Geoarchaeology:Formation Processes

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Site Formation Processes
Many of the commonest field questions asked by archaeologists of geoarchaeology relate to site formation processes. Site deposits accumulate as a series of sediments which are altered by post-depositional processes. As such geoarchaeology is uniquely placed to study the way in which these deposits have accumulated and the manner in which they have been modified. Geoarchaeology can help with understanding the origin of the materials, the sequence and nature of deposit formation, the relative speed of sediment accumulation and the stability of surfaces, as well as identifying losses in the record due to erosion and post-depositional preservation issues.

Geoarchaeology may also help with the interpretation of human construction and artefact materials and practices.

The main geoarchaeological research questions related to site formation processes concern:
 * Pre-construction landsurface: Buried, pre-construction landsurfaces are a potential source of palaeoenvironmental information. Pollen grains (if preserved) and the soil type can provide information on local climate, vegetation, soil fertility and land management practices (references).
 * Construction methods and materials: Geoarchaeological techniques can provide information on the source of construction materials such as clay or turf, and may also provide information on the way in which they were used. For example the micromorphology of plaster and floor layers can provide information about the original construction processes and the frequency of reapplication or repair to the surface (references).
 * Anthropogenic processes (dumping, floor layers etc.): Geoarchaeology can help to distinguish between natural and anthropogenic deposits. The identification of redeposited "natural" for example can be important in determining the end-point of useful excavation. Geoarchaeology may also provide information about the survival of stratigraphy and hence can be used to infer the degree of lost information and the integrity of individual deposits.
 * Natural erosion and deposition processes: Geoarchaeology can help to identify the source and mode of deposition of natural deposits, for example whether deposits are water or wind lain, whther they were deposited in moving or still water, and whether a particular deposit is colluvium. Geoarchaeology can also help identify unconformities in the stratigraphic record that relate to periods of erosion (references).
 * Soil forming processes: Soils (pre-construction landsurface) may be buried beneath archaeological structures or monuments, they may be redeposited construction and land management processes, and they may also develop in-situ within sedimentary sequences. These soils contain information regarding the processes that formed them; these processes are in turn are related to climate, vegetation, hydrology (wetness), parent materials and humans. As such soils can help interpret past environments, if redeposited they may contain evidence as to their source, and they may also contain evidence of past human activity preserved in their chemistry and groundmass. Soils that develop in-situ in sedimentary sequences are also indicative of a period of relative stability (little erosion or deposition); the degree of soil development may provide an indication of the length of any stable phases.
 * Post-depositional change / taphonomy: Most post-depositional or taphanomic changes are related to soil-formation or processes in the burial environment, hence geoarchaeological techniques are particularly effective at identifying, understanding and predicting preservation of artefacts, environmental remains and stratigraphy.

Techniques used to study site formation processes
Because of the range of questions linked to site formation processes, many different techniques have been used effectively. In general however, studies of site formation are interested in sedimentary processes, hence sedimentological techniques are most routinely used including (but not restricted to):
 * Coring
 * Particle size distribution
 * Microscopy
 * Micromorphology
 * X-radiography

Studies of post depositional change may also require more soils related and monitoring techniques, including:
 * Soil pH
 * Pedogenic iron fractionation
 * Monitoring

Case studies
Case Studies of the use of geoarchaeology to address question of site formation include:
 * Calcareous features from the excavations at Godmanchester, Cambridgeshire.

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