Sequence filling and evolutionary model of the Lower Cambrian Maidiping-Qiongzhusi formations in Sichuan Basin and on its periphery

The Lower Cambrian Qiongzhusi Formation in the Sichuan Basin and on its periphery is rich in shale gas resources and has been proven to be one of the important shale gas pay zones in the basin. Due to the deep burial depth, few data and complex geological conditions, the research on its sequence stratigraphy has been relatively weak, having seriously restricted the follow-up research and development. The study on the Early Cambrian tectono-sedimentary setting of the Sichuan Basin and on its periphery, coupled with lithology, rock color, logging curve, trace elements, paleontology, seismic reflection event and other characteristics, is carried out to further explore the sequence stratigraphy of the Maidiping-Qiongzhusi formations, with the idea for the sequence division proposed. As a result, the Maidiping-Qiongzhusi formations are divided into four third-order sequences from bottom to top. By revealing the spatial distribution pattern of the sequence stratigraphy, we establish a sequence evolutionary model of “differential sedimentation in early narrow basin, and stable sedimentation in later wide basin” for the Maidiping-Qiongzhusi formations in the Sichuan Basin and on its periphery under the control of global plate extensional activity. The sequence evolutionary model will be of help to deepening understanding of the Cambrian tectono-sedimentary setting in the Sichuan Basin, promoting geological research on sedimentary reservoirs, and serving the exploration and development of deep shale gas.