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The marine-continent transitional mud shale in Upper Carboniferous Benxi Formation is a potential shale gas exploration target in the eastern Ordos Basin. Based on the systematic observation and sampling analysis of representative profiles and key well, the influencing factors and development pattern of organic-rich mud shale in Benxi Formation of Liulin-Zizhou area, the eastern Ordos Basin were studied, and the development pattern “slow subsidence, terrigenous organic matter supply, and enclosed preservation” of marine-continent transitional organic-rich mud shale was established. The results show that the organic-rich mud shale in Benxi Formation of Liulin-Zizhou area, the eastern Ordos Basin mainly belongs to Jinci and Pangou members, and the lithofacies is mainly clay mud shale with a small amount of siliceous mud shale; the abundance of organic matter is high, and the type is mainly humic; the coal-forming plants flourish in the region because of the hot and humid climate in Benxi depositional period, and result in an abundant supply of organic matter for the sedimentary water; the transgression occurs in the eastern Ordos Basin under the tectonic background of slow subsidence; the high salinity of anoxic water at the bottom maintains reduction environment in the barrier island-lagoon-neritic muddy shelf sedimentary system, which provides a favorable zone for the preservation and enrichment of sedimentary organic matter. [ABSTRACT FROM AUTHOR]

Datangpo Formation of Nanhua System in Shennongjia area of Hubei belongs to interglacial deposit, and the understanding of its sedimentary strata and paleoenvironment is limited at present. Based on the field geological investigation of Datangpo Formation of Nanhua System in Shennongjia area, the paleoenvironmental characteristics of Datangpo Formation and their significance for oil and gas exploration in this area were systematically studied by using the data of element geochemistry analysis. The ratios of CaO/(CaO+Fe), Sr/Ba, Rb/K, K/Na indicate that the sedimentary water salinity of Datangpo Formation is low-medium, and the sedimentary water salinity in the Dajiuhu section is higher than that in the Songluo section. Based on the relevant parameters of oxidation-reduction sensitive elements including the ratios of V/(V+Ni)and Ni/Co, and Ceanom, the results show that Datangpo Formation of Nanhua System in Shennongjia area deposits in a weak oxidation-weak reduction water environment. The CIA, ICV, ratios of Sr/Cu, Sr/Ba, Rb/Sr and Mg/Ca, and the content of Sr indicate that the paleoclimate of Datangpo Formation during the deposition period is a warm and humid climate. Comprehensive analyses of TOC, paleontology and the contents of Cu and Ba show that the warm and humid climate, and water conditions during the deposition period of Datangpo Formation are very suitable for the mass reproduction of aquatic algae, and provide sufficient organic matters for the high-quality source rocks of Datangpo Formation. [ABSTRACT FROM AUTHOR]