Dating Ancient Burial Mounds in Denmark: – Revealing Problematic Ancient Charcoal

The National Museum of Denmark and the Department of Geography at the
University of Copenhagen have collaborated on a project investigating burial
mounds near early Medieval churches. The aim was to identify a possible
continuity in cult sites across the shift to Christianity in the late Viking Age.
Charcoal samples from 18 mounds were radiocarbon dated but the results
showed they were far older than expected. Control dating undertaken on burial
mounds of known age confirmed that charcoal in the mound fill can at least be
up to 3000 years older than the mound itself. As charcoal can survive in the
surface soil layer for millennia, in spite of ploughing, bioturbation and frost, it
may also dominate the charcoal pool of the grass or heather turfs used in the
mound construction. Therefore, the article concludes, charcoal cannot be used
to securely date archaeological features built with turfs and it is important to be
aware of the possible presence of very old charcoal when selecting material for
dating archaeological features, even those which otherwise would be judged
unaffected by material from earlier archaeological periods.