MIDDLESBORO IMPACT CRATER

Type: Complex
Age Ma: <300 (geological dating)^a
Diameter: 6 km
Location: N 36° 37’ W 83° 44’

^a The Appalachians are the weathered and worn remains of mountains that date to the formation of the supercontinent Pangaea 300 million years ago.

A generalized tectonic map of the southern interior lowlands of the United States which shows the locations of the Wells Creek, Flynn Creek, Middlesboro impact structures, Howell Structure and Nashville Dome with respect to three concentric faults (after Roddy, 1968: 293).

The Middlesboro impact crater is located in the southern Appalachian Mountains containing the town of Middlesboro Ky.

The Middlesboro Basin is the unique development of a circular, alluviated, topographic depression in a part of the Appalachian Plateaus that is characterized by rugged hillsides, narrow V-shaped valleys, and a minimum of flat bottom land. The relatively broad expanse of the basin with its low, rolling hills contrasts sharply with the fringing mountains which rise 1,000 to 1,900 feet above the valley floor. Nearly all the lowland, about 4 miles in diameter, is occupied by the city of Middlesboro. The conspicuously different topography and the intense deformation of rocks underlying the basin have attracted geologic interest since the investigations describing the physiography of the basin and noted the deformed condition of the underlying rocks. Recent geologic mapping indicates that meteoric impact is the probable mode of origin.

Evidence of meteor impact is indicated by the structurally high and intensely shattered core, which may be the result of rebound from an impact explosion. Diminishing deformation outward from the center, a marginal syncline, and upturned beds on the periphery of the basin are also suggestive of meteor craters. (ENGLUND and ROEN 1962)

Did the Middlesboro, Kentucky, bolide impact event influence coal rank?

James C.Hower, Stephen, F.Greb, Kenneth, W.Kuehn, Cortland, F.Eble

The Middlesboro Basin, southeastern Kentucky, occurs on the Cumberland Overthrust Sheet and includes a ca. 5.5-km diameter impact structure. The Lower and Middle Pennsylvanian coal-bearing strata are faulted, with some evidence for shock metamorphism. The event post-dated the latest-Pennsylvanian–early-Permian thrusting and was likely prior to late-Mesozoic entrenchment of drainages. The impact of a 0.5-km meteor traveling at ca. 60,000 km/h would release about 1 EJ, the approximate equivalent of the instantaneous combustion of 30 Mt of coal.

The central uplift at Middlesboro provides a means of studying shock metamorphic events in sedimentary targets and provides insight into central uplift formation in complex craters. Results indicate that, following the shock wave passage, the center of the structure ‘rebounded’ in a brittle fashion. So, although fluidization may quantitatively explain the behavior of target rock material in some impacts, rise of the central uplift in some impact structures may occur by minor displacements along faults in target rock.

Geological profile of the Middlesboro impact crater preserved in sedimentary target rock.

Middlesboro, Kentucky; viewed from the Pinnacle Overlook.

The Middlesboro Crater bolide point of impact. We took this image on our post solar eclipse USA crater tour, 2017.

References

Black, D. F. B., Cryptoexplosive structure near Versailles, Kentucky. U.S. Geology Survey Professional Paper 501-B, pp. B9-12. 1964.

Cockell, C. S., Lee, P., The Biology of Impact Craters – a review. Biol. Rev., 77, P. 279 – 310. 2002.

Dietz, R. S., Shatter cones at the Middlesboro structure, Kentucky. Meteoritics, v. 3, pp. 27-29. 1966.

Englund, K. J., Roen, K.J. and DeLaney,A.O., Geology of the Middlesboro north quadrangle, Kentucky. U.S. Geological Survey Geologic Quadrangle Map GQ-300, scale 1:24,000. 1964.

Englund, K. J., Geology of the Middlesboro south quadrangle, Tennessee-Kentucky-Virginia. U.S. Geological Survey Geologic Quadrangle Map GQ-301, scale 1:24,000. 1964.

Englund, K. J., Roen, J. B., Origin of the Middlesboro basin, Kentucky. U.S. Geological Survey Professional Paper 450-E, pp. E20-E22. 1963.

Grieve, R. A. F., The record of impact on Earth: Implications for a major Cretaceous/Tertiary impact event. Geological Society of America, Special Paper 190, pp. 25-37. 1982.

Gurov, E. P., Gurova, E. P., Impact structures on the Earth’s surface (in Russian). Geologicheskii Zhurnal, v. 47, pp. 117-124. 1987.

Masaitis, V. L., Danilin, A.N., Maschak, M.S., Raykhlin, A.I., Selivanovskaya, T.V. and Shadenkov,Ye.M., The Geology of Astroblemes (in Russian). Leningrad, Nedra, 231 p. 1980.

Milam, K. A., Kuehn, K. W., Middlesboro, KY: Further evidence for an impact origin, 1999 GSA Annual Meeting – Denver, Colorado. Abs. No. 52183. 1999.

Seeger, C. R., Geophysical investigations of the Versailles cryptoexplosion structure, and the Middlesboro basin cryptoexplosion structure, Kentucky (abstract). EOS, v. 51, p. 342. 1970.

Steinemann, C. F., A gravity study of the Middlesboro cryptoexplosive structure. Thesis, University of Kentucky, 41 p. 1980.