Late quaternary shell deposits in Northwestern Sri Lanka: New data on chronology, stratigraphy, and contents

Identifying shell-bearing deposits in Late Quaternary coastal landscapes is challenging due to preservation biases and post-depositional alterations. In Sri Lanka, Late Quaternary shell deposits in the Iranamadu Formation are linked to past human-environment interactions; however, their origin, distribution, and taphonomic histories remain uncertain. This study analyzes shell-bearing deposits in the Mannar-Jaffna Seaboard to assess their formation and archaeological significance, highlighting stratigraphic and taphonomic uncertainties in the Late Quaternary coastal record. We observed chronological inconsistencies between AMS radiocarbon and U-Th dating results within the same shell-bearing contexts, with ages ranging from approximately 36, 000 cal BP (AMS ¹4C) to around 3600 cal BP (U-Th), suggesting species-specific diagenetic alteration. While shell middens are considered direct evidence of human activity, findings indicate that alterations to shell remains necessitate considering subtle indicators, such as shell casts. Middle Paleolithic and microlithic artifacts in basal gravels of the Iranamadu Formation, dated to the Late Quaternary, raise questions about their association with shell-bearing layers. These deposits reflect a stratigraphic palimpsest shaped by natural and cultural processes. Our findings highlight the complexities of studying open-air shell deposits, despite the availability of predictive models that can help locate these sites. The need for systematic Late Quaternary research in Sri Lanka is underscored, as it contributes to discussions on early coastal archaeology.