Characteristics of strike-slip inversion structures of the Karatau fault and their petroleum geological significances in the South Turgay Basin, Kazakhstan

The Karatau fault is one of the important strike-slip faults in central Asia, and the South Turgay Basin is located towards its northern end. Detailed seismic interpretation indicated that the strike-slip tectonism of the Karatau fault weakened gradually from west to east in the South Turgay Basin. Typical flower structures developed on the section, and strike-slip faults showed an echelon pattern on planar view. The Karatau strike-slip fault affected the South Turgay Basin in two periods: (1) The South Turgay strike-slip pull-apart rift basin formed as a result of regional extensive stress in the Early-Middle Jurassic, characterized by the juxtaposition of horsts and grabens. The formation of horsts provided favorable reservoir spaces for later hydrocarbon accumulation, and different filling stages of grabens controlled different reservoir-forming factors in grabens. (2) Two stages of tectonic inversion occurred in the Late Jurassic and Late Cretaceous and played a crucial role in the final shape of the structure in the South Turgay Basin. The oil and gas migrated to form reservoirs and mainly concentrated in the horsts, graben slopes and in both sides of the strike-slip fault zone. In the case of the degree of accumulation of petroleum, the factor explaining why horsts are better than grabens is the strike-slip pull-apart of the South Turgay Basin, and the structure inversion of the South Turgay Basin explains why the west graben is better than the east one. Overall, the Karatau strike-slip fault played a very important role in the formation of the South Turgay Basin and its hydrocarbon accumulations.