Discovery of Intracratonic Rift in the Upper Yangtze and Its Control Effect on the Formation of the Anyue Giant Gas Field

Abstract —According to drilling and seismic data, the Late Sinian–Early Cambrian intracratonic rift was found in the Deyang–Anyue area of the Upper Yangtze craton. This rift is controlled by a tensional fault and extends in the N–NW direction with a N–S length of 320 km and an E–W width of 50–300 km. After three stages of the rift evolution, i.e., the formation stage, development stage, and dying stage, a favorable near-source accumulation assemblage formed. The research results indicate that: (1) the sedimentation stage of the Late Sinian Dengying Formation is the rift formation stage, during which trough-basin facies sedimentation is developed in the rift, while platform marginal-facies mounds and shoals are developed on both sides, controlling the formation and distribution of high-quality reservoirs in the Dengying Formation; (2) the sedimentation stage of the Early Cambrian Meishucun–Qiongzhusi Formation is the rift development stage, during which deep-water continental-shelf facies argillaceous rocks accumulated in the rift with a thickness of 500–1000 m, indicating the sedimentation of high-quality source rocks; (3) the sedimentation stage of the Canglangpu Formation is the rift dying stage, terminating the evolution history of the intracratonic rift by gap filling. The intracratonic rift is a key factor for the formation of the Anyue giant gas field, where the high-quality source rocks provide abundant gases for the giant gas field. A regional lateral sealing occurred during the rapid rise of the western paleouplift in Central Sichuan during the Late Yanshan–Himalayan period, favorable for the preservation of the Gaoshiti–Moxi giant gas field on the eastern wing of the rift. The intracratonic rift and its role in giant gas accumulation provide a significant reference for deep oil and gas exploration in paleocratonic basins.