School of Earth Sciences - Theses
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ItemThe Variation of atmospheric carbon dioxide,methane and nitrous oxide during the holocene from ice core analysis(University of Melbourne, 2004)Recent studies have demonstrated that the atmospheric concentrations of radiatively important greenhouse gases, including methane (CH4), carbon dioxide (CO2), nitrous oxide (N2O) and carbon monoxide (CO), have significantly increased during the past 200 years due to anthropogenic emissions. Analysis of air trapped in polar ice cores allows for past atmospheric variations due to natural climate conditions to be investigated, placing recent changes in a historical context. In this thesis new high- precision, multispecies measurements of atmospheric trace gas concentrations during the Holocene have been produced by analysing the air trapped in the ice at Law Dome, East Antarctica (66�46'08"E, 112�48�28�S). The ice core records are well-dated, have high age resolution and overlap with modem instrumental records due to the high accumulation rate at the drilling sites. The combination of high age resolution, precise dating and high precision measurements allows for subtle, decadal-scale variability to be detected. The multispecies measurement technique allows for biogeochemical causes of variations to be identified. The first part of this study focused on the late Holocene period (AD 0 to 1975). New high-precision records of CH4, CO2, N2O and CO have been produced for this period. The CH4 and CO2 measurements are used to build upon the existing Law Dome records of these gases during the last 1000 years, to validate and further define previously observed variations. The new measurements extend the records of these gases by another 1000 years. As a consequence of the multispecies measurement technique it has been possible to also measure N2O and CO during this period. These new measurements highlight the atmospheric response to the Little Ice Age (LIA) cooling (AD 1550 to 1800), particularly a 10 ppm decrease in atmospheric C02 between AD 1550 and 1600. A stabilization of CO2 during the 1940s was also confirmed in the Law Dome record. Increased data density during this period shows that the atmospheric CO2 mixing ratio stabilized at ~310 ppm between 1937 and 1955. New signals were observed in the extended records, including a 100 ppb increase in the CH4 concentration between AD 0 and 1800, which is probably the result of increasing pre-industrial anthropogenic emissions. The second part of this study focussed on the CO2 and CH4 response to a rapid, abrupt cooling at 8,200 years BP. The Law Dome (DSS) measurements are complemented by four measurements of NorthGRIP (Greenland) ice core. A decrease of at least 52 ppb CH4 is observed in the DSS record, and a decrease of at least 62 ppb is observed at NorthGRIP during the same period. A smaller CO2 response of 4 to 5 ppm is seen in both the records. The CH4 signal is used to improve the chronologies of these ice cores by synchronising with other well-dated CH4 records, specifically GRIP (Greenland) and Dome C (Antarctica).
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ItemThe structural evolution, tectonics and hydrocarbons of the offshore Otway Basin, SE Australia( 2003)The offshore Otway Basin is part of Australia's passive southern margin, in which two separate rift-phases between the Tithonian? and Maastrichtian formed numerous depocentres. The research presented has analyzed and described the structural styles in the offshore Otway Basin and constructed a model of the basin's evolution since the Late Jurassic. The Otway Basin has been divided into four structural zones from north to south. Zone I comprises the onshore area and most of the shelf along the margin. Deep halfgraben developed during the first rift phase with characteristic horst and graben in Palaeozoic basement. To the south, zone I is bound by the Hinge Zone. Structural zone II covers the entire deepwater part of the Otway margin, characterized by a very thick Late Cretaceous section with pervasive Turonian faulting in the east and saucer-shaped depocentres in the west. Large halfgraben controlled deposition of the post-Turonian sedimentation in the eastern Otway Basin. Negative flower structures document strike-slip faulting. Strongly thinned lower laminated continental crust underlies this zone, limited to the south by the Outer Margin Highs. Domino faulting formed halfgraben and less commonly graben in Structural Zone III, the Outer Margin Highs. The base of the Outer Margin High sediments represents a regional decollement surface and domino faulting occurred along a second-generation decollement. Structural zone III is limited to the south by the continent-ocean-boundary with oceanic crust in structural zone IV. In the Shipwreck Trough, halfgraben died out against an accommodation zone which developed into the Shipwreck Fault with strike-slip offset .The regional stress regime indicate sinistral strike-slip movement along this fault zone. In the southwest Shipwreck Trough, four Turonian to early Coniacian syn-rift phases can be distinguished formed through footwall collapse to the north of the Hinge Zone. Differences in the amount of extension in the basin are accommodated along strike-slip faults such as the Shipwreck Fault. Sedimentation rates between 89 and 83 Ma increased whilst extension rates declined. Since approximately 83Ma sedimentation rates declined exponentially in phase with extension rates. Regionally, rapid Turonian extension formed a wide graben system between Antarctica and Australia. With the serpentinization of exhumed mantle peridotite in the Outer Margin Highs during the Coniacian in the east and Turonian in the west, the crustal deformation mechanism changed from mainly pure shear to simple shear along the newly established decollement. Fast spreading since the Mid Eocene caused gravitational collapse of the margin. Changes in heat flow possibly correlate with a change in deformation style in the continental crust. Parallel developments of sedimentation-rate and extension-rate suggest that most of the subsidence was structurally related. The Shipwreck Trough hydrocarbon fairway probably continues south into the Sorrell Basin. Possible stagnant conditions in deeper water offshore across the Hinge Zone might have enhanced the organic content of the Belfast Mudstone creating potential oil source rocks. Deepwater lntra-Paaratte reservoirs are not proven, but the alternating reflective to non-reflective seismic facies might indicate interbedded sands and shales. Large rollover anticlines would make excellent traps in the deepwater Otway Basin.
