Abstract: Impact of an Astrobleme on Coal Mining in Part of the Eastern Kentucky Coal Field
GREB, STEPHEN F., and CHESNUT, DONALD
R., Jr., Kentucky Geological Survey, University of Kentucky, Lexington, KY
Mining of the Path Fork and Hance coals near Middlesboro in southeastern Kentucky is locally disrupted by the Middlesboro astrobleme, an inferred celestial impact structure. The impact structure has been previously mapped and consists of an inner region of deformed strata 3 mi (4.8 km) wide, bordered by a ring of arcuate faults, most exhibiting down-to-the-axis displacement. The center of the feature contains a rebound structure, in which strata from the Lower Pennsylvanian Lee sandstones have been brought to the surface. The impact is post-Late Pennsylvanian, pre-Quaternary in age. All that remains is the eroded, circular core of the impact structure, which provided the flat land upon which Middlesboro was settled.
Small, unmapped faults between or splintering off of the mapped rim faults are the most common mining problem. Analysis of mine maps shows that several deep mines stopped along unanticipated rim faults associated with the impact structure. A recent excavation on the north rim intersected several normal faults, brecciated and highly deformed gray shales, and a coal tilted almost on end. On the southern rim, surface mines have also recently crossed unmapped faults. Between two faults, a doubling of coal beds was reported. Local brecciation of the Hance coal along one of the faults, and dips of more than 40 %, have been documented. Sudden loss of coal, changes in coal dip, and brecciation related to the astrobleme affect mining in a way that is, as far as we know, unique to this area.
AAPG Search and Discovery Article #90930©1998 AAPG Eastern Section, Columbus, Ohio