In recent years, the first member of Maokou Formation (MF1) has demonstrated favorable resource potential for carbonate petroleum exploration in the Sichuan Basin. However, discrepancies in the understanding of its sedimentary environments and paleogeography have hindered further exploration planning. Based on drilling data and field outcrop observations, this study integrates detailed analysis of drilling sequences and stratigraphic thickness variations in the Sichuan Basin with geochemical and seismic data to delineate the MF1 sedimentary paleogeographic characteristics. By identifying the top and basal boundaries of the MF1, the interval is subdivided into three fourth-order sequences (MSQ1, MSQ2, and MSQ3). Each sequence comprises a transgressive systems tract (TST) and a highstand systems tract (HST), exhibiting sequence stratigraphic features of prolonged transgressive phases and short regressive phases, with northward thickening and southward thinning trends. Within the basin-scale sequence stratigraphic framework, this study reveals that the Sichuan Basin transitioned from a stable carbonate ramp deposition during the Qixia Stage to a differentiated uplift-sag transition during the Maokou Stage. This shift was driven by continuous sea-level rise under prolonged transgression and the expansion of the Mianlue Ocean in the north. In the southern basin, syngenetic dolostones, argillaceous limestones with high terrigenous input, and salt crystals indicate a deep-water, restricted depositional environment. In contrast, northern regions are characterized by abundant shallow-water reef-building biota. The overall stratigraphic thickening toward the north and thinning toward the south reflect a rimmed open-platform depositional framework characterized by northern reef-shoal complexes and southern lagoon systems during the MF1 deposition.