GEOLOGIC MAP OF THE TELL CITY QUADRANGLE, WEST-CENTRAL KENTUCKY: NEW FEATURES AND QUESTIONS WITH 1:100,000-SCALE MAPS

The Digital Geologic Mapping Program at the Kentucky Geological Survey is digitizing 1:24,000-scale, 7.5-minute geologic quadrangle maps, which are being used to create seamless, 1:100,000-scale 30 x 60 minute geologic quadrangle maps. The new 1:100,000-scale maps reveal features not previously recognized at either the 1:24,000 scale or at the statewide 1:500,000 scale. Regional drainage, erosional, and depositional patterns revealed on the maps, along with correlation of surface faults with basement structure, pose new questions about potential geologic relationships. Geospatial analysis and compilation of a variety of data sources are being used to address these new questions.

The map of the Tell City 30 x 60 minute quadrangle in west-central Kentucky shows that limestones and shales of upper Meramecian (Mississippian) age cover the eastern and northeastern portions of the quadrangle. Chesterian (Mississippian) rocks dominate the central portion of the quadrangle, as part of the Dripping Springs Escarpment. Pennsylvanian sandstones and conglomerates occupy the Western Kentucky Coal Field, in the western portion of the quadrangle. The Rough Creek Fault System and associated Rough Creek Graben run east-west along the southern portion of the quadrangle. Two significant fault splays run northeast-southwest off of the Rough Creek Fault System.

Interesting networks of drainage features trend across the quadrangle from the coal field to the karstic terrane of the east. The Chesterian outcrop pattern exhibits an angular, blocky form that is reflected in the drainage patterns. These linear patterns may be related to basement structure and they, in turn, have an effect on the deposition of younger sedimentary rocks.

Additionally, examination of aeromagnetic and seismic data reveals distinctive patterns in the basement geology. The Proterozoic Louisville Thrust Fault, bounding the eastern edge of the English Basin, is interpreted to correspond in part to the positions of overlying Paleozoic fault systems. Proterozoic thrusting was possibly followed by several episodes of wrenching. There is some indication that the Paleozoic wrench faults, interpreted from reflection-seismic data, correspond with the northeast-oriented faults and both the northwest- and northeast-oriented trends in the outcrop pattern.