Masters Degrees (Geology)

Permanent URI for this collectionhttps://hdl.handle.net/10413/6622

Browse

Now showing 1 - 20 of 58

Hydrogeological and hydrochemical characterisation of the area around the Kusile Power Station, Mpumalanga.
(2022) Dlamini, Andile Eugene.; Demlie, Molla Bekele.
Abstract available in PDF.
Investigating potential aquifers for managed aquifer recharge using treated wastewater around the greater Ethekwini District Municipality.
(2022) Msweli, Hlengiwe Fortunate.; Demlie, Molla Bekele.
Abstract available in PDF.
Stratigraphy and sedimentology of the Molteno formation in the Elliot and Indwe area, Cape Province.
(1981) Christie, Angus David Mackay.; Tavener-Smith, Ronald.
Abstract in PDF file.
Local-to micro-scale structural controls on shear-zone-hosted gold mineralisation, Ngubevu area, Natal Thrust Front, Tugela Terrane, South Africa.
(2021) Chagi, Onele.; Carranza, Emmanuel John Muico.; Hoyer, Lauren.
The research described in this dissertation focused on shear-zone-hosted precious and base metal mineralisation in the Ngubevu area, in the Natal Thrust Front of the Tugela Terrane in the Natal Metamorphic Province of South Africa. This province forms part of a 400-km-wide metamorphic belt referred to as the Namaqua-Natal Metamorphic Province, which stretches from the Northern Cape on the west coast to KwaZulu-Natal on the east coast of the country. Unlike the western Namaqualand Metamorphic Province, which is well-explored and well-exploited for several mineral deposits, the Natal Metamorphic Province is relatively poorly explored. One reason for this is that the nature of structural controls on mineralisation in the Natal Metamorphic Province is poorly understood. In the research described in this dissertation, known occurrences of shear-zonehosted precious and base metal deposits in the Golden Eagle and Champion Mines in the Ngubevu area, which have been described in the literature, were studied in the micro-scale, and the findings obtained were integrated with existing knowledge of regional- to local-scale deformation in the Tugela Terrane, in order to deduce the structural controls of such mineralisation in the area. The micro-scale data, studied by spatial analytical methods (i.e., point pattern analysis, Fry analysis, fractal analysis and shape analysis) show that the mineralisation in the area operated in at least two spatial scales, within each thin section sample, of at most 0.005 μm and at least 0.002 μm and that, within each thin section sample, the occurrence of shear-zone-hosted precious and base metal deposits is non-random as they exhibit clustered and/or regular spatial distributions. Microfractures in the area generally show major northerly trends in their alignments. Likewise, microscale mineral distributions show NNE–SSW and NNW–SSE trends in their orientations. These findings suggest that N–NE-directed compression controlled the occurrence and distribution of shear-zone-hosted precious and base metal mineralisation in the Ngubevu area. This N–NEdirected compression and thrusting during deformation (D1) controlled the circulation and concentration of mineralising hydrothermal fluids in the Natal Thrust Front. These hydrothermal fluids formed quartz veins along nearly E–W-trending foliations resulting in mineralisation in the clustered and regular spatial patterns observed in the micro-scale.
Characterisation of groundwater and surface water interaction in the eThekwini Metropolitan District, KwaZulu-Natal, South Africa.
(2021) Mtshali, Sphindile.; Demlie, Molla Bekele.
Abstract available in PDF.
The structural evolution of the Bumbeni Complex and Bumbeni Ridge and its relationship with Gondwana break-up: insights from high resolution aeromagnetic data and field mapping.
(2021) Ncume, Mawande.; Hoyer, Lauren.; Hicks, Nigel.
The Bumbeni Complex is the remnant of a Cretaceous volcanic centre (~133 Ma) that is now exposed along the southern end of the Lebombo Mountain Range, adjacent to the cover sequences that infill the Zululand Basin in northern KwaZulu-Natal, South Africa. The Bumbeni Complex forms the western limit of the north-east trending Bumbeni Ridge and postdates the rocks of the Karoo Large Igneous Province. The comparison of field relationships, structural data, high-resolution aeromagnetic data and borehole logs are used to determine the formation and structural evolution of the Bumbeni Complex and Bumbeni Ridge by understanding the tectonic regimes responsible for the development of the brittle deformation structures in the study area. These events are then correlated with the regional tectonic events related to Gondwana break-up, thus further constraining the timing of deformation and possible formation mechanisms of the Bumbeni volcanism. The rhyolites of the Jozini Formation (Lebombo Group) provide a basement to the rocks of the Bumbeni Complex. These rhyolites are characterised by a N-S oriented eastward dipping normal and dextral strike-slip faults and associated planar systematic joint sets. These fractures are representative of a dextral strike-slip regime, interpretable on a dextral Riedel shear system. The presence of these dextral strike-slip faults suggests that a rotation in the paleo-stress regime from a vertical 1 to a horizontal NE-SW oriented 1 have occurred during deformation, which may be related to the second deformation event (175–155 Ma) attributed here to stage two of Gondwana break-up. These structural deformation patterns developed in the Jozini Formation are absent in the rocks of the Bumbeni Complex, suggesting