Biostratigraphic and Depositional Implications of the Palynomorphs Recovered from OI-1 Borehole, Eastern Benin Basin

Abstract

Palynostratigraphy and depositional conditions of Paleogene sediments from the eastern Benin Basin were investigated from ditch cutting samples obtained from the OI-1 borehole. The study aimed at delineating the palynological zones penetrated by the borehole and reconstruct the depositional history of the sediments. Sample were subjected to standard palynological sample processing techniques involving crushing, maceration / digestion, decarbonisation, sieving and mounting of palynomorphs on glass slides. The samples yielded fairly abundant palynomorphs (dinocysts and sporomorphs). Dinocyst assemblages comprises dominantly of gonyaulacoid taxa such as Spiniferitespseudofurcatus, Spiniferitesramosus, Paleocystodiniumaustralium, Paleocystodinium sp., Operculodiniumcentrocarpum, Homotryblium spp. Lingulodinium sp., and Polysphaeridiumzoharyi while the peridinioid groups which occur in lesser proportions are represented by Lejeunecystahyalina, Selenopemphix sp., Senegalium sp., Apectodinium sp., and Subtilisphaera sp. The sporomorph (pollens and spores) assemblages comprises of pollens which include Pachydermitesdeiderixi, Striamonocolpitesrectostriatus, Proxapertitescurcus, Proxapertitesoperculites, Monoporitesannulatus, Longapertitesvaneendenburgi, Longapertitesmarginatus, Psilatricolporitescrassus, Retibrevitrocolporites triangularis, Preadapolissp. andBombacaciditesannae. Spores recovered within the section include Cyathiditesminor, Verrucatosporites sp., Laevigatosporites sp. and Polypodiaceoissporites sp. The freshwater alga, Botryococcusbraunii occur in rare counts within the uppermost part of the section. The fairly rich palynomorph assemblage allow for the delineation of the borehole section into two informal palynozones designated palynozones A and B. The zones correlate to established palynozones of Paleogene – Neogene Niger Delta and Pan-tropical zones of Africa and dated Paleocene - Eocene. The dominance of the gonyaulacoid dinoflagellate cysts within interval 90 – 308 m of the borehole section suggest the prevalence of distal shelf depositional conditions. The increased pollen percentage and rare to total absence of dinocysts within the upper, approximately 60 m portion of the borehole section is indicative of shoaling of the basin, increased terrigenous input and deposition in near shore setting. The occurrence of Botryococcusbraunii at 12 m and 51 m suggest freshwater, fluvial input due to progressive shoaling of the basin.

Publication Info:

Author: Adebambo, B.A. , Oyelami, A.B. , Ojenabor, F. and Oyeyemi, I

Volume: 60

Issue: September

Published By: Journal of Mining and Geology Vol. 60(2) 2024. pp. 229 - 239 © Nigerian Mining and Geosciences Society (NMGS), 2024-09-01