Characteristics and significance of biomarker compounds of Linxi Formation hydrocarbon source rocks along Taohaiyingzi section in Zhalute basin, Inner Mongolia

Based on gas chromatography and gas chromatography mass spectrometry techniques, the authors studied the characteristics of biomarker compounds of Linxi Formation hydrocarbon source rocks along Taohaiyingzi section in Zhalute basin, and analyzed the information and geological and geochemical significance indicated by sources of organic matter, sedimentary environment, the degree of the thermal evolution of organic matter and some other factors. Gas chromatography peaks of saturated hydrocarbons from Linxi Formation source rocks show "the frontal peak type" of the single peak distribution and the C23-dominant main peak of carbon. This indicates that the main sources of organic matter were mixed organic matter; Pr/Ph ratios range from 0.3 to 0.6, suggesting a strongly reducing sedimentary environment. Molecular fossil assemblages of Linxi Formation source rocks have abundant tricyclic terpane with long side chains and high level of gammacerane, and show dominant distribution of C27 steranes. Gammacerane ratios range from 0.15 to 0.29, with an average of 0.19, implying that Linxi Formation hydrocarbon source rocks were formed in an environment of micro-saltwater water to half-saltwater water; the hopanes/steranes ratios are mainly between 0.6 and 1.0, with an average of 0.84, implying that bacteria and algae had almost the same contribution to organic matter. The abundance of C27 steranes is high, and the ratio of C27 steranes/C29 steranes is 1.13, showing that alga was the main source of hydrocarbon precursors.