藏北高原双湖地区中侏罗统海相油页岩生物rn标志化合物分布特征及其意义

摘要

Abundant biomarkers, including n-alkanes, isoprenoid, steranes and terpanes, ha v e been detected by GC-MS from the middle Jurassic oil shales in the Shuanghu ar ea, n orthern Tibet plateau.N-alkanes contain carbon number nC12-nC 35 with a relativel y wide range,nC15, nC16 or nC17 as the highest pea k. Examination of the relative abundance show a dominance of low carbon molecular components in the n-alkane . Pr/Ph ratio in oil shales range from 0.77 to 1.59, and it fluctuates in the vert ical section. The upper and lower part of the oil shales have slight predominanc e of pristane, whereas phytane dominates in the middle part of the oil shale seq uence. C30-hopane is the most abundant in the hopane series. According to the relat ively abundance, pentacyclic triterpane > tricyclic terpane > quartcyclic terpan e. Sterane ΣC27/ΣC29 ratio ranges from 0.79 to 1.20, and Σ(C2 7+C28) > ΣC29. The carbon number distribution of the steranes show a slight predominance of C 27 components over C29 in the lower part of the oil shales and a slight domi nance of C29 component over C27 in the upper part of the oil shales sequen ce. C27-dias terane/ C27-sterane ratio range from 0.51 to 3.63, which also fluctuate in the v ertical section. It indicates organic matter of algael origin, with proper ratio contribution from terrestrial sources. The organic matter in the oil shales is mature. Different Pr/Ph and C27-diasteranes/C27-steranes proved e specially usefu l in assessing variation in depositional environment and recognizing preservatio n potential of the organic matter.%重点报道了藏北双湖地区中侏罗统海相油页岩的生物标志化合物特征，首次在该层位油页岩中检出丰富的正烷烃、类异戊二烯烷烃、萜类化合物及甾类化合物。正烷烃图谱呈单峰形，nC15、nC16或nC17为主峰碳，轻烃组份占有绝对优势，OEP值0.93～1.01，无明显的奇偶碳数优势分布；Pr/Ph值为0.77～1.59，在剖面序列中呈波动分布，显示弱植烷优势或姥鲛烷优势；藿烷以C30占优势，萜烷相对丰度五环三萜烷>三环萜烷>四环萜烷；规则甾烷∑（C27+C28）>∑C29，∑C27/∑C29值为0.79～ 1.20，在剖面序列中下部C27甾烷略占优势，上部C29甾烷略占优势，重排甾烷C27/规则甾烷C27值为0.51 ～3.63，在剖面序列中具有显著的波动性，同时检出了少量孕甾烷和4-甲基甾烷。有机质母质构成中，既有丰富的藻类等低等水生生物，可能还有一定比例陆生高等植物输入混合的特点。油页岩处于成熟阶段，整个油页岩剖面序列具有一致的热演化程度。剖面中部油页岩具有极高的原始生产力，氧化-还原条件也是控制油页岩TOC和沥青“A”含量在剖面垂向变化的重要因素。