Geochemical Study of the Sedimentary Environment and Its Organic Matter Enrichment Mechanism in Qingshankou Formation Shale,Gulong Sag,Songliao Basin
[Objective]The paleosedimentary environment of the Gulong shale is the basis for the prediction of shale oil desserts.[Methods]Based on the salinity of modern lakes in Songliao Basin,the common and trace elements,rare earth elements,and biomarkers of the Gulong shale,the geochemical characteristics of the sedimentary environ-ment and the enrichment mechanism of the organic matter were studied.[Results]The results show that during the formation of the Gulong shale,the climate was warm and humid,a freshwater brackish water reduction environment was developed,paleoproductivity was high,the sedimentational rate was low,and the water body was deep,which provided a geological basis for the formation,preservation,and enrichment of organic matter. The paleoclimate index,chemical index of alteration (CIA) during the shale deposition period was 63-74 and was dominated by a warm and humid climate. During the shale deposition period,the paleosalinity w(Sr)/w(Ba) was between 0.23-1.00,which was a fresh-brackish water environment,and w(V)/w(V+Ni) was between 0.6-0.9,a dysoxic-anoxic environ-ment. The paleowater depth was 25-117 m,indicating a semi deep-to-deep lake deposition. The (La/Yb)N value fluc-tuated between 0.90-1.41,representing a low sedimentational rate.[Conclusions]The enrichment of organic matter in the Gulong shale was caused by the favorable coupling of paleoclimate,paleosalinity,paleowater depth,sedimen-tation rate,and paleoproductivity. The research results can effectively guide the prediction,exploration,and devel-opment of Gulong shale oil desserts in Songliao Basin.
万方数据
维普
