OCS Study

BOEM 2020-024

US Department of the Interior

Bureau of Ocean Energy Management

Office of Renewable Energy Programs

Developing Protocols for 

Reconstructing Submerged 

Paleocultural Landscapes and 

Identifying Ancient Native American 

Archaeological Sites in Submerged 

Environments: 

Geoarchaeological Modeling
OCS Study

BOEM 2020-024

US Department of the Interior

Bureau of Ocean Energy Management

Office of Renewable Energy Programs

Developing Protocols for 

Reconstructing Submerged 

Paleocultural Landscapes and 

Identifying Ancient Native American 

Archaeological Sites in Submerged 

Environments: 

Geoarchaeological Modeling

March 2020

Authors: David S. Robinson, Carol L. Gibson, Brian J. Caccioppoli, and John W. King

Prepared under BOEM Award M12AC00016

by

The Coastal Mapping Laboratory

Graduate School of Oceanography, University of Rhode Island

215 South Ferry Road

Narragansett, RI 02882
i

DISCLAIMER

Study collaboration and funding were provided by the US Department of the Interior, Bureau of Ocean 

Energy Management, Environmental Studies Program, Washington, DC, under Agreement Number 

M12AC00016 between BOEM and the University of Rhode Island. This report has been technically 

reviewed by BOEM and it has been approved for publication. The views and conclusions contained in 

this document are those of the authors and should not be interpreted as representing the opinions or 

policies of the US Government, nor does mention of trade names or commercial products constitute 

endorsement or recommendation for use.

REPORT AVAILABILITY

To download a PDF file of this report, go to the US Department of the Interior, Bureau of Ocean Energy 

Management Data and Information Systems webpage (http://www.boem.gov/Environmental-StudiesEnvData/), click on the link for the Environmental Studies Program Information System (ESPIS), and 

search on 2020-024. The report is also available at the National Technical Reports Library at 

https://ntrl.ntis.gov/NTRL/.

CITATION

Robinson, DS, Gibson CL, Caccioppoli BJ, King JW. 2020. Developing protocols for reconstructing 

submerged paleocultural landscapes and identifying ancient Native American archaeological sites in 

submerged environments: geoarchaeological modeling. Sterling (VA): US Department of the Interior, 

Bureau of Ocean Energy Management. OCS Study BOEM 2020-024. 175 p.

ABOUT THE COVER

Left image: United States Geological Survey (USGS) stratigraphic framework of the subsurface 

continental shelf off Rhode Island. 

Upper panel shows an idealized stratigraphic section with a simplified description of each stratigraphic 

unit after Needell et al. (1983a). Lower panel shows an excerpt of a seismic reflection profile obtained by 

the project team south of Narragansett Bay and interpreted according to the established stratigraphic 

framework illustrated in the upper panel. (Illustration by Carol Gibson and Brian Caccioppoli.)

Right image: BOEM Marine Archaeologist and Environmental Studies Coordinator, Melanie Damour,

examines quartz chipping debris found at the newly identified “West Beach UW-1” (RI 2719) submerged 

site, Block Island, RI. (Photograph by David Robinson.)
ii

ACKNOWLEDGMENTS

The modeling effort required a large interdisciplinary, multi-cultural team with a wide range of 

knowledge and technical skills. The following individuals and organizations were involved in the initial 

(and subsequent) project workshops, and in the fieldwork, data analyses, and data interpretation that 

together informed the preparation of this modeling report:

• AECOM: Jean Pelletier

• Aroostook Band of Micmacs: Norman Bernard; Fred Corey; and Rick and Tammy Getchell

• Coastal Environments, Inc.: Amanda Evans

• Connecticut State Archaeologist’s Office: Brian Jones

• CR Environmental, Inc.: Christopher Wright

• Eastern Connecticut State University: Bryan Oakley

• Lenape Indian Tribe of Delaware: Dennis Coker

• Mashantucket (Western) Pequot Tribal Nation Historic Preservation Office: Kathleen 

Knowles and Nakai Clearwater Northup

• Massachusetts Board of Underwater Archaeological Resources: Victor Mastone

• Massachusetts Historical Commission: Jonathan Patton

• Mashpee Wampanoag Tribal Historic Preservation Office: Ramona Peters and David Weeden

• Mohegan Tribal Historic Preservation Office: Elaine Thomas

• Narragansett Indian Tribe: Leah Hopkins; Chali Machado; Norman Machado

• Narragansett Indian Tribal Historic Preservation Office: John Brown, IV; Max BrownGarcia; Doug Harris; Muckquashim Hopkins; and Kiowa Spears

• National Oceanic and Atmospheric Administration Coastal Resources Center/Northeast 

Regional Ocean Council: Katie Lund

• National Oceanic and Atmospheric Administration Office of Ocean Exploration and 

Research: Brian Kennedy and Catalina Martinez

• Nipmuc Nation/Project Mishoon: Cheryl Stedtler

• Northeast Underwater Research, Technology and Education Center, University of 

Connecticut: Ivar Babb

• Public Archaeology Laboratory, Inc.: Joseph Waller, Jr.

• Rhode Island Coastal Resource Management Council: Grover Fugate
iii

• Rhode Island Historical Preservation & Heritage Commission: Timothy Ives and Charlotte 

Taylor

• Shinnecock Indian Nation: Chenae Bullock; Arrow Johnson; and Gerrod Smith

• United States Army Corps of Engineers, New England District: Marcos Paiva

• United States Department of the Interior, Bureau of Ocean Energy Management: David 

Ball; Brandi Carrier; Melanie Damour; Jennifer Ewald; William Hoffman; Douglas Jones; Brian 

Jordan; and James Moore

• United States Department of the Interior, United States Geological Survey, Woods Hole 

Coastal and Marine Science Center: William Schwab

• University of Connecticut: Kevin McBride

• University of Maine (Orono): Daniel Belknap

• University of Rhode Island Graduate School of Oceanography, Coastal Mapping 

Laboratory (staff, students, associates, and volunteers): Monique LaFrance-Bartley; Danielle 

Cares; Michael Dalton; Sean Davis; Sierra Davis; Jorgen Dencker; Carol Gibson; Casey Hearn; 

Clifford Heil; Mitchell Kennedy; Taylor Losure; Chali Machado; Norman Machado; Cameron 

Morissette; Robert Pockalny; Neil Redmond; Michael Robinson; Noah Robinson; and Sean 

Scannell

• University of Rhode Island Graduate School of Oceanography, Inner Space Center: Dwight 

Coleman; Alex DeCiccio; Andrea Gringas; and Gail Scowcroft 

• University of Rhode Island Coastal Resource Center/Rhode Island Sea Grant: Jennifer 

McCann

• University of Rhode Island Geosciences Department: Jon Boothroyd; Simon Engelhart

• University of Ulster, School of Geography and Environmental Sciences: Kieran Westley

• Vrije Universiteit Amsterdam: Philip Verhagen

• Wampanoag Tribe of Gay Head (Aquinnah): Elizabeth James Perry; Jonathan Perry; and 

Bettina Washington

• The 2015 and 2016 captains and crews of the University of Rhode Island’s R/V Endeavor

Special thanks to the individuals who provided assistance and logistical support during project 

fieldwork: Alberta and Michael Baccari; Vincent Carlone (Block Island Police Department); Barbara and 

Raymond Chace (Ponaug Marina); John and Robin Cooney; Andrew Gallonio; Maryellen Hall; Anya 

Hansen (University of Rhode Island); Joseph Houlihan (Block Island Ferry); Thomas Jacques; Joseph 

Mangiafico (University of Rhode Island); Kevin McBride (University of Connecticut); Clifford Payne 

(Payne’s Dock); David and Leann Pickering; and Christopher and Gretchen Willis
iv

Contents

List of Figures...............................................................................................................................................vii

List of Tables................................................................................................................................................. x

List of Abbreviations and Acronyms............................................................................................................. xi

Lexicon........................................................................................................................................................xiii

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

1.1 Project Inception............................................................................................................................1

1.2 Document Context and Scope ......................................................................................................1

2 Geoarchaeological Modeling Overview ................................................................................................4

2.1 What is a Geoarchaeological Model? ................................................................................................4

2.1.1 Components of a “Good” Model..................................................................................................4

2.2 Use of Predictive Models for Paleocultural Sensitivity Assessments ...........................................5

2.2.1 Overview of Theoretical Concepts..............................................................................................5

2.2.2 Current Use of Geoarchaeological Models in Submerged Environments ..................................6

2.3 Challenges with Modeling in Submerged Environments ............................................................10

2.4 Key Points ...................................................................................................................................12

3 Development of the Project Modeling Process...................................................................................13

3.1 Best Practices from Project Workshop .......................................................................................13

3.2 Defining the Scope of the Project Model.....................................................................................13

3.3 The Project Modeling Process ....................................................................................................16

4 Application of Modeling Process to Project Study Area, Step 1: Desktop Study ..............................18

4.1 Geographic and Temporal Limits of the Study Area...................................................................18

4.2 Tribal Engagement......................................................................................................................19

4.3 Geologic Context.........................................................................................................................20

4.3.1 Overview .............................................................................................................................20

4.3.2 Development of an Offshore Regional Subsurface Geologic Framework ..........................22

4.3.3 Overview of the Subsurface Stratigraphic Framework of the Southern New England 

Continental Shelf.................................................................................................................................27

4.3.4 Key Points ...........................................................................................................................28

4.4 Sea Level Change History in the Study Area..............................................................................29

4.4.1 Overview .............................................................................................................................29

4.4.2 Implications for Paleolandscape Reconstruction and Predictive Modeling in the Project 

Area 30

4.4.3 Key Points ...........................................................................................................................31

4.5 Paleocultural Context ..................................................................................................................31

4.6 Previous Modeling in the Project Area........................................................................................33
v

5 Application of Modeling Process to the Project Study Area, Step 2: Developing and Assessing 

Paleoshoreline Models................................................................................................................................35

5.1 Introduction and Goals ................................................................................................................35

5.2 Relative Sea Level Change Models for Southern New England ................................................35

5.3 Paleoshoreline Reconstructions for the Project Study Area .......................................................37

5.4 Results ........................................................................................................................................38

5.5 Implications for Predictive Modeling ...........................................................................................39

5.5 Recommendations ......................................................................................................................45

5.5 Key Points ...................................................................................................................................47

6 Application of Modeling Process to Project Study Area, Step 3: Developing a Regional Stratigraphic 

Model...........................................................................................................................................................47

6.1 Introduction and Goals ................................................................................................................47

6.2 Field Methodology and Data Processing for Model Dataset.......................................................49

6.2.1 USGS Legacy Study: Rhode Island Sound ..............................................................................49

6.2.2 Project Follow-Up Study: EN580 Cruise .............................................................................49

6.3 Results .............................................................................................................................................50

6.3.1 USGS Legacy Data...................................................................................................................50

6.3.2 Project Data—EN580 Survey ...................................................................................................55

6.4 Discussion: Assessment of Legacy Data....................................................................................57

6.4.1 Equipment Resolution and Technical Quality .....................................................................57

6.4.2 Geological Interpretations.........................................................................................................59

6.5. Regional Stratigraphic Model......................................................................................................61

6.6 Key Points ...................................................................................................................................67

7 Application of Modeling Process to Project Study Area, Step IV: Model Testing Through Local Case 

Study Analyses ...........................................................................................................................................68

7.1 Greenwich Bay Area ...................................................................................................................69

7.1.1 Introduction and Goals ........................................................................................................69

7.1.2 Cedar Tree Beach Archaeological Investigation.................................................................71

7.1.3 Greenwich Bay Geological Investigation ............................................................................83

7.1.4 Gorton Pond Paleoenvironmental Investigation................................................................102

7.1.5 Implications for Predictive Modeling..................................................................................107

7.1.6 Key Points .........................................................................................................................109

7.2 Block Island: West Beach .........................................................................................................109

7.2.1 Introduction and Goals ......................................................................................................109

7.2.2 Field Methodology.............................................................................................................114

7.2.3 Results ..............................................................................................................................114

7.2.4 Implications for Predictive Modeling..................................................................................124
vi

7.3 The Mud Hole............................................................................................................................124

7.3.1 Introduction and Goals ......................................................................................................124

7.3.2 Field Methodology.............................................................................................................127

7.3.3 Results ..............................................................................................................................129

7.3.4 Implications for Predictive Modeling..................................................................................135

7.3.5 Key Points .........................................................................................................................137

7.4 The AMI.....................................................................................................................................138

7.4.1 Introduction and Goals ......................................................................................................138

7.4.2 Field Methodology.............................................................................................................140

7.4.3 Results ..............................................................................................................................140

7.4.4 Implications for Predictive Modeling..................................................................................143

8 Conclusions.......................................................................................................................................143

References................................................................................................................................................146

Appendix A: Pre-contact Cultural Chronology for Project Study Area......................................................165
vii

List of Figures

Figure 3-1. Flow chart showing the relationship between the models developed for this report................17

Figure 4-1. Location of case study areas selected for model assessment and testing. .............................19

Figure 4-2. USGS seismic reflection profile tracklines surveyed between 1975 and 1981. .......................23

Figure 4-3. Vibracores obtained in the vicinity of the USGS seismic reflection data..................................24

Figure 4-4. USGS stratigraphic framework of the subsurface continental shelf off Rhode Island..............28

Figure 5-1. Paleoshoreline reconstructions for 3,000 yBP in the study area..............................................40

Figure 5-2. Paleoshoreline reconstructions for 6,000 yBP in the study area..............................................41

Figure 5-3. Paleoshoreline reconstructions for 8,000 yBP in the study area..............................................42

Figure 5-4. Paleoshoreline reconstructions for 10,000 yBP in the study area............................................43

Figure 5-5. Paleoshoreline reconstructions for 11,000 yBP in the study area............................................44

Figure 5-6. Comparison of a digital elevation model of the contemporary seafloor of Buzzards Bay, 

Massachusetts, (upper panel) with the elevation of the eroded surface of Pleistocene glacial drift in the 

same area produced by "backstripping" (lower panel). ..............................................................................46

Figure 6-1. Seismic reflection tracklines from 1980 USGS legacy dataset (black) and 2016 EN580 followup cruise (red). ............................................................................................................................................48

Figure 6-2. Surficial geology of western Rhode Island Sound from Needell et al. (1983a),.......................51

developed from geophysical survey data....................................................................................................51

Figure 6-3. Depth below sea level to deepest acoustic reflector compiled from seismic ...........................52

reflection profiles, from Needell et al. (1983a). ...........................................................................................52

Figure 6-4. Depth below sea level to the post-glacial unconformity (fu1) compiled from seismic reflection 

profiles, from Needell et al. (1983a)............................................................................................................53

Figure 6-5. Interpreted seismic reflection profiles from research cruise EN-580........................................56

Figure 6-6. Seismic reflection survey tracklines in Block Island Sound......................................................58

Figure 6-7. Comparison of seismic reflection profile resolution..................................................................59

Figure 7-1. Location of study locations within the Greenwich Bay area. ....................................................68

Figure 7-2. Seismic reflection profile obtained in the Cedar Tree Beach area prior to the initiation of the 

Submerged Paleocultural Landscapes Project...........................................................................................70

Figure 7-3. Plots of contoured magnetic data from the 2013 Greenwich Bay (Cedar Tree Beach) 

gradiometer survey. ....................................................................................................................................75

....................................................................................................................................................................76

Figure 7-4. Example of plotted 2013 VSP survey data acquired at 20-m spaced probe points distributed 

along “Transect B” in the Greenwich Bay (Cedar Tree Beach) geoarchaeological study area..................76

Figure 7-5. Excerpted processed VSP data documenting the desiccated and cracked organic sediments 

comprising the formerly subaerial paleolandsurface stratum encountered at the location of Cedar Tree 

Beach “Selective Probe S2” approximately 1.25 m below the bay floor’s surface. ....................................77

....................................................................................................................................................................78

Figure 7-6. Distribution of systematic (20-m grid) and selective VSP probe point locations within the 

Greenwich Bay (Cedar Tree Beach) geoarchaeological study area...........................................................78

....................................................................................................................................................................79
viii

Figure 7-7. Visual features of interest (inset images) at Selective VSP Probe Point S2 and Systematic 

VSP Probe Point B17, which were subsequently examined through underwater archaeological excavation 

of 1 x 1 m DTUs at both locations...............................................................................................................79

Figure 7-8. Quartz chipping debris recovered during the underwater excavation of Greenwich Bay (Cedar 

Tree Beach) Selective VSP Probe Point Dredge Test Unit S2...................................................................80

Figure 7-9. Plant macrofossils (left column images) recovered during the underwater archaeological 

excavation of Greenwich Bay (Cedar Tree Beach) Selective VSP Probe Point Dredge Test Unit S2.......82

Figure 7-10. Tree macrofossils (left column images) recovered during the underwater archaeological 

excavation of Greenwich Bay (Cedar Tree Beach) Selective VSP Probe Point Dredge Test Unit S2.......82

Figure 7-11. Overview map of the Cedar Tree Beach study area (top panel) and Greenwich Bay (bottom 

panel). .........................................................................................................................................................83

Figure 7-12. Seismic reflection survey lines from the Cedar Tree Beach study area and the locations of 

collected vibracores. ...................................................................................................................................86

Figure 7-13. Example CHIRP seismic reflection profile from Greenwich Bay............................................87

Figure 7-14. Processed seismic reflection line C-C’, with interpreted seismic reflectors and correlated with 

seismic reflection line 2 from Morissette (2013)..........................................................................................88

Figure 7-15. Seismic reflection line B-B’ with W-E vibracore transect........................................................88

Figure 7-16. Physical properties and initial core descriptions of vibracore CTB VC-10_1. ........................90

Figure 7-17. Physical properties and initial core descriptions of vibracore CTB VC-10_2. ........................91

Figure 7-18. Physical properties and initial core descriptions of vibracore CTB VC-14. ............................92

Figure 7-19. Physical properties and initial core descriptions of vibracore CTB VC-9. ..............................93

Figure 7-20. Physical properties and initial core descriptions of vibracore CTB VC-6. ..............................94

Figure 7-21. Physical properties and initial core descriptions of vibracore CTB VC-5. ..............................95

Figure 7-22. Physical properties and initial core descriptions of vibracore CTB VC-4. ..............................96

Figure 7-23. Comparison of an age model for Greenwich Bay (A) and relative sea level curves for 

southern New England (B, C). ....................................................................................................................99

Figure 7-24. Visualizations of interpolated depths to reflector fu1 (post-glacial fluvial unconformity) using 

seismic reflection profiles obtained at three trackline spacings................................................................101

Figure 7-25. Location of Gorton Pond cores.............................................................................................102

Figure 7-26. Summary pollen diagram for Gorton Pond...........................................................................104

Figure 7-27. Core log from Gorton Pond Livingston core 15-1.................................................................106

Figure 7-28. Lake level reconstruction for Sluice Pond, Massachusetts. .................................................107

Figure 7-29. Block Island (West Beach) geoarchaeological study area locations....................................110

Figure 7-30. Map showing the location of Block Island (circled in red) relative to regional moraine 

locations across southern New England...................................................................................................111

Figure 7-31. Representative stratigraphic sediment profile of the upland sections in the Block Island (West 

Beach) study area (Sirkin 1996). ..............................................................................................................112

Figure 7-32. Northernmost intertidal peat deposit with tree stumps in original growth positions within the 

Block Island (West Beach) Study Area.....................................................................................................115

Figure 7-33. Representative profile of the eroded and exposed profile of the coastal wetland and upland 

topography onshore in the Block Island (West Beach) Study Area..........................................................115
ix

Figure 7-34. Quartz chipping debris constituting the West Beach UW-1 Site (RI 2719) discovered 

embedded in subtidal, exposed, and stratified organic paleosols in the Block Island (West Beach) study 

area. ..........................................................................................................................................................117

Figure 7-35. Exposed and preserved submerged stratigraphy within the Block Island (West Beach) Study 

Area in the vicinity of the West Beach UW 2 Site (RI 2720).....................................................................118

Figure 7-36. Archaeological diver examining extensive subtidal area of preserved and exposed tree 

stumps and root mat visible embedded in the exposed surface of paleosols present in the vicinity of the 

West Beach UW-2 Site (RI 2720). ............................................................................................................120

Figure 7-37. Charred wood (top image), burnt ground surface (middle image), and quartz chipping debris 

(bottom image) comprising the identified elements of the subtidal West Beach UW-2 Site (RI 2720).....121

Figure 7-38. Location of sediment cores obtained at Wash Pond, Block Island, Rhode Island...............122

Figure 7-39. Bathymetry and side-scan sonar mosaic from West Beach study area, Block Island, Rhode 

Island.........................................................................................................................................................123

Figure 7-40. Illustrations of the Mud Hole study area. ..............................................................................125

Figure 7-41. Coverage map of high-resolution geophysical data collected by the URI Graduate School of 

Oceanography in August 2012. ................................................................................................................128

Figure 7-42. Map showing the locations of vibracores collected by the R/V Endeavor (cruise EN-565) from 

the Mud Hole study area...........................................................................................................................129

Figure 7-43. Characterization of backscatter intensity from side-scan imagery.......................................130

Figure 7-44. Mapped spatial extents of sedimentary features identified in side-scan imagery................131

Figure 7-45. Processed seismic reflection line 8, with interpreted seismic reflectors...............................134

Figure 7-46. Processed seismic reflection line 18, with interpreted seismic reflectors.............................134

Figure 7-47. Vibracore VC-15 location and depth plotted against seismic reflection line 18. ..................135

Figure 7-48. Location of the Area of Mutual Interest (AMI) study area.....................................................139

Figure 7-49. Channel feature from the AMI CHIRP seismic reflection data. ............................................141

Figure 7-50. Glaciolacustrine sediment from the AMI CHIRP seismic reflection data..............................142
x

List of Tables

Table 5-1. Comparison of relative sea level models for southern New England used for paleoshoreline 

reconstructions in the project study area. ...................................................................................................38

Table 6-1. Subsurface stratigraphic framework for the continental shelf south of Narragansett Bay, as 

described by Needell et al33. (1983a, b, c). ...............................................................................................54

Table 6-2. Regional subsurface stratigraphic model for the study area. ....................................................63

Table 7-1. Water depths of Gorton Pond Cores. ......................................................................................103

Table 7-2. Datums used for Gorton Pond age model...............................................................................105

Table 7-3. Sea level rise models for the study area. ................................................................................136
xi

List of Abbreviations and Acronyms

APE area of potential effect

AMI Area of Mutual Interest

AMS accelerator mass spectrometry

BITS Block Island Transmission System

BIWF Block Island Wind Farm

BOEM Bureau of Ocean Energy Management

BP before present

ca. circa

CHIRP compressed high intensity radiated pulse

cm centimeter(s)

CML Coastal Mapping Laboratory

CPT cone penetration tests

CRMC Coastal Resource Management Council

CTB Cedar Tree Beach

DOI Department of the Interior

DTU dredge test units

ESPIS Environmental Studies Program Information System

ESRI Environmental Systems Research Institute, Inc

ft foot/feet

fu1, fu2 post-glacial fluvial unconformity

GIS geographic information system

GNSS Global Navigation Satellite System

GRAPE Gamma Ray Attenuation and Porosity Evaluator

in inch(es)

km kilometer(s)

kyBP thousands of years before present

Ku coastal plain and continental shelf sediments

LGM Last Glacial Maximum

lb pound(s)

m meter(s)

mm millimeter(s)

mu marine unconformity

MGSL Marine Geological Samples Laboratory

mm millimeter(s)

MSL mean sea level

NEPA National Environmental Policy Act

NHPA National Historic Preservation Act

NIT Narrangansett Indian Tribe

NITHPO Narragansett Indian Tribal Historic Preservation Office

nT nanoTesla

ROV remotely operated vehicle

RSL relative sea level

OCS Outer Continental Shelf

OSV ocean survey vessel

Qdm glacial end moraine deposits

Qdo glacial drift deposits

Qfe post-glacial fluvial and estuarine sediments
xii

Qpt marine sediments

Pzz pre-Mesozoic bedrock

RIHPHC Rhode Island Historical Preservation & Heritage Commission

RI OSAMP Rhode Island Ocean Special Area Management Plan

s second(s)

TIN Triangular Irregular Network

URI-GSO University of Rhode Island-Graduate School of Oceanography

USACE US Army Corps of Engineers

USGS United States Geological Survey

UTM Universal Transverse Mercator

VSP visual sediment probe

yBP year(s) before present

yr year(s)
xiii

Lexicon

Some of the most common terms associated with submerged cultural sensitivity assessments have 

multiple meanings that can create significant confusion between research partners from diverse 

backgrounds. This lexicon clarifies the usage of these terms in this report.

Archaeological Site: A geographic area where physical remains (i.e., features and artifacts) 

correlating to past human activity are present.

Paleo: A prefix meaning ancient. Frequently used to refer to the geological past. For example, 

“paleoclimate” literally means “ancient climate.” “Paleo” is a general term that does not imply a 

particular time period in the past. The prefix “paleo” should never be confused with, or used 

interchangeably with the term “prehistoric,” which is offensive to Tribal communities, because it 

implies to them that their ancestral culture does not have a history.

Paleoenvironment: Ancient environment, describing the ecological and climatic characteristics 

of the ancient land surface. For example, an ancient land surface may be characterized by lakes 

and rivers, with vegetation indicative of cold climates. Note that this term refers to the natural 

environment only, without any implication regarding the cultural use or importance of the 

environment.

Paleotopography: Ancient topography, describing the physical configuration of the ancient land 

surface, frequently with respect to elevation. Note that this term refers to the natural 

environment only, without any implication regarding the cultural use or importance of a 

geographic area.

Paleolandscape: The combination of the paleotopography and paleoenvironment of a 

geographic area, including the landforms of a region in the aggregate. A portion of territory that 

could have been viewed at one time from one place. Using the term “paleolandscape” should 

imply a comprehensive understanding of the natural environment in a geographic area. Note 

that this term refers only to the physical characteristics of an area, not to the cultural use or 

importance of the area.

Paleolandscape Fragment: A landform or portion of a landform that was part of a 

paleolandscape. For example, a paleochannel is a paleolandscape fragment. It represents only 

a portion of a more complex landscape that may have been dominated by rivers, but also 

consisted of marshes, uplands, and other sub-environments.

Paleocultural Landscape: An ancient landscape that was inhabited or modified by 

humans, and/or a landscape that is perceived by contemporary Tribal communities as having 

cultural importance to them since ancient times.

Paleocultural Sensitivity: The potential for paleocultural sites to be present within a given 

geographic area. 

Paleocultural Sensitivity Assessment: An assessment in which cultural and environmental 

variables are examined to determine the potential for paleocultural sites to be present within a 

given geographic area.
xiv

Paleocultural Site: A site with evidence of ancient cultural activity or importance. 

Paleocultural Site Identification Survey: A geoarchaeological survey done to identify 

paleocultural sites within a given geographic area.

Reconstruction: A representation of something that no longer exists or cannot be viewed 

directly based on scientific and cultural data obtained through evidence-based geoscientific, 

archaeological, and ethnographic research. The focus of reconstructions can be geographically, 

chronologically, and culturally narrow or broad according to the types of data available and the 

needs and goals of the project.

Study, Survey, or Project Area: The geographic location that is being investigated, and where 

activities such as geophysical surveying or archaeological identification or investigation 

activities take place. These locations should not be called “sites” unless physical remains 

associated with past human history are present.
xv

“Unless reliable paleoenvironmental reconstructions can be generated, it is clear that we 

must proceed with caution.”

(Kvamme 2006)
1

1 Introduction

1.1 Project Inception

The Outer Continental Shelf (OCS) of the United States is increasingly becoming the focus of renewable,

oil, and gas development to meet the nation’s energy objectives. Consideration of the effects this 

development may have on submerged Tribal historic properties is a legislatively mandated responsibility 

for Federal agencies, including the United States Department of the Interior’s (DOI) Bureau of Ocean 

Energy Management (BOEM), which reviews and permits these undertakings. It is also a significant 

concern for individual States, Tribal Historic Preservation Offices (THPOs), other regulatory agencies, 

stakeholders, and researchers that participate in the environmental review process for offshore 

development projects. During BOEM’s 2011 Atlantic Wind Energy Workshop, participants identified the 

development of geospatial databases of known submerged Tribal cultural sites, and the development of 

standardized methodologies for identifying them, as critical data needs (Cahill et al. 2011).

In response to these needs, the Coastal Mapping Laboratory (CML) at the University of Rhode Island’s 

Graduate School of Oceanography (URI-GSO) and its research partners, the Rhode Island Coastal 

Resource Management Council (CRMC) and the Narragansett Indian Tribal Historic Preservation Office 

(NITHPO), submitted a joint proposal to BOEM in 2012 entitled, “Developing Protocols for 

Reconstructing Submerged Paleocultural Landscapes and Identifying Ancient Native American 

Archaeological Sites in Submerged Environments” (hereafter, “the project”). This proposal led to a 

cooperative agreement between URI and BOEM, with CRMC and NITHPO as research partners, to 

conduct a five-year study consisting of multidisciplinary investigations of five nearshore and offshore 

areas in Rhode Island waters. The overall goals of the project were to refine and enhance the following:

• The current understanding of submerged paleocultural landscape distribution on the Rhode Island 

OCS, especially landscapes of Tribal significance

• The identification of paleocultural landscapes of importance to southeastern New England Tribes

These goals were to be met through the development and testing of “best practices” for five interrelated 

processes that are considered essential for assessing cultural sensitivity of submerged environments and 

identifying submerged Tribal cultural sites: 1) paleoenvironmental reconstruction; 2) paleolandscape 

reconstruction; 3) Tribal engagement; 4) geoarchaeological modeling; and 5) model testing/submerged 

sites identification survey. This document focuses on the geoarchaeological modeling component of the 

project.

1.2 Document Context and Scope

Geoarchaeological modeling is based on the generally accepted theories that there is an association

between past human activities and different types of paleolandforms and paleoenvironments, which 

results in a material culture expression sometimes preserved within the present landscape in a predictable 

manner. This association has been used with some success in terrestrial contexts onshore to develop 

models that predict where cultural materials may be located (Kvamme 2006; Verhagen and Whitley 

2012). One of the objectives of the project was to examine whether geoarchaeological modeling could be 

applied effectively in the submerged environment to assist in making informed cultural resource 

management decisions for the OCS.
2

Initially, BOEM's scope for the project included the development of a predictive model for the Rhode 

Island OCS based on information compiled from a three-day workshop convened at the start of the project

(CML, URI-GSO 2015). The workshop was designed to foster and support initiation of an open and 

respectful exchange of information, ideas, and values between representatives from the Tribal, agency, 

and research communities within a collaborative research partnership framework. Subject-specific 

presentations and discussion sessions for the workshop's first day included these topics: the project's 

legislative framework and BOEM’s current survey guidelines, Tribal values and information, and current 

knowledge of impacts of sea level rise and marine transgression. Current methods for performing 

submerged paleolandscape reconstruction, predictive modeling, site identification, and excavation were 

also discussed. The second day of the workshop consisted of topical discussions intended to provide the 

necessary information for developing best practices for undertaking submerged paleolandscape 

reconstructions, predictive modeling of site locations, integrating Tribal oral histories into predictive 

models, identifying and reconstructing submerged paleolandscapes, and identifying and excavating sites. 

The third and last day of the workshop consisted of a private meeting and workshop debriefing for Tribal 

members, followed by a final open-forum discussion between the Tribes, BOEM, and URI project 

participants.

Although the workshop was an excellent venue for individuals from diverse backgrounds to interact and 

share information, it revealed significant gaps in the available geoarchaeological data and accessible 

Tribal oral tradition information considered necessary for completing the project’s modeling effort. It also 

revealed that developing a standardized methodology for modeling was a more complex and challenging

task than originally anticipated. Additionally, the workshop clarified that mutually beneficial and 

culturally sensitive relationships between the diverse groups engaged in the project needed further 

development before effective collaboration could take place. These challenges could not be fully 

addressed within a three-day workshop format.

In response to the results of the workshop, the project's modeling process was altered, and organized into 

the following six sequential steps:

1. Conduct a thorough literature review to understand the current state of knowledge regarding the 

use of archaeological predictive models in submerged environments

2. Conduct a detailed desktop study to synthesize the current state of geoarchaeological knowledge 

in the study area into geospatial format

3. Develop a modeling process that can be applied to any geographic area to assist with locating and 

characterizing preserved paleocultural landscapes

4. Develop regional sea level change and stratigraphic models to assist with locating and 

characterizing preserved paleolandscapes or paleolandscape fragments on the Rhode Island OCS

5. Apply the modeling process and model (developed in steps 3 and 4 above) to the project study 

area by conducting geoarchaeological investigations in five diverse case study areas

6. Develop recommendations about the use of predictive models in submerged environments, 

specifically with respect to identifying paleocultural landscapes of Tribal significance

This document presents the results of the tasks outlined above. Section 1 provides the context for the 

project's modeling task, and Section 2 provides a synthesis of the key geoarchaeological modeling 
3

concepts that are necessary to understand the potential applicability of terrestrial modeling to the 

submerged environments. Section 3 presents a process for submerged study area characterization that can 

be applied to a variety of geographic areas and used when diverse types, amounts, and resolution of data 

are available. Section 4 compiles the results of a comprehensive desktop study that was conducted in the 

project area as the basis for the modeling tasks in this report. Sections 5 and 6 present two regional 

models for the study area based on the data obtained through the desktop study. Section 7 summarizes the 

results of archaeological and/or geological investigations of five case study areas in Rhode Island waters 

and discusses the implications of these studies for geoarchaeological modeling of submerged 

environments. Finally, Section 8 identifies conclusions and recommended next steps to further refine the 

concepts presented in this report.
4

2 Geoarchaeological Modeling Overview

2.1 What is a Geoarchaeological Model?

The term “model” is used within a scientific research context to describe a wide variety of procedures and 

outcomes that vary significantly according to research subject and application. In this document, the term 

model is defined as an object, illustration, or process that helps to visualize or predict something, or to test 

a hypothesis. A model can be outcome-based, meaning that it is a digital or physical representation of 

something created for visualization purposes, or it can be process-based, meaning that it consists of a 

framework of steps and actions that can be applied to various datasets to test a hypothesis. For example, a 

representation of a planned building created by a 3D printer is an output-based model. As long as the user 

is comfortable with the technical specifications of the printer, the focus of the model is not the process 

that creates it, but the object that the printer produces. In contrast, a flowchart of geoprocessing steps 

necessary to identify the association between soil types and land use in a geographic area is a processbased model. The flowchart provides a structured framework of repeatable, interconnected steps. The 

resulting map, or output, of this type of model is important, but the framework used to create the map is 

considered to be the model, because it can be applied to a variety of different datasets to test diverse 

hypotheses. Data used in modeling can be quantitative or qualitative. Use of one over the other is 

dependent upon the amount and types of data that is available, and the purpose and goals for developing a 

model.

In archaeological research, a model is a conceptual tool that is used to assess and characterize 

“archaeological sensitivity”—that is, the relative probability of encountering an archaeological site within 

a given area. The outcome of these models, whether created from qualitative/phenomenological data or as 

a result of the processing of quantitative data using multivariate statistical analyses, are most often 

archaeological sensitivity maps that illustrate the horizontal extent of differentially defined sensitivities 

usually categorized into three zones: “high sensitivity,” where archaeological sites are most likely;

“medium sensitivity” where sites are less likely; and “low sensitivity” where sites are unlikely. In 

practice, these maps are then used for a variety of purposes that include the planning of different types, 

resolutions, and extents of archaeological investigations and land-use planning and management (e.g., 

inventorying site types, site locations, and environmental characteristic of particular area and identifying 

gaps in those data, determining the historical significance and best use of an area, protecting and reducing 

natural and anthropogenic impacts to an area, etc.). Current environmental attributes are those most often 

correlated with archaeological site location data to model archaeological sensitivity. These environmental 

attribute data are often readily available in geospatial formats for use in digital archaeological modeling 

research. In the case of geoarchaeological modeling, environmental attributes that are considered also 

include those related to geology, geomorphology, and geochronology.  

The inherent ambiguity of the term “model” requires that, in all cases, the type of model being produced, 

the processes used to create it, and the outcomes and products that are expected from it need to be 

clearly described and defined, as well as reproducible and testable. This type of clarification is not merely 

a matter of semantics, but is necessary for understanding and establishing the data requirements, goals, 

methods, workflow, and outcomes of a model.

2.1.1 Components of a “Good” Model

The accuracy with which an archaeological model predicts or characterizes a given phenomenon when 

tested through field investigation and data acquisition is a function of its performance or validity. By 

comparing model predictions against identified archaeological site locations, it is possible to determine, 
5

with specifiable confidence, how accurately a model performs. It is, in fact, this very approach that 

imparts confidence in a model and allows it to be used as a predictive tool. Iterative validation, 

evaluation, and field testing of a model are essential to demonstrating and improving the model’s 

performance. Validation, or consistency testing, involves identifying any conceptual and factual errors 

that might have been incorporated into the model, such as errors in underlying theories, or unreliability 

and bias in the environmental and archaeological datasets. Evaluation, or performance testing, involves 

comparing model outcomes with existing archaeological knowledge and data and is generally 

accomplished using statistical methods. Finally, field investigation is essential to test and, if necessary, 

refine the original theories underlying the model (CML, URI-GSO 2015; Verhagen 2008; Verhagen and 

Whitley 2012). Additional elements of a “good” model or good modeling practice include the following:

• Transparency and reproducibility, resulting from clearly specified model-building steps

• Applicability to future situations

• The ability to be optimized to the available data set, allowing the best possible prediction based 

on available information

• The ability to specify uncertainties inherent in sensitivity predictions

• The ability to provide an explanatory framework to support why sensitivities are assigned as 

“low,” “medium,” or “high” (CML, URI-GSO 2015; Verhagen 2008; Verhagen and Whitley 

2012)

2.2 Use of Predictive Models for Paleocultural Sensitivity Assessments

2.2.1 Overview of Theoretical Concepts

Although a comprehensive description of the theoretical aspects of predictive modeling in archaeological 

research is beyond the scope and purpose of this document (see Judge and Sebastian 1988), a discussion 

of basic theoretical concepts underlying the approach to assessing paleocultural sensitivity within the 

project’s study areas is necessary. Predictive modeling’s theoretical roots are traceable to the “New” or 

“Processual Archaeology” of the late 1960s, and the application of scientifically based statistical models 

for the prediction of site density based on the relationship between the characteristics of the natural 

environment with the location of human settlement, which were only ever applied to terrestrial 

archaeological contexts (Judge and Sebastian 1988; Verhagen and Whitley 2012). The general underlying 

theoretical basis for archaeological predictive modeling is that: 1) past human behavior is patterned with 

respect to natural and cultural/social environments; 2) we can learn something about ancient humans and 

past human behavior and their interactions with these environments by observing and recording the 

relationships between ancient human material residues (i.e., the archaeological record) and these natural 

and cultural/social environmental features; and 3) we can predict where sites may and may not be located 

based on these relationships and their observed patterning.

By the 1980s, and continuing up to the present, predictive modeling approaches had bifurcated into two 

primary lines of research, consisting of either a largely theoretical series of models based on the use of 

eco-systemic structures and relationships to identify spatial suitability, or a series of models based on 

extrapolating environmental variables from the landscape in a quantitative fashion, from which 

correlative statistical summaries could be built and applied to areas not yet surveyed (Verhagen and 

Whitley 2012).
6

The latter of these two approaches involving statistical extrapolation methods is often referred to as an 

“inductive,” “correlative,” or “data-driven” modeling approach. It compares known site data, usually 

acquired in a controlled survey area with “environmental” data sets, such as distance to water, soil type,

slope, etc., and then extrapolates the correlations found to areas where no site information exists, usually 

by means of logistic regression. The role of archaeological theory on site location preference is very 

limited in these inductive models, with little or no attention paid to ideas on how people may have used 

and perceived the landscape in the past.

In contrast to the inductive modeling approach, “deductive,” “explanatory,” or “theory driven” 

approaches to modeling use archaeological site information to look for correlations for hypothesis testing 

purposes. Hypotheses of settlement location preferences are the basis for these models, which are created 

using relatively simple GIS-based analysis tools, such as weighted overlays. These models were mainly 

used in locations without much site information. Often, they are relatively unsophisticated models, to the 

point of being “intuitive” or “expert judgment” models based on phenomenology. Phenomenology is a 

qualitative research method that involves the direct investigation and description of the perceptions, 

perspectives, and understandings people have based on their experiences with a phenomenon of interest. 

By studying the perspectives of multiple participants, a researcher can begin to make generalizations 

regarding the phenomenon of interest from the perspective of those that have lived the experience. In this 

case, the phenomenon experienced has been the identification of submerged paleocultural landscapes and 

archaeological deposits within them. Virtually all of the archaeological modeling that has been done to 

date for the submerged environment may be described as phenomenological in nature. 

Unfortunately, a dichotomy has arisen in the objectives of using predictive modeling in archaeology. On 

one hand, usually in the context of cultural resource management work, predictive models are employed 

as tools for minimizing field effort, rather than as explanatory research tools for understanding patterns in 

the spatial distribution of archaeological sites (Verhagen and Whitley 2012). Oftentimes, the primary 

intention of the application of predictive modeling is to enhance the cost-effectiveness of the research 

being done, rather than the investigation and explanation of spatial patterning of archaeological sites. 

These types of applications tend to be overly simplistic, ineffective, and ultimately not particularly useful 

for any audience. On the other hand, predictive modeling applications in academic research are often 

explanatory and useful, but only to a small group of scholars, and their complexity makes them 

impractical for environmental management. 

Regardless of the type or degree of sophistication of the modeling that is developed and applied in a 

particular instance, clarity of what is being modeled is essential: a “systemic context” (the living 

behavioral state of past human groups or societies) or an “archaeological context” (the static, 

nonbehavioral state of archaeological materials comprising the physical record of archaeological study)

(Kvamme 2006:13). From a cultural resource management standpoint, the goal seems to be the modeling 

of the latter. In approaching this goal, it is equally important to model and map where archaeological sites 

are unlikely to occur as it is to model and map where they are likely to exist. 

2.2.2 Current Use of Geoarchaeological Models in Submerged Environments

At the time of their publication, BOEM’s Office of Renewable Energy Programs’ 2017 revised version of 

their “Guidelines for Providing Archaeological and Historic Property Information Pursuant to 30 CFR 

Part 585” represented the most current guidance and recommendations from a Federal agency regarding 

the use of geoarchaeological models in submerged environments. The purpose of these guidelines was to 

provide offshore renewable energy developers and their marine archaeological consultants with 

recommended methods for characterizing and identifying pre-contact period historic properties that could 

be affected by proposed offshore renewable energy development activities reviewed and permitted by 

BOEM. These pre-contact historic properties would be Native American cultural sites and archaeological 
7

deposits that dated from the time prior to European contact and were once part of a terrestrial landscape 

inundated by global sea level rise during the Late Pleistocene and Holocene and eligible for or listed in 

the National Register of Historic Places. The BOEM Guidelines were not intended as a one-size-fits-all 

methodology, but, instead, as a foundational framework for designing historic property identification 

surveys for specific areas and activities that would provide sufficient information for BOEM to fulfill its 

National Historic Preservation Act (NHPA) and National Environmental Policy Act (NEPA) review 

responsibilities. The 2017 BOEM Guidelines remain (as of 2019) the current and most widely utilized 

standard methods for geoarchaeological modeling in U.S. waters, in large part because most of the marine 

geoarchaeological work currently being performed there is associated with BOEM-reviewed offshore 

energy development activities. 

BOEM’s current geoarchaeological modeling guidelines adopt ideas and methods that have been 

developed during the course and as a result of this study, as well as those of the applied and academic 

research conducted since the 1970s to inform archaeological sensitivity assessment and submerged 

paleocultural site identification in the U.S. and abroad (e.g., Benjamin 2010; Benjamin et al. 2011; CEI 

1977; Dunbar et al. 1992; Edwards and Merrill 1977; Evans 2016; Faught 1996, 2004, 2014; Fischer 

1987, 1995; Fischer and Sørensen 1983; Flatman and Evans 2014; Flemming 2004; Gaffney et al. 2007; 

Gagliano 1974, 1977, 1983; Gagliano et al. 1982; Garrison et al. 2012; Gifford 1983, 1990; ICA 1979; 

Johnson and Stright 1992; Kelley et al. 2012; Pearson et al. 1986, 1989; Pedersen et al. 1997; Van Andel 

and Llanos 1984; Westley et al. 2011). However, it is primarily during the past two decades and 

especially over the last 10 years that focused interest in submerged paelocultural landscapes archaeology 

has grown and led to new research and fieldwork seeking to address current methodological, modeling, 

and theoretical questions in the discipline. Much of this more recent work has been driven in response to 

the anticipated impacts to the sea floor from current and planned expansion of conventional and 

renewable offshore energy infrastructure, as well as the expanded offshore sand and gravel resource 

extraction that is increasingly needed for shoreline stabilization due to a recent acceleration in the rise of 

global sea level. Greater recognition of the potential presence of previously unidentified submerged precontact period archaeological sites that could be impacted by the planned increases in federally permitted 

offshore activities has created an increasingly urgent need for better geoarchaeological maps and models 

for threatened areas of the sea floor—usable tools for identifying and characterizing paleocultural 

landscapes and the archaeological sites present within them—based on new geoarchaeological, 

paleontological, and indigenous cultural information and insights. 

Substantively little has changed, however, regarding the fundamental need for more geoarchaeological 

data, since the publication of Benjamin et al’s 2011 edited volume, Submerged Prehistory. As Benjamin 

et al. note in that volume, “the study of submerged prehistory is still in its infancy...” with “...countless 

inundated prehistoric sites, from marine, brackish, and freshwater environments worldwide...yet to be 

discovered and studied.” More to the point, in regards to the current use of geoarchaeological modeling, is 

the problem that Peeters (2011) describes in the same volume—that the data points from which reliable 

(geoarchaeological) models for further research offshore can be produced is presently insufficient. Given 

this situation, an essential priority of the discipline must be the collection of more data. More experiences 

and observations from the field are needed from which phenomenologically based generalizations and 

testable hypotheses and models can be created. Beginning with the extremely limited data that is 

available, preliminary working hypotheses and “bold assumptions about what may be expected” need to 

be considered and coarse models developed and tested to refine them, so that it is possible to progress 

from a “primarily hypothetical world to a real one” in the future geoarchaeological models for the 

offshore environment (Peeters 2011). 

