Non-residential Projects: Deep Stratigraphic Corehole
June 1, 2007
At the Hope Plantation in North Carolina, the USGS Geologic Discipline (GD) Eastern Earth Surface Processes Team has been drilling a deep stratigraphic corehole. The drilling was conducted using a wireline continuous-core drill rig and a 21⁄2-inch drill bit to a targeted depth of about 900 feet. The USGS Water Resources Discipline (WRD) will log the core samples to determine the thickness of the aquifers and confining units, and provide daily updates during the active drilling period, collect and test saline pore water samples as practical, and provide a borehole geophysical logging support. A ground water monitoring piezometer may be installed at this site. The GD will obtain geologic and paleontologic samples sufficient to define the stratigraphic units at this location.
The reason that this area is of special interest is that it lies slightly southeast of a zone of anomalously rapid eastward drop-off of the geologic layers of the Coastal Plain. One category of rapid drop-offs, called monoclines, occurs because the layers near the surface are draping downward over one or more deeply buried faults. The presence of faults in this area would significantly complicate the geologic and hydrologic interpretation of the subsurface geology, so it is necessary to determine if faults are present in order to accurately interpret the geology of this area. Drilling on both sides of this monocline-like feature will allow us to determine whether any faults are present and, if so, the amount and timing of movements on the fault(s) over the last 110 million years.