A PXRF-based chemostratigraphy and provenience system for the Cooper’s Ferry site, Idaho

Loren G. Davis, Shane J. Macfarlan, and Celeste N. Henrickson

Correlating archaeological finds with their associated stratigraphic context is elementary to modern excavation methods. Although micro-contextual approaches can provide invaluable perspectives, ascribing primary depositional status and associative context has traditionally been a qualitative exercise. To improve the empirical nature of this process as part of new excavations at the Cooper’s Ferry site in western Idaho, we established a chemostratigraphic framework that enables us to quantitatively relate the elemental geochemistry of sediments associated with artifacts and other samples back to a master lithostratigraphic sequence. We subjected a total of 151 PXRF readings from six lithostratigraphic units to multiple discriminant function analysis, which led to the identification of characteristic elements. To test the site’s chemostratigraphic framework, we collected PXRF readings from an infilled rodent burrow, which visually appeared to contain mixed sediments from multiple lithostratigraphic units. Statistical analysis could not relate the rodent burrow’s sedimentary geochemistry well to any of the known lithostratigraphic units, thus marking it as potentially disturbed. This methodological approach allows us to make quantitative correlations between stratigraphic units across the site and most importantly, enables us to independently evaluate whether objects from any part of the site are in direct association with “anomalous” or “regular” sediments.

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