Palynological Investigation of a Type Section of Early Maastrichtian Arimogija – Okeluse Shale Sequence, Dahomey (Benin) Embayment, Southwestern Nigeria

Abstract

Biostratigraphy of an exposed section of Arimogija – Okeluse shale sequence was carried out through the use of palynological tool to determine the stratigraphic age and paleoenvironment of deposition of the sequence. The facies is light grey in color and fissile. The section belongs to Foveotriletes margaritae assemblage zone characterized by diagnostic forms such as Buttinia andreevi, Retidiportes magdalenensis, Periretisyncolpites spp, Cingulatisporites ornatus, Auriculiidites sp, Constructipollenites ineffectus, and Monocolpopollenites sphaeroidites. Other important features of the shale section are the relatively high frequency of Monosulcites sp and Leiotriletes sp; co-occurrence of Distaverrusporites simplex, Tetracolpites sp, Monocolpites marginatus, Longapertites spp, Syncolporites sp, and Zlivisporites blanensis. All these forms are known to depict Maastrichtian age. However, Early Maastrichtian age is suggested for Arimogija - Okeluse shale based on the fact that it lacks features such as acme occurrence of Longapertites marginatus and appearance of Spinizonocolpites baculatus which define Middle and Late Maastrichtian ages respectively. The paleoenvironment of deposition of the Arimogija - Okeluse shale is marginal marine characterized by co-occurrence of dinoflagellate cysts such as Andalusiellasp (Peridinacean form), microforaminiferal wall lining; algae - Botryococcus braunii and Pediasrum sp.

Key words: Biostratigraphy, Facies, Outcrop, Marker form and Paleoenvironment