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Seabed Maps Showing Topography, Ruggedness, Backscatter Intensity, Sediment Mobility, and the Distribution of Geologic Substrates in Quadrangle 2 of the Stellwagen Bank National Marine Sanctuary Region Offshore of Boston, Massachusetts

Scientific Investigations Map 3530
Coastal/Marine Hazards and Resources Program
Prepared in cooperation with the National Oceanic and Atmospheric Administration
By:  and 
https://doi.org/10.3133/sim3530

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Abstract

The U.S. Geological Survey, in cooperation with the National Marine Sanctuary Program of the National Oceanic and Atmospheric Administration, has conducted seabed mapping and related research in the Stellwagen Bank National Marine Sanctuary (SBNMS) region since 1993. The area being mapped using geophysical and geological data includes the SBNMS and the surrounding region, which totals approximately 3,700 square kilometers (km2) and is subdivided into 18 quadrangles. The seabed is a glaciated terrain that is topographically and texturally diverse. Quadrangle 2, the subject of this scientific investigations map, has a mapped area of 209 km2 and has water depths that range from about 19 meters (m) on the Stellwagen Bank crest to about 68 m in the Stellwagen Basin. Seven map types, each at a scale of 1:25,000, depict seabed topography, ruggedness, backscatter intensity, distribution of geologic substrates, sediment mobility, distribution of fine- and coarse-grained sand, and substrate mud content. These maps show the distribution of geologic substrates across the southwestern part of Stellwagen Bank, in Stellwagen Basin to the west and southwest of the bank, and in Little Stellwagen Basin and the western part of Race Point Channel to the south of the bank. Interpretations of multibeam sonar bathymetric and seabed backscatter imagery, photographs, video imagery, and grain-size analyses were used to create the geology-based maps. Data from 733 stations were analyzed, including 656 sediment samples. The geologic substrate maps of quadrangle 2 show the distribution of 19 geologic substrates that represent a wide range of textures, such as rippled and immobile sand, immobile muddy sand and sandy mud, sand that partially veneers gravel, and a boulder ridge. Mapped substrates are characterized by sediment grain-size composition, surface morphology, substrate layering, the mobility or immobility of substrate surfaces, and water depth range. This scientific investigations map portrays the major geological elements (substrates, topographic features, and processes) of environments in quadrangle 2. It is intended to provide a foundation for research into present and past sediment transport processes in a complex terrain, provide insights into the ecological requirements of invertebrate and vertebrate species that utilize the various substrates, and support seabed management in the region.

Introduction

The U.S. Geological Survey and the National Marine Sanctuary Program of the National Oceanic and Atmospheric Administration have been cooperating to research and map the Stellwagen Bank National Marine Sanctuary (SBNMS) region since 1993. The SBNMS region lies offshore of Boston, Massachusetts, and extends from Race Point Channel in the south to the southern part of Jeffreys Ledge in the north (fig. 1). This region is subdivided into 18 quadrangles with a combined area of approximately 3,700 square kilometers (km2). This scientific investigations map (SIM) presents maps of quadrangle 2 at a scale of 1:25,000 (1 centimeter [cm] on the map represents 250 meters [m] on the seabed) that show the physical characteristics of the seabed. Geospatial datasets of seabed topography, sediment mobility, and the distribution of geologic substrates for quadrangle 2 are provided in a data release associated with this report (Valentine and Cross, 2024a). The mapped area (209 km2) includes the southwestern part of Stellwagen Bank called Southwest Corner (about 19 m minimum water depth), the western part of Race Point Channel and Little Stellwagen Basin that separate Stellwagen Bank from Cape Cod to the south, and Stellwagen Basin in the western and southwestern part of the mapped area (about 68 m maximum water depth).

Quadrangle 2 includes parts of Stellwagen Bank, Stellwagen Basin, Little Stellwagen Basin, and Race Point Channel.
Figure 1.

Map showing the location of quadrangle 2 (highlighted in yellow) of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts. The numbered grid indicates the 18 quadrangles of the U.S. Geological Survey multibeam sonar substrate-mapping project. The dashed line represents the Stellwagen Bank National Marine Sanctuary boundary. Bathymetric contours are labeled in meters and the contour interval is variable. Figure modified from Valentine and Cross (2024c).

The Stellwagen Bank region is a glaciated terrain and, as described in Valentine (2019), bank sediments have been reworked during several episodes of submergence and emergence by rising and falling sea level since the Last Glacial Maximum. Present processes of erosion and transport are the result of currents generated by large storms from the northeast (Butman and others, 2008; Warner and others, 2008) that produce bedforms on the seabed of the bank down to about 50 m water depth. Tidal currents are generally too weak (Butman and others, 2007) to move the coarse-grained sand on the bank. Quadrangle 2 lies approximately 35 kilometers (km) east of the Massachusetts coast and just to the northwest of Cape Cod’s northernmost extent. At present, no sediment is transported from land into the map area except perhaps from the northern margin of Cape Cod onto the southern margin of Race Point Channel.

A geologic substrate is a surface or volume of sediment or rock material where physical and biological processes occur, such as the movement and deposition of sediment, the formation of bedforms, and the attachment, burrowing, feeding, reproduction, and sheltering of organisms (Valentine, 2019). A sedimentary substrate is characterized and identified by sediment composition (mud, sand, and gravel), the distribution of grain diameters, seabed structures (for example, ripples, burrows, and attached organisms), substrate layering (for example, finer sediment partly veneering coarser sediment), sediment movement, and water depth range. Substrates in quadrangle 2 range in composition from mobile coarse-grained sand and coarse-grained sand overlying gravel (on the bank and in the channel) to a boulder ridge (in the channel) to muddy fine-grained sand and fine-grained sandy mud (at depth in Stellwagen Basin and Little Stellwagen Basin). Layered substrates are generally in the form of a sand substrate that partially veneers a gravel substrate.

Seabed properties of quadrangle 2 are shown in a series of seven map types. Three maps show seabed topography (map A), ruggedness (map B), and backscatter intensity (map C). The other maps are interpretive and show the distribution of 19 geologic substrates (map D), the mobility or immobility of substrates (map E), the dominance of fine- or coarse-grained sand in substrates (map F), and the mud content of substrates (map G).

Several of the map types in this SIM (A, B, and C) have been published previously as parts of regional maps at a scale of 1:60,000 (Valentine, 2005); they are presented here at higher resolution (1:25,000 scale). Map A was previously published at a scale of 1:25,000 (Valentine and others, 2000, 2010), but it did not show the distribution of boulder ridges. Maps D–G show new interpretations of geologic substrate composition, substrate mobility, sand content, and mud content.

This SIM follows the design of companion SIMs that show the same seabed properties for quadrangle 5 (Valentine and Cross, 2024b, c), which adjoins quadrangle 2 to the north, and for quadrangle 6 (Valentine and Gallea, 2015), which adjoins quadrangle 2 to the northeast. This SIM for quadrangle 2 and SIM 3515 for quadrangle 5 (Valentine and Cross, 2024c) use the same wording in places to describe the study, regional geology, and other shared features.

The purpose of this SIM is to provide a range of information about the distribution of physical attributes of the seabed in the SBNMS region at a scale (1:25,000) that is appropriate for the density of data. High-resolution substrate maps can serve as a foundation for further study of seabed processes (such as present and past sediment transport), support ecological studies of vertebrate and invertebrate species that use these substrates as habitat, and support planning and managing usage of the seabed.

Methods

The process of mapping geologic substrates in quadrangle 2 followed the principles of substrate characterization and identification as described in Valentine (2019). Geologic substrates were identified by analyzing video imagery of the seabed, multibeam sonar and backscatter imagery of the seabed, and grain sizes of sediment samples. The collection and processing of the multibeam sonar bathymetric and backscatter data presented here are described in Valentine (2005). The locations of stations (areas where data such as sediment samples or video imagery were collected) were digitally plotted on a multibeam sonar image of sun-illuminated seabed topography in a Portable Document Format (PDF). The boundaries of geologic substrates were digitally drawn by hand on this image based on the interpretation of the data described in this SIM. After the geologic substrates were identified, they were digitized in a geographic information system (GIS) and were then used to create three other interpretive maps. These maps characterize the substrates on the basis of the mobility or immobility of their surfaces, the dominance of fine- or coarse-grained sand, and the mud content. Table 1.1 in appendix 1 lists new data layers and previously published data that were used to compile the maps for quadrangle 2.

Grain-size classifications for sediment as used in this study are given in table 1. Composite grain-size classifications for sediment as used in this study are given in table 2.

Table 1.    

Grain-size classifications for sediment as used in this study of quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts.

[To convert particle diameter (D) in millimeters (mm) to phi units (φ): φ = − log2D = −3.3219 log10D. To convert particle diameter in phi units to mm: D = 2–φ. Table from Valentine and Cross (2024c)]
Grade1 Grain size
Particle diameter range1
(millimeters)		 Phi grade scale2
Gravel, boulder 256 to <4,096 − 8 to −11
Gravel, cobble 64 to <256 −6 to −7
Gravel, very coarse pebble 32 to <64 −5
Gravel, coarse pebble 16 to <32 −4
Gravel, medium pebble 8 to <16 −3
Gravel, fine pebble 4 to <8 −2
Gravel, granule 2 to <4 −1
Sand, very coarse 1 to <2 0
Sand, coarse 0.5 to <1 1
Sand, medium 0.25 to <0.5 2
Sand, fine 0.125 to <0.25 3
Sand, very fine 0.062 to <0.125 4
Silt 0.004 to < 0.062 5 to 8
Clay < 0.004 9 and higher
Mud (silt and clay) < 0.062 5 and higher
Table 1.    Grain-size classifications for sediment as used in this study of quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts.
1

Described in Udden (1914), Wentworth (1922), Folk (1954), and Blair and McPherson (1999).

2

Described in Krumbein (1936).

Table 2.    

Composite grain-size classifications for sediment as used in this study of quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts.

[To convert particle diameter (D) in millimeters (mm) to phi units (φ): φ = − log2D = −3.3219 log10D. To convert particle diameter in phi units to mm: D = 2–φ. Table from Valentine and Cross (2024c)]
Composite grade Grain size
Particle diameter range
(millimeters)		 Phi grade scale
Gravel2 (G2) 8 to <64 −3, −4, and −5
Gravel1 (G1) 2 to <8 −1 and −2
Coarse-grained sand (cgS) 0.25 to <2 2, 1, and 0
Fine-grained sand (fgS) 0.062 to <0.25 4 and 3
Boulder gravel (bG) 256 to <4,096 −8 to −11
Cobble gravel (cG) 64 to <256 −6 to −7
Pebble gravel (pG) 2 to <64 −1 to −5
Table 2.    Composite grain-size classifications for sediment as used in this study of quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts.

Naming and abbreviation conventions for components of sediment and nonsediment classes and the mobility and layering properties of substrates are given in table 3 and are described below (from Valentine [2019], table 5). A sediment class based on grain-size analysis contains one or more aggregates and (or) composite grades (Valentine, 2019, table 1). For example, a muddy, gravelly, coarse-grained sand (mgcgS) is a sediment class containing three components: mud (an aggregate), gravel (an aggregate), and coarse-grained sand (a composite grade), in order of increasing weight percent. A sediment class based on a visual analysis of seabed imagery would be, for example, a pebble, cobble gravel (pcG), a sediment class consisting of pebbles and cobbles (each a composite grade), not in order of increasing abundance. A nonsediment class, also based on a visual analysis of seabed imagery, contains components such as shell deposits, rock outcrops, or semiconsolidated mud. Properties of seabed mobility (presence or absence of ripples) and substrate layering are also based on a visual analysis of seabed imagery. An unlayered substrate contains one sediment class (for example, muddy, fine-grained sand [mfgS]) or one nonsediment class (for example, rock outcrop [R]). A layered substrate contains at least two sediment classes or a sediment class and a nonsediment class (for example, a rippled, coarse-grained sand; partial veneer on immobile, semiconsolidated mud [r_cgS / i_scM]). In the present approach to substrate identification, the need to construct two-part names that are both informative and brief can produce names for two (or more) substrates in which geologic substrate symbols are unique but the abbreviations for the descriptive parts of the names are identical, for example A1 r_cgS and K r_cgS.

Table 3.    

Naming and abbreviation conventions for components of sediment and nonsediment classes and the mobility and layering properties of substrates in quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts.

[Not all of the terms in this table are applicable to quadrangle 2. See tables 1 and 2 for grain-size classifications of sediment class components. Table from Valentine (2019, table 5). Terms: >, greater than; ≥, greater than or equal to; <, less than; ≤, less than or equal to]
Name Abbreviation Portion of sediment, in weight percent
Mud M M≥50
Muddy m M≥10 to <50
Sand S S≥50
Sandy s S≥10 to <50
Fine-grained sand fgS fgS≥50
Fine-grained sandy fgs S≥10 to <50; fgS>cgS, fgS–cgS is >10
Coarse-grained sand cgS cgS≥50
Coarse-grained sandy cgs S≥10 to <50; cgS>fgS, cgS–fgS is >10
Coarse- and fine-grained sand cgfgS S≥50; fgS>cgS, fgS–cgS is ≤10
Coarse- and fine-grained sandy cgfgs S≥10 to <50; fgS>cgS, fgS–cgS is ≤10
Fine- and coarse-grained sand fgcgS S≥50; cgS>fgS, cgS–fgS is ≤10
Fine- and coarse-grained sandy fgcgs S≥10 to <50; cgS>fgS, cgS–fgS is ≤10
Gravel G G≥50
Gravelly g G≥25 to <50
Gravel G Presence of gravel
Pebble gravel p Presence of pebbles
Cobble gravel c Presence of cobbles
Boulder gravel b Presence of boulders
Rock outcrop R Presence of rock outcrop
Shell deposit Sh Presence of shell deposit
Shelly sh Presence of shells
Semiconsolidated mud scM Presence of semiconsolidated mud outcrop
Rippled r Presence of rippled sediment, implies mobility
Immobile i Presence of sediment with no ripples, implies no movement
Rippled and immobile r_i Presence of both rippled and immobile sediment
“Partial veneer on” / Indicates layered substrates. For example, “r_cgS / i_pcbG” means “rippled, coarse-grained sand; partial veneer on immobile, pebble, cobble, boulder gravel”
Table 3.    Naming and abbreviation conventions for components of sediment and nonsediment classes and the mobility and layering properties of substrates in quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts.

