| Cambrian Longwangmiao Formation was in the sedimentary environment of distally-steepening slope in Sichuan Basin and its peripheral area, in which nearshore tidal flat, internal slope, middle ramp and external ramp developed successively from west to east. Sichuan Basin was mainly located in the internal slope. The internal slope can be further divided into shallow internal slope, restricted internal slope and open internal slope, in which five subfacies develop, including grain beach, interbeach sea, lagoon, restricted lagoon and tidal flat. Two short-term cycles of transgression-regression, including an upper and a lower ones, developed in longitude during Longwangmiao sedimentation. The upper cycle developing in the shallow internal slope, in which grain beach and sea interbeach subfacies are predominant, is composed of thick calcarenite dolostone, oolitic dolostone and fine-crystalline dolostone in lithology. The lower cycle developing in restricted internal slope and open internal slope, in which two groups of lagoons and tidal flats develop, is predominantly composed of micrite in lithology. Dolomitization is general in the upper cycle. Gypsum and salt rock develop in the restricted internal slope due to limited environment and low energy. It is suggested that the main controlling factors include:(1) paleostructures controlling the sedimentary system and sedimentary facies, (2) the sea-level changes controlling the vertical superimposition and evolution of sediments, and (3) paleo geomorphology and water energy controlling the sediment type and microfacies. A slope sedimentary model is put forward and it is deduced that the favorable reservoirs distribute in the Anyue-Nanchong-Jian′ge area. |
