Mineralogy and Geochemical Evidence of the Late Early Miocene Aridification Intensification in Xining Basin Caused By the Northeastern Tibetan Plateau Uplift

Abstract:

A typical inland aridification is present in Central Asia, global cooling, the retreat of Para-Tethys Sea and Tibetan Plateau uplift have been thought to be the main driving forces of the climate change in interior Asia during Cenozoic. However, only few terrestrial climate records from the Asian inland were extended to the late Oligocene-early Miocene, it is still unclear the evolution of aridification before the middle Miocene and which of these driving forces plays the key role. Here, a sedimentary, mineralogy and geochemical proxies record of the early Miocene sedimentary sequence (ca. 22.1 to 16.7 Ma) from Xining Basin was present in this paper, which locates in the northeastern side of Tibetan Plateau. Mineralogical and geochemical parameters show obvious two stages climate change. During ~ 22.1-19 Ma (Unit I), the enrichment of I/S (irregular mixed-layers of illite and smectite) content, high values of a*/L* and much stronger chemical weathering degree reveal a warm and humid climate condition. During 19-16.7 Ma (Unit II), the increase of chlorite and dolomite contents, the upward decrease of a*/L* and much weaker chemical weathering than Unit I suggest evidently increased aridity since ca. 19 Ma. Comprehensive comparisons among records from the central western China demonstrate that the aridification since ca. 19 Ma is widespread in northeastern of Tibetan Plateau. The early Miocene episodic uplift of the north and northeastern Tibetan Plateau, especially, the uplift of Laji Shan at ~22 Ma, possibly have played a key role in the aridification of the Xining Basin.