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ItemEnvironmental fate and transport of TNT in soil at the former explosives factory Maribyrnong( 2002)Highly toxic explosives compounds can potentially contaminate soil and groundwater and pose extended environmental hazard due to their persistence. Explosives contamination within soils was investigated at the former Explosives Factory at Maribyrnong (EFM), by sampling and spectrophotometric / HPLC analysis. The environmental fate and transport of 2,4,6-trinitrotoluene (TNT) was assessed via batch and microcosm testing to quantify the influence of key subsurface sinks, adsorption, and transformation, and hence evaluate natural attenuation as a remediation option. A five tonne crystalline TNT source zone was delineated within soils at the base of a TNT process waste lagoon. This source was found to be supplying aqueous TNT loading to subsurface soils and groundwater, with the resultant plume localised to the shallow clay sequence due to a combination of natural attenuation processes and hydrogeological constraints. Freundlich described sorptive partitioning was found to be the main TNT sink at EFM (KF= 29 mL/g), while transformation rates were moderate (3.86 x 10-4 hr-1) due to aerobic conditions, and TNT toxicity inhibiting microbial degradation. Slow groundwater migration toward the Maribyrnong River (0.7 m/yr) and upward hydraulic gradients within underlying sand and gravel aquifers serve to increase TNT residence time within the clay aquitard, leading to increased interaction with adsorptive substrates and microbes and/or elements of the soil matrix responsible for aerobic transformation. Remediation of the contaminated lagoon may involve removal and treatment/landfilling of the top 1m of soil, then refilling with an impermeable capping allowing ongoing natural attenuation of residual TNT at depth via anaerobic degradation and sorption.
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ItemAustralian Neoproterozoic glaciation: a study of the Sturtian glacial deposits in the Arkaroola region, Northern Flinders Ranges South Australia( 2005)The late Proterozoic Sturtian glacigenic succession exposed in the Arkaroola region of the Northern Flinders Ranges record the earliest of two global Neoproterozoic `Snowball' glacial events in the Adelaide Geosyncline, South Australia. Two stratigraphically disparate glacigenic units were recognised in the late Sturtian succession in the Arkaroola region, a subaerially deposited glacial till - the Merinjina Tillite, and an unclassified glaciomarine diamict unit. The Merinjina Tillite unit preserves a five-fold lithostratigraphy, hosting englacial melt-out deposits, glaciolacustrinal sediments and dominated by a massive to poorly-bedded tillite unit deposited directly from glacier ice. The glaciomarine diamictite preserves down-slope mass-flow deposits, as well as turbidite sequences, slumping and sediments from glacial fall-out including dropstones embedded in laminated muddy-shale and is interpreted as a basin-margin marine deposit. Palaeocurrent analyses across the Northern Flinders Ranges and stratigraphic reviews of analogous Sturtian glacigenic deposits elsewhere in the Northern Flinders Zone suggest palaeotidal influence from the north-north-west and indicate a north-north-west-sloping basin margin in the Northern Flinders Zone. Two major palaeoclimatic phases were recognised in glacigenic rocks the Arkaroola region. A glacial advance phase is represented by the advance of continental glacial sediments, across a topographically-elevated, subaerial surface and extending down-slope into a submarine basin. The other, represented regionally by dropstone shales, is interpreted as glacial retreat and the termination of Sturtian `Snowball Earth' conditions. A rise in palaeo-atmospheric temperatures is inferred, causing melting of continental and marine ice-sheets and resulting in a regionally-extensive marine transgression. The slight increase in water temperature during glacial retreat is believed to have triggered carbonate precipitation and the ultimate deposition of cap dolomites which overly the glacigenic sediments across the Adelaide Geosyncline.
