Sedimentary facies of the Second Member of the Jialingjiang Formation in the central-southern Sichuan transition zone and its distribution characteristics

Abstract：The Lower Triassic Jialingjiang Formation in the central and southern Sichuan transitional zone may be divided into three facies(restricted platform, evaporative platform and open platform), eight subfacies (open subtidal zone, intraplatform bank, intraplatform embryonic bank, restricted lagoon, intraplatform shallow, restricted tidal flat, evaporative lagoon, evaporative tidal flat) and 18 microfacies. Regional correlation of vertical and lateral sedimentary facies of the 2nd Member of the Jialingjiang Formation indicates that laterally the sedimentary facies of the member are homogeneous and less varied, while vertically the sedimentary facies variation shows synchroneity in a vast areal extent. The 2nd Member of the Jialingjiang Formation is divided into five mapping units. By using the method of combining the single factor analysis and dominant facies method and the outcomes of sequence stratigraphic research, the paper relatively accurately exhibits the distribution and evolution of sedimentary facies of different facies of the 2nd Member of the Jialingjiang Formation. The relatively sea-level change and the microgeomorphology of alternating uplifts and depressions in the carbonate platform together control the distribution and evolution of sedimentary facies. The 2nd Member of the Jialingjiang Formation consists predominantly of restricted platform and evaporative platform facies. The facies belts that are advantageous to the formation of reservoirs are intraplatform embryonic bank and restricted tidal flat subfacies. Intraplatform embryonic banks are developed in relative high-energy zones near the transitional zone between tidal flats and lagoons. Restricted tidal flats are distributed widely.