The grain size end-members of aeolian deposits and their implications in the Menyuan Basin, northeastern Qinghai-Tibet Plateau

The northeastern Qinghai-Tibet Plateau is located at the intersection of the Asian monsoons and Westerlies, serving as a significant site for studying atmospheric circulation variations. The Menyuan Basin is characterized by extensive aeolian deposits, and the loess-paleosol sequence within the basin preserves abundant provenance and aerodynamic information. This research utilizes parametric grain size end-member (EM) analysis on the Yahecun profile within the Menyuan Basin, in conjunction with optically stimulated luminescence dating, to elucidate the composition, transport, and sedimentary processes of grain size. The study’s key findings are as follows: (1) Five distinct grain size groups were identified, each corresponding to specific transport mechanisms. EM1 (2.19 μm) is indicative of pedogenesis; EM2 (10 μm) represents suspended particles transported over long distances by the Westerlies; EM3 (31.67 μm) signifies regional wind-driven floating dust; EM4 (59.18 μm) is associated with coarse silt carried by nearby winter monsoons; and EM5 (120.23 μm) corresponds to local sand mobilized by strong winter monsoons. (2) The variability of EMs is controlled by different factors. EM1 is influenced by moisture of the East Asian summer monsoon and Westerlies. EM2 is governed by the position of the Westerlies. EM3 is regulated by local circulations including surface vegetation and a diminished winter monsoon. EM4 and EM5 are shaped by winter monsoon driven by high-latitude insolation, global ice volume, and the Atlantic meridional overturning circulation. (3) The deposition of loess in Menyuan integrates components from distant, intermediate, and proximal sources. The deserts and alluvial fans in Central Asia, the Qinghai-Tibet Plateau, and areas adjacent to the Menyuan Basin serve as major source regions for the Yahecun profile. Additionally, fluvial sediments, glacial lacustrine deposits, and alluvial fans within the basin significantly contribute to the provenance of coarse particles in the Menyuan loess.