Preliminary Archaeointensity Reference Curve for the "Four Corners" Region of the American Southwest

A preliminary high quality archeointensity reference curve was developed for the last 2000 years for the Four Corners region of the American Southwest. This region includes the states of New Mexico, Arizona, Colorado and Utah. The curve is derived from two data sources: new data collected during the course of this study and previously published data filtered for the highest quality. New paleointensity experiments were conducted using the IZZI protocol on three hundred and four specimens from fifty-seven baked pottery fragments collected from nine archaeological sites near Santa Fe, New Mexico. Anisotropy of remanence is a common problem in archaeological material so we conducted anisotropy experiments to correct for this behavior. In addition, we evaluated the effect of cooling rate in our specimens and adjusted intensity values accordingly. The corrected intensity estimates for successful samples were converted to Virtual Axial Dipole Moments (VADMs). Stylistic evidence, historical documentation, dendrochronology, and 14C analyses provide age constraints with up to decade resolution for the VADM results. Previously published archaeointensity values were retrieved from the GeoMAGIA database (Brown et al., 2015). The accuracy of the data and metadata retrieved from the database was verified and corrected, when necessary, from the original publications. These corrected data were filtered for the highest quality: a statistical "n" greater than or equal to three, a VADM standard deviation less than or equal to 5%, and an age sigma of less than or equal to 150 years. The resulting archaeointensity curve varies in magnitude from approximately 80 ZAm2 during the 7th century to a peak of roughly 145 ZAm2 during the 14th century. During this interval the field increased in magnitude at a rate of 9.3 ZAm2 per century. Since the 14th century the field has been decreasing in magnitude at generally the same rate.