Provenance, Tectonic Setting, Source Area Weathering and Paleoenvironment of the Ilaro Formation, Dahomey Basin, Nigeria

Abstract

The provenance, tectonic setting, source area weathering and paleoenvironment of the Ilaro sandstone of the Dahomey basin have been assessed using geochemical studies. The source area analyses suggest that the sediments were derived from felsic, intermediate and mafic sources with contributions from recycled quartz-rich older sediments. The Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), Plagioclase Index of Alteration (PIA), Mineralogical Index of Alteration (MIA), higher Al/K ratio and the A-CN-K ternary plot of the studied samples suggests that the sediments were derived during intense chemical weathering of the source area. The Th/U-Th plot showed a wide trend above the upper crust value; the overall scenario suggests that weathering conditions were high and not constant during sedimentation. Tectonic discrimination diagrams shows the samples plotting mainly in the active continental margin and passive margin zones. The paleoenviromental and paleoclimatic results suggest that the Ilaro sandstone was deposited in mostly oxic humid conditions in a non-marine deltaic environment and the paleosalinity based on low Sr/Ba ratio indicates low saline water during deposition and a continental enviroment of deposition

Keywords: Ilaro Formation, Provenance, tectonic, weathering, paleoenviroment