Spectroscopic, petrographic, chemical analyses and luminescence dating of historical mortar from the Western Portic ground mosaics of Northern Sacred Agora (WPNSA) at Laodicea ancient city (Deni̇zli̇-Turkey)

Abstract

 Detailed petrographic and geochemical properties of WPNSA ground mosaic mortar were determined by multi-analytical approaches, and its construction history was revealed by the OSL dating method. The ground mosaics of WPNSA in Laodicea are observed in an area of 20x14 m2, partially deteriorated. The ground mosaic mortar exhibits 5 layers which consist of statumen, rudus (coarse grained mortar with 3-4 cm thickness), nucleus (fine grained mortar with 2-3 cm thickness), bedding mortar (1-2 mm thickness), and tesselatum. Transitions between layers are not obvious. Mortar samples were obtained by mixing weak graded “fine sand” aggregates with the lime binder (aggregate to binder ratio is 1:2 by volume). Aggregates consist of marble, mica schist, quartzite, serpentinite, gabbro, harzburgite, limestone, travertine, ceramic, quartz, calcite, mica minerals, pyroxene fragments. Shrinkage cracks and lime lumps are commonly observed in mortar samples. The WPNSA mortar samples generally show similar features, indicating that there was no change in the raw material as well as on the application technique used during the construction. The archaeological record together with the Optically Stimulated Luminescence (OSL) ages indicate that the ground mosaic in WPNSA was built up between the middle of the 4^th century and the beginning of the 5^th centuries AD, and then the building was abandoned by the great earthquake at the beginning of the 6^th century.