Stratigraphic and Structural Controls on Deformation Around a Thrust Belt Recess

Brian S. Cook
University of Kentucky, Department of Earth and Environmental Sciences Lexington, Kentucky 40506 USA; [email protected]

Sinuous map traces around salients and recesses characterize orogenic thrust belts. In a well-defined Appalachian recess in Georgia (USA), two distinct regional strike directions intersect at approximately 45°; fault intersections and interference folds enable tracing of both structural strikes. The intersection and fold interference exemplify a long-standing problem in volume balancing of palinspastic reconstructions of sinuous thrust belts. Cross sections generally are constructed perpendicular to structural strike, parallel to the assumed slip direction. An array of cross sections around a structural bend may be restored and balanced individually; however, restorations perpendicular to strike across intersecting thrust faults yield an imbalance in the along-strike lengths of frontal ramps. The restoration leads to a similar imbalance in the surface area of a stratigraphic horizon, reflecting volume imbalance in three dimensions.

Around the recess in Georgia, tectonically thickened weak stratigraphic layers--mainly shales of the Cambrian Conasauga Formation and Mississippian Floyd Shale--accommodated ductile deformation associated with the folding and faulting of the intervening Cambrian-Mississippian regional stiff layer. The exposed stiff-layer structures in Georgia may be analogous to those over shale-dominated ductile duplexes (mushwads), which are being developed for natural gas elsewhere in the Appalachian thrust belt.

AAPG Search and Discovery Article #90083 © 2008 AAPG Foundation Grants in Aid