Abstract: A mega-complex shallowing-upward sequence, ranging from deep ramp
carbonates, open platform carbonates to restricted platform carbonates and evaporates, was formed in Sichuan region during the ingression from Dongwu Movement(Later Permian)through Yinzhi Movement(Middle Triassic).Pe-trological and geochemical studies of the reservoir showed that the multiple migration of hydrocarbon, dominantly liquid before Cretaceous and gaseous after Neogene, occured during the thermal一evolution of hydrocarbon .The multiple migration resulted in the mixing and accumulation of noncognate gaseous hydrocarbon in the upper part of the mega-complex sequence.They were finally sealed by evaporates, as seen in the gas reservoirs discovered .So more exploration will be significant in the salt-bearing basins of Later Permian一Midle Triassic in Sichuan basin.

Key words: Sedimentary history Regressive sequence Hydrocar