Regional connectivity, differentiation and biogeography of three species of the genus Lutjanus in the western Indian Ocean
- Authors: Morallana, Jonas Moqebelo
- Date: 2014
- Subjects: Lutjanus -- Indian Ocean , Biogeography -- Indian Ocean , Phylogeography -- Indian Ocean , Lutjanus -- Geographical distribution , Lutjanus -- Variation , Mitochondrial DNA , Animal genetics , Variation (Biology)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5369 , http://hdl.handle.net/10962/d1013293
- Description: Snappers of the genus Lutjanus are small to large predatory fishes occurring in inshore circumtropical and subtropical waters throughout the world. These fishes support fisheries across their distribution range. Within the Western Indian Ocean (WIO), previous studies on Lutjanus kasmira revealed limited spatial genetic differentiation, whereas Lutjanus fulviflamma showed high genetic connectivity. The phylogenetic relationships among WIO snappers are unknown. Previous studies in the Indo-Pacific (IP) did not include any WIO representatives. This study examined (1) the phylogeographic patterns in Lutjanus bohar, L. fulviflamma and L. lutjanus to understand the origins and factors influencing the distribution of diversity in the region, (2) how the physical environment, biological, and ecological factors influence genetic diversity, (3) the placement of WIO snappers in context to those from the IP, as well as the placement of taxa not included previously, (4) extent of differentiation among conspecifics from the two regions, and (5) the relationship of the Caesionidae to the Lutjanidae. Samples were sourced from across the WIO and from peripheral localities, where possible. DNA sequence data were generated from two mitochondrial gene regions (cyt-b and NADH-2) and a nuclear gene region (S7 intron 1). Data were analysed under a phylogeographic framework to examine genetic structure, diversity and differentiation among identified regions for each of the three species. Other sequence data were generated from two mitochondrial gene regions (COII and 16S rDNA) to examine the phylogenetic placement of WIO snappers in context of the IP snappers and the relationship of the Caesionidae to the Lutjanidae. Lutjanus bohar and L. fulviflamma displayed high genetic diversity, but lower diversities were observed for L. lutjanus. Genetic differentiation was observed between Mozambique and Maldives in L. bohar. Lutjanus fulviflamma was differentiated in South Africa, Mozambique, Mauritius and Thailand, while differentiation was observed between Kenya and Tanzania in Lutjanus lutjanus. Overall, low genetic differentiation and high connectivity were observed for each of the three species. This differentiation may result from intrinsic features of the species and extrinsic features of the environment, whereas the connectivity is mainly influenced by the pelagic larval duration. These patterns of differentiation are in accordance with a proposed vicariant biogeographic hypothesis for the origins of regional faunas of the IP. Phylogenies were similar to those published, with additional taxa not altering the previous groupings found. Conspecifics from the two regions clustered together, with varying degrees of differentiation among the WIO and IP, depending on the species. Members of the Caesionidae were nested within Lutjanidae, suggesting that morphological characters separating the two families are taxonomically insignificant. This affirms previous notions that the Caesionidae should be a subfamily within the Lutjanidae. This is the first multi-gene study, examining differentiation in multiple species of snapper over a wide geographic area in the WIO, and the results of this study could have potential implications for fisheries management and conservation.
- Full Text:
- Date Issued: 2014
- Authors: Morallana, Jonas Moqebelo
- Date: 2014
- Subjects: Lutjanus -- Indian Ocean , Biogeography -- Indian Ocean , Phylogeography -- Indian Ocean , Lutjanus -- Geographical distribution , Lutjanus -- Variation , Mitochondrial DNA , Animal genetics , Variation (Biology)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5369 , http://hdl.handle.net/10962/d1013293
- Description: Snappers of the genus Lutjanus are small to large predatory fishes occurring in inshore circumtropical and subtropical waters throughout the world. These fishes support fisheries across their distribution range. Within the Western Indian Ocean (WIO), previous studies on Lutjanus kasmira revealed limited spatial genetic differentiation, whereas Lutjanus fulviflamma showed high genetic connectivity. The phylogenetic relationships among WIO snappers are unknown. Previous studies in the Indo-Pacific (IP) did not include any WIO representatives. This study examined (1) the phylogeographic patterns in Lutjanus bohar, L. fulviflamma and L. lutjanus to understand the origins and factors influencing the distribution of diversity in the region, (2) how the physical environment, biological, and ecological factors influence genetic diversity, (3) the placement of WIO snappers in context to those from the IP, as well as the placement of taxa not included previously, (4) extent of differentiation among conspecifics from the two regions, and (5) the relationship of the Caesionidae to the Lutjanidae. Samples were sourced from across the WIO and from peripheral localities, where possible. DNA sequence data were generated from two mitochondrial gene regions (cyt-b and NADH-2) and a nuclear gene region (S7 intron 1). Data were analysed under a phylogeographic framework to examine genetic structure, diversity and differentiation among identified regions for each of the three species. Other sequence data were generated from two mitochondrial gene regions (COII and 16S rDNA) to examine the phylogenetic placement of WIO snappers in context of the IP snappers and the relationship of the Caesionidae to the Lutjanidae. Lutjanus bohar and L. fulviflamma displayed high genetic diversity, but lower diversities were observed for L. lutjanus. Genetic differentiation was observed between Mozambique and Maldives in L. bohar. Lutjanus fulviflamma was differentiated in South Africa, Mozambique, Mauritius and Thailand, while differentiation was observed between Kenya and Tanzania in Lutjanus lutjanus. Overall, low genetic differentiation and high connectivity were observed for each of the three species. This differentiation may result from intrinsic features of the species and extrinsic features of the environment, whereas the connectivity is mainly influenced by the pelagic larval duration. These patterns of differentiation are in accordance with a proposed vicariant biogeographic hypothesis for the origins of regional faunas of the IP. Phylogenies were similar to those published, with additional taxa not altering the previous groupings found. Conspecifics from the two regions clustered together, with varying degrees of differentiation among the WIO and IP, depending on the species. Members of the Caesionidae were nested within Lutjanidae, suggesting that morphological characters separating the two families are taxonomically insignificant. This affirms previous notions that the Caesionidae should be a subfamily within the Lutjanidae. This is the first multi-gene study, examining differentiation in multiple species of snapper over a wide geographic area in the WIO, and the results of this study could have potential implications for fisheries management and conservation.