Virtually all of the marine geoarchaeological studies conducted to date (2019) in the U.S. and abroad 

must be considered as developmental in nature and more narrowly applicable to the specific activites and 

areas for which they were designed. Collectively, though, they represent general progress towards 
8

achieving an accepted, standardized, systematic methodology that may be applied more broadly to the 

open-ocean offshore environment of the U.S. OCS. Synthesis of the different geoarchaeololgical 

modeling approaches coalesced in the BOEM 2017 Guidelines has produced several basic methodological 

elements currently being used in modeling. These elements include:

• Review of relevant geological and archaeological literature

• Reconstruction of sea level and shoreline location changes over time

• Characterization of onshore archaeological site types, ages, cultural affiliations, and distribution 

patterning for correlation with identified submerged paleolandscape types

• Analysis and interpretation of sub-bottom profiler and other types of remote sensing data, and 

geotechnical testing data (i.e., sediment cores and other types of sediment samples) to determine 

whether geomorphic features of the formerly subaerial landscape (e.g., terraces, flood plains, and 

river, bay, lagoon, and paleochannel margins, etc.), dating from the geological period(s) 

associated with human habitation, are preserved and buried beneath more recent marine 

sediments on the sea floor within the areas being studied

• Paleolandscape reconstruction that delineates areas of high potential for the presence of precontact archaeological sites based on the analysis and synthesis of the area’s geomorphologies 

and documented onshore site patterning within those types of geological deposits. 

Currently used geoarchaeological models developed for formerly glaciated locations and environments 

that have been tested and proven valid, or that are of particular interest because of the advancements they 

represent in their approach and methods, are few in number and are all European in origin. They include 

the long-standing “Danish Topographical Model” or “Danish Fishing Site Model,” developed over 30 

years ago for the nearshore coastal waters of Denmark (Fischer 1987, 1993, 1995), and more recently 

published models for the Netherlands (Vos et al. 2012) and Northern Ireland (Westley et al. 2014). 

The Danish Topographical or Fishing Site model is a simple, non-quantitative, phenomenological model 

that was developed from interviews with elder local fishers and field surveys conducted in the mid-1980s 

and identified stratified layers of submerged paleolandscapes containing cultural features (e.g., a hearth) 

and artifacts dating from the Mesolithic (ca. 14,500 to 5,900 years before present [yBP]) and Kongemose 

(ca. 8,400 to 7,400 yBP) cultural periods. The presence of these submerged cultural features and artifacts 

was closely associated with the former topographic locations of ancient fishing sites where the trapping 

and netting of fish took place (e.g., at bay, river, and stream mouths, in narrows, and between nearshore 

islands and point bars [Fischer 1987, 1993, 1995]). The effectiveness of the Danish Fishing Site Model 

and its use of existing bathymetry as an indicator for predicting the possible locations of submerged 

cultural sites was tested at the time it was conceived and determined to have an efficacy greater than 80 

percent (Fischer 1995). Widespread employment of the model during subsequent survey projects 

conducted throughout Denmark’s coastal waters over the past four decades has proven similarly effective. 

Today, there are thousands of submerged Stone Age archaeological sites that have been identified in 

Danish waters by researchers and recreational scuba divers. Although the Danish Fishing Site Model has 

some limitations (non-quantitative, singular activity focus, the use of modern bathymetry as an indicator 

of paleolandscape topography, and sites that are exposed on the sea floor or have shallow burial depths), 

given that ancient coastal peoples worldwide have engaged in fishing activities, it seems likely that the 

Danish Fishing Site Model would nonetheless have broad applicability for identifying fishing site 

archaeological deposits in other regions of the world, including in U.S. waters. 
9

Another geoarchaeological model with methodological elements of interest was developed recently by 

Vos et al. (2012) during a cultural resource management marine archaeological investigation conducted as 

part of a harbor deepening project in the coastal waters of the Netherlands. The study provides a current 

and more complex example of process modeling that is a distinctly articulated, systematic, phased 

approach. Most significantly, the model acknowledges one of the more pressing methodological 

limitations of underwater archaeological survey—that “an underwater archaeological study will be carried 

out with substantially less sampling than an equivalent terrestrial archaeological study.” The Vos et al. 

(2012) model sought to address the issue by determining and testing areas with the highest archaeological 

potential, as determined through paleoenvironmental reconstruction and paleolandscape modeling, and 

the placement of archaeological finds known from terrestrial excavations into their paeloenvironmental 

context (Vos et al. 2012:940). Unlike the Danish Fishing Site Model, the Vos et al. (2012) model is not 

restricted to coastal or paleolandscape elements favorable to fishing, but instead focuses on examining the 

entirety of identified preserved paleolandsurfaces, and in the case of this particular study, paleolandscape 

geomorphologies that were initially deeply buried (20 m below sea level) prior to harbor dredging that 

took place as part of the project and removed 17 m of overlying marine sediments. The phases of the Vos 

et al. (2012) geoarchaeological modeling approach included the following:

• Phase 1: Desktop study of existing data and the development of a “Geological Layer Model” 

identifying paleolandsurfaces from those data and estimating the most likely approximate depth 

of possible archaeological remains (significantly, cone penetration tests (CPT), coincident and 

correlated with borehole data, were used) 

• Phase 2: Full area site investigation, following harbor dredging down to 17 m below sea level, 

involving remote sensing (single and multichannel Compressed High Intensity Radiated Pulse 

[CHIRP] and “sparker” sub-bottom profiling and multibeam bathymetric survey), and additional 

CPTs and borings to update and refine the Geological Layer and Paleolandscape Models

• Phase 3: High-detail site investigation resulting in an archaeological potential map and 

preliminary archaeological site and depth selection

• Archaeological Sampling: Focused on high-probability locations identified in the previous 

research phases 

Preliminary paleoenvironmental reconstruction conducted by Vos et al. (2012) identified depths below 

sea level that archaeologically relevant geological layers were most likely to be found. Use of resistance 

and friction parameters obtained from existing CPTs were correlated with existing boring data and then 

translated into identifiable indicators of specific lithological units and their interfaces. These were then 

grouped into a representative geological layer profile section model and a reconstructed digital surface 

model for the identified layers in the study area. This geological layer model provided a rough estimate of 

the layers and depth levels associated with the highest archaeological potential. In the case of the Vos et 

al. study area, the flanks of river dune sands deposited on the margins of rivers extending across a braided 

Pleistocene floodplain, and the bases of Early Holocene layers of deltaic peat and clay deposited 

subsequently onto the river dune sands as a result of rising sea level were identified as having the highest 

archaeological potential and chosen for archaeological sampling. Underwater excavation of three 

sampling locations, measuring 6 x 16 m, 9 x 12 m, and 2 x 3 m (in four areas), sieved through 10 mm and 

2 mm mesh, resulted in the recovery of a very large number of finds (N=46,067). The finds consisted of 

charcoal, flint, and fragments of burned and unburned animal bones, and were the first in situ scientific 

proof for hominin occupation of the western Netherlands in the Early and Middle Mesolithic (Vos et al. 

2012). Vos et al. (2012)’s systematic, phased, multidisciplinary, integrated-data approach is an example 
10

of a current geoarchaeological modeling effort that could have broader applicability elsewhere, including 

in the waters of the U.S. 

Middle Holocene paleogeographic reconstructions and an archaeological site potential model developed 

for a coastal area in Northern Ireland by Westley et al. (2014) provide additional methodological 

advances for current geoarchaeological modeling in areas where marine sedimentation rates are relatively 

high and paleolandsurfaces are buried. Using legacy boring data, seismic profiles, and sediment cores, 

Westley et al. (2014) improved upon previous reconstructions that utilized modern bathymetry as a proxy 

for submerged and buried paleotopography (rendered potentially less accurate by the effects of postsubmergence erosion or deposition) by employing a “backstripping” methodology in their digitial 

modeling to “remove” 2.5 to 10 m of accumulated modern marine sediments from identified buried 

paleolandscape surfaces in order to obtain a more accurate reconstruction of the past landscape. Westley 

et al. (2014) also utilized available sea level rise models to constrain the range of possible sea levels that 

they apply to their backstripped digital paleolandscape model to reconstruct marine transgression during 

the Early to Middle Holocene. Given the crucial role that paleolandscape reconstructions and marine 

transgression projections play in archaeological research by providing the physical context for predicting 

archaeological site locations produced by past human activities, Westley et al’s methodological 

contributions to geoarchaeological modeling are important to consider. 

2.3 Challenges with Modeling in Submerged Environments

Geoarchaeological modeling for study areas located in submerged environments presents challenges that 

are different from those that are encountered when developing archaeological models for terrestrial 

environments. These challenges are significant and presently preclude the application of sophisticated 

quantitative archaeological modeling approaches that have been developed and used for onshore study 

areas, due to the very limited number of identified paleocultural sites on the United States’ continental 

shelf. The challenges include visibility, access, scale, and resolution. Seeing, surveying, identifying, 

accessing, and conducting archaeological testing of a submerged paleolandscape requires very different 

methodologies and produces different types of data than what is typical done for or available from the 

archaeological investigation of paleolandscapes on land. Unlike on land, where it is possible for a person 

to physically access, walk across, and visually observe broadly and identify a paleolandscape, and 

comparatively easy and inexpensive to complete comprehensive site assessments and archaeological 

surveys to identify archaeological sites within it, elements of the paleolandscape that are preserved in 

submerged environments are not easily visible. They are obscured by 1) the water in which they are 

submerged, both from the surface above the water, as well as below the surface due to limited underwater 

visibility; 2) overlying marine sediments that have accumulated on top of and buried them; 3) the 

massively transformative effects associated with the erosion and redistribution of sediments that occur 

during the marine transgression process and the geomorphological changes that occur post-submergence, 

which together result in the incomplete preservation of the submerged paleolandscape; 4) the equally 

incomplete present understanding of how much, what, where, and why remnants of the submerged 

paleolandscape are preserved; and 5) the absence of comprehensive, detailed, high-resolution mapping 

and visual documentation of the seafloor.

The amount of pre-existing high-resolution geologic and paleoenvironmental data that is publicly 

available for modeling the submerged environment is limited by the challenges associated with accessing, 

surveying, and identifying submerged paleolandscapes on and under the seafloor. Basic information about 

the extent and locations of preserved remnants of the submerged paleolandscape, the geomorphologic 

characteristics of those landscapes, the processes that lead to their preservation or destruction, and the 

submerged sites that would be found within them is all but absent from the literature. Modelers working 
11

in submerged contexts have almost no pre-existing archaeological site data available to them regarding 

the locations, types, dates, sizes, and distributions of archaeological sites in the submerged environment.

In contrast, the onshore terrestrial environment has been continuously occupied by Native people for 

more than 10,000 years, and archaeological research on the material culture and available ethnohistorical 

records associated with that habitation has been ongoing for more than a century. Thousands of terrestrial 

cultural and archaeological sites have been identified onshore throughout the region as a result of surveys 

conducted by archaeologists who have most often been equipped with little more than a mode of 

transportation to get them to and from their study areas, a shovel, a trowel, a shaker-screen for sifting 

excavated soils, a camera, a field notebook and pencil, and a handheld GPS unit.

Submerged environment survey and site identification, on the other hand, requires use of research vessels, 

specially trained and educated marine scientists (i.e., oceanographers, marine geophysicists, marine 

geologists, archaeologists, paleontologists, etc.), and a suite of expensive marine surveying and sediment 

sampling equipment to conduct marine geophysical surveying and geotechnical sampling just to be able 

to access and “see” the seafloor/sub-seafloor and the sediments and stratigraphy that comprise it. In 

situations where conditions allow, actually observing the seafloor and conducting visual reconnaissance 

survey or targeted subsurface sampling/testing is possible only using specially trained and educated 

archaeological divers or archaeologist-guided and expensive remotely operated vehicles (ROV). Some 

offshore areas are characterized by marine conditions that make diving, ROV operations, or extensive onsite sampling/testing logistically problematic or impossible (e.g., where water depth is extreme, 

underwater visibility poor, high seas or strong currents prevalent, or where bottom composition interferes 

with the collection of high-resolution geophysical data or geotechnical sediment samples).

Other important challenges are related to scale and resolution. Although there is a significant amount of 

existing marine geological survey data and a substantial resulting body of literature describing, 

interpreting, and modeling post-glacial sea level rise and characterizing basic sea floor stratigraphy at 

multiple locations on the continental shelf, regional marine geological survey approaches followed to date 

are, by their nature, large in scale and coarse in resolution. Models for sea level rise are generally 

presented as smooth curves that average differences in data points and do not capture the episodic 

fluctuations, periods of “still-stand,” and chaotic ways that sea level rise would have progressed in 

actuality across the variable terrain of the continental shelf’s pre-submergence paleolandscape as it was 

inundated. Geophysical data acquired to develop the regional stratigraphic model for offshore sediments 

are generally acquired along widely spaced (e.g., 2 km apart) primary survey transects. Geotechnical 

sampling data complimenting the geophysical survey data can be limited. As a result, modeling the 

“human-” or “micro-scale” aspects of these paleoenvironmental changes is not yet possible without finer 

scale, higher resolution marine geological and archaeological data (Leary 2011:75-84). 

For the submerged environment, the most immediately pressing question to be answered is not yet

“Where and how did ancestral peoples interact with the formerly terrestrial paleocultural landscape?” but 

rather “Did any remnant elements of the paleocultural landscape that ancient people could have interacted 

with survive the inundation process intact and undisturbed?” If intact remnants of the now submerged 

paleolandscape are identified, a variety of additional questions must also be asked and answered:

• How disturbed are the surviving remnants of the paleolandscape?

• Is it possible to identify and discern primary, secondary, or tertiary contexts in 

preservedsubmerged paleolandscape sediment strata?

• How deeply are they buried?

• How far do they extend?

• What kinds of paleoenvironments are represented where cultural sites may have existed in the 

past, based upon what we know from the observed relationships of cultural sites and 
12

paleoenvironments seen in the onshore archaeological record and as recorded in Tribal histories 

and traditions?

• Why have they survived?

• What are the geologic and oceanic conditions and processes that contribute to preservation?

• Can these variables be identified, measured and predicted?

Answering these questions will be essential for eventually developing the kinds of sophisticated 

quantitative archaeological predictive models for submerged environments that are presently available 

and being used in the archaeological sensitivity assessments of onshore study areas (see Verhagen and 

Whitley 2012).

In the case of developing a model for this project’s study areas, the challenges included the basic ones of 

visibility, access, scale, and resolution, as outlined above. There is a limited amount of high-resolution 

marine geological data that is available for the Rhode Island OCS, particularly from Block Island 

southwards. Data available in the study area and northward is generally regional-scale reconnaissancelevel survey data, except in a small number of areas that have been studied more intensively. Although

the pre-existing regional data and its interpretation are of high quality, and their resolution is adequate for 

providing a regional geologic framework, it is inadequate for the purpose of identifying preserved 

remnants of the submerged paleolandscape. It is also inadequate for identifying specific elements of those 

preserved paleolandscape remnants that could then be correlated with similar preserved environments 

onshore and their associated archaeological and ethnohistorical data to assess and model their 

archaeological sensitivity. Meeting these challenges will require a combination of focused, highresolution marine geophysical survey, geotechnical sediment sampling, sediment dating, analyses, and 

interpretation to further resolve the regional stratigraphic framework, to identify preserved remnants of 

the submerged paleolandscape, and to isolate specific environmental elements of it that can then be 

considered and modeled archaeologically.

2.4 Key Points

• The term “model” must be clearly defined in the context of each unique discussion or project.

• Unless specified, the term “model” in this report is defined as a process, object, map of two or 

three dimensions, or illustration that helps to visualize or predict something, or to test a 

hypothesis.

• In all cases, the type of model being produced, the processes used to create it, and the outcomes 

and products that are expected from it need to be clearly described and defined, as well as 

reproducible and testable. 

• Iterative validation, evaluation, and field testing of models is essential to demonstrating and 

improving the model’s performance, identifying any conceptual or factual errors, and assessing 

the reliability and any bias in the environmental and archaeological datasets used in the model’s 

development.

• Geoarchaeological modeling in submerged environments presents unique challenges of visibility 

and access that are very different from those encountered when modeling in terrestrial 

environments onshore. 

• Currently, the absence of archaeological site data and the limited amount of high-resolution 

comprehensive geological and geophysical data that exist for the submerged environment 

preclude applying quantitative terrestrial archaeological predictive models to underwater areas.
13

3 Development of the Project Modeling Process

3.1 Best Practices from Project Workshop

The initial project workshop summarized then-current (i.e., in 2013) approaches to assessing the 

archaeological sensitivity and predicting the potential for sites to be present within a given submerged 

study area. The resulting discussions that followed generated a number of ideas and general comments 

from the workshop’s diverse group of participants representing academic research, applied 

sciences/industry, Federal and state agencies, and THPOs. A synthesis of the key “take away” messages 

regarding predictive models is presented below. A more detailed discussion is available in a separate 

project deliverable entitled “Developing Protocols for Reconstructing Submerged Paleocultural 

Landscapes and Identifying Native American Archaeological Sites in Submerged Environments: Best 

Practices” (Section 3.7) (Robinson et al. 2018).

• A model is only as good as the data that is used to create it, and a model incorporates assumptions 

and biases that directly affect the results of the model.

• The current amount of archaeological site data for the OCS is extremely limited. Only a handful 

of sites have been identified in submerged contexts offshore, and most of them have been close to 

shore and not in Federal waters.

• Models are a “best educated guess” simplification of reality and should never be viewed as 

reality. 

• Models should never be the primary decision-making tool for cultural resource management.

• Models must be tested to assess their accuracy and should never be used without being tested.

• Models that attempt to identify ancient Tribal cultural sensitivity are incomplete without 

ethnohistorical input and cultural insights from contemporary Tribal peoples.

The project team incorporated all of these concepts into the development of the modeling process, the 

regional models, and the acquisition of new data for model testing that is discussed later in this document.

3.2 Defining the Scope of the Project Model 

Given the inherent ambiguity in the meaning of the term “model” and the nature and scope of its

application to addressing archaeological research problems, it is important to clearly define why a model 

is necessary, and the goals, processes, and expected outcomes of the model(s) being employed. It is also 

important to identify the potential issues and challenges that may be associated with the modeling task so 

that their impacts on the model are clearly understood at the beginning of the process.

The scope of the Submerged Paleocultural Landscapes Project models was established by the questions 

and responses summarized below. These questions provide a useful starting point for any modeling effort.

Responses specific to the project are highlighted in bold.
14

1. What is the specific task that the model is being applied to?

• Developing a greater understanding of where culturally sensitive paleolandscapes and 

archaeological sites may be located on the continental shelf in southern New England.

2. Why is a model necessary for this task?

• Modeling provides a starting point and theoretical framework for focusing research, testing 

hypotheses, and identifying and understanding observable patterning in the preservation and 

distribution of submerged paleolandscapes and their associated ancient Tribal archaeological sites.

Focused research and hypothesis testing are necessary and especially important given:

o The early developmental nature of submerged paleolandscapes archaeology as an

emergent research discipline.

o The extremely limited amount of baseline archaeological data available for the continental 

shelf. 

o The limited coverage and availability of high-resolution marine geological data.

o The significant costs and logistical challenges associated with accessing, mapping, and 

sampling the sea floor. 

3. What is the definition of the term “model” as it will be applied to this task?

• An object, illustration, or process that assists with visualizing or predicting something, or is used to 

test a hypothesis. Multiple types of interconnected models can be used for a single task.

4. What are the goals of the model(s) developed for this task?

• Develop a modeling process that is understandable by diverse groups of stakeholders.

• Develop a modeling process that is applicable to multiple geographic areas, can be used when 

differing types and amounts of data are available, and that is applicable to “real life”

circumstances.

• Develop a tiered modeling process that begins with a thorough geological characterization of the 

study area on a regional scale, and progresses to a local assessment of paleocultural sensitivity by 

applying what is known from terrestrial archaeological research to predict the age(s), density, likely 

distribution, and types of sites that may associated with preserved paleolandscapes.

• Address the unique challenges of working in submerged environments (see Section 2.5.2, and 

Question 8 below).

• Avoid the pitfalls of previous predictive models that are not testable, not reproducible, and/or that 

use subjective environmental variables such as “near” (i.e., sites will be located near water bodies).

5. What types of data will be used to develop the model(s)?

• Publicly available archaeological, geophysical, and geological legacy data for southern New 

England.

• Archaeological, geophysical, and geological data previously collected by the project team and 

project collaborators.

• Publicly available Tribal oral traditions and histories.
15

• Newly acquired archaeological, geophysical and geological data for the Greenwich Bay area, West 

Beach (Block Island), the Mud Hole, and northern Rhode Island Sound.

6. What are the expected outcomes of the model(s)?

• A flow chart illustrating a modeling process that can be applied to diverse geographic areas.

• Illustrations showing projected hypothetical paleoshoreline locations based on the application of 

sea level rise models to present bathymetry for the project study area at key times in the geological 

and archaeological past.

• An improved understanding of the relationship between the broader regional subsurface 

stratigraphy and the local preservation of paleolandscapes that could be culturally sensitive.

• An improved understanding of the pre- and post-inundation topographies and environments that 

preserve submerged paleocultural landscapes and the density, distribution, type, and time period 

of the archaeological sites likely to be present within them.

• An improved understanding of the survey methodologies best suited to identifying, mapping, and 

reconstructing paleocultural landscapes in submerged environments.

7. How will the model be tested?

• By conducting archaeological, geophysical, geological, and paleoenvironmental data acquisition 

and analyses of five case study areas representing diverse nearshore and offshore environments.

8. What are the major challenges associated with model development for this task?

• The amount, resolution, and types of pre-existing data that are available will have a significant 

effect on the model.

• Currently, there are very few submerged ancient Tribal archaeological sites that have been located 

on the continental shelf, so the modeling task cannot be based on archaeological data in the same 

way that it would be for terrestrial locations onshore with extensive archaeological datasets.

• There is currently an incomplete understanding of how, why, and where paleolandscapes or 

paleolandscape fragments survived (or did not survive) the marine inundation process.

• Characterizing the regional geology in submerged environments relies almost exclusively on remote 

sensing technology and interpretations of acoustic data.

• Obtaining and analyzing sediment cores to ground-truth geophysical data, and developing an 

absolute age model with radiocarbon dates, is expensive, time consuming, and a significant drain 

on project resources.

• Methods for culturally appropriate access and use of Tribal cultural knowledge in the model(s) 

requires additional attention and the development of trusting and mutually cooperative 

relationships.
16

3.3 The Project Modeling Process

Identifying submerged paleocultural landscapes on the continental shelf requires a modeling approach 

that differs substantially from archaeological predictive modeling in terrestrial environments. Before 

potential cultural sensitivity can be assessed, the landscapes or landscape fragments that have survived 

post-glacial sea level rise, and that represent environments that could have been inhabited by ancient 

Tribal peoples, must first be located and characterized. Therefore, the modeling process requires a 

thorough understanding of subsurface geology and sea level change history on a regional scale, not just 

for a local study area.

The modeling process discussed in this document begins with a thorough desktop study to synthesize the 

current state of geoarchaeological knowledge in the study area and to assess the applicability of existing 

data to the modeling task. It then uses the compiled desktop study data to develop two types of regional 

geological models that are applied at the local level to five case areas. This approach differs substantively 

from previous approaches that have been applied in southern New England within the context of 

compliance archaeology projects, whose research focus is limited by design to within the localized 

vertical and horizontal boundaries of a proposed project’s area of potential effect (APE). In addition, the 

modeling process presented in this report is unique because it does not assess paleocultural sensitivity 

based on the presence or absence of isolated geologic features, such as a paleochannels. Instead, once a 

regional geological framework is developed, geologic facies are identified that may represent the time 

frame and paleoenvironments associated with occupation by ancestral Tribal peoples.

Two types of models1 are presented, which are organized in sequential tiers. Tier 1 is a process-based 

model that outlines all of the steps necessary to begin identifying and characterizing paleocultural 

landscapes in submerged environments. Because this model is a sequence of general tasks, it is applicable 

to any geographic location and can be used with varying amounts of data. Tier 2 models are illustrations 

and hypotheses that result from applying individual steps in Tier 1 to the regional project study area. Two 

Tier 2 models are developed for the southern New England continental shelf: 1) maps showing 

hypothesized paleoshoreline positions at key times in the past; and 2) illustrations that present a 

preliminary hypothesis about where preserved paleocultural landscapes may be located based on the 

subsurface stratigraphy of the region. Note that there is currently not enough geophysical data in the study 

area to create a regional geographic map of potential paleolandscape locations based on subsurface 

stratigraphy (see Section 4.1 of this report), so this model is not presented in the form of a map. Instead, it

identifies basic geologic facies in representative seismic reflection profiles that may include strata in 

which are preserved archaeologically sensitive remnant elements of the submerged paleocultural 

landscape. Tier 2 models are applied to local case study areas, and are tested and revised by interpreting 

newly acquired data. Figure 3-1 is a flow chart illustrating the relationship between each of the models.

Corresponding steps are summarized below. 

1. Conduct a thorough desktop study to synthesize the geological and archaeological context of the 

study area. Identify previous research that has been conducted both regionally and locally. Assess 

the quality of the data and compile any legacy datasets that will be used for the project into a 

geospatial database. (An additional report produced as part of the Submerged Paleolandscapes 

Project, entitled “Developing Protocols for Reconstructing Paleocultural Landscapes and 

Identifying Native American Archaeological Sites in Submerged Environments: Best Practices,”

(Robinson et al. 2018) provides detailed recommendations about how to assess and compile 

legacy data).

1 To review, a model as defined in this report is an object, illustration, or process that assists with visualizing or predicting 

something, or is used to test a hypothesis. 
17

Figure 3-1. Flow chart showing the relationship between the models developed for this report.

2. Use exiting relative sea level change curves and the highest-resolution bathymetric datasets 

available to create preliminary reconstructions of approximate regional paleoshoreline position(s) 

applicable to the study area. This step has two purposes: 1) provide preliminary visualizations 

illustrating which portions of the study area may have been subaerially exposed at key times in 

the past that are associated with human habitation; and 2) visualize the difference between 

paleoshoreline positions resulting from various sea level models available of the study area.

These visualizations should be regarded as hypotheses that require testing and verification at the 

local level.

3. Develop a regional stratigraphic model that identifies where paleolandscapes may be preserved 

based on the surficial and subsurface stratigraphy of the area. The goal of this step is to develop a 

broad understanding of the timing and processes associated with regional subsurface and surficial

geology. It is essentoal to reconstruct and understand the complete subsurface stratigraphic 

sequence, beginning with acoustic basement and proceeding upwards to the seafloor. Focusing 

the reconstruction only on the depth likely to be impacted by a proposed construction project, or 

assuming that deeply buried sediments are too old to be culturally sensitive, may produce 
18

inaccurate or incomplete assessments of potential cultural sensitivity. Using the reconstructed 

subsurface stratigraphic framework, identify the geological facies that represent the time frame in 

which humans could have inhabited the study area, and the types of paleoenvironments (lake, 

marsh, upland, etc.) that these facies are inferred to represent. Assess the extent to which those 

landscapes or landscape fragments appear to have been impacted by post-glacial sea level rise. 

4. Test the model developed in step 3 at the study area(s). Acquire and interpret additional 

geophysical data and sediment cores to ground-truth the acoustic interpretations. If preserved 

paleolandscapes are identified, then conduct a paleoenvironmental assessment (examining sieved 

sediments for foraminifera, diatoms, pollen, etc.) to provide additional detail about the 

characteristics of the paleolandscape. If acquired and interpreted data demonstrate the presence of 

relict, preserved paleolandforms, then assess the paleocultural sensitivity of the represented 

landforms based on results from engagement and dialog with Tribal research partners, and from a 

review of the results of local and regional archaeological investigations of analogous landforms 

on shore. 

Sections 4-7 of this report demonstrate how the modeling process discussed above was applied to the 

Submerged Paleolandscapes Project study area.

4 Application of Modeling Process to Project Study Area, Step 1: 

Desktop Study

The term “desktop study” refers to the compilation, synthesis, and summary of pre-existing, publicly 

available geophysical, geotechnical, archaeological, and cultural data and information about a given study 

area at the time when the investigation is initiated. Performance of a desktop study does not involve 

acquiring new field survey data. Conducting a thorough desktop study is a critical first step in the 

modeling process. Data that is synthesized as the result of a desktop study can be used to produce 

working regional models, which can then be tested with new data acquisition at local study areas. A 

separate report generated for the Submerged Paleolandscapes Project (Robinson et al. 2018) details “best 

practices” for conducting desktop studies and recommended content. The subject headings and discussion 

presented below follow these protocols.

4.1 Geographic and Temporal Limits of the Study Area

The modeling process and resulting models presented in this report were designed to apply to the southern 

New England continental shelf, and in particular to Rhode Island Sound and the eastern portion of Block 

Island Sounds. Figure 4-1 illustrates the specific areas that were targeted for new data acquisition, and/or

analysis of legacy data. Archaeological, geophysical, and/or geological data from each of these locations 

were used to develop the models. Because one of the goals of the modeling process was to thoroughly 

understand the submerged subsurface regional geology of the study area, the project’s vertical depth of 

interest extends from acoustic basement as defined in seismic reflection profiles, upwards to the sea floor, 

and into the intertidal, beachface, backshore, and dune areas at Cedar Tree Beach (Greenwich Bay area) 

and West Beach (Block Island area). The time period for which paleocultural sensitivity and site potential 

was assessed extends from ca. 24,500 to 450 yBP, spanning the “Pre-Clovis” through “Late Woodland” 

pre-European contact archaeological periods.
19

Figure 4-1. Location of case study areas selected for model assessment and testing.

4.2 Tribal Engagement

An integral element of this project and modeling effort was the engagement with the Tribal communities 

who have cultural connections to the study area to discuss the study, to understand specific Tribal 

concerns and priorities associated with the project’s study areas, and to incorporate Tribal suggestions, 

concerns, and priorities into the project’s research. This engagement was realized through the formal 

research partnership that was established with the NITHPO at the start of the project, and through the 

informal collaborative relationships that were initiated and developed over the course of the study with 

Tribal representatives from the Aroostook Band of Micmacs, Lenape Indian Tribe of Delaware, 

Mashantucket (Western) Pequot Tribal Nation, Mashpee Wampanoag Tribe, Narragansett Indian Tribe 

(Niantic), Nipmuc Nation, Shinnecock Indian Nation, and Wampanoag Tribe of Gay Head (Aquinnah), 

who participated in the initial and interim project workshops, fieldwork, and report preparation and 

review. 
20

4.3 Geologic Context

4.3.1 Overview

Mainland Rhode Island is composed of three general physiographic regions. The first, a narrow coastal 

plain with elevations of less than 100 ft, occurs along the shore and in the area around Narragansett Bay. 

The second, characterized by gently rolling uplands with elevations up to 200 ft, lies to the north and east 

of the Bay. A third region, comprising the western two-thirds of the state, consists of hilly uplands mostly 

between 200 and 600 ft in elevation. Narragansett Bay, a north-south trending estuary with approximately 

420 miles of shoreline and multiple tributaries, dominates the eastern part of the state (Terwilliger 

Consulting, Inc. 2015). 

Immediately offshore of Rhode Island, the Atlantic Ocean is divided into two areas: 1) Block Island 

Sound, which encompasses the area seaward of the southwestern coast of the state and north of Block 

Island; and 2) Rhode Island Sound, which is located south of Narragansett Bay and east of Block Island 

Sound. The water depth on the continental shelf in the study area ranges from intertidal at the coast to 

approximately 65 m offshore, with the deepest areas occurring as isolated basins that may represent 

portions of buried pre-glacial channels in the underlying bedrock (McMaster and Ashraf, 1973a, b, c).

The seafloor consists of a mosaic of benthic environments characterized by mud, silt, sand, coarse sand, 

cobbles/gravel, and boulders associated with modern marine processes and Pleistocene glacial deposition 

(RI CRMC 2010). Some of the seafloor sedimentary environments are transitory and are subject to 

erosion, sediment transport, reworking, sorting and deposition by oceanographic processes, whereas 

others, such as deposits of glacial till, are more stable (RI CRMC 2010).

Much of Rhode Island’s contemporary terrestrial landscape results from glacial processes. The bedrock 

geology of the state consists of igneous, metamorphic, and sedimentary rocks that are between 136 and 

570 million years old (Quinn 1997). Bedrock outcrops occur frequently around Narragansett Bay and in 

other isolated areas, but much of the landscape is draped by a heterogeneous blanket of glacial sediments 

that were deposited during multiple advances and retreats of the Pleistocene ice sheets (Terwilliger 

Consulting Inc 2015). A similar geological pattern occurs offshore in Narragansett Bay and on the 

continental shelf in the study area, where seismic reflection studies have identified glacial and modern 

marine sediments overlying pre-Mesozoic bedrock and Cretaceous coastal plain deposits (McMullen et al. 

2009 a, b; Needell et al. 1983 a, b, c; Needell and Lewis 1984; Oakley 2012; O'Hara and Oldale 1980; 

Peck and McMaster 1991). The offshore subsurface stratigraphy of the study area is discussed in detail in 

Section 4.1.1 of this report.

Several glaciations and intervening non-glacial episodes are thought to have affected southern New 

England in the Pleistocene (Stone and Borns 1986; Boothroyd and Sirkin 2002). There is uncertainty 

regarding how many episodes of glacial ice sheet advance covered southern New England, but at a 

minimum, the Laurentide Ice Sheet advanced to the contemporary continental shelf during the Illinoian 

period (200–120 thousands of years ago), and again during the late Wisconsinan (Stone et al. 1998; 

Caccioppoli 2015). The late Wisconsinan ice sheet reached its terminal position south of Montauk, New 

York and Block Island approximately 26,000 yBP (Boothroyd and Sirkin 2002; Peltier and Fairbanks 

2006). This event is associated with a global lowstand of sea level, which is estimated to have been 

approximately 120 m below present (Peltier and Fairbanks 2006; Oakley and Boothroyd 2012). 

As the ice began to retreat northwestward from its terminal position after 26,000 yBP, a complex 

sequence of recessional moraines (Boothroyd and Sirkin 2002) were deposited across the study area, and

remain significant features in the contemporary terrestrial and seafloor topography. Block Island is 

composed of a thick moraine complex deposited during this glacial episode (Boothroyd and Sirkin 2002).
21

Cosmogenic-nuclide exposure ages for these moraines provide an estimate of when the ice margin 

occupied those locations. The Charlestown moraine, a significant west/east trending topographic feature 

across the southern coast of Rhode Island, appears to have been deposited approximately 21,300 yBP 

(Balco et al. 2009; Balco and Schaefer 2006), and the Whale Rock End Moraine, located at the entrance 

to the West Passage of Narragansett Bay, is inferred to have been deposited between 20,300 yBP (Balco 

et al. 2009) and 20,550 yBP (Oakley and Boothroyd 2012). These dates indicate the continental shelf in 

the study area would have been ice free approximately 4,700–5,700 years after the ice had reached its 

terminal position south of Block Island (i.e., 21,300–20,300 yBP). By approximately 19,500 yBP,

Narragansett Bay is inferred to have been ice free, although the ice remained in the watershed until at 

least 19,300 yBP (Oakley 2012; Oakley and Boothroyd, 2012).

Although portions of the continental shelf may have been subaerially exposed during the very early postglacial period as the ice retreated, large glacial meltwater lakes occupied much of the study area, 

including what is now Narragansett Bay. These were formed by the impoundment of glacial meltwater 

behind bedrock outcrops, sediment dams, or blocks of stagnant ice as the ice sheet retreated (Bertoni et al. 

1977; Lewis and Stone 1991; Lewis and DiGiacomo-Cohen 2000; Oakley 2012; Oakley and Boothroyd 

2013; Caccioppoli 2015). Thick glaciolacustrine deposits associated with these lakes are visible in seismic 

reflection profiles throughout the study area (Needell et al. 1983 a, b, c; O’Hara and Oldale 1980; Klotsko 

and Driscoll 2018), suggesting that the lakes persisted for thousands of years (Uchupi et al. 2001), first as 

pro-glacial lakes fed by glacial meltwater, and then as meteoric lakes after the ice had completely receded 

from the area (J. Boothroyd, personal communication, June 5, 2012). Estimates of the geographical area 

occupied by the lakes have been developed by Oakley (2012), suggesting that they covered an extensive 

area of what is now the southern New England continental shelf. However, the exact locations of their 

shorelines, and how those shorelines changed over time, is not yet well constrained. 

Drainage of the glacial lakes on the continental shelf and in the Narragansett Bay area is inferred to have 

occurred approximately 16,000 yBP, as post-glacial isostatic rebound elevated the land surface (Koteff 

and Larsen 1989; Koteff et al. 1993; Lewis and DiGiacomo-Cohen, 2000; Oakley 2012). Smaller lakes 

may have persisted in deep basins in the study area, but this hypothesis is based on contemporary 

geomorphology and has not been tested (J. Boothroyd, personal communication, June 5, 2012). Once the 

lakes drained, much of the study area was subaerially exposed prior to post-glacial sea level rise and is 

thought to have been characterized by fluvial and estuarine environments (Needell et al. 1983a, b, c). As 

sea level rose, marine inundation progressed from south to north, indicating that the Block Island, Mud 

Hole, and the Area of Mutual Interest (AMI) study areas on the contemporary continental shelf would 

have transitioned to marine conditions several thousand years prior to the Greenwich Bay study area in 

central Narragansett Bay. Illustrations of projected hypothesized paleoshoreline positions during the postglacial period are presented in Section 5 of this report. 

Although the general deglacial chronology presented above has been well established by a variety of 

interdisciplinary studies, the precise dates associated this chronology are still being refined. There is 

currently a lack of extensive radiocarbon ages and correlated varve sequences in southeastern New 

England (Oakley and Boothroyd 2013). In addition, the margins of error associated with varve 

chronology correlation, cosmogenic-nuclide (Balco and Schaefer 2006), and radiocarbon dating can range 

from hundreds to thousands of years. These margins of error should be clearly understood when 

identifying paleolandscapes that may have been available for occupation by ancient Tribal peoples. 

Additional chronological information specific to each of the five study areas, if available, is provided with 

the case studies discussed later in this report.
22

4.3.2 Development of an Offshore Regional Subsurface Geologic Framework

The five study areas identified for this project include a coastal/nearshore location in central Narragansett 

Bay (Cedar Tree Beach/Greenwich Bay), a coastal/nearshore island location approximately 12 miles 

offshore (West Beach, Block Island), and three submerged areas on the Rhode Island continental shelf 

(western Rhode Island Sound, Mud Hole, and the AMI) (Figure 4-1).

Although these areas are separated by tens of kilometers, they share the same regional geologic history 

that is key to identifying and characterizing preserved paleolandscapes. The distinction between terrestrial 

and submerged environments is obvious in the contemporary landscape, but ancestral Tribal peoples who 

occupied this area interacted with a landscape that was very different from contemporary conditions. 

Pleistocene glaciations lowered sea level substantially, with the result that part of what is now the 

submerged continental shelf off Rhode Island was once a continuation of the current terrestrial landscape, 

and was available for habitation. However, glacial processes, post-glacial marine inundation, and 

contemporary oceanographic conditions have either destroyed, significantly altered, and/or buried these 

ancient landscapes during and after submergence. Surviving paleolandscapes may not exist in a 

geographically continuous manner, and may be incomplete representations of the original ancient 

environment. Because these landscapes are now submerged and frequently buried beneath recent marine 

sediments, reconstructing their characteristics relies heavily on high-resolution seismic reflection 

profiling, which provides vertical acoustic “slices” of the sub-seabed. By identifying the ages, 

sedimentary units, and processes associated with the acoustic signatures visible in sub-bottom profiles, it 

is possible to identify where terrestrial paleolandscapes may be preserved, and what type of ancient 

environment (upland, marsh, lake, etc) they may represent.

4.3.2.1 Foundation Studies

The subsurface stratigraphy of the inner continental shelf off southern New England consists of sediments 

deposited by Pleistocene and Holocene glacial and post-glacial processes, unconformably overlying 

Cretaceous/Tertiary deposits and pre-Mesozoic bedrock. This framework was established by a series of 

geophysical studies beginning in the mid-20th century (Ewing et al. 1940; Oliver and Drake 1951; Frankel 

and Thomas 1966; Schafer and Hartshorn 1965; Hoskins and Knott 1968; Savard 1966; Tagg and Uchupi 

1967; McMaster et al. 1968; Grim et al. 1970; Oldale and Uchupi 1970; McMaster and Ashraf 1973a, b, 

c; Sirkin 1976; Bertoni et al. 1977; Gordon 1980; McMaster et al. 1980; McMaster and Fredrich 1985). 

Many of these investigations employed the technique of sequence stratigraphy, which involves 

identifying prominent acoustic reflectors in seismic reflection profiles, associating these reflectors with 

specific geological facies, processes, and time periods, and then correlating these units between tracklines 

to produce an inferred regional characterization of subseafloor sediments. In addition to providing a 

preliminary characterization of the subsurface acoustic signatures in southern New England continental 

shelf, these early studies also focused on establishing the relationship between the stratigraphic sequences 

seen in seismic reflection profiles and the bedrock and glacial geologic history that concurrent research 

established for the terrestrial environment in southern New England (Goldsmith 1962, 1982; Schafer 

1961; Sirkin 1974, 1976, 1982; Hermes and Boothroyd 1981).

The conclusions resulting from this early research were refined by three extensive, high-resolution 

seismic surveys conducted by the United States Geological Survey (USGS) in Long Island, Block Island, 

and Rhode Island Sounds between 1975 and 1981 (“the USGS studies”) (O’Hara and Oldale 1980; 

McMaster 1984; Needell et al. 1983a, b, c; Needell and Lewis 1984; Poppe et al. 2002, McMullen et al. 

2009 a, b). Over 2,000 km (1,243 mi) of seismic reflection data was acquired in a systematic pattern 

(approximately 2-km trackline spacing) across the continental shelf off southern New England 

(Figure 4-2). Limited side-scan sonar data was also obtained along selected tracklines. Data acquired 

during these surveys defined the characteristics associated with acoustic basement in seismic reflection 
23

profiles; detailed the types, thicknesses, and regional distribution of the subsurface Pleistocene/Holocene 

glacial and post-glacial sedimentary sequences; and identified regional acoustic reflectors interpreted to 

represent significant unconformities between stratigraphic units. A series of associated maps was also 

produced to illustrate inferred depths to regional reflectors, and thicknesses of stratigraphic units 

throughout the study areas (O’Hara and Oldale 1980; Needell et al. 1983b; Needell and Lewis 1984; 

Poppe et al. 2002; McMullen et al. 2009 a, b). When combined with the earlier research, the results of 

these surveys produced a comprehensive, reconnaissance-level characterization of the geologic 

framework and depositional history of the inner continental shelf off southern New England (see Section 

4.1.2 of this report) (Poppe et al. 2002; McMullen et al. 2009 a, b).

Figure 4-2. USGS seismic reflection profile tracklines surveyed between 1975 and 1981.

4.3.2.2 Validation of Acoustic Interpretations

Sediment cores and borings: The geological framework developed by the USGS foundation studies is 

primarily based on interpretation of seismic reflection profiles and the technique of sequence stratigraphy. 

“Ground-truthing” of the acoustic interpretations through analysis of sediment cores or borings has not 

yet been conducted in a systematic regional manner. Sixteen vibracores (Figure 4-3, purple dots) were 

acquired as part of the USGS geophysical survey off southeastern Massachusetts (Figure 4-2, closely

spaced purple tracklines) to provide information about the geologic history of the area, identify potential 

sand and gravel resources (O’Hara and Oldale 1980, McMullen et al. 2009b) and to develop a local postglacial sea level rise model for the area (Oldale and O’Hara 1980). Vibracores were not collected during 
24

either the Rhode Island Sound (Figure 4-2, black tracklines) or the Block Island Sound (Figure 4-2, green 

tracklines) survey. However, in 1988, 6 vibracores were obtained on USGS tracklines in Block Island and 

Rhode Island Sounds (Figure 4-3, blue dots) as part of a larger study to assess non-energy resources 

(sand, gravel, minerals) on the southern New England continental shelf and to investigate the subsurface

geology in the area (Neff et al. 1989; Poppe et al. 2002). Three of these cores (Figure 4-3, cores 88-12, 

88-13, 88-14) are within the Submerged Paleolandscapes Project study area and will be discussed in more 

detail in Section 6.1 of this report as part of an assessment of legacy data. 

Figure 4-3. Vibracores obtained in the vicinity of the USGS seismic reflection data. 

Purple dots show the location of cores obtained in 1976 to develop a sea level rise model of the area. Blue dots show 

the location of cores obtainted in 1988, as part of an unrelated study to identify minerals resources on the OCS.

Later studies that examined vibracore or borehole data from Rhode Island or Block Island Sounds 

include:

1. An investigation of the origin and evolution of Quaternary sediments in West Passage, 

Narragansett Bay using seismic stratigraphy, and multidisciplinary analyses of sediment samples 

obtained from borings collected near the Jamestown Bridge. Results of this study suggest a 

subsurface stratigraphic framework for western Narragansett Bay that is very similar to the 

framework developed for the Rhode Island continental shelf by the USGS studies, but a 

correlation between these two sets of findings was not made by the authors (Peck and McMaster
25

1991). The results of this study will be discussed in more detail in Section 6.3 of this report as 

part of the case study of Greenwich Bay.

2. A preliminary paleoenvironmental characterization of an approximately 15-km2 area south of 

Block Island using CHIRP sub-bottom profiles and analyses of 9 sediment cores (Coleman and 

McBride 2008). This study focused on identifying relict geomorphic features interpreted from the 

CHIRP profiles and identified the associated depositional environments. No attempt was made to 

correlate these findings to the larger regional framework previously developed by the USGS.

3. A geoarchaeological marine site characterization study of a submarine cable linking a windfarm 

southeast of Block Island to mainland Rhode Island. Multibeam bathymetry, side-scan sonar, 

magnetic intensity measurements, vibracores, and shallow and intermediate sub-bottom profiles 

were acquired along the proposed cable corridor. Surface and subsurface conditions were 

assessed for engineering and design purposes, shallow hazards, and the potential impact of subseabed cable installation on submerged cultural resources. Analyses focused on characterizing 

conditions within a narrow APE centered on the proposed cable installation corridor

(approximately 300 m wide horizontally on the seafloor with 3.3 m of subsurface depth) 

(Robinson 2012 a,b; Ocean Surveys Inc [OSI] 2012).