Map A. Sun-Illuminated Topography and Boulder Ridges

Map A shows seabed topographic imagery of quadrangle 2, which is a glaciated terrain modified by postglacial sediment-transport processes. This imagery is derived from multibeam sonar bathymetric data contoured at a 5-m interval. Water depths range from about 19 m on Southwest Corner (the shallowest part of Stellwagen Bank) to about 68 m in Stellwagen Basin to the west. There is one large boulder ridge in the mapped area, which is ≥1 m in height and is shown as a semitransparent polygon overlying topographic imagery. This ridge represents an area of 0.4 km2 in this quadrangle (table 4).

Table 4.    

Area of the seabed mapped as boulder ridges in quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts.

[Boulder ridges are segregated into two height categories, <1 meter (m) in height and ≥1 m in height. Data in columns 3 and 4 are rounded to one decimal place. Areas of the seabed mapped as boulder ridges and bedrock outcrops in all 18 quadrangles in the Stellwagen Bank National Marine Sanctuary region are listed in table 1 of map F of Valentine (2005). Table format from Valentine and Cross (2024c). Terms: ≥, greater than or equal to; <, less than; km2, square kilometer]
Region Area
(km2)		 Area of boulder ridges that are
<1 m or ≥1 m in height (km2)		 Area of boulder ridges that are
<1 m or ≥1 m in height (percent)
<1 m ≥1 m <1 m ≥1 m
Quadrangle 2 209 0.0 0.4 0.0 0.2
Table 4.    Area of the seabed mapped as boulder ridges in quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts.

Southwest Corner is the shallowest part of Stellwagen Bank (about 19 m minimum water depth). It extends southwestward into the southern part of Stellwagen Basin. The southernmost extent of the bank’s crest line is located on Southwest Corner; the line trends northeastward and subsequently northward in quadrangle 2. Southwest Corner is separated from Stellwagen Basin by a steep slope that lies in water depths of 25 to 50 m. Stellwagen Basin lies at the foot of Southwest Corner at 55 m and deepens to the west where it reaches depths of about 68 m in quadrangle 2. The northwestern flank of Southwest Corner is incised by a short north-south-trending valley. South of this valley, the steep slope that separates the bank from Stellwagen Basin extends southeastward and then turns northeastward around Southwest Corner and forms the northern boundary of Race Point Channel and Little Stellwagen Basin. Together, Little Stellwagen Basin (about 60 m water depth) and the western part of Race Point Channel (45–60 m water depth) separate Stellwagen Bank to the north from Cape Cod to the south. The southeastern corner of the quadrangle includes the deep part of the northern slope of the Cape Cod mainland; however, this corner is not mapped because multibeam sonar data were not collected there.

Other seabed surface features that are visible in the multibeam topographic imagery include a smooth, sinuous, east-west-trending boulder ridge (lat 42°07.4′ N., long 70°14.0′ W.) in Race Point Channel east of Southwest Corner; this ridge likely represents a glacial moraine or esker that was partly buried by postglacial sediment movement. Smaller, well-defined, nested arcuate ridges are present south of Stellwagen Bank (lat 42°09.5′ N., long 70°15.7′ W.) and are interpreted to represent sedimentary features deposited from a glacial icefall that flowed from the bank southward into the channel. A similar icefall deposit is present in quadrangle 6 to the northeast (Valentine and Gallea, 2015). A low, wide, curved, east-west-trending ridge lies on the northern margin of Race Point Channel and its western end abuts Southwest Corner; this ridge is interpreted to represent a moraine that is partially buried in sediment transported southward from Stellwagen Bank. Other features that are visible in the topographic imagery include sand hummocks on the bank surface and the triangular, rippled sand deposit (lat 42°12.0′ N., long 70°20.0′ W.) that extends southward into quadrangle 2 from quadrangle 5 to the north (Valentine and Cross, 2024c). This deposit is interpreted to be formed by one or more sediment transport events of unknown age. It displays long wavelength (40–50 m) sand ripples and an irregular leading edge, which are interpreted to form by episodic sediment transport. A presumed shipwreck is present on Stellwagen Bank (lat 42°11.65′ N., long 70°16.30′ W.). To view maps and descriptions of glacial and postglacial seabed topography and the distribution of boulder ridges and bedrock outcrops in the entire SBNMS region, see maps A, B, and F of Valentine (2005). For further description of topographic features in this quadrangle, see the map and explanation of sun-illuminated topography in Valentine and others (2000, 2010).

Topographic contours were generated at 5-m and 1-m intervals from bathymetric data collected by a Simrad EM1000 multibeam sonar echo sounder that was used in the mapping survey (Valentine and others, 1998). The 5-m contours accurately represent the morphology of topographic features such as large and small banks, valleys, and the boulder ridge. However, because they do not adequately show the irregular relief of the seabed in some areas, they are supplemented by 1-m contours on maps B and D–G where a boulder ridge, small sediment mounds, bedforms, and edges of sand sheets are present. In areas of relatively featureless seabed where only minor changes in water depths occur, the 1-m contours are not shown because the process of contouring produces incoherent patterns of lines that misrepresent the topographic complexity (Valentine, 2019).

Map B. Seabed Ruggedness

Map B shows the results of an analysis of multibeam sonar bathymetric data to calculate seabed ruggedness, which is a measure of changes in elevation (water depth) over small areas. This kind of analysis is useful for identifying steep features where ruggedness values rapidly increase over short distances, and for delineating features in relatively smooth areas that are subtly expressed by seabed topography. The seabed ruggedness measure is based on a terrain ruggedness index (TRI) developed by Riley and others (1999) to quantify topographic heterogeneity on land. The TRI of Riley and others (1999) measures the sum change in elevation between a central grid cell (pixel) and its eight neighboring grid cells, which is computed by squaring the eight differences in elevation, summing the squared differences, and taking the square root of the sum. Here, a seabed ruggedness index is used to measure changes in elevation more directly by calculating the average change in elevation between a central pixel and its eight neighbors, which is computed by averaging the absolute values of the eight differences in elevation (see map D of Valentine [2005]). Comparing the two methods, a central pixel (representing a positive feature) with an elevation (water depth) value of 10 m and eight neighboring pixels with values of 15 m would have a TRI sum change value of 14.1 m using the method of Riley and others (1999), and a seabed ruggedness of 5.0 m using the method employed here.

For map B, seabed ruggedness values were calculated as the average change in water depth between a central 13-m pixel and the eight pixels that surround it, an area measuring 39 × 39 m. Subsequently, a smoothing filter was applied to the ruggedness index image. This filter calculated the mean of the seabed TRI value of each pixel and its eight neighboring pixels. On map B, the seabed ruggedness index values are represented by 13 colors ranging from lavender to dark red. Map colors represent the average change in elevation, in centimeters, and are shown in 10-cm increments in the >30- to 100-cm range (7 colors), in 50-cm increments in the >100- to 200-cm range (2 colors), and in 100-cm increments in the >200- to 600-cm range (4 colors). For example, on the map, dark blue represents central pixels having an average elevation change of >70 to 80 cm with respect to their surrounding eight-pixel areas. Average changes in elevation of less than or equal to 30 cm are not shown in color.

Table 5 shows the area of seabed that is represented by four ruggedness intervals. Ruggedness values in the 0- to 30-cm range represent an area of 205 km2 (98 percent) of the total 209 km2 mapped area of the quadrangle. Seabed ruggedness reaches a high of >400 to 500 cm in very small areas on the steep slope that separates Southwest Corner from Stellwagen Basin to the west and Little Stellwagen Basin and Race Point Channel to the south. The ruggedness analysis successfully identified changes in elevation of the transitional slope between Stellwagen Bank and Stellwagen Basin. The relatively gentle slope on the western flank of Stellwagen Bank, northwest of Southwest Corner, lies in water depths of 50 to 55 m and has a ruggedness value of >30 to 80 cm. The slope of Southwest Corner proper is variable. In its western part, the slope lies in depths of 35 to 50 m and has a ruggedness value of up to 300 cm. In its southwestern part, the slope lies in depths of 30 to 50 m and has a ruggedness value of up to 400 cm. In its southern part, the slope is less steep, lies in depths of 30 to 50 m, and has a ruggedness value of up to 300 cm. In its southeastern part, the steepest slope of Southwest Corner lies in depths of 30 to 50 m and has a ruggedness value of up to 500 cm. Farther to the east, because of the presence of the icefall deposit described above, the slope lies at shallower depths of 30 to 40 m and has a ruggedness value up to only 150 cm. Still farther east, the slope lies in depths of 40 to 50 m and is much less steep, having a ruggedness value up to 80 cm. A small portion of the base of the slope that separates Little Stellwagen Basin from Cape Cod is present in the southeastern corner of the mapped area; in the 45- to 55-m water depth interval, it has a ruggedness value of up to 50 cm. The ruggedness analysis did not identify the boulder ridge in Race Point Channel. To view maps and a description of seabed ruggedness and slope angle of the entire SBNMS region, see maps D and E, respectively, of Valentine (2005).

Table 5.    

Area of the seabed represented by ruggedness intervals in quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts.

[Areas of seabed are represented by four ruggedness intervals of 0–30 centimeters (cm), >30–100 cm, >100–200 cm, and >200–500 cm in quadrangle 2. Data in columns 3 and 4 are rounded to one decimal place. Areas of seabed represented by ruggedness intervals in all 18 quadrangles of the Stellwagen Bank National Marine Sanctuary region are listed in table 1 of map D of Valentine (2005). Table format from Valentine and Cross (2024c). Terms: >, greater than; km2, square kilometer]
Region Area
(km2)		 Area of seabed within four ruggedness intervals (km2) Area of seabed within four ruggedness intervals (percent)
0–30 cm >30–100 cm >100–200 cm >200–500 cm 0–30 cm >30–100 cm >100–200 cm >200–500 cm
  Quadrangle 2 209 204.8 3.2 0.6 0.3 98.1 1.7 0.3 0.1
Table 5.    Area of the seabed represented by ruggedness intervals in quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts.

Map C. Backscatter Intensity and Sun-Illuminated Topography

Map C shows imagery of seabed backscatter intensity and sun-illuminated topography derived from multibeam sonar data. Backscatter intensity is a measure of the strength of sound waves reflected from the seabed. Hard substrates reflect sound waves more strongly than soft substrates. When color coded and mapped, backscatter intensity reveals patterns that are a useful preliminary guide for delineating the geographic extent of substrates. On map C, the backscatter intensity index shows values represented by an eight-color range from blue to red (1–8). Values from 1 to 3 (blue to blue-green) represent relatively soft substrates, values from 3 to 6 (blue-green to yellow) represent substrates of intermediate hardness, and values from 6 to 8 (yellow to red) represent relatively hard substrates. Backscatter intensity patterns, when used in concert with sediment grain-size analyses and interpretations of video and photographic imagery of the seabed, can be used to characterize and identify geologic substrates. It is not possible to recognize the substrates mapped in quadrangle 2 by relying on backscatter intensity alone.

The highest backscatter values are located on the upper northwestern flank of Southwest Corner in 28 to 35 m water depth and represent substrate AA, a pebble, cobble gravel seabed that lies beneath a partial veneer of rippled, coarse-grained sand (for descriptions of substrates, see the section “Map D. Distribution of Geologic Substrates” below). The area mapped as substrate AA also includes samples of substrates A1 and A3 that are not mappable as coherent units at 1:25,000 scale. In Race Point Channel, seabed features that display a mixture of high and intermediate backscatter are interpreted to represent gravel features partly covered by sand. These features include arcuate ridges of a glacial icefall deposit (substrate AD) and a sinuous gravel ridge or glacial moraine (substrate AE) that lie in the northern part of the channel at the foot of Stellwagen Bank. Samples of these two substrates (AD and AE) are not mappable as coherent units at 1:25,000 scale. An east-west topographic and backscatter high (substrate C) that lies in Race Point Channel is interpreted to be a boulder ridge that represents a glacial moraine or esker (compare maps A, C, and D). A single survey line that trends northwest to southeast across the bank, as well as less pronounced survey lines in other parts of quadrangle 2, represent local high backscatter values that are artifacts of the multibeam echo sounder survey and were possibly caused by ship motion that was not fully accounted for by the attitude sensors of the sonar system.

