On the performances of the single-aliquot regenerative-dose (SAR) protocol for Chinese loess: fine quartz and polymineral grains

Abstract

This paper presents the results of a study which assesses the performances of the single-aliquot regenerative-dose (SAR) protocol in fine quartz and polymineral grains (4– 11 μ m ) obtained from the Luochuan loess–paleosol section on the central Loess Plateau, China. Fine quartz was isolated from polymineral grains, with the grain mineralogy confirmed by infrared (IR) stimulation detection. The fine quartz optically stimulated luminescence (OSL) results obtained yielded a stratigraphically consistent equivalent dose ( D e ) distribution for the Luochuan loess–paleosol sequence deposited during the last glacial–interglacial. The performances of the infrared stimulated luminescence (IRSL) signal and the optically stimulated luminescence signal after infrared exposure ([post-IR] OSL) for polymineral grains were estimated by a comparison with that of fine quartz. Our results suggest that the IRSL D e value is underestimated in relatively old samples (about > 50 Gy ) probably due to anomalous fading of the natural IRSL signal. We propose that the ratio of IRSL vs. [post-IR] OSL signal provides a measure of the degree of fading of the IRSL signal. It is confirmed that the [post-IR] OSL signal after sufficient IR exposure provides a better performance than that of the IRSL signal in Chinese loess, not only for the Holocene samples, but also for the last glacial samples. A suitable IR exposure time prior to measurement of the [post-IR] OSL signal can be obtained by determination of the plateau region of a plot of the [post-IR] OSL D e value vs. IR exposure duration. The results obtained suggest that both quartz OSL and polymineral [post-IR] OSL signal can produce consistent D e estimates for the loess–paleosol succession. The linear modulation technique was used to explain the good performance of [post-IR] OSL signal in D e determination.