Characteristics of 

Estuarine Sediments of 

The United States

GEOLOGICAL SURVEY PROFESSIONAL PAPER 742

Prepared in cooperation with the U.S. Federal 

Water Pollution Control Administration
Characteristics of 

Estuarine Sediments of 

The United States

By DAVID W. FOLGER

GEOLOGICAL SURVEY PROFESSIONAL PAPER 742

Prepared in cooperation with the U.S. Federal 

Water Pollution Control Administration

A compilation of data, essentially an atlas, on 

texture and composition of bottom sediments, 

including geologic and hydro logic factors 

that influence them, in 4.5 estuaries

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1972
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress catalog-card No. 72-600206

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402 - Price $1.25 (paper cover)

Stock Number 2401-2112
CONTENTS

Abstract_ ________________________

Introduction _______________________

Scope and purpose of the study_ 

Sources of information_________

Format______________________

Setting.___________________

Sediment texture ___________

Sediment composition. ______

Acknowledgments__ ___________

Area summaries.___________________

Penobscot Bay, Maine._________

Boston Harbor, Mass__ _________

Cape Cod Bay, Mass__________

Nantucket Bay, Mass-__________

Buzzards Bay, Mass___________-

Narragansett Bay, R.I__________

Moriches Bay, N.Y_____________

New York Harbor, N.Y. and N.J. 

Chesapeake Bay, Md. and Va_ 

Rappahannock River, Va__ ______

Albemarle Sound, N.C__________

Pamlico Sound, N.C____________

Core Sound, N.C_____________

Newport River Estuary, N.C____

Bogue Sound, N.C-------_______

Charleston Harbor, S.C________

Biscayne Bay, Fla______________

Florida Bay, Fla____________

Whitewater Bay, Fla__________

Gullivan Bay, Fla______________

Port Charlotte Harbor, Fla______

Tampa Bay, Fla______________

Apalachicola Bay, Fla___________

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Area summaries Continued

St. Joseph Bay, Fla_______.- _. 44

Pensacola Bay, Fla____--_-_-_--__-----------__- 46

Mobile Bay, Ala___________________ _______ 48

Mississippi Sound, Miss, and Ala_________________ 49

Breton and Chandeleur Sounds, La_______________ 51

Barataria Bay, La______________________________ 53

Sabine Lake, Tex. and La______________________ 54

Trinity River Delta and Upper Trinity Bay, Tex___ 55

Brazos River Delta, Tex___________-----------_ 57

Matagorda Bay, Tex_______-__-___--_--_-----__- 58

San Antonio Bay, Tex_________________________ 60

Aransas Bay, Tex ______ __ ____________ 62

Laguna Madre, Tex __________________________ 63

Baffin Bay, Tex____ __- - - 65

San Francisco Bay, Calif_____________-_-_-----_- 67

Yaquina Bay, Oreg_______-______----__--------- 69

Willapa Bay, Wash________ _ 70

Grays Harbor, Wash_____________-_______---___- 72

Bellingham Bay, Wash______ 74

Puget Sound, Wash-_____________-_-----_-_--__- 78

Nisqually River Delta, Puget Sound, Wash___-____ 80

Deep Inlet, Alaska__________-____-_-_-------_- 82

Summary of the characteristics of sediments in estuaries

and estuarine zones of the United States _________ 84

Setting, ________ - 84

Geology and bathymetry._________-_--_-_--_ 84

Hydrology-_______-____-____---_-_--------- 86

Sediment texture._____________________---_--__- 87

Sediment composition_--_____-__---_--_--------- 88

Organic carbon._________________----------- 88

Mineralogy.______-_______---_-_----------- 89

References cited-___________________--_-_---_------_ 90

ILLUSTRATIONS

FIGURE 1. Map of the United States showing the estuaries, lagoons, embayments, and deltas described in this report 

