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Dating recent floodplain sediments in the Hawkesbury‐Nepean River system,eastern Australia using single‐grain quartz OSL
Authors:Anna K Sim  Kristina J Thomsen  Andrew S Murray  Geraldine Jacobsen  Russell Drysdale  Wayne Erskine
Institution:1. Environmental and Climate Change Research Group, University of Newcastle, , Callaghan, NSW, 2308 Australia;2. Centre for Nuclear Technologies, Ris? Campus, DTU, , DK‐4000 Roskilde, Denmark;3. Nordic Laboratory for Luminescence Dating, Department of Geoscience, Aarhus University, , Aarhus, Denmark;4. Institute for Environmental Research, Australian Nuclear Science and Technology Organisation, , Kirrawee DC, NSW, 2232 Australia;5. Resource Management and Geography, University of Melbourne, , Melbourne, 3010 Vic, Australia;6. Environmental Research Institute of the Supervising Scientist, , Darwin, NT, 0801 Australia
Abstract:Two fluvial sediment cores taken from a floodplain of the Hawkesbury‐Nepean River system in the Sydney region, eastern Australia are dated using Optically Stimulated Luminescence (OSL) to provide a reliable chronology essential for the management and planning of water resources. Nine charcoal 14C (AMS) dates constrain these OSL ages. Quartz extracted from seven OSL samples from each of the cores was measured using both single‐grain and multi‐grain OSL techniques. Three of the single‐grain natural dose distributions appear to be well bleached, but the others appear to be incompletely bleached to various degrees. Three minimum‐age models (MAM, MAMUL and IEU) are applied to the single‐grain dose distributions. We conclude that these models give consistent age estimates. For one of the cores it appears to be necessary to use a minimum‐age model to obtain accurate ages, but in the other core incomplete bleaching is probably less important than postdepositional mixing and mixing during sampling. As a result, the burial age is probably best estimated using the weighted average of the individual single‐grain dose estimates. The application of multi‐grain OSL techniques to these samples results in an average apparent age overestimation of ~200 years, which is significant for these samples, but negligible for sediments older than a few thousand years. The intention is that the chronology obtained in this study will be used in conjunction with a proxy flood record, derived from floodplain sediments, to gain an understanding of the long‐term variability in periods of high and low rainfall in eastern Australia.
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