Study on sedimentary facies of middle Triassic Leikoupo Formation of the southern area in Central Sichuan Basin

The middle Triassic Leikoupo Formation of the southern area in Central Sichuan Basin may be divided into three facies (open platform, restricted plat form and evaporative platform), four subfacies (subtidal zone, lagoon, intertidal flat and supratidal flat) and 17 microfacies.The sedimentary facies of Leikoupo Format ion laterally changed little, and the lithology was unified.In this area, evaporate was well-developed horizontally, while longitudinally the sedimentary facies variation was synchronous in whole.By using the method of single factor analysis and dominant facies, and combining the outcomes of sequence stratigraphy research, Leikoupo Format ion is divided into seven mapping unit s,which relatively accurately exhibits the distribution and evolution of sedimentary facies.The relatively sea-level change and the microgeomorphology of alternating uplift and depressions in the carbonate plat form controlled the distribution and evolution of sedimentary facies.The Leikoupo Formation consists predominantly of restricted platform facies. The favorable facies belt to the forming of petroleum reservoirs is intraplatformal bank microface, which developed in the high-energy zones near the transitional zone between upper intertidal zone and lagoons in the 1st sub-member of the 1st member of Leikoupo Formation.