Palaeoecologic and Palaeoclimatic Inferences from Calcareous Nannofossils in Western Lobe Offshore, Niger Delta

Abstract

In support of the ongoing temporal palaeoenvironment and palaeoclimatic reconstructions of the Neogene sediments, this study attempts to detail the paleo-proxies recovered from DEL-1 Well, western offshore Niger Delta. The standard smear slide method enabled the recovery of well-preserved calcareous nannofossils that depict early to mid–Miocene (NN4–NN5) sediments. The up-hole relationships between the nannofossil accumulation rate (NAR), the relative abundance of Discoaster and coccolith size of Reticulofenestra show step by step collapse of sea surface stability from early to middle Miocene. The lower horizons (8000–9460 ft) exhibit a low NAR, relatively high Discoaster abundance and relatively large Reticulofenestra size to suggest a deep thermocline and nutricline that characterise oligotrophic conditions in less warm-water induced climate. Conversely, upper horizons (5225–6550 ft) exhibit a high NAR, relatively low Discoaster abundance and relatively small Reticulofenestra size to suggest a shallow thermocline and nutricline that characterise eutrophic conditions in warm-water induced climate. The relative abundance of Helicosphaera carteri within the mid-NN5 suggests mesotrophic conditions within a stressed environment, with the possible occurrence of carbonate crash events. The combined parameters indicate gradual eutrophication and collapse of sea surface stability favouring nutrients and influx of terrestrial sediments in the ocean water as it progressed from early to middle Miocene. The abundance of the palaeo-proxies assemblages suggests hyposaline waters in a neritic environment that prevailed during the warm climatic condition.