Abstract
The study is aimed at determining the source-weathering, paleo-redox and paleoclimatic conditions of soil from Ode Irele area of Ondo State, Nigeria. X-Ray Fluorescence (XRF) and the Laser Ablation Inductively Coupled Plasma-Mass Spectrometry ICP-MS) analyses wereusd to determine the major, trace and rare earth element compositios used for the study. The Chemical index of alteration (CIA), Chemical index of weathering (CIW), Plagioclase index of alteration (PIA), Mineralogical index of alteration (MIA), Th/U nd a plot of CIA against Al2O3 as well as the A-CN-K Ternary diagram suggest a high degree of weathering of the source rocks. The positive correlation between Al2O3 with TiO2, K2O, Fe2O3 and MgO implies that they occur in clay minerals formed from weathering. The average K2O/Al2O3 ratios of the investigated samples is ≈0.006, which suggests prevalence of clay minerals relative to other minerals. Low U/Th ratio ranging between 0.14 and 0.50 (average 0.18) relative to PAAS (0.21) and UCC (0.26) suggests deposition under oxic conditions. V/Vi + Ni ratios indicate suboxic to anoxic environment of deposition. However, plots of V/V+ Ni vs Ni/Co and V/Cr vs Ni/Co indicate oxic, dysoxic and suboxic to anoxic environments all suggesting deposition under oxic and suboxic conditions. The Ode Irele sediments was deposited in low saline water with a strong continental rather than marine influence in an arid and semi-arid climatic condition; the low average ratio of P2O5/Al2O3 (0.014) is in unison with freshwater environments.
Highlights
The use of major, trace and rare earth elements of siliciclastic sedimentary rocks is an important tool as they are sensitive indicators of source rocks [1], weathering erosion dynamics [2], tectonic settingpaleoweatherng conditions, paleo climate and post depositional changes [3][11]
The present study aims at identifying the weathering characteristics, paleo-redox and paleoclimati conditions of the soil from Ode Irele through the use of major, trace and rare earth elements
Al2O3 correlates positively with K2O, suggesting that potassium is an important trace constituent of clay mineral. These correlations suggest that potassiumbearing minerals exert substantial control over the Al2O3 distribution, which infers that the contents of the clay minerals primarily control the contents of these elements [30]
Summary
The use of major, trace and rare earth elements of siliciclastic sedimentary rocks is an important tool as they are sensitive indicators of source rocks [1], weathering erosion dynamics [2], tectonic settingpaleoweatherng conditions, paleo climate and post depositional changes [3][11]. Rare earth elements Hf and Zr have been used to reflect the characteristics of their parent rocks. Authors such as [12]-[17] have used other geochemical parameters to infer the paleo-redox conditions of ancient sediments. Obasi is an Associate Professor in the Department of Geology of the Ekiti State University, Ado Ekiti, Nigeria. His research interests are in the areas of geochemistry, mining and economic geology. Madukwe is a Senior Lecturer in the Department of Geology, Ekiti State University, Ado Ekiti Nigeria. His research area covers soft rock geology and geochemistry T. Olaosun is a post graduate masters' student in the Department of Geology of the Ekiti State University, Ado Ekiti, Nigeria
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