Pre-drift reconstructions of the Atlantic place the continental margin off the middle Atlantic region of the United States against the continental margin off northwest Africa. An implication of this reconstruction is that the opposing continental margins would be mirror images if the two margins formerly had been joined and then had separated and had undergone parallel development. Relevant sections of the outer continental shelf, continental slope, continental rise, and abyssal plain off northwest Africa between Point Durnford, the Spanish Sahara, and Cape Timiris, Mauritania, and off Cape Hatteras, United States, were investigated with continuous seismic reflection (air gun), magnetic, and bathymetric profiles.

Geophysical data and regional geology from the two continental margins disclose some similarity in their stratigraphic framework. Mesozoic through Cenozoic coastal-plain strata dip seaward at low inclinations (<5°) under much of the continental shelf of both continents. Paleozoic-Precambrian crystalline rocks are exposed along the landward margin of the coastal plain and apparently incline seaward as basement

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beneath the coastal-plain strata. The continental rises are formed by a seaward-thinning wedge of sedimentary strata inclined nearly parallel with the sediment-water interface (<1°).

However, development of the two continental margins differs. Sedimentary strata of the northwest African margin are deformed by intrusive bodies and by structures which resemble horsts and grabens. An extensive offshore Triassic and/or Aptian salt-dome province extends from Morocco to Senegal. The eastern Canary Islands and the Cape Verde Islands are a strongly folded Jurassic through Eocene fold belt. Sedimentary strata of the Hatteras margin, in contrast, are relatively undeformed except for structures which can be explained by massive rotational slumping and gravitational gliding. The sedimentary strata of neither continental slope nor rise show the effects of compressive stresses expected in models of sea-floor spreading by convection currents that turn downward at the continental margins.

Thus, the opposing continental margins investigated are not mirror images as might be expected if the two margins had been joined and then had separated and had undergone parallel development. Although much of the stratigraphic framework of the two continental margins appears to be similar, their development differs.

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