School of Earth Sciences - Theses
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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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ItemHydromorphology of within-channel river benches( 2008)The fluvial morphology of a river channel is a function of the river’s hydrologic and sediment regime. Within-channel river benches are a fluvial feature widely identified in the international literature as geomorphically and ecologically important. Despite this recognition the relationship between bench morphology and the flow regime is poorly understood. The aim of this thesis is to identify the components of the flow regime responsible for the formation and destruction of within-channel benches. Opinions on the formative flows for benches are highly varied with reports that benches are formed by flows which just inundate the bench; to low-flow periods and sub-bankfull flows; bankfull flows and the annual flood; and moderate, medium and catastrophic sized floods. A large body of research also treats benches as a static morphology. Opinions on destructive flows are similarly varied. There is little empirical evidence for these suggestions. A bench is most commonly referred to as comprising a horizontal (planar) surface which results from within-channel deposition, but the term is also used to describe bars, floodplains and erosional features. The inability of researchers to agree on the relationships between bench morphology and river hydrology is influenced by the lack of a consistent definition and classification for benches. To adequately address the aim this thesis is presented in two parts: Part A addresses bench nomenclature and provides a sound basis for Part B which addresses the processes of bench formation and destruction. (for complete abstract open document)
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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 tectonic history of the Ruker Province, southern Prince Charles Mountains, East Antarctica: implications for Gondwana and Rodinia( 2006-12)Within the Ruker Province of East Antarctica, there is evidence for several key geological events that have occurred coincidently with periods of dynamic earth evolution. A detailed evaluation of the tectonic history of the region is therefore required. This research focuses on the tectonic development of the Ruker Province. The main aspects of this research can be summarised as follows: (1) an evaluation of the gross crustal architecture of the region through the development of a new stratigraphic and structural framework; (2) new U-Th-Pb (LA-ICPMS) age data from detrital zircon grains extracted from thick metasedimentary units that comprise a major component of the Ruker Province; (3) new 40Ar/39Ar data from metamorphic minerals to determine the cooling history of the province; (4) mineral equilibria modelling of metamorphic mineral assemblages to constrain pressure-temperature (P-T) conditions during key orogenic events; (5) a kinematic analysis of brittle/ductile deformation features. Ideas developed from these new data provide inferences on the assembly and dispersion of the late Proterozoic super-continents Rodinia (c. 1000 Ma) and Gondwana (c. 500 Ma).
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ItemA new perspective on melt inclusions: development of novel in-situ analytical protocols( 2006-08)Novel techniques for in-situ lead isotope analysis of melt inclusions using multicollector inductively coupled plasma mass spectrometry, and parallel Faraday cup and ion counter detection have been developed. These provide for measurement of the critical 204Pb isotope, which has been unavailable in melt inclusion Pb isotope studies, but requires on-line determination of 200Hg to correct for 204Hg isobaric interferences. External standardisation allows for effective mass fractionation correction and ion counter gain calibration. An off-line Tau correction was applied and standard glass analyses suggest that this correction provides more accurate and precise results.
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ItemContinental tectonics and landscape evolution in south-central Australia and southern Tibet( 2006-09)The Indo-Australian Plate is actively deforming at its margins and within its interior. In south-central Australia, more than 3000 km from the closest active plate boundary, a geomorphically rugged and apparently youthful mountain range has developed, rising up to 1.1km above the adjacent flat-lying outback plains. These ‘Flinders’ and ‘Barrier’ Ranges are seismically active and bound by major reverse fault scarps with clear evidence for Plio-Quaternary displacements, implying that young and active intraplate tectonism has played a fundamental role in their development. Palaeoseismic investigations and optically stimulated luminescence (OSL) chronology indicate faulting occurred in response to a series of large magnitude (~M6.6 to M7.3) palaeo-earthquakes with recurrence intervals of ~1:20,000 to~1:80,000 yrs and long-term fault slip rates of ~50 m Myr-1. Geomorphic observations and 10Becosmogenic nuclide dating indicate surprisingly high and spatially variable rates of bedrock erosion from fault-affected catchments in the Flinders Ranges. Slowly eroding bedrock summit surfaces have been uplifted up to 12 m in the last 60,000-100,000 years relative to more rapidly eroding valley floors and bounding piedmonts, indicating Late Quaternary increases in elevation and relief in response to intraplate tectonism and erosion. However, both facies changes and sediment aggradation-dissection cycles in alluvial fan sequences are out-of-synch within dividual tectonic events, indicating that an aspect of climate (aridification, changing flood frequency-magnitude distributions) has governed the spatial-temporal distribution of range front sedimentation.
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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.
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ItemGlobal changes in synoptic activity with increasing atmospheric CO2( 2005-11)Over the last century, increases in anthropogenic greenhouse gases and global temperature in the atmosphere has drawn our attention to changes in extra tropical cyclones which influence daily weather patterns in the mid and high latitudes and redistribute energy, momentum and moisture across the globe. This study is aimed at examining changes in extra tropical cyclones: observed over the past two decades using the NCEP-DOE reanalysis II data (NCEP2); and simulated in the CSIRO Mark2 atmosphere-ocean coupled general circulation model (GCM) with increasingCO2. Furthermore, we attempt to explore the physical mechanisms driving such changes by modelling idealised experiments with the Melbourne University atmospheric GCM. The Melbourne University cyclone finding and tracking scheme is utilised to detect and track cyclones observed in NCEP2 and simulated in the two models. The study demonstrates significant changes in Southern Hemisphere (SH) cyclone features from 1979-2000. SH cyclones have decreased in their number at the surface but increased at the 500 hPa level. On the other hand, SH cyclone physical features such as intensity, radius and depth have significantly increased over the two decades at the mean sea level and 500 hPa level. Moreover, cyclones became vertically better organized in both hemispheres, and particularly in the SH. The changes in the characteristics of Northern Hemisphere (NH) cyclones were statistically less significant than their SH counterparts in the period of 1979-2000. Results from the coupled climate model simulation with enhanced CO2 suggest general reductions in cyclone frequency and intensity throughout the troposphere between the surface and500 hPa level but increases in cyclone radius and organization of vertical structure. These changes are persistent throughout the entire transient run with increasing CO2 and during a 100 year stabilisation period. It is found in the CSIRO simulation with enhanced CO2 that the geographical changes of cyclone features are similar in both hemispheres and between the surface and 500 hPa level. Furthermore, we conclude that some observed changes in extra tropical cyclone features seem to follow the patterns of simulated changes with increasing CO2 from 1xCO2 to 2xCO2 particularly in the SH. Modelling latitudinal temperature gradient at different levels of the troposphere has revealed that the warming over the tropics at the upper troposphere causes cyclone frequency and depth to increase in the high latitudes but decrease in the mid latitudes. By contrast, the warming over the high latitudes at the lower troposphere results in decreases in the cyclone features in the high latitudes but increases in them in the mid latitudes. Therefore, the warming over the tropics seems to play an important role in the changes in SH summer cyclone frequency and depth appearing in the simulation with enhanced CO2, whereas the warming over both tropics and high latitudes affects the changes in SH winter cyclone features. In the NH, the change in latitudinal temperature gradient seems less influential in the changes of cyclone features than it does in the SH.