Geochemistry of the Ogwashi-Asaba Formation, Anambra Basin, Nigeria: Implications for Provenance, Tectonic Setting, Source Area Weathering, Classification and Maturity

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Author(s) Madukwe, H.Y. | Bassey, C.E.
Pages 312-327
Volume 4
Issue 7
Date July, 2015
Keywords Ogwashi-Asaba, Sandstone, Weathering, Mafic, Provenance, Tectonic, Paleoclimate
Abstract

Geochemical analysis was carried out on the sandstone facies of the Ogwashi-Asaba Formation in the Anambra Basin, to infer their classification, maturity, paleoclimate, provenance, tectonic setting and source-area weathering. The sandstones are continental sands that can be classified as non-calcareous lithic arenites that contains both sodic and ferromagnesian potassic sandstones. They are chemically immature and formed under semi-humid/humid conditions. The sandstones are mineralogically less stable and more prone to reactivity during supercritical CO2 exposure. The weathering indices: CIA, CIW, PIA and MIA values and the A–CN–K diagram indicates moderate weathering of the source material, it also shows that the sediments may have come from more than one source. QFL provenance diagram plotted mainly in the recycled orogen field, these recycled sands may be sourced from associated platform or passive margin basins. Provenance discrimination diagram shows that The Ogwashi-Asaba sandstones plotted in the mafic igneous provenance field suggesting a mafic Precambrian Basement Complex source plus inputs from recycled older sediments from the Anambra basin and Mid Niger basin. Tectonic discrimination diagrams reveals that the Ogwashi-Asaba Formation is of the passive margin setting. For the sandstone facies of the Ogwashi-Asaba Formation, all the major elements were depleted except Fe. The depletion of the mobile elements may be due to leaching during the formation of clay minerals during chemical weathering. The immobile Fe element was highly enriched, suggesting that it may be from a source rich in Fe minerals or the ferruginisation of the sediment, while the depletion of the immobile Si may be due to fractionation.

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