CENOZOIC TECTONIC EVOLUTION OF SOUTHEASTERN NORTH AMERICA: EVIDENCE FOR PASSIVE MARGIN UPLIFT?

While more than a century old, the notion that southeastern North America records a history of tectonic uplift during Cenozoic time deserves renewed attention. Existing models of sedimentary basin evolution do not readily explain the onshore exposure of Late Cretaceous and Tertiary strata of the Atlantic Basin over a distance of >2000 km (from New Jersey to the Yucatan Peninsula). The absence of such similar stratigraphic sequences on the exposed Atlantic margins of South America, Africa, and Eurasia appear to preclude a simple explanation of lowering of global sea level on a passive (subsiding?) North American margin. Regional topographic anomalies such as the Blue Ridge Escarpment (an ~500 m step in topography, traceable for >1200 km along the Appalachians) and the Eastern U.S. drainage divide (that deviates considerably from the Appalachian topographic divide) likewise suggest a landscape that has been tectonically perturbed in Cenozoic time. A relatively thin stratigraphic cover over much of the Atlantic margin of North America, with numerous unconformities, may be as much a result of periodic tectonic uplift as of eustatic sea level variations during the Cenozoic. Abundant examples of structural deformation of the Coastal Plain section attest to a tectonic history on this passive margin that has yet to be understood within a geodynamic context. Widespread deposition of coarse clastic deposits (Upland unit and equivalents) along much of the Atlantic margin and Mississippi embayment may mark a critical tectonic period, although repeated episodic uplift cannot be ruled out. Any geodynamic explanation for these observations should honor the apparent amplitude (100's of m to km), wavelength (2000 km), and Cenozoic age of the uplift.