Lithostratigraphy, sedimentation and evolution of the Volta Basin in Ghana

Abstract

We present a revised lithostratigraphy for the Voltaian Supergroup of Ghana, based on a review of existing literature, interpretations of remotely sensed data and reconnaissance field survey of the Volta Basin. These strata thicken eastwards, to a maximum of between 5 and 6 km adjacent to the PanAfrican Dahomeyide orogen. They began to accumulate some time after about 1000 Ma, along the margin of an epicontinental sea. Initial sedimentation, comprising the age-equivalent Kwahu and Bombouaka Groups, shows a cyclical mode of deposition controlled by eustatic changes in sea-level that produced a range of nearshore marine, littoral and terrestrial environments. A major erosional interval was followed by deposition of the 3-4 km thick Oti-Pendjari Group. Basal tillites and associated sandy diamictons are correlated with the Marinoan (end-Cryogenian) glaciation, indicating a maximum depositional age of about 635 Ma. The overlying cap carbonates and tuffs were deposited within a shallow epeiric sea bordered by a volcanically active rift system. The main part of the group records the transition from a rifted passive margin to a fully developed foreland basin receiving marine flysch in the form of argillaceous strata interbedded with highly immature wacke-type sandstones and conglomerates. Maximum accommodation space was developed within a foredeep adjacent to the Dahomeyide belt. Towards the end of the orogenic phase, the foredeep succession became partially inverted and then was buried under coarse terrestrial, red-bed molasse of the Obosum Group

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

“…It consists of three disconformable subdivisions which are well presented in northern Togo as Dapaong, Fosse-aux-Lions and Yemboure groups (Deynoux et al, 2006). The lower Tossiegou formation (Affaton et al, 1980) overlies the basement crystalline rocks in the north (Figure 1) and this formation dips southwards taking it beneath the Poubogou formation (Carney et al, 2010). The formation is characterized by quartzitic sandstones with micaceous sandstone records in some of its exposures with ripple marks features.…”

“…Bombouaka group in Togo is largely accepted as the lateral equivalence of the Kwahu group of Ghana (Affaton et al, 1980), studies in its Togo extension reveals that the 500 m thick sedimentary strata of the Bombouaka group was deposited in fluvial, deltaic and nearshore or foreshore environments (Carney et al, 2010;Affaton et al, 1980). The Gambaga-Nakpanduri area of the northeastern Volta basin of Ghana is the lateral equivalence of the southeastern Kwahu group.…”

Pan-African Paleostresses and Reactivation of the Eburnean Basement Complex in Southeast Ghana (West Africa)

“…The Stable Zone corresponds to the southeastern margin of the Guinea [14] or Leo-Man Shield and its Neoproterozoic cover represented by the Volta Basin [1,5,9]. In southeast Ghana, the Stable Zone is mainly composed of Archean to Paleoproterozoic rocks involved in the Eburnean thermotectonic events and stabilized at the end of this orogeny (2000 ± 200 Ma).…”

“…Outcrops at the Nkurakan site are characterized by massive bands of quartzites or quartzitic sandstones with limited black shale intercalations. These facies belong to the Mpraeso Formation (lower part of Bombouaka or Kwahu Supergroup, [5]). Decimetric bands with SE dips (N50-35SE) are cut by strike-slip faults that are assembled around the ESE-WNW to SE-NW trending (N115 to N140) dextral and ENE-WSW to E-W trending (N75 to N95) sinistral.…”

“…It includes three distinct structural domains [1][2][3][4][5] (1) the southeastern margin of the West african craton (WAC) consisting of Archean to Paleoproterozoic assemblages that underwent the Eburnean Orogeny (2000 ± 200 Ma); (2) the Neoproterozoic Volta Basin represented by its lower and middle megasequences (Bombouaka and Oti Supergroups); (3) the frontal structural units of the Pan-African Dahomeyide Orogenic Belt (600 ± 50 Ma).…”