Coffee Bluff: Stratigraphy, Palynology, and Plant Macrofossils From a Late Pleistocene Deposit in Middle Georgia
Coffee Bluff is a section of Ocmulgee River alluvium extending for over four meters through the Holocene epoch back to the late Pleistocene. The upper 1.2 m of the section consist of fining-upward depositional cycles which represent stabilization of this river terrace within the past 10,000 years. Underlying a strongly developed soil toward the base of this upper deposit and extending to a depth of ~350 cm bls are coarser and more poorly sorted sands. At the base of these cross-bedded sands and extending beneath the present river grade for appxoximately 50 cm, there is an organic sand rich in plant macrofossils.
Based upon two radiocarbon dates obtained on plant macrofossils, the organic sand in the lower part of the Coffee Bluff section spans at least 5,000 years from 38,700 14C yr BP to 33,700 14C yr BP. Pollen analyses of four samples (2 upper, 2 lower) by D. Peteet and F. Rich are similar in the counts for major taxa [Quercus (oak) , Carya (hickory), and Pinus (pine)]. Some minor components are different, reflecting water level differences among the samples. Overall, a mesic broad-leaved floodplain forest assemblage is represented, though it had much less pine and more hickory than today, suggesting cooler conditions regionally. The macrofossil presence of wetland taxa such as Chamaecyparis thyoides (Atlantic white cedar) and Nyssa (tupelo) as well as aquatics such as Naias, Nuphar, Potamogeton, and Rynchospora suggest episodic higher standing water at times, while the very low LOI (3%) within a sandy matrix is suggestive of a depositional environment with considerably more energy than in the lake or bog environments which most typically host late Pleistocene pollen assemblages.