4. Two recent studies (Sheldon 2012 and Caccioppoli 2015) utilized cores and borehole data to 

extend the USGS subsurface stratigraphic framework south of the original USGS survey area.

Results of these studies are discussed in Section 4.3.2.4 of this report.

Regional age control: In addition to the lack of systematic core data to verify the offshore regional 

geologic framework developed through sequence stratigraphy, comprehensive age control of the 

subsurface characteristics of the southern New England continental shelf have not yet been developed.

Much of the interpretation of the processes and timing associated with the subsurface geological record is 

based on an overall understanding of the regional glacial and post-glacial history of the area, and 

correlation between the acoustic record and terrestrial outcrops. The only study (Oldale and O’Hara 1980) 

that applied absolute dates to the regional seismic reflection interpretations discussed above (Poppe et al. 

2002; McMullen et al. 2009 a, b; Needell et al. 1983 a, b, c) was conducted using samples from 

vibracores collected in eastern Rhode Island Sound (Figure 4-3, purple dots), which were acquired to 

accompany the USGS geophysical survey conducted in that area (O’Hara and Oldale 1980; McMullen et 

al. 2009b). Radiocarbon dates were obtained from 22 peat and shell samples, with resulting ages ranging 

from > 35,000 yBP (referenced to 1950) for two fragments of Upper Cretaceous lignite occurring in

glacial outwash deposits, to 830 (+ 200) for a shell fragment occurring in sand and gravel. Intermediate 

dates were obtained that defined approximately 1,000-year intervals between 13,500 (+ 1,000) and 1,340 

(+ 200). This Late Pleistocene–Holocene chronology was used to produce a post-glacial sea level rise 

curve for southeastern Massachusetts (Oldale and O’Hara 1980) that is still referenced by contemporary 

researchers. Additional sources of regional age control include:

• Radiocarbon dates from borings collected in southwestern Narragansett Bay (Peck and McMaster

1991)

• Radiocarbon dates from shell and peat marsh samples, obtained to develop local sea level rise 

models (Engelhart et al. 2009; Engelhart 2010; Engelhart et al. 2011; Engelhart and Horton 2012; 

O’Hara and Oldale 1980)

• Four radiocarbon dates from shell material collected in sediment cores south of Block Island, 

obtained to assist with a preliminary paleoenvironmental characterization for the area (Coleman 

and McBride 2008)
26

• Correlations between varve sequences identified in cores from the Providence River (Upper 

Narragansett Bay), the North American Varve Chronology and cosmogenic exposure ages from 

glacial moraines (Oakley and Boothroyd 2013)

• Varve chronologies and cosmogenic-nuclide analyses of moraine deposits for southern New 

England (Balco et al. 2009; Balco and Schaefer 2006; Balco et al. 2002)

Each of the investigations discussed above was focused in small geographic areas on the Rhode Island 

continental shelf, and was not designed to systematically ground-truth the extensive seismic reflection 

dataset collected by the USGS between 1975 and 1981. Detailed re-examination and/or reinterpretation of 

these data could assist with refining the regional stratigraphic framework developed by the USGS, but is 

beyond the scope of the Submerged Paleolandscapes Project.

4.3.2.4 Follow-Up Research

The geologic framework produced by the series of foundation studies discussed above was developed 

through expert analysis of the stratigraphic record. Despite the lack of extensive coring studies or absolute 

age data, it continues to be the generally accepted interpretation of the stratigraphic sequences and 

associated processes that characterize the continental shelf off southern New England (see Section 4.1.2 

of this report). Other subsequent research has helped to refine regional Pleistocene glacial and interglacial

stratigraphy (Stone and Borns 1986; Stone and Sirkin 1996; Boothroyd and Sirkin 2002; Oakley 2012; 

Oakley and Boothroyd 2012; Oakley and Boothroyd 2013) and bedrock geology (Hermes et al. 1994) of 

southern New England, as well as provide important insight into the stratigraphy, depositional history and 

processes associated with the deglacial history of the region (Lewis and Stone 1991; Lewis and 

DiGiacomo-Cohen 2000; Oakley 2012; Oakley and Boothroyd 2013). Each of these follow-up studies 

contributed essential detail that is necessary to understand the regional subsurface record, but did not 

focus on ground-truthing the seismic reflection data collected earlier and did not result in substantial 

revisions to the existing geologic framework established by earlier research.

Only three investigations have specifically re-examined the regional geological framework developed by 

the USGS studies:

1. Goss (1993) refined the Quaternary geologic history of Block Island Sound by correlating welllog records and sedimentary facies visible in terrestrial outcrops on mainland Rhode Island to the 

seismic reflection data acquired in by the USGS seismic surveys. This study resulted in additional 

detail regarding the characteristics and processes associated with glacially derived sediment 

occurring stratigraphically above acoustic basement in the study area. 

2. Sheldon (2012) conducted a multidisciplinary investigation utilizing seismic stratigraphy, and 

sedimentologic and lithostratigraphic analyses to investigate the subsurface stratigraphy of the 

continental shelf approximately 3 nautical miles southeast of Block Island, Rhode Island. The 

purpose of this investigation was specifically to ground-truth the subsurface stratigraphic 

framework derived from the USGS seismic reflection studies by examining newly acquired 

geophysical data and down-hole logs and core samples from eight approximately 70-m borings. 

The results of this study indicated that the regional subsurface stratigraphic framework identified 

by the USGS also extends south of the USGS study area on the continental shelf. Additional 

details regarding the Cretaceous and Late Pleistocene/Early Holocene depositional environments 

represented by the stratigraphic record are also provided by this study.
27

3. Caccioppoli (2015) provided similar confirmation of the regional framework south of the USGS 

survey area by examining CHIRP seismic reflection profiles and vibracore data obtained at “The 

Mud Hole,” an anomalously deep depression located in southern Rhode Island Sound. This 

research was the subject of a Master of Science thesis conducted at the University of Rhode 

Island as part of Submerged Paleocultural Landscapes Project, and will be discussed in detail in 

Section 6.5 of this report.

None of these investigations listed above included absolute age determinations, although Sheldon (2012) 

used mineralogical analyses to confirm the age of the Cretaceous deposits occurring at the base of the 

stratigraphic sequence in the southern portion of the southern New England continental shelf.

4.3.3 Overview of the Subsurface Stratigraphic Framework of the Southern New 

England Continental Shelf 

The research reviewed above resulted in the creation of a regional subsurface stratigraphic framework for 

the southern New England continental shelf. A simplified stratigraphic sequence consists of five geologic 

units (Needell et al. 1983a) separated by three regional acoustic reflectors interpreted to represent 

erosional unconformities. These deposits can be grouped into three general packages according to age 

(Figure 4-4).

As shown in Figure 4-4, two ancient units at the base of the stratigraphic sequence represent preMesozoic bedrock (Pzz) and, in the southern part of the study area, Cretaceous continental shelf and 

coastal plain deposits (Ku). These two units are separated from the overlying sediments by a prominent 

acoustic reflector (fu2)interpreted to be an unconformity representing approximately 64 million years of 

material that is absent due to erosion by Pleistocene glaciers. Above this unconformity are two sequences 

of Pleistocene/Early Holocene age deposited by glacial and post-glacial processes. The lowermost 

Pleistocene unit (Qdo and/or Qdm) was identified as “glacial drift” and is inferred to consist of till, 

morainal deposits, ice-contact sediments, outwash, glaciolacustrine deposits, and sediments deformed by 

overriding glacial ice (Needell et al. 1983a). This unit is separated from the younger one above it by a 

regional unconformity inferred to represent subaerial exposure of the landscape after the Wisconsinan ice 

retreated (fu1). Late Pleistocene/Early Holocene sediments thought to be associated with fluvial and 

estuarine deposition (Qfe) occur above this reflector. At the top of the stratigraphic sequence, a third

unconformity caused by marine inundation (mu) represents erosion of these fluvial and estuarine deposits 

by post-glacial sea level rise. Holocene marine sediments (Qpt) deposited by modern marine processes 

overly this unconformity (Needell et al. 1983a). Geographic variations in the presence, spatial extent, and 

composition of each of these stratigraphic units occur throughout the southern New England continental 

shelf. This stratigraphic sequence, and its importance with respect to reconstruction of paleolandscapes in 

the study area, will be discussed in more detail in Section 6 of this report, when a preliminary 

paleocultural sensitivity model is developed for the Submerged Paleolandscapes Project area.
28

Figure 4-4. USGS stratigraphic framework of the subsurface continental shelf off Rhode Island. 

Upper panel shows an idealized stratigraphic section with a simplified description of each stratigraphic unit. Note that 

the thicknesses of the stratigraphic units in this illustration are not to scale. Lower panel shows an excerpt of a 

seismic reflection profile obtained by the project team south of Narragansett Bay and interpreted according to the 

established stratigraphic framework illustrated in the upper panel. 

4.3.4 Key Points

• The terrestrial and submerged topography in the study area has been significantly impacted by 

Pleistocene glaciations. Understanding the processes and sedimentary deposits associated with 

glaciation, as well as the glacial and deglacial chronology of the region, is necessary to identify 

the location of potentially preserved paleolandscapes that could have been inhabited by ancient 

Native peoples.

• The overall deglacial chronology of the study area is well established, but there is currently a lack 

of region-wide absolute dates needed to develop a detailed timeline. Margins of error associated 

with varve chronology correlation, cosmogenic-nuclide, and radiocarbon dating can range from 

hundreds to thousands of years. These margins of error should be clearly understood when 
29

identifying paleolandscapes that may have been available for occupation by ancestral Tribal 

peoples.

• The subsurface framework of the southern Rhode Island continental shelf consists of five 

stratigraphic units and three regional acoustic reflectors thought to represent unconformities 

(Figure 4-4). This framework was developed by expert analysis of the stratigraphic record but is 

based primarily on decades-old, reconnaissance-level (approximately 2-km trackline spacing) 

seismic reflection profiles using the technique of sequence stratigraphy.

• Sediment cores have not been collected in a systemic manner to ground-truth the seismic 

reflection data, although the cores that have been obtained (O’Hara and Oldale 1980; Needell and 

Lewis 1984; Thomas 1985; Poppe et al. 2002; McMullen et al. 2009b; Sheldon 2012; 

Caccioppoli 2015) confirm the USGS geophysical interpretations at a regional level.

• Radiocarbon dates are available for samples collected from16 vibracores associated with the 

USGS survey in eastern Rhode Island Sound. Absolute dates to ground-truth the sequence 

stratigraphy in other areas of Block Island and Rhode Island Sounds are not yet available.

• Large data gaps significantly impact the current ability to develop a high-quality regional 

paleolandscape reconstruction for the continental shelf off southern New England, but a

reconnaissance-level stratigraphic framework has been developed.

4.4 Sea Level Change History in the Study Area

4.4.1 Overview

An accurate reconstruction of Late Pleistocene and Holocene post-glacial sea level change is needed to 

identify the areas on the continental shelf that were once sub-aerially exposed and available for 

occupation by ancient Tribal peoples and to understand the extent to which these landscapes survived 

marine inundation. The following synthesis provides a regional overview of post-glacial sea level change 

in southern New England. A detailed discussion of specific sea level rise models applicable to the 

Submerged Paleolandscapes Project study area is presented later in this report.

The Laurentide Ice Sheet advanced across the New England landscape in the Late Wisconsin period,

reaching its maximum extent approximately 26,000 years ago before beginning to retreat back out of

southern New England. Retreat of the ice sheet approximately 26,000 yBP caused sea level to rise from 

its global lowstand approximately 120 m below present sea level and rapidly accelerate by 15 kyBP 

(Peltier and Fairbanks 2006; Oakley and Boothroyd 2012). There remains some uncertainty regarding 

how quickly isostatic rebound of the land surface began following the retreat of the ice sheet. Oakley and 

Boothroyd (2012) favor a delayed onset approximately 16 kyBP, whereas geophysical models support 

concurrent rebound and retreat (Roy and Peltier 2015). Regardless, by 16 kyBP, isostatic rebound was 

likely outpacing sea level rise for 2,000 years at the Late Wisconsinan terminal margin near Block Island.

In coastal New England, uplift followed a 0.85 m/km rebound profile towards the northwest at 331 

degrees, based on measurements of delta elevations representing formerly horizontal water levels in proglacial lakes (Koteff et al. 1993; Oakley and Boothroyd 2012).

By the Early Holocene, sea level was still rising rapidly in southern New England, and isostatic rebound 

had been mostly completed (Engelhart and Horton 2012; Oakley and Boothroyd 2012). From 8–4 kyBP 

sea level rise still remains poorly constrained, however reconstructions of sea level from basal sea level 

index points from salt marshes in Connecticut reveal sea level rise had slowed to 1.7 mm/yr between 6 
30

and 4 kyBP (Engelhart and Horton 2012). The Atlantic Ocean began to inundate the stream systems cut 

into the drained lake-beds in present-day Long Island, Rhode Island and Block Island Sounds, marking a 

transition to an estuarine depositional environment. Estuarine sands, silts, clays, and freshwater peats are 

thought to overlie fluvial channel fill (O’Hara and Oldale 1980; Needell et al. 1983a, b, c; Needell and 

Lewis 1984).

A prominent transgressive wave-cut surface, often called the “ravinement,” is observable in regional 

seismic reflection data (from Rhode Island Sound: O’Hara and Oldale 1980; Needell et al. 1983a, b, c; 

from Block Island Sound: Needell and Lewis 1984; from Long Island Sound: Lewis and Stone 1991), 

representing erosion of the landscape by post-glacial sea level rise. Fine-grained marine sediment 

conformably drapes the ravinement surface in deeper basins that are less prone to erosion by bottom 

currents. Shallower regions are more commonly covered with coarser reworked beach sand and gravel 

(O’Hara and Oldale 1980; Needell et al. 1983a, b, c; Needell and Lewis, 1984; Lewis and Stone, 1991).

4.4.2 Implications for Paleolandscape Reconstruction and Predictive Modeling in the 

Project Area

Sea level change curves have two significant implications for paleocultural sensitivity modeling. First, 

they are frequently used to develop hypotheses regarding the general location of paleoshorelines in the 

geologic past, and therefore can be used to identify areas on the continental shelf that may have been 

subaerially exposed and available for human habitation. Although this process can be generally 

instructive, the discrepancies discussed above between the various relative level rise models available for 

southern New England must be taken into consideration during their use, especially when developing 

illustrations of projected paleoshoreline positions. Even relatively small degrees of error in the vertical 

dimensions of sea level change curves can translate into significant horizontal variations in the 

reconstructed geographic positions of paleoshorelines. For example, at 4,000 yBP, relative sea level is 

estimated to be 7 m below its present level using the Roy and Peltier (2015) curve and 3 m below present 

using the Oakley and Boothroyd (2012) curve. The 4-m vertical discrepancy between these two curves 

will impact the projected hypothetical location of the paleoshoreline at this time by significantly more 

than 4 m horizontally.

Second, the amount and rate of sea level change has a significant impact on paleolandscape preservation 

and archaeological sensitivity (i.e., the potential for archaeological sites to be present). Sea level rise and 

the marine transgression of the land is a predominantly destructive process termed “shoreface retreat,” 

wherein previously deposited sediments on land are eroded by powerful wave and current processes as 

the shoreline moves inland (Waters 1992). Because of the erosive force of water, much of the marinetransgressed landscape that was once terrestrial on the southern New England continental shelf has been 

significantly altered or destroyed through erosion that occurred during and after inundation. Slower rates 

of sea level rise allow for the greater development of coastal features, such as berms, barrier beaches, 

coastal wetlands, and marshes. These features together form an ecologically rich and diverse landscape 

abundant in plant and animal resources that would have been attractive for human utilization and 

habitation. Greater usage of this landscape would inevitably have resulted in a higher volume of material 

culture residue deposited into the archaeological record. In contrast, higher rates of sea level rise inundate 

and erode coastal areas more rapidly, thereby preventing the formation of coastal features typical of more 

stable shorelines. This, in turn, would lead to there being potentially less deposition of material cultural 

into the archaeological record, and, therefore, fewer sites. An exception to the generally destructive nature 

of rapid sea level rise are those isolated instances where the marine transgression of the land occurs by a 

process known as “stepwise retreat,” during which coastal landforms and sediments are drowned 

suddenly and left in place as the surf and breaker zones jump from the active shoreline to a point further 

inland (Waters 1992). The exact rate of sea level rise associated with preservation or erosion of coastal 
31

features varies according to local pre-inundation topography, post-inundation bathymetry, prevailing 

wind, wave, and current regimes, and geomorphology and geology.

During the past 4,000 to 5,000 years, the northeast coast of the U.S. has remained relatively stable, with 

sea level rise rates of approximately 2 mm or less (Engelhart et al. 2011), which may assist with 

predicting where paleolandscapes could be preserved from that time period. Predictions become more 

difficult moving further back in time. It may be necessary to focus on specific time intervals where 

geologic information provides clues about possible landscape formation and preservation. Other time 

periods in which very rapid inundation occurred should also be examined, because rapid drowning of 

landscape features may protect them from erosion.

4.4.3 Key Points

• Sea level change reconstructions can assist with visualizing generally areas of the continental 

shelf that were subaerially exposed during key time periods of human habitation. Discrepancies 

between projected paleoshoreline positions for southern New England should identified and 

discussed in all illustrations.

• The presence or absence of preserved elements of paleolandscapes inundated by sea level rise is 

likely to be largely a function of localized variables, such as pre- and post-inundation 

topography/bathymetry, prevailing wind, wave, and current regimes, and 

geomorphology/geology. The amount and rate of sea level rise will also likely influence the 

extent to which paleolandscapes are preserved. 

4.5 Paleocultural Context

A regional understanding of the archaeological and paleocultural context of the project’s marine study 

areas, based on knowledge of ancient Tribal contact period human settlement and land use documented in 

the available archaeological record for the adjacent onshore area, as well as in shared accounts of the 

Narragansett’s Tribal oral history, is important for understanding and modeling how the archaeological 

expression of these activities may be manifested in the submerged paleocultural landscapes potentially 

preserved offshore. Information sources particularly relevant for understanding this context synthesized 

and summarized in this document are the two recently produced archaeological reports on investigations 

conducted in coastal Rhode Island (the southern coast of mainland Rhode Island and the coast of Block 

Island) by McBride et al. (2016) and Waller and Leveillee (2016), prepared for RIHPHC and NPS as part 

of a Hurricane Sandy Disaster Relief Grant. Also informative were the transcribed contents of an 

interview conducted in 2010 by URI researchers with the late Dr. Ella Sekatau, former Narragansett 

Indian Tribal (NIT) Medicine Woman and Ethnohistorian, as part of the development of the Rhode Island

Ocean Special Area Management Plan (URI 2010), as well as the comments by John Brown, NITHPO

and Medicine Man, and Doug Harris, Preservationist for Ceremonial Landscapes and Deputy NITHPO, 

recorded in a 2012 documentary film prepared for the Rhode Island Deepwater Wind Energy Project (TPI

2012). 

Pre-contact period cultural chronologies developed by archaeologists for the onshore portion of southern 

New England adjacent to the project study area are based on the presence and distributions of specific 

artifact types and the associated radiocarbon dates obtained at the archaeological sites where the artifacts 

were found. These archaeological data are compiled from the accumulated results of decades of academic 

archaeological research, professional cultural resource management surveys, and serendipitous reported 

spot-finds by the public and avocational archaeologists. From the distributions and dates of these

catalogued cultural materials may be inferred patterns of past human behavior based on evidence of
32

ancient land use, resource utilization, and, in some cases, elements of ceremonial practices. These patterns 

may then be used in assessments and modeling of the archaeological sensitivity (i.e., the likelihood for 

there to be cultural deposits) within a given project study area. Given that the only submerged sites known 

in the project study area were the few that were found during this study, virtually all of the archaeological

data available for modeling in the offshore environment comes from the onshore terrestrial record.

Consequently, it must be acknowledged that different, as-yet identified, site types, cultural materials, and 

represented time periods may exist in submerged contexts that are not found on shore. 

Archaeologists working onshore in southern New England over the last several decades have developed a 

basic cultural chronology for the region that is essentially a theoretical model developed from inferences 

based on decades of archaeological research. This chronology is used to characterize and organize the 

region’s human past during the pre-European contact (“Pre-contact”) period. The chronology is divided 

into three principal archaeological time periods: “PaleoIndian” (ca. 12,500–10,000 yBP); “Archaic” (ca. 

10,000–3,000 yBP); and “Woodland” (ca. 3,000-450 yBP). The latter two of these time periods is then 

subdivided into “Early,” “Middle,” and “Late” subperiods. An additional, distinct period—the 

“Transitional Archaic” (ca. 3,000-2,500 yBP)—is also included in the sequence between the Late Archaic 

and Early Woodland Periods. A “Late PaleoIndian” (ca. 10,000–8,000 yBP) Period is also sometimes 

included in discussions about southern New England’s PaleoIndian Period. For this study and report, the 

reader is directed to McBride et al. (2016) and Waller and Leveillee (2016) for detailed descriptions of the 

Contact Period and Post-contact Period elements of the archaeological and cultural context chronology.

There is now unequivocal archaeological evidence of a human presence in the Americas predating the 

typical ca. 12,500 yBP start date for the onshore southern New England cultural chronology

corresponding to an archaeological period called the “Pre-Clovis” (ca. 24,000–12,500 yBP) (Dillehay 

1989; Halligan et al. 2016; Raghaven et al. 2015; Skoglund et al. 2015). However, the potential for 

cultural sites dating from the Pre-Clovis Period to exist within the limits of the Laurentide glacial ice

sheet’s maximum extent (corresponding with the locations of Long Island [New York], Block Island 

[Rhode Island], and Martha’s Vineyard and Nantucket [Massachusetts]), must be considered extremely 

remote given of the massive impacts to the glaciated land surface that occurred as a result of the advance, 

retreat, and melting of the ice sheet. The same may not be said, however, of the potential for Pre-Clovis 

Period sites to be submerged and embedded in sediments further out on the continental shelf, beyond the 

limits of the Late Pleistocene southern New England glacial maximum, where it is possible there was a 

human presence that produced archaeological sites that survived inundation and are present within 

preserved remnants of submerged paleocultural landscape. Thus, the Pre-Clovis Period is included in the 

chronology here. 

Hypothetically, the rapidly changing environment that characterizes the Late Pleistocene to Early 

Holocene time period should have produced an archaeological record of site types that is highly variable 

because of the need for flexible responses in social and resource utilization behaviors to the rapidly 

changing environmental conditions (Jones 1998). Increasingly, evidence of lowered water levels and an 

emergent correlation between large wetlands and major water bodies and ancient Native American 

archaeological sites suggests that water (inland and coastal) and its associated food resources were critical 

factors in site selection. Hypotheses are now proposed that assert large Early and Middle Archaic Period 

archaeological sites in proximity to large lakes, rivers, and extensive wetlands with inlets and outlets 

flushing their respective systems may have been more common on the coastal plain submerged by the 

rising sea level (McWeeney and Kellogg 2001), however, they are not represented in the terrestrial 

archaeological record onshore. It is perhaps for this reason that certain site types (especially large coastal 

occupations and very small interior camps and resource extraction locations) seem to be lacking or are 

very rare in the terrestrial archaeological record, as it presently known (Jones 1998). With few exceptions, 

virtually all documented PaleoIndian and Early Archaic Period finds reported throughout New England 

lack detailed contextual information. As archaeological data provides but a single lens through which to 
33

view, interpret, and understand past human and environmental histories, also incorporated into the 

archaeological and paleocultural context here are elements of the Narragansett Indian Tribe’s oral history 

traditions, as provided in the interview with Dr. Sekatau that was included in the Rhode Island Ocean 

SAMP (URI 2010), and as supplemented by Mr. Brown and Mr. Harris’s comments (TPI 2012). For 

example, Native oral traditions also point to a coastal focus for the ancestral Narragansett. According to 

Dr. Sekatau, “Enishkeetompauog minnimussinnock,” is a Native description that applied to the 

Narragansett and translates to “people of the small bays and inlets” (URI 2010). Dr. Sekatau also noted 

during her interview:

Our existence depended upon what the territories embraced directly from the salt water, 

marshes, and sweet [freshwater] waterways that flowed from inland springs, ponds, and 

seeps...The salt waters gave much to the Natives...The marshes around the sweet and the 

saltwater, and even mixtures of sweet-water joining saltwater, played a most important 

role in the existence of the Narragansett Indian peoples...They utilized saltwater fish, 

mammals, and shellfish, as well as the sweet-water fish, shellfish, and mammals. These 

creatures were used for food, clothing, parts of decorations, and shelter (URI 2010). 

Taken together, the available archaeological record for the adjacent onshore area and shared accounts of 

the Narragansett’s Tribal oral history provide an indication for the relationship between ancient human 

activity and the submerged paleocultural landscapes potentially preserved offshore that can be used to 

inform the archaeological sensitivity model. 

4.6 Previous Modeling in the Project Area

Previous modeling efforts in the project area have been limited to preliminary assessments of pre-contact 

period archaeological sensitivity conducted as part of four different studies: 1) URI 2010; 2) Garrison et 

al. 2012; 3) Robinson et al. 2012a; and 4) Robinson et al. 2012b. The first study (URI 2010) was 

associated with the development of the Rhode Island Ocean Special Area Management Plan (RI 

OSAMP). Included in the RI OSAMP document (see Chapter 4: Cultural and Historic Resources) were a 

brief geological context; a transcription of an oral account of Narragansett Tribal history as provided 

during an interview conducted by the URI with (the now late) Dr. Ella Sekatau, Narragansett Tribal 

Ethnohistorian and Medicine Woman; and a brief paleogeographic landscape reconstruction accompanied 

by projected paleoshoreline location maps that applied the Peltier and Fairbanks (2006) sea level change 

model to existing bathymetry within the RI OSAMP study area. The paleogeographic landscape 

reconstruction indicated ancient people could have occupied the part of the continental shelf located 

within the limits of the RI OSAMP study area between about 12,000 and 6,000 yBP when sea level was

modeled to be between about -55 to -6 m below its present level (Peltier and Fairbanks 2006). 

Narragansett Tribal oral traditions shared by Dr. Sekatau seem to agree with the accepted geoscientific

data regarding sea level rise, as today’s Narragansett think about what was and how far the Atlantic Plains 

extended before the water covered them. Narragansett oral tradition also indicates the RI OSAMP study 

area was occupied by ancient Tribal peoples prior to the last glaciation, and that these people moved south

with the last glacial advance and back northward to present-day Rhode Island as the glacier's retreated. 

Access to the “sweet” (i.e., fresh water) and salt waters along the coast was apparently very important to 

the ancient Tribal peoples, because of the abundance the waters offered them in terms of resources for 

food, clothing, and shelter. The marshes, in particular, seem to have played a most important role in the 

existence in the ancient and ancestral Narragansett peoples (URI 2010).

The second study (Garrison et al. 2012) was funded by BOEM to supplement and update two previous 

BOEM (then “Minerals Management Service”) studies of portions of the Atlantic OCS that were carried 

out nearly 40 years ago (ICA 1979; SAI 1981). These two studies collectively covered the area from the 
34

Bay of Fundy to Key West and provided a broad overview of the geology, pre-contact period history, and 

sea level rise data that could affect submerged pre-contact period site preservation, as well as a predictive 

model for locating post-contact period shipwrecks. The Garrison et al. (2012) study built upon the ICA 

1979 and SAI 1981 studies by exploring more recent research on pre-contact period settlement patterns, 

archaeological research, and relative sea level curves to refine the earlier predictive models for locating 

intact, submerged pre-contact archaeological sites and shipwrecks on the OCS. Sections 1.2.2 and 2.4 of 

the Garrison et al. (2012) report focused specifically on the southern New England region and 

summarized regional geology, sea level change, anticipated impacts from marine transgression, and 

conditions likely to lead to submerged paleolandscape and pre-contact period site preservation. The study 

also assessed general archaeological sensitivity for the OCS extending across Federal waters east of the 

southern New England region. The Garrison et al. (2012) assessment defined three categories of 

archaeological sensitivity based on the general projected locations of paleo-sea levels. The first category 

was “no sensitivity.” The no sensitivity area lies below the projected -107 m sea level lowstand

corresponding with the Last Glacial Maximum (LGM) of ca. 22,000 yBP and is an area presumed to have 

always been under water and never subaerially exposed in the archaeologically documented history of a 

human presence in southern New England. The second category was “Low Sensitivity.” This area lies 

between the -107 m and -70 m sea levels, the latter of which corresponds to ca. 12,000 yBP and the time 

around which the onshore archaeological record provides the first evidence of a human presence in the 

region. The Low Sensitivity area recognizes that although there is not yet any archaeological evidence for 

a human presence in the region predating 12,000 yBP, it does not mean that it does not exist, particularly 

on the now submerged portions of the OCS that were south or east of the glacial terminus and exposed 

land prior to 12,000 yBP. The final category was “High Sensitivity.” The high sensitivity area includes 

the portion of the shelf that extends between the -70-m sea level of ca. 12,000 yBP and the 3-mile 

nearshore limit of Federal waters, which corresponded closely with sea level at around 6,000 yBP. It is 

within this portion of the Garrison et al. (2012) southern New England study area that there was exposed 

land available for habitation by ancient Tribal peoples between ca. 12,000–6,000 yBP. These ancient 

peoples would have been associated with today’s PaleoIndian, Early Archaic, and early part of the Middle 

Archaic archaeological periods.

The third and fourth studies (Robinson et al. 2012a and b) were conducted in support of the Federal and 

state permitting requirements associated with the development of Deepwater Wind’s Block Island Wind 

Farm (BIWF) and Block Island Transmission System (BITS) projects. Both of these studies involved, for 

the first time, active participation of Tribal historic preservation specialists in the development of each 

project’s marine geoarchaeological research design and in the execution of the field research and data 

analyses. Reporting produced from each study provided brief summaries of the geologic and paleocultural 

contexts, and interpretations and recommendations based on the examination of marine geotechnical 

samples (i.e., deep borings and vibracores). The studies processed marine geophysical data collected 

within each project’s offshore APE. Robinson et al’s (2012a and b) assessments ultimately concluded that

though there was potential for submerged sites to be preserved within the BIWF and BITS project areas, 

review of geotechnical and geophysical data indicated that no archaeologically sensitive submerged 

paleolandforms were present within either project APE. However, indicators of preserved paleolandforms 

submerged and buried below the maximum depth of the BITS project’s anticipated impacts were 

observed in the sub-bottom profiler data. 
35

5 Application of Modeling Process to the Project Study Area, 

Step 2: Developing and Assessing Paleoshoreline Models

5.1 Introduction and Goals

Identifying culturally sensitive locations on the continental shelf first requires an understanding of where 

and when currently submerged areas may have existed as terrestrial landscapes that were available for 

human occupation. In southern New England, the amount and location of habitable land on the 

continental shelf was associated with the timing of Late Wisconsinan glacial ice retreat, and the rate and 

magnitude of post-glacial sea level rise. As described above, Garrison et al. (2012) developed a regional 

archaeological sensitivity model for the southern New England continental shelf by combining sea level 

rise hypotheses with archaeological information. Areas of the continental shelf that were submerged 

during the LGM were identified by Garrison et al. (2012) as having no sensitivity because they were 

never subaerially exposed and inhabitable land. Low sensitivity areas were those that were subaerial 

between the LGM and the PaleoIndian archaeological period, representing a time when areas of the 

continental shelf were subaerially exposed before the earliest archaeological record of human habitation 

in the northeast. High sensitivity areas were inferred to be subaerial and inhabitable beginning around 

12,000 yBP, the time of the earliest dated archaeological evidence of human habitation in the region, up 

to ca. 6,000 yBP, the date corresponding to the approximate location of the subaerially exposed shelf and 

the Garrison et al. (2012) study area’s shoreward Federal waters limit.

Inclusion of this type of modeling in research designs for marine archaeological compliance studies 

performed for offshore development projects is a growing concern. Models of hypothesized 

paleoshoreline locations are often developed by applying pre-existing sea level rise models to the 

contemporary bathymetric surface in a given study area using geospatial computer software. In theory, 

this type of modeling can be used to develop hypotheses regarding archaeological sensitivity based on the 

timing and extent of the shelf’s exposure and potential inhabitability by humans. However, these types of 

models incorporate assumptions and sources of error have significant impacts on reconstructed 

paleoshoreline positions. The purpose of the following discussion is to apply this approach to create 

paleoshoreline models for the Submerged Paleolandscapes Project study area, evaluate the results, and 

provide recommendations about using this type of modeling for future paleocultural sensitivity 

assessments.

5.2 Relative Sea Level Change Models for Southern New England

The first step in reconstructing the hypothetical locations of paleoshorelines for the study area is to select 

a sea level change curve that can be used to estimate the location of the sea surface at key times in the 

past. The chronology, rate, and magnitude of relative sea level rise following glacial retreat is a function 

of the complex relationship between coastal topography, eustatic flooding, sedimentation, and isostatic 

rebound of the Earth’s crust as the weight of the ice overburden is removed (McMaster 1984). Sea level 

change curves are developed using varying methodologies and data types, and incorporate these variables 

to different degrees. The purpose of this step is not to evaluate the detailed methodology used to construct 

each curve, but only to choose one that is considered the most robust curve for the rate and timing of sea 

level rise within the study area by researchers in the field. 

The relative sea level (RSL) curves that have been developed for southern New England vary 

significantly. Four models are referenced most frequently:
36

1. Roy and Peltier (2015): These RSL curves were created to compare models of glacial isostatic 

adjustment with the extensive sea level indicator database developed by Engelhart et al. (2011)

(see item 2 below). Specifically, iterative improvements of both the ice loading deglaciation 

history (“ICE-6G_C”) and mantle viscosity (“VM6”) models for the U.S. Atlantic coast were 

examined, with particular emphasis on assessing the influence of the glacial “forebulge” collapse 

on isostatic adjustment, and therefore on post-glacial sea level rise. Overall, Roy and Peltier’s 

combination of the ICE-6C_C and VM6 models produced an RSL curve that is in good 

agreement with the Engelhart et al. (2011) (see item 2 below) database of index points. In the 

southern New England area (specifically the “Southern Massachusetts”, “Connecticut,” and 

“Long Island” regions in the Engelhart et al. [2011] study), the agreement is particularly good 

between 0 and approximately 4,500 yBP. For time periods earlier than approximately 4,500 yBP, 

Roy and Peltier’s RSL curves indicate that sea level was lower than suggested by the terrestrial 

and marine-limiting data points. Therefore, the Roy and Peltier model may imply that more of the 

continental shelf was exposed before 4,500 yBP than the database of Engelhart et al. (2011) 

suggests.

2. Engelhart et al. (2011): This dataset consists of 492 RSL index points for the Atlantic Coast of 

the U.S. and 344 limiting dates, which constrain the minimum or maximum limits of former sea 

level. The majority of the index points are from 6,000 yBP to the present time, with only 7% 

older than 6,000 yBP, and most are derived from investigation of salt marshes. Sixteen regional 

sea level curves along the U.S. East Coast were produced using this extensive dataset. The 

“southern Massachusetts,” “Connecticut,” and “Long Island” curves are geographically closest to 

the Submerged Paleolandscapes Project study area. In this investigation, particular attention was 

given to strict quality control, consistent methodology between study areas, and accurate 

estimates of error (Engelhart et al. 2011), resulting in a robust dataset.

3. Oakley and Boothroyd (2012): This RSL curve focuses on the area of the late Wisconsinan 

terminal ice margin south of Block Island, Rhode Island. It differs methodologically from Roy 

and Peltier (2015) as it is not dependent on ice sheet loading and the solid Earth geophysics 

associated with glacial isostatic adjustments, but instead considers the algebraic difference 

between delayed isostatic adjustment and a best-fit eustatic sea level curve. The uplift profile 

resulting from isostatic rebound is recorded by formerly horizontal water levels of pro-glacial

lakes, which project onto a linear plane. Oakley and Boothroyd (2012) argue that no measurable 

isostatic rebound occurred prior to 16,000 yBP and may have been delayed as late as 14,000 yBP,

due to projected water levels and drainage of Glacial Lake Hitchcock, which occupied the 

present-day Connecticut River Valley. The mechanism proposed for delayed isostatic rebound is 

that the lithosphere underlying southern New England behaved as a rigid “crustal block”. This 

viewpoint is not in agreement with viscous mantle models, which favor contemporaneous uplift 

and ice retreat. In addition, the RSL curve proposed by Oakley and Boothroyd (2012) is in poor 

agreement with the Long Island and Connecticut RSL curves produced by Roy and Peltier (2015) 

from 4 to 0 kyBP, which is significant because of the excellent agreement of the Long Island and 

Connecticut RSL curves with the RSL index points over this time interval from the Engelhart et 

al. (2011) database. However, the Oakley and Boothroyd (2012) approach produced an important 

sea level change model that incorporates previously published data (Oldale and O’Hara 1980; van 

de Plassche et al. 1998; Donnelly and Bertness 2001; Peltier and Fairbanks 2006), with an expert 

understanding of deglacial geology and processes in southern New England.

4. Oldale and O’Hara (1980): The RSL curve proposed by Oldale and O’Hara was constructed 

based on radiocarbon dating of terrestrial peats and marine shells identified in vibracore samples 

obtained from the continental shelf in eastern Rhode Island Sound. Each dated sample served as 

either terrestrial limiting (RSL below) or marine limiting (RSL above). This approach helps to 
37

constrain sea level in space and time, and the proposed RSL curve represents a best fit of these 

limiting dates. Compared to the rigorous quality control measures applied for the RSL index 

points by Engelhart et al. (2011), each dated sample is subject to more error and uncertainty, 

including the assumption that the sample had remained in place following deposition. This curve 

was derived from a small study consisting of 22 radiocarbon dates, but is useful for constraining 

sea level change in the southeastern Massachusetts area.

Overall, the Roy and Peltier (2015) RSL curves appear to be most robust due to their agreement with RSL 

index points of Engelhart et al. (2011) and the overall performance of the latest geophysical models in all 

regions along the U.S. East Coast. However, the lack of index points earlier than approximately 

6,000 yBP is problematic for testing these models. The Oakley and Boothroyd (2012) RSL model 

incorporated radiocarbon dates earlier than 6,000 yBP, including those from the Oldale and O’Hara 

(1980) study, and presents a RSL hypotheses that serves as an important comparison.

5.3 Paleoshoreline Reconstructions for the Project Study Area

Because multiple RSL curves for southern New England exist and vary significantly, two were selected as 

the basis for paleoshoreline reconstructions for the project study area. The Roy and Peltier (2015) curve 

was chosen because it incorporates the most recent geophysical understanding of post-glacial isostatic 

rebound and is also in generally good agreement with the sea level index point database of Engelhart et al. 

(2011). Use of this model effectively combines recent geophysical and geological data as applied to 

reconstructing sea level change. The Oakley and Boothroyd (2012) model was also selected because it 

was developed using an alternative view of post-glacial isostatic rebound and combines a detailed 

understanding of southern New England glacial geology with previously published sea level data (van de 

Plassche et al. 1998; Donnelly and Bertness 2001; Peltier and Fairbanks 2006), including the Oldale and 

O’Hara (1980) data from southeastern Massachusetts. 

Ten paleoshoreline reconstructions were created that correspond with five archaeological time periods in 

southern New England:

1. 3,000 yBP: beginning of the Early Woodland Period

2. 6,000 yBP: beginning of the Late Archaic Period

3. 8,000 yBP: beginning of the Middle Archaic Period

4. 10,000 yBP: beginning of the Early Archaic Period

5. 11,000 yBP: mid-PaleoIndian Period

For each time period, two paleoshoreline reconstructions were created for comparison, one based on the 

Roy and Peltier (2015) RSL curve, and the other on the Oakley and Boothroyd (2012) RSL curve. 

Reconstructions were not developed for time periods more recent than 3,000 yBP because the 

comparatively small amount of sea level change that occurred in that time frame would not be easily 

visible on a regional map. In addition, reconstructions were not created for time periods earlier than 

11,000 yBP because both the Roy and Peltier (2015) and Oakley and Boothroyd (2012) RSL models 

suggest that inundation of the project study area did not begin until approximately 11,000 yBP.

Roy and Peltier (2015) developed 16 RSL curves for distinct geographic regions associated with the 

Engelhart et al. (2011) index points. The closest regions to the Submerged Paleolandscapes Project study 

area are Connecticut and Long Island to the west, and southeastern Massachusetts to the east. Because the 

project study area does not correspond to any of these regions but occurs geographically in between them, 

paleoshoreline reconstructions based on the Roy and Peltier (2015) were created by averaging the sea 

levels from each of these three nearby regions at the desired age. Table 5-1 summarizes the 
38

paleoshoreline ages (represented in yBP) and corresponding sea level data (represented as meters below 

present) for each RSL model.

Table 5-1. Comparison of relative sea level models for southern New England used for 

paleoshoreline reconstructions in the project study area.

Estimates of RSL (meters below present) for five ages (years before present) based on the average of 

the Roy and Peltier (2015) models for Connecticut (CT), Long Island (LI), and southeastern 

Massachusetts (SE MA), and the Oakley and Boothroyd (2012) model for Block Island. RSL values in this 

table are approximations obtained from visual inspection of published graphs.

Age

(yBP)

Roy & Peltier Oakley & Boothroyd

CT LI SE 

MA Average Block Island

3,000 4 4 4 4 2

6,000 15 17 16 16 6

8,000 33 36 34 34 13

10,000 48 53 49 50 30

11,000 55 64 57 59 50

Maps of hypothesized paleoshorelines were created for each time period using the information in 

Table 5-1, and ESRI’s ArcInfo software. The “Northeast Atlantic 3 Arc-Second Coastal Relief Model”

(National Geophysical Data Center 1999) was selected as the bathymetric base surface because it is 

available as a seamless raster grid for the entire study area, including Narragansett Bay. For each 

paleoshoreline reconstruction, the sea level value derived from the Roy and Peltier (2015) and Oakley and 

Boothroyd (2012) RSL curves was applied to the contemporary bathymetric surface to generate a new 

raster surface illustrating hypothesized areas of subaerial exposure and submergence. For example, the 

Oakley and Boothroyd (2012) RSL curve indicates that sea level near Block Island was approximately 6 

m below present at 6,000 yBP. Using the ArcInfo “Raster Calculator” tool, the contemporary bathymetric 

surface was made “shallower” by 6 m, because water depths are inferred to have been shallower if sea 

level was lower. Areas of the contemporary bathymetric raster that emerged above 0 m in elevation as a 

result of this calculation are considered to be exposed land at 6,000 yBP, and areas below 0 m in elevation 

are considered submerged. The new raster was then color coded so that all areas above 0 m are shaded 

green, and all areas below 0 m are represented in blue. This process was completed twice for each of the 

ages listed in Table 5-1, once using the average Roy and Peltier (2105) sea level for Connecticut, Long 

Island, and southeastern Massachusetts, and again using the Oakley and Boothroyd (2012) RSL curve.

5.4 Results

Figures 5-1 through 5-5 illustrate the paleoshoreline hypotheses produced by applying two RSL curves to 

a contemporary bathymetry in the study area. The results using the Roy and Peltier (2015) and Oakley 

and Boothroyd (2012) data are presented side by side at each time interval for comparison. Although both 

RSL curves are based on a combination of carefully researched, high-quality geophysical and geological 

data, they produce substantially different paleoshoreline reconstructions, primarily as a result of differing 

hypotheses regarding the timing and extent of isostatic rebound in the study area. Both models indicate 

that most of the continental shelf in the study area was submerged by 6,000 yBP, and therefore 

uninhabitable after that time. However, they differ significantly regarding the submergence of the 

Narragansett Bay area at 6,000 yBP. According to the Roy and Peltier (2015) reconstruction, the northern 

part of Narragansett Bay, including Greenwich Bay, would have been exposed land at that time, whereas 

the Oakley and Boothroyd model suggests that much of the same area was submerged. Significant 

variation between the two models is visible at 8,000 yBP, when the Oakley and Boothroyd (2012) RSL 

curve results in most of the continental shelf in the study area being submerged, whereas the Roy and 
39

Peltier (2015) model suggests that large areas were subaerially exposed and potentially available for 

human habitation. The discrepancies between the two models are even more pronounced at 10,000 yBP. 

These differences have a significant impact on identifying what areas of the continental shelf may have 

been available for human habitation at key times in the past, particularly for the earlier archaeological 

time periods when the absence of extensive RSL index points makes it difficult to test the models.

5.5 Implications for Predictive Modeling

The paleoshoreline reconstruction models illustrated in Figures 5-1 through 5-5 were viewed by the 

project team as graphical hypotheses regarding the general timing of when different parts of the overall 

study area may have been inundated and were, therefore, no longer part of a terrestrial landscape 

accessible for human habitation. The principal implication for these modeled time and geographically 

transgressive paleoshorelines is that the general position of the shoreline acts as a control over the 

possible ages, types, sizes, and predicted densities and distributions of archaeological sites that could be 

present within a particular area. Although there is the potential for sites dating from the earlier periods in 

the pre-contact period archaeological chronology (i.e., prior to ca. 11,000 yBP) to be present throughout 

this project’s entire study area, there would be no potential for former habitation sites from periods postdating the inundation of a progressively larger portion of the study area to be present. For example, based 

on the projected shoreline locations, there was essentially no potential for encountering, and no need to be 

considering and applying what is known from the archaeological record about, Woodland Period sites 

during the geoarchaeological investigations of the Mudhole or AMI study areas. Having even a general 

idea of where shorelines may have been located at particular times of interest in the past is a simple way 

of focusing attention and resources on a specific time period and range of expected site types and 

distributions. 
40

Figure 5-1. Paleoshoreline reconstructions for 3,000 yBP in the study area.
41

Figure 5-2. Paleoshoreline reconstructions for 6,000 yBP in the study area.3
42

Figure 5-3. Paleoshoreline reconstructions for 8,000 yBP in the study area.
43

Figure 5-4. Paleoshoreline reconstructions for 10,000 yBP in the study area.
44

Figure 5-5. Paleoshoreline reconstructions for 11,000 yBP in the study area.
45

5.5 Recommendations

Although paleoshoreline models of this type are straightforward to generate with geospatial software, this 

type of model incorporates several sources of uncertainty:

1. Methodological variations: The development of sea level change models is an extremely complex 

process that incorporates several types of data and varying methodologies. For many study areas, one 

generally accepted model does not yet exist. Individuals who are interested in developing 

paleoshoreline reconstructions need to choose between available models, sometimes without a 

thorough understanding of how the models were constructed, the underlying assumptions, and 

margins of error.

