Southern Appalachian Laurentian margin initial drift-facies sequences: Implications for margin evolution

Abstract

In the Appalachian orogen, the Neoproterozoic(?)–Lower Cambrian Chilhowee Group represents the initial drift-facies deposits along and across the eastern Laurentian continental margin following rifting. In the Southern Appalachians, this group forms thrust sheets along the west flank of the Talladega–Blue Ridge belt. Where the base is unfaulted, it lies depositionally above Ocoee Supergroup rift-facies rocks or Grenville basement. Regionally, the Chilhowee grades up into the Lower Cambrian Shady Dolomite, the initial deposits of the marginwide Cambrian–Ordovician carbonate bank. Sequences more interior to the orogen, including the Kahatchee Mountain Group (Talladega belt), the Nantahala and Brasstown Formations (western Blue Ridge), and the Hollis Quartzite (Pine Mountain belt), are considered to be correlative with the Chilhowee based upon similarities in lithostratigraphic sequence, sequence stratigraphy, sandstone provenance, and paleocurrent studies. Assuming an autochthonous Pine Mountain window, palinspastic restorations of foreland thrusts suggest that the Chilhowee Group restores essentially astride that window, and Chilhowee-equivalent units in the Talladega–Blue Ridge belts, in turn, restore farther southeast. This places the respective sequences southeastward in the order of increasing thickness and depth to basement from the base of the carbonate bank facies, with units restored farthest southeast having the most distal marine characteristics. Retro-deformation of thrust belt structures and the Pine Mountain cover sequence restores the Kahatchee Mountain Group at least to the subsurface position of the Wiggins-Suwannee suture, the southeastern limit of Laurentian continental crust, indicating that this group's basement was subducted beneath Gondwanan or peri-Gondwanan crust, and that the basement of even more outboard Laurentian sequences (e.g., eastern Blue Ridge) was overridden even farther.