ANALYSIS OF A REGIONAL MIDDLE PALEOZOIC UNCONFORMITY ALONG THE DISTALSOUTHEASTERN LAURENTIAN MARGIN, SOUTHERNMOST APPALACHIANS - IMPLICATIONS FOR TECTONIC EVOLUTION

The highly allochthonous Talladega belt in the southernmost Appalachia n orogen of Alabama and Georgia represents the most completely preserv ed outboard fragment of the early Paleozoic Laurentian continental mar gin in this part of the orogen. Palinspastic restoration indicates tha t 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 originate d as a continental promontory during the opening and initial closing o f the Iapetus ocean. Because continental promontories protrude oceanwa rd along a continental margin, any significant early deformation of th is margin should be recorded within this thrust sheet. Regional geolog ic mapping has revealed a middle Paleozoic regional unconformity withi n this belt, and distortion of this unconformity by late Paleozoic reg ional folding provides for examination of subcrop geometries below the unconformity over a large area (similar to 640 km(2)). Retrodeformati on of the late Paleozoic folds indicates that only very mild deformati on predated the unconformity. The origin of this early deformation is unclear. Possibilities include very mild contractional deformation dur ing the Taconic orogeny, or folding associated,vith wrench or extensio nal faulting during Silurian(?)-Devonian Acadian successor-basin forma tion. If the latter is the case, then no vestiges of Taconic deformati on can be found in this outboard fragment of the margin, implying that a major continental promontory at the southwesternmost Laurentian mar gin may have escaped any significant effects of this orogeny.