SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES • NUMBER 11

Underwater Television Survey of the

Atlantic Outer Continental Margin

near Wilmington Canyon

Daniel J. Stanley and Peter Fenner

AUGf

SMITHSONIAN INSTITUTION PRESS

City of Washington

1973
ABSTRACT

Stanley, Daniel J., and Peter Fenner. Underwater Television Survey of the

Atlantic Outer Continental Margin near Wilmington Canyon. Smithsonian

Contributions to the Earth Sciences, number 11, 54 pages, 18 figures, 1973.—

The study summarizes the results of an underwater television survey of the sea

floor at the shelfbreak and at the head of Wilmington Canyon off the Middle

Atlantic States. Distributions are shown for bottom currents and sedimentary

structures, suspended matter, bottom firmness, bottom lithology, shell percentage, and fauna. A number of man-made objects on the sea floor in this area is

documented. The Appendix is a listing of observations made at 26 stations.

These data, based on direct visual observation of the sea floor, serve to complement earlier marine geological investigations made in this region. Mapping

shows that surficial outer shelf and canyon head sediments at the shelfbreak are

undergoing modification by both bottom current processes and bioturbation and

that at the present time the Wilmington Canyon is receiving sediment mainly

from the adjacent margin. Gravel, oyster banks, and near-vertical cavernous

cliffs occurring at depths between 100 and 200 m are relict features related to

eustatic changes of sea level that affected the outer continental margin during the

Pleistocene.

OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded

in the Institution's annual report, Smithsonian Year. SI PRESS NUMBER 4785. SERIES COVER

DESIGN: Aerial view of Ulawun Volcano, New Britain.

Library of Congress Cataloging in Publication Data

Stanley, Daniel J.

Underwater television survey of the Atlantic outer continental margin near Wilmington

Canyon.

(Smithsonian contributions to the earth sciences, no. 11)

1. Continental margins—United States. 2. Television in oceanography. I. Fenner, Peter,

1937— joint author. II. Title. III. Series: Smithsonian Institution. Smithsonian contributions to the earth sciences, no. 11.

QE1.S227 no. 11 [GC84.2.U5] 550'.8s [551.4'614'6] 72-13421

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

Washington, D.C. 20402 - Price 65 cents (paper cover)
Underwater Television Survey of the

Atlantic Outer Continental Margin

near Wilmington Canyon

Daniel J. Stanley and Peter Fenner

Introduction

This publication represents an effort to make

available in one place all of the source data obtained during an underwater television survey as

one of a series of investigations concerned with sedimentation patterns on the outermost reaches of the

broad continental shelf bordering the Middle Atlantic States. Direct visual observations relating to

bottom sediment types and the distribution of

faunal elements are presented here for the first

time.

The present series of investigations includes a

morphologic and subbottom reconnaissance (Kelling and Stanley, 1970), a photographic and bottomsampling program (Stanley and Kelling, 1968), and

water-mass configuration and movement studies

(Fenner et al., 1971; Lyall et al., 1971). Direct observation of bottom neocurrent activity, water-mass

movement, and sediment transport was made by

underwater television and was in part reported on

elsewhere (Stanley et al., 1972). This, a relatively

novel observational technique, has been used with

success in other areas (Stamp, 1953; Eddy et al.,

1967; Drapeau, 1970).

The specific area we examined by the underwater

television technique is about 175 km southeast of

Delaware Bay, at the head of Wilmington Canyon

Daniel J. Stanley, Division of Sedimentology, Smithsonian

Institution, Washington, D. C. 20560. Peter Fenner, Governors

State University, Park Forest South, Illinois 60466.

and at the break between the outermost continental

shelf and upper continental slope (Figure 1). It was

selected in accordance with the overall plan for

this series, in which successive cruise itineraries

were conditioned by the results of previous determinations, e.g., of bathymetry, structure and stratigraphic setting, water mass, and bottom type and

aspect.

Sedimentation in canyons heading in deep water

far from land remains enigmatic. Our studies have

led us to infer that the head of the Wilmington

Canyon has, both now and in the recent geologic

past, trapped sediment moving on the outer shelf.

