Research On Petrological Characteristics And Diagenesis Of The Lower Triassic Jialingjiang Formation In Libi Gorge Of Chongqing Area,Eastern Sichuan Basin

Libi Gorge is located in Yanjing town of Hechuan area, which is to the north ofChongqing city, eastern Sichuan Basin. Its structural position is on the west side ofhigh and steep structures in East Sichuan, belong to the axis–South East Wing of Libigorge anticline which is a branch of the Huaying Mountain brush structures. Alongthe Jialing River, there are continuous Triassic strata exposed surface. Thispaper choose Jialingjiang Formation in Libi gorge section as the research object,combining field observations with laboratory analysis, based on the theories ofsedimentary petrology, carbonate sedimentology, lithofacies-paleogeography and soon, through the measured data of the outcrops, comprehensive using thin sectionidentification, cathodoluminescence, electron microprobe, scanning electronmicroscopy and other technical means, research the characteristics of the carbonaterocks, sedimentary facies and diagenesis of the study area. We have identified thecomponents, structure and types of the rocks, analyzed the depositional environment,diagenesis types and diagenetic environment, and established diagenetic sequence.Based on the results of field observations and thin section analysis, we considerthat the rock types of the study area should be divided into three major categories oflimestone, dolomite and salt breccia, and on this basis subdivided into8subclassesof sparry grain limestone, microcrystalline particles limestone, particle micrite-containing particles micrite, laminated micrite, vermiculate micrite, crystallinelimestone, microcrystalline dolomite, crystalline dolomite. During Jialingjiang phase,the sedimentary facies of the study area are restricted platform and evaporationplatform, and further divided into3subfacies of the lagoon, tidal flat and evaporation tidal flat on the basis of rock characteristics. During Jialingjiang phase, thesedimentary facies of the study area are restricted platform and evaporation platform,and further divided into3subfacies of the lagoon, tidal flat and evaporation tidalflat on the basis of rock characteristics.Jialingjiang Formation has experienced complex diagenetic processes. The typesof diagenesis are various, and mainly include mud crystallization, compaction,pressure solution, calcite cementation, dolomitization, recrystallization, fracturing,dissolution, silicification, degypsification, and formation of authigenic minerals suchas pyrite, fluorite, celestite and glauconite. The characteristics of the diagenesisindicate the study area has experienced the submarine-sea undercurrent diageneticenvironment and atmosphere diagenetic environment in the penecontemporaneousperiod and burial diagenetic environment in the diagenesis stage.