THE ATLANTIC CONTINENTAL SHELF AND 

SLOPE, A PROGRAM FOR STUDY 

K. 0. Emery and John S. Schlee 

GEOLOGICAL SURVEY CIRCULAR 481 

WuhinPm,IMB 
United States Department of the Interior 

STEWART 1.. UDALL, SBCRBTAitY 

Geological Survey 

THOMAS B. NOLAN, OIRBcroll 

Free on application to the t}.S. Geological Survey, Washington 25, D. C. 
Introduction - - - - - - - - - - - - - - -

Facilities - - - - - - - - - - - - - - - -

Programs of study - - - - - - - - - - -

Topography- - - ... - ... - - - ... - - - - ... 

Sediments - - - - - - - - - - - - - - -

Lithology- - - - ... - - - - - - - - - - -

The research vessel Gosnold to be 

used for the geological investigaCONTENTS 

Page 

1 Programs of study (cont'd) 

1 Structure- - - - - -- - - - - - - - - -

2 Water- - - - - - - - - - - - - - - - - -

2 Biology - - - - - - - - - - - - - - - - ... 

3 Broad aspects of the project - - - - - -

4 References- - - - - - - -- - - - - - - -

FIGURES 

Page 

tion - - - - - - - - - - - - - - - - Frontispiece 

4. Blocks of conglomerate and fossiliferous sandstone dredged 

from the top of the northern 

1. Profile made with a precision slope of Georges Bank- - - - - - -

echo sounder across sand waves 

on the continental shelf near 

Cape Cod - ·... - - - - - - - - - - - 3 

2. Large Campbell grab made by 

Logan Smith of Wilmington, California- - - - - - - - - - - - - - - 5 

3. Piston corer overside and ready 

to be lowered to the bottom - - - - 6 

iii 

5. Typical record made by a continuous seismic profiler- - - - - -

6. Shaker table used to sieve.sediment samples collected with 

the large Campbell grab- - - - - -

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The Atlantic Continental Shelf and Slope 

a Program for Study 

By K. 0. Emery and John S. Schlee 

INTRODUCTION 

For many years the work of land geologist has 

stopped at the water's edge and that of marine 

geologists started at the same line. This division of interests came about partly because of 

the differences in geologic tools needed in the 

~wo environments, and partly through limitations 

m charters of organizations sponsoring the 

geologic work. Future progress in both environments will be sped by cooperative studies of 

continental margins. To geologists, these margins are significant because they are areas of 

gr.eat crustal mobility and may, therefore, contain the key to our understanding of the growth, 

and perhaps of the origin, of continents. Most 

sedimentary rocks that geologists study on 

land were formed in a shallow marine environment. If we are to evaluate the many factors 

such as source areas, composition climate 

transporting agents, and diagenesis' that hav~ ~olded the lithified end product, we must first 

discover the relationships between unconsolidated sediments and their shallow-water marine 

environments. Moreover, within the strata of 

many continental margins are structural and 

stratigraphic traps containing petroleum, and 

a. thorough study of the margins may lead to 

discovery of additional traps. 

. In 1~62, the Congress authorized a program 

m mar me geology by the U.S. Geological Survey, 

and the Survey in turn entered into an agreement with Woods Hole Oceanographic Institution 

for a five-year joint investigation of the Continental Shelf and slope off the Atlantic coast of 

the United States. The Survey provides the financial support for the work, , and scientists 

from both organizations are engaged in the 

study. The interests and abilities of the two 

organizations complement each other in this 

study. Several other organizations are also 

cooperating in certailn aspects of the work· 

chief among these are the Bureau of Commer~ cial Fisheries, which is processing benthic 

biological samples, and the Coast and Geodetic 

Survey, which is supplying smooth sheets of 

soundings taken by its many ships in the past, 

and during the course of the investigation. Still 

other organizations, mostly universities are 

involved through their interests in special ~rob­ lems in such fields as taxonomy, chemistry, and 

and oceanographic training. 

The area of the study extends from the border 

between Maine and Canada to the southern tip 

of Florida, a distance of about 2,500 km (see 

cover). It was chosen because of the probable 

continuity of strata from land to sea floor and 

because some of the strata now expos~d in 

outcrops on land were originally deposited 

under conditions probably similar to those now 

existing on the nearby sea floor. 