2-4. Map of Penobscot Bay, Maine, showing 

2. Bathymetry.________________________________-______----_---_--------------------------

3. Texture and organic carbon content of bottom sediments___________-__-__----__-_---------

4. Subbottom sediment texture______-___-------_---_-_-_-_-__------------------------------

5-7. Map of Boston Harbor, Mass., showing 

5. Bathymetry._______________________________________-___-_-_-----_-_-------------------

6. Texture of bottom sediments-_______________________------------------------------------

7. Organic carbon content of bottom sediments__________________________--_-_--------------

8, 9. Map of Cape Cod Bay, Mass., showing 

8. Bathymetry______________________________-_____-_---__---__----_----------------------

9. Texture and organic carbon content of bottom sediments _______________--_-_-------------

m

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2

4

4

4

5

6

6

7

7
IV CONTENTS

Page 

FIGURES 10-12. Map of Nantucket Bay, Mass., showing 

10. Bathymetry._________________________________________________________________________ 8

11. Texture of bottom sediments..-....--..------------------------------------------------ 8

12. Calcium carbonate content of bottom sediments._________________________________________ 8

13, 14. Map of Buzzards Bay, Mass., showing 

13. Bathymetry..___________________________________________ _____ __________ 9

14. Texture and organic carbon content of bottom sediments.__________________________________ 9

15. Bathymetric map and columnar sections of Narragansett Bay, R.I__________________________________ 10

16. Map of Narrangansett Bay, R.I., showing texture and organic carbon content of the bottom sediments.. 11 

17-19. Map of Moriches Bay, N.Y., showing 

17. Bathymetry,_____________________________________________________________ 12

18. Texture of the bottom sediments--...-------.------------------------------------------- 12

19. Total organic matter content of sediments _____________________________________________ 13

20-23. Map of New York Harbor, N.Y. and N.J., showing 

20. Depth below sea level to crystalline rock or consolidated sediments._________________________ 14

21. Bathymetry________.____________________._-_____________-_---_--_---_-__-_-_----__.__ 14

22. Texture of the bottom sediments..______________________________________________________ 15

23. Total organic matter and organic carbon content of bottom sediments.______________________ 15

24-26. Map of Chesapeake Bay showing 

24. Bathymetry---.-.----___________---_____-_______________-_-.____-_____---_----__-____ 17

25. Texture of the bottom sediments...____________-_-____---____-_-_----------------_--_-_- 17

26. Percentage of organic carbon content of bottom sediments-_______________-_----_-_--______ 18

27. Bathymetric map of the Rappahannock River Estuary, Va___________-____-_------__-___-__-__-_-_- 19

28. Map and cross section of the Rappahannock River Estuary showing texture of bottom sediments.________ 19

29. Map of the Rappahannock River Estuary showing organic carbon content of bottom sediments________ 20

30, 31. Map of Albemarle Sound, N.C., showing 

30. Bathymetry.____________----___________________-___-_-___------_-_--__----__-___-_-_. 21

31. Texture and organic carbon content of the bottom sediments.______________________________ 21

32-35. Map of Pamlico Sound, N.C., showing 

32. Bathymetry.__________---____---______.____.________-_-_--__-___--__-___-_-_----_.-_. 22

33. Texture of the bottom sediments.___________________-_--_____-------_--_--_----__-_-_-_- 22

34. Oxidizable organic matter and organic carbon content of the bottom sediments. ________ ______ 23

35. Calcium carbonate content of bottom sediments_________________________________________ 23

36-38. Map of Core Sound, N.C., showing 

36. Bathymetry._____-_______---_.-___.___.___.___._.______--__________________________ 24

37. Texture of the bottom sediments______-------------------------------------------_-_--_- 25

38. Calcium carbonate content of bottom sediments..__-___-_-___-_-_-_-_-_-___-_-_-__----__-- 25 

39-41. Map of Newport River Estuary, N.C., showing 

39. Bathymetry-_______________________________-___-_-_______-__---_---_-----___- 26

40. Texture of the bottom sediments.____________________________________-_-_--_-_---_--_--- 27

41. Calcium carbonate content of bottom sediments_____-__-_-_-_-_----_-------_----_-----_-_- 27

42-45. Map of Bogue Sound, N.C., showing 

42. Bathymetry._________________________________-____-_-___-_-_---_---_------------__- 28

43. Median diameter of bottom sediments-__________________-___,___-__----__-----_-------_- 29

44. Clay content of bottom sedlments_____------_----_-------------------------------------- 29

45. Oxidizable organic matter content of bottom sediments.__________-_-__--_-__--_-_---____-- 29

46-48. Map oT Charleston Harbor, S.C., showing 

46. Bathymetry____-._.._-_____-__________________-__-__-__----___--------------_---_----- 30

47. Median diameter of sediments and distribution of shoals composed mostly of clay___________-_ 30

48. Organic carbon content of bottom sediments_______________________________-----_----_-- 31

49-52. Map of Biscayne Bay, Fla., showing 

49. Bathymetry__-________________________________-___-__------___----------------------- 32

50. Texture of the bottom sediments.____________________________-_--_-__-_---_------------- 32

51. Quartz content of the bottom sediments________________-______----__-_----------------- 33

52. Calcium carbonate content of bottom sediments _______ ___________________---_----__-__ 33

53. Bathymetric map of Florida Bay, Fla___________________________-_--_-__----_----------------_- 34

54-56. Map of White water Bay, Fla., showing 

54. Structure contours on the surface of the Miami Oolite.___________________-------------_--- 35

55. Ratios of sand to silt for the calcium carbonate and quartz fractions of bottom sediments._____ 35

56. Organic carbon content of bottom sediments__---_--______----__-_------------------------ 36

57-59. Map of Gullivan Bay, Fla., showing 

57. Bathymetry_________________________________-____--___--_---------------------------- 37

58. Texture of the bottom sediments______-_-_------_--_------------------------------------ 37

59. Calcium carbonate content of bottom sediments.....-.-....------------------------------- 38
CONTENTS V

Page 

FIGURES 60-63. Map of Port Charlotte Harbor, Fla., showing 

60. Bathymetry-________--_-_________________________________________________________ 38

61. Texture of the bottom sediments_____________-__-_______________________________________ 39

62. Organic carbon content of bottom sediments_______-__-____-__-___________________________ 39

63. Calcium carbonate content of bottom sediments___---___--_-_--_--________________________ 40

64-66. Map of Tampa Bay, Fla., showing 

64. Bathymetry__________________________________________________________________________ 40

65. Texture of the bottom sediments-_---___----_--_________________________________________ 41

66. Calcium carbonate content of bottom sediments_________________________________________ 41

67-70. Map of Apalachicola Bay, Fla., showing 

67. Bathymetry______________--_-_________ ___-____-__--_-___-______.___ __________ 42

68. Texture of the bottom sediments-__---____-__-__---______-___-_---___________-__________ 42

69. Organic carbon content of bottom sediments____________________________________________ 43

70. Calcium carbonate content of bottom sediments._________________________________________ 43

71-74. Map of St. Joseph Bay, Fla., showing 

71. Bathymetry._________________________________________________________________________ 44

72. Texture of the bottom sediments____________----_--_--_---------_-_-__--_-_-___-_-______ 44

73. Organic carbon content of bottom sediments____________________________________________ 45

74. Calcium carbonate content of bottom sediments_________________________________________ 45

75, 76. Map of the Pensacola Bay system, Florida, showing 

75. Bathymetry__________________________________________________________________________ 46

76. Texture of the bottom sediments_________-____--_---___-----_-_-_---_-_-_-_--___________ 47

77, 78. Map of Mobile Bay, Ala., showing 

77. Bathymetry..---.----.___________________________________________________________ 48

78. Texture of the bottom sediments__________-_---------_----_-----_-_---_------_----_-___- 48

79-82. Map of Mississippi Sound, Miss, and Ala., showing 

79. Bathymetry____________________________________________________ 49

80. Texture of the bottom sediments.._____-____-__-_-_-________-__-_---_-_-_____---_-_-_-_- 50

81. Organic carbon content of bottom sediments-____________________________________________ 50

82. Calcium carbonate content of bottom sediments____-_-______-__-___-_-----_-_-_-_-_-_-____ 51

83-86. Map of Breton and Chandeleur Sounds, La., showing 

83. Bathymetry.__________._-_____________________________________________ 52

84. Texture of the bottom sediments.-_____________-___-_____-_--____------__------_----_--- 52

85. Total organic matter in bottom sediments.-______________________________________________ 52

86. Shell content of bottom sediments______________--________-______-_----____--___-_-_-_- 52

87-90. Map of Barataria Bay, La., showing 

87. Bathymetry...____________________________---_______-___-___------__---_-----_-_-_- 53

88. Texture of the bottom sediments___-____-_--_-_--__-_-_--_-_--_-_-_---------_---_------- 53

89. Organic carbon content of bottom sediments_________________________-_-_-___-_-_-_-_--- 54

90. Calcium carbonate content of bottom sediments_________________________________________ 54

91, 92. Map of Sabine Lake, Tex. and La., showing 

91. Bathymetry__-_________________________-________-____--_---_---_-------------------_- 55

92. Texture of the bottom sediments___-____-___-----------------_-------------------------- 55

93, 94. Map of Trinity River Delta and Upper Trinity Bay, Tex., showing 

93. Bathymetry.___________________________________.______ 56

94. Texture of the bottom sediments__-_____-_--------_-_-_-----------_--------------------- 56

95. Map arid cross sections of Trinity River Delta showing texture of the sediments._____-_-___--_---_-_- 57

96. Map of the Brazos River Delta in 1964_________________________________----_--------_--------- 57

97. Map and columnar sections of the Brazos River Delta, Tex., showing texture of delta, bottom, and subbottom sediments in 1952___________________________-__________----_-----------_----------- 58

98, 99. Map of Matagorda Bay, Tex., showing 

98. Bathymetry__________________________________________-_-__-__------_------------- 59

99. Texture of the bottom sediments.._________-_-_-_-_-___--_------_---------_------------- 59

100-102. Map of San Antonio Bay, Tex., showing 

100. Bathymetry-_________________________________________-_---__-----------__------ 60

101. Texture of the bottom sediments..._-__-______-___--____-_---_-_----------------------- 61

102. Calcium carbonate content of bottom sediments____________-____--_-_----------------- 61

103-105. Map of Aransas Bay, Tex., showing 

103. Bathymetry.-________________________________ - - 62

104. Texture of the bottom sediments..._____________________-__---__----------------------- 62

105. Calcium carbonate content of bottom sediments_______--__---_-_---_------------------- 63

106. Map of Laguna Madre, Tex., showing bathymetry.__-_-____-__----_----------------------------- 64

107. Geologic cross sections of Laguna Madre, Tex________-________-__---_----_ --------------------- 64
VI CONTENTS

Page 

FIGURES 108, 109. Map of Laguna Madre, Tex., showing 

108. Texture of the bottom sediments-----_-----------------_---_-________________________ 65

109. Calcium carbonate content of the fine fraction of bottom sediments._______________________ 65

110, 111. Map of Baffin Bay, Tex., showing 

110. Bathymetry_____-__.___-__-_- ____ -----------_-----_-________________________ 66

111. Texture of the bottom sediments_-__-----------_-----_-_-__-___._______________________ 66

112-114. Map of the San Francisco Bay system, California, showing 

112. Bathymetry _ _ __________________ 67

113. Texture of the bottom sediments______----_--_-----__-__-_-____________________________ 68

114. Organic carbon content of bottom sediments _--------_-______________________________ 68

115-118. Map of Yaquina Bay, Oreg., showing 

115. Bathymetry ________________________ ____-__--___ _________________________ 70

116. Texture of the bottom sediments_-_--_-----------------_---_-__________________________ 71

117. Organic carbon content of bottom sediments___________________________________________ 71

118. Calcium carbonate content of bottom sediments._ _--_-_---_-_____-____________________ 72

119, 120. Map of Willapa Bay, Wash., showing 

119. Bathymetry___________ _ . _.______________ 73

120. Texture of the bottom sediments.._____________________________________________________ 73

121. Graph showing the relation of organic carbon content to mean grain size of bottom sediments in Willapa

Bay, Wash. ____________ __ ___-_._____._ ____ __ ______________ 74

122. Map of Willapa Bay, Wash., showing organic carbon content of bottom sediments____________________ 74

123-126. Map of Grays Harbor, Wash., showing 

123. Bathymetry._______________ _ _____________________ _________________ 75

124. Texture of the bottom sediments_______--___-_-__------_---____________________________ 75

125. Organic carbon content of bottom sediments___________________________________________ 76

126. Heavy-mineral content of bottom sediments______---__--_---____________________________ 76

127-130. Map of Bellingham Bay, Wash., showing 

127. Bathymetry... ________________ ___ ______________________________________ 77

128. Texture of the bottom sediments____-_____-_-___--_--___---____________________________ 77

129. Wood fragment content of the coarse fraction of bottom sediments.________________________ 78

130. Shell and Foraminifera content of the coarse fraction of bottom sediments_________________ 78

131, 132. Map of Puget Sound, Wash., showing 

131. Bathymetry.__________________-___________________________________________ 79

132. Texture of the bottom sediments-______--_-_-___-_-----_____________-__________________ 79

133-135. Map of Nisqually Delta and Nisqually Reach, Wash., showing 

133. Bathymetry. ____________________________________________________________________ 80

134. Sand (>62 microns) content in bottom sediments of the Nisqually Reach___________________ 81

135. Medium sand (0.25-0.5 mm) content in bottom sediments of the Nisqually Reach__________ 81

136-139. Maps of Deep Inlet, Alaska, showing 

136. Bathymetry.--___--_--_-___-_-_______ ___ _ ________________________________ 82

137. Texture of the bottom sediments.______________________________________________________ 83

138. Organic carbon content in bottom sediments___________________________________________ 83

139. Calcium carbonate content of bottom sediments________________________________________ 84

TABLES

Page 

TABLE 1. Average composition, in percent, of the coarse fraction of sediments in each environment in Moriches Bay,

