Sedimentary microfacies of the Lower Triassic Jialingjiang Formation in Shizhu,Chongqing,China

The rocks developed in the Lower Triassic Jianglingjiang Formation in Shizhu of Chongqing represent the typical types in the carbonate platform of the upper part of the Yangtze platform.By measuring the profile in the field and analysing the microfacies indoor and according to the normal microfacies and carbonate platform model of Wilson(1975),eight types of microfacies are recognized.They are marlite;bioclastic-intraclastic packstone;bioclastic marl;bioclastic wackstone;bioclastic packstone;oncolith,ooid,alga calcarenite;bioclastic biodisturbed marlite;foraminifer packstone.The order combination of 8 types of microfacies in the study area composes three carbonate platform subfacies,that is,evaporate platform,restrctied platform and open platform subfacies.According to the longitudinal and transverse changes of the sedimentary facies,a sedimentary facies model is built.The evolvement of the sedimentary facies model is well controlled by two transgression-regression cycles with relative sea level changes.The research provides important and basic geological data for the regional geological research and oil and gas exploration and development.