FACILITIES 

The research vessel for work at sea is a rec.ent.ly converted small Army freighter (Frontispiece), renamed Gosnold in honor of a sea 

captain who explored the region near Woods 

Hole in 1602. She is steel hulled 30m long 

6.4-m beam, 2.5-m draft, and of 250 gross ton~ 

nage. Diesel-powered (275 h. p.) with a variable-pitch propeller, she cruises at 13 kmjhour 

but can also idle near zero speed. Fuel, water, 

and food capacities permlt a 3,000-km cruising 

range, well in excess of the maximum range 

needed for the work. Bunking and other facilities are adequate for 15 persons. Approximately 100 days per year will be spent at sea; 

cruises will be about one month long and spaced 

a montb or two apart. 

1/ 

- Woods Hole Oceanographic Institution, Woods Hole, Mass. 

2/ . - U.S. Geological Survey, Woods Hole, Mass. 

1 
Navigation equipment includes gyrocompass 

and pelorus, automatic pilot; radar, Loran a, 

Loran C, and radio direction-finder. Three 

winches are arranged to work over the port 

side. For light high-speed work in shallow 

depths, a bathythermograph winch carrying 

300m of 4 -mm stainiess steel cable is used. 

Light deep-water work is done with a hydrographic winch carrying 6,000 m of 6-mm stainless steel cable. The heavy work will be handled 

with a trawl winch having 3,000 m of 12 -mm nontwist cable of 13-tons breaking strength. To help 

handle heavy gear on board and overside, an 

articulated crane capable of lifting nearly one 

ton at its maximum extension of 6 m is situated 

near the middle. of the main working deck. Most 

of the navigational and other electronic equipment is. housed in a laboratory just below and 

forward of the bridge. Sam p 1 e processing, 

chemical analyses, and other work are conducted 

in a portable van fastened to the deck just forward of the electronics laboratory. Several 

such vans belong to the different groups that 

will use Gosnold for their studies; each van, 

modified to a particular project's needs, can be 

hoisted . aboard for each cruise to replace a van 

previously used by another group. 

Supporting the ship's work are laboratories 

ashore, comprising an area of about 300 sq m 

for this program. The laboratories are well 

equipped with drafting facilities and map enlargers for study of topography, and with balances, sieves, settling tubes and cylinders, 

chemical apparatus, microscopes, X-ray, pH 

meters, and spectrophotometer for studies of 

sediments and rocks. In addition,the Woods Hole 

Oceanographic Institution has available a digital 

computer, salinometers,photographic and drafting facilities, electronic and machine shops, and 

a large file of unpublished information relating 

to coastal and off-shore waters. There are also 

available for consultation many workersat Woods 

Hole who possess special knowledge and experience in water characteristics, marine biology, 

and shoreline geology. The Geological Survey 

support services include map-making facilities, 

extensive collections of foraminifera and\l"OCks,. 

and radiocarbon dating and analytical chemical 

laboratories. 

The study is being conducted by both Woods 

Hole Oceanographic Institution and the U.S. Geological Survey; scientists from both organizations are participating jointly. In the first year's 

activity existing data have been compiled, and 

new information from Gosnold cruises has been 

2 

gathered and organized. The men involved in 

the study and their areas of responsibility are 

as follows: 

K. 0. Emery, WHOI, scientist in charge of the 

study 

Donald J. Casey, USGS, river discharge and 

general sediments 

T. G. Gibson, USGS, micropaleontologist 

John C. Hathaway, USGS, X-ray and mineralogy 

Jobst Hi.ilsemann, WHOI, general sediment 

chemistry 

R. M. Pratt, WHOI, lithology and topography 

John S. Schlee, USGS, Project Chief, stratigraphy and texture of sediments 

A. R. Tagg, USGS, sedimentology and mineralogy 

James V. A. Trumbull, USGS, coarse fractions and sediment texture 

Elazar Uchupi, WHOI, underwater topography 

and areal sediment mapping 

Still·to be added to the staff are a geophysicist, 

a geochemist, and a hydrologist. 

