Abstract

Large meandering paleochannels on the flood plain of the middle Ogeechee River in southeast Georgia represent wet paleoclimate during late Pleistocene and early Holocene time and show no indication of downcutting in response to eustatically lower sea level. Radiocarbon dates indicate that the paleomeanders were active at ∼31–28 ka and ∼8.5–4.5 ka. Bivariate regression models that correlate modern channel dimensions to the discharge of low-magnitude floods (1–5 yr recurrence interval) indicate that paleodischarge of floods during those times was at least double that of modern floods, thus suggesting a wetter paleoclimate. These data corroborate independent studies of pollen and paleoclimate simulations that indicate wet early to middle Holocene (9–3 ka) conditions that were characterized by intensified monsoonal circulation. Paleoclimate conditions at ∼31–28 ka are less well known. Our analysis of the middle Ogeechee River flood plain indicates the absence of base-level response (downcutting) to eustatic sea-level lowering because the beds of the paleochannels are at approximately the same elevation as the bed of the modern channel. This supports recent arguments that the geomorphic response of coastal-plain streams to sea-level lowering is most apparent in deltaic and shelf environments and may not be recognized very far upstream from the coast.

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