- Full Text:
- Date Issued: 2014
The factors affecting self-regulation through the analysis of physiological, psychological and behavioural measures during task-switching
- Authors: Chaplin, Caley
- Date: 2013 , 2013-07-16
- Subjects: Human multitasking -- Physiological aspects , Human multitasking -- Psychological aspects , Fatigue , Boredom , Attention , Mental fatigue , Human information processing , Decision making , Labor productivity , Industrial hygiene , Employees -- Workload
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5135 , http://hdl.handle.net/10962/d1006027 , Human multitasking -- Physiological aspects , Human multitasking -- Psychological aspects , Fatigue , Boredom , Attention , Mental fatigue , Human information processing , Decision making , Labor productivity , Industrial hygiene , Employees -- Workload
- Description: Individuals are required to manage multiple tasks which require strategic allocation of time and effort to ensure goals are reached efficiently. By providing the worker with autonomy over their work, performance and worker well-being have improved. This increased control allows individuals to organize work according to the needs of the body, which prevents fatigue leading to improved productivity. When given the option, humans tend to switch between tasks frequently. This behaviour can be used to determine the change in self-regulation strategies. An understanding of human task-switching behaviour is important for the design of job rotation systems. However, there is a lack of evidence explaining the factors motivating the need to switch between tasks. This study aims to use physiological, subjective and behavioural measures to explain the factors influencing selfregulation through the act of task-switching. Three primary hypotheses were developed to explain the factors underlying taskswitching behaviour. It was hypothesized that the degree of boredom experienced, the effort required to perform the task and the resource usage induced by the task are factors responsible in deciding task switching behaviour. Participants (17 males and 17 females) switched freely between five different information-processing tasks for the 45 minutes. Participants were allowed to switch back and forth between tasks and did not have to conduct all five tasks. The following measures were recorded during the experiment: subjective measures of boredom, mental effort, task frustration and perceived performance of the tasks; energy consumption and physiological measures of effort (HR, HRV and body temperature) and behavioural measures, including duration and frequency of task. Perceived boredom was found to differ among the tasks and before and after the experiment. The average boredom rating at each task transition for all tasks exceeded a score of 2.5 out of a possible 4. There were no significant changes in physiological measures between the beginning and end of the task trials. However, changes in physiological measures showed a decrease in effort investment following task transition. Heart rate variability was lower for externally-paced tasks than for self-paced tasks, despite the differences in cognitive demands. The most frequent task-switch combination occurred between tasks of high and low cognitive demand. The least frequent task-switching combination occurred between tasks of similar characteristics, which produced no differences in physiological responses. Task-switching behaviour was influenced by the degree of boredom, and therefore more time was spent on less monotonous tasks. The level of physiological effort required for the task affected task-switching behaviour. Task switches were made before any changes in effort took place in an attempt to maintain task efficiency. It appears plausible that a task switch was made to reduce effort investment and activation levels. The type of information processing resources used by different tasks affected the task-switching combinations. Individuals tended to switch between tasks of differing resources so that those in limited supply were able to replenish. Therefore the findings from this study can potentially be used to improve the design of job rotation systems. Such improvements may enhance productivity and worker well-being by inhibiting the onset of down regulation and fatigue processes. This study showed that autonomy is necessary for individuals to regulate behaviour to suit human needs. , Microsoft� Office Word 2007 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Date Issued: 2013
- Authors: Chaplin, Caley
- Date: 2013 , 2013-07-16
- Subjects: Human multitasking -- Physiological aspects , Human multitasking -- Psychological aspects , Fatigue , Boredom , Attention , Mental fatigue , Human information processing , Decision making , Labor productivity , Industrial hygiene , Employees -- Workload
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5135 , http://hdl.handle.net/10962/d1006027 , Human multitasking -- Physiological aspects , Human multitasking -- Psychological aspects , Fatigue , Boredom , Attention , Mental fatigue , Human information processing , Decision making , Labor productivity , Industrial hygiene , Employees -- Workload
- Description: Individuals are required to manage multiple tasks which require strategic allocation of time and effort to ensure goals are reached efficiently. By providing the worker with autonomy over their work, performance and worker well-being have improved. This increased control allows individuals to organize work according to the needs of the body, which prevents fatigue leading to improved productivity. When given the option, humans tend to switch between tasks frequently. This behaviour can be used to determine the change in self-regulation strategies. An understanding of human task-switching behaviour is important for the design of job rotation systems. However, there is a lack of evidence explaining the factors motivating the need to switch between tasks. This study aims to use physiological, subjective and behavioural measures to explain the factors influencing selfregulation through the act of task-switching. Three primary hypotheses were developed to explain the factors underlying taskswitching behaviour. It was hypothesized that the degree of boredom experienced, the effort required to perform the task and the resource usage induced by the task are factors responsible in deciding task switching behaviour. Participants (17 males and 17 females) switched freely between five different information-processing tasks for the 45 minutes. Participants were allowed to switch back and forth between tasks and did not have to conduct all five tasks. The following measures were recorded during the experiment: subjective measures of boredom, mental effort, task frustration and perceived performance of the tasks; energy consumption and physiological measures of effort (HR, HRV and body temperature) and behavioural measures, including duration and frequency of task. Perceived boredom was found to differ among the tasks and before and after the experiment. The average boredom rating at each task transition for all tasks exceeded a score of 2.5 out of a possible 4. There were no significant changes in physiological measures between the beginning and end of the task trials. However, changes in physiological measures showed a decrease in effort investment following task transition. Heart rate variability was lower for externally-paced tasks than for self-paced tasks, despite the differences in cognitive demands. The most frequent task-switch combination occurred between tasks of high and low cognitive demand. The least frequent task-switching combination occurred between tasks of similar characteristics, which produced no differences in physiological responses. Task-switching behaviour was influenced by the degree of boredom, and therefore more time was spent on less monotonous tasks. The level of physiological effort required for the task affected task-switching behaviour. Task switches were made before any changes in effort took place in an attempt to maintain task efficiency. It appears plausible that a task switch was made to reduce effort investment and activation levels. The type of information processing resources used by different tasks affected the task-switching combinations. Individuals tended to switch between tasks of differing resources so that those in limited supply were able to replenish. Therefore the findings from this study can potentially be used to improve the design of job rotation systems. Such improvements may enhance productivity and worker well-being by inhibiting the onset of down regulation and fatigue processes. This study showed that autonomy is necessary for individuals to regulate behaviour to suit human needs. , Microsoft� Office Word 2007 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Date Issued: 2013
The feasibility of stock enhancement as a management tool for dusky kob (Argyrosomus japonicus) in South Africa
- Authors: Palmer, Ryan Michael
- Date: 2008
- Subjects: Argyrosomus -- South Africa , Argyrosomus -- Genetics , Fishery management -- South Africa , Fish stocking -- South Africa , Fisheries -- South Africa , Marine ecology -- South Africa , Fish culture -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5281 , http://hdl.handle.net/10962/d1005125 , Argyrosomus -- South Africa , Argyrosomus -- Genetics , Fishery management -- South Africa , Fish stocking -- South Africa , Fisheries -- South Africa , Marine ecology -- South Africa , Fish culture -- South Africa
