IS BLACKBEARD ISLAND ON THE GEORGIA COAST THE SOUTHERN TIP OF ST. CATHERINES SPIT?

The morphology of the spit at the southern end of St. Catherines Island records episodes of deposition interrupted by erosion spanning more than 3000 years of progradation (based on archaeological data). Deposition of recurved spits leads to sets of concordant beach ridges that are convex towards the sea while erosion and overwash produce long, narrow marsh hammocks that are concave to the sea and truncate older structures. This pattern extends about 3.5 miles north to a distinctive erosional lineament, called Zapala scarp, that marks the former limit of Sapelo Sound. North and west of this lineament, on Cracker Tom Hammock, the pattern of beach ridges is quite different; depositional contacts are cuspate and concave towards the sea while erosional contacts are linear and sub-parallel to the modern shore. A similar pattern is observed on Blackbeard Island and leads us to conclude that Blackbeard Island formed by the breaching of the older part of St. Catherines spit. In order to substantiate this hypothesis it will be necessary to confirm the absolute ages of both the older and younger parts of the spit by luminescence dating.

The breaching of spits and straightening of inlets on the Georgia coast is a predictable consequence of the Holocene transgression, which has increased the volume of the tidal prism thus favoring tidal over wave processes.