Petrographic Quartzite Source Discrimination in the Upper Gunnison Basin, Colorado: Implications for the Archaeological Study of Prehistoric Hunter-Gathers

Abstract

Recently (Pitblado et al. 2008, 2013), an interdisciplinary team of archaeologists and geologists collaborated to develop a protocol for sourcing quartzite in the Upper Gunnison Basin, Colorado where archaeological assemblages are commonly over 90 percent quartzite (Dalpra and Pitblado 2016). Investigations from this research program have concluded that two techniques, when used in tandem, offer the best discriminatory results: geochemical characterization via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and petrography (Pitblado et al. 2008). The following study briefly reviews the results of geochemical fingerprinting of Gunnison Basin quartzite, but focuses primarily on the results of petrographic analysis. The results demonstrate the discriminatory power of petrography on quartzite through a Basin-wide study functioning as a proof of concept. This Basin-wide analysis is followed by a more in depth look at two prehistorically used quarry locations analyzing both cobbles and outcrops. It is important to not just demonstrate differences between the sources, but also the variability within each source. The petrographic research is one step toward the ultimate goal, to develop a quartzite-sourcing protocol for the Gunnison Basin to enable “matching” cultural chipped stone assemblages to the likeliest raw material sources. This will allow researchers to reconstruct prehistoric land-use strategies in the Gunnison Basin with more precision than has been possible before.