Description: Central Asia is a large-scale source of dust transport, but it also held a prominent changing hydrological system during the Quaternary. A 223 m long sediment core (GN200) was recovered from the Ejina Basin (synonymously Gaxun Nur Basin) in NW China to reconstruct the main modes of water availability in the area during the Quaternary. The core was drilled from the Heihe alluvial fan, one of the world’s largest alluvial fans, which covers a part of the Gobi Desert. Grain-size distributions supported by endmember modelling analyses, geochemical-mineralogical compositions (based on XRF and XRD measurements), and bioindicator data (ostracods, gastropods, pollen and non-pollen palynomorphs, and n-alkanes with leaf-wax ∂D) are used to infer the main transport processes and related environmental changes during the Pleistocene. Magnetostratigraphy supported by radionuclide dating provides the age model. Grainsize endmembers indicate that lake, playa (sheetflood), fluvial, and aeolian dynamics are the major factors influencing sedimentation in the Ejina Basin. Core GN200 reached the pre-Quaternary quartz- and plagioclase-rich “Red Clay” formation and reworked material derived from it in the core bottom. This part is overlain by silt-dominated sediments between 217 and 110m core depth, which represent a period of lacustrine and playa-lacustrine sedimentation that presumably formed within an endorheic basin. The upper core half between 110 and 0m is composed of mainly silty to sandy sediments derived from the Heihe that have accumulated in a giant sediment fan until modern time. Apart from the transition from a siltier to a sandier environment with frequent switches between sediment types upcore, the clay mineral fraction is indicative of different environments. Mixed-layer clay minerals (chlorite/smectite) are increased in the basal Red Clay and reworked sediments, smectite is indicative of lacustrine-playa deposits, and increased chlorite content is characteristic of the Heihe river deposits. The sediment succession in core GN200 based on the detrital proxy interpretation demonstrates that lake-playa sedimentation in the Ejina Basin has been disrupted likely due to tectonic events in the southern part of the catchment around 1 Ma. At this time Heihe broke through from the Hexi Corridor through the Heli Shan ridge into the northern Ejina Basin. This initiated the alluvial fan progradation into the Ejina Basin. Presently the sediment bulge repels the diminishing lacustrine environment further north. In this sense, the uplift of the hinterland served as a tipping element that triggered landscape transformation in the northern Tibetan foreland (i.e. the Hexi Corridor) and further on in the adjacent northern intracontinental Ejina Basin. The onset of alluvial fan formation coincides with increased sedimentation rates on the Chinese Loess Plateau, suggesting that the Heihe alluvial fan may have served as a prominent upwind sediment source for it.

Description: Wir leben in einer Zeit des Klimawandels, der sich unter anderem im Schwund polarer Eismassen zeigt. Dieses Phänomen ist in der Erdgeschichte nicht außergewöhnlich. Außergewöhnlich ist allerdings die momentane Ursache dafür, das menschliche Klimaexperiment. Ein Blick in die Vergangenheit zeigt, dass das Antlitz der Erde nicht nur vom Kommen und Gehen von Ozeanen und Gebirgen sowie vagabundierenden Kontinenten diktiert wurde, sondern auch stets vom natürlichen Klimawandel geprägt war. Aus der Vergangenheit können wir lernen, welche Umweltbedingungen uns künftig unter den prognostizierten künftigen Szenarien des Klimawandels erwarten könnten. Lagen Teile Afrikas vor 300 Millionen Jahren unter Gletschern begraben, so lebten vor 150 Millionen Jahren die Dinosaurier in einer uns fremdartigen Welt mit eisfreien Polen und weit verbreitet unter tropisch bis subtropischen Bedingungen. Heute erleben wir eine Welt mit ewigem Eis in der Antarktis und schwankenden Eisausbreitungen in der Arktis, Nordamerika und Europa. So ist die norddeutsche Landschaft ein Erbe der letzten Eiszeit vor 20.000 Jahren, als skandinavische Eisschilde bis nach Schleswig-Holstein und Brandenburg reichten und die Nordseeküste nördlich von England lag. Das heutige Nordseebecken wurde von Tundra eingenommen, so wie wir sie heute aus Ostsibirien kennen. Die heutige Arktis mit grönländischem Eis, sibirischem Dauerfrost und Meereis am Nordpol stellt einen Rest dieser eiszeitlichen Welt dar. Die Frage ist, wie lange noch? Inzwischen hat der Umweltwandel auch die Antarktis erreicht. Der Vortrag beleuchtet die geowissenschaftliche Vorgehensweise zu diesem Erkenntnisgewinn. Das Spektrum der Forschungsansätze reicht von der traditionellen Feldgeologie in abgelegen Regionen bis hin zu modernen Forschungsschiffeinsätzen und der Heimarbeit im Labor und am Rechner.

Description: The Beenchime-Salaatinsky Crater (BSC) is located west of the Olenyok River in Northern Yakutia, ~ 260 km south-west of Tiksi and the Lena Delta. The age and origin (volcanic versus meteoritic) of this crater is poorly understood. The key scientific interest in re-visiting the BSC is the reappraisal of the Quaternary sedimentation dynamics for a better understanding of the sediment history and thickness in the basin. This aides for an assessment, if the site is prospective for a deeper drilling of a Quaternary (or Cenozoic) sediment archive. Soil pits and auger cores from slopes and lowland terrain in the basin were sampled and studied to infer sediment ages and transport dynamics. This also included a thermokarst lake placed in the centre of the basin. Studied properties include grain-size distribution, organic carbon and nitrogen contents (TOC and TN), heavy mineral compositions, δ13C of organic carbon, 14C ages from sediment, δ18O and δD from ground ice and waters, and lake bathymetry from GPR profiling, in addition. We conclude that the crater floor in the BSC is underlain by fluvial/alluvial sediments from the MIS 3 period. Thermokarst lake formation took place during the Holocene Thermal Maximum between 7600 and 6100 cal yr BP. The lake has been shrinking hereafter. Fluvial/alluvial sedimentation along the drainage pattern was active again between 5700 to 1500 cal yr BP, and it was flanked by the accumulation of peaty and organic-rich sediments and the formation of ice-wedge polygons.