Sedimentary deposits are important aquifers in many parts of the world and in order to explore, develop and manage these aquifers, it is necessary to determine the relationship between the hydrogeologic properties and sedimentary facies (aquifer characterization). Within a sedimentary hydrogeologic system, the environment of deposition and the resulting distribution of grain sizes, texture, and facies associations within different individual aquifer bodies influence variations in hydraulic properties. Successful prediction of the quality of the aquifer is dependent on the accurate mapping of both lithologic units and hydrogeologic parameters. In this project, the influence of petrophysical characteristics of the sedimentary rocks to the quality of the aquifer is investigated with a view to finding a correlation between these characteristics, the type and nature of sedimentary rocks present and their hydrogeologic properties. Investigation methods involved the use of geophysical wireline log data, lithological core logging, thin section microscopy and X-Ray Diffraction analysis. All this was done to characterize the sedimentary rocks in terms of composition, grain size and diagenesis. Porosity tests were also performed on the samples collected while permeability data was collected from the Department of Natural Resources and Mines (DNR & M), Australia. The basins of interest for this project are the Bowen Basin in Australia and the Kalahari Basin in Botswana. The two basins are similar, though structurally different. The basins are similar in the sense that they have got similarity in their rock sequence. All the work done on the Bowen Basin and the results obtained are extrapolated to the similar Kalahari Basin. The units of the Bowen Basin are underlain by the Late Carboniferous to Early Permian Camboon Volcanics. The Permian units include the Buffel, Barfield, Flat Top, and Gyranda Formations and the Baralaba Coal Measures. The Triassic units are the Rewan Group, Clematis Sandstone and Moolayember Formation. Within the Bowen Basin the Permian units are generally argillaceous and therefore have generally low porosities and permeabilities and also give low resistivity (RES) base lines and high gamma ray (GR) baselines. However where fractured, the units yield some water from the shale. Boreholes drawing water from the Barfield, Flat Top and Gyranda Formations tap the fractured shales. The Triassic aquifers present a different picture. The best aquifers with high porosities and permeabilities are of the Triassic age and their distribution is influenced by their proximity to the source area. Sedimentary rocks of the Triassic age in the Bowen Basin become more argillaceous at more distal positions from the source area. The Rewan Group in particular shows this trend and hence better aquifers within the Rewan are those close to the source area. The Kalahari Basin Karoo stratigraphy commences with the Late Carboniferous to Early Permian glaciogenic sedimentary rocks of the Dwyka Group. The Dwyka Group is overlain by the argillaceous Permian to Early Triassic sedimentary rocks of The Ecca Group and the Beaufort Group. Overlying the Beaufort Group is the Lebung Group (lower Mosolotsane Formation-dominantly mudstone and siltstone sequence and upper Ntane Sandstone Formation- aeolian sandstone). Basaltic lavas of the stormberg Lava Group cap the Karoo stratigraphy. Few groundwater studies in the Karoo of the Kalahari Basin have shown that the Ecca Group does not posses good aquifer characteristics because of its argillaceous nature. However, thin arenaceous interbeds within the Ecca Group have yielded some groundwater. Non-measurable quantities of groundwater have been recorded from boreholes sunk in the Beaufort Group. Few boreholes penetrating the Mosolotsane Formation yielded very little groundwater whereas Ntane Sandstone have yielded a fair amount of groundwater. Groundwater yield from the Stormberg Lava Group is related to the presence of fractures.
| Identifer | oai:union.ndltd.org:ADTP/291094 |
| Creators | Lasarwe, Reneilwe |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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