Characteristics of Lithofacies Paleogeography of Cambrian in Sichuan Basin

Typical sedimentary facies are identified through integrated studies of outcrops,cores,well logging data,and combined with single factor analysis and comprehensive mapping,lithofacies paleogeography of each period of Cambrian in Sichuan Basin is determined. Depositional topography is higher in the west of the basin than in the east. Land source clastic rocks are mainly deposited in west basin and carbonate sediments are developed in the central-east of the basin. There exist two and a half transgression-regression circles in the Cambrian in Sichuan Basin. The first transgression took place in Qiongzhusi period of the early Cambrian,hydrocarbon source rocks are deposited in shallow continental shelf. The first regression took place in Changlangpu period of the early Cambrian,land source clastic supply is sufficient and delta,clastic shoreland sedimentary facies are developed. Bank facies carbonate reservoirs are mainly deposited in Longwangmiao period of the early Cambrian ( the second transgression) and Xixiangchi period of the middle-late Cambrian ( the third transgression) ,in the higher topography of the restricted platform psammitic bank and oolitic beach carbonates are deposited,with the psammitic bank mainly developed in the central-west basin and oolitic beach mainly developed in central-east basin,and in the west-south of the basin there exist inherited lagoon sediments.