Atlantic Continental Shelf and Slope 

of the United States 

Geologic Background 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 529·A 

Atlantic Continental 

Shelf and Slope of 

The United States 

Geologic Background 

By K. 0. EMERY 

GEOLOGICAL SU.RVEY PROFESSIONAL PAPER 529-A 

A background discussion for a comprehensive 

investigation of the marine geology and associated 

hydrology of the Atlantic continental margin 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1966 
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress catalog-card No. 79-604860 

First printing 1966 

Second printing 1967 

Third printing 1972 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 - Price 30 cents (paper cover) 
CONTENTS 

Page 

Abstract___________________________________________________________________________________ A1 

Introduction_______________________________________________________________________________ 1 

General program________________________________________________________________________ 1 

Acknowledgmen~----------------------------------------------------------------------- 4 

Topography________________________________________________________________________________ 6 

Sedimentology______________________________________________________________________________ 9 

Lithology__________________________________________________________________________________ 12 

Structure__________________________________________________________________________________ 13 

Water and biology__________________________________________________________________________ 17 

~ethods of studY--------------------------~------------------------------------------------ 19 

References cited_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 21 

ILLUSTRATIONS 

Page 

FIGURE 1. Distribution of the wider continental shelves of the world and the comparative level of geological knowledge_----- A2 

2. Schematic diagram showing the sources of contributions to geological knowledge of the continental margins of 

theworld_________________________________________________________________________________________ 3 

3. Area of investigation in the joint U.S. Geological Survey-Woods Hole Oceanographic Institution program------ 5 

4. Part of world map made by Diego Ribero in 1529-------------------------------------------------------- 7 

5. Photographs of TIRCS television transmissions showing sections of the Atlantic coast ________ ---------------- 8 

6. Sedimen~ off the Atlantic coast of the United States classified by texture, contributing agent, and age_________ 11 

7. Generalized preliminary geologic map of continental shelf and slope _______________ ------------------------- 14 

8. Axes of trenches off the Atlantic coast_ _______________________ ------------------------------------------ 15 

9. Structural section inferred from seismic data for continental shelf, slope, and rise south of Massachuset~- _ _ _ _ _ _ _ 16 

10. Isotherms and isohalines of winter and summer seasons for surface waters off the Atlantic coast __ - ------------- 18 

11. The research vessel Gosnold _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 20 

12. Schematic distribution of ship time and of laboratory time________________________________________________ 21 

III 

THE ATLANTIC CONTINENTAL SHELF AND SLOPE OF THE UNITED STATES 

GEOLOGIC BACKGROUND 1 

By K. 0. EMERY 

ABSTRACT 

This report is the first of a series that describe the geological, 

biological, and hydrological characteristics and the geological 

history of the continental shelf, slope, and rise o:I:Y the Atlantic 

coast of the United States. The reports are the result of a 

5-year program that is being conducted jointly by the U.S. 

Geological Survey and the Woods Hole Oceanographic Institution with extensive collruboration of the U.S. Bureau of Commercial Fisheries and other organizations. The geological work 

consists of field and laboratory investigations of topography, 

sediments, rocks, and structure. Mineralogy, paleontology, 

geochemistry, and economic geology are iududed. Oomplemelllting- the geological work are studies of biology (the d·~stribution 

and nature of pelagic anu benthic organisms) and hydrology 

(the contribution to the ocean of fresh water by stream runo:I:Y 

and the processes by which this water becomes mixed with 

oceanic water) . 

Topographic charts constructed during the program reveal 

deep irregular topography in the Gulf of Maine and o:I:Y Nova 

Scotia produced by glacial erosion and deposition. On the continental shelf most irregularities, such as terraces and sand 

waves, are formed by marine processes. In deeper water, 

submarine canyons, aprons superimposed upon the continental 

rise, and broad flat abyssal plains are caused or influenced by 

turbidity currents. Structural deformation is shown on the 

topographic charts by prominent bends of the continental slope. 

A suite of well-distributed l·arge bottom samples disclO'SeS a 

broad belt of coarse-grained relict sediment deposited during 

the transgression of the ocean across the shelf during postglacial time. These sediments were contributed to the ocean 

by streams that carried glacial melt water in the north, or 

drained areas of weathered rock in the central and southern 

parts of the region. Modern coarse-grained detrital sediments 

are restricted to the nearshore zone, but modern fine-grained 

sediments largely blanket the deep Gulf of Maine and the still 

deeper continental slope and rise. Modern calcareous biogenic 

sediments dominate at the south on the continental shelf, on 

the Blake Plateau, and at greater depths. 

Dredge and other samples from the ocean bottom show that 

the unconsolidated Pleistocene and Recent sediments overlie 

strata of Pliocene and Miocene age on most of the continental 

shelf. In areas of deeper water are discontinuous outcrops of 

rocks that are as old as middle Cretaceous on the continental 

slope and as old as Paleozoic in the Gulf of Maine. 

Continuous seismic profiles reveal that the Pleistocene and 

Recent .sediments are 10-60 meters thick throughout most of 

the shelf and that they unconformably overlie the older strata. 

Several reflecting horizons within the sediments indicate interruptions in deposition, possibly during times of glacially lowered 

sea level. The profiles also show local downwarping of Pliocene and Miocene strata at the top of the continental slope, 

a possible result of downwarping. Earlier and greater tectonic 

activity is indicated by structural trenches in the vicinity of 

the continental slope, those at the north being filled to over1 Contribution No. 1772 of the Woods Hole Oceanographic Institution. 

Based on work done under a program ronducted jointly by the U.S. 

Geological Survey and the Woods Hole Oceanographic Institutwn and 

financed by the U.S. Geological Survey. 

flowing with Cretaceous and later sedimentary strata and those 

at the south being incompletely filled. Clearly, the topography, 

sedimentology, lithology, and structure are closely interrelated 

and cannot be completely isolated one from the other. 

INTRODUCTION 

GENERAL PROGRAM 

In September 1962 the U.S. Geological Survey and 

the Woods Hole Oceanographic Institution began a 5-

year joint program to study the marine geology 

of the continental margin off the Atlantic coast of the 

United States. The Survey provides the financial support for the work, and the two organizations provide an 

approximately equal number of personnel for field and 

laboratory work. Several laboratories of the U.S. Bureau of Commercial Fisheries are also cooperating. 

The geological work consists of field and laboratory 

investigations of topography, sedimentology, lithology, 

and structure. Mineralogy, paleontology, geochemistry, and economic geology are included among the geological investigations. Complementing the geology are 

studies of biology and hydrology. 

This is the first comprehensive study of marine geology organized for the continental margin of such a 

large region. Studies by many individuals encompassed most aspects of marine geology off southern California (Emery, 1960), but the work was random and 

distributed throughout a long period, about 25 years 

for the most intense phase. A more direct and specifically organized study was conducted for the continental shelf of part of the Gulf of Mexico as a project 

of the American Petroleum Institute (Shepard, Phleger, and van Andel, 1960); however, the work was 

largely restricted to Recent sediments and associated 

biology. European and Asiatic studies of the continental shelf and slope are somewhat like those of southern 

California; the studies have been random and performed over a long period of time by many workers. 

The European studies are also limited by national boundaries. The varying intensity of effort has resulted in 

uneven knowledge of the marine geology of the continental shelves and slopes of the world. As indicated 

by figure 1, the best known (but not well known) continental shelves are those that border the most industrialized countries. Less is known about the adjacent 

continental slopes and still less about the continental 

rises that are farther sea ward and deeper. 

Al 
D Poorly known 

~Moderately known 

.Best known 

FIGURE I.-Distribution of the wider continental shelves of the world and the comparative level of geological knowledge of them prior to 1962. Shelves 

indicated as poorly known have little other than general topographic information; those listed as better known have some additional information on 

sediments, on lithology, or on structure; those which are indicated as best known have some data in all four fields. 

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GEOLOGIC BACKGROUND A3 

A subjective breakdown of the sources of interest and 

effort that have produced data about the continental 

shelves and slopes of the world is given in figure 2. 

