Obsidian source classification and defining “local” in early Holocene Southeast Alaska

Despite the ubiquity of obsidian in early Holocene archaeological assemblages across Southeast Alaska, artifact sourcing using bi-plots and Principal Component Analysis has been hampered by the highly correlated geochemistry of two major sources: local Aguada Cove on Suemez Island, and distant Mount Edziza, in the Coast Mountain range. Partial Least Squares Discriminant Analysis (PLS-DA) models constructed with device-specific portable X-ray fluorescence (pXRF) source catalogs benefit from the precision of individual pXRF machines and the ability of PLS-DA to handle highly correlated data sets to provide a source classification system that complements existing methods. Of the known obsidian sources in or near Southeast Alaska, four are identified in early Holocene archaeological assemblages: Obsidian Cove and Aguada Cove on Suemez Island, Mount Edziza in the Coast Mountain Range, and a newly identified source on Zim Creek, Kupreanof Island. A comprehensive reanalysis of early Holocene microblade cores (101 cores from 13 archaeological sites) across Southeast Alaska confirms the presence of exotic obsidian from Mount Edziza in one of the oldest sites, alongside possible evidence of landscape learning: testing of the obsidian source on Kupreanof Island. The dominance of the Obsidian Cove source for microblade core production supports hypotheses framing Northwest Coast microblade core morphology as an adaptation to the small nodules of raw material available at the source. A simple distance-decay model indicates no relationship between core reduction intensity and distance from the source, suggesting high forager mobility characterized by regular trips to Suemez Island (a voyage of up to 380 km) throughout the early Holocene.