The 3D seismic characteristics and significance of the strike-slip faults in the Tazhong area (Tarim Basin, China)

The eastern part of Tazhong area in the Tarim Basin consists of three sets of vertical strike-slip faults oriented in north-northeast (36 degrees azimuth), east-northeast (68 degrees azimuth), and west-northwest (126 degrees azimuth) directions that cut the strata from Cambrian to Carboniferous. The fault belts indicate significant horizon upwarp and downwarp deformations and variations in their stratigraphic thickness on seismic profiles. Through detailed interpretation of the 3D seismic data, we consider that these phenomena reflect the different stress properties and active stages of the faults. The horizon upwarp and downwarp within the fault belts correlated respectively to the decrease and increase in stratigraphic thickness within the fault belts in comparison to the coeval counterpart of the bilateral fault blocks. For the same fault, different stratigraphic intervals express different types of horizon deformation and thickness changes. The horizon downwarp and the contemporaneous stratigraphic thickening inside the fault belts suggest the transtensional actions of the fault. The horizon upwarp and the contemporaneous thinning within the fault belts suggest transpressional actions of the fault. Based on this, we inferred the active periods of the three sets of strike-slip faults. The north-northeast-striking faults were formed in the late Ordovician Sangtamu Formation. This set of faults experienced four stages, i.e., sinistral transpression, sinistral transtension, static, and transtension. The east-northeast and west-northwest-striking faults initiated in the mid-Cambrian period as coupled transtension. Activity ceased in the west-northwest faults after the mid-Cambrian and in the east-northeast faults during the late Ordovician. The three sets of strike-slip faults all affect the formation of the hydrothermal dissolution reservoirs that are distributed in the Ordovician carbonate rocks.