Several studies on modern mollusk shells and fish otoliths that mimicked ancient cooking practices simulated a thermally induced diagenesis associated with heat exposure, where high temperatures accelerated a process that naturally would require thousands of years (e.g., Andrus and Crowe, 2002 Larsen, 2015 Li et al., 2015 Milano et al., 2016Müller et al., 2017 Lindauer et al., 2018 Aldeias et al., 2019). Conversion of bioaragonite into inorganic calcite also takes place as a solid-state reaction, but generally at higher temperatures (≥300☌ Milano et al., 2016Staudigel and Swart, 2016 Milano and Nehrke, 2018). We also show that macroscopic visual modifications and mineralogical characterization of discarded shellfish might be indicative of specific cooking activities versus secondary burning. The construction of shallow earth ovens might entail an increased archaeological visibility, and some diagnostic signatures of in situ hearths can be obtained by fire below roasting activities. Our results suggest that similar shellfish roasting procedures will largely create microstratigraphic signatures of anthropogenically reworked combusted material spatially “disconnected” from the actual combustion locus. Our experimental design focused on three main types of roasting procedures: the construction of shallow depressions with heated rocks (pebble cuvette experiments), placing shellfish on top of hot embers and ashes (fire below experiment), and by kindling short-lived fires on top of shellfish (fire above experiments). An interdisciplinary geoarchaeological approach, combining micromorphology, FTIR (in transmission and ATR collection modes), TGA and XRD, was used to establish a baseline on the mineralogical transformation of heated shells from aragonite to calcite and diagnostic sedimentary traces produced by roasting fire features. In this paper, we investigate the microarchaeological traces and archaeological visibility of shellfish cooking activities through a series of experimental procedures with direct roasting using wood-fueled fires and controlled heating in a muffle furnace.
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