School of Earth Sciences - Theses
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ItemGeologic expressions of faulting and earthquake strong ground motions in intraplate bedrock terrains( 2019)Australian earthquakes offer unique opportunities to investigate environmental and landscape effects of reverse rupturing faults. All historic surface-rupturing earthquakes have occurred in arid, low-relief, bedrock dominated areas with little to no anthropogenic influence. Environmental earthquake effects identified following the 2016, reverse-mechanism, MW 6.1 Petermann earthquake in remote central Australia are categorised with the Environmental Seismic Intensity scale, the first application of this scale for an Australian earthquake. The intensity and distribution of environmental damage demonstrates strong asymmetry due to fault geometry, with damage increasing towards the surface rupture rather than epicentral region. The direction and distances of 1,437 co-seismically displaced rock fragments (chips) in the near-field of the Petermann earthquake provide a dense proxy-record of strong ground motions, both along- and across-rupture. Chips record preferred azimuths of displacement that are attributed to rupture fling effects. This unprecedented geological proxy-record of the distribution, directivity and intensity of strong ground motions has important implications for hazard analysis in the near-field of reverse earthquakes. Fine-scale mapping of the 2016 Peterman surface rupture and secondary fractures using field, drone-derived and remote-sensing datasets indicates surface rupture characteristics vary with changes in surface geology. Deformation zones are wider and less recognizable in granular materials (e.g. dunes, alluvium) compared with those in proximal bedrock. Kinematic analysis of bedrock fractures indicates sinistral-reverse faulting, consistent with published focal mechanisms, and a maximum compressive stress orientation generally consistent with the inferred regional SHMax orientation. Trenching and 10Be cosmogenic nuclide erosion rates provide preliminary evidence of absence for prior rupture on the Petermann faults within the last 200 to 400 kyrs. The 2016 earthquake is therefore hypothesized to be the first to rupture this fault in the near surface. Analyses of geological and geophysical data from ten moderate magnitude (MW 4.7 – 6.6) historical surface-rupturing earthquakes in cratonic Australia indicate that rupture likely propagated along pre-existing Precambrian bedrock structures. Six of seven events show evidence of multi-fault rupture across 2 to 6 discrete faults of greater than 1 km length, placing these events as some of the most structurally complex earthquake ruptures identified globally for this magnitude. No unambiguous geological evidence for preceding surface-rupturing earthquakes is present. This raises important questions regarding the recurrence behaviour of intraplate stable continental region faults, with implications for seismic hazard analysis. In summary, this thesis explores observational, seismic, and remote-sensing data of surface rupturing earthquakes in Australia to provide new (i) data regarding the recurrence patterns of Australian earthquakes (ii) insights into basement controls on these earthquakes (iii) and methods to quantify seismic directionality behaviour common to reverse earthquakes globally. These contribute to better understanding the why, what, when, where of intraplate earthquakes, and how seismic hazard varies across diverse tectonic and crustal environments.
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ItemCryogenian iron formations: glaciation and oxygenation( 2018)The Cryogenian Period (720–635 Ma) experienced extreme glaciations broadly coincident with a transformation of the Earth’s surface oxidation state, supercontinent breakup, and the evolution of complex animal multicellularity. However, the cause-and-effect relationships of these events are unresolved. The Cryogenian ice ages, known as ‘Snowball Earth' events, would have placed important constraints on the biosphere, and it remains unclear what role global refrigeration played in setting the stage for eukaryotic diversification and the origin of animals. The Cryogenian also experienced the deposition of iron-rich marine chemical sediments (iron formations), representing the first episode of global iron formation deposition in over one billion years. This shift in iron cycling highlights complexities in seawater chemistry and oxidation state during this time, and these iron formations offer valuable insights into Cryogenian palaeoenvironments. Iron formations from Cryogenian glacial successions in Namibia, USA and Australia were studied in order to investigate Cryogenian iron formation genesis and elucidate the relationships between glaciation, ocean chemistry, oxygenation and biotic evolution. In-depth sedimentology, stratigraphy and petrography reveals that these iron formations are intimately associated with Sturtian glacial sediments and are interpreted have been deposited in a range of glaciomarine environments. Geochemical analysis of these chemical sediments permits the reconstruction of Cryogenian ocean chemistry and the synglacial palaeoredox landscape. Multiple geochemical proxies, including rare earth element and iron isotope systematics, indicate widespread marine anoxia with increasing seawater oxidation with proximity to the ice shelf grounding line. A genetic model is proposed whereby the mixing of oxygenated glacial fluids with ferruginous seawater led to the deposition of iron formations in glacial successions during the Cryogenian. Atmospheric oxygen trapped in glacial ice was likely an important oxidant source, delivered to Cryogenian glaciomarine environments via subglacial meltwater outwash. This meltwater supply may have been crucial in establishing oxygenated marine habitats for eukaryotes, including early animals, during Snowball Earth. Multi-million-year oxidation of the oceans via this mechanism may have also set the stage for a Neoproterozoic marine oxygenation event.
