Wells in the North Carolina coastal plain penetrate the Paleogene at depths from 0 to 750m. Lithofacies represented by the cuttings are relatively easy to recognize in plastic-impregnated thin sections of cuttings. They include: quartz sands, shelly sandstones, and terrigenous mudstones (estuarine/lagoon, or prodelta facies); quartz sands and sandy mollusk-fragment grainstones (shoreface and lagoon); phosphatic hardgrounds (inner- to mid-shelf current and wave swept non-depositional surface); bryozoan and echinoderm grainstones/packstones (midouter shelf); and fine skeletal wackestones and planktonic marls that are locally dolomitized (slope). Cuttings were used, in conjunction with wireline logs, to construct lithologic columns for the wells. Over 24 depositional sequences (15 to 30m thick) can be recognized, which are characterized by major landward, followed by seaward shifts of the facies. LSTs in the wells are characterized by abundant quartz sandstone/mudstone; TSTs are represented by an upward decrease in siliciclastic material and an increase in outer shelf skeletal carbonate and lime mud; HSTs show a gradual increase in siliciclastics and molluscan sands. Major marine glauconitic and phosphatic hiatal surfaces are common at the MFS of depositional sequences, but also occur in other systems tracts and relate to marine erosion/nondeposition. This approach is allowing detailed tracing of facies between wells and mapping of facies thickenings and pinchouts. It is also providing a more refined facies-based sequence stratigraphic framework for the subsurface of the North Carolina coastal plain.
AAPG Search and Discovery Article #90925©1999 AAPG Foundation Grants-in-Aid