EGU General Assembly 2022  

Pelagic sediments are boring as they result from monotonous processes: after death, calcareous and/or siliceous phytoplankton and zooplankton (with minor contributions of clayey particles) very slowly settle on the ocean floor. Pelagic sedimentation, therefore, closely corresponds to the productivity of surface waters while being controlled by ocean chemistry, fertility, temperature and depth-size of the basin. The biological pump extracts nutrients and carbon from the photic zone to form organic matter which, however, fails to reach the deep ocean, unless exceptionally unusual conditions are established. Some phytoplanktonic organisms, though, have invented biomineralization and many mineralized parts accumulate at the seafloor as oozes, later diagenetically transformed into pelagic limestone and, more sporadically, chert.  

Arguably, the modern ocean originated in the Early Triassic when a group of phytoplankton learned, by chance or by necessity, to calcify. Since then, coccolithophores developed the ability to secrete a variety of coccoliths/nannoliths and coccospheres. Coccolithogenesis, in a sense, continued to take snapshots that we can use to assess the functioning and dynamics - at various time resolutions- of the ocean, the largest and oldest ecosystem on our planet. My talk will try to provide data and interpretations of good and bad times for Mesozoic coccolithophores, with the ultimate goal of sharing with you my understanding of what a "normal" ocean was, what was its resilience to global perturbations, and which were the tipping points.In Jurassic and Cretaceous oceans calcareous nannoplankton were already widespread from coastal to open oceanic settings and of enough abundance and diversity to be rock-forming. Their variations somehow correlate with environmental global change, although getting from correlation to causality is not always straight forward. Mesozoic ocean anoxic events (OAEs) represent some of the most dramatic disruptions of the global carbon cycle and the geological records of OAEs have been thoroughly investigated to understand how the Earth system has overcome such extreme stress. Quantitative studies reveal major shifts in nannofossil assemblages with species-specific variations in size and major decreases in abundance, especially of the dominant rock-forming taxa. The absence/rarity of calcareous nannofossils at the peak of the OAE perturbation is primarily interpreted as the result of a major change in ocean alkalinity (and development of acidification) that possibly hindered biocalcification. However, none of the nannoplankton forms experiencing a calcification crisis got extinct: they recovered when the paleoenvironment returned to a pre-perturbation state, although slowly and partially.

Calcareous nannoplankton evolution is marked by spectacular speciation episodes (some of them anticipating and accompanying OAEs) in absence of extinctions. Furthermore, Jurassic and Cretaceous nannoplankton underwent accelerated originations during times of prolonged stability that, apparently, may have triggered innovative ways of coccolith/nannolith calcification. After decades of research devoted to environmental perturbations, we know very little about the unstressed ocean. Yet to understand/model how to stop and/or reverse the current global change, we should first know the characteristics of a calm, stable, normal ocean. What concentrations of atmospheric CO2? What fluctuations in chemistry, fertility, temperature? What variations in marine biota? The answers are written in the boring pelagic limestones!

How to cite: Erba, E.: Tiniest story-tellers of the largest ecosystem: calcareous nannofossils and the Mesozoic ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2899, https://doi.org/10.5194/egusphere-egu22-2899, 2022.

Sharp changes in lithology and increases in grain size and sedimentation rate of sedimentary sequences from tectonically active basins are often used to indicate regional neotectonic activity. However, these conventional methods have been challenged by others who argue that the sedimentary evidence used to infer tectonism could be climatically induced. Therefore, some forms of independent evidence or sedimentary criteria are required to discriminate between these two alternatives.

Seismites, sedimentary units preserved in subaqueous stratigraphic sequences that are caused by seismic shaking, are reliable indicators of regional tectonic activity. Subaqueous paleoseismology, can extend the record of strong earthquakes and augment the understanding of fault zone tectonic activity by studying seismites preserved in subaqueous sedimentary sequences. Here, we use the Dead Sea Basin (Middle East) and the Qaidam Basin (NE Tibet) as examples to further understand regional neotectonic activity from the perspectives of subaqueous paleoseismology.

The Dead Sea Basin is the deepest and largest continental tectonic structure in the world. In situ folded layers and intraclast breccia layer in the ICDP Core 5017-1 that recovered from the Dead Sea depocenter are identified as earthquake indicators, based on their resemblance to the lake outcrop observations of seismites that are known to be earthquake-induced. Based on the Kelvin-Helmholtz instability, we model the ground acceleration needed to produce each seismite by using the physical properties of the Dead Sea deposits. We invert acceleration for earthquake magnitude by considering regional earthquake ground motion attenuation, fault geometry, and other constraints.

Based on the magnitude constraints, we develop a 220 kyr-long record of Mw ≥7 earthquakes. The record shows a clustered earthquake recurrence pattern and a group-fault temporal clustering model, and reveals an unexpectedly high seismicity rate on a slow-slipping (~5 mm/yr) plate boundary. We also propose a new approach to establish the seismic origin of prehistoric turbidites that involves analyzing in situ deformation that underlies each turbidite. Moreover, our sedimentological data validate a long-lasting hypothesis that soft-sediment deformation in the Dead Sea formed at the sediment-water interface.

The Qaidam Basin is the largest topographic depression on the Tibetan Plateau that was formed by the ongoing India-Asia collision. The northeastward growth of Tibet formed a series of sub-parallel NW-SE-trending folds over a distance of ~300 km in the western Qaidam Basin. A long core was drilled in the basin on the crest of one such fold, the Jianshan Anticline. Sedimentological analysis reveals micro-faults, soft-sediment deformation, slumps, and detachment surfaces preserved in the core, which we interpret as paleoearthquake indicators. The core records five seismite clusters during 3.6-2.7 Ma. This suggests that the rate of tectonic strain accommodated by the folds/thrusts in the region varies in time and thus reveals episodic local deformation. During the clusters, regional deformation is concentrated more in the fold-and-thrust system than along regional major strike-slip faults.

This kind of research provides a fresh perspective for understanding regional tectonism by linking paleoseismic events and recurrence patterns with regional deformation, and can expand the ability of paleoseismology to understand the history of regional tectonics.

How to cite: Lu, Y., Waldmann, N., Wetzler, N., Moernaut, J., Bookman, R., Biasi, G. P., Strasser, M., Fang, X., Hubert-Ferrari, A., Alsop, G. I., Agnon, A., and Marco, S.: Subaqueous Paleoseismology: Fresh perspectives on sedimentary response to regional tectonics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1439, https://doi.org/10.5194/egusphere-egu22-1439, 2022.

The late Mesoproterozoic to early Neoproterozoic strata in the Yangtze Block hold a key position in deciphering the tectonic evolution of the South China Block and implicate upon the reconstruction of the Rodinia supercontinent. The sedimentological, geochronologic, and geochemical data on the Kunyang Group, southwestern Yangtze Block, were evaluated for a better understanding of the regional geodynamics and refinement in its paleoposition in the Rodinia supercontinent. Our findings constrain the deposition of the Kunyang Group sediments occurring during 1152 Ma and 1000 Ma, under a stable environment with alternating neritic and littoral facies sedimentation. In contrast, deposition of the Meidang Formation, traditionally thought to represent the upper part of the Kunyang Group, continued up to 866 Ma in an active setting at varying basin depths and hydrodynamic conditions. Moderate to high SiO₂ contents (57.7-95.4 wt%), highly variable K₂O/Na₂O ratios (0.01-55.8), and critical trace element abundances (Zr: 57.6-578 ppm, Th: 1.95-28.3 ppm, Sc: 0.75-24.3 ppm), detrital zircon age distribution, sedimentological characteristics, and bimodal magmatism cumulatively underline a transition from continental rift to passive continental margin setting, followed by an active continental marginsetting. The onset of oceanic subduction below the SW-NW margin of the Yangtze Block caused a hiatus in sedimentation, marked by an unconformity between the Kunyang Group and Meidang Formation.

Paleocurrent data, zircon U-Pb ages, and Lu-Hf isotopic characteristics indicate that the Kunyang Group received detritus from some interior sources and exotic terranes, such as the Gawler Craton in Australia, the Transantarctic Mountains in East Antarctica, and the Ongole domain in the Eastern Dharwar Craton of India. The Yangtze Block was likely located to the west of Australia and East Antarctica and north of India in the Rodinia supercontinent. Paleocurrent data also confirm an external location for the Yangtze Block in the Rodinia paleogeographic configuration.

How to cite: Sun, L., Wang, W., Lu, G., Xue, E., Huang, S., Pandit, M. K., Huang, B., Tong, X., Tian, Y., and Zhang, Y.: Neoproterozoic geodynamics of South China and implications on the Rodinia configuration: the Kunyang Group revisited, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-117, https://doi.org/10.5194/egusphere-egu22-117, 2022.

We present geophysical and sedimentological data acquired during the 59^th cruise of the P/V Akademik Ioffe (September – October 2021) from the eastern North Atlantic. Two sediment cores AI-59022 and AI-59027 were recovered southwest of the Western Gap entrance sill (water depth 4872 m) and from the western slope of the Josephine seamount (water depth 3282 m), respectively.  The collected data is valuable for reconstructions of the Pleistocene to Holocene sedimentary record and recognizing the influence of near-bottom currents on sediment deposition in the study areas.

Using high-resolution sub-bottom profiling, sediment waves (up to 50 m in amplitude) were found southwest of the entrance sill of the Western Gap. The presence of ripples and scours north of this sill also indicate elevated bottom current velocities in the gap which is in agreement with direct current velocity measurements (30 cm/s). Given that temperatures of <2 °C, which are characteristic of the AABW (Morozov et al., 2010), were recorded by CTD profiling near the seafloor, it is possible that AABW has played a significant role in shaping the sedimentary and morphological features in the Western Gap.

On the western slope of the Josephine seamount, a contourite drift intercalated with mixed features was identified, characterized by multiple, continuous sub-parallel reflections.  High-resolution sub-bottom profiling has also allowed us to identify a distinct erosional furrow at 1410 m (water depth). The depth of this feature corresponds to the present depth of the Mediterranean Outflow Water and may be related to the erosive passage of MOW currents.

The sponge species Pheronema carpenter was also observed on the western slope of the Josephine seamount. This species is typically associated with areas of high productivity, and possibly with regions of enhanced bottom tidal currents which promote the resuspension of organic matter. Thus, the presence of this sponge indicates elevated near-bottom hydrodynamic activity in the Josephine seamount area.

The dataset across the western slope of the Josephine seamount was supported by an IO RAS state assignment (№0128-2021-0012), whereas the study in the Western Gap was financed by RFBR (№20-08-00246).

How to cite: Urazmuratova, Z., Bashirova, L., Kuleshova, L., Glazkova, T., Rikhman, M., Kazakova, D., and Rodrigues, S.: Recognizing the effect of modern and paleo bottom currents across deep-marine basins: insights from sedimentological and geophysical data across the Western Gap and Josephine Seamount (NE Atlantic), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-535, https://doi.org/10.5194/egusphere-egu22-535, 2022.

The Cenozoic shallow marine deposits of the External Prebetic of Alicante (SE Iberian Peninsula) shows a rich association of benthic foraminifera, dominated by hyaline walled macroforaminifera such as myogypsinids, lepidocyclinids and nummulitids. This study analyses the microbiofacies and systematics of benthic foraminifera at genus and species level in the stratigraphic sections of "El Barranc dels Molins", in the surroundings of the locality of Ibi, and in the Natural Park of "El Carrascal de la Font Roja", nearby the city of Alcoi. The aim of this work is to develop a biostratigraphic study complemented by a sequential stratigraphic analysis and a palaeoenvironmental and depositional interpretation.

The section of Ibi includes benthic foraminifera characteristic of the Upper Eocene and the Oligocene, corresponding to SB zones 19 to 23 (Priabonian-Chattian). The Upper Eocene assemblage includes: Borelis vonderschmitti, Orbitolites aff. armoricensis, Nummulites fabianii, Nummulites sp., Discocyclina sp., Asterocyclina sp., Silvestriella tetraedra, Asterigerina rotula, Fabiania cassis, Halkyardia maxima, Chapmanina gassinensis and Acervulina linearis. The Oligonene species identified are: Pennarchaias glynnjonesi, Peneroplis thomasi, P. flabeliformis, Sorites sp., Sivasina egribucakensis, Borelis pygmaeus, B. inflata, Amphistegina bohdanowiczi, A. mammilla, Risananeiza pustulosa, Heterostegina assilinoides, Cycloclypeus carpenter and C. mediterraneus.

This work extends the stratigraphic distribution of Archaias sp. and Sorites sp. to the Chattian (SBZ 23) in the Tethys. It also confirms the extension of the range of Cycloclypeus mediterraneus and Amphistegina mammilla, and the presence of large-sized Victoriella conoidea (more than 3 mm in length) in the Upper Chattian of the Prebetic Domain.

In both localities, the identification of larger foraminifera and other fossil fauna, such as scleractinian corals, indicate a low-latitude shallow marine environment, at a depth of less than 40 metres. The vertical repetition of microbiofacies observed throughout the studied record is consistent with inner carbonate platform environments outgoing aggrading. This high-stand aggrading system was punctuated by low-stand regressive pulses that ended with the subaerial exposure of the inner platform, as indicated by the presence of several Microcodium horizons.

How to cite: Granero Ordóñez, P., Ferràndez-Cañadell, C., and Herrero Matesanz, C.: Cenozoic larger foraminifera and palaeonvironmental reconstruction from the Prebetic Domain (SE Spain), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1086, https://doi.org/10.5194/egusphere-egu22-1086, 2022.

How to cite: Phujareanchaiwon, C., Chenrai, P., and Laitrakull, K.: Interpretation and Reconstruction of Depositional Environment and Petroleum Source Rock Using Outcrop Gamma-ray Log Spectrometry From the Huai Hin Lat Formation, Thailand, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1519, https://doi.org/10.5194/egusphere-egu22-1519, 2022.

The Yinggehai Basin (YGHB) and Qiongdongnan Basin (QDNB) has received a large amount of terrigenous sediment from different continental blocks since the Paleogene, preserving Cenozoic sedimentary records of the Tibetan Plateau uplift, the tectonic activity of the adjacent plate, and climate change in Southeast Asia. Large scale of oil and gas reservoirs have been discovered in the YGHB and QDNB recently, but the provenance of the marine sediments in this area are poorly understood. In this study, sandstone samples were taken from drilling cores in the joint area of YGHB and QDNB, and cover all Oligocene, Miocene and Pliocene formations. The trace element, rare earth element (REE) and detrital zircon U-Pb geochronology of sedimentary rocks from the Oligocene to Pliocene is examined in this study to investigate the temporal and spatial variations in provenance since the early Oligocene. The Red River has been supplying sediments with positive Eu anomalies from basic-ultrabasic metamorphic and volcanic parent rocks to most parts of two basins, while Hainan Island has delivered sediments with negative Eu anomalies from granitic and sedimentary parent rocks to the eastern slope area of YGHB. The U-Pb ages of detrital zircon range from 3000 to 30 Ma, suggesting that sediment input is derived from multiple sources. Importantly, the Upper Oligocene Formation contained exclusively Cenozoic, Mesozoic, Palaeozoic, and Proterozoic zircon ages, and the age spectrum showed two major peaks at ca. 245 and 423 Ma, indicates that Upper Oligocene sediments in the northwestern area of the QDNB may have originated from the Red River, which had four major peaks at 254, 418, 751, and 1848 Ma, suggesting that sediments from the Red River entered the QDNB as early as the Late Oligocene. Detailed analyses of these components indicate that both the Red River and Hainan are likely the major sources of the sediments in the two basins, with additional minor contributions from Central Vietnam.

How to cite: meng, F.: Linking source and sink: geochemistry and zircon U-Pb geochronology provenance record of drainage systems in potential provenance area and Yinggehai-Qiongdongnan Basin, South China Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1780, https://doi.org/10.5194/egusphere-egu22-1780, 2022.

The Eocene sediments along the eastern Adriatic coast, deposited in the Dinaric foreland basin, are characterized by an abundance of larger benthic foraminifera (LBF). Representatives of the Nummulites are abundant in limestones deposited in oligotrophic, euphotic to mesophotic carbonate ramp settings and in deep basin sediments (being redeposited in mass - transport deposits). Nummulite-rich Lutetian to Bartonian sediments occur in the northwestern part of the basin and Bartonian to Priabonian in the SE part. For this study, nummulite tests from 60 thin sections of shallow-water limestones collected in the northern and southern parts of the foreland basin were examined in detail. The foraminiferal tests from the different areas show signs of mechanical, biological, or chemical degradation, which varies greatly depending on the area. The study of Lutetian carbonates from Istria and Northern Adriatic region has shown that 2 to 5% of all Nummulites tests show boring marks. The A– and B– generation representatives were equally affected by bioerosion. The traces are small and randomly distributed holes near to the outer walls. The Nummulites tests of Bartonian – Priabonian (Hvar Is., Pelješac) are more frequently bioeroded, about 10% of all specimens show boring marks, and preferably B-generation specimens are destroyed. Destruction varies from multiple holes of the same size distributed in a line along the test diameter to complete destruction of the internal test structure. There is a kind of size selection of the bioeroders, because the boring marks in the B-generation tests are larger, than those in the A-generation tests. The more intense bioturbation suggests greater biological competition in the middle to outer ramp settings around the Middle Eocene Climate Optimum in this part of the Neotethys. There are several possible causes for this: (i) a slightly higher seawater temperature around the MECO led to a higher occurrence of bioeroders (even the appearance of some new forms, such as the recorded crabs from the eastern Neotethys, Schweitzer et al., 2007), or (ii) a difference in sedimentation rate (burial history) between the two areas, or (iii) the Lutetian LBF assemblages were more resistant to biological destruction?

Schweitzer, C.E., Shirk, A.M., Ćosović, V., Okan, Y., Feldmann, R.M. and Hosgor; I.: New species of Harpactocarcinus from the Tethys Eocene and their paleoecological settings, Journal of Paleontology, 81/5, 1091-1100, 2007.

This study is conducted within the framework of the scientific project IP-2019-04-5775 BREEMECO, funded by the Croatian Scientific Foundation.

How to cite: Ćosović, V., Aljinović, D., Bucković, D., Čančar, M., Felja, I., Galovic, I., Horvat, M., Kurtanjek, D., Pejnović, I., Pezelj, Đ., Tomašić, N., and Coric, S.: Preservation of Nummulites tests in shallow-water limestones regarding the Middle Eocene Climate Optimum (Dinaric foreland basin, Croatia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2039, https://doi.org/10.5194/egusphere-egu22-2039, 2022.

The Pikermian chronofauna is associated with C₄ vegetation and the potential hominin Graecopithecus freybergi in Greece and Bulgaria and forms part of the Old World Savannah Paleobiome. This study provides a new magnetostratigraphy for thestratigraphic interval that includes the Haliminhanı and Hayranlı mammal sites from the central Anatolian Sivas Basin (Turkey), which show high faunal similarities to the Pikermian chronofauna.

Dated sites harboring Pikermian fauna in Turkey, Greece, and Bulgaria range in age between 11 and 7.3 Ma. Based on biostratigraphy, the Haliminhanı and Hayranlı fossil horizons were previously placed within European Mammal Neogene (MN) zones MN11-MN12 (ca. 9 to 7 Ma). A new magnetostratigraphy in 140 m thick continental deposits refines the age estimate to 8.0–6.5 Ma for the fossil mammal-bearing levels of the Sivas Basin.

Negative covariance between δ¹³C and δ¹⁸O values of bulk carbonate from the fluvio-lacustrine beds indicates an open lake hydrology; δ¹³C and δ¹⁸O values suggest a positive water balance and no significant long-term changes in hydrology and primary productivity within the lake that once covered the Sivas Basin. Two intervals of increased δ¹³C (by ca. 6–8‰) within the section are followed by a similar decrease over total time intervals of ca. 150 kyr. An increase of biogenic productivity can increase δ¹³C in lacustrine carbonate and may either result from changes in nutrient input or temperature. The absence of simultaneous changes in δ¹⁸O during peaks in δ¹³C make temperature an unlikely driver and we therefore conclude that nutrient input adjustments to the basin were responsible for the two peaks in δ¹³C.

Our results suggest that the Pikermian chronofauna of the Sivas Basin thrived under relatively stable local hydrological and climatic conditions. In the Sivas Basin, the Pikermian fauna flourished well into the Messinian, as opposed to Greek and Bulgarian sites where faunal turnover was observed under a cooling climate and mid-latitude desertification across the Tortonian-Messinian boundary.

Key words magnetostratigraphy, stable isotope geochemistry, mammal stratigraphy, late Miocene, Pikermian, central Anatolia

References Böhme et al. (2017). PLoS ONE, https://doi.org/10.1371/journal.pone.0177347; Böhme et al. (2018). Global and Planetary Change, https://doi.org/10.1016/j.gloplacha.2018.07.019 ; Meijers et al. (2018). Earth and Planetary Science Letters, https://doi.org/10.1016/j.epsl.2018.05.040; Meijers et al. (2020). Geosphere, https://doi.org/10.1130/GES02135.1; Meijers et al. (2022). Newsletters on Stratigraphy, https://doi.org/10.1127/nos/2021/0623

How to cite: Meijers, M. J. M., Kaya, F., Peynircioglu, A., Bibi, F., Pehlevan, C., Mulch, A., and Langereis, C. G.: Magnetostratigraphy of the Pikermian fauna-bearing late Miocene central Anatolian Sivas Basin (Turkey), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2958, https://doi.org/10.5194/egusphere-egu22-2958, 2022.

There is a wide range of data behind the concept that the late Pliensbachian–early Toarcian span (184.5–181.5 Ma) was a time of Earth-scale palaeoenvironmental changes. Rapid global warming, sea-level rise, perturbations in the carbon cycle and the development of widespread anoxia, known as the early Toarcian Oceanic Anoxic Event (T-OAE), are deemed amongst the major biogeochemical disturbances in the Mesozoic. A biotic crisis in the marine realm, with ~30% taxonomic loss, known as the early Toarcian mass extinction (T-ME), was broadly recognized. Many studies linked the T-OAE and the T-ME with the eruption of the Karoo–Ferrar igneous province in the southern hemisphere. The volcanism–warming–anoxia–extinction link has been well established and continues to collect evidence in numerous sites from around the world. The T-OAE has been indicated in several Bulgarian stratigraphic sections to date. The latter represent inner-shelf deposits of the Moesian Basin, which was developed proximal to the southern Eurasian passive continental margin. The overall depositional trend fits into the regressive phase of the second-order Ligurian (R6) T-R cycle, which is widely recognizable in the Jurassic basins of NW Europe. Locally, the deposition took place within a rapid late Pliensbachian–early Toarcian transgression, followed by a gradual regression to the mid-Bajocian times. It is related with widespread condensations and a collapse of the carbonate platform productivity. The manifestations of anoxia have been weak and more enhanced at post-T-OAE levels. Oxygen deficiency was evidenced in narrow and diachronous redox intervals with elevated TOC contents, V/Cr, V/(Ni+V) and Th/U ratios, and smallest mean framboid diameters. The δ¹³C_bel and δ¹⁸O_bel profiles showed similar trends to coeval European sections, in having a decline in oxygen-isotope signatures and rising in carbon-isotope values, both of >3‰, around the Pliensbachian/Toarcian (P/T) boundary. A decrease in ⁸⁷Sr/⁸⁶Sr ratios through the upper Pliensbachian, reaching a minimum around the P/T boundary, and followed by gradual increase throughout the Toarcian was also recorded. The isotope data revealed an increased freshwater influx and rapid seawater warming. The warming was attributed to the eruption of the Karoo-Ferrar, reflected by enrichments in mercury (Hg) recorded as a shift in sedimentary Hg/TOC ratios and concomitant with the δ¹³C_bel and δ¹⁸O_bel excursions. A biotic crisis was recorded amongst the benthic (bivalve and brachiopod) faunas and considered to be part of the T-ME. Both bivalves and brachiopods displayed clear NW European affinity, but characteristic ‘black shale’ taxa are virtually absent. A loss of ~40% of extinct bivalve species was evidenced around the P/T boundary. In brachiopods, the loss is even greater, with a prominent P/T boundary-hiatus and straggling occurrences above it, consisting mainly of autochthonous taxa. In the absence of ‘true’ anoxic setting, the T-OAE–T-ME link remains unclear. Therefore, rapid warming rather than oxygen deficiency has been driving the T-ME in the Moesian Basin.

This account takes part of the National Science Program “Environmental Protection and Reduction of Risks of Adverse Events and Natural Disasters”, approved by the Resolution of the Bulgarian Council of Ministers (No. 577/17.08.2018).

How to cite: Metodiev, L., Koleva-Rekalova, E., Georgieva, M., and Stoylkova, T.: Palaeoenvironmental changes in the Moesian Basin (Bulgaria) during the Toarcian, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3697, https://doi.org/10.5194/egusphere-egu22-3697, 2022.

Bed-parallel, fibrous calcite veins are widespread within Eocene, lacustrine, laminated organic-rich source rocks in the Dongying Depression of Bohai Bay Basin, East China. Such veins mainly occur in the horizontal organic-rich laminae (composed of horizontal banded lamalginites) of mature source rocks, with higher TOC and lower carbonate contents than the adjacent non-vein sections vertically. They are products of diagenesis accompanying burial, and their formation was coeval with hydrocarbon generation and expulsion from the initial fracture opening and subsequent dilation, which was evinced by the occurrence of medium plane (calcite+bitumen) and primary hydrocarbon inclusions in the fibrous calcites. Petrographically primary two-phase (oil+gas) hydrocarbon inclusions, and coeval aqueous inclusions are distributed either within individual fibrous calcite grains or between two adjacent fibres. In rare cases, inclusions with only liquid hydrocarbons were observation. The hydrocarbon liquid shows various UV-fluorescence colours (brownish, yellow, yellow-green, green), indicating different composition of oil from less mature to relatively high maturity. The micro-spectrofluorimetry of yellow-green fluid inclusions contains the two dramatic peaks (511 nm and 568 nm) of yellow and green fluorescence, suggesting that it was the by-product by fractionation. In addition, many bitumen-bearing oil inclusions could also be observed in the fibrous calcite veins. Consequently, we surmise that immiscibility and heterogeneous trapping of liquid hydrocarbon, bitumen and aqueous solution during the fibrous calcite growth are the best explanation for these above features. The PVT calculation by use of isochores intersection of oil inclusions and aqueous inclusions, combined with study of the burial history show that veins were formed during the Oligocene Dongying sedimentary stage (32.8-24.6Ma). We conclude the fluid overpressure up to approximately twice (2x) the hydrostatic value (i.e., ~0.5–0.6x lithostatic) are the most common during the hydrocarbon generation and primary migration. The highest degrees of overpressure are recorded by the rare monophase petroleum inclusions. The resulting isochores of these highest density inclusions project to pressures that overlap with the lithostatic gradient. Thus, we contend that vein dilation in the absence of lithostatic fluid pressure suggested a primarily steady-state process, in which dilation was accommodated and offset by concomitant narrowing of the adjacent wall rock laminae. And this process was likely driven by dissolution of CaCO₃ from adjacent wall rocks, coupled with the later reprecipitation of calcite into the nascent horizontal fractures.

How to cite: Wang, M., Chen, Y., and Matthew, S.-M.: Fluid features during hydrocarbon generation and expulsion from laminated source rocks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3705, https://doi.org/10.5194/egusphere-egu22-3705, 2022.

3300 km of newly collected 2D seismic reflection data across the Falkland Plateau, acquired during cruise MSM81 (2019) allowed for mapping of two distinct bottom-simulating-reflection (BSR) features, which are mostly pronounced within the western and southern sectors of the Falkland Plateau Basin (FPB-BSR) and the eastern sector of the Falkland Trough (FT-BSR). The nature of these BSRs is investigated by means of their reflection characteristics and seismic expressions and is concluded to be associated with silica diagenetic fronts. In absence of a proximal borehole, age information is derived through correlation with the Deep Sea Drilling Project Leg 36 Sites 327 and 330 and Leg 71 Site 511, on the easternmost proximity of the FPB, along the seismic profiles. It is argued in this study, that despite their similar origin, presumably in connection to an Opal A/CT diagenetic front, FPB- and FT-BSR display dissimilar geometrical characters. While the FPB-BSR is by definition a true BSR, which mimics the present seafloor, the geometrical extent of the FT-BSR, which shows parallelism with a shallower buried (Early/Middle Miocene?) reflector, favors a fossilized diagenetic front parallel to a paleo-isotherm. Palaeoceanic and palaeomorphologic implications are brought based on observed depth properties of the BSRs by considering different scenarios for the geothermal gradients. The observations suggest the absence of up to a few hundred meters of sedimentary deposits which presumably have been eroded due to the erosive action of the bottom currents.

How to cite: Najjarifarizhendi, B. and Uenzelmann-Neben, G.: Active versus arrested silica diagenetic front: Implications on the Palaeoceanographic evolution across the Falkland Plateau, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3751, https://doi.org/10.5194/egusphere-egu22-3751, 2022.

The analysis of fossil specimens under ultraviolet (UV) light represents a powerful tool in palaeontology. It has been frequently applied in this field only in the last twenty years, although it was discovered at the beginning of the 20^th Century. Up to now this technique has been applied mainly on mollusc shells, but the number of studies dealing with other taxa, like vertebrate specimens, is increasing. Despite this, the analysis of fossil specimens under UV light represents a technique still not fully comprehended; the knowledge of the best procedure of sample preparation and photography still needs to be clarified and new data are required to better understand the real potential of this method. Here, we have tested different preparation (bleached vs not bleached specimens) and photographic techniques to define a protocol for UV analysis of fossil specimens and have explored its main applications analysing specimens from different stratigraphic contexts (from the Permian to the Holocene, from Oman to Italy), having different biominerals (calcite, aragonite, bioapatite and silicified and phosphatized specimens) and belonging to invertebrate and vertebrate taxa (bivalves, gastropods, brachiopods, fish, crustacean and reptile); also, we use two different wavelengths: the commonly used 365 nm, and the 440 nm, a “borderline wavelength” here adopted for the first time. Our results indicate that bleach treatment is not recommended for calcite-shelled brachiopods, whereas is suggested for aragonite-shelled molluscs. We show that UV photography enhances morphological characters and colour patterns and allows to distinguish soft-bodied fossils from the matrix, having important implications in several palaeontological fields and no limitations for its application in invertebrate or vertebrate specimens. Also, the use of UV light provides an inexpensive method to detect man-made interventions in fossil specimens and thus fake fossils. However, the nature of the biomineral and shell microstructures cause different UV responses, whereas the stratigraphic context affects specimen preservation influencing pigment preservation.

How to cite: Crippa, G. and Masini, S.: How UV light photography can be of help to palaeontologists?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3774, https://doi.org/10.5194/egusphere-egu22-3774, 2022.

River deltas have long been considered as important carbon sinks. However, the presence of shallow gas (mainly composed of methane) and the processes of delta erosion caused by diminished sediment supply bring complexities to the present situation. This study investigates the response of the gas charged deposits in the Yangtze subaqueous delta to erosion process based on historical bathymetric data and the dataset obtained from a seismic survey. Both seismic and bathymetric data reveal a prominent erosion belt at water depth ranging from 5-20 m, extending from the southwest to the northeast in the nearshore area of the Yangtze subaqueous delta. Erosion is severe in the south while slight in the north area due to the differences in hydrodynamic condition, sediment erodibility and sensitivity to sediment reduction. Seabed erosion reduces the thickness of cap bed, as well as overburden pressure at gas front, making it easier for gas to seep through the sediment column and bypass the process of anerobic oxidation of methane within the SMT (an important methane filter). The spatial coincidence between the shallower gas front and pockmarks also indicates that sea bed erosion accelerates gas seeping activities. It expected more greenhouse gas would be expelled into atmosphere under the impact of bed erosion induced by ongoing decline of riverine sediment supply.

How to cite: Chen, Y., Deng, B., Zhang, W., and Gao, S.: Response of shallow gas charged Holocene deposits in the Yangtze Delta to erosion induced by diminished sediment supply: Increasing greenhouse gas emission, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3993, https://doi.org/10.5194/egusphere-egu22-3993, 2022.

The Opalinus Clay, an argillaceous to silty claystone formation, is known in Switzerland as being the selected host rock for deep geological disposal of high-, intermediate- and low-level radioactive waste. Since the 1990s, various properties of the Opalinus Clay have been studied within the framework of the Nagra (National Cooperative for the Disposal of Radioactive Waste) deep drilling campaigns and the Mont Terri Project (international research program dedicated to the investigation of claystone). The Opalinus Clay succession was deposited during the Late Toarcian to Early Aalenian in an epicontinental sea covering central Europe.

Although the Opalinus Clay is relatively homogeneous at formation-scale compared to other Mesozoic formations in northern Switzerland, significant lithological variations occur at lower scales. Besides m-scale lithofacies variations, high, intra-facies lithological variability occur at dm- to cm-scale. The facies diversity is primary attributed to regional differences in depositional, environmental and diagenetic conditions. In order to harmonize petrographic descriptions in an objective and quantitative way within all fields of research related to the Opalinus Clay, a subfacies classification scheme has been developed (SF1 to SF5, applied mostly on Mont Terri drill cores). The subfacies are distinguished by parameters such as texture (grain size, bedding, fabric and colour) and composition (nature and mineralogy of components). The five subfacies types can be further refined by additional attributes and sedimentary characteristics (biogenic, diagenetic, structural).

Subfacies descriptions are crucial to understand the lateral and vertical facies variability at regional scale. Moreover, accurate petrographic descriptions are a crucial prerequisite to many geotechnical studies and the prediction of petrophysical properties.

The main goal of the present study is to define a subfacies classification model covering the entire Opalinus Clay succession of the Mont Terri rock laboratory and successions deposited further to the east. Nagra is currently investigating three potential sites for radioactive waste storage within the Opalinus Clay in northern Switzerland. Nine new drill cores are used to apply the subfacies classification scheme. If necessary, the subfacies classification scheme will be adapted considering regional facies heterogeneities. Based on the new subfacies classification, depositional models for the Opalinus Clay will be refined.

How to cite: Zimmerli, G., Lauper, B., Deplazes, G., Jaeggi, D., Wohlwend, S., and Foubert, A.: Harmonisation of Opalinus Clay descriptions in Northern Switzerland: towards a uniform Subfacies Classification Scheme, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4605, https://doi.org/10.5194/egusphere-egu22-4605, 2022.

Combined with a series of analysis and test data such as seismic, core, drilling, logging and carbon oxygen isotope, this paper analyzes the reservoir differences of the East Zone, middle zone and West zone of the third member of Liushagangzu in the steep slope zone of Weixinan Sag, Beibuwan Basin, analyzes the main reservoir controlling factors of the three zones, and summarizes the reservoir development model. In the study area , reservoir diversity is mainly affected by five factors; 1) Structural factors: structural factors control trap types. In the study area , West zone and middle zone fans mainly develop glutenite deposits controlled by linear provenance, and structural traps are developed; The East zone mainly develop glutenite deposits controlled by point provenance, and lithologic traps are developed. 2) Sedimentary facies factors: sedimentary facies types control reservoir characteristics. Fan delta sedimentary system is developed in the three zones in the study area. The main dominant sedimentary microfacies are underwater distributary channel, with large sand body thickness, low matrix and cement content The main characteristics are the development of primary and secondary pores. 3) Sand thickness factors: sandstone thickness mainly controls the oil and gas bearing property of the reservoir. Taking the oil and gas bearing property of 50% as the boundary, the sand thickness of the West Zone in the study area is 3m; The sand thickness of the middle zone is 5m; The sand thickness of the East Zone is 8m; 4) Physical factors: physical factors mainly control reservoir classification. In the study area ,type I conventional reservoirs (porosity > 12%, permeability > 10md) are mainly developed in the West Zone; middle zone mainly develops type II low permeability reservoir (porosity 6-12%, permeability 1-10md); West Zone mainly develops type III tight reservoir (porosity < 6%, permeability < 1md) 5) Diagenetic facies factors: diagenetic facies factors control the reservoir type. In the study area, West Zone mainly develops weakly compacted and weakly cemented diagenetic facies (type I diagenetic facies); middle zone mainly develops medium compaction medium dissolution and strong compaction medium strong dissolution diagenetic facies; East Zone mainly develops strong compaction medium strong dissolution diagenetic facies. Combined with reservoir control factors and reservoir differences in steep slope zone, two types of multi-factor control reservoir prediction models are summarized: steep slope zone prediction model and conversion zone prediction model. The high-quality reservoir in the steep slope zone is mainly in the middle of the sand body, mainly medium coarse sandstone. The organic acid + atmospheric fresh water two-stage acid fluid is active, the dissolution is strong, and the dissolved substances migrate out of the system. The intergranular dissolved pores, intragranular dissolved pores and matrix dissolved pores are developed, and the physical properties are the best. The high-quality reservoirs in the conversion zone are mainly located in the middle of the sand body, mainly medium coarse sandstone, dissolved by organic acid fluid, developed intergranular dissolved pores, intragranular dissolved pores and matrix dissolved pores, and have the best physical properties.

How to cite: liu, S.: Study on Reservoir Diversity Controlled by Multiple Factors:Anexample from Liushagangzu 3rd member of Northern Steep SlopeZone in Weixinan Depression ,Beibuwan Basin, South China Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4941, https://doi.org/10.5194/egusphere-egu22-4941, 2022.

Several episodes of strong climate change and environmental perturbation marked the Early Jurassic, and culminated during the Toarcian Oceanic Anoxic Event (T-OAE), characterised by widespread deposition of organic-rich shales. Exceptionally preserved fossils of marine vertebrates and invertebrates have been discovered in the Toarcian shales of NW Europe, but the potential links between the occurrences of these exceptionally preserved fossils and the T-OAE remain poorly investigated. Paleontological excavations realized in Toarcian strata near Lodève (Grands Causses Basin, southern France) have yielded several specimens of marine vertebrates and abundant invertebrate fauna. We have developed a multiproxy approach (ammonite biostratigraphy, X-ray diffraction-bulk mineralogy, Rock-Eval pyrolysis, stable isotopes, trace element, phosphorus and mercury contents) to place these findings in a well-defined temporal and paleoenvironmental context, and hence constrain the factors that led to their extraordinary preservation. The Jenkyns Event interval, unambiguously identified at the base of the Toarcian organic-rich shales by a 5‰ negative carbon isotope excursion, records higher mercury fluxes, which suggest a causal link with intense volcanic activity of the Karoo–Ferrar large igneous province. This interval is very condensed and unfossiliferous, and might have been deposited under abnormally low-salinity conditions. Our data exhibit that the deposition of the vertebrate-yielding horizons post-dated the T-OAE by several hundreds of ka, and took place during a prolonged period of widespread oxygen-deficiency and high carbon burial. Our results indicate that the unusual richness in vertebrates of the studied site can be explained by a combination of regional factors such as warming-induced, prolonged seafloor anoxia, and more local factors, such as extreme condensation owing to reduced dilution by carbonate and detrital input.

How to cite: Bomou, B., Suan, G., Schlögl, J., Grosjean, A.-S., Suchéras-Marx, B., Adatte, T., Spangenberg, J., Fouché, S., Zacaï, A., Gibert, C., Brazier, J.-M., Perrier, V., Vincent, P., Janneau, K., and Martin, J. E.: Toarcian marine vertebrate preservation in the Grands Causses Basin (France), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6008, https://doi.org/10.5194/egusphere-egu22-6008, 2022.

