Archeomagnetic dating of some Pre-Columbian pottery fragments from northern Mesoamerica: Implications for the chronology of central Mexico during the Epiclassic period

We present the results of a combined rock-magnetic and archeomagnetic study carried out on ceramic samples of the Buenavista archeological site, Valle de Ojocaliente, Zacatecas. Based on archeological considerations, it is believed that the main sedentary occupation of the site took place during the Epiclassic period of the Mesoamerican chronology. Ten out of fifteen ceramic fragments were selected for Thellier-Coe archeointensity experiments on the basis of magnetic properties. According to the mean archeointensity values obtained samples were divided in two groups: Group (I) yielded intensities varying from 40.3 ± 1.6 to 45.6 ± 1.1 μT, with an average value of 42.7 ± 2.4 μT. Group II shows internal variation from 28 to 31 μT, and a corresponding mean value of 30 μT. Based on the average values, the most probable archeomagnetic age for group I lies in the interval [647 AD 855 AD], which is in excellent agreement with the estimated chronology of the site. In regard to group II, such a low AI value is not predicted by any of the available global models for Mesoamerica for the last 3 k years. Thus, under the geophysical point of view, an earlier date and/or different provenance for these pieces are possible.