Palaeodunes intercalated in loess strata from the western Chinese Loess Plateau: Timing and palaeoclimatic implications

摘要

Dune systems represent important palaeoenvironmental archives and therefore provide valuable information on past climate conditions of dryland regions. This study reports on several palaeodunes (thickness ca. 10-20 m) intercalated in thick loess accumulations, located in the Lanzhou area of the western Chinese Loess Plateau. The intercalated dune sands are well-sorted and have a typical aeolian dune structure, with distinct cross-bedded sand layers. The chronology for these palaeodunes and the related loess sediments was established by quartz optically stimulated luminescence (OSL) dating of 19 samples. The dating results indicate that sand dune accumulation occurred at ca. 35-25 ka, which implies a period of increased aridity during dune formation. This interpretation is in contrast to previously retrieved data from lake archives of the nearby deserts (e.g. Tengger and Badain Jaran desert), indicating a humid episode during marine isotope stage 3 (MIS 3). The previously proposed humid MIS 3a may not be universal over all of northwest China.