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2 2011

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IRSL and post-IR IRSL residual doses recorded in modern dust samples from the Chinese loess plateau

Buylaert J.-P., Thiel Ch., Murray A. S., Vandenberghe D. A. G., Yi S., Lu H.

Geochronometria

2011

Vol. 38, no. 4

432-440

Using a set of modern/young (0 to about 200 years old) dust samples collected from the Chinese Loess Plateau the bleachability of IRSL measured at 50°C (IR50) and post-IR50 elevated temperature IRSL (measured at 225°C and at 290°C) is investigated by measuring the apparent (residual) doses recorded by these signals. Doses recorded by quartz OSL are used as a reference. Allowing for differences in dose rates it seems that both IRSL and post-IR IRSL signals yield residual doses that are significantly larger than the doses measured in quartz. These residual doses can be largely explained by thermal transfer caused by preheating. Nevertheless, we advise against the use of a low temperature preheat (<200°C) with IR50 to date loess samples because, as has been reported before, the signal appears to be thermally unstable. In general, we conclude that it may not be advisable to apply post-IR IRSL dating to Chinese loess samples where residuals of up to ~20 Gy are a significant fraction of the total dose. However, these residuals quickly become unimportant when dating older samples, and this is the age range in which post-IR IRSL dating is likely to be most useful.

A high resolution optical dating study of the Mostiştea loess-palaeosol sequence (SE Romania) using sand-sized quartz

Vasiliniuc S., Timar-Gabor A., Vandenberghe D. A. G., Panaiotu C. G., Begy R. CS., Cosma C.

Geochronometria

2011

Vol. 38, no. 1

34-41

We report on SAR-OSL dating of closely-spaced samples from the loess-palaeosol sequence near Mostiştea lake (Danube Plain, SE Romania). We used sand-sized quartz and a SAR protocol that involved a preheat of 10s at 220°C and a test dose cutheat to 180°C. It is shown that these thermal pretreatments isolate a quartz OSL signal that is dominated by the fast component. The behavior of this signal in the SAR protocol is then documented. The ratio of the measured to given dose tends to lie slightly but systematically above unity (~5% on average) and the recycling ratio below unity (~6% on average); for all samples, the recuperated signal is negligible. Within analytical uncertainty, the nineteen optical ages are internally consistent and agree with the predictions from a palaeomagnetic age-depth model. Although it may be possible to optimize the SAR measurement procedure, the optical ages already confirm the chronostratigraphic position of the uppermost welldeveloped palaeosol in that it formed during MIS 5.The established chronology allows correlating the sequence near Mostiştea lake with that near Mircea Vodă that we investigated earlier.