The caves and palaeocaves from the Cradle of Humankind (Cradle), South Africa preserve a rich fossil record of early hominin evolution representing at least three genera: (Australopithecus, Paranthropus, early Homo) and have consequently been the subject of much research. Direct dating of the South African caves had long been hampered by the perception the sedimentary fills are not amenable to direct radiometric dating. The last decade has, however, seen major advances in the ability to reliably date the fossil sites. While some dating methods have been applied directly to fossils and their encasing sediments, the most precise and consistent results come from uranium lead (U-Pb) dating of cave carbonates, known as flowstones and a relatively large dataset places the cave deposits and fossils between 3 and 1.5 Ma. Coupled with the dating issues, there is a second, long held view that the stratigraphy of these sites is too complex and, in many cases, unresolvable. However, coupled with the advances in direct dating the flowstones, there has been a considerable change in understanding of the depositional setting and stratigraphy of these ancient caves. Here we present a model to demystify the stratigraphy and sedimentology of the cave deposits and offer a set of facies which can be applied, in modified site-by-site basis, at all the fossil localities throughout the Cradle. Sedimentary facies vary laterally, depending on the distance from the cave entrance, with entrance facies characterised by coarse-grained material, even piles of boulders. Hydrodynamic sorting winnows finer material and bone into the deeper reaches of the cave resulting in red-brown layered or massive sediments. These clastic sediments are almost all externally derived, and in our model are correlated to times during which the cave entrances are more open; we argue these time windows correlate to a drier external hydroclimate. The stacked occurrence of flowstones and these clastic sediments point to these conditions, both how open the caves are and the general climate state, have oscillated repeatedly in the past. The U-Pb flowstone chronology pins the flowstones and their deposition to specific time windows and investigations into the bigger climatic picture are ongoing. This has the potential to provide a detailed palaeoenvironmental context for the rich early human fossil record, as well as provide otherwise rare southern hemisphere terrestrial records of hydroclimate variability.

How to cite: Edwards, T. and Pickering, R.: A simple sedimentological model demystifying the complexity of fossil bearing cave deposits in the Cradle of Humankind, South Africa., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6299, https://doi.org/10.5194/egusphere-egu22-6299, 2022.

Introduction. Deposits of the Belokatay Formation were studied in four quarries in Belyanka region and Kirikeevo region (Belokataisky District, Bashkortostan). All of these careers are quite similar to each other. The Belokatay Formation is represented by polymictic conglomerates with rare layers of fine-medium-grained polymictic sandstones. The composition of the pebbles is extremely diverse - there are fragments of all types of rocks - sedimentary (70%), magmatic (20%), metamorphic (10%). Sedimentary rocks: pelitomorphic limestones, fragments of coral reefs and organogenic-detrital limestones. Igneous rocks - basaltoids and granitoids. Metamorphic rocks - shales, gneisses, quartzites. The roundness of all the pebbles is very good, there are no angular fragments. The size: more than 70% of fragments – 5-10 cm, which accords to a medium-grained conglomerate (although rare boulders, as well as smaller pebbles, are also sometimes found).

Materials and methods. We analyzed thinsections of matrix rocks and individual fragments in the amount of 60 pieces, identified foraminifera from pebbles of organogenic limestones, and also examined some samples for the presence of conodonts and other fauna.

Results and discussion. The diversity of the composition of the fragments, their consistent size and good roundness, as well as their high thickness (more than 700 meters) indicate that the formation accumulated in a very active hydrodynamic environment. In literary sources, faults are reported - but they were not found on our territory. On the other hand, in the conglomerates vertically layers of sandstones were found. Perhaps these are not layers, but olistoplaks from older formations. However, olistoplaks, as well as faults, only confirms a very active environment. The main source of material for this formation was the Ural Orogen located to the east of the trough. When the mountains were uplifting, fragments of rocks of different formations were demolished into this basin. And not only the rocks of the orogen could be eroded, but also the sediments, which filled the trough earlier (Late Carboniferous-Permian). The formation of sediments of the Ural foredeep has certain patterns: from the bottom up the section, there is an alternation of coarse-grained rocks (including the Belokatay Formation) and fine-rhythmic flysch strata. The formation of Ural foredeep occurs simultaneously with the collision. There are several stages in this process. The accumulation of the Belokaty Formation characterizes the beginning of one of the stages of collision, as the rocks change – from flysch to conglomerates.

Financial support. The research has been funded by RFBR and CNF as a part of the research project № 19-55-26009 Czechia_a

How to cite: Volodina, E., Tevelev, A., Borisenko, A., and Koptev, E.: Composition and accumulation conditions of the Belokatay Formation of the Lower Permian (Middle Urals), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6404, https://doi.org/10.5194/egusphere-egu22-6404, 2022.

Animal body size provides information about the trophic position and reproductive strategies of species, and the presence of environmental stressors. The distribution of body sizes in fossils can be easily measured, making it an important tool for paleoecological studies. However, preservational and collection biases might influence the primary measurements and thus the results. Intuitively, smaller specimens of the same species should be more prone to destructive processes such as fracturing and dissolution. It is often assumed that body size distributions in death assemblages reflect those in living populations. We test this assumption.
Using the body size distributions in monospecific assemblages of Devonian ammonoids, we show that common depositional environments yield distinct distributions of conch sizes. We then simulate postdepositional conditions in recent analogues of these environments. If conch size is proportional to robustness (or disintegration rate), sedimentation rates and mixing intensities characterizing these recent analogues allow us to reconstruct conch size distributions observed in Devonian counterparts of these environments.
The results show that shape parameters of body size distributions (skewness and kurtosis) are modified in predictable ways in sedimentary environments. This implies that fossil body size distributions are not a direct reflection of ecological signals, but can be altered by postdepositional processes. We conclude that parameters of body size distributions, such as mean and dispersion, may not be comparable with parameters in standing populations. If changes in these parameters coincide with changes in the depositional environment, the effect of (post)depositional processes needs to be considered.

How to cite: Hohmann, N., Buchwald, S., Korn, D., Klug, C., De Baets, K., and Jarochowska, E.: Postdepositional Controls on Fossil Body Size Distributions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6816, https://doi.org/10.5194/egusphere-egu22-6816, 2022.

Lemnos Island (NE Aegean Sea) was inhabited since the Paleolithic times, as is suggested by archaeological evidence from the hunting campsite of Ouriakos (~12.000 BP). The Agia Bay, in the vicinity of Ouriakos site, is located on the southeastern coast of Lemnos Island. The coastal area today is characterized by aeolian sandy deposits (dunes), while a small river is discharging in the bay. The systematic investigation of a 15.5-m long sediment core from the coastal plain of Agia aims to set light to the paleoenvironmental evolution of the area. The exhaustive study of the faunal and floral remains of the deposits, including benthic foraminifera, ostracoda, molluscs, pollen and NPPs was further supported by sedimentological, micromorphological and elemental analyses, magnetic susceptibility measurements and radiocarbon dating.

Four main evolutionary stages are identified: (1) at the base of the sequence the fluvial activity is dominating the sedimentation in the area, while progressively seawater intrusions are observed as suggested by reworked marine foraminifera and mollusc specimens (2) before ~7000 BP a restricted fresh water wetland is formed, characterized by land snails, Cyperaceae and the presence of aquatic plant seeds (3) after ~7000 and until ~5000 BP a connection of the wetland to communication to the sea is established as indicated by the occurrence of euryhaline foraminifera (Ammonia tepida, Haynesina germanica), ostracoda (Cyprideis torosa, Cyprinotus salinus) and mollusc (Cerastoderma glaucum, Abra sp., Hydrobia sp.) assemblages accompanied by marine dinoflagellate cysts and charophytes (4) after ~5000 BP a nearshore environment is developed due the sea-level rise, characterized by Peneroplis pertusus, rotaliids and miliolids as well as Loxoconcha sp., Cerithium sp. and reworked foraminifera and mollusc specimens. Pollen assemblages record the occurrence of mixed deciduous oak forest with Ulmus and Carpinus/Ostrya in the island interior, while agricultural activities are inferred by pollen indicator species.

How to cite: Theocharidis, N., Koukousioura, O., Kouli, K., Gkouma, M., Aidona, E., Syrides, G., and Efstratiou, N.: An interdisciplinary approach for reconstructing environmental evolution since the mid Holocene, in Agia (Lemnos Island, Greece), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6973, https://doi.org/10.5194/egusphere-egu22-6973, 2022.

Zoological collections of extant taxa allow assessment of biodiversity only for the past few centuries, when it was already affected by human activity. To understand present-day diversity declines, documenting biodiversity changes in fossil taxa and the drivers behind these shifts is crucial. We present an ongoing project on arthropod palaeodiversity as a case study. In this project, arthropods – particularly arachnids – in different amber deposits are examined to assess the effect of ecosystem shifts and climate variability on biodiversity from the Eocene until today and to analyze evolutionary trends and biogeographical scenarios. We aim to compare past changes with current diversity trends in order to better predict the future of our arachnid fauna.

How to cite: Loria, S. F., Kottoff, U., and Harms, D.: Assessing past arthropod diversity - a case study for Eocene ecosystems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8602, https://doi.org/10.5194/egusphere-egu22-8602, 2022.

Improved knowledge of the connection between striking variations in the abundance and coiling direction of the trochospiral planktic foraminiferal genus Morozovella and early Eocene carbon-cycle changes, is presented in this study as deriving from new data recorded from the Pacific Ocean (Shatsky Rise, Ocean Drilling Program Sites 1209, 1210). This location spans the Early Eocene Climatic Optimum (EECO; ~53-49 Ma), the interval when Earth surface temperatures and atmospheric pCO₂ reached the maximum peak of entire Cenozoic (Zachos et al., 2001, Sciences; Anagnostou et al. 2016, Nature; Inglis et al., 2020 Clim. Past). A significative impact of the EECO on planktic foraminiferal assemblages has recently been recorded in previous works from the Atlantic Ocean, where a definitive marked decline in abundance, diversity, test-size and change in coiling direction of the mixed-layer symbiont-bearing genus Morozovella, took place within the first ~600 kyr of this interval (Luciani et al., 2016 Clim. Past; Luciani et al. 2017 Paleoceanogr.; Luciani et al., 2017 GloPlaCha; D’Onofrio et al., 2020 Geosciences; Luciani et al., 2021 GloPlaCha). As registered in Atlantic sites, in the tropical Pacific Ocean Sites 1209 and 1210, the morozovellids drop permanently their relative abundance at the carbon isotope excursion (CIE) known as J event (~53 Ma), which marks the EECO beginning. A second major change affected all the morphologically defined species of Morozovella (possibly criptic species) at the Atlantic Ocean, resulting in a switch from dominant dextral to sinistrally coiling preference, within ~200 kyr after the K/X event (~52.8 Ma). Although the coiling direction preference of Morozovella at Shatsky Rise changed from dominant dextral to dominant sinistral after the K/X event as well as in the Atlantic sites, here the switch occurred with a delay of ~200 kyr. The recorded modifications clearly reflect important changes in evolution or environment. These changes may include temperature increase and pH decrease that could have reduced the symbiotic relationship and induced calcification crisis. Searching for the driving causes of the observed variations, our data clearly demonstrate their wide geographic and possibly global character and the evident relationship between the environmental perturbations occurred in the mixed-layer at the EECO and the striking changes on planktic foraminiferal assemblages during the first ~800 kyr of this intriguing interval.

How to cite: Filippi, G., Luciani, V., D'Onofrio, R., Westerhold, T., Wade, B. S., and Dickens, G. R.: Dramatic decline and change in coiling direction of planktic foraminifer Morozovella at the Early Eocene Climatic Optimum (EECO; ~53-49 Ma) from the Pacific Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8704, https://doi.org/10.5194/egusphere-egu22-8704, 2022.

Dinosaurs and pterosaurs, critical components of late Mesozoic terrestrial biomes, have thus far never been reported in-situ from deposits immediately below the Cretaceous-Paleogene (KPg) boundary. Strata from the KPg boundary preserve worldwide evidence of a massive cosmic impact that resulted in grave consequences for Earth’s biota, triggering a rapid global mass extinction that ultimately claimed ~75% of species. While trends in long-term biotic effects are well-documented, little is known about the fate of biota coeval with the impact because well-preserved fossil evidence is lacking for that brief time interval. Here we report the first-known occurrences of in-situ dinosaur and pterosaur remains coincident with the KPg boundary, providing a vantage point that is closer in temporal proximity to the Chicxulub impact than any prior known records for these clades. The fossils, preserved in a Chicxulub impact-triggered surge deposit and mass-death assemblage in the Hell Creek Formation, U.S.A., consist of a well-developed semi-articulated prenatal pterosaur in ovum and partially articulated remains of a subadult ornithischian dinosaur (Family Thescelosauridae). Examination via synchrotron rapid scanning X-ray fluorescence (SRS-XRF), scanning electron microscopy (SEM), and traditional light microscopy revealed extensive preservation of soft tissue consisting of distinct signatures of organic residues as well as three-dimensional structure. The pterosaur embryo, which comprises the first known from the Late Cretaceous and the only example thus far from North America, contributes information pivotal to understanding the prenatal development and early ontogeny of these animals from a time interval for which no such data exists. The ornithischian (c.f. Thescelosaurus sp.) dinosaur, which includes a remarkably complete articulated hind limb enclosed within three-dimensional lithified tubercular skin envelope, provides important data regarding the osseous and soft-tissue anatomy of the Thescelosauridae. In addition to contributing invaluable new anatomical and physiological insights, these specimens constitute the first conclusive evidence of the direct participation of pterosaurs and dinosaurs in the terminal-Cretaceous extinction event.

How to cite: DePalma, R., Unwin, D., Oleinik, A., Burnham, D., Gurche, L., Klingler, J., Larson, P., Beasley, T., Bergmann, U., Edwards, N., Wogelius, R., Egerton, V., and Manning, P.: Terminal-Cretaceous Dinosauria and Pterosauria from a Cretaceous-Paleogene mass-death assemblage, Hell Creek Formation, U.S.A., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8957, https://doi.org/10.5194/egusphere-egu22-8957, 2022.

Recognition of the Permian/Triassic boundary in Saudi Arabia by previous researchers using a variety of methods has resulted in placement of the boundary at different stratigraphic levels. In this study, we discovered two lithological horizons containing fossil fish teeth (sharks and Actinopterygii) in different stratigraphic positions within the Khartam Member of the Khuff Formation. Thin-section petrography initially revealed the fossil fish teeth, while XRF, XRD, SEM, and QEMSCAN techniques were used to confirm the presence of biogenic apatite. Fish teeth collected from the two stratigraphic levels in the Khartam Member show distinct and different morphological features. The fossil assemblage recovered from the lower unit belongs to the classes Euselachii and Actinopterygii, while fish teeth from the upper unit belong to the shark genus Lissodus.  The stratigraphic position of the recovered Lissodus microfossils supports the previous placement of the Permo/Triassic boundary by Vaslet et al. (2005) and Crasquin-Soleau et al. (2006), who placed the boundary exactly at the stratigraphic boundary between the Lower and Upper Khartam Members. The results of this study do not corroborate the boundary placement by Eltom et al. (2016), who placed the Permo/Triassic boundary in a higher stratigraphic position within the Upper Khartam Member. Lissodus species are common from the Early Triassic to Late Cretaceous, suggesting new paleontological evidence for the placement of the Permo/Triassic boundary in Saudi Arabia.

How to cite: Babiker, J., Humphrey, J., Al-Ramadan, K., Payne, J., Kaminski, M., and Alqubalee, A.: Fish fossil remains from the Khartam Member, Khuff Formation in Central Saudi Arabia: Implications for placement of the Permo/Triassic Boundary, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9154, https://doi.org/10.5194/egusphere-egu22-9154, 2022.

There is consensus since the last IPCC report that the rate of climate warming related to high CO₂ pressure is generating a strength of the greenhouse state thus the comprehension of marine ecosystems resilience is a pressing humankind issue. The long-term response of the biota under elevated temperatures and CO₂ concentrations remains uncertain because modern studies are limited in time.  The geological archive offers the key opportunity to evaluate the resilience of planktic foraminifera on a long-term perspective. Planktic foraminifera are important marine calcifiers, regulating biogeochemical cycles, abundant in marine sediments since the Cretaceous, and largely adopted for paleoecological and paleoceanographic reconstructions as they are extremely sensitive to environmental parameters. The Early Eocene Climatic Optimum (EECO, ~ 53-49 Ma) is a crucial interval of Earth’ history to investigate as recording the maximum temperature and pCO₂ of the entire Cenozoic (Zachos et al., 2001, Sciences; Anagnostou et al. 2016, Nature; Inglis et al., 2020 Clim. Past). Our recent research shows that the EECO markedly impacted the planktic foraminifera communities by inducing an important turnover as recorded from the latitudinally spaced Atlantic sites 1051, 125 and 1263. Specifically, the mixed-layer symbiont-bearing genus Morozovella, that dominated tropical-subtropical early Paleogene assemblages, abruptly and permanently declined its abundance (up to one-third), size, and diversity at the EECO beginning, close to the carbon isotope excursion known as the J event (~ 53 Ma) whereas the abundance and diversity of Acarinina markedly increased (Luciani et al., 2016 Clim. Past; Luciani et al. 2017 Paleoceanogr.; Luciani et al. 2017 GloPlaCha; D’Onofrio et al., 2020 Geosciences). In addition, the Morozovella morphospecies (or criptic species) display different coiling direction (the ability to add chambers in clock- or counter-clock wise) that was dominantly dextral below the EECO and becoming dominantly sinistral at the EECO, within ~ 200 kyr after the carbon isotope excursion known as K/X event (~ 52.8 Ma) (Luciani et al. 2021 GloPlaCha). Therefore, the sinistral morphotypes represent the main survivors at the expense of dextral forms, that were less resilient to the EECO stressors. Our stable carbon and oxygen data on dextral and sinistral morphotypes performed below and above the major coiling shift, show that sinistral morphotypes typically have lower δ¹³C values. The lower δ¹³C signatures of the sinistral specimens, suggests that they were less dependent on their photosymbiotic partnerships, possibly migrating slightly deeper in the mixed-layer. This strategy could have made them able to better tolerate the pressure occurring during the EECO. Our record strongly advises on a causal relationship to chemical-physical modifications in the surface waters, possibly to the temperature increase. Preliminary Mg/Ca derived paleotemperatures through (LA)-ICP-MS from Site 1263 reveal that Morozovella crater and M. subbotinae record a greater warming at the EECO than Acarinina coalingensis and A. soldadoensis. The higher rise in temperature recorded by morozovellids may explain the reduced symbiotic relationship, even though further geochemical analyses are in progress to explore the influence of other potential stressors such as pH decrease.

How to cite: Luciani, V., D'Onofrio, R., Gandolfi, A., Dickens, G. R., Wade, B. S., Tiepolo, M., and Cannaò, E.: Planktic foraminiferal resilience to the Early Eocene Climatic Optimum (EECO, ~53-49 Ma) at the Atlantic Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9230, https://doi.org/10.5194/egusphere-egu22-9230, 2022.

Producing geologically reasonable subsurface reservoir models which also honor wellbore and seismic data is still a major challenge for geoscientists at a range of energy and mining industries. Models based purely on geostatistics usually don’t satisfy the expected representation of geological concepts, while process-based models can hardly be constrained by subsurface data. Our research project GEOPARD aims to add a new tool in this context by providing a process-mimicking approach. In this method, sedimentary units are placed in 3D space constrained by subsurface data while simultaneously following a set of geological rules. This contribution aims to share and discuss the methodological workflow under development, from the geological domain, to test this method on the shoreface accumulation system. The first major step of the workflow is to specify the geological unit(s) to be modelled, which must be of interest as a control upon reservoir heterogeneity and of an adequate scale for representation. Afterwards, geological rules can be defined. These can be classified as (i) element geometry, scale, and infill specifications, (ii) basic element-set rules, which define the expected relationship between a set of geological units, and (iii) advanced element-set rules, which define how these relationship between elements might change over a sedimentary sequence. Each set of rules is linked to appropriate references for justification and exemplified from virtual outcrops of the Blackhawk Formation at Central Utah, which is one of the most studied and best-preserved examples of this type of depositional system. Feedback from the modelling domain is itself incorporated into refining the geological rules, resulting in an iterative effort to improve the methodology. Testing the method in these type of accumulation systems, that can be said to follow relatively straight-forward rules, are key before advancing into systems which typically exhibit more complex sedimentary architecture. We expect that the development of this modelling method can be a powerful tool to produce more useful models for oilfield assessment and development, CO2 storage projects, hydrocarbon exploration, among many others.

How to cite: Argüello Scotti, A., Haug Eide, C., Aarnes, I., Skauvold, J., and Hauge, R.: Defining the basic rules that describe long-term shoreface dynamics: A process-mimicking approach for reservoir modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9355, https://doi.org/10.5194/egusphere-egu22-9355, 2022.

The Rif chain is located on the western edge of the Apennine-Maghrebian Chain. It is classically subdivided into three main superimposed tectonic domains: The Internal, Flysch Basin, and the External domains. The latter regroups three sub-domains: Intrarif, Mesorif, and Prerif. The present work is based on new geological mapping with lithostratigraphic logging and sampling for geochemical analysis from Lower-Middle Jurassic sedimentary successions belonging to the Prerif sub-domain. Four stratigraphic sections have been analyzed (Jbel Zerhoune, Dhar Nsour I and II, and Jbel Outita section). The Lower Jurassic successions are mainly characterized by alternating marls with limestones, bioclastic limestone, and calcareous sandstones, whereas the Middle Jurassic ones are mainly represented by calcareous sandstones and bioclastic limestones, both alternating with marly intervals.

The collected fifteen samples have been examined using Laser Ablation–Inductively Coupled Plasma–Mass Spectrometry (LA-ICP-MS) and X-Ray Fluorescent (XRF) for Elemental geochemical analysis to provide new insights about provenance, source rocks, paleoweathering, mechanical sorting/recycling, and geodynamic setting.

The elemental geochemistry (Major, Trace, and Rare Earth Elements) reveals that major oxides concentrations (SiO₂, Al₂O₃, MgO, and K₂O) are relatively close to the Post-Archean Australian Shales (PAAS) except for MnO and Na₂O, which show a depletion trend, while Cao and Sr display an enrichment, also Zr, Hf and REEs show low concentrations and indicate weak recycling processes. In order to characterize the provenance, we used a combination of the Cr/V vs. Y/Ni plot, the Cr/Th vs. Th/Sc plot, and the elemental ratios of provenance (La/Sc, Th/Sc, Th/Co, Th/Cr, and Cr/Th). Various discriminant diagrams were used to reveal the paleoweathering intensity, sorting, and maturity of sediment during their source to sink fate. The Chemical Index of Alteration (CIA) shows values varying from 49.09 % to 77.01 %. Th/Sc versus Zr/Sc ratios and the Al2O3-Zr-TiO2 plots have been used to assess the sorting related to the fractionation of sediment during their transport. This is also corroborated by the relatively high values of the compositional variability index (ICV) of Jbel Zerhoune and Dhar Nsour (I and II) and Jbel Outita (ICV<1 and ICV>1, respectively). We also used multidimensional discriminant function diagrams to characterize the geodynamics setting on the analyzed samples.

The main expected results and related interpretations reveal that the provenance of the lower-Middle Jurassic sediments mainly indicates a supply from felsic source rock areas as attested by prevalent enrichment in Sr and probably from a minor mafic supply. The chemical index of alteration indicates a low to moderate degree of source area weathering. The Th/Sc versus Zr/Sc ratios and the Al2O3-Zr-TiO2 recycling plots, and the depletion of Hf and Zr reflect poor mechanical sorting and recycling processes which are confirmed by the high ICV values indicating that almost all samples are immature first-cycle sediments with unweathered detrital minerals. The analyzed sediments have been deposited within a passive margin controlled by a rifting/drifting geodynamic evolution of the northern African margin during the Early-Middle Jurassic.

How to cite: Kairouani, H., Abbassi, A., Zaghloul, M. N., and El Mourabet, M.: Stratigraphy, Provenance, and Geodynamic setting of the Lower-Middle Jurassic succession in the Prerif foreland basin (Rif Chain, Morocco), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9404, https://doi.org/10.5194/egusphere-egu22-9404, 2022.

The scientific community is increasingly focused on the study of past climate analogues to better comprehend future implications of global warming on marine ecosystem and biogeochemical cycles. Through an integrated calcareous plankton and geochemical approach, we examined the Terche and Madeago (NE Italy) Tethyan sections, that encompass the hyperthermal Eocene Thermal Maximum 2 (ETM2, ~54 Ma). The ETM2 shares similarities with the current climate context such as global warming, carbon cycle perturbations, high pCO₂ and ocean acidification, thus representing a key event in which investigate links between climate and biotic changes.

Our planktic foraminiferal and calcareous nannofossil records show significant, though transient, changes in both the sections across this event. Our record of multiple dissolution proxies from both the sections ensures that dissolution did not affect calcareous plankton assemblages. Planktic foraminifera exhibit a marked increase in warm index surface-dweller Acarinina paralleled by a decline in abundance of the deeper-dweller chiloguembelinids and subbotinids. This implies that the ETM2 warming impacted the entire upper water column. Both chiloguembelinids and subbotinids, recognized as eutrophic and colder taxa, may have suffered, beside warming, of reduced food supply at the thermocline due to the increased surface-water remineralization of organic matter as induced by the significant warmth. Increase of Cretaceous calcareous nannofossils testifies reworking related to enhanced hydrological cycle that also generated input of nutrients from land. Surface water eutrophication during the ETM2 was inferred by rise in calcareous nannofossil eutrophic indices. This group proved to be more sensitive to the nutrient supply rather than warming. The ETM2 consequence on marine calcifiers test-size were not previously explored. We provide here new evidence of a striking test size reduction in planktic foraminiferal assemblages (up to 40%) during the ETM2 that involved both the surface and deeper-dweller taxa that is particularly marked at Madeago. Although loss of symbionts (bleaching) is known to affect test calcification, it cannot represent a likely cause in the studied case as both symbiotic and asymbiotic planktic foraminifera were affected at the same scale across the ETM2. The increased abundance of small placoliths Toweius and Ericsonia indicates that size reduction also impacted nannofossils, though to a lesser degree.

We collected Hg (ppb), TOC (wt%) and Hg/TOC (ppb/wt%) data throughout our sections to test whether the reduction in size was related to environmental stressors not commonly linked to the ETM2. An increase in Hg was indeed detected in both sections at the base of the ETM2 and not corresponding to the intervals of reworking. Coeval submarine igneous events in this area might have introduced biolimiting metals thus involving the calcareous plankton productivity and possibly affecting test sizes. We hypothesize that the striking plankton dwarfism here recorded across the ETM2 is the result of the combined effect of paleoenvironmental perturbations induced by this event and increase in biolimiting metals. Our study alerts on possible consequences related to intense warming as associated to igneous events. Further data from different locations are needed to evaluate the geographic extension of impact on test-size variations in calcareous plankton assemblages.

How to cite: D'Onofrio, R., Luciani, V., Schmidt, D. N., Barrett, R., Fornaciari, E., Giusberti, L., Frija, G., and Adatte, T.: Test-size reduction of Tethyan calcareous plankton at the ETM2: combined effect of global warming and biolimiting metals?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9591, https://doi.org/10.5194/egusphere-egu22-9591, 2022.

The Cretaceous-Paleogene (KPg) boundary is demarked by two critical and intimately linked events: a global-scale impact caused by a massive extraterrestrial body, and a resultant catastrophic planet-wide mass-extinction, with pivotal long-term consequences for life on Earth. The site of impact has been identified as the ~180 km wide Chicxulub crater complex [Yucatan peninsula, Mexico] based on strong geochemical, sedimentological, and temporal evidence. However, the impactor, which was obliterated on contact during the cratering process, has eluded identification. Previous studies struggled to identify the projectile based on scant geochemical and isotopic traces admixed with the ejecta and melt-rock, plus a single heavily altered microscopic fragment possibly from the impactor. While those efforts helped to rule out some potential sources and narrowed down the best potential candidates to a CM, CR, or CO carbonaceous chondrite, the data was insufficient to provide an incontrovertible diagnosis, and the identity of the Chicxulub projectile remained a critical missing detail. Here we describe new, exceptionally-preserved fragments of cosmic origin that were directly associated with Chicxulub impact ejecta from a temporally constrained KPg boundary site in North Dakota (U.S.A.). The fragments occur as inclusions within unaltered glassy ejecta spherules, which likely protected them against chemical and physical degradation, leading to their marked preservation. The spherules themselves were also uniquely preserved in amber, which inhibited their usual breakdown to smectitic clay. Geochemical examination of the inclusions were undertaken using electron microprobe, laser-ablation inductively-coupled-plasma-mass-spectroscopy, and synchrotron X-ray techniques. Results provide multiple lines of evidence that support a cosmic origin and chemistry indicative of a CM subtype carbonaceous chondrite, offering new support of prior hypotheses. The data is also in agreement with projectile residues from the Chicxulub impact fallout. In addition to its utility in reconstructing the dynamics of the Chicxulub event, this data helps provide extra dimension to our understanding of major impact processes and their effects on Earth.

How to cite: Manning, P., DePalma, R., Maurrasse, F., Burnham, D., Gurche, L., Klingler, J., Larson, P., Beasley, T., Oleinik, A., Geraki, T., Ignatyev, K., Egerton, V., and Wogelius, R.: The identity of the Chicxulub impactor: KPg ejecta-encapsulated meteoric fragments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9638, https://doi.org/10.5194/egusphere-egu22-9638, 2022.

Of the many biocrises that occurred during the Devonian period, the most studied ones are the end-Devonian Kelwasser event (Frasnian-Famennian Boundary) and the Hangenberg event (Devonian-Carboniferous Boundary). However, the Middle Devonian crisis are receiving an increasing attention. The crisis occurring immediately before the Eifelian-Givetian Boundary (ensensis conodont zone) is known as the Kačák event. It has essentially been identified by time-specific lithofacies in deep-environment settings where pelagic faunas (conodonts, ammonoids, dacryoconaridids) suffered extinctions. On the Belgian neritic carbonate shelf system the Kačák event has been identified, in the lower part of the Hanonet Formation where a complex faunal turnover took place but with few changes in the depositional settings as known in deeper environments. The event is also recognised on a palaeobiological base as the pre-crisis Old World Realm fauna-dominated assemblages are suddenly facing the invasion of East American Realm fauna such as siphonophrentid and heliophillid rugose corals. After the crisis, these corals are very uncommon and the Old World Realm assemblages become largely dominant again. This palaeobiological criterion is proposed to help, especially when the typical pelagic guides are missing, in the identification of the Kačák event.

How to cite: Jamart, V. and Denayer, J.: The late Eifelian (Middle Devonian) Kačák event and its effects on rugose coral palaeobiodiversity (Ardennes, Belgium), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9898, https://doi.org/10.5194/egusphere-egu22-9898, 2022.

Around 37% of the Mediterranean territory is covered with polyploid angiosperms, of which the genus Linum occupies a considerable region. Linum is the most diversified genus of the plant family Linaceae that comprises a “family pair” of Hugonioideae distributed in tropical regions and Linoideae mainly distributed in temperate to subtropical regions. We provide the oldest fossils of Linaceae, comparable to the living genera Linum and Reinwardtia, from the Late Cretaceous Infratrappean Deccan volcano sedimentary sequences of Maharashtra, India. The phylogenetic analysis conducted by combining the morphological characters of the pollen fossils recovered and the pollen morphological as well as molecular characters of extant species of Linaceae reveals that the family originated in the wet and warm tropical zones of South America in the Late Cretaceous. Thereafter, the family dispersed to Africa giving rise to the lineage of Linoideae that further diverged into two main clades, one of which evolved either on seasonally wet areas of Kohistan-Ladakh Island arc (KLIA) or on the Indian Plate in Maastrichtian-Paleocene. The second clade encompassing the genus Linum originated on seasonally wet areas of Africa and later dispersed to Mediterranean region via Boreotropical route in Paleocene where it adapted to seasonally dry climatic conditions that prevailed during late Eocene. The family further expanded its geographical range and spread to Eurasia, and to North America via Bering land bridge. We also propose the dual colonization of Linaceae in India. The seasonally wet lineages dispersed from Africa to India via KLIA in the Maastrichtian-Paleocene. Whereas, the seasonally dry lineages of Linum migrated from Eurasia into India probably during the Oligocene when the climatic conditions were dry and warm arid. The decline in global temperature towards the end of Eocene escalated the diversification rates within Linaceae that is currently found in the regions of meso- and microthermal climate. The next major shift in diversification rate was detected on the crown node of North American Linaceae during the Middle Miocene Climate Transition.

How to cite: Bansal, M., Nagaraju, S., Murthy, S., Farooqui, A., and Prasad, V.: Palaeobiogeographic evolution and climatic adaptation within the plant family Linaceae, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12752, https://doi.org/10.5194/egusphere-egu22-12752, 2022.

DeepStor-1 is the exploration well to the Helmholtz research infrastructure "DeepStor". DeepStor focuses on the investigation of high-temperature heat storage at the rim of the fromer oil-field „Leopoldshafen“. It is located about 10 km north of the city of Karlsruhe (Germany). The DeepStor-1 well is planned to reach the Pechelbronn group at 1‘460 m, i.e. it includes nearly the entire Oligocene sediments at the site. Seismic investigation reveal a structurally undisturbed section that below 200 m depth covers the Landau, Bruchsal, Niederrödern and Froidefontaine Formations. Cores will be taken from the entire section below 820 m. In addition to coring, the logging program is planned to include besides technical logging, a caliper-, self-potential-, temperature-, dual latero-, natural gamma spectrometry-, neutron-gamma porosity-, sonic-, elemental capture spectroscopy-, as well as image-logs in the sections 215-820 m as well as 820-1460 m. Drilling of DeepStor-1 is planned between 2022 and 2023.

How to cite: Eva, S., Bauer, F., Steiner, U., Frieg, B., and Kohl, T.: DeepStor-1 exploration well at KIT Campus North (Upper Rhine Graben, Germany), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-640, https://doi.org/10.5194/egusphere-egu22-640, 2022.

The Izu-Bonin Mariana (IBM) convergent margin is located in the NW Pacific Ocean (12° N to 35° N) and represents, to the best of our knowledge, the only setting where recent episodes of serpentinite mud volcanism took place. The IBM arc-system started to form around 50-52 Ma when the Pacific Plate began to subside below the Philippine Plate and the eastern Eurasian Margin. On the Mariana forearc system, which constitutes the southward region of the IBM, a high number of large serpentinite mud volcanoes formed between the trench and the Mariana volcanic arc. Their origin is linked to episodic extrusion of serpentinite mud and fluids along with materials from the upper mantle, the Philippine plate, and the subducting Pacific plate to the sea floor, through a system of forearc faults. Among them, Fantangisña seamount was drilled during IODP Expedition 366. Cored material comprises serpentinite mud and ultramafic clasts that are underlain by nannofossil-rich forearc deposits and topped by pelagic sediments.

Integrated calcareous nannofossil and planktonic foraminifera biostratigraphy was performed on Sites U1497 and U1498, which are at the top of the serpentinite seamount and on its most stable southern flank, respectively. A total of nine bioevents were recorded in this study, permitting the establishment of a valid age-depth model for Site U1498A which allows for the definition of the latest phase of activity of Fantangisña serpentinite mud volcano. In particular, the emplacement of the mud production was detected between 6.10 (Late Miocene, Messinian) to 4.20 (Early Pliocene, Zanclean). This time interval is defined by nannofossil bioevents LO Reticulofenestra rotaria and FO of Discoaster asymmetricus. Furthermore, our analyses reveal that the latest stage of the serpentinite mud activity occurred 4 Ma later than the age proposed by a previous study (10.77 Ma) and is coeval with the initiation of the rifting in the Mariana Trough recorded at 7-6 Ma.

The age depth model also shows a rapid shift in sedimentation rates (11.80 to 94.71 m/Myr) during the Middle Pleistocene, which corresponds to a change in deposition of distinct serpentinite mud units, likely associated with the regional tectonic activity (different stages of seamount accretion and subduction and/or changes in the forearc extension related to the slab rollback).

How to cite: Del Gaudio, A. V., Piller, W. E., Auer, G., and Kurz, W.: Dating the serpentinite mud production of Fantangisña seamount using calcareous nannofossils and planktonic foraminifera biostratigraphy (IODP Expedition 366)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1019, https://doi.org/10.5194/egusphere-egu22-1019, 2022.

The Arctic is both a contributor to climate change and a region that is most affected by global warming. Despite this global importance, the Arctic Ocean is the last major region on Earth where the long-term climate history remains poorly known. Major advances in understanding were achieved in 2004 with the successful completion of IODP Expedition 302: Arctic Coring Expedition – ACEX – implemented by ECORD, marking the start of a new era in Arctic climate exploration. Although the ACEX results were unprecedented, key questions related to the Cenozoic Arctic climate history remain unanswered, largely due to a major mid-Cenozoic hiatus (or condensed interval) and partly to the poor recovery of the ACEX record. Building on ACEX and its cutting-edge science, IODP Expedition 377: Arctic Ocean Paleoceanography (ArcOP) has been scheduled for mid-August to mid-October 2022. The overall goal of ArcOP is the recovery of a complete stratigraphic sedimentary record on the southern Lomonosov Ridge to meet the highest priority paleoceanographic objective: the continuous long-term Cenozoic Arctic Ocean climate history with its transition from the early Cenozoic Greenhouse world to the late Cenozoic Icehouse world. Furthermore, sedimentation rates two to four times higher than those of ACEX will permit higher-resolution studies of Arctic climate change in the Neogene and Pleistocene. Key objectives are related to the reconstruction of the history of circum-Arctic ice-sheets, sea-ice cover, Siberian river discharge, and deep-water circulation and ventilation and its significance within the global climate system. Obtaining a geologic record of a 50-60 million year time span will provide opportunities to examine trends, pat­terns, rates, causes, and consequences of climate change that are important and relevant to our future. This goal can be achieved through (i) careful site selection, (ii) the use of appropriate drilling technology and ice management, and (iii) applying multi-proxy approaches to paleoceanographic, paleoclimatic, and age-model reconstructions.

In August 2022, a fleet of three ships, the drilling vessel “Dina Polaris” and the powerful icebreakers “Oden” and “Viktor Chernomyrdin”, will set sail for a location on Lomonosov Ridge in international waters far from shore (81°N, 140°E; 800-900 m of water depth). There, the expedition will complete one primary deep drill site (LR-11B) to 900 meters below seafloor (mbsf) which is twice that of the ACEX drill depth – certainly a challenging approach. Based on detailed site survey data, about 230 m of Plio‐Pleistocene, 460 m of Miocene, and >200 m of Oligocene‐Eocene sedimentary sequences might be recovered at this site. In addition, a short drill site (LR-10B) to 50 mbsf will be supplemented to recover an undisturbed uppermost (Quaternary) sedimentary section to ensure complete recovery for construction of a composite section spanning the full age range through the Cenozoic.

In this talk, background information, scientific objectives and an update of the status of planning and implementation of the ArcOP Expedition will be presented. For further details we refer to the ArcOP Scientific Prospectus (https://doi.org/10.14379/iodp.sp.377.2021).

How to cite: Stein, R., St.John, K., and Everest, J.: The Cenozoic Arctic Climate and Sea Ice History - Scientific objectives, challenges and implementation update of IODP Expedition 377 (ArcOP), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1277, https://doi.org/10.5194/egusphere-egu22-1277, 2022.

International Ocean Discovery Program (IODP) conducted a series of expeditions between 2014 and 2016 that were designed to address the development of monsoon climate systems in Asia and Australia. Significant progress was made in recovering Neogene sections spanning the region from the Arabian Sea to the Japan Sea and south to western Australia. High recovery by advanced piston core (APC) technology has provided a host of semi-continuous sections that have been used to examine monsoonal evolution. Use of half APC was successful in sampling sand-rich sediment in Indian Ocean submarine fans. The records show that humidity and seasonality developed diachronously across the region, although most regions show drying since the middle Miocene and especially since ~4 Ma, likely linked to global cooling. The transition from C3 to C4 vegetation often accompanied the drying, but may be more linked to global cooling. Western Australia, and possibly southern China diverge from the general trend in becoming wetter during the late Miocene, with the Australian monsoon being more affected by the Indonesian Throughflow, while the Asian Monsoon is tied more to the rising Himalaya in South Asia and to the Tibetan Plateau in East Asia. The monsoon shows sensitivity to orbital forcing, with many regions having a weaker summer monsoon during times of Northern Hemispheric Glaciation. Stronger monsoons are associated with faster continental erosion, but not weathering intensity, which either shows no trend or decreasing strength since the middle Miocene in Asia. Marine productivity proxies and terrestrial environmental proxies are often seen to diverge. Future work on the almost unknown Paleogene is highlighted, as well as the potential of carbonate platforms as archives of paleoceanographic conditions.

