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SSP – Stratigraphy, Sedimentology & Palaeontology

SSP1.1 – Open session on stratigraphy, sedimentology and palaeontology

EGU21-13333 | vPICO presentations | SSP1.1

The recovery of early vertebrates and reef ecosystems following the late Silurian carbon isotope excursion: the Burgen outlier, Gotland, Sweden

Emilia Jarochowska, Oskar Bremer, Alexandra Yiu, Tiiu Märss, Henning Blom, Thomas Mörs, and Vivi Vajda

The Ludfordian Carbon Isotope Excursion (LCIE) reached the highest known δ13C values in the Phanerozoic. It was a global environmental perturbation manifested in a rapid regression attributed to glacial eustasy. Previous studies suggested that it has also heavily affected the diversity of conodonts, early vertebrates and reef ecosystems, but the timing of the crisis and recovery remained complicated owing to the lateral variability of δ13C values in epeiric platforms and rapid facies shifts, which drove faunal distribution. One of the best records of this interval is available in the Swedish island of Gotland, which preserves tectonically undisturbed strata deposited in a Silurian tropical carbonate platform. We revisited the world-renowned collection of the late Lennart Jeppsson, hosted at the Swedish Museum of Natural History, Stockholm, which holds the key to reconstruct the dynamics of faunal immigration and diversification following the LCIE. Here we focus on the Burgen erosional outlier, which remained a mystery, as it had been correlated with the excursion strata, but preserved a high diversity of conodonts and reefal ecosystems. We re-examined key outcrops and characterized macro- and microfacies, as well as chemostratigraphy and unpublished fauna in the collection. Strata in the Burgen outlier represent back-shoal facies of the Burgsvik Oolite Member and correspond to the Ozarkodina snajdri Conodont Biozone. The shallow-marine position compared to the more continental setting of coeval strata in southern Gotland, is reflected in the higher δ13Ccarb values, reaching +9.2‰. The back-shoal succession in this outcrop includes reefs, which contain a large proportion of microbial carbonates and have therefore been previously compared with low-diversity buildups developed in a stressed ecosystem. However, the framework of these reefs is built by a diverse coral-stromatoporoid-bryozoan fauna, indicating that a high microbial contribution might be a characteristic of the local carbonate factory rather than a reflection of restricted conditions. In the case of conodonts, impoverishment following the LCIE might be a product of facies preferences, as the diverse environments in the outlier yielded at least 20 of the 21 species known from the Burgsvik Formation in Gotland. Fish diversity also returned to normal levels following the LCIE with an estimated minimum of 9 species. Thelodont scales appear to dominate samples from the Burgen outlier, which is in line with previous reports. Our observations highlight how palaeoenvironmental reconstructions inform fossil niche and diversity analyses, but also how fossil museum collections continuously contribute new data on past biodiversity.

How to cite: Jarochowska, E., Bremer, O., Yiu, A., Märss, T., Blom, H., Mörs, T., and Vajda, V.: The recovery of early vertebrates and reef ecosystems following the late Silurian carbon isotope excursion: the Burgen outlier, Gotland, Sweden, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13333, https://doi.org/10.5194/egusphere-egu21-13333, 2021.

Knowledge on the early development of vegetated landscapes mostly arrives from the floodplain successions where both paleosols and plant body fossils can be assessed. Due to better preservation in the sedimentary record, the shallow-marine carbonates avail much broader areas of former land surface preserved at disconformities, although the associated fossil floras are usually not preserved there. This study demonstrates how much can be learned from this underused sedimentary archive. Many dozens of subaerial exposure surfaces are assessed in cores from cyclic peritidal carbonates of the Emsian – early Eifelian age. These surfaces range from incipient erosional surfaces with few solution features, through paleokarst profiles penetrating to ≥1.0 m underneath disconformities, to thick (>1m) calcretic-clayey paleosols where the parent limestone is ultimately disintegrated into floatbreccia. The studied succession also contains numerous palustrine carbonate intervals, which is the earliest known occurrence of a typical palustrine facies in coastal carbonate plain environment (calcimagnesian paleo-landscape) and is nearly coeval with the earliest occurrence of palustrine facies in the floodplain succession of Svalbard. None of paleokarst and paleosol profiles contain traces of vascular-plant root penetration, and only palustrine facies exhibit swarms of thin (0.5-1.5 mm in diameter) rhizoliths. These findings are within the context of Devonian paleosols on marine carbonate substrates where root traces and laminar calcretes are extremely rare, and no instances of root penetrations are trackable from pre-Givetian, as well as from the Famennian carbonate strata. Despite δ13C and δ18O signatures demonstrating partial diagenetic reset of isotopic composition in studied formations, the moderate δ13Cvpdb offset towards lighter values is detected in two thicker paleosols (-3.0 to -8.0‰ in calcretic matrix vs. -1.0 to -4.5‰ in parent limestone). However, instances of δ13C offset in pre-Late Devonian calcretes are rare and their attribution to plant-derived CO2 is doubtful. It is inferred that the land surface in calcimagnesian landscapes remained a primary desert long after the advent of vascular plants in more favorable wetland settings. Furthermore, for the entirety of Devonian and well into the Carboniferous time, the area involved in primary deserts (surfaces never colonized by embryophytes) must have been much broader than the vegetated conduits of continental runoff, as seed reproductive strategy emerged only in the mid-Famennian, and no plant adaptations to aridic habitats enter the fossil record until Pennsylvanian. The embryophytic green cover of even older, pre-Devonian land was confined to very specific amphibian loci. The negligible biomass this pioneer, ground-level green skin was likely able to achieve contests the hypothetical link between the emergence of thallophyte-grade vegetation and the Late Ordovician event of atmospheric oxygenation and decarbonization. The very gradual, on the scale of first hundred(s) Myr, evolutionary expansion of land plants and correspondently slow increase in their aerial coverage and biomass, is at odds with the hypothetical teleconnection between the spread of terrestrial vegetation, Devonian anoxic events, and biotic crises in the marine realm. Eruption activity in LIP(s) was likely a main driving force in the mid-Devonian switch to the widespread anoxic deposition in shelfal seas known as the Kačák Event.

How to cite: Kabanov, P.: Early-Middle Devonian paleosols and palustrine beds of NW Canada in the context of land plant evolution and global spreads of anoxia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9024, https://doi.org/10.5194/egusphere-egu21-9024, 2021.

Jurassic successions of the northern part of the Friuli (a.k.a. Dinaric or Adriatic) Carbonate Platform (hereinafter FAD) are best exposed along the Trnovski Gozd Plateau in SW Slovenia. A major stratigraphic unit, known as the Trnovo (Ternowaner) oolite has been considered as a classical, textbook example of a highly productive carbonate platform system exporting oolite sediments to the adjacent deep water depositional settings, producing massive bodies of resedimented oolite, such as the Vajont Limestone of the Belluno Basin. Whereas the stratigraphy of the basinal units in the eastern southern Alps and NW Dinarides is well constrained, coeval shallow marine depositional sequences of FAD Carbonate Platform lack a reliable chronostratigraphic framework.

We performed Sr isotope analysis of brachiopod shells and belemnite rostra from two stratigraphic levels at the base and above the Trnovo oolite unit (TOU). Suitability of the fossil material was controlled by selecting skeletal parts without fractures and lacking evidence of alteration due to diagenesis and weathering. The ultrastructure of specimens was inspected in resin-embedded polished thin sections under a petrographic microscope, supported by cathodoluminescence and SEM examination, including EDS semi-quantitative elemental analysis of skeletal parts in thin sections and slabs. For chemical analysis, powdered samples were drilled from thin section wafers and analysed for 87Sr/86Sr (stratigraphy), d13C, d18O, Ca, Mg, Sr, Fe, Mn and Rb (diagenetic alteration control).

The elemental quantification was performed at Jožef Stefan Institute on an Agilent 8800 Triple-Quad Mass Spectrometer and Sr isotopic analysis on a Nu plasma II Multi-Collector MS. Additional 87Sr/86Sr measurements were performed at UCM Madrid on a IsotopX TIMS. The numerical values were calculated from published Sr curves.

Brachiopod species from a lumachelle directly overlying a condensed interval in the base of TOU have been considered indicative for the early Toarcian. However, 87Sr/86Sr values obtained from rynchonellid brachipod shells ranged from 0.707109 to 0.707122, corresponding to numerical ages of either 184.7 ± 0.4 Ma (late Pliensbachian) or 181.8 ± 0.5 Ma (early Toarcian). Belemnites from the Limestone with chert, an informal unit overlying TOU, yielded 87Sr/86Sr values from 0.706838 to 0.706862, that fit two intervals of the Sr isotope curve, i.e., 162.5 ± 1.9 Ma (latest Callovian-early Oxfordian) and 159.4 ± 1.7 Ma (middle to late Oxfordian), respectively. In both cases, the duality in results is caused by their proximity to the Sr curve minima.

These ages open several important questions about the geometry and depositional history of the northern FAD platform system. Despite of a limited accuracy of our results, the age range for TOU clearly spans (at least) late Toarcian and almost whole middle Jurassic, while the age of the supposedly time-equivalent basinal unit, the Vajont Limestone, falls into the late Bajocian-Bathonian interval. Furthermore, our sedimentological re-examination of the classical TOU localities has not shown characteristics of in-situ oolite production environments but, on contrary, evidence of deeper marine deposition marked by beds of carbonate mudstone, including most typical rosso-ammonitico-type facies, associated with (resedimented) oolite and crinoidal facies, similar to parts of the succession of the Vajont Limestone.

How to cite: Božič, D., Košir, A., Mušič, M., and Štrok, M.: Stratigraphic constraints on the Jurassic carbonate platform succession of Trnovski Gozd, SW Slovenia: Strontium isotope dating of brachiopods and belemnites, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12099, https://doi.org/10.5194/egusphere-egu21-12099, 2021.

EGU21-2335 | vPICO presentations | SSP1.1

Petrographic and geochemical fingerprinting of flints from the type-Maastrichtian (SE Netherlands and NE Belgium): implications for flint formation and provenance

Hannah Van der Geest, Johan Vellekoop, Pim Kaskes, Matthias Sinnesael, John Jagt, Patrick Degryse, and Philippe Claeys

The chalk deposits of the type-Maastrichtian, in the SE Netherlands and NE Belgium (the Liège-Limburg region), are characterized by abundant flint layers. Since prehistoric times, flints from this region have been used as raw materials for tool making. While the formation, cyclicity and lithostratigraphy of flint layers from the type-Maastrichtian have been previously studied, their stratigraphic, lateral and internal geochemical and petrological variability are still poorly constrained, posing challenges for tracing the provenance of flint tools. Therefore, in the context of the Maastrichtian Geoheritage Project, we are analysing in-situ flint samples macroscopically, microscopically and with micro-X-ray fluorescence (µXRF). The flint samples were collected from a 50-m-thick interval from the Upper Cretaceous Gulpen Formation at the former ENCI quarry (NL) and the Hallembaye quarry (BE). In contrast to averaged outcomes of bulk or portable X-ray fluorescence techniques commonly used for provenance studies of flints in geoarchaeology, the use of µXRF has the advantage of offering insights into the internal variability and heterogeneity of flints, by displaying relative distributions of major and trace elements within flint samples. Our preliminary results show that flint nodules from the Gulpen Formation can be subdivided based on composition. Flint layers in the middle part of this formation (Vijlen Member) show a high contribution of micrite, in addition to silica, and display a heterogeneous distribution of elements such as Ca, S, K, Fe, Rb and Sr, while flint layers from the overlying Lixhe 1-3 members consist predominantly of silica and have a more homogeneous distribution of chemical elements. Both types of flint layers contain biogenic inclusions, such as fragments of sponge spicules, echinoids, shells and benthic/planktic foraminifera, and other minerals, including iron sulphides and glauconite, but with a different abundance. The observed heterogeneity and variability within the flint nodules might not only be useful for tracing the provenance of flint tools, but could also provide insights into the complex formation of flints.

How to cite: Van der Geest, H., Vellekoop, J., Kaskes, P., Sinnesael, M., Jagt, J., Degryse, P., and Claeys, P.: Petrographic and geochemical fingerprinting of flints from the type-Maastrichtian (SE Netherlands and NE Belgium): implications for flint formation and provenance, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2335, https://doi.org/10.5194/egusphere-egu21-2335, 2021.

EGU21-5576 | vPICO presentations | SSP1.1

Kerguelen Plateau – outstanding Southern Indian Ocean archives of Cenozoic climatic and oceanographic changes

Eleen Zirks, Thomas Westerhold, Matthias Schneider, and Gabriele Uenzelmann-Neben

Previous scientific ocean drilling expeditions have revealed that sediments deposited in the Kerguelen Plateau region have the potential to provide an out-standing chronicle of regional and global climate changes. In particular, this area is an excellent location to monitor subantarctic and high-latitude climate dynamics and obtain far-field information documenting Antarctic climate history in a world warmer than today.

Here we report first results from site survey RV Sonne cruise SO272 that sailed January 11 to March 4 2020 from Port Louis, Mauritius, to Cape Town, South Africa. During the cruise ~4000 km of high resolution seismic reflection data were recorded along 18 seismic profiles across the central and southern Kerguelen Plateau. At 11 stations sediment cores with recoveries of up to 10m were retrieved [GU1] to complement the seismic studies and provide ages of the outcropping sediment at the sea floor. Three gravity cores targeted the Labuan Basin recovering Plio-Pleistocene diatom ooze with drop stones and rhythmic changes in reflectance. Eight gravity cores targeted the Raggatt Basin with the main objective to penetrate through the upper undifferentiated layer of surface sediment and probe the below much older outcropping sediment. Carbonate rich sediments were successfully retrieved at three locations with microfossil assemblages of late Eocene age. X-ray fluorescence core scanning, benthic stable isotope and bio-stratigraphic data will be presented. Seismic and geological datasets will form the base for an IODP full proposal to drill a complete Miocene to Paleocene high latitude sediment package, build upon the #983-Pre IODP proposal.

How to cite: Zirks, E., Westerhold, T., Schneider, M., and Uenzelmann-Neben, G.: Kerguelen Plateau – outstanding Southern Indian Ocean archives of Cenozoic climatic and oceanographic changes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5576, https://doi.org/10.5194/egusphere-egu21-5576, 2021.

EGU21-15868 | vPICO presentations | SSP1.1

The Role of Diagenesis in the Apparent Rise of Diatoms

Sophie Westacott, Noah Planavsky, Ming-Yu Zhao, and Pincelli Hull

Diatoms are one of the most dominant primary producers in the ocean today and largely control the modern marine silica cycle. Their ecological expansion in the Cenozoic is thought to have lowered silica concentrations by two orders of magnitude and has been linked to the rise of grasslands and baleen whales. According to the fossil record much of diatoms' rise to dominance occurred in the past 20 m.y.; however, silicon isotope evidence suggests an earlier expansion. Using a diagenetic model and collated deep sea drill core data, we examine how changes in bottom-water temperature and sedimentation rates over the past 65 m.y. affected the burial efficiency of biogenic silica. We find that once taphonomic potential is taken into account there is no support for the traditionally recognized ~5-20 Ma increase in diatom abundance. These results help reconcile interpretations based on geochemical and fossil data, and add to mounting evidence pushing back the evolution of the modern silica cycle to before 20 Ma and possibly earlier than 40 Ma.

How to cite: Westacott, S., Planavsky, N., Zhao, M.-Y., and Hull, P.: The Role of Diagenesis in the Apparent Rise of Diatoms, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15868, https://doi.org/10.5194/egusphere-egu21-15868, 2021.

Facies analysis of the Cergowa Beds of the Polish and Slovak Outer Carpathians shows that this deep-marine siliciclastic unit was deposited by a spectrum of gravity flows ranging from high to low density, which deposited three facies associations (A, B and C). Association A consists of very fine- to medium-grained sandstones with mudstone and coal clasts, granules and rich in coalified organic matter fragments. Sandstones beds reach 8 m in thickness, are massive and subordinately parallel laminated (Ta and Tab). They are interpreted as resulting from incremental, rapid deposition from collapse of a near-bed layer (Ta, Tab) and laterally sheared near-bed layer (Tb) below high-density, turbulent flows and steady turbidity currents or, in case of mud-rich sandstones, en masse deposition by debris flows. Association B comprises very fine- and fine-grained sandstones with mud and coal clasts, granules and coalified plant fragments and detritus. They are massive, parallel- and ripple cross-laminated (Tab, Tabc, Tbc), reach 2 m in thickness and contain mudstone intercalations up to 50 cm. These sandstones seem to have originated from a combination of incremental deposition by high-density turbidity currents (Tab, Tb), low-amplitude bedload waves at the upper stage planar lamination in more dilute turbidity current (Tb) and suspension of fully turbulent and dilute turbidity currents (Tbc, Tc). Association C consists of very fine- to fine-grained sandstones and siltstones with fine organic detritus and minor mud clasts. Parallel- and ripple cross-lamination (Tbc, Tbcd) dominate, bed thickness of sandstones and siltstones amounts to 1-50 cm and mudstones reaches 200 cm. Association C was deposited by transformation of waning, dilute and fully turbulent turbidity currents from ripples into lower stage planar lamination.

Sandstone and mudstone beds at Lipowica (Poland) contain three types of coalified terrestrial organic matter. Based on their morphology and size these are: (i) coalified plant detritus dispersed in B and C associations, (ii) coalified plant fragments forming elongated lenses in A and B associations and (iii) coalified fragments of tree trunks occurring in A and B facies. Petrographic components of organic matter represented by collotelinite, telinite, gelinite and fusinite with co-occuring framboidal pyrite indicate terrestrial plants affected by fast gelification and burial processes of varying intensity. The size of the plant fragments supplied to the Dukla basin is positively correlated with indicators of hydrodynamic regimes suggested by their hosting sediments. Namely, the larger the fragments, the higher flow energy and steadier and longer lasting sustained sediment delivery.

Sedimentary features of the Cergowa Beds suggest deposition out of gradually aggrading sustained turbulent sandy gravity flows primarily controlled by hyperpycnal effluents from a delta. Palaeocurrent data and comparison of mineral composition of sandstone infilling a hollow coalified tree trunk at Lipowica quarry with sandstone beds of the hosting succession suggest provenance from shelf fringing the emergent Silesian Ridge, which acted as a source area to the west of the basin. The depositional age NP23 and NP24 during the Oligocene eustatic sea-level fall implies that the delta supplying the Cergowa basin was located at the edge of this shelf.

How to cite: Pszonka, J., Wendorff, M., Zielińska, M., and Godlewski, P.: Facies and provenance of deep marine sediment gravity flows with fragments of coalified land plants at Lipowica, the Cergowa Beds (Oligocene), Outer Carpathians of Poland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13609, https://doi.org/10.5194/egusphere-egu21-13609, 2021.

EGU21-1738 | vPICO presentations | SSP1.1

Biogenic native Sulfur linked to the Neogene deposits from the Riffian Corridors (Northern Morocco): preliminary study and characterization

Laila Boubkari, Otmane Raji, Mohammed Achalhi, Muhammed Ouabid, and Jean Louis Bodinier

Elemental sulfur in sedimentary rocks is commonly associated with evaporites and authigenic carbonates. The genesis of this evaporite hosted native sulfur has been traditionally considered as a result of bacterial sulfate reduction under specific geological and paleogeographic conditions. Some biogenic sulfur occurrences are found in the Mediterranean area associated with the Neogene formations (e.g. Hellin, Lorca, Teruel, Sicily). They are described as interbedded layers in large evaporitic sequences or as sulfur nodules enclosed in secondary gypsum or carbonate deposits. Quite similar geological settings are present in Northern Morocco where several sediment-hosted sulfur showings were noted. However, these potential sulfur occurrences in the Pre-Rif and post-nappe Neogene basins have not been studied and still basically unknown. This work aims to explore these occurrences and assess their potentials using preliminary field, mineralogical and geochemical data. Several potential areas were identified at the Tortono-Messinian formations of Oued Amlil, Arbaa Taourirt, Taghzout Tassa, and Boudinar basins. They show favorable settings composed mainly of gypsiferous marls, carbonate, and organic matter-rich black sediments. In terms of sulfur contents, preliminary XRD data confirmed the presence of elemental sulfur and geochemical analyses show total sulfur content reaching 18.5 wt.%. However, further fieldwork combined with advanced mineralogical and isotopic geochemistry is still necessary for this area to try understanding their paragenesis in comparison with other similar Mediterranean occurrences.

How to cite: Boubkari, L., Raji, O., Achalhi, M., Ouabid, M., and Bodinier, J. L.: Biogenic native Sulfur linked to the Neogene deposits from the Riffian Corridors (Northern Morocco): preliminary study and characterization, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1738, https://doi.org/10.5194/egusphere-egu21-1738, 2021.

EGU21-24 | vPICO presentations | SSP1.1

Ongoing biogenic silica diagenesis — Interstitial-water chemical signals

Shahab Varkouhi, Nicholas J. Tosca, and Joseph A. Cartwright

Biogenic silica diagenesis leads to abrupt changes in the physical properties of host sediment across the depth of an opal-A to opal-CT transition zone. Predicting the present-day diagenetic state of this reaction boundary, i.e., active versus arrested opal-A to opal-CT transition zones, is imperative to constraining the diagenetic factors that impact dramatic variations in the physical state of sediment. This study assesses whether there are present-day signatures of active silica diagenesis in the interstitial water, and corroborates the potential for pore-water chemistry for distinguishing between ongoing precipitation of diagenetic opal and arrested reaction fronts. Interstitial-water chemistry, mineralogy, and thermodynamic analyses of the Ocean Drilling Program Sites 794 and 795 demonstrate that solubility equilibrium is reached with respect to opal-CT in the transition zones accommodated by the Neogene biosiliceous sediments in the Sea of Japan. Even though the dissolution of biogenic opal is triggering reverse-weathering processes, the equilibrium reached with respect to diagenetic opal strongly suggests that the dissolved silica depression across the transition zones is essentially influenced by ongoing transformation of opal-A to opal-CT. Owing to abrupt petrophysical variations linked to opal-CT precipitation, the interstitial profiles of major ions and primary parameters have also been impacted by silica diagenesis. The extremely low dissolved-silica diffusion fluxes in the sediment, the very low permeability of the sediment capturing silica diagenetic transformations, and the marked pore-water loss at the depth of the transition zone all support the fact that the dissolved species have not been diffused in the sediment at rates comparable to those by pore-water advection due to sediment porosity drop. Advective and diffusive mechanisms, however, appear to have ceased recently because they have failed to smooth out the traces of ongoing biogenic silica diagenesis.

How to cite: Varkouhi, S., Tosca, N. J., and Cartwright, J. A.: Ongoing biogenic silica diagenesis — Interstitial-water chemical signals, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-24, https://doi.org/10.5194/egusphere-egu21-24, 2021.

SSP1.2 – Achievements and perspectives in scientific ocean and continental drilling

EGU21-8407 | vPICO presentations | SSP1.2 | Highlight

Foresight, hindsight, IODP and science communicaton

Carol Cotterill, Sharon Katz Cooper, Angela Slagle, and Carl Brenner

There aren’t many circumstances that require looking into the future to decide what people will be interested in about the past, while writing in the present. Dr. Roz Coggan wasn’t kidding when she drew a picture of a scientific ocean drilling vessel and labelled it as a Time Machine! So how do we go about communicating the science in the sediments, the cliff-hangers in the cores?

Since 1966, the scientific community has looked to the oceans, and the natural laboratories hidden beneath them, to answer fundamental questions concerning the composition, structure, and key processes of the Earth, unravelling geochemical, biological, physical, structural, climatic and geohazard-related complexities along the way. As the current phase of scientific ocean drilling (IODP) is drawing to an end, an international team has drafted a new vision for the future of this inspiring and unique program, released officially in Fall 2020.

The 2050 Science Framework for Scientific Ocean Drilling consists of seven Strategic Objectives and five Flagship Initiatives. Spanning all of these are four Enabling Elements - key facets that facilitate research activities, enhance outputs, and maximise their impact. Enabling Element 1 covers the broader impacts and outreach associated with scientific ocean drilling, including highlighting the societal relevance of its research topics, inspiring and training the next generation of ocean scientists, addressing knowledge sharing and collaborations, and working towards greater diversity and inclusion in geoscience. These are not small issues to address, and overall Enabling Element 1 sets an aspirational target for science communication going forward:

“Using a variety of social media and web-based platforms, data and results will be broadly disseminated to educators, policymakers, and the public, securing scientific ocean drilling’s position as the authoritative source of information about the Earth system.” (Koppers and Coggon, 2020)

We believe that with such broad aims, now is the time to formulate large-scale strategies for science communication. By bringing in aspects of strategy and branding, stirred together with a good dose of umbrella narratives, we aim to develop a transmedia approach to science communication, taking different present audiences on unique journeys into the past with an eye on the future. We will need to assess framing and relevance, the power of storytelling to communicate facts, and how best to ensure that our activities contribute to excitement about learning the unfolding stories of the Earth. Now is the perfect time to initiate this effort, and it is hoped that this review of multiple aspects of Science Communication, Public Engagement and branding can help begin these discussions.

“What is it that we human beings ultimately depend on? We depend on our words. We are suspended in language. Our task is to communicate experience and ideas to others”. Niels Bohr

Original illustration by GeoProse from the 2050 From Koppers, A.A.P., and R. Coggon, eds. 2020. Exploring Earth by Scientific Ocean Drilling: 2050 Framework.

How to cite: Cotterill, C., Katz Cooper, S., Slagle, A., and Brenner, C.: Foresight, hindsight, IODP and science communicaton, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8407, https://doi.org/10.5194/egusphere-egu21-8407, 2021.

EGU21-1904 | vPICO presentations | SSP1.2 | Highlight

INTERACTION: INTeraction between lifE, Rifting And Caldera Tectonics In OkataiNa

Cécile Massiot, Craig Miller, Matthew Stott, Pilar Villamor, Hiroshi Asanuma, Eric Boyd, Matteo Lelli, David D. Mcnamara, Santanu Misra, Doug R. Schmitt, Guido Ventura, Pujun Wang, Ludmila Adam, Edward Bertrand, Fabio Caratori Tontini, Geoff Kilgour, Sarah D. Milicich, Alex Nichols, and Francesco Parisio

Calderas are major volcanic features with large volcanic and seismic hazards. They also host diverse microbiota, provide heat, energy, mineral and economic benefits. Despite their scientific and socio-economic importance, we still do not completely understand calderas and the interactions between volcanism, tectonism, fluid circulation and the deep biosphere because in-situ and subsurface observations are sparse.

The Okataina Volcanic Centre (OVC) in Aotearoa New Zealand, is one of two active giant calderas of the Taupō Volcanic Zone within the rapidly extending continental intra-arc Taupō Rift. This superb natural laboratory has: 1) numerous past eruptions of varied size and style, 2) documented co-eruptive earthquakes, 3) vigorous hydrothermal manifestations, 4) diverse microbial communities in hot springs but unknown in the subsurface.

We propose to establish a scientific drilling programme at the OVC to address:

  • What are the conditions leading to volcanic eruptions; and volcano-tectonic feedbacks in intra-rift calderas?
  • What controls fluid circulations in active calderas/rift regions?
  • Does subsurface microbial community composition vary with tectonic and/or volcanic activity?

High temperatures complicate drillhole design, restrict data collection and prevent exploration of the biosphere. By targeting the cooler parts of the caldera, this project will use conventional engineering to maximise sampling (drill cores and fluids), downhole logging and establish long-term observatories.

Two preliminary drill targets are suggested: (1) in the centre of the caldera; (2) through the caldera margin. Drill data will provide a comprehensive record of past activity, establishing eruption frequency-magnitude relationships and precursors. Combined with well-known fault rupture history, the relative timing of tectonic and magmatic activity will be untangled. Drill data will unravel the relationships between the groundwater and hydrothermal systems, magma, faults and stress, informing thermo-hydro-mechanical regional caldera models with findings applicable worldwide. Drill cores and a dedicated fluid sampler triggered by nearby earthquakes will reveal the composition, function and potential change of microbial activity in response to rock and fluid variations.

The programme is informed by indigenous Māori, regulatory authorities and emergency managers to ensure scientific, cultural, regulatory and resilience outcomes. The programme will underpin 1) community resilience to volcanic and seismic hazards; 2) sustainable management of groundwater and geothermal resources, and 3) understanding of subsurface microbial diversity, function and geobiological interactions. At these early stages of planning, we invite the scientific community to contribute to the concept of this project in the exceptional OVC settings and strengthen linkages with other ongoing research and scientific drilling programmes.

How to cite: Massiot, C., Miller, C., Stott, M., Villamor, P., Asanuma, H., Boyd, E., Lelli, M., Mcnamara, D. D., Misra, S., Schmitt, D. R., Ventura, G., Wang, P., Adam, L., Bertrand, E., Caratori Tontini, F., Kilgour, G., Milicich, S. D., Nichols, A., and Parisio, F.: INTERACTION: INTeraction between lifE, Rifting And Caldera Tectonics In OkataiNa, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1904, https://doi.org/10.5194/egusphere-egu21-1904, 2021.

EGU21-14486 | vPICO presentations | SSP1.2

Afar Dallol Drilling – ONset of sedimentary processes in an active rift basin (ADD-ON): Scientific drilling targets in the Afar (Ethiopia)

Anneleen Foubert, Tesfaye Kidane, Derek Keir, Balemwal Atnafu, and the ICDP ADD-ON Team

Since the early days of the continental drift theory, the Afar triangle developed into an ideal field laboratory where the onset of continental and future oceanic rifting can be studied in detail. The Danakil Depression is the northern portion of the Afar triangle, bordered to the west by the Ethiopian Plateau and to the East by the Danakil Horst, and characterised by active rifting since Oligocene times. Seismo-stratigraphic interpretations based on industrial seismic sections, core and borehole data evidence the presence of Pleistocene evaporite units to a depth of about 900 m below the Dallol salt pan (central Danakil Depression, northern Afar). However, to date no sub-salt sedimentary core records have been available from the central part of the rift basin filled with likely more than 1.5 km of sediments.

The ADD-ON drilling project aims to get access to the sub-salt sedimentary archives of the Danakil basin. The overall goal is to understand sedimentary facies evolution in an active rift setting paced by global environmental fluctuations and their interplay with volcano-tectonic events. Having future access to scientific core records will give new insights into (1) the mechanical understanding of intermittent and incipient basin dynamics in an initial extensive continental rift basin: from rifting towards the development of passive margins, (2) East African climatic changes and Hominin evolution, (3) the limits of the deep biosphere in extreme hypersaline and high-temperature environments below the salt deposits, (4) natural fluid flow in an active geothermal system, and (5) monitoring of active faults, earthquakes and volcanic events in remote areas. Moreover, deep scientific drilling in Afar will be necessary in the rapid assessment of geothermal potential, the quest for ground water resources and advanced Potash exploitation.

How to cite: Foubert, A., Kidane, T., Keir, D., Atnafu, B., and ADD-ON Team, T. I.: Afar Dallol Drilling – ONset of sedimentary processes in an active rift basin (ADD-ON): Scientific drilling targets in the Afar (Ethiopia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14486, https://doi.org/10.5194/egusphere-egu21-14486, 2021.

The Prees-2 fully cored borehole was drilled in November and December 2020 and captures a thick biostratigraphically complete, hemipelagic marine record for the Triassic-Jurassic boundary and for the Hettangian, Sinemurian and lower Pliensbachian stages.  The borehole is sited at the centre of the Prees Jurassic outlier in the Cheshire Basin, Shropshire, England. The overall JET project, funded principally by ICDP, NERC, and DFG, aims to construct a fully integrated age model and timescale for the Early Jurassic combining new data from the Prees core with data generated from the historic Llanbedr (Mochras Farm) borehole in NW Wales.  The new timescale and a wide range of geological data are then being used to reconstruct and understand diverse aspects of the Early Jurassic Earth system, and to provide constraints on astronomical solutions for solar system dynamics over this crucial time interval that links oceanic records of the Cenozoic and later Mesozoic to continental records of the Triassic.  The Prees-2 borehole was drilled to a total depth of 656 m below rig floor, and the Early Jurassic succession comprises mudstone, limestone, and siltstone, which is fossiliferous throughout and includes many biostratigraphically significant ammonite fossils. Diverse trace fossil assemblages are also observed, and lithological cyclicity is apparent through the Jurassic on a scale of about one metre, compatible with interpretations of Milankovitch cyclicity in the precession band based on analysis of Mochras core. Core recovery was largely at 100% and the core quality is excellent. A suite of downhole logs was obtained and ongoing work at the British Geological Survey Core Scanning Facility is generating a high-quality, high-resolution geochemical and geophysical dataset that will provide a fundamental basis for further core-log integration, astrochronology and palaeoenvironmental work.

How to cite: Hesselbo, S. and the JET Science Party: Initial results from coring at Prees, Cheshire Basin, UK, and future plans for the Early Jurassic Earth System and Timescale Project (JET), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12304, https://doi.org/10.5194/egusphere-egu21-12304, 2021.

EGU21-3930 | vPICO presentations | SSP1.2

A successfully finished ICDP deep borehole of 7108m (SK2)in the Cretaceous Songliao Basin of Northeast China

Pujun Wang, Yongyi Zhu, Youfeng Gao, Xiaoqiao Wan, Yangguang Ren, Shuxue Wang, Xuejiao Qu, Qi'an Meng, Yongjian Huang, Qinghua Huang, Haibo Liu, and Chengshan Wang

A series of ICDP deep boreholes of SK1), SK2 and SK3 have been drilled in the Songliao Basin of NE China during 2006 to 2021. The deepest and the most attractive SK2 is with bottom depth of 7108m and super long Continuous coring footage of 4380m. With the long-term working process, we have some special experiences that may be useful to others. The first is that ICDP financial support may cover only a small part of the total cost. But the fishing effect is crucial. That is to say, when we are trying to get financial support, the most important thing above all is generally the reason why do we want to spend the money for. Because of its widely accepted peer review international level program, ICDP funding ,no matter big or small, can always give us strong and convictive argument for the money usage, especially when we are trying to get funded from government organizations and/or companies those are interested in high level research of global aspects. The second is that an ICDP project can be forward in different ways. A step by step procedure is also a very functional way. For example, at the beginning of our ICDP long marching, we got ICDP technical support when we worked on SK1 in 2006. This turned to a key step for the following procedure. Three years later in 2009, we got ICDP funded. The third is that drilling and coring are costly. We may save a lot of money if we can combine ICDP pure research of global aspects with local industry interests. Petroleum companies related to the Songliao Basin kindly provided us all the available data including well-logs, core samples and 3D-seismic data for free. So that, we did not spend any money for the pre-drilling research. And more so, based on these precise data we got very good prediction of the subsurface stratigraphic sections we may meet while drilling, which are very important information for the plans of drilling engineering.

Why we want to drill the deep boreholes of the SK2 coupled with SK1 and SK3.

At first, we hope to obtain a continuous and complete Cretaceous terrestrial coring succession. Situated on the eastern margin of the Eurasian Plate, the Songliao Basin accumulated the most continuous and the highest resolution geological records of Cretaceous terrestrial sedimentary-volcanic successions in the world. The whole Cretaceous sequence is over 10km thick.

Secondly, we hope to establish a high-precision terrestrial stratigraphic framework of the region.

Thirdly, we hope to study the Cretaceous conditions concerning paleo-environment of the lakes in the Songliao Basin and adjacent areas. At last, research on paleoclimatic aspects in northeastern Asia based on the collected precise lake deposits. And then, According to the knowledge acquired from the global warming process in the Cretaceous in NE Asia, especially during the stages of intense fossil fuel accumulation episodes, we may have the opportunity try to find some similarities to the global warming trend that human being is facing now.

How to cite: Wang, P., Zhu, Y., Gao, Y., Wan, X., Ren, Y., Wang, S., Qu, X., Meng, Q., Huang, Y., Huang, Q., Liu, H., and Wang, C.: A successfully finished ICDP deep borehole of 7108m (SK2)in the Cretaceous Songliao Basin of Northeast China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3930, https://doi.org/10.5194/egusphere-egu21-3930, 2021.

EGU21-6969 | vPICO presentations | SSP1.2

New data from ICDP borehole SK2 and its constraint on the beginning of the Lower Cretaceous Shahezi Formation in the Songliao Basin, NE China

haibo liu, Pujun Wang, Youfeng Gao, Yongkang Yin, and Honghao Li

The Songliao Basin is one of the largest non-marine petroliferous basins in the globally and contains nearly complete Cretaceous terrestrial sedimentary records. The Shahezi Formation is a thick terrestrial clastic sedimentary succession deposited during the rift period of the Songliao Basin. Accordingly, it is significant for research on initial basin history restoration and global continental–marine stratigraphic correlation, to certificate the deposition time of the Shahezi Formation. This formation is always met when wells are drilled in fault basins of the Songliao Basin, and its outcrops are discontinuously distributed along the southeastern margin of the basin. Limited by the discontinuous cores and outcrops, previous studies on the deposition time of the Shahezi Formation were lack of direct evidence.

Borehole SK2 of ICDP was located in the thickest part of the Shahezi Formation in the northern Songliao Basin. It drilled into and traversed the Shahezi Formation from 3,335.99 m to 5,960.00 m, cored all the strata of this 2,624.01 m interval, and obtained 2,503.86 m of core with a coring rate of 95.79%. This core, which can be regarded as a continuous high-resolution terrestrial geological record, provides the basic material to study greenhouse climate events in the Cretaceous and interpret oil and gas generation processes in the basin.

Based on centimeter-scale core observation, the Shahezi Formation is mainly composed of variegated conglomerate, gray sandstone, and black mudstone. It is a sedimentary succession of fan-delta facies and lake facies.

One sedimentary tuff layer with a thickness of almost 1 m was found at a depth of 5,943.19 m, close to the bottom of the Shahezi Formation in SK2. The weighted mean age of 117.9 ± 1.6 Ma (MSWD = 0.15, N=15) provides a reference for the beginning of the deposition of the Shahezi Formation. One rhyolitic crystal tuff layer approximately 6 mm thick was found at a depth of 5,958.62 m at the bottom of the formation. The weighted mean age of 118.2 ± 1.5 Ma (MSWD = 0.18, N=19) is interpreted as the eruption age of the tuff sample. These weighted mean ages provide the best estimate of the beginning of deposition of the Shahezi Formation.Taking other studies into account, the deposition rate of the Shahezi Formation without compaction correction was calculated as about 460 m/Ma. This rate is much faster than the deposition rate of other periods in the Songliao Basin. The Shahezi Formation was deposited approximately from 118 to 111 Ma, from the middle Aptian to early Albian.

The study of the high-resolution stratigraphic sequence and deposition time of the Shahezi Formation is a key to know the process of hydrocarbon generation in the basin. It provides a foundation for the correlation between terrestrial sedimentation in the Songliao Basin and global continental–marine stratigraphy. Also, it should have positive significance for other studies, such as CNS, OAE1a, OAE1b, ORB1, Cretaceous paleogeography and paleoclimate, change in the drifting direction of the subducting Pacific Plate, and other contemporaneous global geological events.

How to cite: liu, H., Wang, P., Gao, Y., Yin, Y., and Li, H.: New data from ICDP borehole SK2 and its constraint on the beginning of the Lower Cretaceous Shahezi Formation in the Songliao Basin, NE China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6969, https://doi.org/10.5194/egusphere-egu21-6969, 2021.

In the Songliao Basin, the existence of lower Mesozoic strata remains a debatable issue. Previous studies indicated the absence of Triassic to Lower and Middle Jurassic strata in northeastern China because of uplift and erosion events associated with the return of geo-synclinal folds and orogenic movement during the Late Permian–Early Jurassic. To date, geochronological studies of intrusive and metamorphic rocks in the basement of the Songliao Basin have also confirmed Carboniferous, Permian, and Late Jurassic ages for the basement formations in general. In the International Continental Scientific Drilling Project (ICDP) in the Songliao Basin, radiometric dating has been carried out for the entire drilling core of the SK-2 east borehole. As a result, we have discovered Triassic volcanic-sedimentary strata in the basement of the Songliao Basin. Laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb geochronology was used in this research. Errors in individual analyses by LA-ICP-MS are given at the 1σ level, whereas errors in pooled ages are given at the 95% (2σ) confidence level. Triassic volcanic-sedimentary strata revealed by the SK-2 east borehole consist of andesitic volcanic breccias at the bottom; andesites, sandstones, and conglomerates in the middle; and andesites at the top. The total thickness of these strata is over 500 m. The formation age of the andesite at the depth of 6,031.9 m is 242.4 ± 2.1 Ma (MSWD = 0.06, n = 7). The youngest peak age of the sandstone at the depth of 6,286.2 m is 242.2 Ma. The formation age of the andesite at the depth of 6,286.2 m is 242.6 ± 1.5 Ma (MSWD = 1.02, n = 18). This study demonstrates that in the Songliao Basin, there are not only Carboniferous and Permian strata, but also a Triassic volcanic-sedimentary succession in the basement of the basin. The SK-2 drilling core reveals that this volcanic-sedimentary sequence has great thickness. These Triassic volcanic-sedimentary strata provide new clues for the study of the origin and development of the Songliao Basin. As both volcanic and sedimentary rocks can be oil and gas reservoirs, this discovery also provides a new target for oil and gas exploration deep in the Songliao Basin.

How to cite: Yin, Y., Wang, P., Gao, Y., and Liu, H.: Triassic volcanic-sedimentary strata in the basement of Songliao Basin, discovered by International Continental Scientific Drilling Borehole, SK-2, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1874, https://doi.org/10.5194/egusphere-egu21-1874, 2021.

EGU21-538 | vPICO presentations | SSP1.2

Collisional Orogeny in the Scandinavian Caledonides (COSC): Some preliminary results from drilling of the 2.276 km deep COSC-2 borehole, central Sweden

Christopher Juhlin, Bjarne Almqvist, Mark Anderson, Mark Dopson, Iwona Klonowska, Oliver Lehnert, Rodolphe Lescoutre, Henning Lorenz, Christophe Pascal, Sandra Piazolo, Nick Roberts, Jan-Erik Rosberg, and Chin-Fu Tsang

COSC investigations and drilling activities are focused in the Åre-Mörsil area (Sweden) of central Scandinavia. COSC-2 was drilled with nearly 100% core recovery in 2020 to 2.276 km depth with drilling ongoing from mid-April to early August. Drilling targets for COSC-2 included (1) the highly conductive Alum shale, (2) the Caledonian décollement, the major detachment that separates the Caledonian allochthons from the autochthonous basement of the Fennoscandian Shield, and (3) the strong seismic reflectors in the Precambrian basement.

Combined seismic, magnetotelluric (MT) and magnetic data were used to site the COSC-2 borehole about 20 km east-southeast of COSC-1. Based on these data it was predicted that the uppermost, tectonic occurrence of Cambrian Alum shale would be penetrated at about 800 m, the main décollement in Alum shale at its stratigraphic level at about 1200 m and the uppermost high amplitude basement reflector at about 1600 m. Paleozoic turbidites and greywackes were expected to be drilled down to 800 m depth. Below this depth, Ordovician limestone and shale with imbricates of Alum shale were interpreted to be present. Directly below the main décollement, magnetite rich Precambrian basement was expected to be encountered with a composition similar to that of magnetic granitic rocks found east of the Caledonian Front. The actual depths of the main contacts turned out to agree very well with the predictions based on the geophysical data. However, the geology below the uppermost occurrence of Alum shale is quite different from the expected model. Alum shale was only clearly encountered as a highly deformed, about 30 m thick unit, starting at about 790 m. Between about 820 and 1200 m, preliminary interpretations are that the rocks mainly consist of Neo-Proterozoic to Early Cambrian tuffs. Further below, Precambrian porphyries are present. The high amplitude reflections within the Precambrian sequence appear to be generated by dolerite sheets with the uppermost top penetrated at about 1600 m. Several deformed sheets of dolerite may be present down to about 1930 m. Below this depth the rocks are again porphyries.

A preliminary conclusion concerning the tectonic model is that the main décollement is at about 800 m and not at 1200 m. Also the thickness of the lowermost Cambrian/uppermost Neoproterozoic sediments on top of the basement is much greater than expected (hundreds of meters instead of tens of meters) and likely to have been thickened tectonically. Detailed studies are required to assess the actual importance of the “main décollement” and the degree, type and age of deformation in its footwall. We can also conclude that the Precambrian basement is very similar to the Dala porphyries succession that are typically present farther south.

An extensive set of downhole logging data was acquired directly after drilling. Borehole seismic measurements in 2021 will help to define and correlate seismic boundaries with lithology and structures in the core. Unfortunately, work for describing the geology of the drill core in detail is still on hold due to Covid-19.

How to cite: Juhlin, C., Almqvist, B., Anderson, M., Dopson, M., Klonowska, I., Lehnert, O., Lescoutre, R., Lorenz, H., Pascal, C., Piazolo, S., Roberts, N., Rosberg, J.-E., and Tsang, C.-F.: Collisional Orogeny in the Scandinavian Caledonides (COSC): Some preliminary results from drilling of the 2.276 km deep COSC-2 borehole, central Sweden, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-538, https://doi.org/10.5194/egusphere-egu21-538, 2021.

EGU21-2321 | vPICO presentations | SSP1.2

Core-log-seismic integration in metamorphic rocks at the ICDP drilling project COSC-1, Sweden

Judith Elger, Christian Berndt, Felix Kästner, Simona Pierdominici, Jochem Kück, Bjarne S. G. Almqvist, Christopher Juhlin, and Henning Lorenz

Continental collision causes deformation in the crust along shear zones. However, the physical and chemical conditions at which these zones operate and the deformation processes that enable up to hundreds of km of tectonic transport are still unclear because of the depth at which they occur and the challenges in imaging them. Ancient exhumed collision zones allow us to investigate these processes much better, for example at the COSC-1 borehole in the central Scandinavian Caledonides. This study combines data from the COSC-1 borehole, such as downhole logging and zero-offset vertical seismic profile data, with 2D and 3D seismic measurements to provide constraints on the spatial lithological and textural configuration of the Seve Nappe Complex. This is one of the few studies that shows that core-log-seismic integration in metamorphic rocks allows to identify the spatial distribution of major lithological units, even though the methodology was originally developed for sedimentary basins in the hydrocarbon industry. Especially gamma ray logs in combination with density data are powerful tools to distinguish between mafic and felsic lithologies in log-core correlation. Reflections in the Seve Nappe Complex are not as distinct as in greater depths but continuous, and our results indicate that they are primarily caused by compositional rather than textural changes. Several of the reflections can be linked to magmatic intrusions, which have been metamorphically overprinted. Their setting indicates that the Seve Nappe Complex consists of the remnants of a volcanic continental margin. It appears that in spite of the metamorphic overprint around 417+/-9 Ma, the original configuration of the volcanic passive margin is partly preserved in the Seve Nappe Complex and that it outlasted continent-continent collision, including the nappe emplacement. Thus, an integration of borehole and three-dimensional geophysical data can image lithological changes that can then be extrapolated in three dimensions to arrive at a better understanding of the composition and geometry at mid-crustal levels. Furthermore, our results suggest that ductile-deformed middle crustal reflectivity is primarily a function of pre-orogenic lithological variations which has to be considered when deciphering mountain building processes.

How to cite: Elger, J., Berndt, C., Kästner, F., Pierdominici, S., Kück, J., Almqvist, B. S. G., Juhlin, C., and Lorenz, H.: Core-log-seismic integration in metamorphic rocks at the ICDP drilling project COSC-1, Sweden, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2321, https://doi.org/10.5194/egusphere-egu21-2321, 2021.

EGU21-10044 | vPICO presentations | SSP1.2 | Highlight

Innovative Exploration Drilling and Data Acquisition – Test Center (I-EDDA-TC), Örebro, Central Sweden

Bjarne Almqvist, Maria Ask, Linus Brander, Stefan Buske, Christoph Büttner, Rüdiger Giese, Ulrich Harms, Christopher Juhlin, Jochem Kück, Carl Linden, Henning Lorenz, and Jan-Erik Rosberg

Increasing the effectiveness of exploration for mineral resources is vital to meet future societal, economic and environmental challenges. Effective exploration drilling for mineral resources is an area where industrial innovation plays an important role. Measurements-while-drilling, data acquisition and next generation logging sondes represent three important areas that need development in the mineral exploration sector. Despite this need, there is a lack of test beds that allow to test novel drilling equipment. This limits the development and implementation of equipment with technology that has been proven, but does not yet fulfil the requirements of a product on the commercial market. Although a variety of test sites exist throughout Europe, they are constrained to existing infrastructure, which limits users to pre-existing conditions that may not fit their purpose or need. The I-EDDA-TC provides a unique environment for the development of drilling, and related, equipment used for exploration of mineral resources.

The regional geology around the test center site is dominated by Svecokarelian age granitoid intrusive and acid volcanic rocks (rhyolites) that strike east-west and dip sub-vertical. During 2019 and 2020, two boreholes were drilled at the test center site, as part of an EIT Raw Materials upscaling project. The first borehole is a fully cored 970 m deep borehole drilled with diamond bit (HQ dimension). The second borehole was drilled in the late summer of 2020, and is a 200 m deep percussion-drilled borehole with ~220 mm diameter. Here we present a preliminary synthesis of results from a geophysical survey, borehole logging and geological logging of drill core.

In summer 2019 a comprehensive geophysical surveying program was performed at the site, including 3D high resolution seismic, 2D deeper seismic with a large vibrator source, a series of high-resolution resistivity profiles and magnetic profiles. The 3D seismic data provided detailed velocity information in the near-surface at the site, allowing interpretation of depths to the groundwater table and bedrock in 3D. Data gained from two downhole logging campaigns provides a robust base for the detailed differentiation and characterization of the formations. A first look on the data shows well defined correlations amongst the various geophysical downhole parameters. Geological logging focused both on material properties (e.g. mineralogy, grain-size, texture, alteration and mineralization) and rock mass (joints and RQD). Magnetic susceptibility and ultrasonic pulse velocity were measured at regular intervals along the full core length, and 66 specimens were prepared and analysed with respect to porosity, density, abrasivity, major chemical elements, indirect tensile strength and uniaxial compressive strength. The integrated analysis of core data, surface and borehole seismic data, and the continuous logging profiles allows for the 3-dimensional characterization of the underground below the test center platform, as well as provides reference data for assessment of work conducted at the site (e.g. development of geophysical instruments, testing of drillabilaty and wear on drill bits). Our results will be open access published so that data can be compared to drilling and instruments test of commercial and academic parties utilizing this testing facility in future.

How to cite: Almqvist, B., Ask, M., Brander, L., Buske, S., Büttner, C., Giese, R., Harms, U., Juhlin, C., Kück, J., Linden, C., Lorenz, H., and Rosberg, J.-E.: Innovative Exploration Drilling and Data Acquisition – Test Center (I-EDDA-TC), Örebro, Central Sweden, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10044, https://doi.org/10.5194/egusphere-egu21-10044, 2021.

EGU21-6259 | vPICO presentations | SSP1.2

Rock strength and time dependent deformation of borehole breakouts in the ICDP Outokumpu deep borehole

Simona Pierdominici and Maria Ask

While the mechanical properties of plate boundaries are relatively well known and characterized by earthquake occurrence, intraplate regions are still largely “terra incognita”, especially in cratonic shields where only seldom and very few data related to the state of the stress field are available. The only way to detect such data and understand the geological and physical processes responsible for the present stress field in an intraplate area is to carry out in-situ measurements of stress-induced deformation in a borehole over time. We had a unique and extraordinary opportunity to measure and investigate the time-dependent deformation in an aseismic area directly in-situ inside the 2500 m Outokumpu open borehole in eastern Finland. The stress data acquired in 2006 and 2011 have been analysed and show that a slow but continued deformation of the upper part of the Earth‘s crust, albeit unexpected, is still ongoing. The continuous formation and development of stress-induced borehole enlargements in a tectonically very stable and almost aseismic area is unforeseen and raises questions of global importance. For this, two complementary approaches were conducted: identification of breakout zones and rock physics measurements on selected drill cores. We compared the two datasets to study the changes of breakout geometry and to quantify the growth of the breakouts in this time span from differences in width, length and depth. For the second method, UCS experiments were conducted providing unconfined compressive strength on specimens collected from above, middle and below breakout zones, and rough estimates of the static Young’s modulus based on the initial length and axial travel of the load frame. The sample height-diameter (H:D) ratio of available drill cores was less than required in testing standards (ASTM D7012, 2014, ISRM 1999). The relatively small grain size of drill cores allowed drilling of smaller-diameter subcores that in most cases fulfilled or exceeded the minimum H:D ratio (1.7<H:D<2.3). We realized that also along the same lithology some zones are affected by enlargements and other remain undamaged. Therefore, we performed the geomechanical analyses on specimens from the same lithology but not affected by failures. Fifty-one uniaxial compressive tests were conducted on specimens belonging to four main rock types at different depths: biotite gneiss, diopside tremolite skarn, micaschist and serpentinite. Results from geomechanical test show UCS values range from 27 to 245 MPa with an average of 102 MPa and a standard deviation of 42, while the elastic Youngs modulus range from 3 to 20 GPa with an average of 7.3 GPa and a standard deviation of 2.8. Most samples collected within breakout zones have UCS values from 40 to 170 MPa and H:D ratio from 1.8 to 2.0, less that required by the standards. The samples outside of the breakout zones show UCS values from 27 to 186 MPa, and H:D ratio from 1.7 to 2.3. The hypothesis for testing was that borehole breakouts were formed in weaker rocks. Our results does not confirm this hypothesis, but the observed time-dependent deformation in Outokumpu borehole is interesting and calls for further studies.

How to cite: Pierdominici, S. and Ask, M.: Rock strength and time dependent deformation of borehole breakouts in the ICDP Outokumpu deep borehole, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6259, https://doi.org/10.5194/egusphere-egu21-6259, 2021.

EGU21-8887 | vPICO presentations | SSP1.2

Identification of a fault zone beneath Moxa observatory (Central Germany): evidence from combining logging, rock physical measurements, and geophysical profiling

Valentin Kasburg, Todor Valchev, Andreas Goepel, Cornelius Octavian Schwarze, and Nina Kukowski

Geophysical observatories aim to decipher natural processes taking place in very different parts of the Earth’s interior by recording long time series of various signals related to these processes. As such signals, e.g. fluctuations of deformation or temperature, may be very small, complementary information e.g. from climate stations and very good knowledge of geological structures in the vicinity of an observatory is indispensable. Moxa Geodynamic Observatory, belonging to Jena university is located in a remote area in the Palaeozoic Thuringian Slate Mountains, which however, is characterized by complex subsurface structures with regard to fluid transport and hydrology, including a suspected fault beneath the observatory.

Information about the subsurface beneath the observatory and its geological structures is available from various near-surface geophysical surveys including numerous geo-electrical profiles. These were used to undertake 3D resistivity tomography.

Here we use rock physical measurements, including thermal conductivity, permeability and seismic velocities, on core material from the research drill hole next to the observatory building to characterise the silty greywackes. This data set is complemented by the evaluation of logging data and inspection of long-term temperature data obtained from records of an optical fibre deployed in the borehole to characterize the drilled rocks and identify sections which may favour ground water transport. We also identified fissures from the acoustic televiewer and thus found several depth intervals which could represent a fault zone. Finally we used this information and the results of the resistivity tomography to propose a structural model for the subsurface including the position and type of the suspected fault zone.

How to cite: Kasburg, V., Valchev, T., Goepel, A., Schwarze, C. O., and Kukowski, N.: Identification of a fault zone beneath Moxa observatory (Central Germany): evidence from combining logging, rock physical measurements, and geophysical profiling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8887, https://doi.org/10.5194/egusphere-egu21-8887, 2021.

EGU21-617 | vPICO presentations | SSP1.2 | Highlight

A 220,000-year-long continuous large earthquake record from the central Dead Sea Fault

Yin Lu, Nadav Wetzler, Nicolas Waldmann, Amotz Agnon, Glenn Biasi, and Shmuel Marco

Large earthquakes (magnitude ≥ 7.0) are rare, especially along slow-slipping plate boundaries. Lack of large earthquakes in the instrumental record enlarges uncertainty of the recurrence time; the recurrence of large earthquakes is generally determined by extrapolation according to a magnitude-frequency relation. We enhance the seismological catalog of the Dead Sea Fault Zone by including a 220,000-year-long continuous large earthquake record based on seismites from the Dead Sea center (ICDP Core 5017-1). We constrain seismic shaking intensities via computational fluid dynamics modeling and invert them for earthquake magnitude. Our analysis shows that the recurrence time of large earthquakes follows a power-law distribution, with a mean of ≤ 1400±160 years. This mean recurrence is significantly shorter than the previous estimate of 11,000 years for the past 40,000 years. Our unique record confirms a clustered earthquake recurrence pattern and a group-fault temporal clustering model, and reveals an unexpectedly high seismicity rate on a slow-slipping plate boundary.

Our results suggest that researchers may underestimate the seismic hazard potential of similar slow-slipping faults with irregular rupture. Our study highlights the potential of in situ deformed sediment layers in a subaqueous environment as a strong-motion paleo-seismometer to record long seismic sequences covering multiple recurrence intervals of large earthquakes. Long records are vital for accurate hazard assessment. Our quantitative method of seismic record reconstruction, with paleo-earthquake intensity (ground acceleration) and magnitude estimation, may also prove suitable for similar subaqueous environments along other faults.

How to cite: Lu, Y., Wetzler, N., Waldmann, N., Agnon, A., Biasi, G., and Marco, S.: A 220,000-year-long continuous large earthquake record from the central Dead Sea Fault, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-617, https://doi.org/10.5194/egusphere-egu21-617, 2021.

EGU21-5321 | vPICO presentations | SSP1.2 | Highlight

Half-precession signals in Lake Ohrid and their spatial and temporal connection to proxy records in the European realm

Arne Ulfers, Christian Zeeden, Silke Voigt, and Thomas Wonik

Lake Ohrid is located on the Balkan Peninsula between Albania and North Macedonia. It is considered Europe’s oldest lake and thus is a valuable archive for studies that focus on the change of local (hydro-)climate during the last 1.36 million years (e.g., Francke et al. 2016; Wagner et al. 2019). During an International Continental Scientific Drilling Program (ICDP) campaign in 2013, geophysical downhole logging by the Leibniz Institute for Applied Geophysics acquired continuous datasets of physical properties. Additionally, 2100 m of sediment core was obtained from different sites, the deepest with a length of 570 m (Wagner et al. 2014).

Investigations of half-precession (HP) cycles (~9,000 – 12,000 years) have been given only a small role or have been completely neglected in previous cyclostratographic studies. In this study we focus on HP signals in Lake Ohrid and investigate the temporal variability of this signal over the last one million of years. Next to a connection of HP cycles to interglacials, we see a more pronounced correlation of the HP signal to natural gamma radiation logs in the younger part of the record.

We relate the results from Lake Ohrid to a variety of proxy records from the European mainland and marine sediment cores from the Atlantic and the Mediterranean. Certain patterns, such as the increased visibility of the HP signal in interglacials, occur in most records, but differences, like variations in the amplitude modulation of the filtered HP signal, need to be investiagted in more detail. Nevertheless, the HP cycles are contained in all of the investigated sites, although the records are influenced by different climatic systems. This illustrates that HP signals cannot be connected to a certain climatic system, but can occur simultaneously in records with different proxy signal origins.

HP cycles are a relevant part of natural climate variability - also in Europe - and allow a more detailed investiagtion of sedimentary systems.

 

References:

Francke, A., Wagner, B., Just, J., Leicher, N., Gromig, R., Baumgarten, H., … & Giacco, B. (2016). Sedimentological processes and environmental variability at Lake Ohrid (Macedonia, Albania) between 637 ka and the present, Biogeosciences , 13, 1179–1196.

Wagner, B., Wilke, T., Krastel, S., Zanchetta, G., Sulpizio, R., Reicherter, K., …. & Vogel, H. (2014). The SCOPSCO drilling project recovers more than 1.2 million years of history from Lake Ohrid, Sci. Drill. , 17, 19-29.

Wagner, B., Vogel, H., Francke, A., Friedrich, T., Donders, T., Lacey, J. H., … & Zhang, X. . (2019). Mediterranean winter rainfall in phase with African monsoons during the past 1.36 million years, Nature , 573(7773), 256-260.

How to cite: Ulfers, A., Zeeden, C., Voigt, S., and Wonik, T.: Half-precession signals in Lake Ohrid and their spatial and temporal connection to proxy records in the European realm, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5321, https://doi.org/10.5194/egusphere-egu21-5321, 2021.

EGU21-14232 | vPICO presentations | SSP1.2

IODP Expedition 379: Late Miocene to Pleistocene shelf to rise processes in the Amundsen Sea, West Antarctica, from seismic correlation

Karsten Gohl, Johanna Gille-Petzoldt, Gabriele Uenzelmann-Neben, Rachel Lamb, Johann Klages, Julia Wellner, Sandra Passchier, Claus-Dieter Hillenbrand, Steven Bohaty, Frederichs Thomas, and German Leitchenkov and the IODP Expedition 379 Scientists

The West Antarctic Ice Sheet (WAIS) is thought to be highly sensitive to climatic and oceanographic changes. Modelling infers that the WAIS likely had a very dynamic history throughout the Neogene to the present. A complete collapse of the WAIS would result in a global sea level rise of 3.3 to 4.3 m, yet there is large uncertainty on predicting its future behavior and its contribution to sea level rise. Geological constraints on the past behavior of the WAIS are relatively sparse and mainly based on records from the Ross Sea sector. In particular, records of time intervals with climatic conditions similar to those expected for the near and distant future, such as the Pliocene, are needed. Deglaciation of the WAIS in the Amundsen Sea sector is hypothesized to have triggered WAIS collapses during past warm times. Drill records from the International Ocean Discovery Program (IODP) Expedition 379 provide continuous late Miocene to Pleistocene sediment sequences from a drift on the continental rise, allowing the assessment of sedimentation processes from cold and warm times. In particular Site U1532 recovered an expanded sequence of Pliocene lithofacies with an excellent paleomagnetic record allowing for very high-resolution, sub-orbital scale climate change studies of the previously sparsely sampled eastern Pacific sector of the West Antarctic margin. At both Sites U1532 and U1533, sediments characterized by high microfossil content and high abundance of ice-rafted debris alternate with laminated terrigenous muds and are interpreted to result from cyclic deposition under interglacial and glacial conditions, respectively. Deep-sea channels likely mark the pathways of terrigenous detritus that was transported downslope from the Amundsen Sea shelf via turbidity currents or other gravitational transport processes predominantly during glacial periods. The association of lithological facies predominantly reflects an interplay of these downslope and contouritic sediment transport processes as well as phases of increased pelagic and hemipelagic sediment input. Correlation of the seismic stratigraphy at the drill sites on the rise with that of the continental shelf of the Amundsen Sea Embayment allowed us to identify massive prograding sequences that expanded the outer shelf seaward by about 80 km by frequent advances of grounded ice across the shelf mainly during Pliocene times. The preservation of buried grounding zone wedges visible in seismic profiles from the shelf is explained by (hemi)pelagic sedimentation during prolonged periods of ice retreat. This can be correlated with an extended warm middle Pliocene period chronologically constrained by the drill records. The contrast between sediments deposited under cold and warm climate conditions indicates that this WAIS sector was highly dynamic in the Pliocene.

How to cite: Gohl, K., Gille-Petzoldt, J., Uenzelmann-Neben, G., Lamb, R., Klages, J., Wellner, J., Passchier, S., Hillenbrand, C.-D., Bohaty, S., Thomas, F., and Leitchenkov, G. and the IODP Expedition 379 Scientists: IODP Expedition 379: Late Miocene to Pleistocene shelf to rise processes in the Amundsen Sea, West Antarctica, from seismic correlation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14232, https://doi.org/10.5194/egusphere-egu21-14232, 2021.

EGU21-14391 | vPICO presentations | SSP1.2 | Highlight

IODP Exp. 374 provides clues into the Antarctic Ice Sheet contribution to sea level changes

Laura De Santis, Denise Kulhanek, and Robert McKay

The five sites drilled during International Ocean Discovery Program (IODP) Expedition 374 recovered the distal geological component of a Neogene latitudinal and depth transect across the Ross Sea continental shelf, slope and rise, that can be combined with previous records of ANDRILL and the Deep Sea Drilling Project Leg 28. This transect provides clues into the ocean and atmospheric forcings on marine ice sheet instabilities and provides new direct constraints for reconstructing the Antarctic Ice Sheet contribution to global sea level change. Site U1521 recovered a middle Miocene record that allows identification of the different processes that lead to the expansion and retreat of ice streams emanating from the East and West Antarctic Ice Sheets across the Ross Sea continental shelf. This site also recovered a semi-continuous, expanded, high-resolution record of the Miocene Climatic Optimum in an ice-proximal location. Site U1522 recovered a Pleistocene to upper Miocene sequence from the outer shelf, dating the step-wise continental shelf–wide expansion and coalescing of marine-based ice streams from West Antarctica. Thin diatom-rich mudstone and diatomite beds were recovered in some intervals that provide snapshot records of a deglaciated outer shelf environment in the late Miocene. Site U1523 targeted a Miocene to Pleistocene sediment drift on the outermost continental shelf and informs about the changing vigor of the eastward flowing Antarctic Slope Current (ASC) through time. Changes in ASC vigor is a key control on regulating heat flux onto the continental shelf, making the ASC a key control on ice sheet mass balance. Sites U1524 and U1525 cored a continental rise levee system near the flank of the Hillary Canyon. The upper ~50 m at Site U1525 belong to a large trough-mouth fan deposited to the west of the site. The lower 100 m at Site U1525 and the entire 400 m succession of sediment at Site U1524 recovered near-continuous records of the downslope flow of Ross Sea Bottom Water and turbidity currents, but also of ASC vigor and iceberg discharge. Analyses of Exp. 374 sediments is ongoing, but following initial shipboard characterization, the intial results of sample analysis, the correlation between downhole synthetic logs and the associated seismic sections provide insight into the ages and the processes of erosion and deposition of glacial and marine strata. Exp. 374 sediments are providing key chronological constraints on the major Ross Sea seismic unconformities, enabling reconstruction of paleo-bathymetry and assessment of the geomorphological changes associated with Neogene ice sheet and ocean circulation changes. Exp. 374 results are fundamental for improving the boundary conditions of numerical ice sheet, ocean, and coupled climate models, which are critically required for understanding past ice sheet and global sea level response during warm climate intervals. Such data will enable more accurate predictions of ice sheet behavior and sea level rise anticipated with future warming. 

How to cite: De Santis, L., Kulhanek, D., and McKay, R.: IODP Exp. 374 provides clues into the Antarctic Ice Sheet contribution to sea level changes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14391, https://doi.org/10.5194/egusphere-egu21-14391, 2021.

EGU21-11360 | vPICO presentations | SSP1.2 | Highlight

Quaternary Environmental Changes in the Corinth Rift Area: the IODP 381 Palynological Record

Eugenia Fatourou, Aikaterini Kafetzidou, Konstantinos Panagiotopoulos, Fabienne Marret, Sofia Papadopoulou, Katerina Kouli, and the Expedition 381 Science Team

The new sedimentary record from the Gulf of Corinth (south Greece), retrieved within the IODP Exp. 381: Corinth Active Rift Development, is a new archive registering environmental and climatic variability continuously over the last one million years. The Gulf of Corinth, strategically located at the southernmost tip of the Balkan Peninsula, is a semi-enclosed basin that is sensitive to climate forcing and sea level fluctuations. The Gulf was repeatedly isolated from the Mediterranean Sea during glacial/low-stand intervals, resulting in the amplification of paleoenvironmental gradients (McNeill et al., 2019).

The “Quaternary Environmental Changes in the Corinth Rift Area: the IODP 381 palaeovegetation record (QECCoRA)” project aims to analyse how climate variability affected the development of local vegetation and marine ecosystems in response to glacial/interglacial cycles, using palynological analysis (terrestrial and aquatic palynomorphs). The main goals are: a) to study the glacial-interglacial vegetation history in the southernmost Balkan tree refugium at a millennial scale b) to constrain the timing of Quaternary extinctions of relict tree taxa, and c) to decipher the alternation between marine and isolated intervals and its impact on aquatic ecosystems and the depositional environment using the aquatic palynomorph record.

The first results of the microscopic analysis show significant shifts of the vegetation composition in response to climate variability, nevertheless the fluctuation in vegetation cover appears less pronounced. Dinoflagellate cysts show distinct alternations between marine and brackish conditions revealing changes in surface water salinity, productivity, and temperature. Ongoing palynological analysis will produce a skeleton paleoenvironmental record that will contribute to further analyses carried out within the IODP Exp. 381 Science team.

 

The QECCoRA project is supported by the Hellenic Foundation of Research and Innovation (H.F.R.I., Project Number: 1026)

 

Reference

McNeill LC, Shillington DJ, Carter GDO, Everest J, Gawthorpe R, Miller C, Phillips M, Collier R, Cvetkoska A, De Gelder G, Diz Ferreiro P, Doan M-L, Ford M, Geraga M, Gillespie J, Hemelsdael R, Herrero-Bervera E, Ismaiel M, Janikian L, Kouli K, Le Ber E, Li S, Maffione M, Mahoney C, Machlus M, Michas G, Nixon C, Oflaz SA, Omale A, Panagiotopoulos K, Pechlivanidou S, Sauer S, Seguin J, Sergiou S, Zhakarova N, Green S, High-resolution record reveals climate-driven environmental and sedimentary changes in an active rift, Scientific Reports, 9:3116, 2019, https://doi.org/10.1038/s41598-019-40022-w

How to cite: Fatourou, E., Kafetzidou, A., Panagiotopoulos, K., Marret, F., Papadopoulou, S., Kouli, K., and 381 Science Team, T. E.: Quaternary Environmental Changes in the Corinth Rift Area: the IODP 381 Palynological Record, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11360, https://doi.org/10.5194/egusphere-egu21-11360, 2021.

EGU21-11278 | vPICO presentations | SSP1.2

Pleistocene sea surface temperature, monsoonal hydrological variability and OMZ extension in the Northern Indian Ocean (Maldives Sea)

Montserrat Alonso-García, Teresa Rodrigues, Carlos Alvarez-Zarikian, Mária Padilha, Chimnaz Diana Nadiri, Mayuri Inoue, Hodaka Kawahata, and Fatima Abrantes

The Maldives Inner Sea is a natural sediment trap located in the northern Indian Ocean affected by the South Asian Monsoon (SAM) seasonal reversing wind and precipitation patterns, which drives modern oceanography in the region, including variations in oceanic productivity and in the extension of the oxygen minimum zone (OMZ) of the Northern Indian Ocean. In 2015, International Ocean Discovery Program (IODP) Expedition 359 drilled eight sites (U1465-U1472) in the Maldives Inner Sea aligned in two east-west transects north and south of the Goidhoo atoll in order to unravel the unread history of this region intimately linked to the SAM. In this work, we studied mid and late Pleistocene sediments from IODP Site U1467 (4°51.031′N, 73°17.020′E; 487 m water depth). Our study is focused on the last ~1.2 Ma in order to evaluate changes in the SAM linked to the emergence of the 100 ka cycles during the Mid-Pleistocene Transition (MPT). Lipid biomarkers have been analyzed with the aim of reconstructing sea surface temperature (SST, using the alkenone unsaturation index, Uk’37), past surface ocean productivity (using total alkenone concentration) and bottom water oxygenation (BWO, using a ratio between n-alkan-1-ols and n-alkanes). Additionally, data from scanning x-ray fluorescence (XRF) from this site has been used to provide information about the winter and summer monsoon intensity and ostracod assemblages allowed us to identify changes in BWO and possibly the influence of Antarctic Intermediate water in the region.

At present, seasonal SST variation is rather small in the Maldives Inner Sea (less than 1ºC) and our reconstructed SST record also shows very small variability between glacial and interglacial periods (less than 1ºC), but with strong coherence with other Indian Ocean and equatorial records. Our SST record shows rather warm temperatures before MIS 30, with muted glacial-interglacial variability. After MIS 30, both glacial and interglacial temperatures show a decreasing trend until MIS 22, which represents the first interval with considerably colder glacial SST. Between MIS 22 and 13, SST remains relatively warm, not showing large changes between glacial and interglacial periods. It is remarkable the absence of lukewarm interglacials during this interval. The BWO record shows a similar pattern and can also be divided in the same intervals. BWO starts to increase during glacial periods at MIS 22, which is supported by the ostracod assemblages. This indicates a contraction of the OMZ during glacial periods. Starting at MIS 12, glacial periods show colder glacial SST and enhanced ventilation. The terrigenous elements (K, Fe, Al, Ti) from XRF suggest an increase in aridity at MIS 22, with stronger winter monsoon (higher aridity) during glacial periods, in agreement with the n-alkanes record. The comparison of IODP Site U1467 reconstructions with other records provides key information to improve our understanding of the evolution of SAM, global climate and ocean circulation during the Pleistocene.

How to cite: Alonso-García, M., Rodrigues, T., Alvarez-Zarikian, C., Padilha, M., Nadiri, C. D., Inoue, M., Kawahata, H., and Abrantes, F.: Pleistocene sea surface temperature, monsoonal hydrological variability and OMZ extension in the Northern Indian Ocean (Maldives Sea), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11278, https://doi.org/10.5194/egusphere-egu21-11278, 2021.

EGU21-10739 | vPICO presentations | SSP1.2

Footprints of palaeocurrents in sedimentary sequences of the Cenozoic across the Maurice Ewing Bank

Banafsheh Najjarifarizhendi and Gabriele Uenzelmann-Neben

High-resolution 2D multichannel seismic data collected by the Alfred Wegener Institute in 2019 across the Maurice Ewing Bank, the high-altitude easternmost section of the Falkland Plateau in the SW South Atlantic, are integrated with information from DSDP Leg 36, Sites 327, 329, and 330 and Leg 71 Site 511. A seismostratigraphic model is defined, including five units ranging in age from the Middle Jurassic to Quaternary and are interpreted with respect to the evolutional history of the oceanic circulations in the South Atlantic sector of the Southern Ocean. Sedimentary sequences of late Cretaceous and early Paleogene include little and restricted evidence of current activity, attributable to shallow-intermediate depth connections between the developing South Atlantic and Southern Ocean. In contrast, sedimentary sequences of the late Eocene/Oligocene and Neogene reveal a strong history of current-related erosion and deposition. These features exhibit specific water-depth expressions attesting to the long-term activity of different water masses, in stable circulation patterns as those of the present day. We thus suggest that proto-Upper and -Lower Circumpolar Deep Waters have been shaping the bank since the Oligocene. This implies that this bathymetric high has been acting as a barrier for the deep and bottom water masses flowing within the Antarctic Circumpolar Current since its establishment about the Eocene-Oligocene boundary.

How to cite: Najjarifarizhendi, B. and Uenzelmann-Neben, G.: Footprints of palaeocurrents in sedimentary sequences of the Cenozoic across the Maurice Ewing Bank, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10739, https://doi.org/10.5194/egusphere-egu21-10739, 2021.

EGU21-7844 | vPICO presentations | SSP1.2

The Upper Cretaceous foraminiferal record of IODP Site U1512 (Great Australian Bight, Indian Ocean)

Erik Wolfgring, Michael A. Kaminski, Anna Waśkowska, Maria Rose Petrizzo, Eun Young Lee, Carmine Wainman, and Trine Edvardsen

Site U1512 was drilled during Expedition 369 of the International Ocean Discovery Program (IODP), which is located in the Great Australian Bight, southern Indian Ocean. It provides exceptional insights into the benthic foraminiferal biostratigraphy and paleoecology of a high southern latitude restricted marginal marine basin during the Late Cretaceous hot greenhouse climate and the rifting between Australia and Antarctica. The sedimentary sequence recovered at Site U1512 presents a rare record of a deep water agglutinated foraminifera (DWAF) community from the Southern High Latitudes. The Cretaceous record at Site U1512 covers the lower Turonian through Santonian (nannofossil zones UC8b to UC12/CC10b to CC16, H. helvetica to Marginotruncana spp. - Planoheterohelix papula - Globotruncana linneana planktonic foraminifera zones). Diverse benthic foraminiferal assemblages yield many new taxa that are yet to be described.

Agglutinated forms dominate the assemblage in most intervals. In lower to mid Turonian and Santonian strata, calcareous benthic as well as planktonic foraminifera are frequent. Abundant radiolaria are recovered from the mid Turonian, and they increase up-section and exceed 50% of the microfossil assemblage. We documented a diverse benthic foraminiferal assemblage consisting of 162 taxa (110 agglutinated and 52 calcareous). The most common taxa of the DWAF assemblage are tubular (i.e., Kalamopsis grzybowskii, Bathysiphon spp.) and planispiral forms (i.e., Ammodiscus spp., Haplophragmoides spp., Buzasina sp., Labrospira spp.).

The Turonian strata yield highly abundant Bulbobaculites problematicus and Spiroplectammina navarroana. The presence of the agglutinated foraminiferal marker taxa Uvigerinammina jankoi and Bulbobaculites problematicus provides a tie-point to the Tethyan DWAF biozonation of Geroch and Nowak (1984). The composition of foraminiferal assemblages and the increase in radiolaria abundance suggest unstable environmental conditions at Site U1512 during the early Turonian through Santonian. These characteristics refer to changes in bathymetry associated with changing ocean chemistry. Results of quantitative analyses of the benthic foraminiferal assemblages indicate a restricted paleoenvironmental regime, dictated by changes in paleobathymetry, unstable patterns in ocean circulation, and the discharge of a nearby river delta system.

References: Geroch, S., Nowak, K., 1984. Proposal of zonation for the Late Tithonian – late Eocene. based upon arenaceous Foraminifera from the Outer Carpathians, Poland, 225-239, In: Oertli, H.J. (Ed.), Benthos ´83; 2nd international 915 Symposium on Benthic Foraminifera, Pau (France) April 11-15, 1983, Elf Aquitaine, ESO REP and TOTAL CFP, Pau and Bordeaux.

 

How to cite: Wolfgring, E., Kaminski, M. A., Waśkowska, A., Petrizzo, M. R., Lee, E. Y., Wainman, C., and Edvardsen, T.: The Upper Cretaceous foraminiferal record of IODP Site U1512 (Great Australian Bight, Indian Ocean), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7844, https://doi.org/10.5194/egusphere-egu21-7844, 2021.

EGU21-6414 | vPICO presentations | SSP1.2

Effect of early Oligocene cooling on the deep-sea benthic foraminifera at IODP hole 1138A, Kerguelen Plateau (Southern Ocean)

Rakesh Kumar, Abhayanand Singh Maurya, and Dharmendra Pratap Singh

Benthic foraminifera are typical unicellular marine fauna forming calcareous tests that are commonly used as a proxy to infer the past climatic variabilities. To study the benthic foraminiferal response, we collected 146 samples from IODP hole 1138A, the Southern Ocean (Indian Sector, water depth of 1140 m). We computed various diversity parameters of benthic foraminifera, i.e., Shannon-weaver index (H(S)), Equitability (E'), Hurlbert's diversity index (Sm), Fisher's alpha index (α), and Species richness (S). The calculated diversity indices with the abundance of dominant early Oligocene (33.5 to 31.2 million years ago) benthic foraminifera taxa reveal significant palaeoceanographic changes viz. cooling and warming events in the Southern Ocean. The early Oligocene interval exhibits an unusual condition at hole 1138A dominated by high oxygen species, intermediate food supply, well-ventilated, cold, and corrosive bottom water condition. The calculated values of all diversity parameters increase from 33.7 Ma to 32.8 Ma while attaining the maximum from 32.8 Ma to 32.2 Ma, followed by a decreasing trend. The highest value of diversity parameters coincides with the Oi-1 events. The relative increase in the species diversity between Oi-1 (33.5 Ma) and Oi-1b (31.7 Ma) events correspond to the brief interruption of Warm Saline Deep Water (WSDW). The enhanced values of low species diversity by high seasonality and relatively cold, strong bottom-water currents after Eocene-Oligocene Transition (EOT; 33.9 Ma) and after Oi-1b (31.7 Ma) event relates to the intensification of Antarctic Circumpolar Current (ACC) and Antarctic Bottom Water (AABW) along with the substantial buildup of the southern hemisphere glaciation. The abrupt decrease of abundance of species such as Nuttallides umbonifera, Astrononion echolsi, and Uvigerina peregerina at the end of the studied interval (31.3 Ma) further corroborates the major southern hemisphere glaciation. The present study of the benthic foraminiferal abundance and diversity indices therefore reveals the cooling of the Southern Ocean at early and late stages of the studied interval interrupted by a short-lived warming event. The study further enhances the understanding of paleo-marine ecology by evaluating the response of deep-sea benthic foraminifera to global climate change.

Keywords: Kerguelen Plateau, Benthic Foraminifera, Southern Ocean, early Oligocene

How to cite: Kumar, R., Maurya, A. S., and Singh, D. P.: Effect of early Oligocene cooling on the deep-sea benthic foraminifera at IODP hole 1138A, Kerguelen Plateau (Southern Ocean), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6414, https://doi.org/10.5194/egusphere-egu21-6414, 2021.

EGU21-3152 | vPICO presentations | SSP1.2

Disentangling controls and orbital pacing of South-East Atlantic carbonate deposition since the Oligocene (30-0 Ma)

Anna Joy Drury, Diederik Liebrand, Thomas Westerhold, Helen M. Beddow, David A. Hodell, Nina Rohlfs, Roy H. Wilkens, Mitchell W. Lyle, David B. Bell, Dick Kroon, Heiko Pälike, and Lucas J. Lourens

The evolution of Cenozoic climate since 30 million years ago (Ma) has broadly chartered the transformation from a unipolar to a bipolar world. Highly resolved records of carbonate content (%CaCO3) can provide insight into regional responses to shifting climate, cryosphere and carbon cycle dynamics. Here, we generate the first South-East Atlantic %CaCO3 record spanning 30-0 Ma, derived from X-ray fluorescence (XRF) ln(Ca/Fe) data collected at Ocean Drilling Program Site 1264, located on the Angola Basin side of the Walvis Ridge (SE Atlantic Ocean). We present a comprehensive and continuous depth and age model for the entirety of Site 1264 (~316 m; 30-0 Ma), which constitutes a key reference framework for future palaeoclimatic and palaeoceanographic studies at this location.

We can identify three phases with a distinct orbital imprint on South-East Atlantic CaCO3 deposition, broadly occurring across major developments in climate, the cryosphere and/or the carbon cycle: 1) strong ~110 kyr eccentricity pacing prevails during Oligo-Miocene global warmth (~30-13 Ma); 2) eccentricity-modulated precession imprints more strongly after the mid Miocene Climate Transition (mMCT) (~14-8 Ma); 3) strong obliquity pacing prevails in the late Miocene (~7.7-3.3 Ma) following the increasing influence of high-latitude processes.

The lowest %CaCO3 (92-94%) occur between 18.5-14.5 Ma, potentially reflecting increased dissolution or decreased productivity, probably caused by widespread early Miocene warmth. Around 14 Ma, the increased sensitivity to precession at Site 1264 is associated with an increase in mass accumulation rates (MARs) and could reflect increased regional CaCO3 productivity and/or an influx of less corrosive deep water following regional changes in surface and/or deep-water circulation after Antarctic reglaciation across the mMCT.

The highest %CaCO3 and MARs indicate the late Miocene Biogenic Bloom (LMBB) occurs between ~7.8-3.3 Ma at Site 1264, which is broadly, but not exactly, contemporaneous with the LMBB in the equatorial Pacific Ocean. Global similarities in the expression of the LMBB may reflect an increased nutrient input into the global ocean resulting from enhanced aeolian dust and/or glacial/chemical weathering fluxes, whereas regional variability in the timing and amplitude of the LMBB may be driven by regional differences in cooling, continental aridification and/or changes in ocean circulation during the latest Miocene.

How to cite: Drury, A. J., Liebrand, D., Westerhold, T., Beddow, H. M., Hodell, D. A., Rohlfs, N., Wilkens, R. H., Lyle, M. W., Bell, D. B., Kroon, D., Pälike, H., and Lourens, L. J.: Disentangling controls and orbital pacing of South-East Atlantic carbonate deposition since the Oligocene (30-0 Ma), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3152, https://doi.org/10.5194/egusphere-egu21-3152, 2021.

EGU21-2600 | vPICO presentations | SSP1.2

Using borehole gamma-ray spectroscopy to detect tephra layers in lacustrine deposits: An example from Lake Chalco, central Mexico 

Mehrdad Sardar Abadi, Christian Zeeden, Arne Ulfers, Katja Hesse, and Thomas Wonik

Lacustrine sediments are archives of past environmental conditions. In recent decades, multinational ICDP efforts have conducted lake drilling projects to encode the potential of paleoclimate signals. Gamma-ray spectroscopy is a particularly useful tool as it is non-destructive, fast, and affordable even in cased boreholes. Gamma radiation can be used to identify elemental isotopes in the geological record, which is used for stratigraphic correlation and paleoclimatic investigations. 

However, some lake sediments contain tephra layers with specific gamma-ray signatures, presenting a challenge for extracting the primary signals caused by environmental and climatic agents. Here, we use the sediments of Lake Chalco in central Mexico to propose a protocol to identify tephra layers embedded in other sediments using high-resolution spectral gamma-ray spectroscopy. This facilitates dividing the overall sediment column into representative horizons of tephra and non-tephra.

Among the upper 300 m of the lake deposit, our index detected 363 tephra layers, while 388 total tephra layers (≥1 mm in thickness) were reported from the core description of the same borehole, predicting 92% of tephra layers documented in the lake deposits from core descriptions. We suggest that not only the strength of the gamma-ray signal but also the composition of its constituent energy channels can be used to detect embedded tephra layers.

How to cite: Sardar Abadi, M., Zeeden, C., Ulfers, A., Hesse, K., and Wonik, T.: Using borehole gamma-ray spectroscopy to detect tephra layers in lacustrine deposits: An example from Lake Chalco, central Mexico , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2600, https://doi.org/10.5194/egusphere-egu21-2600, 2021.

EGU21-1232 | vPICO presentations | SSP1.2 | Highlight

Himalayan-Tibetan Erosion is not the Cause of Neogene Global Cooling

Peter Clift and Tara Jonell

Does uplift and erosion of the Himalaya-Tibetan Plateau drive Cenozoic global cooling? We test this classic hypothesis put forward by Raymo and Ruddiman (1992) that suggests enhanced erosion in the Himalaya-Tibetan Plateau drove long-term Cenozoic global cooling through the chemical weathering of siliciclastic sediment. Here we examine three Asian marginal drainage systems (the Indus, Mekong and Pearl) where marine scientific drilling has yielded detailed seismic surveys and geochemical datasets that critically permit sediment mass flux and therefore chemical weathering flux budgets to be made. By compiling suitable bedrock endmember compositions for the fresh bedrock sources, it is possible to calculate the chemical weathering flux and relative CO2 consumption rates for each drainage system into the early Miocene. We correct for evolving provenance of sediment delivered to the offshore and test the sensitivity of our calculations to selected bedrock endmembers, in light of the abundant mafic bedrock exposed Indus and Mekong systems. Appropriate Upper Continental Crust endmembers were further validated using data compiled from the GEOROC database. Regardless of which endmembers were used, calculations demonstrate that the total rate of CO2 consumption decreased by 50% between ~16 and 5.3 Ma, especially within NW Himalaya as onshore erosion slowed and provenance shifted away from mafic arc units in the suture zone. This direct test of the uplift-erosion-weathering hypothesis establishes that chemical weathering fluxes did not increase during the Neogene and cannot be responsible for the drawdown of atmospheric CO2 during that time period. Either additional mechanisms have been driving global cooling since 16 Ma or CO2 consumption via chemical weathering is taking place in other areas outside the Himalaya-Tibetan Plateau.

How to cite: Clift, P. and Jonell, T.: Himalayan-Tibetan Erosion is not the Cause of Neogene Global Cooling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1232, https://doi.org/10.5194/egusphere-egu21-1232, 2021.

EGU21-16035 | vPICO presentations | SSP1.2

Trace metal concentrations and OH defects in quartz from Amazon River sands & and perspectives for application to the marine record

Dominik Jaeger, Roland Stalder, Cristiano Chiessi, André Sawakuchi, and Michael Strasser

EGU21-13902 | vPICO presentations | SSP1.2

Evidence of 8.2-ka event in Southeast Asia inferred from marginal marine sediments off Kallang River Basin, Singapore

Yama Dixit, Stephen Chua, Yu Ting Yan, and Adam Switzer

The Maritime Continent (MC) is located within the Indo-Pacific Warm Pool, which is known as the largest area of warm sea surface temperatures with the highest rainfall on Earth that drives the global atmospheric and hydrologic circulation. The complex climatic system of the MC is controlled by large-scale phenomena such as the seasonal migration of the Intertropical Convergence Zone which causes the northwest and southeast monsoon circulation in the region as well as tropical Indo-Pacific climate phenomena, the Indian Ocean Dipole in the west and the El Niño-Southern Oscillation operating to the east of the MC. In addition to interactions of these climate phenomena, their influence varies across the region due to island topography and ocean–atmosphere fluxes. Despite dedicated efforts, a comprehensive picture of the impacts of abrupt climate events such as the ‘8.2 ka event’ during the Holocene on the MC has proved elusive. Here we use sedimentology and stable isotopes of benthic foraminifera collected from the marginal marine sediments off the Kallang River Basin, Singapore to reconstruct paleoenvironmental history of the early-mid Holocene. Owing to the high sedimentation rate (~4.4 mm/yr), the timing and nature of the ‘8.2 ka event’ was examined in detail in this region making this an invaluable and unique archive to study up to sub-centennial changes. Comparison of the Kallang record with other high-resolution marine and absolutely dated terrestrial archives speleothems revealed that the timing of the onset of ‘8.2 ka event’ in the western IPWP region lags the cooling in the North Atlantic and that of Asian and Indian monsoon failure, by ~100years possibly implying a north-south signal propagation. The termination of the ‘8.2 ka event’, however may have occurred near synchronously between high and low tropical regions at ~7.96ka BP possibly linked via both atmospheric and oceanic processes.

 

How to cite: Dixit, Y., Chua, S., Yan, Y. T., and Switzer, A.: Evidence of 8.2-ka event in Southeast Asia inferred from marginal marine sediments off Kallang River Basin, Singapore, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13902, https://doi.org/10.5194/egusphere-egu21-13902, 2021.

EGU21-8980 | vPICO presentations | SSP1.2

Alternatives to zircon in sedimentary provenance analysis: A case study in detrital garnet U-Pb and trace-element analysis
not presented

Chris Mark, Laura Stutenbecker, Sergio Andò, Gary O'Sulivan, and J. Stephen Daly

Provenance analysis of clastic sediment is a powerful tool to track the evolution of hinterland tectonics and sediment routing systems, for which detrital U-Pb geochronology has proved a popular and rapidly-growing technique. However, >90% of published studies employ zircon (3,691/3,933 results for the keywords detrital geochronology; Clarivate Analytics Web of Science), a mineral which exhibits strong fertility bias towards felsic to intermediate igneous sources, and is rare in metamorphic settings in the absence of anatexis (e.g., Moecher & Samson, 2006). Thus, the development of complementary proxies is desirable. Garnet group minerals are particularly promising because garnet is dominantly formed in metamorphic settings and is a rock-forming mineral in several common metamorphic lithologies; it is thus typically abundant in clastic sediment sourced from orogenic terranes. Moreover, it can incorporate sufficient U to be dated in-situ by the U-Pb method (e.g., Millonig et al., 2020).

Here we focus on the Oligo-Miocene pro-foreland basin of the European Alps. Evolving from a distal marine to a fluvial-alluvial environment affected by at least one major marine incursion, the basin preserves a rich record of tectonic and climatic change in the hinterland. We report detrital garnet U-Pb and trace-element data acquired by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), which we integrate with compositional data obtained by energy- and wavelength-dispersive X-ray spectroscopy (Stutenbecker et al., 2019), and crystallographic data from Raman spectroscopy. We integrate these results with detrital apatite, rutile, and zircon U-Pb data, and discuss the implications for Alpine tectonics and drainage evolution, and future potential for detrital garnet U-Pb analysis.    

Millonig, L., et al., 2020. Earth Planet. Sci. Lett. 552, 116589, doi: 10.1016/j.epsl.2020.116589

Moecher, D., & Samson, S., 2006, Earth Planet. Sci. Lett. 247, 252–266, doi: 10.1016/j.epsl.2006.04.035

Stutenbecker, L., et al., 2019, Solid Earth 10, 1581–1595, doi: 10.5194/se-10-1581-2019

How to cite: Mark, C., Stutenbecker, L., Andò, S., O'Sulivan, G., and Daly, J. S.: Alternatives to zircon in sedimentary provenance analysis: A case study in detrital garnet U-Pb and trace-element analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8980, https://doi.org/10.5194/egusphere-egu21-8980, 2021.

EGU21-8738 | vPICO presentations | SSP1.2

Reconstructing provenance changes in sediments supplying the South East African margin

Ellie Pryor, Ian Hall, Morten Andersen, Daniel Babin, Yue (Merry) Cai, Steven Goldstein, Sidney Hemming, Jeroen van der Lubbe, and Margit Simon

Sediment provenance is of key importance for understanding transport history and characterising sediment source regions in the marine and terrestrial environment. Radiogenic isotopes are widely used to identify inland and coastal sediment origins. They document changes in detrital terrigenous sediment fluxes which can be related to continental hydrological variability. Understanding sediment sources to the ocean is a pre-requisite before interpreting past climate archives in marine sediment cores.

South African coastal drainage basins are composed of various geological units, each reflected by different radiogenic isotope signals in the sediment. In addition to the age and nature of their source rocks, the sediment type influences this radiogenic signature.

Here, we present a review of the present-day radiogenic isotopic fingerprints of South African river catchments signals from new river sediment samples with the aim to gain a broad spatial coverage of the source rocks in the region and their relative contributions of terrigenous sediment delivered to the ocean. This information will be applied to marine sediment core MD20-3591 (36° 43.707 S; 22° 9.151 E, water depth 2464m), located offshore South Africa which has the potential to record both Agulhas Current and terrestrial variability. The core site receives a significant amount of terrigenous material from the African continents via riverine input. During the last glacial period, these rivers flowed across the continental shelf within a subdued incised valley. The Gourritz River catchment drains the Cape Supergroup and Karoo Supergroup, typical of these southern drainage basins, whereas the eastern Cape rivers drain the Karoo Supergroup geological unit which is capped by the Drakensberg basalts.

We are using the knowledge gained from these new South African terrestrial river sediment samples to identify the sources and transport pathways of the terrigenous sediments in MD20-3591. Of particular interest is the sensitivity of the radiogenic isotopic signatures to grain size variabilities and how this relationship can help to define local or distal sediments. These records will allow us to explore variability in regional hydroclimate in relation to the abundant archaeological evidence of cultural and technological innovations of Middle Stone Age humans in southern Africa.

How to cite: Pryor, E., Hall, I., Andersen, M., Babin, D., Cai, Y. (., Goldstein, S., Hemming, S., van der Lubbe, J., and Simon, M.: Reconstructing provenance changes in sediments supplying the South East African margin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8738, https://doi.org/10.5194/egusphere-egu21-8738, 2021.

EGU21-6250 | vPICO presentations | SSP1.2

Geochemical evidence of tropical cyclone controls on shallow-marine sedimentation (Pliocene, Taiwan) 

Shahin Dashtgard, Ludvig Löwemark, Pei-Ling Wang, Romy Setiaji, Yu-Yen Pan, and Romain Vaucher

 Shallow-marine sediment typically contains a mix of marine and terrestrial organic mate­rial (OM). Most terrestrial OM enters the ocean through rivers, and marine OM is incorpo­rated into the sediment through both suspension settling of marine plankton and sediment reworking by tides and waves under fairweather conditions. River-derived terrestrial OM is delivered year-round, although sediment and OM delivery from rivers is typically highest during extreme weather events that impact river catchments. In Taiwan, tropical cyclones (TCs) are the dominant extreme weather event, and 75% of all sediment delivered to the surrounding ocean occurs during TCs.

Lower Pliocene shallow-marine sedimentary strata in the Western Foreland Basin of Taiwan comprises mainly completely bioturbated intervals that transi­tion upward into strata dominated by tidally generated sedimentary structures, indicating extensive sediment reworking under fairweather conditions. Physical evidence of storm deposition is limited. However, lower Pliocene strata contain OM that is effectively 100% terrestrial OM in sediment that accumulated in estimated water depths <35 m. The overwhelming contribution of terrestrially sourced OM is attributed to the dominance of TCs on sedimentation, whereby ∼600,000 TCs are estimated to have impacted Taiwan during accumulation of a ~200 m long succession. In contrast, the virtual absence of marine OM indicates that organic contributions from suspension settling of marine OM is negligible regardless of the preserved evidence of extensive reworking via fairweather processes (i.e., waves and tides). These data suggest that (1) even in the absence of physical expressions of storm deposition, TCs still completely dominate sedimentation in shallow-marine environments, and (2) the organic geochemical signal of preserved shallow-marine strata is not reflective of day-to-day depositional conditions in the environment.

How to cite: Dashtgard, S., Löwemark, L., Wang, P.-L., Setiaji, R., Pan, Y.-Y., and Vaucher, R.: Geochemical evidence of tropical cyclone controls on shallow-marine sedimentation (Pliocene, Taiwan) , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6250, https://doi.org/10.5194/egusphere-egu21-6250, 2021.

The late Miocene provides the chance to assess the changing boundary conditions on a warmer world than present. While the climate variability is well understood for the oceanographic records, the water availability and dynamics in terrestrial environment in the densely populated East Asian remains enigmatic. Little is known about the precipitation response to the Antarctic ice-sheets during this time interval. To understand this critical relationship between low- and high-latitude climates, we use a new indicator based on the carbonate variability in Red Earth on the northern Chinese Loess Plateau to reconstruct water availability throughout the interval (7.5–6.9 Ma). Our high-resolution reconstructions show that the carbonate leaching/reprecipitation cycle is dominantly forced by the astronomical parameter obliquity (40-kyr) that is in accord with the Antarctic ice-volume controlled oceanography records at ~7 Ma. Supported by goethite and hematite records in the same site, soil temperatures and precipitations are fully coupled, interpreted as marking the climate pattern of Asian monsoon during the late Miocene. Cyclic correlation between the carbonate variability and the goethite, hematite data, reveal that the obliquity controlled precipitation oscillations were superimposed on a long-term increase of the Asian monsoon, which was synchronous with intensifification of climate cooling, the declining of partial pressure of carbon dioxide, and the growing of Antarctic ice-volume. Combined with the atmospheric- and oceanic-adjustments, we suggest that the cross-equatorial pressure gradient has led to the rise of Asian monsoon.

How to cite: He, T.: High-Resolution Carbonate Variability in Red Earth Deposits: Implications for Water Cycling Dynamics during the Late Miocene, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2962, https://doi.org/10.5194/egusphere-egu21-2962, 2021.

Hole U1473 (32° 42.3622’ S; 57° 16.6880’ E), located on the summit of Atlantis Bank at the ultra-slow spreading Southwest Indian Ridge was drilled to 789.7 m below seafloor (mbsf) during IODP Expedition 360. It consists of massive gabbros cut by nearly 400 felsic veins, which are evolved, SiO2- enriched lithologies comprising ~1.5 vol% of the drill core. They vary in composition from diorite to trondhjemite. For their formation, 3 endmember models are discussed: (1) fractional crystallization; (2) hydrous anatexis of mafic rocks; (3) liquid immiscibility in an evolved MORB system.

Mineral assemblages in the felsic veins include mainly plagioclase, amphibole, Fe-Ti oxides ± quartz and minor zircon, apatite, ± titanite, ± biotite, ± K-feldspar.

Vein minerals often show strong zoning, which is especially expressed in amphiboles clearly visible by their variation in color ranging from brown to green corresponding to compositions from pargasite via pargasitic amphiboles, magnesiohornblendes to tremolite/actinolite. Moreover, zoning patterns can be observed in plagioclases from the veins, in which their An contents vary from An34 down to An5. This is distinctly lower than in the plagioclases of the host gabbros, which are virtually unzoned.

Clinopyroxenes at the contact between felsic vein and host gabbro show reactions either towards orthopyroxene or amphibole. TiO2 in brown pargasites in the host rock at the contact is enriched (up to ~4.6 wt%), whereas counterparts of the same crystals in the felsic veins are distinctly lower in TiO2 varying from ~2.5 wt% down to 0.1 wt% TiO2, associated with variation in color from brown to green. Calculated equilibrium temperatures based on Ti-content in amphibole (Ernst & Liu, 1998), consequently lead to higher formation temperatures for amphiboles in the host gabbro (up to ~1000 °C) compared to their counterparts in the veins, ranging from ~890 °C to ~500 °C.

Amphiboles contain ~0.2 wt% F and distinctively lower contents in Cl (with one exception found). Most amphiboles at the contact show a core-rim evolution trend with decreasing F and increasing Cl content, implying a magmatic formation with increasing influence of processes involving a hydrothermal fluid. Only one out of twenty-two investigated samples shows a trend vice versa.

The record of eutectic crystallization expressed by granophyric structures of quartz and plagioclase indicates that the felsic veins crystallized from a melt.

Ernst, W. G., & Liu, J. (1998). Experimental phase-equilibrium study of Al-and Ti-contents of calcic amphibole in MORB—A semiquantitative thermobarometer. American mineralogist, 83(9-10), 952-969.

How to cite: Engelhardt, A., Koepke, J., and Holtz, F.: IODP Hole 1473A (Atlantis Bank, SWIR) - Formation of felsic veins in gabbros: reactions at the contact between felsic melt and host rock, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2356, https://doi.org/10.5194/egusphere-egu21-2356, 2021.

EGU21-6496 | vPICO presentations | SSP1.2 | Highlight

Material, Magnetic, and Microbial Features of a Submarine Inflow ZoneTraversed by SUSTAIN Drill Cores, Surtsey Volcano, Iceland

Jacob Peterson, Marie Jackson, Joshua Marquardt, Peter Lippert, Nobumichi Tamura, Pauline Bergsten, Pauline Vannier, Alexandra Klonowski, Stephen Knobloch, Viggo Marteinsson, and Magnus Gudmundsson

A series of basaltic eruptions from 1963 to 1967 off the southern coast of Iceland produced the oceanic island of Surtsey. Investigations of this volcanic system provide a time-lapse window into the real-time alteration of basaltic tephra through interactions with meteoric water in a subaerial tuff cone and with seawater in submarine deposits. In 1979, a 181 m core was recovered from a borehole (SE-01) on the eastern flank of the Surtur vent. In 2017, the ICDP-supported SUSTAIN drilling project drilled two vertical cored boreholes (SE-02a, SE-02b) to 151 and 187 m below surface (m b.s.) parallel to the 1979 borehole, and an additional angled cored borehole (SE-03) to 354 measured depth. These newly recovered cores, in comparison with the 1979 core, have promoted research into alteration processes within the volcano over the half century since its eruption. The scientific drilling undertaken in both 1979 and 2017 provides data critical to investigating mechanisms and rates of mineralogical change in basalt, evolving material and magnetic properties, and the characterization of basalt-hosted microbial communities.

            Previous research, including mineralogical analyses and geophysical downhole logging, reveals a weakly altered region at ~143-155 m b.s. that corresponds with a submarine zone of cool seawater inflow.  The purpose of this study is to better understand processes in this zone by examining SE-02b drill core samples taken at 141.6 m b.s. (83-86 °C) with mineralogical analyses and at 148 m b.s. (83-84 °C) with magnetic analyses and microbial community analyses. Mapping of the weakly-consolidated basaltic tuff at micrometer-scale using synchrotron X-ray micro-diffraction and micro-fluorescence studies shows that the basalt is primarily composed of fresh sideromelane glass, volcanic crystals, and open voids. Olivine and labradorite are the principal volcanic minerals; they have begun to alter to lizardite and aluminous tobermorite, respectively. The basaltic glass has begun to alter to nanocrystalline clinochlore and smectitic clay mineral, mainly nontronite and montmorillonite. The abundance of fresh glass, however, confirms a weakly altered region of the volcano. Uniaxial and cubic single domain titanomagnetite is the principal magnetic remanence carrier in the glass, whereas the magnetic minerals in more highly altered zones of lapilli tuff, only a few meters distant, are more oxidized and exhibit different magnetic anisotropies, consistent with the growth of secondary titanomaghemite. The properties of magnetic remanence remained relatively stable in the cool seawater inflow zone but changed very rapidly during fluid-rock interactions at higher hydrothermal temperatures. The microbial community detected in the drill core sample at 148 m b.s. from SE-02b is dominated by taxa generally found in seawater such as Psychromonas, Glaciecola, Marinomonas and suggests a possible infiltration of microbial taxa from the seawater to the submarine deposit. This anomalously permeable, poorly-consolidated horizon provides a strong contrast to the characteristics of the well-lithified lapilli tuff deposits and demonstrates the potential for substantial variability in mineralogical, magnetic and microbial submarine processes in other Surtseyan volcanoes and seamount structures.

