Most orogenic belts exhibit broadly arcuate regional map-view trends of structural patterns. Commonly, the inflection between opposing curves (recesses and salients) is a transverse zone marking a linear array of along-strike contrasts in regional structure and stratigraphy. Analysis of such transverse zones can provide insight into the processes affecting orogenic curvature. Curvature is especially distinctive along the west flank of the Appalachians, where the tightest salient/recess juncture is a thinned-skinned transverse zone in Georgia, separating the Alabama recess and Tennessee salient, and extending entirely across the width of deformed Laurentian cover rocks. This zone's most notable feature is a large oblique hanging-wall ramp within the frontal metamorphic allochthon formed during Alleghanian collisional events. The basal décollement steps several kilometers stratigraphically upward across this ramp from Proterozoic basement and its overlying Late Proterozoic rift sequence (Tennessee salient), southwestward into basal Cambrian and younger rocks (Alabama recess). This ramp resulted from oblique sinistral displacement of the allochthon against an earlier, east-facing, dextral continental margin transform fault that initially separated adjacent rifted margins of opposite polarity. Differences in the distribution, thickness, and facies of units indicate that important variations in basin geometry existed across the curvature inflection before Paleozoic deformation, suggesting that the orogenic curvature in part results from an inherited basin architecture. Translation of the allochthon over the ramp caused deflection of the tectonic transport trajectory, major cross folding, and rotation of earlier structures. Associated out-of-plane deformation propagated outward across the foreland, producing the array of thinned-skinned transverse structures aligned into the transverse zone.

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