School of Geography - Theses
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ItemThe morphology and evolution of rock coasts over eustatic cycles in temperate, wave dominated environments( 2019)Rock coasts comprise 80% of the world’s shorelines and about 50% of the Victorian coast. Their morphology and evolution over time is the result of marine and subaerial erosional processes that carve features such as sea cliffs, shore platforms, and sea stacks out of the landscape. Rock coasts, therefore, evolve over multiple sea level cycles and create dynamic landscapes on an interglacial timescale. Sea level has risen and fallen over geologic time, with coastal features being formed during sea level high stands. While most coastal landforms found along the modern coast were formed over the past 6,000 years, older coastal features have also been preserved over multiple eustatic cycles, both above and beneath modern sea level. As coastal landforms are formed at or very near sea level, preserved paleo-shoreline features can be used as proxies to reconstruct past sea levels on a regional scale, which had not previously been done for the coast of Victoria, Australia. In this study, an integrated aerial LiDAR and bathymetric multibeam dataset from +20 to -80 m water depth was used to precisely map and quantify the morphology of the rock coast features along the coast of Victoria from Port Fairy in the west to Wilsons Promontory in the east and to analyze the relation between the features’ elevations and the sea levels at which they first formed. This was completed for both the modern coastline as well as paleo-shoreline landforms found 50-60 m below modern sea level, where the offshore geology reflected the onshore geologic units, allowing for an analogous study. These preserved features are believed to have formed during the MIS 3 high stand, during which time sea level most closely matched their average present depths. The culminating results provide not only the first study of the precise morphology of these submerged features in Victoria but also have wider applications for modelling sea level and rocky coast evolution in other temperate, wave dominated environments.
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ItemSpeleothem-based explorations of millennial-scale climate change in southern Australasia( 2018)Understanding the way Earth responds to rapid climate change is critical for understanding future climate scenarios. The best natural examples of rapid climate change are found in millennial-scale climate events recorded in Greenland ice cores over the Last Glacial Period (120-12 ka). These occur concurrently with similarly-paced, gradual warming events recorded in Antarctic ice cores. Understandings of the transition between Greenland-like and Antarctic-like millennial-scale climate events are limited by a lack of appropriate records from the southern mid-latitudes. However, calcite cave formations (speleothems) have the potential to record high-resolution millennial-scale climate change in this region. This study looks at three southern mid-latitude cave sites, develops or improves palaeoclimate reconstructions from each, compares these to external records of millennial-scale climate change, and assesses the suitability of each site for future millennial-scale palaeoclimate reconstructions. Palaeoclimate reconstructions were produced based on U-Th dating, stable isotope analysis and trace element analysis techniques. The first ever high-resolution palaeoclimate record from Naracoorte, Australia from the Last Glacial Period was produced, which suggested that millennial-scale climate change here was influenced by changes in the activity of the southern westerlies. The first ever palaeoclimate record from Wombeyan, Australia was produced, which suggested that millennial-scale climate change here was confounded by both tropical and mid-latitude climate effects. An existing palaeoclimate record from Nettlebed was improved upon and reinterpreted, which supported previous findings that millennial-scale climate in Nettlebed is influenced by the intensity of the southern westerlies. Naracoorte and Nettlebed demonstrated good potential for future millennial-scale palaeoclimate reconstructions, although Naracoorte is limited by a lack of speleothem samples from the Last Glacial Period. Wombeyan demonstrated poor potential for future millennial-scale palaeoclimate reconstructions due to its confounded climate signature, and high U-Th age uncertainties due to low speleothem uranium concentrations. These findings have implications for the future study of millennial-scale climate change, by presenting brand new millennial-scale palaeoclimate reconstructions and demonstrating how future millennial-scale palaeoclimate reconstructions can be developed from a critically under-sampled region.