Geochemical Characterization of Campanian – Maastrichtian Shale's from Akukwa andAmansio

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Geochemical Characterization of Campanian – Maastrichtian Shale's from Akukwa andAmansio

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Abstract

The Campanian-Maastrichtian (CM) shales from Akukwa and Amansiodo exploratory wells in the Anambra Basin, southeastern Nigeria were subjected to X-ray Fluorescence (XRF) and Inductively coupled plasma mass spectrometry (ICPMS) analysis. This is to determine the chemical composition of the shales and the reconstruction of the weathering, provenance and depositional environments under which the shales were formed. The % of SiO2, Al2O3, Fe2O3 andCaO of the shales inAkukwa andAmansiodo wells contain average values of 35.2%, 11.1%, 8.21% and 1.82% and 63.8%, 15.9%, 4.74% and 0.51% respectively. The 78 - 99% CIA and 97 – 99% PIA values of the CM shales in the two wells are very high and suggest extreme chemical weathering. K2O/Na2O versus PIA, (K2O+Na2O) versus PIA, Na2O% versus PIA, CaO% versus PIA and K2O% versus PIA plots, which show a substantial decrease in the quantity of Na2O, CaO and K2O and the high PIA values further confirms the intense chemical weathering. The plots of TiO2 versus Al2O3 and TiO2 versus Ni indicate that the shales are the product of intermediate to felsic rocks while the low Cr/Ni ratios (1.16–5.16 and 1.28–2.77) indicate a felsic origin. The bivariate discriminant function of the shales indicates a passive paleotectonic setting under humid and partly semiarid conditions as suggested by the binary plot of SiO2 wt.% versus (Al2O3 + K2O+Na2O)%. The Ni/Co ratio of 1.70 and the Cu/Zn ratio of 0.48 of the shales suggest deposition in an oxic conditions. This is further supported by the V/Cr and U/Th ratios below 1.20 indicating an oxic depositional environment. The V and Ni cross plots indicate that most of the investigated Akukwa andAmansiodo samples have input from marine or marine-terrestrial sources under oxic conditions.


Publication Info:

Author: Haruna, K.A.1*and Ojo, O.J.2

Volume: 59

Issue: September

Published By: Journal of Mining and Geology Vol. 59(2) 2023. pp. 181 - 197, 2023-09-01

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