RAPID SCOUR, SAND RIM CONSTRUCTION, AND BASIN MIGRATION OF A CAROLINA BAY IN SOUTHEASTERN NORTH CAROLINA

Ongoing geomorphological fieldwork at Herndon Bay in northern Robeson County, North Carolina, has revealed evidence for rapid bay basin scour and landform migration. LiDAR data show a regressive sequence of sand rims that partially backfill the remnant older bay basin, with bay migration of more than 600 meters to the northwest. Similarly, other bays in the region show evidence of significant migration.

A series of Geoprobe® cores (n=4), basal OSL samples (n=3), and GPR data were collected along transects that cross-cut multiple bay sand rims along the bays southeastern margin. Cores were subsequently analyzed to determine basic lithologies, grain-size statistics of lithologic units (i.e., lithofaces), and magnetic susceptibly. These data, along with GPR data and OSL age estimates are used to reconstruct landform geomorphology and provide a geochronology for bay rim development. Evidence suggests bay migration, including scouring of the underlying mud facies. This migration is punctuated by periods of high-energy shoreline processes leading to the development of a regressive sequence of bay sand rims with basal muddy sands incorporated into the earliest sand rims. Single grain OSL place the initial formation of each sand rim from oldest to most recent as ca. 31.8 +/- 3.9, 29.6 +/- 3.1, and 27.2 +/- 2.8 ka. This chronology indicates that migration and rim construction events occurred during early MIS 2. Elsewhere in the Southeast, source-bordering eolian dunes attest to considerably greater average wind speeds, prevailing winds out of the west and southwest, and sparse tree-cover during this time (e.g., Swezey et al. 2013). Evidence for high-energy subaqueous basin scour and rapid construction of multiple sand rims at Herndon Bay is consistent with strong prevailing winds and ecological reconstructions of the late Pleistocene Southeast. The fact that these landforms can migrate, yet maintain their characteristic oval shape, orientation, and rim sequences demonstrate that Carolina bays are oriented lakes shaped by lacustrine processes. Clear evidence of basin scour into the underlying Tertiary marine sandy clays reveal that Carolina bay are capable of creating, shaping, and migrating through their own basins while backfilling remnant basins with a regressive sequence of paleoshorelines.