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Appendix 1: Early Fields - palaeoenvironmental methods and peat stratigraphies

Astrid E. Caseldine

As part of the investigation of early fields in North Wales (Smith et al. 2011), samples were taken for palaeoenvironmental analysis with a view to elucidating the environmental histories of the areas concerned and, in particular, land use changes associated with the field systems. The pollen records from Cwm Cilio and Braich y Gornel also provided an opportunity to see if there was evidence for spatial variation in vegetation history and land use within the region.

Sampling

Samples for pollen analysis were taken during the excavations at Cwm Cilio, Braich y Gornel and Muriau Gwyddelod, Fronhill, and pollen cores were recovered from nearby peat deposits at Cwm Cilio and Braich y Gornel. In addition, samples for charcoal identification and bulk samples for charred plant remains were taken during the excavations at Cwm Cilio and Muriau Gwyddelod, Fronhill.

Methods

Pollen

Sub-samples were taken from the pollen columns and prepared following standard procedures (Moore et al. 1991), including acetolysis to remove cellulose and treatment with hydrofluoric acid and fine sieving to remove minerogenic material. Lycopodium spores were added as a marker and to enable pollen and charcoal concentrations to be calculated (Stockmarr 1971). Pollen and spores were identified using the keys in Moore et al. (1991) and Andrew (1984) as well as a modern reference collection. Fungal spores possibly indicative of animal dung (Buurman et al. 1995, van Geel 1978, van Geel et al. 1981, van Geel et al. 2003) were also identified and counted. A sum of 300 total land pollen grains was counted where concentrations were sufficiently high, but where concentrations were low the count was based on 300 Lycopodium spores. The results from the pollen cores are shown as percentage total land pollen (TLP) for land pollen types whilst aquatics and spores are expressed as percentage TLP plus the respective group. Fungal spores and algae are expressed as a percentage of TLP. Microscopic charcoal was counted and is expressed as concentration data. Pollen nomenclature is modified from Moore et al. (1991) using Bennett (Bennett 1994, Bennett et al. 1994). The pollen core diagrams were prepared using TILIA (Grimm 1991-93) and TGView (Grimm 2004). Stratigraphically constrained cluster analysis using CONISS (Grimm 2004) was used to aid zonation of the pollen core diagrams. The results from the pollen samples from the archaeological sites are expressed as a percentage of the total (including total land pollen, spores and indeterminate pollen) and as a percentage of total land pollen (excluding spores and indeterminate pollen).

Plant macrofossils

The bulk plant macrofossil samples were sieved through a stack of sieves to recover charred plant remains. The finest mesh used was 250μm. In addition, pollen sievings from the two pollen sites were also examined for plant macrofossil remains. The remains were examined using a Wild M5 stereomicroscope and identified with the help of identification texts (e.g. Schoch et al. 1988, Cappers et al. 2006) and a seed reference collection. The results from the pollen sievings are included in the stratigraphic descriptions. No charred plant remains other than wood charcoal were recovered from the bulk samples.

Charcoal identification

Charcoal samples were fractured to produce clean sections in three views: transverse, radial longitudinal, and tangential longitudinal, and examined with a Leica DMR microscope with incident light source. Identification was by reference to wood anatomy texts (Schweingruber 1978; Schoch et al. 2004). Nomenclature follows Stace (1995).

Radiocarbon Dating

Samples for AMS dating were taken from the pollen columns using standard procedures and submitted to Beta Analytic Inc. in Florida. Details of the samples and the results are presented in Table A and discussed with the pollen evidence.

Results

Peat stratigraphies

Cwm Cilio

0–15 cm Fibrous peat including turf mat. Not retained.

15–54 cm Dark brown relatively unhumified fibrous peat with Sphagnum present especially c 36 cm.

54–63 cm Dark brown increasingly humified fibrous herbaceous peat.

63–75 cm Dark brown-black moderately humified fibrous herbaceous peat with Juncus seeds. Charcoal present, particularly c 66cm.

75–88cm Dark brown increasingly humified fibrous peat with Juncus and Potentilla seeds.

88–98 cm Dark brown-black humified peat with Juncus seeds.

98–115 cm Very dark greyish-brown silty humified peat with Juncus seeds.

Braich y Gornel

0–4 cm Turf mat.

4–5 cm Very dark brown base of turf mat.

5–37 cm Dark brown fibrous herbaceous peat. Potentilla and Juncus seeds present.

37–40 cm More humified band of fibrous peat. Potentilla seeds present.

40–48 cm Dark brown fibrous herbaceous peat with Carex, Potentilla and Ranunculus seeds.

48–56 cm Increasingly humified fibrous peat with Juncus seeds and charcoal present.

56–68 cm Dark brown moderately humified and well humified silty peat. Juncus and Potamogeton seeds and charcoal present.

68–84 cm Dark greyish-brown silty peat with Juncus seeds and charcoal.

84–100 cm Peaty silt with Juncus seeds and charcoal.

See Table A: Radiocarbon dates from Cwm Cilio and Braich y Gornel pollen cores


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