内蒙古扎鲁特盆地陶海营子剖面林西组烃源岩生物标志化合物特征及意义

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

采用气相色谱、气相色谱-质谱技术,研究了扎鲁特盆地陶海营子剖面林西组烃源岩的生物标志化合物特征,剖析其蕴含的有机质生源、沉积环境、有机质热演化程度等方面的信息及地质地球化学意义。林西组烃源岩饱和烃气色谱以"前峰型"的单峰分布为主,主峰碳以C23为主,表明有机质来源以混合有机质为主;Pr/Ph值主要介于0.3～0.6之间,植烷优势较明显,指示为强还原的沉积环境。林西组烃源岩具有"长侧链的三环萜烷丰富、伽马蜡烷含量高和C27甾烷分布占优势"的分子化石组合特征,伽马蜡烷比值为0.15～0.29,平均值为0.19,说明林西组烃源岩形成于微咸水—半咸水环境;藿烷与甾烷的含量比值主要分布于0.6～1.0之间,平均值为0.84,表明细菌和藻类对有机质的贡献大致相当;C27甾烷丰度较高,C27(甾烷)/C29(甾烷)的比值为1.13,表明生烃母质生源构成是低等水生生物藻类来源的有机质特征。

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 abun dance 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.