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ItemIsotopic disequilibrium in granitic systems: the origins of heterogeneity in granites and implications for partial melting in the crust and petrogenetic models( 2017)Unravelling the processes involved in granite magmatism is essential to our understanding of the continental crust, its formation and evolution. Radiogenic isotope systems are commonly employed to this end, but the behaviour of these systems may not be as simple as is often assumed. Understanding the causes of isotopic complexity in granite suites is the aim of this research. By modelling the disequilibrium partial melting of isotopically heterogeneous protoliths the different compositions of the melt, source and restite for a range of hypothetical scenarios have been calculated. Results demonstrate that the melt produced may have Sr, Nd and Hf isotope compositions distinct from both the protolith and restite. A corollary is that restite-bearing magmas may exhibit different isotope compositions than their melts, a feature which should be preserved as a difference between the Hf isotope compositions of bulk-rock samples and their magmatic zircon populations. The same modelling also suggests that a single source rock can produce melts with diverse isotope compositions. The predictions of this modelling have been tested by analysing S- and I-type granites from the Lachlan Fold Belt, southeastern Australia, including iconic examples of restite-bearing rocks. Comparisons of Hf isotope compositions between bulk-rocks and their magmatic zircons reveal discrepancies (ΔεHfbulk-zircon) ranging from -0.6 to +2.5 ε units for I-type granites. This intra-sample Hf isotopic heterogeneity is interpreted to represent disequilibrium between the melt and restite assemblage. The ΔεHfbulk-zircon values are consistent with calculated ΔεHfmagma-melt values (from -4.2 to +7.4) based on the disequilibrium amphibole dehydration melting of 0.5-1.0 Ga meta-igneous protoliths. S-type granites also record differences between their bulk-rock and magmatic zircon Hf isotope compositions; however, the disparity is more subtle. Both positive and small negative ΔεHfbulk-zircon values are observed, consistent with modelling the partial melting of isotopically heterogeneous meta-sedimentary protoliths. In addition to low-temperature granites, case studies of two high-temperature I-type granitoid suites (Boggy Plain and Wallundry) have also been conducted. Both display a weak coupling between geochemical parameters that have been interpreted previously to indicate the involvement of assimilation and fractional crystallisation (AFC) processes. Positive ΔεHfbulk-zircon values obtained in the Boggy Plain Suite support the existing petrogenetic model in which basaltic melt becomes variously contaminated by material derived from the continental crust. The positive value is explained by retention of earlier-crystallised, more radiogenic phases in isotopically evolved, more felsic samples. In contrast, the Wallundry Suite is characterised by negative ΔεHfbulk-zircon values caused by the presence of unmelted components of its contaminant. A complex interplay of contamination, crystallisation, melt segregation and interaction between magma batches is required to account for the Wallundry Suite isotope data. The results of this study indicate that disequilibrium partial melting can produce within-suite isotopic variability without recourse to assimilation or mixing processes (1) in mafic to felsic samples caused by the progressive separation of melt from its isotopically distinct restite assemblage; and (2) via the extraction of multiple batches of isotopically distinct melts produced from a single source as anatexis proceeds. Furthermore, the isotope variation resulting from restite unmixing may be distinguished from magma mixing by decoupling of the Rb-Sr, Sm-Nd and Lu-Hf isotope systems. Importantly, the isotopic discrepancy between bulk-rock granite samples and their magmatic zircon populations suggests that the most mafic bulk-rock granite samples of a given suite, not magmatic zircon, provide the most accurate estimate of source rock Hf isotope compositions. This raises concerns regarding the ubiquitous use of zircon Hf isotope data to constrain crustal growth models.