The hypothesis that sediment is being funneled

downslope through the Canyon was assessed in a

previous paper (Stanley and Kelling, 1968).

Data presented herein were gathered during a

cruise (RoS4) made aboard the USCGC Rockaway

(WAGO377) from 11 to 18 July 1968.

ACKNOWLEDGMENTS.—We thank the U.S. Coast

Guard Oceanographic Unit for ship time and the

captain, officers, and men of the USCGC Rockaway

for their help in carrying out the work at sea. Dr.

G. Kelling, University of Wales, helped in the

planning phases of this cruise as well as in the

collection of data. We were also aided by Dr.

D. J. P. Swift, Marine Geology and Geophysical

Laboratory, National Oceanographic and Atmospheric Administration, Mr. J. A. Good, Hydro

Products, and Messrs. G. Bloomer, D. Eby, E.

Gruenstein, and D. Kersey. Messrs. H. Sheng and
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

38°40'

38*30'

TV STATION

(DEPTH IN FATHOMS)

N. MILES

2 3

0 1 2 3

KILOMETERS

73°30'
NUMBER 11

<- FIGURE 1 Television stations occupied in and near the head

of Wilmington Canyon east of the Middle Atlantic States in

July 1968. Data collected along the station tracks are shown

in Appendix. Depth in this and other charts given in fathoms

(1 fathom — 1.83 m).

L. B. Isham, Smithsonian Institution, helped with

drafting. Dr. G. Kelling and Dr. H. D. Palmer,

Westinghouse Ocean Research Laboratory, criticized the manuscript. We alone take responsibility

for errors that may remain. Financial support was

provided by Smithsonian Research Foundation

grant nos. 233770 and 234230 (D. J. S.) and Governors State University (P. F.).

Area of Study

Details of the physiography and topography of

the area studied are given by Kelling and Stanley

(1970). Figure 1 shows the ship's track at the 26

television stations occupied during a period of very

low wind and fairly calm seas. Bottom control,

necessary to keep to a planned track, was based on

bathymetric records and PESR (Precision Echo

Sounding Recorder) records taken continuously

throughout the cruise.

Methods and Techniques

Video monitoring and recording equipment were

continuously manned during all times when the

underwater television rig was submerged (at depths

to 426 m). The system included a light source,

suspended penetrometer, and vaned compass attached to the frame on which the camera was

mounted (Figure 2). The compass (diameter, 7.5

cm) serves as scale.

Greenwich Mean Time was used as the basic

reference for all notations and recordings of

continuously monitored data—bathymetry and

bottom-viewing—and for regularly made observations—navigational fixes, course changes, weather

observations, and hourly expendable bathythermograph, surface-water temperature, and salinity records.

In addition to written notes, the videotape recorder was used to record a running commentary

of sightings, data collected, and speculations on

explanations of observations. The audio track of

B

FIGURE 2.—Photographs on deck of USCGC Rockaway

showing underwater rig used on cruise RoS4: A, television

gear, mounted in a steel frame (120 cm x 120 cm x 120 cm),

and large stabilizing vane was lowered off the stern and

kept just above the sea floor as the ship drifted; B, camera

(a) [Hydrp Products Model TC 100], 1000-watt mercury

vapor light (b) mounted in cage and attached to 460 m

long cable. Compass (c) was suspended far enough from

frame to be free from the effects of its magnetic field.

Tapered and scaled shaft (penetrometer, d) was hung below

all other equipment so as to be in view when striking sea

floor.
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FIGURE 3.—Features such as oriented polychaete tubes (Station 19, 346 m), on upper slope west of the Canyon, provide

information on botton currents. In this sequence, note the

realignment of tube (in rectangle) resulting from turbulence

caused by the cage motion above the sea floor.

the videotapes was later found to be extremely

helpful in reconstructing observations and organizing conclusions.

Details on light and camera angles, technical

data on instruments used, and operating conditions

for the gear are given elsewhere (Stanley et al.,

1972). The photographs in the plates of the present paper are, for the most part, reproductions of

images stored on one tape, transferred to another,

kinescoped, photographed, then enlarged and made

into new negatives with prints for use here. These

fifth generation reproductions have suffered much

in the process.

