A comparative study of detrital zircon ages from river sediment and rocks of the Karoo Supergroup (Late Carboniferous to Jurassic), Eastern Cape Province, South Africa : implications for the tectono-sedimentary evolution of Gondwanaland’s southern continental margin
- Authors: Bowden, Laura Leigh
- Date: 2014-06-26
- Subjects: River sediments - South Africa - Eastern Cape , Sedimentary rocks - South Africa - Eastern Cape , Zircon - South Africa - Eastern Cape , Karoo Supergroup , Gondwana (Continent)
- Type: Thesis
- Identifier: uj:11608 , http://hdl.handle.net/10210/11320
- Description: M.Sc. (Geology) , The Mzimvubu River, situated in the Eastern Cape Province of South Africa, drains essentially strata of the Late Carboniferous to Jurassic Karoo Supergroup with minor intersection of the underlying Devonian Msikaba Formation near the mouth of the river at Port St. Johns. Rock- and river sediment samples were collected at specific points from within the Mzimvubu River drainage basin, based on changes in the geology through which the rivers flow. Detrital zircon age population data was obtained by LA-ICP-MS for each sample in order to meet the two-fold objective of the study; firstly to investigate the reliability of using detrital zircon grains as indicators of sedimentary provenance and secondly to determine possible source areas for the Karoo strata and underlying Msikaba Formation. Through the comparison of detrital zircon age population data for the rock units of the Karoo Supergroup and Msikaba Formation to that of the river sediment, it is concluded that detrital zircon grains hold value in deciphering the geological history of a sedimentary basin. This interpretation is based on similar distributions and trends that are present in both the zircon age populations of the rock- and sediment samples. However, complexities associated with detrital zircon analysis pertaining to rock type and depositional settings are noted and therefore certain procedures that can be implemented during field sampling have been suggested in this study so as to ensure accurate results are obtained. This will further ensure that reliable interpretations of the geological history of a sedimentary basin are achieved. Additionally, by utilising the detrital zircon population data obtained in the first part of the study in conjunction with published scientific data, the provenance of the Karoo Supergroup in the southeastern part of the Main Karoo Basin has been determined. From this data it was determined that, especially the upper part of the Karoo Supergroup in the Eastern Cape Province of South Africa, was deposited much later than previously thought and that many of the stratigraphic layers in the Karoo Basin were deposited coevally in different parts of the basin with lithostratigraphic boundaries being time-transgressive. Ultimately the data allowed for the construction of a tectono-sedimentary model to explain the deposition of the upper Cape- and Karoo Supergroups that started with the deposition of the Msikaba Formation in a passive continental margin setting, to deposition of the lower part of the Karoo Supergroup in an Andean type of foreland basin, with rifting starting during the times of deposition of the Molteno Formation. The deposition of the Molteno-, Elliot- and Clarens Formations took place as Gondwanaland was breaking apart coeval with the formation of the Karoo Igneous Province.
