Prepared in cooperation with the Massachusetts Office of Coastal Zone Management

Shallow Geology, Sea-Floor Texture, and Physiographic 

Zones of the Inner Continental Shelf From Aquinnah to 

Wasque Point, Martha’s Vineyard, and Eel Point to

Great Point, Nantucket, Massachusetts

Open-File Report 2018–1181

U.S. Department of the Interior

U.S. Geological Survey
Cover. North-looking oblique aerial view of topography and bathymetry of Martha’s Vineyard and Nantucket, Massachusetts. Image 

by the U.S. Geological Survey.
Shallow Geology, Sea-Floor Texture, 

and Physiographic Zones of the Inner 

Continental Shelf From Aquinnah to 

Wasque Point, Martha’s Vineyard, and 

Eel Point to Great Point,

Nantucket, Massachusetts

By Elizabeth A. Pendleton, Wayne E. Baldwin, Seth D. Ackerman, David S. Foster, 

Brian D. Andrews, William C. Schwab, and Laura L. Brothers

Prepared in cooperation with the 

Massachusetts Office of Coastal Zone Management

Open-File Report 2018–1181

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DAVID BERNHARDT, Acting Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2019

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

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Suggested citation:

Pendleton, E.A., Baldwin, W.E., Ackerman, S.D., Foster, D.S., Andrews, B.D., Schwab, W.C., and Brothers, L.L., 2019, 

Shallow geology, sea-floor texture, and physiographic zones of the inner continental shelf from Aquinnah to Wasque 

Point, Martha’s Vineyard, and Eel Point to Great Point, Nantucket, Massachusetts: U.S. Geological Survey Open-File 

Report 2018–1181, 37 p., https://doi.org/10.3133/ofr20181181.

ISSN 2331-1258 (online)
iii

Acknowledgments

This research was done in cooperation with the Massachusetts Office of Coastal Zone 

Management. This manuscript benefited from thoughtful scientific reviews by Jason Chaytor 

and Ben Gutierrez of the U.S. Geological Survey.

v

Contents

Acknowledgments........................................................................................................................................iii

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................1

Geographic Setting...............................................................................................................................3

Geologic Setting....................................................................................................................................3

Depositional History .............................................................................................................................3

Previous Work .......................................................................................................................................6

Methods...........................................................................................................................................................6

Bathymetric and Backscatter Composite.........................................................................................6

Seismic Stratigraphic and Surficial Geologic Mapping.................................................................8

Sediment Samples and Sediment Texture Classification Schemes...........................................10

Sediment Texture Mapping...............................................................................................................10

Physiographic Zones..........................................................................................................................12

Results ...........................................................................................................................................................12

Seismic Stratigraphy and Geologic Interpretation .......................................................................12

Sediment Texture and Distribution...................................................................................................24

Physiographic Zones..........................................................................................................................24

Discussion.....................................................................................................................................................29

Synthesis of Maps ..............................................................................................................................29

Geologic History and Framework.....................................................................................................29

Glacial Recession ......................................................................................................................30

Holocene Depositional Setting................................................................................................30

Summary........................................................................................................................................................31

References Cited..........................................................................................................................................31

Appendix 1. Links to Geospatial Data Layers ......................................................................................37

Figures

1. Location map of the Martha’s Vineyard and Nantucket study sites, and inset

map locating the study area within southern New England .................................................2

2. Map showing a digital elevation model of the study area.....................................................4

3. Map showing glacial moraines on land and submerged on the continental shelf,

ice-front locations for southern New England, and glacial lakes and

associated spillways....................................................................................................................5

4. Map showing a composite backscatter image of the study area, created from

a series of published backscatter images................................................................................7

5. Map showing tracklines of chirp seismic-reflection profiles used to interpret

surficial geology and shallow stratigraphy ..............................................................................9

6. Map showing locations of observations of sea-floor composition used to aid the

geophysical and geologic interpretations..............................................................................11

7. Diagram showing Barnhardt and others (1998) bottom-type classification

based on four basic sediment units: rock, gravel, sand, and mud.....................................12
vi

8. Map showing the distribution of confidence levels for sediment texture and

physiographic zone interpretations.........................................................................................13

9. Seismic stratigraphic section showing units and major unconformities interpreted

within Vineyard Sound and eastern Rhode Island Sound ...................................................14

10. Chirp seismic-reflection profile A–A' with seismic stratigraphic interpretation.............15

11. Chirp seismic-reflection profile B–B' with seismic stratigraphic interpretation.............16

12. Geologic sections (C–C', D–D', and E–E') illustrating the general distributions

and thicknesses of seismic stratigraphic units and major unconformities in the 

Martha’s Vineyard and Nantucket, Massachusetts, study sites........................................17

13. Chirp seismic-reflection profile F–F' with seismic stratigraphic interpretation ..............18

14. Chirp seismic-reflection profile G–G' with seismic stratigraphic interpretation.............19

15. Map showing the surficial geology from this study and Baldwin and

others (2016) with equivalent onshore geology.....................................................................20

16. Map showing the elevation of the late Wisconsinan to early Holocene

regressive unconformity Ur, which identifies the eroded surface of Pleistocene

glacial drift offshore ...................................................................................................................22

17. Map showing the thickness of postglacial fluvial and estuarine (Qfe) and

Holocene nearshore marine (Qmn) sediments......................................................................23

18. Map showing the distribution of sediment textures within the study area ......................25

19. Map and photographs showing sediment textures offshore of western and

southern Martha’s Vineyard......................................................................................................26

20. Map and photographs showing sediment textures offshore of

northern Nantucket....................................................................................................................27

21. Map showing the distribution of physiographic zones ........................................................28

Tables

1. Data sources for bathymetry, backscatter, and seismic-reflection profile

interpretations for the south and west shore of Martha’s Vineyard and the north

shore of Nantucket, Massachusetts .........................................................................................8

2. Confidence levels assigned to sediment texture and physiographic zone polygons

on the basis of the data used in the interpretation...............................................................12
vii

Conversion Factors

International System of Units to U.S. customary units

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

kilometer (km) 0.5400 mile, nautical (nmi) 

meter (m) 1.094 yard (yd) 

Area

square kilometer (km2) 0.3861 square mile (mi2)

Datum

Vertical coordinate information is referenced to North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the World Geodetic System of 1984 (WGS 84) 

in a geographic coordinate system.

Elevation, as used in this report, refers to distance above the vertical datum.

Supplemental Information

Particle size in phi units may be converted to millimeters (mm) as mm=2−phi.

Abbreviations

CZM Massachusetts Office of Coastal Zone Management

DEM digital elevation model

GIS geographic information system

ka kiloannum, thousands of years before the present

kHz kilohertz

lidar light detection and ranging

mpp meter per pixel

USGS U.S. Geological Survey

Shallow Geology, Sea-Floor Texture, and Physiographic 

Zones of the Inner Continental Shelf From Aquinnah to 

Wasque Point, Martha’s Vineyard, and Eel Point to

Great Point, Nantucket, Massachusetts

By Elizabeth A. Pendleton, Wayne E. Baldwin, Seth D. Ackerman, David S. Foster, Brian D. Andrews,

William C. Schwab, and Laura L. Brothers

Abstract

A series of interpretive maps that describe the shallow 

geology, distribution, and texture of sea-floor sediments, and 

physiographic zones of the sea floor along the south and west 

shores of Martha’s Vineyard and the north shore of Nantucket, 

Massachusetts, were produced by using high-resolution geophysical data (interferometric and multibeam swath bathymetry, light detection and ranging [lidar] bathymetry, backscatter 

intensity, and seismic-reflection profiles), sediment samples, 

and bottom photographs. These interpretations are intended 

to aid statewide efforts to inventory and manage coastal and 

marine resources, link with existing data interpretations, and 

provide information for research focused on coastal evolution 

and environmental change. Marine geologic mapping of the 

inner continental shelf of Massachusetts is a statewide cooperative effort of the U.S. Geological Survey and the Massachusetts Office of Coastal Zone Management.

Introduction

The geologic framework and seabed character of the 

coastal zone of Massachusetts is complex, heterogeneous, and 

controlled by the antecedent geology. Previous studies in the 

region defined the geology and texture of the sea floor on the 

basis of widely spaced geophysical tracklines and vibracores 

(O’Hara and Oldale, 1980, 1987) or sediment samples (Ford 

and Voss, 2010). In this study, high-resolution geophysical 

datasets at full sea-floor coverage, supplemented with sediment samples and bottom photographs, provide the basis for 

detailed surficial to shallow stratigraphic geologic maps, highresolution sediment texture maps, and physiographic zone 

delineations that were previously unfeasible because of a lack 

of high-quality, high-density sea-floor mapping data.

Purpose and Scope

This report describes the shallow geologic framework, distribution of sea-floor texture, and physiographic 

zones of the Massachusetts coastal zone between Aquinnah 

and Wasque Point on Martha’s Vineyard, and between Eel 

Point and Great Point on Nantucket, Massachusetts (fig. 1). 

Interpretations are provided as geospatial data layers in a 

companion data release (appendix 1; Pendleton and others, 

2018, https://doi.org/10.5066/P9E9EFNE). This research was 

carried out as part of a cooperative sea-floor mapping program 

(https://woodshole.er.usgs.gov/project-pages/coastal_mass/) 

between the U.S. Geological Survey (USGS) and the Massachusetts Office of Coastal Zone Management (CZM). This 

cooperative effort fosters data collection and the production 

of interpretive geospatial datasets that can be used by managers and scientists to delineate marine resources, assess 

environmental change, inventory marine habitats, and support 

research concerning sea-level change, sediment supply and 

budget, and coastal evolution (Massachusetts Office of Coastal 

Zone Management, 2015).

The maps presented in this report are based on interpretation of high-resolution seismic-reflection profiles, swath 

bathymetry, acoustic backscatter, bottom photographs, and 

sediment samples collected within nearshore regions (less 

than about 30-meter [m] water depth; Denny and others, 2009; 

Andrews and others, 2014, 2018; Ackerman and others, 2016); 

bottom photographs and sediment samples (Ackerman and 

others, 2016); and sediment texture databases (Ford and Voss, 

2010; McMullen and others, 2012) modified by CZM (Emily 

Huntley, CZM, unpub. data, 2012). This report is the fifth in a 

series of geologic interpretative datasets and reports (Pendleton and others, 2013, 2015; Foster and others, 2015; Baldwin 

and others, 2016) about Massachusetts State waters that have 

been published as part of the USGS and CZM cooperative 

mapping agreement.
2 Shallow Geology, Sea-Floor Texture, and Physiographic Zones Offshore Martha’s Vineyard and Nantucket, Mass. Buzzards Bay Nantucket Sound ATLANTIC OCEAN Muskeget Channel Vineyard Sound

Elizabeth Islands

Monomoy

Island

Nomans

Island

Tuckernuck

Island

Muskeget

Island Wasque Point

Eel

Point

Great

Point Edgartown

Oak 

Bluffs

Tisbury

Coskata

WEST

YARMOUTH

Coatue

Martha's Vineyard

Nantucket

Falmouth

Aquinnah

Chatham

Mashpee Harwich

Chilmark

MV site

ACK site

MA

NH

ME

CT RI

ATLANTIC 

OCEAN

70° 70°20' 70°40' 71°

41°40'

41°30'

41°20'

41°10' 0 10 20 KILOMETERS 5

0 6 12 NAUTICAL MILES 3

Figure 1. The Martha’s Vineyard and Nantucket study sites, and inset map locating the study area within southern New England. Swath bathymetry, acoustic backscatter, and chirp seismic-reflection data were collected in the area inside the red polygons. Land is depicted from a hillshaded relief image of Massachusetts (Massachusetts Office of Geographic Information [MassGIS] 2005 data). Medium gray is from the hillshade relief maps derived from the continuous bathymetry and elevation models of the Massachusetts coastal zone and continental shelf (Andrews and others, 2018). MV, Martha’s Vineyard; ACK, Nantucket.
Introduction 3

Geographic Setting

Martha’s Vineyard and Nantucket are the two largest 

islands in southeastern Massachusetts and are approximately 

6 and 45 kilometers (km) south of Cape Cod, respectively 

(fig. 1). The study area includes the inner continental shelf just 

west and south of Martha’s Vineyard, between Aquinnah and 

Muskeget Channel, and north of Nantucket Island, between 

Tuckernuck Island and Great Point (fig. 1). The two sites 

described in this study are (1) an area that lies along the open 

Atlantic coast of Martha’s Vineyard, referred to as the Martha’s Vineyard site and (2) another mostly protected area that 

lies on the north side of Nantucket within Nantucket Sound, 

referred to as the Nantucket site. The Martha’s Vineyard site 

occupies nearly 38 km of shoreline offshore of the south and 

west of Martha’s Vineyard and has a mean water depth of 

approximately 18 m (below North American Vertical Datum 

of 1988 [NAVD 88]; fig. 2). This area reaches depths exceeding 30 m south and east of Nomans Island. The Nantucket site 

covers roughly 12 of the 17 km of Nantucket Sound that lies 

between North Point and Great Point, has a mean water depth 

of 12 m below NAVD 88, and gently shallows to the south 

toward Nantucket Harbor.

