The Floors of the Oceans

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Abstract
The Physiographic Diagram: Atlantic Ocean, Sheet 1, which portrays the North Atlantic between 17° and 50° North Latitude, is the first of a projected series of diagrams. The diagram is based on continuous echo-sounding traverses made by research vessels. The relief shown on the profiles was sketched in perspective using the technique introduced by Lobeck. Between sounding profiles the relief is speculative, based on extrapolation of trends noted in the profiles. The area of the diagram is divided into three major physiographic regions which are in turn subdivided into the following categories of provinces. CONTINENTAL MARGIN Category I Continental Shelf Epicontinental Seas Marginal Plateaus Category II Continental Slope Marginal Escarpments Landward Slopes of Trenches Category III Continental Rise Marginal Trench–Outer Ridge Complex Marginal Basin–Outer Ridge Complex OCEAN BASIN FLOOR Abyssal Floor Abyssal Plains Abyssal Hills Abyssal Gaps and Mid-Ocean Canyons Oceanic Rises Seamount Groups MID-OCEANIC RIDGE Crest Provinces Rift Valley Rift Mountains High Fractured Plateau Flank Provinces Upper Step Middle Step Lower Step Each province is defined, briefly described, and illustrated with profiles and photographs of echo-sounding records. The boundaries of the physiographic provinces, defined solely by bottom topography, show good correlation with variations in crustal structure as determined by seismic-refraction measurements and with anomalies of the gravity and magnetic fields. In addition, the province boundaries correlate well with distribution patterns of bottom sediments. The physiographic provinces are thus really morpho-tectonic provinces. The precise correlation of topographic provinces and structure observed in specific sections can thus be extrapolated along province boundaries to deduce the geology in large areas where no geophysical work has been done. The tectonic map of the Atlantic prepared in this manner will be presented in a subsequent publication.

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