Department of Geology, Federal University Oye-Ekiti, Oye-Ekiti, Nigeria.
Department of Geology, Chukwuemeka Odumegwu Ojukwu University, Uli, Nigeria.
Sci Rep. 2020 Jun 2;10(1):8991. doi: 10.1038/s41598-020-65462-7.
Paleogene deposits are extensively exposed in the Eastern Dahomey (Benin) sedimentary Basin in southwestern Nigeria. Outcrop logging and sampling of lithological sections were systematically carried out at the Ibese Quarry, in order to re-establish the age of sediments and reconstruct their depositional environment using samples rich in organic-walled microfossils. Two formations were recognized; the Ewekoro and Akinbo Formations. Two main lithological units were identified; limestones and carbonaceous shales. Minor lithologies include ferrugineous sandstones and glauconite. Results from the palynological examination show that terrestrial palynomorphs (spores and pollen) dominate over the marine dinoflagellates cyst species in the samples recovered from the Ewekoro Formation, while samples from the Akinbo Formation recorded high abundance with less diversity of the marine dinoflagellates cysts over the terrestrial sporomorph. Age determination/correlation was achieved based on selected stratigraphic index taxa recovered. The samples from Ewekoro Formation were dated as late Early Paleocene to early Middle Paleocene, based on the presence of the following pollen key-taxa: Proxapertites operculatus, Retidiporites magdalenensis, Spinizonocolpites baculatus, Mauritidiites crassiexinus, Scabratriporites simpliformis, and Echitriporites trianguliformis. The samples from the Akinbo Formation were assigned late Middle Paleocene to late Paleocene, based on the presence of the following pollen key-taxa: Proxapertites operculatus/cursus, Grimsdalea polygonalis, Retibrevitricolpites triangulatus, Psilatricolporites operculatus, Retistephanocolpites williamsi, Bombacidites sp., Apectodinium homomorphum, and Apectodinium quinquelatum. The environmentally significant palynomorph species indicated differences in paleodepositional environments, ranging from shallow marine in the Ewekoro Formation at the base, up the stratigraphic sequence, to marginal marine (estuarine) depositional environment in the overlying Akinbo Formation.
古近纪沉积物在尼日利亚西南部的多哥东部（贝宁）沉积盆地中广泛暴露。为了利用富含有孔虫微体化石的样品重建沉积物的年龄并重建其沉积环境，在 Ibese 采石场进行了露头测井和岩性剖面采样。确定了两个地层；Ewekoro 组和 Akinbo 组。确定了两个主要的岩石单元；灰岩和含碳页岩。次要岩性包括铁砂岩和海绿石。孢粉学研究结果表明，在从 Ewekoro 组采集的样品中，陆地孢粉（孢子和花粉）比海洋沟鞭藻孢囊种占优势，而在 Akinbo 组的样品中，海洋沟鞭藻孢囊的丰度较高，陆地孢粉的多样性较低。根据选定的地层指标分类群的恢复情况进行了年龄测定/对比。根据以下花粉关键分类群的存在，确定 Ewekoro 组的样品年代为晚始新世至早中新世：Proxapertites operculatus、Retidiporites magdalenensis、Spinizonocolpites baculatus、Mauritidiites crassiexinus、Scabratriporites simpliformis 和 Echitriporites trianguliformis。根据以下花粉关键分类群的存在，确定 Akinbo 组的样品年代为中晚始新世至晚古新世：Proxapertites operculatus/cursus、Grimsdalea polygonalis、Retibrevitricolpites triangulatus、Psilatricolporites operculatus、Retistephanocolpites williamsi、Bombacidites sp.、Apectodinium homomorphum 和 Apectodinium quinquelatum。环境意义重大的有孔虫微体种表明，古沉积环境存在差异，从 Ewekoro 组底部的浅海，到沿地层序列向上的边缘海（河口）沉积环境，再到上覆的 Akinbo 组。
