Assessing the effectiveness of the double-SAR protocol in isolating a luminescence signal dominated by quartz

The effect of the presence of feldspars that can be shown to exhibit anomalous fading is investigated using the double-SAR protocol. This protocol has been suggested as a method of isolating an optically stimulated luminescence (OSL) signal dominated by quartz from a polymineralic mixture of grains. The progressive removal of feldspars from the silt-sized fraction of sediments from Bignell Hill, Nebraska, is also investigated using chemical treatment with hydrofluorosilicic acid for different durations; the appropriate treatment duration for these sediments is identified as being 7 days. For untreated material, the double-SAR protocol yields IRSL and [post-IR] OSL signals that are both dominated by feldspars and that give the same value for the equivalent dose (D-e) determination. However, for material treated with hydrofluorosilicic acid for 7 days, the IRSL and [post-IR] OSL signals have distinctly different characteristics and appear to be dominated by feldspar and by quartz, respectively. Furthermore, the D-e values determined for the feldspar-dominated IRSL signal are about half those obtained for the quartz-dominated [post-IR] OSL signal. This demonstrates that the double-SAR protocol is not always capable of isolating a quartz-dominated signal; clearly, in some circumstances it is necessary to apply a chemical pre-treatment to remove the contribution from feldspars prior to any luminescence measurements being made.