Geological-geochemical approach to "sourcing" of prehistoric chert artifacts, Northwestern Alaska

A new type of approach to prehistoric chert sourcing using both geology and geochemistry is introduced and illustrated by a study conducted in northwestern Alaska. Correlation of each chert artifact with its geological source is based on the idea that both the artifact and its source have identical geologic history characterized by unique petrological and geochemical signatures. A regional database of the petrological and geochemical signatures for each chert source is constructed and artifacts from prehistoric sites located in the region are then compared to the database to determine artifact source. Data are obtained by instrumental neutron activation analysis, electron microprobe analysis, X-ray diffraction analysis, optical microscopy, and hand specimen study. Immobile elements provide depositional environment and provenance signatures (Al, Ce_n/Ce_n*, La_n/Ce_n, and Eu_n/Sm_n) for artifact-outcrop correlation. Minerals and mobile elements provide diagenetic and metamorphic signatures as well as signatures related to local variability which discriminate outcrops belonging to the same stratigraphic units. Artifacts are correlated with outcrops by superimposing their chemical data on geochemical fields of outcrops obtained by descriptive statistics at 1,2, and 3 standard deviations from the means. Two hundred eighty-nine artifacts from 57 prehistoric sites were compared with 12 chert varieties sampled hi nine outcrops in the western Brooks Range. Four outcrops were firmly correlated with 51 artifacts and determined as prehistoric chert quarries. Sourcing resulted in maps of geographic and cultural distribution of quarry cherts among prehistoric sites in northwestern Alaska. The geological-geochemical approach to prehistoric chert sourcing is applicable to any region.