The south coast of Martha’s Vineyard east of Chilmark 

is primarily a low-relief, gently south-sloping sand and gravel 

plain that is incised by linear, shore-perpendicular coastal 

embayments (drowned valleys) fronted by welded barrier 

beaches and spits (Uchupi and Oldale, 1994). The Atlantic 

coast of Aquinnah and Chilmark, including Gay Head and 

Squibnocket Point, is higher but also more variable in elevation. These areas are distinctly rockier than the southeast 

coast of Martha’s Vineyard. Between cliffed areas are lower 

elevation pocket and welded barrier beaches, backed by 

coastal ponds.

The north coast of Nantucket, west of Nantucket Harbor, consists of low, unconsolidated cliffs fronted by a sandy 

beach along Nantucket Sound. The coast along the east side 

of Nantucket from Great Point to Coskata is a barrier spit 

that shelters the study site, and another spit that builds from 

Coskata to the west encloses Nantucket Harbor. The latter spit 

is between 100 and 500 m wide, with a straight sandy beach 

facing Nantucket sound and a sandy, cuspate coast facing into 

Nantucket Harbor.

Geologic Setting

The geologic framework of Martha’s Vineyard and 

Nantucket is controlled by the underlying bedrock and coastal 

plain and continental shelf units, subsequent Pleistocene 

glaciations, and Holocene sea-level rise (O’Hara and Oldale, 

1980, 1987). Basement rocks of Triassic and Cretaceous 

ages underlie the islands at depths below the land surface 

of between 150 and 300 m on Martha’s Vineyard and up to 

500 m on Nantucket (Oldale, 1969; Zen and others, 1983). 

The basement is unconformably overlain by coastal plain and 

continental shelf deposits (Woodsworth and Wigglesworth, 

1934; Kaye, 1964a, b, 1980; Oldale and others, 1973; Folger 

and others, 1978; Hall and others, 1980; O’Hara and Oldale, 

1980, 1987; Oldale and O’Hara, 1984). These deposits are 

composed of unconsolidated to semiconsolidated sand, silty 

clay, and gravel, and they represent a wedge of coastal plain 

and continental shelf strata that dips and thickens to the south 

(Weed and others, 1974; O’Hara and Oldale, 1980, 1987; 

Siegel and others, 2012).

Glacial drift, deposited during the Illinoian and Wisconsinan Ages of the Pleistocene, unconformably overlies the 

basement rocks and coastal plain and continental shelf deposits (Woodsworth and Wigglesworth, 1934; Kaye, 1964a, b; 

O’Hara and Oldale, 1980, 1987; Oldale, 1981, 1982, 2001; 

Oldale and others, 1982; Uchupi and others, 1996; Masterson 

and others, 1997; Stone and DiGiacomo-Cohen, 2009). The 

glacial drift includes poorly sorted tills and moraines, which 

suggest ice-proximal deposition, and moderately to well sorted 

and stratified glaciofluvial and glaciolacustrine units, which 

indicate ice-distal deposition (Kaye, 1964a; b; Oldale and 

Barlow, 1986; Stone and DiGiacomo-Cohen, 2009).

Postglacial deposits primarily consist of material that has 

been winnowed from the glacial drift by marine and fluvial 

processes during the late Pleistocene and Holocene (O’Hara 

and Oldale, 1980, 1987; Oldale, 1982, 2001). The oldest postglacial deposits are fluvial and estuarine units that fill glaciofluvial channels and other topographic lows on the surface of 

the glacial drift (O’Hara and Oldale, 1980, 1987). The Holocene marine transgressive unconformity separates the older 

units from younger overlying postglacial marine deposits. The 

marine units primarily consist of shelf sand bodies offshore 

of Martha’s Vineyard, including thin and discontinuous sand 

veneers, ebb-tidal deltas, and sorted bedforms (Goff and others, 2005), but the modern marine unit on the north side of 

Nantucket is a muddy sand sheet (O’Hara and Oldale, 1987).

Depositional History

Between 28 and 25.5 thousand years before present (ka), 

the Buzzards Bay and Cape Cod Bay lobes of the Wisconsinan Laurentide Ice Sheet reached their maximum southern 

extents near Martha’s Vineyard and Nantucket (fig. 3; Uchupi 

and others, 1996; Oldale, 2001; Balco and others, 2002; 

Uchupi and Mulligan, 2006; Balco, 2011). The overburden of 

the advancing ice front locally deformed and thrusted previously deposited glacial drift and underlying coastal plain and 

continental shelf units into the terminal moraines that now 

form the western and northeastern coasts of Martha’s Vineyard 

and Nantucket, respectively (Woodsworth and Wigglesworth, 

1934; Kaye, 1964a, b; Oldale and Eskenasy, 1982; Oldale and 

O’Hara, 1984; Oldale, 2001; Stone and DiGiacomo-Cohen, 

2009). The Buzzards Bay ice lobe deposited the end moraine 

that makes up Nomans Island and the western side of Martha’s 

Vineyard, and the Cape Cod Bay lobe deposited the end 

moraines present on the eastern side of Martha’s Vineyard and 
4 Shallow Geology, Sea-Floor Texture, and Physiographic Zones Offshore Martha’s Vineyard and Nantucket, Mass. Nantucket Sound ATLANTIC OCEAN Martha's Vineyard Nantucket Muskeget Channel

Elizabeth Islands

Tuckernuck

Island

Muskeget

Island

Vineyard 

Sound

Elizabeth Islands

Chilmark Aquinnah

Gay Head

Squibnocket

Point

Wasque 

Point

Nomans

Island

Katama

Bay

South 

Beach

A

A

B

B

Great Point

Nantucket 

Harbor Eel Point

North Point

70° 70°20' 70°40'

41°30'41°25'41°20'41°15'

70°30' 70°40' 70°50'

41°20'

41°15'

70°4' 70°8' 70°12'

41°24'41°22'41°20'41°18'41°16'

EXPLANATION

Depth, in meters

(NAVD 88)

High : 0Low : -30

0 8 16 KILOMETERS 4

0 4 8 NAUTICAL MILES 2

0 6 12 KILOMETERS 30 3 6 NAUTICAL MILES 1.5

0 3 6 KILOMETERS 1.50 3 NAUTICAL MILES 1.5

Figure 2.

A digital elevation model of the study area, A, west and south of Martha’s Vineyard and 

B, north of Nantucket, Massachusetts, clipped from a 

continuous bathymetry and elevation model published by Andrews and others (2018). High rugosity and relief are most often associated with rocky areas, whereas smooth, low-relief regions tend to be blanketed by fine-grained sediment deposits. NAVD 88, North American Vertical Datum of 1988.
Introduction 5

EXPLANATION

 End moraines

 Submerged end moraines

 Ice fronts

 Outlet spillway

Geology mapped by Larsen (1982), Ridge (2004), Stone and others (2005), Uchupi and Mulligan 

(2006), Boothroyd (2008), Stone and DiGiacomo-Cohen (2009), and Stone and others (2011). 

Base from National Oceanic and Atmospheric Administration and U.S. Geological Survey

Universal Transverse Mercator Projection, Zone 19, WGS84

72° W 71°30’ 71° 70°30’ 70°

42°30’ 42° N 41°

Modified from Oldale and Barlow (1986) Sandwich moraine

Buzzards Bay

moraine

Nantucket

moraine Martha’s Vineyard

moraine

Charlestown

moraine Point Judith

moraine

Block Island

Montauk Point

Massachusetts

Rhode

Conn. Island

Muskeget

Channel

glacial lake

Cape Cod Bay

glacial lake

Nantucket Sound

glacial lake

Wampanoag

Upper

Lower

Buzzards Bay

lobe

Narragansett

Bay lobe

Cape Cod

Bay lobe

South

Channel

lobe

 Glacial lake

Figure 3. Glacial moraines on land and submerged on the continental shelf (compiled from Stone and others, 2005; Boothroyd, 2008; 

Stone and DiGiacomo-Cohen, 2009; and Stone and others, 2011), ice-front locations for southern New England (from Ridge, 2004), and 

glacial lakes and associated spillways (compiled from Larson, 1982; Uchupi and Mulligan, 2006). Inset illustrates the relative locations of 

four lobes of the Laurentide Ice Sheet in southeastern New England (modified from Oldale and Barlow, 1986). Figure is from Baldwin and 

others (2016), modified from Foster and others (2015).
6 Shallow Geology, Sea-Floor Texture, and Physiographic Zones Offshore Martha’s Vineyard and Nantucket, Mass.

on Nantucket (Larson, 1982; Oldale and Barlow, 1986; Oldale, 

2001; Stone and DiGiacomo-Cohen, 2009). Coarse and poorly 

sorted till and ice-contact material were deposited proximal to 

the ice lobe termini, whereas finer grained and stratified fluvial 

outwash, lacustrine, and delta material was deposited beyond 

the ice front. Ice-contact deposits associated with the Buzzards 

Bay lobe are around western Martha’s Vineyard, whereas 

stratified drift deposits associated with the Cape Cod Bay lobe 

formed the expansive outwash plains on Martha’s Vineyard 

and Nantucket south and offshore of the terminal moraines 

(Kaye, 1972; Oldale and Barlow, 1986; Stone and DiGiacomoCohen, 2009).

The outwash plains of Martha’s Vineyard were subsequently incised by north-south-trending sapping valleys that 

continued onto the continental shelf (O’Hara and Oldale, 

1980; Uchupi and Oldale, 1994; Goff and others, 2005; Stone 

and DiGiacomo-Cohen, 2009). These groundwater drainage 

systems formed as a result of the high hydrostatic heads and 

shallow water table associated with proglacial lakes to the 

north and the high permeability of the outwash sediments 

(Uchupi and Oldale, 1994). The glacial landscape south of 

Martha’s Vineyard was modified as an eroding drift sheet 

exposed at the surface, until approximately 10 to 8 ka when 

sea level began to rise (O’Hara and Oldale, 1980; Gutierrez 

and others, 2003). Subsequently, oceanographic processes 

began reworking, winnowing, and redistributing fine-grained 

material from the glacial drift (O’Hara and Oldale, 1980; Goff 

and others, 2005). Sand bodies began accumulating on the 

shelf, sandy beaches formed along the south and west coast of 

Martha’s Vineyard fronting outwash plains and moraines, and 

sapping valleys were progressively drowned.

In Nantucket Sound, proglacial lake deposits and a 

postglacial drainage network carved through outwash, and 

glaciodeltaic sediments underlie a deposit of Holocene estuarine and marine sediments (fig. 3; Larson, 1982; O’Hara and 

Oldale, 1987; Uchupi and Mulligan, 2006). Sheltered marine 

conditions along the north shore of Nantucket have resulted 

in the deposition of a modern muddy sand sheet between 

Great Point and North Point, and barrier spits have enclosed 

Nantucket Harbor (Rosen 1972; O’Hara and Oldale, 1987).

Previous Work

O’Hara and Oldale (1980, 1987) conducted comprehensive geologic mapping studies of eastern Rhode Island 

Sound, Vineyard Sound, and Nantucket Sound. They collected 

widely spaced (approximately 2,000 m apart) boomer seismicreflection profiles, sidescan sonographs, and vibracores. Their 

interpretations described the broad stratigraphic framework in 

a series of subsurface and sea-floor geologic maps, including 

structural contours of depths to the surfaces of pre-Quaternary 

coastal plain and continental shelf units, Quaternary glacial 

units, and isopachs of glacial and postglacial sediments. 

