This investigation explored the potential of using 40Ar/39Ar dating to help fingerprint the source of stone archeological artifacts. As a preliminary investigation, we determined the age of obsidian from one of the principal sources of obsidian in Alaska, the BatzaTena archeological site. The BatzaTena (Indian River) obsidian site in west-central Alaska is thought to be the source for many obsidian artifacts found in northern Alaska. The BatzaTena obsidian occurs as subround pelletal fragments up to 10 cm long and are thought to have formed as residual inclusions ('marekanites' or 'Apache tears' in hydrated perlitic volcanic glass. Several fresh obsidian fragments were analyzed by 40Ar/39Ar step heating. The samples show no evidence of alteration and age spectra from the samples are flat with an average age of 41 Ma. This age is consistent with stratigraphic controls and probably reflects the eruptive age of the obsidian.
If 41 Ma obsidian is unique to this site, then these results may be used along with Instrumental Neutron Activation Analysis, X-ray Fluorescence microprobe and hydration measurements (compiled by John Cook at the Bureau of Land Management) to provide a distinctive 'finger print' to identify artifacts derived from BatzaTena. Laser 40Ar/39Ar dating techniques would allow for small (<1 mm) fragments from actual artifacts to be dated without destroying the entire sample.
There are few accounts of reliable 40Ar/39Ar ages obtained from terrestrial glass samples older than ~10 Ma. The BatzaTena study indicates that reliable ages may be obtainable from old obsidian elsewhere.
Internal University of Alaska funds. Scientific personnel: Paul Layer and John Cook (U.S. Bureau of Land Management)