- Description: The dusky kob, Argyrosomus japonicus, is a popular South African “line fish” whose stocks have dwindled to dangerously low levels of between 1% and 4.5% of pristine spawner biomass per recruit. A. japonicus stocks are currently managed by means of minimum size restrictions and daily bag limits, and as a result of the inability of these measures to facilitate the recovery of the species over a realistic time frame, the need for an alternative management plan has become apparent. Given the status of the stock and management regime, stock enhancement appears to be an appropriate option to be investigated. This study evaluates the feasibility of stock enhancement as a possible management tool to assist with the recovery of this important South African linefish species. By evaluating the genetic and ecological implications related to stock enhancement, identifying a suitable tagging method for post-release monitoring, and evaluating the economic feasibility of such a programme, any fatal flaws would become immediately apparent. This coupled with the required framework for the development of a management plan for stock enhancement of A. japonicus provides direction further research and actions required in order to utilise stock enhancement as a management tool. Due to the nature of stock enhancement, there are several ecological and genetic issues that arise from such a programme. These issues were reviewed and the issues that were relevant to stock enhancement of A. japonicus identified. Ecological concerns that arose included those of competition, disease and seed quality, while genetic issues were concerned mainly in the possible loss of genetic variability and consequent reduction in fitness of the stock. Fortunately the technology exists to evaluate the effects and likelihood of these problems occurring as well as to minimise the likelihood of them occurring. By taking a scientific approach to stock enhancement, hatchery management, and release strategies can be manipulated in such a way as to minimise any negative effects that may be caused. Both ecological and genetic effects of stocking indicate a need for post-release monitoring of stock enhancement programmes. Stock enhancement requires a post-release monitoring programme, which in turn relies on an ability to distinguish between hatchery reared and wild fish. A study was conducted to evaluate the suitability of coded wire tags (CWT), visual implant fluorescent elastomers (VIFE), and oxytetracycline (OTC) as a means of distinguishing between hatchery reared and wild A. japonicus, for the purpose of a post-release monitoring programme. OTC appeared to be the most suitable as it produced 100% retention over a five month period compared to 62% and 61% for VIFE and CWT respectively. OTC is therefore suggested as a tagging method for the purpose of post-release monitoring of the stock enhancement of A. japonicus. To evaluate a possible funding option for stock enhancement of A. japonicus in South Africa, a willingness-to-pay survey, based on a “user pays” approach using recreational fishing permits as a vehicle for payment, included 102 recreational anglers in the Plettenberg Bay area. The survey showed that generally anglers were willing to pay more than the current amount for the recreational fishing permit. This promising result, coupled with the fact that there are approximately 450 000 recreational anglers leads to the belief that there is potential for a substantial increase in the funds generated for the Marine Living Resources Fund through recreational anglers. Stock enhancement should not be ruled out on the basis of economic feasibility yet as there is potential for it to be sustained by the users of the resource. An A. japonicus juvenile production costing model was created taking into account setup and running costs of a hatchery for A. japonicus, based on known parameters from existing facilities, and adjusting them to meet the requirements of a stock enhancement facility. Estimates varied according to the number and size of fish for release (values which can only be decided upon after further research), with setup estimated to be between R 10 000 000 and R 30 000 000 and annual running costs between R 2 400 000 and R 6 700 000 annually. These figures were dependant on the size and number of fish being produced, with production ranging between 100 000 and 5 000 000 fish of between 50 mm and 150 mm, and a broodstock of 150 individuals. Given the need for alternative management of A. japonicus in South Africa and the lack of evidence to suggest that it is an unfeasible option, this project has found no reason why further investigation into the use of stock enhancement for the management of A. japonicus should not proceed further provided the fishery is shown to be recruit limited. The technology and ability to overcome possible ecological and genetic problems exists, a suitable means of tagging for post-release monitoring exists, as does a realistic funding option. There is a substantial amount of research that must be done prior to stocking, for which a base framework is provided.
- Full Text:
- Date Issued: 2008
- Authors: Palmer, Ryan Michael
- Date: 2008
- Subjects: Argyrosomus -- South Africa , Argyrosomus -- Genetics , Fishery management -- South Africa , Fish stocking -- South Africa , Fisheries -- South Africa , Marine ecology -- South Africa , Fish culture -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5281 , http://hdl.handle.net/10962/d1005125 , Argyrosomus -- South Africa , Argyrosomus -- Genetics , Fishery management -- South Africa , Fish stocking -- South Africa , Fisheries -- South Africa , Marine ecology -- South Africa , Fish culture -- South Africa
- Description: The dusky kob, Argyrosomus japonicus, is a popular South African “line fish” whose stocks have dwindled to dangerously low levels of between 1% and 4.5% of pristine spawner biomass per recruit. A. japonicus stocks are currently managed by means of minimum size restrictions and daily bag limits, and as a result of the inability of these measures to facilitate the recovery of the species over a realistic time frame, the need for an alternative management plan has become apparent. Given the status of the stock and management regime, stock enhancement appears to be an appropriate option to be investigated. This study evaluates the feasibility of stock enhancement as a possible management tool to assist with the recovery of this important South African linefish species. By evaluating the genetic and ecological implications related to stock enhancement, identifying a suitable tagging method for post-release monitoring, and evaluating the economic feasibility of such a programme, any fatal flaws would become immediately apparent. This coupled with the required framework for the development of a management plan for stock enhancement of A. japonicus provides direction further research and actions required in order to utilise stock enhancement as a management tool. Due to the nature of stock enhancement, there are several ecological and genetic issues that arise from such a programme. These issues were reviewed and the issues that were relevant to stock enhancement of A. japonicus identified. Ecological concerns that arose included those of competition, disease and seed quality, while genetic issues were concerned mainly in the possible loss of genetic variability and consequent reduction in fitness of the stock. Fortunately the technology exists to evaluate the effects and likelihood of these problems occurring as well as to minimise the likelihood of them occurring. By taking a scientific approach to stock enhancement, hatchery management, and release strategies can be manipulated in such a way as to minimise any negative effects that may be caused. Both ecological and genetic effects of stocking indicate a need for post-release monitoring of stock enhancement programmes. Stock enhancement requires a post-release monitoring programme, which in turn relies on an ability to distinguish between hatchery reared and wild fish. A study was conducted to evaluate the suitability of coded wire tags (CWT), visual implant fluorescent elastomers (VIFE), and oxytetracycline (OTC) as a means of distinguishing between hatchery reared and wild A. japonicus, for the purpose of a post-release monitoring programme. OTC appeared to be the most suitable as it produced 100% retention over a five month period compared to 62% and 61% for VIFE and CWT respectively. OTC is therefore suggested as a tagging method for the purpose of post-release monitoring of the stock enhancement of A. japonicus. To evaluate a possible funding option for stock enhancement of A. japonicus in South Africa, a willingness-to-pay survey, based on a “user pays” approach using recreational fishing permits as a vehicle for payment, included 102 recreational anglers in the Plettenberg Bay area. The survey showed that generally anglers were willing to pay more than the current amount for the recreational fishing permit. This promising result, coupled with the fact that there are approximately 450 000 recreational anglers leads to the belief that there is potential for a substantial increase in the funds generated for the Marine Living Resources Fund through recreational anglers. Stock enhancement should not be ruled out on the basis of economic feasibility yet as there is potential for it to be sustained by the users of the resource. An A. japonicus juvenile production costing model was created taking into account setup and running costs of a hatchery for A. japonicus, based on known parameters from existing facilities, and adjusting them to meet the requirements of a stock enhancement facility. Estimates varied according to the number and size of fish for release (values which can only be decided upon after further research), with setup estimated to be between R 10 000 000 and R 30 000 000 and annual running costs between R 2 400 000 and R 6 700 000 annually. These figures were dependant on the size and number of fish being produced, with production ranging between 100 000 and 5 000 000 fish of between 50 mm and 150 mm, and a broodstock of 150 individuals. Given the need for alternative management of A. japonicus in South Africa and the lack of evidence to suggest that it is an unfeasible option, this project has found no reason why further investigation into the use of stock enhancement for the management of A. japonicus should not proceed further provided the fishery is shown to be recruit limited. The technology and ability to overcome possible ecological and genetic problems exists, a suitable means of tagging for post-release monitoring exists, as does a realistic funding option. There is a substantial amount of research that must be done prior to stocking, for which a base framework is provided.
