School of Earth Sciences - Theses
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ItemCovariances in the weather and the influence on an Australian large-scale renewable electricity system( 2014)Sometime in the future Australia’s demand for electricity will undoubtedly need to rely on significant amounts of Renewable Electricity (RE). Fossil fuels are inherently non-renewable and their dwindling supply will force investment in alternatives. There is therefore a need to research how such increased penetrations of RE resources will be managed. Installed across large areas, a National Electricity Market (NEM) with increased contributions from RE will be affected by large-scale meteorological variability. The synoptic scale (100s-1,000s of km and days-weeks) weather systems are of particular interest. This thesis examines how synoptic scale weather variability might affect a future highly RE dependent Australia using two approaches. Approach one (Part 1 of the thesis) identifies the common synoptic scale weather systems from a reanalysis data set (ERA-Interim) and then analyses the availability of wind and solar associated with each weather type. Approach two (Part 2) utilises data from a regional model (ACCESS-R) as part of an electricity model that maximises the contribution of wind and solar electricity in meeting the demand of Australia. The influence of the weather systems identified in Part 1 on the optimised electricity network is then analysed. Part 1 of this thesis utilises the European Centre for Medium Range Weather Forecasting (ECMWF) reanalysis product ERA-Interim from 1989-2009 and for the Austral region (6S,105E) → (49.5S,165E). The Self-Organising Map (SOM) technique is then used to identify commonly occurring features in the ERA-Interim Mean Sea-Level Pressure (MSLP) field. The SOM technique converts the time series of MSLP to a time series of commonly occurring MSLP patterns, or weather types. The weather types are then analysed for their tendency to be associated with either high or low wind and solar potential. Some autumnal MSLP patterns are shown to be associated with very low wind speeds and solar irradiance for most of the Australian continent, while other summertime patterns show good potential for extracting wind and solar electricity. Following this an analysis of just the wind field demonstrates that decorrelation in the wind field is reached at a distance of approximately 1,300km. Part 2 of this thesis focuses on optimising renewable electricity capacity to meet electrical demand, using data from the Bureau of Meteorology’s high resolution regional weather model, ACCESS-R, for the period 2010-2011. The ACCESS-R data, in tandem with electrical demand data from the Australian Electricity Market Operator and a Genetic Algorithm, are utilised to investigate the influence of synoptic scale variability on a largely RE-based network. Wind and solar installations from locations across the ACCESS-R grid are optimally placed to maximise their contribution to meeting the electrical demand of 2010-2011. A gas-fired back-up system is deployed to cover moments when the combination of wind and solar cannot meet demand. The gas usage is made expensive to minimise its use, yet it is found that gas is still needed throughout the 2010-2011 period to cover moments when both the wind and solar are low. An investigation is then undertaken to determine any large-scale links to the minima in renewable generation. The common weather types identified in Part 1 are utilised in Part 2. By assigning SOM weather types to the 2010-2011 period it is shown that some regimes either adversely or favourably affect the net output of the optimised system. In particular, a late autumn and a summer weather type are shown to be significantly associated with very low RE output. The persistence and re-occurrence of low RE events shows that most episodes of low RE last for less than six hours and such low RE events have a mean return period of more than a week. Increasing the cost of transmission results in installed RE capacity contracting to four large wind stations and it is shown that the NEM region exhibits four distinct wind regimes. The wind regimes are highly uncorrelated and the minimum distance between regime locations reflects an approximate, but identical to Part 1, optimisation-based decorrelation length of 1,400km. In combination, Parts 1 and 2 of this thesis illustrate some of the issues that a future high penetration RE network might need to overcome. Knowledge of the influence of detrimental/favourable weather phenomena will be critical when designing and/or maintaining a large-scale renewable electricity network for Australia—in particular, knowledge of the decorrelation length-scale in the wind field.