How to cite: Peterson, J., Jackson, M., Marquardt, J., Lippert, P., Tamura, N., Bergsten, P., Vannier, P., Klonowski, A., Knobloch, S., Marteinsson, V., and Gudmundsson, M.: Material, Magnetic, and Microbial Features of a Submarine Inflow ZoneTraversed by SUSTAIN Drill Cores, Surtsey Volcano, Iceland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6496, https://doi.org/10.5194/egusphere-egu21-6496, 2021.

EGU21-4080 | vPICO presentations | SSP1.2

The influence of tectonic migration of ocean floor on (bio-)geochemical and diagenetic processes in subseafloor sediments from the Nankai Trough off Japan

Male Köster, Myriam Kars, Florence Schubotz, Man-Yin Tsang, Yuki Morono, Fumio Inagaki, Verena B. Heuer, Sabine Kasten, and Susann Henkel

(Bio-)geochemical processes in subseafloor sediments are closely coupled to global element cycles. To gain an improved understanding of changes in (bio-)geochemical conditions on geological timescales, we investigate sediment cores from a 1180 m deep hole in the Nankai Trough offshore Japan (Site C0023). The sediment cores were taken during International Ocean Discovery Program (IODP) Expedition 370 (Temperature Limit of the Deep Biosphere off Muroto), which aimed at exploring the prerequisites and limits of deep microbial life [1]. Over the past 15 Ma, Site C0023 has moved ~750 km relative to its present-day geographic position from the central Shikoku Basin to the Nankai Trough due to motion of the Philippine Sea plate [2]. During its tectonic migration, Site C0023 has experienced significant changes in depositional and thermal conditions as well as resulting (bio-)geochemical processes.

By combining a large set of complementary pore-water, solid-phase and rock magnetic data with sedimentation rates and sediment ages, our aim is to (1) reconstruct the evolution of (bio-)geochemical processes, especially the cycling of iron, along the tectonic migration, and to (2) investigate if iron(III) minerals are still available to serve as energy substrate for microbial respiration in the deep sediments. Our results demonstrate that a transition from organic carbon-starved conditions with predominantly aerobic respiration processes to an elevated carbon burial environment with increased sedimentation occurred at ~2.5 Ma. Higher rates of organic carbon burial as a consequence of an increased nutrient supply and primary productivity likely stimulated the onset of organoclastic iron and sulfate reduction, biogenic methanogenesis and anaerobic oxidation of methane. A significant temperature increase by ~50°C across the sediment column associated with trench-style sedimentation since ~0.5 Ma potentially increased the bioavailability of organic matter and enhanced biogenic methane production. The resulting shifts in reaction fronts led to a diagenetic transformation of iron (oxyhydr)oxides into pyrite in the lower organic carbon-starved sediments several millions of years after burial. We also show that high amounts of iron(III), which were preserved in the deeply buried sediments due to carbon-starved conditions are still available as energy substrate for microbially mediated processes at Site C0023.

Our study emphasizes that depositional and thermal changes ultimately driven by the tectonically induced migration have the potential to strongly influence and control geochemical conditions and (bio-)geochemical processes within the whole sediment column. Such studies are needed to gain a fundamental understanding of the coupling between depositional history, (bio-)geochemical processes and the resulting diagenetic overprint on geological timescales, thereby linking the sedimentary iron, sulfur and carbon cycles.

References:

[1] Heuer, V.B. et al., 2020. Science 370: 1230-1234.

[2] Mahony, S.H. et al., 2011. Bulletin 123: 2201-2223.

How to cite: Köster, M., Kars, M., Schubotz, F., Tsang, M.-Y., Morono, Y., Inagaki, F., Heuer, V. B., Kasten, S., and Henkel, S.: The influence of tectonic migration of ocean floor on (bio-)geochemical and diagenetic processes in subseafloor sediments from the Nankai Trough off Japan, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4080, https://doi.org/10.5194/egusphere-egu21-4080, 2021.

EGU21-13015 | vPICO presentations | SSP1.2 | Highlight

Magma plumbing system and associated hydrothermal vents in the Guaymas Basin - geometry and implications

Christophe, Y. Galerne, Daniel Lizarralde, Christian Berndt, Florian Neumann, Tobias, W. Höfig, Joann M. Stock, Manet, E. Peña-Salinas, Raquel Negrete-Aranda, and Andreas, P. Teske and the Expedition 385 Scientists

We document the geometry of a massive sill at the root of an approximately 20-m high and 800 m-wide ring of hydrothermal formations, termed Ringvent, located 28.5 km off-axis on the northwestern flanking regions of the actively rifting Guaymas Basin (Gulf of California). Using petrophysical data collected during the IODP Expedition 385 and processed 2D seismic profiles, we present evidence on the mechanics of sill emplacement and how the related hydrothermal vent conduits were constructed. The currently active moderate-temperature hydrothermal vent field indicates that, despite being cold and crystallized, the magma plumbing system, is tapping into a deeper geothermal source of the basin. The vent system roots at the vertical end of the magma plumbing system with the top of the sill located at a depth range of 80 to 150 m below the seafloor. Our research aims at constraining how far deep the geothermal fluids are coming from, and identifying how close the hydrothermal system is from a steady-state condition, to draw implications for how frequently such a system may arise in nascent ocean basins.

How to cite: Galerne, C. Y., Lizarralde, D., Berndt, C., Neumann, F., Höfig, T. W., Stock, J. M., Peña-Salinas, M. E., Negrete-Aranda, R., and Teske, A. P. and the Expedition 385 Scientists: Magma plumbing system and associated hydrothermal vents in the Guaymas Basin - geometry and implications, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13015, https://doi.org/10.5194/egusphere-egu21-13015, 2021.

EGU21-4267 | vPICO presentations | SSP1.2

Multi-level fluid monitoring to understand the origin of transients

Heiko Woith, Kyriaki Daskalopoulou, Martin Zimmer, Tomáš Fischer, Josef Vlček, Jakub Trubač, Jan-Erik Rosberg, Tomáš Vylita, and Torsten Dahm

Anomalies in timeseries are frequently reported in the context of earthquake precursor studies. The state of knowledge can be summarized as follows: (i) significant anomalies exist, (ii) seismo-tectonically induced anomalies might exist, (iii) anomalies of non-tectonic origin exist and may look very similar to tectonic ones. Thus, presumably only a fraction of all reported precursors is real in the sense that they are of seismo-tectonic origin. A key problem in earthquake prediction research is to understand the origin of an anomaly and thus the separation of internal and external drivers like e.g. rainfall.  

State-of-the-art fluid monitoring techniques allow for a high temporal resolution compared to the low-resolution discrete sampling approach used in the last decades. A unique approach will allow to monitor ascending fluids along a vertical profile in a set of drillings from a depth of a few hundred metres to the surface. This setup can provide hints on the origin of temporal variations related to the opening of fault-valves, admixture of crustal fluids to a background mantle-flow or the release of hydrogen during fault rupturing. Gas migration velocities can thus be measured directly from the arrival times of anomalies at different depth levels. In addition, potential admixtures of mantle fluids with crustal or meteoric fluids during the ascent to the Earth’s surface can be quantified.

A prototype of a multi-level gas monitoring system has been implemented at a mofette. Mofettes are gas emission sites where CO2 ascends through long-lived, narrow channels from the deep crust and possibly the Earth’s upper mantle and thus provide natural windows to magmatic processes at depth. The primary objective of our research on mofettes is to clarify physical links between fluid properties, their pathways and the relation to swarm earthquakes. The Hartoušov mofette field with an estimated daily CO2 flux between 23 and 97 t over an area of about 350,000 m2 has been chosen as a key site in the frame of the ICDP project: “Drilling the Eger Rift: Magmatic fluids driving the earthquake swarms and the deep biosphere.” It is located in the Cheb Basin, which terminates the Czech part of the Eger Rift to the West and is known for recurring earthquake swarms and mantle degassing. Gas and isotope compositions will be continuously analyzed in-situ at different depth levels (30 m, 70 m, 230 m) reached by three adjacent boreholes.

How to cite: Woith, H., Daskalopoulou, K., Zimmer, M., Fischer, T., Vlček, J., Trubač, J., Rosberg, J.-E., Vylita, T., and Dahm, T.: Multi-level fluid monitoring to understand the origin of transients, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4267, https://doi.org/10.5194/egusphere-egu21-4267, 2021.

EGU21-5904 | vPICO presentations | SSP1.2 | Highlight

Borehole logging and temperature measurements with the MARUM-MeBo sea bed drilling technology: Recent developments and scientific applications

Tim Freudenthal, Michael Riedel, and Heinrich Villinger

The MARUM-MeBo sea bed drilling technology is developed since 2004 at the MARUM Center for Marine Environmental Sciences at the University of Bremen (Freudenthal and Wefer, 2013). Presently two drill rigs are in operation for drilling and coring down to more than 70 m (MARUM-MeBo70) and 200 m (MARUM-MeBo200), respectively. The robotic drill rig with the required drill tools is deployed on the seabed, where the drill string for conducting coring is assembled during the drilling operation. In addition to wireline core barrels a temperature probe can be used for measuring formation bottom hole temperature at discrete drilling depths by pushing the probe about 15 cm into the base of the bore hole. The temperature is logged for about 10 – 15 minutes in order to allow for dissipation of the frictional heat generated during pushing and equilibration to formation temperature. When the temperature measurement is completed, the probe is recovered out of the drill string and the drilling operation can be continued.

The trip out of the drill string after reaching the target drill depth can be used for logging of the geophysical properties within the borehole and the adjacent formation. A memory logging tool is lowered into the drill string with the sensor part penetrating through the drill bit. When the drill string is tripped out the probe is raised together with the drill string inside the borehole and conducts the geophysical measurements. This method called “logging while tripping” is especially suitable for unconsolidated sediments and logging in unstable borehole conditions, since the drill string stabilizes the borehole above the sensor part during the logging operation. For the MeBo drill rigs we have spectrum gamma ray, magnetic susceptibility, dual induction and acoustic probes available. The latter is also equipped with a temperature sensor for measuring borehole temperature. 

In this presentation we show examples from MeBo drilling campaigns where core drilling, borehole logging and formation temperature measurements where combined. A focus of this presentation is the analysis of borehole temperature measurements during trip out. We investigate how geothermal flux and lithological changes (i.e. thermal conductivity) influence the bore hole temperature measurement by modeling the temperature evolution within the borehole during drilling and trip out.

  

References:

Freudenthal, T and Wefer, G (2013) Geoscientific Instrumentation, Methods and Data Systems, 2(2). 329-337. doi:10.5194/gi-2-329-2013

How to cite: Freudenthal, T., Riedel, M., and Villinger, H.: Borehole logging and temperature measurements with the MARUM-MeBo sea bed drilling technology: Recent developments and scientific applications, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5904, https://doi.org/10.5194/egusphere-egu21-5904, 2021.

SSP1.3 – Mass Extinctions, Volcanism, Impacts and Extreme Environmental Changes

EGU21-16391 | vPICO presentations | SSP1.3

Ocean sulfate scarcity as a pre-condition for Large Igneous Province driven mass extinction

Robert J. Newton, Tianchen He, Jacopo Dal Corso, Paul Wignall, Ben Mills, and Alex Dunhill

Records of sulfur cycling during mass extinction events increasingly show that they are associated with rapid shifts in the sulfur isotope composition of seawater indicative of low concentrations of ocean sulfate [1-4]. These events are also often associated with the spread of anoxic conditions in the marine realm. We propose a feedback mechanism whereby the production of methane in marine sediments increases in proportion to decreasing sulfate and consumes bottom water oxygen, thus acting as a positive feedback on spread of anoxic waters. This can be further amplified via increased weathering or recycled fluxes of phosphate enhancing productivity [e.g. 5], the effects of increasing temperature on the rate of methanogenesis and the additional suppression of marine sulfate via increased pyrite burial.

We propose that sulfate drawdown occurs prior to climate forcing and other extinction drivers imposed by large igneous province (LIP) eruption. The likely mechanism for the drawdown of sulfate prior to these extinction is the removal of sulfate from the oceans as gypsum in evaporite deposits. Several large mid-Phanerozoic mass extinctions have clear evidence of increased evaporite deposition prior to, or approximately coincidental with LIP eruption and extinction.

If this idea is correct, the biological impact of a LIP will partly depend on the sulfate status of the ocean at the time of its eruption, and may at least partly explain the observation that whilst many mass extinctions are associated temporally with a LIP, not all LIPs seem to cause mass extinctions.

1. Newton, R.J., et al., Geology, 2011. 39(1): p. 7-10.

2. Song, H., et al., Geochimica et Cosmochimica Acta, 2014. 128(0): p. 95-113.

3. Witts, J.D., et al., Geochimica et Cosmochimica Acta, 2018. 230: p. 17-45.

4. He, T., et al., Science Advances, 2020. 6(37): p. eabb6704.

5. Schobben, M., et al., Nature Geoscience, 2020. 

How to cite: Newton, R. J., He, T., Dal Corso, J., Wignall, P., Mills, B., and Dunhill, A.: Ocean sulfate scarcity as a pre-condition for Large Igneous Province driven mass extinction, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16391, https://doi.org/10.5194/egusphere-egu21-16391, 2021.

EGU21-9548 | vPICO presentations | SSP1.3 | Highlight

Broadscale evaluation of the sedimentary Hg proxy for volcanism – insights from data compilation

Joost Frieling, Isabel Fendley, and Tamsin Mather

Over the past few years, mercury (Hg) concentrations in (predominantly) marine sediments have gained widespread attention as a far-field, high-temporal resolution proxy for deep-time enhanced volcanic activity. The primary focus of these Hg studies has been a range of events in the past 500 million years; mostly larger and smaller mass extinctions and periods of high-amplitude climate change. As a result, sedimentary Hg data reinforced the notion many of these events are indeed coeval with and hypothesized causally connected to large igneous provinces (LIPs). 

However, relatively poor constraints on long-term dispersal of emissions through the marine and terrestrial biosphere, accumulation and preservation mechanisms of Hg pose difficulties for its use as a qualitative proxy for enhanced volcanic emissions. As a result, using sedimentary Hg for detailed modeling of Hg cycling or past gaseous emissions of magmatic volatiles, e.g. carbon and sulfur, and by extension environmental impact, remains speculative.

The use of Hg normalization to common Hg-binding sedimentary components such as organic carbon (TOC), Fe or Al provides a basic means of comparing relative Hg loading within a sedimentary sequence. Yet, normalizing Hg to these major sedimentary components relies on simple linear relations and this approach often leaves substantial variance. While the high Hg concentrations have usually been ascribed to variability in volcanic activity, there are likely other factors that may invoke changes in the Hg concentrations in sediments, or mask Hg emitted by volcanism such as amount or type and flux of organic matter being deposited in basins and oxygenation of water and local sediments.

To evaluate potential confounding factors, we compiled published Hg, TOC and bulk and trace element data, modern and deep-time events, periods with and without known anomalous volcanic activity and cover a range of depositional settings. We find that the depositional setting, as inferred from lithology and bulk sediment chemistry exerts a major control on the overall concentrations of Hg. Differences in Hg loading between time-correlative deposits persist after normalization to major sedimentary components, likely as a result of a complex interplay between various spatial and environmental factors. Our data compilation further allows us to explore the potential of establishing a range for background Hg values and variability through different periods of geological deep-time. Collectively, such constraints can aid the understanding of changes induced by environmental factors or volcanic emissions and inform Hg-cycling models.

How to cite: Frieling, J., Fendley, I., and Mather, T.: Broadscale evaluation of the sedimentary Hg proxy for volcanism – insights from data compilation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9548, https://doi.org/10.5194/egusphere-egu21-9548, 2021.

EGU21-12461 | vPICO presentations | SSP1.3

A sequence of temporally separated element peaks; the fingerprint of a biogeochemical event initiated by sedimentary exhalative (SEDEX) brine expulsion

Michiel Arts, Bradley Cramer, Mikael Calner, Christian Rasmussen, Alyssa Bancroft, Stephan Oborny, Emma Hartke, Ellie Biebesheimer, and Anne-Christine Da Silva

The Ireviken Biogeochemical Event (IBE) consists of the Ireviken Extinction Event (IEE) and is superseded by the Ireviken positive d13Ccarb Excursion (ICIE). During the Ireviken Extinction Event 80% of the conodont species and 50% of the trilobite species went extinct and Acritarchs, chitinozoans, graptolites, corals, and brachiopods communities were severely affected as well. Currently there are no indications that the Ireviken Biogeochemical event can be linked to a LIP or a bolide impact which are the usual triggers for most known biogeochemical events. The IBE has been tentatively linked to SEDEX brine expulsion, however convincing high-resolution data supporting the SEDEX brine expulsion theory was lacking.

The Altajme core from Gotland Sweden covers the entirety of the Ireviken Biogeochemical Event and using an ITRAX XRF core scanner  we were able to create a new dataset with a 1cm(~150-400 yr.) resolution. This dataset enables us to shed new light on the origin of the IBE and serves as a template for a cyclostratigraphic age model (using the detrital proxies of Ti and Al) which puts the IBE within a precise temporal framework.

The occurrence of peak values of Nb, Mn, Cu, Ba, Pb, Zn, As, Ag in the Altajme core follows the temporal sequence of element peaks which is characteristic for the cooling of a hydrothermal system. A Pb:Zn ratio of >1 and low Cu/(Zn+Pb) ratio categorises the hydrothermal system as being the sedimentary exhalative (SEDEX) brine expulsion type system. Through these results we can undoubtedly link the Ireviken Biogeochemical Event to a SEDEX brine expulsion. Numerous SEDEX style ore deposits of Proterozoic to Cenozoic age are known, but it has been difficult to connect them with similarly aged biogeochemical events.  This study demonstrates that through extremely high resolution XRF/element data we can observe the far-field signature of a SEDEX brine expulsion and thus showing us the way to recognize more biogeochemical events triggered by SEDEX brine expulsions. 

How to cite: Arts, M., Cramer, B., Calner, M., Rasmussen, C., Bancroft, A., Oborny, S., Hartke, E., Biebesheimer, E., and Da Silva, A.-C.: A sequence of temporally separated element peaks; the fingerprint of a biogeochemical event initiated by sedimentary exhalative (SEDEX) brine expulsion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12461, https://doi.org/10.5194/egusphere-egu21-12461, 2021.

EGU21-9955 | vPICO presentations | SSP1.3

Field evidence for coal combustion links the 252 My-old Siberian Traps with global carbon disruption

Linda Elkins-Tanton, Steven Grasby, Benjamin Black, Roman Veselovskiy, Omid Ardakani, and Fariborz Goodarzi

The Permo-Triassic Extinction was the most severe in Earth history. The Siberian Traps eruptions are strongly implicated in the global atmospheric changes that likely drove the extinction. A sharp negative carbon isotope excursion coincides within geochronological uncertainty with the oldest dated rocks from the Norilsk section of the Siberian flood basalts. The source of this light carbon has been debated for decades.

We focused on the voluminous volcaniclastic rocks of the Siberian Traps, relatively unstudied as potential carriers of carbon-bearing gases. Over six field seasons we collected rocks from across the Siberian platform and show the first direct evidence that the earliest eruptions particularly in the southern part of the province burned large volumes of a combination of vegetation and coal. Samples from the Maymecha-Kotuy region, from the Nizhnyaya Tunguska, Podkamennaya Tunguska, and Angara Rivers all show evidence of high-temperature organic matter carbonization and combustion.

Field evidence indicates a process in which ascending magmas entrain xenoliths of coal and carbonaceous sediments that are carbonized in the subsurface and also combusted either through reduction of magmas or when exposed to the atmosphere. We demonstrate that the volume and composition of organic matter interactions with magmas may explain the global carbon isotope signal, and have significantly driven the extinction.

How to cite: Elkins-Tanton, L., Grasby, S., Black, B., Veselovskiy, R., Ardakani, O., and Goodarzi, F.: Field evidence for coal combustion links the 252 My-old Siberian Traps with global carbon disruption, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9955, https://doi.org/10.5194/egusphere-egu21-9955, 2021.

EGU21-13733 | vPICO presentations | SSP1.3 | Highlight

Deep marine anoxia of the southern Panthalassa during the Permian-Triassic – global impacts of the Siberian Traps

Stephen Grasby, David Bond, Paul Wignall, Runsheng Yin, Lorna Strachan, Satoshi Takahashi, and Omid Ardakani

The deep-water record of marine anoxia across the Permo-Triassic mass extinction (PTME) is highly controversial; both the length of time and severity of anoxic conditions are uncertain. Panthalassa Ocean circulation models show varying results, ranging from a well-ventilated deep ocean to rapidly developing northern, but not southern, latitude anoxia in response to Siberian Traps driven global warming. To address this uncertainty we examined a southern paleo-latitude pelagic record. Trace metal and pyrite framboid data show bottom water euxinc conditions developed in the southern Panthalassa Ocean at the PTME, coincident with enhanced volcanic activity indicated by Hg geochemistry. While a global deep-ocean euxinic event at the PTME placed extraordinary stress on marine life, southern surface waters appear to have recovered more quickly as radiolarian populations return several million years before they do in northern Panthalassa.

How to cite: Grasby, S., Bond, D., Wignall, P., Yin, R., Strachan, L., Takahashi, S., and Ardakani, O.: Deep marine anoxia of the southern Panthalassa during the Permian-Triassic – global impacts of the Siberian Traps, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13733, https://doi.org/10.5194/egusphere-egu21-13733, 2021.

EGU21-12938 | vPICO presentations | SSP1.3 | Highlight

Raman estimates of the thermal effect on tree trunks in the Siberian Traps lavas and volcaniclastics

Alexander G. Polozov, Sverre Planke, John A. Millett, Dmitrii A. Zastrozhnov, Kirill V. Ponkratov, Dougal A. Jerram, and Henrik H. Svensen

Tree trunks in lava flows and volcaniclastics of the Siberian Traps witness volcanic activity's violent and rapid onset. Carbonized and petrified trees preserve the peak metamorphic temperatures, which can be estimated using Raman spectroscopy. We have conducted a Raman study of the tree trunks and wooden fragments trapped in the Siberian Traps volcaniclastics and lavas on the Tunguska basin's northwestern region (Norilsk area). The first sample set was taken from volcaniclastic rocks of the Kureika River. The second sample set was collected from the lowermost lava flow of Ivakinskaya Formation that erupted directly on the end-Permian boggy surface (Tunguska Group of Carboniferous-Permian age) and from the coal-bearing inter lava seam at Red Rocks outcrop near Talnakh. The third sample set was taken from in the basal part of the Ivakinskaya Fm lowermost lava flow erupted in a shallow water basin with pillow basalt formation (Ore Brook near Norilsk). The fourth sample set was taken from an open coal pit with shallow dolerites intruded into the late Permian part of the Tunguska Group (near Kajerkan). We analyzed carbonized wood with a Renishaw InVia Qontor with 532 nm laser and processed all spectra with Henry et al. (2018) recommendations. The peak metamorphic temperature was calculated from Deldicque et al. (2016) equation 2. The tree trunks of the first sample set (Kureika River volcaniclastics) have a narrow median temperature range (430-468oC with one sample of 612oC). The second sample set from tree trunks in lavas and the coal-bearing inter lava seam (Red Rocks near Talnakh) ranges between 343-658oC and 742-764oC. The third sample set from pillow basalt at the basal part of Ivakinskaya Fm. (Ore Brook near Norilsk) also has a narrow temperature range (503-535oC with one sample of 650oC). The last sample set from the open coal pit (near Kajerkan) has a wide median temperature range (388-632oC).

We explain these variations by different styles of the Siberian Traps eruption. At the Kureika River, the end-Permian forest was buried and carbonized by tephra. At the Talnakh area, lava flow erupted on the boggy surface, whereas in the Norilsk area, the lava flow erupted into the freshwater basin.

 

Henry, D.G. et al. (2018). Int. J Coal Geol, 191: 135-151

Deldicque, D. et al. (2016). Carbon, 102: 319-329

How to cite: Polozov, A. G., Planke, S., Millett, J. A., Zastrozhnov, D. A., Ponkratov, K. V., Jerram, D. A., and Svensen, H. H.: Raman estimates of the thermal effect on tree trunks in the Siberian Traps lavas and volcaniclastics, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12938, https://doi.org/10.5194/egusphere-egu21-12938, 2021.

EGU21-15598 | vPICO presentations | SSP1.3

High-resolution Sampling and Photogrammetry of the Permian-Triassic Boundary Within the Festningen Profile, Svalbard

Lars Eivind Augland, Sverre Planke, Valentin Zuchuat, Morgan Jones, Kim Senger, Peter Betlem, Tom Birchall, William Hagopian, and Henrik Svensen

The Permian period ended with a mass extinction event about 252 million years ago. A likely trigger of the mass extinction was the eruption of large volumes of magma which had moved through the Tunguska Basin in Siberia. The renowned Festningen section in the outer part of Isfjorden, western Spitsbergen, offers a c. 7 km long nearly continuous stratigraphic section of Lower Carboniferous to Cenozoic strata, where the end-Permian extinction interval is well-exposed. Tectonic deformation associated with the Paleogene West Spitsbergen fold-and-thrust-belt tilted the strata to near-vertical, allowing easy access along the shoreline. The section is a regionally important stratigraphic reference profile and is a key locality for geologists visiting Svalbard. The main objective of our fieldwork in September 2020 was to collect closely spaced mudstone (0.25 to 1 m interval) and ash layer (6 layers of 0.5 to 1.5 cm thickness) samples across the Festningen Permian-Triassic boundary for chemostratigraphic and geochronological assessments. Carbon isotope data reveal a well-defined negative deltaC13 excursion in the lower part of the Vardebukta Fm. Zircons are present in most of the ash layer samples and these will be dated at the University of Oslo TIMS U-Pb Isotope Geology Laboratory. In this contribution, we will also present a new digital outcrop model of the P-Tr boundary section acquired using a UAV (Mavic 2 Pro, 20MP Hasselblad camera). During acquisition, the maximum drone speed was set to 1 meter/second (i.e., “tripod mode”), and photographs were taken automatically at set time intervals (e.g., 1 photo every 5 seconds ≈ meters). The digital outcrop model offers a pixel resolution of 7.27 mm/pixel. The Festningen model will be available online through the Svalbox.no geoscience data platform.

How to cite: Augland, L. E., Planke, S., Zuchuat, V., Jones, M., Senger, K., Betlem, P., Birchall, T., Hagopian, W., and Svensen, H.: High-resolution Sampling and Photogrammetry of the Permian-Triassic Boundary Within the Festningen Profile, Svalbard, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15598, https://doi.org/10.5194/egusphere-egu21-15598, 2021.

EGU21-10813 | vPICO presentations | SSP1.3 | Highlight

Tracing volcanic emissions from the CAMP volcanism in the sedimentary and biotic record

Sofie Lindström, Sara Callegaro, Joshua Davies, Christian Tegner, Bas van de Schootbrugge, Gunver K. Pedersen, Nasrrddine Youbi, Hamed Sanei, and Andrea Marzoli

The end-Triassic mass extinction (ETME) is thought to have been caused by voluminous, pulsed volcanic activity of the Central Atlantic Magmatic Province (CAMP). Over the last decades, various geochemical signals and proxy records, including δ13C, pCO2, iridium and other platinum-group elements, mercury, polycyclic aromatic hydrocarbons (PAH), charcoal and SO2, have been directly or indirectly attributed to CAMP magmatism. Here, we compile and discuss these various records in a stratigraphic framework to present a cohesive chain of events for the CAMP and the end-Triassic mass extinction. Mercury and iridium anomalies  indicate that CAMP activity commenced prior to the onset of the marine extinctions (as marked by the last occurrence of the Triassic ammonoid Choristoceras marshi or closely related species), and a negative δ13C excursion in organic matter (the Marshi CIE). This CIE may be explained by input of light carbon to the atmosphere from CAMP lavas of the Tiourjdal and Prevalent groups. Pedogenic carbonate below and above the Prevalent group in North America indicates a more than twofold increase in atmospheric pCO2. Subsequent n-alkane C-isotopes, and stomatal pCO2 data seem to indicate a temporary cooling after the Marshi CIE, which is consistent with climate models incorporating volcanic emissions of both CO2 and SO2. Records of excess iridium and Hg/TOC indicate intensified magmatism during the extinction interval. Tectonic and perhaps epeirogenic (i.e. doming due to rise of magma) activity is suggested by the occurrence of multiple and widespread seismites in Europe. Atmospheric pCO2 proxies indicate global warming, which culminated contemporaneously with a second negative CIE (the Spelae CIE) at the level of the first occurrence of the ammonoid Psiloceras spelae, the index taxon fot the Triassic−Jurassic boundary (TJB). Global warming at this level is corroborated by increased wildfire activity testified by charcoal and pyrolytic PAH records. Just prior to the increase in pCO2 from stomatal proxy data, fossil plants exhibit SO2-induced damage indicating excess sulfur dioxide deposition priot to and across the TJB. This coincides with increased ratios of heavy molecular PAHs (coronene/benzo(a)pyrene) in sediments, which may suggest metamorphism of organic sediments also occurred across the TJB. This suggests that thermogenic release of light carbon and sulfur from sill intrusions in the Trans-Amazonian basins, where both evaporate- and organic-rich sediments are known to have been intruded, may have played an important role during the course of the ETME. Geochemical traces of magmatism, i.e. Ir and Hg, appear to have gradually disappeared during the Hettangian, suggesting that later phases of CAMP were less voluminous. Stomatal proxy data from Greenland and n-alkane C-isotope data from the UK, together with oxygen isotope data from carbonate fossils in the UK, may indicate that the global warming at the Spelae CIE was succeeded by another short-term cooling event. A gradual decrease in δ13C culminated at the top-Tilmanni CIE, marking the beginning of a long-term steady state with more negative C-isotope values than prior to the ETME. At this time, terrestrial ecosystems appear to have stabilized globally and ammonoids had begun to rediversify.

How to cite: Lindström, S., Callegaro, S., Davies, J., Tegner, C., van de Schootbrugge, B., Pedersen, G. K., Youbi, N., Sanei, H., and Marzoli, A.: Tracing volcanic emissions from the CAMP volcanism in the sedimentary and biotic record, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10813, https://doi.org/10.5194/egusphere-egu21-10813, 2021.

EGU21-11189 | vPICO presentations | SSP1.3 | Highlight

Deep CO2 from the Central Atlantic Magmatic Province during the end-Triassic mass extinction

Manfredo Capriolo, Andrea Marzoli, László E Aradi, Sara Callegaro, Jacopo Dal Corso, Robert J. Newton, Benjamin J. W. Mills, Paul B. Wignall, Omar Bartoli, Don R. Baker, Nasrrddine Youbi, Laurent Remusat, Richard Spiess, and Csaba Szabo

Throughout Earth’s history, the coincidence in time between Large Igneous Province eruptions and mass extinctions points out a potential causality, where volcanic degassing may drive the global-scale climatic and environmental changes leading to biotic crises. The volcanic activity of the Central Atlantic Magmatic Province (CAMP, ca. 201 Ma), one of Earth’s most voluminous Large Igneous Provinces, is synchronous with the end-Triassic mass extinction event, among the most severe extinctions during the Phanerozoic. Combining different in situ analytical techniques (optical microscopy, confocal Raman microspectroscopy, EMP, SEM-EDS, and NanoSIMS analyses), bubble-bearing melt inclusions within basaltic rocks revealed the abundance of CO2 (up to 1.0 wt.%) in CAMP magmas [1]. Gaseous COand solid elemental C, alternatively preserved by gas exsolution bubbles within melt inclusions mainly hosted in clinopyroxene crystal clots, represent direct evidence for large amounts of volcanic CO2 (up to 105 Gt) emitted into Earth’s surface during the entire CAMP activity [1]. The entrapment conditions of these melt inclusions within clinopyroxene aggregates constrain the degassed CO2 to a mantle and/or lower-middle crustal origin, indicating a deep source of carbon which may favour rapid and intense CAMP eruption pulses. Each magmatic pulse may have injected CO2 into the end-Triassic atmosphere in amounts similar to those projected for the anthropogenic emissions during the 21st century [1]. Therefore, volcanic CO2 degassed during CAMP eruptions likely contributed to end-Triassic global warming and ocean acidification with catastrophic consequences for the biosphere.

 

[1] Capriolo et al. (2020), Nat. Commun. 11, 1670.

How to cite: Capriolo, M., Marzoli, A., Aradi, L. E., Callegaro, S., Dal Corso, J., Newton, R. J., Mills, B. J. W., Wignall, P. B., Bartoli, O., Baker, D. R., Youbi, N., Remusat, L., Spiess, R., and Szabo, C.: Deep CO2 from the Central Atlantic Magmatic Province during the end-Triassic mass extinction, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11189, https://doi.org/10.5194/egusphere-egu21-11189, 2021.

EGU21-1069 | vPICO presentations | SSP1.3

Early Jurassic phytotoxicity due to Hg-remobilization

Remco Bos, Sofie Lindström, Hamed Sanei, Irene Waajen, Appy Sluijs, and Bas van de Schootbrugge

The Central Atlantic Magmatic Province (CAMP) eruptions are generally regarded as the main driver of major environmental change and mass-extinction across the Triassic-Jurassic (TJ) boundary (~201.3 Ma), but the exact mechanisms linking volcanism and extinction, resilience, and recovery remain poorly constrained. Volcanogenic mercury (Hg) has been implicated as the cause for mutations in spores/pollen indicating severe ecological stress in terrestrial vegetation. Indeed, elevated sedimentary Hg concentrations coincide with the extinction interval at multiple sites across Europe. Here we show, palynological and geochemical records that gives insight in the dynamics between the Hg cycle and terrestrial vegetation, indicating repeated phytotoxicity in Early Jurassic deposits.

The abundance of mutagenic spores and the concentration of Hg are quantified in shallow marine sediments in the Schandelah-1 core (northern Germany) across the T/J boundary and the Early Jurassic (Hettangian). The results show increased mutagenic spore abundances with accompanying Hg/TOC anomalies across the end-Triassic extinction and within the lowermost Hettangian. This is consistent with studies from Sweden and Denmark and therefore confirming synchronous mutagenesis in and around coastal European margins. In addition, the Hettangian of Schandelah contains a record of long-term vegetational disturbance in the form of recurrent fern spikes and elevated mutagenic spore intervals, accompanied by Hg/TOC anomalies of similar magnitude. This suggests an overall link between volcanogenic pollution and vegetational disturbance. Based on qualitative analyses of organic matter (OM), which show an overall positive correlation between Hg concentration and terrestrial indicators, alternative sources for sedimentary Hg-enrichment such as vegetation reservoirs should be considered. This characterization of OM indicates an intermediate step in the Hg cycle, likely mediated by vegetation and/or climate feedbacks.

Atmospheric Hg-loading via volcanism can explain the synchronous enrichments of Hg concentrations at the TJ boundary interval in multiple sites across the globe. In contrast, the Hettangian anomalies of Schandelah-1, appear to be mainly driven by environmental/ecological perturbations corresponding to intensifying warm/humid conditions. Extreme seasonality alternating between high rainfall and droughts, perhaps due to eccentricity maxima, leading to increased soil erosion, wildfires and transport/degradation of terrestrial OM could potentially recycle and redistribute Hg long after initial deposition. These implications suggest a more dominant role of climate-induced Hg-remobilization, rather than direct volcanic emissions, to the mutagenesis in terrestrial vegetation. This could, in addition, lead to asynchronous and local impacts mainly in the proximity of landmasses.

How to cite: Bos, R., Lindström, S., Sanei, H., Waajen, I., Sluijs, A., and van de Schootbrugge, B.: Early Jurassic phytotoxicity due to Hg-remobilization, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1069, https://doi.org/10.5194/egusphere-egu21-1069, 2021.

The End-Triassic Mass Extinction (ETME) is one of the five major mass extinctions of the Phanerozoic. The deposition of ooids is atypically high in the direct aftermath of major extinction events, including the ETME. Ooids were intensively investigated both petrographically and sedimentologically in the past decades; but only recently their potentialities as archives for the original chemical composition of the oceans where they formed, have gained awareness. Here we present stratigraphical, sedimentological and geochemical aspects for a mid-Norian-Hettangian section from the Emirates.

Petrographic analyses provided a detailed morphological classification of post-ETME coated grains, supported by point counting of two isochronous geological sections. FE-SE-EDX imaging unraveled peculiar µm-scale features linked to morphology, diagenesis and biotic interaction in the cortex. LA-ICP-MS analyses were performed for specific major and trace elements. Post-extinction oolites show high variability in size and development of the cortex. They range from small (~ 300 µm) and superficial coating, to bigger (up to 800 µm) and well developed. The degree of micritization highlights different oxic conditions in the diagenetic environment. LA-ICP-MS analyses give insights into seawater redox conditions during ooids formation, siliciclastic contamination, diagenetic processes and the role of bacterial strain in shaping the ooids. Petrographical and geochemical data point out to a calcitic deposition of these ooids as odd with the general consideration that the Late Triassic to Early Jurassic was part of the Aragonite sea. This has major implication on the understanding of the carbonate saturation in the oceans just after the mass-extinction and on the interpretation of several proxies as the C and Ca isotope-system.

 

 

How to cite: Urban, I. and Richoz, S.: Calcite interval in aragonite seas: Geochemical characterization of post-extinction oolites at the Triassic-Jurassic boundary and their implications, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12423, https://doi.org/10.5194/egusphere-egu21-12423, 2021.

EGU21-2799 | vPICO presentations | SSP1.3

A novel marine phosphorus record from Lower Jurassic belemnites?

Ailsa Roper, Clemens Ullmann, Crispin Little, Simon Poulton, Paul Wignall, Tianchen He, and Robert Newton

Studying the long-term evolution of nutrient cycles and their interaction with other biogeochemical cycles is essential to understand Earth’s history. Marine nutrient cycling forms a key control on the cycling of carbon and oxygen in the bio- and geospheres. Here, we focus on phosphorus, which is the ultimate limiting nutrient on geological timescales and a potential driver of past intervals of marine anoxia/euxinia. Despite its importance, obtaining direct information on spatial and temporal variations in marine phosphorus concentrations has proved challenging. Recent work has demonstrated the potential for calcium carbonate-associated phosphorus in corals to record water-column phosphorus (e.g., LaVigne et al., 2008; 2010). Building on this approach, we are investigating the use of other calcitic fossils as a proxy for water column phosphorus concentration, focussing on belemnites, an extinct group of nektic molluscs.

We have developed and optimised a method to quantify phosphorus in the belemnite rostrum, and initially applied this method to samples from the upper Sinemurian to the Toarcian in the Lower Jurassic. During this time there were major climatic and environmental events in the latest Pliensbachian and early Toarcian, which are thought to have been driven by large scale volcanism of the Karoo-Ferrar Large Igneous Provinces (LIP). Of particular interest are an icehouse event during the Pliensbachian, and a warming event during the Toarcian which coincided with widespread ocean anoxia (the Toarcian Ocean Anoxic Event [TOAE]) and a second order mass extinction event (the Early Toarcian Mass Extinction).

We will present P/Ca results from method development tests and collections of belemnites from the Sinemurian to the Toarcian from a number of sites in the European Epicontinental Sea (EES). Pilot data show similar trends in belemnite phosphorus concentrations at different sites in the EES, including a sharp peak during the TOAE. We will also discuss the impact of inter-species variation on belemnite phosphorus concentrations, as well as internal variability in phosphorus concentrations in individual belemnites, to determine the potential impact of these variables on the reconstruction of water column phosphorus concentrations. 

LaVigne, M., Field, M. P., Anagnostou, E., Grottoli, A. G., Wellington, G. M., Sherrell, R. M. (2008). Skeletal P/Ca tracks upwelling in Gulf of Panamá coral: Evidence for a new seawater phosphate proxy. Geophysical Research Letters 35.

LaVigne, M., Matthews, K. A., Grottoli, A. G., Cobb, K. M., Anagnostou, E., Cabioch, G., Sherrell, R. M. (2010). Coral skeleton P/Ca proxy for seawater phosphate: Multi-colony calibration with a contemporaneous seawater phosphate record. Geochimica et Cosmochimica Acta 74: 1282–1293.

How to cite: Roper, A., Ullmann, C., Little, C., Poulton, S., Wignall, P., He, T., and Newton, R.: A novel marine phosphorus record from Lower Jurassic belemnites?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2799, https://doi.org/10.5194/egusphere-egu21-2799, 2021.

EGU21-2730 | vPICO presentations | SSP1.3

Toward a quantitative framework for assessing the global severity of Oceanic Anoxic Events

Matthew Clarkson, Timothy Lenton, Claudine Stirling, Alexander Dickson, and Derek Vance

Oceanic anoxia is a common response to past climate perturbations and often invoked as a direct cause of mass extinctions and faunal turnover events. During the Phanerozoic, there are numerous events that show qualitatively similar expressions of de-oxygenation, including ‘black shale’ development and distinct geochemical disturbances on global or local scales. These perturbations can be broadly grouped together as Oceanic Anoxic Events (OAEs), but their similarities, and differences, require greater quantification.

Advances in geochemistry over the last decade mean we are approaching a point where such a quantified comparison is possible. In particular, uranium isotopes (δ238U) have become established as an important tool for estimating the global extent of seafloor anoxia, overcoming the geographic limitations of relying on local proxy records. Typically, records from oxic marine carbonates, that are thought to track seawater trends, show negative U isotope excursions that reflect the preferential removal of isotopically heavy 238U into anoxic sediments. Here we present a compilation of δ238U datasets for a series of past climate perturbations, including the Permo-Triassic mass extinction, mid-Cretaceous OAE 2 and the PETM. In combination with a dynamic biogeochemical model, we explore the use of such datasets as a quantitative framework for comparing the ‘severity’ of OAEs. We highlight the strengths and weaknesses of the U isotope approach and outline important guidelines for considering δ238U records and the temporal relationship to other proxy datasets, such as δ13C and temperature.

How to cite: Clarkson, M., Lenton, T., Stirling, C., Dickson, A., and Vance, D.: Toward a quantitative framework for assessing the global severity of Oceanic Anoxic Events, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2730, https://doi.org/10.5194/egusphere-egu21-2730, 2021.

EGU21-893 | vPICO presentations | SSP1.3

A new record of the Toarcian oceanic anoxic event from Scotland (UK) and environmental responses

Wenhan Chen, David Bryan Kemp, Tianchen He, and Chunju Huang

The early Toarcian oceanic anoxic event (T-OAE, ~183 Ma) was characterized by a prominent environmental perturbation, likely associated with a large amount of 12C-enriched carbon released into the global ocean-atmosphere system. This effusion caused a marked disruption to the global carbon cycle and propagated a series of remarkable changes in ocean chemistry and climate. Although the T-OAE has been recognized worldwide, clear geographic differences in the character of the event and its environmental effects have been recognized. Here, we present new geochemical data from a lower Toarcian succession on the Isle of Raasay, NE Scotland (Hebrides Basin, Northwest European Shelf). Organic carbon isotope data through the Raasay section reveal a pronounced negative excursion, similar to that recognised globally. The excursion interval is enriched in organic matter, and redox sensitive element data suggest that suboxic bottom water conditions contemporaneously occurred, likely interspersed with anoxic episodes. Our findings contrast with evidence of more pervasive anoxia/euxinia in nearby basins, and emphasize how deoxygenation was spatially variable within the T-OAE. Inorganic geochemical data and sedimentological observations suggest a significant enhancement in chemical weathering and coarse-grained detrital flux during the T-OAE on Raasay. These findings support evidence from other localities for a strengthening of hydrological cycling in response to global warming during the T-OAE.

How to cite: Chen, W., Kemp, D. B., He, T., and Huang, C.: A new record of the Toarcian oceanic anoxic event from Scotland (UK) and environmental responses, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-893, https://doi.org/10.5194/egusphere-egu21-893, 2021.

EGU21-11835 | vPICO presentations | SSP1.3

Record of the Toarcian oceanic anoxic event in the Grands Causses Basin (southern France) and its implications for vertebrate preservation

Brahimsamba Bomou, Guillaume Suan, Jan Schlögl, Anne-Sabine Grosjean, Baptiste Suchéras-Marx, Thierry Adatte, Jorge Spangenberg, Stéphane Fouché, Axelle Zacai, Corentin Gibert, Jean-Michel Brazier, Vincent Perrier, Peggy Vincent, Kévin Janneau, and Jeremy E. Martin

Paleontological excavations realized by our group in Toarcian shales (Lower Jurassic) of the Grands Causses Basin in Roqueredonde (Hérault, France), yielded several specimens of marine vertebrates. The newly discovered specimens are partly or entirely preserved in anatomical connection and include a partial ichthyosaur skeleton with soft tissues, and a 4 m-long thalattosuchian longirostrine marine crocodile. A multi-proxy approach has been developed (XRD-bulk and clay mineralogy, Rock-Eval pyrolysis, phosphorus and mercury contents) in order to replace these findings in a well-defined temporal and paleoenvironmental context, and hence constrain the factors that led to their remarkable preservation. The fossiliferous succession exposes a 3 m-thick upper Pliensbachian interval of marl and nodular carbonate beds, overlain by a 3 m-thick interval of lower Toarcian laminated shales and limestone beds. Our high-resolution ammonite biostratigraphy, combined with inorganic and organic carbon isotope chemostratigraphy, shows that the fossiliferous Toarcian strata were deposited at a time of global warming and major carbon cycle perturbation known as the Toarcian Oceanic Anoxic Event (T-OAE). The studied succession shows several similarities with the classical coeval fossiliferous levels of the Posidonia Shale in SW Germany, including high organic matter and hydrocarbon contents as well as extremely reduced sedimentation rates. These results indicate that the unusual richness in well-preserved vertebrates of the studied site can be explained by a combination of warming-induced, low salinity and stratified waters, prolonged seafloor anoxia and reduced dilution by low carbonate and terrigenous input due to rapid sea-level rise. Our results also reveal a significant peak in mercury at the base of the T-OAE interval, consistent with that recorded in several coeval sections (e.g. Portugal, Morocco, Argentina, Chile). This mercury anomaly, most likely resulting from intense volcanic activity Karoo-Ferrar large igneous province, suggests that widespread exceptional vertebrate preservation during the T-OAE was initiated by a suite of severe environmental perturbations ultimately triggered by intense volcanic emissions.

How to cite: Bomou, B., Suan, G., Schlögl, J., Grosjean, A.-S., Suchéras-Marx, B., Adatte, T., Spangenberg, J., Fouché, S., Zacai, A., Gibert, C., Brazier, J.-M., Perrier, V., Vincent, P., Janneau, K., and Martin, J. E.: Record of the Toarcian oceanic anoxic event in the Grands Causses Basin (southern France) and its implications for vertebrate preservation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11835, https://doi.org/10.5194/egusphere-egu21-11835, 2021.

The Albian–Cenomanian transition is stratigraphically still poorly constrained in deep-water environments below the CCD. For this reason, the recognition of the OAE1d in such sedimentary records is extremely rare. Our high-resolution carbon-isotope (δ13Corg) stratigraphy of the Upper Albian and Lower Cenomanian turbidite/hemipelagic succession, accumulated in the marginal Silesian Basin of the Western Tethys, made it possible to identify the interval corresponding to the OAE1d. It has been recognized within two lithostratigraphic units of the Silesian Nappe of the Outer Carpathians (the Lower and Middle Lgota Beds), which are composed mostly of turbidite sediments containing a large amount of bioclastic material occurring in the silty and sandy fraction (locally over 70%). Bioclasts were redeposited from marginal shelf of the European Platform. The hemipelagic non-calcareous claystones which separate the turbidite sequences contain deep-water agglutinated foraminiferal (DWAF) assemblages, and are devoid of calcareous benthic foraminifers.

Using the analysis of the DWAF morphogroups, as well as changes in the benthos abundance and its taxonomic composition in relation to the characteristics (colour and TOC content) of hemipelagic sediments, we indicated changes in the environmental conditions that took place during the OAE1d at the bottom of the Silesian Basin. The most abundant horizons of organic-rich shales are characteristic of the lower part of the OAE1d succession corresponding to the Pialli Level from the Umbria-Marche Basin, although thin intercalations of black shales are also present along the upper part of this succession, where the hemipelagic sediments are dominated by green-coloured shales. The variability of organic matter in the studied sediments only slightly correlates with the abundance of the DWAFs and with their taxonomic composition. The more visible features in the latest Albian agglutinated benthos concern relative proportions of foraminiferal morphogroups which correspond to life-style and feeding strategies, and in this way reflect changes in selected environmental parameters. It seems that fluctuations in the morphogroup distribution along the OAE1d succession reflects the influence of two groups of factors: (i) oxygen concentration in bottom waters (low in the older part of the OAE1d, with fluctuations in the younger part of this isotope event), and (ii) the organic carbon flux that was linked to the onset of a massive redeposition of biogenic material from the European shelf. The last factor is related to the sea level fall during the 3-rd order regressive cycle.

How to cite: Bąk, K., Zbigniew, G., and Bąk, M.: Oceanic Anoxic Event 1d (late Albian) in deep-water sediments of the Outer Carpathians, Poland; Carbon isotope and agglutinated foraminiferal records, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4149, https://doi.org/10.5194/egusphere-egu21-4149, 2021.

EGU21-13968 | vPICO presentations | SSP1.3

The Cenomanian–Turonian Oceanic Anoxic Event 2 and the Late Turonian-Coniacian Event in the Mexican Interior Basin

Fernando Nunez, Azucena Colin-Rodríguez, Thierry Adatte, Lourdes Omaña-Pulido, Pura Alfonso, Teresa Pi, Alexander Correa-Metrio, Ricardo Barragán, Mario Martínez-Yáñez, and Juan Josué Enciso Cárdenas

In the modern ocean, deoxygenation is a major consequence of climate change induced by eutrophication and expansion of oxygen minimum zones.  To better understand the exact mechanisms that promote the development of anoxia requires observations not available at human time scale, and therefore demand the study of intervals of rapid warming in the geologic past. During the Cretaceous Period, massive submarine volcanism during the construction of Large Igneous Provinces gave rise to the development of several episodes of widespread oxygen-depleted waters and enhance organic carbon deposition, including the  Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE 2) and the  Late Turonian–Coniacian Event (LTCE). In this study, we reconstruct climate and oceanographic conditions in the Mexican Interior Basin during these events, a key area that connected the Western Interior Seaway to the equatorial Atlantic Tethyan water mass. To accomplish this, we applied an integrated multi-proxy approach that includes sedimentological, microfacies, mineralogical and geochemical data from a upper Cenomanian–lower Coniacian section.

Organic-rich sediments were accumulated during the initial stage of OAE 2 and the middle stage of LTCE (Hitchwood Event), under increasingly warm and humid conditions, as evidenced by high chemical index of alteration (CIA) values. High detrital index (DI) values coupled with high phosphorus mass-accumulation rates suggest that this scenario increased detrital and nutrients fluxes. Eutrophic-anoxic/dysoxic marine conditions are corroborated by the highest TOC values coinciding with significant enrichments in redox- and productivity-sensitive trace elements. Moreover, they are supported by the abundant presence of radiolarians and filaments in the OAE 2 interval, and the occurrence of opportunistic foraminifera in the LTCE interval. Oxygen-depleted bottom waters are also indicated by Mo–U systematics and a small-sized population of pyrite. The onset of the Mexican Orogen tectonic uplift together with upwelling intensified the transference of nutrients and enhanced organic matter burial during the initial stage of OAE 2. In the mid-OAE 2 δ13C trough interval equivalent to the Plenus Cold Event, bioturbated sediments with low TOC values accumulated during a short episode of cold climate conditions reflecting the southward flow of boreal water throughout the Mexican Interior Basin. The minimum δ34Spy value occurring within the OAE 2 interval in the Mexican Interior Basin is lower than elsewhere due to a local increase in sulfate concentrations.

How to cite: Nunez, F., Colin-Rodríguez, A., Adatte, T., Omaña-Pulido, L., Alfonso, P., Pi, T., Correa-Metrio, A., Barragán, R., Martínez-Yáñez, M., and Enciso Cárdenas, J. J.: The Cenomanian–Turonian Oceanic Anoxic Event 2 and the Late Turonian-Coniacian Event in the Mexican Interior Basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13968, https://doi.org/10.5194/egusphere-egu21-13968, 2021.

EGU21-8748 | vPICO presentations | SSP1.3

Onset of Oceanic Anoxic Event 2 in the Lower Saxony Basin – Insights fromhigh-resolution stable isotope stratigraphy and geochemical modelling

Pia Müller, Ulrich Heimhofer, and Christian Ostertag-Henning

The Oceanic Anoxic Event (OAE) 2 spanning the Cenomanian-Turonian boundary (93.5 Ma)
represents a major perturbation of the global carbon cycle and is marked by organic-rich
sediments deposited under oxygen-depleted conditions. In many studies the eruption of the
Caribbean LIP is considered to be the cause for rapidly increasing CO2 concentrations and
resulting global warming accompanied by widespread oceanic anoxia. In the Lower Saxony
Basin of northern Germany, the deposits of the OAE 2 are exposed in several industry drill
cores. In this study, the lower part of the OAE 2 has been studied in the HOLCIM 2011-3 drill
core. Sedimentary rocks are composed of limestones, marly limestones, marls and black
shales and have been analysed with a high-resolution stable isotope approach
(approximately one sample every 2 cm) combined with geochemical modelling. Using stable
carbon isotopes, bulk rock parameters and petrographic analysis, the onset of OAE 2 has
been investigated in detail. The high-resolution δ13C curve exhibits overall stable values
around 3 ‰ before the onset of the Plenus event. This background level is interrupted by
three short-lived and small but significant negative carbon isotope excursions (CIEs) down to
δ13C values of 2.5 ‰, 2.7 ‰ and 1.9 ‰. Immediately before the main rise in the Plenus bed,
a longer-lasting negative CIE down to 2.8 ‰ is observed, preceding the large positive CIE of
the OAE 2 to values of 5.2 ‰ over 33 ka. Thereafter, the δ13C values decrease to 3.5 ‰ over
a period of approximately 130 ka. The results can be correlated with the lower-resolution
data set of Voigt et al. (2008) but enable a more accurate characterization of the subtle
features of the CIE and hence events before and during this time interval. Carbon cycle
modelling with the modelling software SIMILE using a model based on Kump & Arthur (1999)
reveals that the negative excursion before the Plenus bed can be explained by a massive
volcanic pulse releasing of 0.95*1018 mol CO2 within 14 ka. This amount corresponds to only
81 % of the calculated volume of CO2 release during emplacement of the Caribbean LIP by
Joo et al. (2020). In the model the volcanic exhalation increases atmospheric CO2
concentrations. This will increase global temperatures, intensify the hydrological cycle and
thus increase nutrient input into the ocean, resulting in an expansion of the oxygen minimum
zone, the development of anoxic conditions and an increase in the preservation potential for
organic material. In the model enhanced primary productivity and organic matter preservation
can be controlled by the implemented riverine phosphate input and the preservation factor for
organic matter. For the positive anomaly, the riverine phosphate input must be nearly
doubled (from 0.01 μmol/kg PO4 to 0.019 μmol/kg) for the period of the increasing δ13C
values (app. 33 ka), with a concomitant rise of the preservation factor from 1 % to 2 %. This
model scenario accurately reproduces the major features of the new high-resolution δ13C
record over the onset of the OAE 2 CIE.

How to cite: Müller, P., Heimhofer, U., and Ostertag-Henning, C.: Onset of Oceanic Anoxic Event 2 in the Lower Saxony Basin – Insights fromhigh-resolution stable isotope stratigraphy and geochemical modelling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8748, https://doi.org/10.5194/egusphere-egu21-8748, 2021.

EGU21-11868 | vPICO presentations | SSP1.3

The Oceanic Anoxic Event 2 organic record in the South Iberian Paleomargin.

Carolina Fonseca, João Graciano Mendonça Filho, Matías Reolid, Luís Vítor Duarte, and Carine Lézin

The Cenomanian—Turonian boundary is marked by one of the warmest periods of the Mesozoic, associated with high pCO2 levels and global sea-level highstands. Coupled to these extreme conditions is a massive magmatic episode, the establishment of worldwide marine anoxia, the deposition of organic-rich facies, and perturbations of the global carbon cycle, the so-called Oceanic Anoxic Event 2 (OAE2). In order to define the organic facies variability, this stratigraphic interval was analysed in the Baños de la Hedionda, a reference section positioned in the W part of the Internal Subbetic, representing the sedimentary record of a pelagic plateau located in the most distal part of the South Iberian Paleomargin. Regarding this goal, a high resolution study was developed on the Capas Blancas Formation (Capas Blancas, Black radiolaritic shales, and Boquerón members – Mb.), using organic petrographic and geochemical techniques. Carbon isotopic profile, for the isolated kerogen (δ13Ckerogen), displays a positive excursion of ~2.5‰ observed in the Black radiolaritic shales Mb., which is in accordance with the worldwide recognized trend for the OAE2 isotopic record.

The pre-OAE2 is represented by the Capas Blancas Mb., with the majority of the samples of this unit showing no organic matter (OM) recovery (0.01—0.57 wt.% total organic carbon; TOC). Palynofacies analysis displayed an association co-dominated by the Amorphous and Palynomorph groups. The Amorphous Group is characterized mostly by marine phytoplankton-derived amorphous OM (AOM), while the Palynomorph Group is co-dominated by freshwater microplankton (Zygnemataceae and Closterium) and choanoflagellates, with some specimens of marine microplankton, sporomorphs, and zoomorphs being also identified. The mixture of freshwater and marine components suggest deposition in a platform environment with shallow depths and oscillating oxygen regimen (oxic to dysoxic conditions). The freshwater components are most likely transported into the marine system due to the lower amorphization state, with the source area being in high proximity.

The OAE2, represented by the Black radiolaritic shales Mb., is characterized by a dominance of: (i) marine phytoplankton-derived AOM; (ii) plate-like bacterial AOM; and, (iii) sheet-like bacterial AOM with a cratered aspect (0.36—31.48 wt.% TOC). Choanoflagelates (with high degree of amorphization) at the base of the unit, zooclasts, sporomorphs, and solid bitumen are also present. The change in the organic facies suggests the occurrence of a transgressive phase. This organic facies is indicative of a relative sea level rise, with O2 conditions deteriorating with the emplacement of reducing conditions, possibly related to an increase in primary productivity.

The post-OAE2, recognized in the Boquerón Mb., is characterized by a co-dominance of marine phytoplankton-derived AOM and palynomorphs, namely zoomorphs, and high percentages of opaque phytoclasts (below 0.25 wt.% TOC). Nevertheless, kerogen displays a reworked character and, therefore, data should be used with caution.

Furthermore, this study constitutes the first record of Closterium in sediments from the Cretaceous, and the first identification of choanoflagellates, the closest living relatives of Metazoa, in the fossil record.

How to cite: Fonseca, C., Mendonça Filho, J. G., Reolid, M., Duarte, L. V., and Lézin, C.: The Oceanic Anoxic Event 2 organic record in the South Iberian Paleomargin., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11868, https://doi.org/10.5194/egusphere-egu21-11868, 2021.

EGU21-8200 | vPICO presentations | SSP1.3

The recovery of the biological pump across the K/Pg boundary in the GSSP of El Kef, Tunisia

Joep van Dijk, Julio Sepúlveda, Laia Alegret, Heather Birch, Timothy Bralower, Heather Jones, Michael Henehan, Pincelli Hull, Mohamed Hedi Negra, Andy Ridgwell, Ursula Röhl, Johan Vellekoop, Thomas Westerhold, Jessica Whiteside, and Richard Zeebe

The study of Earth’s Big Five mass extinctions provides insight into the resilience of ecosystems to environmental perturbations. Earth’s most recent mass extinction at the Cretaceous/Paleogene boundary (K/Pg) was caused by the impact of an asteroid in the Yucatan peninsula rather than by intense volcanism. Mass extinctions among marine calcareous nannoplankton heavily disrupted the marine food web resulting in a severe weakening of the ocean’s biological pump. The timing and heterogeneous nature of the recovery of the biological pump remain poorly resolved in the neritic zone in the aftermath of the impact. Here, we address the evolution of the biological pump across the K/Pg at the Global Boundary Stratotype Section (GSSP) at El Kef, Tunisia using high-resolution compound-specific carbon isotope records (δ13Cbiomarker) of non-calcareous marine phototrophs from an outer shelf to upper bathyal setting of the southwestern Tethys Ocean. We use δ13Cbiomarker to reconstruct εp, which is a function of the community structure of marine phototrophs, their rate of carbon fixation, and the concentration and isotopic composition of aqueous CO2. We then use our εp record to constrain the recovery of the biological pump in this region while considering the composition of marine phytoplankton, the assemblage and isotopic composition of benthic foraminifera, state-of-the-art physiological models for εp, and carbon cycle simulations using cGENIE. Our results indicate that the recovery of the biological pump in the outer shelf-upper bathyal zone likely outpaced the recovery in the open ocean. This is in agreement with the selective extinctions among phytoplankton at the K/Pg, with most survivors that would later repopulate open-ocean sites being adapted to neritic environments.

How to cite: van Dijk, J., Sepúlveda, J., Alegret, L., Birch, H., Bralower, T., Jones, H., Henehan, M., Hull, P., Hedi Negra, M., Ridgwell, A., Röhl, U., Vellekoop, J., Westerhold, T., Whiteside, J., and Zeebe, R.: The recovery of the biological pump across the K/Pg boundary in the GSSP of El Kef, Tunisia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8200, https://doi.org/10.5194/egusphere-egu21-8200, 2021.

EGU21-10700 | vPICO presentations | SSP1.3

Paroxysmal Deccan Eruptions linked to End-Cretaceous Mass Extinction

Thierry Adatte, Gerta Keller, Jorge E. Spangenberg, Paula Mateo, Jahnavi Punekar, Johannes Monkenbusch, Nicolas Thibault, Sigal Abramovich, Blair Schoene, Michael P. Eddy, Kyle Samperton, and Syed F.R. Khadri

The Chicxulub impact in Mexico and Deccan volcanism in India are both linked to the end-Cretaceous mass extinction but the relative timing of the impact, volcanic eruptions, and environmental changes remain controversial, precluding a full assessment of their respective roles. Mercury anomalies within the stratigraphic record have recently been proposed as atmospheric fallout of continental large igneous provinces (LIPs), and these anomalies are associated with all five major mass extinctions in Earth’s history. If this proxy is robust, it could provide a record of volcanism directly correlated to mass extinctions and in the case of the End-extinction, the Chicxulub impact. To test this hypothesis, we analyzed mercury in the late Maastrichtian from the base of C29r to the Cretaceous-Paleogene boundary (KPB) n the astronomically tuned Elles section in Tunisia, and correlate this chemostratigraphic record with recent high-precision U-Pb geochronology of Deccan volcanism. Our results support that Hg is a robust indicator of LIP volcanism, and directly links Deccan volcanism to rapid global climate changes, ocean acidification and increasing environmental stress during the last 320-340 kyr of the Maastrichtian. Furthermore, our time-resolved Hg record and U-Pb resolved eruption volumes reveal paroxysmal volcanic eruptions (~30% by volume) during the final 35 kyr leading up to the KPB mass extinction.

How to cite: Adatte, T., Keller, G., Spangenberg, J. E., Mateo, P., Punekar, J., Monkenbusch, J., Thibault, N., Abramovich, S., Schoene, B., Eddy, M. P., Samperton, K., and Khadri, S. F. R.: Paroxysmal Deccan Eruptions linked to End-Cretaceous Mass Extinction, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10700, https://doi.org/10.5194/egusphere-egu21-10700, 2021.

EGU21-400 | vPICO presentations | SSP1.3

Evidence for contemporaneous Deccan volcanic aerosol deposition preceding the K-Pg boundary at El Kef, Tunisia

Steffanie Sillitoe-Kukas, Munir Humayun, Thierry Adatte, and Gerta Keller

The cause of the Cretaceous-Paleogene extinction remains debated between an asteroid impact and volcanism. Precise geochronology showed that the extinction coincided with a voluminous phase (Poladpur eruption) of Deccan volcanism (Schoene et al., 2019). Paleontological evidence indicates that microfossil diversity declined about 300,000 years before the K-Pg boundary, synchronous with the onset of Deccan volcanism (Keller et al. 2009). High concentrations of Ir in the K-Pg boundary supported the asteroid hypothesis but recent work indicates that siderophile accumulation at the K-Pg in El Kef is secondary (Humayun et al., this conf.). Here, we critically examine existing element data for the K-Pg boundary and examine new results at the El Kef site, Tunisia, for volcanogenic volatile element accumulation associated with the contemporaneous Deccan eruptions. In this study, we analyzed 60 elements by laser ablation ICP-MS in search of these volcanic aerosol enrichments in the K-Pg sediments at El Kef, Tunisia. A study of siderophile element distribution at global K-Pg sites found that the Ru/Ir ratio is sub-chondritic. Mixing of upper continental crust (Ru/Ir> CI) with a chondritic impactor fails to explain this trend. Volcanic aerosol emissions for Ir are well known but there is less data available for Ru. Relative emission rates of Ru were found to be lower than those of Ir for the Kudryavy volcano (Yudovskaya et al., 2008), so a possible explanation of the sub-chondritic Ru/Ir ratio observed in global K-Pg sites involves deposition of volcanic aerosols in sediments. We also modeled the effect of adding volcanic aerosols to sediments approximated compositionally as upper continental crust (UCC) to find that Re, Cd, Os and Ir are the first elements to become enriched in sediments by volcanogenic aerosol deposition. Sediments from El Kef below the K-Pg boundary are enriched in both Re and Cd. On a plot of Cd vs. Re, the K-Pg sediment from El Kef falls on a mixing line between volcanic aerosol (Erta Ale volcano) and UCC. Sediment at 3 cm above the K-Pg boundary has little enrichment of either Cd or Re, interpreted here to indicate that this sediment was deposited in the interlude between the Poladpur and the Ambenali eruption phases of the Deccan. The availability of chemical proxies of volcanogenic aerosol deposition in sediments enables direct correlation between fossil evidence and the contemporaneous intensity of volcanic outgassing, the likely destroyer of life by the Deccan eruptions (Keller et al., 2020).

How to cite: Sillitoe-Kukas, S., Humayun, M., Adatte, T., and Keller, G.: Evidence for contemporaneous Deccan volcanic aerosol deposition preceding the K-Pg boundary at El Kef, Tunisia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-400, https://doi.org/10.5194/egusphere-egu21-400, 2021.

EGU21-366 | vPICO presentations | SSP1.3

Pyrite Oxidation Controlled Siderophile Element Accumulation on the K-Pg Boundary at El Kef, Tunisia

Munir Humayun, Steffanie Sillitoe-Kukas, Thierry Adatte, and Gerta Keller

In a transformative contribution, Alvarez et al. (1980) discovered the iridium anomaly at several K-Pg boundary locations that they attributed to an extraterrestrial impact that triggered the end-Cretaceous extinction. The absence of a suitable mechanism by which to concentrate siderophile elements in the boundary clay drove the argument for an extraterrestrial origin of the iridium. They made the observation that fallout from a fireball would be expected to create a uniform distribution of Ir in the clay layer and puzzled over the scale of lateral variation in Ir observed even then. A detailed global study of the siderophile element (Ru, Rh, Pd, Ir, Pt Au) distribution at the K-Pg boundary found non-chondritic patterns concluding that some post-depositional process(es) must have affected the elemental distribution (Goderis et al., 2015). Such processes would mobilize siderophile elements into the surrounding strata. Here, we applied laser ablation ICP-MS, a microanalytical technique, to investigate the distribution of 60 elements, with an emphasis on the siderophile elements, in a vertical transect at the K-Pg boundary at El Kef, Tunisia, to search for elemental transport in or out of the K-Pg clay layer. The K-Pg boundary at El Kef consists of irregular mixed layers of clay, goethite and gypsum with marls above and below. The siderophile elements are concentrated in the goethite-rich component with a distinctly terrestrial crust pattern, albeit super-enriched, with prominent negative Pt anomalies indicative of deposition from an oxidized solution. The Fe/Se ratio indicates an origin of the goethite by oxidation of sedimentary pyrite. Iron oxyhydroxides are effective substrates for the binding of trace metal oxyanions from solution. The extreme enrichment of siderophile elements reflects long-term concentration of siderophile elements from percolating oxidized groundwaters at El Kef. The sulfuric acid produced by pyrite oxidation was neutralized by calcium carbonate in the marls to form gypsum. Selenium (normally a sulfur analog) is undetectable in the El Kef gypsum endmember (Se/S~0), unlike marine gypsum, supporting a formation by pyrite oxidation. This observation potentially explains the ubiquitous non-chondritic siderophile patterns observed globally and the variable Ir enrichments that puzzled geochemists since Alvarez et al. (1980). In view of this observation, siderophile element enrichment in the K-Pg layer can no longer be taken as unambiguous evidence of an extraterrestrial impact.

How to cite: Humayun, M., Sillitoe-Kukas, S., Adatte, T., and Keller, G.: Pyrite Oxidation Controlled Siderophile Element Accumulation on the K-Pg Boundary at El Kef, Tunisia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-366, https://doi.org/10.5194/egusphere-egu21-366, 2021.

EGU21-2058 | vPICO presentations | SSP1.3

Planktonic foraminiferal and geochemical record across the Cretaceous-Paleogene boundary (K-Pg): evidence from the Neo-Tethys, Turkey

Ali Uygar Karabeyoglu, Valentin Lorenzo, Jorge Spangenberg, Sevinç Özkan-Altıner, Demir Altıner, and Thierry Adatte

The end-Cretaceous mass extinction is a unique event such that it potentially coincides with both the Chicxulub bolide impact and the Deccan volcanism. Among these two drivers, the role of the Deccan volcanism is crucial to decipher if there is a causal relationship between volcanism and environmental stress, and if so, how stressed the environment was during the latest Maastrichtian. To assess the cause-and-effect relationship between Deccan volcanism and climate change and mass extinctions, high-resolution biostratigraphy, quantitative species analysis coupled with geochemical measurements have been performed on complete sections of Mudurnu-Göynük and Haymana basins (Turkey).

Detailed quantitative study on planktonic foraminifera of the Haymana Basin revealed that planktonic foraminiferal community in the latest Maastrichtian is dominated by ecological generalists with small, simple morphologies (e.g., Heterohelix, Globigerinelloides, Guembelitria). Among them low oxygen tolerant Heterohelix globulosa is the most dominant taxa and their abundance changing with the presence of stress marker Guembelitria cretacea. In all sections, the K/Pg boundary itself is characterized by 2-3 mm thick reddish oxidized layer which corresponds to sudden annihilation of large, ornamented ecological specialists (e.g., Globotruncana, Rugoglobigerina, Racemiguembelina). Right after the boundary, there is an acme of calcareous dinoflagellate cysts (Thoracosphaera) and a surge of Guembelitria cretacea indicate ecosystem collapse in post-K/Pg environment.

On the other hand, detailed quantitative analysis shows a systematic reduction in the species richness throughout the Plummerita hantkeninoides Zone corresponding to the final 150 kyr of the Cretaceous. Proliferations of the Guembelitria cretacea through late Maastrichtian is known as an indicator of high terrigenous influx; therefore, enhanced food resources. The high sedimentation rates observed in all the studied sections might be linked to increased greenhouse conditions due to Deccan volcanism leading to enhanced weathering. Overall, our multiproxy approach including quantitative biostratigraphy and geochemical analyses highlights the influence of the Deccan volcanism by releasing high amounts of atmospheric CO2 and SO2, leading to the climatic changes and associated biotic stress, which predisposed faunas to eventual extinction at the K/Pg boundary.

How to cite: Karabeyoglu, A. U., Lorenzo, V., Spangenberg, J., Özkan-Altıner, S., Altıner, D., and Adatte, T.: Planktonic foraminiferal and geochemical record across the Cretaceous-Paleogene boundary (K-Pg): evidence from the Neo-Tethys, Turkey, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2058, https://doi.org/10.5194/egusphere-egu21-2058, 2021.

EGU21-2625 | vPICO presentations | SSP1.3

Multi-proxy study of the Cretaceous-Paleogene (K-Pg) boundary in deep-sea turbiditic sediments in the Uzgruň section (Outer Flysch Carpathians, Czech Republic)

Šimon Kdýr, Tiiu Elbra, Miroslav Bubík, Petr Schnabl, and Lilian Švábenická

The composite profile, with 4 studied sections, is located near the Uzgruň village (Czech Republic) next to a small stream. The profile is composed of Late Maastrichtian to Palaeocene flysch sediments and the K-Pg boundary is set in claystones within this turbiditic setting. Ongoing research of local paleoenvironment and stratigraphy is based on paleo- and rock-magnetic methods, micropaleontology and geochemistry to obtain more detailed view of the local situation during the K-Pg extinction event. Based on biostratigraphy, two dinocyst zones (Bubík et al., 2002): Palynodium grallator and Carpatella cornuta (first occurrence in the Danian), two calcareous nannofossil zones in the Upper Maastrichtian, and the agglutinated foraminifer zone Rzehakina fissistomata in the Paleogene were distinguished. Biostratigraphic data support the K-Pg boundary interval. The uppermost Maastrichtian is indicated by nannofossil species Micula prinsii, UC26dTP zone. Basal Paleogene non-calcareous strata contain dinocyst Carpatella cornuta and agglutinated foraminifers of Rzehakina fissistomata zone. The presence of low-latitude nannofossil taxa M. prinsii and Ceratolithoides kamptneri show input of warm waters during the uppermost Maastrichtian. Several rock-magnetic methods, such as acquisition of Isothermal remanent magnetization (IRM), acquisition of Anhysteretic remanent magnetization (ARM), Anisotropy of magnetic susceptibility (AMS), Field dependence of magnetic susceptibility (HD) and Frequency dependence of magnetic susceptibility (FD), were applied to estimate behaviour and origin of magnetic particles. Natural remanent magnetization (NRM) values of samples range from 0.09 to 2.48 mA/m. Volume normalized magnetic susceptibility (MS) show values from 130 up to 1197 SI*10-6. There is no increase observed in MS across stratigraphic boundary due to turbiditic evolution of sediment. Due to character of sediments, we applied alternating field (AF) demagnetization and used principal component analysis (PCA; Kirschvink, 1980) for estimation of characteristic remanent component. Most of the K/Pg sections worldwide have well documented Iridium anomaly. In Uzgruň, the preliminary results show that although the values are not as pronounced, the Ir at K-Pg boundary is still higher than in surrounding sediments. For tracing of Deccan traps effect we plan to apply mercury (Hg)/total organic carbon (TOC) stratigraphy. TOC content of 20 pilot samples is low, but not under detection limit of the instrumentation (mean value 0.92 wt%). One sample reached value 4.41 wt% of TOC. Sulphur contents are reaching 1 wt%, but several samples were under detection limit of the instrumentation. Sulphur concentrations suggest more reduction conditions of burial.

Current research is supported by Czech Science Foundation project no. 19-07516S and is in accordance with research plan no. RVO67985831.

Bubík, M., Adamová, M., Bąk, M., Franců, J., Gedl, P., Mikuláš, R., Švábenická, L., & Uchman, A. (2002). Výsledky výzkumu hranice křída/terciér v magurském flyši u Uzgruně. Geologické výzkumy na Moravě a ve Slezsku, 9, 18–22

L. Kirschvink (1980), The least-squares line and plane and the analysis of palaeomagnetic data, Geophysical Journal International, 62(3), 699–718, https://doi.org/10.1111/j.1365-246X.1980.tb02601.x

How to cite: Kdýr, Š., Elbra, T., Bubík, M., Schnabl, P., and Švábenická, L.: Multi-proxy study of the Cretaceous-Paleogene (K-Pg) boundary in deep-sea turbiditic sediments in the Uzgruň section (Outer Flysch Carpathians, Czech Republic), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2625, https://doi.org/10.5194/egusphere-egu21-2625, 2021.

EGU21-5005 | vPICO presentations | SSP1.3

The rock magnetism and biochronology of boundary events across the Cretaceous-Paleogene transition in Slovakia.

Tiiu Elbra, Šimon Kdýr, Petr Schnabl, Petr Pruner, and Jan Soták

Western Carpathians transitional sequence of Upper Cretaceous (e.g. Gosau Group) and Paleogene (e.g. Myjava-Hričov Group) sediments provide good premise for studying the Cretaceous-Paleogene boundary (K-Pg) as well as other end-Cretaceous to Middle Eocene events. In Slovakia, the Late Cretaceous formations of Gosau localities can be found in Brezovské Karpaty Mts, Myjava Upland and Mid Váh Valley. To gain insights to local changes in global cataclysm event, a combined study of planktonic bioevents and magnetic properties across K-Pg was studied in two Western Carpathians drilled sections, Žilina (Mid-Váh Valley region) and Kršteňany (Upper Nitra Depression).

The Žilina-Hradisko drill core (ZA-1) is 75 m long and overturned in position. The micropaleontological research of the ZA-1 drill core provides a stratigraphic data ranging from the Late Maastrichtian to Early Ypressian. The ZA-1 sequence reveals distinct changes in magnetic properties and bioproductivity, particularly at the K-Pg. Although most of the drilled sequence displays paramagnetic behavior and low remanent magnetization (average magnetic susceptibility 142μSI and NRM <1mA/m, respectively), at the K-Pg and during first half of Danian – up to base of P2 biozone, markedly higher magnetic susceptibility (MS) and NRM values were observed. This change could mostly be attributed to increased concentration of magnetic fraction and probably illustrates the paleoenvironmental changes as a result of the K-Pg event. The K-Pg interval is also marked by the presence of increased amount of superparamagnetic particles. A mixture of low and high coercivity minerals were detected throughout the drill core, with S-ratio varying between 0.2-0.9 (at K-Pg 0.6-0.9). An additional study of mercury (Hg) content, in combination with total organic carbon (TOC), of ZA-1 samples, reveals a short time enhanced (Hg/TOC >100ppb/wt%), possibly volcanogenic, Hg input during Late Maastrichtian 40cm below K-Pg and later in the second half of P1 biozone in Danian, but seems to indicate either weak or no correlation with magnetic properties. The Kršteňany section consists of two boreholes, KRS-1 and KRS-3, and comprises Late Cretaceous – Middle Eocene formations. Similarly to ZA-1, most of the KRS-3 displays paramagnetic behavior (MS <300μSI) and low NRM (<2mA/m). However, contrary to ZA-1, the distinct changes in magnetic properties at K-Pg interval were not observed. The Maastrichtian portion of KRS-3 displays elevated, but decreasing towards K-Pg, MS values due to considerable weathering and increased hematite and/or goethite content in red-bed formation in the bottommost part of the core. Paleocene sequence through middle Ypresian shows lowest MS with higher (in pelagic sequences) and lower (in siliciclastic sequences) MS zones, probably following transgressive-regressive cycles.

The research was supported by Czech Science Foundation project no. 19-07516S and by VEGA agency no 2/0013/20, and is in accordance with research plan no. RVO67985831.

How to cite: Elbra, T., Kdýr, Š., Schnabl, P., Pruner, P., and Soták, J.: The rock magnetism and biochronology of boundary events across the Cretaceous-Paleogene transition in Slovakia., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5005, https://doi.org/10.5194/egusphere-egu21-5005, 2021.

The Kara astrobleme is one of the biggest meteoritic craters which is set at the Baydarata Bay of the Kara sea (European Arctic Zone, Russia). It is a result of the catastrophic impact event occurred close to the K/Т extinction. The Kara astrobleme is the largest European crater at the modern erosion level.  At present it is estimated with the diameter from rim to rim about 65 km. While, some scientists have proposed its larger initial size – up to 120 km diameter, but no any well presented proof has been provided for the hypothesis. In 2015-2019 we have provided wide geological observations at the Kara crater and the near-set Ust`-Kara area (UKA) impactites. We have found for the first time that the UKA impactites, described in earlier Russian scientists publications as a synchronic independent crater of the same bolide, can be presented with bottom-flow impactites from the Kara crater (Shumilova et al., 2020). The found bottom-flow impactites abundant with belt-like impact melt bodies enriched in coesite and liquation structures similar to the Kara UHPHT vein and vein-like melt bodies with UHPHT impact glasses. Thus, they belong to UHPHT impactites. According to our air-bird view observations and impactites outcrops description at the UKA we support the hypothesis of the larger Kara crater getting 100-120 km in diameter of the initially originated size. Such giant meteorite event should be followed by catastrophic effects at the planet level, such as mass extinction. The present accepted Kara impact event age followed by the most recent measurements by 40Ar-39Ar method is equal to 70.3 ± 2.2 Ma (Trieloff et al., 1998), that is a bit earlier than the Cretaceous/Tertiary boundary (K/Т) mass extinction at 66 Ma. But, previously, Kara age has been proposed by 65.7 Ma as a probable K/T impact (Kolesnikov et al., 1988; Nazarov et al., 1992). According to different data, the Kara event age lies within the range from 60 to 81 Ma (Masaitis & Mashchak, 1982; Nazarov et al., 1989; Kolesniov et al., 1990; Koeberl et al., 1990). It is clear that the accuracy of the age measurements depend on the quality of the studied samples, including their crystallinity, velocity of impact melt cooling and alteration, and from the used type of a method. By the moment, we have found out “in situ” crystallized zircons within the just discovered real UHPHT impact melt glasses (Shumilova et al., 2018, 2020). The UHPHT glasses do not have any alteration, thus, they can be used for accurate age measurements. Taking a future possibility for more accurate age analysis in the nearest future we can propose a correct vision of the possibility of the giant Kara influence to K-T mass extinction or other ecological effects. In any case following to the giant size of the Kara event touched the sedimentary rocks abundant with black shales and carbonates, which should be a result of essential atmospheric changes. The study has been supported by the Russian Science Foundation project #17-17-01080.

How to cite: Shumilova, T.: The Kara astrobleme size, age and potential paleo-ecological effects of the impact event (European Arctic Zone, Russia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8523, https://doi.org/10.5194/egusphere-egu21-8523, 2021.

EGU21-12788 | vPICO presentations | SSP1.3 | Highlight

Enhanced volcanism associated to the emplacement of the North Atlantic Igneous Province during the PETM evidenced by mercury anomalies in Pyrenean foreland sections

Maxime Tremblin, Hassan Khozyem, Jorge E. Spangenberg, Charlotte Fillon, Sylvain Calassou, Arnaud Grauls, Eric Lasseur, Jean-Yves Roig, Olivier Serrano, François Guillocheau, Thierry Adatte, and Sébastien Castelltort

The Paleocene-Eocene thermal maximum (PETM; ~55.6 Ma) is one of the most pronounced and the best known of the transient hyperthermal events of the Paleogene. The PETM is characterized by global warming, a significant perturbation of the carbon cycle, and a large perturbation of the biosphere. This extraordinary event is recorded by sharp negative carbon excursions (NCIE) in both oceanic and terrestrial carbonates. The sequence of events triggering this disturbance and the source of the 13C-depleted carbon for the NCIE remains controversial. External perturbation such as volcanism, associated with the setup of the North Atlantic Igneous Province (NAIP), is suspected to be one of the mechanisms responsible for this abrupt climate upheaval. One proxy for investigating the possible link between the establishment of the NAIP and perturbation associated with the PETM is to study mercury (Hg) concentrations record in marine and continental sedimentary successions.

In this study, we present new high-resolution mercury and stable isotopic records from peripheral basins of the Pyrenean orogen across the PETM. The four studies sections vary from continental to bathyal deposit environment and offer the potential to evaluate how major climatic disturbances are associated with the PETM record through a continental to marine transect.

The data obtained reveal the occurrence of two main NCIEs. Based on biostratigraphy and similarity of shape and amplitude of the isotopic excursions with global records, the largest NCIE is interpreted as the PETM. This sharp excursion is preceded by another one that we interpreted as the Pre-Onset Excursion (POE), founded in some other profiles worldwide. These two NCIEs are systematically associated with important mercury anomalies, whatever the environment considered. Increase in Hg contents shows no correlation with clay or total organic carbon contents, suggesting that the influences of local processes or Hg scavenging by organic matter appear to be insignificant. These results show that multiple pulses of volcanism, probably associated with the emplacement of the NAIP, contributed to the onset and the long duration of the PETM. In addition, our study highlights the possibility to get reliable information about past extreme climate events from sedimentary successions even if deposited within active tectonic domains.

This work is financed and carried out within the framework of the BRGM-TOTAL Source-to-Sink project.

How to cite: Tremblin, M., Khozyem, H., Spangenberg, J. E., Fillon, C., Calassou, S., Grauls, A., Lasseur, E., Roig, J.-Y., Serrano, O., Guillocheau, F., Adatte, T., and Castelltort, S.: Enhanced volcanism associated to the emplacement of the North Atlantic Igneous Province during the PETM evidenced by mercury anomalies in Pyrenean foreland sections, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12788, https://doi.org/10.5194/egusphere-egu21-12788, 2021.

EGU21-13017 | vPICO presentations | SSP1.3

Astronomical calibration of a key Early Eocene Boreal section: implications for the climate response to the North Atlantic Igneous Province

Nicolas Thibault, Thierry Adatte, and Jorge E. Spangenberg

Sections of the Fur formation exposed on the islands of Fur and Mors (N. Jutland, Denmark) expose well-preserved diatomites and over 140 interbedded ash layers spanning >1 Myr of the Early Eocene from the top part of the Paleocene-Eocene Thermal Maximum (PETM; 55.9 Ma). The Fur Formation is a Konzentrat-Lagerstätten with an extremely rich fish fauna as well as numerous exquisitely preserved invertebrates, vertebrates, plant material, and siliceous microfossils. Due to its peculiar bentonite record, the Fur formation also constitutes a reference for the North Sea area, recording phases of active North Atlantic Igneous Province (NAIP) volcanism. Recently, a sea-surface temperature (SST) record was derived from Tex86 values for this formation, showing anomalously cool SSTs immediately after the PETM (~11–23°C, Stokke et al., 2020) while near-freezing bottom-water temperatures (BWTs) have been inferred from clumped isotopes analysis of giant glendonite crystals (Vickers et al., 2020). The section is constrained by three radiometric dates of ash layers but cyclostratigraphic analysis of the section has proved difficult due to the apparent homogeneity of the diatomite and multitude of interbedded ash layers. We performed a high-resolution analysis of the magnetic susceptibility and carbon isotopes on bulk organics (δ13Corg) from across the top PETM to the top of the Silstrup Mb. The magnetic susceptibility depicts all the apparent ash layers as well as additional hidden ash layers with peaks of various heights, and thus constitutes an excellent stratigraphic tool for its potential of correlation to other sections and deep-sea sites of the North Atlantic. Our δ13Corg record is characterized throughout by periodicities of 65 to 90 cm and 3.6 m that match well precession and short-eccentricity cycles. Long-term trends and filtered 100 kyr cycles from our record correlate very well to the recent benthic δ13C Cenozoic compilation, leading to an astronomical calibration of the section which spans ~1300 kyr from 55.88 to 54.6 Ma. Our calibration allows for a precise illustration of the drastic contrast between the post-PETM warm tropical SSTs/BWTs and the surprisingly cool SSTs/BWTs of the North Sea.

References

Stokke, E.W., et al., 2020, Earth and Planetary Science Letters 544, 116388.

Vickers, M.L., et al., 2020, Nature Communications 11, 4713.

How to cite: Thibault, N., Adatte, T., and Spangenberg, J. E.: Astronomical calibration of a key Early Eocene Boreal section: implications for the climate response to the North Atlantic Igneous Province, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13017, https://doi.org/10.5194/egusphere-egu21-13017, 2021.

EGU21-3731 | vPICO presentations | SSP1.3

Large-scale siliciclastic input during the Paleocene-Eocene Thermal Maximum in the North Sea Basin

Simin Jin, David Kemp, David Jolley, Manuel Vieira, and Chunju Huang

The Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) was the most marked climate warming event of the Cenozoic, and a potentially useful deep time analogue for understanding environmental responses to anthropogenic carbon emissions and associated warming. The response of sedimentary systems to the large-scale climate changes of the PETM are, however, still uncertain. Here, we present an extremely thick (~140 m) record of the PETM in cores from a well in the North Sea, offshore UK. In this well, a thick Paleocene-Eocene interval is developed owing to uplift of the East Shetland Platform in the late Paleocene. Carbon isotope data through this well, coupled with detailed sedimentological analysis, show that the PETM interval is contemporaneous with >200 sandstone turbidites layers. Mud deposition without turbidites dominated sedimentation below and above the PETM. These observations support previous work from other localities highlighting how climate warming during the PETM likely drove substantial changes in hydrological cycling, erosion and sediment supply. Spectral analysis of turbidite recurrence in the PETM interval suggests that the abundance of turbidites was modulated in part by ~21 kyr astronomical precession climate cycles, further emphasizing a potential climatic control on turbidite sedimentation. In detail, we note a kiloyear-scale time lag between onset of the PETM carbon isotope excursion and the appearance of turbidites in the succession, highlighting a delay between PETM carbon release and warming and the basin-wide response in sediment supply.

How to cite: Jin, S., Kemp, D., Jolley, D., Vieira, M., and Huang, C.: Large-scale siliciclastic input during the Paleocene-Eocene Thermal Maximum in the North Sea Basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3731, https://doi.org/10.5194/egusphere-egu21-3731, 2021.

EGU21-12452 | vPICO presentations | SSP1.3

Chemical weathering response to extreme global warming during Paleocene-Eocene Hyperthermals, Southern Pyrenees, Spain

Rocio Jaimes-Gutierrez, Thierry Adatte, Emmanuelle Puceat, Jean Braun, and Sebastien Castelltort

The Paleocene and early Eocene were periods yielding multiple hyperthermal events. The most pronounced of them was the Paleocene-Eocene Thermal Maximum (PETM), which was characterized by an abrupt increase in global temperature (5–8 °C) over a short time (20 ka). A negative carbon isotope excursion marks the onset of the PETM, which resulted in the fast injection of CO2 into the ocean-atmosphere system, triggering global climatic changes. Geochemical, mineralogical, and sedimentological markers record the resulting increase in continental weathering. This is important, as enhanced chemical erosion influences both the CO2 concentration in the atmosphere and ocean acidity, generating a feedback mechanism. Hence, constraining the rates and intensity of weathering response can further clarify the causes for the PETM and Eocene hyperthermals. This study focuses on the well-preserved Pyrenean foreland basin and intends to assess the continental chemical weathering response of the sediment routing system during the PETM. Clay mineralogy is a climate-sensitive proxy, which records changes in continental erosion. Therefore, clay mineral proportions will be analyzed using X-ray diffraction and major element chemistry on clay-rich samples from the entire source-to-sink system (continental to deep marine deposits). Kaolinite and smectite will be separated from the detrital clay fraction and further subjected to δ18O and δD isotopic analysis for paleoclimatic reconstruction. The combined Lu-Hf and Sm-Nd isotope systems in the clay fraction of the sediments will be used to track the evolution of chemical weathering intensity. The outcome of this project will serve to validate numerical models to understand erosion as a function of rapid climatic change. This topic is of keen interest, as the PETM and its sedimentological signal work as a natural analog for anthropogenically-induced climatic change. The project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant Agreement No 860383.

How to cite: Jaimes-Gutierrez, R., Adatte, T., Puceat, E., Braun, J., and Castelltort, S.: Chemical weathering response to extreme global warming during Paleocene-Eocene Hyperthermals, Southern Pyrenees, Spain, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12452, https://doi.org/10.5194/egusphere-egu21-12452, 2021.

EGU21-10340 | vPICO presentations | SSP1.3

The incidence of unusual test morphologies of Eocene Larger benthic foraminifera: An example of Paleogene Adriatic Carbonate Platform

Vlasta Ćosović, Jelena Španiček, Katica Drobne, and Ervin Mrinjek

The Paleogene Adriatic carbonate platform(s) existed within the Central NeoTethys (around 32 N paleolatitude) from the Danian to the late Eocene (Bartonian/Priabonian) and produced a succession of limestones up to 500 m thick, rich in larger benthic foraminifera (LBF). The Eocene sediments are widely distributed along the eastern Adriatic coast and have been studied for many years. Taking into account the climatic changes that took place within the Eocene (Early Eocene and Middle Eocene climatic optima, known as EECO, MECO), special attention was paid to the composition of shallow-marine foraminiferal assemblages. The studies reveal the following trends: (1) the alveolinid-dominated assemblages were replaced by nummulitid-dominated assemblages around the MECO; (2) the greater species and morphological diversity (spherical, ellipsoid, extremely elongated fusiform) of the alveolinid fauna was evident at the EECO; (3) the nummulitid-dominated fauna was characterized by less diversified assemblages compared to the alveolinid ones and by the co-occurrence of scleractinian corals, coralline red algae and aborescent foraminifera. The occurrence of twin embryos has been assigned to the early Eocene in the alveolinid populations, especially in Alveolina levantina and A. axiampla (in some sections, the frequency is greater than 5%), and these coalesced embryos have the same size as the single form (usually they are smaller). The LBF assemblages of Middle Eocene showed a greater frequency of doubled adult tests (Orbitolites sp., Nummulites sp.). The origin of these unusual morphologies is poorly known, usually described as the results of stressful conditions. Considering the timing of the appearance of such morphologies, temperature and associated changes in the shallow-marine environment could be the cause.

This study is carried out as part of the scientific project IP-2019-04-5775 BREEMECO, funded by Croatian Scientific Foundation.

How to cite: Ćosović, V., Španiček, J., Drobne, K., and Mrinjek, E.: The incidence of unusual test morphologies of Eocene Larger benthic foraminifera: An example of Paleogene Adriatic Carbonate Platform, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10340, https://doi.org/10.5194/egusphere-egu21-10340, 2021.

EGU21-15570 | vPICO presentations | SSP1.3 | Highlight

Coring of the Paleocene-Eocene Thermal Maximum (PETM) in Denmark: ICDP Project PVOLC

Morgan Jones, Ella Stokke, Sverre Planke, Lars Augland, Henrik Svensen, Christian Tegner, Appy Sluijs, Joost Frieling, Tamsin Mather, and Ritske Huismans

The Paleocene-Eocene Thermal Maximum (PETM) is recognized as one of the potential analogues in the geological record for present-day global warming. The aim of the International Continental Scientific Drilling Program (ICDP) project PVOLC is to test the hypothesis that voluminous magmatism in sedimentary basins in the NE Atlantic triggered the PETM. Two ICDP boreholes are planned to core the boundary in the Limfjorden area in Denmark in 2022. PVOLC will be conducted in conjunction with IODP Exp 396 on the mid-Norwegian continental margin. The North Atlantic Igneous Province (NAIP) was is a large igneous province (5–10 million km3 magma) that coincided with both the opening of the NE Atlantic Ocean and the greenhouse conditions of the early Paleogene. The close temporal correlations suggest a possible causal relationship between the NAIP and both the climatic and tectonic changes around 56– 54 Ma. In particular, the main acme of NAIP activity occurred across the Paleocene–Eocene Thermal Maximum (PETM), an extreme hyperthermal event that represents the warmest conditions of the last 60 million years. The NAIP is among several proposed candidates for driving global warming through CO2/CH4 emissions, both by magmatic degassing and through contact metamorphism around shallow intrusions in organic rich sedimentary basins. What is needed to refine the role of the NAIP during the PETM are key sedimentary sequences that contain abundant volcanic and climatic proxies in the same section, thereby allowing a precise geochronology of events to be attained. The sediments exposed on the Fur island, Denmark, are a key sequence of PETM and post-PETM strata with little thermal overprint and hundreds of well-preserved volcanic ash layers from the NAIP. The effects of Quaternary glaciotectonism have disturbed this key stratigraphic interval at Fur, but seismic surveys indicate that undisturbed strata are found a few km to the south. The ICDP PVOLC project plan is to drill both the Paleocene-Eocene and the Cretaceous-Paleocene boundaries, hopefully recovering pristine cores suitable for high-resolution geochemical and climatic studies.

How to cite: Jones, M., Stokke, E., Planke, S., Augland, L., Svensen, H., Tegner, C., Sluijs, A., Frieling, J., Mather, T., and Huismans, R.: Coring of the Paleocene-Eocene Thermal Maximum (PETM) in Denmark: ICDP Project PVOLC, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15570, https://doi.org/10.5194/egusphere-egu21-15570, 2021.

EGU21-15114 | vPICO presentations | SSP1.3 | Highlight

Mid-Norwegian continental margin magmatism and Paleogene global climate change: An overview of the upcoming International Ocean Discovery Program (IODP) Expedition 396

Sverre Planke, Ritske Huismans, Christian Berndt, Laurent Gernigon, Stefan Buenz, Jan Inge Faleide, Morgan T. Jones, Henrik H. Svensen, Dougal A. Jerram, John M. Millett, and Reidun Myklebust

Continental breakup between Greenland and NW Europe in the Paleogene was associated with transient massive magmatism and a global hot-house named the Paleocene-Eocene Thermal Maximum (PETM). The International Ocean Discovery Program (IODP) Expedition 396 will study the cause of this magmatism and its climate implication by drilling up to nine boreholes across the Vøring and Møre continental margins in August-September 2021. The expeditions will be conducted in conjunction with ICDP project PVOLC which plan to drill the Paleogene sequences in a more distal setting in Denmark in 2022. The NE Atlantic conjugate volcanic rifted margins are characterized by extensive break-up magmatism recorded by basalt flows, volcanogenic sediments, magmatic underplates, and intrusive complexes in sedimentary basins and the crust. Massive injection of magma into organic-rich sedimentary basins is a likely mechanism for triggering short-term global warming during the Paleocene-Eocene Thermal Maximum (PETM). A key objective of this expedition is to document the nature and explain the causes and consequences of excess magmatism during breakup as the large amount of magmatism cannot be easily be explained by passive decompressional melting of sub-lithospheric mantle with a normal potential temperature. New constraints on 1) melting conditions, 2) timing of magmatism, 3) spatial and temporal variations, 4) eruption environment, 5) sedimentary proxy data, and 6) temporal resolution of magmatism and climate change events are required to resolve current controversies. Systematic IODP drilling is a way to provide these constraints and will allow the development of a quantitatively testable framework for volcanic rifted margin formation and consequences for global climate change. New 3D seismic data collected by the industry and academia during the past few years have provided unique imaging of the basalt and sub-basalt sequences and allowed for optimal planning of the drill sites for scientific purposes. Additional holes are located along and outboard of the continent-ocean boundary to constrain the temporal evolution of the breakup magmatism. Two of the scientific drilling aims of this cruise are to core Paleogene sequences across the PETM and to drill one of the thousands of hydrothermal vent complexes to attain a proximal record of NAIP activity. This will give vital information on the proximal environmental disturbances during the NAIP emplacement.

How to cite: Planke, S., Huismans, R., Berndt, C., Gernigon, L., Buenz, S., Faleide, J. I., Jones, M. T., Svensen, H. H., Jerram, D. A., Millett, J. M., and Myklebust, R.: Mid-Norwegian continental margin magmatism and Paleogene global climate change: An overview of the upcoming International Ocean Discovery Program (IODP) Expedition 396, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15114, https://doi.org/10.5194/egusphere-egu21-15114, 2021.

SSP1.11 – Evolution of restricted evaporitic basins: paleogeography, hydrogeochemistry, climate and ecosystems

EGU21-15511 | vPICO presentations | SSP1.11

Evaporite dynamics and their effects on global climate and oxygen

Graham Shields and Benjamin Mills

Evaporite weathering and deposition are seldom in balance even on million-year time-scales with grand depositional events superimposed against a background of more slowly varying weathering. Despite such imbalance, biogeochemical models generally assume that evaporite weathering and deposition rates are equal on all time scales. Changes in evaporite dynamics through time will likely impact oxidant budgets through the sulfur cycle and we have shown this to have been especially significant during Proterozoic times. Recently, we proposed that imbalances between evaporite weathering and deposition can also affect climate through the process of carbonate sedimentation. Calcium sulfate weathering supplies calcium ions to the ocean unaccompanied by carbonate alkalinity, so that increased carbonate precipitation strengthens greenhouse forcing through transfer of carbon dioxide to the atmosphere. Conversely, calcium sulfate deposition weakens greenhouse forcing, while the high depositional rates of evaporite giants may overwhelm the silicate weathering feedback, causing several degrees of planetary cooling. Non-steady-state evaporite dynamics and related feedbacks have hitherto been overlooked as drivers of long-term carbon cycle change. In this talk, we illustrate the importance of evaporite deposition, in particular, by showing how a series of massive depositional events contributed to global cooling during the mid–late Miocene. Further studies are required to quantify gypsum deposition over time and its possible effects on deoxygenation of the surface environment, especially at times of mass extinction, as well as on climate.

How to cite: Shields, G. and Mills, B.: Evaporite dynamics and their effects on global climate and oxygen, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15511, https://doi.org/10.5194/egusphere-egu21-15511, 2021.

EGU21-15911 | vPICO presentations | SSP1.11

Evaporation rate from bare sandstone surfaces in humid climate

Tomá Weiss, Martin Slavík, and Jiří Bruthans

Evaporation from porous rock is not only a significant part of the earth-atmosphere water balance but it also plays a crucial role in weathering processes. In the case of salt weathering, the evaporation rate directly influences the amount of precipitated aggressive salts. Evaporation also strongly affects frost, hydric and biogenic weathering, since they are influenced by water content and its temporal changes. Without proper quantification of the evaporation loss, it is not possible to thoroughly explain and/or predict the development of moisture content and its spatial distribution within natural rock outcrops. Despite its importance, the study of evaporation from porous rocks has seen little scientific focus so far. In our study (Slavík et al., 2020), we measured the evaporation rate from bare surfaces of sandstone under field microclimate on a roughly monthly interval for about one year. The measurement was performed using sandstone cores with a set depth of the vaporization plane (i.e. the area where most of the phase change from liquid to vapour occurs in the subsurface) and we used a simple Fick’s law of diffusion for calculations of the evaporation rate from the cores. The calculations required only a laboratory-measured water-vapour diffusion coefficient of the sandstone, in-situ seasonally measured vaporization plane depth, and logs of air humidity and temperature. The analysis of measured and calculated evaporation rate revealed that far the most important single factor influencing the evaporation rate is the depth of the vaporization plane. Other factors such as the microclimate characterised by temperature and relative humidity were of lesser importance and the calculated evaporation rate reasonably follows measured values with Pearson correlation coefficient r > 0.81. The experimental setup of evaporation rate measurement, for its simplicity and price, should find use in studies with high-number measuring sites or even locations with a risk of apparatus damage. Our measurements were performed in a humid continental climate and the suggested approach should be verified in more arid environments.

Figure: Goodness‐of‐fit between measured and calculated evaporation rate. Dashed line represents the identity line (calculated values equal to measured values).

This research was funded by the Czech Science Foundation [GA19-14082S].

References: Slavík, M., Bruthans, J., Weiss, T., Schweigstillová, J. (2020): Measurements and calculations of seasonal evaporation rate from bare sandstone surfaces: Implications for rock weathering. Earth Surface Processes and Landforms 45, 2965–2981.

How to cite: Weiss, T., Slavík, M., and Bruthans, J.: Evaporation rate from bare sandstone surfaces in humid climate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15911, https://doi.org/10.5194/egusphere-egu21-15911, 2021.

EGU21-12510 | vPICO presentations | SSP1.11

Hydroclimatic Controls on Salt Fluxes and Halite Deposition in the Dead Sea and the Shaping of “Salt Giants”

Ido Sirota, Raphael Ouillon, Ziv Mor, Eckart Meiburg, Yehouda Enzel, Ali Arnon, and Nadav Lensky

As the only deep hypersaline, halite‐precipitating lake on Earth today, the Dead Sea is the
single modern analog for investigating the mechanisms by which large‐scale and thick salt deposits,
known as “salt giants”, have accreted in the geological record. We directly measure the hydroclimatic forcing
and the physical limnologic processes leading to halite sedimentation, the vertical thermohaline structure,
and salt fluxes in the Dead Sea. We demonstrate that changes in these forcing lead to strong seasonal
and regional variations in the stratification stability ratio, triggering corresponding spatiotemporal
variations in thermohaline staircase formation and diapycnal salt flux, and finally control the thickness of
the halite layer deposited. The observed staircase formation is consistent with the mean‐field γ instability,
causing layering in double‐diffusive convection. We show that double diffusion and thermohaline staircase
formation drive the spatial variability of halite deposition in hypersaline water bodies, underlying and
shaping “salt giants” basin architecture.

How to cite: Sirota, I., Ouillon, R., Mor, Z., Meiburg, E., Enzel, Y., Arnon, A., and Lensky, N.: Hydroclimatic Controls on Salt Fluxes and Halite Deposition in the Dead Sea and the Shaping of “Salt Giants”, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12510, https://doi.org/10.5194/egusphere-egu21-12510, 2021.

