Tutorial:Post-Burial Effects
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[edit] The effects of post-burial modification
The effect these changes have on deposits as seen in the field and the laboratory will depend on the nature of the soil and on the magnitude of the change.
Compression can lead to the loss of pore space and soil structure, resulting in the apparent thinning of individual deposits and horizons. Compression can also lead to artefacts adopting a sub-horizontal orientation, as well as to the fracturing and compression of fragile pieces.
Other effects include overprinting of the original profile by post-burial features such as iron redistribution (grey reductions, pans, nodules and mottles) associated with waterlogging and anaerobic soil conditions. This can result in the loss of information about sedimentary boundaries and depositional contexts as colour differences are obscured. The effects of gleying are amongst the commonest seen in archaeological sites. Gleying results in the development of hydromorphic patterning whose strong colours can obscure boundaries. Iron pans can develop where more oxygen penetrates the deposit or where the pH is higher (the soil is more alkaline). Particular care must be taken where iron pans appear to follow context boundaries as they rarely follow depositional boundaries faithfully and can create a false impression.
The on-going degradation of organic matter, results in the loss of both environmental and soil information. In oxidised conditions the loss of organic matter from buried A horizons can make field identification of buried soils difficult. The loss of fine organic matter, clay and silt from buried horizons by translocation can also destroy evidence of depositional stratigraphy as the fine matrix is lost leaving only sand, gravel and coarse artefacts in-situ. Textural and colour differences may be completely obliterated in extreme cases leaving the artefacts without context.
The preservation of organic and inorganic artefacts and ecofacts is affected by biological and chemical weathering. The principle drivers for which are soil pH, soil moisture and the soil redox conditions. The effect of these weathering processes can include the loss or obscuring of surface detail below corrosion products or precipitates, the alteration of the chemical structure of the artefact, the physical disruption of artefacts and even the complete loss of physical remains.
More information on favourable conditions of preservation can be found here.