2. Lack of dataset access: Obtaining an age and corresponding sea level through visual inspection of a 

printed graph, instead of from the numerical data used to construct the graph, is imprecise. However, 

many published papers provide only a summary graph of the sea level model, and the actual datasets 

are not available for general use.

3. Uncertainty regarding the necessity of “backstripping”: Applying sea level change curves to 

contemporary bathymetric surfaces assumes that the contemporary seabed is an accurate 

representation of the terrestrial paleolandscape. Seismic reflection profiles from the southern New 

England continental shelf (Needell et al. 1983a, b, c) indicate that previously terrestrial 

paleolandscapes have often been significantly altered by post-glacial sea level rise and frequently are 

buried beneath contemporary marine sediments. The contemporary bathymetric surface may display 

hints of any underlying preserved paleolandsurfaces but primarily represents contemporary 

oceanographic conditions. “Backstripping,” a technique of digitally removing overlying Holocene 

marine sediments from seismic reflection profiles, can be applied to produce paleolandsurfaces that 

are potentially more accurate. Figure 5-6 illustrates an example of this approach for the Buzzards Bay 

area off the southeastern coast of Massachusetts (Foster et al. 2016). The differences between the 

contemporary bathymetric and backstripped surfaces are obvious, but the impact of these differences 

on regional paleoshoreline reconstructions has not yet been tested. In addition, backstripping and the 

subsequent creation of a continuous paleolandscape surface require an extensive database of closely

spaced seismic reflection profiles, which are not available for many study areas.

4. Sources of archaeological data: The archaeological evidence of earliest human habitation in the 

northeast is only one source of information to constrain the time frame that previously terrestrial 

landscapes could have been inhabited by humans. Contemporary Tribal culture teaches that Tribal 

peoples have “always been here” and have always been an integral part of the landscape. Focusing 

only on the archaeological evidence of earliest human habitation in a region does not incorporate 

Tribal oral history or cultural values, and may incorrectly identify landscapes that are older than the 

“PaleoIndian” period as having no cultural sensitivity.

5. Oversimplification of paleoenvironmental conditions: Assessing cultural sensitivity based only on 

locations of marine submergence does not incorporate other paleoenvironmental conditions that 

would make portions of the paleolandscape uninhabitable. For example, in southern New England, 

extensive glacial lakes occupied the continental shelf immediately after glacial ice retreated.

Submerged lacustrine areas would have been unsuitable for human habitation but would be displayed 

as “subaerially exposed” in paleoshoreline reconstructions based only on sea level rise models.

Similarly, during the early post-glacial period in southern New England, some areas of the continental 
46

shelf may have been exposed while others were still occupied by the retreating ice sheet, and would 

have not been available for human habitation.

Figure 5-6. Comparison of a 

digital elevation model of the 

contemporary seafloor of 

Buzzards Bay,

Massachusetts, (upper 

panel) with the elevation of 

the eroded surface of 

Pleistocene glacial drift in 

the same area produced by 

"backstripping" (lower 

panel). 

The upper panel was developed 

from swath interferometric, 

multibeam, and single-beam 

bathymetry at a 10-m horizontal 

resolution. The lower panel shows 

the result of digitally removing the 

sediment that is located 

stratigraphically above the eroded 

surface of Pleistocene glacial drift. 

Image from Foster et al. 2016.

For these reasons, regional paleoshoreline reconstructions should be used cautiously, and should never be 

used as the basis for management decisions. These types of models should be regarded as one of many 

sources of information that can inform the assessment of potential cultural sensitivity in submerged areas, 

but must always be tested at the local level with geophysical, geological, and archaeological analyses. 
47

5.5 Key Points

• In the Submerged Paleolandscapes Project study area, both the Roy and Peltier (2015) and 

Oakley and Boothroyd (2012) RSL curves suggest that the continental shelf was mostly 

submerged after 6,000 yBP. Significant uncertainty about the location of paleoshorelines exists 

prior to that time.

• Paleoshoreline reconstructions based on contemporary bathymetry and RSL curves incorporate 

several types of uncertainty and should be used with caution.

• Regional reconstructions of hypothesized paleoshoreline locations should never be used to make 

management decisions or to identify specific submerged areas that may or may not be culturally 

significant. These decisions should be made based on stratigraphic, sediment core, and 

paleoenvironmental analyses for a study area at the local level.

6 Application of Modeling Process to Project Study Area, Step 3: 

Developing a Regional Stratigraphic Model

6.1 Introduction and Goals

Once the Tier 1 model has been developed that estimates which parts of the continental shelf may have 

been subaerially exposed during the inferred period of human habitation, the next step is to develop a 

regional stratigraphic model that can be used to identify and characterize the geologic facies in the 

subaerially exposed areas that are most likely to contain culturally sensitive terrestrial paleolandscapes. 

Specifically, the goals of the stratigraphic model are as follows:

• Provide guidance about the process needed to characterize the subsurface stratigraphy in the 

study area

• Understand the regional geologic processes, facies, and chronology that are responsible for the 

regional pattern of subsurface stratigraphy

• Identify the geologic facies in seismic reflection profiles that meet the following criteria and are 

most likely to contain paleolandscapes that could have been inhabited by ancestral Tribal people:

• Are associated with the timeframe that humans could have inhabited the area

• Represent terrestrial paleolandscapes and paleoenvironments that were suitable for human 

habitation

Note that this model does not focus on identifying archaeological sites, but instead is designed to locate 

paleolandscapes or paleolandscape fragments that could contain sites. The outcome of the model is a table 

that ranks each of the regional stratigraphic units in the study area from “most likely” through “least 

likely” to contain paleolandscapes that could have been occupied by humans, based on the time frame and 

geological environments represented by each unit. Local testing of the model at five case study locations 

is described in Section 7 of this report.
48

The development of a stratigraphic model for submerged environments requires an expert understanding 

of the regional subsurface and surficial geology in the study area and a significant amount of high-quality 

seismic reflection data. As discussed in Section 4.1.1, the USGS developed a subsurface stratigraphic 

framework for the southern New England continental shelf based on geophysical data acquired between 

1975 and 1981 (Figure 4-4). The survey conducted in 1980 south of Narragansett Bay (Needell et al. 

1983a, b, c; McMullen et al. 2009a) provides reconsaissance-level subsurface coverage for much of the 

Submerged Paleolandscapes Project study area (Figure 6-1). However, because the dataset is almost 40 

years old and has not been extensively ground-truthed, it was first necessary to assess its quality before 

using it as the basis for a stratigraphic model. The discussion below focuses only on the subset of the 

complete USGS dataset that was collected in 1980 south of Narragansett Bay (Needell et al. 1983a, b, c; 

McMullen et al. 2009a) (see Figure 6-1). However, because the USGS interpretations were based on the 

complete dataset collected between 1975 and 1981, this stratigraphic model is also pertinent to the entire 

southern New England continental shelf delineated by the surveying tracklines shown in Figure 4-4.

Figure 6-1. Seismic reflection tracklines from 1980 USGS legacy dataset (black) and 2016 EN580 

follow-up cruise (red).
49

6.2 Field Methodology and Data Processing for Model Dataset

6.2.1 USGS Legacy Study: Rhode Island Sound

Approximately 580 km of seismic reflection and side-scan sonar data were collected simultaneously by 

the USGS in 1980, south of Narragansett Bay (see Figure 6-1) (Needell et al. 1983 a, b, c; McMullen et 

al. 2009a) at approximately 1–2 km trackline spacing. Seismic reflection data were acquired using a 

towed EG&G Uniboom system and were printed on an EPC Laboratories, Inc (EPC) recorder at a 

quarter-second sweep rate. The Uniboom system emitted acoustic pulses with frequencies of 400 Hz to 8 

kHz. Acoustic energy reflected back to the ship from the sea floor and subsurface was detected by a 

hydrophone array and converted to an electric signal. The signal was then amplified and filtered to a 400-

to 4,000-Hz bandpass. The resulting data have 1- to 2-m vertical resolution (McMullen et al. 2009a). The 

depth to prominent acoustic reflectors was determined using an assumed compressional wave velocity of 

1,500 m/s for water and sediments of Holocene age and 1,800 m/s for sediments of Pleistocene age. Sidescan sonar data was acquired using an EDO Western system, with a 100m scan range on either side of the 

ship. Ship positioning was determined using Long Range Aids to Navigation (LORAN-C) navigation, 

with an absolute accuracy of 185 to 463 m (U.S. Coast Guard 1992). Navigation fixes were recorded 

manually every 15 minutes and at major course changes. Ship speed averaged about 9 km/h during the 

seismic surveys (McMullen, et al. 2009a).

In 2009, the USGS converted the original analog data from the 1980 study to digital format in response to 

ongoing interest in the dataset. Seismic data were scanned and converted to several universally readable 

digital image formats, as well as SEG-Y files. Navigation data were converted from LORAN-C time 

delays to latitudes and longitudes, summarized in space-delimited text files, and navigation tracklines 

were produced in ESRI ArcGIS format. These data, as well as associated maps and summaries, were 

released as an Open-File Report accessible to the public online (McMullen et al. 2009a). Because the 

original analog data had been converted and updated to digital format, and associated metadata was 

available, no additional data processing was necessary to utilize it for the Submerged Paleocultural 

Landscapes Project. Trackline files, seismic profiles, and metadata were downloaded from the online 

USGS Open-File Report (McMullen et al. 2009a) and imported into ArcGIS and SonarWiz for 

visualization, analysis and comparison with newly acquired data.

6.2.2 Project Follow-Up Study: EN580 Cruise

In 2016, the project team conducted a short seismic reflection survey in a portion of the study area 

previously studied by the USGS in 1980 (see Figure 6-1). The goals of this cruise were to 1) compare the 

resolution of the 1980 USGS survey data to data acquired with modern seismic reflection profiling 

equipment; 2) compare the geological framework interpretations made based on the 1980 data with 

interpretations based on newly acquired, higher resolution data; and 3) determine whether this legacy 

dataset could be used as the basis for a regional stratigraphic model to support paleolandscape 

reconstructions and paleocultural sensitivity modeling. Three test profiles (Figure 6-1, red lines) were 

acquired to fill data gaps between the 2-km trackline spacing of the 1980 survey and for comparison with 

the 1980 legacy data.

Surveying was conducted onboard the URI's R/V Endeavor, a 185-foot research vessel specifically 

equipped for scientific data acquisition. Seismic reflection profiles were obtained using an HMS-620 

Bubblegun system operating in the 70–700 Hz frequency range, which allows penetration through coarser 

surficial sediment and increased depths below the seafloor. The system consists of the Bubble Gun sound 

source (electromagnetic, contained air) mounted below a catamaran, powered by the HMS-620 

transceiver including single or dual power supplies and a single channel receiver. A 24-element 
50

hydrophone array or streamer is interfaced to the receiver for input of reflected acoustic signals. The

receiver features basic signal functions including initial gain amplification and a bandpass filter with low 

and high cutoff options. The sound source and streamer are towed astern of the vessel and outside the 

propeller wash to minimize ambient noise on the hydrophones and interference to the Bubble Gun 

transducer. Seismic data were recorded (SEG-Y format) together with GPS positions by SonarWiz 

Version 5 acquisition software on a topside notebook computer. The computer was interfaced to the 

HMS-620 transceiver for triggering and data transfer via a Chesapeake Technologies, Inc. (CTI) analog 

interface console.

Seismic reflection data was processed and analyzed using SonarWiz Version 6 (CTI) sub-bottom software 

package, which allows the user full control over signal processing functions such as filtering, stacking, a 

variety of gain adjustments, and other file manipulation options. SonarWiz also features 3D visualization 

(fence diagrams) for inspection of profile intersections and sub-bottom data trends. Because the vertical 

axis of the seismic records is signal travel time and not material thickness, a conversion from time to 

depth was performed using an average sediment velocity of 5,000 ft s-1 (1,524 m s-1

). This value is typical 

for saturated, unconsolidated marine sediment in the shallow subsurface. Given the reconnaissance-level 

nature of this study, vertical adjustments for tide (~3 ft [0.9m] tide range) were done manually within 

SonarWiz to check intersections. 

6.3 Results

6.3.1 USGS Legacy Data 

The results of the 1980 USGS geophysical survey south of Narragansett Bay are synthesized by three 

sources. The first (Needell et al. 1983a) is a concise, peer-reviewed journal article that summarizes the 

acoustic stratigraphy and interpreted geologic framework of the study area based on seismic reflection 

profiles and presents three maps showing 1) the hypothesized surficial geology of the study area (Figure 

6-2); 2) the depth below sea level to the deepest acoustic reflector (Ku/fu2) (Figure 6-3); and 3) the depth 

below sea floor to a prominent acoustic reflector interpreted to be the “post-glacial unconformity” (fu1)

(Figure 6-4). The second and third sources (Needell et al. 1983b, c) are USGS Field Study Reports that 

provide additional, larger maps and interpreted seismic reflection images. Illustrations of the thicknesses 

of glacial drift, end moraine deposits, and Holocene deposits (Needell et al., 1983b) are included in these 

reports and are available for online viewing and download as part of a USGS legacy digital data 

compilation (McMullen et al. 2009a). Each of these visualizations were created by interpreting the 

seismic reflection and side-scan sonar data acquired along 1- to 2-km survey tracklines and interpolating 

between the tracklines to construct a hypothesized regional representation of surficial and subsurface 

geology throughout the entire study area.

The USGS survey south of Narragansett Bay indicates that the subsurface geology in the Submerged 

Paleolandscapes Project study area consists of five stratigraphic units, separated by three prominent 

regional acoustic reflectors. These reflectors were interpreted to represent unconformities whose geologic 

nature was inferred from outcrops, bottom-sediment samples, and borehole data within the area, in 

adjacent areas, and from stratigraphic positions similar to geologic units in eastern Rhode Island Sound 

(O'Hara and Oldale 1980). The presence, characteristics, and composition of the stratigraphic units and 

unconformities are geographically variable but can be combined to form a generalized subsurface 

stratigraphic framework for Rhode Island Sound south of Narragansett Bay. The acoustic and geologic 

characteristics of each of these units, as interpreted by Needell et al. (1983a), is summarized in Table 6-1

in stratigraphic order (oldest units are listed at the bottom and youngest at the top of the table).
51

Figure 6-2. Surficial geology of western Rhode Island Sound from Needell et al. (1983a), developed 

from geophysical survey data. 

Acoustic units represented by three-letter codes: PzZ - bedrock; Ku - coastal plain strata; Qdm - glacial end moraine 

deposits; Qdo - glacial drift; Qfe - fluvial and estuarine deposits; Qpt - marine deposits.
52

Figure 6-3. Depth below sea level to deepest acoustic reflector compiled from seismic reflection 

profiles, from Needell et al. (1983a).

North of the heavy dashed line, the reflector is inferred to be bedrock surface; south of the heavy dashed line, the 

reflector is inferred to be the surface of coastal plain and continental shelf strata.
53

Figure 6-4. Depth below sea level to the post-glacial unconformity (fu1) compiled from seismic 

reflection profiles, from Needell et al. (1983a). 

Dashed lines indicate hypothesized thalwegs of post-glacial streams.
54

Table 6-1. Subsurface stratigraphic framework for the continental shelf south of Narragansett Bay,

as described by Needell et al. (1983a, b, c).

Stratigraphic units are shown in white boxes, and regional reflectors are shaded with light orange. The thickness of 

each row in the table is the result of the table contents and is not representative of the relative thicknesses of 

stratigraphic units. 

Feature Code Interpretation Age Acoustic Signature and Notes

Qpt Marine deposits Holocene/Recent • Geographically variable

• Not always present

mu Erosional unconformity 

caused by post-glacial 

marine inundation

Holocene • Smooth, flat-lying reflector

Qfe Post-glacial fluvial and 

estuarine deposits

Late Pleistocene/

Early Holocene

• Internal reflectors flat to gently dipping, or 

locally cross-bedded

fu1

Erosional unconformity 

caused by post-glacial 

fluvial erosion of the 

landscape prior to 

marine inundation

Late Pleistocene

• Same as sea floor (mu) in some 

locations:

o Smooth, continuous reflector

• When overlain by younger deposits: 

o Reflector smooth to highly irregular 

and channelized

Qdo or Qdm

Qdo: Glacial “drift”

• Till

• Ice-contact drift 

• Glaciofluvial 

outwash

• Glaciolacustrine

• Ice-deformed drift

Qdm: 

• End moraine 

deposits

Late Pleistocene

(associated with 

Late Wisconsinan 

glaciation)

May be earlier 

Pleistocene in 

some areas

• Acoustically variable

o Ice-deformed drift: highly irregular, 

short, discontinuous internal 

reflectors

o Glaciofluvial outwash: continuous, 

flat to gently dipping reflectors

o Glaciolacustrine deposits: welllaminated reflectors

o End moraines: acoustic signature 

dependent on geographic location; 

reflectors sometimes absent, 

sometimes continuous and welldefined, slightly irregular at top and 

base

• Variable thicknesses

• Geographically variable

fu2 Erosional unconformity 

caused by glacial 

processes

Pleistocene

• Deepest identifiable reflector

• Overlies Ku in southern study area

o Continuous, smooth in this area

• Overlies Pzz in northern study area 

o Strong, continuous, highly irregular 

in this area

• Traceable from outcrops near shore

Ku

Coastal plain and

continental shelf 

deposits forming a 

cuesta with a northfacing escarpment

Cretaceous/

Early Tertiary • Only occurs in southern 1/3 of study area 

Pzz Crystalline bedrock Paleozoic • Limited or no acoustic penetration
55

6.3.2 Project Data—EN580 Survey

The seismic reflection profiles obtained by the project team in 2016 as a preliminary follow-up to the 

USGS survey south of Narragansett Bay are shown in Figure 6-5. The three additional seismic reflection 

lines were run with the same W-E orientation and in between existing USGS legacy data lines

(Figure 6-1). The newly acquired seismic reflection data have the advantage of improved resolution and 

modern image processing software, allowing the existing framework to bias new interpretations would 

run the risk of missing previously unidentified features. For this reason, interpretations of these data were 

made in a manner consistent with the existing framework; however, the acoustic characteristics of each 

identified seismic unit were carefully considered before correlating with the older USGS data. 

Several seismic units and erosional unconformities were identified and later correlated with the existing 

geologic framework.

• Qpt: Post-marine transgression marine sediment. Qpt is acoustically transparent or exhibits flatlying to gently dipping internal reflectors. In most places, Qpt is a thin veneer of marine sediment 

(< 5 m), except near the western channel where thicknesses reach 10 m in Line 3, and was 

deposited post transgression in a low energy marine setting (Figure 6-5).

• mu: A flat-lying to gently dipping, laterally continuous reflector interpreted as an erosional 

marine unconformity (ravinement surface). Reflector mu is best observed in the western half of 

the seismic reflection lines and reaches its maximum depth of 47 m below sea level near the 

western channel cut by fu1 in Line 3 (Figure 6-5). Marine transgression and wave-cutting are 

identified as the erosional processes leading to the formation of mu. Where mu is not buried 

below marine sediment, it is thought that the modern-day seafloor also comprises mu as it 

continues to erode or is depositionally inhibited by storm-induced bottom currents.

• Qfe: Post-glacial fluvial and estuarine sediment. Qfe exhibits some flat-lying and gently dipping 

internal reflectors, or otherwise acoustically featureless sediment, and ranges 5–25 m in 

thickness. Qfe unconformably fills the channels cut by fu1, locally overlying Qdo.

• fu1: A channelized, discontinuous, and irregular reflector interpreted as an erosional 

unconformity formed by post-glacial fluvial erosion that cuts channels into glacial deposits (Qdo).

The channel depths reach a maximum of 55 m below sea level near the prominent westernmost 

bedrock channel, with several shallower channels towards the east varying in depths from 40–50 

m below sea level.

• Qdo: Undifferentiated “glacial drift” composed of glaciolacustrine, glaciofluvial outwash, till,

and ice-contact/ice-deformed drift sediment. Because this seismic unit spans several depositional 

environments, the acoustic characteristics vary drastically. Glaciolacustrine sediment is 

characterized by parallel, draped laminated internal reflectors and is the most recognizable and 

widespread in the seismic reflection profiles. Till exhibits more chaotic internal reflectors and are 

found locally draping the underlying bedrock. Qdo unconformably fills the large pre-existing

bedrock valleys, found as deep as 100+ m and outcropping in some places at the seafloor. In 

places, the thickness of Qdo exceeds 60 m.

• fu2: A strong and continuous reflector interpreted as an erosional conformity. It cuts and truncates 

Pzz, is highly irregular, and varies in depth from 30–100+ m below sea level. It is thought that fu2

represents millions of years of erosion by a well-established fluvial drainage system that was 

possibly further eroded during Pleistocene glaciation.
56

• Pzz: Acoustic basement (no acoustic penetration) wherever present. Interpreted to be Paleozoic 

crystalline bedrock as it lies to the north of the coastal plain erosional remnant and associated 

cuesta. Because the area lies just to the south of Narragansett Bay, it is thought that Pzz

represents a submerged portion of the Narragansett Basin bedrock.

Figure 6-5. Interpreted seismic reflection profiles from research cruise EN-580. 

Three west-east and parallel FSI Bubble Gun seismic reflection profiles were acquired in June 2016 aboard the R/V 

Endeavor. Profile ‘A’ is the northernmost line, and Profile ‘C’ is the southernmost line. Refer to Figure 6-1 for location 

of EN-580 seismic reflection profiles.
57

6.4 Discussion: Assessment of Legacy Data 

The data acquired by the USGS reconnaissance cruises between 1975 and 1981 (“the USGS legacy data”) 

continue to provide the generally accepted understanding of the regional subsurface geologic framework 

for the southern New England continental shelf. Before applying it to contemporary modeling efforts, two 

aspects of the dataset require assessment: 1) resolution and technical quality; and 2) geological 

interpretations.

6.4.1 Equipment Resolution and Technical Quality

Interpretations of seismic reflectors and units from the newly acquired EN-580 seismic reflection data 

discussed above are in good agreement with the USGS legacy data. Both datasets reveal the same general 

geological framework characterized by several episodes of erosion and deposition, including glaciation 

and marine transgression. The EN-580 data reveals finer scale detail compared to the USGS legacy data 

due to technological improvements in both acquisition and post-processing. Legacy data were analog 

records where all signal-to-noise improvements were performed during acquisition. Modern seismic 

reflection systems such as the Bubble Gun generate digital records where significant data quality 

improvements can be made by advanced image processing techniques in post-processing.

An additional comparison between Bubble Gun and legacy USGS seismic reflection data can be made 

using data obtained by the project team in for a concurrent project (BOEM-URI Grant and Cooperative 

Agreement M14AC00011, Identification of Sand and Gravel Resources in Rhode Island While Working 

Toward a Better Understanding of Storm Impacts on Sediment Budgets; Period of Performance: July 29, 

2014–May 29, 2018). Bubble Gun seismic reflection data were collected in Block Island Sound during a 

geophysical cruise conducted in August 2015 (Figure 6-6). Although the primary objective of the study 

was to identify and characterize the thickness of sand and gravel deposits in Federal waters, a portion of 

the geophysical survey was specifically designed to re-run a legacy USGS seismic reflection trackline 

using the Bubble Gun to compare data quality, and to determine if new interpretations match the existing 

geologic framework. When comparing the two collocated datasets, it is immediately clear that the Bubble 

Gun provides much improved resolution (Figure 6-7). Acoustic basement, interpreted as crystalline 

bedrock in Block Island Sound, is easily identifiable in both the Bubble Gun and legacy data, with better 

detail gained from the Bubble Gun. Much greater disparities in resolvable detail are noticed in shallower 

sediments. The rhythmic character of glaciolacustrine sediment stands out much more clearly in the 

Bubble Gun data and the heterogeneity of glacial deposits (Qdo) is far more apparent. The lateral 

continuity of the post-glacial fluvial unconformity (fu1) is also drastically more apparent and internal 

acoustic character of post-glacial fluvial/estuarine deposits (Qfe), and post-transgression marine 

sediments (Qpt) are more easily identified. 

A similar assessment of USGS legacy seismic reflection data was recently described in Klotsko and 

Driscoll (2018). In this study, high-resolution CHIRP seismic reflection data from Block Island Sound 

revealed a Holocene-glacial sediment contact that was not imaged in the legacy data. For this reason, the 

thickness of glaciolacustrine sediment was underestimated in this study area prior to newly acquired 

CHIRP seismic reflection data. Although the newly acquired the CHIRP data provided new evidence 

supporting catastrophic lake drainage as opposed to gradual lake drainage, it did not change the general 

geologic framework from the legacy data at a regional scale.

Additional CHIRP seismic reflection data would be useful as there are significant improvements in 

resolution achieved with these higher frequency systems (10s of cm vertical resolution). Both the EN-580 

and USGS legacy data used lower frequency seismic reflection systems that achieve better penetration, 

which are well suited to reconnaissance scale geological interpretations, especially where the seafloor 

geology is not well known. This advantage of better acoustic penetration in a wider range of sediment is 
58

offset by lower resolution, particularly with the first return from the seafloor which obscures the upper 1–

2 m of sediment. CHIRP systems in fine-grained (fine sand, silt, clay) sediments produce excellent 

records; however, coarse-grained sediments can quickly attenuate the signal leading to insufficient 

acoustic penetration. Using only a CHIRP system when a geological framework is not well established 

makes it difficult to put observed reflectors into context. Supplemental CHIRP seismic reflection data 

could help to refine identification and interpretation of more archaeologically significant sediment, such 

as seismic units Qfe and Qdo, and should be considered in future surveys.

Figure 6-6. Seismic reflection survey tracklines in Block Island Sound. 

Red survey lines were collected aboard the R/V Endeavor during research cruise EN-565 in 2015 and the R/V 

Shanna Rose in 2016. Black survey lines are part of the 1980 USGS legacy data.
59

Figure 6-7. Comparison of seismic reflection profile resolution. 

Yellow line in map delineates collocated seismic reflection lines. Blue frames delineate the region of comparison, also 

indicated as a blue line in map view. Blue arrows show a subsurface feature easily observed in the URI-GSO data 

that is undistinguishable in USGS legacy data.

6.4.2 Geological Interpretations

The subsurface stratigraphic framework developed by the USGS studies is based on early investigations 

of the bedrock and glacial history of southern New England (see Section 4.1.1.1 of this report) and expert 

interpretation of the acoustic record. Despite the improved resolution produced by contemporary seismic 

reflection profiling equipment, the newly acquired data discussed above supports the overall regional 

geological framework developed by the USGS studies. Subsequent research also supports the USGS 

regional framework, but the legacy interpretations of the acoustic dataset have never been ground-truthed

in a comprehensive manner. Two recent studies (Sheldon 2012; Caccioppoli 2015) specifically sought to 

revisit the interpretations of the USGS legacy dataset by examining sediment core/borehole data and 

additional seismic reflection surveys; both confirmed the regional geologic framework presented by 

Needell et al. (1983a, b, c) but noted local variations. A third study (Klotsko and Driscoll 2018) identified 

glaciolacustrine deposits in CHIRP seismic reflection profiles that were not visible in a portion of nearby 

Uniboom data from the USGS legacy survey of Block Island Sound, but did not ground-truth this 

interpretation with cores or borings. These studies, and the comparison between newly acquired data and 

the USGS data discussed above, indicate that the USGS studies can be used as the basis for a preliminary 

regional stratigraphic model. However, caution should be exercised when applying it to site-specific 
60

paleolandscape reconstructions on a smaller scale. The following issues should be considered when using 

the dataset.

Reconnaissance-level trackline spacing: The 1980 USGS survey was conducted with a 1–2 km 

trackline spacing and, with the exception of a small area immediately south of Narragansett Bay, crossing 

lines are limited (see Figure 6-1). This resolution was designed for a comprehensive reconnaissance-level 

survey across a broad geographic area but is not adequate to develop a regional map of potential 

paleolandscape locations by correlating between survey tracklines. The coarse trackline spacing is 

particularly problematic because of the geographic variability and heterogeneity of sedimentary deposits 

noted in the interpretation of acoustic reflectors (Table 6-1 above). For example, stratigraphic unit Qdo is 

interpreted to represent sediments associated with several glacial depositional environments that are 

present in some geographic areas and absent in others. Unit Qfe represents both fluvial and estuarine 

sediments that are also present in some areas and absent in others. This type of geographic variability 

makes “connecting the dots” between widely spaced tracklines unwise without additional supporting data.

A paleochannel or other landscape feature that is visible in one seismic reflection profile is not necessarily 

the same feature, or even the same age, as a similar one that appears in another profile 2 km away, 

although the regional processes that created both features may be related. The interpretive maps presented 

by the USGS studies (see Figures 6-2, 6-3, and 6-4) are illustrations of the possible regional distribution 

of stratigraphic units, but these interpolations are hypotheses that have not yet been tested. Until 

additional data can be collected to refine the characteristics and distribution of the subsurface stratigraphic 

units in Rhode Island Sound, regional-scale interpolations between widely spaced seismic reflection 

profiles should be avoided for modeling purposes. However, the data can be used to develop a 

preliminary regional stratigraphic model for the southern New England continental shelf that can be tested 

locally, as will be discussed in Section 6.5 of this report.

Limited sediment core data: Sediment cores or borings have not yet been acquired in a systematic 

manner to verify the interpretations of the USGS seismic reflection data. The geological interpretations 

for each stratigraphic unit are based largely on the analysis of acoustic signatures and the technique of 

sequence stratigraphy. The importance of analyzing sediment cores to ground-truth paleoenvironmental 

interpretations based on seismic reflection data is illustrated by the results of a 1988 coring study that was 

designed to assess non-energy (sand, gravel, and mineral) resources on the southern New England 

continental shelf (see Figure 4-3, cores 88-9 through 88-14) (Neff et al. 1989; Poppe et al. 2002). Three 

vibracores from this investigation were obtained in the Submerged Paleolandscapes Project area south of 

Narragansett Bay. Coring targets were selected based on the previous interpretations of the USGS seismic 

reflection profiles in the area, and sedimentological data was compared with the acoustic interpretations.

Core 88-12 was chosen to gain information about the three uppermost acoustic units identified in a nearby 

USGS seismic reflection profile. Although the authors of this study (Neff et al. 1989) did not use the 

naming scheme of the USGS studies (see Table 6-1) to identify these units, they would represent Qpt, Qfe 

(estuarine), and Qfe (fluvial), respectively. Analysis of grain size samples and diatom floras from core 

88-12 confirmed the previous acoustic interpretation (Neff et al. 1989), and a prominent contact visible in 

the core between Units 4 and 3 (Qpt and Qfe, respectively) appears to represent the Holocene marine 

unconformity identified as mu in the USGS studies (see Table 6-1).

Correspondence between the USGS acoustic interpretations and sediment core data at core locations 

88-13 and 88-14 was less clear. The target of both cores was surficial Pleistocene glacial drift deposits, 

which had been inferred by Needell et al. (1983b) and Neff et al. (1989) to occur at these locations.

Glacial drift deposits would correspond to unit Qdo using the naming scheme of the USGS studies (see 

Table 6-1 above). Instead, analysis of core 88-13 suggested that the upper 303 cm of sediments 

represented Holocene marine shelf deposits (Qpt) that may have been composed of reworked glacial 

sediments. This unit was underlain by sediments suggestive of a Holocene low energy estuarine basin 

(Qfe) or glaciolacustrine environment (Qdo). A sharp contact was identified in the core between these 
61

units, which may represent the regional acoustic reflector identified as mu by the USGS studies, although 

the exact depositional history of the lower unit was unclear. Results from core 88-14 also appear to 

contradict the acoustic interpretations. The target location was characterized by zones of parallel, wavy to 

flat-lying reflectors interspersed with chaotic reflectors. Analysis of core 88-14 indicated that a thin 

(approximately 46 cm) veneer of marine sediments overlies 303 cm of sediments of uncertain origin in 

this area, which were hypothesized to represent marine sediments composed of reworked glacial drift 

(Qpt) or possibly glacial outwash (Qdo). The contacts between facies in this core were gradational, 

suggesting that the regional acoustic reflectors identified in the USGS studies (Needell 1983 a, b, c; Table 

6-1) may not occur in this area, or may not represent erosional unconformities. 

Although these cores support the overall regional geologic framework proposed by the USGS studies, 

they indicate that direct correlation between the acoustic units visible in seismic reflection profiles and 

specific paleoenvironments at a local level require significant additional refinement. Because both the 

Qdo and Qfe units are interpreted to represent a variety of geographically variable depositional 

environments, analysis of sediment cores will be necessary to refine the acoustic interpretations and 

develop accurate paleolandscape reconstructions. In addition, verification that the three regional acoustic 

reflectors fu2, fu1, and mu represent unconformities cannot be confirmed without analysis of sediment 

cores.

Absence of absolute dates: Because sediment cores have not yet been acquired to support the USGS 

studies south of Narragansett Bay, absolute dates are not available to verify the ages of the stratigraphic 

units and unconformities identified by analyses of seismic reflection profiles. Approximately 16 

vibracores were obtained as part of the 1975 USGS survey east of the 1980 study area (see Figure 4-3, 

purple dots) (Oldale and O’Hara 1980; McMullen et al. 2009b) and 22 radiocarbon dates were obtained 

from peat and shell samples acquired from these cores. These dates provide important time control for the 

stratigraphy of the continental shelf south of Massachusetts; however, applying them to the project study 

area south of Narragansett Bay requires correlation of local stratigraphic units across a large geographic 

area, which may be problematic due to the wide trackline spacing of the seismic reflection surveys and 

the apparent heterogeneity of sedimentary facies. 

Acoustic resolution: As discussed above, the Uniboom system used for the USGS studies produced good 

results for characterizing the entire subsurface stratigraphic package in the study area, but it lacks detailed 

resolution in shallowly buried sediments. Identification of regional unconformities is necessary to 

understand the relative ages of depositional units. Distinguishing fu1 from mu, and identifying their 

spatial extent, is problematic in some areas because these reflectors occur in shallow sediments with 

lower acoustic resolution. In addition, Klotsko and Driscoll (2018) identified glaciolacustrine deposits in 

Block Island Sound that are visible in CHIRP seismic reflection data but are not visible in nearby USGS 

Uniboom data, suggesting that the local resolution of the USGS legacy data may be variable. 

6.5. Regional Stratigraphic Model

If the USGS legacy datasets are used with caution, they provide an important starting point for 

paleolandscape reconstruction and paleocultural sensitivity assessment in the project study area. A 

preliminary regional stratigraphic model can be developed to identify which subsurface geologic facies

may contain paleolandscapes or paleolandscape fragments that were suitable for human occupation. This 

requires an understanding of the age, geological environments, and geological processes represented by 

the subsurface stratigraphy in the study area. 

The subsurface stratigraphy identified by the USGS studies suggests that much of the geologic record of 

Rhode Island Sound is the result of Pleistocene and Holocene glacial and post-glacial processes.
62

Crystalline bedrock (unit Pzz) and Cretaceous/Early Tertiary coastal plain and continental shelf sediments 

(Ku) form the ancient base of the stratigraphic sequence, representing geological environments that are 

tens to hundreds of million years old. During the Pleistocene, multiple advances and retreats of glacial ice 

significantly eroded the ancient bedrock and Cretaceous sediments, resulting in a regional unconformity 

(fu2). This unconformity represents several million years of missing sediments that were deposited 

between the Early Tertiary and Pleistocene Periods and were subsequently removed by glacial erosion. 

The Late Pleistocene (Wisconsinan) ice advance depressed the land surface and lowered sea level, 

resulting in subaerial exposure of much of what is now the continental shelf. A heterogeneous blanket of 

glacial “drift” sediments (Qdo) and end moraines (Qdm) were deposited across the continental shelf on 

top of unconformity fu2 and the ancient basal units. During deglaciation, the continental shelf was 

occupied first by glacial lakes (portions of Qdo) that formed between the retreating ice and end moraines 

and then was exposed subaerially (unconformity fu1) when the glacial lakes drained. This post-glacial, 

Late Pleistocene/Early Holocene landscape was characterized by streams flowing south and 

southwestward towards Block Island Sound, which eroded (fu1) the earlier glacial and glaciolacustrine 

sediments (Qdo and Qfm) and produced fluvial deposits (Qfe). As sea level rose, post-glacial valleys 

were partly filled by fluvial, freshwater peat, estuarine, and salt marsh deposits (Qfe). Transgressing seas 

eroded the sea floor (mu), exposing the ancient basal bedrock and coastal plain outcrops in some places

and depositing marine sediments (Qpt). In some parts of the contemporary sea floor south of Narragansett 

Bay, marine sediments are being deposited over the unconformity (mu) produced by the post-glacial 

marine transgression, but in much of the study area, bottom sediments may be composed of older 

geographic units (Needell et al. 1983a).

Table 6-2 presents a regional subsurface stratigraphic model that is applicable to the southern New 

England continental shelf and to Narragansett Bay, developed from the USGS legacy dataset. Although 

the USGS studies were focused on the southern New England continental shelf and did not extend into 

Narragansett Bay, several later investigations (McMaster 1984; Peck and McMaster 1991; Oakley 2012; 

Oakley and Boothroyd 2012; Oakley and Boothroyd 2013) suggest that the subsurface stratigraphy of 

Narragansett Bay is correlative with the continental shelf off Rhode Island. This is not unexpected, 

because the geologic processes that resulted in the stratigraphy of both areas were similar, despite 

variations in local topography. Therefore, the model below is applicable to the entire Submerged 

Paleolandscapes Project study area. Each geologic unit is presented in stratigraphic order (most recent at 

the top of the table and oldest at the bottom) and described according to the likelihood of containing 

paleolandscapes or paleolandscape fragments that may have been associated with occupation by ancestral 

Tribal peoples. The inferred age and paleoenvironment of each unit in the subsurface stratigraphy is 

summarized, along with associated rationale and cautionary notes. This table may be used in conjunction 

with Table 6-1 if additional information about the characteristic acoustic signature of each unit is desired.

Note that the ranking system is based only on the inferred age and paleoenvironment of each stratigraphic 

unit and is not a cultural sensitivity assessment based on inferences about the behavior or preferences of 

ancestral Tribal people. The focus of this model is to identify geologic facies in the study area that are 

most likely to contain paleolandscapes or paleolandscape fragments that could have been occupied by 

ancient humans, not to make inferences regarding the importance of these landscapes to ancient or 

contemporary Tribal peoples. This is a regional model that must be tested and refined at each local study 

area to which it is applied. 
63

Table 6-2. Regional subsurface stratigraphic model for the study area.

Qpt and mu:

Represents a marine or dynamic/erosional shoreface landscape unavailable for

human habitation or unlikely to preserve its evidence.

Hypothesis: Qpt was deposited during the time period associated with human occupation of the study 

area but represents a submerged marine environment unavailable for human habitation. The reflector mu 

represents a marine shoreface environment that was dynamic/erosional and is therefore likely to be 

disturbed, with little potential for preservation of contextually intact cultural deposits.

Approximate Age: Marine inundation (date of inundation varies according to 

geographic location) to present

Rationale: The regional reflector mu (also called the “ravinement surface” by contemporary 

researchers) is interpreted to represent an unconformity produced by erosion of the subaerially 

exposed land surface by wave action as sea level rose and the shoreface transgressed across the 

landscape. Because the facies Qpt overlies mu, Qpt is inferred to be younger than the age of mu and 

marine in nature. The age of both of these units varies according to geographic location. Post-glacial 

sea level rise in the study area progressed from south to north, indicating that mu and Qpt are older 

at continental shelf locations and more recent in the Narragansett Bay area. Marine transgression of 

the study area appears to have begun approximately 11,000 yBP. Qpt and mu are inferred to have 

been formed after this time.

Paleolandscape Type: Marine (Qpt) and dynamic shoreface (mu) 

Rationale: The USGS studies defined Qpt sediments as “marine deposits” associated with deposition 

in a submerged environment. Therefore, they represent a paleoenvironment unavailable for human 

habitation and only likely to contain cultural material associated with maritime cultural activity (e.g., 

vessel and fishing gear remains).

Qfe and fu1:

Most likely to represent, or be associated with, elements of the paleolandscape 

that could have been inhabited and utilized by humans.

Hypothesis: Qfe was deposited during the time period associated with human occupation of the study 

area and may represent, or be associated with, archaeologically sensitive terrestrial paleolandscapes. 

Approximate Age: < 16,000 yBP to marine inundation (date of inundation varies 

according to geographic location)

Rationale: The regional reflector fu1 defines the base of Qfe sediments and was identified by the 

USGS studies as an unconformity resulting from subaerial exposure of the continental shelf that 

occurred after glaciers receded and the glacial lakes drained, but before marine inundation.

Subsequent studies (Koteff and Larsen 1989; Koteff et al. 1993; Lewis and DiGiacomo-Cohen, 2000; 

Oakley 2012) indicated that drainage of glacial lakes on the southern New England continental shelf 

occurred approximately 15,000–16,000 yBP. Because the geologic unit Qfe overlies fu1, it is assumed 

to be younger than the age of fu1 and therefore less than approximately 16,000 years old. The earliest 
64

dated archaeological evidence of human habitation in southern New England is ca. 11,000 yBP, 

suggesting that Qfe represents sediments deposited during a time of possible human habitation.

Paleolandscape Type: Fluvial and estuarine

Rationale: The USGS studies concluded that Qfe represents fluvial and estuarine deposits associated 

with stream or river systems that developed on the subaerially exposed continental shelf prior to 

marine inundation. This hypothesis is based on the presence of channel-like features in the fu1

reflector and qualitative correlation of the acoustic signature of this unit with acoustically similar valley 

fill deposits in nearby Martha’s Vineyard Sound (O’Hara and Oldale 1980) and Buzzards Bay (Robb 

and Oldale 1977), which were ground-truthed with a small sediment core study. This facies is also 

hypothesized to contain estuarine deposits, resulting from the initial stages of marine inundation. Both 

fluvial and estuarine sediments are deposited in submerged environments, which obviously are 

unsuitable for human habitation. However, in a broader sense, fluvial and estuarine systems are 

complex landscapes that consist of a variety of environments, particularly at their margins and 

between them. For example, a landscape dominated by rivers also contains marshes and dry upland 

areas. Therefore, some of the sub-environments associated with fluvial and estuarine systems are 

likely to have been suitable for human habitation and use. Because Qfe currently is characterized only 

at a reconnaissance level, it is unclear what aspects of the fluvial and estuarine systems are preserved 

and included in this broadly defined sedimentary facies. However, the age range, deposition on the 

exposed shelf, and presence of fluvial and estuarine deposits in this facies suggests a paleolandscape 

that could have been occupied by and utilized by humans. Cultural deposits could also extend into fu1.

Cautions: 

• This facies has not been adequately defined with sediment cores, radiocarbon dates, and/or 

contemporary high-resolution seismic reflection data. It may represent a variety of geographically 

variable depositional environments, some of which are archaeologically sensitive and some of 

which are not.

• Acoustic resolution of the USGS seismic reflection data is sometimes poor in shallowly buried 

sediments, which interferes with a precise interpretation of this facies.

• The hypotheses that the fluvial component of this facies represent geographically continuous 

stream/river channels, and that fu1 is a geographically continuous surface (Needell et al. 1983a, 

b, c), is based on qualitative correlation of features identified in seismic reflection profiles 

obtained at 2-km trackline spacing. Because Qfe appears to be geographically heterogeneous, 

this hypothesis must be tested by higher resolution surveys.

• The acoustic reflector fu1 is an important marker for Qfe sediments, because it defines the base 

of the Qfe unit. However, its geographic continuity has not been examined in detail. In some 

areas, fu1 and Qfe appear to be absent, and poor acoustic resolution in the upper part of the 

seismic reflection profiles interferes with detailed interpretation of the acoustic signatures. 
65

Qdo, Qdm and fu2:

Lower probability to represent paleolandscape elements associated with human 

habitation, except as outcrops in a younger landscape.

Hypothesis: Qdo and Qdm represent deposits formed on a landscape dominated by glacial ice. This 

landscape is associated with a time frame older than documented human habitation of the study area. 

However, if either Qdo or Qdm deposits persisted as outcrops in the post-glacial period, they could have 

been part of a landscape occupied by humans.

Approximate Age: 26,000–16,000 yBP?

Rationale: The reflector fu2 is inferred to represent a regional unconformity produced by Pleistocene 

erosion of underlying bedrock and Cretaceous/Tertiary coastal plain deposits. Qdo and Qdm are 

located stratigraphically above fu2, but below fu1, indicating that they are associated with a time 

period in between these two features. Because there is some uncertainty about the number of 

glaciations that occupied southern New England during the Pleistocene, identifying a definitive age 

for Qdo, Qdm, and fu2 is problematic. The USGS studies hypothesized that the Qdo and Qdm were 

largely associated with the Late Wisconsinan glaciation, which reached its terminal extent 

approximately 26,000 yBP in the study area. Qdo consists of both ice margin sediments deposited 

when glacial ice occupied the study area, and glaciolacustrine sediments deposited as the ice was 

receding northwards. Drainage of the glacial lakes in the study area is thought to have occurred 

approximately 16,000 yBP. Therefore, the Qdo and Qdm facies would have been deposited between 

approximately 26,000 yBP, when the ice was at its maximum extent, and 16,000 yBP, when the 

glacial lakes drained. 

