The Neoproterozoic strata of the Sichuan Basin are a key target for oil and gas. To evaluate the hydrocarbon evolution and its relationship with tectonic events in the Micang Shan uplift, northernmost Sichuan Basin, we apply solid bitumen geochemistry (bitumen reflectance and fluorescence) and Re-Os geochronology. The geochemistry of the solid bitumen indicates that it is highly mature pyrobitumen that formed contemporaneously with dry-gas generation during oil thermal cracking. The pyrobitumen is enriched in both Re (∼106–191 ppb) and Os (∼3030–5670 parts per trillion). The Re-Os isotope data imply an Early Jurassic date for pyrobitumen formation, which coincides well with age estimates from fluid-inclusion data and basin modeling. The Re-Os date for pyrobitumen formation coupled with previously presented apatite fission-track (AFT) analysis show that exhumation of the Neoproterozoic strata occurred during the Cretaceous in the Micang Shan uplift. This extensive uplift led to the erosion of any potential gas reservoirs and surface exposure of bitumen-bearing Neoproterozoic strata. In contrast, the more southern and central portions of the Sichuan Basin have experienced less severe exhumation and, as a result, Neoproterozoic-sourced gas systems are present. This study shows that, through the combined application of Re-Os and AFT methodologies, the timing of gas generation and subsequent erosion of any potential gas reservoirs in the Micang Shan uplift, northern Sichuan Basin, can be quantified. Moreover, the Re-Os and AFT data illustrate the potential to constrain the timing of gas generation in petroleum systems worldwide.

The coexistence of numerous Mississippi Valley-type (MVT) Pb–Zn deposits and oil/gas reservoirs in the world suggests a close genetic relationship between mineralization and hydrocarbon accumulation. The Wusihe MVT Pb–Zn deposits are located along the southwestern margin of the Sichuan Basin. Based on the spatiotemporal relation between Pb–Zn deposits and paleo-oil/gas reservoirs, ore material sources, and processes of mineralization and hydrocarbon accumulation, a new genetic relationship between mineralization and hydrocarbon accumulation is suggested for these deposits. The Wusihe Pb–Zn deposits are hosted in the Ediacaran Dengying Formation dolostone, accompanied by a large amount of thermally cracked bitumen in the ore bodies. The Pb–Zn deposits and paleo-oil/gas reservoirs are distributed along the paleokarst interface; they overlap spatially, and the ore body occupies the upper part of the paleo-oil/gas reservoirs. Both the Pb–Zn ore and sphalerite are rich in thermally cracked bitumen, in which µm sized galena and sphalerite may be observed, and the contents of lead and zinc in the bitumen are higher than those required for Pb–Zn mineralization. The paleo-oil/gas reservoirs experienced paleo-oil reservoir formation, paleo-gas reservoir generation, and paleo-gas reservoir destruction. The generation time of the paleo-gas reservoirs is similar to the metallogenic time. The source rocks from the Cambrian Qiongzhusi Formation not only provided oil sources for paleo-oil reservoirs but also provided ore-forming metal elements for mineralization. Liquid oil with abundant ore-forming metals accumulated to form paleo-oil reservoirs with mature organic matter in source rocks. As paleo-oil reservoirs were buried, the oil underwent in situ thermal cracking to form overpressure paleo-gas reservoirs and a large amount of bitumen. Along with the thermal cracking of the oil, the metal elements decoupled from organic matter and H₂S formed by thermochemical sulfate reduction (TSR) and minor decomposition of the organic matter dissolved in oilfield brine to form the ore fluid. The large-scale Pb–Zn mineralization is mainly related to the destruction of the overpressured paleo-gas reservoir; the sudden pressure relief caused the ore fluid around the gas–water interface to migrate upward into the paleo-gas reservoirs and induced extensive metal sulfide precipitation in the ore fluid, resulting in special spatiotemporal associated or paragenetic relations of galena, sphalerite, and bitumen.