Study the effect of irradiation, optical bleaching and heating on the thermal stability of OSL signals of quartz from dune sands in northern China

Variability in the thermal stability of quartz OSL signals has been observed for Late Quaternary sediments in different geographic setting in China. In this study, quartz grains were extracted from the Taklimakan Desert and the Hunshandake sandy land and the thermal stability of their quartz OSL signals were further investigated. Firstly, quartz aliquots of Taklimakan Desert were measured by using pulse annealing tests. It was found that the quartz from the Taklimakan Desert exhibited highly variable pulse annealing curves, showing the significant differences in the thermal stability of quartz OSL signals. Secondly, laboratory irradiation, optical bleaching and heating experiments were designed to test their effects on the thermal stability of quartz OSL signals. To compare the thermal stability among different quartz aliquots more efficiently, the thermal remnant ratio (TRR) was used as the proxy for the thermal stability, which was measured by using the ratios of the remnant OSL signals measured after cut-heat to 280 °C to those measured after cut-heat to 240 °C in the simplified pulse annealing tests. For the quartz samples from the Taklimakan Desert, it was found that the operated cycles of dosing and bleaching have relatively insignificant effects on the TRR values of quartz OSL. For the effect of heating on TRR value, it is dependent on samples. When the initial TRR value of quartz OSL is significantly less than 0.9, heating to high temperatures (e.g. ≥400 °C) has significant effect on the TRR value of quartz OSL. When the initial TRR value of quartz OSL is equal to or larger than 0.9, the effect of heating on the TRR value is not obvious. Such results suggest that different heating history of quartz plays an important role in the thermal stability of the quartz OSL signal. Thirdly, the TRR values of quartz OSL of Taklimakan Desert were compared with those of Hunshandake sandy land. For the Taklimakan Desert, it was found that only a part of the quartz grains exhibit TRR values equal to or larger than 0.9. In comparison, the TRR values for the majority of quartz grains from the Hunshandake sandy land are equal to or larger than 0.9. Such results demonstrate the different heating histories of quartz grains between the Taklimakan Desert and the Hunshandake sandy land, i.e. only a part of quartz grains from the Taklimakan Desert suffered from high temperature heating, while the majority of quartz grains from the Hunshandake sandy land suffered from high temperature heating during geological past. The different heating histories of quartz grains between the Taklimakan Desert and the Hunshandake sandy land are consistent with the different geological settings of the two regions. Our studies suggest that the proxy (i.e. TRR) of the thermal stability of quartz OSL has advantages over luminescence sensitivity for distinguishing the provenance of sediments with different heating histories.