Two-dimensional balanced restoration of salt structures and analysis of restored cross sections in the western Kuqa depression

The Paleogene gypsum-salt rocks were deposited in the western Kuqa depression at the southern piedmont of Tian Shan. Trillions of cubic meters of nature gas fields were discovered within the Mesozoic strata below the gypsum-salt layer, an important gas source for the west-east gas transmission in China. The sub-salt in Kuqa depression is a target for oil and gas exploration. At present insufficient understanding of the formation mechanism of the salt structure, which requires restoration of salt structure balance, hinders gas exploration. We have, in this paper, by integrating seismic, drilling and surface geological data from four selected sections of the western Kuqa depression, undertaken tectonic balance restoration using the StructureSolverTM (SS) restoration software developed by StructureSolver Company. We have restored the seismic image before compression deformation of the supra-salt layer, salt layer, and sub-salt layer to rebuild the pattern of the seismic profiles before compression deformation. The results reveal that two stages of salt structures were developed in the western Kuqa depression: piercing salt dome developed in the Oligocene to Miocene, and extruded salt structures developed in the Pliocene to Quaternary. Under compaction, the salt dome developed in the early stage evolved into salt sheets and salt walls, thrust faults and salt anticlines developed in the supra-salt layer, and imbricated thrust faults and critical-taper wedge developed in the sub-salt layer. The differential loading of the overlying salt layer (gravity) was the reason for the development of the salt dome in the western Kuqa depression. The salt domes in the western Kuqa depression are distributed in front of the piedmont alluvial fan and on both sides of Quele alluvial fan. Critical taper wedge developed in the sub-salt layer in western Kuqa depression. The critical taper wedge theory is used to study the relationship between the slope of the top surface of the wedge and the angle of the bottom detachment layer. The slope of the top surface changes abruptly signifying variation in the angle of the detachment layer, thus indicating that the Paleozoic basement normal fault was involved in the wedge. © 2020, Science Press. All right reserved.