Provenance and Tectonic Setting of Amasiri Sandstone (Turonian) in Ugep Area, Southern Benue Trough, Nigeria: Evidences from Petrography and Geochemistry
The petrographic and geochemical study of sandstones of Eze-Aku Formation (Turonian) outcropping in Ugep area southern Benue Trough Nigeria was carried out to ascertain the sandstone provenance and tectonic setting. Field studies show that the sandones occur in linear, parallel northeast-southwest trending ridges alternating with shale sequence. The sandstone facies show coarsening upward sequence, slightly bioturbated, cross-stratified, rippled bedded which infer foreshore to shallow marine below wave base. Petrographic studies show the occurrence of quartz, feldspar, rock fragments and muscovite. The calculated framework grains suggest feldsparthic (subarkosic) sandstone. The geochemical analysis of the major elements of the sandstones show that they are enriched in SiO2, TiO2, Al2O3 and Fe2O3 and depleted in K2O, Na2O, MgO and CaO. Tectonic setting discrimination plot diagrams based on major elements suggest the provenance for the sandstones to be of metamorphic and igneous rocks of Passive Continental Margin Basin. The results of petrographic and geochemical study suggest Oban Massif and Cameroon Basement as the source regions for the sandstone which are characterized by humid climate and low-relief during the Turonian.
