AGE OF THE LAY DAM FORMATION, TALLADEGA BELT, SOUTHERNMOST APPALACHIANS: STRATIGRAPHIC AND STRUCTURAL CONSTRAINTS

The age and origin of the Lay Dam Formation in the Alabama-Georgia Talladega belt of the southernmost Appalachians has been a source of debate. The lowermost unit of the Talladega Group, the Lay Dam Formation consists of >2 km of metamorphosed turbidites, arkosic conglomerates, and diamictites. Diamictites contain clasts derived from both the underlying Cambrian-Ordovician Sylacauga Marble and older Kahatchee Mountain Groups, in addition to granite and granitic gneiss derived from Grenville basement, and probably represent sediment deposited in the proximal portions of a submarine fan derived from uplifts to the south-southeast. Many workers have interpreted the Lay Dam as having been deposited unconformably above the underlying Sylacauga Marble and Kahatchee Mountain strata and in conformable stratigraphic contact with overlying Devonian to lowermost Missippian(?) shelf strata of the upper Talladega Group, assigning it a Silurian to Early Devonian age. Other workers, however, have suggested the Lay Dam represents Ocoee equivalent Neoproterozoic rift basin deposits which have been tectonically emplaced along a thrust fault atop younger strata of the Sylacauga Marble and Kahatchee Mountain Groups. These alternate interpretations are based, in part, on the relationship between the Lay Dam and a number of granitoid bodies in the northeastern segment of the Talladega belt (northwest Georgia) as well as structural interpretations from the basal Lay Dam contact and lithologic comparisons in the southwestern segment of the Talladega belt (Alabama). We present a comprehensive analysis of the stratigraphic and structural constraints on the age of the Lay Dam and argue that the bulk of geologic data does not support this alternate interpretation. Both the age and tectonic setting of the Lay Dam Formation are key to understanding the Paleozoic history of this portion of the Laurentian margin.