Sedimentary facies and sequence stratigraphy in the Lower Triassic Jialingjiang Formation, Sichuan Basin, China

The Lower Triassic Jialingjiang Formation is an important oil and gas exploration target in the Sichuan Basin. The lithofacies mainly consists of clastic rocks, carbonates, and evaporates, which represents a transition from continental to marine depositional environment. The Jialingjiang Formation of the Sichuan Basin is a typical epeiric carbonate platforms. The study area contains four types of facies, including mixed tidal flat facies, open platform facies, restricted platform facies, and evaporitic platform facies. Based on the analysis of cores and logging data, two types of type II sequence boundaries were identified, which are, respectively, local exposure unconformity boundary and lithology and lithofacies transformation boundary. The Jialingjiang Formation is divided into three third-order sequences and six system tracts. Thus, we establish a connected multi-well sequence stratigraphic framework based on typical single-well sequence stratigraphic division. The sedimentary evolution of the Jialingjiang Formation was divided into three major sedimentary periods and six stages, with rising and falling of the sea level, mixed tidal flat, open platform, and restricted platform prograded first, and then restricted platform and evaporitic platform retrograded. It also shows that the open platform shoal and restricted platform tidal flat have oolitic limestone and algal dolomite with good-quality physical properties and are the favorable reservoir facies belt for hydrocarbon exploration and development.