DISTRIBUTION CHARACTERISTICS AND GENESIS OF THE LOWER CAMBRIAN GYPSUM SALT ROCKS IN THE SICHUAN BASIN, CHINA

From the late Early Cambrian to the Middle Cambrian, the Sichuan Basin has a tectonic pattern of "two uplifts and a depression", and the arid and hot climate has created favorable conditions for the development of the gypsum salt rocks. In this paper, the rock types and their distribution characteristics of the Lower Cambrian gypsum salt rocks in the Sichuan Basin were clarified by using field outcrops, drilling profiles, thin sections and regional geological survey data. At the same time, the genesis of the gypsum salt rocks was discussed through analysis of salt sources, lithologic combinations and paleoenvironment. The results show that the Lower Cambrian gypsum salt rocks in the Sichuan Basin is mainly developed in the Lower Cambrian Long-wangmiao Formation (Qingxudong Formation), which forms multiple sedimentary centers with wide distribution, large variation, multiple interlayers, multiple gypsum rocks and less salt rocks. The salty substances in the salt rock are mainly derived from seawater. In the arid and hot and relatively closed paleoenvironment, the strong evaporation makes the seawater salinity increase significantly. At this time, the main lithology is the combination of dolomite or mud (sand) rock interbeded with gypsum salt rock, or gypsum salt rock interbeded with dolomite, or gypsum salt rock interbeded with dolomite or shale. The gypsum salt rock in the southeastern part of the Sichuan Basin is mainly formed in the lagoon environment, while the northeastern part of Chongqing city and the southwestern part of the Sichuan Basin are lagoon and evaporative tidal flat environments.