Displays

SSP1.9

What role did climate dynamics play in human evolution, the dispersal of Homo sapiens within and beyond the African continent, and key cultural innovations? Were dry spells, stable humid conditions, or rapid climate fluctuations the main driver of human evolution and migration? In order to evaluate the impact that different timescales and magnitudes of climatic shifts might have had on the living conditions of prehistoric humans, we need reliable and continuous reconstructions of paleoenvironmental conditions and fluctuations from the vicinity of paleoanthropological and archaeological sites. The search for the environmental context of human evolution and mobility crucially depends on the interpretation of paleoclimate archives from outcrop geology, lacustrine and marine sediments. Linking archeological data to paleoenvironmental reconstructions and models becomes increasingly important.

As a contribution towards a better understanding of these human-climate interactions the conveners encourage submission of abstracts on their project’s research on (geo)archaeology, paleoecology, paleoclimate, stratigraphy, and paleoenvironmental reconstructions. We especially welcome contributions offering new methods for dealing with difficult archive conditions and dating challenges. We hope this session will appeal to a broad audience by highlighting the latest research on paleoenvironmental reconstructions in the vicinity of key sites of human evolution, showcasing a wide variety of analytical methods, and encouraging collaboration between different research groups. Conceptual models, modelling results and model-data comparisons are warmly welcomed, as collaborative and interdisciplinary research.

Keynote speaker:

Prof. Dr. Andrew Cohen (University of Arizona) will talk on:
Continental scientific drilling: A game changer for understanding ecosystem evolution in Africa.

Dr. Annette Hahn (MARUM, University of Bremen) will talk on:
Driving forces of southern African hydroclimate: integrating source to sink and multi-archive studies.

Public information:
During the two time slots of our chat, on Fri 8 May, 08:30–10:15 (Block I) and 10:45–12:30 (Block II), all of the -so far- 10 abstracts with uploaded display material will be open for discussion. The conveners will moderate the chat discussion. We will discuss the abstracts in the order in which they appear in the program and within the allocated time slot of the Block. After we call an abstract, we will ask the author to provide the chat room with a 1-2 line summary of their work (best to copy-paste a pre-written sentence). Then we can proceed to Q&A. We kindly ask all chat room participants to keep the chat on subject, and not to disrupt the Q&A.

Kindly try to upload your display no later than Thursday evening, to avoid technical difficulties during the session, and we will also make time to discuss your contribution too. Don't hesitate to share your science!

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Co-organized by GM10
Convener: Verena E. FoersterECSECS | Co-conveners: Annett Junginger, Inka MeyerECSECS, Janina Bösken, Christian ZeedenECSECS
Displays
| Fri, 08 May, 08:30–12:30 (CEST)

Files for download

Session summary Download all presentations (206MB)

Chat time: Friday, 8 May 2020, 08:30–10:15

Chairperson: Verena Foerster, Christian Zeeden
D796 |
EGU2020-20138
Anya Crocker, B. David Naafs, Thomas Westerhold, Rachael James, Matthew Cooper, Ursula Röhl, Richard Pancost, Colin Osborne, David Beerling, and Paul Wilson

The Sahara is the largest hot desert on Earth and the source of about half of the world’s atmospheric dust which acts to fertilize the Atlantic Ocean and Amazon Basin. The timing and cause of Saharan desert inception are vigorously debated, but northern Africa is widely suggested to have dried progressively with global cooling through the late Cenozoic, favoring both desert and C4-grassland savanna expansion. We present a wide range of data, encompassing sediment geochemistry and grain size distributions, plant wax isotopic signatures and lithogenic radiogenic isotopes to explore when and why desert conditions were established on North Africa. Our work on North Atlantic deep-sea sediments reveals persistent waxing and waning of Saharan dust input, with astronomically forced aridity in the interior of northern Africa more than three times earlier than the widely invoked date for the onset of desert conditions and no major changes in dust source regions over the last 11 Myr. This result strongly suggests that the Saharan desert is older and more dynamic than previously documented. Our data also challenge suggestions of a simple long-term escalation of northern African aridity driving an associated grassland expansion and provide a new framework from which to assess floral and faunal evolutionary outcomes on Africa, including the expansion of the C4-savanna ecosystem and the development of our hominid ancestors. 


D797 |
EGU2020-10826
Stefanie Kaboth-Bahr, Asfawossen Asrat, Andrew S. Cohen, Walter Düsing, Verena Foerster-Indenhuck, Henry Lamb, Mark A. Maslin, Frank Schäbitz, and Martin H. Trauth

It has been a long-standing and passionately discussed hypothesis that important developments in human origins over the last 6-8 Ma coincided with environmental change, including cooling, drying, and wider climate fluctuations. However, testing these hypotheses is difficult as both high resolution climate records and fossil records of early human populations are often incomplete and poorly dated. Thus, to better understand the role that past African climate changes might have played in the evolution and dispersal of our ancestors, in particular Homo sapiens, we have developed a ~620,000 year record of humidity variability from the Chew Bahir basin situated in southern Ethiopia. This 293 m composite lacustrine sediment succession was compiled from two parallel cores HSPDP-CHB14-2A and 2B collected as part of the Hominin Sites and Paleolakes Drilling Project (HSPDP) in 2014. We utilized the log(K/Zr) ratio determined by micro X-ray fluorescence (μXRF) scanning to analyse past moisture changes in the Chew Bahir basin. By placing our results into the existing framework of marine and terrestrial proxy records from various parts of Africa and its surrounding oceans we document a close coupling between the spatio-temporal distribution of African rainfall and sea-surface temperature changes in the Indo-Pacific realm on orbital time scales. We argue that this coupling is facilitated by shifts in the Walker and Hadley circulations in response to insolation variability at the same time.

D798 |
EGU2020-19743
Richard Clark-Wilson, Simon Armitage, and Ian Candy

Orbitally-driven humid phases in arid regions such as the Arabian and Saharan Deserts have played an important biogeographic role in ancient human dispersals, range expansions/contractions and population structure. The timing and regional climatic pattern of humid phases has been shown by multiple long-term continuous palaeoenvironmental records from both marine and terrestrial (speleothems and long palaeolake cores) archives. These attest to episodic humid phases across this region in line with peak interglacial periods over the Pleistocene. However, these records lack detailed information at the scale at which humans interact with the environment, meaning these interactions are poorly understood. To address this, we apply multi-proxy palaeoenvironmental analysis to interdunal carbonate/siliceous sediment beds that formed during episodic humid phases over the past c. 500,000 years in the western Nefud Desert, Saudi Arabia. While such deposits are short relative to many marine, speleothem and palaeolake records, they provide “snapshots” of the palaeoenvironmental conditions experienced by ancient humans. Importantly, these deposits are often directly associated with Lower and Middle Palaeolithic archaeology, demonstrating they were an important locus for ancient human activity during humid phases.

Our analysis demonstrates that humid intervals related to MIS 11, 9, 5e and 5a follow a simple environmental pattern where relatively stable interdunal lake bodies existed through a single humid phase. In contrast, MIS 7 is climatically complex as the sediment record demonstrates a dynamic hydrological system fluctuating between lacustrine and palustrine conditions within a single humid interval. Where available, diatom or invertebrate palaeoecology data consistently indicate predominantly fresh waters across multiple humid intervals, and this is supported by a lack of evaporitic minerals (i.e. gypsum and halite) through all sequences. We therefore argue that the western Nefud Desert has repeatedly provided vital freshwater resources for ancient humans and other fauna over the past c. 500,000 years.

D799 |
EGU2020-7679
Heidi Tanttu, Christine Cocquyt, Dirk Verschuren, and Elie Verleyen

Lake Chala is a c. 90 m deep meromictic, oligotrophic crater lake near Mt. Kilimanjaro in equatorial East Africa. This sub-humid tropical region experiences two rainy seasons separated by a long dry season in June-August, when deep mixing fuels the epilimnion with nutrients resulting in increased phytoplankton primary production. Within the ICDP DeepCHALLA project, a 215-m long, continuous sediment sequence was obtained, which provides a unique opportunity to study long-term climate dynamics and aquatic ecosystem response during the past c. 260 000 years. Here we analyzed fossil pigments and diatom assemblages to reconstruct temporal dynamics in the lake’s phytoplankton community structure with millennial-scale resolution. Fossil pigments were analyzed using high-performance liquid chromatography, and a minimum of 400 valves were counted and identified with best-possible taxonomic discrimination from sediment samples taken at c. 800-yr intervals throughout the last glacial cycle (back to c. 160 kyr BP) and at c. 1600-yr intervals throughout earlier lake history. The most abundant pigments were zeaxanthin and lutein, reflecting the presence of cyanobacteria and green algae. Despite the high diatom content of the sediments, the diatom marker pigment fucoxanthin was almost absent, which we attribute to its labile nature. A small cyclotelloid diatom resembling the tychoplanktonic species Discostella stelligera at the base of the sequence probably reflects open-water conditions with the proximity of littoral habitats during the early filling stages of lake ontogeny. High proportions (20-50%) of an Encyonema species at c. 240-230 kyr BP indicate increased availability of benthic habitats, possibly because of a marked low-stand at the time of early sediment infilling when the central ash cone on the basin floor was still exposed. A phase of abundant needle-like Nitzschia and generally higher, yet fluctuating, pigment concentrations suggest a relatively moist environment with deep water and a stable stratification at c. 220-140 kyr BP. After c. 140 kyr BP, Afrocymbella barkeri appears for the first time, and from then onwards until the modern times the diatom community is composed of fluctuating abundances of Afrocymbella and needle-like Nitzschia taxa. The highest diatom biovolumes yet pronounced low carotenoid concentrations occur during the Afrocymbella-dominated (up to 100 %) intervals between c. 110 and 90 kyr BP and between c. 22 and 17 kyr BP, which broadly coincide with the MIS5 African megadrought and the Last Glacial Maximum, respectively. This suggests that during those time periods, the lake experienced pronounced dry and windy climate conditions, which triggered relatively deep mixing. This probably enhanced internal nutrient cycling and the injecting of oxygen to the bottom waters, which facilitated diatom growth in the epilimnion and resulted in pigment degradation in the hypolimnion. Superimposed on these long-term patterns, we found many short-term fluctuations in the appearance of different Nitzschia taxa, which may reflect stochastic colonization and extinction events, rather than actual climate-driven changes in the abiotic environment of Lake Chala.

