Principles of stratigraphic analysis
1. Clustering

December 2010 - G. Buccellati
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     Stratigraphic clustering refers to the way in which elements in contact, in the physical space, can be linked so as to denote temporal sequences.
     The physical contact is what can in fact be observed and documented. As such it is the starting point of all archaeological analysis. The individual instances of contact are defined as part of emplacement, and are measured as part of volumetry. What lies beyond is the clustering of these points of contacts into groupings that subsume all the pertinent primary observations. From this we derive, in a properly arguable fashion, the depositional process and the overall sequencing.


     The notion of contact presupposes the identification of discrete entities, the elements. The contact is not mere juxtaposition. From various factors, such as texture, alignment of components, organization of planes and volumes, etc., we may plausibly argue for different types of contact. In other words, the clustering is hierarchical, and supports the basic inferences about the depositional process that is to be assumed.
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     That space can be translated into time is the basic postulate that underlies the inferential process. For instance, having distinguished (though emplacement) two vertical planes as a cut vs. a face (texture, alignment, hardness, etc.), we may argue that a face is contemporary with the element behind it, whereas a cut is subsequent to it.
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     The notion of clustering finds its prime realization in the concept of stratum. This is a cluster of elements arranged according to the type of contact, and sorted according to nesting criteria that result in discrete wholes. These wholes are defined by the congruence of the elements in contact (e.g., a series of pits cut into a single accumulation), and by broad elements that extend to an entire volumetric unit (e.g., a floor that covers the entire surface of a locus).
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Phases and horizons

     Phases and horizons extend the notion of clustering beyond the sphere of immediate contact. They are, in effect, non-contact clusterings of contact based clusters (the latter being represetned by tha strata).
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