Geochemistry of the Paleocene saline lake in the southwestern Jianghan Basin, Central China: implications for provenance, tectonic setting, and palaeoclimate

As an important sedimentary area of mineral resources in central and eastern China, the Jianghan Basin has received more and more attention. In recent years, thick evaporites and potassium and lithium-rich brine ores have been discovered in the Paleocene strata in the southern Jianghan Basin, which provides a material basis for studying the genesis of evaporites in central and eastern China. This paper aims to further understand the provenance, tectonic setting and paleoenvironment of the Paleocene Shashi Formation in the south of Jianghan Basin through the study of whole-rock geochemistry, so as to provide theoretical basis for the formation of evaporite. The chondrite-normalized REE distribution pattern of the Shashi Formation’s siltstones are characterized by enriched LREE and flat HREE similar to those of UCC with negative Eu anomalies. Combined with the geochemical element ratio discriminant diagram, such as Al 2 O 3 -TiO 2 , Zr/Sc-Th/Sc, Hf-La/Th, and La/Sc-Co/Th, these samples were sourced from felsic source rocks. Moreover, the discriminant diagrams of K 2 O/Na 2 O-SiO 2 /Al 2 O 3 , La-Th-Sc, and Th-Co-Zr/10 suggest that the samples were formed under the tectonic settings of active continental margin and continental island arc. The discriminant diagrams of Zr/Sc-Th/Sc and Al 2 O 3 -Zr-TiO 2 show that all samples were not affected by recycling and hydraulic sorting. The weathering indices (CIA, CIW, PIA, and ICV) and the diagram of Al 2 O 3 -(CaO + Na 2 O)-K 2 O suggest that mild chemical weathering in the source area under arid climatic condition. And the palaeoclimatic indicators of Sr/Cu, Ga/Rb, and C-value indicate that the climate was cool and arid. According to the geochemical data and previous studies, the Paleocene sediments in the southwest of the Jianghan Basin were from felsic source rocks, and formed in the tectonic background of active continental margin and continental island arc, and the climate was mainly arid and cold.