70°13' 70°10' 70°08' 70°06' 70°04' 70°02'

42°18'

42°19'

70°13' 70°11' 70°09' 70°07' 70°05' 70°03'

42°14'

42°16'

42°18'

42°19'

42°14'

42°16'

70°11' 70°09' 70°07' 70°05' 70°03'

70°12' 70°10' 70°08' 70°06' 70°04'

42°17'

42°15'

42°13' 42°13'

42°15'

42°17'

70°12'

70°02'

Sheet 1.—Seabed geology

Map D.—Distribution of Geologic Substrates

Seabed Maps Showing Topography, Ruggedness, Backscatter Intensity, Sediment Mobility, and the

Distribution of Geologic Substrates in Quadrangle 6 of the Stellwagen Bank National Marine Sanctuary Region 

Offshore of Boston, Massachusetts

By

Page C. Valentine and Leslie B. Gallea

2015

Any use of trade, firm, or product names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government

Digital files available at http://pubs.usgs.gov/sim/3341/

Suggested citation: Valentine, P.C., and Gallea, L.B., 2015, Seabed geology, sheet 1 of Distribution of

geologic substrates, map D of Seabed maps showing topography, ruggedness, backscatter 

intensity, sediment mobility, and the distribution of geologic substrates in quadrangle 6 of the 

Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts: U.S. 

Geological Survey Scientific Investigations Map 3341, scale 1:25,000, 

http://dx.doi.org/10.3133/sim3341.

ISSN 2329-132X (online)

http://dx.doi.org/10.3133/sim3341

Prepared in cooperation with the

National Oceanic and Atmospheric Administration

Scientific Investigations Map 3341

Map D, sheet 1

Mercator projection

Geodetic Reference System 1980; North American Datum of 1983

Longitude of central meridian 70°19' W; latitude of true scale 41°39' N

False easting 0 m; false northing 0 m

This map is not intended for navigational purposes.

SCALE 1:25 000 

ONE CENTIMETER ON THE MAP REPRESENTS 250 METERS ON THE SEA FLOOR 

1 .5 0 1 2 3 4 KILOMETERS

1 .5 0 1 2 NAUTICAL MILES 

CONTOUR INTERVAL 5 METERS

ADDITIONAL 1-METER CONTOURS INCLUDED TO SHOW BOTTOM ROUGHNESS

DATUM MEAN LOWER LOW WATER

MIDDLE

NINETY

BANK

EAST

NINETY

BANK

SOUTH

NINETY

BANK

NORTH 

NINETY

BANK

STELLWAGEN BANK NATIONAL MARINE SANCTUARY

N I N E T Y M E T E R B A N K S

STELLWAGEN BANK

A1 r_cgS

B r_cgS / i_cbG

D1 i_cgS / pcbG

C i_cbG

E i_cgS

D2 i_mcgS / pcbG

F i_cgS / pcbG

F i_cgS / pcbG

G2 i_mfgS

G1 i_mfgS

A2 i_cgS

A1 r_cgS

D2 i_mcgS / pcbG

A1 r_cgS

D1 i_cgS / pcbG

C i_cbG

E i_cgS

F i_cgS / pcbG

G1 i_mfgS

G2 i_mfgS

B r_cgS / i_cbG

D2 i_mcgS / pcbG

A2 i_cgS

DESCRIPTION OF MAP UNITS

[Grain-size composition of each map unit is given as mean weight percent for each grain-size category 

(table 5). Weight percent values may not add to 100 due to rounding. Texture characteristics for 

substrates B, D1, D2, and F represent the partial sediment veneer overlying gravel. Substrate unit names 

(tables 6, 7) describe sediment grain-size composition, surficial morphology, sediment layering, and the 

mobility or immobility of their surfaces. See Conversion Factors for grain-size classification of 

sediment grades (Wentworth, 1922) and composite sediment grades of this study. Sand is divided into 

two composite grades: fine-grained sand (fgS; 0.062 to <0.25 mm) and coarse-grained sand (cgS; 0.25 

to <2mm). Gravel is also divided into two composite grades: Gravel1 (G1; 2 to <8 mm) and Gravel2 (G2; 

8 to <64 mm). Abbreviations: r, rippled; i, immobile; m, muddy (≥10 weight percent mud); fgS, 

fine-grained sand; cgS, coarse-grained sand; G1, Gravel1; G2, Gravel2; p, pebble; c, cobble; b, boulder. 

The notation “i_cGS / pcbG” means “immobile, coarse-grained sand; partial veneer on pebble, cobble, 

boulder gravel.” See Mapping Methods for further explanation]

Rippled, coarse-grained sand—Substrate A1 is a mobile sand deposit on the upper 

flank of Stellwagen Bank. Depth range is 30 to 56 m. Mean weight percents per 

grain-size category: mud, <1; sand, 90 (fgS, 3; cgS, 88); gravel 9 (G1, 8; G2, 1). 

Substrate A1 is equivalent to the mobile portion of adjacent substrate B; and it is 

similar to adjacent immobile substrate A2 which lies at deeper depths (53–77 m) 

on the lower flank of Stellwagen Bank and contains more fine-grained sand (11 

weight percent)

Immobile, coarse-grained sand—Substrate A2 is an immobile sand deposit on the 

lower flank of Stellwagen Bank. Depth range is 53 to 77 m. Mean weight 

percents per grain-size category: mud, 1; sand, 83 (fgS, 11; cgS, 72); gravel, 16 

(G1, 11; G2, 5). Substrate A2 is similar to adjacent mobile substrate A1 which lies 

at shallower depths (30–56 m) and contains less fine-grained sand (3 weight 

percent). It contains less mud and fine-grained sand than substrate E.

