The Quaternary Geomorphological Evolution of the River Murray Mouth and Lakes Region, Southern Australia

University of Wollongong Research Online University of Wollongong Thesis Collection 1954-2016 University of Wollongong Thesis Collections 2015 The Quaternary geomorphological evolution of the River Murray mouth and lakes region, southern Australia Deirdre Dymphna Ryan University of Wollongong Follow this and additional works at: https://ro.uow.edu.au/theses University of Wollongong Copyright Warning You may print or download ONE copy of this document for the purpose of your own research or study. The University does not authorise you to copy, communicate or otherwise make available electronically to any other person any copyright material contained on this site. You are reminded of the following: This work is copyright. Apart from any use permitted under the Copyright Act 1968, no part of this work may be reproduced by any process, nor may any other exclusive right be exercised, without the permission of the author. 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Recommended Citation Ryan, Deirdre Dymphna, The Quaternary geomorphological evolution of the River Murray mouth and lakes region, southern Australia, Doctor of Philosophy thesis, School of Earth and Environmental Sciences, University of Wollongong, 2015. https://ro.uow.edu.au/theses/4539 Research Online is the open access institutional repository for the University of Wollongong. For further information contact the UOW Library: [email protected] The Quaternary geomorphological evolution of the River Murray mouth and lakes region, southern Australia A thesis submitted in fulfilment of the requirements of the award of the degree of Doctor of Philosophy from The University of Wollongong by Deirdre Dymphna Ryan BSc. MSc. School of Earth and Environmental Sciences 2015 I, Deirdre Ryan, declare that this thesis, submitted in fulfilment of the requirements for the award of Doctor of Philosophy, in the School of Earth and Environmental Sciences, University of Wollongong, is wholly my own work unless otherwise referenced or acknowledged. The document has not been submitted for qualifications at any other academic institution. Deirdre Ryan August 2015 Murray Mouth So this is where it ends at last! Half a continent poured out through the long tide-swept sand - the snout of bars, the crunch of wet shells shining, and at night the swinging stars! No guard of honour from great old trees, no bustle of ships or wharves, no city lights, no high bluffs or banks, not even a nation's thanks. Only the long low beaches on and on, and in the white sandhills a gap, a smoothness lying, and a channel, a rip, a strange wild stir... Who would wish it other? Alone, unmarred, the spirit of the land it springs from slips to rest. Sardonic old saunterer, here at last Is death and burial in the line of surf - free as the south wind edged with agate, no ships or sewers, smoke or smear of oil, no lumber, roadways or tilled soil. only a great old river at its end, silently, unrecognised by light or bell, swept under the wild hooves of the South and blessed only by the ponderous pelican's farewell. Colin Thiele, 1970 Murray Mouth, South Australia Abstract This thesis examines the Quaternary geomorphological evolution of the River Murray Mouth region of southern Australia in the context of increasing aridity and fluctuations in eustatic sea level and climate. The region is located at the northern margin of the Coorong Coastal Plain, which preserves a long terrestrial record of Quaternary sea-level highstands within the Bridgewater Formation, a sedimentary succession of coastal carbonate aeolianites with associated beach and back-barrier lagoon facies. The stratigraphic record within the study area has been obscured by long term regional subsidence due to its location adjacent to the uplifting Mount Lofty Ranges, erosion by the River Murray and the dunefields of siliceous Molineaux Sands deposited under continental conditions during periods of glacially low sea levels. Unravelling the depositional record within this region assists in understanding localised variations in the sea-level record, the position of the River Murray during eustatic sea- level fluctuations and the dichotomy of sedimentary successions between the terrestrial, arid climates of glacial periods and marginal marine, wetter climates of interglacial periods. The development of the Pleistocene coastline has been extrapolated from the modern beach-barrier-lagoon analogue, following the principle of uniformitarianism. Pleistocene sedimentary successions were recognised by facies architecture and lithology with depositional and diagenetic environments determined through petrographic analyses. The correlation of the sedimentary successions was based on their morphostratigraphic relationships and geochronological analyses using amino acid racemisation, thermoluminescence, optically stimulated luminescence and radiocarbon methods. The results of these analytical techniques were correlated with the Coorong Coastal Plain sea-level highstand record and the oxygen isotope record. The calcium carbonate content of the Bridgewater Formation aeolianite in the study area is regionally variable and lower than the Coorong Coastal Plain equivalents with consequently higher quartz content. This is attributed to terrestrial sediment input by the River Murray, the quartz-rich character of the offshore shelf environment, i continental siliceous dune development during periods of lowered sea level and the reworking of sediments during sea-level transgressions. Extensive recycling of sediments in the region is reflected in a lack of characteristic features on quartz grains from interglacial and glacial sedimentary successions indicative of depositional environment, the ubiquitous presence of reworked quartz and carbonate skeletal grains throughout interglacial sedimentary successions as revealed by AAR analysis of whole-rock samples and individual foraminifer tests. This research has revealed an extensive record of Pleistocene deposition, most likely correlating with the earliest recognised deposit of the Bridgewater Formation on the Coorong Coastal Plain. The early Pleistocene barriers are composite features deposited when the orbitally driven cycles of eustatic sea level and climate change transitioned from obliquity (41 ka) to eccentricity (100 ka). The middle Pleistocene record within the study area is best represented by MIS 7 (191-243 ka) aeolianites forming Sturt Peninsula. The remaining middle Pleistocene record is minimal reflecting ongoing rates of subsidence and high potential for erosion in the region, hindering the ability to draw conclusions regarding the height of interglacial sea level. The longest Pleistocene sedimentary succession is found at Point McLeay, a topographic high in the study are since at least MIS 11 (374-424 ka). The last interglacial shoreline (MIS 5e, 130 109 ka) is the best preserved exhibiting regional variability in sedimentary characteristics and preservation as a result of sediment source, environment of deposition, calcrete development and position in the landscape. The distribution of Bridgewater Formation throughout the Pleistocene and orientation of the coastline has been affected by differential rates of uplift across the Coorong Coastal Plain and dominant longshore drift to the northwest. Both factors have helped to constrain the position of the River Murray to the northern coastal plain where it has been located since its initiation following the demise of Lake Bungunnia. The orientation of the early Pleistocene ranges was also influenced by the granitic basement feature, the Padthaway Ridge. The subsidence in the Murray Mouth has resulted in closely-spaced, onlapping or stacked sedimentary successions of middle to late Pleistocene age that have been subjected to erosion and reworking by the River Murray and Southern Ocean during successive sea-level highstands. The preservation of ii interglacial and glacial sedimentary successions reflects the differential rates of uplift in the region, their proximity to the River Murray and the height of successive sea-level highstands which, on the southern Australia coastline, has returned to within 6 m. Sedimentary successions within the region of subsidence are more susceptible to the migration and erosive force of the River Murray and the Southern Ocean during sea- level transgressions. Erosion by the river delivers sediment to the continental shelf which is redistributed within the continental dunefields of siliceous sand during periods of glacially lowered sea level. During sea-level transgressions these dunefields are reworked and the sediment is redelivered to the coastline bringing full circle the sediment recycling characteristic of the region. The low preservation potential of sedimentary successions in the region reaffirms the River Murray Mouth identity as a failed delta. iv ACKNOWLEDGEMENTS First and foremost thanks must go to my supervisors Professor Colin Murray- Wallace,

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