Geochemical Discriminant for Provenance Characterization and Palaeogeography of Shales from Dahomey Embayment, Southwestern Nigeria

摘要

Thegeochemical compositions [major, trace and Rare Earth Elements (REE)] ofCretaceous-Tertiary shales fromGbekebo-1 well were used to characterize provenance, paleogeography, sourcearea weathering and tectonic setting of the study area located in thesouthwestern part of the Dahomey Embayment, Nigeria. Core samples (eight) ofshales were obtained and analyzed geochemically using the combined methods ofmajor elements Fusion Inductively Coupled Plasma (FUS-ICP) and trace elementsFusion Inductively Coupled Plasma Emission/Mass Spectrometry (FUS-ICP/MS). AnA-CN-K (Al2O3-CaO + Na2O-K2O)ternary plot, geochemical discriminant function of major elements and chondritenormalized plots of REE suggest an upper continental crust provenance of felsicto intermediate or mixed igneous rocks of tonalite to granodiorite composition.High values of chemical index of alteration (CIA, 82.22 - 96.39) and chemicalindex of weathering (CIW, 88.10 - 99.17) indicated a palaeogeographic conditionmarked by wet tropical climate where intense chemical weathering and erosionprevailed. The Cretaceous-Tertiary shales from Gbekebo-1 well are inferred tohave been deposited in passive margin setting based on various geochemicaltectonic setting discrimination diagrams.