The Sources and Transport Dynamics of Eolian Sediments in the NE Tibetan Plateau Since 6.7 Ma

Abstract

AbstractThe red clay and loess‐paleosol sediments of the Xiaoshuizi and Halagu planation surfaces of the northeastern Tibetan Plateau (TP) provide insights into the response of paleo‐atmospheric circulation and surface processes to TP uplift and global climate changes. We present silicate Sr‐Nd isotope compositions and bulk sediment grain‐size parameters of the red clay and loess‐paleosol sequences, with the aim of reconstructing changes in the transporting wind systems and sediment source regions. The results indicate that the red clay on the planation surface was transported mainly by the westerlies from the Tarim Basin and the Qilian Mountains, while the loess‐paleosol sediments were transported mainly by the East Asian winter monsoon (EAWM) from the Badain Jaran Desert, Tengger Desert, and Qaidam Basin. These shifts in transport mechanism and source were likely related to major changes in the topography of the TP and the expansion of Northern Hemisphere glaciation since the Middle Pliocene. In addition, we reconstructed the evolution of the paleo‐atmospheric circulation from the Late Miocene to the Middle Pliocene. During the Late Miocene, both the paleo‐EAWM and East Asian summer monsoon (EASM) were weak, and westerly winds dominated the climate of the study area. During the Early Pliocene, both the paleo‐EAWM and EASM exerted an increasing influence on the study area. We ascribe the slight enhancement of the paleo‐EAWM to the gradual growth of the northern TP and the significant enhancement of the paleo‐EASM to global climate changes.