TERRANE ACCRETION AND TECTONIC HISTORY OF THE SOUTHERN MARGIN OF LAURENTIA

Along the Iapetan rifted margin of Laurentia, from Ordovician into Permian, tectonic accretion drove thrusting, foreland subsidence, and clastic-wedge progradation of the Appalachian-Ouachita orogen. Foreland subsidence and clastic-wedge deposition accompanied diachronous Taconic (Ordovician–Silurian) arc accretion along the eastern margin of Laurentia between Newfoundland and the Alabama promontory. A passive margin persisted west of the Alabama promontory, from which a Taconic oceanic arc probably extended SW. An Acadian (Devonian–Mississippian) clastic wedge migrated SW, accompanying dextral transpression, terrane accretion, and pull-apart basins, a scenario that continued to Permian N of the New York promontory.

Multiple Gondwanan terranes were accreted during the Alleghanian-Ouachita orogeny along the Iapetan rifted margin that had been modified by Taconic and Acadian accretion from the Alabama promontory northward. The Suwannee terrane was accreted by dextral transpression at the Suwannee suture zone, which cuts across the Carolinia terrane and W onto Grenville-age crust on the corner of the Alabama promontory. Accretion of the Sabine terrane and arc-forearc complex onto the passive margin in the Ouachita embayment began in Mississippian; accretion of the Coahuila terrane in the Marathon embayment began earlier in the Mississippian. On the SW side of the Alabama promontory, a SW-thickening, NE-prograding Mississippian–Pennsylvanian clastic wedge fills the Black Warrior foreland basin, which dips SW beneath the NW-striking Ouachita thrust front. The clastic wedge interfingers with two SW-thinning and deepening Mississippian carbonate ramps; Pennsylvanian clastic facies prograde NE over the carbonate facies. The same facies patterns prevail in the Appalachian thrust belt, indicating the extent of the greater Black Warrior (Ouachita) foreland basin. Subsequent Appalachian NW-directed thrusting, associated with accretion of the Suwannee terrane, imbricated the Ouachita clastic wedge and truncated the NW-striking Ouachita thrust front. Farther NE in the Tennessee embayment, a Mississippian–Pennsylvanian W-prograding clastic wedge merges with the Black Warrior clastic wedge above the youngest part of the Mississippian carbonate bank.