Probably the first need for knowledge about the continental shelf was for navigation in the Mediterranean 

Sea. For example, 2,400 years ago Herodotus mentioned that on approaching Egypt by ship sailors found 

mud bottom at a depth of 20 meters, about one day's 

sailing from shore. About 100 years ago, charting of 

the shelves reached a peak in lead line sounding, and a 

few decades ago other large advances resulted from 

application of electronics to echo sounding and precise 

positioning. General scientific studies of the continental shelves and slopes to learn the nature and distribu-

~,ion of marine plants and animals, the geological composition of the bottom, and the interrela:tionships of 

topography and water movements greatly increased 

wbout the time of the Challenger Expedition during the 

1870's. Since then the studies have continued mostly in 

universities. During World War II, much information 

was obtained about the surfaces of continental shelves 

owing to military requirements for predicting the beNAVIGATION 

NATURAL 

SCIENCE 

MILITARY 

INDUSTRY 

Fishing 

havior of sound during searches for submarines, for 

designing minefields, and for planning amphrbious 

operations. Some of the findings were published shortly after the war, but most of them remained unpublished in the interest of military security. In recent years 

military investigations have largely been confined to 

the deep-sea floor. 

A fourth field which has contributed to knowledge 

of the continental shelves is industry. Fishermen long 

ago recognized the ecological dependence of edible fish 

and mollusks upon bottom materials. The petroleum 

industry turned toward active exploration of the shelves 

only a little more than 15 years ago as the demand for 

oil increased. Probably the knowledge of stratigraphy 

and structure of the shelf that the petroleum industry 

gained during these years exceeds the gains from all 

other sources, but publication of results has been limited 

by proprietary considerations. From all sources, published knowledge (upon which future substantial advances depend) is presently at its highest level, and the 

number of full-time professional and semiprofessional 

investigators is greater than ever before. Nevertheless, 

.. · .. ·.· .......... ··.·· ....... · ··· .... ; .. '• . ·.·: ..... · ... • ... ~--·: ..... · ............... . 

10,000 1000 100 10 

YEARS BEFORE PRESENT 

FIGURE 2.-Sources of contributions to geological knowledge of the continent,al margins of the world by those 

whose main interests are navigation, natural science, military, and industry. Dashed lines represent 

estimates of unpublished knowledge. 
A4 .Aa'LANTIC CONTINENTAL SHELF AN[) SLOPE OF THE UNITEJ> STATES 

many gaps remain: What was the origin and geological 

history of the present continental, shelves and slopes~ 

Did similar features exist during early geological 

times·~ How uniformly do the strata from the adjacent 

land area extend sea ward under the shelves~ 

The Atlantic continental margin was chosen as the 

site for concentrated effort of the Geological SurveyWoods Hole Oceanographic Institution program for 

many reasons. The region is important because it borders the most densely populated part of the country 

and thus is an area of considerable fishing and shipping 

activity. Nearness to markets also should promote active exploitation of any mineral resources that may be 

discovered or e~lored, such as petroleum, sand and 

gravel, phosphate, and manganese oxide. Many geological studies have been made of the adjacent land by 

government, industry, and university geologists whose 

results can be extrapolated sea ward to aid in the interpretation of new marine data; in turn, the measurement of phenomena in the existing marine environment 

can be used to interpret depositional conditions of ancient sedimentary strata now on land. Many geologic,al 

studies have been made in this marine region, even more 

than 100 years ago, but most of these studies were based 

upon methods, now Obsolete, and most involved only 

small areas. A reconnaissance of the entire region will 

provide a general framework of knowledge into which 

the results of past and future detailed studies can be 

examined in proper perspective. Once the distribution 

of properties and the general geological history of the 

region is known, studies of processes will be easier to 

make and to evaluate. The increased attention being 

given to oceanography doubtlessly will result in the 

planning and making of many detailed studies during 

the future. As a matter of fact, one of the difficulties 

experienced throughout this general program was the 

temptation to divert 'too much effort into investigating 

interesting details, many of which can be solved by individuals or small groups having limited resources. 

The area of this investigation (fig. 3), occupies a 

coastal belt about 2,500 kilometers long. Nearest shore 

is the continental shelf, which ranges in width from less 

than 1 kilometer off Florida to more than 420 kilometers 

off Maine; it averages about 135 kilometers. The total 

area is 420,000 square kilometers, of which one-fourth 

is within the Gulf of Maine north of Georges Bank. 

Adjojning the continental shelf off Florida is the Blake 

Plateau, an art!R of about 180,000 square kilometers. 

Ordinarily the continental slope borders the continental shelf, but off Florida it lies seaward of the Blake 

Plateau and is termed the "Blake Escarpment." Considered together, the continental slope and the Blake 

Escarpment have an average width of 30 kilometers and 

an area of about 62,000 square kilometers. The total 

area of all the sea floor from shore to the base of the continental slope is about 662,000 square kilometers, about 

the same as the area of all 13 States northeast of North 

Carolina. Seaward of the Blake Escarpment is an irregular area containing the Blake Ridge; it extends to 

the 5,000-meter contour and encloses about 207,000 

square kilometers. Elsewhere, the continental slope is 

boarded by the continental rise, a broad gently sloping 

plain which has a width as great as 500 kilometers and 

an area of nearly 700,000 square kilometers. Still farther seaward, the continental rise grades into a broad 

flat abyssal plain. Of necessity, the program of study 

is focused mostly upon the continental shelf with progressively less concentration on the continental slope, 

the Blake Plateau, and the continental rise and its ~ssociated abyssal plain. 

Marine geology, the central field to he investigated 

in this program, consists of ·four main and closely interrelated subfields: topography, sedimentology, lithology, 

and structure. Know ledge of each subfield is necessary 

for an understanding of the origin df major features 

of the sea floor such as the continental shelf and slope 

and even for an understanding of many ·minor features. 

No longer can we say, as did Shepard in 1928 (p. 1157), 

"Coastal charts afford almost the only means by which 

we can study continental shelves." 

The term "topography" includes both shoreline and 

ocean bottom configuration. By sedime~tology is 

meant, broadly, the nature and origins of unconsolidated materials ranging from boulders through clay 

sizes, whether of detrital, biogenic, authigenic, or other 

origins, and their contents of living organisms as well as 

dead or fossil remains. Lithology refers to the description of the consolidated rocks whether of sedimentary, 

igneous, or metamorphic origin and regardless of their 

age. Structure describes the attitude of the rocks with 

respect to each other and to overlying sediments, 

whether massive, bedded, folded, or faulted. 

ACKNOWLEDGMENTS 

The writer is indebted to the members df the staff 

assigned to this program of marine geology for information and discussion of the results of their work on 

different aspects of the program. One or two years of 

fi~ld and laboratory work was completed prior to the 

end of 1964 by the following: Elazar Uchupi, Woods 

Hole Oceanographic Institution, topowaphy and structure; R. M. Pratt, Woods Hole Oceanographic Institution, deep-sea topography and sediments; John Schlee, 

U.S. Geological Survey, sediment texture and stratigraphy; Jobst H iUsemann, Woods Hole Oceanographic 

Institution, orgltnic analyses df sediments; J. C. Hath-
GEOLOGIC BACKGROUND 

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SEAMOUNT CHAIN 

BERMUDA 

RISE 

PLATEAU 

PLAIN 

0 250 500 KILOMETERS 

FIGURE 3.-Area of inve~tigation in the joint U.S. Geological SurvPy-Woods Hole Oceanographic Institution 

program. 

A5 
A6 AoTLA.NTIC CONTINENTAL SIHE·LF AND SLOPE OF THE UNITEiD STATES 

away, U.S. Geological Survey, minera;logy; James 

V. A. Trumbull, U.S. Geological Survey, sand fractions 

of sediments; R. K. Paul, Woods Hole Oceanographic 

Institution, •and A. R. Tagg, U.S. Geological :Survey, 

continuous seismic profiling; R. H. Meade, U.S. Geological Survey, hydrology; F. T. Manheim, U.S. Geological ·Survey, geochemistry; T. G. Gibson, U.S. 