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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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ItemThe low-temperature thermochronology of cratonic terranes( 2006)Cratonic terranes present many problems for geologists attempting to define those regions of the continental crust that are the core of today's continents. Inherent in the term is the great passage of time, and typically, the term defines consolidated Archaean or Proterozoic crust (Park and Jaroszewski, 1994). Cratons are further distinguished on the basis of tectonic activity. Marshak and his colleagues (1999) suggest that the lack of penetrative deformation or metamorphism is a useful definition but they further narrow this with the restriction of a Precambrian timeframe. Central to either view is the assumption of stability and perhaps senescence. And, since many aspects of geological research involve the detection of stratigraphic, structural or mineralogical change, stability implies a lack, or at least a minimum, of change. Thus the absence of these traditional markers of geological evolution or change, related to these processes, presents significant challenges in the study of cratons. This is particularly so in shield areas - those cratons with exposed basement rocks (Park and Jaroszewski, 1994). The extraordinary age of shield rocks and their apparent preservation at the surface, has encouraged research into the mechanics of landscape development and the individual evolution of landforms in the landscape, particularly by geomorphologists. From within this environment many thought provoking ideas have been proposed to explain the breadth of observations pertaining to almost every aspect of landscape process in these terranes. According to Summerfield (1991) the models of Davis, Penck, King and Budel have had the most impact in this field. The ideas presented by these workers remain a cornerstone in our understanding of the earth's surface, but in detail and in practice, the models have been shown to be antiquated. Nevertheless, landform evolution models such as those of L.C. King (1967) have held sway in southern Africa and elsewhere long after the underlying assumptions have been shown to lack validity. The purpose of this thesis is to investigate key aspects of landscape evolution in two regions, central Australia and southern Africa, where models have been espoused, arguing for extraordinary surface stability or alternatively a simple erosional history or pediplanation. Contemporary thermochronological techniques now permit us to investigate these regions in previously unavailable detail. The primary technique used in this work was apatite fission track analysis and an introduction to the fundamentals of the method is given in Chapter 1. The theoretical and practical aspects of the fission track method provided the basis for an innovative approach presented in Chapter 2. TASC is a scheme for analysing the raw fission track data so as to extract additional information about the rock's thermal history prior to undertaking traditional inverse modelling techniques. This method (recently described by the author in Ehlers et al., 2005) proved to be a powerful complement to the routine fission track analysis undertaken as part of the Australian and African case studies. Although first proposed for geological use in the 1960's, the fission track technique really only gained serious application with a number of technical and theoretical breakthroughs in the 1980's. Since then, growing understanding of the processes of annealing and how they might be modelled has allowed the technique continue developing. Chapter 3 is a discussion of this topic that expands on material previously published by the author and colleagues (Gleadow et al., 2002) and presents additional new work. Nevertheless, despite it's wide application in tectonic and basin studies amongst others, there remain many improvements to be made and problems to be solved. As part of this project, research into several areas presented the author with opportunities to contribute toward improvement in the apatite fission track technique, that have the potential to aid the study of cratonic terranes. The chlorine content of apatite has a profound influence on the sensitivity of the mineral for recording thermal events. Few current annealing models are capable of comprehensively addressing the variation of chlorine and other trace elements that appear to play a role in the annealing process. This issue is addressed in Chapter 4 where a universal annealing model is proposed to deal with the wide chemical variability observed in real apatites. For this theme, a fresh consideration of established empirical mathematical models was undertaken and all the current published annealing data was considered. Modern inverse modelling is based on a series of robust, but nonetheless empirical, equations that have withstood the test of time. However, with the aim of developing a more realistic and thus predictive model, Chapter 5 introduces an alternative, physicochemical to modelling the thermal annealing of fission tracks. This work attempts to draw firmer links between the processes of fission track formation, the mechanics of diffusion and the predicted response to variable temperature regimes. The first of the case studies is presented in Chapter 6 and is a comprehensive investigation of the long-term landscape evolution of the Davenport Ranges in the central Australian Craton. The study employs traditional petrographic methods as well as thermochronology and combines cosmogenic isotope analysis in an assessment of early landscape models. This chapter expands on work previously published by the author and co-workers (Belton et al., 2004) and has implications for our understanding of landscape evolution in the broader context of the Australian Craton. In order to maximise temperature sensitivity in slow cooled terranes, the relatively new thermochronological technique of (U-Th)/Helium analysis of apatite was tested on a suite of central Australian samples. The inconclusive results of this experiment prompted an investigation into the possible causes, and an important baseline study was conducted (Chapter 7). The study has implications for routine application of this new thermochronometer in cratonic and other terranes. More importantly the research identified a potential new thermochronometer with an even greater temperature sensitivity and near surface application for use in future landscape studies. Chapter 8 documents a larger, craton-wide study of the Mesozoic to recent landscape evolution of the Zimbabwe Craton. This work builds on material presented in earlier chapters and provides a broader view of the nature of crustal cooling, structural reactivation and landform development in the cratonic setting of southern Africa.
