Empirical assessment of beta dose heterogeneity in sediments: implications for luminescence dating

• Published in: Quaternary Geochronology
• Main Authors: Smedley, Rachel, Duller, Geoff, Rufer, Daniel, Utley, James
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2020
• Subjects: Ice Sheet
• Online Access: http://livrepository.liverpool.ac.uk/3074692/; https://doi.org/10.1016/j.quageo.2020.101052; http://livrepository.liverpool.ac.uk/3074692/1/Smedley%20et%20al.%20Accepted%20QG_MANUSCRIPT.pdf; http://livrepository.liverpool.ac.uk/3074692/7/Smedley%20et%20al.%202020%20%28QG%29%20-%20beta%20heterogeneity.pdf

Optically stimulated luminescence (OSL) dating of single grains is often required to determine an accurate age for partially-bleached sediment by identifying those grains with OSL signals that were well bleached prior to burial. However, single-grain De distributions are typically characterised by greater amounts of scatter in comparison to multiple grains. Here we investigate the scatter in single-grain De distributions of quartz from 56 proglacial samples associated with the retreat of the last British-Irish Ice Sheet. Our findings provide the first empirical dataset showing that beta-dose heterogeneity can impact the extrinsic scatter in single-grain De distributions, in addition to partial bleaching in nature. The additional scatter in single-grain De distributions caused by beta-dose heterogeneity suggests that it is inappropriate to apply a fixed threshold to determine between well-bleached and partially-bleached De distributions, but the skewness of the De distributions could alternatively be used. Autoradiography and QEMSCAN analyses show that there was a negative relationship between the relative standard deviation (RSD) of the beta-dose heterogeneity and the beta dose-rate. This relationship offers the opportunity to infer the RSD of the beta-dose heterogeneity for each sample using just the beta dose-rate, instead of acquiring empirical data for every sample. For this large suite of sedimentary samples, we observe a minimum OD of 20 % arising from the effects of beta-dose heterogeneity (Fig. 3e), which should be added (in quadrature) to the intrinsic OD to determine σb for the minimum age model (MAM) to calculate accurate OSL ages and prevent underestimation of the burial age.