Introduction 11
Nomenclature and classification of deep-sea relief 11
Units of depth and slope 12
Continent and ocean 16
Continental margin 17
Definition and general categories 17
General categories 17
Category I provinces 17
Category II provinces 18
Category III provinces 19
Regional description of continental margin 21
Benches and terraces of the continental margin 41
Geology and geophysics of continental-margin physiographic
provinces 51
Seismicity of the continental-margin provinces 51
Magnetic anomalies and continental-margin physiographic
provinces 51
Crustal structures and continental-margin provinces 52
Sediment distribution and physiographic provinces of the
continental margin 53
Past, present, and future of the continental-margin
provinces 53
Ocean-basin floor 55
General description 55
Abyssal plains 55
General discussion 55
Regional description 57
Abyssal hills 61
Definition and distribution 61
Regional description 63
Origin of abyssal-hills topography 65
Other major features of the abyssal floor 66
Abyssal gaps 66
Mid-ocean canyons 66
Regional description 66
Origin of abyssal-floor topography 74
Oceanic rises 74
Definition and distribution 74
Regional description 74
Seamounts of the ocean-basin floor 78
Seismicity of the ocean-basin floor 80
Ocean-basin floor provinces and crustal structure 80
Mid-oceanic ridges 83
Definition 83
Mid-Atlantic Ridge 83
Provinces of the Mid-Atlantic Ridge 84
General statement 84
Crest provinces 84
Flank provinces 95
Azores Plateau 97
Azores-Gibraltar Ridge 98
Atlantis-Plato-Cruiser-Great Meteor Seamount Chain 98
Geology and geophysics of Mid-Atlantic Ridge physiographic
provinces 98
Seismicity of the Mid-Atlantic Ridge 98
Sediments and physiographic provinces of the
Mid-Atlantic Ridge 99
Rocks of the Mid-Atlantic Ridge 99
Crustal structure of the Mid-Atlantic Ridge provinces 100
Origin of the Mid-Atlantic Ridge 103
Sub-bottom reflections recorded on PDR records and
physiographic provinces 05
Summary of province characteristics 107
BIBLIOGRAPHY 109
INDEX 115
ILLUSTRATIONS
PLATES
FOLLOWING
PLATE 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
PAGE
FIGURE
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
TABLE PAGE
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.
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.