MIDDLESBORO IMPACT CRATER
by: Charles O’Dale
- 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.
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.
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