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ItemThe stratigraphy and palaeontology of Cape Vani, Milos, Greece( 2005)Milos, dominated by Pliocene-Recent explosive calc-alkaline volcanics, is in the active Aegean Arc. This project investigated the microfauna and depositional environment of a sequence associated with the only terrestrial white smoker field in the world. White smokers occur in a volcaniclastic-hosted Mn-Fe-Ba deposit in a 1 km2 rift basin associated with dacite intrusives. Although the sediments are extensively hydrothermally altered, they have sedimentary structures and yield a variety of micro- and macrofossils. The typical microfaunal assemblage comprises Miliolinids (e.g. Quinqueloculina spp.; Triloculina spp.) and Elphidiids (Elphidium spp.). In the absence of any planktonic foraminifera, this assemblage is typical of inner shelf palaeodepths from around 10-50m. The occurrence of this fauna with echinoderm spines indicates an open marine setting with normal salinity levels. The associated coarse-grained burrowed facies with symmetrical ripples and hummocky cross stratification and a macrofauna of molluscs (e.g. pectinids, Mytilus, fish teeth) further indicates a shallow marine setting. Terrestrial artiodactyl megafauna occur at three levels in tuff and trough cross-laminated fluvial deposits suggesting close proximity to a regressive shoreline. Macrofauna were probably killed by tephra, rapidly disarticulated and removed into a shallow marine environment. The sequence is unconformably overlain by coarse-grained alluvial fan to braided river deposits deposited when Milos became emergent. Barite-silica white smokers derive from the ingress of and leaching by seawater into basement and overlying volcanics. Palaeontological-boiling data shows the fluid was at 165-140°C and the extremophile echinoderm spicule microfauna dominated because forams were unable to live in warm silica-laden turgid fluids with a high heavy metal content.
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ItemStratigraphy and sedimentology of Cryogenian carbonates, Flinders Ranges, South Australia( 2011)The Adelaide Geosyncline of South Australia contains a Neoproterozoic-aged sedimentary succession consisting of a complex accumulation of sedimentary formations and units recording a diverse and unique depositional record. A detailed stratigraphic and sedimentological investigation of the interglacial period within the Cryogenian-aged Umberatana Group of the Northern and Central Flinders Ranges reveals a complex array of sedimentary successions lying between the Sturtian and Marinoan glacial deposits. In the Northern Flinders Ranges a major unconformity separates the Sturtian and Marinoan-aged sedimentary successions in the area. This forms a sub-aerial erosion surface with terrestrial and marginal marine sediments directly above the Angepena and Balcanoona formations in their respective localities. This exposure surface is here correlated with the previously documented submarine unconformity between the Yankaninna Formation and the underlying deep marine Tapley Hill Formation. This erosional event provides a chronostratigraphic marker horizon that coincides approximately with the previously defined Sturtian-Marinoan time series boundary in the Northern Flinders Ranges. These stratigraphic relationships also constrain lateral facies relationships between the Oodnaminta Reef Complex (Balcanoona Formation) and the Angepena Formation. Similarly, the shallow water Weetootla Dolomite is correlated with the deeper water carbonates of the Yankaninna Formation. In the Northern Flinders Ranges the Angepena Formation occurs as a marginal marine red-bed succession consisting of supratidal mudstones which are interbedded with subtidal and intertidal carbonates. The Angepena Formation is interpreted as a coastal mudflat succession that formed as a shoreward, laterally equivalent facies of the extensive carbonate platforms (reefs) of the Balcanoona Formation. Sedimentological and geochemical investigation of the Angepena Formation reveal that the unit contains a diverse accumulation of shallow marine carbonates including ooidal sands, tepee buckled algal mats, intraformational breccia (palaeo-caliche) and fenestral-bearing microbial deposits. The stratigraphic and sedimentological relationship within the interglacial successions of the Umberatana Group of the Northern Flinders Ranges are found to extend well over a hundred kilometres southwards into regions of the Central Flinders Ranges. The post-glacial Sturtian-aged Tapley Hill Formation records a near-identical depositional record to the Tapley Hill Formation of the Northern Flinders Ranges. In the Central regions, the Tapley Hill Formation is overlain by deep-marine carbonates and calcareous shales of the Wockerawirra Dolomite and Sunderland Formations respectively. The base of the Wockerawirra Dolomite is defined by an erosional surface, which is directly correlated to the unconformity found overlying the