Geo-materials selection and procurement strategies in Copper Age menhirs production at Allai (central-western Sardinia, Italy)

In the 1990s a group of anthropomorphic menhirs were found into the walls of the Nuraghe Arasseda, in Allai (central-western Sardinia, Italy). They probably belonged to a Copper Age sanctuary of III millennium BC, and were reused as a building material by nuragic people during the II millennium BC. In modern times three of these megaliths were removed from the Nuraghe Arasseda and exposed at the Sardinian archaeological museum of Laconi. After testing the reliability of a non-destructive archaeometric approach, a study concerning the source provenance and the technological properties of the raw materials employed for the menhirs production were carried out. On eight geological samples (two of which come from an ancient quarry) collected from the Monte Ironi volcanic outcrop of Allai, visual examination and instrumental measurements were performed. Chemical analyses by portable X-Ray Fluorescence spectrometry (pXRF), Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) were carried out to determine the coherence between the analytical data collected by the different techniques [1], to characterise the stone raw material and to evaluate its chemical intra-source variability. On the three menhirs from Arasseda, in accordance with preservation of archaeological heritage, visual inspection and non-destructive pXRF measurements were achieved only. By means of a comparison between pXRF data collected on artefacts and geological samples, it was possible to indicate the Monte Ironi unit as the geo-source of two out of three Arasseda menhirs. Powder X-Ray Diffraction (PXRD) measurements were useful to recognize the technological properties of the Monte Ironi stone and to reconstruct the criteria adopted during Copper Age in selecting geo-materials for sculptural purposes. To the knowledge of the authors, this is the first research study on the Arasseda menhirs by means of chemical and physical methods (the second one on Sardinian menhirs [2]), and one of the few archaeometric studies recently developed on European megaliths. [1] D. Mitchell, P. Grave, M. Maccheroni, E. Gelman, Geochemical characterisation of north Asian glazed stonewares: a comparative analysis of NAA, ICP-OES and non-destructive Pxrf, Journal of Archaeological Science 39, 2921–2933, 2012. [2] M. Serra, V. Mameli, C. Cannas, Eneolithic menhirs of Laconi (central Sardinia, Italy): from provenance to technological properties, Journal of Archaeological Science: Reports 5, 197-208, 2016