Marine black shales are important to geologists, because they are not only potential sources and reservoir rocks for shale gas/oil, but also, their deposition could influence the climatic and oceanic environments. Here, a detailed study of the shales in the Dalong Formation in South China was conducted to understand the changes in continental weathering and upwelling and their influences on organic matter accumulation in the late Permian. The results revealed that the deposition of the Dalong and Daye Formations could be divided into five stages, with the highest TOC values (>2%) being observed in stages 2 and 4, intermediate TOCs (~1% to 2%) being observed in stages 1 and 3, and the lowest TOC values (<1%) being observed in stage 5. This study attributed the enhanced organic matter accumulation in stages 2 and 4 to enhanced continental weathering (high CIA values and δ²⁶Mg values) and intense upwelling (high Mo/TOC ratios and low δ¹³C_org and Co_EF × Mn_EF values), both of which contributed to high primary productivity and increased anoxia of the bottom waters, further leading to the accumulation of organic matter. Overall, both enhanced continental weathering and upwelling contributed to the development of anoxia, even euxinia, of the seawater and further triggered an end-Permian mass extinction (EPME).

Based on numerous microfossils in Mesozoic of North Carnarvon Basin in Australia, the Mesozoic paleoclimate and paleoenvironment were analyzed, the paleogeographic background and development model of Mesozoic high-quality source rocks were investigated and discussed. Variation of microfossil species and their relative contents in Mesozoic different intervals indicates changes of paleoclimate and paleoenvironment. The paleoclimate shows a cycle variation of arid–humid–arid–humid, the regression occurred in the Early Triassic–Late Triassic and the transgression occurred in the Late Triassic–Late Cretaceous. Four sedimentary facieses including delta facies, littoral facies, restricted sea facies and open sea facies were developed in the Mesozoic. The open sea was mainly developed in the Early Triassic, the delta was distributed in the Middle–Late Triassic, the restricted sea was especially well developed in the Jurassic, and the restricted sea and open sea were mainly distributed in the Cretaceous. Characteristics of microfossil assemblage in these four sedimentary facies are dramatically different. From the delta facies, littoral facies, restricted sea facies to open sea facies, content of pollen gradually decreases, but content of the dinoflagellate+acritarch gradually increases. The delta facies and littoral facies are dominated by the pollen. In the restricted sea facies, content of the pollen is equivalent to that of the dinoflagellate+acritarch. The open sea facies is dominated by the dinoflagellate and acritarch. Supply of sediment and formation of organic matter are influenced by the paleoclimate and paleoenvironment, and type of organic matter is controlled by the microfossil assemblage. Based on the palaeogeographic background, paleoclimatic condition and microfossil assemblage, two developmental models of the Mesozoic source rocks such as the development model of terrestrial organic matter under the background of large delta and the development model of mixed organic matter under the background of the restricted sea, were proposed.

The upper Permian Dalong Formation in western Hubei Province is a crucial strategic successor for shale gas development in South China. However, the geological controls on reservoir pore development, particularly the influence of organic–inorganic interactions on the pore system, remain poorly understood. This restricts the precise optimization of shale gas exploration targets in this formation. To investigate the pore development characteristics and main controlling factors of the Dalong Formation shale reservoirs, this study takes the DFS from the Shuanghe section in western Hubei as the research object. X-ray diffraction (XRD), argon-ion polishing-scanning electron microscopy (SEM), and N₂/CO₂ gas adsorption–desorption technologies were integrated to achieve qualitative characterization and quantitative assessment of the pore network, with analyses of pore size distribution. The results show that the pores of the DFSs are dominated by interparticle pores and organic matter pores, and the pore structures of organic-rich and organic-lean shales exhibit significant differentiation characteristics. The quartz in the DFSs are mainly of diagenetic origin, and authigenic quartz cementation blocks primary intergranular pores, exerting a significant negative effect on pore development. In contrast, the smectite-to-illite transformation promotes the development of interlayer micropores, leading to a good positive correlation between clay mineral content and micropore volume, as well as specific surface area. Organic matter abundance is the core controlling factor for the construction of micro–nano pore networks. This study clarifies the dominant mechanisms of pore development driven by organic–inorganic interactions in the DFS. Authigenic diagenetic quartz impedes pore development, while smectite-to-illite transformation promotes micropore formation. Organic matter abundance is the dominant control on the micro-nanopore system. This study lays a critical geological theoretical foundation for the exploration evaluation and target selection of shale gas in the Dalong Formation.