Sammendrag
Geochemical analyses of the South African shellfish species Turbo sarmaticus, commonly found in southern coast Middle and Later Stone Age assemblages, are essential for long-term paleoclimate reconstructions. A critical concern is the potential effects of alteration of the original δ18O values of the Turbo sarmatius operculum. Archeological shell remains usually represent food waste. In addition to post-depositional diagenesis, they can also be exposed to the effects of pre-depositional treatments, such as cooking. Thermal behavior and conversion temperatures can vary between different shellfish species, making it necessary to establish a species-specific reference base. In this study, temperature-related mineralogical and isotopic alterations in live-collected specimens of Turbo sarmaticus are evaluated experimentally through different cooking methods and temperatures. We performed laboratory-based heating experiments in a controlled environment in addition to realistic simulations of prehistoric shellfish cooking practices with wood-fueled fires. Since heat can also be generated during the sampling process, we tested the effects of the drilling speed on operculum mineralogy and δ18O values during the sampling. Our results demonstrate the relationship between δ18O values and aragonite-calcite mineral transition in different experimental settings, and whether this relationship can be used to estimate which archaeological Turbo sarmaticus opercula can be reliably used for paleoclimatic reconstructions.
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