- Full Text:
- Date Issued: 2008
An investigation into the neuroprotective properties of curcumin
- Authors: Daniel, Sheril
- Date: 2003
- Subjects: Turmeric -- Therapeutic use , Nervous system -- Degeneration -- Prevention
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3753 , http://hdl.handle.net/10962/d1003231 , Turmeric -- Therapeutic use , Nervous system -- Degeneration -- Prevention
- Description: An increasing number of studies show that nutritional antioxidants such as vitamin E and polyphenols are capable of blocking neuronal death in vitro and may have therapeutic properties in animal models of neurodegenerative diseases including Alzheimer’s and Parkinson’s diseases. In the present study, the neuroprotective ability of one such polyphenolic antioxidant, curcumin, was investigated. Curcumin is the yellow curry spice derived from turmeric, and is widely used as a dietary component and herbal medicine in India. Most neurological disorders are postulated to have an oxidative or excitototoxic basis. Thus the effects of curcumin on oxidative stress in the rat brain were investigated. Curcumin, administered to the rat in vivo and in vitro, was able to exert protective effects on oxidative damage in the brain, induced by cyanide, a mitochondrial inhibitor. Curcumin also offered protection against quinolinic acid induced lipid peroxidation, and this protection was extended to lipid peroxidation induced by metals such as lead and cadmium in the rat brain. Experiments conducted on the pineal gland revealed an increased production of the neuroprotective hormone melatonin in presence of curcumin in vivo. The hippocampus is functionally related to vital behaviour and intellectual activities and is known to be a primary target for neuronal degeneration in the brains of patients with Alzheimer’s disease. Histological studies were undertaken to assess the effects of curcumin on lead induced toxicity on the rat hippocampus, the results of which show that curcumin affords significant protection to the hippocampus of the lead treated rats. This study also sought to elucidate possible mechanisms by which curcumin exerts its neuroprotective capabilities. Curcumin was found to inhibit the action of cyanide on the mitochondrial electron transport chain, one of the most common sources of free radicals. Electrochemical, UV/VIS and Infrared spectroscopy were used to characterise interactions between curcumin and the metals lead, cadmium, iron (II) and iron (III). Curcumin was shown to directly chelate these metals with the formation and isolation of two new curcumin complexes with lead, and one complex each with cadmium and iron (III). These results suggest chelation of toxic metals as a mechanism of neuroprotection afforded by curcumin. The need for neuroprotective agents is urgent considering the rapid rise in the elderly population and the proportionate increase in neurological disorders. The findings of this study indicate that curcumin, a well-established dietary antioxidant, is capable of playing a bigger role in neuroprotection, which needs to be further explored and exploited.
- Full Text:
- Date Issued: 2003
- Authors: Daniel, Sheril
- Date: 2003
- Subjects: Turmeric -- Therapeutic use , Nervous system -- Degeneration -- Prevention
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3753 , http://hdl.handle.net/10962/d1003231 , Turmeric -- Therapeutic use , Nervous system -- Degeneration -- Prevention
- Description: An increasing number of studies show that nutritional antioxidants such as vitamin E and polyphenols are capable of blocking neuronal death in vitro and may have therapeutic properties in animal models of neurodegenerative diseases including Alzheimer’s and Parkinson’s diseases. In the present study, the neuroprotective ability of one such polyphenolic antioxidant, curcumin, was investigated. Curcumin is the yellow curry spice derived from turmeric, and is widely used as a dietary component and herbal medicine in India. Most neurological disorders are postulated to have an oxidative or excitototoxic basis. Thus the effects of curcumin on oxidative stress in the rat brain were investigated. Curcumin, administered to the rat in vivo and in vitro, was able to exert protective effects on oxidative damage in the brain, induced by cyanide, a mitochondrial inhibitor. Curcumin also offered protection against quinolinic acid induced lipid peroxidation, and this protection was extended to lipid peroxidation induced by metals such as lead and cadmium in the rat brain. Experiments conducted on the pineal gland revealed an increased production of the neuroprotective hormone melatonin in presence of curcumin in vivo. The hippocampus is functionally related to vital behaviour and intellectual activities and is known to be a primary target for neuronal degeneration in the brains of patients with Alzheimer’s disease. Histological studies were undertaken to assess the effects of curcumin on lead induced toxicity on the rat hippocampus, the results of which show that curcumin affords significant protection to the hippocampus of the lead treated rats. This study also sought to elucidate possible mechanisms by which curcumin exerts its neuroprotective capabilities. Curcumin was found to inhibit the action of cyanide on the mitochondrial electron transport chain, one of the most common sources of free radicals. Electrochemical, UV/VIS and Infrared spectroscopy were used to characterise interactions between curcumin and the metals lead, cadmium, iron (II) and iron (III). Curcumin was shown to directly chelate these metals with the formation and isolation of two new curcumin complexes with lead, and one complex each with cadmium and iron (III). These results suggest chelation of toxic metals as a mechanism of neuroprotection afforded by curcumin. The need for neuroprotective agents is urgent considering the rapid rise in the elderly population and the proportionate increase in neurological disorders. The findings of this study indicate that curcumin, a well-established dietary antioxidant, is capable of playing a bigger role in neuroprotection, which needs to be further explored and exploited.
