ABSTRACT

Northeastern Gulf Coast data reveal the right-lateral fault zone along which Paleozoic North America (NA) moved southeast (present directions) alongside the northeastern edge of future South America (SA), to where incomplete subduction beneath a broad forearc basin on SA's leading edge converted the sedimentary fill of an extensive embayment within eastern-southern NA into the Ouachita thrust belt. Throughout all this, SA was firmly joined to future Africa on the northeast to form the western part of the nearly immobile Gondwana element of the Pangean supercontinent. On the southeastern (Alabama) promontory east of this lateral fault zone the Appalachian thrusts were driven by a similar African forearc basin, which became completely obducted onto NA as suturing of the contiguous Suwannee terrane shut down the orogeny. These convergent relationships left no space between the American continents for the conventional remnant ocean or microcontinents, although the relict forearc basin south of the Ouachitas did continue to accumulate mostly shallow marine sediments into Late Permian time.

By Late Triassic, however, crustal extension somewhat south of the Ouachita Mountains was forming the series of Interior rift (or salt dome) basins, at both ends of which new wrench faults striking slightly east-of-north transferred the extension southward to the DeSoto Canyon and South Texas rift (or salt dome) basins. The basement of the Wiggins arch south of the eastern (Mississippi) Interior rift basin was originally part of the SA craton south of the forearc basin, presumably associated with a volcanic arc. It was left with NA when, after about 60 miles (95 km) of extension, the rifting "jumped" southward across it and other outer basement highs to begin opening the deep Gulf of Mexico basin.

The east-of-north strike of the Late Triassic wrench faults suggests that this crustal extension was caused by right-lateral translation of North America around the bulge of northwestern Africa. About 400 miles (650 km) of this places Cape Hatteras against Africa's Cape Blanc, in the partly-open Gulf configuration from which the magnetic data in the Central North Atlantic Ocean indicate that drifting began in Middle Jurassic time. The reality of this translation is confirmed by widespread Late Triassic rifting in western North Africa and between it, NA and future Europe; the latter was still loosely attached to northern NA and so separated simultaneously from North Africa as the Gulf of Mexico opened. This enabled the Tethys sea to advance southward along the proto-Atlantic rifts as far as Cape Hatteras, leading to deposition of voluminous Late Triassic "red beds" and evaporites in these rifts.