GEOPROBE DRILLING TO COLLECT STRATIGRAPHIC DATA FROM THE SOUTHEASTERN ATLANTIC COASTAL PLAIN PROVINCE: METHODS FOR PROCESSING CORE IN THE FIELD

North Carolina Geological Survey (NCGS) geologists utilize the Model 5400 Geoprobe drill rig to collect undisturbed samples of unconsolidated subsurface materials to provide accurate on-site descriptions of sedimentary facies, stratigraphic boundaries, and tentative correlations between neighboring cores within the Coastal Plain province of the southeastern United States.

Cores (2-in diameter) are collected in 4-foot intervals using the Macro-Core MC5 Soil Sampling System: a continuous, discrete sampling method developed specifically to obtain undisturbed samples encased in plastic core tubes within the metal core barrel.

The geologists’ field set-up consists of several workstations: three folding tables for each step of processing core on-site, one sawhorse for washing open cores, one sawhorse for cleaning rods, and the side of the box truck to prepare the core barrel and associated tools for upcoming runs.

To conduct field work safely and efficiently, a minimum of three people, optimally four, are required at a drill site: the licensed driller, assistant geologist, and the Senior Coastal Plain Principal Investigator (PI). The assisting geologist works with the licensed driller and PI to aid in all facets of drilling and processing the core at the drill site. The assisting geologist assistant communicates information from the licensed driller to the PI and vice versa. The licensed driller oversees drilling operations and prepares the core barrel for each run. The PI rinses, photographs, and logs the cores. The PI sketches a graphic log on-site using a standardized method of textural classification that is independent from the composition (Farrel et al., 2013).

Geoprobe core data, comprehensive geomorphic landform analysis from LiDAR, and three-dimensional subsurface mapping techniques can be used to produce high-quality descriptions of sedimentary facies and relict landforms and create a sequence stratigraphic framework.

Drilling to define subsurface materials is necessary for mapping the Coastal Plain, especially in areas where well-preserved outcrops of Coastal Plain strata are rare due to flat and rolling topography.