ABSTRACT

In the past several years, the new and far reaching hypothesis of crustal spreading has survived all critical tests and at present has almost earned the title of fact. The scientific community has accepted sea-floor spreading and continental drift as reality, thus ending nearly a half-century of debate. Magnetic anomaly data over the oceans has provided the kingpin quantitative analysis of large crustal movements on the surface of the earth. The geomagnetic pattern combined with seismic reflection and seismic refraction data from the continental margins permits a detailed insight into the evolution of the continental margin. Sedimentary patterns in the western North Atlantic depict a story of a widening Atlantic basin with time. During the Cretaceous, a strong thermohaline bottom current circulation pattern developed, creating and shaping the present thick sedimentary deposits of the marginal rises. The reconstruction of the evolution of the continental margins leaves us the inevitable conclusion that the present day Atlantic was once a small and confined basin similar to the present day Red Sea. The recent findings of metallic sulfides in the so-called Red Sea hot holes raised the distinct possibility that similar but fossil deposits underlie the rifted continental margins.

Potential hydrocarbon drilling sights as seen in the diapiric structures of the Gulf of Mexico and the Mediterranean Sea have raised the possibility that foundered shallow continental seas presently lie at oceanic depth. Similar such diapiric structures have been found in 2500 fathoms of water, in the open Atlantic northwest of the Cape Verde Islands, thus raising the possibility that the now oceanic continental rises of the Atlantic are foundered shallow epicontinental seas which existed in the proto- Atlantic Ocean in the Triassic times. If hydrocarbons or metallic sulfides do exist beneath the thick sedimentary wedges of the rifted continental margins, they represent long-term economic resources which may be tapped in future decades or by future generations.

In recent years exciting new data has been presented supporting the concept of sea-floor spreading, the age of prominent seismic reflected within the ocean floor and on ocean basin sedimentary processes. The combination of these findings perhaps permits on to look at the time dependency of sedimentary processes in a growing ocean basin. The concept of an ever widening oceanic basin as response to ridge growth, was first suggested by Heezen (1959) and later popularized in a more unified theory by Hess (1962) and Dietz (1961). Vine and Matthews (1963) and Pittman and Heirtzler (1966) have recently given strong support to the idea that the mid-ocean ridge is truly spreading away from its crest at rates of 1–6 cm per year. The ideas of continental drift (Wegener, 1922) have been bantered about in the geologic literature for several decades and only recently with the magnetic evidence and seismological evidence of sea-floor spreading concepts have these become somewhat accepted. Reconstruction of the pre drift and configuration of the continents around the Atlantic are shown to be quite good, if the ocean is closed by the 500 fathoms contour (Bullard, et al., 1965)

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