High-Resolution Sequence Stratigraphic Framework and Sedimentary Evolution of the Chang 7 Member of the Yanchang Formation, Zhidan Area, Ordos Basin, China

The Chang 7 Member in the Zhidan area of the Ordos Basin is a strategic target for the exploration and development of continental shale oil. However, a systematic understanding of high-resolution sequence stratigraphic division, the spatial distribution of sand bodies and sedimentary facies, sedimentary evolution, and its controlling factors remains insufficient. Guided by high-resolution sequence stratigraphy, this study integrates core observations, well logging, and mud logging data from the Zhidan area. By employing signal processing techniques such as synthetic prediction error filtering analysis and well-to-well profile correlation, a high-precision sequence stratigraphic framework was established. Based on this framework, the spatial distribution of sand bodies and sedimentary facies was meticulously characterized, and the sedimentary evolution process along with its controlling factors was thoroughly discussed. The results indicate that the Chang 7 Member in the Zhidan area was deposited within a complete third-order cycle, which can be further subdivided into two fourth-order cycles. The sedimentary facies are predominantly characterized by a meandering river delta front–lake–turbidite fan system. From the Chang 73 to the Chang 71 depositional periods, the delta front prograded from north to south toward the center of the lake basin. Concurrently, the sand bodies evolved from thin-bedded deposits to multi-layered stacked and laterally extensive continuous deposits. The sedimentary infilling of the Chang 7 Member was synergistically controlled by tectonic subsidence, paleogeomorphology, paleoclimate, provenance supply, and base-level changes. As the base level transitioned from an accelerated rise to a decelerated rise, the depositional process shifted from retrogradation to progradation. This study not only provides significant insights into the sequence stratigraphy and sedimentary evolution of the Zhidan area but also holds great implications for promoting the exploration and development of continental shale oil and gas.