The Sedimentary Sequence, Main Chemical Elements And The Monsoon Environmental Evolution Since 150 KaB.P.as Indicated By Chagelebulu Stratigraphical Section, Southeast Of Badan Jaran

There are 25 sedimentary cycles made up of aeolian palaeo-dune sands, loess, palaeosol, lacustrine facies and alluvial-hillslope sandy soils and gravels in Chagelebu section, Badan Jaran Desert . Analyses of the main chemical elements in the section shows that the contents of Al2O3; Fe2O3+FeO, CaO, MgO, K2O, Na2O and TiO2in the lacustrine facies, loess and palaeosol are higher than those in the aeolian palaeo-dune sands, but the contents of the SiO2 take on converse change, which constitutes 25 element-change cycles corresponding withabove-mentioned sedimentary cycles since 150ka B.P. The regulation of distribution, gathering and migration of each element in the section are corresponded with the fluctuations of its gathering and leach coefficient. The study shows that both stable elements Al2O3, Fe2O3+FeO, TiO2 and unstable elements CaO, MgO, Na2O, K2O can all gather in the warm and humid climate , which is related to its special low-lying depression. Comprehensive analysis of the main chemical elements indicates that, the element-change cycles are resulted from the alternative change between dry cold and windy and mild to warm-humid climates since the late Pleistocene. The change reason was induced by NW and SE swings of the winter and summer monsoons of East Asia during glacial and interglacial periods.This paper also makes a preliminary correlation between average values of the different periods of main elements in Chagelebu section and oxygen isotope phases. The result indicates that at warm phases MIS 1, MIS 3 and MIS 5, the values of SiO2 contents are lower and values of Al2O3, Fe2O3+FeO, CaO, MgO, K2O, Na2O, TiO2higher, that at cold phases MIS 2 and MIS4, their changes are converse, and that values of SiO2 contents are higher, and the rest elements lower. Therefore it is considered that the climate of multi-cycles of dry -humid and cold-warm and its changes recorded by the chemical elements since 150ka B.P .in Chagelebu section , is coupled ,in origin , with the cold-warm phases of the past global changes, at least on the larger time scales.