012 luminescence dating

012 luminescence dating

Optically stimulated luminescence dating of sand-dune formed within the Little Ice Age. Authors: /afrocolombianidad.info Bibliographic Code. Luminescence (IRSL) to date low-energy fluvial sediments that formed after correction of the Upper , DOI /afrocolombianidad.inforev Blair MW . Oct 20, The optically stimulated luminescence (OSL) signals currently used are appropriate for mineral grains whose previous radiation history was.

The only evidence of partial bleaching in these samples was the skewness of the distributions with maximum single grain doses up to 8 Gy; nevertheless, the agreement of small aliquot with single grain results suggests that the majority of grains were well bleached in these flood samples.

Study of modern samples from south-western coastal plain of Taiwan gave residual ages between few a and 12 ka Jain et al, unpublished data, tab. Wallinga et al found an excellent age agreement in the range 1 to 13 ka between OSL and independent 14C ages for fluvial samples from the Rhine. Nevertheless, they measured an OSL age of years for a years old sample; this offset was attributed to partial bleaching, as thermal transfer in these samples was not sufficient to explain the over-estimate.

A later comparison of dose estimates from three different grain sizes from this sample gave ages ofand a unpublished data reported in Wallinga, These relative ages are surprising, considering the lower preheat in the former case, but nonetheless support the partial bleaching hypothesis.

This is due to occasional lack of independently datable materials or dating methods in the age range of interest. Commonly used age controls can be grouped into the following categories: The average ages show large scatter and significant age offset in the near surface samples.

The samples came from a 6 m stack of flood deposits at the junction a minor tributary, Tuggerangong Creek with the Murrumbidgee river, near Canberra. OSL ages show a depth wise increase and agree well with the 14C ages where available. OSL ages from fluvial deposits older than years are summarised in table 2 together with their independent age control. Note that all the ages reported in this section are those obtained from the average OSL of multiple grains, hence partial bleaching, as observed in the modern samples is expected to give an age over-estimate of the order of few years to few thousands years.

One has to keep in mind the absolute age of the sample in question; for example, a year age offset due to partial bleaching would be hidden in the OSL uncertainties associated with a 50 ka sample.

Nevertheless, for relatively younger samples few thousand years old this should be detectable and can be tested in the following case studies.

012 luminescence dating

The estimation of doses from single grains indicated that the over-estimate was due to averaging of OSL from poorly bleached grain in the multiple grain analysis single aliquot results and that single grains could be used to derive the correct dose estimate.

The minimum dose calculated using radial plots Galbraith, was consistent with the known age. Similarly, Colls et al. They differentiated between well bleached and poorly bleached samples based on the significance of the correlation between De values and natural OSL signals; on this basis the sample T4 was identified as partially bleached and gave an average age about twice that of the expected age tab.

On the other hand T2 and T3 were identified as well bleached and gave ages consistent with the expected age range.

Optically stimulated luminescence dating of sand-dune formed within the Little I

Despite the significant age offset in a recent a old sample see previous sectionWallinga et al. This comparison gave them confidence to extend the dating range beyond 14C and also provide an empirical correction for the age under-estimation in feldspars. Strickertsson and Murray analysed samples from freshwater Boiling- Allered and Younger Dryas sediments from Denmark.

They carried out a comparison of OSL ages using different methods: They found good agreement between all the methods for the fluvial samples; however the OSL ages were slightly younger than the independent ages. There was a good agreement between the OSL ages and earlier thermoluminescence TL ages suggesting that the samples were indeed well bleached.

The principles of Luminescence Dating

Houlmark-Neil- sen reported in Murray and Olley, has two 14 ka samples from Late Glacial lacustrine deposits in Denmark where he has found satisfactory agreement with independent age control.

A lacustrine sand deposit from northern Russia gave OSL age of On one of the channel belts Pve, they had an associated radiocarbon age, while on the other two channel belts, there were only minimum radiocarbon age estimates for the surfaces. All the optical ages obtained by them agreed well with the geomorphological relationships and the existing radiocarbon age controls.

In many cases the OSL samples were collected from deposits adjacent to those dated by 14C. There was a good agreement between the expected ages in the age range ka and the quartz ages fig. The reason for this overestimate was, however thought to be, errors in the dose rate calculations; and equivalent doses Equivalent dose and age determination on samples older than yrs. The unpublished data Houmark-Nielsen taken from Murray and Olley, Taking the average dose rates from the adjacent OSL samples removed this apparent discrepancy.

