Sedimentary and petrofacies analyses of the Amasiri Sandstone, southern Benue Trough, Nigeria: Implications for depositional environment and tectonic provenance

• Lithofacies and petrofacies gave clues on depositional and tectonic settings.
• The sandstones are essentially feldspathic and arkosic arenites.
• Provenance area is the uplifted continental block related to a rifted Benue Trough.
• Amasiri Sandstone is a product of storm (mass flow) and tidal shelf processes.
• Paleoclimatic evaluation indicates semi-arid to semi-humid climatic regimes.

This study was undertaken to determine the depositional environment, provenance and tectonic setting for the Turonian Amasiri Sandstone, southern Benue Trough, Nigeria, using lithofacies analysis and re-appraisal of petrography of the sandstones. Local stratigraphy and field relationships show a thick succession of shales alternating with elongate/parallel sandstone ridges extending eastwards from Akpoha to Amasiri through Itigidi and Ugep to Apiapum areas. Lithofacies analysis reveals 9 lithofacies suggestive of storm (mass flow) and tidal shelf processes. These include dark grey to black laminated shale/silty mudstones, bioturbated mudstones, coquinoid limestones, very fine-grained bioturbated sandstones with shell hash/debris in places and limestone rip-up clasts, massive and chaotic sandy conglomerate with rip – up clasts, fine to medium-grained, parallel laminated sandstone, hummocky cross-stratified, massive, medium to coarse-grained sandstones, medium to very coarse-grained, planar cross-bedded sandstone, with clay-draped foresets and Ophiomorpha burrows, and coarse-grained trough cross-bedded sandstone. Petrofacies analysis identifies the sandstones as feldspathic and arkosic arenites. Ternary plot of framework mineralogy indicates derivation from an uplifted continental block related to the nearby Oban Massif and Cameroon Basement Complex.