D800 |
EGU2020-11005
Simon Kübler, Stephen Mathai Rucina, Maurice Obunga, Eileen Eckmeier, Donjá Aßbichler, and Geoffrey Charles Plume King

We have studied the importance of geological and soil edaphic factors for the location and duration of inhabitance of hominin sites in the southern Kenya Rift, East Africa. Using examples from the Lake Magadi-Olorgesailie region, we demonstrate that field mapping and analytical techniques derived from geology and soil science can provide important information for research in early hominin migration and land use.

The Lake Magadi-Olorgesailie region is located in the center of the ~60-km wide rift floor and characterized by a complex network of sub-parallel, nearly vertical, fault escarpments. The largest area of the rift floor is covered by trachyte flows, while other volcanic rocks including basalts, phonolites and carbonatites are located around Mt. Olorgesailie, Mt. Esayeti, Mt. Suswa and Singaraini. The Mid Pleistocene Olorgesailie site is famous for an unusual abundance of hominin artefacts, fossil mammals and palaeoenvironmental indicators, preserved in sediments spanning ~1.2 to <0.4 Ma and has been the subject of wide-ranging and intensive studies on hominins and their archeology. Other important hominin sites in the region are located in the Koora Graben, and in the vicinity of Lake Magadi. 

We have analyzed the chemical composition of a large number of geological and soil samples in the southern Kenya Rift, in order to understand the control of geochemical and tectonic processes on the release and distribution of vital soil nutrients.    

Results show that in the study region volcanic, tectonic and related pedogenic processes created a complex suite of landscape features potentially advantageous for human habitation. Analysis of soil samples from the main volcanic and metamorphic rocks as well as from sedimentary deposits shows that soil edaphic properties are closely correlated with the chemical composition of the parent materials and that deficiencies of soil nutrients are reflected in the mineralogy of the volcanic rocks. Particularly, deficient levels of calcium are sourced in the lack of calcium-bearing minerals in soils developed on trachytic rocks. Further, we show that soil nutrient distributions correlate with the relief created by tectonic faulting. We observed a significant increase of the concentrations of Ca, Mg, P in soils, with proximity to active normal faults.

 We suggest that the combination of complex terrain and patchy nutrient distributions created narrow migration corridors potentially exploited by animals and the humans who hunted them. Our study implies that tectonics, geology and related soil edaphics have been important drivers for human habitation and strategic land use. Knowledge of these processes and their impact on past human-landscape interactions contributes to a broader understanding of how landscapes influenced hominin behavior and subsistence strategies in prehistoric time.

D801 |
EGU2020-4855
Ny Riavo G. Voarintsoa, Antsa Lal’Aina J. Ratovonanahary, Zafitafika Miandrisoa Rakotovao, and Steven Bouillon

Madagascar, an island located ~300km off the eastern coast of Africa, is a natural laboratory to study paleoclimate and paleoenvironment. It holds a key position in the Indian Ocean and in Africa, as information from it has particularly helped fill gaps in paleoclimate reconstruction in the Southern Hemisphere, where such information is still scarce. Madagascar is seasonally visited by the Intertropical Convergence Zone (ITCZ) and experiences monsoon during austral summers. Furthermore, it hosts caves where speleothems can be found. Speleothems preserve a range of continuous geochemical records, mainly stable isotopes, that allow scientists to predict changes happening in the past.  In Madagascar, speleothem studies have revealed distinct early, mid, and late Holocene climatic regimes that were linked to the latitudinal migration of the ITCZ, and the monsoonal responses associated with the migration. Other speleothem studies revealed evidence of the African Humid Period, rapid climate changes, and most importantly the shift in δ13Cc starting ca. AD 800, that was attributed to anthropogenic activities. Although information from these speleothems is unquestionably significant, there are still gaps in isotopic proxies interpretation, mainly in linking modern environments where these speleothems grew and the signals they preserve. Such modern information is however fundamental to calibrate paleo-based climate and environmental reconstructions in Madagascar, which could be a key to refine their past interpretation. In this study, we performed an in-cave spatial test to understand kinetic isotope effect in Anjohibe Cave and to define oxygen isotopic fractionation between speleothem carbonate and its parent water and carbon isotopic fractionation between speleothem carbonate and the corresponding dissolved inorganic carbon (DIC). Results have been compared with modern calibration studies on speleothems from other locations worldwide, and we found that our data fit within the empirical relationship for cave-specific CaCO3-H2O isotope fractionation, grouping a range of monitored caves worldwide, 1000 ln α = 16.1 (103T-1(°K))–24.6 of Tremaine et al. (2011). Other physico-chemical parameters in Anjohibe Cave have also been measured, and they will be used to discuss potential linkages with the spatial variability in the  modern speleothem stable isotopic values and their corresponding parent water and DIC.

Tremaine, D.M., Froelich, P.N., Wang, Y., 2011. Speleothem calcite farmed in situ: Modern calibration of δ18O and δ13C paleoclimate proxies in a continuously-monitored natural cave system. Geochim Cosmochim Acta 75, 4929-4950.

D802 |
EGU2020-1504
| solicited
| Highlight
Andrew S. Cohen

Over the past 20 years a series of scientific drilling campaigns around Africa have yielded exciting new information about the evolutionary ecological history of that continent. Most of these records have come from highly resolved lacustrine deposits with rapid sedimentation rates, and primarily, though not exclusively, have come from the East African Rift Valley, spanning the last ~3.5Ma. Important insights about both lacustrine and terrestrial ecosystem evolution have emerged, including ones with implications for the ecological context of human evolution. During the transition from the Late Pliocene warm period into the Quaternary, phytoliths, charcoal, pollen and leaf wax records are reshaping our understanding of fine scale structure of landscape vegetation transformation, and the implications these changes had for resources and cover that mammals (including early hominins) relied upon.  Pleistocene drill core paleoecological records from Lake Malawi have provided evidence for transformations of that lake’s ecosystem, including water column mixing, transparency and nutrient recycling, that help explain the explosive phylogenetic radiation of that lake’s extraordinary endemic cichlid fish fauna. And high-resolution records from that same lake spanning the time of the ~75ka Toba super-eruption allow us to test and falsify hypotheses linking volcanic activity to wholesale transformation of the African ecosystem, including purported links to modern human population bottlenecks. These valuable archives will in the future be complemented by even longer records from Africa’s oldest lake, L. Tanganyika, allowing us to build a comprehensive picture of African ecosystem evolution extending back to the late Miocene.

D803 |
EGU2020-1724
| Highlight
Axel Timmermann

It still remains unclear what caused the disappearance of Neanderthals during the last glacial period. To determine whether their demise was mainly due to abrupt climate change, interbreeding or competition, I use a spatially resolved numerical hominin dispersal model that simulates the interaction of Anatomically Modern Humans and Neanderthals in the rapidly varying climatic environment of the last ice age. The numerical simulations, which are in good agreement with archeological and fossil data, document that rapid temperature and vegetation changes associated with Dansgaard-Oeschger events played no discernible role in Neanderthal extinction. Instead, the emerging resource competition in Eurasia between Homo sapiens and Neanderthals, along with low levels of interbreeding were the primary drivers for the demise of Neanderthals. 

D804 |
EGU2020-5588
Hervé Bocherens, Hugues-Alexandre Blain, Mikael Fortelius, Juha Saarinen, Christian Sanchez Bandera, José Antonio García-Solano, Deborah Barsky, Carmen Luzón, and Juan Manuel Jiménez Arenas

The Guadix-Baza Basin (Granada Province, Southern Spain) is the richest area in Western Europe for the study of early hominin dispersal and evolution, having yielded the earliest localities with evidence of hominin occupation (a deciduous human molar, lithic industries and cutmarks) together with a rich large and small vertebrate assemblage dated to around 1.4 Ma. A key question is whether environmental changes were involved in the arrival of hominins in this region at this time. To answer this question, possible environmental differences between one older site lacking evidence for hominin occurrence (Venta Micena VM, ~1.6 Ma) and younger sites with undisputable evidence (Barranco León BL and Fuente Nueva-3 FN3, ~1.2-1.5 Ma) were investigated using various approaches, including carbon and oxygen isotopes in tooth enamel, tooth wear analysis, ecometrics and microvertebrates (amphibians, reptiles, mammals) as proxies for palaeoclimate.

Tooth enamel powders were collected from herbivorous mammal specimens from the three sites. For several specimens, enamel was sampled serially to document intra-annual dietary and/or habitat changes for the studied individuals. A large diversity of herbivorous taxa was sampled, including cervids, bovids, equids, rhinoceros, hippopotamus and mammoths. The analyses were conducted at the University of Tübingen (Senckenberg Centre for Human Evolution and Palaeoenvironment).

Carbon isotopic results from the three sites showed that the plants foraged by herbivores were essentially of C3 photosynthetic pathway (trees, shrubs and C3-grass adapted to mild growth season), which is consistent with the results of tooth wear analysis indicating browsing or mixed feeding with browsing preference for most taxa. The consumption of some C4 plants for some herbivores has been detected only in Barranco León, which is consistent with the results of palaeoclimatic investigations based on ecometrics and microvertebrate fauna, indicating a particularly wet and warm climate for this site compared to both others and colder conditions in Venta Micena, the site devoid of hominins. Oxygen isotopic results seem to be essentially related to browsing (high values) versus grazing (lower values) and to different habitats (lowest oxygen isotopic values for semi-aquatic hippos). The differences in isotopic results among taxa are in agreement with those of dietary preferences from mesowear tooth analysis. In addition, in a context of still Mediterranean climate with 4-months aridity during summer, isotopic variations within teeth suggest in some cases significant changes in foraging through a year, which could be related to local seasonal changes or mobility across areas with different vegetation types.

The first results of this multidisciplinary research project financed by the Leakey Foundation and a General Research Project from the Andalusian Regional Government help us to refine the palaeoenvironmental reconstruction around the time of the earliest arrival of hominins in Southern Spain. In combination with the climatic data provided by ecometrics and microvertebrate investigations, it allows us to develop a more detailed framework for the interpretation of the carbon and oxygen isotopic data from tooth enamel in a Mediterranean climate context, which corresponds to the type of climatic conditions where the earliest hominins occur in Europe in the Early Pleistocene.

D805 |
EGU2020-10806
Carlo Mologni, Lamya Khalidi, Marie Revel, Laurent Bruxelles, Jessie Cauliez, Fabien Arnaud, Emmanuel Malet, Eric Chaumillon, Thibault Colombier, Gourguen Davtian, Laure Schenini, Clément Ménard, and Isabelle Crevecoeur

Throughout the last 20 ka, tropical Africa was the site of significant hydrological changes related to variations in the intensity of the African monsoon. Recent studies conducted in lake and deltaic sedimentary records suggest that gradual long-term monsoon humid oscillations (African Humid Period ~14 – ~6 ka) were punctuated by centennial-scale episodes of hyperaridity (HS1, YD, 8.2 ka, 4.2 ka). These abrupt hydrological changes could have caused drastic transformations in landscape patterns, providing favourable ecosystems, but also produced arid environments that may have restricted human exploitation of the landscape.