Legacy reports by Robb and Oldale (1977) and O’Hara and 

Oldale (1980, 1987) and two products of the USGS and CZM 

cooperative program (Foster and others, 2015; Baldwin and 

others, 2016), all of which focused on areas of Buzzards Bay 

and Vineyard and Nantucket Sounds, provided a foundation 

for this report. The geology and shallow structure of the south 

shore of Martha’s Vineyard between Squibnocket Point and 

Wasque Point have not been previously published. Surficial 

geologic maps of Martha’s Vineyard and Nantucket by Oldale 

and Barlow (1986) and Stone and DiGiacomo-Cohen (2009) 

were used to correlate onshore and offshore geologic units 

where possible.

Methods

This section describes how the interpretations presented 

in this report and the companion data release (Pendleton and 

others, 2018, https://doi.org/10.5066/P9E9EFNE) were generated. Detailed descriptions of software, source information, 

scale, and accuracy assessments for each dataset are provided 

in the metadata files for geospatial data layers in the data 

release. High-resolution bathymetric, acoustic-backscatter, and 

seismic-reflection data collected by the USGS, the National 

Oceanic and Atmospheric Administration, and the U.S. Army 

Corps of Engineers provide nearly full coverage of the sea 

floor in the 265-square-kilometer (km2) study area (fig. 1, 

table 1). The geophysical data, sediment samples, and seafloor photographs/video allowed for interpretation of sea-floor 

composition and shallow subsurface stratigraphy at finer 

scales and resolutions than previously possible. However, the 

interpretations have limitations, which primarily arise from 

the types, quality, and density of data from which they were 

made. Pendleton and others (2013) provide detailed discussion regarding the limitations associated with these surficial 

mapping methods. Consequently, qualitative confidence levels 

were assigned to some interpretations and must be considered 

when surficial maps are used to guide management decisions 

and research.

Bathymetric and Backscatter Composite

A continuous bathymetry and elevation model published 

by Andrews and others (2018) that uses previously published 

elevation data covers the entire study area (fig. 2) and provided the seamless bathymetric data source for this study. Vertical resolutions of the source data range from unknown, for 

lead-line soundings, to 0.1 m, for interferometric, multibeam, 

and light detection and ranging (lidar) swath bathymetric data.

A seamless acoustic-backscatter image was also created 

(fig. 4) from data previously published by the USGS (table 1). 

All source backscatter imagery was mosaicked into a composite GeoTIFF by using PCI Geomatica (version 10.1) with a 

resolution of 5 meters per pixel (mpp).
Methods 

7

Nantucket Sound

ATLANTIC OCEAN

Martha's Vineyard

Nantucket

Muskeget

Channel

Elizabeth Islands

Nomans

Island

Tuckernuck

Island

Muskeget

Island

Vineyard 

Sound

A

B

A B

70° 70°20' 70°40'

41°30'41°25'41°20'

41°15'

70°30' 70°40' 70°50'

41°20'41°15'

70°4' 70°8'

41°22'41°20'

41°18'

0 8 16 KILOMETERS 4

0 4 8 NAUTICAL MILES 2

0 6 12 KILOMETERS 3

0 4 8 NAUTICAL MILES 2

0 2 4 KILOMETERS 1

0 2 NAUTICAL MILES 1

EXPLANATION

Backscatter intensity

High : 200Low : 20

Figure 4. A composite backscatter image of the study area, A, south and west of Martha’s Vineyard and B, north of Nantucket, Massachusetts, at 5-meter resolution, created from a series of published backscatter images (table 1). Areas of high backscatter intensity (light tones) have strong acoustic reflections and suggest boulders, gravels, and generally coarse sea-floor sediments. Areas of low backscatter intensity (dark tones) have weak acoustic reflections and are generally of finer grained material such as muds and fine sands. Regularly spaced striping is an artifact of the surveys.
8 Shallow Geology, Sea-Floor Texture, and Physiographic Zones Offshore Martha’s Vineyard and Nantucket, Mass.

Table 1. Data sources for bathymetry, backscatter, and seismic-reflection profile interpretations for the south and west shore of 

Martha’s Vineyard and the north shore of Nantucket, Massachusetts.

[kHz, kilohertz]

Vessel Date Bathymetry Acoustic backscatter Seismic reflection Citation

Megan T. Miller1 2007 SEA SWATHplus 234-

kHz interferometric 

sonar system

Klein 3000 dualfrequency sidescan 

sonar

EdgeTech Geo-Star FSSB 

subbottom profiling 

system and an SB–0512i 

towfish

Denny and others 

(2009)

Megan T. Miller and 

Scarlet Isabella1

2009–2011 SEA SWATHplus 234-

kHz interferometric 

sonar system

Klein 3000 dualfrequency sidescan 

sonar

EdgeTech Geo-Star FSSB 

subbottom profiling 

system and an SB–0512i 

towfish

Andrews and others 

(2014)

Scarlet Isabella1 2013 SWATHplus 234-kHz 

interferometric sonar 

system

SWATHplus 234 kHz 

and EdgeTech 4200 

at 100 and 400 kHz

EdgeTech Geo-Star FSSB 

subbottom profiling 

system and an SB–0512i 

towfish

Ackerman and others (2016)

Various1,2,3 1887–2016 Lead-line, single-beam 

sonar, multibeam sonar, 

interferometric sonar, 

and light detection and 

ranging (lidar)

None None Andrews and others 

(2018)

1

Data collected by the U.S. Geological Survey.

2

Data collected by the National Oceanic and Atmospheric Administration.

3

Data collected by the U.S. Army Corps of Engineers.

Seismic Stratigraphic and Surficial Geologic 

Mapping

Approximately 2,800 kilometers of seismic-reflection 

profiles, collected between 2007 and 2013 (table 1, fig. 5), 

were interpreted in The Kingdom Suite (version 8.8). The 

profiles were collected by using chirp sonars with broadband 

frequencies of 0.5 to 12 kilohertz (kHz) or narrow-band frequencies centered around 3.5 kHz. Legacy seismic-reflection 

data (O’Hara and Oldale, 1980, 1987; McMullen and others, 

2009) were used in the interpretations for general correlation 

with the seismic stratigraphy interpreted in previous studies. 

Interpretations of shallow stratigraphy and surficial geology 

were conducted in the time domain (two-way traveltime) and 

consisted of (1) identifying and defining seismic stratigraphic 

units on the basis of seismic facies, and digitizing reflectors 

(horizons) defining the boundaries between individual seismic 

stratigraphic units; and (2) digitizing the extent over which 

each of the defined seismic stratigraphic units crops out on the 

sea floor.

Two-way traveltime values for the postglacial seismic 

unit were exported and converted to thickness in meters by 

using a constant seismic velocity of 1,500 meters per second. 

The resulting isopach values were imported into ArcGIS 

as point features (easting, northing, thickness) and used to 

generate an interpolated digital elevation model (DEM) with 

a 40-mpp resolution. The isopach map of postglacial sediment 

was added to the DEM of regional swath bathymetry (fig. 2) 

to produce a DEM of the unconformity defining its base of 

postglacial material (40-m cell size, relative to NAVD 88).

The digitized sea-floor outcrops for each seismic unit 

were imported into ArcGIS as point features (easting, northing, seismic unit) and used to guide manual digitizing of 

polygons representing discrete areas of seismic-unit outcrop. 

The resulting polygon dataset provides a seamless representation of surficial geology for the seismic-reflection survey area. 

The surficial geology polygons also provide insight into the 

likely sediment texture at the sea floor based on the glacial or 

postglacial origin and depositional environment inferred from 

the seismic interpretation. The geologic observations were 

incorporated into surficial sediment texture mapping.

High-density seismic-reflection data were collected only 

within the areas surveyed by the USGS between 2007 and 

2013 (table 1, fig. 5). As a result, surficial geology polygons 

derived from the seismic interpretations are less extensive 

than the polygons of sea-floor sediment texture and physiographic zones, which cover areas equivalent to the composite 

bathymetry (fig. 2).
Methods 

9

Nantucket Sound

ATLANTIC OCEAN

Martha's Vineyard

Nantucket

Muskeget

Channel

Elizabeth Islands

Nomans

Island

Tuckernuck

Island

Muskeget

Island

Vineyard 

Sound

A

B

A B

70° 70°20' 70°40'

41°30'41°25'41°20'41°15'

70°30' 70°40' 70°50'

41°20'41°15'

70°4' 70°8'

41°22'41°20'41°18'

0 8 16 KILOMETERS 4

0 4 8 NAUTICAL MILES 2

0 6 12 KILOMETERS 30 4 8 NAUTICAL MILES 2

0 2 4 KILOMETERS 10 2 NAUTICAL MILES 1

EXPLANATION

200720112012

Figure 5. Tracklines of chirp seismic-reflection profiles (table 1) used to interpret surficial geology and shallow stratigraphy, A, south and west of Martha’s Vineyard and B, north of Nantucket, Massachusetts.
10 Shallow Geology, Sea-Floor Texture, and Physiographic Zones Offshore Martha’s Vineyard and Nantucket, Mass.

Sediment Samples and Sediment Texture 

Classification Schemes

Sediment sample databases of Ford and Voss (2010), 

McMullen and others (2012), and Ackerman and others (2016) 

were supplemented with visual descriptions from National 

Oceanic and Atmospheric Administration nautical charts 

and sea-floor photographs compiled by CZM (fig. 6; Emily 

Huntley, CZM, written commun., 2014). This study uses the 

Barnhardt and others (1998) sediment texture classification 

scheme (fig. 7). The Barnhardt and others (1998) system is 

based on four basic, easily recognized sediment units (as measured in grain size, based on Wentworth, 1922): rock (R; grain 

size greater than 64 millimeters [mm]), gravel (G; grain size 

2 to 64 mm), sand (S; grain size 0.062 to 2 mm), and mud 

(M; grain size less than 0.062 mm). Because the sea floor is 

often not a uniform mixture of these units, the classification 

is further divided into 12 composite units, which are two-part 

combinations of the 4 basic units (fig. 7). This classification is 

defined such that the primary texture, representing more than 

50 percent of an area’s texture, is given an uppercase letter, 

and the secondary texture, representing less than 50 percent of 

an area’s texture, is given a lowercase letter. If one of the basic 

sediment units represents more than 90 percent of the texture, 

only its uppercase letter is used. The units defined under the 

Barnhardt and others (1998) classification within this study 

area are R, gravelly rock (Rg), sandy rock (Rs), and muddy 

rock (Rm); G, rocky gravel (Gr), sandy gravel (Gs), and 

muddy gravel (Gm); S, gravelly sand (Sg), muddy sand (Sm), 

and rocky sand (Sr); and M, rocky mud (Mr), gravelly mud 

(Mg), and sandy mud (Ms).

Sediment Texture Mapping

The texture and spatial distribution of sea-floor sediment 

were mapped qualitatively in ArcGIS by using acoustic-backscatter intensity, bathymetry, lidar, geologic interpretations, 

bottom photographs, and sediment samples. The highest data 

resolution that was available was used to map sea-floor sediment texture, typically 2 to 5 m in water depths less than 30 m. 

First, sediment texture polygons were outlined by using backscatter intensity data to define changes in the sea floor based 

on acoustic return (fig. 4). Areas of high backscatter intensity 

(light tones) have strong acoustic reflections, suggest boulders and gravels, and generally are characterized by coarse 

sea-floor sediments. Areas of low backscatter intensity (dark 

tones) have weak acoustic reflections and generally are characterized by fine-grained material such as muds and fine sands.

The polygons were then refined and edited by using 

gradient, rugosity, and hillshaded relief images derived from 

interferometric and multibeam swath bathymetry and lidar 

at the highest resolution available (fig. 2). Areas of rough 

topography and high rugosity typically are associated with 

rocky areas, whereas smooth, low-rugosity regions tend to 

be blanketed by fine-grained sediment. These bathymetric 

derivatives helped to refine polygon boundaries where changes 

from areas of primarily rock to areas of primarily gravel may 

not have been apparent in backscatter data but could easily be 

identified in hillshaded relief, rugosity, and slope data.

The third data input was the stratigraphic and geologic 

interpretation of seismic-reflection profiles, which further 

constrained the extent and general shape of sea-floor sediment distributions and rocky outcrops and also provided 

insight concerning the likely sediment texture based on the 

pre-Quaternary, glacial, or postglacial origin (figs. 5; O’Hara 

and Oldale, 1980, 1987; Foster and others, 2015; Baldwin and 

others, 2016).

