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.