The good agreement between the 14C and OSL ages suggests that there is no partial bleaching in the samples of Chen et al. This is surprising as the analysis of modern samples from the same basin in Taiwan gave ages from few hundred years up to 12 ka discussed above.

In general, there is an excellent agreement between OSL and independent ages for the Late Glacial period, with the exception of the data of Folz et al. They had a robust 14C age framework in their archaeological sites in a palaeochannel of river Seine.

012 luminescence dating

The OSL ages were self consistent and showed a broadly similar variance as the radiocarbon ages. These authors failed to find any convincing argument for explaining the age over-estimation. These results are enigmatic and are not included in the analysis reported in the later sections, since they cannot be confidently attributed to partial bleaching. Chronostratigraphy of the tectonically subsiding southwestern coastal plain of Taiwan reproduced from Chen et al.

OSL ages show a good agreement with independent 14C ages from several core sediments up to last 27 ka, and were used to further extend the dating range to OIS 5.

Aspects of Archaeology: Thermoluminescence Dating

This allowed a comparison with the global sea level curve for last ka and estimation of the rates of subsidence in different parts of the basin.

The large uncertainty in the OSL age arises from scatter in the multiple aliquot measurements; this may have been accentuated by partial bleaching, if any. The OSL age of a younger sample The authors claim that they got better agreement by using the dose discrimination method from the single grain for deposits; unfortunately, however, an independent assessment of their data is difficult because independent age control is presented only for one sample tab.

Nevertheless, the multiple-aliquot age calculated using in-situ measured water content for this sample agreed well with the tephrachronology. OSL zeroing has been found to be complete or nearly complete in big river systems in different climatic settings such as the Ganga, Mississippi Jain et al, unpublished resultsColorado Stokes et al, ; Ward et al, and Loire Stokes et al, ; Colls et al, in the source-distal situations, and in semi-arid Indian rivers Jain et al, unpublished results; Thomas et al, This is perhaps due to multiple recycling of sediment during repeated deposition and erosion in the large river drainage systems, and fluvio-aeolian interactions and ephemeral streams in semi-arid systems.

Significantly higher residual ages are found in flood sediments from other river systems. The average OSL based residual ages for modern samples are distributed asymmetrically The data in figure 7a makes no discrimination between different laboratory procedures employed for dose measurement; thus the data include a few ages derived using high temperature preheats which could have resulted in significant thermal transfer e.

Colls et al, and so age offsets that are partly laboratory artefacts. This is perhaps due to OSL averaging from multiple grains even in the single aliquot studies. From studies based on small aliquots Olley et al, ;it is clear that at least some proportion of the grains are well bleached even in turbid floods, and hence the single grain approach should significantly improve our recovery of an accurate minimum dose from poorly-bleached modern samples.

Some encouraging results using single grains in relatively older known-age samples are provided by Olley et al and Thomas et alalthough this approach is still in the developmental stage.

For recent samples less than years, there exists clear evidence of partial bleaching in both small-aliquot dose distributions and average age offsets; however the deviation from the expected ages is much less then what would be expected from the modern samples shown at 1 on the independent age axis in fig.

From the average OSL based ages for samples older than years, convincing evidence of age over-estimates due to partial bleaching are found only in two samples of 1. The ratios of the average OSL age to independent age are plotted in figure 8a and agree well with the line of unit ratio.

There are occasional samples giving an age over-estimation that almost certainly does not arise from partial bleaching unknown problems - Folz et al, and dosimetry problems, Chen et al, ; these data are shown in figure 8a but not used in the line fitting of figure 8b.

Further, it is encouraging to note that the OSL ages are in agreement with the minimum-age data obtained using independent methods available for some samples Rittenour et al, ; Mol et al, The data span two orders of magnitude lka to ka and the fitted line has a slope of 1.

It seems from the above discussion that there is an inconsistency between the residual ages obtained from modern samples and those from a stratigraphie context; the degree of offset tends to be large in modern samples, Fig.

012 luminescence dating

There was a clear evidence of partial bleaching in these samples and the minimum ages reported in a few studies were based on small aliquot or single grain dose-distribution analysis tab. However, it must be acknowledged that the number of samples in each of these A luminescence imaging system based on a CCD camera. Radiation Measurements 27 2: Optical dating of single sand-sized grains of quartz: Radiation Measurements 32 5—6: Stimulation of luminescence using green light emitting diodes.

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Surface dating by luminescence: An overview : Geochronometria

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