Segmental Differences and Driving Mechanisms of Sequence Architecture in Early–Middle Ordovician Platform Margin, Tarim Basin

The Ordovician platform margin belts in the Tarim Basin are key targets for deep carbonate hydrocarbon exploration. Their sequence architecture and spatial differences exert critical controls on the distribution of high-quality reservoirs. Taking the Early–Middle Ordovician platform margin belts in the Lunnan–Fuman–Gucheng area as the research object, this study systematically characterizes the sequence framework, sedimentary architecture, and segmented differential characteristics based on seismic, drilling, logging, and thin section data, using sequence stratigraphy, seismic facies analysis, and sedimentary mapping. The results show that five sequence boundaries are identified, dividing the Lower–Middle Ordovician into two second-order sequences and four third-order sequences. Seven types of mound-shoal seismic facies are developed, and three structural models are recognized from north to south: aggradation–weak retrogradation in the Lunnan section, weak aggradation–strong retrogradation in the Fuman section, and strong aggradation–weak retrogradation in the Gucheng section. It is revealed that differential subsidence caused by back-arc extension of the Altyn orogenic belt and the paleogeomorphic barrier effect of the Tadong Low Uplift collectively controlled the segmented architecture and migration evolution of the platform margin belts. The findings clarify the differential structural patterns of platform margins and provide a geological basis for hydrocarbon exploration in Ordovician platform margin reef-shoal complexes in the Tarim Basin.