Fine-grained sedimentary characteristics and influencing factors of the Lower Cambrian Qiongzhusi Formation in Sichuan Basin and on its periphery

Abstract

The Lower Cambrian Qiongzhusi Formation in Sichuan Basin and on its periphery is rich in shale gas resources, and it has become one of the important shale gas development intervals in Sichuan Basin. Controlled by complex sedimentary setting, the silty shale reservoir in Qiongzhusi Formation has various lithofacies and strong heterogeneity longitudinally, which restricts the exploration and development of shale gas. Therefore, it is urgent to study the sedimentary characteristics, sedimentary facies and sedimentary models. Based on the previous understanding of tectonic setting and sequence stratigraphy, and through detailed analysis of rock data, well logging data, geochemistry data and paleontology data, this paper clarifies the Early Cambrian sedimentary background of combined ocean-paleoland influence, moderate water depth and widespread reduction of Sichuan Basin and its periphery. The paper also believes that the Qiongzhusi Formation is mainly deposited in shore facies and continental shelf facies. The continental shelf facies are dominated, including shallow water continental shelf subfacies and deep water continental shelf subfacies. Based on the analysis of the combined action of wave and tide, seawater evaporation, suspension, rising ocean current, sedimentary paleogeomorphology and other fine-grained sedimentary influencing factors, and combined with the spatial distribution characteristics of sediments, the fine-grained sedimentary model of the Lower Cambrian Qiongzhusi Formation in Sichuan Basin and on its periphery is established, i.e., in the early stage of sedimentation, the effect of differential sedimentation is significant, the sequence thickness varies greatly, and the sedimentary characteristics and influencing factors differ greatly in different regions. In the middle stage of sedimentation, the effect of differential sedimentation is diminished and the difference of sequence thickness decreases continuously. In the late stage of sedimentation, with steady sedimentation, it enters the "open basin" stage, and the sequence thickness tends to be consistent.

Keywords

• fine-grained sedimentation
• sedimentary model
• sedimentary environment
• qiongzhusi formation
• lower cambrian
• sichuan basin