Assessing mussel shell diagenesis in the modern vadose zone at Lyon's Bluff (22OK520), Northeast Mississippi

This study considers the chemical alteration of archaeological freshwater shell above the water table at the Lyon's Bluff site (22OK520), a single-mound and village complex located in east-central Mississippi, and the changes in trace element concentrations between unfired and fired shell. Thin-section petrography, X-ray diffraction, cathodoluminescence, and scanning electron microscopy analyses were conducted on archaeological shell from four natural layers from Unit 20N20W, over a depth of 80 cm and spanning 450 years. ICP–MS analysis also was conducted on a modern freshwater shell subjected to kiln firing. Microscopy results indicate a pristine aragonite crystal structure in the archaeological samples. ICP–MS data show that certain trace elements within the modern shell maintain their concentration after firing at 500 °C. The broader implications are: 1) that diagenetic alteration does not hinder chemical sourcing of shell at Lyon's Bluff, and 2) that certain trace elements are more reliable than others, namely Sr²⁺, Al²⁺, Ba²⁺, and Mn²⁺, when conducting trace element provenance studies on fired-shell temper.