How to cite: Clift, P., Betzler, C., Clemens, S., Christensen, B., Eberli, G., France-Lanord, C., Gallagher, S., Holbourn, A., Kuhnt, W., Murray, R., Rosenthal, Y., Tada, R., and Wan, S.: A Campaign of Scientific Drilling for Monsoon Exploration in the Asian Marginal Seas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1509, https://doi.org/10.5194/egusphere-egu22-1509, 2022.

The Nankai Trough is a locus of slow slip, low frequency earthquakes and M_w>8 classical earthquakes. It is assumed that high pore pressure contributes substantially to earthquake dynamics. Hence, a full understanding of the hydraulic regime of the Nankai accretionary prism is needed to understand this diversity of behaviors. We contribute to this understanding by innovatively integrating the drilling and logging data of the NanTroSEIZE project. We focus on the toe of the accretionary prism by studying data from Hole C0024A drilled and intersected the décollement at 813 mbsf about 3km away from the trench.

Down Hole Annular Pressure was monitored during drilling. We perform a careful quantitative reanalysis of its variation and show localized fluid exchange between the formation and the borehole (excess of 0.05m³/s), especially in the damage zones at the footwall of the décollement.

Pore pressure was estimated using Eaton’s method on both drilling and sonic velocity data. The formation fluids are getting significantly over-pressurized only a few hundred meters from the toe of the accretionary prism near the décollement with excess pore-pressure (P*≈0.04–4.79MPa) and lithostatic load (λ≈88-0.96 & λ*≈0.1-0.62 ) contributing to maximum 62% of the overburden stress.

The hydraulic profile suggests that the plate boundary acts as a barrier inhibiting upward fluid convection, as well as a lateral channel along the damage zone, favouring high pore pressure at the footwall. Such high pressure at the toe of the subsection zone makes high pressure probable further down in the locus of tremors and slow slip events.

How to cite: Pwavodi, J. and Doan, M.-L.: Direct evidence of high pore pressure at the toe of the Nankai accretionary prism, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1679, https://doi.org/10.5194/egusphere-egu22-1679, 2022.

International Ocean Discovery Program (IODP) Expedition 386, Japan Trench Paleoseismology (offshore period: 13 April to 1 June 2021; Onshore Science Party: 14 February to 14 March 2022) was designed to test the concept of submarine paleoseismology in the Japan Trench, the area where the last, and globally only one out of four instrumentally-recorded, giant (i.e. magnitude 9 class) earthquake occurred back in 2011. “Submarine paleoseismology” is a promising approach to investigate deposits from the deep sea, where earthquakes leave traces preserved in the stratigraphic succession, to reconstruct the long-term history of earthquakes and to deliver observational data that help to reduce uncertainties in seismic hazard assessment for long return periods. This expedition marks the first time, giant piston coring (GPC) was used in IODP, and also the first time, partner IODP implementing organizations cooperated in jointly implementing a mission-specific platform expedition.

We successfully collected 29 GPCs at 15 sites (1 to 3 holes each; total core recovery 831 meters), recovering 20 to 40-meter-long, continuous, upper Pleistocene to Holocene stratigraphic successions of 11 individual trench-fill basins along an axis-parallel transect from 36°N – 40.4°N, at water depth between 7445-8023 m below sea level. These offshore expedition achievements reveal the first high-temporal and high spatial resolution investigation and sampling of a hadal oceanic trench, that form the deepest and least explored environments on our planet.

The cores are currently being examined by multimethod applications to characterize and date hadal trench sediments and extreme event deposits, for which the detailed sedimentological, physical and (bio-)geochemical features, stratigraphic expressions and spatiotemporal distribution will be analyzed for proxy evidence of giant earthquakes and (bio-)geochemical cycling in deep sea sediments. Initial preliminary results presented in this EGU presentation reveal event-stratigraphic successions comprising several 10s of potentially giant-earthquake related event beds, revealing a fascinating record that will unravel the earthquake history of the different along-strike segments that is 10–100 times longer than currently available information. Post-Expedition research projects further analyzing these initial IODP data sets will (i) enable statistically robust assessment of the recurrence patterns of giant earthquakes, there while advancing our understanding of earthquake-induced geohazards along subduction zones and (ii) provide new constraints on sediment and carbon flux of event-triggered sediment mobilization to a deep-sea trench and its influence on the hadal environment.

How to cite: Strasser, M., Ikehara, K., Everest, J., and Maeda, L. and the IODP Expedition 386 Science Party: IODP Expedition 386 “Japan Trench Paleoseismology”: Mission Specific Platform Giant Piston Coring to track past megathrust earthquakes and their consequences in a deep-sea subduction trench., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1729, https://doi.org/10.5194/egusphere-egu22-1729, 2022.

The NE Atlantic conjugate volcanic rifted margins are characterized by extensive breakup-related magmatism recorded by basalt flows, volcanogenic sediments, magmatic underplates, and intrusive complexes in sedimentary basins and the crust. Onset of this voluminous magmatism is concomitant with the global hot-house climate in the Paleogene, and the injection of magma into organic-rich sedimentary basins is a proposed mechanism for triggering short-term global warming during the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma).

The aims of IODP Exp. 396 (August-September 2021) were to drill three transects on the mid-Norwegian continental margin to sample 1) hydrothermal vent complexes formed by eruption of hot fluids and sediments above sill intrusions (Modgunn Transect), 2) Paleogene sediments, with particular focus on the Paleocene-Eocene transition (Mimir Transect), and 3) basalt and sub-basalt sequences across the volcanic rifted margin and the initial oceanic crust (Basement Transect). A total of 21 boreholes were drilled, successfully coring all nine primary and one alternate sites. A comprehensive suite of wireline logs was collected in eight boreholes. Most of the sites were located on industry-standard 3D seismic reflection data, whereas additional high-resolution 2D and 3D P-Cable site survey data were acquired across six sites which were highly useful during the Mimir and Modgunn transect drilling. In total, more than 2000 m of core were recovered during 48 days of operations, including more than 350 m of basalt, 15 m of granite, and 900 m of late Paleocene to early Eocene sediments. Drilling was done using a combination of RCB, XCB, and APC drill bits, commonly with half-advances (c. 5 m) to optimize core recovery. Particularly high recovery (almost 100%) was obtained by half-length APC coring of Eocene sediments in two holes on the outer Vøring Margin, whereas basaltic basement recovery was above 60% in seven holes.

Expedition 396 probed the key elements of a typical volcanic rifted margin and the associated sedimentary archive. Of particular importance is the Modgunn Transect, where we drilled five holes through the upper part of a hydrothermal vent complex with a very expanded Paleocene-Eocene Thermal Maximum (PETM) interval dominated by biogenic ooze and volcanic ash deposits. The expedition also recovered an unprecedented suite of basalt cores across a volcanic rifted margin, including both subaerial and deep marine sheet flows with inter-lava sediments and spectacular shallow marine pillow basalts and hyaloclastites, as well as high-resolution interstitial water samples to assess sediment diagenesis and fluid migration in the region. Lastly, we recovered the first cores of sub-basalt granitic igneous rocks and upper Paleocene sediments along the mid-Norwegian continental margin. Collectively, this unique sample archive offers unprecedented insight on tectonomagmatic processes in the NE Atlantic, and links to rapid climate evolution across the Cenozoic.

How to cite: Planke, S., Berndt, C., Huismans, R., Buenz, S., Alvarez Zarikian, C. A., and Scientists, E.: Operations and Initial Results from IODP Expedition 396: Mid-Norwegian Continental Margin Magmatism and Paleoclimate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1917, https://doi.org/10.5194/egusphere-egu22-1917, 2022.

Sulfate reduction is the quantitatively most important process to degrade organic matter in anoxic marine sediment and has been studied intensively in a variety of settings. Guaymas Basin, a young marginal ocean basin, offers the unique opportunity to study sulfate reduction in an environment characterized by organic-rich sediment, high sedimentation rates, and high geothermal gradients (100-958°C km^-1). We measured sulfate reduction rates (SRR) in samples of the International Ocean Discovery Program (IODP) Expedition 385 using incubation experiments with radiolabeled ³⁵SO₄^2- carried out at in-situ pressure and temperature. Site U1548C, outside of a circular hydrothermal mound above a hot sill intrusion (Ringvent), has the highest geothermal gradient (958°C km^-1) of all eight sampling sites. In near-surface sediment from this site, we measured the highest SRR (387 nmol cm^-3 d^-1) of all samples from this expedition. At Site U1548C SRR were generally over an order of magnitude higher than at similar depths at other sites. Site U1546D also had a sill intrusion, but it had already reached thermal equilibrium and SRR were in the same range as nearby Site U1545C, which is minimally affected by sills. The wide temperature range found in the stratigraphic section at each drill site leads to major shifts in microbial community composition with very different temperature optima. At the transition between the mesophilic and thermophilic range around 40 to 60°C, sulfate-reducing activity appears to be decreased, particularly in more oligotrophic settings but shows a slight recovery at higher temperatures.

How to cite: Nagakura, T., Schubert, F., and Kallmeyer, J. and the IODP Exp. 385 Scientists: Biological sulfate reduction in deep subseafloor sediment of Guaymas Basin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2525, https://doi.org/10.5194/egusphere-egu22-2525, 2022.

A fourth of the global seabed sediment volume is buried at depths where temperatures exceed 80 °C, a previously proposed thermal barrier for life in the subsurface. Here, we demonstrate, utilizing an extensive suite of radiotracer experiments, the prevalence of active methanogenic and sulfate-reducing populations in deeply buried marine sediment from the Nankai Trough subduction zone, heated to extreme temperature (up to ~120 °C). Sediment cores were recovered during International Ocean Discovery Program (IODP) Expedition 370 to Nankai Trough, off the cost of Moroto, Japan. The steep geothermal gradient of ~100 °C km^-1 allowed for the exploration of most of the known temperature range for life over just 1 km of drill core. Despite the high temperatures, microbial cells were detected almost throughout the entire sediment column, albeit at extremely low concentration of <500 cells per cm³ in sediment above ~50 °C. In millions of years old sediment a small microbial community subsisted with high potential cell-specific rates of energy metabolism, which approach the rates of active surface sediments and laboratory cultures. Even under the most conservative assumptions, potential biomass turnover times for the recovered sediment ranges from days to years and therefore many orders of magnitude faster than in colder deep sediment.

Our discovery is in stark contrast to the extremely low metabolic rates otherwise observed in the deep subseafloor. As cells appear to invest most of their energy to repair thermal cell damage in the hot sediment, they are forced to balance delicately between subsistence near the upper temperature limit for life and a rich supply of substrates and energy from thermally driven reactions of the sediment organic matter.

How to cite: Schubert, F., Beulig, F., Adhikari, R. R., Glombitza, C., Heuer, V., Hinrichs, K.-U., Homola, K., Inagaki, F., Jørgensen, B. B., Kallmeyer, J., Krause, S., Morono, Y., Sauvage, J., Spivack, A., and Treude, T.: Microbial survival through high metabolic rates in a deep and hot subseafloor environment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2909, https://doi.org/10.5194/egusphere-egu22-2909, 2022.

The sedimentary infill of glacially overdeepened valleys (i.e. eroded structures below the fluvial base level) are, together with glacial geomorphology, the best-preserved (yet underexplored) direct archives of extents and ages of past glaciations in and around mountain ranges. ICDP project DOVE (Drilling Overdeepened Alpine Valleys) Phase-1 investigates five drill cores from glacially overdeepened structures at several complementing locations along the northern front of the Alps and their foreland. Two of these drill sites, both in the former reaches of the Rhine Glacier, have been successfully drilled in 2021 with excellent core recovery of 95 %: i) The borehole in Basadingen in Northern Switzerland reached a depth of 253 m, and ii) The Tannwald site in Southern Germany consists of one cored borehole to 165 m and two nearby flush boreholes; all three sites will allow a series of crosshole geophysical experiments. Three previously drilled legacy cores from the Eastern Alps are included in the DOVE Phase-1: iii) a core from Schäftlarn, located in the Isar-Loisach glacier catchment, was drilled in 2017 down to a depth of 199 m; iv) the Neusillersdorf drill site, located in the southern German Salzach Foreland glacier area, recovered a sequence down to 136 m (incl. 116 m of Quaternary strata); and v) the drill site Bad Aussee in Austria is located in the area of the Traun Glacier at an inneralpine location. It recovered almost 900 m of Quaternary sediments.

All the sites will be investigated with regard to several aspects of environmental dynamics during the Quaternary, with focus on the glaciation, vegetation, and landscape history. For example, the geometry of overdeepened structures will be investigated using different geophysical approaches (e.g. seismic surveys) to better understand the process of overdeepening. Sedimentological analyses in combination with downhole logging, investigation of biological remains and state-of-the-art geochronological methods will allow to reconstruct the filling and erosion history of the troughs. We expect significant and novel data relating to the extent and timing of the past Alpine glaciations during the Middle-to-Late Quaternary glacial-interglacial cycles. Besides these basic scientific goals, this proposal also addresses a number of applied objectives such as groundwater resources, geothermal energy production, and seismic hazard assessment.

A successful DOVE Phase-1 will lay the ground for an upcoming Phase-2 that will complete the panalpine approach. This follow-up phase will investigate paleoglacier lobes from the western and southern Alpine margins through drilling sites in France, Italy and Slovenia.

How to cite: Anselmetti, F. and Buechi, M. and the ICDP-DOVE Team: Drilling Overdeepened Alpine Valleys (ICDP-DOVE): Age, extent and environmental impact of Alpine glaciations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3165, https://doi.org/10.5194/egusphere-egu22-3165, 2022.

The Re–Os isotopic system is a powerful tool for both geochronology and tracing various geochemical processes. Because the Os isotopic ratio (¹⁸⁷Os/¹⁸⁸Os) distinctly differs between modern seawater (∼1.06) and hydrothermal fluid (∼0.13), the Re–Os isotopic system is potentially a sensitive tracer of subseafloor fluid flow and the release or uptake of hydrogenous/magmatic Re and Os. The effect of alteration on the Re–Os budget in oceanic crust has been examined for mid-ocean ridge basalt (MORB) and lower oceanic crustal gabbro. In contrast, applications of the Re–Os system in intraoceanic arc settings are limited mainly to fresh igneous rocks; the role of hydrothermal alteration has not yet been examined.

Here, we provide a depth profile of Re–Os geochemistry at Site U1527, located on the NW caldera rim of the Brothers volcano hydrothermal field in the Kermadec arc, which was drilled during International Ocean Discovery Program (IODP) Expedition 376 in 2018. Volcaniclastic rocks from Hole U1527C that had experienced various degrees of high- and low-temperature hydrothermal alteration were analyzed for bulk chemical composition as well as Re–Os concentrations and isotopes. The concentration of Re varied from 0.172 to 18.7 ppb, and that of Os ranges from 9.7 to 147.1 ppt. Hydrothermal alteration usually resulted in the Re uptake by rocks, but a part of Re was released into the ocean by later oxidative weathering. Compared with Re, Os mobility resulting from hydrothermal alteration was limited. Before alteration, our samples likely had homogenous ¹⁸⁷Os/¹⁸⁸Os of between 0.13 and 0.14, whereas alteration added hydrogenous Os to some drill core sections in two different ways. Elevated ¹⁸⁷Os/¹⁸⁸Os with Ba enrichment and abundant pyrite occurrence suggests Os precipitation induced by subseafloor mixing of seawater and high-temperature hydrothermal fluid. The highest Re and Os concentrations at Hole U1527C, found in the same interval, were associated with high concentrations of Bi, Sb, and Tl. In contrast, elevated ¹⁸⁷Os/¹⁸⁸Os without Ba and Os enrichment can be explained by adsorption of seawater-derived radiogenic Os onto Fe hydroxide during seawater ingress into volcaniclastic rocks with a high matrix volume.

Intense Re enrichment at Hole U1527 relative to the high-temperature alteration zone in altered MORB may be related to abundant pyrite precipitation and high Re content in primary arc magmas. We propose that degassed Re from shallow intraoceanic arc magmas may be sequestered by subseafloor high-temperature alteration. Part of the stored Re might also be released into the ocean by later oxidative seawater circulation and seafloor weathering, raising a question about the role of alteration zones in the Re cycle in subduction zones. This study is one of the first attempts to apply the Re–Os system to altered rocks in arc settings, and future research should provide more information about the fate of Re in intraoceanic arcs and the detailed role of hydrothermal alteration in the Re cycle on the Earth.

How to cite: Ishida, M., Nozaki, T., Takaya, Y., Ohta, J., Chang, Q., Kimura, J.-I., Nakamura, K., and Kato, Y.: Re–Os geochemistry of altered dacitic rock at Site U1527, IODP Expedition 376: Implications for the Re cycle in intraoceanic arcs, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3372, https://doi.org/10.5194/egusphere-egu22-3372, 2022.

The innovative, new drilling technique of the Hipercorig platform (Harms et al., 2020, https://doi.org/10.5194/sd-28-29-2020) enables to recover undisturbed long cores of sediment archives, and hence allows us to study past environmental conditions and changes. Here we present initial results from the Hipercorig Hallstatt History (H³) lake drilling campaign 2021, which succeeded to recover two parallel cores (core A: 41m, core B: 51m) from 122 m water depth providing a high-resolution record, within the UNESCO World Heritage Cultural Landscape Hallstatt-Dachstein/Salzkammergut, Austria. The Hallstatt-Dachstein region has a history of over 7,000 years of human salt mining and is one of the oldest documented cultural landscapes worldwide.

We present physical- and litho-stratigraphy based on borehole logging (of hole B), non-destructive core logging data, visual core and lithofacies description, Core-Log-Seismic-Correlation and initial age modelling using ¹⁴C dating. The core logging covers (i) x-ray computed tomography, (ii) multi-sensor-core-logger data with Gamma-Ray attenuated bulk density, magnetic susceptibility and visible light photo spectroscopy. The upper ~15 m of the sediment profile can be unambiguously correlated with previous cores (Lauterbach et al., submitted) thus confirming that the sediments are truly representative for Lake Hallstatt. The entire stratigraphic succession comprises two major lithostratigraphic units: The Holocene unit (0-40 m below lake floor (mblf)) and the Late Pleistocene unit (> 40 m). The Holocene unit consists of variably laminated (sub-mm to 5 mm) dark gray clayey-silty carbonate mud interbedded with up to 5.5 m thick mass-movement deposits and thick turbidites. The Late Pleistocene sedimentary succession comprises very thin bedded (1-3 cm) medium gray silty clayey carbonate mud, with some laminated (<1 cm) intervals and multiple cm-thick light gray turbidites. Within the Late Holocene unit, there is a prominent yellowish gray clastic interval of ~4 m with faintly mm- to cm-scale laminated sediments. Another remarkable characteristic of the Holocene unit is the occurrence of at least four major mass-movement deposits containing pebbles (up to 3 cm in diameter) and six thick turbidite deposits >1 m with different sediment colors and compositions.

Detailed multi-proxy analyzes of the Lake Hallstatt cores will provide new insights into the early history of human settlement and salt mining in this Alpine region and their relation to environmental and climatic conditions and meteorological and geological extreme events.

How to cite: Ortler, M., Brauer, A., Fabbri, S. C., Kowarik, K., Kueck, J., and Strasser, M.: Hipercorig Hallstatt History (H3) reveals a high-resolution Late Pleistocene to Holocene sediment record at Lake Hallstatt (Salzkammergut, Austria), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3428, https://doi.org/10.5194/egusphere-egu22-3428, 2022.

Assessing the moisture history of Central Mexico reveals the responses of tropical areas to variation in past climate. Central Mexico has several long-lived lakes, which are potentially important paleoclimate archives. Lake Chalco in Central Mexico contains a ~300 m lacustrine sequence, which were deposited over a period of ~500,000 years. We conducted Spectral Gamma Ray (SGR) measurements across the lacustrine deposits of Lake Chalco to reconstruct the moisture availability over the past. The SGR data reflect the presence of naturally occurring radioactive elements including potassium (⁴⁰K) and the equilibrium decay series of uranium (U) and thorium (Th). Natural sources of gamma radiation in lacustrine deposits of Lake Chalco are from volcanic ash deposition and detrital input of eroded sediments containing radioactive elements. However, redox conditions in the lake water influence the mobility of soluble U through conversion to more stable reduced phases. To extract the primary non-volcanic signals, we detected and removed signals from embedded tephra layers in the lacustrine sediments of Lake Chalco. We developed a moisture proxy by calculating the probability of authigenic U distributed across the lake sediments. We expect that an increasing U content in proportion to the content of K and Th indicate redox conditions in lake bottom water as a result of rising lake level. To evaluate this moisture proxy, we examined differences in the percent of the diatom species that are indicative of a deeper lake from literature. Results suggest that Lake Chalco likely formed prior or within MIS13, and the lake level rose gradually over time until the interglacial period of MIS9. Moisture levels are higher during the interglacial than glacial periods and interglacial periods show higher moisture variability. While glacial periods have less moisture, two periods, MIS6 and MIS4, still have a higher likelihood of authigenic U and more moist conditions. In order to determine potential regulators of moisture, we compared models containing the drivers of Earth’s orbital cycles, carbon dioxide and sea surface temperature. Carbon dioxide, eccentricity, and precession are all key drivers of the moisture content of Lake Chalco over the past 500,000 years. High levels of atmospheric CO₂ have a positive effect on the moisture in Mexico while eccentricity and precession consistently have negative effects on lake moisture. Obliquity and δ¹⁸O have weaker effects on moisture in Mexico, probably due to the equatorial high-altitude region far away from poles, oceans and ice sheets.

How to cite: Abadi, M., Zeeden, C., Ulfers, A., and Wonik, T.: Reconstructing the moisture availability of Central Mexico over the past 500,000 years using borehole logging data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3534, https://doi.org/10.5194/egusphere-egu22-3534, 2022.

The Main Marmara Fault (MMF) in NW Turkey south of Istanbul is a segment of the North Anatolian Fault Zone (NAFZ) that constitutes a right-lateral continental transform fault.  Several well-documented strong (M7+) earthquakes indicate that the MMF poses a great risk to the Istanbul metropolitan region. A 150 km long stretch of the MMF has not ruptured since 1766 and the recurrence time of 250 yrs for M7+ events derived from historical records indicate that the fault is overdue. We introduce a new project addressing how the rheological configuration of the lithosphere in concert with active fluid dynamics within the crust and mantle influence the present-day deformation along the MMF in the Marmara Sea region. We test the following hypotheses: (1) the seismic gap is related to the mechanical segmentation along the MMF which originates from the rheological configuration of the crust and lithosphere; (2) variations in deformation mechanisms with depth in response to variations in temperature and (fluid) pressure exert a first-order control on the mode of seismic activity along the MMF, and, (3) stress and strain concentrations due to strength and structural variability along the MMF can be used as an indicator for potential nucleation areas of expected earthquakes. To assess what mechanisms control the deformation along the MMF, we use data from the ICDP GONAF observatory (International Continental Drilling Programme – Geophysical Observatory at the North Anatolian Fault) and a combined work flow of data integration and process modelling to derive a quantitative description of the physical state of the MMF and its surrounding crust and upper mantle. Seismic and strain observations from the ICDP-GONAF site are integrated with regional observations on active seismicity, on the present-day deformation field at the surface, on the deep structure (crust and upper mantle) and on the present-day stress and thermal fields. This will be complemented by numerical forward simulations of coupled thermo-hydraulic-mechanical processes based on the observation-derived 3D models to evaluate the key controlling factors for the present-day mechanical configuration of the MMF and to contribute to a physics-based seismic hazard assessment.

How to cite: Scheck-Wenderoth, M., Cacace, M., Heidbach, O., Bohnhoff, M., Nurlu, M., Fernandez Terrones, N., Bott, J., and Gholamrezaie, E.: Deformation mechanisms along the Main Marmara Fault around the ICDP-site GONAF, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3538, https://doi.org/10.5194/egusphere-egu22-3538, 2022.

The global reservoir of submarine gas hydrates is favored by the cold temperature of oceanic bottom water and the generally low geothermal gradients along passive continental margins. The continental margins of the land-locked Mediterranean basin are a remarkable exception for the lack of evidence of extensive presence of gas hydrates. Using public data of the physics and chemistry of the subsurface available from 44 Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) wells as lithologic logs, downhole temperature measurements, and pore water salinity values, and observed physical characteristics of bottom waters, we model the theoretical methane hydrate stability zone (MHSZ) below the seafloor and in the water column.

We find important positive pore water salinity anomalies in the subsurface indicating the pervasive presence of concentrated brines up to saturation concentration of halite and gypsum (> 300 ‰). The resulting sub-bottom MHSZ is thinner by up to 90-95% with respect to its thickness calculated assuming constant salinity with depth equal to bottom waters salinity. In the Eastern Mediterranean deep basins the thickness of the subsurface MHSZ is largest (up to ~ 350 m) and the anomaly induced by subsurface brines is highest (~ -300 m), while in the Alboran, Western Mediterranean, Tyrrhenian, Sicily Channel, Adriatic and Aegean basins the MHSZ, where present, thins to less than 100 m with mostly negligible anomaly induced by the presence of subsurface brines.

Modelling results suggest that subsurface brines can produce dramatic reductions of the thickness of the MHSZ only where the geothermal gradient is low (Eastern Mediterranean). We have modelled the same brine-induced limiting effect on the thickness of the MHSZ in synthetic cases of high and low heat flow to simulate Western and Eastern Mediterranean subsurface thermo-haline conditions. The salinity effect is attenuated by the thermal effect in the Western Mediterranean that produces the most relevant thinning of the MHSZ.

The distribution of the MHSZ resulting from the modelling coincides well with the distribution of the Late Miocene salt deposits which limit further the possibility of formation of gas hydrates acting as low permeability seal to the up-ward migration of hydrocarbon gases.

This modelling exercise provides a robust explanation for the lack of evidence of widespread gas hydrates on Mediterranean continental margins, with the exception of areas of local methane upward advection such as mud volcanoes, and it outlines a number of local hydrate-limiting factors that make this basin unfavorable to gas hydrate occurrence.

How to cite: Corradin, C., Camerlenghi, A., Giustiniani, M., Tinivella, U., and Bertoni, C.: Legacy DSDP and ODP data suggest a paradigm shift in methane hydrate stability in the Mediterranean Basin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3793, https://doi.org/10.5194/egusphere-egu22-3793, 2022.

The characteristics of half-precession (HP) cycles (~9,000 - 12,000 years) is still poorly understood, despite their appearance in numerous records. We analyse HP signals in a variety of different marine and terrestrial proxy records from Europe and the Atlantic Ocean, investigate the temporal evolution of the HP signal from the early/middle Pleistocene to the present, and evaluate the potential of the HP to reflect the connectivity of climate systems over time.

We apply filters on the datasets that remove the classical orbital cycles (eccentricity, obliquity, precession) and high frequency signals, and focus on the bandwidth of HP signals. Wavelet annalysis and correlation techniques are used to study the evolution of specific frequencies through the different records.

In addition to a connection of HP cycles with interglacials, we observe a more pronounced HP signal in the younger part of several proxy records. Besides, we observe a trend of more pronounced HP signals in low latitude records compared to high latitudes. This is in agreement with the assumption that HP is an equatorial signal and can be transmitted northward via various pathways. The appearance of HP signals in mid- and high-latitude records may thus be an indicator for the intensity of the transporting mechanisms. We suggest that the African Monsoon plays a major role in this context, as its magnitude directly influences the climate systems of the Mediterranean and Southern Europe. In order to better understand the African climate variability, both equatorial marine and terrestrial records will be examined with respect to HP.

How to cite: Ulfers, A., Zeeden, C., Voigt, S., Sardar Abadi, M., and Wonik, T.: Half-precession signals in marine an terrestrial records – connecting IODP/ICDP sites from the equatorial Atlantic to Greenland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4022, https://doi.org/10.5194/egusphere-egu22-4022, 2022.

Together with amphibole and garnet, epidote-group minerals are one of the three most important heavy minerals found in orogenic sediments (Garzanti and Andò, 2007). Their chemical composition and optical properties vary markedly with temperature and pressure conditions, and thus provide useful information in provenance analysis on the metamorphic grade of source rocks.

The aim of this study is to devise an efficient and quick method, with micrometric resolution to distinguish among the different species of the epidote group during routine point-counting of heavy-mineral slides, which can be applied on a vast ranges of grain-sizes from fine silt to medium sand.

The geochemical variability of epidote-supergroup minerals from different source rock collected in different sectors of the Alpine orogenic belt was first investigated by coupling Raman Spectroscopy, Scanning Electron Microscopy, and Energy-dispersed X-ray Spectroscopy (SEM-EDS). The geochemical composition, optical properties, and Raman fingerprints of these standard epidote grains were described and in-house database of Raman spectra was created, combining geochemical data and Raman response in the low wavenumbers region and OH stretching bands. A program, written in Matlab® language, has been established which allows to obtain a quick estimate of the amount of iron from the Raman spectra in the clinozoisite-epidote series.

Raman spectra of detrital epidotes contained in turbiditic sediments of the Bengal Fan (IODP Expedition 354) were next compared with Raman spectra of epidote-group standards to determine their composition. The identification and relative amount of detrital epidote, clinozoisite and zoisite in silt- and sand-sized deep-sea sediments contribute to constrain the metamorphic grade of Himalayan source rocks, reconstruct the erosional evolution of the Himalayan orogen, and provide information on climate change and strengthening of the Indian Ocean monsoon throughout the Neogene and Quaternary.

Key words: epidote, provenance, Himalaya, Raman spectroscopy, Microprobe analyses, optical microscope.

Garzanti, E., Andò S., 2007. Plate tectonics and heavy-mineral suites of modern sands. In: Mange, M.A., Wright, D.T. (Eds.), Heavy Minerals in Use, Developments in Sedimentology Series, 58. Elsevier, Amsterdam, pp. 741-763.

How to cite: Limonta, M., Andò, S., Bersani, D., France-Lanord, C., and Garzanti, E.: Raman identification of epidote-group minerals in turbiditic sediments from the Bengal Fan (IODP Exp. 354): a complementary tool to better constrain metamorphic grade of source rocks., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6161, https://doi.org/10.5194/egusphere-egu22-6161, 2022.

A 6-meter drill core from Merensky Reef, Bushveld Complex, South Africa, was scanned in detail with a drill core scanner based on Laser Induced Breakdown Spectroscopy (LIBS). The purpose of the investigation was to visualize variations in the chemical composition along the core, and following a mineral classification of the LIBS data, of variations in the mineral chemical composition, e.g. of Fe/Mg, Cr/Al, and Ca/Na ratios, as well.

The LIBS technology is based on atomic emission spectroscopy, in which the excitation of the atomic species occurs in-situ on the sample surface. The excitation source was a pulsed 50 mJ 1064 nm Nd:YAG laser, and the emitted light was collected with a high-resolution wide-range echelle spectrograph with CCD detector. This approach for measuring mineral chemical ratios such as Mg/Fe, Cr/Al, and Ca/Na, is based on the strength of LIBS in detecting chemical variations using intensity ratios within a single matrix, which in this application is one single particular type of mineral phase. For validation purposes, selected samples were analysed with bulk chemical analysis and electron probe microanalysis as well.

Distinct trends could indeed be extracted from the 6 m core section through the Merensky Reef. From a saw-cut core surface without further preparation, a continuous record could be extracted consisting of Mg/Fe of orthopyroxene, Ca/Na of plagioclase, bulk chemical patterns, modal composition, and direct neighbourhood. The data can be used to highlight the presence of unusual patterns and to relate them to Ni, Cu, PGE or other mineralization. When applied to different core sections, it may become an important tool for comparing lateral variability of diagnostic horizons in vertical sequences in layered intrusions such as Merensky Reef and UG-2.

How to cite: Meima, J., Rammlmair, D., Junge, M., and Nikonow, W.: Continuous measurement of Mg/Fe and Ca/Na ratios with scanning Laser Induced Breakdown Spectroscopy in 6 meter of drill core through Merensky Reef, Bushveld Complex, South Africa, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7513, https://doi.org/10.5194/egusphere-egu22-7513, 2022.

The Main Zone of the Bushveld Complex in South Africa is the most voluminous but least studied part of the world’s largest igneous intrusion. Modal layering is poorly developed compared with the units above and below (Upper and Critical Zones, resp.), and most of the ca. 3000 meter-thick Main Zone consists of monotonous gabbronorite, occasionally grading into norite and anorthosite. An exception is the ultramafic “Pyroxenite Marker” near the top of the Main Zone, which is present regionally in the complex and represents a major event of magma recharge into the chamber. However, studies of drillcore through the Main Zone in the Bushveld Northern limb (Ashwal et al., 2005; Hayes et al., 2017) found evidence for layering by periodic variations in rock density at vertical length-scales of 40 to 170 m. This implies there were many more episodes of magma recharge than previously thought.

Our study in the Eastern Limb of the complex tests if cryptic layering in the Main Zone is a local phenomenon or is regionally developed like the Pyroxenite Marker. The first step, reported here, was a vertical profile of bulk density data (Archimedes method) for a 1450 m section of the upper Main Zone below the Pyroxenite Marker. Samples were taken at 1 to 5 m intervals and the results show several intervals of density variations at length-scales of 30 to 120 m, comparable to those previously described in the Northern Limb. Periodicity in density changes is not so well developed as in the earlier study, and we identified several 50 to 75 m intervals where density variations are below 0.05 g/cm³. The second step of the study will use multispectral and laser-induced breakdown spectroscopy (LIBS) scanning to provide modal mineralogy profiles of the same drillcore samples used for density measurement. After cryptic modal layering is documented in this way, follow-up petrologic-geochemical studies at the layer boundaries will aim to characterize the composition and temperature of the magmas involved.

For this project the Bushveld Complex Drilling Project (BVDP) provided access to the BH7771 borehole, donated by Impala Platinum’s Marula mine.

References:

Ashwal, L..D., Webb, S.J. and Knoper, M.W. (2005) S. Afr. Jour. Geol., 108, 199-232.

Hayes, B., Ashwal, L.D., Webb, S.J. and Bybee, G.M. (2017) Contrib. Mineral. Petrol., 172, 13.

How to cite: Trumbull, R. B., Veksler, I. V., Nikonov, W., and Rammlmair, D.: How was the Bushveld Complex assembled? A search for cryptic layering in ICDP drillcores from the Main Zone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8339, https://doi.org/10.5194/egusphere-egu22-8339, 2022.

The Late Miocene deposits in the Sorbas Basin (Spain) have been of an extreme importance in the understanding of the Messinian Salinity Crisis (MSC) events (5.97-5.33 Ma). They consist of four formations. The pre-crisis Abad marls topped by the evaporitic Yesares gypsum member, followed by two non-evaporitic units known as the Sorbas and Zorreras members. Those deposits have been widely explored and studied thanks to the numerous outcropping sections in the basin.

The ‘SaltGiant’ European Training Network held a training school in October 2021 in the Sorbas Basin, where four boreholes (named SG0, 1, 2 and 3) covering most of the Messinian Salinity Crisis sequence, were drilled, cored and logged in this context along an overall thickness of about 175 m. The drillings took place inside and in the vicinity of the Torralba gypsum mine. It allowed for the first time in the scientific non-industrial domain, access to a continuous and non-outcropping succession of the Messinian deposits in the Sorbas basin. In addition to the recovered cores, borehole geophysical data were obtained from the four holes and digital images of the area were collected with a drone. Prior to the drilling, an OBO (Outcrop / Behind Outcrop) workflow was followed, which will allow integrating the outcrop and subsurface data by combining the 3D geometry of geobodies with geophysical information.

Optical borehole wall images provide mm-scale images of the borehole walls, highlighting the sedimentological and structural characteristics of the deposits. Downhole geophysical measurements included acoustic velocity, electrical resistivity and natural spectral gamma ray, which allowed determining the petrophysical characteristics of the penetrated lithologies. In addition to the petrophysical logs, a Vertical Seismic Profiling was performed in holes SG2 and SG3, including a multi-offset VSP survey in hole SG3.

The petrophysical characterization of the Messinian deposits will provide a reference case study for the lithologic characterization of MSC deposits in the subsurface elsewhere. VSP analysis provided an in-field preliminary seismic velocity evaluation in the encountered formations. Preliminary results confirm the astronomical precession-driven cyclicity observed elsewhere in the Messinian gypsum. Further processing and analyses of the large amount of acquired data will lead to identifying the astronomical and possibly higher-frequency cyclicity in the post-evaporitic deposits in the Sorbas member.

How to cite: Raad, F., Pezard, P., Viseras, C., Sierro, F. J., Yeste, L. M., Aguila, J. J., Jerez, P., Schleifer, A., Meneghini, F., Bellezza, C., Lofi, J., Camerlenghi, A., and Aloisi, G.: ‘SaltGiant’ drilling in the Sorbas Basin: Structural, Petrophysical and Geochemical characterization of the Messinian Salinity Crisis deposits, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8952, https://doi.org/10.5194/egusphere-egu22-8952, 2022.

The Oman Ophiolite is the largest and best-investigated piece of ancient oceanic lithosphere on our planet. This ophiolite was target of the Oman Drilling Project (OmanDP) within the frame of ICDP (International Continental Scientific Drilling Program) which aimed to establish a comprehensive drilling program in order to understand essential processes related to the geodynamics of mid-ocean ridges, as magmatic formation, cooling/alteration by seawater-derived fluids, and the weathering with focus on the carbonatisation of peridotites.

Over two drilling seasons, the OmanDP has sampled the Samail Ophiolite sequence from crust to basal thrust. The total cumulative drilled length is 5458 m, with 3221 m of which was at 100% recovery. These cores were logged to IODP standards aboard the Japanese drilling vessel Chikyu during two description campaigns in summer 2017 and 2018. 

Here we present the main results of the working groups of the Universities Hannover and Kiel, focusing on the magmatic accretion of the Oman paleoridge. During 5 field campaigns these groups established a 5 km long profile through the whole crust of the Oman ophiolite by systematic outcrop sampling, providing the reference frame for the 400 m long OmanDP drill cores. The profile contains 463 samples from the mantle, through gabbros up to the dike/gabbro transition. Identical samples have been analyzed by several methods (bulk rock geochemistry, mineral analysis, Isotope geochemistry, EBSD analysis).

The results allow implication on the mechanism of accretion of fast-spreading lower oceanic crust. Depth profiles of mineral compositions combined with petrological modeling reveal insights into the mode of magmatic formation of fast-spreading lower oceanic crust, implying a hybrid accretion mechanism. The lower two thirds of the crust, mainly consisting of layered gabbros, formed via the injection of melt sills and in situ crystallization. Here, upward moving fractionated melts mixed with more primitive melts through melt replenishments, resulting in a slight but distinct upward differentiation trend. The upper third of the gabbroic crust is significantly more differentiated, in accord with a model of downward differentiation of a primitive parental melt originated from the axial melt lens located at the top of the gabbroic crust. Our hybrid model for crustal accretion requires a system to cool the deep crust, which was established by hydrothermal fault zones, initially formed on-axis at very high temperatures.

How to cite: Koepke, J., Garbe-Schönberg, D., Mock, D., and Müller, S.: A profile through fast-spreading oceanic crust in the Oman ophiolite: reference frame for the crustal drillings within the ICDP Oman Drilling Project, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10040, https://doi.org/10.5194/egusphere-egu22-10040, 2022.

Insights into the climate variability of western Africa during the Pleistocene epoch have thus far been limited by the lack of well-dated, high-resolution terrestrial climate archives. The missing information on the climate evolution of western African hampers our understanding of the proposed pan-African evolution of our species. The ~294 m lacustrine sedimentary sequence raised from Lake Bosumtwi by the International Continental Drilling program in 2004, encompassing the last ~1.1 Ma, offers the best opportunity provide a climatic benchmark record in western Africa. However, the establishment of a chronology for this record has proven challenging. To try and improve our understanding of the climatic evolution during the last ~1.1 Ma in western Africa, we will use the high-resolution downhole logging data (natural gamma ray, GR) and magnetic susceptibility data from core logging from Site 5, which is situated in the centre of Lake Bosumtwi. To maximise the robustness of this record we will try to correlate data from downhole logs with core data. This approach has help improve interpretation of logging signals and environmental reconstructions for other long lake records, such as e.g. Lake Ohrid.

