Aridification recorded by lithofacies and grain size in a continuous Pliocene-Quaternary lacustrine sediment record in the western Qaidam Basin, NE Tibetan Plateau

摘要

The Pliocene-Quaternary aridification of the Asian interior is key to understanding the impacts of global cooling and Tibetan Plateau uplift and the potential linkage to North Pacific Ocean biochemical processes and global changes. However, there is a lack of detailed continuous Pliocene-Quaternary paleoclimatic records from the Asian interior because most climatic records have been obtained from discontinuous coarse sediment outcrops around the rims of inland basins. Here, we provide a continuous, high-resolution 3.1 Myr record of grain size from the well-dated SG-3 borehole in the western Qaidam Basin on the northeastern Tibetan Plateau, NW China. The results reveal a long-term upward coarsening trend in grain-size that can be divided into three phases: (i) 3.1-1.1 Ma, laminated fine sediments (fine to medium silts) containing scattered gypsum crystals and interbedded by thin beds of marl; (ii) 1.1-0.15 Ma, massive medium to coarse silts interbedded by beds of mirabilite; (iii) 0.15-0 Ma, coarse silts containing thin layers of mirabilite, halite, bloedite, and polyhalite. This pattern reflects the upward shallowing and shrinking of the lake from a brackish lake to a salt lake, and then to a playa, suggesting a long-term stepwise drying of the Asian interior since the Late Pliocene, probably forced by global cooling and uplift of the Tibetan Plateau.