SCLEROCHRONOLOGICAL DETECTION OF SHORT TERM EVENTS IN ARCHAEOLOGICAL SITES: EXAMPLES FROM THE GRAVELINE MOUND SITE, MISSISSIPPI, AND THE SAPELO SHELL RING COMPLEX, GEORGIA, USA

Mollusk sclerochronology records from archaeological sites are used to estimate season of capture with increasing regularity. Precision of such estimates is typically limited to differentiating between wet and dry periods, warm and cool periods, or 4 periods approximating astronomical seasons. However, it is also possible to use such records in concert with other archaeological data to identify events (singular or cyclic) of significantly shorter duration. This is a relatively novel tool that may help circumvent the analytical precision of radiometric and stratigraphic age dating methods that are limited to multi-decadal scale resolution. Application of this method is complicated by a number of factors related to the archaeological context of the samples and the characteristics of the mollusk species involved.

Two contrasting examples illustrate how archaeological context matters. The Woodland period Graveline Mound Site in coastal Mississippi contains numerous features rich in Rangia cuneata clam and Crassostrea virginica oyster shells. Sclerochronological oxygen isotope data combined with the unique nature of the deposits indicates that several features represent short-term events, perhaps lasting less than one day. Such events seem to have occurred primarily during warm months and the site was not occupied year round. In contrast, the Archaic Period Sapelo Island Shell Rings appear to have been occupied year-round with near continuous deposition of C. virginica and Mercenaria spp. clam shells. The resulting complex and massive shell deposits make it more difficult to resolve a single event; however evidence for one such deposit was identified.

In both examples some shells contained oxygen isotope profiles that contradicted these seasonality estimates and undermined arguments concerning short terms events. These anomalous data may be the result of depositional processes, irregular growth periodicities in the mollusks, and/or the collection of dead shells by site occupants. Nonetheless, sclerochronology may permit insight into human activities that would otherwise be difficult to detect.