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

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∑ (C₂₇+C₂₈) >∑C₂₉,∑C₂₇/∑C₂₉值为 0.79～ 1.2 0,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 0.5 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”含量在剖面垂向变化的重要因素.

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

Abundant hiomarkcrs, including n-alkancs, isoprcnoid, stcrancs and tcrpancs, have been detected by GC-MS from the middle Jurassic oil shalcs in the Shuanghu area northern Tibet plateau.N-alkancs contain carbon number nC₁₂-nC₃₅ with a rclativclv wide range,nC₁₅,nC₁₆ or nC₁₇ as the highest peak.Examination of the relative abundance show a dominancc of low carbon molecular components in the n-alkanc.Pr/Ph ratio in oil shalcs range from 0.77 to 1.59, and it fluetuatcs in the vertical section.The upper and lower part of the oil shalcs have slight predominance of pristanc, whereas phytune dominates in the middle part of the oil shale sequence.C₃₀-hopanc is the most abundant in the hopanc series.According to the rclativclv abundance, pcntacvclic tritcrpanc>tricvclic tcrpanc>quartcvclic tcrpanc.Stcranc ∑C₂₇/C₂₉ ratio ranges from 0.79 to 1.20} and ∑(C₂₇+C₂₈)>∑C₂₉.The carbon number distribution of the stcrancs show a slight predominance of C₂₇ components over C₂₉ in the lower part of the oil shalcs and a slight dominance of C₂₉ component over C₂₇ in the upper part of the oil shalcs sequence.C₂₇-diastcranc/ C₂₇-stcranc ratio range from 0.51 to 3.63,which also fluctuate in the vertical section.It indicates organic matter of algacl origin with proper ratio contribution from terrestrial sources.The organic matter in the oil shalcs is mature.Different Pr/Ph and C₂₇-diastcrancs/C₂₇-stcrancs proved cspcciallv useful in asscssing variation in dcpositional environment and recognizing preservation potential of the organic matter.