Tracing the provenance of the amphorae from underwater sites by archaeometric analysis: The case of Torre Santa Sabina (Apulia, southern Italy)

This thesis deals with the archaeometric study of ceramic materials and in particular of a set of amphorae, from the underwater archaeological site of Torre Santa Sabina (Apulia region, Southern Italy), dating back to the Republican period (late 2nd century BCE). The main aim of this study is to define the provenance of the amphorae found in the underwater shipwrecks and to verify their possible local origin. For this purpose, the amphorae fragments form Torre Santa Sabina underwater site was compared with a set of amphorae fragments recovered from the ancient local production centers of Apani and Giancola (defined as reference groups). Petrographic, mineralogical, and chemical analyses were carried out on 19 samples from Torre Santa Sabina and 11 samples from Apani and Giancola. All the specimens were analyzed by polarized-light microscopy, X-ray Powder Diffraction (XRPD), X-ray fluorescence (XRF) and Scanning Electron Microscope (SEM). The polarized-light microscope analysis provides information on the textural features of the ceramic bodies and the nature and type of inclusions allowing the characterization of the different fabrics. The underwater samples showed heterogeneity both in terms of amphora forms and the textural characteristics of the ceramic bodies. Overall, two macro-groups were identified: one characterized by groundmass of a more carbonate nature and the other one rich in the terrigenous component. This subdivision is also reflected by the mineralogical and chemical composition of the potsherds. XRPD analysis was used to determine the mineralogical composition of the ceramic bodies. Quartz, K-feldspar, muscovite/illite, plagioclase, hematite, pyroxenes, and calcite are the main phases detected; gehlenite was detected in some samples from Apani and Giancola, while sulfur-based mineral phases, as pyrite, were detected only in underwater samples as post-depositional alteration phases. XRF results showed a fairly similar chemical composition among the underwater samples, although they represent amphorae of different types. Some trace elements, like sulfur, show greater variability as they are linked to the precipitation of post-depositional secondary phases, especially pyrite (FeS2). A more in-depth observation by SEM was performed on some representative samples, allowing us to better analyze the microstructural features of the ceramic bodies and also confirm the occurrence of pyrite in the underwater samples. The results revealed compositional similarities between marine and terrestrial fragments suggesting Apani and Giancola as potential production centers of some of the underwater amphorae found on the TSS seabed. In particular, the “Ovoidal Adriatic” type shows the greatest similarity to the products from these local centers, mainly for grain-size distribution of inclusions and the presence of fossil traces. However, a few fragments differ significantly from the others in both mineral-petrographic and chemical characteristics, indicating different places of origin in Mediterranean areas such as Italian Tyrrhenian side (probably Campania region) and North Africa. These outcomes shed light on the nature of the submerged cargo and enhance our knowledge of the site and its role in ancient maritime trade routes across the Mediterranean.