New stratigraphic data on the Eocene Ameki formation, southeastern Nigeria

Abstract

The Eocene Formi Formation in southeastern Nigeria consists, in its type area, of the following four lithologic units, in ascending order: (1) silty to fine calcareous sandstone; (2) grey to dark shale with interacaltions of siltstone; (3) silty to fine argillaceous sandstone; and (4) fine to coarse pebbly sandstone. A palaeoecological study of the fauna of these units is presented. The most significant fossils are the foraminifera comprising chiefly of calcareous benthonic forms. The dominant families are Miliolidae and Nonionidae. Arenaceous forms are absent, while planktonic forms, which are rare, are represented by the generaGlobigerina and Globorotalia. The ostracod assemblage is mainly dominated by the shallow water genera, Togoina, Buntonia, Loxoconcha, Paracypris, Bythocypis, Costa, Basslerites and Cytherella. Based on an integrated analysis of lithologic and faunal data, the following depositional environments are suggested for the Ameki Formation, in ascending order: subtidal and intertidal zones of the shelf environment; barrier ridge, outer lagoon, inner lagoon and beach ridge of the near-shore environment. The water temperature of the Ameki sea was partly influenced by the Bengeula Current.