Geochemical Characterization of Four Quaternary Obsidian Sources and Provenance of Obsidian Artifacts from the Middle Stone Age Site of Gademotta, Main Ethiopian Rift

Abstract

Twenty‐six Middle Stone Age obsidian artifacts from the Gademotta Formation were instrumentally characterized by energy dispersive X‐ray fluorescence. Analysis of artifacts from the type locality enabled sampling of a greater time depth while avoiding the uncertainties in previous results on artifacts sampled from a “disturbed” context at Kulkuletti. Moreover, the analysis here of source samples from Alutu, Worja, and the previously unstudied Bora and Ficke sources in the broader region offers a better understanding of prehistoric lithic raw material procurement. The local Worja source, an aphyric obsidian excellent for tool production, substantially dominates the assemblage. Bora, another aphyric obsidian in the wider region, is also present, but not common. The vitrophyric Ficke and Alutu obsidian sources with abundant sanidine phenocrysts were not present in the archaeological assemblage, and likely did not compete with Worja and Bora for tool production. At least one artifact appears to be from an as yet unknown source, thus confirming results of previous studies. A few artifacts share similar geochemical composition with the Worja and Bora sources, thus highlighting the complexity of obsidian source studies in this part of the rift where multiple geographically close sources may share similar crustal material.