Thermal evolution and maturation of Sinian and Cambrian source rocks in the central Sichuan Basin, Southwest China

The Sichuan Basin is among the basins with the most abundant oil and gas resources in China. The Sinian and Cambrian strata are the most important source rocks. Previous studies of the thermal history of the central Sichuan Basin have focused on the Late Paleozoic and studies of the Early Paleozoic thermal history are not available in literature and the thermal evolution of the Sinian and Cambrian source rocks are yet to be examined. A new thermal history was reconstructed using integrated thermal indicators, including apatite and zircon (U-Th)/He, zircon fission tracks, and equivalent vitrinite reflectance. The modeled results indicated that the heat flow was relatively low (<65 mW/m2) from the Sinian to Early Permian. During the Middle-Late Permian, the heat flow reached a maximum value (75-100 mW/m2) which may have been controlled by the heating effect of the Emeishan mantle plume and crustal extension. Following the Triassic, the heat flow gradually decreased to its present value of 60-70 mW/m2. The maturity histories of the source rocks, modeled based on the new thermal histories, indicate that the Sinian and Cambrian source rocks were slowly maturing during the Early Paleozoic, underwent rapid maturation during the Mesozoic, and reached the dry-gas stage during the Late Cretaceous. These new data on the thermal history and source rock maturity histories of the central Sichuan Basin provide new insights to guide oil and gas exploration of the basin.