Optical dating, using Optically Stimulated Luminescence (OSL) was first Furthermore, ESR dating is not applicable to feldspars because of the lack of a Review and assessment of the potential of post-IR IRSL dating. Optical dating of sediment using optically stimulated luminescence has be- come important . It is the aim of this review to explain the basis of OSL dating, to identify the most important .. Consequently, there is no universal best approach for OSL dating; in particular cir- research effort by OSL specialists. OPTICAL DATING: A NON-SPECIALIST REVIEW. M.J. Aitken. Research Laboratory for Archaeology, 6 Keble Road, Ox]brd OX1 3Q J, U.K.. Optical dating was.
The procedure is however more complicated, as artificial irradiation leads to the trapping of electrons in unstable traps of the mineral crystal lattice. Luminescence Profile In the process of making a ceramic vessel, the soft clay vessel must be heated in a kiln to harden it.
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Optical dating a non specialist review -
The process of firing the vessel releases the trapped electrons energy , and resets the thermoluminescence clock to zero.
The process of accumulation of electrons energy and then release when heated occurs every time the ceramic vessel is reheated. What an archaeologist would be able to measure using this technique is the last time the vessel was heated above degrees Celcius, either at the time the vessel was first fired or the last time it was heated if it was used as a cooking vessel. In the laboratory, the release of electrons can be induced through heating or the use of a laser beam. The intensity of the light emmisions luminescence can be measured to determine the amount of time that has passed since the vessel was last heated and the present laboratory heating of the vessel.
How is a Luminescence Sample Processed? A small sample is cut out of the artifact being dated. An equivalent dose DE of nuclear radiation is determined for every artifact through the application of artificial doses of nuclear radiation through heating or exposure to a laser light beam to subsamples of the artifact to scale the signal. Next the burial dose rate DR is determined by measuring the radioactivity in portions of the sample grains and surrounding sediments.
This method is applicable to samples that range in age from a few hundred years to several hundred thousand years. The Limitations of Luminescence Dating Using this technique, almost any rock mineral or ceramic sample can be directly dated. However, it works best when dating heated grains in ceramics, obsidian, burned flint, and burned sediments. This test is important because feldspars are not only stimulated by infrared light, but also by the blue or green light used for quartz.
Hence, the presence of feldspar contaminates the luminescence one wishes to record from quartz. A similar test is not necessary when the analyses focus on feldspar grains, because the quartz grains which may be present in the aliquots are insensitive to infrared stimulation; iv a measurement of anomalous fading for feldspar. This test may be performed using a SAR protocol including variable delays between irradiation and measurement of the signal to estimate the fading to be estimated.
Accurate ages are then obtained by inserting this fading in a correction model Huntley and Lamothe, ; Auclair et al. Determination of the equivalent dose De using statistical models 14The SAR protocol creates as many equivalent doses as aliquots, with the exception of those which had to be discarded after the tests.
In the case of aeolian sediments, all of the analysed grains are assumed to be well bleached, and all the Dehave a similar value, which can be used to calculate the age of the sediment. However, partial or incomplete bleaching is common, especially if the transport history was short or the exposure to sunlight was insufficient, as can be the case for fluvial sediments.
This partial bleaching can be homogeneous all the grains being incompletely bleached in the same proportion or heterogeneous differential bleaching. In this latter case the Dedistribution shows a scattering fig. Some aliquots can present a very high palaeodose, which greatly overestimate the age of the last transport event. This explains why the mean is not appropriate in estimating the accurate equivalent dose.
It is therefore necessary to use a statistical model. Several models have recently been developed. It will also overestimate the equivalent dose in the presence of a partially bleached sediment. As for the sampling strategy the choice of the model depends upon the kind of sediments and presupposes a discussion between the field and luminescence specialists Bailey and Arnold, Comparison with independent age control may also be very useful, as shown by H.
The relevance of these models increases with the number of aliquots. The number of 50 aliquots is sometimes considered as a minimal value to ensure a reliable equivalent dose determination Rodnight, , but it is important to keep in mind that the number of aliquots to be measured depends on the sample and increases with the scattering.
Applications and place of OSL in geomorphological research in France 15The physical principles of the optical dating method, and its reliability for quartz and for feldspars from silty to sandy sediments, have resulted in optical dating being applied to a diverse range of sedimentary environments, as described in several journal papers see for example special issue of Boreas 1, The aim of this section is to review the applied representative studies dealing with OSL in France.
As in other countries, the first dating of sediments was based on thermoluminescence Wintle et al. The first OSL applications tab. Loess deposits were successfully dated especially in NW France.
Several loess-palaeosol sequences Engelmann et al. Most of the research focused on the last interglacial-glacial cycle Antoine et al. Coastal sands from the North Sea or Channel coastlines were also optically dated for more than one decade. The dating of raised beaches Balescu et al, ; Regnault et al, ; Coutard et al. At the same time the dating of young Holocene dunes Clarke et al.
The first OSL dating of fluvial sediments from French rivers also started at the end of the s, despite the problem of differential bleaching being for a long time considered as a major hindrance in applying luminescence dating to fluvial sediments Wallinga, Improvements in the detection of the partial bleaching e. Fluvial deposits of the Seine River have been locally dated both in its lower reach middle Pleistocene estuarine silts; Balescu and Lamothe, ; Balescu et al. A more extensive dataset was provided for the Loire basin Straffin et al.