EGU21-14573 | vPICO presentations | SSP1.11

Microbial sulfur cycling during the formation of Primary Lower Gypsum in Mediterranean marginals basins

Laetitia Guibourdenche, Pierre Cartigny, Francesco Dela Pierre, Marcello Natalicchio, and Giovanni Aloisi

During the first phase of the Messinian Salinity Crisis, massive amounts of sulfate (SO42-) have been sequestred in the form of up to 200m thick gypsum deposits (Primary Lower Gypsum) in Mediterranean marginal basins. The sulfur isotopic composition of the sulfate ion of this unit (δ34SSO4) (on average 22.3 ‰) strongly suggests that gypsum was formed by concentration of marine sulfate. Interestingly, the preservation of sulfide globules within the gypsum and marls interbeds suggests that the basin sulfate was not only involved in gypsum formation but a fraction was also reduced through microbial sulfate reduction. Moreover, filamentous fossils interpreted to be the remnants of sulfide oxidizing bacterias are entrapped in this gypsum and indicate, together with the occurrence of sulfide globules and dolomite, that an active biogeochemical sulfur cycling was active at the time of Primary Lower Gypsum deposition. To investigate the role of this active sulfur cycling in Mediterranean marginal basins, we analyzed the multiple sulfur isotopic composition of sulfate and sulfide minerals (δ34S andΔ33S)from Primary Lower Gypsum of the Vena del Gesso basin (Italy). Whereas the isotopic composition of gypsum (δ34SSO4 from 21 to 24‰ and Δ33SSO4 from -0.001 to 0.049‰) display very homogenous values that are close to those of the Messinian ocean (δ34SMSC ~22±0.2‰ and Δ33SMSC~0.039±0.015), the analyzed reduced sulfur compounds display a wide range of variability  with -36 to +9‰ in δ34S and -0.017 to 0.125‰ in Δ33S. This suggests huge hydrologically-driven redox variations during Primary Lower Gypsum deposition in the Vena del Gesso basin, possibly involving intermittent stratification of the water column and an active microbial cycling of sulfur.

How to cite: Guibourdenche, L., Cartigny, P., Dela Pierre, F., Natalicchio, M., and Aloisi, G.: Microbial sulfur cycling during the formation of Primary Lower Gypsum in Mediterranean marginals basins, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14573, https://doi.org/10.5194/egusphere-egu21-14573, 2021.

EGU21-12551 | vPICO presentations | SSP1.11

Low-salinity Mediterranean gypsum deposits: chemical vs biological products

Giovanni Aloisi, Marcello Natalicchio, Laetitia Guibourdenche, Antonio Caruso, and Francesco Dela Pierre

Large deposits of gypsum accumulated in the marginal basins of the Mediterranean Sea during the Messinian Salinity Crisis. These form the marginal portions of the Mediterranean Salt Giant (MSG) that also occupies the deep, central Mediterranean basins. Although the marine, evaporitic origin of the MSG is undisputed, the analysis of gypsum fluid inclusions and of gypsum-bound water (d18OH2O and dDH2O) suggest that marginal basin gypsum formed from low- to moderate-salinity water masses (5 - 60 ‰), rather than from high-salinity brines (130 - 320 ‰), as expected during the evaporation of seawater. We present a new set of water isotope and fluid inclusion salinity data that extends the low salinity signature of gypsum to include five Mediterranean Sea marginal basins: Caltanissetta Basin (Sicily), Sorbas Basin (Spain), Piedmont Basin and Vena del Gesso Basin (northern Italy) and Catanzaro Trough (Southern Italy). With a simple geochemical model we explore the salinity-d18OH2O-dDH2O evaporation path and the 87/86Sr and d34SSO4 composition of the Mediterranean Sea subject to a variety of evaporation conditions and mixing ratios with continental runoff. This approach suggests that evaporation and mixing with continental runoff - including freshwater transiting via the Paratethys - cannot lead to the observed geochemical signature of MSC gypsum deposits. An alternative process that decouples the saturation state with respect to gypsum from salinity must have been active. We are exploring the possibility that the biogeochemical sulfur cycle leads to spatially and temporally localized gypsum supersaturation conditions via the production of SO42- by the oxidation and disproportionation of reduced sulfur compounds.

How to cite: Aloisi, G., Natalicchio, M., Guibourdenche, L., Caruso, A., and Dela Pierre, F.: Low-salinity Mediterranean gypsum deposits: chemical vs biological products, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12551, https://doi.org/10.5194/egusphere-egu21-12551, 2021.

EGU21-5791 | vPICO presentations | SSP1.11

Applicability of carbonate reference materials as matrix-matched standards for in-situ LA-ICPMS U-Pb dating of Sulphates 

Aratz Beranoaguirre, Iuliana Vasiliev, and Axel Gerdes

Recent developments on analytical capabilities in the field of in-situ laser ablation mass spectrometry (LA-ICPMS) have expanded the applications of U-Pb geochronometers in low-U minerals such as carbonates (Roberts et al. 2020) or garnets (Millonig et al., 2020). The rapid development of the technique requires well-characterized, matrix-matched reference materials, which are essential for ion probes or LA-ICPMS due to potential matrix effects. However, given the unavailability of standards for some minerals, the use of non-matrix-matched standards, i.e. reference materials that are different to the sample, have been also addressed (Piccione et al., 2019).

In this contribution, we explored the possibility of using carbonate reference materials for in-situ U-Pb dating of sulphates. For that purpose, we selected samples from the Messinian Salinity Crisis because their ages are well established by cyclostratigraphy and thus can be compared with ages obtained by LA-ICPMS analysis. Data was acquired using a RESOLution 193 nm ArF excimer laser coupled to a (I) sector field ICP-MS (ElementXR) or (II) multicollector ICP-MS (Neptune Plus).

The majority of the samples (27 out of 32) failed due to the elevated common-Pb content and low 238U/204Pb ratios. Nevertheless, five of the samples showed greater amounts of U and U/Pb ratios of up to 600; therefore, regression lines could be drawn and ages are calculated with 5-10 % of uncertainty. These ages obtained are within error of the cyclostratigraphic ages already published (Vasiliev et al., 2017).

 

Millonig et al., (2020) Earth Planet. Sci. Lett. 552, 116589; Piccione et al. (2019) Geosphere 15 (6), 1958– 1972; Roberts et al. (2020) Geochronology 2, 33–61; Vasiliev et al. (2017) Palaeogeogr. Palaeoclimatol. Palaeoecol. 471, 120-133.

How to cite: Beranoaguirre, A., Vasiliev, I., and Gerdes, A.: Applicability of carbonate reference materials as matrix-matched standards for in-situ LA-ICPMS U-Pb dating of Sulphates , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5791, https://doi.org/10.5194/egusphere-egu21-5791, 2021.

EGU21-14007 | vPICO presentations | SSP1.11

The hydrochemical genesis of groundwater brines of the Eastern arm of the Makgadikgadi basin.

Fiona Motswaiso, Jiajie Wang, Kengo Nakamura, Noriaki Watanabe, and Takeshi Komai

Hydrochemistry of groundwater brines of the eastern part of the large playa deposit in the Makgadikgadi basin in northern Botswana has been analyzed. Brine samples were collected from 37 production and monitoring wells in this area. Brine samples for analysis were filtered to 0.45 and analyzed for major and minor anions and cations as well as trace species. The results of the hydrochemical analysis revealed that the major element chemistry of these samples from the area is dominated by Na and Cl with minor components of K, CO3, HCO3, and SO4, and depleted in Ca and Mg, which is typical of seawater or coastal water. The brine type is Na-Cl type. However, the exact mechanism of the genesis of the brines is still ambiguous, hence comparison curves of Na/C1 against seawater concentration factor (SCF) and Ca/Mg against (SCF) in order to ascertain the brine genesis geochemically were employed. The relationship between the current results to previous seawater freezing and evaporation experiments by other researchers indicated that the brines were formed by seawater evaporation. Observed variations in hydrogeochemistry and salinity with depth support the results of previous studies indicating downward infiltration of brackish waters and evaporative and/or mixing processes. With respect to minor and trace element analysis, A comparison of measured concentrations of trace elements to their concentration in seawater when normalized against the concentration of chloride, it can be seen that the saline groundwater brines in the area are enriched in a number of trace elements including W, Th, Se, Pb while depleted in Sr. Enrichments in all of these elements which would be expected to exhibit conservative behavior in the brines suggest that the origin of the brine is not restricted to the simple evaporation of seawater or but to a combination of end members enriched in these elements such as riverine and groundwater inputs.

How to cite: Motswaiso, F., Wang, J., Nakamura, K., Watanabe, N., and Komai, T.: The hydrochemical genesis of groundwater brines of the Eastern arm of the Makgadikgadi basin., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14007, https://doi.org/10.5194/egusphere-egu21-14007, 2021.

EGU21-5785 | vPICO presentations | SSP1.11

Seismic evidence of the Messinian events in the Adriatic basin

Alessandra Lanzoni, Anna Del Ben, Edy Forlin, Federica Donda, and Massimo Zecchin

The Adriatic basin represents one of several restricted basins located in the Mediterranean Area. It consists of the foreland of three different orogenic belts: the Dinarides to the East, active during the Eocene, the Southern Alps to the North, active since the Cretaceous time, and the Apennines to the West, active since the Paleogene. The Apennines had a primary role during the Messinian Salinity Crisis (MSC), conditioning the connection between the Adriatic basin, the Ionian basin, and the proto-Tyrrhenian basin. During the Messinian, the present Adriatic Sea was characterized by shallow water domains, where gypsum evaporites initially deposited and often successively incised or outcropped. 

In the past 50 years, a massive dataset, composed of 2D multichannel seismic data and boreholes, was collected, covering almost the whole Adriatic basin in the Italian offshore. In this work, we interpreted the Plio-Quaternary base (PQb), based on available public datasets and on seismic profiles present in literature, which provided regional information from the northernmost Trieste Gulf (Northern Adriatic Sea) to the Otranto Channel (Southern Adriatic Sea). Here, we propose the PQb time-structural map, obtained by analyzing more than 600 seismic profiles. The PQb represents both the Messinian erosion and/or the top of the Messinian evaporites. It is characterized by a high-amplitude reflector, commonly called “horizon M” in the old literature. Principal findings concerning the Messinian event are summarized as below: 

-The Northern Adriatic (Gulf of Trieste, Gulf of Venice, Po delta, Kvarner Area) reveals widespread channelized systems produced by the initial decrease of the sea level, followed by subaerial erosion, related to further sea level decrease. High-grade erosion involved the nearby Adriatic carbonate platform in the Croatian offshore, where deep valleys, filled with Last Messinian or post- Messinian sediments, cut through the limestones.

-The Central Adriatic (from the Po delta to the Gargano Promontory) displays a higher evaporites accumulation than the northern sector. Meanwhile, the Mid-Adriatic Ridge was already developing, along with the Apennine Chain, which was in a westernmost position. Erosional features in the deeper area are related to channelized systems, which followed the evaporites deposition. Meanwhile, also the Mid-Adriatic Ridge was affected by erosion.

-The Southern Adriatic (from the Gargano Promontory to the Otranto Channel) is characterized by the Mesozoic Apulia carbonate platform, covered by a thin Cenozoic sequence affected by subaerial erosion or non-deposition. The platform margin and the slope leading to the deepest South Adriatic basin, where a Messinian gypsum layer, also recorded in the Albanian and Croatian offshore, shows a lower level of upper erosion.

In general, we notice strongly variable thicknesses of the horizon M, which is related to submarine erosion (channels), subaerial erosion (discontinuous surfaces), non-deposition (possible unconformity), and tilting toward the surrounding chains (deepening horizons). In this work, we evaluate these different components from a regional point of view.  

How to cite: Lanzoni, A., Del Ben, A., Forlin, E., Donda, F., and Zecchin, M.: Seismic evidence of the Messinian events in the Adriatic basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5785, https://doi.org/10.5194/egusphere-egu21-5785, 2021.

EGU21-10081 | vPICO presentations | SSP1.11 | Highlight

Modelling the vertical motions of the Alboran Sea since the Messinian salinity crisis: Topographic reconstruction and glacial-isostatic sea-level effects 

Hanneke Heida, Daniel Garcia-Castellanos, Ivone Jiménez-Munt, Ferran Estrada, Gemma Ercilla, Sophie Coulson, and Jerry Mitrovica

The Messinian Salinity Crisis (MSC) was caused and terminated by changes in the Atlantic-Mediterranean connectivity in the western end of the Alboran Basin, a complex tectonic area affected by the Iberia-Africa collision and the presence of a subducted lithospheric slab beneath the Betic-Rif orogen.

The isostatic, tectonic and erosional effects on surface topography work on different spatial and temporal scales, and their relative contributions to the changes in connectivity and subsequent evaporite deposition and sea-level drop are difficult to constrain.

We perform 2D-planform flexural isostatic modeling using the Messinian Erosion Surface imaged in the Alboran Basin to reconstruct the topography and vertical motions of this region since the end of the MSC. The results constrain the original depth of the Messinian erosional features to test their consistency against the various models proposed for Mediterranean sea-level changes during the MSC.
We apply Glacial Isostatic Adjustment theory to quantify the time response of these vertical motions to the large MSC-related mass shifts (salinification, evaporite deposition and a kilometer-scale sea-level drop),  and their gravitational effects on sea-level in the Mediterranean. In particular, models for the Strait of Gibraltar allowus to identify the potential role of these effects as feedback mechanisms influencing the rates and duration of changes in the Atlantic-Mediterranean connectivity at the straits.  We will explore the possible implications of these for the timing of the closure of the last Atlantic-Mediterranean seaway.

How to cite: Heida, H., Garcia-Castellanos, D., Jiménez-Munt, I., Estrada, F., Ercilla, G., Coulson, S., and Mitrovica, J.: Modelling the vertical motions of the Alboran Sea since the Messinian salinity crisis: Topographic reconstruction and glacial-isostatic sea-level effects , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10081, https://doi.org/10.5194/egusphere-egu21-10081, 2021.

The Nahr Menashe Unit (NMU), which forms the uppermost part of the Messinian succession,  is one of the most cryptic and elusive sedimentary units present in the Levant basin (Eastern Mediterranean). We use a high-resolution 3D seismic dataset from offshore Lebanon to propose a new interpretation for its formation and evolution. The NMU varies laterally across the basin both in thickness and internal seismic characteristics. The variably coherent cyclic seismic packages affected by fracturing, faulting suggests that the NMU represent a reworked, layered evaporite succession interbedded with siliciclastics derived from both the Lebanon Highlands and the Latakia Ridge. Widespread semi-circular depressions, random linear imprints, passive surface collapsing and residual mound features within the NMU suggest that post depositional diagenetic and/or strong dissolution process often affected its evaporite-rich subunits. The well-known extended valley and tributary channel systems characterising the uppermost NMU shows mainly erosional rather than depositional features. Erosion started after deposition of NMU as a consequence of the maximum base level fall during the last phase of the Messinian Salinity Crisis (MSC). The channel and valley system were subsequently infilled by layered sediments here interpreted to represent post-MSC deep water marine reflooding. In conclusion, our analyses suggest the NMU can be interpreted as a mixed evaporite-siliciclastic system deposited in a shallow marine or marginal environment, which subsequently experienced fluvial erosion and later burial by transgressive/high-stand sediments.

How to cite: Kabir, S. M., Iacopini, D., Hartley, A., Maselli, V., and Oppo, D.: The role of the Nahr Menashe in the Messinian Salinity Crisis: formation, dissolution and fluvial incision of the top evaporite unit in the NE Levant Basin, Eastern Mediterranean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10318, https://doi.org/10.5194/egusphere-egu21-10318, 2021.

EGU21-8853 | vPICO presentations | SSP1.11

Climate and carbon cycle changes drive the hydrographic configuration of the eastern Mediterranean through the Tortonian-Messinian Transition

Evangelia Besiou, George Kontakiotis, Assimina Antonarakou, Andreas Mulch, and Iuliana Vasiliev

The Late Miocene has been considered one of the most climatically stable periods of the Cenozoic, time span characterized by minor long-term cooling and ice growth. Especially, the Tortonian-Messinian Transition is recognized as a priority for paleoenvironmental reconstruction and climate modelling due to the significant paleoenvironmental changes preceding the Messinian Salinity Crisis (MSC; 5.97-5.33 Ma). Here, we present stable oxygen (δ18O) and carbon (δ13C) isotopes measured on benthic and planktonic foraminifera from Potamida section (Crete Island, eastern Mediterranean). The δ18O results indicate a decoupling between the surface and the bottom water column starting before the Tortonian-Messinian boundary. The difference between planktonic and benthic oxygen isotope signals (Δδ18O) further provides an estimate of the degree of water column stratification during that time. The δ13C data indicate a generally trend towards lighter values as an excellent illustration of the Late Miocene Carbon Isotope Shift (LMCIS; 7.6-6.6 Ma) due to progressive restriction of the Mediterranean basin, with the exception of the 7.38-7.26 Ma time interval where significantly heavier δ13C values are documented in both records. Such changes in carbon cycle seem to be most pronounced in the planktonic foraminiferal record (surface waters) through a 6-cycle development indicative of a cyclic productivity pattern during the latest Tortonian. The entire record is substantiated by sea surface temperature (SST) estimates based on TEX86 biomarker based proxy. The reconstructed SST record shows that a warm phase characterized the late Tortonian sea surface (~27⁰C), time followed by a strong, steady cooling starting with earliest Messinian, when the SSTs dropped to values as low as 20⁰C. The outcome of the combined stable isotope and biomarker based SST data hint to increased salinity in the surface waters already before the Messinian, while at the Tortonian-Messinian Transition, the conditions in the surface waters changed towards cooler (~24⁰C) and normal salinity conditions.

How to cite: Besiou, E., Kontakiotis, G., Antonarakou, A., Mulch, A., and Vasiliev, I.: Climate and carbon cycle changes drive the hydrographic configuration of the eastern Mediterranean through the Tortonian-Messinian Transition, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8853, https://doi.org/10.5194/egusphere-egu21-8853, 2021.

EGU21-8711 | vPICO presentations | SSP1.11

The eastern Mediterranean pre-MSC brine pool as an analogue for future subtropical hydroclimate

George Kontakiotis, Geanina Butiseaca, Assimina Antonarakou, Vasileios Karakitsios, Stergios D. Zarkogiannis, Evangelia Besiou, Konstantina Agiadi, Efterpi Koskeridou, Danae Thivaiou, Andreas Mulch, and Iuliana Vasiliev

During the Late Miocene the Mediterranean Sea experienced severe disruption of its connectivity to the Atlantic Ocean, highlighted by a rapid sea-level drop, culminating to the Messinian Salinity Crisis (MSC; 5.97-5.33 Ma). Such a paleoceanographic change, triggered by the cumulative effect of climate and tectonics, caused high-amplitude fluctuations in the hydrology of the entire basin, and further influenced the geological history of the Mediterranean Sea. Although a consistent pattern of the paleoclimate has started to emerge, we currently lack a continuous sea surface salinity (SSS) record linking the timing of sea surface temperature (SST) variations, sea-level fluctuations, and the overall environmental change, particularly for the pre-evaporitic period. Initial viewpoints of a linear and gradual salinity increase prior to the onset of the MSC have been recently revised and replaced by highly variable salinity-related patterns representative of the stepwise restriction of the Mediterranean Sea. Here we use the combined Tetra Ether (TEX86-) and/or alkenone unsaturation ratio (UK′37) based SSTs and oxygen isotopes (δ18O) from the cyclic marl-sapropel sedimentary succession of Agios Myron section (north-central Crete, Greece) to assess hydroclimate changes during that time, and we finally present the first record of SSS in the eastern Mediterranean Sea for the earliest Messinian (7.2–6.5 Ma). The relatively stable marine conditions after the Tortonian/Messinian boundary, expressed through a cool and fresh upper water column, significantly changed at ∼6.9 Ma, when an important reversal in the heart of the Messinian cooling trend supplemented by a coherent hypersaline water column took place. The observed SST and SSS patterns provide context for a two-fold evolution of this event (centered at 6.9–6.8 and 6.72 Ma), which finally led to the onset of a brine pool into the eastern Mediterranean basin. The transitional character of the following time interval (6.7–6.5 Ma) marks another important step in the basin restriction with a wider range of salinity fluctuations from highly saline to diluted conditions and enhanced water column stratification prior to the deposition of evaporites. Overall, this evolution supports the concept of a stepwise restriction of the Mediterranean Sea associated with substantial hydroclimate variability and increasing environmental (thermal and salinity) stress, and further confirms its position as a preferred laboratory for developing new conceptual models in paleoceanography, allowing the investigation and scale assessment of a phenomenon with high chances of representing a future analogue scenario.

How to cite: Kontakiotis, G., Butiseaca, G., Antonarakou, A., Karakitsios, V., Zarkogiannis, S. D., Besiou, E., Agiadi, K., Koskeridou, E., Thivaiou, D., Mulch, A., and Vasiliev, I.: The eastern Mediterranean pre-MSC brine pool as an analogue for future subtropical hydroclimate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8711, https://doi.org/10.5194/egusphere-egu21-8711, 2021.

EGU21-5409 | vPICO presentations | SSP1.11

Multiple crises before the big crisis: Early Messinian Eastern Mediterranean paleoclimate reconstruction inferred from biomarkers and stable isotopes (Crete, Greece)

Geanina-Adriana Butiseaca, Marcel T. J. van der Meer, Giorgos Kontakiotis, Konstantina Agiadi, Assimina Antonarakou, Andreas Mulch, and Iuliana Vasiliev

Messinian Mediterranean (7.24‒5.33 Ma) was a highly dynamic environment governed by global climatic and regional tectonic activity. The impact of these two environmental factors is highly distinguishable especially during the latest Messinian (5.97–5.33 Ma), when the famous Messinian salinity crisis (MSC) affected the Mediterranean realm. However, the interplay between climate and tectonics is less studied for the earliest Messinian. Here we use biomarker analysis, coupled with compound-specific hydrogen (δ2H) and carbon isotopes (δ13C), to track changes in the hydrological budget, mean annual air temperature (MAAT), vegetation and reconstruct the sea-land climate conditions in Eastern Mediterranean between 7.2‒6.5 Ma. Our data from Agios Myron section on Crete (Greece) confirms a series of drastic environmental changes in the Eastern Mediterranean during the mentioned time interval. δ2H values of alkenones indicate highly evaporitic events accompanied by shifts in vegetation, from dominant >C3 plants to marked increasing dominance of C4, with recurrence of C3 vegetation at ~6.99 and 6.78 Ma respectively. The MAAT data indicate average values of 14⁰C and the overall trend suggests an orbitally paced continental climate, with maximum temperatures registered during eccentricity maxima. The reconstructed paleo-soil pH record follows a stepwise increasing trend towards slightly-alkaline soils, supporting an enhanced open vegetation contribution resulting from the ongoing continentalisation. These results provide new insights into the Messinian environmental conditions of the Mediterranean Sea, suggesting an ongoing restriction after 7 Ma, with multiple restrictive phases marked by increasing intensity until the final MSC event.

How to cite: Butiseaca, G.-A., van der Meer, M. T. J., Kontakiotis, G., Agiadi, K., Antonarakou, A., Mulch, A., and Vasiliev, I.: Multiple crises before the big crisis: Early Messinian Eastern Mediterranean paleoclimate reconstruction inferred from biomarkers and stable isotopes (Crete, Greece), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5409, https://doi.org/10.5194/egusphere-egu21-5409, 2021.

EGU21-12945 | vPICO presentations | SSP1.11

Seawater temperature, productivity and marine fish metabolism in the Messinian eastern Mediterranean

Konstantina Agiadi, Danae Thivaiou, Geanina Butiseaca, George Kontakiotis, Eva Besiou, Stergios Zarkogiannis, Assimina Antonarakou, Efterpi Koskeridou, Andreas Mulch, and Iuliana Vasiliev

Reconstructing paleoceanographic conditions for the entire water column remains challenging, due to the lack of proxies for seawater parameters below surface waters, which could be used to validate models. Fish otoliths and ostracods are used here to obtain biogeochemical proxy data of sea surface/bottom temperature and productivity, as well as the biological response of marine fishes to paleoenvironmental change. Our study area is located in the eastern Mediterranean Sea (Heraklion basin, Crete Island). During the Messinian age (specifically between 7.2 and 6.5 Ma), the Mediterranean–Atlantic connection was restricted leading to a strongly stratified water column. We study the sea surface and bottom conditions under these conditions.

Stable oxygen isotopes on ostracod valves (Bairdoppilata sp.) reflect the combined effect of bottom-water temperature and salinity changes. For fishes however, this depends on each species lifestyle. We analyzed two very common species: 1) Bregmaceros albyi, a surface-water pelagic species, and 2) Lesueurigobius friesii, a demersal fish dwelling on the sea bottom. Our hypothesis was that the stable oxygen isotopic ratios on B. albyi otoliths would reflect surface-water conditions, whereas those on L. friesii would correspond to bottom-water conditions. Furthermore, we obtained δ13C values for the same ostracod and otolith specimens. Stable carbon isotopic ratios in invertebrate shells indicate biological productivity, since carbon fractionation takes place as a single-step process during biomineralization. However, fish otolith aragonite mineralization is more complicated, involving more than one fractionation steps, and carbon is obtained from seawater, but also from diet. Therefore,  otolith δ13C is considered a proxy of the fish’s field metabolic rate, reflecting its ability to continue to grow and reproduce despite environmental change.

Our results show that B. albyi δ18O values correlate well with those derived from planktonic foraminifera shells, whereas L. friesii δ18O is in agreement with ostracod values, thereby confirming our hypothesis. Moreover, ostracod and foraminifera δ13C follow the same decreasing pattern. However, otolith δ13C remains stable, even after 6.8 Ma, when high-amplitude salinity variations prevail. This suggests that fish maintained their capacity to grow and reproduce despite significant changes in seawater conditions at least until 6.5 Ma. However, whether this reflects their resilience to these environmental changes or an adaptation mechanism such as reducing their growth rate or shifting their trophic preferences remains a mystery.

How to cite: Agiadi, K., Thivaiou, D., Butiseaca, G., Kontakiotis, G., Besiou, E., Zarkogiannis, S., Antonarakou, A., Koskeridou, E., Mulch, A., and Vasiliev, I.: Seawater temperature, productivity and marine fish metabolism in the Messinian eastern Mediterranean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12945, https://doi.org/10.5194/egusphere-egu21-12945, 2021.

EGU21-1475 | vPICO presentations | SSP1.11

Environmental change across the onset of the Messinian salinity crisis in the northern Mediterranean (Piedmont Basin, NW Italy)

Mathia Sabino, Marcello Natalicchio, Daniel Birgel, Francesco Dela Pierre, and Jörn Peckmann

In the late Miocene, the Mediterranean Basin became a restricted basin because of its progressive tectonic isolation from the Global Ocean. The almost complete halt of the Atlantic-Mediterranean water exchange about 6 Ma ago triggered the deposition of the Mediterranean Salt Giant during the Messinian salinity crisis (MSC; 5.97-5.33 Ma). The environmental conditions, which developed at the onset and during the MSC, are still debated since the evaporites buried beneath the modern Mediterranean seafloor are mostly inaccessible and the marginal successions contain scarce or no body fossils. Aiming to improve our knowledge on the environmental conditions at the onset of the MSC, we investigated the sedimentary record of intermediate palaeobathymetric settings (200-1000 m) from the Piedmont Basin (NW Italy) through a multidisciplinary approach (petrography, organic geochemistry). Shale/marl couplets deposited after the MSC onset are lateral time equivalents of shallow water (<200 m) shale/gypsum couplets deposited during the first phase of the crisis (5.97-5.60 Ma). Our results suggest that the MSC onset coincided with an intensification of water column stratification, most likely favoured by enhanced freshwater input due to moister climate conditions. No evidence of hypersaline conditions was found at the onset of the crisis, but rather normal marine conditions seem to have persisted at least in the upper water column, influenced by freshwater discharge. A stable chemocline apparently separated an upper water layer from a stagnant deeper-water body typified by reducing conditions. These physicochemical changes in the water column governed the sedimentary facies distribution during the first phase of the MSC.

How to cite: Sabino, M., Natalicchio, M., Birgel, D., Dela Pierre, F., and Peckmann, J.: Environmental change across the onset of the Messinian salinity crisis in the northern Mediterranean (Piedmont Basin, NW Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1475, https://doi.org/10.5194/egusphere-egu21-1475, 2021.

EGU21-2126 | vPICO presentations | SSP1.11

Geochemical and micropaleontological evidence of the Messinian Salinity Crisis preconditioning phase in the West Alboran Basin  

Francesca Bulian, Tanja J. Kouwenhoven, Francisco J. Sierro, and Wout Krijgsman

The Messinian Salinity Crisis (MSC), still highly discussed within the scientific community, affected the Mediterranean Sea between 5.97 and 5.33 Ma and led to the deposition of huge evaporite accumulations both in its marginal and deep basins. During this profound palaeoecological change, the connections between the Atlantic Ocean and Mediterranean Basin were extremely reduced or even non-existing creating an environment where evaporation was dominant. However, the isolation from the global ocean was not a sudden change but most probably a stepwise process. At 7.17 Ma the first signs of restriction are visible in the sedimentological and micropaleontological records all over the Mediterranean.

Particularly, several Italian, Greek and Cypriot locations register a reduced deep water marine ventilation to the sea floor since 7.17 Ma ago as reflected in the higher abundance of benthic low oxygen foraminifer species, indicators of stressed conditions like Bolivinia spp., Bulimina aculeata, Uvigerina peregrina. In these locations, the start of the progressive Mediterranean isolation coincides with the beginning of a more regular occurrence or even the first appearance of sapropel levels which further confirms the increasingly adverse conditions and increasingly dysoxygenated bottom waters. On the other hand, apart from the first opal-rich deposits in the Sorbas basin (Southern Spain) and the Messadit section (North-East Morocco), evidence from the Western Mediterranean is lacking and no studies have focused so far on the 7.17 Ma event.

In this view, we conducted a detailed benthic foraminifer and stable isotope study of West Alboran Sea Site 976 before and after the 7.17 Ma event. This new record highlights the imprint that the early Atlantic-Mediterranean gateway restriction had on the Mediterranean sedimentological record, in a location proximal to the Messinian Gateways. Here, even if anoxic bottom water conditions were never reached, the benthic foraminifer association, paired with the benthic foraminifer carbon isotope record suggest a perturbation of the bottom water circulation and a decrease in bottom water oxygen levels starting ~7.17 Ma. In addition, a comparison of Western-Eastern Mediterranean records enabled us to make assumptions regarding the Mediterranean scale circulation before and after the 7.17 Ma event.

How to cite: Bulian, F., Kouwenhoven, T. J., Sierro, F. J., and Krijgsman, W.: Geochemical and micropaleontological evidence of the Messinian Salinity Crisis preconditioning phase in the West Alboran Basin  , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2126, https://doi.org/10.5194/egusphere-egu21-2126, 2021.

EGU21-5974 | vPICO presentations | SSP1.11

The onset of the Messinian Salinity Crisis recorded by a new marginal basin succession in the Caltanissetta Basin (Sicily, IT).

Athina Tzevahirtzian, Antonio Caruso, Giovanna Scopelliti, and Attilio Sulli

The fresh new cores 3AGN2S02 and 3AGN2S04 located in the deformed foredeep of the Gela Thrust System, locally known as Caltanissetta Basin, represent an opportunity for a better comprehension of the Messinian events, as well as for the reconstruction of the Sicilian evaporitic Basin architecture. The entire ‘early Messinian stage’ (7.2-5.96Ma) preceding the Messinian Salinity Crisis (MSC) has been already investigated in the Caltanissetta Basin. Even though the Tripoli Formation and ‘Calcare di Base’ (‘CdB’) have been widely studied for a long period of time, many aspects remain unclear. The ‘CdB’ has been commonly considered to represent the first evaporitic unit of the Messinian succession in Sicily. Different ages obtained in the underlying Tripoli deposits from various Sicilian outcrops display a diachronous onset of the MSC (Rouchy & Caruso, 2006). However, Manzi et al. (2011) propose an alternative interpretation for the ‘CdB’, suggesting that it does not belong exclusively to the onset of the MSC, but it is made of three carbonate facies belonging to different MSC stages. A detailed sedimentological, geochemical and petrographic study of the two cores allowed us to evidence the paleoceanographic changes that affected the central Mediterranean Sea during the transition from marine to restricted conditions, up to the onset of the MSC, and to observe the differences between the marginal and the deep basins of the Caltanissetta Basin, enhanced by the ongoing regional tectonics. Facies characterization made it possible to confirm the nature of the sediments of the cores, reflecting distinct depositional environments. A lithological transition passing from the Tripoli Formation to the complex ‘CdB’ carbonates alternating with shales is observed (3AGN2S04). This CdB appears to be laterally equivalent to gypsum and salts at site 3AGN2S02. In the brecciated facies of the ‘CdB’, evaporite pseudomorphs are also present, implying early stage diagenesis. Furthermore, our analyses gave us insights of strong oscillations in hypersaline conditions with freshwater inputs controlled by Milankovitch’s cycles. Moreover, the 3AGN2S04 core is characterized by the repetition of sedimentary successions due to the later development of a thrust system, which can be an important hint concerning the morphological and structural evolution of the Caltanissetta Basin. These new data are fundamental for stratigraphic reconstructions, comparing them with the already well-calibrated reference section of Falconara-Gibliscemi but also with other outcrops located in the various depocenters of the Caltanissetta Basin. The local transition from the uppermost part of the Tripoli cycles to the ‘CdB’ reflects the worsening of the marine connections, implying that during late Messinian broadly constant stressed environmental conditions existed in the central Mediterranean shelves. We conclude that since the onset of the MSC, marine inputs were not important enough to balance the effects of the climate fluctuations and the evaporation/precipitation budget in the individualized semi-closed settings.

How to cite: Tzevahirtzian, A., Caruso, A., Scopelliti, G., and Sulli, A.: The onset of the Messinian Salinity Crisis recorded by a new marginal basin succession in the Caltanissetta Basin (Sicily, IT)., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5974, https://doi.org/10.5194/egusphere-egu21-5974, 2021.

EGU21-14836 | vPICO presentations | SSP1.11

Calcareous nannoplankton paleofluxes in the early Pliocene sapropels of the South Aegean Sea, NE Mediterranean: biogenic carbonate contribution and paleoecological implications 

Elisavet Skampa, Maria Triantaphyllou, Margarita Dimiza, Agnieszka Arabas, Alexandra Gogou, and Karl-Heinz Baumann

Calcareous nannoplankton, one of the major contributors to marine primary production, not only responds quickly to variations in environmental conditions, but provides excellent means of first-order biostratigraphy. In our study we use early Pliocene sediments from the Cretan Sea (South Aegean; DSDP- Leg 42A, Site 378). The location of the record allows us to investigate formation processes of the Zanclean sapropelic layers in South Aegean Sea, and unravel the effects of monsoonal activity, as well as characterize any high latitude teleconnections of the area, prior to the mid-Pliocene warm period. The obtained nannofossil biostratigraphy provided the first-order bed-to-bed age control during the time interval of 5.08-3.98 Myrs, enabling the astronomical tuning of the marly–sapropelic cycles 12-59 to the target-curves.

Geochemical analysis  (total organic carbon, oxygen, nitrogen, organic and carbonate carbon stable isotopes) were performed, revealing variations in carbon cycle and paleoceanographic conditions, as also variability in the redox conditions of the basin. Planktonic foraminifera δ18O and δ13C records are comparable to the global and Mediterranean Sea stacks, revealing warmer conditions in between approx. 5.08-4.9, in accordance to high summer insolation variation values. The quantification of the early Pliocene nannoplankton paleofluxes, indicated approximately two times higher average accumulation rates for the past export production during the sapropelic layers in respect to the non-sapropelic intervals; suggesting that primary productivity was a major component of the sapropelic formation procedures. Overall, calcareous nannofossil assemblage was dominated by Reticulofenestra spp. <5μm (up to 74%) followed by Florisphaera profunda (up to 64%). Other major species of the assemblage composition were Umbilicosphaera spp., Calcidiscus spp. and Helicosphaera spp. F. profunda showed an increase in paleofluxes within the sapropelic layers, coupled with relatively decreased accumulation rates of the upper photic zone taxa and high stratification index, thus suggesting an ecological depth-separation of the water column and a nutrient-rich lower photic zone.

 

Acknowledgments
We acknowledge support of this work by the Action ‘National Network on Climate Change and its Impacts – CLIMPACT’, funded by the Public Investment Program of Greece (GSRT, Ministry of Development and Investments). E. Skampa has been granted with a scholarship from the State Scholarships Foundation. This research is co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Programme « Human Resources Development, Education and Lifelong Learning» in the context of the project “Strengthening Human Resources Research Potential via Doctorate Research” (MIS-5000432), implemented by the State Scholarships Foundation (ІΚΥ).

How to cite: Skampa, E., Triantaphyllou, M., Dimiza, M., Arabas, A., Gogou, A., and Baumann, K.-H.: Calcareous nannoplankton paleofluxes in the early Pliocene sapropels of the South Aegean Sea, NE Mediterranean: biogenic carbonate contribution and paleoecological implications , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14836, https://doi.org/10.5194/egusphere-egu21-14836, 2021.

SSP1.13 – The future of lakes: how can our knowledge about ancient and modern lakes contribute to anticipate the evolution of lacustrine systems over the next decades, up to 2100?

EGU21-14808 | vPICO presentations | SSP1.13 | Highlight

The future decline in lake levels puts an evolutionary giant at risk

Matthias Prange, Sri Nandini-Weiss, Thomas Wilke, and Frank Wesselingh

Continental drying in response to global warming will entail declining lake levels all over the world. Falling lake levels will have many far-reaching consequences that are underappreciated, but affect the livelihoods and economies of millions of people. A massive warning signal is the projected twenty-first century water level drop of up to 18 m in high emissions scenarios for the Caspian Sea, the largest lake in the world, which could hit stakeholders unprepared. Such a catastrophic drop in the Caspian Sea level would lead to a surface area decrease of 34% including the loss of the highly productive northern Caspian shelf and important wetlands such as the Volga Delta and other Ramsar sites. The disappearance of the vast shallow shelves, which are major food suppliers for fish and birds, will devastate native and endemic fish species, the Caspian seal and a richness of molluscs and crustacean species unique to the lake. The falling water level will not only threaten the unique ecosystem, but will also have severe impacts on regional economies and geopolitical stability.

In the first part of this presentation, we discuss the extent of twenty-first century projected continental drying on a global scale and its potential effect on worldwide lake levels. In the second part, we focus on the Caspian Sea and discuss the potential impacts of water level fall on biodiversity and ecosystem services. Finally, we address the question to which extent paleoclimates can be used as analogs for future global warming scenarios with respect to changes in the Caspian Sea level.

How to cite: Prange, M., Nandini-Weiss, S., Wilke, T., and Wesselingh, F.: The future decline in lake levels puts an evolutionary giant at risk, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14808, https://doi.org/10.5194/egusphere-egu21-14808, 2021.

EGU21-15440 | vPICO presentations | SSP1.13

Projecting thermal stratification and hypolimnetic oxygen conditions by coupling paleolimnological and 1D lake model approaches

Jean-Philippe Jenny, Olivia Itier, Victor Frossard, David Etienne, and Jean Guillard

Climate change raises many questions about the future of lakes’ thermal regime and hypolimnetic oxygen conditions. One dimensional models have been widely implemented over that last years 1–3, but most of these models are calibrated against very few years of limnological records, potentially limiting the robustness in long-term reconstructions and preventing inclusion of future scenarios. To analysis the variability and the effects of climate change on thermal regime and oxygen conditions of deep hard-water lakes, we relayed on paleolimnological records and 1D thermal lake model calibrated against time series of limnological data collected by the French Observatoire des LAcs (OLA). Continuous sediment records on four peri-alpine lakes (Lake Geneva, Lake Annecy, Lake Bourget and Lake Aiguebelette) were analysed using micro-XRF Mn-Fe ratio as proxy to infer near-annual trends of oxygen conditions for the past 300 years4. Past hypoxia dynamics were further inferred from varved records preserved in sediment cores5. General Lake Model (GLM), i.e. a 1-D modelling tool, has been constrained by climate data derived from meteorological observations and CMIP6 simulations in order to reconstruct and forcast stratification regims for the next century. Our paleolimnological results show that fluctuations in hypoxic volumes since the 1950s were great and that these fluctuations were essentially driven by climatic factors, legitimating the use of thermal model approaches for future projections of hypolimnetic oxygen conditions. In this line, thermal regime simulations based on GLM forecast an intensification in thermal stratification and an increase in volumes of water warmer than 9°C over the period 1850-2100 with potential consequence for hypolimnetic oxygen conditions and ecological habitats. Coupling model and paleolimnological approaches seem a promising way to examine the evolution of lakes in the past, and to realistically anticipate the future of lakes for the next decades.

How to cite: Jenny, J.-P., Itier, O., Frossard, V., Etienne, D., and Guillard, J.: Projecting thermal stratification and hypolimnetic oxygen conditions by coupling paleolimnological and 1D lake model approaches, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15440, https://doi.org/10.5194/egusphere-egu21-15440, 2021.

EGU21-527 | vPICO presentations | SSP1.13 | Highlight

Wind effects change in Taihu Lake with climate change background

Sien Liu, Qinghua Ye, and Jie Zhou

Large shallow lakes globally are threatened by eutrophication, and climate change is believed to aggregate the situation. Wind, as the most important momentum source and the major contributor to consistently change the hydrodynamic patterns inside the large shallow lakes, is highly susceptible to climate change. Taihu Lake, which is the 3rd largest shallow lake in China and pertains crucial social and economic values, is chosen in this study as an example. Due to climate change, the wind condition of Taihu Lake shows a significantly decreasing trend of wind speed and the frequency of extreme wind events. Previous studies have paid little attention to the climate change effects on wind hydrodynamics and its implications on water quality has not yet been thoroughly described. Here in this study, we use a well-calibrated and validated three-dimensional Delft3D model to investigate the spatial and temporal heterogeneity of wind induced hydrodynamics and its water quality implications with climate change. The model results give a prediction of less current speed, lower wave height and bottom shear stress compared to the reference scenario, while the three dimensionality of flow field remains. Further, water age is used to demonstrate the influence of external nutrient sources, i.e. the input from adjacent river networks in the basin. Large water ages are observed and potentially it would enhance the accumulation of nutrients and deterioration of water quality.

How to cite: Liu, S., Ye, Q., and Zhou, J.: Wind effects change in Taihu Lake with climate change background, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-527, https://doi.org/10.5194/egusphere-egu21-527, 2021.

Lacustrine sedimentation, which is considered to be relatively simple, can be dominated by high-energy wind-driven process. Qinghai Lake, located at the northeastern margin of the Qinghai-Tibet Plateau, western China, is a typical “wind-driven lake”, of which the sedimentation and evolution of shorelines are impacted by prevailing wind. In this research, Buha River Delta and Hargai River Delta, located at the northwestern and northeastern of the lake respectively, are studied through field investigation and remote sensing images analysis. The outcrop section of Buha River Delta is characterized by channel lag deposits, planar cross-beds, and trough cross-beds, indicating a dominant effect of river. However, the section of Hargai River Delta displays planar cross-beds, as well as swash cross-beds (beach deposits) and high-angle cross-beds dip to land (washover deposits), revealing a combined effect of river and waves. Remote sensing images in recent 40 years showed that Buha River Delta remained a stable shape except for the migration of mouth bars, which may be caused by lake level fluctuation. Nevertheless, Hargai River Delta has recorded a noteworthy change in its appearance, which was characterized by the formation of a barrier bar outside the estuary. Meteorological Data reveals that the Qinghai Lake is mainly affected by north-west wind and north wind, thus Buha River Delta is located at the leeward side, while Hargai River Delta is situated at the windward side and significantly influenced by high-energy wind-driven lake currents and waves. When the prevailing wind direction is oblique to the lake shoreline, the coastal current parallel to the shoreline formed by the decomposition of wind-driven waves would transport the clastic materials provided by Hargai River and then deposit them along the lake bank, finally forming a barrier bar parallel to the shoreline. This study reveals that wind-driven process could have totally different effects on either side of a “wind-driven lake”, thus can help us anticipate the evolution of shoreline landform of a “wind-driven lake” in the near future.

How to cite: Liu, C. and Jiang, Z.: The effect of prevailing wind on shoreline landform evolution - Illustrated by the case of Buha River Delta and Hargai River Delta in the Qinghai Lake, western China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3716, https://doi.org/10.5194/egusphere-egu21-3716, 2021.

EGU21-1850 | vPICO presentations | SSP1.13

Using fossilised pigments to understand cyanobacterial blooms in New Zealand lakes

Jonathan Puddick, Carrie Page, Donato Romanazzi, Katie Gunning, Jamie Howarth, Adelaine Moody, Jenny Dahl, Xun Li, Sebastian Naeher, Lizette Reyes, Claire Shepherd, Marcus Vandergoes, and Susie Wood

Phytoplankton (including cyanobacteria) are a natural component of lake ecosystems and are the base of many food webs. However, changes in the lake catchment, the lake itself and the wider environment (e.g., climate change) can alter the composition of phytoplankton communities. Of recent concern is the increase in the abundance of cyanobacteria and the formation of blooms in many of New Zealand’s low-land lakes (>30% of those that are monitored). Because regular monitoring data does not stretch back more than 10-30 years and many lakes are not regularly monitored, it is difficult to ascertain whether the intensity of present-day blooms are a new phenomenon or are part of a pre-existing cycle. The pigments produced by cyanobacteria (and other phytoplankton) are deposited in lake sediment and can be extracted from sediment cores and surface sediment samples. Analysis of these pigments by high-performance liquid chromatography has allowed us to reconstruct the historical phytoplankton community from nine New Zealand lakes and to track the emergence of cyanobacteria in impacted lakes. We will present data on the performance of different cyanobacteria pigment indicators and several case studies to demonstrate how fossilised pigment data can be used to understand shifts in lake phytoplankton communities.

How to cite: Puddick, J., Page, C., Romanazzi, D., Gunning, K., Howarth, J., Moody, A., Dahl, J., Li, X., Naeher, S., Reyes, L., Shepherd, C., Vandergoes, M., and Wood, S.: Using fossilised pigments to understand cyanobacterial blooms in New Zealand lakes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1850, https://doi.org/10.5194/egusphere-egu21-1850, 2021.

EGU21-3436 | vPICO presentations | SSP1.13

Clearer than mud? Using environmental DNA to track historical shifts in lake communities.

John Pearman, Laura Biessy, Georgia Thomson-Laing, Lizette Reyes, Claire Shepherd, Jamie Howarth, Andrew Rees, Xun Li, Marcus Vandergoes, Susie Wood, and Team Lakes380

A continuous record of environmental history is stored in lake sediments providing an avenue to explore current and historical lake communities. Traditionally paleolimnological methods have focussed on macroscopic indicators (e.g. pollen, chronomids, diatoms) to investigate environmental changes but the application of environmental DNA techniques has enabled the investigation of microbial communities and other soft bodied organisms through time. The ‘Our lakes’ health; past, present, future (Lakes380)’ project aims to combined traditional and molecular methods to explore shifts in biological communities over the last 1,000 years (pre-human arrival in New Zealand). Sediments cores have been collected from a wide diversity of lakes across New Zealand and 16S rRNA gene metabarcoding approaches of both DNA and RNA applied to reveal how microbial community changes across time and especially in response to the arrival of humans and associated changes to the landscape and lake environments. We further investigate the changes in inferred metabolic potential of the microbial communities as the taxonomic composition of the lake differs over time. Finally, we combine these novel molecular methods with hyperspectral scanning and pollen data to increase the knowledge of changes in lake communities and identifying the timing of changes in lake health. The combination of methodologies provides a greater understanding of the environmental history of lake systems and will help to inform management decisions relating to the restoration and protection of lake health.

How to cite: Pearman, J., Biessy, L., Thomson-Laing, G., Reyes, L., Shepherd, C., Howarth, J., Rees, A., Li, X., Vandergoes, M., Wood, S., and Lakes380, T.: Clearer than mud? Using environmental DNA to track historical shifts in lake communities., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3436, https://doi.org/10.5194/egusphere-egu21-3436, 2021.

EGU21-3706 | vPICO presentations | SSP1.13 | Highlight

Bloom Story: reconstructing historical cyanobacterial communities in six contrasting New Zealand lakes

Maïlys Picard, Xavier Pochon, Andrew Rees, Jamie Howarth, Marc Schallenberg, Chris Moy, Marcus Vandergoes, Ian Hawes, and Susie Wood

Anthropogenic nutrient enrichment, hydrological modifications, and introduced species are contributing to an increase in the frequency and intensity of cyanobacterial blooms. This study aimed to document the evolution of cyanobacterial assemblages over time and explore the drivers of cyanobacterial blooms. Environmental DNA was extracted from sediment cores dating back approximately 1,000-years collected from six New Zealand lakes (Rotoehu, Pounui, Wairarapa, Paringa, Johnson, Hayes). Samples were analysed using cyanobacterial 16S rRNA metabarcoding and droplet digital PCR. Picocyanobacteria had the highest relative abundance. Marked shifts in species composition were observed over time but species varied between lakes. Marked shifts in total abundance (from ddPCR data) were observed through time in all lakes, and the metabarcoding data revealed these abundances to be bloom-forming taxa only in impacted lakes. Historical cyanobacterial communities seemed to be mostly influenced by anthropogenic activities and the geographic location of the lakes. Comparison with other paleolimnological proxies suggests land-use and non-native fish as key drivers in species and abundance shifts. Sedimentary environmental DNA analysis can complement traditional paleo-approaches, and provide novel information on microbial communities, and new insights into causes and consequences of cyanobacterial blooms.

How to cite: Picard, M., Pochon, X., Rees, A., Howarth, J., Schallenberg, M., Moy, C., Vandergoes, M., Hawes, I., and Wood, S.: Bloom Story: reconstructing historical cyanobacterial communities in six contrasting New Zealand lakes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3706, https://doi.org/10.5194/egusphere-egu21-3706, 2021.

EGU21-8920 | vPICO presentations | SSP1.13

Environmental drivers of plankton and sediment microbial communities along latitudinal and vertical gradients in the deepest freshwater lake (Baikal, Southern Siberia)

Purificacion Lopez-Garcia, Guillaume Reboul, Gwendoline David, Ludwig Jardillier, Nataliia Annenkova, Paola Bertolino, Ana I. Lopez-Archilla, Konstantin Vershinin, and David Moreira

Understanding how abiotic and biotic factors influence microbial community assembly and function is crucial to understand ecological processes and predict how communities will respond to environmental change. Lake Baikal (Russian Federation) is the oldest, deepest and most voluminous freshwater lake on Earth, resembling in several respects sea environments. It thus offers a unique opportunity to test the effect of horizontal versus vertical gradients in community structure. Since climate change is rapidly affecting Siberia and Lake Baikal, this information can be useful both, as a reference for future monitoring of the lake and to help predictions about how local communities change as a function of environmental parameters. In order to address these questions, in 2017, we carried out a comprehensive sampling of Lake Baikal water columns and sediments along a North–South latitudinal gradient (ca. 600 km) across the three major basins of the lake, from coastal to pelagic areas and from surface to the deepest zones (0.5 to 1450 m deep). We then applied metabarcoding approaches based on 16S and 18S rRNA gene amplicon sequencing to characterize the composition of microbial communities, in particular, both prokaryotes and eukaryotes in sediments and microbial eukaryotes (0.2-30 µm cell size) in plankton (65 samples from 17 water columns). As expected, depth had a strong significant effect on protist community stratification in the water column. The effect of the latitudinal gradient was marginal and no significant difference was observed between coastal and surface open water communities. Co-occurrence network analyses showed that epipelagic protist communities were significantly more interconnected than in the dark water column. Surprisingly, Baikal benthic communities (13 sites) displayed remarkable stability across sites and seemed not determined by depth or latitude. Comparative analyses with other freshwater, brackish and marine sediments confirmed the distinctness of Baikal benthic communities, which show some similarity to marine and hydrothermally-influenced systems likely owing to its high oligotrophy, depth and fault-associated seepage. Metagenomic analyses of sediment samples show a wide metabolic potential of Baikal benthos and highlight the relative importance ammonia-oxidizing archaea in upper sediment layers.

How to cite: Lopez-Garcia, P., Reboul, G., David, G., Jardillier, L., Annenkova, N., Bertolino, P., Lopez-Archilla, A. I., Vershinin, K., and Moreira, D.: Environmental drivers of plankton and sediment microbial communities along latitudinal and vertical gradients in the deepest freshwater lake (Baikal, Southern Siberia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8920, https://doi.org/10.5194/egusphere-egu21-8920, 2021.

EGU21-4533 | vPICO presentations | SSP1.13

Microbialites as bioindicators of lake hydric dynamics: the evolution of microbial populations and mineralogy of Mexican lacustrine microbialites along an alkaline-saline gradient

Miguel Iniesto, Karim Benzerara, David Moreira, Nina Zeyen, Rosaluz Tavera, Damien Daval, and Purificación López-García

Modern microbialites are frequently studied as analogues of ancient microbialites, the oldest of which date back to ~3.5 Ga. These organo-sedimentary structures are generated by complex microbial communities developing under specific physicochemical conditions, such that fossil microbialites attest for past microbial ecosystems. Lacustrine microbialites, in contrast with marine ones, show a large range of morphologies and mineralogical compositions, including various carbonate and non-carbonate (e.g. Mg-silicates) phases. Major dominant prokaryotic groups (e.g. Cyanobacteria, Planctomycetes or Alphaproteobacteria) and taxa‐associated functions (e.g. oxygenic and anoxygenic photosynthesis) appear conserved across microbialite ecosystems. However, the evolution of the microbial community and/or the chemical and mineralogical composition of lacustrine microbialites with the hydrogeochemistry of lakes remains undescribed. In the present work, we analysed the mineralogical and chemical composition, including major and trace element composition of microbialites as well as their microbial community using samples from ten crater lakes of the Trans‐Mexican volcanic belt along an alkalinity-salinity gradient. We also characterized lake hydrochemistry and planktonic communities to compare them with those of microbialites. We found a large diversity of microbialites in terms of mineralogical composition which was primarily controlled by orthosilicic acid (H4SiO4) concentrations and Mg/Ca ratios of the solutions. In addition, microbialite size correlated positively with salinity, (Mg/Ca)aq ratio and alkalinity. Our observations suggest that alkalinity values above 1.23 mM and salinity above 0.08 g.L-1 constitute potential chemical threshold above which lacustrine microbialites can occur. The composition of both prokaryotic and the eukaryotic microbialite-associated communities varied significantly across lakes, correlating with the alkalinity and salinity gradient. Moreover, microbialite-associated communities were clearly distinguishable from their surrounding planktonic communities, being more similar to those of microbialites from distant and chemically different lakes than to planktonic communities present in the same lake. In fact, we identified a microbial core of 247 operational taxonomic units shared by all lake microbialites. This core, mainly dominated by Cyanobacteria, Bacteroidetes, Planctomycetes, Chloroflexi, Alphaproteobacteria and Gammaproteobacteria, represented up to 40% of the relative abundance of the community in lakes displaying the highest alkalinity and most conspicuous microbialites (Alchichica and Atexcac). This suggests a prominent ecological role for those organisms in microbialite formation. We could also show that, in Lake Alchichica, microbialites formed very rapidly on inert surfaces (e.g. plastic) with rates of ~0.6 (and up to 1) mm/year and that nascent hydromagnesite and aragonite-rich microbialites harboured communities   similar to the mature ones in native microbialites. Our study establishes a connection between the chemical, mineralogical and microbial composition of microbialites and the hydrogeochemical evolution of lakes. Alkalinity and salinity gradients reflect lake hydrological balance and status along an evaporation progress trend and/or weathering intensity of the surrounding bedrocks. In this context, microbial communities associated with modern lacustrine microbialites may possibly be used as indicators for management/prediction of limnologic states along alkalinity-salinity gradients.

 

How to cite: Iniesto, M., Benzerara, K., Moreira, D., Zeyen, N., Tavera, R., Daval, D., and López-García, P.: Microbialites as bioindicators of lake hydric dynamics: the evolution of microbial populations and mineralogy of Mexican lacustrine microbialites along an alkaline-saline gradient, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4533, https://doi.org/10.5194/egusphere-egu21-4533, 2021.

EGU21-5331 | vPICO presentations | SSP1.13

Microbial community composition seasonality and drift over years in small freshwater ecosystems

Ludwig Jardillier, Gwendoline David, Philippe Deschamps, Paola Bertolino, David Moreira, Benjamin Alric, Gwendal Restoux, Emma Rochelle-Newall, Elisa Thébault, Marianne Simon, and Purificación López-García

Small freshwater ecosystems are highly diverse, widely distributed, may be identified as major actors in greenhouse gas fluxes and are potential stocks of freshwater for human usages. In principle, they are more sensitive to environmental disturbance than large aquatic ecosystems because their small volumes provide low buffering capacity. However, little is yet known about their microbial biodiversity and function and how it is structured over time. Yet, understanding the structuring of microbial primary producers, predators, parasites and degraders in these ecosystems is essential to appreciate and model their functioning in the next decades. We investigated the spatial distribution and temporal dynamics of microorganisms of the three domains of life (bacteria, archaea, microbial eukaryotes) at the intra- (seasonal) and inter-annual (pluri-annual) scale in five small freshwater ecosystems. We focused on four ponds and a brook located in northwestern France under temperate climate that we studied for eight years (2011-2019) at seasonal frequency. Microbial diversity was assessed through Illumina MiSeq sequencing of 16S and 18S rDNA amplicons. Several abiotic parameters (physical and chemical) were measured in situ and in the laboratory to characterise the environmental conditions. Multivariate statistical analyses were conducted to identify temporal patterns and link them to environment changes. Microbial communities differed among the ecosystems despite their spatial proximity, likely due to differences in local environmental conditions. Microbial eukaryotic and prokaryotic communities exhibited seasonal temporal patterns and a shift in composition over the years. Microbial communities experienced a strong turnover at the seasonal scale leading to a low fraction (< 2%) of recurrent taxa. In each ecosystem, the measured physico-chemical parameters slightly influenced the microbial community variance over time. These results suggest that biotic interactions but also dormancy, immigration and genetic evolution superimpose to environmental selection through time. Understanding their interplay will be essential to explain microbial community composition change in these ecosystems. 

How to cite: Jardillier, L., David, G., Deschamps, P., Bertolino, P., Moreira, D., Alric, B., Restoux, G., Rochelle-Newall, E., Thébault, E., Simon, M., and López-García, P.: Microbial community composition seasonality and drift over years in small freshwater ecosystems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5331, https://doi.org/10.5194/egusphere-egu21-5331, 2021.

In paleontological context, fish remains are frequently collected and constitute a large part of the lake macro-fossil assemblages. In the presentation, examples from continental Africa chosen in lakes of different dimension, shape and history (mainly Malawi, Chad and Turkana) will illustrate how fish fossil study potentially provides a wide range of information on the paleoenvironment (water salinity, temperature, oxygenation, seasonality, etc.) and the paleogeography (watershed connections) of the lake and its basin. It is based on the knowledge of the ecology and phylogeny of the species and through dedicated biogeochemical and sclerochronological studies of their bones and teeth that also constitute paleo-bio-archives that recorded certain environmental information. Alongside the results extracted from each dedicated study, their combination provide new information and show the gain of extracting different and independent informations from the same object or from objects from the same assemblage, and notably in the case of lake-fish assemblages. For example, the combination of the knowledge on a fish paleo-ecology in a lake with results of a biogeochemical study of their remains can evidence change in the hydrographical regime between successive lake deposits. Finally, fish study also allow an interpolation of change in paleoenvironments at different time scales and their integrative study as paleoenvironmental proxy should be more widely included in the evolution of lakes in the past. The multi-time scale and proxy study enabled on fossil fish is sensible for transfer to predict modern lake evolution.

How to cite: Otero, O.: Fossil fish species and assemblage are relevant integrative paleo-biogeo-archives in ancient lakes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16142, https://doi.org/10.5194/egusphere-egu21-16142, 2021.

The northern Turkana Depression of the East African Rift System in Northern Kenya and Southwestern Ethiopia has one of the most complete and well-documented late Cenozoic continental fossil records worldwide, including remarkable finds of early hominins and associated African Cenozoic vertebrates. Most previous paleoenvironmental reconstructions of the depression were developed using terrestrial vertebrate faunas and paleolandscapes, leaving freshwater ecosystems and associated hydrosystems (lakes, tributaries, river deltas, and wetlands) largely unaddressed. African Cenozoic freshwater mollusks were long considered to be good biostratigraphic indicators, given that their communities are able to represent long phases of morphological stability and at other times rapid morphological changes. However, to what extent changes in freshwater mollusk assemblages match with changes in sedimentary landscapes and lake level fluctuations remains unclear. Here, we address this question through integrative studies on Plio-Pleistocene fossil freshwater mollusks assemblages. Specifically, we are developing a taxonomic framework on fossil freshwater bivalves belonging to the families Unionidae, Iridinidae, Etheriidae and Corbiculidae to create a standardized overview of stratigraphically well-characterized fossil assemblages. Subsequently, we integrate this paleontological dataset with sedimentological characterizations of the depositional environments in which shell beds accumulated at high resolution around faunal turnover events. A detailed reconstruction of environmental changes and how these changes affected freshwater ecosystems in the northern Turkana Depression may allow us to recognize key environmental drivers that triggered faunal turnover events. Such an understanding of drivers from the past perhaps provides our best hope to anticipate how future environmental changes will alter freshwater ecosystems in tropical Africa, and, ultimately, the availability of various freshwater resources on which humanity depends.

How to cite: Andrade, J., Schuster, M., Nutz, A., and Van Bocxlaer, B.: A perspective on Plio-Pleistocene hydrosystems of the northern Turkana Depression (East African Rift System) reconstructed from the study of freshwater mollusk communities, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12114, https://doi.org/10.5194/egusphere-egu21-12114, 2021.

EGU21-4634 | vPICO presentations | SSP1.13

Hydro-climatic fluctuations and their impact on Lake Abhe environments (Ethiopia & Djibouti): a lesson from the past 10,000 years

Carlo Mologni, Laurent Bruxelles, Fabien Arnaud, Pierre Sabatier, Anne-Lise Develle, Emmanuel Malet, Eric Chaumillon, Mathieu Schuster, Gourguen Davtian, Jessie Cauliez, Marie Revel, and Lamya Khalidi

Throughout the last 14 ka, tropical Africa experienced significant hydrological changes that were mainly driven by the orbital precession cycle, which controls the intensity of the African monsoon. Recent studies conducted in lake and deltaic sedimentary records suggest that long-term monsoon humid oscillations (African Humid Period / AHP ~14 – ~6 ka) were punctuated by centennial-scale episodes of hyperaridity. However, the abrupt or gradual aridification modalities since the end of the AHP and the modalities of the centennial-scale episodes, as well as their impacts on past and current environments are still debated.

The Lake Abhe basin in the Central Afar region (Ethiopia & Djibouti) is the endorheic receptacle of freshwater originating in the Ethiopian Highlands, and represents a hydro-sedimentary system sensitive to hydro-climatic changes in East Africa. Today it is characterized by residual lakes (Gamari and Afambo lakes) and a hyper-arid climate, while during the AHP, the Abhe basin was occupied by a Mega-lake and by humid environmental conditions. Holocene climatic disruptions drastically changed the landscapes and ways of life along this basin.  

The aim of this study is to describe, interpret and estimate the impact of hydro-climatic oscillations on the evolution of Lake Abhe’s littoral lacustrine environments and palaeolandscapes since the AHP from different viewpoints.

Indeed, this research combines paleoclimatological and geomorphological studies based on a new set of 14C ages on two lacustrine cores and on several morpho-sedimentary outcrops spanning the Early to Late Holocene. Our results allow us to: a) refine the temporal occurrence and the hydrological modalities of the AHP including short-term arid episodes linked to Younger Dryas and 8.2 ka North Atlantic events; b) recognise some paleo-shoreline geomorphic features linked to lake level fluctuations, as well as the development littoral pedological horizons and the activation/shutdown of the perilacustrine fluvial network during humid and arid events; c) track these changes until the present day, and discuss their evolution scenario in the near future.

Comparing with other regional climatic records, we show how Lake Abhe basin was highly reactive to East African monsoonal regimes, and how current hydrological changes could impact its environments.      

How to cite: Mologni, C., Bruxelles, L., Arnaud, F., Sabatier, P., Develle, A.-L., Malet, E., Chaumillon, E., Schuster, M., Davtian, G., Cauliez, J., Revel, M., and Khalidi, L.: Hydro-climatic fluctuations and their impact on Lake Abhe environments (Ethiopia & Djibouti): a lesson from the past 10,000 years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4634, https://doi.org/10.5194/egusphere-egu21-4634, 2021.

Existing fan-delta depositional models for lacustrine basins do not adequately address significant wave- and storm-related processes. However, in many lakes, such high-energy processes can be effectively driven by winds. As such, the prevailing wind direction determines the progradation direction of wind-induced waves. Observations from modern cases show that wave-dominated deposits commonly exist on one side of the lake, and their sedimentary processes are completely distinct from those on the opposite side, such as in Qinghai Lake in China. However, equivalent deposits have seldom been identified from subsurface data. We present an ancient example from the Upper Tongbomiao Formation in the Tanan Depression (Tamtsag Basin, Mongolia), which was previously interpreted as a fan-delta depositional system. Based on extensive core investigations, eighteen lithofacies, six lithofacies associations and two genetic deposition systems are identified, and a new sedimentological interpretation is proposed for the Upper Tongbomiao Formation containing a wave-dominated clastic shoreline system in the western half-graben dip slope (W-DS) and a fluvial-dominated fan-delta system in the eastern half-graben (E-HG). Sediments within the E-HG unit are grouped into the three lithofacies associations of braidplain, fan-delta front and prodelta, while those within the W-DS unit comprise dominantly alluvial fan, wave-reworked beach, storm-affected shoreface and offshore sediments. Several factors contribute to the preservation of these two distinct sedimentary systems that developed on opposite shores of the lake: (i) the southeast to northeast prevailing wind direction during the deposition period; (ii) a gentle paleotopographic slope in the W-DS unit, while a steep one in the E-HG unit; (iii) a climate shift toward more humid climatic condition from Lower to Upper Tongbomiao Formation intensified hydrodynamic conditions that were able to rework the sediments distributed in the W-DS unit. Finally, we discuss their implications for the future development of shoreline morphology of continental lakes affected by a monodirectional prevailing wind.

How to cite: Xinyu, X., Zaixing, J., and Li, W.:  Wind-induced waves and storms in fan-delta lacustrine successions: New observations from Tanan Depression, Tamtsag Basin, Mongolia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1624, https://doi.org/10.5194/egusphere-egu21-1624, 2021.

EGU21-6447 | vPICO presentations | SSP1.13

The Late-Quaternary morphostratigraphic record of glaciation, paleoseismicity and postglacial environmental changes in fjord-lakes of Québec-Labrador 

Patrick Lajeunesse, Annie-Pier Trottier, Antoine Gagnon-Poiré, Alexandre Normandeau, Etienne Brouard, Antoine Morissette, and Geneviève Philibert

Hydroacoustic surveys were conducted in eight fjord-lakes of Québec-Labrador in order to analyse their Late-Quaternary geomorphological and stratigraphic record of glaciation, paleoseismicity and postglacial environmental changes. This large morphostratigraphic dataset provided a unique opportunity to establish a conceptual model of the evolution for fjord-lakes in relation to deglaciation, glacio-isostatic rebound, sediment fluxes and paleoseismicity. The analysis of the morphology and distribution of many morainic deposits into the fjord-lakes (hummocky moraines, morainic sills and morainic complexes) allows relating their formation to the glacial erosion potential, as well as to climatic and topographic controls. During past glaciations, a topographic sill was left uneroded at the opening of valleys due to the decrease in the glacial erosion potential associated with the lateral extension of the glacier down-ice; this bedrock sill created in turn an anchoring point to the ice during deglaciation. Hummocky moraines were documented at the outlet of five fjord-lakes that are located within the deepest and narrowest valleys of the studied systems. Based on our analysis of these sublacustrine landform-sediment assemblages, fjord-lakes constitute distinct sedimentary systems that should be differentiated from typical fjord system (i.e., in marine waters). The large-scale landforms contained in the fjord-lakes of Québec-Labrador (i.e., esker, moraines, gullies, lateral banks, turbidity channels and circular cavities) are inherited from their past subglacial, glaciomarine and paraglacial conditions, while only small deltaic bedforms (i.e., sediment waves and crescent-shaped bedforms) were formed in postglacial times. The present-day hydrological regime of fjord-lakes of Québec-Labrador is considered river-driven, except for the lakes located near active seismic zones where widespread postglacial mass-movements are documented.

How to cite: Lajeunesse, P., Trottier, A.-P., Gagnon-Poiré, A., Normandeau, A., Brouard, E., Morissette, A., and Philibert, G.: The Late-Quaternary morphostratigraphic record of glaciation, paleoseismicity and postglacial environmental changes in fjord-lakes of Québec-Labrador , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6447, https://doi.org/10.5194/egusphere-egu21-6447, 2021.

EGU21-15787 | vPICO presentations | SSP1.13

Geomorphology of the lakebed and sediment deposition during the Holocene in Lake Visovac

Nikolina Ilijanić, Slobodan Miko, Ozren Hasan, Dea Brunović, Martina Šparica Miko, Željka Sladović, Ivona Ivkić Filipović, Natalia Šenolt, and Gordana Goreta

Lake Visovac is a tufa barrier lake on the Krka River between Roški slap (60 m asl) and Skradinski buk (46 m absl) waterfalls, included in the Krka national park as primarily unaltered area of exceptional natural value. Paleolimnological research was conceived to address a lake evolution and depositional environments through the geophysical survey and collection of the lake sediment cores. A high-resolution bathymetric map was obtained using a multibeam sonar. The average lake depth varies between 20 and 25 m. Sediment cores were investigated to extract physical properties, sedimentological, mineralogical, geochemical and paleoecological records constrained by the radiocarbon chronology, to understand what was happening to both the landscapes and lakescapes of Lake Visovac during the last 2.000 cal yr.

Significant findings of the project are geomorphological features on the lake bottom: submerged sinkholes of various sizes (up to 40 m deep); submerged tufa barriers in the area of Kalički kuk (southern part of Lake Visovac) at the depths of 15 and 17 m, followed by a series of buried cascade tufa barriers at the depth of 25 m covered with up to 10 m of Holocene lake sediments; submerged vertical tufa barrier up to 32 m-high near the mouth of Čikola River; submerged landslides, small (river) fan structures characterized by sediment waves. Ground-penetrating-radar (GPR) data have been acquired due to the presence of gas-saturated sediments over a large area of the lake, that limited the use of high-resolution acoustic profiling. A total thickness of sediments is up to 40 m. High resolution paleoenvironmental record through the Late Holocene gives evidence of high sedimentation rates in Lake Visovac, variable soil erosion impact on lake sediment composition and carbonate authigenic sedimentation. Higher organic carbon is observed in the last 50 years due to changes in land cover and reforestation. Pleistocene lake sediment outcrops occur up to 20 m above the present lake levels indicating higher lake levels as a consequence of higher elevation of tuffa barriers. Kalički kuk, which lies up to 20 m above present lake level, is a remnant of these barriers which have been dated to MIS5. Results allow us to interpret the environmental and evolutionary dynamics of Lake Visovac in the following way: lake level more than 20 m higher than today in mid-Pleistocene with significantly larger lake volume in Lake Visovac, with active Kalički kuk and Skradinski buk waterfalls; lower lake-level at the beginning of the Holocene when several small lakes existed in isolated basins in the area of Lake Visovac. The tufa barrier at Skradinski buk started to grow faster than the Kalički kuk barriers and waterfalls resulting in their flooding and submergence during the Holocene. The tufa barrier at Skradinski buk has grown 15 m since then. This study demonstrates the role of geomorphological lakebed characteristics in reshaping our understanding of the environmental changes and the future of Lake Visovac.

The research was conducted as part of the project funded by the Krka National Park and CSF funded QMAD project (IP-04-2019-8505).

How to cite: Ilijanić, N., Miko, S., Hasan, O., Brunović, D., Šparica Miko, M., Sladović, Ž., Ivkić Filipović, I., Šenolt, N., and Goreta, G.: Geomorphology of the lakebed and sediment deposition during the Holocene in Lake Visovac, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15787, https://doi.org/10.5194/egusphere-egu21-15787, 2021.

To understand the long-term patterns of atmospheric circulation in Eurasia, current paleoclimatic reconstruction syntheses lack accurate data for the Near East. In this semi-arid zone, precipitation is the key factor to be studied that strongly controls ecosystems and human societies. Few data are available from Lake Sevan (1900.52 m above sea level, 1,279 km², 38.2 km3 as of January 1, 2021), the largest fresh-water lake in the Near East, whose past level variations may document seasonal to millennial precipitation changes.

We present here the preliminary results of the interdisciplinary Sevan-up Project. Its ambition is to develop a high resolution lake level reconstruction (which is expected to be preserved from the influences of long ecological processes and from human activities) and other climatic proxies (from pollen and molecular biomarker) in view to quantify precipitation changes during the Holocene.

The Early Holocene climate characteristics (strong seasonality) and environment (prevalence of steppe ecosystems) may raise an analogous model of future conditions in the Near East which will be affected by enhanced continentalism. The study of littoral and deep sedimentary deposits will potentially reveal the consequences of past variations in lake levels on its hydrodynamic functioning and trophic status. These results will give crucial information on how to improve the lake's water management with the goal to reach a sustainable use and a better ecological state. Indeed, seasonal stratification onsets and trophic status dramatically changed since the man-made water-level fall during the Soviet times (40% of its volume).

How to cite: Joannin, S. and the Sevan-upians: Past variations of Lake Sevan (Armenia, lesser Caucasus): documenting climate triggers for the Near East and delivering insights for a sustainable management, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14576, https://doi.org/10.5194/egusphere-egu21-14576, 2021.

EGU21-8467 | vPICO presentations | SSP1.13 | Highlight

Quantifying recent lake level changes in Patagonia (Argentina and Chile): Back to the future?

Daniel Ariztegui, Clément Pollier, and Andrés Bilmes

Lake levels in hydrologically closed-basins are very sensitive to climatically and/or anthropogenically triggered environmental changes. Their record through time can provide valuable information to forecast changes that can have substantial economical and societal impact.

Increasing precipitation in eastern Patagonia (Argentina) have been documented following years with strong El Niño (cold) events using historical and meteorological data. Quantifying changes in modern lake levels allow determining the impact of rainfall variations while contributing to anticipate the evolution of lacustrine systems over the next decades with expected fluctuations in ENSO frequencies. Laguna Carrilaufquen Grande is located in the intermontane Maquinchao Basin, Argentina. Its dimension fluctuates greatly, from 20 to 55 km2 water surface area and an average water depth of 3 m. Several well-preserved gravelly beach ridges witness rainfall variations that can be compared to meteorological data and satellite images covering the last ~50 years. Our results show that in 2016 lake level was the lowest of the past 44 years whereas the maximum lake level was recorded in 1985 (+11.8 m above the current lake level) in a position 1.6 km to the east of the present shoreline. A five-years moving average rainfall record of the area was calculated smoothing the extreme annual events and correlated to the determined lake level fluctuations. The annual variation of lake levels was up to 1.2 m (e.g. 2014) whereas decadal variations related to humid-arid periods for the interval 2002 to 2016 were up to 9.4 m. These data are consistent with those from other monitored lakes and, thus, our approach opens up new perspectives to understand the historical water level fluctuations of lakes with non-available monitoring data.

 

Laguna de los Cisnes in the Chilean section of the island of Tierra del Fuego, is a closed-lake presently divided into two sections of 2.2 and 11.9 km2, respectively. These two water bodies were united in the past forming a single larger lake. The lake level was  ca. 4 m higher than today as shown by clear shorelines and the outcropping of large Ca-rich microbialites. Historical data, aerial photographs and satellite images indicate that the most recent changes in lake level are the result of a massive decrease of water input during the last half of the 20th century triggered by an indiscriminate use of the incoming water for agricultural purposes. The spectacular outcropping of living and fossil microbialites is not only interesting from a scientific point of view but has also initiated the development of the site as a local touristic attraction. However, if the use of the incoming water for agriculture in the catchment remains unregulated the lake water level might drop dangerously and eventually the lake might fully desiccate.

These two examples illustrate how recent changes in lake level can be used to anticipate the near future of lakes. They show that ongoing climate changes along with the growing demand of natural resources have already started to impact lacustrine systems and this is likely to increase in the decades to come.

How to cite: Ariztegui, D., Pollier, C., and Bilmes, A.: Quantifying recent lake level changes in Patagonia (Argentina and Chile): Back to the future?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8467, https://doi.org/10.5194/egusphere-egu21-8467, 2021.

EGU21-9168 | vPICO presentations | SSP1.13 | Highlight

Impact of urban development on waterbodies during medieval and early modern ages in Bad Waldsee (Germany)

Kristin Haas, Kim J. Krahn, Sara Saeidi Ghavi Andam, Rik Tjallingii, Matthias Hinderer, Elena Marinova, Manfred Rösch, and Antje Schwalb

Seasonally laminated lacustrine sediments of Lake Stadtsee, located in the city of Bad Waldsee (Southern Germany), offer a continuous archive that allows a unique and yearly correlation of sedimentary signals and historic documents since medieval times. Comparison of the economic and environmental history of an urban centre will provide detailed insight into how the history of a city and its periphery region affected lake development and water quality, and how fast water quality and aquatic ecosystem recovered from human impact and activities. An interdisciplinary research team consisting of geologists, biologists, and historians from various universities and institutions has been established and started its work recently. The common goal of the different working groups and disciplines is to investigate temporally highly resolved sediment records of diatom and pollen spectra, geochemical proxies, and sediment facies of profundal sediment cores from Lake Stadtsee and to compare and calibrate these results with historic documents, stock books, archive records, dendrochronology records, and maps. So far, continuous geochemical sediment records of Lake Stadtsee were acquired non-destructively using X-ray fluorescence (XRF) core scanning. These element intensity records of the major elements (e.g. Al, Si, K, Ca, Ti, Fe) were measured every 2 mm. Sampling and subsequent analyses (e.g. pollen, PAH, isotopes) are ongoing.

Overall, the environmental impact of socio-economic development for the preindustrial development phase of a city from AD 1200 to 1800 will be assessed for the first time. The research will focus on the effects of population growth or decrease, farming intensity, economic production, trade activity in relation to environmental, and climate change, including catastrophic events such as fires and floods. The results will provide important insights about the response of urban surface waters to changing emissions of the city and the long-term behaviour of persistent pollutants on lakes. The project will thereby contribute to the knowledge of historic human impact on the environment in Germany, pre-medieval reference conditions, and the limits of resilience of aquatic systems. Thus, it will target the past environmental footprint of anthropogenic induced events on urbanized lake ecosystems and help to understand the mechanism behind such processes in the future.

How to cite: Haas, K., Krahn, K. J., Saeidi Ghavi Andam, S., Tjallingii, R., Hinderer, M., Marinova, E., Rösch, M., and Schwalb, A.: Impact of urban development on waterbodies during medieval and early modern ages in Bad Waldsee (Germany), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9168, https://doi.org/10.5194/egusphere-egu21-9168, 2021.

EGU21-14459 | vPICO presentations | SSP1.13 | Highlight

Anticipating the evolution of the Fitri lake system: temporalities of an overflowing flood and its socio-ecological consequences

Raimond Christine, Yalikun Tashi, Créteaux Jean-François, Berge-Nguyen Muriel, Schuster Mathieu, and Sylvestre Florence

The Sahel, located at the southern edge of the Sahara is defined as the transitional boundary of the Sahara, whose aridification since the late Holocene has profoundly affected landscapes, human occupation and ecosystems. Current climate change, characterized by an increase in temperature, raised the idea of aridification and the disappearance of surface water in the Sahelian zone. However, in central Sahel, the trend towards increasing open water surfaces seems to be confirmed over the last decade, particularly during extreme rainfall episodes. Here, we show the current changes of Lake Fitri, a remnant of the mega-lake Chad during the Holocene 6,000 years ago, whose seasonal flooding has reached unequaled levels in the last 50 years. This terminal and shallow lake and spreading out over a vast flat sedimentary plain irrigates a variable surface area. During exceptional rainy years such as the current one (2020-2021), the waters from the Batha river basin (main tributary of Lake Fitri), in the Sahelian zone, can reach the Chari catchment area (main tributary of Lake Chad) by passing through a succession of basins.

The diachronic analysis of Landsat images combined with ground-based observations recorded during the year 2020-2021 will be compared with the previous available time-series, in particular the monthly series already analysed for the year 2015 (Yalikun and al., 2019). The results confirm the trend towards the extension of the lake and the "outflow" of its waters to the west. These observations raise many questions related to the definition of a lake and its precise shoreline in this context. We will also specify the consequences in terms of the recomposition of the social-ecological system (changes in land use, recomposition of activity systems and access to natural resources, governance issues). Finally, we will discuss the timing of the changes observed in the short (annual, decade), medium (25 years), long and very long term (Holocene), on the comparability of these changes and on the elements to be considered in order to envisage the future evolution of such sahelian social-ecological system.

How to cite: Christine, R., Tashi, Y., Jean-François, C., Muriel, B.-N., Mathieu, S., and Florence, S.: Anticipating the evolution of the Fitri lake system: temporalities of an overflowing flood and its socio-ecological consequences, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14459, https://doi.org/10.5194/egusphere-egu21-14459, 2021.

SSP2.1 – Phanerozoic Stratigraphy, Paleoenvironments, and Paleoclimate

EGU21-4555 | vPICO presentations | SSP2.1 | Highlight

Long-term sedimentary cycles of the Phanerozoic; insights from the integration of global stratigraphic datasets and tectonic modelling

Jean-Christophe Wrobel-Daveau, David Ray, Gareth Carroll, Michael G. Tetley, Graham Baines, Mike Simmons, and Frans van Buchem

The Phanerozoic sedimentary record documents a diverse series of cyclic patterns of sedimentation that reflect multiple drivers of change (e.g. climate, eustasy, tectonics, biotic evolution) operating over a range of time scales (days to hundreds of million years). While short-term cycles can be easily identified within the rock record and have frequently been related to the Milankovitch cycles, medium-term (a few tens of million years) and long-term (hundreds of million years) cycles are less-well-resolved. Notably the identification of medium- and long-term cycles are reliant upon global scale studies, which are typically hampered by low stratigraphic resolution or address sedimentary changes indirectly through proxies (e.g. sea-level models, geochemical trends). Moreover, such difficulties have resulted in uncertainties as to the drivers and durations of medium- and long-term cycles.

To adequately address this challenge, an integrated approach is required, combining 1) large sedimentary and global events datasets, 2) a high-resolution sequence stratigraphic model, and 3) plate tectonic and digital palaeo-elevation modelling.

We present the preliminary results of an industry-led study of medium- to long-term Phanerozoic cycles in global sedimentation and an assessment of the drivers of these cycles. Our study is based upon a spatially- and temporally-enabled global dataset of sedimentary records, obtained from over 8,500 wells. The sedimentary data contained within the wells have been standardised using a hierarchical classification of sediment types and divided into time slices based upon sequence stratigraphic interpretations, and the identification of age calibrated maximum flooding surfaces derived from the Neftex Global Sequence Stratigraphic Model. This approach allows the Phanerozoic sedimentary record to be subdivided into 132 time slices and the proportion of different sedimentary compositions preserved for each time slice can be reported as a percentage. The resultant analysis identifies medium- to long-term cycles in the proportions of siliciclastics, carbonates and evaporites.

There are two long-terms trends apparent from our data, and these have been analysed by a palinspastic reconstruction of each time slice using our digital palaeo-elevation and tectonic models. The first trend is a progressive decrease in the proportion of carbonates relative to siliciclastics, such that carbonates represent ~50% of Cambrian sediments and ~30% of Neogene sediments. This appears linked to early Palaeozoic low latitude continental configurations favouring carbonate sedimentation. The second trend is a notable increase in evaporites from the Late Permian to Late Jurassic (5% to 10%, from a Phanerozoic average of <2%) this appears linked to the Pangea super-continent configuration and persists until its breakup. In addition, other lesser breakup events appear linked to increases in evaporites.

Medium-term cycles are identifiable as significant shifts in the global proportions of siliciclastics relative to carbonates. There is a hierarchical arrangement to these cycles, both in terms of duration and severity of change, suggestive of multiple drivers. An initial comparison with known glaciations, major biotic events impacting carbonate producers and orogenies appears to explain many of these cycles.

How to cite: Wrobel-Daveau, J.-C., Ray, D., Carroll, G., Tetley, M. G., Baines, G., Simmons, M., and van Buchem, F.: Long-term sedimentary cycles of the Phanerozoic; insights from the integration of global stratigraphic datasets and tectonic modelling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4555, https://doi.org/10.5194/egusphere-egu21-4555, 2021.

EGU21-11148 | vPICO presentations | SSP2.1

Macroevolution and megaclimate: revealing the domains of the Court Jester and biotic equilibration

Andrej Spiridonov and Shaun Lovejoy

The fundamental question of the biodiversity dynamics field is whether global diversity of organisms is driven by multiple random forces resulting in unsteady pattern or is it constrained by sufficiently strong biotic interactions. The first set of hypotheses is combined under the umbrella of the “Court Jester”, reflecting non-steady nature of the process. The latter set of hypotheses is sometimes combined under the header of the “Red Queen”, an epitomization of perpetual change at constant equilibrium diversity level. Based on the Haar fluctuation analyses of the classical Sepkoski database and Paleobiology Database occurrence based biodiversity data, it was revealed that both datasets show that marine animal genus level diversity is characterized by the two regimes.  The first, up to time scales of 30 to 40 Myrs, has a positive scaling exponent implying that fluctuations diverging with time scale i.e. behaviour like the Court Jester that is apparently unstable. The second regime, at longer time scales has a negative fluctuation exponent so that on average anomalies converge, the system is appears stable: a biodiversity regulating Red Queen regime. The smaller scale diverging regime (unstable) is characterized by nearly the same scaling exponent as megaclimate paleotemperatures, suggests a causal connection with diversity.

To investigate this further, we use a new multi-scale Haar fluctuation correlation analysis to quantify the scale by scale correlations.   We found a persistent trend of increasing correlation of macroevolutionary rates with the surface water temperatures with increasing time scales. At the same time, the diversity shows increasingly negative correlations with the temperatures at longer time scales, which suggest that positive largest scale temperature fluctuations although increased biotic turnover had a regulating effect on the global marine animal diversity levels.

Based on the consideration of dominant processes at the longest time scales we propose that the equilibration of biota is a result of continuous geodispersal and consequently mixing and competition of regional biotas, which becomes increasingly more likely on the deca-million-year time scales.

We conclude that the Earth system processes play a significant role in driving both diverging and equilibrating global biodiversity regimes: both Court Jester and Red Queen regimes may operate, with the former dominant up to ≈ 40 Myrs, and the latter at longer time scales.

How to cite: Spiridonov, A. and Lovejoy, S.: Macroevolution and megaclimate: revealing the domains of the Court Jester and biotic equilibration, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11148, https://doi.org/10.5194/egusphere-egu21-11148, 2021.

EGU21-10132 | vPICO presentations | SSP2.1

Enhanced paleo-wildfire occurrences caused by marine organic carbon burial during the Late Devonian Frasnian–Famennian mass extinction

Man Lu, YueHan Lu, Takehitio Ikejiri, and Richard Carroll

The Frasnian–Famennian (F–F) boundary is characterized by worldwide depositions of organic-rich strata, a series of marine anoxia events and one of the biggest five mass extinction events of the Phanerozoic. Due to the enhanced burial of organic matter, a coeval positive carbon isotope (δ13C) excursion occurred around the F–F boundary, raising questions about carbon cycle feedbacks during the mass extinction. In this study, we test the hypothesis that enhanced burial organic carbon during the F–F mass extinction led to the rise of paleo-wildfire occurrences. Here, we reconstructed paleo-wildfire changes across the F–F boundary via analyzing fossil charcoal (inertinites) and pyrogenic polycyclic aromatic hydrocarbons (PAHs) from an Upper Devonian Chattanooga Shale in the southern Appalachian Basin. Our data show low abundances of inertinites and pyrogenic PAHs before the F–F transition and an increasing trend during the F–F transition, followed by a sustained enhancement through the entire Famennian interval. The changes in paleo-wildfire proxies suggest a rise of wildfires starting from the F–F transition. Furthermore, we quantified the amount of organic carbon burial required to drive the observed δ13C excursion using a forward box model. The modeling results show an increased carbon burial rate after the onset of the F–F transition and peaking during its termination. The comparison of the carbon burial rate and wildfire proxies indicates that widespread organic carbon burial during the F–F transition might cause elevated atmospheric oxygen levels and hence increased occurrences of wildfires. In addition, chemical index alteration index and plant biomarkers suggest a drying climate initiated during the F–F transition, implying that the enhanced carbon burial probably result in the climate change and amplify the wildfire occurrences.

How to cite: Lu, M., Lu, Y., Ikejiri, T., and Carroll, R.: Enhanced paleo-wildfire occurrences caused by marine organic carbon burial during the Late Devonian Frasnian–Famennian mass extinction, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10132, https://doi.org/10.5194/egusphere-egu21-10132, 2021.

EGU21-1128 | vPICO presentations | SSP2.1

Multidisciplinary palaeoenvironmental characterisation of the late Permian Matinde Formation, Mozambique 

Gilda Lopes, Zélia Pereira, Paulo Fernandes, Márcia Mendes, João Marques, and Raul C.G.S. Jorge

The Muarádzi Sub-basin is part of the Moatize-Minjova Basin (MMB), an important Karoo aged coalfield in Tete Province, Mozambique. It is a WNW-ESE trending, elongated sedimentary basin located in the eastern part of the MMB, whilst during the late Permian was situated in the southern-central part of Gondwana. In this study, we undertook a multidisciplinary approach involving the lithological, palynofacies, and palynological analysis of samples collected from 3 coal exploration boreholes (DW11, DW21, and DW141) collected from this sub-basin. A total of 99 core samples were collected and studied, allowing for the characterisation of depositional environments and existing palaeofloras for this sub-basin.

The palynological data indicates that all the successions have a Lopingian age, and a vast lowland fluvial setting existed in an area controlled by tectonic movements associated with a continental rifting phase. Correlation between the three sections enabled the recognition of an initial meandering fluvial system affected by repeated flooding events that changed to a braided river. The palynofacies corroborate the interpreted fluvial model and the palynological record obtained.

The existence of a humid and warm climate during the Lopingian led to the development of vast floodplains and diversified wetland types, typical of lowland settings recorded in the analysed samples. The palynofacies analysis also indicate that the thick coal beds’ development is associated with deposition in anoxic to dysoxic environments. Furthermore, the Glossopteris Province vegetation, responsible for the coal development in the Muarádzi Sub-basin, is documented in the palynological assemblages, allowing for the characterization of a flora dominated by glossopterids (Protohaploxypinus and Striatopodocarpites) and gymnosperm pollen (Alisporites). The palaeofloral analysis based on palynological data also shows that associated ferns (e.g., Osmundidacites senectus, Thymospora pseudothiessenii), sphenophytes (e.g., Calamospora) and lycophytes (e.g., Lundbladispora, Kraeuselisporites) were common in this area. Additionally, upland vegetation indicators in the palynological assemblages, as monosaccate pollen grains, are rare, indicating that upland regions were distant from the studied sections.

 

Acknowledgements

This research was fully supported by the project PALEOCLIMOZ (PTDC/CTA-GEO/30082/2017), funded by Fundação para a Ciência e Tecnologia, Portugal. The authors would also like to acknowledge the financial support of the Portuguese Foundation of Science and Technology (FCT) to CIMA through UIDP/00350/2020.

 

How to cite: Lopes, G., Pereira, Z., Fernandes, P., Mendes, M., Marques, J., and Jorge, R. C. G. S.: Multidisciplinary palaeoenvironmental characterisation of the late Permian Matinde Formation, Mozambique , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1128, https://doi.org/10.5194/egusphere-egu21-1128, 2021.

EGU21-1346 | vPICO presentations | SSP2.1

Constraining the age of the first pulse of continental rifting associated with the breakup of Pangea in Southwest Iberia

Margarida Vilas-Boas, Niall W. Paterson, Zélia Pereira, Paulo Fernandes, and Simonetta Cirilli

The Algarve Basin is a Mesozoic sedimentary basin located in southern Portugal. The basin was initiated by rifting associated with the opening of the North and Central Atlantic Ocean during the initial breakup of Pangea. Sedimentation commenced with continental red beds, which unconformably overlie folded and faulted late Carboniferous strata. The red bed succession (Silves Sandstones) consists mainly of sandstones and conglomerates at the base, overlain by variegated mudstones interbedded with siltstones and dolomites (Silves Mudstones, Siltstones and Dolomites). The sandstones were deposited in alluvial environments, and the mudstones in alluvial to shallow lacustrine environments. Upper Triassic (Carnian to Norian) macrofossils are scarce in the red bed succession, occurring predominantly in the upper beds of the succession above the Silves Sandstones, and do not accurately constrain the age of the beginning of the Algarve Basin.

A palynological study of a new road cut outcrop of Silves Sandstones, located in central Algarve, was undertaken in order to ascertain its age. A 3 m thick bed of grey siltstones located ca. 2.5 m above the unconformity yielded age-diagnostic palynomorphs, which date the onset of sedimentation in the basin. Samples from the latter bed yielded a moderately well preserved, low diversity palynomorph assemblage, which is dominated by Aulisporites astigmosus, Converrucosisporites sp. and Tulesporites briscoensis. Other taxa present in the assemblage include Alisporites sp., Calamospora sp., Cycadopites sp., Deltoidospora sp., Ovalipollis cf. ovalis, Triadispora sp., and Vallasporites ignacii.

The dominance of A. astigmosus together with V. ignacii is indicative of an early Carnian age based on comparison with independently dated sections described elsewhere in Europe. This new dating evidence thus constrains the beginning of sedimentation in the Algarve Basin to the earliest Late Triassic. The co-occurrence of T. briscoensis and A. astigmosus suggests a mixing of palynofloral elements typical of North American and central European Carnian assemblages respectively, which is consistent with the intermediate position of Portugal between those regions. The dominance of phytoclasts and the absence of marine palynomorphs confirms a continental depositional environment as also suggested by sedimentary lithofacies.

Acknowledgements

The authors would like to acknowledge the financial support of the Portuguese Foundation of Science and Technology (FCT) with the scholarship with the reference SFRH/BD/144125/2019 and would also like to acknowledge the financial support of the FCT to CIMA through UIDP/00350/2020.

How to cite: Vilas-Boas, M., W. Paterson, N., Pereira, Z., Fernandes, P., and Cirilli, S.: Constraining the age of the first pulse of continental rifting associated with the breakup of Pangea in Southwest Iberia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1346, https://doi.org/10.5194/egusphere-egu21-1346, 2021.

EGU21-14318 | vPICO presentations | SSP2.1

Clumped isotope evidence for polar warmth and reduced salinity during the Early Jurassic

Thomas Letulle, Guillaume Suan, Mikhail Rogov, Mathieu Daëron, Arnauld Vinçon-Laugier, Bruno Reynard, Gilles Montagnac, and Christophe Lécuyer

Greenhouse climates are periods characterized by high atmospheric CO2 levels and the absence of large continental icecaps, conditions that define most of the Phanerozoic eon. Fossil record and proxy data from the Cretaceous-Early Paleogene (145-33 My) greenhouse interval suggest increased polar warmth and reduced latitudinal gradient. Such features are challenging for most climate models. They imply either misinterpretation of paleoenvironmental data or an underestimation of climate sensitivity under greenhouse climate. Here we present a new record from polar (>80°) paleolatitudes of the Early Jurassic (~180My) global warming episode known as the Toarcian Oceanic Anoxic Event. Carbonate clumped isotope (Δ47) thermometry and stable isotope analyses (δ18Oc, δ13C) were performed on pristine aragonite bivalve shells from the Polovinnaya River succession (N Siberia) recording exceptionally low burial. Reconstructed growing season temperatures of 9.7±5.2 to 19.0±3.4 °C and water δ18Ow values of −4.6±1.2 to −2.2±0.8‰VSMOW imply increased warmth and significant freshwater contribution in the Toarcian Arctic seas, in line with coeval Siberian paleobotanical data. The unusually low δ18Ow values confirm the incorrectness of assuming a spatially uniform δ18Osw value for calculation of δ18O-derived paleotemperatures. The inferred Early Jurassic polar sea surface temperatures are in good agreement with independent high latitude proxy data from Cretaceous and Eocene warming events. Together with coeval sea surface temperatures data from the western Tethys Ocean, our new data suggest a strong reduction of latitudinal temperature gradients during the Toarcian relative to modern gradients. The reconstructed polar warmth and reduction in latitudinal temperature gradient are substantially higher than those simulated by most climate models of the Jurassic to Eocene greenhouse periods, and support the increasing amount of data and models indicating an increase of climate sensitivity with CO2 levels. Our results bring critical new constraints for model simulations of Jurassic temperatures and δ18Osw values and suggest that high climate sensitivity is the hallmark of greenhouse climates since at least 180 My.

How to cite: Letulle, T., Suan, G., Rogov, M., Daëron, M., Vinçon-Laugier, A., Reynard, B., Montagnac, G., and Lécuyer, C.: Clumped isotope evidence for polar warmth and reduced salinity during the Early Jurassic, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14318, https://doi.org/10.5194/egusphere-egu21-14318, 2021.

EGU21-8206 | vPICO presentations | SSP2.1

Recurrent global carbon cycle disturbances during the Aalenian: Evidence from France and Chile

Alicia Fantasia, Thierry Adatte, Jorge E. Spangenberg, Emanuela Mattioli, Enrique Bernárdez, Nicolas Thibault, François-Nicolas Krencker, and Stéphane Bodin

The Jurassic was punctuated by several episodes of abrupt environmental changes associated with climatic instabilities, severe biotic crisis, and perturbations of the global carbon cycle. Over the last decades, the Toarcian Oceanic Anoxic Event (Early Jurassic, ~183 Ma) and the early Bajocian Event (Middle Jurassic, ~170–168 Ma) have attracted much attention because they represent such episodes of global and severe environmental change. Bracketed in between the Toarcian and the Bajocian, the Aalenian stage (Middle Jurassic, ~174-170 Ma) has received less attention, although there is some evidence from Tethyan and Boreal records that it was a time of environmental changes marked by marine biotic turnovers. The lack of knowledge about the Aalenian palaeoenvironments leaves a gap in our understanding of the wider context of the Toarcian and Bajocian events and hence of environmental feedback mechanisms surrounding Mesozoic carbon cycle perturbations. In this study, we provide a high-resolution, biostratigraphically well-defined carbon isotope records (δ13Corg and δ13Ccarb) combined to Rock-Eval data for the upper Toarcian–lower Bajocian interval from two expanded marl/limestone alternation successions from France (French Subalpine Basin) and Chile (Andean Basin). The comparison with available records from the Tethyan and Boreal domains highlights that medium-term δ13C fluctuations are reproducible across different palaeoceanographic settings from both hemispheres and between different carbon substrates. The new high-resolution dataset highlights the complexity of the Aalenian δ13C record, including previously identified δ13C shifts and hitherto undescribed fluctuations. This study provides one of the most expanded high-resolution chemostratigraphic reference records for the entire Aalenian stage, and shows compelling evidence from both hemispheres that it was a time marked by recurrent perturbations to the global carbon cycle and environmental changes.

 

How to cite: Fantasia, A., Adatte, T., Spangenberg, J. E., Mattioli, E., Bernárdez, E., Thibault, N., Krencker, F.-N., and Bodin, S.: Recurrent global carbon cycle disturbances during the Aalenian: Evidence from France and Chile, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8206, https://doi.org/10.5194/egusphere-egu21-8206, 2021.

EGU21-11871 | vPICO presentations | SSP2.1

Assessing orbital vs. volcanic control on carbon cycle during the Early Cretaceous

Mathieu Martinez, Beatriz Aguirre-Urreta, Marina Lescano, Guillaume Dera, Julieta Omarini, Maisa Tunik, Tomas Frederichs, Heiko Pälike, Luis O'Dogherty, Roque Aguado, Miguel Company, and Jose Sandoval

The interval from the Valanginian to the Barremian stages (137–121 Ma; Early Cretaceous) is punctuated by several episodes of environmental changes, accompanied by shifts in weathering intensity on the continents and changes in the Tethyan neritic carbonate production. We synthetize here the astrochronology of two recent studies performed in the Neuquén basin, Vocontian Basin and Subbetic Domain (Aguirre-Urreta et al., 2019; Martinez et al., 2020), anchored to CA-ID-TIMS U-Pb ages, which conclusions have been included in the Geologic Time Scale 2020 (Gale et al, in press). We applied this time scale to a compilation of carbon-isotope ratio from belemnites and proxies of detrital supply in the Tethyan area (Vocontian Basin and Subbetic Domain). From this compilation, we show that the episodes of environmental changes are paced by a 2.4-Myr cycle and, with a lower amplitude, a 1.2-Myr cycle. In addition, the new time scale shows the synchronicity between the Weissert Event and the Parana-Etendeka Large Igneous Province. In the series of carbon-isotope ratios measured on belemnite rostra, the amplitude of the 2.4-Myr cycle is twice higher during the Valanginian than in the Late Barremian and three times higher than in the Hauterivian and Early Barremian, suggesting that the activity of the Parana-Etendeka Large Igneous Province amplified the initial orbital forcing to trigger the environmental changes observed during the Mid-Valanginian.

Reference:

Aguirre-Urreta, B., Martinez, M., Schmitz, M., Lescano, M., Omarini, J., Tunik, M., Kuhnert, H., Concheyro, A., Rawson, P.F., Ramos, V.A., Reboulet, S., Noclin, N., Frederichs, T., Nickl, A.-L., Pälike, H., 2019. Interhemispheric radio-astrochronological calibration of the time scales from the Andean and the Tethyan areas in the Valanginian–Hauterivian (Early Cretaceous). Gondwana Research 70, 104-132. https://doi.org/10.1016/j.gr.2019.01.006.

Gale, A.S., Mutterlose, J., Batenburg, S., in press. Chapter 27: The Cretaceous Period, in: Gradstein, F.M., Ogg, J.G., Schmitz, M.D., Ogg, G.M. (Eds.) Geologic Time Scale 2020. Elsevier BV, Amsterdam, The Netherlands, pp. 1023–1086.

Martinez, M., Aguado, R., Company, M., Sandoval, J., O’Dogherty, L., 2020. Integrated astrochronology of the Barremian Stage (Early Cretaceous) and its biostratigraphic subdivisions. Global and Planetary Change 195, 103368. https://doi.org/10.1016/j.gloplacha.2020.103368.

How to cite: Martinez, M., Aguirre-Urreta, B., Lescano, M., Dera, G., Omarini, J., Tunik, M., Frederichs, T., Pälike, H., O'Dogherty, L., Aguado, R., Company, M., and Sandoval, J.: Assessing orbital vs. volcanic control on carbon cycle during the Early Cretaceous, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11871, https://doi.org/10.5194/egusphere-egu21-11871, 2021.

EGU21-1279 | vPICO presentations | SSP2.1

Volcanism and carbon cycling in the High Arctic during the Late Jurassic – Early Cretaceous

Madeleine L. Vickers, Mads E. Jelby, Jennifer M. Galloway, Lawrence Percival, Feiyue Wang, Hamed Sanei, Kasia K. Śliwińska, Gregory D. Price, Clemens V. Ullmann, Iben W. Hougård, Ivar Midtkandal, Tamsin Mather, and Christoph Korte

Arctic carbon cycling and its regional climate have been observed to deviate from global trends in the Late Jurassic and across the Jurassic–Cretaceous boundary interval, but appear to recouple with global trends in the Early Cretaceous (Galloway et al., 2019; Jelby et al., 2020). We investigate the possible link between these observed trends and volcanism by examining the mercury (Hg) and other element records from Arctic sites in Svalbard (Norway) and the Queen Elizabeth Islands, Canada. We assess whether pulsed phases of the High Arctic Large Igneous Province, or the globally significant emplacement of Paraná-Etendeka or Greater Ontong-Java Plateau, are expressed by stratigraphic Hg trends recorded in the studied sites of Arctic Canada and Svalbard, and how any signals correlate with the regional stable carbon-isotope (δ13C) record. We compare these new data to Hg and δ13C records from other globally distributed sites, focusing on the carbon isotope excursion (CIE) intervals: the Arctic-wide Volgian CIE (“VOICE”), the global Valanginian positive CIE (“Weissert Event”), and the global early Aptian CIE associated with Ocean Anoxic Event 1a (OAE1a).

How to cite: Vickers, M. L., Jelby, M. E., Galloway, J. M., Percival, L., Wang, F., Sanei, H., Śliwińska, K. K., Price, G. D., Ullmann, C. V., Hougård, I. W., Midtkandal, I., Mather, T., and Korte, C.: Volcanism and carbon cycling in the High Arctic during the Late Jurassic – Early Cretaceous, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1279, https://doi.org/10.5194/egusphere-egu21-1279, 2021.

EGU21-10135 | vPICO presentations | SSP2.1

Cretaceous Black Shales in the Pacific: The Equatorial Position Hypothesis

Max J. Bouwmeester, Lydian Boschman, Nienke Berends, Jeremy D. Owens, Ben C. Gill, and João P. Trabucho Alexandre

Although anoxia is rare in modern oceans, the marine stratigraphic record is punctuated by sedimentary and geochemical evidence for episodes of widespread oceanic anoxia. The last time in Earth history that a large volume of the ocean became anoxic was in the middle Cretaceous: black organic-carbon-rich muds were repeatedly preserved on the deep seafloor during oceanic anoxic events (OAEs).

