Abstract
This study was carried out with a view of using an innovative approach (strictly geochemical) in determining the origin of Sandstone Formation within the Southern Bida Basin. The Lokoja Formation (Sandstone) unconformably overlies the basement complex. It consist of sandstones, which crop out around Lokoja area between Felele and Koton-Karfi. Field observations show that lithology includes conglomerates at the base, with coarse-grained to fine-grained sandstones, siltstones and claystones overlying it. Analysis of the collected ten (10) outcrop samples from the study area aided in the deduction of geochemistry, classification and period of deposition of the sandstone facies of the Lokoja Formation. The geochemical analysis revealed the major oxides and the heavy minerals that are present in the samples. From the geochemical analysis of the samples at different locations revealing the major oxides, the percentage of SiO2 in the selected sample compared to the other oxides is very high.Al2O3, Fe2O3, CaO, MgO, MnO, P2O5, K2O, Na2O and SO3were all found to decrease as SiO2 increases. A major reason for this is clastic mixing. The low values observed from the result of ratio of SiO2/ Al2O3 indicate that the collected samples have a high degree of clayness, which can suggest mineralogical immaturity. Al2O3/ (CaO+MgO+Na2O+K2O) ratio has been reported useful in the determination of stability of mobile oxides. This was applied in this work, where positive values obtained (2.73 to 8.27)indicate the presence of stable mobile oxides in the Lokoja Formation sandstone facies.The Zircon Tourmaline Rutile (ZTR) Index for the selected samples range from 30% to 44% with an average of 38%. All the selected samples have Zircon –Tourmaline –Rutile maturity index less than 75% suggesting that nearly all the sediments are mineralogically immature to sub mature. The heavy minerals recovered from the selected samples of the Lokoja sandstone show that the origin of the collected samples from the basin is mainly sedimentary.KEYWORDS: Provenance, Bida Basin, Geochemical, Maturity, Stability, Clayness.
Highlights
The Mid-Niger Basin otherwise known as the Bida basin or the Nupe basin is classified as an intracratonic basin which trends in a NorthwestSoutheast direction (Figure 1)
The Fe2O3/K2O ratio ranges from 0.33 to 3.93 having an average of 1.86; samples with low SiO2/ Al2O3ratio and a higher Fe2O3/K2Oratio should be mineralogically less stable.Al2O3/ (CaO+magnesium oxide (MgO)+Na2O+K2O) ratio can be used in determining the stability of mobile oxides as proposed by Gill and Yamane (1996)
Sandstone facies of the Lokoja Formation has been categorized using a set of approved guidelines
Summary
The Mid-Niger Basin otherwise known as the Bida basin or the Nupe basin is classified as an intracratonic basin which trends in a NorthwestSoutheast direction (Figure 1). Adeleye and Dessauvagie (1972) documented fourmappable stratigraphic units in the central parts of the Bida basin (Around Bida town) This includes; the Bida Sandstone, the Sakpe Ironstone, the Enagi Siltstone and the Batati Formation. Rock exposures of the Patti Formation occur between Koton-Karfi and Abaji This Formation consists of fine to medium, grey and white sandstone, carbonaceous silts, shale and oolitic ironstones. Herringbone cross stratification occur within the Patti Formation, just around the fine-grained sandstones This is an indication of an abrupt change in the current direction when the sands were deposited in the varying environments. According to Braide (1992b), predominance of argillaceous rocks (as shown in figure 5) in the Patti Formation requires suspension and settling of finer sediments in a low energy environment This Formation is the topmost unit in the southern Bida basin. The oolites range in thickness from 23 to 44 ft. and have been deposited in a shallow marine environment
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