Abstract Thiophenic compounds can provide significant geochemical information and may be used as paleoenvironmental indicators as long as their biological origins and formation pathways are understood. To this end, we investigated the structures, distribution, δ13C and δ34S values of specific thiophenic compounds extracted from immature sedimentary rocks from the Upper Cretaceous (Ghareb Formation, Shefela Basin, Israel). Isoprenoidal alkylthiophenes (ATs) showed a general trend of depletion in their 13C and 34S relative to the normal (linear) ATs extracted from the studied samples. In addition, a consistent enrichment of up to 2‰ in 13C and 8‰ in 34S of methylated ATs (m/z= 111), relative to non-methylated ones (m/z= 97), was recorded. This suggests that AT precursors derived from different organisms and diagenetic pathways that later affected their sulfurization mechanisms. The large variation of ∼15 ‰, in the δ34S values of individual ATs, along with the general trend of 13C depletion with increasing Tmax, suggests that ATs formed by a set of diagenetic processes of mild thermochemical alteration. The δ13C values of benzothiophenes (BTs) were enriched in 13C relative to the rest of the organic sulfur compounds, by ∼3‰ on average. This in turn suggests that BTs were generated mainly by sulfurization and subsequent ring closure, or aromatization of 13C-enriched aromatic/ alkyl cyclohexane compounds with unsaturation and/or functional groups in their alkyl chain. Such 13C-enriched precursors can be generated from carotenoids and terrestrial compounds (e.g., by lignin degradation). The large variation in δ34S values of individual BTs of ∼15 ‰, suggests that the BTs in our samples were formed during diagenesis and did not experience advanced thermal alteration processes. Therefore, their occurrence in immature sedimentary rocks might be used as a proxy for early thermochemical alteration that cannot be detected using conventional geochemical indicators, such as Tmax. The combination of structural, 13C and 34S investigations of individual organic sulfur compounds enhanced an understanding of their sulfurization pathways and origins, which in turn may expand their utilization as paleoenvironmental indicators.

中文翻译：

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烷基和苯并噻吩的碳和硫同位素组成提供了对其起源和形成途径的见解

摘要 噻吩化合物可以提供重要的地球化学信息，只要了解其生物起源和形成途径，就可以用作古环境指标。为此，我们研究了从上白垩统（以色列谢菲拉盆地 Ghareb 组）未成熟沉积岩中提取的特定噻吩化合物的结构、分布、δ13C 和 δ34S 值。与从研究样品中提取的正常（线性）AT 相比，类异戊二烯烷基噻吩 (AT) 的 13C 和 34S 显示出普遍的消耗趋势。此外，相对于非甲基化 ATs (m/z= 97)，甲基化 ATs (m/z= 111) 的 13C 和 34S 中高达 2‰ 的一致富集被记录到。这表明来自不同生物体和成岩途径的 AT 前体后来影响了它们的硫化机制。单个 ATs 的 δ34S 值的 ∼15‰ 的大变化，以及随着 Tmax 增加 13C 消耗的总体趋势，表明 ATs 是由一组温和的热化学改变的成岩过程形成的。相对于其余有机硫化合物，苯并噻吩 (BT) 的 δ13C 值在 13C 中平均富集约 3‰。这反过来表明 BTs 主要是通过硫化和随后的闭环或芳构化产生的，富含 13C 的芳香族/烷基环己烷化合物在其烷基链中具有不饱和度和/或官能团。这种富含 13C 的前体可以从类胡萝卜素和陆生化合物（例如，通过木质素降解）。单个 BTs 的 δ34S 值的巨大变化约为 15‰，表明我们样品中的 BTs 是在成岩过程中形成的，并且没有经历高级的热蚀变过程。因此，它们在未成熟沉积岩中的出现可能被用作早期热化学蚀变的代表，而这些变化是使用 Tmax 等常规地球化学指标无法检测到的。对单个有机硫化合物的结构、13C 和 34S 研究的结合增强了对其硫化途径和起源的理解，这反过来可能扩大它们作为古环境指标的利用。因此，它们在未成熟沉积岩中的出现可能被用作早期热化学蚀变的代表，而这些变化是使用 Tmax 等常规地球化学指标无法检测到的。对单个有机硫化合物的结构、13C 和 34S 研究的结合增强了对其硫化途径和起源的理解，这反过来可能扩大它们作为古环境指标的利用。因此，它们在未成熟沉积岩中的出现可能被用作早期热化学蚀变的代表，而这些变化是使用 Tmax 等常规地球化学指标无法检测到的。对单个有机硫化合物的结构、13C 和 34S 研究的结合增强了对其硫化途径和起源的理解，这反过来可能扩大它们作为古环境指标的利用。