Geochemical Characteristics and Climatic Environmental Significance of Holocene Loess on South Qinghai Lake Shore

Qinghai Lake, located in Northeast Qinghai-Tibet Plateau, is the biggest inland lake in China. Many research results with regard to Holocene environmental evolution in Qinghaie lake area have been achieved by analyzing the lacustrine sediments. The Holocene loess section at Heimahe on south Qinghai lake shore was found to contain an ashes layer of ancient human activity at about 2 m thick and it was dated to be {11 200} a BP. From the section 21 samples have been taken to test the chemical contents of CaCO_(3), CaO, MgO and Sr element, and the oxygen and carbon stable isotopes of carbonate. The CaCO_(3), CaO, MgO and Sr components contained in acid-solution fraction have been proven to be the reliable geochemical indicators for distinguishing the paleaosol from loess, and oxygen and carbon stable isotopes could reveal the climatic and environmental change in the process of loess aggradation. The distributing curves of chemical components of CaCO_(3), CaO, MgO and Sr in the section all exhibited two peaks and three valleys, according to which we divided Heimahe loess section into two strata, the upper one is loess and the lower one is paleosol, the paleosol is made up of two sub-layers. The distribution curves of δ~(18)O and δ~(13)C in the section also have remarkably shown the cold climate event at about {8 400} a BP and the climatic change from warm-humid to cold-dry since New Glaciation period. The results are similar to the research results in East Kunlun Mountains and Loess Plateau.