藏北高原双湖地区中侏罗统海相油页岩生物标志化合物分布特征及其意义

Characteristics of Biomarker Compounds and Its Implication of Middle Jurassic Oil Shale Sequence in Shuanghu Area, Northern Tibet Plateau

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～ 1.0 1,无明显的奇偶碳数优势分布 ;Pr/Ph值为 0 .77～ 1.5 9,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∑ (C2 7+C2 8) >∑C2 9,∑C2 7/∑C2 9值为 0 .79～ 1.2 0 ,在剖面序列中下部C2 7甾烷略占优势 ,上部C2 9甾烷略占优势 ,重排甾烷C2 7/规则甾烷C2 7值为 0 .5 1～ 3 .6 3 ,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”

Abundant biomarkers, including n alkanes, isoprenoid, steranes and terpanes, have been detected by GC—MS from the middle Jurassic oil shales in the Shuanghu area, northern Tibet plateau.N alkanes contain carbon number n C 12 n C 35 with a relatively wide range, n C 15 , n C 16 or n C 17 as the highest peak. 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 vertical section. The upper and lower part of the oil shales have slight predominance of pristane, whereas phytane dominates in the middle part of the oil shale sequence. C 30 hopane is the most abundant in the hopane series. According to the relatively abundance, pentacyclic triterpane > tricyclic terpane > quartcyclic terpane. Sterane ΣC 27 /ΣC 29 ratio ranges from 0.79 to 1.20, and Σ(C 27 +C 28 ) > ΣC 29 . The carbon number distribution of the steranes show a slight predominance of C 27 components over C 29 in the lower part of the oil shales and a slight dominance of C 29 component over C 27 in the upper part of the oil shales sequence. C 27 diasterane/ C 27 sterane ratio range from 0.51 to 3.63, which also fluctuate in the vertical 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 C 27 diasteranes/C 27 steranes proved especially useful in assessing variation in depositional environment and recognizing preservation potential of the organic matter.