USE OF CORES, BOREHOLE GEOPHYSICAL LOGS, AND HIGH-RESOLUTION SEISMIC-REFLECTION DATA TO DELINEATE PALEOCHANNELS UNDERLYING THE U.S. MARINE CORPS AIR STATION, CHERRY POINT, NORTH CAROLINA

The U.S. Marine Corps Air Station, Cherry Point, North Carolina, is located in southeastern Craven County, in the Coastal Plain physiographic province. The Air Station is underlain by four fresh-water aquifers -- the surficial, Yorktown, and the upper and lower Castle Hayne. Deeper aquifers contain saline water. The upper and lower Castle Hayne aquifers serve as the principal water supply for the Air Station. Beneath the Air Station, the upper Castle Hayne aquifer is composed of sands and sandy shell beds of the Pungo River Formation and limestone of the River Bend Formation. The lower Castle Hayne aquifer is composed of interbedded limestones, sandy limestones, and calcareous sands of the Castle Hayne Formation. The aquifers are separated by clay confining units that are locally discontinuous due to depositional and erosional truncations, including some that are associated with paleochannels.

Paleochannels are remnants of river and stream channels that have been filled with sediments and overlain by younger units. Geological and geophysical methods were used to locate the paleochannels that breach one or more of the confining units above the Castle Hayne aquifer. Stratigraphic test holes were drilled for the collection of core material and installation of wells. Geophysical logs were made in the test holes. The core material was used to describe the subsurface geology and to correlate units along high-resolution seismic-reflection profiles collected between the test holes.

Lithologic descriptions were made on the cores, which also provided information on formation contacts, ages, and relative hydrologic properties. Borehole geophysical logs, particularly natural gamma logs, were used to correlate stratigraphic relations relative to other test holes. High-resolution seismic-reflection profiles were used to correlate stratigraphic units between test holes and to identify discontinuities in the confining units. In combination, the core descriptions, borehole geophysical logs, and seismic-reflection data were used to create hydrogeologic sections at the Air Station.