NEW GEOLOGIC MAPPING OF THE UP-DIP COASTAL PLAIN IN CENTRAL NORTH CAROLINA

Detailed geologic mapping in up-dip Coastal Plain sediments in fifteen 7.5-minute quadrangles in the Raleigh 1:100,000 sheet has resulted in an extensive database of 355 drill holes. Continuous coring was performed at 183 sites and power-auger samples were collected at another 172 sites for a total of 9,120 feet drilled over the past 5 years as part of the STATEMAP program sponsored by the U.S. Geological Survey. Total depths range from 2-feet to 90-feet and the cores have, for the most part, recovered the entire sedimentary section in this area. Basement topography and regional scarps have influenced the sediment distribution and thickness with scarp toes occurring at about 170-feet, 225-feet, 250-feet, and 300-feet. Cretaceous and Tertiary units have been mapped and are identified based on lithology and limited biostratigraphic control. The siliciclastic Cretaceous section is up to 55-feet thick and consists of sandy clays, coarse- to very coarse-grained sands, and fine-grained clayey well-sorted sands. The Tertiary section is characterized by marine shelly sand and clay, fine-grained well-sorted micaceous sand and fine- to medium-grained clayey sand and is up to 70-feet thick. Gravel lags are common where the sediments rest directly on crystalline basement rocks. Results to-date suggest that the Cretaceous section correlates with the Upper Cretaceous Cape Fear Formation. The Tertiary section is interpreted to be one transgressive-regressive event in the Pliocene, resulting in the depositon of the lower to upper Pliocene Yorktown Formation. Cores presented here represent the most widespread lithofacies mapped to-date.