PROGRAMS OF STUDY 

Several kinds of geological information are to 

be obtained. To visualize the shelf and slope 

and to interpret Recent and Pleistocene geologic 

history, studies of topography and sediments are 

apt to be most rewarding. For pre-Pleistocene 

history, studies of lithology and structure contribute more. Tools and procedures for each of 

these fields of investigation differ both aboard 

ship and in the laboratory ashore. 

Topography 

Existing data on the topography of the Contiinental Shelf and continental slope come mainly 

from pre-1940 surveys by the U.S. Coast and 

Geodetic Survey. Some ofthesedata(thosewhich 

relate to the area between Massachusetts and 

North Carolina) were contoured and published 

by Veatch and Smith in 1939. Soundings by the 

Coast and Geodetic Survey and others from Lamont yeological Observatory and from the Navy 

Oceanographic Office served as the basis for a 

chart of the North Atlantic, including the Atlantic 

coastal margin, drawn by Heezen, Tharp, and 

Ewing (1959). Several more detailed charts of 

sma.ller areas have been made, but because of 

their local nature, these charts are not summarized here. 

The Continental Shelf, about 2, 500 km long, 

slopes outward from shore to the shelf-break at 

a depth which increases from about 50 meters 

off Florida to 120 meters off New England. The 

average width of the shelf is about 170 km, but 
it ranges from less than 15 km off Florida to 

500 km in the Gulf of Maine. The total area is 

about 510,000 sq km, of which nearly half is in 

the Gulf of Maine (for simplicity considered here 

as Continental Shelf). The surface of the Continental Shelf is a plain made somewhat irregular 

by glacial features in the Gulf of Maine by numerous submarine valleys, most of which only 

indent the shelf-break, by submerged wave-cut 

cliffs along most of its length, and by sand waves 

on Georges Bank and elsewhere (fig. 1). 

Beyond the shelf break is a complex array of 

of continental slope, marginal plateau, and continental rise. The continental slope is steep 

(averaging 5°), and it descends to between 900 

and 3,000 m. The average width is about 50 km 

and the area is about lSO,OOOsqkm. Along most 

of its length, the continental slope is cut by submarine canyons. Benches, believed to have been 

produced by outcrops of resistant strata, occur 

along part of its length. 

At the base of the continental slope is a broad 

apron, the continental rise. Much of the shallower part may be of structural origin, but the 

deeper part is probably a fan of debris deposited 

by turbidity currents. At its toe is an abyssal 

plain 5,000 to 5,500 m deep. The average width 

of the continental slope, marginal plateau, and 

continental rise between the shelf-break and the 

5,000-m contour is 550 km, and the total area 

is about 1,400,000 sq km. 

Contour charts of the Continental Shelf and 

slope are being prepared from most existing 

soundings; the charts will be contoured at 10-m 

intervals on the shelf and at 200-m intervals 

on the slope. The results of new surveys by 

the Coast and Geodetic Survey will be incorporated as they become available. ln addition, 

sounding lines will be run about 18 km apart 

with the Precision Depth Recorder (whi~h records in meters) aboard Gosnold during the 

course of sampling operations and in certain 

small areas where detailed studies of topography 

are desired. The contour charts will serve as 

base maps for other studies. Profiles obtained 

aboard Gosnold will supplement contours in providing a basis for Physiographic studies which 

should include delineation of areas shaped by 

different erosion and depositional agents, the 

positions of ancient shorelines of glacially lowered sea levels, and the extent of postglacial 

warping, as well as the perennial inferences 

about submarine canyons. 

Sediments 

Sediments of the Continental Shelf have been 

studied over a long period of time. Stetson 

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( 1938) examined sediments along widely spaced 

traverses of the entire shelf. Shepard and 

Cohee ( 1936) analyzed many c 1 o s e 1 y spaced 

samples off New York and Connecticut. The only 

modern study, and one that also overlaps on to 

the continental slope, is that of Moore and Gorsline ( 1960) on the area off southeastern United 

States. Reconnaissance study of sediments beyond the Continental Shelf has been made by the 

Lamont Geological Observatory and reported 

in a series of papers culminating in a summary 

paper by Ericson, Ewing, Wollin, and Heezen 

( 1961 ). Many other .studies have been made of 

sediments in estuaries and on be ache s, but 

all are on local scale and unrelated. 

