Luminescence Dating in Fluvial Settings: Overcoming the Challenge of Partial Bleaching

Abstract

OpticallyFluvial stimulatedPartial bleaching luminescence (OSLOptically Stimulated Luminescence (OSL)) dating is a versatile technique that utilises the two most ubiquitous minerals on Earth (quartz or K-feldspar) for constraining the timing of sediment deposition. It has provided accurate ages in agreement with independent age control in many fluvialFluvial settings, but is often characterised by partial bleachingPartial bleaching of individual grains. Partial bleachingPartial bleaching can occur where sunlight exposure is limited and so only a portion of the grains in the sample was exposed to sunlight prior to burial, especially in sediment-laden, turbulent or deep water columns. OSLOptically Stimulated Luminescence (OSL) analysis on multiple grains can provide accurate ages for partially bleached sediments where the OSLOptically Stimulated Luminescence (OSL) signal intensity is dominated by a single brighter grain, but will overestimate the age where the OSLOptically Stimulated Luminescence (OSL) signal intensity is equally as bright (often typical of K-feldspar) or as dim (sometimes typical of quartz). In such settings, it is important to identify partial bleachingPartial bleaching and the minimum dose population, preferably by analysing single grains,Single grains and applying the appropriate statistical age modelAge models to the dose population obtained for each sample. To determine accurate OSLOptically Stimulated Luminescence (OSL) ages using these age modelsAge models, it is important to quantify the amount of scatter (or overdispersion) in the well-bleached part of the partially bleached dose distribution, which can vary between sediment samples depending upon the bedrock sources and transport histories of grains. Here, we discuss how the effects of partial bleachingPartial bleaching can be easily identified and overcome to determine accurate ages. This discussion will therefore focus entirely on the burial dose determination for OSLOptically Stimulated Luminescence (OSL) dating, rather than the dose-rate, as only the burial doses are impacted by the effects of partial bleachingPartial bleaching.