TRACE ELEMENT CHARACTERIZATION OF DISTINCT OBSIDIAN FLOWS WITHIN THE COSO VOLCANIC FIELD, CALIFORNIA BY LASER ABLATION ICP/MS AND ARCHAEOLOGICAL IMPLICATIONS

The Coso Volcanic Field (CVF) has been a major source of toolstone for prehistoric populations for at least the past 12,000 years. Hundreds of small prehistoric quarries exist within the CVF, the most notable being the "Colossal Quarry" first described by Harrington (1951) on the south-facing side of Sugarloaf Mountain, a large Tertiary rhyolite dome. Geochemical sourcing of CVF obsidian for archaeological studies has been an important tool in assessing prehistoric trading patterns in eastern California, and the CVF source was first characterized using X-ray fluorescence in the later 1970s. Subsequent work by Hughes (1988) demonstrated the occurrence of four distinct geochemical subsources of obsidian within the CVF (Joshua Ridge, West Sugarloaf, Sugarloaf Mountain, West Cactus Peak).

We examined obsidian from Joshua Ridge, West Sugarloaf, Sugarloaf Mountain, and West Cactus Peak by Laser Ablation ICP/MS. This technique allows for quick and non-destructive trace element analysis of obsidian and other solids making it a promising tool for archaeogical investigations. Obsidian samples were analyzed for a suite of 25 trace elements including rare earth elements. The samples exhibited a generally similar trace element composition but differences in Rb, Ba, Zr, Sr, Ce, Dy, Eu, and Sm were large enough to allow distinction of the different source areas. An attempt was also made to distinguish obsidian from four different quarries on Sugarloaf Mountain. However, the composition of obsidian from these quarries was too similar to allow unequivocal identification.

References: R.E. Hughes Geoarchaeology: An International Journal 3, 253 (1988) M.R. Harrington The Masterkey 25, 14 (1951).