The Abhe Lake basin in the Central Afar region (Ethiopia & Djibouti) is the endorheic receptacle of freshwater and terrigenous inputs from the Ethiopian Highlands, and is a hydro-sedimentary system sensitive to hydroclimatic change. Since 2014, in the context of the VAPOR-Afar and PSPCA programs (in Ethiopia and Djibouti respectively), we have intensified scientific investigations over this basin with the objective of exploring the evolution of Holocene hydroclimatic change, its impact on landscapes and on prehistoric human behaviour during one of the most forcible transitions in human history, that from a dominantly hunter-gathering way of life to the food production societies one.

We present the first results of this research that combines paleoclimatological, geomorphological and geoarchaeological studies based on a new set of 14C datations on two lacustrine cores, on several morpho-sedimentary outcrops and on 8 new archaeological sites spanning the Early to Late Holocene. Our results allow us to: a) refine the temporal occurrence and the modalities of the African Humid Period and of the 8.2 and 4.2 ka hyperarid episodes, coupling paleolake-level reconstitution and lacustrine sediment analysis (paleolimnology, geochemistry); b) evaluate the impact of these hydroclimatic oscillations on perilacustrine sedimentary formation processes, especially for pedogenic formations; c) and better understand the relationship between environmental change and the development of one of the most important economic and cultural innovations, that of domestication.  

D806 |
EGU2020-7055
Jiaoyang Ruan and Axel Timmermann

Human fossil and archeological findings indicate that Anatomically Modern Humans (AMHs) may have migrated from Africa into Eurasia multiple times during the last glacial period. However, mtDNA-based genetic data (haplogroup L3 & its daughters M, N) appear to be more consistent with a single wave dispersal ~ 70-60 ka, coinciding with one of the driest periods in northeastern Africa. 

To reconcile this discrepancy and better understand the migration routes and interactions of different groups of AMHs, we developed a new version of the Hominin Dispersal Model (HDM, version 2). The phenomenological reaction diffusion model simulates a realistic human dispersal in a spatio-temporally varying climatic environment.  In our configuration, we introduce a group which represents individuals which dispersed into Asia prior to 60 ka and a group which migrated into Eurasia post-60 ka. An ensemble of parameter sensitivity experiments suggests that their interaction caused a characteristic east-west gradient in admixture across Eurasia, which is consistent with latest genetic datasets, which reveal a faint signal of pre-60 ka dispersal waves in Southeast Asians and individuals from Papua New Guinea. Moreover, our simulations provide new insights into possible migration routes of AMHs. Based on this analysis we propose a new hypothesis to explain the increased Neanderthal DNA percentage in present-day Asians relative to Europeans.

D807 |
EGU2020-7304
Lucas Bittner, Marcel Bliedtner, Dai Grady, Graciela Gil-Romera, Catherine Martin-Jones, Bruk Lemma, Henry F. Lamb, Cindy De Jonge, Hanno Meyer, Bruno Glaser, and Michael Zech

Our knowledge of East African paleoclimate is largely based on marine core and paleolimnological reconstructions. Accordingly, more humid climatic conditions such as the African Humid Period (AHP) are usually associated with summer insolation-driven increased monsoonal precipitation and the movement of the Congo Air Boundary.

In order to contribute to this discussion and to reconstruct the paleoclimate of the afro-alpine Bale Mountains, Ethiopia, within the DFG Research Unit 2358 ‘The Mountain Exile Hypothesis: How humans benefited from and re-shaped African high-altitude ecosystems during Quaternary climate changes’ we re-cored Lake Garba Guracha. This site represents one of the best dated Late Glacial - Holocene continuous, high altitude (3950 m asl) paleoenvironmental archives in East Africa.
We investigated sugar and lipid biomarkers and their compound-specific stable oxygen and hydrogen isotopic composition (δ18Osugar and δ2Hn-alkane) to infer past hydrological patterns. The δ18Osugar record reflects lake water and can thus be used to reconstruct lake evaporation history.

Our results suggest that a virtually permanent lake overflow existed from about 10 to 7 cal. ka BP, whereas the period from about 7 to 5 cal. ka BP is characterised by increased lake evaporation. We present initial results of δ18Odiatom analyses and organic geochemical and XRF data that document dominant minerogenic input during the Late Glacial and increased input of almost exclusively aquatic organic matter from 11 cal. ka BP on. Reconstructed mean annual temperatures (n=20, -2.2 to 2.5°C), inferred from brGDGT-based proxies, indicate that colder conditions prevailed in the high-altitude Bale Mountain ecosystem during the Younger Dryas.

D808 |
EGU2020-5600
Alexis Nutz, Mathieu Schuster, Doris Barboni, Ghislain Gassier, Jean-François Ghienne, and Jean-Loup Rubino

The Turkana Depression consists of several Oligocene to Pliocene North-South oriented half-grabens that connect the Ethiopian and Kenyan rift valleys within the eastern branch of the Cenozoic East African Rift System. In the northern portion of the Turkana Depression, exposed on the west side of modern Lake Turkana, is the Nachukui Formation that consists of a > 700 m pile of fluvial-deltaic-lacustrine sediments deposited between 4.2 and 0.7 Ma. The Nachukui Fm is a world-class fossil-bearing succession into which more than 500 hominin fossils were discovered, including major discoveries for the understanding of Human evolution and more than 100 archaeological sites. Most significant discoveries include Australopithecus anamensis, Kenyanthropus platyops, Paranthropus aethiopicus, Paranthropus boisei and specimens of Homo (i.e., H. rudolfensis and H. erectus) and early members of H. sapiens, as well as the earliest evidence of Acheulean stone tool technology and, more recently, the most primitive Lomekwian stone tool technology.

            Palaeoenvironmental changes may have had a strong influence on evolution, including that of the human lineage. However, in the Turkana Depression, palaeoenvironments are still very partially reconstructed and the respective role of climate and tectonism is still debated. Here, we used the interpretation of depositional environments, the delineation of depositional sequences and a record of d13C in pedogenic carbonates (i.e. paleovegetation proxy) to reconstruct 1) palaeolake Turkana fluctuations between ca. 4 and ca. 1.2 Ma and 2) the successive sedimentary palaeoenvironments and resulting landscapes that characterized the West Turkana area during the same time interval.

            Facies and sequence analyses reveal that palaeolake Turkana experienced eight low-frequency transgression-regression (T-R) cycles between ca. 4 and ca. 1.2 Ma; superimposed lower amplitude and shorter duration T-R cycles are also locally identified revealing subordinate-order fluctuations. In the same time, two different palaeolandscapes (labelled type-1 and type-2) alternated through times revealing variations in sediment supply coming from the western rift shoulder. A statistical treatment of the d13C record using a modified k-mean clustering allows us to confront a paleovegetation proxy and the sedimentological record. This combined approach reveals that the evolution of rainfall over the Ethiopian dome (i.e., drainage basin of the Omo river) controlled long-term palaeolake Turkana fluctuations during the Plio-Quaternary period while tectonism likely controlled the occurrence of different palaeolandscapes in West Turkana forced by changes in the rate of sediment supply.

            Finally, our study shows that traditional methods of basin geology (i.e., facies and sequence analysis) are key tools to provide large-scale paleolandscape reconstructions and palaeolake fluctuations needed for investigating the interactions between hominins and palaeoenvironments. Such a powerful procedure, however, is rare for hominins sites and has yet to be integrated in the workflow utilized by the paleontology and archeology communities.

This is a contribution of the Rift Lake Sedimentology project (RiLakS).

D809 |
EGU2020-8481
| solicited
Annette Hahn, Hayley Cawthra, Green Andrew, Humphries Marc, Schefuß Enno, and Zabel Matthias

Southern Africa is located at the interface of sub-tropical and temperate climate zones as well as between two major warm and cold ocean current systems (Agulhas and Benguela), respectively. This makes it a key region for understanding global climate dynamics and highly sensitive to future climatic change. A growing number of paleo-archives have revealed small-scale climatic dipoles in this region and the driving mechanisms of the complex climatic variability often in this region remain unclear. Several regional studies have suggested a synchronicity with the southern hemisphere and thus inferred a direct insolation forcing while others have observed a synchronicity with northern hemispheric climate and associated this with a teleconnection mechanism. In order to decipher the complex climatic processes affecting this region it is necessary to integrate on- and offshore paleo-archives as well as various paleo-environmental indicators (proxies). For the correct interpretation of the various proxies a source to sink approach is necessary determining the origin of the different terrestrial sedimentary components and their potential alterations during transport and deposition. With a focus on marine and lacustrine sedimentary archives along the west, south, and east coast of southern Africa we are now able to reconstruct Late Quaternary climate variability on regional scales. We propose a new conceptual model describing latitudinal shifts of rainfall zones as tropical and temperate climate systems shift over glacial and interglacial cycles. New insights allow us to resolve some of the apparent contradictions between paleoclimate records from the region. 

 

D810 |
EGU2020-9748
Annett Junginger and Simon Kuebler

Landscapes form the basis for the development of human habitats. Studying human-landscape interactions thus requires an understanding of the character and evolution of landscapes on different temporal and spatial scales. In Africa, key anthropological sites are often associated with the tectonically active sectors of the East African Rift. But the landscapes inhabited by our ancestors have undergone massive changes over time, changes driven by climatic variability as well as long-term geomorphological and tectonic processes. River courses have changed, lakes expanded and then disappeared, and volcanic and tectonic activity formed steep fault scarps and barriers. Here we present a review of archaeological, paleo-climatological, paleo-limnological, tectonic and soil nutrients data sets of the southern Ethiopian and Kenyan Rift System in Eastern Africa of the past 1 Million years. Results suggest that tectonic processes and climatic change created a unique suite of landscape features potentially advantageous for human inhabitance. The combined analysis thus allows the quantification of styles and rates of surface modification, which in turn can be used for reconstructing ancient landscapes.

D811 |
EGU2020-22010
Josephine Mahony, Ellen Dyer, and Richard Washington

The Serengeti National Park is famous for the biological phenomenon of the annual wildebeest migration. This migration is reliant on unique local precipitation conditions: a rainfall gradient stretching across the park, the strength and inclination of which alters from month to month. Given the ecological significance and the complexity of the regional precipitation, a detailed study of the region’s climatology is essential for understanding why these precipitation patterns exist, and whether they are likely to change.

