Paper No. 27-6
Presentation Time: 8:00 AM-12:00 PM
WAS ST. ANDREWS SOUND BETWEEN JEKYLL AND CUMBERLAND ISLANDS, GEORGIA, A FORMER MOUTH OF THE ALTAMAHA RIVER?
Judging by the separation between Pleistocene bluffs on Jekyll and Cumberland islands, St Andrews Sound was formerly the widest inlet on the Georgia coast. It is currently partially infilled by Holocene spits prograding, both from Jekyll Island in the north and Cumberland Island in the south. Sands from the older part of Jekyll spit (>2500 BP) yield an unusual amount of coarse grained muscovite suggesting the inlet may once have been occupied by a river draining from the Piedmont, presumably the Altamaha. In order to test this hypothesis a program of vibracoring has been initiated on Little Cumberland Island. Preliminary results show that Little Cumberland consists of a sequence of recurved spits (Sanctuary Ridge, East Ridge etc.) that prograde to the north and were once likely attached to Pleistocene uplands in the south. Erosion due to Brockington and Christmas creeks currently separates Holocene stratigraphy into older and younger inlet fill sequences. Coarse grained muscovite is present in some older sands associated with East Ridge but not apparently in younger deposits.
Work continues in order to provide radiometric ages for the various beach ridges and associated inlets as well as to determine the provenance of the mica; whether from the shoreface (longshore transport) or more likely from the backbarrier via the low-country between the Silver Bluff and Princess Anne barriers, or perhaps by way of Buffalo Swamp and Turtle River; both possible routes for an ancestral Altamaha.