Intermediate backscatter values are located on the bank and represent rippled, coarse-grained sand substrates A1 and A3. The low to intermediate backscatter values in part of Little Stellwagen Basin and in Stellwagen Basin (in the south-central and southwestern part of the mapped area) represent substrate P (a muddy, fine-grained sand) in shallower water and substrate R (a fine-grained sandy mud) in deeper water. An east-to-west increase in water depth and a decrease in backscatter intensity documents the transition from mobile, coarse-grained sand in Race Point Channel (substrates Y and Z) to immobile, fine-grained sand and fine-grained sandy mud in Little Stellwagen Basin and Stellwagen Basin (substrates P and R).

Map D. Distribution of Geologic Substrates

Map D shows the distribution of 19 geologic substrates characterized by grain-size composition, the distribution of grain diameters in the sediment, surface morphology, substrate layering, the mobility or immobility of the substrate surfaces, and water depth range. Bathymetric contours are drawn at 5-m intervals, except in some areas of complex seabed with low relief where they are drawn at 1-m intervals.

Data from 733 stations were analyzed, including 656 sediment samples. Map D, sheet 1 shows the distribution of geologic substrates and the locations of stations where sediment samples were collected or the locations of the ends of video drifts if no sediment was collected. Sediment was usually collected at the end of video drifts. Map D, sheet 2 shows the distribution of geologic substrates and sun-illuminated topography, but not the locations of data stations. Data from these stations were used to identify and map the substrate polygons.

See Valentine and Cross (2024d) for the results of grain-size analyses of sediment samples and the assignment of stations to substrates. See tables 6 and 7 (which follow the “References Cited”) for descriptions and comparisons of substrate properties, water depth ranges, and substrate areas. See Valentine (2019) for a complete description of the methodology developed for sediment classification and for substrate characterization, identification, and mapping.

The geologic substrates of quadrangle 2 were formed by the glacial processes of erosion and deposition, were subsequently modified by the effects of rising postglacial sea level, and are presently affected by storm-wave generated currents (Valentine, 2019). A discussion of the morphology and origin of topographic features in this quadrangle can be found in Valentine and others (2000, 2010).

Substrates range widely in character in quadrangle 2 and include the following: rippled, fine-grained sand; immobile, fine-grained sand; rippled, coarse-grained sand; immobile, muddy, fine-grained sand; immobile, fine-grained sandy mud; rippled, gravelly, coarse-grained sand that partially veneers gravel; and a large boulder ridge. The shallow surface of Stellwagen Bank is covered by relatively coarse sediments, including coarse-grained sand and a complex substrate of sand partially veneering gravel. The relatively steep western and southern slopes of Southwest Corner are transition zones of increasing water depth where the coarse-grained sand of the bank gives way to muddy, fine-grained sand and fine-grained sandy mud of Stellwagen Basin.

The middle western flank of Stellwagen Bank is partly covered by a sheet of sand (substrate H) with irregular leading edges (red line on maps A and D–G) that indicate episodic sediment movement on the western slope of the bank. This movement of substrate H is likely caused by storm-wave generated currents. However, the timing of the movement is not known.

The quality of substrate identification and mapping depends on the spatial density of samples and observations available to interpret multibeam sonar imagery. Fewer samples are required to identify substrates where the substrate boundaries align with topographic features and sonar backscatter intensity patterns. More samples are required where multibeam imagery indicates seabed features and substrates are complex, and also where they are relatively uniform but are present in an area of changing water depths.

Substrates are mapped in three ways, depending on the density of the data. First, substrates are mapped as irregular-sided polygons (in this context meaning polygons with many vertices and smooth edges) if the density of data allows for their extent to be mapped with some confidence. In quadrangle 2, 13 of the 19 substrates are mapped as irregular-sided polygons. Second, substrates are mapped as straight-sided polygons (in this context meaning angular polygons with relatively few vertices and sides) if transitions between substrates are ambiguous because data are sparse. The straight-sided polygons alert the user that there is uncertainty as to the areal extents of the substrates. In quadrangle 2, only substrate AA is mapped as a straight-sided polygon. This polygon is drawn to surround an area of high backscatter where the seabed is texturally highly variable and is characterized by varying portions of sand and gravel (compare maps C and D). Contacts are not drawn for irregular-sided or straight-sided polygons because contacts indicate a degree of certainty that is usually not warranted in marine substrate mapping. Third, deposits of six substrates (A1, A3, AD, AE, AF, and AH) that occur within the bounds of other mapped substrates and that are too few to be mapped as coherent units at 1:25,000 scale are shown as magenta square symbols on map D, sheet 1. Substrates A3, AD, AE, AF, and AH are only shown as magenta square symbols whereas substrate A1 is mapped as a coherent unit in most locations.

Description of Map Units (Substrates)

[The grain sizes of sediment samples collected from each substrate are given as mean weight percents for each aggregate (mud, sand, and gravel) and composite grade (fine-grained sand, coarse-grained sand, gravel1, and gravel2). See Valentine (2019) for descriptions of aggregates and composite grades. Weight percent values were rounded and may not add up to 100 or other summed values, for example, sand, 99 (fgS, 16; cgS, 82). Aggregates and composite grades are abbreviated and given in order of increasing weight percent in the name of each substrate. For example, a muddy, fine-grained sand (mfgS) contains more fine-grained sand than mud. Sand is divided into two composite grades: fine-grained sand (fgS; 0.062 to <0.25 millimeters [mm]) and coarse-grained sand (cgS; 0.25 to <2 mm). Fine-grained sand (3 and 4 phi combined) is transported as suspended load, and coarse-grained sand (0, 1, and 2 phi combined) is transported as bed load (Valentine, 2019). Gravel is also divided into two composite grades: gravel1 (G1; 2 to <8 mm) and gravel2 (G2; 8 to <64 mm). Gravel (in the form of pebbles, cobbles, and boulders) that could not be sampled was identified using visual analysis of video and photographic imagery. Grain-size characteristics for the one layered substrate (AA) represent the sampled sediment that partially veneers gravel. Substrate unit names describe the mobility or immobility of their surfaces, sediment grain-size composition, and sediment layering. For example, the notation “r_cgS / i_pcbG” means “rippled, coarse-grained sand; partial veneer on immobile, pebble, cobble, boulder gravel.” See table 3 for further explanation]

A1 r_cgS—Rippled, coarse-grained sand.—Substrate A1 is a mobile, coarse-grained sand deposit that covers the southwestern part of Stellwagen Bank. Its mapped area in quadrangle 2 is 51.7 km2, or 24.7 percent of the quadrangle area. The water depths of the stations range from 19 to 48 m and the water depth of the mapped substrate ranges from 19 to 55 m. Substrate A1 reaches its deepest depths of 55 m along the base of the slope below Southwest Corner. Mean weight percents of aggregates and composite grades are as follows: mud, <1; sand, 97 (fgS, 2; cgS, 95); gravel, 3 (G1, 3; G2, <1). Substrate A1 extends northward onto the crest and western flank of Stellwagen Bank in quadrangle 5 (Valentine and Cross, 2024c), onto the eastern flank of the bank in quadrangle 6 (Valentine and Gallea, 2015), and onto the southeastern flank of the bank in the adjoining quadrangle to the east of quadrangle 2. The substrate is dominantly coarse-grained sand and is very low in mud and fine-grained sand content. Storm-wave generated sand ripples with wavelengths of 0.5 to 1.0 m are present on the surface, and the orientation of ripple crests varies from north-south to northwest-southeast. The ripples are symmetrical and well shaped (sometimes with narrow, sharply defined crests and sometimes with broad crests hosting secondary ripples) when first formed by storm-wave generated currents, but they are subsequently rounded by biological disturbance and flattened by bottom-tending fishing gear. Some samples of substrate A1 were collected from within the area mapped as substrate AA, but they are not mappable as a coherent unit at 1:25,000 scale; the locations of these samples are shown by magenta square symbols on map D, sheet 1, and are identified in Valentine and Cross (2024d). Substrate A1 is similar to substrate A3 in that they both have similar mud and sand content, lie at similar water depths, and are rippled substrates. However, substrate A3 contains much more fine-grained sand (16 weight percent) and each sample from A3 generally contains 10 weight percent or more of fine-grained sand, mostly as 3-phi sand, and its surface is covered with smaller ripples. Substrate A1 is texturally similar to substrate Z (also a rippled, coarse-grained sand) but they are separated geographically and lie at different water depths; substrate Z lies south of Stellwagen Bank in greater water depths in Race Point Channel. Substrate A1 is also texturally similar to substrate AG that lies far to the south on the southern margin of Race Point Channel.

A3 r_cgS—Rippled, coarse-grained sand.—Substrate A3 is a collection of mobile, coarse-grained sand deposits that lie chiefly on the southwestern part of Stellwagen Bank within the area occupied by substrates A1, AA, and AB. The water depths of the stations range from 19 to 59 m. Mean weight percents of aggregates and composite grades are as follows: mud, 1; sand, 99 (fgS, 16; cgS, 82); gravel, <1 (G1, <1; G2, 0). Substrate A3 is also present within the area of substrate A1 on the crest and western flank of the bank in quadrangle 5 to the north (Valentine and Cross, 2024c) and it also extends onto the southeastern flank of the bank in the adjoining quadrangle to the east of quadrangle 2. Substrate A3 is similar to substrate A1 in that it is a rippled, coarse-grained sand with a very low mud content. It differs from A1 in that samples of A3 generally contain 10 weight percent or more of fine-grained sand (mostly as 3 phi sand) and its surface ripples are much smaller, with wavelengths of 10 to 20 cm. Substrate A3 is also similar to substrate A2, which lies on the far eastern flank of Stellwagen Bank in quadrangle 6 to the northeast (Valentine and Gallea, 2015). Substrates A2 and A3 both contain more fine-grained sand than substrate A1, but A2 has less fine-grained sand than A3, is immobile, and lies at greater water depths (53–77 m). Samples of substrate A3 were collected from within the area mapped as substrates A1, AA, and AB, but they are not mappable as coherent units at 1:25,000 scale; the locations of these samples are shown by magenta square symbols on map D, sheet 1, and are identified in Valentine and Cross (2024d).

C i_cbG—Immobile, cobble, boulder gravel.—Substrate C is a boulder ridge. This feature lies in the middle of the western part of Race Point Channel and is interpreted to be a boulder ridge based on video and multibeam topographic imagery. Its mapped area in quadrangle 2 is 0.5 km2, or 0.2 percent of the quadrangle area. It is represented by only two stations (4651 and 4652) in quadrangle 2. The water depths of the two stations are both 58 m and the water depth of the mapped substrate ranges from 55 to <60 m. One sample was collected, which was from the rippled, coarse-grained sand that partially veneers the gravelly margins of the boulder ridge. Weight percents of aggregates and composite grades of the one sample are as follows: mud, 1; sand, 88 (fgS, 15; cgS, 73); gravel, 10 (G1, 10; G2, 0). The boulder ridge is a linear feature that trends east to west; its eastern part is bounded by substrate Z and its western part by substrate Y. Deposits of substrate C also occur in quadrangle 5 to the north (Valentine and Cross, 2024c) and more commonly in quadrangle 6 on the eastern flank of Stellwagen Bank and on the tops of the Ninety Meter Banks (Valentine and Gallea, 2015).

H r_fgS—Rippled, fine-grained sand.—Substrate H is a mobile, fine-grained sand deposit that lies on the southwestern flank of Stellwagen Bank. Its mapped area in quadrangle 2 is 1.0 km2, or 0.5 percent of the quadrangle area. The water depths of the stations range from 39 to 42 m and the water depth of the mapped substrate ranges from 37 to 42 m. Mean weight percents of aggregates and composite grades are as follows: mud, 1; sand, 99 (fgS, 89; cgS, 10); gravel, 0 (G1, 0; G2, 0). Substrate H extends northward along the lower western flank of Stellwagen Bank into quadrangle 5 (Valentine and Cross, 2024c). The surface of the substrate is characterized by low, long-wavelength (approximately 40–50 m) ripples that are visible in multibeam topographic imagery. Shell deposits are present in ripple troughs. Substrate H is bounded downslope by substrate K (a rippled, coarse-grained sand) and upslope by substrate A1 (also a rippled, coarse-grained sand). This juxtaposition of fine- and coarse-grained sand deposits suggests that substrate K was overridden by the fine-grained sand of substrate H and that later H was overridden by the coarse-grained sand of substrate A1. Thus, the long-wavelength ripples of the surface of substrate H are likely relict and the substrate may not be mobile at present. The timing of such a mass movement event or events is not known. Substrate H texturally resembles substrate L, an immobile, muddy, fine-grained sand (which lies at deeper depths and is separated from substrate H by substrate K on the western flank of the bank) in its ratio of fine- to coarse-grained sand content, but substrate H contains less mud.

K r_cgS—Rippled, coarse-grained sand.—Substrate K is a mobile, coarse-grained sand deposit that lies on the southwestern flank of Stellwagen Bank, northwest of Southwest Corner. Its mapped area in quadrangle 2 is 5.9 km2, or 2.8 percent of the quadrangle area. The water depths of the stations range from 41 to 56 m and the water depth of the mapped substrate ranges from 40 to 56 m. Mean weight percents of aggregates and composite grades are as follows: mud, 1; sand, 99 (fgS, 19; cgS, 80); gravel, 0 (G1, 0; G2, 0). Substrate K extends northward into quadrangle 5 along the lower western flank of Stellwagen Bank near the eastern end of Southwestern Spur (Valentine and Cross, 2024c). The substrate is dominantly coarse-grained sand and is low in mud, but it contains an appreciable amount of fine-grained sand (and 3 phi sand is more abundant than 4 phi sand). To the east, upslope in shallower water, substrate K is bounded by the rippled, fine-grained sand of substrate H (which multibeam topographic imagery suggests has encroached upon substrate K) and by the rippled coarse-grained sand of substrate A1. To the west, in deeper water, substrate K is bounded by the immobile, muddy, fine-grained sands of substrates L and P. Thus, substrate K, a coarse-grained sand, lies between fine-grained substrate H (upslope) and substrates L and P (downslope), indicating that K was not deposited by present-day sedimentary transport processes; its depositional history is unclear. Substrate K is bounded to the south by substrate X, an immobile, fine-grained sand that lies in a small valley that incises the bank adjacent to Southwest Corner.

