ORGANIC GEOCHEMISTRY OF THE SOURCE ROCKS IN THE DONGYING FORMATION OF THE SOUTH BOZHONG SUBSAG

This paper is devoted to the studies of organic matter abundance, type, maturity, parent matter source and depositional environment of the source rocks in the Dongying Formation of the south Bozhong subsag. Analysis results of organic carbon, kerogen, rock pyrolysis, chloroform bitumen "A", group components, Ro, saturated hydrocarbon chromatography-mass spectrometry are collected for the purpose of resource evaluation and source comparison. Results suggest that E₃d₃ is a high-quality source rock with rather high content of organic carbon. Rock pyrolysis experiments and kerogen maceral observation proves that the organic matters of the source rocks of the Dongying Formation are dominated by type Ⅱ₁-Ⅱ₂; The biomarkers are relatively low in Pr/Ph and Gamma-paraffin index, and the combination of Pr/nC₁₇ and Ph/nC₁₈ indicates a weak reduction and fresh-brackish water dominated shallow-lacustrine environment in which the Dongying Formation was deposited. The distribution of n-alkanes, high content of C₂₉ steranes, 4-methylsteranes, C₁₉/C₂₃ tricyclic terpanes and C₂₄ tetracyclic terpanes /C₂₆ tricyclic terpanes suggest that the organic matters are coming from a mixed source, with certain amount of terrigenous input. The parameters of Ro, CPI, OEP, C₂₉20S/(20S+20R), C₂₉ββ/(αα+ββ) and Ts/Tm confirm that the source rocks of the E₃d₃ have matured and started to generate substantial amount of hydrocarbons. However, the E₃d₂ still remain in the stage of low maturity, and the E₃d₁ in the stage of low maturity and/or even immature.