the deformation in the Lebombo Group occurred prior and/or during the eruption and intrusion of the Bumbeni Complex. The aeromagnetic data defines four distinct magnetic domains (Domains 1–4), which are separated by distinct regional magnetic discontinuities and are defined by their structural framework. Domain 1 occurs in the SW of the study area and is characterised by N-S oriented wide lineaments (low frequency, deep seated), and correlate with the Lebombo Group and are likely related to the N-S oriented faults occurring in the Jozini Formation rhyolites. The formation of these structures is here associated with the E-W orientated spreading attributed to the initial stages of Gondwana break-up (~180–175 Ma). Domains 2, 3 and 4 mainly display E-W and NE-SW oriented high frequency shallow structures, which cross-cut each other suggesting that the shallow structures occurred at different times and post-date the occurrence of the deep structures. These structures are related to the second deformation event which is constrained between stages 2 and 3 (175–135 Ma). The field evidence reveals that the Bumbeni Complex comprises basaltic and rhyolitic rocks of the Mpilo and Fenda Formations, respectively, indicating bimodal volcanism typical of rift related extension. The bimodal volcanism is most likely related to local extension associated with the upwelling of the continental lithospheric mantle. The position of the Zululand Basin boreholes (ZD and ZG) in relation to the aeromagnetic anomalies and the geomagnetic timescale, reveal that the Bumbeni Complex comprise NE-striking remanent and non-remanently magnetised plutonic bodies. These NE-striking plutonic bodies, which are a result of ascended magma occur in the southeast and northeast of the study area, delineated from the aeromagnetic data, and are indicative of emplacement during positive and negative polarity periods which prevailed during the Cretaceous. The position of the Bumbeni Complex and extension of the volcanism along the Bumbeni Ridge is correlated with a once-active E-W trending spreading centre located in the Northern Natal Valley at ~133–125.3 Ma, based on its paleo-position. Thus, the Bumbeni event is attributed to a combination of these processes. This event is likely a volcanic centre that formed along a failed rift system.
Index testing and assessment of the suitability of bentonite from the Imerys Bentonite Mine, for use in geosynthetic clay liners.
(2020) Patel, Ahmad.; Hingston, Egerton Daniel Christian.
Geosynthetic Clay Liners (GCLs) have become a suitable substitute for compacted clay liners. Their use centre on liquid impoundments, such as to prevent leachates from landfills seeping into the groundwater system and as sealant in tailings dam. GCLs are thin sheets of bentonite encased between two geotextiles. The main component of GCLs is bentonite, which formed as an alteration product of volcanic ash, comprised mainly of montmorillonite. Bentonite exists as either sodium bentonite or calcium bentonite, depending on the type of montmorillonite present within it. To perform as an effective hydraulic barrier, sodium bentonite is the preferred type due to its high-water retention characteristics and swelling potential. Often times, the bentonite does not meet the desired swell index. As such, a process known as activation is undertaken, whereby soda ash (Na2CO3) is mixed with borderline quality bentonite. This study investigated the suitability of bentonites from the Imerys mine in the Western Cape Province of South Africa for use in GCLs. In this research, both activated and non-activated bentonites were investigated. X-Ray diffraction analysis was conducted on the bentonites in order to determine their bulk mineralogical composition. Swell index test, fluid loss test, plate water absorption tests and Atterberg limits test were also conducted on samples of activated and non-activated bentonites. Furthermore, swell index tests were conducted to investigate the extent of beneficiation over time. The XRD results reveal that activated and non-activated bentonite have a smectite content of approximately 58 % and 67 % respectively with the major impurity being quartz. The swell index of non-activated bentonite was significantly lower than the activated bentonite. However, the activated bentonite did not swell to the required minimum of 24 ml/2g as it did not achieve full activation. Activated samples of bentonite tested at different times subsequent to activation reveal that the activation requires at least 4 weeks for the ideal ratio of 1:50, soda ash to bentonite, to fully activate. The fluid loss results also displayed results slightly above the required minimum, of 18 ml, as a result of the low swell index. Activated and non-activated bentonite has an absorption capacity of approximately 133 % and 121 %. The plasticity index is 101 % for activated bentonite, 15 % higher than non-activated bentonite. Moreover, a moderate correlation between plate water absorption and liquid limit was found for activated bentonite. The activated bentonite from Western Cape is suitable for use in GCLs provided the blend of bentonite is not of very low quality and sufficient time is given for activation to reach completion. Imerys bentonite is a medium quality bentonite with borderline index properties that requires beneficiation and time to achieve complete activation.
Hydrochemical characterisation of Northern KwaZulu-Natal historic coal mining districts, Northeastern South Africa.
(2018) Mduduma, Hlumela.; Demlie, Molla Bekele.