Tapley Hill Formation in the Northern Flinders Ranges (Sturtian-Marinoan series boundary). This stratigraphic relationship indicates the Wockerawirra Dolomite and Sunderland Formations of the Central Flinders Ranges are direct correlatives of the Yankaninna Formation of the Northern Flinders Ranges. The regionally widespread carbonate platform complexes of the Balcanoona Formation in the Northern Flinders Ranges preserve a unique history of the depositional record within the middle Umberatana Group of the Adelaide Geosyncline. Cessation of reef development coincides with a major regression event situated immediately below the Sturtian-Marinoan boundary. The regional consistency of the stratigraphic features found at the Sturtian-Marinoan boundary (i.e. unconformities) suggests that regional scale mechanisms, such as glacio-eustasy, were probably active during this otherwise ‘interglacial’ succession of the Cryogenian-aged Umberatana Group.
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ItemMetamorphism of granulite facies metapelites( 2004)This thesis involves a study of metamorphism and partial melting in granulite facies metapelites from three regions, the Larsemann Hills and the Rauer Group of east Antarctica, and Fishery Bay in southern Eyre Peninsula of South Australia. Along with the metamorphic study, $^40Ar/^39Ar$ thermochronological dating was also undertaken for the first two areas to constrain the timing of tectonothermal events and syn- to post-tectonic cooling history. (From Abstract)
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ItemGeochronology of Timor-Leste and seismo-tectonics of the southern Banda Arc( 2009)Arc–continent collision is a significant plate boundary process that results in crustal growth. Since the early stages of evolution are often obscured in mature orogens, more complete understanding of the processes involved in arc–continent collision require study of young, active collision settings. The Banda Arc presents an exceptional opportunity to study a young arc–continent collision zone. This thesis presents aspects of the geology and geochronology of Ataúro and the Aileu Complex of Timor-Leste, and the tectonics of the Banda Arc. U–Pb dating of detrital zircons from the Aileu Complex by LA-ICPMS show major age modes at 270–440 Ma, 860–1240 Ma and 1460–1870 Ma. The youngest zircon populations indicate a maximum depositional age of 270 Ma. The detrital zircon age populations and evidence for juvenile sediments within the sequence favours a synorogenic setting of deposition of sediments sourced from an East Malaya – Indochina terrane. Previous uncertainty in aspects of the cooling history for the Aileu Complex is resolved with 39Ar/40Ar geochronology of hornblende. Cooling ages of 6–10 Ma are established, with the highest metamorphic grade parts of the Complex yielding the older ages. Cooling ages of 10 Ma imply that metamorphism of the Aileu Complex must have commenced by at least ~12 Ma. Metamorphism at this time is attributed to an arc setting rather than the direct result of collision of the Australian continent with the Banda Arc, an interpretation consistent with the new provenance data. Geological mapping of Ataúro, an island in the volcanic Banda Arc north of Timor, reveals a volcanic history of bi-modal subaqueous volcanism. 39Ar/40Ar geochronology of hornblende from dacitic lavas confirms that volcanism ceased by ~3 Ma. Following the cessation of volcanism, coral reef marine terraces have been uplifted to elevations of 700 m above sea level. Continuity of the terraces at constant elevations around the island reflects regional-scale uplift most likely linked to sublithospheric processes such as slab detachment. North of Timor, the near complete absence of intermediate depth seismicity beneath the inactive segment of the arc is attributed to a slab window that has opened in the collision zone and extends to 350 km below the surface. Differences in seismic moment release around this slab window indicate asymmetric rupture, propagating to the east at a much faster rate than to the west. If the lower boundary of this seismic gap signifies the original slab rupture then the slab window represents ~4 m.y. of subsequent subduction and implies that collision preceded the end of volcanism by at least 1 m.y. Variations in seismic moment release and stress state across the transition from subduction of oceanic crust to arc–continent collision in the Banda Arc are investigated using earthquake catalogues. It is shown that the slab under the western Savu Sea is unusual in that intermediate depth (70–300 km) events indicate that the slab is largely in down-dip compression at this depth range, beneath a region of the arc that has the closest spacing of volcanoes in the Sunda–Banda arc system. This unusual state of stress is attributed to subduction of a northern extension of the Scott Plateau. Present day deformation in the Savu Sea region may be analogous with the earliest stages of collision north of Timor.
