Abstract: Sequence Stratigraphy of Paleogene Non-tropical Mixed Carbonate Siliciclastic Units, North Carolina Coastal Plain

COFFEY, BRIAN P., Virginia Tech, Dept. of Geol. Sciences, Blacksburg, VA

This project will document the sequence stratigraphic development of potential reservoir facies on a Tertiary non-tropical, mixed carbonate/siliciclastic ramp, using a combination of outcrops, cores, wireline logs, well cuttings, and seismic reflection profiles. Preliminary study of outcrops, shallow cores, and well cuttings from the North Carolina coastal plain suggests that the major facies include: terrigenous barrier-lagoon complexes, widespread nondepositional inner ramp (a hardground surface of wave abrasion), and outer ramp bryozoan-echinoderm-dominated facies grading downslope into deep water marls.

The study will involve detailed logging of continuous cores and quarry sections along structural highs, which will be tied into the deeper subsurface using thin sectioned plastic-impregnated cuttings (3 to 5 m spacing) from numerous exploratory wells. The cuttings preserve both grain types and intergranular calcite cements and show limited mixing up section.

Sequence boundaries in outcrops and wells are marked by concentration of quartz sand and phosphate hardgrounds and pebble layers. This data will be integrated with existing biostratigraphic frameworks to construct detailed lithologic cross-sections across the basin, which will be tied into the seismic stratigraphic database to correlate between wells, determine the seismic expression of bounding surfaces, and define stratal geometries of this ramp succession.

Reservoir facies distribution and seismic response for nontropical mixed carbonate-siliciclastic ramps are poorly known, because most studies have concentrated on tropical carbonate platforms. Potential reservoirs on these passive margin ramps are coastal sand bodies and outer ramp (25-100 m water depth) swell-wave washed bryozoan-echinoderm grainstones, which contrast markedly with the reefal, bank, and oolite reservoirs of most well-studied tropical platforms.

AAPG Search and Discovery Article #90931©1998 AAPG Foundation Grants-in-Aid