IDENTIFYING GEOLOGICAL SOURCES FOR ANASAZI AND COHONINA CERAMIC RAW MATERIALS IN THE EASTERN GRAND CANYON REGION THROUGH PETROGRAPHIC ANALYSIS

Due to the geological heterogeneity of north-central Arizona, petrographic studies of prehistoric archaeological ceramics from the region hold considerable promise for resolving the movement of ceramic materials across the Coconino Plateau. Our ongoing program of petrographic analysis of Anasazi and Cohonina ceramics and geological source materials from the eastern Grand Canyon region aims to: 1) assess the compositional variation between Anasazi and Cohonina ceramics; and 2) identify the unknown geological origins of Anasazi and Cohonina ceramic raw materials.

Our research demonstrates substantial compositional and textural differences between Anasazi gray wares and Cohonina gray wares. The coarse fractions (all inclusions silt-sized and larger) of Anasazi gray wares are principally composed of moderate-to-well sorted, medium-to-coarse sand-sized grains of monocrystalline and polycrystalline quartz, with small and highly variable proportions of feldspars and sedimentary lithics. Although the coarse fractions of Cohonina gray wares are also dominated by monocrystalline quartz, the texture of quartz grains in Cohonina gray wares is markedly different than that in Anasazi gray wares, as characterized by poor sorting with an average grain size of medium sand and highly variable grain morphology. Furthermore, in contrast to Anasazi gray wares, all Cohonina gray wares have a moderate abundance of feldspars and a small abundance of mica. Quantitative analysis by point counting has documented statistically significant differences between Anasazi and Cohonina gray wares in the abundance of five types of inclusions: 1) polycrystalline quartz; 2) K-feldspar; 3) plagioclase; 4) mica; and 5) sedimentary lithics. The inclusions in Anasazi gray wares are consistent with derivation from subarkosic sandstones in the Permian Kaibab Fm and/or the Triassic Chinle Fm on the Coconino Plateau. However, the inclusions in Cohonina gray wares are more consistent with sources such as arkosic sandstones in the Mesoproterozoic Dox Fm and/or juvenile sedimentary materials associated with Paleoproterozoic and Mesoproterozoic granitic rocks in the inner Grand Canyon. Therefore, our research suggests fundamentally different patterns of ceramic resource procurement for the Anasazi and Cohonina gray ware traditions.