Finally, sediment texture data and bottom photographs 

were used to verify and refine the classification of the sediment texture polygons. Samples with laboratory analysis 

data, rather than qualitative descriptions, were preferred for 

defining sediment texture throughout the study area. Bottom 

photographs were also used to qualitatively define sediment 

texture, particularly in areas dominated by gravel- to bouldersize material. Many of the sediment type polygons did not 

contain sample information. For these polygons, sediment 

textures were extrapolated from similar sea-floor polygons that 

contained samples and produced similar acoustic-backscatter 

and seismic-reflection properties.

Sediment texture polygons were assigned one of four 

confidence levels on the basis of the type and quality of data 

used to define them (table 2). The confidence levels were 

attached as an attribute in the geographic information system 

(GIS) for each sediment texture polygon (fig. 8). Level-one 

confidence areas contain the widest variety of high-resolution 

geophysical data and the highest quality of sediment sample 

data. Level-two areas share the same variety of geophysical data but do not contain data from sediment samples that 

were analyzed quantitatively in the laboratory. Many leveltwo areas consist of gravel or gravelly sediment from which 

there was no attempt to collect a physical sample, or sample 

attempts recovered no material. This lack of samples is a 

common problem because either most bottom samplers are 

incapable of sampling gravel and cobble, or sufficient material 

cannot be collected for accurate quantitative laboratory analysis. Because level-three areas were designated in the absence 

of seismic-reflection data and possibly sediment samples with 

laboratory analyses, these areas are considered to have slightly 

less confidence than level-one and level-two areas. Level-four 

areas have substantially lower confidence because the primary 

component of the Barnhardt and others (1998) classification, acoustic reflectivity, is lacking. Consequently, levels one 

through three are generally considered “high confidence,” and 

level four is considered “low confidence” (table 2).
Methods 11

Nantucket Sound

ATLANTIC OCEAN

Martha's Vineyard

Nantucket

Muskeget

Channel

Elizabeth Islands

Nomans

Island

Tuckernuck

Island

Muskeget

Island

Vineyard 

Sound

A

B

A B

70° 70°20' 70°40'

41°30'41°25'41°20'

41°15'

41°20'41°15'

70°30' 70°40' 70°50' 70°4' 70°8'

41°22'41°20'41°18'

EXPLANATION

Sediment analysisBottom photographVisual description

0 8 16 KILOMETERS 4

0 4 8 NAUTICAL MILES 2

0 6 12 KILOMETERS 30 3 6 NAUTICAL MILES 1.5

0 2 4 KILOMETERS 1

0 2 NAUTICAL MILES 1

Figure 6. Locations of observations of sea-floor composition used to aid the geophysical and geologic interpretations, A, south and west of Martha’s Vineyard and B, north of Nantucket, Massachusetts (Ford and Voss, 2010; McMullen and others, 2012; Emily Huntley, Massachusetts Office of Coastal Zone Management, written commun., 2014). Blue dots indicate visual descriptions made from sediment grab samples, vibracore tops, or sea-floor photographs/video, or visual descriptions obtained from National Oceanic and Atmospheric Administration nautical charts (generally near the shoreline). Magenta dots indicate sediment grab samples that were analyzed in a laboratory to obtain grain-size statistics. Processed samples are preferred over those that were only described visually. Bottom photograph locations, indicated by yellow dots, are generally associated with sites where samples were collected and grain-size statistics were processed.
12 Shallow Geology, Sea-Floor Texture, and Physiographic Zones Offshore Martha’s Vineyard and Nantucket, Mass.

Figure 7. Barnhardt and others (1998) bottom-type classification 

based on four basic sediment units: rock (R), gravel (G), sand (S), 

and mud (M). Twelve additional two-part units represent 

combinations of the four basic units. In the two-part units, the 

primary texture (greater than 50 percent of the area) is given an 

uppercase letter, and the secondary texture (less than 50 percent 

of the area) is given a lowercase letter. Only the uppercase letter 

is used for areas where more than 90 percent of the texture is 

represented by one basic sediment unit. Figure is modified from 

Barnhardt and others (1998).

Physiographic Zones

Based on geologic maps produced for the western Gulf 

of Maine (Kelley and Belknap, 1991; Kelley and others, 1996; 

Barnhardt and others, 2006, 2009), and western Massachusetts 

Bay, the Merrimack Embayment, Cape Cod Bay, Buzzards 

Bay, Vineyard Sound, and western Nantucket Sound (Pendleton and others, 2013, 2015; Foster and others, 2015; Baldwin 

and others, 2016), the sea floor in the Martha’s Vineyard and 

Nantucket sites was divided into physiographic zones, which 

are delineated on the basis of sea-floor morphology and dominant sediment texture. Physiographic zone mapping allows 

for efficient characterization of large areas by using a variety 

of data sources that separately may not provide full sea-floor 

coverage. The zones were defined qualitatively in ArcGIS by 

using the same data sources and digitization techniques used 

to derive sediment texture and distribution.

Results

Seismic Stratigraphy and Geologic 

Interpretation

Four primary seismic stratigraphic units and three major 

unconformities were interpreted within the seismic survey 

area (figs. 5 and 9–14). Interpreted seismic profiles (figs. 10, 

13, and 14) illustrate the typical geometry of the seismic units 

and unconformities throughout the Martha’s Vineyard and 

Nantucket sites. Figure 12 contains interpreted geologic cross 

sections for one area north of Nantucket and two areas within 

the Martha’s Vineyard study site. Figure 15 contains the surficial geologic map derived from mapping the areal extents of 

geologic unit outcrops on the sea floor. Correlations between 

our geologic interpretations, which are modified from Foster 

and others (2015) and Baldwin and others (2016), and those 

of O’Hara and Oldale (1980, 1987) for eastern Rhode Island 

Sound, Vineyard Sound, and western Nantucket Sound are 

summarized in figure 9. Our interpretations of the seismic stratigraphy generally agree with the previous studies (O’Hara and 

Oldale, 1980, 1987) where there is overlap. The higher density 

and spatial resolution of the new data allowed us to build on 

the previous interpretations and provide more detailed surficial 

and shallow subsurface geologic maps than previously available. However, the newly acquired chirp data did not provide 

adequate penetration for reliable mapping of the deep Pleistocene and pre-Quaternary units; therefore, discussion of the 

deeper stratigraphy mostly relies on previous interpretations 

that were based on more widely spaced but more deeply penetrating boomer seismic data and vibracores.

Table 2. Confidence levels assigned to sediment texture and physiographic zone polygons on the basis of the data used in the 

interpretation.

[The spatial distribution of polygons and associated confidence levels are shown in figure 8. lidar, light detection and ranging]

Confidence level Bathymetry Acoustic

backscatter

Seismic

reflection

Sediment sample 

(laboratory analysis)

Sediment sample 

(visual analysis)

Bottom

photograph

One (high) Swath Yes Yes Yes Yes Possible

Two (high) Swath Yes Yes No Yes Possible

Three (high) lidar No No Yes Yes Possible

Four (low) lidar No No No Yes Possible
Results 13

A

B

Nantucket Sound

ATLANTIC OCEAN

Martha's Vineyard

Nantucket

Muskeget

Channel

Tuckernuck

Island

Muskeget

Island

Vineyard 

Sound

A

Wasque 

Point

Katama

Bay

South 

Beach

Chilmark

Aquinnah

Gayhead

Nomans

Island

Squibnocket

Point

B

North Point

Nantucket 

Harbor

Great Point

Eel Point

70° 70°20' 70°40'

41°20'

41°15'

70°30' 70°40' 70°50'

41°20'41°15'

70°4' 70°8' 70°12'

41°24'41°22'41°20'41°18'

41°16'

EXPLANATION

Confidence

1234

0 8 16 KILOMETERS 4

0 4 8 NAUTICAL MILES 2

0 6 12 KILOMETERS 30 2 4 NAUTICAL MILES 1

0 2.5 5 KILOMETERS 1.250 3 NAUTICAL MILES 1.5

Figure 8. The distribution of confidence levels for sediment texture and physiographic zone interpretations (table 2), A, south and west of Martha’s Vineyard and B, north of Nantucket, Massachusetts.
14 Shallow Geology, Sea-Floor Texture, and Physiographic Zones Offshore Martha’s Vineyard and Nantucket, Mass. Qfe Qdf Qdt Qfe QdoPzZ Qdm Qfe Qd Ku TKu(?)

1From O’ Hara and Oldale (1980).2From O’Hara and Oldale (1987).3This study, modified after Baldwin and others (2016) and Foster and others (2015).

Pleistocene end moraine (Qdm), glacial till and ice contact deposits (Qdt) - Drift composed of poorly sorted mud, sand, gravel, and boulders that produce rugged topography where they crop out at the seafloor. While seismic penetration is typically limited, these units produce chaotic reflectors with common diffraction hyperbolae. Underlie Ut and Ur, and overlie the fluvial unconformity Ul. Equivalent in part to Qdo1

and Qd2 (glacial drift), and Qdm1 (Buzzards Bay moraine).

Holocene fluvial and estuarine - Fluvial sands and gravels, and estuarine sands and muds (locally > 10 m thick) that fill incised fluvial valleys. Produces vertically laminated, horizontal to concave-up reflectors and zones of acoustic transparency; local indications of cut-and-fill. Bounded above by Ut and below by the regressive unconformity (Ur). May include Pleistocene deposits or younger Holocene 

marine deposits. Equivalent in part to Qfe1 and 2 (fluvial and estuarine).

Late Cretaceous, Tertiary, and (or) early Pleistocene age coastal plain and continental shelf deposits and possibly pre-Wisconsinan age glacial drift (QTKu?) - Undifferentiated pre-Wisconsinan glacial drift (Qpw?) and (or) earlier Pleistocene and pre-Quaternary coastal plain and continental shelf units (TKu?) that represent the acoustic basement of seismic survey. Ul is a major unconformity that has vertical relief 

up to 140 m(1,2), but was only observed in lines west of Chilmark. Neoproterozoic to early Paleozoic (PzZ) bedrock deposits were not 

recognized in this study.

Ku

Qdl

Qdm

Pleistocene glaciofluvial (Qdf, outwash) - Stratified drift composed of sand and gravel that produce vertically laminated, roughly horizontal to broadly undulating reflectors, cut-and-fill structures, and zones of acoustic transparency. Underlies Ut and Ur, and typically overlies 

glaciolacustrine (Qdl) and glacial till (Qdt). Equivalent in part to Qdo1 and Qd2 (glacial drift).

Pleistocene glaciolacustrine (Qdl, glaciodeltaic and lake floor) - Stratified drift composed of mud and sand that produce strong to weak, vertically laminated, horizontal to gently dipping reflectors. Underlies Ut and Ur, and typically drapes glacial till (Qdt) and moraine (Qdm). 

Equivalent in part with Qdo1 and Qd2 (glacial drift).

Qpw(?)

Qmn Qm Qm Qb Qb

Qd

Holocene nearshore marine (Qmn) - Mostly sandy deposits (typically < 2 m but up to 14 m thick) that form shoals, ebb-tidal deltas, transgressive sand sheets, and sorted bedforms within the Martha’s Vineyard study site. Qmn at the Nantucket study site is thicker (typically greater than 4 m) and muddy sand. In both sites the unit is generally acoustically transparent with faint, flat-lying reflectors. Overlies transgressive unconformity (Ut). Equivalent to Qb1 and 2 (marine beach and bar).

TRANSGRESSIVE UNCONFORMITY (Ut

)

REGRESSIVE UNCONFORMITY (Ur

)

FLUVIAL UNCONFORMITY (U)

l

Vineyard Sound

and eastern Rhode

Island Sound1

Nantucket

Sound2

South of Martha’s 

Vineyard and 

north of Nantucket3

Seismic stratigraphic units and major unconformities

Holocene Pleistocene Pre-Pleistocene

Quaternary Pre-Quaternary

QTKu(?)

