Relationships between human activity and the magnetic properties of soils: a case study in the medieval site of Roissy‐en‐France

Magnetic prospection of archaeological sites depends strongly on the susceptibility, χm, of the upper layer of soils and on their ferrimagnetic mineral content. The minerals involved may be authigenic, biogenic or anthropogenic (by firing). To characterize and identify different ferrimagnetic minerals in several archaeological soils, we performed thermomagnetic and hysteresis measurements on a set of samples. Pedological and micromorphological analyses allow us to determine the relationship between pedological and human activities (ferruginization and anthropogenic objects) and their magnetic parameters. Maghemite was identified by the thermomagnetic curves as the main ferrimagnetic mineral in these archaeological sediments. The link between ferruginization and high magnetic susceptibility is complex. However, a correlation between the ratio of susceptibility to saturation magnetization, χm/Js, and the abundance of anthropogenic objects was observed. In association with magnetic susceptibility and remanent coercive field, we can provide an estimation of human alteration of the sediments. The thermomagnetic curves and a comparison between heated natural sediment and the anthropogenically altered sediments may provide an estimate of the furnace temperature. Copyright © 1999 John Wiley & Sons, Ltd.