ICP-MS AND PETROGRAPHIC IDENTIFICATION OF GEOCHEMICAL DIFFERENCES BETWEEN ARCHAEOLOGICAL CERAMICS FROM TERRESTRIAL AND SUBMERGED ENVIRONMENTS, LA ALTAGRACIA PROVINCE, DOMINICAN REPUBLIC

Geochemical studies of archaeological ceramics often assume little to no post-depositional change to the chemical composition of the artifact. The goal of this project is to test the null hypothesis that there are no measurable geochemical differences between ceramic assemblages from an underwater cavern site and assemblages from terrestrial sites in the same province of the same age. We integrate ICP-MS trace element analysis, MC-ICP-MS lead (Pb) stable isotope analysis, and thin-section petrography to examine potential post-depositional alterations in archaeological ceramics recovered from freshwater submerged cavern sites in La Altagracia Province, Dominican Republic. Ceramics sampled in this study are sherds from low-fired vessels recovered from contemporaneous archaeological sites dating to the Late Ceramic Age (ca. 500-1500 CE).

Analysis of ICP-MS results indicates statistically significant (P<0.01) variation between assemblages in the concentrations of ten trace elements (V, Cu, Zn, As, Sr, Zr, Cs, Ta, Tl, U), leading to a rejection of the null hypothesis. MC-ICP-MS results show a wider range of Pb isotope ratios between ceramics recovered from a submerged site than terrestrial sites, leading to further investigation of Pb isotope variation in unfired clay from the study area. Thin section microscopy documented increased porosity in samples from an underwater context, indicating potential loss of material due to dispersion of clay platelets in water. Results suggest that ceramic artifacts recovered from underwater sites may be unsuitable for inclusion in studies that assume the geochemical composition of a ceramic artifact is a direct proxy for that of the original vessel. Results of this study may impact sampling design of future ceramic analyses and contribute to understandings of underwater archaeological site formation.