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ItemLate Neogene stratigraphy and sedimentation across the Murray Basin, southeastern Australia( 2007)The Late Neogene sedimentary sequence of the Murray Basin provides an excellent opportunity to examine paleoenvironmental change across southeastern Australia. A detailed stratigraphic analysis of sediments deposited within the basin in the last 10 Ma was undertaken to assess the influence of tectonic and eustatic processes on deposition. Stratigraphic observations and radiogenic isotope analysis reveals the onset of deposition by 7.2 Ma with a transgressive episode that deposited the marine marls of the Bookpurnong Beds. Deposition was restricted to the central and eastern parts of the basin due to the Hamley Fault. In the west, subsurface elevation contours indicate the presence of incised paleodrainage channels above Miocene limestones, which facilitated the formation of a large estuary system at 5.3 Ma. The sediments of the Norwest Bend Formation were deposited within this western region, while further east, the Loxton-Parilla Sands strandplain deposited over 214 coastal ridges. The basal parts of this unit occur as lateral equivalents to the sediments of the Lower Norwest Bend Formation (in the west). Topographic and magnetic data reveal that tectonism was active during this period and resulted in the erosion and truncation of strandlines. Tectonic evidence and an estimated minimum 28,037 year cyclicity between strandline sets, suggests that the Loxton-Parilla Sands strandlines do not represent an unbroken record of glacioeustatic change. The subaerial exposure of these sediments at approximately 3.0 Ma caused the formation of a calcareous karst above the Norwest Bend Formation and a ferruginous and/or silicious cap (the Karoonda Surface) above the Loxton-Parilla Sands. The stratigraphic position of these surfaces are indicative of a regional widespread unconformity. The Douglas-Blackburn paleodrainage system in western Victoria was dammed during the Mid-Late Pliocene by uplift associated with the Padthaway High, which caused the formation of a 400,000 km2 lacustrine system, known as Lake Bungunnia. Topographic analysis indicates that Lake Bungunnia comprised at least four distinct sub-basins with water depths of up to 30 metres, with lake shorelines indicating that active tectonism occurred during this period. The resulting lack of sediment input to the coast caused the formation of the Kanawinka Escarpment, a large erosional scarp along the southern margin of the Padthaway High. The geomorphology of the modern Murray Basin can be directly attributed to the demise of the Lake Bungunnia system. Movement along the Morgan Fault in the west at approximately 700 Ka, resulted in the draining and progressive drying of Lake Bungunnia as a breach was created along the Padthaway High. The Murray River gorge as observed today was incised following this episode. The modern Murray River (and playa lakes such as Lake Tyrell) occupy the lowest elevations along the former sub-basins of Lake Bungunnia. The Late Neogene sedimentary sequence across the Murray Basin illustrates a complex interaction of eustatic and tectonic processes on deposition. Sedimentation within strandline, estuarine and lacustrine systems, particularly in the western Murray Basin, display evidence of significant tectonic control. This highlights the important role that neotectonic processes have played in shaping southeastern Australia.