The aeolian sedimentary system along the transition between the Qilian Shan and northern Chinese drylands during the late Quaternary

Abstract

Central Asia hosts different large-scale wind systems (i.e., Westerlies, the Asian monsoon system) which interact along the transition between the Tibetan Plateau, the Chinese Loess Plateau, and northern Chinese deserts. This study focuses on the distribution of (mainly) aeolian sediments, involved geomorphological processes, and palaeoenvironmental implications in this transition zone between high mountains and deserts during the late Quaternary. A sample set of almost 800 sedimentological samples and 58 Optically Stimulated Luminescence (OSL) samples was obtained from the Qilian Shan mountain range and its northern foreland. Different geomorphological settings were sampled to assess spatial and temporal distribution patterns and evaluate geomorphological influences and palaeoenvironmental changes among sediment properties. Between the Qilian Shan (<5700 m asl) and its foreland basins (Hexi Corridor; <2000 m asl), a sediment classification based on grain size analysis yields six major sediment types which are distributed in three major sedimentological landscape units along an altitudinal cross section: I) Periglacial debris and glaciofluvial sediments above 3800 m asl. II) Primary loess is dominantly preserved between 3800 and 2000 m asl. III) Below 2000 m asl aeolian sands alternate with lacustrine deposits and gravel gobi surfaces (Nottebaum et al., 2014). Focusing on loess grain size, a significant fining trend is evident with increasing altitude. An increased contribution from far distant dust sources caused by stronger Westerly influence in altitudes >3000 m asl leads to a larger fine silt proportion. Additionally, steep mountain topography restricts the fluvial sand supply compared to flat foreland topography where rivers tend to aggradation (Nottebaum et al. 2014). Loess deposition started during the PleistoceneHolocene transition at around 12 ka (Zhang et al. 2015). Statistical decomposition of loess grain size distributions THESIS ABSTRACT