Browsing by Author "Gwavava, Oswald"

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    Geochemistry of the mudrocks and sandstones from the Bredasdorp Basin, offshore South Africa: Implications for tectonic provenance and paleoweathering
    (De Gruyter, 2021-10-12) Baiyegunhi, Temitope Love ; Liu, Kuiwu ; Gwavava, Oswald ; Baiyegunhi, Christopher ; Rapholo, Maropene
    An inorganic geochemical investigation of mudrocks and sandstone from the southern Bredasdorp Basin, off the south coast of South Africa was carried out to unravel the provenance, paleoweathering, and tectonic setting of the basin. Seventy-seven representative samples from exploration wells E-AH1, E-AJ1, E-BA1, E-BB1, and E-D3 underwent geochemical analysis involving major and trace elements. The major oxide compositions show that the sandstones could be classified as sub-arkose and sublithic arenite. The provenance discrimination diagrams based on major oxide geochemistry revealed that the sandstones are mainly of quartzose sedimentary provenance, while the mudrocks are of quartzose sedimentary and intermediate igneous provenances. The discrimination diagrams indicate that the Bredasdorp sediments were mostly derived from a cratonic interior or recycled orogen. The bivariate plots of TiO2 versus Ni, TiO2 against Zr, and La/Th versus Hf as well as the ternary diagrams of V–Ni–Th∗10 suggest that the mudrocks and sandstones were derived from felsic igneous rocks. The tectonic setting discrimination diagrams support passive-active continental margin setting of the provenance. Also, the closely similar compositions of the analysed samples and recent sedimentary rocks of the East African Rift System perhaps suggest a rifted basin tectonic setting for the Bredasdorp Basin. Chemical index of alteration (CIA) indices observed in the sandstones suggest that their source area underwent low to moderate degree of chemical weathering. However, the mudrocks have high CIA indices suggesting that the source area underwent more intense chemical weathering, possibly due to climatic and/or tectonic variations.
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    Groundwater Potential Zones Assessment Using Geospatial Models in Semi-Arid Areas of South Africa
    (MDPI, 2023-10-06) Adesola, Gbenga Olamide; Thamaga, Kgabo Humphrey; Gwavava, Oswald; Pharoe, Benedict Kinshasa; Frappart, F.
    Water resources are under tremendous pressure as a result of the growing demand for water to meet human needs. Hence, it is necessary to delineate groundwater potential zones (GWPZs) to sustainably develop and manage groundwater resources. In this study, the geospatial-based analytical hierarchy process (AHP) and frequency ratio (FR) techniques were used to identify the GWPZs. Seven factors (geology, rainfall, slope, lineament density, soil, drainage density, and land use/land cover), which partially or entirely influence the groundwater potentiality of an area, were accessed separately and later combined to create GWPZ maps. Weights and ranks were assigned to the factors to perform the AHP model using existing knowledge. The FR was performed by calculating the percentage ratio between the dependent variable (boreholes) and the independent variable (factors). The preparation of the contributing factors and the creation of the resulting models was done using ArcGIS 10.8. The final GWPZ maps were classified into five zones: very low, low, moderate, high, and very high. About 80 boreholes in the study area were randomly subset into training and testing datasets; 58% were used for model training, and the remaining 42% were used for validation purposes. The receiver operating characteristic (ROC) curves for the GWPZs models were generated, and the areas under the curves (AUC) were calculated. Validation of the models shows that the FR model is more efficient (85.3% accuracy) than the AHP model (83.2% accuracy). The findings show that the AHP and FR models are reliable and can be adopted to characterize GWPZs in arid or semi-arid environments.
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    Hydrological Evaluation of the Groundwater Potential in the Fractured Karoo Aquifer Using Magnetic and Electrical Resistivity Methods: Case Study of the Balfour Formation, Alice, South Africa
    (Wiley, 2023-09-06) Adesola, Gbenga Olamide; Gwavava, Oswald; Liu, Kuiwu; Szalai, S.
    The study is aimed at evaluating the groundwater accumulations present in Alice using magnetic and electrical resistivity measurements to examine the trends of structural elements and characterize the groundwater resource for borehole drilling. The magnetic maps show a low magnetic linear structure moving northwest to southeast direction, which may be caused by fractures. The linear high intensities were probably caused by dolerite dykes, while dolerite sills caused broader high-intensity areas. The depth slices show that the near-surface magnetic structures are visible to a depth of about 19 m, and the deep-seated structures are found at a depth of about 31 m, possibly deeper. Twenty-five vertical electrical soundings (VES) of the Schlumberger array were measured with AB/2 varying between 1.5 m and 250 m across the study area. The VES interpretation showed four geoelectric layers composed of HK and HA curve types. The geoelectric layer’s thicknesses are (1) topsoil from 0.4 to 1.8 m, (2) weathered layer from 0.8 to 17.5 m, and (3) weathered/fractured layer from 9.9 to 143.9 m; the third layer could be the productive water-bearing zones, and (4) bedrock layer has an infinite thickness. The layers have resistivity values of 20-5752 Ωm, 3-51 Ωm, 136-352 Ωm, and 44-60428 Ωm, respectively. A correlation of the VES with the borehole log indicated a well-matched result. The magnetic and electrical resistivity surveys provided a detailed subsurface structure and helped identify possible fractures that could act as a passage for groundwater.
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    Petrographic Analysis of the Sandstones and Mudstones in Alice, Eastern Cape Province, South Africa: Implications for Groundwater Potential
    (MDPI, 2023-07-21) Adesola, Gbenga Olamide; Gwavava, Oswald; Liu, Kuiwu; Martínez, J.
    Aquifers’ storability potential in Alice, comprising rocks of the Beaufort Group in the Karoo Supergroup, is examined based on the mineralogical and diagenetic implications of sandstones and mudstones. This investigation is focused on SEM + EDX analysis, petrographic study, porosity, and density determination. The SEM + EDX and petrographic studies show that the rocks are fractured and porous and contain minerals like quartz, feldspar, lithics, mica, kaolinite, calcite, and illite. The primary diagenetic processes that affect the groundwater storage of the rocks are cementation via authigenic minerals, mineral replacement, the dissolution of minerals, and recrystallization. The existence of fractured and dissolution pores improves the groundwater storage capacity. Ten rock samples were selected for density and porosity measurements. The porosity result shows that mudstone has the highest porosity value of 2.56%, while sandstone has the lowest porosity value of 0.85%. This is due to mudstone having numerous pore spaces compared to sandstone. The density of mudstone ranges from 2.5763 to 2.6978 g/cm3 , while the density of sandstone ranges from 2.5908 to 2.6820 g/cm3. The secondary porosity is the main porosity for the reservoir rocks. The pores and fractures observed in the rocks act as channels for groundwater, which influence the aquifers’ storability in the study area. The techniques used in this research help us to efficiently understand the factors that control aquifers’ storability to assist with groundwater exploration.