High-resolution stratigraphy at a coastal drillhole determined from a continuous core profile and a borehole geophysical log

Lithologic descriptions of continuous core interpreted in conjunction with borehole geophysical logs were used to established high-resolution hydro- and geostratigraphic profiles and to determine thicknesses of hydrologic and geologic units at CR-622 in the coastal plain of North Carolina. Borehole geophysics was used to adjust the position of core loss within each cored interval and to supplement lithology to determine the stratigraphy of missing segments of core. The surficial aquifer has some small inclusion of clay and is thinner here than anticipated. The Yorktown confining unit rests on an unconformity, distinguishing the aquifer from the aquitard and corresponds to the geologic units. Borehole geophysics identified this anomaly which might have otherwise been missed. The Pungo River Aquifer immediately overlies the upper Castle Hayne confining unit. The Castle Hayne confining unit is comprised of the Pungo River Formation. In other areas of the Coastal Plain, the lower part of the Pungo River Formation is a confining unit on top of the River Bend Formation and separates the Pungo River Aquifer from the upper Castle Hayne Aquifer. A resulting hydrologic and stratigraphic column of the upper Cretaceous, Tertiary and Quaternary showing a generalized relation between geologic and hydrologic units beneath Cherry Point Air Station is presented. Present are the Yorktown, Pungo River and Castle Hayne Aquifers. The geologic units are Eocene -- Castle Hayne, Miocene -- Pungo River, Pliocene -- Yorktown, Pleistocene -- James City and Flanner Beach, and the topsoil is Holocene-undifferentiated. The Oligocene -- River Bend Formation is absent, and an unconformity exists between the Pungo River Formation and the Castle Hayne Formation. Although some geophysical logs produce non-unique lithologic solutions, a complete normal stratigraphic profile may be obtained with the addition of continuous core. Curve characteristics within geophysical logs provide precise identification of transitional sequences and can be used to calibrate lithostratigraphy. The interpretation of borehole geophysical logs in conjunction with the lithology developed from continuous core can be used to produce high-resolution hydro- and geostratigraphic profiles.