REEXAMINATION OF SEVERAL EARLY (LOWER) PLEISTOCENE FORMATIONS IN THE CONTEXT OF SEQUENCE STRATIGRAPHY, SURRY PALEOSHORELINE COMPLEX, NORTH CAROLINA COASTAL PLAIN

The Surry Scarp, defined at Surry, VA, is a regional-scale (Atlantic-Gulf of Mexico) paleoshoreline with a toe of ~30 m that separates the Sunderland and Wicomico Terraces. Mapping in Virginia defined several Early Pleistocene units near the scarp. These are the Bacons Castle (west of scarp), Windsor, and Charles City Formations (both east of scarp), and the Moorings Unit (shoreline affiliated complex). The three formations, or alloformations, have similar stratigraphic descriptions; all are presumably unconformity bounded units that fine upward and include variegated gravel, sand, silt and clay. The principal defining factors for these units, in reality, are geomorphic surfaces, rather than unique stratigraphic signatures.

In North Carolina, an along-strike four-quadrangle area that includes the Surry Paleoshoreline is the focus of detailed mapping of correlative Early Pleistocene deposits—geomorphology defined from LiDAR is integrated with subsurface analysis from cores. The goal is to examine facies and bounding surfaces for the Quaternary section (maximum thickness ~ 22m) along profiles that transect specific geomorphic surfaces, and to integrate sequence stratigraphy with traditional formation mapping. This first cut interpretation starts with the assumption that the Surry Paleoshoreline geomorphically marks the transition between normal (western facies) and forced (eastern facies) regression deposits during a major transgressive-regressive cycle in the basal Quaternary.

Using a series of cross sections constructed from graphic logs and core photographs, the following concepts are discussed for the Early Pleistocene in the context of Virginia’s stratigraphic nomenclature and the Surry Paleoshoreline: the sequence boundary for the Quaternary; the overlying transgressive systems tract (TST); the maximum flooding surface (MFS) in shelf muds to the east; the high stand systems tract (HST) including proximal and distal facies; and, correlations to marine isotope stages. Other concepts to address are: continuously deposited sedimentary facies above the basal sequence boundary of the Quaternary; parasequences; small-scale repetitive facies cycles emplaced during falling stage; younger sequence boundaries and alloformations; and the maximum surface of forced regression.