Distribution Law Of Granulated Beaches And Control Of Weathering Crust In The Middle Permian Maokou Formation In Eastern

According to core data, thin section and logging information, we studied about the regularities of distribution of grain beach and it’s effects on the development of weathering crust karst,which is located in Maokou Formation of middle Permian in eastern Sichuan Basin. Results indicated that Maokou Formation was a sets of open marine platform facies sedimentation in our study area, affected by the varying sea-stand elevation. Maokou Formation formed a typical beach multicycle phase particles grainstone sedimentation on the micro landform highland of Kaijiang palaeohigh. in addition, the grain beach was primary developed in Mao2A sub-member, Mao2B sub-member and Mao3member. The type of the study rock is mostly bioclast limestone and algal limestone, while calcarenite take the second place, characterized by Shallowing upward sequence development, thinner Single beach, larger cumulative thickness and good lateral continuity. Since seawater retreated Yangzi platform which was forced by Tungwu movement in the late Permian, resulted in up to7-8Ma depositional break and formed karst weathering crust. At this stage, high-energy grain beach facies was the primary control on the development of karst, manifest as that other low-energy facies developed less karst. The karst which was primary controlled by polycyclic superimposed Grain beach presents the characteristics of layered development. Consequently, the forecast works on the karst reservoir in aim position should based on the advantageous reservoir facies, then take overprint of krast into consideration to find the area which may host high-energy beach in the basin, and this understanding is very important for the next to oil and gas exploration of the Maokou Formation in the study area.