Analysis of a regional middle Paleozoic unconformity along the distal southeastern Laurentian margin, southernmost Appalachians; implications for tectonic evolution

The highly allochthonous Talladega belt in the southernmost Appalachian orogen of Alabama and Georgia represents the most completely preserved outboard fragment of the early Paleozoic Laurentian continental margin in this part of the orogen. Palinspastic restoration indicates that this Alleghanian thrust sheet was originally located at or near this continental margin. The Talladega belt is within a structural recess (Alabama recess) in the orogen, which is interpreted to have originated as a continental promontory during the opening and initial closing of the Iapetus ocean. Because continental promontories protrude oceanward along a continental margin, any significant early deformation of this margin should be recorded within this thrust sheet. Regional geologic mapping has revealed a middle Paleozoic regional unconformity within this belt, and distortion of this unconformity by late Paleozoic regional folding provides for examination of subcrop geometries below the unconformity over a large area ( approximately 640 km (super 2) ). Retrodeformation of the late Paleozoic folds indicates that only very mild deformation predated the unconformity. The origin of this early deformation is unclear. Possibilities include very mild contractional deformation during the Taconic orogeny, or folding associated with wrench or extensional faulting during Silurian(?)-Devonian Acadian successor-basin formation. If the latter is the case, then no vestiges of Taconic deformation can be found in this outboard fragment of the margin, implying that a major continental promontory at the southwesternmost Laurentian margin may have escaped any significant effects of this orogeny.