摘要
The geochemical compositions [major, trace and Rare Earth Elements (REE)] of Cretaceous-Tertiary shales from Gbekebo-1 well were used to characterize provenance, paleogeography, source area weathering and tectonic setting of the study area located in the southwestern part of the Dahomey Embayment, Nigeria. Core samples (eight) of shales were obtained and analyzed geochemically using the combined methods of major elements Fusion Inductively Coupled Plasma (FUS-ICP) and trace elements Fusion Inductively Coupled Plasma Emission/Mass Spectrometry (FUS-ICP/MS). An A-CN-K (Al<sub>2</sub>O<sub>3</sub>-CaO + Na<sub>2</sub>O-K<sub>2</sub>O) ternary plot, geochemical discriminant function of major elements and chondrite normalized plots of REE suggest an upper continental crust provenance of felsic to intermediate or mixed igneous rocks of tonalite to granodiorite composition. High values of chemical index of alteration (CIA, 82.22 - 96.39) and chemical index of weathering (CIW, 88.10 - 99.17) indicated a palaeogeographic condition marked by wet tropical climate where intense chemical weathering and erosion prevailed. The Cretaceous-Tertiary shales from Gbekebo-1 well are inferred to have been deposited in passive margin setting based on various geochemical tectonic setting discrimination diagrams.
The geochemical compositions [major, trace and Rare Earth Elements (REE)] of Cretaceous-Tertiary shales from Gbekebo-1 well were used to characterize provenance, paleogeography, source area weathering and tectonic setting of the study area located in the southwestern part of the Dahomey Embayment, Nigeria. Core samples (eight) of shales were obtained and analyzed geochemically using the combined methods of major elements Fusion Inductively Coupled Plasma (FUS-ICP) and trace elements Fusion Inductively Coupled Plasma Emission/Mass Spectrometry (FUS-ICP/MS). An A-CN-K (Al<sub>2</sub>O<sub>3</sub>-CaO + Na<sub>2</sub>O-K<sub>2</sub>O) ternary plot, geochemical discriminant function of major elements and chondrite normalized plots of REE suggest an upper continental crust provenance of felsic to intermediate or mixed igneous rocks of tonalite to granodiorite composition. High values of chemical index of alteration (CIA, 82.22 - 96.39) and chemical index of weathering (CIW, 88.10 - 99.17) indicated a palaeogeographic condition marked by wet tropical climate where intense chemical weathering and erosion prevailed. The Cretaceous-Tertiary shales from Gbekebo-1 well are inferred to have been deposited in passive margin setting based on various geochemical tectonic setting discrimination diagrams.
作者
O. Innocent Ejeh
O. Innocent Ejeh(Department of Geology, Delta State University, Abraka, Nigeria)
