Provenance change and continental weathering of Late Permian bauxitic claystone in Guizhou Province, Southwest China

Abstract

Known as the Guadalupian-Lopingian boundary (GLB), the unconformity between the Guadalupian (Middle Permian) and Lopingian (Late Permian) is widespread in the South China Block. This boundary presents an important period with actives of the Emeishan Large Igneous Provenance (ELIP), the regression and the mass extinction. In Zunyi and Liupanshui areas of Guizhou Province, southwestern China, marine deposits of the Middle Permian Maokou Formation were covered by the terrigenous deposits of the Upper Permian Longtan Formation, the bauxitic claystone at the bottom of the Longtan Formation indicates the exposure during the Middle - Late Permian transition. The provenance of this bauxitic claystone in the South China is complicated, previous studies argue that the flood basalt and submarine volcanic rocks in the ELIP and the aeolian tuff in the Indochina Block are potential sources. In this study, new mineralogical, geochronological and geochemical data are got from the NW Guizhou, our new data constrain the age of bauxitic claystone in Zunyi and Liupanshui are 262.1 ± 1.5 Ma and 267.0 ± 2.7 Ma, respectively. Combined with trace element geochemical analysis, the source materials of bauxitic claystone in Zunyi is mainly derived from the intermediate-acid extrusive rocks in the ELIP, while the provenance of bauxitic claystone in Liupanshui is derived from the submarine volcanic activities during the initial stage of the ELIP. From the central area of ELIP to the outer area, the provenance of early Late Permian sediments transforms from the volcanic rocks of ELIP to Paleo-Tethys magmatic arc. Mass balance calculation and geochemical multivariate statistical methods show that the bauxitic claystone in Zunyi experienced two groundwater level variations in the land surface leaching stage, and Fe2O3、P2O5、HREE show similar geochemical behaviors. HREE is adsorbed by iron phase minerals and phosphate minerals, resulting in simultaneous migration. Our study also finds that paleogeographic location is an important factor for Late Permian bauxitization in South China. The different paleogeographic location determines the supply mode of provenance, provenance lithology, exposure time, leaching degree and other factors.