The Middle Permian carbonate rock microfacies in the Wansheng district, Chongqing

The samples of the Middle Permian carbonate rock outcrops examined in this paper were mainly (collected) from the Wansheng district, Chongqing. The Qixia and Maokou Formations both of which are (assigned) to the Middle Permian in age, consist of marine siliciclastic and carbonate rocks. The carbonate deposits account for about 80 per cent of the sedimentary rocks in the study area. According to textural-genetic classification, grain types, sedimentary structures and fossils, the carbonate rocks herem can be recognized as ten types of microfacies, including lime mudstone, fusulinid wackestone, pelleted bioclastic wackestone, bioclastic-intraclastic packstone, algal-mat (patellate) packstone, oolitic intraclastic packstone/grainstone, foraminiferal packstone, bioclastic packstone, green algal grainstone, and bioclastic grainstone. It is inferred from the microfacies division and microenvironmental analysis that the Middle Permian strata were deposited in the littoral, restricted platform and open platform environments. A facies model has been constructed for the above-mentioned depositional environments.