OCS Study

BOEM 2016-015

U.S. Department of the Interior

Bureau of Ocean Energy Management

Gulf of Mexico OCS Region

Cooperative Agreement

Coastal Marine Institute

Louisiana State University

Coastal Marine Institute

Examining and Testing Potential 

Prehistoric Archaeological Features on 

the Gulf of Mexico Outer Continental Shelf
OCS Study

BOEM 2016-015

Published by

U.S. Department of the Interior

Bureau of Ocean Energy Management

Gulf of Mexico OCS Region

Cooperative Agreement

Coastal Marine Institute

Louisiana State University

Coastal Marine Institute

Examining and Testing Potential

Prehistoric Archaeological Features on

the Gulf of Mexico Outer Continental Shelf

Author

Amanda M. Evans

February 2016

Prepared under BOEM Cooperative Agreement

by

Louisiana State University

Coastal Marine Institute

Baton Rouge, Louisiana 70803
iii

DISCLAIMER

This report was prepared under contract between the Bureau of Ocean Energy Management 

(BOEM) and Louisiana State University. This report has been technically reviewed by BOEM, 

and it has been approved for publication. Approval does not necessarily signify that the contents 

reflect the views and policies of BOEM, nor does mention of trade names or commercial 

products constitute endorsement or recommendation for use.

REPORT AVAILABILITY

To download a PDF file of this Gulf of Mexico OCS Region report, go to the U.S. Department of 

the Interior, Bureau of Ocean Energy Management, Environmental Studies Program Information 

System website and search on OCS Study BOEM 2016-015.

This report can be viewed at select Federal Depository Libraries. It can also be obtained from the 

National Technical Information Service; the contact information is below.

U.S. Department of Commerce

National Technical Information Service

5301 Shawnee Rd.

Springfield, Virginia 22312

Phone: (703) 605-6000, 1(800)553-6847

Fax: (703) 605-6900

Website: http://www.ntis.gov/

CITATION

Evans, A.M. 2016. Examining and Testing Potential Prehistoric Archaeological Features on the 

Gulf of Mexico Outer Continental Shelf. U.S. Department of the Interior, Bureau of 

Ocean Energy Management, Gulf of Mexico OCS Region, New Orleans, LA. OCS Study 

BOEM 2016-015. 208 p.

ABOUT THE COVER

The cover image of an inset terrace with possible shell deposits, as seen from the 2007 survey 

data acquired in GA 426 (survey line 6), was initially reported in the NTL-compliant survey. The 

image shows vertical fix marks (150 m intervals) and scale lines (10 ms intervals).
iv

ACKNOWLEDGEMENTS

Funding for this project was provided by a Coastal Marine Institute cooperative agreement (No. 

M07AC13373) between the Bureau of Ocean Energy Management (BOEM) and Louisiana State 

University’s Department of Geography and Anthropology. Patrick Hesp was the Principal 

Investigator for this cooperative agreement. An earlier draft of this report was prepared as a 

doctoral dissertation by the author and submitted to Louisiana State University (LSU). The 

dissertation has been significantly expanded, revised, and corrected, and is the basis of this final 

report. Any errors remain the sole responsibility of the author. 

The following individuals gave their time, effort, and expertise towards the overall grant project, 

and allowed their work to be referenced in this report: Brooks Ellwood, Laurie Anderson, Sophie 

Warny, Barun Sen Gupta, Graziela da Silva, Floyd DeMars, and Linda Cummings. Graduate 

research assistants Jennifer Gardner and Elizabeth Cory Sills provided field and laboratory 

assistance. Radiocarbon dates were processed under contract to Beta Analytic. Fourier 

Transform Infrared (FTIR) spectroscopy and pollen analysis were completed under contract by 

PaleoResearch.

It would not have been possible to conduct this research without the assistance of Nedda Taylor 

and Linda Strain with the LSU Department of Geography and Anthropology, for their assistance 

and expertise in grant management and administration.

The following individuals provided technical assistance, expertise, and support for this project: 

Alan Craig and Gary Sayers with Survey Equipment Services; Joe Marlbrough, Van Domangue, 

Carl Sevin, and Cindy Sevin with the R/V Acadiana and the Louisiana Universities Marine 

Consortium (LUMCON); Nancy DeWitt with the U.S. Geological Survey; Tim Dellapenna with 

Texas A&M University, Galveston; James Brooks with TDI Brooks; Vaught Bryant with Texas 

A&M University; Dave Conlin with the National Park Service Submerged Resources Center; 

Charlie Pearson and Rich Weinstein with Coastal Environments, Inc.; Melanie Stright with the 

former Minerals Management Service; Rob Floyd with Marine Surveys, LLC; Glen Doran with 

Florida State University; Michael Faught with Panamerican Consultants, Inc.; David Jarzen with 

University of Florida; Sean Kemnuir, Mike Wenger, Mike Bureau, John Windhaus, Mike 

Leavitt, Wesley Schneider and Nathan Lozano with the M/V Thunderforce and American 

Vibracore Services; Tom Oliver, Jerry Cook, Steve Garrett, Greg Schexnider, Chris Chaney, 

Ryan Newchurch, Curtis Chaney, Anthony Hidalgo, Mike Tripp, Matt Keith, Rick Clemmons, 

Donald Spicer, CD Schempf, Randy Bergeron, Teresa Bowman, and Dana Montgomery with 

Tesla Offshore; and Dave Ball, Melanie Damour, Jack Irion, and Ron Brinkman with BOEM,

and Chris Horrell, Olivia Adrian, Christy Tardiff, and Deborah Epperson with the Bureau of 

Safety and Environmental Enforcement (BSEE).

Special thanks are due to Tesla Offshore for donating supplemental survey services to this 

project for use in preparing the final report. Erin Voisin provided assistance with formatting the 

final report to adhere to BOEM guidelines. Matt Keith volunteered countless hours to the project

and commented on various drafts of the final report.
v

INTRODUCTION

Funding for this project was awarded to Principal Investigator Patrick Hesp through Coastal 

Marine Institute (CMI) cooperative agreement No. M07AC13373 between the Bureau of Ocean 

Energy Management (BOEM) and Louisiana State University (LSU). Oversight of data 

collection, fieldwork, and laboratory analyses was conducted by the author. The purpose of this 

study was to conduct geophysical survey and physical sampling at four high-probability features 

in the Gulf of Mexico (GOM), which were identified for their prehistoric archaeological 

potential. Two of these features, located in Galveston 356 and High Island 160, were required for 

inclusion in the study by BOEM. The remaining sites were selected during the course of research 

and include Outer Continental Shelf (OCS) leasing area/block numbers High Island 178 and 

Galveston 426. 

BOEM requires oil and gas operators to conduct pre-disturbance archaeological assessments of 

geophysical data, in compliance with Section 106 of the National Historic Preservation Act. For 

this study, 204 reports that had sub-bottom acoustic data were reviewed and additional sites were 

selected for inclusion. After the study sites were selected, new geophysical surveys were 

conducted to better image the sites using tighter track intervals. Coring sites were identified 

based on the interpreted geophysical data. Coring operations were conducted on board M/V 

Thunderforce. All cores were inventoried on the vessel, and alternate coring sites were selected 

when field conditions precluded the acquisition of previously planned cores. In total, 30 cores 

were acquired as part of the study, from High Island 178, High Island 160, Galveston 426, and 

Galveston 356. 

Chapter 1 discusses the Federal requirement for archaeology on the OCS, middle-range theory as 

applied to understanding submerged landscapes, and contextual archaeology. Chapter 2 details 

the modern marine environment, and the recent history of sea level changes that inundated the 

formerly subaerial landscape, which formed the geographical environment during prehistoric 

times. Sea level transgression is a source of landscape modification; however, these 

modifications must be delineated from anthropogenic—or human-induced—changes. Chapter 3 

introduces known patterns of human behavior from the Paleoindian and Early Archaic Periods, 

which are the cultural-chronological periods that coincide temporally with subaerial exposure of 

the OCS. Elements of the operational environment expected on the OCS are identified from 

contemporaneous sites located in modern terrestrial settings, and are outlined as indices for 

middle-range theory-building. Chapter 4 details previous investigations of submerged prehistoric 

landscapes in general. Specifically, Chapter 4 discusses a series of previous studies from the 

GOM region that provide information on indices useful in identifying modified landscapes on 

the OCS. Chapter 5 discusses in detail the methodology used in this study, which relies 

exclusively on the use of geophysical data in the identification of modified landscapes, rather 

than the presence of artifacts. Results of this investigation are presented in Chapter 6 (acoustic 

survey) and Chapter 7 (coring and sediment analyses). Chapter 8 includes a discussion of the 

results as they apply to middle-range theory and the identification of geographical, operational, 

and modified environments. A summary of the utility of geophysical data in a spatial application 

of middle-range theory used to identify elements of the real environment are presented in 

Chapter 9, along with their implications for submerged cultural resource management. Several 
vi

appendices are included, providing detailed information on sea level curves used in this study 

(Appendix A), individual logs for each core (Appendix B), and supplemental reports utilized in 

the discussion of real environments (pollen analysis, Appendix C). 

A previous draft of this report was prepared under guidelines for electronic theses and 

dissertations and submitted to Louisiana State University by the author. Following submission, 

the text of the dissertation was significantly revised, corrected, and expanded in preparation of 

this final report. It is suggested that readers cite this final study report when referring to the 

project. 
vii

CONTENTS

ACKNOWLEDGEMENTS..........................................................................................................IV

INTRODUCTION ......................................................................................................................... V

CONTENTS.................................................................................................................................VII

LIST OF FIGURES ......................................................................................................................IX

LIST OF TABLES..................................................................................................................... XIV

ABBREVIATIONS AND ACRONYMS....................................................................................XV

1. SUBMERGED PREHISTORIC LANDSCAPES AND CULTURAL RESOURCE 

MANAGEMENT...................................................................................................................... 1

1.1 Federal Requirements for Offshore Archaeology............................................................... 1

1.2 Submerged Landscapes and Middle-Range Theory ........................................................... 3

1.3 Contextual Archaeology and the “Real” Environment....................................................... 4

1.4 “Real” Environments on the OCS....................................................................................... 5

2. PHYSICAL LANDSCAPE: SETTING AND RECONSTRUCTION....................................... 6

2.1 Sediment Stratigraphy......................................................................................................... 7

2.2 Sea Level Change ............................................................................................................. 10

2.2.1 Sea Level Change and Archaeology ................................................................... 13

2.2.2 Late Quaternary Sea Level Change in the GOM ................................................ 14

2.3 Diachronic Reconstruction and Site Preservation Potential ............................................. 19

2.4 Summary........................................................................................................................... 22

3. ARCHAEOLOGICAL EVIDENCE AND THE PHYSICAL LANDSCAPE......................... 23

3.1 Defining the Temporal Period of Interest ......................................................................... 23

3.2 Migration Routes and Dates.............................................................................................. 23

3.3 Material Culture and Paleoindian Subsistence ................................................................. 24

3.3.1. Louisiana ............................................................................................................ 26

3.3.2. Texas .................................................................................................................. 28

3.4 Modified Environments as Evidence of Human Occupation ........................................... 29

3.5 Prehistoric Occupation Potential in the Coastal Zone ...................................................... 31

4. SUBMERGED PREHISTORIC ARCHAEOLOGY AND THE GOM................................... 33

4.1 Developing a Predictive Model for Submerged Site Location ......................................... 33

4.2 Thirty Years of Submerged Prehistoric Archaeology....................................................... 35

4.3 Submerged GOM Landscapes Methodology.................................................................... 37

4.4 Towards an Updated Predictive Model............................................................................. 40

5. METHODOLOGY ................................................................................................................... 43

5.1 Geophysical Remote Sensing ........................................................................................... 43

5.1.1 Acoustic Survey: Overview................................................................................. 43

5.1.2 Sub-bottom Profilers ........................................................................................... 45
viii

5.1.3 Sub-bottom Interpretation ................................................................................... 46

5.1.4 Survey Methodology .......................................................................................... 47

5.2 Physical Sampling............................................................................................................. 48

5.2.1 Coring Methodology .......................................................................................... 50

5.3 Sediment Analysis Methodologies ................................................................................... 55

5.3.1 Grain Size Analysis............................................................................................. 56

5.3.2 Magnetic Susceptibility....................................................................................... 56

5.4 Presentation of Results........................................................................................... 59

6. SUB-BOTTOM PROFILER DATA ........................................................................................ 61

6.1 High Island Area 160........................................................................................................ 61

6.2 High Island Area 178........................................................................................................ 68

6.3 Galveston area 356............................................................................................................ 73

6.4 Galveston Area 426........................................................................................................... 81

6.5 Discussion......................................................................................................................... 86

7. SEDIMENT CORING AND ANALYSES .............................................................................. 89

7.1 High Island area 160 ......................................................................................................... 89

7.2 High Island Area 178........................................................................................................ 96

7.2.1 Interpreted Levee Feature.................................................................................... 97

7.2.2 Interpreted Terrace ............................................................................................ 111

7.3 Galveston Area 356......................................................................................................... 119

7.4 Galveston Area 426......................................................................................................... 123

7.4.1 Interpreted Shell Deposit................................................................................... 127

7.4.2 Interpreted Inset Terrace Profile........................................................................ 138

8. “REAL” ENVIRONMENTS.................................................................................................. 143

8.1 Geographical Environments............................................................................................ 143

8.1.1 Characterizing Geographical Environments ..................................................... 143

8.1.2 Younger Deweyville Terrace ............................................................................ 150

8.2 Operational Environments.............................................................................................. 152

8.2.1 Magnetic Susceptibility..................................................................................... 152

8.2.2 Shell Resources ................................................................................................. 157

8.2.3 Pollen and Fourier Transform Infrared Analysis .............................................. 159

8.3 Modified Environments.................................................................................................. 164

8.4 Summary......................................................................................................................... 165

9. CONCLUSIONS AND RECOMMENDATIONS ................................................................. 167

9.1 Conclusions and Future Research................................................................................... 167

9.2 Recommendations for Submerged Cultural Resource Management.............................. 169

10. LITERATURE CITED......................................................................................................... 175

Appendix A Sea-Level Curves.............................................................................................. 195

Appendix B Core Logs.......................................................................................................... 209

Appendix C Pollen and FTIR Reports.................................................................................. 311
ix

LIST OF FIGURES

Figure 1.1. Gulf of Mexico region ................................................................................................. 2

Figure 2.1. Map showing study areas in relation to relict river channels ...................................... 7

Figure 2.2. Sub-bottom profiler sample of acoustic data depicting a preserved river channel...... 9

Figure 2.3. Global sea level curves demonstrate the variability within the record at different 

positions on the Earth in the recent past. .................................................................. 12

Figure 2.4. Comparison between selected published sea level curves constructed from data 

specific to the northwestern GOM. ........................................................................... 15

Figure 2.5. Composite sea level curve for the northwestern GOM. ............................................ 18

Figure 4.1. Archaeological site buried by and preserved within estuarine sediments ................. 38

Figure 4.2. Hypothetical model of prehistoric archaeological sites associated with a channel 

feature. ...................................................................................................................... 39

Figure 5.1. Sub-bottom profiler data (2–10 kHz) recorded over Sabine Bank, offshore Texas .. 46

Figure 5.2. R/V Acadiana at the LUMCON dock ....................................................................... 48

Figure 5.3. M/V Thunderforce with stern-mounted A-frame, as seen from starboard. ............... 51

Figure 5.4. Pneumatic vibracore rig on the deck of the M/V Thunderforce. ............................... 52

Figure 5.5. Pneumatic vibracore rig being lifted on the deck of the M/V Thunderforce. ........... .53

Figure 5.6. Sediment color variations are visible in High Island 178, core no. 5, sections A–

E. ............................................................................................................................... 54

Figure 5.7. Shell fragments recovered in the drill bit from core no. 1, GA 426. .......................... 54

Figure 5.8. Shells observed in GA 426 core no. 10, between sections D and E............................55

Figure 5.9. Sub-bottom profiler data sample of stratified sediments within a relict river 

channel offshore Galveston. ..................................................................................... 58

Figure 6.1.1. Annotated pinger profiler image of survey line 55 shows the levee feature 

identified in 1995. ................................................................................................ 62

Figure 6.1.2. Annotated interpretation map of HI 160 near the reported shell midden; map is 

oriented north up. ................................................................................................. 62

Figure 6.1.3. Annotated sub-bottom profiler image of survey line 504 shows a feature 

similar to the interpreted shell midden (circled in yellow) originally identified in 

1995..................................................................................................................... 63

Figure 6.1.5. Contours depict the survey area as interpreted from all available data................... 67

Figure 6.1.6. Annotated sub-bottom profiler image of survey line 505 shows the midden-like 

 feature (circled in yellow) and sag zones associated with the channels

 (highlighted in red)............................................................................................... 68

Figure 6.2.1. Contours depict the channel system as interpreted from the 2007 data set............ 69
x 

Figure 6.2.2. Annotated sub-bottom profiler image of survey line 4 shows the levee 

 feature (circled in yellow) identified in 2007 with the channel horizon (red) and 

 ravinement surface (green). .................................................................................. 70

Figure 6.2.3. Contours depict the channel system as interpreted from the 2008 data sets. ........ 71

Figure 6.2.4. Annotated sub-bottom profiler from line 506A shows the levee feature 

(circled in yellow) previously identified in 2007, as well as the channel horizon 

(red) and interpreted ravinement surface (green)................................................. 71

Figure 6.2.5. Annotated sub-bottom profiler image from line 508 of a second possible 

levee feature (circled in yellow) identified from the 2008 survey data .............. 72

Figure 6.2.6. Contours depict the channel system as interpreted from all available data 

sets (2007, 2008, 2009, and 2011). ...................................................................... 73

Figure 6.3.1. Annotated sub-bottom profiler image from line 4 of a possible levee 

feature (circled in yellow) identified from the 2005 survey data .........................74

Figure 6.3.2. Contours depict the channel system and possible midden (highlighted in 

red) as interpreted from the 2005 data ..................................................................75

Figure 6.3.3. Contours depict a detailed view of the channel system and levee 

immediately adjacent to the interpreted midden...................................................76

Figure 6.3.4. Contours depict the channel system and levee adjacent to the reported 

midden ..................................................................................................................77

Figure 6.3.5. Annotated sub-bottom profiler data illustrate differences in reflection of

the same subseafloor strata caused by survey line orientation ..............................78

Figure 6.3.6. Annotated sub-bottom profiler image from line 203 illustrates the typical 

sediment reflection of the subseafloor strata. .......................................................79

Figure 6.3.7. Contours created from all of the available data depict the channel system

and the extents of the interpreted midden. ............................................................80

Figure 6.4.2. Annotated sub-bottom profiler image of survey line 6 depicts the 

topographic feature (yellow) and inset terrace (cyan) identified from the 2007...82

Figure 6.4.3. 3-D wireframe representation of the channel system as interpreted in GA

426 from the 2008 data set. ...................................................................................83

Figure 6.4.4.

Figure 6.4.5.

Contours depict the channel system as interpreted from the 2008 data set............ 84

Annotated sub-bottom profiler image from survey line 504 illustrates the 

topographic feature (yellow) previously identified in 2007 .................................85

Figure 6.4.6. Annotated sub-bottom profiler image from survey line 502 ..................................85

Figure 6.4.7. Contours depict the channel system as interpreted from the 2008 and 2011 

supplemental data set............................................................................................86

Figure 6.5.1. Landform depth ranges from the High Island Area are plotted on the sea-level

curve in green; Galveston Area landform depth ranges are plotted in blue. .........88
xi

Figure 7.1.1. Annotated interpretation map of HI 160 near the reported shell midden 

showing the differing pipeline positions for Segments Nos. 2834 and 2832 ........90

Figure 7.1.2. Core locations are depicted on the channel system contours as interpreted 

from the data. .........................................................................................................92

Figure 7.1.3. Cores no. 3, 12, 10, and 11 (left to right) are shown against the survey line 

closest to the core sites (line 507). .........................................................................93

Figure 7.1.4. Cores no. 7 (left) and 9 (right) are shown against the survey line closest to 

the core sites (line 504)..........................................................................................95

Figure 7.1.5. Magnetometer interpretation map of HI 160 .......................................................... 96

Figure 7.2.1. Core locations are depicted on the interpreted channel system contours as 

interpreted from the three available data sets (2007, 2008, and 2009). .................98

Figure 7.2.2. Annotated sub-bottom profiler image of core no. 1 location ...................................99

Figure 7.2.3. Annotated sub-bottom profiler image of survey line 504, with core no. 2 

location .................................................................................................................99

Figure 7.2.4. Annotated sub-bottom profiler image of survey line 507, showing core no. 5

location .................................................................................................................99

Figure 7.2.5. Annotated sub-bottom profiler image of survey line 506 showing core no. 6

location ...............................................................................................................100

Figure 7.2.6. Annotated sub-bottom profiler image of survey line 505 showing core no. 7.......100

Figure 7.2.7. Core log prepared for no. 2 ....................................................................................102

Figure 7.2.8. Core log prepared for no. 7 ....................................................................................103

Figure 7.2.9. Core log prepared for No. 6 ...................................................................................104

Figure 7.2.10. Core log prepared for No. 5 ..................................................................................105

Figure 7.2.11. Core logs superimposed over the acoustic profile depict the sedimentary 

units and their representative places on the acoustic profile. .............................107

Figure 7.2.12. Comparison of grain size S-curves based on samples from HI 178 core no. 7.....108

Figure 7.2.13. Diagram depicting magnetic susceptibility data obtained from cores no. 2, 

7, 6, and 5 (as collected west-east), and interpreted sedimentary horizons. .......109

Figure 7.2.14. Annotated diagram depicting magnetic susceptibility data obtained from 

cores no. 2, 7, 6, and 5 ........................................................................................110

Figure 7.2.15. Core log prepared for no. 1 ...................................................................................112

Figure 7.2.16. Core log no. 1 superimposed over the acoustic profile depicts the 

sedimentary units and their representative places on the acoustic profile. .........113

Figure 7.2.17. Diagram depicting grain size (graphic mean) and magnetic susceptibility data

obtained from core no. 1, with sedimentary units provided for correlation. .......117
xii

Figure 7.2.18. Magnetic susceptibility curve from core no. 1 samples with conventional 

radiocarbon ages plotted at depth. ......................................................................118

Figure 7.3.1. Core locations are depicted on the interpreted channel system contours as 

interpreted from the data.....................................................................................120

Figure 7.3.2. Cores no. 2, 1, 8, 7, 3, and 9 (left to right) are shown against a composite 

image of the acoustic profile closest to the core sites.........................................121

Figure 7.3.3. Cores no. 4, 5, and 6 (left to right) are shown against the acoustic profile 

closest to the core sites .......................................................................................122

Figure 7.3.4. Lab photo of core no. 6 at 360 cmbs (142 in.). .....................................................123

Figure 7.4.1. Contours depict the channel system as interpreted from the combined data 

sets.......................................................................................................................125

Figure 7.4.2. Core locations are labeled on the channel system contours as interpreted 

from the combined data sets. ..............................................................................126

Figure 7.4.3. Annotated sub-bottom profiler image of survey line 502 showing the common

 surface location for cores no. 1, 9, and 11 (left) and core no. 10 (right) ............128

Figure 7.4.4. Annotated sub-bottom profiler image of survey line 504 showing the 

surface locations for cores no. 6 (left), 7 (middle), and 8 (right).......................128

Figure 7.4.5. Annotated sub-bottom profiler image of survey line 507 showing the 

location for core no. 4 ........................................................................................129

Figure 7.4.6. Annotated sub-bottom profiler image of survey line 506 showing the 

location for core no. 5 ........................................................................................129

Figure 7.4.7. Core logs prepared for cores no. 1, 9, and 11 ......................................................131

Figure 7.4.8. Core logs prepared for cores no. 10 and 2 ...........................................................132

Figure 7.4.9. Core logs superimposed over the acoustic profile depict the sedimentary 

units and their representative places on the acoustic profile .............................133

Figure 7.4.10. Composite photograph of core no. 10, section E, with densely packed shell.......133

Figure 7.4.11. Graphic mean grain size curve for core no. 10. ....................................................135

Figure 7.4.12. Diagram depicting magnetic susceptibility data obtained from cores no. 10 

and 9 with their interpreted sediment horizons. .................................................136

Figure 7.4.14. Core logs prepared for nos. 6, 7, and 8 .................................................................139

Figure 7.4.15. Core logs superimposed over the acoustic profile depict the sedimentary 

units and their representative places on the acoustic profile. ............................140

Figure 7.4.16. Graphic mean grain size curve for core no. 6. ......................................................141

Figure 8.1.1. Measured P-wave velocities for HI 178 cores no. 6 and 7 compared to the 

average speed of sound. .....................................................................................145

Figure 8.1.2. Measured P-wave velocities for GA 426 cores no. 1, 9, and 11 compared

to the average speed of sound. ...........................................................................146
xiii

Figure 8.1.3. Measured P-wave velocities for GA 426 cores no. 6, 7, and 8 compared to 

the average speed of sound. ...............................................................................147

Figure 8.1.4. Composite sea level curve with radiocarbon dates and estimated ages 

(based on acoustic profiles) shown. ...................................................................149

Figure 8.1.5. Possible evidence of oxidation within core no. 10, HI 160, at a depth of 4 

m (13 ft.) below seafloor. ..................................................................................151

Figure 8.2.1. Magnetic susceptibility curve from HI 178 core no. 1 with radiocarbon dates 

annotated at depth; charcoal horizon is at 1.21 m (3.97 ft.) below seafloor......154

Figure 8.2.2. Magnetic susceptibility curves from HI 178 core nos. 2, 6, and 7. .......................155

Figure 8.2.3. Magnetic susceptibility curves from GA 426 cores no. 1, 9, 10, and 11 

with radiocarbon dates annotated at depth. .......................................................156

Figure 8.2.4. Magnetic susceptibility curves from GA 426 core nos. 6, 7, and 8. .....................157
xiv

LIST OF TABLES

Table 2.1. Sea level sequence for Sabine-High Island Areas...................................................... 17

Table 2.2. Scour estimates based on oceanographic modeling.................................................... 21

Table 3.1. Chronology of archaeological sites with absolute dates greater than 12,000 yrs BP. . 24

Table 3.2. Comparison of early cultural periods in the northwestern GOM region ..................... 26

Table 4.1. Correlation of terrestrial landforms, cultural period, and effectiveness of survey 

techniques................................................................................................................. 34

Table 7.1. Core penetration and sediment recovery, HI 160 ....................................................... 91

Table 7.3. Representative grain sizes for core no. 10, HI 160..................................................... 94

Table 7.4. Radiocarbon sample results for core no. 3, HI 160 .................................................... 94

Table 7.5. Core penetration and sediment recovery, HI 178 ....................................................... 97

Table 7.6. Representative grain sizes for core no. 7, HI 178..................................................... 106

Table 7.7. Representative grain sizes for core no. 1, HI 178..................................................... 114

Table 7.8. Radiocarbon sample results for core no. 1, HI 178 .................................................. 116

Table 7.9. Core penetration and sediment recovery, GA 356.................................................... 119

Table 7.10. Representative grain sizes for core no. 2, GA 356 ................................................. 122

Table 7.11. Representative grain sizes for core no. 8, GA 356 ................................................. 122

Table 7.12. Radiocarbon sample results for core no. 6, GA 356............................................... 123

Table 7.13. Core penetration and sediment recovery, GA 426.................................................. 127

Table 7.14. Representative grain sizes for core no. 10, GA 426 ............................................... 134

Table 7.15. Radiocarbon sample results for core no. 10, GA 426............................................. 136

Table 7.16. Representative grain sizes for core no. 6, GA 426 ................................................. 141

Table 8.1. P-wave velocities of specific materials..................................................................... 147
xv

ABBREVIATIONS AND ACRONYMS

BML below mud line

BOEM Dept. of the Interior, Bureau of Ocean Energy Management

BSEE Dept. of the Interior, Bureau of Safety and Environmental Enforcement

BSF below seafloor

BSL below sea level

cal yrs BP calibrated years before present

cmbs centimeters below surface

GOM Gulf of Mexico

kHz kilohertz

kya thousand years ago

m meter

m/sec meters per second

M/V motor vessel

MMS Dept. of the Interior, Minerals Management Service

ms millisecond

NHPA National Historic Preservation Act

NOAA National Oceanic and Atmospheric Administration 

NOAA 

CSC

National Oceanic and Atmospheric Administration

Coastal Services Center

nm nautical miles

NTL Notice(s) to Lessees

OCS Outer Continental Shelf

ppT parts per thousand

μm micron

USCG U.S. Coast Guard

Vp Primary-wave (P-wave) velocity

yrs BP years before present
1

1. SUBMERGED PREHISTORIC LANDSCAPES AND CULTURAL 

RESOURCE MANAGEMENT

Underneath the waters of the Gulf of Mexico (GOM), the seafloor hides evidence of resources 

important for the economic development of the United States. Oil and gas reserves created by 

geological processes, upwardly migrating hydrocarbons that feed biological communities and 

benthic species, and fish and shellfish resources are all extracted or harvested from the waters 

offshore of Texas and Louisiana. Competing economic interests for GOM resources are 

regulated by the federal government, which has jurisdiction over waters extending from three

(Louisiana) to nine (Texas) nautical miles (nm) offshore to the edge of the Exclusive Economic 

Zone, located 200 nm offshore (NOAA CSC 2009). The densest area of offshore development 

and resource extraction in the northwestern GOM is on the Outer Continental Shelf (OCS), 

which is defined as those portions of the seabed and submarine sediments adjacent to the 

shoreline and extending out to a depth of 200 m (656 ft.) below sea level (BSL) (UNESCO 

1958). 

 

1.1 FEDERAL REQUIREMENTS FOR OFFSHORE ARCHAEOLOGY

Beginning in the 1960s, federal legislation was drafted specifically to balance the protection of 

the U.S.’s cultural and natural heritage against development pressures. Specifically, the National 

Historic Preservation Act (NHPA) was passed in 1966 (and amended several times thereafter), 

and requires that all federal undertakings consider the effects of the activity on potential cultural 

resources within the area of proposed effect (NPS 2006). Federal undertakings are those 

activities which occur on federal land, require a federal permit, or involve the use of federal 

funding (NPS 2006). Due to other legislative acts, the NHPA is the only mechanism that requires 

consideration of archaeological resources on the OCS (Evans 2014). Following the passage of 

the NHPA, the responsibility for archaeological resources on the OCS was vested with the

Bureau of Land Management, which at the time managed all OCS oil and gas leases. In 1982, the 

Minerals Management Service (MMS), a new agency within the Department of the Interior, was 

created with the specific purpose of managing OCS oil and gas permitting, leasing, and revenue 

(U.S. Congress 1983). MMS was superseded by the formation of the Bureau of Ocean Energy 

Management, Regulation, and Enforcement in 2010, followed by the permanent split into three

agencies: the Bureau of Ocean Energy Management (BOEM), the Bureau of Safety and 

Environmental Enforcement (BSEE), and the Office of Natural Resources Revenue (ONRR) in 

2011.

To fulfill its NHPA responsibilities, BOEM and BSEE (and all preceding agencies) issue Notices 

to Lessees (NTL) that give oil and gas industry operators the guidelines and reporting 

requirements necessary for federal permit applications. Specific to archaeology, NTL 2005-G07 

outlines the current requirements for surveys and reports used to identify the two types of 

resources most likely to be encountered on the OCS, which are historic sites (e.g., shipwrecks, 

lighthouses, ballast piles) and drowned sites representing prehistoric occupation or exploitation 

dating from the Late Pleistocene, when sea-levels were lower than at present (BOEM 2005). 

Previous studies conducted on behalf of BOEM and its predecessors were commissioned 
2

specifically to determine the highest probability areas of the GOM for the presence and 

occurrence of archaeological resources (CEI 1977; Garrison et al. 1989; Pearson et al. 2003). 

Despite the indefensible use of studies featuring unvalidated models to delineate areas requiring 

archaeological survey, survey requirements are somewhat vague. Survey guidelines published in 

NTL 2005-G07 Appendix I, Section III do not provide a maximum water depth for areas in 

which prehistoric archaeological survey assessments are required. This means that prehistoric 

archaeological surveys and assessments are required along the entire OCS (Figure 1.1).

Figure 1.1. Gulf of Mexico region with the modern shoreline and approximate extent of the 

subaerially exposed continental shelf at approximately 200 m (656 ft.) isobath (Evans and Keith 

2011a:167).

The research reported in this study expands on previous studies to identify potential prehistoric 

features on the GOM OCS (CEI (1977; Gagliano et al. 1982; Pearson et al. 1986). Previous 

investigations of prehistoric sites on the OCS over the last 30 years have treated the GOM as two 

distinct zones. In the Eastern Planning Area, off the coast of Florida, prehistoric sites have been 

investigated using direct survey methodology, including divers using a self-contained underwater 

breathing apparatus (SCUBA), to document assemblages of prehistoric artifacts in the karst 

environment (Johnson 1992:101; Faught and Donoghue 1997). In the Central and Western 

Planning Areas, including the areas offshore Louisiana and Texas, predictive models guide 

geophysical remote sensing surveys in the tentative identification of relict landforms that may 

contain archaeological deposits (CEI 1977; Pearson et al. 1986; Johnson 1992:101). Although 

features have been identified as potential archaeological deposits by their geophysical and 

sedimentary characteristics, no prehistoric site in the Western or Central Planning Areas has been 

verified by the presence of material culture. Because physical sampling is not required for 

prehistoric site assessments conducted for NTL-compliant surveys, it is unlikely that material 

culture will be identified. The purpose of this study is therefore focused on maximizing the 

utility of acoustic profiling (geophysical survey) in identifying prehistoric landscapes, and 

physical sampling of previously reported features to refine the spatial extent of high-probability 

areas for site occurrence on the OCS. 
3

1.2 SUBMERGED LANDSCAPES AND MIDDLE-RANGE THEORY

The search for buried and submerged sites is based on contextual archaeology, which, as defined 

by Butzer (1982:7), relies less on the discovery of artifacts than on examining sites as an 

expression of human agency, or decision-making. In the northwestern GOM this is an important 

analytical tool used to more specifically delineate areas where submerged prehistoric landscapes 

are most likely to be found on the OCS. When examined as part of a network within the human 

ecosystem, the location of archaeological sites becomes somewhat predictable, based on the 

presence of various factors required to sustain a given population. In the northwestern GOM, a 

contextual approach to submerged prehistoric archaeology is necessary because the formerly

exposed surfaces on which sites were created were buried by sediment before being inundated by 

rising sea-levels, making the identification of artifacts extremely unlikely. Using a predictive 

model for human preferences within the landscape, contextual archaeology then relies on 

empirical methods of physical geography applied to middle-range theory.

Middle-range theory was first developed for use in sociology following World War II as a way to 

conceive of social systems and societal functions (Raab and Goodyear 1984:256). As used by 

R.K. Merton in the 1940s (Herbert 1996), the goal of middle-range theory was to allow empirical 

testing of theories based on abstract human behavior that would be otherwise untestable. 

According to Raab and Goodyear (1984:258), there is little direct discussion of the sociological 

origins of middle-range theory in the archaeological literature, despite its prevalence and 

association with the New Archaeology. Instead, they argue that middle-range theory’s goals of 

linking empirical data with higher order theoretical constructs have been usurped by an emphasis 

on site formation process modeling (Raab and Goodyear 1984:258). Though Raab and Goodyear 

(1984:258–259) illustrate that some studies over-emphasize site formation processes without 

relating the evidence back to social constructs of human behavior, middle-range theory should 

not be categorically dismissed as a viable tool in submerged landscapes archaeology. 

Two of the most influential works using middle-range theory in archaeology, authored by Lewis 

Binford (1978, 1981), demonstrated that empirical data may be tied to hypotheses of past human 

behavior through observations of modern human behavior. From the sociological and 

archaeological perspectives, middle-range theory is used to bridge empirical data with theories 

concerning past cultural patterns of behavior, which may be too abstract or generalized to be 

testable. Binford’s (1978) initial use of middle-range theory applied knowledge of modern 

human technologies and their effects on faunal materials to models of past technologies and 

evidence of prehistoric butchering, moving backwards from the known to the unknown using 

discrete variables to derive probable hypotheses of similar technologies used in the past. 

In one of the first studies to explicitly address the use of middle-range theory in underwater 

archaeology, Rik Anuskiewicz (1992:92) stated that geophysical signatures and their correlation 

with archaeological sites form empirical data consistent with middle-range theory building. Data 

produced through geophysical prospection are then tested against models of human behavior, 

which are intended to provide meaning to the empirical observations represented by the data 

(Anuskiewicz 1992:92). Anuskiewicz (1992) was writing specifically about magnetometer data 

as an indicator of the presence of submerged nautical sites (e.g., shipwrecks, ballast piles). His
4

work demonstrated that the empirical data (measurable magnetic anomalies) led to the 

identification of sites (shipwrecks) which in turn provided information about the local maritime 

culture. Middle-range theory, he wrote, is useful in explaining how the past is perceived by 

researchers rather than how it is explained (Anuskiewicz 1992:92).

Typically used in temporal studies, middle-range theory is applied here spatially to translate what 

is known about prehistoric site patterns and interactions (which is the basis of contextual 

archaeology), from a given time period on land to the OCS as a way to model where sites would 

have been located. Perceived archaeological indices have been identified through previous 

research on prehistoric landscape occupation and exploitation patterns, resulting in indices for 

landscape identification that can be observed through geophysical survey. In other words, by 

identifying locations that prehistoric people preferred to occupy and resources that were 

selectively exploited on land, archaeologists can extend those behavioral patterns spatially to 

areas that are now underwater.

1.3 CONTEXTUAL ARCHAEOLOGY AND THE “REAL” ENVIRONMENT 

Archaeologists study past human behavior and build patterns by up-scaling data observed at the 

micro-scale, or site, to the regional, cultural, or temporal scales. An archaeological site is defined 

differently depending on the purpose, but generally is defined as a spatially-delimited 

accumulation of cultural material that has sufficient quantity and quality to allow inferences to be 

made about behavior occurring at that location (Butzer 1982:259). Sites are critical to 

reconstructing past human behavior, but non-sites or data occurrences may still provide 

information needed to inform patterns of available resources (Butzer 1982:260). This is an 

essential point of understanding to the current study, because prehistoric artifacts are unlikely to 

be identified on acoustic profiling data, whereas environments can be recorded and reconstructed 

from geophysical data.

In geography, environments may have both a real and a perceived character. Real environments 

are composed of three elements: the geographical environment, the operational environment, and 

the modified environment (Butzer 1982:253). The geographical environment, or the physical 

landscape, is that which is available for occupation and exploitation by a human population 

(Butzer 1982:253). The operational environment consists of the resources available for 

subsistence within the overall geographical environment (Butzer 1982:253). The modified 

environment is defined by Butzer (1982:253) as the space where “frequent or effective activity 

results in tangible modification” of the landscape. Without knowledge of the real environment, it 

is difficult, if not impossible, to explore the human dimensions of a place, including motives, 

preferences, and traditions (Butzer 1982:254). The perceived environment consists of elements 

from the geographical and operational environments that a human population may or may not be 

aware of, and which influence decisions. Real and perceived environments are not diametrically 

opposed, but do not completely overlap. It is not possible, however, to make inferences about the 

perceived environment without knowledge of the real environment. 

The only previous study of submerged environments on the GOM OCS was conducted off the 

Sabine River Valley (Pearson et al. 1986), in water depths up to 12 m (39 ft.); however,
5

regulatory guidelines are vague about defining a maximum water depth for prehistoric site 

potential assessment. The published guidelines for archaeological survey refer simply to “OCS

blocks that have a high probability for containing prehistoric archaeological resources” as 

requiring survey at line spacing intervals less than or equal to 300 m (984 ft.) (BOEM 2005). No 

maximum water depth is defined as the limit for potential prehistoric resources; however, testing 

has been conducted only in shallow water depths near the State-Federal jurisdiction boundary 

(Pearson et al. 1986). For the purposes of this study, select locations with high-probability 

features (identified from a review of industry surveys on file with BOEM) at depths of 15 m (49 

ft.) to 35 m (115 ft.) were selected and subjected to geophysical survey and physical sampling.

After the geophysical data was analyzed, geographical, operational, and modified environments 

were identified in buried and submerged contexts through a spatial application of middle-range 

theory. The purpose of the work described in this report was to test and refine the areas and 

methods used to identify “real environments” (as defined above) that would have supported 

human populations.

1.4 “REAL” ENVIRONMENTS ON THE OCS

The physical landscape of the OCS is not static, but has experienced significant change over the 

last 18,000 years. This study aimed to use geophysical data to identify three specific types of 

environment that are presently submerged on the OCS, as they relate to possible prehistoric 

archaeological sites. The geographical environment that was subaerially exposed during the Last 

Glacial Maximum presents a largely unexplored (archaeologically) landscape that could have 

been exploited by prehistoric populations. The identification of operational and modified 

environments allows archaeologists to narrow down possible areas of human occupation within 

the context of the OCS. The geophysical data, however, record the entire subseafloor profile, and 

not just the areas of interest. 
6

2. PHYSICAL LANDSCAPE: SETTING AND RECONSTRUCTION

The search for submerged and buried prehistoric archaeological landscapes is predicated on an 

accurate assessment of the landscape from the point in time when it could have been occupied to 

the present. The synchronic reconstruction of the landscape, or reconstruction of a specific place 

at a given point in time, provides information about exploitable resources that would have been 

necessary to support populations, and discrete areas within the landscape where evidence of past 

occupation is most likely to be found. Diachronic reconstruction of that same place provides 

information about changes to the site over time that influence preservation of any archaeological 

materials from their time of deposition, and influence secondary site formation processes. 

Reconstruction of geologic and climatic events from the time of occupation through to the 

present is necessary to interpret the stratigraphy under analysis. Although geologists tend to 

examine strata from the bottom up, archaeologists address stratigraphy from a top-down 

perspective, starting with the present surface and moving backwards through time with depth. 

Geologic formations and processes on the northwestern GOM OCS are interpreted in this study 

from the top down. 

Sediment stratigraphy in the GOM, from the Jurassic Period (201.3–145 million years ago) to the 

Holocene Epoch (Late Quaternary Period beginning 11,700 calendar years before present), can 

be up to 20 km (12 mi.) thick (Galloway 2011:33). Coleman et al. (1991:325) estimate Late 

Quaternary sediment thickness at approximately 3.6 km (2.2 mi.) on the Texas and Louisiana 

shelf, where the areas under investigation are located. Core samples acquired as part of this 

study, and discussed in subsequent chapters, measure approximately 6 m (20 ft.) long, and 

therefore capture only a fraction of the Gulf’s Late Quaternary stratigraphic profile. The topdown approach is conducive for the types of analyses used in this study, which begins with the 

identification of known modern marine sediment at the seafloor and works backward through 

time with depth. 

The sites selected for this study are located in the northwestern portion of the OCS offshore of 

south-central Texas and western Louisiana. The only other published study conducted on 

submerged archaeological landscapes in the Western Gulf focused on the Sabine River Valley 

and examined areas where current maximum water depths are approximately 12 m (39 ft.) BSL 

(Pearson et al. 1986). Despite this limited testing, conservative estimates suggest that prehistoric 

landscapes may exist on the shelf at areas where current water depths exceed 50 m (164 ft.) BSL 

(Gagliano 1984:14) The current study sites are located in the High Island and Galveston federal 

lease protraction areas and represent current water depths ranging from 15 m (49 ft.) to 35 m

(115 ft.) BSL. These sites are located within and between the relict Sabine, relict Trinity/San 

Jacinto, and relict Brazos River valleys (Figure 2.1). 
7

Figure 2.1. Map showing study areas in relation to relict river channels; High Island is outlined in red; 

Galveston is outlined in blue (modified from Simms et al. 2008).

2.1 SEDIMENT STRATIGRAPHY

The GOM is a small ocean basin that developed through the opening of the North and South 

American tectonic plates (Galloway 2011:33). Formation of the Gulf basin was complete by 

approximately 140 million years ago (Bird et al. 2011:14). Since then, the basin has experienced 

multiple episodes of uplift, erosion, and sedimentation, resulting in the present stratigraphic 

sequence (Galloway 2011:47). Relevant to this study, the northwestern and northeastern GOM

represent two distinct geologic zones. The northeastern Gulf is characterized by an underlying 

carbonate platform and the surficial Mississippi-Alabama-Florida (MAFLA) sand sheet 

(Coleman et al. 1991). Geologically, the northwestern Gulf is completely different, characterized 

by alluvial sediments built up along the wide, shallow continental shelf (Coleman et al. 1991). 

High rates of sedimentation in the northwestern Gulf during the Pleistocene Epoch are attributed 

to Quaternary glacial periods that controlled sediment transport systems, forming the 

stratigraphic sequences observed in data collected as part of this scope of work. During the 

Holocene Epoch, sediment accretion has been most pronounced at the Mississippi River deltas 

with limited to no appreciable sediment accretion on the western flank of the OCS (Curray 1960; 

Bernard 1970).
8

Because of the presence of recoverable oil and gas reserves in the northern GOM, significant 

efforts have been made to map geologic formations and develop sedimentary models in this 

region (Holmes 2011:195). Curray’s 1960 analysis of Holocene sediments resulted in the 

identification of four distinct surficial sediment zones in the present northwestern GOM (ranging 

across Texas and Louisiana). The zones were created by assessing heavy mineral assemblages 

and correlating surficial deposits with their source; Mississippi River sediments were found in

the greatest concentration near the modern delta, but were distributed within all of the identified 

zones (Curray 1960:235). Curray’s findings illustrate that the Mississippi River has had the most 

significant impact on shelf sedimentation rates and patterns during the Late Quaternary. 

Mississippi and weathered Mississippi River sediments are found in greatest abundance in the 

central and central Louisiana regions (as identified by Curray). In contrast, the western area 

consists of a mix of primarily Mississippi, weathered Mississippi, and Colorado River sediments 

with smaller amounts of Brazos, Trinity, and Neches River sediments in the western extent of the 

western area (Curray 1960:247). 

Subsequent studies of Holocene sediment structures and thicknesses support Curray’s earlier 

assessment that the thickest zone of recent sediment deposition is located around the mouth of 

the modern Mississippi River. Bernard (1970:Plate 17) estimates approximately 45–90 m (148–

295 ft.) of recent (or post-glacial) sediment close to the modern Balize Delta, with sediments 

thinning to less than 8 m (26 ft.) on portions of the shelf located west of the Atchafalaya Basin.

Areas offshore of Texas are shown to have little to no recent sediment, with some exposed areas 

of Beaumont, or late Pleistocene, sediment (Bernard 1970:Plates 17, 18; Berryhill 1984). Soil 

borings analyzed by McClelland Engineers (1979) identified a similar pattern; the majority of 

recent sedimentation were located closest to the modern Balize delta, and there was little to no 

active sediment deposition along the northwestern margins of the GOM. The modern Mississippi 

River drainage basin, which includes the Atchafalaya Basin, deposits approximately 2.34x1012

kg (230 million tons) of sediment annually (Holmes 2011:198). These sediments are deposited 

preferentially along the Louisiana coast. The Brazos and Colorado Rivers deposit approximately 

1.12x1010 kg (11 million tons) along the south-central Texas portions of the modern continental 

shelf (Holmes 2011:198). Due to the low gradient of the offshore OCS, sediments are distributed 

over a wide area in the northwest, resulting in low levels of gross accumulation.

The GOM OCS is relatively wide and shallow; measuring approximately 87 km (54 mi.) wide at 

the Rio Grande and a maximum 209 km (130 mi.) wide at the Texas-Louisiana border (Curray 

1960:223). Average seafloor gradients become shallower from southwest to northeast; average 

gradient is 2.2 m (7.3 ft.) per statute mile at the Rio Grande, 1.8 m (6 ft.) per mile at the Brazos 

River Delta, 1 m (3.2 ft.) per statute mile at the Texas-Louisiana border, and less than 0.3 m (1 

ft.) per mile at the Recent Mississippi delta (Curray 1960:223; Bernard and LeBlanc 1965:137). 

The modern seafloor in the GOM is composed of a mixture of sand, silts, and clays deposited 

along a gradual slope. Significant bed forms are virtually non-existent. A few areas of naturally

occurring topographic relief are located on the shallow shelf; features such as salt outcrops, 

pinnacles, and mud mounds are located closer to the shelf-slope break. There is little indication 

from seafloor morphology that significant portions of the shallow OCS were part of a fluvial 

plain during lower sea-level periods in the recent past (Nelson and Bray 1970:55). All evidence 
9

of these channels and their related features have been buried by sediment accretion following the 

most recent marine transgression. Investigations of formerly subaerial landscapes therefore 

require the ability to image and examine subseafloor sediments, which is most commonly 

achieved through acoustic profiling.

Acoustic profiling provides a top-down image that represents strata of varying acoustic 

impedance. Depending on the strength of the acoustic returns, a profile is generated that depicts 

strata of varying thicknesses and signal strength, represented visually by dark and light horizons

(Figure 2.2). Features such as channels, levees, and inset terraces can be identified from the 

acoustic profile. In addition, interpretations can be made of sediment types and consistencies, 

including water-logged sediments, sands, biogenic gas, and peat deposits (e.g., Whelan et al. 

1977; Plets et al. 2007).

Figure 2.2. Sub-bottom profiler sample of acoustic data depicting a preserved river channel (outlined 

in red) and levees (circled in yellow) underneath modern marine sediment (shaded in green) (data 

courtesy of Tesla Offshore).

In this study, acoustic profiling is the first step in identifying potential prehistoric landscapes. 

The study sites are located in proximity to the relict Sabine, Trinity-San Jacinto, and Brazos 

Rivers. During the Last Glacial Maximum, these rivers extended across the newly exposed OCS, 

carving channels and creating a fluvial landscape that included inset terraces and natural levees. 

As sea level began to rise, the river systems backed up the shelf, depositing sediments and filling 

the most recently entrenched channels. Sediments deposited during the Holocene and Late 

Pleistocene represent distinct depositional events and episodes attributable to changes in sea 

level and regional climate (Frazier 1974). These episodes are visible on the acoustic profiling 

data and form the basis of the depositional sequence paradigm, in which subaerial erosion 

surfaces are interpreted as sequence boundaries because of the strong influence of glacio-eustasy 

(Galloway 2011:38). 

Offshore entrenched river valley fill typically consists of alluvial and deltaic sediments overlaid

by marine, deltaic, or coastal interdeltaic deposits (Bernard and LeBlanc 1965:138). Offshore

sedimentary sequences are unconformably deposited on eroded and/or subaerially weathered 

surfaces correlating with major glacial stages (Bernard and LeBlanc 1965:138). Fisk observed 

that each Quaternary depositional sequence consisted of gravelly basal sands fining upwards to 

sands, silts, and clays, followed by an erosional surface on which the sequence was again 

repeated (Bernard and LeBlanc 1965:141). Glacial stages include net lowering and lower-than-
10

modern sea level substages, and interglacials include net rising, and high-standing sea-level 

substages (Bernard and LeBlanc 1965:139). 

Sea level change has altered the extent and shape of the OCS repeatedly during the Pleistocene.

The geographical environment available to prehistoric human populations was expanded and 

minimized by these progradations and transgressions; it also was altered and reworked by these 

same mechanisms. Sea level position is useful in determining areas of potential prehistoric 

landscapes. Because people did not live underwater, sea level curve data are used to estimate the 

possible time period of exposure for a given sediment horizon. Final inundation—the most recent 

inundation as sea level approached the present high-stand—marks the last possible date for 

potential occupation by prehistoric populations before the landscape became part of a submerged 

environment. 

2.2 SEA LEVEL CHANGE

Some of the first scientific observations and hypotheses about sea level change were made in the

mid-1700s (Pirazzoli 1991:1). Early explanations for the rise and fall of sea level were attributed 

to diminishing global water supplies, evaporation, and crustal movement on the Earth’s surface 

(Pirazolli 1991:1). In 1885, Suess developed the concept of eustatic sea level change, or uniform 

vertical displacement of the ocean surface on a global scale, which influenced sea level change 

studies well into the 20th century (Pirazolli 1991:1–2). The concept of glacio-isostatic changes in 

sea level was introduced by Daly (1934) and correlated sea level change to glacial melt and land 

subsidence (Pirazolli 1991:2). Early sea level studies were characterized by an assumption that 

the interconnectedness of the Earth’s oceans would result in uniform eustatic sea level change, 

and that data from any tectonically stable region was representative of global sea level at that 

point in time (Pirazzolli 1991:4). Current understanding is that sea level is geographically and 

temporally dynamic. Factors that influence eustatic sea level at any given time may include 

changes in ocean volume, water mass, and water density (Pirazolli 1991:6). Overall global 

patterns are influenced locally by relative changes associated with regional land uplift or 

subsidence, meteorological or atmospheric events, gravity, and eccentricity (Pirazolli 1991:6).

Sea level change can be assessed by identifying evidence of former shoreline stands and related 

environments, and by absolute dating of samples taken from sediment and ice. Sea level 

indicators include naturally occurring features such as sediment deposits, erosion features, corals, 

fossils, shells, or plant remains, as well as anthropogenic materials such as archaeological 

artifacts (Pirazolli 1991:10–16). These indicators will provide evidence only of possible 

shoreline positions and translations or patterns of change. In and of themselves, they do not 

provide dates of shoreline positions. Isotope analysis is a commonly accepted method for 

determining ages, or age ranges, for specific samples. Radiocarbon dating is one of the more 

common isotopic analyses used to determine absolute date ranges, and has been in use since the 

1950s (Pirazolli 1991:19). More recently, the marine oxygen isotope record has been used by 

scientists to date global climate change, as well as correlate eustatic sea level changes (Chappell 

et al. 1996; Thacker and Ellwood 2007). Despite the seeming reliability of absolute dates, 

caution must be exercised when using and comparing sea level curve data. As Pirazolli stated 

(1991:21), many sea curves are created by extrapolating change among discrete data points, 
11

without regard to estimates of error. Line graphs of age/depth below modern sea level represent 

an oversimplified interpretation of sea level change. Error ranges for individual data points allow 

for a more comprehensive, although more complex, visualization of sea level change within a 

given data set (e.g., Balsille and Donoghue 2004). Furthermore, oscillations and reversals 

become exaggerated at smaller time intervals. Positive and negative alternations of sea level 

observed at a time scale on the order of a thousand years are likely to become insignificant 

within the overall pattern of sea level change when viewed on a scale of tens of thousands of 

years (Pirazolli 1991:21). The issue of scale becomes pertinent when sea level curves are applied 

to archaeology in the Western Hemisphere, where the record of human habitation is about 15,000 

years (Figure 2.3). 

At the local or site level, researchers rely on sediment data to correlate climate conditions with a 

relative site age. Geochemical properties and physical assemblages within the sediment matrix 

can be tested at the local level and correlated over regions. This process is essential to 

determining a successful age range since sea level curve data and even marine oxygen isotope 

records are determined at the regional scale or larger, without accommodating for local 

variations.

Global rates of sea level change can be assessed using a variety of data sets and correlative 

methods. Chappell et al. (1996) modeled global sea levels by cross-referencing UraniumThorium (U-Th) dating of coral reef terraces in Papua New Guinea with delta-O-18 (δ18O)

curves from deepwater marine sediment cores. Toscano and Macintyre (2003) produced a sea 

level curve specific to the western Atlantic region using calibrated carbon-14 (14C) and U-Th 

absolute dates derived from coral reefs and mangrove peat samples. While rates of change vary 

among data sets, most eustatic sea level models indicate that sea levels were approximately 140 

to 125 m (459 to 410 ft.) lower than present mean sea level at the end of the Last Glacial 

Maximum (Bailey and Flemming 2008; Bird 1993:14).

Changes in the relative position of a given shoreline involve complicated processes. A discussion 

of sea level change at the end of the Last Glacial Maximum should address more than the 

increasing quantity of water introduced to global basins by melting glaciers. Sea level rise can be 

attributed to either eustatic or isostatic change (Lewis 2000). Eustatic change refers specifically 

to a rising sea level in relation to a stable land surface, and is most often attributed to changes in 

climate (Lewis 2000). Isostatic sea level change is measured on a more localized scale, and is 

given as the vertical displacement between stable sea level and the elevation of the land surface 

(Lewis 2000:526). Isostatic changes can be attributed to sediment load compaction, fluid 

extraction, and other localized changes in conditions, and are generally associated with 

subsidence (Lewis 2000). Oscillations and differences in early global sea level curves may be 

attributed to data that were obtained from areas now characterized as subsiding coasts, rather 

than resulting from faulty data (Pirazolli 1991:4). 
12

Figure 2.3. Global sea level curves demonstrate the variability within the record at different positions on the Earth in the recent past.

-140.00

-120.00

-100.00

-80.00

-60.00

-40.00

-20.00

0.00

20.00

0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 45,000

Depth Below Modern Sea-level (meters)

Radiocarbon Age (years BP)

Global Sea-level Curves

Chappell et al.

1996

Toscano and

McIntyre 2003

Fairbanks

1989, 1990
13

2.2.1 Sea Level Change and Archaeology

Eustatic sea level rise has significantly impacted the archaeological record of early coastal 

cultures. Archaeological sites related to the earliest inhabitants of the Gulf coast area likely are 

located on the now-submerged continental shelf (Lewis 2000). According to Lewis (2000:531), 

no true coastal sites associated with these populations have been identified because the location 

of the coastal zone relative to those cultural periods is on now-inundated portions of the 

continental shelf. 

The majority of researchers agree that sea level change is a locally specific phenomenon. 

Therefore, reconstructions must include some measure of local variability within trends that 

would otherwise suggest uniform rates of global sea level change (Lewis 2000). As early as 

1965, Bernard and LeBlanc (1965:140) cited factors that complicate the construction of sea level 

curves based on radiocarbon dates. Complications may arise from, but are not limited to, 

sediment compaction and local subsidence, recognition of marsh and swamp peats, range of peat 

formation relative to water depth, and habitat extent within the water column (Bernard and 

LeBlanc 1965:140). Awareness of these complications has led to re-evaluations of regions once 

considered to reflect homogenous rates of sea level rise, and have demonstrated high rates of 

local variability (Lewis 2000). Global patterns of sea level change are insufficient for a study of 

localized impacts to archaeological sites related to rates of sea level rise. According to Dott 

(1992:2):

...we have come to realize that the problem of isolating an unambiguous eustatic 

signal is even more complex than prior generations could imagine. This is 

because there are so many complex feedbacks among glacial isostasy and glacial 

eustasy, hydro-isostasy affecting the entire world ocean through changing water 

volume, tectonic eustatic effects, erosional and sedimentational isostasy, 

compaction and decompaction of sediments, and even changing evaporative 

potential over the oceans.

Estimates for sea level position during the Last Glacial Maximum indicate a difference of -140 m

(-459 ft.) from the modern sea level stand, and estimates of sea level rise indicate a change of 

approximately 1 m (3 ft.) per century between 18,000 and 6,000 year ago (18–6 kya) (Bird 

1993:14). Sea level rise is commonly described as oscillating. Regressions or pauses interrupt 

periods of continual rise. However, some argue that oscillations are the result of statistical 

aberrations within the data (Bird 1993:14). The rate and timing of sea level rise are complicated 

by many factors including tectonic uplift or localized subsidence (Bird 1993:14). Subsidence and

downwarping commonly occur along coastal deltas due to the accretion of fluvial sediment (Bird 

1993:17). Downwarping also may occur as a result of hydro-isostatic subsidence, especially 

along low-lying shallow continental shelves, as the weight of deepening water compresses soft 

sediments such as peat (Bird 1993:17-18).

The variability in different sea level curves results in great difficulty for archaeologists 

attempting to reconstruct shoreline changes within time periods of several hundred, or even 

several thousand years. To be useful in archaeological settings, rates of sea level rise must be 

accurate at the site-specific level. 
14

2.2.2 Late Quaternary Sea Level Change in the GOM

Archaeologists have argued for the construction of regional sea level curves (Ricklis 2004). 

Global curves, such as those proposed by Chappell et al. (1996), can accurately demonstrate 

general climate trends. However, global models can overwhelm or mask distinct regional 

patterns (Ricklis 2004:183). The importance of a regionally accurate curve was demonstrated by 

archaeologists working at a 10,700 yr BP site in Florida. Attempts to reconstruct the shoreline 

position at the time the site (8JE1004) was occupied using global curves resulted in estimates of 

sea levels 10–70 m (33–230 ft.) below present mean sea level (Balsillie and Donoghue 2004). In 

this case, the scale of the global data resulted in sea level positions too gross to make finite 

assessments of a short interval in the recent past. 

The sequence of sea level change in the northwestern GOM was summarized by Simms et al. 

