STRAIN ANALYSIS ON THE BASAL CONTACT OF THE LAY DAM FORMATION, TALLADEGA BELT, ALABAMA

The Talladega belt (western Blue Ridge) of the southernmost Appalachian Mountains in Alabama and Georgia contains the most distal Paleozoic shelf facies strata of the Laurentian margin along the Alabama promontory. The belt consists mostly of lower greenschist facies metasedimentary rocks lying in the hanging wall of the Talladega-Cartersville fault, separating it from the underlying foreland fold and thrust belt, and in the footwall of the Hollins Line and Allatoona faults, separating it from the overlying Ashland-Wedowee belt (eastern Blue Ridge). The Lay Dam Formation, at the stratigraphic base of the Talladega Group, consists of metaturbidites, arkosic metaconglomerates, and metadiamictites. Diamictitic strata contain clasts from both the underlying Sylacauga Marble and Kahatchee Mountain Groups, as well as clasts of Grenville basement gneiss, and represents deep water sediments deposited along the Laurentian margin proximal to basement and cover uplifts. The contact between the Lay Dam and the Sylacauga Marble has been alternatively interpreted as a fault, a locally faulted unconformity, and an unconformity. Reports of sheath folds and S-C fabrics have led some workers to suggest that the basal contact of the Lay Dam is a fault accommodating tens of kilometers of displacement. However, our work along this contact in the region of Jumbo, Alabama, is not supportive of this interpretation. Strain analysis at the basal contact of the Lay Dam near Jumbo, including Rf/Φ analysis of a diamictite, suggests that deformation is more likely associated with regional metamorphism common to units above and below the contact and not faulting. As such, we argue that the contact between the Lay Dam Formation and underlying Sylacauga Marble Group is a locally sheared unconformity with minimal displacement associated with ductility contrasts, and has not accommodated the tens of kilometers of offset argued for by other workers. The nature of the basal Lay Dam contact is important in interpretations of the Paleozoic tectonic history of the southernmost Appalachians.