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ItemBiogeochemical arsenic cycling in the hydrothermal acid-sulfide springs at Waiotapu, New Zealand: implications for the evolution of arsenic resistance( 2014)Active acid-sulfide hot springs provide modern analogs for the geothermal systems of the early Earth where microbial metal(loid) resistance may have first evolved. One metal(loid) that potentially presented a critical geochemical challenge to the earliest biological processes is arsenic, present at high concentrations in the hot springs at Waiotapu on the North Island of New Zealand. Particularly of interest is the moderately acidic sulfidic Champagne Pool that features dissolved arsenic concentrations of up to 4.2 mg L-1. The biogeochemical arsenic cycle in Champagne Pool follows reaction paths that are not yet fully understood with respect to biotic versus abiotic contributions, but involve strong coupling to the biogeochemical sulfur cycle. In this PhD study, I quantified arsenic species at Champagne Pool via HPLC-ICPMS and detected arsenic oxyanions, arsenic thioanions and methylated arsenic species. Arsenite was the dominant species at Champagne Pool’s inner pool, rim and outflow channel (55% – 75% of total arsenic concentration), with dithio- and trithioarsenates forming 18% – 25% of total arsenic concentration. In the outflow channel, dimethylmonothioarsenate comprised up to 9% of total arsenic concentration, while on the highly siliceous outflow terrace „Artist’s Palette“, thioarsenates were the dominant species at 55% of total arsenic concentration. I also quantified the redox sensitive sulfur species sulfide, thiosulfate, sulfate and elemental sulfur via UV-VIS and HPLC-UV spectrometry. Sulfide and sulfate were measured at their maximum concentration in Champagne Pool and at the adjacent outflow terrace, respectively; whereas sulfite, not quantified in this study, could possible contribute up to 30% to the total sulfur concentration at the individual sites. Elemental sulfur, not included in the sulfur mass balance, reached its measured maximum concentration at the outflow terrace. Phylogenetic analysis of 16S ribosomal RNA genes of the whole microbial community obtained via metagenomic sequencing revealed the dominance of Sulfurihydrogenibium at all sites, with an elevated archaeal population including Thermofilum and Sulfolobus at the rim and outflow channel of Champagne Pool. This analysis revealed several phylotypes closely related to known sulfur oxidizing as well as sulfur reducing microorganisms. Functional gene analysis linked sulfur metabolizing genes to sulfur speciation results, supporting the potential for microbially mediated sulfur-dependent transformation of arsenite to thioarsenate species. Metagenomic analysis revealed genes encoding for the arsenate reductase ArsC at all sites, which, given the wide thioarsenate species distribution, suggests a possible early evolution for arsenate resistance in the absence of oxygen. Furthermore, the absence of the arsenite oxidase encoding gene aio at all sites suggests the priority of an arsenite detoxification mechanism over the energy conserving arsenite oxidation. Finally, the detection of methylated arsenic, a solely biogenic arsenic species, only at the outflow channel, and in conjunction with a significant increase in Aquificaceae, indicates a potential role for methyl transferases from this lineage in the evolution of thermophilic arsenic resistance. My PhD study highlights microbial contributions to coupled arsenic and sulfur cycling in an acid-sulfide hot spring that have implications for understanding the evolution of microbial arsenic resistance in sulfidic geothermal environments.
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ItemAerosol contributions to speleothem geochemistry( 2014)There is developing interest in cave aerosols due to the increasing awareness of their impacts on the cave environment and speleothems. This study presents the first multidisciplinary investigation into cave aerosols and their potential contribution to speleothem geochemistry. Aerosols are shown to be sourced from a variety of external emission processes, and transported into cave networks. Both natural (marine sea-spray, terrestrial dust) and anthropogenic (e.g. vehicle emissions) aerosol emissions are detected throughout caves. Internal cave aerosol production by human disruption has also been shown to be of importance in caves open to the public. Aerosols produced from floor sediment suspension and release from clothing causes short term high amplitude aerosol suspension events. Cave aerosol transport, distribution and deposition are highly variable depending on cave situation. Cave morphology, ventilation, and environmental conditions will influence how aerosols are distributed through cave networks. Aerosol deposition monitoring in Obir Cave, Austria has shown the significance of cave chamber size in aerosol transport, with large open chambers presenting higher levels of deposition. Modern monitoring of suspended aerosol concentrations, CO2 and temperature in Gough’s Cave, Cheddar Gorge have presented a strong relationship with cave ventilation processes. Temporal variations of aerosol levels have demonstrated the ability of aerosol monitoring to record seasonal ventilation shifts, beyond anthropogenic influences. Aerosol minima (based on 24 hours) provide a representation of natural aerosol