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

Thomsen, K.J., Murray, A.S., Jain, M., Bøtter-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 °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 °C) and a remaining IRSL signal is measured at an elevated temperature (100 s at 225 °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 °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 g2days = 1.62 ± 0.06%/decade, n = 24; assuming logarithmic fading) are significantly lower than those measured at 50 °C (mean g2days = 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 °C over an age range from a few ka to >260 ka. However, the correction factor for anomalous fading is only 39% of that of the conventional IR at 50 °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.