Geological Survey, Foraminifera; and J. E. H·azel, U.S. 

Geological Survey, Ostracoda. Appreciation is also due 

cooperating investigators of benthic biology of the U.S. 

Bureau of Commercial Fisheries, R. W. Wigley (Woods 

Hole, Mass.), 'and A. S. Merrill (Oxford, Md.) . 

TOPOGRAPHY 

The earliest records of marine geology along the Atlantic coast are the sagas of the Vikings, A.D. 1000-1006 

(Th6rdarson, 1930), which contain cryptic references 

to coastal forms and shore materials of Newfoundland 

and perhaps of Nova Scotia and the Gulf of Maine. 

Five centuries later, Columbus' four cruises, 1492-1504 

(Morison, 1942) provided coastal charts much farther 

south, in the Caribbean Sea, and initiated a great period 

of discovery. One of the first charts of the entire Atlantic coast of the United States was d~awn by Diego 

Ribero in 1529, from information largely obtained during a cruise of Estevan Gomez between Newfoundland 

and Cuba in 1524-1525. The map (fig. 4) contains 

many identifiable coastal features ·and even depicts the 

Gulf Stream, which had been discovered earlier by 

Ponce de Leon (Stommel, 19'58, p. 1-2). 

Continued exploration during the following three 

centuries contributed many details of coastal configuration, but the best charts were still inadequate for the 

growing shipping and fishing industries, and .they led 

to many shipwrecks. Consequently, in 1807 Congress 

established the "Survey of the Coast" under the direction of Ferdinand Hassler (Roberts, 1957). In 1878 

the name of the organization was changed to the Coast 

and Geodetic Survey, whose function in marine surveying until about 1960 was largely confined to waters bordering the United States and its territories. A parallel 

charting organization within 'the U.S. Navy was established in 1830 as the "Depot of Charts and Instruments" 

under the direotion of Lt. Charles Wilkes. In 1842, 

command of the depot was assigned to Lt. Matthew 

Maury, who greatly expanded its functions so that in 

1866 it became the Navy Hydrographic Office (now the 

U.S. Naval Oceanographic Office). This office chiefly 

charts deep waters and foreign coasts. Using precise 

triangulation, each organization prodnced charts of the 

shorelines as early as 1816. Aerial photography has 

accelerated and improved chart making. Still further 

gains are indicated through the future use of satellites, 

which presently provide instructive but coarse-lined 

television pictures of the earth's surface (fig. 5) ; these 

pictures duplicate in a few minutes the coastal outlines 

which previously required many years of shipboard 

surveying. 

Ease of access has led university faculty members to 

make many studies of the shoreline. One of the most 

industrious workers was N. S. Shaler, who described 

many aspects of coastal geology between 1860 and 1905 

and completed a fine study of beaches and marshes 

(Shaler, 1895). Later, a cl8tf8ic book on shoreline features was written by Johnson (1925), and in it, he 

developed a classification of shore forms. Popular 

interest in the shore for building sites and for summer 

recreation during recent decades has led to an increase 

in engineering problems. Many of these problems have 

been studied by the Beach Erosion Board (now the 

Coastal Engineering Research Center, Corps of Engineers, U.S. Army) either directly or by contract with 

universities. 

Most early soundings in the ocean were confined to 

the continental shelf, where lead lines sufficed. These 

records formed the basis for the first sounding chart 

published by the Survey of the Coast, the New York 

area, in 1835. In deeper water, sounding proved to be 

far more difficult, owing to uncertainty in determining 

the instant of arrival of the lead weight at the bottom. 

Several techniques were proposed by Maury ( 1855, p. 

200-216) for making deep-sea soundings, but by 1912, 

Murray and Hjort ( 1912, p. 131) could report only 

1,873 soundings greater than 1,000 fathoms in the entire 

North Atlantic Ocean. As a result, the chavts of 

Maury (1855, pl. 11) and Murray and Hjort (1912, 

map II) show the deep-sea floor off the United States 

in only the most rudimentary fashion. Beginning in 

the early 1920's, sounding by acoustic echo became routine because of its speed and convenient underway operation. Later improvements through continuous recording (about 1935) and precision timing (about 

1955) vastly increased the value of echo sounding. 

About 1,500,000 soundings on the continental shelf and 

slope off the eastern lTnited States have been compiled 

on plotting (smooth) sheets of the Coast and Geodetic 

Survey, most of the soundings having been taken since 

1930. Several tens of thousands of soundings in deep 

water farther sea ward resulted mostly from expeditions 

of Lamont Geological Observatory and 'Voods Hole 

Oceanographic Institution, as well as from general compilations of the U.S. Naval Oceanographic Office. 

Among the more significant studies of topography off 

the Atlantic coast based upon echo soundings are those 

of Veatch and Smith ( 1939) for the continental shelf 

and slope, and of Heezen, Tharp, and Ewing ( 1959) 
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FIGURE 4.-Part of world map made by Diego Ribero in 1529. One of the first maps to show entire Atlantic coast of the United States. 

Easily identifiable pointBi are irregular east coast of Newfoundland, Penobscot Bay (exaggerated scale, trending northward), Cape 

Cod (named appropriately Cabo de Arenas), and Florida. Reproduced from a copy in Y~J.'le University Library. 

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A8 Nl'LANTIC CONTINENTAL S'HEiLF AN1

D SLOPE OF THE UNITED STATES 

FIGURE 5.-Photographs of TIROS television transmissions showing sections of the Atlantic coast of the United States viewed 

from a height of about 650 kilometers during 1963. (From Goddard Space Flight Center, TIROS Station, Wallops 

Island, Va.) 

for the continental slope, continental rise, and abyssal 

plains. A great deal of attention has been given the 

numerous submarine canyons that indent the continental shelf and extend to the base of the continental 

slope and beyond; important contributions were made 

by Shepard ( 1934) , Veatch and Smith ( 1939) , and 

Heezen, Tharp, and Ewing ( 1959). Interpretations of 

topography also have been made for Georges Bank 

(Shepard, Trefethen, and Cohee, 1934), the Gulf of 

Maine (Johnson, 1925, p. 255-314; Murray, 1947), and 

the Bay of Fundy (Shepard, 1930). 

The most pressing need at the beginning of the program was a general topographic chart for the entire 

region between Nova Scotia and the tip of Florida. 

Accordingly, charts were constructed on the basis of all 

pertinent smooth sheets of the Coast and Geodetic Survey and of the Canadian Hydrographic Service for the 

continental shelf and slope and of the many unpublished 

sounding lines of Woods Hole Oceanogntphic Institution and Lamont Geological Observatory for the continental slope, the Blake Plateau, the continental rise, 

and the deep sea. A general chart of the region (scale 

1: 5,000,000) was compiled by Pratt (unpub. data) to 

depict the relation of the continental margin to 'the deep 

sea. A oot of three more detailed sheets (scale 1 : 1,000,-

000) was drawn by Uchupi (1965; unpub. data) for the 

continental shelf, slope, twd rise. Secondary charts, still 

more detailed and of larger scale, illustrate certain features such as basins, sand waves, and terraces. All 

these charts are sources of information for making inferences about the sediment, lithology, and structure of 

the region and thence of its geological history, and some 

of them also serve ·as bases for plotting information obtained from samples and other benthic data. 

Most of the continental shelf off the Atlantic coast 

fits the classical concept of a shelf as a region of low 

relief sloping gently seaward. The depth of ·its outer 

edge varies between 80 and 140 meters, spanning the 
GEOLOGIC BACKGROUND A9 

world average of 132 meters (Shepard, 1963, p. 257) and 

lying close to the estimate of 159 meters for the maximum lowering of sea level during Pleistocene glaciations (Donn, Farrand, and Ewing, 1962). Most of the 

area of the shelf is well below present wave base, which 

is about 20 meters, as estimated from the position at 

which waves begin to refract and transmit energy to the 

sea bottom. The rising sea level of interglacial and 

postglacial times left several terraces of both erosional 

and depositional origin and many submerged bars which 

once may have separated long lagoons from the open sea. 

