Electronic Theses and Dissertations (PhDs)
Permanent URI for this collectionhttps://hdl.handle.net/10539/38011
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Item Late Triassic to Early Jurassic ecology: An insight into diet and trophic levels using non-traditional Ca isotopes(University of the Witwatersrand, Johannesburg, 2023-07) Davechand, Priyanka; Bybee, Grant; Choiniere, JonahThe diet and trophic structuring of organisms in deep time is poorly understood, making comparison of ancient and modern ecosystems challenging. Proxy data (e.g., dental morphology, jaw muscle reconstruction) remain the most common mode of palaeodietary inference, but the correlative strength of these proxies remains untested due to a lack of direct evidence and an incomplete sampling of palaeobiodiversity. These major challenges in palaeodietary reconstruction can be overcome using novel geochemical markers in fossilised tooth enamel, which provide direct evidence of palaeodiet and trophic relationships. Traditional stable isotopes of carbon, oxygen, and nitrogen have been used in the past to infer palaeodiets, but these elements are susceptible to diagenetic alteration during fossil preservation and require large sample amounts for assays. In contrast, non-traditional calcium (δ44/42Ca) isotopes are less susceptible to diagenesis and require significantly smaller sample amounts. This, together with the fractionation that Ca isotopes undergo as a bio-essential element, allows δ44/42Ca to be utilised on a broad range of palaeontological questions including assessing dietary range and trophic level. The diverse ecosystems of the Elliot Formation (Karoo Supergroup) in South Africa are represented by abundant fossils of a variety of reptilian and mammalian stem lineages that coexisted during the latest Triassic–earliest Jurassic interval (218–190 Ma). The broad range of body sizes, inferred dietary preferences, and phylogenetic positions make the Elliot palaeoecosystems an ideal natural laboratory in which to apply palaeodietary isotopic tools. This dissertation aims to assess the palaeotrophic divisions of the Elliot Formation vertebrates using non-traditional δ 44/42Ca isotopes. This research uses ion-exchange chromatography on vertebrate tooth enamel to assess the palaeodietary preferences of Elliot Formation reptilian and mammalian lineages. To obtain these data, existing techniques for sample preparation of non-traditional δ 44/42Ca isotopes were modified and optimised at the Wits Isotope Geoscience Laboratory (WIGL) at the University of the Witwatersrand. δ 44/42Ca analysis was conducted on a variety of specimens across a broad range of amniote lineages, ranging from: dinosaurs such as presumed herbivorous sauropodomorphs Massospondylus and Aardonyx, the presumed omnivorous ornithischian (Lesothosaurus and Heterodontosaurus), and the presumed carnivorous theropod Megapnosaurus; to cynodont therapsids (Tritylodon, Pachygenelus and Scalenodontoides); to pseudosuchians such as the crocodylomorphs Protosuchus and Orthosuchus and earlier branching taxa (‘rauisuchians’ and poposauroids). A leaching procedure was also tested to ensure that the results produced were not influenced by diagenetic biases. Once consistent and reproducible methods were finalised, column chemistry and Multicollector-Inductively Coupled Plasma Mass Spectrometery (MC-ICPMS) analysis was conducted on the different Karoo-aged specimens. There are various outcomes from this dissertation. One important outcome was the optimisation of time for Ca separation using ion-exchange chromatography. This allowed for a shorter chemical preparation time and increased the number of analyses completed per session. Another improvement of the method was that the leaching procedure can be used to control for any diagenetic biases by removing secondary calcite in samples as old as those from the Triassic–Jurassic period. Elliot taxa were then analysed, and significant differences were found between δ 44/42Ca values of large carnivorous pseudosuchians (‘rauisuchians’; -0.45 ‰ to -1.17 ‰) and co occurring herbivorous sauropodomorph genera (-0.26 ‰ to -0.69 ‰). These results indicated that non-traditional δ 44/42Ca isotopes can be used to understand trophic structures and palaeodiets in ecosystems at least 210 million years old. We also found that while some taxa had δ44/42Ca isotope values in-line with their presumed diets, other taxa had more diverse diets than initially presumed. δ 44/42Ca-enriched values in this study provide evidence for herbivory in crocodylomorph and the oldest theropod. There is also a possibility of an omnivorous diet for presumed herbivorous Lesothosaurus as the δ 44/42Ca values are relatively depleted to other herbivores. In addition to diet, calcium plays a major role in the formation of reptilian eggs and there are documented changes in δ 44/42Ca values during the reproductive cycle. To assess this in a living system, Crocodylus niloticus, was analysed to understand if δ 44/42Ca could be used to identify the difference in sex based on the δ 44/42Ca values. No isotopic differences were found between the juvenile male and female Crocodylus niloticus samples. Testing these important ecological principles in temporally constrained formations allows us to understand the historical nature of biodiversity changes, especially across periods when environments on Earth were experiencing extreme conditions. The ability to determine factors such as palaeodiet and palaeotrophic range will enable the development and improvement of palaeoecological analysis. This research presents the first ever δ 44/42Ca values on Karoo-aged vertebrate fossils and will have a large impact on how palaeoecological reconstruction is conducted in the future