QUANTIFYING THE SCALE OF AGE MIXING OF HOLOCENE MOLLUSK ASSEMBLAGES FROM IFRI OUDADANE ARCHEOLOGICAL SITE, MOROCCO, NW AFRICA

The chronology and stratigraphy of archeological settings are often complex to disentangle because ancient human activity interferes with the natural sedimentary deposition process. As a result, significant time-averaging, or age-mixing of remains that are not contemporaneous, may occur at different sections in the stratigraphy, which in turn, could lead to environmental misinterpretations of the investigated record.

The coastal Mediterranean site in Northeast Morocco, Ifri Oudadane embraces a rare relatively continuous Holocene archeological succession with extensive accumulations of harvested marine shells that provide key clues into past subsistence strategies and paleoclimate. Stratigraphic evidence suggests two main cultural periods, Epipaleolithic (pre-food production) and Neolithic (post-food production), which is further subdivided into Early Neolithic A, B, and C. In the current work, numerous harvested shells of the topshell Phorcus turbinatus (Gastropoda:Trocoidea) were radiocarbon dated using the cost effective, novel carbonate-target radiocarbon dating method to assess the chronology and quantify the degree of age mixing for these mollusk assemblages. Results from this study indicate that calcitic and aragonitic layers of the same shell yielded statistically equivalent ages, and therefore, both minerals can be used for radiocarbon dating when pristinely preserved. Uncalibrated radiocarbon results retrieved from the same archeological phases suggest that harvested shells exhibit multi-centennial age mixing (between 300 to 700 ¹⁴C years) that could not be explained by analytical imprecisions alone. This research is the first to illustrate the multi-centennial scale of time-averaging in Ifri Oudadane mollusk assemblages and suggest the need for individually dating specimens in future paleoclimate investigations.