Paleotemperature And Its Potash-forming Effect In Early And Middle Triassic In Eastern Sichuan Basin

Sichuan basin is one of the important marine salt-forming basins found in China.According to previous studies, the thickness of the slat-bearing strata in Sichuan Basin is about one thousand meters, and there were many minerals rich in potassium such as polyhailte and leonite, precipitated during the formation of the middle-lower Triassic Sichuan salt basin, which can be divided into six stages, suggesting a promising prospecting.This paper focused on the Changping 3rd and ZK-2 wells distributed in the eastern Sichuan Basin, discussed about the process of the enrichment of potassium,based on the previous studies, homogenization temperature of fluid inclusions,petrographic and geochemical characteristics and some other data obtained during our work.According to our study on the fluid inclusions from the halilith in the eastern Sichuan Basin, we found many primary fluid inclusions preserved in the halite, which can directly reflect the paleo-temperature of seawater in the early Triassic. The result of homogenization temperature of the primary fluid inclusions range from 17.7℃ to63.5℃, which is consistent with the temperature(32℃~61℃) calculated by isotopic data in the same area. As thus, we confirm that the paleo-temperature of the seawater during the period of salt-formation is high, suggesting a rather warm paleo-climate in eastern Sichuan in the early-middle Triassic.Combining the geochemical data of the analyzed samples from Changping 3rd and ZK-2 wells and the coefficients of K, Mg, Br and Cl, we suggest that the orange polyhalite halilith in the Changping 3rd well has experienced the heaviest evaporation and concentration of the seawater, in other words, in the period of and the T1J4-2, the evaporation and concentration of the brine was strongest. Besides, the coefficients of Br and Cl reveal that potassium-slat began to precipitated in the easter Sichuan during the period of T1J4-2.The formation of salt and potassium deposits was genetic-linked with the rather warm paleoclimate in Triassic, and also well controlled by and the special structures,especially the Luzhou-Kaijiang dome. The paleotemperature of the seawater had an important effect on the rate of evaporation and the concentration of the brine, while the paloe-structures provided a stable and closed place for the process. Considering the paleo-temperature and paleo-structures in the eastern Sichuan Basin, we suggest that condition in the period of T1J4-2h is more favorable for formation the salt and potassium deposits than the period of Badong.