(2008) as follows. The end of Late Wisconsin period glacial conditions, referred to as the Last 

Glacial Maximum (oxygen isotope stage 2 [OIS2]), occurred approximately 22 kya to 17 kya 

and resulted in shoreline progradation to approximately 90–120 m (295–394 ft.) below present 

mean sea level. Shoreline transgression began again approximately 17 kya, rising rapidly until 

approximately 6 kya. Although most researchers agree on this basic pattern of sea level change, 

the rates and details of change are debated. 

A review of sea level curve data produced by Ricklis (2004) for the northern GOM region 

suggests that sea level rise over the last 20,000 years consists of a discontinuous pattern of 

change. The curve hypothesized by Ricklis (2004) entailed sequential periods of rapid sea level 

rise, consisting of glacial meltwater pulses, interrupted by periods of slow sea level rise, 

stillstands, or slight regressions. This revised model does not exhibit the same sea level 

oscillations that appear in earlier works, which differ from Ricklis’ sequence and each other (i.e., 

Curray 1960; Frazier 1974; Morton et al. 2000; Figure 2.4). Individual sea level curves are 

provided in Appendix A.

In 2004, the Florida Geological Survey published a comprehensive survey report that compared 

high-resolution data on sea level change since the Late Pleistocene for the northeastern GOM

region (Balsillie and Donoghue 2004). The study included 22 data sets specific to the region 

(Balsillie and Donoghue 2004), and compared a statistical analysis of the regional data with the 

eustatic global curve developed by Siddall et al. (2003) from delta-O-18 (δ18O, a measure of the 

ratio of stable isotopes oxygen-18:oxygen-16 [18O: 16O]) analyses of foraminifera from Red Sea 

sediment cores. The researchers found that the regional data sets were consistent with trends 

illustrated in the global eustatic curve from approximately 18,000 yrs BP until approximately 

6,000 yrs BP (Balsillie and Donoghue 2004). In the northeastern GOM data sets, two trends 

emerged, both of which differed from the eustatic global curve. The global eustatic curve since 

6,000 yrs BP resembles the sea level oscillations reported by Frazier (1974). The GOM data 

depict pulses of sea level rise more on par with those hypothesized by Ricklis (2004).

This assessment is specific to the northeastern GOM, where the carbonate platform and seafloor 

sands are less susceptible to isostatic change than the alluvial sediments characteristic of the 

northwestern GOM.
15

Figure 2.4. Comparison between selected published sea level curves constructed from data specific to the northwestern GOM.

-120.00

-100.00

-80.00

-60.00

-40.00

-20.00

0.00

20.00

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000

Depth Below Modern Sea-Level (meters)

Radiocarbon Age (years BP)

Selected NW Gulf of Mexico Sea Level Curves

Curray 1960 Frazier 1974 Morton et al. 2000
16

A review of sea level curve data published by Milliken, Anderson, and Rodriguez (2008) argues 

for rapid, possibly episodic, rates of sea level rise in the northern GOM region during the early 

Holocene, followed by slower, nearly continuous rates of rise during the middle to late 

Holocene. Specifically, the authors identified several Holocene-era flooding events: ca. 9,800–

9,500 cal yrs BP; ca. 8,900–8,500 cal yrs BP; ca. 8,400–8,000 cal yrs BP; and ca. 7,400–6,800 

cal yrs BP. These flooding events are generally correlated with climate events, such as an 8,200 

cal yr BP event associated with a glacial meltwater pulse related to mass wasting of the 

Laurentide ice sheet (Milliken, Anderson, and Rodriguez 2008). Correlated data from peat 

samples and Donax species (bivalves) suggests that sea level ranged 3–10 m (10–33 ft.) below 

present mean sea level from 8,000 to 4,000 cal yrs BP (Milliken, Anderson, and Rodriguez 

2008). Based on evidence from their study, Milliken, Anderson, and Rodriguez (2008) argue that 

sea level rise was rapid in the middle Holocene, but did not reach present levels until after 4,000 

cal yrs BP. Sea level rise from the late Holocene occurred at an approximate rate of 0.4–0.6 

mm/yr, and was variably influenced along the Gulf coast by localized subsidence (Milliken, 

Anderson, and Rodriguez 2008). 

The most notable area of disagreement in regional curves is within the last 10,000 years of sea 

level change. Unlike the previously discussed models, Blum et al. (2008) argue that landforms 

along the Gulf coast, including samples from Texas and Alabama, indicate that present mean sea 

level was reached by approximately 6.7 kya. This model contradicts most other sea level curves, 

which indicate that sea level was rapidly rising until approximately 2–5 kya (Blum et al. 2008).

One explanation for the difference in rates of sea level rise within the GOM is the local 

expression of both eustatic and isostatic change resulting in simultaneously different patterns of 

transgression (Simms et al. 2008). Subsidence rates for the Gulf region are estimated to increase 

from several centimeters per thousand years onshore to approximately one meter per thousand 

years at the shelf edge (Simms et al. 2008). This isostatic change occurs in tandem with eustatic 

sea level rise. Rates of subsidence and compaction have been studied along the deltaic plains of 

the Mississippi River. However, the impacts of both isostatic and eustatic sea level rise serve to 

demonstrate the difficulty in calculating local rates of sea level rise from global, and even 

regional, data sets. Even within regionally discrete areas, sea level curve data are not always 

consistent. Nelson and Bray (1970:66) compared radiocarbon dates from brackish shells, marine 

shells, and wood and peat samples to create a sea level curve specific to the Sabine-High Island 

Area. They developed a primary sequence of events (Table 2.1), but noted the existence of 

numerous outliers within their data set.
17

Table 2.1. Sea level sequence for Sabine-High Island Areas

Date Range 

(yrs BP) Description

Minimum Depth 

Below Modern 

Sea Level

18,200 10,200

Subaerial exposure along portions of the OCS, 

freshwater entrenchment of the Sabine River 

along a wide, flat plain

35 m (117 ft.)

10,200 9,400

Rapidly rising sea level; brackish waters 

intrude upstream but remain contained within 

river channels

22 m (73 ft.)

9,400 8,660 Rising sea level, brackish waters breach 

channels but remain within river valley 19 m (62 ft.)

8,660 7,800 Falling sea level, re-entrenchment of river 

channels 22 m (72 ft.)

7,800 6,660

Stable sea level; sedimentation remains 

confined within the river valley, which now 

forms a brackish, estuarine lagoon

22 m (72 ft.)

6,600 5,650 Rapidly rising sea level (approx. 1.6 

m/century) 15 m (50 ft.)

5,650 3,600 Slower rate of sea level rise 1.8 m (6 ft.)

3,600 2,800 Slowest rate of sea level rise (approx. 0.27 

m/century) --

Source: Nelson and Bray (1970:67–70)

Although the work of Nelson and Bray (1970) represents a detailed account of sea level rise, 

their research is restricted in area to the Sabine River valley. It also represents an area in which 

numerous data points were collected within one locality and is therefore anomalous among other 

sea level data sets for the northwestern Gulf. Despite the detailed nature of Nelson and Bray’s 

sea level sequence, it varies significantly from other regional reconstructions. Milliken, 

Anderson, and Rodriguez’s (2008) suggested sea levels were 3–10 m (10–33 ft.) below present 

from 8,000 to 4,000 yrs BP, the same time during which Nelson and Bray estimated sea levels 

were 2–22 m (6.5–72 ft.) below present. Sea level curves are generally consulted by 

archaeologists to determine when a given location on the OCS was last exposed to subaerial 

weathering, and if that time coincides with likely periods of human occupation. Because of the 

complexity of sea level rise patterns, and the need to address landscapes in areas with variable 

data sets, a single pre-existing sea level curve was not selected for use in this study. Instead, 

locally and regionally specific curves were deconstructed, and their data points combined into a 

cumulative data set along an X-Y axis, where the X axis represents time and the Y axis 

represents depth below modern sea level (Figure 2.5; Curray 1960; Shepard 1960; Nelson and 

Bray 1970; Frazier 1974; Morton et al. 2000; Blum et al. 2001; Tornqvist et al. 2006; Blum et al. 

2008). A four-point polynomial average was plotted along the sea level curve, depicting the 

general trend of sea level rise within the region. The calculated average depicts a generalized 

pattern of sea level rise, but does not account for outliers within the data set. Minimum and

maximum lines were created for the composite curve because the original data sets for many of 

the locally specific sea level curves could not be obtained, and the necessary error distributions

(as used by Balsillie and Donoghue 2004 and advocated by Pirazolli 1991) were not available. 
18

Figure 2.5. Composite sea level curve for the northwestern GOM.

-110.00

-100.00

-90.00

-80.00

-70.00

-60.00

-50.00

-40.00

-30.00

-20.00

-10.00

0.00

10.00

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000

Depth Below Modern Sea-level (meters)

Radiocarbon Age (years BP)

Sea-level Data Points from the Northwestern Gulf of Mexico

Radiocarbon Dates

Four-point 

Polynomial Trend 

Line

Minimum and 

Maximum 

Sources:

Curray 1960;

Shepard 1960; 

Nelson and Bray 1970; 

Frazier 1974; 

Morton et al. 2000; 

Blum et al. 2001; 

Tornqvist et al. 2006; 

Blum et al. 2008
19

From an archaeological perspective, the minimum and maximum dates provide an objective 

range for correlating the age of an identified landscape feature with the potential for human 

occupation, since site-specific issues such as sediment compaction or regional subsidence will 

affect the feature’s age relative to any pre-existing sea level curve. The minimum and maximum 

lines allow the archaeologist to correlate a feature’s depth with times of potential subaerial 

exposure and final inundation relative to cultural chronological periods and dates of known 

human habitation in the region. This date range can be refined through physical sampling of the 

feature and absolute dating of samples. 

2.3 DIACHRONIC RECONSTRUCTION AND SITE PRESERVATION POTENTIAL

The northwestern GOM is considered a high-probability area for the preservation of prehistoric 

archaeological sites due to the presence of the various river valleys that were entrenched on the 

subaerial OCS (CEI 1977; BOEM 2005). However, one cannot argue for evidence of prehistoric 

occupation simply because the geographical environment was available for human exploitation. 

A study of submerged landscapes requires that any evidence of occupation or exploitation be 

preserved in situ. Preservation begins with the creation of the archaeological site, and continues 

through inundation and eventual transformation of that location into an open-water marine 

environment.

Studies on site preservation potential specific to the northwestern GOM (CEI 1977; Pearson et 

al. 1986; Waters 1992) have demonstrated that relict river channels represent the optimum place 

for site preservation. As demonstrated in Nelson and Bray’s (1970) sea level rise sequence, river 

channels and ultimately river valleys fill with brackish water and become low-energy estuaries or 

lagoons during the initial stages of sea level rise. Archaeological sites located within these river 

valleys become buried underneath newly deposited estuarine sediments, which eventually fill the 

channels and valley so that they are topographically indistinguishable from the surrounding 

seafloor. Localized subsidence into estuarine peats also would have encouraged the preservation 

of archaeological materials, as they would have been below the immediate seafloor sediments at 

the time of final inundation (Lewis 2000; Weinstein et al. 2012). As the shoreline begins to 

translate over the site, the high energy surf zone impacts the newly deposited sediments and 

surrounding paleosols, leaving any landscape features underneath the estuarine transgressive 

zone (defined here as the maximum depth to which sediments were scoured and eroded during 

sea level rise) protected from erosion. The Nelson and Bray (1970), Blum et al. (2008), and 

Milliken, Anderson, and Rodriguez (2008) studies demonstrate the various rates of sea level rise 

at any given time. All sea level curves from these studies imply the movement of the shoreline. 

In terms of site preservation potential, shoreline change includes the movement of the high 

energy surf zone across the continental shelf. For any given location on the OCS, estimates of 

time during which that portion of the shelf was undergoing active erosion as part of the high 

energy surf zone will vary from hundreds to thousands of years, depending upon the sea level 

curve being used. Following stabilization of the shoreline, and depending on the depth of the 

buried feature, its long-term preservation is dependent on oceanographic processes, especially 

scour and erosion, impacting the marine environment.
20

The GOM OCS is characterized as a micro-tidal, low-energy environment (Curray 1960:231–

234). Diurnal and mixed diurnal tidal fluctuations in the GOM typically average less than 0.3 m

(1 ft.). However, tidal ranges are highly variable during meteorological events; hurricaneinduced tides in the GOM often exceed 3 m (10 ft.) (Curray 1960:233). Wave conditions are 

normally low to moderate; average deepwater wave periods range from 3 to 8 seconds, and 

waves rarely exceed 1 m (3 ft.) in height (Curray 1960:231). These small-size waves generally 

are only capable of moving sediment in the shallow surf zone (Curray 1960:231). Shallow water 

sediments are principally sands and coarser-grained material than that found on the continental 

shelf, since sands fall out of suspension before silts and clays and are therefore preferentially 

deposited along the coast (Masselink and Hughes 2003). Under bed stress and flow conditions,

cohesionless sands “behave individually.” In contrast, silts and clays (grain size less than 63

micron [μm]) are electrostatically charged and therefore cohesive (Masselink and Hughes 

2003:124). According to Masselink and Hughes (2003:124), “the dynamic behavior of cohesive 

sediment depends less on single-grain properties and more on bulk-sediment properties (e.g., floc 

size and water content).” 

Sediments on the OCS are generally considered to be at equilibrium. Fine-grained sediments 

correspond to areas with weaker currents (Whitehouse 1998:62). Hurricane waves and tidal 

currents disrupt this equilibrium and are responsible for reworking and modifying sediments on 

the shelf (Curray 1960:234). According to Curray (1960:233), “a velocity of 35cm/second is ... 

the approximate mean velocity at 1 meter above the bottom which is required to pick up and 

move fine quartz sand,” although actual net transport also requires unidirectional flow and a 

velocity gradient that extends to the seafloor. Using hindcast wind/wave data for normal wave 

conditions in the GOM, Curray estimated that areas in water depths less than 10 fathoms (18 m 

or 60 ft.) experienced bottom velocities greater than or equal to 35 cm/second for more than 500 

hours per year, or approximately 5% of the time (1960:233). 

Due to the relatively minor impact of normal current and tidal conditions, the majority of 

pronounced episodes of erosion and scour recorded in the uppermost sedimentary record stem 

from discrete or punctuated events, such as extreme storms, or anthropogenic impacts, such as 

dredging. Anthropogenic activities such as trawling, construction, and dredging have occurred on 

the GOM OCS with increasing regularity for the last hundred years (Evans et al. 2009; Evans 

and Keith 2011a, 2011b). Trawling has resulted in the occasional isolated find of archaeological 

materials. Otter trawl nets and their associated equipment typically only disrupt the uppermost 20

cm (8 in.) of sediment (FAO 2005). Dredging and construction can have a much deeper impact, 

but are more likely to be regulated on the OCS. No finds of prehistoric artifacts have been 

reported from either of these activities offshore in the northwestern Gulf. Extreme storm events 

impact the OCS with some regularity. When applied to actual hurricane wave statistics, Curray’s 

(1960:233) calculations for sediment transport velocities indicated that areas in water depths 

between 10 and 15 fathoms (18–28 m; 60–90 ft.) experienced storm induced scour less than once 

every 18 months. All of the areas included within this study are located in depths that, according 

to Curray’s estimates, experience bottom current velocities sufficient to result in transport and 

scour of fine, cohesionless sands at least once every 18 months. 

 

To accurately assess the potential for sediment scour and erosion of seafloor sediments resulting 

from extreme storm events, computer modeling of sediment transport was conducted under 
21

contract by Deltares for each of the study areas (Galveston and High Island), at water depths of 

15.5 and 31.0 m (50.8 and 101.7 ft.) BSL (Rego et al. 2011; modeling was conducted jointly 

with another BOEM-funded project, and those results are reported in Evans et al. 2012). The 

modeling incorporated H*WIND data for recent hurricanes and simulated hydrodynamics and 

waves using proprietary Delft3D-FLOW and Delft3D-WAVE models in the GOM basin using a 

rectangular model of 10km resolution around the datum points. Smaller, curvilinear models of 50 

m (164 ft.) maximum resolution were also created with Delft3D-FLOW and Delft3D-WAVE to 

simulate localized conditions. For each site curves were created that represented model results 

for both loose and consolidated sediment types. Hurricane surface wind speed data were

prepared by the National Oceanic and Atmospheric Administration (NOAA) and are available as 

real-time analyses of tropical cyclone surface wind observations (H*WIND). Delft3D-FLOW is 

a three-dimensional hydrodynamic model that simulates horizontal and vertical water movement 

on the continental shelf. Delft3D-WAVE is designed to simulate the transformation and 

propagation of “random, short-crested, wind-generated waves in coastal waters” (Rego et al. 

2011).

Based on the results of the oceanographic modeling, each of the study areas experienced some 

degree of maximum scour potential during recent hurricane events (Table 2.2). Sediment 

porosity and plasticity were not measured for the datum sites; therefore, to provide a range of 

expected conditions, both a loose and consolidated bed scenario were modeled for the specific 

grain sizes found at each sample site located within the study areas. For loose bed scenarios, 

maximum scour was reduced by between 70% and 91% following sediment redeposition 

(calculated 7 days after each modeled storm and reported as “net” scour; Table 2.2).

Table 2.2. Scour estimates based on oceanographic modeling

Hurricane Bed Scenario Scour Type Study Area

High 

Island Galveston

Ike

Loose Maximum 1.0 m 1.3 m

Net 30 cm 30 cm

Consolidated Maximum 0.2 cm 0.24 cm

Net 0.03 cm --

Rita

Loose Maximum 84 cm 60 cm

Net 10 cm + 5 cm

Consolidated Maximum 0.2 cm 0.10 cm

Net ~ 0 cm --

At the Galveston datum, sediment redeposition resulted in net sediment accretion. This datum 

was the only site to display accretion following a hurricane event. Under consolidated bed 

scenarios, maximum scour was reduced by 85% to 99% following sediment redeposition (Rego 

et al. 2011). Hurricanes can cause seafloor scour above a potentially preserved landscape feature. 

In some cases, sediment resettles on the seabed, resulting in a reduced amount of net scour over 

the feature. Depending on the depth of burial of a specific feature below the modern seafloor, the 

feature may be protected from both long-term processes and extreme punctuated scour events. 
22

2.4 SUMMARY

Lowered sea levels during the Late Wisconsinan glacial period transformed the OCS from a 

marine environment to a subaerial plain entrenched by numerous river channels. As sea level 

began to recede following maximum glacial conditions, these same rivers retreated backwards up 

the shelf, changing freshwater systems to brackish lagoons before finally reverting to open 

marine systems. Evidence of the former landscape was buried underneath these lagoons and 

estuaries, the overlying sediment serving as a protective sediment layer during shoreline 

transgression and, in some cases, subsequent storm events. Geologic studies suggest that 

Pleistocene surfaces exposed as dry land on the OCS are buried under thin veneers of recent 

sediment in the northwestern GOM. Investigations into sediment scour during extreme storm 

events indicate that storm-induced scour may be followed by re-deposition of sediment, resulting 

in minimal net scour, or in some cases net sediment accretion. Based on an assessment of 

geologic and oceanographic conditions, it is accurate to say that geographical, operational, and 

modified environments may lie preserved on the OCS at depths accessible to researchers. 
23

3. ARCHAEOLOGICAL EVIDENCE AND THE PHYSICAL LANDSCAPE

3.1 DEFINING THE TEMPORAL PERIOD OF INTEREST

The formerly subaerial OCS defines the geographical as well as temporal setting for this study.

Based on a range of sea level curves, the modern shoreline position was reached by 

approximately 4,000 yrs BP at the latest or as early as 6,800 yrs BP (as shown in Chapter 2, 

Figure 2.6), by which time the OCS had been completely transformed into an open marine 

environment. The establishment of the modern shoreline serves as a terminus ante quem for 

occupation of the OCS, which correlates with the Middle Archaic cultural period. Sea level 

decline during the most recent glaciation, the Late Wisconsin, started as early as 35,200 yrs BP 

(Frazier 1974:10), predating any known occupation of North America. Previous estimates for the 

arrival of humans into North America adopted a terminus post quem of 11,500 yrs BP. 

Increasing numbers of sites older than 11,500 yrs BP have been identified that preclude the use 

of a single specific date for the beginning of possible occupation in North America (Table 3.1). 

The ambiguous timing of the arrival of the first Americans makes is difficult to determine an 

exact date before which one can stop looking for possible prehistoric archaeological sites.

3.2 MIGRATION ROUTES AND DATES

In the search for archaeological landscapes on the OCS, the dates of subaerial exposure, and 

therefore the potential for human landscape exploitation, are first correlated with the dates of 

known occupations within the region. A fundamental question in archaeology is the timing of the 

arrival of North America’s first inhabitants and their route of entry into and across the landscape. 

The peopling of the New World is a complicated topic in which hypotheses have been tested 

and, in some cases, revised in light of new evidence. As a science, archaeology is restricted to 

the data that have been collected. Researchers must be ready to account for newly discovered 

data that can, and have, challenged the dominant paradigm. As discussed in the previous chapter 

(Chapter 2. Physical Landscape), the landscape of the present-day northwestern GOM region has 

changed significantly since the Last Glacial Maximum. The coastal margins and modern 

shorelines are very different than when the first inhabitants entered North America. Current 

models of early prehistoric population density, subsistence, and interaction are based on evidence 

found from inland terrestrial settings, where artifact preservation rates have in many cases 

restricted the archaeological record to discussions of stone tools. Keeping in mind the diachronic 

landscape, significant portions of the modern-day coast have been altered by sea level rise and 

associated landscape changes have contributed to a potentially biased archaeological record. 

What is known is that though modern humans have been in the GOM region since approximately 

11,000 yrs BP (Ricklis 2004; Rees 2010), new discoveries continue to push back the dates for 

potential occupation (e.g., Waters et al. 2011).
24

Table 3.1. Chronology of archaeological sites with 

absolute dates greater than 12,000 yrs BP.

Site Location Method Dates Source

CA-SRI-512W California C14 11,350–12,000 cal yrs BP Erlandson et al. 

2011:1181

Daisy Cave California C14 11,950–12,780 cal yrs BP Rick, Erlandson, 

and Vellanoweth 

2001:598

Paisley Caves Oregon C14 12,300 RCYBP Gilbert et al. 

2008:786

Page-Ladson Florida C14 12,480 yrs BP Faught 2008:675

Monte Verde II Chile C14 12,500 yrs BP Bonnichsen and

Lepper 2005:14

Meadowcroft 

Rockshelter

Pennsylvania C14 12,000–15,000 yrs BP Adovasio and

Pedler 2005:26

Miles Point 

(18TA365)

Maryland C14 / 

OSL

13,200 yrs BP Lowery et al. 

2010:1472

Debra L. 

Friedkin 

(41BL1239)

Texas OSL 13,200–15,500 yrs BP Waters et al. 

2011:1599

Topper (8AL23) South 

Carolina

OSL 15,200 +/- 1,500 cal yrs BP Goodyear 2005:107

Cactus Hill 

(44SX202)

Virginia C14 / 

OSL

15,000–17,000 RCYBP Goodyear 2005:107

3.3 MATERIAL CULTURE AND PALEOINDIAN SUBSISTENCE

Projectile points and other lithic tools often are used as proxy indicators of subsistence strategies. 

Subsistence strategies are a complete cultural package, incorporating environmental variables 

such as climate and available natural resources, or the operational environment, to create a 

culture’s unique way of life, or more specifically the foods that prehistoric people ate, and the 

tools and techniques used to acquire those resources and to manipulate them into edible food 

(Price and Feinman 2008:26). Paleoindians were the first cultural group to occupy what is now 

North America. They are routinely described as nomadic hunter-gatherers who subsisted on large 

herbivore game animals, or megafauna (Milanich 1994:38). The Early Paleoindian diet probably 

consisted of a variety of terrestrial game animals such as mammoth, mastodon, bison, caribou, 

and elk, and gathered foods, such as berries, nuts, seeds, roots, smaller game animals, and fish 

(Kelly and Todd 1988:233). Kelly and Todd (1988) have referred to Early Paleoindian 

populations as “high technology foragers” who relied primarily on faunal food sources. Based on 

archaeological evidence recovered to date, early Paleoindian groups were sparsely located within 

North America. They probably lacked local knowledge of new floral food resources during 

migration, and this suggests a primary dependence on hunting. Early Paleoindian subsistence 
25

lacked geographical specialization, since low population densities allowed groups to use large 

hunting ranges (Anderson 1996; Kelly and Todd 1988; Milanich 1994).

Anderson (1996:32–34) states that Paleoindians who settled in the southeastern region of what is 

now the United States initially used a generalized foraging strategy with a preference for hunting 

and frequent changes in hunting radii. Therefore, Paleoindians did not stay in any given place for 

extended periods of time. This subsistence system resulted in scattered sites of low density. He 

further argues that this pattern was likely true of earlier initial occupations. The mobile lifestyle 

associated with this type of subsistence is supported by the Paleoindian archaeological record. As 

noted by Kelly and Todd (1988:235), the artifact assemblage of Early Paleoindians included 

several similar artifact types, such as scrapers, beaked gravers, and bifaces, with little regional 

variation. This lack of regional types led Kelly and Todd (1998:235) to suggest that Paleoindians 

across different environments lived a relatively similar lifestyle. Similar Paleoindian artifacts 

have been identified from areas across the U.S., spanning various ecosystems. According to 

Milanich (1994:48), many of these stone tools were unifacial, and likely served multiple 

purposes. People may have found travel easier with a smaller number of general purpose tools

than with a greater number of highly specialized tools.

According to Anderson (1996:50), bands of Paleoindians became “place-oriented” once they 

found resource rich areas from which they could stage hunting trips, creating a locus for their 

subsistence range. The establishment and use of large staging areas contributed to the 

development of regional traditions observed within later Paleoindian assemblages (Anderson 

1996:50). Subregional specializations likely developed due to differences in resource base, local 

climate, and physiography (Anderson 1996:51). 

In the northeastern Gulf coast region, archaeologists have found evidence of sub-regional 

adaptations in later Paleoindian subsistence strategies, probably necessitated by local climate 

fluctuations (Milanich 1994:40). One such example is the oasis model (Dunbar and Waller 1983; 

Dunbar 1983, 1991), which posits an adaptation to specific freshwater sources, such as tertiary 

karst sinkholes and shallow lakes in the dry, arid Florida interior. Paleoindians exploited the 

sinkholes and lakes, not only as their own freshwater source, but also as hunting sites, since 

game animals utilized the same water sources (Milanich 1994:41). As of 1994, Milanich reported 

that 92% of all diagnostic Paleoindian artifacts found in Florida were recovered from the tertiary 

karst regions. This finding has profound implications for the Paleoindian archaeological record 

in Louisiana and Texas, where freshwater sources, such as rivers, have experienced significant 

alteration. Modern shoreline positions were reached approximately 6,800 to 4,000 years ago, 

based on the sea level curve presented in Chapter 2 (Figure 2.6). Given that prehistoric peoples 

were known to have been in the Gulf region since at least 11,500 yrs BP, areas of the nowsubmerged OCS may have been inhabited by Paleoindian and even Archaic period peoples.

Paleoindians did not conceptualize or live within boundaries such as modern geopolitical

divisions of landscape. Because much of the information in the archaeological record is 

generated through state-permitted activities and NHPA-compliant surveys, the data needed to 

address this time period often are organized by, and classified within state boundaries (Table 

3.2). Typologies and cultural chronologies may be developed on a state or micro-regional basis. 
26

Table 3.2. Comparison of early cultural periods in the northwestern GOM region

Louisiana Southeast Texas

Middle Archaic a 7,950–3,950 yrs BP Archaic Coastal b 5,000–2,200 yrs BP

Early Archaic a 9,950–7,950 yrs BP Archaic Inland b 8,000–1,500 yrs BP

Late Paleoindian a 10,750–9,950 yrs BP

Middle Paleoindian a 11,450–10,750 yrs BP

Early Paleoindian a 13,450–11,450 yrs BP Paleoindian b 11,500–8,000 yrs BP

Sources: (a) adapted from Rees 2010; (b) Ricklis 2004

3.3.1. Louisiana

Compared to other southeastern states, southern Louisiana has few identified Paleoindian 

archaeological sites. According to Rees (2010:40), the most well documented Paleoindian and 

Early Archaic sites are located on Tertiary uplands. Landscapes in the west-central and 

northwestern portions of the state account for over half of all known Paleoindian sites in 

Louisiana. Paleoindian sites in southern Louisiana have been identified on Pleistocene surfaces. 

These sites often include the remains of megafauna in the assemblage, such as the Salt Mine 

Valley site (16IB23), the Tapir site (16IB66), Côte Blanche Island (16SMY79), Trappey 

Mastodon (16LY63), and Above the Mastodon (16WF63) (Rees 2010:37).

The archaeological site at Avery Island (16IB23) has produced evidence of the earliest known 

occupation in coastal Louisiana. Avery Island (16IB23) is a large salt piercement dome located 

in present day Iberia Parish, in south-central Louisiana (Gagliano 1967:iii). Unlike an island that 

is surrounded by water, the salt piercement dome’s distinct vegetation and relative relief creates 

a distinct boundary, separate from the surrounding swampy landscape (Gagliano 1964:1). 

Underlying salt deposits have uplifted localized areas of sediment, creating topographic highs 

with a maximum elevation of 46 m (152 ft.) above the surrounding landscape (Gagliano 1964:1). 

The earliest evidence for human occupation at Avery Island dates to what was defined locally as

the Early Recent Stage, 18,000–5,000 yrs BP, by Gagliano (1967:101). The Early Recent Stage 

includes the entire Paleoindian period and part of the Archaic Period as defined by Louisiana’s 

cultural chronology (Table 3.2). Radiocarbon dates from excavations in 1968 provided absolute 

dates of 12,000 (+/- 400) yrs BP and 10,900 (+/- 300) yrs BP (Neuman 1984:63). Fossils of 

Pleistocene megafauna such as mastodon and giant bison were recovered from Avery Island 

deposits suggesting an abundance of game animals utilizing the surrounding environment 

(Gagliano 1967:39). The interpreted hunter-gatherer populations present at Avery Island are 

believed to have visited the site seasonally. Artifacts include a small number of sharp-edged 

scrapers and cutters (Gagliano 1967:102).

Avery Island is one of several sites in Louisiana that links Early Paleoindians with Pleistocene 

megafauna. At the Trappey Mastodon site, mastodon faunal remains including teeth and 
27

fragments of a mandible, scapula, and tibia were recorded in situ (Neuman 1984:65). Two 

corner-notched projectile points also were recorded at this site, though there is no direct evidence 

that the projectile points were used to hunt, kill, or butcher the animal (Neuman 1984:65). Early 

Paleoindians in Louisiana, and throughout North America, are described as hunter-gatherers. 

There is limited evidence for Louisiana-specific subsistence systems within the Paleoindian 

archaeological record. However, analogies with other Early Paleoindian populations suggest that 

hunter-gatherers exploited mastodon and Bison antiquus among other megafaunal species (Rees 

2010:37). Later Paleoindians in Louisiana became adept at hunting mammals such as deer 

(Neuman 1984:69). Despite the lack of direct evidence of Paleoindian and Early Archaic 

subsistence systems, archaeologists have created models of subsistence based on landscape 

reconstructions which detail the available fauna and flora, and correlate that information with 

archaeologically excavated tools that were used in food procurement and processing. This type 

of modeling can produce an accurate interpretation of subsistence systems because of the 

relationship between available resources and the technologies required to utilize and process 

them. As summarized by Gagliano (1984:26): 

...it is conceivable that a coastal system could have high biological productivity 

and produce a great annual yield of biomass, but this biomass may not be readily 

accessible to people living in the area there if their technology is inadequate to 

harvest or to utilize key species, or both.

Artifacts such as stone tools are commonly used to identify and differentiate prehistoric cultures 

due to their abundance in the archaeological record. Organic materials such as textiles, clothing, 

and food remains, which could have identified specific populations, often are not preserved 

within terrestrial settings, and are unavailable as direct evidence. The Paleoindian and Early 

Archaic cultural periods in Louisiana are therefore defined by their tool assemblages, which 

include projectile points such as Clovis, San Patrice, untyped lanceolate, Folsom, Plainview, 

Dalton, Pelican, and Scottsbluff styles. Tools were made from both exotic and local materials 

such as chert, petrified wood, and sandstone (Rees 2010:43–51). In prehistoric archaeology, an 

emphasis on stone tools, specifically projectile points, exists because these materials do not 

deteriorate significantly over time. In many cases, they are the only surviving artifacts at sites 

from early archaeological contexts (Young et al. 1994:209). Unfortunately, projectile points can 

be and have been disarticulated from their archaeological context by any number of processes,

including erosion, fluvial migration and associated reworking, and human modification of the 

landscape (Schiffer 1987; Gagliano 1984). Due to significant modification of the southern 

Louisiana landscape by river channel migration, the perceived geographical density of 

Louisiana’s Paleoindian sites is more likely attributed to excellent site preservation conditions in 

the north rather than low occupation densities in the south (Rees 2010:51; Gagliano 1984:40). 

Based on existing archaeological evidence, the Late Paleoindian period in Louisiana is 

characterized by a decrease in population mobility coupled with an increase in total population 

(Rees 2010:53). In the archaeological record, this increase in regionalization is demonstrated 

through the abundance of regional projectile point types, including bifurcate and stemmed points, 

and a decrease in the use of exotic materials in tool production (Rees 2010:54). The projectile 

points of the Late Paleoindian and Early Archaic periods generally were smaller, more complex 

technologies than those used by Paleoindians to hunt megafauna. The change in lithic 
28

technologies is generally attributed to climatic shifts following the Last Glacial Maximum, 

which resulted in an abundance of smaller animals such as deer and fish that replaced megafauna 

as the primary subsistence (Rees 2010:54). Another reason for the diversification of projectile 

point types during the Early Archaic period, according to Rees (2010:57) was related to the 

manner in which projectile points were hafted, or fastened to spears, and used. The atlatl, or 

spear thrower, was first used in Louisiana during the Early or Middle Archaic periods (Rees 

2010:67). Continuing through the Middle Archaic period, increasingly sedentary populations 

exploited more diverse resources such as aquatic species and wild plants that could be gathered 

(Rees 2010:60). Middle Archaic subsistence adaptations appear in the archaeological record in 

the form of increased types of stone tools, including manos, metates, abraders, and mortar and 

pestles used to process plant foods. Other significant adaptations include the development of 

intensive middens and human burials (Rees 2010:59–60).

3.3.2. Texas

As is the case in Louisiana, few Paleoindian sites have been identified along the coastal regions 

of southeast Texas. Most of the Early Paleoindian sites in this region are found within or 

associated with stream drainage areas (Stright 1986; Ricklis 2004:184). According to Ricklis 

(2004:184), the majority of recovered Paleoindian projectile points were created from highquality lithic materials that are exotic to southeast Texas, suggesting that early populations 

introduced these materials to the coastal region through migration or trade. 

One of the earliest sites in southeastern Texas, McFaddin Beach (41JF50), contains a large 

quantity of Early Paleoindian projectile points. McFaddin Beach is a 32-km (52-mi.) long area 

along the modern Texas coast in Jefferson County, located west of Sabine Pass (Stright 1999:2). 

Eustatic sea level rise and a lack of modern sediment inputs have resulted in net beach erosion.

Artifacts that date from the Paleoindian period through to the historic era have been redeposited 

along the shore for decades (Stright 1999:5). Although the source or sources of these artifacts

have not been identified, the artifacts and their secondary context have been studied by amateur 

and professional archaeologists since the 1970s (Stright 1999:10). According to Stright 

(1999:15), the area surrounding McFaddin Beach was an upland ridge above the now-relict 

Sabine River valley during lower sea level stands, approximately 11,500 yrs BP. 

Analysis of 880 artifacts recovered from the McFaddin Beach site indicated that the largest 

single percentage of the assemblage, 43% of the total artifacts, date to the Paleoindian period, 

11,500–8,000 yrs BP (Stright 1999:112). According to Stright (1999:112), the next time period 

most represented in the assemblage is the Middle Archaic, 4,500–1,300 yrs BP. The majority of 

the artifacts recovered from the McFaddin Beach site were identified as projectile points (Stright 

1999:115). McFaddin Beach is an impressive, but unusual, assemblage. The majority of 

Paleoindian sites in southeastern Texas, particularly along the modern coast, consist of isolated 

finds or scatters, such as site 41GV101. This site is located off the coast of Bolivar Peninsula 

near Crystal Beach and consisted of a single Clovis point (Texas Historical Commission [THC] 

1988). Archaeologists have historically placed great emphasis on the correlation between 

projectile point types and game animals when modeling prehistoric subsistence strategies. Early 

models showed a continuum within the Paleoindian period in which Clovis megafauna hunters 

transitioned to Folsom bison hunters, becoming generalized hunter-gatherers in the Archaic 
29

period (Bousman et al. 2004:75). In this same vein, lanceolate projectile points were universally 

attributed to big game hunting (Bousman et al. 2004:75).

Supplemental evidence from faunal remains suggests that the correlation between game size and 

projectile point type is oversimplified. Faunal evidence from Texas sites such as Aubrey, 

Lubbock Lake, and Lewisville suggests a broader range of game animals that included 

megafauna such as mammoth, camel, horse, bison, and giant armadillo, and smaller vertebrates 

and invertebrates including fish, turtle, alligator, deer, and rabbit (Bousman et al. 2004:75). As is 

the case in Louisiana, stone tools provide evidence of subsistence systems, and offer insight into 

specific activities. Due to the abundance of lithic tools, Paleoindian sites in Texas have been 

subdivided into three types: food procurement or consumption sites; butchering or processing 

sites; and campsites (Bousman et al. 2004:76–78). Contrary to the idea of Paleoindians as 

exclusively big game hunters, some archaeologists hypothesize that prehistoric populations that 

occupied what is now classified as the modern coastal zone exploited estuarine resources (Evans 

and Keith 2011a:166–167). According to Newcomb (1961:329), Paleoindian and Early Archaic 

populations exhibited some maritime adaptations, but maintained ties with inland populations 

rather than adopt a completely maritime subsistence. Aten (1983:11) developed a similar 

interpretation of coastal Texas’ prehistoric populations, stating: 

...to suggest that the peoples of the upper coast were adapted to maritime life is to 

substantially stretch the point; a much more appropriate descriptor is strandlooper, 

as South African coastal scavenger-hunter-gatherer-collectors are commonly 

called.

3.4 MODIFIED ENVIRONMENTS AS EVIDENCE OF HUMAN OCCUPATION

The Pleistocene landscapes on the OCS were created through episodic changes in environmental 

conditions at both the regional and local scales, beginning in the late Quaternary Period and 

extending into the Holocene Epoch (Hill 2007:13). Humans, however, do not merely live on a 

landscape. Humans actively modify their landscape, matching their subsistence objectives with 

available resources, and modifying natural processes to better meet their needs (Butzer 1982:32). 

As previously discussed, the lithic record of Paleoindians and Early Archaic populations 

demonstrates a growing specialization within the form of projectile points. This pattern has been 

interpreted as a change in hunting patterns from megafauna to smaller game animals coupled 

with increasing resource diversification. Environmental evidence from this same time period 

indicates a changing climate, suggesting that early inhabitants adapted their subsistence systems 

to take advantage of the changing conditions.

The climate of North America at the end of the Last Glacial Maximum was largely controlled by 

the presence of the Cordilleran and Laurentide ice sheets, which influenced prevailing weather 

patterns by pushing circulation patterns to the south, causing a southward shift of climate zones 

(Burroughs 2005:78–79). The GOM experienced less of a decrease in temperature than waters 

closer to the ice sheets, resulting in an exaggerated temperature gradient from north to south 

across the United States (Burroughs 2005:79,99). Northern Florida and the Gulf coast 

experienced conditions more commonly found across modern southern New England; faunal 
30

evidence indicates average July temperatures in southern Missouri during the Heinrich 2 event 

were 10–12 degrees Celsius lower than at present (Burroughs 2005:99). 

According to Burroughs (2005:82), temperature fluctuations related to the Last Glacial 

Maximum had a significant impact on local populations, especially cooling temperatures 

associated with Heinrich events that likely rendered large portions of the northern landmass 

inhospitable to human habitation. Warming occurred between 10,000 and 8,200 years ago, 

resulting in increased precipitation out of the GOM during summer (Burroughs 2005:183). 

Conditions in the Gulf coastal regions of Mexico were conducive to wild plant use and land 

clearance (Pohl et al. 2007). Human adaptation to climate shifts at this time period include 

nascent plant cultivation and domestication, with the earliest dates for domestication of maize 

(Zea mays) by 9,100 yrs BP (Pohl et al. 2007:6870); other cultigens such as squash (Cucurbita 

pepo) developed between 9,000 and 7,000 yrs BP (Story 1985:37-38; Galinat 1985:247). 

Evidence of cultivation is found in preserved pollen grains, but these are not the only ecological 

evidence of human landscape manipulation. Anthropogenic fires have been studied through 

analyses of charcoal and pollen (Fowler and Konopik 2007:165). 

Fire was used for several purposes in the Gulf coast region during the Paleoindian and Early 

Archaic periods. Though it can be difficult to differentiate lightning-induced fires from 

anthropogenic causes, fire is associated with Paleoindian game hunting. Paleoindians are known 

to have used fires to create barriers, forcing game animals into areas more conducive for capture 

(Fowler and Konopik 2007:166). Fire also was used to clear landscapes in the fall and winter, 

encouraging pioneer plant species or species associated with secondary succession. Collection of 

nuts was facilitated by landscape clearance (Fowler and Koponik 2007:166). During the Early 

Archaic period, fire was still used in hunting, but was applied in indirect ways. Rather than 

creating barriers to trap game animals, Early Archaic populations used fire to burn areas within 

the landscape, maintaining habitats that were attractive to specific game animals (Fowler and 

Koponik 2007:166–167). Landscape clearance through burning, occurring most often in the fall 

and winter months, served a social purpose by creating large open areas for seasonal gatherings 

of several small bands (Fowler and Koponik 2007:166).

Conclusive evidence of human habitation does not rely solely on the presence of anthropogenic 

artifacts. Evidence of anthropogenic landscape manipulation in the form of species selection or 

landscape clearance may be found within sedimentary strata (Thomas 1989:314–315; Hill 

2007:6–7). A 1982 study by researchers with Coastal Environments, Inc., conducted on behalf of 

the National Park Service, examined sedimentary signatures of anthropogenic activity within 

terrestrial sites along the northwestern GOM. In some cases macro-sedimentary characteristics 

can be identified from physical samples, such as the presence of exotic shell in a non-natural 

habitat, an abundance of worked shell, or unnaturally large percentages of a specific shell type or 

size (Gagliano et al. 1982:53). Signatures of fire can be identified beyond the presence of 

charcoal. Chemical alterations of sediments such as oxidation of clays, or particularly the 

presence of baked clay, have been cited as indicators of human activities (Gagliano et al.

1982:90). Areas of crushed shell or mechanically packed sediment may indicate an intensive 

activity area (Gagliano et al. 1982:90). Depending on the type of sampling conducted, artifacts 

may not be collected from formerly subaerial landscapes on the OCS. However, their absence 

does not preclude the ability to identify areas of potential human occupation or activity.
31

3.5 PREHISTORIC OCCUPATION POTENTIAL IN THE COASTAL ZONE

Subsistence strategies are intrinsically linked to site location; the variables incorporated into a 

specific subsistence strategy can be used to delineate areas of probable site location or 

interaction. McFaddin Beach and Avery Island are located along and near the present-day 

shoreline. Reconstructions of the shoreline position 11,000 years ago indicate that McFaddin 

Beach was located in a woodland environment—a low-density forest with open spaces allowing 

for sunlight but offering limited shade. Avery Island, at the time of Paleoindian occupation, was 

at the boundary between the woodland and coastal zones (Aten 1983:145). This distinction is 

important because models of prehistoric populations in the northwestern Gulf coast area have 

stated that the highest population densities are located in the deltaic (near a river mouth) and 

littoral (shoreline) zones (CEI 1977:314–324; Aten 1983:138). If population densities are 

greatest near the shoreline, then a larger density of sites should be expected where the deltaic and 

littoral zones occurred during lower shoreline positions, areas that are presently underwater. 

Reviews of prehistoric settlement patterns indicate that prehistoric populations had an observable 

preference for the coastal zone (Aten 1983; Westley and Dix 2006). In terms of locating Gulf 

coast Paleoindian or Early Archaic sites, this finding is an important point. Any definition of 

“coastal zone” implies a temporally constrained period during which terrestrial and marine 

processes interact within a given area (Masselink and Hughes 2003). What was the coastal zone 

at the time of possible Paleoindian and Early Archaic occupation is now located underwater, 

having been submerged during sea level transgression related to climate changes at the end of the 

Last Glacial Maximum (CEI 1977; Faught and Donoghue 1997; Pearson et al. 1986; Stright 

1986). According to Aten (1983), prehistoric population density increases from the woodland 

into the prairie setting, and is highest in the coastal zone. This finding would suggest that a 

search for evidence of Paleoindian and Early Archaic culture would be most successful in the 

areas with the highest density at the time of occupation. 

As discussed in Chapter 2, geographical environments, and potentially prehistoric archaeological 

sites, may have survived sea level transgression. Previous studies have demonstrated the 

potential for offshore submerged archaeological site preservation in the northwestern GOM

region (CEI 1977; Pearson et al. 1986). Investigations in other parts of the world have identified 

prehistoric sites in submerged offshore contexts (Masters and Flemming 1983; Benjamin et al. 

2011; Evans et al. 2014). 

33

4. SUBMERGED PREHISTORIC ARCHAEOLOGY AND THE GOM

Interest in the geology of continental shelves is often interrelated with economic development. 

In the GOM, recoverable oil and gas reserves located offshore have instigated research in aid of 

energy extraction industries. Open water oil and gas drilling began in the 1890s, with drilling 

rigs built on piers extending from the shore (Evans and Keith 2011b; National Commission 

2011). In 1937, the world’s first freestanding drilling structure was built in the GOM. The 

structure was located one and a half miles from shore in approximately 4.3 m (14 ft.) of water 

(National Commission 2011). In 1947, the first successful well was drilled out of sight of land, 

approximately 17 km (10.5 mi.) offshore of Louisiana, in 6 m (20 ft.) of water (National 

Commission 2011). Geologic and geophysical studies were necessary to identify oil and gas 

fields, as well as to determine if near-seafloor sediments were stable enough to support 

installation of pipelines and placement of drilling rigs. Though much of the GOM geologic and 

geophysical research has been published, more exists as grey literature reports, including studies 

conducted by oil and gas operators and studies funded by the U.S. government in efforts to 

manage oil and gas operations.

In the U.S., oil and gas industry activities on the OCS are regulated by the U.S. Department of 

the Interior’s (USDOI) Bureau of Ocean Energy Management (BOEM) and Bureau of Safety 

and Environmental Enforcement (BSEE). As discussed in Chapter 1, BOEM and BSEE have a 

responsibility under the NHPA to consider the impacts of federal undertakings on cultural 

resources within the area of potential effect. Beginning with the first archaeological Notice To 

Lessees (NTL) in 1974, survey guidelines addressed both the presence of historic shipwrecks and 

submerged prehistoric sites on the continental shelf, requiring archaeological assessments 

prepared by a qualified marine archaeologist in order for an operator to obtain approval to drill a 

well or install a pipeline. 

4.1 DEVELOPING A PREDICTIVE MODEL FOR SUBMERGED SITE LOCATION

To develop accurate survey guidelines and assessment requirements, the National Park Service 

(NPS) funded a study in the early 1970s to determine the archaeological potential of the GOM 

OCS. The final report divided the results between prehistoric potential for sites on the nowsubmerged portions of the OCS (Vol. 1), and the potential for historic shipwrecks (Vol. 2) (CEI 

1977). The goals of the study included development of a predictive model for the identification 

of the most likely resources to be found on the OCS, and the highest probability areas for the 

occurrence of these resources. The methodology outlined by the authors was one of the earliest 

publications specific to submerged archaeological landscape research, and their 

recommendations still serve as the basis for methodologies used in modern studies. 

The predictive model developed by researchers with Coastal Environments Inc., or CEI, (1977) 

began with the identification of distinct geologic systems and landforms found within each 

discrete region of the GOM, from the Rio Grande to the Florida Keys, with a focus on Late 

Quaternary formations. Sea level position (including fluctuations), climate changes, and geologic 

history were then correlated with each type of geologic landform in order to determine the 
34

likelihood of their preservation through to the modern period. Landforms with the highest rates 

of predicted preservation were then correlated with similar landforms in modern terrestrial 

settings to determine any association with archaeological sites or prehistoric human habitation. 

According to the study’s authors, prehistoric cultural resources do not occur randomly, and their 

results argued for correlations between specific landform types and artifacts or other evidence of 

past human behavior (Table 4.1; CEI 1977:331). The authors then made correlations between 

types of landforms and the effectiveness of different survey techniques in identifying these same 

features in submerged contexts. 

Table 4.1. Correlation of terrestrial landforms, cultural period, and effectiveness of survey 

techniques

Landform Cultural Period Survey Effectiveness

Early Archaic Paleoindian Sub-bottom 

Profiler

Piston Corer

Quarry Sites V V Low Not effective

Salt Dome Sites V V High Medium

Spring/Sinkhole Sites V V High Medium

Valley Margin Sites V P Low Not effective–Low

Natural Levee Sites V V High Not effective–Low

Point Bar Sites V V High Not effective–Low

Bay Margin Sites V V Low Not effective–Low

Coastal Dune Lake 

Sites V V High Medium

Shell Middens U U High Not effective

Key: V (verified or known correlation); P (probable correlation); U (unknown) 

Source: CEI 1977:333,340

The CEI (1977) study examined geographical environments across the entire GOM; however, 

not all of the final recommendations are applicable to all environments. The authors suggested 

that any investigation of submerged prehistoric resources take a three-step approach beginning 

with remote sensing of the area through either small-scale bathymetry or sub-bottom profiling to 

resolve the upper 9 m (30 ft.) of sediment coupled with acquisition of a grab or drag sample of 

seafloor sediments (CEI 1977:341). If a probable site was indicated by the data acquired in Step 

1, then subsequent data should be collected, either in the form of side scan sonar imagery of the 

area, bottom cores, and/or additional grab or drag samples (CEI 1977:341). The final step, if 

warranted, was recommended as underwater photography/videography, box core sampling, and 

or diver investigation (CEI 1977:341). The majority of the recommendations, such as 

bathymetric survey or diver photography, assume that the landform is exposed at the seafloor, 

which is appropriate for the northeastern GOM, where, for example, sinkholes and river channels 

are readily apparent on bathymetric and side scan sonar data due to the underlying karst 

formations (Faught and Donoghue 1997; Adovasio and Hemmings 2011). Based on geologic 
35

reconstructions of sea level rise at the end of the Last Glacial Maximum (Chapter 2) 

methodologies used in the northwestern GOM must assume that relict landforms such as those 

specified by CEI (1977) will be buried below the modern sediment and not readily apparent at 

the seafloor.

The methodologies created as a result of the 1977 study were developed for use on landforms 

identified as correlating with archaeological sites through construction of a predictive model for 

site occurrence. While the predictive model identified specific landforms and general areas for 

research, the cultural groups included within this model were highly mobile hunter-gatherers

with scant material culture (Aten 1983; Neuman 1984; Ricklis 2004). The predictive model 

included geological reconstruction and landscape change modeling, but recognized that a paucity 

of artifacts would likely exist at submerged sites. Cultural signatures of human occupation were 

therefore identified that went beyond artifacts, such as potsherds and lithics, to include signatures 

more likely to be recovered in core samples, such as the presence of shells, faunal fragments, 

black earth, burned rock, charcoal, and pollen (CEI 1977:172). 

In the thirty years since the creation of the dominant archaeological site prediction and 

preservation model used in the GOM (CEI 1977), subsequent studies have been conducted 

worldwide that add to the theory and methodology of investigating submerged prehistoric sites. 

4.2 THIRTY YEARS OF SUBMERGED PREHISTORIC ARCHAEOLOGY

In 1981, in recognition of advances in paleo-coastline reconstruction, archaeologists, 

anthropologists, geologists, and oceanographers were invited to participate in a symposium 

addressing Quaternary coastlines and prehistoric archaeology. The resulting papers were 

published in one of the first edited volumes on the subject (Masters and Flemming 1983). The 

participants in this symposium noted that, at that time, the majority of submerged prehistoric 

artifacts were the result of chance finds by recreational SCUBA divers, fishermen, or activities 

related to offshore construction (Masters and Flemming 1983:611). Site discovery, they 

maintained, depended on both physical preservation of the site and its ease of detection (Masters 

and Flemming 1983:622). The participants presented diverse case studies ranging in location 

from Siberia to Australia, but concluded that several methodologies could be universally applied 

to site prediction and detection. According to their findings, at minimum, local geomorphology 

has to be reviewed to identify three things: an area with high preservation potential; the presence 

of recognizable features (such as shell middens); and an operational environment that includes 

basic human requirements such as access to fresh water, protection from environmental 

exposure, and/or availability of food (Masters and Flemming 1983:623). The primary 

recommendation for survey and identification of prehistoric features stemming from the 1981 

symposium was similar to the methodology outlined by CEI (1977): chiefly, bathymetric or 

subseafloor survey conducted at tight intervals (no greater than 150 m [492 ft.]). The authors 

stressed, however, that this type of survey cannot prove without doubt the existence of 

prehistoric sites; it can only identify the most probable areas in which sites could be preserved 

(Masters and Flemming 1983:624).

In 1982, Gagliano et al. published the results of a study that analyzed terrestrial analogues for

potential offshore deposits. The study, developed under contract for the National Park Service, 
36

analyzed core samples from verified terrestrial prehistoric sites along the Gulf coast. Lab 

analyses of sediment core data indicated that the following variables were credible indicators of 

modified environments: grain size, pollen content, geochemical composition, point-counts,

foraminifera species identification, and radiocarbon dating of appropriate samples (Gagliano et 

al. 1982). Recognizing that site identification could not be dependent upon the presence of 

anthropogenic artifacts, the terrestrial corollaries were developed so that landforms could be 

tested for indicators of prehistoric archaeological site occurrence without the presence of obvious 

anthropogenic artifacts such as projectile points (Gagliano et al. 1982:115). 

To test the effectiveness of the predictive model and recommended methodology proposed by 

the 1977 and 1982 reports, the former Minerals Management Service (MMS), now BOEM,

funded a study in the early 1980s, concentrated in the relict Sabine River Valley on the GOM 

OCS (Pearson et al. 1986). This area was identified as an ideal test area because of a wealth of 

pre-existing geologic data (e.g., Nelson and Bray 1970) and existing subseafloor survey data 

conducted on behalf of oil and gas operators and available to the researchers through the funding 

agency (Pearson et al. 1986:xix). Eight target areas were selected for inclusion in the project 

based on a review of existing shallow high resolution seismic data, and then subjected to a 

seismic survey at a transect interval of 152.4–304.8 m (500–1,000 ft.) to relocate features of 

interest. Once features were identified, an additional seismic survey using a 30.5-m (100-ft.) 

transect interval was employed to delineate those features (Pearson et al. 1986:53–76). Survey 

grids were located in the Sabine Pass, High Island, and Galveston federal lease areas; current 

water depths in these areas range from approximately 8 m (27 ft.) to 16 m (54 ft.) and are 

referenced to mean lower low water (MLLW) (NOAA 2006). Vibracores were acquired from 

five (5) of the surveyed areas, including Sabine Pass lease blocks 3, 6, and 9, and High Island 

Area lease blocks 18 and 49; cores measured 12 m (40 ft.) in length. The cored areas ranged in 

water depth from approximately 8 m (27 ft.) to 12 m (40 ft.) (NOAA 2006). Vibracores were 

planned for additional areas, but adverse weather conditions precluded further coring operations. 

The collected cores, 76 in total, were subjected to a series of laboratory analyses in efforts to 

identify potential signatures of anthropogenic activity (Pearson et al. 1986:76–80), as identified 

by the Gagliano et al. (1982) study. No artifacts or distinctly human-made materials were 

recovered within the cores; however, two cored features included sediments exhibiting 

characteristics of archaeological deposits. One sampling site was interpreted as a possible shell 

midden, dating to approximately 8,055 +/- 90 yrs BP, and the second was interpreted as an area 

of burnt bone dating to approximately 8,500 yrs BP (Pearson et al. 1986:xxiii,127–162). The 

study’s authors were hesitant to identify the features as concrete evidence of human occupation, 

but stated “that they more closely resemble archaeological deposits than known natural deposits” 

(Pearson et al. 1986:162).

The results of the Sabine River Valley study supported the theories behind the predictive model 

created for use in the GOM and demonstrated the complicated task of identifying discrete 

archaeological features from buried contexts offshore. The northwestern GOM is unique from 

many other published submerged prehistoric contexts in that archaeological data are not simply 

submerged, but also buried underneath a seafloor which gives little to no indication of the 

underlying features. Despite the identification of potential archaeological features in cores from 

Sabine Pass lease block 6, no further sampling was conducted offshore for prehistoric 

archaeology in the northwestern GOM before the start of the current project.
37

The Sabine River Valley study was not the only study to investigate submerged prehistoric 

resources. Numerous studies have been conducted around the world, but are distinct from the 

Sabine River Valley study in that these other sites are exposed at the seafloor, located in 

relatively shallow water depths, or some combination thereof (Johnson and Stright 1992; Browne 

1994; Faught and Donoghue 1997; Momber 2000; Dix et al. 2004; Benjamin et al. 2011; Evans 

et al. 2014). Some research projects have avoided the complications of working in submerged 

environments by using evidence from terrestrial contexts to address changes in human 

subsistence and coastal settlement patterns instigated by changing climate conditions (Bailey and 

Parkington 1988). Despite systematic studies and surveys, a significant amount of data have been 

uncovered accidently, such as the Cinmar blade off of the U.S. Atlantic coast, which was 

recovered by a commercial dredging operation in the 1970s (Stanford and Bradley 2012). 

Estimates suggest that approximately 550 submerged prehistoric archaeological sites have been 

identified globally, dating from the Lower Paleolithic/Early Pleistocene periods, or within the 

last approximately 2.5 million years (Dix et al. 2004:5). This is contrasted with approximately 

10,834 prehistoric sites recorded in the state of Louisiana alone (Rachel Watson, LA Division of 

Archaeology, personal communication).

Despite 30 years of research in locations ranging from Beringea to Argentina, the methodology 

used in submerged prehistoric research has remained relatively unchanged from the CEI 1977 

recommendations. As outlined by Gaffney and Thomson (2007:4) the most common techniques 

used in the investigation of submerged prehistoric contexts include high resolution 2-D seismic 

(sub-bottom) profiling, high resolution 3-D seismic profiling, high resolution bathymetric 

mapping, and seabed sampling and shallow coring. The acquired remote sensing data or 

sediment samples/cores are then put into a locally specific context. These paleolandscape 

reconstructions remain critically dependent upon accurate understandings of sea level, including 

isostatic and eustatic changes, and rates of sedimentation or erosion (Dix et al. 2004:13–30). 

4.3 SUBMERGED GOM LANDSCAPES METHODOLOGY

In the GOM, the existing predictive model for submerged prehistoric site occurrence was created 

by extrapolating observed terrestrial settlement patterns onto the formerly exposed continental 

shelf. Additional data acquired since the creation of the first predictive model (CEI 1977) have 

supported the hypothesis that prehistoric sites in coastal Texas and Louisiana occur near fresh 

water sources, and that inhabitants occupied or exploited landforms associated with fluvial 

systems, including naturally occurring levees and inset river terraces (Pearson et al. 1986; Ricklis 

and Blum 1997). For example, a regional survey of 23 terrestrial archaeological sites along 

coastal Texas resulted in an observable pattern of site location (Ricklis and Blum 1997). 

Archaeological deposits were identified on landward channel margins in close proximity to 

shorelines, but at elevations above the effects of surf zone dynamics that could potentially bias 

the archaeological record by eroding, reworking, or destroying sites before they could be 

preserved (Ricklis and Blum 1997). 

Archaeological data are used to reconstruct patterns of past human behavior. After data have

been located and documented, site level observations can be correlated with environmental 
38

climate reconstructions on the local, regional, and global scales to accurately identify cultural 

chronologies and subsistence patterns (Thacker and Ellwood 2007). Land and water are both 

active mechanisms impacting the coastal environment and influence long-term coastal 

archaeological site distribution patterns (Lewis 2000). Paleoenvironmental reconstructions

depend upon both synchronic and diachronic processes. As discussed in detail in Chapter 2, 

synchronic reconstructions are used to develop a static landscape at a given point in time, 

determine when a potential area may have been subaerially exposed, and correlate that time 

period with possible occupations in the Gulf coast region. Diachronic reconstructions determine 

how the landscape changed over time, illustrating the geomorphological processes related to site 

inundation and identifying key processes impacting site preservation potential. Both of these 

models are essential for determining if a geographical environment may contain in situ

archaeological deposits (Waters 1992). 

