Field Analysis:SASSA Burning

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Has this deposit been affected by burning in-situ?
This query aims to distinguish between redeposited residues of burning and the site of burning itself such as a hearth or camp fire. To score highly the deposit should have:
 * Clear, gradual or diffuse lower and lateral boundaries.
 * A similar mineralogy to a comparable ‘unburnt’ context, if one is available. This refers explicitly to stone and sand grain type rather than grain size or texture as this can be affected by burning as soil particles weld together.
 * The presence of vesicles – these will only form where the soil temperature is sufficiently high to cause nitrogen and sulphur in soil organic matter to be released as gases.
 * Any charcoal present should have a predominantly horizontal orientation, except where disturbed by bioturbation, and is likely to be most frequent at or towards the top of the deposit.
 * A soil crust that is intact or at least not highly disturbed except where bioturbation has been high.

There are other changes brought about by burning, which have not been considered here but which the user should be aware of. These include a coarsening of texture, a reduction in overall porosity, a reduction in organic matter content, and an increase in density. These were not used in this case because the potential heterogeneity of anthropogenically redeposited material could not be sufficiently taken into account. Changes in soil colour have not been relied on here, because they can be confused with the effects of seasonal waterlogging.

Field interpretations often have a high degree of uncertainty associated with them, this can be reduced if appropriate field and post-excavation analyses are carried out. Magnetic susceptibility is a key analysis in determining the presence of burnt materials. The use of field probes can be very helpful for field-level interpretation, whilst laboratory based magnetic susceptibility analyses can provide additional information. Micromorphology may provide information about whether burning was in-situ or whether the material is redeposited. Electron Spin Resonance has also been used to study hearth sites.

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