Sedimentary System of Platformal Trough of Feixianguan Formation of Lower Triassic in Northern Sichuan Basin and Its Evolution

Kaijiang-Liangping trough existed for 700 My.controlled the deposition of Feixianguan Formation of lower Triassic in the northern Sichuan Basin. In the short period of the trough existed, relativelysymmetrical carbonate rock sedimentary system that be analogous to Wilson facies pattern could be formed in its both sides. Through researching on petrology data of detailled drilling, outcrop and so on, Feixianguan Formation mainly developed six types of sedimentary facies including evaporate platform, restricted platform, open-platform, platform marginbeach, slope and basin facies. The basin facies that was shallower than deep-sea basin which mainly developed dark marl and lime mudstone; the depositonal characteristics of the slope facies are distinct, but shelf facies poor developed which may be for the sake of the depth of the trough, because it is so small; with the gradual close of the trough, seawater became shallow, the characteristics of the depositional evolution from basin facies to slope, platform margin beach, open-platform, restricted platform and evaporate platform within the trough are dinstinct; to the top of the Member 4 of Feixianguan Formation, all of the Northern Sichuan basin were deposited equally by restricted platform facies or evaporate platform facies. The period of the trough existed is so short that the course of evolution of sedimentary facies is quite clear in plane and longitude. With the gradual close of the trough, seawater receded toward to open sea, platform margin oolitic beaches moved toward to trough too, that was open sea, growing horizons of them rised gradually at the same time.