Figure 9. Units and major unconformities interpreted within Vineyard Sound and eastern Rhode Island Sound by O’Hara and Oldale (1980), within Nantucket Sound by O’Hara and Oldale (1987), and modified from Foster and others (2015) and Baldwin and others (2016) for this study. m, meter.
Results 15

Two-way traveltime, in milliseconds

Depth, in meters

A A'

WEST EAST

0

15

30

Depth, in meters

Two-way traveltime, in milliseconds Qdm or Qdt Qdt Qdm Buzzards Bay lobe Cape Cod Bay lobe QTKu(?) Qdf Qdl Ut Ul

0

1020304050

0

15

30

0

1020304050

0 0.5 1 MILE0 1 2 KILOMETERS

Figure 10. Chirp seismic-reflection profile A–A' with seismic stratigraphic interpretation. This profile illustrates the stratigraphy offshore of Martha’s Vineyard, Massachusetts, from Squibnocket Beach to Chilmark. See figure 9 for descriptions of stratigraphic units and major unconformities (indicated by red and black lines). Deposits of the Martha’s Vineyard moraine (Qdm) that crop out at the sea floor are draped by Buzzards Bay lobe ice-contact deposits (Qdt) to the west and glaciofluvial and glaciolacustrine (Qdf and Qdl) deposits inferred to be from the Cape Cod Bay lobe to the east. To the southwest, Buzzards Bay lobe end moraine deposits (Qdm) extend over deformed older drift deposits or coastal plain deposits (QTKu?). See figure 15 for profile location. A constant sound velocity of 1,500 meters per second was used to convert two-way traveltime to depth in meters.
16 Shallow Geology, Sea-Floor Texture, and Physiographic Zones Offshore Martha’s Vineyard and Nantucket, Mass.

B'

SOUTHEAST NORTHWEST

B

Two-way traveltime, in milliseconds

Depth, in meters

Two-way traveltime, in milliseconds

Depth, in meters

gas

gas

Qmn

Qmn

Qmn

Qfegas

Qdf

Qfe

Ut Ur

multiple

X-SECTION

' C-C

15

30

203040

203040

15

30

0 0.5 1 MILE

0 1 2 KILOMETERS

Figure 11. Chirp seismic-reflection profile B–B' with seismic stratigraphic interpretation. This profile illustrates the stratigraphy north of Nantucket, Massachusetts, from offshore to onshore. See figure 9 for descriptions of stratigraphic units and major unconformities (indicated by red and orange lines). A relatively thick blanket of modern nearshore marine sediments (Qmn) sits unconformably on top of Holocene estuarine and fluvial deposits (Qfe; O’Hara and Oldale, 1987). Glaciofluvial (Qdf) sediments are interpreted to lie below the Holocene sediments. See figure 15 for profile location. Dashed vertical black line indicates intersection with cross section 

C–

C'. A constant 

sound velocity of 1,500 meters per second was used to convert two-way traveltime to depth in meters.
Results 17

Depth, in meters

PROFILE

B-B'

?

?

?

SOUTHWEST

C C'

NORTHEAST

Depth, in meters

NORTHWEST

D D'

SOUTHEAST

Depth, in meters

E'

NORTH SOUTH

E

15

30

15

30

15

30

0 0.5 1 MILE

0 1 2 KILOMETERS

0 0.25 0.5 MILE

0 0.5 1 KILOMETER

0 0.5 1 MILE

0 1 2 KILOMETERS

Holocene nearshore marine

Holocene fluvial and estuarine

Pleistocene glaciofluvial drift

Pleistocene till or ice-contact drift

Pleistocene moraine

Sea floor

Ut

Ur

EXPLANATION

Ul

Qmn

Qfe

Qdf

Qdt

Qdm

Figure 12. The general distributions and thicknesses of seismic stratigraphic units and major unconformities in the Martha’s Vineyard 

and Nantucket, Massachusetts, study sites. The geologic sections (C–C', D–D', and E–E') were produced from chirp seismic-reflection 

profile interpretations. See figure 9 for descriptions of stratigraphic units and unconformities. Geologic section locations are indicated 

on figure 15. The Ul fluvial unconformity is a dashed line to denote that it is discontinuous and (or) inferred.
18 Shallow Geology, Sea-Floor Texture, and Physiographic Zones Offshore Martha’s Vineyard and Nantucket, Mass.

Two-way traveltime, in milliseconds

Depth, in meters

NORTH

F

F'

SOUTH

Two-way traveltime, in milliseconds

Depth, in meters

PROFILE

' G-G

Qfe

Qmn

Qfe

Qfe

Qdf

Qdf

Ut Ur Qmn

Qfe

0

10203040

0

15

30

102040

0

30

0

15

30

0 0.5 1 MILE0 1 2 KILOMETERS

Figure 13. Chirp seismic-reflection profile F–F' with seismic stratigraphic interpretation. This profile illustrates the stratigraphy across the shelf west of South Beach on Martha’s Vineyard, Massachusetts. See figure 9 for descriptions of stratigraphic units and major unconformities (indicated by red and orange lines). This profile shows a series of across-shelf fluvial or groundwater sapping channels (Qfe; Uchupi and Oldale, 1994) carved into glaciofluvial sediments (Qdf) deposited by the Cape Cod Bay lobe of the Laurentide Ice Sheet. At the southern side of the profile, the chirp data indicate that another glaciofluvial unit (not shown) is interpreted below the overlying Qdf unit. Modern nearshore marine sediments (Qmn) locally lie unconformably on top of the Holocene fluvial and glaciofluvial sediments. Qmn units are often associated with sorted bedforms oriented perpendicular to the coast (Goff and others, 2005). See figure 15 for profile location. Dashed vertical black line indicates intersection with profile 

G–

G'. A constant sound 

velocity of 1,500 meters per second was used to convert two-way traveltime to depth in meters.
Results 19

Two-way traveltime, in milliseconds

G'

EAST WEST

G

Depth, in meters

Qdf

Qfe

Qmn

Qfe Qfe

Qmn Ut U

r

PROFILE' F-F

Two-way traveltime, in milliseconds

Depth, in meters

0

15

0

0

102030

0

15

30

0

102030

0 0.5 1 MILE0 1 2 KILOMETERS

Figure 14. Chirp seismic-reflection profile G–G' with seismic stratigraphic interpretation. This profile illustrates the stratigraphy along the shelf near South Beach on Martha’s Vineyard, Massachusetts. See figure 9 for descriptions of stratigraphic units and major unconformities (indicated by red and orange lines). This profile shows two sets of fluvial or groundwater sapping channels (Qfe; Uchupi and Oldale, 1994) carved into glaciofluvial sediments (Qdf) deposited by the Cape Cod Bay lobe of the Laurentide Ice Sheet. Modern nearshore marine sediments (Qmn) locally lie unconformably on top of the Holocene fluvial and glaciofluvial sediments (Qfe). Qmn units are often associated with sorted bedforms oriented perpendicular to the coast (Goff and others, 2005). See figure 15 for profile location. Dashed vertical black line indicates intersection with profile F–F'. A constant sound velocity of 1,500 meters per second was used to convert two-way traveltime to depth in meters.
20 Shallow Geology, Sea-Floor Texture, and Physiographic Zones Offshore Martha’s Vineyard and Nantucket, Mass.

A

B

Nantucket Sound

ATLANTIC OCEAN

Muskeget

Channel

Vineyard 

Sound

Martha's Vineyard

Nantucket

Elizabeth Islands

Tuckernuck

Island

Muskeget

Island

B

B'

C

C'

A A'

D

D'

E

E'

F

F'

G G'

A

Nomans

Island

Wasque 

Point

Katama

Bay

South 

Beach

Chilmark Aquinnah

Gayhead

Squibnocket

Point

Nomans

Island

Wasque 

Point

B

North Point Nantucket 

Harbor

Great Point

Eel Point

70° 70°20' 70°40'

41°30'41°25'41°20'41°15'

70°30' 70°40' 70°50'

41°20'41°15'

70°4' 70°8' 70°12'

41°24'

41°22'41°20'41°18'

41°16'

EXPLANATION

Geology

Qmn

Qfe

Qdf

Qdl

Qdt

Qdm

0 8 16 KILOMETERS 4

0 4 8 NAUTICAL MILES 2

0 6 12 KILOMETERS 30 3 6 NAUTICAL MILES 1.5

0 3 6 KILOMETERS 1.5

0 3 NAUTICAL MILES 1.5

Figure 15. Surficial geology from this study and Baldwin and others (2016) with equivalent onshore geology (adapted from Stone and DiGiacomo-Cohen, 2009), 

A, south and west of Martha’s Vineyard and 

B, north of Nantucket, Massachusetts. The areal extents over which offshore subsurface geologic units 

crop out at the sea floor were interpreted from seismic-reflection data. See figure 9 for detailed descriptions of the offshore geologic units. Holocene sediment veneers too thin to be detected in the seismic data (less than approximately 0.5 meter) may overlie outcrops of older units locally. The bathymetric hillshade relief map is derived from the composite bathymetry in Andrews and others (2018). Black lines indicate chirp profile locations, and magenta lines indicate geologic section locations. Surficial geology interpreted by Baldwin and others (2016) in Vineyard Sound is shown for regional context and continuity. Qdm, Pleistocene glacial moraine—Martha’s Vineyard moraine; Qdt, undifferentiated Pleistocene glacial till and ice contact; Qdl, Pleistocene glaciolacustrine (glaciodeltaic and lake floor); Qdf, Pleistocene glaciofluvial (outwash); Qfe, Holocene fluvial and estuarine; Qmn, Holocene nearshore marine.
Results 21

In ascending order, the four primary seismic stratigraphic 

units are (1) undifferentiated coastal plain and continental 

shelf deposits of Late Cretaceous(?), Tertiary(?), and (or) early 

Pleistocene(?) age and possibly glacial drift of late Pleistocene (pre-Wisconsinan?) age (QTKu?); (2) glacial drift of late 

Pleistocene (Wisconsinan) age (Qd); (3) postglacial fluvial and 

estuarine deposits of Holocene age (Qfe); and (4) Holocene 

postglacial marine deposits (Qmn). These are separated by 

three regional unconformities: Ul, Ur, and Ut (fluvial, regressive, and transgressive, respectively, fig. 9). In addition, glacial 

drift deposits (Qd) are divided into subunits on the basis of 

seismic facies, stratigraphic position, and spatial distribution.

The lowermost stratigraphic unit mapped in previous 

studies within and adjacent to this area is of coastal plain and 

continental shelf deposits of Late Cretaceous(?), Tertiary(?), 

and (or) early Pleistocene(?) age and possibly glacial drift 

of pre-Wisconsinan(?) age (Woodsworth and Wigglesworth, 

1934; Kaye, 1964a, b, 1980; Folger and others, 1978; Hall 

and others, 1980; O’Hara and Oldale, 1980, 1987; Oldale and 

O’Hara, 1984; Uchupi and Mulligan, 2006; Foster and others, 2015; Baldwin and others, 2016). However, because of 

the shallow penetration of the chirp seismic data used in this 

study, units below the unit inferred to be deposits of late Pleistocene (Wisconsinan) age (Qd) were not frequently observed. 

Qd is divided into four subunits—end moraine (Qdm), glacial 

till and ice-contact (Qdt), glaciolacustrine (Qdl), and glaciofluvial (Qdf) deposits—on the basis of their seismic facies, 

defined by internal reflections as well as their relative stratigraphic positions and spatial distributions. Qd subunits were 

generally recognized in chirp profiles as outcropping units, 

where they were present in the relatively shallow subsurface 

(less than about 40 milliseconds two-way traveltime), or when 

they were unobscured by the primary sea-floor multiple.

The end moraine (Qdm) and glacial till and ice-contact (Qdt) subunits produce similar seismic facies, consisting 

of irregular, high-amplitude surface reflections and chaotic 

and discontinuous internal reflections with common diffraction 

hyperbolae that often mask subunits (figs. 9 and 10). Chaotic 

reflections within Qdm and Qdt and hyperbolic diffractions 

where these units intersect the sea floor are interpreted as 

acoustic signatures of poorly sorted, relatively coarse drift and 

boulders. Qdm is specifically inferred to represent till associated with the Martha’s Vineyard end moraine (fig. 10). Qdt 

units are present at the sea floor in discrete locations in the 

western part of the Martha’s Vineyard site (fig. 15) and are 

interpreted to represent outcrops of supraglacial or subglacial 

stagnation till, lodgment till, or deformation till.

