Late Holocene vegetation and palaeoenvironmental history of the Dunadd area,Argyll, Scotland: chronology of events

This paper focuses on the chronology and environmental significance of a sediment sequence from an alluvial locality in the vicinity of the historic site of Dunadd, Scotland. It outlines the rationale and statistical validity of an age model derived for a sequence of floodplain sediments from which detailed pollen-stratigraphical and plant macrofossil records have been derived. A series of radiocarbon dates are calibrated using a Bayesian modelling approach, the results of which can be refined by incorporating two independent age estimates based on tephra layers of known age. Analysis of the entire floodplain sequence for volcanic glass shards revealed the presence of discrete but geochemically very similar tephra layers within the upper (late Holocene) part of the sequence. Comparison with published geochemical data obtained from Icelandic tephras of historical age indicates strong statistical correlations with the Hekla 1947 AD and Hekla 1510 AD. While the Hekla 1510 AD tephra has previously been reported from sites within Britain and Ireland, the Dunadd sequence affords the first record of the Hekla 1947 AD tephra layer within Scotland. When the ages and stratigraphic positions of both tephra layers are incorporated into the Bayesian age model, an overall centennial to decadal precision for the late Holocene is achieved, with archaeological and environmental transitions discriminated with highest-likelihood age uncertainty ranges of 20–50 years at 95% confidence. The local environmental record is assessed in the light of this new chronological framework: the data support previously reported proposals for two periods of significant climatic deterioration with increased wetness, the first during the early Medieval period and the second during the late 16th and 17th centuries AD.