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The effect of aromatization on the isotopic compositions of hydrocarbons during early diagenesis
Organic Geochemistry ( IF 3 ) Pub Date : 1994-10-01 , DOI: 10.1016/0146-6380(94)90067-1
K H Freeman 1 , C J Boreham , R E Summons , J M Hayes
Affiliation  

Polycyclic aromatic hydrocarbons with varying degrees of aromatization were isolated from the Eocene Messel Shale (Rheingraben, Germany). The high abundances of these compounds and their structural resemblances to cyclic triterpenoid lipids are consistent with derivation from microbial rather than thermal processes. Compounds structurally related to oleanane contain from five to nine double bonds; those within a series of aromatized hopanoids contain from three to nine. All are products of diagenetic reactions that remove hydrogen or methyl groups, and, in several cases, break carbon-carbon bonds to open rings. Aromatized products are on average depleted in 13C relative to possible precursors by l.2% (range: l.5% enrichment to 4% depletion, n = 9). The dependence of 13C content on the number of double bonds is not, however, statistically significant and it must be concluded that there is no strong evidence for isotopic fractionation accompanying diagenetic aromatization. Isotopic differences between series (structures related to ursane, des-A-ursane, des-A-lupane, des-A-arborane, and possibly, des-A-gammacerane are present) are much greater, indicating that 13C contents are controlled primarily by source effects. Fractionations due to chromatographic isotope effects during HPLC ranged from 0.1 to 2.8%.

中文翻译:

芳构化对早期成岩过程中碳氢化合物同位素组成的影响

从始新世 Messel 页岩 (Rheingraben, Germany) 中分离出具有不同芳构化程度的多环芳烃。这些化合物的高丰度及其与环状三萜类脂质的结构相似性与微生物而非热过程的衍生一致。结构上与齐墩果烷相关的化合物含有 5 到 9 个双键;一系列芳香化hopanoids中的那些包含三到九个。所有这些都是去除氢或甲基的成岩反应的产物,并且在某些情况下,会破坏碳-碳键以开环。相对于可能的前体,芳香化产品在 13C 中平均消耗 1.2%(范围:1.5% 富集到 4% 消耗,n = 9)。然而,13C 含量对双键数量的依赖性不是,统计显着,必须得出结论,没有强有力的证据表明伴随成岩芳构化的同位素分馏。系列之间的同位素差异(存在与 ursane、des-A-ursane、des-A-lupane、des-A-arborane 和 des-A-gammacerane 相关的结构)要大得多,表明 13C 含量主要受到控制按源效应。由于 HPLC 中的色谱同位素效应而产生的馏分范围为 0.1% 至 2.8%。
更新日期:1994-10-01
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