ILLUSTRATIONS

PLATES

PLATEFOLLOWING PAGE
1.Physiographic diagram: Atlantic Ocean, Sheet 1 (In separate tube)
2.Preliminary chart of Hudson Submarine Canyon[20]
3.Representative PDR records from continental rise of northeastern United States[32]
4.PDR records from continental slope and Blake Plateau[32]
5.PDR records from outer ridge east of the Blake Plateau and from the Blake-Bahama Abyssal Plain[32]
6.PDR record of outer ridge showing sub-bottom horizon[32]
7.Tracings of PDR records across continental slope and part of the Blake Plateau[36]
8.PDR records European continental rise and Biscay Abyssal Plain[38]
9.Representative PDR records of continental margin and abyssal floor southwest of Canary Islands[38]
10.PDR record of abyssal hills, southeast of Bermuda Rise[38]
11.Ocean bottom photographs of the continental margin and ocean basin floor[38]
12.PDR record of Biscay Abyssal Plain[52]
13.PDR records of Madeira Abyssal Plain and the Madeira Rise[52]
14.PDR records of Mid-Ocean Canyon No. 2 and canyons at Vema Gap[58]
15.Ocean-bottom photographs of seamounts[58]
16.Representative PDR records from Bermuda Rise[78]
17.PDR record, Bermuda Scarp Zone[78]
18.PDR record, Upper Step Mid-Atlantic Ridge[78]
19.Ocean-bottom photographs; Mid-Atlantic Ridge[78]
20.Physiographic provinces, Atlantic Ocean[122]
21.Control chart[122]
22.Six trans-Atlantic topographic profiles[122]
23.Index chart showing locations of profiles of Plates 24, 25, 26 and Figure 45[122]
24.Thirty-four profiles of the continental margin: western North Atlantic[122]
25.Twenty-three profiles of the continental margin of Europe and Africa[122]
26.Crustal structure and continental-margin provinces[122]
27.Five topographic profiles, western North Atlantic[122]
28.Distribution of deep-sea sands in relation to physiographic provinces[122]
29.Earthquake epicenters, North Atlantic[122]
30.Location of PDR records and bottom photographs reproduced as illustrations.[122]

FIGURES

FIGUREPAGE
1.Method of preparation of physiographic diagram[4]
2.Precision depth recorder (PDR) sounding lines obtained by research vessels[6]
3.Good, but nonprecision sounding lines obtained by research vessels[7]
4.Major basins of the North Atlantic, after Wüst (1940)[12]
5.Sound-velocity corrections for echo soundings[13]
6.Conversion diagram for degrees, per cent grade, feet per statute mile, and gradient[14]
7.Gradients from 1:5 to 1:8000 shown at 40:1 vertical exaggeration[15]
8.Outline of submarine topography[15]
9.Major morphologic divisions: North Atlantic Ocean[16]
10.Three categories of continental-margin provinces[17]
11.Two east-west profiles of Southeast Newfoundland Ridge[22]
12.Laurentian Channel[23]
13.Eastern Channel, Gulf of Maine[23]
14.Submarine canyons off the Scotian Shelf[24]
15.Continental-margin provinces: Type profile off northeastern United States[26]
16.Tracings of PDR records of continental and insular slopes[28]
17.Cross sections of Hudson Submarine Canyon[32]
18.Tracing of PDR record of Blake Escarpment[34]
19.Continental-margin provinces: Type profiles off northwest Africa[40]
20.Georges Bank canyons[44]
21.Two projected profiles of Georges Bank canyons[45]
22.Geologic section at Cape Hatteras, Virginia[46]
23.Correlation of structural benches off northeast United States[48]
24.Geologic section: Western Europe based on refraction measurements[49]
25.Index chart, location of abyssal hill profiles illustrated in Figures 26 and 27[62]
26.Eleven profiles, Abyssal Hills Province, western Atlantic[62]
27.Eight profiles, Abyssal Hills Province, eastern Atlantic[63]
28.Tracing of PDR record, abyssal hills, southeast of Bermuda Rise[64]
29.Northwest Atlantic Mid-Ocean Canyon[67]
30.Eight east-west profiles showing Northwest Atlantic Mid-Ocean Canyon[68]
31.Forty-eight cross sections of Northwest Atlantic Mid-Ocean Canyon[69]
32.Long profile of Northwest Atlantic Mid-Ocean Canyon[70]
33.Tracing of PDR record across Theta Gap[73]
34.Natural scale profile, Kelvin Seamounts[77]
35.Crustal sections in various physiographic provinces, determined by seismic-refraction measurements[81]
36.Index to natural-scale Mid-Atlantic Ridge profiles reproduced in Figures 37-41[84]
37.Natural-scale Mid-Atlantic Ridge profile 1A[85]
38.Natural-scale Mid-Atlantic Ridge profile 1B[86]
39.Natural-scale Mid-Atlantic Ridge profile 1C[87]
40.Natural-scale Mid-Atlantic Ridge profile 2A[88]
41.Natural-scale Mid-Atlantic Ridge profile 2B[89]
42.Type profile, provinces of the Mid-Atlantic Ridge[90]
43.Tracing of PDR record, Rift Valley, Rift Mountains, High Fractured Plateau, and Upper Step[91]
44.Tracing of PDR record, Western Rift Mountains[92]
45.Twenty-six rift valley profiles, Mid-Atlantic Ridge[93]
46.Five representative profiles, crest and western flank of Mid-Atlantic Ridge[94]
47.Axial profile of the Mid-Atlantic Ridge[96]
48.Profile of total magnetic intensity and topography, Mid-Atlantic Ridge[101]
49.Physiographic provinces and trans-Atlantic structure[102]

TABLES

TABLEPAGE
1.Characteristics of continental rise, northeastern United States[27]
2.Characteristics of continental rise, northwest Africa[41]
3.Depths of prominent continental-shelf terraces[42]

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.

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.