Sedimentary Evolutionary Processes of Platform Margin Shoal of Maokou Formation in the Jiange-Yuanba Area, Sichuan Basin

Carbonate reservoirs are of great significance for global hydrocarbon exploration. In recent years, platform‑margin carbonate reservoirs have received increasing attention due to substantial oil and gas discoveries. The Sichuan Basin is located on the northern margin of the South China Plate, and the Middle Permian Maokou Formation was deposited during a critical period of accelerated closure of the Paleo‑Tethys Ocean. As a key exploration target in the basin, early exploration was concentrated in inner platform areas of southern and central Sichuan. However, recent high‑yield gas flows from the Jiange–Yuanba area have revealed great exploration potential in its platform‑margin facies belts. Previous studies have proposed conflicting depositional models for the Maokou Formation in this region, including rimmed platform, carbonate ramp, and evolutionary ramp‑to‑restricted platform models. Although the development of platform‑margin facies has been widely recognized, understanding of sedimentary sequences in northwestern Sichuan remains limited by scattered well and outcrop data. High‑resolution seismic research is therefore urgently needed to better constrain sedimentary processes of platform‑margin systems under extensional tectonic settings. This study integrates logging, core, and 3D seismic data to establish a comprehensive analytical framework for platform‑margin facies. Research methods include sequence‑constrained sedimentological analysis, seismic stratigraphy, and seismic geomorphology. Synthetic seismograms are used to calibrate core‑scale lithology with seismic‑scale reflections. By combining lithofacies analysis with seismic interpretation, sedimentary evolution and paleogeographic maps of the Maokou Formation are reconstructed. Three main conclusions are obtained. First, the Maokou Formation is divided into three third‑order sequences (SQ1–SQ3). SQ1 shows relatively gentle paleotopography, while SQ2–SQ3 display distinct south‑thick and north‑thin differential subsidence. Second, the depositional system evolved from an early gentle carbonate ramp to a progradational rimmed carbonate platform in the middle–late stages. Third, SQ1 only developed scattered low‑energy shoals on subtle paleohighs, whereas SQ2–SQ3 formed well‑developed NW–SE‑trending and vertically stacked platform‑margin shoal complexes. These shoal bodies represent large‑scale high‑quality reservoirs and major exploration targets. This study clarifies the spatiotemporal evolution of platform‑margin facies and provides a practical reference for Maokou Formation exploration in the Sichuan Basin.