Research On Petrological Characteristics And Diagenesis Of The Third And Fourth Members Of The Lower Triassic Jialingjiang Formation In Baimiaozi Gorge Of Chongqing Area

As an important petroliferous marine carbonate strata in Sichuan basin, the Lower Triassic Jialingjiang Formation has attracted a lot of people to study on it, these studies focused on the characteristics of sedimentary facies, reservoir characteristics and diagenesis, but these studies are limited to the particular structure or areas, lack of specially research or insufficient system deeply on the petrology characteristics and diagenesis of the Jialingjiang Formation carbonate in eastern Sichuan area, it can not exactly reflect the regional sedimentary characteristics, therefore, it is necessary for a depth research on the carbonate petrology characteristics of the Jialingjiang Formation in eastern sichuan area. Baimiaozi Gorge is located in Beibei area, which is to the eastern Sichuan Basin. Its structural position is on the west side of high and steep structures in East Sichuan, belong to the axis West Wing of Guanyin gorge anticline which is a branch of the Huaying Mountain brush structures. The tectonic line of this area mainly is the North East. Along the Jialing River, there are continuous Triassic strata exposed surface. This paper choose Jialingjiang Formation in Baimiaozi gorge section as the research object, combining field observations with laboratory analysis, based on the theories of sedimentary petrology, carbonate sedimentology and so on, systematic research the characteristics of the carbonate rocks, sedimentary facies and diagenesis of the third-fourth members of the Jialingjiang formation carbonate.The rock types of the third-fourth members of the Jialingjiang formation in Baimiaozi Gorge are abundant, most of mainly is carbonate, followed by salt dissolved breccia. The main rock type of the third member is limestone, including sparry grain limestone, microcrystalline particles limestone, containing particles micrite and micrite. The main rock types of the fourth member are dolomite and salt breccia, including microcrystalline dolomite, crystalline dolomite and salt dissolved breccia, micrite and crystalline limestone. Through the microscopic observation and cathode luminescence, we have been expounding the characteristic of all kinds of rock. Based on previous studies, combined with field phenomenon, petrology characteristic and paleontology characteristics, we have analysised the sedimentary environment of the third and fourth members of Jialingjiang formation, the sedimentary facies of the study area are open platform, restricted-evaporation platform and platform evaporite, and further divided into 5 subfacies, the depression and the beach in the open platform, lagoon, tidal flat and evaporation tidal flat.The third and fourth members of Jialingjiang Formation in Baimiaozi Gorge has experienced complex diagenetic processes. The types of diagenesis are various, including mud crystallization, calcite cementation, compaction and pressure solution, dissolution, dolomitization, recrystallization, fracturing, degypsification. From the special characteristics of rock fabric and all kinds of diagenesis, we can identify the study area has experienced the seawater undercurrent diagenetic environment of and atmosphere environment in the penecontemporaneous period, burial diagenetic environment in the diagenesis stage and table generating rock environment in supergene stage.