FARMVILLE, WALSTONBURG AND FOUNTAIN QUADRANGLES: A FIRST CUT INTEGRATION OF SURFICIAL MAP UNITS, FACIES ANALYSIS AND SEQUENCE STRATIGRAPHY NEAR THE EARLY PLEISTOCENE SURRY PALEOSHORELINE COMPLEX, COASTAL PLAIN, NORTH CAROLINA

Despite its wide use, sequence stratigraphy is not yet included in stratigraphic codes. Recent mapping on the Coastal Plain of North Carolina (Farmville, Walstonburg and Fountain quadrangles) focuses on integrating facies analysis and sequence stratigraphy to help define the Quaternary section. This area includes the Surry Scarp, a prominent, regional-scale paleoshoreline complex on the Atlantic Coastal Plain that is associated with several correlative Early Pleistocene stratigraphic units depicted on the Coastal Plain Map of Virginia: the Bacon’s Castle, Windsor and Charles City Formations, and the informal Moorings Unit, a barrier island complex.

Our questions are: What is the sequence stratigraphic framework of Early Pleistocene strata near the Surry paleoshoreline? What methods help define its chronostratigraphy? How are facies and their bounding surfaces packaged in the context of this framework? Which surfaces should be utilized to define formations, members, and smaller-scale units? How are map units related to relict geomorphic features, global coastal onlap cycles, marine isotope stages, systems tracts, and parasequences?

The NC Coastal Plain, notorious for its low relief, few outcrops, recurring facies, and extensive wetland cover, required a non-traditional method, called three-dimensional (3D) subsurface mapping, to define and map its surficial units, establish type sections, and address the science issues (above). The USGS developed the 3D mapping method in the 1970s for COGEOMAP to define surficial map units in areas with relict geomorphic features. The method helps reduce data density and the cost of subsurface analysis. It combines landscape analysis with targeted subsurface analysis using exploration methods along key transects. Stratigraphy is established along cored profiles that crosscut landforms. New surficial units are regionally extrapolated using landform analysis to broad areas that lack data.

We present maps and cross sections that are products of the 3D analysis, and acknowledge existing data gaps. Interpreted cross sections integrate facies analysis, sequence stratigraphy, and stratigraphic nomenclature. An idea tested is that the Surry shoreline marks the transition from normal to forced regression, and that each unit is a chronostratigraphic slab.