164-1 Radiocarbon Dating Mollusk Shells: Challenges, Advances, and Best Practices

Session: Advances and Applications of Geochemistry in Archaeology

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Radiocarbon dating is a critical tool for establishing site chronologies and reconstructing formation processes at archaeological sites worldwide. However, directly dating mollusk shells (marine, freshwater, or terrestrial) presents persistent challenges due to significant and variable radiocarbon age offsets. These offsets stem from a range of factors that introduce "old" carbon into shell carbonates, ranging in scale from localized or species-specific effects to regional trends. This presentation examines the causes and consequences of these offsets, drawing on case studies from North America. We explore the “good, the bad, and the ugly” of shell dating, clarify common misconceptions, and offer practical guidance for archaeologists and geoscientists working with these materials. We also highlight recent methodological advances such as improved pretreatment protocols, compound-specific dating techniques, refined regional correction factors (ΔR), and emerging statistical approaches that are improving the accuracy and interpretive power of shell-based chronologies. Still, the reliability of shell dates is highly contingent on contextual data, including species ecology, depositional setting, hydrology, and local geology. Despite the challenges, mollusk shells remain a valuable and often necessary resource for constructing robust chronological frameworks, particularly where organic materials are poorly preserved. When approached critically and with contextual awareness, shell radiocarbon dates can meaningfully inform archaeological and paleoenvironmental narratives across diverse landscapes.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-5138

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