鄂尔多斯盆地西南缘奥陶系马家沟组烃源岩饱和烃特征研究

Saturated Hydrocarbon Biomarkers in the Source Rock of the Ordovician Majiagou Formation in the Southwest Ordos Basin

奥陶系马家沟组是鄂尔多斯盆地下古生界的烃源岩层系之一,为了进一步认识马家沟组烃源岩的地球化学特征,本文以鄂尔多斯盆地西南缘典型剖面烃源岩样品为研究对象,利用GC-MS分析方法对研究样品的饱和烃馏分进行了分析。研究表明鄂尔多斯盆地西南缘马家沟组烃源岩岩性不同,其生物标志化合物分布特征也存在差异。根据生物标志化合物特征推断,马家沟组各类源岩的沉积环境为盐度较高的还原环境,灰岩沉积环境的氧化性略高于灰质泥岩;灰岩的有机质母质来源以低等水生生物和微生物为主,而灰质泥岩有高等植物来源的有机质混入,有机质的热演化程度均达到成熟阶段;马家沟组各类源岩有机质均经历过降解作用,且碳质泥岩中有机质遭受的降解作用要强于灰岩。

The Ordovician Majiagou formation in the Ordos basin is one of the potential source rocks in Lower Paleozoic formations.In this paper,samples were collected from typical sections in the sourthwest margin and saturated hydrocarbon fractions were detected by gas-chromatography/mass-spectrometry （GC-MS） to further understand the geochemical characteristics of source rocks in the Majiagou formation.The results indicated that,based on lithological differences,the distributions of biomarker compounds in Majiagou formation source rocks of the southwest margin of the Ordos basin are obviously different.According to the biomarker characteristics of source rocks,we believed that Majiagou formation source rocks were formed in a high salinity and reduced environment,and the oxidizing of limestone source rock was a little higher than that of mudstone.The material source of limestone source rocks was dominated by low grade aquatic lives and microorganisms,while organic matter from higher plants were mixed into mudstone source rocks.Thermal evolution of all source rocks had reached a mature stage.Organic matter of all source rocks had experienced degradation,and organic matter in lime mudstone suffered stronger degradation than in limestone.