Geochemical characteristics of loess and paleosols in Yili Basin, NW China

Systematic geochemical studies on loess-paleosol sequences in Yili Basin, Xinjiang, NW China are carried out. Major and trace element composition, REE abundances, isotope systematics such as Rb-Sr, Sr-Nd and Sm-Nd are reported to characterize loess and paleosol in Yili Basin. Based on the major and trace element abundance, the paleosols from steppe zone can be distinguished from the loess by decarbonatation and higher contents of stable and relatively stable elements, such as Al2O3, TiO2, K2O and Rb, whereas the paleosols from desert steppe zone do not show distinct difference of major and trace elements concentration between loess and paleosols. Pedogenesis is thought to be influenced strongly by climate, especially by precipitation. REE patterns of Yili loess and paleosols are remarkably uniform with (La/Yb)(N) approximate to 7.6, this value is smaller than that of the upper continental crust (UCC), (La/Yb)(N) approximate to 9.0. Negative Eu anomalies, expressed in Eu/Eu* ratios vary from 0.61 to 0.82. Rb-Sr isotopic systematics of the loess-paleosols show a well-correlated pseudo-isochron which reflects the mixing of two components, i.e., the silicate material with high Rb-87/Sr-86 ratios and high (87)Nr/Sr-86 ratios and the carbonate materials with low Rb-87/Sr-86 and low Sr-87/Sr-86 (0.710). Neodymium isotopic compositions of Yili loess-paleosols are uniform with epsilon (Nd)(0) varies from -9.0 to -8.0, obviously higher than Luochuan loess-paleosols, from -9.3 to -10.4. The geo chemical evidences suggest that the Yili loess is an aeolian deposit and its material source and accumulating environment differs from the Central Loess Plateau.