Sedimentary facies and depositional environments of the neoproterozoic sediments of the Gambaga-Nakpanduri massifs, Voltaian Basin

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.

An overview of the geology of Tanga onshore basin: implication for hydrocarbon potential, Tanzania, East Africa

“…3b), conglomeratic sandstones and rudaceous materials around the Ngole Bridge. The sandstone which was observed at Ngole Bridge was formed in high energy level environment depositional materials (Abu 2018). Late Cretaceous regression of sea leaving behind clastic sediments of sandstones together with shales of continental origin has been collaboratively reported for the EARS by Rop et al (2016).…”

“…5). The Umba river sediment are the initial strata starting with coarse materials, high energy deposits very shorter time, deposited during glacial time (Abu 2018;Abu et al 2020), this interpretation Rop et al (2016) interpretation of a regional glaciation in the East Africa Rift System (EARS). This is also the lower part of the lower Tanga beds, following the sandstones or conglomeratic sandstone towards the mudstone in the river, are the fine layered siltstones which later moved into the middle Karoo beds.…”

“…These chemical sediments consisting of dolomitic marbles and dolomitic limestones formed in a deep marine environment, although carbonate materials could be detrital, this at Tanga basin are without sedimentary structures to support their detrital status (Pettijohn 1975), this can, however, be investigated further. The argillaceous facies immediately follows the carbonates also in a quite water environment and by a low energy water medium (Abu 2018;Abu et al 2020) of oxygen poor environment. The presence of dropstones observed in some exposures supports a glacial depositional environment where regression and transgression action of water (Trompette et al 1998;Klein and Ladeira 2004) would have controlled this group of facies, and this is part of the larger arenaceous facies class.…”

“…These conglomeratic sandstones ( Fig. 5) of the Carboniferous-Permian are the most probable unconformity indicators (Abu 2018) marking the boundary between the underlying dominant carbonates, dolomitic and subordinate sandstone lower unit of the basin (Fig. 5).…”

“…These siltstones are exposed at a road cutting with characteristic parallel and cross-laminations of varying thickness indicating the variable energy of the depositional media. The presence of cross-lamination is supportive of a shallow marine oxygenated environment of deposition (Stow 2005;Abu 2018). This unit is an argillaceous formation/unit with alternating detrital materials of claystone, mud stone and siltstone (Fig.…”