Equivalent dose determinations for polymineralic fine-grains using the SAR protocol: application to a Holocene sequence of the Chinese Loess Plateau

A single-aliquot regenerative-dose (SAR) protocol, involving stimulation of the same disc with an infra-red laser diode followed by blue LEDs, was applied to polymineralic fine-grains. Infra-red stimulated luminescence (IRSL) and (post-IR) optically stimulated luminescence (OSL) ages are presented for a series of 19 fine-grain (4-11 mum) samples, taken from a loess section (Duowa) in the western Chinese Loess Plateau. There an significant differences between the equivalent doses and, thus, the ages for the IRSL and (post-IR) OSL measurements. Three potential explanations an investigated: incomplete bleaching prior to deposition; thermal transfer of charge; and initial sensitivity change. The question regarding which sequence of ages [IR or (post-IR) OSL] is correct (if either) is not resolved, although the 19 (post-IR) OSL ages yield more consistent results. It is proposed that the 'double' SAR protocol employed may not be correctly monitoring the sensitivity changes relating to either (or both) Natural signals. (C) 2000 Elsevier Science Ltd. All rights reserved.