Sediment will be collected as short-core or 

grab samples (fig. 2) about 18 km apart on lines 

about 18 km apart across the Continental Shelf. 

Adherence to a grid will not be strict, because 

allowance must be made for variations of sediment related to topographic features. At the 

approximate spacing of one sample per 350 sq 

km, a total of about 1,500 samples would be obtained. Probably about 2,000 samples will be 

obtained in order to portray more accurately 

certain local variations. A fine start has been 

provided by a suite of about 300 samples collected on such a grid spacing in the Gulf of Maine; 

these were obtained during 1959-61 by the Bureau of Commercial Fisheries in an effort to 

relate fish populations to sediment characteristics (Wigley, 1961 ). Laboratory studies will 

be made of texture carbonate, organic carbon, 

and nitrogen contents and ofmineralogy, including clays and . coarse fractions. These parameters are usually sufficient to determine the 

origin of sediments. Sediments on the continental 

slope to be investigated will be obtained by taking 

several hundred cores with the piston corer 

(fig. 3 ). These cores will allow study of the distribution of calcium carbonate and organic matter with depth, as well as changes in pore-water 

chemistry and rates of deposition. 

The coarse grid of sediment sampling can be 

considered good reconnaissance, and it will certainly allow the delineation of areas of glacial, 

organic, authigenic, residual, relict, and modern 

detrital sediments (Emery, 1960, p. 198-208), 

and establish a framework for more-detailed 

studies of the shelf, including sediments of the 

past. 

Lithology 

Rocks cropping out on the Continental Shelf and 

in the submarine canyons were dredged by Stetson (1949}, particularly in the region between 

4 

Massachusetts and Virginia. Little rock sampling has been done elsewhere on the shelf. The 

best places for dredging are, of course, the walls 

of canyons, the shelf-break, and the face of the 

steeper parts of the continental slope (fig. 4). 

Stetson's work will be extended and detail added 

with possibly 300 well-distributed dredgings 

made from Gosnold. Additional .rock samples 

may come from cores--both incidental and intentional. Cores have the advantage over dredgings 

of being more precise in depth and position, but 

the disadvantage of being less representative of 

an area and less certain of success. Eventually, 

some offshore drilling will be done to confirm 

interpretations derived from outcrops and from 

geophysical work. 

Preparation and preliminary investigation of 

the rock samples will be undertaken at Woods 

Hole, in addition to the sorting and identification 

of most rock types in the predominantly igneous 

and metamorphic pebbles and boulders of glacial 

till and ice rafting. Final identification and correlation of sedimentary rocks in place will be 

made mostly or largely at the Geological Survey 

in Washington, where the staff is familiar with the 

lithology of the adjacent land, and where type 

rock sam p 1 e s and representative fossils collected from outcrops during many years are 

available. Also, the Geological Survey is making 

a compilation of Coastal Plain subsurface stratigraphy. 

The identification and study of rock specimens 

obtained from the sea floor may provide new information on the continuity or facies changes of 

strata well known in outcrop on land. Strata 

cropping out on land, particularly the Tertiary 

strata, consist largely of nonmarine sediments, 

but probably these grade seaward into their marine equivalents. 

Structure 

Many refraction and reflection seismic lines 

have been run across the Continental Shelf by 

Ewing and associates at Lamont Geological Observatory (a representative report is one by 

Drake, Ewing, and Sutton, 1959). Some have been 

carried farther seaward by the same group and 

by Hersey, Bunce, Wyrick, and Dietz (1959) of 

the Woods Hole Oceanographic Institution. 

Other kinds of geophysical data are needed 

more urgently at present. Chief of these are 

continuous reflection seismic profiles (fig. 5) 

of the type obtained by sparker and thumper. 

