High Resolution Biostratigraphic, Sequence Stratigraphic and Paleoenvironmental Analyses of Motun 1 Well, Niger Delta, Nigeria

Abstract

Osazuwa A. Ogbahon and Motunrayo O. Afolabi

High resolution biostratigraphy of Motun -1 well from offshore Niger Delta was undertaken to determine the age and depositional setting of the stratigraphic succession in the well. The study involved integrated foraminiferal, calcareous nannofossil and palynological analysis using standard preparation techniques of wet sieving, smearing and pipette method as well as Hydrofluoric (HF) and Hydrochloric (HCl) acids maceration techniques respectively. This was complimented by the sedimentological description of samples. The samples yielded exclusively benthic foraminiferal fauna with moderate diversity consisting of eleven species belonging to seven genera of calcareous benthic and three (3) species belonging to three genera of arenaceous benthic foraminifera. They include Bolivina, Lenticulina, Quinqueloculina, Cristellaria, Ammobaculites, and Textularia. The recorded calcareous nannofossil consists of nine genera and 27 species, including Helicosphaera ampiaperta, Sphenolitus heteromorphus, Pontosphaera multipora, and Cyclicargolithus floridanus. The palynological data consists of highly diversified assemblages dominated by pollen, comprising 42 species and seven species of spores and subordinate amount of dinocysts (one species). They include Monoporites annulatus, Zonocostites ramonae, Magnastriatites howardi, Belskipolis elegans, Crassoretitriletes vanraadshooveni, and Leiospheridia sp. The well is dated early to middle Miocene (NN4 –NN5) based on the occurrence of marker species Helicosphaera ampliaperta and Sphenolithus heteromophus which corresponds Echitricolporites –Crassoretitriletes vanraashooveni zone (P680-P720). One maximum flooding surface identified on the bases of maximum diversity and abundance of calcareous nannofossil assemblage composition is placed at the 7680 ft depth and dated 16 Ma. The environment of deposition fluctuated between middle neritic and inner neritic to littoral, including coastal deltaic settings based on deductions from sedimentological and foraminiferal data.

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