baseline conditions without diurnal anthropogenic influences. Aerosols have shown a quicker recovery to natural background levels when compared to CO2 and T, making aerosols a sensitive and effective monitoring tool. When used in combination with more established monitoring methods, suspended aerosol monitoring is a beneficial addition to cave environmental studies. Theoretical modelling and calculations based on modern aerosol monitoring have established that aerosol contributions are highly variable. In some instances, modern aerosol supply is sufficient to account for speleothem geochemistry concentrations entirely. Aerosol contributions are of greatest significance under slow growth or hiatus scenarios and high aerosol deposition scenarios. Geochemical and stratigraphical analysis of a flowstone core from Gibraltar has highlighted the importance of hiatus events for future aerosol studies. Hiatus events provide a unique opportunity to investigate the type and amount of aerosol deposition and accumulation. Marine aerosol contributions have been quantified in the Gibraltar flowstone core and account for 18.5% of speleothem Sr. Sr isotopic analysis has confirmed the significance of marine aerosol contributions. Flowstone analysis has also demonstrated the ability of speleothems to record shifts in the supply of highly radiogenic terrestrial dust. Bio-aerosol deposits and bacterial colonisation have been identified as a potential source of trace element bioaccumulation and flowstone coloration in Yarrangobilly Caves, Australia. Bio-aerosols have shown to be deposited throughout cave networks. Inorganic aerosol deposition may provide a nutrient supply to cave surfaces allowing for, and sustaining microbial colonisation.
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ItemNeoproterozoic seas: ocean chemistry and marine carbonate mineralogy( 2014)The step-wise oxygenation of the ocean-atmosphere system is arguably one of the most profound processes in Earth history, affecting most surficial Earth processes. The last major oxygenation of the oceans is believed to have occurred in the Neoproterozoic Oxygenation Event (~800-540 Ma), and is implicated as a trigger for the rise of animal life. However, the timing of this event is not well constrained, both due to geochronological problems with Neoproterozoic stratigraphy; and because of the inherent uncertainty in ocean oxygenation proxies. Furthermore, there is now evidence for a more complex Neoproterozoic ocean chemical history, including return to strongly anoxic and ferruginous conditions. An additional complication in the understanding of Precambrian marine environments is the abundance of dolomite in Proterozoic successions. A recently discovered series of dolomitic reef complexes in the Neoproterozoic Adelaide Fold Belt, Australia, and Otavi Belt, Namibia, improve our understanding of Precambrian marine conditions. Stratigraphic and petrological analysis suggests that synsedimentary marine dolomite precipitation was pervasive within these reefs. Newly described dolomite cements have optical properties, chemical zonation and cathodoluminescent characteristics indicating that they were direct marine precipitates. Dolomite precipitation during marine diagenesis in these reef complexes suggests that the oceans of the Cryogenian were chemically different to those of the Phanerozoic. Marine dolomite precipitation appears to be linked to anoxic, magnesium-rich ocean conditions. These newly documented primary marine dolomite cements preserve information about conditions in the parent seawater via their petrographic properties and geochemistry. Being constrained by sedimentology, carbonate geochemistry provides a window into Cryogenian ocean chemistry and structure. Geochemical results reveal a pronounced chemical stratification where a thin veneer of oxic surface waters existed above a peritidal redoxcline with anoxic, strongly ferruginous seawater at depth. These conditions describe a ferro-sulfidic ocean and encompass some of the most extreme anoxia yet documented during the late Precambrian. A return to Archean-like ocean conditions at this time suggests large-scale disruption of the ocean system during the Neoproterozoic. These conditions may be linked to extreme climatic fluctuations at this time, perhaps induced by ocean stratification in this Neoproterozoic ‘Stagnant Earth’. When analysed in stratigraphic framework, variations in carbonate mineralogy provide a record of ocean oxygenation during the Neoproterozoic. New sedimentological and stratigraphic constraints for the Namibian Otavi Belt provides a context for this variation and has also led to the discovery of new Cryogenian reef complexes. When correlated with the Adelaidian succession, the distribution of marine cements in these sequences reflects changing seawater conditions. Pre-Sturtian, Neoproterozoic oceans precipitated both dolomite and aragonite and developed widespread marine anoxia prior to glaciation. Interglacial Cryogenian oceans were extremely anoxic and ferruginous, with widespread dolomite precipitation. In contrast, late Cryogenian and Ediacaran oceans hosted abundant aragonite precipitation recording a gradual decline in marine dolomitisation. The deepening of the oceanic chemocline during this interval suggests that these seas were likely to have been moderately oxygenated, paving the way for the large-scale radiation of animal life.