Data concerning most variables, save navigational

specification (see Figure 1, for all locations), are

FIGURE 4.—Sequence of photographs made from video tapes

shows turbulence initiated as compass strikes muddy bottom

(A) (Station 18, 134 m). After a few seconds (B) mud

brought into suspension is slowed by SSE moving current and

then (c) the cloud begins movement to the S and SSW

(about 10 cm/sec) and out of view. Compass diameter,

7.5 cm.
38°40'

38°30

38°IO'

•• current

w ripple marks

worm tubes

aligned shells

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N. MILES

0 1 2 3

KILOMETERS

FIGURE 5.—Chart showing evidence of neocurrent activity in and near the head of Wilmington

Canyon (from Stanley et al., 1972). Arrows depict direct observation of sediment movement

of currents above the bottom (based on sediment movement or heeling over of sessile fauna).

Indirect evidence of recent current activity (based on alignment of ripple mark crests, polychaete tubes and aligned shells) is also depicted.
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

listed in the Appendix. Summarized are raw observational and interpretative data such as: station

number and physiographic location; date and time;

depth; inferred bottom-sediment texture; resistance

to penetration (firmness); the nature, orientation,

and dimension of ripple marks and other features

indicating current movement, including oriented

organic structures; velocity of suspended sediment

movement along the bottom; nature and distribution of shell fragments; and the relative amounts

of materials suspended in the water near the bottom.

A partly edited, untitled version of a short film,

and the more than 20 hours of videotapes from

which it was made, are available from the Sedimentology Laboratory, National Museum of Natural History.

Suspended Matter and Bottom Currents

Suspended matter and current activity were observed everywhere throughout the area of study—

on the outermost continental shelf, shelf break,

canyon head proper, and upper slope—but not uniformly developed. Ripple marks, aligned polychaete tubes (Figure 3), and shells were used to

infer current directions, and particles streaming

along the sea floor past a fixed object of known

size provided a means for measuring bottom-current

velocities (Figure 4). Data included in the Appendix are fully discussed in Stanley et al. (1972).

In sum, current activity ranged from barely detectable to about 20 cm/sec and did not follow a

uniform pattern (Figure 5). There is, however,

a net southerly and downslope orientation to current flow within the Canyon. Medium to large

concentrations of suspended matter just above the

sea floor (Figure 6) help explain the generally poor

clarity of photographs made in earlier surveys of

this area (Stanley and Kelling, 1968). Figure 6 depicts a rather subjective classification of concentrations of suspended matter, and shows that higher

concentrations most often occur higher on the shelf

side of the shelfbreak. There is also a suggestion

of a slight westward offset of the medium-clarity

water from the Canyon axis, particularly in the

headward part, which may reflect large scale motion of shelf and slope water in this region during

the period of the survey.

38*30'

FIGURE 6.—Chart showing distribution of layer of suspensionrich water above the sea floor as observed by television.

During the period of the cruise (11 to 18 July 1968) somewhat higher concentrations of suspended sediment were noted

in the area landward of the shelfbreak than in the Canyon

head proper. A slight westward offset away from the Canyon

is also observed.

Firmness of the Sea Floor

Penetration into the sea floor of a scaled stainless steel shaft (see penetrometer in Figure 2nd)

provides a relative scale of bottom firmness. Areas

of deep (> 24 cm), medium (15-24 cm), and shallow penetration (< 15 cm) were thus designated

and mapped (Figure 7).

Data summarized in the Appendix show that

most of the sea floor of the outer shelf and uppermost slope regions not near the Canyon is characterized by low to very low penetration. This

firm surface is indicative of a shelly, gravelly sand

cover. A zone of medium penetration occurs at the

very head of the Canyon and along much of its

eastern wall to a depth of about 200 to 450 m and

appears to be indicative of sandy mud, silt, clay,

or mixtures of these grades. The least firm sedi-
NUMBER 11

38*30'

PENETRATION

shollow | 1 dttp

medium (DEPTH IN FATHOMS)

N. MILES

FIGURE 7.—Chart indicating bottom firmness, based on

amount of penetration of scaled shaft into the surficial sediment. Generally firmer sediment on the east canyon wall

reflects the presence of coarser sediment tongues draping

on that wall as opposed to the west wall.

ments occur in the Canyon proper and a distributary canyon cut into the shelf west of the head and

reflect a soft clay or ooze bottom (Figure 8). On

the western margin, the contact between firm and

soft surfaces is more abrupt, and tends to occur

at a shallower depth than on the eastern wall, appearing near the shelfbreak.

