Abstract A detailed study of organic facies and palynological assemblages was carried out on 11 samples of potential hydrocarbon source rocks of the Pimenteiras Formation, an outcropping at the western edge of the Parnaiba Basin, Brazil. The main objectives are to characterize the depositional paleoenvironment and hydrocarbon source potential. The selection of this outcrop occurred in the function of its preservation and accessibility, and the samples collection observed 1 m of vertical spacing. Generally, the organic matter and the palynomorphs showed a good state of preservation and fluorescence. The most notable spores and acritarchs and phycomates species were discussed in light of international biozones, and the chronostratigraphic range defined as Late Eifelian - Latest Frasnian in age. TOC results show ranges from 0.40 to 2.91%, with most samples showing greater than 1%, thereby holding a high potential generation. The S1 values were virtually null, and the S2 peak ranged from 0.9 to 5.33 mg/g. The kerogen 435 °C, and the ICE between 4.0 and 4.5 demonstrating the material immaturity. For the palynofacies associations definition, only 10 out of the 25 total quantified of subgroups of kerogen categories were considered in the counting of 300 particles. A dendrogram constructed based on these results through cluster analysis, revealed four palynofacies, as follows: I constituted mainly by palynomorphs (acritarchs, prasinophytes and sporomorphs); II – Dominance of Translucent organic matter (cuticles, epidermal tissue and translucent phytoclasts with and without structure); III - Dominance of Opaque/non-fluorescent (opaque phytoclasts and non-fluorescent AOM) and IV - Dominance of AOM fluorescent (amorphous organic matter with fluorescence). The palynomorphs are the most abundant constituents of all studied kerogen. Quantitative analysis based on the distribution of palynomorphs groups throughout the section indicates the dominance of sporomorphs in the palynological assemblages from the Middle Devonian aged samples. On the other hand, occurred the predominance of microplankton elements in the Late Devonian aged samples. Thus, the depositional paleoenvironment was established as a distal oxic mud-dominated shelf with the deltaic influence of the Late Eifelian to Late Givetian, and there is a tendency distal (dysoxic-anoxic ‘shelf’) from the Frasnian, which indicates the maximum flooding surface.

中文翻译：

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巴西 Parnaiba 盆地 Pimenteiras 组中晚泥盆世有机相和孢粉学

摘要 对巴西 Parnaiba 盆地西部边缘的 Pimenteiras 组潜在烃源岩的 11 个样品进行了有机相和孢粉组合的详细研究。主要目标是表征沉积古环境和烃源潜力。该露头的选择发生在其保存和可达性的功能上，样本采集观察到1 m的垂直间距。总体上，有机质和孢粉体表现出良好的保存和荧光状态。根据国际生物带，讨论了最显着的孢子、acritarchs 和 phycomates 物种，并将年代地层范围定义为晚埃菲尔时代 - 最新弗拉斯尼亚时代。TOC 结果显示范围从 0.40 到 2.91%，大多数样品显示大于 1%，因此具有很高的生成潜力。S1 值几乎为零，S2 峰的范围为 0.9 至 5.33 mg/g。干酪根 435 °C，ICE 介于 4.0 和 4.5 之间，表明材料不成熟。对于孢粉相协会定义，在 300 个粒子的计数中，仅考虑了干酪根类别的 25 个量化亚组中的 10 个。基于这些结果通过聚类分析构建的树状图揭示了四种孢粉相，如下： I 主要由孢粉类（acritarchs、prasinophytes 和 sporomorphs）组成；II – 半透明有机物的优势（角质层、表皮组织和半透明的植物细胞，有无结构）；III - 不透明/非荧光（不透明植株和非荧光 AOM）的优势和 IV - AOM 荧光（具有荧光的无定形有机物）的优势。孢粉体是所有研究过的干酪根中最丰富的成分。基于整个部分孢粉形组分布的定量分析表明孢子形在来自中泥盆世年龄样品的孢粉组合中占主导地位。另一方面，晚泥盆世老化样品中出现了微浮游生物元素的优势。因此，沉积古环境被确立为受埃菲尔期晚期至吉维天晚期的三角洲影响的远侧含氧泥质陆架，从弗拉斯尼期开始存在远侧（缺氧-缺氧“陆架”）趋势，表明最大洪水期表面。