Discovery of tephra on the Grabow 15 floodplain site, northern Germany

An investigation of the late Palaeolithic ‘Federmesser’ floodplain site of Grabow 15 reveals the presence of ‘cryptotephra’ (non-visible volcanic ash) in a disturbed late Holocene deposit which overlies the late-glacial archaeology. Geochemical analyses demonstrate the tephra originates from Iceland; most likely from an eruption of the volcano of Askja. In the late Holocene there are two known eruptions of Askja: the historical AD 1875 eruption and the earlier ‘Glen Garry’ tephra, which is only known as a horizon outside of Iceland. Although similarity of composition prevents these contenders being distinguished on their geochemistry alone, nevertheless, the presence of such volcanic glass at the site of Grabow demonstrates the potential for applying tephrostratigraphy in archaeological settings, especially in regions where multiple ash footprints are known to be present. The presence of very low numbers of volcanic glass shards in an adjacent river palaeochannel suggests the presence of another, potentially important, tephra in the region. However, failure to obtain a geochemical signature leaves open the origin of the ash and questions whether it constitutes a primary fall event.