Sediment history mirrors Pleistocene aridification in the Gobi Desert (Ejina Basin, NW China)
Authors: Schwamborn Georg , Hartmann Kai , Wünnemann Bernd , Rösler Wolfgang , Wefer-Roehl Annette , Pross Jörg , Schlöffel Marlen , Kobe Franziska , Tarasov Pavel E. , Berke Melissa A. , Diekmann Bernhard 
Published: July 2020

Abstract. 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 δD) are used to infer the main
transport processes and related environmental changes during the
Pleistocene. Magnetostratigraphy supported by radionuclide dating provides
the age model. Grain-size 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 110 m 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 0 m 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.