An archeomagnetic analysis of burnt grain bin floors from ca. 1200 to 1250 AD Iron-Age South Africa

Recognition of the rapid decay of Earth’s magnetic field over the last 150 years, chronicled in magnetic observatory and satellite data, highlights the need for a higher resolution record of geomagnetic field behavior over the past millennium. Such a record would help us better understand the nature of the recent dramatic changes. A limitation of the existing database is undersampling of the Southern Hemisphere. Here we investigate the potential of obtaining archeomagnetic data from Iron-Age burnt grain bins from southern Africa. These structures preserve oriented material that can record both paleodirections and paleointensity information. Directional data collected from three sites (ca. 1200–1250 AD) fall 9–22° to the East of predictions. Thellier–Coe and Shaw paleointensity results differ from model values by ∼15%. The consistency of results between the three sites suggests that further investigations of these materials with different ages could markedly improve the current spatial distribution of the archeomagnetic database.

► We report burnt grain bins as a source of archeomagnetic data from South Africa.
► We present directions and intensities derived from Thellier–Coe and Shaw experiments.
► Results differ from global model predictions suggesting local structure in the field.