Creating an Archaeomagnetic Dating Curve for Minnesota: Assessing the potential of Minnesota ceramic sherds to accurately record field intensity

Abstract

Precise dating of heat treated Minnesota artifacts is hampered by a scarcity of material suitable for radiocarbon dating, and uncertainties in stylistic dating of material culture (often > ± 500 years). Archaeomagnetic dating has the potential to refine the ages of nondiagnostic ceramics and other heated artifacts, but has not been implemented in Minnesota, as the region lacks a well-constrained reference curve. For this study, we analyze a collection of 21 ceramic sherds with differing material characteristics and ages, representative of the kinds of ceramics commonly found in southwest Minnesota. We performed rock magnetic analyses to better characterize the sherds, determining that the majority of specimens contain a range of magnetic grain sizes and compositions (magnetite/maghemite, goethite, and hematite). Archaeointensity experiments based on the IZZI method were encouraging, with approximately 86% of specimens showing promise under a modified version of the SELCRIT2 selection criteria. These results indicate that the construction of an archaeomagnetic reference curve for Minnesota (MARC) is feasible, and can be used as a tool to better constrain archaeological dates and the geomagnetic field in the state and surrounding area. Future work on this topic will deal with populating the MARC using archaeointensities and available radiocarbon dates.