Transverse to the shelf are channels cut by streams during the low stages of sea level; one channel off the Hudson River has remained partly open, but others are completely filled. Elsewhere between Nova Scotia and 

Cape Hatteras, the shelf edge is indented by the heads 

of submarine canyons. In the north, particularly within the Gulf of Maine, very irregular topography remains from direct erosion and deposition by Pleistocene 

glaciers. 

The continental slope is steeper than the continental 

shelf, but most of it is gentler than 5°. North of Cape 

Hatteras the slope is deeply cut by submarine canyons, 

and south of the cape it is interrupted by the broad 

Blake Plateau, whose surface is at depths of 500-1,100 

meters (Pratt and Heezen, 1964). Blake Plateau was 

probably shaped by faults, as was the offset of the continental slope between New York and a point southeast of 

Boston (fig. 3). Although sediments mantle the continental slope, numerous outcrops of rock on the slope or 

on the sides of its submarine canyons indiGate that structural deformation of some sort probably played a large 

role in shaping it. The seaward limit of the continental 

slope gradually deepens from 1,400 meters off Nova 

Scotia to 2,500 meters off Cape Hatteras; farther south 

off the Blake Plateau the slope extends to a depth of 

5,000 meters. 

At the base of the continental slope is the continental 

rise, a depositional apron sloping seaward at a declivity generally between 0°35' and 0°05'. Its base is 

near the 5,000-meter-depth contour, which is as far as 

500 kilometers beyond the base of the continental slope. 

Crossing the continental rise are many prolongations of 

the submarine canyons that occur on the continental 

slope. At a depth of about 5,000-meters the continental 

rise merges with the abyssal plains, which are among the 

flattest large physiographic features of the earth. Topographic, sedimentary, and stratigraphic evidence indicate that the continental rises and abyssal plains formed 

by deposition of sediments from turbidity currents. 

Continued development of sounding devices may 

eventually render ordinary echo sounding as obsolete 

as lead line sounding is today. Water is nearly opaque 

to light and radio frequencies as compared with sound; 

therefore, increased attention is being given to special 

uses of sound in exploration. Typical new (since 1955) 

devices are sideways pingers used for acoustically 

sweeping a broad area of sea floor parallel to the ship's 

track, narrow-beam sound sources for reducing side 

echoes and obtaining true slopes, and high-energy sound 

sources for gaining knowledge of subbottom structures. 

SEDIMENTOLOGY 

Study of the sediments on the sea floor serves chiefl~ 

to illuminate processes of deposition and the geological 

history of Pleistocene and post-Pleistocene times. Understanding of these sediments requires a knowledge of 

both horizontal and vertical distribution patterns. 

Simpler of the two patterns to investigate is the horizontal one; it is also the more important from the viewpoint of simultaneously revealing the distribution and 

density of benthic animals that contribute to the sediments and partly rework them. 

Small samples of the sediments from the ocean bottom were obtained during the past century by the tallowed lead originally used for making shallow soundings. Using some of these samples, Pourtales (1850) 

first described the sediments off New Jersey, and later, 

using 9,000 samples, he made a map showing the types of 

sediments along the entire coast (Pourtales, 1870, 1872). 

Supplementary information for Blake Plateau was provided by Agassiz (1888). About 700 lead line and small 

snapper samples were examined and 200 were analyzed 

by Shepard and Cohee (1936) to determine the characteristics of sediment on the continental shelf off the 

Middle Atlantic States. With the advent of echosounding methods, the collection of small ocean bottom 

samples largely ceased ; however, navigational charts 

commonly retain bottom notations inherited from early 

surveys. These notations served as the basis for drawing bottom-sediment charts of the Gulf of Maine by 

Shepard (1939) and for much of the Atlantic coast by 

the Oberkommando der Krieg-smarine (1943). 

Special snapper samples were collected by Stetson 

(1938) along 13 profile's and analyzed in the laboratory 

to learn more of the distribution patterns. Still other 

snapper and larger samples were obtained by the U.S. 

Bureau of Commercial Fisheries during fisheries 

studies. One set of samples is from Georges Bank 

(Wigley, 1961b) and the Gulf of Maine; another is 

from the shelf off Florida and Georgia (Moore and 

Gorsline, 1960). Sediments of small bays have been 

studied by many workers associated with universities. 

The Woods Hole Oceanographic Institution and the 

Lamont Geological Observatory have also made major 

contributions to knowledge of sediments on the con-
AlO ATLANTIC CONTIN'EtNTAL SHELF AND SLOPE OF THE UNITED STATES 

tinental slope, the Blake Plateau, and the deep-sea floor, 

mostly through coring operations (Stetson, 1949; Ericson, Ewing, Wollin, and Heezen, 1961). 

A general distribution map of the sediments on the 

continental shelf was compiled by Uchupi (1963) from 

past publications. This map revealed patterns due to 

regional differences in sources and environment, but 

these patterns are complicated and partly obscured by 

differences in sampling devices and density of sampling 

and by differences in intensity of study of the samples. 

In the present program, a new set of samples was needed 

for studies using modern and uniform techniques. To 

cover the entire region with a reasonable number of 

samples, a grid was so chosen that samples were obtained 

at intervals of about 18 kilometers (10 nautical miles). 

Thus there is one sample for each 300 square kilometers, 

or a total of about 1,400 samples for the continental 

shelf. Samples of the continental slope and the Blake 

Plateau are more widely spaced owing to greater depth 

(longer time required for sampling) and to a presumed 

more uniform distribution pattern of sediments; these 

comprise about 600 samples. During 1960 and 1961, 

samples at about 400 of the grid points within the Gulf 

of Maine, Georges Bank, and Nantucket Shoals were 

obtained by the Bureau of Commercial Fisheries Biological Laboratory at Woods Hole as part of a study of 

the relation of benthic animals to bottom materials· ' these samples are available for the sediment studies. 

Collection of the additional necessary 1,600 surface samples was completed by the summer of 1965. 

The samples of the Bureau of Commercial Fisheries 

were obtained with a Smith-Mcintyre grab (Smith and 

Mcintyre, 1954) which recovers material from an area 

of 0.1 square meter. Within the present program, sampling was done with the much larger Cam_pbell grab, 

which samples 0.6 square meter. Fitted into the interior of the grab is a light and a camera that takes a 

photograph of the bottom while the grab is being lowered and when it is 1 meter above the bottom (Menzies 

Smith, and Emery, 1963). Representative parts of each 

sample were removed aboard ship for later sediment 

analyses in the laboratory (color, coarse fractions, granulometry,, clay and other mineralogy, and contents of 

calcium carbonate and organic matter), and for study 

of enclosed foraminifers and ostracodes. The remainder of the sample was screened on a sieve having !-

millimeter openings. Fine material that passed 

through the sieve was discarded overside and the coarse 

fraction preserved in formalin for later sorting and removal of all organisms at the Bureau of Commerc;al 

Fisheries Biological Laboratory at Woods Hole. 

Gravels were also retained to complete the information 

on grain-size distribution. 

In addition to sampling from aboard ship, collections 

of beach sediments and observa,.tions of beach slope 

and other characteristics were made at 18-kilometer 

intervals along the entire coast. This work, under the 

direction of John M. Zeigler of theW oods Hole Oceanographic Institution, is being coordinated with the offshore program to gain maximum benefit for both 

studies. 

Preliminary inspection of the samples enabled the 

construction of distribution maps of texture (granulometry), contributing agent, and age (fig. 6). The 

map of texture shows irregularity of pattern, but sands 

dominate throughout most of the shelf southwest of 

the Gulf of Maine. In the Gulf of Maine the rugged 

coast and irregular sea floor are accompanied by rock 

and boulder bottoms, but deep areas are thickly covered by silt and clay which remain because of the protection from wave action provided by the broad 

embayment and the lee of the shallow Georges Bank 

(Hathaway, Hiilsemann, Schlee, and Trumbull, 1965). 

