HOLOCENE PALEOCHANNEL AND MEANDER SCAR DEPOSITS ON UPATOI CREEK, WEST-CENTRAL GEORGIA

Upatoi Creek is a tributary of the Chattahoochee River in west central Georgia south of the Fall Line. The Upatoi has incised into its former flood plain, forming the T1 terrace about 3 to 4 m above stream level. We describe sediments exposed by cut-bank erosion and in a meander scar 150 m to the west.

The base of the cut bank, is covered. The rest of the exposure is composed of a 2.5 to 4 m, layered sequence of detrital sediments whose grain-size grades from coarse gravel at the base to silty very-fine sand near the top. The top is a modern soil. The sequence begins with a sandy pebble conglomerate up to 1 m. The gravel consists of subangular to subrounded quartz and quartzite; sand is angular to rounded, monocrystalline quartz and rounded feldspar. Above the conglomerate is a tabular unit composed of pebbly, very coarse, poorly sorted sand with large scale tabular cross-bedding. Layer 3 is a fine to coarse, moderately to well sorted sandstone, with small scale, cross-bedding, dipping to the west. This sandstone passes upward into the T1 terrace soil. This fining-upward sequence formed by point-bar migration.

At the south end of the cut bank, layer 3 is only 60 cm thick and is overlain by silty, fine grained sand with thin laminations and small burrows. Above this is a channel-form unit 2 m thick of silty clay containing palynomorphs. This unit represents an ox bow lake filled with silty clay.

The meander scar on the T1 terrace is the same ox bow exposed in the cut bank A 2 m core consists of silty, structureless, clay with palynomorphs recording a drier, diverse early Holocene forest with Quercus and Pinus. Increases in Nyssa indicate wetter conditions by the mid-Holocene. Forests continue to be dominated by tupelo until historic times, when their decline indicates a lowering of the water table due to incision of Upatoi Creek. Charcoal and organic matter yielded radiocarbon dates of 9,940 ±220 yr and 10,310±220 yr.

Our analyses of the sedimentology and palynology of Upatoi paleochannel deposits reflect the same climate conditions in the lower Chattahoochee River drainage as reported by Leigh in eastern Georgia.