How to cite: Zeeden, C., Vinnepand, M., Kaboth-Bahr, S., Gosling, W., Kück, J., and Wonik, T.: Assessing the well logging data from the Lake Bosumtwi (Ghana), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10406, https://doi.org/10.5194/egusphere-egu22-10406, 2022.

At the Hikurangi convergent margin the Pacific plate is subducted westward beneath the Australian plate. This margin has been the location of major earthquakes as well as slow slip events related to the ongoing subduction. Drill site U1518 which was drilled during IODP Expedition 375, 73 km offshore Gisborne (New Zealand), targeted the Papaku fault, a splay fault of the major decollement in sediments of the frontal accretionary prism. We selected samples from the mostly hemipelagic, weakly consolidated mudstones in the fault zone, as well as from hangingwall and footwall. In order to investigate localized and distributed deformation in the fault zone, we analysed composition, microstructure and crystallographic preferred orientation (CPO). For that we applied µXRF measurements and optical microscopy, as well as synchrotron texture analysis at DESY in Hamburg.

The samples from hanging- and footwall sediments show a relatively homogeneous microstructure with local compositional layering. While CPO strength in the hangingwall is slightly increasing with depth for all analysed clay mineral phases, the CPO in the footwall samples is in general lower and does not show a clear trend with depth. This might be interpreted as different deformation histories in hangingwall and footwall which is in accordance with previous studies. Fault zone samples show a variety of microstructures, such as mingling of different sedimentary components, locally overprinted by microfaults. CPO strength in the faulted sediments is also variable, with zones showing strong alignment of phyllosilicates and zones showing weak alignment of phyllosilicates. Variations in CPO and variable distribution of sedimentary components indicate a heterogeneous deformation within the fault zone which might be due to local compositional variations.

How to cite: Kühn, R., Greve, A., Kilian, R., Mizera, M., and Stipp, M.: Heterogeneous deformation across the Papaku fault, Hikurangi accretionary prism, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11265, https://doi.org/10.5194/egusphere-egu22-11265, 2022.

The emissions of volcanic gases over the Earth’s history have played a major role in changing the chemistry of the terrestrial atmosphere with implications for life development and sustainability (Kasting and Catling 2003). Sedimentary rocks record geological processes that occurred at the interface between water and/or surface and atmosphere such as volcanic eruptions and other (extra)terrestrial catastrophic events. In the last decade, anomalous concentrations of mercury (Hg) in the sedimentary record have been used as a global tracer of extensive volcanism, although other sources of Hg must be taken into account as massive wildfires and continental weathering (Grasby et al. 2019). In this ongoing study, we aim at establishing the relation between geochemistry and mineralogy to explain the occurrence of Hg anomalies in sedimentary rocks distributed at regional scale. We investigated the Bonarelli level, a 0.87-m thick layer made of organic-rich shales, that outcrops at Valle della Contessa section in Gubbio (Italy). This layer records the Oceanic Anoxic Event 2 (OAE2; Cenomanian-Turonian, ~93 Ma), an event likely triggered by submarine volcanic emission of High Arctic and Caribbean large igneous provinces (Turgeon and Creaser 2008).

We collected rock samples from ~1 m below up to ~1 m above the Bonarelli level every 5 to 10 cm including the confining limestones. Measurements of absolute Hg concentrations were performed using the Direct Mercury Analyzer (DMA-80 Tricell) and combined with the mineralogical abundance at each layer determined by X-ray diffraction (XRD). Additional measurements were carried out to determine the concentrations of trace elements using the inductively coupled plasma-mass spectrometry (ICP-MS). Analyses of δ¹³C and total organic carbon (TOC) were also performed on the collected samples.

Preliminary results show low Hg concentrations measured in the limestones less than 20 μg/kg, but anomalous high contents up to ~1600 μg/kg within the Bonarelli level. These high Hg concentrations correlate positively with chalcophile elements such as Cu, Ni and Fe. XRD semi-quantitative analysis show that oxidized (barite, jarosite) and reduced (pyrite) S-bearing minerals are among the minerals occurring in the Bonarelli level that, along with the organic matter, are good candidates to host the Hg released to the atmosphere by extensive volcanic eruptions.

Kasting, J. F., & Catling, D. 2003. Annual Review of Astronomy and Astrophysics, 41(1), 429-463.

Grasby, S. E et al. 2019. Earth-Science Reviews, 196, 102880.

Turgeon, S. C., & Creaser, R. A. 2008. Nature, 454(7202), 323-326.

How to cite: Marras, G., Brandano, M., Tomassetti, L., Morelli, G., Rimondi, V., Aldega, L., Barberio, M. D., Preto, N., and Stagno, V.: Geochemical and mineralogical investigations of the Bonarelli level (Gubbio, Italy): evidence of Hg anomalies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-377, https://doi.org/10.5194/egusphere-egu22-377, 2022.

The Valanginian Weissert Event (~134 Ma) represented the first major carbon-cycle disturbance of the Cretaceous Period, characterized in the sedimentary record by a prolonged positive excursion in carbon-isotope ratios. The event has been widely linked with climate cooling, documented in several geographic regions; however, some areas show minimal evidence of temperature change at that time, or even warming and enhanced humidity around the onset of the event. Moreover, although the carbon-isotope excursion has generally been attributed to enhanced burial of organic matter, there is no evidence of widespread marine anoxia that would have promoted such deposition. Consequently, key questions remain regarding the causes of climate and environmental degradation during the early Valanginian. Understanding changes in volcanic activity and silicate weathering rates through late Berriasian to early Valanginian times is crucial for resolving this debate, as both processes influence atmospheric pCO₂ levels and global temperatures. In particular, volcanism associated with formation of the Paraná-Etendeka large igneous province (LIP) during the Valanginian has long been proposed as the ultimate trigger of the Weissert Event via carbon emissions and greenhouse warming,but weathering of juvenile LIP basalts could equally have caused climate cooling.

In this study, we investigated the osmium-isotope composition (¹⁸⁷Os/¹⁸⁸Os) of deep-marine organic-rich Berriasian–Valanginian sediments from two proto-Atlantic Ocean archives (DSDP sites 534 and 603). Given the palaeoenvironmental setting of the two sites, the recorded ¹⁸⁷Os/¹⁸⁸Os seawater compositions of the proto-Atlantic should be representative of the global ocean. We find that seawater ¹⁸⁷Os/¹⁸⁸Os shifted from ~0.6 to ~0.75 during the latest Berriasian, suggestive of an increased flux of radiogenic osmium to the ocean during that time, likely resulting from enhanced weathering of the continental crust. Interestingly, however, there is no evidence of global climate warming during the late Berriasian that would have caused this weathering. Following the late Berriasian radiogenic shift, seawater osmium gradually changed to a more unradiogenic isotopic composition (~0.45) during the early Valanginian; the lowest ¹⁸⁷Os/¹⁸⁸Os values correlating with both the peak in the Weissert Event carbon-isotope excursion and evidence for climate cooling. This unradiogenic shift could reflect a decline in weathering of radiogenic crustal material; however, it also stratigraphically correlates with geochronological and geochemical evidence for the time of maximum igneous activity on the western (Paraná) part of the Paraná-Etendeka LIP. Therefore, we conclude that the early Valanginian shift to unradiogenic ¹⁸⁷Os/¹⁸⁸Os seawater compositions resulted from erosion of juvenile primitive basalts, suggesting that combined weathering of the continental crust and the Paraná-Etendeka LIP played a key role in causing the global cooling associated with the Weissert Event.

How to cite: Percival, L., Selby, D., Robinson, S., Goderis, S., and Claeys, P.: Osmium-isotope records of volcanism and weathering before and during the Valanginian Weissert Event, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-779, https://doi.org/10.5194/egusphere-egu22-779, 2022.

Large Igneous Provinces (LIPs) are commonly correlated with global climate change, and environmental, as well as biological, crises. These are short-lived igneous events, typically much less than 5 Ma, can erupt more than 1 Mkm³ of volcanic rocks, while potentially emplacing over 500,000 km³ of upper crustal intrusions. As a result, LIPs represent some of the most rapid periods of lithospheric growth, generating enormous volumes of mafic upper crust. Detailing the duration and pace of these high flux magmatic events has, however, is hampered by a lack of high-precision geochronology. We focus on the Karoo LIP in southern Africa as a natural laboratory for testing models on the formation of mafic upper crust through large-volume mafic LIP intrusions. The Karoo LIP is comprised of a suite of basaltic lava flows, sills, dike swarms, and was emplaced during the early Toarcian. Approximately 340,000 km³ of sills are interlaid within Karoo Basin sedimentary rocks. Differential uplift, erosion and availability of drill core material allows for sampling of the entire intrusive succession in the basin.

We report new high-precision U-Pb zircon and baddeleyite ages, Hf isotope compositions and apatite volatile compositions from sills emplaced from base to top of the Karoo Basin. Using these data, we are able to address several fundamental questions of LIP emplacement: (1) what is the total of intrusive LIP magmatism within the Karoo Basin; (2) is there variable magma flux during assembly of the intrusive complex; (3) is there is a relationship between age and structural position of sills within the basin; (4) is it justified to correlate the intrusion of the LIP with global climate change at this level of precision; (5) does the composition and extent of thermogenic degassing vary throughout the basin?

Our new data indicate that the 340,000 km³ of intrusive magmas were emplaced in approximately 500 kyr, solidifying new mafic upper crust through a downward stacking assembly, and that the entirety of intrusive magmas were emplaced within the uncertainty of the early Toarcian oceanic anoxic event. This pulsed assembly is in agreement with atmospheric models that require pulsed degassing of the basin to cause the observed early Toarcian isotope excursions. In addition, these data also indicate that dolerite sills throughout the basin assimilated sedimentary wall rock during crystallization, which helped facilitate zircon crystallization within pegmatitic pods interfingered within the sills. Finally, volatile compositions preserved in apatite indicate that thermogenic wallrock-sill interactions significantly affected the final volatile compositions of the sills, and trace the release of LIP-driven gases from the basin.

How to cite: Gaynor, S. P., Augland, L., Svensen, H. H., and Schaltegger, U.: Lithospheric and Atmospheric Changes Associated with Rapid, Pulsed Assembly of Mafic Upper Crust: Assembly of the Karoo LIP Intrusive Complex, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3162, https://doi.org/10.5194/egusphere-egu22-3162, 2022.

Direct evidence of intense chemical weathering induced by volcanism is rare in sedimentary successions. Here, we undertake a multiproxy analysis (including organic carbon isotopes, mercury (Hg) concentrations and isotopes, chemical index of alteration (CIA), and clay minerals) of two well-dated Triassic–Jurassic (T–J) boundary sections representing high- and low/middle-paleolatitude sites. Both sections show increasing CIA in association with Hg peaks near the T–J boundary. We interpret these results as reflecting volcanism-induced intensification of continental chemical weathering, which is also supported by negative mass-independent fractionation (MIF) of odd Hg isotopes. The interval of enhanced chemical weathering persisted for ~2 million years, which is consistent with carbon-cycle model results of the time needed to drawdown excess atmospheric CO₂ following a carbon release event. Lastly, these data also demonstrate that high-latitude continental settings are more sensitive than low/middle-latitude sites to shifts in weathering intensity during climatic warming events. 

How to cite: shen, J.: Intensified continental chemical weathering and carbon-cycle perturbations linked to volcanism during the Triassic–Jurassic transition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3179, https://doi.org/10.5194/egusphere-egu22-3179, 2022.

The mid-Cretaceous (~120 Ma to ~90 Ma) is a well-known greenhouse period in the Earth’s history that was punctuated by multiple dramatic paleoceanographic changes known as oceanic anoxic events (OAEs). Among these OAEs, OAE2 occurred near the Cenomanian-Turonian boundary (CTB, ~93.9 Ma) and represents one of the most pronounced OAEs. OAE2 is widely believed to be triggered by submarine volcanism, primarily based on proxy records from the Northern Hemisphere in which a large osmium isotope excursion indicative of volcanism precedes the carbon isotope excursion (CIE) of OAE2. However, the timing and mechanism of the global initiation of OAE2 remain elusive in part due to the lack of detailed osmium-isotope proxy records across the OAE2 intervals in the Southern Hemisphere. Here we report a high-resolution initial osmium isotope (¹⁸⁷Os/¹⁸⁸Os_i, Os_i) and δ¹³C_org record from a highly expanded OAE2 interval in southern Tibet, China that was deposited in the northern margin of India Plate in eastern Tethys in the Southern Hemisphere. The Os_i record documents three distinct Os_i shifts toward unradiogenic compositions with increasing amplitudes at ~95.1 Ma, ~94.8 Ma, and ~94.5 Ma, respectively, indicating episodic, intensifying volcanism with the highest intensity episode at ∼94.5 Ma. In addition, the large Os_i excursion at ~94.5 Ma is followed by an ∼200 kyr Os_i minimum concomitant with a cooling interval as revealed by an overall broad minimum interval of the difference of the paired δ¹³C_carb and δ¹³C_org. This cooling interval is broadly synchronous with the Plenus Cold Event (PCE) recorded in the Northern Hemisphere. Furthermore, the large Os_i excursion paradoxically lags the onset of OAE2 by ∼50 kyr at the Tibetan section. Comparison with and re-examination of the expanded OAE2 record of the Yezo Group (Japan) and those from the western interior seaway (WIS) in North America reveal the regional difference in the phasing relationship between the large Os_i excursions and the CIEs of OAE2. Intriguingly, the large Os_i excursions occurred during a near synchronous global transgression at ~94.5 Ma that led to increased connectivity of global oceans. Taken together, these results suggest that enhanced ocean connectivity was essential in helping trigger the global onset of OAE2 at ~94.5 Ma.

How to cite: Li, Y.-X., Liu, X., Selby, D., Liu, Z., Montañez, I., and Li, X.: Deciphering the global onset of Oceanic Anoxic Event 2 (OAE2) in the mid-Cretaceous greenhouse world, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3366, https://doi.org/10.5194/egusphere-egu22-3366, 2022.

The End Triassic Extinction (ETE), one of the “big five” of the Phanerozoic, caused a severe loss of biodiversity both in the continental and in the marine realm. The ETE has been linked with enhanced volcanism of the Central Atlantic Magmatic Province (CAMP), which injected a large amount of CO₂ in the ocean-atmosphere system, triggering major paleoenvironmental perturbations including climate change, ocean acidification and marine anoxia.

In the marine realm, shallow-water benthic biocalcifiers of subtropical carbonate platforms were severely affected, with reef-building scleractinian corals and calcisponges, large megalodontid bivalves, involutinid benthic foraminifers and dasycladalean algae being among the most famous victims. In the classical localities of the Northern Calcareous Alps and Transdanubian Range, the ETE coincides with the demise of the Dachstein-type carbonate platform, which is generally sharply overlain by relatively deep-water facies of outer ramp to basinal environment. This stratigraphy has been interpreted as recording subaerial exposure of the carbonate platform, associated to a sea-level drop in the late Rhaetian that generated a hiatus of variable and generally poorly constrained duration, followed by drowning during transgression in the Early Jurassic.

A different stratigraphic evolution is recorded in some areas of the southern Tethyan margin (i.e., the southern Apennines and Sicily in southern Italy, Greece, the United Arab Emirates and Oman) where carbonate platform facies persist across the Triassic/Jurassic boundary. Stratigraphic sections in these areas are particularly significant to document the evolution of biodiversity of shallow-water benthic biocalcifiers across the ETE interval.

In this study we present new data on the stratigraphic distribution and changes in abundance of benthic foraminifers in two latest Triassic–earliest Jurassic carbonate platform sections of the southern Apennines (Italy) and Pelagonian domain (Greece). We document a decline in diversity and abundance of involutinid benthic foraminifers predating the extinction of several genera in the latest Rhaetian. Carbon isotope profiles of the studied sections show a complicated pattern of repetitive high-frequency negative excursions, seemingly related to local paleoenvironmental and/or early diagenetic features. However, by integrating bio- and carbon isotope stratigraphy we are able to correlate the studied sections with other persistent carbonate platform sections and with reference sections of the Lombardy Basin and of the Northern Calcareous Alps.

How to cite: Falzoni, F., Montanaro, A., Iannace, A., and Parente, M.: The record of the End Triassic Extinction in southern Tethyan carbonate platforms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3986, https://doi.org/10.5194/egusphere-egu22-3986, 2022.

Massive release of volcanic gases into the ocean-atmosphere system during geologically short periods of time is often invoked as the main trigger of episodes of global paleoenvironmental perturbations, and a link has been proposed between some mass extinction events, OAEs and the activity of Large Igneous Provinces. However, establishing a precise correlation between sections where the volcanic deposits of LIPs are preserved and marine sections, which hold the key records of global biotic and paleoenvironmental changes, is not a trivial effort.  During the past 15 years, mercury concentration in sedimentary rocks has emerged as a useful proxy for bracketing intervals of LIPs activity, because Hg is primarily introduced into the atmosphere, and from there into the sedimentary record, through volcanic inputs. 
The end-Triassic extinction (ETE), one of the big five mass extinction of the Phanerozoic, has been linked to the volcanic activity of the Central Atlantic Magmatic Province (CAMP). Correlation by radiochronologic dating of CAMP basalts has been further supported in recent years by detection of mercury anomalies in marine deposits of key sections recording the ETE, including the Kuhjoch GSSP in the Northern Calcareous Alps (Austria), St Audrie’s Bay (UK) and the New York Canyon (Nevada, USA). However, as the Hg proxy is investigated in more and more sections, a complicated pattern is emerging, which indicates that depositional and diagenetic processes can produce Hg anomalies unrelated to LIP magmatism. For this reason, it is important to test the proxy across a wide range of depositional environments. 
In this study, we present a high-resolution record of Hg concentration in an uppermost Triassic-Lower Jurassic carbonate platform section of the Pelagonian Domain (Greece). In this section the ETE is marked by the abrupt disappearance of megalodontid bivalves and involutinid benthic foraminifers. By integrating bio- and high-resolution carbon isotope stratigraphy, we correlate the studied section with reference sections for which a record of Hg concentration across the ETE has been published. Furthermore, we use facies analysis and geochemistry to unravel the role of local depositional and diagenetic processes in overprinting the global signal of volcanism on Hg concentration.

How to cite: Montanaro, A., Falzoni, F., Iannace, A., Adatte, T., and Parente, M.: Mercury anomaly as a proxy for volcanism in an isolated carbonate platform during the end-Triassic mass extinction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4901, https://doi.org/10.5194/egusphere-egu22-4901, 2022.

Large Igneous Provinces (LIPs) are accumulations of igneous rocks representing periods of intense volcanism in Earth’s history. The timing of the emplacement of many LIPs corresponds with global climatic perturbations and mass extinctions, leading to the hypothesis that their occurrence is implicated in these events. However, detailed investigations into these hypotheses are typically restricted to studies of individual events (e.g. the Siberian Traps emplacement at the Permian-Triassic boundary), and single forcing mechanisms (e.g. carbon emissions). As a result, it is often unclear what the overall impact of LIP emplacement was on climate in Earth’s history.

In this work, we present the results of the first integration of LIP degassing and weathering to a long-term model of global carbon cycling. We use the SCION climate-chemical model, which allows for both the addition of LIP degassing as a CO₂ forcing mechanism, and the introduction of LIPs as highly weatherable terranes on the Earth surface. In this way, we can estimate both the warming impact LIPs may have had on climate change in the past, through carbon degassing, but also the cooling effect they would have had, through enhanced silicate weathering. Our work shows the importance of LIP location on weathering rates, with those which are emplaced in the mid-latitudes having the biggest cooling impact.

Comparison of our reconstruction with previous estimates of Phanerozoic climates show that the inclusion of LIPs enhances model-data comparability. This is particularly clear in the late Triassic, and Cretaceous periods, where previous model reconstructions overestimated atmospheric CO₂ and global temperature. Our findings suggest LIP weathering is an important factor mitigating global climate change through the Phanerozoic.

How to cite: Longman, J. and Mills, B. J. W.: The role of Large Igneous Provinces in controlling long-term Phanerozoic climate change, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5403, https://doi.org/10.5194/egusphere-egu22-5403, 2022.

Perceived mercury (Hg) enrichments and elevated ratios of Hg to total organic carbon (Hg/TOC) in sedimentary rocks have often been linked to volcanism from large igneous provinces (LIPs) and mass extinctions, prompting the hypothesis that elevated Hg concentrations are a proxy for intense volcanism from LIPs.  However, primary Hg and TOC contents of sedimentary rocks can be altered by secondary processes, for example, intense weathering [1].  Before endorsing cause-and-effect between volcanic Hg emissions and biotic crises or mass extinctions, the magnitude of measured Hg and Hg/TOC anomalies in weathered outcrop samples must be compared to equivalent units in core samples, where the outcrop sample provides, in effect, a minimum concentration value.  

Here, we investigate the effects of incipient weathering on Hg contents and Hg/TOC ratios.  We quantify the behavior of Hg during incipient weathering by determining Hg concentrations in visually pristine black shales from outcrops of the Upper Permian Ravnefjeld Formation in East Greenland, comparing these data to equivalent intervals acquired from drill core taken from a plateau 7 km from the outcrop.  Directly correlative Upper Permian shales (drill core) from the mid-Norwegian shelf further enhance our comparison.  Using detailed geochemistry and principal component analysis (PCA), we characterize the main host phases of Hg and relate different Hg contents from pristine samples from East Greenland and the mid-Norwegian shelf to different Hg inputs during shale deposition.  Importantly, we show the vulnerability of Hg contents and Hg/TOC ratios to incipient weathering of fresh-appearing outcrops of organic-rich shale.  

Working with drill core rather than outcrop samples is essential to circumvent the problem, and to provide accurate Hg concentration data for primary events in the paleo-record.

[1] Charbonnier, G., Adatte, T., Föllmi, K.B., and Suan, G. (2020) Effect of intense weathering and postdepositional degradation of organic matter on Hg/TOC proxy in organic-rich sediments and its implications for deep-time investigations. Geochemistry, Geophysics, Geosystems, 21(2).

Funding – HS acknowledges the support of ACS-PRF award #59965-ND2 supporting AIRIE PhD student JP.  Drill cores were acquired from GEUS under Petromaks grant (NFR 180015/S30).  Colorado State University-Geosciences provides no funding for the personnel and operation of the AIRIE Program and its Re-Os laboratories. 

How to cite: Park, J., Stein, H., Georgiev, S., and Hannah, J.: Degradation of mercury (Hg) signals on incipient weathering refines use of Hg as a volcanic paleoproxy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5955, https://doi.org/10.5194/egusphere-egu22-5955, 2022.

Massive volcanic eruptions of the Deccan coincided with the end-Cretaceous mass extinction. Precisely dating when the most intense eruptions occurred is challenging because the resolution of geochronological techniques does not yet resolve events shorter than 20 kiloannum (ka). Volcanic eruptions outgas volatile metals, e.g., Cd, Te and Hg, along with SO₂ and other gases that may have contributed to high-stress environments for planktic foraminifera the 200 ka preceding the end-Cretaceous. Trace metals like Cd accumulate in sediments by deposition of aerosols, where the excess Cd reflects the intensity of volcanic emissions. Models show high frequency, low effusion rate eruptions result in low Cd enrichments, whereas low frequency, high effusion rate eruptions, the type likely to lead to deadly consequences, result in high enrichments of Cd within the sediments. The KPg section at Elles represents a middle neritic depositional environment with an average sedimentation rate of 4.7 cm/1,000 years for the late Maastrichtian. A series of sediment samples (marly limestone to shale) were taken from about 1 meter above the boundary to about 15 meters below the boundary. Elemental compositions of sediments (50 elements) were obtained by solution ICP-MS. Cadmium abundances ranged from values close to upper continental crust (UCC) to values approximately eight times higher. Such high enrichments were found in sediments from the 100 ka period preceding the boundary corresponding to the Poladpur phase of Deccan volcanism. A lack of correlation between Zn, P₂O₅, and Mo below the boundary suggest the Cd enrichments are not from an influx of biogenic detritus or TOC burial. Above the boundary, there is a 25 ka period of normal shale Cd values interpreted here to represent the period between the Ambenali and Poladpur phases. We have previously shown from the neighbouring El Kef section, representing ~ 10 ka, that Cd and Re are correlated in proportions similar to those from intraplate volcanoes. The Cd data for Elles complement Te and Hg data, all of which demonstrate the presence of volcanogenic trace metals over most of the period of the Poladpur phase of the Deccan eruption. Cadmium as a tracer enables better correlation between foram-based chronology and intense pulses of the Deccan eruption. The data obtained thus far confirm that the period prior to the extinction was dominated by intense volcanism followed by relative quiescence during the earliest Danian recovery with important implications for the cause of the extinction.

How to cite: Sillitoe-Kukas, S., Humayun, M., Adatte, T., and Keller, G.: Evidence of high effusion Deccan volcanism proceeding the KPg boundary at Elles, Tunisia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6736, https://doi.org/10.5194/egusphere-egu22-6736, 2022.

The Deccan flood basalt province in India was erupted within < 1 Myr and overlaps in age with the Cretaceous-Paleogene boundary (KPB) extinction event, and the Chicxulub impact in Mexico. Consequently, the role of Deccan volcanism in the KPB extinction is debated, and it has also been proposed that the Chicxulub impact triggered the largest Deccan lava formations (Poladpur, Ambenali and Mahabaleshwar (PAM)), which represent approximately 70% by volume of the total Deccan and may have been erupted within 500,000 years. Recent geochronological data studies debate whether the onset of the PAM eruptions began at the KPB as consequence of the Chicxulub impact, or whether the PAM lavas were erupted in several pulses, beginning several tens of thousands of years before the KPB (e.g., Sprain et al. 2019, Schoene et al., 2019).

The Rajahmundry Traps on the eastern side of India are believed to represent either the distal ends of voluminous Ambenali and Mahabaleshwar lava flows (e.g., Baksi et al. 1994), or lavas which were erupted locally through fault-controlled fissures unrelated to Deccan volcanism (Manikyamba et al. 2015). In contrast to lavas of the Main Deccan Province, the three separate lava flow units at Rajahmundry are interbedded with sediments, which constrain their age relative to the KPB (Keller et al. 2008; Fendley et al. 2020).

Here we present new major and trace element data for lavas from Rajahmundry and from the Main Deccan Province, and correlate the lavas from Rajahmundry with the younger formations of the Deccan Traps using machine learning algorithms. We find that flows of the Poladpur (lower flow), Ambenali (middle flow) and Mahabaleshwar (upper flow) formations are all present at Rajahmundry, confirming these as an eastward extension of the Deccan Traps. The geochemical classification is consistent with published paleomagnetic and geochronological data for these lavas. Our study shows that some Poladpur lava flows were of sufficient volume and were erupted rapidly enough to flow approximately 1000 km across the Indian subcontinent. The ages of sediments at Rajahmundry imply that eruption of the Poladpur Formation and thus the onset of voluminous PAM volcanic activity began close to the KPB (and Chicxulub impact), and at least the youngest Poladpur flows were emplaced in the Danian.

How to cite: Hoyer, P., Regelous, M., Adatte, T., and Haase, K.: Linking the Deccan lava stratigraphy with the end-Cretaceous extinction and impact – new insights from Rajahmundry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7033, https://doi.org/10.5194/egusphere-egu22-7033, 2022.

The Permian-Triassic boundary mass extinction (PTBME) is recognized as the most severe extinction of the Phanerozoic and has been causally linked to the Siberian Traps Large Igneous Province (STLIP) volcanism (e.g., Burgess and Bowring, 2015; Svensen et al, 2009; Sanei et al., 2012). This link is suggested based on the approximate temporal coincidence of STLIP magmatism and sedimentary successions straddling the PTB, which bear evidence of faunal extinction as well as elevated mercury (Hg) concentrations. However, several marine successions spanning the Late Permian to Early Triassic do not have elevated Hg content or are not synchronous in terms of their Hg concentration “anomalies” and the PTB interval (e.g., Sial et al., 2020). Furthermore, Hg sequestered in marine sediments may differ in provenance and its depositional pathways (Yager et al., 2021), complicating the use of Hg anomalies as a direct and reliable proxy for volcanism. This study investigates Hg concentrations and Hg isotopic composition together with total organic carbon (TOC) content, organic carbon δ¹³C values and element concentrations from two deep-water PTBME sedimentary sections in the Nanpanjiang basin, south China, spanning the Late Permian to Early Triassic. The Hg anomaly in these successions is found to coincide with the nadir of the negative C-isotope excursion close to the PTB. However, based on both the fossil associations as well as precise U-Pb ages for volcanic ash layers within these successions, these anomalies are of Griesbachian age. Hg isotope compositions support a volcanic origin and constant provenance for the Hg across the entire interval studied. These features, together with the common occurrence of volcanic ash beds throughout the investigated successions, are compatible with regional volcanic arc magmatism as a probable source of the Hg. The present results highlight that elevated Hg concentrations in marine successions straddling the PTB in south China cannot be unequivocally linked to STLIP volcanism.

References

Burgess, S. D., and Bowring, S. A., 2015, High-precision geochronology confirms voluminous magmatism before, during, and after Earth’s most severe extinction: Science Advances, v. 1, no. 7, p. e1500470.

Sanei, H., Grasby, S. E., and Beauchamp, B., 2012, Latest Permian mercury anomalies: Geology, v. 40, no. 1, p. 63-66.

Sial, A., Chen, J., Lacerda, L., Korte, C., Spangenberg, J., Silva-Tamayo, J., Gaucher, C., Ferreira, V., Barbosa, J., and Pereira, N., 2020, Globally enhanced Hg deposition and Hg isotopes in sections straddling the Permian–Triassic boundary: Link to volcanism: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 540, p. 109537.

Svensen, H., Planke, S., Polozov, A. G., Schmidbauer, N., Corfu, F., Podladchikov, Y. Y., and Jamtveit, B., 2009, Siberian gas venting and the end-Permian environmental crisis: Earth and Planetary Science Letters, v. 277, no. 3-4, p. 490-500.

Yager, J. A., West, A. J., Thibodeau, A. M., Corsetti, F. A., Rigo, M., Berelson, W. M., Bottjer, D. J., Greene, S. E., Ibarra, Y., and Jadoul, F., 2021, Mercury contents and isotope ratios from diverse depositional environments across the Triassic–Jurassic Boundary: Towards a more robust mercury proxy for large igneous province magmatism: Earth-Science Reviews, p. 103775.

How to cite: Edward, O., Paul, A. N., Bucher, H., Bagherpour, B., Baud, A., Adatte, T., Sonke, J., Schaltegger, U., and Vennemann, T.: Mercury isotope evidence for sustained regional volcanism in south China before and after the Permian-Triassic boundary, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8013, https://doi.org/10.5194/egusphere-egu22-8013, 2022.

Deep-water agglutinated foraminifera (DWAF) are investigated from the lower Paleocene of the Contessa Highway section in the Umbria-Marche Basin in Italy. In the lowermost meter of the Paleocene, corresponding the P0, Pa, and lowermost P1 planktonic foraminifera zones, a total of 46 species of DWAF are observed. A comparison with the uppermost Maastrichtian DWAF assemblages documented by Cetean (2009) yields a combined total of 94 DWAF species over the Cretaceous/Paleogene boundary interval at Contessa Highway. Of these, 49 species are listed as extinction taxa, nine are survivor taxa, 19 are Lazarus taxa, and 17 taxa display first occurrences in the Paleocene.

The record of DWAF in the Contessa Highway section displays a moderate decrease in diversity across the K/Pg boundary, followed by a gradual recovery in the first meter of the Paleocene. The lower Paleocene record is characterized by blooms of opportunistic species belonging to the genera Reophax, Subreophax, Repmanina, and Spiroplectinella. The K/Pg boundary interval records a major change in the proportions of DWAF morphogroups, from a suspension-feeding community in the Maastrichtian to one dominated by epifaunal detritivores in the lower Paleocene, reflecting a fundamental change in the nature of marine primary productivity following the bollide impact. 

How to cite: Kaminski, M., Hikmahtiar, S., and Cetean, C.: Deep-Water Agglutinated Foraminifera from the Contessa Highway Section, Umbria-Marche Basin, Italy: Assemblage turnover at the Cretaceous/Paleogene Boundary, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9536, https://doi.org/10.5194/egusphere-egu22-9536, 2022.

The Late Maastrichtian Deccan volcanic pulses contributed to a cumulative biotic stress that set the stage for the Cretaceous-Palaeogene boundary (KPB) mass extinction. The high-flux emissions of volcanogenic CO₂ and SO₂ into the atmosphere likely led to ocean acidification. The resultant carbonate crisis has been hypothesized as a key stressor for marine calcifying biota such as planktic foraminifera. The final ~50 ky of the Cretaceous at Bidart (France) record a unique concurrence of anomalous bulk-rock low magnetic susceptibility, high Hg/TOC, and high planktic foraminifera fragmentation index. This study documents new evidence of a biological (calcification) crisis in the geochemical and taphonomic Deccan benchmark interval.

The onset of the hypothesized acidification interval (~0.5 m below KPB) coincides with abrupt changes in the relative abundances of the heavily calcified globotruncanid (~30 to ~17%) and larger biserial tests (~38 to ~55%). The absolute abundances of target groups/species however show a marked decline in both the biserials and globotruncanids. The counts per gram within the benchmark fluctuate considerably. At the KPB, the relative abundances of robust tests are high, partly due to taphonomic overestimation. However, absolute abundances unequivocally show a decline in all analyzed groups e.g., globotruncanids, biserials, racemiguembelinids and Planomalina brazoensis. The benchmark interval also records smaller-than-average test sizes of Globotruncana arca, Globotruncana mariei, Heterohelix globulosa, Pseudoguembelina hariaensis, Pseudotextularia elegans, Pseudoguembelina carsayae, Pseudoguembelina palpebra, Rugoglobigerina rugosa and P. brazoensis, indicating intraspecific dwarfing. This same interval also records a measurable decrease in the test-wall thickness amongst adult (>150 µm) specimens of H. globulosa, R. rugosa, P. elegans, P. brazoensis, further substantiating a carbonate crisis. The interpolation of geochemical, taphonomic and the new biological evidences strongly validate an ocean acidification event spanning ~50 ky preceding the KPB, a duration more consistent with Deccan volcanism as the cause.

How to cite: Punekar, J., Patra, S., and Keller, G.: On Planktic Foraminifera Calcification Crisis in the Deccan Benchmark Interval of Bidart, France, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10083, https://doi.org/10.5194/egusphere-egu22-10083, 2022.

After 42 years, the debate over the end-Cretaceous mass extinction still rages with arguments made for Chicxulub impact and Deccan volcanism as the real cause of this catastrophe. We briefly review the evidence for the pre-KPB age of the Chicxulub impact based on the primary impact spherule layer, which we link to Deccan volcanism based on the global mercury (Hg) fallout from Deccan eruptions. Mercury from volcanic eruptions is distributed around the world during its atmospheric residence time of 6 months to one year, after which it rains out over land and oceans. Major pulsed volcanic eruptions yield high Hg concentrations during fallout, which we termed Extreme Events (EE). We identified 20 of these Hg extreme events during the last 550 ky of the late Maastrichtian in sequences from Tunisia, Israel, Egypt and Mexico. At Elles, Tunisia, we dated these events (EE1 to EE20) based on orbital cyclicity and biostratigraphy with precision of one cycle (20 ky) with an error margin of 10-20 ky (Keller et al., 2020). We linked these dates to U-Pb zircon ages of the Deccan Traps with similarly high precision (Schoene et al., 2019). The resulting mercury stratigraphy yielded excellent age control linking Deccan eruption pulses across the globe. Results from two localities in NE Mexico revealed the Chicxulub impact crashed into Yucatan above the base of the Plummerita hantkeninoides zone CF1 and EE6 at about 200 ky prior to the KPB mass extinction. This deposit is unlike any other of the over 100 reworked spherule layers mixed with abundant shallow water debris. This oldest and primary impact spherule layer consists of compressed pure melt rock glass and glass spherules that settled rapidly to the deep seafloor. The environmental effects of this large impact were short-lived and caused no species extinctions. The effects of this 10 km-sized bolide impact had been vastly overrated.

The KPB mass extinction was identified between the longest lava flows across India to the Krishna-Godavari Basin and into the Bay of Bengal. Based on peak Hg fallout, we identified these volcanic eruptions as the largest most rapid sequence of pulsed events in Tunisia, Israel, Egypt and Mexico, all coinciding with the rapid mass extinction observed in India. The mass extinction began with the onset and ramp-up of pulsed Deccan eruptions resulting in toxic and acidic waters that caused 50% species extinctions. Extremely rapid large pulsed eruptions followed and resulted in the longest lave flows and hyperthermal warming that caused the rapid demise of all but one species, the disaster opportunist Guembelitria cretacea. Deccan eruptions quickly diminished after the mass extinction and climate cooled rapidly giving rise to the first new species. Volcanic eruptions remained low and cool temperatures persisted through the early Paleocene interrupted by a smaller eruption phase about 100 ky after the mass extinction.  These data reveal that Deccan volcanism caused the KPB mass extinction without any extraterrestrial aid.

Keywords: Chicxulub, Deccan Volcanism, Mass Extinction, Mercury Stratigraphy, Age control

How to cite: Keller, G., Grasby, S., Khozyem, H., Punekar, J., Mateo, P., and Adatte, T.: Chicxulub Impact’s Real Age & Mass Extinction’s Real Cause, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11901, https://doi.org/10.5194/egusphere-egu22-11901, 2022.

Our systematic study of the spatial-temporal evolution of magmatism in the Deccan Traps   Large Igneous Province provides new data from the Malwa Plateau(MP) subprovince, which lies north of the comparatively well-studied Western Ghats. 40Ar/39Ar analysis was performed by incremental laser heating of multigrained plagioclase aliquots, in multiple (typically 4) experiments per sample.  Achievable precision is strongly anticorrelated with Ca/K of the plagioclase, reaching ~0.1% (pooled plateau ages, 1 s.d. intralaboratory precision) for some samples with Ca/K< 80. Results have been obtained from samples between ~100-800 m elevation, spanning virtually the entire exposed stratigraphy of the MP. Most of the MP overlaps in age with the older Kalsubai and Lonavala subgroups (~66.3 to 66.0 Ma) of the Western Ghats(WG), but MP basalts do not align with traditional WG chemical stratigraphy suggesting multiple contemporaneous eruptive centers and magma systems. The lowest (134 masl) lava dated is 66.8 ±0.07 Ma, significantly older than anything yet dated in the WG but identical to the result of Schöbel et al. (2014) for a stratigraphically low lava elsewhere in the MP. This is consistent with the consensus that the inception of volcanism progressed generally from North to South. Collectively, our data indicate a much slower mean lava accumulation rate for the basal MP, increasing sharply from 66.4 to 66.2 Ma and slowing by the Cretaceous-Paleogene boundary (KPB). MP lava accumulation rates decrease around the time of the KPB coincident with when eruption rates are inferred to increase in the WG. At similar elevations, our results overlap with the age model presented by Eddy et al. (2020) based on U/Pb dating of zircons from presumed silicic ashes preserved in red boles between lava flows, however our data span about twice their elevation range encompassing the lower portions of the section where we obtained the oldest ages. Our results indicate that the peak lava extrusion in the MP coincided closely with the Late Maastrichtian Warming Event (Barnet et al., 2017).

How to cite: Tholt, A., Renne, P., Vanderkluysen, L., Pande, K., Mohabey, D., and Dhobale, A.: 40Ar/39Ar dating of the Malwa Plateau subprovince, Deccan Traps, India, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11928, https://doi.org/10.5194/egusphere-egu22-11928, 2022.

