CROSS SECTION CONSTRUCTION FOR THE STRATIGRAPHIC CHARACTERIZATION OF PLIOCENE-PLEISTOCENE DEPOSITS OF THE NORTH CAROLINA COASTAL PLAIN, FALKLAND 7.5 MINUTE QUADRANGLE

Traditional geologic mapping methods (boots on the ground) are insufficient to characterize the geology and stratigraphy of the Atlantic Coastal Plain of eastern North Carolina. Due to low relief, sparse outcrops, recurring facies, and extensive wetlands cover, a non-traditional mapping method is needed. Three-dimensional (3D) subsurface mapping combines geomorphic landscape analysis with focused subsurface analysis that includes cores collected along specific profiles transecting landforms.

Data are collected from a four-quadrangle study area that includes the Early Pleistocene Surry Paleoshoreline of eastern North Carolina. This is a geomorphically complex area that features relict barrier islands, beach and shoreface, beach ridge accretion plains, longshore bars, spits, embayed areas, lagoons, tidal channels, etc. Mapping occurs at 1:24,000 and 1:8,000 scale in quarter-quad sections. The most recent data represent the southwest and southeast quarter-quad sections of the Falkland quadrangle.

Sediment cores (1.75” in diameter) are collected with a Geoprobe Macro-Core MC5 Soil Sampling System. After careful cleaning, the cores are used to construct simplified graphic logs showing principal grain size and generalized structures at 1 cm = 4 ft scale. These field logs are then scanned into Adobe Illustrator and used to create geologic cross sections with a horizontal scale of 1 in = 500 ft and a vertical scale of 1 in = 8 ft (62.5x vertical exaggeration). ArcGIS software provides the topographic profile and the specific location of each core along the transect. Outlines visually enhance the grain size portion of each graphic log. Depth scales, grain size cards, core labels, and a line marking current sea level are all added to the cross section. Correlating the graphic logs reveals preliminary surficial units ranging from coarse sandy gravels to sandy muds, mixed siliciclastic and bioclastic muddy sands and gravels, and interdistributary heterolithic strata. These cross sections are vital in developing a regional facies model of the North Carolina Coastal Plain.