N. ¥______________________________________________,_____________________________________ 13

2. Physical, mineral, and chemical characteristics of sediments in Florida Bay, Fla______________________ 35
CHARACTERISTICS OF ESTUARINE SEDIMENTS 

OF THE UNITED STATES'

By DAVID W. FOLGER

ABSTRACT

The texture and composition of bottom sediments in the estuarine zones of the United States are a function of the geologic, bathymetric, and hydrologic settings in which they were 

deposited. On the northeast and northwest coasts, where sediment supply has been inadequate to fill many of the deep 

drowned river valleys or glacially scoured estuaries, clay and 

silt in the deep central parts of the bays most commonly grade 

shoreward and seaward into sand. On the Oregon and northern 

California coasts, where both sediment supply and tidal range 

are large, clay and silt are commonly swept from the deep 

channels and deposited on marginal tidal flats. On the gulf 

coast, where tidal ranges are small and where rivers transport 

abundant fine material to the coast, estuaries are generally 

shallow. Silt and clay near the center of these bar-built estuaries and lagoons grade into sand around the margins. 

Deltas are common in many of the gulf coast bays and have, in 

several, prograded across the estuarine zone onto the continental shelf.

Most bottom sediments that accumulate in the estuarine zone 

consist of terrigenous detritus, biogenic debris, and pollutants. 

Organic carbon generally makes up less than 5 percent of the 

bottom sediments except in swampy areas, fjords, or where 

pollutants are abundant. Inorganic constituents are mostly 

quartz, feldspar, and clay minerals. In general, illite and 

chlorite are the most abundant clay minerals on the northeast 

coast; kaolinite predominates on the southeast Atlantic coast 

and in the eastern Gulf of Mexico; and montmorillonite is common along the coasts of the western Gulf of Mexico and the 

Pacific Ocean. Shell debris is locally abundant in many areas 

but is dominant only in areas far from terrigenous sources.

INTRODUCTION 

SCOPE AND PURPOSE OF THE STUDY

The available information concerning the characteristics of sediments deposited in 45 estuaries, lagoons, 

embayments, and deltas of the United States has been

1 Contribution 2482 of the Woods Hole Oceanographlc Institution, 

based on work done under a program conducted jointly by the U.S. 

Geological Survey and the Woods Hole Oceanographlc Institution In 

cooperation with the U.S. Federal Water Pollution Control Administration and financed mostly by the U.S. Federal Water Pollution Control 

Administration.

assembled, summarized, and presented in this report 

(fig. 1); 17 of the areas are on the Atlantic coast, 20 on 

the gulf coast, and eight on the Pacific coast. This 

compilation of summaries represents much of the available data on the estuarine zone and thus provides an 

opportunity to compare coastal sedimentary deposits 

and the processes responsible for them.

This study was undertaken by the U.S. Geological 

Survey and Woods Hole Oceanographic Institution in 

cooperation with the U.S. Federal Water Pollution 

Control Administration as part of the response to 

Public Law 89-753, which instructed the U.S. Secretary of the Interior to assemble, coordinate, and organize all existing pertinent information on sedimentation in estuarine zones, and to identify the problems 

and areas where further research and study are required.

SOURCES OF INFORMATION

Information in this report has been drawn from published sources and unpublished material including 

M.S. theses, Ph. D. theses, and a few raw data that 

mostly deal with organic carbon concentrations and 

clay mineralogy. U.S. Geological Survey water-supply 

papers and U.S. Coast and Geodetic Survey (U.S.C. 

& G. S.) tide tables were used throughout the report 

and therefore have not been cited. For simplicity of 

presentation, source material for each area is listed only 

briefly at the end of the summary section on the area, 

but reference to specific sources is given for the illustrations and complete references are listed at the back of

the report.

FORMAT

The data for each area are presented in the following format: 

Setting

Geology

Bathymetry

Hydrology
CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

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AREA SUMMARIES

Sediment texture

Bottom

Subbottom 

Sediment composition

Organic carbon

Mineralogy

Other 

References

Illustrations that accompany each summary generally represent bathymetry, sediment texture, and 

organic carbon distribution in the bottom sediments. 

Geologic cross sections and maps showing the distribution of calcium carbonate or other mineral constituents 

are included where sufficient data are available.

SETTING

The geologic, bathymetric, and hydrologic characteristics of each area are discussed because each affects directly the composition and distribution of sediment. Specifically, the summary of geology includes 

the type and age of the sedimentary and other rocks 

contiguous with and underlying the area; hydrology 

includes the mean rate of fresh-water inflow, salinity 

distribution, tidal range, and current velocities; bathymetry is presented in feet rather than meters, because most available maps have been adapted or taken 

directly from U.S. Coast and Geodetic Survey charts.

SEDIMENT TEXTURE

Most statistical data concerning sediment texture 

were derived from mechanical analyses of sediment 

samples. In several areas, however, estimates of texture 

are based in part on optical examination. Textural 

classes presented in the illustrations are based mostly 

on sample median and mean diameters and, in a few 

areas, on modal diameters. Where only numerical data 

are available, values have been grouped into classes 

according to a slightly modified form of Inman's 

(1952) classification; where textural data from several 

references are available, the most compatible information has been used. Maps of sediment sorting, skewness, and kurtosis were considered too specific for the 

scope of this report and have not been included.

SEDIMENT COMPOSITION

In most of the studies summarized herein, the organic constituents of sediments were recorded as either 

carbon or nitrogen. Total organic matter (weight loss 

after treatment with hydrogen peroxide) and oxidizable organic matter were also reported. Organic carbon 

and (or) organic matter are, therefore, the only parameters cited in this report that indicate the amount of 

natural organic material and organic pollutants retained by the sediments. Techniques used to measure

organic carbon content include those of Popoff (1927), 

Krogh and Keys (1934), Allisson (1935), Niederl and 

Niederl (1942), Dennen (1957), Walkely-Black (in 

Jackson, 1958, p. 219), and Curl (1962). Gas analyzers 

that were used for these measurements include Leco, 

Beckmann, and Coleman.

The distribution of various mineral species in the 

estuarine zone has been investigated thoroughly in only 

a few areas. Most available data are summarized in the 

text, but for most areas only the distribution of minerals composed of calcium carbonate is presented 

graphically.

ACKNOWLEDGMENTS

Many thanks are due R. H. Meade of the U.S. Geological Survey, who assembled much of the information used in this report and offered helpful suggestions 

and guidance in preparing the manuscript. J. C. Hathaway of the U.S. Geological Survey and Susan Kadar 

of Woods Hole Oceanographic Institution provided 

many useful raw data that were collected during recent joint U.S. Geological Survey-Woods Hole Oceanographic Institution continental shelf surveys. D. S. 

Gorsline of the University of Southern California, H. 

G. Goodell of Florida State University, and B. W. 

Nelson of the University of South Carolina also supplied helpful information. Frances Williams of Woods 

Hole Oceanographic Institution prepared the illustrations.

AREA SUMMARIES

PENOBSCOT BAY, MAINE

SETTING

Geology. Lower and middle Paleozoic metasedimentary rocks and granite are exposed on the islands 

and on the western shore of Penobscot Bay; silicic 

intrusive rocks crop out on the eastern side. Thin 

patchy deposits of Pleistocene glacial till occur mostly 

in depressions and valleys.