This M.Sc. dissertation reports the results of a hydrogeochemical study undertaken on historical coal mining districts of northern KwaZulu-Natal (KZN) Province, South Africa. The research catchment covers an area of about 12945 km2, located in the head waters of the Tugela River Basin or the uThukela Water Management Area (WMA). The main aim of the study was to assess the effectiveness of the rehabilitation undertaken by the South African Government on the various defunct/abandoned historical coal mines in northern KZN in improving surface water and groundwater quality in the region. Characterisation of surface water and groundwater water in terms of their interconnection, flow and hydrochemistry were undertaken. Primary (original data) and secondary data and information were collected, collated and analysed to understand the hydrogeochemical conditions of the region. The original data collected through a series of field campaigns within the study area, were complimented with secondary data from the Department of Water Affairs and Sanitation (DWS) monitoring programme, the KZN Groundwater Recourse Information Project (GRIP), the National Groundwater Archives (NGA) and borehole logs, hydrochemical and borehole yield data from various reports. The results of the study reveal that since the beginning of groundwater monitoring in 2010, the groundwater has been characterised by circumneutral waters. Time series EC, SO42- and Fe2+ data reveal no incongruities apart from a few episodes of elevated concentrations. Surface water hydrochemical analyses revealed peaks in EC coupled with low pH at varied sampling points which are presumed to be impacts from Acid Mine Drainage (AMD). Time series saturation states of groundwater with respect to calcite and dolomite indicate that groundwater remains oversaturated with respect to these minerals but under saturated with respect to gypsum as a result of carbonate AMD neutralization reactions. Trace metal data reveal no anomalous concentrations both in surface water and groundwater samples as a result of the circumneutral hydrogeochemical conditions. Major ion hydrochemical data show two main groundwater hydrochemical facies in the study area, namely most upstream boreholes are characterized by Na-Ca-HCO3-SO4 and most downstream boreholes are characterised by Ca-Mg-HCO3-SO4 hydrochemical water types. All surface water and groundwater samples have δD and δ18O isotopic values that plot on or below the Local and Global Meteoric Water Lines, indicating recharge from meteoric source with some evaporation mainly within the rehabilitated mine dumps. The detectible tritium signal in the shallow aquifers reflect recent active recharge taking place.
Hydrogeological and hydrochemical investigation of the Durban Metropolitan District, Eastern South Africa.
(2018) Ndlovu, Minenhle Siphesihle.; Demlie, Molla Bekele.
Population and economic growth within the Durban Metropolitan region in eastern South Africa has increased the demand for water supply. This ever-increasing demand means that all available water supply sources including groundwater will be looked at, particularly in urban and peri-urban areas. However, the state of the groundwater resource in the region is poorly understood. This study aims to contribute towards improved understanding of the state of groundwater resources in the Metropolitan District through an integrated hydrogeological, hydrochemical and environmental isotope investigations. Results of hydrogeological and hydrogeochemical characterization identified at least five hydrostratigraphic units of varying hydraulic and hydrochemical characteristics. 1) The weathered and fractured Granitic basement aquifers of the Mapumulo Group and Oribi Gorge Suite characterized by average borehole yield and transmissivity (T) of 1.2 l/s and 3.9 m2/day, respectively, with hydrochemical facies of Ca-Mg-HCO3. 2) The fractured Natal Group sandstone, characterized by average borehole yield and hydraulic conductivity (K) of 5.6 l/s and 2.8 m/day, respectively with Na-Mg-HCO3-Cl as dominant water type; 3) The fractured aquifers of the Dwyka Group diamictite and tillite are characterized by average borehole yield of 0.4 l/s and T of 1.3 m2/day and Na-Cl-HCO3 as the dominant water type; 4) The Vryheid Formation, which is part of the Ecca Group, is characterized by a mean borehole yield of 2.5 l/s, T of 4.9 m2/day, K of 0.17 m/day and Na-Cl-HCO3 water type; 5) The intergranular primary aquifers of the Maputaland Group which consists the Bluff, Berea Formations and recent alluvium and estuarine deposits (locally called harbour beds Formation) have average borehole yield of 14.8 l/s and transmissivity of up to 406 m2/day with a mainly Na-Cl-HCO3 hydrochemical signature. The region receives mean annual precipitation (MAP) of 935 mm/yr of which 9.2% infiltrates to recharge the various aquifers. Environmental isotope information (2H, 18O and 3H) indicated that groundwater recharge is of modern precipitation. Groundwater tritium values of 37.4 and 92 TU are measured around the Bul Bul Drive and Bisasar Road Landfill sites, respectively, indicating groundwater contamination from landfill leachate leakage. Based on the main hydrogeological, hydrogeochemical and environmental isotope findings, a regional hydrogeological conceptual model is developed that characterizes the hydrogeological and hydrochemical conditions of the Durban Metropolitan region.
Geotechnical characterization and slope stability analyses of the Town Bush Valley, Pietermaritzburg, South Africa.
(2018) Singh, Keval.; Hingston, Egerton Daniel Christian.; Demlie, Molla Bekele.