Using multiple observational datasets, we studied the spatial distribution of annual and monthly climatological precipitation. We carried out harmonic analysis and cluster analysis to identify areas with similar annual cycles. We then examined regional wind, moisture and precipitation patterns on seasonal, monthly and diurnal timescales.

We found that the large-scale wind circulation patterns dictate the basic structure of the annual cycle over the region. However the shape of the annual cycle was distinctly different in 5 parts of the region, with varying peak rainfall months and dry season rainfall totals. Analysis of the diurnal wind patterns showed that the regional seasonality is strongly augmented by the lake and land breeze from Lake Victoria, and the interactions between this local source of moisture and the complex topography of the East African rift. This leads to a low-level convergence zone between the prevailing large-scale easterlies, and westerlies from Lake Victoria over the Serengeti in the afternoon. This in turn results in the rainfall gradient across the region, the orientation of which changes depending on the mid-tropospheric wind direction.

D812 |
EGU2020-11488
Frank Schäbitz, Verena Foerster, Asfawossen Asrat, Andrew S. Cohen, Melissa S. Chapot, Jonathan R. Dean, Alan Deino, Daniel M. Deocampo, Walter Duesing, Christina Günter, Annett Junginger, Stefanie Kaboth-Bahr, Henry F. Lamb, Christine Lane, Melanie J. Leng, Stefan Opitz, Rachel Lupien, Helen M. Roberts, Christopher Bronk Ramsey, and James Rusell and the HSPDP and CRC806 Science team

Humans have been adapting to more demanding habitats in the course of their evolutionary history. Nevertheless, environmental changes coupled with overpopulation naturally limit competition for resources. In order to find such limits, reconstructions of climate and population changes are increasingly used for the continent of our origin, Africa. However, continuous and high-resolution records of climate-human interactions are still scarce.

Using a 280 m sediment core from Chew Bahir*, a wide tectonic basin in southern Ethiopia, we reconstruct the paleoenvironmental conditions during the development of Homo sapiens. The complete multiproxy record of the composite core covers the last ~600 ka , allowing tests of hypotheses about the influence of climate change on human evolution and technological innovation from the Late Acheulean to the Middle/Late Stone Age, and on dispersal within and out of Africa.

Here we present results from the uppermost 100 meters of the Chew Bahir core, spanning the last 200 kiloyears (ka). The record shows two modes of environmental change that are associated with two types of human mobility. The first mode is a long-term trend towards a more arid climate, overlain by precession-driven wet-dry alternation. Through comparison with the archaeological record, humid episodes appear to have led to the opening of ‘green’ networks between favourable habitats and thus to increased human mobility on a regional scale. The second mode of environmental change resembles millennial-scale Dansgaard-Oeschger and Heinrich events, which seem to coincide with enhanced vertical mobility from the Ethiopian rift to the highlands, especially in the time frame between ~65–21 ka BP. The coincidence of climate change and human mobility patterns help to define the limiting conditions for early Homo sapiens in eastern Africa.

___________________

* cored in the context of HSPDP (Hominin Sites and Paleolakes Drilling Project) and CRC (Collaborative Research Centre) 806 “Our way to Europe

D813 |
EGU2020-5233
Gabriele Arnold, Claudia Szczech, Asfawossen Asrat, Andrew S. Cohen, Verena Foerster, Frank Schäbitz, Henry Lamb, and Martin H. Trauth

This paper reports on the application of advanced hyperspectral analysis to support the non-destructive study of samples from long sediment cores (up to 280 m coring depth) collected under the Hominin Sites and Paleolake Drilling Program (HSPDP) in the Chew Bahir region of southern Ethiopia. For this purpose, the bidirectional reflectance of 35 core samples from different core depths in the wavelength range from 0.25 to 17 µm was measured. It can be directly compared with spectral remote sensing data of the corresponding land surface areas. We examined the relationship between the derived mineralogical and geochemical properties of the core samples to test for linkage to the hydroclimate history of the region. Using XRD and µXRD methods, it has been shown that an illitization of the smectites and an octahedral Al-to-Mg substitution occurs in the phyllosilicate materials present during phases that have been associated with increased salinity and alkalinity due to enhanced evaporation (Foerster et al., 2018). These processes are found to be accompanied by potassium fixation and they are associated with the increase of the layer charge due to the authigenic changes of the octahedral composition. Reflection spectroscopy is a suitable method for studying such mineralogical properties.

We investigated the spectral properties over a wide spectral range from UV to MIR. This enables detection of absorption bands of crystal field transitions of transition metal ions in the UV/VIS range and to detect the characteristic bands of OH, H2O, M-OH lattice vibrations in the NIR. It also allows the study of the fundamental vibration bands as well as other typical MIR features like the Christiansen band or transparency features of silicates and thus helps to reconstruct weathering paths.

The results show that the main mineralogical components are clays of the smectite group. The samples are rich in montmorillonite and show variable concentrations of calcite. The clays are composed of tetrahedral coordinated, corner-connected SiO4 for which Si is partially substituted by Al and of edge-linked Al (OH)6 octahedrons in which part of the Al is substituted by Mg and which are layered by OH and H2O groups. Thus all reflectance spectra show the characteristic absorption bands at 1.4 µm (OH), 1.9 µm (H2O), 2.2 µm (Al-OH), and 2.3 µm (Mg-OH). Their band depth ratios derived from continuum removed spectra have been used to characterize the clay structure within different climate periods. The results support the model of illitization and potassium fixation during dry climate intervals. In addition, the spectral indicators determined in the MIR can be used to specify the mineralogical properties of silicates and other materials in terms of their geochemical composition. In summary, the method is suitable for examining the main mineralogical components of Chew Bahir core samples and enables confirmation of climate-driven wet and dry weathering processes in the formation of phyllosilicates.


Foerster, V. et al., (2018) Towards an understanding of climate proxy formation in the Chew Bahir basin, southern Ethiopian Rift. Palaeogeography, Palaeoclimatology, Palaeoecology, 501, 111-123.

D814 |
EGU2020-18292
Verena E. Foerster, Asfawossen Asrat, Andrew S. Cohen, Melissa S. Chapot, Alan Deino, Daniel M. Deocampo, Walter Duesing, Christina Guenter, Annett Junginger, Stefanie Kaboth-Bahr, Henry F. Lamb, Christine Lane, Christopher Bronk Ramsey, Helen M. Roberts, Céline Vidal, Frank Schaebitz, and Martin H. Trauth

What role did climate dynamics play in the evolution and dispersal of Homo sapiens within and beyond Africa, and in key cultural innovations? Were gradual climatic changes, rapid shifts from wet to dry, or short-term climate flickers the main driver of human evolution and migration? As a contribution towards an enhanced understanding of those possible human-climate interactions the Chew Bahir Drilling Project, part of the Hominin Sites and Paleolakes Drilling Project (HSPDP) and the Collaborative Research Center (CRC) 806 “Our way to Europe”, recovered two ~280 m-long sediment cores from a deep, tectonically-bound basin in the southern Ethiopian rift in late 2014. The Chew Bahir record covers the past ~600 ka of environmental history, a critical time period that includes the transition from the Acheulean to the Middle Stone Age, and the origin and dispersal of Homo sapiens.

 

Here we present the results from our multi-proxy study of the Chew Bahir 280 m-long composite core, providing a detailed and high-resolution record of eastern Africa’s climate oscillations during the last ~600 ka. To determine sediment age we used a Bayesian model to combine ages derived from radiocarbon dating of ostracodes, optically-stimulated luminescence (OSL) dating of quartz, Argon-Argon (40Ar/39Ar) dating of feldspar grains from some key (micro)tephra layers, and correlation on the basis of geochemistry of a tephra unit in the core to a known and dated tephra in the outcrop. We used high-resolution geophysical and geochemical indicators, such as the established aridity proxy K, sediment colour and authigenic minerals to differentiate between climate fluctuations on different time scales and magnitudes.

 

Our results show that the full proxy record from Chew Bahir can be divided into three phases with similar trends in central tendency and dispersion. Phase I from ~600 to ~430 kyr BP shows a long-term shift from humid to arid conditions while slightly increasing the variability and ending with the most extreme oscillations between full humidity and extreme aridity. The transition into Phase II (~430 to ~200 kyr BP) is marked by a pronounced millennial-scale humidity increase. Phase II reflects generally more humid conditions and there is evidence of double humidity increase tendency. Firstly, between ~430 and ~315 kyr BP (Phase IIa), and again from ~280 to ~195 kyr BP (Phase IIb), with only slight changes in long-term variability. Since ~200 kyr BP (Phase III), a long-term aridification trend sets in, similar to Phase I, but with a distinct increase in variability and amplitudes. All of these changes would have had significant implications for shaping our ancestors’ living environments, both broadening and limiting their options in response to the different degrees and rates of climatic stress. The Chew Bahir record, one of the very few long terrestrial environmental records from continental eastern Africa, can contribute to testing the influence of low versus high latitude climate change in driving the expansion, contraction and fragmentation of early human habitats.

D815 |
EGU2020-13026
Walter Duesing, Asfawossen Asrat, Andrew S. Cohen, Verena S. Foerster, Stefanie Kaboth-Bahr, Hauke Kraemer, Henry F. Lamb, Norbert Marwan, Helen M. Roberts, and Frank Schaebitz

The sediment cores of the Chew Bahir drilling project, part of the Hominin Sites and Paleolakes Drilling Project (HSPDP), from southern Ethiopia, were used to reconstruct climatic changes by analyzing the sediment geochemistry with high-resolution XRF scanning. To interpret the multidimensional XRF dataset we computed a principal component analysis. We used the first principal component (PC1) to detect changes in variability by running a windowed standard deviation analysis and additionally a change point analysis to detect the exact timing of variability changes. 

 

Additionally we used the established Chew Bahir log(K/Zr) aridity proxy, representing clay mineral chemistry- detrital input ratio and compared it to a new Chew Bahir climate indicator, the log(Ca/Ti) proxy, an evaporation signal that is probably inversely related to lake level stands. We find that the log(Ca/Ti) record is also an exceptionally good climate indicator because, compared to the established log(K/Zr) proxy, it reacts with greater amplitude to insolation-controlled signals such as orbital precession. This is confirmed by the log (Ca/Ti) record showing a very clear signal during the African Humid Period, which is however less pronounced in the log(K/Zr) record.

