Testing the potential of an elevated temperature IRSL signal from K-feldspar

Thomsen, K.J., Murray, A.S., Jain, M., Botter-Jensen, L [2008. Laboratory fading rates of various luminescence signals from feldspar-rich sediment extracts. Radiat. Meas. 43, 1474-1486] have identified a number of feldspar signals which show significantly less anomalous fading than the conventional IRSL signal stimulated at 50 degrees C and detected in the blue-violet region of the spectrum. One of these was the post-IR IR signal in which first an IR bleach is carried out at a low temperature (e.g. 100 s at 50 degrees C) and a remaining IRSL signal is measured at an elevated temperature (100 s at 225 degrees C: detection in the blue-violet region). It is the latter signal that is of interest in this paper. We test such a post-IR IR dating protocol on K-feldspar extracts from a variety of locations and depositional environments and compare the results with those from the conventional IR at 50 degrees C protocol. Based on laboratory tests (recycling ratio, recuperation, dose recovery) we show that our SAR protocol is suitable for these samples. The observed post-IR IR fading rates (mean g(2days) = 1.62 +/- 0.06%/decade, n = 24: assuming logarithmic fading) are significantly lower than those measured at 50 degrees C (mean g(2day), = 3.23 +/- 0.13%/decade, n = 24). The signal is bleachable in nature although residual doses of the order of a few Gy are to be expected. After fading correction the ages are indistinguishable from those measured by IR at 50 degrees C over an age range from a few ka to >260 ka. However, the correction factor for anomalous fading is only similar to 39% of that of the conventional IR at 50 degrees C signal. This smaller correction factor makes the new post-IR IR ages Much less dependent on the inherent assumptions included in the fading correction model. (C) 2009 Elsevier Ltd. All rights reserved.