Abstract: Exploration on both sides of the Mianyang-Changning Tensional Trough has achieved good results, but there are still controversies regarding the characteristics, genesis and control effects on hydrocarbon accumulation of the tensional trough, which restrict further exploration deployment. For this purpose, based on regional seismic lines and key exploratory well data, the study focuses on the sequence sedimentary filling and unconformity characteristics of the Lower Cambrian inside the Mianyang-Changning Tensional Trough. The results indicate that the Mianyang-Changning Tensional Trough extends nearly north-south and can be divided into inner, middle and outer zones horizontally. Vertically, the trough interior developed two stages of filling sedimentation, two stages of widespreadsedimentation and two stages of sedimentary onlap unconformities,the two stages of filling in the first member of the Maidiping Formation and the first and second members of the Qiongzhusi Formation are the direct causes of abnormally increased stratigraphic thickness in the trough. The two stages of sedimentary onlap unconformities developed at the bottom of the two stages of filling sedimentary bodies, indicating two stages of basement subsidence in the study area; the episodic activity of the Xingkai taphrogeny is the internal driving force for the two stages of basement subsidence and also the internal cause for the formation of the tensional trough. The development of the tensional trough can be divided into juvenile, mature, and senescent stages, with the early Qiongzhusi period being the mature stage; the tensional trough mainly controls the development of Lower Cambrian source rocks and the source-reservoir matching of the Dengying Formation. The steep slope zone on the eastern side has high-quality source rock development and good spatial source-reservoir matching, making it the enrichment zone for Dengying Formation oil and gas reservoirs and the main direction for future exploration. This understanding has certain guiding significance for the next step of exploration in the Dengying Formation of the Sichuan Basin.

Key words: filling sedimentation, formation and evolution, Mianyang-Changning Tensional Trough, Sichuan Basin