Such seismic profiling is planned for Gosnolg to 

be done mostly at night. The records should 

reveal the thickness and distribution ofpostgla-
Figure 2.-Large Campbell grab made by Logan Smith of Wilmington, California 

5 
Figure 3.-Piston corer overside and 

to be lowered to the bottom 

cial deposits, the wave-erosion terraces beneath 

these deposits, and the presence of filled extensions of submarine canyons. The presence or 

absence of sediments mantling the continental 

slope, or extending from the shelf down the slope, 

are important criteria for estimating the relative roles played by erosion and deposition in 

forming the Continental Shelf and the slope. Even 

more important, the profiles should indicate the 

6 

st:ructural attitudes of the strata underlying the 

shelf; regional seaward dips are shown by many 

unpublished recordings, but probably folds and 

faults are present locally. It is expected that at 

the end of the five-year study the entire shelf and 

slope will be crossed by seismic profiles at intervals averaging perhaps 36 km. 

Water 

Data on characteristics of water above the 

Continental Shelf and slope are more abundant 

than in other fields of interest; and, so, water 

sampling will constitute but a minor part of the 

work. Among the studies which will be made 

are those on relationships of water movement 

to transportation of sediment and erosion of the 

bottom. Internal waves, particularly those of 

tidal period, are of considerable interest in this 

respect, and their proper study is best carried 

out by anchored buoys. Similarly, direct me asurements of currents near the bottom may be related to other work now being done at Woods Hole, 

and to estuarine studies by the Geological Survey. 

Studies of sea level recorded at tide gages indicate that water discharged by rivers into the 

ocean accounts for seasonal and perhaps longterm changes of sea level. Chemical and energy 

relationships of this runoff may permit it to serve 

as. a useful tracer for following water movements 

on the shelf. Plans are also being formed for the 

examination of the characteristics of interstitial 

water of the sediments in order to learn more 

of the methods by which early diagenesis ofsediments occurs. Much of this chemical work will 

be done in association with R. M. Garrels and 

Raymond Siever of Harvard University. 

Biology 

Many of the surface sediments will be sampled 

with a large (250 kg) grab which recovers about 

0.2 cubic meter of muddy sediment from an area 

of 0.6 square meter. Within the grab is mounted 

a camera which takes a photographofthebottom 

just before the device touches bottom. Comparison of photograph and bottom sample has revealed interesting differences during preliminary work, and the photographs show attitudes 

and relationships of organi~ms difficult to infer 

from the disturbed condition in samples. As in 

previous work on the Pacific coast, the samples 

will be sieved in a shaker table on deck (fig. 6) 

to separate the organisms larger than about 1 mm 

in diameter from smaller organisms. On return 

to shore, the preserved organisms will be turned 

over to the Bureau of Commercial Fisheries for 

determination-Of associations and ofbiomasses of 

(Continued on p. 10) 
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northern slope of Georges Bank 
DEPTH 

,::1 IN FATHOMS 

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Figure 5. -Typic al record made by a continuous seismic pro filer. 
Figure 6.-Shaker table used to sieve sediment samples collected with the large 

Campbell grab 

9 
major categories of organisms by R. L. Wigley 

and Arthur S. Merrill. Geologic reasons for inclusion ofthis phase include: the need to determine the effects of mixing activities by benthic 

animals; the fact that a small to large percentage 

of the sediment consists of organic remains; and 

previously observed indications that points of 

escape of fresh water are marked by colonies of 

freshwater worms. 

Some data on plankton and productivity to supplement existing information may be obtained 

through collaboration with biologists at Woods 

Hole Oceanographic Institution, who are chiefly 

concerned with these questions. This kind of 

information will be needed to interpret the distribution of organic matter in the sediments and 

to aid in the study of foraminiferal ecology. 

BROAD ASPECTS OF THE PROJECT 

Information exists about the Continental Shelf 

and slope in many parts of the world, but nowhere 

can it be considered very complete. General 

topography is known, but usually detailed knowledge is lacking; witness, for example, the much 

higher concentration of known submarine c·anyons in the best-sounded regions--United States, 

Europe, and Japan. The world distribution of 

submerged terraces is even less well known 

than are canyons, because terraces require better soundings. Although probably no new large 

canyons will be found on the Atlantic coast, it 

is likely that new soundings and seismic profiles 

will reveal the presence of and much about the 

nature of submarine terraces. This knowledge 

should stimulate interest in further investigation 

of the extent and depth of such terraces elsewhere 

in the world. Similarly, the presence or absence 

of a blanket of sediment which extends from the 

Continental Shelf down the continental slope will 

indicate whether or not this slope progrades by 

deposition. Such conclusions can be applied to 

other areas after a relatively small effort is 

spent on testing in these areas. 

