Strongest chemical weathering in response to the coldest period in Guyuan, Ningxia, China, during 14-11 Ma.

Abstract

Moisture evolution in Central Asia including Northwest China shows less similarity with its surroundings and attracts a growing number of studies. In this study, a well-dated thick lacustrine sequence is chosen in Northwest China and detailed geochemical analysis is conducted during the Middle Miocene Climate Transition (MMCT, 14–11 Ma). The multi-proxy records (Na2O/Al2O3, CIA, Rb/Sr) revealed that chemical weathering was the strongest during 11.85–11 Ma, the coldest period in 14–11 Ma as evidenced by the global deep-sea oxygen isotope records. Accordingly, we conclude that global climate cooled during MMCT and reached the coldest during 11.85–11 Ma. Thus, the westerly circulation became the strongest during this period, which brought more water vapor to Northwest China and the chemical weathering was significantly improved. On the other hand, the significant decrease in temperature led to the marked weakening of evapotranspiration, and thus the effective humidity was relatively increased. Both aspects contribute greatly to the significant enhancement of chemical weathering in eastern Central Asia. This weathering history of the sediments in the northeastern Tibetan Plateau is of great scientific significance to understanding tectonism and climate change in Asia during MMCT.