Most data concerning sediment distribution in the 

estuary are limited to the western part. The thickness 

of unconsolidated material varies from zero (in areas 

where bedrock is exposed) to a maximum of approximately 150 feet (46 m (meters)) northwest of Vinalhaven Island. Southwest of the island, however, in the 

deepest part of the bay, little sediment has accumulated.

Bathymetry. The smooth bottom near the head of 

the estuary, which is cut by channels 2 to 18 feet (0.6- 

5.5 m) deep and as much as 90 feet (27 m) wide, 

grades southward into predominantly irregular topography. The bay deepens to a maximum depth of about 

540 feet (165 m) southeast of Rockland, and it shoals 

southward from there (fig. 2).

460-197 O - 72 - 2
CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

FIGURE 2. Bathymetry (in feet) of Penobseot Bay, Maine 

(from Osterieher, 1965).

COARSE SAND

a MEDIUM -VERY 

FINE SAND

SILT 

E3 CLAY

FIGUKE 4. Subbottom sediment texture, Penobseot Bay, 

Maine. Interpreted from data of Osterieher (1965). In area 

A, bottom clay grades down into sand; in area B, clay 

predominates to the depth of core penetration; in area C, 

silt or sand at the bottom becomes finer with depth.

Hydrology. Average fresh-water discharge at the 

mouth of the Penobseot River is approximately 470 

m 3/sec (cubic meters per second). Except during 

periods of high runoff, salinity ranges from about 25 

parts per thousand at the head of the bay to 32.5 parts 

per thousand at the mouth; the latter salinity is typical of Gulf of Maine water. The mean tidal range exceeds 10 feet (3m), and currents in the bay are dependent primarily on the tidal cycle. Flow velocities 

at the surface during the ebb tide exceed those during 

flood, while at the bottom the situation is reversed. 

Off Rockland, a maximum current velocity of 1.0 knot 

(50 cm/sec (centimeters per second)) was measured at 

the surface and 0.7 knot (35 cm/sec) at the bottom. 

Higher values are common in restricted channels. During winter months sea states may become severe in unprotected areas of the bay.

FIGUKE 3 (left). Texture and organic carbon content of bottom 

sediments in Penobseot Bay, Maine. Grain-size distribution 

of sediment is based on data of Osterieher (1965); carbon 

values are from Hathaway (1971).
AREA SUMMARIES

SEDIMENT TEXTURE

Bottom. Silty clay and clay predominate throughout most of the estuary, but sand is abundant near 

mouths of rivers and close to shore. The very fine sediment at the head of the bay grades southward into silt 

and subsequently to sand at the mouth of the bay 

(fig. 3).

Subbottom. Only the upper 10 feet (3 m) of section has been cored. At the head of the bay, the predominant silt and clay at the surface grades down into 

sand. Most sediment, however, is silty clay (smallest 

particle size measured is 2 microns) throughout the 

estuary to the depth of core penetration. Silt persists 

with depth only in the mouth of the estuary and in a 

few nearshore areas (fig. 4).

SEDIMENT COMPOSITION

Organic carbon (samples analyzed by the Leco gas 

analyzer). Measurements have been made for only 

five samples (fig. 3). Fine material deposited near the 

mouth of the Penobscot Eiver contains the greatest 

amounts of organic carbon (2.1 percent), and sands 

south of Vinalhaven Island contain less than 1 percent.

Mineralogy. In samples collected at the locations 

shown in figure 3, quartz and feldspar are the most 

abundant minerals (70 percent) in the sediment fraction coarser than silt. In the fine sediment, illite, chlorite, and minor kaolinite make up 70 to 80 percent of 

the minerals present.

Color, burrowing, and age. Silt and clay are mostly 

olive gray; sandy layers are lighter in color. Throughout the bay, wood fragments are common and shell 

detritus is generally confined to thin zones. Burrowing 

is most common near the head of the bay. Wood lying 

close to or in a prominent acoustic subbottom reflector 

10 to 50 feet (3-15 m) below the bottom has been 

dated as 7,390 ± 500 years old.

REFERENCES

E. L. Gory (unpub. data of the U.S. Naval Hydrographic Office, 1959), Hathaway (1971), Ostericher 

(1965).

BOSTON HARBOR, MASSACHUSETTS

SETTING

Geology. Boston Harbor is a topographic basin underlain by Paleozoic clastic sedimentary rocks interbedded with andesitic volcanic rocks. Bedrock surrounding the harbor is covered with as much as 200 

feet (61 m) of glacial drift.

In the harbor itself, glacial detritus ranges in thickness from zero (bedrock is exposed on several islands)

to more than 100 feet (30 m). Overlying Holocene 

black mud, present over most of the area, ranges in 

thickness from less than 10 feet (3m) to more than 

40 feet (12 m).

Bathymetry. The bottom is generally smooth, but 

rises abruptly to the shores of the many islands, which 

consist mostly of drumlin till. The depth averages less 

than 20 feet (6 m), but is maintained by dredging at 

a depth of approximately 40 feet (12 m) in the major 

ship channels (fig. 5).

Hydrology. The Charles, Mystic, and Chelsea 

Rivers contribute fresh water to the inner harbor at 

an approximate rate of 10 to 20 m 3 /sec. Salinities 

range from 1 part per thousand near the river mouths 

to more than 32 parts per thousand between the islands 

farthest from land. The average tidal range is about 

9 feet (2.7 m). The greatest current velocity approaches 2 knots (100 cm/sec) between Deer Island 

and Long Island, but in most areas velocities are less 

than 1 knot (50 cm/sec).

SEDIMENT TEXTURE

Bottom. Clayey silt predominates throughout most 

of the harbor. Coarsest material is limited to areas adjacent to the mainland and to the islands (fig. 6).

SEDIMENT COMPOSITION

Organic carbon (samples analyzed by the Dennen 

(1957) spectrographic technique). In 98 percent of

FIGURE 5. Bathymetry (in feet) of Boston Harbor, Mass, 

(from U.S.C. & G.S. Charts 240 and 246.)
6 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

FIGURE 6. Texture ot bottom sediments in Boston Harbor, 

Mass. Modified from Mencher, Copeland, and Payson (1968).

FIGURE 7. Organic carbon content of bottom sediments in 

Boston Harbor, Mass. Modified from Mencher, Copeland, 

and Payson (1968).

the sediment, organic carbon content ranges from 1 to 

15 percent. Coal and coke fragments predominate in 

the organic matter of the 62- to 1,000-micron size 

fraction, whereas finely divided organic material, 

probably mostly composed of sewage, is concentrated 

in the silt and clay fractions. The distribution of organic carbon is related both to the location of sewage

outfalls and to the water circulation in the harbor

(fig-7).

Mineralogy. Sand consists of 80 to 90 percent 

rounded clear quartz grains and 5 to 10 percent black 

frothy coke and coal fragments. Silt grains are almost 

entirely angular vitreous quartz. The finest material is 

composed of chlorite, illite, and probably muscovite 

plus some quartz and feldspar.

The Holocene mud is soupy to gelatinous and is 

black to dark gray; shell detritus forms 1 to 30 percent of it. Mussel banks are common.

REFERENCES

Bumpus and Day (1952), Bumpus and others 

(1953), Mencher, Copeland, and Payson (1968).

CAPE COD BAY, MASSACHUSETTS

SETTING

Geology. Crystalline rocks (Dedham Granodiorite) 

crop out on the western margin of Cape Cod Bay and 

have been cored on Cape Cod. These rocks are overlain 

by patchy deposits of semiconsolidated and consolidated sediments and a thick section of glacial debris. 

The present configuration of the bay was determined 

largely by glacial processes superimposed on an erosional surface of low relief.

Sediments in the bay include thin, unconsolidated 

Pleistocene and Holocene detritus, glacial till, and 

unconsolidated Tertiary and Cretaceous (?) deposits. 

This sedimentary section ranges in thickness from less 

than 100 feet (30 m) at the western margin of the 

bay to approximately 550 feet (166 m) near the eastern margin.

Bathymetry. The smooth bottom of the bay has an 

average depth of over 100 feet (30 m) and a maximum depth of 220 feet (66 m). A well-defined shelf 

borders the western side; and two northeast-trending 

ridges, probably recessional moraines, extend across 

the bay (fig. 8).

Hydrology. Fresh-water inflow to the bay is very 

small and salinities are essentially the same as those 

in the open sea except in a few protected embayments 

along the coast. Mean tidal range is approximately 

9 feet (2.7m).

