Standardised growth curves for optical dating of sediment using multiple-grain aliquots

The single aliquot regenerative dose (SAR) protocol offers the opportunity of exploring, relatively simply, the existence of a ‘universal’ growth curve for use in dating using optically stimulated luminescence (OSL). A test dose is used in the SAR procedure to monitor and correct for sensitivity change occurring either over the burial period, or as a result of thermal pretreatments during the measurement procedure. However, this test dose can also be used to correct for variations in signal intensity between individual aliquots, thus enabling the comparison of growth response with dose for many different aliquots and samples, even for measurements made using different instruments. In this paper, the growth characteristics of coarse-grained quartz and polymineral fine-grains are examined using data obtained as part of the SAR procedure. Following standardisation of these data for differences in the test dose response and the magnitude of the test dose used, distinct and reproducible patterns of growth are observed and mineral-specific standardised growth curves (SGCs) are defined for multiple-grain aliquots. An equivalent dose for a sample can then be determined based only on measurements of the natural luminescence signal intensity (Ln) and the response to an artificial irradiation dose (Tn). This equivalent dose, determined using the SGCs defined for quartz and polymineral fine-grains, is compared to that determined using a conventional SAR measurement procedure, for a large number of samples and aliquots. Using an SGC, accurate estimates of equivalent dose may be made based solely on measurements of Ln and Tn, thus potentially speeding up the measurement process. This has obvious benefits where it is necessary to examine a large number of aliquots.