Geochemistry of rare earth elements of purple soil layers in the Middle-Lower Cretaceous Xiaoba Formation, Pushi area, Xichang

Geochemical characteristics of rare earth elements (REEs) in medium-alpine areas are of great significance to understanding regional ecological environment. In this paper, four typical soil profiles of the Middle-Lower Cretaceous Xiaoba Formation in Pushi area of Xichang City are systematically sampled and analyzed, and the characteristics of geochemical distribution, migration and enrichment of 14 kinds of rare earth elements such as La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu are studied detailedly. The results show that the contents of rare earth elements in the same kind of soils formed by different types of parent rocks are different under similar environments. The contents of rare earth elements in representative profiles of mudstone-purple soil profile (PM0909), sandstone-purple soil profile (PM03-3), silty mudstone-purple soil profile (PM04-4) and argillaceous siltstone-purple soil profile (PM0924) are 126.870 mg/kg, 116.472 mg/kg, 163.926 mg/kg and 175.231 mg/kg, respectively. The differences of rare earth element contents in each profile are closely relate to the lithology of soil parent rocks and the contents of clay minerals. Clay minerals have a certain adsorption effect on rare earth elements. The Chondrite-normalized distribution patterns of rare earth elements of 4 rock-soil profiles in Pushi area show an obvious "V" right-tilted model, with an obvious negative Eu anomaly and relatively flat curve of heavy rare earth elements. The Chondrite-normalized distribution patterns of rare earth elements of 4 rock-soil profiles in Pushi area belong to the light rare earth enrichment type, which is related to the difference of chemical properties of REEs leaching and parent rocks during the formation of soils. The migration coefficients of different parent rocks are various, and the high values of migration coefficient mainly distribute in the bottom of the sedimentary layer (B) and the parent layer(C) of in each profile, indicating the results of the leaching and deposition of REEs and the adsorption and desorption of clay minerals. The results of this study can provide a theoretical support for the large-scale eco-geological research in Daliangshan area.