Organic mounds and tracks, ripple marks, other

primary sedimentary structures, and the nature of

the sediment cloud produced by instruments hitting the sea floor, all aided in further interpretation of the bottom firmness.

These techniques help to define the generally

abrupt "mud line," a boundary, despite tradition,

not strictly parallel to the shelfbreak.

Major Lithological Types

The contoured regional distribution of major

surficial sediment textural types is shown in Figure

FIGURE 8.—Sequence showing deep penetration (at least 24

cm) of scaled shaft in soft sediment on the west wall of the

canyon head (Station 16A, 256 m) .

9. The categories shown are: (a) rock ledges (Figure 10) and bedrock obviously discernible directly

from the videotapes, and large broken rock talus

(Figure 11); (b) admixtures of pebbles, shell and
73*,30'

38*30'

FIGURE 9.—Chart showing distribution of major lithological

types in the study area. Note presence of rock outcrops in

the canyon head near the shelfbreak, and the draping of

sand and gravel on the east wall well into the canyon. The

"mud-line" is not strictly parallel to the shelfbreak indicating that spill-over and off-shelf processes have been active

in recent time.

FIGURE 10.—Sequence showing cavernous rock outcrop just

below the shelfbreak on the west wall of the Canyon (Station 16, 120-130 m). This unit forms low "cliffs" with a

relief of 5 to 10 m, and is populated by numerous fish and

occasional lobsters. The rock is poorly consolidated at the

surface as indicated by breaking of outcrop by the penetrometer.
NUMBER 11

coarse sand (also directly discernible from tape),

locally including finer sediment (Figure 12); (c)

admixtures of medium to fine sand and sandy silt,

generally indicated by degree of penetration of the

penetrometer, and the presence of associated features such as ripple marks amply illustrated in

Stanley and Kelling (1968; and also detected by

direct observation when cage is at rest on sea floor);

and (d) mud, including silty and stiff clay, as

judged by appearance on the monitor, amount of

penetration, and as indicated by the character of

the mark made on the bottom or the nature of the

sediment cloud raised by the cage and suspended

instruments (Figure 8).

Categories b and c generally include shelly sands.

The character of sedimentary structures and organic tracks, burrows and mounds ("lebensspuren")

provide additional evidence of the nature of bottom sediment type.

Views of rock outcrops along the canyon walls

provide some of the more spectacular footage of the

television tapes. The most obvious outcrops of

bedrock occur on the west side of the canyon wall.

There, large clifflike protruding edges of some exposures of cavernous rock occur at depths ranging

from 110 to 135 m (Figure 10). Locally, the exposures are sufficiently friable to be easily broken

by the weight of the penetrometer. On the eastern

side of the canyon, rock exposures were found to

be different in character; they form isolated patches

with numerous flat-lying surfaces frequently burrowed but not particularly cavernous. Texture of

the bedrock appears to be medium to fine. The

patchy occurrence of outcrops shown in Figure 9

is in part an artifact resulting from the sample net

and subsequent plotting. Furthermore, in the

areas west of the canyon where we found outcrops,

they tended to be continuous, running perhaps for

hundreds of meters; on the eastern side, however,

the outcrops occur as smaller patches (< 1000 m2)

throughout the area where they are plotted. The

paired nature of outcroppings across the canyon is

also, in part, an artifact resulting from the sample

grid.

The coarser surficial sediment consisting of

gravel and coarse sand (areas of very low penetration) was found covering much of the outermost

shelf area in the vicinity of the canyon, in waters

generally less than 180 m deep; however, these

FIGURE 11.—Rock outcrops of the type shown in Figure 10

fail ("rock fall"), thus producing boulders and cobbles

encountered at deeper depths in the Canyon and on the

upper slope. Here a sequence of photographs (Station 12,

278 m) show a large (> 1 m diameter) shell-encrusted block

resting on mud. Note fish on rock (B) .
10 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FIGURE 12.—Concentrations of large pelecypod valves including oysters (A) and gravel on the

upper slope just west of the Canyon (Station 19, 196 m). These patches of anomalous sediment

types are relict deposits probably related to eustatic lower stands of sea level.

coarser grade sediments tend to drape into deeper

water along the eastern canyon wall. Pebbles and

cobbles were observed to depths of at least 320 m

at Station 8.

