Exploring dryland dynamics with portable luminescence readers

Luminescence signals using portable luminescence readers (port-OSL) are insightful tools for exploring sample relative age and casting additional light on sediment characteristics, used back in the laboratory or in the field. Sand-rich dryland environments are a useful testing ground for using port-OSL, owing to the likelihood of complete signal bleaching before burial. We have been exploring the extent to which it is possible to produce generalized chronologies that approximate sediment burial age in different locations and geomorphic settings. Our approach compares port-OSL signals with ages established using standard luminescence dating protocols for quartz, as a form of port-OSL first-order ‘calibration’ (e.g. Stone et al., 2015; 2019; Nitundil et al., 2022). The rationale for this work is to provide landscape-scale assessments of Quaternary environmental change in a cost-effective and time-effective manner.

In this study we present samples from dunes in four regions within southern African dunes (re-measured in 2022 to provide a consistent analytical sequence and data processing approach) and from the Thar Desert in western India. This represents n=26 for the Namib Sand Sea, n=32 for the western Kalaha-ri, n=22 for the southern Kalahari, and n=44 for the Thar (and may include further regions, if samples are available before June 2023). We also present samples from palaoelake shorelines in the former megalake Makgadikgadi sequence (n=73 from Lake Ngami, n=40 from Lake Mababe and n=36 from Makgadigadi).

We find the port-OSL calibrations are region specific with coherent regional groupings, and strong coefficients of correlations for the dune datasets. However, those from the lake shorelines define a weaker correlation with sample age. We explore the influence of sample composition data (such as quartz to feld-spar rations and particle size distribution) and inherent port-OSL signal brightness (using a subset of southern African dune and lake shoreline samples).