The construction of settlements over zones of instability is increasing the impact of disasters across the world both in developed and developing nations. Many areas in the greater Pietermaritzburg region in South Africa, such as the Town Bush Valley, are prone to slope instability due to the terrain morphology and high intensity rainfall. This study has investigated the geotechnical conditions at the Town Bush Valley, in Pietermaritzburg. A geotechnical characterization of the Town Bush Valley has been undertaken in order to understand the geotechnical conditions prevailing on site. Furthermore, two critical slopes were selected for slope stability analyses to investigate the conditions under which failure would occur. The method of analyses chosen was the Morgenstern and Price method using the Rocscience, SLIDE software. The analyses involved a deterministic approach and a probabilistic approach. In the deterministic approach, all the input variables were considered as constant values. In the case of the probabilistic approach, the effective shear strength parameters were chosen as the random variables in order to account for their uncertainty. Prior to the analyses, sensitivity analysis was conducted in order to see the effect of the effective shear strength parameters, c´ and φ´, on the factor of safety. Various scenarios, including groundwater conditions and surcharge load, were considered during the analyses. Results from the site characterization show that the site is characterized by heterogeneous talus material, which is underlain at depth by shales of the Pietermaritzburg Formation and sandstones of the Vryheid Formation. Particle size analysis, Atterberg Limits Determination and consolidated-drained triaxial tests were undertaken on the talus material. The slope stability analyses show that the probabilistic approach presents a better insight into the assessment of the slope than a deterministic approach in accounting for the uncertainty in the geotechnical parameters. The random behaviour of the geotechnical parameters was quantified through various probabilistic functions. The various functions derived during probabilistic slope stability analyses, allowed for an assessment of the reliability of the data sets. Keywords/Phrases: Deterministic slope stability analysis; Phreatic surface; Probabilistic slope stability analysis; Random variables; Town Bush Valley
Marine geology of the East London continental shelf.
(2017) Dlamini, Nontuthuzo Patricia.; Green, Andrew Noel.; Wiles, Errol Avern.; Dladla, Nonkululeko Nosipho.
This dissertation examines the marine geology of the continental shelf offshore East London, on the east coast of South Africa. High-resolution seismic, multibeam bathymetric and backscatter tools are employed to reveal the stratigraphic, geomorphic and oceanographic controls on the shelf development. Eight seismic units (A-H) are revealed and comprise Campanian-age limestones of the Igoda Formation at their base, with an overlying transgressive stratigraphic package associated with the last deglaciation. A subaerial unconformity transects the shelf and is infilled by Late-Pleistocene to Holocene-age material of Unit C. Overlying the subaerial unconformity in other places are isolated shoreface deposits of Unit B. Unit D comprises a series of aeolianites and beachrocks which form palaeo-shorelines at -100 and -60 m. They are mantled to landward by the back-barrier deposits of Unit E, and to seaward by the disaggregated barrier deposits of Unit F. Unit G comprises shoreface deposits and is interfingered with Unit H, a series of rhodoliths that mantle the modern day seafloor. Multibeam data reveal extraordinarily preserved palaeo-shorelines which are the outcrop expression of Unit B. The most seaward of these form barrier islands and associated back-barrier segmented coastal waterbodies that evolved to planform equilibria before being overstepped. These are bordered by large, well-preserved parabolic dunefields that signify planform equilibrium with high-rates of sediment supply. These shorelines formed during the Bǿlling-Allerod stillstand and were overstepped by Melt Water Pulse (MWP) 1-A. A -60 m shoreline is preserved as an isolated drumstick barrier, and a series of cuspate spits that are welded onto palaeo-embayments in Gondwana-aged bedrock. These formed during the Younger Dryas slowstand and were overstepped by MWP-1B. Underfilled incised valleys are still exposed at the seafloor along these palaeo-embayments and formed due to rapid transgression and limited marine sediment supply during the conditions associated with MWP-1B. They are currently being filled by the submerged prodeltas of the contemporary drainage systems. Backscatter data reveal eight acoustic facies (A-H). These units all show marked current sweeping of the shelf, with dredge samples revealing gravels that fill in erosional furrows, or form streamers and ribbons. The AMS C14 dating of the rhodolith fields of Unit H indicates that the vigorous Agulhas Current has continuously swept the shelf since ~7400 years BP, post MWP 1-B. This has caused the sediment starvation of most of the shelf, and has transported much of the available sediment to the deep sea via the shelf-indenting canyon systems of the area.
Hydrogeochemical and environmental isotope characterization of the CO₂ springs along the Bongwana Fault, its impact on fresh water resources and implications for carbon capture and storage (CCS) in South Africa.
(2018) Nkwane, Mzikayise.; Demlie, Molla Bekele.
