Variation in the radiocarbon age of different fractions of peat: A case study from Ahrenshöft, northern Germany

• Published in: Quaternary geochronology 2011-12, Vol.6 (6), p.550-555
• Main Authors: Brock, F., Lee, S., Housley, R.A., Bronk Ramsey, C.
• Format: Article
• Language: English
• Subjects: Cryptotephra; Humic acid; Humin; Peat; Radiocarbon dating
• ISSN: 1871-1014; 1878-0350
• DOI: 10.1016/j.quageo.2011.08.003

Peat is notoriously difficult to radiocarbon date as it is composed of a heterogeneous mix of organic materials of different radiocarbon ages and at different stages of humification. Different chemical fractions (most frequently humin and humic acid) have been observed to yield significantly different radiocarbon ages from some peat deposits. Here we present humin and humic acid dates on a range of grain-size fractions of peat from the open-air archaeological site of Ahrenshöft LA 58 D, northern Germany, which were measured to confirm the identity of the source of cryptotephra found at the site. Both the humin and humic acid ages increased with increasing grain size, and for all but one sample the humic acid fraction was younger than the corresponding humin date. When calibrated the 6 dates from the horizon containing the cryptotephra spanned a time period of up to 1500 years, and are insufficiently conclusive to definitively resolve which eruption is responsible for the observed ash horizon. ► We 14C date humin and humic acids from different grain-sized fractions of peat. ► The peat was sampled from the open-air archaeological site at Ahrenshöft, Germany. ► Humin ages increased with increasing grain size due to rootlet contamination. ► Unexpectedly, humic acid ages also increased with increasing grain size. ► We find humic acid ages are generally younger than corresponding humin ones.