Abstract Outcrops of Neogene carbonates of the North Brazilian platform occur exclusively along the equatorial coast and represent some of the few existing examples of Neogene carbonate systems of the Atlantic coast of South America. The Pirabas Formation (early-middle Miocene) is the northernmost part of this platform. Although onshore mainly consists of small and scattered outcrops, it considerably extends in the subsurface keeping record of relevant geological and paleontological episodes of tropical South American history. Intending to improve the knowledge of South American carbonate and providing a solid basis for future comparisons between the Pirabas Basin and other, largely subsurface, Cenozoic basins, this research investigates the Aricuru outcrops by combining a standard petrographical and paleontological approach with advanced microCT analyses. The Aricuru area is characterized by mixed siliciclastic-carbonate sand-sized deposits, which probably deposited after the early Miocene according to the palynological assemblage. The bioclastic fraction of the rock is dominated by benthic foraminifera (mostly soritids, amphisteginids, small rotaliids, and small miliolids, typical of marginal marine environments), bryozoans, calcareous algae (Halimeda), echinoderms and mollusks. The abundant siliciclastic fraction together with the taxonomic composition of the foraminiferal, echinodermal, crustacean, ichnofossil and fish assemblages indicates deposition in a tropical coastal environment featuring both protected and more exposed sectors. The carbonate system probably developed under abundant nutrient supply, which fostered heterotroph suspension feeders over hermatypic corals. The demise of this system was most likely caused by a growth in siliciclastic input due to increased rainfall in the coastal area. The sedimentary evolution of the Pirabas Formation is similar to the one of the Foz do Amazonas Basin, and fits well with the general evolutionary trend of Cenozoic carbonate factories of the region, indicating the potential of the Pirabas subsurface record for understanding other Cenozoic basins, their paleoenvironmental significance, and their potential as oil, gas and water reservoirs.

中文翻译：

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来自南美洲西大西洋赤道边缘的中新世杂碳酸盐系统：Pirabas 地层

摘要 巴西北部台地新近系碳酸盐岩露头仅沿赤道海岸出现，代表了南美洲大西洋沿岸新近系碳酸盐岩系统的少数几个现有实例。Pirabas 组（早中新世）是这个平台的最北端。虽然陆上主要由小而分散的露头组成，但它在地下有相当大的延伸，记录了南美洲热带历史的相关地质和古生物事件。打算提高对南美碳酸盐岩的认识，并为将来皮拉巴斯盆地与其他主要在地下的新生代盆地进行比较提供坚实的基础，这项研究将标准的岩相学和古生物学方法与先进的显微 CT 分析相结合，对 Aricuru 露头进行了调查。Aricuru地区以硅质碎屑-碳酸盐混合砂粒沉积为特征，根据孢粉组合可能沉积于早中新世之后。岩石的生物碎屑部分主要是底栖有孔虫（主要是海鞘类、两栖类、小型轮虫类和小型兔科动物，典型的边缘海洋环境）、苔藓动物、钙质藻类（Halimeda）、棘皮动物和软体动物。丰富的硅质碎屑部分以及有孔虫、棘皮动物、甲壳动物、鱼化石和鱼类组合的分类组成表明沉积在热带沿海环境中，具有受保护和更暴露的部分。碳酸盐系统可能是在丰富的营养供应下发展起来的，这在雌雄同体的珊瑚上形成了异养悬浮饲养者。该系统的消亡很可能是由于沿海地区降雨量增加导致硅质碎屑输入增加所致。Pirabas 组的沉积演化与 Foz do Amazonas 盆地相似，与该地区新生代碳酸盐岩工厂的总体演化趋势吻合，表明 Pirabas 地下记录对于了解其他新生代盆地、它们的古环境意义，以及它们作为石油、天然气和水库的潜力。该系统的消亡很可能是由于沿海地区降雨量增加导致硅质碎屑输入增加所致。Pirabas 组的沉积演化与 Foz do Amazonas 盆地相似，与该地区新生代碳酸盐岩工厂的总体演化趋势吻合，表明 Pirabas 地下记录对于了解其他新生代盆地、它们的古环境意义，以及它们作为石油、天然气和水库的潜力。该系统的消亡很可能是由于沿海地区降雨量增加导致硅质碎屑输入增加所致。Pirabas 组的沉积演化与 Foz do Amazonas 盆地相似，与该地区新生代碳酸盐岩工厂的总体演化趋势吻合，表明 Pirabas 地下记录对于了解其他新生代盆地、它们的古环境意义，以及它们作为石油、天然气和水库的潜力。