Revealing paleosalinity and paleoclimatic characteristics in Dawenkou Formation of the Paleogene in Huanggang Depression, eastern China: An integrated geochemical and palynological analysis

The variations in paleosalinity and paleoclimate significantly influence the deposition and distribution of rock salt deposits. Understanding these variations is therefore essential for advancing knowledge of salt resource formation and supporting exploration efforts. In this study, we use an integrated approach combining geochemical and palynological proxies to reconstruct paleosalinity and paleoclimate during the salinization period of the Paleogene Dawenkou Formation, based on core samples from the ZK04 borehole in the Huanggang Depression, eastern China. The analysis identifies three distinct salinity phases spanning the late Eocene to early Oligocene: hyposaline water to mesosaline conditions, mesosaline to hypersaline conditions, and a return to hyposaline conditions. The intermediate hypersaline phase is particularly notable for a significant increase in both salinity and aridity, as evidenced by salinity-sensitive proxies such as the B/Ga ratio, boron excess (B_xs), corrected Sr/Ba, and sulfur-to-total organic carbon (S/TOC) ratios. Among these, the B/Ga ratio emerges as the most reliable indicator for reconstructing paleosalinity. The findings highlight the primary role of arid climatic conditions and elevated salinity in driving rock salt deposition in the Dawenkou Formation and offer valuable insights into the environmental controls on salt formation in other comparable basins worldwide.