The upper Cretaceous Lokoja Formation is the earliest deposited stratigraphic unit in the intracratonic Bida Basin, Nigeria. It consists predominantly of sandstone and offers a potential hydrocarbon reservoir in the basin. In this study, we investigated the bulk elemental (major, trace and rare earth elements) and mineralogical compositions of the sandstones for the determination of their compositional maturity, tectonic setting, source and weathering history. The sandstone geochemical data indicates that the samples contain moderate amount of SiO 2 and Al 2 O 3 with average values of 78.3 % and 9.75 % respectively. Relatively high average values of K 2 O (1.59 %) and Na 2 O (1.52 %) and low Fe 2 O 3 (2.56 %), MnO (0.05 %), TiO 2 (0.31 %) and P 2 O 5 (0.018 %) were obtained. Plots of relevant geochemical elements reveal that the sandstones are predominantly arkose and litharenite types with minor sub-litharenites. Application of some trace element geochemical proxies; La/Co (11.78), Th/Co (1.32), La/ Th (7.04) and Eu/Eu* (0.82) to constrain the source history suggest protolith dominated by felsic rock. Relatively low average values of ΣREEs (12.81) and ΣHREEs (1.52) support the felsic provenance of the sandstones and the tectonic setting discriminant function plots indicate passive margin depositional basin. Paleo-weathering plot reveals a moderate humid climatic condition and the mean values of CIA (79.21), CIW (90.51), PIA (66.55) and A-CN-K diagram indicates low to moderate chemical weathering in the source area and compositional immaturity for the sediments. This study concludes that the sandstones of the Lokoja Formation are immature and were derived from the faulted blocks of granitic basement rocks at the margin of the basin and deposited proximally.
The need for construction materials in the rapidly developing areas around Federal Capital Territory, Abuja, Nigeria cannot be overemphasized and this study was undertaken in line with this need. The study area, located about 60km from Abuja, is underlain predominantly by shales and claystones of the Patti Formation. These argillaceous rocks may offer locally sourced construction material if they meet certain specifications, however to date, there has not been a geotechnical study of these rocks. The geotechnical properties and the mineralogy of the shale and claystone were investigated to evaluate their suitability for civil engineering works. Particle size distribution, Atterberg limits and X-ray diffraction analyses were performed on fifteen shale and claystone samples collected from three localities (along an approximately 25km transect) for determination of their geotechnical properties and mineralogical composition. Mineralogical data obtained show the samples are dominated by kaolinite with minor amount of montmorillonite. Quartz and minor amounts of microcline, rutile and anatase dominate the non-clay mineral fraction. Particle size data indicate high proportion of fines and they are well graded. The Atterberg limits indicate that the samples have average values of liquid limit of 51%, plastic limit of 23%, plasticity index of 29% and shrinkage limit of 13%. These indicate they are of medium compressibility, low to medium shrink/swell potential, marginal expansive rating and low permeability. High bulk specific gravity (average of 2.61) suggests the samples are inorganic and this is supported by the consistency limits values. Generally, the results indicate the shale and claystone can be useful as stabilizing materials in civil engineering works. In addition, the marginally expansive nature of the shale and claystone, low permeability and intermediate to high plasticity may make them suitable as road subgrade.Keywords— activity, Bida Basin, Gerinya, Kaolinite, plasticity, Patti Formation
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