The Full‐Glacial Vegetation of Northwestern Georgia

Two small ponds in Bartow County, Georgia, northwest of Atlanta, originated by subsidence of unconsolidated surface deposits into solution hollows in the underlying lower Paleozoic Knox Dolomite. The pond sediments consist of copropelic clays 250—400 cm thick with well—preserved plant remains, covered by as much as 150 cm of colluvial deposits with moderately to poorly preserved plant fossils. The clays yield radiocarbon dates of 20,100 and 22,900 BP near their base, contemporaneous with the main Wisconsin glaciation. The full—glacial sediments are rich in pollen and plant macrofossils. The pollen assemblage is dominated by Pinus (pine), with small amounts of Picea (spruce), Quercus (oak), Ostrya type (hophornbeam), and herbaceous types. It closely resembles published full—glacial pollen assemblages from southeastern North Carolina. Pinus banksiana (jack—pine) and Picea sp. are represented by fossil needles at many levels, and the rich macroflora of aquatics shows a marked phytogeographical relationship with the modern flora of northern New England. A floristic displacement of about 1,100 km would be needed to account for the presence of this flora in Georgia. Deciduous trees, primarily Quercus and Ostrya type, may have had a minor role in the full—glacial vegetation. In the postglacial an early Quercus—dominated phase is followed by a Pinus—dominated phase, which lasts to the present. Familiar southern tree genera such as Liquidambar (sweet gum) and Nyssa (black gum) appear to have migrated into the region in postglacial time. Species that occur primarily on the Coastal Plain but have disjunct occurrences at the two ponds and farther into the central United States, such as Itea virginica (Virginia willow) and Psilocarya nitens (sedge), first appear in the fossil record in the postglacial. It is supposed that they and perhaps other "Coastal Plain disjuncts" migrated into their present localities during the postglacial.