Mechanism of Organic Matter Enrichment in the Wufeng Formation-Longmaxi Formation Shale in the Upper Yangtze Platform
The study takes the shale at the bottom of the Wufeng-Longmaxi Formation in the Upper Yangtze Platform as the research object.The organic matter enrichment mechanism of this set of black shale was studied through the test of organic carbon content,major,trace and rare earth elements and other data.The results show that:the shale at the bottom of the Wufeng-Longmaxi Formation in the study area was deposited in a passive continental margin setting with tectonic stability,which was conducive to the enrichment of organic matter;different geological factors exert varying degrees of control over organic matter enrichment,wherein paleoproductivity has shown a non-significant impact on the organic matter enrichment in the bottom shales of the Wufeng-Longmaxi Formation.Conversely,terrestrial input has produced a diluting effect to some extent;during the sedimentation period of the bottom shales in the Wufeng-Longmaxi Formation,the environmental conditions were characterized by dysoxic-anoxic and moderately stagnant settings,which were highly favorable for the accumulation and preservation of organic matter.However,due to a slightly more open water body environment during the deposition period at the base of the Longmaxi Formation compared to that of the Wufeng Formation,there exists a certain degree of difference in the controlling influence of the water body environment on the preservation of organic matter in the two sets of black shales from both formations.The organic matter enrichment in the two sets of shales from the Wufeng Formation and Longmaxi Formation exhibits distinct differences.The organic matter enrichment of the shale of the Wufeng Formation is controlled by productivity-retention environment,and the organic matter enrichment of the shale at the bottom of the Longmaxi Formation is controlled by conservation-open-upwelling ocean current.
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