Abstract Previous geochemical studies carried out in the Parnaiba Basin (Brazil) show that natural gas deposits, whose source rock is formed by the shales of the Pimenteiras Formation (PF; Devonian), stimulated new research to understand the petroleum system. Despite previous studies of PF, it's characterization with emphasis on the biomarker content is still incipient. In this work, the organic matter (OM) of outcrop samples of the Pimenteiras Formation outcrop samples was investigated through diagnostic biomarkers, to evaluate paleoenvironmental conditions of deposition, the thermal evolution, and the organic matter type. The general distribution of hydrocarbons suggested that the samples present low thermal evolution, marine depositional paleoenvironment, and dysoxic conditions. The molecular parameters based on steranes, hopanes, Pr/C17 and Ph/C18, presence of n-C25, n-C27 and n-C29 n-alkanes showed strong evidence of marine origin OM with higher plant input. The data also suggested that OM was not affected by igneous intrusions, being below the oil window. Also, the isomers 4α(methyl)- and 4β(methyl)-24-ethylcholestane and 24-n-propylcholestane have been detected, which are indicative of a marine depositional system. Aromatic carotenoids and derivatives suggest that euxinic conditions have reached the photic zone, an environment conducive to the preservation of organic matter.

中文翻译：

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泥盆纪皮门泰拉斯组烃源岩中脂肪族和芳香族生物标志物的分布及古环境意义

摘要 先前在 Parnaiba 盆地（巴西）进行的地球化学研究表明，其烃源岩由 Pimenteiras 组（PF；泥盆纪）页岩形成的天然气矿床刺激了新的研究以了解石油系统。尽管之前对 PF 进行了研究，但它的表征重点仍然是生物标志物含量。在这项工作中，通过诊断生物标志物研究了 Pimenteiras 组露头样品的露头样品的有机质 (OM)，以评估沉积的古环境条件、热演化和有机质类型。碳氢化合物的一般分布表明样品呈现低热演化、海洋沉积古环境和缺氧条件。基于甾烷、藿烷、Pr/C17 和 Ph/C18，n-C25、n-C27 和 n-C29 正构烷烃的存在显示了海洋来源 OM 和较高植物输入的有力证据。数据还表明，OM 不受火成岩侵入的影响，位于油窗以下。此外，还检测到异构体 4α(甲基)-和 4β(甲基)-24-乙基胆甾烷和 24-n-丙基胆甾烷，这表明存在海洋沉积系统。芳香族类胡萝卜素和衍生物表明，euxinic 条件已经达到了光区，这是一个有利于有机物质保存的环境。已检测到异构体 4α(甲基)-和 4β(甲基)-24-乙基胆甾烷和 24-n-丙基胆甾烷，表明存在海洋沉积系统。芳香族类胡萝卜素和衍生物表明，euxinic 条件已经达到了光区，这是一个有利于有机物质保存的环境。已检测到异构体 4α(甲基)-和 4β(甲基)-24-乙基胆甾烷和 24-n-丙基胆甾烷，表明存在海洋沉积系统。芳香族类胡萝卜素和衍生物表明，euxinic 条件已经达到了光区，这是一个有利于有机物质保存的环境。