FORMATION AND LANDSCAPE EVOLUTION OF CAROLINA BAYS

Carolina Bays are elliptical depressions on the North American Atlantic Coastal Plain. Their elliptical shape and common orientation became obvious when aerial photography revealed their ubiquity. Underlying stratigraphy, sediment properties, ground penetrating radar, geomorphic setting, and radiocarbon ages from cores at the 300 ha Juniper Bay in Lumberton County, North Carolina, suggest a model for Carolina Bay formation and evolution. Reference bays in the nearby Cape Fear River Valley also contribute to our understanding. A rising Plio-Pleistocene Atlantic Ocean buried with sandy sediments an incised Cretaceous landscape of heterogeneous older marine deposits, and the subsequent receding ocean left a dune system parallel to the coast. The upper coastal plain was periodically reworked by winds during the Pleistocene, and periods of dry climate reworked the interdune areas leaving blowouts. When water tables came back up and/or precipitation increased during wetter climates, these depressions filled with water perched on the clayey Cretaceous sediments underlying the area, and grew under the influence of wind and water into features that began to resemble the Bays we see today. The Cretaceous strata, which contain a variety of sediments reflecting changes of coastal environments over short distances, are responsible for the various hydrologic regimes observed in Carolina Bays.

Climate shifts, with the most intense shifts tied to advances and retreats of Northern Hemisphere glaciers, and the associated rise and fall of sea level, resulted in multiple episodes of Bay creation and growth. Underlying sediments controlled the size and depth of Bays, and in conjunction with prevailing wind direction, produced overlapping Bays and Bays within Bays. Radiocarbon ages indicate periodic activity extending into the Holocene, with paleosols and tree fragments buried by sediment infilling. Horseshoe lakes in Bays represent an intermediate stage of Bay infilling. In the last stages of Bay infilling, only pockets of open water exist. Organic soils cover the surface of what was once an open lake. The landscape approaches equilibrium until the next time water tables and precipitation drop, and rejuvenation, growth, and the creation of Bays resumes.