The Songon-M'Brathé shell midden (Ivory Coast): microstratigraphic evidence of human activities and paleoenvironmental evolution in the Late Holocene

Abstract

This study explores the site formation and paleoenvironmental evolution of the Songon-M’Brathé shell midden in Ivory Coast through microstratigraphic analysis. Using geoarchaeological and dating techniques—including micromorphology, µ-XRF elemental mapping, radiocarbon dating, and thermoluminescence—the human occupation at the site is dated from the 7th to the 17th centuries CE. The earliest deposits reflect periodic flooding from a paleochannel of the Agnéby River, embedding organic matter and pottery fragments, marking early human activity in a dynamic floodplain. A subsequent phase of prolonged water saturation led to the formation of a hydromorphic gley deposit, indicating a temporarily abandoned wetland. Later layers reveal anthropogenic inputs, with combustion by-products followed by shellfish remains linked to cooking and dumping activities, alongside evidence of trampling. A hiatus in the midden’s formation is marked by overbank sediments with secondary calcitic cementation, signifying discontinuities in human occupation. Post-depositional reworking includes bioturbation and agricultural disturbances. As the first microstratigraphic study of a shell midden in Ivory Coast, this research expands African shell midden data to tropical regions, incorporates open-air contexts that had not previously been examined from this perspective, and refines their chronological framework. These findings enhance the understanding of human–environment interactions in tropical coastal settings, contributing to broader geoarchaeological research on shell middens as a global phenomenon.