Archaeologists have hypothesized that sites on the OCS are most likely to be preserved by 

sediment deposition related to a low energy environment that covers the site prior to 

transgression of the high energy surf zone. According to Pearson et al. (1986), prehistoric sites 

have the highest probability for preservation when they are located within, or underneath, the 

estuarine transgressive zone in channel features and channel fill (Figure 4.1). An example of a 

site found within channel fill is a campsite located next to an oxbow lake when the water table 

was low. Episodes of overbank flooding from the nearby river and sediment deposition would 

eventually cover the site. Prehistoric sites on the offshore continental shelf may also be preserved 

when they are buried by sediments in a low energy environment prior to sea level rise and 

subsequent marine inundation, such as sites located on floodplains and inset river terraces 

(Pearson et al. 1986; Stright 1986; Lewis 2000). According to Waters (1992:279), Quaternary 

archaeological deposits on the continental shelf are most likely to be preserved within drowned 

river channels below the ravinement surface (Figure 4.2). For use in this archaeological study, 

the “ravinement surface” is defined as the erosional unconformity that marks the maximum 

depth of transgression-related disturbance (Waters 1992:277).

Figure 4.1. Archaeological site buried by and preserved within estuarine 

sediments (CEI 1977).
39

Figure 4.2. Hypothetical model of prehistoric archaeological sites 

associated with a channel feature. 

Sites are located (A) interbedded in levee sediments, (B) within floodplain 

sediments, (C) on the natural levee surface, and (D) within the channel fill 

(Waters 1992:142).

The typical method for determining site preservation potential for submerged prehistoric sites 

calculates the maximum depth of erosion and scour in relation to the depth of the potential 

feature below the seafloor and the thickness of any protective sediment overburden. 

Archaeological site formation processes are well documented for different terrestrial landforms

(e.g., Schiffer 1987), but few quantitative studies have been published for submerged 

archaeological sites (e.g., Muckelroy 1978; Quinn 2006; Evans et al. 2014). Notable exceptions 

include studies conducted in areas dominated by sand and gravel, which do not compare with the 

behavior of silts and clays like those found on the northwestern GOM OCS (e.g., Quinn et al. 

1997; Quinn 2006). In the submerged environment, hydrodynamic and physical site formation 

processes have been quantitatively modeled as they pertain to historic shipwreck sites (McNinch, 

Wells, and Trembanis 2006; Foecke et al. 2010). McNinch, Wells, and Trembanis modeled the 

environmental characteristics and geomorphology of the Beaufort tidal inlet in North Carolina, 

site of the 18th century shipwreck interpreted as Blackbeard’s flagship, Queen Anne’s Revenge

(QAR). They modeled wave height and direction, wave-driven and mean current, and sediment 

transport in order to determine effective rates and depth of scour (McNinch, Wells, and 

Trembanis 2006). The goal of the QAR project was to determine effective management 

strategies for the wreck site, and to assess the potential for artifact movement within the site 

matrix. The lack of quantitative studies for submerged prehistoric site formation processes is 

likely attributed to the lower number of confirmed sites as compared to the number of known 

shipwrecks.

The study conducted at Beaufort Inlet highlights a fundamental challenge for archaeologists 

attempting to study submerged prehistoric site formation. In the GOM region, prehistoric sites 

would have been in place and impacted by any combination of physical processes during sea 

level rise including, but not limited to: deposition of sediment overburden; erosion by lateral 
40

channel migration or channel avulsion; scour within the high energy surf zone; and storm surge 

(Waters 1992). Essentially, submerged prehistoric sites form from the bottom up; the sites are 

already in place and the water rises over the top of them. This is fundamentally different from 

historic shipwreck sites, which form from the top down as the materials are introduced to the 

seabed and become incorporated into the site matrix (McNinch, Wells, and Trembanis 2006; 

Muckelroy 1978; Stewart 1999; Stanbury 2003). An understanding of submerged prehistoric site 

formation processes in the GOM region depends upon an explicitly geomorphological and 

geoarchaeological approach. Initial surveys for prehistoric sites offshore will predominantly rely 

on limited testing, such as the extraction of sediment cores. Therefore, sediment analyses, which 

can correlate offshore sediments with local climate changes, and potentially, absolute dates for 

sea level rise, must be utilized (Pearson et al. 1986; Stright 1986). 

4.4 TOWARDS AN UPDATED PREDICTIVE MODEL

It has been argued by CEI (1977), Gagliano et al. (1982), Pearson et al. (1986), Stright (1986, 

1991), Waters (1992), and Faught and Donoghue (1997), among others, that more information 

about the earliest Gulf coast inhabitants may be preserved on portions of the now-submerged 

continental shelf. The predictive model and methodology in use since the late 1970s appears to 

remain valid, with some minor adjustments based on new research. 

If submarine archaeological sites are to be found ... we must be able to predict the 

approximate location of sites so as to minimize the search area, and the conditions 

must be known which will maximize the chance of survival of material

(Flemming 1983:138).

The existing predictive model for prehistoric archaeological resources in the northwestern GOM

is fundamentally a spatial application of middle-range theory in archaeology. The model is built 

on the assumption that a pattern of site locations, constructed from data at what would have been 

inland sites, can be translated accurately to what was the coastal zone at the time of occupation. 

To date, no evidence has been found of marine exploitation by either Paleoindian or Early 

Archaic peoples in the northwestern GOM. Rather than a lack of marine exploitation, the case 

may be that the evidence simply has not been found yet. Almost all archaeological evidence from 

the northwestern GOM has been recovered from terrestrial settings which were inland at the time 

of occupation, and does not represent evidence from what would have been contemporary coastal 

occupations. According to Dix et al. (2004:199), a fundamental assumption of predictive models 

is that settlement patterns are strongly influenced by environmental factors. Generally, predictive 

models include the following types of variables: topography, hydrology, geomorphology, 

available resources (food, water, raw materials), and social processes (symbolic, political, or 

economic) (Dix et al. 2004:201–202). 

Synchronic reconstructions of possible site locations and diachronic reconstructions of landscape 

change in the GOM are both driven by and dependent upon an accurate understanding of sea 

level change. Dated sediments or deposits from high-probability landforms must correlate with 

both the date ranges of subaerial exposure and potential human occupation in order to be viable 

locations for site occurrence. Correlations are created by scaling up site level data from a specific 

location to compare with regional or even global models of sea level change and climate trends.
41

It is necessary to make a critical assessment of the validity and applicability of any sea level data 

set used, as errors are known to occur in almost all data sets (Dix et al. 2004:208). To address the 

inherent errors within a given data set, a new sea level range was prepared for this study 

(presented in Chapter 2), incorporating several locally specific northwestern GOM sea level 

curves and focusing on the minimum and maximum times of probable exposure, rather than a 

single curve depicting final inundation. 

 

Diachronic landscape reconstruction is related to site formation process modeling (Schiffer 

1987). Qualitative models of underwater site formation have been developed by Muckelroy 

(1978), Stewart (1999), and Stanbury (2003), among others, and include both cultural and 

environmental factors that can affect the seabed at or near an archaeological site. Environmental 

processes of site formation include bioturbation, gravity, tides and currents, waves, seismic 

activity, sedimentary movement (e.g. mud flows), and regional climate (Stewart 1999). Waters 

(1992:278) modeled underwater site formation processes specifically related to prehistoric sites 

and identified variables that encourage site preservation including: the energy level of coastal 

processes and the depth of effective erosion; strength and frequency of punctuated storm events; 

the cohesiveness of site matrix sediments; the amount of subsidence before inundation; the 

gradient of the continental shelf; tidal range; and sediment import and export. Transgressive 

shorelines also impact upstream river valleys, causing a shift to the entire system. Diachronic 

landscape reconstructions must recognize all potential sources of site preservation or erosion, 

including lateral fluvial migration, avulsion stages, and river valley entrenchment. One of the 

driving mechanisms of diachronic change in the GOM since the Late Pleistocene is sea level 

change, reinforcing the need for a locally accurate sea level change data set. 

The existing model for submerged prehistoric site occurrence and preservation used in the 

northwestern GOM was originally developed in 1977. Subsequent research on submerged 

prehistoric landscapes worldwide demonstrates that the basis of the GOM model is still valid, 

and represents basic methodology. Additional research in sea level rise and climate change data 

from the last thirty years complements, rather than contradicts this model. New sea level curve 

data specific to the northwestern GOM is the most important recent contribution to synchronic 

modeling of the region, as it allows archaeologists to best determine the time span associated 

with final inundation. Previous studies have used a single curve, which may not account for local 

variability caused by subsidence or isostatic uplift. The expanded curve used in this study is not 

intended to produce an absolute date of final inundation, but for the purposes of archaeological 

inquiry provides the most likely periods of subaerial exposure therefore allowing the 

archaeologist to determine if the area is suitable for continued investigation.

Sediment analyses, such as those identified by Gagliano et al. (1982), are useful in identifying 

sediments that have been altered by anthropogenic activity, such as those within a midden. At 

issue in submerged prehistoric landscape reconstruction, however, is that cores or physical 

samples may not be from anthropogenic features, but the geographical environment on which 

anthropogenic features are located. The ability to identify the climate, environment, and age of a 

given landscape is necessary before in-depth archaeological research can be justified at a given 

location offshore. Additional geophysical techniques, not included in the 1977 predictive model, 

are included in this research as a means of identifying climate proxy indicators, sediment ages, 

and evidence of diachronic landscape change necessary for prehistoric site preservation.

43

5. METHODOLOGY

Late Pleistocene and early Holocene landscapes on the OCS in the northwestern GOM have been 

inundated by rising sea levels, and buried in place by associated sediment accretion. These 

buried geographical environments may contain evidence of operational and even modified 

environments related to Paleoindian and Early Archaic populations. Unlike submerged 

prehistoric sites in other parts of the world (discussed in Chapter 4), the emphasis in the 

northwestern GOM is not on artifacts or even sites, but rather on the identification of the 

geographical environments in which archaeological sites would have been preserved prior to sea 

level rise. The first step in identifying and verifying these features, and any subsequent sites, 

consists of geophysical remote sensing, especially acoustic profiling, to identify subseafloor 

horizons and depositional events. 

5.1 GEOPHYSICAL REMOTE SENSING

All of the studies reviewed as part of this research include unanimous recommendations that 

remote sensing survey of the seafloor, using either side scan sonar or sub-bottom profiling

sensors, should be the first step in examining submerged prehistoric features. Geophysical 

instruments that are routinely used in the search for terrestrial and submerged archaeological 

sites include both passive and active sensors (e.g., Herz and Garrison 1998:147; Benjamin 2010; 

Evans and Voisin 2011). In the search for buried prehistoric features in terrestrial contexts, subsurface imaging through ground penetrating radar and magnetic survey has been used to locate 

prehistoric sites or features that indicate human habitation or exploitation. Submerged 

archaeological features may also be identified through the use of geophysics; however, the 

methods and tools are adapted to meet the specific challenges presented by the submerged 

environment. Marine geophysical data are often acquired during a towed survey; the geophysical 

sensor is towed behind a boat along a predefined survey grid and positioning is maintained by a

GPS mounted on the vessel. The range of magnetic survey intervals typically used for marine 

surveys are unlikely to reliably identify short duration or low intensity anomalies such as those 

caused by hearths or other anthropogenically altered sediments unless the sensor happens to pass 

directly over or in the immediate vicinity of the anomaly’s source. Unlike terrestrial sites, which 

may be surveyed at sub-meter magnetometer sampling intervals, line intervals of 15–30 m (49–

98 ft.) (or greater) are more often used for marine surveys (CEI 1977; Garrison et al. 1989; 

BOEM 2005; Enright et al. 2006; Camidge et al. 2010). The use of towed acoustic sensors, 

particularly sub-bottom profilers, is therefore the preferred method for the identification of 

buried geographical environments offshore. 

5.1.1 Acoustic Survey: Overview

Acoustic sensors are used in marine surveys because of the superior ability of sound waves to 

propagate through the water column and seafloor sediments. Sound waves are preferred over 

electromagnetic waves, such as x-ray and ultra-violet rays, which have limited penetration of less 
44

than 1 m (3 ft.) in water, and visible light (Wille 2005:9). In contrast, sound waves of varying 

frequencies can travel through the water column to depths ranging from 100 m to 10,000 km

(328 m to 16,093 mi.) (Wille 2005:9). Acoustic sensors include side scan sonar, multibeam 

bathymetry fan echosounders, single-beam bathymetry profilers, and sub-bottom profilers. All 

acoustic sensors operate by emitting a fixed or variable frequency signal and recording both the 

amount of time it takes the signal to return to the transceiver (known as the speed of sound in 

two-way time travel), and the strength and direction of the returned signal, also known as 

backscatter (Wille 2005:42–60; Blondel 2009:18–22). Acoustic data are used to reconstruct 

either 2D plan view images (e.g., multibeam or side scan sonar) or profiles of the seafloor and 

subseafloor structures (e.g., single-beam bathymetry and sub-bottom profiler) (Wille 2005:42–

60). 

Geologic conditions in the northwestern GOM create a unique environment for submerged 

prehistoric archaeological sites. As discussed in Chapter 2, the influx of sediment from the Rio 

Grande to the Mississippi Rivers has filled in relict river channels that incised across the OCS

during the Last Glacial Maximum (Nelson and Bray 1970; Anderson 2007:20–46). Unlike river 

systems in other parts of the world, including the eastern GOM, evidence of these relict channels 

is not visible at the seafloor; therefore, side scan sonar and multibeam bathymetry are not useful 

tools for submerged prehistoric research in the northwestern Gulf. The identification of 

geographical environments offshore Texas and Louisiana is dependent upon careful 

interpretation of subseafloor sediment horizons (CEI 1977; Pearson et al. 1986; Stright 1986; 

Evans and Keith 2011a).

Imagery based on sound requires interpretation; although acoustic images may appear similar to 

photographs, they represent data that must be interpreted (Evans and Voisin 2011). Sound 

images are produced when an object has a different acoustic impedance than its surroundings.

Acoustic impedance is defined mathematically as the product of the speed of sound and density

where a change in either density or speed of sound will produce an acoustic echo (Wille 

2005:29). The ability to measure depth from acoustic data is dependent upon the actual speed of 

sound in two-way time travel that exists when the data are recorded, which is itself the product of 

temperature, density, and salinity levels within the water column. In the absence of a velocity 

cast that records the true speed of sound, data can be interpreted for marine environments by 

using the average speed of sound in salt water, which is 1,500 meters/second two-way time 

travel (Wille 2005:27). Recorded acoustic signals generate images but do not have a genuine 

color. Typical sound images are black and white with a large and dynamic gray scale, although a 

false color scale may be added in post-processing to assist with interpretation or presentation of 

the data (Wille 2005:30). Acoustic data samples provided in the following chapters are displayed 

in gray scale. Sediments of varying densities or acoustic impedance produce different echoes, 

which can be identified on the resulting images as layers of varying color. Variation in acoustic 

impedance may also indicate stratification and a relative record of deposition events. According 

to Wille (2005:30):

...the seabed may have no echo producing layers during even thousands of years 

of continuous sedimentation. On the other hand the presence of a clearly 

discernible layer is an indication of an event of sedimentation, disrupting 
45

continuity. A difference of only one percent and even less in the impedance of 

adjacent layers may appear as a visible horizon. 

Marine geophysical surveys for archaeological resources utilize acoustic data that have been 

collected line by line along a predefined survey grid (BOEM 2005; Wille 2005:49). Independent 

of cost, line spacing intervals used to construct the survey grid are dependent upon many factors 

such as the size of the anticipated feature, but are predominantly controlled by practical survey 

parameters such as water depth, the size of the survey vessel, and its ability to maintain survey 

course heading given prevailing weather conditions. Survey data quality can also be 

compromised due to physical factors that diminish the acoustic signal’s strength or return 

trajectory such as lateral deviation of the towfish due to currents, heave or sea surface conditions, 

boat pitch and/or roll, and towfish height above the seafloor (Edgetech 2003: 3–29; Wille 

2005:38–39). 

5.1.2 Sub-bottom Profilers

Sub-bottom profilers are used to record the seafloor and underlying internal structures of subsurface sediments (Wille 2005:52). Typically, acoustic frequencies of between 3 kilohertz (kHz)

and 16 kHz are used to image the upper 100 m (328 ft.) of sediment (Wille 2005:53). Subbottom profiler data acquisition is a balance between high resolution of detail and depth of data 

penetration. Detailed, high resolution imagery of near-seafloor stratigraphy is achieved by using 

higher frequencies, while penetration into deeper sediment structures is generally accomplished 

using lower frequency signals (Wille 2005:53). 

Sub-bottom data quality is directly related to the type of sediment being imaged. Several factors

can severely compromise sub-bottom data quality, including underconsolidated sediments, the 

presence and amount of interstitial or dispersed biogenic gas, high percentages of sand grains 

within a horizon, or the presence of pore water (Fleischer et al. 2001:103; Whelan et al. 

1977:157–158). Based on studies from the South Pass area in the northwestern GOM, Whelan 

(1977:158) found that when methane concentrations were greater than 30 ml/L within a sediment 

sample (or horizon) the acoustic signal was either completely absorbed or scattered laterally, 

decreasing the strength of the acoustic return. Acoustic data must be reflected back to the 

transducer/receiver to be recorded, therefore the survey medium must have sufficient density or 

consolidation to reflect the signal; dewatered and compacted clays typically produce high quality 

data. Sands, which are uncompressible, contain trapped pore water. Pore water and biogenic gas 

function similarly during acoustic profiling; neither reflects the acoustic signal well, and both 

contribute to signal scattering, resulting in an acoustic void or opacity on the resulting image 

(Figure 5.1).
46

Figure 5.1. Sub-bottom profiler data (2–10 kHz) recorded over Sabine Bank, offshore Texas, 

illustrates the difference of acoustic reflectivity of sands (left) and compacted clays (right). (Data 

courtesy Tesla Offshore, LLC)

5.1.3 Sub-bottom Interpretation

Sub-bottom interpretation for prehistoric archaeology is based on a contextual pattern of site 

preference. Modified environments are best preserved when they are located underneath the 

estuarine transgressive zone. The transgressive zone is defined here as the maximum depth to 

which sediments were scoured and eroded during sea level rise (Pearson et al. 1986; Waters 

1992:279). Depending on the sediments within the survey area, features such as channels, 

channel margins, infilled sediments, levees, and inset terraces can be observed as significant 

depositional events based on their reflective properties. Channel margins and inset terraces may 

exhibit greater consolidation than surrounding sediments, appearing as more reflective horizons 

than under-, or overlying sediments. Channel fill, however, can be more difficult to identify, 

depending upon the degree of consolidation and grain sizes constituting the fill. Well-stratified 

channel fill, deposited slowly over time, or allowed to naturally dewater and compact, will 

appear as parallel to subparallel, distinct reflectors inside the channel margins. Channel fill that is 

deposited quickly, or contains a high degree of sand or deltaic material is less likely to reflect the 

acoustic signal and in some cases may appear as a distinct acoustic void, blanking out all 

underlying strata within an otherwise stratified sediment profile (Edgetech 2003:1–10; Wille 

2005:53). Once channel margins and thalwegs (the site of maximum depth of entrenchment 

within the channel) are identified along survey lines, the channels can be extrapolated across 

survey lines, delineating their horizontal extent. Related features such as levees and inset terraces 

are then identified within the overall channel pattern. Feature depths can be calculated as depth 

below the seafloor (BSF) and depth below sea level (BSL) using half of the average speed of 

sound in two-way time travel, or 750 meters per second (m/sec) (1/2 1,500 m/sec average speed 

of sound in salt water). Depth BSF is calculated as the product of time in milliseconds (ms) at the 

feature of interest multiplied by 0.75 m (2.46 ft.). Depth BSL is calculated by adding the depth 

BSF to the water depth at the interpreted feature. Approximate dates can be determined for an 

interpreted feature by plotting depth BSL on a local sea level curve appropriate to the survey area 

to determine the approximate time of exposure. 
47

5.1.4 Survey Methodology 

Study areas for this project were selected after reviewing a total of 204 shallow hazard and 

archaeological NTL-compliant surveys on file with BOEM. The only other study to survey and 

physically sample sediments on the northwestern GOM OCS for evidence of prehistoric 

exploitation was centered in the Sabine Pass, High Island, and Galveston Areas, in water depths 

ranging from 8 m (27 ft.) to 12 m (40 ft.) (Pearson et al. 1986). To complement the previous 

project, this survey review specifically targeted survey reports in which features were located at 

depths ranging from 15 m (50 ft.) to 40 m (130 ft.) BSL. The original maps, data samples, and 

geologic and archaeological interpretation were reviewed for each report. Existing surveys were 

searched in order to find sub-bottom features that resembled high-probability areas for 

prehistoric site occurrence and preservation (as defined in Chapter 4). When possible, preference 

was given to features based on the availability of the original sub-bottom data. Finally, survey 

features of interest were ranked by their relative depth below the seafloor, with preference given 

to sites closer the seafloor surface (less than 2 m [6.5 ft.] below) and, therefore, more accessible. 

This ranking was done to facilitate future excavation or data recovery in selected survey areas if 

physical sampling indicated a probable anthropogenically modified environment.

The selected study areas were initially identified from industry surveys that utilized between 50-

and 300-m (164- and 984-ft.) survey line spacing for acquisition of sub-bottom data.

Supplemental tie lines were collected perpendicular to the primary survey lines at 900-m (2,952-

ft.) intervals for correlation of geologic features, as required by NTL 2005-G07. New 

geophysical survey grids were designed explicitly for research purposes using grid spacing of 25 

m (82 ft.). The centerline of each new survey usually was designed to reproduce the original 

survey line from which the feature was originally identified, with additional parallel lines to 

either side. Strike lines were designed perpendicular to the primary survey lines, and also utilized 

25-m (82-ft.) line spacing. The 25-m (82-ft.) line spacing was deemed necessary for research 

purposes based on recommendations published in 1982. According to Gagliano et al. (1982) 

survey intervals should be designed with the relative size of the sought after target in mind. The 

need for close interval survey was demonstrated using the example of terrestrial analogues 

within an offshore survey grid. Magnolia Mound, one of the largest recorded shell midden sites 

in Louisiana, was superimposed onto a 150-m (492-ft.) sub-bottom profiler survey grid. It should 

be noted that the line spacing for this hypothetical grid is half the 300-m (984-ft.) line spacing 

maximum allowed for industry NTL-compliant surveys. When placed on the 150-m (492-ft.) 

grid, the Magnolia Mound was intersected by one survey line only (Gagliano et al. 1982:113). 

The first objective of geophysical survey for this study was to relocate the originally reported 

feature; the second objective was to obtain more detailed information about the geographical 

environment by conducting close interval survey around the feature. Four discrete landforms 

were selected for use in this study: two located in High Island Area (HI), and two in Galveston 

Area (GA) based on review of the existing survey reports. 

Geophysical survey was conducted from the R/V Acadiana, an 18-m (59-ft.) survey vessel 

owned and operated by the Louisiana Universities Marine Consortium (LUMCON) out of 

Cocodrie, Louisiana. The vessel is equipped with an A-frame on the back deck, which was used

for deployment of the sub-bottom towfish (Figure 5.2). An Edgetech 3100 series SB-216 sub-
48

bottom profiler with variable chirp frequency settings was selected for this survey work. An 

independent Trimble unit provided differential global positioning system (DGPS) data via the 

U.S. Coast Guard (USCG) WAAS signals to an EZNav navigation system for positioning of the 

towfish. Setback from the antennae to the towfish was entered into EZNav and no cable changes 

were made during individual survey lines. Digital data were recorded using CODA for 

acquisition, post-processing, and interpretation. Equipment was dry-tested to ensure that the 

correct navigation string was input from the navigation system directly into the digital 

acquisition system, and that the chirp signal was emitting from the transducers before 

deployment. The sub-bottom towfish was towed by a Kevlar-reinforced soft data cable, and 

deployed over the stern of the vessel using the survey vessel’s A-frame and winch. 

Recommended tow speeds vary from 3 to 5 knots for this sub-bottom unit model, and the 

Acadiana typically operated at 4 knots. All survey work was conducted between 12 July and 22

July 2008. 

Figure 5.2. R/V Acadiana at the LUMCON dock.

5.2 PHYSICAL SAMPLING

Geophysical survey has been used regularly for the last 40 years to identify sub-surface features 

in marine environments (Blondel 2009; Wille 2005). Measurements of the speed of sound allow 

for accurate measuring of feature depths, but acoustic data, with the exception of sonar 

backscatter, is largely qualitative, or more specifically, relative within a specific data set.

Changes in acoustic impedance may result in the identification of sedimentary episodes, but the 

stratigraphic sequence is relative to differing densities of the profiled sediments and does not 
49

provide definitive sediment age or date of deposition. Physical samples are therefore required to 

provide additional data that can either refute or confirm an interpretation based initially on 

geophysical data.

Ocean cores are recognized for their potential to contribute to climate and geologic 

reconstruction studies. Historically, core acquisition was dependent upon development of a 

practical means of recovery, such as Kullenberg’s invention of the piston corer in the 1940s (Catt 

1986:16). Sediments captured stratigraphically within cores can be tested using a number of 

different methods to develop both relative dating chronologies and absolute dates. Relative 

chronologies are often tied to temperature or climatic fluctuations. An early method of 

determining climate fluctuation was to measure and plot the relative proportions of species of 

temperature-sensitive foraminifera in the sediments (Catt 1986:16). Emiliani developed a 

technique for determining previous water temperatures from the oxygen isotope ratios (18O/16O) 

measured in fossilized foraminifera recovered from core sediments (Catt 1986:17). Radiocarbon 

dating produces absolute dates that are used to anchor relative chronologies constructed using 

other methods within core samples for archaeological studies in the GOM region. Radiocarbon 

dating is effective only until approximately 40,000 yrs BP, which far exceeds the known dates of 

human occupation in the region (Catt 1986:17). 

There are two basic bottom sampling methods for the collection of cores. Cores may be obtained 

from a platform (such as piston cores or vibracores), or collected by divers (including push cores 

and box cores) (Mudroch and Azcue 1995:48). Sediments sampled by divers have been shown to 

retain greater integrity than those sampled remotely (Mudroch and Azcue 1995:54). As described 

by Mudroch and Azcue (1995:54), a comparison of sampling methods used in the study of 

meiobenthos found greater numbers of specimens in the cores collected by divers due to 

disturbance of the sediments during gravity, or drop, core acquisition. According to Mudroch and 

Azcue (1995:54), gravity cores create downwash as they fall through the water column, which 

disperses a significant portion of the superficial sediments, resulting in a biased sample. It must 

be noted that there is no universal bottom sediment sampler; the coring method used must be 

selected with regard to the dominant type of sediment that will be sampled and the desired depth 

of core penetration (Mudroch and Azcue 1995:55).

Actions before and during sediment sampling can alter the physical composition of the 

sediments, which can skew the data analysis results (Mudroch and Azcue 1995:56). Disturbances 

can stem from many actions. In shallow water, vessel movement can create a current that 

disturbs the uppermost sediment layer (Mudroch and Azcue 1995:56). Other sources of 

disturbance may include a pressure wave generated by placement of the coring device, a less 

than vertical coring sleeve that results in a skewed profile, washout of sediments, or sediment 

loss during core retrieval (Mudroch and Azcue 1995:56).

Previous physical sampling of the OCS for prehistoric resources included the use of 12 m (40 ft.) 

cores deployed from a jack-up barge (Pearson et al. 1986). A total of 76 cores were collected at 

that time, with the potential for maximum recovery of 921 m (3,040 ft.) of sediment; actual 

vertical core penetration was 550 m (1,815 ft.) (Pearson et al. 1986:79). Water content and 

sediment compaction were hypothesized to impact the total amount of sediment recovered within 

each core. Sediment content down the core from open ocean samples increases as the water 
50

content decreases. According to Mudroch and Azcue (1995:66), fine-grained sediments in the 

uppermost 20 cm (8 in.) contain 70–80% water, and sediments between 30 and 40 cm (12 and 16 

in.) below seafloor contain 50–60% water. Sediments below 50 cm (20 in.) are typically more 

compacted and exhibit minimal changes in water content (Mudroch and Azcue 1995:66). 

Sediment recovery within the cores acquired for the 1986 study ranged from 34% to 78%; 

average recovery was 55% (Pearson et al. 1986:79).

The degree to which sediment disturbances caused by sampling procedures impact data 

interpretation depends upon the type of analysis being conducted (Mudroch and Azcue 1995:67). 

Contamination profiling or monitoring is dependent upon accurate sampling to the subcentimeter, and requires that the uppermost sediments be captured during the sampling process 

(Mudroch and Azcue 1995:67). Piston corers generally can recover cores ranging 3–20 m (10–66 

ft.) in length with minimal sediment disturbance within the sample (Mudroch and Azcue 

1995:76). They are not appropriate for contaminant sampling, or other studies that require intact 

sediments from the uppermost sediments due to loss of material during the sampling procedure,

but are appropriate for landscape reconstruction that extends several meters below the seafloor 

(Mudroch and Azcue 1995:76).

When cores are collected in areas with sandy, unconsolidated sediments, vibracores are better 

able to penetrate the sediment and recover samples that may be used in geotechnical and 

structural assessments (Mudroch and Azcue 1995:76). Vibration is “the most popular and 

successful technique for increasing the penetration depth of a platform sampler” (Lee 1985:195). 

Vibration can be produced in a single direction by counter rotating pistons, hammers, or 

eccentric weights (Lee 1985:196). Disturbance is expected within vibracore sediment samples 

but has not been found to significantly affect stratigraphy, grain size, or Atterberg limits (Lee 

1985:197). Additionally, vibracore sediment penetration rates may provide rough estimates of in 

situ soil strength (Lee 1985:197), which may be used to infer sediment type and water content. 

Surface procedures further impact the quality of acquired core sediments. Collected cores need to 

be capped on both ends immediately during or following retrieval to the surface to prevent the 

loss of material (Mudroch and Azcue 1995:126). If the core liner is made of clear plastic, “the 

appearance of the sediment core should be recorded prior to subsampling, along with other 

features such as the length of the core; sediment color, texture, and structure; occurrence of 

fauna; etc. (Mudroch and Azcue 1995:126).” Long cores can be sectioned laterally into smaller 

pieces for ease of transportation and/or storage (Mudroch and Azcue 1995:126). In the lab, cores 

that have been sectioned longitudinally and labeled can be wrapped to preserve sediment 

stratigraphy and moisture content, and stored for months (Mudroch and Azcue 1995:142–144).

5.2.1 Coring Methodology 

A total of thirty cores were collected for this research project from the areas previously 

investigated through acoustic survey. It was expected that cores would be acquired from a matrix 

of sand, silt, and clay, therefore a vibracore platform was chosen for maximum penetration depth 

within these various sediment profiles. Given that previous cores for prehistoric archaeological 

research averaged just 55% sediment recovery within a 12 m (40 ft.) core sleeve (Pearson et al. 
51

1986:79), it was decided that a vessel-mounted coring rig with a 6 m (20 ft.) core sleeve would 

be sufficient to capture the strata of interest, and be more cost-effective than coring from a jackup barge. At three of the four sites, at least one core was acquired from the originally interpreted 

feature (see Chapter 7); the remaining core locations were selected from the interpreted 

geophysical data (detailed in Chapter 6). The coring methodology was designed to be inherently 

flexible; the methodology had to be adaptable depending upon observed sediments or possible 

features identified in the field. It was planned that ,if a shell midden was encountered, additional 

cores would be acquired from that location in order to provide sufficient data to determine if the 

feature was natural or anthropogenic. 

Coring operations were conducted from 24 June to 3 July 2009 on board the motor vessel (M/V)

Thunderforce, a dedicated coring vessel operated by American Vibracore Services (Figure 5.3). 

The M/V Thunderforce is a 26-m (85-ft.) long, steel-hulled vessel with twin 12-71 diesel 

engines, a removable stern rail, and a 10,000 lb. stern-mounted A-frame. Coring site coordinates 

were prepared from differential global positioning system (DGPS)-integrated digital sub-bottom 

data with navigation data in the NAD27 state plane coordinate system (SPCS) X/Y (easting and 

northing) pairs and converted to WGS84 Latitude and Longitude in decimal minutes for

integration with the coring vessel’s Nobeltec ProTM software. The Nobeltec ProTM system 

received differential signals provided via Wide Area Augmentation System (WAAS) and U.S. 

Coast Guard (USCG) Reference Station Networks operated by the U.S. Department of Defense 

(DOD). 

The coring rig consisted of a pneumatic vibracore unit with a 6 m (20 ft.) drill pipe and 20 cm (8 

in.) drill bit. Clear, plastic, 10-cm (4-in.) diameter core sleeves were inserted into the drill pipe. 

Following core acquisition the drill bit was removed from the pipe, and sediments from the drill 

bit were collected. The core sleeve was extruded from the drill pipe and cut into pre-determined 

lengths of 0.9 m or 1.2 m (3 ft. or 4 ft.) depending on whether the core was to be frozen (0.9 m [3 

ft.]) or stored in the climate-controlled lab (1.2 m [4 ft.]). Each core section was capped, labeled, 

and measured as soon as it was removed from the drill pipe. 

Figure 5.3. M/V Thunderforce with stern-mounted A-frame, as seen 

from starboard.
52

The vessel was positioned above each core location as a “live boat”—no anchors were set. The 

coring rig was lifted from the back deck of the vessel and lowered into position on the seafloor 

using the vessel’s stern-mounted A-frame and winch (Figures 5.4 and 5.5). The pneumatic 

vibracore was powered by a surface-supplied air compressor. Core penetration depths and rate of 

penetration were monitored on the vessel using a penetrometer connected to a laptop computer 

and recorded when possible.

Figure 5.4. Pneumatic vibracore rig on 

the deck of the M/V Thunderforce.
53

Figure 5.5. Pneumatic vibracore rig 

being lifted on the deck of the M/V 

Thunderforce.

On Saturday, 27 June and Sunday, 28 June 2009, a total of six (6) cores were acquired south of a 

previously reported feature in High Island (HI) lease block 160, where water depths are 

approximately 15 m (49 ft.) BSL. Due to confusion over the location of the Shell 4-inch pipeline 

(Segment No. 2834), which was reportedly located approximately 9 m (30 ft.) due north of the 

reported feature, coring options at the HI 160 grid were limited (see Chapter 6, Section 1). The 

pipeline is listed as abandoned in place, meaning it should be empty of all remaining product.

However, permission could not be obtained from the pipeline’s listed owner before operations to 

allow coring within 150 m (492 ft.) of the pipeline. Due to safety operating procedures, the 

coring vessel also required that operations maintain a 150 m (492 ft.) radius away from the 

published position of the pipeline. This meant that alternate coring locations had to be selected in 

the field to substitute for the desired core locations originally planned over the feature of interest. 

The presence of the Shell 3-inch pipeline (Segment No. 2832) located to the north of Segment 

No. 2834 further limited coring options to the north of the reported feature; therefore, all cores 

were collected south of the reported shell midden. 

On Sunday, 28 June, a total of five (5) cores were acquired from features in HI 178 where water 

depths are approximately 12–15 m (39–49 ft.) BSL (Figure 5.6). One of the pre-planned core 

sites (core no. 4) was located approximately 412 m (1,352 ft.) inside the eastern boundary of a 

dedicated Fairway. Approval could not be obtained from the U.S. Coast Guard and the Captain 

of the Port of Houston to conduct coring at this location. Core no. 4 was a low priority location

and was removed from the coring plan, and replaced with an alternate core location selected in 

the field. 
54

Figure 5.6. Sediment color variations are visible in High 

Island 178, core no. 5, sections A–E.

On Monday, 29 June and Tuesday, 30 June, a total of nine cores were acquired from and in the 

vicinity of a previously reported possible archaeological feature in Galveston (GA) lease block

356, where water depths are approximately 26–27 m (85–89 ft.) BSL. On Tuesday, 30 June and 

Wednesday, 1 July, a total of ten (10) cores were acquired from features in GA 426 where water 

depths are approximately 27–31 m (89–102 ft.) BSL. Following acquisition of core no. 1 in GA 

426, moderately-sized shell fragments were observed in the drill bit (Figure 5.7). 

Figure 5.7. Shell fragments recovered in the drill bit from core no. 1, GA 426. 

 

Based on the identification of shell fragments in the drill bit section of core no. 1, the decision 

was made in the field to acquire additional cores at that location. While attempting to core a 

second time at core no. 1 (labeled as Core no. 9), the crew experienced difficulty with the 

penetrometer cable. Failure of the penetrometer meant that field personnel were unable to verify 

core depths during drilling. Core no. 9 achieved a maximum penetration of 4.6 m (15 ft.) below 

the seafloor (BSF), missing the observed feature from core no. 1 which had a maximum depth of 

5.8 m (19 ft.) BSF. Various repairs were attempted on the penetrometer, and two additional cores 
55

were acquired at this same location (cores no. 10 and no. 11). The decision to acquire more 

samples from the shell feature was made to provide a sufficient sample size to determine if the 

observed shell deposit is natural or anthropogenic (Figure 5.8). 

Figure 5.8. Shells observed in GA 426 core no. 10, between sections D and E. 

Following core acquisition at GA 426, the project wrapped up after having acquired, sectioned, 

capped, labelled, and inventoried thirty cores. The vessel returned to Port Fourchon, Louisiana 

and the cores were offloaded for immediate transport to the H.J. Walker Geomorphology Lab at 

Louisiana State University (LSU). Refrigerated cores were transported inside a separate vehicle 

and immediately placed in cold storage at LSU. The remaining cores were unloaded at the 

Walker Lab for sampling and analysis.

5.3 SEDIMENT ANALYSIS METHODOLOGIES

Before being opened, all individual core sections were run through a Geotek multi-sensor core 

logger (MSCL) by lab assistant Jennifer Gardner at the LSU School of Coast and the 

Environment. The MSCL recorded primary wave (P-wave) velocity and magnetic susceptibility 

(as volume-specific values). P-wave velocity was recorded as μsec (seconds per foot) and 

processed to calculate the speed of sound through the various strata as m/sec. These data were 

used to correlate sediment strata with their measured depths as estimated from the acoustic 

profile data. Volume-specific measurements of magnetic susceptibility were recorded to identify 

stratigraphic sequences within the sediment profile, and specifically any data irregularities (or 

spikes) that could indicate an erosional unconformity. The core logger is equipped with a 10 cm

(4 in.) sensor for recording magnetic susceptibility measurements. Following core logging, all 

cores were returned to the Walker lab where they were sectioned longitudinally. One half was 

immediately wrapped in plastic core sleeves, labeled, and sealed as an archived sample. The 

other half was photographed in the lab, and logs were made describing each section’s 

stratigraphy, Munsell color, sediment type (based on qualitative data), horizon thickness, and any 

observed inclusions. Cores were subsampled for additional analyses, including measurements for 

grain size, magnetic susceptibility, and carbon dating. Additional research was undertaken by 
56

specialists analyzing preserved pollen and foraminifera, and performing Fourier Transform 

Infrared (FTIR) spectroscopy (Appendix C). 

5.3.1 Grain Size Analysis 

The extensive literature regarding the sediment distribution on the OCS of the GOM indicates 

that the sediments between the Mississippi Delta and the Mexican border are one of two types; 

transgressive nearshore sands or shelf muds (Curray 1960; Balsam & Beeson 2003). More 

specifically, the OCS of Texas, Louisiana, Mississippi, Alabama, and north Florida is dominated 

by river-transported terrigenous sediments. Major portions of the Texas and Louisiana shelf are 

covered with clay and varying amounts of sand, silt, and organics (Allison et al. 2000; Gordon et 

al. 2001; Balsam & Beeson 2003; Ellwood et al. 2006).

The areas investigated as part of this study are located offshore Texas and Louisiana, and the 

most likely sediments to be analyzed are principally quartz sands and muds. The latter are 

modern, suspended, and transported during river high-flow stages, storms, and hurricanes, and 

preferentially deposited during calm conditions. Sand layers are predominantly relict and 

deposited near the coastline by transgressive events (Curray 1960) or can be attributed to and/or 

reworked by storms or hurricanes. Limited sandy sediment is being supplied to the nearshore or 

shelf areas at the present time (Bentley et al. 2002). Grain size is an important indicator in 

reconstructing sedimentary structures and the controlling “hydrodynamics of deposition” (Wells 

2001:157). Specific environments exhibit distinct sedimentary characteristics, which can be 

identified through grain size. Peat deposits exhibit high percentages of very-fine clay and silt;

mudflats contain a combination of clay, silt, and molluscan fauna; and marsh sediments contain 

highly organic sand to clay (Wells 2001:159–162).

Grain size samples were collected from units identified during preparation of core descriptions 

(from Munsell colors) to refine the final core log. Samples were collected and placed into labeled 

Whirl-Pak® bags. Grain size analysis was conducted by lab assistant Cory Sills using a laser 

particle counter at the LUMCON facility. Results were exported into MS Excel; both median and 

mean grain sizes were calculated following procedures outlined by Folk (1980) and Shackley 

(1975).

5.3.2 Magnetic Susceptibility 

Magnetic susceptibility measurements can be described generally as a measurement of the 

concentration of iron-containing grains within a sediment sample (Thacker and Ellwood 2007). 

Magnetic susceptibility should not be confused with remnant magnetization, which is used to 

determine polarity and measured in areas devoid of a magnetic field (Ellwood and Burkart 1996; 

Ellwood et al. 2004). According to Thacker and Ellwood (2007:164), geological studies of

magnetic susceptibility are possible because soil minerals, especially iron-rich sediments, “are 

more easily magnetized in the presence of an inducing magnetic field.” In archaeology, magnetic 

susceptibility has been used to identify anthropogenic activities such as organic refuse disposal 

and repeated burning, as occurs in hearths (Evans and O’Connor 1999). A different application 
57

of magnetic susceptibility, however, may aid in linking local data from submerged contexts to 

regional data sets. Measurements of magnetic susceptibility may be used to develop a proxy 

record of climate conditions within a sediment profile, facilitating relative dating of strata, and 

reconstruction of diachronic changes in a given area. 

Soil forming processes, or pedogenesis, are controlled by five variables: climate, the activities of 

organisms within the sediment profile, relief, parent material, and time (Goldberg and Macphail 

2006). Chemical changes during pedogenesis can result in mineral oxidation and in situ

development of magnetic grains and iron oxides including magnetite and maghemite (Ellwood et 

al. 2004; Ellwood and Burkhart 1996). There is a direct relationship between magnetic 

susceptibility and the amount of iron-containing grains in a given sediment sample; generally, 

the higher the amount of iron-containing grains, the higher the measurement of magnetic 

susceptibility (Ellwood and Burkart 1996). 

Pedogenesis and eolian (wind-blown) processes are the two primary mechanisms controlling 

deposition of sediments resulting in an observable magnetic susceptibility trend. Magnetic

susceptibility levels can be impacted by other processes that can potentially alter the observed

climate trend. These include deposition from other sources, such as alluvial (water-born) 

systems, unconformities caused by non-deposition or erosion, or post-depositional mixing or 

alteration (Harrold et al. 2004). 

Climate, as previously stated, is one of the five controlling factors for pedogenesis, with 

temperature and moisture playing important roles in determining rates of pedogenesis (Goldberg 

and Macphail 2006; Ellwood et al. 2004). Increases in temperature and moisture typically result 

in increased production of magnetite and maghemite (Ellwood et al. 2004). Variations in climate 

can therefore be inferred from sediment stratigraphy as variations in the amount of magnetic 

grains, and therefore the measure of magnetic susceptibility (Ellwood et al. 2004). The use of

magnetic susceptibility in archaeological projects has demonstrated the utility of correlating local 

site magnetic susceptibility curves with global climate patterns (Ellwood et al. 2004; Thacker 

and Ellwood 2007). 

Magnetic susceptibility has been used in archaeological studies, but it must be noted that

magnetic susceptibility data have inherent limitations—in and of itself, the data will only result 

in a relative curve of conditions and change. Magnetic susceptibility data do not, by themselves, 

indicate an age for the sampled sediments nor do they provide absolute temperature values 

(Thacker and Ellwood 2007). Magnetic susceptibility data can be used to create a general pattern 

of warmer versus cooler climate trends, creating a relative dating profile that must then be tied to 

the stratigraphic record using radiometric or biological absolute ages (Thacker and Ellwood 

2007). 

Climate correlation using magnetic susceptibility data works in a variety of environmental 

settings. Measurements of magnetic susceptibility from Chinese loess deposits were used to 

create a data curve that directly correlated with the marine oxygen isotope record developed by 

Imbrie et al. (Ellwood et al. 2004). In the Chinese loess data, higher magnetic susceptibility 

levels correlated with a warmer and wetter climate, while lower values correlated with relatively 

colder and drier climate conditions (Ellwood et al 2004). In this same example, pedogenesis was 
58

the main source of deposition within the warmer climate sediments, while eolian deposition 

accounted for sediments with the lower measured magnetic susceptibility values deposited 

during colder climate periods (Ellwood et al 2004). In a separate application, sediment data from 

Hall’s Cave, Texas demonstrated that magnetic susceptibility data were a more accurate 

indicator of the end of full glacial climate conditions than sediment lithology (Ellwood and Gose 

2006). 

According to Holliday (2004), magnetic susceptibility is useful for determining buried soils, 

especially in areas with thick, stratified sequences. Although Holliday specifically refers to the 

utility of magnetic susceptibility in correlating stratified soils within loess deposits, formerly 

exposed sediments on the OCS can exhibit well-preserved stratified layers (Figure 5.9). 

Figure 5.9. Sub-bottom profiler data sample of stratified sediments within a relict river 

channel offshore Galveston.

Vertical scale lines are in 150-m (492-ft.) intervals; horizontal scale lines are in 10-ms (25-ft) 

intervals. (Image courtesy Tesla Offshore, LLC.)

Magnetic susceptibility data have proven effective in studies of marine sediments (Ellwood et al. 

2006). A study of magnetic susceptibility values measured from surface sediment samples 

throughout the GOM allowed researchers to model sediment flow and distribution in the offshore 

environment (Ellwood et al. 2006). Sediment profiles on the OCS consist of modern marine 

sediments overlying buried soils (Bernard 1970; Coleman and Roberts 1988; McClelland 

Engineers 1979). Existing estimates of middle to late Holocene sediment overburden state that 

thickness ranges from less than 1 m (3 ft.) to approximately 8 m (26 ft.) along portions of the 

OCS near the Texas-Louisiana border (Bernard 1970; McClelland Engineers 1979; Berryhill 

1984). 

One of the limitations in using magnetic susceptibility data is the potential for disruption of 

observable climate trends (Harrold et al. 2004). According to Harrold et al. (2004) disruptions 

can be caused by unconformities within the sediment profile, post-depositional mixing, and 

deposition from fluvial (river or stream) systems. All of the potential sources for disruption are 

anticipated within a sediment profile of a fluvial landform that underwent shoreline 

transgression. Although these disruptions may restrict the ability to use the magnetic 

susceptibility data to correlate climate change, it may be possible to correlate the expected 
59

unconformities or disruptions across multiple samples to determine the local expression of 

regional climate events. 

Sediment samples, depending on the core, were collected either continuously or at regular 

intervals from a vertical sediment column in 2 cm3 plastic sampling boxes. Materials such as 

limestone, bone, or calcium create mass within a sample but are non-magnetic and not related to 

climate change (Thacker and Ellwood 2007). Samples in this study were not screened prior to

magnetic susceptibility measurement; therefore, samples that include these types of materials 

may produce artificially lower magnetic susceptibility values (Thacker and Ellwood 2007). 

Samples were weighed and normalized for mass. Mass-specific measurements were chosen as a 

supplemental analysis for this study because volume-specific measurements, such as those 

recorded during core logging, can introduce unnecessary error to the interpretation because of 

potential sediment compaction within samples (Thacker and Ellwood 2007). Prepared samples 

were measured using a balanced coil induction system, also referred to as a susceptibility bridge 

(Dearing 1994; Thacker and Ellwood 2007). The magnetic susceptibility bridge was calibrated 

daily, as well as after several hours of continuous measurements within the same day, using 

values from the National Bureau of Standards or other conventional sources (Ellwood and 

Burkhart 1996). 

5.4 Presentation of Results

The results of site-specific acoustic survey and coring and sediment analyses are presented in the 

following chapters (Chapters 6 and 7). These results are supplemented with data provided by 

other researchers (e.g., Warny et al. 2012, Appendix C) and from samples sent to commercial 

labs for preparation and analysis (Appendices C and D). Following core logging, organic 

samples appropriate for radiocarbon, or 14C dating, were selected from individual cores. 

Radiocarbon dates were obtained from shells, charcoal, and sediment samples. Sub-samples were 

not collected from every individual core, but were collected from all four geographic areas from 

which cores were collected (HI 160, HI 178, GA 356, and GA 426). Samples were sent to Beta 

Analytic Inc. for radiocarbon dating and are detailed in the following chapters. Pollen samples 

were acquired from cores within the HI 178 and GA 426 survey grids to provide additional detail 

about environments that were initially identified as possible operational environments. 

61

6. SUB-BOTTOM PROFILER DATA

Multiple data sets were available for review and used as part of this study. A total of 204 

industry surveys completed under NTL survey guidelines (NTL-compliant) were initially 

reviewed in order to select locations with possible archaeological features for further study. 

References are cited for the industry survey on file with BOEM, with the archaeologist’s name 

given first (in the case of an archaeological and shallow hazards combined report). Where 

multiple data sets are referenced, the data are referred to by the year in which they were 

acquired; however, in some cases the final report on file with BOEM (and cited in the references 

for this report, Chapter 10) has a later date. Areas selected for survey represent targeted depths of 

15–35 m (49–115 ft.) BSL, and are located in High Island (HI) Area lease blocks 160 and 178, 

and in Galveston Area (GA) lease blocks 356 and 426.

6.1 HIGH ISLAND AREA 160

A possible shell midden was identified in Block 160, High Island Area, during an archaeological 

and shallow hazard survey in the spring of 1995 and reported to the MMS (now BOEM and 

BSEE) (Landry and DuVal 1995). The original survey data were not available for review as part 

of this study, but copies of the original survey report that identified the feature (Landry and 

DuVal 1995), and a subsequent lease survey report that included a sub-bottom data assessment 

over the southwestern half of Block 160 (Saltus and El Darragi 2002) were made available. 

Acoustic (sub-bottom) profiling data was collected as part of the current scope of work and was 

acquired in 2008. Supplemental acoustic profiles and magnetometer data were collected in 2011 

for use in this study.

 

The 1995 report was based on an assessment of survey data over the northeastern portion of 

Block 160, and included 3.5 kHz pinger sub-bottom profiler data acquired at 50-m (164-ft.) 

intervals along survey lines that were arbitrarily oriented north-south (Landry and DuVal 1995). 

According to the sub-bottom data assessment, the pinger system resolved approximately 14.5 m 

(48 ft.) of sediment below the seafloor; data quality was intermittently compromised by the 

presence of interstitial gas (Landry and DuVal 1995:21). From the report, Landry and DuVal 

(1995:26) state:

In the southwestern portion of the survey area in Block 160, on Line 55, a moundlike acoustically amorphous feature was recorded adjacent to a well preserved 

relict channel on the edge of the terrace. It is a single line event. The mound is 

about 115 feet wide and about 8 feet high. It is buried below 12 feet of sediment. 

This feature may represent a prehistoric shell midden. It should be avoided.

According to the archaeological interpretation, the shell midden was located on the younger of 

two observed Deweyville terraces. Buried channels with margins at observed depths of 2.7–7.6 

m (9–25 ft.) BML were recorded to the south of the feature, and Deweyville/Holocene floodplain 

deposits (3–13 m; or 10–42 ft. BML) are located to the north (Figures 6.1.1 and 6.1.2). Based on 

regional studies, this area is reported to have been submerged by 6,500 yrs BP (Landry and 
62

DuVal 1995:24), and could therefore have been available to Paleoindian and Early Archaic 

populations.

Figure 6.1.1. Annotated pinger profiler image of survey line 55 shows the levee feature 

(circled in yellow) identified in 1995.

Vertical scale lines are in 150-m (492-ft.) intervals; horizontal scale lines are in 7.5-m (25-ft.) intervals 

(modified from Landry and DuVal 1995).

Figure 6.1.2. Annotated interpretation map of HI 160 near the reported shell midden; map is oriented 

north up.

(Modified from Landry and DuVal 1995.)

A second NTL-compliant survey was consulted as part of this study (Saltus and El Darragi 

2002). Although the 2002 survey area did not overlap with the 1995 survey, the two grids are 

contiguous, and the sub-bottom assessment provided independent verification of the presence 

and approximate depths of the buried channels interpreted from the 1995 data set. The 2002 

survey data were not available for review, and the report included few sub-bottom data examples 

(Saltus and El Darragi 2002).
63

A new survey grid was designed around the interpreted feature in order to relocate the reported 

shell midden and to provide close-interval data around the midden to determine its spatial extent. 

The new survey grid was centered on the interpreted shell midden, with survey lines oriented 

north-south and east-west. In addition to the survey lines originally planned, additional survey 

lines were added in the field. The resulting data were interpreted digitally and contoured. 

Significant heave was recorded on the sub-bottom profiles that could not be processed out of the 

survey data, therefore supplemental survey lines (501–510) were designed for use in illustrating 

the data in this report. These lines were recorded by Tesla Offshore’s survey vessel M//V Nikola

in 2011 while in transit between regularly scheduled work at no cost, and included magnetometer 

data acquisition (see Chapter 7, Section 1 for magnetometer discussion).

The sub-bottom profiling data acquired as part of this scope of work recorded a feature similar in 

appearance and location to the interpreted shell midden identified in 1995 (Figure 6.1.3). The 

feature was clearly visible on survey lines 504, 505, and 506, which were oriented north-south 

along the same axis as the 1995 survey data. According to the 1995 report, the midden was 

recorded on a single survey line and was not visible on the adjacent survey lines located 50 m

(164 ft.) to the west and east. The 1995 midden measured 35 m (115 ft.) along-track (north to 

south) and had approximately 2.4 m (8 ft.) of measured relief. It was buried approximately 3.7 m 

(12 ft.) below the seafloor. The 1995 data did not have any tie lines located near the reported 

shell midden, therefore the east-west extent of the feature was estimated at less than 100 m (328 

ft.), based on its absence in the adjacent survey lines.

Figure 6.1.3. Annotated sub-bottom profiler image of survey line 504 shows a feature 

similar to the interpreted shell midden (circled in yellow) originally identified in 1995. 

Vertical scale lines are in 150-m (492-ft.) intervals; horizontal scale lines are in 7.5-m (25-ft.)

intervals; data have been reversed horizontally to appear in the same orientation as the 1995 data 

for direct comparison; north is at left. 

The survey grid designed for the current study included both north-south and east-west survey 

lines across the reported shell midden. As stated above, the midden-like feature was apparent on 

survey lines 504, 505, and 506 (oriented north-south). The feature measured between 

approximately 42 m (140 ft.; line 504) to approximately 31 m (100 ft.; line 506) in length along

the north-south track. The feature has approximately 1.5–2.4 m (5–8 ft.) of relief and is buried 
64

approximately 3.9–4.9 m (13–16 ft.) below the seafloor. Perpendicular survey lines 508 and 509 

intersected the feature along an east-west axis, and revealed a much larger feature than 

previously interpreted (Figure 6.1.4).

Figure 6.1.4. Annotated sub-bottom profiler image of survey line 509 shows the west (left) to east 

(right) extent of the midden-like feature (circled in yellow).

The feature measures approximately 94 m (310 ft.) in length along the east-west oriented track and is 

approximately 5 m (16 ft.) BML. Vertical scale lines are in 150-m (492-ft.) intervals; horizontal scale 

lines are in 7.5-m (25-ft.) intervals.

The midden-like feature was not observed on survey line 510 (located 25 m [82 ft.] north) or any 

of the other adjacent survey lines. It is possible that the feature, which appears to taper on the 

ends, is not acoustically distinguishable from the surrounding sediments on additional survey 

lines. Based on measurements from the east-west survey lines the feature is approximately 46 m 

(152 ft.) along-track on survey line 508, increasing to approximately 95 m (312 ft.) along-track 

on survey line 509, with approximately 1.5–1.8 m (5–6 ft.) of relief, and is buried approximately 

4.9 m (16 ft.) below the seafloor. The feature appears to have dual peaks (one on each end; 

Figure 6.1.4); however, this may be due to vertical exaggeration of the acoustic data display as 

opposed to an accurate representation of the feature’s preserved shape.

Based on the sub-bottom data acquired as part of this project’s scope of work, it appears that the 

reported midden is located along a topographic ridge between an entrenched channel system to 

the south and a floodplain to the north (Figure 6.1.5), which correlates with the interpretation 

discussed the 1995 report. The midden was originally recorded on a single survey line; however,

the data acquired as part of this study indicate that the feature is significantly larger, oriented 

along a northwest to southeast axis, and measures approximately 152 by 53 m (500 by 175 ft.) 

overall (Figure 6.1.5).
67

Figure 6.1.5. Contours depict the survey area as interpreted from all available data.

The 1995 shell midden location is indicated by the red diamond; the red shaded area in the inset shows the 1995 

location within the context of the midden as interpreted from the new data. The survey lines are superimposed over the 

channel system in black. Depths are in meters below the seafloor; north is at top.
68

Sediments deposited on top of the midden feature appear to drape over the structure and do not 

appear to have eroded the midden. Sediments overlying the associated channels are observed to 

sag into the entrenched channels. The observed sagging indicates that the overlying sediments 

were deposited quickly, or subaqueously; in both cases the sediments did not have sufficient time 

to de-water and compact prior to conversion of the area into an open marine system (Figure 

6.1.6).

Figure 6.1.6. Annotated sub-bottom profiler image of survey line 505 shows the midden-like feature 

(circled in yellow) and sag zones associated with the channels (highlighted in red). Vertical scale lines 

are in 150-m (492-ft.) intervals; horizontal scale lines are in 7.5-m (25-ft.) intervals; north is at left.

6.2 HIGH ISLAND AREA 178

Four separate data sets were available for use surrounding a possible prehistoric feature first 

identified in an NTL-compliant archaeological report in Block 178, High Island Area. The first 

data set was an oil and gas industry lease block survey report that originally identified the 

channel system and feature (Keith and Pryor 2007). The digital sub-bottom data acquired for the 

2007 report were made available for analysis and reinterpretation as part of this study. Acoustic 

(sub-bottom) profiling data were collected as part of the current study’s scope of work and were 

acquired in 2008. A separate industry pipeline survey was conducted in 2009 and overlapped the 

channel system and feature of interest identified in the 2007 lease block report. Data collected as 

part of the 2009 survey were made available for use in this study (Keith and Evans 2009). 

Supplemental acoustic profiles were collected by Tesla Offshore in 2011.

 

Numerous near-surface channels were recorded at HI 178 during an NTL-compliant shallow 

hazards and archaeological survey conducted in October 2007 (Keith and Pryor 2007). The grid 

utilized for data acquisition was designed with survey lines oriented parallel to the northern 

boundary of an existing fairway, approximately northwest to southeast. Sub-bottom profiler 

survey lines were spaced 150 m (492 ft.) apart. Four tie-lines were designed perpendicular to the 

primary lines and spaced 900 m (2,953 ft.) apart (Keith and Pryor 2007). The existing digital 

data set was used to create a new near-seafloor contour map depicting the interpretation and the 

survey lines (Figure 6.2.1). 

Sag zones
69

Figure 6.2.1. Contours depict the channel system as interpreted from the 2007 data set. The area of 

interest is indicated by the red diamond. The survey lines are superimposed over the channel system in 

black; primary survey lines are spaced 150 m (492 ft.) apart. Depths are in meters below the seafloor; 

image is oriented north up.

Interpretation of the sub-bottom data identified up to 1.5 m (5 ft.) of strongly to moderately 

reflective stratified sediment, which was interpreted as Holocene in age, overlying weakly 

reflective to acoustically opaque sediments (Keith and Pryor 2007). Paleochannels were 

observed within the lower sedimentary unit, with observed margins identified at depths of 1–1.5 

m (3–5 ft.) below the seafloor; observed thalwegs were up to 16.6 m (55 ft.) below the seafloor. 

An area of archaeological interest was identified along the margin of a large channel feature, 

which appeared to be intact below the interpreted modern sediment horizon (Figure 6.2.2). Based 

on a sea level curve developed by CEI (1977), the feature was estimated to have been exposed as 

dry land and available for occupation prior to 6,000 yrs BP, after which it was inundated by 

rising sea levels (Keith and Pryor 2007). The 6,000 yrs BP estimate for final inundation would 

have left the area available for exploitation by Paleoindian and Early Archaic populations. The 

feature was recommended for avoidance during future lease activities, and no further testing was 

required at that time. 
70

Figure 6.2.2. Annotated sub-bottom profiler image of survey line 4 shows the levee feature (circled in 

yellow) identified in 2007 with the channel horizon (red) and ravinement surface (green). Vertical scale 

lines are in 150-m (492-ft.) intervals; horizontal scale lines are in 7.5-m (25-ft.) intervals (modified from 

Keith and Pryor 2007).

