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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 We re-examined key outcrops and characterized macro- and microfacies, as well as chemostratigraphy and unpublished fauna in the collection.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.