Abstract:

The conflict between thick-skinned and thin-skinned thrust belt hypotheses in the southern Appalachians has been conclusively decided in favor of the thin-skinned interpretation by seismic surveys and drilling results. Balanced cross sections are a logical development stemming from the thin-skinned thrusting hypothesis. Three detailed balanced sections across the region (northern Alabama, Knoxville area, and Blacksburg area) are compared with the early thin-skinned and thick-skinned models of Rodgers, Cooper, and Chamberlin. In Virginia, Cooper’s hypothesis about the order of thrusting and synchronous evolution of structures associated with basement fault motion have been disproved by modern mapping, fabric, and paleontologic work. In northeast Tennessee, the no-basement hypothesis has been relatively well established since the work of Rich. In the Alabama-Georgia segment, discussion continues about the origin of some major structures. Balanced section concepts require that the sections be restored to their pre-deformational configurations.

In retrospect, the geologic reasoning based on surface stratigraphic thicknesses and structural styles should have convinced us of the thin-skinned nature of thrusts without the seismic data that seemed essential at the time. The COCORP seismic results should have been no surprise had the geologic reasoning of balanced sections been believed.

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