Tutorial:Burial As Preservation

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Burial as a process of preservation
Many of the most archaeologically destructive processes occur within the topsoil zone, in particular physical processes of bioturbation, cultivation, trampling, freeze-thaw, erosion etc. Burial acts as a mechanism for preservation by isolating the archaeology from these potentially destructive processes. The rate of deposition and the depth of burial are key factors in preservation. Stratigraphic preservation is likely to be better in deep, rapidly buried deposits. Shallow burial means the deposits become incorporated (or welded) within the newly developing soil profile and over time may be completely destroyed.

The depth at which deposits are effectively isolated from the surface differs according the soil type, and particularly to the soil texture. The maximum depth of root penetration, bioturbation and soil development is generally less in heavy, clay-rich materials than in lighter sandy deposits. This means that stratigraphy buried beneath 0.5m of heavy clay may be better preserved than if it was buried beneath 1m of coarse sand. Likewise stony or compacted layers can help prevent root and biological penetration. The exact depth of burial required for isolation is highly dependant on local conditions.

The rate of burial also has an effect on preservation. The slower the rate of burial the longer it is before the deposits are actually isolated, and in particular, protracted periods of stability in the depositional record can lead to erosion and/or soil formation. The loss of stratigraphy to soil processes in modern topsoil is taken for granted, but as deposits accumulate, past periods of soil formation may also have destroyed buried stratigraphy.

Burial may also result in changes to soil moisture that can favour preservation. As the ground surface rises, either through natural deposition or anthropogenic constructions such as mottes and burial mounds, the ground water table also rises. Perched water tables can also develop where there are clay rich or compacted deposits.

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