POROSITY DEVELOPMENT ACROSS THE CRETACEOUS-EOCENE UNCONFORMITY IN SOUTHEAST NORTH CAROLINA

The unconformity between the Cretaceous Peedee Formation and the Eocene Castle Hayne Formation was examined in a 2.5 m core from New Hanover County, North Carolina. The Rocky Point Member of the Peedee Formation (base of core) has large moldic pores with average long axes of 7-10 mm and comprising about 21% of the rock volume. Castle Hayne Formation (upper core) porosity is also primarily moldic but pores are smaller with average long axes in the 2-4 mm range and comprising 3-13% of the rock volume. The unconformity is bound by a thin (0.3 m) carbonate-cemented quartz wacke of the Island Creek Member of the Peedee Formation below and a 0.2 m phosphate pebble conglomerate with micritic matrix of the Castle Hayne Formation above. Porosity in the Island Creek is occluded except for minor moldic porosity associated with local concentrations of molluscs. Porosity in the conglomerate (7%) is associated primarily with solution seam concentrations of siliciclastic sediments. Controls on porosity include the size and nature of the bioclasts, relative abundance of siliciclastic material, and duration of exposure of the unconformity.