Thermal Evolution History Reconstruction of the Dengying Formation to Longmaxi Formation in the Micangshan Uplift Area, Based on Multiple Paleothermometers and Basin Modelling Techniques

ABSTRACT Evaluation of shale maturity in strata lacking vitrinite is a significant challenge in unconventional oil and gas geology research. Maturity and thermal evolution history of the Lower Silurian and underlying formations of the Micangshan Uplift are poorly understood. This study focuses on the Dengying–Longmaxi formations in the Micangshan Uplift, conducting analyses of clay mineral composition, illite crystallinity, bitumen reflectance, bitumen laser Raman spectroscopy, thermal conductivity and heat production rate measurements. These are integrated with apatite fission track data to reconstruct the burial–thermal evolution history. The results indicate: (1) the source rocks have illite crystallinity ranging from 0.49 to 0.88, R b from 1.23% to 3.5%, R o from 1.16% to 2.68%, indicating a high to over‐mature stage. (2) Bitumen laser Raman spectroscopy reveals Rmc R o values of 1.57% to 3.54% and B R o values of 1.53% to 3.66%, suggesting high organic matter maturity. (3) the maximum paleogeotemperature experienced since the Lower Palaeozoic ranges from 180°C to 222°C, with a geothermal gradient of 3.1°C/100m to 3.9°C/100 m. (4) the study area has undergone four tectonic uplifts since 550 Ma, with maturity evolving from low to over‐mature. Regional uplift and denudation since 150 Ma halted further heating. The complex tectonic–thermal evolution of Dengying–Longmaxi shale since the Late Palaeozoic, coupled with favourable paleogeotemperature, maturity, porosity and adsorption capacity evolution, suggests significant shale gas exploration potential, warranting further resource exploration and evaluation.