In the past few years, new geologic and geophysical data from the continental margin and the ocean-basin floor have permitted a more detailed reconstruction of the evolution of the continental margin off the east coast of the United States. Application of the Vine-Mathews hypothesis of sea-floor spreading suggests that continental rifting in the North Atlantic began in Late Triassic or Jurassic time. Triassic redbeds of the Newark Series may represent the stage of rifting presently seen in the African Rift Valley. The continental block or coastal plain has prograded slowly seaward (15 km during Tertiary time) and its surface has subsided slowly (5 cm/1,000 years) but remained near sea level during Cretaceous-Tertiary time.

Seismic reflection profiles, bottom morphology studies, long sediment cores (more than 300), and bottom photographs (350 stations) demonstrate that southerly flowing deep-ocean currents have constructed and shaped the large margin sedimentary wedges of the continental rise and outer ridges. This southerly flowing North Atlantic deep water is--and has been--eroding, transporting, and depositing sediment parallel with the regional contours. The present sediment surface of the lower continental rise (0-10 m) is marked by a distinct sedimentary facies of current-produced alternating thin silt laminations with hemipelagic lutites.

Seismic reflectors horizon A (Upper Cretaceous) can be traced beneath the large (1-2-km thick) sedimentary wedge of the Blake-Bahama outer ridge and also beneath the continental rise on the north, and shows that these features have been lapped adjacent to the continental block in post-Cretaceous time. The initiation of this unique sedimentary process can be linked to the growth of a strong pattern of thermohaline circulation in the North Atlantic with the widening of a growing North Atlantic basin during the Cenozoic.

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