Obsidians of Pantelleria (Strait of Sicily): A Petrographic, Geochemical and Magnetic Study of Known and New Geological Sources

Silvio G Rotolo,Alessandra Correale,Fabio Speranza,Pierangelo Romano,Gregor Hahn,Franco Foresta Martin,Leonardo Sagnotti,Mariangela La Monica,Maria Luisa Carapezza,Alastair G.E Hodgetts,Gaia Siravo,Manuela Nazzari

doi:10.1515/opar-2020-0120

Abstract

Abstract This paper provides new petrochemical and paleomagnetic data from obsidian sub-sources on the island of Pantelleria, exploited since the Neolithic. Data has been obtained from 14 obsidian samples from 4 locations: Fossa della Pernice (2 sites), Salto la Vecchia and Balata dei Turchi. Here, we aim to better characterize these obsidians using a cross-disciplinary and multi-analytical approach, to further understand their archaeological significance. Major element analyses (EMP) have enabled two compositional super-groups to be distinguished: (i) Fossa della Pernice, less peralkaline and (ii) Balata dei Turchi–Salto la Vecchia, distinctly more peralkaline and having almost identical chemical patterns. Trace element analyses (LA-ICP-MS) corroborate major element groupings, with the Balata dei Turchi–Salto la Vecchia super-group being further characterized by a pronounced negative europium anomaly. Glass H2O contents (FT-IR) reveal an overlap among all the sub-sources (H2O = 0.1–0.3 wt. %). Magnetic methods have refined the petrochemical groupings, permitting further distinction between Balata dei Turchi–Salto La Vecchia and the Fossa della Pernice super-groups. The occurrence of sub-microscopic (< 1 μm) ferromagnetic minerals results in different magnetic susceptibility and Natural Remanent Magnetization values and allows the best distinction among the products from the chosen sites. When compared with obsidian tools excavated from Bronze-age settlements on the island of Ustica (230 km NE of Pantelleria), 12% are distinctly peralkaline, indicating their provenance to be from the Balata dei Turchi sub-source.

Highlights

Throughout the Neolithic, until the Bronze age, obsidian was a widely used geological material across the circumMediterranean, primarily used for the manufacturing of stone tools and weapons
When major element analyses (Table 2) are plotted in the FeOtot vs. Al2O3 diagram (Macdonald, 1974) two groups can be clearly distinguished, displaying different clusters (Figure 7): – Obsidian samples from Fossa Pernice 1 (FP 1) and Fossa Pernice 2 (FP 2) sites are almost identical in their major element contents and are remarkably higher in Al2O3 and lower in FeO, i.e. are less peralkaline (P.I. = 1.4–1.5), with respect to the Salto La Vecchia (SLV)-Balata Dei Turchi (BDT) super-group (P.I. = 2.2). – Samples belonging to SLV-BDT groups are indistinguishable among themselves, but, if compared with FP samples, are distinctly more peralkaline
During the late Neolithic to Bronze age (i.e. 6th to 2nd millennium BCE), two principal obsidian localities were present in the south-western Mediterranean Sea: Lipari and Pantelleria

Summary

Introduction

Throughout the Neolithic, until the Bronze age, obsidian was a widely used geological material across the circumMediterranean, primarily used for the manufacturing of stone tools and weapons. Petrographic and geochemical characteristics have a great efficacy in distinguishing between the above two petrochemical groups, but somehow lose their discriminating power if a given group within the same geological context has different sub-sources

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Conclusion