of palaeosciences.Item Naturally occurring asbestos (NOA) and asbestos contamination of the environment: Implications for in-situ risk assessment and rehabilitation(University of the Witwatersrand, Johannesburg, 2023-01) Schapira, Jessica Shaye; Bolhar, Robert; Master, Sharad; Rumbold, KarlThe risk associated with asbestos minerals is an enduring global concern, especially with regards to exposure at the sources. The risks connected to exposure in their natural contexts (i.e., derelict mine sites and naturally occurring asbestos) form the subject of this study. These sites are plentiful throughout Southern Africa (and Africa) and are considered as unconfined, thereby constituting large environmental and human health risks. Asbestos in these settings is not inherently hazardous unless dispersed from its sources into environmental systems, such as the atmosphere, where it may be inhaled. Compared to occupational asbestos exposure, environmental sources present unique challenges with respect to their potential risks. Literature focused on these sites is lacking and without extensive knowledge the risks remain greatly unknown, and thus asbestos site assessment frameworks are imperative. South Africa, with its geological richness, allows for all aspects of environmental asbestos to be studied in its natural context. In this research, mineral fibres from derelict asbestos mine sites were characterised mineralogically and geochemically to identify and assess their human health hazard potential, to define the degree of toxicity and to determine the potential negative environmental effects. High concentrations of heavy metals, including copper, iron, magnesium, manganese and zinc detrimental to human health and environmental functioning were measured in these fibrous minerals using X-ray fluorescence (XRF) . The chemical stability of four asbestos minerals was studied using batch isothermal dissolution tests in acidic solutions and their stability determined as follows: chrysotile < crocidolite < amosite < anthophyllite. Significant inferences can be made regarding the persistence of asbestos particles in their natural environments from dissolution kinetics mechanisms. The mineralogical, geochemical, and microbiological characterisation of solid asbestos mine waste rock substrates indicate that their properties, such as low macro and micronutrients and lack of properties of true soils, strongly alkaline pH and low to zero microbial abundance and diversity present significant challenges to rehabilitation strategies. Such parameters are identified as important baseline conditions that need to be considered prior to rehabilitation implementation, if long-term, self-sustaining ecological restoration is to be achieved on these sites. Present bio-solutions to ensure asbestos mine land rehabilitation success are discussed and the potential of using available agronomic bio-fertilisers (microbial strain Pseudomonas fluorescens) is examined. The growth-based assays indicate that this micro-organism is suitable for an environmental biotechnology applied to ecosystem restoration of asbestos-mining lands. Naturally Occurring Asbestos (NOA) occurrences are highly dependent upon the geological conditions, and understanding these in a large variety of settings may allow the development of predictive strategies necessary for in situ identification and hazard assessment required for health risk mitigation in the context of mining and other geologically disruptive activities. A variety of natural asbestos rock samples was examined, showing how geological databases relevant for predicting natural occurrences of asbestos provide baseline data required for mitigating asbestos exposure risks.Item Late Quaternary Palynological Studies at Lake St Lucia, KwaZulu-Natal(University of the Witwatersrand, Johannesburg, 2023-08) Effiom, Angela Charles; Neumann, Frank; Bamford, MarionPalynological studies were done on lacustrine sediments deposited during the last ~6300 and about ~2000 cal yrs BP in Mkhuze Swamp, which drains into the most northern part of Lake St Lucia located in the Indian Ocean Coastal Belt Biome of KwaZulu-Natal, eastern South Africa. The aim was to reconstruct the past vegetation and to infer past climate fluctuations as well as human disturbances to complement growing evidence from other disciplines about these questions in the area. Following standard palynological methods, samples from two cores Mkhuze River Delta (MKD-1, long core) and Mkhuze swamp (MK24-1, short core) were extracted and analyzed. Palynological results for both cores show a dominance of Poaceae (20-90%) suggesting a strong influence of grassy woodland savanna. Spirostachys pollen dominated the arboreal spectra of the pollen profile in MK24-1, but it dominated the arboreal pollen spectra for the last 2600 cal yrs BP in MKD-1 as Podocarpus pollen dominated the arboreal spectra from 6300-2600 cal yrs BP indicating a change from a forested environment to a more open woodland environment. The results also show that the mid Holocene was humid with high precipitation and high sea level while the late Holocene was warm, dry with Marine influence (more sea water flowing into the lake due to high evaporation and low fresh water supply caused by drought). Similar pollen fluctuations were observed in records from Lakes Eteza and Sibaya also located within the Indian Ocean Coastal Belt Biome. The presence of Pinus pollen at the top of the profiles suggests the onset of European settlement when pines were introduced for timber production. Other published pollen records from the region in the last ~7000 cal BP show a general trend from a mesic forested environment towards an open woodland environment with grasses which is due to climate change.