Succession of palynomorphs from the early Eocene of Gbekebo-1 well in S.W. Nigeria

Abstract

Subsurface samples from the Early Eocene section of the Imo Shale, obtained from Gbekebo-1 well, yielded microfloras on which some zonal divisions are based. The microfloras reflect from below upwards the close of a marine transgression. The lowest microfloras (samples 37 to 35) are almost exclusively dominated by different dinoflagellate cyst assemblages each characterising a distinct stage in a transgressive-regressive cycle. The younger microfloras (up to a depth of 681 metres) progressively assume a more terrestrial nature composition of land-derived pollen and spores, some of which reach large grain sizes. Samples 37 to 35 indicate transgressive-regressive cycle whilst sample 34 shows considerable land derived palynomorphs. The Apectodinium dominated intervals (regressive) suggest lagoonal, estuarine or brackish water influence whilst Impletosphaeridium ligospinosum and Monoporites annulatus dominated horizon indicate the final closing stage of the marine transgressive phase and beginning of regressive phase. A large monocopate pollen, Proxapertites tertiaria reported by earlier workers from the Paleocene of Nigeria and Colombia, and typical of the Paleocene Plamae province, has been recovered in the present study. Its presence implies that the prevailing climate was tropical.