L i_mfgS—Immobile, muddy, fine-grained sand.—Substrate L is an immobile, muddy, fine-grained sand deposit that lies on the lower, western flank of Stellwagen Bank. Its mapped area in quadrangle 2 is 0.7 km2, or 0.3 percent of the quadrangle area. The water depths of the stations range from 50 to 58 m and the water depth of the mapped substrate ranges from 49 to 58 m. Mean weight percents of aggregates and composite grades are as follows: mud, 9; sand, 90 (fgS, 75; cgS, 15); gravel, 0 (G1, 0; G2, 0). Substrate L extends northward along the lower western flank of Stellwagen Bank into quadrangle 5 (Valentine and Cross, 2024c). It lies between substrate K (upslope; mud content 1 weight percent) and substrate P (downslope; mud content 23 weight percent) in a region where mud content increases with increasing water depth from bank to basin. Note that substrate L is identified as a muddy, fine-grained sand even though the threshold of ≥10 weight percent mud (table 6) is not met (Valentine, 2019) because substrate L extends northward from quadrangle 2 into quadrangle 5 where the mud threshold is met. As is the case in quadrangle 5, substrate L in quadrangle 2 is texturally different from its bounding substrates K and P in mud, coarse-grained sand, 3-phi sand, and 4-phi sand content; in topographic position; and in water depth. Substrate L in quadrangle 2 is texturally equivalent to substrate G1 that occurs off the eastern flank of Stellwagen Bank in quadrangle 6 (Valentine and Gallea, 2015) in much greater water depths (85–171 m). Substrate L is texturally similar to substrates X and AB but is geographically separated from them.

P i_mfgS—Immobile, muddy, fine-grained sand.—Substrate P is an immobile, muddy, fine-grained sand deposit that lies in Stellwagen Basin, bounds the southwestern part of Stellwagen Bank, and extends southeastward into adjacent Little Stellwagen Basin at the western approach to Race Point Channel. Its mapped area in quadrangle 2 is 76.1 km2, or 36.5 percent of the quadrangle area. The water depths of the stations and the mapped substrate range from 51 to 68 m. Mean weight percents of aggregates and composite grades are as follows: mud, 23; sand, 76 (fgS, 68; cgS, 8); gravel, <1 (G1, <1; G2, 0). Substrate P extends northward within Stellwagen Basin into quadrangle 5 (Valentine and Cross, 2024c). In quadrangle 2, substrate P abuts several texturally varied substrates to the east along the topographic transition from Stellwagen Bank into Stellwagen Basin and Little Stellwagen Basin. These substrates, from north to south, are muddy, fine-grained sand (L), coarse-grained sand (K), fine-grained sand (X), coarse-grained sand (A1), fine-grained sand (AB), and coarse-grained sand (Y). To the southwest, in somewhat deeper water of Stellwagen Basin, it abuts fine-grained sandy mud (substrate R). Substrate AF (a rippled, fine-grained sand) occurs at five stations in the easternmost part of substrate P and is interpreted to represent a transition area between substrates P and Y.

R i_fgsM—Immobile, fine-grained sandy mud.—Substrate R is an immobile, fine-grained sandy mud deposit that lies in Stellwagen Basin in the southwestern part of quadrangle 2. Its mapped area in quadrangle 2 is 29.3 km2, or 14.0 percent of the quadrangle area. The water depths of the stations and the mapped substrate range from 60 to 64 m. Mean weight percents of aggregates and composite grades are as follows: mud, 68; sand, 32 (fgS, 29; cgS, 3); gravel, <1 (G1, <1; G2, 0). Substrate R is bounded to the east by substrate P, a muddy, fine-grained sand with a lower mud content (23 weight percent). Substrate R is also present in quadrangle 5 to the north (Valentine and Cross, 2024c). Although deposits of substrate R in quadrangles 2 and 5 are not contiguous, they are similar in terms of grain-size composition (both contain 50 to <90 weight percent mud), water depth range, geographic setting, and the presence of fish and crab burrows.

X i_fgS—Immobile, fine-grained sand.—Substrate X is an immobile, fine-grained sand deposit that lies in a small valley located on the western flank of Southwest Corner. Its mapped area in quadrangle 2 is 1.2 km2, or 0.6 percent of the quadrangle area. The water depths of the stations and the mapped substrate range from 44 to 55 m. Mean weight percents of aggregates and composite grades are as follows: mud, 5; sand, 95 (fgS, 82; cgS, 13); gravel, <1 (G1, <1; G2, 0). It is bounded to the northwest and north by the rippled, coarse-grained sand of substrate K and to the east at shallower depths by the rippled, coarse-grained sand of substrate A1. Substrate X is bounded to the south and southwest at deeper depths by the muddy, fine-grained sand of substrate P in Stellwagen Basin. Substrate X is an immobile, fine-grained sand that is texturally very similar to substrate AB but separated from it geographically. Substrate AB is a rippled, fine-grained sand (44–63 m water depth) that is present on the southern flank of the bank facing Race Point Channel.

Y r_cgS—Rippled, coarse-grained sand.—Substrate Y is a mobile, coarse-grained sand deposit that lies in the western part of Race Point Channel between Stellwagen Bank to the north and Cape Cod to the south. Its mapped area in quadrangle 2 is 22.4 km2, or 10.7 percent of the quadrangle area. The water depths of the stations and the mapped substrate range from 54 to 64 m. Mean weight percents of aggregates and composite grades are as follows: mud, 4; sand, 95 (fgS, 36; cgS, 59); gravel, 1 (G1, 1; G2, 0). The northern part of substrate Y lies at somewhat shallower depths (≤60 m) than the southern part (>60 m). Substrate Y is bounded by the rippled, fine-grained sand of substrate AB to the north and rippled, coarse-grained sand of substrate Z to the east. To the west it abuts the immobile, muddy, fine-grained sand of substrate P in Stellwagen Basin and Little Stellwagen Basin. Substrate C, interpreted to be an east-west-trending boulder ridge, extends eastward from substrate Y into the area occupied by substrate Z.

Z r_cgS—Rippled, coarse-grained sand.—Substrate Z is a mobile, coarse-grained sand deposit that lies in Race Point Channel between Stellwagen Bank to the north and Cape Cod to the south. Its mapped area in quadrangle 2 is 6.4 km2, or 3.1 percent of the quadrangle area. The water depths of the stations range from 51 to 56 m and the water depth of the mapped substrate ranges from 50 to 60 m. Mean weight percents of aggregates and composite grades are as follows: mud, 2; sand, 98 (fgS, 9; cgS, 89); gravel, 1 (G1, 1; G2, <1). Substrate Z is bounded to the north by substrate AB (rippled, fine-grained sand), to the west by substrate Y (rippled, coarse-grained sand), and to the south by substate AC (rippled, coarse-grained sand). Although substrates Y and Z are both coarse-grained sands, substrate Z lies at somewhat shallower depths and has a higher coarse-grained sand content (89 weight percent) than substrate Y (59 weight percent), which lies at somewhat deeper depths in the western entrance to Race Point Channel. Substrates Z and AC are texturally similar, but the surface of AC displays large bedforms visible in multibeam topographic imagery. Substrate Z also is texturally similar to (but separated geographically from) both substrate A1 on Stellwagen Bank to the north and substrate AG on the southern margin of Race Point Channel to the south. Substrate C, interpreted to be an east-west-trending boulder ridge, extends westward from substrate Z into the area occupied by substrate Y.

AA r_gcgS / i_pcG—Rippled, gravelly, coarse-grained sand; partial veneer on immobile, pebble, cobble gravel.—Substrate AA is a layered substrate of mobile sand that partially veneers immobile, pebble, cobble gravel and lies on the southwestern part of Stellwagen Bank, north of Southwest Corner. Its mapped area in quadrangle 2 is 1.4 km2, or 0.7 percent of the quadrangle area. The water depths of the stations and the mapped substrate range from 27 to 35 m. Mean weight percents of aggregates and composite grades of the sediment partial veneer that overlies gravel are as follows: mud, <1; sand, 55 (fgS, 6; cgS, 49); gravel, 45 (G1, 16; G2, 29). Substrate AA is surrounded by substrate A1. The area occupied by substrate AA includes deposits of substrates A1 and A3 as bedforms that are flattened by fishery trawling and dredging and are subsequently re-formed by storm-wave generated currents; therefore, at times, the seabed is gravel partially covered by sand and represents substrate AA and, at other times, the seabed is fully covered by sand and represents substrates A1 and A3.

AB r_fgS—Rippled, fine-grained sand.—Substrate AB is a mobile, fine-grained sand deposit that lies in the northern part of Race Point Channel on the southern flank of Stellwagen Bank. Its mapped area in quadrangle 2 is 11.7 km2, or 5.6 percent of the quadrangle area. The water depths of the stations and the mapped substrate range from 44 to 63 m. Mean weight percents of aggregates and composite grades are as follows: mud, 4; sand, 96 (fgS, 71; cgS, 25); gravel, <1 (G1, <1; G2, 0). Substrate AB is bounded to the north by the rippled, coarse-grained sand of substrate A1 on Stellwagen Bank; to the south by the rippled, coarse-grained sands of substrates Y and Z in Race Point Channel; and to the west by the immobile, muddy, fine-grained sand of substrate P in Stellwagen Basin. The fine-grained sand that characterizes substrate AB has likely been transported southward from Stellwagen Bank by storm-wave generated currents from the north and northeast. Within the area occupied by substrate AB, deposits of two substrates occur that are represented by too few samples to be mappable as coherent units at 1:25,000 scale in quadrangle 2. One, substrate AD, is a rippled, coarse-grained sand that overlies a series of nested, arcuate gravel ridges that are observed in multibeam topographic imagery and are interpreted to represent a glacial icefall deposit at the foot of Stellwagen Bank. The other, substrate AE, is a rippled, coarse-grained sand that overlies a topographic feature interpreted to be a gravel ridge or moraine that lies southeast of Southwest Corner. Substrate AD contains more coarse-grained sand and less fine-grained sand than substrate AE. Substrate AB is texturally similar to substrates L and X that lie on the western slope of Stellwagen Bank.

AC r_cgS—Rippled, coarse-grained sand.—Substrate AC is a mobile, coarse-grained sand deposit that lies in a small part of Race Point Channel in quadrangle 2; however, most of the substrate lies in the adjoining quadrangle to the east. Its mapped area in quadrangle 2 is <0.1 km2, or <0.1 percent of the quadrangle area. The water depth of the mapped substrate in quadrangle 2 is approximately 60 m. No sediment samples of this substrate were collected in quadrangle 2. Weight percents of aggregates and composite grades of the one sample collected from substrate AC in the adjoining quadrangle are as follows: mud, 2; sand, 98 (fgS, 12; cgS, 86); gravel, <1 (G1, <1; G2, 0). Substrate AC is interpreted to be a rippled, coarse-grained sand because its surface displays large bedforms observable in multibeam topographic imagery. These bedforms trend northwest to southeast, approximately normal to the trend of Race Point Channel. Although substrate AC was not sampled in quadrangle 2, it is mapped as extending a short distance into quadrangle 2 from the adjoining quadrangle to the east based on the presence of its distinctive bedforms observed in the multibeam sonar topographic imagery.

AD r_cgS—Rippled, coarse-grained sand.—Substrate AD is a collection of mobile, coarse-grained sand deposits that lie on several partly buried, nested, arcuate gravel ridges that are interpreted from multibeam topographic imagery to represent a glacial icefall deposit at the foot of the southern slope of Stellwagen Bank in the northern part of Race Point Channel. The water depths of the stations range from 44 to 45 m. Mean weight percents of aggregates and composite grades are as follows: mud, 1; sand, 92 (fgS, 10; cgS, 82); gravel, 6 (G1, 6; G2, 0). Four samples of substrate AD were collected from within the area mapped as substrate AB, but they are not mappable as a coherent unit at 1:25,000 scale; the locations of these samples are shown by magenta square symbols on map D, sheet 1, and are identified in Valentine and Cross (2024d). Substrate AD is texturally similar to substrate AE, which also is an unmappable substrate lying within the area of substrate AB, but AD has a higher weight percent of coarse-grained sand.

AE r_cgS—Rippled, coarse-grained sand.—Substrate AE is a collection of mobile, coarse-grained sand deposits that lie on a partly buried feature that is interpreted from multibeam topographic imagery to be a gravel ridge or moraine that is located in the northern part of Race Point Channel near the southern margin of Stellwagen Bank. The water depths of the stations range from 49 to 54 m. Mean weight percents of aggregates and composite grades are as follows: mud, 3; sand, 95 (fgS, 34; cgS, 61); gravel, 2 (G1, 2; G2, <1). Five samples of substrate AE were collected from within the area mapped as substrate AB, but they are not mappable as a coherent unit at 1:25,000 scale; the locations of these samples are shown by magenta square symbols on map D, sheet 1, and are identified in Valentine and Cross (2024d). Substrate AE is texturally similar to substrate AD, but AE has a higher weight percent of fine-grained sand.

