Optically Stimulated Luminescence (OSL) dating.

Radial plot of the equivalent dose (D_e) values obtained from 49 individual grains of quartz from sample JQ200-OSL1. Filled circles denote the 46 values used to calculate the weighted mean D_e for OSL age determination, and open triangles are the three values identified as outliers (Table 1). Each point represents the D_e value for a single grain. It can be read off the radial axis by extending a line from zero on the ‘standardised estimate’ axis through the point of interest, and the ‘relative error’ on this D_e can be read by projecting a vertical line to intersect the horizontal axis. The ‘precision’ is the reciprocal of the relative error, so the most precise D_e estimates lie furthest to the right. The grey band is centred on the weighted mean D_e estimated using the Central Age Model. Individual D_e values that are consistent at 2σ with this weighted mean fall within the grey band. This D_e distribution is overdispersed by 23±4%, which is typical for well-bleached samples of quartz that have not been disturbed since burial. See Galbraith and Roberts [71] for further explanation of statistical aspects of D_e estimation and display in OSL dating.