Geochemical characteristics of Chengdu clay and their implications for provenance and weathering intensity

Abstract：The chemical composition of late Pleistocene Chengdu clay in Chengdu plain shows that SiO2 (75.24% on average), Fe2O3 (14.12% on average) and Al2O3 (5.81% on average) are dominant chemical compositions, Chengdu clay has an overall similarity in geochemical characteristics to the UCC. In comparison with the loess of northern China, Chengdu clay has higher TiO2/Al2O3, Zr/Al, Zr/Ti and Y/Al ratios, and lower Eu/Eu?鄢, LaN/SmN and LaN/YbN ratios. These features coincide with those of the Quaternary deep soil in Chengdu plain, which suggests local sources for the Chengdu clay in this region; nevertheless, Chengdu clay is quite different from the loess of northern China. The average chemical index of alteration (CIA) of Chengdu clay is 78.59, higher than that of the loess of northern China. Chengdu clay has experienced the intermediate K removal weathering stage, and Ca, Na, Mg and K seem to have been the main mobile elements in the weathering process. In comparison with the loess of northern China, Chengdu clay has greater depletion of Na, Mg, K and Ca, indicating a stronger weathering intensity.