Source Area Weathering, Paleo-Environment and Paleo-Climatic Conditions of Soils from Bitumen Rich Ode Irele Area of Ondo State, Nigeria

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.