TIMING OF EVENTS IN THE EASTERN OUACHITA OROGEN

Ouachita allochthons of Cambrian–Mississippian off-shelf passive-margin facies and Mississippian–Pennsylvanian synorogenic turbidites overlie a Cambrian–Mississippian passive-margin carbonate shelf along the Alabama-Oklahoma transform fault at the Iapetan margin of Laurentian continental crust. Tectonic loading drove Atokan subsidence of the Arkoma foreland basin, into which the Ouachita frontal thrust belt propagated. The Maumelle chaotic zone and Benton central uplift form an accretionary prism at the leading edge of an arc complex, including the southern Ouachita thrust belt within a forearc basin. Farther south, post-orogenic strata of the Mesozoic–Cenozoic Gulf Coastal Plain cover the arc complex. A thick forearc-basin deposit fills a remnant ocean basin between the transform margin of Laurentian crust and the accreted Sabine microcontinental terrane, which includes a continental-margin arc. Within the forearc basin, seismic reflection clearly images an angular unconformity; data from drill holes document deformed Atokan and older Ouachita turbidites overlain by shallow-marine Desmoinesian–Guadalupian strata in a successor basin, marking the end of contractional deformation in the Ouachita internides. In the exposed Ouachita foreland, the youngest strata involved in contractional deformation are middle Desmoinesian.

The Ouachita thrust belt plunges eastward in central Arkansas beneath the Gulf Coastal Plain. Data from deep drill holes and seismic reflection show that the frontal thrust belt and Benton central uplift strike eastward and curve to southeastward in Mississippi. Beneath the Gulf Coastal Plain in eastern Mississippi, the west-striking Appalachian frontal thrust fault truncates the southeast-striking Ouachita structures, indicating that Appalachian thrusting post-dated Ouachita thrusting. Northeast-striking Appalachian thrust faults in Alabama also imbricated the southeastern part of the greater Black Warrior basin in the foreland of the southeast-striking Ouachita thrust belt, where foreland subsidence and clastic-wedge deposition began in Late Mississippian. The time of Appalachian thrusting is indicated also by metamorphic cooling ages of ~300 Ma in the leading part of the Suwannee suture, coincident with accretion of the Suwannee terrane.