- Full Text:
- Date Issued: 2003
The bioaccumulation of platinum (IV) from aqueous solution using sulphate reducing bacteria: role of a hydrogenase enzyme
- Authors: Rashamuse, Konanani Justice
- Date: 2003
- Subjects: Sulfur bacteria , Bioremediation , Enzymes -- Metabolism , Platinum , Platinum compounds , Reduction (Chemistry) , Hydrogenation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4003 , http://hdl.handle.net/10962/d1004063 , Sulfur bacteria , Bioremediation , Enzymes -- Metabolism , Platinum , Platinum compounds , Reduction (Chemistry) , Hydrogenation
- Description: The enzymatic reduction of a high-valence form of metals to a low-valence reduced form has been proposed as a strategy to treat water contaminated with a range of metals and radionuclides. Metal reduction by sulphate reducing bacteria (SRB) is carried out either chemically (involving reduction by hydrogen sulphide) or enzymatically (involving redox enzymes such as the hydrogenases). While reduction of metal ions by hydrogen sulphide is well known, the enzymatic mechanism for metal reduction is poorly understood. The aims of this study were to investigate the role of SRB in facilitating platinum removal, and to investigate the role of a hydrogenase in platinum reduction in vitro. In order to avoid precipitation of platinum as platinum sulphide, a resting (non-growing) mixed SRB culture was used. The maximum initial concentration of platinum (IV), which SRB can effectively remove from solution was shown to be 50 mg.l⁻¹. Electron donor studies showed high platinum (IV) uptake in the presence of hydrogen, suggesting that platinum (IV) uptake from solution by SRB requires careful optimization with respect to the correct electron donor. Transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analysis indicated that platinum was being precipitated in the periplasm, a major area of hydrogenase activity in SRB. Purification of the hydrogenase by ammonium sulphate precipitation (65%), Toyopearl-Super Q 650S ion exchange and Sephacry 1 S-100 size exclusion chromatography revealed that the hydrogenase was monomeric with a molecular weight of 58 KDa, when analyzed by 12% SDS-PAGE. The purified hydrogenase showed optimal temperature and pH at 35°C and 7.5 respectively, and a poor thermal stability. In vitro investigation of platinum reduction by purified hydrogenase from mixed SRB culture showed that hydrogenase reduces platinum only in the presence of hydrogen. Major platinum (IV) reduction was observed when hydrogenase was incubated with cytochrome C₃ (physiological electron carrier in vivo) under hydrogen. The same observations were also noted with industrial effluent. Collectively these findings suggest that in vitro platinum reduction is mediated by hydrogenase with a concerted action of cytochrome C₃ required to shuttle the electron from hydrogenase.
- Full Text:
- Date Issued: 2003
- Authors: Rashamuse, Konanani Justice
- Date: 2003
- Subjects: Sulfur bacteria , Bioremediation , Enzymes -- Metabolism , Platinum , Platinum compounds , Reduction (Chemistry) , Hydrogenation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4003 , http://hdl.handle.net/10962/d1004063 , Sulfur bacteria , Bioremediation , Enzymes -- Metabolism , Platinum , Platinum compounds , Reduction (Chemistry) , Hydrogenation
- Description: The enzymatic reduction of a high-valence form of metals to a low-valence reduced form has been proposed as a strategy to treat water contaminated with a range of metals and radionuclides. Metal reduction by sulphate reducing bacteria (SRB) is carried out either chemically (involving reduction by hydrogen sulphide) or enzymatically (involving redox enzymes such as the hydrogenases). While reduction of metal ions by hydrogen sulphide is well known, the enzymatic mechanism for metal reduction is poorly understood. The aims of this study were to investigate the role of SRB in facilitating platinum removal, and to investigate the role of a hydrogenase in platinum reduction in vitro. In order to avoid precipitation of platinum as platinum sulphide, a resting (non-growing) mixed SRB culture was used. The maximum initial concentration of platinum (IV), which SRB can effectively remove from solution was shown to be 50 mg.l⁻¹. Electron donor studies showed high platinum (IV) uptake in the presence of hydrogen, suggesting that platinum (IV) uptake from solution by SRB requires careful optimization with respect to the correct electron donor. Transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analysis indicated that platinum was being precipitated in the periplasm, a major area of hydrogenase activity in SRB. Purification of the hydrogenase by ammonium sulphate precipitation (65%), Toyopearl-Super Q 650S ion exchange and Sephacry 1 S-100 size exclusion chromatography revealed that the hydrogenase was monomeric with a molecular weight of 58 KDa, when analyzed by 12% SDS-PAGE. The purified hydrogenase showed optimal temperature and pH at 35°C and 7.5 respectively, and a poor thermal stability. In vitro investigation of platinum reduction by purified hydrogenase from mixed SRB culture showed that hydrogenase reduces platinum only in the presence of hydrogen. Major platinum (IV) reduction was observed when hydrogenase was incubated with cytochrome C₃ (physiological electron carrier in vivo) under hydrogen. The same observations were also noted with industrial effluent. Collectively these findings suggest that in vitro platinum reduction is mediated by hydrogenase with a concerted action of cytochrome C₃ required to shuttle the electron from hydrogenase.
