Positive Inversion Structure in Fusha Structure Zone of Southwest Depression of Tarim Basin and Its Significance to Petroleum Geology

The intensive fold-thrust deformation is developed in Fusha structure zone of southwest depression of Tarim basin. The structural deformation of gypsum-mudstone in Paleocene is more intensive and has the features of positive inversion structure. Lots of normal faults, formed in early extensive environment of Jurassic-cretaceous, were compressed and inverted in Himalayan movement. Positive inversion faults at high angle were developed in the south. Imbricate thrust faults were developed in the center. Deformation is rather weakly in the northern frontier. Accordingly, Fusha structure zone can be divided into three belts, including inverted fault uplift anticline belt, wedge-like imbricate belt and thrust frontier belt. The inversion deformation is more intensive in western and southern part of Fusha structure zone than in the east and north. By anglicizing the evolution of regional structure´s environment, horizontal compression and vertical shear generated in western Kunlun´s fold-uplifting, make the pre-existing normal faults easier to invert. By evaluating structural traps formed in positive inversion, it is considered that, in inverted fault-uplift anticline belt, the large scale, low relief, shallow bury and highly confirmed traps with thin superposition gypsum-mudstone layers were developed, and they were seriously destroyed by thrust faults. Oil and gas dissipated easily. In wedge-like imbricate belt, the small scale, high relief, deep bury and lowly confirmed traps with thick superposition gypsum-mudstone layers were developed, which is favorable for the preservation of oil and gas. Lower relief and formation litho-logical trap were developed in thrust frontier belt.