Geochemistry and Petrographic Analysis of Sandstone Facies of Eze-Aku Formation in Amasiri Area, Lower Benue through Nigeria: Implications for Provenance and Tectonic Setting.

Abstract

This study was undertaken to determine the provenance and tectonic setting for the sandstones of Eze-Aku Formation in Amasiri area through evaluation and re-appraisal of the petrography and geochemistry of sandstones. Local stratigraphy and field relationship show that the lithologic succession consists of thick sequence of shale alternating with sandstone ridges trending NE-SW direction. Two units were delineated namely: Unit I which is composed of calcareous/ siliceous sandstone and dark grey shale, and Unit II which consists of friable and slightly consolidated pebbly sandstone belonging to Turonian sediments. Analysis and interpretation of the sedimentary structures, mostly cross-beds and structures of quartz grains indicates that the sandstones were derived primarily from granitic Basement complex rocks from the Oban Massif in a humid paleoclimate. Petrographic analysis show that the sandstones essentially contain quartz, feldspar and few rock fragment and are classified as subarkosic sandstone using calculated framework grains. The application of Q-F-RF diagram, suggest plutonic igneous and metamorphic rocks, from the Craton interior, recycled Orogen and transitional continental field as the provenance for the sandstones. The geochemistry of the major element oxides (SiO₂, Fe₂O₃, Na₂O, Al₂O₃, K₂O, MgO, MnO, TiO₂ and SO₃) suggests the Active Continental Margin as the tectonic setting of the area.

Keywords: Amasiri area, Benue Trough, sandstones, geochemistry, petrography