PALYNOLOGY AND PALEOECOLOGY OF LATE PLEISTOCENE TO HOLOCENE, ORGANIC-RICH, PALEOMEANDER/RIMSWAMP DEPOSITS IN SOUTH CAROLINA AND GEORGIA

Many previous studies of late Pleistocene to Holocene pollen in the southeastern US have been conducted on sediments at the bottoms of small lakes. In contrast, studies reported herein were conducted at selected paleomeander sites occurring at the edges of river floodplains, where relatively persistent groundwater seepage from the valley bluffs enhanced preservation of organics and created a sedimentary sequence represented by a basal oxbow lake deposit (containing occasional layers of fibric aquatic peat), overlain by a groundwater-fed, often slightly domed, sapric to hemic peat deposit with occasional, thin, clay-rich flood layers. These kinds of sites (rimswamp peatlands) are much more complicated than pond sites because of their considerable content of local in situ vegetation; but, once the depositional model is identified, these very common floodplain deposits can provide not only regional climate records (where few other records exist), but also, useful additional records of local vegetational changes resulting from changes in hydrology, water chemistry, fires, and other natural, as well as anthropogenically-derived, events.

The rimswamp peatland deposits studied include: (1) Muck Swamp in Congaree River floodplain, Congaree Nat. Park, SC; (2) Damon Swamp, in Great Pee Dee River floodplain, SC; (3) Hite Bowl Swamp in a tributary of the Chattahoochee River, GA; and, (4) Peat Bay located on the Savannah River floodplain, SC. Cores from these sites contained gaps in sedimentation and basal ages ranged from about 21,000 ka at Muck Swamp to 2,000 ka at the Hite Bowl site. Regional changes in climate were readily detectable in palyno-flora from these sites, including: (1) pre-9500 ka cool, dry regional climates, but local sedimentation within oxbow lakes containing Nuphar and later Nymphaea; (2) Nyssa dominance beginning at about 8500-9500 ka; (3) hardwoods typical of present Southeast beginning dominance after about 8500 ka at nearly all SC, GA and FL sites. In contrast, although Taxodium appears after about 3000-5000 ka at all of southernmost pond sites (from GA to FL), Taxodium was not as common or was absent in most of the SC and NC rimswamp peatland sites; also, most SC sites tended to correlate better with NC sites than with sites in GA and FL.