Chlorine isotope analysis of Triassic salt rock and geological significance of ancient salt lake in Sichuan Basin, China

In the northeastern Tethys Ocean in the early-middle Triassic, the Sichuan Basin was one of three regions where marine strata developed. Several periods of transgressions and regressions during that time contributed to the development of marine evaporites. The presence of extremely thick evaporites is a basic geological condition for potash formation that is exhibited in the Sichuan Basin, which has been an important region for the exploration of marine potash. The evaporites in the Sichuan Basin are abundant in bromine and possess high bromo-chloro coefficients. Although chlorine isotope values vary significantly within regions, they are relatively low and are similar to the negative values found in the Hechuan and Changshou areas. Comparative studies have been conducted regarding chlorine isotope values in the Sichuan Basin and in other prominent potash-forming basins with results, indicating that sea water concentrations had reached the late stages in the early-middle Triassic and a potential presence of potassium and magnesium salts.