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

摘要

Correlating archaeological finds with their associated stratigraphic context is elementary to modernexcavation 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 sitein western Idaho, we established a chemostratigraphic framework that enables us to quantitatively relatethe elemental geochemistry of sediments associated with artifacts and other samples back to a masterlithostratigraphic sequence.We subjected a total of 151 PXRF readings from six lithostratigraphic units tomultiple discriminant function analysis, which led to the identification of characteristic elements. To testthe site’s chemostratigraphic framework, we collected PXRF readings from an infilled rodent burrow,which visually appeared to contain mixed sediments from multiple lithostratigraphic units. Statisticalanalysis could not relate the rodent burrow’s sedimentary geochemistry well to any of the knownlithostratigraphic units, thus marking it as potentially disturbed. This methodological approach allows usto 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.