CL1.2.1

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.

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 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.

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.

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.

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 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.

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.

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.

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.

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 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.