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ItemThe weather and climate of Australia at the Last Glacial Maximum( 2005)The global climate has experienced four glacial cycles in the last 420,000 years, with each cycle characterised by a prolonged period of cooling culminating in maximal glaciation followed by a brief warm period. The most recent period of maximal glaciation is termed the Last Glacial Maximum (LGM) and occurred about 21,000 years ago. We currently live in one of the warm periods. The global climate is changing, and it is becoming more important to understand the extremes of the climate system and how well our modelling capability can capture those extremes. There has been a modelling intercomparison project established to examine how global general circulation models compare in simulating past climates, including the LGM. Analysis and comparison of these model results has been presented for many parts of the globe, but there has not been a comparison of the different model results over the Australian region. This thesis aims to fill that gap and explore the simulated LGM weather and climate of Australia and its drivers in more detail. Comparison with proxy evidence is also undertaken, and inconsistencies seen in the literature addressed. The Australian climate at the LGM was believed to be generally cooler, drier and possibly windier from proxy evidence in the literature. In the comparison done here the mean temperature and precipitation fields from most models show cooler and drier conditions, with some seasonal variability, but there are some strong outliers. It was found that the differences were not dependent on model resolution, but that the surface parameterisations were highly important for these fields. The shifts in the circulation were examined both in the model results and with a study of the non-linear link between the wind, surface moisture and dunes, which are a proxy for past winds. All the models simulate a southward shift in the westerlies in the Australian region. This is strongly driven byte prescribed sea-surface temperatures. Australia's current wind regime is conducive to dune building. However, the binding effect of soil moisture (or vegetation) is strong enough to limit present day movement, whereas in the drier climate at the LGM there was a capacity for sand movement. The analysis of dune orientations did not produce conclusive evidence for how the westerlies might have shifted at the LGM. An apparent enigma in the proxy evidence at the LGM is the high lake levels in Australia’s south east, while most inland lakes were dry. Previous authors believed that the precipitation was still low, but the high lake levels were driven by lowered potential evaporation. The hydrological cycle was generally depressed in the LGM simulations, but the potential for evaporation remained high. Thus an alternative hypothesis is posed based on increased run off due to a known shift in the vegetation types and a lag in the timing of the run off due to snowmelt. The analysis here shows that our capacity to simulate climates quite different from the present is still developing, but that model results can help explain apparent inconsistencies in the reconstruction of past climates from proxies.
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ItemVertical structure Of atmospheric trace gases over Southeast Australia( 2000-01)Trace gas (CO2 and its carbon and oxygen isotopes, CH4, CO, H2 and N2O) vertical profile data above Cape Grim, Tasmania for the period April 1992 to February 1997 are investigated. A climatology of the distribution of each trace gas has been compiled from statistical treatment of the raw data. These climatologies are useful for verification of transport model outputs. Here, the CO2 climatology is compared to simulation results from two transport models (Melbourne University Transport Model and TM2Z) using three different sets of CO2 fluxes separately (compiled with different methods by different authors). Large discrepancies are found between simulations and observations, especially in the free troposphere (4-6 km). By considering emission ratios, trajectories, satellite fire counts and simulation with biomass burning fluxes, the influence of tropical biomass burning plumes on the southeastern Australian region in the austral winter/spring is studied and quantified. This identification process requires a multiple-species approach where the large CO anomalies and the unexpected behaviour of H2 are most revealing. The frequent presence of burning plumes in the mid troposphere complicates one of the original motivations for the Cape Grim Overflight Program, which is to estimate the air-sea exchange of CO2 in this region. A suggestion arising from analysis of pre-1992 aircraft sampling in this region was that the regional CO2 air-sea flux south of Australia is exceptionally large.