The glaciolacustrine (Qdl) and glaciofluvial (Qdf) subunits represent stratified drift of late Pleistocene age that was 

deposited by glacial meltwater. The glaciolacustrine seismic 

facies is characterized by vertically laminated, horizontal to 

gently dipping reflections of variable amplitude. Qdl reflections are undulatory where they conformably drape the 

irregular surfaces of Qdm or Qdt and where they have been 

deformed. The seismic signature of Qdl is interpreted to 

represent varved, relatively fine grained, glaciodeltaic or glaciolacustrine deposits. The glaciofluvial (Qdf) seismic facies 

is characterized by zones of acoustic transparency along the 

south shore of Martha’s Vineyard, but less continuous units are 

present as undulatory, or gently to steeply dipping laminated 

reflections, chaotic and discontinuous reflections, or cut-andfill structures (figs. 10–13 and 14). Generally, seismic-reflection data penetration was not adequate for mapping the base 

of Qdf; however, Qdf is observed to overlie other Qd subunits 

locally, and its variable seismic character indicates a variety of 

outwash morphologies.

The medium-to high-amplitude, irregular to undulating 

seismic reflection Ur (regressive) unconformity delineates the 

eroded upper surface of Qd (figs. 11, 13, and 14) and represents the regressive unconformity of late Wisconsinan to early 

Holocene age (fig. 16). The Ur surface contains subsurface 

valleys that deepen progressively offshore from the drowned 

valleys of Martha’s Vineyard and toward the eastern margin 

of the Nantucket site. These morphologies resulted through a 

combination of glacial lake drainage, meltwater fluvial erosion, and later fluvial erosion during the early Holocene. Ur

 is 

a composite unconformity that merges with the Ut (transgressive) unconformity outside of glaciofluvially eroded areas.

The remaining two primary stratigraphic units that 

overlie the Qd unit represent primarily Holocene fluvial and 

estuarine (Qfe) and nearshore marine (Qmn) deposits (figs. 9 

and 17). Qfe is the lowermost of these deposits, and where 

present, it fills the deepest portions of the Martha’s Vineyard 

valleys and the Nantucket Sound basin formed by Ur. Qfe 

produces seismic signatures that include laminated, horizontal 

to concave-up reflections, cut-and-fill structures, and zones 

of near acoustic transparency (figs. 11, 13, and 14). Qfe units 

are interpreted to consist of late Pleistocene and Holocene 

fluvial deposits, as well as younger Holocene estuarine fill 

related to marine transgression. Qfe deposits are thickest 

where they form the youngest fills within the major channel 

trunks in the Pleistocene drainage network (figs. 11 and 17). In 

some locations north of Nantucket, biogenic gas, presumably 

produced in the organic-matter-rich estuarine sections of Qfe, 

attenuated the seismic signal and prevented interpretation of 

underlying units.

Seismic reflector Ut, a medium-amplitude, mostly flatlying, and continuous reflector, is interpreted to represent the 

Holocene marine transgressive unconformity and generally 

defines the boundary between Holocene marine (Qmn) deposits and older underlying units. Ut

 is a composite unconformity 

that merges with Ur wherever Qfe is absent (figs. 11 and 13).

The Holocene marine (Qm) seismic facies is characterized by medium- to low-amplitude, flat-lying to steeply dipping, laminated reflections and zones of acoustic transparency 

(figs. 11, 13, and 14). Qmn deposits are composed primarily 

of sand and some gravel and form the beaches and bars along 

the shorelines, as well as shoals, sand ridges and sheets, and 

smaller bedforms on the sea floor (figs. 15 and 17).
22 Shallow Geology, Sea-Floor Texture, and Physiographic Zones Offshore Martha’s Vineyard and Nantucket, Mass. Nantucket Sound ATLANTIC OCEAN Martha's Vineyard Nantucket Muskeget Channel Tuckernuck Island Muskeget Island

A

B

Vineyard 

Sound

Nomans

Island

Wasque 

Point Chilmark

Aquinnah

Squibnocket

Point

A

Nomans

Island

Wasque 

Point

Katama

Bay

South 

Beach

Chilmark

Aquinnah

Gayhead

Squibnocket

Point

Katama

Bay

North Point

Nantucket 

Harbor

Great Point

Coskata

B

North Point

Nantucket 

Harbor

Great Point

Eel Point

Coskata

70° 70°20' 70°40'

41°20'41°15'

70°30' 70°40' 70°50'

41°20'41°15'

70°4' 70°8' 70°12'

41°24'41°22'41°20'41°18'41°16'

70°4' 70°8' 70°12'

41°24'41°22'41°20'41°18'41°16'

EXPLANATION

Elevation of regressive

unconformity, inmeters (NAVD 88)

High : -5Low : -35

0 8 16 KILOMETERS 40 4 8 NAUTICAL MILES 2

0 6 12 KILOMETERS 3

0 2 4 NAUTICAL MILES 1

0 2.5 5 KILOMETERS 1.250 3 NAUTICAL MILES 1.5

Figure 16. The elevation (referenced to the North American Vertical Datum of 1988 [NAVD 88]) of the late Wisconsinan to early Holocene regressive unconformity Ur, which identifies the eroded surface of Pleistocene glacial drift offshore of 

A, southern Martha’s Vineyard and 

B, northern Nantucket. Ur represents a composite unconformity where it 

locally merges with the Holocene transgressive unconformity (Ut). The surface illustrates the topographic morphologies of prominent glacial features in the shallow subsurface.
Results 23

Nantucket Sound

Martha's Vineyard

ATLANTIC OCEAN

Nantucket

Muskeget

Channel

Tuckernuck

Island

Muskeget

Island

A

B

Vineyard 

Sound

Nomans

Island

Wasque 

Point Chilmark

Aquinnah

Gayhead

Squibnocket

Point

A

Nomans

Island

Wasque 

Point

Katama

Bay

South 

Beach

Chilmark

Aquinnah

Gayhead

Squibnocket

Point

Katama

Bay

North Point

Nantucket 

Harbor Eel Point

Coskata

B

North Point

Nantucket 

Harbor

Great Point

Eel Point

Coskata

70° 70°20' 70°40'

41°20'41°15'

70°30' 70°40' 70°50'

41°20'41°15'

70°4' 70°8' 70°12'

41°24'41°22'41°20'41°18'41°16'

EXPLANATION

Postglacial sediment

thickness, in meters

High : 16Low : 0

0 8 16 KILOMETERS 40 4 8 NAUTICAL MILES 2

0 6 12 KILOMETERS 3

0 2 4 NAUTICAL MILES 1

0 2.5 5 KILOMETERS 1.25

0 3 NAUTICAL MILES 1.5

Figure 17. The thickness of postglacial fluvial and estuarine (Qfe) and Holocene nearshore marine (Qmn) sediments A, west and south of Martha’s Vineyard and B, north of Nantucket, Massachusetts.
24 Shallow Geology, Sea-Floor Texture, and Physiographic Zones Offshore Martha’s Vineyard and Nantucket, Mass.

Sediment Texture and Distribution

Sediment texture and distribution were mapped for more 

than 265 km2 of the inner shelf (fig. 18) by using the Barnhardt 

and others (1998) classification (fig. 7). The data were interpreted at scales ranging from 1:8,000 to 1:25,000, depending on the resolution of the source geophysical grids and the 

density of the sample data.

Sediments within the study area represent nearly all 

particle sizes. Sediment texture ranges from muddy sands 

primarily north of Nantucket to pebbles, cobbles, and boulders 

where tills and moraine deposits are exposed at the sea floor 

(figs. 15 and 18–20). Both coarse- and fine-grained sediment 

exist in all water depths; however, rocky textures are generally most prevalent along the nearshore margin of southwestern Martha’s Vineyard (figs. 18 and 19). Rocky textures are 

least concentrated east of Chilmark and north of Nantucket 

(figs. 18–20). Overall, the distribution of samples in the texture database for the study area is 62 percent sand, 33 percent 

mud, and 5 percent gravel by weight.

Sand (greater than 0.062 mm to 2 mm) is the dominant 

bottom sediment type within the study area and is interpreted 

to cover 92 percent of the sea floor by area (fig. 18). Sand is 

most extensive east of Chilmark. Muddy sediments, which 

include silt- and clay-size particles less than 0.062 mm in 

diameter, cover 1 percent of the sea floor by area within the 

Martha’s Vineyard study site but are present in the Nantucket 

site in nearly 70 percent of the sea floor by area. Gravel or 

particles greater than 2 mm but less than 64 mm (−1 to −6 phi) 

in diameter are interpreted to be the primary sediment cover in 

less than 1 percent of the sea floor. Primarily rocky areas are 

interpreted to cover about 7 percent of the sea floor by area 

and are most prevalent adjacent to morainal headland deposits 

on the western and southwestern sides of Martha’s Vineyard 

(figs. 15, 18, and 19). Photographs document the presence of 

gravel and cobble in rocky areas where sediment sampling 

devices were unable to recover large-diameter particles, suggesting that gravel and rock are underrepresented in sediment 

sample data in this area.

Physiographic Zones

The areal distribution of physiographic zones in the 

offshore part of the study area (265 km2) was interpreted at 

a scale ranging from 1:8,000 to 1:25,000, depending on the 

resolution of the source geophysical grids (fig. 21).

Rocky zones are rugged areas, which often exhibit high 

bathymetric relief, ranging from ridges to relatively flat, 

gravel-covered plains with boulders several meters in diameter. Although coarse-grained sediments are locally present in 

all physiographic zones, they dominate the sea floor in rocky 

zones. Rocky zones are common from Gay Head to Chilmark 

(12 percent of the sea floor by area) but are absent throughout the rest of the Martha’s Vineyard study site and north 

of Nantucket.

Zones of coastal embayments include much of the study 

area north of Nantucket. Coastal embayments cover 38 km2, or 

about 14 percent, of the study area.

Ebb-tidal deltas are present on the eastern edge of the 

Martha’s Vineyard site, where the western edge of the large 

Muskeget Channel ebb-tidal delta can be identified in the 

geophysical data. Ebb-tidal delta zones compose just less than 

2.5 percent of the sea floor within the entire study area.

Hard-bottom plains tend to have low bathymetric 

relief and a coarse sediment texture consisting of primarily 

gravel, sand, and rock. Hard-bottom plains account for about 

1.5 percent of the sea floor and are on the western side of 

Martha’s Vineyard, adjacent to rocky zones associated with 

morainal deposits.

Nearshore ramps are areas of gently sloping sea floor 

with generally shore-parallel bathymetric contours. These 

zones are primarily interpreted as sand-rich sediment, although 

small exposures of cobbles and boulders locally crop out on 

the sea floor. Nearshore ramps are the primary physiographic 

zone on the south side of Martha’s Vineyard, east of Chilmark. 

Within the entire study area (Martha’s Vineyard and Nantucket), nearshore ramps are the most abundant physiographic 

zone, accounting for nearly half of the sea floor by area, which 

is likely a result of the substantial amount of open-ocean inner 

shelf offshore of southern Martha’s Vineyard (fig. 21).

Shelf valleys are elongate depressions that extend offshore, often perpendicular to the trend of the coastline, and 

slope gently seaward. Shelf valleys represent about 11 percent 

of the study area in total, but they are absent east of Chilmark. 

They likely existed there as well but may have been reworked 

into a broad sand sheet during transgression. These zones are 

interpreted to have formed by fluvial erosion during periods of 

lower-than-present sea level and are most commonly dominated by sandy textures.

