Miocene Seismic Stratigraphy, Structural Framework, and Sea-Level Cyclicity: North Carolina Continental Shelf

Abstract

Preliminary interpretations of over 1000 km of high-resolution seismic reflection data, supplemented by over 100 9-m vibracores, have delineated the shallow stratigraphic and structural framework for several Miocene depositional sequences overlying the Carolina platform in the area of Onslow Bay, North Carolina. Comparison of the observed stratigraphy with published seismic, gravity, magnetic, and core hole data indicates that the distribution, thickness and depositional pattern of each sequence has been controlled by: 1) the regional tectonic framework; 2) several, local structural features; and 3) numerous, relative, sea-level functions.

A broad zone of phosphate-rich, Miocene sediments and rocks crops out at mid-shelf across the northern segment of the Carolina Platform. This outcrop belt trends northeast-southwest, and extends from Frying Pan Shoals off Cape Fear to the middle shelf off Bogue Banks. Older Tertiary and Cretaceous sequences crop out southwest of Frying Pan Shoals owing to the presence of the Cape Fear Arch, a mid-Carolina Platform high. In the vicinity of Bogue Banks, the Miocene sequences abruptly change strike and run parallel to the north-south oriented White Oak Lineament. North of Bogue Banks, the Miocene depositional sequences thin and/or pinch out over the Cape Lookout High, which is presently thought to be a pre-Miocene, erosion-originated paleoptopographic feature. In southwestern Onslow Bay the Miocene sequences change strike and thicken along a third local structure, herein referred to as the Cape Fear Monocline. Several shallow Miocene outliers, which are the surficial expression of subbottom “flexures,” were also identified in this area. These structures are deformational in origin, and may be a consequence of differential movement along deep-seated structures within the Carolina Platform.

The Miocene depositional sequences and associated unconformities indicate several cycles of relative sea-level change. Comparison of the Miocene relative sea-level cyclicity with the proposed global eustatic sea-level curve of Vail and others (1977) depicts a potentially strong correlation. However, the present lack of high-resolution biostratigraphic data precludes exact correlations.