Characterisation and OSL dating of mortars from the crypt of Saint Seurin basilica in Bordeaux: revealing the history - Archive ouverte HAL Accéder directement au contenu
Chapitre D'ouvrage Année : 2016

Characterisation and OSL dating of mortars from the crypt of Saint Seurin basilica in Bordeaux: revealing the history

Résumé

As an important cradle of early Christianity in Bordeaux, the Saint Seurin basilica represents a significant monument for the history of the city. The church was constructed on the older remains attributed recently to a Late Antiquity mausoleum [1]. During the archaeological excavations in 2014, nine stratigraphic levels were identified in the crypt. However, since the crypt was subjected to numerous reconstructions, the discontinuity of the stratigraphic levels in many zones complicates the archaeological interpretations and the absence of written sources does not allow clarifying the development of this old structure. Therefore, the archaeometric study of mortars was realized in order to shed light on the complex history of the crypt in the Early Medieval Period. The archaeometric study of mortars had dual objective: first to compare the mortars sampled in different zones and levels of the crypt in order to reveal the extent of different building phases and possibly to identify the changes in preparation technology of mortar, second to date selected mortar samples by optically stimulated luminescence (OSL) applying the new methodology by single grain technique recently developed in the Bordeaux laboratory IRAMAT-CRPAA [2]. The basic premise in dating of mortar by optically stimulated luminescence is that quartz in the sand used for making mortar is optically zeroed during the preparation process. The moment to be dated is the last exposure of mortar to light, before being embedded within the masonry and hidden from light. Because the quartz in mortars is heterogeneously bleached, every single grain is analysed [3]. For OSL dating application, the individual archaeological doses are measured by OSL on individual quartz grains extracted from the mortar, and the mean annual dose is determined by on-site dosimetry (environmental component of the radioactivity) and by high resolution low back ground gamma spectrometry of natural radio nuclides of te mortar sample (beta and alpha components). In addition to those measurements, the mortar has to be studied by using EDX-SEM cartography, autoradiography beta and ICP-MS in order to evaluate microdosimetric effects at the grain size scale. The characterization of mortars includes the combination of petrographic, mineralogical and chemical analysis in order to distinct the groups of samples corresponding to different building phases and to attempt identifying the provenance of the aggregate [4]. The first results indicate the construction of the mausoleum between the half of the 4th and 5th century AD and several reconstructions are emerging between the 5th and the 10th century AD. The paper represents an interdisciplinary approach where physicians, specialists in archaeometry and archaeologists worked in a narrow collaboration contributing to the better understanding of the history of this unique monument. [1] Michel A (2012) Autour de l'identification des mausolées: le cas de Saint-Seurin de Bordeaux. Mausolées & Églises, IVe-VIIIe siècle, Hortus Artium Medievalium, 18/2/2012. [2] Urbanová P, Guibert P (2015) New insights towards the dating of Roman and medieval mortars by Optically Stimulated Luminescence (OSL) : comparison of case studies. Proceedings of the 5th International Congress on Construction History, Chicago, Etats-Unis, 3-7/6/2015, 499-508. [3] Urbanová P, Hourcade D, Ney C, Guibert P (2015) Sources of uncertainties in OSL dating of archaeological mortars: the case study of the Roman amphitheatre Palais-Gallien in Bordeaux. Radiation Measurements, 72: 100-110 [4] Miriello D, Barca D, Bloise A, Ciarallo A, Crisci G, De Rose T, Gattuso C, Gazineo F, La Russa M, (2010a) Characterisation of archaeological mortars from Pompeii (Campania, Italy) and identification of construction phases by compositional data analysis. Journal of Archaeological Science 37: 2207-2223
Fichier principal
Vignette du fichier
Urbanova et al HMC 2016.pdf (349.36 Ko) Télécharger le fichier
Origine : Fichiers produits par l'(les) auteur(s)
Loading...

Dates et versions

hal-02535095 , version 1 (07-04-2020)

Identifiants

  • HAL Id : hal-02535095 , version 1

Citer

Petra Urbanová, Pierre Guibert, Nadia Cantin, Anne Michel. Characterisation and OSL dating of mortars from the crypt of Saint Seurin basilica in Bordeaux: revealing the history. Ioanna Papayianni; Maria Stefanidou; Vasiliki Pachta. Proceedings of the 4th Historic Mortars Conference HMC2016 10th-12th October 2016, Santorini, Greece, Laboratory of Building Materials Laboratory of Building Materials Department of Civil Engineering Aristotle University of Thessaloniki, pp.179-186, 2016, 978-960-99922-3-7. ⟨hal-02535095⟩
67 Consultations
34 Téléchargements

Partager

Gmail Facebook X LinkedIn More