Superposed evolution of Sichuan Basin and its petroleum accumulation

According to previous research and petroleum exploration data,the Sichuan Basin existing in the Yangtze Plate has been researched.The basin has undergone five evolution stages:Sinian faulted basin evolution,Cambrian-Silurian faulted basin evolution and inversion, Carboniferous-Permian-Middle Triassic basin evolution,Late Triassic foreland basin and Jurassic-Early Cretaceous large intra-continental basin evolution and the Late Cretaceous-Cenozoic uplift evolution.Sinian,Cambrian-Silurian basin evolution was controlled by the peripheral NE-trending faults;basin strata are clastic,evaporite and carbonate rocks;the basement has a structural pattern of west uplifting and east depressing.The late Middle Ordovician tectonic events formed the Chuanzhong Uplift,and the late Silurian tectonic events led to the uplift and erosion of the basin as a whole.After a late Silurian tectonic deformation and uplift,the Carboniferous- Middle Triassic basin was characterized by epicontinental sedimentary evolution of carbonates and gypsum-salt rock;the basement has a structural pattern of southwest uplifting and northeast depressing in this stage.In the end of Maokou sedimentary stage,tectonic events led to the uplift and erosion of the basin;in the end of Middle Triassic,tectonic events formed the Luzhou-Kaijiang palaeohigh.The Late Triassic foreland basin was superimposed on the early marine basins;the basement has a structural pattern of east uplifting and west depressing in this stage.The Jurassic-Early Cretaceous basin is a large intracontinental faulted basin;in the end of the Jurassic,tectonic events formed eastern Sichuan structural zone;in the end of early Cretaceous,tectonic events led to the demise of the basin and the overall uplift.The Late Cretaceous-Cenozoic sediment was confined in the southwest of the Sichuan Basin.The evolution of superposed basins formed several sets of organic-rich source rocks,such as Sinian,Lower Cambrian, Wufeng Formation of Upper Ordovician,Longmaxi Formation of Lower Silurian,Liangshan Formation and Longtan Formation of Permian,coal-bearing formation of upper Triassic and lower Jurassic.The gypsum,salt,mud and coal-bearing rocks developed in the Cambrian,Silurian,Permian,Lower-Middle Triassic,Upper Triassic and Jurassic were distributed with vertical superimposition and horizontal composite joint.These seal and source rocks formed high-quality combinations within the basin,which is the basis of hydrocarbon enrichment.A high-quality reservoir was developed under each set of high-quality cap.The good reservoir-traps combination has become a necessary condition of oil and gas accumulation.There formed lower,middle and upper assemblages of exploration formations in the basin.Exploration results show that the palaeohigh,paleoslopes and ancient source rocks controlled the oil and gas distribution of the basin.