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Methodological study on single grain OSL dating of mortars: Comparison of five reference archaeological sites

Urbanová P., Guibert P.

Geochronometria

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2017

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Vol. 44, no. 1

77--97

EN

The paper focuses on single grain OSL dating of quartz extracted from known age archaeological mortars, potentially representing a new tool for dating the construction of historical buildings. Apart from SG-OSL measurements and annual dose rate determination, the samples are systematically studied by means of optical microscopy, EDX-SEM cartography and beta autoradiography in order to evaluate the possible microdosimetric heterogeneity of each sample, arising principally from local variations of potassium content. Besides the practical aspects concerning sampling, preparation and appropriate choice of measurement conditions, the paper aims at the differences in microstructure and in elementary composition between different mortars and attempts to evaluate the impact of these aspects on the dispersion of equivalent dose distributions. Finally, archaeological doses (paleodoses) are calculated by using central age model (CAM), minimum age model (MAM) and internal-external consistency criterion (IEU). The appropriateness of these models for the exploitation of the measured SG-OSL data as well as for a hypothesis on the estimation of the input parameter needed to run these models are discussed. Three categories of mortars were identified: samples without any exploitable SG-OSL signal, samples that could have been reliably dated and poorly bleached samples affected by microdosimetric variations whose dating still remains complicated. Finally, the hypothesis on distinguishing between reliable and questionable dating results is raised and the potentials of the method for dating mortars are pointed out.

2

Coarse versus fine-grain quartz optical dating of the sediments related to the 1985 Ms7.1 Wuqia earthquake, northeastern margin of the Pamir salient, China

Yang H., Chen J., Porat N., Li T., Li W., Xiao W.

Geochronometria

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2017

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Vol. 44, no. 1

299--306

EN

Optical dating of earthquake related sediments were investigated including one modern sample and three samples from a trench excavated across the 1985 Ms7.4 Wuqia Earthquake surface rupture. The results indicated that equivalent dose (De) values vary with grain size and the method used for De determination. The residual dose of the modern sample is 0.1 ka ( 0.2+0.2−0.1 Gy) for the quartz single grain measurements. Only 1.5–3.6% of the grains have a detectable OSL signal. Single grain quartz ages are similar to the expected ages. Fine grain quartz results overestimate the De values and are much older than single grain quartz and coarse grain quartz small aliquot standardized growth curve (SA-SGC) ages. Single grain quartz OSL dating may be optimal for dating earthquake related deposits, but SA-SGC can save measurement time and has potential for dating some poorly bleaching samples.

3

Application of different protocols and age-models in OSL dating of earthen mortars

Panzeri L., Cantù M., Martini M., Sibilia E.

Geochronometria

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2017

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Vol. 44, no. 1

341--351

EN

In this study, OSL dating was applied to earthen mortars, consisting in a quartz-rich aggregate dispersed in silty-clayey matrix. The samples were taken from two independently dated structures in Cremona, Northern Italy (Palazzo Raimondi, 1495–1499 AD and Palazzo Soldi, 1770–1790 AD). The evaluation of the equivalent dose (De) was attempted with both the multigrain and the single grain protocols using the 150–250 μm quartz fraction. The reliability and effectiveness of the various statistical methods in identifying the well-bleached samples were tested. The use of the multi-grain technique gave unreliable results, due to the high amount of poorly bleached grains. With the single-grain technique, more promising results were obtained: in particular, the un-log MAM3 and IEU models allowed an accurate evaluation of the mortar expected age in most cases, even if the precision is still relatively low.

4

Quartz single grain OSL sensitivity distributions : implications for multiple grain single aliquot dating

Rhodes E.J.

Geochronometria

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2007

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Vol. 26

19-29

EN

A simple probabilistic numerical model was used to construct synthetic De distributions by combining the simulated OSL from grains of different sensitivities and with various simulated De values. This is useful for exploring the complex patterns generated by summing the signals from many grains in real, multiple grain OSL dating scenarios, and demonstrates that the form of the sensitivity distribution has a significant effect on the identification of mixed dose populations in multiple grain single aliquot methods. I describe the simple numerical model and its implementation. I present measured quartz single grain OSL sensitivity distributions for an aeolian dune sample from the Simpson Desert, Northern Territory, Australia, and from a suite of 9 fluvial sediments from Namadgi National Park, Australian Capital Territory, Australia, to illustrate effects that result from natural differences. Minimum age model determinations of synthetic De values are used to assess the validity of dose values estimated from multiple grain single aliquot measurements.