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3.4 Palaeoenvironmental evidence

See Appendix 1, Appendix 2 and Figure 6

3.4.1 Soil micromorphology by Richard I. Macphail

Two thin-section samples, M104 and M105, were examined from Cwm Cilio. The former was from a buried soil on the downhill side of a lynchet, below primary and secondary banks, and the latter was from a buried soil below a post-medieval boundary. The results are discussed below, and supported by Table 1 and Table 2 and Figures 7.4 and 7.15, 7.16, 7.17, 7.18, 7.19, 7.20, 7.21, 7.22.

Figure 7: Soil micromorphology

Figure 7.1

Figure 7.2

Figure 7.3

Figure 7.4

Figure 7.5

Figure 7.6

Figure 7.7

Figure 7.8

Figure 7.9

Figure 7.10

Figure 7.11

Figure 7.12

Figure 7.13:

Figure 7.14

Figure 7.15

Figure 7.16

Figure 7.17

Figure 7.18

Figure 7.19

Figure 7.20

Figure 7.21

Figure 7.22

Figure 7.23

Figure 7.24

Trench 1, Context 11 (primary and secondary bank-buried soil)(M104):
This is a heterogeneous, moderately stony humic coarse silty–very fine sandy soil, composed of very humic (A1h) and humic (A12h) mineral soil, and 1–2mm-size rounded clasts of minerogenic (Bw) soil (Figures 7.15, 7.16, 7.17). Occasional fine charcoal (max. 6mm), very fine charcoal and a trace of likely burned mineral material occur. The soil is present as sub-angular aggregates which are being currently worked into thin excrements.

Soil is formed in coarse silty–very fine sandy drift. Context 11 is probably a humic 'Ap' colluvial soil containing rounded eroded clasts of subsoil (of upslope origin), with very fine and fine charcoal relict of clearance (?)/management by fire. It can be suggested that this is an arable soil (ploughsoil colluvium), which went out of use allowing some reworking by acidophyle fauna and development of humic topsoil.

Trench 3, Context 9 (see Figure 6E. IA/RB? field below post-med boundary)(M105):
The thin section records the moderately mixed junction between compact minerogenic subsoil and overlying fine pellety humic soil, which contains rare inclusions of subsoil, trace amounts of fine charcoal and possible weakly burned angular mineral material (Figures 7.4 and 7.18, 7.19, 7.20, 7.21, 7.22). An example of 'ancient' vesicular arbuscular mycorrhizae is present (cf. Braich y Gornel M8, Figures 7.9, 7.10). The subsoil is characterised by moderately broad organo-mineral excrements. Occasional roots occur including a 10mm-wide example of bracken root.

Context 9 encompasses a weakly biologically worked anomalous junction between a minerogenic acid brown earth subsoil formed in coarse silt–very fine sand-size drift, and a more strongly acidic and humic topsoil. Possible burned material and trace amounts of fine charcoal suggest that the upper soil is partially anthropogenic. The lower soil appears to be truncated.

Discussion:
At Trench 1, the soil (Context 11) can be considered to be the remains of a cultivated colluvial soil, where plough-eroded brown earth subsoil (just downhill of the lynchet) occurs as rounded clasts. In situ acid brown earth subsoil is present in Trench 3, and here it seems to have been truncated. It can be noted that at Romano-British Chysauster, Cornwall, rounded acid brown earth subsoil clasts were found as evidence of plough erosion and colluvial soil accumulation in lynchets (Smith et al. 1996). Eroded soil clasts are typical of ploughsoil colluvium, although again textural pedofeature indications of ploughing were not observed (Jongerius 1970, Jongerius 1983, Kwaad and Mücher 1977, Kwaad and Mücher 1979, Macphail 1992, Mücher 1974). Subsequently, and again as at Chysauster, the soils have developed into more acid humic topsoils, presumably reflecting the current pasture land use. The site is located within an area of cambic stagnohumic gley soils (Wilcocks 1 soil association, Rudeforth et al. 1984) formed on drift from Palaeozoic sandstones, mudstones and shale, and these soils can be very acid when not limed (Rudeforth et al. 1983). Clearly, the soils chosen for agriculture are better drained and less acid compared to the dominant soils locally, even whilst abandonment was followed by acid soil development.

3.4.2 Soil pollen by Astrid E. Caseldine

Two samples were examined from sample 103 from the buried soil (11) pre-dating the field bank. The results are presented in Table 3. Pollen preservation was relatively poor and concentrations were low but slightly higher in the lower sample, perhaps indicating some pollen movement down the profile. Quercus and Corylus avellana type pollen dominated the assemblage, indicating oak and hazel woodland in the area. A decline in Quercus and increase in Corylus possibly suggests a shift towards more secondary hazel woodland in the area. There is also some evidence for alder and birch woodland. Poaceae (grasses) pollen is quite frequent, reflecting grassland but weed taxa are rare.

3.4.3 Charcoal by Astrid E. Caseldine

Charcoal (Table 4) from the buried soil (11) at Cwm Cilio comprised oak (Quercus spp.) and hazel (Corylus avellana), indicating the presence of oak and hazel woodland in the area. However, the hazel charcoal gave a date of 1910–1740 cal BC (SUERC-33062) while a fragment of oak charcoal gave a date of 5210–4990 cal BC (SUERC-33063), demonstrating that the charcoal related to different periods of fire activity, namely the Later Mesolithic and the Early Bronze Age, and is probably residual. It is possible that the charcoal represents deliberate woodland clearance activity rather than the results of natural fires. The oak charcoal may be derived from primary oak woodland while the hazel may represent secondary woodland.


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