EVOLUTIONARY PROCESS OF THE CLIMATE OF LOP NUR REGION OF XINJIANG SINCE MID-PLEISTOCENE

Climate variability since the mid-Pleistocene is studied from the proxies in core LS2 drilled in the Lop Nur region (N39°46'39.3″, E88°23'18.2 ″) in the eastern Tarim basin, Xinjiang, China. Geochemical properties, including CaCO₃ content, total organic carbon content (TOC) and total nitrogen content (TN), have been determined to reconstruct the environmental evolution of the area since the mid-Pleistocene. Change of sedimentary facies of Lop Nur region since the mid-Pleistocene is documented through the lithology of sediments. From bottom to top, the sedimentary facies of LS2 core can be classified into shallow lacustrine, shore-lacustrine, shallow lacustrine, shore-lacustrine and shore-lacustrine to aeolian deposites, with thickness of 12 m, 46 m, 11 m, 28 m and 18 m respectively. Evolutionary process of the climate can be divided into seven stages:Ⅰ(depth of 115~103 m), changing from warm-dry to cold-dry; Ⅱ (depth of 103~82 m), alternating between cold-wet and warm-dry; Ⅲ (depth of 82~67 m), relatively warm and dry; Ⅳ (depth of 67~57 m), relatively cold-wet; Ⅴ (depth of 57~46 m), relatively warm and dry; Ⅵ (depth of 46~18 m), three warm-dry climate fluctuations folded in the cold-wet climate background; Ⅶ (depth of 18~0 m), intensified arid. This study shows that the sedimentary environment is dominated by shallow lacustrine to shore-lacustrine facies during mid-Pleistocene, while mainly aeolian deposits since the late Pleistocene. The hydrothermal characteristics of climate mainly have been following the form of "cold wet-warm dry" in the region since mid-Pleistocene.