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Three Appalachian Orogenies: Their Influence on Sedimentation in the Southern-Central Appalachian Foreland Fold-Thrust Belt and Beyond

Robert D. Hatcher
University of Tennessee-Knoxville, Knoxville, TN

The southern and central Appalachian foreland records the effects of three orogenies in both the sedimentary and deformational record. The diachronous Taconian orogeny produced foredeep sedimentation during the Middle (southern) and Late (central) Ordovician, producing some 3 km of sediment in the south (Sevier-Paperville), and possibly 5 km in the central (Martinsburg) Appalachians. This event was probably related to loading of the outer margin by obducted arc volcanic rocks and ophiolites. Deformation effects in the foreland were minimal, except for dynamic loading producing the foredeep and a peripheral bulge farther into the continent.

The mid-Paleozoic Acadian (and Neoacadian) orogeny produced the Devonian Catskill delta, and Devonian shale, which propagated southwest from a source in New England. This and the Neoacadian (latest Devonian-early Mississippian) event are related to collision of the peri-Gondwanan Carolina-Avalon terrane. This event also produced folding and some faulting far into the southern Appalachian foreland that was truncated by the pre-Chattanooga Shale (latest Devonian-early Mississippian) unconformity. The Chattanooga Shale and overlying Mississippian clastic units form the clastic wedge of the Neoacadian orogeny.

The late Mississippian to Permian Alleghanian orogeny produced uplift in the internal parts of the Appalachian orogen that first spread sediment in a large late Mississippian to Early Permian delta complex from the Appalachian chain into the Midwest. The delta was then deformed as Africa collided with North America propagating thrust faults first into the crystalline crust, then into the foreland. Deposition continued farther west as the eastern foreland was being deformed. These events provide the structural and depositional framework within which the petroleum systems and hydrocarbon traps of the Appalachians developed.