Rippled, coarse-grained sand; partial veneer on immobile, cobble, boulder 

gravel—Substrate B is a layered substrate of mobile sand overlying immobile 

gravel on the shallow flank of Stellwagen Bank. Depth range is 36 to 58 m. 

Mean weight percents per grain-size category: mud, <1; sand, 92 (fgS, 5; cgS, 

86); gravel, 8 (G1

, 7; G2, 1). Cobbles and boulders are identified on the basis of 

video and photographic imagery. Boulder ridges (substrate C) are present. The 

mobile sand layer of substrate B is equivalent to adjacent mobile substrate A1 

Immobile, cobble, boulder gravel—Substrate C is immobile gravel that forms 

topographic ridges where cobbles and boulders are piled upon one another and are 

separated by voids. It is identified on the basis of video and photographic images 

of mapped topographic ridges. It is present on the flank of Stellwagen Bank 

where it is associated with substrate B (36–58 m) and substrate D1 (50–83 m), 

and on the tops of North, East, and Middle Ninety Banks where it is associated 

with substrate D2 (87–105 m). Equivalent to boulder ridges <1 m and ≥1 m on 

Maps A, E, F, and G

Immobile, coarse-grained sand; partial veneer on pebble, cobble, boulder 

gravel—Substrate D1 is a layered substrate of immobile sand overlying immobile 

gravel on the flank of Stellwagen Bank. Depth range is 50 to 83 m. Mean weight 

percents per grain-size category: mud, 4; sand, 50 (fgS, 16; cgS, 34); gravel, 45 

(G1

, 11; G2, 34). Pebbles, cobbles, and boulders are identified on the basis of 

video and photographic imagery. Boulder ridges (substrate C) are present. 

Substrate D1 is similar to substrate D2 which lies at deeper depths (87–105 m) on 

the tops of North, East, and Middle Ninety Banks and has higher mud content (12 

weight percent)

Immobile, muddy, coarse-grained sand; partial veneer on pebble, cobble, boulder 

gravel—Substrate D2 is a layered substrate of immobile sand overlying immobile 

gravel on the tops of North, East, and Middle Ninety Banks. Depth range is 87 to 

105 m. Mean weight percents per grain-size category: mud, 12; sand, 76 (fgS, 22; 

cgS, 55); gravel, 12 (G1, 8; G2, 4). Pebbles, cobbles, and boulders are identified 

on the basis of video and photographic imagery. Boulder ridges (substrate C) are 

present. Substrate D2 is similar to substrate D1 which lies at shallower depths 

(50–83 m) on the flank of Stellwagen Bank and has lower mud content (4 weight 

percent)

Immobile, coarse-grained sand—Substrate E is an immobile sand deposit on the 

lower flank of Stellwagen Bank. Depth range is 66 to 122 m. Mean weight 

percents per grain-size category: mud, 4; sand, 82 (fgS, 18; cgS, 64); gravel, 14 

(G1

, 9; G2, 5). Boulder ridges are absent. Substrate E is similar in mud content to 

substrate D1 and contains more mud and fine-grained sand than substrate A2

Immobile, coarse-grained sand; partial veneer on pebble, cobble, boulder 

gravel—Substrate F is a layered substrate of immobile sand overlying immobile 

gravel on the flanks of the Ninety Meter Banks. Depth range is 90 to 148 m. 

Mean weight percents per grain-size category: mud, 9; sand, 69 (fgS, 25; cgS, 

44); gravel, 22 (G1, 13; G2, 9). Pebbles, cobbles, and boulders are identified on 

the basis of video and photographic imagery. Boulder ridges are absent. 

Substrate F is similar to substrates D1 and D2, except that F lies at deeper depths, 

and the partial veneer of coarse grained sand on the gravel is more extensive

Immobile, muddy, fine-grained sand—Substrate G1 is an immobile muddy sand 

deposit in valleys between Stellwagen Bank and the Ninety Meter Banks. Depth 

range is 85 to 171 m. Mean weight percents per grain-size category: mud, 10; 

sand, 88 (fgS, 78; cgS, 10); gravel, 1 (G1

, 1; G2, 1). Substrate G1 is similar to 

substrate G2 which lies at deeper depths (125–185 m) and has higher 4 phi sand 

(58 weight percent) and higher mud content (23 weight percent)

Immobile, muddy, fine-grained sand—Substrate G2 is an immobile muddy sand 

deposit in deep parts of valleys lying between the Ninety Meter Banks. Depth 

range is 125 to 185 m. Mean weight percents per grain-size category: mud, 23; 

sand, 77 (fgS, 77; cgS, 1); gravel, 0. Substrate G2 has the highest mud content of 

all substrates in quadrangle 6

Merrimack River

0 20 km

CAPE COD

CAPE

ANN

Plymouth

Provincetown

BOSTON

MAS SACHUSETTS

BAY

GULF

OF

MAINE

71°00'W 70°45'W 70°30'W 70°15'W 70°00'W

Location Map.—Shows quadrangle 6 (highlighted in yellow). Stellwagen Bank 

National Marine Sanctuary boundary is shown as a dashed line. Bathymetric 

contours are labeled in meters.

40

200

100

100

100

100

80

80

80

80

40

80

80

40

100

80 40

40

CAPE COD BAY

8

5

9

10 11 12

4

1 2 3

14 15

16 17 18

13

7

42°45'N

42°30'N

42°15'N

42°00'N

41°45'N

6

Gloucester

RACE POINT CHANNEL

STELLWAGEN BASIN

STELLWAGEN

BANK

TILLIES BANK

JEFFREYS LEDGE

U.S. Department of the Interior

U.S. Geological Survey