Calcareous nannofossils biostratigraphy of well Uche 1, Offshore Lagos, Eastern Dahomey Basin, South Western Nigeria

Abstract

Well Uche 1 drilled in the offshore of Dahomey Basin was biostratigraphically analyzed, based on its calcareous nannofossils content. Thirty analyzed samples were collected from the Well at an interval range of 20m at a depth of 1284m- 1860m. The microscopic examination of the processed samples was carried out (using simple smear method) and this was found useful in the identification of the different biostratigraphic zones present. Moreover, it is equally found useful in age determination. In all, fifteen (15) calcareous nannofossil species (Braarudosphaera bigelowii, Calcidiscus leptoporus, Coccolithus nitescens, Coccolithus pelagicus, Coronocyclus nitescens, Discoaster deflandrei, Discoaster druggii, Discoaster sp (6rays), Helicosphaera cateri,Pontosphaera multipora, Reticulofenestra haqii (3-5 microns), Reticulofenestra pseudoumbilicus (5-7 microns), Reticulofenestra pseudoumbilicus (>7 µ), Sphenolithus moriformis, Triquetrorhabdulus carinatus) were identified and used for biozonation and identification of significant time surfaces. The distribution of the calcareous nanofossil species in the well enabled the establishment of zones belonging to the Early Miocene; NN2 zone. The most abundant calcareous nannofossils identified are Triquetrorhabdulus carinatus, Cyclicargolithus abisectus and Discoaster druggi. Two biozones of calcareous nannofossils were identified from the well as well as three significant surfaces.