Sedimentary and geochemical evidence for oceanic anoxia during OAEs comes mainly from the Atlantic and Tethys Oceans. Data from the Pacific Ocean, which was the largest ocean basin in the middle Cretaceous, is scarce and equivocal. Based on black shales deposited at depths of about 500–1500 m on seamounts, Monteiro et al. (2012) have suggested that at least 50 vol% of the ocean was anoxic at the climax of Cretaceous oceanic anoxia during the late Cenomanian. They also included a single black shale at DSDP Site 585 in the Mariana Basin as evidence for anoxia in the deep Pacific. We will show, however, that this is a mud turbidite reworked from shallower water.

For this study, we reviewed all available data and publications from scientific drilling that recovered Cretaceous sediments in the Pacific Ocean. The little available Cretaceous record from the Pacific consists mainly of well-oxidized sediments. The exceptions are black shales that occur at depths of about 500–1500 m on seamounts. Takashima et al. (2011) have shown that the Asian and North American continental margins of the Pacific were indeed oxic for most of the late Cenomanian OAE. 

We used a new paleomagnetic reconstruction of the Pacific plate back to 150 Ma to show that all investigated Cretaceous organic-carbon-rich sediments in the Pacific Ocean were deposited while the site was located in the Equatorial Divergence Zone (10°S to 10°N). We therefore argue that organic matter deposition in the Pacific Ocean might not have been directly related to OAEs, but rather be associated with the passage of seamounts beneath the equatorial belt of high productivity.

Several authors have challenged suggestions that OAEs were characterized by globally pervasive anoxic deep water and pointed to the difficulty in sustaining whole-ocean anoxia, even in warm oceans. We agree and our results show that oceanic anoxia in the Pacific is a local phenomenon superposed on a global trend of expanded oxygen minima in the ocean.

How to cite: Bouwmeester, M. J., Boschman, L., Berends, N., Owens, J. D., Gill, B. C., and Trabucho Alexandre, J. P.: Cretaceous Black Shales in the Pacific: The Equatorial Position Hypothesis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10135, https://doi.org/10.5194/egusphere-egu21-10135, 2021.

EGU21-8630 | vPICO presentations | SSP2.1

Campanian biostratigraphy and paleoenvironments, a case study from the Central Srednogorie Zone, Central Bulgaria

Docho Dochev, Michael Wagreich, and Polina Pavlishina

The Central Srednogorie Zone of Bulgaria represents a chain of strike-slip and pull-apart basins, part of the of the peri-Tethyan arc/back-arc basin system. The Upper Cretaceous volcano-sedimentary sequence in the western part of the Central Srednogorie Zone, forms two strips, spanning the Turonian-Maastrichtian interval. This succession is represented by basal siliciclastic sediments, an interval with magmatic rocks followed by volcanoclastic and epiclastic deposits, covered by white, red, grey limestones, with fast transition to sandy low-density turbidites. One of the most representative and continuous sedimentary record in the Panagyurishte strip is exposed east of the Petrich village (Petrich section).  

The base of the Petrich section is composed of the rocks from the so-called lower epiclastic unit (Coniacian-Santonian), followed by grey, pink to variegated limestones of the Mirkovo Formation (Santonian-Campanian). The middle and upper part of the section consists of muddy-sandy turbidites of the Chugovitsa Formation (Campanian-Maastrichtian). The lower part of this formation, the Voden Member, composed of grey thin bedded marls with rare sandstones beds, has yielded a comparatively rich macro- and microfossil record. Upwards, thin to medium bedded sandstones and marls are in alternation, with documented mudstone dominated intervals.  

The present study of the Petrich section is focused on integrated biostratigraphical analysis, based on three important fossil groups for the Campanian – inoceramid bivalves, nannofossils and dinoflagellate cysts. The study in progress creates a comprehensive calibrated dataset, in which the nannofossil and dinoflagellate cyst ranges and inoceramid occurrences, provide valuable markers for age assessment and stratigraphic subdivision of the Campanian. The presence of the nannofossil Ceratolithus aculeus marks a middle to late Campanian age, followed by a typical late Campanian assemblage including Broinsonia parca parca, Reinhardtites levis and rare Eiffellithus eximius. A high diversity dinocyst association is identified and ranges of key Campanian species as Corradinisphaeridium horridum, Raetiaedinium truncigerum, Palaeohystrichophora infusorioides and Cannosphaeropsis utinensis provided valuable markers for the stratigraphic subdivision of the Campanian. Typical middle Campanian “Inoceramusellipticus and “Inoceramusagdjakendsis were documented from the Voden Member. The paleoenvironmental analysis, based on dinocyst assemblages and palynofacies data, suggests stable open-marine depositional environment and oligotrophic conditions, with normal marine productivity and nutrient availability during the Campanian in the basin.

Acknowledgements. The study is part of the Bilateral Bulgarian-Austrian collaboration within project KP-06-Austria/9.

How to cite: Dochev, D., Wagreich, M., and Pavlishina, P.: Campanian biostratigraphy and paleoenvironments, a case study from the Central Srednogorie Zone, Central Bulgaria, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8630, https://doi.org/10.5194/egusphere-egu21-8630, 2021.

EGU21-12656 | vPICO presentations | SSP2.1

A multistratigraphic study of the Campanian Postalm section (Northern Calcareous Alps, Austria)

Michael Wagreich, Erik Wolfgring, Johann Hohenegger, Jaume Dinarès-Turell, Christoph Spötl, and Benjamin Sames

The Postalm section in the Gosau Group (Northern Calcareous Alps) exposes pelagic deposits of northwestern Tethyan origin. We present a magneto-, bio- and chemostratigraphic assessment of this Santonian to uppermost Campanian record, as well as a cyclostratigraphic model for the Tethyan Campanian based on three independently assessed proxies; the δ13C signature, the elemental ratio of Fe and the thickness of limestone/marl couplets (Wolfgring et al., 2021).

The Santonian/Campanian transition is characterised by condensed greyish packstones, the Campanian strata exhibit a succession of limestone-marl couplets that represent orbital precession of an approximate duration of 20ka. A magneto- and biostratigraphic (based on planktonic foraminifera and calcareous nannofossils) framework is supported by carbon isotope and strontium stratigraphy.

The Sr isotope record matches the data for the Upper Cretaceous and suggests no major gaps in the Postalm succession. A robust cyclostratigraphic assessment of three independently assessed data series (L/M couplets, Fe and δ13C) resulted in the identification of eighteen 405 ka eccentricity cycles spanning the middle to upper Campanian (Contusotruncana plummerae to Gansserina gansseri Zones or CC17/UC15 to CC23/UC16 nannofossil zones).

Carbon isotope stratigraphy identifies the LCE (Late Campanian Event) and possibly the SCBE (Santonian Campanian Boundary Event). Magneto- and biostratigraphic data, in particular the position of the top of the R. calcarata planktonic foraminifera Zone, the position of the LCE and the top of Chron C32r.1r served as primary tie points and constraints to match the floating cyclostratigraphic model to the Laskar solution and to compare it to other cyclostratigraphic solutions and reference sections for the upper Campanian.

References: Wolfgring, E., Wagreich, M., Hohenegger, J., Böhm, K., Dinarès Turell, J., Gier, S., Sames, B., Spötl, C., Jin, S., 2021. An integrated multi-proxy study of cyclic pelagic deposits from the north-western Tethys: The Campanian of the Postalm section (Gosau Group, Austria), Cretaceous Research, 120, 104704, doi.org/10.1016/j.cretres.2020.104704.

How to cite: Wagreich, M., Wolfgring, E., Hohenegger, J., Dinarès-Turell, J., Spötl, C., and Sames, B.: A multistratigraphic study of the Campanian Postalm section (Northern Calcareous Alps, Austria), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12656, https://doi.org/10.5194/egusphere-egu21-12656, 2021.

EGU21-2182 | vPICO presentations | SSP2.1

The benthic foraminiferal response to the mid-Maastrichtian event in the Maastrichtian-type area

Iris Vancoppenolle, Johan Vellekoop, Monika Doubrawa, Pim Kaskes, Matthias Sinnesael, John Jagt, Philippe Claeys, and Robert P. Speijer

The mid-Maastrichtian event (MME), ~69 Ma, represents a global negative δ13C excursion which is linked to the extinction of inoceramid bivalves and latitudinal migration of planktonic foraminifera. While the actual extinction of inoceramids was diachronous across the globe, the decline of this important fossil group is generally linked to environmental changes across the mid-Maastrichtian interval. The MME is potentially related to changes in oceanic circulation. While the MME, and associated decline of inoceramids, has been recorded from a variety of deep-sea sites, little is known about the MME signature in shallow epicontinental environments.

Recently, the MME has been recorded for the first time from the type-Maastrichtian, in the Maastricht-Liège region (The Netherlands and Belgium), in newly generated bulk carbonate carbon isotope records from the Hallembaye quarry (NE Belgium) and former ENCI quarry (SE Netherlands). These quarries are approximately 8 km apart. The type-Maastrichtian succession was deposited in a shallow subtropical sea during the Late Cretaceous. As the stratigraphic position of the MME is now constrained in the type-Maastrichtian record, this succession presents an interesting opportunity for studying the signature of this event in a relatively shallow epicontinental basin. Therefore, we are generating high-resolution benthic foraminiferal assemblage data and species-specific carbon and oxygen stable isotope records across the MME interval at these two quarries, in order to unravel biotic and environmental expressions of the MME in the Maastrichtian type area. This is done using the high-resolution sample set acquired in the context of the Maastrichtian Geoheritage Project. Our preliminary data show a distinctive acme of the benthic foraminifer Cuneus trigona in the interval that roughly that corresponds to the MME, potentially caused by a change in quality of the organic matter that reached the sea bottom, highlighting local environmental and oceanographic perturbations across this event.

How to cite: Vancoppenolle, I., Vellekoop, J., Doubrawa, M., Kaskes, P., Sinnesael, M., Jagt, J., Claeys, P., and Speijer, R. P.: The benthic foraminiferal response to the mid-Maastrichtian event in the Maastrichtian-type area, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2182, https://doi.org/10.5194/egusphere-egu21-2182, 2021.

EGU21-12647 | vPICO presentations | SSP2.1 | Highlight

A terrestrial temperature peak in the first millennia after the Cretaceous-Paleogene Boundary 

Gregory Price, Emily Dearing Crampton-Flood, Rhodri Jerrett, Sabine Lengger, Bart van Dongen, David Naafs, Richard Pancost, Aris Lempotesis-Davies, and Paul McCormack

The Cretaceous-Paleogene (K-Pg) boundary marks one of the five major mass extinctions of the Phanerozoic. A bolide impact and flood basalt volcanism compete as triggers for the extinction, but their relative roles remain contentious. This is in part related to a paucity of robust measurements of temperature change at millennial time scales across the K-Pg boundary. Using the distribution of branched tetraether lipids in samples collected from coals (fossil peats), we present the initial findings of an ongoing study attempting to reconstruct temperatures across North America in the latest Cretaceous to earliest Paleogene. The glycerol dialkyl glycerol tetraether (brGDGTs) palaeotemperature proxy – which has been successfully applied to temperature reconstructions in the Pleistocene and Holocene – is being applied to a succession of fossil peats (lignites) that span the K-Pg boundary at ten sites from Colorado in the south to the North West Territories in the north. The Iridium anomaly that is synonymous with bolide impact at the K-Pg boundary can be used as a datum to correlate the coals. Data derived from coals deposited at a latitude of ~55 °N in Saskatchewan (Canada), are interpreted to reveal millennial-scale records of terrestrial mean annual air temperature (MAAT) for an interval spanning the latest Maastrichtian and earliest Paleogene. The MAAT record peaks at 28 °C ~1 ka (+ 4 ka/- 0.3 ka) after the K-Pg boundary, and subsequently recovers to pre-event values in the subsequent ~ 5 ka (+30 ka/-2 ka). Our unique record is consistent with an abrupt increase in atmospheric CO2 that has been widely documented at this time. 

How to cite: Price, G., Dearing Crampton-Flood, E., Jerrett, R., Lengger, S., van Dongen, B., Naafs, D., Pancost, R., Lempotesis-Davies, A., and McCormack, P.: A terrestrial temperature peak in the first millennia after the Cretaceous-Paleogene Boundary , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12647, https://doi.org/10.5194/egusphere-egu21-12647, 2021.

EGU21-8008 | vPICO presentations | SSP2.1

Astronomical calibration of paleoclimatic and planktic foraminiferal events of the Cretaceous-Paleogene transition at Zumaia, Spain

Vicente Gilabert, Sietske J. Batenburg, Ignacio Arenillas, and José A. Arz

The main trigger for the Cretaceous/Paleogene boundary (KPB) mass extinction is still subject of intense debate. The co-occurrence of the Chicxulub impact (Yucatan, Mexico) and massive Deccan Traps volcanism (India) during Chron C29r hinders disentangling their climatic and environmental effects. Unravelling the influence of Deccan volcanism on the KPB extinction and other Maastrichtian and Danian perturbations requires more accurate age calibrations and duration estimates of biotic and climatic events. Here we integrate existing astrochronologies of the Zumaia section, allowing us to produce a refined cyclostratigraphic calibration of the main planktic foraminiferal and paleoclimatic events recorded across the KPB in the well-know Zumaia section (NW, Spain).

At Zumaia, the KPB is marked by a ~8 cm-thick dark clay bed, with low values of %CaCO3 and δ13C. The Chicxulub ejecta-rich airfall layer has been identified at the base of the dark clay bed, but it is partially masked within a 1–2 cm-thick diagenetic calcitic layer. At Zumaia, the KPB has been astronomically calibrated at 66 Ma (compatible with radioisotopic ages), and the duration of dark clay bed is estimated at ~10 kyr. The first appearances (FA) of the Danian planktic foraminiferal index-species Parvularugoglobigerina longiapertura, Parvularugoglobigerina eugubina, Eoglobigerina simplicissima, Parasubbotina pseudobulloides, Subbotina triloculinoides and Globanomalina compressa have been orbitally tuned at Zumaia, to have occurred at 8, 30, 45, 70, 210, and 475 kyr after the KPB. Specimens of Plummerita hantkeninoides have been identified for the first time in the Maastrichtian of Zumaia, and its first occurrence is dated at ~100 kyr before the KPB. Based on d13C data, we have identified the late Maastrichtian Warming Event (LMWE), the early Danian Dan-C2 and the Lower-C29N events. Additionally, a bloom of the eutrophic/opportunist genus Chiloguembelitria, interpreted as a period of environmental stress, has also been recognized above and separate from the KPB clay bed. Besides the KPB, the main paleoclimatic/paleoenvironmental events have been astronomically calibrated at Zumaia as follows: the LMWE between 270 and 120 kyr before the KPB, the Dan-C2 event between 205 and 305 kyr after the KPB, the Lower-C29N event between 520 and 595 kyr after the KPB, and the Chiloguembelitria bloom between 100 and 305 kyr after the KPB. According to this chronology, we conclude that the LMWE and early Danian Chiloguembelitria bloom seems to coincide in time with major volcanic pulses of the Deccan Traps, unlike the Dan-C2 and Lower-C29N events, which appear to have been driven by orbital forcing. Regardless of the cause of climatic and environmental events, all these perturbations appear unrelated to the KPB mass extinction event. It supports the hypothesis that the influence of Deccan volcanism on planktic foraminiferal assemblages during the Maastrichtian and Danian was limited.

How to cite: Gilabert, V., Batenburg, S. J., Arenillas, I., and Arz, J. A.: Astronomical calibration of paleoclimatic and planktic foraminiferal events of the Cretaceous-Paleogene transition at Zumaia, Spain, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8008, https://doi.org/10.5194/egusphere-egu21-8008, 2021.

EGU21-1662 | vPICO presentations | SSP2.1

Microfossil evidence for the EECO and MECO events in the Eocene sediments of the Isle of Wight, UK.

Malcolm Hart, Pritpal Mangat, and Meriel Fitzpatrick

The Paleogene section of Whitecliff Bay (Isle of Wight) is one of the most complete onshore successions in North West Europe (see Curry, 1965, 1966). The microfossil assemblages have been investigated by many micropaleontologists and the succession of foraminifera, ostracods, calcareous nannofossils, pteropods, diatoms, charophytes and dinocysts have been described in varying levels of detail. The planktic foraminiferal datum (Wright, 1972; Murray et al., 1989) in the Lower Eocene and the occurrence of larger foraminifera in the mid-Eocene provide evidence of incursions of warm water taxa that may be recording the presence of the Early Eocene Climatic Optimum (EECO) and the Middle Eocene Climatic Optimum (MECO) although these occurrences could equally be caused by changes in palaeogeography, glacio-eustasy and the general depositional environment.

Over a period of over 40 years samples have been collected from both the cliff succession and, at times of lowered sediment levels, on the foreshore which can often provide 100% exposure of the succession. Preservation of microfossil assemblages in samples is always better when collected from the foreshore while the cliff succession often records no calcareous (e.g., foraminifera) or siliceous microfossils (e.g., diatoms).

Both EECO and MECO are recorded as being brief, transient events while the palaeontological variations look to be of an altogether longer duration. Stable isotope data are limited (Dawber et al., 2011) and, at the present time, do not provide precise confirmation of isotope excursions precisely synchronous with the palaeontological distributions. Nevertheless, the evidence of northward migration by warm-water taxa is quite distinctive and worthy of still further investigation. In the case of MECO, the presence of Nummulites spp., Alveolina fusiformis and corals is certainly suggestive of warm-water migration into the northern confines of the Anglo-Paris-Belgian Basin.

Curry, D., 1965. The Palaeogene Beds of South-East England. Proceedings of the Geologists’ Association, 76(2), 151‒173.

Curry, D., 1966. Problems of correlation in the Anglo-Paris-Basin. Proceedings of the Geologists’ Association, 77(4), 437‒467.

Dawber, C.F., Tripati, A.K., Gale, A.S., MacNiocaill, C., Hesselbo, S.P., 2011. Glacioeustasy during the middle Eocene? Insights from the stratigraphy of the Hampshire Basin, UK. Palaeogeography, Palaeoclimatology, Palaeoecology, 300, 84–100.

Wright, C.A., 1972.  The recognition of a planktonic foraminiferid datum in the London Clay of the Hampshire Basin. Proceedings of the Geologists’ Association, 83, 413‒419.

Murray, J.W., Curry, D., Haynes, J.R., King, C.,1989. Palaeogene. In: Jenkins, D.G., Murray, J.W. (eds), Stratigraphical Atlas of Fossil Foraminifera [2nd Edition] (eds), British Micropalaeontological Series, Ellis Horwood Ltd, Chichester, 490‒536.

How to cite: Hart, M., Mangat, P., and Fitzpatrick, M.: Microfossil evidence for the EECO and MECO events in the Eocene sediments of the Isle of Wight, UK., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1662, https://doi.org/10.5194/egusphere-egu21-1662, 2021.

EGU21-12976 | vPICO presentations | SSP2.1

Charophyte biostratigraphy of continental deposits in a filled-karst system: A case study from the Eocene bauxite cover-sequence at Gánt (Vértes Hills, Hungary)

Khaled Trabelsi, Benjamin Sames, Michael Wagreich, Miklós Kázmér, Andrea Mindszenty, and Carles Martín-Closas Martín-Closas

The Eocene ‘‘blue hole” freshwater limestones from the bauxite cover-sequence at the Gánt karst system (Vértes Hills), Transdanubian Central Range, north-western Hungary, have yielded rich charophyte assemblages of higher taxonomic and biostratigraphic interest. The taxonomic study of this flora allows revision and emendation of the species Raskyella peckii and facilitates the definition of a new evolutionary anagenetic lineage based on three successive anagenetic varieties of this species which were formerly considered as separate species or subspecies: Raskyella peckii var. peckii (early Lutetian–early Bartonian), Raskyella peckii var. caliciformis (early Bartonian), and Raskyella peckii var. vadaszii (late Bartonian). Based on these, we propose a new local charophyte biozonation with the new Raskyella peckii Superzone (Lutetian–Bartonian), subdivided into three successive charophyte partial range zones: The ‘Raskyella peckii peckii Zone’ (Lutetian–lowermost Bartonian) is locally characterized by an assemblage of R. peckii peckii, Gyrogona caelata forma caelata, G. caelata forma monolifera and Nitellopsis (Tectochara) palaeohungarica. The ‘Raskyella peckii caliciformis Zone’ (lower Bartonian) includes the local assemblage of R. peckii var. caliciformis, G. caelata forma caelata, G. caelata forma monolifera, G. caelata forma baccata, Nitellopsis (Tectochara) palaeohungarica and Chara media. The ‘Raskyella peckii vadaszii Zone’ (upper Bartonian) is composed of the local assemblage of R. peckii var. vadaszii, G. caelata forma bicincta, G. caelata forma baccata, G. caelata forma fasciata, G. tuberosa, Psilochara polita, Psilochara sp., Chara media and Chara subcylindrica. Future research may show the new local biozonation as applicable to whole Europe and complementing the current European charophyte biozonation. Our results show that the sequences from Gánt previously regarded as upper mid-Eocene (upper Lutetian–lower Bartonian) appear to comprise a longer chronostratigraphic interval, i.e. lower Lutetian till upper Bartonian, with also has implications on the understanding of the regional stratigraphy of the Transdanubian Central Range during the Eocene.

How to cite: Trabelsi, K., Sames, B., Wagreich, M., Kázmér, M., Mindszenty, A., and Martín-Closas, C. M.-C.: Charophyte biostratigraphy of continental deposits in a filled-karst system: A case study from the Eocene bauxite cover-sequence at Gánt (Vértes Hills, Hungary), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12976, https://doi.org/10.5194/egusphere-egu21-12976, 2021.

EGU21-10985 | vPICO presentations | SSP2.1

Calcareous nannofossils from the Tasman Sea (IODP Site U1509): biochronology, paleoclimatic evolution and bulk stable isotopes across the Eocene-Oligocene Transition

Allyson Viganò, Edoardo Dallanave, Laia Alegret, Thomas Westerhold, Rupert Sutherland, Gerald R. Dickens, and Claudia Agnini

About 34 Ma, the Warmhouse climate state switched into the Coolhouse state, when a rapid drop in temperature and the establishment of permanent continental ice-sheet on the Antarctic continent occurred (1).

This event, which is referred to as the Eocene-Oligocene transition (EOT; lasted ~500 ka) represents one of the most prominent transitions of the entire Cenozoic. During the EOT, calcareous nannoplankton experienced significant changes in the assemblage coinciding with the long-term cooling and modifications in the sea-surface water conditions (2, 3), suggesting a cause-effect relationship between the onset of the first sustained Antarctic glaciation and the response of phytoplanktonic communities.

We generated a high-resolution calcareous nannofossil and geochemical datasets (δ18O, δ13C and % CaCO3) from IODP Site U1509 (New Caledonia Trough) (4) with the final aim to provide an overview of the paleoclimatic and paleoceanographic evolution of the study area across the EOT. Our bio-magnetostratigraphic results, consistent with shipboard data (5), were compared along with other existing records recovered from Indian Ocean, Equatorial Pacific and Atlantic Ocean in order to critically evaluate the reliability, reproducibility and synchroneity of all the biohorizons taken into consideration and to obtain a clearer global perspective. 

According to major trends and shifts in the assemblage, the ~5 Myr study interval was subdivided into 4 distinct phases, which were also identified based on changes observed in 1) a number of diversity indices (i.e., species richness, dominance, H-index and evenness), 2) the warm-oligotrophic taxa abundance (Discoaster saipanensis, D. barbadiensis and Ericsonia formosa), 3) the principal component (PC1 and PC2) scores, and 4) bulk stable isotopes and carbonate content. The observed changes are interpreted as an overall decline of warm-oligotrophic communities and, conversely, the incoming of genera better adapted to cooler and more eutrophic conditions.

The most prominent shift in the assemblage occurred during a time window of ~520 kyr, the precursor phase, with relatively high bulk δ18O and % CaCO3 values, that predated the phase of maximum glacial expansion (Earliest Oligocene Glacial Maximum – EOGM) (6) and documented the permanent loss of the late Eocene k-selected community, characterized by warm and oligotrophic taxa.

References

1. T. Westerhold et al., Science. 369, 1383–1388 (2020).

2. T. Dunkley Jones, P. R. Bown, P. N. Pearson, J. Syst. Palaeontol. 7, 359–411 (2009).

3. H. K. Coxall, P. N. Pearson, in Deep-Time Perspectives on Climate Change: Marrying the Signal from Computer Models and Biological Proxies, Micropaleontology Society Special Publication, M. Williams, A. M. Haywood, J. Gregory, D. N. Schmidt, Eds. (Geological Society, London, 2007), pp. 351–387.

4. R. Sutherland, G. R. Dickens, P. Blum, the Expedition 371, Int. Ocean Discov. Progr. (2017), doi:10.14379/iodp.pr.371.2018.

5. R. Sutherland et al., Tasman Front. Subduction Initiat. Paleogene Clim. Proc. Int. Ocean Discov. Program, 371 Coll. Station. TX (International Oce. 371, 1–35 (2019).

6. Z. Liu, S. Tuo, Q. Zhao, X. Cheng, W. Huang, Chinese Sci. Bull. 49, 2190–2197 (2004).

How to cite: Viganò, A., Dallanave, E., Alegret, L., Westerhold, T., Sutherland, R., Dickens, G. R., and Agnini, C.: Calcareous nannofossils from the Tasman Sea (IODP Site U1509): biochronology, paleoclimatic evolution and bulk stable isotopes across the Eocene-Oligocene Transition, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10985, https://doi.org/10.5194/egusphere-egu21-10985, 2021.

EGU21-10907 | vPICO presentations | SSP2.1

Hunting down the late Miocene-early Pliocene biogenic bloom in the Tasman Sea: an integrated study at IODP Site U1506

Maria Elena Gastaldello, Claudia Agnini, Edoardo Dallanave, Thomas Westerhold, Adriane R. Lam, Michelle K. Drake, Gerald R. Dickens, Rupert Sutherland, and Laia Alegret

The latest Miocene-early Pliocene biogenic bloom is a poorly understood paleoceanographic event that has been traditionally related to increased primary productivity; and associated changes in the marine carbon cycle. In order to identify this event in the Tasman Sea, we carried out an integrated study at IODP Site U1506. First, we have constructed an age model based on an integrated approach (i.e. biostratigraphy, astrocyclostratigraphic tuning). This permits the identification of the precise position as well as the duration of the biogenic bloom in the Tasman Sea but also the calculation of sedimentation rates across the study interval. In this framework, we generated quantitative micropaleontological records (benthic and planktic foraminifera and calcareous nannofossils) and a low-resolution carbon and oxygen stable isotope records on Cibicidoides mundulus and Trilobatus sacculifer across an interval spanning from 233.50 to 81.75 m CSF-A (Tortonian, late Miocene to Zanclean, early Pliocene). Quantitative assemblage work and statistical analyses on the resulting dataset point to increased export productivity in the lower part of the interval (between CNM15 and CNM18, Backman et al., 2012), as inferred from benthic foraminiferal assemblages dominated by taxa (e.g. Uvigerina and Ehrenbergina) that have been reported to be common across the biogenic bloom in the Indian Ocean (Dickens and Owen, 1999). The paleoecological analysis of these assemblages suggests eutrophic conditions at the seafloor and low oxygen concentration of bottom waters.

Reference

Backman, J., Raffi, I., Rio, D., Fornaciari, E., & Pälike, H., 2012. Biozonation and biochronology of Miocene through Pleistocene calcareous nannofossils from low and middle latitudes. Newsletters on Stratigraphy, 45(3), 221–244.

Dickens, G.R. and Owen, R.M., 1999. The latest Miocene-early Pliocene biogenic bloom: A revised Indian Ocean perspective. Marine Geology, 161: 75-91.

Acknowledgments

University of Padova DOR grant, CARIPARO Foundation Phd scholarship.

Spanish Ministry of Economy and Competitiveness and FEDER funds (PID2019-105537RB-I00).

How to cite: Gastaldello, M. E., Agnini, C., Dallanave, E., Westerhold, T., Lam, A. R., Drake, M. K., Dickens, G. R., Sutherland, R., and Alegret, L.: Hunting down the late Miocene-early Pliocene biogenic bloom in the Tasman Sea: an integrated study at IODP Site U1506, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10907, https://doi.org/10.5194/egusphere-egu21-10907, 2021.

EGU21-6900 | vPICO presentations | SSP2.1

The Mid-Brunhes Event: a second stage for the Middle Pleistocene Subseries?

Martin J. Head, Jan Zalasiewicz, Adele Bertini, and Liping Zhou

The Middle Pleistocene Subseries and Chibanian Stage were officially defined in 2020 through ratification of the Global Boundary Stratotype Section and Point (GSSP) at Chiba, Japan (Suganuma et al., in press).  Their shared base at 774.1 ka represents the approximate midpoint of the Early–Middle Pleistocene transition, a 1.4–0.4 ka interval marked by a progressive increase in the amplitude of climate oscillations and shift towards a quasi-100 ky frequency.  They currently both extend to the base of the Upper Pleistocene Subseries dated provisionally at ~129 ka (Head et al., in press).  Global stages have not traditionally been employed for the Quaternary owing to the long use of global subseries and regional stages.  Global stages are nonetheless required for formal subdivision of the International Chronostratigraphic Chart, and their acceptance in subdividing both the Holocene and Pleistocene Series has become increasingly evident.  The Middle Pleistocene Subseries and Chibanian Stage are currently identical in extent.  With this in mind, we consider the possibility of subdividing the Middle Pleistocene by introducing a second stage, which would shorten the duration of the Chibanian and increase its utility.  There has been increasing recognition of the ‘Mid-Brunhes Event’ (Jansen et al., 1986) more recently termed the ‘mid- Brunhes Transition’ (Yin, 2013; Barth et al., 2018), an abrupt step-change to increased amplitude of the quasi-100 kyr cycles and warmer interglacials from MIS 11 onwards. The base of this new stage would reasonably be placed around the MIS 12–MIS 11 transition (Termination V, ~420 ka), a level clearly recognised in the marine record. This level appears to approximate the bases of the Holsteinian, Hoxnian, Likhvinian, and Zavadivian regional stages across northwestern and central Europe, the Russian Plain, and the Ukrainian Loess Plain; and can be traced across the Chinese Loess Plateau (Cohen and Gibbard, 2020).  The possibility of a second stage will initially be explored by publication of a position paper. If this attracts sufficient support, a Working Group of the International Subcommission on Quaternary Stratigraphy will be established to analyse the case more formally.

Barth, A.M., Clark, P.U., Bill, N.S., He, F., Pisias, N.G., 2018.  Climate evolution across the Mid-Brunhes Transition. Climate of the Past 14, 2071–2087.

Cohen, K., Gibbard, P., 2020. Global chronostratigraphical correlation table for the last 2.7 million years v.2019 (Poster version), Mendeley Data, V3, doi: 10.17632/dtsn3xn3n6.3

Head, M.J., Pillans, B., Zalasiewicz, J.A., in press. Formal ratification of subseries/subepochs for the Pleistocene Series/Epoch of the Quaternary System/Period. Episodes.

Jansen, J.H.F., Kuijpers, A., Troelstra, S.R., 1986. A mid-Brunhes climatic event: Long-term changes in global atmosphere and ocean circulation. Science 232, 619–622.

Suganuma, Y., Okada, M., Head, M.J. et al., in press. Formal ratification of the Global Boundary Stratotype Section and Point (GSSP) for the Chibanian Stage and Middle Pleistocene Subseries of the Quaternary System: the Chiba Section, Japan.  Episodes.

Yin, Q., 2013. Insolation-induced mid-Brunhes transition in Southern Ocean ventilation and deep-ocean temperature. Nature 494: 222–225.

How to cite: Head, M. J., Zalasiewicz, J., Bertini, A., and Zhou, L.: The Mid-Brunhes Event: a second stage for the Middle Pleistocene Subseries?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6900, https://doi.org/10.5194/egusphere-egu21-6900, 2021.

EGU21-12664 | vPICO presentations | SSP2.1

Preliminary results of a multidisciplinary study of the buried peatland and host sediments of the Moscow-Valdai age (Dmitrov, Moscow region, Russia)

Ekaterina Ershova, Svetlana Sycheva, Svetlana Kuzmina, Inna Zuganova, Pavel Panin, and Margarita Meteleva

The poster presents preliminary results of multidisciplinary studies of a 5-m section of Middle and Late Pleistocene deposits found in a quarry near the town of Dmitrov, Moscow region. The section includes Moscow fluvioglacial sands, alluvium, lake sapropels, and a layered lens of peat overlain by Valdai cover loams with large cryogenic deformations. The sediments were described and analyzed for pollen, plant macrofossils, and insect remains. The results of pollen analysis suggest that the deposits were formed during the second half of the Mikulino (Eemian) interglacial and during the transition to the Valdai (Weichselian) Glaciation (MIS 5e to MIS 5d). The pollen diagram reflects the replacement of deciduous forests by coniferous forests and the subsequent replacement of closed dark coniferous forests by open communities dominated by birch, shrubs, light-demanding grasses, and Artemisia. Seeds and fruits of wetland and aquatic plants, including endocarps of the extinct species Potamogeton sukaczevii, were found in samples from peat and underlying lake sediments. This may indicate the Mikulino or Early Valdai age of the studied deposits. The entomological fauna indicates the predominance of coastal and marsh species. Environmental conditions were relatively cool, rather characteristic of the late Interglacial. It is expected to obtain micromorphological, physicochemical characteristics of the sediments, as well as OSL dates to clarify the age of the sediments. This work was supported by RFBR, grant N19-29-05024 mk.

How to cite: Ershova, E., Sycheva, S., Kuzmina, S., Zuganova, I., Panin, P., and Meteleva, M.: Preliminary results of a multidisciplinary study of the buried peatland and host sediments of the Moscow-Valdai age (Dmitrov, Moscow region, Russia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12664, https://doi.org/10.5194/egusphere-egu21-12664, 2021.

SSP2.3 – SSP2.3 Integrated Stratigraphy - Recent advances in reconstructing Earth System and human dynamics.

EGU21-9491 | vPICO presentations | SSP2.3 | Highlight

Progress in assessment of the Anthropocene Series in the Geological Time Scale (GTS)

Colin N. Waters, Jan Zalasiewicz, and Mark Williams

The Anthropocene as a concept originated in 2000, suggested by Paul Crutzen in an Earth System science context. Only later was it considered as a putative geological series, including in GTS2012 (Zalasiewicz et al. 2012). This was barely three years after the establishment of the Anthropocene Working Group (AWG), tasked by the Subcommission on Quaternary Stratigraphy to examine the Anthropocene for potential inclusion in the GTS and to formulate a definition. In GTS2012 a likely generalised stratigraphic signature was postulated to comprise: a) lithostratigraphic signals, both direct modification of the landscape and indirect influences on sedimentary facies through rapidly modifying drivers; b) sequence stratigraphic signals due to modern sea-level rises, envisaging a near-future marine transgression; c) biostratigraphic signals through increased extinction rates, range changes especially through unprecedented rates of species invasions; and d) chemostratigraphic signals including inorganic and organic contaminants, isotopic shifts of carbon and nitrogen and fallout from nuclear bomb testing. By the time of GTS2020 (Zalasiewicz et al. 2020), not only could specific examples of temporal variations in many of these proxies be demonstrated, but also numerous new proxies, such as inorganic crystalline mineral-like compounds, microplastics, fuel ash and black carbon had been demonstrated and more information was available on the scale of human terraforming of landscape and anthropogenic modification of river systems. Further, the intervening eight years had seen a strengthening of the evidence of climate warming, sea-level rise and ocean acidification.

In GTS2012, three levels for the beginning of the Anthropocene were considered: the Early Holocene; the onset of the Industrial Revolution; and the mid-20th century, and only the first option was definitively excluded. GTS 2020 was able to report the findings of the AWG that the Anthropocene represented “geological reality”, was best considered at epoch level, should be linked with the plethora of proxies that initiate or show marked perturbations at around the 1950s and is best defined using a GSSP. In GTS2020, the ongoing task of researching potential GSSP candidate sections for the Anthropocene Series was also outlined and this work is anticipated to be completed by 2022. The eleven current sites encompass diverse environments that will best preserve the extensive range of proxies suitable for characterising the prospective Holocene–Anthropocene transition. All sections will be in borehole/drill cores, most showing annually resolved laminations that can be independently dated radiometrically to confirm a complete succession extending back to pre-Industrial times. The strengths and weaknesses of distinct environments are discussed in GTS2020 for lake deposits, marine anoxic basins, estuaries and deltas, speleothems, glacial ice, coral reefs, trees and peat. The evidence collected already suggests that the Anthropocene may be widely recognised and delineated as a sharply distinctive chronostratigraphic unit reflecting major Earth System change that will have geologically lasting consequences.

Zalasiewicz, J., Crutzen, P.J. & Steffen, W. 2012. Chapter 32: The Anthropocene. The Geologic Time Scale 2012. https://doi.org/10.1016/B978-0-444-59425-9.00032-9 

Zalasiewicz, J., Waters, C. & Williams, M. 2020. Chapter 31: The Anthropocene. The Geologic Time Scale 2020. https://doi.org/10.1016/B978-0-12-824360-2.00031-0

How to cite: Waters, C. N., Zalasiewicz, J., and Williams, M.: Progress in assessment of the Anthropocene Series in the Geological Time Scale (GTS), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9491, https://doi.org/10.5194/egusphere-egu21-9491, 2021.

EGU21-6919 | vPICO presentations | SSP2.3

Subdivision of the Quaternary System: formal subseries and new corresponding stages for the Pleistocene and Holocene

Martin J. Head, Philip L. Gibbard, and Jan Zalasiewicz

The Holocene and Pleistocene series/epochs have each long been divided into Early, Middle and Late subseries/subepochs, although their formalization had been complicated by the hitherto absence of this rank from the International Chronostratigraphic Chart.  On 14th June 2018, the Holocene was formally subdivided into the Greenlandian, Northgrippian and Meghalayan stages/ages and their corresponding Lower/Early, Middle, Upper/Late subseries/subepochs, each defined by a Global Boundary Stratotype Section and Point (GSSP). The GSSP for the lowermost stage, the Greenlandian, is that of the Holocene as previously defined in the NGRIP2 Greenland ice core, and dated at 11,700 yr b2k (before 2000 CE). The GSSP for the Northgrippian is in the NGRIP1 Greenland ice core, and dated at 8236 yr b2k, whereas that for the Meghalayan is located in a speleothem from Mawmluh Cave, Meghalaya, northeast India with a date of 4250 yr b2k (Walker et al., 2018).  The Pleistocene Series/Epoch of the Quaternary System/Period has been divided unofficially into three subseries/subepochs since at least the 1870s.  On 30th January 2020, two proposals were ratified: 1) the Lower Pleistocene Subseries, comprising the Gelasian Stage and the superjacent Calabrian Stage, with a base defined by the GSSP for the Gelasian Stage, the Pleistocene Series, and the Quaternary System, and currently dated at 2.58 Ma; and 2) the term Upper Pleistocene, at the rank of subseries, with a base currently undefined but provisionally dated at ~129 ka.  The Middle Pleistocene and its corresponding Chibanian Stage/Age had meanwhile been formalized on January 17, 2020 with a GSSP in the Chiba section, Japan.  The GSSP is placed 1.1 m below the directional midpoint of the Matuyama–Brunhes Chron boundary, at the base of a regional lithostratigraphic marker, the Ontake-Byakubi-E tephra bed, in the Chiba section. The GSSP has an astronomical age of 774.1 ka and is placed just below the top of Marine Isotope Substage 19c.  These ratifications nominally complete the official division of the Quaternary into subseries/subepochs, although the Upper Pleistocene and its corresponding stage remain to be defined by GSSP.  The Anthropocene is currently an unofficial unit, while analysis of potential candidate GSSP locations is progressing in preparation for a formalization proposal.  If approved, it would terminate the Holocene at around the year 1952, assuming it is defined at series/epoch rank.

Head, M.J., Pillans, B., and Zalasiewicz, J.A., in press. Formal ratification of subseries/subepochs for the Pleistocene Series/Epoch of the Quaternary System/Period. Episodes

Suganuma, Y., Okada, M., Head, M.J., et al., in press. Formal ratification of the Global Boundary Stratotype Section and Point (GSSP) for the Chibanian Stage and Middle Pleistocene Subseries of the Quaternary System: the Chiba Section, Japan.  Episodes

Walker, M., Head, M.J., Berkelhammer, M. et al., 2018.  Formal ratification of the subdivision of the Holocene Series/Epoch (Quaternary System/Period): two new Global Boundary Stratotype Sections and Points (GSSPs) and three new stages/subseries. Episodes 41(4): 213–223. 

How to cite: Head, M. J., Gibbard, P. L., and Zalasiewicz, J.: Subdivision of the Quaternary System: formal subseries and new corresponding stages for the Pleistocene and Holocene, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6919, https://doi.org/10.5194/egusphere-egu21-6919, 2021.

EGU21-9373 | vPICO presentations | SSP2.3

New methods for quantitative climate reconstructions applied to the Levant

Timon Netzel, Andreas Hense, Thomas Litt, and Andrea Miebach

On his migration out of Africa, anthropological modern human had to cross the Levant, among other places. Today, there are many different climatic zones, which are particularly evident along the Jordan Valley. For example, the Dead Sea and the Sea of Galilee in Israel are reservoirs of climate proxies and reflect climate variability during the Holocene, based on pollen and plant remains in their lake sediments.

In addition to plant information, speleothems are also useful as climatic proxies. They have been studied in many caves in the Levant. From their isotopic data, conclusions can be drawn about the climate in specific periods and areas. One task is their appropriate use in terms of quantitative climate reconstruction.

Another topic is the consideration of age uncertainties in paleoclimatology and their influence on reconstruction techniques. For this purpose, it is advantageous to use mathematical formulations that are easy to implement and calculate.

Based on data from a sediment core of Sea of Galilee we will discuss and present results for the following sequence of points: the mathematical formulation of climate reconstruction using Bayesian hierarchical models, the computation of transfer function connecting proxy information with physical climate data using machine learning techniques, and the inclusion of age uncertainty based on the output from the latest BACON version.

How to cite: Netzel, T., Hense, A., Litt, T., and Miebach, A.: New methods for quantitative climate reconstructions applied to the Levant, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9373, https://doi.org/10.5194/egusphere-egu21-9373, 2021.

EGU21-8634 | vPICO presentations | SSP2.3

Holocene landscape instability in the context of a loessic early Upper Palaeolithic open-air site in the Middle Danube Basin

Stephan Pötter, Wei Chu, Janina J. Nett, and Philipp Schulte

The palaeoanthropological record of Western Romania is a prime archive of the early modern human presence in Southeastern Europe. Regional stratified early Upper Palaeolithic open-air and karstic sites enable us to infer temporal and spatial patterns of early modern human behaviour in various geomorphological settings. However, open-air sites are often prone to reworking processes caused by local landscape instabilities. The pristine archaeological and palaeoenvironmental stratigraphic evidence is often overprinted by fluvial and slope processes. Therefore, heavily reworked sites are often neglected by researchers. Nevertheless, reworked archaeological and sediment sequences are crucial archives of landscape evolution because they record fluctuations in subsequent erosional and depositional phases. Here, we present the results of a multi-proxy geoarchaeological investigation of the Upper Palaeolithic site of Temereşti Dealu Vinii. This site is located in the Bega Valley, a well-known area for early Upper Palaeolithic open-air localities. Despite the identification of various Upper Palaeolithic cultural units, the artefacts show no discernible horizontal or vertical distribution patterns and stratigraphic inconsistencies. Geochemical and granulometric data aided by luminescence and radiocarbon dating as well as stratigraphic evidence suggest a sub-continuous hydrological sorting over short transport distances during the Holocene. Consistent luminescence ages and characteristics suggest that erosion and deposition occurred sub-continuously during this period. This record of landscape dynamics is consistent with other archives from the area that show evidence for anthropogenically induced phases of soil erosion during the Holocene. This study highlights the importance of reworked archaeological sites such as Temereşti Dealu Vinii not only as viable archives of human presence during the Late Pleistocene – but also as valuable records of subsequent landscape evolution. Detailed analyses of post-depositional disturbances of archaeological sites enable us to improve the accuracy of early modern human behavioural interpretations, and to better contextualise sites such as Temereşti Dealu Vinii within the assemblage of both “in-situ” and reworked loessic Upper Palaeolithic localities in the Danube Basin to evaluate the importance of palaeogeography for human occupation

How to cite: Pötter, S., Chu, W., Nett, J. J., and Schulte, P.: Holocene landscape instability in the context of a loessic early Upper Palaeolithic open-air site in the Middle Danube Basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8634, https://doi.org/10.5194/egusphere-egu21-8634, 2021.

EGU21-6295 | vPICO presentations | SSP2.3

CLIMATE@COA project: Climate and human adaptation during the Last Glacial Period in the Côa Valley region (Portugal)

Luca Dimuccio, Thierry Aubry, Lúcio Cunha, and Nelson Rodrigues

In Portugal, climate fluctuations of Late Pleistocene are well-known from marine record on the western Iberian continental margin, particularly of Marine Isotope Stages 4, 3 and 2, and they include various events of secular abrupt climate changes. During cooling phases the Heinrich Events (HE) occurred, corresponding to episodes of massive ice-discharges from Northern Hemisphere ice sheets. Furthermore, several climate phases with relatively warmer conditions, known as Dansgaard-Oeschger (D-O) cycles, characterized by an abrupt warming (D-O event) followed by a more gradual cooling, took place in-between HE. This pronounced climate instability that characterizes the Last Glacial Period between ca. 80-12 ka is recorded in a variety of marine and terrestrial archives worldwide. It had a recognized impact on the bioclimatic zones and, possibly, on the Neanderthal and Anatomically Modern Human (AMH) settlements of Iberia.

Based mainly on the study of geoarchaeological records preserved in caves and rock-shelters of Iberia, a correlation framework with climate shifts has been proposed to explain the observed discontinuities between sequences containing late Middle and early Upper Palaeolithic remains. Moreover, a climate driven model has been advanced to explain the chronological differences between northern and southern Pyrenean data by a later dispersion of AMH and the persistence of last Neanderthals in Southern Iberia, which were interpreted as a direct impact of HE4 (40-38 ka) in the distribution of large ungulate populations.

Despite all these data, the exact impact of HE on terrestrial systems, the evaluation of the latitudinal differentiation of their impact and time-gap, as well as the correlation between periods of relative stabilization/soil formation and the D-O events remain to be clearly established. In addition, the whole framework relating to the Middle-to-Upper Palaeolithic transition has been excessively dependent on karst archives and it should be investigated in other geomorphological settings - among these the fluvial and Iberian plateau (“Meseta”), both present in the Côa Valley region (Douro Basin, north-east of Portugal). Alluvial and colluvial deposits preserved in the Côa Valley (e.g. at the Cardina-Salto do Boi, Quinta da Barca Sul, Penascosa, Fariseu, Olga de Ervamoira sites) have demonstrated to be a valuable record of information about Late Pleistocene sedimentary processes, depositional environments, and hunter-gatherer’s behaviour at local and regional scales.

In this context, the CLIMATE@COA project (COA/CAC/0031/2019), funded by the Fundação para a Ciência e Tecnologia (FCT), proposes an integrated multi/interdisciplinary approach based on the stratigraphical, sedimentological, geochemical, geomorphological, geoarchaeological, and geochronological analyses of terrestrial record (natural and cultural) preserved in the Côa Valley and surrounding plateau areas, with the aim to develop an evolutionary model for the region and to deduce the environmental forcing factors for such evolution - namely climate and ecosystem changes. In addition, the project’s data will allow to define better the chronology of the transition between Neanderthal and AMH and to infer on land use and social organization in its environmental context.

How to cite: Dimuccio, L., Aubry, T., Cunha, L., and Rodrigues, N.: CLIMATE@COA project: Climate and human adaptation during the Last Glacial Period in the Côa Valley region (Portugal), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6295, https://doi.org/10.5194/egusphere-egu21-6295, 2021.

EGU21-8644 | vPICO presentations | SSP2.3

U-Th dated late Pleistocene tufas linked to human occupation in the semi-arid southern Kalahari

Jessica von der Meden, Jayne Wilkins, Benjamin Schoville, Kyle Brown, and Robyn Pickering

Ga-Mohana Hill North Rockshelter (GHN) in the Northern Cape Province of South Africa is situated within the Summer Rainfall Zone, in the semi-arid (~300-400mm mean annual rainfall) southeastern edge of the Kalahari Basin. This location is significant as the dominant narrative for the evolution of modern humans has focused on Middle Stone Age archaeological sites along the southern cape coast of South Africa, with coastal resources and favourable climate conditions argued as key factors in driving the evolution of Homo sapiens. Semi-arid regions in the interior of South Africa, such as the southern Kalahari Basin, are often considered to have been too dry to sustain significant human occupation and activity, and have thus been overlooked. However, GHN does indeed preserve rich stratified Middle and Later Stone Age deposits, as well as abundant large relict tufa deposits that cover the surrounding hillside. These tufas, which are ambient temperature, freshwater calcium carbonate deposits, are indicative of past periods of flowing surface waters and shallow pools on the hillside. Laser ablation trace element mapping was used to pre-screen the tufa samples to target layers with high 238U and little to no 232Th concentration for U-Th dating. The resultant ages show that the tufa system at Ga-Mohana was active during five distinct intervals over the last 110 ka, three of which closely coincide with the timing of human occupation at the site, itself dated via OSL. The coincidence of tufa formation and human occupation suggests that the tufa-forming waters were a critical resource to human populations living in the area. This hitherto undiscovered source of fresh water, more than 600 km inland and as far back as 110 ka, stands to challenge the notion of an empty and arid interior.

How to cite: von der Meden, J., Wilkins, J., Schoville, B., Brown, K., and Pickering, R.: U-Th dated late Pleistocene tufas linked to human occupation in the semi-arid southern Kalahari, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8644, https://doi.org/10.5194/egusphere-egu21-8644, 2021.

EGU21-3008 | vPICO presentations | SSP2.3

Paleoclimate and vegetation reconstruction of Abric Romani (Capellades, Spain) during MIS-3, 4, and MIS-5 (a-d)

Demet Biltekin, Francesc Burjachs, Josep Vallverdú, Warren D. Sharp, Regina Mertz-Kraus, M. Gema Chacón, Palmira Saladié, James L. Bischoff, and Eudald Carbonell

Paleoclimate and vegetation reconstruction of Abric Romani (Capellades, Spain) during MIS-3, 4, and MIS-5 (a-d)

Demet Biltekin1,2, Francesc Burjachs1,3,4, Josep Vallverdú1,4, Warren D. Sharp5, Regina Mertz-Kraus6, M. Gema Chacón1,4,  Palmira Saladié1,4, James L. Bischoff5, Eudald Carbonell1,4

 

1Institut Català de Paleoecologia Humana i Evolucio Social (IPHES), Zona Educacional 4, Campus Sescelades URV, edifici W3, 43007 Tarragona, Spain.

2Istanbul Technical University, Eurasia Institute of Earth Sciences, Ayazağa Campus, Maslak, Sarıyer, 34469, Istanbul/Turkey

3ICREA, Barcelona, Catalonia, Spain.

4URV, Universitat Rovira i Virgili, Facultat de Lletres, Avinguda Catalunya, 35, 43002 Tarragona, Catalonia, Spain.

5Berkeley Geochronology Center, Berkeley, CA 94709, United States.

6Institute for Geosciences, Johannes Gutenberg University, Mainz, Germany.

 

This new pollen data provides the vegetation and climate history during ca. 110 ka-55 ka BP from Abric Romaní archaeological site using pollen analysis of a 30 m-long sedimentary sequence. The beginning of the MIS 3 starts an abundance in steppes and herbs, indicating cold and dry climate in the region. However, this was replaced by a slight increase in deciduous Quercus and Mediterranean trees. During the MIS 4, the pollen records reflect a predominance of Artemisia steppes and herbaceous communities (Poaceae and Asteraceae families), indicating dry and cold conditions in Abric Romaní. The MIS 5 was well recorded with its substages, including 5a, 5b, 5c and 5d. The MIS 5d is characterized by Pinus and Artemisia steppes with herbaceous assemblages. The higher abundance of Artemisia during the second part of the MIS 5b, reflecting cold and dry climate, while temperate forest and Mediterranean trees decline. Mélisey II stadial was marked by an increase in Artemisia and herbs. This suggests that cold climatic conditions existed during this time period. The abundance of oaks during the MIS 5c indicate warmer and humid climate in the region. Other deciduous and broadleaved forest developed as well, including Ulmus, Viburnum, Juglans and Castanea. A short cooling Montaigu event was also recorded within this interstadial, which is dominated by a high percentage of Ericaceae with Artemisia. The first part of the MIS 5a is characterized by Corylus, Carpinus, Hedera, Ulmus, Betula, pointing to warmer climatic conditions. In contrast, the high amount of Artemisia steppes may indicate an enhanced degree of continentality during the second half of the MIS 5a in the north-eastern Iberian Peninsula.

Keywords: paleovegetation, climate, pollen analysis, Late Pleistocene, Spain

How to cite: Biltekin, D., Burjachs, F., Vallverdú, J., Sharp, W. D., Mertz-Kraus, R., Chacón, M. G., Saladié, P., Bischoff, J. L., and Carbonell, E.: Paleoclimate and vegetation reconstruction of Abric Romani (Capellades, Spain) during MIS-3, 4, and MIS-5 (a-d), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3008, https://doi.org/10.5194/egusphere-egu21-3008, 2021.

Isotopic fluctuation of certain stable isotopes, notably Oxygen, provide important information on paleoenvironmental change along geological times. However, interpreting isotopic change along continental series depends on our ability to understand its recording, for instance in soils or in mammal teeth. In the case of continental series yielding most of available information on hominid diversification and expansion within and beyond Africa, isotopic information even seems to show discrepancies depending on the archive. In our study, we use isotopic composition in crocodilian tooth enamel. We assume that, for these ectotherms that regulate their temperature, isotopic composition recorded in their teeth mainly depends on drinking water, itself depending on precipitation. Moreover, crocodilian fossil teeth are abundant and widely distributed within continental series, thus constituting an interesting archive. We sampled crocodilian teeth from the Shungura Formation (Lower Omo Valley, Ethiopia), which spans major steps of human evolution between 3.6 Ma and ~1.0 Ma, tentatively correlated with major environmental changes in eastern Africa (intensification of seasonal contrasts, increasing aridity and landscape opening). The analyses of δ18O of hundreds of crocodilian teeth have identified environmental changes. Whereas the isotopic composition of paedogenic carbonates displays a different trend over time, that of crocodilian teeth relates changes already observed in mammal teeth, notably a major shift between 2.6 Ma and 2.3 Ma toward more arid conditions. Our study indicates that crocodilian teeth are a relevant archive of environmental change in continental contexts, and calls for further study to strengthen interpretations of isotopic composition in fossil archives. 

How to cite: Gardin, A., Pucéat, E., Garcia, G., Boisserie, J.-R., and Otero, O.: Stable isotope composition of crocodilian teeth provides new information on climatic change in the East-African Rift along the Plio-Pleistocene period (Shungura Formation, Lower Omo Valley Ethiopia) , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5203, https://doi.org/10.5194/egusphere-egu21-5203, 2021.

EGU21-3991 | vPICO presentations | SSP2.3

Variations in sedimentology, mineralogy and geochemistry on a turbiditic continental margin during an early Eocene negative carbon isotope excursion

Naroa Martínez-Braceras, Aitor Payros, Javier Arostegi, and Jaume Dinarès-Turell

Expanded deep-marine sedimentary successions were deposited on the North Iberian continental margin in Eocene times. These deposits are well exposed along accessible coastal cliffs of the Biscay province, being of great interest for paleoenvironmental and paleoclimatic studies. This study dealt with the 110 m-thick lower Ypresian (early Eocene) succession from Solondota, which is mainly composed of hemipelagic limestones and marls interspersed with abundant turbidites.

Biomagnetostratigraphic and geochemical records allowed correlation of a prominent negative carbon isotope excursion (CIE) with the Ypresian hyperthermal event J, also known as C24n.2rH1. In order to disentangle the environmental evolution of the Solondota turbiditic area during the CIE, high-resolution sedimentological, geochemical (stable isotopes, major, minor and trace elements) and mineralogical (general and clay mineralogy) studies were carried out. The large size of the dataset hindered straightforward identification of relevant variables and interpretation of their relationships. However, a multivariate analysis provided invaluable information about significant trends and variations in the dataset, avoiding empirical or arbitrary selection of representative elements. A good correspondence was found between some elemental trends obtained from the analysis and the sedimentological and mineralogical records. Major and minor elements from the hemipelagic fraction across the Solondota CIE suggest a temporarily more humid continental climate, which caused increased terrigenous material input into the marine environment. While fine-grained terrigenous sediment boosted hemipelagic carbonate dilution, the coarser terrigenous sediment was transported by temporarily more frequent and voluminous turbidity currents. Thus, the results from the Solondota CIE show similarities with deep marine records from other early Eocene minor hyperthermal events. Taking everything into account, this study demonstrates the validity of deep-marine turbiditic successions for providing reliable sedimentological, mineralogical and geochemical records of paleoclimatic significance. Indeed, the expanded nature of turbiditic continental margin successions provides paleoenvironmental records at very high resolution, enriching, and perhaps improving, the commonly condensed and sometimes discontinuous record of hemipelagic-only successions.

 

Research funded by the Spanish Government project MCI PID2019-105670GB-I00 and the Basque Government project IT-930-16. NM-B received a pre-doctoral grant from the Basque Government and a post-doctoral Dokberri grant from the University of the Basque Country.

How to cite: Martínez-Braceras, N., Payros, A., Arostegi, J., and Dinarès-Turell, J.: Variations in sedimentology, mineralogy and geochemistry on a turbiditic continental margin during an early Eocene negative carbon isotope excursion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3991, https://doi.org/10.5194/egusphere-egu21-3991, 2021.

EGU21-13175 | vPICO presentations | SSP2.3

GTS2020: The Paleogene Period

Robert P. Speijer, Heiko Pälike, Christopher J. Hollis, Jerry J. Hooker, and James G. Ogg

It’s nearly forty years ago that ‘A Geologic Time Scale 1982’ appeared (Harland et al. 1982); it was succeeded by major updates in 1989 (Harland et al. 1990), 2004 and 2012 (Gradstein et al. 2004, 2012 – known as GTS2004 and GTS2012, respectively). The primary rationale was “to show as clearly as we can how such a scale has been constructed” (Harland et al. 1982). Each update was about twice the length of the previous version. Consistently aiming to achieve a common language with respect to chronostratigraphic units and geological time, these books have served as state-of-the-art summaries for the entire geological community, both in academia and industry. The last two time scale books contained a discrete and extensive chapter devoted entirely to the stratigraphy of the Paleogene, summarizing information on all stages, established GSSPs, various biozonations and the creation of the time scale  (Luterbacher et al. 2004; Vandenberghe et al. 2012). After a three-year-long preparation GTS2020 was published in November 2020.

All Paleocene and Oligocene stages (Danian, Selandian, Thanetian, resp. Rupelian, and Chattian) have formally ratified definitions and so have the Ypresian, Lutetian, and Priabonian stages of the Eocene. We anticipate that the Global Boundary Stratotype Section and Point (GSSP) for the Bartonian Stage still requires more research before all stages of the Paleogene (66-23 Ma) are formally defined. Paleogene marine microfossil groups (planktonic and larger benthic foraminifera, calcareous nannofossils, radiolarians, organic-walled dinoflagellate cysts) provide robust zonation schemes for regional to global correlation and are integrated within the magneto-biochronological framework. Since land mammal faunas are also increasingly being studied with an integrated magnetostratigraphic and/or chemostratigraphic and geochronologic approach, their age calibrations have considerably been improved since GTS2012. Stable isotope analysis and XRF (X-ray fluorescence) scanning have become key tools in Paleogene high-resolution stratigraphy, correlation, and time scale construction. Stable oxygen and carbon isotope records also provide insight into trends in paleoclimate and carbon cycling, such as the warming trend starting in the middle Paleocene and culminating during the Early Eocene Climatic Optimum, and the subsequent cooling leading to a change from greenhouse to icehouse conditions at the onset of the Oligocene. Numerous short-term isotope excursions mark high climatic variability, expressed in hyperthermal (transient global warming) events (62-40 Ma) and cooling/glaciation events (38-23 Ma). At the same time, these stable isotope excursions provide accurate stratigraphic constraints and enable land-sea correlations, such as for the Paleocene-Eocene Thermal Maximum, the “Mother of all hyperthermals.” Orbital tuning of sedimentary cycles, calibrated to the geomagnetic polarity and biostratigraphic scales, has greatly improved the resolution of the Paleogene time scale over the last two decades. We now have astronomical age control for almost all geomagnetic polarity reversals, but differences between published age models still persist through the “Eocene astronomical time scale gap” spanning Chrons C20r through C22n (43.5-49.5 Ma).

How to cite: Speijer, R. P., Pälike, H., Hollis, C. J., Hooker, J. J., and Ogg, J. G.: GTS2020: The Paleogene Period, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13175, https://doi.org/10.5194/egusphere-egu21-13175, 2021.

EGU21-4806 | vPICO presentations | SSP2.3

Cyclostratigraphy of a type-Maastrichtian chalk record, based on high-resolution geochemical analysis of the Gulpen Formation, NE Belgium 

Jarno Huygh, Johan Vellekoop, Matthias Sinnesael, Pim Kaskes, John Jagt, and Philippe Claeys

Cyclostratigraphic studies on carbonate successions have proved invaluable for understanding palaeoclimate and for constructing improved, high-resolution age models of the Late Cretaceous. Whereas carbonate strata from the type-Maastrichtian from the Netherlands and Belgium have provided a wealth of palaeontological data, so far, dating of these deposits has relied mainly on biostratigraphy and preliminary attempts at cyclostratigraphy. The existing basic cyclostratigraphic framework is based principally on apparent cyclic variations in bioclast composition and suggested Milankovitch-paced flint cycles. Until now, these strata have not yet been examined using a cyclostratigraphic approach based on high-resolution multi-proxy geochemical data sets. Within the scope of the Maastrichtian Geoheritage Project, we attempt to construct an improved astrochronological age model for Maastrichtian chalk deposits of the Gulpen Formation.

We have carried out a high-resolution elemental composition analysis of the Lower to Middle Maastrichtian chalk succession exposed at the Hallembaye (Kreco) quarry, NE Belgium. Approximately 460 chalk samples were collected every 5 cm over a 23-metre-thick stratigraphic interval and analysed as homogenised powders using micro X-ray fluorescence. This extensive elemental data set is used to evaluate (regular) changes in palaeoenvironmental conditions over time. Additionally, stratigraphic comparison of variations in elemental concentrations in the chalk with the occurrence of flint layers provides insights into potential diagenetic alterations. 

Preliminary results display promising trends with potential for the development of a cyclostratigraphic age model for the Gulpen Formation. Significant correlation between the main matrix elements calcium and silica might suggest a relationship between silica-depleted chalk and occurring flint layers throughout the chalk succession. Additionally, observed rhythmic variations in elements including - but not limited to - titanium, aluminium and potassium might exemplify changing palaeoenvironmental conditions. This improved astrochronological age model can be compared with age-equivalent astrochronologies and will, in combination with ongoing carbon isotope stratigraphy work, enable a better dating of the geological and biological records from the type-Maastrichtian. 

How to cite: Huygh, J., Vellekoop, J., Sinnesael, M., Kaskes, P., Jagt, J., and Claeys, P.: Cyclostratigraphy of a type-Maastrichtian chalk record, based on high-resolution geochemical analysis of the Gulpen Formation, NE Belgium , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4806, https://doi.org/10.5194/egusphere-egu21-4806, 2021.

EGU21-11977 | vPICO presentations | SSP2.3

The rhythmic expression of mid-Cretaceous Oceanic Anoxic Event 2 at IODP Sites U1513 and U1516 (southwest of Australia) 

Sietske Batenburg, Kara Bogus, Matthew Jones, Kenneth Macleod, Mathieu Martinez, and Iodp Exp 369 Scientists

The widespread deposition of organic-rich black shales during the mid-Cretaceous hothouse at ~94 Ma marked a climatic extreme that is particularly well studied in the Northern Hemisphere. The expression of Oceanic Anoxic Event 2 (OAE 2) in the NH was characterised by low oceanic oxygen concentrations, likely caused by the input of nutrients through volcanism and/or weathering in combination with a peculiar geography in which the proto-North Atlantic was semi-restricted (Jenkyns, 2010; Trabucho Alexandre et al., 2010). The extent of water column anoxia outside the North Atlantic and Tethyan domains remains poorly resolved, as few Southern Hemisphere records have been recovered that span OAE 2, and only a portion of those Indian and Pacific Ocean localities experienced anoxia and organic matter deposition (Dickson et al., 2017; Hasegawa et al., 2013).

 

Here we present new results from IODP Expedition 369 offshore southwestern Australia. Sedimentary records across the Cenomanian-Turonian transition from Sites U1513 and U1516 in the Mentelle Basin (Indian Ocean) display rhythmic lithologic banding patterns. The OAE 2 interval is marked by a dramatic drop in carbonate content and the occurrence of several thin organic-rich black bands. The spacing of dark bands within a rhythmic sequence suggests a potential orbital control on organic matter deposition at our study sites. Time series analyses of high-resolution (cm-scale) elemental data from XRF-core scanning reveal the imprint of periodicities that can be confidently linked to Earth’s orbital parameters. The new OAE 2 records from Sites U1516 and U1513 allow us to i) evaluate existing time scales over the Cenomanian-Turonian transition, and ii) investigate the mechanisms leading to a recurrent lack of oxygen in the Indian Ocean.

 

Climatic mechanisms translating changes in insolation to variations in organic matter deposition may have included variations in nutrient input from nearby continents and shifts in water column structure affecting local to regional stratification versus deep water formation and advection. Investigating ventilation of the deep sea during the OAE2 interval is of heightened relevance as current global warming is leading to a worldwide expansion of oxygen minimum zones (Pörtner et al., 2019).

 

References:

Dickson, A.J., et al., 2017. Sedimentology 64, 186–203.

Hasegawa, et al., 2013. Cretaceous Research 40, 61–80.

Jenkyns, H.C., 2010. Geochemistry, Geophysics, Geosystems 11, Q03004.

Pörtner, H.O., et al., 2019. IPCC Intergovernmental Panel on Climate Change: Geneva, Switzerland.

Trabucho Alexandre, J., et al., 2010. Paleoceanography 25, PA

How to cite: Batenburg, S., Bogus, K., Jones, M., Macleod, K., Martinez, M., and Exp 369 Scientists, I.: The rhythmic expression of mid-Cretaceous Oceanic Anoxic Event 2 at IODP Sites U1513 and U1516 (southwest of Australia) , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11977, https://doi.org/10.5194/egusphere-egu21-11977, 2021.

EGU21-12170 | vPICO presentations | SSP2.3

Astronomical calibration of the OAE1b, Col de Pré Guittard, Vocontian Basin, France

Fatima-Zahra Ait-Itto, Mathieu Martinez, Jean François Deconinck, Danny Boué, and Stéphane Bodin

The Cretaceous period was punctuated by several episodes of widespread deoxygenation of the sea floor referred to as Oceanic Anoxic Events. The OAE1b around the Aptian - Albian boundary is characterized by a series of black shales deposits, namely Jacob, Kilian, Paquier and Leenhardt levels. They are well documented in the Vocontian Basin, and their equivalent have been observed in different basins across the globe. Disagreement of more than a million of years exist about the timing of these events, leaving vast uncertainties about the causes of these recurring environmental changes. In order to better understand the relation between the climate perturbation and anoxic events during the Aptian-Albian period, we have focused on high-resolution investigations of magnetic susceptibility of Col de Pré-Guittard section, Drôme, France (GSSP of the Albian Stage; Kennedy et al., 2017). This section in the Blue Marls Formation consists of monotonous dark-grey marlstones interrupted by limestone beds and organic-rich layers. Spectral analyses were conducted on a magnetic susceptibility signal sampled every 5 cm. From this, we detected the record of the eccentricity, obliquity and precession cycles. We used the 100-kyr eccentricity cycles to construct an orbital time scale and shows that the interval starting above the Jacob level and ending above the Leenhardt level contains 21 repetitions of the 100-kyr eccentricity in the magnetic susceptibility data, leading to a duration of ca. 2.1 Myr. This duration is significantly shorter than the duration of 4 Myr provided by the current geologic time scale (Gale et al., 2020) but agrees with the U-Pb ages anchored to a δ13Corg curve from the High Arctic (Herrle et al., 2015).

References:

Gale, A.S., Mutterlose, J., Batenburg, S., 2020. Chapter 27: The Cretaceous Period, in: Gradstein, F.M., Ogg, J.G., Schmitz, M.D., Ogg, G.M. (Eds.) Geologic Time Scale 2020. Elsevier BV, Amsterdam, The Netherlands, pp. 1023–1086.

Herrle, J., Schröder-Adams, C.J., Davis, W., Pugh, A.T., Galloway, J.M., Fath, J., 2015. Mid-Cretaceous High Arctic stratigraphy, climate, and Oceanic Anoxic Events. Geology 43, 403–406.

Kennedy, J.W., Gale, A.S., Huber, B.T., Petrizzo, M.R., Bown, P., Jenkyns, H.C., 2017. The Global Boundary Stratotype Section and Point (GSSP) for the base of the Albian Stage, of the Cretaceous, the Col de Pré-Guittard section, Arnayon, Drôme, France. Episodes 40, 177–188.

How to cite: Ait-Itto, F.-Z., Martinez, M., Deconinck, J. F., Boué, D., and Bodin, S.: Astronomical calibration of the OAE1b, Col de Pré Guittard, Vocontian Basin, France, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12170, https://doi.org/10.5194/egusphere-egu21-12170, 2021.

EGU21-718 | vPICO presentations | SSP2.3

Astronomical tuning of the Aptian Stage

Gabriele Gambacorta, Cinzia Bottini, Giulia Faucher, Alessandro Grippo, Helmut Weissert, and Elisabetta Erba

We present a new astronomical tuning for the Aptian stage, based on the combined record of the Piobbico Core (Umbria-Marche Basin, central Italy - this study) and the Cismon Core (Belluno Basin, northwestern Italy - Malinverno et al., 2010).  Integrated bio-chemostratigraphy is available for both cores, granting their chronostratigraphic characterization and highest correlability.

A continuous high-resolution greyscale log of the Piobbico Core, obtained after full reprocessing of core photos, was used as input for the cyclostratigraphic analysis. Evolutionary spectral analysis reveals unstable frequencies throughout the record, indicative of uneven sedimentation rates ranging from about 2 to about 9 m/My. Reconstructed sedimentation rate model is based on the optimal fit of the long-eccentricity ~405-kyr-cycle. Changes in accumulation rate were further validated by applying the evolutionary coefficient analysis of the stratigraphic series, with the main components of the La2010a astronomical solution used as targets. Estimated variations in sedimentation rate well reflect the major lithofacies variations, from marlstone-dominated to marly limestone-dominated intervals, and the relative changes in biogenic components along the succession.

Results of the cyclostratigraphic analysis indicate that orbital forcing controlled the depositional patterns. Visual variations in the greyscale log, further supported by spectral analysis, highlight an evident cyclicity related to long- and short-eccentricity orbital periodicities. The combined short- and long-eccentricity amplitude envelope of the tuned record shows significant long-term modulations in the short eccentricity bands. Frequencies related to precession index fit as well with the La2010a astronomical model. The calibration with the theoretical astronomical solution allowed to define a consistent age model for the studied succession.

The tuned greyscale log of the Piobbico Core (this study) was merged with the tuned FMI resistivity log of the Cismon Core (Malinverno et al., 2010) in order to obtain a composite record covering the entire Aptian time interval and determine the duration of the Aptian time interval.  In addition, by anchoring the results of the cyclostratigraphy to the U-Pb absolute age of 113.1 ± 0.3 Ma for the Aptian/Albian boundary, we provide a new estimate for the age of the Barremian/Aptian boundary, currently placed at the base of the M0r polarity Chron. The ~405 ky-tuned Piobbico and Cismon merged record indicates a duration of 9.77 My for the Aptian, and an age of 122.87 ± 0.3 Ma for the Barremian/Aptian boundary.

How to cite: Gambacorta, G., Bottini, C., Faucher, G., Grippo, A., Weissert, H., and Erba, E.: Astronomical tuning of the Aptian Stage, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-718, https://doi.org/10.5194/egusphere-egu21-718, 2021.

EGU21-15701 | vPICO presentations | SSP2.3

Global carbon isotope signal in the Middle Triassic on Svalbard

Victoria S. Engelschiøn, Øyvind Hammer, Fredrik Wesenlund, Jørn H. Hurum, and Atle Mørk

Several carbon isotope curves were recently published for the Early and Middle Triassic in Tethys. Recent work has also been done on the Early Triassic of Svalbard, but not yet for the Middle Triassic. This work is the first to measure δ13C for different Middle Triassic localities on Svalbard, which was then part of the Boreal Ocean on northern Pangea. Our aim is to understand the controls on the Svalbard carbon isotope curve and to place them in a global setting.

Correlating Triassic rocks around the world is interesting for several reasons. The Triassic Period was a tumultuous time for life, and the Arctic archipelago of Svalbard has shown to be an important locality to understand the early radiation of marine vertebrates in the Triassic. Much effort is also made to understand the development of the Barents Sea through Svalbard’s geology.

Carbon isotope curves are controlled by depositional environment and global fluctuations. Global factors such as the carbon cycle control the long-term carbon isotopic compositions, while short-term fluctuations may reflect the origin of organic materials in the sediment (e.g. algal or terrestrial matter), stratification of the water column, and/or surface water productivity. Carbon isotopes can therefore be useful to understand the depositional environment and to correlate time-equivalent rocks globally.

The dataset was collected through three seasons of fieldwork in Svalbard with localities from the islands Spitsbergen, Edgeøya and Bjørnøya. Detailed stratigraphic sampling has resulted in high-resolution δ13C curves. These show three strong transitions; 1) on the boundary between the Early and Middle Triassic, 2) in the middle of the formation and 3) at the Middle and Late Triassic boundary. Several Tethyan localities show a possibly similar Early-Middle Triassic signal. Current work in progress is sedimentological analysis by thin sections and X-ray fluorescence spectroscopy (XRF) to further understand the sedimentary environment.

How to cite: Engelschiøn, V. S., Hammer, Ø., Wesenlund, F., Hurum, J. H., and Mørk, A.: Global carbon isotope signal in the Middle Triassic on Svalbard, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15701, https://doi.org/10.5194/egusphere-egu21-15701, 2021.

There's no doubt that nowadays detrital zircon U-Pb geochronology is actually required method of sedimentary basins analysis. Furthermore, this approach may have a lot of applications, such as a stratigraphic correlation. Here we present the first results of U–Pb LA–ICP–MS dating of detrital zircon from the Permian-Triassic red beds located within the Moscow Basin of the East European platform. Two outcrops have been studied: the Zhukov Ravine P/T boundary reference section and the Nedubrovo strata with uncertain stratigraphic position (uppermost Permian or lower Triassic?).

U–Pb ages of detrital zircon grains have been obtained for two samples – the Upper Permian and Lower Triassic age, which were taken in the proximity to the Permian–Triassic boundary in the Zhukov Ravine. Corresponding age distributions show contrasting provenance of the studied sedimentary rocks, pointing out that principal change in source of clastic material occurred on the Paleozoic-Mesozoic boundary. It means that detrital zircon U–Pb geochronology can be used as an additional independent tool for stratigraphic correlation of the Permian-Triassic red beds, at least within the Moscow Basin. We demonstrate this in the case of the Nedubrovo section with debated (Permian or Triassic?) stratigraphic position: the obtained data on detrital zircons persuasively suggests Early Triassic age of the Nedubrovo strata.

This study is supported by the Russian Foundation for Basic Research (project no. 18-05-00593).

How to cite: Chistyakova, A. and Veselovskiy, R.: Stratigraphic correlation of the Permian-Triassic red beds constrained by detrital zircon geochronology: Moscow basin, East European platform, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10294, https://doi.org/10.5194/egusphere-egu21-10294, 2021.

EGU21-9588 | vPICO presentations | SSP2.3

An integrated Bayesian stratigraphic correlation approach for the Cambrian Explosion

Matthias Sinnesael, Andrew R. Millard, and Martin R. Smith

The Cambrian Explosion is characterised by a large diversification of life. The precise nature of this major evolutionary event is heavily debated, featuring anomalously fast versus more gradual evolutionary scenarios. Our ability to distinguish between such scenarios hinges on the quality of global correlations and corresponding timescales. With Cambrian temporal uncertainties often in the order of millions of years, establishing such correlations and timelines is a challenging task. Here, we present a novel approach to this problem based on a probabilistic Bayesian conceptual framework. Major advantages of the Bayesian approach include the consideration of multiple information sources in a single analysis and explicit uncertainty formulations.

In the absence of good index fossils, early Cambrian correlations rely heavily on carbon isotope chemostratigraphy and ‘expert-based’ correlations. Inspired by approaches in the radiocarbon community, we have been exploring representations of stable carbon isotope variations using random walk and spline fitting models. Implementation is undertaken using Markov-chain Monte-Carlo (MCMC) approaches. Temporal calibration is mainly dependent on published state-of-the-art U-Pb zircon dating. Our model also allows for the use of different sedimentary facies. Simultaneous analysis of several sections and multiple stratigraphic variables will allow each section to inform the correlation of every other, leading to a single, objectively derived and quantitative reference curve. Ultimately, the aim is to have a coupled Bayesian model setup of both stratigraphy and morphological evolution of the fossil record. These models will better inform us on the origins of diverse animal-dominated ecosystems and their impact on Earth processes.

How to cite: Sinnesael, M., Millard, A. R., and Smith, M. R.: An integrated Bayesian stratigraphic correlation approach for the Cambrian Explosion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9588, https://doi.org/10.5194/egusphere-egu21-9588, 2021.

EGU21-5082 | vPICO presentations | SSP2.3

Synchronizing Rock Clocks in the Cambrian

Zhengfu Zhao, Nicolas Thibault, Tais W. Dahl, Niels H. Schovsbo, Aske L. Sørensen, Christian M.Ø. Rasmussen, and Arne T. Nielsen

Profound environmental and biological changes took place during the Cambrian, yet, compared to other Phanerozoic intervals, the Cambrian time framework remains poorly constrained, which severely hinders a detailed understanding of the timing and progression of these major geological events. In this study, we report a radiometrically anchored astrochronologic framework across the late Cambrian interval, using high-resolution aluminum (Al) series (1 mm resolution) through the Alum Shale Formation in Scania, southernmost Sweden, based on the fully cored Albjära-1 well. Significant cycles with periods of 405 kyr (long eccentricity), 108 kyr (short eccentricity), 30.4 kyr (obliquity) and 18.8 kyr (precession), associated with long-term amplitude modulation of obliquity and precession, confirmed the orbital imprint on late Cambrian climate. Using the U-Pb dating at 486.78±0.53Ma for the Cambro-Ordovician boundary as anchor point, our timescale spans from ~483.9 to ~500.0 Ma, covering 7 trilobite superzones and 3 graptolite zones. The calibration indicates ages of 491.2±0.54 Ma, 493.9±0.67 Ma, 497.3±0.67 Ma and 500.4±0.67 Ma for the lower boundaries of provisional Stage10, Jiangshanian, Paibian and Guzhangian stages, respectively. This radiometrically anchored astrochronology also provides precise age constrains on regional superzones or even biozones within Scandinavia, and hopefully pave the way for better understanding the late Cambrian major geological events globally.

How to cite: Zhao, Z., Thibault, N., Dahl, T. W., Schovsbo, N. H., Sørensen, A. L., Rasmussen, C. M. Ø., and Nielsen, A. T.: Synchronizing Rock Clocks in the Cambrian, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5082, https://doi.org/10.5194/egusphere-egu21-5082, 2021.

EGU21-15112 | vPICO presentations | SSP2.3

New high precision U-Pb CA-ID-TIMS zircon ages from the Ediacaran in Namibia

Fabio Messori, Ulf Linnemann, Mandy Hofmann, Johannes Zieger, Gerd Geyer, Patricia Vickers-Rich, and Maria Ovtcharova

The Ediacaran records a transition from a planet largely dominated by microscopic organisms to macroscopic multicellular organisms during the Phanerozoic. Temporal calibration of the record of changing climates and coevally diversifying biota is crucial to understand how metazoan life gained an early foothold on Earth.

A causal link between climate-driven environmental perturbations and biotic changes is generally accepted. However, a chronological relationship is needed to prove which event acted as a trigger for the biological turnover, i.e. extinction or the development of new organizational levels. A connection between environmental perturbations associated with the appearance and disappearance of the Ediacaran biota is profoundly complicated because of the scarcity of available geochronological and chemostratigraphical records. Therefore, it is crucial to expand existing datasets for this period, particularly through additional chronology.

The Nama Group in southern Namibia serves as a unique archive for major geobiological changes across the Ediacaran–Cambrian transition exemplified by a near complete section through the terminal Ediacaran. The region exposes the full stratigraphic range of the Nama assemblage and records several environmental perturbations. Establishing a precise timeframe of the terminal Ediacaran environmental and biological changes in Nama group enables a much-enhanced understanding of the nature and rates of the evolutionary changes.

Following pioneering research by Grotzinger et al. (1995), the Ediacaran–Cambrian boundary in Namibia has recently been dated ca. 2 Ma younger than previously assumed [1]. Additional high-precision U-Pb CA-ID-TIMS zircon ages from silicified tuffs of the Nama Group allow additional insights for the timeframe of the entire terminal Nama. Our results indicate that (i) the oldest ash bed in the Zaris subbasin is 547.3 Ma old, which makes it more than 0.5 Ma younger than the previously dated tuff in the same subbasin; (ii) a newly explored section at the base of the terminal Ediacaran Spitskop Member near the MTC tower (Witpütz Nord farm) revealed a slightly younger age of 539 Ma, which permits a precise correlation of this section with the Swartpunt section and indicates the position of the Ediacaran-Cambrian boundary.

[1] Linnemann, U. et al., (2019) Terra Nova 31(1) 49-58.

How to cite: Messori, F., Linnemann, U., Hofmann, M., Zieger, J., Geyer, G., Vickers-Rich, P., and Ovtcharova, M.: New high precision U-Pb CA-ID-TIMS zircon ages from the Ediacaran in Namibia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15112, https://doi.org/10.5194/egusphere-egu21-15112, 2021.

Reconstructing the high-resolution astrochronology framework for the Ediacaran is critical to fully understand the evolution of the sedimentary environment and the carbon cycle in South China. The Ediacaran was perhaps one of the most important intervals in the Earth's sedimentary environment and biological evolution history, which witnessed the carbon isotope perturbation frequently, the emergence and evolution of metazoans, and the extreme climate change. There are many controversies for the characteristics and origin of these geological, biological and extreme climate events due to the lack of continuous and high-resolution astronomical time scale in the Ediacaran. We here propose to study the systematic cyclostratigraphic analysis of the Doushantuo Formation based on the Jiulongwan section in South China, and then use the long-eccentricity (405-kyr) for astronomical tuning to establish continuous and high-resolution astrochronologic framework, which would provide chronological constraints on carbon isotope negative  excursions, biological evolution and the extreme climate change for the Ediacaran. In order to reveal the inner correlation of the onset age, sequence of these major geological events as well as biological evolution in the Doushantuo Formation on the Ediacaran. Moreover, we also try to discuss the astronomical orbits-forcing factor that may lead to the occurrence and evolution of these major geological events, which would provide scientific evidence for studying the global climate change in the future.

How to cite: Sui, Y., Wang, Z., and Huang, C.: Astronomical time scale for the  Doushantuo Formation ofEdiacaran in South China: Implications for the duration of the negative δ13C excursion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6880, https://doi.org/10.5194/egusphere-egu21-6880, 2021.

SSP2.6 – The physical record of the Anthropocene in geological archives

EGU21-3226 | vPICO presentations | SSP2.6 | Highlight

Progress in the formalisation of the Anthropocene GSSP

Simon Turner and the AWG-HKW-MPIWG Anthropocene GSSP

The Anthropocene Working Group (AWG) has assembled scientific teams to analyse stratigraphic successions, as potential stratotypes, in order to facilitate a formal submission to the Subcommission on Quaternary Stratigraphy. The aim is to seek ratification of the Anthropocene as a geological epoch starting in the mid-twentieth century. Stratigraphic records, including a range of novel materials, geochemical and biological signals spanning the mid-twentieth century interval of unprecedented human activity and industrialisation, are being gathered by international teams of scientists, working on eleven contrasting depositional settings from around the planet. Interwoven with this scientific process to define a Global Boundary Stratotype Section and Point (GSSP), from which a specific year for the onset of the Anthropocene will be established, is a decades long collaborative exploration of the Anthropocene between the AWG, Haus der Kulturen Welt (HKW) and Max Planck Institute for the History of Science (MPIWG).  

While the compilation of stratigraphic data to define a new epoch is as old as the science of geology, the demarcation of one within living history that signifies human activity as a global geological agent is unparalleled. Similarly, there is no precedent of a stratigraphic formalisation process being pivotal to the framing of so much contemporary social, ecological, artistic, historical and political thought. In May 2022 along with the publication of the results and data, an exhibition including a discursive and performative programme will occur at HKW in Berlin as a public forum for the scientific, cultural and socio-political impact of the geochronological research carried out by the international research project on the Anthropocene.

This presentation provides an introduction to the interdisciplinary and collaborative research project between the AWG, HKW and MPIWG. The talk will introduce the prospective sites and stratigraphy of the proposed successions and an update on progress towards the official ratification of the GSSP, as well as collaborative artistic and cultural work embedded in the process.

How to cite: Turner, S. and the AWG-HKW-MPIWG Anthropocene GSSP: Progress in the formalisation of the Anthropocene GSSP, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3226, https://doi.org/10.5194/egusphere-egu21-3226, 2021.

EGU21-6685 | vPICO presentations | SSP2.6

Dynamics of biotic and abiotic markers of the Anthropocene at Jasper Ridge Biological Preserve, California, USA

M. Allison Stegner, SeanPaul La Selle, Brian Sherrod, Anthony Barnosky, and Elizabeth Hadly

Human activities changed our planet over the course of the Holocene, but the scale of impacts increased dramatically around the mid-20th century, representing the start of the Anthropocene. These pervasive anthropogenic impacts, including pollution, road-building, the rise of plastics, etc., are comparable in magnitude, uniqueness, and geologic perseverance to global changes that mark previous major geologic time intervals. To identify the preservable global and local signals that might be used to characterize the Anthropocene, we examine sediment cores from Searsville Reservoir, a 129-year-old reservoir located in the eastern foothills of the San Francisco Peninsula. We collected eight sediment cores ranging from 7.4 to 8.5 meters in length that appear to have bottomed out on the pre-reservoir surface, indicating average sedimentation rates of 6 to 7 cm per year. This exceptionally high sedimentation rate allows us to explore the Anthropocene geologic record on a sub-annual scale.

Our analyses to date include sedimentary DNA (sedDNA), pollen, computed tomography (CT) scanning, Carbon and Nitrogen isotopes, radionuclides, Mercury, and X-ray fluorescence (XRF). We find a strong relationship between sediment type and both sedDNA and pollen frequency: sedDNA and pollen are more abundant in the thin, low-density units that are thought to be associated with lower sedimentation rates and high organic inputs during the dry season. SedDNA analyses successfully identified a diversity of insects and vertebrates to the species level, including invasive fish and mosquitos. Computed tomography scans of the cores revealed >300 distinct layers ranging in thickness from <1mm to ~30mm. Many of the thicker laminae show upward-fining, indicative of individual storm events. Sediment density generally decreases from the bottom to the top of the cores, consistent with both sediment compaction and increasing organic inputs as the reservoir filled with sediment and eutrophied. δ15N declined over the record, reflecting global δ15N depletion due to fossil fuel combustion and artificial nitrogen fertilization for agriculture. δ13C was fairly stable prior to around 1950, then became highly variable, possibly related to changes in aquatic productivity (algal blooms) that began in the 1950s. A sharp and well-defined peak in 137Cs provides evidence of nuclear testing in the 1950s and ‘60s, and serves as a secure chronological tie point for the year 1963. The 137Cs peak correlates well with the chronology estimated by counting back suspected annual couplets of high density (wet season)/low density (dry-season) sediments. Our analyses reveal a complex interplay between local and global human impacts at Searsville Reservoir, and document the onset of the Anthropocene epoch at fine scale. Searsville is particularly appropriate as a candidate Global Boundary Stratotype Section and Point for the Anthropocene not just because of the unique and highly resolved nature of the sediments, but because the record itself is a direct consequence of human activity—the emplacement of a dam.

How to cite: Stegner, M. A., La Selle, S., Sherrod, B., Barnosky, A., and Hadly, E.: Dynamics of biotic and abiotic markers of the Anthropocene at Jasper Ridge Biological Preserve, California, USA, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6685, https://doi.org/10.5194/egusphere-egu21-6685, 2021.

EGU21-15133 | vPICO presentations | SSP2.6

A biostratigraphic record of Anthropocene ecological change in one of the world's most invaded aquatic ecosystems, San Francisco, CA.

Stephen Himson, Mark Williams, Mary McGann, Neil Rose, Ian Wilkinson, Jan Zalasiewicz, and Colin Waters

Modification of ecosystems through the introduction of non-native species (neobiota) is one part of the major human impact on the biosphere. Neobiota are now present worldwide and often significantly outnumber native fauna and flora. In many places they have left a distinctive biostratigraphic record of anthropogenic changes to the biosphere in the 20th century. Few ecosystems have been as severely affected by the arrival of neobiota as San Francisco Bay. Some 234 introduced species comprising up to 97% of individuals and in some places up to 99% of the biomass are known to be present in the bay (Cohen and Carlton, 1998). Among the multitude of neobiotic species established are Trochammina hadai, a benthic foraminifer that is native to Japan and was introduced in 1983 (McGann 2008), and Potamocorbula amurensis, a bivalved mollusc native to the Amur River region of East Asia that was introduced in 1986 (Carlton et al. 1990). Here we present sediment core data showing the arrival and proliferation of T. hadai and P. amurensis in addition to three introduced ostracod species, Spinileberis quadriaculeata, Eusarsiella zostericola and Bicornucythere bisanensis. The introduction of T. hadai is thought to have occurred through ballast water exchange from trans-Pacific shipping, and has produced a major perturbation to the foraminiferal record of San Francisco Bay. Pb-210 radiometric dating has established a high-resolution chronology for the core and analysis of fly ash particles (Rose 2015) emitted from coal-fired power stations allow time horizons, and the chronologies they define, to be correlated to a further 18 cores collected across the bay. This quantifies both the temporal and spatial extent of a human-induced biostratigraphic assemblage of neobiota, one that is correlatable with a biostratigraphic record of changes to ecosystems across the world in the late 20th century.

 

Carlton, J.T., Thompson, J.K., Schemel, L.E. and Nichols, F.H. 1990. Remarkable invasion of San Francisco Bay (California, USA), by the Asian clam Potamocorbula amurensis. I. Introduction and dispersal. Marine Ecology Progress Series, 81-94.

Cohen, A.N. & Carlton, J.T. 1998. Accelerating invasion rate in a highly invaded estuary. Science 279, 555-558.

McGann, M. 2008. High-resolution foraminiferal, isotopic, and trace element record from Holocene estuarine deposits of San Francisco Bay, California. Journal of Coastal Research 24, 1092-1109.

Rose, N.L. 2015. Spheroidal carbonaceous fly ash particles provide a globally synchronous stratigraphic marker for the Anthropocene. Environmental Science & Technology 49, 4155-4162.

How to cite: Himson, S., Williams, M., McGann, M., Rose, N., Wilkinson, I., Zalasiewicz, J., and Waters, C.: A biostratigraphic record of Anthropocene ecological change in one of the world's most invaded aquatic ecosystems, San Francisco, CA., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15133, https://doi.org/10.5194/egusphere-egu21-15133, 2021.

EGU21-3744 | vPICO presentations | SSP2.6

Americium-241 in peat bogs as a marker of the beginning of the Anthropocene: examples from Europe and North America.

Andrii Oleksandrenko, Peter Appleby, Tommy Noernberg, and William Shotyk

Americium-241 (241Am) is present in the terrestrial and aquatic environment around the globe as a result of the atmospheric testing of high yield thermonuclear weapons carried out mainly in the 1950s and 1960s. Radioactive debris (including mainly 137Cs, 90Sr, and various Pu isotopes) from the tests was injected high into the stratosphere where it was rapidly dispersed around the world. Over a period of months this material slowly returned to the troposphere, and from there was quickly removed by wet and dry fallout onto the earth’s surface. Amounts of 241Am in freshly deposited weapons test debris were essentially zero. Its presence today is through in-growth from its short-lived precursor 241Pu (half-life 14.4 years). By this process concentrations of 241Am have steadily increased with time and will continue to do so through to around 2040. Widely considered to be immobile in soils and sediments, with its well-known origins and long half-life (432 years), 241Am is in many ways an ideal chronostratigraphic marker of the nuclear age. Calculations show that the 241Am record in any ideal natural archive is a faithful representation of the history of weapons test fallout. Beginning in the early 1950s, fallout reached a peak in 1963 and then declined rapidly following the implementation of the test ban treaty. A number of scientists have proposed that the weapons test fallout peak could be used to mark the start of the Anthropocene. Various geological archives preserve the record of fallout, though with varying degrees of fidelity. They include polar snow and ice, marine and lacustrine sediments, and peat bogs. Bogs are ombrotrophic peatlands in that the plants growing there receive nutrients and contaminants exclusively from the atmosphere. The purpose of this study is to determine the fidelity of 241Am records in peat bog cores.
Specifically, we compare the position of the 241Am concentration peak with the 1963 depth determined by 210Pb dating. We use 39 peat cores from Europe, North America, and Indonesia collected by our team during the past 30 years for studies of atmospheric deposition of trace metals, all of which had been independently dated using 210Pb. We find that 18 of the cores provide an excellent agreement between the 241Am and 210Pb dates, 12 were in good agreement, and 9 agreed poorly. Possible reasons for the discrepancy in the 9 cores with the poor agreement are 1) the sensitivity of the gamma spectrometer for detecting 241Am, and 2) disruptions to the fallout records caused e.g. by disturbances to the peat bog or changes in the peat topography or hydrology. Small scale horizontal and vertical variations in bogs help explain why in a triplicate of peat cores collected from Wildseemoor in the Black Forest of Germany, excellent agreement was found in one core, good agreement in a second, and poor agreement in the third. A peat core collected from Gola di Lago, a small fen in Switzerland, showed excellent agreement; this suggests that samples from minerotrophic peatlands may also be useful to mark the start of the Anthropocene.

How to cite: Oleksandrenko, A., Appleby, P., Noernberg, T., and Shotyk, W.: Americium-241 in peat bogs as a marker of the beginning of the Anthropocene: examples from Europe and North America., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3744, https://doi.org/10.5194/egusphere-egu21-3744, 2021.

EGU21-15795 | vPICO presentations | SSP2.6

Tracking the South Pacific convergence zone variability and recent acidification reconstructed from tropical corals

Sara Todorović, Henry C. Wu, Braddock Linsley, Delphine Dissard, Henning Kuhnert, Albert Benthien, Klaus-Uwe Richter, Markus Raitzsch, and Jelle Bijma

Massive tropical corals represent one of the most important natural archives of modern climate change. Coral based reconstructions give us the possibility to extend the instrumental oceanographic records and observe hydrographic variability on seasonal to interdecadal scales in tropical oceans. South Pacific convergence zone (SPCZ) variability, Interdecadal Pacific Oscillation (IPO) and El Niño-Southern Oscillation (ENSO) events are major drivers of global climate and may exert control on regional CO2 absorption, outgassing and pH variability.

Porites sp. corals from Tonga and Rotuma (Fijian dependency) are being analyzed for multi-proxy (e.g. Sr/Ca, δ18O, δ13C, δ11B, B/Ca) reconstructions of sea surface temperature and salinity (SST, SSS) and carbonate chemistry, on a monthly to annual resolution. Preliminary data of the Rotuma Porites sp. coral shows δ18O has been decreasing by 0.004 ‰ per year at the end of the 20th century, suggesting freshening and/or warming of the surface water. In the same period, we observe a δ13C decrease of 0.017 ‰ per year in-line with the anthropogenic CO2 driven Suess effect. Initial results of the δ11B Tonga Porites sp. show high interannual variability, and a strong trend of decrease of -0.0626 ‰ per year in the last five decades of the record (1949-2004) suggesting acidification. The results are in agreement with published coral-based reconstructions from the region.

When completed, the new records will facilitate exploring the effects of modern anthropogenic influence on ocean carbonate system and pH variation, and the relationship between them and interannual and decadal-interdecadal climatic fluctuations.

How to cite: Todorović, S., C. Wu, H., Linsley, B., Dissard, D., Kuhnert, H., Benthien, A., Richter, K.-U., Raitzsch, M., and Bijma, J.: Tracking the South Pacific convergence zone variability and recent acidification reconstructed from tropical corals, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15795, https://doi.org/10.5194/egusphere-egu21-15795, 2021.

Mid-Late Holocene stratigraphy beneath the town of Bologna, in northern Italy, records an upward increase in the amount, thickness, width and connectivity of anthropogenic deposits and a parallel decrease in alluvial sediments. Anthropogenic deposits, spanning from the Neolithic to the Present, occur at three stratigraphic intervals separated by alluvial strata.

The lower interval, dated to the Neolithic-Early Eneolithic, includes sparse lithic, ceramic and copper artefacts, post holes, charcoals, shallow wells and ditches. These evidences of human presence are scattered along a pedogenized horizon developed during a phase of river stability lasting more than 3 millennia. Early Eneolithic rests are aligned along paleo river courses.

The second horizon consists of an uninterrupted archaeological sequence spanning from the Late Bronze Age to the Late Antiquity. Late Bronze and Iron Age remains include ceramic and metal artefacts, charcoals, huts, dwellings, wells, ditches, and cemetery sites. Iron age remains are pervasive and their distribution is irrespective of riverbed location. The elevated number of dwellings and cremation jars testifies to a significant local population growth. A dense grid of ditches and embankments denotes a widespread control of the drainage network. Roman deposits include large dwellings, public buildings, productive sites, wells, aqueducts, ditches, landfills, roads, bridges, cemetery sites. Romans introduced in the geological record huge amounts of anthropogenic materials with high preservation potential such as bricks and mortars. Large quantities of different rock types were imported from European and Mediterranean areas. These materials constitute a laterally continuous horizon buried at depth of 3-4 metres, which testifies to the development the colony of Bononia, founded in 189 BC. The amount and connectivity of roman rests, decreases away from the historical centre, where large farms, reclaimed lands and centuriae highlight an anthropogenically modified rural landscape. Fluvial gravels deposited since the Roman period are commonly enriched in brick clasts.

The uppermost anthropogenic interval is dated to the last millennia. Its base is a time-transgressive erosional surface which testifies to the progressive expansion of the Bologna urban area, with a minor pulse dated to Middle Ages (1200-1300 AD) and a major to the last 70 years. Particularly, in the 20th century the urban area of Bologna became 20 times larger and merged with adjacent villages. Post-1950 deposits are up-to-30 m thick and deeply cut into older stratigraphic units. Concrete, metal, and plastic are the most abundant materials. The last 70 years also record the spread of pollutants within shallow acquifers and dramatically increased subsidence rates due to water withdrawal.

Anthropogenic deposits beneath Bologna record an overall upward transition from a river-dominated to a man-dominated environment. Iron Age and Roman deposits represent the first evidence of a landscape heavily modelled by human activities. However, the thickness, lateral extent and pervasiveness of post-1950 anthropogenic units support the recently proposed idea to place the base of the Anthropocene in the mid-20th century.

How to cite: Bruno, L.: From a river- to a man-dominated environment. Insights from the geo-archaeological record of Bologna (northern Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10221, https://doi.org/10.5194/egusphere-egu21-10221, 2021.

EGU21-11930 | vPICO presentations | SSP2.6

Tracing the Anthropocene bomb-spike in urban strata of Vienna

Maria Meszar, Karin Hain, Michael Wagreich, Kira Lappé, Martin Mosser, Katrin Hornek, Veronika Koukal, Constance Litschauer, and Nikolaos Piperakis

Urban anthropogenic strata forms the layered archaeosphere in the underground of large cities. In a transdisciplinary project involving geosciences, isotope physics and urban archaeology, funded by the Vienna Science and Technology Fund (WWTF), we looked for artificial isotopes in urban layers around the proposed starting date of the Anthropocene in the middle of the 20th century. The tested archaeological site is situated in the heart of Vienna, in a park area at Karlsplatz, adjacent to the renovated Vienna Museum. Excellent and detailed 3D archaeological stratigraphy sets age constraints around 1922, post-1945, and around the 1960s. A layer on top of the WWII rubble that fills fundaments of a 1922 building post-dates 1945, and pre-dates the finishing shaping of the human-made park ground of 1959, the date of the opening of the Vienna Museum. We focused on the fine-grained (clayey-sandy) sediment matrix on top of the WWII rubble, at the base of and mixed with backfilled soil material. The sieved fraction below 2 mm grain size was dried and pulverised. This sediment sample was prepared for chemical separation of actinides which were then analysed by Accelerator Mass Spectrometry (AMS) using the setup at the Vienna Environmental Research Accelerator (VERA, Isotope Physics Group). We identified several artificial radionuclides including U-236, Np-237, Pu-239, Pu-240. Isotope ratios like Pu-240/Pu-239 and in particular U-233/U-236, which was only recently introduced as anthropogenic tracer by the VERA group, clearly point to atmospheric atomic bomb fallout material of the 1950s to 1960s. A significant input of Chernobyl (1986) material can be excluded based on the ratio Pu-241/Pu-239. Thus, the 1952-1964 bomb-spike as the possible primary (GSSP) marker of the Anthropocene can be identified and used even in coarse urban anthropogenic sediments of big cities, exemplifying the correlation potential of these radionuclide markers.

How to cite: Meszar, M., Hain, K., Wagreich, M., Lappé, K., Mosser, M., Hornek, K., Koukal, V., Litschauer, C., and Piperakis, N.: Tracing the Anthropocene bomb-spike in urban strata of Vienna, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11930, https://doi.org/10.5194/egusphere-egu21-11930, 2021.

SSP2.7 – Responding to change: Propagation of environmental signals during landscape transience

EGU21-14746 | vPICO presentations | SSP2.7

Under what conditions do climatic variations lead to incision of alluvial fans? Insights from coupled catchment-fan system in the lab

Stéphane Bonnet, Valeria Zavala-Ortiz, and Sébastien Carretier

EGU21-8313 | vPICO presentations | SSP2.7

Landscape response to the Mid-Pleistocene Transition (MPT) and higher frequency climate change in the Central Andes

Elizabeth Orr, Taylor Schildgen, Stefanie Tofelde, and Hella Wittmann-Oelze

Theory suggests that the response time of alluvial-channel systems to perturbations in climate can be related to the magnitude and direction of the forcing, and the length of the system; shorter systems may record a higher frequency of forcing compared to longer systems. The Toro Basin in the Eastern Cordillera of NW Argentina has preserved a suite of alluvial-fan deposits at the toe of the western flanks of the Pascha Range. Farther downstream, a series of cut-and-fill terraces have been linked to 100-kyr climate cycles since ca. 500 ka (Tofelde et al., 2017). The upper basin fan sequence therefore presents an excellent opportunity to explore (1) how climate-induced channel responses may or may not propagate downstream, and (2) the differences in landscape response to forcing frequency as a function of stream length when comparing the upper to the lower basin fan/terrace sequences. 

 

The abandonment ages of eight fan surfaces based on our new 10Be-derived exposure ages of 30 boulders and a 10Be depth profile define two sets of fans: the first set records fan-surface activity and abandonment between ca. 800 and 500 ka, and the second set records activity within the last 100 kyr. By comparing the fan stratigraphy and surface ages with paleoenvironmental records, we can explore whether the complete fan sequence can be explained by the local expression of shifts in regional and global climate.

 

The older set of fans records an important phase of incision within the basin, punctuated by periods of surface stability and aggradation, between ca. 800 and 500 ka. We argue that this net incisional phase, which has been recognised within other intermontane basins throughout the Central Andes, was likely triggered by prolonged and enhanced global glacial cycles following the Mid-Pleistocene Transition (MPT). A period of relative fan surface stability followed in the upper basin, while 100-kyr cut-and-full cycles persisted downstream, suggesting a disconnect in the behaviour of the two regions.

 

The younger set of fans reflect higher frequency climate forcing, possibly the result of precessional forcing of climate (ca. 20-kyr timescales) without significant net incision. Within these climatic cycles, fan surface activity can be correlated to periods of enhanced warming and aridity within the Central Andes and the previous global interglacial. The incision and abandonment of these surfaces then coincide with periods of increased humidity from an intensified monsoon, regional glaciation and global cooling. The lack of this high-frequency signal farther downstream provides field support for theoretical predictions of a filtering of high-frequency climate forcing with increasing channel length.

 


Tofelde, S., Schildgen, T.F., Savi, S., Pingel, H., Wickert, A.D., Bookhagen, B., Wittmann, H., Alonso, R.N., Cottle, J. and Strecker, M.R., 2017. 100 kyr fluvial cut-and-fill terrace cycles since the Middle Pleistocene in the southern Central Andes, NW Argentina. Earth and Planetary Science Letters, 473, p.141-153.

