GEOCHEMICAL SOURCING OF OBSIDIAN AT ZETO POINT, ADAK ISLAND, AK: IMPLICATIONS FOR PREHISTORIC UNANGAN RESOURCE ACQUISITION

We collected samples of rare obsidian fragments and other worked lithic fragments from three occupation levels discovered during an archeological excavation at Zeto Point, Adak Island. The only known outcrop of fresh obsidian in the Aleutians is some 800 km distant from Adak on Akutan Island. We examined the trace element compositions of the samples from the potential source outcrop and the archaeological fragments to determine statistically the similarity of the samples. Determining the source of the Zeto Point obsidian artifacts has major implications for an ongoing study of 1) Unangan (Aleut) resources acquisition, 2) human impact on subarctic ecosystems prior to European contact, 3) travel and trade patterns between Unangan groups, many of whom were in conflict perhaps due to resource competition in a marginal habitat. We conducted trace element analysis (i.e. LIL, REE, and HFSE) at the Pacific Centre for Isotopic and Geochemical Research (PCIGR) at the University of British Columbia (UBC). Using Inductively Coupled Plasma Mass Spectrometry (ICP-MS), ten samples were selected and analyzed in total; five worked lithic fragments from Zeto Point, four of which were obsidian and one of which was a glassy rhyodacite or andesite, and five samples of the Akutan obsidian, in addition to analytical standards and duplicates. The analytical results show the composition of the Adak obsidian samples to be within the analytical error of the compositions of the Akutan obsidian; there is no significant compositional difference between the two groups. The single glassy rhyodacite/andesite differs significantly in composition from the both the Zeto Point obsidian and the Akutan obsidian.