Paleolandscape Type: Glacial and early post-glacial

Rationale: The USGS studies indicate that Qdo is composed of a variety of deposits, including till, 

ice-contact drift, glaciofluvial outwash, ice-deformed “drift,” and glaciolacustrine sediments. Each of 

these deposits is associated with a landscape occupied by glacial ice. The time frame of these 

deposits is older than the documented archaeological evidence of human occupation in this area. If 

human occupation did occur in this time frame, the glacial landscape close to the ice margin 

(represented by deposits Qdo and Qdm) would have been an inhospitable (although theoretically 

possible) place for human habitation. During the early post-glacial period, glacial lakes occupied large 

areas of the continental shelf in the study area (represented by portions of unit Qdo), although the 

exact extent has not yet been defined. The glaciolacustrine deposits associated with unit Qdo also 

were deposited during a time frame prior to documented human habitation of the region, but if 

humans did occupy the area during this time, any exposed land around the glacial lakes could have 

been inhabited. Erosion of the Qdo surface would have been widespread. Preservation of any cultural 

deposits within it would have been localized and limited to preserved outcrops in younger sediments. 

Until additional evidence becomes available that humans occupied the study area prior to ca. 12,500 

yBP, Qdo and Qdm are considered unlikely to represent paleolandscapes that were inhabited by 

humans. However, if either Qdo or Qdm deposits persisted as outcrops in the post-glacial period, 

they could have been part of a later landscape that was inhabited by humans.

Cautions: 

• This facies has not been adequately defined with sediment cores, radiocarbon dates, and/or 

contemporary high-resolution seismic reflection data. It represents a variety of ice-contact and 

early post-glacial environments that are acoustically and geographically variable.

• The USGS studies hypothesized that Qdo and Qdm were associated with the Late Wisconsinan 

glacial period but also suggested that these deposits may have been associated with an older 

glaciation in some parts of the study area. Radiocarbon dates will be necessary to clearly define 

the chronology of these units.
66

Ku and Pzz:

Does not represent paleolandscape elements associated with human habitation, 

except as outcrops in a younger landscape.

Hypothesis: The stratigraphic units Ku and Pzz are associated with a time period that is millions of 

years older than the global human archaeological record. These units could only represent 

paleolandscapes occupied by humans if they persisted as outcrops with elements that were preserved 

when humans inhabited the study area. 

Approximate Age: Tens-of-millions (Ku*) to > 245 million yBP (Pzz) 

* The unit Ku is identified as "Late Cretaceous–Early Tertiary" but has not been assigned a specific date.

Rationale: The age of each of these units is inferred to correspond to bedrock identified and 

mapped on the southern New England mainland (Oliver and Drake 1951; Tagg and Uchupi 1967;

Hermes et al. 1994).

Paleolandscape Type: Coastal plain and continental shelf (Ku) metasedimentary, 

igneous, and metamorphic bedrock (Pzz)

Rationale: The geologic environments of these units is inferred to correspond to similar units

identified and mapped on the southern New England mainland. Because they are significantly older 

than even the global archaeological record of human habitation, they cannot be associated with 

human habitation unless they occurred as outcrops in a younger landscape.
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6.6 Key Points

• The USGS legacy studies resulted in the development of a subsurface stratigraphic framework for 

the southern New England continental shelf. This framework is based primarily on the technique 

of sequence stratigraphy and the interpretation of seismic reflection profiles obtained at 

approximately 2-km trackline spacing. The USGS interpretations have not been systematically 

ground-truthed with sediment core data or radiocarbon dates. However, the limited amount of 

subsequent studies that have been conducted in the study area confirm the regional stratigraphic 

framework developed by the USGS, while noting local variations in geologic facies and acoustic 

signatures.

• Comparison between the USGS legacy dataset and several newly acquired seismic reflection 

profiles indicates that contemporary geophysical surveying equipment produces higher resolution 

data but does not significantly alter the general subsurface stratigraphic framework for the 

southern New England continental shelf developed by the USGS.

• A regional stratigraphic model was developed for this project from the USGS legacy dataset, 

which identifies the geologic facies in the study area that are most likely to contain 

paleolandscapes or paleolandscape fragments that could have been occupied by ancient humans.

Note that this model is based only on the inferred age and paleoenvironments of geologic facies. 

It is not designed to make inferences regarding how ancestral Tribal people interacted with those 

landscapes or the cultural importance of those landscapes.

• The stratigraphic model developed for this report is a regional model that must be tested and 

refined at each local study area to which it is applied. Ground-truthing of the model with 

contemporary high-resolution geophysical equipment, sediment core analysis, and radiocarbon 

dates is essential at each local study area.

• The cautionary notes included with the facies descriptions in the model should be carefully 

considered when the model is applied. 

• Accurate application of the stratigraphic model to local study areas requires expert interpretation 

of the seismic reflection data by individuals who are experienced in interpreting geophysical data 

and who are thoroughly familiar with the regional geologic history of the study area.

Interpretation of the sediment core data necessary to ground-truth the acoustic interpretations 

requires similar expertise. Applying the model without this level of expertise may result in 

inaccurate conclusions regarding the location, type, and preservation of paleolandscapes that may 

be of cultural significance to Tribal peoples.
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7 Application of Modeling Process to Project Study Area, Step IV: 

Model Testing Through Local Case Study Analyses

Four case study areas were selected to test the Tier 1 and Tier 2 models discussed above and to refine data 

collection methodologies. A diverse range of environments was targeted in order to provide a variety of 

data types and data collection situations. The Greenwich Bay area (Figure 4-1) represents an interior 

study area in the central Narragansett Bay region, and its three sub-areas (Gorton Pond, Cedar Tree 

Beach, and the Greenwich Bay sub-seafloor) were targeted for multidisciplinary analyses (Figure 7-1).

Figure 7-1. Location of study locations within the Greenwich Bay area.

Basemap: ESRI ArcGIS Online “World Imagery”
69

The nearshore location of the Greenwich Bay study areas simplified the logistics of field data collection 

and provided the project team with an accessible and cost-effective location for model testing and 

refinement. It also served as an analog for locations that are now submerged offshore but were once 

nearshore environments prior to post-glacial marine inundation. The West Beach (Block Island) study 

area (Figure 4-1) was chosen as a “data bridge” between the nearshore and offshore investigations. Block 

Island currently is located approximately 11 miles offshore of mainland Rhode Island and is therefore 

exposed to oceanographic conditions and associated with the offshore stratigraphic record, but the study 

area at West Beach is located in the beach, intertidal, and shallow subtidal zone. This combination of 

nearshore and offshore characteristics at West Beach provided an opportunity to investigate 

paleolandscape preservation and paleocultural sensitivity in a unique environment. The Mud Hole and 

AMI areas (Figure 4-1) served as offshore study locations that were targeted for geophysical and 

geological investigations to refine the test the offshore stratigraphic model and to understand whether 

elements of the formerly terrestrial paleolandscape survived post-glacial marine transgression. The 

specific goals of each study area are discussed in more detail below.

At each case study area, a primary goal was to educate Tribal research partners in the application and use 

of geophysical survey equipment and non-disturbance marine remote sensing survey methods. Fieldwork 

considered comments and recommendations that were voiced by Tribal participants during the project’s 

initial workshop in March of 2013. As such, the work progressed in three phases, progressing from the 

least to most in investigative techniques, with an overall goal of minimizing the disturbance to the 

seafloor as much as possible during the performance of all phases of the field investigations. 

7.1 Greenwich Bay Area

7.1.1 Introduction and Goals

Archaeological and geological investigations in the Greenwich Bay area were focused in three locations:

1) Greenwich Bay itself, which is a major sub-embayment on the west-central margin of Narragansett 

Bay that drains into the larger Narragansett Bay estuary system; 2) Cedar Tree Beach, which forms the 

northwestern shoreline of Greenwich Bay; and 3) Gorton Pond, which is a small kettle pond located 

approximately 1 km (0.62 mi) from the Apponaug Cove, which forms the northwestern extent of 

Greenwich Bay (Figure 7-1). Hundreds of pre-contact period stone artifacts have been found by local 

residents in the exposed swash zone of Cedar Tree Beach. These artifacts do not exhibit significant 

marine growth or water-wear, suggesting that they originate from a nearby paleocultural landscape. 

Possible sources are archaeological deposits formerly situated in an ancient low-relief upland now being 

eroded by the northwardly migrating beach or in a partially eroded and buried submerged paleocultural 

landscape immediately offshore of the beach. The presence of a buried and submerged paleocultural 

landscape was suggested by detailed CHIRP sub-bottom sonar survey data acquired by the URI-GSO 

project team prior to the initiation of the Submerged Paleocultural Landscapes Project. These data 

depicted an acoustic reflector consistent with a marine bench or flat extending about 100 to 150 m off of 

Cedar Tree Beach out to the margin of a buried paleochannel near the current modern channel going 

across Greenwich Bay and into Apponaug Cove (Figure 7-2). This feature, combined with the large 

number of artifacts previously found and the protected environment within Greenwich Bay, presented a 

unique opportunity for conducting systematic, multi-phased geoarchaeological field investigations and 

field training. 
70

Figure 7-2. Seismic reflection profile obtained in the Cedar Tree Beach area prior to the initiation 

of the Submerged Paleocultural Landscapes Project.

Upper panel shows the location of the survey trackline. Lower panel illustrates the seismic reflection profile from this 

location. The red arrow shows the location of a marine bench that was hypothesized to represent a portion of a 

paleolandscape that may have been associated with the artifacts found on Cedar Tree Beach. 

Each of the three locations within the broader Greenwich Bay study area was targeted for a specific 

purpose. The primary goals for each area are outlined below.

Greenwich Bay: Characterize the subsurface stratigraphy of Greenwich Bay to:

• Develop a hypothesis regarding the relationship between preserved Late Pleistocene/Early 

Holocene paleolandscapes and the archaeological evidence at Cedar Tree Beach.

• Test the stratigraphic model developed for the continental shelf of southern New England 

(Section 6 of this report) at an inland location to determine if the regional model is applicable to 

the Narragansett Bay area.

Cedar Tree Beach: Test and evaluate phased, systematic no- and low-impact geoarchaeological 

survey methodologies (close-interval [i.e., 1-m track line spacing] gradiometric survey, visual 
71

sediment probing, and excavation of 1 x 1 m underwater dredge test units [DTUs]) for identifying 

submerged paleocultural landscapes. In addition, test the hypotheses that: 

• An element of the paleolandscape is preserved submerged and buried off of Cedar Tree Beach.

• This paleolandscape may have been utilized by pre-contact period inhabitants and, therefore, 

could be a source of some of the pre-contact period stone artifacts appearing in Cedar Tree 

Beach’s swash zone.

Gorton Pond: Develop a paleoenvironmental framework for the Greenwich Bay area for 

approximately the past 15,000 years by investigating proxy indicators of vegetation change and fire 

frequency obtained from sediment core samples.

7.1.2 Cedar Tree Beach Archaeological Investigation

7.1.2.1 Introduction and Goals

The marine archaeological fieldwork conducted in the shallow waters off of Cedar Tree Beach was

intended to meet multiple goals using a systematic, phased approach employing different types of lowimpact surveying and subsurface sampling techniques to:

• Test the hypotheses that a) an element of the paleolandscape was preserved submerged and buried 

off of Cedar Tree Beach; and b) that this paleolandscape may have been utilized by pre-contact 

period human inhabitants and, therefore, could be a source of some of the pre-contact period 

stone artifacts appearing in Cedar Tree Beach’s low-energy swash zone.

• Test and evaluate the combination of close-interval (i.e., 1-m track line spacing) systematic 

gradiometric survey, systematic and selective visual sediment probing, and selective excavation 

of 1 x 1 m underwater DTUs as methods of a phased approach to identifying and characterizing 

submerged paleocultural landscapes.

• Work with Tribal research partners to apply and use non-disturbance and low-disturbance marine 

remote sensing geoarchaeological survey methods.

7.1.2.2 Overview of Field Methodology

Field methodologies designed and employed in the Cedar Tree Beach study area (Figure 7-1)

incorporated comments and recommendations voiced by Tribal and non-Tribal participants in the 

project’s initial March 2013 workshop (CML, URI-GSO 2015). As such, the work progressed in phases 

from less- to more-invasive investigation techniques with an overall goal of minimizing the disturbance to 

the bay floor as much as possible during the performance of all phases of the Cedar Tree Beach field 

investigations. A more detailed description of the field methodologies employed at Cedar Tree Beach is 

included in the Project Field Report (Caccioppoli et al. 2018).

The first phase was a close-interval (1-m spaced survey transects) systematic gradiometric survey that 

was performed over a single 50 x 200 m study area, the northern edge of which was centered on the area 

where the greatest concentration of artifacts was found by Robin Cooney, long-time member of the Cedar 

Tree Point community. Similar gradiometric surveys performed in terrestrial contexts onshore have 

proven effective at identifying buried cultural sites, particularly stone-oven, fire pit, and kiln features, 

where subtle, localized changes in the Earth’s magnetic field are detectable to gradiometers. Acquisition 
72

of high-resolution magnetic data within the study area was processed and contoured to reveal subtle, lowamplitude, anomalous deflections (possibly associated with cultural features) in the Earth’s ambient 

magnetic field. Once located, these magnetic anomalies were then targeted for selective subsurface testing 

that included minimally invasive visual sediment probing, followed by, if warranted, selective excavation 

of 1 x 1 m underwater DTUs.

The gradiometric survey was conducted using a total field intensity Geometrics G-858 magnetometer 

operated in gradiometer mode (i.e., with two fixed magnetometer sensors oriented vertically on a boom 

and spaced about 1-m apart). The gradiometric survey was accomplished by walking across the exposed 

intertidal and submerged shallow sub-tidal portions of the nearshore mudflat off of Cedar Tree Beach at a

spring low tide (i.e., the tide with the greatest distance between high and low tide that occurs when the 

Moon is either new or full, and the Sun, the Moon, and the Earth are aligned, strengthening their 

collective gravitational pull on the Earth’s water). Prior to initiating the survey of each line, the end-points 

of planned survey track lines were acquired using a handheld Garmin GPS and marked with flagged 

stakes, so that the surveyor could use the stakes for visual referencing while walking and collecting data 

along the transects. A digital left-right indicator on the gradiometer unit also helped with tracking course 

heading along survey transects. The 1-m interval of the planned survey track lines optimized the density 

of coverage of the study area and increased the gradiometer’s capacity to detect small features, such as 

might be caused by individual hearths. Gradiometer sensitivity was set at 0.01 nanoTesla (nT) or less, 

with data sampling set to 0.1 s. These settings yielded approximately one reading per 5 cm over-ground at 

normal walking/wading speeds of 1.5 m/s. Each magnetometer was fixed for gradiometric operation and 

was maintained at heights of 1 and 2 m above the harbor floor’s surface. Positioning along surveyed lines 

was recorded in real time with the data from each magnetometer sensor. The quality of the acquired data 

was determined to be acceptable relative to the requirements of the survey, with minor magnetic noise 

typical of the Geometrics 858 system noted during data processing. None of the observed magnetic noise 

was significant enough to obscure magnetic features that were observable in the total field data or in the 

filtered data that was post-processed and plotted.

The second phase of the geoarchaeological field investigations performed in the Cedar Tree Beach study 

area involved the systematic subsurface testing the sediments, which was accomplished using two 

different methods. The initial subsurface testing method consisted of the systematic visual inspection and 

video documentation of subsurface sediments (in plan-view) at 33 locations distributed on a 20-m grid 

across the entire study area, and at 10 selective locations where magnetic anomalies of interest were 

identified in the post-processed magnetic data. The visual inspection of the subsurface sediments was 

achieved using a unique and minimally invasive technological approach termed “visual sediment 

probing,” a technique first applied in a marine archaeological research context by one of this report’s 

authors (Robinson) to ground-truth and identify the sources of marine magnetometer anomalies buried 

under the seafloor during the survey of a proposed submarine cable corridor off of Long Island, New 

York. Visual investigation of the Cedar Tree Beach study area’s sediments using the visual sediment 

probe (VSP) was justified based on a) the results of the gradiometric survey that had identified multiple 

magnetic anomalies; b) the presence of the submerged and buried marine bench or flat seen in the preexisting sub-bottom profiler data (Figure 7-2); and c) the presence of hundreds of pre-contact period 

artifacts that were found at Cedar Tree Beach. The principal goals of the visual sediment probing phase of 

fieldwork were the following:

• Determine the source of the magnetic anomalies identified during the gradiometric survey

• Determine whether or not the marine bench or flat had been previously a subaerially exposed 

paleocultural landscape with inherent archaeological sensitivity
73

• Determine whether or not excavation of 1 x 1 m subsurface underwater archaeological DTUs was 

warranted, and, if so, where

• Introduce and gain experience working with our Tribal research partners in developing minimally 

invasive, subsurface visual sediment probing technologies and field methods, and conducting data 

post-processing and interpretation

An average VSP probing depth of 2 m below the surface of the bay floor was targeted, as this depth was 

considered to be a realistic maximum depth for the planned next element of the subsurface testing (i.e.,

underwater excavation of 1 x 1 m DTUs) in the event that the VSP survey’s results warranted it. 

Based on the results of the VSP subsurface testing results, two probe points (selective VSP probe point 

“S2” and systematic VSP probe-point “B17”) were selected for an additional phase of subsurface testing 

involving excavation of 1 x 1 m DTUs centered at their locations. Reacquisition of the precise locations 

of these VSP probe-points was facilitated by the presence of small depressions left behind in the bayfloor 

by the VSP probing. Excavation of 1 x 1 m underwater DTUs is, like all archaeological excavation, 

inherently destructive; however, it provided a larger physical “window” through which to observe, 

sample, and document the geoarchaeological record in plan and profile. From a scientific research 

perspective, as long as the excavation is conducted properly and well-documented, the information gained 

is generally thought to justify the destruction of the excavated portion of the investigated cultural site. 

This is a perspective that is not shared generally by Tribal people, for whom the Earth, and the ancestral 

cultural sites that are a part of it, have inherent spirituality that is best left undisturbed and protected from 

destruction. In essence, virtually all archaeological sampling or excavation is seen as an unwanted 

disturbance. Out of respect for the importance of this perspective, the originally planned underwater 

archaeological excavations of six 1 x 1 m DTUs was reduced to just the two DTUs, representing a nearly 

70 percent decrease in the amount of disturbance to the seafloor caused by this particular phase of the 

geoarchaeological field investigation at Cedar Tree Beach. Justification for excavating these two locations 

was that they would provide information that would enable the further evaluation of the extent, nature, 

and content of the preserved, stratified, and formerly subaerial sediments within the full study area, and 

would provide an opportunity for evaluating the phased methodology employed in determining the 

presence/absence of paleocultural deposits at the two sampled locations. The field plan and the overall

research design associated with the Cedar Tree Beach fieldwork included a contingency response plan 

covering the appropriate steps and coordination for addressing an unanticipated discovery of ancient 

human remains or a human burial, which was reviewed and approved by BOEM, the RIHPHC, and the 

NITHPO prior to the initiation of fieldwork.

Underwater excavation was conducted over three separate field deployments in June, July, and October of 

2014 by a team of archaeological divers from URI-GSO, NITHPO, and BOEM working together to 

excavate two DTUs underwater by hand, assisted by an 8 cm-diameter induction dredge. A 1 x 1 m 

square x 30 cm tall x 7 mm thick clear plexiglass cofferdam was employed to prevent the lessconsolidated uppermost sediment stratum of silty sand from slumping in during excavation. Excavation 

was conducted following natural stratum changes, or in 10 cm levels when individual strata exceed 10 cm 

in thickness. All excavated materials were screened through one of two different sizes (3 and 6 mm) of 

nylon mesh by attaching nylon mesh bags to the end of the dredge’s exhaust hose. Excavators switched to 

the finer mesh bags once excavation depths approached the buried paleosol stratum that was targeted for 

testing. The mesh bag was changed with a new bag at each change in stratum, or each 10 cm level, as they 

were attained. Each dredge bag’s contents were examined and sifted by topside personnel and evidence of 

artifacts and ecofacts were retained, bagged (to keep them wet), labeled, and then inventoried when 

brought back to the laboratory at URI-GSO for final processing, analysis, and cataloging of their contents.

Upon completion of the excavation, the DTUs were backfilled with plastic bags of clean builder’s sand.

The plastic sand-filled bags were used to assist in identifying the excavated units in the event that 
74

additional archaeological excavation work is ever undertaken again in the Cedar Tree Beach study area.

The upper 20 cm of the DTUs were then filled by dumping the clean builder’s sand into the top of the 

unit, so that the plastic bags were not visible and the bay floor was as close to its natural appearance as 

possible. 

7.1.2.3 Results and Discussion

The phased, systematic application of different types of no- and low-impact marine geoarchaeological 

surveying and subsurface sampling methods conducted at Cedar Tree Beach produced results that met the 

objectives and goals of the work that was planned. Geoarchaeological evidence acquired through the 

combination of close-interval systematic gradiometric survey, systematic and selective VSP probing, and 

selective excavation of two 1 x 1 m underwater DTUs confirmed that:

• A stratified element of the paleolandscape correlating with the marine bench or flat seen in subbottom data (see Figure 7-2) was preserved submerged and buried off of Cedar Tree Beach.

• Cultural materials were present in this element of the paleolandscape, thus indicating its 

utilization by pre-contact period human inhabitants and high potential for being a point of origin 

for some of the pre-contact period stone artifacts that have appeared in Cedar Tree Beach’s lowenergy swash zone.

• No- and low-impact marine remote sensing and subsurface testing geoarchaeological survey 

methods can be used effectively in identifying and characterizing preserved elements of the 

submerged paleocultural landscape and cultural deposits within them.

Gradiometric survey performed as the initial phase of marine geoarchaeological fieldwork identified 

numerous magnetic anomalies, visible as yellow and red areas in the plots of contoured magnetic data 

from the 2013 Greenwich Bay (Cedar Tree Beach) gradiometer survey comprising Figure 7-3. Some of 

these anomalies were clearly associated with visible modern, post-contact period ferrous metal cultural 

debris and structures (e.g., automobile parts and other debris, as well as the steel fasteners in the wooden 

groins extending into the water from the beach), while others were of the detectable size (i.e., 

approximately 0.5 to 3 m in duration) and intensity (i.e., 15 to 30 nT) to be suggestive of representing 

possible hearth or hearth-like paleocultural features, as indicated in reviewed literature on the subject 

(Jones and Munson 2005; Slater, et al. 2000).

Imaging subsurface sediments in the study area with the VSP provided an efficient and expedient, lowimpact, first-pass approach for evaluating the gradiometric and sub-bottom profiler data. The VSP’s

unique perspective on subsurface sediments is different from that obtained from coring. The VSP allows

researchers to see sediments in plan as each stratum is encountered (illustrated in the data presentation in 

Figure 7-4), rather than in profile, as sediments are seen in cores. Seeing the sediments in plan-view made 

it possible to more easily identify and image the formerly subaerial paleolandscape surface, which was 

clearly recognizable by its desiccated/sunbaked and cracked appearance, as shown in Figure 7-5.

Indicators of subaerial exposure are detectable in the sediment profile of a split core (e.g., increased 

sediment density and color change due to oxidation) they are just less obvious. An additional unique 

capability of the VSP was its dynamic recording of the physical properties of sediments. These properties

were observable as the internal water flow of the VSP washed over and through the probed sediments. A 

final benefit of the VSP was that it allowed for real-time monitoring, so that probing operations could be 

halted if evidence of a culturally sensitive feature was encountered (e.g., bone indicative of a possible 

human burial). Although VSP probing proved expedient and effective, it must be considered 

complimentary to, rather than a replacement for, subsurface sediment sampling/coring. 
75

Figure 7-3. Plots of contoured magnetic data from the 2013 Greenwich Bay (Cedar Tree Beach) 

gradiometer survey. 

The upper image presents the Earth’s total magnetic field-strength data. The lower image presents the derivative of 

the magnetic gradient (i.e., the slope of the difference between magnetic readings), accentuating magnetic anomalies 

of potential interest that were targeted for VSP inspection. 
76

Figure 7-4. Example of plotted 2013 VSP survey data acquired at 20-m spaced probe points 

distributed along “Transect B” in the Greenwich Bay (Cedar Tree Beach) geoarchaeological study 

area. 

Plot consists of sequenced plan-view images of changes to sediment strata recorded at each VSP probe point in 25 

cm intervals down to a maximum target depth of 2 m below the surface of the bay floor. Images are frame-grabs from 

video that was recorded by a self-lit camera mounted in the tip of the VSP (a modified hydro-probe). The location of 

Transect B is illustrated in Figure 7-6 by the yellow dots in the row labeled "B."
77

Figure 7-5. Excerpted processed VSP data documenting the desiccated and cracked organic 

sediments comprising the formerly subaerial paleolandsurface stratum encountered at the 

location of Cedar Tree Beach “Selective Probe S2” approximately 1.25 m below the bay floor’s 

surface.

In total, 41 VSP points were probed. Figure 7-6 shows the distribution of the systematic (20-m grid) and 

the 10 selective VSP probe point locations within the Greenwich Bay (Cedar Tree Beach) 

geoarchaeological study area. Only two of the systematic VSP locations targeted for investigation were 

not probed. One was at the location of a wooden groin and the other was located on shore. VSP data 

produced visual evidence of archaeologically sensitive, formerly subaerial sediments, as well as possible 

cultural features/artifacts. Formerly subaerial sediments were observed at several of the probed locations. 

Locations with evidence of paleolandsurfaces were organized hierarchically based on their predicted 

information potential. Two areas with the greatest information potential were selected for subsurface

archaeological testing/excavation: VSP probe-point “S2” and systematic VSP probe-point “B17.” These 

two points are located at opposite ends of the study area. Their positions and contents of interest are 

illustrated in Figure 7-7.
78

Figure 7-6. Distribution of systematic (20-m grid) and selective VSP probe point locations within the Greenwich Bay (Cedar Tree Beach) 

geoarchaeological study area. 

VSP probe points are superimposed onto a plot of the gradiometric survey results. Magnetic anomalies appear as orange-red areas in the data and were 

selectively targeted for VSP inspection (note the locations of VSP Transect “B” and VSP Selective Probe “S2”).
79

Figure 7-7. Visual features of interest (inset images) at Selective VSP Probe Point S2 and Systematic VSP Probe Point B17, which were 

subsequently examined through underwater archaeological excavation of 1 x 1 m DTUs at both locations. 

Inset images show a thin, formerly desiccated, cracked organic layer of stratified paleosols preserved on top of a thick loess deposit at Selective VSP Probe Point 

S2 (lower left image), and what appears to be a small primary flake of a dark-colored chert chipping debris at the location of Systematic VSP Probe Point B17 

(upper right image). The inset image at Systematic VSP Probe Point B1 includes what appears to be a thin layer of charcoal (this location was not subjected to 

underwater excavation). 
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VSP probe-point S2 was selected, because it contained a visibly oxidized, desiccated/sunbaked, 

archaeologically sensitive organic stratum at approximately 1.3 m below the surface of the sub-tidal 

bayfloor (see Figure 7-7). VSP probe-point B17 was selected, because it contained stratified organic 

sediments and what appeared to be a single piece of lithic chipping debris, as well as wood and charcoal 

approximately 1.5 m below the bayfloor surface (see Figure 7-7). Subsurface investigation of the two

VSP probe-points, located at opposite ends of the Cedar Tree Beach study area, provided more broadly 

spaced windows into the stratigraphy of the area. 

Excavation of the 1 x 1 m DTUs’ S2 and B17 terminated at depths of 1.5 and 1.8 m, respectively, below 

the bayfloor surface. The sidewalls of both DTUs were fragile and proved challenging to maintain. The 

stratigraphic sequence and visual evidence of a formerly subaerial paleolandscape surface observed in 

VSP S2 at 1.35–1.45 m below the bayfloor surface were confirmed by the excavation of DTU S2.

Examination and sorting of the archaeologically excavated paleolandscape surface stratum in DTU S2 

produced the first pre-contact period artifact—a single piece approximately 1.5 x 2.0 cm of high-quality 

quartz chipping debris—discovered as a result of a multi-phase, systematic geophysical/geotechnical 

survey of a submerged context (Figure 7-8). This discovery constituted a major technical find and project 

achievement, as it confirmed the presence of cultural materials within a documented, intact, stratified 

paleosol deposit identified by the research team, which was composed primarily of Tribal field specialists 

and data analysts.

Figure 7-8. Quartz chipping debris recovered during the underwater excavation of Greenwich Bay 

(Cedar Tree Beach) Selective VSP Probe Point Dredge Test Unit S2. 

These cultural materials were encounted in a submerged and buried, contextually intact, freshwater wetland 

paleolandsurface stratum that was located 135–145 cm below the surface of the bayfloor surface (photographs by 

David S. Robinson [URI-GSO]).

Underwater archaeological subsurface testing in DTU B17 encountered a stratified, organic-rich, formerly 

subaerial paleolandsurface stratum overlying a loess sediment layer (oxidized at its upper limit) at 

approximately the same depth below the seafloor (1.3–1.45 m as was seen in the systematic VSP data 

acquired at B17 and was found preserved in DTU S2. Preserved paleolandscape sediments in DTUs B17 

and S2 (approximately 200 m apart), as well as observations from other VSP probe points across the 

study area, suggested the stratified paleolandscape surface may have been more extensive within the 

Cedar Tree Beach (CTB) study area (and possibly beyond it) than originally thought, based on the 

project’s 2013 VSP probing alone.
81

As in the case of DTU S2, roots from an as-yet identified species of paleo-vegetation were preserved in 

their original growth position extending from the formerly subaerial paleolandsurface stratum into the 

upper surface of the underlying loess sediments. Unlike the relatively few roots seen in DTU S2, 

however, DTU B17 contained a relative abundance of them, as well as greenish-colored leaves/blades that 

were visible above the rootlets in the organic paleolandsurface stratum’s matrix. The finer and more 

dispersed roots of the vegetation observed in DTU B17 were different than the comparatively robust and 

densely packed roots of the common reed (Phragmites), which were observed and documented in 

sampled exposed peat deposits present onshore on CTB. Instead, they bear a closer resemblance to those 

of widgeon grass (Ruppia maritima), a salt-tolerant freshwater grass that grows in oxygenated sediments 

of fresh to brackish, non-turbid shallow water in coastal marshes. The presence of the in situ paleovegetation mat in its original growth position is significant, as it is a strong indicator of the lack of 

inundation-related disturbance to the paleolandsurface’s sediment matrix in which it was found.

Macro- and microscopic examination and sorting of materials excavated from the paleosols in DTU S2 

and B17, combined with observations from the visual sediment probing data and from the DTU’s during 

excavation, produced some basic results that are significant to the project, paleoenvironmental 

reconstruction, and modeling. Pre-contact period artifacts (i.e., quartz chipping debris) were recovered 

from a submerged and stratified, formerly subaerial paleolandsurface deposit that was identified through 

systematic, phased field research and data analysis by a joint-team of Tribal and non-Tribal researchers. 

This tells us that not only was a stratified paleolandsuface deposit preserved in Greenwich Bay, but that it 

contained cultural materials that were preserved in that stratified context as result of the activities of the 

ancient Native people who were occupying that now submerged and buried paleolandsurface at CTB. 

In addition to the cultural material recovered through underwater archaeological excavation, an 

assemblage of paleobotanical macrofossils was also recovered and identified. This assemblage included: a 

goosefoot (Chenopodium) seed; a grape seed; acorns; a maple seed; and numerous pondweed 

(Potamogeton) seeds, visible in Figure 7-9, as well as miscellaneous fragments of twigs, bark, and 

charcoal. Images of as-yet identified paleo-vegetation in its original growth position in the 

paleolandsurface stratum was documented in HD underwater video and samples of this vegetation were 

recovered from each excavated DTU (S2 and B17). Microscopic examination of the sediment sample 

recovered from the interface between the paleoslandsurface stratum and underlying loess in DTU S2 

revealed no indications of a marine environment (e.g., the presence of foraminifera). The combined

presence of desiccated and cracked organic-rich paleolandsurface sediments overlying a deposit of loess

that were observed in the VSP, the absence of foraminifera or any other marine floral or faunal remains, 

and the presence of pond weed seeds, along with terrestrial floral materials (e.g., acorns, maple seed, 

walnut or hickory shell husks, etc.), displayed in Figure 7-10, together suggest preservation of a 

paleoenvironment that was a topographically low and frequently wet, but sometimes exposed, muddy area 

(i.e., a flood plain) that was a resource-rich, intermediate environmental zone—a potential zone of 

intensive human activity—that was situated between adjacent uplands and the freshwater stream or small 

river that once occupied the natural channel in Greenwich Bay.
82

Figure 7-9. Plant macrofossils (left column images) recovered during the underwater 

archaeological excavation of Greenwich Bay (Cedar Tree Beach) Selective VSP Probe Point 

Dredge Test Unit S2.

These macrofossils were encountered in a submerged and buried, contextually intact, organic, freshwater wetland 

paleolandsurface stratum that was located 135–145 cm below the surface of the bayfloor. 

Figure 7-10. Tree macrofossils (left column images) recovered during the underwater 

archaeological excavation of Greenwich Bay (Cedar Tree Beach) Selective VSP Probe Point 

Dredge Test Unit S2. 

Macrofossils were encountered in a submerged and buried, contextually intact, organic, freshwater wetland 

paleolandsurface stratum located 135–145 cm below the surface of the bayfloor.
83

7.1.3 Greenwich Bay Geological Investigation

7.1.3.1 Introduction and Goals

Greenwich Bay is a shallow (2.6 m mean depth), 12-km2 estuary, with connection to the West Passage of 

Narragansett Bay. Cedar Tree Beach, described in Section 7.12 above, is located on the northweast coast 

of Greenwich Bay (Figure 7-11).

Figure 7-11. Overview map of the Cedar Tree Beach study area (top panel) and Greenwich Bay 

(bottom panel). 

Aerial imagery prepared by the URI Environmental Data Center, and projected in the NAD83 Rhode Island State 

Plane Feet 3800 coordinate system.
84

The purpose of the geological surveying in Greenwich Bay was to support the archaeological 

investigations at Cedar Tree Beach by identifying and characterizing submerged preserved terrestrial 

deposits and/or paleolandscapes offshore of Cedar Tree Beach and to determine if the subsurface 

stratigraphic framework established for the southern New England OCS applies to Greenwich Bay. In 

addition, geophysical surveying was conducted in order to investigate how improving seismic reflection 

profile trackline spacing affects paleolandscape reconstruction where high-resolution data exist.

7.1.3.2 Geologic Setting and Previous Work

The preferential erosion and lowered topography of the Rhode Island Formation led to the establishment 

of a south-flowing drainage system through Narragansett Bay during the Tertiary Period, representing 

nearly 60 million years of erosion (McMaster 1984). A prominent bedrock valley referred to as the 

(proto-) Blackstone River was traced from north of Providence through Greenwich Bay, connecting to a 

trunk valley in the west passage of Narragansett Bay (Upson and Spencer 1964). Subsequent modification 

by Pleistocene glaciation resulted in the widening and deepening of drainage valleys, followed by 

deposition of up to 40 m of Quaternary sediments in upper Narragansett Bay, mostly filling the drainage 

valleys (McMaster 1984). This thick sequence of sediment is composed of ground moraine tills, stratified 

outwash, and glaciodeltaic and glaciolacustrine deposits (Peck and McMaster 1991). The glacial deposits 

enclosing Greenwich Bay are described by Boothroyd and McCandless (2003), with glacial deltaic 

deposits to the north and south of Greenwich Bay, ice-marginal deposits to the west, and coarse tills to the 

east.

Twenty-four CHIRP seismic reflection profiles collected by URI-GSO in 2006 from Greenwich Bay and 

interpreted by Morissette (2014) describe the post-glacial depositional environments and sediments of 

now submerged Greenwich Bay. Acoustic basement was constrained as bedrock or where shallow, a 

progradational glacial fan. A thick sequence (typically > 30 m) of glaciolacustrine deposits was found to 

overlie acoustic basement throughout the bay, consisting of both proximal and distal seismic facies. The 

rhythmic internal reflectors draping the underlying topography are consistent with glaciolacustrine 

sediments identified in most of Narragansett Bay (Peck and McMaster 1991; Boothroyd and McCandless 

2003; Oakley 2012).

Morissette (2014) reports the existence of paleochannels incising glaciolacustrine sediments. These 

paleochannels form a tributary system, consistent with seismic reflector R2 reported by McMaster (1984) 

and a regional fluvial unconformity fu1 (O’Hara and Oldale 1980; Needell et al. 1983a, b, c; Needell and 

Lewis 1984). The presence of paleochannels is associated with the drainage of Glacial Lake Narragansett, 

which likely did not begin until the onset of isostatic rebound, but remains poorly constrained (Oakley

2012). A paleo-stream originating from modern-day Apponaug Cove passed just to the south of Cedar 

Tree Beach, joining a trunk channel approximately midway through Greenwich Bay (Morissette 2014).

Glacial deposits are truncated by a diachronous ravinement surface representing marine transgression 

through Greenwich Bay. Inundation of Greenwich Bay was at first confined to the paleo-streams, 

progressively flooding the subaerially exposed lakefloor. The timing of marine inundation of Greenwich 

Bay is somewhat contested. Based on the RSL curve generated by Oldale and O’Hara (1980), McMaster 

(1984) proposed an inundation age of 5,500 yBP. A study by Vinhateiro et al. (2007) reported an AMSdated shell from a sediment core collected in western Greenwich Bay dated to 6,500 yr BP. Morissette 

conservatively placed the age of paleo-streams as > 6,000 yBP.

Estuarine sediments overlie the ravinement surface and were deposited as Greenwich Bay transitioned to 

an estuary during the Holocene. In the seismic reflection profiles, estuarine sediment is nearly 

acoustically transparent suggesting the fine-grained nature of these sediments (Morissette 2014). Benthic 

geologic habitat mapping by Oakley et al. (2012) details the surficial geology of Greenwich Bay. The 
85

deeper, central basin of Greenwich Bay appeared as a featureless, low backscatter region in the side-scan 

imagery and is reported as fine-grained silts. Near the mouth of Greenwich Bay, sand sheets with some 

tidal/wave bedforms are predominant. Along the margins of Greenwich Bay, a shallow (< 1 m) 

depositional platform composed of sand, some gravel and shells can be traced to the beaches. Cedar Tree 

Beach falls under this categorization and marks the westernmost extension of the northern depositional 

platform. The coves of Greenwich Bay are primarily dredged channels or composed of clay, silt, and 

organic matter.

In Morissette (2014), three-dimensional paleolandscape reconstructions were attempted using the 2006 

CHIRP seismic reflection dataset with 300-m line spacing. Reflectors including acoustic basement, 

paleochannels and the ravinement surface were digitized using CTI SonarWeb software and interpolated 

in ESRI ArcGIS software, producing continuous surfaces. Morissette reported the prevalence of 

interpolation artifacts that arose due to the widely spaced seismic reflection profiles and the absence of 

perpendicular crossing lines. Nevertheless, the general morphology of the paleolandscapes was captured 

in these interpolated surfaces.

7.1.3.3 Overview of Field Methodology

Cedar Tree Beach

During the spring and summer of 2015, a seismic reflection survey was performed within the Cedar Tree 

Beach study area at 20-m line spacing perpendicular to the shoreline, and crossing lines paralleling the 

shore (Figure 7-12). Due to shallow bathymetry along this depositional platform, and the importance of 

collecting data as near to the beach as logistically possible, the survey was conducted at high tide. The 

data were acquired using a surface-towed “catamaran” style Benthos CHIRP III seismic reflection system 

and an Applanix POS MV inertially aided navigation system. All data were logged using SonarWiz 5 

acquisition software. Data quality was monitored during acquisition and parameters were modified in the 

field as needed (see field report for additional details). A total of six vibracores (Figure 7-12) were also 

collected along Cedar Tree Beach, using a pontoon boat as a coring platform. A submersible Rossfelder 

P-3 vibracoring head was affixed to a 4-in PVC tube, into which the sediment was recovered. Successful 

vibracores were capped and transported to the URI-GSO Marine Geological Samples Laboratory (MGSL) 

and stored near 4°C in a sediment core refrigerator.

The physical properties of each vibracore were logged and imaged using the non-destructive Geotek 

MSCL system. Parameters logged at a 1-cm resolution included Gamma Ray Attenuation and Porosity 

Evaluator (GRAPE) density, magnetic susceptibility, electrical resistivity, compressional wave (P-wave) 

velocity, and travel times. Initial core descriptions were recorded noting observed changes in color 

(referenced to the Munsell system of color notation), lithology, grain size, and presence of organic matter.
86

Figure 7-12. Seismic reflection survey lines from the Cedar Tree Beach study area and the 

locations of collected vibracores.

Survey lines are shown with red and blue lines. Vibracores are shown with yellow dots. Survey lines A-A’, B-B’ and CC’ overlap vibracore transects and are discussed in further detail. Seismic reflection line 2 was collected in 2006 and 

provides a stratigraphic framework for Greenwich Bay.

3-D Paleolandscape Reconstruction of Central Greenwich Bay

A total of 25 NE-SW trending CHIRP seismic reflection profiles (100- to 200-m line spacing) and 7 

perpendicular crossing profiles (300-m line spacing) were collected in June–July 2015. The seismic 

reflection system, software, and acquisition techniques were the same as the Cedar Tree Beach survey 

(see Caccioppoli et al. 2018 for detailed description). The new CHIRP seismic reflection data 

supplements a 2006 CHIRP survey such that when combined, the data achieves 100-m line spacing and 

300-m crossing line spacing throughout Greenwich Bay.

Raw digital seismic reflection data were imported into CTI SonarWiz 6 processing software. Each 

seismic reflection profile was bottom tracked and signal gains were applied to improve image quality. A 

subset of 13 NE-SW trending seismic reflection profiles and 3 perpendicular crossing lines located in 

central Greenwich Bay were selected for paleolandscape reconstruction. These 16 seismic reflection lines 

were selected due to excellent seismic penetration and relative absence of gas-bearing sediment.

Seismic reflector fu1 was identified and digitally traced in each seismic reflection profile using SonarWiz 

6 software (Figure 7-13). The thicknesses of traced reflectors fu1 were then calculated and exported as 

points (delimited xyz text files). The depth of reflector fu1 was then converted from milliseconds to 

meters using an assumed two-way travel velocity of 1,500 ms-1

, a value that is valid for unconsolidated 

saturated sediment and in agreement with previous p-wave seismic velocity findings from a sediment core 

in Greenwich Bay (Vinhateiro et al. 2007).
87

Figure 7-13. Example CHIRP seismic reflection profile from Greenwich Bay. 

Shaded blue area shows depth to reflector fu1, treated as a thickness and exported an “.xyz” file for use in the 

interpolated paleolandscape surface.

The processed xyz point text files were brought into a geospatial environment using ESRI ArcMap 10.2 

as points with elevations. The points were then interpolated as a continuous surface using the Terrain 

interpolation method. Terrains are a robust, specialized variant of Triangular Irregular Network (TIN) 

surfaces that are well suited for datasets exceeding many thousands of points such as those generated by 

sonar and LiDAR. The terrain was then converted to a raster using the Terrain to Raster Conversion 

toolset. The resulting raster represents the depth to reflector fu1 below mean sea level (MSL). 

This outlined procedure was repeated, generating three interpolated surfaces. The first surface contains all 

interpreted seismic reflections lines within our study area. The second surface is based on the on all NESW oriented seismic reflection lines, excluding perpendicular crossing lines. The final surface uses only 

the older CHIRP seismic reflection lines collected in the original 2006 survey.

7.1.3.4 Results and Discussion

7.1.3.4.1 Cedar Tree Beach

Seismic Reflection Profiles and Correlation with Previous Studies

The combination of very shallow water depths and a highly reflective seafloor resulted in the poor 

performance of the CHIRP seismic reflection system. Best penetration occurred in the westernmost study 

area, where water depths were slightly deeper and surficial sediments finer. Two reflectors were identified 

in the CHIRP data. The deepest reflector observed is south dipping and discontinuous, and reaches a 

depth of approximately 5 m (seismic line C-C’) (Figures 7-12, 7-14). This reflector is also observed in 

seismic line B-B’ at approximately 1.5 to 2.5 m depth (Figures 7-12, 7-15). A shallower, prominent flatlying reflector is observed 1 to 1.5 m below the seafloor in the western portion of the seismic line (Figure 

7-14). 
88

Figure 7-14. Processed seismic reflection line C-C’, with interpreted seismic reflectors and correlated with seismic reflection line 2 from 

Morissette (2013). 

See text for explanation of reflectors and interpretations of lithology

Figure 7-15. Seismic reflection line B-B’ with W-E vibracore transect. 

See Figure 7-12 for location of seismic line. Dark red, red, blue and green core sections represents Lithology 1, 2 3 and 4, respectively. See text for explanation of 

reflectors and interpretations of lithology.
89

Despite limited penetration, the two identified reflectors were correlated with the regional stratigraphic 

framework and with reflectors reported in Morissette (2014). The deepest seismic reflector identified was

the lithological change at the marine unconformity (mu), representing Holocene marine transgression and 

the truncation of underlying glaciolacustrine sediments (Figure 7-14). The marine unconformity is 

referred to as the ravinement surface (R1) in Morissette (2014). The shallowest reflector identified in 

seismic reflection profiles B-B’ and C-C’ is represented by a dashed green line in Figure 7-14. This 

reflector has not been described in previous studies, likely due to its shallow depth and confinement to the 

depositional platform. This reflector lies ~1 m below the estuary floor and represents a change in physical 

properties within the estuarine sediment.

Several other reflectors and sedimentary units were only observed in seismic reflection line 2 from

Morissette (2014) and were correlated with the regional stratigraphic framework. A well-defined 

paleochannel, referred to as PC in Morrissete (2014) and part of reflector fu1 in the regional stratigraphic 

framework, dissects glaciolacustrine sediment (Figure 7-14). Filling these channels is post-glacial fluvial 

sediment and estuarine sediment, referred to as Qfe in the regional stratigraphic framework (Figure 7-14).

Overlying the marine unconformity (mu) and Qfe is marine sediment (Qpt in the regional framework).

The reflector mu exists at a depth of approximately 6–8 m below present sea level in seismic reflection 

profile 2, and more or less parallels the depth of the estuary floor. Extrapolation of mu to the north, and 

approximately following the slope of the estuary floor results in good depth agreement with a reflector 

identified in seismic reflection profile C-C’ (this study) (Figure 7-14).

Physical Properties and Stratigraphic Correlation of Vibracores

Physical properties from the seven vibracores were plotted using Delta Graph 5 software (Figures 7-16 to 

7-22). Additionally, a down-core plot of reflection coefficient was calculated for each vibracore. The 

trends in magnetic susceptibility, P-wave travel time, GRAPE density, and reflection coefficient were 

analyzed based off the plotted data and four distinct lithologies were identified and are discussed below.