The levee feature in HI 178 was included in this study because it is shallowly buried, located less 

than 2 m (6.5 ft.) BML, and appeared to meet the criteria for high-probability features for 

archaeological site occurrence and preservation as defined by CEI (1977) and Waters (1992). 

Like the reported shell midden in HI 160, the channel horizon in HI 178 represented preserved 

high-probability features at a depth of approximately 15 m (49 ft.) BSL, within the range 

targeted by this study. A new acoustic survey grid was designed and centered on the interpreted 

feature, with survey lines oriented north-south and east-west. Two perpendicular survey lines 

were added to run through the middle of the interpreted feature. Additional survey lines were 

created so that ten lines extended to each direction of the reported feature. All survey lines were 

450 m (1,500 ft.) in length, and spaced at 25 m (82 ft.) intervals (Figure 6.2.3); the survey was 

conducted on 21 July 2008. In addition to the 42 survey lines originally planned, eight survey 

lines were added in the field to provide broader-scale imaging of the channels in the area. These 

lines were oriented diagonal to the primary survey lines (northwest to southeast, and southwest 

to northeast) to approximate the orientation of the 2007 survey lines. The resulting data were 

digitally interpreted and contoured. Significant heave was recorded on the acoustic profiles that 

could not be processed out of the survey data. Supplemental survey lines (501–509) were 

designed over the interpreted features of interest for use in illustrating the data in this report. 

These lines were recorded by Tesla Offshore’s survey vessel M/V Nikola in 2011 while in transit 

between regularly scheduled work at no cost to the current study.

The survey grid designed as part of this study’s scope of work, and acquired in 2008, was 

designed for two purposes: to record more detail of the area immediately surrounding the 

potential levee, and to accurately delineate the boundaries of the interpreted feature. Longer lines 

were added in the field to collect data over features observed during acquisition (represented by 

the 100 and 200 series lines). The high-density 2008 data, which was collected at 25 m (82 ft.) 

intervals, reflect greater variability within the channel’s margins than seen in the 2007 data, and 

depict the channel wrapping around the northern boundary of the survey area (Figure 6.2.3). The 
71

interpreted levee (as identified from the 2007 data) was visible on the 2008 data (Figure 6.2.4), 

and an additional area of interest was observed to the northwest. This second area was 

interpreted as a possible levee or terrace (Figure 6.2.5).

Figure 6.2.3. Contours depict the channel system as interpreted from the 2008 data sets. The site of 

interest is indicated by the red diamond. The survey lines are superimposed over the channel system 

in black; primary survey lines are spaced 25 m (82 ft.) apart. The 100 and 200 series lines were added 

in the field. Depths are in meters below the seafloor; image is oriented north up.

Figure 6.2.4. Annotated sub-bottom profiler from line 506A shows the levee feature (circled in yellow) 

previously identified in 2007, as well as the channel horizon (red) and interpreted ravinement surface 

(green). Vertical scale lines are in 150-m (492-ft.) intervals; horizontal scale lines are in 7.5-m (25-ft.)

intervals.
72

Figure 6.2.5. Annotated sub-bottom profiler image from line 508 of a second possible levee feature 

(circled in yellow) identified from the 2008 survey data; also shown are the channel horizon (red) and 

interpreted ravinement surface (green). Vertical scale lines are in 150-m (492-ft.) intervals; horizontal 

scale lines are in 7.5-m (25-ft.) intervals.

Following acquisition of the acoustic survey data in 2008, a proposed pipeline survey was 

conducted between HI 154 and HI 178 in November 2009 (Keith and Evans 2009). Those data 

were made available for inclusion in the current study. 

The 2009 survey grid included the channel margin and levee identified from the 2007 data, and 

correlated with the interpreted 2008 data (Keith and Evans 2009). The 2009 survey grid also 

included supplemental coverage over the secondary feature of interest identified from the 2008 

data. The 2009 grid was designed with survey lines oriented parallel to a proposed pipeline route, 

approximately northwest to southeast. Survey line orientation was similar to the 2007 survey 

grid. Sub-bottom profiler survey lines were spaced 50 m (164 ft.) apart, and eight tie lines were 

designed perpendicular to the primary survey lines and spaced 900 m (2,953 ft.) apart (Keith and 

Evans 2009). The sub-bottom interpretation correlated strongly with the two previous data sets 

and identified a moderately to strongly reflective surficial unit approximately 0.6–1.5m (2–5 ft.) 

thick overlying weakly reflective to acoustically opaque sediments. Buried paleochannels were 

observed in the eastern extent of the survey grid, correlating with the approximate margins of 

buried paleochannels as interpreted from the 2007 and 2008 surveys. Channel margins were 

observed within the upper 0.6–1.8 m (2–6 ft.) of sediment while entrenched thalwegs were 

observed to depths of 15 m (52 ft.). Sub-bottom data from the southeastern portion of the 2009 

survey grid were incorporated into the 2007 and 2008 contour data, and provide a significant 

amount of additional detail (Figure 6.2.6).
73

Figure 6.2.6. Contours depict the channel system as interpreted from all available data sets (2007, 

2008, 2009, and 2011). Survey lines are superimposed in the following colors: 2007 in green, 2008 in 

black, 2009 in purple, and 2011 in gray. Depths are in meters below the seafloor; north is at top.

6.3 GALVESTON AREA 356

A possible shell midden was identified in Block 356, Galveston Area, during an archaeological 

and shallow hazards survey in the winter of 2005 and reported to the MMS (Floyd and Keith 

2005; Figure 6.3.1). Four separate data sets were available for use in interpreting the reported 

midden in GA 356. The original survey data (2005) were available for review and contoured as 

part of this study. Supplemental survey data were acquired over the possible midden by Tesla 

Offshore in 2006 and made available for use in this study. Acoustic (sub-bottom) profiling data 

were collected in 2008 as part of the current scope of work. Supplemental acoustic profiles were 

collected by Tesla Offshore in 2011 for use in this study at no cost.
74

Figure 6.3.1. Annotated sub-bottom profiler image from line 4 of a possible levee feature (circled in 

yellow) identified from the 2005 survey data; also shown are the channel horizon (red) and interpreted 

ravinement surface (green). Vertical scale lines are in 150-m (492-ft.) intervals; horizontal scale lines 

are in 7.5-m (25-ft.) intervals; north is at left.

The 2005 report was based on an assessment of survey data over all of Blocks 355 and 356, and 

included 2–10 kHz chirp sub-bottom profiler data acquired at 300-m (984-ft.) intervals along 

survey lines that were arbitrarily oriented north-south (Floyd and Keith 2005). According to the 

sub-bottom data assessment, approximately 22.9 m (75 ft.) of sediment was resolved on the subbottom profiles. These sediments are interpreted to consist of approximately 1.5–2.4 m (5–8 ft.) 

of silty sand of probable Holocene age overlying Pleistocene Beaumont Clay and probable Late 

Wisconsin-aged channels with observed margins at depths of approximately 1.5 m (5 ft.) BML 

(Floyd and Keith 2005:4). The 2005 digital data set was used to create a new near-seafloor 

contour map, depicting the interpretation from survey lines 2 through 7 (Figure 6.3.2). According 

to the report (Floyd and Keith 2005:4):

The shallow channel margins at 5 feet below the seafloor could contain preserved 

archaeological material. Specific prehistoric material could be preserved in the 

elevated levee deposit and possible shell midden... This preserved feature is 5 

feet below the seafloor and exhibits the same characteristics seen at shell middens 

on existing archaeological sites across south Louisiana. This site...should be 

avoided by 200 feet when selecting drilling locations.
75

Figure 6.3.2. Contours depict the channel system and 

possible midden (highlighted in red) as interpreted from the 

2005 data, lines 2 (west) through 7 (east). Survey lines are 

shown in gray. Depths are in meters below the seafloor; north 

is at top.

The interpreted shell midden was located along channel margins that, according to the report, 

could have been inhabited by Paleoindian groups prior to final inundation approximately 10,000 

yrs BP (Floyd and Keith 2005:4). 

Following the site’s identification in 2005, supplemental survey data were acquired over the area 

in 2006 by Tesla Offshore. Five survey lines were run in multiple directions over the interpreted 

midden (Figure 6.3.3). The initial view of the possible midden from survey line 4 (2005 data) 
76

depicted an area of highly reflective sediment resembling a plateau just under the interpreted 

ravinement surface. The midden’s boundaries were plotted by interpolating between the northern 

and southern extents of the feature from two adjacent survey lines, providing a rough 

approximation of the feature. The 2006 supplemental data depicts much more variability within 

the elevation of the levee and interpreted midden.

Figure 6.3.3. Contours depict a detailed view of the channel system and 

levee immediately adjacent to the interpreted midden (the extents as 

identified in 2005 are shown in red). Survey lines are shown in gray. 

Depths are in meters below the seafloor; north is at top.

The possible midden feature in GA 356 was included in this study because it is shallowly buried, 

located less than 2 m (6.5 ft.) BML, and appeared to meet the criteria for high-probability 

features for archaeological site occurrence and preservation as defined by CEI (1977) and Waters 

(1992). The possible midden represents a preserved high-probability feature at a depth of 

approximately 30 m (98 ft.) BSL, within the range targeted by this study. A new survey grid was 

designed around the interpreted feature in order to relocate the reported shell midden and to 

provide expanded coverage around the 2006 supplemental data (Figure 6.3.4). The new survey 

grid was centered on the interpreted shell midden, with survey lines oriented north-south and 

east-west. The resulting data were digitally interpreted and contoured. Significant heave was 

recorded on the sub-bottom profiles that could not be processed out of the survey data, therefore 

supplemental survey lines were designed for use in illustrating the data in this report. These lines 

were recorded by Tesla Offshore’s survey vessel M/V Nikola in 2011 while in transit between 

regularly scheduled work at no cost to the current study.
77

Figure 6.3.4. Contours depict the channel system and levee adjacent to 

the reported midden (the extents of the possible midden as identified in 

2005 are shown in red). Survey lines are shown in gray. Depths are in 

meters below the seafloor; north is at top.

After reviewing all of the available data it is apparent that the plateau-shaped midden feature is

not as distinct on subsequent data as it is on the 2005 data. In fact, survey line direction and 

orientation were observed to variably influence the acoustic returns recorded along the subbottom profiles (Figure 6.3.5). 
78

Figure 6.3.5. Annotated sub-bottom profiler data illustrate differences in reflection of the 

same subseafloor strata caused by survey line orientation (heading line 204 [top] = 0°; heading line 

509 [bottom] = 180°). Vertical scale lines are in 150-m (492-ft.) intervals; horizontal scale lines are 

in 7.5-m (25-ft.) intervals.

In all cases, sub-bottom profiles recorded a strongly reflective seafloor underlain by 

approximately 0.9–1.5 m (3–5 ft.) of acoustically undifferentiated to weakly reflecting sediment 

that in turn overlies approximately 2.4 m (8 ft.) of strongly to moderately reflecting parallel 

bedded sediment, outside of the channel system. Acoustic penetration is largely attenuated 

underneath this sedimentary unit (Figure 6.3.6). Within the entrenched channels, recorded 

channel fill appears as either subparallel bedded sediments or acoustically opaque sediments. 

Acoustic opacity of the channel fill is likely caused by the presence of biogenic-gas enriched 

sediment (Whelan et al. 1977). 
79

Figure 6.3.6. Annotated sub-bottom profiler image from line 203 illustrates the typical 

sediment reflection of the subseafloor strata. Vertical scale lines are in 150-m (492-ft.) intervals; 

horizontal scale lines are in 7.5-m (25-ft.) intervals.

The combined data sets correlate in depicting a topographic high area with strongly to 

moderately reflecting sediments on the margins of an entrenched channel oriented northwest to 

southeast (Figure 6.3.7). It is unclear from the data whether or not the plateau-like midden, as 

interpreted from the 2005 data, depicts an intact archaeological deposit. 

Acoustically opaque

Seafloor

Parallel bedded

Weakly reflecting
80

Figure 6.3.7. Contours created from all of the available data depict the 

channel system and the extents of the interpreted midden. The survey 

lines are superimposed over the channel system in black; primary survey 

lines are spaced 300 m (984 ft.) apart. Depths are in meters below the 

seafloor; image is oriented north up. 

 
81

6.4 GALVESTON AREA 426

A high-probability feature for prehistoric archaeological site occurrence and preservation was 

recorded in GA 426 during an NTL-compliant shallow hazards and archaeological survey 

conducted in December 2007 (Keith and Geresi 2008). Water depths in this survey area were 

approximately 30.5 m (101 ft.) BSL. The grid utilized for data acquisition was designed with 

survey lines arbitrarily oriented north-south. Sub-bottom profiler survey lines were spaced 300 m

(984 ft.) apart, and five tie-lines were designed perpendicular to the primary lines (oriented eastwest) and spaced 900 m (2,953 ft.) apart (Keith and Geresi 2008; Figure 6.4.1). 

 Figure 6.4.1. Contours depict the channel system as re-interpreted from the 2007 data set. The site of 

interest is indicated by the red diamond; an outcropping feature is outlined in green. The survey lines 

are superimposed over the channel system in black; primary survey lines are spaced 300 m (984 ft.) 

apart. Depths are in meters below the seafloor; image is oriented north up.

The interpretation of the 2007 sub-bottom data identified a very thin veneer of probable 

Holocene sediment immediately underlain by the probable Holocene-Pleistocene unconformity. 

East-west trending channels and channel fragments were identified in the survey area, with 

channel margins located at depths ranging from 1.5–4.5 m (5–15 ft.) below the seafloor.

Observed thalwegs were up to 8.8 m (29 ft.) below the seafloor (Keith and Geresi 2008). Two 

distinct channels were identified in the central portion of the survey area, separated by a 

topographic rise that reaches a minimum depth of approximately 1.5 m (5 ft.) below the seafloor. 

At least one inset terrace was identified on sub-bottom data within the southern margin of the 

northern channel approximately 3.8 m (12.5 ft.) below the modern seafloor, and below the 

interpreted ravinement surface (Figure 6.4.2). Based on a sea level curve developed by CEI 

(1977), the topographic rise between the two channels was estimated to have been exposed as 

dry land and available for occupation prior to 10,500 yrs BP and the inset terrace before 11,000 

yrs BP, after which these features were inundated by rising sea-level (Keith and Geresi 2008). 
82

Figure 6.4.2. Annotated sub-bottom profiler image of survey line 6 depicts the topographic feature 

(yellow) and inset terrace (cyan) identified from the 2007 data set with the channel horizon (red) and 

interpreted ravinement surface (green). Vertical scale lines are in 150-m (492-ft.) intervals; horizontal 

scale lines are in 7.5-m (25-ft.) intervals; north is at right (modified from Keith and Geresi 2008).

Geophysical data also recorded an outcropping diapir approximately 780 m (2,575 ft.) south of 

the interpreted channel system (Keith and Geresi 2008). Uplifted sediments associated with the 

interpreted diapir were recorded on processed 2-D seismic data to depths of 1.2 seconds (900 m

[2,953 ft.]) BSL before the signal was completely attenuated (Keith and Geresi 2008). The 

diapir, which likely represents upwardly mobile salt, was also observed on the sonar data and 

was associated with outcropping features as recorded on the sonar, sub-bottom, and bathymetry 

data (Keith and Geresi 2008). The probable salt diapir was not identified as a high-probability 

feature for prehistoric archaeological site occurrence, but could have contributed to the local 

environment and served as an exploitable resource. 

The interpreted features in GA 426 were selected for inclusion in this study because of their 

shallow depth below the seafloor and apparent similarity to high-probability features for 

archaeological site occurrence and preservation as defined by CEI (1977) and Waters (1992). As 

with the reported midden feature in GA 356, the area in GA 426 represents a channel system at a 

depth of approximately 30 m (98 ft.) BSL, which is within the targeted depth range for this 

study. A new survey grid was created as part of the scope of work, and centered on the 

topographic feature. Two perpendicular survey lines were oriented over the middle of the feature 

as plotted from the 2007 data. Additional survey lines were created so that twenty survey lines 

extended to the east and west of the interpreted feature, oriented north-south, and spaced at 25-m 

(82-ft.) intervals. Due to the east-west orientation of the channels, tie lines were designed over 

the grid at approximately 150-m (492-ft.) intervals. All survey lines were 900 m (1,500 ft) in 

length (Figure 6.4.3). The acquired data were interpreted digitally and contoured. Significant 

heave was recorded that could not be processed out of the survey data. Additional survey lines 

were designed over the interpreted features of interest for use in illustrating the feature further 

(lines 501-511) and were acquired by Tesla Offshore’s survey vessel M/V Nikola in 2011 while 

in transit between regularly scheduled work at no cost to the current study.
83

The 2008 data set was designed to provide detailed coverage of the inset terraces observed on

either side of the topographic feature in the 2007 data, and to more accurately delineate the 

feature’s boundaries. The 2008 data indicate greater variability within the channel’s margins than 

was plotted from the 2007 data, which is not unexpected since the 2007 interpretation was based 

on data acquired at 300-m (984-ft.) intervals. The 25-m (82-ft.) interval data acquired in 2008 

depict greater variability along the X, Y, and Z axes, although it is apparent that inset terraces are 

preserved to both sides of the topographic feature (Figures 6.4.3 and 6.4.4). Maximum channel

entrenchment is variable, and it is likely that discontinuous reflectors may be the result of 

reduced data reflection relative to survey line orientation.

Figure 6.4.3. 3-D wireframe representation of the channel 

system as interpreted in GA 426 from the 2008 data set. 
84

 

Figure 6.4.4. Contours depict the channel system as interpreted from the 2008 data set. The 

site of interest is indicated by the red diamond. The survey lines are superimposed over the channel 

system in black; primary survey lines are spaced 25 m (82 ft.) apart. Depths are in meters below the 

seafloor; image is oriented north up.

The interpreted topographic feature and inset terrace associated with the southern margin of the 

northern channel were relocated during the 2008 survey (Figure 6.4.5). During data 

interpretation, it became apparent that a highly reflective feature was associated with the inset 

terrace, representing a deposit with greater density than the surrounding sediments (Figure 6.4.6). 

This feature was hypothesized to represent either hard-packed sediment or shell.
85

Figure 6.4.5. Annotated sub-bottom profiler image from survey line 504 illustrates the topographic 

feature (yellow) previously identified in 2007, as well as the inset terrace (cyan), channel horizon (red), 

and ravinement surface (green). Data have been reversed to mimic the same orientation as the 2007 

image. Vertical scale lines are in 150-m (492-ft.) intervals; horizontal scale lines are in 7.5-m (25-ft.)

intervals; north is at right.

Figure 6.4.6. Annotated sub-bottom profiler image from survey line 502 of the extended inset terrace 

(cyan) with highly reflective feature (circled in yellow) identified from the 2008 survey. Also shown are 

the channel horizon (red) and ravinement surface (green). Vertical scale lines are in 150-m (492-ft.) 

intervals; horizontal scale lines are in 7.5-m (25-ft.) intervals; north is at right.

The channel system as interpreted from the data acquired as part of this study includes two 

distinct channels, but it is not possible to determine from the acoustic data alone whether or not 

the channels were contemporaneously active (Figure 6.4.7).
86

Figure 6.4.7. Contours depict the channel system as interpreted from the 2008 and 2011 supplemental 

data set. The site of interest is indicated by the red diamond. The survey lines are superimposed over 

the channel system in black; 2008 survey lines are spaced 25 m (82 ft.) apart. Depths are in meters 

below the seafloor.

6.5 DISCUSSION

The interpreted terraces and levees associated with the channel systems in HI 160, HI 178, GA 

356, and GA 426 are located at depths ranging from 1.5 m to 6 m (5–20 ft.) below the seafloor. 

Based on the sea level curve created for this study, the landforms in High Island Area (Blocks 

160 and 178) could have been exposed as dry land until between 5,000 and 10,200 yrs BP. The 

features in Galveston Area (Blocks 356 and 426) could have been available for occupation until 

final inundation between 7,800 and 11,800 yrs BP (Figure 6.5.1). Contours based on the acoustic 

data have been used to generate plan view maps of the formerly exposed landscape, and indicate 

areas similar to high-probability landforms for prehistoric site occurrence and preservation. 

These features appear to be buried by a thin veneer of sediment, but have not been truncated or 
87

significantly eroded by overlying sediment units, with the possible exception of some erosion of 

the reported midden feature in GA 356. Sea level curve data indicate that landforms in all four of 

the survey areas would have been exposed and available for occupation and/or exploitation 

during the Paleoindian period. HI 160 and 178 may have remained exposed as late as the Archaic 

period. Without physical samples it is not possible to definitively ascertain the dates of these 

landscape features or their potential for prehistoric archaeology.

The geophysical survey represented just one phase of field work required to identify 

landforms—and more important—assess the potential for buried prehistoric landscapes in the 

northwestern GOM. Sub-bottom data are a relative data set and do not provide an accurate age of 

interpreted features, therefore physical sampling is necessary to verify the interpretation of 

geophysical data. As stated by Wille (2005:56):

Sediment acoustics needs verification by coring and probing regarding 

mineralogy, chemistry, and fossils. But it can reveal on its own even very weak 

reflecting horizons and is peerless in verifying whether a core stratification is only 

a local peculiarity or a symptomatic regularity over an extended ocean region.
88

Figure 6.5.1. Landform depth ranges from the High Island Area are plotted on the sea-level curve in green; Galveston Area landform depth 

ranges are plotted in blue. Both areas are at depths correlating with known occupations in the Gulf region.

-110.00

-100.00

-90.00

-80.00

-70.00

-60.00

-50.00

-40.00

-30.00

-20.00

-10.00

0.00

10.00

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000

Depth Below Modern Sea-level (meters)

Radiocarbon Age (years BP)

Sea-level Data Points from the Northwestern Gulf of Mexico

Radiocarbon Dates

Four-point 

Polynomial Trend 

Line

Minimum and 

Maximum 

Sources:

Curray 1960;

Shepard 1960; 

Nelson and Bray 1970; 

Frazier 1974; 

Morton et al. 2000; 

Blum et al. 2001; 

Tornqvist et al. 2006; 

Blum et al. 2008
89

7. SEDIMENT CORING AND ANALYSES

Cores were acquired from the interpreted features identified from the acoustic survey profiles in 

HI 160, HI 178, GA 356, and GA 426. Coring locations were selected prior to the start of 

fieldwork. In some cases planned cores had to be moved or cancelled in the field. Due to the 

presence of over-consolidated sediments, not all cores recovered the full 6 m (20 ft.) maximum 

sample. A penetrometer was used to monitor coring depth and potential refusal on all cores, but 

malfunctioned during acquisition of several samples while on location at GA 426. Following 

acquisition, all cores were opened in the lab at Louisiana State University. The observed 

sediment stratigraphy within each core was correlated with the acoustic impedance observed on 

the recorded profiles. Distinct landforms and environmental features were evident within the 

sediment profiles, while sediment sub-sampling allowed for the identification of discrete 

variables such as radiocarbon age and sediment grain size. 

The following sections detail the results of the coring operations and describe sediments 

observed within the collected cores. Figures provide comparisons between the logged cores and 

their corresponding locations on the acoustic profiles. It should be noted that the sub-bottom data 

does not exactly match the core locations and should be used as an approximation of 

stratification based on the survey line closest to the core location. Cores are 10 cm (4 in.) in 

diameter, and the sub-bottom profile represents a 10-cm (4-in.) swath recorded along-track. The 

coring rig was positioned from the surface and lowered onto the seafloor. No anchors were set,

and the vessel was held on location by the captain in generally flat to calm sea states. Due to 

positioning margins of error, and the limitations of the data, the sub-bottom profiles and cores do 

not match up exactly. Core locations as plotted on the sub-bottom contours should also be 

considered a best approximation of subseafloor conditions. Contours are based on 25-m (82 ft.) 

interval data, and are interpolated between survey lines. Contours were generated using Surfer 

10, and included algorithms specifically selected to introduce the least amount of interpolation 

beyond the extents of the data. Figures are therefore presented as representative illustrations of 

the data.

7.1 HIGH ISLAND AREA 160

Following data interpretation, all available data were used to locate and define areas for physical 

sampling. During preparation of the coring maps it became apparent that two different positions 

were reported for each of two pipelines in the immediate vicinity of the interpreted shell midden. 

According to the 1995 survey and resulting report, the Shell 4-inch (10 cm) pipeline (Segment 

No. 2834) was located approximately 160 m (530 ft.) directly north of the shell midden, and the 

Shell 3-inch pipeline (Segment No. 2832) was located approximately 303 m (1,000 ft.) to the 

north-northeast. Both pipelines should have been far enough from the reported shell midden to 

allow coring, since typical safety standards in the GOM require operators to maintain a distance 

of 150 m (500 ft.) from published positions of pipelines during ground disturbing activities. In 

the process of preparing new maps for submission to BOEM in compliance with Geology and 

Geophysics Notifications guidelines, different positions than those shown on the 1995 survey 

maps were discovered for Segments No. 2834 and 2832 based on publicly available, published 
90

as-built data (Figure 7.1.1). The published position for the Shell 4-inch (10 cm) pipeline 

(Segment No. 2834) plotted less than 10 m (30 ft.) north of the reported shell midden, and the 

Shell 3-inch pipeline (Segment No. 2832) plotted approximately 260 m (860 ft.) to the northnortheast. The sub-bottom data acquired as part of this study were scrutinized to determine if 

acoustic diffractions consistent with pipelines could be observed within the recorded profiles.

Unfortunately, the diameters of the two pipelines (3-inch and 4-inch) are too small to be clearly 

resolved on sub-bottom data. Pipelines must typically have a diameter of at least 8 in. (20 cm) to 

be resolved in acoustic profiles (Tian 2008; Evans and Voisin 2011).

Figure 7.1.1. Annotated interpretation map of HI 160 near the reported shell midden showing the 

differing pipeline positions for Segments Nos. 2834 and 2832 (modified from Landry and DuVal 1995).

According to the 1995 report, the magnetometer data verified the locations of man-made features 

in the survey grid, including “nine Shell 3-inch Pipelines” and “six Shell 4-inch Pipelines” 

(Landry and DuVal 1995:12). The report does not specify the source of the plotted locations, nor 

are Segment numbers associated with the “verified” pipelines. The report contains no discussion 

of any variation between reported pipeline positions and pipeline positions as found from the 

magnetometer data. Attempts to contact Shell, the listed pipeline owner, before coring operations 

were unsuccessful. Shell is no longer the owner of the offshore lease for Block 160, including the 

pipelines, and the pipelines themselves have been plugged and abandoned in place. No 

explanation could be found for the discrepancy in pipeline positions.
91

Coring locations were selected based on the combination of available and interpreted sub-bottom 

data. Once in the field, however, the coring operator indicated that safety protocols required a 

minimum safety buffer of 150 m (500 ft.) from the published positions of any pipelines within 

the area. The pipeline positions as indicated by the 1995 survey are not published; they are 

located in a proprietary survey report and as such are not considered a publicly available source. 

Therefore, the pipeline positions as plotted from the BOEM-managed database were used by the 

coring operator. A magnetometer was not available for the coring vessel to deploy to identify the 

pipelines’ actual positions. Because no other data was available to refute or confirm the disputed 

positions of the two Shell pipelines, alternate core locations were selected in order to adhere to 

the minimum 150 m (500 ft.) buffer. This meant that cores could not be taken directly from the 

interpreted shell midden.

All cores from the High Island 160 area were acquired on 28 June 2009. Core recovery ranged 

from 76% to 91% of the possible 6-m (20-ft.) maximum; sediment recovery within each core 

ranged from 92% to 100% (Table 7.1).

Table 7.1. Core penetration and sediment recovery, HI 160

Core No.

Maximum 

Core Depth 

(m)

Maximum Core 

Depth (%)

Sediment 

Recovery (m)

Sediment 

Recovery (%)

3 5.43 91.0 5.12 94.3 

7 5.15 85.8 4.88 94.8

9 4.57 76.2 4.18 91.5

10 4.72 78.7 4.57 96.8

11 4.82 80.3 4.80 99.6

12 5.36 89.3 5.10 95.1

Due to the unresolved issues related to pipeline positions in the coring area, none of the planned 

cores could be acquired. After consulting the interpreted sub-bottom data in the field, cores no. 7 

and 9 were placed as far north towards the reported midden feature as possible, while 

maintaining the 150 m (492 ft.) buffer around the reported pipeline position (Figure 7.1.2). Cores 

7 and 9 are approximately in line with core no. 10 along a north-south axis. Cores no. 3, 12, 10, 

and 11 were intended to form a west-east profile across the interpreted channel system and 

associated margin. 

Once the cores were opened it became apparent that the captured sediments did not experience 

the high degree of visual variability anticipated from the horizons visible on the acoustic profiles.

Stratigraphic units were created by assessing the color of the sediments as defined by the 

Munsell color chart; relative texture (as an estimate of sand vs. silt); presence of mottling, 

inclusions, or intrusive lenses; and presence/quantity of shell.
92

Figure 7.1.2. Core locations are depicted on the channel system contours as interpreted from the 

data. The midden feature as originally reported and as interpreted from the current data are shown in 

red along line 509. The survey lines are superimposed over the channel system in black. Depths are in 

meters below the seafloor; image is oriented north up.

Cores no. 3, 12, 10, and 11 formed a transect across the southern portion of the survey area. 

Based on the interpreted contours, cores 3 and 12 were inside of the interpreted channel that 

curved around a topographic ridge, on which core 10 was located. Core no. 11 was located along 

the eastern slope of the same topographic ridge as core no. 10, where the ridge drops back into 

the eastern curve of the same channel from which cores 3 and 12 were taken. Cores no. 10 and 

11 should contain sampled sediments related to the interpreted Younger Deweyville terrace as 

identified from the 1995 survey report (Landry and DuVal 1995).

Cores no. 3 and 12 were sampled in close proximity to one another, but exhibit significant 

variability. Core no. 3 contains soft, gritty textured sediment with visible shell, intrusive sand,

and shell-filled lenses, and an anomalous area of black probable organic sediment at a depth of 

230 centimeters below surface (cmbs) (91 in.) that is not present in core no. 12 until a depth of 

440 cmbs (173 in.). It is probable that these cores were acquired in channel sediments that are 

subangular, and represent similar deposition events at different depths, based on the horizon’s 

angle of repose within the channel.
93

Cores no. 10 and 11 exhibit similar sedimentary units, but as with cores no. 3 and 12, the units 

observed in core 10 occur at different depths than in core 11 (Figure 7.1.3). This is likely because 

the thickness of modern sediments is different between the two cores, offsetting the strata.

Figure 7.1.3. Cores no. 3, 12, 10, and 11 (left to right) are shown against the survey line closest to the 

core sites (line 507). Image is not to scale. Core logs are truncated at 420 cmbs (165 in.).

Physical samples were collected from cores no. 3 and 10 for grain size analysis; one sample was 

collected per unit based on the initial core description. Raw grain size values were plotted as scurves, then calculated as both median grain size and graphic mean and rounded to the nearest 

hundredth (Tables 7.2 and 7.3). The data were intended to assist in defining the Deweyville 

terrace.
94

Table 7.2. Representative grain sizes for core no. 3, HI 160

Sample 

No. 

Sample Depth 

(cmbs) 

Median (Mdmm) Graphic Mean

Mz (mm)

Wentworth 

Classification

1 61 0.12 0.111 very fine sand

2 190 0.009 0.020 medium silt

3 211 0.025 0.029 medium silt

4 245 0.006 0.019 medium silt/fine silt 

5 381 0.0345 0.034 coarse silt / medium 

silt

6 465 0.0056 0.011 medium silt/fine silt

Table 7.3. Representative grain sizes for core no. 10, HI 160

Sample 

No. 

Sample Depth 

(cmbs) 

Median (Mdmm) Graphic Mean

Mz (mm)

Wentworth 

Classification

1 24 0.12 0.165 fine sand/very fine 

sand

2 140 0.009 0.037 coarse silt / medium 

silt

3 290 0.025 0.014 medium silt

4 340 0.006 0.038 coarse silt/fine silt

5 414 0.0345 0.038 coarse silt

Samples were collected from core no. 3 for radiocarbon dates (Table 7.4). A large scallop shell 

observed in interpreted estuarine fill was dated to provide an absolute date for a horizon 

observable across multiple survey lines. Additional samples were collected from within the 

probable organic sediment observed in core no. 3 at a depth of approximately 250 cmbs (98 in.). 

It was hypothesized that this sedimentary unit was the same as similar units observed at deeper 

depths within cores 12, 10, and 11.

Table 7.4. Radiocarbon sample results for core no. 3, HI 160

Sample Sample 

Depth (cmbs) 

Conventional Radiocarbon 

Age (yrs BP)

Calibrated (2 Sigma) 

Radiocarbon Age (yrs BP)

B-1 41 4,090 +/- 40 4,020–4, 240

C-2 243 8,210 +/- 60 9,010–9,400 

C-3 263 8,340 +/- 40 9,270–9,470

Cores no. 7 and 9 were sampled in close proximity to one another but exhibit significant 

variability (Figure 7.1.4). Core no. 7 is most similar in appearance to core no. 11. Both were 

acquired near or along the slope of an interpreted ridge that slopes into a channel, and both 

exhibit relatively uniform sediments interrupted by occasional sand lenses. 
95

Core no. 9 is the most dissimilar core acquired from this area, and is also closest in proximity to 

the interpreted midden. Based on the sub-bottom data, core no. 9 should represent Holoceneaged sediment draped over the top of the buried channel system. The sediments within core no. 9 

contain intrusive lenses of sand and shell within the overall sediment stratigraphy, suggesting 

interruptions or erosion occurring within the context of overall deposition.

Figure 7.1.4. Cores no. 7 (left) and 9 (right) are shown against the survey line closest to the core sites 

(line 504). Image is not to scale.

Following acquisition of the cores from HI 160, supplemental sub-bottom survey lines were 

acquired over the survey grid (lines 501–510, as discussed in Chapter 6, Section 1). During 

planning and design of the supplemental grid, magnetometer data acquisition was added to the 

scope of supplemental work at HI 160. Although the data was not acquired in time to verify the 

pipelines’ positions relevant to coring operations for this study, the midden represents a probable 

shell deposit. Without physical samples it will not be possible to determine if this deposit 

represents an anthropogenic midden, or a naturally occurring reef feature. The magnetometer 

data is necessary to clarify pipeline positions in the event that future coring is performed at this 

location.
96

Magnetometer data was acquired using a Marine Magnetics total field magnetometer. Data were 

recorded digitally, and interpreted using proprietary MagPick software. Magnetic anomalies with 

characteristics indicative of large quantities of ferromagnetic material were recorded close to the 

pipeline positions as reported in the 1995 survey (Figure 7.1.5). It is not clear where the 

published pipeline positions came from for Segments No. 2832 and 2834, but the magnetometer 

data clearly indicate that no ferromagnetic material is present along those plotted locations, and 

that coring may be attempted at HI 160 while maintaining a 150-m (492-ft.) buffer from existing 

pipelines.

Figure 7.1.5. Magnetometer interpretation map of HI 160; map is oriented north up 

(modified from Landry and DuVal 1995). Magnetic anomalies are indicated by red triangles and 

represent data recorded from lines 501 to 510.

7.2 HIGH ISLAND AREA 178

All cores from the High Island 178 area were acquired on 28 June 2009. Core recovery ranged 

from 50% to 100% of the possible 6-m (20-ft.) maximum; sediment recovery within each core 

ranged from 72% to 97% (Table 7.5).
97

Table 7.5. Core penetration and sediment recovery, HI 178

Core No.

Maximum 

Core Depth 

(m)

Maximum Core 

Depth (%)

Sediment 

Recovery (m)

Sediment 

Recovery (%)

1 4.96 83 4.80 97

2 4.18 70 3.62 87

5 6.33 105 4.93 78

6 3.82 64 2.74 72

7 2.99 50 2.81 94

Once the cores were opened it became apparent that cores no. 2, 5, 6, and 7 reflected similar 

sedimentary units. Despite the similarity of the acoustic profiles, the observed sediment 

stratigraphy in core no. 1 represents a unique area within the channel system, and is unlike any of 

the other cores from the HI 178 area. Cores no. 2, 5, 6, and 7 are located on opposing margins of 

the same channel feature (Figure 7.2.1). Cores no. 2, 6, and 7 are located on a probable naturally

occurring levee and associated terrace, and core no. 5 is on the opposite channel margin. The 

location of core no. 1 is interpreted as a separate inset terrace. The approximate core locations 

are outlined on the acoustic profiles for all cores in HI 178 (Figures 7.2.2–7.2.6).

7.2.1 Interpreted Levee Feature

Cores 2, 7, and 6 represent an approximate west-east transect 170 m (558 ft.) long across an 

interpreted levee bounded on three sides by a channel. Core no. 5 is located 625 m (2,051 ft.) 

away, on the eastern side of the same channel, in-line with cores 2, 7, and 6 along a 

northwestern-southeastern axis. Core no. 5 was interpreted as having probable Holocene 

sediment to a depth of approximately 3 m (10 ft.) BSF where a horizon of increased reflectivity 

suggested the depth of the subaerially exposed Pleistocene surface. Cores 2, 7, and 6 were 

interpreted as having approximately 1–2 m (3–6 ft.) of Holocene sediment overlying the 

interpreted subaerially exposed Pleistocene surface. Once opened, the cores reflect this general 

pattern of sedimentation. Beginning in the west with core no. 2, soft, cohesive, probable modern 

marine and estuarine sediments occur from the top of the core to a depth of 142 cmbs (56 in.) 

(Figure 7.2.7). These sediments contain shell hash lenses and evidence of bioturbation. A 

horizon of stacked shell, including individual pieces measuring 6 cm by 3cm (2 in. by 1 in.), 

immediately underlies the probable Holocene sediments to a depth of 160 cmbs (63 in.). The 

remaining sediments within core no. 2 consist of silty sand interspersed with carbonate nodules 

and exhibit substantial lenses of oxidized sediment.
98

Figure 7.2.1. Core locations are depicted on the interpreted channel system contours as interpreted from the three available data sets (2007, 

2008, and 2009). The 2008 survey lines are superimposed over the channel system in black; primary survey lines are spaced 25 m (82 ft.) apart. 

Depths are in meters below the seafloor.
99

Figure 7.2.2. Annotated sub-bottom profiler image of core no. 1 location (outlined in red). Vertical 

scale lines are in 150-m (492-ft.) intervals; horizontal scale lines are in 7.5-m (25-ft.) intervals.

Figure 7.2.3. Annotated sub-bottom profiler image of survey line 504, with core no. 2 location

(outlined in red). Vertical scale lines are in 150-m (492-ft.) intervals; horizontal scale lines are in 7.5-m

(25-ft.) intervals.

Figure 7.2.4. Annotated sub-bottom profiler image of survey line 507, showing core no. 5 location

(outlined in red). Vertical scale lines are in 150-m (492-ft.) intervals; horizontal scale lines are in 7.5-m

(25-ft.) intervals.
100

Figure 7.2.5. Annotated sub-bottom profiler image of survey line 506 showing core no. 6 location

(outlined in red). Vertical scale lines are in 150-m (492-ft.) intervals; horizontal scale lines are in 7.5-m

(25-ft.) intervals.

Figure 7.2.6. Annotated sub-bottom profiler image of survey line 505 showing core no. 7 location

(outlined in red). Vertical scale lines are in 150-m (492-ft.) intervals; horizontal scale lines are in 7.5-m

(25-ft.) intervals.

Core no. 7 represents the feature originally identified from the 2007 survey data. Like core no. 2,

the uppermost sediments consist of probable modern marine and estuarine sediments with 

occasional disarticulated shell fragments; however, this unit does not extend past 93 cmbs (37 

in.) (Figure 7.2.8). The remaining sediments within core no. 7 consist of silty sand exhibiting 

increased oxidation with depth. Unlike core no. 2, only a single carbonate nodule was identified, 

at a depth of 248 cmbs (98 in.). 

Core no. 6 is more similar to core no. 2 than it is to core no. 7, despite its closer proximity to core 

no. 7. The uppermost sediments of core no. 6 consist of probable modern marine and estuarine 

sediments to a maximum depth of 191 cmbs (75 in.) (Figure 7.2.9). This uppermost unit contains 

discrete lenses of shell hash and disarticulated shell fragments, as well as evidence of 
101

bioturbation. An intrusive shell hash lens is present between 90.5 and 108.5 cmbs (35.6 and 42.7 

in.). Sediments within the remainder of the opened core consist of silty sand interspersed with 

dark staining, possibly indicative of organic material, and exhibits increasing oxidation with 

depth.

Core no. 5 consists of approximately 63.5 cm (25 in.) of probable modern marine and estuarine 

sediment overlying silty sand to a depth of 493 cmbs (194 in.) (Figure 7.2.10). Substantial 

carbonate nodules are located within the silty sand horizon, beginning at 152 cmbs (60 in.); 

evidence of bioturbation is not evident below a depth of 90 cmbs (35 in.).

Based on the contoured acoustic survey data, core no. 5 is outside of the channelized area and 

likely represents modern marine sediments over an estuarine transgressive unit that overlies the 

formerly exposed Pleistocene surface. Cores no. 2, 7, and 6 form a profile across a natural levee 

feature, which is overlain by modern marine sediment and an estuarine transgressive unit of 

variable thickness. Acoustic survey contours depict the probable Pleistocene-aged levee at depths 

ranging 1–2 m (3–7 ft.) BSF, which is reflected by the sediment units from these cores (Figure 

7.2.11).

Sedimentary units were initially developed based on qualitative features such as sediment texture 

and Munsell color; additional attributes such as presence or degree of oxidation and bioturbation 

were also used to separate cores into discrete sedimentary units. Following core descriptions and 

initial assessment, physical samples were collected for grain size analysis and mass-specific 

measurements of magnetic susceptibility.
102

Figure 7.2.7. Core log prepared for no. 2 (full 

size core logs are in Appendix B).
103

Figure 7.2.8. Core log prepared for no. 7 depicts the 

sediment units, as well as P-wave measurements (m/s) and

magnetic susceptibility (volume-specific) as measured from the 

Geotek MSCL (full size core logs are in Appendix B).
104

Figure 7.2.9. Core log prepared for No. 6 (full size core 

logs are in Appendix B).
105

Figure 7.2.10. Core log prepared for No. 

5 depicts the sediment units, as well as Pwave measurements (m/s) and magnetic 

susceptibility (volume-specific) as measured 

from the Geotek MSCL (full size core logs are 

in Appendix B).
106

Physical samples were collected from core no. 7 for grain size analysis; one sample was 

collected per unit based on the initial core description. Raw grain size values were plotted as scurves, then calculated as both median grain size and graphic mean and rounded to the nearest 

hundredth (Table 7.6; Figure 7.2.12). Due to the similarity of the observed sedimentary units, 

results from core no. 7 were assumed to be representative across cores no. 2, 5, and 6.

Table 7.6. Representative grain sizes for core no. 7, HI 178 

Sample 

No. 

Sample Depth 

(cmbs) 

Median (Mdmm) Graphic Mean

Mz (mm)

Wentworth 

Classification

1 6 0.075 0.088 very fine sand

2 52 0.049 0.063 coarse silt/very fine 

sand

3 97 0.035 0.069 coarse silt/very fine 

sand

4 128 0.01 0.043 fine silt/coarse silt

5 172 0.045 0.073 coarse silt/very fine 

sand

6 240 0.106 0.098 very fine sand

Magnetic susceptibility was used in this study for multiple reasons: 1) to determine if the 

observed stratigraphy correlated with discrete depositional events as indicated by the magnetic 

susceptibility values; 2) if plotted magnetic susceptibility data would result in the identification 

of additional units not apparent through qualitative analysis; 3) to detail charcoal horizons or 

units with significant charcoal; and 4) to serve as a proxy climate indicator. Unlike magnetic 

susceptibility measurements obtained from the Geotek MSCL, which were obtained as volumespecific values, independent magnetic susceptibility measurements were made specific to the 

individual mass of each sample. Cores no. 2, 7, 6, and 5 were sampled continuously from the top 

of the core down through the interpreted marine and estuarine sediments, into the Pleistocene 

surface where observed oxidation suggested subaerial exposure (Figure 7.2.13).
107

Figure 7.2.11. Core logs superimposed over the acoustic profile depict the sedimentary units and their representative places on the acoustic 

profile. Core logs and the acoustic profile are shown at the same vertical scale; horizontal scales are not equal.

No. 2 No. 7 No. 6 No. 5
108

Figure 7.2.12. Comparison of grain size S-curves based on samples from HI 178 core no. 7.

0

10

20

30

40

50

60

70

80

90

100

355 300 250 212 180 150 125 106 90 75 63 53 45 38 31 15.6 7.8 3.9 2 0.98 0.49 0.24 0

Cumulative %

um

HI178-7 Grain Size Comparison

Sample 1

Sample 2

Sample 3

Sample 4

Sample 5

Sample 6
109

Figure 7.2.13. Diagram depicting magnetic susceptibility data obtained from cores no. 2, 7, 6, and 5 (as collected west-east), and interpreted 

sedimentary horizons.
110

Figure 7.2.14. Annotated diagram depicting magnetic susceptibility data obtained from cores no. 2, 7, 6, and 5 (as collected west-east) 

depicting the probable ravinement surface indicating the maximum depth of modern marine sediments (as indicated in brown), the lower 

boundary of the probable estuarine sediment unit deposited during sea-level transgression (as indicated in red), and an anomalously low range 

of magnetic susceptibility values that may indicate a discrete period of lower temperatures following the Last Glacial Maximum (as indicated in 

green).
111

Each of the magnetic susceptibility curves prepared from cores no. 2, 7, 6, and 5 depict a general 

trend in which the uppermost magnetic susceptibility values are relatively high, but exhibit 

significant variability to a depth of approximately 50 cmbs (20 in.) (Figure 7.2.14). The 

uppermost sediments likely represent modern marine sediments that have experienced 

punctuated episodes of scour, mixing, and redeposition that have created unconformities within 

an overall increasing magnetic susceptibility trend. The next sequence of magnetic susceptibility 

values is located between depths of 60 and 100 cmbs (24 and 39 in.) and represents a trend of

magnetic susceptibility values that are slightly lower than the overlying horizon and exhibit less 

variability. The base of this sequence is identified by a significant increase from the next 

underlying magnetic susceptibility value sequence, which represent the lowest values recorded in 

each profile. These values likely represent a distinctly different depositional environment, but 

without absolute dates it is not possible to determine the exact time period represented by this 

unit. Core no. 6 was the deepest profile measured for mass-specific magnetic susceptibility

values and indicates that sediments within the lowest unit of the magnetic susceptibility profile 

represent a completely different depositional environment. Profiles from cores no. 2, 7, and 5 are 

truncated at the top of this horizon but the shift is evident by the few data points within this 

horizon, and suggests that this sequence is found in all cores.

7.2.2 Interpreted Terrace

Core no. 1 was acquired from an interpreted terrace feature located approximately 550 m (1,820 

ft.) north-northwest of cores no. 2, 6, and 7. This terrace is bounded on the west, north, and east 

by a channel, with a channel fragment or possible meander loop bounding the southern margin. 

Core no. 1 was interpreted as having probable Holocene sediment to a depth of approximately 1–

1.5 m (3–5 ft.) BSF where a horizon of increased reflectivity suggested the depth of the 

subaerially exposed terrace surface. The sedimentary structure observed in core no. 1 was much 

more complex than the sequence observed in cores no. 2, 7, 6, and 5, suggesting a different 

depositional environment/sequence. 

The uppermost sediments of core no. 1 consist of approximately 119 cm (47 in.) of soft, 

cohesive, probable modern marine sediment occurring from the top of the core, with discrete 

lenses of shell hash (Figure 7.2.15). Unlike any of the other HI 178 cores, the next sedimentary 

unit observed in core no. 1 consists of soft, well-consolidated sediment interspersed with peat or 

other highly organic material and charcoal flecks. A 2-cm (0.8-in.) thick charcoal lens is 

contained within this unit starting at a depth of 122 cmbs (48 in.). This unit continues to a depth 

of 277 cmbs (109 in.) and contains two other intrusions: a 1-cm (0.4-in.) thick lens of silty sand 

located at a depth of 144 cmbs (57 in.), and a 4-cm (1.5 in.) thick lens of cohesive sediment 

lacking any organic material located at a depth of 181.5 cmbs (71.5 in.). A unit of silty sandy 

sediment, similar to those observed in cores no. 2, 7, 6, and 5 that begins at a depth of 277 cmbs 

(109 in.) and continues to the end of the recovered sediment, exhibiting increased oxidation with 

depth. The observed sedimentary sequence correlates with the expected stratigraphy from the 

acoustic profile (Figure 7.2.16).
112

Figure 7.2.15. Core log prepared for no. 

1 depicts the sediment units, as well as 

P-wave measurements (m/s) and

magnetic susceptibility (volumespecific) as measured from the Geotek 

MSCL (full size core logs are in 

Appendix B).
113

Figure 7.2.16. Core log no. 1 superimposed over the acoustic profile depicts the sedimentary units and their representative places on the 

acoustic profile. The core log and acoustic profile are shown at the same vertical scale; horizontal scales are not equal.

Core No. 1
114

As with the previous cores, sedimentary units were initially developed based on qualitative 

features such as sediment texture and Munsell color. Additional attributes such as presence or 

degree of oxidation and bioturbation were also used to separate cores into discrete sedimentary 

units. Following core descriptions and initial assessment, physical samples were collected for 

grain size analysis and mass-specific measurements of magnetic susceptibility.

Physical samples were collected from core no. 1 for grain size analysis; samples were collected 

at regular 10-cm (4-in.) intervals down the core. Additional samples were acquired between 

intervals when a distinctly different sediment horizon was encountered that would otherwise 

remain unsampled. Raw grain size values were plotted as s-curves, then calculated as both 

median grain size and graphic mean and rounded to the nearest hundredth (Table 7.7; Figure 

7.2.17). 

Table 7.7. Representative grain sizes for core no. 1, HI 178 

Sample 

No.

Sample Depth 

(cmbs)

Median (Mdmm) Graphic Mean

Mz (mm)

Wentworth 

Classification

1 10 0.081 0.088 very fine sand

2 20 0.05 0.071 coarse silt/very fine 

sand

3 30 0.031 0.041 coarse silt

4 40 0.044 0.048 coarse silt

5 50 0.042 0.047 coarse silt

6 60 0.053 0.064 coarse silt/very fine 

sand

7 70 0.031 0.045 coarse silt

8 80 0.021 0.045 medium/coarse silt

9 90 0.031 0.055 coarse silt

37 93 0.023 0.050 medium/coarse silt

38 96 0.014 0.034 fine/coarse silt

10 100 0.031 0.053 coarse silt

39 104 0.006 0.013 very fine/fine silt

40 107 0.010 0.029 fine/medium silt

11 110 0.008 0.022 fine/medium silt

41 112 0.006 0.011 very fine/fine silt

12 115 0.003 0.005 clay/very fine silt

42 117 0.003 0.005 clay/very fine silt

43 119 0.007 0.024 very fine/medium silt

13 120 0.003 0.006 clay/very fine silt

14 124 0.003 0.005 clay/very fine silt

44 126 0.003 0.004 clay

45 128 0.003 0.005 clay/very fine silt

46 130 0.004 0.008 clay/very fine silt

47 135 0.003 0.006 clay/very fine silt

15 140 0.002 0.003 clay
115

Sample 

No.

Sample Depth 

(cmbs)

Median (Mdmm) Graphic Mean

Mz (mm)

Wentworth 

Classification

16 143 0.004 0.006 clay/very fine silt

17 150 0.004 0.012 clay/fine silt

18 160 0.003 0.004 clay

19 170 0.021 0.060 very fine/medium silt

20 180 0.004 0.007 clay/very fine silt

21 183 0.004 0.006 clay/very fine silt

22 190 0.004 0.006 clay/very fine silt

23 200 0.042 0.055 coarse silt

24 210 0.021 0.033 medium/coarse silt

25 220 0.019 0.027 medium silt

26 230 0.018 0.032 medium/coarse silt

27 240 0.015 0.022 fine/medium silt

28 250 0.013 0.017 fine/medium silt

29 260 0.011 0.015 fine silt

30 270 0.005 0.007 very fine silt

31 280 0.018 0.025 medium silt

32 290 0.009 0.015 fine silt

33 300 0.011 0.014 fine silt

34 310 0.014 0.015 fine silt

35 320 0.013 0.015 fine silt

36 330 0.005 0.007 very fine silt

Core no. 1 was sampled continuously for magnetic susceptibility from the top of the core down 

through the interpreted marine and estuarine sediments, into the Pleistocene surface where 

observed oxidation suggested a former period of subaerial exposure (Figure 7.2.17).

The magnetic susceptibility curve prepared from core no. 1 depicts a general trend in which the 

uppermost magnetic susceptibility values are relatively high, but exhibit significant variability to 

a depth of approximately 70 cmbs (28 in.) (Figure 7.2.17). It is probable that these uppermost 

sediments represent modern marine sediments that have experienced punctuated episodes of 

scour, mixing, and redeposition that have resulted in fluctuating magnetic susceptibility values. 

A sharp decline in magnetic susceptibility values exists from 70 to 100 cmbs (28–39 in.), at 

which point magnetic susceptibility values remain consistently low to a depth of 190 cmbs (75 

in.). A noticeable spike in magnetic susceptibility values is present at 122 cmbs (48 in.), 

correlating with the charcoal lens observed in the core. Magnetic susceptibility values increase 

significantly from 190 to 210 cmbs (75–83 in.), at which point magnetic susceptibility values 

represent a third, distinct sequence of mid-range values with internal variability.

Samples were selected from core no. 1 for radiocarbon sampling to provide absolute ages for use 

in correlating the magnetic susceptibility data. Since the charcoal lens represented a unique 

horizon specific to core no. 1, samples were taken above, below, and within this unit. All 

samples were submitted to Beta Analytic for testing (Table 7.8). Calibrated ages were calculated;
116

however, conventional radiocarbon ages are used in subsequent figures to allow direct 

comparison against previous sea level data sets (Figure 7.2.18).

Table 7.8. Radiocarbon sample results for core no. 1, HI 178 

Sample Sample 

Depth (cmbs) 

Conventional Radiocarbon 

Age (yrs BP)

Calibrated (2 Sigma) 

Radiocarbon Age (yrs BP)

1 97–100 7,420 +/ 50 7,780–7,970

2 114–115.5 7,720 +/- 50 8,070–8,310

3 121.5–122 8,530 +/- 60 9,460–9,550

4 125 8,630 +/- 40 9,530–9,670

5 170.5 8,600 +/- 70 9,480–9,700

6 202 8,790 +/- 40 9,670–9,920
117

Figure 7.2.17. Diagram depicting grain size (graphic mean) and magnetic susceptibility data obtained from core no. 1, with sedimentary units 

provided for correlation.
118

 

Figure 7.2.18. Magnetic susceptibility curve from core no. 1 samples with conventional radiocarbon 

ages plotted at depth.

7,420 +/- 50 BP

8,530 +/- 60 BP

Charcoal 

8,630 +/- 40 BP

8,600 +/- 70 BP

8,790 +/- 40 BP

7,720

+/- 50
119

7.3 GALVESTON AREA 356

All cores from the Galveston 356 leasing area were acquired on 29 and 30 June 2009. Core 

recovery ranged from 74% to 105% of the possible 6-m (20-ft.) maximum; sediment recovery 

within each core ranged from 91% to 99% (Table 7.9).

Table 7.9. Core penetration and sediment recovery, GA 356

Core No.

Maximum 

Core Depth 

(m)

Maximum Core 

Depth (%)

Sediment 

Recovery (m)

Sediment 

Recovery (%)

1 4.45 74.2 4.28 96.2 

2 6.13 102.2 5.86 95.6

3 6.16 102.7 6.08 98.7

4 6.34 105.7 6.12 96.5

5 6.34 105.7 6.05 95.4

6 5.10 85.0 4.65 91.2

7 4.42 73.7 4.18 94.6

8 4.91 81.8 4.68 95.3

9 4.60 76.7 4.34 94.3

Based on the combined data interpretation, numerous cores were planned for the interpreted

midden feature reported prior to the current study. Cores no. 1, 2, 8, 7, 3, and 9 were placed 

southwest to northeast along the central axis of the reported midden (Figure 7.3.1). If the feature 

represented a midden then it was assumed that multiple samples would be necessary to discern a 

natural from an anthropogenic deposit. Cores no. 4, 5, and 6 were located along an 

approximately north-south axis outside of the channel margins to the west of the reported midden 

feature. Cores no. 4, 5, and 6 were collected as a control for comparison against the cores 

collected from within the boundary of the interpreted midden. 
120

Figure 7.3.1. Core locations are depicted on the interpreted 

channel system contours as interpreted from the data. The midden 

feature as reported is shown in red between lines 201 and 203. 

The survey lines are superimposed over the channel system in 

black. Depths are in meters below the seafloor.

Cores collected from within the boundary of the interpreted midden feature were hypothesized to 

be similar in stratigraphy; however, this was not the case once the cores were opened (Figure 

7.3.2). This may be due to variability within the thickness of the overlying, modern marine 

sediment.
121

Figure 7.3.2. Cores no. 2, 1, 8, 7, 3, and 9 (left to right) are shown against a composite image of the 

acoustic profile closest to the core sites (lines 508, 503, and 505, left to right). Black dashed lines 

indicate breaks between survey lines; red line approximates core location. Image is not to scale. Core 

logs are truncated at 420 cmbs (165 in.). 

Cores 1, 2, 3, and 9 exhibited relatively uniform stratigraphic units generally devoid of intrusive 

lenses or inclusions. Cores no. 7 and 8, however, contained similar units characterized by 

interbedded lenses of sand and silt at depths of 86–191 cmbs (34–75 in.) and 82–228 cmbs (32–

90 in.), respectively. A similar unit of interbedded lenses was observed in core no. 4, which was 

collected away from the interpreted midden feature (Figure 7.3.3).
122

Figure 7.3.3. Cores no. 4, 5, and 6 (left to right) are shown against the acoustic profile closest to the 

core sites (lines 501, 506, and 504, left to right). Black dashed lines indicate breaks between survey 

lines; red line approximates core location. Image is not to scale. Core logs are truncated at 420 

cmbs (165 in.).

Physical samples were collected from cores no. 2 and 8 for grain size analysis; one sample was 

collected per unit based on the initial core description. Raw grain size values were plotted as scurves, then calculated as both median grain size and graphic mean and rounded to the nearest 

hundredth (Tables 7.10 and 7.11). 

Table 7.10. Representative grain sizes for core no. 2, GA 356 

Sample 

No.

Sample Depth 

(cmbs)

Median (Mdmm) Graphic Mean

Mz (mm)

Wentworth 

Classification

1 34 0.045 0.057 coarse silt

2 80 0.0078 0.045 coarse silt/fine silt

3 120 0.0039 0.038 very fine silt

4 185 0.0039 0.006 fine/very fine silt

5 308 0.038 0.043 coarse silt

6 426 0.18 0.140 fine sand

7 510 0.106 0.101 very fine sand

Table 7.11. Representative grain sizes for core no. 8, GA 356 

Sample

No.

Sample Depth 

(cmbs)

Median (Mdmm) Graphic Mean

Mz (mm)

Wentworth 

Classification

1 41 0.045 0.057 coarse silt

2 98 0.0039 0.027 medium silt/very fine 

silt

3 116 0.0056 0.006 fine silt
123

Sample

No.

Sample Depth 

(cmbs)

Median (Mdmm) Graphic Mean

Mz (mm)

Wentworth 

Classification

4 152 0.0056 0.023 medium silt/fine silt

5 159 0.075 0.069 very fine sand

6 188 0.0056 0.008 fine silt

7 192 0.106 0.088 very fine sand

8 332 0.0078 0.039 coarse silt/fine silt

9 432 0.1 0.095 very fine sand

Samples were collected from core no. 6 for radiocarbon dates (Table 7.12). A thick horizon of 

black organic sediment was selected for testing. This horizon was not on the area identified as a 

midden deposit, but was located near a topographic high point, farther outside of the channel 

system (Figure 7.3.4). 

Table 7.12. Radiocarbon sample results for core no. 6, GA 356

Sample Sample Depth 

(cmbs) 

Conventional Radiocarbon 

Age (yrs BP)

Calibrated (2 Sigma) 

Radiocarbon Age (yrs BP)

E-1 360 9,830 +/- 50 11,190–11,300

E-2 412 10,460 +/- 50 12,150–12,650

Figure 7.3.4. Lab photo of core no. 6 at 360 cmbs (142 in.).

7.4 GALVESTON AREA 426

Coring locations were selected from the combined 2007 and 2008 geophysical data (Figures 

7.4.1 and 7.4.2). Based on the interpreted sub-bottom data, cores no. 1 and 2 were placed across 

the topographic feature as identified from the 2008 data, and represented the westernmost cores. 

