Modeling the Chronology of a Late Precontact Site Using Radiocarbon and Trade Good Dates: Middle Grant Creek

Late precontact- and contact-period sites often produce multiple sources of chronological information, including stratigraphy, radiocarbon dates, European trade goods, and pottery seriation patterns. In this article, we describe a step-by-step approach to incorporating such information in an OxCal-based Bayesian chronology model, with special emphasis on incorporating trade-good dating into radiocarbon-based modeling. The Middle Grant Creek site in Illinois is an American Indian site that has yielded a number of European copper and brass trade goods along with extensive ceramic, faunal, floral, and lithic artifacts. Our modeling addresses issues resulting from an inversion in the radiocarbon calibration curve during the late precontact period and produces surprisingly different results depending on the boundary conditions applied to the model. We consider the probabilities produced by the models, propose the most likely chronology for Middle Grant Creek, and provide detailed OxCal scripts and examples that other researchers may adapt to their circumstances and preferences. We also describe lessons learned related to chronological modeling of sites where the radiocarbon curve contains significant inversions.