Several distinct lithologies have been identified through the analysis of seismic reflection profiles 

collected for this study, correlation of seismic reflection data with previous studies, and analysis of 

physical properties of vibracores.

Lithology 1: Estuarine Deposition Modified by Anthropogenic Processes

Previous studies have established the usefulness of magnetic susceptibility for stratigraphic correlation of 

coring sites (Bloemendal et al. 1988; Corbin 1989). Changes in the concentration of magnetic minerals in 

sediments are responsible for changes in measured magnetic susceptibility values, therefore, as 

sedimentation rates increase at a given site, fluxes of magnetic material will covary based on the 

concentration of magnetic minerals. Corbin (1989) used this relationship as a proxy for sedimentation 

rates in Narragansett Bay. Piston cores analyzed in Corbin (1989) from Apponaug Cove and Greenwich 

Bay show a very similar trend in magnetic susceptibility, with high values within the upper 40–60 cm, 

and trending towards a low background value down-core. Vibracores collected from Cedar Tree Beach 

exhibited high amplitude variability with up to four distinct peaks in magnetic susceptibility, with the 

core logging sampling interval of 1 cm. These peaks were absent from the piston cores in Corbin (1989), 

which is likely due to the difference in sampling interval (3-cm subsamples). Additionally, the amplitude 

of peaks in magnetic susceptibility increased with nearness to shore. 
90

Figure 7-16. Physical properties and initial core descriptions of vibracore CTB VC-10_1. 

Numbers refer to correlated peaks in magnetic susceptibility. Green line represents a down-core transition to background values of magnetic susceptibility. Dashed 

red line represents a core break. Dashed black line labeled “A” is a tie point with CTB VC-10_2 and CTB VC-14. Red line (R1) indicates a change in lithology 

characterized by the presence of coarse sand and gravel. See text for interpretations of lithology.
91

Figure 7-17. Physical properties and initial core descriptions of vibracore CTB VC-10_2. 

Numbers refer to correlated peaks in magnetic susceptibility. Green line represents a down-core transition to background values of magnetic susceptibility. Dashed 

red line represents a core break. Dashed black line labeled “A” is a tie point with CTB VC-10_1 and CTB VC-14. See text for interpretations of lithology.
92

Figure 7-18. Physical properties and initial core descriptions of vibracore CTB VC-14. 

Numbers refer to correlated peaks in magnetic susceptibility. Green line represents a down-core transition to background values of magnetic susceptibility. Dashed 

red line represents a core break. Dashed black line labeled “A” is a tie point with CTB VC-10_1 and CTB VC-10_2. Red line (R1) indicates a change in lithology 

characterized by the presence of coarse sand and gravel. See text for interpretations of lithology.
93

Figure 7-19. Physical properties and initial core descriptions of vibracore CTB VC-9. 

Numbers refer to correlated peaks in magnetic susceptibility. Green line represents a down-core transition to background values of magnetic susceptibility. Dashed 

red line represents a core break. Red line (R1) indicates a change in lithology characterized by the presence of coarse sand and gravel. Blue line represents a 

change in lithology. See text for interpretations of lithology.
94

Figure 7-20. Physical properties and initial core descriptions of vibracore CTB VC-6. 

Numbers refer to correlated peaks in magnetic susceptibility. Green line represents a down-core transition to background values of magnetic susceptibility. Dashed 

red line represents a core break. Red line (R1) indicates a change in lithology characterized by the presence of coarse sand and gravel. See text for interpretations 

of lithology.
95

Figure 7-21. Physical properties and initial core descriptions of vibracore CTB VC-5. 

Numbers refer to correlated peaks in magnetic susceptibility. Green line represents a down-core transition to background values of magnetic susceptibility. Dashed 

red line represents a core break. See text for interpretations of lithology. 
96

Figure 7-22. Physical properties and initial core descriptions of vibracore CTB VC-4. 

Numbers refer to correlated peaks in magnetic susceptibility. Green line represents a down-core transition to background values of magnetic susceptibility. Dashed 

red line represents a core break. Red line (R1) indicates a change in lithology characterized by the presence of coarse sand and gravel. See text for interpretations 

of lithology.
97

Corbin (1989) reported that metal concentrations reached background values at a depth very similar to 

magnetic susceptibility and occurred at the interface of two distinct lithologies. Similarly, magnetic 

susceptibility of the vibracores from this study reached background values at a distinct density change, 

indicated by a high amplitude peak in the reflection coefficient. The base of Lithology 1 is correlated with 

the tie point in Corbin (1989), where magnetic susceptibility and metal concentrations reach background 

values, which was dated to approximately 1880 A.D. (138 yBP). This age serves as minimum age of the 

base of Unit 1, as the increase in magnetic susceptibility predated the increase in metal concentrations in 

the Apponaug Cove and Greenwich Bay piston cores. The increase in magnetic susceptibility and 

sedimentation rates are the result of land clearance by European settlers, which increased erosion rates 

and changed the composition of sediments entering Greenwich Bay (Corbin 1989). A well-established 

proxy for European settlement and land clearance is the “Ambrosia rise,” the presence of ragweed pollen 

grains representing a vegetation shift due to European settlement. Morissette (2014) reporting on an 

unpublished study by King et al. (1993) identified an age of ~340 yBP for the Ambrosia rise specific to 

Gorton Pond, a freshwater kettle pond < 2 km from Cedar Tree Beach. It is therefore proposed that 340 

yBP is a maximum age of the base of Unit 1. According to the radiocarbon-dated Rumex pollen rise 

observed in sediment cores from Succotash Marsh, East Matunuck, RI, the date of land clearance in 

southern New England occurred ~209–281 yBP (1734–1806 A.D.). This date range is closer to the 

widespread and regional European-style agricultural land clearance ca. 1,700 (Donnelly and Berntness

2001). Based on initial core descriptions, grain size of Unit 1 decreases with distance from the shoreline, 

with numerous marine shells and shell hash present. The base of this lithology is correlated with green 

reflector from seismic reflection line 2 (Figure 7-14), representing an upper facies of marine sedimentary 

unit (Qpt).

Lithology 2: Open Estuarine Deposition

Based on initial core descriptions, sediment within this unit fines downward, with increasing fraction of 

silt and mud. Shells become less common down-core through this lithology. In vibracore CTB VC-10_1, 

a scallop shell was preserved at the very top of this lithology (Figure 7-16). In Greenwich Bay, scallops 

are an indicator species for good water quality. Prior to anthropogenic eutrophication, Greenwich Bay 

supported a thriving scallop fishery. Declines in eelgrass due to eutrophication have greatly reduced 

scallop populations (John King, personal communication, October 25, 2015). This lithology is correlated 

with sedimentary unit Qpt from the regional framework and represents the onset of open estuarine 

deposition within the Cedar Tree Beach study area, truncated at the top by the onset of estuarine 

deposition modified by anthropogenic activities in surrounding upland areas.

Lithology 3: Ravinement and Onset of Estuarine Deposition

The identification of Lithology 3 is dependent on observations of coarse-grained sediments during initial 

core descriptions. In most cores, sub-angular to angular coarse sand to gravel are sparsely embedded 

within this unit, becoming more prevalent towards the bottom of this lithology. Lithology 3 ranges in 

down-core depth from 73 to 189 cm and is shallowest near shore. The coarse sand and gravel do not 

exhibit distinct layering in any of the cores. It is hypothesized that rising sea level left a coarse lag deposit 

prior to onset of estuarine deposition that was subsequently mixed with finer grained sediment by 

bioturbation.

The top of Lithology 3 is correlated with seismic reflector mu from seismic reflection line 2, representing 

the marine unconformity (ravinement surface) (Figure 7-14). In the down-core plots of reflection 

coefficient there are no prominent reflectors that are associated with the ravinement. However, the 

ravinement surface is clearly observable in seismic reflection profiles 2 and C-C’ (Figure 7-14). This 

disparity most likely arises from the differing vertical resolutions between the Geotek MSCL system and 

the CHIRP seismic reflection system. The absence of high amplitude reflectors representing the 
98

ravinement in the core is likely due to the small (1- to 2-cm) sampling interval of the Geotek MSCL 

system and the lack of a distinct layer of coarse sand and gravel due to bioturbation effects. Conversely, 

the 20- to 40-cm vertical resolution of the CHIRP seismic reflection system is thought to average the 

acoustic impedance of sparsely distributed coarse sand generating a weak reflector.

The ravinement surface is a diachronous feature, and therefore the depth at which it is observed 

corresponds to an inundation age based on RSL rise. A previously unpublished study created an age 

model for an approximately 7-m sediment core collected in western Greenwich Bay (Vinhateiro et al. 

2007) (Figure 7-23). Calibrated radiocarbon-dated shells determined a basal age of ca. 6,500 yBP. The 

depth of the ravinement surface at the southern edge of the Cedar Tree Beach study area is estimated to be 

approximately 5.50 m below present-day sea level. Based on the age model produced by Vinhateiro et al. 

(2007), submergence of Cedar Tree Beach would have begun approximately 6,000 yBP. This closely 

agrees with the RSL curve constructed for Block Island by Oakley and Boothroyd (2012), which yields an 

inundation age of ca. 5,800 yBP (Figure 7-23). Comparison with RSL curves for southern New England 

constructed by Roy and Peltier (2015) yields a much younger inundation age, approximately 3,300 yBP 

(Figure 7-23). The Connecticut RSL curve presented in Roy and Peltier (2015) was determined as 

appropriate for Greenwich Bay, RI, based on the measured distance (ca. 2,450 km) from the approximate 

center of mass of the Laurentide Ice Sheet near the western shore of Hudson Bay. A plot of the rates of 

Late Holocene RSL rise against the distance from the ice sheet center of mass presented in Engelhart et 

al. (2009) yields a subsidence rate of ca. 1 mm/yr at a distance of 2,450 km, a rate which is nearly 

identical to that of Connecticut (1.1 ± 0.1 mm/yr). The predicted RSL curves from geophysical models fit 

well with robust RSL indicators, especially from 4,000 to 0 yBP (Roy and Peltier 2015). For this reason, 

an inundation age closer to 3,300 yBP must be strongly considered.

Lithology 4: Terrestrial / Glaciolacustrine Deposition

Lithology 4 was only recovered in vibracore CTB VC-9, however, characterization of the physical 

properties associated with this boundary suggests that several vibracores likely penetrated, or came very 

close to penetrating this lithology (Figure 7-19). At 231 cm sediment depth, a light tan silt and clay unit 

with oxidation stains and a disturbed appearance was recovered, to a depth of 247 cm. A very high 

amplitude magnetic susceptibility peak and prominent reflection was observed within this lithology, 

where background values predominated in the overlying lithology. CTB VC-6 also shows a high 

amplitude peak in magnetic susceptibility at the very bottom of the vibracore, at a down-core depth of 

approximately 188 cm (Figure 7-20). These two vibracores have a similar density trend at peak in 

magnetic susceptibility, characterized first by a sharp decrease in density, followed by a sharp increase in 

density, occurring over a 10-cm interval at the bottom of the core.

Lithology 4 is inferred to be non-estuarine deposits, and is likely glaciolacustrine sediment (Qdo in the 

regional stratigraphic framework). Morissette (2014) reported very thick sequences (up to 42 m) of 

varved pro-glacial lake floor sediments truncated by the ravinement surface. Lithology 4 represents the 

top of the glacial deposits. Oxidized sediment may represent a period of subaerial exposure, as the proglacial lake in Greenwich Bay was drained, and streams cut in to the exposed lake floor as is indicated by 

the paleochannel identified in seismic reflection line 2.

Due to the poor performance of the CHIRP seismic reflection system along the Cedar Tree Beach 

depositional platform, no seismic reflector is correlated with this change in lithology.
99

Figure 7-23. Comparison of an age model for Greenwich Bay (A) and relative sea level curves for 

southern New England (B, C). 

The horizontal red lines intersect a depth of 5.5 m below present sea level, representing the depth of the ravinement 

surface at the seaward edge of the Cedar Tree Beach study area. The Greenwich Bay age model agrees more 

closely with the RSL curve produced by Oakley and Boothroyd (2012), with an inundation age of ~5,800 yr BP. 
100

7.1.3.4.2 3-D Paleolandscape Reconstruction of Central Greenwich Bay

The methodology outlined above describes the process of generating three-dimensional (x, y position and 

z elevation) continuous surfaces from reflectors traced across seismic reflection profiles. When a seismic 

reflector has inferred geological attributes, the 3-D expression of the reflector represents a 

paleolandscape. Paleolandscapes are best visualized like bathymetry, where depth contours are filled and 

colorized displaying the variation in depth across the study area. In the case of a paleolandscape, the 

generated surface represents the depth to a sub-seafloor feature (instead of depth to seafloor for 

bathymetry).

As is intuited, increasing the number of seismic reflection profiles from which the 3-D paleolandscape 

reconstruction is based results in a much more detailed continuous surface (Figure 7-24). When only four 

seismic reflection profiles were incorporated into the reconstruction (Figure 7-24c), depths exceeding 

11 m form a broad trough and appears to follow the trend of bathymetric contours (Figure 7-23, nautical 

chart basemap). However, as additional seismic reflection lines are incorporated, this broad trough 

becomes more discontinuous and irregular (Figure 7-24 a, b). Without crossing lines incorporated into the 

reconstruction (b), an apparent sill separates two deeper basins. Incorporating the crossing lines (Figure 7-

24a) reveals that the deeper basins are narrowly connected by a channel. Because this channel axis is 

aligned with the trend of the crossing line, it is absent in both reconstructions b and c, despite being nearly

100 m in width. This example illustrates the importance of crossing lines when planning paleolandscape 

reconstructions.

The fu1 reflector is a prominent regional seismic reflector described throughout this report (Figure 7-13).

It represents a fluvially eroded terrestrial surface underlain by glacially deposited sediment. Throughout 

Greenwich Bay, fu1 truncates glaciolacustrine sediment that was deposited when Glacial Lake 

Narragansett occupied Greenwich Bay following the retreat of the Late Wisconsinan icesheet. As the 

post-glacial lake occupying Greenwich Bay and, more broadly, Narragansett Bay drained, the lakebed 

was subaerially exposed and subsequently was fluvially eroded. The fu1 reflector and paleolandscape 

represents what remains of the subaerially exposed lakebed.

Within this study area subset in Greenwich Bay, there does not appear to be a strongly developed 

dendritic drainage pattern, but a partially interconnected series of basins. This is in general agreement 

with the paleochannels mapped by Morissette (2014); however, a better-defined tributary drainage system 

was described as occupying Greenwich Bay than is observed in this reconstruction. Similar post-glacial 

drainage features have been described in southern New England and were attributed to spring-sapping 

erosion from high water tables immediately following lake drainage (e.g., Uchupi and Oldale 1994; 

Boothroyd and August 2008).
101

Figure 7-24. Visualizations of interpolated depths to reflector fu1 (post-glacial fluvial unconformity) 

using seismic reflection profiles obtained at three trackline spacings. 
102

7.1.4 Gorton Pond Paleoenvironmental Investigation

7.1.4.1 Introduction and Goals

Gorton Pond is a 13.7 m deep freshwater glacial kettle lake located at the headwaters of Greenwich Bay 

in Warwick, Rhode Island (Figure 7-25). The sedimentary record contained within the lake is potentially 

approximately 19,000 years old, based on the estimated age of the associated glacial moraine (Morrissette 

2014). Several core locations (Figure 7-25) were sampled in order to obtain a long regional 

paleoenvironmental record for use in the Submerged Paleolandscapes Project. The results of studies from 

a long core from the deep basin in Gorton Pond are summarized in Morrisette (2014). Additional cores 

were subsequently taken in shallower basins to test for lake level changes (Figure 7-25). The water depths 

at the core locations are summarized in Table 7-1.

Figure 7-25. Location of Gorton Pond cores. 

The location of cores obtained within Gorton Pond are illustrated by yellow dots, with call-out boxes indicating core 

names.
103

Table 7-1. Water depths of Gorton Pond Cores.

Core Location Water Depth (m)

GP13 13.0

LC1 & LC2 13.0

15-1 3.8

15-2 9.6

15-3 5.5

The primary goals of the Gorton Pond studies were to:

• Develop a paleoenvironmental framework for the Greenwich Bay area for approximately the past 

15,000 years, by investigating proxy indicators of vegetation change and fire frequency obtained 

from sediment core samples.

• Test the efficacy of proxy indicators for detecting climate change and human activity in the 

sedimentary record, and try and distinguish changes in the paleoenvironmental record that were 

due to climate change from those that might indicate human activities within the watershed.

7.1.4.2 Geological Setting and Previous Work

Gorton Pond is a kettle pond that formed from the melting of calved ice blocks that were originally buried 

beneath glacial derived sediments and are often found with either glacial moraines or glacial outwash 

plains (Morrisette 2014). Previous glacial geology summarized in Morrisette (2014) indicates that the age 

of the basal sediments in Gorton Pond is between 17,800–18,800 calendar years old. Little multi-proxy 

paleoenvironmental work had been conducted on Rhode Island kettle lakes prior to Morrissette (2014).

Studies of Gorton Pond and an additional kettle pond known as Silver Lake, located about 30 km south of 

Gorton Pond near the south coast of Rhode Island, were conducted as part of the Submerged 

Paleolandscapes Project as a follow-up to Morrissette (2014).

7.1.4.3 Geological Setting and Previous Work

The field methodology used to study Gorton Pond is summarized in Morrisette (2014) and Caccioppoli et 

al. (2018). In short, a piston coring system (Glew et al. 2002) was deployed from a 10 m pontoon boat in 

the summer of 2013 to obtain a approximately 1.2 m surface core, and an approximately 6.4 m long core 

from the deep basin of the lake. During the winter of 2015, additional cores were obtained using the same 

coring methods in shallower basins from a frozen ice surface (Caccioppoli et al. 2018). These cores were 

obtained to detect major climate-induced lake level fluctuations during the Holocene period.

7.1.4.4 Results and Discussion 

The majority of the results from multi-proxy studies of the long core from the deep basin of Gorton Pond 

are summarized in Morrisette (2014). One important result was the construction of a hydrogen isotope 

paleotemperature curve for the region that spans from the present back to approximately 16,000 calendar 

years ago (Morrissette 2014). Subsequent studies have been done to construct a paleo-vegetation record 

or the same interval. A summary pollen diagram for Gorton Pond is shown in Figure 7-26. The 

chronological information used to estimate the age model is shown in Table 7-2.
104

Figure 7-26. Summary pollen diagram for Gorton Pond. 

Pollen type and charcoal are shown on the x axis as percentages of the total grains counted at each depth interval. The age model is estimated from the pollen 

datums and radiocarbon dates shown in Table 7-2.
105

Table 7-2. Datums used for Gorton Pond age model.

Previous studies (Delcourt and Delcourt 2004) have shown that intervals of elevated percentages of 

ragweed pollen, an indicator of forest clearance/disturbance, in conjunction with elevated inputs of 

charcoal, are evidence of human activities within the watershed. Two major intervals, between 9,200–

7,000 years ago and 400 yBP–present, of contemporaneously elevated ragweed pollen and charcoal inputs 

are shown in Figure 7-26. 

The lithological results from the depth transect of cores summarized in Table 7-1 are interesting because 

core 15-1, obtained at 3.8-m water depth, contains a sand layer at 3.35-m depth in the core (Figure 7-27). 

This sand layer indicates that the core site was dry at that time and that the lake level was more than 7 m 

lower in the past. Studies are ongoing but the sediments above the sand layer are approximately 1,000–

1,500 years old. Therefore lake levels in Gorton Pond were more than 7 m lower than present at that time. 

The lack of a comparable layer at site 15-3 located in 5.5 m of water indicates that the drop in lake level 

was more than 7 m but less than approximately 9 m.

The increase in ragweed and charcoal during the interval of 400 yBP to present is coincident with the 

contact period and time of European settlement and subsequent development in the Gorton Pond 

watershed. This time interval is one of well-documented forest clearance and extensive human 

disturbance (Morrisette 2014). The interval between 9,200–7,000 years ago is one of relatively stable 

temperatures (climate) as indicated by hydrogen isotope studies (Morrisette 2014). For this reason the 

observed increase in ragweed pollen and charcoal input to Gorton Pond may be indicative of an earlier 

interval of disturbance within the watershed by indigenous people (Delcourt and Delcourt 2004).

Late glacial and Holocene lake level fluctuates of up to 20 m have been observed in a high-resolution 

study of Sluice Pond in southern Massachusetts (Hubeny et al. 2015). The Sluice Pond lake level record is 

shown in Figure 7-28. The interval between 5,500–1,000 years contains two times of lake levels that are 

10–15 m lower than present, separated by a short interval approximately 3,000 years ago that had lake 

levels that were 5 m lower than present. In addition, lake levels up to 10 m lower than present have been 

observed during the interval between 5,500–1,000 years ago have been observed by King et al. (2015) in 

Silver Lake, located in southern Rhode Island. For these reasons the approximately 7–9 m drop in lake 

level in Gorton Pond that ended 1,000–1,500 years ago is interpreted to be part of a regional time of 

significantly drier climate in southern New England.

The sediments of Gorton Pond contain two intervals of extensive human disturbance within the watershed 

as indicated by ragweed pollen and charcoal inputs. The younger interval of disturbance is welldocumented in the written historical record. Further work on the older interval is underway to look for 

cultural material, e.g., microdebitage. The sediments of Gorton Pond and other regional lake records 

document dramatic changes in lake level during the Holocene. The interval 5,500–1,000 years ago is one 

of drier climate. Further work is underway to examine the possible relationship between human 

populations and climate prior to, during, and after this dry interval.

Composite Depth 

(cm)

14C Age

(yBP)

Error

( + years)

Calendar Age

(yBP)

Error

( + years)

0 0 0 0 0

110 (Ragweed rise) -- -- 338 25

180 1,840 30 1,859 87

303 6,140 30 7,117 103

416 9,570 40 10,986 182

475 10,310 40 12,165 123
106

Figure 7-27. Core log from Gorton Pond Livingston core 15-1.

Core was obtained in 3.8-m water depth. Down-core density and magnetic susceptibility (MS) are shown at left, 

compared to the core image and description at right.

organic 

mud

sand
107

Figure 7-28. Lake level reconstruction for Sluice Pond, Massachusetts.

Diagram from Hubeny et al. (2015).

7.1.5 Implications for Predictive Modeling

7.1.5.1 Archaeological Investigations

The phased, systematic application of different types of Tribally sensitive no- and low-impact marine 

geoarchaeological surveying and subsurface sampling methods (i.e., close-interval systematic 

gradiometric survey, systematic and selective VSP probing, and selective excavation of underwater 

DTUs) conducted on a localized scale at Cedar Tree Beach demonstrated that:

• Identifying, characterizing, and documenting preserved elements of the submerged paleocultural 

landscape is technologically possible and logistically feasible.

• Identifying cultural deposits preserved within the preserved paleolandscape is technologically 

possible and logistically feasible.

• It is possible for submerged and buried sediment strata associated with a resource-rich, 

archaeologically sensitive element of the formerly subaerial paleolandscape located in the 

intermediate environmental zone (e.g., a floodplain) between a freshwater stream/small river and 

adjacent uplands to survive the marine transgression process intact within protected, lowerenergy, shallow water, estuarine embayment environments.

• The root mat of thick peat deposits that can form along coastal areas on top of terrestrial strata as 

sea level rises and shorelines move inland act as a protective layer inhibiting erosion and 

destruction of the underlying paleolandscape surface.

The implication of these findings to modeling is that elements of similarly situated paleolandscapes 

located at the margins of former water bodies can be preserved underwater, and, consequently, may have 

higher archaeological sensitivity than other types of sea floor strata. 
108

7.1.5.2 Geological Investigations

Several seismic reflectors representing unconformities and sedimentary sequences were identified in the 

extensive seismic reflection surveys in Greenwich Bay. Previous work by Morissette (2014) did not 

conform to regional geologic framework nomenclature, despite similar findings. The inconsistent 

nomenclature between these previous works can be challenging, and therefore we have summarized the 

correlated reflectors and sedimentary sequences below. For the discussion of predictive modeling, the 

regional geologic framework nomenclature developed by the USGS legacy studies (Sections 4 and 6, and 

Figures 4-4 and 6-5 in this report) will be used for consistency purposes within this report.

• Qpt: Post-transgression marine sediment. The uppermost sediment identified in seismic 

reflection profiles from Greenwich Bay is post-marine transgression estuarine/marine sediment. It 

is easily identified by its nearly acoustically transparent character and was referred to as U4 in 

Morissette (2014). This sediment overlies the ravinement surface and is correlated with the Qpt 

post-transgression marine sediment in regional geologic framework studies.

• mu: Ravinement surface. The ravinement surface, an erosional unconformity due to wave-cutting 

during marine transgression was identified throughout Greenwich Bay. It has been referred to as 

the R1 reflector in Morissette (2014) and is correlated with the mu reflector reported in regional 

geologic framework studies.

• Qfe: Fluvial and estuarine sediments. Fluvial and estuarine sediment filling paleochannels 

associated with reflector fu1 and unconformably overlying glaciolacustrine sediment were not 

discussed in previous works. This sediment is confined to the paleochannels and underlies the 

ravinement surface and is referred to as Qfe in regional geologic framework studies.

• fu1: Post-glacial fluvial unconformity. Previous work by Morissette (2014) describes reflectors 

interpreted as paleochannels that were eroded into the underlying glaciolacustrine deposits. This 

post-glacial fluvial unconformity is ubiquitous throughout the sub-seafloor geological framework 

of Narragansett Bay, Block Island, and Rhode Island Sounds and is referred to as fu1 in several 

earlier studies (e.g., Needell et al. 1983a, b, c). Although fu1 is described as a continuous drainage 

system connecting the upper portions of Narragansett Bay to the present-day continental shelf, the 

paleolandscape reconstruction of fu1 within Greenwich Bay suggest that the connectivity may not 

have been completely continuous in the central basin of Greenwich Bay (Figure 7-24). 

• Qdo: Glaciolacustrine sediments. Glaciolacustrine sediments with thicknesses of up to ~40m 

were identified in Greenwich Bay. Morissette (2014) separated glaciolacustrine into several 

different seismic units (U1, U2, U3), suggesting that there were slight differences in depositional 

environments and conditions. More broadly, the glaciolacustrine sediment is correlated with the 

“Qdo” depositional sequence described in regional geologic framework studies. 

Of the described sedimentary units and reflectors observed within Greenwich Bay, only two are most 

likely to be paleoculturally sensitive. At the base of the stratigraphic unit, acoustic basement is inferred to 

consist of bedrock or stratified glacial deposits, which underly Greenwich Bay and served as the basin 

where glacial meltwater formed a glacial lake. Thick deposits of glaciolacustrine sediment overlie 

acoustic basement, suggesting that acoustic basement had not been subaerially exposed since before 

Wisconsinan glaciation. Also unlikely to be culturally sensitive is Qpt, as it represents sediment that had 

been deposited after marine conditions had been established in Greenwich Bay. Only Qdo and Qfe are 

likely to be paleoculturally sensitive in Greenwich Bay. Glaciolacustrine sediment (Qdo) would only 

become sensitive following lake drainage and subaerial exposure of the lakebed. Similarly, Qfe may be 

culturally sensitive, particularly any sediment deposited in a fluvial environment. Although fluvial 
109

processes are erosional at stream thalwegs, deposition can occur at the margins and in a floodplain, 

particularly as stream levels lower. Any improvements in seismic reflection profile spacing only improves 

paleolandscape reconstruction and should be considered when planning paleocultural sensitivity 

assessments.

7.1.6 Key Points

• Several different depositional sequences were identified in seismic reflection profiles in 

Greenwich Bay:

o Acoustic Basement: bedrock or deltaic sediment (Pzz in the regional geologic 

framework)

o Units 1–3: glaciolacustrine sediment (Qdo in regional geologic framework)

o Unit 4: estuarine sediment (Qfe and Qpt in regional geologic framework)

• Two reflectors were identified in seismic reflection profiles in Greenwich Bay:

o Paleochannel: post-glacial fluvial erosion (fu1 in regional geologic framework)

o R1: ravinement surface (mu in regional geologic framework)

• Non-marine sediment “Lithology 4” was recovered in a single vibracore from Cedar Tree Beach 

and is inferred to be glaciolacustrine sediment (Qdo).

• Marine inundation at Cedar Tree Beach occurred when sea level reached -5.5 m below presentday sea level and is constrained between 6,000 and 3,300 yBP.

• Significant improvements in 3-D paleolandscape reconstruction of the post-glacial fluvial 

unconformity (fu1) surface occurred when reducing seismic reflection profile spacing from 300 m 

to 100 m and when incorporating crossing lines (spaced 300 m apart in this case).

• It is possible to identify, characterize, and document preserved elements of the submerged 

paleolandscape and cultural deposits within them.

• Resource-rich, archaeologically sensitive, topographically low, margins of former water bodies 

on the paleolandscape can survive the marine transgression process intact, particularly when 

jacketed by a thick vegetative root mat and when situated in protected, lower-energy, shallow

water, estuarine embayment environments. 

• The sediments of Gorton Pond and other regional lake records document dramatic changes in lake 

level during the Holocene. The interval 5,500–1,000 years ago is one of drier climate.

7.2 Block Island: West Beach

7.2.1 Introduction and Goals

7.2.1.1 Geologic Background

Block Island is a 5.8-km wide by 9.3-km long island situated 14.9 km south of mainland Rhode Island 

and 22.8 km northeast of Montauk Point, New York. It is surrounded to the northwest by Block Island 

Sound, to the northeast by Rhode Island Sound, and to the south by the Atlantic Ocean (Figure 7-29).
110

Figure 7-29. Block Island (West Beach) geoarchaeological study area locations.

Note locations of URI-identified subtidal archaeological sites (RI 2719 and RI 2720) and Mashantucket Pequot 

Museum and Research Center-identified terrestrial archaeological sites (RI 2622 and RI 2623).

Much of the island’s geology was shaped and deposited by the Wisconsinan glaciation as a recessional 

moraine just north of the terminal end moraine that formed immediately south of Block Island about 

21,000 years ago. Block Island is part of a west-east trending series of moraines and glacially created 

islands in southern New England that extend from Long Island, New York, to the west and to Nantucket, 

Massachusetts, to the east (Figure 7-30) (McBride et al. 2016). 
111

Figure 7-30. Map showing the location of Block Island (circled in red) relative to regional moraine 

locations across southern New England.

Source: after Skehan 2001, as modified from Mather 1952, Koteff 1974, and Larson 1982

Block Island is composed of stratified morainal material (i.e., rock debris ranging in size from boulders to 

gravel to sand) deposited at the interlobate contact of the Hudson-Champlain and Narragansett BayBuzzards Bay glacial ice lobes (McBride et al. 2016; Boothroyd and Sirkin 2002). The island’s north and 

south ends are morainal deposits. They are divided by the Block Island’s “Great Salt Pond” but joined by 

two barrier spits on the east and west sides of the pond. The northern of these two upland areas, where the 

West Beach study area is located, is called “Corn Neck.” Corn Neck is a recessional moraine that 

occupies an area of about 2.5 km2. Its elevation rises gradually from the south to northeast reaching a 

maximum of 42.7 m above sea level. Its topography has been described as “hummocky” and is dotted 

with kettle ponds and coastal ponds. 

Sediments on Corn Neck consist of a sheet of upper glacial drift overlying an older, lower drift sheet 

deposited by an earlier glaciation, as well as masses of Cretaceous sediment. The younger drift covers 

most of the island and is characterized by glacial deposits and landforms associated with the Late 

Pleistocene melting and receding of the Laurentide Ice Sheet. The uppermost element of this glacial 

sequence consists, in part, of a type of till known as “melt-out” till, which was deposited during the final 

wasting of the area’s glacial ice. After the ice receded, the climate remained cold, and strong winds blew 

across the barren, recently exposed land surface adjacent to the ice. Wind-blown silt or “loess” was swept 

off of the exposed glacial deposits and redeposited as an “eolian mantle” of sediment on top of the melt-
112

out till. This eolian mantle overlies most of the glacial deposits in southern Rhode Island, including the 

upland till mantle and lowland morphosequences (Boothroyd and Sirken 2002). A layer of loess 1-m 

thick can be found in places on Block Island, including in the West Beach study area. As the climate 

warmed and glacial ice receded further northward, the barren sediments on the surface of the deglaciated 

landscape weathered and became vegetated. Organic components accumulated on the surface of the loess 

and gave rise to a silty-sandy variety of organic soil known as “loam.” In places along the coast, as sea 

level rose and beaches migrated inland, sand dunes formed on top of this old soil (“paleosol”) surface.

Organic soils rich in partially decomposed organic plant debris were formed in lowlands, wetlands 

(swamps and marshes), and ponds that were significantly different in composition than paleosols in the 

upland areas. Pollen, spores, seeds, needles, leaves, and other tough plant structures are preserved in these

layers of highly organic “peat.” Many glacial lakes have been filled-in with lake bottom sediment and 

then covered with peat. These layers of sediment provide a record of post-glacial vegetation and climate 

in their assemblages of tree, shrub, and herb pollen (Sirkin 1996). Elements of all of these various strata 

are present within the West Beach study area (Figure 7-31). 

Figure 7-31. Representative stratigraphic sediment profile of the upland sections in the Block 

Island (West Beach) study area (Sirkin 1996).
113

7.2.1.2 Justification and Goals

The West Beach study area was selected for marine geoarchaeological reconnaissance field investigations

as part of the project because of its unique combination of environmental, geological, and archaeological 

variables. West Beach is located on the western shore of the northern or Corn Neck moraine end of Block 

Island on a low- to high-energy beach that is a much more dynamic environment than exists in the Cedar 

Tree Beach/Greenwich Bay study area. West Beach faces the coastal waters of Block Island Sound where 

there is 25 km of fetch from winds out of the northwest. Westerly winds are dominant on Block Island 9.7 

months out of the year between September and July. Southerly winds dominate during the remaining 2.3 

months of the year from July to September. 

The West Beach study area’s onshore component includes preserved elements of a low-relief, coastal 

upland paleocultural landscape that are preserved at two previously identified locations, Rhode Island 

Historical Preservation & Heritage Commission- (RIHPHC-) registered archaeological sites, RI 2622 and 

RI 2623. These archaeological sites are interpreted to be the cultural material residue left behind by 

activities that took place at ancient Native seasonal (likely Springtime) fishing camps dating from the 

Early to Middle Woodland archaeological periods (ca. 3,000–1,000 yBP) (McBride et al. 2016). Portions 

of upland paleocultural landscape elements preserved at West Beach and the intact stratigraphy above and 

below them were exposed in plan and profile after the dune deposits overlying them were stripped and 

eroded by wind and waves associated with Hurricane Sandy in 2012. The preserved upland paleocultural 

landscape elements are backed and interspersed by lowlands containing fresh water wetlands and small, 

shallow, freshwater ponds. Seaward elements of West Beach’s upland paleolandscape areas are eroded 

and completely absent from the beach, the intertidal, and the subtidal portions of the study area. In 

contrast, large highly organic peat and paleosol deposits, some containing tree stumps and root mat still in 

growth positions (also presumably exposed by Hurricane Sandy), are preserved onshore in the intertidal 

and in the subtidal—the places corresponding to what had been lowlands, wetlands, and coastal ponds 

that were/are interspersed between the onshore uplands. The presence of nearby onshore archaeological 

deposits, the apparent preferential preservation of the lower elevation paleocultural landscape elements 

(i.e., remnants of lowlands—wooded wetlands, marsh, and pond basins), and the unknown extent of their 

preservation offshore together made the location attractive for conducting marine geoarchaeological 

investigations. The overall goals of these investigations were to learn more about the nature of the

preservation of these paleocultural landscape elements and the archaeological deposits they contained out 

in West Beach’s subtidal zone. 

The goals of the 2015–2016 reconnaissance investigations were met by accomplishing the following 

fieldwork objectives:

• Examine and preliminarily map visually (with the recorded observations of archaeological divers 

and underwater video documentation), as well as through marine geophysical remote sensing 

survey, West Beach’s exposed intertidal and subtidal paleolandscape elements and obtain small 

samples of organic materials within them for radiocarbon dating.

• Obtain sediment cores from Wash Pond and West Beach’s subtidal paleolandscape elements for 

paleoenvironmental analysis and radiocarbon dating to assess how much, if any, of these

archaeologically sensitive upland coastal geological features and their cultural deposits were 

preserved in the water.

• Visually examine and video-document transects extending out into the subtidal zone coastal from 

West Beach’s previously identified onshore back-beach dune locations of archaeological sites RI 

2622 and RI 2623 to assess the preservation of the different paleolandscape strata and the 

possible extent of the archaeological sites offshore.
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7.2.2 Field Methodology

Marine geoarchaeological field investigations conducted for the project in the West Beach study area 

included the following methods:

2015:

• May 29, June 14: onshore walk-over survey of the beach, GPS mapping, and intertidal organics 

small sample collection of intertidal tree stumps and exposed peat deposits

• June 21–27: geoarchaeological visual examination/video documentation, GPS mapping of 

subtidal transects, subtidal organics small samples collection, and collection of subtidal artifacts 

discovered in situ (two pieces of small stone chipping debris) by archaeological divers from 

BOEM and URI

• June 25: depth survey and sediment coring in Wash Pond (shallow fresh water pond backing 

West Beach)

2016:

• May 2–14: onshore, intertidal, and subtidal geoarchaeological visual examination/video 

documentation; GPS mapping; and subtidal organics small sample collection by archaeological 

divers from BOEM and URI

• May 3–9: vessel-based geophysical remote sensing survey of the subtidal zone with Edgetech 

6205 side-scan sonar system, Benthos CHIRP III sub-bottom profiling system, and Applanix POS 

MV positioning system

• June 16: geoarchaeological visual examination/video documentation of subtidal area and 

collection subtidal artifact discovered in situ (one large piece of stone chipping debris) by 

archaeological divers from NITHPO and URI

Detailed descriptions of the field methodologies employed at West Beach are included in the Project Field 

Report (Caccioppoli et al. 2018). 

7.2.3 Results

Initial walkover surveys of the West Beach study area documented five areas of intertidal peat deposits 

(designated “Peat Areas 1 through 5”). Several of the peat deposits appeared to extend out into the water a 

significant distance (ca. 50 m) beyond the low-tide level, based on the dark appearance of the seafloor in 

areas of exposed peat, which contrasted with the otherwise lighter-colored sandy areas of the seafloor. 

The northernmost of these exposed intertidal peat areas contained three tree stumps distributed roughly 

perpendicular to the axis of the beach, as well as multiple small sapling stumps, all of which were in 

growth positions (Figure 7-32). The tree and sapling stumps were also surrounded by tree root mat, which 

presumably helped hold together the sediment matrix in which they had grown. The exposed peat was 

observed to contain rocks and woody fragments (roots and branches of varying diameter and size)

embedded in it. The observed stratigraphy in the areas of the intertidal with exposed peat consisted of 

1) an overlying upper layer of coarse sand, gravel, cobbles, and boulders; 2) a middle layer of peat; and 

3) a lower layer of brown (oxidizing to gray) loess with organic inclusions.
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Figure 7-32. Northernmost intertidal peat deposit with tree stumps in original growth positions 

within the Block Island (West Beach) Study Area. 

The AMS dates for the peat were ca. 900 yBP. Dates for the stumps closest to shore and furthest offshore were CAL 

BP 430–375 and CAL BP 730–670, respectively. (Photograph by David S. Robinson [URI-GSO]).

Examination of the preserved paleocultural upland stratigraphy at the locations of archaeological sites RI 

2622 and RI 2623 revealed a stratigraphic sequence consistent with that described by Sirkin (1996:141, 

Figure 25) for a “twenty-foot bluff, West Beach.” The observed stratigraphy consisted of a variablethickness veneer of overlying recent dune sands, underlain by a thin paleosol layer of dark brown to black 

organic sandy loam. The sandy loam paleosol layer overlays a thick stratum of a lighter-colored, brown 

loess. The thick visible basement stratum consisted of a hard, concrete-like, glacial melt-out till. The 

stratigraphic profile observed where archaeological site RI 2623 is located included the paleolandscape’s 

upland feature containing the RI 2623 cultural deposit. This upland feature extended northward, sloping 

downward into a topographic depression or lowland area (Figure 7-33).

Figure 7-33. Representative profile of the eroded and exposed profile of the coastal wetland and 

upland topography onshore in the Block Island (West Beach) Study Area. 

Note the wetland basin filled-in by displaced beach sand and cobbles (left side of the image) and the dune-topped 

low-relief upland low-relief bluff (right side of the image) with its distinct, but thin, dark organic paleosol stratum 

overlying a thick loess stratum, which overlies a thick melt-out till stratum at its base. This particular upland location 

corresponds with the location of a Middle Woodland Period archaeological site (RI 2623) identified by archaeologists 

from the Mashantucket Pequot Museum & Research Center in 2015 (McBride et al. 2016). (Photograph by David S. 

Robinson [URI-GSO]).
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Within this lowland were highly organic sediments associated with a wetland or pond margin that 

transitioned into highly organic lagoonal mud indicative of a shallow pond basin. This variable 

paleolandscape profile provided an excellent proxy for interpreting the multiple exposed paleolandscape 

strata visible in a more planar orientation in the intertidal and subtidal zones that were then investigated 

by the project’s diving archaeologists.

Fieldwork performed by BOEM, NITHPO, and URI archaeological divers in the intertidal and subtidal 

zone of the West Beach study area focused mainly on the visual exploration, mapping, and 

characterization of the subtidal area’s surface. Portions of the subtidal zone that were examined included 

the areas seaward of the five exposed intertidal deposits of peat, as well as subtidal areas seaward of the 

RI 2622 and RI 2623 onshore archaeological sites. A 100-m long x 50-m wide subtidal survey area,

oriented along the axis of the beach and extending southward from the location of the northernmost 

exposed intertidal peat deposit, was mapped by the archaeological divers. Systematic visual survey of this 

subtidal area was accomplished by installing a 100-m long baseline tape onshore, parallel to the axis of 

the beach, from which a series of 10-m spaced, 50-m long, tape-measure survey transects were extended 

perpendicular to the baseline out into the water. Each of these transects was surveyed visually and videodocumented by the archaeological divers who also recorded their observations on underwater slates. The 

GPS positions of the ends of the baseline and survey transects, as well as features of interest (marked with 

a buoy), were recorded at the surface using a handheld Garmin GPS, which reported positional accuracies 

of +/- 2.5 m. 

In addition to the systematic visual survey of the seafloor, the archaeological divers also performed nonpatterned visual survey and exploration of the subtidal zone. During this phase of the subtidal area’s 

examination, two pieces of quartz chipping debris were found in situ, embedded in the subtidal portion of 

the northernmost peat deposit (i.e., the deposit containing the intertidal tree stumps) (Figure 7-34). The 

find was video-documented underwater in real time when it was discovered and its GPS location 

recorded. The identified artifacts were then recovered by URI, photo-documented, inventoried, and are

presently in storage at the URI-GSO CML until a permanent repository is designated by the RIHPHC.

The site where the artifacts were found, “West Beach UW-1,” was reported to the RIHPHC and added to 

their archaeological site inventory as RI 2719, the state’s first registered subtidal ancient Native 

archaeological site; cultural material found in a subtidal context off of Cedar Tree Beach is considered to 

be an extension of the previously identified intertidal “Cedar Tree Point” site (RI 2311).

Additional non-patterned visual survey conducted seaward of the southernmost of the five exposed 

intertidal peat deposits encountered a broad expanse of multiple exposed and stepped submerged 

paleolandscape strata extending from the seaward margin of the exposed area of intertidal peat out about 

100 m offshore into water approximately 5 m in depth. Video documentation and radiocarbon dating of 

this seaward progression of the stepped sub-tidal strata recorded a stratigraphically and 

paleoenvironmentally differentiated sequence of lowland (wetland margin/pond basin) sediments that was 

similar to that which was observed onshore in the exposed profile of upland, wetland, and pond basin

stratigraphy at RI 2623. Progressing from the sea towards shore, in the subtidal was observed glacial 

melt-out till, an overlying eolian mantle of loess thickening towards shore, topped by organic paleosols 

associated with both a wooded wetland margin and a pond basin (Figure 7-35). Overlying the wooden 

wetland margin paleosols were three distinctly separate peat layers. Micro- and macro-fossil elements of 

these distinct peat layers record their transition from two freshwater marsh environments to a salt marsh

environment. Radiocarbon-dated samples from multiple elements of this preserved subtidal remnant of 

West Beach’s paleocultural landscape provided evidence of the sequencing and timing of the area’s

transition from a wooded low area, to a marsh, to a beach, and then to an inundated marine environment.

These dates, organized from shallowest water depth/closest to shore, to the deepest depth/furthest from 

shore were reported by BETA Analytic as: 735–870 cal yBP; 1,295–1,225 cal yBP; 3,330–3,290 cal yBP; 

and 6,635–6,580 cal yBP.
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Figure 7-34. Quartz chipping debris constituting the West Beach UW-1 Site (RI 2719) discovered 

embedded in subtidal, exposed, and stratified organic paleosols in the Block Island (West Beach) 

study area.

Photographs by Melanie Damour (BOEM) (upper image) and David S. Robinson (URI-GSO) (lower image).
118

Figure 7-35. Exposed and preserved submerged stratigraphy within the Block Island (West Beach) 

Study Area in the vicinity of the West Beach UW 2 Site (RI 2720). 

Photographs by David S. Robinson (URI-GSO)

WB Loess Stratum
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Embedded in the surface of the organic paleosols corresponding to a preserved subtidal remnant lowland 

area of the paleolandscape were four tree stumps in growth positions surrounded by extensive tree root 

mat (Figure 7-36). Next to one of the four stumps was about a 2-m long toppled trunk section lying 

embedded in the paleosols. Also observed and documented in the surface of the organic lowland paleosol 

was a possible hearth feature, consisting of about a 1-m diameter area of burned ground surface (Figure 7-

37). Microscopic analysis of a sample of sediments from within this possible hearth feature found 

evidence of heated sediments and charcoal. Embedded in this burned area was a large piece of wellpreserved, naturally shaped/broken, and charred wood. The burned area of the paleolandsurface and 

charred wood were surrounded by a concentrated assemblage of small cobbles that appeared to have been 

heated. Also present and associated with the possible hearth feature was a large primary flake of quartz 

chipping debris embedded in the surface of unburned organic paleosols, less than 1 m away from the 

possible hearth feature (Figure 7-37). This artifact and possible hearth feature together comprise the 

“West Beach UW-2” site, which was also reported to RIHPHC and entered into their archaeological site 

inventory as RI 2720, the second subtidal ancient Native archaeological site registered in Rhode Island 

waters. 