Natural CO²-rich springs at the Bongwana area in Eastern South Africa emanate from three sites along an 80 km long North-South trending Bongwana Fault. The geological unit that outcrops along the extent of the Fault are the Dwyka Group rocks that are made up of mainly tillites and subordinate sandstones, shales and conglomerates. The objectives of this M.Sc. study is to characterize these CO²-rich springs and assess their impacts on shallow groundwater and surface water chemistry and consequently to understand the implication of a failed CCS facility. Groundwater and surface samples were collected both at CO² emission and CO²-free springs, boreholes and streams around the length of the studied fault zone for the analyses of major ions, trace elements and environmental isotopes. Additionally, specific electrical conductivity (EC), total dissolved solids (TDS), pH, temperature, dissolved oxygen (DO), redox potential (Eh), total alkalinity, CO³²- and HCO³- concentrations were determined onsite. The results indicate that all the travertine cone springs located near Umtamvuna River are characterized by Na-Ca-Mg-HCO3 water types, while boreholes from shallow groundwater and river samples show Ca-Na-Mg-HCO³ types. Stable isotope (δ18O and δ2H) composition of the travertine cone springs shows a major negative shift from the meteoric water lines with δ18O and δ2H values ranging from -7.78 to -6.52 ‰ and -21.5 to -17.9 ‰, respectively. While, the stable isotopic composition of shallow groundwater reflects local and modern meteoric recharge. These observations indicate that the reservoir and source of recharge for the deep circulating groundwater are different from the shallow groundwater. Based on onsite hydrogeological, hydrogeochemical, and environmental isotope observations, a hydrogeological conceptual model is proposed, which states that the groundwater recharge for deep circulating groundwater is to the west of the Bongwana fault, located at a higher altitude. From these altitudes, groundwater percolates through deep fractures and faults to greater depths. As groundwater percolates through the rock, it interacts with minerals and the initial recharge chemistry and isotopic composition is altered along the groundwater flow paths. At depth, groundwater dissolves carbonate rocks and as a result CO² is generated. The dissolution of CO² in groundwater further drives the leaching of the formation minerals along the flow path. Near the surface, CO² exsolves and travertine mainly composed of calcite, amorphous silica and iron hydroxides is formed. Geochemical inverse modelling and bivariate correlation among groundwater hydrochemical parameters for travertine springs indicate that the major geochemical processes that are responsible for the observed chemical composition are the dissolution of calcite, dolomite, Pyrite, Goethite, K-feldspars, fluorite, albite and sylvite and the precipitation of calcite, amorphous silica, iron hydroxide, iron carbonates, kaolinite and CO² gas. The carbonate minerals are attributed to the dissolution of carbonate rocks at depth. Feldspars are common from the Dwyka Group Diamictites, whereas the plagioclase feldspar (albite) is probably originating from the recharge area outside of the Dwyka group or leached from the granitic and metamorphic fragments contained within the Dwyka tillites. These inverse modelling results are supported by the saturation indices (SI) for calcite and dolomite in these springs which range from 0.74 to 0.82 and from 0.24 to 1.35, respectively indicating oversaturation with respect to these minerals and subsequent precipitation out of the aqueous solution. The precipitation of calcite, amorphous silica and iron carbonates were confirmed by the XRF, XRD and thin section results of the travertine rock samples. Acidic pH conditions (5.5), elevated TDS (5937 ppm), EC (3271 mS/m) and high trace metals concentration were detected in all CO² emission sites compared to CO² free streams, springs and boreholes. These results clearly show the impacts of CO² on groundwater and surface water quality within the vicinity of emission points. Therefore, it appears that natural CO² emission along the Bongwana fault have impacted the ambient groundwater and surface water quality at the emission sites rendering it unfit for human consumption due to elevated concentration of dissolved constituents above safe drinking standards. The implication of this to CCS in South Africa is the fact that any unintended CO² leakage into fresh groundwater and surface water resources from a failed subsurface storage facility may impact freshwater resources. Thus, strict scientific site selection protocols and properly designed monitoring systems are required to minimise the risk.
Submarine canyon evolution of the Southwest Cape continental margin.
(2017) Palan, Kreesan Jonah.; Green, Andrew Noel.; Wiles, Errol Avern.; Sink, Kerry.
Submarine canyons are diverse geomorphological systems that are characterised by a wide variety of geomorphic and sedimentary processes. The complexities that arise during their evolution reveal changes in the tectonic and eustatic setting that actively sculpt continental margins. Newly acquired high-resolution bathymetry reveals 15 submarine canyon systems, most of which were previously undocumented, and a large fluid seep/pockmark field off the Cape continental margin of the west coast of South Africa. These are hosted in the Orange Basin, South Africa’s largest gas producing basin. High resolution 2D seismic reflection and borehole data were used to establish a general seismic stratigraphy in which eight units are defined (Seismic Facies 1 – 8). Five key unconformity bounding surfaces are delineated (surfaces A – E) and related to major fluctuations in sea-level. Surface A marks the Albian sedimentation in the basin, B defines the Turonian – Conacian boundary and is imprinted by the first palaeo-canyons of the area, C characterises the Maastrichtian – Danian boundary and correlating with another episode of canyon formation, D marks the Palaeocene – Eocene surface, above which an assumed Oligocene canyon system was formed, and E defines the Mid-Miocene unconformity correlating to a pulse of uplift of the hinterland and further canyon incision. The modern-day canyons observed from multibeam bathymetry are suspected to have initiated in the Pliocene. The contemporary canyon morphologies vary, with many canyon features yet to be described in the literature. These morphologies are broadly classed into linear, sinuous, hooked and shelf-indenting types. Pockmarks are situated in close proximity to the sinuous, hooked and shelf-indenting canyon types and were quantified using hydrological extraction techniques to a total of 2219. These pockmarks represent the terminus of stratigraphic fluid migration from an Aptian gas reservoir, evidenced in the form of blowout pipes and brightened reflectors. Various pockmark morphologies are exhibited including circular, elongate, crescentic, composite and stringed-types. This pockmark morphological diversity is explained through localised bottom current controls which modify a point-sourced circular pockmark to establish the more complicated morphologies. The morphometric analyses of the canyons suggest contemporaneous down- and upslope eroding paradigms, that later were dominated by the influences of vertical fluid flows and gas seepage. It is proposed that fluid flow plays a key role in establishing the morphological variability of canyons along the Cape continental margin. Vertical fluid migration within the study area has the potential to mobilise sediments, evidenced by the occurrences of blowout pipes, pockmarks and neighbouring mass wasting deposits. The youngest (or most immature) canyons are considered to be the linear-types, produced by the amalgamation of intra-slope rills and with a notable absence of fluid flow features. Succeeding these are the sinuous canyons, their sinuous form dictated by the spatially irregular control of fluid flow on the sea-floor stability. The hooked canyons are defined by their arcuate heads and dense pockmark associations, suggesting further fluid flow interaction around the canyon head, producing erosion patterns associated with neither up, nor downslope mass wasting. A single shelf indenting/breaching canyon is observed. This is considered the most mature canyon system. The meandering mid-components of this canyon formed by fluid-interactions, however slumping may have been of sufficient magnitude to have extended beyond the pockmark fields, the canyon head thus gaining access to sediment flows from the upper slope. The head then subsequently retrogressed beyond the shelf-break to its present position. This thesis provides the first opportunity for a glimpse into seafloor fluid venting and escape features from the South African margin and how they affect canyon morphologies.
