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.

In the process of diagenesis and burial of sedimentary basins, basin fluid activities participate in the process of hydrocarbon accumulation and metal mineralization. Understanding the evolution of basin fluid is of great significance in revealing the related hydrocarbon accumulation and mineralization. Paleo-reservoirs are closely associated with Carlin-type gold deposits in the Nanpanjiang-Youjiang Basin, South China. Calcite, the fluid activity product, is closely related to bitumen and gold-bearing pyrite. By integrating petrographic, cathode luminescence, and fluid inclusion analysis, as well as the relevant chronological results of predecessors, this paper attempts to establish the relationship between fluid evolution, hydrocarbon accumulation, and gold mineralization. Two types of calcite (black/gray and white) developed in the Banqi-Yata-Laizishan area, the Nanpanjiang-Youjiang Basin. Black/gray calcite is symbiotic with bitumen and features dark red colors in cathode luminescence. Many hydrocarbon inclusions developed along with fluid inclusion analysis at low homogenization temperatures (65.7~173.1 °C). Combining the previously reported U-Pb ages (~250–230 Ma) of this kind of calcite with some geochemistry data on the associated reservoir and gold deposit, this calcite records the consecutive hydrocarbon accumulation and Carlin-type gold mineralization from the Late Permian to the Late Triassic periods controlled by Indosinian tectonic movement. The white calcite featuring bright red in cathodoluminescence is symbiotic with gold-bearing pyrite and realgar, and the associated fluid inclusions have high homogenization temperatures (128.2~299.9 °C). Combined with regional tectonic background and isotopic chronology (~140–106 Ma), it seems to record the early Cretaceous Carlin-type gold mineralization controlled by the subduction of the paleo-Pacific plate in the late Yanshanian period.

Introduction: The lower Cambrian Niutitang Formation shale in the western margin of the Xuefeng uplift (WMXU), South China, possesses favorable material conditions including significant thickness, high organic carbon content, and high thermal maturity. However, industrial shale gas has not been discovered in this region, suggesting that preservation conditions may be the key limiting factor. Methods: In this study, we comprehensively analyzed the preservation conditions of shale gas in the Niutitang Formation using paleofluid analysis, including calcite carbon–oxygen isotope analysis, fluid inclusion analysis, and in situ calcite LA-ICP-MS U–Pb dating. Results: The results show that calcite veins in WMXU exhibit negative carbon and oxygen isotopes, low Z values, and low-salinity brine inclusions, indicating exogenous fluid infiltration and poor sealing conditions. Calcite U–Pb dating reveals one reliable paleofluid episode at 84.4 ± 2.9 Ma, corresponding to the middle–late Yanshanian strike-slip movement. A Neogene episode at ca. 17 Ma is inferred from apatite fission-track thermochronology and fluid inclusion data. Discussion: We propose that large-scale fractures and detachment surfaces at the base of the Niutitang Formation provided pathways for gas escape, with the Yanshanian and Himalayan tectonic movements being the critical periods for shale gas loss. These findings provide important insights for shale gas exploration in structurally complex areas.