A GEOARCHAEOLOGICAL INVESTIGATION on THE ORIGIN OF SANIDINE-BEARING VOLCANIC TEMPER IN POTTERY SHERDS FROM THE FOUR CORNERS AREA

An important question in Southwestern archaeological research is how social and economic ties between prehistoric groups changed through time. The chemical and mineralogical matching of ceramic temper to source areas is a vital piece of information that has been used to address this question. It has been proposed in previous studies that sanidine-bearing temper found in sherds in the Four Corners region were sourced from the Chuska Mountains of New Mexico. This hypothesis is based mostly on interpretation that poikilitic sanidine in the sherds is texturally similar to sanidine in “trachyte” flows of the Navajo volcanic field (NVF) that are exposed at Narbona Pass.

Our recent research on mafic volcanic rocks in the Navajo volcanic field reveals that sanidine is present at more rock-outcrop sites than previously documented. In addition, poikilitic is a common textural variety of sanidine found in many of the NVF rocks. On the basis of our preliminary findings, we argue that petrographic traits of sanidine-rich sherd fragments are not a reliable means to constrain the source rock of the temper. We thus challenge the hypothesis that all “trachyte” used for manufacturing ceramics in the Mesa Verde region of Colorado was derived solely from the Chuska Mountains of New Mexico. If other source areas were used, then this would imply a lesser degree of ceramic temper importation from the Chuska Mountains to Chaco Canyon. In addition, this would lessen the evidence supporting the strong economic and political influence of Chaco Canyon on other regions during its florescence (around A.D. 1040–1135).

In this presentation we summarize our current state of knowledge about the potential source rocks for sanidine-bearing temper materials in the Four Corners region, and the implications on previous hypotheses. We will also discuss our preliminary results of major and trace element geochemical data for sanidine from sherds and potential source rocks obtained from electron microprobe studies, and highlight the pros and cons of different chemical analyses and methodologies to identify different temper materials.