Petrographic and geochemical investigations on the volcanic rocks used in the Punic-Roman archaeological site of Nora (Sardinia, Italy)

Abstract

The research focuses on the geochemical and petrographic characterisation of volcanics that were used in the Roman city of Nora archaeological site. These rocks formed during the Late Eocene–Miocene orogenic Sardinian magmatic activity (38–15 Ma), were used as construction materials (ashlars, decorative frame, etc.) and as aggregate in the ancient mortars of some important buildings of Nora (e.g. Roman theatre, first century ad). Several samples coming from the Roman theatre (taken as study cases) and other ancient buildings and artefacts of Nora village were studied and chemically petrographically analysed. To define their provenance, analytical data of major and trace elements by XRF method were compared with those of several volcanics coming from the sector around the Nora archaeological site and from Sulcis area, frequented in ancient times by Romans. To highlight the geochemical discriminant markers or affinities between the sample populations of volcanics, factorial analysis was used, taking some significant variables: SiO2, Na2O, K2O, L.o.I, Al2O3, Rb, Ba, Sr. The results of this research allow also defining the aspects of stone quarry extraction and construction technologies used in the Roman period.