THE SOURCE ROCKS OF MESOPROTEROZOIC TIELING FORMATION IN LINGYUAN-NINGCHENG BASIN: Biomarker Characteristics and Implication

Based on gas chromatography and gas chromatography-mass spectrometry, the paper studies the characteristics of biomarker compounds in the source rocks of Tieling Formation in Lingyuan-ningcheng Basin, and analyzes the organic source, sedimentary environment and thermal evolution degree of organic matter, as well as geochemical implication. The saturated hydrocarbon gas chromatography of source rocks is front-peak type unimodal distribution dominated, with the main peak carbon mostly nC₁₈, indicating that the organic matter is mainly derived from lower organism. The Pr/Ph ratio mainly ranges from 0.16 to 0.73, with obviously more phytane, indicating a strongly reducing sedimentary environment. The source rocks of Tieling Formation are characterized by abundant long-side chain tricyclic terpane, high content of gamacerane and dominant distribution of C₂₇ sterane, with Ga/C₃₀H of 0.10-0.31, averagely 0.19, reflecting the source rocks were formed in slight saline water-brackish water environment. The Ts/Tm ratio of 0.54-1.19 (averagely 0.88) shows the thermal evolution degree of source rocks is relatively high. The ratio of sterane/hopane contents is mainly in the range of 0.24-0.59, averagely 0.42, reflecting the lower organism of algae contributes little to organic matter, while the microorganisms such as bacteria contribute a lot. The sterane in the source rocks are L-shape with dominant C₂₇ sterane, indicating the hydrocarbon generating parent material is of lower aquatic biological organism origin.