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 μm) samples, taken from a loess section (Duowa) in the western Chinese Loess Plateau. There are significant differences between the equivalent doses and, thus, the ages for the IRSL and (post-IR) OSL measurements. Three potential explanations are 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.