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Age and origin of alluvial sediments within and flanking the Mt Lofty Ranges, southern South Australia: a Late Quaternary archive of climate and environmental change

2010; Taylor & Francis; Volume: 57; Issue: 2 Linguagem: Inglês

10.1080/08120090903416260

1440-0952

Robert P. Bourman, J.R. Prescott, D. Banerjee, N. F. Alley, Solomon Buckman,

Pleistocene-Era Hominins and Archaeology

Abstract Quaternary alluvial sediments occur within and on the flanks of the Mt Lofty Ranges of southern South Australia. Within the ranges they occupy colluvium-filled bedrock depressions, alluvial-fan sequences at hill/plain junctions and river terraces that flank major streamlines in both locations. Sediments ranging in age throughout the Quaternary have been identified, but this paper focuses on those deposits of Late Quaternary age. Luminescence dating has verified a Last Interglacial age (132–118 ka) for the most widespread of the alluvial units, the Pooraka Formation. A younger, Marine Isotope Stage 3, alluvial unit, in places containing bones of the extinct marsupial Diprotodon, has also been identified. Deposition of the alluvial sediments is associated with relatively warmer and wetter conditions, whereas the valleys that they occupy were eroded under drier climatic conditions. A more widespread occurrence of Stage 3 units is expected to be present but has not yet been verified. Cold, arid environments are inferred from the presence of dunes (∼18 ka) deposited during the Last Glacial Maximum when stream valleys were incised. Grey/black mid-Holocene alluvium (Waldeila Formation), forming present-day floodplains and low river terraces, equates with the Holocene Hypsithermal. The sequence of climatic changes revealed by these sediments is correlated with evidence of Late Quaternary climatic change from other Australian locations. The identification of equivalent units in different tectonic settings reveals that sedimentation is largely climatically driven although active tectonism may accelerate the supply of sediments available for transport. Key Words: climate changeluminescence dating, megafaunaMt Lofty RangesPooraka FormationQuaternarySouth Australiaterrestrial sediments Acknowledgements We are grateful to the owners of the property containing the Diprotodon bones, Mr and Mrs Clarke, for drawing them to our attention and for facilitating access. Neville Pledge is thanked for identifying the bones, and G. Robinson, L. Waldron and P. Martinaitis for field assistance. PIRSA provided support funding the luminescence dating of the Burra Creek samples. The luminescence dating was also assisted by grants 96/080 and 98/P008 from the Australian Institute of Nuclear Science and Engineering and the Archaeometry Special Fund of the Physics Department, University of Adelaide. We are grateful to Gerald Nanson for providing useful feedback on an early version of the paper. Philip Roetman is thanked for preparing the illustrations. Funding for dating of the Sellicks Creek samples was provided by the University of South Australia. We appreciate the critical reviews of the paper by Colin Murray-Wallace and Nick Harvey. We thank the referees Paul Hesse and Wolfgang Preiss for their insightful improvements to the paper: we are particularly indebted for having our attention drawn to the most important and informative work of the late D. L. G. Williams.