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Uranium mineralisation and provenance analyses of the Karoo supergroup in the Springbok Flats Coalfield, South Africa
- Authors: Nxumalo, Valerie
- Date: 2020
- Subjects: Karoo Supergroup , Uranium ores , Uranium - Metallurgy
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/458609 , uj:40741
- Description: Abstract: The Springbok Flats Coalfield (SFC) is situated in a c. 60 km wide, 200 km long, SW-NE trending basin that stretches from c. 50 km N of Pretoria to 50 km S of Polokwane in the Limpopo Province. In this study, the distribution, nature and origins of uranium (U) mineralisation in the Karoo Supergroup of the SFC were investigated by a variety of methods, which includes; 1) facies analysis on borehole cores to understand the depositional environments, 2) geochemistry and mineralogical composition of the sedimentary rocks to understand the elemental concentrations and distributions (including uranium) and 3) provenance studies using U-Pb detrital zircon geochronology to indicate potential source areas of the clastic sediments. The geology of the SFC is largely known from borehole cores, as the Karoo Supergroup succession in the coalfield is poorly exposed. A total of five boreholes were drilled for this study, from the northeast (NE) to the central (C) and the southwest (SW) sectors of the SFC. The stratigraphy of the Karoo Supergroup in the SFC spans the Late Carboniferous to Early Jurassic. It is broadly similar to that of the main Karoo Basin (MKB), as well as to the Waterberg and Tshipise coalfields to the north of the MKB, and the Kalahari Karoo Basin (KKB) in Botswana, even though some units are absent. The basal part of the SFC consists of the fluvial-dominated lower Vryheid Formation (Fm), which is associated with swamp deposits of the lower Coal Zone (LCZ). The LCZ is only developed in the SW sector of the SFC and reaches a thickness of about 10 m. The lower Vryheid Fm is conformably overlain by a coarsening-upward successions of the upper Vryheid Fm, representing deltaic deposits, which are in turn overlain by the upper Coal Zone (UCZ). The LCZ and UCZ are cyclic deposits in the swamp characterised by a number of coal seams, alternating with in part carbonaceous as well as noncarbonaceous mudstones. The coal seams are dominated by alternating bands of bright to moderately bright coals and carbonaceous mudstones. The UCZ is conformably overlain by thick massive mudstones of the Beaufort Group equivalent, believed to represent deposits from suspension in a lacustrine environment. The Beaufort Group equivalent is unconformably overlain by the Molteno Fm, interpreted to have been deposited in fluvial environments under oxidising conditions. The Molteno Fm is in turn overlain by the Elliot Fm, which is dominated by very dusky red oxidised mudstones and siltstones, sandstones and conglomerates with fossil bone fragments occurring towards the NE sector of the SFC. The uppermost part of the Karoo Supergroup is represented by the Clarens Fm, consisting predominantly of aeolian sandstones. The Karoo sedimentation in the SFC was terminated by the extrusion of the Letaba Fm basalts, which are equivalent to those of the Drakensberg Group in the MKB. , Ph.D. (Geology)
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Geological controls on no. 4 seam roof conditions at New Denmark Colliery, Highveld Coal Field, Karoo Basin, South Africa
- Authors: Stanimirovic, Jasmina
- Date: 2009-01-28T09:43:30Z
- Subjects: Facies (Geology) , Coal , Stratigraphic geology , Sedimentology , Mine roof control , Karoo Supergroup , Mpumalanga (South Africa)
- Type: Thesis
- Identifier: uj:14849 , http://hdl.handle.net/10210/1971
- Description: M.Sc. , The coal-bearing Permian Vryheid Formation of the Ecca Group (Karoo Supergroup) was investigated at New Denmark Colliery, situated in the north east section of the Karoo Basin, South Africa. The lithostratigraphy of the sequence is defined in terms of conventional lithostratigraphic terminology but also by applying detailed genetic stratigraphic schemes that have previously been proposed for the adjacent coalfields. The succession is divided up into depositional sequences named after the underlying and overlying coal seams, the No. 2, 3, 4 and 5 seam sequences. The sedimentary succession was divided up into five facies, namely: conglomerate facies, sandstone facies, interlaminated sandstone-siltstone facies, siltstone facies and coal facies. These were interpreted hydrodynamically. Facies assemblages were then interpreted palaeoenvironmentally. Glacial, fluvial, deltaic and transgressive marine sequences were responsible for forming this sedimentary succession. Attention was then focussed on the main economic No. 4 seam, which is mined underground at the colliery. Detailed subsurface geological cross-sections, core sequences and isopach maps of the No. 4 seam coal and the lithologies above, were used to determine specific aspects of the depositional environment that could contribute to unstable roof conditions above No. 4 seam. Coarsening-upward deltaic cycles, fining-upward bedload fluvial cycles, glauconite sandstone marine transgressions and crevasse-splay deposits are recognized in the overlying strata. Poor roof conditions occur parallel to palaeochannel margins because the interbedded channel sandstone and adjacent flood plain argillites cause collapsing along bedding plane surfaces. Rider coals overlying thin crevasse-splay sequences in close proximity to the No. 4 seam, create one of the most serious roof conditions; complete collapse occurs along the rider coal contact with the underlying splay deposits. Differential compaction of mudrock/shale/siltstone over more competent sandstone causes slickensided surfaces that weaken the roof lithologies. Correct identification of these sedimentological features will enable the prediction of potential poor roof conditions during mining operations and mine planning.
