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.