Medium to finer grade sand and sandy silt tend

to cover the upper margins of the canyon proper

and are, in fact, the predominant textural types

serving as the upper canyon head fill. This lithological type is also the predominant facies in those

areas of the shelf not covered by gravel and coarse

sand.

The predominantly muddy facies are located axially and extend shelfward to depths of about 90 m

at the very northward sector of the canyon head.

Similarly, mud can be found in tributary canyons

entering the canyon proper. The "mud line" cannot be well defined on the west canyon wall because

television stations generally did not extend to the

same depths as on the east wall (i.e., drift of the

ship prevented the television cage from hanging

vertically).

The sediment textural distribution confirms earlier conclusions based on bottom photography

(Stanley and Kelling, 1968), subbottom (Kelling

and Stanley, 1970) and current studies (Fenner et

al., 1971), and more generalized data that sand
NUMBER 11 11

spill-over from the outer shelf into the Canyon has

continued until recent time and may still be an

active process at present. As a result, sand is a

predominant fraction in certain parts of the canyon

head.

Shell Fraction in Surficial Sediments

Shell is one of the predominant components of

surficial sandy sediment on the continental shelf.

This fraction, mostly whole or fragmented disarticulated pelecypod valves, accounts for more than

30 percent of the total sediment. Shell content

tends to vary inversely with depth, the decrease of

shell amount coinciding roughly with the break in

slope. On the eastern canyon margin, however, the

distribution of shell-rich sediment coincides with

that of the sand-rich sediment, draping from the

shelf edge into deeper water.

A scale of relative shell abundance was devised

(Figure 13). Outermost shelf sediment was found

generally to contain more than 25 percent shell,

while patches of shell-deficient sediment occur on

the shelf in the vicinity of gravel and coarse sand

patches.

Local concentrations of large pelecypods and

gravel occur between about 130 and 200 m (Figure

12). It is possible that certain of these may be

remnant oyster banks of the type found in other

sectors of the Atlantic shelf at lesser depths (Merrill et al., 1965; Emery, 1968) and dating from low

stands of sea level during the Pleistocene Epoch.

Fauna and Bioturbation

Living fauna is a common element in all videotapes, and the organic forms observed have been

grouped into four generalized categories and their

distribution is summarized on Figure 14: (a) nonshelled swimming forms, mostly fish (Figures 10;

15c, D; 17C) and, locally, squid (Figure 16); (b)

shelled bottom dwellers, e.g., pelecypods (Figure

38"40'.

38*30'

73",30'

38*4O'/

28-tOX I I I N >25X

(DEPTH IN FATHOMS)

N. MILES

FIGURE 13.—Chart showing distribution of shell (including

whole and fragmental matter) , in surficial sediment. Note

rapid decrease in shell percentage in water depths below

shelfbreak.

38*30"

cru.tac.ans \JIJ\ ^ ypo j : ChlnOld> 1

[]• ] «l«h n««ft (DEPTH IN FATHOMS)

N. MILES

KILOMETERS

FIGURE 14.—Distribution of major benthic organisms as observed with television. Note sharp faunal breaks between th~

outer shelf and the Canyon head.
12 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FIGURE 15.—Organisms in the water mass above the sea floor: A, concentration of planktonic

forms at northern end of Canyon head (Station 7, 238 m) ; B, shrimp on east wall of Canyon

(Station 11A, 302 m) ; c, D, school of small fish on the upper slope west of Canyon (Station 19,

347 m).

12), bryozoans, and echinoderms; (c) soft-bodied

bottom dwellers, e.g., sea pens (Figure 17A), COelenterates (Figure 17B), and worms; (d) crustaceans, including mainly crabs (Figure 17D),

shrimps (Figure 15B), lobsters, and sea spiders.