- Full Text:
- Date Issued: 2003
A comparative photostability study of four propyl piperzine-substituted phenothiazines
- Authors: Drummond, Patricia Mary
- Date: 1997
- Subjects: Phenothiazine
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3756 , http://hdl.handle.net/10962/d1003234 , Phenothiazine
- Description: Four structurally related phenothiazines available in South Africa in a variety of dosage forms and as fine chemicals were investigated to ascertain whether their structural differences in terms of the 2-chloro-/ trifluoromethyl-substituents on the phenothiazine nucleus and the methyl-/ ß-hydroxethyl groups on the piperazine ring accouning for the differences in pharmacological activity can be correlated with their photostability².The four propyl piperazine-substituted derivatives are ranked in the following decreasing order of neuroleptic activity: fluphenazine> trifluoperazine> perphenazine > rochlorperazine. In order to assess their photostability an HPLC method was developed and validated for linearity, accuracy and precision, selectivity, limit of detection and quantitation and ruggedness. Preliminary solution photostudies under controlled light conditions (UV, sunlight, fluorescent light) indicated that the rate of degradation followed first-order kinetics with perphenazine the most susceptible to.photodegradation under all light conditions studied. In vitro and in vivo metabolism yielding the 5-sulphoxide and its reported presence on decomposition of the phenothiazines25 led to the development of a synthetic procedure suitable for the sutphoxides of all four derivatives based on the method proposed by Owens et al. in order to provide standards for comparison in the photostudies⁷. Since ICH regulations require that impurities> 0.1 % are examined and identified⁷⁴ and semi-preparative isolation of photoproducts proved unsuccessful, LC-MS having been well documented for structural.elucidation⁷⁵ ⁷⁵ ⁷⁶ ⁷⁷ was used to characterize solution (UV, sunlight, fluorescent light) and preliminary solid (UV) photostudies. The chloroderivatives underwent dechlorination and sulphoxidation with subsequent photosubstitution in the case of prochlorperazine to yield the 2-hydroxy derivative and sulphoxidation of the dechloro-derivative of perphenazine. The sulphoxides of both trifluoperazine and fluphenazine were formed with further oxidation to the respective sulphones occurring. Preliminary solid state (UV) photostudies showed fluphenazine to be the least stable with 30.71 % degradation as opposed to 7.57% for prochlorperazine, 4.28% for perphenazine and 7.10% for trifluoperazine witn sulphoxidation observed to be. the major degradation pathway. Since in vitro metabolism of perazine derivatives is reported to occur via N-oxidation, N-demethylation, sulphoxidation and aromatic hydroxylation¹⁸ it does appear that there is some correlation between metabolic and photoproducts. However the fact that solution (UV) photostudies indicates trifluoperazine to be the most and perphenazine the least stable does not concur with the proposed order of pharmacological activity.
- Full Text:
- Date Issued: 1997
- Authors: Drummond, Patricia Mary
- Date: 1997
- Subjects: Phenothiazine
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3756 , http://hdl.handle.net/10962/d1003234 , Phenothiazine
- Description: Four structurally related phenothiazines available in South Africa in a variety of dosage forms and as fine chemicals were investigated to ascertain whether their structural differences in terms of the 2-chloro-/ trifluoromethyl-substituents on the phenothiazine nucleus and the methyl-/ ß-hydroxethyl groups on the piperazine ring accouning for the differences in pharmacological activity can be correlated with their photostability².The four propyl piperazine-substituted derivatives are ranked in the following decreasing order of neuroleptic activity: fluphenazine> trifluoperazine> perphenazine > rochlorperazine. In order to assess their photostability an HPLC method was developed and validated for linearity, accuracy and precision, selectivity, limit of detection and quantitation and ruggedness. Preliminary solution photostudies under controlled light conditions (UV, sunlight, fluorescent light) indicated that the rate of degradation followed first-order kinetics with perphenazine the most susceptible to.photodegradation under all light conditions studied. In vitro and in vivo metabolism yielding the 5-sulphoxide and its reported presence on decomposition of the phenothiazines25 led to the development of a synthetic procedure suitable for the sutphoxides of all four derivatives based on the method proposed by Owens et al. in order to provide standards for comparison in the photostudies⁷. Since ICH regulations require that impurities> 0.1 % are examined and identified⁷⁴ and semi-preparative isolation of photoproducts proved unsuccessful, LC-MS having been well documented for structural.elucidation⁷⁵ ⁷⁵ ⁷⁶ ⁷⁷ was used to characterize solution (UV, sunlight, fluorescent light) and preliminary solid (UV) photostudies. The chloroderivatives underwent dechlorination and sulphoxidation with subsequent photosubstitution in the case of prochlorperazine to yield the 2-hydroxy derivative and sulphoxidation of the dechloro-derivative of perphenazine. The sulphoxides of both trifluoperazine and fluphenazine were formed with further oxidation to the respective sulphones occurring. Preliminary solid state (UV) photostudies showed fluphenazine to be the least stable with 30.71 % degradation as opposed to 7.57% for prochlorperazine, 4.28% for perphenazine and 7.10% for trifluoperazine witn sulphoxidation observed to be. the major degradation pathway. Since in vitro metabolism of perazine derivatives is reported to occur via N-oxidation, N-demethylation, sulphoxidation and aromatic hydroxylation¹⁸ it does appear that there is some correlation between metabolic and photoproducts. However the fact that solution (UV) photostudies indicates trifluoperazine to be the most and perphenazine the least stable does not concur with the proposed order of pharmacological activity.
- Full Text:
- Date Issued: 1997
Progestin receptor heterogeneity in a breast cancer cell line
- Authors: Levy, Anita Rochelle
- Date: 1995
- Subjects: Breast -- Cancer , Hormone receptors , Cancer cells -- Growth -- Regulation , Progesterone -- Receptors , Cellular control mechanisms
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4039 , http://hdl.handle.net/10962/d1004100 , Breast -- Cancer , Hormone receptors , Cancer cells -- Growth -- Regulation , Progesterone -- Receptors , Cellular control mechanisms
- Description: Anti-oestrogens act via the oestrogen receptor whether they compete with the hormone for binding to the receptor and therefore interfere with DNA binding or inhibit transcriptional activity. These receptors exist as a large 85 complex and/or a small 45 form on sucrose density gradients. High performance ion-exchange chromatography has confirmed that the oestrogen and progestin complex is present in various isoforms. Progestin receptor heterogeneity could be influenced by the presence of oestrogens and anti-oestrogens in the culture media of hormone-dependent neoplastic cells. Cell culture methods offer the opportunity to test effects of specified components in repeated experiments on a homogeneous population of cells. MCF-7 and T47-D human breast cancer cell lines were conditioned to grow in a serum-free environment. There was no difference in cell proliferation rates, nor in their oestrogen or progestin receptor levels when compared to the same cells grown in conventional media. Receptors were present mainly in the large molecular 85 form. Both the MCF-7 and T47-D breast cancer cells showed an increase in proliferation rate with the addition of oestrogen or diethylstilbestrol. There was a corresponding loss of progestin receptor levels and an alteration in the high performance ion-exchange isoforms. Flow cytometry confirmed differences in the S-phase components of the cells following exposure to oestrogens. The proliferation rates of the cell lines as well as their progestin receptor levels decreased when treated with tamoxifen or the hydroxylated tamoxifen. There were marked changes on high performance ion-exchange chromatography profiles. DNA ploidy and S-phase showed signs of toxicity and there was an increase in cellular debris. The MCF-7 and T47-D human breast cancer cell line retained response to antioestrogen saturation.