AF r_fgS—Rippled, fine-grained sand.—Substrate AF is a collection of mobile, fine-grained sand deposits that lie at the western end of Race Point Channel in Little Stellwagen Basin. The water depths of the stations range from 62 to 64 m. Mean weight percents of aggregates and composite grades are as follows: mud, 4; sand, 95 (fgS, 62; cgS, 33); gravel, 1 (G1, 1; G2, 0). Five samples of substrate AF were collected from within the easternmost part of the area mapped as substrate P, but they are not mappable as a coherent unit at 1:25,000 scale; the locations of these samples are shown by magenta square symbols on map D, sheet 1, and are identified in Valentine and Cross (2024d). The substrate AF samples lie near the boundary of substrate P (an immobile, muddy, fine-grained sand) and substrate Y (a rippled, coarse-grained sand that lies to the east in Race Point Channel) and are interpreted to represent a textural transition area between substrates P and Y.

AG r_cgS—Rippled, coarse-grained sand.—Substrate AG is a mobile, coarse-grained sand deposit that lies on the southern flank of Little Stellwagen Basin north of Cape Cod and extends eastward into the adjoining quadrangle to the east. Its mapped area in quadrangle 2 is 0.4 km2, or 0.2 percent of the quadrangle area. It is represented by only two stations (1425 and 4646) in quadrangle 2, one in the mapped area and one located nearby to the south in the unmapped southeastern part of quadrangle 2. The water depths of the stations range from 55 to 58 m and the water depth of the mapped substrate ranges from about 55 to about 60 m. Mean weight percents of aggregates and composite grades of the two samples are as follows: mud, <1; sand, 100 (fgS, 5; cgS, 95); gravel, 0 (G1, 0; G2, 0). Storm-wave generated sand ripples are present on the surface of substrate AG. The substrate likely extends southward into shallowing water depths on the northern margin of Cape Cod, but this area of quadrangle 2 is unmapped due to a lack of multibeam sonar data. Substrate AG is similar to substrate AH, an unmappable substrate that abuts it to the west. Substrate AH is also a rippled, coarse-grained sand that lies along the northern margin of Cape Cod, but it contains much more fine-grained sand (16 weight percent) than substrate AG (5 weight percent). Multibeam topographic and backscatter imagery indicate that substrate AG is a recognizable feature that extends eastward along the northern slope of Cape Cod into the adjoining quadrangle to the east.

AH r_cgS—Rippled, coarse-grained sand.—Substrate AH is a collection of mobile, coarse-grained sand deposits that lie on the southern flank of Little Stellwagen Basin. It is represented by only two stations (1424 and 4645) in quadrangle 2. The water depths of the two stations are both 61 m. One sample was collected from the area mapped as substrate Y (near its southern margin) and the other was collected in the unmapped southeastern part of the quadrangle. Mean weight percents of aggregates and composite grades are as follows: mud, <1; sand, 100 (fgS, 16; cgS, 84); gravel, 0 (G1, 0; G2, 0). The substrate is likely present in the unmapped area to the south of substrate Y, in shallowing water depths on the northern margin of Cape Cod. The two samples of substrate AH are not mappable as a coherent unit at 1:25,000 scale; the locations of these samples are shown by magenta square symbols on map D, sheet 1, and are identified in Valentine and Cross (2024d). Storm-wave generated sand ripples are present on the surface of substrate AH. The substrate has a lower mud content and a higher coarse-grained sand content than substrate Y. Substrate AH is similar to substrate AG that abuts it to the east. Substrate AG is also a rippled, coarse-grained sand that lies along the northern margin of Cape Cod, but it contains much less fine-grained sand (5 weight percent) than substrate AG (16 weight percent). Substrate AH is texturally similar to substrate A3, but it is recognized as a separate substrate because it is separated geographically from deposits of A3 by Race Point Channel.

Map E. Sediment Mobility

Map E shows the distribution of 19 geologic substrates of map D grouped into four substrates based on surface mobility, as determined by the presence or absence of sand ripples observed in video, photographic, and multibeam topographic imagery (tables 6 and 7; Valentine and Cross, 2024d). The four mapped substrates are (1) mobile sediment (unlayered sand substrates with rippled surfaces), (2) mobile and immobile sediment (layered substrates of mobile sand that partially veneers immobile gravel), (3) immobile sediment (unlayered sand or mud substrates with immobile surfaces), and (4) boulder ridges ≥1 m in height.

Some stations have been fished using otter trawls and scallop dredges. These activities temporarily disturb and flatten sand ripples so that video and photographic imagery sometimes show no evidence of sand ripples at the time of acquisition. The sand ripples are later re-formed by storm-wave generated currents. The presence of broken shells is often an indicator of fishing disturbance. When a site that occurred within an area mapped as a rippled substrate did not display ripples at the time of imaging due to fishing disturbance, that site is still interpreted to be a rippled substrate under natural conditions.

In quadrangle 2, substrate mobility decreases with increasing water depth westward from Stellwagen Bank to Stellwagen Basin. The boundary between mobile and immobile sediment on the western flank of the bank lies at 50 to 55 m water depth, approximately along the downslope margins of substrates A1, H, and K. By contrast, in Race Point Channel (south of Stellwagen Bank), where all substrates exhibit rippled surfaces, substrates are mobile at water depths of up to 64 m.

Of the 13 unlayered substrates with mobile surfaces in quadrangle 2, 4 are on Stellwagen Bank (A1, A3, H, and K) and 9 are in the Race Point Channel region (Y, Z, AB, AC, AD, AE, AF, AG, and AH). On Stellwagen Bank, substrate A1 is a rippled, coarse-grained sand (19–55 m water depth) that occupies the bank top and its upper western flank to about 40 m and its southern flank to about 55 m. Substrate A3 is also a rippled, coarse-grained sand (19–59 m water depth) and is an unmappable substrate present in the areas occupied by substrates A1, AA, and AB. Substrates H (a rippled, fine-grained sand; 37–42 m water depth) and K (a rippled, coarse-grained sand; 40–56 m water depth) are both present on the western flank of Stellwagen Bank. In the Race Point Channel region, substrates Y (54–64 m water depth) and Z (50–60 m water depth) are rippled, coarse-grained sands that occupy the western part of the channel. Substrate AB is a rippled, fine-grained sand (44–63 m water depth) that lies at the base of Stellwagen Bank along the northern margin of Race Point Channel. Substrate AC is a rippled, coarse-grained sand (60 m water depth) that occupies a small area in the channel along the eastern margin of quadrangle 2, but it lies primarily in the adjoining quadrangle to the east. Substrates AD (44–45 m water depth) and AE (49–54 m water depth) are rippled, coarse-grained sands that are unmappable substrates and lie in the area occupied by substrate AB. Substrate AF is a rippled, fine-grained sand (62–64 m water depth) that is an unmappable substrate and lies in the eastern part of substrate P. Substrate AG is a rippled, coarse-grained sand (55–60 m water depth) that lies on the southern margin of Race Point Channel. Substrate AH is a rippled, coarse-grained sand (61 m) that is an unmappable substrate and lies in and near the southern part of the area occupied by substrate Y.

The one layered substrate that has an upper mobile substrate that partially veneers a lower immobile substrate is substrate AA, a rippled, gravelly, coarse-grained sand. Substrate AA forms a partial veneer on an immobile, pebble, cobble gravel substrate (27–35 m water depth) that lies on the upper western flank of Stellwagen Bank.

The four substrates that have immobile surfaces are substrates L, P, R, and X. Substrate L is an immobile, muddy, fine-grained sand (49–58 m water depth) that lies at the base of the western flank of Stellwagen Bank. Substrate P is an immobile, muddy, fine-grained sand (51–68 m water depth) that occupies Stellwagen Basin and a portion of Little Stellwagen Basin west and southwest of Stellwagen Bank. Substrate R is an immobile, fine-grained sandy mud (60–64 m water depth) that lies in Stellwagen Basin, in the southwestern part of the quadrangle. Substrate X is an immobile, fine-grained sand (44–55 m water depth) that lies in a small valley that incises the southwestern flank of Stellwagen Bank.

Substrate C is a boulder ridge that is ≥1 m in height. It is a mappable feature of piled cobbles and boulders in Race Point Channel at 55 to 60 m water depth.

Map F. Distribution of Fine- and Coarse-Grained Sand and Boulder Ridges

Map F shows the distribution of fine- and coarse-grained sand that characterize the composition of unlayered (or the upper layer of layered) geologic substrates shown on map D. There are two substrate groups in which either fine- or coarse-grained sand dominate the sand fraction (table 6).

The fine-grained sand group consists of six substrates (H, L, P, X, AB, and AF) that have ≥50 mean weight percent sand, of which the largest portion is fine-grained sand (3 and 4 phi combined). These substrates occur primarily on the western flank of Stellwagen Bank, in Stellwagen Basin, in the western part of Little Stellwagen Basin, and along the southern margin of Stellwagen Bank in Race Point Channel. Substrate R is also included in the mapped fine-grained sand group; it is a fine-grained sandy mud that occurs in Stellwagen Basin in the southwestern part of quadrangle 2. Although it is a sandy mud, substrate R is included in the fine-grained sand group to draw attention to its large sand content (32 weight percent), of which most (29 weight percent) is fine-grained sand, and to acknowledge the likely transport of fine-grained sand from Stellwagen Bank into Stellwagen Basin. Substrate R is also observed in quadrangle 5 to the north and is similarly grouped there (Valentine and Cross, 2024c).

The coarse-grained sand group consists of eleven substrates (A1, A3, K, Y, Z, AA, AC, AD, AE, AG, and AH) that have ≥50 mean weight percent sand, of which the largest portion is coarse-grained sand (0, 1, and 2 phi combined). These substrates occur on Stellwagen Bank, on its western flank, in Race Point Channel, and in the eastern part of Little Stellwagen Basin.

Also shown on the map is substrate C. This substrate consists of a single boulder ridge in quadrangle 2.

Most substrates in quadrangle 2 display an increase of fine-grained sand and mud content with increasing water depth west of Stellwagen Bank; this increase is interpreted to be the result of fine-grained sediments winnowed from sands on Stellwagen Bank and in Race Point Channel being transported downslope into Stellwagen Basin. Substrate K (a coarse-grained sand; 40–56 m water depth) is an exception to this observation because it lies downslope of substrate H (a fine-grained sand; 37–42 m water depth); this relation indicates that substrate K is an older deposit that was not formed by present-day sedimentary transport processes. This relation between substrates K and H is also observed in quadrangle 5 to the north (Valentine and Cross, 2024c).

Map G. Distribution of Substrate Mud Content and Boulder Ridges

Map G shows the mud content of 18 sedimentary substrates of map D grouped using a seven-tier scale based on mean weight percent mud content (table 6). The seven ranges of mud content, in mean weight percent, are as follows: <1; 1 to <5; 5 to <10; 10 to <20; 20 to <50; 50 to <90; and ≥90. Mud content increases from <1 to 68 mean weight percent with increasing water depth southwestward from Southwest Corner (19 m water depth) into Stellwagen Basin (68 m water depth). Also shown on the map is a boulder ridge unit (equivalent to substrate C).

Substrate mud contents and their equivalent geologic substrates from map D, water depths, and locations are listed below:

  • • Substrates containing <1 weight percent mud (A1, AA, AG, and AH; 19–61 m water depth) occupy the shallow crest of Stellwagen Bank, its upper western flank, and the northern slope of Cape Cod along the southern margin of Race Point Channel.

  • • Substrates containing 1 to <5 weight percent mud (A3, H, K, Y, Z, AB, AC, AD, AE, and AF; 19–64 m water depth) occupy the western flank of Stellwagen Bank and Race Point Channel.

  • • One substrate containing 5 to <10 weight percent mud (X; 44–55 m water depth) occupies the small valley that incises the southwest flank of the bank.

  • • One substrate containing 10 to <20 weight percent mud (L; 49–58 m water depth) occupies the lower western flank of the bank. Substrate L contains 9 weight percent mud in quadrangle 2 and 10 weight percent mud in the adjoining quadrangle 5 (Valentine and Cross, 2024b, c). For continuity with substrate L in quadrangle 5, and because the mean mud content of substrate L in quadrangles 2 and 5 differs by only 1 weight percent, substrate L is mapped in the 10 to <20 weight percent mud category in quadrangle 2.

  • • One substrate containing 20 to <50 weight percent mud (P; 51–68 m water depth) occurs in Stellwagen Basin at the base of the western flank of the bank and in Little Stellwagen Basin at the western entrance to Race Point Channel.

  • • One substrate containing 50 to <90 weight percent mud (R; 60–64 m water depth) occurs in Stellwagen Basin in the southwest part of the mapped region and is characterized by the presence of fish and crab burrows.

  • • Substrate C contains 0 weight percent mud and is shown as a boulder ridge ≥1 m in height on map G.

Tables 6 and 7

Table 6.    

Properties of geologic substrates in quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts.

