Tectonic characteristics and their shale gas geological significance of the Mesozoic-Paleozoic in Jiaoshiba area, the Sichuan Basin

Through 2D and 3D seismic interpretation and application of balanced cross section technique, basement structure, and tectonic characteristics and its evolution of the Mesozoic-Paleozoic of Jiaoshiba area, the Sichuan Basin are analyzed in this study. The results show that there are two types of structures in the study area. The first type is basement-involved structure, which is characterized by five structural patterns and assemblages, including back thrust anticlines, ramp syncline, imbricate thrusting, positive flower wrench and “Chinese character”-shaped wrench. The other type is cap detachment structure, which is characterized by five structural patterns and assemblages, including fault-propagation or fault-bend, fault-slipping, imbricate thrusting, imbricate ramp and thrust wedge. Additionally, the Early and Middle Yanshanian period are two major tectonic deformation periods. During the Early Yanshanian period, the nearly horizontal westwards detachment and decollement-nappe structures occurred along the interface between the Mesozoic-Paleozoic and the basement and the interfaces within the basement, resulting in the anticline-syncline alternating Zhuluoshan fold. The Jiaoshiba area between Fangdoushan fault and Datianchi anticline is within a broad compressional synclinorium structural background. During the Middle Yanshanian period, the detachment of the middle-deep burial basement in the eastern trough-like fold belt caused intensive westward thrusting, and then led to the formation of the tectonic framework of obduction-thrust-overthrust in the Jiaoshiba area. The double-layer back-thrusting anticline and faulted fold belt in the flanks were formed in Jiaoshiba area after three deformation episodes, including basement-involved imbricate thrusting-cap rock decollement-left-lateral transpression. Furthermore, Shimen faulted fold belt is characterized by multi-layer detachment folding structure and Wujiang fault-fold belt is characterized by detachment and left-lateral transpression structure. The tectonic deformation properties and types, decollement degree of the Longmaxi and Wufeng Formations, and layer-slipping structural fractures are the major tectonic factors controlling the shale gas play. © 2016, Editorial Office of Oil and Gas Geology. All right reserved.