Nearshore morphological changes and their relation to wave-induced forcing at Isipingo embayment, KwaZulu-Natal.
(2017) Shanganlall, Arissa.; Green, Andrew Noel.; Loureiro, Carlos Manuel.
The nearshore zone is one of the most active sedimentary environments on the continental shelf, frequently impacted by energetic wave conditions and storm–generated waves and flows. Despite its proximity to the beach and shoreline, the nearshore is a difficult domain to study and little is understood with regards to its response to storm waves and the agents responsible for the morphological evolution of the region. Previous research has provided insight into the nearshore, however high-resolution approaches to gain a three dimensional understanding of these environments are still lacking. This is especially true in geologically constrained environments as coastal embayments. Advances in the acquisition and analysis of high- resolution multibeam bathymetry of the nearshore, coupled with wave modelling techniques, can provide an improved understanding of coastal response to high energetic wave conditions and the subsequent morphological changes that result from the impact of storm events. Detailed nearshore multibeam bathymetric surveying conducted at the Isipingo embayment before and after the 2017 winter season provided a framework to analyse the seasonal morphological changes that were driven by winter storms along the KwaZulu-Natal coastline. High-resolution bathymetric grids were implemented in the hydrodynamic model SWAN (Simulating Waves Nearshore) to simulate the nearshore wave field of Isipingo embayment for a variety of wave conditions. Morphological changes were evaluated in conjunction with wave-induced forcing to determine the potential for sediment mobilisation. Spectral wave modelling results of the wave field and bed shear stresses agree with the observed morphological changes. Significant erosion and deposition occurred in the shallower regions (5 m to 14 m) of the study area and along the northeast and southwest sections of the embayment. Modelling results presented in this study indicate that the spatial variation and distribution of orbital bottom velocities and bed shear stresses are strongly dependent upon the bathymetric configuration of large-scale bedforms and the magnitude of the nearshore wave field. Consequently, the greater the energy of the wave conditions (i.e. as a result of major storm events) the greater the wave-induced forcing, which causes the change of the bedforms and the morphological evolution of the nearshore. Large-scale features such as shoreface-connected ridges, rippled scour depressions and large subaqueous dunes tend to increase the significant wave height and the bed shear stresses acting on the seabed. Thus, waves are focussed towards the NE headland resulting in an extensive zone of erosion in the embayment. The main geological constraints at the embayed region of Isipingo are imposed by the NE and SW headlands and the shoreface-connected ridges. Such constraints drive the development of topographically controlled rips against the NE headland, set up by the prevalent south-north longshore current, and the shadowing effect of the SW headland also contributes to the observed erosional (NE region) and accretion (SW region) patterns on the nearshore. The hydrodynamic forcing of rippled scour depressions and shoreface connected ridges control the persistence of the non-stationary rip currents of the NE section of the embayment. As a consequence, the absence of rip activity at the centre of the embayment creates a relatively stable region. Additionally, the study reveals that the patterns of morphological change in the nearshore mimic those of the apparent rotation of the beach, explained by the breathing mode described from other embayments. Model simulations of extreme storm events depict that the morphological change is driven by an energetic wave field, and the wave induced orbital motions and bed shear stresses have a strong bathymetric imprint. This study demonstrates the usefulness of high-resolution bathymetry in understanding nearshore morphological change. In providing a complete three dimensional image of changes at incredibly high-resolutions, and with high (2-3 month) temporal resolution, an increased level of understanding of the nearshore changes seaward of bars can be garnered. This includes rip-dynamics, erosion patterns, geological control on wave-forcing and seasonal accretion/erosion monitoring. These are areas which have not yet received attention in this level of detail and in which it is demonstrated that good results can be obtained.
Seismic, geochemical and sedimentological characteristics of storm deposits from the Durban continental shelf, South Africa.
(2015) Dixon, Shannon Louise.; Green, Andrew Noel.