Details about these different paleolandforms, the conditions that allowed them to be preserved, and the 

prevailing paleoenvironmental conditions that were represented on site were all noted and considered 

during the performance of the West Beach marine geoarchaeological fieldwork. Small samples of the 

different strata represented in the paleolandforms, including the exposed, burned surface of the paleosols 

within the potential hearth feature, the tree stumps, and the paleosols from which they had grown were 

collected for micro- and macroscopic analysis and AMS radiocarbon dating.

In addition to the systematic and non-patterned archaeological diver survey of the West Beach underwater 

archaeological sites, two 50-m transects extending seaward of the onshore low-relief upland areas 

containing archaeological sites were visually examined and video-documented to assess how much, if 

any, of these archaeologically sensitive upland coastal geological features and their cultural deposits were 

preserved across the beach and subtidal zone, and out into the water. In both cases, it was evident that the 

upland geological stratigraphy and the archaeological deposits that they contained had been completely 

removed by erosion. Only a small area of the basement stratum of glacial melt-out till was observed 

exposed from beneath marine sediments a short distance out into the water off of the RI 2623 location.

Coring operations were conducted in two locations within Wash Pond at locations that were 1) near its 

deepest central area that was thought to contain the thickest sediment record; and 2) on the pond’s 

western edge, just beyond the slope of the over-wash sand deposit (Figure 7-38). These locations were 

chosen to provide the most complete paleoenvironmental and storm records possible. Both biological 

cores recovered adequately long sections and terminated in a stiff layer, precluding the need for additional 

cores of this type in the pond. Although biological core WP15-2Bio missed the sediment-water interface, 

WP15-1LC did not. A Livingston core was also taken at the western coring site, managing two drives for 

a cumulative recovered length of 130 cm. This core started from a depth of 74 cm (the upper section 

already represented by the biological core from this site) and consisted of two drives (74–176 cm and 

176–204 cm). The water depths at the two coring sites were similar at approximately 2.1 m, the maximum 

observed depth of the pond. The Wash Pond cores were found to contain highly organic lagoonal mud 

with outwash sand in the upper sediments, particularly in the core sample from the more western coring 

site. These results indicate that Wash Pond is likely to have been one of the numerous seaward-reaching 

topographic lows interspersed between topographic highs in the northern Block Island paleolandscape 

that filled with water over time and remained wet as West Beach’s inland-migrating dune zone formed a 

dam along the depression’s western edge and trapped water within it. 
120

Figure 7-36. Archaeological diver examining extensive subtidal area of preserved and exposed 

tree stumps and root mat visible embedded in the exposed surface of paleosols present in the 

vicinity of the West Beach UW-2 Site (RI 2720). 

Photographs by David S. Robinson (URI-GSO).
121

Figure 7-37. Charred wood (top image), burnt ground surface (middle image), and quartz chipping 

debris (bottom image) comprising the identified elements of the subtidal West Beach UW-2 Site 

(RI 2720).

Photographs by David S. Robinson (URI-GSO).
122

Figure 7-38. Location of sediment cores obtained at Wash Pond, Block Island, Rhode Island.

WP15 designates the core name. The abbreviations “Bio” or “Liv” lindicates the type of coring system used. “Bio” is a 

biological-type coring system with < 2m coring capacity, which is optimized for use in flocculent or loosely compacted 

sediments and is designed to retrieve the sediment-water interface intact. “Liv” is a Livingston-type coring system,

which can obtain longer cores by recovering 1–1.5 m core sections through multiple drives in the same cased hole.

Marine geophysical remote sensing survey operations in the subtidal portion of the West Beach study area 

utilizing the Edgetech 6205 side-scan sonar system, Benthos CHIRP III sub-bottom profiler system, and 

the Applanix POS MV positioning system were run at a trackline spacing of 30 m with the side-scan 

sonar system’s range set at 25 m, producing a total potential swath width of 50 m, dependent on water 

depth. The CHIRP sub-bottom profiler was run at a 63-ms repetition rate and towed 10–15 m aft of the 

survey vessel’s stern. The side-scan sonar system was successful in acquiring high-resolution acoustic 

imaging (side-scan and bathymetric data) (Figure 7-39) from the surface of the sea floor in the subtidal 

portion of the West Beach study area, with bedforms, such as scour marks and sand waves, easily 

observed in both datasets. The CHIRP’s penetration was limited due to the coarse seafloor geology (i.e., 

sand, gravel, cobbles, and boulders) visibly prevalent in the area, as well as the thin or absent veneer of 

sediments overlying the hard basement stratum of concrete-like glacial melt-out till observed in the area 

by the project’s archaeological divers. 
123

Figure 7-39. Bathymetry and side-scan sonar mosaic from West Beach study area, Block Island, Rhode Island.

Both images benefit from magnification to visualize the details of the data.
124

Coring locations within the subtidal portion of the West Beach study area were selected after reviewing 

the processed side-scan data to identify fine-grained areas. When arriving at the coring locations, it was 

determined that the seafloor geology was too coarse for both biological cores and vibracores. After 

physically probing the seafloor in numerous locations to find sites adequate for coring, coring operations 

were abandoned, and no cores were collected. 

7.2.4 Implications for Predictive Modeling

Terrestrial archaeologists conducting site identification surveys in 2015 along West Beach were able to 

observe, examine, and identify archaeological sites onshore within the upland and lowland 

paleolandscape stratigraphy in the back-beach zone that was recently exposed in plan and profile by 

Hurricane Sandy’s powerful winds and waves. The project’s diving archaeologists were able to observe in

West Beach’s intertidal and subtidal zones the preserved lowland element of this same paleolandscape 

stratigraphy, presumably exposed and visible also because of the recent erosion caused by Hurricane 

Sandy. The implications for predictive modeling resulting from the geoarchaeological investigation of the 

West Beach study area may be summarized as follows:

• Sea level rise and the concomitant process of shoreface retreat appears to have the greatest impact 

on upland geological formations, which were observed at West Beach to be completed eroded 

and absent from the explored intertidal and subtidal stratigraphy.

• In contrast, lowland elements of the paleolandscape (i.e., the margins and basins of coastal ponds, 

marshes, and swamps) were found to be preserved. Preservation of these lowland areas is 

hypothesized to be the result of multiple factors that include the following: the degree of 

protection afforded by their local pre-inundation topographic situation; the rate of sea level rise 

and the slope of the seafloor—rapid inundation through stepwise retreat of the shoreface causing 

the erosive surf zone to jump inland of the flooded topographic low; the infilling and burial of the 

submerged low by displaced upland sediments; and the armoring effect of the thick root mat of 

peaty deposits in the upper stratigraphy of lowlands. 

• Well-drained, upland paleolandforms are typically among the most archaeologically sensitive 

areas identified in onshore archaeological predictive models. Their absence from the intertidal 

and subtidal stratigraphy indicates that any model developed for a submerged oceanic context is 

going to need to be significantly different from existing models developed for onshore contexts. 

Greater consideration needs to be given to the types and range of past human activities that may 

be represented in the archaeological record found in the preserved elements of the 

paleolandscape’s lowlands and margins of water bodies when modeling archaeological sensitivity 

in a submerged context. 

7.3 The Mud Hole

7.3.1 Introduction and Goals

The Mud Hole is an anomalously deep (up to 60 m) elongated depression in the seafloor at the southern 

edge of the Rhode Island Sound, located approximately 15 km southeast of Block Island, RI (Figure 7-

40). The long axis of the trough is oriented approximately SW-NE, measuring 30 km in length and 

approximately 8 km wide along the shorter axis. The trough is shallower and broader towards the north, 

becoming deeper and branching into two distinct channels towards the south. Adjacent to the Mud Hole’s 

west and east margins are submerged segments of the Block Island-Martha’s Vineyard terminal end 

moraine, which delineate the maximum extent of Late Wisconsinan glacial ice. These end moraine 
125

segments are the result of glaciotectonic upthrust of older sediment and till (Poppe et al. 2012) and 

currently form bathymetric highs compared to the surrounding seafloor, at approximately 30- to 35-m 

depth. The Mud Hole interrupts these broad ridges as a bathymetric low.

Figure 7-40. Illustrations of the Mud Hole study area.

(A) Overview map showing the position of the Mud Hole (black inset), Late Wisconsinan terminal end moraine 

(dashed red line), recessional end moraine (dashed black line), and adjacent water bodies. (B) Fledermaus scene 

depicting the bathymetry of the Mud Hole and related bathymetric features.
126

The deglacial chronology of the Rhode Island Sound can be summarized in three distinct phases, with the 

Mud Hole potentially playing a key role in determining how the paleolandscape transformed.

1. Formation of Glacial Lakes: Glacial ice began its retreat from its maximum extent at the 

terminal end moraine. Meltwater became trapped north of the terminal end moraine, forming 

large glacial lakes in the Rhode Island, Block Island, and Long Island Sounds (Bertoni et al. 

1977; Lewis and Stone 1991). Lake levels were controlled by erosion at spillways and isostatic 

rebound. There is ample evidence that glacial lakes had formed behind the terminal end moraine 

in present-day Rhode Island, Block Island, and Long Island Sounds; evidence includes direct 

sampling (e.g., Bertoni et al. 1977) and inferences from seismic reflection data (e.g., Needell et 

al. 1983a, b, c; Lewis and DiGiacomo-Cohen 2000). The proximity of the Mud Hole to the 

southern edge of glacial lake Rhode Island and its low topography have led to the hypothesis that 

it served as a spillway for glacial lakes that once occupied present-day Rhode Island Sound 

following the retreat of glacial ice (Oakley 2012).

2. Drainage of Glacial Lakes: It is reported that glacial lakes of the inner continental shelf mostly, 

if not completely drained by approximately 15,500 yBP, leading to subaerial of exposure of the 

lakefloor (Lewis and DiGiacomo-Cohen 2000). Isostatic rebound likely accelerated lake drainage.

As erosion at the Mud Hole continued, lake levels would have continued to lower. With the Mud 

Hole serving as a topographic low, it may have remained a small post-glacial lake longer than the 

rest of the Rhode Island Sound.

3. Marine Transgression: Rising eustatic sea level during deglaciation advanced the shoreline 

from its -120 m position at the edge of the continental shelf to its modern-day position. Due to its 

depth, the Mud Hole would have been inundated earlier than the rest of the Rhode Island Sound, 

and may have also transitioned to a quiescent marine setting, diminishing the erosional effects of 

marine transgression and leading to better chances of preserving older sediments. Conversely, if 

the Mud Hole served as a chokepoint for the proto-Rhode Island Sound, tidal currents may have 

scoured and deepened the Mud Hole.

Critical to understanding the potential for preservation of terrestrial paleolandscapes and/or paleocultural 

resources is whether the Mud Hole was deepened prior to or following marine inundation. It was 

hypothesized that deepening of the Mud Hole by fluvial processes would have caused it to flood more 

quickly during marine transgression, creating an environment more conducive to preservation. If 

additional deepening occurred due to tidal scour, much of the underlying sediment may have been eroded, 

with little potential preservation of terrestrial paleolandscapes or paleocultural resources. The potential for 

the preservation of pre-inundation sediments sets the Mud Hole apart from most other areas of the inner 

continental shelf, where it is expected that up to 2 m of sediment may have been eroded due to marine 

transgression (Koteff et al. 1993). For this reason, the Mud Hole was selected as a study site to assess 

paleocultural sensitivity in an offshore setting.

The following goals were outlined to help address the Mud Hole’s paleocultural sensitivity and potential 

for preservation of paleolandscapes:

• Determine how strongly the seismic stratigraphy from the CHIRP seismic reflection data 

correlates with the existing geologic framework for the Rhode Island Sound

• Investigate if the high-resolution geophysical data support the hypothesis that the Mud Hole 

served as a spillway
127

• Better understand how significantly episodes of erosion and deposition have modified the postglacial landscape

7.3.2 Field Methodology

A suite of geophysical data including interferometric side-scan (swath bathymetry and backscatter) and 

CHIRP seismic reflection data were collected in August 2012 on the EPA operated Ocean Survey Vessel 

(OSV) Bold. The combined Teledyne Benthos C3D/CHIRP III pole-mounted sonar system allowed for 

simultaneous collection of interferometric and sub-bottom data, respectively. Data from a total of 37 

survey lines spaced 500 m, trending WNW–ESE, surveyed perpendicular to the deep channel-like 

portions of the Mud Hole were collected (Figure 7-41). No data from crossing lines (lines run 

perpendicular to the trend of the survey) were obtained. Side-scan swath width was approximately 500 m, 

providing nearly complete coverage of the study area. Bathymetric swath width was significantly 

narrower than side-scan swath width, depending on water depth. Data acquisition was controlled by OIC

GeoDAS software for the interferometric side-scan data. Chesapeake Technologies SonarWiz software 

was used for CHIRP seismic reflection data acquisition. Position, heading, attitude, heave and velocity 

data were obtained by an Applanix POS MV Inertially aided Real-Time Kinematic Global Positioning 

System. Nearly 260 km of sub-bottom data and ~130 km2 of interferometric side-scan data were 

collected. CHIRP seismic reflection data achieved a maximum of 90 m penetration. The system produced 

a CHIRP waveform with a 2–7 kHz frequency band transmitted at a 1/8 second repetition rate. Raw data 

were recorded in SEG-Y format. Interferometric side-scan raw data were recorded in .OIC file format 

(Ocean Imaging Consultants proprietary file format).

Vibracoring operations took place in August 2015 during the RIEP EN-565 cruise aboard the R/V 

Endeavor. The cruise began with geophysical surveying in Block Island Sound on an unrelated effort. On 

August 25, and the R/V Endeavor transited to the Mud Hole study area and coring operations began. Prior 

to deployment, the Rossfelder P-3 Vibro-Percussive coring system was prepared and assembled. Plastic 

core liners were inserted into the 6-m core barrels. The core barrel, cutter, and catcher were assembled 

and attached to the vibracore head. To ensure that the entire vibracoring assembly remained upright in 

deep water during deployment and recovery, a purpose-built assembly with a series of weights and floats 

was utilized. The entire coring assembly was then deployed aft of the stern, using a cable winch run 

through the stern A-frame. Two deck-mounted air-tugger winches were used in tandem to prevent the 

coring assembly from swinging with vessel motion. As the vibracoring system was being deployed, 

diligent field notes were kept noting latitude/longitude, water depth, time, and measurements of cable 

tension. Just before the vibracoring system reached the bottom, the system was powered on. The cable out 

and cable tension were monitored to determine when a full core/refusal was achieved. Before recovery, 

the vibracore system was powered off. Once on deck, the core barrel assembly was removed from the 

vibracore head, and the core liner extruded from the core barrel. The recovered sediment length was 

measured, and the core was packaged and placed in cold storage. These vibracoring methods were 

repeated at each subsequent station. Coring operations were continued during daylight hours and lasted 

until Thursday, August 27, with 16 cores attempted and 15 successfully recovered (Figure 7-42). At the 

end of coring operations, each vibracore was cut into 1.5 m segments and was labeled and packaged for 

transport back to URI-GSO.
128

Figure 7-41. Coverage map of high-resolution geophysical data collected by the URI Graduate 

School of Oceanography in August 2012.

The data includes interferometric sonar and CHIRP seismic reflection profiles. Shown in this figure is a mosaic of 

side-scan imagery overlaying the RI Ocean SAMP RI Coastal Bathymetry raster dataset produced by the University 

of Rhode Island’s Environmental Data Center. Numbers correspond to the survey lines, referred to within this text.
129

Figure 7-42. Map showing the locations of vibracores collected by the R/V Endeavor (cruise EN565) from the Mud Hole study area.

7.3.3 Results

7.3.3.1 Data Processing

Sub-bottom profiles were processed in 2015 using Chesapeake Technology Inc. SonarWiz 5 processing 

software. Navigation data were inspected and fixes were calculated for each of the 37 sub-bottom profiles 

where applicable. Each profile was bottom tracked and processed to adjust for signal attenuation and 

improve signal to noise using signal gains. Attempts were made to process out a persistent diagonal 

striping data artifact across all seismic images with no success. A 1,500 ms-1 sound velocity was used for 

all seismic images, a valid value for saturated and unconsolidated sediment. Seismic reflectors identified 

in each processed image were traced using the SonarWiz Digitize Reflectors tool. The reflectors were also 

displayed in map view such that the 2D spatial extent and continuity of the reflectors could be 

ascertained.

Side-scan data had been previously post-processed shortly following the Bold 2012 cruise using OIC 

CleanSweep. Each swath was bottom tracked, and across track signal gains were applied to compensate 

for signal attenuation. Look-up tables were used to compensate for along-track variability in color. Sidescan swaths were mosaicked at 1-m pixel resolution and exported as a GeoTIFF spatially referenced in 

the Universal Transverse Mercator (UTM) Zone 19N projected coordinate system. Two interpretative 

maps were generated in ESRI ArcMap 10 software: backscatter and surficial sedimentary environments 

by delineating changes in backscatter and bedforms respectively (Figure 7-43, Figure 7-44).
130

Figure 7-43. Characterization of backscatter intensity from side-scan imagery.
131

Figure 7-44. Mapped spatial extents of sedimentary features identified in side-scan imagery.
132

Several types of bedforms and sediment features were identified in the side-scan mosaic. Megaripples, 

defined as sandwaves with wavelengths between 2–20 m, and crest-to-trough heights of 0.6–2 m were 

prominent in shallower portions (< 40 m depth) of the study area. Megaripples indicate a sedimentary 

environment in which the seafloor is being actively reworked due to unidirectional current flow. The 

WNW–ESE trend of the megaripple crests suggests a NNE migration direction, likely due to storminduced bottom currents. Erosional outliers and scour depressions were commonly observed in the 

souther half of the study area, at depths shallower than 40 m and in areas of mixed backscatter intensity.

These scour depressions were characterized by having higher acoustic backscatter compared to the 

surrounding seafloor and are crescent shaped. It is speculated that the coarse, rough seafloor causes 

turbulent bottom current flow, enhancing erosion and inhibiting deposition. Boulders are distributed 

primarily in the southern portions of the study area, with the exception of the deepest locations. They can 

be identified in the side-scan imagery as highly reflective points, creating a speckled seafloor appearance.

Trawl marks were also identified in areas of low backscatter and are mostly confined to the deepest, finegrained portions of the study area, where sediment reworking and deposition allow for preservation of 

these anthropogenic features.

7.3.3.2 Identified Sediments and Correlation with Geologic Framework

Several seismic reflectors and seismic units were identified within the Mud Hole study area. Acoustic 

penetration was highest where surficial sedimentology was predominantly fine-grained. In coarse 

sediment, particularly in the southern portion of the study area, signal attenuation limited penetration 

approximately 5–10 m below seafloor. Identified reflectors and sedimentary units were correlated to the 

regional seismic stratigraphy developed in earlier studies (Needell et al. 1983a) and the naming 

convention remains consistent.

Ku and Reflector fu2: Ku is the lowest observed sedimentary unit within the Mud Hole study area. The 

internal character is unknown due to lack of acoustic penetration beyond reflector fu2, and thus only the 

surface of Ku can be characterized. Ku varies in depth from nearly outcropping (Figure 7-45) to greater 

than 90 m below sea level, where it can no longer be resolved. Ku is interpreted to be the highly eroded 

coastal plain remnant. The coastal plain strata are composed of semi-consolidated to unconsolidated 

marine sands, silts, and clays that were primarily deposited in the Late Cretaceous Period (Flint 1963; 

McMaster et al. 1968; Sheldon 2012). Early lower resolution but more deeply penetrating seismic 

reflection studies report parallel internal bedding distinctive of coastal plain sediments, none of which 

was observed in this study (McMaster et al. 1968). Correlation with Ku is therefore limited to 

stratigraphic position and expected depth to the truncated surface. Previous works within the Rhode 

Island Sound report a similar depth to the coastal plain surface in the vicinity of Block Island (McMaster 

and Ashraf 1973c).

The deepest reflector identified within the study area, fu2 is inferred to be an erosional unconformity, 

incising Ku. The surface is strongly reflective and strongly attenuates the seismic signal. Reflector fu2 is 

only traceable in the northern half of the study area due to lack of acoustic penetration elsewhere. It is 

characterized as a smooth, shallowly westward dipping surface in the northern study area becoming a 

deep channel. The character of fu2 becomes more obscured towards the south and eventually is no longer 

visible due to the coarse surficial geology attenuating the CHIRP seismic signal. fu2 represents the 

fluvially eroded surface of the underlying coastal plain strata during eustatic sea level lowstands of the 

Late Tertiary and Early Quaternary periods and subsequent widening and deepening by episodic 

glaciations during the Pleistocene Epoch. North of the Mud Hole, Fu2 forms the north facing cuesta. The 

possibility that reflector fu2 could represent an erosional contact between the most recent glacial deposits 

and pre-Wisconsinan glacial deposits has been considered, and without direct sampling cannot be fully 

ruled out. However, the alignment of the valley axis defined by fu2 and the direction of glacial advance 

suggests that the most recent Wisconsinan glaciation would have likely removed most if not all of the 
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earlier glacial deposits and continued to widen and scour the pre-glacial valley. In addition, preWisconsinan glacial deposits have only been found locally outcropped on the outer islands (Long Island, 

Block Island, Martha’s Vineyard, Nantucket), due to glaciotectonic upthrust of pre-glacial material 

(Poppe et al. 2012). The study area is dissimilar to this geologic configuration, and thus the interpretation 

that fu2 represents an erosional unconformity separating pre-glacial and glacial deposits is favored.

Sedimentary Unit Qdo, Qdm, and Discontinuity fu1: Sedimentary unit Qdo unconformably overlies Ku 

and shows considerable thicknesses (up to 45 m). The internal character of Qdo exhibits continuous 

parallel internal reflectors (Figure 7-45). The thickness of seismic unit Qdo is generally controlled by the 

depth of fu2, and thus the deposits are thickest where fu2 assumes a deep incised valley configuration.

Regional seismic reflection studies have considered glacial deposits as one seismic unit, Qdo; however,

these studies recognized that the glacial deposits (Qdo) are made up of unconsolidated tills, stratified 

outwash and glaciolacustrine deposits (O’Hara and Oldale 1980; Needell et al. 1983a, b, c; Needell and 

Lewis 1984). The closely spaced, rhythmically layered, continuous internal reflectors draping the 

underlying topography are diagnostic of glaciolacustrine sediments. Qdo is interpreted to be pro-glacial

delta/lakefloor deposits composed of varved silt and clay. As the ice sheet retreated, meltwater became 

impounded north of the terminal moraine deposits, flooding areas of low topography

Sedimentary unit Qdm overlies discontinuity fu2 south of seismic reflection line 18. Acoustic penetration 

is significantly reduced due to coarse surficial geology, making it difficult to determine the thickness of 

Qdm; however, the internal character is observed in several sub-bottom profiles as discontinuous 

stratification and chaotic and parabolic internal reflectors (Figure 7-46). Qdm is composed of 

unconsolidated till and glaciotectonically upthrust sediment deposited as portions of the terminal end 

moraine as the Late Wisconsinan ice sheet reached its terminal position approximately 26 kyBP. 

Reflector fu1 truncates Qdm, forming two distinct paleochannels (west and east). The depth of fu1 is 

approximately 60 m and nearly constant wherever observable in the study area. Both the western and 

eastern paleochannels are observed in the southern half of the study area and become progressively 

narrow towards the south. The reflector fu1 represents a fluvial unconformity that cuts into the underlying 

glaciolacustrine sediment as glacial lakes drained through the spillways to the south. At the Mud Hole, fu1

represents the spillway that cuts through the end moraine (Qdm).

Sedimentary Unit Qfe, Discontinuity mu, and Seismic Unit Qpt: Sedimentary unit Qfe overlies 

reflector fu1, partially filling the paleochannels. The base of Qfe is strongly reflective, with hummocky, 

chaotic, and discontinuous internal reflectors. This lowermost channel fill obscures the true channel 

depth. Acoustically transparent sediment overlies the strongly reflective fill, and is < 5 m in thickness.

Qfe is interpreted as a transgressive sequence consisting of channel-fill sand, silt and clay, freshwater peat 

and marsh, and estuarine silt and clay (O’Hara and Oldale 1980; Needell et al. 1983a, b, c; Needell and 

Lewis 1984). Qfe represents a transition from an erosive fluvial environment to an estuarine depositional 

environment as marine inundation began. It is likely that the lower portion of Qfe partially fills the 

spillway channels with channel-fill gravel, sands, and silts. Presumably diachronous estuarine deposits 

composed of finer silts and clays overlie the emplaced channel fill, as sea level began to inundate the 

study area.

Reflector mu is a prominent reflector in the northern half of the study area characterized as a continuous, 

smooth surface that truncates seismic unit Qdo. This reflector forms a channel beginning with seismic 

reflection line 8 (reaching a maximum depth of 70 m) to line 16 (up to 60-m depth); it is not observable in 

any lines to the south. Reflector mu represents the wave-cutting ravinement with marine transgression and 

tidal scour in the eastern channel where depths reach 70 m.
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Figure 7-45. Processed seismic reflection line 8, with interpreted seismic reflectors.

Trackline location is highlighted in red on the index map at right. See text for explanation of discontinuities and seismic units.

Figure 7-46. Processed seismic reflection line 18, with interpreted seismic reflectors.

Trackline location is highlighted in red on the index map at right. See text for explanation of discontinuities and seismic units.
135

Sedimentary unit Qpt is nearly acoustically transparent and homogenous though some discontinuous, flatlying internal reflectors occasionally are seen. With the exception of the channel cut by mu, where Qpt 

thickens ~12 m and most of this seismic unit is no thicker than 1–2 m. Qpt is not observed where seafloor 

depths < 40 m. Qpt is interpreted as a drape of fine-grained sand and silt deposited as the Mud Hole 

transitioned to a low energy marine setting during the Holocene. Qpt was directly sampled by vibracores 

and found to contain fine sand and silt, shells, and shell fragments (Figure 7-47).

Figure 7-47. Vibracore VC-15 location and depth plotted against seismic reflection line 18.

A lithology change from marine/estuarine sediments to glaciolacustrine sediments occurs at a sub-bottom depth of 

3.90 m.

7.3.4 Implications for Predictive Modeling

Several of the sedimentary units and reflectors observed within the Mud Hole study area can be 

considered for paleocultural sensitivity. Ku and fu2 underlie glacially deposited sediment, and therefore 

do not represent a landscape that would have existed during human habitation. Qpt is also disqualified 

from sensitivity as it represents sediment that had been deposited after marine conditions had been 

established at the Mud Hole. Qdm is potentially sensitive; however, assessment of surficial geology and 

bedforms indicate that the moraine deposits have been reworked by modern bottom currents. Preservation 

potential is thus thought to be low. These constraints leave only Qdo and Qfe as potentially sensitive 

sedimentary units with some caveats. Qdo, characterized as glaciolacustrine and moraine sediment, would 

only become sensitive following lake drainage and subaerial exposure of the lakebed. Assuming the lake 

had drained completely from the Mud Hole, ravinement and subsequent tidal currents (mu) eroded and 

reworked the terrestrial landscape. It appears that the disturbance may have been accentuated in the east 

channel of the Mud Hole, where up to 10 m of Qdo may have been eroded. The depth of the east channel 

reaches 70 m, shallowing southward to 60 m at the spillway. This positive N-S gradient is incompatible 

with stream drainage, and it is thought that tidal scour occurred before sea level overtopped the adjacent 

moraine segments. Similarly, Qfe has some potential for sensitive sediments, particularly any sediment 

identified as fluvial. Fluvial processes are erosional at stream thalwegs, or during high flow, but can form 

stratified deposits at the margins and in a floodplain.
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In addition to the spatial considerations for paleocultural sensitivity, there are also temporal 

considerations that rely on a well-constrained deglacial chronology. The Mud Hole study area is first 

considered to be habitable when glacial ice had retreated north of the study area. A conservative estimate 

of the onset of habitability is 21,000 yBP, when the ice margin was well north of the Mud Hole at the 

Charlestown-Point Judith recessional end moraine position (Oakley and Boothroyd 2012). The end of 

habitability is controlled by RSL rise and inundation of the study area. Earliest inundation, and the 

establishment of estuarine conditions at the Mud Hole is constrained between 12,800 and 10,700 yBP 

based on the southern New England RSL curve and backstripping of marine sediments (Table 7-3). Full 

inundation of the Mud Hole study area occurred when sea level reached -35 m, constrained between 

10,800 to 8,000 yBP. The date range from 21,000–8,000 yBP represents the maximum period of time in 

which habitable conditions existed at least in part of the Mud Hole study area, however, the habitability of 

one particular location would likely have been transient as the basin evolved. The following outlines the 

limitations to habitability in three distinct phases in the evolution of the Mud Hole while considering the 

large uncertainties that exist with the timing of marine inundation.

Table 7-3. Sea level rise models for the study area.

Publication Location

Calendar Age 

(yBP)

Methods 60 m

below

sea 

level

35 m

below

sea 

level

Oldale &

O’Hara

1980

SE

Massachusetts

10,966 

to

10,708

8,845 

to 

8,294

• Radiocarbon-dated peat and shells from vibracores

• Calibrated agebased on original radiocarbon data 

were calculated by Caccioppoli (2015) using the 

CALIB v.7.1 software (Stuiver et al. 2019)

• Range reflects error (2-sigma)

Oakley &

Boothroyd

2012

Block Island 12,800 10,800

Best-fit curve of previous RSL studies and delayed 

onset of isostatic rebound based on paleolake water 

levels

Roy &

Peltier

2015

Connecticut 11,500 8,400

Mantle viscosity model (VM6) and deglaciation model 

ICE-6G_C combined with Engelhart et al. (2011) RSL

curves reconstructed from salt marshes

Roy &

Peltier

2015

Long Island 10,800 8,000

Mantle viscosity model (VM6) and deglaciation model 

ICE-6G_C combined with Engelhart et al. (2011) 

RSL curves reconstructed from salt marshes

Phase 1: Formation of Post-Glacial Lake 21,000 yBP to 16,000 yBP: As the ice retreated from the 

recessional end moraine position 21,000 yBP, meltwater lakes were already forming in present-day 

Rhode Island Sound north of the end moraine segments. Lake water level control was shifted to the Mud 

Hole by 21,000 yBP with coalescence of Glacial Lakes Block Island and Rhode Island (Oakley 2012).

Fluvial erosion formed the west and east spillway channels in the southern Mud Hole, the path through 

which the lakes drained towards the Atlantic Ocean. The Mud Hole study area was part of Glacial Lake 

Rhode Island, constraining the habitable area to the topographic highs along the moraines.
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Phase 2: Accelerated Lake Drainage 16,000 yBP to 12,800 yBP: The interpreted acceleration of 

isostatic rebound of the glacially depressed land surface occurred ~16,000 yBP. The rebound tilted the 

land surface, accelerating the drainage of Glacial Lake Rhode Island. Glacial Lake Connecticut was 

drained by 15,500 yBP (Lewis and DiGiacomo-Cohen 2000), and because of the interconnectedness with 

Glacial Lake Rhode Island, a similar timing for drainage of Glacial Lake Rhode Island is inferred. Prior to 

marine inundation, much of the study area would be considered habitable if pro-glacial lake levels 

lowered significantly.

Phase 3: Transition to Estuarine Conditions 12,800 yBP to 8,000 yBP: According to local RSL rise 

curves, marine inundation reached the spillway depth of -60 m between 12,800 and 10,800 yBP and 

began to infiltrate the eroded spillways at the southern extent of the Mud Hole study area. Estuarine 

conditions that were originally confined to the thalwegs of the channels, inundated further into the protoRhode Island Sound. Tidal constriction due to the topographically higher moraines likely enhanced tidal 

scour of the eastern channel, eroding up to 10 m of glacial lakefloor sediment, to 70 m depth (10 m below 

spillway depth). Full marine conditions were established between 10,800 and 8,000 yBP, when sea level 

had risen to ~35 m below present, overtopping the glacial moraines and relaxing tidal constriction.

Habitability of the Mud Hole study area began as early as 12,800 yBP after the complete drainage of 

Glacial Lake Rhode Island and prior to the beginning of marine inundation, and declined until the study 

area was fully inundated and uninhabitable.

7.3.5 Key Points

• The Mud Hole was selected as a submerged offshore study site for establishing best practices for 

assessing paleocultural sensitivity.

• 37 CHIRP sub-bottom profiles, side-scan, and 15 vibracores were obtained from 2012–2015 over 

two research cruises. 

• The seismic stratigraphy from the CHIRP seismic reflection data correlated easily with the 

existing Rhode Island Sound geologic framework in Needell et al. (1983a, b, c). Several 

sedimentary units were identified:

o Ku: Unconsolidated coastal plain sediment of Late Cretaceous age

o Qdo: Glacial sediment from Late Wisconsinan glaciation, with potentially older glacial 

deposits, including glaciolacustrine, glaciofluvial, till and stratified outwash

o Qdm: Glacial moraine sediment composed of till and stratified glacial outwash

o Qfe: Post-glacial fluvial and estuarine sediment deposited after glacial lake drainage and 

as marine transgression began to flood the Mud Hole

o Qpt: Marine sediment deposited when sea level had risen and the Mud Hole transformed 

into a low energy depositional basin

Several seismic reflectors were also identified at the Mud Hole:

o fu2: Fluvial unconformity, incision of the coastal plain remnant during Tertiary and Early 

Quaternary Age, and additionally scoured by Pleistocene glaciation
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o fu1: Fluvial unconformity, incision of the Late Wisconsinan glacial surface during 

drainage of glacial lakes

o mu: Marine unconformity, ravinement due to Holocene marine transgression and locally 

due to tidal scour

• There is ample evidence that the Mud Hole served as a spillway for Glacial Lake Rhode Island.

Two distinct channels were identified with spillway depths 60 m below present-day sea level.

These channels cut through terminal end moraine segments, though they may have been modified 

by tidal currents during marine inundation.

• The post-glacial landscape has been modified significantly by several geological processes. First, 

drainage of Glacial Lake Rhode Island through the topographic low at the Mud Hole caused 

fluvial erosion in the spillway channels. Marine inundation appears to have further scoured the 

east channel of the Mud Hole, likely due to tidal scour when sea level had not fully overtopped 

the end moraine segments. This is evidenced by a marine backstripped depth of 70 m in the east 

channel, suggesting 10 m of localized erosion in that channel. Elsewhere, ravinement was 

probably negligible. There are thick marine deposits in the basin of the Mud Hole, exceeding 6 m 

thickness as is observed in the CHIRP sub-bottom data as well as verified by vibracores.

• Spatial and temporal constraints were placed on paleocultural sensitivity in the Mud Hole. Qdo, 

Qdm, and Qfe are considered to be potentially paleoculturally sensitive. The degree to which they 

are sensitive is dependent on how these sediments were modified by marine inundation and 

tidal/bottom currents. Qdm, composed of end moraine sediment, was likely eroded by ravinement 

and reworked by modern bottom currents. This is supported by the presence of bedforms in 

surficial geology. Qdo and Qfe where there was limited fluvial erosion (fu1) or marine erosion 

and reworking (mu) are likely the most sensitive.

• Human habitation at the Mud Hole would have theoretically been possible following the retreat of 

glacial ice. By 21 kyBP, glacial ice had retreated to the Charlestown-Point Judith-Buzzards Bay 

end moraine position, which serves as a conservative boundary for human habitation at the Mud 

Hole. Glacial lakes formed in the present-day Rhode Island Sound and Mud Hole, and were 

thought to have fully drained by 15.5 kyBP. Between 12.8 and 8 kyBP, marine inundation 

progressively transitioned the Mud Hole to a shallow estuarine marine setting. Therefore, 

between 15.5 and 12.8 kyBP, the Mud Hole is thought to have been most conducive to human 

habitation.

7.4 The AMI

7.4.1 Introduction and Goals

The AMI is located in Federal waters approximately 25 km SE of Block Island and 45 km due south of the 

Sakonnet River (Figure 7-48). The study area is nearly square: 15 km (N-S) by 15 km (W-E). Water depths 

generally increase from north to south through the study area ranging from approximately 35 to 55 m. The 

bathymetry is generally featureless and absent of any large-scale features. The Mud Hole is immediately 

adjacent to the northwest of the study area. The northern portion of the AMI encompasses a submerged 

segment of the Block Island-Martha’s Vineyard terminal end moraine consisting of deposits from the Late 

Wisconsinan icesheet at its furthest extent. It is here where the shallowest portions of the study area are 

found. Towards the south, depths increase with distance away from the end moraine segment.
139

Figure 7-48. Location of the Area of Mutual Interest (AMI) study area.

The primary goal of the AMI study area was to investigate whether bathymetry can be used as a proxy for 

underlying paleolandscapes and to assess paleocultural sensitivity. Studies that rely exclusively on 

bathymetry for paleolandscape reconstructions with the assumption that the seafloor expression closely 

resembles the subsurface geology should be met with skepticism. Investigation of the AMI study area 

using a CHIRP seismic reflection system set out to address if areas with featureless bathymetry are 

indicative of a featureless subsurface. Similarly, the goal of this study was to determine if bathymetry can 

fully mask the presence of buried paleolandscapes in submerged areas. The results of these goals will help 

us judge just how predictive bathymetry is of underlying paleolandscapes.
140

7.4.2 Field Methodology

Interferometric side-scan (swath bathymetry and backscatter) and CHIRP seismic reflection data were 

collected in August 2011 on the EPA operated OSV Bold. The combined Teledyne Benthos C3D/CHIRP 

III pole-mounted sonar system allowed for simultaneous collection of interferometric and sub-bottom 

data. Trackline spacing for the survey was 150 m, trending NW–SE. Side-scan swath width exceeded 

trackline spacing leading to a full coverage dataset. Data acquisition was controlled by OCI GeoDAS 

software for the interferometric side-scan data. Chesapeake Technologies SonarWiz software was used 

for CHIRP seismic reflection data acquisition. Position, heading, attitude, heave, and velocity data were 

obtained by an Applanix POS MV Inertially aided Real-Time Kinematic Global Positioning System.

Nearly 225 km2 of interferometric side-scan data were collected. CHIRP seismic reflection data achieved 

a maximum of 90-m penetration. The system produced a CHIRP waveform with a 2–7 kHz frequency 

band transmitted at a 1/8-s repetition rate. Raw data were recorded in SEG-Y format. Interferometric sidescan raw data were recorded in “.OIC” file format (Ocean Imaging Consultants proprietary file format).

7.4.3 Results

7.4.3.1 Data Processing

Sub-bottom profiles were processed using Chesapeake Technology Inc. SonarWiz 5 processing software.

Navigation data were inspected and fixes were calculated for each sub-bottom profile where applicable.

Each profile was bottom tracked and processed to adjust for signal attenuation and improve signal to 

noise using signal gains. Attempts were made to process out a persistent diagonal striping data artifact 

across all seismic images with no success. A 1,500-ms-1 sound velocity was used for all seismic images, a 

valid value for saturated and unconsolidated sediment. Due to the limited amount of acoustic penetration 

achieved by the CHIRP seismic reflection system, very few seismic reflectors were identified, most of 

which were not spatially continuous. For this reason, reflectors were not systematically traced and 

interpretation of the subsurface was greatly impeded. 

7.4.3.2 Characterization of the Seafloor and Subsurface

The CHIRP seismic reflection system performed poorly due to coarse surficial sediment. In most places, 

acoustic penetration was approximately 0–10 m, except in several noteworthy areas. Several channel-like 

features (Figure 7-49) were identified with some continuity in adjacent lines, none of which can be 

confidently correlated with any of the regional reflectors.

The majority of identified reflectors within the AMI study area are shallow (10–15 m below seafloor) and 

laterally discontinuous. A channel-like feature was identified and observed in three adjacent lines (Figure 

7-49). Much of the seafloor geology appears to be coarse, with many boulders observed along the 

seafloor, especially near Cox Ledge. Rhythmic laminated sediment is occasionally observed in the 

northwest AMI, near the Mud Hole and Cox Ledge, and interpreted to be glaciolacustrine deposits 

(Figure 7-50). Some profiles also show a thin veneer of acoustically transparent sediment, interpreted to 

be fine-grained marine sediment. The lack of lateral continuity of identified reflectors as well as the lack 

of acoustic penetration makes subsurface geological interpretation not possible within this study area. A 

lower frequency seismic reflection system would provide better acoustic penetration in this area, where 

coarse surficial sediments impeded the CHIRP signal.
141

Figure 7-49. Channel feature from the AMI CHIRP seismic reflection data.

Top panel shows the full extent of the seismic reflection profile. Black inset is an expanded view, shown in the middle 

panel. A discontinuous channel feature is seen within this profile.
142

Figure 7-50. Glaciolacustrine sediment from the AMI CHIRP seismic reflection data.

Top panel shows the full extent of the seismic reflection profile. Black inset is an expanded view, shown in the middle 

panel. Discontinuous, parallel reflectors are interpreted as glaciolactustrine deposits.
143

7.4.4 Implications for Predictive Modeling

Although the CHIRP seismic reflection system performed inadequately in the AMI, several lessons were 

learned that are significant when designing future surveys for predictive modeling purposes.

• Bathymetry is not a reliable predictor of subsurface geology. In many places, a drape of 

contemporary and/or reworked marine sediment buries older and potentially more 

archaeologically sensitive sediments. This can range from a thin veneer to locally much thicker 

deposits where there are buried channels. The bathymetry only reveals the modern marine 

landscape, which has no significance for predictive modeling of paleolandscapes. 

• In areas of unknown surficial geology, it is recommended that two seismic reflection systems be 

used to characterize the subsurface. In favorable conditions, a CHIRP system can produce very 

high-resolution (< 1 m vertical) records, revealing finer scale changes than other lower frequency 

systems. It is for this reason that the CHIRP is often favored and recommended by regulating 

bodies for marine archaeological survey. Where surficial geology is coarse (medium sand and 

coarser) the CHIRP signal is often attenuated very quickly, with almost no penetration below the 

seafloor. A lower frequency system like the Bubble Gun achieves far better penetration in coarser 

sediment with some compromise in vertical resolution. Running the two systems simultaneously 

is preferable when there is no frequency band overlap between the systems as this offers several 

benefits. First, the data are collocated allowing for redundancy. The ability to better contextualize 

and interpret the subsurface is also greatly benefited by two systems. Spatial changes in sediment 

distribution within a study area may lead to variable performance of the CHIRP. Having a lower 

frequency system that performs well in all environments will help interpretation consistency 

throughout the study area. Even where the CHIRP works well, it may be difficult to interpret the 

CHIRP data within the geologic framework without a more complete record (e.g., identifying all 

sediments above crystalline bedrock).

8 Conclusions

The processes and datasets necessary to identify areas of cultural sensitivity in submerged environments 

differ significantly from those utilized in terrestrial environments. In terrestrial environments, information 

from a wide range of identified archaeological sites can be used to create hypotheses about how ancestral 

Tribal people interacted with the landscape, and the remnants of those ancient landscapes can be visited 

and analyzed by researchers and contemporary Tribal representatives, in most cases with relative ease. On 

the continental shelf, very few Tribal archaeological sites have been identified. Previously terrestrial 

paleolandscapes that could have been inhabited by ancestral Tribal peoples are hidden from view by 

marine waters and are frequently buried beneath meters of recently deposited sediments. In addition, 

paleolandscapes that may have once been suitable for human habitation often have been significantly 

altered by post-glacial marine transgression and modern marine processes, and may have been eroded and 

be entirely absent from the offshore geological record, or exist only as geographically discontinuous 

fragments of formerly terrestrial strata and paleoland surfaces. Conversely, the greater preservation of 

organic elements of cultural sites in submerged contexts may make what is known of archaeological site 

types and assemblages from terrestrial contexts a poor proxy for modeling offshore site types and 

distributions. Identifying and reconstructing paleolandscapes in submerged environments is completely 

dependent on geophysical remote sensing techniques and the analysis and correlation of sediment coring 

data, except in cases where oceanographic conditions also allow for visual investigation and subsurface 

sampling by scientific divers or ROVs. For these reasons, applying traditional or advanced archaeological 

predictive modeling concepts and techniques to the continental shelf is problematic.
144

Modeling cultural sensitivity in submerged environments requires a unique approach that distinguishes 

between models designed to understand cultural systems and those designed to understand natural, nonhuman systems. Although these two types of models may be related, they should not be viewed as 

interchangeable. Models of cultural systems seek to recreate how ancient peoples interacted with and 

viewed their landscape, so that locations of material culture deposits can be predicted. Models of natural 

systems are focused only on understanding how the non-human, natural world functions and has changed 

over time. Currently, the primary question to be answered about Tribal cultural sensitivity on the 

continental shelf is not how ancient Tribal peoples interacted with their landscape, but instead whether 

any of the landscapes that they could have interacted with have been preserved and, if so, what type of 

landscapes they were, and where they are located. Answering the latter question requires the development 

of models for natural systems only. Attempting to apply a cultural sensitivity model to a landscape first 

requires the identification and characterization of that landscape. For submerged environments on the 

continental shelf, this is the current challenge.

This report discusses the state of knowledge regarding archaeological predictive modeling both in 

terrestrial and submerged environments, and discusses the difficulties with applying terrestrial cultural 

sensitivity models to the continental shelf. In response to increasing offshore energy development 

pressures and the immediate need to understand where submerged paleolandscapes might be located to 

avoid impacting them, a new approach involving the development of a regional stratigraphic model is 

presented for use as a guide for the comprehensive geological characterization of local study areas within 

the region. This regional model approach was designed to assist with identifying where submerged, 

culturally sensitive paleolandscapes are likely to be located and to inform detailed geoarchaeological 

analyses at a study area of interest, rather than to make inferences about how ancestral Tribal peoples 

interacted with those landscapes, or their cultural importance. Although the regional stratigraphic model 

presented in this report focuses on the southern New England continental shelf, the following principles 

and process used to construct it can be applied to any location:

1. Reconstruct the entire subsurface stratigraphic framework of a study area from acoustic 

basement upwards to the seafloor. In this preliminary step, avoid focusing only one one facies or 

on one type of landform.

