Estimation of equivalent dose using quartz isothermal TL and the SAR procedure

Abstract

Optically stimulated luminescence (OSL) from quartz is now widely applied to the dating of Quaternary sediments. Unfortunately, quartz OSL ages are often limited to 100–200 ka by the saturation level of the dose–response curve (∼300 Gy), unless the annual dose from the surrounding sediments is sufficiently low. Quartz thermoluminescence (TL) has been used in the past to date beyond this range, but this signal is no longer widely employed because of the poor reproducibility obtained from multiple-aliquot procedures, and because of the greater uncertainty in the degree of bleaching compared to the OSL signal. Here we investigate, for the first time, the possibility of using the quartz isothermal thermoluminescence (ITL) signal at 310 °C for dating sediments from various depositional environments. The single-aliquot regenerative-dose (SAR) procedure is shown to be applicable to this signal, and a protocol is developed. Dose recovery tests are used to examine the reliability of the new protocol for equivalent dose ( D e) estimation using quartz ITL. The D e values obtained using the new protocol are compared to those from conventional SAR OSL. We estimate D e values as high as 550±50 Gy, corresponding to a luminescence age of 147±13 ka, for a natural loess sample from Korea. Our results suggest that quartz ITL shows potential for dating samples well beyond the OSL age range. The new ITL SAR protocol has several advantages common to all applications of the SAR procedure: D e estimation from a single aliquot using interpolation, excellent reproducibility, high throughput (allowing routine testing of protocol performance), and the ability to examine the distribution of D e within a sample.