Provenance and Tectonic Setting of Amasiri Sandstone (Turonian) in Ugep Area, Southern Benue Trough, Nigeria: Evidences from Petrography and Geochemistry

bstract - The p et rographic and geochemical study of sandstones of Eze - Aku Formation (Turonian) outcropping in Ugep area souther n 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 SiO 2 , TiO 2 , Al 2O 3 and Fe 2O 3 and depleted in K 2 O, Na 2 O, MgO and CaO. Tectonic setting discrimination plot d iagrams 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. Keyw ords : eze- aku fo rmation, petrography, geoche - mistry, sandst