DIACHRONOUS TECTONIC LOADING AND SYNOROGENIC CLASTIC WEDGES ALONG THE SOUTHERN APPALACHIAN-OUACHITA OROGEN

The late Paleozoic southern Appalachian-Ouachita orogen curves around the Alabama promontory and Ouachita embayment of the Iaptean rifted margin of southern Laurentia. Taconic and Acadian phases of the Appalachian orogen are not expressed west of the Alabama promontory, and a passive margin persisted around the Ouachita embayment. Diachronous late Paleozoic orogenic events overprinted the entire southern Laurentian margin, including accretion of terranes, tectonic loading of the continental margin, foreland subsidence, cratonward progradation of synorogenic clastic wedges, and propagation of foreland thrust belts.

Along the Ouachita orogen, synorogenic deposition began in Middle Mississippian (338 Ma) in a forearc basin or incipient trench at the leading edge of the Sabine continental terrane and continental-margin arc. In the eastern Ouachita embayment, tectonic loading, foreland subsidence of the Black Warrior basin, and northeastward progradation of a synorogenic clastic wedge onto Laurentian crust began in Late Mississippian (332 Ma), indicating collision of the Sabine terrane with the Alabama-Oklahoma transform margin. By Middle Pennsylvanian (313 Ma), westward migration of tectonic loading by emplacement of the accretionary prism of the Sabine forearc complex on the Laurentian margin resulted in foreland subsidence and clastic-wedge deposition in the Arkoma foreland basin.

Separate tectonic loading on the east side of the Alabama promontory and westward progradation of a synorogenic clastic wedge began in Middle Mississippian (340 Ma). Pennsylvanian clastic facies prograded farther west, merging with northeastward prograding Black Warrior clastic facies above a Mississippian carbonate shelf on the Alabama promontory.

Later foreland subsidence and northwestward progradation of a synorogenic clastic wedge began in middle Early Pennsylvanian (315 Ma) on the corner of the Alabama promontory, reflecting continent-continent collision of Laurentia with the Suwannee (Africa) terrane, and driving northwest-directed Appalachian thrusting. Northeast-striking Appalachian thrust faults imbricated the northeast-prograding clastic wedge in the Black Warrior (Ouachita) foreland basin and truncated northwest-striking Ouachita thrust faults along the southwest side of the basin.