Geochemical characteristics and environmental significance of Talede loess-paleosol sequences of Ili Basin in Central Asia

摘要

The loess-paleosol deposit in Central Asia is a sensitive indicator of the evolution of the quaternary pa-leoclimate in the Westerlies, providing insight into the quaternary climate history and its relationship with global climatic changes. Based on the geochemical analysis of elemental composition of densely sampled strata from Talede loess-paleosol sequence in the Ili Basin, the results showed that SiO_2 had the highest major elements content, followed by A1_2O_3. The order of compositional abundance of major elements was generally as follows: SiO_2 ＞ A1_2O_3 ＞ CaO ＞ Fe_2O_3 ＞ MgO ＞ Na_2O ＞ K_2O. Trace elements (i.e. Rb, Sr, Sc, Ni, Cu, Ga, Mo, Y, Pb, Th) in the paleosol layers (i.e. S_o, S_m, S_l) and the loess layer of L_1 were enriched relative to underlain loess (L_2) horizons, except for the contents of Zr, Cs, Nd, and La in paleosol layers. All of geochemical proxies, such as enrichment factor, Rb/Sr ratio, eluvial coefficient (K_i) and chemical weathering index, display no obvious differentiation in the Talede loess-paleosol deposit. The results indicate that the weak chemical weathering, greater evaporation and low effective moisture in Ili Basin, are to a degree weaker than those in the China Loess Plateau and the climate was warm-dry during the interglacial period. In addition, the loess of Ili area is rich in schistose minerals and implies that the loess may come from the deserts of Central Asia and it may be closely related to the widespread aridification of Central Asia.