Savanna Journal of Basic and Applied Sciences 4(1):1-7
Stratigraphy and Palynology of the Late Miocene Lignite Facie in Abia and Imo States Coastal Plain Sediments, Niger Delta, Southeastern Nigeria
Obuseh, J. O. and Ola-Buraimo, A. O.
ABSTRACT
Coastal field geology of the Abia and Imo States were undertaken with a view to studying the lithostratigraphy section of the outcrops present in gullies, along streams, in the mines and to date the lignite beds present within the Ogwashi-Asaba Formation. Field study method employed in the litho-description of the outcrops involved composition, textural characteristics, structures, fossil content, ichnofossil, bioturbation, accessory minerals and post depositional effects. Palynology laboratory slide preparation went through processes of decarbonization, digestion, filtration of the organic debris with 10 µm sieve, maceral separation with heavy liquid and mounting of the macerals on glass slides before examination under the B-150 OPTIKA scientific microscope. Lithologic sequence is characterized at the base by lignite, overlain by whitish and brownish siltstone beds constituting OgwashiAsaba Formation and stratigraphically equivalent to Agbada Formation. Overlying the Agbada Formation is Benin Formation comprising of conglomerates, poorly sorted sandstones, mudstones of varying colours of light grey to reddish brown silty mudstones, 3.5m thick laterite and topmost regolith layer deposited in continental environment. The lignite beds were palynologically dated Late Miocene, belonging to Echiticolpirites spinosus zone of P800/P830 subzone. The lignite palynomorphs that characterize the erected zone are Multiareolites formosus, Anthocerus sp., Nmphae lotus, Elaeis guineensis, Zonocostites ramonae, Retitricolporites irregularis, Monoporites annulatus, and Psilatricolporites crassus. Other stratigraphically important forms present are Retibrevitricolporites obodoensis, Echiperiporites estalae, Canthium type, and Brevitricolpites guinetti. The lignite was suggested to be deposited in the vegetated brackish environment of Late Miocene depocenter in Niger Delta, Nigeria.
