Dating environmental change using magnetic bacteria in archaeological soils from the upper Thames Valley, UK

An archaeomagnetic date has been recovered from an organic rich sediment at the base of an alluviated ditch section found during archaeological excavations near the village of Yarnton, Oxford, UK. The magnetic minerals carrying this remanence include greigite and biogenic magnetite, derived from magnetotactic bacteria, that both indicate the presence of a micro-aerobic environment. It is proposed that the archaeomagnetic date from this material indicates the onset of floodplain conditions at the site due to increased population pressure and intensification of land clearance in the late British Iron Age.