During coring operations, core no. 2 was moved away from core no. 1 to test the lateral extent of 

the shell deposit observed within the sleeve for core no. 1. Cores were not acquired in numerical 

order and during operations core no. 3, which had been intended to sample a laterally migrating 

terrace extending north of the topographic feature, was cancelled in the field due to its proximity 
124

to the already acquired cores no. 7 and 8. Core no. 4 was positioned over a possible levee to the 

south of the southernmost channel. Core no. 5 was selected as an offsite control in an area of 

parallel bedded sediment with no visible channeling, located between the southernmost channel 

and the outcropping diapir feature. Core no. 6 was positioned over the topographic feature as 

identified from the 2007 data. Cores no. 7 and 8 were positioned due north of core no. 6 in order 

to test the interpreted inset terrace extending northward from the topographic feature. Core no. 9 

was originally planned adjacent to core no. 4 in order to increase the likelihood of coring through 

the possible levee feature; however, core no. 9 was collected from a different location while in 

the field. Core no. 9 was relocated in order to acquire additional samples from the same surface 

location as core no. 1 after densely packed shell was observed in the core sleeves during 

extrusion from the coring barrel. A combination of factors, including the presence of densely 

packed shells in the core sleeves for cores no. 1 and 9, resulted in the acquisition of two 

supplemental cores from Galveston Area 426. Cores no. 10 and 11 were acquired using the same 

surface location as core no. 1. Although the vessel drifted north during live-boat placement of the 

coring rig prior to acquisition of core no. 10, the intent was to acquire a large enough sample 

from the shell feature to determine if it represented a naturally-occurring reef or anthropogenic 

deposit. A total of 10 cores were acquired from this study area. Actual locations of all cores are 

shown in Figure 7.4.2.

All cores from the Galveston 426 leasing area were acquired on 30 June and 1 July 2009. Core 

recovery ranged from 65% to 101% of the possible 6-m (20-ft.) maximum; sediment recovery 

within each core ranged from 95% to 101% (Table 7.13).
125

Figure 7.4.1. Contours depict the channel system as interpreted from the combined data sets. The 

topographic feature is indicated by a red diamond. The survey lines are superimposed over the channel 

system. Primary survey lines are spaced 25 m (82 ft.) apart; 500 series lines were acquired in 2011. 

Depths are in meters below the seafloor.
126

Figure 7.4.2. Core locations are labeled on the channel system contours as interpreted from the 

combined data sets. The 2008 survey lines are superimposed over the channel system in black. Primary 

survey lines are spaced 25 m (82 ft.) apart; 500 series lines were acquired in 2011. Depths are in meters 

below the seafloor. Red diamonds indicate core locations.
127

Table 7.13. Core penetration and sediment recovery, GA 426

Core 

No.

Maximum 

Core Depth 

(m)

Maximum Core 

Depth (%)

Sediment 

Recovery (m)

Sediment 

Recovery (%)

1 5.92 98 5.80 98

2 5.42 90 5.45 101

4 6.12 101 6.04 99

5 4.54 75 4.45 98

6 5.99 99 5.89 98

7 4.74 78 4.50 95

8 5.43 90 5.25 97

9 4.48 74 4.29 96

10 5.95 98 5.87 99

11 3.94 65 3.90 99

Once the cores were opened, it became apparent that cores no. 1, 2, 9, 10, and 11 reflected 

similar sedimentary units related to a significant shell deposit (Figure 7.4.3). Cores no. 6, 7, and 

8 form a profile across the southern margin of the northernmost channel, including an inset 

terrace (Figure 7.4.4). Core no. 4 (Figure 7.4.5) represents a possible intact levee, while core no. 

5 (Figure 7.4.6) represents parallel to subparallel sediments outside of the channel system. Cores 

no. 4 and 5 represent isolated samples and are not included in the following discussion. 

7.4.1 Interpreted Shell Deposit

Cores 1, 9, and 11 represent a significant shell deposit located between two channels on the 

western boundary of the area surveyed in 2008. Core no. 10 is located 106 m (350 ft.) north of 

the common surface location for cores no. 1, 9, and 11; core no. 2 is located approximately 197 

m (650 ft.) east of the common surface location. All five cores were interpreted as having 

probable Holocene sediment to a depth of approximately 1.5 m (5 ft.) BSF, at which point the 

channel system and associated features appeared to be relatively intact. 
128

Figure 7.4.3. Annotated sub-bottom profiler image of survey line 502 showing the common surface location for cores no. 1, 9, and 11 (left) 

and core no. 10 (right) outlined in red. Vertical scale lines are in 150-m (492-ft.) intervals; horizontal scale lines are in 7.5-m (25-ft.) intervals; 

north is at right.

Figure 7.4.4. Annotated sub-bottom profiler image of survey line 504 showing the surface locations for cores no. 6 (left), 7 (middle), and 8 

(right) outlined in red. Vertical scale lines are in 150-m (492-ft.) intervals; horizontal scale lines are in 7.5-m (25-ft.) intervals; north is at right.
129

Figure 7.4.5. Annotated sub-bottom profiler image of survey line 507 showing the location for core no. 

4 outlined in red. Vertical scale lines are in 150-m (492-ft.) intervals; horizontal scale lines are in 7.5-m

(25-ft.) intervals; north is at right.

Figure 7.4.6. Annotated sub-bottom profiler image of survey line 506 showing the location for core no. 

5 outlined in red. Vertical scale lines are in 150-m (492-ft.) intervals; horizontal scale lines are in 7.5-m

(25-ft.) intervals; north is at right.

Core no. 1 was the first core acquired through the shell deposit, and, once opened, was found to 

contain approximately 85 cm (33 in.) of probable Holocene sediment with discrete shell lenses. 

This same sedimentary unit was found in cores no. 9 and 11, which were collected from the same 

surface location (Figure 7.4.7). The penetrometer, used to monitor core depth and potential 

refusal, was not functioning properly during acquisition of cores at this surface location, 

therefore cores were timed and withdrawn after an estimated duration, resulting in artificially 

shortened samples in cores 9 and 11. The next sediment unit across all three cores represents 

possible estuarine sediments with organic material. This unit overlies sediment units that include 
130

increasing amounts of coarser grained material with depth that overlie the densely packed shell 

deposit. The shell deposit continues past the captured ends of cores no. 1 and 11, but does not 

persist to the end of core no. 9 likely because of stratigraphic mixing caused by the common 

surface location.

Similar stratigraphic units were identified in cores no. 10 and 2, located due north and due east of 

cores no. 1, 9, and 11, respectively. The uppermost sedimentary unit in core no. 10 is the same as 

those within cores no. 1, 9, and 11; all four cores are within 106 m (350 ft.) of one another. 

Although core no. 2 lacks this same sedimentary unit at the top of the core, the remaining 

sequence is similar to that of core no. 10 (Figure 7.4.8). Core no. 10 contains approximately 220 

cm (87 in.) of densely packed shell, similar to core no. 1, while core no. 2 has a much thinner 

lens of densely packed shell overlying coarse grained sediment with evidence of oxidation.

Based on the contoured acoustic survey data, all five cores are located along the ridge of a 

topographic high area between the two observed channels. It is apparent that the shell deposit is 

concentrated in the area surrounding cores no. 1, 9, 10, and 11, but extends to a lesser extent to 

the east at least as far as core no. 2. Though the shell deposit is a significant feature, variable 

horizons are evident when the acoustic profiles and sediment units are compared (Figure 7.4.9 

and 7.4.10).

Sedimentary units were initially developed based on qualitative features such as sediment texture 

and Munsell color; additional attributes such as presence or density of shell and degree of 

oxidation were also used to separate cores into discrete sedimentary units. Following core 

descriptions and initial assessment, physical samples were collected for grain size analysis and 

mass-specific measurements of magnetic susceptibility from representative cores.
131

Figure 7.4.7. Core logs prepared for cores no. 1, 9, and 

11 depict the sediment units (full size core logs are in 

Appendix B).

Core no. 1 Core no. 9 Core no. 11
132

Figure 7.4.8. Core logs prepared for 

cores no. 10 and 2 (full size core logs are 

in Appendix B).

Core no. 10 Core no. 2
133

Figure 7.4.9. Core logs superimposed over the acoustic profile depict the sedimentary units and their 

representative places on the acoustic profile. Core logs and the acoustic profile are shown at the same 

vertical scale; horizontal scales are not equal. North is at right.

Figure 7.4.10. Composite photograph of core no. 10, section E, with densely packed shell.

Physical samples were collected from core no. 10 for grain size analysis; one sample was 

collected every 10 cm (4 in.) down the core for the first 2 m (7 ft.). The remaining samples were 

collected from the dense shell deposit at arbitrary levels based on the ability to capture enough 

sediment between shells for processing. Raw grain size values were plotted as s-curves, then 

calculated as both median grain size and graphic mean and rounded to the nearest hundredth 

(Table 7.14; Figure 7.4.11). Median grain sizes were generally smaller than the calculated 

graphic mean size. Sediment classes range from fine sand to very fine silt; no clay was observed 

within the calculated grain sizes. Due to the similarity of the observed sedimentary units, results 

from core no. 10 were assumed to be representative for similar units within cores from this area 

within GA 426. 

Core 

no. 1

Core 

no. 11

Core 

no. 9

Core 

no. 10
134

Table 7.14. Representative grain sizes for core no. 10, GA 426

Sample 

No.

Sample Depth 

(cmbs)

Median (Mdmm) Graphic Mean

Mz (mm)

Wentworth 

Classification

1 10 0.082 0.093 very fine sand

2 20 0.031 0.065 coarse silt/very fine 

sand

3 30 0.036 0.054 coarse silt 

4 40 0.038 0.044 coarse silt

5 50 0.034 0.042 coarse silt 

6 60 0.028 0.045 medium/coarse silt

7 70 0.045 0.083 coarse silt/very fine 

sand

8 80 0.098 0.108 very fine sand

9 90 0.017 0.062 medium/coarse silt

10 100 0.005 0.007 very fine silt

11 110 0.007 0.015 very fine/fine silt

12 120 0.058 0.063 coarse silt/very fine 

sand

13 130 0.087 0.077 very fine sand

14 140 0.070 0.070 very fine sand

15 150 0.066 0.068 very fine sand

16 160 0.053 0.059 coarse silt

17 170 0.022 0.046 medium/coarse silt

18 180 0.084 0.073 very fine sand

19 190 0.078 0.070 very fine sand

20 200 0.069 0.063 very fine sand

21 250 0.090 0.088 very fine sand

22 280 0.071 0.064 very fine sand

23 330 0.102 0.084 very fine sand

24 390 0.010 0.044 fine/coarse silt

25 464 0.012 0.042 fine/coarse silt

26 550 0.102 0.202 very fine/fine sand
135

Figure 7.4.11. Graphic mean 

grain size curve for core no. 10.

Core no. 10 was sampled continuously for magnetic susceptibility from the top of the core down 

through the interpreted marine and estuarine sediments and throughout the entire shell deposit. 

The upper half of core no. 9 was sampled at arbitrary intervals, based on stratigraphy but reflects 

a similar pattern of magnetic susceptibility values (Figure 7.4.12).

Each of the magnetic susceptibility curves prepared from cores no. 9 and 10 depict a general 

trend in which the uppermost magnetic susceptibility values are relatively higher than values at 

the bottom of the core, but exhibit a significantly increased unit between depths of 50 and 100 

cmbs (20 and 39 in.). Similar peaks within the magnetic susceptibility data recorded during core 

logging indicate that this unit is a real artifact of the sedimentary record and is not a spike within 

the data. 

Samples were selected from core no. 10 for radiocarbon sampling to provide absolute ages for 

use in correlating the magnetic susceptibility data. All samples were submitted to Beta Analytic 

for testing (Table 7.15). Calibrated ages were calculated; however, conventional radiocarbon 

ages are used in text and in subsequent figures to allow direct comparison against previous sea 

level data sets.

0

100

200

300

400

500

600

0.000 0.100 0.200

Grain Size (MZ mm)
136

Figure 7.4.12. Diagram depicting magnetic susceptibility data obtained from cores no. 10 and 9 with 

their interpreted sediment horizons.

Table 7.15. Radiocarbon sample results for core no. 10, GA 426 

Sample Sample Depth 

(cmbs) 

Conventional 

Radiocarbon Age 

(yrs BP)

Calibrated

(2 Sigma)

Radiocarbon Age 

(yrs BP)

1 39 9,890 +/ 50 10,610–11,050

2 85 9,870 +/- 50 10,600–11,020

3 105 9,980 +/- 50 11,250–11,640

4 106 10,070 +/- 60 11,320–11,840

5 149 41,660 +/- 620 Outside of 

calibration range

6 254 38,880 +/- 900 Outside of 

calibration range

7 390.5 >43,500 ---

8 460.5 >43,500 ---

Radiocarbon ages suggest a long history of sediment deposition within the upper 3 m (10 ft.), 

spanning over 33,000 years. When correlated with the magnetic susceptibility curve for core no. 

10, the radiocarbon ages demonstrate that the sedimentary units have been formed as punctuated 

events, rather than one continuous event (Figure 7.4.13).
137

Figure 7.4.13. Magnetic susceptibility curve from core no. 10 samples with conventional 

radiocarbon ages plotted at depth.

-600

-500

-400

-300

-200

-100

0

3.00E-08 1.30E-07 2.30E-07 3.30E-07 4.30E-07 5.30E-07

MS (m3/kg) and Conventional Radiocarbon Age

9,890 +/ 50 BP

9,870 +/- 50 BP

9,980 +/-50 BP 

10,070 +/-60 BP

41,660 +/-620 BP

38,880 +/-900 BP

>43,500 BP

>43,500 BP
138

7.4.2 Interpreted Inset Terrace Profile

Cores 6, 7, and 8 represent a profile along an interpreted inset terrace on the southern margin of 

the northernmost channel surveyed in 2008. The interpreted Holocene sediment depth increases 

from core no. 6, which represents the highest point along the channel margin, to core no. 8, 

ranging from approximately 1.5 m (5 ft.) to 3 m (10 ft.) BSF (Figure 7.4.4) as calculated from 

the acoustic profiles. 

Core no. 6 is located on the upper margin of the channel, and captured the longest sediment 

profile of the three cores (Figure 7.4.14). With varying intrusions, this unit was observed 

consistently in cores no. 7 and 8 to depths of 130–165 cmbs (51–65 in.). Cores no. 6 and 7 are 

most similar in profile, and it is likely that the variable unit thicknesses across the cores is 

attributed to the slope on which core no. 7 was acquired, grading into the channel system. The 

second sedimentary unit in these cores features oxidized sediment, suggesting these sediments 

were exposed as dry land in the past. Core no. 8 lacks this same unit and instead features a thin 

horizon of consolidated sediment streaked with dark, probable organic material. The third 

sedimentary unit in all three cores consists of densely packed shell with oxidized sediment. 

Underlying sediments in core no. 6 transition from gritty sediment with few scattered shells at 

the bottom of the shell deposit to sediments streaked with possible organic flecks throughout. 

Core no. 7 has the same gritty sediment with evidence of oxidation at the bottom of the shell 

deposit but lacks the organic-streaked sediment unit. This may be because core no. 7 is the 

shortest of the series and did not penetrate into this sediment unit. The lowest sedimentary units 

in core no. 8 include alternating lenses of sandy and organic streaked sediment, suggesting this 

area experienced repeated episodes of deposition and scour, possibly during terrace formation.
139

Figure 7.4.14. Core logs prepared for nos. 6, 7, and 8

depict the sediment units (full size core logs are in 

Appendix B).

Core no. 6 Core no. 7 Core no. 8
140

Based on the contoured acoustic survey data, the three cores should not have uniform 

stratigraphic units as they represent different elevations of the channel’s inset terrace and margin 

(Figure 7.4.15). 

Figure 7.4.15. Core logs superimposed over the acoustic profile depict the sedimentary units and their 

representative places on the acoustic profile. Core logs and the acoustic profile are shown at the same 

vertical scale; horizontal scales are not equal. North is at right.

As with the previous cores, qualitative attributes were used to distinguish sedimentary units. 

Physical samples were collected subsequently from core no. 6 for grain size analysis; one sample 

was collected within each qualitative unit, and from intrusive lenses observed within units. Raw 

grain size values were plotted as s-curves, then calculated as both median grain size and graphic 

mean and rounded to the nearest hundredth (Table 7.16; Figure 7.4.16). Median grain sizes were 

generally smaller than the calculated graphic mean size. Sediment classes range from very fine 

sand to very fine silt; no clay was observed within the calculated grain sizes. Due to the 

similarity of the observed sedimentary units, results from core no. 6 were assumed to be 

representative for similar units along this channel margin. 

Core 

no. 6

Core 

no. 7

Core 

no. 8
141

Table 7.16. Representative grain sizes for core no. 6, GA 426

Sample 

No.

Sample Depth 

(cmbs)

Median (Mdmm) Graphic Mean

Mz (mm)

Wentworth 

Classification

1 39 0.025 0.038 medium/coarse silt

2 93 0.010 0.023 fine/medium silt

3 112 0.075 0.072 very fine sand

4 140 0.092 0.082 very fine sand

5 181 0.031 0.054 coarse silt 

6 216 0.027 0.051 medium/coarse silt

7 246 0.006 0.013 very fine/fine silt

8 267 0.045 0.059 coarse silt

9 309 0.090 0.098 very fine sand

10 383 0.007 0.024 very fine/medium 

silt

11 434 0.016 0.036 medium/coarse silt

12 523 0.077 0.069 very fine sand

Figure 7.4.16. Graphic mean grain size 

curve for core no. 6.

0

100

200

300

400

500

0.000 0.020 0.040 0.060 0.080 0.100

Grain Size (MZ mm)

143

8. “REAL” ENVIRONMENTS

It was hypothesized at the beginning of this project that geographical, operational, and modified 

environments could be identified on the OCS through a spatial application of middle-range 

theory using indices recorded from geophysical survey and sampling. Site formation process 

variables were identified as they relate to environmental changes from a subaerial landscape to 

the modern marine environment on the OCS (Chapter 2). Terrestrial patterns of landscape 

exploitation demonstrated the types of landforms most likely to be associated with 

archaeological sites, providing guidance for the identification of the geographical environment 

(Chapter 3). Additional indices of anthropogenic activity were culled from previous studies in 

the GOM region and from other submerged contexts (Chapter 4), and were identified from some 

of the geophysical data sets (Chapters 6 and 7). Geographical and operational environments were 

identified in both survey areas, and two possible examples of modified environments were 

identified from the geophysical and environmental data.

8.1 GEOGRAPHICAL ENVIRONMENTS

As defined by Butzer (1982:253) and used in this study, the geographical environment is that 

which is available for occupation and exploitation by a human population. It is one of many 

sediment horizons visible on acoustic profiles, but through an examination of horizon depth and 

age, relative to the archaeological record, it is possible to place specific horizons and their 

associated landforms within a context of possible occupation and exploitation. A combination of 

acoustic data, primary wave velocity, and radiocarbon dates were used to characterize the 

geographical environments recorded in each survey area. One possible geographical 

environment, a younger Deweyville Terrace, was also tested as part of this scope of work. 

8.1.1 Characterizing Geographical Environments 

The physical landscape, or geographical environment, available for possible exploitation by 

human populations was readily identified from the acoustic profile data. At close interval survey 

line spacing (25 m [82 ft.]), depths for the interpreted landscape horizons for the survey areas 

were contoured. The resulting renderings (provided in Chapters 6 and 7) effectively stripped off 

the overlying sediments, consisting of modern marine and estuarine strata, leaving the 

paleolandscape visible. In this manner it was possible to identify paleochannels as possible 

freshwater resources, as well as inset terraces and intact topographic features. Both the inset 

terraces and topographic features have been previously identified as indicators for prehistoric site 

occurrence and preservation. Based on a qualitative assessment of the acoustic profile data it was 

possible to identify the geographical environment in each survey area from the corresponding 

geophysical data. Gross landscape interpretation was based on an assumption that sub-surface 

depths for the interpreted landscape could be calculated using an assumed constant speed of 

sound. 

Acoustic survey profiles were interpreted by using the average speed of sound in saltwater 

(1,500 m/sec) to calculate depth. Minimum and maximum depths for observed features within 
144

each horizon were then plotted against the composite sea level curve presented in Chapter 2 to 

determine if the paleolandscape dated to a time correlating with known occupation of the Gulf 

coast region. In all survey areas it was assumed that the average speed of sound would be 

accurate enough to determine depth within the shallow sub-surface. Following this method, the 

geographical environments in the High Island and Galveston leasing areas dated to 

approximately 5,000–10,200 yrs BP, and 7,800–11,800 yrs BP respectively (as previously 

presented in Figure 6.3.1). Although these are wide ranges for possible occupation, they correlate 

with the Paleoindian and Early Archaic cultural-chronological periods in Texas and Louisiana. 

This was sufficient evidence to continue forward with environmental sampling (coring) in each 

area.

All of the cores acquired from this study were logged prior to opening using a Geotek multisensor core logger, which produced primary wave, or P-wave, velocity profiles for each core 

section. The P-wave data were initially recorded in μsec (seconds per foot) and processed to 

calculate downcore acoustic wave penetration in m/sec. Acoustic data profiles are recorded 

within the sub-bottom profiler as a function of time, therefore using the average speed of sound 

in two-way time travel each second of data is equivalent to 750 m (2,461 ft.) in depth. The 

acoustic data profiles displayed in this study are presented on a millisecond (ms) scale; 

horizontal scales are plotted in 10 ms intervals, therefore 10 ms are equal to 7.5 m (24.6 ft.), or 1 

ms is equal to 0.75 m (2.46 ft.).

The actual speed of sound was found to vary considerably within each survey area, and between 

neighboring cores. This suggests that age estimates based on depths calculated using the average 

speed of sound may contain errors. In the HI 178 survey area, measured P-wave velocity from 

cores no. 6 and 7, when plotted against the average speed of sound, demonstrate this variability 

(Figure 8.1.1). The sub-bottom profiler data is a visual representation of the changes in velocity 

between the different strata, representing changes in acoustic impedance.

The measured P-wave velocities within HI 178 ranged from a minimum of 1,100 m/sec to a 

maximum 1,825 m/sec. When calculated as depth, 1 ms of data is equal to a vertical distance of 

0.55–0.913 m (1.8–2.99 ft.). Depths calculated from the acoustic profiles using the average speed 

of sound are therefore accurate within a margin of 0.36 m (1.2 ft.). This error does not 

significantly impact the date ranges for landscape age as determined using constant velocityderived depths on the composite sea level curve. 
145

Figure 8.1.1. Measured P-wave velocities for HI 178 cores no. 6 and 7 compared to the average 

speed of sound.

Cores from GA 426 show similar variability in the P-wave profiles (Figures 8.1.2 and 8.1.3). The 

measured P-wave velocities within the interpreted shell deposit in GA 426 range from a 

minimum of 915 m/sec (3,002 ft./sec) to a maximum 1,800 m/sec (5,906 ft./sec) while those 

along the interpreted channel margin range from 980 m/sec to 1,835 m/sec (3,215 ft./sec to 6,020 

ft./sec). Depths calculated within the shell deposit are considered accurate within a margin of 

0.44 m (1.44 ft.), while depths along the channel margin profile are accurate within a margin of 

0.43 m (1.41 ft.). 

In addition to their utility in calculating accurate depths below the seafloor, seismic wave 

velocities have been used to characterize marine sediments in geology for over 40 years (Ayres 

and Theilen 1999:431). In engineering applications, abrupt changes in P-wave velocity are used 

to identify stratigraphic features, such as the presence of groundwater tables, within 1-m (3-ft.) 

depth accuracy (Bellana 2009:14). Normal marine sediments exhibit increased shear strength at 

the seafloor due to compression caused by the weight of the overlying water column (Ayres and 

Theilen 1999:433), but the P-wave profile under the water/sediment interface may be used to 

categorize lithologic facies (Hamilton and Bachman 1982). Of specific application to the cores 

from this study, mean grain size and percent clay fraction directly impact velocity (Hamilton and 

Bachman 1982:1899). 

0

0.5

1

1.5

2

2.5

3

3.5

4

900 1100 1300 1500 1700 1900

Depth below seafloor (meters)

Speed of sound (meters/second)

Speed of Sound in Two-Way Time Travel: Actual vs. Average

Average Velocity

HI178-6

HI178-7
146

Figure 8.1.2. Measured P-wave velocities for GA 426 cores no. 1, 9, and 11 compared to the average 

speed of sound.

Primary-wave (P-wave) velocities (Vp) for sediments within the study area ranged from 905 

m/sec to 2,067 m/sec (2,969 ft./sec to 6,781 ft./sec), both of which were recorded in the GA 356 

cores. Mid-range values within this data set correlate with measured P-wave velocities of marine 

sediments, which can be between 1,400 and 1,700 m/sec (4,593 and 5,577 ft./sec) (Ayres and 

Theilen 1999:434). Previous studies have correlated marine sediments and Vp, producing 

expected values for material type and sediment classes (Table 8.1). 

Velocity is impacted by many factors, for example decreasing in direct relation to decreasing 

sediment porosity and water content; therefore, similar sediment types may react differently 

under various conditions (Ayres and Theilen 1999:434). P-wave velocity in clay particles varies 

from approximately 200 to 1,400 m/sec (656–4,593 ft./sec) when dry but increases to 1,200–

2,200 m/sec (3,937–7,218 ft./sec) when wet, suggesting that it may be possible to correlate grain 

size and P-wave velocity with prolonged subaerial exposure. In the case of the shell deposit 

identified in GA 426, core depths correlating with the densest areas of shell show Vp that is 

consistently lower than the average (1,500 m/sec [4,921 ft./sec]). No corresponding P-wave 

velocities could be found for shell mounds or middens, therefore it is assumed that the P-wave 

values recorded in the core logs are based on the sediment within these dense shell horizons, and 

that air pockets trapped between imbricated shells account for the velocity slow-downs observed 

within the Vp profiles.

0

1

2

3

4

5

6

800 1000 1200 1400 1600 1800

Depth below seafloor (meters)

Speed of sound (meters/second)

Speed of Sound in Two-Way Time Travel: Actual vs. Average

Average Velocity

GA426-1

GA426-9

GA426-11
147

Figure 8.1.3. Measured P-wave velocities for GA 426 cores no. 6, 7, and 8 compared to the average 

speed of sound.

Table 8.1. P-wave velocities of specific materials

Material type Sediment classification Vp (m/sec)

Air b 320

Water b 1,500

Ice b 3,200

Clastic sediment b 1,400–5,300 

Very fine sand a 1,709

Silty sand a 1,658

Sandy silt a 1,644

Silt a 1,615

Sand-silt-clay a 1,582

Clayey silt a 1,546

Silty clay a 1,517 

Sandstone b 4,300

Salt b 3,800–5,200

Source: (a) Hamilton and Bachman 1982; (b) Bormann et al. 2012

 

0

1

2

3

4

5

6

900 1100 1300 1500 1700 1900

Depth below seafloor (meters)

Speed of sound (meters/second)

Speed of Sound in Two-Way Time Travel: Actual vs. Average

Average Velocity

GA426-6

GA426-7

GA426-8
148

Acoustic profiling has been consistently referred to as the first step in searching for submerged 

prehistoric environments, but typically relies on data acquired using an assumed, or average, 

velocity of sound. The measured P-wave profiles from cores acquired in this study demonstrate 

that horizon depths calculated from the acoustic survey data were accurate within approximately 

half a meter. This is an important finding given that much of the survey work done to identify 

potential prehistoric geographical environments in the GOM consists entirely of acoustic 

profiling, without the benefit of supplemental physical samples; however, there is not a direct 

correlation between geographical environment depth and time range of subaerial exposure. 

Depths calculated from P-wave velocities or even assumed speeds of sound were plotted on sea

level curves in order to determine the potential dates of exposure and final inundation, but do not 

always accurately indicate the horizon’s age. Radiocarbon testing was conducted on sediment 

and shell samples obtained from cores in all four areas. The geographical landscape in High 

Island was dated to approximately 5,000–10,200 yrs BP using the composite sea level. 

Radiocarbon dates from samples between 16.4 and 17.4 m (53.8 and 57 ft.) BSL yielded absolute 

dates of 7,420 +/- 50 yrs BP [7,780–7,970 cal yrs BP] from HI 178, while samples from 

approximately the same depths in HI 160 yielded absolute dates of 8,210 +/- 60 yrs BP [9,010–

9,400 cal yrs BP]. The absolute dates correlated with the expected dates of landscape exposure as 

indicated from the acoustic profile depths (Figure 8.1.4). 

Radiocarbon dates represent a much larger age range in the Galveston Area. The geographical 

environment was dated between 7,800 and 11,800 yrs BP using the composite sea level curve. In 

GA 356, samples collected from depths of 30.1 and 30.6 m (98.8 and 100.3 ft.) BSL returned 

dates of between 9,830 +/-50 yrs BP [11,190–11,300 cal yrs BP] and 10,460 +/- 50 yrs BP 

[12,150–12,650 cal yrs BP]. Dates from samples in GA 426 taken at depths between 31.3 and 

35.9 m (102.7 and 117.8 ft.) BSL yielded absolute dates ranging from 9,890 +/ 50 yrs BP 

[10,610–11,050 cal yrs BP] to greater than 43,000 yrs BP. The GA 426 dates from the shell 

deposit (core no. 10) suggest either a long period of exposure with little to no sediment accretion 

followed by a punctuated period of deposition, or a significant unconformity within the profile 

possibly caused by scour or sediment removal. No other radiocarbon dates were run from the 

Galveston Area. Therefore, it is not possible to state with certainty if samples from similar total 

depths BSL on other geographical features, such as the inset terrace indicated by cores no.6, 7, 

and 8, are any younger or if the shell deposit represents an anomaly in the radiocarbon profile of 

this geographical landscape. What is clear from the GA 426 radiocarbon dates is that the 

uppermost sections of the shell deposit were exposed, or in the shallow sub-surface, and possibly 

available for exploitation as part of the operational environment during periods correlating with 

known human occupation of the Gulf coast.
149

Figure 8.1.4. Composite sea level curve with radiocarbon dates and estimated ages (based on acoustic profiles) shown.
150

8.1.2 Younger Deweyville Terrace 

The channel system identified in HI 160 consists of broad channels abutted by an interpreted 

younger Deweyville terrace and a Deweyville/Holocene floodplain. Cores were collected across 

the interpreted Deweyville terrace. Although depths were not given for the younger Deweyville

terrace, the Deweyville/Holocene floodplain was reportedly located 3–12.8 m (10–42 ft.) BSF 

(Landry and DuVal 1995). The three principle studies on prehistoric offshore archaeology in the 

GOM (CEI 1977; Gagliano et al. 1982; and Pearson et al. 1986) identify Deweyville terraces as 

high-probability areas for archaeological site occurrence and preservation. According to Pearson 

et al. (1986:xxi) the Deweyville is characterized by “an initial, hard reflector beneath which there 

is a void or little indication of variability in the sediments.” This may be differentiated from 

Pleistocene sediments, which are typically well stratified, parallel deposits of the 

Beaumont/Prairie formation.

In the 1944 Mississippi River Commission report, Fisk delineated four major Quaternary terraces 

in the GOM; the Williana, Bentley, Montgomery, and Prairie (also known regionally offshore 

Texas as Beaumont) terraces (Bryant et al. 1991). Following Fisk, Bernard created a revised 

typology for Gulf terraces, identifying and defining Deweyville terraces in his 1950 dissertation. 

Prior to Bernard, all post-Beaumont Prairie sediments had been classified as undifferentiated, 

Holocene-aged strata (Blum, Morton, and Durbin 1995). The genesis of Deweyville terraces has 

been debated in the geologic literature. Fisk’s earlier model postulated that the post-Beaumont 

Prairie strata represented Wisconsinan channel incision during post-glacial sea level rise (Blum, 

Morton, and Durbin 1995). According to Bernard, the Deweyville terraces resulted from cyclic 

transgressive and prograding shorelines during the Late Wisconsin, but recent research points to 

a diverse package of climate change conditions including larger mean annual discharge rates, 

changes in local groundcover, changes in annual and seasonal precipitation, and even the 

occurrence of “superfloods” (Blum, Morton, and Durbin 1995).

 

To avoid ambiguity implied by the use of the term “terrace,” Autin proposed the term “complex” 

to refer to a specific geomorphologic horizon or temporally related horizons with a common 

sedimentary sequence possibly indicative of multiple depositional events (Bryant et al. 1991:17). 

The standard structural chronology for the Lower Mississippi Valley proposed by Fisk was 

revised by Autin et al. (1991) to include four complexes; Upland, Intermediate, Prairie, and 

Deweyville. According to Autin et al. (1991), the Deweyville complex is located between the 

Prairie and Holocene floodplains, and may consist of multiple degradational tiers. Deweyville 

complex features can be located above the modern flood plain, and sediments are typically 

coarser than either older Prairie Complex sediments or more recent Holocene sediments (Autin 

et al. 1991). Deweyville complex sediments can contain several meters of oxidized sand-silt-clay 

that fines downward into a sand-gravel matrix up to 12 m (39 ft.) in thickness (Autin et al. 1991). 

More recently, Blum, Morton, and Durbin (1995:54) suggested that the Deweyville features 

should be interpreted as “unconformity-bounded allostratigraphic units” because although some 

terraces were not expressed on the surface, they all share a common age, genetic origin, and 

morphological significance. Additionally, sediments in Colorado valley Deweyville profiles are 

gravelly or sandy, with minimal silty overburden, which correlates with the sediment description 
151

provided by Autin et al. 1991 (Blum, Morton, and Durbin 1995). Soils of the Deweyville 

Complex are markedly different than those of surrounding complexes, consisting of ultisols and 

weathered alfisols, a result of drainage from older, higher terrace structures (Autin et al. 1991).

Ages for the Deweyville Complex are derived locally. Previously, the Deweyville Complex was 

believed to relate to sea level rise at the end of the Late Wisconsin, effectively 18,000 yrs BP 

(Autin et al. 1991). Estimates published in 1991 for Deweyville features in the Gulf Coast region 

vary from 8,000 to 30,000 yrs BP for different phases of terrace formation (Autin et al. 1991). 

Newer evidence has not identified an exact date for the Deweyville Complex and has instead 

created target date ranges. 

Bernard’s original identification of the Deweyville terraces noted that the channel dimensions for 

this horizon were much larger than modern channels (Blum, Morton, and Durbin 1995). This 

observation has been supported by subsequent studies that noted Deweyville terraces tend to 

exhibit well-preserved relict channel features that are larger than more recent features on the 

modern floodplain surfaces (Heinrich 2006).

Cores in the HI 160 area reached a subseafloor depth of 4.57–5.43 m (14.99–17.81 ft.) BSF, and 

should have been sufficient to reach the interpreted younger Deweyville terrace on which the 

interpreted shell midden was located at a depth of 3.6 m (11.8 ft.) BSF. The cores, however, do 

not show overwhelming evidence of the Deweyville terrace, as defined above, within the 

captured sediments. The cores represent fine sandy sediments at the seafloor underlain by coarse, 

medium, and fine grained silts that do not uniformly become finer downward. No evidence of 

sand-gravels was observed at depth. Sediments in the bottom section of core no. 10 exhibit

evidence of oxidation (orange staining) but consist of silty sediment devoid of sand or other 

coarser grained material (Figure 8.1.5). The cores in HI 178 exhibit significantly more evidence 

of oxidation than sediments recovered from HI 160. The cores in HI 160 consist largely of silts, 

with varying fractions, which is inconsistent with the minimal silty overburden for Deweyville 

sediments as defined by Autin et al. (1991). It is entirely possible that the cores from HI 160 did 

not capture sediments deep enough to sample the interpreted Deweyville terrace. However, based 

on qualitative descriptions that include such evidence as oxidation, it is more likely that the cores 

along inset terraces in HI 178 represent sediments from the Deweyville complex.

Figure 8.1.5. Possible evidence of oxidation within core no. 10, HI 160, at a depth of 4 m (13 ft.) below 

seafloor. 
152

8.2 OPERATIONAL ENVIRONMENTS

Four distinct features were identified within the overall geographical environments in HI 178 and 

GA 426, including two inset terraces (HI 178 and GA 426), an intact topographic feature (HI 

178), and a shell deposit (GA 426). By themselves, these features do not confirm or refute the 

possible presence of humans on the OCS, but they do form a landscape available for exploitation. 

It is necessary then to identify any resources available for subsistence, which would create an 

operational environment within the geographical landscape.

The cultural chronological periods that coincide with subaerial exposure of the geographical 

environments in High Island and Galveston leasing areas include both the Paleoindian and Early 

Archaic periods. Both periods include populations of hunter-gatherers who left scant evidence of 

their presence in terms of material culture. In a review of prehistoric sites between Sabine Lake 

and Corpus Christi, Texas, Aten (1971:1–2) found that the most common type of archaeological 

site was the shell midden, which ranged in extent from refuse deposits created during temporary 

occupation to periodic occupation over hundreds of years. Relative to operational environments, 

these shell middens typically consisted of clam, oysters, faunal materials, and, in later prehistoric 

periods, pottery and projectile points (Aten 1971:1–2). 

Given the paucity of artifacts associated with Paleoindian and Early Archaic period sites, and the 

relatively small core diameter used for physical sampling, it is not surprising that no artifacts 

were identified in any of the cores recovered in the study areas. It is still possible, however, to 

identify elements within the landscape that could have supported anthropogenic subsistence 

systems. Proxy data indicated by the magnetic susceptibility profiles provide evidence of 

possible climate conditions, while shell samples and pollen analysis provide evidence of 

available fauna and flora capable of supporting subsistence.

8.2.1 Magnetic Susceptibility

As discussed in Chapter 5, magnetic susceptibility has been used to identify anthropogenic 

activities and evidence of prehistoric activity (Evans and O’Connor 1999). As used in this study, 

measurements of magnetic susceptibility are used to develop a proxy record of climate conditions 

within each core sediment profile, since increases in temperature and moisture typically result in 

higher magnetic susceptibility values. By itself, the magnetic susceptibility profile is merely a 

relative profile devoid of absolute dates. As previously stated in Chapter 5, magnetic 

susceptibility data have inherent limitations; in and of itself the data will only result in a relative 

curve of conditions and change. Magnetic susceptibility data from the study areas cores have 

been tied into the stratigraphic record using the absolute radiocarbon dates obtained during lab 

analyses. 

An archaeological application of magnetic susceptibility data serving as a climate proxy was 

conducted in inland Texas, and demonstrates its utility within the Gulf coast region. In fact, 

sediment data from Hall’s Cave, Texas demonstrated that magnetic susceptibility data were a 

more accurate indicator of the end of full glacial climate conditions than sediment lithology 

(Ellwood and Gose 2006). 
153

Data compiled by Ellwood and Gose (2006) correlated local climate variations and magnetic 

susceptibility data from Hall’s Cave, Texas with global events to create a timeline of climate 

change. Full glacial conditions existed between approximately 14 and 19 kya BP, a trend 

supported by lower relative magnetic susceptibility values. An anomalously high range of

magnetic susceptibility values recorded at Hall’s Cave at approximately 17–17.5 kya BP 

correlates with the global date of 16,800 +/- 255 for the Heinrich H1 event, which resulted in 

milder conditions along the western Atlantic and Gulf coast regions (Ellwood and Gose 2006). A 

steady increase in magnetic susceptibility values, which was consistent with changes noted in the 

faunal assemblage, suggested that the end of full glacial conditions occurred at the site by 14,200 

yrs BP (Ellwood and Gose 2006). An overall warming trend 2–14 kya BP was interrupted by a 

temporally restricted decrease in magnetic susceptibility values between 11–14 kya BP. This 

decrease approximately correlated with the Younger Dryas climate event, which has been dated 

to 11.5–12.5 kya BP (Ellwood and Gose 2006). 

From 8,250 to 8,050 yrs BP, magnetic susceptibility values at the Hall’s Cave site increased, a 

pattern which was correlated with the 8,200 yrs BP event, hypothesized as the final pulse of 

glacial meltwater into the GOM (Ellwood and Gose 2006). Data from the Greenland Ice Sheet 

Project (GISP) 2 identified this meltwater pulse as occurring 8,250–8,180 yrs BP, although this 

event could not be identified in all of the GISP cores (Ellwood and Gose 2006). At roughly 4,300 

yrs BP, an anomalous increase in magnetic susceptibility values at the Hall’s Cave site was 

correlated to a 4,400 yrs BP event in British Columbia, and interpreted as an increase in rainfall 

that subsequently increased volume to the marine system (Ellwood and Gose 2006). 

Magnetic susceptibility was measured in two ways for this study: as mass-specific and volumespecific values. Volume magnetic susceptibility profiles were recorded continuously down each 

core section during core logging. Individual cores were sampled either continuously or at 

intervals as mass-specific values during lab sampling and analyses. Mass-specific magnetic 

susceptibility measurements are preferred over volume-specific magnetic susceptibility due to 

the potential for introduced error related to potential sediment compaction within samples 

(Thacker and Ellwood 2007). Mass-specific measurements were not always conducted as 

continuous samples, however, and the use of arbitrary levels resulted in overly simplified curves. 

In future studies it is suggested that continuous sampling be conducted to allow for direct 

comparison with P-wave, grain size, and radiocarbon results. To allow for continuous curves, 

volume-based measurements are presented in the following graphics.

Magnetic susceptibility curves for HI 178 and GA 426 indicate relatively similar values for 

measured magnetic susceptibility between 7,000 and 10,000 yrs BP (Figures 8.2.1, 8.2.2, 8.2.3, 

and 8.2.4). The dominant magnetic susceptibility values within this period measured 

approximately 6.0E-8 to 8.0E-8 m3

/kg (cubic meters per kilogram). Spikes and oscillations 

observed within the data are most likely attributed to shells or sediment unconformities caused 

by erosion, but may also represent artifacts of the core logging process. Core sections were 

logged unopened, in the core sleeve liners, complete with the caps at each end of the individual 

core sections. The plastic caps and air pockets at the end of some cores may have resulted in 

erroneous spikes at the top and/or bottom of core sections. Not all core sections had observed 

data errors. Therefore, the following graphs include all data points, and the locations of core 

section caps are annotated on the complete core logs (Appendix B).
154

Figure 8.2.1. Magnetic susceptibility curve from HI 178 core no. 1 with radiocarbon dates 

annotated at depth; charcoal horizon is at 1.21 m (3.97 ft.) below seafloor.

Of particular interest on the magnetic susceptibility curves is that the inset terrace features from 

both HI 178 and GA 426 appear to have fewer data oscillations than geographical features with 

high elevation, suggesting fewer stratigraphic interruptions. Core no. 1, HI 178 in particular has 

very few oscillations within the magnetic susceptibility curve, and the one spike that does appear 

at a depth of 1.20 m (3.9 ft.) is attributed to the charcoal layer observed in the sediment lithology. 

The interpreted topographic feature from HI 178, cores no. 2, 6, and 7, shows significant spikes 

in the uppermost 60 cm (24 in.) of data, with the most variability observed on core no. 6, which 

was also the highest point on the topographic feature. It is very likely that scour related to sea 

level transgression and subsequent storms has impacted the uppermost stratigraphy, a hypothesis 

supported by the presence of discrete shell and/or sand lenses within the uppermost sedimentary 

units (Appendix B). Climate, as indicated by the magnetic susceptibility curves from HI 178,

appears to have remained relatively consistent during the period of subaerial exposure and 

possible occupation.

7,420

7,772 8,530

8,630

8,600

8,790

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

-100 -50 0 50 100

Depth below seafloor (meters)

Measured MS value (E-8 (m3/kg))

Volume-specific MS Profiles, HI 178 Interpreted Inset Terrace

HI178-1

Radiocarbon dates
155

Figure 8.2.2. Magnetic susceptibility curves from HI 178 core nos. 2, 6, and 7.

Magnetic susceptibility curves for the shell deposit noted in GA 426 demonstrate a possible 

warming period within the overall magnetic susceptibility profile, occurring between 10,070 yrs 

BP [11,320–11,840 cal yrs BP] and 9,890 yrs BP [10,610–11,050 cal yrs BP]. This same 

interpreted warming trend is apparent in the terrace profile of cores no. 6, 7, and 8, but to a lesser 

degree. This potential warming trend does not correlate with any previously known climate 

trends identified from terrestrial settings in the Gulf coast region, such as Milliken et al.’s (2008) 

Holocene-era flooding events, or the 8,200 yrs BP event which was associated with an increased 

meltwater pulse. Cores no. 6 and 8 do provide some indication of a possible locally specific 

cooling event, such as the Younger Dryas (approximately 12,000 yrs BP). Each magnetic 

susceptibility profile depicts higher than modern magnetic susceptibility values at depth, overlain 

by a sequence of lower than modern magnetic susceptibility values. The depths of these lower 

and higher magnetic susceptibility values are not consistent across the cores, but this is likely due 

to the fact that the geographical surface of core no. 6 was at a higher elevation than the 

interpreted contemporary terrace surface at core no. 8.

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

-100 -50 0 50 100

Depth below seafloor (meters)

Measured MS value (E-8 (m3/kg))

Volume-based MS Profiles, HI 178, Interpreted Topographic Feature

HI 178-2

HI178-6

HI 178-7

Volume-specific
156

Figure 8.2.3. Magnetic susceptibility curves from GA 426 cores no. 1, 9, 10, and 11 with 

radiocarbon dates annotated at depth.

Complications arise when attempting to compare magnetic susceptibility profiles across cores in 

both survey areas. With the exception of cores no. 1, 9, and 11 in GA 426, the cores represent 

discrete surface locations where the observed geographical landscape is at a different depth 

below the seafloor than in the adjacent cores. Oceanographic modeling of storm related scour 

indicates that the seafloor in HI 178 and GA 426 is likely to experience episodes of scour, 

followed by redeposition of sediments, resulting in mixed and possibly scrambled near-surface 

stratigraphy at least once every 18 months (Curray 1960; Rego et al. 2011). Based on the core 

logs and the observed sediment lithology, it is expected that modern marine and possible 

estuarine sediments represent the uppermost sections of each magnetic susceptibility profile, and 

it is therefore expected that these areas will exhibit magnetic susceptibility data interruptions due 

to scour.

9,890

9,870

9,980

10,07041,660

38,880

>43,500

>43,500

0

1

2

3

4

5

6

-100 -50 0 50 100

Depth below seafloor (meters)

Measured MS value (E-8 (m3/kg))

Volume-based MS Profiles, GA 426 Shell Deposit

GA426-1

GA 426-9

GA 426-10

GA 426-11

Radiocarbon Dates

Volume-specific
157

Figure 8.2.4. Magnetic susceptibility curves from GA 426 core nos. 6, 7, and 8.

8.2.2 Shell Resources

Prehistoric shellfish and marine exploitation is not uncommon, especially in areas where 

terrestrial resources are lacking (Erlandson et al. 2008, 2011). Areas in California’s Channel 

Islands provide evidence of marine exploitation dating to approximately 10,000 yrs BP 

(Erlandson et al. 2008). However, most Paleoindian and Early Archaic sites in the northwestern 

GOM are associated with projectile points and faunal remains from land mammals (as discussed 

in Chapter 3). This fact is not to suggest that marine exploitation did not occur in the GOM 

during the Paleoindian and Early Archaic periods. Instead, evidence to that effect is not likely to 

have been preserved at what would have been inland sites far removed from the contemporary 

coastline. Estuarine exploitation is more typical of GOM sites, and Rangia cuneata (Gulf Wedge 

Clam) shells were a focus of the previous investigation of offshore landscapes (Pearson et al. 

1986). Shells collected within the cores from HI 178 and GA 426 have been used to assist in 

identifying stratigraphic sections, and also serve as climate indicators.

Donax shells were identified in almost all of the cores, as intrusive lenses in the uppermost 

sediments. The two dominant Donax species, texasianus and variabilis (Coquina clams) are 

typically found in the surf zone, or intermediate shallow surf zone (Tunnell et al. 2010:373). 

Living Donax occur at depths of up to 11 m (36 ft.); their presence within the uppermost core 

0

1

2

3

4

5

6

-100 -50 0 50 100

Depth below seafloor (meters)

Measured MS value (E-8 (m3/kg))

Volume-specific MS Profiles, GA 426 Inset Terrace

GA 426-6

GA 426-7

GA 426-8
158

sediments suggests mixing of modern marine sediments and discrete storm deposit layers 

(Tunnell et al. 2010:373). 

Representative shells and shell fragments collected from HI 178 core no. 2 at depths of 81 and 93 

cmbs (32 and 37 in.) include the species Anadara transversa (Transverse Ark) and Mulinia

lateralis (Dwarf Surf Clam). Both are bivalves that are abundant in bays (Hicks 2010:39). Dwarf 

surf clams are not tolerant of high-energy environments and are typically found in calm water,

mid-bay environments where salinity ranges from 15 to 35 parts per thousand (ppT) (Hicks 

2010:39). Their presence on the topographic high feature along a channel margin may be 

explained as preferential deposition following flooding events or possible deposition on the 

channel margins following exploitation by another organism. The shells identified in core no. 2 

were not likely the result of either intensive or extensive human exploitation, due to the relatively 

small numbers recovered, but this does not preclude their exploitation by other species.

Shells within the deposit identified across GA 426, especially cores no. 1, 2, 9, 10, and 11 are 

composed almost exclusively of Crassostrea virginica (Eastern Oyster). This species is known 

to occur in areas with moderate salinity (12 to 25 ppT) and are found in naturally accumulating 

reefs (Hicks 2010:41). Oyster reefs are formed over successive generations as new organisms 

attach to and live on the shell substrate of their predecessors (Hicks 2010:41). Naturally 

occurring reefs of Crassostrea virginica have been identified off the Texas coast measuring 6–8 

km (3.5–5 mi) in length (Hicks 2010:41). The uppermost portions of some large reefs are 

exposed to air at low tides, which may explain oxidation observed in the sediment profiles along 

the upper boundaries of shell deposits within the cores from GA 426. Tidally exposed portions of 

oyster reefs located in the intertidal zone, referred to as “hogbacks,” may consist entirely of dead 

oyster shells (Hicks 2010:41). Living portions of oyster reefs are typically subtidal (Hicks 

2010:41). It is possible that the oyster reef identified in GA 426 extends below the maximum 

core depths; documented oyster reefs in San Antonio Bay extend to depths of 24 m (80 ft.) below 

the seafloor, and date to more than 8,500 yrs BP (Hicks 2010:41). 

The dates obtained from Crassostrea virginica shells within the deposit in core no. 10 are too old 

to coincide with known human occupations in the region. There is additional evidence to suggest 

that this is a naturally occurring deposit. In many cases, articulated shells were discovered, and 

no evidence of worked shell was observed on any of the recovered samples. One sample in 

particular, recovered from core no. 10 at a depth of 235 cmbs (93 in.), consisted of an intact, 

articulated Crassostrea virginica, whose largest valve contained sediment infilling with barnacle 

plates and fragments, and whose inner surface contained encrusted bryozoans (Laurie Anderson, 

personal communication). This pattern is consistent with an oyster shell in situ within a reef 

environment.

Shells recovered from the uppermost portions of the shell deposits indicate a transition to a baylike environment, and possible sea level transgression. Cores no. 6 and 7 contained specimens 

identified as Anomalcordia auberiana (Venus clam), and Terebra protexta (Fine-Ribbed Auger 

snail) among the uppermost Crassostrea virginica deposits. Terebra protexta are found just 

offshore at depths of less than 1 m (3 ft.) BSL to depths of more than 100 m (328 ft.) BSL 

(Tunnell et al. 2010:240), while Anomalcordia auberiana are located in hyposaline bays (Tunnell 

et al. 2010:357). 
159

A single Geukensia demissa (Ribbed mussel) specimen was identified from the lower boundary 

of estuarine sediment in core no. 8, GA 426, immediately overlying the Crassostrea virginica

deposit, at approximately 160 cmbs (63 in.). Geukensia demissa are filter-feeders commonly 

found attached to the stalks of Spartina (Morris 1973:17) and indicate a low energy, sedimentrich environment. This shell may signify transition of the area into an estuarine environment 

related to sea level rise.

8.2.3 Pollen and Fourier Transform Infrared Analysis

Pollen samples were acquired from the inset terrace indicated by core no. 1, HI 178 and the shell 

deposit in GA 426 (cores no. 2, 9 and 10). Pollen samples from HI 178 core no. 1 were analyzed 

by two independent labs; Dr. Sophie Warny at Louisiana State University examined one set of 

pollen samples, and a second set was analyzed by PaleoResearch Institute (Appendix C). All 

samples from GA 426 were analyzed by researchers at PaleoResearch Institute.

Pollen samples were acquired from core no. 1, HI 178 and analyzed closest to the charcoal 

horizon, from depths of 116, 124, and 135 cmbs (46, 49, and 53 in.). Analysis by Warny et al. 

(2012) indicated preserved examples of Hornworts (Anthocerotophyta) within the samples 

acquired above and below the charcoal horizon (located at 121.5 cmbs [47.8 in.]). Hornworts are 

one of three phyla of bryophyte (non-vascular land plants), along with liverworts and mosses 

(Warny et al. 2012:7). In terms of environmental reconstruction, and specifically identification of 

the operational environment, the presence of hornworts provides a significant amount of 

information. Hornworts require a damp environment and are often found on streams, river banks, 

and wet floodplains. They are associated with shady, moist areas that correlate with warm and 

relatively wet conditions conducive to swamp development but are not salt-tolerant, suggesting a 

freshwater environment (Warny et al. 2012:14). Hornworts have a very fine tolerance for 

moisture; they cannot survive desiccation, nor can they be permanently submerged (Warny et al. 

2012:14), suggesting a relatively stable water level. The core’s location on an inset terrace 

correlates with the environmental requirements for successful hornwort colonization, and 

provides additional details about this potential freshwater resource. Also noted in the pollen 

profile for the sediment samples from HI 178 were abundant Helianthoid (including members of 

the sunflower family) and Chenopodiaceae (including species of the goosefoot family). 

Chenopodiaceae are related to Amaranthaceae and commonly referred to as “cheno-ams” 

(McConnell 1998:179). Chenopodiaceae are a common pollen species associated with 

prehistoric sites and have been found in diverse environments ranging from Australia 

(McConnell 1998) to submerged contexts off the coast of Israel (Galili and Weinstein-Evron 

1985) to the eastern (McLauchlan 2003) and southwestern United States (Hill 1966). They are 

commonly associated with pioneering species in areas that have been cleared or denuded (Coile 

and Artaud 1997). In addition to their nutritional use, Chenopodium have been used variously as 

a vermifuge and insecticide, and for medicinal purposes in a variety of cultures (Core 1967:206; 

Coile and Artaud 1997:4).

Two samples surrounding the charcoal lens in core no. 1, at depths of 121 and 123 cmbs (47 and 

48 in.) , were examined by PaleoResearch Institute for pollen analysis and Fourier Transform 
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Infrared (FTIR) spectroscopy, which was used to identify organic residue. Probable Thalictrum

(meadow-rue) pollen dominated the samples, followed by Poaceae (true grasses) pollen

indicative of large grass populations (Cummings and Logan 2011:12). Additional species 

identified through pollen analysis included: Quercus (oak) and Cheno-am pollen (goosefoot and 

saltbush); and Juglans, Pinus, and Alnus pollen (walnut, pines, and wetland-adjacent alder). 

Some examples of diploxylon (having two fibrovascular bundles per leaf) Pinus (red pine) pollen 

were observed. According to Cummings and Logan (2011:12), smaller quantities of Artemisia, 

Low- and High-spine Asteraceae, Boraginaceae, Cyperaceae, Fabaceae, Plantago, and 

Rosaceae were also identified, and represent “sagebrush or wormwood, marshelder or similar 

plants, other members of the sunflower family, wild onion or a similar plant, members of the 

borage, sedge, and legume families, plantain, and a member of the rose family.” The pollen 

identified from the sediments surrounding the charcoal horizon supports the earlier pollen 

interpretation that the surrounding environment was a meadow with adjacent freshwater 

remaining at relatively stable levels. 

FTIR analysis of the sediments from the same horizons as the pollen resulted in the identification 

of the following: Achillea (yarrow) stems, Cicuta (hemlock) stems, Poaceae (grass family) stems 

and joints, Helianthus (sunflower) seed shells, and Prunus (choke cherry) and Ribes (currant) 

fruit. These plant species are consistent with the interpretation of a meadow environment, with 

some species also found in drainages (Cummings and Logan 2011:12-13). FTIR analysis 

identified polysaccharide galactoglucomannan (water-soluble hemicellulose), indicative of 

woody and fibrous tissues from coniferous plants (Gymnosperms) (Cummings and Logan 

2011:13). FTIR peaks correlating with the amino acid glutamate indicate the presence of fish 

within the sample; however, this is expected for sediment recovered from below the seafloor in a 

modern marine environment (Cummings and Logan 2011:13). 

At the time the sediments immediately above and below the charcoal horizon were deposited, the 

inset terrace surrounding core no. 1 was subaerially exposed. Plant species identified include 

sunflowers, goosefoot, chokecherry, and currants, all of which would have provided ample 

subsistence to foragers, including most commonly black bears, raccoons, chipmunks, deer mice, 

and birds (USDA NRCS 2004). While there is no direct evidence of exploitation by human 

populations at this location, historic Native American populations are known to have exploited 

chokecherry, goosefoot, and sunflower seeds (Hill 1966; Core 1967; McLauchlan 2003; USDA 

NRCS 2004). Cultivation of several of these species is known, but from later periods in 

prehistory (McLauchlan 2003). Indirectly, animals known to consume these species can also be 

interpreted as part of the operational environment, since this location would have been an ideal 

place for Paleoindian and Early Archaic hunters to target game animals.

Pollen and FTIR analysis was initially conducted on a sample from the dense shell concentration 

within core no. 9, GA 426, at a depth of 399 cmbs (157 in.); this sample was submitted before 

the radiocarbon dating results determined the antiquity of the reef structure. The pollen record 

for this sample had high amounts of Quercus, indicating the presence of oak trees (Cummings 

and Logan 2011:10). Additional species identified include: Betula, Carya, Pinus, and Ulmus

(hickory, pine, and elm trees); diploxylon Pinus pollen (red pine); and a large quantity of 

Poaceae pollen (grasses) (Cummings and Logan 2011:10). Cheno-am pollen frequency

suggested the presence of saltbush, goosefoot, or a similar plant. Additional species identified 
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included: Low- and High-spine Asteraceae, Cyperaceae, Eriogonum, Phlox, and Rosaceae

(marshelder and rabbitbrush/sunflower, sedges, wild buckwheat, phlox); and possibly Prunus

(chokecherry) (Cummings and Logan 2011:10). The presence of the Low-spine Asteraceae

(including daisies) and Cyperaceae (sedges) suggests that the area was part of a wetland. This is 

consistent with conditions necessary for oyster reef development. 

FTIR analysis of this same sample provided additional species identification, all of which were 

consistent with the interpretation of a wetland environment with adjacent areas capable of 

supporting terrestrial plant species. It is probable that these plants would have grown in areas 

adjacent to estuarine zones and river channels. According to Cummings and Logan (2011:11),

some of these additional species are similar to those surrounding HI 178 and include: Achillea

(yarrow) stems; Schoenoplectus (bulrush) stems; Cicuta (hemlock) stems; Helianthus

(sunflower) seed shells; ground Cheno-am seeds; dried, ground Thalia dealbata (alligator flag) 

seeds; dried Cylindropuntia (cholla cactus) buds; and wet Sambucus (elderberry). Of note among 

the FTIR results is the identification of matches consistent with cricket proteins and reptilian, 

probably turtle, blood (Cummings and Logan 2011:11).

Following the return of radiocarbon dates for the shell deposit in GA 426, additional samples 

were submitted for pollen analysis, targeting the top of the shell deposit, and the interpreted 

estuarine sediments that date more closely to periods of possible human occupation. These 

samples were prepared from core no. 2 at depths of 104, 131, and 136 cmbs (41, 52, and 54 in.), 

and from core no. 10 at depths of 86 and 105 cmbs (34 and 41 in.).

Identified pollen species observed from core no. 2, at a depth of 136 cmbs (54 in.), resulted in a 

pollen profile similar to the previously examined sample from core no. 10, at a depth of 399 

cmbs (157 in.) (Cummings and Varney 2011). The dominant species, which included pine, 

hickory, oak, elm, sunflower, sagebrush, and marshelder, suggest proximity to a wetland with an 

adjacent open area and elevated ground (Cummings and Varney 2011:2). Of particular interest in 

this sample was a moderate amount of charcoal, visible in the sedimentary unit as “organic 

staining throughout” (Appendix B). 

