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Phosphates in archaeology
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History of use in archaeology
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Accuracy and validity of the methodology
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Performing a phosphate analysis survey
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Summary
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Phosphate Analysis: interpretive possibilities

Phosphate analysis is useful as an archaeological site and/or feature location technique, but its value is magnified through application to use-of-space modeling within identified sites.  Phosphate analysis can be used to locate and interpret ‘clean’ and ‘dirty’ activity areas (Matthews et al1997: 293), including sleeping areas (Terry et al. 2004: 1243), food consumption/production/storage areas (Sanchez et al. 1999: 56), areas where refuse was deposited (Crowther 1998: 118) and some craft areas (Eidt and Wood 1974: 44).  Phosphate analysis can also be used to interpret less archaeologically tangible components of use-of-space such as the placement of entryways (Yerkes et al. 2002: 865) and pathways (Parnell et al. 2002: 336), which can help interpret how people were creating and using their own landscapes.  Phosphate analysis is a valuable source of information in this regard, because in many cases these features cannot be identified through conventional archaeological excavation.  

For example, on the promontory fort of Gubadoon (fig.) phosphate analysis was able to determine: 1) the site was never used for sedentary occupation 2) two areas were identified as areas of more intensive use, these areas are the most exposed and most protected portions of the fort, 3) phosphate rich material decomposed against a wall or bank to form the phosphate increase in the most protected area, 4) access to the headland was regulated and 5) traversal of the headland, once access was gained, was not regimented.  These factors suggest used of the headland as a look-out point (most exposed) with associated basecamp (most protected), access was likely limited to only several individuals at a time and use of the fort was more utilitarian than symbolic in nature.  On other tested promontory forts phosphate analysis showed the pathways that crossed the headlands were much more well-defined and the ways in which certain areas were accessed was controlled through the placement of stone and earthen features.    The identification of this possible use, and the positive elimination of settlement as a possible use of the site, have not been previously suggested for promontory forts. 
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Phosphate patterning on the Gubadoon headland (Ullrich 2010)

The ability of phosphate analysis techniques to accurately identify archaeological features, as well as less tangible components, makes phosphate testing highly applicable to a large variety of archaeological sites.  The utilization of this information to create use-of-space models helps determine land-use patterns over sites, allows for greater trends between sites to be identified and aids in the archaeological interpretation of large- and small-scale intra-site dynamics.  A better understanding of the accuracy and applicability of the method, as well as how to link specific phosphate patterns to the location and function of on-site features and uses, is important to making phosphate analysis results both accessible and of greater value to archaeologists.  


Johanna Ullrich, Ph.D.