Late Quaternary climates and river channels of the Atlantic Coastal Plain, Southeastern USA

Abstract: Late Quaternary river patterns and sedimentation styles reflect past climate changes in Atlantic drainages of eastern Georgia and the Carolinas. Past climate episodes for the region are summarized from pollen and eolian sedimentary records that exhibit correlation to major changes in river channel patterns. Records of past river responses are derived from luminescence and radiocarbon dated landforms and strata. Slow tectonic uplift does not explain temporal changes in channel patterns. Drainage networks have not received meltwater from continental or mountain glaciers. Eustatic influence would have been most pronounced on the now-submerged continental shelf prior to 6 ka and currently manifests only within 60–80 km of the present highstand shoreline. Human impact overshadows climatic changes during historic time, but was negligible during prehistoric time. The late Quaternary fluvial system primarily responded to climatic fluctuations that drove changes in vegetation, precipitation, and runoff patterns. Prehistoric meandering paleochannels of the Holocene stand as important references to guide “natural” channel rehabilitation efforts. During the coldest climate phases of the late Wisconsin stage (ca. 30–16 ka), when forest vegetation was sparse and interspersed with grasses and herbs, many rivers and streams were braided with eolian dunes on the floodplains. The terminal Wisconsin stage (ca. 16–11 ka) exhibited rapid warming and forest expansion characterized by pronounced change from braided to meandering patterns with intermediate forms of sandy scroll-bar patterns. The Younger Dryas cold excursion is not readily apparent in the regional fluvial record. Unusually large meandering channels of the terminal Wisconsin stage continue into the first half of the Holocene and indicate significantly larger bankfull flood discharges during those times than during the last half of the Holocene. Bankfull channels during the last half of the Holocene retained meandering patterns, but decreased to modern-like dimensions, suggesting more modern-like flood regimes. No clear fluvial response occurs to the presumed middle Holocene climatic optimum (Hypsithermal), the Medieval warm period and Little Ice Age, or to recent instrumentally-observed fluctuations in climate, but little research has been done in these realms. [Copyright &y& Elsevier]