Local structures such as faults and folds can 

generally be expected to be associated with 

structures known on land. However, the great 

tectonism of many continental slopes suggests 

that other kinds of folds and faults may be associated with the outer Continental Shelf and 

the slope; such structures may be closely related, and found in this environment in many 

parts of the world. The deeper seated downfolds 

of crustal rocks beneath the Continental Shelf 

and slope off the Atlantic and Gulf coasts of the 

United States and off England may be a common 

characteristic of continental margins to be discovered elsewhere when adequate s e ism i c 

studies are made. 

Sediments on outer continental shelves and 

slopes have a family resemblance throughout 

the world, because modern detrital sediments 

generally have not 'yet covered those relict from 

glacially lowered s~a levels. The same lack of 

cover by modern detrital sediments has permitted the accumulation of slowly deposited 

organic and authigenic sediments near the shelf 

break. Comparison of sediments on the Atlantic 

shelf with those of fairly well studied areas in 

the same latitudes off southern California and off 

the Asiatic coast (Niino and Emery, 1961) should 

provide evidence of the controls exerted by water 

temperature and salinity and by contributions 

from land. These inferences can subsequently 

be applied more certainly than in the past toestimation of facies control within ancient strata. 

Fortunately, the Atlantic Coastal Plain and Continental Shelf are underlain by Tertiary sedimentary rocks which were probably deposited 

in an environment somewhat similar to the existing one. Therefore, application of the knowledge gained from modern sediments can be applied directly to ancient strata. 

In the same vein, sedimentary structures similar to those in modern sediments have been 

used by Potter and Glass (1958) to infer the environment of deposition in ancient sedimentary 

rocks. These structures are among the most 

obvious features of rock outcrops studied by land 

geologists. Not only have they been helpful in 

determining environments, but they also have 

aided in deducing the ancient geography. Similar 

sorts of structures will be encountered in the 

cores taken on the shelf and slope. Here we will 

have an opportunity to see what types of structures are indicative of different environments, 

through correlation with other properties such 

as type of benthic fauna present. 

Studies of the types outlined above must be 

regional in extent even though based on widely 

spaced samples. Detailed studies of small areas 

cannot have the necessary breadth of land and 

sea-floor environments. The Atlantic Gontinental Shelf is sufficiently large for this general 

framework study, because it covers 20° of latitude and has an area equaling that of all the 

New England states plus New YorkandPennsylvania, or 5 percent of the total United States. 

The continental slope, of course, has an additional large area, and the continental rise even 

more. 

The labor of constructing a general environmental framework is such that many interesting 

10 
questions of d i age n e s is must be temporarily 

passed up or only sketchily investigated at first. 

Many of these process problems will be investigated as time and opportunity permit. Among 

these are questions of alteration of organic matter leading to petroleum, the changes of interstitial waters with time and depth of burial, and 

migration of sand waves in formation of sheet 

sands. Clearly, most process problems can best 

be investigated when a sufficient level of understanding is reached concerning origin, transportation, and deposition of the particular source 

materials, including their enclosing sediments. 

This means that the topography and water movements must be known far better than at present. 

Lastly, we may expect that the results of the 

general study will have considerable application 

to future recovery of oil and gas and to mining 

of such sea-floor deposits as manganese and 

phosphorite. Certainly we cannot now foresee 

the full benefits of a study which is the first of 

its kind and which is now just beginning. 

REFERENCES 

Drake, C. L., Ewing, M., and Sutton, G. H., 1959, 

Continental margins and geosynclines: The 

east coast of North America north of Cape 

Hatteras: Physics and Chemistry of the 

Earth, v. 3, p. 110-198, Pergamon Press. 

Emery, K. 0., 1960, The Sea off Southern California: A modern habitat of petroleum: 

New York, John Wiley & Sons, 366p. 

Ericson, D. B., Ewing, M., Wollin, G., and Heezen, B. C., 1961, Atlantic deep-sea sediment 

cores: Geol. Soc. America Bull., v. 72, 

p. 193-286. 

Heezen, B. C., Tharp, Marie, and Ewing, M., 

19 59, The floors of the oceans, 1. The North 

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