The Durban shelf is a wave-dominated, high energy setting, characterised by submerged shorelines at depths of ~60 m, backed to landward by low-relief backbarrier depressions. The exposure at the seafloor of a back-barrier/lagoon complex, coupled with the general high wave energy of the shelf makes for a unique opportunity to examine records of marine storminess, preserved as tempestites in the shelf stratigraphy. This thesis examined a variety of ultra-high resolution seismic data, coupled with multibeam bathymetry, core and sedimentological data. High resolution XRF, XRD and other provenance proxies were also examined in order to reveal cycles of storminess that have impacted the lower shoreface offshore Durban. These are integrated with a rigorous geochronological framework. The seismic sections revealed two distinct packages which comprise the unconsolidated shoreface (Unit A and B). These are further subdivided into an upper five packages (Sub-unit B1-B5 and sub-unit A-Ai). Cores that penetrated this sediment enabled a further correlation with that of the bounding surfaces, sediment compositions and the nature of individual sub units. Unit A and Ai are considered incised valley fills corresponding to organic-rich fine sand of the central basin and flood tide delta deposits with a distinctly higher terrigenous sediment signature in comparison to the overlying sediment packages. The tidal ravinement surface (tRS) is restricted to the incised valley where it separates unit A and Ai. The wave ravinement surface (WRS) truncates the incised valley fills and is overlain by unconsolidated material of unit B. Sub-units B3 and B4 are storm associated deposits which are of particular interest to this study. Sub-unit B3 comprises a number of high energy deposits, namely mudballs; these deposits consist of organic rich material indicative of storm winnowing of an exposed muddy backbarrier (such as presently occurring along sectors of the adjoining coastal plain). This is corroborated by the geochemical analyses of the mudballs which displays significantly higher concentrations of terrigenous elements (Si, Al, K, Ti and Rb), in comparison to the surrounding sediment, indicative of a terrigenous sediment origin. The centre of the mudball was dated at 9 850 ± 50 cal yrs BP. The outer veneer dates to 3 835 ± 35 cal yrs BP and represents the final phase of deposition in the lower shoreface. The mudballs are encased in coarse sediment, dominated by Ca and Sr elemental concentrations, suggestive of a marine origin. Sub-unit B4 consists of alternating horizons of storm generated gravel horizons displaying increased marine elemental signatures, interbedded with finer sediment with increased terrigenous concentrations indicative of fair-weather conditions. It was found that horizons of coarser material had higher elemental signatures of Ca and Sr indicating a predominantly marine input into the system. These horizons are intercalated with finer material with distinctly higher concentrations of elements associated with terrigenous source material that represents fair-weather suspension settling of terrestrial materials. Based on modelling of the largest experienced contemporary marine storm (Hs = 8.5 m), it is clear that storm waves do not significantly rework gravelly sediment on the lower shoreface, especially in the areas of smooth seafloor where the cores are situated. Bathymetry of the area shows no contemporary evidence for storm scour or gravel deposition. As the palaeo-tempestites date to a time when sea level occupied a similar position to that of today, it is logical to assume these represent much larger storm events than are commonly experienced. This study shows for the first time a period of increased storminess in the Indian Ocean between 6 480 ± 40 cal yr BP to 4 595 ± 35 cal yr BP; a time linked to a strongly positive Indian Ocean Dipole (IOD) anomaly and increased sea surface temperatures (SST). With further global warming, it appears that Durban may be more vulnerable to large marine storms as the associated changes in atmospheric circulation patterns and oceanic currents promote the formation of positive IOD phenomena.
Catchment hydrological modelling using ArcSWAT : a study of the Ingula pumped storage scheme (IPSS) catchments, South Africa.
(2017) Ngubane, Zesizwe.; Demlie, Molla Bekele.
Abstract available in PDF file.
Structure and evolution of the Zinkwazi and Umdloti barrier spit and inlet systems along the KwaZulu-Natal coastline, South Africa.
(2017) Pillay, Talicia.; Green, Andrew Noel.
Abstract available in PDF file.
A geochemical study of the Theta Reef of the Frankfort Mining Complex in the Sabie-Pilgrim's Rest Goldfield South Africa.
(2015) Metz, Alexander Richard.; McCourt, Stephen.; Elburg, Marlina Augusta.
