Stratification Patterns and Petroleum Geological Significance of Intra-Cratonic Strike-Slip Faults in Major Basins of Central-Western China

The widespread development of intra-cratonic strike-slip faults has been confirmed by exploration activities, with successive major discoveries such as the Shunbei and Fuman oilfields along these fault zones. In recent years, the extensive acquisition and in-depth application of 3D seismic data have further substantiated the distinct characteristic of vertical stratification along strike-slip faults. This recognition holds significant implications for advancing fundamental geological theories of cratonic basins and for pioneering novel domains in hydrocarbon exploration.This study focuses on the Tarim, Sichuan, and Ordos basins in central-western China. Addressing the scientific question regarding the vertical stratification of strike-slip faults, it systematically synthesizes developmental patterns, genetic mechanisms, and petroleum geological significance through comprehensive investigation, comparative analysis, and integrated interpretation. The research yields five key findings.(1) Strike-slip fault stratification is a localized phenomenon within cratonic superimposed basins, rather than a regionally extensive characteristic. It is prominently developed in the Tabei-Tazhong area of the Tarim Basin, the central Sichuan Basin, and the southwestern Ordos Basin. (2) Within these three major cratonic superimposed basins, strike-slip fault stratification exhibits four principal manifestations. ① Major regional unconformities serve as the primary detachment interfaces for vertical fault segmentation; ② Vertical stacking between different structural layers occurs in both strike-parallel and strike-divergent configurations; ③ Within individual structural layers, strike-slip faults may not be fully penetrative vertically, often separated by interval zones of appreciable thickness; ④Stratification characteristics are not exclusively controlled by basement fault reactivation.(3) Strike-slip fault stratification is classified into two genetic types: inter-layer stratification (between structural layers) and intra-layer stratification (within a single structural layer). In the Tabei-Tazhong area, central Sichuan, and southwestern Ordos Basin, the inter-layer type exhibits "two-layer", "three-layer", and "four-layer" architectures, respectively. The intra-layer type is characterized by faults terminating within specific strata, with significant interval zones-such as within the Upper Ordovician, Lower Cambrian, Carboniferous-Permian, and Lower Triassic formations, respectively-where faulting is absent, constituting crucial vertical separations.(4) Strike-slip fault stratification is governed by three essential conditions: a stable crystalline basement, a thick sedimentary cover, and compressional stress. Inter-layer stratification is primarily controlled by polyphase regional stress fields, whereas intra-layer stratification is mainly influenced by the downward attenuation of contemporaneous tectonic stress and variations in deep structural settings.(5) The stratification patterns of strike-slip faults not only corroborate the existence of regional vertical tectonic decoupling within cratonic superimposed basins but also provide a framework for understanding the deep-seated mechanisms governing vertically stratified and independently accumulated hydrocarbon reservoirs in cratonic interiors. Currently, studies in the Ordos Basin demonstrate that the downward convergence zones of stratified strike-slip faults are frequently associated with the most severe drilling fluid losses. This understanding offers important theoretical support for drilling program design and early warning during engineering operations.