四川盆地西部二叠纪成都—三台火山古隆起的发现及其对沉积储层的控制作用OA

Based on core observations,thin section identification,well logging and seismic data of the Permian strata in the western Sichuan Basin,this study systematically discusses the constraints of Middle and Late Permian two-phase volcanism on paleotectonic evolution and sedimentary filling.It further reveals a long-neglected Chengdu-Santai volcanic paleo-uplift developed continuously in the study area and clarifies its controlling effects of formation and evolution on sedimentary reservoirs.The results indicate that two suites of volcanic rocks are developed in the Permian strata of western Sichuan Basin.The lower volcanic rocks of the Middle Permian Maokou Formation are predominantly composed of basalt and volcanic breccia,whereas the upper volcanic rocks of the Upper Permian Longtan Formation are mainly basalt and volcaniclastic rocks,recording two episodic volcanic eruption events that occurred in the middle depositional stage of the Maokou Formation and the early depositional stage of the Longtan Formation.Paleogeomorphological reconstruction shows that the volcanism during the middle Maokou depositional stage initially formed the embryonic paleo-uplift on the western Sichuan carbonate platform.Continuous vertical stacking and lateral expansion of volcanic materials during the early Longtan depositional stage finally shaped a sub-elliptical paleo-uplift plunging northeastward.This paleo-uplift extends approximately 200 km northeastward along its major axis,with a minor axis ranging from 70 km to 110 km in the east-west direction.The uplift high is located in the Well area YS1-YT1,with a maximum relative relief of 300 m.Affected by late tectonic activities and persistent sedimentary filling and leveling,the paleo-uplift completely disappeared during the deposition of the third member of the Feixianguan Formation.Formed by the synergistic effect of the clockwise northward rotation and drift of the South China Plate and mantle plume hotspot activity during the Permian,this paleo-uplift dominated the paleogeographic pattern of the central and western Sichuan Basin during its development.Specifically,tidal flat-barrier shoal sedimentary systems developed around the volcanic highland during the middle to late Maokou depositional stage,and high-energy facies belts were widely distributed around the volcanic paleo-uplift during the Changxing depositional stage.This study confirms that the volcanic paleo-uplift and its peripheral zones are favorable hydrocarbon exploration areas for the Maokou and Changxing formations,providing a new perspective for Permian oil and gas exploration in the Sichuan Basin.