柴达木盆地北部滩间山群碳沥青地球化学特征与成因

摘要

固体沥青研究由于其组成的复杂性、形成机制与影响因素的多变性而面临很多难题.在柴达木盆地北部联合沟地区滩间山群发现大量厚层碳沥青，对盆地内的资源勘探具有重要价值.通过野外地质填图以及有机地球化学分析与盆地模拟，对碳沥青的空间分布特征、地球化学特征与成因进行了探讨.结果表明：碳沥青呈NW—SE 向分布在滩间山群 a 段的砂岩与灰岩中；碳沥青中氯仿沥青“A”含量低，族组分中饱和烃与芳烃含量低，而非烃与沥青质含量高；饱和烃与芳烃碳同位素组成偏轻，碳沥青等效镜质体反射率在3．74％~4．72％之间，达到过成熟阶段；饱和烃气相色谱呈后峰形单峰态；油岩对比发现碳沥青与石炭系、侏罗系烃源岩不具有对比性，与滩间山群 a 段泥岩具有可对比性；碳沥青成因与晚泥盆世、早二叠世岩浆侵入有关，两期热事件使烃源岩生成的原油热变质成重油、沥青，甚至碳沥青.%It is difficult to study solid bitumen because of the complexity of bitumen component and the variability of formation mechanism and influencing factor.It is very important that a lot of thick-layer anthraxolites from Tanj ianshan Group in Lianhegou area,the northern of Qaidam Basin were discovered. Through field geological survey, organic geochemical analysis and basin simulation, the spatial distribution,geochemical characteristics and origin of anthraxolite were discussed.The results show that anthraxolite is distributed in sandstone and limestone of member a of Tanj ianshan Group with NW-SE trend;contents of chloroform asphalt “A”are low in anthraxolite,contents of saturated and aromatic hydrocarbons are also low in group component,but contents of non-hydrocarbon and asphaltene are high;carbon isotope compositions of saturated and aromatic hydrocarbons are light,and anthraxolite is at the stage of over-maturity with the equivalent vitrinite reflectance of 3.74%-4.72%;gas chromatogram of saturated hydrocarbon has single peak and odd carbon preference at the range of high carbon number;according to the oil-rock correlation,anthraxolite is not comparable with Carboniferous and Jurassic hydrocarbon source rocks,but is comparable with mudstone from member a of Tanjianshan Group;the origin of anthraxolite is related to Late Devonian and Early Permian magmatic intrusion events,which make crude oil generated by hydrocarbon source rock to heavy oil,bitumen and even anthraxolite.