SEDIMENT TEXTURE

Bottom. Sand and gravel are most abundant along 

the margins of the bay. To seaward, medium to fine 

sand grades into clay and silt in deeper water. Sand 

occurs locally throughout the area, especially on topographic highs where fine material has been winnowed 

out. Silt and clay are mostly restricted to protected 

embayments near shore and to the deep central part 

of the bay (fig. 9).
AREA SUMMARIES

FIGURE 8. Bathymetry (in feet) of Cape Cod Bay, Mass. 

(from Hough, 1942.)

FIGURE 9. Texture (modified from Hough, 1942) and organic 

carbon content (from Hathaway, 1971) of bottom sediments in Cape Cod Bay, Mass.

SEDIMENT COMPOSITION

Organic carbon (samples analyzed by the Leco gas 

analyzer). Of the five measurements available, four 

were made in areas where sand predominates. Of these 

four, the highest measurement of organic carbon content was 0.6 percent, and the other three were less than 

0.2 percent. The one value in a sample taken in the 

silt-clay area was 1.5 percent.

Mineralogy. Analyses have been made only at the 

five locations shown in figure 9. Coarse sand and gravel 

consist of quartz (90-95 percent) and feldspar (5-10 

percent); fine to medium sands are 75 percent quartz 

and feldspar plus 25 percent illite and chlorite; and 

the clay and silt is 45 percent quartz and feldspar and 

55 percent layered silicates.

Color. The finest sediment is generally brownish 

green to black, and sands are light brown. Shell debris 

is sparse.

REFERENCES

Hathaway (1971), Hoskins and Knott (1961), Hough 

(1942),Oldale (1969).

NANTUCKET BAY, MASSACHUSETTS

SETTING

Geology. Nantucket Bay is bordered on the south 

and east by detritus deposited as part of the terminal 

moraine of Wisconsin Glaciation. A postglacial cuspate 

spit isolates the bay on the northwest from Nantucket 

Sound. Pleistocene (?) marine rocks crop out near the 

east end of Nantucket Island and probably underlie 

the reworked glacial material which covers the entire 

bottom of the bay. Basement depth is approximately 

1,500 feet (460 m).

Bathymetry. Shoals are abundant throughout the 

bay and water depths are generally less than 20 feet 

(6m). The depth reaches a maximum of about 30 feet 

(10 m) in the channel at the harbor entrance (fig. 10).

Hydrology. Only a few small streams flow into the 

bay. Available salinity measurements, however, vary 

little from 31 parts per thousand throughout the entire 

bay. The mean tidal range is about 3 feet (0.9 m). 

Maximum velocities of tidal flow are between 0.6 and 

4 knots (30-200 cm/sec.).

SEDIMENT TEXTURE

Bottom. Gravel, composed of both shell fragments 

and glacial material, occurs near the harbor entrance 

and in the channel that leads into the central harbor. 

Very coarse sand is associated with shoals that extend from cusps on the northwest and southeast sides 

of the bay. Grain size decreases uniformly to silt and 

clay where depths are greater in the widest parts of 

the bay. Material less than 32 microns in diameter 

generally is present in areas deeper than 16 feet (5 m)

(fig. 11).

SEDIMENT COMPOSITION

Organic carbon (samples analyzed with the Leco 

gas analyzer). High concentrations of organic carbon 

(2-3 percent) occur in the deepest areas of the three 

basins. Where eel grass is particularly abundant 

anomalously high values (10-20 percent) apparently
CHARACTERISTICS OF ESTUARINE SEDIMENTS EST THE U.S.

FIGURE 10. Bathymetry (in feet) of Nantucket Bay, Mass. Modified from Lidz (1965).

I E3 MEDIUM SANO

VERY FINE-FINE SANo 

SILT

FIGURE 11. Texture of bottom sediments in Nantucket Bay, Mass. Modified from Lidz (1965).

FIGURE 12. Calcium carbonate content (in percent) of bottom sediments in Nantucket Bay, Mass, (from Lidz, 1985).
AREA SUMMARIES 9

may be present, but most are less than 3 percent. Sand, 

which covers most of the bottom, generally contains 

less than 1 percent organic carbon.

Mineralogy. Quartz constitutes approximately 90 

percent and feldspar 10 percent of the light-mineral 

fraction. Heavy minerals, mostly magnetite and ilmenite, make up a maximum of 3 percent of the total 

assemblage. Layered silicates, in contrast to their 

abundance in most bays and estuaries in the area, are 

notably sparse. Carbonates that consist mostly of large 

shell fragments and Foraminifera are most abundant 

in the silts and clays and locally in gravel (fig. 12).

Color. Sediment color varies from white to light 

gray in quartz sands to dark greenish gray in muds. 

A reddish color in some sands may be relict or may be 

due to staining by iron-rich water flowing into the bay 

from contiguous swamps.

REFERENCES

Lidz (1965), Oldale (1969), D. W. Folger and L. G. 

Toner (unpub. data, 1970).

BUZZARDS BAY, MASSACHUSETTS

SETTING

Geology. Thick glacial deposits overlie the Dedham 

Granodiorite which crops out intermittently on the 

northwestern shore of Buzzards Bay. A terminal moraine of Wisconsin Glaciation forms the Elizabeth 

Islands and isolates the bay from Vineyard Sound. 

Few subsurface data are available within the bay. 

Basement was cored at a depth of about 300 feet (90 

m) below the bottom in Woods Hole Harbor. Geophysical profiles within the bay itself indicate that 

crystalline rocks are present between about 30 and 

200 feet (9-60 m) below the bottom. Most of the sedimentary material is probably Pleistocene glacial debris, 

but available seismic velocity data do not preclude the 

presence of older strata. No data are available on the 

thickness of Holocene sediments.

Bathymetry. Most of the bay is less than 50 feet 

(15 m) deep, but depressions near the mouth reach a 

depth of 140 feet (42 m). The dissected, hummocky 

topography on the northwest side of the bay becomes 

smoother with increasing distance from the mainland 

(fig. 13).

Hydrology. Fresh-water inflow from a few small 

streams on the mainland is small. Variations in salinity are accordingly also small and generally range 

from 29.5 to 32.5 parts per thousand. Semidiurnal

FIGURE 14 (right). Texture (modified from Moore, 1963) and 

organic carbon content (from Hathaway, 1971) of bottom sediments in Buzzards Bay, Mass.

FIGURE 13. Bathymetry (in feet) of Buzzards Bay, 

Mass, (from Moore, 1963).

EXPLANATION

GRAVEL G23 MEDIUM SAND

IO) VERY COARSE SAND I" :l FINE SAND

C3 COARSE SAND EI3 SILT AND CLAY

 -/.ORGANIC CARBON
10 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

tides have a range of about 3 to 4 feet (0.9-1.2 m). 

Tidal currents in the bay are mostly less than 1 knot 

(50 cm/sec). Velocities are higher only in channels 

between islands on the margin of the bay.

SEDIMENT TEXTURE

Bottom. The sediments in the southeastern part of 

the bay where topography is smoothest are primarily 

silts and clays. Fine detritus has also been trapped 

near shore in embayments. The complex distribution 

of sand is apparently due to current and wave action. 

Gravel occurs near shore in shallow water (fig. 14).

SEDIMENT COMPOSITION

Organic carbon. The total organic content in 20 

sediment samples collected in 1934 averaged approximately 2 percent. The technique used to obtain this 

value was not reported.

Six recent measurements (Leco gas analyzer) are 

less than 0.3 percent organic carbon in sand samples 

and range from 0.8 to 1.7 percent in silt and clay samples (fig. 14).

Mineralogy. In the few samples analyzed, sand is 

composed of quartz (as much as 90 percent) and feldspar (as much as 30 percent). Illite makes up approximately 50 percent of the clay and silt.

REFERENCES

Hathaway (1971), Hough (1940), Moore (1963), 

Murray (1968), Oldale (1969).

NARRAGANSETT BAY, RHODE ISLAND

SETTING

Geology. Narragansett Bay is located in a structural depression (Narragansett basin) filled with Carboniferous sedimentary and metasedimentary rocks. 

Precambrian and lower Paleozoic rocks crop out on the 

western shore. The position of the three main channels 

is controlled by bedrock valleys.

Bathymetry. North of Prudence Island the smooth 

bottom averages 20 feet (6m) in depth. Two dredged 

channels are maintained at a depth of approximately 

24 feet (7 m). To the south topography is rougher, 

especially in the narrow channels (fig. 15). A maximum depth of more than 150 feet (45 m) occurs in the 

narrow channel at the bay mouth, between Conanicut 

Island and Newport Neck.

