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Basement is defined, for the purposes of this discussion, as the metamorphic and (or) igneous rocks below
which there is no known stratigraphic or structural break.
At least 300 holes have penetrated basement beneath the Mesozoic and Cenozoic sediments of the Atlantic Coastal Plain between New York and Georgia. Approximately 90 per cent of them penetrated basement at elevations above--1,000 feet M.S.L. The 10,054-foot Esso #1 Hatteras Light well, which encountered the top of basement at--9,954 feet M.S.L., is deepest.
Drill hole plus meager geophysical data support the following tentative conclusions.
Precambrian and Paleozoic metamorphic and igneous (including volcanic) rocks, similar to those exposed on the Piedmont to the west, constitute basement. Many of these rocks have been highly fractured and sheared.
Part of the rocks accumulated in a pre-Mesozoic eugeosyncline.
From at least late Mesozoic time the basement surface has played the role of a differentially warping platform.
At least four periods of diastrophism are known to have occurred in this area.
The regional structural (and topographical) trend is northeast-southwest.
The surface of the basement may be characterized as an old age erosion surface--commonly referred to as the Fall Zone peneplain--with sporadic fault troughs, ridges, valleys, and "arches."
Locally some of the rocks have been weathered to depths exceeding 150 feet.
The basement surface dips generally seawardly from 15-40 feet per mile (with about 35 feet per mile typical) to approximately the--2,250-foot M.S.L. contour; seaward from this contour it steepens to about 100-125 feet per mile.
Oil may occur in commercial quantities in weathered zones on or fractured zones in the basement or in sedimentary rocks that lens out against topographic highs on the basement surface.
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