The lower Cambrian Niutitang shales, as one of target intervals with the greatest potential for shale gas exploration and development, have attracted much attention. Nevertheless, the organic matter enrichment mechanisms of the lower Cambrian Niutitang shales need further study, especially in the hydrothermal active zone. In this study, samples from ND1 well in western Hubei Province, middle Yangtze region, South China, were investigated for the controlling factors of organic matter accumulation of Lower Cambrian Niutitang shales by detailed petrographic, mineralogic, and geochemical proxies. The results show that hydrothermal activity and sea level fluctuation controlled the redox conditions and paleoproductivity of seawater and ultimately controlled the organic matter accumulation of Niutitang formation. In the Niu-1 member, the intense hydrothermal events lead to a suboxic to anoxic environment, which is conducive to the organic matter preservation. However, low sea level strengthens the restriction of water mass and reduced nutrient upwelling into the shelf, leading to decreased marine primary productivity, which was ultimately responsible for depleted organic matter accumulation in the Niu-1 member. In the Niu-2 member, the anoxic-euxinic environment and high paleoproductivity, driven by continuous hydrothermal activity and rising sea level, were the main factors controlling the enrichment of organic matter. In the Niu-3 member, the dysoxic to oxic condition plus low primary productivity, caused by the disappearance of hydrothermal activities and sea-level fall, resulted in the unfavorable organic matter accumulation. The results of this paper enrich the model of organic matter enrichment in the lower Cambrian black shale in the middle Yangtze region.

Understanding the pore structure of high-rank coals is essential in evaluating gas storage and transport. Here, twelve semianthracite samples from the early Permian Shanxi Formation were investigated by proximate analysis, optical microscopy, low-temperature N₂ adsorption, and fractal analysis, coupled with diffusion coefficient modeling. The coals exhibit diverse pore types (plant-cellular, interparticle, and dissolution pores) shaped by coalification and minerals and show Type IV (a) isotherms with H4 hysteresis loops, indicating complex pore networks. Pore-size partitioning reveals that mesopores and macropores dominate total pore volume, whereas mesopores contribute most of the specific surface area. The pore structure exhibits strong fractal characteristics with an average comprehensive fractal dimension (F_c) of 2.628. The calculated gas diffusion coefficient decreases monotonically with increasing pressure from 1 MPa to 5.8 MPa, with a more pronounced decline at low pressure, indicating a clear pressure-dependent attenuation effect. Diffusion capacity is weakly related to average pore diameter but shows positive correlations with total pore volume and, particularly, macropore volume. Multiple linear regression further demonstrates that pore volume structure is the dominant control on diffusion under both low- and high-pressure conditions, with the relative importance ranked as macropores > mesopores > micropores. Macropores provide the main low-resistance transport framework, mesopores serve as transitional pathways linking storage and transport domains, whereas micropores mainly contribute to gas storage and may even suppress apparent diffusion when overly developed. These results reveal a clear functional differentiation of multiscale pore systems and highlight that gas migration in semianthracite is jointly governed by pore size distribution, connectivity, tortuosity, and fractal network topology.