Abstract The Pirabas Formation (early to middle Miocene) from the equatorial margin of North Brazil is characterized by a shallow-marine carbonate platform with high fossil diversity and abundant micro- and macrofossil remains. The Pirabas Formation represents a unique carbonate system along the Atlantic margin of South America that developed before the onset of the Amazon delta. We studied the palaeontology and lithofacies of outcrops of the uppermost Pirabas Formation and found that was deposited in a coastal marine environment with marginal lagoons under the influence of a tidal regime and tropical storms. The remains of calcareous algae, molluscs, crustaceans, echinoiderms, bryozoans, solitary corals, fish and marine mammals, together with foraminifera, ostracods and other marine microfossils, shaped a biogenic framework, that together with the post-depositional processes of dissolution of skeletal grains, is responsible for the mean packstone-floatstone porosity of 14.9%. The palaeontological framework and the petrophysical characterization of the carbonate rocks from the uppermost Pirabas Formation outcrop represent a baseline to interpret the entire Pirabas Formation in the subsurface stratigraphic sections (cores) of this important Neogene unit. Considering that carbonate rocks account for ~50% of oil and gas reservoirs around the world, this research provides a model for Neogene tropical carbonate deposits useful for carbonate petroliferous reservoirs in the Brazilian equatorial basins.

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来自皮拉巴斯组（巴西北部）的古生物框架用作赤道碳酸盐台地的潜在模型

摘要 巴西北部赤道边缘皮拉巴斯组（早中新世）以浅海碳酸盐台地为特征，具有丰富的化石多样性和丰富的微化石和大型化石遗存。Pirabas 组代表了一个独特的碳酸盐系统，沿着南美洲大西洋边缘，在亚马逊三角洲形成之前就形成了。我们研究了 Pirabas 组最上层露头的古生物学和岩相，发现它在潮汐机制和热带风暴的影响下沉积在具有边缘泻湖的沿海海洋环境中。钙质藻类、软体动物、甲壳类动物、棘皮动物、苔藓动物、独居珊瑚、鱼类和海洋哺乳动物的遗骸，与有孔虫、介形动物和其他海洋微化石一起，形成了一个生物框架，再加上骨骼颗粒溶解的沉积后过程，造成了 14.9% 的平均灰岩-浮石孔隙度。来自 Pirabas 组最上部露头的碳酸盐岩的古生物框架和岩石物理特征代表了解释这一重要新近系单元地下地层剖面（岩心）中整个 Pirabas 组的基线。考虑到碳酸盐岩占全球石油和天然气储层的约 50%，这项研究为新近纪热带碳酸盐沉积提供了一个模型，可用于巴西赤道盆地的碳酸盐含油气储层。来自 Pirabas 组最上部露头的碳酸盐岩的古生物框架和岩石物理特征代表了解释这一重要新近系单元地下地层剖面（岩心）中整个 Pirabas 组的基线。考虑到碳酸盐岩占全球石油和天然气储层的约 50%，这项研究为新近纪热带碳酸盐沉积提供了一个模型，可用于巴西赤道盆地的碳酸盐含油气储层。来自 Pirabas 组最上部露头的碳酸盐岩的古生物框架和岩石物理特征代表了解释这一重要新近系单元地下地层剖面（岩心）中整个 Pirabas 组的基线。考虑到碳酸盐岩占全球石油和天然气储层的约 50%，这项研究为新近纪热带碳酸盐沉积提供了一个模型，可用于巴西赤道盆地的碳酸盐含油气储层。