Abstract: Significant breakthroughs have been made in the exploration of two types of shale gas, poor and rich in organic matter, in the Qiongzhusi Formation of the groove facies area in the Sichuan Basin. However, the degree of organic matter enrichment, shale gas reservoir characteristics, and formation conditions are significantly different from those of the Longmaxi Formation. Through comprehensive analysis of the lithology, grain size, mineral composition, organic carbon content, hydrocarbon generating organisms, and trace elements of the shale in the groove facies area of the Qiongzhusi Formation, we clarify the structural pattern of the "two platforms sandwiching one trough" in the central and western parts of the Qiongzhusi Formation during the Early Cambrian. The unique extensional tectonic background constructed a relatively stable semi open and semi closed environment for the sedimentation of the Qiongzhusi Formation shale. The high accommodation space and abundant input of terrestrial debris have laid the material foundation for the widespread development of the Qiongzhusi Formation silty shale. The changes in sedimentary water bodies and microfacies during the Qiongzhusi period in the Jingyan and Ziyang areas are the main reasons for the alternating development of two types of shale: poor organic matter and shale with rich organic matter. Therefore, a shallow water subfacies and deep water subfacies shale development model for the Qiongzhusi Formation in the groove facies areaa of the Sichuan Basin has been established, which has important reference value and guiding significance for the exploration of new types of shale gas under the background of extensional structures.

Key words: Qiongzhusi Formation, groove facies area, geochemical characteristics, sedimentary environment, shale development model