2. Thoroughly understand the geological processes and chronology responsible for each 

stratigraphic unit in a regional context.

3. Identify the geologic facies (if any) that are a) associated with the time frame of human 

habitation in the area; and b) represent terrestrial environments that could have been inhabited 

by humans.

4. Conduct detailed paleoenvironmental reconstructions and archaeological surveys of the facies 

identified in step 3 above.

This process places each study area in a well-characterized regional context that can be refined at the 

local level. The emphasis on developing a regional context differs substantively from previous approaches 

that have been applied in southern New England within the context of compliance archaeology projects, 

whose research focus is limited by design to within the localized vertical and horizontal boundaries of a 

proposed project’s APE. In addition, the modeling process presented in this report is unique because it 

does not assess paleocultural sensitivity based on the presence or absence of isolated geologic features, 

such as a paleochannels. Instead, once a regional geological framework is developed, geologic facies are 

identified that may represent the time frame and paleoenvironments associated with occupation by 

ancestral Tribal peoples.
145

For now, until a more comprehensive understanding is developed regarding the extent to which 

paleolandscapes are preserved on the continental shelf and the circumstances that lead to their 

preservation, this approach is recommended to provide the most accurate understanding of where

submerged paleolandscapes with the potential to contain cultural sites may be located. Although a 

substantial amount of additional research is needed to improve the geoarchaeological understanding of 

submerged environments, conducting this research provides excellent opportunities to improve the 

capacity for agencies, researchers, and Tribes to determine collaboratively the presence/absence of 

submerged paleocutural landscapes in a positive, culturally sensitive, and mutually satisfactory manner.

In addition to developing a regional stratigraphic model that can assist with identifying where 

paleocultural landscapes may be located, this report presents the results of more localized geological and 

archaeological analyses at five case study areas in nearshore and offshore Rhode Island waters. The 

regional stratigraphic model was tested at each location where applicable within the southern New 

England region, specifically, at Cedar Tree Beach (Greenwich Bay area) and West Beach (Block Island),

where submerged ancient Tribal cultural material was identified in the locally preserved expressions of 

what appears to be the regional geological facies Qfe. Qfe was identified in the stratigraphic model as 

most likely to contain paleolandscapes or landscape fragments of cultural significance because it appears 

to represent terrestrial environments that existed on the OCS after the large post-glacial lakes drained 

(approximately 16,000 yBP) but before marine inundation (date depends on location). Geophysical and

geological investigations at the Mud Hole indicated the stratigraphic model was applicable south of the 

geographic area associated with the USGS legacy surveys on which it was based, and a similar conclusion 

was reached at Greenwich Bay, located north of the USGS survey area. This suggests that the model can 

be applied across a broad geographic region. It can also be used to assist with paleocultural landscape 

identification at the local level if it is ground-truthed with high-resolution seismic reflection surveys using 

both CHIRP and Bubblegun systems, sediment core analyses, and, when logistically feasible, scientific 

diver or ROV visual investigation and subsurface sampling.

Several surveying methodologies were also explored and refined at the case study areas. The acoustic 

quality of the USGS legacy seismic reflection profiles was compared to data acquired with current 

geophysical systems at a test location south of Narragansett Bay, and the current BOEM recommendation 

to use CHIRP seismic reflection systems to characterize the subsurface stratigraphy of a study area was 

investigated at Greenwich Bay, the Mud Hole, the AMI. This methodological research will assist with 

accurately collecting the geophysical and geological data needed to develop effective and accurate

paleolandscape reconstructions in the future.
146

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Appendix A: Pre-contact Cultural Chronology for Project Study Area

A.1 Pre-Clovis Period (ca. 24,500–12,500 yBP)

The timing of the initial peopling of the eastern seaboard remains a question among archaeologists and is 

a topic of debate between them and the region’s Native peoples. Archaeologists cite the accumulating 

body of genetic and radiocarbon-dated archaeological evidence that support their hypotheses. These 

hypotheses center on the idea that ancient human populations migrated into the Americas from 

northeastern Asia over land and by water along interior and coastal routes in multiple migratory pulses 

spanning a period lasting more than 10,000 years (Dillehay and Meltzer 1991; Erlandson 2002; Fiedel 

2001; Jablonski 2002; Kraft et al. 1983; McBride et al. 2016; Powell 2005; Ridge 2004). In contrast, 

Native oral traditions from the region indicate to Native peoples that they have always been here, since 

time immemorial (CML, URI-GSO 2015), and that people of southern New England and Rhode Island 

returned to the area as glaciers receded—implying they had been present before the area’s glaciation—a 

position stated unequivocally by the Narragansett Indian Tribe’s Dr. Sekatau: “We the Narragansett 

People, know that our peoples evolved on this side of the world and did not come from elsewhere” (URI 

2010).

By the start of the Pre-Clovis Period, glacial ice had reached its point of maximum advance southward 

and stretched east-to-west across today’s Long Island, Block Island, Martha’s Vineyard, and Nantucket 

islands, and the waters now between and north of them. With all of New England covered by glacial ice, 

there would have been no opportunity for cultural materials from this period to have been deposited into 

the archaeological record of the ice-covered landscape. At the start of the period, however, sea level was 

more than 100 m below its current level and the coastline was out near where the edge of the continental 

shelf is today, approximately 150 km to the south of the present southern New England coastline. 

Remains of terrestrial plant life (e.g., large chunks of peat-like deposits containing multiple kinds of 

organic materials and interspersed with wood fragments) and terrestrial and coastal animal life (e.g., 

mammoth, mastodon, and walrus) are reported to have been found serendipitously in bottom-dragging 

offshore commercial fishing gear over the last 50 years as far offshore as Georges Banks (i.e., 100 km) 

(Edwards and Emery 1966; Emery et al. 1965; Emery et al. 1967; Whitmore et al. 1967). These finds 

have provided intriguing clues about the former nature and possible preservation of elements of a now

submerged paleolandscape that once was exposed on today’s continental shelf and available for human 

occupation. Equally compelling is the NIT’s oral tradition, as recalled by Mr. Harris based on what he 

heard said by Dr. Sekatau, which was that “...more than 15,000 years ago, that the ocean waters began to 

rise overnight and inundate our villages and people had to evacuate” (TPI 2012). This oral tradition of the 

Narragansett comports with the marine geological record indicating that during the course of this period, 

global temperatures generally rose, glacial ice melted, and the ice sheet’s margin retreated northward. As 

the glacier melted, water returned to the world’s oceans, and sea level rose rapidly. With this rapid rise in 

sea level, more and more of the shelf progressively became submerged, and the positions of the 

paleoshorelines retreated rapidly inland, as well.

Archaeological research has produced data that has led most archaeologists to conclude that following the 

retreat of thick glacial ice from the region between 18,000 and 16,000 yBP, the subaerially exposed 

portions of the now submerged study area, if inhabited, were probably initially populated by bands of 

highly mobile ancient people. Again, the timing of the post-glacial population of the Eastern Seaboard by 

ancient Native peoples is a topic of debate. Contributing to this debate are the discovery of apparent 

cultural strata and artifacts predating the PaleoIndian archaeological Period Clovis culture or fluted point 
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tradition, such as those found at the “Topper Site” in South Carolina and the “Cactus Hill Site” in 

Virginia. The latter of these two sites is situated on a river terrace within the coastal plain, highlighting 

the fact that environments such as these were attractive for occupation. Similarly, an averaged date of 

15,960 radiocarbon years BP from reported cultural strata at the Meadowcroft Rock Shelter Site in 

Pennsylvania predates accepted Clovis dates in the Northeast by nearly 3,000 years (Adovasio 1993). The 

advance and subsequent retreat of thick glacial ice across southern New England ca. 15,000 to 16,000 

yBP is often assumed to have eradicated any evidence for Pre-Clovis occupation of the region, and no 

Pre-Clovis finds are known from onshore (or offshore) contexts in New England or in Rhode Island. 

A.2 PaleoIndian Period (ca. 12,500 to 10,000 yBP)

The earliest unequivocal archaeological evidence for human habitation of New England is associated with 

two PaleoIndian Period Clovis Culture sites dating from ca. 11,000 yBP: the 11,120 ± 180 radiocarbon 

years BP “Vail Site” in Maine (Gramly 1982), and the “Sands of the Blackstone Site” in Massachusetts 

with an averaged date of 10,903 radiocarbon years BP (Leveillee 2016). Traditional archaeological 

interpretations of PaleoIndian Period settlement and subsistence patterns are that ancient peoples of the 

period were generally organized into small groups of nomadic hunters that hunted large migratory 

animals, such as mastodon, caribou, bison, or elk (Dragoo 1976; Kelly and Todd 1988; Snow 1980; 

Waguespack and Surovell 2003). PaleoIndian Period subsistence data from archaeological sites in the 

New England-Maritimes (Meltzer and Smith 1986; Spiess et al. 1998) and the Great Lakes (Stothers 

1996) regions indicate people living then hunted mainly caribou. The relative absence of migratory or 

megafaunal animal remains from PaleoIndian Period archaeological contexts in southern New England 

has caused some to question the “specialized subsistence model” in the region (Dincauze 1993; Ogden 

1977). The late archaeologist, Dr. Dena Dincauze (1990), argued that PaleoIndian Period people living in 

southern New England were more generalized in their subsistence strategies, hunting and gathering 

opportunistically available animal and plant species. Jones and Forrest (2003) have concurred with 

Dincauze, arguing that the higher abundance of small PaleoIndian Period encampments relative to larger 

base camps in the region may be characteristic of a PaleoIndian Period settlement and subsistence pattern 

wherein hunters and foragers had adjusted to resource unpredictability likely tied to climatic shifts. 

Resource-rich freshwater glacial ponds and wetlands were widely distributed across the deglaciated New 

England landscape and likely supported a relatively abundant and more climatically stable diversity of 

plant and animal species suitable for human consumption and use. Following the thinking of Jones and 

Forrest, smaller groups would have been better equipped than larger groups, via adaptive flexibility, to 

utilize available resources in southern New England.

PaleoIndian Period sites and artifacts are comparatively rare in New England’s archaeological record. 

Tool assemblages from southern New England PaleoIndian sites typically include non-local (chert and 

jasper) lithic materials and extra-regionally (e.g., Massachusetts, New Hampshire, Maine) available 

rhyolites. The places where PaleoIndian Period sites and artifacts are found suggests that settlement and 

subsistence activity of that time were focused along interior post-glacial wetlands, glacial lakes, and 

riverine settings. Known PaleoIndian Period artifacts from southern Rhode Island are limited to an 

isolated fluted projectile point find from along the shores of Chapman Pond in Westerly (Turnbaugh 

1980), fluted projectile point finds and a spurred end scraper from the Great Swamp Management Area of 

South Kingstown (George et al. 1993) and a single fluted biface from the South Wind Site (RI 1006) 

located on Wickford Harbor in nearby North Kingstown (Leveillee and Van Coughyen 1990). No 

PaleoIndian sites have been identified on Block Island, but fossil evidence for the presence of elk on the 

island during the period, and Dr. Sekatau’s statement that her ancestors in the region “hunted very large 

animals, including migratory elk” (URI 2010), suggests that there may have also been an as-yet 

archaeologically identified PaleoIndian Period presence there (McBride et al. 2016:79). 
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A.3 Archaic Period (ca. 10,000 to 3,000 yBP)

The Archaic Period is interpreted from the archaeological record to have represented a time of increasing 

population and settlement complexity by ancient Native peoples within the southern New England 

woodlands. The Archaic has been subdivided into Early, Middle, and Late subperiods. 

Paleoenvironmental and archaeological evidence indicates there were increased diversification of food 

resource utilization and the establishment of Tribal territories during the Archaic Period. Archaic Period 

peoples appear to have subsisted primarily through hunting and gathering with a settlement pattern 

characterized by exploratory forays and seasonal relocations within circumscribed territories (Dincauze 

1975). 

A.3.1 Early Archaic Period (ca. 10,000 to 7,500 yBP)

The Early Archaic Period coincided with the commencement of the Holocene Epoch, ca. 10,000 years 

ago. The Early Holocene was marked by warmer and drier conditions than the preceding Pleistocene 

Epoch. The Early Archaic Period archaeological record indicates ancient people of this time had a 

generalized subsistence base hunting available animals, including deer and elk, and harvesting a wide 

range of woodland and wetland vegetation and nuts, particularly hazelnuts, which tended to grow near 

wetlands, and wetland tubers (cattail, bulrush, water lily, and arrowroot) (Dumont 1981; Forrest 1999, 

Kuehn 1998; Meltzer and Smith 1986; Nicholas 1987). Early Archaic Period sites identified in southern 

New England and in Rhode Island have typically been concentrated around large glacial lake basins, the 

perimeters of ponds, marshes, and very productive wooded wetlands, particularly at the headwaters of 

major rivers (Pfeiffer 1986; Taylor 1976; Turnbaugh 1980). The association of Early Archaic Period sites 

with wetland locations implies that wetland environments were one of the most important loci of human 

activity during the Early Archaic Period (Jones and Forrest 2003; Nicholas 1987).

Early Archaic Period bifurcate-based projectiles are made almost exclusively from non-local and extraregional lithic materials. This suggests that people living during the Early Archaic Period either were 

comparatively highly mobile or maintained active trade networks in the region (Waller and Leveillee 

2002). Recent archaeological data from Connecticut (Forrest 1999) and the Gulf of Maine region of 

northern New England (Robinson 1992) suggest that some southern New England Early Holocene 

populations utilized a distinct quartz lithic technology producing quartz “microliths” for use in composite 

tools (Forrest 1999). The ubiquitous nature of quartz in regional artifact assemblages raises the possibility 

that some Early Archaic sites and assemblages are being misidentified as later occupations. The 

settlement patterning of the microlith tool-makers appears markedly different from that of the Early 

Archaic Period’s bifurcate-based stone projectile-makers in that it includes large “residential” base camps 

with subterranean pit houses occupied for extended periods of time (ca. 8,800 to 8,200 yBP). The 

archaeological evidence of subterranean pit houses found at the “Sandy Hill Site” on the Mashantucket 

Pequot reservation in southeastern Connecticut is an example of one of these Early Archaic large 

residential base camps (Forrest 1999; Jones and Forrest 2003). Small, short-duration sites resulting from 

logistical forays undoubtedly supplemented larger residential sites in the Early Archaic settlement 

patterning. Jones and Forrest (2003) interpret the Early Archaic’s semi-residential settlement pattern in 

southeastern Connecticut as an adaptive response to more predictable and readily abundant resources. The 

identification of a semi-subterranean pit house associated with a LeCroy Bifurcate complex at the 

Weilnau Site in Ohio (Stothers 1996), and the more recent discoveries of two pit houses dated to 7,830 ± 

130 and 8,110 ± 90 radiocarbon years BP at the Whortleberry Site in Dracut, Massachusetts (Dudek 

2005), may imply a previously unknown/unrecognized degree of sedentism for the Early Archaic Period 

peoples in portions of the Northeast and Great Lakes regions. Paleobotanical remains (acorns, hazelnuts, 

blackberry/raspberry, and goosefoot) from the Whortleberry Site suggest a summer occupation that 

possibly extended into the winter. Apparent differences in identifiable artifact assemblages (quartz 
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microlith composite tools v. bifurcate-based projectile points) and settlement systems suggests the

possibility that two distinct Early Archaic Period populations occupied the southern New England 

landscape during the Early Holocene (Forrest 1999).

Archaeological evidence of Early Archaic habitations in Rhode Island is scarce, consisting of low-density 

recoveries of diagnostic bifurcate-based projectiles from the nearby Pawcatuck River Drainage in 

Washington County (Turnbaugh 1980) and from the Bear Swamp in Exeter (Waller and Leveillee 2002).

The large Congdon Collection gathered in proximity to the Great Swamp in South Kingstown contains 

Kirk corner notched and bifurcate-based projectiles, both of which are diagnostic of the Early Archaic 

Period. In addition to temporally diagnostic projectile points, an Early Archaic presence in South 

Kingstown may be indicated by an uncalibrated radiocarbon ages of 8,510 ± 90 radiocarbon yBP from the 

Bouchard Site along Glen Brook in Usquepaug (Davin 1985) and 8,510 ± 140 yBP from the village of 

Rocky Brook. The low frequency of Early Archaic finds is suggestive of brief occupations by highly 

mobile peoples (Waller and Leveillee 2002). On Block Island, the Historical Society has a number of 

Early Archaic projectile points in its collections. Unfortunately, all of these points lack specific 

provenience information. The points are distinct from those found on the Rhode Island mainland in that 

they are all made from quartz and quartzite, presumably from locally available beach cobbles. In contrast, 

the lithic materials used in Early Archaic Period points found on the mainland are made almost 

exclusively from lithic materials from outside of southern New England. By the Early Archaic, Block 

Island was separated from the mainland, although only by a short distance easily crossed in a canoe. It 

may be that there was a resident population of people living on Block Island during the Early Archaic 

who were not participating in extra-regional exchange networks (McBride et al. 2016). 

A.3.2 Middle Archaic Period (ca. 7,500 to 5,000 yBP)

The Middle Archaic Period is generally correlated with the beginning of a warmer and wetter Atlantic 

climatic phase and a broadening of ecosystems at about 7,500 yBP. The appearance of oak, hickory, 

beech, and chestnut forests provided more predictable and stable plant and animal food resources to 

humans living in the area during this period. A dramatic increase in the number of Middle Archaic Period 

sites in southern New England indicates resident populations in the region were firmly established by ca. 

7,500 yBP. Overall, Middle Archaic Period culture is conceptualized as having been based primarily on 

hunting and gathering with more permanent residential bases from which foraging activities were 

conducted within circumscribed territories that may have coincided with major river drainage systems. 

Middle Archaic sites are commonly associated with waterfalls in major river drainages, as well as with 

wetlands and coastal settings. Large base camps established along extensive wetland systems, the 

appearance of heavy chipped-stone woodworking tools (possibly used for making log boats), net sinkers, 

and the common presence of fish remains in the archaeological record of Middle Archaic sites all point to 

water-focused subsistence (Bunker 1992; Dincauze 1976; Dincauze 2000; Doucette 2005; Doucette and 

Cross 1997; Jones 1999; Maymon and Bolian 1992; McBride et al. 2016). 

Models of settlement for the Middle Archaic suggest two types of sites. The first reflects large group 

activities sited on flood plains and low terraces of major rivers and streams and in association with marsh, 

swamp, and estuarine environments to maximize access to a diverse, abundant, and predictably reliable 

resource base. The second reflects small group activities, such as hunting and gathering forays from base 

camps or staging areas that are located in a broader range of environmental settings. Smaller logistical 

camps and hunting-and-gathering sites supplemented the base camps. Subsistence activities reflected at 

these sites included the harvesting of anadromous fish, hunting and foraging, and fishing and shellfish 

collection. An increase in the complexity of seasonal rounds is conjectured based on the broad range of 

resources available throughout the period (McBride 1984). Adzes, gouges, and axes suggest heavy 

woodworking and possibly the making and use of dugout canoes and other wooden structures. 
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A preference for regionally available lithic raw materials (quartzite and rhyolite) with lesser amounts of 

locally available materials, namely argillite, is reflected in the site collections databases. The correlation 

between regional lithic material types and Middle Archaic materials led Dincauze (1976) to theorize that 

Native American band or Tribal territories were established within major river drainages, and that the 

scheduling of subsistence activities, such as the seasonal pursuit of anadromous fish species, may have 

developed in response to territoriality (Dincauze and Mulholland 1977).

The location of many of Rhode Island’s known Middle Archaic sites indicates the region’s interior 

wetland environs were especially targeted for settlement. Documented Middle Archaic sites are more 

numerous in Rhode Island relative to the earlier periods. Non-local and extra-regional lithic materials 

such as quartzite and varieties of rhyolite dominate Middle Archaic assemblages. Middle Archaic sites 

have been identified along the shores of Larkin Pond (Waller and Leveillee 2001) from the Gallo 2 Site in 

South Kingstown (Leveillee 1998) and the Great Swamp Management Area (Leveillee and Lance 2008).

Middle Archaic Period archaeological sites are very common on Block Island, and the materials from 

them are well represented in the collections of the Block Island Historical Society and of local collectors. 

Their locations indicate a marked preference for the larger wetlands on the island, including the salt 

ponds, when they were freshwater ponds. Middle Archaic artifacts were all recovered from 

“multicomponent sites” (i.e., sites with artifacts and features dating from more than one archaeological 

period), indicating some continuity in the use of the larger freshwater wetlands on the island from the 

Middle Archaic through the Woodland archaeological periods (McBride et al. 2016). However, as 

McBride et al. (2016) note, it is important to consider that the paleoenvironmental contexts of these 

Middle Archaic and Woodland components would have been quite different. The location of the coast 

would have been many hundreds of meters further away during the Middle Archaic Period than it was 

during the Woodland Period. Consequently, the Middle Archaic Period sites would have been associated 

with inland wetlands and ponds, while the nearby Woodland Period sites would have been proximal to the 

ocean and coastal wetlands and ponds. 

A.3.3 Late Archaic Period (ca. 5,000 to 3,000 yBP)

The Late Archaic archaeological period correlates with a time of adjustment to environmental change and 

apparent population increase with sites associated with the period both larger and more numerous than 

during previous periods. The climate continued its warming trend and became somewhat drier, reaching a 

period of maximum oscillation between about 5,000 and 3,000 yBP. A particularly high density of Late 

Archaic sites is associated with large wetland systems after about 4,200 yBP (McBride et al. 2016). 

Vegetation during the Late Archaic archaeological period is dominated by a fully temperate deciduous 

forest, which included more hickory and pine and less oak. This resulted in a more open forest canopy 

with a higher carrying capacity. The period also correlates with the marked decrease in the rate of sea 

level rise. Stabilization of sea level appears to be associated with increased populations of shellfish, 

anadromous fish, and other riverine, estuarine, and marsh resources, which were better able to become 

established with more stabilized sea levels. As a result, the archaeological record from the Late Archaic 

reflects a more intensive focus on the high-yield and highly predictable food resources associated with 

riverine and estuarine environments, particularly the collection of oysters and clams. A mosaic of 

archaeological sites created as result of multi-generational land use provides evidence of intensive and 

repeated reuse of the Northeast’s swamps and wetlands and repetitive longer-term occupations of lands 

near large interior wetland basins and along regional waterways (McBride et al. 2016). The focus on 

fishing and shellfish gathering is evident in the large shell middens found along the coast (Kraft 1985). 

This apparent transition to a coastal focus could be the result of the stabilization of sea levels and 

coastlines (relative to earlier periods) and a concomitant establishment of resource-rich marshes and 
170

estuarine systems with extensive shellfish beds that were attractive to Late Archaic populations.

Alternatively, it could also be the result of a data filtering bias. This data filtering bias could be attributed 

to the preferential preservation of shell as compared to other resources, such as fish bone. It could also be 

attributed to the current terrestrial bias in the archaeological data due to the virtual absence of underwater 

archaeological research and subsurface testing and excavation conducted to date within the former coastal 

areas that were exposed during earlier cultural periods, but are now submerged (Westley and Dix 2006).

Late Archaic Period archaeological sites are well represented on Rhode Island’s mainland. The density of 

Late Archaic archaeological deposits and an apparent reliance on locally available lithic materials (quartz, 

quartzite, and argillite) is suggestive of increased Native American sedentism for the period (Dincauze 

1975). Seasonal and multi-occupation Late Archaic campsites were created as a result of the harvesting of 

an expansive variety of resources. Shellfish harvesting and use, first observed during the Middle Archaic, 

appears to have intensified, perhaps because as the rate of coastal inundation decreased, estuaries, more 

extensive salt marshes, and tidal mud flats were established (Braun 1974; Lavin 1988). The overlapping 

mosaic of archaeological sites created during generations of land use attest to intensive utilization of the 

Northeast’s swamps and wetlands and occupation along regional waterways, particularly after around 

4,200 yBP. The high density of Late Archaic sites in a wide range of habitats, coupled with the large 

number of artifacts attributed to the period, is suggestive of a large regional population utilizing a broad 

spectrum of resources (Dincauze 1975; McBride 1984).

The Late Archaic archaeological period is associated with three distinctive archaeologically defined 

cultural “traditions”: the “Laurentian,” the “Small Stemmed,” and the “Susquehanna.” Each tradition is 

identified by its well-defined time periods based on radiocarbon-dated sites and associated diagnostic 

tools, distinct lithic tool morphologies/technologies and preferences for different types of raw materials, 

settlement patterns, and ceremonial practices, all of which have been documented archaeologically.

The Laurentian Tradition is the earliest cultural expression of the Late Archaic archaeological period in 

the Northeast. Materials associated with Laurentian occupations include woodworking tools (hones and 

adzes), ground slate points and knives, ulus, simple bannerstones, and broad-bladed and side-notched 

projectile points (Ritchie 1980:79). Lithic materials used in Laurentian Tradition tool manufacture include 

quartzites, volcanics, and some argillites. Laurentian Tradition sites in southeastern Connecticut and 

Rhode Island contained very high percentages of Plainfield Formation quartzite, obtained primarily from 

bedrock outcrops or cobbles found in eastern Connecticut or far western Rhode Island. Laurentian 

Tradition site distributions on the mainland in the region imply an interior settlement focus associated 

with small, mobile groups of hunter-gatherers who occupied sites for short-durations while targeting 

specific resources, and moved their site locations on a fairly regular basis within well circumscribed 

territories (McBride 1984; McBride et al. 2016). Laurentian Tradition cultural materials have been 

recovered from multiple mainland sites in Rhode Island, which include South Kingstown’s RI 781 and 

Gallo 2 sites and an Otter Creek projectile point find in the Great Swamp Management Area, and the Bear 

Swamp 2 Site in Exeter, dating from 3950 ± 70 radiocarbon yBP (Waller and Leveillee 2002). An 

apparent focus on uplands led Ritchie (1980) to suggest an essentially interior riverine adaptation for 

Laurentian groups; however, one of the most significant Laurentian Tradition sites discovered and 

investigated archaeologically in southern New England to date is the recently identified Harbor Pond Site 

(RI 2554) out on Block Island, the presence of which suggests a broader focus that included coastal areas 

(Waller 2013). Located in very close proximity to Harbor Pond, Trims Pond, and the Great Salt Pond 

(which would have been a freshwater pond at the time), the site contains one of the largest and most 

varied lithic assemblages (projectile points, a ground-stone axe, a ground-stone celt, and drills) ever 

identified in a Laurentian site in southern New England. Equally significant are the sources of the raw 

materials used to make the tools in this assemblage. Although the majority of the Block Island Harbor 

Pond Site assemblage was made from quarried Plainfield Formation quartzite identical to what is found 
171

on mainland sites, the presence of cortex on quartzite debitage from the site indicates the utilization of 

raw materials obtained from beach cobbles on the island. The Harbor Pond Site provides evidence that 

suggests there was a year-round Late Archaic resident population of Laurentian Tradition people on 

Block Island by at least 5,000 yBP (and maybe earlier) (McBride et al. 2016). 

The Small Stemmed tradition is a Late Archaic cultural tradition that appears to continue into the 

Woodland Period (Mahlstedt 1985). Regional archaeological data indicates Small Stemmed tool-makers 

relied on a quartz cobble tool technology (McBride 1984). Quartz cobbles from glacial outwash, 

riverbeds, or coastal contexts were the most common sources of raw material for Small Stemmed 

chipped-stone tools. In addition to quartz, Narragansett Basin argillite was also utilized preferentially for 

the production of Small Stemmed projectile points in Rhode Island. The database of Late Archaic Small 

Stemmed tradition sites in Rhode Island is quite extensive (e.g., RI 781, RI 247, RI 1116, RI 2008, etc.). 

The distribution of these points suggests that the Small Stemmed tool-makers occupied an environmental 

niche focused on the region’s interior wetlands (Waller and Leveillee 2002). The Small Stemmed 

tradition settlement pattern is consistent with that described by McBride (1984) for Connecticut with large 

base camps concentrated along the well-drained, resource-rich banks of streams, ponds, and interior 

wetlands, supplemented by task-oriented, short-duration sites where specific resources were sought 

(Waller and Leveillee 2002). The occurrence of Narragansett Bay argillite at Small Stemmed tradition 

Native American archaeological sites in the region indicates the importance that this lithic raw material 

played in the Late Archaic Small Stemmed settlement patterning. Small Stemmed projectile points are 

well represented from all of the collections from Block Island and are often recovered from the island’s 

multicomponent sites that also yield Laurentian Tradition and Woodland Period artifacts (McBride et al. 

2016).

A.4 Transitional/Terminal Archaic Period (ca. 3,600 to 2,500 yBP)

The Transitional Archaic Period bridges the Archaic and Woodland periods and is recognized in southern 

New England through Susquehanna tradition cultural materials and sites. An extensive trade network, 

increased burial ceremonialism, and stone tool making technologies markedly different from the 

antecedent Late Archaic traditions characterize the Transitional Archaic Period. Radiometric and 

stratigraphic information from some southern New England archaeological sites indicate the Susquehanna 

tradition was temporally contemporaneous with the Late Archaic Small Stemmed tradition sites (Filios 

1989, 1999). The Susquehanna tradition in southern New England commenced with the Atlantic Phase 

(ca. 3,600 yBP) and terminated with the Orient Phase (ca. 2,600 yBP), coincident with the beginning of 

the Early Woodland Period (ca. 3,000–1,600 yBP) (Dincauze 1972; Ritchie 1980). The peoples associated 

with these phases, although differing in some ways from one another, shared similar cultural 

commonalities (lithic technologies, cultural materials, and/or settlement and subsistence data) to place 

them within the collective Susquehanna archaeological tradition.

New technological developments associated with the Susquehanna tradition included the manufacture of 

steatite vessels and broad-bladed tool forms (Atlantic, Susquehanna Broad, Coburn, and Orient Fishtail 

projectile points/knives), which either developed out of the local populations or were introduced to the 

region by peoples migrating into New England. Steatite bowl use, technology, and trade had its 

beginnings approximately 3,600 years ago following the Atlantic Phase, peaked between 3,400 and 2,900 

yBP, and fell into disuse by the end of the Orient Phase, perhaps because of the introduction and 

widespread use of ceramic vessels (Sassaman 1999). Regionally available steatite outcrops included the 

Oaklawn steatite quarry in Cranston, the Manton Avenue Quarry in Providence, and the Ochee Springs 

steatite quarry in Johnston. Broad and thin Susquehanna tradition bifaces were ideally suited for knives 

and possibly woodworking implements and are in marked contrast to the more linear, elongated, narrow, 

and thicker piercing Small Stemmed projectiles. Susquehanna tradition chipped-stone tools were 
172

commonly manufactured from a variety of lithic materials that included regionally available rhyolites, 

quartzite, and non-local cherts. A reliance on readily available lithic materials, such as quartz, argillite, 

and some rhyolites, is apparent by the final Orient Phase of the Susquehanna tradition. The manufacture 

and use of heavy steatite vessels by Susquehanna tradition peoples implies a trend towards increased 

sedentism by resident populations. The predominance of non-local lithic materials in Susquehanna 

tradition cultural assemblages implies the existence of a broad exchange network between different 

Susquehanna Tradition peoples across the region (McBride et al. 2016).

The Transitional Archaic settlement pattern on the mainland was oriented towards coastal or riverine 

settings with a subsistence base focused on the acquisition of riverine or estuarine flora and fauna that 

included fish, nuts, and small- to medium-sized mammals (Pagoulatos 1988). There is also evidence of 

increased use of floodplain seed plants, such as Chenopodium (goosefoot) (McBride et al. 2016).

Susquehanna tradition sites are markers of the Transitional Archaic Period and are best known from 

regional cremation cemetery complexes, such as the Vincent, Watertown Arsenal, and Millbury III sites 

in Massachusetts (Dincauze 1968; Leveillee 2002), and the Bliss and Griffin sites in Connecticut (Pfeiffer 

1986). Transitional Archaic Period burials in Rhode Island are reported in the Pawtuxet River drainage 

from the Flat River Site in Coventry (Fowler 1968), from Charlestown (Fowler 1964), and at the West 

Ferry Site in Jamestown (Simmons 1970). Susquehanna artifacts have been recovered from the South 

Wind Site along Wickford Harbor (RI 667) in North Kingstown; from Deerskin Landing in Perryville;

and from the RI 1854, Peninsula, and RI 1371 sites in Charlestown (Waller and Leveillee 2016). 

Transitional Archaic sites are also prevalent around noted steatite quarries, such as the Furnace Hill Brook 

and Phenix Avenue sites near the Oaklawn steatite quarry in Cranston (Waller and Leveillee 1998). On 

Block Island, Susquehanna Tradition projectile points are common in Block Island collections; however, 

no Susquehanna tradition occupation sites have been isolated from the multicomponent sites identified on 

the island. Other than diagnostic projectile points, the only other Susquehanna tradition-associated artifact 

found on Block Island was a steatite stone bowl fragment (McBride et al. 2016). 

A.4.1 Woodland Period (ca. 3,000 to 450 yBP) 

The Woodland archaeological period was a time of very dynamic development for southern New 

England’s indigenous peoples and generally involved a transition from a more mobile foraging way of 

life towards a more sedentary existence (McBride et al. 2016; Waller and Leveillee 2016). The Woodland 

Period has traditionally been interpreted as reflecting an abandonment of the Archaic subsistence pattern 

of hunting/gathering/fishing, replacing, or supplementing it with the adoption of horticulture and ceramic 

technology (Snow 1980). However, the transition from the Archaic Period into the Woodland Period does 

not reflect a strictly linear evolution from one stage to the next. Radiometric and stratigraphic data 

indicate that a Susquehanna tradition presence overlapped in time with the Late Archaic Small Stemmed 

tradition and Early Woodland Period, and the archaeological record supports a continued diversification 

of food resources, an increased reliance on shellfish and maritime resources, refinement in pottery 

manufacturing, the maintenance of long-distance trade and exchange networks, and eventually year-round 

coastal or riverine settlement with evidence for horticulture. It is during the Early Woodland Period (ca. 

3,000 to 1,600 yBP) on the mainland that the first documented evidence appears in the archaeological 

record for the regular and seasonal harvesting of shellfish and non-anadromous fish, marking a trend 

towards the increased reliance on coastal and maritime resources that continues throughout the entirety of 

the Woodland Period. The Woodland Period settlement and subsistence patterns reconstructed for the 

population on Block Island, as well as the observed lithic technology, are very different from those for the 

people inhabiting the mainland coast, exhibiting a much stronger maritime subsistence focus than that 

which is found in mainland sites, even after the adoption of maize horticulture (McBride et al. 2016). 

Faunal assemblages from Block Island Woodland Period sites indicate an overwhelming orientation to 

marine mammals, migratory birds, and fish of coastal and marine species with the only terrestrial resource 
173

occurring in high numbers being mast products, such as hickory, hazel, and acorn nuts (McBride et al. 

2016). Block Island Woodland Period Lithic technology is also significantly different than that of the 

mainland and is described as an “expedient technology” that includes very few form tools as compared to 

what is found in mainland sites (Tveskov 1992; McBride et al. 2016). Although there is a wide variety of 

lithic raw materials abundantly available in cobble form on Block Island’s beaches, there appears to have 

been little effort expended to make or curate more formal tools (e.g., knives, scrapers, or drills) during the 

Woodland Period (McBride et al. 2016). Tools do not appear to have been made carefully for durability 

and longevity, but, instead, appear to have been considered expendable and were made quickly and easily 

by splitting and modifying readily available beach cobbles to produce a usable edge or tip for scraping, 

cutting, or piercing. Like the Archaic Period, the Woodland archaeological period is also subdivided into 

Early, Middle, and Late subperiods. 

A.4.2 Early Woodland Period (ca. 3,000 to 1,600 yBP)

Early Woodland Period settlement patterns on the mainland were characterized by medium-sized seasonal 

camps situated in a variety of ecological zones (uplands, river valleys, and coastal zones). Early 

Woodland peoples do not seem to have been as mobile as were the people of the Archaic Period, but still 

organized their movements to follow changes in the seasonal abundance of resources. Coastal habitation 

sites and shell midden deposits found along saltwater and estuarine margins from Maine to New York 

reflect the increasing dependence on shellfish and other marine resources during the Early Woodland 

Period. On the mainland, there are generally fewer identified Early Woodland Period sites as compared to 

those from earlier periods. This may be related to a problem of determining what constitutes diagnostic 

artifact assemblages for the period (Juli and McBride 1984). The positive association of some Small 

Stemmed projectile points with Early Woodland radiocarbon dates indicates that some Early Woodland 

assemblages have been misidentified as older Late Archaic materials. Early Woodland archaeological 

deposits have traditionally been identified through the presence of Meadowood, Lagoon, and Rossville 

type projectile points, as well as grit-tempered, cord-marked Vinette I ceramic styles in the absence of 

radiocarbon dates. The under-representation of Early Woodland Period occupations in the regional 

archaeological record has also led to speculation that there was a population decline for the period 

(Dincauze 1974; Lavin 1988). Fiedel (2001) hypothesized that either climatic or environmental changes, 

sociocultural change, or epidemics may have contributed to an “Early Woodland collapse.” Recent 

paleoenvironmental analyses of sediment cores recovered from Sluice Pond (Lynn, Massachusetts) 

(Hubeny et al. 2015), Silver Lake (South Kingstown) (King et al. 2015), and Gorton Pond (Warwick) (for 

this project) (John King, personal communication, 2016) seem to support a climate change-related 

hypothesis, as analyses of sediments from all three ponds indicate a significant period of warmer and drier 

climatic conditions persisted for a majority of the time between ca. 5,100 and 1,300 yBP. Nevertheless, 

the regional database of archaeological data appears to support the idea of a population decline for the 

period (Fiedel 2001). 

Settlement appears to have intensified along the estuary margins of Narragansett Bay and Rhode Island’s 

south coast during the Early Woodland Period. This intensification seems to correspond with decreased 

rates of sea level rise and coastal inundation, and the resultant stabilization of shorelines, approximately 

3,000 years ago. Radiocarbon dates ranging from 2,720 +/- 120 yBP to 2,110 +/- 120 yBP obtained from 

the Greenwich Cove shell midden site on Greenwich Bay/Narragansett Bay, indicate shell-fishing 

intensified around Narragansett Bay during the Early Woodland. Small- to medium-sized temporary or 

seasonal Early Woodland archaeological sites have been identified all around Narraganset Bay. They 

follow a settlement pattern that is typical for the mainland in other parts of southern New England, but 

very different from the pattern identified on Block Island associated with large, semi-permanent or 

permanent occupations with a stronger maritime subsistence focus than found on mainland Early 

Woodland sites. These villages were complimented by temporary and task-specific sites throughout the 
174

interior of the island associated with ponds and wetlands. Dating from as early as 2,700 yBP, the 

identified Block Island Early Woodland Period sites represent the first permanent villages in southern 

New England until after the advent of maize horticulture on the mainland ca. 1,500 years later. Very few 

Early Woodland projectile points have been identified on Block Island. Archaeological excavations there 

at the Early Woodland Period village site (RI 1428) recovered over 10,000 artifacts and pieces of 

debitage. Almost all were of quartz, indicating a strong preference for it that lasted through the Middle 

Woodland Period on the island (Tveskov 1992, 1997). 

A.4.3 Middle Woodland Period (ca. 1,600 to 1,000 yBP)

Middle Woodland Period archaeological site distribution throughout the region on the mainland reflects a 

continued focus on coastal or riverine ecosystems with a trend towards fewer, but larger, seasonal camps 

along rivers, large wetlands, and coastal zones with a corresponding increase in small, temporary and 

task-specific sites in the interior (Hecker 1995; McBride et al. 2016). The introduction, adoption, and 

subsequent intensification of horticulture in the Northeast has been interpreted by archaeologists as 

substantially altering previously established settlement and subsistence patterns of Archaic Period hunters 

and gatherers (Snow 1980). Horticulture had important impacts on the Native subsistence and settlement 

base for southern New England, as it initially supplemented and later supplanted the pre-existing focus on 

hunting and gathering of the Middle Woodland Period. The earliest evidence of domesticated agricultural 

products in the region dates to around 1,000 yBP, coincident with the end of the period, suggesting a 

“late” reliance on horticulture (Bendremer and Dewar 1994). More recent analyses of food residues from 

cooking pots suggest that maize and squash were present in the Finger Lakes region of New York as early 

as around 1,350 yBP (Hart et al. 2003). Middle Woodland Period sites in southeastern New England are 

commonly marked by a high occurrence of non-local chert, jasper, and various amounts of hornfels from 

the Blue Hills area south of Boston (Luedtke 1987; Ritchie and Gould 1985). The use of Boston Basin 

lithics and exotic cherts and jaspers is in contrast to the almost exclusive use of quartz and argillite 

materials dating to the Early Woodland Period, except on Block Island, where the preference for quartz 

and argillite persisted through the Middle Woodland Period. The relative frequency of “exotic” raw 

materials from Middle Woodland sites implies the existence of long-distance exchange networks 

extending from Labrador to Pennsylvania and beyond (Dragoo 1976; Fitting 1978; Snow 1980). Through 

established trade networks, southern New England’s Native cultures remained peripheral to, though 

influenced by, the prominent Hopewell culture situated in America’s midwestern region (Kostiw 1995). 

Middle Woodland components are known from both interior and coastal settings in Rhode Island, but are 

more common along the coast. Middle Woodland Period cultural materials were recovered from the RI 

1818 shell midden archaeological site located along the western edge of Point Judith Pond in South 

Kingstown. Small limited-focus Middle Woodland Period archaeological deposits are documented at the 

Hoskins Park Site (RI 1007), RI 670, RI 141, the ER Site, and the Habitat Site in North Kingstown, while 

a Middle Woodland site dating from 1,650 yBP was reported from the Walmsley Lane Site near Tower 

Hill on the North Kingstown and South Kingstown town line (Harrison and Leveillee 1996). Hornfels 

chipping debris collected from the YMCA Site (RI 141) located on the northeast shore of the 

Pettaquamscutt River in Saunderstown (North Kingstown) is also likely to Middle Woodland Period in 

age. Very few Middle Woodland points have been identified on Block Island. This may be a result of the 

island’s population’s making and use of bone points of various types, which were more effective than 

stone points for hunting large marine species, such as seal and sturgeon (McBride et al. 2016).

A.4.4 Late Woodland Period (1,000 to 450 yBP)

The nature and distribution of Late Woodland Period settlement and subsistence patterns contrast sharply 

with the preceding Middle Woodland patterns. Coastal and estuarine resources continued to be a focus for 
175

coastal groups, but with introduction of maize horticulture, sedentary villages appeared for the first time 

in riverine and coastal areas on the mainland (McBride et al. 2016). Late Woodland Period settlement 

types reconstructed from archaeological evidence in coastal areas included specialized resource 

procurement sites (shell middens, hunting and processing camps, lithic workshops, etc.), small domestic 

sites, and larger semi-permanent and permanent hamlet and village sites (McBride 1984). Maize 

horticulture was the most important element of most Late Woodland subsistence economies between ca. 

800 and 700 yBP (McBride et al. 2016). With intensive maize horticulture came the need, refinement, and 

advances in storage technology to ensure that ample maize would be available through the winter months 

and that a sufficient supply of seed crop would be available for the next season. Increased reliance on 

storage led to be people being more tethered to specific areas and localized regions. The result was 

decreased mobility, wherein residential mobility was abandoned in favor of logistical mobility, with a 

corresponding increase in the quantity of logistical temporary and task-specific sites within a 

community’s territory, as interior upland and coastal resources were sought be small groups on behalf of 

their associated village (McBride et al. 2016).

Increasing populations and the reduction in communal mobility influenced the development of formative 

Late Woodland territories and increasingly complex social structures. Social complexity, the formation of 

political alliances, and the establishment of Tribal territories appear to have developed during the period 

(Mulholland 1988). Many researchers believe “intensive” maize horticulture must have been inextricably 

linked with population growth and Native American sedentary settlement, reasoning that only such a 

productive subsistence economy could reliably support large communal populations. McBride and Dewar 

(1987) have countered, arguing that large settlements could have developed independently of horticulture, 

especially in ecologically rich settings such as coastal environments and estuaries, where there is a rich 

and reliable maritime or estuarine (fish and shellfish) base.

The Late Woodland Period is associated with an improvement in ceramic technology and production. 

Late Woodland artifacts represented in the regional archaeological record include triangular Madison and 

Levanna type projectile points and cord-wrapped, stick-impressed, and incised ceramics. Diagnostic 

Levanna projectile points were most often manufactured of quartz, argillite, as well as rhyolites derived 

from the Lynn Volcanic Suite and Blue Hills Area of northeastern Massachusetts and the Boston Basin, 

respectively; or coastal cobbles that were carried in glacial drift. The Midwestern trade in cultural items 

continued into the Late Woodland. However, the importance of the Late Woodland’s Midwestern trade 

had diminished relative to that of the preceding Middle Woodland.

The Late Woodland Period is well represented along the margins of South Kingstown’s and southern 

Rhode Island’s salt water estuaries. Large concentrations of Late Woodland materials have been 

recovered from settlement sites, such as the Potters Pond Site and larger resource extraction sites, such as 

RI 1818, and around Great Salt Pond on Block Island. Native American settlements that arguably qualify 

as “villages” have recently been the focus of archaeological investigation near Ninigret Pond in 

Charlestown and along the upper Point Judith tidal estuary in Narragansett (Leveillee et al. 2006). Lowdensity recoveries of Late Woodland projectiles are also reported from southern Rhode Island’s interior. 

Nevertheless, the relatively fewer Woodland sites and low-density recoveries from the interior might be 

reflective of seasonal relocations of peoples for hunting and collecting purposes as the ancestral 

Narragansett Indians began to establish their characteristic coastally based settlement pattern (Waller and 

Leveillee 2002). A cluster of Late Woodland archaeological sites that include domestic village and 

ceremonial mortuary sites discovered since 2,000 indicates the formation of an ancestral Narragansett 

homeland at the headwaters of the Point Judith Pond saltwater estuary in South Kingstown and 

Narragansett during the period (Harrison and Leveillee 1996; Leveillee et al. 2006; Waller 2000; Waller 

et al. 2018).
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