Establishing the modern-like differential climate of the Qaidam Basin, northeast Tibetan Plateau, since ca. 9 Ma: Implications of the effect of interactions between tectonics and atmospheric circles on paleoclimate

The Qaidam Basin plays a key role in understanding the Cenozoic tectonic and climatic evolution of the northeast Tibetan Plateau. Despite its significance, how the interactions of tectonics and atmospheric circulations at different scales have established the modern-like climatic pattern in the region remains unclear. In this study, grain-size analysis was subjected to the late Cenozoic sediments of the Dahonggou Section in the northeastern Qaidam Basin to reveal the paleoclimatic evolution of the Qaidam Basin. The upward increase of mean grain size and coarse grain content (i.e., hydatogenic-origin content) and decrease of fine grain content (i.e., eolian-origin content) in the Dahonggou Section indicate a trend to an enhanced precipitation condition since the deposition period of the Shangyoushashan Formation (ca. 9 Ma, according to the recent geochronological framework), consistent with previous results (i.e., in the Huaitoutala Section and Nanbaxian areas) along the northeastern Qaidam Basin. By contrast, previous studies suggest that the southwestern Qaidam Basin (i.e., in the Honggouzi Section and KC-1, SG3, ZK402, and F2 boreholes) displayed less precipitation and thus a more arid climate at the same time. Such a differential climate pattern, i.e., less precipitation on the southwestern and more on the northeastern Qaidam Basin, is quite similar to the state of the present climate, suggesting that the modern-like climate of the basin may have been established at least since ca. 9 Ma. Through analyzing the present moisture source and wind field, we suggest that the differential climate of the Qaidam Basin since ca. 9 Ma is a result of an integrated effect of the westerlies on a global scale, the atmospheric subsidence at the northeast margin of the Tibetan Plateau due to plateau uplift on a regional scale, and the atmospheric upwelling at the south slope of the elevated Qilian Shan due to its uplift on a local scale. This study sheds new light on the effect of interactions between tectonics and atmospheric circles of different scales on the paleoclimate of a specific region.