The nonshelled swimming forms are most common just within the Canyon proper, and especially

on the west margin of the Canyon. Localized concentrations of fish and plankton (Figure 15A) are

also noted on the shelf north of the canyon reentry. Like the fish themselves, fish "nests" are

concentrated in fine-grained sediment below the

shelfbreak. As detailed in the previous section,

pelecypod and related fragments dominate the surficial shelf sediments and decrease notably beyond

the shelfbreak. The distribution of echinoderms

is generally irregular and patchy, but locally single

faunal types predominate (see Appendix).

Crustaceans are more commonly observed below

the shelfbreak, the larger forms (i.e., lobsters) frequently concentrating in or near the cavernous rock

outcrops where benthic fish are also abundant.

Sea pens and coelenterates are limited depthwise below the shelfbreak and, together with

worms, are most abundant in finer grained sediment within the Canyon. They locally dominate
FIGURE 16.—Sequence showing squid moving past television

cage and releasing ink, in the head of Canyon (Station 6,

148 m).

the faunal assemblage along the west margin of

the Canyon. One area distinguished by this assemblage was also observed just northeast of the

very head of the Canyon. The concentration of

worm burrows increases canyonward beyond the

shelf break (Stanley, 1971a). These burrowing organisms not only modify the strength of sediment,

but also contribute to the addition of suspended

sediment in the water mass (worms were seen ejecting small clouds of mud as the cage moved slowly

above the bottom). Fish also were seen stirring the

bottom, and they are important in modifying the

sea floor and contribute in a small way to the sediment in suspension (Stanley, 1971b).

Man-made Objects

Human artifacts constitute minor but, in our

opinion, significant components of the sea floor in

the study area which lies below the east coast

shipping lane. Considering our very limited field

of view, even the dozen or so whole, large, objects

observed during a 5-day period suggest that there is

a growing amount of material accumulating even

at this distance from shore.

Observations of such materials included bottles

(Stations 5, 12), cans (Station 3A), paper (Station

19; Figure 18), and a large polelike object. Materials of smaller size were not recorded, and in

most cases would have been very difficult to observe due to the camera's motion through the water.

The high percentage of artificial fibers filtered from

water samples collected in this area on a subsequent

cruise (Lyall et al., 1971) attests to the importance

of man-introduced materials on this sector of the

outer continental margin.

Fenner et al. (1971) have shown that this region

is one of significant bottom-current activity, hence

we can speculate that only a short period of time

has elapsed since the objects observed were deposited. The origin of one bottle with a distinct

shape was identified, though not recorded on videotape (this type of bottle had been commercially
14 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

D

FIGURE 17.—Example of benthic organisms in the study area: A, large worm tubes extruding

from the sea floor on east wall of Canyon (Station 8, 320 m) ; B, anemones on uppermost slope

east of Canyon (Station 12, 312 m) ; c, benthic fish (outlined) extending out of large mud

depression on west wall of Canyon (Station 13, 267 m) ; and D, crab moving past penetrometer

on upper slope east of Canyon (Station 12, 311 m).

introduced only a half-year or so before the cruise).

Considerably more man-made objects are presumably buried in the sediment.

Conclusions

Examination of the sea floor and mapping of the

outer Atlantic margin near the head of Wilmington Canyon with underwater television supplements observations made in earlier surveys of this

region. Among features of particular interest are:

(1) the apparent intensity of bottom-current activity and the abundance of suspended matter

above the sea floor in the depth range from G5 to

430 m, even though the survey was made in very

calm weather and low sea state; (2) the abundance

of benthic organisms and intensity of reworking

(bioturbation) throughout the study area; (3) the

draping of sandy sediment tongues on the east wall

into the Canyon axis, and the shallower position

of the "mud line" near the shelfbreak on the west

Canyon wall; (4) the exposure of cavernous rocky
NUMBER 11 15

cliffs on the west wall concentrated between 110

and 135 m depth; (5) the concentration of pelecyFIGURE 18.—Sequence (A-C) of videotape showing compass

catching long paper on the upper slope west of Canyon

(Station 19, 200 m) .

pods, including oysters, and gravel in pockets between 130 and 200 m; and (6) the significant

number of large man-made objects even in this area

located far from land.

