STRATIGRAPHIC INVESTIGATION OF NGOR – 1 WELL BORNU BASIN, NIGERIA

Abstract

One hundred and seventy ditch cutting samples retrieved from Ngor – 1 well, Bornu Basin have been subjected to biostratigraphic study using their foraminifera, nannofossils, palynomorphs content as well as the textural characteristics of the cuttings. The project was design to establish the ages and paleo-environment of the sequences penetrated by a section of the well for better understanding of the geological events in the basin. A simple standard laboratory preparation method was used for the analysis. Silisiclastic sediments (shale and sand) with occasional subordinate calcareous materials characterizes the sedimentary succession penetrated by the well and this enable identification of the following formations in the basin: Chad, Kerri-Kerri, Gombe, Fika, Gongila, Bima, Gongila, Fika, Gombe, Kerri-kerri, Chad. Although four (4) species of planktics were recovered, the section has eight (8) species of arenaceous benthics dominated by environmental diagnostics species such Ammobaculities spp., Ammobaculities bauchensis and Haplophragmoides spp. Based on the continuous occurrence of Heterohelix globulosa, one foraminifera zone was however recognised, namely: G.aesyptiaca – G.elevata zone. The Ngor – 1 well penetrated the Triorites africanensis – Droseridites senonicus/Spinizonocolpites baculatus zones, which are further correlated with Donea Mutabilis – Watzielia articulata zones and allowed the establishment of six local palynozone. A Cenomanian – Eocene age has been assigned to the studied section of Ngor – 1 well based on the palynozones. The entire well section is barren of nannofossils. Inference of the paleodepositional environment of the sequences penetrated by the well was made based on faunal abundance and diversity of foraminifera. This has been integrated with the lithologic description of the wells. The planktic/benthic foraminifera ratio and presence/absence of ostracod and dinoflagellates as well as non-occurrence of nannofossils enabled a subdivision of the sequence penetrated by Ngor – 1 studied into environment that fluctuated from Continental to marginal and open marine. The occurrence of Botryococcus brauni throughout the studied section of the well suggests the availability of source rock, which calls for further geochemical studies in the basin.