Palynostratigraphy and palaeoenvironmental characterization and evidence of Oligocene in the terrestrial sedimentary basin, Bingerville area, Southern Cte dIvoire, Northern Gulf of Guinea

摘要

A palynological investigation of two shallow boreholesin Anna, Bingerville area, at 13 km Northwest Abidjan, Southern Côte d’Ivoire,yielded rich and relatively well-preserved dinoflagellate cyst’s assemblages that allowed recognition of Oligocene age. This recognition was based on global dinoflagellate cyst events, including mainlyLejeunecystaspeciesrepresented by cf.Lejeunecysta communis,L. lata,L. pulchra,Lejeunecystasp.cf.L.granosa, cf. L. globosa, L. beninensisand otherPheolodinium magnificum, P. africanum, Selenopemphix nephroïdesandCordosphaeridium inodes. They are associated to terrestrial spores and pollen grains such asMagnastriatites howardii,Spirosyncolpites spiralis,Perfotricolpites digitatus, Retitricoporites irregularis, Retimonocolpites irregularis, Pachydermites diederixii,Psilatricolporites operculatusandPunctodiporites harrisii.The palynostratigraphic interpretations are based on a comparison with calibrated dinoflagellate cyst ranges from several reference sections, mainly in the peri-atlantic and incidentally peri-pacific basins. This study showed changes in the relative abundances of different species or groups of morphologically related species. These changes are palaeoenvironmentally controlled,indicating a deposition occurred between the continental nearshore and marginal marine areas under continental influence. The prevalence of peridinioid dinocysts assemblage suggests deposition in a subtropical province whereasterrestrial pollen grains and spores provided by plants of coastal vegetation dominated by pteridophyts and angiosperms evoke mangrove and swamp forests. These new palynological data, notably the presence of Oligocene especially in the Ivorian terrestrial basin north of the so called “faille des lagunes”, specifies and modifies the previous local stratigraphic scale.