 

To gain a deeper understanding of the climate cycles and their temporal evolution, we computed a continuous wavelet transformation (CWT) for each of the climate proxies, and studied temporal changes in their cyclicity. Our results indicate that in addition to the precession cycle (~ 20 kyr), the Chew Bahir climate record contains earth eccentricity cycles (~ 100 kyr), as well as half-precession cycles during high eccentricity. During low eccentricity (450-350 kyr ago), we find reduced variability, three of five changes in standard deviation, damped precession and half precession cycles, and an abrupt transition from dry to wet climate, possibly due to climatic change in high latitudes which may be related to the Mid-Bruhnes event (MBE). 

 

The results confirm that during high eccentricity the tropics are insolation controlled, largely independent of the high latitudes, whereas during low eccentricity the climate of tropical eastern Africa is sensitive to climatic drivers other than precession, possibly originating from high latitudes. Such a period occurring 450 to 350 kyr ago could have led to large regional differences in moisture availability and may have affected early humans by habitat separation, which by isolating populations, resulted in technological diversification. This possible scenario may help to explain the technological transition from Middle Stone Age (MSA) to Acheulean technology that was documented in the Olorgesailie basin during the same time period. 

 

D816 |
EGU2020-4660
Martin H. Trauth, Asfawossen Asrat, Andrew S. Cohen, Walter Duesing, Verena Foerster, Stefanie Kaboth-Bahr, Hauke Kraemer, Henry Lamb, Norbert Marwan, Mark A. Maslin, and Frank Schaebitz

The Chew Bahir Drilling Project (CBDP) aims to test possible linkages between climate and evolution in Africa through the analysis of sediment cores that record Quaternary environmental changes in the Chew Bahir basin. In this statistical project we used recurrence plots (PRs) together with a recurrence quantification analysis (RQA) to distinguish two types of variability and transitions in Chew Bahir and compare them with the ODP 967 wetness index from the eastern Mediterranean. The first type of variability are slow variations with cycles of ~20 kyr and subharmonics of this cycle. In addition to the these cyclical wet-dry fluctuations in the area, extreme events often occur, i.e. short wet or dry episodes, lasting for several centuries or even millennia, with rapid transitions between wet and dry episodes. The second type of variability is characterized by relatively low variation on orbital time scales, but significant century-to-millennium-scale variations with increasing frequency in the course of an episode of type 2 variability. Within this type of variability there are extremely fast transitions between dry and wet, and vice versa, within a few decades or years, in contrast to those within type 1 which have transitions lasting several hundred years. Type 1 variability probably reflects the influence of precessional forcing in the lower latitudes at times of increased eccentricity, with the tendency towards extreme events, whereas type 2 variability seems to be linked with minimum values of the long (400 kyr) eccentricity cycle, and there does not seem to be a link with atmospheric CO2 levels. The different types of variability and transitions certainly had a completely different influence on the availability of water, food and shelter, and hence eastern Africa’s biotic environment, including the habitat of H. sapiens.

Chat time: Friday, 8 May 2020, 10:45–12:30

Chairperson: Annett Junginger, Janina Bösken, Inka Meyer
D817 |
EGU2020-18611
Peter Nickolaus, Monika Markowska, Hubert Vonhof, Hervé Bocherens, Ashley Martin, Bahru Zinaye, Markus Fischer, Asfawossen Asrat, and Annett Junginger

In the context of human evolution and dispersal in Africa, it is important to understand past climate conditions and changes as possible drivers of these processes. One of the most recent climatic events was the end of the African Humid Period (AHP) at around 5 ka BP. This was marked by a decrease in precipitation following a long wet-phase in northern and eastern Africa, which caused many lakes to decrease in size or even desiccate. Although the termination of the AHP is well known, the timing and rate of the transition from wet to dry conditions is still heavily debated. To investigate the termination of the AHP at a high temporal resolution (subdecadal and subannual), fossil stromatolites and Etheria elliptica shells from paleo-shorelines in the Chew Bahir Basin, southern Ethiopia, were collected. Today, Lake Chew Bahir is a deltaic swamp, however in past pluvials a large lake was present that likely overflowed and connected to other basins similar to other amplifier lakes in the East African Rift System. Radiocarbon dating, oxygen and carbon stable isotope analyses, trace element analyses and petrographic mapping of stromatolite laminae structure were conducted. A strong correlation between δ18O and δ13C shows that paleo-lake Chew Bahir likely experienced highly evaporative conditions and indicate an endorheic state of the basin in times of stromatolite growth at 7.1, 5.8, 4.7 and 4.6 ka BP. Furthermore, our findings suggest highly fluctuating environmental conditions during these times and demonstrate that the transition to drier conditions was not a strictly linear trend. In summary, the stromatolites and Etheria elliptica shells are an excellent environmental archive due to their high temporal resolution, precise dating (± 30 yrs) and an indication of the paleo-lake water depth. These types of records provide insights to past changes in freshwater availability, the variability of which would have had large consequences for humans living in the region.

D818 |
EGU2020-2975
Inka Meyer, Maarten Van Daele, Niels Thange, Dirk Verschuren, and Marc De Batist

Terrigenous particles deposited in all kinds of sedimentary records (terrestrial, marine and lacustrine) have proven to yield valuable information for reconstruction of paleo-climate and paleo-environments. Natural sediments typically represent a mixture of deposits of diverse provenance, potentially supplied by different transport processes, expressed in a bi-or poly-modal grain-size distribution. Recently, complex mathematical-statistical end-member models have been developed to disentangle the different sub-populations within one grain-size distribution, which are then assumed to represent a distinct sediment fraction that has a single provenance and/or was transported by the same process to the site of deposition.

Here we present end-member modeling results of the terrigenous sediment fraction in a 25-kyr sediment sequence from Lake Chala (Kenya/Tanzania), revealing valuable information on climate and environmental change in equatorial East Africa since the Last Glacial Maximum (LGM). Calculated end members could be related to distinct source areas and transport processes, namely to fine aeolian dust, fine-grained soil runoff, coarser aeolian dust from proximal sources and coarse erosive material originating from the crater rim surrounding the lake. Variations in the occurrence of distal versus proximal dust is suggested to be a reliable indicator for changes in East African monsoon circulation. During Northern Hemisphere cold periods, such as the LGM and Younger Dryas (YD), wind systems associated with the Intertropical Convergence Zone (ITCZ) were pushed southward, causing a more intense influence of the NE monsoon at Lake Chala. This resulted in high amounts of fine dust originating from the Horn of Africa region. At the same time, SE monsoon circulation was diminished due to a reduced atmospheric pressure gradient between the Asian/Indian continent and the Indian Ocean. Influx of coarse dust from proximal sources, which are mostly located east of Lake Chala, was impossible due to the weaker SE monsoon circulation. After termination of the YD, rapid reestablishment of the SE monsoon in the Early Holocene is recorded by an abrupt increase in the influx of coarse dust.

Lake Chala sediments contain one of the few continuous and high-resolution climate records in East Africa spanning the past 25 kyr, providing detailed information on long-term climate variation in an area highly sensitive to hydrological variations. Subdividing the clastic sediment fraction into statistically robust end members produces multiple quantitative and independent proxies to help reconstruct this region’s climate and environmental history.

D819 |
EGU2020-12966
Elena A. Hensel, Ralf Vogelsang, Tom Noack, and Olaf Bubenzer

Rock shelter and cave sites can be suitable archives for archaeological remains and environmental records if the right conditions are complied with. There are a few sediment stratigraphies in the Horn of Africa that preserved information about human occupation during the Upper Pleistocene and Holocene. Unfortunately, little is known about human settlement in Ethiopia during the period corresponding to MIS 2 due to discontinuous archaeological records. The project A1, within the framework of the Collaborative Research Centre 806 (CRC 806 – “Our Way to Europe”), focuses on Late Pleistocene stratigraphies and paleoenvironments of northeast African sites. In this context, during excavations at the Sodicho Rockshelter in the southwestern Ethiopian Highlands, a complex stratigraphy with evidence of several human occupation phases was exposed.

This poster presents the latest research results of the Sodicho Rockshelter. It displays first radiocarbon ages and the site formation processes according to a selection of sedimentological and geochemical methods to understand human settlement history in this tropical environment. A multi-proxy approach has been chosen to detect possible rapid or gradual changes in depositional conditions in the rock shelter. The sedimentological records suggest that the depositional and post-depositional processes varied significantly over time in response to external environmental changes and the use of the shelter by humans. For instance, lithic assemblages in anthropogenic influenced layers alternate with thick volcanic ash layers. In addition, a sterile, clayish horizon refers to a period of increased precipitation and could thus provide evidence for an African Humid Period. The Sodicho Rockshelter could validate the current state of research and possibly close the chronostratigraphic gap.

D820 |
EGU2020-10635
Mahmoud Abbas, Stephanie Neuhuber, Roman Garba, Denis Štefanisko Štefanisko, Dominik Chlachula, and Zhongping Lai

The paleohydrology and geomorphology of southeastern Arabia after 130 ka suggests complex climatic records in the area considered a potential route for human dispersal Out of Africa. Understanding the past hydrological systems is essential to relate the lithic assemblages at the surface to a habitable environment. Climatic records such as speleothems can in combination to sedimentological evidence provide crucial data on the potential formation and persistence of paleo-water bodies and human livelihood.  The transition of a more humid period in the past to the presently harsh environment of southeastern Arabia and its relationship with human occupation is one long-term focus of this project. The information on timing, permanency and depth of these paleo-water bodies in Central and Southern Oman are yet lacking.

An initial geo-archaeological investigation has been carried out in south-central Oman (al-Wusṭā Governorate) and southern Oman (Ẓufār Governorate) as part of TSMO (Trilith Stone Monuments of Oman) archaeological expedition During TSMO field campaign. The OSL samples were collected from fluvial, colluvial and valley sediments in the main study area of al-Duqm, south-central Oman, and the reference area of Mudayy, south of Oman in Ẓufār. At both locations we logged several sediment profiles that mainly consist of well-rounded boulders, imbricated gravels and coarse-grained sediments intercalated with sporadic sand lenses. The sediments suggest fluvial transport in a perennial river and differ significantly from today’s ubiquitous angular Wadi-sediments. At both locations we found reddish sediment that might originate from fluvially reworked soil and would indicate not only the presence of water but also enough moisture to facilitate soil forming processes. Preliminary XRD scans from samples in Ẓufār identified calcite, quartz, feldspar and the sheet silicates illite and kaolinite. The clay fraction of this material has been separated and analyzed to determine the exact minerals that might be typical for soil formation in the B-horizon. Sediments in the Mudayy area are – similarly to al-Duqm - composed of river sediments with well-rounded imbricated gravels but in contrast to further north, they are covered by aeolian (loess) sediments. This captures the transition of fluvial deposition to aeolian deposition and thus a transition of the environmental setting during the time of formation. The Mudayy area in southern Oman is associated with Middle Paleolithic lithic tools of Levallios/Nubian complex technology as well as early-middle Holocene stone tools. The main research area of al-Duqm revealed several new Middle Palaeolithic sites with preferential Levallois facie with some influence of Nubian complex suggesting the landscape with favorable local environmental conditions, forming a possible human refugium between the harsh northern and southern borderlands. The understanding of Quaternary geomorphic, sediment and erosion processes, paleoclimate reconstruction, techno-typological analysis of lithic tools and cosmogenic nuclide dating of the raw material procurement sites in al-Duqm can shed more light on occupation and movement of human population on Arabian Peninsula during the Late Pleistocene.

