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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.

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Combined dating methods applied to building archaeology: the contribution of thermoluminescence to the case of the bell tower of St Martin's church, Angers (France)

Blain S., Guibert P., Prigent D., Lanos P., Oberlin C., Sapin C., Bouvier A., Dufresne P.

Geochronometria

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2011

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Vol. 38, no. 1

55-63

EN

St Martin's church, Angers, is emblematic of the problems raised in pre-12th century history of architecture. In view of the importance of this building, it was necessary to attempt to define its dating and this study particularly focuses on its bell-tower. In addition to the conclusion resulting from the interpretation of written sources and typological criteria positioning the construction of the site at the beginning of the 11th century, not only a significant number of 14C dates were carried out on charcoals from the masonry structures, but also independent dating by archaeomagnetism and thermoluminescence were performed on bricks from the bell-tower. The whole results from these three different methods agree and indicate the lower level of the bell tower was likely built in the 9th century, disputing evidence to the theory of construction in the 11th century of the church. Presented here are the detailed results obtained from the thermoluminescence (TL) dating analysis.

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Dependence of luminescence characteristics of irradiated quartz with the thermal treatment and consequences for TL dating

Roque C., Guibert P., Duttine M., Vartanian E., Chapoulie R., Bechtel F.

Geochronometria

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2004

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Vol. 23

1-8

EN

The dependence of luminescence properties of archaeological quartz pebbles with their thermal history is investigated and consequences for TL-dating are examined; the archaeological samples studied were collected from Solutrean layers at Laugerie Haute West rock shelter (Dordogne, France). This study is supported by a simulation experiment carried out on a natural quartz, using a combined approach by Cathodoluminescence (CL), Thermoluminescence (TL) and Electron Paramagnetic Resonance (EPR) techniques. The quartz grains used were given a high beta dose, then independent aliquots were annealed in air at a temperature varying from 300 degrees C to 900 degrees C. It has been observed that the TL growth with dose, after annealing and re-irradiation, evolved from a linear behaviour to a marked supralinear one according to annealing temperature linked respectively with a partial or a total thermal drainage of charges in deep traps. Consequently, during the TL-dating process of materials anciently heated at low temperature in the past (between 300 degrees C and 500 degrees C approximately), a special care has to be taken by adopting an annealing treatment that approaches the filling state of trapped charges that the samples had after the archaeological zeroing. This necessary new requirement strengthens accuracy and reliability of TL-dates obtained at Laugerie Haute.