Dating recent floodplain sediments in the Hawkesbury- Nepean River system, eastern Australia using single-grain quartz OSL.

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 ¹⁴ C ( 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, MAM_UL 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. [ABSTRACT FROM AUTHOR]