D821 |
EGU2020-1756
Elke Zeller and Axel Timmermann

It has long been hypothesized that long and short term climate changes influenced early human evolution and dispersal. With the use of paleoclimate, archeological, genetic, and climate model data, we can infer climate factors that influenced dispersal and possible migration routes. Recent research has shown that with the use of data from these different disciplines, we can model human dispersal and interactions with the environment at a group level. However, decision-based questions such as push vs. pull scenarios and what is the optimal time to move are challenging to answer using classical differential-equation based models. With the use of individual-based modeling (IBM), we can connect archeological research with paleoclimate (modeling) data and build possible dispersal scenarios.

IBM has long been used in ecology to research the overall behavior of a group based on decisions made by individuals. In IBMs, each individual is modeled as a discrete agent who decides its action based on the environment and relation to other agents, thereby allowing for more individual variation and adaptation than is possible with classical differential-equation and difference-equation models.

Here we present some preliminary results from our climate forced IBM. Climate variables such as net primary production, temperature, and rainfall were obtained from a transient simulation of the LOVECLIM intermediate climate model. These climate factors were used for movement decisions and influence the birthrate and life span of the agents. We show the most likely dispersal routes for different climate scenarios and the role of dispersal strategies (push vs. pull).

D822 |
EGU2020-15470
| solicited
Konstantin Klein, Yaping Shao, and Masoud Rostami

Archaeological records indicate that human population experienced frequent decline and growth as humans were on their way to populate the whole planet. Our hypothesis is that climate and environment were the main drivers for human existence and dispersal. Based on this hypothesis, we develop a Lagrangian Constraint Random Walk Model (CRW) to simulate the dispersal of hunter-gatherers. Human existence potential (HEP) is estimated using climate/environment model data, supported by archaeological evidence. The CRW simulates the movement of individual humans with a stochastic differential equation. While the movement of the individuals has a random component, it is constrained by a drift term which depends on the HEP. Population growth and decline are represented using a birth and a death term. Sociological elements of hunter-gatherers, such as population pressure, conflicts, and cooperation, are considered in the model. With the CRW, we estimate human mobility and dispersal based on the statistical behavior of a large ensemble of individuals. Furthermore, by varying the external factors and hence the HEP, we evaluate the response of hunter-gatherer societies to climate change. We will present the model and a case study on the mobility of hunter-gatherers on the Iberian Peninsula during the Last Glacial Maximum.

D823 |
EGU2020-3401
| solicited
Kantapon Suraprasit and Hervé Bocherens

How climatic and environmental conditions contributed to early human migration between mainland and island Southeast Asia during the Pleistocene is one of the most hotly debated topics in paleoanthropological communities today. As Peninsular or Southern Thailand is regarded as an obligatory pathway for humans and mammals during their dispersal between these two terrestrial areas, the understanding of paleoenvironments and vegetation covers in this region is highly relevant. The hypothesis of a “savanna corridor” or a band of open vegetation (seasonal forests and grasslands) stretching from Central Thailand to Java during several periods of lowering sea level and exposed land bridges though the Pleistocene has been suggested for explaining the facilitated route of early humans and associated large mammals in migrating out of mainland Southeast Asia towards Sundaland southwards. However, the existence of savanna grasslands in Peninsular Thailand during the Pleistocene has rarely been demonstrated due to the scarcity of available proxies.

Here we reconstructed the Pleistocene vegetation and environments of the region using stable isotope analyses of mammalian tooth enamel from the channel cave deposits of Tham Phadan (Nakhon Si Thammarat Province in Peninsular Thailand) where diversified large mammal fossils were collected. The mammal fauna is tentatively attributed to a late Middle to early Late Pleistocene age according to the presence of an extirpated spotted hyaena Crocuta crocuta ultima. The stable carbon isotope results, ranging from -13.9‰VPDB to +4.3‰VPDB, reveal that an open vegetation/forest-grassland mosaic was dominant in this region, unlike the present-day landscapes that are mostly covered by rainforests, thus confirming the existence of a savanna corridor in Peninsular Thailand during that time. The extreme southward distribution of some grassland-related taxa (such as spotted hyaenas and Himalayan gorals), which were common in mainland Southeast Asia during the Pleistocene, reflects the habitat continuity from north to south of Thailand. However, the lack of fossil records of these two taxa in Peninsular Malaysia and the islands of Indonesia suggests that the open vegetation band did not extend far beyond the transequatorial region. Further investigations of the Pleistocene mammal faunas in the Thai-Malay Peninsula will be helpful to identify such a corridor and to examine the paleobiogeographic affinities of Southeast Asian large mammals in the future, providing empirical data for understanding the timing and pathways of human migrations into island South-East Asia.

D824 |
EGU2020-20692
Valerie Trouet, Tom De Mil, Matthew Meko, and Jan Van den Bulcke

High-resolution annual precipitation and temperature proxies are largely lacking in Southern Africa, partly due to the scarcely available tree species that are suitable for dendrochronology. Clanwilliam cedar (Widdringtonia cedarbergensis) from Cape Province, South Africa, is a long-lived conifer with distinct tree rings and thus a strong dendroclimatic potential. However, the climatic signal in its tree-ring width (TRW) is weak and other tree-ring parameters such as density need to be explored to extract climatic information from this proxy. Here we investigate the climatic signal of density parameters in 17 Clanwilliam cedar samples (9 trees) collected in 1978 (Dunwiddie & LaMarche, 1980). We use a non-destructive X-ray Computed Tomography facility to develop minimum density (MIND) and maximum density (MXD) chronologies from 1900 until 1977. EPS for both density series exceeded 0.85. For the period 1930-1977 (reliable instrumental records), MIND correlates negatively with early-growing season precipitation (Oct-Nov), whereas MXD correlates negatively with end-of-season (March) temperature. The spatial correlation between MIND and spring precipitation spans the winter rainfall zone of South Africa. Clanwilliam cedar can live to be 356 years old and the current TRW chronology extends to 1564 CE. Full-length density chronologies for this long-lived species could provide a precipitation reconstruction for southern Africa, a region where historical climate observations are limited and where societal vulnerability to future climate change is high.

References:

Dunwiddie, P. W., & LaMarche, V. C. (1980). A climatically responsive tree-ring record from Widdringtonia cedarbergensis, Cape Province, South Africa. Nature, 286(5775), 796–797.

D825 |
EGU2020-2944
Paul Strobel, Roland Zech, Marcel Bliedtner, Julian Struck, Bruno Glaser, Michael Zech, Michael E. Meadows, and Torsten Haberzettl

Hydrogen isotope analyses of leaf wax n-alkanes (δ2Hwax) are widely applied to reconstruct paleoclimate changes. To date, it has proved difficult to disentangle past changes in the isotopic signal of precipitation (δ2Hp) and other fractionation factors, e.g. evapo-transpirative enrichment. Oxygen isotopes from hemicellulose sugars (δ18Osugar) have been proposed to complement δ2Hwax and enable more robust paleohydrological reconstructions by coupling both isotopes. However, up to now, there is a lack of studies analysing both water isotopes in South Africa.

Therefore, we analysed δ2Hwax and δ18Osugar from topsoils from South Africa to evaluate the coupled isotope approach on modern reference material as an initial step towards more robust paleohydrological reconstructions. The results indicate that δ2Hwax significantly correlates with δ2Hp values for growing season precipitation. However, no correlation exists between δ18Osugar and growing season δ18Op. While the apparent fractionation εapp 2H, i.e. the difference between δ2Hwax and δ2Hp, is relatively constant and not affected by climate, εapp 18O correlates significantly with both potential evapotranspiration and the aridity index, indicating a strong influence of evapo-transpirative enrichment on δ18Osugar. Coupling δ18Osugar and δ2Hwax facilitates the reconstruction of δ2Hp and δ18Op in South Africa with a 1σ accuracy of ± ~27‰ and ± ~3.7‰, respectively, and relative humidity (RH) with a 1σ accuracy of ± ~17%.

In a second step, we applied the coupled isotope approach to a 14.6 m long sediment core to complement geochemical and sedimentological analyses. The core is from Vankervelsvlei, a fen near the southern Cape coast located 152 m above mean sea level within the year‑round rainfall zone of South Africa. Our results show relatively high values for δ2Hwax between 7,020 +200/‑270 and 4,770 +280/‑230 cal BP. Conventionally, this would be interpreted to indicate more arid conditions (referring to the ‘amount effect’ or enhanced evapo-transpirative enrichment). However, corresponding reconstructed RH values are high and point to more humid conditions. Thus, we interpret the higher δ2Hwax (as well as the isotopically positive reconstructed precipitation) to reflect changing moisture sources, i.e. more summer precipitation related to greater prominence of the Easterlies. Enhanced RH as well as increased wind speed inferred from high wind driven allochthonous input (Al, Sr, Ti), is associated with a maximum in obliquity during that time. Drier and less windy conditions are indicated between 4,770 +280/‑230 and 2,820 +350/‑330 cal BP, as suggested by lower δ2Hwax and reconstructed precipitation, low RH and reduced wind driven allochthonous input. Moister conditions persisted between 2,820 +350/‑330 and 1,620 +430/‑280 cal BP and are followed by a ~1 kyr dry period. Moisture levels have been increasing since 640 +90/‑100 cal BP.

