Optical dating of an aeolian deposit on the Murrumbidgee floodplain

Optical dating of quartz grains from an aeolian deposit using multiple aliquot additive-dose and regenerative-dose growth curves, combined using the Australian slide method, produced ages slightly exceeding the C-14 2 sigma age range of 3470-4230 yr from charcoal fragments from the same horizon. A slightly greater degree of scatter was observed about the additive-dose growth curve than about the regenerative-dose growth curve, raising the possibility that the sample might have been composed of grains containing different palaeodose (P) as a result of incomplete predepositional bleaching. This possibility was first investigated using small aliquots ( similar to 10 grains) and a single-aliquot regenerative-dose (SAR) protocol. Asymmetric P distributions were observed, initially interpreted as supporting the presence of a partially bleached population. Single grains of quartz were then examined to determine if several discrete P populations could be resolved, thereby providing information on reworking events, and larger aliquots were then measured in an attempt to reconcile the "Australian slide" findings with the small aliquot and single-grain results. (C) 2000 Elsevier Science Ltd. All rights reserved.