Jeptha Knob, Kentucky, a probable meteorite impact structure

Abstract

AbstractJeptha Knob is a deformed structure, 4.5 km in diameter, composed entirely of carbonate rocks in the stable craton of North America. At Jeptha Knob, conventional evidence of meteorite impact, shock metamorphism, has not been found. I used calcite twin analysis to test the hypothesis that Jeptha Knob is a meteorite impact crater. Calcite twinning gives differential stresses of >170 MPa in rocks that were 600 to ≈800 m below the surface when the rocks were deformed. Under these conditions, high differential stresses cannot be explained by tectonic processes. In addition, twin intensities are >150 twins/mm which are >50% higher than the highest twin intensities observed in limestone from a wide variety of tectonic settings. Twin intensities and differential stresses are the same magnitudes as those found at Serpent Mound, a proven impact structure. Consistent with meteorite impact, differential stresses increase toward the center of the structure. If one accepts that Jeptha Knob is a marine impact crater, then (1) the presence of high temperature (>250°C) thick twins in calcite from a resurge deposit; (2) the extensive dolomitization of the central uplift with water/rock ratios >1.0; and (3) two episodes of calcite twin recorded incremental strains, are explained.