Dating the Glen Garry tephra: a widespread late-Holocene marker horizon in the peatlands of northern Britain

The distal Icelandic tephra known as the Glen Garry layer has been dated by AMS C-14 at eight ombrotrophic peat bogs from northern England and Scotland. The geochemistry of all the tephra layers is consistent with there being only one Glen Garry tephra, rather than two or more from eruptions of the same volcanic source. At seven of the sites, all in Scotland, the tephra layer was bracketed by 1 cm contiguous samples below, at and above the horizon. At the one English site, Walton Moss, Cumbria, a suite of 16 AMS dates was applied to a 116 cm section of a peat core containing the tephra. The resulting dates were calibrated and wiggle-matched using the BCal and Bpeat programmes to give an estimated age for the Glen Garry tephra of 2176 cal. BP, with a 2 sigma range of 2210 - 1966 cal. BP. This 244 year range is an improvement on the 410 years calibrated date range for the date without the wiggle-match. This age estimate will allow future work on peat profiles and other sediments containing the tephra to use the date as a pinning-point in age/depth models and obviate the need for radiocarbon dating at this period.