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Lithostratigraphy, depositional environments and sedimentology of the Permian Vryheid Formation (Karoo Supergroup), Arnot North, Witbank Coalfield, South Africa
- Authors: Uys, Joanne
- Date: 2009-04-30T09:28:39Z
- Subjects: Stratigraphic geology , Sedimentology , Facies (Geology) , Lithofacies , Karoo Supergroup , Mpumalanga (South Africa)
- Type: Thesis
- Identifier: uj:8338 , http://hdl.handle.net/10210/2464
- Description: M.Sc. , This work documents the lithostratigraphy and interpreted depositional environments of the Permian Vryheid Formation in the most northern proximal setting yet studied in the Witbank Coalfield. Data from 924 boreholes from two mining companies (Anglo Operations Ltd. and Xstrata Coal Ltd.) drilled over 50 years, covering an area of 910km2 revealed a 35m sequence of terrigenous clastic sedimentary rocks containing two coal seams. These seams are numbered No. 1 at the base and No. 2 at the top. Delineation of facies type, facies assemblages, lateral facies distributions and computer-based three-dimensional modeling facilitated the interpretation of the palaeodepositional environments. Eleven lithofacies are defined and interpreted hydrodynamically. Facies classification is based primarily on grain size and sedimentary structures. The modeling of the borehole information uses the finite element method to interpolate the thickness, roof and floor surfaces and trend of each seam and inter-seam parting between boreholes. The spatial position of the boreholes is defined using a digital terrain model that represents the current surface topography. Lateral distributions were correlated by repositioning the boreholes using the base of the No. 2 seam as a datum. Glaciofluvial, glaciolacustrine, bed-load (braided) fluvial and constructive progradational deltaic environments are interpreted in the study area. Fluvial channel sequences are dominant and cause the thinning of the coal seams below channel axes as well as splitting of both the No. 1 and No. 2 seams. Glaciofluvial influences also affect the lower portion of the No. 1 seam. Basement palaeotopography restricts the distribution of the lower splits of the No. 1 seam. The coals either ‘pinch-out’ or are absent above basement highs but blanket the adjacent low-lying areas. In contrast to the greater Witbank Coalfield, but concurrent with other studies in the more northern proximal regions, fluvial systems dominate over deltaic systems in the study area. Glaciodeltaic, fluviodeltaic and anastomosed channel fluvial systems recognized in the remainder of the Karoo Basin were fed by the braided fluvial systems in the study area. The close proximity of the study area to the northern edge of the basin accounts for the subtle differences in lithostratigraphy and interpreted depositional environments when compared with more distal sites to the south. For example, glaciofluvial clastic sediment input in the lower portions of the No. 1 seam and post-Karoo erosion that has removed the overlying seams; the deltaic progradational sequence, above the No. 2 seam, occurs twice in succession and the bioturbation, that has become characteristic of sedimentary sequence of the Vryheid Formation above the No. 2 seam in the central and southern parts of the Karoo Basin, is not as identifiable. These differences are explained by the extreme proximal location of the study area on the northern basin margin relative to the remainder of the Karoo Basin.
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Laser ablation ICP-MS age determination of detrital zircon populations in the Phanerozoic Cape and Lower Karoo Supergroups (South Africa) and correlatives in Argentina.