The continental slope ·along the entire coast appears to 

be mantled with clay and silt. Sediments on the continental rise and abyssal plains are clays interbedded 

with fine sands and coarse silts. 

Several different sediment sources are represented on 

the continental shelf off the Atlantic coast, as they are 

on many other continental shelves of the world. Near 

Miami the warm water is conducive to deposition of 

biogenic calcium carbonate; thus shell sands dominate 

on the southwestern end of the continental shelf. Similarly, foraminiferal sands or silts characterize the top 

of Blake Plateau, and reef corals and algae are present 

on the nearby Bahama Islan~s. On most of the continental shelf, river-contributed detrital sands and silts 

are the chief sediment, although between New York and 

Georges Bank the the rivers probably consisted mostly 

of glacial melt water. True glacial and ice-rafted sediments having a wide range of grain sizes are typical 

of the continental shelf off Nova Scotia and bank tops 

in the Gulf of Maine. The continental slope and rise 

receive sediments from the same sources as the shelf but 

after considerable mixing, particularly at great depth 

and on the abyssal plains. Accordingly, we can expect 

a south-to-north change of sediment source from biogenic to fluviatile to glacial, each somewhat blurred by 

subsequent reworking by marine agents (fig. 6). 

Comparison with other regions indicates that the 

sediments vary transversely from shore to deep water 

owing to differences in extent of reworking by waves 

and currents and to differences in age (Emery, 1960). 

Continental shelves whose sediments have been studied 

carefully have a generally narrow belt of modern sediment that shows a sea ward decrease in grain size from 
25 

Silt 

~ 

~ 

and clayW ashinrlon ~ 

Sandy 

~ 

~ 

silt 

AGENT 

~ Fluviatile 

Glacial 

-

Biogenic 

Authigenic 

-Biogenic 

s· 

BooOOn')j Ji 

PLANATION 

AGE Washington 

~ Modern 

.. 

Relict 

5' 

FIGURE 6.-Sediments off the Atlantic coast of the United States classified by texture, contributing agent, and age. The charts are based upon inspection 

of about 1,600 samples prior to detailed laboratory analyses. 

~ 

~ t"l 

9 

c 

t:C 

> 

~ ge 

0 

~ t::; 

> ..... 

..... 
A12 .Afl'LA.NTIC CONTINENTAL SHEiLF AND SLOPE OF THE UNITED STATES 

gravels or coarse sands on the beaches to fine sands 

offshore. On open shelves, such as occur along most of 

the Atlantic coast, this belt of sediments extends to 

depths of about 20 meters and is usually only a few 

kilometers wide. Within areas protected by coastal 

configuration (estuaries and lagoons) and areas protected by submerged barriers (Gulf of Maine), the belt 

is wider, extends to deeper water, and contains sediments as fine as clay sizes (fig. 6). Sediments on the 

main expanse of the continental shelf are commonly 

coarse grained and iron stained and contain shells of 

animals that lived in water shallower than that at the 

sampling site. These sediments evidently are relict, 

deposited at a time of glacially lowered sea level. More 

than a single relict age can be represented, as shown 

for example by thick sands overlying gravels. Modern 

sediments have failed to cover these older ones, mainly 

because insufficient time has elapsed since sea level 

reached its present position (about 5,000 yr ago) for 

sediments derived from rivers or from erosion of sea 

cliffs to fill estuaries and progFade very far sea ward. 

Corroboration of the antiquity of these sediments is 

provided by the recovery and radiocarbon dating 

(8,000-11,000 yrs before the present) of shallow-water 

mollusks and intertidal peat from the continental shelf 

(Merrill, Emery, and Rubin, 1965; Emery, Wigley, and 

Rubin, 1965). 

Waves and currents atop the continental shelf provide enough turbulence to cause much of the clay and 

fine silt components of the modern sediment to bypass 

the outer half of the shelf and reach deeper water sites 

of deposition. Owing to lack of burial under detrital 

sediments, accumulations of slowly deposited authigenic 

glauconite, phosphorite, and manganese oxide are common near the outer edge of the continental sh~lf. The 

same conditions of slow deposition allow residual 

sediments (reworked from outcrops of older strata) to 

compose a recognizable percentage of the total sediment. 

This residual component tends to concentrate the more 

resistant grains, such as quartz but also locally glauconite and phosphorite. A last type of sediment, biogenic, can be deposited any place on the continental 

shelf and is not related to distance from shore. 

The fine-grained components of modern sediments 

that bypass the continental shelf a-t:.e deposited partly 

on the continental slope, giving :rise to massive deposits 

containing little evidence of bedding. Those components that reach even deeper water may become interbedded with coarser sediments contributed by turbidity 

currents. These currents bring coarse-grained nearshore sediments to deep water especially in areas where 

submarine canyons reach close inshore (Emery, 1960, 

p. 217-219). Submarine canyons off the Atlantic coast 

have heads that are now far from shore and inaccessible 

to nearshore sediments. Therefore, turbidity currents 

probably contribute far less sediment to- this deep-sea 

region now than during glacial times of lower sea level, 

when the shore was closer to the heads of the canyons 

and when the extensions of the canyons across the continental shelf were free of their present fills of sediment. 

Once the provinces of surface sediments have been 

outlined and the controlling agencies inferred, the positions for collection of long cores can be established. 

These cores require considerable effort, both in the field 

and in the laboratory; thus positions for them must be 

carefully selected for maximum scientific information. 

Piston coring is most productive in areas of finegrained sediments (basins in the Gulf of Maine, the 

protected Long Island Sound, a few areas of the open 

continental shelf, the continental slope, and the continental rise). Cores may be as long as 10 meters and 

have diameters of 6-15 centimeters depending upon the 

kind of sediments and the use intended for particular 

cores. Some short ( 1- to 2-m) cores are a vail81ble from 

earlier sampling with open-barrel gravity corers by staff 

members of Woods Hole Oceanographic Institution. 

Areas of sandy sediment on the continental shelf cannot be sampled satisfactorily with such corers, but they 

may be cored with a vibropiston corer (Kudinov, 1957). 

Most cores will undergo analyses similar to those of the 

surface sediments, plus radiocarbon dating to determine 

rates of deposition, and analyses of interstitial waters 

. to investigate possible diagenesis of the sediments and 

their included waters. A box sampler (Reineck, 1963) 

is also being used to examine minor features of stratification and effects of burrowing animals; this sampler 

is essentially a corer 30 centimeters in diameter. 

LITHOLOGY 

Rocks cropping out on the continental margin have 

been sampled mostly by university research workers, 

but because of the high cost, both in time and money, 

the study is still in its infancy. Among the earliest 

reports of rock outcrops is tha;t of Shepard, Trefethen, 

and Cohee ( 1934), ~ ho reported its recovery from 

Georges Bank on anchors. Later, Stetson ( 1949) 

dredged rocks from the sides of New England submarine canyons. Cores from the Blake Escarpment and 

the Blake Plateau have included rock and also sediments containing Foraminifera reworked from older 

sedimentary strata (Ericson, Ewing, Wollin, and 

Heezen, 1961). Borings made by Zeigler, Hoffmeister, 

Giese, and Tasha (1960) along the shores of Cape Cod 

penetrated Eocene nonmarine strata. Other wells were 

drilled by engineering firms to test foundations for 

light towers and radar towers at many places along the 
GEOLOGIC BACKGROUND A13 

coast; many of these test wells penetrated late Tertiary 

sedimentary strata. 

In the future a great advance over the largely hit-ormiss dredging method is likely to result through the 

proper use of two new tools, manned submersibles and 

oceanic drilling from ships. Both are in early stages 

of development, but even so they have made significant 

contributions to the knowledge of the lithology of the 

sea floor. The submersible can bring a trained observer 

to outcrops to map strata and select specimens (Moore, 

1963; Terry, 1964). Deep-sea drilling has boon accomplished in experimental borings off Ca;lifornia and 

Mexico (National Research Council, AMSOC Committee, 1961), the first experimental drilling from a ship 

since that at Funafuti in 1896-98 (Halligan, 1904) . 