How to cite: Orr, E., Schildgen, T., Tofelde, S., and Wittmann-Oelze, H.: Landscape response to the Mid-Pleistocene Transition (MPT) and higher frequency climate change in the Central Andes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8313, https://doi.org/10.5194/egusphere-egu21-8313, 2021.

EGU21-12885 | vPICO presentations | SSP2.7

Quantifying competing measures of sediment dynamics on alluvial fans: implications for reconstructing past environmental change

Alexander Whittaker, Sam Brooke, and Mitch D'Arcy

The effects of climate change on eroding landscapes and the sedimentary record remains poorly understood. While sediment routing systems at the Earth’s surface should, in principle, record changes in past environmental boundary conditions, the extent to which landscapes are buffered to high-frequency, high-magnitude climate change is contentious. Mountain catchments and alluvial fans offer one way to address this question, as they are accessible sediment routing systems in which source and sink are closely coupled, sedimentation rates are high, and sediment budgets can be closed. Here we consider the extent to which the granulometry of sediment in stream-flow-dominated alluvial fans records changing environmental conditions. We focus on well-constrained field examples in Death Valley, California, such as the Hanaupah Canyon Fan, which have experienced hydroclimate forcing associated with recent glacial-interglacial cycles. Using field-derived measures of grain size, we compare three complementary methods that have recently been used to reconstruct sediment dynamics on alluvial fans. First, we use a self-similarity analysis of sediment calibre to reconstruct sediment mobility on the fan over time. Second, we use a downstream-fining model to evaluate the extent to which different depositional units on the fans record changing sediment fluxes from source catchments. Finally, we adopt a palaeohydrological approach to reconstruct unit discharges, bed shear stresses and instantaneous sediment transport capacities for fans in the study area, based on field measures of hydraulic geometry and grain size. We evaluate the extent to which these three methods provide consistent results, and we quantify the extent to which grain mobility, water and sediment discharge scale with documented variations in the regional climate. Our work shows that alluvial fans are highly sensitive to palaeo-environmental change, but our findings also illustrate the importance of considering which measures of past climate (particularly averages versus variance) are most relevant for landscape responses and sensitivity to climate change. 

How to cite: Whittaker, A., Brooke, S., and D'Arcy, M.: Quantifying competing measures of sediment dynamics on alluvial fans: implications for reconstructing past environmental change, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12885, https://doi.org/10.5194/egusphere-egu21-12885, 2021.

EGU21-16267 | vPICO presentations | SSP2.7

Debris‐flow and anthropogenic disturbance on 10Be concentration in mountain streams with contrasting structural geomorphic connectivity

Francesco Brardinoni, Reto Grischott, Florian Kober, Corrado Morelli, and Marcus Christl

The understanding of the sediment routing system and source-to-sink dynamics in a catchment is vital as it helps to assess areas undergoing erosion and deposition. This is significant in catchments which undergo active mining activities especially natural sand materials. The role of climate and natural erosional processes is vital in this as mining of sand is also affected by natural replenishment. In present study, we take a case study of a small catchment of 30km length ~ Chharri, situated in arid landscape of Kachchh of western India. Using geomorphic assemblage mapped using remote sensing and field investigation, we identified natural sub-sinks (depocenters) in the Chharri river valley. The investigation was validated by studying sediment profiles of the depocentral landforms in seasonal time series (pre-monsoon and post monsoon sessions). The changes in morphology, sediments accumulations were integrated to assess the natural sand replenishment in areas which had been undergoing mining activity. Based on time series data it was deduced that the small catchments in dry-land environments, the sand production and dynamics is modulated by type of vegetation, pattern in precipitation and human intervention. The results of such source-to-sink study have long-term implications on sand replenishment, mining activity and landscape evolution of such river basins.

How to cite: Singh, A. K. and Bhatt, N.: Geomorphic variability and sediment dynamics in small catchments of dryland environments: Application into sand mining, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2426, https://doi.org/10.5194/egusphere-egu21-2426, 2021.

EGU21-12642 | vPICO presentations | SSP2.7

Understanding fluvial aggradation styles through physical modelling: Are we able to distinguish changes in water discharge and/or sediment supply (upstream drivers) from changes in base-level (downstream forcing) on river aggradation?  

Stephen E. Watkins, Guy Simpson, Laure Guerit, Frédéric Arlaud, Valentin Marguin, Marine Prieur, Nikhil Sharma, Maxime Tremblin, Luis Valero, Abdallah S. Zaki, and Sébastien Castelltort

EGU21-7904 | vPICO presentations | SSP2.7

Responses of gravel-bed rivers to periodic climate change

Fergus McNab, Taylor Schildgen, Jens Turowski, and Andrew Wickert

Periodic variation in Earth's orbit leads to variation in temperature and precipitation at its surface that are expected to exert a profound influence on landscape evolution. Indeed, cyclical fluctuations in sediment yield and grain size are a ubiquitous feature of the geological record, and recurrence times of geomorphological features such as fluvial terraces and alluvial fans often appear to reflect orbital periodicities. However, making quantitative interpretations of these records requires a detailed understanding of the ways in which sediment is transported from mountainous source regions along alluvial channels to depositional sinks. Sediment transport processes may dampen (i.e. buffer, 'shred') or amplify climate signals, such as changes in channel elevation or sediment flux, and may introduce a lag between them and the responsible external forcing. Recent modelling studies, mostly focused on the potential transmission of climatic signals to sedimentary archives, have predicted a wide range of behaviour and have proven challenging to test in the field. Here, we aim to clarify this discussion and also consider the potential preservation of climatic signals by fluvial terraces along alluvial channels. Our starting point is a recently developed model describing the long-profile evolution of gravel-bed rivers. This model is the first of its kind to be derived from first principles using physical relationships that have been extensively tested in laboratory settings, and takes a non-linear diffusive form. We employ perturbation theory to obtain approximate analytical solutions to the relevant equations that describe how channel elevation and sediment flux vary in response to periodic fluctuations in discharge and sediment supply. Our solutions contain expressions for response amplitudes and lag times as functions of downstream distance, system 'diffusivity' and forcing frequency. Lag times can be a significant fraction of the forcing period, implying that care is required when interpreting the timings of terrace formation in terms of changes in discharge or sediment supply. We also show that at the onset of periodic forcing, or a change in the dominant forcing period, alluvial channels undergo a transient response as they adjust to a new quasi-steady state. Importantly, this result implies that suites of fluvial terraces can be preserved without the need for significant local base-level fall. Since the expressions presented here are defined in terms of fundamental properties of alluvial channels, they should be readily applicable to real settings.

How to cite: McNab, F., Schildgen, T., Turowski, J., and Wickert, A.: Responses of gravel-bed rivers to periodic climate change, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7904, https://doi.org/10.5194/egusphere-egu21-7904, 2021.

EGU21-10234 | vPICO presentations | SSP2.7

Impacts of climatic changes on fluvial sediment fluxes in north western Europe: The Middle and Late Pleistocene Meuse river system

Ewerton da Silva Guimarães, Ronald T. van Balen, Cornelis Kasse, Freek S. Busschers, and Renaud Bouroullec

Climate change and tectonics can generate signals in a source-to-sink system in the form of changing sediment supply. The study of the propagation of this signal through the system might elucidate how different source-to-sink systems respond to a given perturbation, for instance, the Early to Middle-Pleistocene climate transition. Knowledge on the temporal and spatial responses to such perturbations in a catchment is still limited. Previous studies, with the support of landscape evolution models, demonstrate that several thousands of years might be needed for an extreme-climate-transition-induced signal to propagate through a river catchment (an example of source-to-sink system). The present work aims to contribute to the understanding of how such systems might react when submitted to rapid climate change events by studying the Meuse river catchment. The primary goals are to characterize and quantify the main controls on sediment flux of this fluvial system as a response to the Early to Middle Pleistocene climate transition as well as to assess how climate signals propagated through this source-to-sink system during the last four glacial-interglacial cycles, starting around 450.000 years ago.

To achieve our goals, three main tasks are proposed. In the first stage of this project, with the support of high-resolution DEM and high-resolution sedimentary cores, the different Meuse fluvial terrace maps are updated. For that, a new cross-border fluvial terrace map between the Netherlands, Belgium and Germany is produced. Characterization and mapping of sediment grain-size and provenance is also carried out. The new Meuse terrace map will guide the sampling campaign of Meuse terrace sediments. The samples will be used for cosmogenic-nuclide age-dating of the sampled terraces. Two dating methods will be used depending on how deeply buried and well-preserved the terraces are: burial isochrone (26Al/10Be) where sediment cover thickness is greater than 4,5 – 5 m, and depth profile (10Be) when the terrace surface is well preserved. These methods will be applied to specific terrace steps, in order to date those around the Mid-Pleistocene transition. Beryllium-10 age-dating will possibly also be applied to specific sedimentary levels (cores, outcrops), in order to infer averaged denudation rates and, consequently, the sediment fluxes, during the investigated climatic cycles. During the latter part of the project, all the data will be set in a temporal framework using the cosmogenic dating results and existing age controls.

How to cite: da Silva Guimarães, E., van Balen, R. T., Kasse, C., Busschers, F. S., and Bouroullec, R.: Impacts of climatic changes on fluvial sediment fluxes in north western Europe: The Middle and Late Pleistocene Meuse river system, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10234, https://doi.org/10.5194/egusphere-egu21-10234, 2021.

EGU21-13384 | vPICO presentations | SSP2.7

River discharge variability in the rock record? Disentangling the relative role of flow variability and morphodynamic hierarchies on bedform preservation

Sinead Lyster, Alexander Whittaker, Elizabeth Hajek, Vamsi Ganti, and Peter Allison

River discharge variability is a fundamental control on fluvial morphodynamics and, in principle, stratigraphic architecture. The ability to quantitatively constrain discharge variability from fluvial stratigraphy would newly enable us to reconstruct instantaneous or interannual responses of rivers to climatic perturbation in the geologic past. However, the extent to which we can extract quantitative information about discharge variability from fluvial stratigraphy is currently unknown. Recent experimental work indicates that preserved cross-set geometries can potentially be used to inform formative flow conditions and durations. However, to date, this has not been tested on field examples of ancient fluvial systems. Here we use detailed measurements of cross-sets to assess bedform kinematics and formative flow conditions in fluvial strata of three Late Cretaceous geologic formations: the Blackhawk Formation, Castlegate Sandstone, and Ferron Sandstone, which crop out in central Utah, USA.

Unanimously low coefficients of variation (CV) in preserved cross-set heights of 0.25–0.5 are consistent with the hypothesis that CV<<0.88 arises from preservation of bedforms in disequilibrium conditions, which typically occurs during rapid flood recession in a “flashy” flood hydrograph. Bedform preservation in disequilibrium conditions requires that formative flow durations are shorter than bedform turnover timescales. We reconstruct median turnover timescales of 2–3 days, with a 10–90 percentile range of ~1–10 days, which implies that formative flow durations were of order hours to a few days. These durations are consistent with storm-related flood durations in perennial discharge regimes, as opposed to the more sustained flood durations that are typical of subtropical/monsoonal climate regimes. However, it is also possible that this same CV signature (CV<<0.88) can be achieved simply by the presence of morphodynamic hierarchies, e.g. concurrently migrating bedforms and bars. We explore whether it is possible to disentangle the relative role of formative flow conditions and morphodynamic hierarchies on bedform preservation using our field data, models of flood stratigraphy, and estimates of bedform preservation ratios. Moreover, we identify future steps that will further our ability to quantitatively extract formative flow variability and, ultimately, discharge variability from the rock record. 

How to cite: Lyster, S., Whittaker, A., Hajek, E., Ganti, V., and Allison, P.: River discharge variability in the rock record? Disentangling the relative role of flow variability and morphodynamic hierarchies on bedform preservation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13384, https://doi.org/10.5194/egusphere-egu21-13384, 2021.

There are two main statements of a long-accepted paradigm of fluvial morphodynamics formalized inter alia by S.A. Schumm: (i) changes in fluvial systems strongly depend on exceeding external and / or internal thresholds ​​and (ii) they are always characterized by a nonlinear and asynchronous character. While the first aspect of this paradigm is part of numerous studies on fluvial morphology and river dynamics, the second aspect has so far tended to be sidelined in practical geomorphology.

With particular respect to the field of paleo-environmental research, this is evident from studies that aim at determining ages of Pleistocene river terraces in order to provide a time frame for the reconstruction of paleo-environmental conditions. Typically, numerical dating approaches are only applied to a single location that is supposed to be exemplary for the respective terrace level. Numerical ages determined for this specific location are then extrapolated and interpreted in a generalizing way to derive "THE age" of the river terrace as a whole.

With respect to the concept of asynchronism of fluvial reactions to environmental changes, such an approach seems problematic. In fact, asynchronism implies different sections of a river showing different and specific reactions to environmental changes at a given point in time. For fluvial terraces, this means that the processes controlling their formation may already have started in some sections of a valley, while in other sections they do not yet have any impact on landscape evolution.

In this contribution, we present luminescence ages of fluvial deposits originating from an Upper Pleistocene river terrace in a small valley located in the headwater of the Main River, Germany. Here, several samples from various locations throughout the river longitudinal course have been analysed. The luminescence ages determined for the lowermost part of the valley are significantly older than those from the middle section, which in turn are older than those from the valley’s upper reaches.

Our results suggest a diachronic alignment of sedimentation ages for fluvial deposits, starting with old ages close the mouth of a river and getting progressively younger for locations approaching the upper reaches. If these findings are confirmed in other fluvial systems and are not only the result of specific local conditions, they will be of great relevance for geomorphological research in fluvial landscapes. As a result, the widespread approach of deriving age estimates for fluvial terraces from numerical results merely determined for a single location appears to be inadequate and should be subjected to a critical review.

How to cite: Kolb, T. and Fuchs, M.: Diachronism as process-inherent part of Pleistocene river terrace formation: First results based on luminescence dating for testing a well-established theoretical concept and possible implications for practical field work, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10429, https://doi.org/10.5194/egusphere-egu21-10429, 2021.

EGU21-10532 | vPICO presentations | SSP2.7

Decoding geochemical signals of the Schwalbenberg Loess-Palaeosol-Sequences — A key to Upper Pleistocene terrestrial ecosystem responses in western Central Europe 

Mathias Vinnepand, Peter Fischer, Christian Zeeden, Philipp Schulte, Sabine Fiedler, Olaf Jöris, Ulrich Hambach, Kathryn Fitzsimmons, Charlotte Prud'homme, Zoran Péric, Wolfgang Schirmer, Frank Lehmkuhl, and Andreas Vött

The Schwalbenberg Loess-Palaeosol-Sequences (LPS) in the Middle Rhine Valley, Germany, comprise unprecedented complete records of Upper Pleistocene terrestrial ecosystem response to global climate changes. However, direct correlation of the Schwalbenberg geochemical signals with climate archives of supra-regional northern hemispheric relevance remains complicated. This is due to the complex interplay of pre-, syn-, or post-depositional processes that left their traces in the terrestrial record. In particular, the use of different element ratios to derive weathering indices may be complicated as dust sources change through time, and as ecosystems respond to changing conditions. In this study, we decode interfering geochemical signatures and re-evaluate proxies, commonly applied, regarding their suitability and meaning for understanding the evolution of the Schwalbenberg LPS. We undertake a systematic approach, firstly dividing the 30 m long Schwalbenberg REM3 LPS according to our core description. In a second step, we integrate LOG-ratios indicative of provenance shifts, sediment reworking dynamics and weathering into multivariate analysis. We apply Principle Component Analyses (PCA) and Linear Discriminant Analysis (LDA) to datasets comprising sediments deposited under similar environmental conditions. In doing so, we sensitively quantify subordinate processes and conditions, such as the impact of varying source- and weathering-signals in all proxies. Our results show that in particularly K/Rb and Mg/Ca ratios contain a strong provenance signal in loess deposits, whereas the Ca/Ald ratio (Ald: dithionite extractable) best indicates the maturity state of Gelic Gleysols. Integration of our filtered datasets with a high-resolution age model enables direct correlation of the variability of principal components on sub-millennial scales with Atlantic-driven climate oscillations. More specifically, PC2 appears to reflect changes in mineral dust accumulation and indicates increasing dust input in response to climate cooling towards the end of interstadials, highlighting the accretionary nature of the Schwalbenberg LPS during transitional periods from interstadial to stadial depositional modes.

 

How to cite: Vinnepand, M., Fischer, P., Zeeden, C., Schulte, P., Fiedler, S., Jöris, O., Hambach, U., Fitzsimmons, K., Prud'homme, C., Péric, Z., Schirmer, W., Lehmkuhl, F., and Vött, A.: Decoding geochemical signals of the Schwalbenberg Loess-Palaeosol-Sequences — A key to Upper Pleistocene terrestrial ecosystem responses in western Central Europe , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10532, https://doi.org/10.5194/egusphere-egu21-10532, 2021.

EGU21-12905 | vPICO presentations | SSP2.7

Tracking signal propagation through landscapes using a granular avalanching system

Chloe Griffin, Jonathan Higham, Robert Duller, and Kyle Straub

Landscapes have the ability to transmit environmental signals or inhibit them. The mechanisms by which landscapes do this are largely unquantified, but is probably due to the ability of landscapes to transiently store and release sediment which acts as a medium for energy to propagate. Previous experiments using 1D avalanching rice piles suggest that stochastic collapses can overprint, or shred, periodic sedimentary signals (Jerolmack and Paola (2010), as measured using mass efflux from the experimental rice pile. Jerolmack and Paola (2010) defined a threshold for successful surface signal propagation: Tx, where signals with a period less than Tx are shredded, unless the magnitude of the signal is sufficiently large. We aim to utilise the rice pile to further investigate signal propagation across a landscape, and the thresholds for this, by quantifying inter-particle interactions and the mechanics of how signals propagate using a quasi-2D rice pile model, built using MFiX-DEM code. This open source, physics model utilises individual particles which compose the solid phase whilst treating the fluid as a continuum. The rice grains in the model are represented by spherical particles, where each individual particle, or cluster of particles, can be tracked through each time step using a coordinate axis system, allowing internal dynamics, such as avalanche sizes and sediment residence times, to be quantified. To certify the model replicates the self-organised nature of an experimental rice pile, sensitivity tests were performed by systematically changing two key parameters controlling grain interactions: the friction coefficient and the coefficient of restitution, alongside the sediment flux. To calibrate the results of the sensitivity analysis, mass efflux through time and the corresponding power spectra are compared to real experimental rice pile results and statistical rice pile models. It is hoped this work will provide fundamental insights into how a signal propagates through a landscapes, and how they are shredded in the process.   

How to cite: Griffin, C., Higham, J., Duller, R., and Straub, K.: Tracking signal propagation through landscapes using a granular avalanching system, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12905, https://doi.org/10.5194/egusphere-egu21-12905, 2021.

EGU21-15896 | vPICO presentations | SSP2.7

Quantifying environmental signal propagation and preservation in ancient sediment routing systems using field data

Robert Duller, Stephan Toby, Silvio De Angelis, and Kyle Straub

The assertion that stratigraphy will store environmental signals, such as sediment flux signals related to paleoclimate and tectonics, is debatable because that same stratigraphy can also store signals of autogenic processes that overprint and replace allogenic signals (“shred”). To establish the likelihood that strata will contain allogenic signals, the focus should be on quantifying autogenic processes. Models show that stratigraphic storage of allogenic sediment flux signals will only take place if it exceeds a threshold condition set by autogenic processes. This is supported by experimental and numerical models but its validation is hindered by low spatio-temporal resolution of stratigraphic datasets. We address this by reformulating a theoretical framework that dispenses with the need for exquisite temporal resolution. To demonstrate the applicability of our approach we explore the potential for environmental signal propagation and preservation in two ancient field systems: a small Pleistocene delta in Greece and a larger Eocene sediment routing system in the Spanish Pyrenees. This work demonstrates how short-term system dynamics can be integrated with long-term basin dynamics to provide a framework that assesses the capacity of sedimentary systems to store environmental signals.

How to cite: Duller, R., Toby, S., De Angelis, S., and Straub, K.: Quantifying environmental signal propagation and preservation in ancient sediment routing systems using field data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15896, https://doi.org/10.5194/egusphere-egu21-15896, 2021.

EGU21-12796 | vPICO presentations | SSP2.7

Sediment flux across the south-Pyreneean foreland basin. A contribution to the S2S-Future network. 

Philémon Juvany and Miguel Garcés
 

The early Eocene was a period of the intense collision during the formation of the Pyrenees. The flexural response to loading of the overriding European plate led to the formation of an elongated foredeep on the subducting Iberian plate which connected westward to the Atlantic Ocean. A thrust salient formed in the central Pyrenees, where Mesozoic Cover units travelled southwards on top of Triassic salt detachment. This process resulted in the sequencing of the foreland basin in different isolated sub-basins such as the Ripoll basin in the East, the Tremp-Graus and Ainsa-Jaca basins in central and western south Pyrenees and the Ager basin located south of the Tremp-Graus basin.  The precise timing and surface processes associated to this reorganization of the sedimentary routing system remains not totally understood. Indeed, various sedimentary provenance studies show that the sediments of the Tremp-Graus basin were sourced from a different catchment zone than those of the Ager basin. Besides, the Ripoll basin sediments provenance analysis shows major similarities with the Ager basin, suggesting a common catchment area in the Eastern Pyrenees. However, it has been pointed out that the clastic systems feeding the rapidly subsiding sink of the Ripoll through could not find their way towards the shallower Ager basin. In this PhD project we aim at providing further constraints to the paleogeographic reconstruction and sediment routing systems of the South Eastern Pyrenees in the light of a revised chronostratigraphic scheme. A Source-to-Sink approach will be followed to study the sediment Routing Systems and to decode the climatic and tectonic signal from the sedimentary record. It will follow a volumetric quantification of the sediment budget over the entire foreland, and a comparison with eroded rock volumes of the whole Pyrenees. The resulting revised scenario will seek conciliation of all available data from the stratigraphic, structural, petrologic, geochronologic and sedimentologic datasets with new radiogenic isotopes sedimentary provenance analysis.  

How to cite: Juvany, P. and Garcés, M.: Sediment flux across the south-Pyreneean foreland basin. A contribution to the S2S-Future network. , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12796, https://doi.org/10.5194/egusphere-egu21-12796, 2021.

EGU21-3269 | vPICO presentations | SSP2.7

Do grain size patterns from Oligo-Miocene Swiss Molasse sequences reflect shifts in sediment flux through time?

Philippos Garefalakis, Alexander C. Whittaker, Jörg Hermann, David Mair, and Fritz Schlunegger

The formation of large-scale coarsening- and thickening-upward sedimentary sequences is commonly related to mountain belt evolution, where tectonic, lithological or climatic controlled changes (e.g. Whittaker et al., 2010; D’Arcy et al., 2017) have a major influence on the large-scale architecture of the adjacent foreland basin. Furthermore, as proposed by Lane (1955), trends in stratal patterns are also controlled by variations in hydrological conditions such as sediment and water discharge. These changes affect the dynamics of alluvial systems, which are commonly preserved by grain size and stacking patterns. A relation between grain size trends and sediment flux has been in the focus of previous research (e.g. Schlunegger and Castelltort, 2016) yet with a limited dataset only. Here, we extend this approach and investigate whether there exists a direct correlation between grain size patterns and shifts in sediment flux through time at the scale of an entire basin.

The Swiss Molasse basin, our study area, includes three major depositional systems situated in eastern, central and western Switzerland. These systems have been active during Oligocene- to Miocene-times between 31 and 13 Ma (Schlunegger et al., 1997; Kempf et al., 1999). We collected grain size data from several km-thick conglomerate sequences along 16 individual sections using state-of-the-art techniques and compared grain size patterns with published data of sediment flux to the Molasse basin (Kuhlemann et al., 2001).

Preliminary results reveal that from 31 to 21 Ma, both, the median grain size (D50) and the D84 percentiles show an increase from 4.4±0.8cm to 4.8±0.1cm (D50, +10%), and from 8.0±1.4cm to 9.5±1.2cm (D84, +20%). Simultaneously, sediment flux to the entire Molasse basin increased from c. 6’000 km3/Myr at 31 Ma to c. 23’000 km3/Myr at 21 Ma recording almost a fourfold increase (Kuhlemann et al., 2001). A substantial flux reduction at 20 Ma to c. 17’000 km3/Myr was followed by strong fluctuations, reaching c. 15’000 km3/Myr at 13 Ma. However, compared to the peak at 21 Ma, this corresponds to a 30% decrease in sediment discharge. In contrast, during the same time interval, the grain size data record a 20% increase in D50 from 3.7±0.5cm to 4.5±0.4cm and a 40% increase in D84 from 6.2±1.0cm to 8.7±1.0cm, respectively.

The preliminary results thus show that grain size patterns are positively correlated to shifts in sediment flux during Oligocene-times (31 to 21 Ma), but weak to no correlations between sediment flux and grain size trends were observed during Miocene-times (20 to 13 Ma). We interpret this data as showing that surface erosion and topographic development occurred in pace with the geological driving forces such as ongoing continent-continent collision during Oligocene-times. In contrast, we tentatively suggest that the landscape entered a transient stage after 20 Ma when large-scale tectonic exhumation started to interfere with the fluvial processes in the Alpine hinterland, thereby shifting the Alpine topography in a transient state.

 

D’Arcy et al., 2017. Sedimentology, 64, 388-424.

Kempf, O. et al., 1999. Int. J. Earth Sci., 88(2), 253-275.

Kuhlemann et al., 2001. Tectonophysics, 330, 1-23.

Lane, 1955. ASCE Proceedings, 81(745), 1-15.

Schlunegger et al., 1997. GSA Bulletin, 109(2), 225-241.

Schlunegger and Castelltort, 2016. Sci. Rep., 6, 1-11.

Whittaker et al., 2010. Basin Res., 22, 809-828.

How to cite: Garefalakis, P., Whittaker, A. C., Hermann, J., Mair, D., and Schlunegger, F.: Do grain size patterns from Oligo-Miocene Swiss Molasse sequences reflect shifts in sediment flux through time?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3269, https://doi.org/10.5194/egusphere-egu21-3269, 2021.

EGU21-14581 | vPICO presentations | SSP2.7

Selective recording of a tectonic forcing in different grain-size fractions in the Oligocene/Miocene Eastern Alpine Molasse Basin

Julian Hülscher, Edward R. Sobel, Niklas Kallnik, J. Elis Hoffmann, Ian L. Millar, and Anne Bernhardt

Sedimentary archives are the main source of information for climatic and tectonic changes in Earth’s history. We investigate how the tectonically triggered early (28±1 Ma) exhumation of the Tauern Window in the Eastern European Alps is recorded in the Oligocene/Miocene Northern Alpine Foreland Basin (NAFB) in Upper Austria. We combined Nd isotopic compositions on clay-sized bulk sediment and of sand-sized single-grain apatites with additional trace-element geochemistry, fission track (AFT) and U-Pb dating to investigate the timing of when this tectonic signal reaches the sediment archive within these different grain-size fractions.

This well-investigated basin offers an excellent opportunity to investigate environmental signal propagation. From ~27 to 19 Ma, a deep-marine basin-axial, gravity-flow dominated channel controlled the West to East directed sediment transport in the Upper Austrian NAFB. The sediments were sourced in the Eastern and Central Alps. At 19 Ma, channel sedimentation ceased and clinoforms prograded from the southern margin northward into the basin. This change in sediment-routing direction cut off the Central Alpine sediment source.

Drill cuttings of one well on the northern basin slope and drill cores from 12 wells were sampled for clay and the single-grain analysis. Clay eNd values remain stable around -9.7 (±0.5) from 27 to 19 Ma but increase afterwards to -8.7 (±0.2) at 18.3 Ma. In contrast, apatite single-grain results significantly change at 23.3±0.3 Ma from a domination of apatites from low-grade (<upper amphibolite-facies) metamorphic sources, Permo-Mesozoic and late Variscan U-Pb ages and AFT ages >40 Ma to a domination of high-grade metamorphic apatites with late Variscan U-Pb ages and an increasing number of AFT ages <30 Ma. The high-grade metamorphic apatites have slightly more positive eNd values (-2.2 ± 3.9) than the low-grade metamorphic apatites (-4.4 ± 4.2).

The changes in the single-grain data sets have been previously interpreted to mirror the exposure of a new Upper Austroalpine nappe as a consequence of the ongoing early Tauern Window exhumation. The total signal lag time between the beginning of the exhumation and the arrival of the signal within the apatite assemblage in the sedimentary archive is therefore 3.4 to 6 Myrs. The clay eNd values do not record this change in provenance at 23.3±0.3 Ma as they stayed stable until 19 Ma when they increased slightly. This might point towards a delayed recording of the provenance change revealed at 23.3±0.3 Ma by the apatites. The difference in signal recording is caused by the characteristics of the applied methods. Whereas single-grain distributions of orogen-wide sediment-routing systems can be dominated by geographically small areas with high erosion rates and high mineral fertility, bulk-rock methods integrate over the entire drainage area, a process that diminishes extreme values. The disconnection of the Central Alpine sediment source at 19 Ma, increased the relative proportion of the more positive eNd values of the Upper Austroalpine Nappe in the drainage area, leading to an increase in clay eNd values in our data set. Our results show that different information from the hinterland is recorded in the different grain-size fractions and methods.

How to cite: Hülscher, J., Sobel, E. R., Kallnik, N., Hoffmann, J. E., Millar, I. L., and Bernhardt, A.: Selective recording of a tectonic forcing in different grain-size fractions in the Oligocene/Miocene Eastern Alpine Molasse Basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14581, https://doi.org/10.5194/egusphere-egu21-14581, 2021.

EGU21-4070 | vPICO presentations | SSP2.7

The Evolution of the Paleo-Danube Deltas of the Lower Pannonian in the Vienna Basin 

Arthur Borzi, Werner E. Piller, Mathias Harzhauser, Wolfgang Siedl, and Philipp Strauss

ABSTRACT

The Vienna Basin is a rhombohedral SSW-NNE oriented Neogene extensional basin that formed along sinistral fault systems during Miocene lateral extrusion of the Eastern Alps. The basin fill consists of shallow marine and terrestrial sediments of early to late Miocene age reaching a thickness of 5500 m in the central part of the basin. The early Pannonian was a crucial time in the development of the Vienna Basin, as It coincided with the formation of Lake Pannon. The lake formed at 11.6 Ma when a significant regressive event isolated Lake Pannon from the Paratethys Sea, creating lacustrine depositional environments. At that time the delta of the Paleo-Danube started shedding its sediments into the central Vienna Basin. Based on an existing age model delta deposition commenced around 11.5 Ma and continued until 11.1 Ma. These subsurface deltaic deposits of the Hollabrunn-Mistelbach Formation represent the coeval fluvial deposits of the Paleo-Danube in the eastern plains of the North Alpine Foreland Basin. Therefore, the Palaeo-Danube represents an extraordinary case in where coeval fluvial and deltaic deposits of a Miocene river are continuously captured.

This study provides an interpretation of depositional architecture and depositional environments of this delta in the Austrian part of the central Vienna Basin based on the integration of 3D seismic surveys and well data. The mapped delta has an area of about 580 km2, and solely based on the geometry we classify the delta as a mostly river – dominated delta with significant influence of wave – reworking processes. For seven time slices paleogeographic maps are created, showing the interplay between the lacustrine environments of Lake Pannon, delta evolution and fluvial systems incising in the abandoned deltaplain. Onlaps between single deltalobes indicate a northward-movement of the main distributary channel. Approximate water-depth estimates are carried out with in-seismic measurements of the true vertical depth between the topset deposits of the delta and the base of the bottomset deposits. These data suggest a decrease of lake water depth from about 170 m during the initial phase of delta formation at 11.5 Ma to about 100 m during its terminal phase at 11.1 Ma. A major lake level rise of Lake Pannon around 11.1 Ma caused a flooding of the margins of the Vienna Basin, resulting in a back stepping of riverine deposits and termination of delta deposition in the study area.

 

How to cite: Borzi, A., Piller, W. E., Harzhauser, M., Siedl, W., and Strauss, P.: The Evolution of the Paleo-Danube Deltas of the Lower Pannonian in the Vienna Basin , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4070, https://doi.org/10.5194/egusphere-egu21-4070, 2021.

EGU21-13678 | vPICO presentations | SSP2.7

Isostasy amplifies relative sea-level change on continental-scale deltas

Sara Morón, Mike Blum, Tristan Salles, Bruce Frederick, Rebecca Farrington, Xuesong Ding, Claire Mallard, Ben Mather, and Louis Moresi

The nature and contribution of flexural isostatic compensation to subsidence and uplift of passive margin deltas remains poorly understood. We performed a series of simulations to investigate flexural isostatic responses to high frequency fluctuations in water and sediment load associated with climatically-driven sea-level changes. We use a parallel basin and landscape dynamics model, BADLANDS, (an acronym for BAsin anD LANdscape DynamicS) that combines erosion, sedimentation, and diffusion with flexure, where the isostatic compensation of the load is computed by flexural compensation. We model a large drainage basin that discharges to a continental margin to generate a deltaic depocenter, then prescribe synthetic and climatic-driven sea-level curves of different frequencies to assess flexural response. Results show that flexural isostatic adjustments are bidirectional over 100-1000 kyr time-scales and mirror the magnitude, frequency, and direction of sea-level fluctuations, and that isostatic adjustments play an important role in driving along-strike and cross-shelf river-mouth migration and sediment accumulation. Our findings demonstrate that climate-forced sea-level changes set up a feedback mechanism that results in self-sustaining creation of accommodation into which sediment is deposited and plays a major role in delta morphology and stratigraphic architecture.

How to cite: Morón, S., Blum, M., Salles, T., Frederick, B., Farrington, R., Ding, X., Mallard, C., Mather, B., and Moresi, L.: Isostasy amplifies relative sea-level change on continental-scale deltas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13678, https://doi.org/10.5194/egusphere-egu21-13678, 2021.

EGU21-10323 | vPICO presentations | SSP2.7

Assessing the fidelity of leaf wax signals in marine sediments: n-alkane sensitivity to change along a precipitation gradient

Nestor Gaviria-Lugo, Charlotte Läuchli, Hella Wittmann, Anne Bernhardt, Patrick Frings, and Dirk Sachse

Leaf wax n-alkanes are well known higher plant biomarkers. These molecules are widely found in geological archives, where their concentration, average chain length (ACL) and isotopic composition (δ13Calkanes and δ2Halkanes) serve as proxies for changes in continental vegetation and hydroclimate. While mechanistic relationships of these proxies with climate and vegetation are relatively well understood, little is known about the transport of those biomarkers into geological archives. In marine sedimentary records, leaf wax biomarkers are often interpreted to represent the contiguous continental catchments, but few studies have examined the fidelity with which n-alkanes in marine sediments record the corresponding continental conditions.

Here we assess the variability of n-alkane composition in terrestrial and marine sediments from 26°S to 41°S along the Chilean coast. The sample sites are located along a strong vegetation and precipitation gradient, with precipitation ranging from 25 to 2300 mm/yr. We evaluate riverbed sediments from twenty catchments, draining the western slopes of the Andes to the Pacific Ocean and compare the values to the ones of 19 samples from marine surface sediments recovered directly offshore each catchment.

The correspondence between terrestrial and marine n-alkanes signals changes along the precipitation gradient. Where precipitation rates range between 100 to 500 mm/yr, ACL and δ2Halkanes values agree well between continental and adjacent marine sediments. At precipitation rates below 100 mm/yr, ACL and δ2Halkanes values recorded in marine sediments are consistently lower than the ones found in continental sediments. At precipitation rates higher than 500 mm/yr, ACL and δ2Halkanes values registered in marine sediments are consistently higher than in the adjacent catchments.

Multiple factors, including mixing of sediment from different sources along the transport pathway from continent to ocean or variability in catchment storage capacity, likely cause marine n-alkane composition to be offset from their terrestrial source. Nevertheless, the consistent change in behavior along the gradient suggest that precipitation is the dominant factor on the transmission of n-alkane signals along the sedimentary routing systems of the study area. Moreover, since correspondence decreases at high and low precipitation, our data suggest that the sensitivity of the leaf wax biomarker proxy in marine archives towards hydrological change may be subdued due to sedimentary integration. This may have implications for quantitative interpretations derived from n-alkanes and their isotopes in marine paleorecords.

How to cite: Gaviria-Lugo, N., Läuchli, C., Wittmann, H., Bernhardt, A., Frings, P., and Sachse, D.: Assessing the fidelity of leaf wax signals in marine sediments: n-alkane sensitivity to change along a precipitation gradient, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10323, https://doi.org/10.5194/egusphere-egu21-10323, 2021.

EGU21-6237 | vPICO presentations | SSP2.7

Transient landscape response to abrupt precipitation increase at the Pleistocene-Holocene transition, offshore Sumatra

Sarah Mosser, Anne Bernhardt, Mahyar Mohtadi, and Tilmann Schwenk

Active continental margins play a major role in exporting terrestrial sediment to the oceans. Yet, the response of a sediment-routing system to a specific climate change is poorly quantified. The terrestrial-to-marine sediment-routing systems on West Sumatra can be used as a natural laboratory to quantify these changes. Rivers efficiently deliver sediment from the high-relief Barisan mountains to the enclosed marine forearc Mentawai Basin along this active subduction margin. The Holocene climatic history of the region is well known and shows an abrupt precipitation increase at the Pleistocene-Holocene transition (~12 ka BP) as recorded previously in δ18O time-series measured on planktonic foraminifera.

Here we analyze multiple late Quaternary sediment records spanning the last 14 ka from the Mentawai Basin, offshore Sumatra. We use volumetric sediment budgets and multivariate statistics on high-resolution elemental compositions to assess changes in sediment flux and composition based on ~150 km of high-resolution sub-bottom sediment profiles (covering 435 km²) and six sediment cores. Radiocarbon ages were taken at every ~35 cm within the sediment cores.

Our results, from sediment budget calculation and sedimentation rates within the cores, show that absolute rates of sediment supply to the marine forearc basin remained constant throughout the Holocene (542-566 g/m²/yr, 68% quantile, 0.1 and 0.2 cm/yr, respectively). However, the sediment composition varies drastically with comparable patterns all over the basin. The compositional changes are characterized by an 8000-year damped oscillation between terrestrial clastic (Al, Si, Ti, Zr, Fe, K, Rb) and marine authigenic (Ca, Sr) sediment supply. From ~12 to 8 ka BP, the relative amount of clastic rock-forming elements is increasing, then decreasing from ~8 to 4 ka BP, and finally increasing again from 4 ka BP to the present. Using a dynamical system modeling approach, we link the beginning of this oscillation to the abrupt precipitation increase at the interglacial transition at ~ 12 ka BP. We interpret the oscillation to reflect a persistent erosional feedback between physical and chemical weathering caused by ongoing landscape adaptation to the abrupt Pleistocene-Holocene transition. The total amount of sediment accumulation, however, does not follow this trend. Thus, the sedimentary composition shows ongoing landscape transience, whereas the uniform sediment accumulation rates imply a landscape in steady state.

These results have two major implications for future landscape evolution: a) the time scale of landscape transience far exceeds the time scale of abrupt climate transition, b) in this study, the sediment flux to the ocean floor does not mirror landscape transience because the excess terrestrial clastic sediment is compensated by decreased deposition of marine carbonates. These implications call for the implementation of compositional changes of exported sediments into landscape evolution models since so far most landscape models focus on the amount of exported sediment.

How to cite: Mosser, S., Bernhardt, A., Mohtadi, M., and Schwenk, T.: Transient landscape response to abrupt precipitation increase at the Pleistocene-Holocene transition, offshore Sumatra, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6237, https://doi.org/10.5194/egusphere-egu21-6237, 2021.

SSP2.11 – Climate and environmental change: Africa’s past, present and future

EGU21-805 | vPICO presentations | SSP2.11 | Highlight

Northern Hemisphere Glaciation, African Climate and Evolution

Martin H. Trauth, Asfawossen Asrat, Nadine Berner, Faysal Bibi, Verena Foerster, Matt Grove, Stefanie Kaboth-Bahr, Mark A. Maslin, Manfred Mudelsee, and Frank Schaebitz

The hypothesis of a connection between the onset (or intensification) of Northern Hemisphere Glaciation (NHG), the stepwise increase in African aridity (and climate variability) and an important mammalian (including hominin) species turnover is a textbook example of the initiation of a scientific idea and its propagation in science. It is, however, also an example of the persistent popularity of a hypothesis despite mounting evidence against it. The first part of our work analyzes of the history of the scientific idea by seeking its roots, including coincidental meetings and exchanges between of scientists, at project meetings, conferences and workshops. The consequences of this idea are examined and its influence on subsequent scientific investigations both before and after it has been falsified. In the second part of our investigation, we examine why the idea that the high latitudes have a major control on the climate of the low latitudes and thus early human evolution persists. For this purpose, an attempt is made to understand the original interpretation of the data, with special consideration of the composition of the scientific team and their scientific backgrounds and persuasions. Some of the key records in support of the hypothesis of a step-wise transition will be statistically re-analyzed by fitting change-point models to the time series to determine the midpoint and duration of the transition – in case such a transition is found in the data. A critical review of key publications in support of such a connection and a statistical re-analysis of key data sets leads to three conclusions: (1) Northern Hemisphere Glaciation is a gradual process between ~3.5–2.5 Ma, not an abrupt onset, either at ~2.5 Ma, nor at ~2.8 Ma, or any other time in the Late Cenozoic Era, (2) the trend towards greater aridity in Africa during this period was also gradual, not stepwise in the sense of a consistent transition of a duration of ≤0.2 Ma, and (3) accordingly, a step-wise change in environmental conditions cannot be used to explain an important mammalian (including hominin) species turnover.

How to cite: Trauth, M. H., Asrat, A., Berner, N., Bibi, F., Foerster, V., Grove, M., Kaboth-Bahr, S., Maslin, M. A., Mudelsee, M., and Schaebitz, F.: Northern Hemisphere Glaciation, African Climate and Evolution, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-805, https://doi.org/10.5194/egusphere-egu21-805, 2021.

EGU21-8025 | vPICO presentations | SSP2.11 | Highlight

Paleo-ENSO impacted habitat availability for early modern humans

Stefanie Kaboth-Bahr, William D. Gosling, Ralf Vogelsang, André Bahr, Eleanor M.L. Scerri, Asfawossen Asrat, Andrew S. Cohen, Walter Düsing, Verena E. Foerster, Henry F. Lamb, Mark A. Maslin, Helen M. Roberts, Frank Schäbitz, and Martin H. Trauth

Within eastern Africa, Ethiopia stands out for its steep topography, resulting in an altitudinal zonation of climate and vegetation. To understand future vegetation changes, we need information on past vegetation covers and vegetation responses to environmental and climatic changes. Pollen studies are available for low and high elevations in Ethiopia, but they are low in number and limited in spatial coverage. In addition, explicit research to altitudinal patterns of environmental changes are missing. However, archaeological evidence from SW Ethiopia suggests vertical migration of humans in response to humidity fluctuations, highlighting the need for research to spatial dynamics of human activities and vegetation in Ethiopia. On the other hand, sedimentological evidence suggests a millennia long agricultural history in Ethiopia’s highlands and several authors identify this region as a center of plant domestication. 

It is clear that a thorough understanding of the past vegetation cover and its alteration by humans and climate is missing for Ethiopia. These research gaps impede identification of the timing and location of the onset of agriculture in the ancient Ethiopian landscape, resulting in poor understanding of e.g. contemporary degraded landforms. In our study, we aim to reconstruct and quantify the vegetation history along an altitudinal gradient in the Southern Ethiopian Rift Valley and to identify the role of man and climate on this evolution. Therefore, several lakes and swamps are selected as study sites along an altitudinal gradient (1100-3000 m a.s.l.) in the Gamo Highlands near the city of Arba Minch, along the Southern Ethiopian Rift Valley. Here, we will present the results of pollen, charcoal and NPP analyses from two wetland sites situated at 2300 and 3000 m a.s.l. The records show an increase of Afromontane forest taxa around 13 ka BP, at the expense of Montane ericaceous taxa. At 8 ka BP, a shift in the composition of the Afromontane forest is observed, together with a change in the fungal assemblage and decrease of grasses. Around 6 ka BP, Wooded grassland taxa increase simultaneously with Delitschia fungal spores. Montane forest taxa increase again at 2.5 ka BP, together with a shift in fungal spores, followed by an increase in charcoal accumulation during the last millennium. Most of the observed transitions can be linked to other vegetation records from Ethiopia, and reflect responses to climatic changes such as the African Humid Period. However, the exact timing and  nature of the vegetation changes differs substantially between records, and asks for a denser sampling of palaeoecological records across Ethiopia. In this study, we will link the reconstructed vegetation changes with anthropogenic and natural driving forces, and come up with a reconstruction of the long-term landscape development in the study area in SW Ethiopia.   

How to cite: Augustijns, F., Broothaerts, N., and Verstraeten, G.: Reconstructing vegetation changes in the Ethiopian Highlands: 18000 years of Afromontane vegetation dynamics recorded in high altitude wetlands., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1340, https://doi.org/10.5194/egusphere-egu21-1340, 2021.

EGU21-5923 | vPICO presentations | SSP2.11 | Highlight

How dry was the LGM? A Biosphere-Hydrosphere modelling approach for the paleo-lake Chew Bahir and Omo-River catchment in southern Ethiopia

Markus L. Fischer, Felix Bachofer, Martin H. Trauth, and Annett Junginger

The formation of the East African Rift System led to the emergence of large topographical contrasts in southern Ethiopia. This extreme topography is in turn responsible for an extreme gradient in the distribution of precipitation between the dry lowlands (~500 mm a-1) in the surrounding of Lake Turkana and the moist western Ethiopian Highlands (~2,000 mm a-1). As a consequence, the prevailing vegetation is fractionated into a complex mosaic that includes desert scrubland along the Lake Turkana shore, woodlands and wooded grasslands in the Omo-River lowlands and the paleo-lake Chew Bahir catchment, afro-montane forests of the Ethiopian Highlands, and afro-alpine heath in most elevated parts. During the past 25 ka, southern Ethiopia has been exposed to significant climate changes, from a dry and cold Last Glacial Maximum (LGM, 25-18 ka BP) to the African Humid Period (AHP, 15-5 ka BP), and back to present-day dry conditions. These shifts in temperature and precipitation may have affected the vegetation pattern and landscape in the area, but environmental data especially from LGM times are rare. This is because in times of a dry climate the paleo-lake Chew Bahir was dried up and hence the climate record in lake sediments was interrupted.

In this study, we investigate the hydrological conditions during the LGM using a previously-developed lake balance model (LBM) for southern Ethiopia, which is now coupled with a new predictive vegetation model (PVM) to better understand the biosphere-hydrosphere interactions and thus possible precipitation thresholds. The PVM is based on the method of boosted regression trees using elevation and monthly precipitation as input to predict land-cover, tree-cover and vegetation greenness for a ~1 km grid covering the Omo-River, paleo-lake Chew Bahir, Lake Chamo and Lake Abaya catchments. We linked the PVM and the resulting land surface parameters with the LBM to model the impact of a changing land-cover to the actual evaporation. Furthermore, we used the glycerol dialkyl glycerol tetraethers (GDGT) based paleo-temperature and tropical lapse rate reconstructions from Mount Kenya to consider the orographic temperature distribution in southern Ethiopia during the LGM. Using both, we simulated different precipitation amounts from 100% to 50% compared to the modern-day multi-annual averages and their effect on vegetation and lake levels of paleo-lake Chew Bahir. Our biosphere-hydrosphere modelling approach suggests 25 to 30% lower moisture availability during the LGM compared to the modern conditions and provides a high-resolution spatial reconstruction of the potential prevailing vegetation in the southern Ethiopian region.

How to cite: Fischer, M. L., Bachofer, F., Trauth, M. H., and Junginger, A.: How dry was the LGM? A Biosphere-Hydrosphere modelling approach for the paleo-lake Chew Bahir and Omo-River catchment in southern Ethiopia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5923, https://doi.org/10.5194/egusphere-egu21-5923, 2021.

EGU21-12530 | vPICO presentations | SSP2.11

The highest altitude paleoecological record of early pastoralism in Africa

Graciela Gil-Romera, Lucas Bittner, David A. Grady, Laura S. Epp, Götz Ossendorf, Mekbib Fekadu, MIchael Zech, Lars Opgenoorth, Georg Miehe, and Henry F. Lamb

The advent of pastoralism in Eastern Africa is one of the most significant cultural transformations in the continent’s history. Traditionally, herding origins and its spreading routes have been studied in the lowlands and described as a complex and lengthy process that began before 4 ka BP and lasted until 1.3 ka BP. This cultural transition has long been argued to have been a process involving both environmental change and population movements. Given the current patchy archaeological data, most studies studies conclude that no single factor can be identified as a driver of the onset of herding in Eastern Africa, but almost all evidence is from lowland areas. The higher elevations of the Eastern African mountains are sensitive to climate and environmental change, so may be ideal for testing hypotheses of human-environmental relationships. However, the history of pastoralism in the African highlands, especially its connection with regional herding migrations and Holocene climate change, has thus far been poorly explored with few available records.

In this contribution, we provide evidence of early pastoral activities at high altitude in the Bale Mountains of southwest Ethiopia. We present a 4000-year multiproxy palaeoecological lacustrine sequence from Garba Guracha, a cirque lake at 3950 m asl, combining palaeoclimatic and palaeoenvironmental proxies. Our record indicates the distinctive presence of faecal fungal spores (Sporormiella, Cercospora, Podospora) and the expansion of pollen and sedaDNA from ruderal plants as early as 3.5 ka. To our knowledge, this is the highest altitude record of early animal husbandry traces on the continent. Coeval with the expansion of pastoralism indicators in Garba Guracha, we find important changes in the lake’s diatom community, as well as climate fluctuations reconstructed from biomarkers; these may be critical for understanding human occupation at high altitudes. However, archaeological studies conducted in the Garba Guracha basin have proved unfruitful in finding permanent settlements of herders, suggesting hypotheses of seasonal resource use.

We discuss different scenarios of pastoral expansion on the Eastern African highlands under changing local climates, as well as the general context of pastoralist migration across Eastern Africa.

How to cite: Gil-Romera, G., Bittner, L., Grady, D. A., Epp, L. S., Ossendorf, G., Fekadu, M., Zech, M., Opgenoorth, L., Miehe, G., and Lamb, H. F.: The highest altitude paleoecological record of early pastoralism in Africa, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12530, https://doi.org/10.5194/egusphere-egu21-12530, 2021.

EGU21-3453 | vPICO presentations | SSP2.11

Analysis of paleosol-based proxies from the Turkana Basin through paleo-landscape and paleoclimate reconstruction

Margaret Manning, Catherine Beck, and Emily Beverly

The Turkana Basin is world famous for its extensive outcrops that provide insights into the paleoclimate and paleolandscapes in which hominins evolved over the past ~4 Ma. The Nachukui Formation, part of the Omo Group, reflects basin-wide dynamic processes of interlaced sequences including floodplains, deltas, and river systems throughout the Plio-Pleistocene. Paleosols associated with floodplains of the fluvial systems provide a valuable window into better understanding key intervals within this record and are frequently associated with fossiliferous fluvial sequences. This study analyzed three paleosols taken from outcrops of the Kaitio and Natoo Members of the Nachukui Formation. In particular, the Kaitio Mmb was assumed to be simply a lacustrine environment deposited during the longest-lived part of Paleolake Lorenyang (~1.7-2 Ma). However, recent studies have worked to provide a more comprehensive understanding of this member, indicating it was a far more dynamic lacustrine margin than previously recognized. This research builds upon this stratigraphic framework to integrate paleosol-based geochemical proxies to better reconstruct the paleoclimate and paleoenvironment of West Turkana Kaitio (WTK). This includes 1) x-ray fluorescence (XRF) elemental analysis of bulk sediment, and 2) stable isotope analysis on both bulk sediment and pedogenic carbonates. These data allowed us to make estimates of mean annual precipitation (MAP), vegetation type, and paleotemperatures. Using the CalMag and CIA-K weathering indices, the MAP estimates range from 351-933 mm of rain/year, with the means for both proxies ranging from 351-917 mm with an average MAP of 761.75 mm. The CIA-K weathering index produced MAP values of 503-933 mm with an average 812.88 mm. Compared to modern average rainfall values in the basin (324.1-151.6 mm/yr), our MAP estimates indicate the basin experienced more precipitation in the Plio-Pleistocene than it does today. Pairing the geochemical data with our sedimentological assessment allowed us to better characterize these paleosols for a more in depth understanding of the depositional environment of the Kaitio Member. 

How to cite: Manning, M., Beck, C., and Beverly, E.: Analysis of paleosol-based proxies from the Turkana Basin through paleo-landscape and paleoclimate reconstruction, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3453, https://doi.org/10.5194/egusphere-egu21-3453, 2021.

EGU21-16309 | vPICO presentations | SSP2.11

High-resolution records of grain-size and depositional environment correlated to the Homo erectus Nariokotome Boy site, West Turkana, Kenya

Conner O'Reilly, Catherine C. Beck, Jeroen H. van der Lubbe, Craig S. Feibel, Bruce Wegter, and Andrew S. Cohen

The Turkana Basin in northern Kenya contains a robust record of hominin fossils, including Nariokotome Boy (discovered from the NK3 site), the most complete H. erectus specimen found to date. Understanding the paleoenvironmental context in which hominins such as H. erectus evolved has been an objective of decades of research in eastern Africa. Here, we present a study using grain size analyses to infer the paleoenvironmental conditions responsible for the deposition of the sedimentary sequences directly associated with NK3. We resampled a ~14 m interval at from the West Turkana Kaitio (WTK13) core, collected as part of the Hominin Sites and Paleolakes Drilling Project. This interval ties directly to the outcrop where Nariokotome Boy was recovered. By sampling continuously at 0.5 cm intervals (~7 yrs/sample), we document the paleoenvironment in ultra high-resolution (i.e. a scale relevant to a hominin life) that directly correlates to the NK3 site. Over 350 sediment samples were pre-treated to remove carbonate, biogenic silica, and other organic material from detrital material. Grain size distributions were measured on a Malvern Mastersizer 3000 using wet suspension. Based on these analyses, the interval was dominated by silt, which was further investigated using end-member modeling. A four end-member solution explained on average 99% of the population variability. The bottom of the interval was more coarse-grained, with an abrupt fining transition at 38.83 meter below surface (mbsf), which corresponds with the transition out of a tuffaceous interval (Natoo tuff) and into a pedogenically modified interval. This correlation is significant as the top of this tuff is the surface upon which Nariokotome Boy was recovered. Previous facies and grain size analyses revealed and quantified Turkana’s dynamic lake level history. However, our grain size analysis provides unprecedented resolution for the paleoenvironment during which Nariokotome Boy lived. Our 0.5 cm sampling resolution enables us to quantify depositional changes on a scale comparable with previous descriptive facies analyses and to refine transitions between paleosols, fluvial deposits, and lacustrine deposition at the interface of these three paleoenvironments enabling us to reconstruct a dynamic lakeshore environment during the lifetime of the Nariokotome Boy.

How to cite: O'Reilly, C., Beck, C. C., van der Lubbe, J. H., Feibel, C. S., Wegter, B., and Cohen, A. S.: High-resolution records of grain-size and depositional environment correlated to the Homo erectus Nariokotome Boy site, West Turkana, Kenya, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16309, https://doi.org/10.5194/egusphere-egu21-16309, 2021.

EGU21-7946 | vPICO presentations | SSP2.11

Multiproxy paleolimnological reconstruction of Lake Victoria’s environmental history, East Africa 

Giulia Wienhues, Yunuén Temoltzin-Loranca, Hendrik Vogel, and Martin Grosjean

Lake Victoria (LV), Africa’s largest lake is situated in the African Great Rift Valley. Due to its shallowness (max.68 m; mean 40 m) and limited river inflow, LV is very sensitive to variations in climate and lake level fluctuations. As a result, LV has undergone repeated low stand periods, or even complete desiccation during the Late Pleistocene with profound effects on the aquatic ecosystem. One example is the emergence of a unique biodiversity of endemic cichlid species following the lake’s last desiccation event during the last glacial and subsequent refilling commencing ~15,000 years ago.

In an interdisciplinary project we aim at reconstructing linkages between paleoenvironmental variability, disturbances and adaptive species radiation by combining approaches from paleogenomics, paleoecology and paleolimnology. For this purpose, four sediment cores along a depth-transect (near-shore to offshore), covering ca. the past 14,000 years, are analyzed.

We present first paleolimnological results of long-term changes of using (isotope-)geochemical indicators including: Sedimentary pigments and biogenic silica to infer aquatic productivity supported by micro X-ray Fluorescence (XRF) derived element geochemistry, 13C and 15N, and sedimentary phosphorus fraction analyses providing information on changes in sediment composition.

The results suggest that the infilling of the LV basin was a long-term step-wise process. This is shown by elevated and variable indicators for lithogenic input (e.g Ti, Zr and K) and interpreted as mobilization of substrate from the shorelines by a dynamic lake level prior to its stabilization in the Early and Mid-Holocene.  This process is mainly reflected in the core taken at the greatest water depth (65 m). Simultaneously, the aquatic productivity (BSi and chloropigments) increased rapidly after the refilling of the lake basin in the Late-Glacial. A gradual drying of the climate and a following shift to a more oxygenated water column is observed in the Mid-to Late Holocene indicated by a decline in chemically weathered material (e.g Rb/K & K/Al ratios) and abundance of Mn.

How to cite: Wienhues, G., Temoltzin-Loranca, Y., Vogel, H., and Grosjean, M.: Multiproxy paleolimnological reconstruction of Lake Victoria’s environmental history, East Africa , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7946, https://doi.org/10.5194/egusphere-egu21-7946, 2021.

EGU21-5020 | vPICO presentations | SSP2.11

Lake Chala 2k: the last two millennia of environmental change in equatorial East Africa

Inka Meyer, Irina Papadimitriou, Dirk Verschuren, and Marc De Batist

In order to disentangle natural climate variability from anthropogenically caused variations, environmental reconstructions of the past 2000 years have gained renewed scientific interest during the last ~20 years. Whereas climatic and environmental changes during this period, such as the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) are fairly well expressed in western Europe and the North Atlantic area, knowledge about equivalent changes in African climate and environment (e.g. changes in temperature and precipitation, monsoonal activity and resulting vegetation feedbacks) can be much improved. Here we present new results from Lake Chala, a crater lake in equatorial East Africa, based on sedimentary grain-size distributions. Notwithstanding the relatively minor clastic mineral component, we are able to discriminate between different aeolian and fluviatile sources of terrigenous material and to reconstruct temporal trends in their contribution to the sediment. This can be linked to both local environmental dynamics and changes in the large-scale monsoonal systems over the East African landmass. Our findings point to arid conditions during the MCA and humid conditions during the LIA, in support of regional hydroclimate history as reconstructed from other moisture-balance proxies. The results of this study form an important piece of the puzzle to better understand past changes in African environments, which is a key aspect in the debate about future climate change in one of the most climate-sensitive regions on the planet.

How to cite: Meyer, I., Papadimitriou, I., Verschuren, D., and De Batist, M.: Lake Chala 2k: the last two millennia of environmental change in equatorial East Africa, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5020, https://doi.org/10.5194/egusphere-egu21-5020, 2021.

EGU21-2123 | vPICO presentations | SSP2.11

Vegetation changes and sediment transfers in the catchment of Lake Alaotra, Madagascar

Nils Broothaerts, Vao Fenotiana Razanamahandry, Liesa Brosens, Benjamin Campforts, Liesbet Jacobs, Tantely Razafimbelo, Tovonarivo Rafolisy, Gert Verstraeten, Steven Bouillon, and Gerard Govers

To understand the driving processes for changes in African ecosystems and related problems such as soil degradation, it is crucial to gain insight in the relative importance of human disturbance and climate change. Madagascar is known for its particularly high erosion rates in the central highlands, yet the role of human disturbance versus natural processes are not well understood and is a topic of ongoing debate. Recent studies have challenged the traditional view that the currently observed intense erosion processes and sediment fluxes in Madagascar are mainly driven by recent large-scale deforestation. However, at present almost no quantitative data is available to couple vegetation dynamics and sediment fluxes over time in Madagascar. This study aims to provide more insight in landscape changes (vegetation changes, sediment mobilization and deposition) in central Madagascar, and in the specific role of man and climate. The study focuses on the 1800 km² catchment of Lake Alaotra, located ca 200 km northeast of Antananarivo. Lake Alaotra is formed in a graben system in the highlands of Madagascar, and is the largest freshwater lake of the country (400 km²). A pollen record from the lake was used to reconstruct regional vegetation changes. Radiocarbon dates of extracted pollen provide a detailed chronostratigraphic framework. Augerings and radiocarbon dates from floodplains and marshes in the catchment were used to reconstruct the sediment deposition history. The pollen record and charcoal data shows the vegetation changes over the last 3000 years. The main observed shift in vegetation is a transition from a woodland/grassland mosaic towards an open grassland, starting ca 1850 years ago, which coincides with the onset of human activities. Data on floodplain sedimentation show an increase in accumulation rates in the last 600 years, from ca 1 mm yr-1 to ca 30 mm yr-1, which can be linked to increased hillslope erosion rates during that time period. The sedimentation wave, however, does not reach Lake Alaotra nor the surrounding marshes as floodplains act as a buffer. Overall, this study provides a spatial and temporal integrated reconstruction of vegetation changes in the Lake Alaotra catchment and the link with sediment mobilization and deposition, thereby providing a better understanding of environmental changes in central Madagascar and its driving forces.

How to cite: Broothaerts, N., Razanamahandry, V. F., Brosens, L., Campforts, B., Jacobs, L., Razafimbelo, T., Rafolisy, T., Verstraeten, G., Bouillon, S., and Govers, G.: Vegetation changes and sediment transfers in the catchment of Lake Alaotra, Madagascar, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2123, https://doi.org/10.5194/egusphere-egu21-2123, 2021.

Palaeoproxy records during the Last Glacial Maximum (LGM) in Southern Africa have not offered consistent results regarding hydroclimate of the region. Similarly, models from the Palaeoclimate/Coupled Modelling Intercomparison Project (PMIP/CMIP) show varying results with regards to the movement of the Southern Hemisphere (SH) Westerlies. An equator-wards shift in the SH Westerlies has long been used to account for increased precipitation in Southern Africa during the LGM. Palynological studies have supported this narrative citing the presence of higher precipitation species during the LGM as evidence of increased precipitation. This project uses the fossil charcoal and pollen assemblages from Elands Bay Cave (EBC) and Boomplaas Cave (BPC) to quantify the change in Mean Annual Temperature (MAT) and Total Annual Precipitation (TAP) using the recalibrated age models at both sites to understand the change in hydroclimate of the region. These sites are both spatially and temporally ideal to track changes in the SH Westerlies with both sites recording floral assemblages from the Last Glacial Period, the LGM, and deglaciation at EBC in the Winter Rainfall Zone (WRZ) and BPC in the Year-round Rainfall Zone (YRZ). Both rainfall zones receive precipitation from mid-latitude frontal systems associated with the SH Westerlies. The YRZ is associated with both the mid-latitude frontal systems and tropical disturbances. A database of the modern-day distribution of the taxa identified in the stratigraphy at EBC and BPC was created using the Global Biodiversity Information Facility and paired with modern climate data from WorldClim to perform a Weighted Average – Partial Least Squares (WA-PLS) regression to predict MAT and TAP. Most of the WA-PLS regression models predict temperatures around 7°C at the LGM, consistent with regional records. The predicted TAP at the LGM is mostly lower than that of the Last Glacial Period. In the case of EBC in the WRZ, decreased precipitation is consistent with a decrease in intensity of the frontal system and/or a polewards shift in the SH Westerlies at the LGM. Similarly, decreased precipitation in BPC in the YRZ implies decrease in intensity of frontal systems and/or a polewards shift in the SH Westerlies. This poleward shift in the SH Westerlies has been demonstrated in some climate models, the parameters of which need further interrogation.

How to cite: Khumalo, W., Hare, V., and Pickering, R.: Effect of Southern Hemisphere Westerlies on hydroclimate and seasonality from the Last Glacial Maximum: Using the fossil charcoal and pollen records from Elands Bay Cave and Boomplaas Cave, South Africa, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11197, https://doi.org/10.5194/egusphere-egu21-11197, 2021.

EGU21-12322 | vPICO presentations | SSP2.11

The Holocene African Humid Period from Tibesti mountains (Chad): Contribution of the fossil assemblage and the oxygen isotopic composition from lacustrine diatoms

Yacoub Abdallah Nassour, Sylvestre Florence, Moussa Abderamane, Mazur Jean-Charles, Pailles Christine, Couapel Martine, Sonzogni Corrine, Alexandre Anne, Hoelzmann Philipp, Dinies Michele, and Kröpelin Stefan

During the Holocene (0-11.7 ka BP), the subtropical regions of Africa were characterized by very significant climatic changes. These changes were evidenced by variations in lake levels which reflect the balance between precipitation and evaporation (P-E) at the watershed scale. These climatic conditions are mainly associated with the dynamics of the African summer monsoon in relation with the location of the Intertropical Convergence Zone (ITCZ), which is modulated by summer insolation induced by the Earth's orbital parameters. This mechanism explains the wetter conditions observed from 11 ka BP to 5.5 ka BP in the Sahelo-Saharan zone. This period, called "Green Sahara" or "African Humid Period", was characterized by a green landscape, covered by grasslands and trees, dotted with numerous lakes, and incised by large river networks.
Despite the numerous studies carried out on the African Humid Period, there is a scarcity of data for quantifying source and origin of precipitation. The Lake Chad Basin (BLT) is a key region for paleoclimatic research because of its position reflecting main tropical atmospheric mechanisms and its endorheic morphology amplifying climatic signals. More particularly, the crater palaeolakes of Trou au Natron (Pic Toussidé) and Era Kohor (Emi Koussi) in the Tibesti mountains offer unique sedimentary archives that may record the climatic history of the Sahara.
This work aims to reconstruct the evolution of these crater palaeolakes, thanks to the oxygen isotopic composition of diatoms (18Odiatom), from the termination of the last deglaciation until the African Humid Period. The identification of the fossil diatom assemblages combined with the 18Odiatom values should give insights on the evolution of the limnological parameters, the relative depth, the chemistry, and the water isotopic composition of these palaeolakes.
The measurement of 18Odiatom is carried out using the IR-laser fluorination-isotope ratio mass spectrometry technique at the CEREGE stable isotope laboratory, after dehydration under a flow of nitrogen gas. The diatoms are purified at the CEREGE micropaleontology laboratory after decarbonation and organic matter oxidation. The taxonomic determination of diatoms is carried at CEREGE (France) and at the University of N’Djamena (Chad).
Preliminary results from the two Tibesti mountains records cover the Holocene wet period. They show significant variations in the d18Odiatom values and a distinct evolution of ecosystems as demonstrated by taxonomic assemblage of fossil diatoms. These results are compared with a reconstruction of the d18Odiatom from Lake Chad for the same period. This comparison evidenced substantial data for the reconstruction of the Holocene wet period, in terms of origin of water inflows in the basin, eg Tropical versus Mediterranean and lowland versus mountainous atmospheric processes, and on the reconstruction of the migration and the position of the ITCZ. These two questions are still speculative and will certainly provide data for global climate circulation models which are struggling to reproduce the climate in Saharan latitudes.

How to cite: Abdallah Nassour, Y., Florence, S., Abderamane, M., Jean-Charles, M., Christine, P., Martine, C., Corrine, S., Anne, A., Philipp, H., Michele, D., and Stefan, K.: The Holocene African Humid Period from Tibesti mountains (Chad): Contribution of the fossil assemblage and the oxygen isotopic composition from lacustrine diatoms, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12322, https://doi.org/10.5194/egusphere-egu21-12322, 2021.

EGU21-8608 | vPICO presentations | SSP2.11

Hydroclimate and atmospheric circulation over North Africa through the last two climatic cycles reconstructed from dust deposited off West Africa

Maxime Leblanc, Charlotte Skonieczny, Aloys Bory, Viviane Bout-Roumazeilles, Serge Miska, Romain Abraham, Marion Delattre, Julius Nouet, and Bruno Malaizé

On glacial to interglacial time scales, northern Africa fluctuated between arid to hyperarid states and much wetter conditions called African Humid Periods (AHP). These AHP are characterized by a major transformation of the Saharan hydrological cycle, favoring the development of vast fluvial networks, tropical flora and fauna in a region previously hyperarid. In the present-day context of global warming, it is crucial to understand the environmental mechanisms and responses associated with these dramatic swings between two extreme climatic states in order to improve the climatic projections. Numerous studies have been focused on the last AHP, which occurred at the beginning of the Holocene and corresponds to a period when insolation - governed by precession – and obliquity both reached their maximum almost synchronously, thus complicating the distinction of their respective roles. The study of older AHP corresponding to different orbital configurations is likely to provide some answers. However, finding climatic archives allowing the reconstruction of past changes in the Saharan hydrological cycle on longer timescales remains challenging (e.g., discontinuity of continental archives, preservation of tracers…). In this study, we propose to circumvent this difficulty by studying the Saharan dust deposited in marine sediments of the northeastern Atlantic tropical ocean. In fact, past modifications of Saharan dust deposited off West Africa can provide precious information on changes in environmental conditions in their source areas (aridity, weathering), as well as on changes in the characteristics of their atmospheric transport (pathways and strength). Here, we present a unique high-resolution (1 sample/200yrs) multi-proxy characterization of the dust deposited continuously through the last 240ka - a period punctuated by eight AHP - in the marine core MD03-2705 (18°05N; 21°09W; 3085 mbsl) retrieved from a bathymetric dome, 300 meters above the surrounding seafloor. Considering this particular environmental setting, the terrigenous fraction in this record is assumed to be predominantly of eolian origin. We combine the 230Th-normalized dust flux1 together with grain-size distribution, clay mineralogy and geochemical compositions in order to explore changes in the Saharan hydroclimate and atmospheric circulation over North Africa on millennial to orbital timescales, with a particular focus on the mechanisms associated with the recurrence of the AHP.

1Skonieczny et al., 2019 – Science Advances 5 (1) - eaav1887

How to cite: Leblanc, M., Skonieczny, C., Bory, A., Bout-Roumazeilles, V., Miska, S., Abraham, R., Delattre, M., Nouet, J., and Malaizé, B.: Hydroclimate and atmospheric circulation over North Africa through the last two climatic cycles reconstructed from dust deposited off West Africa, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8608, https://doi.org/10.5194/egusphere-egu21-8608, 2021.

EGU21-8650 | vPICO presentations | SSP2.11

Centennial to millennial-scale variability of Holocene climate and environmental dynamics in the western Mediterranean (Lake Sidi Ali, Middle Atlas, Morocco)

Johannes Schmidt, Cathleen Kertscher, Markus Reichert, Helen Ballasus, Birgit Schneider, Elisabeth Dietze, Rik Tjallingii, Abdelfattah Benkkadour, Abdselam Mikdad, Lukas Werther, Alexander Bolland, Sylvain Pichat, Hans von Suchodoletz, William Fletcher, Steffen Mischke, and Christoph Zielhofer

The Western Mediterranean region including the North African desert margin is considered one of the most sensitive areas to future climate changes. In order to refine long-term scenarios for hydrological and environmental responses to future climate changes in this region, it is important to improve our knowledge about past environmental responses to climatic variability at centennial to millennial timescales. During the last two decades, the recovery and compilation of Holocene records from the subtropical North Atlantic and the Mediterranean Sea have improved our knowledge about millennial-scale variability of the Western Mediterranean palaeoclimate. The variabilities appear to affect regional precipitation patterns and environmental systems in the Western Mediterranean, but the timescales, magnitudes and forcing mechanisms remain poorly known. To compare the changes in Holocene climate variability and geomorphological processes across temporal scales, we analysed a 19.63-m long sediment record from Lake Sidi Ali (33°03’ N, 5°00’ W, 2080 m a.s.l.) in the sub-humid Middle Atlas that spans the last 12,000 years (23 pollen-based radiocarbon dates accompanied with 210Pb results). We use calibrated XRF core scanning records with an annual to sub-decadal resolution to disentangle the complex interplay between climate changes and environmental dynamics during the Holocene. Data exploration techniques and time series analysis (Redfit, Wavelet) revealed long-term changes in lake behaviour. Three main proxy groups were identified (temperature proxies: 2ky, 1ky and 0.7ky cycles; sediment dynamic proxies: 3.5ky, 1.5ky cycles; hydrological proxies: 1.5ky, 1.2ky, 0.17ky cycles). For example, redox sensitive elements Fe and Mn show 1ky cycles and higher values in the Early Holocene and 1.5ky cycles and lower values in the Mid- to Late Holocene. All groups show specific periodicities throughout the Holocene, demonstrating their particular climatic and geomorphological dependencies. Furthermore, we discuss these periodicities relating to global and hemispheric drivers, such as the North Atlantic Oscillation (NAO), El-Niño Southern Oscillation (ENSO), Innertropical Convergence Zone variability (ITCZ) and North Atlantic cold relapses (Bond events).

How to cite: Schmidt, J., Kertscher, C., Reichert, M., Ballasus, H., Schneider, B., Dietze, E., Tjallingii, R., Benkkadour, A., Mikdad, A., Werther, L., Bolland, A., Pichat, S., von Suchodoletz, H., Fletcher, W., Mischke, S., and Zielhofer, C.: Centennial to millennial-scale variability of Holocene climate and environmental dynamics in the western Mediterranean (Lake Sidi Ali, Middle Atlas, Morocco), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8650, https://doi.org/10.5194/egusphere-egu21-8650, 2021.

EGU21-5417 | vPICO presentations | SSP2.11

Climate and land-use effects on hydrological and vegetation signals during the last three millennia in southwestern Morocco

Asmae Baqloul, Enno Schefuß, Martin Kölling, Lydie Dupont, Jeroen Groeneveld, Xueqin Zhao, Hanane Reddad, Lhoussaine Bouchaou, and Ilham Bouimetarhan

The southwest of Morocco is considered to be an area of refuge within the Mediterranean region, hosting the endemic tropical Argan tree. This region is presently subject to severe droughts, desertification, and land degradation, and likely facing increased climate variability and socio-economic stress in the future. Here, we use the stable hydrogen and carbon isotope composition (δD and δ13C) of plant-waxes in a high-resolution marine sediment core (GeoB8601-3) collected off Cape Ghir in southwestern Morocco, in combination with published data on pollen and XRF element ratios from the same archive. We aim to reconstruct the hydroclimate and vegetation history during the last 3000 years. Stable carbon isotope compositions of leaf waxes (δ13Cwax) show that natural vegetation in southwestern Morocco consists of C3 plants. Minor variations in δ13Cwax were positively correlated to changes in stable hydrogen isotope compositions of leaf waxes (δDwax) before 700 CE. Changes in rainfall amounts and water use efficiency indicate a clear vegetation response to precipitation changes and thus to climate forcing. After 700 CE, δDwax and δ13Cwax became de-coupled suggesting that the plant wax discharge and their isotope signals were no longer solely controlled by climate; the waxes likely mainly originate from the lowlands and carry an enriched (dry) δD signal but a depleted 13C signature. The depletion of δ13Cwax correlates with the increase of Argan pollen concentration in the record. The period between ~700 and 900 CE coincides with the Arabization of Morocco which had an impact on the demographic composition of the country leading to new agricultural habits and, as a result, on the land-use triggering a higher erosion of lowland material by the Souss River.

How to cite: Baqloul, A., Schefuß, E., Kölling, M., Dupont, L., Groeneveld, J., Zhao, X., Reddad, H., Bouchaou, L., and Bouimetarhan, I.: Climate and land-use effects on hydrological and vegetation signals during the last three millennia in southwestern Morocco, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5417, https://doi.org/10.5194/egusphere-egu21-5417, 2021.

Abstract: Changes in the global oceanic system have already negatively affected the world’s marine life and the livelihoods of many coastal communities across the world, including in the Middle East' and Eastern Africa's Least Developed Countries (LDCs). Coastal communities in Somalia and Yemen for instance, have been particularly affected by extreme environmental events (EEEs), with an increase in the frequency of tropical cyclones over the past 20 years. Using expert elicitation as a method to generate data to assess and quantify a specific issue in the absence of sufficient and/or reliable data, the authors interviewed selected specialists in or from Somalia and Yemen, from diverse fields of expertise related to climate change, extreme environmental events, disaster risk reduction, and humanitarian affairs. Ten experts followed the elicitation protocol and answered a specific series of questions in order to better quantify the expectable mid-to-long-term climatic and humanitarian levels of risks, impacts, and consequences that climate change and related issues (e.g., sea-level rise, tropical cyclones, and sea surge) may generate in coastal areas along the Gulf of Aden's coastal cities of Aden and Bossaso, in Yemen and Somalia, respectively.

The findings indicate that there is cause for significant concern as climate change is assessed by all interviewees - irrespective of their background -, as very likely to hold a negative to a devastating impact on (fresh) water security, food security, public health, social conflicts, population displacement, and eventually political stability; and to strongly worsen the humanitarian situations in Somalia and Yemen, both in the medium-term (i.e., 2020-2050) and the long-term (i.e., 2020-2100). The authors call on the scientific community to further research the issue of climate change in the understudied coastal areas of the Gulf of Aden, and on the international community to pro-actively and urgently help the local populations and relevant authorities to rapidly and strongly build up their adaptation capacities, especially in the niche of coastal EEEs.

How to cite: Lambert, L., Almehdhar, M., and Haji, M.: Climate Change, Humanitarian Risks, and Social-Political (In)stability Along the Gulf of Aden: Expert Elicitation for the Case of Somalia and Yemen, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7575, https://doi.org/10.5194/egusphere-egu21-7575, 2021.

EGU21-3465 | vPICO presentations | SSP2.11

Mechanisms and effects of dry and wet Sahel epochs

John T Bruun, Katy Sheen, and Mat Collins

The Sahel is Northern African region between the equator and the Sahara desert. It is home to a belt of semi-arid grassland that stretches from the Atlantic and across the continent westward towards the Red Sea. The monsoon type rainfall season that occurs in this region is influenced by the way that moisture transport along this belt region combines along the Inter Tropical Convergence Zone (ITCZ). The Sahel is one of the most productive crop areas of Africa, and if the rains fail – it has long lasting implications for its community. Due to its  planetary location dry conditions pervade the Sahel for most of the year, with food production and livelihoods reliant on the summer monsoon rainy season between July and September. In this study we use (where available) up to 100 years of re-analysis records (GPCC rainfall, NCAR wind and HadiSST ocean data) together with an accurate signal decomposition approach (dominant frequency state analysis, DFSA). With this we assess how the teleconnection influence of the Pacific ENSO and the Atlantic dipole mechanisms influence the dry and wet Sahel rain conditions. The severe Sahelian drought of the 1980’s is shown to be a compounded sequence of drying dynamic effects that combined to occur suddenly over the span of 5-10 years. Our work indicates that dry and wet conditions appear to be related to land-air evaporation and condensation in the vicinity of the Sahel river catchments, with the land locked Lake Chad catchment having a particularly sensitive arid climate. Our latest finding’s help explain how the Atlantic and Pacific physical mechanism influence the Sahel monsoon and its extremes. With an assessment of agricultural data we also show how agricultural growth in the region is impacted by these factors. We present and discuss Africa dry and wet rainfall epoch forecasts over the next 30 years for Sahel based on stable and altered climate hysteresis scenarios.

How to cite: Bruun, J. T., Sheen, K., and Collins, M.: Mechanisms and effects of dry and wet Sahel epochs, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3465, https://doi.org/10.5194/egusphere-egu21-3465, 2021.

EGU21-10196 | vPICO presentations | SSP2.11

Modern pollen distributions and their relationship with environmental gradient in Southern Morocco

Sokaina Tadoumant, Ilham Bouimetarhan, Martin Koelling, Asmae Baqloul, and Lhoussaine Bouchaou

      Terrestrial signals in marine sediment archives are frequently used for paleoclimate reconstructions. A little is known about the origin of terrestrial components such as pollen and spores, organic and inorganic elements in the sedimentary archives. The aims of this study is to investigate the geographic distribution pattern of pollen and spores in southern Morocco in relation to environmental gradients, and different transport mechanisms in order to link temporal variations in marine sediment cores to environmental changes in southern Morocco. Pollen taxa of Argania spinosa, Cichorioideae, Poaceae and Cyperaceae exhibit high percentages and concentrations in the semi-arid Souss Massa basin and the relatively humid Tensift basin accompanied with higher values of Fe/Ca and Ti/Al. Moreover, the simulation between distribution of Olea/Phillyrea and Ti/Al ratio suggests that Olea/Phillyrea are mainly dispersed by wind transport. However, Artemisia and Quercus distributions are limited to the south of High Atlas and the northern Anti Atlas. Chenopodiaceae, Caryophyllaceae , and Amaranthaceae (CCA) show a maximum percentages in littoral sites especially of Souss and Draa basins according to the important production of pollen quantities, the  high values of CCA from north to south of study area are indicated the starts of Saharan-type climate with increasing values of Acacia, Ziziphus, Asphodelus and Tamarix taxa may indicate plants adaptation to droughts, and/or a dominant aeolian transport. The South of Morocco which is known by higher wind inflows and low rainfall during the year occurring as occasional events during the winter, we conclude that pollen are primarily transported by the NE trade winds and occasionally with rivers in the basins.

How to cite: Tadoumant, S., Bouimetarhan, I., Koelling, M., Baqloul, A., and Bouchaou, L.: Modern pollen distributions and their relationship with environmental gradient in Southern Morocco, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10196, https://doi.org/10.5194/egusphere-egu21-10196, 2021.

EGU21-13018 | vPICO presentations | SSP2.11

Extreme weather associated with atmospheric rivers over Morocco

Abdou Khouakhi, Fatima Driouech, Louise Slater, Toby Waine, Omar Chafki, and Otmane Raji

Atmospheric rivers (ARs) are long, narrow, and transient corridors of enhanced water vapour content in the lower troposphere, often connected to the warm sector of extratropical cyclones and associated with strong low-level winds. These features play a major role in the global water cycle and drive weather extremes in many parts of the world. Here, we investigated the characteristics of landfilling ARs, including their frequency and magnitude over Morocco for the period 1979–2020. We used ECMWF ERA5 reanalysis data to detect and track landfilling ARs, and compared different gridded precipitation products (i.e. Integrated Multi-satellite Retrievals for GPM (IMERG), ERA5 Land, and CHIRPS) with a set of gauging stations datasets distributed across Morocco. We assessed AR association with rainfall at the annual and seasonal scales, as well as for extreme rainfall events, in different datasets. Preliminary results indicate that around 20 ARs/year make landfall or have their centroids within 200 km from Morocco. AR occurrence varies spatially and seasonally with highest occurrences in winter (DJF) across northern regions and spring (MAM) in the southern part of country. Rainfall events of up to 250 mm/year are driven by ARs; with the southernmost and driest regions receiving most of their rainfall from ARs. This paper will provide an overview of extreme rainfall and wind associated with ARs across Morocco.

How to cite: Khouakhi, A., Driouech, F., Slater, L., Waine, T., Chafki, O., and Raji, O.: Extreme weather associated with atmospheric rivers over Morocco, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13018, https://doi.org/10.5194/egusphere-egu21-13018, 2021.

EGU21-12310 | vPICO presentations | SSP2.11

Heat Waves Evolution in Senegal under Climate Change

Marie Jeanne G. Sambou, Benjamin Pohl, Serge Janicot, Adjoua Moise Famien, Pascal Roucou, Daouda Badiane, and Amadou Thierno Gaye

Following the high temperatures recorded in the Sahel during 2010 and most recently in May 2013 in the northern part of Senegal where the temperature oscillated between 45 and 50 degrees, significant human deaths were recorded. A good understanding of the dynamics of these heat waves thus become necessary not only to improve the prediction of these events, but also to better assess the impact of future climate change on the occurrence and intensification of these heat waves. To address this issue, simulated CMIP5 daily bias-corrected temperature data interpolated on a 0.5° grid over 1950-2099 have been used by focusing on 3 RCP (Representative Concentration Pathways) scenarios, RCP8.5, RCP4.5 and RCP2.6 . The heat waves in Senegal are defined by relying on exceeding of a moving percentile relative to maximum, minimum and mean temperature during 3 consecutive days over the MAM (March-April-May), the hottest season of the year. Senegal is characterized by a steep zonal temperature gradient from the coast to hinterland. In RCP8.5, the general temperature increase present for the last 60 years (+1.5°C) will continue and reach ~ +5°C in 2100. In this context, at the end of the century the mean temperatures of the western coastal zone will be similar to the present ones of the eastern continental zone, and the warmest spring seasons recorded over the last 15 years will be the norm around 2040. Then exceptional and yet unknown intense heat waves are planned and policy and decision makers will have to anticipate reliable adaptation strategies.

How to cite: Sambou, M. J. G., Pohl, B., Janicot, S., Famien, A. M., Roucou, P., Badiane, D., and Gaye, A. T.: Heat Waves Evolution in Senegal under Climate Change, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12310, https://doi.org/10.5194/egusphere-egu21-12310, 2021.

EGU21-261 | vPICO presentations | SSP2.11

MAX-DOAS measurements of NO2 and HCHO in the city of Kinshasa from 2019-2020

Rodriguez Yombo, Alexis Merlaud, Gaia Pinardi, Emmanuel Mahieu, Martina Friedrich, François Hendrick, Caroline Fayt, Michel Van Roozendael, Richard Bopili Mbotia Lepiba, Djibi Buenimio Lomami, and Jean-Pierre Mbungu Tsumbu

Recent studies in Kinshasa show how much air pollution is present in this large megalopolis of 13 million inhabitants, with levels even exceeding the recommended values (WHO, 2018).

From May 2017 to November 2019, the University of Kinshasa (UniKin: -4.42°S, 15.31°E) has equipped itself with a low-cost instrument operating in single-axis mode. Studies based on measurements made with this instrument have demonstrated the presence of NO2 with highest vertical column densities (VCDs) in June, July and August (R. Yombo, 2020). With this low-cost instrument, information such as aerosol and NO2 profile, which have major impacts on the determination of VCDs could not be obtained, leading to considerable uncertainties in the results obtained.

This work therefore supports the first one as described above, by presenting first results of a new MAX-DOAS (multi-axis differential optical absorption spectroscopy) system built at the IASB, in Belgium, and installed in Kinshsasa at the same location in November 2019. We first present the new MAX-DOAS, which is based on compact Avantes spectrometer (280-550 nm, 0.7 nm FWHM), a small computer, and a scanner.  We describe the analyses for aerosol extinction, HCHO and NO2 using FRM4-DOAS. For these two molecules, we compare with model simulations (GEOS-Chem) and satellite observations (OMI, TROPOMI).

How to cite: Yombo, R., Merlaud, A., Pinardi, G., Mahieu, E., Friedrich, M., Hendrick, F., Fayt, C., Van Roozendael, M., Bopili Mbotia Lepiba, R., Buenimio Lomami, D., and Mbungu Tsumbu, J.-P.: MAX-DOAS measurements of NO2 and HCHO in the city of Kinshasa from 2019-2020, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-261, https://doi.org/10.5194/egusphere-egu21-261, 2021.

SSP2.12 – Polar climate and environmental change throughout geological time

EGU21-10659 | vPICO presentations | SSP2.12

 Middle and Late Jurassic climatic, oceanographic and environmental trends along the Viking Corridor

Iben W. Hougård, Madeleine L. Vickers, Peter Alsen, Mads E. Jelby, Clemens V. Ullmann, and Christoph Korte

Keywords: Late Jurassic; palaeoclimate; Greenland; carbon cycling; Viking Corridor; belemnite stable isotopes

The “polar amplification” effect, whereby the poles experience greater changes in temperature compared to the low latitudes for a given global average temperature change, makes high-latitude isotope records ideally suited to investigate fluctuations in palaeoclimate. The present study investigates palaeoclimatic and oceanographic changes along the Viking Corridor – the narrow seaway that connected the Tethys to the Arctic Boreal Realm during the Middle and Late Jurassic.

Stable-isotope data obtained from belemnites from East Greenland, originating from along the western margin of the Viking Corridor, show a M. Bathonian warming trend, which may indicate the reopening of the corridor after North Sea doming. We also discuss various controls on the carbon-isotope record that may dampen or amplify global signals. Changes in local depositional settings caused partial overprinting of the δ13C record during the Late Jurassic VOICE event.

How to cite: Hougård, I. W., Vickers, M. L., Alsen, P., Jelby, M. E., Ullmann, C. V., and Korte, C.:  Middle and Late Jurassic climatic, oceanographic and environmental trends along the Viking Corridor, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10659, https://doi.org/10.5194/egusphere-egu21-10659, 2021.

EGU21-5021 | vPICO presentations | SSP2.12

Early Cretaceous glendonites of Arctic realm: distributions and their paleoclimate implication

Kseniya Mikhailova, Victoria Ershova, and Mikhail Rogov

In the middle of 20th century glendonites were purposed as an indicator of cold climate. There is no doubt that unique morphology and sizes of pseudomorphs occurring through Precambrian to Quaternary succession indicate uncommon geochemical environment. Here, we present an overview of Early Cretaceous glendonites distribution across Arctic which widely distributed here despite generally greenhouse climate conditions in Early Cretaceous.

Late Berriasian pseudomorphs are known on northeastern Siberia and Arctic Canada. Valanginian glendonites are the widest ones are described from the Northern and Western Siberia, Spitsbergen and the Arctic Canada. Late Hauterivian concretions were studied on Svalbard. Barremian and lower Aptian glendonites are unknown in this area due to wide distributed continental succession, but late Barremian glendonites were reported from the wells drilled on the Barents Sea shelf. Middle and Upper Aptian glendonites are found on Svalbard,  North Greenland, the Arctic Canada and North-East Russia. Lower Albian glendonites are found on Svalbard, islands of Arctic Canada and the Koryak Uplands.

Nowadays it is reliable known that the precursor of glendonites is an ikaite - metastable calcium carbonate hexahydrate, forming in a narrow temperature range from 0-4oC, mainly in near-bottom conditions. Besides low temperature, high phosphate concentrations that occurs due to anaerobic oxidation of methane and/or organic matter; dissolved organic carbon, sulfates and amino acid may favor to ikaite formation as well. However, glendonites associated with terrigenious rocks, often including glacial deposits, that allow to use them as a paleoclimate indicator.

Glendonites show a wide variability in form and size: from single crystal blades to stellate aggregates and rosettes, usually ranged from a few mm to dozens of cm. Mineralogical composition of pseudomorph is represented mainly by three calcite phases determining by CL-light. Both δ18O and δ13C of glendonites are characterized by a broad range of values. Oxygen isotope composition ranges from -14 to -0 ‰ Vienna Pee Dee Belemnite (VPDB), whilst  carbon isotope composition ranges from -52.4 to – 14 ‰ Vienna Pee Dee Belemnite (VPDB).

Based on received data we suggest that δ18O reflects the complex processes involved in ikaite-glendonite transformation, supposing mixing depleted fluids with seawater. Nevertheless, received data coincide with δ18O values reported from Paleozoic-Quaternary glendonites formed in near-freezing environments. Values of δ13C of glendonites is the result of both mixing seawater inorganic carbon and sedimentary organic diagenesis and close to bacterial sulfate reduction and/or anaerobic oxidation of methane or organic matter.

To conclude,  Early Cretaceous climate was warm generally, however studied pseudomorphs point to cold episodes in Late Berriasian, Valanginian, Late Hauterivian, Middle-Late Aptian and Early Albian.

The study was supported by RFBR, project number 20-35-70012.

How to cite: Mikhailova, K., Ershova, V., and Rogov, M.: Early Cretaceous glendonites of Arctic realm: distributions and their paleoclimate implication, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5021, https://doi.org/10.5194/egusphere-egu21-5021, 2021.

EGU21-9571 | vPICO presentations | SSP2.12

Climate changes across Oceanic Anoxic Event 1a: new data from the Boreal realm

Stephane Bodin, Carlette Blok, Jon Ineson, Kresten Anderskouv, Alicia Fantasia, Emma Sheldon, Nicolas Thibault, and Thierry Adatte
Our understanding of the climatic evolution during the early Cretaceous in general, and the Oceanic Anoxic Event 1a (OAE-1a) in peculiar, is widely derived from the investigation of Tethyan localities, leaving large uncertainties about their significance on a global scale. In this study, we have performed high-resolution clay-mineral assemblage analyses in the upper Hauterivian to lower Aptian of the North Jens-1 core, located in the Danish central graben that was part of the Boreal realm. High amount of detrital Kaolinite is observed throughout the core, indicating the presence of a local, kaolinite-rich source. A long-term decline in Kaolinite content is occurring from the lower Hauterivian to the lowermost, pre-OAE-1a Aptian, followed by a sharp rise within the OAE-1a. This trend is similar to the one observed in the Tethyan realm, indicating a supra-regional climatic evolution from humid conditions in the late Hauterivian toward drier conditions in the latest Barremian – earliest Aptian, followed by renewed humid conditions during the unfolding of OAE-1a. Precise timing of climate change during the OAE-1a differs however in between the Tethyan and Boreal realm. Shift toward humid conditions coincides hence with the onset of OAE-1a (segment C3) in the Tethyan realm, followed by a return to drier conditions in the second half of OAE-1a. In the Boreal realm, the onset of OAE-1a is characterized by a relatively dry climate, followed by the installation of humid climate during the mid-OAE-1a (segments C4-C5) that persists through the remainder of the early Aptian. Across latitudinal belts, there is thus a non-linear change in precipitation pattern during the unfolding of OAE-1a. Similar observations have been made for other OAEs, suggesting more complex weathering feedback mechanism during hyperthermal events than generally assumed.

How to cite: Bodin, S., Blok, C., Ineson, J., Anderskouv, K., Fantasia, A., Sheldon, E., Thibault, N., and Adatte, T.: Climate changes across Oceanic Anoxic Event 1a: new data from the Boreal realm, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9571, https://doi.org/10.5194/egusphere-egu21-9571, 2021.

Oceanic anoxic event (OAE) 1a documents a major perturbation of the Early Cretaceous global carbon cycle with severe consequences for the ocean-climate-biosphere system. While numerous studies over the past decades have provided a relatively detailed picture of the environmental repercussions of OAE 1a at low and mid-latitudes, studies from high latitudes, in particular the High Arctic, are limited. In this study, we present a high-resolution carbon isotopic and sequence stratigraphic framework for the lower to lower upper Aptian interval of the Isachsen Formation of the High Arctic Sverdrup Basin (Canada). These data enable us to precisely locate the stratigraphic position of OAE 1a in a deltaic sedimentary environment. The carbon isotope record allows, for the first time, identification of the different carbon isotope segments (CISs) of OAE 1a in the Sverdrup Basin and thereby correlation of the High Arctic record with sections from lower latitudes. Based on this improved chemostratigraphy, we revise the age of upper Paterson Island, Rondon, and Walker Island Members, important regional lithostratigraphic marker units. Whole-rock geochemical data record two episodes of marine incursion into the Sverdrup Basin during OAE 1a (CISs Ap3 and Ap6), which are interpreted as regional maximum flooding surfaces. This information is used in conjunction with detailed sedimentological logs and geochemical grain-size proxies to refine the sequence stratigraphic framework for the upper Isachsen Formation. We propose that transgressive-regressive cycles in the Sverdrup Basin were mainly controlled by the combined effects of eustatic sea-level changes and regional tectonic uplift, potentially related to the emplacement of Alpha Ridge, which culminated at ca. 122 Ma during CIS Ap9.

How to cite: Dummann, W., Schröder-Adams, C., Hofmann, P., Rethemeyer, J., and Herrle, J. O.: Carbon isotope and sequence stratigraphy of the upper Isachsen Formation on Axel Heiberg Island (Nunavut, Canada): High Arctic expression of oceanic anoxic event 1a in a deltaic environment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8196, https://doi.org/10.5194/egusphere-egu21-8196, 2021.

EGU21-10923 | vPICO presentations | SSP2.12

Paleoceanographic reconstructions from planktonic foraminifera across the Cenomanian/Turonian boundary and OAE 2 at southern high latitudes (IODP Site U1516, Mentelle Basin, Indian Ocean, SW Australia) 

Maria Rose Petrizzo, David K. Watkins, Kenneth G. MacLeod, Takashi Hasegawa, Brian T. Huber, Sietske J. Batenburg, and Tomonori Kato

Planktonic foraminiferal population dynamics and stable isotope data are presented to interpret environmental changes across the Cenomanian-Turonian boundary interval at Integrated Ocean Discovery Program (IODP) Expedition 369 Site U1516 in the Mentelle Basin (Indian Ocean, SW Australia). Site U1516 was located at 60°-62°S paleolatitude and it is the first high latitude locality in the Southern Hemisphere where planktonic foraminifera are consistently recorded across the Oceanic Anoxic Event 2 (OAE 2) interval and its associated positive δ13C excursion. Planktonic foraminifera and calcareous nannofossil biostratigraphy and stable isotopic results indicate the presence of a hiatus in the upper Cenomanian that spans the base of the δ13C excursion, thus the record of the onset of OAE 2 is not preserved. Nevertheless, correlation between the δ13C and δ18O profiles at Site U1516 and the European reference section at Eastbourne (England) allow identification of the Carbon Isotopic Excursion and, tentatively, of correlative local cooling consistent with the expression of the Plenus Cold Event at low latitudes.

Absolute abundances of planktonic and benthic foraminifera, and radiolaria combined with δ13C and δ18O measurements of both bulk carbonate and planktonic and benthic foraminifera provide clues concerning the paleoceanographic changes across OAE 2. In the lower part of OAE 2 and coinciding with the trough in the δ13C profile, the planktonic foraminiferal assemblages are dominated by small-sized (125-38 μm) opportunistic species and radiolaria indicating a dominantly eutrophic regime. An increase in benthic foraminiferal abundance may indicate a local increase of oxygenation during the interval of the Plenus Cold Event associated with high δ18O values, as observed at low latitudes. At Site U1516, the middle part of OAE 2 corresponding to the plateau phase of the δ13C profile is masked by absence of carbonate, highest TOC values, and high biogenic silica indicating this interval corresponded to a time of highly stressed eutrophic conditions with possible shoaling of the Carbonate Compensation Depth. Above this interval, bulk isotopic results are characterized by a decrease in δ13C values, CaCO3 increases associated with the abundance of opportunist planktonic species and apparently cyclic fluctuations in the absolute abundance of benthic foraminifera. These observations point to dominantly eutrophic conditions likely affected by upwelling of nutrient-rich and δ13C-depleted intermediate water masses.

Toward the top of OAE 2 across the C-T boundary interval, the planktonic foraminiferal assemblages show changes in composition with an overall increase in species diversity and continued cyclic fluctuations in absolute abundances. These features coupled with the foraminiferal species-specific δ13C and δ18O patterns reveal that Site U1516 occupied a paleoceanographic setting still affected by eutrophy likely related to enhanced input of nutrients. However, the occurrence of species that occupied relatively deep ecological niches indicates there were also episodes of stability with ecological/thermal stratification in the surface waters. This interval also records the highest sea surface water paleotemperatures values estimated as 20°-23°C based on δ18O values of foraminiferal shell and assuming seawater δ18O values of -1‰V-SMOW. Following the OAE 2 event and associated δ13C excursion, stable conditions in the water column were established.

 

 

How to cite: Petrizzo, M. R., Watkins, D. K., MacLeod, K. G., Hasegawa, T., Huber, B. T., Batenburg, S. J., and Kato, T.: Paleoceanographic reconstructions from planktonic foraminifera across the Cenomanian/Turonian boundary and OAE 2 at southern high latitudes (IODP Site U1516, Mentelle Basin, Indian Ocean, SW Australia) , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10923, https://doi.org/10.5194/egusphere-egu21-10923, 2021.

EGU21-10917 | vPICO presentations | SSP2.12

Maastrichtian-Rupelian paleoclimates in the southwest Pacific realm – a critical evaluation of biomarker paleothermometry and dinoflagellate cyst paleoecology at Ocean Drilling Program Site 1172

Peter Bijl, Joost Frieling, Margot J. Cramwinckel, Christine Boschman, Appy Sluijs, and Francien Peterse

Sea surface temperature (SST) reconstructions based on isoprenoid glycerol dialkyl glycerol tetraether (isoGDGT) distributions from the Eocene southwest (sw) Pacific Ocean are unequivocally warmer than can be reconciled with state-of-the-art fully coupled climate models. However, the SST signal preserved in sedimentary archives can be obscured by contributions of additional isoGDGT sources. We here use current proxy insights to assess the reliability of the isoGDGT-based SST signal in 69 newly analysed and 242 re-analysed samples covering the Maastrichtian to Oligocene from ODP Site 1172 (East Tasman Plateau, Australia) following state-of-the-art chromatographic techniques. We then reinterpret the record in context of paleo-environmental and paleoclimatologic reconstructions based on dinoflagellate cysts. Our ~130 kyr-resolution SST record reaffirms previous reconstructions of anomalous warmth in the early Eocene sw Pacific and remarkably cool conditions during the mid-Paleocene. Dinocyst diversity and temperature-sensitive taxa show a strong response to the local SST evolution, supporting the robustness of the marine biomarker record.  In addition, the long-term isoGDGT and dinocyst records provide further support for an apparent temperature control on compositional changes of branched glycerol monoalkyl glycerol tetraethers (brGMGTs), recorded in the same samples.

Soil-derived branched GDGTs (brGDGTs) stored in the same sediments are used to reconstruct mean annual air temperature (MAAT) of the nearby land through the MBT’5me proxy. General trends in SST and MAAT are similar, except for 1) an enigmatic absence of MAAT rise during the Paleocene-Eocene Thermal Maximum and Middle Eocene Climatic Optimum, and 2) a subdued middle–late Eocene MAAT cooling relative to SST. Both dinocyst assemblages and brGDGT indices (the isomerization index) suggest a mid-shelf depositional environment with strong river-runoff during the Paleocene-early Eocene, becoming more open marine thereafter. This trend reflects gradual drying and more seasonal precipitation regime in the northward drifting Australian hinterland. The overall correlation between dinocyst assemblages, biodiversity and SST changes suggests that temperature and associated environmental changes exert a strong influence on the surface-water ecosystem.

How to cite: Bijl, P., Frieling, J., Cramwinckel, M. J., Boschman, C., Sluijs, A., and Peterse, F.: Maastrichtian-Rupelian paleoclimates in the southwest Pacific realm – a critical evaluation of biomarker paleothermometry and dinoflagellate cyst paleoecology at Ocean Drilling Program Site 1172, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10917, https://doi.org/10.5194/egusphere-egu21-10917, 2021.

The Paleocene-Eocene bryozoans such as microporoideans, umbonulomorphs, lepraliomorphs as well as cerioporoidean cyclostomes are successful biota inhabited the marine and glacio-marine sequences in Antarctica. Changes in their taxonomic composition, associated faunas, colony growth-forms, biodiversity, skeletal mineralogy and geochemistry are important environmental/climatic indicators.

The earliest Cenozoic Antarctic bryozoan fossil records (late early Eocene) are well-documented from the shallow-marine–estuarine clastic succession of the lower part (Telm1-2) of the La Meseta Formation of Seymour Island, where the faunas are represented by massive multilamellar colonies, often spectacular in size and dominated by the cyclostome cerioporids and diverse ascophoran cheilostomes. The distinct free-living lunulitiforms, for the first time reported from Antarctica from the Ypresian/Lutetian of the middle part of the La Meseta Fm. (Telm4-6) are represented by the disc-shaped colonies, which are characteristic for the temperate warm, shallow-shelf environment, with the bottom temperature, which are never lower than 10 to 12°C (Hara et al., 2018). The skeletons of the Lunulites, Otionellina, and Uharella are formed by the intermediate-Mg calcite (IMC) with the 4.5 mol% MgCO3. The use of the X-ray diffraction (XRD) and the Laser Raman spectroscopy (Hara et al., in preparation) shows that they build the bimineralic skeletons (with the traces of aragonite, calcite and strontium apatite), which are indicative for the temperate shelf environment, sandy and often shifting substrate. Biogeographically, the free-living lunulitiforms (Lunulites and Otionellina) are valuable climatic indicators, inhabited in the Recent the circumtropical, tropical-subtropical to warm-temperate Australasian sand environments.

Contrary to that, the bryozoans of the Telm6-7 with a scarce lepraliomorphs tentatively assignated to ?Goodonia and accompanied by crustaceans, brachiopods and gadiform fish remains are known from the temperate environments.

The isotopic analyses of the δ18O of the bryozoan skeletons from the lower part of the La Meseta Fm. show the range of the temperature from 13.4°C to 14.6°C (according to the equation given by Anderson & Arthur 1983).

It is worth pointing that the middle Ypresian/early Lutetian bryozoans, which in the stratigraphical profile of the LMF document the nearly 10 MA evolutionary history of the bryozoans are well-correlated with the MECO event, what is also consisted with the isotopic data based on the macrofaunal marine fossil records (Ivany et al. 2008).