The first three observations listed above indicate that surficial sediments, including sand, are

being actively moved by the water mass and continuously reworked by organisms. This current activity results in a net downslope transport from

the shelf edge onto the upper slope and into the

Wilmington Canyon proper. Spill-over from the

shelf onto the east Canyon wall is prevalent. Organisms apparently accelerate this off-shelf process

by modifying the physical properties of the sediment wedge.

The submerged cliffs, gravels, and oyster banks

are relict features resulting from events related to

eustatic lowering of sea level in Pleistocene time.

The cliffs are at depths that suggest that they were

subaerially exposed river- and ocean-cut bluffs. The

gravels, undoubtedly of river origin, help pinpoint

the position of fluvial deposits and coarse deltaic

concentrations formed at the shelfbreak by major

rivers that drained the northeastern United States

and traversed the subaerially exposed continental

shelf during the Pleistocene. The localized oyster

"patches" and other pelecypod concentrations were

also formed when sea level was considerably lower

(at least about 120 m lower), in Wisconsin time.

The presence of man-made objects on the sea

floor below shipping lanes is not in itself surprising. It does serve to emphasize, however, the importance of this type of refuse as an important element of surficial sediments and one likely to

increase unless dumping from ships is more tightly

controlled.

Underwater television has proved a valuable tool,

and its use by marine scientists who plan reconnaissance mapping and regional surveys is advocated. Nothing can surpass this direct visual

examination of the ocean floor.

Literature Cited

Drapeau, G.

1970. Sand Waves on Browns Bank Observed from the

Shelf Diver. Maritime Sediments, 6:90-101.

Eddy, J. E., V. J. Henry, J. Hoyt, and E. Bradley

1967. Description and Use of an Underwater Television

System on the Atlantic Continental Shelf. U. S.
16 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

Geological Survey Professional Paper, 575-C:G72-

C76.

Emery, K. O.

1968. Positions of Empty Pelecypod Valves on the Continental Shelf. Journal of Sedimentary Petrology,

4:1264-1269.

Fenner, P., G. Kelling, and D. J. Stanley

1971. Bottom Currents in Wilmington Submarine Canyon. Nature, Physical Sciences, 229:52-54.

Kelling, G., and D. J. Stanley

1970. Morphology and Structure of Wilmington and Baltimore Submarine Canyons, Eastern United States.

Journal of Geology, 78:637-660.

Lyall, A., D. J. Stanley, H. N. Giles, and A. Fisher, Jr.

1971. Suspended Sediment and Transport at the Shelfbreak and on the Slope. Marine Technology Society Journal, 5:15-27.

Merrill, A. S., K. O. Emery, and M. Rubin

1965. Ancient Oyster Shells on the Atlantic Continental

Shelf. Science, 147:398-400.

Stamp, W. R.

1953. Underwater Television. Scientific American, 188:

32-37.

.Stanley, D. J.

1971a. Bioturbation and Sediment Failure in Some Submarine Canyons. Vie et Milieu, supplement 22,

541-555.

1971b. Fish-produced Markings on the Outer Continental

Margin East of the Middle Atlantic States. Journal

of Sedimentary Petrology, 41:159-170.

Stanley, D. J., P. Fenner, and G. Kelling

1972. Currents and Sediment Transport at the Wilmington Canyon Shelfbreak, as Observed by Underwater

Television. Pages 621-644 in D. J. P. Swift, D.

Duane, and O. H. Pilkey, editors, Shelf Sediment

Transport: Process and Pattern. Stroudsburg,

Pennsylvania: Dowden, Hutchinson & Ross.

Stanley, D. J., and G. Kelling

1968. Photographic Investigation of Sediment Texture,

Bottom Current Activity, and Benthonic Organisms

in the Wilmington Submarine Canyon. U.S. Coast

Guard Oceanographic Report, 22: 95 pages.
Appendix

PAGES 17-28

Data recorded on videotape at 26 stations, outer continental margin near Wilmington Canyon

(period 12 to 16 July 1968 on USCGC Rockaway cruise RoS4) . See Figure 1 for station

location.
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