In May 2021 project PORO-CLIM acquired a new geophysical dataset across the little studied Porcupine and Rockall Plateau passive margins in the Northeastern Atlantic. The project aims to study the initiation of the North Atlantic Igneous Province (NAIP) and test its relationship with the Palaeocene-Eocene Thermal Maximum (PETM) global climate change event. Profile 1, a 400 km long deep seismic (MCS and OBS) profile, contains a continuous latest-Cretaceous to early-Eocene oceanic crustal thickness record that spans the entire emplacement of the NAIP. Oceanic crustal thickness can be directly interpreted as a record of magma productivity and hence mantle temperature. As such Profile 1 encodes the first continuous, sub-million year record of the entire waxing and waning cycle of mantle temperature during the initiation of any of the world’s Large Igneous Provinces.

Thermogenic methane produced by shallow igneous sills within the NAIP sill province and released to the atmosphere through hydrothermal vent systems, together with the carbon dioxide released from the magma itself, are the most likely carbon sources for the PETM ^[1]. Profile 1 is the first whole crustal seismic record across Eriador Ridge, thought to be the thick oceanic crustal trace of the pulse of anomalously hot mantle which drove the pulse of melting which led to NAIP sill province emplacement. Thus the magma productivity record derived from Profile 1 will ultimately help constrain the rate of NAIP thermogenic carbon emissions, further testing the link between NAIP sills and the PETM. This presentation will outline the initial findings from seismic data analysis, including a preliminary magma production record spanning NAIP initiation and the relationship between magma productivity and the PETM. Initial analysis of relative changes in crustal thickness across the record suggest that long-term (>5 My) magma productivity increased from late Cretaceous to early Eocene time, whilst short term (<5 My) magma productivity became more pulsed. The new dataset also shows Eriador Ridge contains a previously unknown double peak in magma productivity. These peaks may potentially be the result of two distinct pulses of anomalously hot mantle, separated by c. 1 Myr, which could imply multiple bursts of gas release from the NAIP around the Palaeocene-Eocene boundary.

[1] Jones, S.M., Hoggett, M., Greene, S.E. and Jones, T.D. Large Igneous Province thermogenic greenhouse gas flux could have initiated Paleocene-Eocene Thermal Maximum climate change. Nat. Commun. 10, 5547 (2019).

How to cite: Knight, H., Jones, S. M., Hopper, J. R., O'Reilly, B. M., and Funck, T.: Project PORO-CLIM initial results: Towards a new oceanic crustal record of magma productivity throughout initiation of the North Atlantic Igneous Province, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12380, https://doi.org/10.5194/egusphere-egu22-12380, 2022.

Drilling undertaken in the 1990s at the Kalkkop impact crater, situated in the semi-arid, Nama-Karoo biome of South Africa, revealed lacustrine sedimentary deposits. This is an invaluable archive for a region synonymous with a paucity of terrestrial-based, continuous, and high-resolution records. In 2019, a new 90 m core was retrieved from the palaeolake and subjected to a detailed sedimentological log. Sedimentary facies analysis was applied to investigate the changes in past depositional environments, themselves reflecting local changes in hydroclimate. Sedimentological evidence indicated deposition in an overall low-energy environment, intermittently interrupted by brief high energy events. Employment of grey scale image analysis on the top 20 m revealed dry conditions persisted for longer and became more frequent towards the present surface. This was inferred by the darker layers referring to more minerogenic input which is associated with wetter conditions and lighter layers suggesting more pure carbonates and linked to dry conditions. This prolonged aridity impacted the longevity and alkalinity of the Kalkkop lake, resulting in carbonate precipitation, silica dissolution, and complete desiccation. Limited biological remains (diatoms, n=5) support this hypothesis. The body of evidence, namely carbonate precipitation and long persistence of arid spells, as well as the extremely low abundance of silica-based biological remains (pollen, diatoms, phytoliths), supports a transition toward a semi-arid environment by ~250 ka. This remarkable new record of past environmental and climatic changes recorded by the Kalkkop palaeolake core is the subject of ongoing research at the University of Cape Town, South Africa.

How to cite: Mpangala, L. E., Kirsten, K., Haberzettl, T., Murungi, M., Mavuso, S., and Pickering, R.: Sedimentary facies analysis and palaeoenvironmental reconstruction of the Kalkkop palaeolake, Eastern Cape, South Africa, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-402, https://doi.org/10.5194/egusphere-egu22-402, 2022.

Konya closed basin, located on the Anatolian plateau, hosted plenty of cultures and civilizations throughout the Holocene. The abundance of archaeological settlements and the current ecological fragility of the basin have increased the scholarly focus on the region. The basin offers a long-term and multi-dimensional record of human-environment interactions that reflect social, environmental, political, and economic processes. Paleolimnology studies are significant to reconstruct the paleoclimate and the paleoenvironment of the region. Sediment cores obtained from the basin, which is known to be paleo lake formerly and its surrounding lakes, provide multiple proxy records. Although plenty of paleoenvironmental studies were conducted in the region, reaching a temporally and regionally homogenous and long-term dataset is not straightforward. First, this research aims to build a paleoenvironmental synthesis of the Konya Basin. Secondly, it aims to reveal the climatic changes in the region throughout the Holocene quantitatively. In this study, Macrophysical Climate Model (MCM) was run with thirty years of observation data from a total of 20 meteorological stations located in and around the study area. The model outputs were compared with the local proxy records (oxygen isotopes and pollen records) obtained from the lacustrine environments of the region. MCM is a heat-budget modeling method to precisely recognize the mean centers of high and low sea-level pressure systems that manage the weather and wind patterns at mid-latitudes. The MCM model allows us to predict meteorological parameters at the interval of 100 years from the present to 40,000 years ago. Preliminary findings from the MCM point to the wetter and warmer periods in the Early Holocene, similar to isotope proxies in the region. Towards the end of the Early Holocene, precipitation decreases, and the driest climatic conditions occur in the Middle Holocene. The model outputs confirm the cessation of the active alluvion process in the Middle Holocene, which was experienced due to the reduction in the seasonality of precipitation. It was seen that increasing trend in winter temperatures during the Holocene for analyzed stations. On the advancing parts of the research, the findings from this study will be used in an agent-based modeling platform to understand the complex human-environment interaction in the region.

How to cite: Erdem, N. and Arıkan, B.: Modeling Holocene paleoclimate of Konya basin and comparison with proxy data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-606, https://doi.org/10.5194/egusphere-egu22-606, 2022.

The Lake Turkana region in northern Kenya and southern Ethiopia is famous for its fossil richness including key sites for human evolution studies. Modern Lake Turkana is the last of numerous mega-paleo-lakes, that has persisted to dry up completely at the end of the last African Humid Period (AHP, 15 – 5 ka). The adjacent paleo-lakes Suguta (2,000 km²) and Chew Bahir (2,500 km²), which are desiccated today, have formed together with paleo-lake Turkana (20,000 km²) a N-S oriented mega-lake during the AHP that has being separated only by small morphological Barriers. While Turkana, Suguta and Chew Bahir have been part of intensive research during the past decades, paleo-lake Chalbi with 10,000 km² in size just 10 km east of Lake Turkana was out of sight for most archaeologists and geoscientist. Here we present the first attempts for enhancing our understanding of the paleoenvironmental consequences of paleo-lake Chalbi close to one of the key regions in human evolution.

How to cite: Fischer, M. L. and Junginger, A.: The Great Lakes of Turkana – a Novel Perspective on the African Humid Period, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-667, https://doi.org/10.5194/egusphere-egu22-667, 2022.

Climate may have played a critical role in early hominin evolution and dispersion, with rapid changes from humid to hyper-arid observed in East African palaeoclimate records. Many studies show linkages between these climate changes and hominin speciation and dispersion; however, few of them have focused on annual to decadal climate variability. This new study presents paleoenvironmental records (diatom assemblages and oxygen isotopes in diatom biogenic silica, d¹⁸O_diatom) from the Ol Njorowa Gorge in Kenya. The study site is located west of the African Rift Valley, from where important hominin dispersals are believed to have taken place. The study site preserves a stratigraphic record of interbedded diatomite beds spanning a key period of theorised hominin dispersals; 150,000 to 80,000 years ago. In this study, diatom assemblages and d¹⁸O_diatomrecords are used to understand past changes in moisture and precipitation patterns over East Africa as well as changes in lake water chemistry. d¹⁸O_diatom has been used in both lacustrine and oceanic settings since the early 2000s. It is however an under-utilised proxy that holds great potential, especially for diatomites from exposed lake beds where carbonate material is scarce or inexistant. The study also uses high resolution scanning XRF data from diatomite blocks to develop an age model for the diatomite beds at an annual timescale.

How to cite: Porchier, C. A., Maslin, M. A., Hill, T., Williams, D. M., Cox, E., Mackay, A. W., Swann, G. E. A., and Leng, M. J.: Paleoenvironmental reconstruction in East Africa at a critical period of hominin dispersion out-of-Africa (150-80 kyr), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1100, https://doi.org/10.5194/egusphere-egu22-1100, 2022.

It has previously been suggested that climate shifts during the last 2 million years played an important role in the evolution of our genus Homo. However, quantifying this linkage has remained challenging. Here we use an unprecedented transient Pleistocene Coupled General Circulation model simulation in combination with an extensive compilation of fossil and archaeological records, to study the spatio-temporal habitat suitability of five hominin species over the past 2 million years. We show that astronomically-forced changes in temperature, rainfall and terrestrial net primary production had a major impact on their observed distributions. During the early Pleistocene hominins primarily settled in environments with weak orbital-scale climate variability. This behaviour changed drastically after the mid-Pleistocene-transition when archaic humans became global wanderers who adapted to a wide range of spatial climatic gradients, which increased  the likelihood for habitat overlap and cladogenic transitions. Our robust numerical simulations of climate-induced habitat changes provide a novel framework to test hypotheses on our human origin.

How to cite: Timmermann, A., Yun, K., Raia, P., Zollikofer, C., Ponce de Leon, M., Willeit, M., Ganopolski, A., Zeller, E., Ruan, J., and Zeller, E.: Simulating climate effects on archaic human habitats and species successions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2707, https://doi.org/10.5194/egusphere-egu22-2707, 2022.

Lake Victoria is the largest tropical lake on the planet. Located in East Africa at an altitude of 1135 m asl, it lies across the limits between two major climatic zones with a temperature and moisture gradient and associated tropical biomes, the rain forest, and the savanna. At higher altitudes > 1200–2500 m a.s.l. temperatures are significantly lower and vegetation forms an Afromontane belt. Primarily triggered by climate shifts, these three biomes and fire regimes have been dynamically interspersing over the last 17,000 years.

Here, we present a robust ¹⁴C chronology mainly based on macroscopic charcoal using the MICADAS system of LARA at the University of Bern, new palynological data used as biostratigraphic control, and the first continuous charcoal record in Lake Victoria to establish the fire history.

Our pollen and macro–charcoal records, support the assumption that throughout time regional fire dynamics are controlled by biome’s changes, and that climate was the main driver of these vegetation shifts at least until the Iron Age. Our results indicate that during the Last Glacial Maxima and Heinrich Stadial 1, under dry and colder climates the savanna was dominating, with low fire regimes before 15,000 cal yr BP and increased fire occurrence between 15,000 and 14,000 cal yr BP. After this period, the Afromontane forest started to expand, and warmer and humid climates promoted the growth of rain forests and reduced fire events, which is particularly observed in the African Humid Period (between ca. 11,500 and 5000 cal yr BP). Subsequently, our records indicate a global maximum of fire occurrence at 5000 cal yr BP, followed by unexpectedly low fire regimes during the Iron Age and the subsequent periods.

This work is part of a SINERGIA project funded by the Swiss National Foundation which seeks to unravel the long-term causes and consequences of Lake Victoria’s ecosystem dynamics with a special focus on the evolution of fish species and other biotas from the late Pleistocene to the present.

How to cite: Temoltzin-Loranca, Y., Gobet, E., Vannière, B., van Leeuwen, J. F. N., Courtney-Mustaphi, C., Wienhues, G., Szidat, S., Grosjean, M., and Tinner, W.: Postglacial fire regime changes and vegetation dynamics at Lake Victoria, Africa, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2788, https://doi.org/10.5194/egusphere-egu22-2788, 2022.

Based on a set of various marine palaeoclimate proxy records, we investigate African climate variations during the past 5 million years. We use a collection of modern approaches from non-linear time series analysis to identify and characterise dynamical regime shifts as changes in signal predictability, regularity, complexity, and higher-order stochastic properties such as multi-stability. We observe notable nonlinear transitions and important climate events in the African palaeoclimate, which can be attributed to phases of intensified Walker circulation, marine isotope stage M2, the onset of northern hemisphere glaciation, and the mid-Pleistocene transition, and relate them to variations of the Earth's orbital parameters.

How to cite: Marwan, N., Donges, J. F., Donner, R. V., and Eroglu, D.: Integrative multivariate study of past African climate variability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6559, https://doi.org/10.5194/egusphere-egu22-6559, 2022.

Genomic data document multiple episodes of interbreeding among Neanderthals, Denisovans and Homo sapiens. When, where and how often the interbreeding between these hominin populations took place remains unclear. Here, we study the Neanderthal-Denisovan admixture during the past 400 thousand years using a novel habitat model that integrates extensive fossil, archeological, and genetic data with unprecedented transient Coupled General Circulation Model simulations of global climate and vegetation. Our Pleistocene hindcast of habitat suitability reveals pronounced climate-driven zonal shifts in the main overlap region of Denisovans and Neanderthals in central Eurasia. These shifts, which influenced timing and intensity of potential interbreeding events, can be attributed to the response of climate and vegetation to past variations in atmospheric CO₂ and northern hemisphere ice-sheet volume. Therefore glacial/interglacial climate swings likely played an important role in archaic human gene flow and genetic diversification.

How to cite: Ruan, J., Timmermann, A., Yun, K.-S., Zeller, E., and Lemmon, D.: Simulating Pleistocene climate effect on archaic human interbreeding, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6682, https://doi.org/10.5194/egusphere-egu22-6682, 2022.

Climate influenced the evolution of hominins, though the mechanisms and scales are still not well understood. We know that long-term climatic variations, such as wet-dry climate cycles and sea-level change, can change landscapes dramatically. Changes in landscapes can drive early hominins to find different locations to settle, but what kind of environments did they prefer and what role did changing climates play in all this? To research this question, we modeled the climate of the past 3 million years using CESM, made a best estimate of the global biome landscape, and compared the results to an extensive archeological database of hominin findings.

This analysis shows us that early hominins living in Africa predominantly lived in open habitats. When hominins expanded northwards, they adapted to more forested landscapes. While they were able to adapt, most hominin locations were found in areas with less variability and higher local biome diversity, suggesting that hominins prefer stable environmental conditions with a variety of resources nearby. This preference for stability and a landscape that offers diverse biomes is seen for all hominins regardless of species.

How to cite: Zeller, E., Timmermann, A., Yun, K.-S., and Raia, P.: Early hominins were variability avoiders and diversity seekers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6824, https://doi.org/10.5194/egusphere-egu22-6824, 2022.

The East African (hydro-)climate response to perturbations during the deglacial transition (e.g. Older and Younger Dryas) is complex and expressed heterogeneously in different paleoclimatic records. Lake Victoria (LV), Africa’s largest lake, desiccated entirely during the dry last glacial (>16.3 kyr BP) and subsequently refilled as climate conditions got more humid, reaching a highstand during the Early Holocene. However, existing sediment records from LV do not have sufficient resolution to fully resolve short-term hydroclimate changes during the deglacial transition (especially between 14 and 11 kyr BP). There is little direct evidence of late-glacial lake level fluctuations in LV so far because intermediate water depth coring sites suitable to record intermittent lowstands are missing.

By analysing sediment cores along a near-shore/shallow water (current water depth 22 m) to offshore/deep water (current water depth 63 m) coring transect covering the past 16,000 years, we aim at a more accurate spatial and temporal reconstruction of LV’s deglacial lake level history in response to regional hydroclimate changes.

Core stratigraphy and geochemical evidence, combined with a robust radiocarbon chronology, demonstrate a stepwise infilling of the Lake Victoria basin after its last complete desiccation (< 16.3 kyr BP). Following the dry late glacial Heinrich 1 event, an intermediate water level prevailed between 16.3 and 14.4 kyr BP, with uninterrupted deposition of fine-grained, organic matter-rich pelagic muds at our deep-water site and coarser, sandy-clay deposits at the near shore site. A second dry episode during the Older Dryas (~14 kyr BP) is marked by an abrupt decline in lake level with deposition of coarse mollusc shell bearing sediments at the near shore site indicating a littoral depositional environment. This shift in hydroclimate in the Lake Victoria basin is congruent with a brief period of cooling and drying during the Bölling/Alleröd (Dansgard Oeschger Event 1), which is also recorded in other East African Lakes. Subsequently, Lake Victoria reached maximum water levels with the onset of the African Humid Period in the early Holocene at around 11 kyr BP, which is expressed by elevated input of chemically weathered material (e.g. Rb/K) and deposition of fine-grained muds at both the near shore and offshore sites.

How to cite: Wienhues, G., Temoltzin-Loranca, Y., Vogel, H., and Grosjean, M.: New sedimentological evidence of Lake Victoria’s palaeohydrological variability during the last deglacial transition (16-10 kyr BP), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7105, https://doi.org/10.5194/egusphere-egu22-7105, 2022.

The chronology of the arrival of Homo erectus on the island of Java is a cornerstone of paleoanthropology. Understanding the dispersal routes of Homo erectus, but also of other hominin lineages in Asia and across Southeast Asia, depends on this timing. Their dispersal across Sundaland, in particular, is challenged by an extremely transient climatic and geological environment during Early Pleistocene. Furthermore, ages of first appearance of Javanese H. erectus remain controversial. New age constraints based on cosmogenic nuclides ¹⁰Be and ²⁶Al produced in situ indicate that H. erectus reached Java and dwelled at Sangiran at least ~1.4 Ma ago and more probably around 1.8 Ma. During this period, Java was just emerging from the sea while the adjacent Sundaland was a vast and continuous expanse of climatically and environmentally hospitable land connecting Java to mainland Asia, which facilitated the prior dispersal of hominins and terrestrial faunas to the edge of Java. This ancient age makes H. erectus the contemporary of the earliest members of the genus Homo in Africa and Asia, and rejuvenates the question of dispersal and evolutionary pathways across Eurasia and Sundaland.

How to cite: Husson, L., Lebatard, A.-E., Zerathe, S., Braucher, R., Noerwidi, S., Aribowo, S., Carcaillet, J., Natawidjaja, D. H., Bourlès, D. L., and Team, A.: Early Pleistocene route to Sangiran opened to Javanese Homo erectus, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7177, https://doi.org/10.5194/egusphere-egu22-7177, 2022.

Understanding the chronology and environmental context of the earliest hominin expansions into Eurasia is of considerable interest in palaeoanthropology, however, our current knowledge is based on a handful of sites.  Dated to 1.85–1.78 Ma, Dmanisi (southern Georgia) is not only the locus of the earliest Homo fossils in Eurasia but has also yielded stone tools and rich assemblages of vertebrate fossils (1,2).  Whilst Dmanisi fundamentally changed our views on the timing of hominin expansions out of Africa and the technological capabilities of these populations, it has long represented a single site in the region, and little is known about the broader environmental context.

The Debed Valley (located in the Lori Depression, northern Armenia) represents a key area in which to improve our understanding of this early hominin expansion. The area lies at the southeast margins of the Javakheti Plateau, a large volcanic province spanning both southern Georgia and northern Armenia. Current chronological study of the Javakheti-derived lavas places the interval of volcanic activity between 2.1 and 1.6 Ma (3,4). The lavas are exposed along the Debed valley and trap sediment sequences below, within, and atop the flows. 

Here, we present the first results of our ongoing paleoenvironmental and geoarchaeological investigations in the Debed valley. We first present a model of landscape evolution during the Early Pleistocene based on detailed geologic and geomorphic mapping in the valley. We then describe preliminary results from two of the key sequences in the valley: 1) the open-air archaeological site of Haghtanak-3, from which a Mode 1 lithic assemblage has been recovered, and 2) the fluvio-lacustrine sequence of Dzoragyugh-1 paleolake.  We discuss the stratigraphic, sedimentological, and chronological (⁴⁰Ar/³⁹Ar and palaeomagnetism) results from each site and provide linkages between these sites, the geomorphic evolution of the Debed valley, and Dmanisi sequence. Through this, we highlight the environmental and archaeological significance of sedimentary archives in northern Armenia for understanding the nature and environmental context of early hominin expansions into Eurasia.  

1) Ferring, R., Oms, O., Agustí, J., Berna, F., Nioradze, M., Shelia, T., Tappen, M., Vekua, A., Zhvania, D. and Lordkipanidze, D., 2011. Earliest human occupations at Dmanisi (Georgian Caucasus) dated to 1.85–1.78 Ma. Proceedings of the National Academy of Sciences, 108, 10432-10436.

2) Mgeladze, A., Lordkipanidze, D., Moncel, M.-H., Despriee, J., Chagelishvili, R., Nioradze, M., Nioradze, G., (2011). Hominin occupations at the Dmanisi site, Georgia, Southern Caucasus: raw materials and technical behaviours of Europe's first hominins. Journal of Human Evolution 60, 571–596.

3) Lebedev, V.A., Bubnov, S.N., Chernyshev, I.V., Chugaev, A.V., Dudauri, O.Z. and Vashakidze, G.T. (2007). Geochronology and genesis of subalkaline basaltic lava rivers at the Dzhavakheti Highland, Lesser Caucasus: K/Ar and Sr-Nd isotopic data. Geochemistry International 45, 211–225.

4) Trifonov, V.G., Lyubin, V.P., Belyaeva, E.V., Lebedev, V.A., Trikhunkov, Ya.I., Tesakov, A.S., Simakova, A.N., Veselovsky, R.V., Latyshev, A.V., Presnyakov, S.L., Isanova, T.P., Ozhereliev, D.V., Bachmanov, D.M. and Lyapunov, S.M. (2016). Stratigraphic and tectonic settings of Early Paleolithic of North-West Armenia. Quaternary International 420, 178– 198.

How to cite: Sherriff, J. E., Adler, D. S., Arakelyan, D., Gasparyan, B., Lauer, T., Preece, K. J., Sier, M. J., and Wilkinson, K. N.: Developing a chronological and environmental framework of Early Pleistocene hominin expansions in the Caucasus region: Current research in northern Armenia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7421, https://doi.org/10.5194/egusphere-egu22-7421, 2022.

The Early Pleistocene dispersal of Homo out of Africa  is a highly studied and debated topic.  One of the controversies centres on the question of what type of environments hominin species expanded out of Africa into. We conducted a literature review of 163 papers published since 2000 studying the environmental settings of the first Out of Africa expansion. We found that the literature is polarised between two types of hypotheses. On one hand there are papers which describe Homo in the Early Pleistocene as inflexible (compared to Homo sapiens) and incapable of persisting in non-savannah environments, e.g. the ‘savannahstan’ hypothesis. On the other hand there are papers which describe Homo as flexible and able to persist in various environment types, e.g. the variability selection hypothesis. By investigating these hypotheses we are able to move closer to answering the question - as Homo dispersed out of Africa, did they diversify to exploit new environments, or remain within the ranges of their African niche? We analysed the reconstructions of early Homo environments included in these papers. We found that the qualitative language used to describe hominin environments is problematic and impedes the formation of clear conclusions about the environments occupied by early Homo species. However, by forcibly quantifying the descriptions used in 69 (of the original 163) papers we found that the research does not strongly support the savannahstan hypothesis. Instead the environments inhabited by Homo are consistently reconstructed as a mix of environment types (grassland, forest, savannah etc.), with a slight skew towards open habitats. Based on these results, we tentatively suggest that Homo exhibited a preference for heterogeneous “edge” environments during the Pleistocene and as they dispersed out of Africa. However,  in order to further investigate the potential preference of Homo for heterogeneous environments and to build confidence in reconstructions of early human environments in general, quantified reconstructions of the vegetation composition and distribution at early Homo sites are needed. 

How to cite: Foister, T., Tallavaara, M., Fortelius, M., and Wilson, O. E.: Homo heterogenus: Variability in Pleistocene Homo environments., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9664, https://doi.org/10.5194/egusphere-egu22-9664, 2022.

The stratigraphic interval spanning the Aptian-Albian transition is marked by a cluster of short-lived marine anoxic episodes referred to as Oceanic Anoxic Event 1b (OAE 1b). These short-lived episodes are, from the oldest to the youngest, the Jacob, Kilian, Paquier and Leenhardt events. We here aim at testing the impact of the long Milankovitch cycles (1.2-Myr and 2.4-Myr) on the recurrence of these oxygen-deficiency episodes by establishing a precise astrochronology of the OAE 1b interval from the Col de Pré-Guittard section (Albian GSSP, Vocontian Basin, SE France). The section belongs to the “Marnes Bleues Formation”, which is a thick (several hundred metres) clayey formation, interrupted by thin limestone beds and black shale layers, slumps and turbidites, all deposited in the hemipelagic part of the Vocontian Basin. Organic-matter carbon isotope ratios and Total Organic Carbon have been measured to precisely locate these events within the Col de Pré-Guittard section. A magnetic susceptibility signal was obtained from 3500 bulk rock samples collected every 5 cm. The sampling was performed on two parts of the Col de Pré-Guittard section to avoid a multi-decametric slump outcropping in one of the two section below the Kilian Level. However, two thin turbidite layers, near the Jacob and the Paquier events, remained unavoidable. Spectral analyses were performed using the Multi-Taper Method and the evolutive Fourier Transforms. These spectral analyses show the pervasive control of the 100-kyr eccentricity cycle and demonstrates a duration of (i) 1.6 Myr from the Jacob to the Kilian events, (ii) 1.5 Myr from the Kilian to the Paquier events, and (iii) 1.0 Myr from the Paquier to the Leenhardt events. Duration do not correspond to long Milankovitch cycles and thus do not favour the sole orbital control on the pacing of the anoxic events of the Aptian-Albian transition. Thus, other global forcing factors, as the volcanism, or local factors, as basin-scale paleoceanographic and climatic changes, have to be considered to explain this recurrence of anoxic conditions in the Vocontian Basin.

How to cite: Martinez, M., Ait-Itto, F.-Z., Boué, D., Deconinck, J.-F., and Bodin, S.: Is there an orbital control on the pacing of anoxia across the Aptian-Albian boundary (~113 Ma)?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10011, https://doi.org/10.5194/egusphere-egu22-10011, 2022.

Multiproxy paleoenvironmental research in Ethiopia is limited to a handful of studies, mostly situated in central and northern Ethiopia. This results in lasting uncertainties about the nature and timing of the vegetation response to climatic changes such as the African Humid Period and the Holocene aridification, and the imprint of human activities on the vegetation.

Here we present the sedimentary ancient DNA (sedaDNA) and XRF results as part of a multiproxy study in the Gamo Highlands in the southern Ethiopian rift valley. A six meter long sediment core spanning the last 18 thousand years was retrieved from a wetland at Gelba at 2300 m asl in the Gamo Highlands. Previous pollen and charcoal analyses on the core showed a past vegetation dominated by Afromontane forest taxa over the entire record. A first shift in the pollen-based reconstructed vegetation was a decrease of afroalpine vegetation around 13 cal. ka BP, with a relative increase of Afromontane forest taxa. Around 7 cal. ka BP wooded grassland taxa increased. At ca. 2.5 cal. ka BP a sudden change in the vegetation was detected, with increased disturbance indicators and charcoal particles.

Samples spanning the entire core we analyzed for their plant DNA content targeting the extracellular DNA. For the last 2.5 cal. ka BP, both extracellular and total DNA extraction was applied to the investigated samples. The results showed similar results for both approaches, whilst them also being complimentary by each detecting additional taxa. The majority of DNA sequences was derived from herbs and wetland plants, indicating a relatively local vegetation signal. A first observable change in the DNA record occurs at 7 cal. ka BP (with e.g. decreasing Convolvulaceae), but the strongest shift is observed in the period 2.5-2 cal. ka BP, with in particular an increase of Lythraceae and Polygonoideae. The DNA analysis has some taxa in common with the pollen analysis, but both proxies complement each other strongly due to the dominant local versus regional signal they provide. Despite the difference in detected plant taxa, the timing of vegetation transitions matches well between both records.

The XRF results show a highly minerogenic sediment input in the late glacial period. From ca. 13 cal. ka BP, a strong decrease in minerogenic input is observed and the sediment becomes more organic. At ca. 7.5 cal. ka BP, the minerogenic input increases again until 3 cal. ka BP, followed by fluctuating levels of minerogenic elements and increasing phosphorus levels in the last 2000 years.

How to cite: Augustijns, F., Giguet-Covex, C., Tilahun, A. K., Broothaerts, N., and Verstraeten, G.: The paleoenvironmental history of the wetland Gelba in the Gamo Highlands of Ethiopia: a Holocene vegetation reconstruction with sedimentary ancient DNA, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10334, https://doi.org/10.5194/egusphere-egu22-10334, 2022.

There are many interdisciplinary theories as to how climate variability impacted hominin migration, and subsequently human evolution. One such hypothesis concerns so-called “green corridors,” in which climate and biome variability periodically opened vegetated corridors between habitable areas. The periodic opening of these corridors may have acted as a pump through uninhabitable barrier regions, allowing for more wide-spread dispersal. We present results from a climate-forced agent-based model that furthers the green corridor hypothesis to include the effect of stochastic resonance in penetrating barrier regions. In other words, while it intuitively makes sense that hominins would explore and disperse as green corridors opened up, the potential for green corridors to act as a dispersal pump likely depended on having the right amount of stochasticity (randomness) in hominin movement to resonate with orbitally-paced climate signals, effectively penetrating these corridors and dispersing into other regions. We integrate data from a 2-million-year CESM model, from the BIOME4 vegetation model, and from archaeological archives to create a map of habitat suitability based on a species-specific climate envelope. This habitat suitability forces the agent-based hominin migration model, in which agents seek more habitable areas and the added randomness in that agent movement is varied. While our conclusions are largely independent of species, we show results from a Homo erectus migration simulation. In my presentation I will discuss how stochastic hominin movement, the opening up of green corridors, and climate variability affected hominin dispersal throughout the Plio-Pleistocene.

How to cite: Lemmon, D., Timmermann, A., Zeller, E., Ruan, J., Yun, K., and Raia, P.: Stochastic Resonance between Climate Variability and Hominin Migration in an Agent-Based Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11141, https://doi.org/10.5194/egusphere-egu22-11141, 2022.

Surveying at the landscape scale to find archaeological sites is a particular challenge in the dryland environments of Arabia, the Sahara and other similar hyper-arid regions. Here we present how novel high-resolution palaeoydrological mapping of the entirety of the Saharo-Arabian desert belt has not only revealed large numbers of palaeolakes, shorelines and past drainage courses, but also proved particularly fruitful for finding new palaeolithic sites, and lacustrine pleistocene proxy records in Arabia. We describe the integrated survey methodologies which have helped us to locate large numbers of new sites in Arabia, including the earliest fossil and footprints of our species in Arabia, thus helping to enhance our understanding of pleistocene climatic change in these deserts, and of Hominin dispersals into and through them.

How to cite: Breeze, P., Drake, N., Manning, K., and Petraglia, M.: Integrated approaches to locating Pleistocene archaeological and proxy sites in drylands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12497, https://doi.org/10.5194/egusphere-egu22-12497, 2022.

Many classical models of landscape evolution in South Africa have previously relied on large-scale, predominantly qualitative, field observations. In recent decades, however, the development of the accelerator mass spectrometer (AMS) has allowed for greater use of cosmogenic nuclide analyses in landscape evolution studies to quantify rates of denudation and establish timescales of landscape development. In South Africa, various field areas and isotopes have been studied to understand the development of the landscape on Quaternary and longer timescales. The aim of our study is to use a cosmogenic nuclide (¹⁰Be) to investigate the development of geographically separate parts of the South African landscape, and so contribute towards the growing database of landscape evolution rates across southern Africa. Samples of granitic bedrock have been collected along the Olifants River (local/original names: Lepelle, Obalule or iBhalule) in the Kruger National Park in the subtropical east and are being compared to samples of similar composition from the Orange River (local/original names: Gariep, Senqu,) near the Augrabies Falls National Park in the arid west. Both rivers have similar multi-channel morphologies (e.g. mixed bedrock-alluvial anabranching).  A comparison of erosion rates along these otherwise similar rivers at opposite sides of the country will enable an investigation of the effects of climatic differences on erosion rates. Results will allow us to test previous, largely qualitative hypotheses of landscape evolution using state-of-the-art cosmogenic nuclide data analysed at the African continent’s only AMS facility.

How to cite: Khosa, R., Tooth, S., Mbele, V., and Pickering, R.: A Tale of Two Rivers: Comparing erosion rates from two sides of the South African landscape, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-312, https://doi.org/10.5194/egusphere-egu22-312, 2022.

The eastern Mediterranean region is located at divergent climatic zones and contrasting precipitation regimes of the humid Mediterranean climate and hyper-arid Saharo-Arabian desert belt. Important sedimentary archives from lakes allow past hydroclimatic variability to be reconstructed using multiple proxies. This can provide useful insight into potential future water budget scenarios. However, problems associated with chronological uncertainty can prevent insight into regional climatic (a)synchronies. The use of isochronous chronological markers of tephra (volcanic ash) can be a powerful tool in correlating palaeoclimatic records, particularly over vast distances with the development of cryptotephra analyses (non-visible volcanic glass shards).

            The TephroMed project aims to precisely synchronise two key ICDP palaeoclimatic records from eastern Mediterranean through the use of tephrostratigraphic investigations: to the north, in the Anatolian region, Lake Van (PALEOVAN, Litt et al., 2014) and to the south, in the Levant, the Dead Sea (DSDDP, Stein et al., 2011). Both records have undergone lake level reconstructions, indicating contrasting past regional responses to large-scale climatic events (e.g. Finne et al., 2019; Neugebauer et al., 2015). Though both records are dated through absolute and relative methods (radiocarbon, U-Th, varve counting, wiggle-matching), inherited large chronological uncertainties do not allow detailed insight into the potential climatic time-transgressive nature between the two sites. Yet, both records have tephra deposits within their lacustrine sediments, highlighting the potential to facilitate the alignment of both records using tephra (Neugebauer et al., 2021).

Here, we present new major and minor element volcanic glass chemical data from several tephra layers from both Lake Van and the Dead Sea ICDP cores. New geochemical data from selected visible tephra layers in Lake Van are given. The cryptotephra results from the Dead Sea show particular significant findings with volcanic glass derived from potentially several volcanic regions within the Mediterranean (e.g. Anatolia, Italy). This new data can help to facilitate a chronological alignment between the Dead Sea, Lake Van and other important climatic archives in the Mediterranean. In addition, it highlights the importance of distal records in understanding past volcanic eruptions. As a result of these findings, we can now start to answer questions associated with regional expression of past climatic events and their temporal transgression.

References

Finné, M., Woodbridge, J., Labuhn, I., Roberts, C.N., 2019. Holocene hydro-climatic variability in the Mediterranean: A synthetic multi-proxy reconstruction. Holocene 29(5), 847–863

Litt, T., Anselmetti, F.S., 2014. Lake Van deep drilling project PALEOVAN. Quat. Sci. Rev. 104, 1-7.

Neugebauer, I., Brauer, A., Schwab, M.J., Dulski, P., Frank, U., Hadzhiivanova, E., Kitagawa, H., Litt, T., Schiebel, V., Taha, N., Waldmann, N.D., DSDDP Scientific Party, 2015. Evidences for centennial dry periods at ~3300 and ~2800 cal. yr BP from micro-facies analyses of the Dead Sea sediments. Holocene 25, 1358-1371.

Neugebauer, I., Müller, D., Schwab, M.J., Blockley, S., Lane, C.S., Wulf, S., Appelt, O., Brauer, A., 2021. Cryptotephras in the Lateglacial ICDP Dead Sea sediment record and their implications for chronology. Boreas 50 (3), 844-861.

Stein, M., Ben-Avraham, Z., Goldstein, S.L., 2011. Dead Sea deep cores: A window into past climate and seismicity. Eos, Transactions American Geophysical Union 92, 453-454

How to cite: Kearney, R., Schwab, M. J., Neugebauer, I., Pickarski, N., and Brauer, A.: The TephroMed project: Precise synchronising of two key palaeoclimatic ICDP records of the eastern Mediterranean using tephra, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-468, https://doi.org/10.5194/egusphere-egu22-468, 2022.

Carbonate based archives, such as speleothems and cold-water corals, yield valuable information on past states of the climate system. The key chronometer to access the deposition times of these archives is ²³⁰Th/U dating, typically measured using multi-collector inductively coupled plasma mass spectrometers (MC-ICP-MS). Here, we present our Python-based data treatment, correction and age calculation algorithm equipped with a graphical user interface (GUI) which ensures reproducibility and allows for customized calculation constants. We outline the relevance of proper data outlier treatment and review hardware settings such as fade-out times of Faraday cups (FC).  Furthermore, we systematically analyse the effect of variation in different MC-ICP-MS raw data corrections as tailing and process blank on the accuracy of the atomic ratios ²³⁰Th/²³⁸U and ²³⁴U/²³⁸U and the ages. To do so, three speleothem samples of different isotopic concentrations and ages were employed. We find that already a variation in tailing of 10 % causes a deviation on the permille level from the actual age for older samples (~150 ka), whilst younger samples are hardly affected. Process blank (instrumental background) measurements in turn affect the youngest samples strongest, as we found that an unnoticed increase of 50 % of the process blank results in a deviation on the percent level for the youngest sample (few hundred years). On contrary, hydride correction is minor for all samples, thus all time scales. In conclusion, the methods presented here permit routine precision levels of isotope analysis in the order of 5 ε units (1 ε-unit = 10^-4).

How to cite: Kerber, I. K., Kontor, F., Eichstädter, R., Schröder-Ritzrau, A., Warken, S., and Frank, N.: Data treatment and systematic analysis of MC-ICP-MS 230Th/238U-dating of secondary carbonates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4751, https://doi.org/10.5194/egusphere-egu22-4751, 2022.

We investigated sediments from three different depositional environments along the northern Argentine continental margin to assess the main processes controlling sediment deposition since the last glacial period. Further, we evaluated how different depositional conditions affect (bio)geochemical processes within sediments. Sediment cores were collected during expedition SO260 in 2018[1]. Two sites are located at ~1100 m water depth north and south of the Mar del Plata Canyon (N- and S-Middle Slope Site). Another site is situated at the lower continental slope at 3600 m water depth (Lower Slope Site). Reliable age constraints of sediments deposited during the last glaciation at the Argentine margin are difficult to obtain due limited amounts of carbonate. We overcame this issue by combining radio-isotope analyses (¹⁴C,²³⁰Th_ex) with sedimentological, geochemical and magnetic data demonstrating that all sites experienced distinct changes over time.

Both, N- and S-Middle Slope Sites, record at least the last 30 ka. The S-Middle Slope Site is dominated by continuously organic carbon-starved and winnowed sandy deposits, which according to geochemical and magnetic data leads to insignificant sulfate reduction and sulfidation of iron (oxyhydr)oxides. Glacial sedimentation rates at the Middle Slope increase northwards suggesting a decrease in bottom-current strength. The N-Middle Slope Site records a transition from the last glacial period, dominated by organic carbon-starved sands, to the early deglacial period when mainly silty and organic carbon-rich sediments were deposited between 14-15 ka BP. Concurrently, glacial sedimentation rates of ~50 cm/ka significantly increased to 120 cm/ka. We propose that this high sedimentation rate relates to lateral sediment re-deposition by current-driven focusing as response to sea level rise. Towards the Holocene, sedimentation rates strongly decreased to 8 cm/ka. We propose that the distinct decrease in sedimentation rates and change in organic carbon contents observed at the N-Middle Slope Site caused the nonsteady-state pore-water conditions and deep sulfate-methane-transition (SMT) at 750 cm core depth. The Lower Slope Site records the last 19 ka. Continuously high terrigenous sediment input (~100 cm/ka) prevailed during the Deglacial, while sedimentation rates distinctly decreased to ~13 cm/ka in the Holocene. Here, pore-water data suggest current steady-state conditions with a pronounced SMT at 510 cm core depth. Our study confirms previous geochemical-modelling studies at the lower slope, which implied that the observed SMT fixation for ~9 ka at specific depth relates to a strong decrease in sedimentation rates at the Pleistocene/Holocene transition[2].

