The geology of the Springbok Flats
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Date
2012
Authors
Nel, Leon
Journal Title
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Publisher
University of the Free State
Abstract
The Springbok Flats constitutes an extensive tract of generally flat country extending from south of Bela Bela north-eastwards to Zebediela Location. This area is located within 28˚00´ and 29˚30´ east and 24˚15´ and 25˚30´ south with a total areal extent of approximately 8 000 km2.
A comprehensive exploration programme commenced in 1976 and was completed in 1982. During the exploration programme 3 000 boreholes were drilled. These borehole data was re-interpreted in conjunction with downhole geophysical surveys in order to create a sedimentological database suitable for the reconstruction of palaeo-environments of the Karoo-aged strata in the Springbok Flats Karoo Basin (SFKB).
Structurally the SFKB comprises two elongated basins i.e. Roedtan Basin (north) and Settlers-Tuinplaats Basin (south). These two basins are bordered by pre-Karoo aged tectonic features i.e. Thabazimbi-Murchison lineament (northern boundary of the Roedtan Basin) and the Droogekloof Fault Zone (northern boundary of the Settlers-Tuinplaats Basin). These tectonic features were continuously active after the deposition of the Karoo strata in the SFKB resulting that the existing SFKB is considered to be a preserved Karoo-aged basin.
Stratigraphically the SFKB was subdivided into 7 distinctive lithostratigraphic units. Lithostratigraphic Unit 1 comprises glacier derived sediments and is correlated with the Dwyka Group of the Main Karoo Basin. Lithostratigraphic Unit 2 is a mega upward coarsening cycle resembling a deltaic deposit. This deltaic deposit is overlain by a cyclothem consisting of Lithostratigraphic Units 3 and 4 respectively. Lithostratigraphic Unit 3 is a composite coal zone. Based on selected seam horizons a coal zone resource of 3492 mt was demarcated. In areas adjacent to palaeotopographical highs uranium is associated with the coal zone and a resource of 363.0 mt with an average grade of 0.40 kg/t U3O8 was calculated.
A prominent regionally developed disconformity marks the commencement of Lithostratigraphic Unit 5. A continuum of fluvial environments including alluvial fans, braided rivers, meandering river systems and anastomosed river systems was postulated as depositional environments for Lithostratigraphic Unit 5.
A lithostratigraphic unit, comprising basal calcrete conglomerates followed by intensely bioturbated siltstone and a lesser bioturbated sandstone respectively, constitutes Lithostratigraphic Unit 6. The texture and sedimentary structures of Lithostratigraphic Unit 7 which overlies Lithostratigraphic Unit 6 is compatible with a typical aeolian deposit. The termination of the Karoo-aged strata in the SFKB is marked by the presence of amygdaloidal basaltic lavas.
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Thesis (Ph.D. (Geology))--University of the Free State, 2012, Geology -- South Africa -- Springbok Flats, Formation (Geology) -- South Africa -- Springbok Flats, Geological Survey (South Africa)