Bitumen from archaeological pots of two Apulian Bronze Age settlements, Monopoli and Torre Santa Sabina: provenance and processing

Evidences of bitumen use were found in several Apulian Bronze Age coastal sites such as Otranto, Roca, Le Pazze (LE), Scoglio del Tonno (TA), Monopoli (BA) and Torre Santa Sabina (BR), but there are no archaeometric data about its source origin or use. Bitumen from archaeological potsherds collected from two Apulia excavations, Monopoli and Torre Santa Sabina, and geological samples from three different areas, Majella, Selenicë and Ragusa, were analysed by GC-MS/MS to assess the geographic origin of the archaeological bitumen. The distribution pattern of steranes and terpanes obtained from archaeological sample is very similar to those ofgeological samples collected from Selenicë.Archeological and Selenicë samples (SBI and SB2) are dominatedby C29 steranes (53–54%) followed by C27 steranes(26–33 %) and only minor proportions of C28 steranes(21%). This bitumen compositional family distinguished by having lower C27 regular steranes and higher C29 regular steranes is inferred to have a non-marine, possibly lacustrine source. Other biomarkers such as gammacerane and oleanane as well as carbon isotopic data on δ13C on asphaltene fractionalso suggested that the bitumen used for pottery came from the same source area in Selenicë. GC-MS was also employed to show the deliberate addition of fats to the archaeological bitumen, probably to lower the quite high softening point (about 120 °C) of Selenicë bitumen. Further, the presence of benzothiophene in selected samples suggests the use at temperatures below 220 °C (benzothiophene boiling point). The processing in such narrow temperature range, exclude direct contact of vessels with flame and points to indirect heating systems (e.g. water-bath heating). Since no direct evidences of use for bitumen were found, and taking into account its occurrence in Apulian coastal sites, its main utilization for caulking is supposed. Only in few cases, bitumen was used as adhesive to repair pottery.