PRELIMINARY FINDINGS OF A RECENTLY DISCOVERED MESOZOIC RIFT BASIN CONCEALED BENEATH COASTAL PLAIN COVER, BERTIE COUNTY, NORTH CAROLINA

In 2004, USGS water resources well BE-110 was drilled in Bertie Co., NC. Beneath 1026 ft of coastal plain cover, the well penetrated Triassic strata that continued to the total depth of the well, 1096 ft. This study is the first to attempt to provide constraints on the size and geometry of the buried basin. Other wells reaching basement in the region are sparse, and provide loose constraints on the areal extent of the basin. Consequently, we conducted a detailed gravity survey to constrain the areal extent and 3-d geometry of the basin. The survey transects are roughly normal to the hypothesized strike of the long axis of the basin. An inversion of the gravity data to further constrain the basin geometry is ongoing. Forward models, using assumed rock densities, suggest a 1 km thick by 3 km wide basin would produce a Bouguer anomaly between 1-3 mGals. This is most likely the maximum size of the basin, as previous aeromagnetic and gravity surveys have failed to produce an observable anomaly.

We investigated and sampled core from well BE-110 in the repository of the NC Geological Survey. Investigation techniques include magnetic susceptibility, thin section petrography, and major and trace element geochemical analysis. Statistical analyses of susceptibility data demonstrate that Triassic strata are distinct from overlying Cretaceous strata. Triassic material has a mean susceptibility of -27.64 (SI), contrasted by a Cretaceous mean value of 46.49 (SI). Initial petrographic analysis suggests a likely tectonic provenance of recycled orogen, sub classified as a collision orogens or foreland uplift, based upon the abundance of quartz clasts identified during point counting. Geochemical studies are focusing on immobile trace element populations (e.g. Th, Zr, La), their respective ratios, and interpretations of these data regarding provenance.

Our results provide insight into the complex tectonic and sedimentary processes operating in continental extensional regimes. Ranging over 1700 km on the eastern seaboard of North America, Mesozoic rift basins offer valuable insight into the tectonic history of the region. These basins are also valuable to society, particularly as water aquifers and hydrocarbon reservoirs.