TRANSITION FROM BRAIDED TO MEANDERING CHANNEL PATTERN AS RECORDED IN THE ALLUVIAL STRATIGRAPHY AT COFFEE BLUFF, TELFAIR COUNTY, GEORGIA

Stratified alluvium at Coffee Bluff in Telfair County, Georgia records the transition from a braided to meandering channel pattern for the Ocmulgee River. Beneath cross-bedded sands which represent a braided stream depositional environment, an organic mat rich in plant macrofossils has been radiocarbon dated to 38,690 +/- 420 yr B.P. The well-preserved plant macrofossils in the dated deposit are dominated by species familiar in the area's contemporary floral communities. Laboratory analysis of a column of twelve samples from the overlying profile shows rapid changes in both mean grain size and sorting for the lower half of the profile, consistent with deposits of a braided stream. At approximately 1.2 m below the land surface there is a change to fining-upward depositional cycles in which both clay accumulation and sediment chemistry indicate a period of landform stability roughly coinciding with the Pleistocene-Holocene boundary at 10,000 yr B.P.