- Full Text:
- Date Issued: 1995
- Authors: Levy, Anita Rochelle
- Date: 1995
- Subjects: Breast -- Cancer , Hormone receptors , Cancer cells -- Growth -- Regulation , Progesterone -- Receptors , Cellular control mechanisms
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4039 , http://hdl.handle.net/10962/d1004100 , Breast -- Cancer , Hormone receptors , Cancer cells -- Growth -- Regulation , Progesterone -- Receptors , Cellular control mechanisms
- Description: Anti-oestrogens act via the oestrogen receptor whether they compete with the hormone for binding to the receptor and therefore interfere with DNA binding or inhibit transcriptional activity. These receptors exist as a large 85 complex and/or a small 45 form on sucrose density gradients. High performance ion-exchange chromatography has confirmed that the oestrogen and progestin complex is present in various isoforms. Progestin receptor heterogeneity could be influenced by the presence of oestrogens and anti-oestrogens in the culture media of hormone-dependent neoplastic cells. Cell culture methods offer the opportunity to test effects of specified components in repeated experiments on a homogeneous population of cells. MCF-7 and T47-D human breast cancer cell lines were conditioned to grow in a serum-free environment. There was no difference in cell proliferation rates, nor in their oestrogen or progestin receptor levels when compared to the same cells grown in conventional media. Receptors were present mainly in the large molecular 85 form. Both the MCF-7 and T47-D breast cancer cells showed an increase in proliferation rate with the addition of oestrogen or diethylstilbestrol. There was a corresponding loss of progestin receptor levels and an alteration in the high performance ion-exchange isoforms. Flow cytometry confirmed differences in the S-phase components of the cells following exposure to oestrogens. The proliferation rates of the cell lines as well as their progestin receptor levels decreased when treated with tamoxifen or the hydroxylated tamoxifen. There were marked changes on high performance ion-exchange chromatography profiles. DNA ploidy and S-phase showed signs of toxicity and there was an increase in cellular debris. The MCF-7 and T47-D human breast cancer cell line retained response to antioestrogen saturation.
- Full Text:
- Date Issued: 1995
Application of high-performance liquid chromatography for the analysis and pharmocokinetics of mephenoxalone
- Authors: Van der Westhuizen, Fiona
- Date: 1988 , 2013-03-06
- Subjects: High performance liquid chromatography , Central nervous system depressants
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3810 , http://hdl.handle.net/10962/d1004385 , High performance liquid chromatography , Central nervous system depressants
- Description: Mephenoxalone is a mild central nervous system depressant with activity resembling that of meprobamate. Since its introduction in 1961 mephenoxalone has been used as an anxiolytic and as a muscle relaxant, although the latter effect is weak. Preliminary studies on the absorption and disposition of mephenoxalone have been conducted in beagle dogs but no pharmacokinetic data from human studies have been reported, except for a single study in which the biotransformation products present in human urine were identified. Methods presently available for the determination of mephenoxalone in biological fluids lack the sensitivity, specificity and precision required for detailed pharmacokinetic studies. In this study, a rapid, sensitive, precise reverse-phase high-performance liquid chromatographic method with ultraviolet detection at 200nm was employed for the determination of mephenoxalone in biological fluids. Serum and urine samples were prepared for chromatographic analysis using simple liquid-liquid extraction techniques. The application of the assay to pharmacokinetic studies in humans is presented. After administration of a single oral dose of 400mg mephenoxalone dispersed in 150ml water to six young, healthy volunteers, the compound was rapidly absorbed with the peak concentration of 8μg/ml occurring after about 1 hour. The elimination half-life was approximately 3 hours. The drug was extensively metabolized with only about 1 percent of the administered dose being excreted unchanged in the urine after 24 hours. The bioavailability of a newly developed mephenoxalone-containing tablet was also investigated. The drug was absorbed more rapidly from the tablet than from the dispersed dose. This was attributed to a shorter in vivo dissolution time on the basis of in vitro tests, but this effect is not expected to be clinically significant. In addition, two human urinary metabolites of mephenoxalone were identified as unconjugated hydroxylated derivatives using thermospray HPLC-mass spectrometry. The plasma protein-binding properties of mephenoxalone were also investigated.
- Full Text:
- Date Issued: 1988
- Authors: Van der Westhuizen, Fiona
- Date: 1988 , 2013-03-06
- Subjects: High performance liquid chromatography , Central nervous system depressants
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3810 , http://hdl.handle.net/10962/d1004385 , High performance liquid chromatography , Central nervous system depressants
- Description: Mephenoxalone is a mild central nervous system depressant with activity resembling that of meprobamate. Since its introduction in 1961 mephenoxalone has been used as an anxiolytic and as a muscle relaxant, although the latter effect is weak. Preliminary studies on the absorption and disposition of mephenoxalone have been conducted in beagle dogs but no pharmacokinetic data from human studies have been reported, except for a single study in which the biotransformation products present in human urine were identified. Methods presently available for the determination of mephenoxalone in biological fluids lack the sensitivity, specificity and precision required for detailed pharmacokinetic studies. In this study, a rapid, sensitive, precise reverse-phase high-performance liquid chromatographic method with ultraviolet detection at 200nm was employed for the determination of mephenoxalone in biological fluids. Serum and urine samples were prepared for chromatographic analysis using simple liquid-liquid extraction techniques. The application of the assay to pharmacokinetic studies in humans is presented. After administration of a single oral dose of 400mg mephenoxalone dispersed in 150ml water to six young, healthy volunteers, the compound was rapidly absorbed with the peak concentration of 8μg/ml occurring after about 1 hour. The elimination half-life was approximately 3 hours. The drug was extensively metabolized with only about 1 percent of the administered dose being excreted unchanged in the urine after 24 hours. The bioavailability of a newly developed mephenoxalone-containing tablet was also investigated. The drug was absorbed more rapidly from the tablet than from the dispersed dose. This was attributed to a shorter in vivo dissolution time on the basis of in vitro tests, but this effect is not expected to be clinically significant. In addition, two human urinary metabolites of mephenoxalone were identified as unconjugated hydroxylated derivatives using thermospray HPLC-mass spectrometry. The plasma protein-binding properties of mephenoxalone were also investigated.
