Chemical Weathering Intensity and Element Migration Features of the Xiashu Loess Profile in Zhenjiang

The chemical weathering intensity and element migration features of the Xiashu loess profile in Zhenjiang are studied in this paper.Based on the comparison with other aeolian-dust deposits,i.e.Quaternary loess-palesol and late-tertiary red-clay profiles in the Loess Plateau,and aeolian dust red earth in Xuancheng of Anhui province,we draw the following conclusions:(1)The Xiashu loess profile underwent moderate chemical weathering,which was stronger than that of the loess and palesol in Luochuan,much weaker than that of the aeolian dust red earth in Xuancheng,and similar to that of late-tertiary red-clay in Xifeng.The chemical weathering differences among the studied aeolian-dust deposits were mainly induced by the distinction of the climate condition,which imposed important influence on the geochemical environment through the mean annual temperature and annual precipitation.It seems that the annual precipitation has more important influence on the chemical weathering process.(2)The major elements such as Si,K,Na,Ca,Mg,Mn and P were migrated and leached,while the elements Fe and Ti were slightly enriched during the chemical weathering process.According to the migration ability,the major elements are ranked in the following order:P Na Ca Mg K Fe2+ Si Mn Al Ti Fe3+.The migration features of the major elements reveal that the Xiashu loess finished the primary process of chemical weathering characterized by leaching of Ca and Na,and almost reached the secondary process characterized by leaching of K.Except the elements Sr and Ga,other trace elements such as Th,Ba,Cu,Zn,Co,Ni,Cr and V were enriched during the chemical weathering process.And this enrichment might be caused by both the biogeochemical process and the adsorption of trace elements by clay mineral and organic materials during the chemical weathering.(3)The difference of element migration down the Xiashu loess profile reveals that the climate was warm and wet at the early-middle stage of the Middle Pleistocene(before 0.24 Ma),however,bearing the feature of an alternate dry and wet fluctuation.At the end of the Middle Pleistocene,it became dry and cool,which resulted in the weakest weathering and element migration.At the early stage of the Late Pleistocene,the paleoclimate became warm and wet again,which led to rather strong pedogenesis and the formation of the paleosol S1 in the Xiashu loess profile.As a whole,the paleoclimate generally became drier and cooler in this region from the beginning of the Middle Pleistocene.