During the Holocene, total organic and inorganic carbon contents, inorganic carbon mass accumulation rates and XRF Si/Al ratios (preserved diatom flux) increase at our sites. We relate this to increased primary production in surface waters and less terrigenous input along the continental margin. Our multidisciplinary approach presents improved age constraints at the northern Argentine Margin and demonstrates that lateral/vertical sediment transport and deposition was strongly linked to Glacial/Interglacial variations in bottom currents, seafloor morphology, sea level and sediment supply. The dynamic depositional histories at the three sites still exert a significant control on modern sedimentary (bio)geochemical processes.

[1]Kasten et al. (2019).Cruise No. SO260. Sonne-Berichte.

[2]Riedinger et al. (2005).Geochim. Cosmochim. Acta. 69.

How to cite: Melcher, A., Miramontes, E., Geibert, W., Henkel, S., Wilckens, H., Pape, T., Köster, M., Volz, J., Frederichs, T., Bozzano, G., Chiessi, C., Chidolue, N. C., Ngui, O. S., Schwenk, T., and Kasten, S.: Strong changes in depositional conditions during the Late Glacial and the Holocene along the northern Argentina Continental Margin: a multiproxy approach., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8328, https://doi.org/10.5194/egusphere-egu22-8328, 2022.

Refined dating techniques and high-precision radiocarbon dating have enabled more accurate age controls for paleoenvironmental reconstruction of lake systems. However, low bioproductivity and the influence of old carbon have a profound impact on radiocarbon dating series of non-varved sediment records from Arctic lakes. Geochronological tools such as software systems for age-depth modeling provide sophisticated justifications for age-depth relationships. But because there are many different tools available with varying underlying mathematical methods and models, the model output can show diverging results, e.g., for problematic sediment cores with scatter age dating points. A detailed comparison of the results of individual modeling system is therefore often tedious and potentially error-prone. Due to time constraints and a lack of alternative options, users typically only select and apply one modeling system to provide a geochronological timeframe for paleoenvironmental interpretation. Therefore, we introduce our “Linked age and depth modeling” (LANDO) approach that links five modeling systems (Bacon, Bchron, clam, hamstr, Undatable) in a single multi-language Jupyter Notebook. LANDO reduces the effort of using established modeling systems for both single and multiple dating series and makes the results directly comparable. In addition, we introduce an ensemble age-depth model that uses the output from all models to create a data-driven, semi-informed age-depth relationship. In our talk we will highlight our adapted fuzzy change point method, in which we used independent proxy data to evaluate the performance of each modeling system in representing lithological changes. LANDO is already publicly available on GitHub: https://github.com/GPawi/LANDO.

How to cite: Pfalz, G., Diekmann, B., Freytag, J.-C., Syrykh, L., Subetto, D. A., and Biskaborn, B. K.: Using LANDO as a universal wrapper for applying multiple age-depth modeling systems for sediment records from Arctic lake systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8743, https://doi.org/10.5194/egusphere-egu22-8743, 2022.

Radiocarbon (¹⁴C) dating is the standard method for obtaining the age of marine sediments of Holocene and late Pleistocene age. For accurate calibrations, however, this tool relies on precise knowledge of the local radiocarbon reservoir age of the surface ocean, i.e. the regional difference (ΔR) from the average global marine calibration dataset. This parameter has become impossible to measure from modern material samples because of ¹⁴C contamination from extensive testing of thermo-nuclear bombs in the second half of the twentieth century. The local reservoir age can thus only be calculated from the radiocarbon age of samples collected before AD 1950 or from sediment records containing absolute age markers, derived from e.g. tephrochronology or paleomagnetism.

Knowledge of the marine reservoir age around Greenland is sparse and relies on work by a few studies, represented by measurements clustered in local patches. In this study we add new radiocarbon measurements on samples from historical mollusk collections from Arctic expeditions of the late 19^th and early 20^th Century. The 92 new samples are from central east Greenland and the entire western Greenland coast. Although the new data is mostly coastal, it includes a few deeper sites from the Labrador Sea and northeastern North Atlantic Ocean, where deep waters were found to be very young. Together with existing measurements, the new results are used to calculate average ΔR values for different regions around Greenland, all in relation to Marine20, the most recent radiocarbon calibration curve. Despite the significant addition of new measurements, very few data exist for southeastern Greenland, while no data at all is available for the Arctic Ocean coast in northern Greenland.

How to cite: Pearce, C., Özdemir, K. S., Forchhammer, R. C., Detlef, H., and Olsen, J.: The radiocarbon reservoir age of coastal Greenland waters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8868, https://doi.org/10.5194/egusphere-egu22-8868, 2022.

On earth, Calcium-41 is produced as a cosmogenic isotope via neutron capture process, leaving a natural isotopic abundance of 10^-15 on earth surface. Calcium is also of vital importance for the metabolism of biological organisms. Consequently, analysis of the long lived radioactive isotope Calcium-41 is of great importance in geoscience, archeology and life sciences. The half-life of Calcium-41 is 1.03 x 10⁵ years. It is a good candidate in dating rock and bone samples ranging from 50,000 to 1,000,000 years old.

The available techniques for trace analysis of Calcium-41 include accelerator mass spectrometry (AMS) and resonance ionization mass spectroscopy (RIMS). The detection limit of RIMS is on the level of 10^-11 due to the interference of Potassium-41, which is difficult to remove from the sample. The analysis with high-energy AMS is more expensive than the table top apparatus, and it also faces similar problem as RIMS method.

We develop an atom trap trace analysis(ATTA) apparatus for Calcium-41 analysis to the sensitivity of 10^-16 abundance level by one day of single atom counting. ATTA uses laser tuned at the resonant wavelength for a specific element and isotope to slow down and capture single atom by fluorescence radiation. It has a very high selectivity of element and isotope, which is more advantageous than AMS and RIMS to avoid isobar interference. ATTA has been used in analysis of Krypton-81, Argon-39 dating of the hydrological samples. This work on high sensitivity Calcium-41 analysis is very promising in dating the geochemical sample to determine the exposure ages of rocks or in cosmochemistry for investigations on terrestrial ages.

How to cite: Xia, T., Xia, T.-Y., Sun, W.-W., Zhu, H.-M., Jiang, W., and Lu, Z.-T.: Analyzing Ca-41 sample at E-16 abundance level with cold atom trap techniques, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9533, https://doi.org/10.5194/egusphere-egu22-9533, 2022.

Coral microatolls allow for the reconstruction of relative sea level (RSL) and the inference of tectonic deformation along tropical coastlines over the Holocene. Microatolls track RSL with unparalleled vertical precision, and their annual banding allows us to count years precisely over an individual coral’s lifetime; however, RSL histories reconstructed from multiple corals depend on accurate and precise radiocarbon (¹⁴C) or uranium-thorium (²³⁰Th) ages.

We collected coral microatoll slabs from sites in Ilocos Region, northwestern Luzon, Philippines, and dated them with ¹⁴C and ²³⁰Th techniques. Notably, initial RSL reconstructions for some sites disagreed markedly depending on the dating technique used. Attempts to replicate geochronologic analyses have shown that the coral skeletons are susceptible to diagenesis, complicating efforts to accurately determine coral ages.

We are developing a strategy to overcome this limitation. We extracted multiple samples from each microatoll slab for paired ¹⁴C and ²³⁰Th dating. The number of annual bands separating any dated sample was used to further constrain the age of the coral; by subtracting the number of years from each dated sample, samples taken from different parts of the slab can produce independent estimates of the outermost preserved band. After excluding anomalously young replicate ¹⁴C ages and samples flagged as partly calcified by x-ray diffraction, we find that ²³⁰Th ages from a single coral disagree at 4σ in 4 of 8 cases, whereas calibrated ¹⁴C dates overlap at 2σ in 8 of 9 cases for an arbitrary radiocarbon marine reservoir correction, ∆R = 0 yr.

Using OxCal and the Marine20 calibration curve, we apply Bayesian statistics to combine ¹⁴C and ²³⁰Th ages, to estimate ∆R, and to determine the coral ages using the best available data. We further analyze the ∆R value for each coral, and account for overdispersion and underdispersion, whilst generating a ∆R value per site, and an overall ∆R value (inclusive of all sites). We find no statistically significant difference in ∆R for each site, and we calculate an overall ∆R of -155 ± 117 yr for sites in Ilocos Region since the mid-Holocene, though century-scale variability in ∆R may occur.

Additionally, to improve the reliability of our dates, our final dating strategy in OxCal is to apply the previously determined ∆R, to a code that places the corals in sequence (based on precise elevation measurements, morphological similarities, and coral die-down events), along with the ¹⁴C dates that are dated to the outermost preserved band.

How to cite: Mitchell, A., Lim, J., Gopal, A., Meltzner, A., Chan, A., Sarkawi, G., Li, X., Cantillep, A. M., Sarmiento, L. F., Komori, J., Yu, T.-L., Shen, C.-C., Gong, S.-Y., Weil-Accardo, J., Maxwell, K., Lin, K., Lu, Y., Wang, X., and Ramos, N.: Geochronologic methods for dating coral microatolls in the Philippines, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11178, https://doi.org/10.5194/egusphere-egu22-11178, 2022.

Loess-paleosol sequences are among the most important and detailed terrestrial records of local climate and environmental changes during the Pleistocene. The Carpathian Basin can offer a unique opportunity to investigate temporal and spatial variations in dust accumulation, since 20-25% of its area is covered by loess and the thickness of these material is considerable (80-90 m at max).

High-resolution data are available for some loess sections (Jingbian, Sanbahuo, Toshan, Dunaszekcső) making it possible to develop reliable age-depth models and to calculate more precise mass accumulation rates (MARs), being among the most important input data of paleoclimate models. However, these measurements are mostly limited at around 50 k age, because they are based on radiocarbon or quartz luminescence ages.  In our project, the 20 m thick loess-paleosol profile at Süttő, in the northern part of the Carpathian Basin, was investigated first. More than 130 luminescence and some radiocarbon samples were collected during the sampling campaign during the winter of 2020-21. A systematic sampling for porosity/density measurement was also carried out parallel to luminescence sampling.

This profile was previously dated by Novothny et al. using multiple aliquot additive dose Infrared Stimulated Luminescence (IRSL), single aliquot regeneration IRSL with fading correction, and it resulted in the deposition period of the dust during MIS 6 - MIS 2. The luminescence ages in this study are calculated based on the Optically Stimulated Luminescence signal of quartz for the younger part of the sequence and using the post-Infrared IRSL signal of polymineral fine-grains for the older than ~50 ka part of the sequence. The samples were collected from every 20 cm, and every 10^th samples are considered as primary or benchmark samples and therefore complete luminescence tests, residual dose, a-value, and fading measurements are carried out on them. The secondary samples are only measured by shortened measurement routine to optimize the measurement strategy and save measurement time.

Age-depth modelling will be carried out using an R-package specially developed for the Bayesian and inverse modelling of luminescence ages. Based on the constructed age-depth models and the already available datasets MARs will be calculated for each MI stages.

Luminescence properties and variation of dose rate may also have a paleo-environmental relevance, e.g. the luminescence sensitivity of the quartz fraction can refer to the provenance of the dust. Dose rate measurements will be performed by two Canberra type gamma spectrometers equipped with a GX2018 extended range Ge detector and a MiDose alpha/beta counter, which also enables microdosimetric analyses and comparison between the different kinds of detectors.

The research was supported by the NKFIH project K 135509.

How to cite: Ágnes, N., György, S., Dávid, F., Gergely, S., Tamás, V., Diána, C., Tamás, B., Gergő, M., Gábor, Ú., and Erzsébet, H.: High resolution luminescence dating of the Süttő loess-paleosol sequence (MIS 6-2) to create an age depth model and calculate mass accumulation rates - as input data for paleoclimate models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11331, https://doi.org/10.5194/egusphere-egu22-11331, 2022.

Our ability to quantify past climate conditions is crucial for understanding and predicting future climate scenarios as well as landscape evolution. One of the most drastic climatic changes in Earth’s history was the Last Glacial Maximum (LGM) where a significant area of the planet’s surface was covered in ice (Clark et al., 2009). However, most reconstructions of the Earth’s past climate rely on the use of climate proxies (e.g. Jones and Mann, 2004 for a review), which are particularly poorly preserved in terrestrial settings previously covered by ice- thus limiting the applicability of existing methods.

Here, we apply feldspar thermoluminescence (TL) surface paleothermometry (Biswas et al., 2018; 2020) to better constrain the temperature history of exposed bedrock surfaces since the Last Glacial Maximum to present day. The aim of this study is to contribute towards a more detailed understanding of glacial and interglacial temperature fluctuations across the Central and Western Alps. Feldspar TL paleothermometry is a recently developed technique that exploits the dependence of trapped charge on temperature (Biswas et al., 2018). The trapped charge is sourced from feldspar’s crystalline lattice. While a TL signal can be extracted between room temperature and 450°C, traps sensitive to typical surface temperature variations (e.g.10°C) are found between 200°C and 250°C (Biswas et al., 2020). As a result, five thermometers (200°C to 250°C in 10°C intervals) can be used together as a multi-thermometer, and subsequently combined with a Bayesian inversion approach to constrain thermal histories over the last50 kyr (Biswas et al., 2020).

The temperature histories of bedrock samples collected down two vertical transects adjacent to the Gorner (Switzerland) and the Mer de Glace (France) glaciers, which have been exposed progressively since the LGM, will be presented. Preliminary results suggest a temperature difference of ∼10 °C in both locations, which is promising and in agreement with past surface temperatures obtained from other studies.

References:

Biswas, R.H., Herman, F., King, G.E., Braun, J., 2018. Thermoluminescence of feldspar as a multi-thermochronometer to constrain the temporal variation of rock exhumation in the recent past. Earth and Planetary Science Letters, 495, 56-68.

Biswas, R.H., Herman, F., King, G.E., Lehmann, B., Singhvi, A.K., 2020. Surface paleothermometry using low temperature thermoluminescence of feldspar. Climate of the Past, 16, 2075-2093.

Clark, P. U., Dyke, A. S., Shakun, J. D., Carlson, A. E., Clark, J., Wohlfarth, B., Mitrovica, J. X., Hostetler, S. W., and McCabe, A. M., 2009. The Last Glacial Maximum. Science, 325 (5941), 710-714.

Jones, P.D., Mann, M.E., 2004. Climate over past millennia. Reviews of Geophysics, 42, 2004.

How to cite: Elkadi, J., Biswas, R. H., Visnjevic, V., Magnin, F., Lehmann, B., King, G. E., and Herman, F.: Constraining Last Glacial Maximum bedrock surface temperatures in the Western Alps using thermoluminescence paleothermometry., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11906, https://doi.org/10.5194/egusphere-egu22-11906, 2022.

Creating high resolution chronologies in sediment sequences is important for understanding past carbon-climate dynamics, including accurately dating the timing of climate events, and calculating carbon accumulation changes through time. Here we present >100 ¹⁴C dates from UNSWs high-throughput MICADAS (Turney et al. 2021) that help answer key questions about carbon-climate dynamics in the Southern Hemisphere. Peatlands from the southern mid-high latitudes have an important role in the global carbon budget but are underrepresented in global syntheses due to paucity of data. Developing accurate age-depth models from peat sequences is notoriously difficult. Outliers are common, with peat being susceptible to issues such as root penetration and in-wash of sediment. With careful consideration to site selection (Thomas et al. 2019) and material preparation (e.g. sieving out root and rootlet material), the age-depth models presented here demonstrate stratigraphic integrity with no evidence of significant outliers, providing robust and detailed chronologies to enable a range of scientific questions to be answered.

To better constrain the understanding of southern peatland dynamics, we collected and radiocarbon-dated 25 basal peats from across sub-Antarctic islands of the South Atlantic region, doubling the existing available data. We then collated basal peat radiocarbon ages from >35°S and analysed their temporal and spatial distribution. We find two distinct phases of peat formation, at ~16,000 cal years BP and ~13,000 cal years BP, independent of northern hemisphere peat growth. Well-constrained age models from these regions (including a 6 m peat sequence with 55 ¹⁴C dates) show changes in carbon accumulation rates that are consistent with these phases. Potential drivers of these phases include growth disruption via the Antarctic Cold Reversal, and the latitudinal movement of the southern hemisphere westerly winds, with implications for future carbon storage in these under-studied regions.

References

Thomas, Z.A., Turney, C.S.M., Hogg, A., Williams, A.N., Fogwill, C.J., 2019. Investigating Subantarctic 14 C Ages of Different Peat Components: Site and Sample Selection for Developing Robust Age Models in Dynamic Landscapes. Radiocarbon 61, 1–19. doi:10.1017/rdc.2019.54

Turney, C., Becerra-Valdivia, L., Sookdeo, A., Thomas, Z.A., Palmer, J., Haines, H.A., Cadd, H., Wacker, L., Baker, A., Anderson, M., Jacobsen, G., Meredith, K., Chinu, K., Bollhalder, S., Marjo, C., 2021. Radiocarbon protocols and first intercomparison results from the Chronos 14Carbon-Cycle Facility, University of New South Wales, Sydney, Australia. Radiocarbon 63(3), 1003–1023. doi:10.1017/RDC.2021.23

How to cite: Thomas, Z., Cadd, H., Turney, C., Haines, H., Marjo, C., Becerra Valdivia, L., Carter, S., and Brickle, P.: Phases of peatland carbon accumulation in the southern mid-latitudes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12232, https://doi.org/10.5194/egusphere-egu22-12232, 2022.

In the search for very old ice, finding the age of the ice is a key parameter necessary for its interpretation. Most ice core dating methods are based on chronological markers that require the ice to be in stratigraphic order. However, the oldest ice is likely to be found at the bottom of ice sheets, where the stratigraphy is disturbed, or in ablation areas, where the classical methods cannot be used. Absolute dating techniques have recently been developed to provide new constraints on the age of old ice. In particular, ⁸¹Kr measurements provide strong dating constraints for the old ice cores. Still, these measurements are limited in deep ice cores because of the large sample size required (5-6 kg). In addition to ⁸¹Kr dating, we discuss here the analytical performances of a new technique for ⁴⁰Ar dating, which allows us to provide a reliable age with 80g of ice rather than 800g, as previously published. Finally, we present two applications for the ⁸¹Kr and ⁴⁰Ar dating on the bottom of the TALDICE and Dome C ice cores.

How to cite: Landais, A., Orsi, A. O., Fourré, E. F., Jacob, R., Crotti, I., Ritterbusch, F., Lu, Z.-T., Yang, G.-M., and Jiang, W.: Absolute dating of deep ice cores with argon and krypton isotopes., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13260, https://doi.org/10.5194/egusphere-egu22-13260, 2022.

²³⁴U-²³⁸U is a powerful geochronometer that can provide absolute ages of secondary carbonates over a greater interval of time than the well-established ²³⁰Th-U. In this study, we apply ²³⁴U-²³⁸U dating techniques to subaqueous calcite deposits in Devils Hole cave, located in the Amargosa Desert (Nevada, USA). Subaqueous calcite deposits record paleo water table elevations within the cave. Previous work used ²³⁰Th-U dating techniques to reconstruct fluctuations in the local water table over the last 350,000 years (Wendt et al. 2018). We have extended the Devils Hole water table record up to and beyond the ²³⁰Th-U dating limit using both ²³⁰Th-U and ²³⁴U-²³⁸U dating techniques. Precise control (±60.5‰) of the initial ²³⁴U/²³⁸U ratio is possible due to its low variability and high correlation with δ¹³C and δ¹⁸O (Li et al., 2020). Resulting ²³⁴U-²³⁸U age uncertainties are on the order of ±16,000 years for 800,000-year old calcite. The new ²³⁴U-²³⁸U ages allow us to extend the Devils Hole water-table record across the full range of deposition. The resulting 800,000-year record reveals local water-table fluctuated on glacial-interglacial times scales, reaching maximum heights of 20m above modern-day levels. The observed orbital- to millennial-scale fluctuations are interpreted to be primarily driven by climate. Assessing the sensitivity of the Devils Hole water table to various climate modes is key to predicting future water availability in this water-stressed region.

Wendt, K. A., Dublyansky, Y. V., Moseley, G. E., Edwards, R. L., Cheng, H. & Spötl, C., 2018, Moisture availability in the southwest United States over the last three glacial-interglacial cycles Science Advances, 4, https://doi.org/10.1126/sciadv.aau1375.

Li, X.; Wendt, K. A.; Dublyansky, Y.; Moseley, G. E.; Spötl, C. & Edwards, R. L., 2020 Novel method for determining ²³⁴U-²³⁸U ages of Devils Hole 2 cave calcite, Geochronology, https://doi.org/10.5194/gchron-2020-26

How to cite: Steidle, S. D., Wendt, K., Edwards, R. L., Dublyansky, Y., and Spötl, C.: U-series dating of water-table fluctuations in Devils Hole cave (Nevada, USA) over the last 800,000 years, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13299, https://doi.org/10.5194/egusphere-egu22-13299, 2022.

Stable oxygen isotopic composition (δ¹⁸O) of CO₂ produced from carbonates in natural archives is a useful proxy for paleo precipitation and paleo temperature reconstruction. However, there exist multiple factors controlling the δ¹⁸O values, the applications of the δ¹⁸O alone for paleoclimate studies are thus limited. Anomaly in ¹⁷O in carbonates, expressed by Δ′¹⁷O=1000*ln(δ¹⁷O/1000+1)-λ*1000*ln(δ¹⁸O/1000+1) is another proxy to independently constrain aspects of climatic variables such as precipitation source variation and kinetic effects during carbonate precipitation. However, to use ¹⁷O anomaly for such studies, the triple oxygen isotope fractionation exponent (θ= lnα¹⁷/lnα¹⁸) must be known precisely. Knowledge of this parameter is central to emerging applications of carbonate triple oxygen isotopes to paleoclimate and paleo-hydrology studies. Though a number of theoretical and experimental studies have been carried out in the last few years, there remains no consensus on 𝛳 value for carbonate-water system, likely due to kinetic isotope fractionation during precipitation.

Here, we measured Δ′¹⁷O in synthetic carbonates as well as in the water from which the carbonates are precipitated to check how reliable the Δ′¹⁷O value of the parent water can be reconstructed from the carbonates or carbonate-digested CO₂. To determine θ_{carbonate_CO2-water} for precipitated carbonates, we synthesized carbonates in the laboratory at temperatures ranging from 10 ⸰C to 66 ⸰C using passive/active CO₂ degassing method. Triple oxygen isotope compositions of the water were determined using water-CO₂ equilibration followed by CO₂-O₂ exchange method and of the carbonate (CO₂ liberated by acid digestion) using CO₂-O₂ exchange method. We analyzed our isotope data for their possible kinetic isotope effect and determined the 𝛳_{carbonate_CO2-water} value for precipitated carbonates. We find that most of our synthetic carbonate samples did not attain the equilibrium. The 𝛳_{carbonate_CO2-water} increases as the disequilibrium effect increases. We determined the θ_{carbonate_CO2-water} from the samples precipitating in equilibrium. Furthermore, we do not find any differences in the 𝛳_{carbonate_CO2-water} value for carbonate precipitated in equilibrium at 25 ⸰C and 35 ⸰C. An important issue of using Δ′¹⁷O in carbonates is to resolve the 𝛳_acid for acid digestion which is resolved in the present study. Additionally, we determined the temperature dependent variation in 𝛳_acid and find no significant changes between 0 ⸰C and 70 ⸰C.

How to cite: Roy, P., Laskar, A., and Liang, M.-C.: Triple oxygen isotope fractionation of carbonate during carbonate precipitation and acid digestion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-626, https://doi.org/10.5194/egusphere-egu22-626, 2022.

Correlative analytical approaches involving high-spatial resolution microscopy techniques allow for the compositional measurements and spatial imaging of materials at the near-atomic scale. By combining electron backscatter diffraction (EBSD) mapping, electron channeling contrast imaging (ECCI), scanning transmission electron microscopy (STEM) and atom probe tomography (APT) on various geological materials such as minerals and glasses, we have successfully documented element mobility regulated by structural defects. Although these techniques were initially developed in the materials sciences, they are now being applied to a broad range of applications within many subdisciplines of geosciences including geochemistry, geochronology, and economic geology. In one set of experiments, we applied a correlative approach on naturally deformed pyrite from an orogenic gold mine in northern Canada to assess the impact of crystal-plastic deformation on the remobilization of trace elements. This study has led us to propose a new paragenetic model for metallic ore deposits in which deformation creates nanostructures that act as traps for base- and precious-metals. By applying our approach on pyrite that is rich with fluid inclusions, we have also documented two processes that led to proposing a new fluid inclusion-induced hardening model, which is in contrast to the more commonly reported weakening effect of fluids on minerals. To broaden the applications of our approach, we have applied the same suite of analytical techniques to a synthetic andesitic glass to assess whether nanoscale chemical heterogeneities can act as nucleation sites for gas bubbles. The combined results demonstrate the existence of nanoscale chemical heterogeneities within the melt and at the bubble-melt interface supporting the hypothesis that homogeneous nucleation could in fact be a variety of heterogeneous nucleation. The interactions between trace elements and structural defects plays a vital role in determining the mechanical properties of minerals, particularly in fluid-rich environments. These sub-nanometer scale exchanges consequently control meso- to tectonic-scale geological processes. Our research work not only demonstrates the latest advancements in analytical microscopy resolving long-standing geological problems but also brings us closer to bridging the gap between the fields of materials sciences and geosciences.

How to cite: Dubosq, R., Schneider, D., Rogowitz, A., and Gault, B.: Unraveling the secrets of the Earth through nanogeology: A correlative microscopy approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1186, https://doi.org/10.5194/egusphere-egu22-1186, 2022.

Understanding earth materials is critical to creating a sustainable, carbon-neutral society. Earth materials control the feasibility of subsurface energy storage, geothermal energy extraction, and are a source of critical elements for future-proof battery technologies. Perturbations to geological systems can also result in hazards, such as human-induced earthquakes. If we want to tackle the current, pressing scientific questions related to sustainable development for a circular economy, there is an urgent need to make multi-scale, multi-dimensional characterisations of earth materials available to a broad spectrum of earth-science disciplines. In addition to the society-relevant topics, the properties of earth materials determine how the Earth workson the most fundamental level.To overcome this challenge, 15 European facilities for electron and X-ray microscopy join forces to establish EXCITE. EXCITE is a Horizon Europe infrastructure project, and enables access to high-end microscopy facilities and to join the knowledge and experience from the different institutions. By doing so, EXCITE will develop community-driven technological imaging advancements that will strengthen and extend the current implementation of leading-edge microscopy for earth-materials research. In particular, the EXCITE strategy is to integrate joint research programmes with networking, training, and trans-national access activities, to enable both academia and industry to answer critical questions in earth-materials science and technology. As such, EXCITE builds a community of highly qualified earth scientists, develops correlative imaging technologies providing access to world-class facilities to particularly new and non-expert users that are often hindered from engaging in problem-solving microscopy of earth-materials.This presentation gives an overview EXCITE, its activities and open calls, and the progress of the first year of the project.

How to cite: Walter, S., Cnudde, V., Plümper, O., and ter Maat, G.: EXCITE: A European infrastructure to promote electron and X-ray microscopy of Earth materials, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2517, https://doi.org/10.5194/egusphere-egu22-2517, 2022.

Due to the fine-grained nature of shale, organic matter particles are generally micro- and nano-scale in size. Functional groups differ between different organic matter types and as such provide unique chemical information for organic matter. Micro-FTIR can provide direct measurement to characterize sample features at the micrometer scale. However, optical diffraction limits its application at the nanometer scale. As a non-destructive high-resolution scanning probe technique, atomic force microscopy (AFM) is very powerful in nanoscale research and has been widely used in the fields of polymers, semiconductors, electrochemistry and biology. To provide a better combination of AFM’s unique advantages with nanoscale chemical analysis, the AFM-IR technique has been developed in recent years and also attracted the attention of geologists to explore the application in geological materials.

In this research, AFM-IR which is a quite new technique in geological research was used to investigate the in-situ geochemical characteristics of organic matter in shale. Nanoscale molecular composition of individual organic particles was captured nondestructively, and the distribution of typical functional groups was displayed via 2D IR mapping. In our samples, both alginite and inertinite display chemical homogeneity. The former is dominated by oxygenated and aliphatic contents which indicates a higher hydrocarbon generation potential, whereas the latter is dominated by aromatic carbon. In contrast, migrated solid bitumen particles show compositional heterogeneities at the nanometer scale as some are aromatic-rich and others are aliphatic-rich. Finally, linking this advanced nanochemical technique to potential applications in subsurface energy was explored. This research demonstrates that AFM-IR is a powerful tool to examine the in-situ nanoscale geochemical characteristics of different organic matter types, which can also provide implications for energy applications.

How to cite: Wang, K., Ma, L., and Taylor, K. G.: In-situ nanoscale geochemical characterization of organic matter in shale by AFM-IR, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3234, https://doi.org/10.5194/egusphere-egu22-3234, 2022.

Geochronology is fundamental for the understanding of rates and mechanisms of Earth processes, including tectonics, crust formation, ore formation and magmatism. Analytical techniques are mostly applied to the mineral zircon, particularly LA-ICPMS and ID-TIMS dating, which offer the required accuracy, precision and analytical throughput to solve outstanding scientific questions. However, zircon can record multiple geological events within discrete crystallographic domains, so it is crucial to ensure that measurements are completed using optimal precision and accuracy while specifically targeting crystal domains of interest to resolve potentially complex zircon systematics. We explore here a case where the combination of xenocrystic and autocrystic growth zones within same crystals, together with decay damage related lead loss, leads to apparently protracted age spectra, which can erroneously be interpreted in terms of magmatic evolution.

We present LA-ICP-MS and ID-TIMS U-Pb zircon data from a Variscan, 335 Ma old granodiorite from the Alpine basement in the Aar massif (Switzerland), which highlight the potential complexities present in zircon samples and address the need for careful zircon pre-treatment. CL imagery of zircon reveals minor but pervasive secondary alteration, leading to the observed excess scatter in LA-ICPMS dates. Chemical abrasion (CA) as a pre-treatment prior to LA-ICPMS analysis significantly reduces this scatter. CA-ID-TIMS analyses of zircon from this sample yield extremely high precision due to very high radiogenic/common Pb ratios (Pb*/Pb_c), with significant ²⁰⁶Pb/²³⁸U scatter. Due to the elevated precision of these analyses, it is possible to resolve a linear discordance for these data. This indicates that Pb-loss is not the only age component observed, and the volume of zircon analyzed via CA-ID-TIMS does not purely reflect Variscan igneous crystallization. Since CL images also show thin and poorly visible metamorphic rims, we carried out a physical abrasion (PA) pre-treatment prior to chemical abrasion to isolate the Variscan zircon zones from later Alpine overgrowth for CA-ID-TIMS analysis. We interpret a high-precision PA-CA-ID-TIMS ²⁰⁶Pb/²³⁸U age of 335.479 ± 0.041/0.096 Ma (internal non-systematic/external systematic error; MSWD=0.27) as best estimate for Variscan zircon crystallization for this sample. This age overlaps with the result of CA-LA-ICPMS analyses when properly accounting for the total analytical uncertainty, including matrix effects on concentration ratio standardization.

From these data we conclude: (1) mixing of two age components in zircon may lead to an apparent protracted range in ²⁰⁶Pb/²³⁸U age, which can be resolved if isotope analyses yield very high Pb*/Pb_c ratios and thus are very precise. At lower precision zircon age spectra can be erroneously interpreted as reflecting protracted growth, since they will overlap concordia due to elevated ²⁰⁷Pb/²³⁵U uncertainties, as well as in between individual ²⁰⁶Pb/²³⁸U ages. (2) By combining physical and chemical abrasion, we can resolve the observed complexities, by selectively analyzing zircon domains of interest while simultaneously mitigating diffusive Pb-loss. (3) This study shows how analytical precision may dramatically impact on scientific interpretation, as less precise data can easily be mistaken to reflect prolonged magmatic growth, rather than two-component mixing with xenocrystic material. This difference can significantly impact the interpreted lifespan of magmatic systems.

How to cite: Schaltegger, U., Gaynor, S. P., Ruiz, M., and Ulianov, A.: Protracted U-Pb age spectra from complex zircon crystals resolved using high-precision geochronology and selective sample pre-treatment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3540, https://doi.org/10.5194/egusphere-egu22-3540, 2022.

Dating of the extrusive parts of large igneous provinces has been a challenge because of the lack of mineral phases that can be dated by high-precision techniques. This is the case for the rapidly emplaced Drakensberg lavas, part of the Karoo LIP in South Africa and Lesotho. The circulation of hot fluids through the lava stack during rapid emplacement of continental flood basalts develops relatively high degrees of fracturing and alteration of the rocks, which often results in the re-opening of isotopic systems and inaccurate dates. This alteration occurs on varying length scales, from the outcrop to the micrometric scales, creating Argon loss in minerals of interest for ⁴⁰Ar/³⁹Ar dating (i.e. plagioclase) and making the procedure of separation for step-heating ⁴⁰Ar/³⁹Ar a tedious and sometimes ineffective task. Here, we re-approach measuring ⁴⁰Ar/³⁹Ar by directly analyzing leached and unleached thin sections without having to go through mineral separation, and therefore effectively eliminating the mixing issue of mechanically separating the plagioclase crystals. Half of each plagioclase aliquot was leached in acid, and then irradiated at the TRIGA reactor (Oregon State). We used a 193nm excimer UV-laser attached to a noble gas extraction and purification line, and an Argus VI mass spectrometer at the University of Geneva on thick sections for in-situ analysis. Plagioclase separates from the same Karoo lava flow samples were previously analyzed for ⁴⁰Ar/³⁹Ar geochronology using step heating, on aliquots of both leached and unleached plagioclase separates, using the same noble gas analytical equipment. This allows for a direct comparison of the in-situ­ analysis, testing the potential differences between the two different analytical systems and a potential way of assessing differences in accuracy between the two. Preliminary results show that accurate ages can be achieved by this technique at the cost of a larger precision.  

How to cite: Antoine, C., Spikings, R. A., Gaynor, S. P., and Schaltegger, U.: 40Ar/39Ar In-Situ Dating of Altered Mafic Rocks in the Karoo Large Igneous Provinces., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3987, https://doi.org/10.5194/egusphere-egu22-3987, 2022.

Hydrous lattice point defects (OH defects) in quartz (SiO₂) occur through coupled substitution of Si⁴⁺ with a trivalent cation (most commonly Al³⁺) and a hydroxyl group (OH^-). These impurities can be used to investigate its host rock’s crystallization history and may therefore also serve as a tracer for sediment provenance analyses, but are also economically relevant (e.g., high purity quartz sources).

Transmission infrared (IR) spectroscopy has proven to be a very effective method to analyze OH defects down to concentrations of a few weight parts per million water equivalent. This technique, however, requires thin (100 to 200 µm), polished quartz wafers that are cut perpendicular to the crystallographic c-axis. Preparation of a statistically significant number (i.e. > 100) of grains using this approach is very time consuming and requires a skilled operator. Furthermore, IR spectral analysis so far does not follow a standardized protocol, possibly introducing individual biases and hampering reproducibility of as well as comparability between datasets.

In this work, we present a new, standardized procedure for sample preparation, measurement, and data analysis of OH defects in quartz. Sample preparation and IR measurements are significantly sped up and simplified and require relatively little specialized laboratory equipment. Additionally, our data analysis is performed largely automated and based on spectral deconvolution and generation of synthetic spectra before quantification, ensuring quick generation of reproducible results. This new protocol may therefore be another step towards making OH defect analysis accessible to a wider range of geoscientific fields.

How to cite: Jaeger, D. and Stalder, R.: Quantification of OH in quartz via infrared spectroscopy – new protocol for sample preparation and spectral analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4954, https://doi.org/10.5194/egusphere-egu22-4954, 2022.

The spatial distribution of mineral phases in a thin section provides information about the mineral reactions and deformation history of the sample. This information is often difficult to obtain using classical optical microscopy or SEM analyses, as the spatial resolution is too small to provide the necessary overview. SEM Automated Mineralogy (AM) delivers false colour mineral phase maps at the full thin section scale. Combined with full-sized PPL and XPL thin section scans, this provides an exceptional high-resolution overview of the mineral content and microstructures. Moreover, SEM-AM provides quantitative information about the mineral and bulk rock compositions, which can subsequently be used in thermodynamic modelling to establish P-T conditions for the entire, or a subset of, the rock sample.

The structural geology group at Utrecht University recently acquired a SEM-EDS system with Automated Mineralogy capabilities. The accuracy of the EDS system was compared against WDS microprobe measurements, while the SEM-AM based bulk rock composition of the thin section was compared against XRF data from the corresponding sample dummy. Subsequently, the SEM-AM bulk rock composition was used as input for thermodynamic modelling using Perple_X. Independent temperature estimates were established using; i) SEM-EBSD based CPO results on quartz, in conjunction with the quartz recrystallization mechanisms and recrystallized grain size; and ii) titanium-in-quartz using nano-SIMS analyses. Further constraints on fluid-rock-melt interactions were obtained by using LA-ICP-MS.

This workflow is applied to samples from the Cap de Creus region in northeast Spain. Located in the axial zone of the Pyrenees, the pre-Cambrian metasediments underwent HT-LP greenschist- to amphibolite-facies metamorphism, are intruded by pegmatite bodies, and overprinted by greenschist-facies shear zones. The SEM-AM workflow allowed to further constrain the prograde and retrograde P-T conditions in the different metamorphic zones. In addition, at the thin section scale, the results show temporal and spatial variations in the mineral reactions that occurred.  

In the near future, this workflow will be refined and included in the broader correlative microscopy workflow that will be applied in the H2020-funded EXCITE project (https://excite-network.eu/), a European collaboration of electron and x-ray microscopy facilities and researchers aimed at structural and chemical imaging of earth materials. The data will be made available in a FAIR manner through the EPOS (European Plate Observing System) data publication chain (https://epos-msl.uu.nl/).

How to cite: Wessels, R., Kok, T., van Melick, H., and Drury, M.: Constraining P-T conditions using a SEM Automated Mineralogy based workflow – an example from Cap de Creus, NE Spain, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6179, https://doi.org/10.5194/egusphere-egu22-6179, 2022.

Identification of unknown micro- and nano-sized mineral phases is commonly achieved by analysing chemical maps generated from hyperspectral datasets, particularly scanning electron microscope - energy dispersive X-ray spectroscopy (SEM-EDX). However, the accuracy and reliability are limited by subjective human interpretation and instrumental artefacts in the chemical maps. At the same time, machine learning has emerged as a powerful method to overcome the roadblocks. Here, we propose a self-supervised machine learning approach to not only identify unknown phases but also unmix the overlapped chemical signals of individual phases with no need for user expertise in mineralogy. This approach leverages the guidance of gaussian mixture modelling (GMM) clustering fitted on an informative latent space of pixel-wise elemental data points modelled using a neural network autoencoder, and deconvolutes the overlapped chemical signals of phases using non-negative matrix factorisation (NMF). We evaluate the reliability and the accuracy of the new approach using two hyperspectral EDX datasets. The first dataset was measured from an intentionally fabricated sample, where seven known mineral particles are physically overlapping with each other as well as the substrate. Without any prior knowledge, the proposed approach successfully identified all major phases and recovered the original chemical spectra of the individual phases with high accuracy. In the second case, the dataset was collected from a potential vehicular source of particulate matter air pollution, where identification of the individual pollution particles is complicated by the complex nature of the sample. The approach once again was able to identify the potential Fe-bearing ultrafine particles and isolate the background-subtracted elemental signal. We demonstrate a robust approach that potentially brings a significant improvement of mineralogical and chemical analysis in a fully automated manner. In addition, the proposed analysis process has been built into a user-friendly Python code with graphical user interface (GUI) for ease of use by general users.

