Formation Mechanism of the Zhongqiu–Dibei Structural Transformation Belt of the Thrust Wedge in the Kuqa Depression,Tarim Basin: Implications from the Sandbox Structure Simulation Experiment

There are abundant oil and gas resources in the Mesozoic–Cenozoic continental sedimentary layer of the Kuqa Depression of the Tarim Basin. The NNE-trending Zhongqiu–Dibei structural transformation belt, located in the transition zone between the Baicheng Sag in the middle of the Kuqa Depression and the Yangxia Sag in the east, is an oil-bearing zone discovered in the Kuqa Depression in recent years. Exploration shows that the oil and gas traps in the Zhongqiu–Dibei structural transformation belt are related to Mesozoic structures involved in strike-slip thrust-fold deformation. In this study, the relationship between the Mesozoic structural deformation assemblage and the competency of the strata was analyzed based on the interpretation results of 3D seismic data and the formation mechanism of the Zhongqiu–Dibei structural transformation belt was demonstrated through the simulation of the sandbox structure. The results showed that the Zhongqiu–Dibei structural belt is a structural transformation belt in the thrust wedge of the Kuqa foreland and differences in the thickness and competency of the Mesozoic strata are the main factors controlling the formation of the structural belt. The Baicheng Sag on the western side of the Zhongqiu–Dibei structural transformation belt is filled with thick Mesozoic strata and contains thick coal seams, mudstone, and other incompetent rocks. During the uplift and southward pressing of the southern Tianshan Mountains, the thrust-fold deformation that developed in the Mesozoic interior spread further by detachment deformation in incompetent strata and its front reached the Xiqiu structural belt on the southern edge of the Baicheng Depression. However, in the Yangxia Sag, with thinner Mesozoic strata and a lack of thicker incompetent strata, coordinated thrust fold deformation developed and the thrust-fold deformation spread relatively near and disappeared in the Dongqiu–Dina structural belt. The differences in the thickness and competency of strata combination characteristics in the Mesozoic along the Zhongqiu–Dibei structural belt dominated the development of the NNE-trending lateral and oblique ramps in the thrust wedge of the Kuqa Depression, which transferred the difference in thrust wedge structural deformation between the Baicheng and Yangxia depressions. Thrust faults and strike-slip thrust-related anticlinal structures controlled by the main ramp and lateral or oblique ramps are the main structural trap styles in the Zhongqiu–Dibei structural transformation belt.