GEOCHEMICAL AND GEOCHRONOLOGICAL OBSIDISN AND RHYOLITE SOURCE AND ARTIFACT FINGERPRINTING: CONSTRAINTS ON PREHISTORIC ALASKA TRADE ROUTES AND RAW MATERIAL ACCESS

Obsidian and rhyolite were important raw materials for prehistoric inhabitants of Alaska and are well-suited for provenance analyses using geochemical techniques (primarily XRF and INAA). Such analyses allow researchers to model prehistoric economic systems, social interactions, and the ways people adapted to landscape and climate change since the last Ice Age. Geochronological analyses provide an additional, but less commonly used, means to understand prehistoric lithic raw material use. 40Ar/39Ar geochronology is especially useful in helping to pinpoint the numerous sources of prehistoric toolstone that have yet to be relocated by geologists or archaeologists because it narrows the search universe to geological formations of specific age. The combination of two finger printing techniques also helps discriminate between sources with similar age or geochemical signatures.

Over the past 20 years a variety of researchers have constructed a catalog of obsidian source signatures consisting of about two dozen distinct obsidian source groups from Alaska and adjacent Yukon Territory. Geological sources have been confirmed for 8 of these sources and the remainder remain undocumented. The three most commonly used sources, Batza Tena in the Koyukuk River drainage, Wiki Peak in the Wrangell Mountains, and Okmok caldera in the Aleutian Islands, account for about 65% of all obsidian found in archaeological sites.

In Alaska we have just started to develop a geochemical and geochronological fingerprint framework for rhyolite artifact to source provenance work. A major problem is that most sources have not been located (i.e., we only know of hypothetical distinct sources from archeological samples from which we've defined geochemical "groups."). In order to refine the search for geological sources we have applied 40Ar/39Ar dating techniques to both artifacts and potential sources and compiled known identified rhyolite outcrops. In the field ground truthing has also assisted in locating and mapping potential rhyolite outcrops.

By combining the prehistoric access and trading history of two different distinct commonly used and well preserved Alaska raw materials we can better reconstruct how variations in extent of glaciations affect the social-economic behavior of the prehistoric peoples of Alaska.