THREE-DIMENSIONAL PALINSPASTIC RESTORATION OF THE UNMETAMORPHOSED APPALACHIAN THRUST BELT IN ALABAMA AND GEORGIA

A new three-dimensional palinspastic restoration for the Appalachian thrust belt in Alabama and Georgia is based on an iterative comparison of balanced cross sections, palinspastic maps at multiple stratigraphic levels, and a basement structure map. Structural cross sections, constrained by surficial and subsurface data, define the structural geometry and palinspastic position of thrust sheets. For cross-section construction, Paleozoic strata are divided into four units: a basal weak unit (mostly Rome and Conasauga strata), a regionally dominant stiff layer (Knox Group), a heterogeneous carbonate-siliciclastic Middle Ordovician-Lower Mississippian succession, and Upper Mississippian-Pennsylvanian synorogenic foreland deposits. The regional décollement is within the basal weak unit above Precambrian crystalline basement, and a few ramps connect to upper-level detachment surfaces in the upper Knox Group and younger strata. Construction of palinspastic maps, using the basement structure map as a visible layer, supports comparison of stratigraphic trends of coeval deposits between adjacent thrust sheets and across basement faults, matching lateral and frontal cut offs, and defining the relation of basement faults to stratigraphy and thrust-belt geometry.

Iterative comparison of basement structure, cross sections, and palinspastic maps suggests that basement faults influenced the stratigraphic distribution of Paleozoic units and the geometry of thrust-belt structures. Variations in structural style across strike are directly related to basement structures, décollement-host stratigraphy, duplexes of the stiff layer, and distribution of upper-level detachments. Along-strike changes in thrust-belt and basement structure are concentrated in transverse zones across the thrust belt.