Identification and origin of bitumen in Neolithic artefacts from Demirköy Höyük (8100 BC): Comparison with oil seeps and crude oils from southeastern Turkey

Two ring-like artefacts from the aceramic Neolithic site of Demirköy Höyük in southeastern Turkey were analysed using geochemical techniques in order to determine whether they were prepared using a bitumen amalgam or not. The artefacts, dated 8100 BC, are early evidence of the innovative use of a petroleum-based material to prepare pieces of ornaments (beads, rings, etc.) for the elite of a Neolithic settlement. In order to trace the source of the presumed bitumen, two oil seeps, Boğazköy and Yeşilli, were sampled. To complete the genetic references, geochemical data on crude oils from the main oil fields from the area were compiled. Basic geochemical data show that bitumen is present in the artefacts. Sterane and terpane patterns, as well as carbon isotopic data on C15+ saturated and C15+ aromatic hydrocarbons, allowed us to conclude that the Demirköy Höyük bitumen and the Boğazköy oil seep were generated from a Silurian source rock. The detailed geochemical characteristics show, however, that the Demirköy Höyük bitumen does not correlate perfectly with the Boğazköy oil. This discrepancy suggests several explanations: the real bitumen source may be elsewhere in the vicinity and has not been discovered or was at the Boğazköy oil seep location but with slightly different properties in Neolithic times, or has disappeared. Another possibility is that the slight molecular differences are due to weathering effects, which affected the pristine bitumen within the archaeological sample.