THE STATUS OF SURFICIAL GEOLOGIC MAPPING AND STRATIGRAPHY ON THE COASTAL PLAIN OF NORTH CAROLINA

Presented here is a status report on surficial geologic mapping and stratigraphy for the Coastal Plain of North Carolina (NC), which covers 44% of the state. In 1985, the NC Geological Survey published a statewide geologic map that showed subcrop formations, rather than surficial geologic units for the Coastal Plain; several exceptions included the Pinehurst and Waccamaw Formations, and Qp for undivided surficials east of the Suffolk Scarp. The reason for this exclusion may be that USGS and university collaborators independently compiled 1:250K Quaternary geologic maps for same area (1986, 1987 paper maps). The NCGS 1985 map biases the user into assumptions that are not valid.

Production of a surficial map for NC’s Coastal Plain, is a multi-phase process that includes a 3D subsurface mapping approach: 1) a landform analysis using high-resolution LiDAR, 2) cores to define stratigraphy underlying landform elements, 3) definition of the hierarchy of stratigraphy (sequence boundaries, facies analysis, ages), 4) a 3D database of units, 5) establishment of type sections, 6) standardized digital map units (DMUs), and, 7) a geologic map derived from the landform map. This process is conducted at the 24K scale and simplified when applying to 100K compilations.

NC’s Coastal Plain includes over 330, 7.5-minute (24K) quadrangles. To date, 1:24K geologic maps exist for only 24 quads. Three quads (EARTH MRI) are currently being mapped. Only 6.5 of the relevant 25 100K-quadrangles are compiled as geologic maps. NCGS plans to remedy this by 2030 by systematically compiling 100K geologic maps for the remaining quads and will begin to integrate them with subsurface data. Bureau of Offshore Energy and Minerals (BOEM) staff recently proposed integrating onshore and offshore geologic data in 100K map areas that include water.

NC is currently establishing type sections for its Pliocene and Quaternary surficial units. Recent detailed mapping (STATEMAP, EARTH MRI) produced 13,600 ft of Geoprobe core in six 24K quadrangles that are available to support this effort (EARTH MRI, Fall Zone and Middle Shorelines Placer Focus Areas). FY22 STATEMAP supports interstate drilling and stratigraphic correlations (VA/NC), and a new multi-state (FL/SC/NC/VA) cooperative supported by the USGS is also established to facilitate this process.