Neolithic and Bronze Age Landscapes of North Mayo: Report 2011

Charcoal analysis from Neolithic and Bronze Age
landscapes of North Mayo,
Lorna O’Donnell
Introduction
Charcoal is the product of chemical reactions that occur when wood is heated (i.e. thermal
decomposition) (Smart and Hoffman 1988, 172). It is frequently found on Irish archaeological
sites, in general in greater quantities than plant remains. Its uses in environmental
archaeology range from being a suitable material for radiocarbon dating, to an
environmental indicator.
This report describes the analysis of wood and charcoal samples from five sites in the Céide
fields complex Co. Mayo, excavated by Prof. Seamas Caulfield, Ms Gretta Byrne and Mr. Noel
Dunne.
During the excavations, bulk samples were taken for future environmental work. Current
funding under the INSTAR grant scheme by the Heritage Council has allowed for processing
and analysis of these samples. Previously, some charcoal analysis was undertaken by Mr.
Donal Synott from the National Botanic Gardens, Glasnevin. In 2010, the author was asked
to assess samples from five of the sites; Glenulra enclosure (E24) (Caulfield et al 2009a),
Glenulra Scatter (92E140) (Byrne et al 2009a), Céide Visitor Centre (E494) (Byrne et al
2009b), Belderg Beg (E109) (Caulfield et al 2009b) and Rathlackan (E580) (Byrne et al 2009c)
(O’Donnell 2010). Following this assessment and further sample processing, 82 samples
were selected for full analysis from the five sites.
The aims of the work are as follows:
• Assess suitable short lived material for radiocarbon dating
• Examine any wood selection strategies on the sites
• Compare woodland flora over time, incorporating other environmental data
Sampling strategy
The sampling strategy on site consisted mainly of targeted sampling of charcoal rich
deposits.
Methodology
Processing
Soil samples were processed in 2009-2010 by means of flotation. Mechanical flotation tanks
were used. This involved the agitation of the soil sample in a water filled tank lined with a
1mm nylon mesh. This releases the lighter environmental material (flot) such as seeds and
charcoal from the soil matrix. This lighter fraction is collected in a sieve of 300μm mesh size.
Once dry, the retent was sorted using a stack of sieves with a mesh size of 4mm, 2mm and
1mm. Charcoal larger than 2mm in size was sorted out of the retent and the flot, all seeds
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