An evaluation of a section of the campano-maastrichtian nkporo shale, anambra basin, south-eastern nigeria: Implications for provenance and palaeoenvironment of deposition Ikhane P.R.1,*, Adeagbo O.A.2, Oyebolu O.O.1, Oladipo O.V.1 1Department of Earth Sciences, Faculty of Science, Olabisi Onabanjo University, Ago-Iwoye, Ogun State, Nigeria 2Department of Geology, Faculty of Science, The Polytechnic, Ibadan, Oyo State, Nigeria *E-mail: ikhane.phillips@oouagoiwoye.edu.ng, phillipsikhane@gmail.com
Online published on 22 May, 2019. Abstract Geochemical evaluation of Anambra Basin was carried out using forty Campano-Maastrichtian shale samples from two wells, drilled within the depocenter of the Basin. This was with a view to determining their origin and distribution of the sediments as well as their palaeodepositional environment. The selected samples which represent the first trangressive phase were analyzed using Inductively Coupled Plasma-Atomic Emission Spectrometer (ICPAES) to determine the elemental concentration. Average elemental abundance in the samples from Well-1 showed 60.1%-SiO2, 17.5%-Al2O3, 3.9%-FeOand 6.3%-MgO, while 59.1% SiO2, 17.6% Al2O3, 3.8% Fe2O3 and 6.0%, MgO were recorded in samples from Well-2. Average concentration of other oxides including MnO, CaO, K2O, NaO and TiO2 was less than 2.7% and the trace elements-Ni, Co, Pb, Be, As, V, Fe, Ce and Mo were less than 0.69 μg/g in samples from both wells. This implies an igneous (granitic) provenance for the sediment. Average K2O value (0.92 μg/g) reflects relatively immature sediments. The SiO2 content in the theoretically inferred magmatic source of these shales is found to range narrowly from 68.7 to 73.7 wt.% (average 70.03 wt.%) for Well-1 and 68.9 wt. % to 70.9 wt. % (average of 69.9 wt %) for Well-2. These values of SiO2 suggest that the source rocks of the shales of the present study are felsic igneous rocks. Average SiO2 content (∼70 wt. %) indicates that the inferred source rocks constituents are high in SiO2, bearing end are members of felsic group of igneous rocks. This is also confirmed on the Al2O3-(CaO+Na2O+K2O)-(Fe2O+MgO) ternary diagram. The depositional environments of these samples were further evaluated using the V/(V + Ni) fractions. It has been reported that a high value (i.e. values close 1) indicates reducing conditions. The V/(V + Ni) values in the study area are relatively high with values ranging from ∼0.616 to∼ 0.675 (an average of ∼0.642) in Well-1 and from ∼0.613 to ∼0.669 (an average of ∼0.640) in Well-2. These values indicate that the source rocks were deposited under an reducing environmental condition. Top Keywords Depocenter, Campano-Maastrichtian, Palaeodepositional, Geochemical, Anambra Basin, Environment. Top |