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Abstract: The Serpent Mound Magnetic Anomaly: Fingerprint of a Meteorite Impact?

Department of Geology and Applied Geology, University of Glasgow, Glasgow, Scotland
Apex Technology, Hershey, PA
Ohio Environmental Protection Agency, Columbus, OH
Ohio Division of Geological Survey, Columbus, OH

We report results of a recent ground total field magnetic survey across the Serpent Mound disturbance. Interpretation of these results suggests the disturbance was caused by a meteorite impact. The survey comprises measurements from approximately 2,000 stations covering an area of about 400 km2. Data editing removed the effects of cultural features such as casings from three abandoned oil wells, fences, and buried cables. We collected data in greenfields as much as possible to avoid this contamination. Global Positioning Satellite stations provided control of locations away from roads. After processing data onto a 500 m2 grid, median filtering attenuated short-wavelength anomalies related to cultural features.

An elongated, closed magnetic high correlates with the center of the disturbance; an associated low occurs across the eastern margin of the disturbance. This positive magnetic anomaly is superimposed on a regional NNW-trending magnetic basement high. In the area of the disturbance, evidence for elevated temperatures or igneous activity is absent within Paleozoic strata. Conversely, gravity, seismic reflection, and petrographic evidence makes a compelling case for a meteorite impact origin of the disturbance. Hence, we propose the cause of the local magnetic anomaly was the passage of meteorite-impact-induced shock waves through the basement causing remagnetization of a volume of magnetic rock beneath the disturbance. Magnetic modeling was performed on the magnetic anomaly, based on an estimated depth to Precambrian basement of 1,300 m from seismic reflection and borehole data. Our model shows that a volume of about 7 km3, given a permanent magnetization of 1 amp/m and superimposed on a regional-scale magnetic body having susceptibility of 0.025 units, will produce the observed magnetic anomaly.

AAPG Search and Discovery Article #90930©1998 AAPG Eastern Section, Columbus, Ohio