The geochemistry and chlorine isotope revealed the origin and evolution of the Late Eocene evaporites in the Qianjiang Depression, Jianghan Basin

The thick evaporites within the Qianjiang depression are frequently considered a significant source of potassium-rich brine in the depression. This study conducted mineralogical, geochemical, and isotopic analyses on the late Eocene evaporites in the Qianjiang depression to investigate the origin and evolution of the evaporites. Based on field core descriptions and microscopic observations, the evaporites are primarily composed of dolomite, anhydrite, glauberite and halite. They display complete salinization cycles involving carbonate, sulfate, and chloride phases, along with two binary sedimentary cycles that sulfate to chloride and carbonate to sulfate. The high 1000 × Br/Cl ratio (0.37) and the low δ 37 Cl value (–0.41 ‰) observed in one sample do not necessarily indicate that the threshold of the potash stage has been reached. Instead, these values are more likely attributable to anomalies arising from the dissolution–recrystallization process. These results collectively suggest that the study area experienced a dry and hot climate, with significant warming and cooling processes, developing different sedimentary sequences. The obvious climate fluctuations during the Late Eocene led to the dominance of halite deposition in the saline lakes.