Astronomical cycle framework and carbonate platform evolution of Permian Longtan Formation–Triassic Feixianguan Formation in Sichuan Basin, SW China

Based on data from cores, well logs, seismic profiles, and carbon isotopic compositions, this study constrains the chronostratigraphic framework using carbon isotopic excursion events and applies cyclostratigraphic methods to establish a high-resolution isochronous stratigraphic framework for the Permian Longtan Formation–Triassic Feixianguan Formation in the Sichuan Basin. Through single-well sedimentary evolution analysis and well-seismic integration, the sedimentary characteristics and the patterns and petroleum geologic significance of carbonate platform evolution during the deposition of the Longtan Formation–Feixianguan Formation are systematically revealed. The results show that the Longtan Formation–Feixianguan Formation exhibits 19 to 22 long eccentricity cycles across the entire basin. The difference in cycle counts is attributed to the significant local absence of the top part of the Permian Changxing Formation. Sedimentation rates gradually increase from the southwest to the northeast of the basin. The sedimentary system is overall controlled by a “high productivity, high supply” background, and jointly influenced by sea-level changes and terrigenous input. The Changxing Formation shows progradational ramp characteristics locally, while the Longtan Formation– Feixianguan Formation presents a carbonate ramp sedimentary model. The “tectonics-climate-astronomy” multi-level synergistic driving mechanism governed carbonate platform development, the regional tectonic setting established the macro-paleogeographic framework and accommodation space configuration for carbonate platform development, while the rhythmic sedimentary infilling and the production intensity of carbonate factories were significantly modulated by paleoclimate and astronomical orbital signals. The three factors exhibited stage-wise synergistic evolution in time and space, collectively driving the formation, development, and demise of carbonate platforms. This study provides a new sedimentary model and basis for an in-depth understanding of sedimentary characteristics and carbonate platform evolution patterns during the Permian–Triassic transition in the Sichuan Basin.