Diagenesis in freshwater mussel shell and its implications for provenance determination – Evidence from the Kinlock Site, 22SU526 (Yazoo Basin, Mississippi, U.S.A.)

Abstract

Freshwater shells from archaeological contexts hold the potential to allow sourcing of shell-tempered ceramics on the basis of their chemical composition. This application, however, requires understanding chemical interaction of shell with the burial environment. Here, we use material recovered at Kinlock (22SU526), a Late Woodland - to Mississippian-period site located in the Yazoo Basin, Mississippi, U.S.A. as a case study to evaluate the presence and impact of diagenesis on Unionid shells. Twenty whole shells recovered from the plow zone and the sub-plow zone are analyzed using a combination of thin sections, Scanning Electron Microscopy, and Inductively Coupled Plasma-Mass Spectrometry. Results show that, contrary to what might be expected, shells from the sub-plow zone are more affected by diagenesis than samples from the plow zone. The chemistry of the shells from the sub-plow zone is affected by modern human contaminants (fertilizers) within a perched water table, and is no longer representative of the original composition of these samples, compromising their use in provenance research. Shells from within the plow zone are less affected by contamination, making them potentially more useful to generate background data for provenance studies.