Research
Petrological and Geochemical Characteristics of Pyroclastics Outcropping in Abakaliki Area Lower Benue Trough, Nigeria
Bakaliki pyroclastics are part of the volcanoclastics of the Lower Benue Trough Nigeria. The petrological and geochemical study of the pyroclastics was carried out; to evaluate and re-appraise their petrology, stratigraphic position and origin which have remained subjects of controversy in the Benue Trough Geology. The pyroclastics outcrop as enlongate and domical bodies that are large and massive. Field relationships indicate that the volcanoclastics occur within the Abakaliki Shale of the Asu River Group and in some places they interbed with the shales. They occur mostly as agglomerates and welded tuffs cut by several quartz filled veins and segregations. The agglomerates are porphyritic with angular fragments of shales embedded in them. The tuffs are very fine grained and aphanitic in texture. Petrographic data obtained from this study show plagioclase and augite as the major mineral constituents with quartz, olivine, calcite and iron oxide as the accessories. Devitrified glass shards are common in the rocks. They are of basaltic composition. Geochemical analysis shows that the pyroclastics are subakaline, tholeiitic rocks of thin continental crust origin. They are classified as basalts, basaltic andesites, dacites and rhyolites
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.
