Developments in optically stimulated luminescence and photo-transferred thermoluminescence dating of young sediments: Application to a 2000-year sequence of flood deposits

This paper demonstrates how optically stimulated luminescence (OSL) and photo-transferred thermoluminescence (PTTL) can be used to date young (0-2000 year-old) flood deposits on the bank of a major river in the Southern Tablelands of southeastern Australia. Quartz grains extracted from these deposits do not show a detectable dose-dependent sensitivity change following optical stimulation. This allows a recently proposed regeneration-based protocol (SARA) to be used to estimate the equivalent dose (D-e) acquired since burial. For the oldest sample, a dependence of D-e on pre-heat temperature is removed by heating to at least 180 degrees C for 10 s before stimulation. Values of D-3 are reported for six samples using both OSL and PTTL. Values ranged between 0.4 and 6.5 Gy, with overall uncertainties usually <7%; the values of D-e obtained using OSL and PTTL are in agreement. Dose rates are calculated from detailed analyses of environmental radionuclide concentrations, and the resulting luminescence dates range from 100 +/- 13 to 1920 +/- 130 years before present; the uncertainties include systematic effects. For two layers where there is age control by C-14 dates, the luminescence dates are in good agreement. Unfortunately, the limitations of the C-14 data preclude firm conclusions about the size of any effective age-residual at deposition for the luminescence samples, although this is likely to be <50-100 years. It is concluded that luminescence dating offers a considerable improvement over other techniques, including C-14, for recently transported fluvial sediments.