Principles of stratigraphic analysis
5. Sequencing

August 2009 - G. Buccellati
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Concepts

     Sequencing is a way of ordering spatial clusters, i.e., strata, phases and horizons.
     An important premise relates to the very nature of the system.
     There are two conflicting principles of operation. On the one hand, one wants to retain full adherence to the principle that contact associations are the fundamental point of reference for all stratigraphic considerations – and contact associations can be described only at the level of the most elemental unit of excavation, i. e., the strata. On the other, one wants to relate these to the wider chronological frame that matches the full historical dimension of the site and of the region, i. e., phases and horizons.
     As a result, strata can only be defined in terms of the unit of excavation, and they change more frequently as the excavation itself proceeds. Phases and even more horizons, on the other hand, require greater permanence. A resolution of this conflict lies in allowing for multple sequences to exist at the same time, with an indexing system that maintains the distinction while making it possible to establish overarching connections. I use the term sequence for the ordering of strata, and frame for the ordering of horizons and phases.
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Indexing

     In my system, strata and phases (but not horizons) are indexed, meaning that each is given a distinct sequential number as part of an element label(e.g., s12 for stratum 12, h6 for phase 6). The elements from each applicable sequence are listed in the constituent section of the analytical portion of the UGR (right hand side, in black), under strata and phases.
     Suffixes identify sub-strata and sub-phases (s12a, h6a).
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Sequences

     A sequence reflects our understanding of the stratigraphy at any given moment in the process of excavations, and in any given operation throughout the archaeological site. The logic of the system requires that strata (to a lesser extent, phases as well) be sequenced independently in each operation, since properly stratigraphic considerations can only apply to contiguous excavations. The sequence may change dramatically even between areas that are very proximate to each other, and may change within the same operation from year to year. Thus, it is indispensable to register the differences, and to keep the correlation among them perfectly clear. To this end a second suffix (preceded by a hyphen) is added to each stratum and phase, indicating the sequence to which it belongs - e.g., s12a-AAC refers to stratum 12, substratum a, in sequence C pertaining to area AA. Such sequences may belong to either a single excavation Unit (s12-A1C) or a broader Area ((s12-AAB): a sequence by area becomes possible as individual units come either in physical contact with each other, or are sufficiently close to allow a logical extrapolation.
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The MZ frame

     In the 2008 season at Mozan we introduced for the first time a sitewide sequence (MZA), which is the one uniformly in use in the current version of the UGR. But more than a proper sequence, this serves as a broad frame of reference within which actual phases, and especially actual strata are identified and defined. In other words, while the same numbers are used to allow for a correlation across chronological lines, this should not be taken to imply that the depositional processes embodied in the different sequences are the same. While the numbers for phases and especially strata may be the same, the definitions for phases and strata will generally differ from area to area, and even from unit to unit.
     In practice, this means that we retain distinct unit and area sequences (e.g., A1A, AAC,...), but assign numbers within the range of the MZ frame (currently MZA). For example, phases 53MZA through 55MZA are richly represented in area AA (where they were labeled as 5aAAG through 5cAAG); they are, however, missing in area JP. Using the MZA sequence simply means that there will be a gap in the numerical sequence of the JP phases: this will call attention to a depositional phenomenon that requires a particular explanation.
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Archival versions

     The different phase/strata generations that were in use for different units and different areas prior to any given date are archived for permanent future reference, even though only the latest one is in use in any given version of the UGR. Thus, for area AA (and various units within it) we reached generation G, and for area JP (and various units within it) we reached generation C. For ease of correlation, all previous sequences are accessible from the MZ sitewide book.
     Some of these sequences have been published in printed reports.

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