D826 |
EGU2020-11782
| solicited
Ana Gomes, Simon Connor, Maria João Martins, Brandon Zinsious, Célia Gonçalves, Delminda Moura, Elena Skosey-LaLonde, João Cascalheira, Jonathan Haws, Judite Nhanombe, Mussa Raja, Paulo Fernandes, Reginelinda Mauelele, Roxane Matias, Sónia Oliveira, Susana Costas, and Nuno Bicho

To better understand Quaternary environmental changes in Southeastern Mozambique and their role in human evolution, it is first necessary to characterized the modern environment of this area and the environmental drivers on their evolution. For this reason, an international and interdisciplinary team interpreted the Inhambane Province’s geology, hydrographic and tectonic maps and open-access satellite imagery and derived products (for morphometric analysis and landscape interpretation). Inhambane province is in a coastal plain composed of a Pleistocene dune system, within which many lakes can be found. Additionally, a comprehensive review of the existing research for the region was conducted, to choose the most suitable lakes from which to collect sediment records for paleoenvironmental reconstructions. The team carried out fieldwork during the summer of 2019 in four of the selected interdunal lakes (Muangue, Nyalonzelwe, Nhambutse and Chivanene). During fieldwork the vegetation cover and the land uses were carefully described, and the lakes water column parameters were measured. Additionally, in the two lakes that presented the longest sedimentological records (Muangue and Nyalonzelwe), an unmanned aerial vehicle (UAV) survey was carried out to create high resolution maps and elevation models of the lakes and their surroundings. UAV flights were carried out at 25 and 60 m height, with a front and side overlap between 60 to 70 %, using georeferenced Ground control points (GCPs). The lakes’ areas vary between 0.4 (Muangue) to 0.8 km2 (Chivanene). The longest sedimentological records were found in lakes with a water level 5 m above the Mean Sea Level (MSL) and surrounded by higher dunes (between 31 and 121 m elevation in relation to MSL). Most of the lake margins are used for agriculture, livestock and housing and some have fish farming. Regarding vegetation, between 16 families and 27 species were identified around Nhambutse and 27 families and 43 species around Muangue. The lakes’ maximum depths vary between 1 (Nhambutse) and 4.6 meters (Muangue). All lakes are freshwater except Nyalonzelwe, which is brackish. On average, surface water pH varies between 7.2 (Chivanene) and 9.12 (Nyalonzelwe). Surface water temperature varies between 25.03 (Nhambutse) and 26.6 ° C (Chivanene). All the collected data highlight the diversity of interdunal lake environments in the Inhambane Province, and how these environments may impact the sedimentological record. This work was supported by project PTDC/HAR-ARQ/28148/2017, funded by the Portuguese Foundation for Science and Technology.

D827 |
EGU2020-11485
Elena Skosey-LaLonde, Ana Gomes, Maria João Martins, Simon Connor, Mussa Raja, Brandon Zinsious, Roxane Matias, Reginelinda Mauelele, Jonathan Haws, Delminda Moura, Gideon Hartman, Célia Gonçlaves, João Cascalheira, Sónia Oliveira, Paulo Fernandes, Susana Costas, and Nuno Bicho

In order to better quantify the role of climate variability in southeastern Africa, and its impact on the evolution and spread of anatomically modern humans, our international and interdisciplinary team cored a series of coastal lakes during the summer of 2019. Here, we present data from lake Nyalonzelwe, one of many interdunal lakes present along the coast in the Inhambane region of southeastern Mozambique. Nyalonzelwe sits 5m above MSL and is bounded by a Pleistocene dune system, reaching between 29-121m in elevation, protecting the lake from the Indian Ocean. The sedimentological record of Nyalonzelwe presents over 6m of stratigraphic variability, including a varve sequence spanning the basal 2m, making it an incredibly rare record of seasonal resolution climate variability and the first record of its kind in Mozambique. Two cores, C1 and C4, with depths of 6.12m and 6.22m respectively, were collected for multiproxy biogeochemical analyses and C14 dating using a Livingstone corer. This work seeks to present the results of Carbon, Hydrogen, Nitrogen (CHN) elemental analysis for core C1, sampled at 10 cm intervals and aragonite/calcite ratios for gastropod assemblages across C4, sampled at 1 cm resolution in preparation for stable isotope analysis.

CHN analysis was conducted using an Elementar model Vario EL III at the University of Algarve CCMAR for both organic and inorganic carbon present in sediment samples from C1. Aragonite/calcite ratios for identified gastropod species, namely Melanoides tuberculata, were collected from individual representatives in samples from C4 with more than 8 individuals present and determined using Fourier Transform Infrared Spectroscopy at the University of Connecticut. Nyalonzelwe cores C1 and C4 are stratigraphically correlated. Together these data represent the first look at Quaternary paleoenvironmental evolution in southeastern coastal Mozambique and the importance of climate (in)stability in the region and its impact on early modern human populations. This work was supported by the project PTDC/HAR-ARQ/28148/2017, funded by the Portuguese Foundation for Science and Technology.

D828 |
EGU2020-21437
| solicited
Ines Bludau, Max Weiss, Ellen Schnabel, Nicholas Thompson, Vangelis Tourloukis, Panagiotis Karkanas, Eleni Panagopoulou, Katarina Harvati, and Annett Junginger

In the fossil-rich sediments of the Megalopolis Basin, southern Greece, the remains of an ancient paleo-lake alternate between detrital units and lignite seams deposited during the Middle Pleistocene. The detrital sediments of MAR-1 (480-420 kyr) between two lignite seams are where lithics and elephant bones with cut-marks have been systematically excavated indicating hominin activity along a paleo-shoreline circa 440 kyr. Based on current knowledge, lignite seams formed during interglacials, while the silty-clay-rich deposits in between were deposited under glacial conditions. However, the paleoenvironmental and paleoclimatic conditions on shorter times-scales, leading to the preservation of hominin activity in the area, remain largely unknown. In order to reconstruct the paleo-environment including paleo-lake levels and thus sedimentation patterns and their governing paleo-climatic factors, we analyzed a high resolution 5-meter long sediment sequence from the archaeological site MAR-1. For the reconstruction, a multiproxy approach was applied using microfossils, grain-size, and geochemical analysis such as total organic carbon, total inorganic carbon, X-ray diffraction, and conventional X-ray fluorescence. Diatoms were often too corroded to be of use, most likely due to a combination of alkaline water conditions and the influence of silicate sponges. The results of the analyses revealed that MAR-1, located between lignite unit II and III, experienced multiple lake level oscillations mostly following insolation changes suggesting that several short-term wet-dry-wet cycles occurred during the investigated period, which must have impacted flora and fauna, including hominins, in the area. This research was conducted under the auspices of the Ephoreia of Paleoanthropology and Speleology, Greek Ministry of Culture, and was supported by the European Research Council (PaGE, CROSSROADS).

D829 |
EGU2020-8414
Hannah Hartung, Jane M. Reed, and Thomas Litt

The Eastern Mediterranean, and the southern Levant in particular, is a key region for palaeoclimatological and palaeoenvironmental research due to its highly complex topography and climatic variability. Our understanding of environmental variability and its possible drivers, and the interaction with migration processes of modern Homo sapiens from a source area in Africa to Europe, is still limited. This is partly because continuous sediment records of sufficient age are rare across the Mediterranean Basin. The deposits of the Dead Sea represent an ideal archive to investigate palaeoenvironmental conditions during human migration phases in the Last Glacial period (MIS 4-2). 

Diatoms (single-celled siliceous algae, Bacillariophyceae) have well-recognised potential to generate high-quality palaeolimnological data, especially in closed-basin saline lakes, but they remain one of the least-exploited proxies in Eastern Mediterranean palaeoclimate research. Here, we present preliminary results of a low-resolution diatom study derived from analysis of sediment deposits of Lake Lisan, the last glacial precursor of the Dead Sea. Sediment cores were recovered during an ICDP campaign in 2010/2011 from the centre of the modern Dead Sea. 18 sediment samples were analysed to investigate (a) the preservation of diatom valves in various evaporitic deposits (b) possible shifts in diatom species composition of Lake Lisan during the Last Glacial period, and (c) if diatoms can be used as proxy indicator for lake-level and, thus, palaeoclimate reconstruction. We focus on a prominent lake-level high stand of Lake Lisan at around 28-22 ka BP, which resulted in the merging Lake Lisan and freshwater Lake Kinneret.

First results show that the diatom preservation is exceptionally good in evaporitic deposits of the sediment cores from Lake Lisan, which is contradictory to the available literature. In contrast to Holocene deposits from the Dead Sea, diatoms are abundant in all analysed samples from laminated deposits from Lake Lisan: the diatom flora is dominated by halophilous benthic diatoms, such as Amphora spp., Halamphora spp. and Nitzschia spp. In phases of lake-level high stands of Lake Lisan, the diatom flora shifts towards a more plankton-dominated freshwater flora containing Aulacoseira spp. and taxa from the Cyclotella-ocellata-species complex.

D830 |
EGU2020-7706
Shaddai Heidgen, Elena Marinova, Raiko Krauß, Oliver Nelle, Martin Ebner, Stefan Klingler, Tatiana Miranda, Jörg Böfinger, Elisabeth Stephan, and Annett Junginger

The Upper Neckar and Ammer river valleys in southwestern Germany correspond to the southwestern limit of the overall distribution of the oldest Linear Bandkeramik (LBK) culture. More than 200 Neolithic sites are known from this region with one of the oldest sites located in the vicinity of the village Ammerbuch-Pfäffingen, around 10 km west of Tübingen, Germany. The archaeological record suggests that settlement activities occurred here between 7260 and 7110 cal BP (or 5310-5160 cal BC). Despite the various activities at the settling site itself, little is known about the environmental impact of the first settlers on the area, ranging from the introduction of farming and animal husbandry with impacts to the forests due to pasture and collection of wood, as well as possible control of water bodies. We here present the first results of a palynological study of two parallel, overlapping 8 m long sediment cores that were retrieved in 2018 from a shallow paleo-lake only a few hundred meters distant from the excavation site. The composite core allows environmental reconstruction of the area between 11540 and 7000 cal BP, based on six radiocarbon dates. Pollen analysis indicates mixed oak forests and an increase of light-demanding vegetation (i.e. Quercus, Corylus, Betula). Current analyses on micro- and macro-charcoal are going to reveal the natural or anthropogenic induced causes of paleo-fire events and Non-Pollen-Palynomorphs (NPP), including dung spores, unravel the possible presence of herbivores (including domestic ones) in the area. The results of the current study and its integration into the bioarchaeological record are relevant even beyond the region providing the usually rarely available paleoecological records from close proximity of an LBK site and thus deliver valuable insights on the environmental settings at the beginning of farming in central Europe.