Hydrology. The volume of fresh water flowing into 

the bay is not great. Mean flow rate for the Taunton 

Eiver is approximately 29 m 3 /sec. Measurements of 

salinity vary between approximately 15 parts per 

thousand at Fall River to 33 parts per thousand near 

the bay mouth. Tidal current velocities are generally

SEA LEVEL -

IOO-

^200-

300-

400-

A' B B'

UNCONSOLIDATED SEDIMENT,^ 

(ESTUARINE SEDIMENT, /r 

OUTWASH, TILL) / =

CONSOLIDATED SEDIMENT 

(CARBONIFEROUS STRATA)

CRYSTALLINE BASEMENT

-SEA LEVEL

-ZOO

-400

-600 

r-8OO

-1000

FIGURE 15. Bathymetry (in feet) of Narragansett Bay, R.I. 

(from McMaster, 1960). Columnar sections A-A' and 

B-B' are based on geophysical data of Birch and Dietz 

(1962).

between 0.5 and 1.0 knot (25-50 cm/sec), but in narrow channels they approach 3 knots (150 cm/sec).

SEDIMENT TEXTURE

Bottom. In the upper bay, silts and clays predominate in the deeper area whereas sand is more abundant 

near shore. Clay, however, rarely constitutes more than 

half the total sediment, and gravel, though ubiquitous, 

is rarely volumetrically important. Sand predominates 

in all three passages from the southern part of the bay
AREA SUMMARIES 11

EXPLANATION I 

 % ORGANIC CARBON

41°45' 

FIGURE 16. Texture and organic carbon content of bottom 

sediments in Narragansett Bay, R.I. Texture data 

modified from McMaster (1960); carbon data from 

Hathaway (1971).

to Ehode Island Sound (fig. 16).

Subbottom. Based primarily on a few test borings, 

Holocene estuarine sediments are 10 to 65 feet (3-20 

m) thick. Locally, plant remains and shell fragments 

are abundant. Poorly sorted underlying unconsolidated 

sediment, approximately 60 to 160 feet (18-50 m) 

thick, is probably made up principally of glacial till 

and outwash. The thickness of Carboniferous basement 

strata, based on seismic refraction measurements (fig. 

15), ranges from approximately 160 feet (50 m) to at 

least 1,000 feet (333 m).

SEDIMENT COMPOSITION

Organic carbon (samples analyzed by the Leco gas 

analyzer). Few measurements of organic carbon content are available. The greatest value (2.3 percent) 

was recorded from the deepest part of Mt. Hope Bay. 

The only other values available for sediments of the 

upper estuary are 1.8 percent and 1.6 percent. In 

Sakonnet Passage and West Passage, values for two

samples are 1.1 percent and 1.7 percent, respectively 

(fig. 16).

Mineralogy. In the northern part of the bay, layered silicates make up between 50 and 70 percent of the 

minerals present in the few samples analyzed. Quartz 

and feldspar make up the remainder. In one sample 

collected in West Passage, where coarser textured sediment predominates, quartz and feldspar constitute 70 

percent of the minerals.

REFERENCES

Berg (1963), Birch and Dietz (1962), Hathaway 

(1971), McMaster (1960), Towe (1959), Upson and 

Spencer (1964), Wilson (1967).

MORICHES BAY, NEW YORK

SETTING

Geology. The irregular shoreline on the northwest 

side of Moriches Bay consists of detritus deposited as 

part of the outwash plain of Wisconsin Glaciation. On 

the southeast the bay is isolated from the Atlantic 

Ocean by a barrier island which is periodically cut by 

an inlet.

Bathymetry. At high tide, the flat-floored bay has 

an average depth of 4 feet (1.2 m) and a maximum 

depth of less than 8 feet (2.4 m). A delta formed by 

material transported landward through Moriches Inlet 

divides the bay into two basins. Irregular shoals that 

project from the barrier island are washover fans and 

former inlet deltas (fig. 17).

Hydrology. Sluggish water circulation within the 

bay is controlled by tides and runoff. Waters are well 

mixed vertically. Most drainage is introduced by the 

Forge River, but seepage is responsible for most fresh 

water present in the bay. Average salinity when 

Moriches Inlet is open is 27 parts per thousand, and 

when closed, about 12 parts per thousand.

SEDIMENT TEXTURE

Bottom. Clayey silt is present in the deepest, central parts of the lagoon and is surrounded by a narrow marginal zone consisting of a mixture of sand, silt, 

and clay. Shallow areas adjacent to the barrier islands 

are sand. Clayey silt covers much of the bottom of 

the Forge River estuary (fig. 18).

SEDIMENT COMPOSITION

Organic matter (dry weight loss after sample digestion with H2O2 ). Lowest values of organic matter 

content, which occur near shore in sand, increase toward the center of the lagoon in clayey silts. Highest 

concentrations (28.7 percent maximum in Seatuck 

Cove) are present in the drowned stream channels 

where duck farms are located (fig. 19).

460-197 O - 72 - 3
12 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

FIGURE 17. Bathymetry (in feet) of Moriches Bay, N.Y. (from Nichols, 1964).

ATLANTIC OCEAN

FIGURE 18. Texture of bottom sediments in Moriches Bay, N.Y. Modified from Nichols (1964).
AREA SUMMARIES 13

ATLANTIC OCEAN

FIGURE 19. Total organic matter content (in percent) of sediments in Moriches Bay, N. Y. (from Nichols, 1964).

Mineralogy. The principal clay minerals illite, 

kaolinite, and montmorillonite occur respectively in 

the following ratios: 7-3-trace in an estuary, 3-7-0 in 

a cove, 8-2-trace in midbay, and 8-0-2 on a barrier 

shoal. In the sand fraction, components are: 90 percent 

quartz, 2 percent muscovite, 3 percent plagioclase feldspar and small amounts of apatite, biotite, potash feldTABLE 1. Average composition, in percent, of the coarse fraction of 

sediments in each environment in Moriches Bay, N.Y.

[Modified from Nichols (1964)]

Midbay _ _ _

Open cove ___

Estuary _ _ ____

Bay mar gin __

Midbay _____

Open cove _ _

Estuary

Bay margin. ___.

Foraminif2. 3 0. 06 3. 7

5. 6 .1 8. 5

________________ 33.2

.5 .05 .1

Mica

________________ 13.7

________________ 20.2

________________ 7.5

________________ .5

Minerals

Light Heavy

78. 8 0.

60.2

57.8

97. 8 1.

Ferruginous Diatoms 

aggregates

0.2 0.

3. 8 1.

. 3

. 2

8

6

8

5

0

3

4

spar, chlorite, chert, and rock fragments. Other components of sediment coarser than 0.062 mm are shown 

in table 1. Heavy minerals (as much as 4 percent in 

inlets) include magnetite, garnet, tourmaline, kyanite, 

and hornblende.

Internal structures. Sands on the margins of the 

estuary are homogeneous and contain no layering. In 

midbay, indistinct mottling of the sediments reflects 

the effects of burrowing organisms.

Color, pH, Eh. In midbay, clayey silts have an 

average pH of 7.8 at the surface and 7.0 at a depth of 

1 cm (centimeter). Eh below the surface ranges from 

-0.5 to -2.5 volts. In drowned stream channels where 

organic material is most abundant, pH values are 6.7 

at the surface and 6.2, 6.4, and 6.4 at depths of 1 cm, 

15 cm, and 30 cm, respectively. These sediments are 

generally black, have an H2S odor, and contain small 

pyrite grains. Sands on the margin of the bay have 

neutral pH and positive Eh.

Coarse fraction. Components of the coarse fraction 

of the sediments are shown in table 1.

REFERENCE

Nichols (1964).
14 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

NEW YORK HARBOR, NEW YORK AND NEW JERSEY

SETTING

Geology. Glacial debris, probably mostly part of 

the terminal moraine of Wisconsin Glaciation, borders 

the Lower Bay and Raritan Bay on the northwest 

(Staten Island) and on the south along segments of 

the New Jersey coastline (fig. 21). Cretaceous deposits 

crop out along cliffs on the southwestern shore. Sandy 

Hook is a postglacial spit. In the Upper Bay and the 

Hudson River, Paleozoic crystalline rocks crop out on 

the east and Triassic intrusives and sedimentary rocks 

crop out on the west. Unconsolidated sediments that 

underlie the harbor probably consist mostly of Cretaceous, glacial, and Holocene deposits and range in

thickness from zero to approximately 1,000 feet (fig. 