Shoal/sand waves are sea-floor zones dominated by linear 

to sinuous bedforms primarily composed of sandy sediments 

that have been reworked from adjacent glacial deposits by 

wave and tidal currents. Water depths range from approximately 10 to 30 m. Shell zones are areas that are nearly completely covered by carbonate shells. High densities of slipper 

shells (Crepidula fornicata) were recognized within areas of 

sea floor north of Nantucket. Shell zones (figs. 20 and 21) and 

sand waves account for just over 5 percent of the sea floor by 

area. Foster and others (2015), Ackerman and others (2016), 

and Baldwin and others (2016) recognized similar accumulations of Crepidula in the central Buzzards Bay basin and 

western Nantucket Sound.
Results 25

Nantucket Sound

ATLANTIC OCEAN

Martha's Vineyard

Nantucket

Muskeget

Channel

Tuckernuck

Island

Muskeget

Island

A

B

Vineyard 

Sound

Nomans

Island

Wasque 

Point Chilmark

Aquinnah

Gayhead

Squibnocket

Point

A

Nomans

Island

Wasque 

Point

Katama

Bay

South 

Beach

Chilmark

Aquinnah

Gayhead

Squibnocket

Point

Katama

Bay

North Point

Nantucket 

Harbor

Great Point

B

Eel Point

70° 70°20' 70°40'

41°20'

41°15'

70°30' 70°40' 70°50'

41°20'41°15'

70°4' 70°8' 70°12'

41°24'41°22'41°20'41°18'41°16'

EXPLANATION

Sediment texture

GGsMsRsSSgSmSr

0 8 16 KILOMETERS 40 4 8 NAUTICAL MILES 2

0 6 12 KILOMETERS 3

0 2 4 NAUTICAL MILES 1

0 3 6 KILOMETERS 1.50 3 NAUTICAL MILES 1.5

Figure 18. The distribution of sediment textures within the study area A, west and south of Martha’s Vineyard and B, north of Nantucket, Massachusetts. The bottomtype classification is from Barnhardt and others (1998) and is based on two part combinations of four basic sediment units that include gravel (G), mud (M), rock (R), and sand (S) (fig. 7). If the texture is greater than 90 percent, it is labeled with a single letter. If the composition of one component is less than 90 percent, it is labeled with two letters, where the first letter is the primary sediment unit (more than 50 percent) and the second letter is the secondary sediment unit (less than 50 percent). Areas interpreted by Baldwin and others (2016) in Vineyard Sound are shown for regional context and continuity.
26 Shallow Geology, Sea-Floor Texture, and Physiographic Zones Offshore Martha’s Vineyard and Nantucket, Mass.

B

A

C

D

E

B

C

D

E

EXPLANATION

Sediment texture

G

Gs

MsRs

SSg

SmSr

Figure 19.

A, Sediment textures offshore of western and southern Martha’s Vineyard. B, Photograph of coarse sand and gravel obtained from a 

section of sea floor classified as primarily sand with gravel (Sg). 

C, Photograph of the sea floor showing sandy sediment within an area classified as 

primarily sand (S). 

D, Photograph from a section of sea floor classified as primarily sand with some mud (Sm). 

E, Photograph from a section of sea 

floor classified as primarily sand (S). The scales of photographs B–E are approximately 60 to 100 cm(?). Bottom-type classification is from Barnhardt and others (1998).
Results 27

B

A

C

D

E

F

B

C

D E F

EXPLANATION

Sediment texture

G

Gs

Ms

Rs

S

Sg

Sm

Sr

Figure 20. A, Sediment textures offshore of northern Nantucket. B, Photograph of the seafloor covered by highly 

concentrated Crepidula fornicata. The sediment below the shells is classified as primarily sand with mud (Sm). 

C, Photograph of the sea floor showing sandy sediment within an area classified as primarily sand (S). D, Photograph 

from a section of sea floor classified as primarily sand (S). E, Photograph from a section of sea floor classified as primarily 

sand with some mud (Sm). F, Photograph from a section of sea floor classified as primarily sand with gravel (Sg) that is 

also blanketed with a fairly dense covering of Crepidula fornicata. Shell zones are outlined with cross-hatching. Bottomtype classification is from Barnhardt and others (1998).
28 Shallow Geology, Sea-Floor Texture, and Physiographic Zones Offshore Martha’s Vineyard and Nantucket, Mass. Nantucket Sound ATLANTIC OCEAN Martha's Vineyard Nantucket Muskeget Channel Tuckernuck Island Muskeget Island

A

B

Vineyard 

Sound

Nomans

Island

Wasque 

Point Chilmark

Aquinnah

Squibnocket

Point

A

Nomans

Island

Wasque 

Point

Katama

Bay

South 

Beach

Chilmark

Aquinnah

Gayhead

Squibnocket

Point

Katama

Bay

North Point Nantucket 

Harbor

Great Point

B

Eel Point

70° 70°20' 70°40'

41°20'

41°15'

70°30' 70°40' 70°50'

41°20'41°15'

70°4' 70°8' 70°12'

41°24'41°22'41°20'41°18'41°16'

EXPLANATION

Physiographic zones

Coastal embaymentEbb tidal deltaHard-bottom plainNearshore basinNearshore ramp

Outer basinRocky zoneShelf valleyShell zoneSand waves

0 8 16 KILOMETERS 4

0 4 8 NAUTICAL MILES 2

0 6 12 KILOMETERS 3

0 2 4 NAUTICAL MILES 1

0 2.5 5 KILOMETERS 1.250 3 NAUTICAL MILES 1.5

Figure 21. The distribution of physiographic zones

A, offshore of Martha’s Vineyard and 

B, north of Nantucket. The physiographic zone classification is adapted from 

Kelley and others (1996), and the zones are delineated on the basis of sea-floor morphology and the dominant texture of surficial material.
Discussion 29

Discussion

Synthesis of Maps

Three of the four primary stratigraphic units (fig. 9) crop 

out at the sea floor in the study area (fig. 15), and the interpretations of surficial sediment texture (fig. 18) and physiographic 

zones (fig. 21) are closely related to the distribution of these 

units. Surficial geologic units may not directly correspond 

with surficial sediment units because geologic units may be 

buried beneath a sediment layer too thin to detect in the seismic data (less than about 0.5 m), or the outcropping unit may 

be winnowed or reworked at the sea floor.

No undifferentiated coastal plain and continental shelf 

deposits of Late Cretaceous(?), Tertiary(?), and (or) early 

Pleistocene(?) age and possibly glacial drift of late Pleistocene (pre-Wisconsinan?) age (QTKu?) were interpreted to 

crop out at the surface in the geophysical and geologic data. 

Small, local areas may crop out but cannot be differentiated 

from Pleistocene end moraine deposits (Qdm) in the chirp data 

because of a lack of penetration, especially in the 2011 dataset 

(Andrews and others, 2014). Thrusted and deformed portions of QTKu(?) are known to compose much of the terminal 

moraine complex along the western margin of Martha’s Vineyard, are exposed along the shore in the Aquinnah cliffs, and 

extend west and south beneath the shallow subsurface (Woodsworth and Wigglesworth, 1934; Kaye, 1964a, b; O’Hara 

and Oldale 1980, 1987; Oldale and O’Hara, 1984). Outcrops 

of Qdm associated with the Martha’s Vineyard moraine are 

mapped at the sea floor west and southwest of Martha’s Vineyard and are interpreted to cover underlying QTKu(?) units. 

Where discontinuous reflectors of QTKu(?) units are identified and interpreted in the chirp data, they are commonly as 

shallow as 5 m below the sea floor. The presence of boulders 

and cobble-sized clasts in bottom photos from Qdm outcrops 

suggests that these units are associated with Rg, Rs, Sr, and 

G surficial sediment textures and rocky physiographic zones 

(figs. 15, 18, and 21).

Late Pleistocene glacial till and ice-contact (Qdt) outcrops are present mostly in the southwestern section of the 

Martha’s Vineyard study site (fig. 15), associated with the 

Martha’s Vineyard moraine. These outcrops contain boulders 

and cobbles and represent sea-floor exposures of ice-contact 

sediments that are buried by younger sediment in adjacent areas. Qdt crops out adjacent to Qdm units offshore of 

Chilmark, is interpreted here as stagnation till, and is locally 

covered by late Pleistocene glaciolacustrine (Qdl), glaciofluvial (Qdf), or Holocene nearshore marine (Qmn) deposits 

(figs. 10 and 15). Qdt is primarily associated with Gs, Sg, and 

S surficial sediment textures and rocky zones and nearshore 

ramp physiographic zones (figs. 15, 18, and 21).

Glaciolacustrine deposits (Qdl) are typically buried 

by younger units but are exposed at the sea floor and fill 

depressions between Qdm and Qdt deposits just offshore of 

Squibnocket Point (fig. 15). Depressions filled with Qdl units 

may have been created by the melting of blocks of stagnant 

ice within or on top of the till or outwash near the ice margin. Glaciofluvial outcrops of late Pleistocene age (Qdf) are 

extensive offshore beyond the extents of Qdm and Qdt and 

east of Chilmark in the Martha’s Vineyard study site. The Qdf 

sediments are interpreted to be primarily associated with Cape 

Cod Bay ice lobe outwash deposits. Qdf and Qdl are in most 

places associated with S or Sg textures and with nearshore 

ramps and shelf valley physiographic zones (figs. 15, 18, 

and 21).

Holocene fluvial and estuarine (Qfe) outcrops in the 

Martha’s Vineyard study site are generally exposed in sublinear to sinuous patterns incising outcrops of Qdf, Qdt, or Qdm 

(fig. 15). Several drainage channels, some of which may also 

be associated with groundwater sapping valleys (Uchupi and 

Oldale, 1994), incise the outwash plain offshore and east of 

Chilmark to Katama Bay (figs. 16 and 17). Qfe is primarily 

associated with the Sg and S surficial sediment types and the 

nearshore ramp physiographic zone (figs. 15, 18, and 21).

A Holocene nearshore marine (Qmn) unit overlies 

parts of each of the other units throughout the study area 

of Martha’s Vineyard and blankets the entire study site of 

Nantucket (fig. 15). Qmn is composed of fine-grained sediments that we interpret to be derived from the erosion, reworking, and winnowing of the older underlying glacial and postglacial sediments. In the Martha’s Vineyard study area, Qmn 

is relatively thin (2 m or less) across much of the shelf but is 

quite thick where it is associated with two large sand shoals 

north and south of Nomans Island. Qmn is also thin (less than 

2 m) along the western side of the Nantucket study site, where 

glaciofluvial material is exposed at the surface on Tuckernuck 

Island and east nearly to Nantucket Harbor (Oldale and Barlow, 1986), but Qmn thickens toward Great Point. Qmn units 

are primarily sandy, coinciding with S, Sg, and Sm surficial 

sediment types (figs. 15 and 18). These units form the sandy 

inner shelf areas of nearshore ramps, coastal embayments, and 

the modern mobile bedforms of ebb-tidal deltas, shell zones, 

and shoal/sand wave zones (figs. 15 and 21).

Geologic History and Framework

Interpretation of the geologic framework and seismic 

stratigraphy offshore of Martha’s Vineyard and north of 

Nantucket was fundamental in developing a foundation for the 

surficial maps presented here, and this interpretation informed 

our understanding of the late Pleistocene to Holocene deposition history of the area. Our interpretations of the geologic 

framework west of Martha’s Vineyard and north of Nantucket 

are compatible with those of O’Hara and Oldale (1980, 1987), 

respectively, and our interpretation of the geologic framework for the inner continental shelf along the south shore of 

Martha’s Vineyard is new. The geologic framework presented 

here as a series of interpretive maps describes the glacial and 

postglacial depositional history that resulted from the retreat 

of the late Wisconsinan Buzzards Bay and Cape Cod Bay ice 

lobes and subsequent Holocene marine transgression. These 

dense, high-resolution data and mapping products refine our 
30 Shallow Geology, Sea-Floor Texture, and Physiographic Zones Offshore Martha’s Vineyard and Nantucket, Mass.

understanding of the shallow geologic framework offshore 

of Martha’s Vineyard and north of Nantucket and foster new 

insights about regional depositional history and the relations 

between near-surface geologic units and sea-floor morphology 

and composition.

Glacial Recession

This mapping describes the interaction between the icecontact material at the margin of the Buzzards Bay ice lobe 

and the outwash plains of the Cape Cod Bay ice lobe along the 

south and west coast of Martha’s Vineyard and also describes 

the retreat of the Cape Cod Bay ice lobe from the terminal 

moraine on Nantucket. Foster and others (2015) and Baldwin 

and others (2016) presented a suite of geologic maps and interpretations, equivalent to those presented here, that describe the 

stepwise recession of the Cape Cod Bay and Buzzards Bay ice 

lobes from the Martha’s Vineyard end moraine through Vineyard and Nantucket Sounds and Buzzards Bay, respectively. 

They described a sequence of proglacial lacustrine, deltaic, 

and fluvial outwash units that filled basins dammed by icemarginal ridges that were subsequently incised by a meltwater 

drainage network. The interpretations presented here build 

on these descriptions of the retreat of the Buzzards Bay and 

Cape Cod Bay ice lobes from an earlier time at their maximum 

positions (Uchupi and others, 1996; Oldale, 2001; Balco and 

others, 2002; Uchupi and Mulligan, 2006; Balco, 2011).

