INTEGRATING SEDIMENTARY FACIES AND WELL-LOG RESPONSE PATTERNS TO IDENTIFY HIGH RESOLUTION SEQUENCES FOR A CALIBRATED CHRONO- AND HYDROSTRATIGRAPHIC FRAMEWORK, EASTERN NORTH CAROLINA COASTAL PLAIN

The U.S. Geological Survey's (USGS) Coastal Carolina Project is a Geologic Division program that collects and analyzes deep geologic cores to develop an integrated, calibrated, chrono- and hydrostratigraphic framework for the Coastal Plain of North Carolina. To date, four deep cores were acquired. In April, 2005, a 265 m (870 ft) deep corehole was drilled at Cove City. The core includes approximately 252 m (723 ft) of Cretaceous section (Cape Fear Formation, Black Creek Group, and Peedee Formations), with the K/T boundary at 51 m (147 ft). Above this is a succession of mostly Paleocene (Mosely Creek) and Eocene strata, with a thin, surficial Quaternary unit.

A team of scientists (USGS, University of North Carolina-Wilmington (UNC-W), NCGS and Clemson University), coordinated by the USGS, subsampled and analyzed the core. The USGS constructed a field log, subsampled for nannofossils, diatoms and pollen, acquired a downhole suite of borehole logs (gamma ray, resistivity, conductivity, temperature), interpreted hydrostratigraphic units, and assigned preliminary ages and stratigraphic nomenclature. Samples for radiometric dating were collected (UNC-W). NCGS photographed the cores, and constructed a lithologically-based graphic log of the core at a scale of 1 in = 1 ft. This log, compiled and analyzed at 1 inch = 10 ft, graphically shows bounding surfaces and sedimentary attributes such as principal grain size class, relative abundance of gravel, sand, and mud, and % carbonate; these are useful in defining sedimentary facies, depositional sequences, aquifers and confining units, and, ultimately, confirming the stratigraphic hierarchy developed from biofacies.

We report here the results of integrating this facies analysis with well-log response patterns, hydrostratigraphic units, alloformations and their ages, and the identification of high resolution sequences. Facies attributes and depositional sequences are defined for hydrostratigraphic units including the Black Creek and Cape Fear aquifers and their confining units. At the basin scale, the high-resolution sequences identified from facies and well log patterns are correlated to a 174 m (570 ft) corehole to basement at Elizabethtown, N.C. Regional facies variations within high resolution, unconformity-bounded sequences are reported.