Eventually, the drill method of sampling rock may become relatively inexpensive and available for nearly 

routine use to recover rock from considerable depth 

beneath the ocean floor even in great depths of water. 

Existing dredge and drill samples generally show 

seaward extensions of strata found in oil wells and 

outcrops of the adjacent land, as shown by the Geologic 

Map of the United States (Stose, 1932) and by the various State geologic maps, and as summarized by Murray 

( 1961) . Also, as on land, the rocks of the continental 

shelf are highly varied. A collection by a diver, John 

M. Zeigler, showed that least one of the shallow banks 

in the Gulf of Maine is a massive outcrop of Paleozoic 

granite (Toulmin, 1957). Other dredgings and photographs of the Gulf bottom reveal widespread boulders 

of igneous, metamorphic, and sedimentary rocks deposited by Pleistocene glaciers or by icebergs. Elsewhere on the shelf, Pleistocene and Recent marine sediments form a surface cover largely concealing older 

strata. 

The results of all known offshore collections of rock 

are summarized in a geologic map (fig. 7) that shows 

the age of rock immediately underlying the Quaternary 

cover of glacial till and marine sediments. This map is 

a simple one commensurate with the paucity of data. 

However, it does indicate Pliocene and Miocene strata 

atop most of the continental shelf, Miocene on the Blake 

Plateau, and rocks only of Eocene or greater age in the 

Gulf of Maine. Rock samples recovered through 1964 

from the continental slope and from submarine canyons 

cut into it include strata of Pliocene, Oligocene, Eocene, 

Paleocene, and Cretaceous age. The Pliocene rocks are 

mainly from near the top of the continental slope and 

the older rocks are from greater depths, but there is 

considerable overlap in depth. This overlap may result from a sampling of talus or it may reflect a downwarp of the continental slope. A downwarp could 

mean that Miocene and Pliocene strata conceal older 

rocks except where they have been removed by erosion 

of submarine canyons or by mass movements at the face 

of the continental slope. A downwarp is also suggested 

by some continuous seismic profiles, but it may be absent 

locally if irregular terraces on the continental slope 

represent the outcropping edges of resistant strata, as 

suggested by Heezen, Tharp, and Ewing (1959). 

Beyond the base of the continental slope (on the continental rise, Blake Ridge) samples obtained to 1964 

consist only of post-Pleistocene sediments. At some 

presently unknown depth there should be a buried 

blanket of Pliocene sediments, underlain by Miocene 

strata. The tops of the seamounts of the New England 

Seamount Chain which protrude through these layers 

are capped by Eocene calcareous sediment (Northrop, 

Frosch, Frassetto, and Zeigler, 1959). 

STRUCTURE 

The structure of the continental margin is so closely 

associated with its origin that if the structure is known, 

the origin should be apparent. Two classes of structural 

data are needed, deep and shallow, and these two classes 

require different methods of measurements. At present 

the most successful method for investigating deep structure is seismic refraction, followed by magnetic and 

gravity measurements. For detailed study of shallow 

structure the best method is continuous seismic profiling. 

Gravity measurements constitute the coarsest geophysical method to be considered here. Bouguer anomalies measured aboard a submarine were computed and 

reported by Ewing, Worzel, and Shurbet (1957). A 

plot of their results indicates an increase from between 

-25 and +50 milligals at the shore between Maine and 

Cape Hatteras through about + 100 milligals near the 

edge of the continental shelf to about + 300 milligals on 

the upper continental rise. This relation merely indicates a sea ward thinning of the crust (Airy theory), a 

seaward increase in density of the crust (Pratt theory), 

or both (Heiskanen theory), with thickness or density 

contours approximately paralleling the shelf edge. The 

change in thickness of the crust is reflected by a decrease 

in depth of the Mohorovicic discontinuity from about 

32 kilometers below sea level under the land and most of 

the continental shelf to between 10 and 15 kilometers 

below sea level in the deep sea. 

Magnetic meaSiirements compiled by Drake, Heirtzler, and Hirshman ( 1963) show several parallel belts of 

positive anomalies alternating with belts of negative 

anomalies and extending along the continental shelf, 

slope, and rise of the entire coast. Off New Jersey these 

belts are offset as though by right-lateral strike-slip 

faulting (fig. 8). Supplementary evinence of this faulting is provided by displacement of Triassic and earlier 

structures on land to the west and by numerous extinct 
A14 ATLANTIC CONTINENTAL SHELF AND SLOPE OF TirE UNITE;D STATES 

0 

75° 

EXPLANATION 

Pliocene and Miocene strata 

Oligocene to Triassic strata 

Dashed pattern indicates discontinuous cover by Pliocene 

and Miocene strata 

Permian and older strata 

250 500 KILOMETERS 

FIGURE 7.-Map of continental shelf and slope showing distribution of pre-Pleistocene strata. 
Washington 

0 

GEOLOGIC BACKGROUND 

0 250 500 KILOMETERS 

FIGURE 8.-Axes of trenches. Numbers indicate thickness of sedimentary fill atop basement rocks that have 

compressional velocities of 5.0-6.4 km per sec. Crosshatched band south of New York marks a zone in 

which magnetic anomalies are oft'set and suggestive of strike-slip faulting. Data from Drake, Ewing, and 

Sutton (1959); Hersey, Bunce, Wyrick, and Dietz (1959); and Drake, Heirtzler, and Hirshman (1968). 

A15 
A16 AfrLANTIC CONTINENTAL SHE1LF AND SLOPE OF THE UNITE,D STATES 

volcanoes in the New England Seamopnt Chain to the 

east. The fault is associated with the bend in the Appalachian Mountains shown by the TIROS photograph 

of the New York region (fig. 5). The offset of the continental slope is approximately parallel to that of the 

Appalachian Mountains, and it amounts to about 220 

kilometers, somewhat less than the movement along 

strike-slip faults off the Pacific coast inferred from displacement of belts of magnetic anomalies (Vacquier, 

Raff, and Warren, 1961). 

Seismic refraction surveys were begun off the Atlantic coast in 1937 (Ewing, Woollard, Vine, and W orzel, 1946), and subsequently many traverses have been 

run at about right angles to the New England coast by 

Ewing and his associates. All these refraction data 

were compiled and summarized by Drake, Ewing, and 

Sutton (1959). Clearly shown in their compilation 

are two trenches formed in basement rocks having 5.0-

6.0 kilometers per second compressional velocity. The 

trenches contain fills of 3.0-6.5 kilometers of materials 

having compressional velocities similar to those of sedimentary rocks overlain by unconsolidated sediments. 

Between the trenches is a ridge which is much shallower 

and nearly reaches sea level at Sable Island off eastern 

Nova Scotia. 

Many other scattered refraction stations were obtained by Hersey, Bunce, Wyrick, and Dietz (1959) 

farther south on the Blake Plateau and the nearby continental shelf. These stations reveal a single broad 

trench in which as much as 10 kilometers of sedimentary 

rocks and sediments rest atop basement rocks having 

a higher compressional velocity ( 5.8--'6.4 km per sec) 

than was reported off New England. In figure 8 this 

trench is shown as possibly being a union of the two 

northern trenches, and its axis is along the Blake Escarpment. If the trench continues beyond the Blake 

Plateau, it probably bends southeastward to join the 

Puerto Rico Trench (Ewing and W orzel, 1954) , where 

a smaller supply of sediment may account for its incompletely filled condition. The surface of basement rocks 

off the entire coast probably represents a submerged 

extension of the Fall Zone peneplain of pre-Cretaceous 

age. A velocity discontinuity within the sedimentary 

fill is considered to be the top of Lower Cretaceous 

strata on the basis of continuity with outcrops and logs 

of wells drilled on land (Ewing, W orzel, Steenland, and 

Press, 1950). As shown by the composite cross section 

of figure 9, Lower ·Cretaceous rocks (semi consolidated) 

compose the bulk of the fill within the trenches. 

