Abstract
The classification of the sediments into facies and the various environments in which the sediments of the northeastern Voltaian basin were deposited has not been clearly described. Using detailed field mapping together with petrographic studies, six sedimentary facies has been identified; F1 is defined by asymmetric wave formed ripple marks, F2 indicates flute casts on micaceous sandy shales, F3 has bifurcated ripple and climbing ripple marks on argillaceous materials at the middle parts of the scarp, F4 is identified by parallel and cross stratifications observed close to the upper parts of the scarp, F5 has a bipolar herringbone cross beds and planar cross beds on quartz rich sediments at the southern parts of the study area and a distinctive well developed burrows (Skolithos) at the southern half of the study area defines facies F6. The sediments are deposited largely in a shallow marine environment, with subordinate fluvial, flood plain, deltaic, aeolian, tidal flats and shoreface/nearshore environments. Although, there exist a suitable depositional environment for the formation of hydrocarbons, the overlying sediments are not thick enough to give the required temperature and pressure conditions for hydrocarbons development in the northeastern fringes of the basin. Paleosol features evident by pseudokarren, like weathering marking the contact between the middle Oti/Pendjari group and the lower Gambaga group of the study area. The sequence of the area is that of a typical shallowing, thickening and coarsening upward sequence. Key words: Clastic sediments, environments, facies sequence, Gambaga-Nakpanduri, massifs.
Highlights
The northeastern Voltaian basin, of the GambagaNakpanduri areas overlies the basement rocks in the northeastern parts of the basin
Sedimentary facies are the products of the environments in which they are found and depositional environment of sediments is usually characterized by certain sedimentary structure(s) which defines the type of sedimentary facies
Different energy levels of the depositional media could reflect variable sedimentary facies as the sedimentary structures will be different with a possible similar composition of the sediments, the grouping of the sediments into facies is principally based on the observed sedimentary structures, which reflects the depositional environments, conditions and processes, the composition and the texture of the sediments (Tucker, 2004; Kavoosi et al, 2009)
Summary
The northeastern Voltaian basin, of the GambagaNakpanduri areas overlies the basement rocks in the northeastern parts of the basin. The Gambaga-Nakpanduri area of the northeastern Volta basin of Ghana is the lateral equivalence of the southeastern Kwahu group. This makes it understandable if we refer to the northeastern areas of the basin as Bombouaka/Gambaga group. In this study of the GambagaNakpanduri areas of the northeastern fringe of the Voltaian, for the first time, the author seeks to analyze the facies and the depositional processes and environment of the sediments, as this will help reveal how suitable the prevailing depositional environments are to hosting source and/reservoir rocks of the oil shows in the basin and to developed a facies sequence for the area
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