For over a century the Sabie-Pilgrim’s Rest Goldfield has been one of the most important gold producers in South Africa. The epigenetic gold deposits are situated at the eastern escarpment of the Eastern Transvaal Drakensberg, approximately 60 km away from the eastern rim of the Bushveld Igneous Complex. The Theta and Bevets Reef of the Frankfort Mining Complex occur within the Neoarchean dolomite of the Malmani Subgroup and the Paleoproterozoic Pretoria Group, respectively, of the Transvaal Supergroup. While the Theta Reef is situated in the dolomites of the Eccles Formation of the Malmani Subgroup, the Bevets Reef is situated at the contact between a conglomerate, also called the Bevets Conglomerate and the shales of the Rooihoogte Formation of the Pretoria Group, therefore providing two different environments for the ore mineralisation. The ore-bearing reefs are represented by quartz-carbonate veins. The ore minerals are pyrite, arsenopyrite, chalcopyrite and minor amounts of minerals of the tetrahedrite-tennantite series. The reefs were emplaced along thrust faults developed parallel to bedding which dips at 4-7° west towards the Bushveld Complex. The thrusts are attributed to forces related to the emplacement of the intrusion. Stable isotope geochemistry revealed that isotopes within a single mineral phase and between two phases are not in isotopic equilibrium. This suggests an episodic mineralisation of the ore-bearing quartz vein. Oxygen and carbon isotopic compositions of 10.9 – 13.8 (fluid) and -4.1 - -2.8 ‰ (calcite), respectively, indicate that the ore forming fluids are most likely of igneous origin and interacted with the rocks of the Transvaal Supergroup. Sulphur isotopic compositions of -1 – 2.3 ‰ (sulphides) show that fluids and metals seem to have originated from the Bushveld Complex. Trace element analysis of ore samples from the most northern section of the Theta Reef shows that the gold content within pyrite is generally low. The common trace elements are Cu, As, Ag Sb, Au, Pb and Bi, occurring as minerals or mineral inclusions of the tetrahedrite-tennantite series. Gold occurs as invisible solid solution and/or as Au-As and/or Au-Sb compound in arsenic rich sulphide minerals and occasionally in association with silver as electrum. The research shows that the intrusion of the Bushveld Complex played a major role in the formation of the gold deposits in the Sabie-Pilgrim’s Rest area being responsible for the mineralizing hydrothermal fluids, the ore metals, the heat budget for the hydrothermal cell and the forces that created the thrust faults that acted as pathways for the circulation of the mineralizing fluids. The circa 2.055Ga age of the Bushveld Complex also provides a maximum age for the Au-mineralization.
Hydrogeological conceptual modeling of the Kosi Bay Lakes system, north eastern South Africa.
(2015) Ndlovu, Mbali.; Demlie, Molla Bekele.
This M.Sc. Thesis focuses on the hydrogeological study of the Kosi Bay Lakes system, located in the north-eastern KwaZulu-Natal (KZN) Province of South Africa. The research catchment covers an area of about 659 km². It is characterised by four interconnected lakes, two isolated lakes and an estuary with a combined area of about 48 km². Two fresh water streams; namely, Sihadhla and Gezisa drain into the lakes. The study was initiated due to information gaps and the importance of the area with respect to conservation, ecology and water resources. The main objectives of the research was to characterize the groundwater and surface systems, in terms of their interconnection, flow and hydrochemistry; conduct a water balance study and develop a conceptual hydrogeological model on the occurrence and interaction of groundwater and surface water within the study area. The study has been undertaken by collecting primary data through a series of field campaigns in April 2013, May 2013 (onsite measurements and water, and water sampling) and October to December 2014 (geophysical data collection and supervision of borehole drilling). Original data generated in this study was complimented with data from KZN Groundwater Resource Information Project (GRIP), the National Groundwater Archives (NGA) and geophysical data, borehole logs, chemistry, and borehole yield data from consultant reports. Geophysical sounding data were calibrated using borehole logs and aquifer pumping tests, which indicate the presence of three hydrostratigraphic units in the study area, namely; the unconfined Holocene cover sands, the Kosi Bay and Port Durnford Formations, and the leaky-confined aquifer made up of the Umkhwelane and Uloa Formations, from top to bottom, respectively. The mean annual precipitation (MAP) for the study area based on data collected at Ingwavuma Kosi Bay and Ingwavuma Manguzi meteorological stations is 939 mm/year. The mean annual groundwater recharge estimated using the chloride mass balance method is 13% of the MAP. Surface water runoff from the catchment to the lakes derived using the Runoff Curve Number method is 14% of the MAP. Evaporation rate from the lakes and evapotranspiration from the catchment area estimated using the Penman and FAO Penman-Monteith approach are 1341 mm/a and 1135 mm/a, respectively. The water balance parameters indicate that inputs into the lakes are greater than the output as indicated by the positive change in storage (ΔS). The lake water balance result was supported by long-term lake level records that show an increasing trend over time. The measured electrical conductivity (EC) for the Kosi Bay Lakes range from 1024 μS/cm (Amanzamnyama) to 24600 (Makhawulani) μS/cm, for the groundwater from 86 to 400 μS/cm and for the streams, it ranges from 227 to 341 μS/cm. The high EC and TDS values of some of the Kosi Bay Lakes are attributed to the high evaporation and connection to the sea through the estuary. The shallow aquifers are characterized by Na-HCO₃-Cl, whereas the deep aquifers have a Na-Ca-Cl hydrochemical facies. All groundwater, stream and lake water samples have δ¹⁸O and δ²H values that plot on the local and global meteoric water lines indicating recharge from meteoric sources. Groundwater in the shallow Holocene aquifer and streams has similar hydrochemical and isotopic signature, indicating strong interconnection. On the other hand, the lakes are characterized by Na-Cl hydrochemical water type and an enriched stable isotopic signal (positive δD and δ¹⁸O signals) indicating evaporation and terminations of the local surface and groundwater flow system. The detectable tritium signal along with the low salinity of groundwater in the shallow aquifer reflect recent (< 50 years) recharge.
Foraminiferal distribution in unconsolidated sediment associated with a marginal coral reef in South Africa.
(2015) Hayman, Stephanie Vivien.; Schleyer, Michael H.; Mackay, Christine Fiona.
Abstract available in pdf file.

Browse

Recent Submissions