Palynostratigraphy and palaeoenvironmental characterization and evidence of Oligocene in the terrestrial sedimentary basin, Bingerville area, Southern Côte d'Ivoire, Northern Gulf of Guinea

A palynological investigation of two shallow boreholes in 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 mainly Lejeunecysta species represented by cf. Lejeunecysta  communis, L. lata, L. pulchra, Lejeunecysta sp. cf. L. granosa, cf. L. globosa, L. beninensis and other  Pheolodinium magnificum, P. africanum, Selenopemphix nephroïdes and Cordosphaeridium inodes.  They are associated to terrestrial spores and pollen grains such as Magnastriatites howardii,  Spirosyncolpites spiralis, Perfotricolpites digitatus, Retitricoporites irregularis, Retimonocolpites  irregularis, Pachydermites diederixii, Psilatricolporites operculatus and Punctodiporites 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 whereas  terrestrial 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.Key words: Palynostratigraphy, palaeoenvironment, Oligocene, sedimentary basin, Côte d’Ivoire