As a hydrocarbon-rich sedimentary basin in China, the Ordos Basin has enormous potential for shale gas resources. The shale of the Upper Carboniferous Benxi Formation is rich in organic matter, however, its palaeoenvironment and organic matter enrichment mode are yet to be revealed. In this study, the geochemical characteristics of the shale of the Benxi Formation in the east-central part of the Ordos Basin were analyzed to investigate its palaeoenvironment. At the same time, the organic matter enrichment modes in different sedimentary facies were compared and analyzed. The results indicate that: 1) the shale of the Benxi Formation was mainly deposited on the continental margin and strong terrestrial clastic input; 2) the deposition period of the Benxi Formation shale had a hot and humid climate with high palaeoproductivity and local volcanic hydrothermal fluid, and a high sedimentation rate with the strong stagnant environment. The bottom water was in dysoxic conditions and a semi-saline deposition environment; 3) multiple factors, such as palaeoproductivity, volcanic hydrothermal, redox conditions, and palaeosalinity interact to influence the enrichment of shale organic matter in Benxi Formation; 4) the organic matter enrichment modes of continental, marine-continental transitional, and marine shales can be classified into three types: “production mode”, “hybrid mode of preservation and production”, and “preservation mode”, respectively. This study provides a reference for the organic matter enrichment mode, shale gas formation conditions, and core area evaluation in these marine-continental transitional shales, and also offers new guidance for exploration ideas for shale gas in different sedimentary facies.

鄂尔多斯盆地作为我国富油气沉积盆地，页岩气资源潜力巨大。上石炭统本溪组页岩富含有机质，但其古环境和有机质富集模式尚未揭示。本研究对鄂尔多斯盆地中东部本溪组页岩地球化学特征进行分析，探讨其古环境。同时对不同沉积相有机质富集模式进行了对比分析。研究结果表明：1）本溪组页岩主要沉积于陆缘，陆相碎屑输入较强；2）本溪组页岩沉积期气候湿热，古生产力高，局部有火山热液，沉积速率高，滞留环境强。底层水体处于低氧条件和半咸水沉积环境；3）古生产力、火山热液、氧化还原条件、古盐度等多种因素相互作用影响本溪组页岩有机质富集；4）陆相、海陆过渡带、海相页岩有机质富集模式可分为“生产模式”、“保存与生产混合模式”、“保存模式”3种类型。该研究为海陆过渡相页岩有机质富集模式、页岩气形成条件及核心区评价提供了参考，也为不同沉积相页岩气勘探思路提供了新的指导。