CHARACTERISTICS OF MAJOR GEOCHEMICAL ELEMENTS OF TACHENG LOESS DEPOSITS IN XINJIANG AND ITS PALEOENVIRONMENTAL IMPLICATIONS

In this paper,we studied the characteristics of major geochemical elements and weathering intensity of the loess deposits at the Tacheng section,Xinjiang,northwest China.Results show that among the oxides of the major geochemical elements,SiO2,Al2O3,CaO,CO3,Fe2O3,MgO,K2O and Na2O occur in a decreasing order in the loess section.There is obvious differentiation of oxides in the palaeosol and loess layers and the average contents of Al2O3,Fe2O3 and CaO were markedly higher in paleosol layers.CaO,Fe2O3,MgO,and K2O were accumulated and Na2O,SiO2,Al2O3 depleted in the section compared to the upper continental crust(UCC).The oxides have different distribution pattern in loess and paleosols and some of the major geochemical elements exhibit different concentrations in the topsoils and the paleosols.Further analysis shows that the Tacheng section had experienced weak chemical weathering after deposition,which was similar to the Yili loess section but far weaker than the loess deposits in the Chinese Loess Plateau and the lower reaches of the Yangtze River.The differentiation of weathering degree between the loess and paleosol was also distinct,indicating that the paloesols have experienced stronger weathering process.However,the eluviation of paleosol layers was weaker than that of loess layers probably resulting from the decline of humidity during the period of pedogenesis.The heat-moisture pattern might exert important effect on the chemical weathering of loess/paleosol sequences in the arid area.