The shallow stratigraphy of the inner continental shelf 

offshore of Aquinnah on the western side of Martha’s Vineyard is characterized by two topographic highs that extend 

southwest from Gayhead and Squibnocket Point (fig. 12). 

These highs are interpreted to be undifferentiated coastal 

plain and continental shelf deposits of Late Cretaceous(?), 

Tertiary(?), and (or) early Pleistocene(?) age or glacial drift 

of late Pleistocene (pre-Wisconsinan?) age (QTKu?) that are 

draped with till associated with the late Wisconsinan Martha’s 

Vineyard moraine. A valley between the till-covered highs is 

filled with glaciofluvial material that was subsequently incised 

by late Pleistocene to early Holocene groundwater sapping 

or fluvial channels, which were subsequently capped with a 

modern sand body during the Holocene transgression (figs. 12, 

16, and 17).

The Buzzards Bay ice lobe is inferred to have deposited 

an apron of end moraine (Qdm) material that extended from 

Chilmark (Stone and DiGacimo-Cohen, 2009) to Nomans 

Island, which is partially buried by stagnation till, glaciolacustrine, and glaciofluvial deposits along the ablating ice 

front. Glaciofluvial deposits cropping out beyond the extent of 

ice-contact deposits likely represent the confluence of meltwater drainage networks of both the Buzzards Bay ice lobe 

and the Cape Cod Bay ice lobe. The surficial geology of the 

south shore of Martha’s Vineyard between Nomans Island and 

Katama Bay transitions abruptly from ice-contact deposits, 

locally capped with younger units, to a broad, massive sheet of 

outwash material that is locally incised or capped by younger 

units (fig. 15). The ice-contact material associated with the 

Martha’s Vineyard moraine of the Buzzards Bay ice lobe(?) is 

inferred to have been in place before and at a higher elevation than the outwash sediments deposited by the Cape Cod 

Bay lobe. The margin of the Buzzards Bay ice lobe may have 

provided a dam for a proglacial lake on the (present-day) shelf 

that subsequently filled with outwash material from the Cape 

Cod Bay ice lobe (fig. 10). A prominent reflector interpreted to 

be coastal plain and continental shelf deposits of Late Cretaceous(?), Tertiary(?), and (or) early Pleistocene(?) age or glacial drift of late Pleistocene (pre-Wisconsinan?) age (QTKu?) 

may have served to maintain some separation between the 

sediments of the ice-contact deposits from the Buzzards Bay 

ice lobe and the outwash sediments from the Cape Cod Bay 

ice lobe, in a way similar to a lateral moraine. Stratigraphy 

within the glaciofluvial deposits of the Cape Cod Bay ice lobe 

east of Chilmark is largely absent, with the exception of a 

reflector within some glaciofluvial (Qdf) units interpreted to 

be overlapping lobes of outwash (fig. 13).

North of Nantucket, the glacial stratigraphy visible in 

the chirp data is limited to glaciofluvial material that presumably overlies glaciolacustrine sediments in the area to the 

north and east of Tuckernuck Island (Uchupi and Mulligan, 

2006). A topographic high that is interpreted as an ice-contact 

ridge deposit likely associated with late Pleistocene deposits 

of Coskata and (or) Great Point (Oldale, 1982; Oldale and 

Barlow, 1986) was incised and separated from the mainland 

ice-contact unit by postglacial drainage along the eastern side 

of the Nantucket study area (figs. 11 and 12).

Holocene Depositional Setting

Postglacial sediments are relatively thick (less than 10 m) 

in a central valley filled with glaciofluvial sediments on the 

inner continental shelf offshore of Aquinnah on the western 

side of Martha’s Vineyard. The glaciofluvial valley cut into 

Pleistocene end moraine (Qdm) and older units is incised 

by a series of postglacial channels, which are truncated by 

a transgressive sand sheet (Qmn; figs. 12 and 15–17). Elsewhere offshore of Aquinnah, postglacial sediments are largely 

absent and morainal deposits crop out at the sea floor (figs. 16 

and 17). Postglacial sediments are also thick between Squibnocket Point and Nomans Island, where a submerged tombololike sand body has accumulated to greater than 10 m thick and 

rests unconformably on glacial ice-contact deposits. Another 

Holocene sand sheet is partially mapped to the southeast of 

Nomans Island, and two postglacial fluvial channels meander 

offshore on either side of Nomans Island. Holocene marine 

sediments are very thin (typically less than 1 m) and discontinuous east of Squibnocket Point, except where postglacial 

fluvial drainage networks are carved through the outwash to 

the west and east of South Beach. Two postglacial channels 

that are not exposed at the surface just west of South Beach, 

coming out of Edgartown Great Pond, are likely older than 

adjacent and shallower fluvial or estuarine channels and may 

owe their origin to groundwater sapping processes described 

by Uchupi and Oldale (1994). An ebb-tidal delta deposit 
References Cited 31

associated with Muskeget Channel caps another large postglacial fluvial channel and the outwash plain on the eastern edge 

of the Martha’s Vineyard study area.

The study area north of Nantucket is covered by a relatively thick (about 5 m) layer of Holocene muddy sand deposited in the semienclosed basin north of Nantucket (figs. 11, 

12, and 17). Qmn is thinnest along the southwestern edge of 

the survey area, where outwash sediments cropping out on 

Nantucket are covered with less than 2 m of reworked sand 

and gravel derived from the outwash. Underlying the modern 

sediment sheet is another relatively thick (about 5 m) deposit 

of late Pleistocene to early Holocene estuarine sediments (Qfe; 

figs. 11 and 12). A vibracore collected by O’Hara and Oldale 

(1987), just west of Great Point and about 100 m north of 

this study area, penetrated the Qfe unit, which was described 

as a peat deposit with a radiocarbon age of 6,830 ±250 years 

before present at a depth of 20.5 m below sea level.

The interpretations of geologic framework presented here 

indicate that the topography of the glacial terrain has had a 

substantial influence over patterns of deposition and erosion as 

Holocene sea level has risen, but less of an influence than in 

Vineyard and Nantucket Sounds (Baldwin and others, 2016), 

where strong tidal currents maintain an equilibrium topography that preserves much of the glacial terrain. Along the south 

and west coasts of Martha’s Vineyard, oceanographic conditions driven by wave energy rather than tidal currents modify 

the sea floor by winnowing and reworking the glacial surface 

into a gently sloping inner continental shelf. The net effect on 

the sea floor is a smoothing of its irregularities over time, such 

that topographic depressions are filled and highs are eroded. 

Coincident with surface smoothing is the tendency to homogenize surficial sediments wherever sediment can accumulate as 

a result of critical shear stress. The long-term (40-year) mean 

significant wave height offshore of the Martha’s Vineyard 

study site is 1.2 m (Cox and Swail, 2001). The Holocene transgression across this energetic open-ocean coast has created 

a sandy and relatively smooth inner shelf, where fluvial and 

glaciofluvial sediments crop out or are buried beneath a thin 

layer of modern shelf sands or sand waves. In areas where 

ice-contact sediments exist at or near the surface, the sea floor 

is more heterogeneous, such that large boulders and cobbles 

associated with till are left in place and finer sediments are 

reworked around the erratics. The semiprotected area between 

Nomans Island and Squibnocket Point provided accommodation space for a large sand body to accumulate (greater than 

12 m thick) in an area where tidal currents and waves refracting around Nomans Island result in sediment accumulation.

The barrier spit that connects Coskata to Great Point 

formed during the Holocene transgression (Shaler, 1889), 

creating a semienclosed basin north of Nantucket that is similar to the Holocene depositional conditions in Buzzards Bay 

described by Foster and others (2015). Quiescent wave and 

tidal conditions have allowed thick (about 10-m) accumulations of late Pleistocene and early Holocene fluvial, estuarine, 

and modern marine sediments, which bury the glacial surface 

locally to depths greater than 20 m.

Summary

The U.S. Geological Survey, in cooperation with the 

Massachusetts Office of Coastal Zone Management, compiled 

previously published seismic-reflection, bathymetric, acousticbackscatter, and sea-floor sediment sample and photograph 

data to investigate the surficial and shallow subsurface geology offshore of Martha’s Vineyard and north of Nantucket. 

The results are a series of composite geophysical maps with 

nearly full sea-floor coverage and detailed interpretive maps 

of the surficial geology and shallow geologic framework of 

the area. Each of the interpretive maps contributes new insight 

into the geologic framework and sedimentary environments at 

a resolution that was previously impossible because of a lack 

of high-resolution geophysical data. The shallow geologic 

framework and surficial geology are a complex and variable 

distribution of sediments and geomorphic features that can be 

primarily attributed to the advances, occupations, and retreats 

of Wisconsinan glaciation and to reworking and deposition 

during the Holocene transgression. Glacial, marine, and terrestrial processes have acted on this region since the late Pleistocene, resulting in a complex geologic history and a heterogeneous sea-floor character. Glacial sediments within the entire 

region are locally overlain by Holocene fluvial, estuarine, and 

marine sand and mud.

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Stanley, R.S., 1983, Bedrock geologic map of Massachusetts: U.S. Geological Survey Unnumbered Series, 3 sheets, 

scale 1:250,000.
Appendix 1

Appendix 1 37

Appendix 1. Links to Geospatial Data Layers

Geospatial data layers described in this report are available in a companion U.S. Geological Survey data release at 

https://doi.org/10.5066/P9E9EFNE (table 1.1; Pendleton and 

others, 2018). All vector data are delivered as Esri shapefiles 

in the geographic coordinate system, referenced to the World 

Geodetic System of 1984 (WGS 84). Raster representations of 

seismic interpretation interpretations are GeoTIFF formats in 

Universal Transverse Mercator projection, Zone 19N, WGS 84 

datum. All spatial data are distributed with Federal Geographic 

Data Committee-compliant metadata.

Table 1.1. Links to geospatial data layers.

Filename and description Federal Geographic Data

Committee metadata Data and metadata download

Backscatter mosaic:

5-m backscatter mosaic from south and west of Martha’s Vineyard 

and north of Nantucket produced from sidescan-sonar and interferometric backscatter datasets

HTML MV_ACK_backscatter_5m.zip

Regressive unconformity:

Elevation of the late Wisconsinan to early Holocene regressive 

unconformity (Ur) offshore of western and southern Martha’s 

Vineyard and north of Nantucket, Massachusetts

HTML MV_ACK_depth2G.zip

Holocene sediment isopach:

Holocene fluvial and estuarine (Qfe) and nearshore marine (Qmn) 

sediment thickness offshore of western and southern Martha’s 

Vineyard and north of Nantucket, Massachusetts

HTML MV_ACK_postGisopach.zip

Surficial geology:

Interpretation of sea floor geologic units for offshore of western 

and southern Martha’s Vineyard and north of Nantucket, Massachusetts

HTML MV_ACK_surfgeology.zip

Physiographic zones:

Physiographic Zones of the Sea Floor offshore of western and 

southern Martha’s Vineyard and north of Nantucket, Massachusetts

HTML MV_ACK_physiozone.zip

Sediment texture:

Sediment Texture of the Sea Floor offshore of western and southern 

Martha’s Vineyard and north of Nantucket, Massachusetts

HTML MV_ACK_sedtexture.zip

Reference Cited

Pendleton, E.A., Baldwin, W.E., Foster, D.F., Ackerman, S.D., 

Andrews, B.D., Brothers, L.L., and Schwab, W.C., 2018, 

Geospatial data layers of shallow geology, sea-floor texture, 

and physiographic zones from the inner continental shelf 

of Martha’s Vineyard from Aquinnah to Wasque Point, and 

Nantucket from Eel Point to Great Point: U.S. Geological 

Survey data release, https://doi.org/10.5066/P9E9EFNE.

For more information about this report, 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 (508) 457–2200

or visit our website at

https://woodshole.er.usgs.gov

Publishing support provided by the

Pembroke Publishing Service Center
Pendleton and others—Shallow Geology, Sea-Floor Texture, and Physiographic Zones Offshore Martha’s Vineyard and Nantucket, Mass.—OFR 2018–1181

ISSN 2331-1258 (online)

https://doi.org/10.3133/ofr20181181