PLIOCENE-PLEISTOCENE CLIMATE CHANGE AT THE NE TIBETAN PLATEAU DEDUCED FROM LITHOFACIES VARIATION IN THE DRILL CORE SG-1, WESTERN QAIDAM BASIN, CHINA

The Pliocene-Pleistocene sedimentologic evolution of the western Qaidam Basin at the NE Tibetan Plateau was studied on the nearly thousand-meter-deep drill core SG-1 (spanning ca. 2.8-0.1 Ma), recovered from the Chahansilatu sub-depression with an average recovery rate of 95%. Lithofacies variation records the regional climatic change in relation to Asian drying and Tibetan Plateau uplift. Sedimentary textures and structures demonstrate a continuous slight coarsening and an increase of evaporites upward. We recognized five lithofacies: (1) gray-black laminated mudstone, (2) gray massive mudstone and siltstone, (3) bedded halite, (4) loose muddy halite, and (5) brownish-yellowish saliferous siltstone and mudstone, representing (1) semi-deep fresh to semi-brackish lake, (2) shallow brackish lake, (3) perennial saline lake, (4) playa saline lake, and (5) saline mudflat conditions, respectively. Variation of the lithofacies through the core demonstrates a clear trend of lake shrinkage since the late Pliocene and the final termination of the Chahansilatu paleolake. Accelerations of lake shrinkages are observed at ca. 2.5 Ma, 2.2 Ma, 1.6 Ma, 1.2 Ma, 0.9 Ma, 0.6 Ma, and 0.1 Ma. Our results suggest that the long-term stepwise drying of the Asian inland may have been forced by the change of the global ice volume.