How to cite: Tung, P.-Y., Sheikh, H., Ball, M., Nabiei, F., and Harrison, R.: Self-supervised Automated Mineralogical and Chemical Analysis for Hyperspectral Datasets, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6787, https://doi.org/10.5194/egusphere-egu22-6787, 2022.

The determination of the electronic structure of iron-bearing compounds at high pressure and high temperature (HPHT) conditions is of crucial importance for the understanding of the Earth’s interior and planetary matter. Information on their electronic structure can be obtained by X-ray emission spectroscopy (XES) measurements, where the iron’s Kβ_1,3 emission provides information about the spin state and the valence-to-core region focusses on the coordination chemistry around the iron and its electronic state. Furthermore, resonant XES (RXES) at the iron’s K-edge reveals even more detailed information about the electronic structure [1].

We present a setup to investigate the electronic structure of iron-bearing compounds in situ at HPHT conditions using XES and RXES. The HPHT conditions are accomplished by diamond anvil cells (DACs) in combination with a portable double-sided Yb:YAG-laser heating setup [2]. The spectroscopy setup contains a wavelength dispersive von Hamos spectrometer in combination with a Pilatus 100K area detector [3]. This setup provides a full Kβ_1,3 emission spectrum including valence-to-core emission in a single shot fashion. In combination with a dedicated sample preparation and use of highly intense synchrotron radiation of beamline P01 at PETRA III, the duration of the measurements is shortened to an extend that in situ XES, including valence-to-core, as well as in situ spin state imaging becomes feasible. The use of miniature diamonds [4] enables RXES measurements at the Fe-K edge. By using different analyzer crystals for the von Hamos spectrometer, simultaneous Kα and Kβ detection are feasible, which provides L-edge and M-edge like information.

The presented sample is siderite (FeCO₃), which is in focus of recent research as it is a candidate for the carbon storage in the deep Earth. Siderite exhibits a complex chemistry at pressures above 50 GPa and temperatures above 1400 K resulting in the formation of carbonates featuring tetrahedrally coordinated CO₄-groups instead of the typical triangular-planar CO₃-coordination. These carbonates are well understood on a structural level but information on their electronic structure is scarce [5-7]. We present information on the sample’s spin state at in situ conditions of about 75 GPa and 2000 K XES Kβ_1,3 imaging  as well as RXES measurements for low and high pressure siderite at ambient temperature conditions for Kα and Kβ emission.

[1] M. L. Baker et al., Coordination Chemistry Reviews 345, 182 (2017)

[2] G. Spiekermann et al.,  Journal of Synchroton Radiation, 27, 414 (2020)

[3] C. Weis et al., Journal of Analytical Atomic Spectroscopy 34, 384 (2019)

[4] S. Petitgirard et al., J. Synchrotron Rad. , 24, 276 (2017)

[5] J. Liu et al., Scientific Reports, 5, 7640 (2015)

[6] M. Merlini et al., American Mineralogist, 100, 2001, (2015)

[7] V. Cerantola et al., Nature Communications 8, 15960 (2017)

How to cite: Albers, C., Sakrowski, R., Spiekermann, G., Libon, L., Wilke, M., Thiering, N., Gretarsson, H., Sundermann, M., Kaa, J., Tolan, M., and Sternemann, C.: Setup to study the electronic structure of iron-bearing compounds in situ at conditions of the Earth’s lower mantle, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7132, https://doi.org/10.5194/egusphere-egu22-7132, 2022.

Next generation, high-resolution datasets to assess the dynamics of geological systems are becoming increasingly important to answer scientific questions that require higher spatial and temporal resolution than the current state-of-the-art. Such questions involve the couplings and feedbacks between tectonic, climatic, and surficial processes that constitute a heavily debated topic in Earth-Systems research. Over the last decades, the insufficient temporal resolution of conventionally derived (U-Th)/He thermochronometric datasets has limited the necessary quantification to track recent changes in erosion rates and relief—two metrics essential to reconstruct the past dynamics of landscapes and evaluate the relative contribution of surface and tectonic processes on erosion.

To overcome this limitation, the ERC-funded COOLER project aims to further the development of high-resolution, ultra-low temperature thermochronology by setting up a world-leading ⁴He/³He laboratory at the University of Potsdam. The centerpiece of the newly established laboratory is a split-flight-tube multi-collector gas-source sector mass spectrometer from Thermo Scientific™ connected to a sample-gas preparation bench, which includes He gas purification equipment along with a diode laser for stepped-heat sample degassing. Important topics of research the instrument will be utilized for include 1) investigation of the glacial imprint on topography, 2) characterization of the couplings between tectonic activity and topographic relief development in response to glaciation, and 3) quantification of glacial erosion relative to fluvial erosion in mountain belts. In addition to serving researchers and students at the University of Potsdam and collaborating institutions, the facility will provide analytical, research, and educational opportunities within the frame of the COOLER project to researchers from across the globe through external workshops.

To illustrate the capabilities of the new laboratory, we present our analytical and experimental methodologies used to obtain reliable high-resolution ⁴He/³He datasets. We focus on accuracy and cross-calibration to ensure minimal analytical bias in our measurements. Growing efforts in the (geo)science community are aimed at establishing best standardization practices and ensuring consistencies between laboratories and/or communities. Accordingly, we focus on ensuring that our methodologies are leading toward a noble-gas standardized method to compare mass spectrometry capabilities over various laboratories, and analytical techniques among the noble-gas communities. Accordingly, our standardized approach, coupled with analytical automation will lead to significant improvement in the accessibility and efficiency of routine ⁴He/³He analyses for geologic applications.

How to cite: Amalberti, J., van der Beek, P., Colleps, C., and Bermard, M.: New high-resolution 4He/3He laboratory at the University of Potsdam: Toward standardized approaches for efficient and reliable routine 4He/3He analyses for thermochronology applications., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7412, https://doi.org/10.5194/egusphere-egu22-7412, 2022.

Volatile organic sulfur compounds (VOSC) are known to occur in natural gas and petroleum reservoirs. These compounds are typically accompanied by H₂S which together, degrade the quality of the petroleum, complicate production due to corrosion of piping, and pose a health risk to workers and local communities. The origins of both H₂S and VOSC in natural gas are only partially understood with the latter being analyzed in only a few cases and its formation processes virtually unknown. Nevertheless, several studies have linked VOSC to H₂S in processes such as thermochemical sulfate reduction (TSR) and kerogen cracking. Hence, VOSC have the potential to act as a proxy for the natural gas and H₂S origins, in-situ TSR and fluid migration pathways.

To better understand the pathways of VOSC formation in natural gas reservoirs, we analyzed natural gas samples (Permian reservoirs, Sichuan Basin, China) and performed a series of pyrolysis experiments. The results of the experiments between methane (CH₄) and H₂S at 360°C for 4-96 hours revealed the only VOSC formed is methanethiol (MeSH) which was identified at ppm concentrations in all experiments. The δ³⁴S values of the MeSH were 2 to 3‰ heavier than the initial H₂S. For comparison, Meshoulam et al., (2021) reported that the reaction between H₂S and pentane (i.e. “wet gas”) that yielded a variety of VOSCs from thiols to methyl-thiophenes in the gas phase and up to methyl-benzothiophenes in the liquid phase. The analysis of natural gases showed that the samples contain a large variety of thiols and sulfides. The diversity of VOSC identified carries some resemblance to that observed by Meshoulam et al., (2021) and may suggest these VOSC are the result of in-reservoir reaction of C₂+ hydrocarbons with H₂S. The analysis of δ³⁴S values of the VOSCs showed they cover a range between +10 to +30‰ while most samples had their VOSC in a narrower range of approximately 8‰. Generally, samples show a positive correlation between H₂S content and VOSCs concentration- thereby implying VOSCs formation in the gas-phase. The δ³⁴S of thiols in five of the samples covered a narrower isotopic range of about 2‰ while the sulfides in the samples spread over a large isotopic range of up to 10‰. This observation suggests the thiols are in isotopic equilibrium with their associated H₂S while the sulfides are not. The reason for this difference is unclear. Further analysis will shed more light on isotopic fractionations between VOSC and H₂S and will thus allow identification of H₂S origins in the studied area.

[1] Meshoulam, A., Said-Ahmad, W., Turich, C., Luu, N., Jacksier, T., Shurki, A., Amrani, A., 2021. Experimental and theoretical study on the formation of volatile sulfur compounds under gas reservoir conditions. Organic Geochemistry, 152, 104175

How to cite: Kutuzov, I., Cai, C., and Amrani, A.: The origins of volatile organic sulfur compounds in natural gas reservoirs, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9146, https://doi.org/10.5194/egusphere-egu22-9146, 2022.

The isotope composition of rainfall provides information on the initial isotope composition of the moisture source, conditions during evaporation and condensation of water vapor, and the rain-out history of an air-parcel. A standard method to analyze the rainfall isotope composition is by using Cavity Ring Down Spectrometry (CRDS). The accuracy of the analysis highly depends on the water isotope standards used, which determines the degree to which absolute values from different labs can be compared. The amount of international water isotope standards like VSMOW2 and SLAP2 primary water standards is extremely limited; therefore the International Atomic Energy Agency recommends calibrating in-house water isotope standards once a year by using VSMOW2 and SLAP2. The isotope range between VSMOW2 and SLAP2 is extreme, with 55.5‰ for d¹⁸O and 427.5‰ for d²H. The isotope range used in a sequence poses a problem for CRDS techniques that are characterized by significant memory effects.

In this study, we compare the behaviors of two different CRDS systems: a Picarro L2140i and a LGR WIA 35EP. We evaluate the relation between isotope differences of subsequent samples and the memory effect. We show that after 100 injections, memory effects may still be visible in hydrogen. Even when the isotope composition of subsequent injections of the same standard or sample does not show a trend anymore, the raw isotope data seems biased towards the isotope composition of multiple different samples or standards run prior. Running long sequences of for example 1100 injections in high precision ¹⁷O mode, also requires several vaporizer septa changes. The timing of a septa change is important, because opening the vaporizer allows water vapor from the atmosphere to enter the otherwise closed system, from which it takes approx. 20 injections to recover to the prior absolute values. Here we aim to provide a more practicle approach to a calibration sequence architecture and number of injections per primary and in-house standards, taking into account the potential drift of the analyzers.

How to cite: Wassenburg, J. A. and Sinha, N.: Improving calibrations of in-house water isotope standards using CRDS and OA-CRDS: memory effects versus drift, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11603, https://doi.org/10.5194/egusphere-egu22-11603, 2022.

High pressure and high temperature experiments performed with laser-heated diamond anvil cells (LH-DAC) are being extensively used in geosciences in order to study matter at conditions prevailing in planetary interiors. Due to the size of the apparatus itself, the samples that are produced are extremely small, on the order of few tens of micrometers. There are several ways to analyze the samples and extract physical, chemical or structural information, using either in situ or ex situ methods. Here, we will compare two nanoprobe techniques, namely nano X-ray fluorescence (nano-XRF) and Nanoscale secondary ion mass spectrometry (NanoSIMS), that can be used to analyze samples synthetized in LH-DAC and recovered using Focused Ion Beam. The two techniques are very different in various aspects, the most important one being that nano-XRF is a deeply penetrative but nondestructive method, whereas NanoSIMS is a surface sensitive and destructive method. The second major difference between the two techniques is that NanoSIMS can probe isotopes, whereas nano-XRF cannot. With both, it is possible to obtain the spatial distribution of chemical elements in the samples.

We used these two nanoprobes to retrieve elemental concentrations and ratios of dilute moderately and highly siderophile elements (few tens of ppm) in quenched experimental melts relevant for the formation of the core of the Earth. We will show those results and discuss the importance of proper calibration for the acquisition of quantifiable results. We have also performed metal–silicate partitioning experiments in which tungsten and molybdenum were incorporated. Those experiments are especially relevant to understand the core–mantle differentiation of the Earth, about 4.5 billion years ago. We will first present and compare metal–silicate partition coefficient obtained by both nano-XRF and NanoSIMS, and second also with results obtained independently by electron microprobe.

How to cite: Blanchard, I., Petitgirard, S., Laurenz, V., Miyajima, N., Wilke, M., Rubie, D., Lobanov, S. S., Hennet, L., Morgenroth, W., Tucoulou, R., Bonino, V., Zhao, X., and Franchi, I.: Chemical Analysis of Trace Elements at the Nanoscale in Samples Recovered from Laser-Heated Diamond Anvil Cell Experiments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13173, https://doi.org/10.5194/egusphere-egu22-13173, 2022.

This presentation describes the structure and morphologies associated with seafloor spreading in the Red Sea inferred from bathymetric, gravity, magnetic and seismic data. We show that the orientation of the structures is consistent with an Arabia-Nubia Euler pole located within the 95% confidence of Ar-Rajehi et al, (2010) Euler pole and with the tectonic model initially proposed by Girdler (1984). At the Red Sea scale, our model shows that a spreading axis extends along its entire length, even though it is mostly covered by allochthonous Middle Miocene salt and Late Miocene minibasins flowing inward from the margins. In the northern Red Sea, oceanic basement is only exposed through small windows within the salt, forming a series of deeps. The seafloor segments symmetrically bisect the new ocean in the south. Right-stepping transform faults that cluster near Jeddah, Zabargad and Ikhwan Islands offset the ridge axis as spreading is getting more oblique towards the Euler Pole. The northern, central and southern Red Sea segments display a well-developed mid-ocean ridge flanked by landward-dipping volcanic basement, typical of slow spreading ridges. In the northern magma poor spreading segment, mantle exhumation is likely at the transition between continental and oceanic crust. Transpression and transtension along transform faults accounts for the exhumation of the mantle on Zabargad Island as well as the collapse of a pull-apart basin in the Conrad deep.

We propose a new structural model for the Red Sea constrained by the geodetic rules of tectonic plates movements on a sphere. Finally, we discuss the effect of the Danakil microplate on the ridge morphology and show that the Arabia-Nubia-Danakil triple junction is likely located further north than previously described, around 18±0.5°N, where we observe a shift in the ridge axis orientation as well as in the spreading orientation.

How to cite: Delaunay, A., Alafifi, A., Baby, G., Fedorik, J., Tapponnier, P., and Dyment, J.: Structure and Morphology of the Mid-Ocean-Ridge in the Red Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1405, https://doi.org/10.5194/egusphere-egu22-1405, 2022.

How to cite: Jolivet, L., Allanic, C., Becker, T., Bellahsen, N., Briais, J., Davaille, A., Faccenna, C., Lasseur, E., and Romanowicz, B.: Continental rifts and mantle convection: Insights from the East African Rift and a new model of the West European Rift System, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1696, https://doi.org/10.5194/egusphere-egu22-1696, 2022.

Corrugated detachments are fundamental crustal structures found in many extensional systems and plate tectonic boundaries, including mid-oceanic ridges and rifted margins. Direct observations of the complete geometry of extensional detachments are rare and our understanding of detachment fault structures and the mechanisms of development of high-angle normal faults and their rotation to lower angles mainly relies on proxy observations, for example seismicity trends, and numerical modelling.

We present interpretations of a high-resolution 3D seismic reflection survey from the hyperextended domain of the Porcupine Basin, Offshore West of Ireland. The 3D data image a highly reflective corrugated surface, the P reflector, that we interpret as an extensional detachment preserved in its slip position that likely developed at the top mantle surface during Jurassic hyperextension of the basin. Within the 3D data, the P reflector covers an area 95 km long and 35 km wide and has a domal shape that is elongate in the N-S direction with a crest at ~6.3 s two way travel time. It is the first time to our knowledge that 3D seismic data has imaged a complete detachment in the hyperextended area of a rifted margin, including its domal shape, the breakaway structures, and the linkage between the steep and shallow segments of the detachment. The resolved texture and geometry of the detachment and its relationship with overlying faults provide a basis for refining current models of detachment formation accommodating extreme extension.

Steep west-dipping faults mark the western frontal margin of the detachment. The steep faults pass eastward into shallower, predominantly west-dipping faults that appear to merge downwards with the P reflector. The P reflector has pronounced E-W corrugations, interpreted to indicate the detachment slip vector. The reflector is also characterised by abrupt changes in dip across N-S transverse ridges. These ridges are spaced on average 10 km apart, they coincide with lines of intersection between the P reflector and large overlying faults, and they often mark the termination of detachment corrugations. We interpret these ridges as recording former locations of the western boundary of the detachment so that they indicate a step-wise westward propagation of the P reflector. While it is generally accepted that detachments develop by oceanward propagation, we suggest that the faceted nature of the detachment indicates that this process is a punctuated one and that the clearly imaged transverse ridges record the oceanward stepping of the detachment with the initiation of a new family of steep faults.

We propose a new concept for the growth of detachments that may be applicable to other detachments that accommodate extreme extension, for example at mid-oceanic slow and ultra-slow spreading ridges.

How to cite: Lymer, G., Childs, C., and Walsh, J.: Punctuated propagation of a corrugated extensional detachment offshore West of Ireland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1799, https://doi.org/10.5194/egusphere-egu22-1799, 2022.

The Afar Depression forms a triple junction between three rift systems: the Red Sea Rift, the Gulf of Aden Rift and the Main Ethiopian Rift. Rifting began in the Oligocene after the eruption of the Ethiopian Flood Basalts. It represents a unique modern example of hotspot-influenced continental breakup. Its emerged position allows detailed field and remote sensing investigations. Important mapping efforts in the area during the 60s and 70s provided very valuable input for the understanding of the local geology but also for the development of global tectonic, volcanological and sedimentary concepts in continental rift settings.

This study presents the compilation of a new geological map which covers the complete Afar depression and includes its Phanerozoic sedimentary and magmatic cover. The map is based on extensive literature research, remote sensing and fieldwork. The geological history of the Afar Depression has also been reviewed. The map evidences the complexity of the rift system with the interaction of distinct tectonic plates, blocks, rift segments, sedimentary basins and volcanic areas that evolve through time and space. This integrative geological map and review is used to reassess and discuss aspects of the style, evolution, kinematics and dynamics of this rift system. Studying this unique modern example of active rifting will help in the better comprehension of rift processes and passive margin development worldwide.

How to cite: Rime, V., Foubert, A., Atnafu, B., and Kidane, T.: New mapping of the Afar Depression: towards the better understanding of rift dynamics in a hotspot-influenced continental rift zone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2208, https://doi.org/10.5194/egusphere-egu22-2208, 2022.

Rifting in Ethiopia is predominantly driven by magmatic intrusion into the rifting crust. Unravelling the dynamics of lithospheric melt migration and storage is paramount to understanding the late-stage development of continental rifts. In particular, extensive geophysical observations of the structure and composition of rifting crust must be supported by petrology to provide a complete picture of rift-related magmatism. We present major element, trace element, and volatile element compositional data for olivine-hosted melt inclusions from the Boku Volcanic Complex (BVC), a monogenetic cone field in the north Main Ethiopian Rift. Through combined CO₂-density-calibrated Raman spectroscopy and secondary ion mass spectrometry we assess the total CO₂ concentrations within the melt inclusions allowing us to estimate pressures of entrapment via CO₂-H₂O solubility models. Our results show that primitive BVC melts carry up to 0.58 wt% CO₂ (mean ~0.2 wt%), with as much as half of the CO₂ in the melt inclusion present within shrinkage bubbles. Volatile solubility models suggest that these melts are stored over a narrow range of depths (10-15 km), consistent with geophysical data and implying the existence of focussed zone of magma intrusion at mid-crustal depths. The expansive range of trace element concentrations in the inclusions illustrate that, at the time of entrapment, compositional heterogeneity remains extant, and melts must therefore be stored in discrete magmatic bodies with limited mixing. Our results have implications for understanding the interplay between magma intrusion and extensional tectonics during continental break-up, such as magmatic compensation of crustal thinning and the thermo-mechanical effects of melt emplacement into the rifting crust.

How to cite: Wong, K., Ferguson, D., Wieser, P., Morgan, D., Edmonds, M., Tadesse, A. Z., and Yirgu, G.: Petrological evidence for focussed mid-crustal magma intrusion in the Main Ethiopian Rift, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2290, https://doi.org/10.5194/egusphere-egu22-2290, 2022.

The continental deposits of the Triassic basins developed along the eastern margin of the Central and North Atlantic show a similar sedimentological evolution, as those of the western margin resulting from the interaction of various processes.

The examples chosen in this work are those of the Mohammedia-Benslimane-ElGara-Berrechid basin MBEB in the Moroccan meseta that we studied in detail in the field, and that we tried to compare with Portugal which is on the same East Atlantic margin.

At the begininig of the Mesozoic, the northwestern part of the African continent was affected by an initial fracturing associated with the early stages of the opening of the Central Atlantic (Atlantic rift) during which several Moroccan Triassic basins are open.

The Mohammedia-Benslimane-ElGara-Berrechid basin is part of the Moroccan western Triassic province, which corresponds to all the basins of the Moroccan Atlantic margin in direct relation with the Atlantic rift. In this basin, an asymmetric rift is set up on the old Hercynian structures during the Carnien-Norien, the paroxysm is reached at the Trias-Lias passage with the installation of basalts (CAMP: Central Atlantique Magmatic Province).

During rifting (syn-rift stage in the Upper Triassic), the MBEB basin experienced three major phases of sediment filling. The first phase is purely continental, the first deposits to arrive in the opening basin are of proximal fluvial origin. Subsequently, the decrease of the paleopente and the rise of the base level generated paleoenvironmental changes in the basin (2nd phase), and the deposition system evolved towards distal environments. During the third phase, the syn-rift sedimentary series recorded a marine incursion in the late Triassic with saliferous sedimentation. This marine intervention is deduced from the presence of a thick saliferous series with a large lateral extension and whose isotopic ratios of sulfur and bromine contents indicate their marine origin. These marine waters are probably of Tethysian origin and are also linked to the opening of the Proto-Atlantic.

In Portugal, the Upper Triassic is represented by two formations in the north of the Lusitanian basin (Palain, 1976): Silves Fm which is fluvial sandstone and Dagorda Fm which includes first dolomites and then evaporites. In this Portuguese basin, the proximal-distal fluvial transition took place at the Norien-Rhétien limit. This also rift-type basin was filled with continental fluvial and alluvial clastic rocks of the Silves Formation, largely derived from the adjacent Iberian highlands of the Meseta. Locally, black shales are present at the top of the Silves and may represent the first marine incursion into the basin.

The comparison between the two basins shows that they followed a similar evolution at the base and in the middle of the series but at the top the MBEB basin presented thick layers of evaporites while that of Portugal presented mainly dolomites attributed to paralic facies.

Palain, C., 1976. Une série détritique terrigene; 'les grès de silves'; Trias et Lias inférieur du Portugal. Mem. Serv. Geol. Portugal, p. 25 (377 pp.)

How to cite: Essamoud, R., Afenzar, A., and Belqadi, A.: Triassic sedimentation on the Eastern Atlantic margin: two examples from Moroccan Meseta and Portugal, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3259, https://doi.org/10.5194/egusphere-egu22-3259, 2022.

Multiple geoscientific studies along the Main Ethiopian and Eastern rifts have revealed that extension via magma intrusion now prevails over plate stretching as the primary mechanism for strain accommodation throughout the crust and mantle lithosphere. However, problematic in this picture is where the Main Ethiopian and Eastern rifts meet, across the low-lying, broadly-rifted, and as-yet poorly-studied Turkana Depression which separates the elevated Ethiopian and East African plateaus. We have so far revealed through body-wave tomography (Kounoudis et al., 2021), that the Depression does not lack mantle dynamic support in comparison to the plateaus, suggesting a significantly thinned crust, resulting from superposed Mesozoic and Cenozoic rifting, most likely explains its low elevations. Slow uppermost-mantle wavespeeds imply the presence of either melt-intruded mantle lithosphere or ponded asthenospheric material below lithospheric thin-spots induced by the region’s multiple rifting phases. To better illuminate the Depression’s lithosphere-asthenosphere system, we conduct a surface-wave analysis to image crust and uppermost-mantle structure using data from the NSF-NERC funded Turkana Rift Arrays Investigating Lithospheric Structure (TRAILS) project broadband seismic network. In particular, we investigate the presence of melt, whether the lithosphere is melt-rich, melt-poor, and/or if ponded zones of asthenosphere exist below variably thinned lithosphere. Group velocity dispersion curves, measured using data from local and regional earthquakes, yield the first high resolution fundamental mode Rayleigh-wave group velocity maps for periods between 4 and 40s for the Turkana Depression. In collaboration with the ongoing TRAILS GPS project, we explore how these results relate to present-day versus past episodes of extension.

Kounoudis, R., Bastow, I.D., Ebinger, C.J., Ogden, C.S., Ayele, A., Bendick, R., Mariita, N., Kiangi, G., Wigham, G., Musila, M. & Kibret, B. (2021). Body-wave tomographic imaging of the Turkana Depression: Implications for rift development and plume-lithosphere interactions. G3, 22, doi:10.1029/2021GC009782.

How to cite: Kounoudis, R., Bastow, I., Ebinger, C., Ogden, C., Ayele, A., Bendick, R., Mariita, N., Kianji, G., Musila, M., and Sullivan, G.: The Crust and Uppermost-Mantle Structure of the Turkana Depression: Insights from Surface-Wave Analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4683, https://doi.org/10.5194/egusphere-egu22-4683, 2022.

During the formation of rifted continental margins, a rift evolves through a number of stages that produce major sedimentary basins and distinct rifted margin domains. While these domains have been classified based on the resulting structures and crustal thickness seen in geophysical data, the evolution of the fault network that produces these domains is not as well understood. Further, margin architecture may be influenced by erosion and sedimentation. Previous studies have qualitatively examined how faults respond to sedimentation during rifting, but there has not been a quantitative study on how variable surface processes efficiency affects fault network properties and the effect this has on rift evolution.

In this study we use a two-way coupling between the geodynamic code ASPECT (Kronbichler et al., 2012) and the surface processes code FastScape (Braun and Willett, 2013) to run 12 high-resolution 2D rift models that represent asymmetric, symmetric, and wide rift types (Neuharth et al., in review). For each rift type, we vary the surface process efficiency by altering the bedrock erodibility (K_f) from no surface processes to low (K_f = 10^-6 m^0.2/yr), medium (10^-5), and high efficiency (10^-4). To analyze these models, we use a novel quantitative fault analysis toolbox that extracts discrete faults from our continuum models and correlates them through space and time (https://github.com/thilowrona/fatbox). This toolbox allows us to track faults and their properties such as the number of faults, their displacement, and cumulative length, to see how they evolve through time, as well as how these properties change given different rifting types and surface processes efficiency.

Based on the evolution of fault network properties, we find that rift fault networks evolve through 5 major phases: 1) distributed deformation and coalescence, 2) fault system growth, 3) fault system decline and basinward localization, 4) rift migration, and 5) continental breakup. Each of these phases can be correlated to the rifted margin domains defined from geophysical data (e.g., proximal, necking, hyperextended, and oceanic). We find that surface processes do not have a large impact on the overall evolution of a rift, but they do affect fault network properties by enhancing strain localization, increasing fault longevity, and reducing the total length of a fault system. Through these changes, they can prolong rift phases and delay continental breakup with increasing surface process efficiency. To summarize, we find that surface processes do not change the overall evolution of rifts, but they do affect fault growth and as a result the timing of rifting.

Braun, J., and Willett, S.D., 2013, A very efficient O(n), implicit and parallel method to solve the stream power equation governing fluvial incision and landscape evolution: Geomorphology, v. 180–181, p. 170–179, doi:10.1016/j.geomorph.2012.10.008.

Kronbichler, M., Heister, T., and Bangerth, W., 2012, High Accuracy Mantle Convection Simulation through Modern Numerical Methods.: Geophysical Journal International, v. 191, doi:doi:10.1111/j.1365-246x.2012.05609.x.

Neuharth, D., Brune, S., Wrona, T., Glerum, A., Braun, J., and Yuan, X.P., (in review at  Tectonics), Evolution of rift systems and their fault networks in response to surface processes, [preprint], doi: https://doi.org/10.31223/X5Q333

How to cite: Neuharth, D., Brune, S., Wrona, T., Glerum, A., Braun, J., and Yuan, X.: Evolution of rift systems and their fault networks in response to surface processes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5758, https://doi.org/10.5194/egusphere-egu22-5758, 2022.

The palaeobathymetric evolution of rifted margins during continental breakup is complex. We investigate the subsidence of Late Triassic to Early Jurassic evaporitic sequences in the proximal and distal parts of the Scotian margin that formed during the opening of the Central Atlantic Ocean.

We use a 3D flexural backstripping technique, which incorporates decompaction and post-breakup reverse thermal subsidence modelling applied to key stratigraphic intervals through the Jurassic down to the Late Triassic base salt. The isostatic evolution of rifted margins depends on crustal thinning, lithosphere thermal perturbation and melt production during rifting and breakup. Quantitative analysis of seismic reflection and gravity anomaly data together with subsidence analysis have also been used to determine crustal thickness variations and ocean–continent transition structure, and to constrain the along strike variability in breakup related magmatism and crustal composition.

Reverse post-breakup subsidence modelling to the Late Triassic base salt restores this horizon at breakup time to near sea level in the proximal domains of the Scotian margin where the continental crust was only slightly thinned during rifting. In contrast, predicted palaeobathymetry of the base salt surface restored to breakup time is greater than 2 to 3 km in the distal parts of the margin where the continental crust was highly thinned (<10km) close to the ocean-continent-transition. One possible interpretation of this is that while the proximal salt underwent post-rift thermal subsidence only, the distal salt was deposited during the latest stage of rifting focused along the distal domains of the Scotian margin, where it underwent additional tectonic subsidence from crustal thinning. This observed difference between the subsidence of proximal and distal salt has been observed elsewhere on the South Atlantic margins (e.g., the Angolan Kwanza margin) and illustrates the complexity of the subsidence and palaeobathymetric evolution of distal rifted margins during breakup.

The deposition of Triassic evaporites occurred before and after the emplacement of the Central Atlantic Magmatic Province (CAMP). The impact of the CAMP on rifting, crustal structure and palaeobathymetric evolution of the Nova Scotia remains to be determined. We do not exclude an additional positive dynamic topography effect at breakup time related to the CAMP magmatic event.

How to cite: Tugend, J., Kusznir, N., Mohn, G., Deptuck, M., Kendell, K., Keppie, F., Morrison, N., and Dmytriw, R.: Palaeobathymetric evolution of the Nova Scotia rifted margin during the Central Atlantic Ocean opening, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5938, https://doi.org/10.5194/egusphere-egu22-5938, 2022.

Early Carboniferous igneous rocks are widespread in the Southern Urals. We have obtained new stratigraphic and isotopic data on plutonic and volcanic complexes, allowing us to determine correlation of their age and to construct a new geodynamic model.

The prevailing tectonic setting in the Southern Urals during the Early Carboniferous was sinistral transtension. Volcanic and plutonic complexes in transtensional zones were synchronously formed along large submeridional orogen-parallel strike-slip faults, but are particularly abundant within two N–S-trending zones: Magnitogorsk and East Ural.

The upper Tournaisian–lower Visean sequence in the Magnitogorsk zone consists mainly of moderately alkaline volcanic rocks, basalt and rhyolite are predominant, but pyroclastic, volcano-sedimentary, terrigenous, and carbonate rocks are also widespread. The middle Visean sequence consists of moderately alkaline basalt, andesite, dacite including lavas, tuffs and tuffites. The thickness of the Lower Carboniferous volcanic group varies from 1200 to 5500 m. The age of the volcanic rocks has been proved by findings of foraminifera in limestone interbeds. The oldest volcanic rocks appear in upper Tournaisian, while the youngest are found in the middle upper Visean. New U–Pb zircon dating using SHRIMP is now in progress.

Volcanic rocks in the East Ural zone occur within a few tectonic sheets. The sequence consists of lavas and tuffs of basalt, basaltic andesite, andesite and rhyolite. The total thickness of the sequence varies from 800 to 1500 m. The age of the sequence is determined by findings of fossil plants as middle Visean.

We studied eight plutons in the Magnitogorsk and six in the East Ural zones. Most of them record several intrusive phases. The composition of the rocks varies from gabbro to granodiorites and granites from normal to moderately alkaline series. We combined our new isotopic data on zircons (SHRIMP) with published ages and came to the following conclusions.

• Two main stages of Early Carboniferous plutonism can be distinguished in the Southern Ural. The first began simultaneously in both zones at the Devonian/Carboniferous boundary (ca. 356–357 Ma) and then changed to volcanic activity at around 346 Ma in the Magnitogosk zone and at around 340 Ma in the East Ural zone, respectively. The second stage began after the termination of volcanic activity and corresponds to 334–327 Ma interval in both zones. So, stages of active volcanism and plutonism alternate in time.
• Early Carboniferous rifting began with intrusion of plutons, usually associated with transtensional zones under oblique collision. The subsequent volcanic stage corresponds to local extension. The next stage of plutonism began just after volcanism termination and marked a cessation of tectonic activity.

The reported study was funded by RFBR and Czech Science Foundation according to the research project № 19-55-26009. Centre of collective usage ‘Geoportal’, Lomonosov Moscow State University (MSU), provided access to remote sensing data.

How to cite: Pravikova, N., Tevelev, A., Kazansky, A., Kosheleva, I., Sobolev, I., Borisenko, A., Koptev, E., Shestakov, P., and Žák, J.: Early Carboniferous rifting in the Southern Urals: New isotopic dating of plutonic and volcanic complexes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6172, https://doi.org/10.5194/egusphere-egu22-6172, 2022.

The East African Rift System (EARS) is the largest active continental rift on Earth. Inherited lithospheric strength variations have played a large role in forming the system’s current geometry. The partly overlapping eastern and western EARS branches encompass the large Victoria continental microplate that rotates counter-clockwise with respect to Nubia, in striking contrast to its neighboring plates.

Both the forces driving rifting in the EARS as a whole and the rotation of Victoria in particular are debated. Whereas some studies largely ascribe the rifting to horizontal mantle tractions deriving from plume-induced flow patterns (e.g., Ghosh et al., 2013), or to more equal contributions of mantle tractions and gravitational potential energy (e.g., Kendall and Lithgow-Bertelloni, 2016), recent work by Rajaonarison et al. (2021) points to a dominant role for lithospheric buoyancy forces in the opening of the rift system. Similarly, other numerical modeling (Glerum et al., 2020) has shown that Victoria’s rotation can be induced through drag of the major plates along the edges of the microplate transmitted along stronger lithospheric zones, with weaker regions facilitating the rotation, without the need for plume-lithosphere interactions (e.g., Koptev et al., 2015; Calais et al., 2006).

With unprecedented data-driven, regional spherical geodynamic numerical models spanning the EARS and the upper 660 km of mantle, we aim to identify the individual contributions of lithosphere and mantle drivers of deformation in the EARS and of Victoria’s rotation. Observational data informs the model setup in terms of crustal and lithospheric thickness, sublithospheric mantle density structure and plate motions. Comparison to separate observations of the high-resolution model evolution of strain localization, melting conditions, horizontal stress directions, topography and horizontal plate motions allows us to identify the geodynamic drivers at play and quantify the contributions of large-scale upper mantle flow to the local deformation of the East African crust.

Calais et al. (2006). GSL Special Publications, 259(1), 9–22.

Ghosh et al. (2013). J. Geophys. Res. 118, 346–368.

Glerum et al. (2020). Nature Communications 11 (1), 2881.

Koptev et al. (2015). Nat. Geosci. 8, 388–392.

Rajaonarison et al. (2021). Geophys. Res. Letters, 48(6), 1–10.

How to cite: Glerum, A., Brune, S., and Ben Mansour, W.: Geodynamic Drivers of the East African Rift System, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7155, https://doi.org/10.5194/egusphere-egu22-7155, 2022.

Fossil carbonate reefs are common along rifts and rifted passive margins. They provide valuable paleoecological and paleogeographical information. Moreover, porous reef buildups are targeted as potential oil and gas reservoirs and sites for gas storage.

The Red Sea and Gulf of Suez contain several generations of reef deposits: (1) syn-rift Early and Middle Miocene reefs that formed along the eroded footwalls of normal faults, and (2) post-rift Pliocene-Holocene coastal reefs that split apart, subsided, and aggraded to form carbonate platforms by salt-driven raft tectonics. The Late Miocene lacks reefs due to evaporitic conditions. This study focuses on the uplifted Early-Middle Miocene reef deposits, which outcrop sporadically along the Arabian and African margins of the Red Sea, particularly the northern half, over a distance of ~1000 km. They are exhumed along the coastal plain at elevations of 50-150 meters. We studied several reefs on the Arabian side and carried out age determination implementing a revised planktonic foraminifera zonation and paleoenvironmental interpretation. We also used satellite images to identify and map similar exhumed reefs on the African side.

The Miocene reefs are located along the eroded footwalls of normal fault scarps that form the first or second marginal half grabens, usually sitting unconformably over the basement. The flat reef and back-reef lagoonal facies are often removed by erosion, but the dipping thick fore-reef talus breccias are preserved. The breccias are an unsorted mix of coral reef and back reef debris and also contain basement clasts. The linear fore-reef talus deposits follow along the fault scarps, revealing paleo-valleys incised into the hanging wall. Placing the reef on the basin-scale helps us distinguish the tectonic influence, accompanied by climate and eustatic sea-level variation, on shallow marine carbonates during rifting.

Mapping all published, newly discovered, and inferred outcrops along the African and Arabian coast of the Red Sea allow us to develop a new tectono-sedimentary model for reef evolution in the syn-rift setting. The proposed model explains the absence of the reef outcrops in the southern areas of the Arabian Red Sea and predicts subsurface zones where reef growth possibly took place. Nature of the contact between reef carbonates and the underlying Precambrian basement in conjunction with the consistently preserved fore-reef zone disclose the uplift history and erosion events prior and post reef growth. In addition, following the reef distribution, we developed a syn-rift paleogeographic model of the Red Sea.

How to cite: Pensa, T., Afifi, A., Delaunay, A., and Baby, G.: Tectonic control on the reef evolution in the Red Sea syn-rift basin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7186, https://doi.org/10.5194/egusphere-egu22-7186, 2022.

Within rifted margins, the necking domain corresponds to the area where drastic reduction in basement thickness leads the crust to attain a wedge-shape. The crustal thinning occurs along detachment fault systems typically recording displacements in the order of 10s of kilometers. These systems commonly shape the crustal taper and eventually the taper break, where crustal thickness is thinned to 10 km or less. In recent years, it has become clear that evolutionary models for detachment fault systems remain unsatisfactory as the well-known principles for smaller magnitude fault systems are not fully applicable to these large-magnitude systems. Consequently, the detailed responses in the foot- and hanging walls and associated basin sedimentation within detachment fault systems and necking domains remain poorly understood compared to those observed in extensional half-graben basins.

We use interpretation of 3D- and 2D seismic reflection data from the Mid-Norwegian rifted margin to discuss the effects of lateral interaction and linkage of extensional detachment faults on the necking domain configuration. We investigate how the structural evolution of these detachment faults interact with the effects of isostatic rollback to produce complex 3D geometries and control the configuration of the associated supradetachment basins. The study area demonstrates how successive incision may induce a complex structural relief in response to faulting and folding. In the proximal parts of the south Vøring and northeastern Møre basins, the Klakk and Main Møre Fault Complexes form the outer necking breakaway complex and the western boundary of the Frøya High. We interpret the previously identified metamorphic core complex within the central Frøya High as an extension-parallel turtleback-structure. The now eroded turtleback is flanked by a supradetachment basin with two synclinal depocenters resting at the foot of the necking domain above the taper break. We attribute footwall and turtleback exhumation to Jurassic-Early Cretaceous detachment faulting along the Klakk and Main Møre Fault Complexes. The study area further demonstrates how detachment fault evolution may lead to the formation of younger, successively incising fault splays locally. Consequently, displacement may occur along laterally linked fault segments generated at different stages in time. Implicitly, the detachment fault system may continue to change configuration and therefore re-iterate itself and its geometry during its evolution.

