The Jurassic sedimentary facies and oil-gas distribution in western Sichuan Basin

During the Jurassic, an interior basin once occupied the western part of the Sichuan Basin, in which the fluvial and lake deposits predominated. The alluvial deposits are common near the Longmen Mountain area. The alluvial plain and floodplain deposits occur in the other parts of the basin. The lakes in the study area may fall, according to lake water regimes, into seasonal lakes, intermittent lakes and perennial lakes. During the (Indosinian), the (Garze)-(Aba) orogenic zone came into being. The climates in the basin recorded a transition from the humid and hot ones to the arid and hot ones. The basin then became a perennial lake during the Early and early Middle Jurassic. The early and middle Yanshanian tectonic movements permitted the fluvial, seasonal lake and intermittent lake facies to be developed. The perennial lake deposits are believed to be most (important) (Jurassic) source rocks and reservoir rocks. The (coarse)-(grained) clastic rocks of the fluvial facies may serve as the (reservoir) (rocks), and the argillaceous rocks of the seasonal lake and intermittent lake facies as the cap rocks, both of which constitute a number of reservoir-seal associations in the Upper and Middle Jurassic strata.