广西百色盆地州景矿第三系褐煤有机地球化学与煤岩学研究 Ⅳ．单化合物碳稳定同位素推断生物标志物起源
Organic Geochemistry and Coal Petrology of the Tertiary Brown Coal in the Zhoujing Mine, Baise Basin, South ChinaⅣ Biomarker Source Inferred from stable carbon Isotope Compositions of Individual Compounds
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摘要: 一个未成熟褐煤抽提物中，高等植物生源化合物的同位素值在全煤碳同位素组成（δ１３Ｃ值－２７．０‰）的±２‰范围内，表明相似成煤植物对这些化合物的贡献，或者其成煤植物经历过相似的生物合成分馏效应。所检测的萜烃类按同位素差异分为两组：二萜类（δ１３Ｃ值－２５．０±１．４‰）和倍半萜类（δ１３Ｃ值－２５．９±１．５‰）平均较全煤样富集１～２％。１３Ｃ，而奥利烷－乌散烷－羽扇烷型衍生物（δ１３Ｃ值－２９．０±０．８‰）平均比全煤样减少１～２‰１３Ｃ。Ｃ15～Ｃ35正烷烃δ１３Ｃ平均值－３２．４±０．６‰，据此表明Ｃ17～Ｃ22和Ｃ22～Ｃ33正烷烃的同位素值与上述平均值没有明显差异。与全煤样相比较，该煤样抽提物的藿烷衍生物１３Ｃ值则减少８～３４‰，标志在成煤过程中甲烷的细菌循环起着作用。Abstract: Compounds derived from higher land plants in an immature brown coal extract are isotopically within ± 2%, of the bulk coal carbon isotopic composition (δ13C of - 27. 0‰), suggesting either that similar species contributed to these compounds or similar biosynthetic fractionations occurred in the plants from which this coal was formed. The terpenoid hydrocarbons form two isotopically distinct groups: the diterpenoids (δ13C of - 25. 0 ± 1. 4‰) and the sesguiterpenoids (δ13C of - 25. 9 ± 1. 5‰) are on average 1 ～ 2‰, enriched in 13C compared to the bulk coal, whereas the oleanane-ursane-lupane derivatives(δ13C of - 29. 0±0. 8‰) are on average 1～2‰, depleted in 13C compared to the bulk coal。 The n-alkanes, ranging from C15 to C35, have a mean δ13C value of - 32. 4± 0.6‰, whereby averages for the C17～C22, and C23～C33 n-alkanes do not significantly differ from the overall average. Hopane derivatives in this coal extract are depleted in 13C compared to the bulk coal by 8～34‰, suggesting that bacterial cycling of methane played a role during the formation of this coal.
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