How to cite: Gresseth, J. L. S., Osmundsen, P. T., and Péron-Pinvidic, G.: Evolution of detachment fault systems within necking domains: insights from the Frøya and Gossa Highs, mid-Norwegian margin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8003, https://doi.org/10.5194/egusphere-egu22-8003, 2022.

How to cite: Ferrante, G., Rivalta, E., and Maccaferri, F.: Spatio-temporal evolution of rift volcanism driven by progressive crustal unloading, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8663, https://doi.org/10.5194/egusphere-egu22-8663, 2022.

Marginal Seas are extensional basins formed in a convergent setting near active subduction zones. They are characterized by a short life (<25 Ma), as well as unstable and changing directions of seafloor spreading. However, the underlying processes involved in their formation from rifting to seafloor spreading initiation are still debated (supra-subduction convection/extension, slab-pull). This problem is further compounded by the fact that our understanding of continental breakup is primarily derived from the evolution of magma-poor and magma-rich Continent-Ocean Transitions (COT) of the Atlantic margins.

In this contribution, we characterize the tectono-magmatic processes acting during continental breakup by investigating the COT structures of three main Marginal Seas located in the Western Pacific, namely the South China Sea, the Coral Sea and the Woodlark Basin. All three examples formed under rapid extension rates and propagation of seafloor spreading. Although each marginal basin has its uniqueness, we show that these three marginal basins are characterized by a narrow COT (typically <~20 km), documenting the sharp juxtaposition of continental crust against igneous oceanic crust. The COT of the three basins shows that final extension is accommodated by the activity of one major low-angle normal fault. This extension is contemporaneous with important magmatic activity expressed by volcanic edifices, dykes and sills emplaced in the distalmost part of these margins. Such narrow COT suggests that a rapid shift from rifting to spreading.

The rapid localization of extensional deformation in a narrow area has major implications for partial melting generation. The evolution of extensional structures is controlled by the interplay of lithospheric thinning, asthenosphere upwelling and decompression melting. High extension rate prevents conductive cooling and lead to focus volcanic activity in a narrow area evolving rapidly in space and time to magmatic accretion. Causes for the fast extensions rates of Marginal Sea rifting are likely controlled by kinematic boundary conditions directly or indirectly controlled by nearby subduction zones. Such mode of breakup is probably not limited to marginal Seas but only enhanced in such settings.

How to cite: Mohn, G., Ringenbach, J.-C., Nirrengarten, M., Tugend, J., McCarthy, A., and Lei, C.: Continental breakup style of Marginal Seas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8715, https://doi.org/10.5194/egusphere-egu22-8715, 2022.

Breakup volcanism along rifted passive margins is highly variable in time and space. The factors controlling magmatic activity during continental rifting and breakup are not resolved and controversial. Here we use numerical models to investigate melt generation at rifted margins with contrasting rifting styles corresponding to those observed in natural systems. Our results demonstrate a surprising correlation of enhanced magmatism with margin width. This relationship is explained by depth-dependent extension, during which the lithospheric mantle ruptures earlier than the crust, and is confirmed by a semi-analytical prediction of melt volume over margin width. The results presented here show that the effect of increased mantle temperature at wide volcanic margins is likely over-estimated, and demonstrate that the large volumes of magmatism at volcanic rifted margin can be explained by depth-dependent extension and very moderate excess mantle potential temperature in the order of 50-80 °C, significantly smaller than previously suggested.

How to cite: Lu, G. and Huismans, R.: Melt volume at Atlantic volcanic rifted margins controlled by depth-dependent extension and mantle temperature, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9420, https://doi.org/10.5194/egusphere-egu22-9420, 2022.

Permian-Triassic rifts of the West Siberian basin compose one of the largest continental rift systems in the world. The Koltogor-Urengoy and Khudosey rifts of meridional strike are the main structures in the eastern part of the basin and are filled mainly by basaltic lavas with clastic sediments. However, in the central part of the West Siberian plate felsic lavas are widespread along with mafic volcanics. Here we present the detailed data on composition of lavas, whole-rock geochemistry, geophysical features and U-Pb ages from the Frolov-Krasnoleninsky region in the central part of the West Siberian basin.

Within the studied region, Permian-Triassic rifts of NW and NE strike are predominant. The main structure is Rogozhnikov-Nazym graben of NW strike, composed of rhyolite-dacitic lavas.  According to the seismic data, this volcanic area comprises multiple local eruptive centers (1-5 km in diameter). Lavas constitute the major part of the volcanic pile, while tuffs are subordinate (up to 15%). Deep boreholes did not reach the base of volcanic sequence, but its thickness exceed 0.5 km.

The main geochemical features of the Rogozhnikov-Nazym volcanics are: 1) acidic composition and increased alkali content; 2) signs of supra-subduction setting: Ta-Nb and Pb anomalies; 3) high ratios of all incompatible trace elements. According to these features, volcanic rocks of the Rogozhnikov-Nazym graben were formed in the setting of post-collisional extension. Furthermore, coeval felsic lavas are widespread in smaller structures of the Frolov-Krasnoleninskiy region and demonstrate similar geochemical characteristics.

We obtained 9 U-Pb (SHRIMP) ages from felsic lavas of the Rogozhnikov-Nazym graben and other rift structures. All samples yielded ages in the range from 254±2 to 248.2±1.3 Ma (Late Permian – Early Triassic). Thus, volcanic activity in the Frolov-Krasnoleninsky region was nearly synchronous to the main phase of Siberian Traps magmatism in the Siberian platform.

Volcanic rocks of the Frolov-Krasnoleninsky region constitute rifts of NW strike (mainly felsic lavas, including the Rogozhnikov-Nazym graben) and NE strike (mainly mafic lavas, geochemically similar to the Siberian Traps basalts). We suggest that orientation of rifts inherits two conjugate strike-slip fault systems, which mark the W-E compression during the preceding collisional event in the Early-Middle Permian, and the mechanism of extension is similar to pull-apart model. The contrasting composition of volcanics can be caused by different-depth zones of magma generation.

The Permian-Triassic volcanics are overlain by continental coal-bearing coarse-grained volcanoclastic sediments of the Chelyabinsk Group (Middle Triassic – Early Jurassic). These deposits fill the local depressions in the paleotopography. The Middle Jurassic clastic Tyumen Formation overlays both volcanic rocks and Chelyabinsk Group, covers almost the entire territory of the Frolov-Krasnoleninsky region and marks the initiation of post-rift subsidence in the West Siberian basin.

How to cite: Smirnova, M., Latyshev, A., Panchenko, I., Kulikov, P., Khotylev, A., and Garipov, R.: Permian-Triassic rifts of the West Siberian basin: evidence of voluminous felsic volcanic activity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9480, https://doi.org/10.5194/egusphere-egu22-9480, 2022.

NE Brazil is scarred by a number of aborted rift basins that developed from the same extensional stresses that lead to the opening of the South Atlantic. Extension started in Late Jurassic times, with the formation of an AfroBrazilian Depression south of the Patos Lineament, and continued through the Early Berriasian along two NS trending axes of deformation: Recôncavo-Tucano-Jatobá (RTJ) and Gabon-Sergipe-Alagoas (GSA). In the Late Berriasian - Early Barremian, rifting jumped North of the Pernambuco Lineament to progress along the NE-SW trending Cariri-Potiguar (CP) axis. In the Late Barremian, approximately coinciding with the opening of the Equatorial Atlantic, rifting aborted along the RTJ and CP axes and continued along the GBA trend eventually resulting in continental break-up. Extension-related magmatic activity seems to have been restricted to break-up along the marginal basins, although dyke swarms bordering the Potiguar basin (Rio Ceará-Mirim) seem to be associated to early extension stages in NE Brazil and three subparallel dolerite dykes, with K-Ar dates of 105±9 Ma, were inferred indirectly from aeromagnetic and outcrop data East of the RTJ axis. Aiming at better understanding the structure and evolution of the syn-rift basins of NE Brazil, a total of 20 seismic stations were deployed between October 2018 and January 2021 along the CP and RTJ trends. The deployment, funded by the national oil company Petrobras, included both broadband and short-period stations borrowed from the Pool de Equipamentos Geofísicos do Brasil. These stations complemented a number of permanent broadband stations belonging to the Rede Sismográfica do Brasil. Receiver functions were obtained for each of the seismic stations from teleseismic P-wave recordings and S-wave velocity models were developed from their joint inversion with dispersion velocities from an independent tomographic study. In the RTJ basins, our results show that the crust is about 41 km thick and displays a thick (5-8 km) layer of fast-velocity material (> 4.0 km/s) at its bottom; in the Potiguar basin, our results show a thinner crust of about 30-35 km underlain by an anomalously slow (4.3-4.4 km/s) uppermost mantle. We argue that those anomalous layers are the result of syn-rift and/or post-rift magmatic intrusions, which would have had the effect of increasing velocity at lower crustal levels under the RTJ basins and decreasing velocity at uppermost mantle depths under the Potiguar basin. If correct, ou interpretation would imply that, in spite of an overall lack of evidence at shallow levels, deep magmatic processes have played a role in the formation and evolution of the syn-rift basins of NE Brazil.

How to cite: Julià, J., Döring, M., and Barbosa, T.: Crustal architecture under the NE Brazil syn-rift basins from receiver functions: Evidence of deep magmatic processes., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9962, https://doi.org/10.5194/egusphere-egu22-9962, 2022.

Since the middle Triassic the long-lived convergent margin of western Gondwana evolved from a relatively steeply inclined into a flat lying slab setting that combined an extensional regime on the backarc side with the telescoping of crustal slices at the continental margin. In the Northern Andes the opening of Late Triassic basins is practically contemporaneous with the outwedging of lower crustal slices, that often alternate with intrusive sheets of S-type granites and mark the limit to a  non-metamorphic roof. A tectonic coupling between backarc collapse and the escape of lower crustal slices can be examined in detail in the northwestern flank of the Sierra Nevada de Santa Marta, a northern-most outlier of the North Andean basement. Remnants of a Late Triassic graben fill attest here to a block tilted toward the hinterland. Its tri-partite sedimentary sequence recycled material sourced from external parts of the continental margin. The basement of a more foreland-oriented block of the Sevilla belt is affected by outward-verging folds, which have formed under greenschist facies conditions in its upper and lower amphibolite conditions in its lower part. The succeeding Inner Santa Marta Metamorphic Belt consists of a stack of high-grade metamorphic basement slices separated by siliciclastic wedges metamorphosed under lower amphibolite conditions. The soles of the basement slices consist of migmatites with remobilized granitic pods and resulting folds oriented in a dip-slip direction. These structures are overprinted by a flattening and a second migmatitic event, which records peak P-T conditions of a lowest crustal level. Accordingly, they contain inclusions of ultramafic rocks. The time-equivalent correspondence between a supracrustal  backarc extension and a foreland-directed stacking of crustal slices suggests some similarity to the model  of a low-viscosity channel of a thickened orogenic crust. An important difference of this flat-slab setting resides, however, in a wholesale mobility of a strongly heated crust that constitutes the backarc and frontal position of this active margin.

How to cite: Avila Paez, M. A., Kammer, A., Conde Carvajal, C. A., Piraquive Bermudez, A., and Gomez Plata, C. N.: Backarc rifting as a response to a crustal collapse at the western Gondwana margin: The Triassic tectonic setting of the Sierra Nevada de Santa Marta, Northern Andes of Colombia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10866, https://doi.org/10.5194/egusphere-egu22-10866, 2022.

Rifted margins are the result of the successful process of thinning and breakup of continents leading to the formation of new oceanic lithosphere. Observations on rifted margins are now integrating an increasing amount of multi-channel seismic data and drilling of several Continent-Ocean Transitions. Based on large scale geometries and domains observed on high-quality long-offset seismic lines, we illustrate a simple classification based on mechanical behavior and magmatic production. Therefore, rifted margins are not divided into opposing types, but described as a combination and continuum that can evolve through time and space from ductile to brittle mechanical behavior on one hand and from magma-poor to magma-rich on the other hand.

For instance, margins such as the Mauritania-Senegal Basin evolve north to south from a magma-poor to a magma-rich margin. Margins such as the Vøring one suffered different rifting episodes evolving from ductile deformation in the Devonian to more brittle and magma-poor rifting in the Cretaceous prior to a final magma-rich breakup in the Paleogene.

Thanks to these examples and to some others, we show the variability of the rifted margins worldwide but also along strike of a single segment and through time along a single margin in order to explore and illustrate some of the forcing parameters that can control the initial rifting conditions but also their evolution through time.

How to cite: Sapin, F.: Rifted margins classification and forcing parameters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11260, https://doi.org/10.5194/egusphere-egu22-11260, 2022.

The breakup of Pangaea in Early Mesozoic times initiated first in the Central Atlantic region, where Triassic to Early Jurassic lithosphere extension led to continental breakup and oceanic accretion. The Central Atlantic rifted margins of NW Africa and eastern North America exhibit complex along-strike variations in structural configuration, crustal geometries, and magmatic budget at breakup. Quantifying these lateral changes is essential to understand the tectonic and geodynamic processes that dominated rifting and continental breakup. The existing seismic refraction lines along the African side and its American conjugate provide good constraints on the 2D crustal architecture of several Central Atlantic margins. However, they are insufficient to quantify the ambiguous lateral variations.

This work examines the central segment of the Moroccan Atlantic margin, which is named here the Sidi Ifni-Tan Tan margin. Using 2D seismic reflection and well data, we quantify the stratigraphic and structural architecture of the margin. We then use this to constrain 2D and 3D gravity models, to predict crustal thickness and types. Ultimately, our results are integrated with previous findings from the conjugate Nova Scotia margin, on the Canadian side, to propose a rift to drift model for this segment of the Central Atlantic and discuss the tectonic processes that dominated rifting and decided the fate of continental breakup.

How to cite: Gouiza, M.: Rift to drift evolution and crustal structure of the Central Atlantic: the Sidi Ifni-Nova Scotia conjugate margins, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11336, https://doi.org/10.5194/egusphere-egu22-11336, 2022.

The East African Rift System (EARS) is the classic example of an active continental rift associated with extension, deformation, lithosphere thinning, and generation of magmas from different mantle domains and depths. Magmatism and tectonics have always been closely linked and their mutual relationships concern many processes such as the kinematics and rates of extension, the passive versus active role of mantle upwelling and magma genesis. In addition, the spatial and temporal variations of the geochemical signature of magmas varies in response to different mantle domains contributing to their genesis (subcontinental lithosphere, asthenosphere and deeper mantle sources).

In this study we carefully screened an exhaustive geochemical database of basalts (including authors’ unpublished data) emplaced in the EARS to decipher the possible connection between different mantle domains, and the evolution and tectonic characteristics of the EARS. The geochemical data were subdivided according to spatial and temporal criteria: from a spatial point of view, the samples were ascribed to five groups, namely Afar, Ethiopia, Turkana depression, Kenya and Tanzania. From a temporal point of view, the magmatic activity of the EARS was subdivided into three main temporal sequences: 45-25 Ma, 25-10 Ma and 10-0 Ma.

The geochemical signature and radiogenic isotopes (Sr, Nd, Pb) of the selected basalts reveal significant spatial and temporal variations and permits to place important constraints on the contribution of subcontinental lithosphere, asthenosphere, and lower mantle in magma genesis

How to cite: Braschi, E., Tommasini, S., Corti, G., and Orlando, A.: Spatial and temporal variation of magmatism in the East African Rift System: influence of tectonics and different mantle domains, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11973, https://doi.org/10.5194/egusphere-egu22-11973, 2022.

When continental lithosphere is extended to break-up it forms two conjugate passive margins. In many instances, these margins are asymmetric: while one is wide and extensively faulted, the conjugate thins more abruptly and exhibits little faulting. Recent studies have suggested that this asymmetry results from the formation of an oceanward-dipping sequential normal fault array and rift migration leading to the observed geometry of asymmetric margins. Numerical models have shown that fault sequentiality arises as a result of asymmetric uplift of the hot mantle towards the hanging wall of the active fault. The preferential localization of strain reinforced by strain weakening effects is random and can happen on either conjugate. However, along the long stretch of the South Atlantic margins, from the Camamu-Gabon to the North Santos-South Kwanza conjugates, the polarity can be very well correlated with the distance of the rift to nearby cratonic lithosphere. Here, we use numerical experiments to show that the presence of a thick cratonic root inhibits asthenospheric flow from underneath the craton towards the adjacent fold belt, while flow from underneath the fold belt towards the craton is favoured. This enhances and promotes sequential faulting and rift migration towards the craton and resulting in a wide faulted margin on the fold belt and a narrow conjugate margin on the craton side, thereby determining the polarity of asymmetry, as observed in nature.

How to cite: Gudipati, R., Pérez-Gussinyé, M., Andres-Martinez, M., Neto-Araujo, M., and Phipps Morgan, J.: Passive margin asymmetry and its polarity in the presence of a craton, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12619, https://doi.org/10.5194/egusphere-egu22-12619, 2022.

The choice of crustal and mantle densities in numerical geodynamic models is usually based on convention. The isostatic component of the topography is, however, in most if not all cases not calibrated to fit observations resulting in not very well constrained elevations. The density distribution on Earth is not easy to constrain because it involves multiple variables (temperature, pressure, composition, and deformation). We provide a review and global analysis of the topography of the Earth showing that elevation of stable continents and active mid-ocean ridges far from hotspots on average is +400 m and -2750 m respectively. We show that density values for the crust and mantle, commonly used for isostatic modeling result in highly inaccurate prediction of topography. We use thermodynamic calculations to constrain the density distribution of the continental lithospheric mantle, sub-lithospheric mantle, the mid-ocean ridge mantle, and review data on crustal density. We couple the thermo-dynamic consistent density calculations with 2-D forward geodynamic modelling including melt prediction and calibrate crustal and mantle densities that match the observed elevation difference. Our results can be used as a reference case for geodynamic modeling that accurately fits the relative elevation between continents and mid-ocean ridges consistent with geophysical observations and thermodynamic calculations. 

How to cite: Theunissen, T., Huismans, R. S., Lu, G., and Riel, N.: Relative continent/mid-ocean ridge elevation: a reference case for isostasy in geodynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12955, https://doi.org/10.5194/egusphere-egu22-12955, 2022.

A holistic understanding of rift initiation, evolution, and variation is made complicated by the difficulties of deep seismic imaging, limited modern examples of continental rifting, and few accessible outcrops of fossil rifted margins. In particular, The temporal structural and rheological evolution of the mantle lithosphere during riftingis poorly constrained. The mantle lithosphere rheology controls lithospheric strength at initiation, but how deformation is partitioned between the crust and mantle,  and how the paths for melt migration from the asthenosphere to the rift surface evolve during rifting is fundamental for our understanding of the rift-to-drift evolution .
Here, we use elastoplastic-viscoelastoplastic modeling in concert with published deep seismic profiles of Atlantic rifted margins and geological insights from the Lanzo peridotite outcrops in the Alps to propose a new mode of extensional tectonics in the subcontinental mantle. We run a series of dynamic models varying initial conditions and mechanisms of deformation localization in the mantle lithosphere consistent with mechanisms of ductile shear zone formation observed at slow spreading centers. Models and geophysical surveys show homologous, sigmoidal reflectors in the mantle, a reversal of fault vergence as seafloor spreading develops, exhumation of the mantle, and increasing magmatic accretion. Geological evidence, along with the coincidence of magmatic accretion and extensional structures in the mantle, suggests that faults in the mantle may serve as conduits for melt, resulting in bright reflectors on seismic profiles.

How to cite: Montiel, N., Massini, E., Lavier, L., and Müntener, O.: Characterizing mantle deformation processes during the rift-to-drift transition at magma-poor margins, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13043, https://doi.org/10.5194/egusphere-egu22-13043, 2022.

Apatite fission track (AFT) thermochronology can resolve thermal histories over a temperature window that spans 50–150°C. Herein, we present a case study from the Peel Plateau, a foreland basin of the Mackenzie Mountains, northern Canadian Cordillera, where we compare three interpretations from a single AFT sample: 1) the central age, and thermal history modelling of 2) a mono-kinetic population and 3) a multi-kinetic population. The AFT sample is derived from a lithic wacke with an Albian depositional age and yields an AFT central age of 67 ± 9 Ma (n: 39). Despite central ages often being interpreted to reflect a sample’s 'cooling age,' laboratory experiments have demonstrated that fission tracks anneal over a wide temperature range, corresponding to the partial annealing zone (PAZ). AFT ages from samples that have undergone multiple burial and exhumation events likely represent partial annealing due to their protracted residence in the PAZ and require thermal history modelling to derive a meaningful geologic interpretation. It is unlikely the Peel Plateau experienced a simple thermal history with rapid cooling through the PAZ, as a regional unconformity separates the Albian and Cenomanian strata across much of the region. Thus, the central age does not necessarily reflect a meaningful thermal event. Thermal modelling the data as a mono-kinetic population predict peak burial temperatures of 118–166°C at 65–92 Ma, however, the sample fails the χ², indicating it does not comprise a single statistical age population. Intra-sample age dispersion is often indicative of samples that comprise multi-kinetic population and grain specific chemistry is known to strongly influence apatite’s annealing kinetics. Most notably apatite with high F content will undergo thermal annealing at lower temperatures than apatite with high Cl content, although numerous other elements (e.g. OH, Mn, Fe) are known to effect annealing kinetics. The r_mro parameter was developed through laboratory annealing experiments, and accounts for compositional controls on apatite’s kinetic behaviour. Apatite grain chemistry was measured via EMPA methods to calculate r_mro values and used to separate AFT samples into two kinetic populations (resulting in pooled ages of 36 ± 5 Ma and 103 ± 12 Ma) that both pass the χ² test. Pooled ages incorporate information of the grains’ pre-depositional history and U-Pb dating can serve as an additional tool to decipher between different kinetic populations. These populations then act as independent thermochronometers capable of resolving different temperature windows. Compared to thermal history model results from mono-kinetic data, the multi-kinetic model predicts significantly lower burial temperatures of 83–93°C, which may have occurred over a longer duration (33–88 Ma). The central age for this sample overlaps with the timing of peak burial predicted by the multi-kinetic model, therefore does not inform us about the cooling history. Ultimately, the purpose of this study is to highlight the importance of assessing multi-kinetic behaviour in sedimentary samples, as these interpretations provide statistically significant age populations and robust thermal history models. Thermal history models that ignore multi-kinetic behaviour may lead to erroneous geologic interpretations.

How to cite: Spalding, J., Schneider, D., and Powell, J.: Central ages, mono-kinetic, or multi-kinetic? Assessing detrital AFT thermochronology in a Cretaceous foreland basin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-61, https://doi.org/10.5194/egusphere-egu22-61, 2022.

Raman Spectroscopy on Carbonaceous Material (RSCM) approach is commonly used to calculate thermal peaks recorded by rocks. A first calibration of the RSCM was developed to measure temperatures ranging from 330°C to 640°C (Beyssac et al., 2002). Its applicability was later expanded to lower temperatures from 200°C to 350°C (Lahfid et al., 2010). Here, we apply the RSCM approach to Digne Nappe area - thrust front of the SW Alps - in order to evaluate the thermal evolution of the sub-Alpine domain from rift to the present. About 150 temperatures have been obtained along seven continuous stratigraphic sections sampled along the strike the whole Digne thrust sheet. The base of the Digne thrust sheet (i.e. the Lias syn-rift carbonates) shows temperatures ranging from 250°C to 330°C. These temperatures are 200-240°C in post-rift marls dated to Callovian-Oxfordian and rapidly drop upsection in the Kimmeridgian-Tithonian carbonates and younger Cretaceous rocks to temperatures below 100-120°C. While these temperatures are seen to decrease from bottom to top we note the lack of well-defined apparent geothermal gradients. One of our section (Serre-Ponçon) structurally positioned beneath the Embrunais-Ubaye thrust sheets is remarkable because the temperatures are rather homogeneous, ranging between 300°C and 350°C along the whole 5km-thick sedimentary pile from the Lias until the Eocene. The regional dataset suggests that the thermal history of the sub-Alpine fold-and-thrust belts varies along-strike and requires the succession of several thermal events. The drop of temperatures observed in the Late Jurassic sediments is interpreted to be related to increasing heat flow during crustal thinning associated to the formation of the Alpine Tethys rifted margin.  The high temperatures observed along the Serre-Ponçon specifically indicate a burial beneath the Embrunais-Ubaye thrust sheets during Alpine orogeny, possibly combined with high geothermal gradients inherited from the Mesozoic Alpine Tethys thinning phase.

How to cite: Célini, N., Mouthereau, F., Lahfid, A., Gout, C., and Callot, J.-P.: Tectono-thermal evolution of the External Western Alps (France): evidence for rift-related thermal event, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3510, https://doi.org/10.5194/egusphere-egu22-3510, 2022.

Temperature is the most important parameter in hydrocarbon generation. Well LKB was drilled to test a section in the Sanga Sanga area of the Neogene Kutei Basin in East Kalimantan. The Sanga Sanga Block contains four large to giant hydrocarbon fields in mid- to upper Miocene deltaic sandstones of the Mahakam Delta, Eastern Kalimantan (Indonesia). Well LKB was drilled to a total depth of 2286 m within a Miocene deltaic sequence. Following the measurement of vitrinite reflectance, the samples are scanned in fluorescence and white light modes to obtain sample descriptions. The mean maximum vitrinite reflectance data provide a basis for inferring some aspects of the thermal history of the sedimentary sequence in well LKB. The well intersected with a small portion of the oil mature level. The conventionally defined principal zone of oil generation (oil window) probably lies in the section from about 1066 to 3962 m. The measured maximum formation temperature at 2286 m is 93,9 ^°C. Assuming a surface temperature of 26 ^°C, the bottom hole temperature (BHT) corresponds to a geothermal gradient of 34,55 ^°C/km. Temperature measurements at intermediate levels give a range of geothermal gradients. The highest temperature gradient results from a single mesurement at depth of about 225 m which would indicate a geothermal gradient of 158,1 ^°C/km. This value is more than three times higher than the gradients obtained from any other measurements downsection. The causes of this extremely high thermal gradient is unknown. Although the presence of faults, overpressured zones, and flux of hot formation water that expelled from deeper parts of the section are possible mechanism, such an extreme geothermal gradient may also be a product of measurement errors that may be related to older reworking and hence it would be more matured. The average geothermal gradient calculated from the other five measurements is more normal by 38,5 ^°C/km.  Modelling the measured levels of maturation using the logging run temperatures gives maturity levels different from those observed. A compromise model that approximately simulates the observed maturity levels can be obtained by assuming a cover loss of about 914 m of sediments since Pliocene, and geothermal gradients respectively of 38 ^°C/km and 30 ^°C/km for pre- and post- Pliocene times, respectively.

How to cite: Jamaluddin, J., Wagreich, M., and Mohamed Sayed, M.: Thermal History of Miocene – Pliocene strata in the Well LKB, Kutei Basin, Indonesia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6545, https://doi.org/10.5194/egusphere-egu22-6545, 2022.

Flexural foreland basins represent first-order geological archives that preserve the record of orogenic processes. These detrital archives provide critical insights into tectonic, climatic and environmental evolution as well as variations in source lithologies, isostasy, eustasy and dynamic lithospheric processes. In this study, we combine published geological data (e.g., facies analysis, magnetostratigraphy, sediment provenance, and carbon and oxygen isotopic records from authigenic minerals) with new zircon U-Pb geochronologic and zircon and apatite (U-Th)/He thermochronologic data from the southern foreland basin of the Alborz Mountains in northern Iran. This orogen, resulting from the Neogene Arabia-Eurasia collision zone, experienced topographic growth and exhumation since ~20 Ma and foreland deposition of a thick pile (> 7 km) of continental red beds.

The foreland-basin fill consists of three major systematic coarsening-upward cycles that each exhibits fine-grained siliciclastic strata at the base with high sediment accumulation rates and younger detrital zircon U-Pb and (U-Th)/He ages (mostly Eocene), followed by coarse-grained sedimentary strata with decreased sediment accumulation rates and older detrital zircon U-Pb and (U-Th)/He ages (> 100 Ma).

The base of each cycle is interpreted as a pulse of enhanced subsidence driven by tectonic loading associated with the growth of new thrust sheets experiencing erosional unroofing. The top of each cycle is interpreted to reflect wanning tectonic subsidence in response to local intra-basinal uplift (cycle 1) as documented by the sedimentary stratal pattern; uplift of the proximal foreland (cycle 3) as suggested by the age distribution of the detrital zircon U-Pb ages, the shift from fluvial to alluvial fan deposits and recycled apatite (U-Th)/He ages from the deepest exhumed red beds. Within these systematic trends, the top of cycle 2 represents an exception as it appears to record an enhanced phase of sediment supply triggered by wetter climatic conditions as documented by oxygen isotope data from paleosols samples.

Overall, our multidisciplinary approach provides a comprehensive overview of the history of a collisional foreland basin, from the forcing mechanisms controlling its stratigraphic architecture and sedimentary composition to its final incorporation into the orogenic wedge associated with basin uplift and erosion.

How to cite: Ballato, P., Stockli, D. F., Hassanzadeh, J., Stockli, L. D., and Strecker, M. R.: The life cycle of a foreland basin: Insights from the Alborz Mountains (Arabia-Eurasia collision zone), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7383, https://doi.org/10.5194/egusphere-egu22-7383, 2022.

The Midland Valley Basin of Scotland (MVS) is a major NE-SW trending, fault-bounded sedimentary basin in central Scotland, UK, comprised predominantly of Carboniferous and Devonian sedimentary rocks. Changing palaeo-environments of the MVS produced alternating successions of sandstone, siltstone, mudstone, limestone and coal. The MVS also experienced folding, fault inversion and development of a widespread unconformity during the latest Carboniferous culmination of the Variscan Orogeny and minor tectonic events thereafter. The MVS’ geological resources played a major role in driving Scotland’s economic, industrial, and cultural development in the 19^th - 20^th. The region was heavily exploited for coal and hydrocarbon energy resources and material for construction, manufacturing, and agriculture. The MVS basin remains as relevant in the 21^st century having been identified as a viable source of low-carbon geo-energy resources (e.g., geothermal energy) and potential for subsurface energy storage (Heinemann et al., 2019).

While the geology of the MVS has been well-studied, thermal and burial history reconstructions have typically relied on techniques focused on the maturation of organic matter (e.g., vitrinite reflectance, VR), which lack quantitative information on timing. Moreover, tracing sediment provenance can be challenging but crucial for understanding the tectonic evolution of the surrounding source region. Here, we present the results of a geochronological and thermochronological investigation of the MVS basin designed to better understand sediment pathways to the basin from surrounding upland regions and the post-depositional thermal history of the MVS. Our data includes zircon and apatite U-Pb data and apatite fission-track (AFT) data from across the basin and AFT data from a UK Geoenergy Observatories borehole in Glasgow.

With our U-Pb data, we identify distant source areas in Greenland, more local source areas in the Scottish Highlands, and recycling of older sedimentary rocks and reworked material in the basin that change through the tectono-magmatic evolution of the basin. Our AFT data and associated thermal history modelling identify three main thermal events: i) Carboniferous-Permian heating; ii) Permian-Mesozoic cooling, and iii) relatively rapid Cenozoic cooling (McKenna, 2021; Hattie, 2021). These are attributed to post-Carboniferous burial followed by post-Permian exhumation. However, ambiguity in some of our models suggests some heating in the Mesozoic may have occurred and, due to the limitations on the temperature sensitivity of the AFT technique, the timing and rate of Cenozoic cooling is poorly resolved. Through our modelling we explore the influence changing palaeo-geothermal gradients has on our thermal history and whether the lower temperature thermochronometer apatite (U-Th)/He can better resolve the most-recent cooling event.

Heinemann, N., Alcalde, J., Johnson, G., Roberts, J. J., McCay, A. T., & Booth, M. G. (2019). Low-carbon GeoEnergy resource options in the Midland Valley of Scotland, UK. Scottish Journal of Geology, 55(2), 93-106.

McKenna, Eamon (2021) The Provenance and thermal histories of the Carboniferous Midland Valley of Scotland, PhD thesis, University of Glasgow.

Hattie, Andrew (2021) Constraining the post-burial history of the central Midland Valley of Scotland using apatite fission track analysis: implications for geothermal energy. MSc(R) thesis, University of Glasgow.

How to cite: Wildman, M., Persano, C., McKenna, E., Hattie, A., and Monaghan, A.: Geology, Geochronology and Geoenergy of Sedimentary Basins: Insights from the Midland Valley of Scotland, UK, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8433, https://doi.org/10.5194/egusphere-egu22-8433, 2022.

The Froan Basin, located on the proximal platform area on the Mid-Norwegian Continental Shelf, contains petroleum-bearing Upper Jurassic syn-rift deposits. Additional isolated Upper Jurassic shallow marine sand bodies have been identified on the Frøya High, but the platform area remains poorly understood in terms of its Late Jurassic tectono-stratigraphic evolution. Improving our understanding, and in particular how fault activity and rift-shoulder uplift influenced rift physiography and the presence of shallow marine reservoirs, is crucial when assessing hydrocarbon prospectivity. In this study, we present a model for the Late Jurassic rift development of the Froan Basin and Frøya High based on seismic interpretation, well data, and reverse subsidence modelling. We show that during the Late Jurassic to Early Cretaceous, major footwall uplift and exposed the western margin of the Froan Basin and Frøya High formed an intra-rift footwall island. Shallow marine areas to the east, immediately adjacent to the footwall island, accumulated shoreface sediments supplied from the eroded footwall. We therefore suggest that the extent of the Late Jurassic shallow marine system was controlled by the magnitude of footwall uplift and geomorphology of the western margin of the platform area.

How to cite: Nakken, L., Chiarella, D., and Jackson, C. A.-L.: Development of a Late Jurassic shallow marine system controlled by footwall uplift in the Froan Basin and Frøya High, offshore Mid-Norway, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10007, https://doi.org/10.5194/egusphere-egu22-10007, 2022.

Located in Northern Morocco, the Rif fold and-thrust belt is mainly made by the remnant of the north African paleo-passive margin and its sedimentary infill. We present in this contribution new field observations combined with paleo-thermal analysis to investigate the formation of the Rif orogenic wedge. Three structural domains are recognized from north to south, namely, the Alboran domain assigned to a meso-Mediterranean continental terrane, the Maghrebian flysch domain that corresponds to the sedimentary cover of the Maghrebian Tethys and the External domain (namely Intrarif, Mesorif and Prerif) that belongs to the former north African margin. The Rif fold and-thrust belt suffered an important Cenozoic Alpine compressional deformation starting from the Late Oligocene-Early Miocene, as a consequence of the closure of the Maghrebian Tethys and the westward translation and docking of the Alboran Domain onto the African margin.

To define the evolution and geometry of thrust sheet stacking and their burial-exhumation paths, a NE-SW regional transect crossing the Maghrebian flysch and the External domains is presented and discussed. A set of 32 samples have been collected for paleo-thermal analysis. The methodological approach consists in combining petrography and Raman micro-spectroscopy on dispersed organic matter, X-ray diffraction of clay minerals and 1D thermal modelling with viable cross section reconstruction and field structural survey.

The highest thermal maturity values along the section (1.00 and 1.15 Ro%) are concentrated in the Cretaceous Intrarif sub-domain (Loukkos and Tangier Intrarifain sub-units) that are structurally squeezed between the Maghrebian flysch domain and the Mesorifain sub-domain. The relationship between organic and inorganic paleo-thermal indicators plotted on Hillier diagram show a thermal signature for the Intrarifain sub-domain typical of continental rift thermal regime. The thermal evolution of the Tangier sub-unit, tectonically overlain by the Numidian-like sandstones has been modelled. The model shows a thermal jump between the two juxtaposed rock units indicating an allochthonous origin of the Numidian-like sandstones, probably detached from the Maghrebian Flysch domain. In the Mesorif sub-domain, data plots on Hillier diagram indicate a continental rift heating regime except for the Lower Miocene Zoumi siliciclastics at the top of it, cropping out between Intrarif and Mesorif sub-domains that falls in a very cold thermal regime, typical of synorogenic basins. The structural relationships between the Cenozoic Zoumi basin and its substratum (Upper Jurassic-Lower Eocene) shows an unconformity where the Paleocene-Eocene is missing, probably indicating a pre-Oligocene compressive phase.

These evidences constrain the geological timing of the Rif belt structuration. According to new models, the whole external Rif deformed between the Early Langhian and Late Tortonian with the front of the chain placed at the boundary between Intrarif and Mesorif, where the Zoumi basin developed during the Late Serravallian-Early Tortonian times.

How to cite: Atouabat, A., corrado, S., Frizon de Lamotte, D., Leprêtre, R., Mohn, G., and Schito, A.: Alpine tectono-thermal evolution of the North African passive paleo-margin incorporated in the Western Rif belt (Northern Morocco), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11175, https://doi.org/10.5194/egusphere-egu22-11175, 2022.

Maturity assessment of solid bitumen is significant for the construction of the thermal evolution history of Sinian carbonate reservoirs in the eastern and central Sichuan Basin because of the absence of vitrinite. Occurrence characteristics of solid bitumen in the Sichuan Basin were investigated by petrography observation. Based on Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy analyses of solid bitumen, the thermal maturity of solid bitumen in the Sinian reservoir was evaluated, and the thermal history of the Sinian reservoirs in the eastern and central Sichuan Basin was further reconstructed. The results show that solid bitumen occurred within intercrystalline pores, intercrystalline dissolution pores, karst caves, fractures, and stylolites in the eastern and central Sichuan Basin. The FTIR spectrums of solid bitumen are characterized by depleted aliphatic carbon and C=O group, and enrichment of aromatic carbon. The FTIR spectrums of solid bitumen indicate that the thermal maturity of solid bitumen in the Sichuan Basin exceeds at least 1.3%. The calculated Ro of solid bitumen in the eastern Sichuan Basin ranges from 3.8 to 4.09%, that of solid bitumen in the central Sichuan Basin ranges from 3.51 to 3.77%, and that of bitumen inclusions in the central Sichuan Basin varies from 3.54 to 3.64% inferred from Raman spectroscopy analysis. The thermal evolution history of Sinian reservoirs in the eastern and central Sichuan Basin can be divided into two heating–cooling stages. At the end of the second heating stage, that is, the Late Cretaceous, the Sinian reservoir reached the highest temperature of 250 °C in the eastern Sichuan Basin and 225 °C in the central Sichuan Basin.

How to cite: Chen, J. and Guo, X.: Maturity assessment of solid bitumen in the Sinian carbonate reservoirs of the eastern and central Sichuan Basin, China: insights from FTIR and Raman spectroscopy analyses, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11719, https://doi.org/10.5194/egusphere-egu22-11719, 2022.

The measurements of soil erosion, sediment transport, and soil deposition due to the tectonic activity regions retard the river basin development. The tectonic activity assessment in this area requires the identification of minimum eroded volume (MEV) and the soil loss (Sl) amount. The MEV, LS, and Hi indices have been used to develop relative tectonic activity Index (RTI) to identify probable zones of Hi, MEV, and SL in the Diyala River Basin (DRB). The results show that the north, north-eastern, and northwestern parts of the (DRB) are situated in the high (RTI) zone. The TIN model is used for estimating the MEV in the DRB and the (RUSLE) model is used for estimating the soil loss in the DRB. The MEV results in the DRB vary from 0 to 845 m3 in some areas. The result of soil loss in the DRB is varied from a minimum value of zero to a maximum of 91.34 t/h/y in some areas. The spatial distribution of MEV and SL in the (DRB) is classified into five types (Low Tectonic Activity, Slight Tectonic Activity, Moderate, High, and Extremely Tectonic Activity). From the results, it was observed that about 25.3% and 24.2% of the total study area are located in the very high relative tectonic activity and low relative tectonic activity zones, respectively. The large percentage of soil loss areas are 28.6% and 26.5% of the total study area are located in the very slight and slight, respectively.

How to cite: Ali, M.: The tectonic  activity assessment using minimum eroded volume and soil loss in Diyala river basin area, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12468, https://doi.org/10.5194/egusphere-egu22-12468, 2022.