Sedimentary responses to the Dongwu movement and the influence of the Emeishan mantle plume in Sichuan Basin, Southwest China: significance for petroleum geology

The various stages of tectonic activity associated with the Dongwu movement (DM) and the associated sedimentary responses in the Sichuan Basin, Southwest China, have been analyzed and their significance for petroleum geology discussed. The analysis was based on the comprehensive analysis of field outcrops, wells, and seismic data. It is proposed that the DM in the Sichuan Basin can be divided into four stages: (1) Stage I occurred during the late Qixia, when the Emeishan mantle plume (EMP) began to rise, causing a fall in relative sea level, leading to subaerial exposure and a subaqueous hiatus. This formed a ramp paleogeographic pattern that was higher in the southwest and lower in the northeast of the basin. (2) Stage II, which occurred during the middle and late Maokou, sees the NE–SW-trending extensional rifting being affected by the EMP, developing from an early localized platform trough to the late widely distributed basin facies in the northern part of the basin. (3) Stage III occurred at the end of the Maokou, when the EMP caused continuous rapid uplift, resulting in a significant fall in relative sea level and a distinct karstification and paleogeomorphological pattern. This led to weakly denudated areas in the southwestern basin, moderately to strongly denudated areas in the southern and central basin, and basically no denudated areas in the northern basin. (4) Stage IV, at the beginning of the Late Permian, was marked by large-scale basaltic eruptions, the activation of basement faults, and hydrothermal modification. These four stages of tectonic activity in the basin reflect the entire evolutionary process of the EMP from its initial weak stage to its strong climax. The four stages, on the one hand, led to the differentiation of sedimentation and provided conditions for diagenesis, thus controlling the development and evolution of reservoir and source rocks. On the other hand, the reactivated faults would have had a significant impact on hydrocarbon migration and accumulation. This study therefore provides a valuable reference for the study of other mantle plume areas around the world.