[Textural properties for unlayered substrates (A1, A3, H, K, L, P, R, X, Y, Z, AB, AC, AD, AE, AF, AG, and AH) are based on grain-size analysis. Textural properties for the layered substrate (AA) are based on grain-size analysis of the upper substrate that partially veneers the lower substrate. The lower substrate is identified on the basis of video imagery and is a combination of pebble, cobble, and boulder gravel. Weight percent values may not add to 100 due to rounding; <1 means >0 and ≤0.5 weight percent. A sand (4, 3, 2, 1, and 0 phi), mud (>4 phi), or gravel (−1, −2, −3, −4, and −5 phi) grain size is termed “significant” in a substrate if its mean weight percent for all samples of a substrate type is ≥10. See tables 1 and 2 for grain-size classifications for sediment. Sediment components of an unlayered substrate (or the upper substrate of a layered substrate) are listed in order of increasing weight percent in the sediment class name. Sediment components of the lower substrate indicate presence/absence and are not listed in order of increasing areal coverage in the sediment class name. See table 3 for an explanation of characters used in substrate names to describe their physical attributes. For stations that represent substrates that could not be mapped as coherent units (A3, AD, AE, AF, and AH), the water depth range of stations is the same as that of the mapped substrate. See Valentine and Cross (2024d) for the results of grain-size analyses of sediment samples and the assignment of stations to substrates. Table format from Valentine and Cross (2024c). Grain-size abbreviations: cgS, coarse-grained sand (2, 1, and 0 phi combined); fgS, fine-grained sand (4 and 3 phi combined); G1, gravel1 (−1 and −2 phi combined); G2, gravel2 (−3, −4, and −5 phi combined). Other terms: ~, approximately; >, greater than; ≥, greater than or equal to; <, less than; ≤, less than or equal to; φ, phi; All, total number of stations; m, meter; max, maximum; min, minimum; mm, millimeter; NS, number of stations with only video or photograph imagery; S, number of stations with sediment grain-size analysis]
Substrate name Substrate name translation Number of stations Station water depth range; mean [mapped substrate depth range] (m) Significant sediment grain sizes Weight percent of aggregates (mud, sand, and gravel), phi grades (4 phi and 3 phi), and composite grades (fgS, cgS, G1, and G2) that occur in each substrate
Phi grade (mean weight percent) Min and max grain diameter (mm); max difference Samples    Mud      4 phi     3 phi      fgS       cgS        Sand         G1         G2     Gravel
A1 r_cgS A1—Rippled, coarse-grained sand S, 342;
NS, 55;
All, 397		 19–48; 27
[19–55]		 2φ (26), 1φ (52), 0φ (17);
Total (95)		 0.25–<2.0;
~1.75		 Range 0–5 0–2 0–9 0–9 64–99 66–100 0–26 0–14 0–34
Mean <1 <1 2 2 95 97 3 <1 3
A3 r_cgS A3—Rippled, coarse-grained sand S, 34;
NS, 1;
All, 35		 19–59; 31
[19–59]		 3φ (15), 2φ (43), 1φ (37);
Total (95)		 0.125–<1.0;
~0.875		 Range <1–3 0–6 7–63 10–70 30–90 94–100 0–4 0–0 0–4
Mean 1 1 15 16 82 99 <1 0 <1
C i_cbG C—Immobile, cobble, boulder gravel S, 1;
NS, 1;
All, 2		 58–58; 58
[55–<60]		 Substrate C is a boulder ridge identified on the basis of video and multibeam sonar imagery. One sediment sample was collected, which was from the rippled, coarse-grained sand that partially veneers the gravelly margins of the boulder ridge.
H r_fgS H—Rippled, fine-grained sand S, 8;
NS, 0;
All, 8		 39–42; 40
[37–42]		 4φ (17), 3φ (72);
Total (89)		 0.062–<0.250;
~0.188		 Range 1–2 4–27 59–89 78–97 2–20 98–99 0–<1 0–0 0–<1
Mean 1 17 72 89 10 99 0 0 0
K r_cgS K—Rippled, coarse-grained sand S, 34;
NS, 4;
All, 38		 41–56; 45
[40–56]		 3φ (16), 2φ (47), 1φ (32);
Total (95)		 0.125–<1.0;
~0.875		 Range <1–5 1–10 3–40 4–47 49–96 95–100 0–<1 0–0 0–<1
Mean 1 3 16 19 80 99 0 0 0
L i_mfgS L—Immobile, muddy, fine-grained sand S, 6;
NS, 0;
All, 6		 50–58; 53
[49–58]		 >4φ (9*), 4φ (24), 3φ (52), 2φ (15);
Total (100)		 >0–<0.50;
~0.50		 Range 6–14 15–31 44–58 65–87 3–29 86–94 0–<1 0–0 0–<1
Mean 9 24 52 75 15 90 0 0 0
P i_mfgS P—Immobile, muddy, fine-grained sand S, 105;
NS, 6;
All, 111		 51–68; 61
[51–68]		 >4φ (23), 4φ (35), 3φ (34);
Total (92)		 >0–<0.250;
~0.250		 Range 8–48 6–59 13–68 39–90 0–38 52–92 0–5 0–1 0–3
Mean 23 35 34 68 8 76 <1 0 <1
R i_fgsM R—Immobile, fine-grained sandy mud S, 18;
NS, 2;
All, 20		 60–64; 62
[60–64]		 >4φ (68), 4φ (22);
Total (90)		 >0–<0.125;
~0.125		 Range 49–91 8–36 1–15 9–47 <1–12 9–51 0–<1 0–0 0–<1
Mean 68 22 6 29 3 32 <1 0 <1
X i_fgS X—Immobile, fine-grained sand S, 9;
NS, 0;
All, 9		 44–55; 50
[44–55]		 4φ (24), 3φ (58), 2φ (13);
Total (95)		 0.062–<0.50;
~0.438		 Range 1–9 12–48 42–69 59–93 1–40 91–99 0–<1 0–0 0–<1
Mean 5 24 58 82 13 95 <1 0 <1
Y r_cgS Y—Rippled, coarse-grained sand S, 29;
NS, 0;
All, 29		 54–64; 60
[54–64]		 3φ (32), 2φ (51);
Total (83)		 0.125–<0.50;
~0.375		 Range <1–11 <1–10 11–47 12–49 46–85 89–100 0–4 0–0 0–4
Mean 4 4 32 36 59 95 1 0 1
Z r_cgS Z—Rippled, coarse-grained sand S, 14;
NS, 1;
All, 15		 51–56; 54
[50–60]		 2φ (43), 1φ (41);
Total (84)		 0.250–<1.0;
~0.75		 Range 1–5 0–2 2–14 2–15 81–96 91–99 0–6 0–2 0–8
Mean 2 1 8 9 89 98 1 <1 1
AA r_gcgS / i_pcG AA—Rippled, gravelly, coarse-grained sand; partial veneer on immobile, pebble, cobble gravel S, 7;
NS, 5;
All, 12		 27–35; 31
[27–35]		 2φ (10), 1φ (17), 0φ (22), −5φ (11);
Total (60)		 0.25–<64;
~63.75		 Range <1–1 0–2 1–15 1–16 28–62 29–72 10–20 15–60 28–71
Mean <1 1 5 6 49 55 16 29 45
AB r_fgS AB—Rippled, fine-grained sand S, 31;
NS, 1;
All, 32		 44–63; 53
[44–63]		 4φ (10), 3φ (61), 2φ (21);
Total (92)		 0.062–<0.50;
~0.438		 Range 1–6 2–26 37–84 48–93 3–48 93–98 0–3 0–<1 0–3
Mean 4 10 61 71 25 96 <1 0 <1
AC r_cgS C—Rippled, coarse-grained sand S, 1;
NS, 0;
All, 1		 ~60
[~60]		 3φ (11), 2φ (44), 1φ (38);
Total (93)		 0.125–<1.0;
~0.875		 Range 2 1 11 12 86 98 <1 0 <1
Substrate AC lies principally in the adjoining quadrangle to the east of quadrangle 2, but it also extends a small distance into quadrangle 2. The single grain-size analysis from this substrate is from a sample collected in the adjoining quadrangle. No samples were collected from this substrate in quadrangle 2.
AD r_cgS AD—Rippled, coarse-grained sand S, 4;
NS, 0;
All, 4		 44–45; 45
[44–45]		 1φ (35), 0φ (40);
Total (75)		 0.5–<2.0;
~1.5		 Range 1–1 <1–3 4–15 6–16 78–87 85–97 2–13 0–0 2–13
Mean 1 1 9 10 82 92 6 0 6
AE r_cgS AE—Rippled, coarse-grained sand S, 5;
NS, 0;
All, 5		 49–54; 52
[49–54]		 3φ (26), 2φ (37), 1φ (17);
Total (80)		 0.125–<1.0;
~0.875		 Range 2–5 6–11 15–33 22–41 51–74 88–97 <1–5 0–2 <1–6
Mean 3 8 26 34 61 95 2 <1 2
AF r_fgS AF—Rippled, fine-grained sand S, 4;
NS, 1;
All, 5		 62–64; 63
[62–64]		 3φ (58), 2φ (28);
Total (86)		 >0.125–<0.50;
~0.375		 Range 1–8 2–8 51–71 53–75 22–44 92–97 0–1 0–0 0–1
Mean 4 4 58 62 33 95 1 0 1
AG r_cgS AG—Rippled, coarse-grained sand S, 2;
NS, 0;
All, 2		 55–58; 57
[~55–~60]		 2φ (86);
Total (86)		 >0.25–<0.50;
~0.25		 Range <1–<1 0–0 5–6 5–6 94–95 100–100 0–0 0–0 0–0
Mean <1 0 5 5 95 100 0 0 0
AH r_cgS AH—Rippled, coarse-grained sand S, 2;
NS, 0;
All, 2		 61–61; 61
[61]		 3φ (16), 2φ (75);
Total (91)		 >0.125–<0.50;
~0.375		 Range 0–<1 0–<1 15–17 15–17 83–85 100–100 0–0 0–0 0–0
Mean <1 <1 16 16 84 100 0 0 0
Table 6.    Properties of geologic substrates in quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts.
*

The mud (>4φ) content of substrate L is provided even though the threshold of ≥10 weight percent is not met (Valentine, 2019) because substrate L extends northward from quadrangle 2 into quadrangle 5 where the mud threshold is met.

Table 7.    

Geologic substrate symbols, names, areas, and brief comparisons to other substrates in quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts.

