The reactivation of pre-existing faults exerts a profound influence on the formation of rift basins and the deformation behaviors within their interiors, however, the specific modes of activation and underlying mechanisms remain unclear. The Enping-17 Sag, located in the tectonically active Pearl River Mouth Basin of the South China Sea, exhibits complex fault geometries and rapid subsidence since the Neogene. Its distinctive coexistence and differential reactivation of inherited fault sets make it an ideal location to investigate structural inheritance and basin evolution. In this study, high-resolution three-dimensional seismic data were employed in conjunction with seismic interpretation, dynamic analysis, and kinematic modeling to investigate the geometric attributes, activity, and genesis of sag-controlling faults. The results reveal that the boundary faults of Enping-17 Sag exhibit significant variations in strike, transitioning from a near N–S-trending in its southern segment to an ENE-trending in its northern segment. In cross-sectional profiles, the northern segment exhibits a ramp-flat geometry and records four distinct depositional periods (Early Wenchang, 49–43 Ma; Late Wenchang, 43–39 Ma; Enping, 39–32 Ma; Zhuhai, 32–23.8 Ma), whereas the southern segment displays a listric geometry, recording two prominent depositional periods (Early Wenchang, 49–43 Ma; Late Wenchang, 43–39 Ma) of tectonic reactivation. The fault displacement-length profile further indicates clear along-strike segmentation of the Enping-17 boundary fault, with variations in fault activity playing a significant role in controlling sag formation and internal structural heterogeneity. The structural evolution of the Enping-17 Sag reflects the interplay between pre-existing fault reactivation and regional tectonics along the northern South China Sea margin. Driven by Pacific Plate subduction and India–Eurasia collision, evolving extensional stresses selectively reactivated NE-trending and N–S-trending basement faults during the Early Eocene, facilitating rapid linkage of northern and southern fault segments. Continued clockwise stress-field rotation in the Middle Eocene promoted the development of new ENE-trending faults, while sustained NE-trending and ENE-trending fault activity in the Late Eocene steered the depocenter northward. Ultimately, segmented fault reactivation and progressive linkage, modulated by regional plate interactions, governed the sag's structural complexity and depositional evolution.

With the theoretical and technological developments related to cratonic strike-slip faults, the Shuntuoguole Low Uplift in the Tarim Basin has attracted considerable attention recently. Affected by multi-stage tectonic movements, the strike-slip faults have controlled the distribution of hydrocarbon resources owing to the special fault characteristics and fault-related structures. In contrast, the kinematics and formation mechanism of strike-slip faults in buried sedimentary basins are difficult to investigate, limiting the discussion of these faults and hydrocarbon accumulation. In this study, we identified the characteristics of massive sigmoidal tension gashes (STGs) that formed in the Shunnan area of the Tarim Basin. High-resolution three-dimensional seismic data and attribute analyses were used to investigate their geometric and kinematic characteristics. Then, the stress state of each point of the STGs was calculated using seismic curvature attributes. Finally, the formation mechanism of the STGs and their roles in controlling hydrocarbon migration and accumulation were discussed. The results suggest that: (1) the STGs developed in the Shunnan area have a wide distribution, with a tensile fault arranged in an en échelon pattern, showing an S-shaped bending. These STGs formed in multiple stages, and differential rotation occurred along the direction of strike-slip stress during formation. (2) Near the principal displacement zone of the strike-slip faults, the stress value of the STGs was higher, gradually decreasing at both ends. The shallow layer deformation was greater than the deep layer deformation. (3) STGs are critical for connecting source rocks, migrating oil and gas, sealing horizontally, and developing efficient reservoirs. This study not only provides seismic evidence for the formation and evolution of super large STGs, but also provides certain guidance for oil and gas exploration in this area.