Even being the more studied of the interior basins of Northeast Brazil, the Araripe Basin still lacks research in organic geochemistry designed to support interpretations of depositional systems and conditions of formation. This work aims to investigate the organic behavior of evaporites and shales from the Santana Group (Lower Cretaceous), as well as discuss their role in the evolution of its depositional systems. A total of 23 samples, 17 shales and six evaporites, were collected in outcrops and quarries. Analyses of Total Organic Carbon (TOC), Total Sulfur (TS), Rock Eval pyrolysis, and the δ³⁴S isotope ratio were performed. The TOC results revealed high organic content for seven intervals, of which only five had high TS content. From the Rock Eval pyrolysis, dominance of the Type I kerogen was verified, thus corresponding to the best type of organic matter (mainly algal) for the generation of liquid and gaseous hydrocarbons. The Lower Cretaceous (probably Aptian) response to the progressive evolution in redox conditions is linked to a remarked Oceanic Anoxic Event (OAE-1a). The TOC/TS ratio suggests variable palaeosalinity, indicating most of the shales were formed under brackish waters with saline influence, yet tending to increase the salinity upwards where hypersaline conditions dominate in the Ipubi Formation. The isotope data also suggest the occurrence of marine ingressions in the depositional systems even prior to the well-documented event of the Romualdo Formation.

中文翻译：

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Santana 群（巴西阿拉里佩盆地）蒸发岩和页岩的有机和同位素地球化学：下白垩统沉积系统演化和全球相关性的线索

即使对巴西东北部的内陆盆地进行了更多的研究，阿拉里佩盆地仍然缺乏旨在支持对沉积系统和形成条件的解释的有机地球化学研究。这项工作旨在研究来自桑塔纳群（下白垩纪）的蒸发岩和页岩的有机行为，并讨论它们在沉积系统演化中的作用。在露头和采石场共采集了 23 个样品，17 个页岩和 6 个蒸发岩。总有机碳 (TOC)、总硫 (TS)、岩石评价热解和 δ ^{34 的分析}进行 S 同位素比值。TOC 结果显示七个区间的有机物含量高，其中只有五个区间的 TS 含量高。Rock Eval 热解证实了 I 型干酪根的优势，因此对应于生成液态和气态烃的最佳有机质类型（主要是藻类）。下白垩纪（可能是 Aptian）对氧化还原条件逐渐演化的反应与显着的海洋缺氧事件 (OAE-1a) 有关。TOC/TS 比率表明古盐度存在差异，表明大部分页岩形成于咸水影响下，但在 Ipubi 组中高盐度条件占主导地位的情况下，盐度倾向于向上增加。