Paleocene faulting within the Beaufort Group, Atlantic Coastal Plain, North Carolina

Postrift faulting in the Atlantic Coastal Plain of the eastern United State s is a focus of several recent studies, particularly because of seismic act ivity associated with areas such as Charleston, South Carolina (earthquake of 1886), Understanding the ancient behavior of fault systems can contribut e to increased awareness of earthquake potential where traditional mechanis ms of earthquake activity are poorly understood. In the coastal plain of ea stern North Carolina, the Graingers wrench zone, a more recently active nor theast-southwest-trending fault system, overprints a Paleocene east-west fa ult trend and preserves evidence of episodic activity during Mesozoic and C enozoic time. The western border of the Graingers basin is coincident with a northeast-southwest-oriented feature delineated on aeromagnetic and gravi ty maps. This northeast-southwest-trending western border fault records mov ement that initially occurred during the Paleozoic, was reactivated during the Triassic-Jurassic and the Cretaceous (Cenomanian and Maastrichtian), an d has been active into the Holocene, Paleocene deformation records a shift in motion from the northeast-southwest trend to the east-west. This shift i n direction controls the present-day distribution of early to late Paleocen e strata of the Beaufort Group. Stratigraphic relationships between the Pal eocene and underlying Cretaceous units suggest that the fault zone propagat ed to the southwest during the late Danian-Selandian and into the Selandian -Thanetian. Post-Paleocene activity of the northeast-southwest-trending fau lts exhibited a down-to-the-east displacement pattern and appears to have a minor component of strike slip, which may offset the older east-west-trend ing structures. Preservation of topographic features, such as a fault-line scarp with as much as 13 m of relief, triangular facets, and extensive ravi nement normal to the scarp orientation, suggest Holocene movement on the fa ults. Historical records indicate seismicity in the area during the latter part of the nineteenth century. The combined northeast-southwest and east-west fabric has geometry similar to those of fault zones in Georgia and seismically active areas of South Ca rolina, The faults that affect the area were probably formed by interaction of the Neuse hinge and the Roanoke Island-Goldsboro fault, which border th e Graingers basin to the south and north, respectively. Differential moveme nt on these larger structures may be the result of compression caused by ch anges in direction of motion of the North American plate.