Research Paper A revised burial dose estimation procedure for optical dating of young and modern-age sediments L.J. Arnold a, * , R.G. Roberts a , R.F. Galbraith b , S.B. DeLong c a GeoQuEST Research Centre, School of Earth and Environmental Sciences, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, Australia b Department of Statistical Science, University College London, London WC1E 6BT, UK c U.S. Geological Survey, 345 Middlefield Rd. MS 977, Menlo Park, CA 94025, USA article info Article history: Received 10 November 2008 Received in revised form 18 February 2009 Accepted 20 February 2009 Available online 6 March 2009 Keywords: Optically stimulated luminescence dating Single-grain Un-logged age models Minimum age model Fluvial sediments Arroyo abstract The presence of genuinely zero-age or near-zero-age grains in modern-age and very young samples poses a problem for many existing burial dose estimation procedures used in optical (optically stimulated luminescence, OSL) dating. This difficulty currently necessitates consideration of relatively simplistic and statistically inferior age models. In this study, we investigate the potential for using modified versions of the statistical age models of Galbraith et al. [Galbraith, R.F., Roberts, R.G., Laslett, G.M., Yoshida, H., Olley, J.M., 1999. Optical dating of single and multiple grains of quartz from Jinmium rock shelter, northern Australia: Part I, experimental design and statistical models. Archaeometry 41, 339–364.] to provide reliable equivalent dose (D e ) estimates for young and modern-age samples that display negative, zero or near-zero D e estimates. For this purpose, we have revised the original versions of the central and minimum age models, which are based on log-transformed D e values, so that they can be applied to un- logged D e estimates and their associated absolute standard errors. The suitability of these ‘un-logged’ age models is tested using a series of known-age fluvial samples deposited within two arroyo systems from the American Southwest. The un-logged age models provide accurate burial doses and final OSL ages for roughly three-quarters of the total number of samples considered in this study. Sensitivity tests reveal that the un-logged versions of the central and minimum age models are capable of producing accurate burial dose estimates for modern-age and very young (<350 yr) fluvial samples that contain (i) more than 20% of well-bleached grains in their D e distributions, or (ii) smaller sub-populations of well- bleached grains for which the D e values are known with high precision. Our results indicate that the original (log-transformed) versions of the central and minimum age models are still preferable for most routine dating applications, since these age models are better suited to the statistical properties of typical single-grain and multi-grain single-aliquot D e datasets. However, the unique error properties of modern- age samples, combined with the problems of calculating natural logarithms of negative or zero-Gy D e values, mean that the un-logged versions of the central and minimum age models currently offer the most suitable means of deriving accurate burial dose estimates for very young and modern-age samples. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Over the last ten years, there have been a number of important methodological and technological advances in optically stimulated luminescence (OSL) dating (e.g. Murray and Roberts, 1997; Roberts et al., 1998; Murray and Wintle, 2000; Bøtter-Jensen et al., 2000) that have permitted (i) a shift away from conventional multiple- aliquot equivalent dose (D e ) estimation procedures towards single- aliquot methods, (ii) improved reliability of D e calculation based on interpolation, rather than extrapolation, of fitted dose–response curves, (iii) routine measurement of large numbers of replicate D e values for different aliquots of the same sample, and (iv) rapid measurement of individual sand-sized grains of quartz with rela- tively small OSL signals. The improvements in precision and accu- racy afforded by these advances, and in particular the use of the single-aliquot regenerative-dose (SAR) protocol, have made it possible to apply OSL dating techniques over increasingly younger timescales, as demonstrated by a number of reliable OSL dating studies of very young (<500 yr) and modern-age sedimentary samples with independent age control (e.g. Olley et al., 1998, 1999, 2004; Bailey et al., 2001, 2003; Ballarini et al., 2003; Singarayer et al., 2005; Madsen et al., 2007; Page et al., 2007; Rustomji and * Corresponding author. Tel.: þ61 242215946. E-mail address: larnold@uow.edu.au (L.J. Arnold). Contents lists available at ScienceDirect Quaternary Geochronology journal homepage: www.elsevier.com/locate/quageo 1871-1014/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.quageo.2009.02.017 Quaternary Geochronology 4 (2009) 306–325