Testing the reliability of quartz OSL ages beyond the Eemian

There is some evidence that optically stimulated luminescence (OSL) dating using the fast component from quartz may underestimate the age by similar to 10% at about 130 ka, or for values of D-e of similar to 150-200 Gy. Any significant underestimate in age, if true, would be inconsistent with the expected values for the stability of the OSL trap. However, the alternative explanation, that the age control provided by the beginning of marine isotope stage 5e is similar to 10% too old, would be very contentious. As part of our continuing investigation of the reliability of quartz ages for older material, we describe results from a deposit on the Seyda River in northern Russia. Quartz was extracted from an organic-rich layer identified as being laid down in either MIS 7.1 (similar to 193 ka) or MIS 7.3 (similar to 215 ka), and U-series dated to 198 +/- 7 ka, and from the immediately overlying fluvial sand. The resulting mean OSL age of 10 samples from these sedimentary units is 207 +/- 12 ka. The results are also discussed in relation to the earlier quartz studies. (C) 2008 Elsevier Ltd. All rights reserved.