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ItemThe petrogenesis of Brazilian kimberlites and kamafugites intruded along the 125° lineament: improved geochemical and geochronological constraints on magmatism in Rondonia and the Alto Paranaiba Igneous Province( 2014)Despite a number of studies, the origin of ultrapotassic magmatism in Brazil remains contentious. In particular, problems relate to the timing of Cretaceous kimberlite and kamafugite magmatism within the Alto Paranaiba Igneous Province (APIP), the origin and relationship between the Cretaceous kimberlites and kamafugites, and the geochemical nature of the Permo-Triassic kimberlite magmatism. Many of these uncertainties arise as a consequence of either the implementation of now superseded analytical techniques or the use of highly altered samples. This study seeks to address these issues by performing state-of-the-art geochemical and geochronological analyses on a number of fresh kimberlite and kamafugite drill core samples situated along the 125° lineament. The first part of the thesis provides a comprehensive geochronological study of Brazilian kimberlites and kamafugites. This is built around a combination of the most recent U/Pb perovskite, Rb-Sr phlogopite, and Ar-Ar phlogopite dating techniques that together provide 33 age estimates, representing 22 separate intrusions, of which 11 are kimberlites and 11 kamafugites. The results are in broad agreement with previously published data, identifying a Permo-Triassic age for the Amazonian kimberlites, and kimberlites and kamafugites of Cretaceous age in the APIP. The new data from this study also support an age decrease from NW to SE within the APIP. However, data from this study suggest that this is not a continuous younging, instead indicating that two distinct magmatic episodes may exist. The data also reveal the presence of an “older” mid Cretaceous cluster (~88 Ma) encompassing Goias and the NW APIP (Southern Goiás and NW Minas Gerais) and a slightly younger Cretaceous cluster (~80 Ma) in the Central/Southern APIP. The importance of these new findings is discussed with reference to previously proposed petrogenetic models and casts doubt on the applicability of the plume-related hypothesis for ultrapossic magmatism in the region. In the second part of the thesis, an in-depth geochemical study of 15 kimberlites and 16 kamafugites from the APIP (27 samples) and Rondonia/Mato Grosso (4 samples) is presented. Bulk rock major and trace element data, together with Nd and Hf isotope determinations are combined with perovskite trace element, Sr and Nd isotope analyses in order to provide a comprehensive geochemical dataset. The elemental and isotopic similarity of the APIP kimberlite to South African transitional kimberlites, the APIP kamafugites to Ugandan and Chinese kamafugites and, for the first time, the Amazonian kimberlites to a mixture of South African Group I and transitional kimberlites is established. The overlapping range in Sr isotopic signatures identified between the APIP kimberlite and kamafugite magmas during previous bulk rock studies is confirmed by in situ perovskite analysis, with APIP kimberlites ranging between 70496 and 0.70596 and APIP kamafugites ranging between 0.70499 and 0.70574. Modelling suggests that this range can not result from contamination and must represent a heterogeneous source component, common in the formation of both rock types. It is argued that the combination of geochemical results is best explained by derivation of both rock types from the heterogeneous subcontinental lithospheric mantle. Kimberlites are believed to have been sourced from carbonated garnet lherzolite whereas the kamafugites were generated from phlogopite and clinopyroxene rich vein assemblages, with small volume MARID type metasomes indicated by the kamafugite Hf signatures. Finally, the geochronological and geochemical information is combined into a petrogenetic model: it is argued that the Cretaceous magmatism is likely not the result of plume heating but is instead a consequence of adiabatic decompression melting of the heterogeneous SCLM caused by extension. In parallel with the study of Brazilian ultrapotassic magmatism the thesis also investigates technical aspects of the U-Pb perovskite dating technique. Using a subset of Indian and Brazilian kimberlite samples, in situ perovskite dating was performed and combined with isotope dilution analysis of the co-magmatic, low uranium phase, titanomagnetite, in an attempt to improve precision of the Tera-Wasserburg regression. The inclusion of the titanomagnetite phase improved precision in all cases and enabled ages to be determined for the Indian samples without recourse to an assumed Stacey-Kramers common Pb value. The investigation also highlights some of the shortcomings associated with using an assumed Stacey-Kramers Pb value for young unradiogenic perovskite samples, whilst also highlighting the circularity of the commonly employed 207Pb correction method.