Anderson T.F., and Arthur M.A.1983. Stable isotopes of oxygen and carbon and their application to sedimentologic and paleoenvironmental problems. SEPM Short Course, 10: 1-151.

Hara U., Mors T., Hagstrom  and Reguero M. A., 2018. Eocene bryozoan assemblages from the La Meseta Formation of Seymour Island. Geological Quarterly, 62: 705-728. 

Hara U., Wrzosek B., and Mors, T. 2020. Calcite and aragonite distribution in the skeletons of bimineralic high-latitude bryozoans in the Raman spectroscopy (in preparation).

Ivany L.C., Lohmann K. C. Hasiuk F., Blake D.B., Glass A., Aronson R.B., and Moody R.M. 2008. Eocene climate record of the high southern latitude continental shelf: Seymour Island, Antarctica. Geological Society of America Bulletin, v. 120, no. 5-6: 659-678.

How to cite: Hara, U.: Environmental/climatic changes during the Eocene: biotic and geochemical evidences based on the bryozoan fauna (Antarctic Peninsula), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15673, https://doi.org/10.5194/egusphere-egu21-15673, 2021.

EGU21-12959 | vPICO presentations | SSP2.12

The timing of fjord formation and early glaciations in North and Northeast Greenland

Vivi Kathrine Pedersen, Nicolaj Krog Larsen, and David Lundbek Egholm

The timing and extent of early glaciations in Greenland, and their co-evolution with the underlying landscape remain elusive. In this study, we explore the timing of fjord formation in Northeast and North Greenland, between Scoresby Sund (70°N) and Independence Fjord (82°N). By determining the timing of fjord formation, we can improve our understanding of the early history of the Greenland Ice Sheet in these regions. We use the concept of geophysical relief to estimate fjord erosion volumes and calculate the subsequent flexural isostatic response to erosional unloading. The timing of erosion and isostatic uplift is constrained by marine sediments of late Pliocene-early Pleistocene age that are now exposed on land between ~24 and 230 m a.s.l. The late Pliocene-early Pleistocene sediments themselves attest to a time of limited ice cover in Greenland, with temperatures as much as 6-8 °C higher than present (e.g. Bennike et al., 2010).

We find that the northern Independence Fjord system must have formed by glacial erosion since the deposition of the marine late Pliocene-early Pleistocene sediments at ~2.5 Ma, in order to explain the current elevation of the sediments by erosion-induced isostatic uplift. In contrast, fjord formation in the outer parts of southward Scoresby Sund commenced prior to the Pleistocene, most likely in late Miocene, and continued throughout the Pleistocene with fjord formation progressing inland. Our results suggest that the inception of the Greenland Ice Sheet began in the central parts of Northeast Greenland before the Pleistocene and spread to North Greenland only at the onset of the Pleistocene. 

References:

Bennike, O., Knudsen, K.L., Abrahamsen, N., Böcher, J., Cremer, H., and Wagner, B., 2010, Early Pleistocene sediments on Store Koldewey, north­east Greenland: Boreas v. 39, p. 603–619, https://doi.org /10.1111/j.1502-3885.2010.00147.x.

How to cite: Pedersen, V. K., Larsen, N. K., and Egholm, D. L.: The timing of fjord formation and early glaciations in North and Northeast Greenland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12959, https://doi.org/10.5194/egusphere-egu21-12959, 2021.

EGU21-8345 | vPICO presentations | SSP2.12

Testing the synchronicity of Pleistocene biostratigraphic events in the central Arctic – Do we have a consistent biostratigraphic framework?  

Flor Vermassen, Helen K. Coxall, Gabriel West, and Matt O'Regan

Harsh environmental and taphonomic conditions in the central Arctic Ocean make age-modelling for Quaternary palaeoclimate reconstructions challenging. Pleistocene age models in the Arctic have relied heavily on cyclostratigraphy using lithologic variability tied to relatively poorly calibrated foraminifera biostratigraphic events. Recently, the identification of Pseudoemiliania lacunosa in a sediment core from the Lomonosov Ridge, a coccolithophore that went extinct during marine isotope stage (MIS) 12 (478-424 ka), has been used to delineate glacial-interglacial units back to MIS 14 (~500 ka BP). Here we present a comparative study on how this nannofossil biostratigraphy fits with existing foraminifer biohorizons that are recognised in central Arctic Ocean sediments. A new core from the Alpha Ridge is presented, together with its lithologic variability and down-core compositional changes in planktonic and benthic foraminifera. The core exhibits an interval dominated by Turborotalita egelida, a planktonic foraminifer that is increasingly being adopted as a marker for MIS11 in sediment cores from the Amerasian Basin of the Arctic Ocean. We show that the new age-constraints provided by calcareous nannofossils are difficult to reconcile with the proposed MIS 11 age for the T. egelida horizon. Instead, the emerging litho- and coccolith biostratigraphy implies that Amerasian Basin sediments predating MIS5 are older than the egelida-based age models suggest, i.e. that the T. egelida Zone is older than MIS11. These results expose uncertainties regarding the age determination of glacial-interglacial cycles in the Amerasian basin and point out that future work is required to reconcile the micro- and nannofossil biostratigraphy of the Amerasian and Eurasian basin.

How to cite: Vermassen, F., Coxall, H. K., West, G., and O'Regan, M.: Testing the synchronicity of Pleistocene biostratigraphic events in the central Arctic – Do we have a consistent biostratigraphic framework?  , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8345, https://doi.org/10.5194/egusphere-egu21-8345, 2021.

EGU21-7522 | vPICO presentations | SSP2.12

Revised Southern Ocean sea surface temperatures over the last 180 ka

David Chandler and Petra Langebroek

Proxy records and climate models suggest that the Last Interglacial (LIG, ~130 to 115 thousand years before present) was characterised by high-latitude air and sea surface temperatures (SSTs) slightly warmer than present, and by mean global sea level a few metres higher. Therefore, the LIG is widely used as an analogue for near-future oceanographic/climatic conditions. Of particular interest is the Antarctic Ice Sheet’s contribution to rapid sea level rise and to Southern Ocean surface freshening, in response to warming. In the Southern Ocean, existing LIG temperature reconstructions suffer from very high variance amongst a low number of individual records. Recent syntheses have focused on the LIG climatic optimum, but conditions during the penultimate glacial are also important for forcing transient climate or Antarctic Ice Sheet simulations. Here we use databases of modern core-top sediments to evaluate the strengths of SST proxies available in the Southern Ocean, and consider their likely sources of bias and variance. By selecting only those paleo-temperature reconstructions which we believe are reliable in this region, we then compile a Southern Ocean SST synthesis covering the penultimate glacial and the LIG. This longer temperature time series can be used as a basis for LIG ice sheet simulations or for climate model development.  

How to cite: Chandler, D. and Langebroek, P.: Revised Southern Ocean sea surface temperatures over the last 180 ka, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7522, https://doi.org/10.5194/egusphere-egu21-7522, 2021.

EGU21-1213 | vPICO presentations | SSP2.12 | Highlight

Reconstructing Antarctic winter sea-ice extent during Marine Isotope Stage 5e

Matthew Chadwick, Claire Allen, Louise Sime, and Xavier Crosta

Marine Isotope Stage (MIS) 5e marks the peak of the last interglacial (130-116 ka) and is an important ‘process analogue’ for understanding the high latitude climatic feedbacks and forcings active under future anthropogenic warming. Antarctic sea-ice extent is a critical component of the Earth’s climate system through its impact on global albedo and its roles in Southern Hemisphere atmospheric and ocean circulation. Published marine sediment core records are located too far north to accurately constrain the timing and extent of the winter sea-ice (WSI) minimum during MIS 5e (Chadwick et al., 2020) and researchers/models have therefore assumed that this minimum occurs synchronously with the Antarctic peak warming in ice core records (Holloway et al., 2017).

This study presents new reconstructions of Southern Ocean WSI extent for MIS 5e based on the diatom species assemblage records in marine sediment cores. These records have robust age models, which allow for the different timings and patterns of WSI retreat throughout the Southern Ocean to be examined. In particular, the difference between the relatively stable WSI extent in the Pacific sector of the Southern Ocean and the more dynamic WSI extent in the Atlantic sector of the Southern Ocean. Using sediment cores located south of 55 oS creates a novel synthesis for assessing the evidence for the considerable MIS 5e WSI reduction (67% in the Atlantic sector) predicted by model simulations (Holloway et al., 2017).

References

Chadwick M., Allen C.S., Sime L.C., Hillenbrand C-D. (2020). Analysing the timing of peak warming and minimum winter sea-ice extent in the Southern Ocean during MIS 5e. Quaternary Science Reviews, 229: 106134.

Holloway M.D., Sime L.C., Allen C.S., Hillenbrand C-D., Bunch P., Wolff E., Valdes P.J. (2017). The Spatial Structure of the 128 ka Antarctic Sea Ice Minimum. Geophysical Research Letters, 44 (21): 11129-11139.

How to cite: Chadwick, M., Allen, C., Sime, L., and Crosta, X.: Reconstructing Antarctic winter sea-ice extent during Marine Isotope Stage 5e, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1213, https://doi.org/10.5194/egusphere-egu21-1213, 2021.

EGU21-15799 | vPICO presentations | SSP2.12

Geochemical and sedimentological responses of Arctic glacial Lake Ilirney, Chukotka (Far East Russia) to palaeoenvironmental change since ~ 51.8 ka BP

Stuart Vyse, Ulrike Herzschuh, Andrei Andreev, Lyudmila Pestryakova, Bernhard Diekmann, Simon Armitage, and Boris Biskaborn

Palaeoenvironmental reconstructions with temporal coverages extending beyond Marine Isotope Stage (MIS) three are scarce within the data sparse region of Chukotka, Far East Russia. The objective of this work was to infer palaeoenvironmental variability from a 10.76 m long, radiocarbon and OSL dated sediment core from Lake Ilirney, Chukotka (67°21´N, 168°19´E). We performed acoustic sub-bottom profiling of the lake basin and analysed high-resolution elements (XRF), organic carbon (TC, TN, TOC), grain-size, mineralogy (XRD) and partly also diatoms and pollen from the core. Our results affirm the application of XRF-based sediment-geochemical proxies as effective tracers of palaeoenvironmental variability within arctic lake systems. Our work reveals that a lake formed during MIS 3 from ca. 51.8 ka BP, following an extensive MIS 4 glaciation in the Ilirney valley. Catchment palaeoenvironmental conditions during this time likely remained cold associated with the continued presence of a catchment glacier until ca. 36.2 ka BP. Partial amelioration reflected by increased diatom, catchment vegetation and lake organic productivity and clastic sediment input from mixed sources from ca. 36.2 ka BP potentially resulted in a lake high-stand ~15 m above the present level and may represent evidence of a more productive palaeoenvironment overlapping in timing with the MIS 3 interstadial optimum. A transitional period of deteriorating palaeoenvironmental conditions occurred ca. 30- 27.9 ka BP and was superseded by periglacial-glacial conditions from ca. 27.9 ka BP, during MIS 2. Deglaciation as marked by sediment-geochemical proxies commenced ca. 20.2 ka BP. Our findings are compared with lacustrine, Yedoma and river-bluff records from across Beringia and potentially yield limited support for a marked Younger Dryas cooling in the study area.

How to cite: Vyse, S., Herzschuh, U., Andreev, A., Pestryakova, L., Diekmann, B., Armitage, S., and Biskaborn, B.: Geochemical and sedimentological responses of Arctic glacial Lake Ilirney, Chukotka (Far East Russia) to palaeoenvironmental change since ~ 51.8 ka BP, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15799, https://doi.org/10.5194/egusphere-egu21-15799, 2021.

EGU21-10823 | vPICO presentations | SSP2.12

Catastrophic ice sheet break-up surrounding Baffin Bay coincident with the Younger Dryas and the Oldest Dryas/ Bølling-Allerød interstadial

Emma Ownsworth, David Selby, Jeremy Lloyd, and Sönke Szidat

The advance and retreat of the Greenland, Innuitian and Laurentide ice sheets (GIS, IIS, LIS) which surrounded Baffin Bay (West of Greenland) have been studied using numerous methods to gain insight into past ice sheet and ice stream dynamics. However, the exact timings, movements and relationships to climate events are still somewhat debated. Utilising osmium isotopes (187Os/188Os) as part of a multi-proxy strategy coupled with absolute age models, an enhanced understanding of the palaeoceanography and palaeoglaciology of this region for last ~40 kyrs is presented.

Carbonate-enriched layers recorded in many cores across Baffin Bay (Baffin Bay detrital carbonate - BBDC) are thought to be sourced from Palaeozoic carbonate rich rocks in the north/north-west of the bay which were covered by the IIS and LIS. Age modelling indicates that core JR175 records BBDC 0 and BBDC 1. Coincident with the BBDC events, hydrogenous 187Os/188Os compositions abruptly become more radiogenic. This suggests that alongside the carbonate delivery from the north of the bay, there is also a radiogenic Os source. Radiogenic Os derives from typically older, continental inputs, such as the Archean/Proterozoic terrains of western Greenland and Baffin Island. The seemingly sudden nature (within 1000 years) of the increase in 187Os/188Os would suggest a catastrophic ice sheet break-up and a period of increased iceberg discharge, or a sudden advance of the glacier outlets closer to the core site from the GIS and/or LIS.These events are also coincident with the Younger Dryas (~12.8 ka BP) and the end of the Oldest Dryas/ beginning of the Bølling–Allerød interstadial (~14.7 ka BP).

During periods of low carbonate enrichment, the 187Os/188Os values are less radiogenic. We invoke this to be a baseline during lower continental erosion periods and/or iceberg delivery, and more influence of oceanic Os from the Atlantic. Indeed, during the last 10 kyrs, 187Os/188Os values gradually decrease to compositions similar to the present day North Atlantic Ocean (~1.0).  This could represent increased mixing of marine Atlantic waters into Baffin Bay and/or a decrease in sediment delivery from all ice sheets representing the gradual retreat of the ice sheets through the Holocene.

In summary our data provide further insight into ice sheet advance, retreat, and sediment provenance within Baffin Bay during the past 40 kyrs, suggesting asynchronous behaviour of the surrounding ice sheets during theYounger Dryas and the end of the Oldest Dryas/ beginning of the Bølling–Allerød interstadial.

How to cite: Ownsworth, E., Selby, D., Lloyd, J., and Szidat, S.: Catastrophic ice sheet break-up surrounding Baffin Bay coincident with the Younger Dryas and the Oldest Dryas/ Bølling-Allerød interstadial, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10823, https://doi.org/10.5194/egusphere-egu21-10823, 2021.

EGU21-15494 | vPICO presentations | SSP2.12

Sedimentary processes on the continental slope north of Kvitøya (northern Barents Sea) – preliminary results from regional bathymetry and sediment cores

Christine Tømmervik Kollsgård, Jan Sverre Laberg, Tom Arne Rydningen, Matthias Forwick, Katrine Husum, and Amando Lasabuda

The continental margin of the northern Barents Sea is a key area for understanding the behavior and dynamics of the northern Barents Sea Ice Sheet, as well as the Arctic ocean circulation pattern during the Last Glacial Maximum, the deglaciation, and the Holocene.

In this study, we investigate the continental slope north of Kvitøya and Nordaustlandet (Svalbard) by analyzing the seabed morphology of the improved IBCAO 4.0 bathymetric grid (Jakobsson et al., 2020) and high-resolution sub-bottom profiles (CHIRP), one giant piston core and three gravity cores (4.61 to 18 m long). We present results from the multi-proxy analysis of the sediment cores, including lithostratigraphy, physical properties, grain-size distribution, XRF core scanning data, and radiocarbon dates.

The morphology of the Kvitøya Trough-Mouth Fan is generally smooth, with furrows 500 m wide and 200-500 m deep stretching from the shelf edge at around 250 m water depth to at least 3000 m water depth into the Arctic Ocean. The morphology of the continental slope east and west of the trough-mouth fan is smooth in the upper parts, and characterized by 3-5 km wide and 200-500 m deep channels and canyons cutting into the slope from a water depth of around 1000 to 3000 m.

The observations from the bathymetric data show that the trough-mouth fan buries channels and canyons, smoothing the morphology of the continental slope. The furrows are likely erosional features resulting from downslope activity such as debris flows and turbidity currents. In the inter-fan areas to the east and west, we interpret that the uppermost smooth morphology results from suspension fallout of sediments from the ocean currents flowing along-slope, indicating that these accumulations are contourites. The rugged topography further downslope possibly represents channel and canyon systems that are only partially buried, likely due to reduced influence from ocean currents at greater water depths. Analysis of the cores provides insight on the sediment properties of the contourites, debris flows, and turbidites, and radiocarbon dates shed light on the interplay and timing of the ocean current regime and the glacial dynamics.

 

Jakobsson, M., Mayer, L.A., Bringensparr, C. et al. The International Bathymetric Chart of the Arctic Ocean Version 4.0. Sci Data 7, 176 (2020). https://doi.org/10.1038/s41597-020-0520-9

How to cite: Kollsgård, C. T., Laberg, J. S., Rydningen, T. A., Forwick, M., Husum, K., and Lasabuda, A.: Sedimentary processes on the continental slope north of Kvitøya (northern Barents Sea) – preliminary results from regional bathymetry and sediment cores, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15494, https://doi.org/10.5194/egusphere-egu21-15494, 2021.

EGU21-10201 | vPICO presentations | SSP2.12

Distribution and paleoecology of benthic foraminifera of Denmark Strait in Holocene and late Pleistocene

Liubov Kireenko, Nina Kozina, and Anna Tikhonova

Holocene and Pleistocene benthic foraminifera assemblage patterns studied from 63 samples in sediment core AMK-5890 collected from Iceland's western slope in the Denmark Strait during the 71th cruise of research vessel"Academic Mstislav Keldysh" in 2018 (Novigatsky A.N, et al., 2018). Core were sampled at 1 cm interval from Holocene and 5 cm from Pleistocene and washed through a 63 micron sieve.

In the first complex of deposits represented by Holocene deposits the total benthic foraminifera abundance reaches highest values 35 000 – 60 000 individuals/g of dry sediment (ind/g of dry sed). In the lower part of the complex, abundance decreases to 10,000 ind/g of dry sed. The species diversity ranges from 25 to 35 species in the sample. Trifarina angulosa is the dominant species (about 60%). The species Cibicides lobatulus is subdominant (25-30%) in the Holocene community which lived in areas with increased hydrodynamic characteristics (Lorenz, 2005). The small group benthic foraminifera (from 2 to 15%) includes Atlantic and boreal species Cassidulina laevigata, Cassidulina neoteretis and Uvigerina peregrina (Sejrup et al, 2004). This database of distribution and ecology of benthic foraminifera indicated that in Holocene favorable living environment (positive bottom temperatures and salinity, close to modern sea), increased productivity and wide influence of Atlantic waters to the north existed. The lower part of complex reflects the epoch of deglaciation.

There are short changes in all measures at the boundary of Holocene and Pleistocene: total benthic foraminifera abundance (1000-400 ind/g of dry sed) and species diversity (<20 species) decreases, and species assemblage is almost completely changes. It allows to identify the second complex that characterizes the transition to glacial deposits. At the top of the glacial complex, the peak of occurrence of Cibicidoides wuellerstorfi (about 25%) associates with a decrease in the influence of meltwater and active hydrodynamics (Struck, 2007). The glacial assemblage consists of two dominant species C. lobatulus (about 35%) and Cassidulina obusta (about 40%). Also, there are Cassidulina reniforme, Elphidium clavatum and Nonion labradoricum, which prefer cold waters and Arctic environmental conditions with the presence of ice cover.

 Acknowledgments: Preparation, processing of samples and micropaleontological analysis was funded by RFBR, project number 20-35-90093. The expedition studies was funded by RPF, project number 14-50-00095, the primary lithological-mineralogical and geochemical studies was funded of the State assignment of the FANO of Russia (№ 0149-2019-0007).

How to cite: Kireenko, L., Kozina, N., and Tikhonova, A.: Distribution and paleoecology of benthic foraminifera of Denmark Strait in Holocene and late Pleistocene, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10201, https://doi.org/10.5194/egusphere-egu21-10201, 2021.

EGU21-10875 | vPICO presentations | SSP2.12

Deglacial records of terrigenous organic matter accumulation off the Yukon and Amur rivers using lignin phenols and long-chain n-alkanes as biomarkers

Mengli Cao, Jens Hefter, Ralf Tiedemann, Lester Lembke-Jene, and Gesine Mollenhauer

Anthropogenic climate change has profound impacts on Arctic temperatures, with consequences for Arctic ecosystems and landscapes, and the stability of organic-rich permafrost deposits. When mobilized, these permafrost deposits might release vast amounts of greenhouse gases. We use periods of past rapid warming in the high latitudes as analogues to study the ecological changes and effects on permafrost stability under climate change. We used marine sediment cores from the Bering and Okhotsk Sea continental margins, off the mouths of the Yukon and Amur rivers, to study two types of terrigenous biomarkers, which trace different terrestrial organic carbon (OC) components and transport pathways, and cover the early deglaciation to the early Holocene. The Yukon basin remains within the permafrost-affected region today, whereas the Amur basin changed from being subject to complete permafrost cover during the last glacial to permafrost-free conditions today. 

Vascular plant-derived lignin phenols were analyzed and compared to published n-alkane content data. The carbon- and sediment-normalized contents of the vanillyl phenols (V), syringyl phenols (S), and cinnamyl phenols (C) phenols (Λ8 and Σ8) reflect the content of lignin dominantly transported by river runoff. The C/V and S/V ratios serve to distinguish between woody and non-woody tissues of angiosperms and gymnosperms. The acid to aldehyde ratios of V and S phenols ((Ad/Al)V and (Ad/Al)S) indicate the degree of lignin degradation. In addition, the ratio of 3,5-dihydroxybenzoic acid to V (3,5Bd/V) likely reflects the wetland extent, while lignin reflects primarily transportation into the marine sediment via surface runoff. In contrast, the n-alkane contents represent primarily terrigenous organic matter eroded from deeper deposits and a second marker for wetland extent via the Paq index. Lignin and n-alkane mass accumulation rates (MAR) can thus be used to reconstruct the mobilization of different carbon pools and the relative timing of the processes leading to their export to the ocean.

The MAR of biomarkers and the wetland indicators 3,5 Bd/V and Paq start to increase in the Bering Sea sediment during the early deglaciation (19-14.6 ka BP), while no obvious change in lignin MAR in the Okhotsk Sea occurred during this time. We observe distinct peaks of mass accumulation rates, wetland indices and indicators for degradation of lignin (Ad/Al) in both sediment cores during the warm Bølling-Allerød (12.9-14.6 ka BP) and Pre-Boreal (9-11.5 ka BP) intervals, and during the Younger Dryas cold spell (11.5-12.9 ka BP). In contrast, in the Okhotsk Sea, the ratios of S/V and C/V did not change before the Preboreal. 

Our biomarker data suggest that the permafrost in the Yukon basin may have started to be remobilized by inland warming leading to wetland development in the early deglaciation, while the onset of permafrost degradation in the Amur basin occurred during the Preboreal.

How to cite: Cao, M., Hefter, J., Tiedemann, R., Lembke-Jene, L., and Mollenhauer, G.: Deglacial records of terrigenous organic matter accumulation off the Yukon and Amur rivers using lignin phenols and long-chain n-alkanes as biomarkers, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10875, https://doi.org/10.5194/egusphere-egu21-10875, 2021.

EGU21-14641 | vPICO presentations | SSP2.12

Southern Hemisphere Westerly Winds and Holocene climate variability on sub-Antarctic South Georgia

Maaike Zwier, Anne Bjune, and Willem van der Bilt

The Southern Hemisphere Westerly Winds play a major role in the global climate system. By driving circulation in the Southern Ocean and its subsequent effect on the upwelling of carbon-rich deep water, the Westerlies affect the oceans ability to take up atmospheric CO2. Furthermore, by impacting temperature conditions and moisture availability, the Westerlies act as a first-order control on local environmental conditions. Uncovering long term natural climatic variability in the sub-Antarctic is therefore crucial to understand how the global system might react under future climate changes. Due to the lack of land mass on the Southern Hemisphere, sub-Antarctic islands are essential for studying climate variability in this region; terrestrial records provide valuable insights into both local and regional surface climate conditions. We use a pollen record from Lake Diamond to provide detailed reconstructions of vegetation and climate on sub-Antarctic South Georgia for the last ~9900 years. Westerly Wind strength and position is inferred from long-distance transport of pollen from South America, Africa, and New Zealand. Additionally, changes in relative pollen abundance of native taxa occupying either upland (cold) or lowland (warm) environments are used to infer local climatic variation, supported by additional sedimentological proxies. On South Georgia we find long-distance transported pollen from several South American taxa, mainly Nothofagus, Ephedra and Asteraceae. They show a general increase in abundance throughout the Holocene, with peak influx between 2800 and 1500 cal yr BP, most likely caused by changes in the strength of the Southern Hemisphere Westerly Winds. In both our record and others, this interval is seen as the end of the Neoglacial period.

How to cite: Zwier, M., Bjune, A., and van der Bilt, W.: Southern Hemisphere Westerly Winds and Holocene climate variability on sub-Antarctic South Georgia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14641, https://doi.org/10.5194/egusphere-egu21-14641, 2021.

EGU21-3651 | vPICO presentations | SSP2.12

Climate related variations in atmospheric nitrous oxide concentration during the Mid- to Late Holocene

Syed Azharuddin, Jinho Ahn, Yeongjun Ryu, and Ed Brook

Nitrous oxide (N2O) is an important greenhouse gas with sources that respond to the biogeochemical processes on land and ocean. The major sources of atmospheric N2O are nitrification and denitrification occurring in terrestrial soils and the ocean. Here we present a new high-resolution atmospheric N2O record obtained from South Pole Ice (SPICE) core site covering the Mid- to Late Holocene (since ~5.5 ka). The N2O analysis was performed in a specialised wet extraction facility installed at Seoul National University that used small ice samples (<20 g) to yield a high precision (average standard deviation of ~1ppb) record. The new N2O data agree well with existing records on the millennial scale and reveal new details on the multi-centennial scale. Our results show a progressive increase in atmospheric N2O during 5.5 to 3.2 ka which correlates well with the increase of marine denitrification around the Arabian Sea (AS) and Peru-Chile Margin (PCM) as well as Indian monsoon precipitation around the same period. A local minimum in N2O is observed around 2.8 ka, possibly related to a sudden decrease in Western Tropical South (WTS) Pacific sea surface temperature and increased La-Nina like conditions which may have supressed denitrification along PCM. These conditions may have further influenced the monsoons and reduced denitrification in land soils. Our record also shows a local N2O maximum around 2.2 ka which may correspond to relaxed La-Nina like conditions around WTS Pacific. Subsequently, the N2O further dropped to attain a pronounced minimum around 1.4 ka. Similar N2O minima are also observed in Styx (Antarctica) and  NEEM (Greenland) ice core records, demonstrating the robustness of the signals.

How to cite: Azharuddin, S., Ahn, J., Ryu, Y., and Brook, E.: Climate related variations in atmospheric nitrous oxide concentration during the Mid- to Late Holocene, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3651, https://doi.org/10.5194/egusphere-egu21-3651, 2021.

SSP3.1 – Limnogeology - reading the geological record of lakes

EGU21-15832 | vPICO presentations | SSP3.1

Paleoenvironmental reconstruction of the central Levantine Corridor during the Pliocene: insights from lacustrine settings 

John Greenlee, Silas Dean, and Nicolas Waldmann

This study aims to reconstruct the paleoenvironmental and climatic conditions affecting the Levantine corridor during the early Pliocene. For the purpose of this study, a ~20 m continuous core sequence was retrieved out of the ~200 m long, tilted Erk el Ahmar sequence previously dated by cosmogenic isotopes to ~3.5 Ma. The record include intercalating units consisting of sands, silts, and clays that were sampled in high resolution in order to analyze a variety of sedimentological and geochemical proxies of past climate and environmental changes. We present new preliminary, high-resolution sedimentological (laser diffraction granulometry), petrophysical (magnetic susceptibility) and compositional (X-ray fluorescence) data along with accompanying statistical analysis performed with an advanced suite of data-science tools. These results reveal new cycles of environmental change in the area, which appears to be orbitally controlled, and include dramatic changes also indicated by discrete strata of fossil fragments. Moreover, cycles of deposition can also provide hints on the major hydrological controlling mechanisms. This project provides new light into favorable conditions for the subsistence of perennial lake environments in the Levantine Corridor, which in turn may have facilitated faunal migration between Africa and Eurasia.

How to cite: Greenlee, J., Dean, S., and Waldmann, N.: Paleoenvironmental reconstruction of the central Levantine Corridor during the Pliocene: insights from lacustrine settings , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15832, https://doi.org/10.5194/egusphere-egu21-15832, 2021.

EGU21-14361 | vPICO presentations | SSP3.1

Depositional history of Lake Chala (Mt. Kilimanjaro, equatorial East Africa) from high-resolution seismic stratigraphy

Aihemaiti Maitituerdi, Maarten Van Daele, Dirk Verschuren, Marc De Batist, and Nicolas Waldmann

Sediments deposited in Lake Chala constitute a high-resolution archive of past climate and environmental change in equatorial East Africa spanning two glacial-interglacial cycles. To correctly interpret the proxy records it contains, it is crucial to understand the evolution of lacustrine sedimentation in this volcanic crater basin since its formation on the lower south-eastern slope of Mt. Kilimanjaro. A dense grid of 37 km high-resolution seismic-reflection profiles allowed the reconstruction of the depositional history of Lake Chala. The seismic-stratigraphic sequence comprises sixteen distinct and finely-stratified units (U1-U16, youngest to oldest), grouped into five major depositional stages. Depositional stage I (U16, ~243-198 ka) marks the initiation of sedimentation in the originally ring-shaped depositional area surrounding two central tuff cones emerging from the basin floor and is characterized by a high rate of sediment accumulation and frequent occurrence of mass-wasting events (MWEs) under conditions of a relatively low lake-surface level compared to today. Depositional stage II (U15-U12, ~198-114 ka) represents the onset of basin-wide sedimentation above the central tuff cones, implying a higher position of the lake surface, less sediment focusing, and a shift to more strictly hemipelagic sedimentation. Multiple large-scale slope failures occurred around the basin periphery accompanying the progressive rise in lake level. Depositional stage III (U11-U8, ~114-97 ka) represents the development of a relatively flat lake floor under a significantly lower lake level, with evidence for strong sediment focusing implying accelerated sediment accumulation in central bottom areas. Depositional stage IV (U7-U4, ~97-20 ka) is again characterized by largely undisturbed hemipelagic sedimentation under mostly high lake-level conditions. However, frequent occurrence of mass-wasting events (MWEs) after ~48 ka resulted in the development of a longer, more gentle bottom slope towards the basin center. Depositional Stage V (U3-U1, ~20 ka BP to Present) represents the most recent period of basin evolution, during which the frequent occurrence of basin-focused sedimentation under a fluctuating lake surface level contributed to the establishment of the present-day very broad and flat basin floor of Lake Chala. Extrapolation of sedimentation rates established for the uppermost part of the sediment sequence, supplemented with basin-morphometric inferences derived from the successive depositional stages, yields an estimated age of ~243 ka for the oldest sediments in Lake Chala.

How to cite: Maitituerdi, A., Van Daele, M., Verschuren, D., De Batist, M., and Waldmann, N.: Depositional history of Lake Chala (Mt. Kilimanjaro, equatorial East Africa) from high-resolution seismic stratigraphy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14361, https://doi.org/10.5194/egusphere-egu21-14361, 2021.

EGU21-12393 | vPICO presentations | SSP3.1

Lake Chala turbidites produced by surficial slope sediment remobilization: A mechanism to bring near-shore macrofossils to the deep basin with only limited time offset

Maarten Van Daele, Violeth Swai, Thijs Van der Meeren, Christian Wolff, Inka Meyer, Nicolas Waldmann, Christine Lane, Marc De Batist, and Dirk Verschuren

In paleoclimate and paleoenvironmental studies, turbidites are usually considered as interruptions of the sedimentary sequence and therefore ignored. However, turbidites are composed of sediments from the (shallow) slopes along the lake’s periphery where fossil assemblages are often different to those in the deep basin. Turbidites may thus be valuable as carriers of this near-shore proxy information to a profundal core site. However, as turbidites are composed of reworked (older) sediments, their fossil content can only be exploited if their “mean time offset” can be readily estimated or ascertained to be minimal.

Several recent studies have shown that turbidites can indeed form as a result of surficial slope sediment remobilization, a process – independent of slope failure – in which only a thin veneer (20 cm) of surficial sediment is being remobilized, for example by earthquake shaking, and subsequently transported by a turbidity current. However, demonstrating that this process is active in a basin and determining the remobilization depth, is challenging, especially in the absence of slope cores. Here we study the turbidite record of the 215 m (~260 kyr) long composite core of Lake Chala in the framework of the ICDP project DeepCHALLA. We analyzed its sediment color at a 0.5-cm interval using a spectrophotometer and determined the average color for each of the 391 thickest turbidites (> 3 datapoints) in the L*a*b* color space. For the entire dataset, we performed a linear regression of the turbidite color against the average color of different intervals (2-55 cm) of laminated sediment below. For each combination of paired values, the highest R² values are found for the upper 7-15 cm of matrix sediment below the turbidites, which can thereby be interpreted as the average remobilization depth. These results are mainly based on the a* value, which shows (i) relatively poor correlations between adjacent intervals of laminated sediment (thereby not smearing the signal), and (ii) the most constant values in sediments from across the basin as determined by short-core transects. Depth-dependent variations of sediment color as determined from these transects further allows to estimate the water depth from which the turbidites were sourced.

Our results show that the sediments of most Lake Chala turbidites are 100-200 yrs older than the laminated sediments upon which they are deposited. We conclude that the turbidites can be used as ‘sampling windows’ to study temporal trends in macrofossils such as ostracods, chironomids and fish teeth, which are much more common along the basin periphery than in the deep basin.

How to cite: Van Daele, M., Swai, V., Van der Meeren, T., Wolff, C., Meyer, I., Waldmann, N., Lane, C., De Batist, M., and Verschuren, D.: Lake Chala turbidites produced by surficial slope sediment remobilization: A mechanism to bring near-shore macrofossils to the deep basin with only limited time offset, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12393, https://doi.org/10.5194/egusphere-egu21-12393, 2021.

EGU21-2997 | vPICO presentations | SSP3.1

Short, sharp shelves: unravelling palaeoenvironmental controls on sediment supply across active rift-margins to deep-water lakes

Tim Cullen, Richard Collier, Robert Gawthorpe, David Hodgson, Marco Maffione, Katerina Kouli, and Haralambos Kranis

Deep-water systems in active rift margins are complex, highly dynamic, and often characterised by short, steep source-to-sink configurations promoting high and sustained sediment supply to substantially underfilled, deep-water depocentres. The timing and character of coarse siliciclastic sediment delivery to deep-water environments in active rift basins is governed by complicated interactions of tectonics, climate, eustasy, and shelf process regime. However, existing sediment-supply models are largely geared towards longer term changes (~106 yrs) in tectonics, or eustatic variability, with relatively limited consideration for higher order (104-105 yrs) changes in catchment sediment flux due to the difficulty in deconvolving controls at these timescales. In the case of deep-lacustrine, syn-rift systems, the excess accommodation resulting from substantial subsidence, limited storage in short or absent shelves, and suppressed water-level variability in lacustrine settings, means climate-controlled catchment sediment flux may become a dominant allogenic control on mesoscale stratigraphic architecture. However, well-constrained conceptual models and examples of the stratigraphic record of sediment supply variability to deep-water syn-rift lakes are rare due to the paucity of exhumed deep-water syn-rift systems.

The West Xylokastro Fault Block, on the southern margin of the Gulf of Corinth, Greece presents an exhumed Early-Mid Pleistocene deep-lacustrine syn-rift fan system of the Rethi-Dendro Formation. The stratigraphic correlation possible in the West Xylokastro Fault Block permits the tying of stratigraphic architecture recorded in the up-dip Ilias fan-delta, supplying sediment to the deep-water realm, and their stratigraphy and palaeoenvironmental record down-dip. Through combining fieldwork, digital-outcrop investigation with palynological and palaeomagnetic sampling of a behind-outcrop research borehole, a chronostratigraphically-constrained palaeoenvironmental record reveals important changes in sediment supply variability to the deep-water consistent with obliquity-paced oscillations of forest coverage and glacial-interglacial climate variability. Integration of the borehole data, with outcrop observations, highlights that thick, laterally pervasive mudstone intervals can be tied to transgressions of the fan delta, interpreted to be related to sediment supply shutdowns. Sediment supply shutdowns occur during the warming phase of the most severe interglacials of the Early Pleistocene, where the palynological record shows the substantial expansion of warm-temperate, forested vegetation biomes. The role of vegetation in governing sediment supply, through hindering sediment erosion and transport from a catchment, has commonly been linked to reduced sediment yields throughout interglacials. However, the observations in the West Xylokastro stratigraphy highlight that such a model may not appropriate for very severe interglacials where highstand conditions may become highly seasonal, with semi-arid or dry summers, but with very large storms in winters and/or too warm to sustain lowland forests. In these conditions more open, scrubland vegetation permits the erosion and transport of coarse-grained material to the deep-lacustrine fan during the interglacial highstand.

The study informs new conceptual models for climate- and vegetation-controlled sediment supply to deep-water in active margins, which highlight the substantial potential complexity of palaeoenvironmental controls on sediment flux. Binary interglacial vs glacial sediment supply models are likely insufficient for characterising the complexity presented by deep-water syn-rift stratigraphy and highlights a greater need for deep-water stratigraphers to identify suitable proxies (such as palynology) for constraining palaeoenvironmental change.

How to cite: Cullen, T., Collier, R., Gawthorpe, R., Hodgson, D., Maffione, M., Kouli, K., and Kranis, H.: Short, sharp shelves: unravelling palaeoenvironmental controls on sediment supply across active rift-margins to deep-water lakes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2997, https://doi.org/10.5194/egusphere-egu21-2997, 2021.

EGU21-15108 | vPICO presentations | SSP3.1

Climate change in Southern Ural according to the Lake Bannoe sediments investigations

Yusupova Anastasia, Kuzina Dilyara, Nurgalieva Nouria, Krylov Pavel, and Antonenko Vadim

The work is devoted to studying the climate change in last millennia in South Ural on the basis of geochemical and petromagnetic data. The object of research is sediments of Bannoe lake sediments, which is located in republic of Bashkortostan (55°35’48”N 58°37’47” E). The average depth of the lake is 10.6 m, the maximum depth of the lake is 28 m, length 4.17 km, average width 1.88 km. The surface area of the lake is 7.7 km2.

Four cores from 3.8-5.14 m long were taken based on seismoacoustic data. Core samples were cut into 2 cm.

For constructing comprehensive paleoenvironmental reconstructions radiocarbon ages of 9 samples from core №3 were determined in the Department of Geosciences of the National Taiwan University (NTUAMS 14C-dating Lab). According the results the age of investigated deposits is Holocene-Pleistocene. For studying climate changes were measured magnetic properties and elemental composition of sediments.

Magnetic susceptibility (MS) was measured using a Multifunction Kappabridge MFK1-FA (AGICO), hysteresis parameters were obtained using the J_meter coercitive spectrometer, and it allows separate measurements of the remanent and induced magnetizations in magnetic fields up to 1.5 T at room temperature, induced magnetization versus temperature. Also element composition of each 5th (10 cm) sample was measured on Bruker S8 Tiger X-ray Fluorescence spectrometer. The output values were corrected with loss on ignition parameter, which was determined through heating samples at 1100 °С for about 2h.

Magnetic susceptibility varies between 0.88 - 7.87·10-7 м3/kg for all cores. The lower part of cores are characterised the largest changes of MS, which indicates a significant change in climatic conditions. Almost all magnetic fractions are presented by pseudo-single domain particles, according hysteresis parameters.

Decomposition of coercitive spectras into para-, ferro-, syperparamagnetic components also gives a lot of information about conditions during sedimentation. Thus, variations of the paramagnetic component reflect the relative growth of material input into the sedimentation basin, as well as the hydrogeological regime of the lake. The ferrimagnetic components of the sediments can be allothigenic and authigenic.

The higher values of MS, paramagnetic component and lithophilic elements (such us Na, K, Al, Si) and lower values of organic matter in lower part of the section displays the beginning of lake accumulation (12691-9963 years) in Late Pleistocene. According to data of chemical weathering intensity, an increase of the weathering is observed between 7908-7343 years (Atlantic), 4750-3998 years (Subboreal), and a decrease of the weathering is appeared between 9963-7908 years (Boreal), 7343-4750 years (Atlantic), 3998 - 892 years (Subboreal and Subatlantic).

This work was funded by the subsidy allocated to Kazan Federal University for the state assignment # 671-2020-0049 in the sphere of scientific activities and partly by RFBR according to the research project № 20-35-90058.

How to cite: Anastasia, Y., Dilyara, K., Nouria, N., Pavel, K., and Vadim, A.: Climate change in Southern Ural according to the Lake Bannoe sediments investigations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15108, https://doi.org/10.5194/egusphere-egu21-15108, 2021.

EGU21-2414 | vPICO presentations | SSP3.1

Deep-water syn-rift sedimentary response to alternating Late Quaternary palaeoenvironments in the Gulf of Corinth (Greece)

Natacha Fabregas, Sofia Pechlivanidou, Robert Gawthorpe, Mary Ford, and Richard Collier

Relatively few detailed studies exist of rift axis depositional systems and the controls on their sedimentology and stratigraphy. Cores from the IODP Expedition 381 (Corinth Active Rift Development) provide a continuous high resolution stratigraphic record of depositional processes operating within this deep-water rift. During the Late Quaternary, the Gulf of Corinth alternated between marine and isolated/non-marine conditions due to intermittent connection with the open ocean across a sill driven by climate-related sea-level fluctuations. In this study we performed bed scale logging of the sedimentary deposits within the eastern Gulf of Corinth in order to understand key controls on sedimentation during the Late Quaternary. High resolution, mm-scale analysis was performed on the first 300 m of core from Site M0079 that records the last two glacial-interglacial cycles and the Holocene (Marine Isotope Stages 1 to 7). The succession is dominated by fine-grained gravity flows (event beds) and hemipelagic sediments. Event beds result from discrete events that interrupt/overprint ongoing low energy sedimentation. As such, these have been abstracted in order to define three main sedimentary unit types. Unit-scale logging was extended to the rest of the succession and to the other drill sites to build a stratigraphic and depositional model covering the last ca. 700 kyr of deposition. Our results show that during interglacial periods (i.e. marine conditions), the sediment record consists mainly of highly bioturbated mud with rarer occurrences of coarser grained sediment. Sedimentary structures and identifiable event beds have largely been lost due to the high degree of bioturbation. In contrast, during glacial periods (i.e. isolated/semi-isolated lake conditions) the deposits are well bedded with a low bioturbation index and background muds alternate with event beds. Transitional strata, between marine and non-marine units, show finely laminated beds rich in aragonite, often becoming more organic rich toward the top. The deepest parts of the core penetrate slumped units and thicker gravity flow deposits. This study allows us to recognise the response to high frequency climatic fluctuations recorded in the sedimentary succession of this deep-water rift.

How to cite: Fabregas, N., Pechlivanidou, S., Gawthorpe, R., Ford, M., and Collier, R.: Deep-water syn-rift sedimentary response to alternating Late Quaternary palaeoenvironments in the Gulf of Corinth (Greece), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2414, https://doi.org/10.5194/egusphere-egu21-2414, 2021.

EGU21-4100 | vPICO presentations | SSP3.1

Catchment vegetation and erosion controls soil carbon cycling in SE Australia during two Glacial-Interglacial complexes

Alexander Francke, Matt Forbes, Haidee Cadd, Julia E. Short, Anthony Dosseto, Jonathan Tyler, John Tibbi, Sam Marx, William Dodson, and Cohen Tim C.

Soil Organic Carbon (SOC) represents with up to 80% the largest part of the terrestrial’s carbon pool. However, it is still highly debated if soil-carbon is a net atmospheric carbon source or sink. This is mainly due to a paucity of information on the SOC’s fate during soil erosion, which controls the interplay between SOC oxidation during soil storage, transportation, and final storage in a sedimentary sink. The southern hemisphere landmasses have the potential to play a dominant role in the SOC - atmosphere carbon cycle, since wetter (dryer) climates can cause the expansion (contraction) of terrestrial biomass in vast continental areas, such as for example in temperate to semi-arid SE Australia.

We herein investigate the interplay between catchment erosion (quantified by means of uranium isotopes), vegetation density (pollen), the wetland’s response (diatoms), and catchment-wide carbon and nitrogen cycling (carbon and nitrogen isotopes) on glacial/interglacial time scales in SE Australia. The analyses are applied to the sediments of Lake Couridjah, which is part of the Thirlmere Lake system located approximately 100 km SE of Sydney. A previous study has shown that Lake Couridjah and its catchment vegetation are highly sensitive to local and regional climate change. Radiocarbon and luminescence dating revealed that recovered lake sediments cover the time interval between ~140 ka and 100 ka, and between ~17.6 cal yr BP and present day. Lake Couridjah is thus one of the very few sedimentary archives providing a continuous archive for the previous interglacial complex in SE Australia, and thus offers an outstanding opportunity to study SOC cycling in a small catchment across different interglacial boundary conditions. The sedimentary analyses are supported by uranium, carbon, and nitrogen isotope analyses of a soil pit from the vicinity of the lake.

Statistical analyses revealed robust phase-relationships between catchment erosion, vegetation density, and carbon and nitrogen cycling during both glacial-interglacial complexes. The data implies that the density of the catchment’s sclerophyll woodland and mid- to understory vegetation - and not the amount of rainfall - has major control on catchment erosion, and, thus, on SOC storage in the catchment. Overall wetter and warmer peak interglacial conditions promote the expansion of dense sclerophyll vegetation, reducing catchment erosion while simultaneously increasing SOC storage as well as lake productivity and lake carbon-storage. The later post-Eemian phase of the preceding interglacial reveals overall cooler climates and a more open sclerophyll vegetation, resulting in faster catchment-wide erosion and reduced SOC and lake-C storage, conditions that are amplified in glacial periods (post-LGM, penultimate glacial period).

How to cite: Francke, A., Forbes, M., Cadd, H., Short, J. E., Dosseto, A., Tyler, J., Tibbi, J., Marx, S., Dodson, W., and Tim C., C.: Catchment vegetation and erosion controls soil carbon cycling in SE Australia during two Glacial-Interglacial complexes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4100, https://doi.org/10.5194/egusphere-egu21-4100, 2021.

EGU21-1048 | vPICO presentations | SSP3.1

Seismic event stratigraphy of tectonic Lake Towuti, Sulawesi, Indonesia: a 15 kyrs record of seismo-turbidites

Nicolas Tournier, Hendrik Vogel, Stefano C. Fabbri, Flavio S. Anselmetti, James M. Russell, Satria Bijaksana, and Sri Yudawati Cahyarini

Located at the triple junction of the Pacific, Eurasian and Sunda plates, the island of Sulawesi in Indonesia is one of the most tectonically active places on Earth. This is highlighted by the recurrence of devastating earthquakes such as the 2018 Mw 7.5 earthquake that destroyed the city of Palu and caused several thousand deaths in central Sulawesi. The majority of large magnitude earthquakes on Sulawesi are related to stress release along major strike-slip faults such as the Palu-Koro fault and its southern extensions the Matano and Lawanopo faults. To date, information on the frequency and magnitude of major events on these faults is limited to instrumental records, whereas information from historical sources and natural archives is completely lacking. Considering the increase in population density and its extension into distant areas, it is important to better quantify the seismic hazard. Therefore, a systemic catalogue of past earthquakes is essential for the understanding of tectonic dynamics of the area.

            Lake Towuti, situated in Eastern Sulawesi, is a key site to study the paleoseismology on the island. The lake lies close to the Matano strike-slip fault and is hence an ideal archive for past earthquakes that have occurred in the surrounding area. Moreover, its morphology allows a temporally continuous sedimentary succession. The large and deep central basins of the lake preserve the deposits linked to seismic activity. We combine high-resolution Chirp seismic data with sedimentary analyses of sediment piston cores to assess the recurrence of major earthquakes (Mw > 6) in the area, which are expressed by earthquake-triggered Mass Wasting Deposits (MWD). Five major seismic-stratigraphic units are identified in the upper 200 milliseconds TWT and show different depositional mechanisms. MWD’s and associated seismoturbidites can be easily distinguished in seismic data and are well preserved in the cored sedimentary successions in the topmost Unit 1.1. Chronologically Unit 1.1 covers the last 15 kyrs and enables the establishment of an event chronostratigraphy for Lake Towuti’s recent past. The most recent MWD likely corresponds to an AD 1924 Mw 6.5 earthquake, which was recorded to the south of Lake Towuti. In addition, 11 seismoturbidites have been observed in the Late Glacial to Holocene (~15 kyrs) sediment succession. These results tentatively suggest an average recurrence of major events every 1300 to 1400 years.

How to cite: Tournier, N., Vogel, H., Fabbri, S. C., Anselmetti, F. S., Russell, J. M., Bijaksana, S., and Cahyarini, S. Y.: Seismic event stratigraphy of tectonic Lake Towuti, Sulawesi, Indonesia: a 15 kyrs record of seismo-turbidites, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1048, https://doi.org/10.5194/egusphere-egu21-1048, 2021.

EGU21-7185 | vPICO presentations | SSP3.1

Preliminary sedimentological investigation of a Holocene lake deposit in the northern Apennines (Italy)

Lionello Morandi, Stefano Segadelli, and Marco Cocuccioni

The lake Moo in the northern Apennines, a 0.15 km2 basin located at an altitude of 1130 m a.s.l., consists of a small marshy area lying within a portion of a flat semi-circular depression surrounded by steep slopes. The site presents a series of geological and geomorphological characteristics which make it an ideal context to observe the results of flood events on the late Holocene sedimentary record of the basin. Our project aims to establish a relationship between recent deposits, instrumental data and modern-age cartography, in order to obtain site-specific parameters to interpret the sedimentary signal produced by floods on our site. The information can be extended back in time to the millennial scale by analysing sediment cores, in order to observe the frequency and magnitude of flood events throughout the Holocene and assess potential relationships with palaeoclimate reconstructions. This contribution discusses the results from five coring campaigns undertaken between 2018 and 2019 for a total thickness of 10.5 m, which allowed the recording of a c. 500 m long transect stretching from the west slope to the open water on the eastern part of the basin. This extended section enhanced our understanding of the deposit on a larger scale, allowing us to relate the new sequences to the ones identified in previous cores, and develop insights into flood-induced sediment gravity flows and their macroscopic physical characteristics (i.e. grain size, sedimentary structures, Munsell colour and types of contact surfaces). The study has led to the observation of possible correlations between various flood events and Holocene periods.

How to cite: Morandi, L., Segadelli, S., and Cocuccioni, M.: Preliminary sedimentological investigation of a Holocene lake deposit in the northern Apennines (Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7185, https://doi.org/10.5194/egusphere-egu21-7185, 2021.

EGU21-6017 | vPICO presentations | SSP3.1

Holocene climate variability and associated paleoenvironmental changes in the eastern lowlands of Guatemala revealed by a lake sediment from Lake Izabal

Edward Duarte, Jonathan Obrist-Farner, Alex Correa-Metrio, and Byron A. Steinman

Sediment records have been widely used to reconstruct Holocene environmental and climate conditions around the world. As new Holocene records from Central America and the Caribbean have become available, new hypotheses have emerged to explain the complex hydroclimate variability in the region. Here we present results from a radiocarbon-dated sediment core recovered from Lake Izabal, eastern Guatemala, that covers the last ~9,500 years. We combined sedimentological, XRF elemental abundances, and principal component (PC) analyses to reconstruct changes in erosion/precipitation, lake productivity, and lake water chemistry during the Holocene. Our results indicate that during the early Holocene, Lake Izabal was a shallow lake with minimal catchment erosion/precipitation as indicated by the abundance of organic-rich mud, coupled with the lowest PC scores and titanium (Ti) abundance of the entire record. An overall increase in the PC scores and a progressive increase in Ti suggest that precipitation/erosion increased from 8,300 to 4,800 cal yr BP and remained high until 1,200 cal yr BP. There was then a significant reduction in erosion and precipitation at ca. 1,200 cal yr BP, as evidenced by a sharp decrease in magnetic susceptibility, terrigenic derived elements, and PC scores. We suggest that the transition towards wetter conditions from the early to the middle Holocene, followed by a stable wet climate until ca. 1,200 cal yr BP, was strongly influenced by a progressive increase in autumn insolation throughout the Holocene, which could have caused an increase in Caribbean sea surface temperatures, increasing moisture availability leading to greater precipitation amounts in the Caribbean coast of Central America.

How to cite: Duarte, E., Obrist-Farner, J., Correa-Metrio, A., and Steinman, B. A.: Holocene climate variability and associated paleoenvironmental changes in the eastern lowlands of Guatemala revealed by a lake sediment from Lake Izabal, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6017, https://doi.org/10.5194/egusphere-egu21-6017, 2021.

EGU21-13577 | vPICO presentations | SSP3.1 | Highlight

How do recent depositional processes changes in high altitude Pyrenean lakes compare with Late Holocene variability? The case of Montmalús Lake (Principality of Andorra, Eastern Pyrenees)

Marcel-Saïd Galofré, Fernando Barreiro, Iván Santamaría, Ramón Copons, Benjamin Komack, and Blas.L Valero

High mountain lakes are pristine ecosystems that archive in their sediments high-resolution records of watershed and lake evolution. Understanding how they have responded to Holocene climate fluctuations and anthropic impacts provides essential information to put into a historical context the magnitude and unique features of the current global change.

The REPLIM project funded by the Interreg program (POCTEFA 2014-2020) has implemented a network of lakes in Spain, France and Andorra to study current and past climate, environmental and anthropic changes in lakes. In August 2017, eight short sediment cores were recovered in Montmalús Lake (2433 m a.s.l., Andorra). We present a paleolimnological reconstruction based on sedimentary facies, chemical (main and trace element) analyses and δ13C and δ15N of bulk organic matter. We developed a robust age model based on 210Pb, 137Cs and 14C dating for the last 2000 years. Moreover, modern lake dynamics have been characterized with continuous water temperature measurements at various depths, periodical water sampling and sediment traps.

The results show large depositional fluctuations in the lake dynamics, especially during the Little Ice Age, with changes in organic matter accumulation, bioproductivity and sources and increased sediment delivery. Sedimentological and geochemical indicators point to the onset of high human impact in the landscape around the 11th century. Also, medieval mining and metallurgic activity from 11th to 14th centuries increased Pb deposition.

The 20th century is characterized by a recovery in organic accumulation and bioproductivity rates. Heavy metal deposition also increased during the late 20th century and started to decrease in the 2010’s decade, without reaching the background values

This study provides the first data on recent changes in lakes from the Principality of Andorra. The results highlight the uniqueness of current global change impacts in alpine lakes and underline the interplay of Great Acceleration and Global Warming processes in these fragile and sensitive depositional systems.

How to cite: Galofré, M.-S., Barreiro, F., Santamaría, I., Copons, R., Komack, B., and Valero, B. L.: How do recent depositional processes changes in high altitude Pyrenean lakes compare with Late Holocene variability? The case of Montmalús Lake (Principality of Andorra, Eastern Pyrenees), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13577, https://doi.org/10.5194/egusphere-egu21-13577, 2021.

EGU21-15522 | vPICO presentations | SSP3.1 | Highlight

Sedimentary dynamics and heavy metal deposition in central Pyrenean high altitude lakes during the last 2000 years

Alejandra Vicente de Vera García, Fernando Barreiro Lostres, Ana Moreno Caballud, María del Pilar Mata Campo, Juan Pablo Corella Aznar, Sergi Pla Rabes, and Blas Lorenzo Valero Garcés

High altitude mountain lakes archive high-resolution records of environmental variability (climatic and anthropic). The REPLIM project funded by the INTERREG program (POCTEFA 2014-2020) has implemented a network to understand current and past changes in Pyrenean lakes. In this work, we compare six high altitude lake records along a W- E transect in the South Central Pyrenees: Acherito (1877 m.a.s.l.), La Sierra (2022 m.a.s.l.), Sabocos (1900 m.a.s.l.), Marboré (2600 m.a.s.l), Urdiceto (2364 m.a.s.l.) and Cregueña (2633 m.a.s.l.).

In each lake we have analyzed short sediment cores across transects applying sedimentological (facies, grain size, sediment composition, thin sections), geochemical (XRF scanner, elemental and trace metals) physical (Magnetic Susceptibility), isotopic (δ13C and δ 15N of bulk organic matter) and biological (diatoms) techniques. The age models have been constructed with 137Cs, 210Pb and 14C dates.

The sedimentary dynamics and heavy metals depositional history for the last 2000 years provides a temporal context for recent changes. Sedimentary facies variability correlates with climate phases and reflect varied human pressures. In general, during the colder and more humid periods, usually associated with glacier advances (LIA and Late Antiquity LIA), higher surface runoff was generated and, therefore, sediment delivery to the lake increased, in some cases with deposition of coarser facies. Intense watershed disturbances due to human impact were noticeable in lower altitude lakes since early medieval times. All lakes show larger sediment rate variability during the last centuries, but the timing of the onset varies. Lakes located at higher altitudes (Marboré and Cregüeña) show larger changes in sedimentation rates and dynamics around the end of the LIA (ca. 1850 CE), while in lower altitude lakes (Sierra, Sabocos, Acherito) occurred later (ca. 1950 CE).  In most lakes, a significant increase in organic matter accumulation started at the end of the 19th century and the trend accelerated since mid 20th century. Diatom and isotopes analyses suggest an increase in lake primary productivity during the last decades. The results indicate that the combined impacts of climate change and increased human pressure in the Pyrenees at the end of the LIA had a greater impact on high-altitude lakes, but recent changes in the 20th century have affected the lakes at all altitudes

All lakes show a similar heavy metal deposition pattern, with enrichment during Roman and Medieval times and a progressive increase since the end of the 18th century (industrialization) and reaching its peak in the middle and late 20th century. Some metals, such as Pb, show a subsequent decline at the end of the 20th century related to the reduction of industrial emissions and the ban on leaded gasoline.

This integrated approach demonstrates the sensitivity of high altitude lake systems to record past changes and highlights the need for multi-archive studies to support regional reconstructions of past environmental and climate changes.

How to cite: Vicente de Vera García, A., Barreiro Lostres, F., Moreno Caballud, A., Mata Campo, M. P., Corella Aznar, J. P., Pla Rabes, S., and Valero Garcés, B. L.: Sedimentary dynamics and heavy metal deposition in central Pyrenean high altitude lakes during the last 2000 years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15522, https://doi.org/10.5194/egusphere-egu21-15522, 2021.

EGU21-15839 | vPICO presentations | SSP3.1 | Highlight

Neotectonic activity in Lake Sils (Engadine, Switzerland) as trigger of tsunamigenic delta collapses?

Stefano C. Fabbri, Valentin Nigg, Benjamin Bellwald, Katrina Kremer, and Flavio S. Anselmetti

Tsunamigenic delta collapses in lacustrine environments are still poorly understood phenomena in terms of their recurrence rate, driving mechanism and hazard potential. A partial collapse of the Isola Delta in Lake Sils (Engadine, Switzerland) with an estimated depositional volume of at least 6.5 million m3 is radiocarbon-dated to 548-797 cal CE and may represent a typical tsunamigenic delta collapse in the Alpine environment. Recent studies propose that this basin-wide tsunami with a run-up height of 2–3 m and an inundation distance of 200 m at the lakeshore highlights the importance to better understand these processes and the associated hazards. The collapse was likely triggered by a strong regional earthquake responsible for several simultaneously triggered mass movements in nearby Lake Silvaplana and Lake Como. Increasingly available datasets from Lake Sils (short cores, high-resolution seismic reflection data, numerical tsunami simulations) are now complemented by multibeam swath bathymetry, providing a high-resolution (1 m grid) model of the lake floor that offers new insights into the failed slope masses, and post-failure basin morphology.

Lake Sils is located in the Upper Engadine in southeastern Switzerland at ~1800 m above sea level and has four major sub-basins (Maloja, Central, Sils & Lagrev Basins). A major tectonic element is the Engadine Fault Line (EFL), an oblique sinistral strike-slip fault that runs along the entire Upper Engadine valley. Its influence on the subaqueous morphology of the Maloja Basin in Lake Sils is expressed in the form of several localized troughs and ridges. It is suspected that the fault also cross-cuts the Isola Delta, possibly causing renewed delta failures in case of reactivation. In fact, recent studies have indicated that there is strong evidence for Quaternary left-lateral transcurrent faulting of the EFL, e.g. offsetting a river gully in the Forno Valley close to Lake Sils.

New bathymetric data from Lake Sils and their morphologic interpretations indicate subaquaeous slope failures, the extent of the Isola Delta collapse, and several trough-ridge features within the southwestern Maloja Basin. The latter are possibly indicative of ongoing faulting in the region since such features strongly suggest rhomboidal pull-apart basins within the Maloja Basin along the EFL. In general, such localized troughs within a lacustrine system are expected to level-out over time due to higher sedimentation rates in preferentially deeper regions of the lake. This study thus highlights the use of high-resolution bathymetric data in identifying the combined effects of deep-seated tectonic zones with shallow lake-floor processes, providing new insights into lacustrine hazard studies.

How to cite: Fabbri, S. C., Nigg, V., Bellwald, B., Kremer, K., and Anselmetti, F. S.: Neotectonic activity in Lake Sils (Engadine, Switzerland) as trigger of tsunamigenic delta collapses?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15839, https://doi.org/10.5194/egusphere-egu21-15839, 2021.

EGU21-7468 | vPICO presentations | SSP3.1

Stratigraphy and sedimentary process in a closed-basin lake in Central Italy during the Anthropocene

Paola Gravina, Beatrice Moroni, Riccardo Vivani, Alessandro Ludovisi, Roberta Selvaggi, and David Cappelletti

Shallow and closed lakes are affected by meteorological and climate variations and are especially sensitive to the change in their hydrological balance. In central Italy, there is the fourth-largest lake of the country, the Trasimeno Lake, whose water level has undergone various fluctuations over the centuries with alternation of flood and drought periods because of its shallow depth and the absence of natural outflows [1].

Sediment archives are used as information records to study chemical, physical, and biological environmental variations and changes in the hydrological budget driven by climatic fluctuations, but this is particularly complicated in shallow lakes due to the multiple perturbative phenomena. A robust study depends on the ability to obtain valid high-resolution geochemical data from lake sediments.

We conducted high-resolution geochemical analysis on three sediment cores about 1 meter long each, collected in Lake Trasimeno. We sectioned at 1  or 2 cm interval, which provided a detailed characterization of the significant changes in lacustrine processes that occurred in the basin during the Anthropocene (~last 150 years) [2], combining quantitative chemical (ICP-OES) and semi-quantitative (XRD and SEM) investigations. Geochemical variables are used as paleolimnological proxies to reconstruct past lake events that occurred within the water column. In particular, we report the study of the endogenic precipitates characteristic of the Trasimeno sediments, whose precipitation processes have been influenced by water fluctuations and anthropogenic impacts.

Given the strong presence of water fluctuations, the investigation period was divided into three distinct phases related to the lake's hydrometric state and characterized by sedimentary compounds of different nature. The endogenic carbonate compounds of calcite (commonly present in the Trasimeno sediments) contain a different Mg percentage during the different hydrometric phases. The lake sediments are particularly rich in Mg-calcite due to both water level changes and biological effects. Moreover, co-precipitation of non-crystalline Ca-P compounds (e.g., apatite type) has been detected during a hydrometric phase characterized by high microorganisms activity. Precipitation processes were triggered in Trasimeno by the growth of nutrient discharge into the lake (since the 1970s) and are currently studied for their importance in controlling eutrophication phenomena.

In conclusion, our findings show that rapid lake responses to water fluctuations and climate variations were transcribed within the sedimentary stratigraphic archives, which underlines their value and high quality in paleoenvironmental and paleohydrological reconstruction.

References:

[1] Frondini, Dragoni, Morgantini, Donnini, Cardellini, Caliro, Melillo, and Chiodini (2019). An En-dorheic Lake in a Changing Climate: Geochemical Investigations at Lake Trasimeno (Italy).Water, 11(7):1319.

 [2] Gaino, E., Scoccia, F., Piersanti, S., Rebora, M., Bellucci, L. G., and Ludovisi, A. (2012). Spiculerecords of Ephydatia fluviatilis as a proxy for hydrological and environmental changes inthe shallow Lake Trasimeno (Umbria, Italy). Hydrobiologia, 679(1):139–153.

How to cite: Gravina, P., Moroni, B., Vivani, R., Ludovisi, A., Selvaggi, R., and Cappelletti, D.: Stratigraphy and sedimentary process in a closed-basin lake in Central Italy during the Anthropocene, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7468, https://doi.org/10.5194/egusphere-egu21-7468, 2021.

EGU21-13837 | vPICO presentations | SSP3.1 | Highlight

Depositional signatures of historical flood and human landscape disturbances in lakes of the northeastern U.S. 

Timothy Cook and Noah Snyder

Sedimentary archives in lakes and ponds are widely used to reconstruct past climatic and environmental conditions, as well as to quantify the environmental impacts of human activity. In this study, we summarize the characteristics of sedimentary deposits associated with different types of disturbances including floods, landslides, timber harvest, and conversion of forested land to agricultural use. We evaluated sediment cores from a network of lakes across the northeastern U.S. The watersheds span a range of topographic and surficial geologic characteristics, and have land-use histories with differing types, timing, intensity, and duration of anthropogenic disturbance. Cores were analyzed to identify distinct event deposits and changes in clastic sediment input indicative of landscape disturbances. While most records span the past millennium, we focus specifically on the period of record that overlaps with historical and instrumental records of events that can be linked to specific sedimentary deposits. Neither hydroclimatic nor human land-use signals are ubiquitous across all watersheds. The identification of distinct flood deposits was limited to higher relief, mountainous watersheds with abundant glacial-age sediment. Distal flood deposits are typically thin (mm to cm scale) and characterized by sharp contacts between dominant gyttja and fine-grained clastic flood layers. Hydrologic disturbances associated with landslide activation (such as occurred during tropical storm Irene in 2011) result in similarly sharp basal contacts between gyttja and clastic sediment. However, these deposits are commonly thicker (10s of cm) and characterized by compositional grading from more clastic to more organic rich sediment, and have complex patterns of textural variability. These signatures reflect a multi-year duration of elevated sediment delivery as the landscape gradually stabilizes and vegetation returns. In contrast, human land cover alteration typically manifests in sediments as a gradual and often prolonged increase in clastic content. Thick (up to 10s of cm), often sandy, texturally graded clastic deposits are distinct from those formed by both hydrologic and human disturbances, and interpreted as a consequence of subaqueous mass movements.

How to cite: Cook, T. and Snyder, N.: Depositional signatures of historical flood and human landscape disturbances in lakes of the northeastern U.S. , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13837, https://doi.org/10.5194/egusphere-egu21-13837, 2021.

EGU21-11911 | vPICO presentations | SSP3.1

The paradox of increasing long-term carbon sequestration in lake ecosystems despite reoligotrophication : the case of four large French perialpine lakes

Julie Rotschi, Isabelle Domaizon, Irene Gregory-Eaves, Andrea Lami, Cécilia Barouillet, David Etienne, Erwan Messager, and Jean-Philippe Jenny

Although lakes only represent a small fraction of the surface of the earth, a growing number of studies have shown that they play a critical role in the global carbon cycle ([i],[ii],[iii]), mediating carbon transfer from land to the atmosphere, and burying organic carbon in their sediments. The magnitude and temporal variability of carbon burial is, however, poorly constrained, and the degree to which lake productivity has influenced lake carbon cycling has not been systematically assessed ([iv]). Here, trends in total organic carbon (TOC) sequestration and primary production are reconstructed from sediment records for the last 300 years in four perialpine deep lakes. We rely on High Performance Liquid Chromatography (HPLC) and geochemical proxies to investigate changes in algal communities. Then, we evaluate the temporal contribution of algal assemblages to the variability of lake primary production, as well as the potential effects on carbon sequestration magnitude. Other contributors to carbon sequestration derived from the IPER RETRO project (2009-2013) are also investigated, such as past oxygen conditions, lake thermal structure or allochthonous supplies of carbon. Our results suggest that despite reoligotrophication of all lakes (e.g., decrease in dissolved phosphorus concentration in water column and relative restoration of diatoms communities ([v])) over the last 3 decades, TOC in lakes sediments is still increasing in the sediment. The study of algal pigments suggests that changes in algal assemblages and oxygen conditions could be responsible of this persistent increase in carbon burial. Future development (e.g., DNA analysis) should provide more detail on algal communities to validate these results.


[i] J. J. Cole et al., ‘Plumbing the Global Carbon Cycle: Integrating Inland Waters into the Terrestrial Carbon Budget’, Ecosystems 10, no. 1 (May 2007): 172–85, https://doi.org/10.1007/s10021-006-9013-8.

[ii] Tom J. Battin et al., ‘Biophysical Controls on Organic Carbon Fluxes in Fluvial Networks’, Nature Geoscience 1, no. 2 (February 2008): 95–100, https://doi.org/10.1038/ngeo101.

[iii] Lars J. Tranvik et al., ‘Lakes and Reservoirs as Regulators of Carbon Cycling and Climate’, Limnology and Oceanography 54, no. 6part2 (November 2009): 2298–2314, https://doi.org/10.4319/lo.2009.54.6_part_2.2298.

[iv] N. J. Anderson et al., ‘Anthropogenic Alteration of Nutrient Supply Increases the Global Freshwater Carbon Sink’, Science Advances 6, no. 16 (April 2020): eaaw2145, https://doi.org/10.1126/sciadv.aaw2145.

[v] Vincent Berthon et al., ‘Trophic History of French Sub-Alpine Lakes over the Last 150 Years: Phosphorus Reconstruction and Assessment of Taphonomic Biases’, Journal of Limnology 72, no. 3 (September 2013): 34, https://doi.org/10.4081/jlimnol.2013.e34.

How to cite: Rotschi, J., Domaizon, I., Gregory-Eaves, I., Lami, A., Barouillet, C., Etienne, D., Messager, E., and Jenny, J.-P.: The paradox of increasing long-term carbon sequestration in lake ecosystems despite reoligotrophication : the case of four large French perialpine lakes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11911, https://doi.org/10.5194/egusphere-egu21-11911, 2021.

EGU21-8820 | vPICO presentations | SSP3.1

Hydroclimate reconstruction of Western Iberia over the last 3600 years - insights from lipid biomarker and specific isotope signal

Ricardo N. Santos, Teresa Rodrigues, Enno Schefuß, Filipa Naughton, Dulce Oliveira, Alexandre Ramos, and Armand Hernández

Located between the temperate and arid climates of Europe and North Africa, Iberia is one of the most climatic vulnerable regions of Europe with more severe and longstanding extreme climate events being expected in this region. The Iberian climate, mainly in winter, is modulated by the North Atlantic Oscillation (NAO). Persistent positive (negative) NAO phases, can lead to significant changes in the North Atlantic westerly wind-belts, resulting in strengthened (weakened) winter precipitation in Western Iberia.

The Iberian Central System mountain range constitutes one of the biggest physical barriers to the moist air masses coming from the Atlantic Ocean. Usually, under low anthropic influence, the high mountain lake ecosystems have sensitive responses to climate and environmental changes, which makes lake sediments a pristine record for paleo reconstructions.

The increasing number of studies on Iberian high lakes depicted a wide spectrum of spatiotemporal variability in climate and environmental conditions for the last few millennia. However, the paucity of archives from the western region hampers the understanding of the effect of major climate forcings on different climate periods.

In this sense, to assess the past hydroclimatic patterns over western Iberia, we study upper 120 cm sediments of a 5 m core retrieved from a high mountain lake in central Portugal (Lake Peixão, Serra da Estrela). The age and depth model provides a robust chronology of the last 3600 years based on four 14C AMS dating on pollen concentrates and 137Cs and 210Pb profiles.

Here we present the preliminary results on sedimentary lipid biomarker (leaf wax n-alkane) and compound-specific hydrogen isotope (δDwax) analysis performed at centennial time scale resolution. n-Alkane characterization, based on diverse indices (e.g., ACL, CPI, Paq, relative percentages, etc.), shows a clear higher plant signal, with a strong odd-over-even carbon predominance of long-chain n-alkanes, and predominance of the C31 homologue. Principal component analysis (PCA) applied to the odd n-alkanes (C17 – C35) concentrations reduced the data dimensionality into two principal components (PC). The PC1 mostly represents total n-alkane concentrations. PC2 has a positive correlation with Paq, C27, and δD signals, while a high negative correlation with ACL. Another important feature of the PC2 signal is its parallelism with NAO index reconstructions.

Our new data show a sensitive response from the lake catchment vegetation to hydroclimatic variability and allow the reconstruction of climatic phases occurring in this region based on plant waxes from Lake Peixão.

Acknowledgments

The financial support for this work was possible through the following FCT project: HOLMODRIVE—North Atlantic Atmospheric Patterns Influence on Western Iberia Climate: From the Late Glacial to the Present (PTDC/CTA-GEO/29029/2017).

How to cite: N. Santos, R., Rodrigues, T., Schefuß, E., Naughton, F., Oliveira, D., Ramos, A., and Hernández, A.: Hydroclimate reconstruction of Western Iberia over the last 3600 years - insights from lipid biomarker and specific isotope signal, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8820, https://doi.org/10.5194/egusphere-egu21-8820, 2021.

EGU21-8379 | vPICO presentations | SSP3.1

Unlocking the power of lake multiproxy analyses by understanding subsurface biosphere processes

Camille Thomas, Hendrik Vogel, and Daniel Ariztegui

Lake sediments bear valuable information allowing multidisciplinary research to address paleoclimatic and paleoenvironmental reconstructions at regional to global scales. Sedimentological, geochemical, paleontological and biological tools are commonly used to tackle these questions, which are generally driven by a set of intricated parameters. Among them, the importance of biogeochemical cycling is largely acknowledged in the lake (paleo-) water columns and has been at the heart of most paleolimnological studies. The way these signals are transferred to lake sediments has largely been studied. However, microbial communities - the principal actors in the biogeochemical cycling framework - keep being active in the sediment, and continue to influence the preservation and retention of organic and inorganic matter while buried. Gathered within the “early diagenesis” black box, these processes, once qualified, can help better interpret the proxies they may influence, and even constitute new ones. Within this work, we provide examples showing that the integration of studies of the subsurface biosphere within geo- and paleo-limnology investigations can help unlock or secure the potential of multiproxy analysis for reconstructing the paleoenvironments, paleoclimates and paleo-ecology of lake basins. The use of now well-developed OMICS methods, through the analysis of environmental and/or ancient DNA and lipids in particular has been coupled to mineralogical, isotopic and magnetic information in the Dead Sea (Levant) to demonstrate the differential preservation of mineralogic and sedimentologic signals along the last two glacial-interglacial cycles (Thomas et al., 2015, 2016; Ebert et al., 2018). Similar signals have been unlocked in Lake Towuti (Indonesia) and in Laguna Potrok Aike (Argentina) (Vuillemin et al., 2015, 2017). In Lake Ohrid (North Macedonia/Albania), environmental DNA has provided limited inputs on that perspective (Thomas et al., 2020), but has shown that ancient/fossil DNA could provide valuable information regarding the lake primary productivity and the status of its watershed land-cover. Integrating OMICS methods to tackle the identity and activity of the ancient and modern subsurface biosphere of lakes therefore holds an immense potential not only for microbiology investigations, but also for paleoclimatic and paleoenvironmental reconstructions.

Ebert et al. (2018) Overwriting of sedimentary magnetism by bacterially mediated mineral alteration. Geology 46, 2–5.

Thomas et al. (2016) Microbial sedimentary imprint on the deep Dead Sea sediment. The Depositional Record 1–21.

Thomas et al. (2020) Weak influence of paleoenvironmental conditions on the subsurface biosphere of lake ohrid over the last 515 ka. Microorganisms 8, 1–20.

Thomas et al. (2015) Impact of paleoclimate on the distribution of microbial communities in the subsurface sediment of the Dead Sea. Geobiology 13, 546–561.

Vuillemin et al. (2015) Recording of climate and diagenesis through fossil pigments and sedimentary DNA at Laguna Potrok Aike, Argentina. Biogeosciences Discussions 12, 18345–18388.

Vuillemin et al. (2017) Preservation and Significance of Extracellular DNA in Ferruginous Sediments from Lake Towuti , Indonesia. Frontiers in Microbiology 8, 1–15.

How to cite: Thomas, C., Vogel, H., and Ariztegui, D.: Unlocking the power of lake multiproxy analyses by understanding subsurface biosphere processes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8379, https://doi.org/10.5194/egusphere-egu21-8379, 2021.

EGU21-8230 | vPICO presentations | SSP3.1

Genomic variation of microbial populations on a continuous 10,000-year sediment sequence from Lake Cadagno (Piora Valley, Switzerland)

Paula Catalina Rodriguez Ramirez, Jasmine Berg, Longhui Deng, Hendrik Vogel, Mark A. Lever, and Cara Magnabosco

Lake Cadagno is a meromictic Alpine lake located in the Piora Valley, Switzerland. In 2019, a 10,000-year (10 m)sediment sequence was collected and found to contain three main lithological units: glacial sediment deposited under oxic conditions; a Mn-rich and organic-matter-rich sediment layer deposited during the transition from an oxic late-glacial lake to the onset of anoxia, and dark, sulfidic sediments deposited during the period of euxinia to the present. This study investigates the relationships between the physical-chemical properties and microorganisms of the sediment sequenceusing genome-resolved and targeted metagenomics.   

Results show that 16S rRNA gene abundance peaks in upper 1-32 cm of the sediment core (108 copies per gram of sediment) and decreases with depth. The abundance of a marker gene for sulfate reduction, dsrB, is positively correlated to 16S rRNA gene copy numbers, decreasing with depth from approximately 108 copies per gram of sediment in the top 30 cm to 104 gene copies per gram of sediment at 900 cm below the sediment depth.  These results suggest that sulfate-reducing microbial communities in surface sediments harvest the bioavailable oxidized sulfur inorganic species. In contrast, the presence of sulfate-reducing genes in sediments with sulfate concentrations below detection may indicate the engagement of microbial populations in sulfur cycling using alternative metabolic strategies (e.g. secondary fermentation).

 

Moreover, a clear differentiation between surface and deep sediment communities is observed. Sequencing of dsrB amplicons show a decrease in dsrB sequence richness with depth and sediment age. A clear transition from a surface section dominated (>80% relative abundance) by Deltaproteobacteria-related dsrB sequences from well-studied groups, to a deeper section below 40 cm dominated by a group of unclassified dsrB sequences most likely related to Firmicutes or Chloroflexi is also observed. The identity of these unclassified dsrB sequences will be determined by genome-resolved metagenomic sequencing (currently in progress). Furthermore, these analyses will give information on the presence of complete sulfate-reduction pathways and/or genes related to sulfur cycling in these microbial groups. By reconstructing the genomes of sulfate reducers and other microbial populations throughout the core, we will investigate whether there are genomic changes associated with the main geochemical trends. This work will enable us to assess the influence of a changing lake with the evolution of sediment-dwelling prokaryotic populations over thousands of years.

 

 

 

How to cite: Rodriguez Ramirez, P. C., Berg, J., Deng, L., Vogel, H., Lever, M. A., and Magnabosco, C.: Genomic variation of microbial populations on a continuous 10,000-year sediment sequence from Lake Cadagno (Piora Valley, Switzerland), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8230, https://doi.org/10.5194/egusphere-egu21-8230, 2021.

EGU21-6915 | vPICO presentations | SSP3.1

Lake microbial communities are not resistant or resilient to repeated large-scale natural pulse disturbances 

Katie Brasell, Jamie Howarth, John Pearman, Sean Fitzsimons, Xavier Pochon, Anastasija Zaiko, Kevin Simon, Marcus Vandergoes, and Susanna Wood

Opportunities to study and understand community level responses to extreme natural pulse disturbances in unaltered ecosystems are rare. Lake sediment records that span thousands of years can contain well resolved sediment pulses, triggered by earthquakes. These paleo-records provide a means to study repeated pulse disturbance and the processes of resistance (insensitivity to disturbance) and ecological resilience (capacity to regain structure, function and process). In this study, DNA preserved in lake sediment layers was extracted from a sediment core from a lake in a near-natural catchment.  Metabarcoding and inferred functions were used to assess the lake microbial community over the past 1,100 years – a period that included four major earthquakes. Microbial community composition and function differed significantly between highly perturbed (postseismic, c. 50 yrs) phases directly after the earthquakes and more stable (interseismic, c. 260 yr) phases, indicating a lack of community resistance to natural pulse disturbances. A decoupling between community structure and function in successive postseismic phases suggest potential functional redundancy in the community. Significant differences in composition and function in successive interseismic phases demonstrates the communities are not resilient to large scale natural pulse disturbances. The clear difference in structure and function, and high number of indicator taxa in the fourth interseismic phase likely represents a regime shift, possibly due to the two-fold increase in sediment and terrestrial biospheric organic carbon fluxes recorded following the fourth earthquake. Large pulse disturbances that enhance sediment inputs into lake systems may produce an underappreciated mechanism that destabilises lake ecosystem processes. 

How to cite: Brasell, K., Howarth, J., Pearman, J., Fitzsimons, S., Pochon, X., Zaiko, A., Simon, K., Vandergoes, M., and Wood, S.: Lake microbial communities are not resistant or resilient to repeated large-scale natural pulse disturbances , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6915, https://doi.org/10.5194/egusphere-egu21-6915, 2021.

SSP3.3 – Volcano-sedimentary processes in broader geological environments

EGU21-9665 | vPICO presentations | SSP3.3 | Highlight

The AD 79 Vesuvius eruption: stratigraphy, lithofacies variations and impact of the pyroclastic current deposits within the archaeological sites of Pompeii and Stabiae (southern Italy)

Ileana Santangelo, Claudio Scarpati, Annamaria Perrotta, Domenico Sparice, Lorenzo Fedele, Giulia Chiominto, Valeria Amoretti, Francesco Muscolino, Carlo Rescigno, Michele Silani, and Massimo Osanna

Plinian eruptions are powerful explosive volcanic events that impact large areas with cubic kilometers of magma emplaced as pyroclastic material accumulated in thick blankets around the volcanic vents. The violence of the emplacement mechanism (i.e., fallout or pyroclastic density currents, PDC) and the sudden burial of the landscape, make these types of eruptions extremely dangerous. Aiming to fully understand these phenomena, an accurate reconstruction of the physical behaviour and the historical record of a volcano is critical as starting point for the assessment of volcanic hazard. In this scenario an excellent case is the worldwide-known Plinian AD 79 Vesuvius eruption, which destroyed Roman towns with large effects preserved in different sites around the volcano. This study reports the results of a collaboration between the Archaeological Park of Pompeii and the University of Napoli Federico II to document the stratigraphic sequence and the type and extent of damage and victims buried under meters of pyroclastic material within the Pompeii and Stabiae archaeological sites. A systematic survey of well exposed outcrops along the recent excavations front allowed us to study in detail the facies variations of the different PDC stratigraphic units and how their distribution is affected even by urban structures. At Pompeii, the stratified ash PDC succession ranges in thickness from few tens of centimetres to two metres and shows considerable vertical and lateral variations in its sedimentological features. The layer associated with the most destructive impact on the Roman buildings shows down-current variation in thickness (0 to 330 cm) and texture. Where it is less than 30 cm thick, the deposit is fine-grained and thinly stratified, with few rounded pumice clasts scattered inside the matrix. Where it thickens, the lower part is rich in coarse pumice lapilli and locally shows well-developed stratifications, while the upper part shows an internal arrangement of alternating layers of fine and coarse ash, forming progressive bedforms. Upwards, the sequence is made up of a succession of plane-parallel ash layers with rare pumice lapilli clasts and diffuse accretionary lapilli. This ash sequence is interstratified with four well-sorted, thin lithic-rich layers that exhibit mantling structures of fall deposits. All PDC layers, except the lowermost, are dispersed across the entire Pompeii area, although some are locally missing as a result of the erosive action of the following PDC. At Stabiae, the ash PDC sequence is 83 cm thick. In few rooms of the Roman villa the ash deposits thicken up to 150 cm. Most of the ash layers identified at Pompeii are recognized also at Stabiae. In the upper part of the sequence a new PDC layer, never reported at Pompeii, is here documented for the first time. Damages are documented inside the more destructive ash layer and even in the upper ash layers, providing new insights about the risk assessment in distal areas.

How to cite: Santangelo, I., Scarpati, C., Perrotta, A., Sparice, D., Fedele, L., Chiominto, G., Amoretti, V., Muscolino, F., Rescigno, C., Silani, M., and Osanna, M.: The AD 79 Vesuvius eruption: stratigraphy, lithofacies variations and impact of the pyroclastic current deposits within the archaeological sites of Pompeii and Stabiae (southern Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9665, https://doi.org/10.5194/egusphere-egu21-9665, 2021.

EGU21-11035 | vPICO presentations | SSP3.3

Plinian eruptions and their impact on human settlements: stratigraphy of the 79 AD Vesuvius fall deposits and detailed study of their downwind and substrate-induced variations inside the archaeological excavations of Pompeii and Stabiae (southern Italy)

Giulia Chiominto, Claudio Scarpati, Annamaria Perrotta, Domenico Sparice, Lorenzo Fedele, Ileana Santangelo, Valeria Amoretti, Francesco Muscolino, Carlo Rescigno, Michele Silani, and Massimo Osanna

Plinian eruptions are highly energetic events that release cubic kilometres of magma in the form of pyroclastic material (pumice, lithic clasts and ash). These products tend to accumulate near the vent with considerable thickness. The rapid burial of the territory around the eruptive centre makes these eruptions extremely dangerous. For this purpose, the renowned 79 AD Vesuvius eruption, which destroyed the ancient cities of Pompeii and Stabiae (where Pliny the Elder founds his death) located respectively 10 and 15 km from the vent, was studied in detailed. The recent excavations carried out in collaboration with the Archaeological Park of Pompeii, both in Pompeii and in the Stabian villas, have shown the complete sequence of products of the 79 AD eruption that destroyed and covered these Roman cities. The discovery of thick sequences of reworked material accumulated during previous excavations, testifies for the presence of underground tunnels dug for the Royal House of Bourbon. Fall products of the 79 AD eruptive sequence, accumulated during the main Plinian phase and the successive sustained column phases, were studied in detail to investigate their sedimentological characteristics and how these were influenced by anthropic structures. Results from field investigation show that in both archaeological sites, fall deposits consist of white and grey pumice lapilli in the lower part of the eruptive sequence (units A and B), and of thin, lithic-rich layers interstratified to ash products emplaced by pyroclastic currents, in the highest part of the pyroclastic deposit (units D, G1, G3, I). A new thin lithic-rich layer (X2) has been observed near the top of the sequence at Stabiae. The internal structure of the Plinian pumice lapilli deposit appears weakly stratified in open areas, while it is strongly stratified near steep roofs (e.g., impluvium areas), where the deposit thickens. The observed stratification is confirmed by a significant variation of sedimentological parameters with the stratigraphic height (e.g., median ranging from -3.5 to -0.1), possibly related to fluctuations in the eruptive parameters. Locally, rolling of pyroclastic clasts on sloped roofs produced a well-stratified deposit with laterally discontinuous layers and rounded clasts. Several roofing-tiles, either intact or in fragments, were recovered at various stratigraphic heights in the pumice lapilli deposit both at Pompeii and Stabiae.  These tiles testify for the progressive collapse of the roofs under the increasing load of the falling lapilli clasts.

How to cite: Chiominto, G., Scarpati, C., Perrotta, A., Sparice, D., Fedele, L., Santangelo, I., Amoretti, V., Muscolino, F., Rescigno, C., Silani, M., and Osanna, M.: Plinian eruptions and their impact on human settlements: stratigraphy of the 79 AD Vesuvius fall deposits and detailed study of their downwind and substrate-induced variations inside the archaeological excavations of Pompeii and Stabiae (southern Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11035, https://doi.org/10.5194/egusphere-egu21-11035, 2021.

The Upper Awash valley runs across a volcano-sedimentary sequence dated from Late Miocene to about 500 my ago. The volcano sedimentary sequence in the Upper Awash valley developed within a closed basin at the western margin of the Main Ethiopian Rift branch and was affected by tephra sedimentation from nearby sources but also from volcanoes from the rift floor, and local fissural/dome eruptions. Dynamic interaction between rift tectonics, volcanic activity, tephra erosion and redeposition created a complex sedimentary environment constituting an exceptional fossil trap. In the area of Melka Kunture, the sediments host numerous fossils and archeological remains of Early-Middle Pleistocene (Oldowan and Acheulean) and Upper Pleistocene age. This is one of the most relevant African locations for researching human evolution.

The valley sequence formed after deposition of the large ignimbrite sheet of the Munesa tuff, within a paleo fluvial system which developed within lateral rift faults. Sedimentation rates significantly decreased after 500 my ago, probably due to decline of the volcanic activity in the area.

The basin stratigraphy consists of a composite sequence of primary (fall and flow) volcanic facies interbedded with reworked sediments emplaced in a low energy floodplain environment. The sequence is dominated by the deposit of one large pyroclastic density current (Kella Tuff) which is a main marker layer dated at 1.2 My. Deposition of the Kella Tuff had deep impact on the area leading to a complete reorganization of the drainage system and river channel migration and development of a disconformity in the southern Melka Kunture area.

Stratigraphic correlation is based on the interpretation of the basin history and evolution and has a crucial relevance not only for the reconstruction of the paleoenvironment but also for the interpretation of the paleontological and archeological data.

 

How to cite: Pioli, L., Mussi, M., and Melis, R. T.: The volcano sedimentary sequence in the Upper Awash valley (Ethiopia): a type case of volcanoclastic sedimentation in a peripheral rift environment , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10151, https://doi.org/10.5194/egusphere-egu21-10151, 2021.

EGU21-14794 | vPICO presentations | SSP3.3

The southernmost occurrence of the volcanic-rich layer of 5.5 Main the Northern Apennines: clues on its deposition

Davide Potere, Gianluca Iezzi, Vittorio Scisciani, Anna Chiara Tangari, and Manuela Nazzari

A volcanic-rich horizon crops along the Northern Apennines chain for about 200 km, in the post-evaporitic sedimentary sequence with an age of 5.5 Ma. Its thickness ranges between 30-200 cm and has been interpreted either as a primary fallout or a giant gravity flow in seawater (Aldinucci et al., 2005; Trua et al., 2010; Cosentino et al., 2013). Here, we focus on the two southernmost occurrences in the Abruzzo region (Central Italy): Castiglione a’ Casauria (CAC 42°14'10'' 13°53'29') and San Vittorino (SVT 42°12'10'' 13°53'29'') villages.

The SVT and CAC deposits are lithified with thickness of 80 and 220 cm, respectively, mildly fractured and greyish to light brown in colour. Four (SVT) and fifteen (CAC) oriented samples coaxial to the field, were cut and polished to expose about 470 and 700 cm2, respectively, of their vertical mesoscopic surfaces. The oriented thin sections and powders were prepared according to these mesoscopic attributes.

The XRPD (X-ray powder diffraction) spectra show the presence of a peculiar prominent large shoulder reflecting significative silicate non-crystalline phase, i.e. volcanic glass, plus faint Bragg reflections indicative of minor amounts of quartz, two feldspars (anorthite and sanidine), clinopyroxene, biotite and montmorillonite. The latter mineral results from post-emplacement and secondary crystallization. In addition, calcite and dolomite XRPD peaks occur with intensity inversely proportional to that of the silicate glass, reflecting the abundance or paucity of sedimentary versus volcanic fractions in sub-layers.

The microscopic 2D textures plus compositional features were investigated by SEM and EPMA. Both volcanic layers are very rich in fine-grained (averaging on 200 mm) and highly sorted glassy ashy clasts, while minerals are very poor (< 5 area%) in agreement with XRPD outcomes. Lithified ashes are mainly blocky in shape and un-broken. The ashes plot in the rhyolitic TAS field and overlap those already reported from other Northern Apennine sites. The amount of volatiles (H2O + CO2) estimated from EPMA average on about 6 wt.%, in agreement with the quantities of LOI determined on both bulk samples.

Field observations coupled with analysis on mesoscopic polished rock slices and thin sections do not shown any significant vertical size gradation and sorting, while fossils are almost absent. By contrast, both volcanic-rich deposits show: sedimentary- and volcanic-rich sub-layers, cm-sized volcanic clasts dispersed prevalently on the uppermost sedimentary sub-layers, cm-sized convolute laminations and slumped pseudo-beds. All these features demonstrate mass transport, soft-sediment deformation and fluid escape in seawater. Nonetheless, the absence of rounded ashy clasts, lithic sedimentary rock and classic Bouma sequence features (typical in coeval and adjacent deposits) mirror for local remobilization of poorly consolidated to loose carbonate and tephra deposits. In parallel, the high sorting of fine ashy clasts suggest a primary deposition from a distal fall-out eruptions. The location and features of both SVT and CAC volcanic-rich layers extend the previously inferred distribution of this ancient volcanic eruption.

References

Aldinucci et al., 2005. GeoActa, 4, 2005, pp. 67-82

Cosentino et al., 2013. Geology, 41, pp. 323-326

Trua et al., 2010. Italian Journal of Geosciences, 129, pp. 269-279

How to cite: Potere, D., Iezzi, G., Scisciani, V., Tangari, A. C., and Nazzari, M.: The southernmost occurrence of the volcanic-rich layer of 5.5 Main the Northern Apennines: clues on its deposition, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14794, https://doi.org/10.5194/egusphere-egu21-14794, 2021.

EGU21-10855 | vPICO presentations | SSP3.3 | Highlight

The Bontău Volcano, Apuseni Mts. (Romania), source for numerous debris avalanche deposits

Gabriel Corneliu Stefan, Viorel Mirea, and Ioan Seghedi

The Neogene volcanism in the western part of Romania is confined to the Apuseni Mountains and surrounding areas. The largest volcanic area is mostly developed in the WNW-ESE oriented, ca. 120 km in length Zărand-Brad-Zlatna Basin.

The Bontău Volcano (Seghedi et al., 2010) is located inside the western part of the Zărand-Brad-Zlatna Basin and it is strongly affected by erosional processes, being crossed in its northern part, from east to west, by the Crișul Alb River.

The Bontău Volcano is known to be active roughly between 14-10 Ma (according to the available K/Ar data) and it has been characterized as a composite or stratovolcano volcano associated with dome complexes, built by calc-alkaline andesitic lavas and pyroclastic deposits (andesite to basaltic andesite). The long-lasting volcanism developed in the Bontău area has a complex build up stages that we recently have found were interrupted by a series of destructive failure events. Several important volcanic collapses of the volcanic edifice took place producing large volcanic debris avalanches followed by numerous debris flows which produced various secondary volcaniclastic deposits that can be observed in different places all around the Bontău volcano. The debris avalanches deposits have not yet been known up to this study. The distribution of the debris avalanche deposits and associated volcaniclastic deposits is the main target of this study. In order to reconstruct Bontău Volcano activity and reconstruct its original morphology we done field observations and sampled the main lithologies to perform petrographic observations and geochemical and isotopic analyses (for the main lithologies).

During our field observations we tried to identify the relationships between debris avalanche deposits and older volcanic bodies (lavas, domes, volcaniclastic). One main important remark is related with the presence of several small basins at the margin of the volcano consisting of a succession of thin planar and cross-bedded sandstone in an alternation of coarse and fine layers associated with discontinuous lapilli trains (including pumices); The deposits are poorly to moderately sorted; with low angle cross lamination in lenses or pockets. Such deposits, as closely associate with debris avalanche deposits have been interpreted as small intra-hummocky basins formed after debris avalanche generation; they are mostly situated at the margins of the volcano.

The presence of multiple debris avalanche deposits can be connected with volcano growing in an extensional environment. We may assume that the long-lived Miocene rift graben system of the Zărand-Brad-Zlatna Basin experienced numerous changes in the fracture propagation and vertical movements that promoted repeated dyke intrusion and facilitated generation of numerous debris avalanches.

Acknowledgements: This work was supported by a grant of the of Ministry of Research and Innovation, CNCS – UEFISCDI, project number PN-III-P4-ID-PCCF-2016-4-0014, within PNCDI III.

How to cite: Stefan, G. C., Mirea, V., and Seghedi, I.: The Bontău Volcano, Apuseni Mts. (Romania), source for numerous debris avalanche deposits, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10855, https://doi.org/10.5194/egusphere-egu21-10855, 2021.

EGU21-14829 | vPICO presentations | SSP3.3

Biostratigraphy and microfacies of the sedimentary sequences within volcano-sedimentary Maden Complex in Southeastern Turkey

Ayşe Atakul-Özdemir, Sevinç Özkan-Altıner, Sesil Tancan, Yavuz Özdemir, Çağrı Mercan, Vural Oyan, and Nilgün Güleç

Maden Complex is a volcano-sedimantary unit, mainly composed of shallow and deep marine sedimentary rocks and associated volcanics. Deep marine units of Maden Complex, exposed between Çatak (Van) and Kozluk (Batman) regions have been studied with a combined sedimentological and paleontological approaches. The following species are recorded within the Melefan formation: Morozovella aragonensis, Acarinina collactea, Acarinina cf. esnehensis, Acarinina soldadoensis, Acarinina boudreauxi, Acarinina bullbrooki, Acarinina mckanni, Acarinina pentacamerata, Acarinina cf. pseudosubsphaerica, Acarinina topilensis, Acarinina esnehensis, Chiloguembelina sp., Globanomalina planoconica, Globanomalina australiformis, Globigerinatheka sp., Parasubbotina hagni, Pearsonites broedermanni, Pseudoglobigerinella bolivariana,   Planoglobanomalina pseudoalgeriana, Pseudohastigerina wilcoxensis,  Subbotina roesnaensis, Subbotina yeguaensis. Based on the defined planktonic foraminiferal species, the unit corresponds to the E7 zone and the depositional age of the formation is proposed as Early Eocene (Ypresian) to Middle Eocene (Lutetian). The deep marine sedimentary sequence mainly consists of pinkish to red colored micritic limestones including shale intercalations. The formation is represented by the pelloidal wackestone-packstone facies and comprises abundant planktonic foraminiferal assemblages.

How to cite: Atakul-Özdemir, A., Özkan-Altıner, S., Tancan, S., Özdemir, Y., Mercan, Ç., Oyan, V., and Güleç, N.: Biostratigraphy and microfacies of the sedimentary sequences within volcano-sedimentary Maden Complex in Southeastern Turkey, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14829, https://doi.org/10.5194/egusphere-egu21-14829, 2021.

EGU21-15060 | vPICO presentations | SSP3.3

Petrolgy of the volcanic/subvolcanic members of the volcano-sedimentary Maden Complex in Eastern Turkey

Yavuz Özdemir, Çağrı Mercan, Vural Oyan, Ayşe Atakul-Özdemir, Nilgün Güleç, and Sevinç Özkan-Altıner

Maden Complex exposed in Eastern Turkey, is a succession of volcano-sedimentary rocks and tectonically overlain by Bitlis Metamorphics and Cretaceous ophiolitic rocks. The succession includes shallow-water deposits and deep marine pelagic sediments intercalated with pillow lavas ranging from a few centimeters to ten meters in diameter. The planktonic foraminiferal assemblages from micritic limestones and zircon U-Pb ages from selected sedimentary rocks indicate the age of Late Ypresian - Early Lutetian. Plagioclase and  clinopyroxenes are the main mineral phases, olivine rarely found as altered phenocrysts. Clinopyroxenes are augite and diopside, and their compositions are ranging between Wo44-51, En27-43, Fe10-21. The anorthite contents of plagioclases are between 32- 67 % in unaltered grains. The crystallization temperatures and pressures obtained from clinopyroxene chemistry are ranging from 1126 to 1250oC and 3 to 8 Kbar, respectively. The majority of the volcanic/subvolcanic rocks are subalkaline-tholeiitic basalts however; a few andesitic and rhyolitic derivatives are also present. The whole – rock and  Sr-Nd-Pb isotope compositions reveal that the  basaltic rocks are originated from E-MORB like asthenospheric mantle source without a subduction component.

How to cite: Özdemir, Y., Mercan, Ç., Oyan, V., Atakul-Özdemir, A., Güleç, N., and Özkan-Altıner, S.: Petrolgy of the volcanic/subvolcanic members of the volcano-sedimentary Maden Complex in Eastern Turkey, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15060, https://doi.org/10.5194/egusphere-egu21-15060, 2021.

SSP3.5 – Bedform morphodynamics on Earth and in extra-terrestrial environments: current understanding of a complex interplay

EGU21-525 | vPICO presentations | SSP3.5 | Highlight

An Evolving Understanding of Enigmatic Large Ripples on Mars

Mathieu Lapotre, Ryan Ewing, and Michael Lamb

Unlike terrestrial sandy deserts, Mars hosts two scales of ripples in fine sand. Larger, meter-scale ripples are morphologically distinct from small, decimeter-scale ripples, and their size, in particular, decreases with increasing atmospheric density. As a result, it was recently proposed that the equilibrium size of the larger ripples is set by an aerodynamic process, which makes them larger under thinner atmospheres. Under this hypothesis, large martian ripples would be distinct from smaller, decimeter-scale impact ripples in a mechanistic sense. Several workers have followed up on these initial observations to either corroborate, counter, or expand upon that hypothesis. Notably, a mechanistic model that not only corroborates the hypothesis that the size of large martian ripples is set by an aerodynamic process but also suggests that they arise from an aerodynamic instability, distinct from the grain-impact instability thought to be responsible for the formation of impact ripples, was developed. Conversely, other workers proposed that large ripples can develop from small impact ripples in a numerical model due to Mars’ low atmospheric pressure. In the latter model, the ripples’ growth-limiting mechanism is consistent with an aerodynamic process, but the large ripples would not be a separate class of ripples – they would simply be a larger version of the small impact ripples. Here, we explore this debate by synthesizing recent advances in large-ripple formation and offer potential avenues to address outstanding questions. Although significant knowledge gaps remain, it is clear that large martian ripples are larger where the atmosphere is less dense. The size of large martian ripples thus remain a powerful paleoclimate indicator.

How to cite: Lapotre, M., Ewing, R., and Lamb, M.: An Evolving Understanding of Enigmatic Large Ripples on Mars, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-525, https://doi.org/10.5194/egusphere-egu21-525, 2021.

EGU21-3429 | vPICO presentations | SSP3.5 | Highlight

Change in the Wind and Climate at the ExoMars 2022 Landing Site in Oxia Planum (Mars).  

Simone Silvestro, Daniela Tirsch, Andrea Pacifici, Francesco Salese, David Vaz, Alicia Neesemann, Ciprian Popa, Maurizio Pajola, Gabriele Franzese, Guseppe Mongelluzzo, Alan Cosimo Ruggeri, Fabio Cozzolino, Carmen Porto, and Francesca Esposito

The ESA/ROSCOSMOS ExoMars 2022 will land in Oxia Planum an area that shows outcrops of clay-rich Noachian-aged phyllosilicates overlaid by an Early Amazonian volcanic dark resistant unit (Adru) [1]. Using HiRISE images, we identified NE-SW (53.9 ± 13.2°) oriented TARs overlying an enigmatic ~EW (95.4 ± 10°) oriented ridge pattern that we interpreted as periodic bedrock ridges (PBRs) [2]. Ridges (~ 38 m spaced) display Y-junctions, show cross-cutting fractures and share the same blocky texture of the bedrock they are associated with. Ridge crestlines are locally found in continuity outside and inside heavily eroded impact craters around the dark upstanding material (Adru) exposed in the center of many craters. These stratigraphic relationships suggest that the ridges (PBRs) formed after the event(s) that eroded the crater rims and thus after deposition of the Adru (2.6 Ga). Ridges are even visible in association with impact crater ejecta and are superimposed by 10-25 m craters and boulders, so they pre-date these impact events. When associated with crater ejecta, ridges locally show two different crests. Both crests are truncated by craters suggesting they were emplaced before the impacts. We interpret this double crest arrangement as megaripples detaching from PBRs. The ejecta deposited over the megaripple-PBRs favored the preservation of the megaripple crests from a subsequent episode/s of erosion that led to the complete exposure of the PBRs on the plain. Because the preserved megaripples are locally visible on the southern edges of the PBRs, the wind that formed the megaripple-PBR system should have blown from N-NNE because the megaripples are located at the downwind side of PBRs [3]. To better understand the relative age of the ridges, we mapped their occurrence on 316 craters in the study area that we qualitatively classified as relatively degraded/old and pristine/young. Results show that ridges are only found in degraded/old craters but are never found inside pristine/young craters. Thus, the ridge forming process was only active in-between the formation of degraded/old and pristine/young craters. A major change in the wind regime occurred during or after the event that exposed the PBRs: N-NNE winds that shaped the PBRs changed into dominant SE winds that led to the deposition of the TARs above the PBR/megaripples. This work unveils a complex history of aeolian erosion and deposition in Oxia Planum during the Amazonian. By visiting PBRs for the first time, the ExoMars 2022 mission will provide further constraints on PBR formation and paleo-winds, shedding light on a past Amazonian environment.

