Structural configuration and its controls on shale oil accumulation of the Wulalike formation at southern section of western margin, Ordos Basin

The Wulalike Formation in the southern Ordos Basin represents an emerging marine shale oil play, with recent discoveries challenging traditional views of its low-TOC and low-porosity potential. The current study integrates 3D seismic data, geochemistry (TOC, R o ), and structural analysis to unravel tectonic controls on shale oil accumulation. The western margin features three structural zones: 1) a reverse-thrust belt (Huianbu-Shajingzi fault), 2) a thrust-extension zone (Yandunshan-Majiatan blocks), and 3) a stable eastern zone. Unlike the northern detachment systems, the southern section exhibits monoclinal thrusts, evidenced by near-vertical Ordovician strata (Qiujianjia section) and high-angle thrusts. Fault analysis highlights that fault activity reached its peak during the Permian-Triassic transition (252–201 Ma), with faults inheriting structural characteristics from Caledonian and Yanshanian-Indosinian orogenies. Early uplift in the south led to lower thermal maturity (R o = 0.83%, TOC = 0.82%) and preserved oil, while the central-north reached gas-window maturity (R o = 1.6%, TOC = 1.13%). Meanwhile, different unconformities in southern versus northern sections reflect differential tectonic evolution. Structurally stable inner thrust-sheet zones (e.g., Shajingzi) retained intact strata and deeper burial, whereas sheet-edge zones underwent erosion and leakage. The Wulalike shale oil model emphasizes tectonic control on preservation, prioritizing inner-sheet zones for exploration in the western margin of the Ordos Basin. These insights redefine prospects for low-TOC shale oil in thrust belts.