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ItemGeochronology and geochemistry of Cenozoic volcanism in relation to epithermal gold mineralisation in western Java, Indonesia( 2014)Western Java in Indonesia is a well known gold deposit district that contains a number of world class ore deposits. The district hosts mainly low-sulphidation epithermal gold deposits and the most important gold deposits occur in the Pongkor, Cibaliung, Cikotok, and Papandayan districts. Although Java has a long record of volcanic activity, little is known of its pre-Pleistocene arc history, particularly in relation to the timing and geochemical evolution of the volcanic successions associated with ore mineralisation. Moreover, much of the available geochronological data for volcanic rocks in the region are based on imprecise K-Ar results. Therefore a combination of 40Ar/39Ar dating techniques and elemental geochemical methods (major and trace element analyses) have been utilised in the current project. Most of volcanic samples from the current study are characterised by enriched LILE and LREE compositions, which are characteristic of calc-alkaline arcs. However, Papandayan basaltic samples exhibit depleted LREE contents, typical of island arc tholeiites. The more enriched LILE and LREE compositions present in some Pongkor samples and Papandayan intrusive rocks, are indicative of high-K calc-alkaline and shoshonite arcs. Trends in Nb/Y, Th/Nb, Ce/Yb, and Ce/La(N) ratios reflect temporal evolution of the arcs, from: i) a primitive arc (low Nb/Y, Th/Nb, Ce/Yb and high Ce/La(N) ratios) characterised by the tholeiite basaltic samples; ii) an evolved arc (high Nb/Y, Th/Nb, Ce/Yb and low Ce/La(N) values) typified by the high K – shoshonite volcanic samples; and iii) a mature arc (with intermediate Nb/Y, Th/Nb, Ce/Yb and Ce/La(N) values) represented by the calc-alkaline volcanic samples. Trace element signatures of La and Ce suggest a broadly similar magma source for all rocks in the region. 40Ar/39Ar dating of volcanic rocks that host gold mineralisation are representative of the western Java magmatic arc, give the oldest age of ca. 18 Ma for the Papandayan district; ages ranging from ~11 Ma to ~9.5 Ma for the Cibaliung district, from ~18 Ma to ~4.5 Ma for the Cikotok district, and the youngest ages from 2.74 ± 0.03 Ma to ca. 2 Ma for the Pongkor district. Adularia crystallisation that is associated with western Java gold mineralisation shows 40Ar/39Ar ages from the oldest to most recent: ca. 18 Ma for the Papandayan district; from 12.44 ± 0.19 Ma to 9.39 ± 0.75 Ma for the Cibaliung district; 5.36 ± 0.46 Ma and 3.43 ± 0.04 Ma for the Cikotok district; and from 2.02 ± 0.03 Ma to 1.80 ± 0.03 Ma for the Pongkor district. Some host volcanic rocks have been affected by hydrothermal alteration, which has resulted in partial resetting of ages towards the time of gold mineralisation. Variation of the mineralisation ages suggests multiple generation of adularia growth in the mineralised veins. The dating results suggest that the magmatic arc across western Java are most likely linked to Southeast Asia tectonic evolution, from Early Miocene counter clock wise rotation of Kalimantan to Late Miocene – Pliocene subduction of the Eurasian continental plate beneath the Indo-Australian oceanic plate. The new and existing age data allow for a reconstruction of the western Java magmatic arc, with three main events identified: an Early Miocene primitive tholeiite arc (20 – 18 Ma), a Middle Miocene mature calc-alkaline arc (13 – 9 Ma) and a Late Miocene – Pliocene evolved high-K calc-alkaline and shoshonitic arc (7 – 2 Ma). The reconstruction indicates that the Early Miocene Papandayan low sulphidation epithermal system (with some indications of high sulphidation activity) is related to a basement comprising thinned island arc crust. In contrast the Miocene – Pleistocene low-sulphidation epithermal mineralisation system of the Cibaliung, Cikotok and Pongkor districts, which is associated with a calc-alkaline arc, was constructed on Sundaland continental crust.