This work is a summary of a manuscript that is currently in press on Geophysical Research Letters: Silvestro et al. 2021, Periodic Bedrock Ridges at the ExoMars 2022 Landing Site: Evidence for a Changing Wind Regime. DOI: 10.1029/2020GL091651.

[1] Quantin-Nataf C. et al. (2021). Astrobiology, 21, N.3.

[2] Silvestro S. et al. (2020). 6th Int. Planet. Dunes Work. 12-15 May, 2020. LPI No. 2188, id.3009.

[3] Hugenholtz C. H. et al. (2015). Aeolian Res. 18, 135–144.

How to cite: Silvestro, S., Tirsch, D., Pacifici, A., Salese, F., Vaz, D., Neesemann, A., Popa, C., Pajola, M., Franzese, G., Mongelluzzo, G., Ruggeri, A. C., Cozzolino, F., Porto, C., and Esposito, F.: Change in the Wind and Climate at the ExoMars 2022 Landing Site in Oxia Planum (Mars).  , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3429, https://doi.org/10.5194/egusphere-egu21-3429, 2021.

EGU21-7814 | vPICO presentations | SSP3.5

Multiscale bedform interactions in a lowland river

Judith Zomer, Suleyman Naqshband, and Ton Hoitink

Multiscale bedforms exist in diverse environments. Globally, trains of small secondary bedforms have been observed in fluvial systems, where they are superimposed on larger fluvial dunes. Yet, we understand little about the morphodynamics of these superimposed bedforms and their interaction with larger bedform scales. It is unclear what their impact is on the overall system functioning, for example in terms of sediment transport and (near-bed) flow dynamics.

Bed elevation data with a high spatiotemporal resolution, obtained during a dedicated field campaign in the river Waal, a main distributary of the river Rhine, have shed light on the morphodynamics of fluvial dunes and superimposed bedforms. Results from the study indicate that superimposed bedforms persist over low-angled lee sides, whereas they disintegrate over lee side angles steeper than . The transport of bed sediment associated with secondary bedform migration is significant. The small bedforms migrate with a celerity that is an order of magnitude larger, from which a transport rate can be inferred that equals and in some sections even exceeds the transport associated with primary river dunes. Where superimposed bedforms disintegrate at or downstream of the dune lee slope, superimposed bedforms fully contribute to the migration of the primary dune. Where they persist over the dune lee side however, the sediment transport inferred from superimposed bedforms over the dune crest might partly contribute to primary dune migration. A significant portion, however, will also be transported over the dune lee side and trough and form an additional transport component. Both the persistence of the superimposed bedforms on the primary dune lee and their size and shape, appear to depend on the primary dune morphology. This is likely related to the flow structure—i.e. the presence of flow separation and the properties of the downstream, turbulent wake—that depends on the primary lee slope angle and height.

In our current work, we build upon this study, and  analyse the morphodynamics of these two bedform scales across a much larger spatial and temporal scale. Small-scale superimposed bedforms appear to be ubiquitous in the river Waal and can be observed across a range of discharge conditions. Our analysis quantifies and predicts when secondary bedform occur and persist over primary lee sides. We further aim to understand how secondary bedform morphology depends on primary dune characteristics as well as environmental conditions such as (changes in) discharge, and the bed sediment properties. In relation to that, we question to what extent superimposed bedforms in turn affect the primary dune morphology, their migration celerity and associated bedload transport.

 

How to cite: Zomer, J., Naqshband, S., and Hoitink, T.: Multiscale bedform interactions in a lowland river, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7814, https://doi.org/10.5194/egusphere-egu21-7814, 2021.

EGU21-213 | vPICO presentations | SSP3.5

Inference of barchan interaction properties from a comparison of theoretical modelling and observation

Dominic Robson, Andreas Baas, and Alessia Annibale

It is well known that barchan dunes are not isolated bedforms but are able to interact with one another both directly, through collisions and the emission/absorption of flux, and indirectly, due to the effects of turbulence in the wake of a dune.  In recent years, wave-tank experiments, continuum simulations, and cellular automata models have enabled researchers to model barchan-barchan interactions.  The findings from these studies have been fed into object-based models of entire fields of barchans and used to predict the size distributions.  Although there has been some success with these techniques, each model has failed to reproduce certain known properties on the field-scale; for instance, that the mean width is constant with downwind distance.  Furthermore, previous attempts have not been based on a theoretical understanding of the role of interactions in determining the dune size distribution, thus limiting their potential as universal models of barchan swarms.

Mean-field models are relatively simple in terms of the mathematics, but have shown some degree of success in the modelling of barchan fields, although previous work has  focused only on specific cases of interaction rules.  We have developed a more general mean-field model which can include many different forms of interaction, making it applicable to a variety of problems, including socio-economic systems as well as fields of interacting barchans.  Despite the generality of our model, we have been able to derive expressions for the dependence of the steady-state size distribution, and its moments, on the choice of interaction rules.  This means that, by making a measurement of the size distribution of a barchan field, we are able to infer properties of the interactions at play. 

To demonstrate the power of such a model we have measured size distributions of several barchan fields in the area of Tarfaya, Morocco.  Measurements were made by recording locations of seven distinct points on each barchan to yield morphometric parameters of each dune and compile the size-distribution.  By comparing the distribution and its moments to those predicted by the model, we can infer certain properties of the interaction rules, such as the relative probabilities of the different forms of collision.  The results show an example of how our model provides a more comprehensive understanding of the way in which dune-dune interactions determine properties on the scale of the field. 

How to cite: Robson, D., Baas, A., and Annibale, A.: Inference of barchan interaction properties from a comparison of theoretical modelling and observation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-213, https://doi.org/10.5194/egusphere-egu21-213, 2021.

EGU21-4919 | vPICO presentations | SSP3.5 | Highlight

Morphology of tidal bedforms, Weser Estuary, Germany

Alice Lefebvre, Gerald Herrling, Anna Zorndt, Knut Krämer, Marius Becker, and Christian Winter

The distribution and morphology of tidal bedforms in the Weser Estuary, Germany, between the tidal limit (Weser-km 0 in Bremen) and the open North Sea (Weser-km 110) has been analysed for a five-year period (2009-2013) based on monthly bathymetric surveys carried out along the main waterway. Bedforms were detected from gridded bathymetry data (2x2 m) and their geometric properties described. In particular, the presence and position of a slip face, here defined as the portion of the lee side steeper than 15°, were determined. In earlier studies, this was shown to be a practical criterion for the presence of a permanent flow separation and a turbulent wake in the lee of bedforms. Here it is used as a simplified indicator of bedform roughness: if a bedform does feature a slip face, it is assumed to be an active roughness element. The results were related to measured river discharge and water levels and modelled flow velocities.

Bedforms properties varied spatially and temporally along the estuary. Along the main bedform field (Weser-km 12 to 55) bedforms were mostly flood-oriented upstream, gradually becoming symmetrical then ebb-oriented downstream. In times of high discharge, all bedforms were more ebb-oriented than in times of low discharge. Bedforms in the Weser Estuary can be described as predominantly low angle dunes and their steepest slope is situated near the bedform crest. The analysed bedforms (in the main navigational channel, which is deepened and constrained) are also very two-dimensional, with little variations of three-dimensionality in time or space.

Although the Weser bedforms are mainly low angle, a significant proportion of bedforms possesses a slip face. This implies that they have a strong potential to induce bed roughness. This roughness is likely to change spatially along the estuary due to the variations of bedform properties, but also vary in time as a function of the tidal phase (ebb and flood) and discharge. This has wide implications in terms of modelling hydrodynamics and sediment transport in estuaries.

How to cite: Lefebvre, A., Herrling, G., Zorndt, A., Krämer, K., Becker, M., and Winter, C.: Morphology of tidal bedforms, Weser Estuary, Germany, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4919, https://doi.org/10.5194/egusphere-egu21-4919, 2021.

EGU21-258 | vPICO presentations | SSP3.5

The measuring of compound dunes – when height becomes a matter of perspective

Leon Scheiber, Jan Visscher, Oliver Lojek, and Torsten Schlurmann

Subaqueous bedforms are a fascinating morphological feature that concerns natural scientists and engineers alike. Under certain conditions, the different scales of these natural seafloor patterns merge into compound dunes consisting of large-scale primary and superimposing secondary bedforms. When it comes to the measuring of these composites, however, scholarly opinion varies depending on the investigator’s perspective. Specifically, compound dunes can either be interpreted as a superposition of their respective constituents, whose individual heights are measured independently after mathematical disintegration, or as one coherent bedform with readily measurable extents. Both methodologies, undoubtedly, have fully legitimate scopes of application, but little is written about the actual discrepancy that can result from signal pre-processing or differing geometric height definitions.

We experienced this problem when recently validating a method for the decomposition of compound dunes by comparison with three alternative approaches, of which two relied on detrending the bed elevation profiles before examination, whereas the third approach (similar to the newly proposed one) assessed unfiltered profiles. Although all tools were applied to the same bathymetric raw data, the statistical values of obtained dune dimensions diverged significantly. Even between approaches that generally showed comparable mean dune lengths, the corresponding height values differed by a factor of 2 or so. These results suggest that detrending or band-pass filtering of bed elevation profiles, as it is commonly applied before dune identification, leads to a systematic underestimation of profile amplitudes and thus dune heights. We therefore recommend refraining from these pre-processing steps in all cases where unambiguous absolute heights are needed. Dune identification from unfiltered bed elevation profiles, in return, necessitates that dune dimensions are calculated in consideration of the inherent inclinations. When analyzing the respective behavior of primary and secondary bedforms and their complex interplay, however, mathematical disintegration is the method of choice and, accordingly, dune height remains a matter of perspective.

How to cite: Scheiber, L., Visscher, J., Lojek, O., and Schlurmann, T.: The measuring of compound dunes – when height becomes a matter of perspective, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-258, https://doi.org/10.5194/egusphere-egu21-258, 2021.

EGU21-16551 | vPICO presentations | SSP3.5

Investigation of the lateral continuity of sandstone bedsets containing hummocky cross stratifications

Guilhem Amin Douillet and Déborah Harlet

Hummocky Cross Stratifications (HCS) are low-angle sedimentary structures found in association to sediments from the offshore transition. They are traditionally interpreted as representing storm-induced bedforms, whereby a combined flow is created including an oscillation component from storm waves and a unidirectional component from a density current, with debate on the intensity of each component. 

 

Here, the lateral evolution of bedsets containing HCS is investigated from field exposures. Drone images were collected from outcrops in the Moroccan Anti-Atlas from the Jbel Bani, a several hundred meters thick succession of shoreface to offshore sandstones and shales deposited during the Late Ordovician. Outcrops were targeted specifically for configurations where a vertical series of HCS sandstone bedsets occurred within silty-shale to flazer background interbeds.

 

Over a few hundred meters of lateral distance, HCS beds are found to splay out into channel cuts. Outside these channel features, individual bedsets are seemingly discontinuous, either amalgamating into underlying beds or laterally passing into ripple beds. This preliminary study offers new insights into the depositional dynamics of HCS sandstone beds, feeding a long-lasting discussion over the last 50 years. 

How to cite: Douillet, G. A. and Harlet, D.: Investigation of the lateral continuity of sandstone bedsets containing hummocky cross stratifications, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16551, https://doi.org/10.5194/egusphere-egu21-16551, 2021.

EGU21-4874 | vPICO presentations | SSP3.5

The influence of the gravitational circulation on estuarine sand dune migration: an idealized modelling approach

Wessel M. van der Sande, Pieter C. Roos, Theo Gerkema, and Suzanne J. M. H. Hulscher

Estuarine sand dunes are – similar to river dunes and marine sand waves – large-scale rhythmic bed patterns. Their characteristics differ from their riverine and marine counterparts, owing to the complex and dynamic estuarine environment. Using an idealized process-based modelling approach, we investigate the effect of the gravitational circulation on estuarine sand dunes.

The gravitational circulation is a residual current typical to estuaries, as it results from a longitudinal salinity gradient. It constitutes a tide-averaged residual flow with an upstream-directed (landward) component at the bed and a downstream-directed (seaward) component at the water surface (Geyer & MacCready, 2014). Sediment transport primarily depends on the bed shear stress (and thus on the flow near the bed), and therefore this residual flow may well be responsible for upstream migration of these bedforms. Observations of sand dunes in the Gironde estuary, France, suggest that this may indeed be relevant to the migration direction of estuarine sand dunes (Berné et al., 1993).  

We incorporated the hydrodynamic features of the gravitational circulation in a morphodynamic model, which is similar to the one of Hulscher (1996). We then perform a so-called linear stability analysis, which shows that bedforms develop as free instabilities of the flat bed.

Results show that a longitudinal salinity gradient may cause upstream migration, provided that the river flow velocity is sufficiently small. During high discharge in the Gironde estuary, the salinity front is pushed outward (van Maanen & Sottolichio, 2018), thus increasing the salinity gradient at the position in the Gironde where the sand wave field is situated. Including this in the model shows that the strengthened gravitational circulation can overpower the increased river flow velocities during high discharge, and thus confirms the observation by Berné et al. (1993). We note that this mechanism is probably limited to estuaries which share similar characteristics as the Gironde estuary, i.e. symmetric tide, well-mixed, little wind and wave influence, and a small residual river flow velocity due to a significant increase in cross-sectional area. Future research will elaborate on the effects of (tidally varying) stratification through implementation of a time- and space dependent eddy viscosity.

References

Berné, S., Castaing, P., le Drezen, E., & Lericolais, G. (1993). Morphology, Internal Structure, and Reversal of Asymmetry of Large Subtidal Dunes in the Entrance to Gironde Estuary (France). Journal of Sedimentary Petrology, 63(5), 780–793. https://doi.org/10.1306/d4267c03-2b26-11d7-8648000102c1865d

Geyer, W. R., & MacCready, P. (2014). The Estuarine Circulation. Annual Review of Fluid Mechanics, 46, 175–197. https://doi.org/10.1146/annurev-fluid-010313-141302

Hulscher, S. J. M. H. (1996). Tidal-induced large-scale regular bed form patterns in a three-dimensional shallow water model. Journal of Geophysical Research, 101(C9), 727–744. https://doi.org/10.1029/96JC01662

van Maanen, B., & Sottolichio, A. (2018). Hydro- and sediment dynamics in the Gironde estuary (France): Sensitivity to seasonal variations in river inflow and sea level rise. Continental Shelf Research, 165(May), 37–50. https://doi.org/10.1016/j.csr.2018.06.001

How to cite: van der Sande, W. M., Roos, P. C., Gerkema, T., and Hulscher, S. J. M. H.: The influence of the gravitational circulation on estuarine sand dune migration: an idealized modelling approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4874, https://doi.org/10.5194/egusphere-egu21-4874, 2021.

EGU21-16081 | vPICO presentations | SSP3.5

BedformsML0, a preliminary metadata language for a large, engineered and freely accessible bed form database

Ronald R. Gutierrez, Frank E. Escusa, Alice Lefebvre, Carlo Gualtieri, Francisco Nunez-Gonzalez, and Marc Roche

Open and data-driven paradigms have allowed to answer fundamental scientific questions in different disciplines such as astronomy, ecology and fluid mechanics, among others. Recently, the need to collaboratively build a large, engineered and freely accessible bed form database has been highlighted as a necessary step to adopt these paradigms in bed form dynamics research.

Most large database architectures have followed the principles of relational databases model solutions (RDBMS). Recently, non-relational (NoSQL) architectures (e.g., key-value store, graph databases, document-oriented, etc.) have been proposed to improve the capabilities and flexibility of RDBMS. Both RDBMS and NoSQL architectures require designing an engineered metadata structure to define the data taxonomy and structure, which are subsequently used to develop a metadata language for data querying. Past research suggests that the development of a metadata language needs a collaborative and iterative approach.

Defining the data taxonomy and structure for bed form data may be challenging because: [1] there is not a standardized protocol for conducting field and laboratory measurements; [2] it is expected that existing bed form data have a wide spectrum of data characteristics (e.g. length, format, resolution, structured or non-structured, etc.); and [3] bedforms are studied by scientists and engineers from different disciplines (e.g., geologists, ecologists, civil and water engineers, etc.).

In recent years, several data repositories have been built to manage large datasets related to the Earth System. One of these repositories is the Earth Science Information Partners, which has proposed standards to promote and improve the preservation, availability and overall quality of Earth System related data. These standards map the roles of participants (e.g., creators, intermediaries and end users) and delivers protocols to ensure proper data distribution and quality control.

This contribution presents the first iteration of a metadata language for subaqueous bed form data, named BedformsML0, which adopts the standards of the Earth Science Information Partners. BedformsML0 may serve as a prototype to describe bed form observations from field and laboratory measurements, model outputs, technical reports, scientific papers, post processed data, etc. Biogeoenvironmental observations associated to bed form dynamics (e.g., hydrodynamics, turbulence, river and coastal morphology, biota density, habitat metrics, sediment transport, sediment properties, land use dynamics, etc.) may also be represented in BedformsML0. It could subsequently be improved in future iterations via the collaboration of professionals from different Earth science fields to also describe subaerial, and extraterrestrial bed form data. Likewise, BedformsML0 can be used as machine search query selection for massive data processing and visualization of bed form observations. 

How to cite: Gutierrez, R. R., Escusa, F. E., Lefebvre, A., Gualtieri, C., Nunez-Gonzalez, F., and Roche, M.: BedformsML0, a preliminary metadata language for a large, engineered and freely accessible bed form database, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16081, https://doi.org/10.5194/egusphere-egu21-16081, 2021.

EGU21-6276 | vPICO presentations | SSP3.5

The variability of river dune shape at high and low flows in a navigable river

Lieke Lokin, Jord Warmink, Anouk Bomers, and Suzanne Hulscher

During low flows, river dunes determine the navigable depth of rivers, influencing the maximum draft of ships. Accurate predictions of the height and location of river dunes during low flows is needed to plan shipping operations in rivers. Currently, little data of dune evolution during low flows is available and analyzed, as most research is focused on high flows and most data is retrieved in flume experiments. However, the scaling from flume to full scale river gives issues with the lee slope angle and secondary bed forms.[LL(1]  Therefore, research on dune evolution on full scale rivers is lacking.

For this research multibeam echo sounding (MBES) measurements of the Waal river, Netherlands, were used. These measurements were done once per two weeks and cover the fairway. The data was made available by Rijkswaterstaat (Department of public works and water management, Netherlands). We developed a method to analyze dune shape in a large dataset of bed data. This method was applied on a stretch of 2 km Waal river, between the cities of Tiel and St. Andries. The research period covers the whole year 2018. This year is characterized by three separate discharge regimes. High water during January until March, median discharge from April until June and extreme low discharges from July until November.

In the first step of the data analysis locations of the primary dunes were determined using a wavelet analysis. At these locations, the dune crests and troughs were identified. With the crests and troughs, the shape characteristics such as dune length, height lee slope angle and propagation speed were determined. The dune characteristics were eventually related to the governing discharge.

The first results show that the river dunes are mobile during extreme low flows. After a transition period of one month, where the discharge drops from the median value towards the low discharge, the dune length and height become statistically stable. While the dune shape in flow direction becomes stable during these low flows the three dimensionality increases, not only in primary dune shape but also the appearance of secondary dunes and ripples. The dune height near the right bank is smaller than in the middle of the river, towards the left bank the height decreases again. The differences between the banks and the middle of the fairway increase as discharge decreases. Also, by visually inspecting the bed profiles at other locations, a similar trend is observed.

The first results show that the location in the river cross-section influences the dune characteristics. These differences increase as the discharge decreases. In further work we will extend the research area over the full length of the Waal river, to give a quantitative analysis supporting our visual results and to include influence of sediment size. As the differences in the cross-section can be found throughout the river, we will also investigate the influence of shipping on the differences in dune shape.

How to cite: Lokin, L., Warmink, J., Bomers, A., and Hulscher, S.: The variability of river dune shape at high and low flows in a navigable river, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6276, https://doi.org/10.5194/egusphere-egu21-6276, 2021.

EGU21-6336 | vPICO presentations | SSP3.5 | Highlight

Quantifying hydraulic roughness from field data: can bed morphology tell the whole story?

Sjoukje de Lange, Suleyman Naqshband, and Ton Hoitink

Bedforms are thought to be a major cause of hydraulic roughness in channels. The geometry of the river bed, shaped by bars, dunes, and ripples, and the spatial and temporal distribution of these, influence the resulting roughness variations. Roughness is a fundamental parameter for understanding river flow behaviour by influencing sediment transport and water level.

Quantification of roughness is challenging since it is not directly measurable in the field. It is therefore inferred from hydrological characteristics, -including water depth, water surface slope, flow velocity, discharge-, as well as morphological characteristics, -such as bedform height-, or derived from calibration of a hydraulic model.

This study contributes to the elucidation of factors influencing hydraulic roughness, and its quantification from field data. Proper quantification of roughness and its spatiotemporal behavior will increase our knowledge in river behavior and will lead to improvement of river management strategies and operational models.

In this research, three methods will be explored, to quantify the spatial distribution of hydraulic roughness in the field. We aim to state the importance of bed morphology for hydraulic roughness and we pursue the auxiliary aim to explore the spatial distribution of bedforms and roughness in our case study area river Waal, the Netherlands.

Method 1 uses the St. Vernant equations (better known as the Chezy equations) to quantify roughness, with as input among others flow velocity, bed slope and water surface slope. This value is seen as the ‘true’  roughness of the river system. Method 2 is a traditionally often used method, where form roughness is obtained from dune characteristics such as height and length via empirical predictors. Method 3 makes use of characteristics of the bed itself, not strictly related to 2D bedform geometry, specifically the inclination of the streamwise local elevation profile, i.e. local topographic leeside angle. Doing so eliminates the necessity of defining dune characteristics, and therefore taking one, often arbitrary, step out of the procedure to quantify roughness.

The three methodologies show the same general trend and order of magnitude of roughness (C=30-70 m0.5/s, mean 42 m0.5/s) however kilometer-scale variations show contrasting patterns. Nor dune geometry neither local topographic leeside angle manage to fully explain the variations in the roughness as obtain from the st. Vernant equations. From this we conclude that bed morphology does not seem to be the only explaining factor for roughness variations. Possible explanations include the low leeside angle of dunes (mean <10°), the influence of man-made structures such as groynes and longitudinal training dams, the influence of fixed gravel layers in sharp bends, river curvature, and cross-sectional variation in river depth (bars) and flow velocity. Further steps will be made to unravel the contributing factors for spatial variation in roughness.

How to cite: de Lange, S., Naqshband, S., and Hoitink, T.: Quantifying hydraulic roughness from field data: can bed morphology tell the whole story?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6336, https://doi.org/10.5194/egusphere-egu21-6336, 2021.

EGU21-9017 | vPICO presentations | SSP3.5

Recent advances on bedform research and application: Process-based to machine learning

Sanjay Giri, Amin Shakya, Mohamed Nabi, Suleyman Naqshband, Toshiki Iwasaki, Satomi Yamaguchi, David C. Froehlich, Biswa Bhattacharya, and Yasuyuki Shimizu

Evolution and transition of bedforms in lowland rivers are micro-scale morphological processes that influence river management decisions. This work builds upon our past efforts that include physics-based modelling, physical experiments and the machine learning (ML) approach to predict bedform features, states as well as associated flow resistance. We revisit our past works and efforts on developing and applying numerical models, from simple to sophisticated, starting with a multi-scale shallow-water model with a dual-grid technique. The model incorporates an adjustment of the local bed shear stress by a slope effect and an additional term that influences bedform feature. Furthermore, we review our work on a vertical two-dimensional model with a free surface flow condition. We explore the effects of different sediment transport approaches such as equilibrium transport with bed slope correction and a non-equilibrium transport with pick-up and deposition. We revisit a sophisticated three-dimensional Large Eddy Simulation (LES) model with an improved sediment transport approach that includes sliding, rolling, and jumping based on a Lagrangian framework. Finally, we discuss about bedform states and transition that are studied using laboratory experiments as well as a theory-guided data science approach that assures logical reasoning to analyze physical phenomena with large amounts of data. A theoretical evaluation of parameters that influence bedform development is carried out, followed by classification of bedform type by using a neural network model.

In second part, we focus on practical application, and discuss about large-scale numerical models that are being applied in river engineering and management practices. Such models are found to have noticeable inaccuracies and uncertainties associated with various physical and non-physical reasons. A key physical problem of these large-scale numerical models is related to the prediction of evolution and transition of micro-scale bedforms, and associated flow resistance. The evolution and transition of bedforms during rising and falling stages of a flood wave have a noticeable impact on morphology and flow levels in low-land alluvial rivers. The interaction between flow and micro-scale bedforms cannot be considered in a physics-based manner in large-scale numerical models due to the incompatibility between the resolution of the models and the scale of morphological changes. The dynamics of bedforms and the corresponding changes in flow resistance are not captured. As a way forward, we propse a hydrid approach that includes application of the CFD models, mentioned above, to generate a large amount of data in complement with field and laboratory observations, analysis of their reliability based on which developing a ML model. The CFD models can replicate bedform evolution and transition processes as well as associated flow resistance in physics-based manner under steady and varying flow conditions. The hybrid approach of using CFD and ML models can offer a better prediction of flow resistance that can be coupled with large-scale numerical models to improve their performance. The reseach is in progress.

How to cite: Giri, S., Shakya, A., Nabi, M., Naqshband, S., Iwasaki, T., Yamaguchi, S., Froehlich, D. C., Bhattacharya, B., and Shimizu, Y.: Recent advances on bedform research and application: Process-based to machine learning, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9017, https://doi.org/10.5194/egusphere-egu21-9017, 2021.

EGU21-6873 | vPICO presentations | SSP3.5

Gravity flow event beds in the middle section of Watermelon Formation in Luanping Basin,eastern China:A new interpretation for its Discovery and genesis.

Cheng Wang

EGU21-16019 | vPICO presentations | SSP3.5

Nonlinear dynamics of sand waves in sediment scarce environments

Johan Damveld, Gaetano Porcile, Paolo Blondeaux, and Pieter Roos

Field observations in the Dover Strait (Le Bot and Trentesaux, 2004) show sandy bed patterns in an environment where sand is scarce. Their morphological features closely resemble tidal sand waves, however, these type of bed forms are characterized by a crest-to-crest spacing which is larger than the wavelength of sand waves in the same surveyed area where sand is abundant. Based on stability theory, Porcile et al (2017) developed a morphodynamic model that was able to explain these features. They found that where the motionless substratum is exposed due to the growth of dunes, the lack of sand affects sediment transport, and consequently the morphology of the bed patterns. Their results also showed that the continuous growth leads to a lengthening of the dunes, and an increasing irregularity of the spacing. The found that their results were supported by the field observations.

Since the model by Porcile et al (2017) is partly based on the perturbation principle, the results are only valid for small amplitude patterns. To further understand the nonlinear behaviour of these sand starved dunes (e.g. shape, height), we here apply the fully numerical sand wave model by Damveld et al (2020). We extend this model by accounting for the presence of a hard substrate just below a thin layer of sand. Moreover, we start with a randomly perturbed bed pattern to give the morphodynamic system the freedom of self-organization.

Preliminary results show that the numerical model is able to reproduce the results found by Porcile et al (2017). In situations where sand is less abundant, wavelengths increase, and so does the spacing irregularity. Moreover, it is found that the average height of the sandy dunes is becoming increasingly smaller with decreasing sand availability. Further analysis should reveal dependencies to different environmental parameters, such as grain size, depth and tidal current strength.

Le Bot, S., & Trentesaux, A. (2004). Types of internal structure and external morphology of submarine dunes under the influence of tide- and wind-driven processes (Dover Strait, northern France). Marine Geology, 211(1), 143-168. doi:10.1016/j.margeo.2004.07.002

Damveld, J. H., Borsje, B. W., Roos, P. C., & Hulscher, S. J. M. H. (2020). Horizontal and Vertical Sediment Sorting in Tidal Sand Waves: Modeling the Finite-Amplitude Stage. Journal of Geophysical Research: Earth Surface, 125(10), e2019JF005430. doi:https://doi.org/10.1029/2019JF005430

Porcile, G., Blondeaux, P., & Vittori, G. (2017). On the formation of periodic sandy mounds. Continental Shelf Research, 145(Supplement C), 68-79. doi:10.1016/j.csr.2017.07.011

How to cite: Damveld, J., Porcile, G., Blondeaux, P., and Roos, P.: Nonlinear dynamics of sand waves in sediment scarce environments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16019, https://doi.org/10.5194/egusphere-egu21-16019, 2021.

SSP3.6 – Mineral archives – insights from modern and ancient marine, terrestrial, and man-made systems

EGU21-2904 | vPICO presentations | SSP3.6 | Highlight

How can computer models help us understand mineral forming processes?

Luca Valentini

The birth (and death) of minerals is controlled by a series of basic physical and chemical processes such as nucleation, growth, dissolution, diffusion and adsorption, which normally occur over time and length scales that are not easily accessible to common experimental investigation methods. However, reconciling these microscopic processes with macroscopic observations may represent a key to the interpretation of the geological archive as well as to optimizing the engineering of geomaterials based on the exploitation of mineral resources.
Motivated by this need, an overview of commonly used numerical techniques for the simulation of mineral forming processes, and their relevant input parameter, is provided, with the aim of assessing the potential and limitations of specific computational tools in different scenarios.
The scope and suitability of methods such as Molecular Dynamics, Kinetic Modelling, Cellular Automata, Monte Carlo and Population Balance are illustrated, with a brief introduction of the theoretical principles, followed by examples of applications to specific case studies.  
Challenges and future perspective, with emphasis on multiscale modelling, are discussed.

How to cite: Valentini, L.: How can computer models help us understand mineral forming processes?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2904, https://doi.org/10.5194/egusphere-egu21-2904, 2021.

EGU21-13041 | vPICO presentations | SSP3.6

Mineral surface reactivity: mechanisms and concepts

Cornelius Fischer

Diagenetic reactions in sediments and sedimentary rocks are controlled by both fluid transport and surface reactivity. In this chapter, the major focus is on the effect of crystal surface reactivity and its variability. The “energetic landscape” of the solid material in contact with the fluid exerts control on reaction type, kinetics, and products. Critical surface processes include sorption, catalysis, dissolution, and precipitation. For diagenetic reactions, the sequence of processes and thus the potential inhibition of subsequent reactions due to surface modifications is of great interest. Consequently, the evolution of porosity and permeability is governed by the chronological sequence of surface reactions during the diagenetic history. This provides feedback to the fluid transport behaviour in the complex porous material. Because of this coupling, numerical approaches address the problem appropriately by the use of reactive transport codes. Pore scale treatment follows mechanisms at the scale of crystal surfaces that form the pore walls of the sedimentary rock. Such surface-chemical exercises require a parametrization that includes mechanistic understanding and connection to first-principles treatment. At larger scales, so-called continuum scale simulation treats fluid transport and fluid-solid reactions in a more generalized quantitative way. While such field-scale treatment is required and applied for multiple challenges, the small-scale mechanistic understanding is still a crucial part of geochemical research. The observed heterogeneity of surface reactivity requires specific upscaling strategies that are not yet reflected in large-scale analysis and predictions.

How to cite: Fischer, C.: Mineral surface reactivity: mechanisms and concepts, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13041, https://doi.org/10.5194/egusphere-egu21-13041, 2021.

Fans and hemispheres comprised of crystals of calcium carbonate that directly grew on the seafloor are an intriguing feature of ancient carbonate environments. Calcium carbonate fans from across Earth history are typically made up of crystals of neomorphosed calcium carbonate that maintain an acicular morphology that is pseudohexagonal in cross – section with blunt terminations, pointing to an aragonite precursor. Crystal fans may occur as isolated bodies, or may form larger aggregates that are sometimes associated with microbialites, and form larger, reef – like structures. Some of the first occurrences of these features are within Neoarchean carbonates, when the crystals fans grew to impressive sizes, with lengths of over 1 m, formed layers of marine cement that reached thicknesses of up to several meters, are laterally continuous over 10s of km or more, and formed across carbonate platform settings from high energy subtidal settings to lower intertidal environments. Crystalline carbonate fans become less common and smaller (cm – scale) in the Paleoproterozoic, and nearly disappear prior to the Neoproterozoic, when they are associated with cap carbonates, and are primarily found in deeper water or outer shelf settings with low sedimentation rates. Seafloor cements are rare during the Phanerozoic, and are typically limited to small geographic areas with unusual sedimentary conditions, or are found in void spaces, where seawater chemistry was able to undergo modifications that would allow precipitation of cement fans. The exception is during the interval of time that followed the Permian – Triassic mass extinction, when small, cm – scale fans and hemispheres are found in Lower Triassic and lowermost Middle Triassic rocks. These cement fans occur in a variety of settings, although they are typically found in deeper water environments. Calcium carbonate fans that formed following the Permian – Triassic extinction may have microbial remains preserved within the cements, and are frequently found in close lateral or stratigraphic association with microbialites. However, some examples of post – extinction carbonate fans appear to have formed abiotically, without any microbial influence. Overall, crystalline calcium carbonate fans signal high levels of calcium carbonate supersaturation in ancient oceans. The initial decline in seafloor cement growth from the Neoarchean into the Proterozoic may have been the result of accelerated micrite production, while Neoproterozoic calcium carbonate fan growth is associated with glacial decay and retreat. Lower Triassic seafloor cements are likely the result of stratification and stagnation of the deep oceans that led to enhanced alkalinity. Calcium carbonate crystal fans are an intriguing feature of ancient carbonates that signal depositional systems and ocean chemistry that is much different from modern ocean, and provide a fascinating glimpse into non – uniformitarian sedimentary environments.

How to cite: Woods, A.: Calcium carbonate crystal fans: Geologic occurrences and controls on growth, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9021, https://doi.org/10.5194/egusphere-egu21-9021, 2021.

EGU21-3365 | vPICO presentations | SSP3.6

Working towards a universal formation model for spheroidal iron (oxyhydr)oxide concretions

Desiree Baker and Sally Potter-McIntyre

Three principal models exist for iron (oxyhydr)oxide concretion formation in the Navajo Sandstone in southern Utah, USA and the most recent model by Yoshida et al. (2018) suggests that calcite concretions are precursors to iron (oxyhydr)oxide concretions. This model could account for the existence of a gradient of carbonate and iron concretions found in both red diagenetic facies (with primary hematite grains coatings retained) and white diagenetic facies (primary hematite grain coatings removed during diagenesis). However, evidence for calcite precursor minerals and an understanding of the fluid chemistries involved in these diagenetic reactions is lacking. This research focuses on spheroidal concretions in the Navajo Sandstone at Coyote Gulch—a site that is down gradient, but upsection from Spencer Flat (the focus of previous work) and tests the hypothesis that calcite concretions are precursors to iron (oxyhydr)oxide concretions. Bulk mineralogy, bulk geochemistry, and petrography provide elemental and mineralogical composition of the concretions and show that the concretions are calcite cemented (~40 wt.%) and the host rock is predominately iron (oxyhydr)oxide cemented (~3 wt.%). The host rock surrounding embedded concretions shows secondary iron (oxyhydr)oxide precipitation and decreases in calcite in transects away from the concretion. These relationships suggest that the calcite concretions formed prior to the precipitation of secondary iron (oxyhydr)oxides and may have provided a localized buffering environment for the precipitation of iron (oxyhydr)oxides. This study also represents an opportunity to determine a universal model for carbonate and iron (oxyhydr)oxide spheroidal concretion formation, and to understand the influence of fluid interactions in the search for subsurface redox reactions to power metabolisms on Earth and Mars.

How to cite: Baker, D. and Potter-McIntyre, S.: Working towards a universal formation model for spheroidal iron (oxyhydr)oxide concretions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3365, https://doi.org/10.5194/egusphere-egu21-3365, 2021.

In his 1897 article on the formation and transformation of solid phases, Friedrich Wilhelm Ostwald described the phenomenon that hydrous sodium chlorate precipitates from an oversaturated solution, despite the fact that this phase is much more soluble than the non-hydrous salt. The fundamental concept, also known as Ostwald’s step rule, is best summarized on page 307 of his article (here translated to English):

“... Such phenomena also frequently occur during melting and condensation of steam and even in homogeneous chemical reactions, and I would like to summarize the previous experiences with this matter in the single phrase that during departure from any state, and the transition to a more stable one, not the under given circumstances most stable state is reached, but the nearest one.“

Despite its major importance for mineral formation under Earth’s surface conditions, this concept is still not fully understood on a mechanistic level. While Ostwald’s step rule is commonly explained with the classical nucleation theory, there are several inconsistencies, especially the conundrum that sometimes stable phases, such as dolomite or quartz, do not form as long as a metastable phase is supersaturated. I propose an alternative interpretation that would be consistent with Ostwald’s (1897) original formulation as well as with several observations from natural environments and laboratory experiments. If “nearest” (in German: “nächstliegend”) is not understood as “thermodynamically most similar”, but as the phase with the lowest kinetic barrier, Ostwald’s step rule should be always valid. The kinetic barrier is surface specific and independent of supersaturation, but it depends on the atomic scale interfacial energy landscape. This concept would better represent the power of Ostwald’s step rule to explain mineral formation processes and how they are affected by chemical and biological influences. New nano-scale analytical techniques in combination with advanced molecular dynamic modelling bear great potential to explain and appreciate the importance of Ostwald’s step rule.

How to cite: Meister, P.: Ostwald’s step rule: a consequence of growth kinetics and nano-scale energy landscape, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8176, https://doi.org/10.5194/egusphere-egu21-8176, 2021.

EGU21-9343 | vPICO presentations | SSP3.6

From poorly-ordered precursors to crystals: Factors contributing to spherulitic growth of dolomite

Juan Diego Rodriguez Blanco and Adrienn Maria Szucs

Dolomite is one of the most abundant carbonate minerals in the geological record, yet it barely forms in the present. The contrast in the abundance of dolomite between geological and modern records combined with the impossibility of synthesizing stoichiometric dolomite in the laboratory at ambient conditions are known as the 'dolomite problem'. This enigma has been in the scope of research for decades, trying to understand dolomite formation, mechanisms and the contributing factors. Dolomite is known to form via two abiotic mechanisms; through (1) dolomitization or (2) dolomite cementation. Also, the contribution of microorganisms can result in biotic dolomite crystallization. The mechanisms of dolomite formation at the molecular and nanoscale in biotic and abiotic environments are relatively well-described, but we still struggle to develop a unified model of dolomite formation in modern and ancient settings. In this contribution, we summarize the development of research related to the dolomite formation processes and in particular the direct dolomite precipitation via spherulitic growth of proto-dolomite.

How to cite: Rodriguez Blanco, J. D. and Szucs, A. M.: From poorly-ordered precursors to crystals: Factors contributing to spherulitic growth of dolomite, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9343, https://doi.org/10.5194/egusphere-egu21-9343, 2021.

EGU21-15510 | vPICO presentations | SSP3.6

An unsuspected biomineralization process in the green algae class Chlorodendrophyceae 

Inés Segovia Campos, Agathe Martignier, Montserrat Filella, and Daniel Ariztegui

Chlorodendrophyceae are a class of unicellular green algae widespread in the aquatic environment (seawater, brackish water, and freshwater) that have recently been discovered to form intracellular carbonates. These mineral inclusions, called micropearls, are mainly composed of hydrated amorphous calcium carbonates (ACC) in which strontium can also accumulate at high concentrations. Under natural and culture conditions, the Sr/Ca ratio of micropearls can be 200 times higher than in their environment, suggesting that Chlorodendrophyceae species may be considered as potential candidates for new bioremediation methods regarding radioactive 90Sr water contamination. Because very little is known about this phenomenon, ongoing experiments with laboratory cultures are providing essential information about the cellular mechanisms involved in this newly discovered biomineralization process and its impact on the geochemical cycles of Ca and Sr.

How to cite: Segovia Campos, I., Martignier, A., Filella, M., and Ariztegui, D.: An unsuspected biomineralization process in the green algae class Chlorodendrophyceae , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15510, https://doi.org/10.5194/egusphere-egu21-15510, 2021.

EGU21-16415 | vPICO presentations | SSP3.6

A comparative study of low-temperature dolomite formation driven by exopolymers from hypersaline microbial mats and clays

Zach Diloreto, Huan Liu, Xiancai Lu, Tomaso Bontognali, and Maria Dittrich

Recent studies have shown that surfaces rich in functional groups can facilitate nucleation of low-temperature (low-T) dolomite. However, to date few experiments have investigated the details of the nucleation mechanisms nor determined how naturally occurring substances influence crystallization pathways of low-T dolomite. In this study we isolated and characterized extracellular polymers (EPS) from a hypersaline sabkha, as well as clay standards and performed mineralization experiments with these surfaces as seed material. Mineralization experiments were carried out in batch reactors in a solution supersaturated with respect to dolomite. Our results showed that over a five-month period the rate of low-t dolomite formation in samples seeded with EPS was significantly higher compared to those seeded with clay. The observed rates were also shorter than previously published experiments using bacterial cultures (e.g., Kenward et al., 2013, Deng et al., 2019). Precipitates from samples seeded with EPS show crystallization of dolomite pre-cursors after several days and assemblages of dolomite crystals from 10-days forward [Figure 1]. Measurements from EPS seeded samples showed significant depletion of Ca and Mg in solution within one week as well as elevated alkalinity that coincided with dolomite crystallization. Samples seeded with clay and control samples without seed materials showed little and no dolomite crystallization, respectively, during the same time-frame. Overall, the results of this work shows that EPS isolated from microbial mats are preferential nucleation surfaces for carbonate precipitation when compared to clays. Additionally, the findings reveal that the properties of nucleation surfaces such as functional group type and concentration are a key factor driving low-T dolomite precipitation.

Figure 1: Dolomite like phases and representative EDS spectra from a solution seeded with EPS.

 

References:

Kenward PA, Fowle DA, Goldstein RH, Ueshima M, González LA, Roberts JA. Ordered low-temperature dolomite mediated by carboxyl-group density of microbial cell walls. AAPG bulletin. 2013 Nov 1;97(11):2113-25.

Liu D, Xu Y, Papineau D, Yu N, Fan Q, Qiu X, Wang H. Experimental evidence for abiotic formation of low-temperature proto-dolomite facilitated by clay minerals. Geochimica et Cosmochimica Acta. 2019 Feb 15;247:83-95.

 

How to cite: Diloreto, Z., Liu, H., Lu, X., Bontognali, T., and Dittrich, M.: A comparative study of low-temperature dolomite formation driven by exopolymers from hypersaline microbial mats and clays, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16415, https://doi.org/10.5194/egusphere-egu21-16415, 2021.

EGU21-7169 | vPICO presentations | SSP3.6

SEM-based mineralogical mapping at the submicrometer-scale of modern Sardinian stromatolites

Juliette Debrie, Dimitri Prêt, Karim Benzerara, and Jean Paul Saint Martin

Stromatolites, i.e. macroscopically laminated carbonate rocks formed by diverse microbial communities, are particularly emblematic geobiological materials since they are the oldest evidence of life-mineral interactions, dated up to 3.5 Gyrs ago.  They are found throughout the history of the Earth and have received strong attention because they provide precious information about microbial paleobiodiversity and paleoenvironments. However, while this information is interpreted based on our knowledge about modern analogs, the latter remains very incomplete. Here, we studied recently discovered modern stromatolites from Mari Ermi1, a coastal pond in Western Sardinia, that seasonally experience severe evaporation and broad salinity variations. For this purpose, we explored the mineralogical composition of these unique sedimentary archives and its spatial variations in order to gain better insight into how mineral phases record the conditions and processes of their formation. We investigated the heterogeneous distribution of minerals using quantitative X-ray chemical maps provided by energy dispersive x-ray spectrometry analyses coupled with scanning electron microscopy (SEM-EDXS). Hyperspectral maps were analyzed using an innovative data treatment method 2 allowing phase recognition within the complex mineral mixtures and solid solutions encountered. This method provided quantitative data on spatial distribution, modal content and associated calculated unit formulas for each identified mineral and phase with a hundred nanometer resolution. Based on these results, we will discuss the origin of the laminations in the stromatolites.

Reference:

1. Saint Martin, J.-P. & Saint Martin, S. Geo-Eco-Marina 21, 35–53 (2015a).

2. Prêt, D. et al. American Mineralogist 95, 1379–1388 (2010).

How to cite: Debrie, J., Prêt, D., Benzerara, K., and Saint Martin, J. P.: SEM-based mineralogical mapping at the submicrometer-scale of modern Sardinian stromatolites, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7169, https://doi.org/10.5194/egusphere-egu21-7169, 2021.

The Danube – Tisza interfluve area in the middle part of the Carpathian Basin harbors numerous mainly groundwater-fed hypersaline (alkaline) ponds which were characterized by carbonate precipitation under varying geochemical, climatic, environmental conditions during the Holocene.  The formation of dolomite attributable to seasonal variations of the climate and concomitant volume, geochemical changes of the groundwater, and the waterbody in these lacustrine environments is a unique feature of the area. A general model of freshwater high magnesium calcite, proto-dolomite, and dolomite precipitation in these lakes has been constructed in the early-mid 1980s via the complex geological, geochemical isotope geochemical investigation of carbonate rocks of extant lacustrine sequences of the mentioned area complemented by geochemical analyses of the lake and groundwater. Seasonal and long-term climate variations are expressed in the form of macro and micro-cycles preserved in the rock record. These however have never been examined in detail.   To unravel and understand the cyclicity present in the mentioned carbonate sequences we need quantitative information on the composition and physical properties of rock. CT analysis of rocks yields data on density differences observable between the building blocks or forming components in the material under study. Groups identified via statistical analysis of the data can be assigned to the various rock-forming components, and these groups can be described quantitatively via statistical parameters characterizing distribution. 3D visualization of the clustered data in the rock samples allows for cross-validation of interpretations. Via studying the vertical and spatial heterogeneity of the identified rock-forming components using their descriptive statistical properties the presence of micro-and macrocycles can be revealed, which serve as a starting point for further investigations to understand the nature and causes of these cycles. We are to present the results of such work done on some carbonate samples of the mentioned area. Research has been carried out within the framework of the University of Szeged, Interdisciplinary Excellence Centre, Institute of Geography and Earth Sciences, Long Environmental Changes Research Team. Support of the Ministry of Human Capacities, Hungary Grants 20391- 3/2018/FEKUSTRAT and NKFIH 129265 are acknowledged. 

 

How to cite: Alzoubi, N., Gulyás, S., and Geiger, J.: Heterogeneity of Holocene freshwater dolomites from central Hungary based on a statistical analysis of rock-forming component properties derived from CT data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6489, https://doi.org/10.5194/egusphere-egu21-6489, 2021.

The Northern Caucasus Carbonate Platform is one example of the carbonate platforms developed through the Northern Peri-Tethys margin during Jurassic and Cretaceous times.  The platform’s age can be identified as Callovian - Valanginian, with the most carbonate production and diversity during Oxfordian-Berriasian. Its composition and features can be obtained by studying the outcrops of carbonate rocks along the Skalisty Ridge of the Northern Caucasus and along with river valleys that cut it. The thickness of carbonate deposits decreases from west to east, from the Mineralovodski uplift to Northern Ossetia and further to the east. Therefore, the Urukh River section is one of the most complete and detailed. The stratigraphy of the section was studied several times, although the section’s sedimentology was never the aim of these studies. Facies interpretation and depositional environments of the Northern Caucasus carbonate platform can be found in previous research at a fairly general level. The microfacies analysis is widely used to reconstruct the facies settings of carbonate sedimentation. Our research is the first attempt to apply the microfacies method for the Jurassic-Cretaceous carbonate deposits of the Urukh river region.

The section is located between Kaluh and Upper Zadalesk villages (Digorsky District, Northern Ossetia) along the Chikola-Matsuta road. The overall thickness of the carbonate sediments here is more than 1 km. The deposits consist of various bedded and massive limestones and dolomites forming high cliffs of the Urukh river valley. They form a monocline with dip angles from 10° to 15-20° in the northern and northeastern dip. The alternation of the marls, clays, and different muddy and clayey limestones can be observed in the section’s Berriassian part. 

The most common microfacies types (MFT) were identified after studying 50 thin-sections. They are compared with the standard microfacies of the carbonate platform and ramp, as well as with the microfacies types identified for the adjacent carbonate platforms of the Northern Peri-Thetys with similar age. The MFTs are represented by layered mudstones and dolomites; oncoid and bioclastic floatstones; well to moderately sorted peloid and bioclastic grainstones and packstones; stromatolite bindstones and dolomites. Among the carbonate particles in grainstones and wackestones, various bioclasts are most common, including micritized shells of benthic foraminifera (including Milliolids), fragments of echinoderms, bivalve shells, and other benthic organisms. They have marine genesis and can form in the inner parts of the carbonate platform.

The formation of the dolomites and stromatolite bindstones is related to supratidal and intertidal environments. The formation of the other MFTs can be linked to the subtidal environments of the inner parts of the carbonate platform or the open-marine conditions in its outer part. 

The obtained data is new for this section and must be compared with data observed in the other sections of the Northern Caucasian carbonate platform to establish its morphology.

How to cite: Mazko, E.: Microfacies of Middle Jurassic - Early Cretaceous Northern Caucasian carbonate platform from Urukh river region (Northern Ossetia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15732, https://doi.org/10.5194/egusphere-egu21-15732, 2021.

EGU21-15898 | vPICO presentations | SSP3.6

Pelagic Sargassum as an emergent high-rate importer of carbonate sediment to tropical Atlantic coastlines

Michael Salter, Chris Perry, Rosa Rodríguez-Martínez, Lorenzo Alvarez-Filip, and Eric Jordan-Dahlgren

The composition of modern carbonate sediments in nearshore tropical marine settings typically reflects a suite of somewhat proximal processes of carbonate production and erosion. Here, we document pelagic Sargassum as an emergent vector of carbonate sediment import to tropical Atlantic and Caribbean shorelines: a process with distal (oceanic) origins that has the potential to impart a distinct record of regional to global change within nearshore sediments. This process arose as recently as 2011, when a major new Sargassum bloom region emerged in the central Atlantic Ocean and resulted in Caribbean, West African, and northern Brazilian shorelines being inundated with Sargassum at unprecedented scales. Subsequent near annual recurrences of these coastal inundations at increasingly large scales suggest they are becoming an established norm. Socio-economic and ecological implications are widespread and potentially serious, and include potential impacts on the established sources and stability of nearshore carbonate sediments. This study, however, focuses on new sediment delivered to these coastal settings in the form of calcareous epiphytic communities that colonise Sargassum (i.e., bryozoans, serpulid worms, and red algae). Our analysis of Sargassum collected from coastal waters of the Mexican Caribbean in 2018 indicates a mean carbonate content of 2.09% wet weight at shoreline arrival. Based on data from 11 sites in Quintana Roo, Mexico (spanning 11.15 km of a 60 km section of shoreline), we further estimate the average drained weight of Sargassum that arrived at the coast during 2018 to have been 7.0x103 kg m-1 of shoreline. Together, these findings indicate that mean import of new carbonate sediment by Sargassum was 179 kg m-1 of shoreline in 2018, which is close to our upper estimate of annual proximal sediment production by Thalassia seagrass epiphytes (210 kg m-1 of shoreline). Prior to the onset of these massive Sargassum inundations, grains recognisable as bryozoan skeletons and serpulid tube casings were rare in coastal sediments of the Mexican Caribbean. Consequently, if these calcareous Sargassum epiphytes that are evidently now being imported in large volumes are retained and preserved, they can be expected to impart a distinct record within these coastal sediments. Although quantitative data on Sargassum inundations from other locations are sparse, numerous reports from the scientific community and the media suggest the scale of these events is comparable for many exposed tropical Caribbean and Atlantic shorelines. This represents the first documentation of pelagic Sargassum as a major vector of coastal sediment import, the significance of which has likely only arisen since the onset of large-scale inundations in 2011.

How to cite: Salter, M., Perry, C., Rodríguez-Martínez, R., Alvarez-Filip, L., and Jordan-Dahlgren, E.: Pelagic Sargassum as an emergent high-rate importer of carbonate sediment to tropical Atlantic coastlines, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15898, https://doi.org/10.5194/egusphere-egu21-15898, 2021.

Such factors as climate, currents, morphology, riverine input, and the source rocks influence the composition of the sediments in the Arctic Ocean. Heavy minerals being quite inert in terms of transport can reflect the geology of the source rock clearly and indicate the riverine input. There is a long history of studying the heavy mineral composition of the sediments in the Arctic Ocean. The works by Vogt (1997), Kosheleva (1999), Stein (2008), and others study the distribution of the minerals both on a sea scale and oceanwide. The current study covers Russian shelf seas: Barents, Kara, Laptev, East Siberian, and Chukchi Seas. To collect the material several data sources were used: data collected by the institute VNIIOkeangeologia during numerous expeditions since 2000 for mapping the shelf, data from the old expedition reports (earlier than 2000) taken from the geological funds, and datasets from PANGAEA (www.pangaea.de). About 82 minerals and groups of minerals were included in the joint dataset. The density of the sample points varied significantly in all seas: 1394 data points in the Barents Sea, 713 in the Kara Sea, 487 in the Laptev Sea, 196 in the East Siberian Sea, and 245 in the Chukchi Sea. These data allowed comparing the areas in terms of major minerals and associations. Maps of prevailing and significant components were created in ODV (Schlitzer, 2020) to demonstrate the differences between the seas and indicate the sites of remarkable changes in the source rocks. Additionally, the standardized ratio was calculated to perform quantitative comparison: the sea average was divided by the weighted sea average and then the ratio of that number to the mineral average was found. Only the minerals present in at least four seas and amounting to at least 20 points per sea were considered. As a result, water areas with the highest content of particular minerals were detected. The ratio varied from 0 to 3,4. Combining the ratio data for various minerals allowed mapping specific groups or provinces for every sea and within the seas.

 

Kosheleva, V.A., & Yashin, D.S. (1999). Bottom Sediments of the Arctic Seas. St. Petersburg: VNIIOkeangeologia, 286pp. (in Russian).

PANGAEA. Data Publisher for Earth & Environmental Science https://www.pangaea.de/

Schlitzer, R. (2020). Ocean Data View, Retrieved from https://odv.awi.de.

Stein, R. (2008). Arctic Ocean Sediments: Processes, Proxies, and Paleoenvironment. Oxford: Elsevier, 602pp.

Vogt, C. (1997). Regional and temporal variations of mineral assemblages in Arctic Ocean sediments as a climatic indicator during glacial/interglacial changes. Berichte Zur Polarforschung, 251, 309pp.

How to cite: Popova, E.: Characteristics of the Russian shelf seas in the Arctic Ocean regarding the content of heavy minerals in surface sediments: new data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1166, https://doi.org/10.5194/egusphere-egu21-1166, 2021.

Mollies Nipple—a butte located in the Grand Staircase-Escalante National Monument (GSENM)—is of special interest because of the presence of unusual alunite and jarosite cements within the caprock. These minerals precipitate in hyperacidic environments (pH1-2) and are not stable over ~pH5; yet they are abundant on Mars where they are used to interpret depositional and diagenetic environments. The caprock at Mollies Nipple is historically interpreted as Navajo Sandstone via photogeologic mapping; however, it is ~200 m above the mapped upper extent of the Navajo Sandstone in this region. The units overlying the Navajo Sandstone have complex stratigraphic relations in this region and the caprock could be the Carmel or Temple Cap Formations, or the Page Sandstone. This study aims to characterize Mollies Nipple through measured sections, mineralogical analyses, palynomorph analysis, and radiometric age dates from ash lenses present in the caprock. The results will better define the stratigraphy of Mollies Nipple and determine the regional correlation of the caprock. Ultimately, this work will contribute to the understanding of how alunite and jarosite were precipitated at Mollies Nipple; why these minerals are still present at Mollies Nipple, and potentially revise the understanding of Martian depositional environments.

How to cite: Walker, J. and Potter-McIntyre, S.: Revising the stratigraphy at Mollies Nipple, Kane County, Utah, USA to better understand the origin of jarosite and alunite cements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8032, https://doi.org/10.5194/egusphere-egu21-8032, 2021.

EGU21-14074 | vPICO presentations | SSP3.6

Analyzing the occurrence of environmental indicator minerals using clustering techniques and mineral networks

Jason Williams, Sally Potter-McIntyre, Justin Filiberto, Shaunna Morrison, and Daniel Hummer

Indicator minerals have special physical and chemical properties that can be analyzed to glean information concerning the composition of host rocks and formational (or altering) fluids. Clay, zeolite, and tourmaline mineral groups are all ubiquitous at the Earth’s surface and shallow crust and distributed through a wide variety of sedimentary, igneous, metamorphic, and hydrothermal systems. Traditional studies of indicator mineral-bearing deposits have provided a wealth of data that could be integral to discovering new insights into the formation and evolution of naturally occurring systems. This study evaluates the relationships that exist between different environmental indicator mineral groups through the implementation of machine learning algorithms and network diagrams. Mineral occurrence data for thousands of localities hosting clay, zeolite, and tourmaline minerals were retrieved from mineral databases. Clustering techniques (e.g., agglomerative hierarchical clustering and density based spatial clustering of applications with noise) combined with network analyses were used to analyze the compiled dataset in an effort to characterize and identify geological processes operating at different localities across the United States. Ultimately, this study evaluates the ability of machine learning algorithms to act as supplementary diagnostic and interpretive tools in geoscientific studies.

How to cite: Williams, J., Potter-McIntyre, S., Filiberto, J., Morrison, S., and Hummer, D.: Analyzing the occurrence of environmental indicator minerals using clustering techniques and mineral networks, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14074, https://doi.org/10.5194/egusphere-egu21-14074, 2021.

EGU21-10140 | vPICO presentations | SSP3.6

The ikaite to calcite transformation: A key to understanding the palaeoclimatic significance of glendonites?

Martin Vickers, Madeleine Vickers, Rosalind Rickaby, Han Wu, Stefano Bernasconi, Clemens Ullmann, Gerhard Bohrmann, Robert Spielhagen, Nicolas Thibault, and Christoph Korte

Keywords: Ikaite; Glendonite; Palaeoclimate; Powder X-Ray Diffraction; Clumped isotope thermometry

Marine sedimentary ikaite is the parent mineral to glendonites, stellate pseudomorphs found throughout the geological record. Glendonites are a controversy in palaeoclimatic studies as there is an ongoing debate as to whether their presence in sedimentary successions may be used as cold-climate indicators. Glendonites are typically found associated with glacial sediments, and for a long time ikaite was believed to only nucleate and grow at temperatures < 7 °C. However, with the successful laboratory synthesis of ikaite at higher temperatures, the climatic significance of glendonites was brought into question. This study uses a combination of physical and inorganic chemistry techniques to demonstrate the variable stability of natural marine sedimentary ikaites over short (minutes to hours) and longer (weeks to months) timescales, both between ikaite samples, and in a given ikaite. We examine the nucleation of calcite from the destabilized ikaite, observing that this process is much more complex than previous studies suggest. We demonstrate that over much longer (e.g. months or more) timescales, natural marine sedimentary ikaites are not stable above 5 °C, and thus glendonite presence in sedimentary successions may be considered cold climate indicators.

How to cite: Vickers, M., Vickers, M., Rickaby, R., Wu, H., Bernasconi, S., Ullmann, C., Bohrmann, G., Spielhagen, R., Thibault, N., and Korte, C.: The ikaite to calcite transformation: A key to understanding the palaeoclimatic significance of glendonites?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10140, https://doi.org/10.5194/egusphere-egu21-10140, 2021.

EGU21-3547 | vPICO presentations | SSP3.6 | Highlight

Nano-scale investigation of co-precipitated subglacial calcite and opal, antarctica 

Silvia Frisia, Péter Németh, Andrea Borsato, John C. Hellstrom, Attila Demény, and Béla Pécz

Calcite crusts from the Elephant Hill Moraine (EHM) (76°17'35" S  157°20'05" E) collected during 1983-84  were interpreted as formed in subglacial environments influenced by hydrothermalism (Faure et al., 1988). More recently, 234U enrichment in these crusts was used to suggest that during the warm MIS 11 interglacial (ca. 400 ka), the ice sheet margin at the Wilkes Basin retreated about 700 km inland (Blackburn et al., 2020). Their 234U data from separate analyses of pure calcite and pure opal crusts suggested that “connate seawater would impart marine signatures to subglacial waters” (Blackburn et al., 2020), with the former associated with massive melting during MIS 11.  However, robust U-series dating by Blackburn et al (2020) was only possible on pure end members of opal and calcite, whilst other EHM crusts did not yield reliable ages and were discarded. The inferred MIS11 ice-loss was then based on a model of 234U accumulation and on those carbonate ages that fit their hypothesis that connate seawater influenced the subglacial environment.

 

Here, we investigated the nanostructure of EMH samples that yielded unreliable U-Th ages, which were too old to fit into the 234U-based model of MIS11 connate seawater influencing subglacial waters. High-resolution transmission electron microscope images showed a complex history of precipitation, dissolution, re-precipitation, including the co-precipitation of nanocrystalline calcite and opal. Co-precipitation was documented by the inclusion of micrometre-scale opal spherules within calcite crystals whose lattice orientation does not change across the spherules and can be explained by the fluid being extremely enriched in silica. The calcite immediately surrounding the opal spherules was characterized by twins and likely a response to sub-ice sheet stress during their precipitation. The calcite-opal mixture partially replaced pre-existing calcite crystals, which appear broken, corroded and pre-date a final, pure calcite void-filling cement. Clearly, these EHM samples document several stages of crystallization, which imply repeated mobilization of chemical species. Preliminary Fluid Inclusion analyses of the crusts yielded a temperature of about 85oC, which inferred that at one stage calcite precipitation may have been influenced by hydrothermalism associated with volcanism.  Our identification of complex crystallization histories for the Elephant Moraine subglacial carbonates opens up alternative formation hypotheses to that proposed by Blackburn et al. (2020) such as the existence of multiple sources of aqueous solutions. Consequently, it is fraught to infer that all the EMH formed from connate marine waters generated 400 ka without dating of multiple phases of calcite precipitation from each sample.

 

References: Blackburn, T. et al. 2020, Nature, 583 (7817), pp.554-559. Faure, G.  et al, 1988, Nature, 332(6162), pp.352-354.

How to cite: Frisia, S., Németh, P., Borsato, A., Hellstrom, J. C., Demény, A., and Pécz, B.: Nano-scale investigation of co-precipitated subglacial calcite and opal, antarctica , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3547, https://doi.org/10.5194/egusphere-egu21-3547, 2021.

Primary phases in carbonate rocks archive a wealth of geochemical information about depositional conditions and environmental changes. Secondary phases may record additional—albeit more cryptic—information, potentially complicating interpretation of primary signatures. The ability to compositionally characterize and date multiple, texturally distinct generations of primary, diagenetic, and metamorphic carbonate phases enables deciphering of complex depositional and post-depositional histories carbonate successions have experienced. Combined trace-element mapping and U-Pb geochronology of calcite in situ (in thin sections) by LA-ICP-MS provides opportunities to assign absolute ages to calcite crystallization and recrystallization with petrographic and geochemical context. We have applied this approach to two samples of apparently pristine, unmetamorphosed Ordovician bioclastic limestones from the Viki drill core (western Estonia), representing the eastern part of the Baltoscandian Basin. The depositional ages of the samples are constrained by biostratigraphic correlation to ca. 460 and 445 Ma (Hints et al., 2014). Several lines of evidence—such as very low organic-matter maturation and properties of clay minerals—indicate that this sequence did not experience temperatures above 100 °C, and likely not above 50 °C, since deposition (Kirsimäe et al., 2020). Optical petrography and backscatter-electron (“BSE”) imaging reveal low-porosity “BSE-bright” calcite spar cement in pore spaces between “BSE-dark” micro-porous calcite bioclasts. Trace-element mapping of several areas (several mm2 each) in each thin section by LA-quadrupole-ICP-MS reveals variably elevated Mn/Sr, U concentration, and U/Pb in the calcite spar cement. The trace-element maps were subsequently used to guide the placement of laser spots for U-Pb dating by LA-multicollector-ICP-MS. Primary bioclastic calcite in both samples has low U/Pb (238U/206Pb < 7) and, thus, does not yield precise Concordia-intercept dates. The primary calcite does, however, yield imprecise intercept dates within uncertainty of the depositional ages. Calcite spar cement has higher U/Pb (238U/206Pb up to ~15.7) and including all analyses, yields intercept dates of ca. 415 Ma in each sample. Additionally, several of the domains with the highest U/Pb from each sample yield slightly younger dates of ca. 400­-380 Ma. The timing of calcite (re)crystallization and cementation identified here overlaps with the timing of continent collision during the Caledonian orogeny in Scandinavia. We tentatively interpret this to be a result of fluid flow in response to the collision far-inboard (>500 km) from the orogenic front. Furthermore, this work demonstrates that apparently pristine carbonates may have experienced recrystallization (or at least chemical-isotopic perturbation) in open systems long after deposition.

References

Hints, O., Martma, T., Männik, P., Nõlvak, J., Põldvere, A., Shen, Y., Viira, V. 2014. New data on Ordovician stable isotope record and conodont biostratigraphy from the Viki reference drill core, Saaremaa Island, western Estonia. GFF 136, 100–104.

Kirsimäe, K., Somelar, P., Jõeleht, A. 2020. Illitization of the lower Cambrian (Terreneuvian) Blue Clay in the northern Baltic Palaeobasin. Estonian Journal of Earth Sciences 69, 200–213.

How to cite: Hagen-Peter, G., Wang, Y., Hints, O., and Lepland, A.: Cryptic secondary cementation of Ordovician limestones in the Baltoscandian Basin, northern Europe, revealed through trace-element mapping and U-Pb dating by LA-ICP-MS, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12547, https://doi.org/10.5194/egusphere-egu21-12547, 2021.

EGU21-511 | vPICO presentations | SSP3.6

Carbonate pore type quantification through digital image analysis – dual-porosity reservoir example of the Arabian Gulf.

Joao Barata, Jorge Gomes, Ana C. Azerêdo, and Luís V. Duarte

The Barremian Upper Kharaib Formation reservoir unit was deposited in a carbonate ramp setting and shows moderate vertical facies variability, transitioning from a wackestone-dominated transgressive phase into a grainstone-dominated regressive phase. A dual-porosity system containing micro and macro-pores characterizes this reservoir, with microporosity as the dominant fraction of total porosity and holding large amounts of hydrocarbons in place. Porosity variations in the reservoir section shows no clear vertical trends, while permeability shows significantly higher values in the regressive phase sediments.

Digital image analysis (DIA) was done on this study using the different methods of visual estimation, colour selection based on histogram analysis and trained machine learning, with the measured area seen as a proxy for the total pore volume. A total of 285 images captured from 142 thin sections from 4 different wells were analysed. Colour selection through automated batch processing was done to quantify total macroporosity in all thin sections, using the petrographic images captured under XPL. Different RGB color codes and tolerance parameters were used in different runs on the same image, in an attempt to address the uncertainty in macroporosity measurements. Machine learning was applied using selected training images and manually classified pixel sets defining 2 classes (porous and non-porous space).

Total macroporosity is separated into interparticle and intraparticle/mouldic porosity (intrafossil porosity and probable dissolution of bioclasts/peloids/intraclasts) based on visual estimations, given that an unambiguous automated classification of these pore types is practically impossible to obtain. Microporosity is estimated to represent more than 60% of the total porosity. Considerable differences exist between the pore networks of the transgressive and regressive phase deposits, with the latter showing stronger heterogeneity and higher average interparticle macroporosity values in grainstone intervals containing coarser carbonate particles and small or no amount of interparticle micrite. These carbonate particles are, however, micritized and contain considerable volumes of microporosity within.

Pore type quantification through DIA can provide an objective, relatively quick and inexpensive methodology to provide useful insights into petrophysical relationships and to complement petrographic observations and core analysis results. Detailed depositional and stratigraphic models coupled with this quantitative data would help to better understand the depositional and diagenetic controls on rock properties variability.

How to cite: Barata, J., Gomes, J., C. Azerêdo, A., and V. Duarte, L.: Carbonate pore type quantification through digital image analysis – dual-porosity reservoir example of the Arabian Gulf., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-511, https://doi.org/10.5194/egusphere-egu21-511, 2021.

EGU21-10145 | vPICO presentations | SSP3.6

Diagenetic complexities of iron oxide cements in Mesozoic sandstones of Utah, U.S.A.

Sally Potter-McIntyre and Marjorie Chan

Stratigraphic units of the Colorado Plateau comprise a remarkable Mesozoic section in Utah. Thse units are ideal for studying sandstone diagenesis where there is established basinal context of depositional facies and tectonics, as well as continuity of exposure. To untangle the complex relationships and diagenetic histories, it is crucial to understand host rock properities (porosity and permeability), authigenic mineralogies (that give clues to fluid composition), diagenetic textures, and age dating. This study is a review and synthesis of previous work that has contributed to the understanding of the diagenetic history recorded in authigenic iron oxide precipitates. We discuss cement generations and mineralogies, fluid chemistries, origins and mobilization of iron, and timing of precipitation. Spheroidal cemented mineral masses (concretions) are common within many Mesozoic units of Utah – most notably the Jurassic Navajo Sandstone.  However, formation of these concretions is still not completely understood. Spheroidal concretions are currently a “hot topic”, especially since the discovery of similar “blueberry” features on Mars with their implications for habitability, and the potential for these nodules to host biosignatures. Several models for spheroidal concretion formation are evaluated. Understanding how iron is mobilized and precipitated and how spheroidal concretions form have implications for similar geometries and mineralogies in many terrestrial regions, but will require continued integrated studies across multiple scales (see Baker and Potter-McIntyre, this session). These scales include the submicroscopic levels of understanding and detecting the potential role of microbes in mineral precipitation, to the larger scale mapping of regional diagenetic coloration and mineral patterns that could represent records of basinal fluids and the response to climate, tectonics, and regional hydrology.

How to cite: Potter-McIntyre, S. and Chan, M.: Diagenetic complexities of iron oxide cements in Mesozoic sandstones of Utah, U.S.A., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10145, https://doi.org/10.5194/egusphere-egu21-10145, 2021.

SSP3.7 – Mixed-Energy Shoreline–Shelf Systems: Processes, Facies and Architecture

EGU21-2895 | vPICO presentations | SSP3.7

Internal mouth-bar variability and differential preservation of coastal-process indicators in low-accommodation deltaic settings 

Anna van Yperen, Miquel Poyatos-Moré, John Holbrook, and Ivar Midtkandal

Mouth bars are fundamental architectural elements of deltaic successions. Understanding their internal architecture and complex interaction with coastal processes (fluvial-, tide- and wave-dominated) is therefore paramount to the interpretation of ancient deltaic successions. This is particularly challenging in low-accommodation systems because they are commonly characterized by a thin, condensed and top-truncated expression. In this study we analyze the exhumed Cenomanian Mesa Rica Sandstone (Dakota Group, Western Interior Seaway, USA), which encompasses a fluvio-deltaic system along a ~450 km depositional dip-parallel profile. The study targets the proximal deltaic expression of the system, using 22 sedimentary logs (total of 390 m) spatially correlated within a ~25 km2 study area at the Tucumcari Basin margin. Analysis of facies distribution, depositional architecture and stratigraphic surfaces mapping reveals a 6–10-m-thick, sharp-based and sand-prone deltaic package, comprising several laterally-extensive (>1.4 km width) mouth bars. Within those, we distinguish four different along-strike sub-environments based on differences in grain size, sedimentary structures, bed thicknesses, and bioturbation indices; these are mouth bar axis, off-axis, lateral fringe to distal lateral fringe deposits, and overall reflect waning depositional energy with increasing distality from the distributary channel mouth. The interpreted mouth-bar components also show internal variability in dominant process regime, with overall river dominance but local preservation of tide influence in the lateral fringe and distal fringe environments. However, mouth-bar deposits amalgamate to form an extensive sand-rich sheet body throughout the study area, in which interflood mudstone to very-fine grained sandstone beds are nearly absent. This indicates a low accommodation/supply (A/S) setting, which promoted recurrent channel avulsion/bifurcation and thus reworking of mouth-bar fringe and distal-fringe sediments, where background coastal processes tend to be better recorded.

Trends in along-strike changes in sedimentary characteristics from axial to lateral environments are also recognized in other wave- and river-dominated deltaic settings as well, where axial components consist of higher energy facies associations resulting from high-density currents, whereas heterolithics become dominant towards the fringes, where there is an alternation of low- and high-density deposits combined with an increased recording of finer-grained facies associations. Complemented with our study, this suggests that internal hierarchy of mouth bars is evident and observed regardless of dominant coastal processes. Consequently, subdivision of mouth bars into different components can reduce complexity of models deriving from a myriad of facies subdivisions, and guide prediction of facies changes and sand distribution in future studies of proximal deltaic settings. Finally, results of this study evidence internal process-regime variability within mouth-bar components. This cautions against relying solely on the preserved deposits at one given location in a system to infer dominant and subordinate coastal processes (e.g. tidal indicators), with a consequent risk of underestimating the true mixed-influence nature of low-accommodation deltaic settings.

How to cite: van Yperen, A., Poyatos-Moré, M., Holbrook, J., and Midtkandal, I.: Internal mouth-bar variability and differential preservation of coastal-process indicators in low-accommodation deltaic settings , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2895, https://doi.org/10.5194/egusphere-egu21-2895, 2021.

EGU21-5702 | vPICO presentations | SSP3.7

The architecture and evolution of shallow water delta mouth bars: examples from the Lower Cretaceous of Spain

Matthew Watkinson, Grant Cole, and Rhodri Jerrett

Improved understanding of delta mouth bar morphodynamics, and the resulting stratigraphic architectures, is important for predicting the loci of deposition of different sediment fractions, coastal geomorphic change and heterogeneity in mouth bar reservoirs. Facies and architectural analysis of exceptionally well-exposed shallow water (ca. 5 m depth) mouth bars and associated distributaries, from the Xert Formation (Lower Cretaceous), of the Maestrat Basin (east-central Spain), reveal that they grew via a succession of repeated autogenic cycles. The formation is part of a mixed clastic-carbonate succession deposited during a time of active faulting and incipient salt tectonism, but in an area away from their direct influence and where wave and tidal reworking were minimal.

An initial mouth bar accretion element forms after avulsion of a distributary into shallow standing water. Turbulent expansion of the fluvial jet and high bed friction results in rapid flow deceleration, and deposition of sediment in an aggradational to expansional bar-form. Vertical bar growth causes flattening and acceleration of the jet. The accelerated flow scours channels on the bar top, which focuses further expansion of the mouth bar at individual loci where the channels break through the front of the mouth bar. Here, new mouth bar accretion elements form, downlapping and onlapping against a readily recognizable surface of mouth bar reorganization. Vertical growth of the new mouth bar accretion elements causes flattening and re-acceleration of the jet, leading to channelization, and initiation of the next generation of mouth bar accretion elements. Thus the mouth bar grows, until bed-friction effects cause backwater deceleration and superelevation of flow in the feeding distributary. Within-channel sedimentation, choking and upstream avulsion of the feeding channel, results in mouth bar abandonment. In this study, mouth bars are formed of at least two to three accretion elements, before abandonment happened. The results of this study contrast with the notion that mouth bars form by simple vertical aggradation and radial expansion. However, the architecture and facies distributions of shallow water mouth bars are a predictable product of intrinsic processes that operate to deposit them.

How to cite: Watkinson, M., Cole, G., and Jerrett, R.: The architecture and evolution of shallow water delta mouth bars: examples from the Lower Cretaceous of Spain, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5702, https://doi.org/10.5194/egusphere-egu21-5702, 2021.

EGU21-13530 | vPICO presentations | SSP3.7

The impact of compaction of clastic sediments on fluvial-dominated delta morphology

A. Aulia Valencia, J.E.A. (Joep) Storms, Dirk-Jan Walstra, Helena van der Vegt, and H.R.A. (Bert) Jagers

Only a limited amount of data is available to quantify the impact of syn-depositional compaction on delta depositional patterns. In this study, we investigate numerically how different scenarios for compaction rate (0 - 10 mm yr-1) drives morphological variations in mud- and sand-rich fluvial-dominated deltas. To do this, a 1D grain-size dependent compaction model was implemented into the open-source Delft3D. This implementation allows deposited sediment to decrease in thickness over time due to the accumulation of newly deposited sediments above. The resultant sedimentary deposits of a prograding delta are post-processed to highlight the changes in depositional patterns under different compaction scenarios. Deposits are classified into sub-environment (e.g., delta top, delta front, and pro delta). The delta top geometry (e.g., area, shape, and rugosity) and the distribution of sediment between different sub-environments are compared. The modeling results verify that the larger compaction-induced subsidence affects accommodation provision. We show that this results in more significant sediment deposition and more evenly distributed sediment across the delta top. Larger compaction results in a smaller area with a more semi-circular shape and less rugose delta top. The modeling results presented here bridges the knowledge gap on the effects of syn-depositional compaction on delta morphology evolution.

How to cite: Valencia, A. A., Storms, J. E. A. (., Walstra, D.-J., van der Vegt, H., and Jagers, H. R. A. (.: The impact of compaction of clastic sediments on fluvial-dominated delta morphology, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13530, https://doi.org/10.5194/egusphere-egu21-13530, 2021.

EGU21-6914 | vPICO presentations | SSP3.7

Landward migration of backwater-mediated delta avulsion sites in response to increase in seasonal lake level: Qaidam Basin, China

Jiaguang Li, Vamsi Ganti, Hao Wei, and Chenglong Li

River deltas grow through episodic channel-jumping events, called avulsions, which have caused some of the deadliest floods in human history. Climate change is threatening to drown river deltas through a global increase in sea level; however, it is unclear how sea-level rise may affect the location of avulsion sites. Theory and experiments indicate that the avulsion sites on lowland deltas emerge within the backwater zone of coastal rivers because of the morphodynamic feedbacks arising from natural flood discharge variability and the nonuniform flows caused by the standing water level in the receiving basin. Under this backwater hypothesis, marine transgression should cause the landward-migration of lobe-scale avulsion locations; however, we currently lack field evidence for this theoretical prediction. Here, we analyze the location of river avulsions on the Sulengguole River that drains into the North Hubusun Lake, Qaidam Basin, China. Using analysis of time-series satellite imagery, we identified 7 lobe-scale avulsions that occurred in the distal portions of the Sulengguole River during the observation period of 1985 to 2010 CE. Satellite imagery revealed that the areal extent of the seasonal water in the lake increased at a rate of 1.89±0.80 km2/yr, likely as a result of increase in extreme precipitation rates. The increase in seasonal lake water areas caused the river mouth of the Sulengguole River to translate landward at a rate of 0.36±0.17 km/yr. We show that the avulsion sites also migrated landward at a commensurate rate of 0.24±0.07 km/yr during this period, consistent with the rate of landward migration of the river mouth. Finally, we show that all 7 avulsions had an avulsion length—streamwise distance of the avulsion site to the river mouth—that scales with the estimated backwater lengthscale (mean of 0.50±0.14 times the backwater lengthscale), consistent with the global compilation of avulsion lengths on large, low-gradient deltas. Our work demonstrates, for the first time, that landward migration of river mouth that would result from relative sea-level rise will cause the avulsion locations to migrate inland in a predictable manner, with implications for the sustainable management of the future of deltas and mitigating flood hazards.

How to cite: Li, J., Ganti, V., Wei, H., and Li, C.: Landward migration of backwater-mediated delta avulsion sites in response to increase in seasonal lake level: Qaidam Basin, China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6914, https://doi.org/10.5194/egusphere-egu21-6914, 2021.

EGU21-3472 | vPICO presentations | SSP3.7

Subsurface heterogeneity patterns that emerge from interacting depositional processes

Brian Willis and Tao Sun

Emergent structures define organizational patterns that spontaneously develop due to interactions between component properties or behaviors of complex dynamic systems, rather than being a simple compilation of the individual parts observed within the system at any one time. Traditional facies models used to predict subsurface lithic variations focus on defining the distribution of depositional environments on Earth’s surface and relating the hierarchy of preserved bedding units to different scales of surficial bedforms. It is increasingly recognized that such static models fail to predict the geometry and character of many types of preserved lithic bodies and discontinuity surfaces unless these observations are placed within the context of the overall evolving system. Numerical depositional process models are presented to show links between evolving depositional patterns and preserved facies patterns within different settings.

     Channel deposit internal variations tend not to be channel shaped, but rather sweet spots within the deposit resemble a string of beads, each formed as individual channel segments meander. Mouth bar deposits generally do not to have the circular to elliptical shape of a modern channel-mouth bedform, but rather tend to be more elongate fingers cut by a diachronous channel filled as river flows are choked off by loss of gradient during progradation. Although the final channel basal erosion surface appears continuous, timelines cross this surface along the length of the deposit. Deltaic shorelines that look identical at a given time preserve very different deposits when the feeding river avulses at different frequency, a condition that can change within an individual deposit formed alternately during periods of sea level rise and fall. Even major stratigraphic surfaces, like lowstand fluvial incision surfaces and wave-ravined falling stage and transgressive surfaces, are likely to gradually emerge from the migration of localized areas of erosion that were never as extensive at any one time as the preserved surface. Such surfaces may be regionally diachronous, with deposits of the same age locally preserved variably above and below the surface. Understanding emergent lithic bodies and internal heterogeneity patterns are fundamental to understanding how deposition is recorded in the rock record and for facies models used to predict how subsurface fluids move through shallow marine deposits.

How to cite: Willis, B. and Sun, T.: Subsurface heterogeneity patterns that emerge from interacting depositional processes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3472, https://doi.org/10.5194/egusphere-egu21-3472, 2021.

The geology of a depositional system can mostly be described by looking at sedimentary structures and sedimentary composition. However, in areas of complex shoreline mixed-process system (influenced by fluvial-tides-marine processes), many factors should be put into consideration. In Brunei, the mixed-sediment types occur extensively. The geology is mainly characterized here by thick Neogene siliciclastic facies ranging from fluvial, tidal and marine sediments deposited during periods of deltaic to shelfal setting, affected also by tectonic events. Due to this, differentiating tide and wave dominated facies is often a major challenge in the region.

In this study, it is emphasized that in order to support interpretations on these transitional facies, specific factors such as ichnofacies and microfossil content can be considered. Pollen and spores are more expected and useful in rather terrestrial systems, whilst in marine environments dinoflagellates, foraminifera and nannofossils could be convenient if preserved. Foraminifera and ichnofossils have the merit to be great indicators of a variety of sub-environments within the complex shallow water system.

The methods involve standard outcrop logging of fluvial, tidal and shallow marine outcrops, identifying lithology and key sedimentary features including trace fossils. Clay-rich samples were checked for microfossil content. Laboratory work involved extracting organic (pollen, spores, dinoflagellates) and calcareous (foraminifera, nannofossils) microfossils and documented them with light microscope (LM), stereo microscope, and Scanning Electron Microscope (SEM).

The results revealed that the most common trace fossil assemblages are the Ophiomorpha, Cruziana and Skolithos ichnofacies, and they refer to proximal marine settings. Among the calcareous microfossils recovered were very few coccolithophorids (Sphenolithus abies and Sphenolithus moriformis), which indicate very rare holomarine conditions, while the following benthic foraminifera genera were identified: Ammonia, Nonion, Elphdium, Elphidiella, Quinqueloculina, Ammobaculites, and Trochammina. Each of these genera have specific environmental requirements concerning hydrodynamics, trophic resources, oxygen content, substrate-type and deltaic influence. Results on pollen and spores, mangrove vegetation is marked by Sonneratia and Rhizophora-types, mixed-dipterocarp by Shorea spp., while peat swamp by Verrucatosporites usmensis and Osmunda sp.. Besides few dinoflagellate cysts (Achomosphaera sp., cf. Exosphaeridium sp., cf. Operculodinium sp., gen indet., Lingulodinium? pycnospinosum and Tuberculodinium vancampoae) and two acrtitarch taxa (Cymatiosphaera sp. and Cymatiosphaera cf. nuda) were found. These findings indicate incomplete sets of parasequences with palaeoenvironments of mixed shallow marine conditions. Mangrove pollen retrieved within tidal sediments indicates mangrove-dominated tide-influenced shoreline, while shoreline with diverse ichnofossils show coastal area connected to wave-dominated upper shoreface/ delta front. The calcareous foraminifera and nannofossil differentiate sediments belonging to lower shoreface to offshore/ prodelta deposits.

How to cite: Roslim, A., Briguglio, A., Kocsis, L., and Goeting, S.: Addressing mixed facies interpretation difficulties by coupling sedimentary data with ichnofacies and microfossil data: an example from several paralic deposits in Brunei Darussalam., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6888, https://doi.org/10.5194/egusphere-egu21-6888, 2021.

The interaction of river and marine processes in the fluvial to marine transition zone (FMTZ) fundamentally impacts sedimentary dynamics and deposition. Heterolithics are important facies within ancient and modern FMTZs but the preserved signal of river flood, wave and tidal variations in heterolithics remains uncertain. This study integrates facies and ichnofacies characteristics of heterolithics in the Lambir Formation (Baram Delta Province, NW Borneo), with information of larger-scale stratigraphic architecture and modern analogue information, to interpret the preserved record of river flood deposits under the influence of tides and waves in an ancient FMTZ. Within the FMTZ of distributary channels, interpreted proximal–distal sedimentological and stratigraphic trends suggest: (1) a proximal fluvial-dominated, tide-influenced subzone; (2) a distal fluvial- to wave-dominated subzone; and (3) a conspicuously absent tide-dominated subzone. During coupled storm and river floods, fluvial processes dominated the FMTZ along major and minor distributary channels and channel mouths, causing significant overprinting of preceding interflood deposits and deposition of thicker, sandier event beds. Intervening interflood deposits are muddier, with increased bioturbation, and may variably preserve sedimentary indicators of tide and wave processes. Despite interpreted fluvial–tidal channel units and mangrove influence implying tidal processes, there is a paucity of unequivocal tidal indicators (e.g. cyclical heterolithic layering). This suggests that process preservation in the FMTZ preserved in the Lambir Formation primarily records episodic (flashy) river discharge, river flood and storm overprinting of tidal processes, and possible backwater dynamics. 

How to cite: Collins, D. and Johnson, H.: Sedimentary signals of fluvial discharge variability under tide and wave influence: Miocene examples in NW Borneo, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14931, https://doi.org/10.5194/egusphere-egu21-14931, 2021.

EGU21-8546 | vPICO presentations | SSP3.7

How to link modern and ancient barrier island systems: Dimensional comparisons and updated sedimentary facies models 
not presented

Cari Johnson, Julia Mulhern, and Andrew Green

Existing depositional and facies models for ancient barrier island systems are primarily based on modern observations. This approach overlooks processes tied to geologic time scales, such as multi-directional motion, erosion, and reworking, and their resulting expressions in preserved strata. We have investigated these and other challenges of linking modern and ancient barrier islands through outcrop studies and through data compilation from the rock record compared to modern barrier island dimensions. Results emphasize key depositional and preservation processes, and the dimensional differences between deposits formed over geologic versus modern time scales. For example, when comparing deposits from individual barrier islands, thickness measurement comparisons between modern and ancient examples do not vary systematically, suggesting that local accommodation and reworking dictate barrier island thickness preservation. A complementary outcrop study focusing on paralic strata from the Upper Cretaceous Straight Cliffs Formation in southern Utah (USA) is used to update models for barrier island motion and preservation to include geologic time-scale processes. Barrier island deposits are described using four facies associations (FA): backbarrier fill (FA1), lower and upper shoreface (FA2), proximal upper shoreface (FA3), and tidal channel facies (FA4). Three main architectural elements (barrier island shorefaces, shoreface-dominated inlet fill, and channel-dominated inlet fill) occur independently or in combination to create stacked barrier island deposits. Barrier island shorefaces record progradation, while shoreface-dominated inlet fill records lateral migration, and channel-dominated inlet fill records aggradation within the tidal inlet. Barrier islands are bound by lagoons or estuaries and are distinguished from other shoreface deposits by their internal facies and outcrop geometry, association with backbarrier facies, and position within transgressive successions. Tidal processes, in particular, tidal inlet migration and reworking of the upper shoreface, also distinguish barrier island successions. In sum, these datasets demonstrate that improved depositional and facies models must consider multidirectional island motion, ravinement, erosion, inlet migration, and reworking when describing processes and predicting barrier island dimensions.

How to cite: Johnson, C., Mulhern, J., and Green, A.: How to link modern and ancient barrier island systems: Dimensional comparisons and updated sedimentary facies models , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8546, https://doi.org/10.5194/egusphere-egu21-8546, 2021.

EGU21-9042 | vPICO presentations | SSP3.7

Variations in physiography, tidal forcing, and bottom shear stress in palaeo-seas: lessons learned from numerical modelling.

Valentin Zuchuat, Elisabeth Steel, Ryan Mulligan, Daniel Collins, and J.A. Mattias Green

The physiography (geometry and bathymetry) of a basin and its latitude are the primary parameters that dictate the tidal dynamics in shoreline–shelf systems. Understanding the impact that changes in physiography have on tides allows researchers to 1) improve interpretations of historical sedimentary processes in shallow-marine basins, and 2) better predict potential variations in tidal dynamics in response to an anthropogenic-driven relative sea level change.

Here, we present an analysis of numerical modelling of tidal propagation in the Upper Jurassic Sundance and Curtis Seas demontrating that basin-scale amplification and dampening of tides occurred in different palaeophysiographic configurations, and more localised amplification relating to tidal harmonics occurred in certain physiographic scenarios. Consequently, palaeophysiography was the primary control on both the magnitude and location of tidal amplification, flow speed, and bed shear stress, whereas secondary controls were initial tidal forcing and bottom drag coefficient.

Simulation results for the palaeophysiography with a 600 m depth at the mouth of the system suggest a distribution of sedimentary facies comparable to those documented in the Upper Jurassic lower Curtis Formation, apart from the innermost Curtis Sea, near to the palaeoshoreline. Sediments potentially supplied by aeolian processes during regression and increased aridity were likely reworked by tides during a subsequent a transgression as the climate became more humid. The palaeophysiography with a 600 m depth at the mouth of the system can therefore be considered a realistic palaeophysiographic configuration for the Sundance and Curtis Seas given the similarities that exist between the predicted distribution of sedimentary facies and their actual distribution in the lower Curtis Formation. In this palaeophysiography, the Sundance Sea and the Curtis Sea would have thus attained a maximum depth of ~240 m and 40-45 m, respectively. In this context, the simulated tidal range in the Curtis Sea would have reached 2.60 m, which would classify the Curtis Sea as a meso-tidal system (2x 1.30 m tidal amplitude).

Finally, using change in palaeophysiographic configuration as a proxy for relative sea-level variations revealed the non-uniqueness (sensu Burgess & Prince, 2015) of sedimentary successions deposited in tide-dominated basin, given that tidal amplification in the system was controlled by palaeophysiographic configuration: one specific succession could be the product of several, equally-valid relative sea-level histories. Reciprocally, the impact of relative sea-level change on different successions is non-unique, since local tidal harmonics and the characteristics of coeval deposition may vary significantly during relative sea level changes.

How to cite: Zuchuat, V., Steel, E., Mulligan, R., Collins, D., and Green, J. A. M.: Variations in physiography, tidal forcing, and bottom shear stress in palaeo-seas: lessons learned from numerical modelling., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9042, https://doi.org/10.5194/egusphere-egu21-9042, 2021.

Low-accommodation shallow-marine systems are often challenging to interpret and map in the subsurface due to their amalgamated/condensed nature, which often falls within sub-seismic resolution. Outcrop examples are significantly rarer and less well documented than moderate to high accommodation systems. Detailed studies of such systems are scarce, and their resulting depositional architecture is still poorly understood.

The late Jurassic shallow-marine deposits of the Intra Draupne Formation were deposited during the lattermost stage of Jurassic rifting in the South Viking Graben. They are found in a small N-S graben, flanked by two highs, the Haugaland (west) and the Avaldsness (east). Deposition took place under low-accommodation conditions on top of a markedly erosive regional unconformity of Middle Jurassic age. In this study, we performed a detailed 1:1 sedimentological core description and interpretation of 20 wells with the aim of providing a redefined, basin-wide and high-resolution sequence stratigraphic model to constrain the tectonostratigraphic evolution of the basin.

The Intra Draupne Formation is typically 15-20 m thick, with minimum and maximum values of 5 and 40 m respectively. The deposits are remarkably coarse-grained, dominated by coarse to very coarse sand and granule to pebble rich packages showing different degrees of textural maturity, ranging from well-rounded and very well-sorted to subangular and poorly-sorted deposits. The deposits are bioturbated with ichnofacies mainly represented by Skolithos and Thalassinoides and locally abundant Fugichnia escape traces. The bioturbation index is typically 2-3.  Deposits are otherwise structureless graded/non-graded or planar/through cross stratified. Differences in the degree of textural maturity, grain-size trends and sedimentary structures are the basis for a depositional model which includes gravity-flow dominated fan delta front and prodelta lobe deposits with variable degrees of tidal and wave modification and reworking in the form of compound tidal dunes/sand ridges and barred shorefaces.

Our results suggest the presence of an Early Kimmeridgian shoreline at the easternmost part of the study area, with westerly sourced fan-fan delta systems and separated from the Haugaland High and the basin-bounding Western Boundary Fault (WBF), by an inferred (non-preserved) coastal plain. In the Late Kimmeridgian, tectonic subsidence associated with the WBF created a major change in the basin configuration; the former shoreline and alluvial systems to the east were disconnected from their original source area and a semi-enclosed and elongated embayment was formed to the west, characterized by low energy conditions and restricted water circulation. During the Tithonian, further tectonic movements and relative sea-level rise, lead to the creation of a fully-connected marine seaway which was characterized by strong tidal currents to the west and more wave-dominated conditions to the east. Reduction of tectonic activity and sea-level rise from Late Tithonian to Early Rhyazanian forced backstepping of the delivery systems and flooding of the source areas promoting a basin-wide period of sediment starvation, which ended with deposition of the open marine Draupne shale.

This study provides information on how shallow-marine systems develop in low-accommodation settings, with implications for paleogeographic reconstructions, sandstone distribution and characterization in other areas, with more limited datasets.

How to cite: Puig López, J. M., Poyatos-Moré, M., and Howell, J. A.: Sedimentological and tectonostratigraphic evolution of a restricted to fully-connected, low-accommodation, shallow-marine basin: The late Jurassic Intra Draupne Formation in the Johan Sverdrup field, Southern Utsira High (Norwegian North Sea), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9271, https://doi.org/10.5194/egusphere-egu21-9271, 2021.

EGU21-16005 | vPICO presentations | SSP3.7

Multi-scale influence of topography on shallow-marine successions associated with long-term transgressions

Miquel Poyatos-Moré, Ernesto Schwarz, Salvador Boya, Luz Elena Gomis-Cartesio, and Ivar Midtkandal

Thick shallow-marine successions associated with long-term transgressions are less well known than their thin, well-sorted counterparts, widely studied due to their potential to form good reservoirs. In these successions, particularly in storm-dominated examples, bioturbation can obliterate primary sedimentary characteristics, making stacking patterns and sequences difficult to define, and challenging our understanding of the main controls in their resulting depositional architecture. This study presents an example from the Jurassic of the Neuquén Basin (Argentina), with the aim to: a) refine the depositional model of a thick, shallow-marine succession associated with a long-term, early post-rift transgression, b) constrain multi-scale controls on stratigraphic architecture and lateral facies variability, and c) discuss their preservation and response to post-depositional processes. To do this, a <300 m-thick succession has been studied along a >10 km continuous exposure, with mapping, sedimentary logging and correlation of stratigraphic units, integrated with subsurface, biostratigraphic and ichnological data. The succession shows an overall retrogradational-aggradational-retrogradational stacking pattern, with several higher frequency regressive units (parasequences and parasequence sets, PSS). The lower part (PSS I) comprises laterally-discontinuous (10's of m) mouth-bars and distributary channel fills, dominated by several m-thick coarsening- and fining-up sandstone packages and m-scale erosive conglomeratic lenses. Above these, the succession (PSS II-IV) is composed by laterally-continuous (>100's of m) storm-dominated lower-shoreface to upper-offshore deposits, dominated by <1m-thick fine-grained and highly bioturbated tabular muddy sandstones and sandy mudstones, with rarely-preserved HCS and bioclastic-rich limestones; their internal characteristics and bed boundaries are diffuse due to pervasive bioturbation, suggesting overall low sedimentation rates and recurrent periods of colonization. The coarse-grained nature and lithology of the mouth bars and channel fills in the lower succession (PSS I) are consistent with a proximal sediment source, associated with erosion of intra-basinal highs. Its variable thickness, lateral distribution and onlap against underlying syn-rift deposits demonstrates partial infill of localized higher-accommodation areas. The well-sorted and finer-grained nature of the shoreface-offshore strata the middle and upper succession (PSS II-IV) indicates a more mature, distal source, with sediment redistributed by longshore currents, and then intensely bioturbated. These deposits display well-defined parasequences internally composed of laterally-continuous bedsets (<5 m-thick). They extend along the entire study area, but show a significant vertical thickness variability. The integration of outcrop and subsurface data mapping (well and seismic) reveals this variability records the stratigraphic response of transgression over a complex, regional-scale ramp-step and underfilled rift topography, which controlled the location of main thickness and facies changes, and promoted areas of favored biogenic reworking. This study offers new insights in how to interpret thick transgressive successions based on primary depositional mechanisms and postdepositional processes, and provides useful tools to understand and predict the nature and potential preservation of these deposits in limited subsurface datasets.

How to cite: Poyatos-Moré, M., Schwarz, E., Boya, S., Gomis-Cartesio, L. E., and Midtkandal, I.: Multi-scale influence of topography on shallow-marine successions associated with long-term transgressions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16005, https://doi.org/10.5194/egusphere-egu21-16005, 2021.

EGU21-10409 | vPICO presentations | SSP3.7

Sedimentology, stratigraphy and clinoform architectures of a siliciclastic shallow-marine platform: insights from the Late Ordovician of the Anti-Atlas (Morocco)

Déborah Harlet, Guilhem Amin Douillet, Jean-François Ghienne, Chloé Bouscary, Philippe Razin, Pierre Dietrich, and Fritz Schlunegger

The Moroccan Anti-Atlas consists of a several kilometers thick sediment pile accumulated on the northern Gondwana platform since the latest Precambrian (Ediacaran). This study focuses on the Ktaoua Group, early Late Ordovician (Mid-Sandbian to Katian) in age, which records a major and multiphase transgressive/regressive cycle above the shallow marine sandstones of the underlying First Bani Group. In the western Central Anti-Atlas, the Ktaoua Group is formed by offshore shales to coastal sandstones organized in regressive parasequences. Here, high-resolution field-based stratigraphy is used to constrain the shelf architecture and clinoforms geometries within the Ktaoua Group.

Whereas the lower part of the Ktaoua Group records parasequences from silty-shale to fine to coarse sandstones with hummocky-cross-stratification (HCS), its upper part oscillates between HCS beds and very coarse sandstones. Ferruginous, condensed horizons usually drape the parasequences. In this study, we investigate the platform geometry through the correlation of the stacking patterns of seventeen stratigraphic logs along an 85 km long, well-exposed cliff. Drone images support the logging and the correlations of the sections by imaging clinoforms geometries.

Several decameters of fine to coarse sandstones can be observed to grade laterally into condensed level(s) within a few kilometers, hence evidencing clinoforms pinching out. The visible orientation of the clinoforms along the cliff exposures show a proximal to distal trend from the south-west to the north-east, in agreement with the overall basin geometry. Three clinoforms with distinct geometries and lateral evolution of facies associations are highlighted. The distal part of a clinoform, 15 m in thickness, pinches out onto the top of the underlying First Bani Group within 7 km. The overlying regressive parasequence, approximatively 50 m thick, remains consistent more than 50 km, and is understood as a prograding clinoform. A third clinoform, capped by a prominent sandstone body constantly thicker than 20 m over ca. 20 km, disappears within its last 3.5 km onto the underlying clinoform. This study offers new details on the progradation and regression geometries along a giant platform within a detailed stratigraphic framework.

We would like to thank the Pacha and the Gendarmerie Royale of Foum-Zguid, the governor of Tata and the different persons who gave their approval and facilitated the use of the drone in the region of Souss-Massa for their precious help.

How to cite: Harlet, D., Douillet, G. A., Ghienne, J.-F., Bouscary, C., Razin, P., Dietrich, P., and Schlunegger, F.: Sedimentology, stratigraphy and clinoform architectures of a siliciclastic shallow-marine platform: insights from the Late Ordovician of the Anti-Atlas (Morocco), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10409, https://doi.org/10.5194/egusphere-egu21-10409, 2021.

EGU21-12287 | vPICO presentations | SSP3.7

Controls on the sedimentary characteristics of shelf-edge deltas in a source-to-sink context

Laura Bührig, Luca Colombera, Nigel P. Mountney, and William D. McCaffrey

Shelf-edge deltas constitute important components of source-to-sink (S2S) systems. They distribute sediment to continental slopes and basin floors from rivers that have prograded across shelves, and due to their scale they form significant sediment accumulations at shelf margins. Because of their intimate relationship with regressive conditions, several geological controls govern their evolution, including relative sea-level changes, sediment budgets, river hydrology, and hydrodynamic processes; these factors are themselves influenced by characteristics of terrestrial catchments and continental shelves, and by climate. Despite their important role in sediment dispersal to shallow- and deep-marine environments, shelf-edge deltas are commonly overlooked in models that describe S2S systems, perhaps because of their relative paucity during the present-day highstand conditions. In subsurface and outcrop, their recognition can be difficult in cases where information with which to constrain the physiographic environment is limited, such that the spatial position of a delta relative to the shelf margin cannot be determined unequivocally.

This study aims to improve our understanding of controls on the sedimentary characteristics of shelf-edge deltas. For this purpose, >40 shelf-edge deltas of Late Triassic to late Quaternary age from >30 globally-distributed shelf-margin successions have been investigated, utilising literature-derived seafloor-, subsurface- and outcrop data. Following a database approach, sedimentary records have been quantitatively analysed in terms of geometry (e.g. dimensions, thickness, gradients) and facies characteristics (e.g. lithology, sedimentary structures) of depositional environments (e.g. delta top, delta front) and architectural elements (e.g. delta lobes, distributary mouth bars). Specific consideration has been given to assessment of palaeoenvironmental setting (e.g. hydrodynamic process regime, margin type, bathymetric setting, palaeolatitude). Moreover, scaling relationships between these properties and attributes of the S2S system (e.g. fluvial-system and catchment attributes, shelf configuration, shelf-slope transition) have been evaluated. Accordingly, the relative importance of controls on the sedimentary characteristics of shelf-edge deltas has been assessed.

This analysis demonstrates that environmental factors influence the sedimentary record of shelf-edge deltas via a complex interplay of dynamic processes and physiography of the S2S segments catchment, shelf and slope. Based on these findings, new facies models for shelf-edge delta types are developed, which are placed in the context of S2S linkages. Outcomes of this study aid the identification and classification of shelf-edge deltas and their preserved deposits, as well as the reconstruction of associated environmental conditions from stratigraphic records.

How to cite: Bührig, L., Colombera, L., Mountney, N. P., and McCaffrey, W. D.: Controls on the sedimentary characteristics of shelf-edge deltas in a source-to-sink context, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12287, https://doi.org/10.5194/egusphere-egu21-12287, 2021.

Abstract: Reservoir assessment of unconventional reservoirs poses numerous exploration challenges. These challenges relate to their fine-grained and heterogeneous nature, which are ultimately controlled by depositional and diagenetic processes. To illustrate such constraints on shale gas reservoirs, this study focuses on lithofacies analysis, paleo-depositional and diagenetic evolution of the Paleocene Patala Formation at Potwar Basin of Pakistan. Integrated sedimentologic, petrographic, X-ray diffraction and TOC (total organic carbon) analyses showed that the formation contained mostly fine-grained carbonaceous, siliceous, calcareous and argilaceous siliciclastic-lithofacies, whereas carbonate microfacies included mudstone, wackestone and packstone. The silicious and carbonaceous lithofacies are considered a potential shale-gas system. The clastic lithofacies are dominated by detrital and calcareous assemblage including quartz, feldspar, calcite, organic matter and clay minerals with auxiliary pyrites and siderites. Fluctuations in depositional and diagenetic conditions caused  lateral and vertical variability in lithofacies. Superimposed on the depositional heterogeneity are spatially variable diagenetic modifications such as dissolution, compaction, cementation and stylolitization. The δ13C and δ15N stable isotopes elucidated that the formation has been deposited under anoxic conditions, which relatively enhanced the preservation of mixed marine and terrigenous organic matter. Overall, the Patala Formation exemplifies deposition in a shallow marine (shelfal) environment with episodic anoxic conditions.

Keywords: Lithofacies, Organic Matter, Paleocene, Potwar Basin, Shale Gas, Shallow Marine.

How to cite: Khan, N., Swennen, R., Weltje, G. J., and Jan, I. U.: Lithofacies, Depositional Environment and Diagenetic Evolution of the Paleocene Patala Formation, Potwar Basin, Pakistan: Implication for Shale Gas Potential, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12555, https://doi.org/10.5194/egusphere-egu21-12555, 2021.

