Organic Geochemistry of Bio-Thermocatalytic Transition Zone in the Lisohe Basin (Ⅱ)── Systematic Variation of Maturity Parameters of Steranes,Terpanes and Aromatics within Bio-Thermocatalytic Transition Zone

Key words: 
• Liaohe Basin /
• bio-thermocatalytic transition zone /
• maturity parameter /
• Sterane /
• terpane

Abstract: Hydrocarbon source rocks in Section Sha-1 and Sha-2 of the eastern depression in Liaohe Basin, dealt with in the present paper, are mainly in an immature stage and of which stereochemical parameters of steranes and terpanes in the soluble organic matter show an abnormal abundance of "geopolymer" isomers. Each parameter is generally over its corresponding threshold value and shows a systematical variation with depth roughly bounded by 2200m to 2300 m, 2500 m, 2700 m and 2770 m, respectively. Meanwhile, maturity parameters of phenanthrene, naphthalene, dibenzofuran and dibenzothiophene series are found to be similar in variation to those of steranes and terpanes. On the basis of the contrast study in detail and the integration of variations of infrared absorption parameters in the original soluble organic matter,the paper points out that variations of maturity parameters of steranes, terpanes and aromatics within the bio- thermocatalytic transition zone are dependent on the evolutionary features of the original soluble organic matter. The paper also qualitatively raises some geochemical identification markers for the bio-thermocatalytic transition zone of the eastern depression in Liaohe Basin. The present results can be applied to the identification of biothermocatalytic transition zone gases or immature and low-mature oils in other different areas.