During the past, shallow structural features of the 

continental shelves had to be inferred from physiography, as was done by Shepard (1930) for the Bay 

of Fundy and by Shepard, Trefethen, and Cohee ( 1934) 

KILOMETERS SOUTH OF MARTHA'S VINEYARD 

0 100 wo o~~~~~~SE~~~------.-----------~ 300 

(/) 

a:: 

~ 2 LJJ 

~ 3 ....1 

~ 4 

~ 5 Ill: 6 LJJ 

0 7 

gL-----------~------------~----------~ 

FIGURE 9.-Structural section inferred from seismic data for 

continental shelf, slope, and rise south of Massachusetts. 

Data are from Ewing, Worzel, Steenland, and Press (1950); 

Drake, Ewing, and Sutton ( 1959) ; and unpublished profiles 

of v;arious dates by S. T. Knott, D. D. Caulfield, and Hartley Hoskins of Woods Hole Oceanographic Institution. The 

abbreviation "my," stands for million years. Inferred ages 

are based on correlation with geology from adjacent land 

·areas. 

for Georges Bank. Where data were available from 

rock dredgings and from wells or outcrops on shore, 

structural ·cross sections could be inferred by interpolation ben~ath the shelf ( Heezen, Tharp, and Ewing, 

1959). In the first systematic acoustic study, Murray 

( 194 7) mapped shallow features beneath acoustically 

highly transparent sediments of the Gull£ of Maine 

using records of ordinary echo sounders. His work 

revealed basin fillings of Recent sediments resting atop 

Pleistocene glacial till and perhaps on older strata. 

Since about 1955, rapid development of high-energy 

low-frequency sound sources has allowed the recording 

of subbottom echoes that can be related to strata as old 

as Cretaceous and as deep as 2,000 meters (Ewing, 

Luskin, Roberts, and Hirshman, 1960; Ewing, Le 

Pichon, and Ewing, 1963; Hersey, 1963). A continuous 

seismic profiler was built especially for this program 

by R. K. Paul assisted by A. R. Tagg and advised by 

members of the Department of Geophysics at Woods 

Hole Oceanographic Institution. This device uses a 

10,000-joule spark source of low-·frequency acoustic 

energy. The data •are printed aboard ship on rolls of 

chemical paper about 45 centimeters wide. Recordings 

on magnetic tape are also made as a source of base data 

for closer study in the laboratory, using V'arious filters 

to amplify the signal over background noise. The average spacing of profiles on the continental margin is 

about 50 kilometers, but closer spacing is provided for 

detailed study of certain features such as basins, submarine canyons, and embayments. 

The seismic profiles show unconformities, faults, 

buried hills and valleys, and depositional irregularities. 

Profiles across Georges Bank show 10-30 meters of hori-
GEOLOGIC BACKGROUND A17 

zontally bedded sediment (proba;bly glacial outwash) 

resting unconformably atop seaward-dipping strata 

(probably Pliocene shales) with some prograding on 

the continental slope. The same unconformity is common beneath other kinds of Pleistocene and post-Pleistocene sediments of the continental shelf between Georges 

Bank and Florida (fig. 9). In a general way, the postunconformity sediments change from dominantly upbuilding to dominantly out-building in a southwesterly 

direction, as though controlled by the greater supply of 

sediments and the generally shallower surface of the 

shelf· toward the south west. The post unconformity 

sediments extend horizontally to outcrops on the sides 

of subm'arine canyons, indicating that canyon cutting 

was subsequent to deposition of these sediments; only 

locally do the sediments dip down the sides of canyons 

as though these sediments were deposited after the canyons had formed. 

Widespread application of continuous seismic profiling is expected to provide much new information on 

the late geological history of the continental margin, as 

well as upon general conditions of deposition of sediments, in these areas. It supplements seismic refraction 

studies, which are more apt to yield data on deep structures, including the shapes of the trenches in which 

thick prisms of sediments have accumulated along the 

coasts of both the Atlantic Ocean and the Gulf of 

Mexico. Striking simil'arities have been shown by 

Drake, Ewing, and Sutton ( 1959') between the trenches 

under the present Atlantic continental shelf and slope 

and those containing Paleozoic sedimentary rocks of 

the Appalachian Mountains. Further speculations 

about the nature of continental accretion by Hess 

(1962) and Dietz (1963) can be tested by these seismic 

techniques as well as by deep oceanic drilling. 

WATER AND BIOLOGY 

The water overlying a marine environment is probably the chief factor governing the distribution and 

kinds of organisms and the nature of the sediments; accordingly, study of the water and biology is warranted 

in this program. A compilation by the author of unpublished data in the files of Woods Hole Oceanographic Institution reveals a large seasonal change in 

both salinity and temperature of the waters off New 

England, in contrast with great uniformity of sa.Iinity 

and temperature in waters off Florida (fig. 10). These 

seasonal changes are the result of greater extremes in 

solar heating, precipitation, and runoff at the north. 

Cape Hatteras constitutes an obvious barrier separating 

waters of these two regions. Cape Cod farther north 

and the tip of Florid-a ~t the south are less important 

barriers. 

Warm salty waters of the. Florida Current pass seaward of Cape Hatteras to become the Gulf Stream, as 

noted by Franklin ( 1786), but masses of this wfl,rm 

water break a way and intrude the region of the continental shelf (Stommel, 1958). A coastal countercurrent 

landward of the Gulf Stream consists of water partly 

derived from the Gulf Stream and partly from land 

runoff. Seasonal changes and year-to-year variations 

in runoff and coastal winds produce changesin the currents atop the continental shelf, particularly in the 

countercurrents. Studies of these changes are based 

upon drift bottles (Bumpus and Lauzier, 1964), current-meter records, and water properties (Bigelow, 

1927). A good example of the effectiveness of water 

properties as tracers is given by the fact that the nearshore countercurrent brings low salinity water from 

runoff as far south as Cape Hatteras. 

Data from the files of the U.S. Geological Survey on 

seasonal and annual stream discharge permit the construction of a water budget for the coastal region. 

Measurements of salinity and related chemical characteristics of streams, estuaries, and shelf waters are being 

compiled from many sources for their possible aid as 

tracers of water movement. 

A direct effect of water properties upon sediments of 

the continental shelf is their control of biogenic calcium 

carbonate. The warm saline waters south of Cape Hatteras result in high concentration (commonly more than 

70 percent) of calcareous sediments such as shells, foraminiferal tests, algae, and corals, whereas the cool, 

more dilute waters of the north are underlain by sediments low in calcium carbonate (commonly about 5 percent). The speed of the Florida Current is so great that 

it has swept parts of the Blake Plateau nearly clean of 

loose sediments, but it does little more than impinge 

upon the continental shelf, and its side eddies and oountercurrents ·are too slow to have much effect upon sediments of the shelf. Instead, the sediments are controlled by the faster currents produced by tides, internal 

waves, and surface waves, listed in their order of importance from deep to shaH ow water; these currents appear to be sufficiently grea.t to be able to transfer the 

finest sediments contributed by streams and shore erosion to deeper water beyond the continental shelf. 

Diatoms and other phytoplankton serve as the food 

base for the animals that live in the ocean. Some of the 

organic matter which they produce by photosynthesis 

escapes ingestion by animals or decomposition by bacteria and is incorporated within the sediments. The 

concentration of this material in the sediments depends 

not only upon its ra;te of production in the overlying 

water, but also upon its rate of burial in the sediments 

and the rate at which it can be oxidized by the overlying 

waters (Emery, 1960). Analyses of the content of organic carbon and nitrogen in the sediments range from 
Al8 ATLANTIC CONTINENTAL SHELF AN!D SLOPE OF THE UNITEiD STATES 

0 500 1000 1500 2000 KILOMETERS 

FIGURE 10.-Isotherms (top) and isohalines (bottom) of winter (JFM) and summer (JAS) seasons for surface 

waters oft' the Atlantic coast. Units are oc and salinity ( o 1 oo). Based upon unpublished data in files of 

Woods Hole Oceanographic Institution from about 1940--61. 
GEOLOGIC BACKGROUND Al9 

almost zero in the coarse sands of Georges Bank to commonly about 2 percent carbon and 0.3 percent nitrogen 

in the clays and silts of the Gulf of Maine and the continental slope. When complete, these measurements will 

be compared to rates of deposition, measurements of primary productivity, and specific organic C<?D-stituents 

such as hydrocarbons, amino acids, and pigments in 

the sediments. Some of the data needed for comparison are available in the literature, but most will be obtained by various workers of several organizations as 

parts of small cooperative studies. 