 

D831 |
EGU2020-22297
Alexandru Petculescu, Virgil Drăgușin, Anca Avram, Sabrina Curran, Luchiana Faur, Radu Irimia, Ionuț Mirea, Chris Robinson, Marius Robu, Ionuț Şandric, Barbara Soare, Claire E. Terhune, Alida Timar-Gabor, and John Woodhead

The Olteț River Valley in southern Romania hosts a large number of fossiliferous sites, the richest of which is Valea Grăunceanului. Based on biochronological estimations, these sites were assigned to the Late Villafranchian (MN17/MNQ1), at ~2.0-1.8 Ma. As yet, no other dating methods were employed and our present study aims to provide the geological and geomorphological background for radiometric and trapped charge dating, as well as for the stratigraphic correlation of these sites. These deposits are represented by fluvial-lacustrine sediments belonging to the Dacian Basin, a part of the Eastern Paratethys domain.

Our approach is to create a regional stratigraphic column onto which to place the fossil sites. We first created a high-resolution 3D model of the surface using UAV technology. Further, we sampled sediments from several sections and determined their grain size and mineralogy. We also sampled pedogenic carbonates and fossil teeth for preliminary geochemical analysis, in preparation for uranium series dating.

Although no human fossils have been found so far in the Olteț River Valley, the site is important for understanding the environment used by early humans to migrate out of Africa. These sites are close both in time and space to important anthropological sites such as Dmanisi, Khapry or Kozarnika, while being part of an area dominated by large water bodies that included the Pannonian, Dacian and Euxinic lakes.

D832 |
EGU2020-2925
Janina Bösken, Nicole Klasen, Daniela Constantin, Ulrich Hambach, Daniel Veres, Christoph Schmidt, Stephan Pötter, Christian Zeeden, Frank Lehmkuhl, and Alida Timar-Gabor

Loess-paleosol sequences are in the focus of paleoenvironmental research because they offer potentially quasi-continuous terrestrial records of environmental change. For the research on paleoenvironments, paleoclimates, and human evolution studies reliable dating approaches are essential. Age models can be based on different methods, e.g. proxy data correlation and chronometric dating approaches. For the Urluia loess-paleosol sequence, which provides a high-resolution record covering the Last Glacial Cycle in the Lower Danube-Black Sea area (Romania), correlative and luminescence age models do not agree with each other (Bösken et al., 2018). While the results of internal quality checks of the luminescence data speaks for a reliable chronology, the radiometric ages of samples assigned to the MIS 4-5 interval based on stratigraphic evidence are significantly overestimated. As ages in the lower half of the section do not increase with depth, field saturation has been suggested, while new measurements indicate that laboratory saturation has not been reached. This contribution presents a detailed luminescence dating approach using OSL and pIRIR protocols for fine-grain quartz and polymineral samples. Furthermore, the geochronology of the Vlasca loess-paleosol sequence that is located at the bank of the Danube ~40 km north of Urluia is presented. The section was chosen because it contains a vast accumulation of loess with one prominent paleosol at the bottom (total height ~27 m), presumably covering a similar time-interval as the Urluia sequence. The dating approach includes fine-grain quartz, coarse-grain quartz, polymineral pIRIR225, and portable OSL measurements. The question whether the observed discrepancy between the dating results and the stratigraphy at Urluia represents a regional pattern and/or possibly intrinsic luminescence properties are responsible will be discussed.

References

Bösken, J., Zeeden, C., Hambach, U., Veres, D., Klasen, N., Brill, D., Burow, C., Obreht, I. and Lehmkuhl, F. (2018). Consistency challenges between correlative and luminescence age models for the last ~150 ka in the Lower Danube Basin loess-paleosol sequences. Geophysical Research Abstracts 20, EGU2018-7986, EGU General Assembly 2018.

D833 |
EGU2020-4723
Stephan Pötter, Janina Bösken, Igor Obreht, Philipp Schulte, Daniel Veres, Ulrich Hambach, Christian Zeeden, Slobodan Marković, and Frank Lehmkuhl

The vast Pleistocene aeolian sediments of the Lower Danube Basin are an important archive of Quaternary palaeoclimate dynamics in Southeast Europe. The intercalation of loess layers and fossil soils, so called loess-palaeosol sequences (LPS) are interpreted as the results of oscillating climate phases in the past. However, the characteristics of these LPS vary quite strongly, since they are influenced by various factors. Those factors are mainly the (palaeo-) climate, the (palaeo-) relief and the availability of source material, which differ notably, even at a regional scale. Taken that into account, it is crucial to consider local characteristics while comparing data from different LPS.

Against this backdrop, we compare two LPS from the dry Bărăgan steppe area in southeast Romania: Vlasca (VLA) and Balta Alba Kurgan (BAK). The two sections are approx. 100 km afar and developed under different geomorphic and climatic situations, resulting in varying accumulation rates and post-depositional alterations. Vlasca is a natural exposure on the left bank of the Danube River, whereas BAK is situated in a road cut, approx. 15 km south of the Carpathian bending. The two sites show remarkable differences concerning accumulation rates, grain size, colour, geochemical characteristics as well as magnetic properties, which are interpreted as the results of sediment availability, depositional milieu and especially post-depositional alterations. The variations and the commonalities are used, together with the chronological framework, to better understand the palaeoclimatic evolution of the Lower Danube Basin within the last glacial cycle and to gauge possible ramifications of palaeoclimatic variations on the migration of modern humans.

D834 |
EGU2020-18353
Philipp Schulte, Tobias Sprafke, and Frank Lehmkuhl

Loess-paleosol sequences are sensitive terrestrial archives of Quaternary aeolian dynamics and paleoclimatic changes. Loess is predominantly formed during glacial periods, whereas soils form during interglacials and interstadials, when dust sedimentation is reduced or absent. Common grain size (GS) based proxies used in loess research mainly reconstruct past sedimentation dynamics. However, the GS distribution of a loess sample is not solely a function of aeolian dynamics; rather complex polygenetic depositional and post-depositional processes must be taken into account.

Here we integrate GS data of primary loess samples from 14 profiles in Europe as baseline to identify and quantify the imprint of local paleoenvironments on GS distribution along vertical loess sections. Our GS data are measured by the same laser diffraction device (Beckmann Coulter LS13320) and available in the database of the Physical Geography laboratory at the RWTH Aachen University. Based on a catalogue of criteria, samples with least signs of weathering and reworking (e.g. low GS mean and good sorting, low magnetic susceptibility, low geochemical weathering proxies) are defined as primary loess of the studied loess sections. GS distributions of these loess samples show little variation, both within individual profiles (temporal) and in a supra-regional comparison (spatial). We calculate an averaged loess sample and interpret it as baseline loess or European Standard Loess. We discuss the significance of deviations from this standard loess related to different geomorphological conditions during deposition and later pedogenetic processes.

D835 |
EGU2020-681
Christian Laag, Ulrich Hambach, Christian Zeeden, Mladjen Jovanović, and Slobodan Marković

Quaternary palaeoenvironmental recorders are particularly in the Northern Hemisphere provided by loess-palaeosol sequences (LPSs). In the Middle Danube basin, these terrestrial archives cover the last million years (Markovic et al., 2015) of the climate history as well as archaeological horizons from occupations by early humans. The Zemun loess site (ZLS, located in the Vojvodina, Northern Serbia) was declared as a protected site, based on artefacts of previous settlements found on the river bench. For providing a stratigraphy for this site and to set the archaeological findings into an environmental and temporal context, the ZLS was investigated by means of environmental magnetic and colorimetric properties. This requires not only to creation of a stratigraphy to be compared to already investigated sites of northern Serbia, but also provides independent age control, carried out by tephrochronology. Therefore, the ZLS contains two important chronological anchor-points, namely the L2-tephra (correlated to Vico Ignimbrite B and dated to 160.6 ± 4 ka, (Mannella et al., 2019)) and the Bag-Tephra (correlated to the Villa Senni eruption and dated to 351-357 ka (Fu et al., 2019)). This tephrochronological timeframe, in combination with the colorimetric and environmental magnetic parameters, witnesses an accumulation of mineral dust, providing insights from glacial to interglacial conditions ranging from marine oxygen isotope stage (MIS) 11 to MIS 4.

 

References

Fu et al. (2019): Chances and challenges in tephrochronology of loess: A case study from the Bag tephra in Serbia. Poster at the XX. INQUA International Quaternary Association Conference 25 – 31 July, Dublin, Ireland.

Mannella et al. (2019): Palaeoenvironmental and palaeohydrological variability of mointain areas in the central Mediterranean region: A 190 ka-long chronicle from the independently dated Fucino palaeolake record (central Italy). Qua. Sci Rev., 210, pp. 190-210.

Markovic et al. (2015): Danube loess stratigraphy – Towards a pan-European loess stratigraphic model. Earth-Sci. Rev., 148, pp. 228-258.

D836 |
EGU2020-13340
Dong-Geun Yoo, Seok-Hwi Hong, Gwang-Soo Lee, Jin-Cheul Kim, Gil-Young Kim, and Yun-Soo Choi

Sequence analysis using borehole samples and high-resolution seismic data in the Nakdong River valley reveals that the Nakdong River valley deposits, approximately 60 - 70 m thick, consist of a set of lowstand, transgressive, and highstand systems tracts that corresponds to a fifth-order (20 ka) sea-level cycle. Four main depositional systems, including ten sedimentary facies, constitute these systems tracts: fluvial, estuary, coastal/shoreface, and delta. The lowstand systems tract (LST), consisting of gravelly sand, forms a fluvial depositional system (Unit I) which fills the thalweg of river valley mainly developed approximately before 12 ka. The transgressive systems tract (TST) can be divided into two depositional systems (Unit II and III). The river-derived sediments were trapped within the paleo-estuary, forming an estuarine depositional system (Unit II) developed between 12 and 6 ka. As the transgression continued, the coarse sediments were deposited and redistributed by coastal processes, resulting in coastal/shoreface depositional system (Unit III). It is characterized by an isolated sand body and thin sand veneer. The HST is composed of deltaic depositional system including delta plain, delta front, and prodelta (Unit IV). During the delta progradation, most coarse-grained sands derived from the river were deposited in the lower delta plain and delta front, forming sand bars and shoals less than 15 m deep. The remaining fine-grained sediments were transported further offshore in a suspension mode and deposited in the inner shelf off the present river mouth, forming a subaqueous prodelta. Radiocarbon and optically stimulated luminescence (OSL) dating suggest that the recent deltaic system was initiated by aggradational and progradational stacking patterns at approximately 8 ka during the last stage of decelerated sea-level rise, and was then followed by a prograding clinoform after the highest sea level at approximately 6 ka.