GRAVITY SURVEY OF A BURIED TRIASSIC RIFT BASIN, BERTIE COUNTY, NORTH CAROLINA

The North Atlantic (NA) rift margin includes of a series of small and large Triassic rift basins along the eastern United States seaboard. This regional rift system is comprised of complex and variable geometries that can be generalized into regions and sedimentary associations (Leleu et al., 2016). Rift basins provided accommodation space for organic-rich Triassic age sediments that may be source rocks for natural gas and petroleum. Dozens of these rift basins have been identified, studied, and characterized due to their economic importance. Most of the studied basins are exposed at the surface and relatively easy to access. Only a few buried basins beneath coastal plain cover strata have been identified and studied. We used primarily geophysical methods to study a buried, recently discovered Triassic rift basin in Bertie County, North Carolina, from a deep core sample that documented Triassic age sedimentary rocks buried underneath approximately 300 meters of Cretaceous and younger sediments and sedimentary rock (Weems et al., 2007).

We used a gravity survey to constrain the dimensions and geometry of rock bodies at depth. More than 200 gravity stations were measured over an area of roughly 1000 square kilometers . Data processing, modeling, and integration with preexisting data was accomplished using Oasis:Montaj software. The buried basin creates a maximum gravity anomaly of approximately 5 mGal. Preliminary modeling of the data suggests the basin is elongate generally SW to NE, and is approximately 20 km wide, 40 km long, and as much as 2 km deep. In cross section, the basis is asymmetrical and wedge-shaped, with a steeply dipping NW margin and a more shallowly dipping SE margin.

The Bertie Basin is small compared to other exposed rift basins in North Carolina such as the Durham/Deep River and Danville Basins. Its more seaward position indicates that formation began later into the rifting event and may be related to reduced size and increased seaward accommodation space. Uplift in the proximal domain, where the exposed basins are located, resulted in significant deformation through erosion and inversion. Burial underneath the Coastal Plain, however, has helped to preserve the Bertie Basin’s original geometry and size which allows for better interpretation of paleo-environments and sedimentary deposition.