20).

Bathymetry. Dissected topography around the 

margin of the Lower Bay grades into the smooth bottom which is present over much of the central area. 

North of the Narrows, rapid shoaling requires frequent 

dredging. Depths are maintained between 40 and 60 

feet (12-18 m) (fig. 21).

Hydrology. The Hudson River accounts for 90 percent of the total fresh-water inflow of 740 m 3/sec into 

the bay. The Raritan and Passaic Rivers bring in most 

of the remaining 10 percent. In the Upper Bay the 

mean tidal range is about 3 to 4 feet (0.9-1.2 m); flood 

currents in the area flow at velocities of 0.8 to 1.8 

knots (40-90 cm/sec) and ebb currents flow from 0.6

FIGURE 20. Depth (in feet) below sea level to crystalline 

rock or consolidated sediments in New York Harbor, 

N.Y. and N.J. (from Crawford and others, 1951).

FIGURE 21. Bathymetry (in feet) of New York Harbor, 

N.Y. and N.J. (from U.S.C. & G.S. Chart 369).
AREA SUMMARIES 15

to 2.5 knots (30-125 cm/see). South of Manhattan the 

estuary is well mixed vertically; to the north it is only 

partly mixed.

SEDIMENT TEXTURE

Available data concerning sediment distribution in 

the area are sparse. Most of the analyzed samples used 

in this study were collected in Earitan Bay with a 

Petersen grab sampler. A few samples were taken in 

the northern part of the Lower Bay and in the Hudson 

Eiver off Manhattan.

Bottom. Sand is present throughout most of the 

Lower Bay. Silt and clay are predominant near the 

mouths of the Raritan and Hudson Rivers and in 

an area west of Sandy Hook. The median diameter of

most of the sand in Raritan Bay ranges from 0.1 to 

0.5 mm (millimeter) (fine to medium sand), and that 

of finer material near Sandy Hook is about 0.03 mm 

(coarse silt). A few analyzed sediment samples from 

the Hudson River off Manhattan have median diameters between 0.008 and 0.060 mm, encompassing almost the whole silt range (fig. 22).

Subbottom. North of the Battery, which is at the 

south end of Manhattan, the few analyzed samples did 

not show significant textural variations to a depth of 

7 feet (2m) below the bottom.

FIGUEE 22. Texture of bottom sediments in New York 

Harbor, N.Y. and N.J. Modified from DeFalco (1967), 

Duke (1961), and Panuzio (1965).

FIGURE 23. Total organic matter and organic carbon content of bottom sediments in New York Harbor, N.Y. 

and N.J. Data on total organic matter content is modified 

from DeFalco (1967); organic carbon content in the Hudson River from Panuzio (1965); and concentrations of 

organic carbon elsewhere from Hathaway (1971).
16 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

SEDIMENT COMPOSITION

Organic matter. Values for total organic matter 

measured in sediment samples of Raritan Bay were 

based on dry weight loss after treatment with H2O2 

(fig. 23). A few values for organic carbon measured 

by the Leco gas analyzer are also shown. The method 

used for measuring organic carbon concentrations in 

the Hudson River was not specified.

The highest concentrations of organic matter in the 

Raritan and Lower Bays are associated with the silt 

and clay near the mouth of the Raritan River and 

near Sandy Hook. Sands throughout the areas generally contain less than 1 percent organic matter. The 

highest values (5-12 percent organic carbon) were reported in shoal areas in the Hudson River. Much of 

the coarse organic debris consists of amphipod tubes, 

wood, and coal.

Mineralogy. Over 90 percent of the sand in the few 

samples analyzed consisted of quartz and plagioclase 

feldspar. Illite, montmorillonite, and quartz predominate in the finer material.

Carbonate. Shells and shell fragments (mostly 

oyster shells) make up 0.1 to 40 percent of the sediment.

REFERENCES

Crawford, Powers, and Backus (1951), DeFalco 

(1967), Duke (1961), Hathaway (1971), Panuzio 

(1965), U.S. Public Health Service (1965), Wilson 

(1967).

CHESAPEAKE BAY, MARYLAND AND VIRGINIA

SETTING

Geology. Chesapeake Bay lies totally within the 

Atlantic Coastal Plain. Sedimentary strata underlying 

the bay and exposed on its shores consist mostly of unconsolidated gravel, sand, clay, and marl of Cretaceous, Tertiary, and Quaternary age. The complex 

dendritic drainage system of the Susquehanna River 

was drowned in the postglacial advance of the sea; this 

formed the largest estuary on the Atlantic coast. The 

shoreline is a classic example of a ria or youthful coast.

Bathymetry. The bay has a mean depth of less than 

25 feet (7.6 m). The deepest area (about 175 feet or 

53 m), between the mouths of the Chester and Choptank Rivers, is part of a sinuous channel that extends 

the length of the bay and may be part of the unfilled 

ancient Susquehanna River valley (fig. 24).

Hydrology. The Susquehanna River accounts for 

about half the average total fresh-water inflow (2,000 

ms/sec) brought to the bay by nine main rivers. Salinity ranges from zero at the head of the estuary to 

about 33 parts per thousand at the mouth. Average 

tidal range is about 3 feet (1m) at Norfolk and declines to about 1.5 feet (0.5 m) near the Potomac River 

mouth. Current velocities may be as high as 3 knots 

(150 cm/sec) but most often are less than 1 knot (50 

cm/sec). Water is generally saturated with dissolved 

oxygen except in summer when it becomes depleted in 

the deep areas.

SEDIMENT TEXTURE

Bottom. Data are taken mostly from Ryan's (1953) 

reconnaissance map that was based on analyses of 209 

bottom samples collected during 15 transects of the 

bay. The results of more recent studies of sediment 

texture, (Biggs, 1967; Harrison and others, 1964; Virginia Institute of Marine Science, 1967; Young, 

1968) are incorporated onto Ryan's map on the basis 

either of the median or arithmetic mean sediment diameter reported (fig. 25). Clayey and sandy silt, present over most of the central parts of the bay, is 

bounded toward shore by fine to medium sand. Gravel 

and coarse sand are sparse except near the mouth of 

the bay.

SEDIMENT COMPOSITION

Organic carbon (samples analyzed with the Leco gas 

analyzer or by the Niederl and Niederl (1942) techniques). Closely spaced samples have been analyzed 

only in the areas off the Patuxent River mouth and 

between the mouths of the Rappahannock and Potomac 

Rivers. Others, located along the bay axis, were collected at about 10-nautical-mile (16 km (kilometers)) 

intervals. Highest concentrations of organic carbon (7 

percent)) occur in sediments of the northern bay (fig. 

26). Coal fragments are abundant on the bottom for a 

distance of approximately 20 miles (37 km) south of 

the Susquehanna River mouth; these probably account 

in part for the high values. South of the Patuxent 

River, few samples contain more than 2 percent organic carbon.

Mineralogy. The sand fraction of the sediment consists mostly of quartz, and equal amounts of feldspar 

occur locally. In the finer material, layered silicates 

(mostly illite, chlorite, and mixed-layer clay) locally 

constitute as much as 50 percent of the minerals. Rock 

fragments are abundant in a few places, mostly near 

the bay mouth. A wide variety of heavy minerals the 

most common of which include hornblende, garnet, and 

hypersthene generally constitute less than 3 percent 

of the sediment by volume.

pH, Eh, and color. In sediments located between 

the mouths of the Rappahannock and Potomac Rivers, 

pH in surface sediments ranges from 7.0 to 8.3. Below 

the bottom, values range from 6.8 to 8.3. The lowest 

values occur in black soupy mud common along the 

axis of the central bay. Iron sulfide minerals appar-
AREA SUMMARIES 17

E- 1 GRAVEL-COARSE SAND 

E23 MEDIUM SAND

FINES VERY FINE SAND 

£4 CLAYEY 8 SANDY SILT

FIGURE 24. Bathymetry (in feet) of Chesapeake Bay, Md. 

and Va. (from Ryan, 1953).

FIGURE 25. Texture of bottom sediments in Chesapeake 

Bay, Md. and Va. Modified from Ryan (1953), Biggs 

(1967), Harrison and others (1964), Virginia Institute of 

Marine Science (1967), Young (1968).
18 CHARACTERISTICS OF ESTUARINE. SEDIMENTS IN THE U.S.

ently are responsible for the black color. Eh values in 

the top inch of black sediment are commonly lower 

than 150 millivolts.

