Paleoenviromental Reconstruction and Organic Matter Accumulation Mechanism for Youganwo Formation Oil Shale in Maoming Basin
To identify the formation background of oil shale and the enrichment mechanism of high-quality intervals are the fundamental works for in-situ upgrading of oil shale reservoir.In this paper,geochemical methods,e.g.,TOC,major and trace element,rare earth element and biomarkers,were carried out to restore paleosedimentary environment as well as discuss organic matter accumulation mechanism.The results suggest that oil shale within the entire interval of Youganwo Formation is rich in organic matter,and the bottom is composed of thin carbonaceous shale,sandstone and lignite.Mo content,Ba/Al,Babio and biomarkers all reflect that Youganwo Formation has high primary productivity,with intermittent"algal bloom"phenomenon.V/(V+Ni),Ceanom,Th/U,pyrite framboids and Pr/n C17-Ph/n C18 crossplot indicate that Youganwo Formation was anoxic environment.Sr/Cu,Rb/Sr and climate index C identify that the climate of Youganwo Formation was warm and humid.Sr/Ba,Ba/Ga,Ca/(Fe+Ca),Al2O3/MgO and gammacerane feature suggest that water of ancient lake is fresh.The ancient lake of Youganwo Formation was semi-deep to deep,proved by Zr/Al,Rb/K and MnO content.Through the correlations between paleo-environmental parameters with TOC content,it is deemed that the warm and humid climate and freshwater environment can provide good conditions for the flourishing of algae,forming high quality productivity,and therefore it determines the quality and development characteristics of Youganwo Formation oil shale.High primary productivity with abundant organic matter sources is the main condition for oil shale formation,and anoxic semi-deep to deep lake environment,as a promoting factor,is conducive to organic matter accumulation and preservation.To sum up,in this paper it proposes the accumulation model of organic matter in high-quality oil shale of Youganwo Formation in the Maoming Basin.
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