CONSTRUCTING A MORPHO-STRATIGRAPHIC MODEL OF THE ATLANTIC COASTAL PLAIN (NORTH CAROLINA) FROM HIGH-RESOLUTION LIDAR WITH IMPLICATIONS FOR INTERPRETING THE SEQUENCE STRATIGRAPHY OF EARLY PLEISTOCENE TRANSGRESSIVE-REGRESSIVE EVENTS

Using the constructivist approach, landform elements on a relict Quaternary landscape were interpreted from high-resolution LiDAR (2004 10 ft DEMS, QL2) to develop a new or revised morpho-stratigraphic model of the Atlantic Coastal Plain in North Carolina. The area targeted is an Early Pleistocene to upper Pliocene landscape that extends from the Walterboro/Kenly paleoshoreline area to the Surry paleoshoreline, environs east, and the associated incised valleys. Included marine terraces are the Coharie, Sunderland, and westernmost Wicomico.

Landform elements were interpreted in 7.5-minute quadrangles in the Rocky Mount 100K sheet and in Drake and Red Oak (Roanoke Rapids 100K). Interpretations were based on elevation grids, derived hillshade, slope and contour lines (1.0, 0.5 and 0.25 m), and orthoimages. Standardized digital map units (DMUs) were applied to each landform element, permitting a regional overview of landscape evolution.

Consequently, the dynamic morpho-stratigraphic response to transgressive-regressive (T-R) cycles was observable and quantifiable, particularly for the Surry and Kenly paleoshorelines. As an example: the Surry shoreline complex (28-32 m) marks the eastern termination of the Sunderland terrace (~50-34 m). A beach-ridge plain may occur at ~33-34m; this may be the highstand systems tract (HST). Associated incised valleys show a downcutting event at 32-34 m that is mappable across the Coastal Plain. Sand platforms and barriers occur at ~28-32 m in the shoreline complex and up incised valleys.

The highstand shoreline at ~30 m marks the transition from normal to forced regression. After the highstand at 30 m, sea-level drops. Landform elements downstep every 1 to 2 m during evolution of this Early Pleistocene falling stage systems tract (FST) (28-20 m). Downsteps are continuous and discrete in the forming incipient incised valleys. The marine ramp seaward of the shoreline is flat with only subtle local downsteps. Downsteps formed by small-scale fluctuations in sea-level during an overall falling stage; each may correlate to a parasequence.

A similar morpho-stratigraphic evolution at 50-60 m occurs in the area of the Kenly paleoshoreline complex. Correlating these sea-level events with specific marine isotope stages (MIS) remains outstanding.