The distribution characteristics of biomarkers in Upper Sinian Doushantuo Forma-tion at YangJiaping

Middle Yangzi Region were studied through analysing three typical samples of limestone

carbonaceous limestone and carbonaceous shale.The biomarkers in Doushantuo Formation include n-alkanes

n-alkylcyclohexanes and methyl-n-alkylcyclohexanes.The content of regular sterane with C

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sterane predominance is much higher than that of rearranged sterane.The contents of tricyclic terpane and pentacyclic triterpane are higher.Gammacerane

carotanes

pristane and phytane are widespread.Biomarkers in Upper Sinian Doushantuo Formation suggest that the organic matter comes from algae and bacteria.The differences of biomarker distribution in lime-stone and shale in Doushantuo Formation indicate that sedimentary environment is the main factor in controlling biomarker distribution

and the stereoiso merization of limestoneis slower than that of shale

suggesting a higher thermal evolution degree of shale than that of limestone.Though the formation in the Middle Yangzi Region is rich in fine or-ganic matter

but it is only possible to have gas-source potential due to the overmature ofthe organic matter.