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Over 2,000 km (1,240 mi) of high-resolution seismic reflection data were "rapidly" reduced to stratigraphic line drawings with a predetermined vertical exaggeration of 100:1 using a graphics digitizing tablet and desk-top computer. These data form the basis of a three-dimensional stratigraphic model for the upper southeastern North Carolina continental margin.
Correlations between the seismic data and drill, core, quarry, and outcrop data from the adjacent emerged coastal plain, supplemented by lithostratigraphic and biostratigraphic analyses of over 200 (9 m [30 ft]) vibracores collected along the seismic lines depicts an internally-consistent chronostratigraphic framework ranging in age from middle Eocene to late Pliocene. Seismic sequence analysis delineates five mid-late Paleogene depositional sequences, each bound by basin-wide unconformities. The distribution of these sequences is regionally controlled by the mid-Carolina Platform high of the Cape Fear Arch and locally influenced by Gulf Stream erosional events.
The Neogene section is an extremely complex, highly variable lithic package consisting of at least ten depositional sequences bound by regional unconformities and associated channels. Preliminary biostratigraphic analyses (both nannoflora and planktonic foraminifera) of vibracores penetrating these sequences suggest they represent high-frequency (4th- and possibly 5th-order) sea-level cyclicity. The seismic data indicate that these short pulse sea-level episodes were primarily low amplitude (<50 m [164 ft]) events. The general distribution for each Neogene sequence, as well as the temporal and spatial relationships of lithofacies changes, seems to be a consequence of a constant interplay between high-frequency sea-level cyclicity and concomitant Gulf Stream dynamics.
The evolving depositional model for the upper southeastern North Carolina margin consists of a few low-frequency (3rd-order) high-amplitude, mid-late Paleogene sea-level events. During their maximum transgression, the western boundary current bypassed the Charleston Bump to the south and impinged on the North Carolina shelf 35 to 40 km (22 to 25 mi) southeast of Cape Fear. These Gulf Stream erosion events deeply scoured the shelf, extending the Blake Plateau to the north. Conversely, the Neogene was dominated by high-frequency, low-amplitude sea level cyclicity. Maximum transgression was relatively lower, forcing the Gulf Stream to be deflected by the Charleston Bump to the south. Consequently, the Neogene sequences comprise a major depositional episode in which the shelf prograded ea t to the present location of the Florida-Hatteras slope.
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