| 17 Oct 2025
Novel insights into the post-IR IRSL200 signal bleachability of single-grain K-feldspars in fluvial modern analogues from the Southern Central Andes, Chile
Abstract. Post-infrared infrared stimulated luminescence (post-IR IRSL) signals from potassium feldspars are gaining prominence in both luminescence dating and luminescence-based sediment tracing techniques. To enhance the accuracy and reliability of these applications, it is essential to develop a comprehensive understanding of how post-IR IRSL signals undergo bleaching. While previous studies have explored post-IR IRSL bleachability using multi-grain approaches, a systematic single-grain investigation on modern analogues has not been conducted. In this study, we examined the bleaching behaviour of the post-IR IRSL200 signal at the single-grain level in eleven modern floodplain samples from the tectonically active Southern Central Andes. Our study demonstrated considerable variation in the mean residual doses observed following two days of laboratory solar simulator bleaching across the sample set. This variability was evident not only between different samples but also among individual grains within the same sample. Thus, we evaluated the influence of bleaching duration, grain-specific geochemical composition, catchment-scale lithological variability, and the size of the natural dose on both laboratory-measured residual doses and remnant doses. Our laboratory bleaching experiments showed consistent post-IR IRSL200 signal behaviour across four different samples, reaching a plateau based on normalised luminescence signal after two days of exposure to solar simulator light. While individual grains exhibited a wide range of bleaching rates, this variability did not account for the spread in residual dose values. Notably, extended light exposure reduced variability in signal intensity, underscoring its role in dose homogenisation. Geochemical analysis of major oxides showed no significant correlation with either residual dose magnitude or bleaching rate, suggesting that mineral composition (including K-concentration) does not influence bleaching efficiency at the individual grain level. Furthermore, bleaching behaviour remained consistent across samples regardless of catchment lithology, with no discernible relationship between lithological units and remnant or residual dose values. Most importantly, we identified a strong positive exponential correlation (R2 = 0.86) between residual dose and natural remnant dose, revealing dose-dependent bleaching efficiency and the presence of a unbleachable component at the time of deposition. By integrating insights on bleachability with the information on the unbleachable component and remnant doses derived from modern analogues, we highlight the limitations of correcting palaeodoses by directly using remanent doses and evaluate three context-sensitive correction strategies. Finally, we discuss how residual dose and the unbleachable component can be leveraged to more reliably identify well-bleached grains, enhancing the accuracy of luminescence-based sediment tracing applications.
Review of Biswas et al., submitted for publication in GChron
Manuscript ‘Novel insights into the post-IR IRSL200 signal bleachability of singlegrain K-feldspars in fluvial modern analogues from the Southern Central Andes, Chile’
Review by Jakob Wallinga, Wageningen University / Netherlands Centre for Luminescence dating.
The authors investigate the resetting of feldspar pIRIR200 signals upon light exposure, using data from both modern fluvial samples and laboratory irradiated and bleached samples. They find that bleaching rates vary between grains, and explore whether these differences can be explained from the chemical composition of the grains. The work and insights gained are original and relevant to the luminescence dating and tracing community, and fit well with the scope of the GChron journal. I would therefor support publication of the work. However, I would suggest that major revisions are needed to improve quality and clarity prior to publication. Below I list the most crucial improvements to be made.
My first concern is the focus of the paper. The manuscript documents a wide range of experiments conducted on a set of samples – a more coherent storyline and choices on which data to include in the main paper would contribute to a more powerful manuscript. At the end of the introduction five aims are listed, which is a lot for a single paper. I would recommend to reduce to a maximum of three aims. In this context, I would suggest to focus on bleachability of individual grains and how it relates to geochemical composition of the grains – as this is the original and unique aspect of the paper. For remnant doses in modern natural samples, the light exposure history (rather than bleachability) is likely to be the decisive factor (as is also discussed in e.g. the associated thesis by Karman—Besson). The remnant dose data is hardly discussed and distracts from the original and important work to investigate bleachability at single grain level. Moreover, I have some serious reservations on the interpretation of the data. As other approaches/assumptions may change the interpretation and hence the conclusions drawn, I would like to re-assess the paper after the authors have implemented the suggestions below – or provide convincing argumentation why they decide not to.
Below I list my major reservations with respect to the data interpretation:
Additional minor comments: