INVESTIGATION OF A POTENTIAL METEORITE IMPACT CRATER, ATLANTIC COASTAL PLAIN, NORTH CAROLINA

Examination of aerial photography from the inner Atlantic Coastal Plain/Piedmont transition identified an anomalous circular feature which was hypothesized to represent the margins of a meteorite impact crater. This feature is approximately 2.5 km in diameter and its margins are outlined by drainages that lie 10 m lower than the topographically higher central area. To test this hypothesis a gravity and magnetic survey was acquired along three north-south and three east-west transects at an average station spacing of approximately 200 m. Gravity readings were measured with a Worden gravimeter and magnetic measurements collected with a Geometrics G-856 magnetometer. The raw gravity was reduced and terrain corrected to calculate the complete Bouguer anomalies. The results indicate that the circular topographic feature lies athwart a gravity high that extends from the north. The total amplitude of the gravity high is approximately 4 mGal. The magnetic data show a northeast-southwest trending magnetic high through the western portion of the feature.

Core samples were recovered from two holes that penetrated the top of phyllitic bedrock beneath approximately 8 m of coastal plain sands and muds. Thin sections of the bedrock were examined to search for the presence of planar deformation features (PDFs), considered to be the definitive features of an impact.

The combined geophysical and petrographic data indicate that this circular topographic feature is not the result of an impact event. Simple impact craters typically exhibit circular gravity lows which result from impact-associated breccias and sedimentary fills. Larger, complex craters may possess a positive gravity signature, denoting the location of the central uplift, but there is no geologic or geophysical evidence to support this interpretation. . Furthermore, the lack of PDFs from the examined thin sections indicates that the phyllite was not subjected to shock metamorphic conditions. A more probable interpretation is the topographic and geophysical signature of this area is a result of the folded Late Proterozoic – Cambrian metavolcanic basement rock and Jurassic diabase dikes.