Integrated Clumped Isotope Thermometry and U-Pb Dating Provide Preliminary Constraints on the Thermal Evolution of Deeply Buried Permian Carbonates: A Case Study from the Yuanba Area, Northern Sichuan Basin

The thermal history of carbonate successions is fundamental to constraining hydrocarbon generation and reservoir diagenesis, yet traditional proxies such as vitrinite reflectance and apatite fission-track analysis are often inapplicable to marine carbonates because organic matter and suitable heavy minerals are scarce. This study evaluates an integrated carbonate isotope (Δ47) thermometry and in situ U-Pb geochronology approach using a micrite matrix and three dolomite-bearing samples from the Upper Permian Changxing Formation in the Yuanba area, northern Sichuan Basin, southwestern China. The measured apparent clumped isotope temperatures (TΔ47) range from 127.8 to 174.6 °C. The micrite matrix yields a U-Pb age of 257 ± 1.2 Ma, consistent with an early depositional or syndepositional origin, whereas the dolomite samples yield younger diagenetic ages. Coupling these time–temperature constraints with an exchange–diffusion model for solid-state reordering provides a preliminary, well-scale thermal scenario for the sampled intervals. The preferred model suggests rapid heating during Late Permian–Early Triassic and Middle Jurassic burial, followed by peak heating to approximately 220 °C in the Late Cretaceous at modeled maximum burial depths exceeding 8000 m, and subsequent cooling during Yanshan–Himalayan uplift and denudation. A conditional maturity model predicts that the underlying Wujiaping Formation source rocks entered the main gas-generation window (1.3% < Ro < 2.6%) by the Middle Jurassic and became overmature during peak heating in the Late Cretaceous. This dual-proxy framework is promising for carbonate-dominated petroleum systems but requires validation with a larger sample set and independent thermal indicators.