The overlying sample from 131 cmbs (52 in.) was collected from the same lithologic unit but 

represented a changing environment. Microscopic charcoal was identified throughout this 

sample, as in the previously discussed sample. An increased amount of oak pollen was identified, 

as well as evidence of alder, juniper, and fir (Cummings and Varney 2011:2). Decreases in the 

amount of High-spine Asteraceae suggest fewer sunflower-type plants, which were replaced by 

increases in marshelder plants (Cummings and Varney 2011:2). Of particular note is the presence 

of Apiaceae, or umbel, which is characteristic of plants including carrot, parsley, dill, fennel, and 

onion (Cummings and Varney 2011:2). An overall increase in preserved pollen from <10,000 

pollen per cc of sediment to >47,000 pollen per cc of sediment indicates that this sedimentary 

unit was part of a stable surface (Cummings and Varney 2011:2). Based on the rapid change in 

radiocarbon age noted in core no. 10, it is very likely that this environment remained relatively 

unchanged for a significant period of time, allowing for growth of the reef, from whose shells the 

radiocarbon ages were derived. 
162

The uppermost sample from core no. 2 was collected from a depth of 104 cmbs (41 in.), and 

indicated an increase in pine from the previously discussed samples. Cummings and Varney 

(2011:3) attributed this to either a decrease in other vegetation resulting in overrepresentation in 

the sample, or a simple increase in the amount of pine within the immediate area. Larger pieces 

of charcoal were identified in this sample; however, pollen amounts in the sample are not low 

enough to suggest complete landscape clearing through fire (Cummings and Varney 2011:3).

Instead, it is more likely that this sample represents an environment with an increased number of 

pine trees. Generally, the pollen record for core no. 2 suggests a relatively stable environment 

over time with an increase in sediment dryness, which is supported by observed oxidation within 

the sediment profile.

Two samples were analyzed from core no. 10, from depths of 85 and 106 cmbs (34 and 42 in.); 

these samples correspond to samples dated for radiocarbon age. The sample from 106 cmbs (42 

in.) dates to 9,890 yrs BP [10,610–11,050 cal yrs BP] and is similar in pollen profile to core no. 

2, at 136 cmbs (54 in.) (discussed above). This pollen profile identified similar species, 

suggesting an environment dominated by grasses, with some pine and oak stands, as well as 

Apiaceae, Artemisia, Low-spine Asteraceae, Caryophyllaceae, Cyperaceae, Plantago, Rosaceae, 

Salix, and Typha. These species indicate a member of the umbel family, sagebrush, members of 

the sunflower family, a member of the pink family, sedges, plantain, a member of the rose 

family, willow, and cattails (Cummings and Varney 2011:4). A total pollen concentration of 

18,000 pollen per cc of sediment suggests a relatively stable surface, and a moderately large 

quantity of microscopic charcoal from this sample provide evidence of a potential surface that 

was exposed and available for exploitation (Cummings and Varney 2011:4).

The overlying sediment sample from 86 cmbs (34 in.) correlates with a radiocarbon age of 9,870 

+/- 50 yrs BP [10,600–11,020 cal yrs BP]. The pollen profile suggests a stable, forested 

landscape interspersed with grassy meadows, with high amounts of hickory, juniper, pine, and 

oak and smaller quantities of alder and hemlock (Cummings and Varney 2011:4). Local 

vegetation in this sample was similar to core no. 2 and included evidence of umbel, sagebrush, 

sunflower, wild buckwheat, legumes, as well as microscopic charcoal (Cummings and Varney 

2011:4). 

As with HI 178, the pollen and FTIR results indicate that the operational landscape of GA 426 

would have supported numerous species of flora available for both hunter-gatherer populations 

and game animals, including species known to have been important to prehistoric cultures in 

other parts of North America (Hill 1966; McLauchlan 2003). Pollen species identified in both 

study areas include Chenopodiaceae (goosefoot family), identified by Warny, and Cheno-ams 

identified by PaleoResearch. During the Middle Archaic (Louisiana)/coastal Archaic (Texas) 

period, approximately 3,950–3,450 yrs BP, Chenopodium (goosefoot family) and Helianthus

(sunflower) were domesticated by prehistoric populations in the eastern United States where they 

were grown on disturbed landscapes, and associated with land clearance (McLauchlan 

2003:557). The dates for the pollen samples in this study are very early compared with known 

dates for cultivation, and there is no other direct evidence to suggest that these plants were being 

modified; however, there are known linkages between these species and land clearance. 

Evidence of microscopic charcoal was noted in the GA 426 samples, but was not evident in the 
163

core lithology as a discrete lens, as was the case in HI 178 core no. 1. Both examples of charcoal, 

however, may provide evidence of a modified environment.
164

8.3 MODIFIED ENVIRONMENTS

People require an operational landscape that will support their subsistence needs. Given enough 

time, people will modify their environment through frequent or effective activity (Butzer 

1982:253). In the case of HI 178 and GA 426, discrete evidence of charcoal within the sediment 

profiles suggests fire, but in neither case is there concrete evidence that the fire was intentional, 

or anthropogenic. 

As identified by Warny et al. (2012:16), charcoal was identified in the same samples as the 

hornwort and cheno-am pollen. It was suggested that the charcoal itself may explain the 

abundance of hornwort species in the pollen profile. Bryophytes, including hornworts, and 

cheno-ams are among the early pioneering species during secondary succession, or 

recolonization of a landscape following a burning event (Coile and Artaud 1997; Warny et al. 

2012:16). No other evidence of charcoal was identified from any of the other cores at HI 178;

however, core no. 1 was an isolated sample. Core no. 1 was acquired from an inset terrace over 

550 m north-northwest of the other cores in this area. Although there is evidence that prehistoric 

populations manipulated the landscape through use of fire (e.g., Fowler and Konopik 2007), it is 

not possible based on a single core to determine if the charcoal in core no.1 represents a locally 

discrete burn feature such as a midden or intentional land clearance. It is just as likely, based on 

the evidence presented here, that the charcoal is related to a naturally occurring fire or lightning 

strike. 

Charcoal was identified from GA 426 in multiple cores, spanning a horizontal distance of 

approximately 106 m (348 ft.). Unlike HI 178, the charcoal identified at this location was 

observed as microscopic fragments throughout a sedimentary unit, and was not located within 

one discrete unit. While it is possible that this charcoal represents a geographical landscape-wide 

burn event, there is insufficient evidence to suggest that the fire(s) was anthropogenic in nature, 

and may just as easily be explained as a wildfire, or lightening-induced burning event.

Two other types of landscape features may indicate a modified environment: middens and 

mounds. The sites in HI 160 and GA 356 were originally interpreted as middens, and the shell 

deposit in GA 426 could be confused on acoustic profiles for an anthropogenic midden. 

Archaeological middens are part of the modified landscape, having either been built up 

intentionally or through continued disposal of food refuse (as in shell middens). Mounds, dating

in Louisiana as early as 6,000 yrs BP (Homburg 1992; Russo 1994), may not include any 

artifacts or faunal remains, but are anthropogenic constructions of selected and altered sediments. 

Previous investigations of mound sites conducted by Gagliano et al. (1982) provide indicators 

that may be used to distinguish archaeological sediments within mounds from surrounding 

sediment horizons. The 1982 study included the Magnolia Mound Site (16SB49), Mound B, and 

the Bayou Blue site (16AL01). Magnolia Mound B is a conical earthen mound, and the Bayou 

Blue site is located on a Pleistocene Prairie terrace above a former channel probably associated 

with the Calcasieu-Red River system (Gagliano et al. 1982). The Bayou Blue site was occupied 

from the Early Archaic period (8,000–6,000 B.P.) through the early ceramic period, and at its 

earliest is roughly contemporaneous with the radiocarbon dates from High Island Area. 
165

Sediment profiles from the Bayou Blue site were classified by Munsell color. Ceramic horizon 

sediments include dark yellowish-brown to yellowish-brown silt (10 YR 4/4; 10 YR 5/6). Preceramic sediments were classified as brown silt with oxidized nodules (7.5 YR 5/6). The Prairie 

Terrace deposits were described as mottled yellowish-red silty clay (5 YR 5/8) (Gagliano et al. 

1982). Grain sizes in the archaeological sediment horizons ranged from silt (4–8 phi units) to 

clay (8 phi units). At the Magnolia Mound site, brown silty clay (7.5 YR 4/2) was added to the 

mound by basket-loading. Grain sizes were all within 4–8 phi units, indicating that sediments 

were classified as silt (Gagliano et al. 1982). 

Cores acquired from the location of the interpreted midden in GA 356 did not reveal any 

evidence of faunal remains or worked shell that would indicate an archaeological midden. 

Sediments, however, especially those units exhibiting interbedded lenses, were examined for 

patterns similar to those observed in terrestrial archaeological mounds. No evidence was 

observed to suggest that GA 356 represents an anthropogenic mound, and the radiocarbon dates 

for this area predate the earliest known mound constructions in the northwestern Gulf by 

approximately 3,500 to 4,500 years. The Monte Santo Bayou Mound ‘A’ dates to approximately 

6,220 +/-140 yrs BP (Saunders 1994) while the next oldest example, the LSU Campus Mounds, 

dates to approximately 5,345 +/-235 yrs BP (Homburg 1992). Although it is possible that earthen 

mounds of anthropogenic origin are preserved offshore, and may be recorded on acoustic 

profiles, GA 356 does not likely represent such a deposit. 

Evidence from High Island and Galveston areas indicate that it is possible to use geophysical 

evidence and environmental data to identify geographical and operational environments;

however, there was no irrefutable evidence of an anthropogenically modified environment at any 

of the study sites. It is possible that subsequent testing could indicate anthropogenic alterations to 

the operational landscape.

8.4 SUMMARY

The geophysical and environmental data were used to successfully identify both geographical 

and operational environments in both of the study areas. The acoustic survey data were used to 

construct contour maps of the interpreted geographical environment. When viewed as part of the 

total data set, the acoustic survey data comprise the single most important data set that form the 

building block on which all subsequent testing was based. 

The use of P-wave data, which have not been extensively cited in published studies of submerged 

landscapes, were effective in correlating the calculated depths of features from the acoustic data 

with the actual depths of features in the observed sediment stratigraphy. Inferences concerning 

sediment type and environmental conditions were based on P-wave data. Specifically, slower 

velocities were correlated with imbricated shells and oxidized sediment to suggest subaerial 

exposure of hogback portions of the GA 426 oyster reef.

Volume-specific measurements of magnetic susceptibility were used to generalize climate 

conditions at each study area. Inferences were made about sediment scour and disturbance based 

on oscillations within the magnetic susceptibility curves, since sediment discontinuities are 

known to cause anomalous spikes.
166

Shell species were identified and used to elucidate the environmental conditions present at that 

depth in the core profile. The oysters and dwarf clams represent potential food resources for 

human populations, but there was no evidence of worked shell or selective disposal of shell 

species/size/seasonality. The shells represent species within a healthy ecosystem, though, and 

contribute information concerning the operational environment.

The pollen and FTIR data provided information on the types of species, allowing inferences to be 

made about the operational environment within each study area at different points in time. The 

HI 178 pollen data suggested a wetland environment with adjacent terrestrial plants, indicative of 

a stable waterline and relatively stable conditions. Species known to have been utilized by 

prehistoric populations were identified in association with the charcoal horizon, and suggest that 

this area would have provided significant resources to any populations in the area. The pollen 

from GA 426 indicated a long period of exposure and a relatively stable environment, with many 

of the same species as HI 178. The GA 426 environment was identified as a meadow-type 

ecosystem with adjacent freshwater. Again, this type of environment would have provided a 

reliable source of diverse resources for a population present in the area.

The modified environment was the most difficult to identify from the collected data. At present, 

there is no conclusive, irrefutable evidence of human modification at any of the study sites;

however, the evidence for potential burning events at HI 178 and GA 426 warrant further 

investigation.
167

9. CONCLUSIONS AND RECOMMENDATIONS

The Bureau of Ocean Energy Management (BOEM) is tasked with protecting the natural and 

cultural environment with regard to energy development on the OCS. Through application of the 

National Historic Preservation Act, BOEM has a responsibility to identify potential and existing 

submerged cultural resources on the OCS. Previous studies have tested environments 

approximately 16.7 km (9 nm) offshore, in up to 12 m (39 ft.) of water, for the presence of 

preserved remains of prehistoric populations. The area covered by previous studies, however, 

covers only a fraction of BOEM’s jurisdiction. The current study sought to expand upon earlier 

work by testing areas in deeper water depths and using different analyses to try and determine 

the most effective methods for paleolandscape identification. This is a critical point to make, as 

no prehistoric archaeological sites on the northwestern GOM OCS have been discovered in situ. 

Given the current NTL survey guidelines for sub-bottom profiling, it is much more likely that 

archaeologists can identify landforms on which prehistoric sites could be located. Prehistoric 

archaeological sites on the OCS correlate with the Paleoindian and Early Archaic Periods, when 

sites are generally low in density and artifacts consist mainly of projectile points or other lithic 

implements that are unlikely to be resolved on acoustic profiles. This presents a significant 

challenge to resource managers. Unlike historic submerged cultural heritage, such as shipwrecks, 

prehistoric sites are not readily apparent on remote sensing data. The question then becomes 

whether to protect only “sites” which may not be identified, or protect landforms that fit the 

model and date to the right time period, but may not contain any archaeological materials. The 

investigation of submerged prehistoric sites in the northwestern GOM region is an archaeological 

task firmly rooted in the physical environment. Various aspects of the real environment, 

including available resources and evidence of modification, can be empirically tested using 

methods of sediment sampling, acoustic surveying, and environmental analysis. Without 

identifying the physical aspects of the environment, it is not possible to make inferences as to 

how the environment was utilized or manipulated, which is at the heart of human behavior and 

archaeology’s ultimate goals. 

9.1 CONCLUSIONS AND FUTURE RESEARCH

The methods used in this study were based on the concept of middle-range theory but applied in 

a spatial rather than temporal manner. Known indices of archaeological sites dating to the 

Paleoindian and Early Archaic periods from terrestrial contexts in Louisiana and Texas were 

applied to geographical environments identified on the OCS dating to similar points in time. A 

combination of acoustic surveying and physical sampling provided all of the data used in this 

study. 

A review of existing sea level curves was conducted, and a new composite curve created 

specifically for use in this study (see Figure 2.5). The composite sea level curve was deemed 

necessary to account for local variations in sea level rise attributed to uplift or subsidence, and 

provide the maximum possible date range for potential subaerial exposure and corresponding 

prehistoric occupation. The composite sea level curve was successful in defining the minimum 

and maximum dates for final inundation at all of the sites; exceptions included the shell sample 
168

from HI 160 (taken from an interpreted subaqueous horizon), and the anomalously old dates 

returned for samples from within the shell deposit in GA 426. If the shell deposit in GA 426 was 

indeed a hogback reef, then the deeper shells could have been dead for some time, while the 

upper portions of the reef were exposed and available for exploitation. Additional dates, such as 

OSL dates from non-shell features in GA 426 may provide a better record of the age-depth 

relationship. If possible, dates at regular intervals should be acquired for the sediment profile 

above and through the shell feature in GA 426 core no. 2, to correlate with the pollen data. 

Additional dates could also be obtained from samples across the channel profile in HI 178, in 

cores 2, 6, 7, and 5. 

Evidence of the operational environments in both HI 178 and GA 426 demonstrate that each area 

supported resources exploited in prehistoric subsistence systems. Independent data sets were 

correlated to provide a more detailed reconstruction of the operational environments, but were 

not without problems. Mass-specific magnetic susceptibility was not measured continuously 

down each core, resulting in magnetic susceptibility profiles with significant gaps between data 

points that did not allow for direct comparison with other data sets. Although volume-specific

magnetic susceptibility measurements may contain erroneous or misleading readings due to 

differential compaction, these measurements were found to be better suited for comparison 

across data sets in this study. If future testing includes mass-specific magnetic susceptibility 

measurements, the samples should be collected continuously down the core. Alternatively, 

volume-specific measurements can be taken and compared with the data acquired in this study.

Future research should continue to search for elements of the real environment in buried and 

submerged contexts through a spatial application of middle-range theory using geophysical data. 

Evidence of fire was identified from Paleoindian-age operational environments in both HI 178 

and GA 426. Charcoal was only identified in one core from HI 178, indicating the fire was 

spatially restricted to the terrace feature sampled by core no. 1. No evidence of fire was indicated 

by the remaining cores, and the charcoal in core no. 1 may refer to either a discrete localized 

burn, such as a hearth, or a terrace-wide burning event that did not reach the other channel 

margin. Additional coring conducted systematically across this terrace feature, or the opening of 

1 by 1 m (3 by 3 ft.) units over the core no. 1 location could help to resolve this question. 

Charcoal identified across several cores in GA 426 suggests a wider burn area, but again it is 

unclear if this is due to a natural fire, or fire that was intentionally set by humans to modify the 

landscape.

Pollen species identified in the cores from both HI 178 and GA 426 represent food sources 

exploited by prehistoric populations, and even species developed as cultigens in later contexts 

(Hill 1966; Core 1967; McLauchlan 2003). In North America, chenopods especially became an 

important staple crop of prehistoric populations, but at later points in time than represented by 

the area in HI 178 (McConnell 1998:181). Without additional cores from the terrace feature 

sampled via core no. 1 at HI 178, it is not possible at this time to determine if the pollen shows

any evidence of cultivation, seasonal selection, manipulation, or is naturally-occurring and 

unmodified. Similarly, pollen data from GA 426 indicated Cheno-ams associated with charcoal. 

This finding alone does not indicate human landscape modification. Future coring or sediment 

sampling strategies should be designed to allow for pollen analysis relative to seasonality or 
169

other indicators that would allow for distinction between likely periods for wildfire so as to 

identify modification of the operational environment.

Cores should be acquired from the probable shell deposit reported in HI 160. Although the 

dimensions of the midden would suggest a naturally-occurring deposit, this cannot be confirmed 

or refuted without physical samples. Based on the success of coring operations through 

sediments at HI 160 and the shell deposit at GA 426, a surface-positioned vibracore unit with 6 

m (20 ft.) core barrels should have sufficient power to capture sediments from the probable shell

deposit. If future coring is planned, magnetometer data from this study can be cited as 

verification that the 1995 survey pipeline positions are correct. The positions indicated by 

publicly available sources, which are likely to be consulted by coring operators prior to 

commencement of operations, are incorrect. Future coring operations at the interpreted shell 

deposit in HI 160 can be conducted while maintaining a 150-m (492-ft.) buffer with the as-found 

pipelines.

9.2 RECOMMENDATIONS FOR SUBMERGED CULTURAL RESOURCE MANAGEMENT

Existing acoustic survey data were used to delineate large-scale geographical environments 

within all four survey areas. In each case, the original NTL-compliant survey had recorded 

evidence of a high-probability landform on one, or possibly two, of the acoustic profiles. In the 

case of the possible midden in HI 160, the feature was seen on one survey line resulting in a 

single along-track measurement. By acquiring additional data perpendicular to the originally 

reported feature, it became evident that the feature was more than four times larger than 

previously estimated. Initially, survey lines were designed for this study as high-density (25-m 

interval [82-ft.]) lines to provide close-up detail of features interpreted from larger scale NTLcompliant surveys that used line spacing intervals of 50 to 300 m (164 to 984 ft.). Closer interval 

data provided much needed detail over the areas of interest, as illustrated by the contoured data 

sets for HI 178 using overlapping 150 m, 50 m, and 25 m (492 ft., 164 ft., and 82 ft.) interval 

data sets (see Figures 6.2.1, 6.2.3, and 6.2.6). The survey line interval was expected to be a 

contributing factor to allow for more detailed mapping of buried features, but survey line length 

also turned out to be an important factor. During data interpretation it became apparent that the 

newly acquired data, gathered at close intervals along short (450 m [1,476 ft.]) survey lines, 

resulted in such an extremely tight view of the area that it was difficult to contextualize the 

feature of interest. Sub-bottom profiling data reflect differences in the acoustic impedance of 

sediments. Because the data are relative to the surrounding sediments, it is necessary to acquire a 

longer profile of the subseafloor before and after the feature of interest. Acoustic profiles of just 

a feature of interest, devoid of its geographical context, are difficult to interpret. Supplemental 

data acquired along 1,000 m (3,281 ft.) long survey lines, and at the same close intervals, as part 

of this project were much more easily interpreted. 

Survey line interval was hypothesized to be a contributing factor to successfully identifying 

landscape features of interest, but based on the results of this study it is also important to 

consider grid orientation. Geophysical grids for NTL-compliant surveys are typically designed in 

one of three ways. First, a survey grid may be designed so that the primary survey lines are 

oriented parallel to the bathymetric contours of the seafloor within the grid. This is done to 
170

minimize the number of cable changes required along the survey line, which are necessary to 

keep different towfish (such as sonar and magnetometer) within their operating specifications. 

Second, a survey grid may be designed along the axis of a proposed development installation or 

irregular survey boundary. For example, a grid may be created so that the primary survey lines 

are oriented parallel to a proposed pipeline route, or as in the case of the original survey report 

for HI 178, along the boundary of an existing fairway. Finally, grids may be developed in an 

arbitrary orientation. In the GOM, many NTL-compliant surveys are designed with primary 

survey lines oriented north-south. Sub-surface channels, however, are best resolved when 

crossed perpendicular to the axis of the thalweg (as in GA 426). Survey lines that follow the axis 

of an entrenched thalweg are more likely to experience acoustic attenuation from sediments 

comprising the channel fill, and therefore have less resolution of the underlying channel 

morphology. It would be easy to recommend that sub-bottom survey lines be designed to cross 

perpendicular to the entrenched channels, but this is a highly impractical recommendation for 

NTL-compliant survey design in the northwestern GOM. 

Sub-surface channels in the study area have been filled and buried in place through the processes 

of sea level transgression and modern marine sediment deposition and are not visible at the 

seafloor. Even in areas where channels are known to exist in the sub-surface, individual channel 

morphology can be highly variable. The only way to design a grid perpendicular to specific 

channels would be to conduct a preliminary, coarse grid survey of the area, map the observed 

channels, and then design a subsequent survey grid perpendicular to the channels. This is a 

prudent strategy for a research study of a specific portion of a channel and should be 

recommended in requests for proposals related to future studies of specific channel systems. A 

more reasonable solution to address channel resolution by NTL-compliant surveys may be to 

review the requirements for tie-lines within a survey grid. Current NTL survey guidelines for 

archaeology require “cross-tie lines spaced at a maximum of 900 meters (2,953 feet)” (BOEM 

2005). By having parallel and perpendicular survey lines, even at coarse intervals, there is more 

opportunity to record and resolve significant subseafloor features and channel morphology. 

Another consideration for grid design is survey line direction. It became apparent during this 

survey that the direction along which a survey line is run has an impact on the acoustic reflection 

of subseafloor sediments. For example, as discussed in Chapter 6, survey lines 204 and 509 were 

run over the GA 356 site using equivalent towfish (2–10 kHz chirp sub-bottom profiler), 

acquisition systems, and similar instrument settings. When displayed at equivalent vertical and 

horizontal scales it is apparent that the reflection of the channel, especially the deepest thalweg, 

differs between the two lines. The primary difference between the two lines, both oriented northsouth, was the direction in which they were run. Survey line 204 was acquired along a heading of 

0° and survey line 509 was acquired along a heading of 180°. Staggering or varying the heading 

along which survey lines are run may increase the likelihood of resolving sub-surface features. 

Standard operating procedures for NTL-compliant surveys typically already require variation of 

line headings, but it bears repeating here for inclusion in future research proposals.

The recommendations for survey data acquisition presented here cannot guarantee success in 

resolving sub-surface channel systems. Acoustic data is based on the recorded velocity of the 

speed of sound, and reflects changes in acoustic impedance. Sediment properties have an 

enormous influence on the quality of the returned acoustic signal. There are simply some 
171

sediments on the OCS that are not conducive to producing high quality acoustic returns (e.g.,

water logged sands and peat). The recommendations made here are suggested to maximize the 

likelihood of resolving sub-surface features using commercially available equipment.

It is debatable whether further 2D sub-bottom profiling at the locations tested in this study will 

result in significantly new information. Different acoustic technologies and data processing 

systems would yield different figures and data representations; however, the geographical 

environment at the study sites is already well understood, and clearly contains operational 

features that correlate with prehistoric populations. The challenge now is to recover sufficient 

data from the sub-surface environment to identify anthropogenic environmental modification. 

This step can only be done through physical sampling of the horizons associated with potential 

human occupation.

Neither this report, nor the previous study that tested sub-surface features on the OCS (Pearson et

al. 1986), has addressed anything in the central GOM. The central GOM OCS presents 

significant challenges to the identification of preserved prehistoric archaeological resources due 

to the presence of the Mississippi River, and its associated deltas. As discussed in Chapter 2, the 

Mississippi River is responsible for the majority of the sediment deposited offshore of Louisiana 

and Texas. Sediments are preferentially deposited near the mouth of the river, with coarser 

grained sediments and biogenic-gas enriched sediments deposited closest to the river’s outflow 

and delta, and finer grained sediments settling out of suspension farthest away from the deltas. 

Based on regional studies, post-glacial sediment accretion is thickest offshore Louisiana, 

meaning that areas that were subaerially exposed and available for prehistoric populations are 

underneath significant quantities (up to 200 m [656 ft.] per Coleman 1976) of sediment that 

contains high percentages of sand and organic matter. All of these factors work against 

producing high quality acoustic profiles of the formerly exposed sediment horizons in the subsurface. Even when acoustic profiles resolve a feature of interest in the central GOM OCS, it 

may not be possible to collect physical samples. Sediment cores collected as part of this study 

were 6 m (20 ft.) in length; cores collected by Pearson et al. (1986) were 12 m (39 ft.) in length. 

Depending upon the thickness of the Holocene sediment overburden, commercially available 

coring rigs may not be able to capture the targeted sub-surface horizon, requiring larger and more 

expensive equipment, without guarantee of success that the cores will provide conclusive 

evidence of archaeological “sites.” 

Physical sampling has been discussed in this report (and elsewhere) as a necessary follow-up to 

remote sensing data acquisition and interpretation. Sediment analyses conducted as part of this 

study were successful in refining the sea level curve constructed specifically for the northwestern 

GOM, and resulted in data that defined an operational environment that would have been 

available for exploitation. The physical samples did not, however, provide indisputable evidence 

of people on the now-submerged landscape. If the resource management goal is to identify and 

preserve (through assignment of avoidance zones) prehistoric archaeological “sites,” then cores 

are insufficient for this task. Using the example of the preserved feature in HI 178, core no. 1, the 

evidence demonstrates that a discrete (or spatially restricted) fire burned on an inset terrace, 

which was elevated above a low-energy freshwater source and surrounded by plant and animal 

resources known to have been exploited by prehistoric populations at a time when people are 

known to have been in Texas and Louisiana. No artifacts were encountered at this location; 
172

however, the core diameter (10 cm [4 in.]) was such that artifacts were not anticipated, even if 

present. Despite the evidence collected, it is not possible to classify this area as an archaeological 

“site.” It does, however, represent a horizon with archaeological potential within the sub-surface.

Avoidance is the most commonly practiced mitigation for possible archaeological sites on the 

OCS. In the course of NTL-compliant surveys, when possible prehistoric archaeological features 

are identified from acoustic survey profiles, that information is reported to BOEM. BOEM then 

has the option to assign an avoidance zone to the feature. As with historic shipwrecks, an 

assigned avoidance zone requires operators to maintain a minimum distance away from a 

potential archaeological resource in order to protect that resource during construction or other 

offshore development activities. From a management standpoint, avoidances protect the 

resource, but from a research standpoint, avoidance usually also means that no additional

evidence is collected from a landform and the acoustic profiles remain the sole source of 

information. Two studies have now been conducted on possible prehistoric sites on the OCS, 

collecting a combined total of 106 sediment cores, ranging from 6 to 12 m (20–39 ft.) in length, 

and all approximately 10.16 cm (4 in.) in diameter. This represents a wealth of vertical and 

chronological data, but spatially accounts for approximately 3.4 m2 (36.6 ft2

) of surface area 

coverage along the entire northwestern OCS. Additional sampling is sorely needed; however, it 

can only be expected to assist in identifying archaeological horizons, as discrete “sites” along 

submerged paleolandscapes are still likely to go undetected.

Management recommendations for survey line intervals, tie lines, and line direction are made 

here within the context of NTL-compliant surveys. NTLs however, are informed by research 

conducted on behalf of BOEM. It is therefore reasonable to suggest that BOEM coordinate 

additional research on prehistoric archaeology as part of their management strategy. The acoustic 

profiling conducted as part of this study used a commercially available sub-bottom profiler of a 

type commonly employed in NTL-compliant surveys. The NTL-compliant surveys already 

collect coarse-interval sub-bottom profiles that, as they did for this study, serve as a resource 

from which to select areas for future research. Research projects may be designed by first 

selecting survey areas from the interpreted sub-bottom maps and data samples on file with 

BOEM that are based on coarse-interval surveys. Selected channel systems and other features 

then could be subjected to close-interval survey using different technologies such as 3D subbottom or ultra-high resolution 3D seismic. Not all of these systems are commonly available on 

the commercial market and require processing beyond the scope of traditional 2D sub-bottom 

systems. The cost and required expertise, plus certain operational limitations required to use 

these systems and process the data, means that they are not yet appropriate for NTL 

requirements, but they could provide important data under research applications. Comparisons of 

the systems on similar features, and across different environments could identify better modeling 

methods (e.g., 3D cube slice) for the subseafloor. There is also a need to gather more physical 

samples, either by acquiring additional cores or making use of archived cores with good 

provenience in order to identify and delineate the spatial extent of archaeological horizons. 

It is suggested here that submerged prehistoric sites be differentiated from historic shipwrecks 

for BOEM mitigation purposes. Specifically, prehistoric resources should be reported and 

classified as landforms or horizons, as opposed to discrete sites. Currently, NTL-compliant 

archaeological assessments are required to report high-probability landforms associated with the 
173

occurrence and preservation of prehistoric archaeological sites. With historic resources, discrete 

coordinates are provided to BOEM for magnetic anomalies, sonar targets, and shipwrecks, which 

are then avoided by assigned distances. With prehistoric assessments, coordinates based on an 

along-track measurement will not necessarily reflect the true size and shape of the landform 

being reported. Using the example from HI 160, the reported feature was 35 m (115 ft.) along a 

north-south axis. In reality, the 1995 survey report identified the northwestern-most extent of a 

diagonal feature 4 times larger than previously reported and extending to the southeast. 

Recommending an avoidance zone for prehistoric landforms is a “best-guess” scenario. 

Prehistoric avoidance zones may be skewed to one side of a feature’s actual shape, insufficient to 

fully protect the landform, or unnecessarily large. It has to be noted that the landform is being 

protected, not necessarily an archaeological site, and as previously stated, avoidances do not 

result in any further data acquisition. It is unlikely that drilling activities on the shelf will impact 

a buried high-probability landform, especially as channel margins are typically avoided as rig 

locations on the OCS (Evans and Keith 2011b). What are more likely to occur are the indirect 

impacts similar to the case of HI 160. Pipelines located (or reportedly located) within 150 m

(492 ft.) of a reported prehistoric landform can preclude the ability to test the feature due to 

safety concerns over the proximity of the installation. Not every reported landform necessitates 

avoidance. Avoidance is key to protecting historically significant sites, but sites are not being 

reported. 

Based on the combined efforts of studies in the northwestern GOM, prehistoric people could 

have been living on the OCS in areas that are currently up to 30 m (98 ft.) BSL and as much as 

48 km (26 nm) offshore. Radiocarbon dates from this study confirm that archaeological horizons 

exist offshore that correlate with known periods of occupation by Paleoindians and Early 

Archaic peoples in Texas and Louisiana. Sediment analyses yielded data representing hospitable 

environments with resources known to have been exploited by prehistoric populations. The 

combined results from this study confirm that geographical and operational environments can be 

detected by geophysical data (acoustic survey and physical sampling). Evidence of modified 

environments or irrefutable evidence of people, however, was not recovered. 

175

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Appendix A

Sea-Level Curves
‐100.00

‐80.00

‐60.00‐40.00‐20.00

0.00

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000

Depth Below Modern Sea‐level (meters)

Radiocarbon Ages (years BP)

Global Sea‐level Curve Based on Peat Samples and Benthic Co

197
‐100.00

‐80.00

‐60.00‐40.00‐20.00

0.00

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000

Depth Below Modern Sea‐level (meters)

Radiocarbon Ages (years BP)

Global Sea‐level Curve Based on Coral Samples from Barbados

198
‐100.00

‐80.00

‐60.00‐40.00‐20.00

0.00

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000

Depth Below Modern Sea‐level (meters)

Radiocarbon Ages (years BP)

Western Atlantic Sea‐level Curve Based on Peat and Coral Samp

199
‐100.00

‐80.00

‐60.00‐40.00‐20.00

0.00

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 

Depth Below Modern Sea‐level (meters)

Radiocarbon Ages (years BP)

Texas Coast Sea‐level Curve Based on Marine Shell

200
‐100.00

‐80.00

‐60.00‐40.00‐20.00

0.00

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18

Depth Below Modern Sea‐level (meters)

Radiocarbon Ages (years BP)

Texas and Louisiana Coastal Sea‐level Curve Based on Oyster S

201
‐100

‐80

‐60‐40‐20

0

0 2000 4000 6000 8000 10000 12000 14000 16000 18000

Depth Below Modern Sea‐level (meters)

Radiocarbon Ages (years BP)

Texas Coastal Sea‐level Curve Based on Peat

202
‐100

‐80

‐60‐40‐20

0

0 2000 4000 6000 8000 10000 12000 14000 16000 

Depth Below Modern Sea‐level (meters)

Radiocarbon Ages (years BP)

Texas Coastal Sea‐level Curve Based on Peat and Shell Sampl

203
‐100.00

‐80.00

‐60.00‐40.00‐20.00

0.00

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000

Depth Below Modern Sea‐level (meters)

Radiocarbon Ages (years BP)

Texas Coastal Sea‐level Curve Based on Peat, Wood, and Rangia 

204
‐100.00

‐80.00

‐60.00‐40.00‐20.00

0.00

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,0

Depth Below Modern Sea‐level (meters)

Radiocarbon Ages (years BP)

Texas Coastal Sea‐level Curve Based on Foraminifera

205
‐100.00

‐80.00

‐60.00‐40.00‐20.00

0.00

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000

Depth Below Modern Sea‐level (meters)

Radiocarbon Ages (years BP)

Western Mississippi River Valley Coastal Margin Sea‐level Cur

206
‐100.00

‐80.00

‐60.00‐40.00‐20.00

0.00

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,0

Depth Below Modern Sea‐level (meters)

Radiocarbon Ages (years BP)

East and Central Texas Coastal Sea‐level Curve

207
209

Appendix B

Core Logs
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

-170

28 June 2009

15.1 m BSL

HI 160

3

OL: Unit 1: Munsell 5GY 4/1 (dark

greenish gray gley 1) gritty texture with

visible shell, 5-8cm orange bay scallop

shell at 9 cmbs

OL: Unit 2: Munsell 10GY 5/1 (greenish

gray gley 1) gritty texture

GW: shell filled burrows, vertical as

opposed to discrete lenses

OL: Unit 2 (continued)

SC: shell lens

OL: Unit 2 (continued)

1200 1700 -20 20

211
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

-340

28 June 2009

15.1 m BSL

HI 160

3

GW: shell filled burrow

OL

SM: sand lens

OL: Unit 2 (continued)

SM: sand lens

OL: Unit 2 (continued): trace of 10YR 2/1

(black) staining, one shell at 218 cmbs

OH: Unit 3: Munsell 2.5Y 4/1 (dark gray)

with mottling of 10YR 2/1 (black) and

10YR 3/3 (dark brown), no grit in texture,

no visible shell

OL: Unit 4: Munsell 5G 5/1 (greenish gray

gley 1), similar to Unit 2 except for

presence of broken shell scattered

throughout

SM: sand lens

OL: Unit 4 (continued)

SM: sand lens (5Y 5/1 gray)

OL: Unit 4 (continued)

-20 20

-20 20

1200 1700

1200 1700

212
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

-440

-450

-460

-470

-480

-490

-500

-510

28 June 2009

15.1 m BSL

HI 160

3

SM: sand lens

OL: Unit 4 (continued)

SM: sand lens

OL: Unit 4 (continued)

SM: sand lens

OL: Unit 4 (continued)

SM: sand lens

OL: Unit 4 (continued): scattered sand

throughtout remainder of Unit, not in

discrete lenses

1200 1700 -20 20

213
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-510

28 June 2009

15.1 m BSL

HI 160

3

214
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

-170

28 June 2009

15.02 m BSL

HI 160

7

OL: Unit 1: Munsell 5GY 4/1 (dark

greenish gray), gritty texture with shell

throughout unit

OL: Unit 2A: Munsell 10GY 5/1 (greenish

gray), well mixed sediments with visible

shell throughout unit, more grit (probable

sand) than Unit 2B

OL: Unit 2B: Munsell 10GY 5/1 (greenish

gray), similar to Unit 2A but with less grit

overall, discrete sand lenses

SC: sand lens

OL: Unit 2B (continued)

SC: sand lens

OL: Unit 2B (continued)

SC: sand lens with observed shell

1200 1700 -20 20

215
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

-340

28 June 2009

15.02 m BSL

HI 160

7

OL: Unit 2B (continued)

SC: sand lens with observed shell

OL: Unit 2B (continued)

SC: sand lens

OL: Unit 2B (continued)

SC: sand lens

OL: Unit 2B (continued)

SC: sand lens

OL: Unit 2B (continued): carbonate nodule

(5Y 5/1 gray, 3 cm diameter) at 310 cmbs

-20 20

-20 20

1200 1700

1200 1700

216
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

-440

-450

-460

-470

-480

28 June 2009

15.02 m BSL

HI 160

7

SC: Unit 3A: Munsell 2.5Y 4/1 (dark gray)

with mottling of 10YR 2/1 (black) and

10YR 3/3 (dark brown) probable organics,

irregular shell at unit transition, but does

not extend into unit

SC: Unit 3B: same as unit 3A but with less

mottling downward, more discrete streaks

of organic staining

SC: Unit 3C: same base Munsell as 3A but

with little to no observed organics

1200 1700 -20 20

217
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

-170

28 June 2009

15.02 m BSL

HI 160

9

OL: Unit 1: Munsell N4/1 (dark gray) gley

1, mottled (10Y 5/1, greenish gray gley)

silty sediment with gritty texture and large

(possible) clam shell 8-10 cmbs, 3cm

whelk shell at 16 cmbs

OH: Unit 2: Munsell 10GY 5/1 (greenish

gray), smooth texture with some visible

shell and discrete shell lenses

SC: sand lens

OH: Unit 2 (continued)

SC: sand lens

OH: Unit 2 (continued)

SC: sand lens

OH: Unit 2 (continued)

SC: sand lens

OH: Unit 2 (continued)

1200 1700 -20 20

218
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

-340

28 June 2009

15.02 m BSL

HI 160

9

SC: sand stringers, not completely

discrete lenses

OH: Unit 2 (continued)

SC: sand lens

OH: Unit 2 (continued)

SC: sand lens

OH: Unit 2 (continued)

SC: sand lens

OH: Unit 2 (continued)

SC : sand lens

OH: Unit 2 (continued)

SC: sand lens

OH: Unit 2 (continued)

GW: shell-filled lens

OH: Unit 2 (continued)

GW: shell-filled lens

OH: Unit 2 (continued)

SC: sand lens

OH: Unit 2 (continued)

OH: Unit 3: Munsell 4/N (dark gray gley 1),

smooth texture with charcoal visible at

306 cmbs, smaller flecks possible organics

throughout

-20 20

-20 20

1200 1700

1200 1700

219
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

28 June 2009

15.02 m BSL

HI 160

9

OH: Unit 4: Munsell N4/1 (dark gray gley

1) mottled with N3/1 (very dark gray gley

1), smooth texture, no visible sand; some

streaks of 10YR 2/1 (black)

OH: Unit 5: Munsell N3/1 (very dark gray

gley 1) smooth texture with inclusions of

10YR 2/2 (very dark brown) possible

organics

OH: Unit 6: Munsell 10GY 5/1 (greenish

gray gley 1) smooth texture, slightly

plasticy, includes diagonal intrusive streak

of 10Y 5/1 (greenish gray) staining that

begins in Unit 5

1200 1700 -20 20

220
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

-170

28 June 2009

15.3 m BSL

HI 160

10

OL: Unit 1: Munsell 5GY 4/1 (dark

greenish gray gley 1), gritty texture with

intact and broken shell pieces throughout

OL: Unit 2: Munsell 10Y 5/1 (greenish gray

gley 1), gritty texture with occassional

shell/sand lenses/burrows

SM: sand lens

OL: Unit 2 (continued)

SM: sand lens

OL: Unit 2 (continued)

SM: sand lens

OL: Unit 2 (continued)

SM: sand lens

OL: Unit 2 (continued)

SM: sand lens with semi-circular pattern

stain of 5Y 5/1 (gray)

OL: Unit 2 (continued)

1200 1700 -20 20

221
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

-340

28 June 2009

15.3 m BSL

HI 160

10

SM: sand lens

OL: Unit 2 (continued)

GW: shell filled burrow

OL: Unit 2 (continued)

SM: sand lens

OH: ribbon of 5Y 5/1 (gray) soft texture

sediment cutting through Unit 2 sediments

(possible burrow)

SM: sand lens, single shell

OL: Unit 2 (continued)

OH: Unit 3: Munsell 2.5Y 4/1 (dark gray)

with mottling of 10YR 2/1 black and 10YR

2/3 (dark brown) possible organics

OH: Unit 4: Munsell 5Y 5/1 (gray) with

some streaks of 10YR 2/1 (black) smooth,

plasticy texture, no visible sand or shell

-20 20

-20 20

1200 1700

1200 1700

222
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

-440

-450

28 June 2009

15.3 m BSL

HI 160

10

OH: Unit 5: Munsell 5Y 5/1 (gray) with

increasing amounts (possible oxidized)

10YR 4/6 (red), smooth texture, very stiff

1200 1700 -20 20

223
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

-170

28 June 2009

15.3 m BSL

HI 160

11

OL: Unit 1: Munsell 5GY 4/1 (dark

greenish gray gley 1) high water content,

gritty texture, visibly broken shells

throughout

OL: Unit 2: Munsell 10GY 5/1 (greenish

gray gley 1), gritty texture, occassional

shell filled burrows and sand lenses

GW: shell filled burrow

OL: Unit 2 (continued)

GW: shell filled burrow

OL: Unit 2 (continued)

SC: sand lens

OL: Unit 2 (continued)

1200 1700 -20 20

224
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

-340

28 June 2009

15.3 m BSL

HI 160

11

SC: sand lens

OL: Unit 2 (continued)

SC: shell lens

OL: Unit 2 (continued)

SC: sand lens

OL: Unit 2 (continued)

SC: sand lens

OL: Unit 2 (continued)

SC: sand lens

OL: Unit 2 (continued)

SC: sand lens

OL: Unit 2 (continued)

SM: small deposit 10YR 3/2 (very dark

grayish brown)

OL: Unit 2 (continued)

SC: sand lens

OL: Unit 2 (continued)

-20 20

-20 20

1200 1700

1200 1700

225
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

-440

-450

-460

-470

-480

28 June 2009

15.3 m BSL

HI 160

11

GW: shell filled burrow

OL: Unit 2 (continued)

OH: Unit 3: Munsell 2.5Y 4/1 (dark gray)

with mottling of 10YR 2/1 (black) and

10YR 3/3 (dark brown), smooth texture, no

grit, no visible shell

OH: Unit 4: Munsell 10YR 2/1 (black)

smooth and plactic, no grit, no visible

shell, very dense material

1200 1700 -20 20

226
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

-170

28 June 2009

15.3 m BSL

HI 160

12

OL: Unit 1: Munsell 5GY 4/1 (dark

greenish gray gley 1) gritty texture, broken

shell pieces throughout, large spondylus

shell at 36 cmbs

OL: Unit 2: Munsell 10Y 5/1 (greenish gray

gley 1), smooth texture with occassional

sand lenses and shell filled burrows

1200 1700 -20 20

227
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

-340

28 June 2009

15.3 m BSL

HI 160

12

SC: sand lens

OL: Unit 2 (continued)

-20 20

-20 20

1200 1700

1200 1700

228
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

-440

-450

-460

-470

-480

-490

-500

-510

28 June 2009

15.3 m BSL

HI 160

12

SC: sand lens

OL: Unit 2 (continued): vertical streak of

5Y 5/1 (gray) color change through the

underlying sand lenses and Unit 2

sediments (350-380 cmbs)

SC: sand lens

OL: Unit 2 (continued)

SC: sand lens

OL: Unit 2 (continued)

SC: sand lens

OL: Unit 2 (continued)

SC: sand lens

OL: Unit 2 (continued)

SC: sand lens

OL: Unit 2 (continued)

SC: sand lens

OL: Unit 2 (continued)

GW: shell filled burrow

OL: Unit 2 (continued)

SC: sand lens

OL: Unit 2 (continued)

OH: Unit 3: Munsell 2.5Y 4/1 (dark gray)

with mottling of 10YR 2/1 (black) and

10YR 2/3 (dark brown) smooth, plastic

texture, no visible sand or shell

1200 1700 -20 20

229
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (usec) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

28 June 2009

15.4 m BSL

HI 178

1

OL: Unit 1: Munsell 5Y3/1 (very dark gray)

soft, cohesive sediment with few, discrete

shells

GW: Shell hash

OL: Unit 1: continued

GW: Shell hash

OL: Unit 1: continued

OH: Unit 2: Munsell 10YR 2/1 (black), soft

cohesive sediment with scattered charcoal

flecks and streaks of 5Y3/1 (very dark

gray)

PT: Charcoal lens

OH: Unit 2: continued

SC: Unit 3: Munsell 5Y 4/1 (dark gray),

muddy sand lens with some broken shell

OH: Unit 4: Munsell 2.5Y 3/1 (dark gray),

mottled sediment with streaks of brown

probable organics throughout

73 92 -20 20

230
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (usec) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

28 June 2009

15.4 m BSL

HI 178

1

OL: Unit 5: Munsell (gley) 4/N4 (dark gray)

well consolidated sediment

OH: Unit 6: Munsell 2.5Y 3/1 (dark gray),

mottled sediment with streaks of brown

probable organics

OH: Unit 7: Munsell (gley) N5/ (gray), well

consolidated sediment with flecks of

organics, large bioturbation burrow

approx. 2 cm in diameter extending from

204 to a depth of 223 cmbs.

SC: Unit 8: Munsell 5GY 5/1 (greenish

gley), more consolidated than Unit 7,

apparent oxidation beginning at 285 cmbs,

becoming more pronounced with depth

-20 20

-20 20

73 92

73 92

231
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (usec) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

-440

-450

-460

-470

-480

28 June 2009

15.4 m BSL

HI 178

1

SC: Unit 9: Munsell 2.5Y 5/3 (light olive

brown) and 5GY 5/1 (greenish gley)

mottled with increased oxidation ranging

from 10YR 4/6 (dark yellowish brown) to

7.5YR 2.5/3 (very dark brown)

73 92 -20 20

232
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (usec) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

28 June 2009

15.4 m BSL

HI 178

2

OL: Unit 1: Munsell 2.5Y 3/1 (very dark

gray), silty sediment with broken,

disarticulated shell

OL: Unit 2: Munsell 5GY 4/1 (dark

greenish gray), silty sediment, intrusive

burrows filled with Unit 1 material, mild

oxidation

OL: Unit 3: Munsell 5GY 5/1 (greenish

gray), silty sediment with broken,

disarticulated shell

GW: Stacked shell lens with significant

oxidation from 153 to 156 cmbs

SM: Unit 4: Munsell 2.5Y 6/2 (light

brownish gray), carbonate nodules

scattered throughout, silty sandy sediment

73 92 -20 20

233
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (usec) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

28 June 2009

15.4 m BSL

HI 178

2

SM: Unit 5: Munsell 2.5Y 6/2 (light

brownish gray), sandy sediment

interbedded with lenses of 5GY5/1

(greenish gray)

Unopened section.

-20 20

-20 20

73 92

73 92

234
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (usec) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

28 June 2009

15.4 m BSL

HI 178

2

235
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (usec) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

28 June 2009

15.4 m BSL

HI 178

5

OL: Unit 1: Munsell 5GY 4/1 (dark

greenish gray), soft, cohesive sediment,

no inclusions

OL: Unit 2: Munsell 5GY 5/1 (greenish

gray), soft, cohesive sediment with shellfilled burrow, some oxidized sediment of

2.5Y 5/4 (light olive brown)

SC: Unit 3: Munsell 5GY 6/1 (greenish

gray) cohesive sediment with some

bioturbation, oxidized sediment of 10YR

6/6 (brownish yellow) and 10YR 3/6 (dark

yellowish brown) increasing with depth.

Carbonate nodules apparent at 152, 169,

176, 208, 215, 220, 231, 266 cmbs.

73 92 -20 20

236
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (usec) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

28 June 2009

15.4 m BSL

HI 178

5

SC: Unit 4: Munsell 10YR 5/4 (yellowish

brown) very fine sandy loam with discrete

lenses of 2.5Y 5/3 (light olive brown)

clayey sediment with nodules.

-20 20

-20 20

73 92

73 92

237
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (usec) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

-440

-450

-460

-470

-480

-490

28 June 2009

15.4 m BSL

HI 178

5

OH: Discrete lens of 10YR 2/1 black,

probable organic-rich sediment

SC: Unit 4: continued

73 92 -20 20

238
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

28 June 2009

15.4 m BSL

HI 178

6

OL: Unit 1: Munsell 5GY 4/1 (dark

greenish gray), sandy silt

GW: Shell hash

OL: Unit 1: continued

GW: Unit 2: Munsell 2.5Y 4/1 (dark gray),

bioturbated unit with shell hash

OL: Unit 3: Munsell 5Y 4/1 (greenish gray),

silty sand with dark streaks (2.5Y 3/1 very

dark gray) that increase in density with

depth

1200 1700 -20 20

239
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

28 June 2009

15.4 m BSL

HI 178

6

SC: Unit 4: Munsell 2.5Y 3/1 (very dark

gray) and 2.5Y 4/1 (dark gray), mottled

sandy sediment

SC: Unit 5: Munsell color 5Y5/1 (gray)

smooth silty sediment with flecks of

2.5Y3/1 (very dark gray)

SC: Unit 6: Munsell color 5Y5/1 (gray) with

oxidized streaks of 10YR5/4 (yellowish

brown)

Unopened section

-20 20

-20 20

1200 1700

1200 1700

240
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

28 June 2009

15.4 m BSL

HI 178

6

241
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

28 June 2009

15.4 m BSL

HI 178

7

OL: Unit 1: Munsell 5GY 4/1 (dark

greenish gray), high water content on

uppermost 12.5 cmbs, silty sediment with

broken, distarticulated shell inclusions

SC: Unit 2: Munsell 5GY 5/1 (greenish

gray), heavily bioturbated with shell fill,

some oxidation of 2.5Y 6/3 (light yellowish

brown)

SC: Unit 3: Munsell 5Y 6/1 (gray), some

bioturbation, some oxidation (2.5Y 5/4 light

olive brown)

SC: Unit 4: Munsell 5GY 6/1 (gray), some

bioturbation, increasing amount of

oxidation (2.5Y 4/4 olive brown) with

depth, isolated shell at 161-164 cmbs

1200 1700 -20 20

242
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

28 June 2009

15.4 m BSL

HI 178

7

SC: Unit 5: Munsell 2.5Y 6/2 (light

brownish gray), heavy oxidation of 2.5Y

5/6 (light olive brown), carbonate nodule at

248-250 cmbs

1200 1700 -20 20

243
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

-170

29 June 2009

26.5 m BSL

GA 356

1

OL: Unit 1: Munsell 10GY 4/1 (dark

greenish gray) gritty texture, some shell

visible, blurred transition into unit 2

OH: Unit 2: Munsell 10Y 4/1 (dark

greenish gray) smooth texture, possible

organics, no visible shell, blurred transition

into unit 3

OH: Unit 3A: Munsell 10GY 5/1 (greenish

gray) smooth texture, no visible shell,

some minor inclusions of N5/ (gray gley 1)

with gritty texture

1200 1700 -20 20

244
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

-340

29 June 2009

26.5 m BSL

GA 356

1

OL: Unit 3B: Munsell 10GY 6/1 (greenish

gray) gritty texture, no shell visible,

transitions into 5G 5/1 (greenish gray gley

1)

OL: Unit 3C: Munsell 10GY 6/1 (greenish

gray) gritty texture, no visible shell

OL: Unit 4: Munsell 10GY 6/1 (greenish

-20 20

-20 20

1200 1700

1200 1700

245
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

29 June 2009

26.5 m BSL

GA 356

1

gray clay) mottled with 2.5Y 6/4 (light

yellowish brown) and 10Y 6/1 (greenish

gray gley 1) gritty texture

OH: intrusive 5G 5/1 (greenish gray) soft

texture

OL: Unit 4 (continued)

1200 1700 -20 20

246
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

-170

29 June 2009

26.3 m BSL

GA 356

2

OL: Unit 1: Munsell 5GY 4/1 (greenish

gray gley 1) grity texture, some visible

shell

OH: Unit 2: Munsell 10GY 5/1 (greenish

gray gley 1) smooth texture no visible shell

or sand

OL: Unit 3: alternating lenses Munsell 5GY

4/1 (dark greenish gray) gritty, 10GY 5/1

(greenish gray gley 1) smooth, 10Y 4/1

(drak greenish gray) gritty, and traces 2.5Y

5/2 (grayish brown) gritty 1200 1700 -20 20

247
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

-340

29 June 2009

26.3 m BSL

GA 356

2

SC: Unit 4: Munsell 10YR 5/2 (grayish

brown) grit with lenses 10YR 5/6

(yellowish brown) grit and 5YR 5/4

(reddish brown) smooth

OL: Unit 5A: Munsell 10GY 5/1 (greenish

gray gley 1) smooth texture with 10YR 5/6

(yellowish brown) grit and 10Y 5/1

(greenish gray) grit, possible charcoal

flake at 237 cmbs

-20 20

-20 20

1200 1700

1200 1700

248
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

-440

-450

-460

-470

-480

-490

-500

-510

29 June 2009

26.3 m BSL

GA 356

2

SC: possible sand

SC: Unit 6: Munsell 2.5Y 5/3 (light olive

brown)grit with streaks 10GY 5/1 (greenish

gray gley 1), some staining of 10YR 4/6

(dark yellowish brown), scattered shell

broken throughout, large shell clusters 537

& 544 cmbs

-20 20

-20 20

1200 1700

1200 1700

249
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-510

-520

-530

-540

-550

-560

-570

-580

29 June 2009

26.3 m BSL

GA 356

2

GW: shell filled burrow

SC: Unit 6 (continued)

250
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

-170

29 June 2009

26.6 m BSL

GA 356

3

OL: Unit 1: Munsell 10Y 4/1 (dark greenish

gray) mottled with 2.5Y 4/3 (olive brown)

and 2.5Y 6/2 (light brownish gray) grit

OL: Unit 2: Munsell 5GY 4/1 (dark

greenish gray) mottled with 5Y 5/3 (olive)

grit

OL: Unit 3: same as Unit 1 with addition of

2.5Y 7/2 (light gray) nodules (probably

carbonate, at 90-97 cmbs) and 5Y 6/2

(light olive) grit

OL: Unit 4A: Munsell 5G 6/1 (greenish

gray gley 1) mottled with (oxidized) 10YR

5/6 (yellowish brown) grit, nodules noted

at 141-145, 174-178, and 233-240 cmbs

1200 1700 -20 20

251
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

-340

29 June 2009

26.6 m BSL

GA 356

3

OL: Unit 4B: same as Unit 4A but with

broken shell throughout

OL: Unit 5A: Munsell 5G 4/2 (grayish

green) grit with 2.5Y 7/2 (light gray) grit,

ground and broken shell

OL: Unit 5B: same as Unit 5A but 2.5Y 7/2

dominant

-20 20

-20 20

1200 1700

1200 1700

252
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

-440

-450

-460

-470

-480

-490

-500

-510

29 June 2009

26.6 m BSL

GA 356

3

SC: Unit 6: Munsell 5Y 6/1 (light olive

gray) grit with some oxidized staining

SC: Unit 7: Munsell 5Y 6/2 (light olive

gray) grit

SC: Unit 8: Munsell 5YR 4/6 (yellowish

red) grit mottled with 2.5Y 6/3 (light

yellowish brown) grit, small pieces shell

throughout, large nodules at 420-426 &

446-449 cmbs

-20 20

-20 20

1200 1700

1200 1700

253
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-510

-520

-530

-540

-550

-560

-570

-580

-590

-600

29 June 2009

26.6 m BSL

GA 356

3

254
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

-170

29 June 2009

26.8 m BSL

GA 356

4

OL: Unit 1: Munsell N4/ (dark gray gley 1),

gritty

OL: Unit 2: Munsell 2.5Y 5/1 (gray) grit

interbedded with sand lenses (N4/1 gley 1

dark gray), some visible shell, 173-184

has higher water content than surrounding

seds

1200 1700 -20 20

255
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

-340

29 June 2009

26.8 m BSL

GA 356

4

OL: Unit 3: Munsell 10GY 4/1 (dark

greenish gray) grit well mixed with 10Y 4/1

(dark greenish gray gley 1)

SC: sand lens (5Y 4/2 light olive gray)

OL: Unit 3 (continued)

OH: silty lens 10Y 5/1 (greenish gray gley

1)

OL: Unit 3 (continued)

-20 20

-20 20

1200 1700

1200 1700

256
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

-440

-450

-460

-470

-480

-490

-500

-510

29 June 2009

26.8 m BSL

GA 356

4

OL: Unit 3 (continued), becomes coarser

with depth

GW: shell including scallop and whelk,

sediments are 5GY 4/1 (drak gray gley 1)

OL: Unit 3 (continued)

-20 20

-20 20

1200 1700

1200 1700

257
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-510

-520

-530

-540

-550

-560

-570

-580

-590

-600

-610

29 June 2009

26.8 m BSL

GA 356

4

GW: whelk shell

OL: Unit 3 (continued)

258
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

-170

29 June 2009

26.8 m BSL

GA 356

5

OL: Unit 1: Munsell 5GY 4/1 (drak

greenish gray gley 1) grit with broken

pieces shell visible throughout

OH: Unit 2: Munsell 5GY 4/1 (dark

greenish gray gley 1) mottled with N3/

(very dark gray gley 1), scattered probable

organics throughout (2.5Y 5/6 light olive

brown and 5GY 2.5/1 greenish black gley

1), no grit, no visible shell

1200 1700 -20 20

259
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

-340

29 June 2009

26.8 m BSL

GA 356

5

OL: Unit 3: Munsell 10Y 4/1 (dark greenish

gray) grit, with possible root/burrow

extending vertically into Unit 4

OH: Unit 4A: Munsell 10BG 6/1 (greenish

gray gley 2), no grit, no visible shell

OL: Unit 4B: same base color as Unit 4A,

mottled with 10BG 6/1 (greenish gray gley

2) silty texture and 10Y 7/1 (light greenish

gray gley 1) grit

-20 20

-20 20

1200 1700

1200 1700

260
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

-440

-450

-460

-470

-480

-490

-500

-510

29 June 2009

26.8 m BSL

GA 356

5

OL: Unit 4C: same colors as Unit 4B but

all coarse grain grit, no viisble shell or

organics

-20 20

-20 20

1200 1700

1200 1700

261
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-510

-520

-530

-540

-550

-560

-570

-580

-590

-600

29 June 2009

26.8 m BSL

GA 356

5

262
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

-170

29 June 2009

26.5 m BSL

GA 356

6

OL: Unit 1: Munsell 5GY 4/1 (dark

greenish gray gley 1) grit

OL: Unit 2: Munsell 10GY 4/1 (dark

greenish gray gley 1) smooth texture

mottled with sand intrusions and scattered

pieces of organic matter (10YR4/6 dark

yellowish brown)

SC: round intrusive accummulation 5GY

4/1 (dark greenish gray) gritty texture

OL: Unit 2 (continued)

1200 1700 -20 20

263
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

-340

29 June 2009

26.5 m BSL

GA 356

6

OH: Unit 3: Munsell 5GY 4/1 (dark

greenish gray gley 1) smooth texture, no

grit, no visible shell; @303 cmbs faint line

of organics visible but no change in color

or texture

OH: Unit 4: Munsell 10Y 3/1 (greenish

gray gley 1) smooth texture with flecked

organics throughout

-20 20

-20 20

1200 1700

1200 1700

264
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

-440

-450

-460

29 June 2009

26.5 m BSL

GA 356

6

CH: Unit 5: Munsell 5Y 2.5/1 (black) soft,

cohesive texture, some organic flecks,

intrudes vertically into Unit 6 to depth of

384 cmbs

OL: Unit 6: Munsell 10Y 4/1 (dark greenish

gray gley 1) grit with some dark staining

(10YR 2/1 black)

