GEOCHEMICAL CHARACTERIZATION OF PREHISTORIC GRAY WARE CERAMICS FROM THE UPPER BASIN REGION OF THE GRAND CANYON, NORTHERN ARIZONA

Chemical characterization of archaeological ceramics can be used to constrain models regarding variation in pottery manufacturing techniques, including identifying types and sources of raw materials. Based on petrographic and strontium isotope analyses, it has been proposed that San Francisco Mountain Gray Ware (SFMGW) and Tusayan Gray Ware (TGW) prehistoric ceramics from the Upper Basin of the Grand Canyon, Arizona, are compositionally distinct. Specifically, SFMGW ceramics were produced from a narrow range of non-local materials whereas TGW ceramics were manufactured from a wide range of materials. To test these inferences, we conducted a comprehensive chemical characterization of a suite of SFMGW and TGW sherds. Major, minor, and trace element XRF data were obtained for 32 SFMGW and 33 TGW sherds. Principal component analysis (PCA) of the number of oxides and trace metals for the 65 sherds was used to investigate elemental patterning. Two mutually exclusive groups were identified, based on variation in K₂O (axis 1), and SiO₂ (axis 2) and MgO (axis 3). Group 1 contains only SFMGW sherds and Group 2 only TGW sherds. Group 1 has minimal variability in K₂O (2.24-4.72 weight percent [wt%]), SiO₂ (61.54-70.13 wt%), and MgO (0.82-1.52 wt%) concentrations while Group 2 has a greater degree of chemical variability: K₂O (0.70-2.55 wt%), SiO₂ (61.23-73.09 wt%), and MgO (0.88-1.71 wt%). These distributions suggest a limited number of raw materials were used to produce SFMGW vessels. In contrast, TGW is compositionally diverse, which suggests multiple source materials were selected for ceramic manufacture. Although not designed to address questions of provenance, results of this study sustain previous interpretations that SFMGW and TGW ceramics were manufactured from distinct source materials.