- Authors: Vorster, Clarisa
- Date: 2014-01-14
- Subjects: Karoo Supergroup , Cape Supergroup , Zircon - South Africa , Zircon - Argentinia , Inductively coupled plasma mass spectrometry , Geochronometry
- Type: Thesis
- Identifier: uj:7897 , http://hdl.handle.net/10210/8789
- Description: Ph.D. (Geology) , The successions of the Cape- and Karoo Supergroups preserve an integrated history of sedimentation along the paleo-Pacific margin of Gondwana from the Paleozoic to the Early Mesozoic. The Cape- and Karoo Supergroups have been well studied with regard to stratigraphy, sedimentary facies and depositional environment. However, the nature and location of their source regions, especially for the changeover from deposition within an Atlantic-type continental margin basin for the successions of the Cape Supergroup to an Andean-type continental foreland basin for some of the units of the Karoo Supergroup, remains poorly understood. In order to shed light on the nature of these source regions, a comprehensive U-Pb detrital zircon study of the successions of the Cape- and lower Karoo Supergroups was launched. A representative number of samples from the upper and lower successions of the Table Mountain- Bokkeveld- and Witteberg Groups of the Cape Supergroup as well as the Dwyka and Ecca Groups of the Karoo Supergroup were collected throughout the western, southwestern and southern Cape region. A few samples of the Dwyka Group were also collected within the more eastern outcrop regions of the succession located in Kwazulu-Natal. The sedimentary rocks of the Natal Group and Msikaba Formation have long been regarded as coeval with the Cape Supergroup. Similar to the successions of the Cape- and Karoo Supergroups, very little is known about their sedimentary source regions. Also, their relative age of sedimentation remains poorly constrained. The U-Pb detrital zircon study of the successions of the Cape- and lower Karoo Supergroups was thus extended so as to include the successions of the Natal Group and Msikaba Formation. The detrital zircon age populations of the successions of the Natal Group and Msikaba Formation would not only improve the present understanding with regards to the sedimentary source regions to these units but would also facilitate the evaluation of possible correlations between these units and the stratigraphic units of the Cape Supergroup. Samples of both the lower Durban Formation and the upper Mariannhill Formation of the Natal Group and the Msikaba Formation (which is presently regarded as being part of the Cape Supergroup) were therefore collected within their respective outcrop regions in the Kwazulu-Natal area. The similarities in litho- and bio-stratigraphy between the successions of the Cape- and Karoo Supergroups and those of the Ordovician to Early Permian successions of the Ventania System and the Ordovician to Silurian successions of the Tandilia System in Argentina have long been recognized. Although the detrital zircon populations of some of the formations within these Systems have been evaluated in the past, it is yet to be determined whether these successions and those of the Cape- and lower Karoo Supergroups have certain source regions in common. In order to facilitate such a comparison, samples of selected units of the Ventania System were therefore collected near Sierra de la Ventania, while a sample of the Balcarce Formation of the Tandilia System was obtained near Mar del Plata. The detrital zircon age populations of the successions of the Ventania and Tandilia Systems were also further evaluated in the light of establishing or confirming a time-correlation between these formations and those of the Cape- and lower Karoo Supergroups. U-Pb age determination of the detrital zircons population of the samples was conducted by means of Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS). Although LA-ICP-MS is a routine, well-established technique where the U-Pb age determination of detrital zircons is concerned, it was yet to be established at the centralized analytical facility of the University of Johannesburg, SPECTRUM, using the instrumentation currently available (i.e. 213nm Nd:YAG laser coupled to Quadrupole-based ICP-MS). The U-Pb age determination of detrital zircons was therefore preceded by a fair amount of instrument optimization and method development. Well studied shortcomings of U-Pb detrital zircon dating by LA-ICP-MS such as laser induced elemental fractionation, mass discrimination effects and as well as the possible occurrence of minor common-Pb needs were addressed and corrected for. The detrital zircon populations of successions in the Cape Supergroup have a distinct major Neoproterozoic to Early Cambrian age component, which can be attributed to an input of detritus from successions related to the Pan-African Orogeny in South Africa, such as the Gariep- and Saldania Belts located towards the north of the Cape Basin. A substantial amount of Mesoproterozoic detrital zircon grains is also present in all the samples from the successions of the Cape Supergroup. These grains of Mesoproterozoic age were probably derived from the Namaqua-Natal Metamorphic Province, which is also regarded as the source of some minor amounts of Paleoproterozoic detrital zircon grains. The near absence of Archean grains from the detrital zircon populations of the successions of the Cape Supergroup is notable, and is thought to be due to the Namaqua-Natal Metamorphic Province acting as a geomorphological barrier at the time of their deposition. The minor Paleozoic (Ordovician to Carboniferous) detrital zircon populations in the samples from the formations of the Cape Supergroup increase progressively upwards through the succession. ....
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