GEOMORPHOLOGY AND ITS RELATIONSHIP TO COASTAL PLAIN STRATIGRAPHY, IMPLICATIONS FOR A REGIONAL MODEL FROM SITE SPECIFIC DATA: LIZZIE RESEARCH STATION, NORTH CAROLINA

The post-Cretaceous stratigraphy of a small site (km X km), the Lizzie Research Site, was studied in detail relative to its geomorphic position, with a series of cores and accompanying gamma logs. A three-dimensional analysis of geomorphology, facies and bounding surfaces in these Pliocene and younger deposits reveals that paleogeography controls the stratigraphic framework of the local coastal plain.

Geomorphically, the site sits between the Surry and Suffolk Scarps, straddling the coast-wise Wicomico plain (24 m above mean sea level (M.S.L.)) and several lower fluvial-estuarine terraces that step down to a drainage with Holocene wetland flats at 12 m (M.S.L). The site is 20 km east of the Surry Scarp, a regional paleoshoreline generated at a sea-level highstand of about 30 m (M.S.L.) in late Pliocene or early Pleistocene time.

A series of structure contour of boundaries and isopach maps of Plio-Pleistocene facies show that the post-Cretaceous section (<25 m) evolved as a series of nested, sand-rich, complex incised valley fills separated by interfluves with distinct marine signatures. Site data appear to indicate that: 1) modern drainages follow paleovalleys that existed prior to the late PlioceneYorktown transgression; and 2) interfluves have been relatively fixed in position for this same period. This suggests structural control over the location of these features. Site data also suggest that faulting has offset Cretaceous units, possibly impacting facies distribution in the overlying section. This is difficult to prove without continuous subsurface data between boreholes, and has widespread implications for regional generalizations.

Site-specific data also provide a road map for extrapolating stratigraphic units across regional geomorphic features. The Wicomico Plain, for example, was generated in association with the sea level highstand at the Surry Scarp, and the subsequent regression. It is underlain by 3 marine sequences of late Pliocene to early Pleistocene age. It is likely that these 3 marine sequences can be correlated regionally across the Wicomico Plain.