De determination of quartz samples showing falling De(t) plots

To determine an equivalent dose (De), the initial signal of the CW-OSL decay curve, supposedly dominated by the fast component, is used. Previous studies suggest that the resulting De however, may be underestimated if thermally unstable medium or slow components are part of the initial decay curve. The De(t) plot has the potential to reveal the “unclean” fast component. We have here studied quartz samples obtained from late Pleistocene floodplain deposits in the Lower Mississippi Valley (LMV), which show decreasing values of De with increasing stimulation time. The deconvolution analysis of CW-OSL signals from these samples confirm the interpretation of the De(t) plots. As a consequence, component-resolved values of De were determined to obtain an accurate estimation of De. Contrary to previous studies, our results indicate that the values of De obtained with the initial signal are not underestimated for our samples containing a thermally unstable medium component.