Palynology and paleoenvironments of the upper araromi formation, Dahomey Basin, Nigeria

摘要

A detailed understanding of the biostratigraphy of the Dahomey Basin in southwestern Nigeria will broaden our knowledge of the Basin which traversed different West African countries especially as Nigeria is working towards increasing her petroleum output. The palynological investigation of eight surface outcrops from Ifon town of the Upper Araromi Formation processed using conventional methods of disaggregation and removal of carbonates and silicates with hydrochloric acid and hydrofluoric acid and further treatment with hot hydrochloric acid (HC1), wet-sieving over a 5-micron sieve and the Branson Sonifier 250 used for the complete removal of silt and clay particles. Each residue was prepared for study as strewn mounts using Loctite. The samples yielded a rich assemblage of Maastrichtian-Paleocene palynomorphs among which were common Ariadnaesporites spinosa, A. nigeriensis, Ariadnaesporites sp., Foveotriletes margaritae, Rugulatisporites caperatus, Distaverrusporites simplex, Cingulatisporites ornatus, Zlivisporis blanensis, with dinoflagellate cysts, diatom frustules and abundant palm pollen Longapertites marginatus, L. vaneendenburgi, L. microfoveolatus, Proxapertites operculatus, Monocolpopollenites sphaeroidites, Spinizonocolpites echinatus, S. baculatus, S. kostinensis, Retidiporites magdalenensis, Mauritidites lehmanii, Tubistephanocolpites cylindricus, Echitriporites trianguliformis, E. longispinosus, Monocolpites marginatus, Retimonocolpites nigeriensis, Racemonocolpites racematus and Arecipites sp. The palynological age assigned to the samples were based on already published ranges of the palynostratigraphically important taxa. The preponderance of these palm pollen, together with diatom frustules and a dinoflagellate cyst suite dominated by Gonyaulaceleans, indicates sediment deposition in a highly productive shallow marine environment.