Ptghni: A new obsidian source in the Hrazdan River basin, Armenia

Here we report our recent discovery of a new obsidian source in central Armenia. Using portable XRF, we were able to chemically identify “Ptghni” obsidian as a previously unrecognized source on the same day that we first encountered it during our field surveys. Obsidian was found in alluvial-lacustrine sediments exposed within the Hrazdan Gorge, where it had been deposited after having eroded from an upstream source. These sediments were covered by mafic lavas and later exposed by downcutting of the Hrazdan River. Based on the stratigraphy of the gorge, the lava flows - and, therefore, the sediments sandwiched between them - predate 441 ka. The composition of Ptghni obsidian does not fit into the chemical trends of known sources in the Gegham and Tsaghkunyats ranges, so its precise volcanic origin remains unknown. Comparisons to unidentified artifacts in the literature revealed no matches, but obsidian sourcing work in Armenia has largely focused on the Holocene, when the Ptghni source might no longer have been accessible. The discovery of Ptghni obsidian is crucial for research into early hominin expansions given that it was an obsidian source available for use as toolstone by hominins during the Early and/or Middle Pleistocene.