[See table 3 for an explanation of characters used in substrate names to describe their physical attributes. Areas were calculated from substrate polygons (Valentine and Cross, 2024a) using Esri’s ArcMap program, version 10.8.1. Areas could not be determined for substrates A3, AD, AE, AF, and AH because they are represented by few samples and are not mappable as coherent units at 1:25,000 scale. Quadrangle 2 has a total mapped area of 209 km2. Table format from Valentine and Cross (2024c). Terms: <, less than; km2, square kilometer; m, meter; nd, no data; wt. pct., weight percent]
Geologic substrate symbol Substrate name Substrate name translation Area of substrate in quadrangle 2 (km2) Area of substrate in quadrangle 2 (percent) Brief description and (or) comparison to other substrates
A1 A1 r_cgS A1—Rippled, coarse-grained sand 51.7 24.7 Substrate A1 (19–55 m water depth) lies on Stellwagen Bank and is equivalent to both substrates A1 and the mobile portion of substrate B in the adjoining quadrangle 5 to the north (Valentine and Cross, 2024c). Substrate A1 is similar to mobile substrate A3, but A1 has a lower content of fine-grained sand (2 wt. pct.) than A3 (16 wt. pct.). Substrate A1 is texturally similar to immobile substrate A2 which lies at greater water depths (53–77 m) on the lower eastern flank of Stellwagen Bank in quadrangle 6 (Valentine and Gallea, 2015) and contains more fine-grained sand (11 wt. pct.).
A3 A3 r_cgS A3—Rippled, coarse-grained sand nd nd Substrate A3 (19–59 m water depth) is similar to mobile substrate A1, but A3 has a higher fine-grained sand content than A1 (see above). Substrate A3 also occurs in quadrangle 5 to the north (Valentine and Cross, 2024c). Deposits of substrate A3 could not be mapped as a coherent unit and are shown by magenta square symbols on map D, sheet 1 (see Valentine and Cross, 2024d). Texturally, substrate A3 is equivalent to substrate K, which lies in a greater water depth range in quadrangle 2 on the western flank of Stellwagen Bank (see below).
C C i_cbG C—Immobile, cobble, boulder gravel 0.5 0.2 Substrate C (55–<60 m water depth) is a boulder ridge whose gravelly margin is partially veneered by a layer of rippled sand. This boulder ridge trends east to west and it lies in Race Point Channel near the eastern border of quadrangle 2. Its eastern part is bounded by substrate Z and its western part by substrate Y.
H H r_fgS H—Rippled, fine-grained sand 1.0 0.5 Substrate H (37–42 m water depth) lies on the western flank of Stellwagen Bank and extends northward into quadrangle 5 (Valentine and Cross, 2024c). Substrate H lies downslope of mobile substrate A1. The weight percent of mud is low in both substrates (A1, <1; H, 1), but H has a much higher fine-grained sand content (89 wt. pct.) than A1 (2 wt. pct.). Substrate H lies upslope of substrate K, a mobile, coarse-grained sand with low mud content (1 wt. pct.).
K K r_cgS K—Rippled, coarse-grained sand 5.9 2.8 Substrate K (40–56 m water depth) lies on the western flank of Stellwagen Bank, downslope of substrates A1 and H, and extends northward into quadrangle 5 (Valentine and Cross, 2024c). It is texturally equivalent to substrate A3. In deeper water to the west, substrate H is bounded by the immobile, muddy fine-grained sands of substrates L and P.
L L i_mfgS L—Immobile, muddy, fine-grained sand 0.7 0.3 Substrate L (49–58 m water depth) lies on the western flank of Stellwagen Bank, downslope of substate K, and extends northward into quadrangle 5 (Valentine and Cross, 2024c). It contains 9 wt. pct. mud and represents the textural transition from a rippled, shallower sand substrate K (1 wt. pct. mud) to an immobile, deeper mud substrate P (23 wt. pct. mud) in Stellwagen Basin. Substrate L in quadrangle 2 is texturally equivalent to substrate G1 that occurs off the eastern flank of Stellwagen Bank in quadrangle 6 (Valentine and Gallea, 2015) in much greater water depths (85–171 m).
P P i_mfgS P—Immobile, muddy, fine-grained sand 76.1 36.5 Substrate P (51–68 m water depth) lies in Stellwagen Basin west of Stellwagen Bank and in Little Stellwagen Basin at the western entrance to Race Point Channel. It extends northward into quadrangle 5 (Valentine and Cross, 2024c). In quadrangle 2, it occupies the transition between substrate R (fine-grained sandy mud) in the basin to the west and textually varied substrates that lie in shallower water to the east, including substrates A1 (coarse-grained sand), A3 (coarse-grained sand), K (coarse-grained sand), L (muddy, fine-grained sand), X (fine-grained sand), Y (coarse-grained sand), and AB (fine-grained sand).
R R i_fgsM R—Immobile, fine-grained sandy mud 29.3 14.0 Substrate R (60–64 m water depth) lies in Stellwagen Basin in the southwestern part of quadrangle 2. It also occurs in quadrangle 5 to the north (Valentine and Cross, 2024c). Substrate R contains a higher mud content (68 wt. pct.) than all other substrates in quadrangle 2. It is bounded to the east by substrate P, a muddy, fine-grained sand with a lower mud content (23 wt. pct.). Fish and crab burrows are present.
X X i_fgS X—Immobile, fine-grained sand 1.2 0.6 Substrate X (44–55 m water depth) lies in a small valley that incises the western flank of Stellwagen Bank. It occupies the transitional area between the immobile, muddy, fine-grained sand of Stellwagen Basin (substrate P) and the rippled, coarse-grained sands of Stellwagen Bank (substrate A1) and its western flank (substrate K). Substrate X is textually similar but geographically separated from substrate AB that is located at the base of Stellwagen Bank in Race Point Channel, but AB is mobile and X is not.
Y Y r_cgS Y—Rippled, coarse-grained sand 22.4 10.7 Substrate Y (54–64 m water depth) lies in the western part of Race Point Channel between the coarse-grained sand of substrate Z in the channel to the east and the muddy, fine-grained sand of substrate P in Little Stellwagen Basin and Stellwagen Basin to the west. Substrate Y has a lower content of coarse-grained sand (59 wt. pct.) than substrate Z (89 wt. pct.). Substrate Y is bounded to the north by the fine-grained sand of substrate AB at the base of Stellwagen Bank and to the south by the coarse-grained sand of substrate AG at the base of the northern slope of Cape Cod.
Z Z r_cgS Z—Rippled, coarse-grained sand 6.4 3.1 Substrate Z (50–60 m water depth) lies in Race Point Channel to the east of substrate Y (also a coarse-grained sand) in somewhat shallower depths. Substrate Z has a higher content of coarse-grained sand (89 wt. pct.) than substrate Y (59 wt. pct.). Like substrate Y, substrate Z is bounded to the north by substrate AB, a fine-grained sand at the base of Stellwagen Bank.
AA AA r_gcgS / i_pcG AA—Rippled, gravelly, coarse-grained sand; partial veneer on immobile, pebble, cobble gravel 1.4 0.7 Substrate AA (27–35 m water depth) lies on the southwestern part of Stellwagen Bank and is surrounded by substrate A1, a rippled, coarse-grained sand. Substrate AA is composed of an upper substrate of rippled, coarse-grained sand which partially veneers the lower gravel substrate. In response to storm-wave generated currents, the mobile sand covers and uncovers the gravel; as a result, deposits of substrates A1 and A3 are also present in the polygon that represents AA.
AB AB r_fgS AB—Rippled, fine-grained sand 11.7 5.6 Substrate AB (44–63 m water depth) lies in the northern part of Race Point Channel at the base of Stellwagen Bank. It is bounded to the north by the coarse-grained sands of substrate A1 on Stellwagen Bank and to the south by substrates Y and Z in Race Point Channel. To the west, it is bounded by the muddy, fine-grained sand of substrate P in Stellwagen Basin. Substrate AB is texturally similar to substrate X. Two unmappable substrates of coarse-grained sand (AD, AE) lie within the area occupied by substrate AB.
AC AC r_cgS AC—Rippled, coarse-grained sand <0.1 <0.1 Substrate AC (about 60 m water depth) lies along the eastern margin of quadrangle 2, south of substrate C. The surface of substrate AC displays large bedforms observable in multibeam topographic imagery. It extends a small distance into quadrangle 2 from the adjoining quadrangle to the east. The single grain-size analysis from this substrate is from a sample collected nearby in the adjoining quadrangle to the east. No samples of this substrate were collected in quadrangle 2.
AD AD r_cgS AD—Rippled, coarse-grained sand nd nd Substrate AD (44–45 m water depth) is represented by deposits at four stations that overlie a series of arcuate gravel ridges located in the area represented by substrate AB at the base of Stellwagen Bank in the northern part of Race Point Channel. Deposits of substrate AD could not be mapped as a coherent unit and are shown by magenta square symbols on map D, sheet 1 (see Valentine and Cross, 2024d).
AE AE r_cgS AE—Rippled, coarse-grained sand nd nd Substrate AE (49–54 m water depth) is represented by deposits at five stations that lie on a partly buried feature interpreted to be a gravel ridge or moraine located in the area occupied by substrate AB at the base of Stellwagen Bank in the northern part of Race Point Channel. Deposits of substrate AE could not be mapped as a coherent unit and are shown by magenta square symbols on map D, sheet 1 (see Valentine and Cross, 2024d).
AF AF r_fgS AF—Rippled, fine-grained sand nd nd Substrate AF (62–64 m water depth) is represented by deposits at five stations in the western entrance to Race Point Channel. Substrate AF samples lie within the area occupied by substrate P, a muddy, fine-grained sand. Substrate AF stations lie in an area of textural transition between substrates P and Y. Deposits of substrate AF could not be mapped as a coherent unit and are shown by magenta square symbols on map D, sheet 1 (see Valentine and Cross, 2024d).
AG AG r_cgS AG—Rippled, coarse-grained sand 0.4 0.2 Substrate AG (about 55 m to about 60 m water depth) is represented by deposits at two stations on the northern margin of Cape Cod in the southeastern corner of quadrangle 2. One of these stations lies in the unmapped southeastern part of the quadrangle. Substrate AG extends into the adjoining quadrangle to the east.
AH AH r_cgS AH—Rippled, coarse-grained sand nd nd Substrate AH (61 m water depth) is represented by deposits at two stations on the south flank of Race Point Channel. One station lies within substrate Y and the other lies in the unmapped southeastern part of quadrangle 2. It is identical to mobile substrate A3, which occurs on Stellwagen Bank to the north, but AH is geographically separated from A3 by Race Point Channel. Deposits of substrate AH could not be mapped as a coherent unit and are shown by magenta square symbols on map D, sheet 1 (see Valentine and Cross, 2024d).
Table 7.    Geologic substrate symbols, names, areas, and brief comparisons to other substrates in quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts.

References Cited

Blair, T.C., and McPherson, J.G., 1999, Grain-size and textural classification of coarse sedimentary particles: Journal of Sedimentary Research, v. 69, no. 1, p. 6–19. [Also available at https://doi.org/10.2110/jsr.69.6.]

Butman, B., Sherwood, C.R., and Dalyander, P.S., 2008, Northeast storms ranked by wind stress and wave-generated bottom stress observed in Massachusetts Bay, 1990–2006: Continental Shelf Research, v. 28, nos. 10–11, p. 1231–1245. [Also available at https://doi.org/10.1016/j.csr.2008.02.010.]

Butman, B., Signell, R.P., Warner, J.C., and Alexander, P.S., 2007, Oceanographic setting, in Bothner, M.H., and Butman, B., eds., Processes influencing the transport and fate of contaminated sediments in the coastal ocean—Boston Harbor and Massachusetts Bay: U.S. Geological Survey Circular 1302, p. 26–33. [Also available at https://doi.org/10.3133/cir1302.]

Folk, R.L., 1954, The distinction between grain size and mineral composition in sedimentary-rock nomenclature: Journal of Geology, v. 62, no. 4, p. 344 –359. [Also available at https://www.jstor.org/stable/30065016.]

Krumbein, W.C., 1936, Application of logarithmic moments to size frequency distributions of sediments: Journal of Sedimentary Petrology, v. 6, no. 1, p. 35–47. [Also available at https://doi.org/10.1306/D4268F59-2B26-11D7-8648000102C1865D.]

Riley, S.J., DeGloria, S.D., and Elliot, R., 1999, A terrain ruggedness index that quantifies topographic heterogeneity: Intermountain Journal of Sciences, v. 5, nos. 1–4, p. 23–27. [Also available at http://download.osgeo.org/qgis/doc/reference-docs/Terrain_Ruggedness_Index.pdf.]

Udden, J.A., 1914, Mechanical composition of clastic sediments: Bulletin of the Geological Society of America, v. 25, no. 1, p. 655–744. [Also available at https://doi.org/10.1130/GSAB-25-655.]

Valentine, P.C., ed., 2005, Sea floor image maps showing topography, sun-illuminated topography, backscatter intensity, ruggedness, slope, and the distribution of boulder ridges and bedrock outcrops in the Stellwagen Bank National Marine Sanctuary region off Boston, Massachusetts: U.S. Geological Survey Scientific Investigations Map 2840, 12 sheets, scale 1:60,000, 1 DVD-ROM. [Also available at https://doi.org/10.3133/sim2840.]

Valentine, P.C., 2019, Sediment classification and the characterization, identification, and mapping of geologic substrates for the glaciated Gulf of Maine seabed and other terrains, providing a physical framework for ecological research and seabed management: U.S. Geological Survey Scientific Investigations Report 2019–5073, 37 p., accessed June 14, 2023, at https://doi.org/10.3133/sir20195073.

Valentine, P.C., Baker, J.L., Unger, T.S., and Polloni, C., 1998, Sea floor topographic map and perspective view-imagery of Quadrangles 1-18, Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File Report 98–138, 1 CD-ROM. [Also available at https://doi.org/10.3133/ofr98138.]

Valentine, P.C., and Cross, V.A., 2024a, Geospatial datasets of seabed topography, sediment mobility, and the distribution of geologic substrates in quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts: U.S. Geological Survey data release, https://doi.org/10.5066/P9UL3LWN.

Valentine, P.C., and Cross, V.A., 2024b, Geospatial datasets of seabed topography, sediment mobility, and the distribution of geologic substrates in quadrangle 5 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts: U.S. Geological Survey data release, accessed March 21, 2024, at https://doi.org/10.5066/P9W9BN3S.

Valentine, P.C., and Cross, V.A., 2024c, Seabed maps showing topography, ruggedness, backscatter intensity, sediment mobility, and the distribution of geologic substrates in quadrangle 5 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts: U.S. Geological Survey Scientific Investigations Map 3515, 8 sheets, scale 1:25,000, 27-p. pamphlet, accessed March 21, 2024, at https://doi.org/10.3133/sim3515.

Valentine, P.C., and Cross, V.A., 2024d, Station locations in quadrangle 2 in Stellwagen Bank National Marine Sanctuary offshore of Boston, Massachusetts where video, photographs and sediment samples were collected by the U.S. Geological Survey from 1993-2019 - includes sediment sample analyses and interpreted geologic substrate, in Geospatial datasets of seabed topography, sediment mobility, and the distribution of geologic substrates in quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts: U.S. Geological Survey data release, https://www.sciencebase.gov/catalog/item/644a79c6d34ee8d4adee0439.

Valentine, P.C., and Gallea, L.B., 2015, 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, 10 sheets, scale 1:25,000, 21-p. pamphlet, accessed June 14, 2023, at https://doi.org/10.3133/sim3341.

Valentine, P.C., Gallea, L.B., Blackwood, D.S., and Twomey, E.R., 2010, Seabed photographs, sediment texture analyses, and sun-illuminated sea floor topography in the Stellwagen Bank National Marine Sanctuary region off Boston, Massachusetts: U.S. Geological Survey Data Series DS–469, accessed June 14, 2023, at https://doi.org/10.3133/ds469.

Valentine, P.C., Unger, T.S., and Baker, J.L., 2000, Sun-illuminated sea floor topography of quadrangle 2 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Geologic Investigations Series Map I–2702, 1 sheet, scale 1:25,000. [Also available at https://doi.org/10.3133/i2702.]

Warner, J.C., Butman, B., and Dalyander, P.S., 2008, Storm-driven sediment transport in Massachusetts Bay: Continental Shelf Research, v. 28, no. 2, p. 257–282. [Also available at https://doi.org/10.1016/j.csr.2007.08.008.]

