PALYNOLOGICAL AND LITHIFACIES APPROACH TO PALEO-ENVIRONMENTAL AND SEQUENCE STRATIGRAPHIC INTERPRETATION OF AMEKI FORMATION OUTCROPPING IN UMUNYA- OGBUNIKE AREAS, NORTHERN NIGER DELTA BASIN. NIGERIA

Palynological analysis and lithofacies have been used to interpret the palaeoenvironment and build a sequence stratigraphic model for outcropping rocks of the Ameki Formation in Umunya-Ogbunike area. Analysed samples for palynomorphs yielded fairly good recoveries including few marine indicator dinoflagellates and foraminiferal wall linings. The miospore assemblage of Margocolporites foveolatus, Retibrevitricolporites triangulatus, Striatricolporites bellus, Psilatricolporites crassus, Scabratriporites ibadanensis, Praedapollis africanus and Retimonocolpites asabaensis suggest a Middle Eocene age (P430 Subzone) for the sequence. Lithofacies analysis identified highly cross bedded sandstone interbedded with grey to light grey claystone lithofacies and a dark grey to black shale lithofacies. Dominant sedimentary structures of the cross bedded sandstone lithofacies include prominent sigmoidal clay-draped foreset beds, tidal bundles, reactivation structures, flaser beds, lenticular beds as well as biogenic structures which include ophiomorpha, chondrites and thallasinoides isp burrows. These indicate deposition in variable high and low energy, tidally-influenced depositional setting. Granulometric analysis suggests deposition of the sandstone lithofacies in agitated shallow marine setting. The marine indicator palynomorphs (dynocysts and acritards) together with the lithofacies therefore suggest deposition of the Ameki succession in low energy offshore to high energy shoreface (subtidal sandwaves) environments with strong tidal signatures, in coastal deltaic-inner neritic settings. Attempt at sequence stratigraphic modeling identified two 4^th or 3^rd order Type 11 sequences - a lower bounded at the top by an erosional unconformity (candidate sequence boundary) and an upper sequence with a maximum flooding surface (MFS) dated 43.2Ma