Luminescence dating of glaciofluvial deposits: A review

Abstract For glacigenic sediments, Optically Stimulated Luminescence (OSL) dating offers an opportunity to date the time of deposition of quartz and feldspar minerals that are ubiquitous within the sediment matrix, rather than relying upon the chance occurrence of organic material for radiocarbon dating. The OSL dating signal or charge accumulates in crystal defects of individual quartz and feldspar minerals through exposure to environmental radiation within their depositional setting. The OSL signal within individual grains can be reset or bleached through exposure to daylight during transportation processes. Thus OSL dating of sediments attempts to determine the time elapsed since burial. Glacigenic sediments present considerable challenges for OSL dating not only in terms of poor bleaching of the OSL signal during the transport and deposition cycle, but also poor quartz luminescence characteristics which are often related to sediment provenance, the nature of the bedrock or source material, and the freshly eroded nature of many such deposits. This paper reviews luminescence dating techniques as applied to glaciofluvial sediments and explores the challenges that such deposits present to the technique. Successful application of OSL techniques can be judged in a number of ways: comparison with the ‘independent’ chronologies is prevalent in the literature, but recently the movement towards measurement of large numbers of small aliquots and single grains allows a more robust assessment of luminescence properties and behaviour for individual samples and ultimately more precise luminescence ages to be determined. For glaciofluvial sediments in particular, it is important to investigate the depositional sub-environment of each sample in relation to the chance of sufficient bleaching during transport and deposition. A lithofacies-based approach to sampling for optically stimulated luminescence dating of these sediments is suggested whereby hypothetically well-bleached deposits are targeted after a detailed investigation into possible environments of deposition. This approach, together with small aliquot/single-grain analysis methodologies should further enhance the likelihood of obtaining a sufficiently bleached sample for OSL dating.