Paleoenvironmental interpretation through the analysis of ostracodes and carbonate microfacies: study of the Jandaíra Formation, Upper Cretaceous, Potiguar Basin

Paleoecological analyses are important tools for the reconstruction of paleoenvironments. This paper had the objective of using analysis of ostracode assemblages and carbonate microfacies of a well (Carbomil) and an outcrop (Quixeré) from the Jandaíra Formation, Potiguar Basin, in order to verify how they corroborate and complement the other. Two paleoenvironments for Carbomil Well (assemblages 1 and 2, respectively marine and brackish to neritic environments) and one for Quixeré Outcrop (assemblage 3, marine environment) were identified through the ostracode assemblage analysis. Thin section analysis allowed the identification of two different facies for Carbomil Well, i.e. bioclastic packstones to wackstones, a marine brackish or restricted marine system; and bioclastic grainstones to packstones, a normal, shallow marine system. High levels of alteration on the samples prevented an adequate analysis of Quixeré Outcrop; however, it seems to point towards a low-energy environment. Overall, information provided by the thin sections corroborate and complement data of the ostracode assemblages, which allowed a higher degree of certainty for the paleoenvironmental analysis.

古生态学分析是开展古环境重建的重要工具。本研究旨在通过对波蒂瓜尔盆地（Potiguar Basin）詹代拉组（Jandaíra Formation）的Carbomil钻井与Quixeré露头的介形类（ostracode）组合及碳酸盐微相（carbonate microfacies）进行分析，验证二者如何相互佐证并互为补充。通过介形类组合分析，研究人员在Carbomil钻井中识别出两种古环境（分别对应组合1与组合2，即海相及半咸水至浅海环境），在Quixeré露头中识别出一种古环境（组合3，海相环境）。薄片分析（thin section analysis）使得我们得以在Carbomil钻井中识别出两种不同的岩相：其一为生物碎屑粒泥灰岩至泥粒灰岩，对应半咸水海相或局限海相体系；其二为生物碎屑颗粒灰岩至粒泥灰岩，对应正常浅海相体系。样品的强烈蚀变程度阻碍了对Quixeré露头的充分分析，但该露头的分析结果似乎指向低能环境。总体而言，薄片分析所获信息可佐证并补充介形类组合的相关数据，使得古环境分析的确定性得到显著提升。