Seawater composition variation in the eastern Sichuan evaporite formation basin: Constraint from 87 Sr/ 86 Sr and major ion compositional evidence of halite

Abstract

Abstract The Hechuan Depression is a secondary depression in central eastern Sichuan and belongs to the Nanchong salt area (central Sichuan salt-forming zone). Palaeotethys seawater entered the secondary depression, and the subbasin gradually became shallower with tectonic changes. In this paper, the content of Sr ranges from 130 to 1316 ppm, which indicates that the water‒rock interaction time was long. The Br content of Jianglingjiang halite ranges from 108 to 191 ppm, and the Br content of the salt rock is mainly controlled by the Br concentration in concentrated seawater. The 1000Br/Cl ratio ranges from 0.18 to 0.51, which has reached the potassium mineral precipitation stage. The global environmental conditions of the Early Triassic were inherited from the late Permian with high temperature, anoxia, water stagnation and other environmental factors. The Sr isotopes of halite samples show that the ratios range from 0.708147 to 0.708256. By comparing the early Triassic SIS curve, which is consistent with the trend between the Smithian and Spathian, it can be basically determined that the evaporites were deposited in the Olenekian.