The animals living in the water and on the bottom 

are closely interrelated with the characteristics of the 

water and of the sediments. As shown long ago by 

Bigelow ( 1926), the nature and distribution of zooplankton contribute to an understanding of the circulation pattern and rate of movement of waters in the 

Gulf of Ma-ine. Pelagic fishes also serve as indicators 

of topography through the indirect control of topography upon overlying waters. Examples are the locations of fishing grounds for cod and other commercial 

fishes above banks in the Gulf of Maine (Rich, 1929), 

and the recent finding and development of an allyear fishery for tuna and swordfish by long-line methods in the heads of submarine canyons off New England 

(Mather and Bartlett, 1962). 

During the past, little information has been available 

concerning the relative abundance of pelagic Foraminifera in waters atop the continental shelves as compared 

with those of the deep sea, although speculation about 

their distribution has served as a basis for some paleoecological interpretations of ancient strata. As· a partial remedy, about 100 large plankton hauls have been 

made for study of the relations of pelagic Foraminifera 

in the water with respect to their remains in the sediments. Pelagic species average less than 1 percent of 

total Foraminifera nearshore, but more than 90 percent 

of the total in deep water of the continental slope. Also 

reasonably common in the sediments of the continental 

shelf are the remains of diatoms and ostracodes, particularly in northern areas. The- ostracodes appear to 

be abundant in areas of dilute sea water off the mouths 

of rivers; thus they may serve as indicators of large contributions of fresh water to the ocean. 

Benthic Foraminifera are among the most ubiquitous 

animals in the sediments. Abundance of their tests 

shows regional zonations that are controlled by temperature, salinity, or other factors. A very sharp 

boundary occurs between warm-water benthic forms on 

the continental shelf and cold-water forms within the 

Gulf of Maine. On the shelf there is a marked increase 

in concentration of Foraminifera with bottom depth, an 

increase from an average of less than 1 test per gram of 

sediment near shore to more than 1,000 per gram on the 

continental slope. Foraminifera are also much more 

abundant on the southern part of the shelf than on the 

northern part. A marked increase in living fauna 

(identified by stains) occurs below 40 meters, and a major increase is at 90-100 meters; changes of many species occur at the same depths. Breaks of this sort will 

permit identification of faunas of dead Foraminifera 

displaced by currents or mass movements. 

The resistant remains of such animals as mollusks, 

corals, and foraminiferans are common constituents of 

the calcareous sediments south of Cape Hatteras, and 

they are present in the sediments farther north. Still 

other animals, including some sponges, fishes, holothurians, and worms destroy calcareous materials by their 

boring, comminution, or digestive activities. From another point of view, the sediments control the distribution patterns of the animals. Examples are the general 

restriction of most brachiopods, bryozoans, tunicates, 

and sponges to bottom areas of rock or boulders. Many 

polychaete worms and certain crustaceans and heart 

urchins are typical of mud bottom, and sand dollars and 

many brittle stars are restricted to sand. The distribution patterns and biomasses of these and other animals 

are being studied by the U.S. Bureau of Commercial 

Fisheries (Wigley, 1961a) as a cooperative part of the 

program. Studies of these larger benthic animals will 

require several years to complete, but a preliminary 

compilation of 37 stations between Nova Scotia and New 

York (Emery, Merrill, and Trumbull, 1965) shows that 

the greatest number of specimens and the highest biomass per unit area occur with gravel and boulders and 

the lowest number are in shell hash. If weighted for 

the area covered by each different kind of sediment between Nova Scotia and New York, the average biomass 

is about 120 grams per square meter, about 60 percent of 

the world average for continental shelves. At most 

stations, either crustaceans or annelid worms are dominant in terms of number of specimens, but at some 

stations echinoderms, mollusks, or bryozoans are dominant. Lack of hard parts in some organisms or their 

early disintegration produces a poor correlation between 

dominant living organisms and potentially dominant 

fossil forms. Comparison of faunas in the nearly 

simultaneous photographs and samples from the ocean 

bottom also yielded a poor correlation, indicating that 

many organisms transgress the simple classification of 

epifauna and infauna. 

METHODS OF STUDY 

A small converted Army ireighter, R/V GoStnOld 

(fig. 11), was outfitted by the Woods Hole Oceanographic Institution and used an average of 100 days per 
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GEOLOGIC BACKGROUND A21 

year to accomplish most fieldwork. Gosnold is steel 

hulled, is 30 meters long, and has a 6.4-meter beam and 

a 2.5-meter draft; her gross tonnage is 250 (Emery and 

Schlee, 1963). Diesel powered ( 250 hp) with a variable 

pitch propeller, the ship can cruise at 7.5 knots (14 km 

per hr) but can maintain steerageway at 3 kilometers 

per hour. Navigation equipment includes Loran A, 

radar, radio direction finder, and gyropelorus. The 

low midship working area is sheltered at the forward 

end by the forecastle and at the after end by the superstructure which houses the bridge, electronics room, and 

most of the living quarters. A portable van is bolted to 

the deck adjoining the superstructure. Sample processing and chemical analyses, together with other shipboard laboratory work, are conducted here. The van 

opens into the forward room of the permanent deck 

structure of the ship where most electronic equipment 

needed for the geologic work is located. For collecting 

large grab samples, dredgings, and cores, a trawl winch 

containing 3,000 meters of 12-millimeter nontwist cable 

of 13-ton breaking strength is installed. Lighter cable 

(6,000 m of 6-mm stainless steel} on a separate drum of 

the same winch is used for lighter work. For nearshore work in shallow waters, R/V A.sterias, about 13 

meters long, was used about 30 days per year. 

Work was done aboard ship and in laboratories ashore 

in each of the four subfields of marine geology : topography, sedimentology, lithology, and structure. In 

addition studies of water and biology were undertaken 

concurrently with geological sampling at sea. First 

priority was given to the construction of topographic 

charts because they are needed for all other investigations (fig. 12). Study of the sediments was advanced 

by the contribution from the U.S. Bureau of Commercial Fisheries of 400 suitable surface samples from the 

Gulf of Maine. Laboratory study of these samples was 

largely finished while R/V Gosnold was being outfitted. 

Subsequently, an additional1,600 surface samples were 

collected. Completion of the sample studies enabled 

the selection of the best sites for more detailed work and 

for cores. 

Rock specimens were included within many of the 

sediment samples, but the major effort in rock dredging 

was withheld until special cruises during the third and 

fourth years, which in turn were followed by intensive 

laboratory studies of lithology and stratigraphy. 

Structural geology, largely inferred from continuous 

seismic profiling, required a larger amount of ship time 

and of equipment preparation than most of the other 

sub.fields of marine geology. Accordingly, its fieldwork was spread throughout the 1963-66 period with a 

year-to-year increase from the first to the third year. 

Interpretation of results of the profiling constituted the 

major effort of the structure program in the fourth year. 

The shipboard work was concentrated in the first 4 

years, leaving the fifth year for cleanup of remaining 

work. Laboratory analyses and report writing continued throughout the period, with preparation of final 

reports spread throughout the entire period. 

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FIGURE 12.-Schematic distribution of ship time (ship-days 

per year) and of laboratory time (man-years per year) 

among the subfi.elds of marine geology being applied to the 

study of the continental shelf and slope o:tr the Atlantic 

coast of the United States. 

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A22 Afl'LANTIC CONTINENTAL SHE,LF AND SLOPE OF THE UNITED STATES 

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GEOLOGIC BACKGROUND A23 

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