OL: Unit 7: Munsell 10Y 5/1 (greenish gray

gley 1) grit with some dark staining (10YR

2/1 black)

OH: Unit 8: Munsell 10Y 4/1 (dark

greenish gray gley 1) smooth texture

1200 1700 -20 20

265
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

-170

29 June 2009

26.9 m BSL

GA 356

7

OL: Unit 1: Munsell 5GY 4/1 (dark

greenish gray gley 1) grit with broken

shells visible

SC: Unit 2A: parallel bedded smooth and

gritty textured sediment in alternating

lenses of 5Y 4/3 (olive) grit, 5G 6/1

(greenish gray gley 1) smooth, 10YR 5/4

(yellowish brown) grit, 10Y 6/1 (greenish

gray gley 1) smooth, and 10YR 5/6

(yellowish brown) grit 1200 1700 -20 20

266
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

-340

29 June 2009

26.9 m BSL

GA 356

7

SC: Unit 2B: same colors and textures as

Unit 2A but no longer sorted, sediments

are mixed, one fleck 10YR 2/1 (black) at

198 cmbs

SC: Unit 2C: same as Unit 2B but with

increasing oxidation with depth, addition of

7.5YR 4/6 (strong brown) cohesive

sediment

-20 20

-20 20

1200 1700

1200 1700

267
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

29 June 2009

26.9 m BSL

GA 356

7

SM: Unit 3: Munsell 2.5Y 7/3 (pale yellow)

grit

1200 1700 -20 20

268
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

-170

30 June 2009

26.6 m BSL

GA 356

8

OL: Unit 1: Munsell 5GY 4/1 (dark

greenish gray gley 1) grit

OL: Unit 2: Munsell 5G 5/1 (greenish gray

gley 1) smooth, with other vertical half of

Unit characterized by 5GY 5/1 (greenish

gray gley 1) grit

SC: Unit 3: parallel bedded smooth and

gritty textured sediment in alternating

lenses of 5Y 5/4 (olive) grit, 10Y 6/1

(greenish gray gley 1) smooth, 2.5Y 5/3

(light olive brown) smooth, and 2.5Y 5/6

(light olive brown) grit

1200 1700 -20 20

269
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

-340

30 June 2009

26.6 m BSL

GA 356

8

SC: Unit 4: mottled sediments with less

overall grit, includes 2.5Y 5/4 (light olive)

smooth, 10Y 6/1 (greenish gray gley 1)

smooth, 2.5Y 6/2 (light brownish gray) grit,

and 5G 5/2 (grayish green gley 1)

smooth; 10YR 5/8 (yellowish brown) grit

appears towards end of unit

-20 20

-20 20

1200 1700

1200 1700

270
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

-440

-450

-460

30 June 2009

26.6 m BSL

GA 356

8

SM: Unit 5: Munsell 10YR 5/4 (yellowish

brown) coasrse grained mottled with 2.5Y

5/3 (light olive brown), broken shell

fragments visible throughout 1200 1700 -20 20

271
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

-170

30 June 2009

26.7 m BSL

GA 356

9

OL: Unit 1: Munsell 5GY 4/1 (dark

greenish gray gley 1) gritty texture with

broken shell fragments visible

OL: Unit 2: Munsell 5GY 4/1 (dark

greenish gray gley 1) gritty texture fining

with depth, occassional shell fragments

visible, some observed organics

OH: Unit 3: Munsell 10YG 4/1 (dark

greenish gray gley 1) smooth texture,

some color variation with 5G 4/1 (dark

greenish gray gley 1) observed

GW: shell filled burrow

OH: Unit 3 (continued)

1200 1700 -20 20

272
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

-340

30 June 2009

26.7 m BSL

GA 356

9

-20 20

-20 20

1200 1700

1200 1700

273
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

30 June 2009

26.7 m BSL

GA 356

9

GW: sand lens

OH: Unit 3 (continued)

SC: Unit 4: Munsell 10Y 4/1 (dark greenish

gray gley 1) smooth texture with streaks

of 2.5Y 3/3 (dark olive brown) possible

organics and lenses of 2.5N/ (black)

MH: Unit 5: Munsell 5Y 2.5/1 (black)

smooth texture, dessicated, mottled with

5Y 7/4 (pale yellow) grit and 7.5YR 4/6

(black) grit

1200 1700 -20 20

274
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

30 June 2009

30.9 m BSL

GA 426

1

OL: Unit 1: Munsell 5Y 4/1 (dark gray)

smooth, consolidated sediment with

scattered, disarticulated shell

GW: Shell hash

OL: Unit 1: continued

GW: Shell hash-filled burrow

OL: Unit 1: continued

OH: Unit 2: Munsell 2.5Y 4/1 (dark gray)

smooth, consolidated sediments with

possible organic streaks, one 1-cm long

disarticulated shell along core edge at 88

cmbs

ML: Unit 3: Munsell 5Y 5/1 (gray) gritty

texture, consolidated sediments with

probable organic streaks of 2.5Y 2.5/1

(black), no visible shell

SM: Unit 4A: Munsell 5GY 5/1 (greenish

1200 1700 -20 20

275
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

30 June 2009

30.9 m BSL

GA 426

1

gray) silty sand sediment with streaks of

2.5Y 6/2 (light olive brown) and 10YR 4/6

(dark yellowish brown) oxidized sediments

and discrete lenses 2.5Y 6/2 (light

brownish gray) sand

GM: Unit 4B: Munsell 5GY 5/1 (greenish

gray) silty sand with increased amount

10YR 4/6 (dark yellowish brown) oxidation,

dense shell concentration throughout unit

GM: Unit 5: Munsell 2.5Y 4/1 (dark gray)

with limited amounts 2.5Y 3/1 (very dark

gray), dense shell concentration

throughout unit

-20 20

-20 20

1200 1700

1200 1700

276
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

-440

-450

-460

-470

-480

-490

-500

30 June 2009

30.9 m BSL

GA 426

1

-20 20

-20 20

1200 1700

1200 1700

277
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-510

-520

-530

-540

-550

-560

-570

-580

30 June 2009

30.9 m BSL

GA 426

1

278
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

1 July 2009

30.7 m BSL

GA 426

2

ML: Unit 1: Munsell 5GY 4/1 (dark

greenish gray) gritty texture sediment with

scattered disarticulated shell fragments

and possible organic streaks

SM: Unit 2: Munsell 2.5Y 4/1 (drak gray)

gritty texture sediment with scattered

disarticulated shell fragments, possible

bioturbation

OH: Unit 3: Munsell 2.5Y 5/1 (gray)

smooth texture sediment with isolated

shell fragment at 117 cmbs, organic

staining throughout

SM: Unit 4: Munsell 2.5Y 5/1 (gray) to

2.5Y 3/1 (very dark gray) mottled

sediment, consolidated with no visible

shell, discrete lenses 2.5Y 5/1 (gray)

probable sand loam

OH: Unit 5A: Munsell 5GY 5/1 (greenish

1200 1700 -20 20

279
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

1 July 2009

30.7 m BSL

GA 426

2

gray) soft cohesive sediment with N4 (dark

gray) organic staining

OH: Unit 5B: Munsell 5GY 5/1 (greenish

gray) with lenses 2.5Y 7/2 (gray) and 2.5Y

5/1 (gray) sand loam, faint organic

staining, 2.5Y 5/6 (light olive brown)

oxidation darkening to 10YR 3/4 (dark

yellowish brown) with depth, no visible

shell

SM: Unit 6: Munsell 5GY 5/1 (greenish

gray) gritty texture consolidated sediment

with 10YR 3/4 (dark yellowish brown)

oxidation, no visible shell or organic

staining

OH: Unit 7: Munsell 5Y 3/1 (very dark

gray), smooth texture consolidated

sediment with discrete shell at 294 cmbs,

probable charcoal at 296 cmbs

GM: Unit 8A: Munsell 5Y 4/1 (dark gray)

smooth texture sediment with dense shell

throughout

-20 20

-20 20

1200 1700

1200 1700

280
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

-440

-450

-460

-470

-480

-490

-500

1 July 2009

30.7 m BSL

GA 426

2

GM: Unit 8B: Munsell 5Y 4/1 (dark gray)

smooth texture sediment with scattered

shell throughout

SM: Unit 9: Munsell 2.5Y 4/1 (dark gray)

gritty texture with occassional organic

staining, no visible shell

-20 20

-20 20

1200 1700

1200 1700

281
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-510

-520

-530

-540

1 July 2009

30.7 m BSL

GA 426

2

282
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

30 June 2009

31.09 m BSL

GA426

4

OL: Unit 1: Munsell 5Y 4/1 (dark gray)

smooth, consolidated sediment with

scattered, disarticulated shell

SM: Unit 2: Munsell 10YR 4/6 (dark

yellowish brown) gritty texture sediment,

disarticulated shell fragments

SM: Unit 3: Munsell 5GY 5/1 (greenish

gray) silty sand sediment with scattered

shell fragments

SM: Unit 4: Munsell 5Y 4/1 (dark gray) silty

sand sediment with scattered shell

fragments

1200 1700 -20 20

283
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

30 June 2009

31.09 m BSL

GA426

4

ML: Unit 5: 2.5Y 4/1 (dark gray) very fine

sandy sediment with organic staining, no

visible shell

OH: Organic staining 5Y 3/1 (very dark

gray)

ML: Unit 5: continued

SM: Unit 6: Munsell 5Y 4/1 (dark gray) and

2.5Y 5/1 (gray) mottled, gritty texture, high

water content sediment with scattered

shell fragments

GW: Shell hash lens

SM: Unit 6: continued

GW: Shell hash lens

SM: Unit 6: continued

OL: Unit 7: Munsell 5Y 4/1 (dark gray)

smooth texture consolidated sediment, no

visible shell

OL: Unit 8: Munsell 5Y 4/1 (dark gray) and

5Y 3/1 (very dark gray) mottled smooth

-20 20

-20 20

1200 1700

1200 1700

284
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

-440

-450

-460

-470

-480

-490

-500

30 June 2009

31.09 m BSL

GA426

4

sediment with scattered shell fragments

throughout

GW: Shell hash lens

OL: Unit 8: continued

GW: Shell hash lens

OL: Unit 8: continued

-20 20

-20 20

1200 1700

1200 1700

285
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-510

-520

-530

-540

-550

-560

-570

-580

-590

-600

30 June 2009

31.09 m BSL

GA426

4

286
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

30 June 2009

31.3 m BSL

GA426

5

OL: Unit 1: Munsell 5Y 4/1 (dark gray)

gritty texture, consolidated sediment with

scattered, disarticulated shell

SM: Unit 2: Munsell 2.5Y 4/4 (olive brown)

and 5Y 4/2 (olive gray) mottled sediment

with gritty texture and visible shell and

fragments

SM: Unit 3A: 5Y 4/1 (dark gray) very fine

probable sand, some 5Y 3/1 (very dark

gray) staining

1200 1700 -20 20

287
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

30 June 2009

31.3 m BSL

GA426

5

GC: Unit 3B: 5Y 4/1 (dark gray) very fine

probable sand, dense shell throughout

unit, with individual pieces fining with

depth

MH: Burrow filled with 5Y 4/4 (olive) sand

loam

GC: Unit 3B: continued

-20 20

-20 20

1200 1700

1200 1700

288
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

-440

30 June 2009

31.3 m BSL

GA426

5

1200 1700 -20 20

289
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

30 June 2009

30.9 m BSL

GA426

6

ML: Unit 1: Munsell 5Y 4/1 (dark gray)

gritty texture sediment with scattered

disarticulated shell fragments and possible

organic streaks

GW: Shell hash filled burrow

OL: Unit 2: Munsell 5Y 4/1 (dark gray)

smooth, consolidated sediment

ML: Unit 3: Munsell 2.5Y 3/1 (very dark

gray) and 5Y 6/1 (gray) mottled sediment,

gritty texture, possible organic staining

SM: Unit 4: Munsell 5Y 6/1 (gray) with

mottled 5Y 4/1 (very dark gray), gritty

1200 1700 -20 20

290
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

30 June 2009

30.9 m BSL

GA426

6

texture consolidated sediments, 2.5Y 6/1

(gray) sand and 10YR 5/8 (yellowish

brown) oxidation that increases with depth

to include 10YR 3/6 (dark yellowish brown)

GC: Unit 5: Munsell 5Y 6/1 (gray) gritty

sediment with articulated shells (~5 cm

diameter)

GC: Unit 6: Munsell 5Y 5/1 (gray) smooth

texture sediment with densely packed

oyster shell decreasing in size with depth

-20 20

-20 20

1200 1700

1200 1700

291
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

-440

-450

-460

-470

-480

-490

-500

30 June 2009

30.9 m BSL

GA426

6

SM: Unit 7: Munsell 5Y 4/1 (dark gray)

gritty texture sediment with no visible shell

GW: Burrow filled with 5Y 3/1 (very dark

gray) sand loam

SM: Unit 7: continued

ML: Unit 8: Munsell 5Y 4/1 (dark gray)

gritty consolidated sediment with organic

streaks and scattered, disarticulated shell

fragments

-20 20

-20 20

1200 1700

1200 1700

292
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-510

-520

-530

-540

-550

-560

-570

-580

30 June 2009

30.9 m BSL

GA426

6

293
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

1 July 2009

30.8 m BSL

GA426

7

ML: Unit 1: Munsell 5Y 4/1 (dark gray)

smooth, consolidated sediment with

scattered, disarticulated shell

GW: Shell hash lens

ML: Unit 1: continued

SM: Unit 2: Munsell 10BG 6/1 (greenish

gray) gritty texture with no visible shell,

and 10YR 5/6 (yellowish brown) oxidation

GC: Unit 3: Munsell 10BG 6/1 (greenish

gray) gritty texture with densely packed

shell throughout unit, and 10YR 5/6

1200 1700 -20 20

294
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

1 July 2009

30.8 m BSL

GA426

7

(yellowish brown) oxidation

GC: Unit 4A: Munsell 2.5Y 4/1 (dark gray)

gritty, consolidated sediment with shell

throughout

GC: Unit 4B: Munsell 2.5Y 4/1 (dark gray)

gritty, consolidated sediment with shell

throughout, 10YR 2/2 (very dark brown)

oxidation present

SM: Unit 5: Munsell 2.5Y 4/1 (dark gray)

gritty, consolidated sediment with

scattered shell fragments, 10YR 2/2 (very

dark brown) oxidation, possible tap root

burrow 1cm wide and filled with 2.5Y 3/2

(dark grayish brown) loam

-20 20

-20 20

1200 1700

1200 1700

295
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

-440

-450

1 July 2009

30.8 m BSL

GA426

7

1200 1700 -20 20

296
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

1 July 2009

30.7 m BSL

GA426

8

ML: Unit 1: Munsell 5Y 4/1 (dark gray)

gritty texture, consolidated sediment with

scattered, disarticulated shell

OH: Unit 2: Munsell gley 5/N (gray)

smooth texture, no visible shell with some

streaks 5Y 4/1 (dark gray)

OH: Unit 3: Munsell gley 4/(N) (dark gray)

smooth texture with some flecks 5Y 2.5

(black) probable organics

ML: Unit 4: Munsell 2.5Y 4/1 (dark gray)

gritty texture, no visible shell

OL: Unit 5: Munsell gley 6/1 (5GY)

(greenish gray) gritty texture with streaks

5Y 2.5/1 (black), Unit 4 sediments intrude

along left side of core, possible burrow

GC: Unit 6: Munsell gley 6/1 (5GY)

(greenish gray) gritty texture mottled with

sandy streaks 5Y 7/1 (light grey),

1200 1700 -20 20

297
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

1 July 2009

30.7 m BSL

GA426

8

increasing amounts 10YR 5/6 (yellowish

brown) oxidation with depth, no visible

shell

SM: Intrusive lens 10YR 5/1 (gray) clayey

sediment

GC: Unit 6: continued

ML: Unit 7A: Munsell 5Y 4/1 (dark gray)

smooth texture sediment with streaks 5Y

2.5/1 (black) organics and discrete lenses

as indicated throughout

SC: Intrusive sandy lens 10YR 5/3 (brown)

ML: Unit 7A: continued

GW: Intrusive shell lens

ML: Unit 7A: continued

SC: Intrusive sandy lens 5Y 4/1 (dark

gray)

ML: Unit 7A: continued

-20 20

-20 20

1200 1700

1200 1700

298
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

-440

-450

-460

-470

-480

-490

-500

1 July 2009

30.7 m BSL

GA426

8

SC: Intrusive sandy lens 5Y 4/1 (dark

gray)

ML: Unit 7A: continued

SC: Intrusive sandy lens 5Y 4/1 (dark

gray)

ML: Unit 7A: continued

SC: Intrusive lens 10YR 4/2 (dark grayish

brown)

ML: Unit 7B: Munsell 5Y 4/1 (dark gray)

smooth texture with 19 lenses 5Y 2.5/1

(black) less than 0.25 cm thick at irregular

intervals throughout unit

SC: Unit 8: Munsell 2.5Y 4/1 (dark gray)

gritty texture sediment with flecks 5Y 2.5/1

(black) and crushed shell

-20 20

-20 20

1200 1700

1200 1700

299
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-510

-520

1 July 2009

30.7 m BSL

GA426

8

300
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

1 July 2009

30.9 m BSL

GA426

9

OL: Unit 1: Munsell 5Y 4/1 (dark gray)

gritty texture, consolidated sediment with

scattered, disarticulated shell, one 3-cm

long fragment at 35 cmbs

GW: Shell hash lens

OL: Unit 1: continued

GW: Shell cluster

OL: Unit 1: continued

OH: Burrow or other organic

OL: Unit 1: continued

OH: Unit 2: Munsell 2.5Y 4/1 (dark gray)

smooth, consolidated sediments, no

visible shell

ML: Unit 3: Munsell 5Y 5/1 (gray) and 5GY

5/1 (greenish gray) mottled, gritty texture,

consolidated sediments with probable

organic streaks of 2.5Y 2.5/1 (black), no

visible shell

1200 1700 -20 20

301
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

1 July 2009

30.9 m BSL

GA426

9

SM: Unit 4A: Munsell 5GY 6/1 (greenish

gray) silty sand sediment with streaks of

2.5Y 6/8 (olive yellow) and 10YR 4/6 (dark

yellowish brown) oxidized sediments and

discrete lenses 2.5Y 5/1 (gray) sand,

carbonate nodules present between 185-

199 cmbs

GM: Unit 4B: Munsell 5GY 5/1 (greenish

gray) silty sand with increased amount

10YR 4/6 (dark yellowish brown) oxidation,

dense shell concentration thinning

towards bottom of unit

OH: Unit 5: Munsell 2.5Y 5/1 (gray)

smooth, consolidated sediments, no

visible shell

ML: Unit 6: Munsell 5Y 4/1 (dark gray) and

5Y 2.5/12 black mottled sediment with

organic staining

OL: Unit 7: Munsell 5Y 5/1 (gray) smooth,

consolidated sediment

GW: Shell hash lens

-20 20

-20 20

1200 1700

1200 1700

302
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

1 July 2009

30.9 m BSL

GA426

9

OL: Unit 7: continued

ML: Unit 8: Munsell 5Y 2.5/1 (black)

cohesive sediment, organic staining, no

visible shell

GC: Unit 9: Munsell 5Y 5/1 (gray) smooth

texture with dense shell throughout

OH: Unit 10: Munsell 5Y 2.5/1 (black),

2.5Y 3/2 (very dark grayish brown), and

5Y 5/1 (gray) mottled, smooth sediment

with organic staining, no visible shell

CH: Unit 11: Munsell 10YR 2/2 (very dark

brown) smooth cohesive sediment, coils

easily, one disarticulated shell fragment at

393 cmbs

SM: Unit 12: Munsell 2.5Y 4/2 (dark

grayish brown) and 5Y 5/1 (gray) mottled

sediment, gritty texture, no visible shell

1200 1700 -20 20

303
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

1 July 2009

30.9 m BSL

GA426

10

OL: Unit 1: Munsell 5Y 4/1 (dark gray)

smooth, consolidated sediment with

scattered, disarticulated shell

GW: Shell hash lens

OL: Unit 1: continued

GW: Shell hash lens

OL: Unit 1: continued

ML: Unit 2: Munsell 5Y 5/1 (gray) gritty

texture, consolidated sediments with

probable organic streaks

OH: Unit 3: Munsell 5GY 5/1 (greenish

gray) smooth, consolidated sediments with

10YR 2/1 (black) staining of organics,

possible charcoal

1200 1700 -20 20

304
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

1 July 2009

30.9 m BSL

GA426

10

SM: Unit 4A: Munsell 5GY 5/1 (greenish

gray) silty sand sediment with streaks of

2.5Y 5/3 (light olive brown) and 10YR 3/4

(dark yellowish brown) oxidized sediments

and possible burrow filled with 10YR 7/2

(light gray) sandy sediment

GC: Unit 4B: Munsell 5GY 5/1 (greenish

gray) silty sand with streaks of 10YR 3/4

(dark yellowish brown) oxidation, dense

shell concentration throughout unit

SM: Unit 5A: Munsell 2.5Y 4/1 (dark gray)

slightly gritty, cohesive sediment that coils

easily, mixed with scattered , discrete shell

fragments

-20 20

-20 20

1200 1700

1200 1700

305
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

-400

-410

-420

-430

-440

-450

-460

-470

-480

-490

-500

1 July 2009

30.9 m BSL

GA426

10

GC: Unit 5B: Munsell 2.5Y 4/1 (dark gray)

slightly gritty, cohesive sediment, dense

shell concentration with articulated shells

SM: Unit 5C: Munsell 2.5Y 4/1 (dark gray)

slightly gritty, cohesive sediment, no

visible shell

GC: Unit 5B: Munsell 2.5Y 4/1 (dark gray)

slightly gritty, cohesive sediment, dense

shell concentration with articulated shells

-20 20

-20 20

1200 1700

1200 1700

306
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-510

-520

-530

-540

-550

-560

-570

-580

1 July 2009

30.9 m BSL

GA426

10

307
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

-160

1 July 2009

30.9 m BSL

GA426

11

OL: Unit 1: Munsell 5Y 4/1 (dark gray)

smooth, consolidated sediment with

scattered, disarticulated shell

GW: Shell hash filled burrow

OL: Unit 1: continued

GW: Scattered shell hash

OL: Unit 1: continued

OH: Unit 2: Munsell 5Y 4/1 (dark gray)

smooth, consolidated sediments with

possible organic streaks, no visible shell

ML: Unit 3: Munsell 5GY 5/1 (greenish

gray) gritty texture, consolidated

sediments with probable organic streaks of

2.5Y 4/1 (dark gray), no visible shell

1200 1700 -20 20

308
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-170

-180

-190

-200

-210

-220

-230

-240

-250

-260

-270

-280

-290

-300

-310

-320

-330

1 July 2009

30.9 m BSL

GA426

11

SM: Unit 4A: Munsell 5GY 5/1 (greenish

gray) silty sand sediment with streaks of

2.5Y 5/6 (light olive brown) and 10YR 3/4

(dark yellowish brown) oxidized sediments

and discrete lenses 2.5Y 7/2 (light gray)

and 2.5Y 5/1 (gray) sand

GC: Unit 4B: Munsell 5GY 5/1 (greenish

gray) silty sand sediment with streaks of

2.5Y 5/6 (light olive brown) and 10YR 3/4

(dark yellowish brown) oxidized

sediments, shell fragments throughout,

uppermost shell pieces bleached

GC: Unit 5: Munsell 5Y 4/1 (dark gray)

smooth texture sediment with dense shell

concentration throughout, including intact,

articulated shells

-20 20

-20 20

1200 1700

1200 1700

309
Collection Date

Water Depth

Core No.

Description

(x 10^-8 (m^3/kg))

Site No.

Scale (cm) Lithology P-wave Velocity (m/s) Magnetic Susceptibility

-340

-350

-360

-370

-380

-390

1 July 2009

30.9 m BSL

GA426

11

310
311

Appendix C

Pollen and FTIR Reports
Environmental significance of abundant and diverse hornwort spores in a potential submerged

Paleoindian site in the Gulf of Mexico

Sophie Warnya*, David M. Jarzenb, Amanda Evansc, Patrick Hespc and Philip Barta

a

LSU Department of Geology and Geophysics, E-235 Howe-Russell, Baton Rouge, Louisiana 70803, USA; bCleveland Museum of

Natural History, 1 Wade Oval, University Circle, Cleveland, Ohio 44106, USA; c

LSU Department of Geography and Anthropology,

Baton Rouge, Louisiana 70803, USA

A palynological analysis of sediments sampled from core HI-178, offshore High Island, Texas, provided a diverse

and well-preserved palynoflora. The main objective was to analyze the environmental conditions at time of

deposition. A secondary objective was to evaluate whether or not this site might have been occupied by Native

Americans by looking for signs of human-driven changes in vegetation. Here we focus on the abundance of

hornwort spores recovered from these samples, review their diversity, compare the fossil spores to modern analogues

and discuss the paleoenvironmental implications of hornwort abundance. Although no direct evidence of human

occupation was found, the pollen and spore assemblage recovered, marked by high abundance and diversity in

spores of hornworts belonging to the families Anthocerotaceae and Notothyladaceae, indicate that this site was most

likely not submerged at the time of deposition; human occupation was therefore possible. This site represents a

coastal low-lying area with ponds or slow-moving waters that provided the humid environment needed for

hornworts to reproduce and thrive under warm climatic conditions.

Keywords: palynology; Gulf of Mexico; Holocene; Anthoceros; Phaeoceros; hornwort

1. Introduction

Hornworts (Anthocerotophyta) are a group of sporeproducing plants that are usually not very abundant in

Cenozoic palynological assemblages; they tend to be

overshadowed by abundant pollen produced by

gymnosperm and angiosperm plants that dominate

most environments since the Paleocene. Hornworts are

one of the three groups of bryophytes. When

recovered, the trilete spores they produced are often

grouped with spores from spore-producing pteridophytes and bryophytes such as the more common ferns

and mosses. Few palynological studies have been

published on hornwort spores alone; only a few

authors (Dettmann 1963; Krutzsch 1963, 1967; Nagy

1968; Jarzen 1979; Hassel de Menendez 1989) have

described or illustrated fossil spores comparable or

belonging to the Anthocerotophyta.

In our recent archeological study of a landscape

sampled off the Texas coast (Figure 1), abundant

spores of the Anthocerotophyta were recovered.

Because of their abundance at the site, a better

understanding of the environmental significance of

this group of land plants was needed to constrain the

type of environment that existed at High Island

at the time of deposition. Hence, this paper reviews

the morphological differences observed in two dominant fossil genera found in offshore Texas, Anthoceros

and Phaeoceros, and discusses the environmental

implications of this group of land plants as they occur

at the High Island site.

2. Background data on fossil site selection

High Island 178 (HI-178) is located approximately

34 km off the shore of Texas, near Galveston Island

(Figure 1). The site is currently located at a depth of

about 16 m below modern sea level (Figure 2). Based

on various studies of sea-level fluctuation reconstructions in the Gulf Coast region, it is possible that the

general area was barely inundated or a few meters (up

to 8 m) above sea floor between 7,000 and 9,200 BP,

depending on the sea-level curve used (Curray 1960;

Shepard 1964; Frazier 1974; Morton et al. 2000;

Tornqvist et al. 2006; Blum et al. 2008; Milliken

et al. 2008) and rates of subsidence (Milliken et al.

2008; figure 3). A geophysical survey was conducted in

June 2008 using a chirp sub-bottom profiler to acquire

acoustic data at 25 m intervals across the study site.

A navigation system was used to follow a predesigned

survey grid and the tow-fish was kept at a constant

*Corresponding author. Email: swarny@lsu.edu

Palynology

2012, 1–20, iFirst article

ISSN 0191-6122 print/ISSN 1558-9188 online

2012 AASP – The Palynological Society

http://dx.doi.org/10.1080/01916122.2012.666507

http://www.tandfonline.com

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setback, which was applied during post-processing. An

average speed of sound in saltwater of 1,500 m s–1

(two-way time travel) was used to calculate depth. All

sub-bottom data were interpreted digitally, with plan

view maps and three dimensional (3D) contours

created to illustrate the relict channel and associated

landforms observed within the survey grid. Age

estimates of interpreted features and existing datasets,

including grey literature reports and proprietary

studies, were correlated with the geophysical data

(Wille 2005). Absolute ages were established by carbon

dating of samples collected from cores acquired in June

and July 2009. Radiocarbon dating of charcoal units

recovered yielded a range of 9,550–9,460 calibrated

years BP.

Due to the variability of anticipated surficial and

subsurface sediments, a pneumatic vibracore rig was

used to acquire cores for this study. The coring rig was

Figure 1. Location map showing the present-day offshore position of the High Island 178 (HI178) site. Structure map of the top

of the Pleistocene surface (contours with numbers) are after Rodriguez et al. (2001). They delineate the Trinity/Sabine incised

valley during oxygen isotope stage 2 sequence boundary.

Figure 2. Transect showing depth of the High Island 178 (HI178) site at present, generated using GeoMapApp. mbsl: meters

below sea level.

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equipped with 6.096 m long, 0.1016 m diameter core

sleeves, and was positioned from the stern of the vessel.

A penetrometer was attached to the rig and recorded

core progress as both depth per second and time per

foot. A penetrometer is an engineering tool typically

used to measure sediment strength. In this case, it was

used to calculate the amount of time the coring rig

took to penetrate 0.3048 m of sediment. This precaution was taken because, in the Gulf of Mexico, some

sediments are difficult to core through. For example,

the Beaumont clay has a typical shear strength of

95,760 Pa. Coring crews usually deploy the rig at a

given location until either the maximum core depth is

achieved (in our case * 6 m) or the depth at which the

rig hits refusal. For our purposes, refusal was defined

as when the rig took more than 2 minutes to core

0.3048 m of depth. Trying to core past refusal can

damage the rig and/or the compressor. To avoid

potential problems, plots of the penetrometer data

graphically depicting depth versus time and depth

versus time per foot were monitored continuously

during drilling operation. Core sleeves were extruded

from the barrel, sectioned, capped and labeled on the

boat before being transported back to Louisiana State

University for processing and sampling in the H. Jesse

Walker Geomorphology Laboratory.

This site is of particular interest to archaeologists

because it was likely located above water at a time

when Paleoindian civilizations lived in Texas. Indeed,

according to Ricklis (2004), southeastern Texas has

been divided into three cultural chronological periods:

the Paleoindian (11,500 – 8,000 BP); the Inland

Archaic (8,000 – 1,500 BP); and the Coastal Archaic

(5,000 – 2,200 BP). The designation ‘Coastal’ refers to

sites located in the modern coastal zone and not the

coastal zone at the time of occupation. The radiocarbon dates place the site between 9,550 and 9,460

calibrated years BP, suggesting these samples fall

within the timeframe of Paleoindian occupation.

Because the HI-178 site was possibly above sea level

at the time when Paleoindian groups lived in Texas,

this site is a prime target for archaeological investigations as it represents a coastal geographic area for

which there is no previously defined cultural affiliation.

In order to look for evidence of possible human

presence 18 core samples were selected from core

sediments, including the layers containing the charcoal

inclusions.

3. Palynological techniques for collection of fossil and

modern spores

The fossil palynomorphs were extracted by standard

palynological techniques as outlined in Traverse

(2007). Specimens for scanning electron microscopy

(SEM) were cleaned in distilled water and a drop of

residue was placed on a SEM stub overnight for

drying. The dried residue was then coated with a thin

gold layer (200 A ̊

 ́

) applied by a glow plasma discharge

for 2 minutes, using a Hummer IITM gold sputter

coater. Photomicrographs of the results of SEM of

fossil Phaeoceros and Anthoceros spores are presented

in Plates 1–3.

To compare the fossil spores to modern spores of

Anthoceros and Phaeoceros, spores of extant species

were obtained via a loan from the Paleobiology

Division of the Canadian Museum of Nature

(CMN), Ottawa, Canada. SEM photomicrographs of

these specimen are illustrated in Plates 4–9. The

general locations where these specimens were collected

are summarized in Figure 4. The spores illustrated

herein were collected from vouchered herbarium sheets

as described by Jarzen and Jarzen (2006) and processed

using the techniques outlined in Jarzen (1979).

4. Results

The HI-178 fossil samples include up to 8% of various

forms of Anthocerotophyta (Plates 1–3). Several of the

different variations in spine length and overall morphology observed are probably derived from a single

species. Jarzen (1979) compared some of the fossil

species of Phaeoceros to modern specimens of the

living genera and concluded that several fossil species

and genera, as recorded from the Cretaceous of North

Figure 3. Relation between sea-level changes in the Gulf

of Mexico during the past 18,000 years and age of the HI

178 core studied (sea-level graphic from Milliken et al.

2008).

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America, are actually morphological variations within

a single taxon. By using a cautious approach as

highlighted in Jarzen (1979) and comparing the fossil

spores (Plates 1–3) to the modern spores (Plates 4–9)

obtained from the herbarium, we obtained information

which helps in the accurate comparison of the fossils to

extant taxa. Based on this evaluation, we concluded

that at least two species are abundant at our site; these

are Phaeoceros laevis (L.) Prosk. and Anthoceros

multifidus Lindb. The remaining forms recovered

were grouped as Anthoceros spp. as they could be

morphological variations within Anthoceros.

All spores show polar differences with a distinctive

trilete mark on the proximal surface and with a

Plate 1. Scanning electron microscope (SEM) photographs of key specimens of fossils of Anthocerotaceae from the High Island

drill hole HI-178, sample 32C, offshore Texas, US (see location 1 on Figure 4). Figures 1–9 show various surface sculpture found

in the fossil specimens of Phaeoceros laevis type, with the granules dispersed in between the branches of the laesurae. The scale

bar represents 10 microns.

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variation of ornamentation (variable density in spines

between species and within the surface of a single

spore, often stubby with broad-based and rounded

edges) on the distal surface.

The fossil spores of Phaeoceros laevis recovered off

the Texas coast resemble very closely those produced

today by hornworts growing in warm environments,

and are characterized by an amb that varies from a

circular to nearly square shape. An important diagnostic feature is the absence of heavy ornamentation

on the laesurae (even less so on the fossil species), and

the consistency of the thickening of the laesurae walls.

The surface sculpturing is essentially restricted to the

area between the arms of the laesurae. The ornamentation is composed of spine-like processes that are

generally broader at the base. Their height tends to

Plate 2. SEM photographs of key specimens of fossils of Anthocerotaceae from the High Island drill hole HI-178, sample 32C,

offshore Texas, US (see location 1 on Figure 4). Figures 1–9 show various surface sculpture found in the fossil specimens of

Phaeoceros spp. type, with more pronounced wall structures. Figures 1–4. Proximal views showing the trilete mark. Figures 5–9.

Distal views. The scale bar represents 10 microns. Note the fluctuation in amb from oval to rounded triangular.

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be somewhat less in the fossil genus, although variation

in this feature has been observed among specimens of

extant species.

The other fossil form found at High Island is

comparable to Anthoceros multifidus. Both fossil and

modern spores are characterized by triangular to

circular amb. The most striking feature is the network

of thick spine-like processes on the distal side of the

spore which is also visible in equatorial view. The bases

of these processes are connected to form a reticulate

pattern separated by wide lumina or depressions,

somewhat larger than the base of the processes

themselves. The proximal side of the spore is covered

in fine to thick granulations, but lacks spines. The

entire proximal surface is characterized by about 20

large depressions in each of the three areas that are

Plate 3. SEM photographs of key specimens of fossils of Anthocerotaceae from the High Island drill hole HI-178, sample 32C,

offshore Texas, US (see location 1 on Figure 4). Figures 1–9 show various surface sculpture found in the fossil specimens of

Anthoceros multifidus type with the spine-like processes and large lacunae. Figures 1–8. Proximal views with the trilete mark

clearly marked by a smoother ridge. Figure 9. Distal side of the spore. The scale bar represents 10 microns.

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divided by the trilete mark. The trilete mark is

expressed by the laesurae that is found broadly opened

in several specimens.

5. Update on the phylogeny and taxonomy of the living

Anthocerotophyta

Before looking into the environmental significance of

the two genera recovered, it is important to understand

their position in the plant kingdom. It is well accepted

that the bryophytes comprise three phyla (hornworts,

liverworts and mosses) that are of particular interest to

geologists and biologists as these are most likely the

first extant lineages in the land-plant tree of life (Shaw

and Renzaglia 2004). It is intriguing to think that the

hornworts were among the first plants to colonize land

in geological history (Villarreal et al. 2010b), with

ancestral traits such as algal-like chloroplast (Vaughn

Plate 4. SEM photographs of key specimens of modern species of Anthocerotaceae from Turkey (see location 2 on Figure 4).

The scale bar represents 10 microns. Figures 1–9 are of specimens of Phaeoceros laevis.

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et al. 1990) and association with nitrogen-fixing

cyanobacteria (Villarreal and Renzaglia 2006). If the

phylum is well established, it is however apparent when

reading the literature that there is a lack of consensus

on hornwort phylogeny. The plant division Anthocerotophyta (Stotler and Crandall-Stotler 1977) indeed

contains only the group of vascular plants referred to

as the hornworts, and they are separated from the

division Bryophyta that is restricted sensu stricto to

mosses and from the Marchantiophyta that is restricted to the liverworts.

Originally, the family Anthocerotaceae as described by Proskauer (1951) only included four genera:

Anthoceros, Phaeoceros, Dendroceros, and Megaceros.

Much work has been done on the hornworts since

Proskauer (1951), separating out various generic

Plate 5. SEM photographs of key specimens of modern species of Anthocerotaceae from Chile (see location 3 on Figure 4). The

scale bar represents 10 microns. Figures 1–9 are of specimens of Phaeoceros skottsbergii, emended Phaeomegaceros skottsbergii

(Duff et al. 2007).

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groups into several families and subfamilies (Hyvo ̈nen

and Piippo 1993; Stotler and Crandall-Stotler 2005;

Duff et al. 2007). A new generally accepted classification includes two classes of hornworts (Figure 5a): the

Anthocerotopsida and a new class, the Leiosporocertotopsida (only including Leiosporoceros). The classification of Anthocerotopsida (all other hornworts)

based on Stotler and Crandall-Stotler (2005) recognizes three genera (Anthoceros, Folioceros, and

Sphaerosporoceros) in the order of Anthocerotales

and seven genera (Dendroceros, Hattorloceros, Megaceros, Mesoceros, Nothoceros, Notothylas, and Phaeoceros) in the order of Notothyladales (Figure 5a).

Stotler and Crandall-Stotler’s classification was recently modified by Duff et al. (2007) who proposed a

more complex classification based on molecular

phylogenetic analyses (Figure 5b). Renzaglia et al.

(2007, 2008), however, caution that more work is

Plate 6. SEM photographs of key specimens of modern species of Anthocerotaceae from Russia (see location 4 on Figure 4).

The scale bar represents 10 microns. Figures 1–9 are of specimens of Anthoceros punctatus.

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needed using sequencing and multigene analyses before

a full comprehensive phylogeny of hornworts can be

fully defined and accepted.

The two genera of interest in our study (Anthoceros

and Phaeoceros) have a similar phylogenic position in

both the Duff et al. (2007) and Stotler and CrandallStotler (2005) classifications (Figure 4). This said, one

of the modern herbarium species discussed here –

Phaeoceros skottsbergii collected in Chile (CANM

#4305, Plate 5) – shows some distinct difference in its

spore morphology. These differences are very uncharacteristic of spores of the Phaeoceros genus: it has a

pronounced central depression or fovea, surrounded

by a circular ridge. This is a very similar structure to

that of spores of a new species defined in 2010 by

Villarreal et al. (2010a), Phaeomegaceros squamuliger.

In their new classification, Duff et al. (2007) proposed

a new genus, Phaeomegaceros, that better fit four

Plate 7. SEM photographs of key specimens of modern species of Anthocerotaceae from Sueca, Spain (see location 5 on Figure

4). The scale bar represents 10 microns. Figures 1–9 are of specimens of Anthoceros multifidus.

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species previously included in the Phaeoceros genus;

they include Phaeoceros skottsbergii as one of them.

The spores of the new Phaeomegaceros genus seem to

have in common a central circular depression surrounded by ridges on the distal surface. Hence, we

follow the new classification of Duff et al. (2007) and

accept that this species is now amended to Phaeomegaceros skottsbergii. New sequencing data presented

by Villarreal et al. (2010a) also support this

classification.

6. Spore, sporophytes and gametophyte of

Anthocerotophyta

Palynologically, it is interesting to note that hornworts

are named for their horn-shaped slender, upright

sporophyte or spore capsule (Figure 6). One unique

feature of hornworts is that the sporophyte, responsible for releasing spores, grows taller with age and is

not dissociated from the gametophyte (Figure 7).

Despite the importance of the sporophyte, hornwort

spores are not often dealt with in palynological studies

Plate 8. SEM photographs of key specimens of modern species of Anthocerotaceae from Japan (see location 6 on Figure 4).

The scale bar represents 10 microns. Figures 1–9 are of specimens of Anthoceros nagasakiensis.

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as they are usually not an abundant component of

Cenozoic palynological assemblages. When found, they

are often grouped with spores of land plants from other

lineages of bryophytes, a fact that is not surprising as

hornworts are the least species-rich lineage of bryophytes with only up to 250 species worldwide as

opposed to *1200 spp. for mosses and 8000 spp. for

liverworts (Villarreal et al. 2010b). Hornworts mainly

differ from liverworts in three main ways: (1) they have

only a few chloroplasts but these can store carbon

dioxide (unlike liverwort choloroplasts); (2) hornworts

do not have oil bodies in their cells; and (3) hornworts

can produce spores for weeks as opposed to a few hours

for the liverworts (Wassilieff 2009). Shaw and Renzaglia (2004) confirmed that latest point by stating that

hornworts are the only plant group that have a constant

production of spores, ensuring dispersal throughout the

growing season.

Plate 9. SEM photographs of key specimens of modern species of Anthocerotaceae from Canada (see location 7 on Figure 4).

The scale bar represents 10 microns. Figures 1–9 are of specimens of Anthoceros ravenellii.

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The presence of well-preserved, abundant and

diverse hornwort spores at HI-178 indicates that the

High Island site (or its proximity) was covered by these

unusual-looking few-centimeter-tall narrow sporophytes embedded on the top of a gelatinous-looking,

ground-cover of gametophyte plants (Figure 6). So,

what does this imply for the type of environmental

conditions that prevailed at the time of deposition?

7. Environmental significance of Anthocerotopsida

Because hornworts require a very specific environment

in which to grow and reproduce, the spore abundance

at the High Island site is interesting. The main goal of

this project was to identify whether this site was, at

least in part, above sea level during the Paleoindian

period, and hence could have been occupied and/or

utilized by humans as early as 9,460 years BP. Here we

Figure 4. Geographic distribution of modern species collected at the Canadian Museum of Nature (CMN), Ottawa, Canada.

Species collected includes two Phaeoceros and four Anthoceros species; a Phaeoceros laevis from Turkey (CANM #4292, Plate 4),

a Phaeoceros skottsbergii from Chile (CANM #4305, Plate 5), an Anthoceros punctatus from Ukraine, USSR (CANM #4295,

Plate 6), an Anthoceros multifidus from Sueca, Spain (CANM #4301, Plate 7), an Anthoceros nagasakiensis from Japan (CANM

#4302, Plate 8), and an Anthoceros ravenellii from British Columbia, Canada (CANM #4306, Plate 9).

Figure 5. Summary of latest hornwort phylogeny as proposed by (left) Stotler and Crandall-Stotler 2005 and (right) Duff et al.

(2007). Gray-shaded box highlights the position of the two genera recovered at our site.

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review the environmental data available on modern

hornworts from the literature to summarize the type of

environmental conditions needed for these primitive

plants to grow.

7.1. Habitat preference

In general, hornworts are found mainly in damp places

such as clay banks, along stream sides, ponds or

swamps or settled on rocks, soil or even tree barks.

Anthoceros species are often found on damp banks

while other genera such as Dendroceros favor swampy

ground (Wassilieff 2009). These plants, although small,

can be found covering large areas of soil or trees. Breil

(1970) conducted a detailed examination of hornworts

and liverworts present at the same latitude as our study

area, but about 170 miles east on the Alabama–Florida

Gulf of Mexico coast. One of the most common

hornworts found at these sites were species of

Anthoceros and Phaeoceros, similar to what we found

in High Island. In this study, Breil (1970) found that

these two genera were strictly found in association with

moist rotten stumps or logs, on moist soil, in moist

quartzitic sand (but rarely on limestone), in ditches,

along streams and riverbanks and commonly on wet

floodplains and in freshwater swamps. While conducting a palynological analysis of non-pollen palynomorphs of Australia, Cook et al. (2011) noted that

Anthoceros spores are generally found in moist shady

environments during warm and wet time intervals

conducive to swamp development.

7.2. Desiccation tolerance

In a review of desiccation-tolerance of hornworts,

liverworts and mosses, Wood (2007) found that out of

all bryophytes, the hornworts had a very low tolerance

for reviving from the air-dried state, with only one

species of hornworts (Dendroceros granulosus) showing

vegetative desiccation tolerance. Wood (2007) further

noted that more experimental analyses are needed on

other species of this group but that, so far, no other

hornwort species have been documented as being

desiccation tolerant. This inability to survive dessication was confirmed by Schuette and Renzaglia (2010)

who also stated that Dendroceros is the only desiccation-tolerant hornwort genus. This current state of

knowledge indicates that finding so many spores of

hornworts in the samples implies that the depositional

environment was constantly moist, allowing these land

plants to thrive and reproduce at the studied site. The

importance of moisture for hornwort development is

confirmed by Bisang et al. (2009) who found that

hornwort occurrence at sites in Europe increases

during time of high humidity level in the air. Bisang

et al. (2009) added that high hornwort abundance is

found during exceptionally wet growing seasons and

concluded that humidity has a strong influence on

hornwort population performance.

7.3. Submergence tolerance

If hornworts dry up and disintegrate very quickly when

not kept moist, they will quickly rot if totally

immersed. Working with closely allied species, Bates

(2009) noted that bryophytes will not survive when

permanently submerged. So, although hornworts

require constant moist conditions, species of true

hornworts (Anthocerotophyta) are likely to die in

submerged conditions. Note that the true hornwort

(Anthocerotophyta) discussed here are not related to

the common aquatic ‘hornwort’ species Ceratophyllum

demersum that is used in aquaria worldwide. This

aquatic plant is actually a cosmopolitan flowering

plant species belonging to the angiosperm family

Ceratophyllaceae and is unfortunately commonly

referred to as an aquatic hornwort, despite the lack

of biological affinity with the Anthocerotophyta.

7.4. Saltwater tolerance

As our studied location is located today in the Gulf of

Mexico, salinity must be considered as a controlling

factor. Although some bryophyte species are found in

marshes where the salinity is low but not zero, the need

to identify the tolerance of hornworts for saline water

is very important at our coastal site. Based on our

review of the literature, it seems clear that hornworts

are essentially found in association with freshwater

habitats. Bates (2009) noted that very few bryophytes

are halophytes and that they would not survive

saltwater spray from the action of waves and tides.

Tiedtje and Teer (1996) discussed hornwort abundance

Figure 6. Photographs of a modern Phaeoceros plant,

growing today in (a) Florida (David Jarzen) and (b)

California (James Crame).

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in freshwater wetlands while studying the feeding

pattern of northern shovelers during overwintering in

Texas. During year 4 of their study, Tiedtje and Teer

(1996) found that the shovelers food source in freshwater wetlands included 37% of hornwort during

middle winter (17 December–22 February) and 26%

during late winter (23 February–6 May), indicating that

these are an important component of these types of

habitat. The fact that hornworts are essentially freshwater species and that they do not tolerate exposure to

saltwater conditions is also of great interest to our

paleoenvironmental reconstruction. Matheson et al.

(2007) reported that a species of hornwort (Ceratophyllum demersum) displays some degree of saltwater

tolerance while judging the efficacy of saltwater

solutions to kill freshwater species. As we discussed

above however, this species should not be included into

the true hornwort Antocerotophyta group. The only

true exception we found regarding the Antocerotophyta is noted by J.C. Villarreal (pers. comm., 2011) who

collected one species of true hornwort (Notothylas

dissecta) near the sea where the specimens were

splashed by the ocean waves, indicating that this

species had some degree of salinity tolerance.

Figure 7. The life cycle (alternation of generations) of the hornworts. The (a) gametophyte generation with its thallus-like body

and rhizoids on the under-surface bears the (b) male antheridium producing the (c) sperm which fertilize the egg within the (d)

female archegonium, giving rise to the (e) sporophyte generation. The mature sporophyte generation – (f) enlarged cut-away

view – develops the sporogeneous cells which upon maturity release the trilete spores and (g) pseudo-elaters, which grow into the

(h) protonema, eventually developing into the (i) young gametophyte generation, completing the life-cycle. (Redrawn and

modified from: http://www.enotes.com/topic/Hornwort.)

Palynology 15

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7.5. Temperature tolerance

When considering the known distribution of hornwort worldwide, data show that the genera Anthoceros and Phaeoceros include some of the most

common and diverse species of hornworts found

throughout the world (Figure 8). The proportions of

species from these two genera in comparison to all

hornworts species average between 47% on the

Indian subcontinent (where diversity in hornworts

is high) to up to 100% for Southern Africa and

Russia (Renzaglia et al. 2007). The modern spores of

species of Anthoceros and Phaeoceros presented in

Plates 4–9 were extracted from specimens collected

in six locations (Chile, Japan, Turkey, Canada,

Spain, and Russia). Clearly, some of these species

were collected in cold to temperate settings such as

Russia or Canada. The literature however shows that

hornwort sporophytes are not able to survive during

winters in these cold regions (Bisang 1995), although

he noted that only few precise population ecological

studies of hornworts have been conducted to date.

Specifically, the species collected in Russia (Anthoceros punctatus) is known to tolerate colder temperatures. Bisang et al. (2009) noted that this species is

found in Switzerland, confined to a region south of

the Alps.

Despite their broad distribution, studies so far

indicate that both Anthoceros and Phaeoceros clearly

favor warmer temperatures and that they are known to

be particularly abundant in tropical regions (Villarreal

et al. 2010b).

7.6. Response to fire

As noted earlier, several charcoal layers were found at

and around depths where hornwort spores are

abundant. This provides potential evidence that the

area was in proximity to sites of wild or potentially

controlled fires. As a twist, the charcoal evidence could

explain the unusual dominance of hornworts. Bates

(2009) noted that bryophytes, although usually

readily destroyed in fires, are often a predominant

plant element in the early recolonization of burned

land.

8. Implications of environmental evaluation for our

Paleoindian landscape

The presence of hornwort spores has important

implications for the type of environment that must

have existed at the High Island site about 9,000 years

BP. Based on the very specific requirements of

hornworts, as discussed earlier, we postulate that the

site was most likely a freshwater swamp or an area

with constant moist soil, possibly close to streams, and

that the site was above sea level during at least part of

the Paleoindian period. The climate of offshore Texas

at that time was indeed likely warm and humid. The

seismic survey data indicate that the site under

investigation was located on natural levees and river

terraces and that the flooding of the HI-178 location

was likely delayed (Figure 2). Furthermore, subsidence

must be considered. The current depth of the studied

site is 16 m below sea level. The radiocarbon dates

Figure 8. Relative distribution of Anthoceros and Phaeoceros species worldwide in comparison to all hornwort species. The data

represented here are based on proportion of hornwort species in the different genera across regions of the world as summarized in

Villarreal et al. (2010b).

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indicate that the area was deposited about 9,500 years

BP. Although this places the site just below or at sea

level at that time using most sea-level rise estimates,

this does not take into account subsidence in the

region. A subsidence rate of 0 would place the site at

0.5 m below sea level, but conservative estimates

indicate that the region subsided by at least 1 mm

per year (Milliken et al. 2008) which would translate to

a 8 m total subsidence since the deposition of the

radiocarbon-dated charcoal (see Table 1 for details).

This clearly supports our premise that the High Island

site was indeed above water and was occupied by

freshwater habitats.

Although no evidence of cultivated grains were

found in our palynological assemblage, we cannot rule

out that Paleoindian populations were present on this

portion of the now-submerged continental shelf or that

they manipulated their environment. A few recent

studies have shown that agricultural practices such as

land disturbance through tillage impact the distribution

of hornworts (Bisang 1998; Bisang et al. 2009). Bisang

(1998) and Bisang et al. (2009) specifically show that

Anthoceros and Phaeoceros were found in abundance in

abandoned stubblefields, but that these two genera

were rare in stubblefields with maize, root-crops, and

fodder-crops. Unfortunately, whether the abundance

of hornworts at our site is a result of landscape

manipulation by Paleoindians is a matter we cannot

evaluate.

9. Conclusions

Two species of hornworts, Phaeoceros laevis (L.)

Prosk. and Anthoceros multifidus Lindb., dominate

the spore assemblage recovered from a potential

Paleoindian landscape sampled offshore High Island,

near Galveston, Texas. Because these plants do not

tolerate being submerged or being in contact with salt

water, the presence of these two species of Anthocerotophyta growing in close proximity to the study area

along with other evidence (e.g. charcoal) strongly

suggests that this site was indeed not submerged at

the time of deposition and that human occupation was

therefore possible at or very near the site. In addition,

since hornworts are commonly one of the first plants

colonizing burnt sites (Bates 2009), a link between

burning (either naturally occurring or human-induced)

and high numbers of hornworts is established. The

types of spore species present represent plants which are

most commonly found today in countries with tropical

climates where these hornworts thrive under moist but

never submerged conditions. The warm, moist high

land on the shelf of the northern Gulf of Mexico was

therefore potentially hospitable to human occupation

between 9,550 and 9,460 calibrated years BP.

Table 1. A range of estimates of subsidence and changes to the core-site elevation corrected with respect to modern sea level

and the lower sea-level elevation existing at 9.5 ka BP. The first column provides the time elapsed since erosion of the Last Glacial

Maximum (LGM) surface and the radiocarbon age of in situ material at the core site (see Figure 1 for LGM contour line). The

last column is the inferred range of core-site elevations corrected for 8.5 ka of subsidence measured with respect to the lower sea

level elevation (–15.5 mbsl) that existed at 9.5 ka BP.

Elapsed time

between 18.0

and 9.5 ka BP (ka)

Average

subsidence

rate (mm a–1)

Total magnitude

of subsidence

between 18

and 9.5 ka (m)

Current-day

elevation at

core site (mbsl)

Core site elevation

corrected for 8.5ka

subsidence (mbsl)

Core-site elevation

relative to sea-level

at 9.5 ka BP (m)

8.5 1.0 8.5 16 7.5 8.0

8.5 0.8 7.6 16 9.2 6.3

8.5 0.6 5.7 16 10.9 4.6

8.5 0.4 3.8 16 12.6 2.9

8.5 0.2 1.9 16 14.3 1.2

8.5 0.1 0.95 16 15.15 0.35

8.5 0 0 16 16 70.5 (mbsl)

Acknowledgements

The authors would like to thank the Bureau of Ocean Energy

Management, Regulation, and Enforcement (BOEMRE)

(formerly Minerals Management Service) for funding this

project (Cooperative Agreement/Award No. MO7AC13373

to P. Hesp). We are indebted to Dr Robert Ireland (currently

with the Smithsonian Institution, Washington, DC) for

guiding DMJ through the collection of modern Anthocerotophyta from vouchered herbarium material at CANM

(Ottawa, Canada). Appreciation is expressed to the Collection staff at the Canadian Museum of Nature (Ottawa) and

especially to Richard Day and Margaret Currie for the loan

of Anthocerotophyta prepared spore slides and residues.

Further, we extend our thanks to Dr Dana Griffin III and

Kurt M. Neubig (Florida Museum of Natural History,

Gainesville, Florida) for their assistance in obtaining photographs of living Anthoceros. Brooks Ellwood, Graziela Miot

da Silva and Barun Sen Gupta (Department of Geology and

Geophysics at LSU) were instrumental in assisting and

advising this study. Susan Jarzen assisted in manuscript and

Palynology 17

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329
slide preparation. 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. Mention of trade names or commercial

products does not constitute their Endorsement by the US

Government.

Author biographies

SOPHIE WARNY is an Assistant Professor

of Palynology in the department of Geology

and Geophysics & at the Museum of Natural

Science at Louisiana State University in

Baton Rouge. She has a long history with

AASP as she won the AASP Student Award

in 1996. She received her Ph.D. from the

Universite ́ Catholique de Louvain, in Belgium working with

Dr Jean-Pierre Suc. Her doctoral dissertation focused on the

Messinian Salinity Crisis. Since graduating, she has been

working on Antarctic sediments that were acquired via the

ANDRILL SMS and the SHALDRIL programs. In 2011,

she received the prestigeous NSF CAREER award to

support her palynological research in Antarctica. Now that

she lives in Louisiana, her research focus has expended to the

Gulf of Mexico region. In addition to her research, she

teaches Historical Geology, Paleobotany, and Micropaleontology. She also manages the education and outreach

programs for the Museum. She currently has a research

group that is composed of four master students and three

Ph.D. students. Since being hired on tenure-track at LSU,

she graduated three students. One is a biostratigrapher at BP,

the other two were recently hired by DEVON and EOG,

respectively. She recently remodeled the CENEX facility, in

Baton Rouge, Louisiana.

DAVID M. JARZEN is a Research

Associate at the Cleveland Museum of

Natural History, in Paleobotany and Palynology. He earned his B.S. degree in 1967

from Kent State University majoring in

Biological Sciences, and two years later

received his M.A. degree in Botany from

the same institution. In 1973 he was awarded the Ph.D. in

Geology from the University of Toronto. His research

interests in the nature of extant and fossil plant life, have

provided extensive field work in all regions of Canada and

the United States, as well as Europe, Africa, Central and

South America, the South Pacific, and to several localities

within Australia. The focus of his work incorporates a global

view aiming to understand the evolution of plant life during

Earth’s history, with an emphasis on fossil floras recorded

from the Paleogene, Neogene and Cretaceous of the world.

Some of his work has been seen in Scientific American, The

Owl Magazine, other popular publications, on the Internet,

and in museum displays in Canada, Australia and the USA.

His work has been incorporated in several radio and

television productions including CBC’s ‘‘Nature of Things’’

with David Suzuki, the PBS NOVA Series, the NHK (Japan)

Series ‘‘The Miracle Planet’’, the National Film Board of

Canada, the Discovery Channel and other North American

cable networks. In 1987 he was an invited Visiting Scholar to

the Department of Geology & Mineralogy of The University

of Queensland, Brisbane, Australia, and in 1991 and 1994 to

the Botany Department of the same university. In 2005 he

was invited to Australia once again, this time to work with

colleagues at the Queensland Museum in Brisbane,

Queensland. In 2003, he was elected as Fellow National to

the Explores Club, and in 2005 he was elected Fellow of the

Ohio Academy of Science. David is listed in American Men

and Women of Science, Who’s Who in Ontario (Canada),

Who’s Who in Canadian Science, Who’s Who in Science and

Engineering, as well as Who’s Who in America and Who’s

Who in the World.

AMANDA M. EVANS is a Ph.D. candidate

in the Department of Geography and

Anthropology at Louisiana State University

in Baton Rouge. She received her Bachelors

degree in Anthropology from Indiana University in 1998, and her Master’s degree in

Anthropology from Florida State University

in 2005. Her doctoral dissertation addresses buried landforms in the Gulf of Mexico and their potential for

prehistoric occupation and exploitation using geophysical

and geotechnical data and physical sampling. Since 2005 she

has served as Senior Marine Archaeologist for Tesla

Offshore, LLC, a full service geophysical survey company.

She is an elected officer for the Advisory Council on

Underwater Archaeology, an appointed director to the

Register of Professional Archaeologists, and Principal

Investigator for a BOEMRE-funded shipwreck study.

PATRICK HESP, who completed BA and

MA degrees in Geography at Massey (1971–

1975). He received his Ph.D. at the University of Sydney in 1981. He is the R.J.

Russell Professor in Geography and Anthropology in the College of Humanities and

Social Sciences at Louisiana State University

where he has been for the past 8 years. He was awarded a

prestigious Fulbright Fellowship for 2011. The award will

provide funding for Dr Hesp to spend three months in

southern Brazil conducting a detailed drilling and dating

program on two coastal barriers, one at Pinheira (in Santa

Catarina state), and the other at Paranagua (in Parana

State). These barriers are characterized by alternating suites

of foredune ridges and parabolic dunes, and provide evidence

of alternating sediment supply and coastal storms, and

climate histories over the past 7000 years. Dr Hesp is an

expert in coastal beach and dune systems, dynamics and

geomorphology, and has spent the past 30 years conducting

research in southern Brazil, as well as in Canada, USA,

Mexico and China. For more information about Dr Hesp

http://www.coastalsystems.co.nz/who_we_are_hesp.html.

