Machine learning approach to Nemrut Dağ and Bingöl obsidians: insights from Tūlūl al Baqarat obsidian prehistoric tools (Iraq, IV millennium BC) and volcanological implications

Abstract

A machine learning approach was employed to determine the source material of nine obsidian blades from the archaeological site of Tulūl al Baqarat (Iraq) employing geo-referenced obsidians from Nemrut Dağ stratovolcano and Bingöl volcanic plateaux as the reference dataset for the investigation. On the obsidian tools were performed chemical analysis using non-invasive and non-destructive techniques. Major and minor elements were determined using a low vacuum SEM-EDS microprobe, while trace elements were analysed using a bench-to-top micro-XRF. To identify the volcanic complex from which the tools were sourced, a geochemical comparison with Turkish obsidian flows was conducted, from the volcano itself to the artefact samples. However, only a machine learning approach proved to be an exhaustive and discriminative method, complemented by well-known geochemical comparisons. The analysed nine obsidian tools display a peraluminous rhyolite composition with a peculiar high Zr content which excludes most obsidian outcrops in Turkish and Armenian volcanic sites as potential original sources. Nevertheless, a machine learning approach applied to selected major, minor, and trace elements indicate the obsidian tools results comparable to Nemrut Dağ mild alkaline rhyolitic obsidians from pre-caldera eruptions. These obsidians are now exposed within the caldera and in Sicaksu outcrop (SE Turkey). Therefore, the artifacts may even be attributed to specific Nemrut Dağ flows using geochemically significant elements in machine learning approach. The provenance of the source from the Nemrut Dağ stratovolcano in south-eastern Turkey, situated along the Turkish route of the Tigris River, supports the hypothesis of a network of trade and broad exchange since the 4th millennium BC, from Turkey and the South Near East, which is presumed to have occurred along the Tigris River up to the shores of the Persian Gulf.