Characterisation of historic mortars related to the possibility of their radiocarbon dating, Mikulčice and Pohansko archaeological sites

0561612 - ÚTAM 2023 RIV SI eng C - Konferenční příspěvek (zahraniční konf.)
Kozlovcev, Petr - Kotková, Kristýna - Frankeová, Dita - Válek, Jan - Viani, Alberto - Maříková-Kubková, Jana
Characterisation of historic mortars related to the possibility of their radiocarbon dating, Mikulčice and Pohansko archaeological sites.
Proceedings of the 6th Historic Mortars Conference - HMC 2022. Ljubljana: University of Ljubljana, 2022 - (Bokan Bosiljkov, V.; Padovnik, A.; Turk, T.; Štukovnik, P.), s. 199-214. ISBN 978-961-6884-77-8.
[Historic mortars conference HMC 2022 /6./. Lublaň (SI), 21.09.2022-23.09.2022]
Grant CEP: GA MK(CZ) DG20P02OVV028
Klíčová slova: historic mortars * characterisation * Mikulčice * Pohansko * stable isotope analyses
Obor OECD: Materials engineering; Archaeology (ARU-G)

The archaeological sites of Mikulčice and Pohansko (South Moravia – the Czech Republic) belong to the oldest and the most important localities of Slavic settlement in Central Europe, related to the 9th century. Their considerable importance is attached to the preserved masonry remnants, which are also one of the oldest lime and stone masonry remains in the Czech Republic. A number of historic mortars sampled from the archaeological sites in Mikulčice and Pohansko were collected in order to study their composition, mortar structural characteristics and raw materials provenance. The aim of this study was not only the comparison and characterisation of the historical mortars from these archaeological sites, but we also evaluated the suitability of these mortars to be dated by 14C analysis. The samples of historic mortars were characterised by several analytical techniques. Polarised light microscopy (PLM) and scanning electron microscopy (SEM-EDS) were used to determine petrographic characteristic and mineralogical composition. Thermal analyses (TA) and quantitative X-ray diffraction (XRD-QPA) were used to determine the chemical and mineralogical composition and hydraulic properties of the studied mortars. Stable isotope analyses (δ13C‰ and δ18O‰) and cathode luminescence (CL) were performed to detect carbonate filler and underburnt lime particles containing geogenic carbon. The collected mortar samples contained a considerable amount of lime particles that can adversely affect the possibility of 14C radiocarbon dating. According to the results of the analyses, the samples from Mikulčice and the samples from Pohansko had a similar character. Mortars were very rich in the binder and contained unburnt limestone fragments that occurred frequently. Unburnt fragments were classified as a micritic limestone and contained sparite rich zones and bioclastic material. This material was determined as Ernstbrunn limestones according to the composition and structure. Stable isotope analysis also suggested that all studied lime samples came from a single source. The presence of geogenic carbonates (not fully burnt lime) affects the resulting 14C age of the analysed samples fundamentally. The character of mortars leads to a discussion on how to adapt the
separating procedures of the individual fractions and avoid geogenic carbon contamination.
Trvalý link: https://hdl.handle.net/11104/0334295