PHILIP BART is an Associate Professor in

the department of Geology and Geophysics

at Louisiana State University in Baton

Rouge. He earned his Ph.D. degree from

Rice University in Houston, working with

Dr John Anderson. He received the Presidential Early Career Award for Scientists

and Engineers (PECASE) in 2001 for his sequence stratigraphic research in Antarctica. One of his other research

interests consists in evaluating the sea-level elevation at the

peak of the LGM based on the acquisition of seismic data in

the northeastern Gulf of Mexico. Thus far, the research

conducted by his group strongly suggests that the LGM sealevel elevations were at *70 meters below present. This work

is important as the scientific community attempts to explain

why Earth climates change abruptly (i.e. a few thousand

years) from full glacial conditions to full interglacial

conditions. If their results are correct, the mechanisms

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invoked to cause this abrupt climatic change need not be as

dramatic as has traditionally been assumed.

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POLLEN AND ORGANIC RESIDUE (FTIR) ANALYSIS OF SAMPLES FROM

 SITES GA426 AND HI178, TEXAS GULF COAST

By

Linda Scott Cummings

and

Melissa K. Logan

With Assistance from

R.A. Varney

and

Mikaela Murphy

PaleoResearch Institute

Golden, Colorado

PaleoResearch Institute Technical Report 10-119

Prepared For

Louisiana State University

Baton Rouge, Louisiana

January 2011

333
INTRODUCTION

Three core samples recovered from two underwater sites (GA426 and HI178) on the

outer continental shelf off the Texas coast in the Gulf of Mexico were submitted for pollen and

organic residue analysis. Two of the samples were examined for organic residues using

Fourier Transform Infrared Spectroscopy (FTIR), and two were examined for pollen. Pollen and

organic residue analysis will be used to determine if the core samples represent sites on land or

deposition of floral remains blown to sea.

METHODS

Pollen

A chemical extraction technique based on flotation is the standard preparation technique

used in this laboratory for the removal of the pollen from the large volume of sand, silt, and clay

with which they were mixed. This particular process was developed for extraction of pollen from

soils where preservation has been less than ideal and pollen density is lower than in peat. It is

important to recognize that it is not the repetition of specific and individual steps in the

laboratory, but rather mastery of the concepts of extraction and how the desired result is best

achieved, given different sediment matrices, that results in successful recovery of pollen for

analysis.

Hydrochloric acid (10%) was used to remove calcium carbonates present in the soil,

after which the samples were screened through 250 micron mesh. The samples were rinsed

until neutral by adding water, letting the samples stand for 2 hours, then pouring off the

supernatant. A small quantity of sodium hexametaphosphate was added to each sample once

it reached neutrality, then the samples were allowed to settle according to Stoke’s Law in

settling columns. This process was repeated with ethylenediaminetetraacetic acid (EDTA). 

These steps remove clay prior to heavy liquid separation. The samples then were freeze dried. 

Sodium polytungstate (SPT), with a density 1.8, was used for the flotation process. The

samples were mixed with SPT and centrifuged at 1500 rpm for 10 minutes to separate organic

from inorganic remains. The supernatant containing pollen and organic remains was decanted. 

Sodium polytungstate again was added to the inorganic fraction to repeat the separation

process. The supernatant was decanted into the same tube as the supernatant from the first

separation. This supernatant was then centrifuged at 1500 rpm for 10 minutes to allow any

silica remaining to be separated from the organics. Following this, the supernatant was

decanted into a 50 ml conical tube and diluted with distilled water. These samples were

centrifuged at 3000 rpm to concentrate the organic fraction in the bottom of the tube. After

rinsing the pollen-rich organic fraction obtained by this separation, all samples receive a short

(20-30 minute) treatment in hot hydrofluoric acid to remove any remaining inorganic particles. 

The samples then were acetolated for 3-5 minutes to remove any extraneous organic matter.

A light microscope was used to count pollen at a magnification of 500x. Pollen

preservation in these samples varied from good to poor. Comparative reference material

collected at the Intermountain Herbarium at Utah State University and the University of

Colorado Herbarium was used to identify the pollen to the family, genus, and species level,

where possible.

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Pollen aggregates were recorded during identification of the pollen. Aggregates are

clumps of a single type of pollen and may be interpreted to represent pollen dispersal over short

distances or the introduction of portions of the plant represented into an archaeological setting. 

Aggregates were included in the pollen counts as single grains, as is customary. The presence

of aggregates is noted by an "A" next to the pollen frequency on the pollen diagram. Pollen

diagrams are produced using Tilia 2.0 and TGView 2.0.2. Total pollen concentrations are

calculated in Tilia using the quantity of sample processed in cubic centimeters (cc), the quantity

of exotics (spores) added to the sample, the quantity of exotics counted, and the total pollen

counted and expressed as pollen per cc of sediment.

Indeterminate pollen includes pollen grains that are folded, mutilated, and otherwise

distorted beyond recognition. These grains are included in the total pollen count since they are

part of the pollen record. The microscopic charcoal frequency registers the relationship

between pollen and charcoal. The total number of microscopic charcoal fragments was divided

by the pollen sum, resulting in a charcoal frequency that reflects the quantity of microscopic

charcoal fragments observed, normalized per 100 pollen grains.

Pollen analysis also includes examination for and identification of algal bodies and

foraminifera tests, when present.

FTIR (Fourier Transform Infrared Spectroscopy)

A mixture of chloroform and methanol (CHM) was used as a solvent to remove lipids

and other organic substances that had soaked into the sediment. This mixture is represented

in the FTIR graphics as CHM. The CHM solvent and sample were placed in a glass container,

and allowed to sit, covered, for several hours. After this period of time, the solvent was pipetted

into an aluminum evaporation dish, where the CHM was allowed to evaporate. This process

leaves the residue of any absorbed chemicals in the aluminum dishes. The residue remaining

in the aluminum dishes was then placed on the FTIR crystal and the spectra were collected. 

The aluminum dishes were tilted during the process of evaporation to separate the lighter from

the heavier fraction of the residue. The lighter and heavier fractions are designated upper

(lighter fraction) and lower (heavier fraction) respectively in the subsequent analysis.

FTIR is performed using a Nicolet 6700 optical bench with an ATR and a diamond

crystal. The sample is placed in the path of a specially encoded infrared beam, which passes

through the sample and produces a signal called an “inferogram.” The inferogram contains

information about the frequencies of infrared that are absorbed and the strength of the

absorptions, which is determined by the sample’s chemical make-up. A computer reads the

inferogram and uses Fourier transformation to decode the intensity information for each

frequency (wave numbers) and presents a spectrum.

FTIR (FOURIER TRANSFORM INFRARED SPECTROSCOPY) REVIEW

Infrared spectroscopy (IR) is the study of how molecules absorb infrared radiation and

ultimately convert it to heat, revealing how the infrared energy is absorbed, as well as the

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structure of specific organic molecules. Infrared spectroscopy has been experiencing a

renaissance for identifying organic substances during the past few decades. It is currently

considered one of the more powerful tools in organic and analytical chemistry. One of the

primary advantages to the FTIR is that it measures all wave lengths simultaneously. It has a

relatively high signal-to-noise ratio and a short measurement time. Each peak in the spectrum

represents either a chemical bond or a functional group. 

Since molecular structures absorb the vibrational frequencies or wavelengths of infrared

radiation, the bands of absorbance can then be used to identify the composition of the materials

under study. In the case of the current research, the portion of the electromagnetic spectrum

between 4000-400 wave numbers is used for identifying organic materials. Carbohydrates,

lipids, proteins, and other organic molecules are associated with specific wave number bands

(Isaksson 1999:36-39).

The infrared spectrum can be divided into two regions--the functional group region and

the fingerprint region. These two groups are recognized by the effect that infrared radiation has

on the respective molecules of these groups. The functional group region is located between

4000 and approximately 1500 wave numbers. The molecular bonds display specific

characteristic vibrations that identify fats, lipids, waxes, lignins, proteins, carbohydrates, etc. 

The fingerprint region, located below 1500 wave numbers, is influenced by bending motions,

which further identify the molecules present. 

Using the FTIR, it is possible to identify different types of organic compounds and

eventually recognize different types of materials such as plant or animal fats or lipids, plant

waxes, esters, proteins, carbohydrates, and more. Specific regions of the spectrum are

important in identifying these compounds.

The results of the identification of specific wavelengths can be compared with

commercial or laboratory-created analytical standards to identify the specific types of bonds

present in different materials. By combining the results of the analysis of individual samples

with all of the reference materials in the PaleoResearch Institute (PRI) library, the percent

match with individual reference items can be displayed. For instance, plant lipids or fats are

identifiable between 3000-2800 wave numbers. A match might be obtained on this portion of

the spectrum with nuts such as hickory, walnut, or acorn, or with animal fats or corn oil. 

Recovery of high level matches with several types of nuts (in this example) indicates that nuts

were processed. If the match with the PRI library is with meats, then the fats matched are more

consistent with those produced by meat than plant parts, such as nuts.

Samples containing many compounds are more difficult to identify – and many

archaeological samples are complex mixtures. Multi-purpose artifacts, such as groundstone,

which could have been used to crush or grind a variety of foodstuffs, or ceramic cooking

vessels, which are expected to have been used to cook many different foods, might present a

mixture problem. Mixtures sometimes have many absorption bands that overlap, yielding only

broad envelopes of absorption and few distinctive features. FTIR analysis is expected to be

particularly valuable in examining fire-cracked rock (FCR), for which few other means of

analysis exist, since the fats, lipids, waxes, and other organic molecules contained in liquids

that seep out of the food being processed become deposited on the rocks during the baking

process. Once again, these rocks might have been present in more than one cooking episode,

thus having the potential to yield a complex signature. The PRI extraction method gently

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removes these organic molecules from the groundstone, ceramics, and/or rocks so that they

can be measured with the FTIR and subsequently identified.

Organic molecules from sediments can be extracted and the sediments then

characterized. This has the potential to be very useful in identifying signatures of the remains

responsible for a dark horizon. For instance, if the dark horizons are the result of decaying

organic matter (plant or animal), the FTIR will yield a signature of decaying organic remains. If

the dark horizons are the result of blowing ash from cultural features, the FTIR signature will be

considerably different. This is an affordable technique for making distinctions between horizons

and identifying cultural horizons.

Carbohydrates

Carbohydrates are a product of photosynthesis in green plants. This group of

compounds is the most abundant found on earth. Carbohydrates is a term that encompasses

three main groups of compounds: 1) sugars, 2) starches, and 3) fibers. To elaborate, sugars

include the simple carbohydrates found in table sugar, honey, natural fruit sugars, and

molasses. Starches and complex carbohydrates are present in legumes, grains, vegetables,

and fruits. Fibers, including cellulose, hemicellulose, and pectin, are present in whole grains,

legumes, vegetables, and fruits (Garrison and Somer 1985:13). Dietary carbohydrates provide

energy for bodily functions, including our ability to digest and absorb other foods. They are the

body’s preferred source of energy, although proteins and lipids also may be converted to

energy. Carbohydrates are so important that an inadequate intake may result in nutritional

deficiencies such as ketosis, energy loss, depression, and even loss of essential body protein. 

On the other hand, excess intake of carbohydrates causes obesity and dental decay.

To understand carbohydrates and their detection with the FTIR, it is important to know

that they are formed of carbon atoms coupled to “hyrates,” such as water, resulting in empirical

formulas of CnH2nOn where “n” represents the number of atoms for C, H, and O, respectively. 

“Biochemically, carbohydrates are polyhydroxy alcohols with aldehyde or ketone groups that are

potentially active” (Garrison and Somer 1985:13). Since carbohydrates are classified according

to their structure and the FTIR detects the bonds between molecules, we will review the simple

sugars (monosaccharides), multiple sugars (oligosaccharides), and complex molecules

(polysaccharides) that are made up of simple sugars.

Polysaccharides

These complex starchy compounds follow the empirical formula: C6H10O5. They are not

sweet, do not crystallize, and are not water soluble. Simply defined, polysaccharides are

complex carbohydrates found in plants as starch and cellulose, and in animals as glycogen. 

Because the FTIR detects the bonds between atoms in molecules, it is important to know that

polysaccharides are formed of repeating units of mono- or disaccharides that are joined

together by glycosidic bonds. Polysaccharides are often heterogeneous. The slight

modifications of the repeating unit results in slightly different wave number signatures on the

FTIR. Types of polysaccharides are descriptive and include storage (starches and glycogen),

structural (cellulose and chitin), acidic (containing carboxyl groups, phosphate groups, and/or

sulfuric ester groups), neutral (presumably without the acid features), bacterial

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(macromolecules that include peptidoglycan, lipipolysaccharides, capsules and

exopolysaccharides), and more. The study of polysaccharides is an ever growing field and

industry, since polysaccharides are important to proper immune function, bowel health, and a

host of other factors that are important in human health. At present there is no comprehensive

study of which plants and animal parts contain which polysaccharides. Research into this field

is currently growing at a rapid pace. Some highlights for the purpose of our discussions are

presented below.

Storage Polysaccharides

Storage polysaccharides are digestible polysaccharides. Starch and glycogen are the

two primary groups of these polysaccharides (Wardlaw and Insel 1996:80-81).

Starch

Starch is the primary digestible polysaccharide in the human diet, and the most

important carbohydrate food source (Murray, et al. 2000:155; Wardlaw and Insel 1996:80).

Starch is composed of long chains of glucose units. “Cooking increases the digestibility

of...starches...making them more soluble in water and thus more available for attack by

digestive enzymes” (Wardlaw and Insel 1996:80). Amorphous starch granules encased in cell

walls burst free when cooked because the granules absorb water and expand. The two primary

constituents of starch are amylose and amylopectin, both of which are a source of energy for

plants and animals (Murray, et al. 2000:155; Wardlaw and Insel 1996:80). When the glucose

chains are long and straight, the starch is labeled amylose. If the chains are short and

branched, they are amylopectin. Shorter chains of glucose (dextrin) are the intermediate

product of the hydrolysis of starch. Glucan, which is often found in association with pectin,

resides in the cell walls of plants and trees and many forms of bacteria and fungi (Stephen

2006). Most people are familiar with beta glucans, which are a diverse group of molecules that

occur commonly in the cellulose of plants, bran of cereals, cell walls of baker’s yeast, and

certain fungi, mushrooms, and bacteria. Some beta glucans may be useful as texturing agents

and soluble fiber supplements. Beta glucans derived from yeast and medicinal mushrooms

have been used for their ability to modulate the immune system. 

Structural Polysaccharides

Structural polysaccharides, which are also known as dietary fiber, are indigestible by

humans and other animals. Structural polysaccharides are primarily composed of cellulose,

hemicellulose, pectin, gum, and mucilage (Wardlaw and Insel 1996:82). “The only

noncarbohydrate components of dietary fiber are lignins, which are complex alcohol derivatives”

(Wardlaw and Insel 1996:82). Lignins are complex alcohol derivatives that make up the noncarbohydrate components of insoluble plant fibers (Wardlaw and Insel 1996:82). As such, they

cannot be digested by the enzymes animals produce (Carlile 1994). Lignin is found in all plants

and is an important component of the secondary cell walls (Lebo, et al. 2001; Martone 2009;

Wardlaw and Insel 1996:82). One of the important functions of lignin is to provide support

through strengthening of the xylem cells of wood in trees (Arms 1995; Esau 1977; Wardrop

1969). In linking plant polysaccharides, lignin provides strength to the cell walls and by

extension to the entire plant (Chabannes, et al. 2001). Because cellulose and chitin provide

structural support to plants and animals they are not water soluble. Cellulose, hemicellulose,

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and pectin are all comprised of simple sugars, and their differences are defined by the various

inclusions, exclusions, and combinations of these sugars, as well as how the sugars are

bonded, and the molecular structure of the sugars of these polysaccharides. 

Cellulose

Cellulose is comprised of a long linear chain of glucose, whereas hemicellulose consists

of shorter branched chains of simple sugars in addition to glucose, including especially xylose,

but also mannose, galactose, rhamnose, and arabinose (Crawford 1981; Updegraff 1969). 

Pectin, however, may be found in either a linear or branched form of simple sugars that is

primarily composed of rhamnose. 

Hemicellulose

Hemicellulose resides in the cell wall structures of many plants, particularly grain and

vegetable plants, and is a component of both insoluble and soluble fibers (Wardlaw and Insel

1996:82). Some specific hemicelluloses include galactan, galactoglucomannan, glucomannan,

glucuronoxylan (GX), and xyloglucan (Walker 2006; Wilkie 1985).

Galactoglucomannan. Galactoglucomannan is a primary component of the woody tissue of

coniferous plants (Gymnosperms) (Bochicchio and Reicher 2003).

Pectin, Gums, and Mucilages

Pectin, gums, and mucilages are soluble fibers found inside and around plant cells that help

“glue” them together (Wardlaw and Insel 1996:82). Pectin is a structural heteropolysaccharide

and common substance found in many plants (apples, plums, gooseberries, and citrus) often

used for its gelling or thickening action. Plant derived gums and mucilages such as gum arabic,

guar gum, and locus bean gum are also used for this same purpose. Arabinan,

arabinogalactan, arabinoglucuronoxylan, and rhamnogalacturonan are some examples of these

types of polysaccharides (Wilkie 1985).

Arabinan. In plants, arabinan is essential for the function of guard cells, which “play a key role

in the ability of plants to survive on dry land, because their movements regulate the exchange

of gases and water vapor between the external environment and the interior of the plant”

(Jones, et al. 2003:11783). 

Arabinogalactan. Arabinogalactan is a sugar found in plant carbohydrate structures,

particularly gums and hemicelluloses. One of arabinogalactan’s many functions is to bond with

proteins to repair damage when it occurs to a plant or its parts (Nothnagel 2000).

Esters

Esters are an important functional group because they are present as flavoring agents

in food and are components of biological compounds such as fats, oils, and lipids. In an ester,

the basic unit of the molecule is known as a carbonyl. The presence of the double peak

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between 3000 and 2800 wave numbers identifies the presence of the aldehyde functional

group, which is present in fats, oils, lipids, and waxes.

There are two important groups of esters, saturated esters and aromatic esters.

Aromatic esters take their name from their ability to produce distinctive odors and are present

as flavoring agents in food. In contrast, saturated esters do not produce distinctive odors. 

Esters are expressed in the FTIR spectrum by three distinct peaks (“the rule of three”) located

at approximately 1700, 1200, and 1100 wave numbers, and a fourth peak in the region between

750 and 700 wave numbers, which represents the CH2 bend associated with aromatic esters. 

The first peak for saturated esters falls in the 1750-1735 range, the second peak lies between

1210 and 1160, and the third peak sits between 1100 and 1030. Saturated esters have a

unique peak to acetates at 1240. This band can be very strong in the signature. The first peak

for aromatic esters falls in the range between 1730 and 1715, the second peak between 1310

and 1250, and the third peak between 1130 and 1100 (Smith 1999:110-112). Distinguishing

between saturated and aromatic esters, which are both components of foods, is easy if all three

bands are present, since they occupy different wave number regions.

Lipids

Lipids that are solid at room temperature are called “fats,” and those that are liquid at

room temperature are referred to as “oils” (Wardlaw and Insel 1996:108). Both forms of lipids

can be detrimental, as well as beneficial, to human health. Consumption of certain animal fats

rich in saturated fatty acids can lead to heart disease, while ingesting omega-3 fatty acids such

as EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) found in fish and other plant

sources are essential to good health.

Fatty Acids

Fatty acids are found in most lipids in the human and animal body, as well as in the

lipids in foods (Wardlaw and Insel 1996:108). Long chains of carbons bonded together which

are then bonded to hydrogens define the structure of fatty acids (Wardlaw and Insel 1996:109). 

A fatty acid is considered saturated if the carbons are connected by single bonds. Saturated

fatty acids are high in animal fats. If the carbon chain has one double bond between two of the

carbons, then the fatty acid is monounsaturated. If there are two or more double bonds

between carbons, then the fatty acid is polyunsaturated.

Essential Fatty Acids

Essential fatty acids, are those lipids critical to human health, such as omega-3 and

omega-6 fatty acids, alpha-lineolic acid, and linoleic acid, that cannot be created within the body

and must be obtained from dietary sources (Wardlaw and Insel 1996:110-111). These

essential fatty acids are part of “vital body structures, perform vital roles in immune system

function and vision, help form cell membranes, and produce hormone like compounds,” and are

necessary to maintain good health (Wardlaw and Insel 1996:111). Diets high in essential fatty

acids, like omega-3 and omega-6, reduce the risk of heart attacks because they minimize the

tendency for blood to clot (Wardlaw and Insel 1996:112). Fish oils contain high concentrations

of omega-3 and omega-6 fatty acids and may be administered as a dietary supplement. 

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Proteins

The human body uses protein from dietary plant and animal sources to form body

structures and other constituents (Wardlaw and Insel 1996:152). “Proteins contribute to key

body functions, including blood clotting, fluid balance, production of hormones and enzymes,

vision, and cell growth and repair” (Wardlaw and Insel 1996:152). This constant regulation and

maintenance of the body requires thousands of different types of proteins that are not all

available within the body (Wardlaw and Insel 1996:152). The majority of the building blocks for

these proteins, which are also known as amino acids, are produced by plants. 

Amino Acids

Within the body, amino acids are linked to form the necessary proteins, making them

not only essential for life, but key to nutrition. Amino acids can be combined in a multitude of

ways to create a vast variety of proteins. Differences between these proteins are distinguished

by the unique arrangements of amino acids. Proteins are created through a process called

translation, in which amino acids are added, one-by-one, to form short polymer chains called

peptides, or longer chains called polypeptides or proteins (Rodnina 2007). The order in which

the amino acids are added is determined by the genetic code of the mRNA template, which is a

copy of an organism’s genes (Creighton 1993). Amino acids are divided into standard and nonstandard types. 

Standard Amino Acids

There are twenty (20) naturally occurring amino acids on earth called standard amino

acids (Creighton 1993). These amino acids are encoded by the standard genetic code and are

found in all forms of life (Creighton 1993). The standard amino acids are broken down into two

different types, essential and nonessential.

Essential Amino Acids 

Eight of the standard amino acids are considered “essential amino acids” because they

are necessary for normal human growth and cannot be synthesized by the human body (Young

1994). Essential amino acids must be obtained from food sources, and include histidine,

isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine (Furst

and Stehle 2004; Reeds 2000; Wardlaw and Insel 1996:154).

Leucine. Leucine is used in the liver, adipose tissue, and muscle tissue. In adipose and

muscle tissue, leucine aids in the formation of sterols, and slows the degradation of muscle

tissue by increasing the synthesis of muscle proteins (Combaret, et al. 2005; Rosenthal, et al.

1974). Common sources of leucine in the diet include beef, fish, shellfish, nuts and seeds,

eggs, and legumes.

Lysine. Lysine is important for calcium absorption, building muscle, recovering from injuries or

illnesses, and the production of hormones, enzymes, and antibodies (Nelson and Cox 2005). 

Plants that contain significant amounts of lysine include legumes, gourds/squash, spinach,

amaranth, quinoa, and buckwheat (Wardlaw and Insel 1996:158). Other dietary sources of

lysine include beef, poultry, pork, fish, eggs, and dairy.

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Nonessential Amino Acids

The majority of the standard amino acids are considered “nonessential,” meaning that

under normal circumstances these amino acids can be manufactured by the human body and

are not required in the diet. However, some amino acids that are normally nonessential may

become an essential part of the diet for a person whose health has been compromised

(Wardlaw and Insel 1996:155). Nonessential amino acids include alanine, arginine,

asparagine, aspartate (aspartic acid), cysteine, glutamate (glutamic acid), glutamine, glycine,

proline, serine, and tyrosine (Furst and Stehle 2004; Reeds 2000)(Wardlaw and Insel

1996:154).

Glutamate. Glutamate, or glutamic acid, is an important molecule in cellular metabolism. It is

the most abundant excitatory neurotransmitter in the nervous system of mammals (Nelson and

Cox 2005). Glutamate is found in dairy products, eggs, and all meats, such as beef, pork,

poultry, wild meats, and fish (Reeds, et al. 2000).

Glutamine. Glutamine is the most abundant and naturally occurring, non-essential amino acid

in the human body. It is one of the few amino acids which directly crosses the blood-brain

barrier (Lee, et al. 1998). The blood-brain barrier is a collection of high density cells joined with

almost impenetrable connections that protect the brain from being exposed to all elements in

the blood, particularly bacteria (Lee, et al. 1998). Unlike many other substances, such as

solutes, which are redistricted from making this passage, glutamine in the blood can easily pass

through these junctions (Lee, et al. 1998). Glutamine is not only found circulating in the blood,

but is also stored in the skeletal muscles (Lee, et al. 1998). At times of illness or injury,

glutamine can be considered a conditionally essential amino acid that must be obtained

temporarily from the diet because the body is unable to synthesize it on its own (Lee, et al.

1998). Glutamine is also beneficial in healing the cells of the gastrointestinal tract by

stimulating regeneration and promoting new cellular growth. Common sources of glutamine in

the diet include beef, chicken, fish, eggs, dairy, legumes, cabbage, beets, spinach, and parsley. 

Nonstandard Amino Acids

Nonstandard amino acids are amino acids that are chemically altered after they have

been incorporated into a protein and/or amino acids that exist in living organisms but are not

found in proteins (Driscoll 2003).

Nucleic Acids

Millions of proteins exist in all living organisms to assist with the daily functions of these

complex systems. Proteins are produced and assembled locally to exact specifications, and a

large amount of information is necessary to properly manage the system. This information is

stored in a set of molecules called nucleic acids. Nucleic acids not only contain the genetic

instructions for the proper development and functioning of living organisms, but also play a role

in copying genetic information to protein (Saenger 1984). The most common examples of

nucleic acids are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

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DISCUSSION

The underwater sites GA426 and HI178 are located on the outer continental shelf off the

Texas coast in the Gulf of Mexico. Both sites were exposed as dry land during the last glacial

maximum, and due to the difference in elevation, were inundated at slightly different time

intervals due to rising sea levels. Although the cultural affiliation of these sites is unknown,

radiocarbon dating of core sediments suggests an early Archaic, or possibly a Paleoindian

association when correlated to terrestrial archaeological sites in Texas and Louisiana. Three

core samples from these sites were examined for pollen and organic residues (Table 1). 

Samples were tested for organic residues using Fourier Transform Infrared Spectroscopy

(FTIR). Pollen and organic residue analysis are used to determine if the core samples

represent sites on land or deposition of floral remains blown to sea. Results from these

analyses will be discussed below by site.

GA426

Site GA426 is located approximately thirty-one miles off the Texas coast 102 feet below

modern sea level. Although exposed during the last glacial maximum, the area was probably

inundated between 7,700 and 10,900 BP, depending on the sea-level curve used. Subaerially

exposed surface located near entrenched river channels would have transitioned to low energy

estuarine zones prior to being inundated. A core sample (GA426-9-G) collected between 399

to 400 centimeters below the sea floor was examined for pollen and organic residues. The unit

from which this sample was recovered is described as a very dark brown smooth textured

clayey sediment. A single isolated shell was observed in this unit. Radiocarbon dates obtained

from sediment above this unit at approximately 105 centimeters below the sea floor were dated

to 9,980 ± 50 BP (Amanda Evans, personal communication, September 28, 2010). Sediments

at the depth (390 centimeters below the sea floor) from which sample GA426-9-G was

recovered were reported as greater than 43,500 BP, so are considered too old to be reliably

radiocarbon dated.

The pollen record for sample GA426-9-G was dominated by Quercus pollen,

representing local growth of oak trees (Figure 1, Table 2). In addition, small quantities of

Betula, Carya, Pinus, and Ulmus pollen were recorded, indicating a mixture of hickory, pine,

and elm trees growing with the oaks. A small quantity of diploxylon Pinus pollen, representing

red, rather than white, pine, was noted. A very large quantity of Poaceae pollen was noted in

this sample, suggesting a dense population of grasses. Phytolith analysis of these sediments

would document the types of grasses growing in the area. The Cheno-am pollen frequency

was moderately large, suggesting local growth of saltbush, goosefoot, or a similar plant. 

Smaller quantities of Low-spine Asteraceae, High-spine Asteraceae, Cyperaceae, Eriogonum,

Phlox, Rosaceae, and Rosaceae striate pollen represent various members of the marshelder

and rabbitbrush/sunflower portions of the sunflower family, sedges, wild buckwheat, phlox, and

two members of the rose family. Striate Rosaceae pollen may represent any of several genera,

although the most likely is Prunus (chokecherry). Members of the Low-spine Asteraceae group,

such as marshelder, are expected as part of wetland communities, as are Cyperaceae and

some of the Cheno-ams.

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Organic residue analysis of the core sample (GA426-9-G) yielded peaks representing

major categories (functional groups) of compounds (4000-1500 wave number), as well as

specific compounds noted in the fingerprint region (1500-400 wave numbers) of the spectrum. 

The functional group peaks indicate the presence of absorbed water and fats/oils/lipids and/or

plant waxes (Table 3). Peaks within the fingerprint region represent the presence of aromatic

and saturated esters; proteins including nucleic acids; the amino acids lysine, glutamine, and

leucine; pectin; humates; and the polysaccharides arabinan and arabinogalactan.

Matches for these peaks include Achillea (yarrow) stems, Schoenoplectus (bulrush)

stems, Cicuta (hemlock) stems, Helianthus (sunflower) seed shells, ground Cheno-am seeds,

dried, ground Thalia dealbata (alligator flag) seeds, dried Cylindropuntia (cholla cactus) buds,

and wet Sambucus (elderberry) (Table 4) probably represent elements of the local vegetation

community. Several of these plants are expected to grow in the vicinity of river channels and

estuarine zones. They include members of the sunflower family that might have been confused

with yarrow, bulrush, hemlock, and alligator flag.

Arabinan identified in the sample suggests the presence of terrestrial plant materials in

the sample representing the core sediments. This compound is unique to land plants because

it is essential for the function of guard cells. These cells “play a key role in the ability of plants

to survive on dry land, because their movements regulate the exchange of gases and water

vapor between the external environment and the interior of the plant” (Jones, et al.

2003:11783).

The presence of the polysaccharide arabinogalactan suggests plant gums and

hemicelluoses are contributing to the signature; however, due to the ubiquitous nature of this

compound in the plant kingdom specific plants cannot be identified.

Other matches were made with crickets and turtle blood. Although matches with

crickets are being detected, it is the protein, and not the chitin, that was identified and matched. 

Therefore, matches with crickets probably indicate the presence of insect protein in the sample,

and not chitin as a proxy for shellfish. Recovery of a match to turtle blood is indicative of blood,

but not necessarily only turtle blood. FTIR distinctions of blood between the major categories of

reptiles/amphibians, land mammals, birds, and fish are considered to be reliable, although

protein residue analysis, based on immunological principles provides more specific

identifications.

Peaks representing the amino acids lysine, glutamate, and leucine suggest the

presence of fish remains in the samples, which is expected for sediments deposited below the

sea floor. These amino acids also are found in crickets and reptiles, and probably are reflecting

compounds present in these matched references, as well. It is possible that organic residues

from fish were integrated into the inundated sediments.

HI178

Site HI178 is located approximately twenty-one miles off the shore of Texas at a depth

of about 52 feet below modern sea level. This location probably was inundated between 7,000

and 9,200 BP, depending on the sea-level curve used. Two core samples (HI178-1-B and

344
12

HI178-1-C) were recovered from a unit described as black sediment with discrete lenses of dark

gray material. Sample HI178-1-B, collected between 120.5 to 121.5 centimeters below the sea

floor, was examined for organic residues using FTIR. Pollen analysis was performed on

sample HI178-1-C, collected from approximately 123 to 124 centimeters below the sea floor. 

Charcoal was visible in this unit as a discrete lens at about 122 centimeters below the sea floor

and continued as scattered fragments to a maximum depth of 142.5 centimeters below the sea

floor. Radiocarbon dating of sediments above and below these samples yielded an

uncalibrated age range of 7,420-8,530 BP suggesting this sample also falls within this time

frame (Amanda Evans, personal communication, September 28, 2010).

Pollen analysis of sample HI178-1-C exhibits a different pollen signature, indicating a

different assemblage of vegetation in this area. Probable Thalictrum pollen dominated the

record, indicating that local vegetation was typical of a meadow. Poaceae pollen was subdominant, representing a large local grass population, which is consistent with this

interpretation. Further clarification of the grass population is possible with phytolith analysis. 

Moderate quantities of Quercus and Cheno-am pollen represent oak and members of the

Cheno-am group that might include goosefoot, saltbush, or others. Recovery of Alnus, Juglans,

and Pinus pollen indicates that alder grew in wetlands and that walnut and pines were part of

the local woodland. Once again, a few diploxylon Pinus pollen were observed, representing red

pines. Recovery of smaller quantities of Artemisia, Low-spine Asteraceae, High-spine

Asteraceae, Allium-type, Boraginaceae, Cyperaceae, Fabaceae, Plantago, and Rosaceae

pollen represents sagebrush or wormwood, marshelder or similar plants, other members of the

sunflower family, wild onion or a similar plant, members of the borage, sedge, and legume

families, plantain, and a member of the rose family. Most of this assemblage of plants is

compatible with an interpretation of meadow vegetation. Globerigina tests were slightly more

abundant than pollen in this sample. Globerigina are a type of foraminifera with a calcium

carbonate outer test. During normal pollen sample extraction calcium carbonates are removed

through the use of hydrochloric (HCl) acid. Foraminifera also have an inner organic form that

survives pollen extraction. It is this portion that was recovered in this sample. Globerigina are

temperature sensitive, although finding published documentation that they represent cooler sea

temperatures has proven extremely difficult. They are commonly reported as forming an “oozy”

deposit on the ocean bottom. Recovery of Globerigina in this sample, which is close to the level

that was radiocarbon dated, points to the possibility of contamination of a total soil organic date

by the organic portion of the interior test. The calcium carbonate outer test should have been

dissolved in the chemical pre-treatment routinely practiced by all radiocarbon labs. The

reported observation of charcoal as a discrete lens in this core and the recovery of a large

quantity (more than 40 times as abundant as pollen) of microscopic charcoal particles in this

sample point to the opportunity to extract this microscopic charcoal and clean it chemically. 

Because even microscopic charcoal fragments can be cleaned more effectively of microscopic

organisms such as bacteria and Foraminifera inner tests than sediment, it is possible that

dating microscopic charcoal from this lens will yield a date more reflective of the time period

represented by that charcoal.

FTIR analysis of the core sample (HI178-1-B) yielded peaks representing functional

group compounds including absorbed water and fats/oils/lipids and/or plant waxes. Other

peaks identified in the fingerprint range indicate the presence aromatic and saturated esters;

protein; the amino acid glutamate; pectin; starch; cellulose and carbohydrates; and the

polysaccharide galactoglucomannan.

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13

The local vegetation community is represented by matches with Achillea (yarrow, a

member of the High-spine Asteraceae group) stems, Cicuta (hemlock) stems, Poaceae (grass

family) stems and joints, Helianthus (sunflower) seed shells, Prunus (choke cherry) and Ribes

(currant) fruit. Most of these plants might be found growing in meadows, although the Prunus is

more likely to grow in drainages.

The presence of the polysaccharide galactoglucomannan suggests woody and fibrous

tissues from coniferous plants (Gymnosperms) are contributing to the signature. This

compound might reflect pines, noted in the pollen record, growing in the area.

Peaks representing the amino acid glutamate indicate fish in the sample, which is

expected for sediment deposits below the sea floor.

SUMMARY AND CONCLUSIONS

Pollen and FTIR analysis of organic residues of samples from GA426 and HI178 provide

a record of probable vegetation for both locations. The pollen record indicates that site GA426

was located closer to an open wooded area that included at least oak and probably also birch,

hickory, pine, and elm, with an understory of grasses. Vegetation also included various

members of the sunflower family, sedges, wild buckwheat, mallow, phlox, and members of the

rose family. FTIR analysis confirms a signature of land plants. Pollen analysis of a sediment

sample from HI178 suggests the presence of a meadow at this location. FTIR analysis is

consistent with this interpretation. Pollen and FTIR analyses combine to indicate that these

sediments were part of the exposed land surface, rather than part of the inundated sea bed, at

the point of sediment deposition. Recovery of large quantities of Globerigina inner tests from

sediments at HI178 points to the possibility that the radiocarbon date for that location is too

young.

346
14

TABLE 1

PROVENIENCE DATA FOR SAMPLES FROM SITES GA426 AND HI178, 

TEXAS GULF COAST

Site Sample

Number

Depth

(cmbs)

Provenience/Description Radiocarbon

Dates

Analysis

HI178 HI178-1-B 120.5 - 121.5 Core sample: charcoal from

discrete lens beginning at

122cmbs, decreasing to

scattered fragments until

142.5cmbs

7420-8530 BP FTIR

HI178-1-C 123 - 124 Core sample: charcoal from

discrete lens beginning at

122cmbs, decreasing to scatter

fragments until 142.5cmbs

7420-8530 BP Pollen

GA426 GA426-9-G 399 - 400 Core sample: sediment > 43900 BP Pollen

FTIR

cmbs = centimeters below sea floor

FTIR = Fourier Transform Infrared Spectrometry

347
15

TABLE 2

POLLEN TYPES OBSERVED IN SAMPLES FROM SITES GA426 AND HI178, 

TEXAS GULF COAST

Scientific Name Common Name

ARBOREAL POLLEN:

Alnus Alder

Betula Birch

Carya Hickory, Pecan

Juglans Walnut

Pinus Pine

Quercus Oak

Ulmus Am erican Elm or, White Elm, W ater Elm 

NON-ARBOREAL POLLEN:

Allium-type W ild onion

Asteraceae: Sunflower fam ily

 Artemisia Sagebrush

 Low-spine Includes ragweed, cocklebur, sumpweed

 High-spine Includes aster, rabbitbrush, snakeweed,

sunflower, etc.

Boraginaceae Borage fam ily

cf. Thalictrum Meadow rue

Cheno-am Includes the goosefoot family and amaranth

Cyperaceae Sedge family

Eriogonum W ild buckwheat

Fabaceae Bean or Legume family

Phlox Phlox

Plantago Plantain

Poaceae Grass fam ily

Rosaceae: Rose family

Rosaceae - striate (includes Purshia, Prunus,

Coleogyne, Crataegus, Malus, and Pyrus)

Rose family - includes bitterbrush, chokecherry,

cherry, plum, peach/nectarine, apricot, almond,

blackbrush, hawthorn, apple, and pear

348
TABLE 2 (Continued)

Scientific Name Common Name

16

Indeterminate Too badly deteriorated to identify

OTHER:

Forams:

 Foraminifera Inner Test Tests

 Globergina Inner Test Tests

Charcoal Microscopic charcoal

Total pollen concentration Quantity of pollen per cubic centimeter (cc) of

sediment

349
17

TABLE 3

FTIR PEAK SUMMARY TABLE FOR SAMPLES FROM SITES GA426 AND HI178, 

TEXAS GULF COAST

Peak Range Represents

GA426-9-G

Core sediment

H178-1-B

Core sediment

3600-3200 Absorbed Water (O-H

Stretch)

3396,3357,

3283

3324,3303

3293,3284,

3278

3000-2800 Aldehydes:

fats, oils, lipids, waxes

2917,2916,

2849

2918/17/16,

2850,2849

1730-1705 Aromatic esters (C=O

Stretch)

1708,1707 1710, 1707/08

1700-1500 Protein, incl.

1650 protein

1655/54,

1637,1617,

1545,1511

1648,

1597,1560,

1546,1542, 1508/07

1653 Proteins (Amide bands, 80%

C=O Stretch, 10% C-N

Stretch, 10% N-H Bend)

1654

1680-1600, 1260,

955

Pectin 1655/54,

1637,1617

1648

1660-1655 Proteins, Nucleic acids 1655

1640-1610,

1550-1485

Lysine (amino acid) NH3

+

bending

1637,1617

1615 Proteins (Glutamine, NH2

Bend)

1617

1560 Glutamate (amino acid) CO2

-

asymmetric stretching

1560

1500-1400 Protein 1464,

1413

1463/62/61,

1459,1420

1465-1455 Protein/lipids 1464 1463/62/61

1490-1350 Protein 1464,

1413,

1376

1463/62/61,

1459,1420,

1364

1377 Fats, oils, lipids, humates

(CH3 symmetric bend)

1376

1375 Leucine (amino acid) CH3

symmetric bending

1376

1375 CH3 Umbrella mode 1376

1170 Lipids 1171,1170

350
TABLE 3 (Continued)

Peak Range Represents

GA426-9-G

Core sediment

H178-1-B

Core sediment

18

1170-1150, 1050,

1030

Cellulose 1163 ,1128

1162 Cellulose 1163

1130-1100 Aromatic esters 1128/27/26/25

1100-1030 Saturated esters 1040,1039 1081

1028-1000 Cellulose

Carbohydrates

1015

1082 Starch 1081

1040 Arabinogalactan (Type II) 1040

1039 Arabinan 1039

934 Galactoglucomannan 935

931 Starch 931

930 Cellulose 930

918 Arabinan 920

889 C-CH2-O Symmetric stretch 888

830 Symmetric C-C-O stretch 831

750-700 Aromatic esters 719 719

722-719 CH2 Rock (methylene) 719 719

351
19

TABLE 4

MATCHES SUMMARY TABLE FOR FTIR RESULTS FROM SITE GA426 AND HI178,

TEXAS GULF COAST

Match

(Scientific Name)

Match

(Common Name) Part

GA426-9-G

Core sediment

(Range)

HI178-1-B

Core sediment

(Range)

Achillea Yarrow Stem 1183-1153 1476-1443

738-690

Cheno-am Goosefoot family and

amaranth

Seed

(ground)

1479-1434

Cicuta Hemlock Stem 1476-1428

1183-1153

1616-1574

Cylindropuntia Cholla cactus Bud

(baked/dried)

1392-1356

1183-1153

Helianthus Sunflower seed Shell 1476-1428

735-711

1616-1574

1481-1440

1174-1150

735-708

Poaceae Grass fam ily Joints 1514-1490

1481-1440

735-708

Stem 1481-1440

735-708

Prunus Choke cherry Fruit 1616-1574

735-708

Ribes Currant Fruit 1481-1440

Sambucus Elderberry Fruit

(boiled/wet)

1479-1434

738-705

Schoenoplectus Bulrush Stem (raw) 1392-1356

735-711

Thalia dealbata Alligator flag Seed

(baked/dried,

ground)

1183-1144

735-711

Cricket W hole 1476-1428

1392-1356

735-711

Turtle Blood 1392-1356

1183-1153

352
HI178-1-B

GA426-9-G

SAMPLE NO.

20

ARBOREAL POLLEN Alnus Betula Carya Juglans Pinus undiff Pinus Diploxylon

20

Quercus Ulmus Allium-type Artemisia LOW-SPINE ASTERACEAE HIGH-SPINE ASTERACEAE BORAGINACEAE

20

cf. Thalictrum

20

CHENO-AM CYPERACEAE Eriogonum FABACEAE Phlox Plantago

20 40

POACEAE ROSACEAE ROSACEAE STRIATE INDETERMINATE Foraminifera Test

20 40

Globergina Test

10

MICROS

PINUS ASTERACEAE ROSA

FIGURE 1. POLLEN DIAGRAM FOR TWO OFFSHORE CORE SAMPLES, GULF CO

AA A

A

353
21

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356
POLLEN ANALYSIS OF CORES FROM SITE GA426,

OFFSHORE NEAR GALVESTON, TEXAS

By

Linda Scott Cummings

and

R. A. Varney

PaleoResearch Institute

Golden, Colorado

PaleoResearch Institute Technical Report 11-079

Prepared for

Louisiana State University

Baton Rouge, Louisiana

November 2011

357
INTRODUCTION

Five sediment samples from two cores collected at site GA426, located approximately

31 miles offshore near Galveston, Texas, were examined for pollen. The site is on an old river

terrace that is now submerged in an estuary or back bay. The site is a possible Paleoindian site

that is expected to date to between approximately 9,000 and 10,000 BP. The area was above

water during the last glacial maximum and was subsequently submerged in the range of 8,400

to 10,000 BP (Patrick Hesp, personal communication, June 7, 2011). Pollen analysis of these

samples provides information about the past vegetation growing in the area and also may be

used to describe the paleoenvironment.

METHODS

Pollen

A chemical extraction technique based on flotation is the standard preparation technique

used in this laboratory for the removal of the pollen from the large volume of sand, silt, and clay

with which it is mixed. This particular process was developed for the extraction of pollen from

soils where preservation has been less than ideal and the pollen density is lower than in peat. It

is important to recognize that it is not the repetition of specific and individual steps in the

laboratory, but rather mastery of the concepts of extraction and how the desired result is best

achieved, given different sediment matrices, that results in successful recovery of pollen for

analysis. 

Hydrochloric acid (10%) was used to remove calcium carbonates present in the soil,

after which the samples were screened through 250-micron mesh. The samples were rinsed

until neutral by adding water, letting the samples stand for 2 hours, then pouring off the

supernatant. A small quantity of sodium hexametaphosphate was added to each sample once it

reached neutrality; then the samples were allowed to settle according to Stoke’s Law in settling

columns. This process was repeated with ethylenediaminetetraacetic acid (EDTA). These

steps remove clay prior to heavy liquid separation. The samples then were freeze dried. 

Sodium polytungstate (SPT), with a density 1.8, was used for the flotation process. The

samples were mixed with SPT and centrifuged at 1500 rpm for 10 minutes to separate organic

from inorganic remains. The supernatant containing pollen and organic remains was decanted. 

SPT again was added to the inorganic fraction to repeat the separation process. The

supernatant was decanted into the same tube as the supernatant from the first separation. This

supernatant was then centrifuged at 1500 rpm for 10 minutes to allow any silica remaining to be

separated from the organics. Following this, the supernatant was decanted into a 50-ml conical

tube and diluted with distilled water. These samples were centrifuged at 3000 rpm to

concentrate the organic fraction in the bottom of the tube. After rinsing the pollen-rich organic

fraction obtained by this separation, all samples receive a short (20–30 minute) treatment in hot

hydrofluoric acid to remove any remaining inorganic particles. The samples then were

acetylated for 3–5 minutes to remove any extraneous organic matter.

A light microscope was used to count pollen at a magnification of 500x. The pollen

preservation in these samples varied from good to poor. Comparative reference material

collected at the Intermountain Herbarium at Utah State University and the University of

358
2

Colorado Herbarium was used to identify the pollen to the family, genus, and species level,

where possible.

Pollen aggregates were recorded during identification of the pollen. Aggregates are

clumps of a single type of pollen and may be interpreted to represent pollen dispersal over short

distances or the introduction of portions of the plant represented into an archaeological setting. 

Aggregates were included in the pollen counts as single grains, as is customary. The presence

of aggregates is noted by an "A" next to the pollen frequency on the pollen diagram. Pollen

diagrams are produced using Tilia 2.0 and TGView 2.0.2. Total pollen concentrations are

calculated in Tilia using the quantity of sample processed in cubic centimeters (cc), the quantity

of exotics (spores) added to the sample, the quantity of exotics counted, and the total pollen

counted and expressed as pollen per cc of sediment.

Indeterminate pollen includes pollen grains that are folded, mutilated, or otherwise

distorted beyond recognition. These grains are included in the total pollen count since they are

part of the pollen record. The microscopic charcoal frequency registers the relationship

between pollen and charcoal. The total number of microscopic charcoal fragments was divided

by the pollen sum, resulting in a charcoal frequency that reflects the quantity of microscopic

charcoal fragments observed, normalized per 100 pollen grains.

DISCUSSION

This site is located approximately 31 miles offshore on the outer continental shelf. The

current water depth is 101' BSL. Although this area is currently underwater, it was exposed as

dry land during the last glacial maximum and probably was inundated between approximately

8,400 and 10,000 BP, depending on which sea level curve is selected. Two cores were

collected on the topographic rise between two entrenched river channels. One speculation is

that this area could have been a low-energy estuarine zone. Small charcoal flecks and/or

organic staining were present in the unit that was cored.

Core 2

The pollen record in Core 2, designated GA-426-2, displays evidence of vegetation

change through time. The samples were collected at depths between 137 and 103 cm below the

sediment surface (Table 1) at this location. The lowest sample was collected at a depth of 136

to 137 cm below the sediment surface. This sample was co-dominated by High-spine

Asteraceae and Cheno-am pollen (Figure 1, Table 2) and also exhibited moderate quantities of

Pinus and Poaceae pollen. This pollen record suggests an open area that supported various

members of the sunflower family, plants in the Cheno-am group, and grasses. Pine trees

probably grew at some distance from this location on more elevated ground. Small quantities of

Carya, Quercus, and Ulmus pollen indicate that hickory, oak, and elm trees also grew in the

area. Recovery of small quantities of Artemisia, Low-spine Asteraceae, Corylus, and Persicaria

pollen indicate that sagebrush, marsh elder or similar plants, hazel, and smartweed also grew

as part of the local vegetation community. The presence of Corylus and Persicaria pollen in this

sample suggests proximity to a wetland. The remainder of the pollen record, however, is more

typical of a meadow. A moderate quantity of microscopic charcoal was observed that might

359
3

represent cultural activity or natural fires in this area. Recovery of foraminifera in this sample

might reflect later inundation of the sediments. The total pollen concentration is calculated at

approximately 9500 pollen per cubic centimeter (cc) of sediment.

The local plant community appears to have changed rapidly, as is recorded in the

sample collected at a depth of 132 cm. This sample records a dramatic increase in Quercus

pollen, indicating an encroachment of oaks. The recovery of small quantities of Alnus,

Juniperus, and Abies pollen indicates local growth of alder, as well as the inclusion of juniper

and fir into stands of conifers that were probably growing at a greater distance from this

location. The presence of Apiaceae suggests growth of members of the umbel family in the

immediate vicinity of the area sampled, or possibly their use or processing by people working in

this area if the charcoal is interpreted to represent a cultural activity area. The dramatic

reduction in High-spine Asteraceae pollen reflects a decrease in the local growth of plants in the

sunflower family. A gradual increase in Low-spine Asteraceae pollen frequencies suggests an

increase in the marshelder (and similar plant) population. This sample is the first to contain

small quantities of Cyperaceae and Rosaceae pollen, and monolete fern spores, reflecting the

local growth of sedges, a member of the rose family, and ferns. The quantity of microscopic

charcoal remains unchanged. The total pollen concentration, however, has increased from less

than 10,000 pollen per cc of sediment to more than 47,000 pollen per cc of sediment. This

increase in total pollen concentration is consistent with the presence of a stable surface.

The sample collected at a depth of 103-105 cm below the surface is noteworthy because

of an increase in Pinus pollen. This change might reflect either an increase in the quantity of

pine trees growing in the area or a decrease in local vegetation that results in an overrepresentation of pollen present through long distance transport. The latter is a possibility,

since this sample exhibited a much larger quantity of microscopic charcoal than did the lower

samples. If a fire was responsible for reducing local vegetation, then there would be little input

from local plants and most of the pollen record would consist of pollen transported on the wind. 

Increases in Pinus pollen would be expected since it is readily transported over long distances. 

The total pollen concentration is more than 20,000 pollen per cc of sediment, slightly less than

half that observed in sample 132. This reduction is not sufficient to warrant an interpretation of

a massive fire that denuded the landscape of vegetation. Therefore, the most reasonable

interpretation is that the quantity of pine trees growing in the region increased. It is also likely

that this sample represents a surface that experienced very slow aggradation through time. The

gradual increase in Low-spine Asteraceae pollen noted in sample 132 continues in this sample,

suggesting local growth of marsh elder-type plants in moderately wet sediments. Persicaria

pollen has dropped out of the record, indicating that the moist ground that supported this type of

knotweed probably did not exist at the time represented by this sample. Other pollen taxa

recovered from this sample are similar to those noted in the underlying sample, sample 132.

The recovery of Alnus and Corylus pollen represents alder trees and hazel shrubs growing

along the local drainage. Plants that are expected to grow along the margins of wetlands are

represented by Apiaceae and Cyperaceae pollen, representing a member of the umbel family

and sedges.

The pollen record for Core 2 indicates moderate sediment aggradation in the lower

(earliest) sample, then surface stabilization in the middle sample, followed by a resumption of

slow sediment aggregation in the uppermost sample. A general increase in dryness is

suggested through time, with pines becoming more abundant on the landscape in the upper

sample. These changes in the pollen record are consistent with vegetational succession as

360
4

communities mature. Evidence for the continuation of wetland communities in the vicinity of the

area sampled continues.

Core 10

Core 10 from site G8 426 was sampled at depths of 104-106 cm and 85-87 cm below

the surface. The sample collected from a depth of 104-106 centimeters was similar in pollen

content to the lowest sample examined from Core 2. This sample also was dominated by

Cheno-am pollen, and the quantity of High-spine Asteraceae pollen was larger in this sample

than the sample above it. The quantities of Pinus and Quercus pollen also were lower in this

sample than in the sample above it, indicating that while pine and oak trees grew in the area,

they were not particularly abundant. The Poaceae pollen frequency was moderately high,

indicating that grasses were an important part of the plant cover. Pollen recovered from this

sample representing trees growing in the area also includes Alnus, Carya, Juglans, and

Juniperus, representing alder, hickory, walnut, and juniper. Although they were noted in small

quantities, recovery of these pollen documents local growth of these trees. Pollen representing

herbaceous or shrubby plants growing in the area (and not mentioned earlier) includes

Apiaceae, Artemisia, Low-spine Asteraceae, Caryophyllaceae, Cyperaceae, Plantago,

Rosaceae, Salix, and Typha, indicating that a member of the umbel family, sagebrush,

members of the sunflower family, a member of the pink family, sedges, plantain, a member of

the rose family, willow, and cattails grew locally. This sample displays a moderately large

quantity of microscopic charcoal, which is consistent with the presence of a cultural layer at this

depth. The total pollen concentration was more than 18,000 pollen per cc of sediment,

suggesting a moderately stable surface.

The upper sample, collected at 86-87 cm, displays slightly elevated Carya, Juniperus,

Pinus, and Quercus pollen frequencies compared to the lower sample, indicating increases in

quantities of hickory, juniper, pine, and oak trees. Recovery of small quantities of Alnus,

Elaeagnus, and Tsuga pollen indicate that alder, silverberry, and hemlock trees also grew in the

area. The herbaceous and shrubby portion of this record is dominated by Poaceae pollen,

which has increased slightly over the quantity observed in the lower sample. Once again, it is

likely that forested areas were interspersed with grassy meadows on the landscape. Recovery

of small quantities of Apiaceae, Artemisia, Low-spine Asteraceae, High-spine Asteraceae,

Cheno-am, Corylus, Cyperaceae, Eriogonum, Fabaceae, Rosaceae, Salix, and Typha pollen

indicate that the local vegetation also included a member of the umbel family, sagebrush,

members of the sunflower family, Cheno-am, hazel, sedges, wild buckwheat, legumes, a

member of the rose family, willow, and cattail. It is likely that plants growing in a wetland

community included plants in the umbel family, marsh elder, hazel, sedges, willow, cattails, and

alder. The quantity of microscopic charcoal was severely reduced in this sample when

compared with the lower samples from this core. The total pollen concentration also was

reduced to approximately 10,000 pollen per cc of sediment. This is consistent with a

moderately stable surface.

The pollen record from Core 10 also exhibits evidence of drying through time and

vegetation succession with maturation of woodland communities, expressed as increases in

Carya, Pinus, and Quercus pollen. Grassy or meadow communities either shrink in size or are

filled in with trees. The lowest sample represents a period of slow sediment aggradation and a

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5

relatively stable land surface, while the upper sample represents an increase in sediment aggradation.

SUMMARY AND CONCLUSIONS

The pollen records from Cores 2 and 10 exhibit similar signals representing local

vegetation communities. The total pollen concentration indicates periods of changing sediment

aggregation. Core 2 sediments aggraded most rapidly in the lower portion that was examined

(sample 137). Sediment aggradation slowed dramatically and a relatively stable surface is

reflected in sample 132. Slow aggradation is indicated in sample 105. A more open vegetation,

possibly wet riparian vegetation community is represented in the lowest sample (137) of this

core, suggesting a disturbed landscape and moderate sediment aggradation. It is likely that the

large quantities of High-spine Asteraceae (sunflower family) and Cheno-am (goosefoot and

related plants) pollen represent vegetation response to this disturbance. The increase in

Poaceae pollen in sample 132 probably represents replacement of many of the plants in the

sunflower family by grasses as the disturbance abates and the surface becomes more stable. 

The Cheno-am frequency declines only slightly at this point. Increases in Pinus and Quercus

pollen indicate that woodlands including pine and oak as the dominant trees increased in

density and/or proximity. This vegetation pattern continues into the uppermost sample (105) as

the woodland vegetation communities mature. The uppermost sample, exhibiting the largest

quantity of microscopic charcoal, represents a relatively mature woodland interspersed with

openings that experienced only slow sediment aggradation.

This general pattern of vegetation succession is also noted in the Core 10 samples, with

the lowest sample containing the largest High-spine Asteraceae and Cheno-am pollen

frequencies and smallest quantities of pollen representing trees. It is interesting that this

signature is observed in a sample that registers slow sediment aggradation rather than rapid

aggradation. As sediment aggradation increases, grasses replace members of the sunflower

family and Cheno-ams, and pine and oak trees become slightly more abundant, which suggests

that the rate of vegetation community maturation was greater than the disturbance caused by

the aggradation of sediments. These records are not exactly the same, but both indicate

proximity to wet riparian communities and exhibit signatures that indicate they represent riparian

meadows at some point. Natural fires or cultural activity is evident in both cores with increases

in microscopic charcoal. General drying through time and woodland community maturation is

indicated in the pollen records from both cores.

362
6

TABLE 1

PROVENIENCE DATA FOR SAMPLES FROM SITE GA-426,

OFFSHORE NEAR GALVESTON, TEXAS

Sample No. Core Depth

(cmbs)

Provenience/Description Analysis

GA-426-10-A-87 10 86-87 River terrace fill Pollen

GA-426-10-B-106 10 104-106 River terrace fill Pollen

GA-426-2-B-105 2 103-105 River terrace fill Pollen

GA-426-2-B-132 2 130-132 River terrace fill Pollen

GA-426-2-B-137 2 136-137 River terrace fill Pollen

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7

TABLE 2

POLLEN TYPES OBSERVED IN SAMPLES FROM SITE GA426,

OFFSHORE NEAR GALVESTON, TEXAS

Scientific Name Common Name

ARBOREAL POLLEN:

Alnus Alder

Carya Hickory, Pecan

Elaeagnus Russian olive

 Juglans Walnut

Juniperus Juniper

Pinaceae: Pine family

 Abies Fir

 Pinus Pine

Quercus Oak

Tsuga Hemlock

Ulmus American Elm or, White Elm, Water Elm 

NON-ARBOREAL POLLEN:

Apiaceae Umbel family

Asteraceae: Sunflower family

 Artemisia Sagebrush

 Low-spine Includes ragweed, cocklebur, sumpweed

 High-spine Includes aster, rabbitbrush, snakeweed,

sunflower, etc.

Caryophyllaceae Pink family

Cheno-am Includes the goosefoot family and amaranth

Corylus Hazel

Cyperaceae Sedge family

Fabaceae Bean or Legume family

Plantago Plantain

Poaceae Grass family

Polygonaceae: Knotweed/Smartweed family

364
TABLE 2 (Continued)

Scientific Name Common Name

8

 Eriogonum Wild buckwheat

 Persicaria Smartweed, Persicaria, Pinkweed

Rosaceae Rose family

Salix Willow

Typha latifolia Cattail

Indeterminate Too badly deteriorated to identify

FERNS:

Monolete Smooth Fern

Trilete Smooth Fern

OTHER:

Foraminifera A group of plankton species

Hystrichosphere Geologic plankton

Charcoal Microscopic charcoal

Total pollen concentration Quantity of pollen per cubic centimeter (cc) of

sediment

365
87

106105132137

SAMPLE NO.

20 40

ARBOREAL POLLEN Alnus Carya Elaeagnus Juglans Juniperus Abies

20 40

Pinus

20

Quercus Tsuga Ulmus APIACEAE Artemisia LOW-SPINE ASTERACEAE

20

HIGH-SPINE ASTERACEAE Caryophyllaceae

20 40

CHENO-AM Corylus CYPERACEAE FABACEAE Plantago

20

POACEAE Eriogonum Persicaria ROSACEAE SalixTypha latifolia

20

INDETERMINATE MONOLETE SMOOTH TRILETE SMOOTH Foraminifera Hystrichos

MICR

PINACEAE ASTERACEAE POLYGONACEAE 

FIGURE 1. POLLEN DIAGRAM FOR TWO CORES FROM SITE GA426, OFFSHORE GALVESTO

A

A

A

A

366
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