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ItemThe hydrogeology of the Gippsland Basin, and its role in the genesis and accumulation of petroleum( 2002)The Gippsland Basin of southeastern Australia is the most energy-rich basin of Australia producing petroleum, gas and brown coal. Three-quarters of the Basin lies offshore and the rest onshore. The basin was initiated as a rift valley, caused by the separation of the Australian continent from the Antarctic followed by a number of tectonic events throughout the basin history. Early Cretaceous sedimentary rocks form the basement, which is in turn covered with Late Cretaceous to Recent sediment of sand, clay, limestone, and brown coal seams. The total thickness of the in-filling sediments offshore attains up to 6000 m, but onshore is up to 1200 m. There are three main acquifer systems, the Hydrostratigraphic Units 2, 4, and 7, all of which are confined. The two lower aquifer systems, Units 4 and 7, contain high temperature groundwater. It is generally agreed that the hydrocarbons offshore have been derived from terrestrial matters including brown coal and ligneous clay offshore. In the present study, the author has developed a case that hydrocarbons offshore being derived not only from the offshore source but also from onshore brown coals and coaly matter and in this hydrocarbon forming processes, groundwater has played a significant role. The Central Deep, in particular, provides favourable conditions for hydrocarbon maturation. Throughout the basin history, the Central Deep has experienced the oil window temperatures. In supporting this hypothesis, geochemical studies on groundwater, brown coal, and hydrocarbons as well as hydrodynamics are presented.
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ItemThe geochronology and thermochronology of the Brockman Creek 01, Melita 01 and Melita 02 kimberlites, Western Australia( 2000-10)Due to the difficulties inherent in dating kimberlites, two independent methods are employed to confirm the unusually old ages of approximately 2 Ga for three occurrences in Western Australia. Phlogopite micas from three kimberlites were dated using 40Ar/39Ar and 87Rb/86Sr dating techniques in order to provide an estimate of the intrusion ages. The high reliability of the age estimates is indicated by the similar results produced by the 87Rb/86Sr method. Argon loss is suspected for phlogopite samples, resulting in the apparently reliable 40Ar/39Ar total fusion ages that do not correspond to previously determined emplacement ages. (For complete abstract open document)
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ItemThe potential for natural attenuation of petroleum hydrocarbons in groundwater: Shell Newport Terminal, Victoria( 2000-10)Groundwater in the fractured and jointed Quaternary Newer Volcanics basaltic aquifer system beneath the Shell Newport Terminal has been contaminated by petroleum hydrocarbons. This petroleum hydrocarbon contamination has resulted from a number of different spill incidents over the terminal's long operation. Petroleum hydrocarbon contamination has led to the formation of a light nonaqueous phase liquid (LNAPL) floating on the water table. Associated dissolved and vapour phases have also developed within the basaltic aquifer. The effectiveness of natural attenuation processes to remediate the petroleum hydrocarbon contamination has been evaluated based on the gas chromatography / mass spectroscopy analysis of LNAPL samples and changes in groundwater geochemistry. Three distinct LNAPL plumes were identified within the Shell Newport Terminal jet facility plume (kerosene source); off-site plume along High 8t (mixed source of leaded petrol, kerosene, and diesel); and black oil fuel gantry plume, which is migrating off-site to Digman Reserve (mixed source of leaded petrol, shell sol A, and diesel). LNAPL ratio analysis revealed only that the samples were degraded compared to their estimated source composition. Further interpretation of ratios was difficult due to constraints involved in source compositions, sampling limitations, heterogeneity of the groundwater system, and high transport velocities of the groundwater compared to LNAPL migration. (For complete abstract open document)
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ItemThe fate of cyanide in groundwater at gasworks sites in south-eastern Australia( 2000-09)The fate and transport of cyanide in groundwater was investigated at gasworks sites in southeastern Australia. Two gasworks sites were investigated during this research: one in Tasmania and the other in Adelaide. The research followed three principal methods of investigation: field work, laboratory work and numerical modelling. The field work was aimed at observing the behaviour of cyanide in highly contaminated groundwater environments. Measured field parameters and laboratory analytical results from groundwater sampling were used to describe the hydrodynamics and hydrochemistry of the groundwater environment, providing a framework for groundwater flow and solute transport modelling. Groundwater and soil samples were also collected for use in laboratory experiments. The results from both field sites indicate contrasting hydrogeological environments, however, inorganic (metallic and non-metallic) and organic contaminants were measured in solution at both sites. The maximum concentrations observed at both sites were up to 5,300 mg/L CN(Total) (Adelaide site) and 21 mg/L CN(Total) (Tasmanian site). Results from geochemical modelling of solutes in groundwater at the field sites indicate that cyanide was predominantly in its free form in solution, with metallo- and alkali-cyanides also present.