Wentworth, C.K., 1922, A scale of grade and class terms for clastic sediments: Journal of Geology, v. 30, no. 5, p. 377–392. [Also available at https://www.jstor.org/stable/30063207.]

Appendix 1. Data Layers and Data for Quadrangle 2

Data used to compile the quadrangle 2 maps of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts, include new data layers and previously published data, as listed in table 1.1 below. The new data layers are available in a data release associated with this report (Valentine and Cross, 2024a).

Table 1.1.    

Data layers and data used to compile maps for quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts.

[Table format from Valentine and Cross (2024b). Terms: ≥, greater than or equal to; <, less than; CSV, comma separated values; GeoTIFF, Geographic Tagged Image File Format; JPEG, Joint Photographic Experts Group; m, meter; NAD 83, North American Datum of 1983; TIFF, Tagged Image File Format]
Data-layer name
and (or) description		 Location of data and associated metadata Source
q2_geologic_interp—Polygon shapefile of the geologic substrate interpretation of the seabed in quadrangle 2. Attribute fields can be used to symbolically illustrate the seven maps presented in this publication https://www.sciencebase.gov/catalog/item/644a7995d34ee8d4adee0435 Valentine and Cross (2024a)
q2_1m_contours—Polyline shapefile of the 1-m contours in quadrangle 2. These contours are used in some areas to reveal small features not shown by 5-m contours https://www.sciencebase.gov/catalog/item/644a79fed34ee8d4adee043d Valentine and Cross (2024a)
q2_13mbathy—32-bit GeoTIFF image of the 13- × 13-m cell-size bathymetry of quadrangle 2 used as a basis for the generation of the 1-m contours and the terrain ruggedness analyses https://www.sciencebase.gov/catalog/item/644a79e1d34ee8d4adee043b Valentine and Cross (2024a)
q2_stations_geology—Point shapefile of station locations and Excel and CSV files of sediment grain-size analyses and assignment of stations to substrate types https://www.sciencebase.gov/catalog/item/644a79c6d34ee8d4adee0439 Valentine and Cross (2024c)
2013-044-FA_video_driftlines.zip—Video transects of the sea floor on Stellwagen Bank during U.S. Geological Survey field activity 2013-044-FA, aboard the R/V Auk, November 5, 15, and 21, 2013 https://doi.org/10.5066/P9N8YJL1 Valentine and Cross (2019)
2014-015-FA_video_driftlines.zip—Video transects of the sea floor on Stellwagen Bank during U.S. Geological Survey field activity 2014-015-FA, aboard the R/V Auk, May 22–23 and 29–30, 2014 https://doi.org/10.5066/P93OZR8C Valentine and Cross (2020b)
2014-066-FA_video_driftlines.zip—Video transects of the sea floor on Stellwagen Bank during U.S. Geological Survey field activity 2014-066-FA, aboard the R/V Auk, November 10, 2014 https://doi.org/10.5066/P9EQM8MK Valentine and Cross (2020d)
2015-017-FA_video_driftlines.zip—Video transects of the sea floor on Stellwagen Bank during U.S. Geological Survey field activity 2015-017-FA, aboard the R/V Auk, May 18–19, 29, and June 3, 2015 https://doi.org/10.5066/P9BG490P Valentine and Cross (2020c)
2015-062-FA_video_driftlines.zip—Video transects of the sea floor on Stellwagen Bank during U.S. Geological Survey field activity 2015-062-FA, aboard the R/V Auk, October 21–22 and November 3–4, 2015 https://dx.doi.org/10.5066/F7N015FS Valentine and Cross (2017)
2016-038-FA_video_driftlines.zip—Video transects of the sea floor on Stellwagen Bank during U.S. Geological Survey field activity 2016-038-FA, aboard the R/V Auk, September 16 and 19, 2016 https://doi.org/10.5066/P91MNNSN Valentine and Cross (2020e)
2019-008-FA_video_driftlines.zip—Video transects of the sea floor on Stellwagen Bank during U.S. Geological Survey field activity 2019-008-FA, aboard the R/V Auk, July 30–31 and August 1, 2019 https://doi.org/10.5066/P93ATKSC Valentine and Cross (2020a)
Seabed observation stations—Video drift track locations, Stellwagen Bank National Marine Sanctuary region https://doi.org/10.3133/sim2840 Valentine (2005)
Seabed observation stations—Sediment sample locations and Excel file of grain-size analyses, Stellwagen Bank National Marine Sanctuary region https://doi.org/10.3133/sim2840 Valentine (2005)
Photographic images of the seabed—Locations of individual photographs, Stellwagen Bank National Marine Sanctuary region https://pubs.usgs.gov/ds/469/DataCatalog/sb_photolocs.zip Valentine and others (2010)
JPEG images of the seabed from quadrangles 1–18 in medium and high resolution, Stellwagen Bank National Marine Sanctuary region https://pubs.usgs.gov/ds/469/html/DataCatalog.html Valentine and others (2010)
Sun-illuminated sea-floor topography and TIFF world file, Stellwagen Bank National Marine Sanctuary region https://doi.org/10.3133/sim2840 Valentine (2005)
Bathymetric contours, Stellwagen Bank National Marine Sanctuary region https://doi.org/10.3133/sim2840 Valentine (2005)
Backscatter intensity, sun-illuminated sea-floor topography, and TIFF world file, Stellwagen Bank National Marine Sanctuary region https://doi.org/10.3133/sim2840 Valentine (2005)
Sea-floor ruggedness and TIFF world file, Stellwagen Bank National Marine Sanctuary region https://doi.org/10.3133/sim2840 Valentine (2005)
Esri binary grid used as the basis for the terrain rugged analyses, Stellwagen Bank National Marine Sanctuary region https://doi.org/10.3133/sim2840 Valentine (2005)
Sea-floor slope and TIFF world file, Stellwagen Bank National Marine Sanctuary region https://doi.org/10.3133/sim2840 Valentine (2005)
Boulder ridges <1 meter in height, Stellwagen Bank National Marine Sanctuary region https://doi.org/10.3133/sim2840 Valentine (2005)
Boulder ridges ≥1 meter in height, Stellwagen Bank National Marine Sanctuary region https://doi.org/10.3133/sim2840 Valentine (2005)
Bedrock outcrops, Stellwagen Bank National Marine Sanctuary region https://doi.org/10.3133/sim2840 Valentine (2005)
Boundary, Stellwagen Bank National Marine Sanctuary https://doi.org/10.3133/sim2840 Valentine (2005)
Quadrangle boundaries, Stellwagen Bank National Marine Sanctuary region https://doi.org/10.3133/sim2840 Valentine (2005)
Table 1.1.    Data layers and data used to compile maps for quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts.

References Cited

Valentine, P.C., ed., 2005, Sea floor image maps showing topography, sun-illuminated topography, backscatter intensity, ruggedness, slope, and the distribution of boulder ridges and bedrock outcrops in the Stellwagen Bank National Marine Sanctuary region off Boston, Massachusetts: U.S. Geological Survey Scientific Investigations Map 2840, 12 sheets, scale 1:60,000, 1 DVD-ROM. [Also available at https://doi.org/10.3133/sim2840.]

Valentine, P.C., and Cross, V.A., 2017, Sea floor sediment samples, seabed imagery, and CTD data collected in Stellwagen Bank National Marine Sanctuary, MA in 2015, U.S. Geological Survey Field Activity 2015-062-FA: U.S. Geological Survey data release, accessed June 14, 2023, at https://doi.org/10.5066/F7N015FS.

Valentine, P.C., and Cross, V.A., 2019, Sea-floor sediment samples, seabed imagery, and CTD instrument data collected on Stellwagen Bank in November, 2013, U.S. Geological Survey Field Activity 2013-044-FA: U.S. Geological Survey data release, accessed June 14, 2023, at https://doi.org/10.5066/P9N8YJL1.

Valentine, P.C., and Cross, V.A., 2020a, Sea-floor sediment samples, seabed imagery, and CTD instrument data collected on Stellwagen Bank in July and August, 2019, U.S. Geological Survey Field Activity 2019-008-FA (ver. 1.1, May 2023): U.S. Geological Survey data release, accessed June 14, 2023, at https://doi.org/10.5066/P93ATKSC.

Valentine, P.C., and Cross, V.A., 2020b, Sea-floor sediment samples, seabed imagery, and CTD instrument data collected on Stellwagen Bank in May, 2014, U.S. Geological Survey Field Activity 2014-015-FA: U.S. Geological Survey data release, accessed June 14, 2023, at https://doi.org/10.5066/P93OZR8C.

Valentine, P.C., and Cross, V.A., 2020c, Sea-floor sediment samples, seabed imagery, and CTD instrument data collected on Stellwagen Bank in May and June, 2015, U.S. Geological Survey Field Activity 2015-017-FA: U.S. Geological Survey data release, accessed June 14, 2023, at https://doi.org/10.5066/P9BG490P.

Valentine, P.C., and Cross, V.A., 2020d, Sea-floor sediment samples, seabed imagery, and CTD instrument data collected on Stellwagen Bank in November, 2014, U.S. Geological Survey Field Activity 2014-066-FA: U.S. Geological Survey data release, accessed June 14, 2023, at https://doi.org/10.5066/P9EQM8MK.

Valentine, P.C., and Cross, V.A., 2020e, Station information, seabed and sample imagery, and CTD instrument data collected on Stellwagen Bank in September, 2016, U.S. Geological Survey Field Activity 2016-038-FA: U.S. Geological Survey data release, accessed June 14, 2023, at https://doi.org/10.5066/P91MNNSN.

Valentine, P.C., and Cross, V.A., 2024a, Geospatial datasets of seabed topography, sediment mobility, and the distribution of geologic substrates in quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts: U.S. Geological Survey data release, https://doi.org/10.5066/P9UL3LWN.

Valentine, P.C., and Cross, V.A., 2024b, Seabed maps showing topography, ruggedness, backscatter intensity, sediment mobility, and the distribution of geologic substrates in quadrangle 5 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts: U.S. Geological Survey Scientific Investigations Map 3515, 8 sheets, scale 1:25,000, 27-p. pamphlet, accessed March 21, 2024, at https://doi.org/10.3133/sim3515.

Valentine, P.C., and Cross, V.A., 2024c, Station locations in quadrangle 2 in Stellwagen Bank National Marine Sanctuary offshore of Boston, Massachusetts where video, photographs and sediment samples were collected by the U.S. Geological Survey from 1993-2019 - includes sediment sample analyses and interpreted geologic substrate, in Geospatial datasets of seabed topography, sediment mobility, and the distribution of geologic substrates in quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts: U.S. Geological Survey data release, https://www.sciencebase.gov/catalog/item/644a79c6d34ee8d4adee0439.

Valentine, P.C., Gallea, L.B., Blackwood, D.S., and Twomey, E.R., 2010, Seabed photographs, sediment texture analyses, and sun-illuminated sea floor topography in the Stellwagen Bank National Marine Sanctuary region off Boston, Massachusetts: U.S. Geological Survey Data Series DS–469, accessed June 14, 2023, at https://doi.org/10.3133/ds469.

Conversion Factors

International System of Units to U.S. customary units

Multiply By To obtain
millimeter (mm) 0.03937 inch (in.)
centimeter (cm) 0.3937 inch (in.)
meter (m) 3.281 foot (ft)
meter (m) 1.094 yard (yd)
kilometer (km) 0.5400 mile, nautical (nmi)
square meter (m2) 10.76 square foot (ft2)
square kilometer (km2) 0.3861 square mile (mi2)
square kilometer (km2) 0.2916 square nautical mile (nmi2)

Abbreviations

>

greater than

≥

greater than or equal to

<

less than

≤

less than or equal to

GIS

geographic information system

PDF

Portable Document Format

SBNMS

Stellwagen Bank National Marine Sanctuary

TRI

terrain ruggedness index

For more information, please contact:

Director, Woods Hole Coastal and Marine Science Center

U.S. Geological Survey

384 Woods Hole Road

Quissett Campus

Woods Hole, MA 02543–1598

WHSC_science_director@usgs.gov

508–548–8700

Or visit our website at:

https://www.usgs.gov/centers/whcmsc

 

Publishing support provided by the USGS, Science Publishing Network, Reston Publishing Service Center

Edited by Zachary P. Younger

Cartography by D. Paul Mathieux

Layout by Jeffrey L. Corbett

Web support by Molly Newbrough

Disclaimers

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested Citation

Valentine, P.C., and Cross, V.A., 2024, Seabed maps showing topography, ruggedness, backscatter intensity, sediment mobility, and the distribution of geologic substrates in quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts: U.S. Geological Survey Scientific Investigations Map 3530, 8 sheets, scale 1:25,000, 27-p. pamphlet, https://doi.org/10.3133/sim3530.

ISSN: 2329-132X (online)

Study Area

Publication type Report
Publication Subtype USGS Numbered Series
Title Seabed maps showing topography, ruggedness, backscatter intensity, sediment mobility, and the distribution of geologic substrates in quadrangle 2 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts
Series title Scientific Investigations Map
Series number 3530
DOI 10.3133/sim3530
Year Published 2024
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Woods Hole Coastal and Marine Science Center
Description Pamphlet: v, 27 p.; 8 Sheets: 26.98 x 35.69 inches or smaller; Data Release
Country United States
State Massachusetts
Other Geospatial Stellwagen Bank National Marine Sanctuary
Online Only (Y/N) Y
Additional Online Files (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details