南羌塘鄂斯玛地区早白垩世沥青地球化学特征及意义

Geochemical characteristics and significance of Early Cretaceous bitumens in Esima area,southern Qiangtang Basin of Tibet

首次在南羌塘安多县鄂斯玛地区早白垩世地层中发现沥青。从沥青有机碳含量、族组分及生物标志化合物方面综合研究了其有机地球化学特征,并进行了油源对比。研究结果表明,样品的有机碳含量为3.42%~75.01%,显示其有较高的沥青含量;族组成中重烃组分(非烃+沥青质)质量分数最高,其次为芳香烃,饱和烃质量分数最低。生物标志物研究表明,沥青的成熟度较高,沥青母岩的沉积环境为还原环境,其有机母质主要为混合来源,特别是藻类做出了重要贡献。运用生物标志化合物的相对含量指标进行油源对比研究表明,沥青可能来源于索瓦组泥岩。该研究成果对南羌塘的油气勘探具有一定意义。

Early Cretaceous bitumens were found for the first time in Esima area in southern Qiangtang Basin.The authors analyzed the organic geochemical characteristics from the bitumen content of organic carbon and group composition and biomarkers in this area and discussed the oil-source correlation.The result reveals that the total organic carbon content of the bituments samples varies inthe range of3.42%~75.01%,in dicating abundant bitumens.The bitumen samples have the highest fraction of heavy hydrocarbons(nonhydrocarbon and asphaltene),followed by aromatics hydrocarbon,and the lowest fraction is saturated hydrocarbon.The maturity of bitumens are not in high maturity and are mainly in the mature stage.The source rock was deposited under reductive conditions,and the original organic matter was algae and high-grade plants,with especially important contribution made by algae.Oil-source correlations were studied by using the biomarkers,and the results show that the bitumens were derived from the Suowa Formation mudstones.The results obtained by the authors are important for oil and gas exploration in southern Qiangtang Basin.