- Full Text:
- Date Issued: 1988
The effect of sewage on the distribution of seaweed at the Bats Cave east bank sewage outfall in East London, South Africa
- Authors: Klenk, Theodore Charles
- Date: 1985 , 2013-03-13
- Subjects: Marine algae -- Dispersal -- South Africa -- East London , Sewage disposal in the ocean -- South Africa -- East London , Plants -- Effect of sewage on
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4238 , http://hdl.handle.net/10962/d1004768 , Marine algae -- Dispersal -- South Africa -- East London , Sewage disposal in the ocean -- South Africa -- East London , Plants -- Effect of sewage on
- Description: In order to determine which seaweeds were unable to survive in the stressed area and how far the effect of the effluent extended along the coast, various methods were applied and carried out over a two-year period between November 1982 and November 1984. Three major long-term studies took place. The first study was to determine the presence or absence of the seaweeds throughout (1) the entire study area and then (2) in areas broken up into sections with known distances from the outfalls. The second method involved statistical evaluations using point intersect methods and photography to produce information to determine species density, diversity, evenness, and to provide the information required to work with a number of ecological equations in the future. The third method incorporated a long-term survey on cleared plots in various sectors of the study area. The recolonization of the plots was recorded over a thirty-week period. (par. 1.1, p. 6-7)
- Full Text:
- Date Issued: 1985
- Authors: Klenk, Theodore Charles
- Date: 1985 , 2013-03-13
- Subjects: Marine algae -- Dispersal -- South Africa -- East London , Sewage disposal in the ocean -- South Africa -- East London , Plants -- Effect of sewage on
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4238 , http://hdl.handle.net/10962/d1004768 , Marine algae -- Dispersal -- South Africa -- East London , Sewage disposal in the ocean -- South Africa -- East London , Plants -- Effect of sewage on
- Description: In order to determine which seaweeds were unable to survive in the stressed area and how far the effect of the effluent extended along the coast, various methods were applied and carried out over a two-year period between November 1982 and November 1984. Three major long-term studies took place. The first study was to determine the presence or absence of the seaweeds throughout (1) the entire study area and then (2) in areas broken up into sections with known distances from the outfalls. The second method involved statistical evaluations using point intersect methods and photography to produce information to determine species density, diversity, evenness, and to provide the information required to work with a number of ecological equations in the future. The third method incorporated a long-term survey on cleared plots in various sectors of the study area. The recolonization of the plots was recorded over a thirty-week period. (par. 1.1, p. 6-7)
- Full Text:
- Date Issued: 1985
Geology of the central and southern domains of the Koras Group, northern Cape Province
- Sanderson-Damstra, Christopher Gerald
- Authors: Sanderson-Damstra, Christopher Gerald
- Date: 1983 , 2013-04-17
- Subjects: Geology -- South Africa -- Cape of Good Hope
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5017 , http://hdl.handle.net/10962/d1006203 , Geology -- South Africa -- Cape of Good Hope
- Description: The Central and Southern Domains of the Koras Group, situated on the Doornberg Lineament, are the structurally preserved remnants of a once more widespread late-syntectonic cover sequence. Detailed examination of the field relationships, lithology and petrography together with new geochemical data (30 analyses) has resulted in the proposal of a new geological succession consisting mainly of two cycles of bimodal basaltic-rhyolitic volcanics with interbedded, immature conglomerates and lithic greywackes. These two cycles, named the Boomrivier and Leeudraai Formations, are overlain by the immature, polymictic orthoconglomerates and red arkosic sandstones of the Kalkpunt Formation. The first volcanic cycle commenced with the Lambrechtsdrif basaltic andesites and was followed, after a short hiatus, by the Swartkopsleegte rhyodacites. The second cycle comprises the Rouxville basalts and basaltic andesites and the Swartkop and Kenilworth rhyolites. Field evidence suggests that eruption of the rhyolitic and basaltic volcanics in the second cycle was contemporaneous. Geochemically, the volcanics can be classified as an "average-K" to high-K, tholeiitic, subalkaline association which exhibits general similarities to other Southern African bimodal associations e.g., the tholeiitic lavas of the Wilgenhoutsdrif Group. The Koras Group is petrologically similar to the Sinclair Sequence which is presently considered to be its coeval equivalent, but the dominantly calc-alkaline character of the Sinclair rocks distinguishes them from the dominantly tholeiitic Koras lavas. In a short literature review, the four main hypotheses for the petrogenesis of bimodal associations: liquid immiscibility, crystal fractionation, two-stage partial melting and separate magma sources, are described and the most feasible explanation for the origin of the Koras lavas is thought to be a "separate magma source" hypothesis in which two cycles of mantle-derived basalts and crustal-derived rhyolites were produced in a zone of high heat flow and erupted in an area of crustal weakness. The middle- or late-Proterozoic Koras Group was formed during unstable tectonic conditions, in a depositional setting that was probably controlled by late folding of the underlying pre-Koras sequences as well as the major strike-slip movement and subordinate dip-slip faulting in the Doornberg Lineament.
- Full Text:
- Date Issued: 1983
- Authors: Sanderson-Damstra, Christopher Gerald
- Date: 1983 , 2013-04-17
- Subjects: Geology -- South Africa -- Cape of Good Hope
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5017 , http://hdl.handle.net/10962/d1006203 , Geology -- South Africa -- Cape of Good Hope
- Description: The Central and Southern Domains of the Koras Group, situated on the Doornberg Lineament, are the structurally preserved remnants of a once more widespread late-syntectonic cover sequence. Detailed examination of the field relationships, lithology and petrography together with new geochemical data (30 analyses) has resulted in the proposal of a new geological succession consisting mainly of two cycles of bimodal basaltic-rhyolitic volcanics with interbedded, immature conglomerates and lithic greywackes. These two cycles, named the Boomrivier and Leeudraai Formations, are overlain by the immature, polymictic orthoconglomerates and red arkosic sandstones of the Kalkpunt Formation. The first volcanic cycle commenced with the Lambrechtsdrif basaltic andesites and was followed, after a short hiatus, by the Swartkopsleegte rhyodacites. The second cycle comprises the Rouxville basalts and basaltic andesites and the Swartkop and Kenilworth rhyolites. Field evidence suggests that eruption of the rhyolitic and basaltic volcanics in the second cycle was contemporaneous. Geochemically, the volcanics can be classified as an "average-K" to high-K, tholeiitic, subalkaline association which exhibits general similarities to other Southern African bimodal associations e.g., the tholeiitic lavas of the Wilgenhoutsdrif Group. The Koras Group is petrologically similar to the Sinclair Sequence which is presently considered to be its coeval equivalent, but the dominantly calc-alkaline character of the Sinclair rocks distinguishes them from the dominantly tholeiitic Koras lavas. In a short literature review, the four main hypotheses for the petrogenesis of bimodal associations: liquid immiscibility, crystal fractionation, two-stage partial melting and separate magma sources, are described and the most feasible explanation for the origin of the Koras lavas is thought to be a "separate magma source" hypothesis in which two cycles of mantle-derived basalts and crustal-derived rhyolites were produced in a zone of high heat flow and erupted in an area of crustal weakness. The middle- or late-Proterozoic Koras Group was formed during unstable tectonic conditions, in a depositional setting that was probably controlled by late folding of the underlying pre-Koras sequences as well as the major strike-slip movement and subordinate dip-slip faulting in the Doornberg Lineament.
- Full Text:
- Date Issued: 1983
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