Foraminiferal patterns and palaeoenvironmental inferences from DEL-1 well, offshore Niger Delta

Abstract

The Miocene Epoch (23.3–5.3 Ma) represents a remarkable time in the Earth's geological history with significant palaeoclimatic and palaeoenvironmental relevance. In this study, microfossils recovered from the DEL-1 (4600–9460 ft) well in the western Detachment Fold Zone, offshore Niger Delta in the Gulf of Guinea were used to construe the age, palaeoenvironment, and palaeoecology of the penetrated successions. Standard foraminiferal analyses were carried out on one hundred and forty-eight (148) ditch cuttings retrieved from the studied interval following standard laboratory and identification procedures. Globigerinatella spp./Catapsydrax dissimilis Concurrent-range Zone (M3/N6), Fohsella birnageae Lowest Occurrence Subzone (M4b/N7), and Orbulina suturalis Lowest Occurrence Zone (M6/N9) of early to middle Miocene were identified. An overall progradational coastal and shelfal facies dominated by argillaceous and arenaceous sediment in the early and middle Miocene is construed, whereas interpreted palaeoenvironment of deposition indicates fluctuation between coastal deltaic, inner, middle, and outer neritic system with some fluvio-marine incursions between 4600 and 9460 ft intervals. The identified early Miocene succession is characterised by significantly high ecological parameters (diversity, evenness, richness), low salinity, and relatively high occurrence of foraminifera faunas compared to the middle Miocene. The relationships between the foraminiferal faunas and environmental factors suggest the local ecologic niche exhibits environmental heterogeneity that might have influenced even distribution of different microhabitat faunal preferences. Whereas the contributing influence of arenaceous sediment on the general dearth of microfossils in the upper section of the well cannot be neglected, the foraminiferal signatures reflect the ubiquitous middle Miocene carbonate crash event, and thus confirm its occurrence in the Gulf of Guinea.