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Appendix 2: Early fields soil micromorphology methods

Richard I. Macphail

Summary

Buried soils from three sites in near-upland areas of north-west Wales were investigated employing six thin sections. Although only these few samples were studied, they do provide localised information for the interpretation of past land use. Soil micromorphology and selected SEM/EDAX analyses found evidence suggesting a colluvial plough soil had been present before pasture development at Braich y Gornel; clayey subsoils formed in drift had been eroded down slope. At Muriau Gwyddelod, Fronhill, acidifying buried pasture soils were found, together with evidence of earlier clearance and the original earthworm-worked brown earth soil. A history of acid brown earth subsoil erosion and the deposition of eroded subsoil clasts down slope was recorded at Cwm Cilio, as probable evidence of arable activity before an ensuing land use change to pasture.

Introduction

Six soil thin-section samples were received from George Smith (Gwynedd Archaeological Trust) from the three sites of Braich y Gornel, Muriau Gwyddelod and Cwm Cilio, in north-west Wales in the spring of 2010. These thin-section samples were studied employing soil micromorphology, as part of research aimed to improve the understanding of early field systems in this region (Smith et al. 2011). Evidence of field use in relationship to soil type and pedogenic development was sought.

Samples and methods

The thin-section samples were from:

Braich y Gornel (Iron Age; M6: buried soils Contexts 4 [within slight lynchet] and 9; M8: buried soil Context 10 [below field boundary tumble].

Muriau Gwyddelod, Fronhill (Iron Age or earlier; M7: buried soil Context 14; M10: buried soil Context 14).

Cwm Cilio (Iron Age/Romano-British/medieval?; M104: buried soil Context 11 [downhill side of lynchet, below primary and secondary banks]; M105: buried soil Context 9 [below post-medieval boundary].

The six samples were impregnated with a clear polyester resin-acetone mixture; samples were then topped-up with resin, ahead of curing and slabbing for 75x50mm-size thin-section manufacture by Spectrum Petrographics, Vancouver, Washington, USA (Goldberg and Macphail 2006, Murphy 1986) (Figures 7.1–7.22).

Thin sections were further polished with 1,000 grit papers and analyzed using a petrological microscope under plane polarized light (PPL), crossed polarized light (XPL), oblique incident light (OIL) and using fluorescent microscopy (blue light - BL), at magnifications ranging from x1 to x200/400. SEM/EDAX quantitative analyses were applied to features in M6 and M8 (see Table 9, Figure 7.23, Figure 7.24). Thin sections were described, ascribed soil microfabric types (MFTs) and microfacies types (MFTs) (see Table 1, Table 7 and Table 14 and Table 2, Table 8 and Table 15), and counted according to established methods (Bullock et al. 1985, Courty 2001, Courty et al. 1989, Goldberg and Macphail 2006, Macphail and Cruise 2001, Stoops 2003). Some 13 features and inclusions were described and counted.

See also Smith et al. 2011


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