SSP3.8 – Glaciations and their terrestrial sedimentary records

EGU21-2756 | vPICO presentations | SSP3.8

Geometry of alpine overdeepenings assessed with gravimetry and 3-D modelling

Dimitri Bandou, Patrick Schläfli, Michael Schwenk, Guilhem A. Douillet, Edi Kissling, Urs Marti, and Fritz Schlunegger

EGU21-5996 | vPICO presentations | SSP3.8

The shape and infill of the Basadingen overdeepened glacial valley from P-wave seismic reflections

Anna-Catharina Brandt, David C. Tanner, Hermann Buness, Thomas Burschil, and Gerald Gabriel

Overdeepened valleys in the Alps allow to probe the glacial sedimentation record, which in turn can illuminate the climatic history. In particular, seismic reflections can be used to extend punctual borehole data (for instance a number of boreholes are to be drilled into Alpine glacial overdeepened valleys as part of the DOVE ICDP project) in the second dimension or even survey a region before drilling begins. Thus, we use detailed, 2-D seismic P-wave profiles to reveal the shape and infill of an overdeepened Rhine glacier valley in the area of Basadingen, near to the German/Swiss border. We acquired two profiles nearly perpendicular to the valley strike, approximately 500 m apart. The first profile was 1246 m long, and consisted of a single spread of 624 geophones. The second profile was 1120 m long and was acquired using 200 3-component geophones using a roll-along method. For both profiles we used a vibro-source with a 12 s linear sweep of 20-240 Hz at every second geophone (two metre spacing), which produced a high fold.

Both seismic images reveal that the overdeepened basin at this location is asymmetrical and circa 260 m deep, although the deepest part (220 m wide) covers only a small portion of the broader main valley. The infill is characterised by at least three unconformities and distinct onlap and erosive boundaries between the sedimentary units. We interpret the infill to represent a highly dynamic sedimentary system. The lower part, within the deepest part of the basin is filled with chaotic sediments and slumping. Above a major unconformity, the upper part contains strongly-dipping reflectors that probably represent a prograding point-bar in a glacio-fluviatile environment that migrated toward the north-east. Beneath the deepest part of the basin we see evidence for faults in the Tertiary Molasse basement, which correlate with known faults at the surface. The faults most likely caused the valley to be sited at this location and they were probably also the cause of the ‘valley in valley’ shape.

A new DOVE research borehole will be drilled in the centre of the valley in 2021. This will bring more light on the sedimentary history and OSL-dating of the material will bracket the timing of the infill.

How to cite: Brandt, A.-C., Tanner, D. C., Buness, H., Burschil, T., and Gabriel, G.: The shape and infill of the Basadingen overdeepened glacial valley from P-wave seismic reflections, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5996, https://doi.org/10.5194/egusphere-egu21-5996, 2021.

EGU21-5899 | vPICO presentations | SSP3.8

3D overdeepened trough morphology revealed as a product of bedrock geology (northern Switzerland)

Lukas Gegg, Marius W. Buechi, Gaudenz Deplazes, Herfried Madritsch, Lorenz Keller, Thomas Spillmann, and Flavio S. Anselmetti

Subglacial overdeepenings are a common element of once glaciated mountain forelands and have considerable implications for society, e.g. in construction projects, water production and radioactive waste disposal. Yet the processes of overdeepening erosion, especially the influence of bedrock lithology and structure, are poorly understood. We present a case study of the Gebenstorf-Stilli Trough in northern Switzerland, a unique overdeepening with complex underlying geology: In contrast to the Molasse-hosted majority of the Alpine foreland overdeepenings, it is to a large part incised into Upper Jurassic limestones and marls. In order to constrain its morphology in 3D, it was targeted with scientific boreholes as well as a seismic campaign based on analysis of surface waves. The results reveal unexpected trough morphology with two nested sub-basins that appear to be closely related to the bedrock geology. We suggest that this morphology is a product of low erosional efficiency in Jurassic limestones in comparison with both underlying marls and overlying Molasse deposits as well as secondary paleoglaciological effects. We further infer that the glacier’s basal drainage system was the main driver of subglacial erosion of the Gebenstorf-Stilli Trough.

How to cite: Gegg, L., Buechi, M. W., Deplazes, G., Madritsch, H., Keller, L., Spillmann, T., and Anselmetti, F. S.: 3D overdeepened trough morphology revealed as a product of bedrock geology (northern Switzerland), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5899, https://doi.org/10.5194/egusphere-egu21-5899, 2021.

Glaciotectonic structures commonly include thrusting and folding, often as multiphase deformation. Here we present the results of a small-scale 3-D P-wave seismic reflection survey of glacial sediments within an overdeepened glacial valley in which we recognise unusual folding structures in front of push-moraine. The study area is in the Tannwald Basin, in southern Germany, about 50 km north of Lake Constance, where the basin is part of the glacial overdeepened Rhine Valley. The basin was excavated out of Tertiary Molasse sediments during the Hosskirchian stage, and infilled by 200 m of Hosskirchian and Rissian glacioclastics (Dietmanns Fm.). After an unconformity in the Rissian, a ca. 7 m-thick till (matrix-supported diamicton) was deposited, followed by up to 30 m of Rissian/Würmian coarse gravels and minor diamictons (Illmensee Fm.). The terminal moraine of the last Würmian glaciation overlies these deposits to the SW, not 200 m away.

We conducted a 3-D, 120 x 120 m², P-wave seismic reflection survey around a prospective borehole site in the study area. Source/receiver points and lines were spaced at 3 m and 9 m, respectively. A 10 s sweep of 20-200 Hz was excited by a small electrodynamic, wheelbarrow-borne vibrator twice at every of the 1004 realized shot positions. We recognised that the top layer of coarse gravel above the till is folded, but not in the conventional buckling sense, rather as cuspate-lobate folding. The fold axes are parallel to the terminal moraine front. The wavelength of the folding varies between 40 and 80 m, and the thickness of the folded layer is on average about 20 m. Cuspate-lobate folding is typical for deformation of layers of differing mechanical competence (after Ramsay and Huber 1987; µ12 less than 10), so this tell us something about the relative competence (or stiffness) of the till layer compared to the coarse clastics above. We also detected small thrust faults that are also parallel to the push-moraine, but these have very little offset and most of the deformation was achieved by folding.

Ramsay, J.G. and Huber, M. I. (1987): The techniques of modern structural geology, vol. 2: Folds and fractures: Academic Press, London, 700 pp.

How to cite: Tanner, D., Buness, H., and Burschil, T.: Near-surface glaciotectonic structures in the sediments of an overdeepened glacial valley revealed by a shallow 3D seismic survey, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8195, https://doi.org/10.5194/egusphere-egu21-8195, 2021.

EGU21-7098 | vPICO presentations | SSP3.8

Retreat of the Rhine Glacier from Lake Constance: Sedimentological and geochemical evidences from a deep lake-basin drillhole

Sebastian Schaller, Michael E. Boettcher, Marius W. Buechi, Laura S. Epp, Stefano C. Fabbri, Natacha Gribenski, Ulrich Harms, Sebastian Krastel, Alina Liebezeit, Katja Lindhorst, Ulli Raschke, David Schleheck, Iris Schmiedinger, Antje Schwalb, Hendrik Vogel, Martin Wessels, and Flavio S. Anselmetti

The modern basin of trinational Lake Constance, between Switzerland, Germany, and Austria, represents the underfilled northern part of a glacially overdeepened trough. It is over 400 m deep and reaches well into the Alps at its southern end. The overdeepening was formed by the numerous glacial advance-retreat cycles of the Rhine Glacier throughout the Middle to Late Quaternary. A seismic survey of Lake Constance revealed a Quaternary sediment fill of over 150 m thickness under the modern lake floor in a maximal water depth of >250 m. This sedimentary sequence represents at least the last glacial cycle with ice-contact deposits at the base on top of the Molasse bedrock overlain by glaciolacustrine to lacustrine sediments. During the successful field test of a newly developed mid-size coring system ("HIPERCORIG"), the longest core ever taken in Lake Constance was recovered with an overall length of 24 m. The drill core, taken in a water depth of 200 m, consists of a nearly continuous succession of lacustrine sediments including over 12 m of pre-Holocene sediment at the base. The entire core was petrophysically and geochemically analyzed, sedimentologically described, and 14 lithotypes were identified. In combination with a 14C- and OSL-based age-depth model, the core was divided into three main chronostratigraphic units. The basal age of ~13.7 ka BP places the base of the section back into the Bølling-Allerød interstadial whereas the overlying strata represent a complete Younger-Dryas and Holocene section.

The sediments offer a high-resolution insight into the evolution of Paleolake Constance from a cold postglacial to a more productive warm Holocene lake. The Late Glacial sections are dominated by massive, m-thick sand beds reflecting episodic sedimentation pulses. They are most likely linked with a subaquatic channel system that is still apparent in today's lake bathymetry despite the Holocene drape. This channel system was fed from a Late Glacial river from the north; provenance analysis of the initially unexpected sands together with hydrologic considerations will document whether this inflowing high-discharge river represented a local catchment (i.e. northern lake shore) or an Alpine signal (i.e. from the south) provided by the Rhine glacier. Tentative pore water hydrogeochemical and isotope analyses indicate a still active flow system at depth. The overlying Holocene section reveals a prominent, several cm-thick double-turbiditic event layer representing the most distal impact of the "Flimser Bergsturz", the largest known rock slide of the Alps that occurred over 100 km upstream the Rhine River at ~9.5 ka BP. Furthermore, lithologic variations in the Holocene section document the varying sediment load of the Rhine and of the endogenic production representing a multitude of environmental changes.

How to cite: Schaller, S., Boettcher, M. E., Buechi, M. W., Epp, L. S., Fabbri, S. C., Gribenski, N., Harms, U., Krastel, S., Liebezeit, A., Lindhorst, K., Raschke, U., Schleheck, D., Schmiedinger, I., Schwalb, A., Vogel, H., Wessels, M., and Anselmetti, F. S.: Retreat of the Rhine Glacier from Lake Constance: Sedimentological and geochemical evidences from a deep lake-basin drillhole, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7098, https://doi.org/10.5194/egusphere-egu21-7098, 2021.

EGU21-14551 | vPICO presentations | SSP3.8

Glacial erosion and subsequent shallowing-up sequence, evidence for two glacial advances into the overdeepened Aare Valley, Switzerland

Michael Schwenk, Patrick Schläfli, Dimitri Bandou, Natacha Gribenski, Guilhem A. Douillet, and Fritz Schlunegger

A scientific drilling was conducted into a bedrock trough in Bern-Bümpliz, a branch of the Aare Valley overdeepening (Switzerland). It is the first scientific drilling in the Bern area that reached the bedrock. We analyzed the 208.5 m-thick succession of Quaternary sediments recovered in this scientific drilling and present the sedimentological results of the campaign. In the retrieved sediments 12 different lithofacies were identified, which were grouped into 5 facies assemblages, and 2 major sedimentary sequences (A = lower, B = upper), which transition into a minor sequence C. Generally, the sedimentary successions of sequences A and B are similar. The lowermost facies assemblage of each sequence consists of a till that was deposited during a period of ice cover. However, the two tills differ from each other. In particular, while the till at the base of sequence A is dominated by large clasts derived from the underlying Molasse bedrock, the till at the base of sequence B has no such Molasse components. Furthermore, the till in sequence A bears evidence for glaciotectonic deformations. Both tills are overlain by thick facies assemblages of subaqueous, most likely glaciolacustrine and lacustrine sediments. Sequence A is characterized by cross-bedded and steeply inclined sand, gravel and diamictic beds which we interpret as deposits of density currents in a subaqueous ice-contact fan system in a proglacial lake. In contrast, the lacustrine sediments in sequence B are considered to record a less energetic environment where the material was most likely deposited in a prodelta setting that gradually developed into a delta plain. Towards the top, sequence B evolves into the fluvial system of sequence C, where large sediment fluxes of a possibly advancing glacier resulted in a widespread cover of the region by a thick gravel unit. Additionally, feldspar luminescence dating was performed on two samples from a sand layer at the top of sequence B. The dating in combination with lithostratigraphic correlations with the sequences encountered in the neighboring scientific drillings to the north (Meikirch) and south of Bern (Thalgut) suggests that sequence B was deposited during Marine Isotope Stage 8 (MIS 8; 300–243 ka).

How to cite: Schwenk, M., Schläfli, P., Bandou, D., Gribenski, N., Douillet, G. A., and Schlunegger, F.: Glacial erosion and subsequent shallowing-up sequence, evidence for two glacial advances into the overdeepened Aare Valley, Switzerland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14551, https://doi.org/10.5194/egusphere-egu21-14551, 2021.

EGU21-12558 | vPICO presentations | SSP3.8

Palaeoenvironmental significance of a large-scale buried ice-marginal landsystem, Skeiðarársandur, SE Iceland

Devin Harrison, Neil Ross, Andrew J. Russell, and Stuart J. Jones

The sedimentary record of Icelandic ice-contact environments provides valuable information about glacier margin dynamics and position, relative sea-level, and the geomorphic processes that drive the evolution of proglacial environments. This important archive has been little exploited, however, with most glacier and sea level reconstructions based on limited sedimentary exposures and surface geomorphic evidence. Although geophysical surveys of Icelandic sandur have been conducted, they have often been of limited spatial scale and focus on specific landforms. We report an extensive (42 km of data within a 24 km2 study area) and detailed (reflections recorded at depths of up to 100 m) low-frequency (40 and 100 MHz) Ground-Penetrating Radar (GPR) survey of the Sandgígur moraine complex, SE Iceland. This transforms our understanding of this landform, with implications for the Holocene glacial history and evolution of Skeiðarársandur and SE Iceland.

The Sandgígur moraines are located on Skeiðarársandur, SE Iceland, down-sandur of large Little Ice Age-moraines of Skeiðarárjökull. They have a relatively subtle surface geomorphic expression (typically 7 m high and 125 m wide), and knowledge of their formation is limited, with no dating control on their age or detailed geomorphic or sedimentological investigations. GPR-data reveals reflections interpreted as large progradational foresets (dip angle: 2.19° – 6.87°) beneath the morainic structure (depth of 100 m). These features are consistent with a sub-aqueous depositional environment before moraine formation, providing potential indications of past relative sea-level limits. GPR profiles in the vicinity of the Sandgígur moraines reveal a much larger (67 m high and 1.25 km wide) and extensive buried moraine complex than that suggested by surface morphology. Indicating that the moraine was a major Holocene ice margin of Skeiðarárjökull. The buried Sandgígur moraine ridge is comprised of a unit of chaotic folded reflections adjacent to a unit of parallel, down-sandur dipping reflections (dip angle: 1.29° – 2.27°) indicative of an ice-contact or end-moraine fan. Possible evidence of buried ice at depth is also present within radargrams surrounding the moraine ridges. Sediment above the morainic bounding surface is interpreted to be dominated by glaciofluvial deposits with an estimated sediment volume of 1.04 km3 over the 24 km2 study area. Potential moraine breaches, possibly caused by high magnitude jökulhlaups (glacier outburst floods) are coincident within the GPR data and the surface geomorphology.

We combine GPR-derived subsurface architecture with the current surface morphology to develop a conceptual model detailing the geomorphic evolution of the moraines and surrounding region, from pre-moraine morphology, to their formation and burial, resulting in the present-day morphology. These results provide new insights into the Holocene to present-day glacial history of Skeiðarárjökull and the controls on sedimentation responsible for the evolution of Skeiðarársandur, with implications for the formation of sandar environments and the Holocene environmental history of SE Iceland.

How to cite: Harrison, D., Ross, N., Russell, A. J., and Jones, S. J.: Palaeoenvironmental significance of a large-scale buried ice-marginal landsystem, Skeiðarársandur, SE Iceland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12558, https://doi.org/10.5194/egusphere-egu21-12558, 2021.

EGU21-12416 | vPICO presentations | SSP3.8

The Drac paleo-valleys: a long-term archive of fluvial dynamics in the periglacial zone of the western French Alps

Vivien Mai Yung Sen, Pierre Valla, and Peter van der Beek

The evolution of the Alpine mountain belt during the Quaternary is strongly controlled by periodic glaciations and deglaciations. The significant erosion during these glacial/interglacial cycles has left very few sedimentary archives to study the surface dynamics within the mountain belt over the last hundreds of thousands of years. Valleys within the periglacial zone are the best candidates to target long-term geological archives in the Alps because they potentially preserve ancient fluvial deposits that have been preserved from glacial abrasion. The Drac River in the French western Alps preserves the alluvial fills of three generations of paleo-valleys, which were filled in response to glacial damming of the river and subsequently re-incised during glacial retreat. Detailed 3D mapping of the paleo-valleys was carried out to constrain their geometry and reconstruct the evolution of the Drac fluvial profile over time. The age of the fills of the three paleo-valleys was constrained by measuring the luminescence signal of feldspars, targeting sandy intervals within the coarse fluvial deposits. Dating these fills allows to quantitatively constrain the alluviation and incision dynamics of the Drac paleo-valleys. The onset of alluviation of the most recent paleo-valley occurred before the Last Glacial Maximum, between 40 ka and 90 ka BP (MIS 3 -5). The fill of the intermediate paleo-valley is dated to the previous cold period at 134±20 ka BP (MIS 6). Finally, the oldest paleo-valley was filled more than 200 ka ago. The filling periods correspond to the global climatic cooling stages and are much longer than the incision phases, which took place during global warm intervals. The pattern of sedimentary filling implies it is controlled by an increase in sediment flux in the context of glacial advance, while the incision phases are due to rapid base-level lowering linked to the retreat of glaciers damming the Drac basin. Complementary luminescence dating is currently carried out on the terraces, at the tops of the fillings, and will lead to a better understanding of the control of glaciations on the dynamics of alluvial deposits in the periglacial zone.

How to cite: Mai Yung Sen, V., Valla, P., and van der Beek, P.: The Drac paleo-valleys: a long-term archive of fluvial dynamics in the periglacial zone of the western French Alps, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12416, https://doi.org/10.5194/egusphere-egu21-12416, 2021.

EGU21-6207 | vPICO presentations | SSP3.8

Present-day sediment dynamics and provenance of the Gornergletscher

Fien De Doncker, Frédéric Herman, Günther Prasicek, Thierry Adatte, François Mettra, and Bruno Belotti

Glacial erosion processes shape the Earth’s surface. Nevertheless, the processes that drive glacial erosion and the subsequent export of sediments are poorly understood and quantified. These processes include ice sliding, which controls erosion by abrasion and quarrying, and meltwater availability, which is essential to flush out sediment stocks that form a protective layer of sediments impeding bedrock erosion. Mapping glacial erosion rates can help understand the role of these different processes through the spatial relationships between the subprocesses and erosion rates. Here we report timeseries of glacial erosion rate maps inferred from the inversion of suspended sediment loads and their provenance. Geographically, we focus on the Gornergletscher complex (VS, Switzerland) where we collected data for the summer of 2017. The erosion rate timeseries are then compared to records of temperature, precipitation and estimates of discharge and turbidity of the meltwater river. Erosional activity seems to increase with rising temperatures and meltwater discharge, leading to an increased proportion of suspended sediments coming from the north-eastern (and occasionally western) side of the glacier. Interestingly, the peak in sediments from the north-eastern side is always preceded by a peak in sediments from the western side of the glacier. Sediments of these two zones are predominant in the suspended load signal when the maximal temperature at the Equilibrium Line Altitude (ELA) is above 10°C and on the rising limb of the hydrograph. Furthermore, the obtained erosion rate maps suggest that sliding velocities are not the only explanatory factor of the erosion rate patterns. We therefore postulate from these preliminary results that the present-day sediment output of the Gornergletscher complex is largely influenced by short term variations in temperature and meltwater availability.

How to cite: De Doncker, F., Herman, F., Prasicek, G., Adatte, T., Mettra, F., and Belotti, B.: Present-day sediment dynamics and provenance of the Gornergletscher, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6207, https://doi.org/10.5194/egusphere-egu21-6207, 2021.

SSP4.1 – Of fossils and humans: how to study deep-time life

EGU21-578 | vPICO presentations | SSP4.1

Insights from big data into the fossilization potential of marine communities

Jack Shaw, Derek Briggs, and Pincelli Hull

Only a small percentage of all life that ever existed is preserved in the rock record. Some animals and environments are particularly unlikely to fossilize—e.g., soft-bodied organisms and high-energy habitats—biasing fossil deposit faunal composition and resultant inferences about macroevolution and macroecology. To estimate the extent of information loss caused by non-preservation we compared diversity data in over 20,000 modern marine assemblages (Ocean Biogeographic Information System; OBIS) with fossil occurrence data (Paleobiology Database; PBDB) to yield a global assessment of assemblage-level fossilization potential as it varies across depth, habitats, and environments. We used two different metrics, taxon fossilization potential and within-environment fossilization potential, to assess the proportion of taxa in a modern community with PBDB occurrences or with PBDB occurrences in the same environment, respectively. Averaged across all 20,000+ marine assemblages, mean taxon fossilization potential is 38% and mean values vary between environments: from 34% in shallow and deep water, 44% in coral reefs, 51% on seamounts, to 15% in pelagic assemblages. Mean within-environment fossilization potential, in contrast, does not exceed 32% (in shallow water), a lower value than that obtained in other studies, and may approach zero (on seamounts and pelagic environments). Differences between these two metrics indicate the large control of environment on fossilization potential. Our results provide a means to include and compare palaeoecological dynamics across a broader range of settings in the fossil record, while accounting for differences in fossilization potential among environments.

How to cite: Shaw, J., Briggs, D., and Hull, P.: Insights from big data into the fossilization potential of marine communities, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-578, https://doi.org/10.5194/egusphere-egu21-578, 2021.

EGU21-14476 | vPICO presentations | SSP4.1 | Highlight

How not to study fossil biomolecules

Julien Alleon and Pierre Gueriau

The search for fossil biomolecules often requires combining many techniques to properly characterize their chemical composition. Recently, it was suggested in 6 papers that conventional Raman spectroscopy (i.e., equipped with a 532 nm laser as the excitation source under continuous illumination) can be used alone to identify diverse remnants or derivatives of biomolecules in animal fossils, with important implications for both evolutionary events and fossilization processes. Unfortunately, the reported claims are not supported by the spectroscopy data provided, which actually result from instrumental artefacts and data processing. Here, we outline the limitations of Raman spectroscopy with respect to the identification of biomolecules in fossil materials, and then describe in detail the origin of the misinterpreted signal. Conventional Raman spectroscopy alone cannot be used to identify fossil biomolecules. Instead, non-conventional Raman spectroscopy, mass spectrometry and infrared and X-ray absorption spectroscopy techniques, are successfully used by paleontologists to identify fossil biomolecules that help understanding both the history of life and the mechanisms of fossilization.

How to cite: Alleon, J. and Gueriau, P.: How not to study fossil biomolecules, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14476, https://doi.org/10.5194/egusphere-egu21-14476, 2021.

EGU21-12201 | vPICO presentations | SSP4.1

Modelling marine ecosystem structure from palaeoecological trait data in the Middle Jurassic Peterborough Member (UK)

Thomas Pavey, Jack O. Shaw, Andrew P. Beckerman, and Alexander M. Dunhill

Reconstructing ancient community assemblages and the ecological relationships between extinct organisms is a major challenge due to the shortcomings of the fossil record. The uncertainty surrounding the life habits of extinct organisms has proven to be a major hurdle for our understanding of the evolution of ecosystem structure through time. One such period of interest is the Mesozoic Marine Revolution (MMR), where escalation is proposed to have driven major changes in marine food webs which led to the establishment of modern marine ecosystem structure. The timing of the MMR is heavily debated, with proposals ranging from an Early Triassic to a Cretaceous/Cenozoic origin. We present a meta-community analysis of the Peterborough Member (Callovian, UK) with the aim of constraining the timing of the MMR. We assigned traits (i.e. body size, feeding mode, motility, tiering) that define interactions in modern systems to all fossil organisms and used rules based on foraging behaviour to model meta-community food web structure. We then compare the modelled Peterborough Member food webs with those of well-constrained modern marine ecosystems to shed light on whether modern marine ecosystem was established by the end of the Middle Jurassic.

How to cite: Pavey, T., Shaw, J. O., Beckerman, A. P., and Dunhill, A. M.: Modelling marine ecosystem structure from palaeoecological trait data in the Middle Jurassic Peterborough Member (UK), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12201, https://doi.org/10.5194/egusphere-egu21-12201, 2021.

EGU21-16394 | vPICO presentations | SSP4.1

Deep Neural Networks for Hierarchical Taxonomic Fossil Classification of Carbonate Skeletal Grains

Sidhant Idgunji, Madison Ho, Jonathan L. Payne, Daniel Lehrmann, Michele Morsilli, Khalid Al-Ramadan, and Ardiansyah Koeshidayatullah

The growing digitization of fossil images has vastly improved and broadened the potential application of big data and machine learning, particularly computer vision, in paleontology. Recent studies show that machine learning is capable of approaching human abilities of classifying images, and with the increase in computational power and visual data, it stands to reason that it can match human ability but at much greater efficiency in the near future. Here we demonstrate this potential of using deep learning to identify skeletal grains at different levels of the Linnaean taxonomic hierarchy. Our approach was two-pronged. First, we built a database of skeletal grain images spanning a wide range of animal phyla and classes and used this database to train the model. We used a Python-based method to automate image recognition and extraction from published sources. Second, we developed a deep learning algorithm that can attach multiple labels to a single image. Conventionally, deep learning is used to predict a single class from an image; here, we adopted a Branch Convolutional Neural Network (B-CNN) technique to classify multiple taxonomic levels for a single skeletal grain image. Using this method, we achieved over 90% accuracy for both the coarse, phylum-level recognition and the fine, class-level recognition across diverse skeletal grains (6 phyla and 15 classes). Furthermore, we found that image augmentation improves the overall accuracy. This tool has potential applications in geology ranging from biostratigraphy to paleo-bathymetry, paleoecology, and microfacies analysis. Further improvement of the algorithm and expansion of the training dataset will continue to narrow the efficiency gap between human expertise and machine learning.

How to cite: Idgunji, S., Ho, M., Payne, J. L., Lehrmann, D., Morsilli, M., Al-Ramadan, K., and Koeshidayatullah, A.: Deep Neural Networks for Hierarchical Taxonomic Fossil Classification of Carbonate Skeletal Grains, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16394, https://doi.org/10.5194/egusphere-egu21-16394, 2021.

EGU21-15332 | vPICO presentations | SSP4.1

Geometric morphometric analysis of different species of Cyprideis deriving from the Early Pleistocene record of Greece.

Ypermachia Dimitriou, Penelope Papadopoulou, Maria Kolendrianou, Maria Tsoni, and George Iliopoulos

The genus Cyprideis is one of the most widespread ostracod representative of the Pleistocene brackish palaeoenvironments. Especially Cyprideis torosa is often found in great numbers and even in monospecific taphocoenoses and for this reason its study is very useful for palaeoenvironmental reconstructions.  The identification of different species of Cyprideis is often complicated and needs careful morphology inspection. This becomes even more difficult in the case of endemic species which present significant similarities with each other.  In this work, we have studied and analyzed several  Cyprideis species (C.torosa, C. frydaci, C.dictyoti, C. pannonica, C. elisabeta, C. seminulum, C. heterostigma) deriving from brackish palaeoenvironments of a Lower Pleistocene marl sequence in Sousaki Basin (Northeastern Corinth Graben, Greece). More specifically size measurements and geometric morphometrics (lateral valve outline of both right and left valves as well as females and males) were used in order to attest the similarities and dissimilarities between the different species and draw conclusions about their origin.  According to the valve outline and the multivariate analysis a close relationship between the valve shape of all Cyprideis species can be noticed. C. torosa is commonly grouped with C. pannonica except in the male right valve where the two species show some differences.  The endemic species C. frydaci and C. dictyoti can be identified by the differences in the right valve of the male and female respectively.  The other species could not be substantially differentiated using just the outline analysis which possibly denotes their common genetic origin.  The valve outline has proved to be a very useful character for recognizing the different species especially when the two valves of both females and males are considered. More analyses of representative species of Miocene and Pliocene Cyprideis are needed in order to establish their phylogenetic relationships and draw conclusions about their common ancestor.

How to cite: Dimitriou, Y., Papadopoulou, P., Kolendrianou, M., Tsoni, M., and Iliopoulos, G.: Geometric morphometric analysis of different species of Cyprideis deriving from the Early Pleistocene record of Greece., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15332, https://doi.org/10.5194/egusphere-egu21-15332, 2021.

The most numerous and diversified Middle Miocene gastropod collection from Northern Croatia, housed at the Croatian Natural History Museum (CNHM), comes from the Zaprešić Brijeg locality near Zagreb. The gastropod-bearing horizon of the Middle Miocene (Langhian, Badenian) age is today no longer visible on the surface, not only in this area but also in other parts of Northern Croatia. The description of the Zaprešić Brijeg locality and fossil collecting methods can be found in the museum archives and published papers. According to these data, gastropods were collected from "sandstones" during the first half of the 20th century (Gorjanović-Kramberger 1894; Šuklje 1929). Among more than 11000 stored gastropod shells from this locality 45 belong to marine, 2 to marine/brackish and 2 to brackish gastropod families. Some families comprise only one or a few representatives, while other are much more common, such as Potamididae (4459 shells), Nassariidae (2428 shells), Clavatulidae (1813 shells), Turritellidae (1253 shells), and Cerithiidae (508 shells). In previously published papers on the Zaprešić Brijeg gastropod fauna (e.g., Gorjanović-Kramberger 1894; Šuklje 1929; Pavlovsky 1957, 1960) the focus was mostly on the taxonomical aspect. While examining the collection, we observed numerous drilling predation marks in a shape of drill holes on marine gastropod shells and provided numerical analysis of predation marks on some common families (Bošnjak et al., submitted). The aim of this study is to continue the division of gastropod families by their palaeoecology (infauna, epifauna) and feeding type (carnivores, suspension feeders, detritivores and grazers), in order to better understand the palaeoenvironmental conditions during the Middle Miocene (Badenian, Langhian) in this area. Non-marine gastropod taxa indicate the freshwater influx and the vicinity of hinterland. Such a rich museum collection can provide further insight into the palaeoecology of the southwestern margin of the Central Paratethys, even though the original fossiliferous horizon is no more available in the field.

References:

Bošnjak, M., Sremac, J., Karaica, B., Mađerić, I. & Jarić, A. (submitted): Mollusk mortal kombat: drilled Middle Miocene gastropods from the south-western margin of the Central Paratethys, Croatia.

Gorjanović-Kramberger, D. (1894): Geology of Samoborsko gorje Mt. and Žumberak Mt. Rad Yugoslav Academy of Sciences and Arts, 120, 1–82. (in Croatian)

Šuklje, F. (1929): Die Mediterranfauna des Zaprešić Brijeg in der Samoborska gora in Kroatien. Bulletin de l'institut geologique de Zagreb, III, 1–52. (in Croatian with German summary)

Pavlovsky, M. (1957): Ein Beitrag zur Kenntnis Miozäner Gastropoden von Zaprešić-Brijeg bei Samobor. Geološki vjesnik, 10 (1956), 51–56. (in Croatian with German summary)

Pavlovsky, M. (1960): Neue Elemente der Fauna von Zaprešić-Brijeg bei Samobor. Geološki vjesnik, XIII (1959), 213–216. (in Croatian with German summary)

How to cite: Bošnjak, M. and Sremac, J.: Middle Miocene gastropods from the southwestern margin of the Central Paratethys, Croatia: Museum collection's insight, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12861, https://doi.org/10.5194/egusphere-egu21-12861, 2021.

EGU21-2593 | vPICO presentations | SSP4.1

Early Miocene mollusc and fish biodiversity at the Proto-Mediterranean–Paratethys marine corridor

Efterpi Koskeridou, Konstantina Agiadi, and Danae Thivaiou

Marine biodiversity is controlled by depth, climate, and ocean connectivity. The early Miocene marine fauna of the proto-Mediterranean is particularly important because this is the time when the connection with the Indo-Pacific realm was disrupted , and the marine biodiversity hotspot shifted toward the southeast, marking the onset of a subtropical gradually oligotrophic regime in the proto-Mediterranean Sea. The Mesohellenic basin in particular, at the northern part of the proto-Mediterranean, was located at the intersection with the Paratethys epicontinental sea. Therefore, the fauna in this area was influenced by the conditions in both basins. In this study, we present the mollusc and fish fauna of the Aquitanian Mesohellenic basin and discuss its paleobiogeographic and evolutionary implications. Comparisons and assessment of faunal similarities of the proto-Mediterranean and adjacent provinces is carried out using ordination methods to treat available data from relevant publications and the Paleobiology Database (PBDB).

This research has been co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Programme “Human Resources Development, Education and Lifelong Learning 2014–2020” in the context of the project “Mollusc and fish migrations in the dynamic environments of the early to middle Miocene in the Mediterranean” (MIS 5047960). 

How to cite: Koskeridou, E., Agiadi, K., and Thivaiou, D.: Early Miocene mollusc and fish biodiversity at the Proto-Mediterranean–Paratethys marine corridor, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2593, https://doi.org/10.5194/egusphere-egu21-2593, 2021.

Conidae is a very diverse family of carnivorous gastropods with over 900 extant species, that present beautiful colour patterns. These patterns can be useful to biologists for the systematic approach, but lack usually in fossil samples, when they are only observed in natural light. Therefore conid species were difficult to distinguish.
To resolve that problem, we use ultraviolet light to reveal the colour patterns of these fossil shells. Here, we present the second part of a PhD project that attempts to clarify the diversity of the Tortonian Conidae from Crete, Greece. The first part of this project already revealed eleven species of Conilithes Swainson, 1840 and Conus (Kalloconus) da Motta, 1991 five of them being new. In the second part, we found seventeen species, of those seven are considered as new. Among them, ten are attributed to Conus (Lautoconus) Monterosato, 1923 and three in Conus (Plagioconus) Tucker & Tenorio, 2009. Finally, a group of four species with special characteristics is discussed and is proposed as a new subgenus.
This project will greatly enrich the knowledge of the family in  the Tortonian of Eastern Proto-Mediterranean. The results will be compared to similar faunas from the Middle-Miocene to Pliocene of Europe, in order to assess the biogeography of this family.

How to cite: Psarras, C., Koskeridou, E., and Merle, D.: Tortonian Conidae of Crete. New species revealed under UV light. Subgenera Conus (Lautoconus), Conus (Plagioconus) and a possible new subgenus., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2543, https://doi.org/10.5194/egusphere-egu21-2543, 2021.

Grotta del Cavallo, a well-known Paleolithic site in Southern Italy (Nardò, Apulia), preserves one of the most important Italian Middle Paleolithic sequences. Its stratigraphic succession records the presence of Neanderthals from Marine Isotope Stage (MIS) 7 to 3, providing substantial insights on their lifeways. Here we present the taxonomic and taphonomic analysis of the bird assemblages associated to Neanderthal occupation. The rich avifaunal assemblages allowed paleoenvironmental and paleoclimatic reconstructions, noticeably improving the reconstruction of the landscape that was exploited by Neanderthals throughout the last glacial-interglacial cycles. Based on the bird taxa identified in the assemblages, Grotta del Cavallo was mainly surrounded by extensive grasslands and shrublands, with scattered open woodland and rocky outcrops, during MIS 7, 6 and 3. The coastal plain, that is currently underwater due to Holocene relative sea-level rise, hosted wetlands in the cooler periods, when it was exposed. In the cool-temperate climatic phase attributed to MIS 3, bird taxa of water and wet environments proportionally increased, as well as coverage-based rarefied richness values. This is possibly due to the expansion of wetland areas, linked to more humid conditions, or to the shorter distance of the wetland settings from the cave, compared to MIS 6 (glacial period). A consequent higher heterogeneity of the landscape is retained to drive the increased richness. The sampling effort allowed to retrieve bird taxa that provided significant paleoclimatic insights, such as Branta leucopsis, an arctic breeder, and other species currently spread at higher altitudes, that reinforce previously obtained geochemical derived inference of climate conditions cooler than the present ones. The bird assemblages also provided the first occurrence ever of Larus genei, the first Italian occurrence of Emberiza calandra, the oldest Italian occurrence of Podiceps nigricollis, and the occurrence of Sylvia communis (a species rarely retrieved in the fossil record). Ordination analyses of the bird dataset detected the drivers of taphonomic degradation and the agents responsible for the accumulation of the avian bones: modifications are mainly due to physical sin- and post-depositional processes, whereas accumulation is mainly attributed to short-range physical processes of sediment accumulation, feeding activities of nocturnal raptors and, to a lesser extent, human activities. In detail, traces found on a few bones suggest that Neanderthals introduced some of the birds in the cave with alimentary purposes, providing the earliest Italian evidence of bird exploitation ever.

How to cite: Carrera, L., Scarponi, D., Martini, F., Sarti, L., and Pavia, M.: Neanderthal landscapes and subsistence strategies during late Quaternary glacial-interglacial periods: insights from the avian assemblages of Grotta del Cavallo (Apulia, Southern Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10115, https://doi.org/10.5194/egusphere-egu21-10115, 2021.

SSP4.2 – CO2 excess and global warming events: newest results on past and current resilience of marine biota

EGU21-10828 | vPICO presentations | SSP4.2

Increase in ecosystem complexity aided organic carbon sequestration during the c. 2.22-2.06 Ga Lomagundi carbon isotope excursion

Frantz Ossa Ossa, Stephan König, Axel Hofmann, Andrey Bekker, Jorge E. Spangenberg, and Ronny Schoenberg

The first dramatic rise in atmospheric oxygen to concentrations above 10-5 present atmospheric level (PAL), known as the Great Oxidation Event (GOE), was initiated during the early Proterozoic Eon c. 2.43-2.32 billion years (Gyrs) ago [1,2].  Although atmospheric O2 concentrations are generally accepted to have remained below 1% PAL for at least 1.5 Gyrs following the GOE [3], high atmospheric O2 build up occurred during the Lomagundi carbon isotope excursion (LE) at the latest stage of the GOE [4]. The LE is the most pronounced and longest-lived carbon isotope excursion in Earth’s history that took place c. 2.22-2.06 Gyrs ago [4,5]. It reflects increased organic carbon (Corg) burial resulting from high primary productivity at the time of high phosphorous flux to the ocean associated with intense acidic chemical weathering of landmasses. However, mechanisms responsible for such high Corg sequestration are not yet fully resolved, nor has it been possible to precisely quantify the magnitude and expansion of oxygenation within the coeval atmosphere-ocean system.

Here, we studied diagenetic concretions of pyrite and carbonate and their host black shales of the Francevillian Group, southeast Gabon, deposited during the LE. Light sulfur (δ34S ‰, VCDT) and carbon (δ13Ccarb ‰, VPDB) isotope ratios indicate that both pyrite and carbonate formed in sediments through microbial sulfate reduction and Corg remineralization, respectively. Selenium isotopic ratios (δ82/76Se ‰, NIST3149) of the pyrite concretions and their host shales are dominated by highly negative values as low as –3‰, which is strong evidence for partial reduction of selenium oxyanions (SeOx2-) in the sediment below an oxygenated seawater column. Collectively, the data suggests an oxygenated water column in the Francevillian Basin with a large SeOx2- reservoir that continuously resupplied these electron acceptors to the sediment and prevented their quantitative reduction. The studied black shales host putative, fossilized large colonial multicellular organisms that had the ability to laterally and vertically migrate within the sediments [6]. We propose that bioturbation by these organisms allowed an increased flux of electron acceptors (e.g., O2, NO3, SeOx2-, SO4-) into the sediments and pushed the microbial sulfate reduction and methanogenesis zones downward. As a consequence, CH4 and H2S generated in these zones were re-oxidized in more oxic upper levels of the sediments, which prevented them from escaping to the water column. An increase in ecosystem complexity thus likely aided Corg sequestration to the sediments and O2 accumulation in the atmosphere-ocean system during the LE.

 

[1] Bekker et al. (2004), Nature, 427, 117–120. [2] Holland (2006), Philos. Trans. R. Soc. B 361, 903–91. [3] Colwyn et al. (2014), Geobiology, DOI: 10.1111/gbi.12360. [4] Karhu and Holland (1996), Geology, 24, 867–870. [5] Bekker (2014), Encyclopedia of Astrobiology, Springer-Verlag, 1–6. [6] El Albani et al. (2019), Proc. Natl. Acad. Sci. USA, 116, 3431–3436.

How to cite: Ossa Ossa, F., König, S., Hofmann, A., Bekker, A., Spangenberg, J. E., and Schoenberg, R.: Increase in ecosystem complexity aided organic carbon sequestration during the c. 2.22-2.06 Ga Lomagundi carbon isotope excursion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10828, https://doi.org/10.5194/egusphere-egu21-10828, 2021.

During the late Pliensbachian–Toarcian interval, several global events were recognized as cooling and sea-level fall, warming, and sea-level rise which were driven by the changes in the concentration of the atmospheric CO2. The latter one caused a second-order mass extinction during the Jenkyns Event in the early Toarcian, which was sedimentologically represented by black shales on the epicontinental carbonate-siliciclastic ramps of the Neotethyan Boreal-Atlantic Foraminiferal Biome (BAFB). While in the distal, hemipelagic-pelagic parts of the Western Neotethys, in the Mediterranean Foraminiferal Biome (MFB, Zsiborás & Görög, 2020, Görög & Zsiborás, 2020) with condensed Ammonitico Rosso carbonates, the black shales are usually missing.

The Bakonycsernye (Hungary) sections gave firstly the opportunity for the investigation of foraminifers from the upper Pliensbachian–Toarcian Ammonitico Rosso successions belong to the MFB. Thus, our goals were to show out the effect of the Jenkyns Event on the foraminiferal assemblages in this biome and based on the literature, to compare them with the ones of the MFB and BAFB.

Foraminiferal fauna was extracted by glacial acetic acid from 22 samples of three sections. Microfacies studies, taxonomic and palaeoecological analyses (abundance, diversity, morphogroups, and ecozones) were used for the evaluation of the palaeoenvironmental changes. For the comparison, a review of the literature was carried out to collect similar quantitative data about the assemblages of other regions.

The upper Pliensbachian was affected by a cooling event and a global sea-level fall (JPlie8) which was characterized by a diverse ammodiscinid-lenticulinid-ichthyolariid-nodosariid mixed epi- and infaunal assemblage in Bakonycsernye. During the rapid global warming and sea-level rise event (JToa1) in the lower Toarcian, ammodiscinids and ornamented ichthyolariids disappeared thus the assemblage changed into a less diverse lenticulinid-nodosariid-polymorphinid infauna-dominated assemblage. In the middle–upper Toarcian, epifaunal grazer spirillinids reigned the assemblages followed by lenticulinids and nodosariids.

The microfossils indicated low to moderate oxygen levels in the upper Pliensbachian–lower Toarcian, high from the middle Toarcian. From then, the opportunist epifaunal spirillinids appeared in mass. They could graze on a microbial and/or fungal biofilm or could be fed on marine snow. Thus, the existence of the main foraminiferal groups depended on the microbial activity which increased during the warmer intervals.

Based on the ratio of the foraminiferal morphogroups, the foraminiferal fauna of Bakonycsernye was similar to others from the Mediterranean Biome and it was remarkably different from Boreal Atlantic ones. The calculated provinciality indices showed no provinciality between the foraminiferal fauna of Bakonycsernye and other Western and Southern European localities in the upper Pliensbachian–upper Toarcian interval. These results also proved the global warming event linked to the increased atmospheric CO2 level caused by the Karoo-Ferrar LIP.

Görög, Á., & Zsiborás, G. (2020). Foraminiferal Faunal Changes in the Upper Pliensbachian–Toarcian Ammonitico Rosso Sections (Bakonycsernye, Hungary). Journal of Foraminiferal Research, 50(4), 342–372.

Zsiborás, G., & Görög, Á (2020). Aalenian–lower Bajocian foraminiferal fauna from the Ammonitico Rosso series of Bakonycsernye (Hungary). Part 2: Palaeoecological and palaeobiogeographical aspects.  Journal of Foraminiferal Research, 50(1): 73–88.

 

How to cite: Görög, Á. and Zsiborás, G.: The biotic response of the Late Pliensbachian–Toarcian foraminiferal assemblages to the environmental perturbations in the pelagic and neritic environments of the Neotethys ocean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13108, https://doi.org/10.5194/egusphere-egu21-13108, 2021.

EGU21-8045 | vPICO presentations | SSP4.2 | Highlight

Surface- and deep-water response to the Early Aptian OAE 1a in the western Tethys

Cinzia Bottini, Victor M. Giraldo-Gómez, Maria Rose Petrizzo, and Elisabetta Erba

The Cretaceous was punctuated by interludes of widespread deposition of organic-rich sediments (black shales) in the oceans and epicontinental seas, named Oceanic Anoxic Events (OAE)s, representing major alterations in the global carbon budget. The early Aptian OAE 1a (ca. 120 Ma) coincided with a global paleoclimatic and paleoenvironmental perturbation which lasted for ca. 1.1 Myrs probably triggered by volcanogenic COemissions associated with the emplacement of the Ontong Java Plateau. To date, there is a comprehensive characterization of OAE 1a paleoceanographic conditions and paleoecology of surface-waters while less information is available for bottom-water evolution. In this regard, benthic foraminifera are ideal to characterize deep-water oxygen levels and the organic carbon flux. We present a high-resolution study of benthic foraminiferal assemblages across OAE 1a in the Cismon Core (western Tethys, Lombardy Basin, Northern Italy). Contrarily to many sites, the Cismon Core yields benthic foraminifera also in the Selli Level thus providing information about deep-water conditions during OAE 1a. Our data are indicative of fluctuations in bottom-water oxygenation and organic-matter flux to the sea-floor prior to, during and after OAE 1a. The integration of the new benthic foraminiferal data with calcareous nannofossil and planktonic foraminiferal datasets is here used to produce a model of surface- to bottom-water paleowater evolution through the latest Barremian-early late Aptian. In particular, the new data show coeval changes in bottom- and surface-waters conditions prior to and at the onset of OAE 1a. Anoxia was reached during the core of the negative carbon isotope anomaly, under maximum warming and higher surface-water fertility. Conversely, the repopulation of benthic foraminifera postponed the plankton recovery. Benthic foraminifera data at Cismon show, for the first time, evidence of a repopulation event during the OAE 1a suggestive for a slight increase in the supply of oxygen to the seafloor during the Selli Level deposition.

How to cite: Bottini, C., Giraldo-Gómez, V. M., Petrizzo, M. R., and Erba, E.: Surface- and deep-water response to the Early Aptian OAE 1a in the western Tethys, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8045, https://doi.org/10.5194/egusphere-egu21-8045, 2021.

EGU21-1004 | vPICO presentations | SSP4.2 | Highlight

Resilience of SW Pacific marine plankton to Cenozoic global warming events

Chris Hollis, Giuseppe Cortese, Martin Crundwell, Claire Shepherd, Erica Crouch, and Joe Prebble

EGU21-7245 | vPICO presentations | SSP4.2

Rise and fall of rotaliids in the Paleocene-Eocene: the influence of climate and trophic competition

Andrea Benedetti, Cesare Andrea Papazzoni, and Francesca Romana Bosellini

It is largely accepted that climate plays a pivotal role in the diversification of shallow-water communities, with special regards to larger foraminifera (LF), also because increase of surface water temperatures is often accompanied by change in trophic conditions. The shift from widespread eutrophic to oligotrophic conditions in shallow seas probably contributed to the LF differentiation during Paleocene-Eocene times. However, there are few recent attempts to quantify the changes in biodiversity and to correlate them with the global climatic events of the Paleogene. We concentrated our attention on the group of rotaliids, resilient taxa that partially survived after the mass extinction occurred at the end of the Cretaceous.

Our data show that their differentiation at genus level was very rapid, reaching its maximum already in the late Danian SB2 Zone. Specific diversification, instead, culminated in late Thanetian SB4 Zone. A second peak in specific diversity is recorded during the Cuisian (upper part of the Ypresian), then rotaliid diversity steadily declined, as long as other groups of larger foraminifers, especially Alveolina and Nummulites, became more competitive and proliferated with a large number of species up to the Bartonian SB17 Zone, when a significant drop in rotaliid biodiversity is recorded.

Differently to other taxonomic groups, i.e., alveolinids and nummulitids, for which a single genus during the whole Eocene generated numerous species, rotaliid genera are usually characterized by a low number of species, possibly due to the re-opening of ecological niches after the abrupt decrease of diversity that followed the PETM event. The competition with other K-strategist LF probably contributed to the decline of rotaliids in the middle Eocene up to the MECO event, where a last dramatic drop is recorded.

The major changes appear strictly linked to warming events such as the Late Danian Event (LDE, starting of the generic diversification of rotaliids), Paleocene Eocene Termal Maximum (PETM, faunal turnover followed by abrupt decrease in both generic and specific diversity), Early Eocene Climatic Optimum (EECO, increase in number of K-strategists under widespread oligotrophic conditions) and Middle Eocene Climatic Optimum (MECO, ultimate drop in diversity and competition with other larger foraminifers).

This study was funded by the Italian Ministry of Education and Research (MIUR), funds PRIN 2017: project “Biota resilience to global change: biomineralization of planktic and benthic calcifiers in the past, present and future” (prot. 2017RX9XXY).

How to cite: Benedetti, A., Papazzoni, C. A., and Bosellini, F. R.: Rise and fall of rotaliids in the Paleocene-Eocene: the influence of climate and trophic competition, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7245, https://doi.org/10.5194/egusphere-egu21-7245, 2021.

EGU21-3360 | vPICO presentations | SSP4.2

Late Oligocene Warming Event (LOWE) possibly preserved on top of a reef drowning sequence in NW Italy: insights from an integrated stratigraphic approach.

Antonino Briguglio, Maria Grazia Vannucci, Clarissa Bruzzone, Simone Crobu, Eleni Lutaj, and Michele Piazza

The Oligo-Miocene Transition (OMT) is one of the most important climatic transitions of younger earth history. This short period of climate warming coincides with a few biotic turnovers. OMT follows the Late Oligocene Warming Event which marks the last warming pulse of a generally cool interval and represents a time frame that could potentially fit well with modern climate change predictions.

The Case Cné section located within the Tertiary Piedmont Basin (TPB) represents a gradual transgressive event, which shows the drowning of a locally developed reef complex and a development of a deeper marine sedimentary setting influenced by gravity flow mechanics. Larger foraminifera association indicate a late Oligocene (SBZ23) time and this seems confirmed by Sr isotopes data.

By usage of sedimentological, semi-quantitative microfacies and geochemical analysis the sedimentary history of the section could be reconstructed and divided into four major phases. 1) The growth and establishment of the reef directly on the metamorphic substrate, 2) its development over the basement and the construction of a modest reefal body, 3) the slow drowning of the reef complex due to enhanced prograding fluvial activity and finally 4) the onset of gravity flows passing to turbiditic influence which cap the transgression and that continue regionally throughout into the Miocene. 

The benthic fauna seems to register the warming period by change in biodiversity and abundance. Below the warming event, larger foraminfera are rather sparse over the section and the benthic community seems dominated by suspension feeders. Toward the top of the section, where the LOWE seems to occur, the gravity flows transport a very large amount of operculinid foraminifera that are well adapted to warm and eutrophic conditions as the ones that possibly characterized the LOWE time span in this tectonically active region.

How to cite: Briguglio, A., Vannucci, M. G., Bruzzone, C., Crobu, S., Lutaj, E., and Piazza, M.: Late Oligocene Warming Event (LOWE) possibly preserved on top of a reef drowning sequence in NW Italy: insights from an integrated stratigraphic approach., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3360, https://doi.org/10.5194/egusphere-egu21-3360, 2021.

EGU21-7735 | vPICO presentations | SSP4.2 | Highlight

Coccolithophores’ efficiency towards CO2 buffering in the Western Pacific Ocean during the last 300 kyr

Manuela Bordiga, Claudia Lupi, Marina Cabrini, and Miriam Cobianchi

The biogeochemical and physical processes occurring in the oceans are pivotal in controlling the atmospheric carbon dioxide (CO2atm) concentration. In particular, the biological pump uptakes CO2atm through photosynthesis, whereas the carbonate pump produces CO2 during CaCO3 production. On the other hand, the accumulation of microbiota-derived carbonates into the deep-sea sediments favors the CO2 surplus buffering during high carbonate dissolution episodes. To unravel the role of calcifying marine microbiota on CO2atm regulation, we studied the microfossil contents from two sectors of the Western Pacific Ocean with potential different behaviors towards CO2 buffering: the Ocean Drilling Program Site 1209 (NW Pacific) and the IMAGES Core MD 97-2114 (SW Pacific). The selected time interval covers the last 300 kyr – i.e. the most recent glacial-interglacial cycles, with particular attention to the Last Interglacial (LIG; 129-116 kyr) which is a good modern-analogue within the geological records. Analyses of calcareous nannofossil assemblages provided data on coccolith carbonate production and fluxes, primary productivity, and carbonate dissolution, which are essential to investigate the carbonate and biological pumps’ efficiency on CO2atm uptake.

Our data confirm that the calcareous nannofossils contributed significantly to the ocean carbon cycle through both the biological and carbonate pumps, constituting up to 50-70% of the carbonate stocked into the sediments of the studied sites. In both the oceanic sectors, we recorded  higher coccolith carbonate fluxes mostly during deglaciations, and thus coccolithophores’ production acted as a negative feedback on CO2atm uptake contributing to the CO2atm abrupt increase which characterizes the deglacial-interglacial transitions of the last 800 kyr. Instead, higher carbonate dissolution episodes generating positive feedback on CO2atm occurred during glacial inceptions and interglacials at Site 1209, and during glacial phases at Core MD 97-2114 due to the stronger intensity of the highly corrosive Deep Western Boundary Current (DWBC). Therefore, changes in coccolithophore production influenced the saturation state of deep waters in a time ranging from 10 to 100 kyr at both sites. The comparison between the two oceanic areas allows identifying significant differences in the processes involved in the CO2 buffering. In the NW Pacific site the biological pump is probably more efficient owing to the high productivity of coccolithophorids together with the presence of diatom blooms during glacial phases. At the southern site the biological pump consists only of coccolithophorids, but the coccolith carbonate fluxes are almost doubled compared to the northern site testifying a major efficiency of the carbonate pump on CO2 production. On the other hand, the higher amount of CaCO3 stocked into the southern sediments and the higher efficiency of the physical pump related to the DWBC strongly contributed to the CO2atm uptake during glacials. Thus, these two oceanic sectors seem to be decoupled and, therefore, it could be possible that their combined effect in a long-term trend can result in a balance.

How to cite: Bordiga, M., Lupi, C., Cabrini, M., and Cobianchi, M.: Coccolithophores’ efficiency towards CO2 buffering in the Western Pacific Ocean during the last 300 kyr, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7735, https://doi.org/10.5194/egusphere-egu21-7735, 2021.

EGU21-9748 | vPICO presentations | SSP4.2

Has (anthropogenic) climate change driven subantarctic Emiliania huxleyi populations beyond their natural state?

Andres S. Rigual-Hernandez, Francisco J. Sierro, José A. Flores, José M. Sánchez-Santos, Ruth S. Eriksen, Andrew D. Moy, Fátima Abrantes, Helen Bostock, Scott D. Nodder, Alba González-Lanchas, and Thomas W. Trull

The global ocean acts as a climate regulator through the uptake of Earth’s excess heat and the absorption of about 30% of anthropogenic CO2 emissions since 1750.  Southern Ocean waters are warming faster than the global ocean average and their low temperatures and moderate alkalinity make this region especially vulnerable to ocean acidification. Coccolithophores are a major group of calcifying phytoplankton and an important component of the Southern Ocean carbon cycle. Controlled laboratory experiments on Emiliania huxleyi (the most abundant coccolithophore) over a broad range of carbonate chemistry scenarios suggest that this taxon may be susceptible to ongoing environmental change. However, it remains uncertain whether Southern Ocean coccolithophore populations have been modified by environmental change during the industrial era. The main reason for this knowledge gap is the lack of observational data since the onset of the Industrial Revolution. In particular, continuous monitoring of key Southern Ocean ecosystems only started a few decades ago, a period insufficiently long to permit assessments of whether anthropogenic impacts on the environment have affected coccolithophore populations beyond their natural state. In order to overcome this limitation, here we take advantage of the preservation capacity of coccolithophores in the sedimentary record to provide a benchmark of their pre-industrial state. We compare the morphotype assemblage composition and morphometric parameters in coccoliths of E. huxleyi from a suite of Holocene-aged sediments south of Tasmania with annual sediment trap records retrieved at the Southern Ocean Time Series observatory in the Australian sector of the Subantarctic Zone. Our results suggest that carbonate dissolution in the sediments reduced the coccolith mass and length of the coccoliths but, coccolith thickness appeared to be decoupled from dissolution. The biogeographical distribution of coccolith thickness in subtropical and subantarctic sediments mirrored the distribution of E. huxleyi morphotypes, highlighting the important role of E. huxleyi assemblage composition on the control of coccolith morphometrics. Moreover, comparison of coccolith assemblages from the sedimentary record with those collected from subantarctic sediment traps indicates that modern E. huxleyi coccoliths are about 2% thinner than those from the pre-industrial Holocene. The subtle change in coccolith thickness is in stark contrast with previous work that documented a dramatic reduction in shell calcification in the planktonic foraminifera Globigerina bulloides that resulted in a shell-weight decrease of 30-35%, most likely induced by ocean acidification. Overall, our results underscore the variable sensitivity of different marine calcifying plankton groups to ongoing environmental change in the Southern Ocean.

How to cite: Rigual-Hernandez, A. S., Sierro, F. J., Flores, J. A., Sánchez-Santos, J. M., Eriksen, R. S., Moy, A. D., Abrantes, F., Bostock, H., Nodder, S. D., González-Lanchas, A., and Trull, T. W.: Has (anthropogenic) climate change driven subantarctic Emiliania huxleyi populations beyond their natural state?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9748, https://doi.org/10.5194/egusphere-egu21-9748, 2021.

EGU21-12620 | vPICO presentations | SSP4.2

The influence of different oxygen regimes on metabolism and behavior of a soft shell clam Mya arenaria

Natascha Ouillon, Stefan Forster, Abigail Jarret, Eugene Sokolov, and Inna Sokolova

Hypoxia is widely distributed in coastal benthic habitats and is driven by warming, nutrient pollution and the diurnal cycles of photosynthesis and respiration. Benthic sessile species, such as the soft shell clam Mya arenaria, are commonly exposed to oxygen fluctuations in their habitats which might negatively impact the performance and metabolism of clams. To determine the effects of different oxygen regime on metabolism and behavior of M. arenaria, we exposed the clams for 21 days to chronic (constant) hypoxia at 20% of air saturation, fluctuating (cyclic) hypoxia (~10-50% of air saturation) and normoxia (100% of air saturation). To mimic conditions occurring in coastal hypoxic zones, CO2 and pH levels varied with the oxygen. We assessed the digging performance, bioirrigation capacity and bioenergetics of the clams. Acclimation to constant or cyclic hypoxia did not affect the oxygen consumption of the clams, but the oxygen consumption rates declined at low ambient oxygen concentrations regardless of the acclimation to different oxygen regimes. Clams acclimated to constant hypoxia mainly used lipids, whereas clams acclimated to cyclic hypoxia used carbohydrates as energy fuel. Clams acclimated to constant or cyclic hypoxia dug slower compared to the clams acclimated to normoxia. Furthermore, bioirrigation capacity decreased in clams acclimated to constant hypoxia. Our results indicate that constant and cyclic hypoxia impair bioturbation and bioirrigation capacity of clams which has implications for their ecological function as ecosystem engineers in benthic soft bottom habitats. 

How to cite: Ouillon, N., Forster, S., Jarret, A., Sokolov, E., and Sokolova, I.: The influence of different oxygen regimes on metabolism and behavior of a soft shell clam Mya arenaria, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12620, https://doi.org/10.5194/egusphere-egu21-12620, 2021.

SSP4.3 – Conservation Paleobiology: insights from deep time to recent past

EGU21-198 | vPICO presentations | SSP4.3

Diel Vertical migration of marine organisms and the biological carbon pump

Jerome Pinti, Tim DeVries, Tommy Norin, Camila Serra-Pompei, Roland Proud, David A. Siegel, Thomas Kiørboe, Colleen M. Petrik, Ken H. Andersen, Andrew S. Brierley, and André W. Visser

Diel Vertical Migration (DVM) is a key feature of pelagic and mesopelagic ecosystems, mainly driven by predator-prey interactions along a time-varying vertical gradient of light. Marine organisms including meso-zooplankton and fish typically hide from visual predators at depth during daytime and migrate up at dusk to feed in productive near-surface waters during nighttime. Specific migration patterns, however, vary tremendously, for instance in terms of residency depth during day and night. In addition to environmental parameters such as light intensity and oxygen concentration, the migration pattern of each organism is intrinsically linked to the patterns of its conspecifics, its prey, and its predators through feedbacks that are hard to understand—but important to consider.

DVM not only affects trophic interactions, but also the biogeochemistry of the world’s oceans.  Organisms preying at the surface and actively migrating vertically transport carbon to depth, contributing to the biological carbon pump, and directly connecting surface production with mesopelagic and demersal ecosystems.

Here, we present a method based on a game-theoretic trait-based mechanistic model that enables the optimal DVM patterns for all organisms in a food-web to be computed simultaneously. The results are used to investigate the contributions of the different food-web pathways to the active component of the biological carbon pump. We apply the method to a modern pelagic food-web (comprised of meso- and macro-zooplankton, forage fish, mesopelagic fish, large pelagic fish and gelatinous organisms), shedding light on the direct effects that different trophic levels can have on the DVM behaviours of each other. The model is run on a global scale to assess the carbon export mediated by different functional groups, through fecal pellet production, carcasses sinking and respiration.

Finally, the model output is coupled to an ocean inverse circulation model to assess the carbon sequestration potential of the different export pathways. Results indicate that the carbon sequestration mediated by fish is much more important than presently recognised in global assessments of the biological carbon pump. The work we present relates to contemporary ecosystems, but we also explain how it can be adapted to fit any pelagic food-web structure to assess the contribution of the active biological pump to the global carbon cycle in past ecosystems.

How to cite: Pinti, J., DeVries, T., Norin, T., Serra-Pompei, C., Proud, R., Siegel, D. A., Kiørboe, T., Petrik, C. M., Andersen, K. H., Brierley, A. S., and Visser, A. W.: Diel Vertical migration of marine organisms and the biological carbon pump, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-198, https://doi.org/10.5194/egusphere-egu21-198, 2021.

EGU21-927 | vPICO presentations | SSP4.3 | Highlight

Ecological Consequences of a Millennium of Introduced Dogs on Madagascar

Sean Hixon, Kristina Douglass, Laurie Godfrey, Laurie Eccles, Brooke Crowley, Lucien Rakotozafy, Geoffrey Clark, Simon Haberle, Atholl Anderson, Henry Wright, and Douglas Kennett

Introduced predators currently threaten endemic animals on Madagascar through predation, facilitation of human-led hunts, competition, and disease transmission, but the antiquity and past consequences of these introductions are poorly known. We use radiocarbon and stable carbon and nitrogen isotope data from the bone collagen of introduced dogs (Canis familiaris) and endemic fosa (Cryptoprocta spp.) in central and southern Madagascar to test for competition between introduced and endemic predators. Isotopic evidence indicates little overlap in diet between ancient dogs and fosa in these regions but leaves open the possibility that dogs competitively exclude fosa. Radiocarbon dates confirm that dogs have been present on Madagascar for at least a millennium and suggest that they briefly co-occurred with the island’s extinct megafauna, which included giant lemurs, elephant birds, and pygmy hippopotamuses. Dogs share a mutualism with pastoralists who also at least occasionally hunt, and this is reflected in deposits at several Malagasy paleontological sites that contain dog and livestock bones along with butchered bones of extinct megafauna and extant lemurs. Dogs on Madagascar have had a wide range of diets during the past millennium, but relatively high stable carbon isotope values suggest few individuals relied primarily on forest bushmeat. The absence of distinct dietary differences between dogs from archaeological and paleontological sites may reflect the absence of discrete feral populations. Our data suggest that dogs were part of a suite of animal introductions beginning over a millennium ago that coincided with widespread landscape transformation and megafaunal extinction.

How to cite: Hixon, S., Douglass, K., Godfrey, L., Eccles, L., Crowley, B., Rakotozafy, L., Clark, G., Haberle, S., Anderson, A., Wright, H., and Kennett, D.: Ecological Consequences of a Millennium of Introduced Dogs on Madagascar, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-927, https://doi.org/10.5194/egusphere-egu21-927, 2021.

EGU21-9134 | vPICO presentations | SSP4.3

Modern and fossil insects body size as a possible proxy to understand environments of the past

Viktor Baranov, Blue Hunter-Moffatt, Sajad Noori, Simon Schölderle, and Joachim T. Haug

The fossil records of Insects is quite rich and abundant, telling a story of the group’s rise through the Paleozoic, with the subsequent conquest of sea, land, freshwater and finally, for the first time in history of animals – air. Fossil insects also can tell us about the environment they lived in. It is relatively common to use insect remnants, especially head capsules of  non-biting midges (Diptera, Chironomidae) preserved in the sediments from the period including several last Ice ages the Holocene (11650 Years BC – Present) to reconstruct temperatures and the climate patterns of the past. Most of the midges in the Holocene are representatives of modern species, which allows us to extrapolate their ecology from the modern representatives of the same species. Based on our knowledge of the temperature preference of this modern species we can quite easily reconstruct and model their temperature preferences in the past.

Reconstruction of the temperature optimums of all the taxa in the community, together with analyses of the other paleoecological proxies (i.e. plant pollen profiles) enables us to assess the range of the temperatures experienced by the area in which midge samples of Chironomidae was obtained in the Holocene and latest Pleistocene. We cannot rely on such ecological extrapolation from the modern animals' ecology for the animal’s fossil records from the deep past, for example from Cretaceous or Triassic periods.

Therefore, we are proposing a more universally applicable climate proxy, independent of our knowledge of the fossil organism’s ecology. Animal size is one of the best candidates for such proxy. It is well known that the body size of the homoeothermic (“warm-blooded”) animals follows (roughly) so-called Bergman rule when size within the group of organisms is increasing from South to North ( i.e. polar bear and Amur tiger are both the northernmost and the largest representatives of their respective groups). We hypothesized that flies (Diptera) are suitable candidates for a quantitative paleoclimate proxy. Flies are very abundant in the fossil records from the mid Triassic (245 Mya) up until modern time. Their size is appears directly negatively correlated with temperature, i.e. representatives occurring further North are larger than the ones from the equatorial regions. This relationship allows us to use the relationships between the insect size and the geographic latitude at which they occur and the temperature at which these insects occur. Here we present a first results from analysis of > 2000 species of Chironomidae from around the globe, in a phylogenetic-constrained framework. First results are showing that non-biting midge’s wing and body size is growing by about 0.02 mm per one degree of geographical latitude, as one moves from the equator, mostly regardless of the phylogenetic position of the species analysed. This first results are showing that Insect size might be a promising proxy for reconstructing the palaeotemperature.

 

 

How to cite: Baranov, V., Hunter-Moffatt, B., Noori, S., Schölderle, S., and Haug, J. T.: Modern and fossil insects body size as a possible proxy to understand environments of the past, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9134, https://doi.org/10.5194/egusphere-egu21-9134, 2021.

EGU21-14604 | vPICO presentations | SSP4.3

Fungi and plant co-variation in Arctic Siberia inferred from sedimentary ancient DNA metabarcoding during the last 45.000 years

Barbara von Hippel, Kathleen R. Stoof-Leichsenring, Luise Schulte, Peter Seeber, Laura S. Epp, Matthias Lenz, Stephanie Scheidt, and Ulrike Herzschuh

Climate change has a great impact on boreal ecosystems including Siberian larch forests. As a consequence of warming, larch grow is possible in areas where climate used to be too cold, leading to a shift of the tree line into more arctic regions. Most plants co-exist in symbiosis with heterotrophic organisms surrounding their root system. In arctic ecosystems, mycorrhizal fungi are a prerequisite for plant establishment and survival because they support nutrient uptake from nutrient-poor soils and maintain the water supply. Until now, however, knowledge about the co-variation of vegetation and fungi is poor. Certainly, the understanding of dynamic changes in biotic interactions is important to understand adaptation mechanisms of ecosystems to climate change.

We investigated sedimentary ancient DNA from Lake Levinson Lessing, Taymyr Peninsula (Arctic Siberia, tundra), Lake Lama, Lake Kyutyunda (both northern Siberia, tundra-taiga transition zone) and Lake Bolshoe Toko (southern Siberia, forest area) covering the last about 45.000 years using ITS primers for fungi along with the chloroplast P6 loop marker for vegetation metabarcoding. We found changes in the fungal communities that are in broad agreement with vegetation turnover. To our knowledge, this is the first broad ecological study on lake sediment cores to analyze fungal biodiversity in relation to vegetation change on millennial time scales.

How to cite: von Hippel, B., Stoof-Leichsenring, K. R., Schulte, L., Seeber, P., Epp, L. S., Lenz, M., Scheidt, S., and Herzschuh, U.: Fungi and plant co-variation in Arctic Siberia inferred from sedimentary ancient DNA metabarcoding during the last 45.000 years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14604, https://doi.org/10.5194/egusphere-egu21-14604, 2021.

EGU21-14457 | vPICO presentations | SSP4.3

A multiproxy reconstruction of vegetation dynamics in the Eastern Alps (Switzerland): combining paleoecological and paleogenetic approaches.

Laura Dziomber, Lisa Gurtner, Maria Leunda, and Christoph Schwörer

Current and future climate change is a serious threat to biodiversity and ecosystem stability. With a rapid increase of global temperatures by 1.5°C since the pre-industrial period and a projected warming of 1.5-4°C by the end of this century, plant species are forced to either adapt to these changes, shift their distribution range to higher elevation, or face population decline and extinction. Today, there is an urgent need to better understand the responses of mountain vegetation to climate change in order to predict the consequences of the human-driven global change currently occurring during the Anthropocene and maintain species diversity and ecosystem services. However, most predictions are based on short-term experiments. There is, in general, an insufficient use of longer time scales in conservation biology to understand long-term processes. Palaeoecological data are a great source of information to infer past species responses to changing environmental factors, such as climate or anthropogenic disturbances.

The last climate change of a similar magnitude and rate as projected for this century was the transition between the last Ice Age and the Holocene interglacial (ca. 11,700 years ago). By analyzing subfossil plant remains such as plant macrofossils, charcoal and pollen from natural archives, we can study past responses to climate change. However, until recently it was not possible to reconstruct changes at the population level. With the development of new methods to extract ancient DNA (aDNA) from plant remains and next generation DNA-sequencing techniques, we can now infer past population dynamics by analyzing the genetic variation through time. Ancient DNA might also be able to reveal if species could adapt to climatic changes by identifying intraspecific variation of specific genes related to climatic adaptations.

We are currently investigating a palaeoecological archive from a high-altitude mountain lake, Lai da Vons (1991 m a.s.l), situated in Eastern Switzerland. We are presenting preliminary macrofossil, pollen and charcoal results to reconstruct local to regional vegetation and fire dynamics with high chronological precision and resolution. In a next step, we will use novel molecular methods, in order to track adaptive and neutral genetic diversity through the Holocene by analyzing aDNA from subfossil conifer needles. The overarching goal of this large-scale, multiproxy study is to better understand past vegetation dynamics and the impact of future climate change on plants at multiple scales; from the genetic to the community level.

 

How to cite: Dziomber, L., Gurtner, L., Leunda, M., and Schwörer, C.: A multiproxy reconstruction of vegetation dynamics in the Eastern Alps (Switzerland): combining paleoecological and paleogenetic approaches., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14457, https://doi.org/10.5194/egusphere-egu21-14457, 2021.

EGU21-3484 | vPICO presentations | SSP4.3

What do shallow cores tell us when drilled in an anthropogenically active delta from northwest Italy?

Carla Altieri, Antonino Briguglio, Cristina Carbone, Sirio Consani, Laura Cutroneo, Irene Geneselli, Arianna Malatesta, Anna Reboa, and Marco Capello

This study aims at checking the quality of the sedimentary record preserved on the deltaic seafloor by analyzing the deposits preserved in 4 shallow cores. These have been collected by scuba diving at four different depths (10m, 20m, 30m and 40m) just in correspondence of the delta of the Entella river, in the Gulf of Tigullio (Western Ligurian Sea - Italy).

The Entella river runs through several onshore sites that can have been potential source of pollution or contamination of the marine system in the past and thus potentially preserved in the sedimentary sequence. Among those sites the possible contamination sources could be caused by extensive human activities such as production and processing of thermoplastic material, vegetable oils, junkyards, several quarries (limestone and slate), landfill of solid urban waste.

The core subsampling was directly performed onboard of the support vessel immediately after underwater collection. In total four cores, with a length comprised between 26 and 44 cm, have been collected. Each core was cut into 2-cm slices, which were then further divided in half.

The first half of sediment has been placed in a plastic bag in order to perform the followed analyses: granulometry, content of organic/inorganic matter by thermogravimetric method, XRPD analyses, C14 radiometric dating and chemical component analysis.

The second half of sediment, stored into a glass jar (to prevent plastic contamination), has been used to search for both agglutinated microplastics on picked agglutinated foraminifera and further microplastics on filters. Filters have been prepared using density separation in supersalty aqueous solution and filtration. Investigations have been performed by optical microscopy and µRaman spectroscopy. Since the analysis of the whole filter is extensively time-consuming, due to the high number of items present, we have tested a statistical approach to optimize the filter investigation.

All the data obtained were processed using the statistical software R. Multivariate analyses have been performed for the granulometry dataset as well as for other data. The results seem to point to specific trends characterized by possible seasonal fluctuations registered in the sedimentary sequence. The mineralogy dataset, investigated by cluster analysis, points to a clear separation of the mineralogical composition of the shallower versus the deeper cores. Interestingly, agglutinated foraminifera (i.e., mostly textulariids) seem to agglutinate large amount of carbon grains and plastics have been not yet observed.

How to cite: Altieri, C., Briguglio, A., Carbone, C., Consani, S., Cutroneo, L., Geneselli, I., Malatesta, A., Reboa, A., and Capello, M.: What do shallow cores tell us when drilled in an anthropogenically active delta from northwest Italy?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3484, https://doi.org/10.5194/egusphere-egu21-3484, 2021.

EGU21-14128 | vPICO presentations | SSP4.3

How can stratigraphy contribute to conservation paleobiology? Insights from a mid-Holocene to present-day transitional system of the Po coastal plain (N Italy)

Giulia Barbieri, Veronica Rossi, Éric Armynot du Châtelet, Simone Da Prato, Ilaria Mazzini, Stefano Claudio Vaiani, and Fabrizio Frontalini

The definition of reference conditions has a major role for the understanding of the present-day and paleoecological quality status on transitional environments. The estuarine quality paradox and the paucity of unimpacted sites make the definition of reference conditions a challenging task. In this context, the integration of biological indicators with stratigraphic data is essential, as the vertical stacking pattern of facies composing the shallow subsurface of modern coastal plains reflects changes in physical-chemical parameters which, in turn, affect (paleo-)biotic communities.

In the Po coastal plain (N Italy), the mid to late Holocene back-barrier succession of the Mezzano Lowland and the adjacent present-day Bellocchio Lagoon offer a unique example of pristine paralic system for comparing reference conditions defined in fossil and modern settings, respectively. Benthic foraminifers and ostracods from the Mezzano succession allowed us to investigate vertical (i.e., temporal) and lateral (i.e., spatial) changes in (paleo-)environmental conditions, in analogy to the lateral variations recorded at the Bellocchio Lagoon.

Both sites present subtidal channel sands almost barren in autochthonous meiofauna and fine-grained lagoon sediments with abundant benthic foraminifers and ostracods mostly represented by euryhaline taxa recording the highest diversity. Intertidal muddy deposits are also recorded, including mud flat clays with abundant oligotypic assemblages dominated by highly-confined benthic foraminifers. In the present study, we demonstrate that changes in modern benthic foraminifer assemblages diversity and composition often interpreted as perturbations of ecological conditions in response to anthropogenic pressures also occur under natural state, as confirmed by paleoenvironmental conditions recorded by ostracods. This reflects the effects of authogenic processes at short time and geographic scales.

How to cite: Barbieri, G., Rossi, V., Armynot du Châtelet, É., Da Prato, S., Mazzini, I., Vaiani, S. C., and Frontalini, F.: How can stratigraphy contribute to conservation paleobiology? Insights from a mid-Holocene to present-day transitional system of the Po coastal plain (N Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14128, https://doi.org/10.5194/egusphere-egu21-14128, 2021.

EGU21-15750 | vPICO presentations | SSP4.3

Climate change influence on calcification of the bivalve Chamelea gallina in the Adriatic Sea: exploring a temporal gradient from the Holocene to modern days

Alessandro Cheli, Arianna Mancuso, Fiorella Prada, Andrea Baseotto, Giuseppe Falini, Stefano Goffredo, and Daniele Scarponi

The Mediterranean striped venus (Chamelea gallina) is a valuable economic species in the Mediterranean Sea. In the last decades the over-exploitation of this fishing resource and the occurrence of several mass mortality events, lead to a strong quantitative decline in clam population density in the Adriatic Sea. Studying the effects of climate-driven changes of environmental factors on C. gallina, therefore, is of increasing interest both from an academic and economic point of view.

Previous studies have mainly focused on population dynamics, shell growth and structure of this species in the present-day Mediterranean Sea. In contrast, there is no information about shell variations in relation to climate-driven environmental change along temporal gradients.

This ongoing study investigates and contrasts variations in shell microstructure and shell growth parameters of C. gallina assemblages from Holocene sedimentary archives of the Northern Adriatic (Italy). Four shoreface-related C. gallina horizons are being evaluated: two from the present-day Adriatic setting and two from the Middle Holocene sedimentary succession of the Adriatic-Po system, when regional sea surface temperatures were higher than today, thus representing a possible analogue for the near-future global warming. Specifically we aim to: 1) determine the life span of selected specimen using three independent ageing methods (shell surface growth rings, shell internal bands and stable isotope composition); 2) determine shell growth parameters and functions concerning linear extension and net calcification rates for each assemblage investigated.

This approach should give access to an archive of ecological responses to past climate transitions and enabling reconstruction of the C. gallina natural range of variability on time-scale well beyond the ecological monitoring or small-scale experiments. Additionally, the young (sub)fossil record should offer insights on the adaptive capacities of C. gallina facing near-future anthropogenic warming and may allow implementation of a more effective management of this economically important bivalve species in the near-future.

How to cite: Cheli, A., Mancuso, A., Prada, F., Baseotto, A., Falini, G., Goffredo, S., and Scarponi, D.: Climate change influence on calcification of the bivalve Chamelea gallina in the Adriatic Sea: exploring a temporal gradient from the Holocene to modern days, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15750, https://doi.org/10.5194/egusphere-egu21-15750, 2021.

EGU21-7694 | vPICO presentations | SSP4.3

Reconstructing the baseline population structure of the exploited bivalve Arca noae in the Northern Adriatic Sea

Saskia Macharia, Rafał Nawrot, Michaela Berensmeier, Ivo Gallmetzer, Alexandra Haselmair, Adam Tomašových, and Martin Zuschin

The Northern Adriatic Sea is one of the most impacted ecosystems worldwide with a long history of anthropogenic impacts, ranging from overfishing and bottom trawling to eutrophication, deoxygenation and pollution. The impact of these multiple pressures on populations of economically important species is often difficult to evaluate due to paucity of long-term monitoring data. The edible bivalve Noah’s Ark shell (Arca noae L.) was intensively harvested in the eastern Adriatic Sea until 1949-1950 when it suffered a catastrophic population collapse due to unknown agents. The assessment of its subsequent recovery is hindered by the lack of data on the population size structure prior to that event. To reconstruct the natural baseline state of populations of A. noae before the onset of extensive harvesting, we studied fossil assemblages from two 1.5-m-long sediment cores collected in the southern Gulf of Trieste (off Piran, Slovenia), both recording the last ~9,500 years.

The abundance and shell length of A. noae remained low in the lower part of the cores but increased strongly within the oyster-Arca shell bed corresponding to maximum flooding and early highstand sea-level phases (6,500-1,000 years ago). In contrasts, the top 8 cm of the core (the late highstand phase), marked by high concentration of pollutants and organic enrichment, contained only few and small (< 10 mm) A. noae shells. Moreover, no living individuals were found in grab samples taken from the two stations suggesting that the dense populations of A. noae, persisting there for several thousand years, were locally extirpated in the 20th century. To evaluate population recovery in other parts of the NE Adriatic, we compared the size distribution of fossil A. noae from the shell bed interval to the previously published data on living populations of this species sampled along Istrian peninsula between 1966 and 1978. Both fossil and extant populations were characterized by similar median size, modal size class and proportion of specimens > 50 mm (minimal legal landing size). These results suggest that within few decades after the 1949-1950 mass mortality event the size structure of populations of A. noae have largely returned to their earlier, natural state. The recovery was spatially variable, however, as attested by the decline of A. noae populations due to loss of suitable shell-bed habitats in the two studied stations off Piran.

How to cite: Macharia, S., Nawrot, R., Berensmeier, M., Gallmetzer, I., Haselmair, A., Tomašových, A., and Zuschin, M.: Reconstructing the baseline population structure of the exploited bivalve Arca noae in the Northern Adriatic Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7694, https://doi.org/10.5194/egusphere-egu21-7694, 2021.

EGU21-15320 | vPICO presentations | SSP4.3

Micro- and macrofaunal responses to major environmental changes in Holocene highstand sediments from the Northern Adriatic Sea

Michaela Berensmeier, Adam Tomašových, and Martin Zuschin

Benthic communities in the Northern Adriatic Sea experienced major environmental and ecological changes during the late Holocene, particularly in the late 20th century due to anthropogenic induced stressors such as hypoxic events. These events lead to mass mortalities and changes in benthic communities. Here, we assess stratigraphic changes in bulk sediment geochemistry and sedimentological attributes to quantify the magnitude and timing of environmental changes and to correlate them to ecological changes. We focus on the reconstruction of the micro- to macrobenthic community composition (foraminifera, ostracods, bivalves and gastropods) prior and after major anthropogenic impacts. We investigate the differences in responses of these taxonomic groups to environmental changes and account for the impact of time-averaging.

The 3-m-long gravity core was collected at 31 m water depth, off the Po prodelta in the western part of the northern Adriatic Sea. The upper 60 cm of the core represent a condensed record determined by sediment bypassing and winnowing during the early and late sea level highstand. In total, 50 shells of the common bivalve Corbula gibba were dated by 14C-calibrated amino acid racemization (AAR) from the upper 30 cm and plant remains were dated by 14C from deeper parts. These analyses show that median shell ages of Corbula decline downcore, from ~50 years in the top 2.5 cm to 1,400 years in the 5-7.5 cm increment, 2,900 years in the 10-12.5 cm increment, and 4,500 years in the 17.5-20 cm increment. Median age in the 28-33 cm increment is again 3,600 years, indicating effects of mixing. The youngest shell corresponds to 24 years BP in the top 2.5 cm and the oldest shell to to 7800 years BP at the base at 30 cm.  The 60 cm-long highstand record can be divided in 4 major intervals:

(1) Early-highstand sediments cover the development of a baseline community. Total abundances of micro-and macrobenthic species increase upwards (2) In the late-highstand sediments (around 12.5-15 cm), micro-and macrobenthic absolute species abundance are highest. Increase in eutrophication and heavy metal pollution is indicated by rising N levels and Pb content in bulk sediments. (3) At 5 cm depth, a major anthropogenic environmental shift indicated by strong pollution (Pb and Hg) and eutrophication (TOC) coincides with a strong decline in micro-and macrobenthic abundance and diversity (4) The surface-mixed layer yields a slight increase in micro-to macrobenthic abundances, next to a slight decrease of heavy metal pollution and eutrophication.

14C-calibrated AAR shell ages indicate a relatively limited, centennial time averaging (measured by interquartile age ranges) of Corbula in the uppermost increment but then show a millennial-scale time-averaging below the uppermost surface-mixed layer. This can be linked to a decrease in bioturbation in the 20th century and to a slight increase in sedimentation rate. Although the record is affected by time-averaging, the micro-and macrobenthic community abundances show a distinct pattern that can be related to environmental changes from geochemical sediment proxies. Benthic foraminifers, ostracods and mollusks abundance show similar responses to sedimentological and geochemical tracers in these condensed sediments.

How to cite: Berensmeier, M., Tomašových, A., and Zuschin, M.: Micro- and macrofaunal responses to major environmental changes in Holocene highstand sediments from the Northern Adriatic Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15320, https://doi.org/10.5194/egusphere-egu21-15320, 2021.

EGU21-9604 | vPICO presentations | SSP4.3

Stratigraphic changes in shell size of a turritellid gastropod in the Holocene fossil record of the Po prodelta (Northern Adriatic Sea)

Angela Scheidl, Michaela Berensmeier, Rafal Nawrot, Paolo G. Albano, Adam Tomašových, and Martin Zuschin

Over the last century, the northern Adriatic Sea has faced multiple ecological threats such as hypoxic events, eutrophication, pollution by heavy metals and plastics, and bottom trawling. These impacts were associated with major changes in the composition of benthic communities, particularly a decline in the abundance of Turritellinella tricarinata (= Turritella communis), the dominant gastropod species in the previously widespread Turritella-biocenosis of the northern Adriatic muddy bottoms. In this study, we reconstruct changes in abundance and size structure of T. tricarinata populations over the last 6000 years to better understand the drivers responsible for its recent decline and to provide a historical baseline for assessing potential recovery.

We studied sediment cores from two locations in the western Northern Adriatic Sea: (1) distal zones of Po prodelta based on a 3-meter-long gravity core collected at 31 m water depth comprising a condensed record of the last ~9,100 years, (2) proximal zones of Po prodelta based on five 1.5-meter-long piston cores taken at 21 m water depth in the Po prodelta, which capture the last 100-150 years. Core chronologies are based on radiocarbon-calibrated amino-acid racemization analyses of bivalve shells.

We analysed changes in the abundance and shell height of T. tricarinata in each increment of the cores. In total, 600 specimens have been measured. All stations show a similar pattern in shell abundance: a climax in the early 20th century and a strong decrease in the late 20th century.

The proximal records of Po prodelta show a negative correlation between abundance and median shell size, with larger size and lower abundance in the late the 20th century, a period characterized by recurrent severe hypoxic events. The 3-meter-long offshore core contains on average smaller specimens, but reflects a similar pattern: the number of larger specimens (>10 mm) and median shell sizes increase slightly towards the core top while total abundance declines. This trend towards larger shell size and lower abundance may reflect the complex effect of nutrient enrichment in a highly disturbed environment. During the last century Turritella communis might experience higher growth rates and lower predation but simultaneously reduced recruitment due to hypoxia and pollution.

How to cite: Scheidl, A., Berensmeier, M., Nawrot, R., Albano, P. G., Tomašových, A., and Zuschin, M.: Stratigraphic changes in shell size of a turritellid gastropod in the Holocene fossil record of the Po prodelta (Northern Adriatic Sea), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9604, https://doi.org/10.5194/egusphere-egu21-9604, 2021.

Differences in the taxonomic or functional composition of living and death assemblages is a key means of identifying the magnitude and drivers of past ecological changes in conservation paleobiology, especially when assessing the effects of anthropogenic impacts. However, such live-dead differences in species abundances can arise not only from ecological (stochastic or deterministic) changes in abundance over the duration of time averaging but also from interspecific differences in the postmortem durability of skeletal remains or from the lifespan of the individuals. Here, we attempt to directly incorporate the effects of durability on species abundances in death assemblages by modeling dead abundance as a function of species’ durability traits and using abundances in living assemblages as a prior. Species inferred to be negatively affected by anthropogenic impacts should be over-represented in death assemblages relative to their abundance in death assemblages predicted by the durability model (rather than just relative to their abundance in living assemblages). Using species-level durability trait data for bivalves (shell size, thickness, mineralogy, shell organic content, and life habit) from the southern California shelf, we find that, among these traits, valve thickness correlates consistently positively and at multiple spatial scales with the log of the dead:live ratio of species abundances, and accounts for ~20-30% of live-dead mismatch. Using this benchmark for the discordance that might be taphonomic in origin, we confirm that the over-representation of epifaunal suspension-feeders and siphonate deposit-feeders in death assemblages of the southern California shelf owes in fact to their ecological decline in recent centuries, even when accounting for their greater durability.

How to cite: Tomašových, A. and Kidwell, S. M.: Testing the effects of durability (shell thickness) on species over-representation in death assemblages, a taphonomic baseline for conservation paleobiology, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13291, https://doi.org/10.5194/egusphere-egu21-13291, 2021.

EGU21-879 | vPICO presentations | SSP4.3

Addressing challenges in biodiversity conservation with fish otolith death assemblages: the state-of-the-art

Konstantina Agiadi and Paolo G. Albano

Fish otoliths are incrementally growing aragonitic elements found in the inner ear of most fishes. They have species-specific morphology that enable species level identification and they are excellent high-resolution recorders of ambient water conditions, enabling the reconstruction of past fish faunas and their environment. Although they have been studied as fossils for almost 150 years, and they are very useful tools for tracking lifestyle and population changes in modern fishes, otolith death assemblages recovered from sea bottom sediments have been studied only much more recently. Still, these fish remains can provide valuable insight into past fish faunas before most anthropogenic impacts, such as climate warming, habitat modification and biological invasions. Here, we present an overview of research done until now on otolith death assemblages highlighting their applications for marine conservation.

How to cite: Agiadi, K. and Albano, P. G.: Addressing challenges in biodiversity conservation with fish otolith death assemblages: the state-of-the-art, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-879, https://doi.org/10.5194/egusphere-egu21-879, 2021.

EGU21-6206 | vPICO presentations | SSP4.3

Radiocarbon dating of individual foram tests show that alleged Lessepsian species are of Holocene age

Paolo G. Albano, Anna Sabbatini, Jonathan Lattanzio, Jan Steger, Sönke Szidat, Quan Hua, Darrell Kaufman, Martin Zuschin, and Alessandra Negri

The Lessepsian invasion – the largest marine biological invasion – followed the opening of the Suez Canal in 1869 (81 years BP). Shortly afterwards, tropical species also distributed in the Red Sea appeared on Mediterranean shores: it was the dawn of what would become the invasion of several hundred tropical species. The time of the Suez Canal opening coincided with an acceleration in natural history exploration and description, but the eastern sectors of the Mediterranean Sea lagged behind and were thoroughly explored only in the second half of the 20th century. Many parts are still insufficiently studied today. Baseline information on pre-Lessepsian ecosystem states is thus scarce. This knowledge gap has rarely been considered by invasion scientists: every new finding of species belonging to tropical clades has been assumed to be a Lessepsian invader.

We here question this assumption by radiocarbon dating seven individual tests of miliolids – imperforated calcareous foraminifera – belonging to five alleged non-indigenous species. Tests were found in two sediment cores collected at 30 and 40 m depth off Ashqelon, on the Mediterranean Israeli shelf. We dated one Cribromiliolinella milletti (core at 40 m, 20 cm sediment depth), three Nodophthalmidium antillarum (core at 40 m, 35 cm sediment depth), one Miliolinella cf. fichteliana (core at 30 m, 110 cm sediment depth), one Articulina alticostata (core at 40 m, 35 cm sediment depth) and one Spiroloculina antillarum (core at 30 m, 110 cm sediment depth). All foraminiferal tests proved to be of Holocene age, with a median calibrated age spanning between 749 and 8285 years BP. Only one test of N. antillarum showed a 2-sigma error overlapping the time of the opening of the Suez Canal, but with a median age of 1123 years BP. Additionally, a thorough literature search resulted in a further record of S. antillarum in a core interval dated 1820–2064 years BP in Turkey.

Therefore, these foraminiferal species are not introduced, but native species. They are all circumtropical or Indo-Pacific and in the Mediterranean distributed mostly in the eastern sectors (only S. antillarum occurs also in the Adriatic Sea). Two hypotheses can explain our results: these species are Tethyan relicts that survived the Messinian salinity crisis (5.97–5.33 Ma) and the glacial periods of the Pleistocene in the Eastern Mediterranean, which may have never desiccated completely during the Messinian crisis and which may have worked as a warm-water refugium in the Pleistocene; or they entered the Mediterranean Sea from the Red Sea more recently but before the opening of the Suez Canal, for example during the Last Interglacial (MIS5e) high-stand (125,000 years BP) when the flooded Isthmus of Suez enabled exchanges between the Mediterranean and the Indo-Pacific fauna. The recognition that some alleged Lessepsian invaders are in fact native species influences our understanding of the invasion process, its rates and environmental correlates.

How to cite: Albano, P. G., Sabbatini, A., Lattanzio, J., Steger, J., Szidat, S., Hua, Q., Kaufman, D., Zuschin, M., and Negri, A.: Radiocarbon dating of individual foram tests show that alleged Lessepsian species are of Holocene age, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6206, https://doi.org/10.5194/egusphere-egu21-6206, 2021.

EGU21-7479 | vPICO presentations | SSP4.3

Tracing migration of larger benthic foraminifera across atolls in the South China Sea

Sulia Goeting, Antonino Briguglio, Laszlo Kocsis, and Amajida Roslim

The distribution of modern benthic foraminifera is studied from offshore reefs of Brunei Darussalam located in northwest Borneo with enhanced siliclastic influence, and from Louisa Reef, an atoll in the Southern Spratly Islands under fully carbonatic environment. The main families of larger benthic foraminifera found from offshore reefs of Brunei are the Calcarinidae, Amphisteginidae and the Operculinidae, while at the Louisa Reef are the Calcarinidae, Amphisteginidae and the Soritidae. Larger benthic foraminifera are mainly concentrated in the tropical regions and in shallow waters, and their distribution depends on important environmental factors such as water depth, sunlight and type of sediment. Migration of LBF has been recorded since the Paleogene from the Americas to Africa and the Mediterranean Sea, and later to the Indo-Pacific where the modern biodiversity hotspot occurs. Hence looking into any possible migration throughout certain groups of LBF could help in understanding their biogeographic distribution through time within the Indo-Pacific region. Along the atolls in South China Sea the marine environments meet their living preferences, hence tracing their presence, distributions, and abundances could shed further light on their regional migration pattern.

How to cite: Goeting, S., Briguglio, A., Kocsis, L., and Roslim, A.: Tracing migration of larger benthic foraminifera across atolls in the South China Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7479, https://doi.org/10.5194/egusphere-egu21-7479, 2021.

EGU21-10057 | vPICO presentations | SSP4.3

Unexpected abundance: Millepora corals in Late Pleistocene reefs of Egypt

Angelina Ivkić, Andreas Kroh, Abbas Mansour, and Martin Zuschin

Coral reefs throughout the world are well known for the dominance of scleractinian corals. However, one group of hydrozoan corals can be very common in modern tropical coral reefs as well: Millepora, the fire coral. The modern Red Sea is particularly well known for its high abundances of Millepora, where the fire coral is dominant on current-exposed reefs. Yet, this hydrozoan has been described as rare in the fossil record throughout the world and the documented abundances in fossil reefs do not match the numbers from modern reefs. The main interpretation to explain this phenomenon so far has been a lower preservation potential of milleporids compared to scleractinians due to differences in skeletal structure.

During an investigation of six Eemian Egyptian reef sites (29 line intercept transects, typically of 20 m length) we found Millepora in 69% of the fossil reef transects. The abundances were comparable to the adjacent modern reefs (65.13% to 0.26%). Preservation of fossil Millepora was good to excellent and in some cases well-preserved pore characters allowed for identification to species level. Our findings seem to be in stark contrast to results and interpretations of earlier studies, which suggest that Millepora is very rare in the fossil record globally. To understand the reason for this mismatch, we compared the associated scleractinian fauna between fossil reefs with and without Millepora presence. Furthermore, as a differentiation between shallower habitats close to the reef edge and deeper habitats along the reef slope was possible, we were able to investigate habitat preferences. Porites abundances were higher in fossil reefs without Millepora. Based on a comparison with modern communities, this suggests that the exposure to water energy might be a decisive factor for Millepora presence in the fossil reef. Therefore, preservation and consecutive investigation of appropriate fire coral-habitats is a pre-requisite for valid comparisons.

Another factor for the mismatch between our results and earlier studies might be a difference in diagenetic conditions that allow preservation of hydrozoan skeletons in the fossil record. Preservation of the investigated Egyptian sites is favored by their young geological age and their geographic location in a desert climate, reducing dissolution by aggressive meteoric waters. Furthermore, the extremely high abundance of Millepora in modern Red Sea coral reefs may in part mitigate the lower preservation potential of the hydrozoan skeleton in comparison with that of scleractinian corals.

How to cite: Ivkić, A., Kroh, A., Mansour, A., and Zuschin, M.: Unexpected abundance: Millepora corals in Late Pleistocene reefs of Egypt, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10057, https://doi.org/10.5194/egusphere-egu21-10057, 2021.

EGU21-16060 | vPICO presentations | SSP4.3

Fossil molluscan fauna reflects zonation of a Late Pleistocene reef of the Red Sea

Anna Haider, Angelina Ivkić, Andreas Kroh, Abbas Mansour, and Martin Zuschin

Many studies focus on modern coral reefs and their associated invertebrate fauna, but not much is known about the paleoecology and diversity of molluscs of Late Pleistocene coral reefs, which were formed during the last interglacial MIS5e. This study is investigating the molluscan assemblage of a Late Pleistocene coral reef in southern Egypt, at the locality Sharm El Luli, in the area of Marsa Alam. The locality is characterized by a variety of reef- and reef associated habitats, including a reef flat, reef slope, a patch reef, and soft bottoms of a lagoon and in the backreef area. We quantitatively and qualitatively sampled 10 sites with a total of 79 samples and collected 2126 shells, which belong to 177 taxa, mostly identified to the species level.   Most taxa were found with the qualitative sampling approach. The most abundant bivalves taxon was the epifaunal, encrusting Chama spp., the most abundant gastropod species was the cerithiid Rhinoclavis vertagus. Regarding the life habitats most bivalve species are infaunal filter feeders, while most gastropods are epifaunal carnivores.    Alpha diversity is highest in the coral patch and in the upper reef region, which implies the reef slope, the reef flat as well as the transition between reef slope and the lagoon. Preliminary statistical results suggest a division in coral-patch, lagoon and backreef as well as a cluster of upper-reef habitats. From these two broad environments can be distinguished: hard bottoms associated to reefs and reef-associated soft bottom environments. The former are best characterized by encrusting taxa such as Chama spp. and Spondylus spp., and by Tridacna maxima and Perigylypta spp., which are well-known reef associates. Gastropods in this environment are predatory conids and cypraeids. All of these species live on - or occur cryptically in - structured hard bottoms. Reef associated-soft bottom environments are best characterized by infauna, such as the tellinid Quidinipagus palatam and the lucinids Anodontia kora and Pillucina vietnamica. Furthermore, many soft bottom gastropod species such as the strombid Gibberulus gibberulus albus, the cerithiid Rhinoclavis vertagus, both with an herbivorous diet, and the nassariid Nassarius fenistratus, a scavenger, can be found here.  A comparison with modern datasets from the Red Sea indicates strong similarities in faunal composition and habitat diversity between fossil and recent reefs.  Furthermore, our preliminary results suggest that Late Pleistocene molluscan assemblages can aid in reconstruction of associated fossil reef habitats. 

How to cite: Haider, A., Ivkić, A., Kroh, A., Mansour, A., and Zuschin, M.: Fossil molluscan fauna reflects zonation of a Late Pleistocene reef of the Red Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16060, https://doi.org/10.5194/egusphere-egu21-16060, 2021.

EGU21-10632 | vPICO presentations | SSP4.3

The effect of preservation on diversity in a Triassic reef basin assemblage

Vanessa Julie Roden, Alexander Nützel, and Wolfgang Kiessling

Taphonomic effects complicate the assessment of variations in biodiversity over time. Most pre-Cenozoic fossil assemblages have been altered through taphonomic effects, such as lithification and aragonite dissolution. Several studies have found alpha (local) and gamma (global) diversity in marine ecosystems to be low in the early Mesozoic and then increase throughout the Mesozoic, reaching a maximum in the Cenozoic.

The Middle to Late Triassic Cassian Formation, exposed in the Dolomites, Southern Alps, northern Italy, comprises tropical reef basin and transported platform assemblages characterized by high diversity and commonly excellent preservation of fossils. The Cassian Formation yields high alpha (mean species richness per locality: 96), beta (mean Jaccard dissimilarity: 0.95), and gamma (1421 invertebrate species) diversity. The high primary diversity is probably due to the tropical reef-associated setting, and its reduced taphonomic alteration caused 4.5 times higher biodiversity to be preserved than in comparable pre-Cenozoic settings. High beta diversity can be explained by the presence of various habitat types and may also have been driven by priority effects. The Cassian fauna, like most comparable modern ecosystems, features a large number of gastropods (39% of all invertebrates, 58% of mollusks are gastropods). Especially small species in the millimeter size range contribute to the large number of gastropod species in the Cassian Formation. Our results support the assumption that the Modern Evolutionary Fauna was already established early in the Mesozoic and that the scarcity of small gastropods in many fossil assemblages is a taphonomic phenomenon. This contradicts the view that the major radiation of gastropods and the generally very strong increase in biodiversity largely took place in the Cenozoic. We suggest that highly complex, gastropod-dominant marine benthic ecosystems are as old as Middle/Late Triassic, pointing to an earlier establishment of the Modern Evolutionary Fauna than previously assumed. An improved eco-space utilization by infaunalization and increased biotic interactions such as a predator/prey escalation may have contributed to the high biodiversity and may reflect early aspects of the Marine Mesozoic Revolution.

How to cite: Roden, V. J., Nützel, A., and Kiessling, W.: The effect of preservation on diversity in a Triassic reef basin assemblage, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10632, https://doi.org/10.5194/egusphere-egu21-10632, 2021.

In order to reveal the response of benthic foraminifera to Cretaceous-Paleogene (K/Pg) boundary event, a high-resolution benthic foraminiferal study was carried out from a land-based Haymana section which is biostratigraphically complete, and once located in the northern branch of the Tethyan Ocean. To this end, 25 samples collected from deep marine succession of the Haymana Basin were quantitatively assessed along with the utilization of quantification of species, morphogroup analysis and diversity indices to establish remarkable changes in biofacies which resulted from the boundary event.

Depositional environment is inferred as upper bathyal (200-600 m) throughout the studied section based on foraminiferal associations. Bathymetric marker species include mainly bi- to triserial forms in Maastrichtian, which favor this interval. Calcareous taxa including Bolivinoides draco,  Eouvigerina subsculptura, Nonionellina sp. 1, Pseudouvigerina plummerae, Pyramidina minuta, as well as species belonging to Gyroidinoides, Laevidentalina, Lagena, Lenticulina, Pullenia, and Sitella are together forming 30% of the whole assemblage in this study, which are also attributed as Shallow Bathyal Assemblage of Widmark and Speijer (1997b) from the upper bathyal environment. Accompanied agglutinated taxa are consisting of Clavuinoides trilatera, Arenobulimina sp., as well as species of Dorothia, Gaudryina, Verneuilina, and Heterostomella, which are reported from low and mid-latitude Slope Deep Water biofacies of Kuhnt et al. (1989). There was probably no paleobathymetric change in the Danian, as it is concluded from the structure of the faunal assemblage. Besides, calcareous taxa are found to be more abundant with respect to agglutinated taxa within the whole section, offering deposition over Carbonate Compensation Depth (CCD) level.

With this study, Eouvigerina subsculptura Acme Zone is newly offered for the uppermost Maastrichtian, and also aligned with Bolivinoides draco Zone, since it is existing as very abundant in all samples. Besides, Angulogavelinella avnimelechi-Anomalinoides rubiginosus Interval Zone (BB1) is assigned for the lowermost Danian section based on marker Paleocene species.

Based on this benthic foraminiferal record, a highly diverse foraminiferal assemblage is observed in the Maastrichtian, then it is replaced with a poor to moderate diversity assemblage in the Danian. This finding is presented by diversity indices (Fisher alpha, Shannon H and Berger Parker). Presence of diverse morphogroups together in the upper Maastrichtian section along with taxa preferring high nutrient levels including E. Subsculptura (11-23%), Sliteria varsoviensis (0-6%), Praebulimina reussi (2-9%), Heterostomella spp. (4-11%) and Sitella spp. (1-13%) suggests meso- to eutrophic conditions in this section. A sudden change in the faunal composition right after the K/Pg boundary offers depleted food flux into the bottom of the basin. Infaunal morpogroups decline after the boundary in the Danian section, whereas epifaunal morphogroups including mostly opportunistic Cibicidoides spp. (17%), increased in number in this section. The timing of this record is coinciding with the worldwide primary productivity collapse and planktonic foraminiferal mass extinction during the K/Pg boundary event.

Keywords: K/Pg boundary, deep sea benthic foraminifera, quantitative assessment, paleoenvironment, Haymana Basin

How to cite: Vardar, E. and Özkan-Altıner, S.: Deep sea benthic foraminiferal record from the Haymana Basin (Turkey): changes in abundance patterns and diversity across Cretaceous-Paleogene boundary, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15764, https://doi.org/10.5194/egusphere-egu21-15764, 2021.

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