REFERENCES

Biggs (1967), Harrison, Lynch, and Altschaeffl 

(1964), Hathaway (1971), Powers (1954, 1957), 

Pritchard (1952), Eyan (1953), Schubel (1968), Virginia Institute of Marine Science (1967), Wilson 

(1967), and Young (1968).

RAPPAHANNOCK RIVER, VIRGINIA

SETTING

Geology. The estuary channel of the Bappahannock River cuts into Quaternary, Tertiary, and Cretaceous sedimentary rocks of the Atlantic Coastal 

Plain. Most of the sediment that is presently accumulating here is transported by the Rappahannock River 

from the weathered crystalline rocks of the Blue Ridge 

and Piedmont provinces.

Bathymetry. In the lower estuary (fig. 27), shallow water on the margins deepens rapidly into the 

narrow central channel where water depths reach almost 80 feet (24 m). In the upper estuary, depths 

range from 20 to 40 feet (6-12 m).

Hydrology. Fresh-water inflow (?« 70 m3/sec) is 

primarily derived from the Rappahannock River. Salinity increases from an average of 1 part per thousand at Tappahannock to 18 parts per thousand at the 

mouth of the estuary in the summer. The mean tidal 

range is about 1.1 feet (0.3 m) at the mouth and 2.3 

feet (0.7 m) near the head. The maximum tidal currents observed are 1.4 knots (70 cm/sec) at ebb tide 

and 1.1 knots (55 cm/sec) at flood tide. Velocities decrease downstream. The water has a pH that ranges 

from 6.5 to 7.0.

SEDIMENT TEXTURE

Bottom. Distribution of sediment (fig. 28) is interpreted from descriptions of sediments collected during nine transects of the estuary. No quantitative data 

such as the median diameter are available. Sand is 

most abundant in the estuary along the margin and 

over a wide area near the mouth. Silt in the deep channel near the mouth gives way to clay with increasing 

distance upstream.

Subbottom. Numerical textural data on subbottom 

sediments are unavailable. The geologic cross section 

near Grey's Point (fig. 28) is based on descriptions 

of sediments penetrated by test borings drilled prior 

to the construction of a bridge.

FIGURE 26. (left) Percentage of organic carbon content of 

bottom sediments in Chesapeake Bay, Md. and Va. , from 

Hathaway (1971); A, from Harrison and others (1964), Virginia Institute of Marine Science (1967), and Young (1968); 

contours from Biggs (1967).
AEEA SUMMARIES 19

\ TAPPAHANN

\

/ \

FIGURE 27. Bathymetry (in feet) of the Rappahannock 

River Estuary, Va. (from U.S.C. & G.S. Charts 534 

and 535).

FIGURE 28. Texture of bottom sediments in Rappahannock River Estuary, Va. Adapted from sediment 

descriptions of Ellison, Nichols, and Hughes (1965). 

Geologic cross section modified from Hack (1957).

SEDIMENT COMPOSITION

Organic carbon (samples analyzed by the Leco gas 

analyzer). Concentrations of organic carbon in 10 

samples collected in the estuary are shown in figure 29. 

Values range from 1.3 to 2.7 percent.

Mineralogy. Detailed studies of minerals in the 

sediments have been confined mostly to the layered 

silicates. Kaolinite, illite, montmorillonite, and vermiculite are abundant in the upper part of the estuary and 

become rather evenly mixed between 20 and 40 nautical 

miles (37-74 km) upstream from the mouth. Chlorite 

and feldspar are confined to the lower estuary, where 

most of the layered silicates decline in abundance.

REFERENCES

Boon and Maclntyre (1968), Bue (1970), Ellison, 

Nichols, and Hughes (1965), Hack (1957), Nelson 

(1960), Nichols and Poor (1967).

ALBEMARLE SOUND, NORTH CAROLINA

SETTING

Geology. Coastal Plain sedimentary rocks of Quaternary age are exposed on the mainland shores of 

Albemarle Sound, except on the western shore where 

the Yorktown Formation of Miocene age borders the 

area. An offshore bar which is part of the North Carolina Outer Banks forms the seaward margin.
20 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

TAPPAHANNOCK

Nautical Mil»s

FIGURE 29. Organic carbon content (in percent) of bottom 

sediments in the Rappahannock River Estuary. Data 

from Boon and Maclntyre (1968).

Bathymetry. Depths increase rapidly with distance 

from shore to the relatively flat floor of the sound (fig. 

30). The maximum depth is almost 30 feet (9m) but 

most of the bottom of the central area of the bay is 

about 18 feet (5.4 m) deep. In Croatan Sound, which 

connects Albemarle Sound with Pamlico Sound to the 

south, depths are less than 12 feet (3.6 m).

Hydrology. Fresh-water inflow from the Eoanoke 

and Chowan Rivers averages about 380 m3/sec. Average salinities range from zero at the western end of 

the sound to about 5 parts per thousand at the eastern 

end. Values are normally 10-15 parts per thousand in 

Croatan Sound, except in the spring when concentrations drop to 3 parts per thousand. Tidal influence on

the water level is slight due to the narrow channels 

that connect the bay with the open sea.

SEDIMENT TEXTURE

Bottom. Most of the available data on sediment 

texture were obtained by microscopic estimates of 

grain size. The coarsest sediments, which consist mostly of fine to medium sand, are concentrated around the 

margins of the sound and grade bayward to silt and 

clay in the deepest areas. Some coarse material is probably carried into the sound by the Roanoke River but 

most is derived from erosion of Quaternary sediments 

on the shores of the sound. Widespread sand deposits 

at the eastern end of the bay and in Croatan Sound 

were probably derived in large part from the Outer 

Banks (fig. 31).

SEDIMENT COMPOSITION

Organic carbon (samples were analyzed by the Leco 

gas analyzer). Eleven samples were analyzed for 

concentrations of organic carbon; 0.1 to 1.4 percent was 

found in sands, and 1.6 to 2.6 percent was found in 

silts and clays of the central bay. Values exceeding 3 

percent were found in sediments in the Chowan River 

and in a smaller drowned stream channel that probably receives much organic matter from adjacent 

swamps. One sample of peat recovered from the Alligator River contained 28 percent organic carbon (fig. 

31).

Mineralogy. Quartz is the most abundant constituent of the sand; feldspars are rare and constitute less 

than 1 percent. Heavy minerals include amphiboles, 

epidote, garnet, ilmenite, magnetite, pyroxenes, staurolite, and zircon. The fine fraction consists mostly of 

kaolinite, illite, dioctahedral vermiculite, and chlorite. 

Kaolinite, which accounts for as much as 80 percent 

of the fine fraction, is relatively more abundant here 

than in any other estuary from which sediments have 

been analyzed on the Atlantic coast. Chlorite is present in concentrations as high as 20 percent and is 

apparently being transported into the estuary from 

the continental shelf.

Carbonate minerals make up less than 0.3 percent 

of the 11 samples analyzed.

Bottom sediments here are more yellowish than 

those in other estuaries on the Atlantic coast. The 

color is apparently due to influx of fine material carried to the area by the Roanoke River prior to the 

construction of the Kerr Reservoir dam, which now is 

located about 90 nautical miles (160 km) west-northwest of the sound.

REFERENCES

Hathaway (1971), Pels (1967), Smith (1967), 

Stanley (1969), Wilson (1967).
AREA SUMMARIES 21

EXPLANATION

MEDIUM SAND

FINE SAND

VERY FINE SAND

SILT

CLAY

% ORGANIC CARSON

FIGURE 30. Bathymetry (in feet) of Albemarle Sound, N.C. (from Pels, 1967).

FIGURE 31. Texture (modified from Pels, 1967) and organic carbon content (from Hathaway, 1971) of bottom sediments in

Albemarle Sound, N.C.
22 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

PAMLICO SOUND, NORTH CAROLINA

SETTING

Geology. West of Pamlico Sound, Quaternary sand 

and clay overlie Tertiary and Cretaceous sediments of 

the Atlantic Coastal Plain. A postglacial barrier island 

system, broken by inlets, isolates the bay from the 

Atlantic Ocean.

Bathymetry. Bluff Shoal (fig. 32) divides the sound 

into two broad basins. Bottom topography in the 

northern area dips smoothly toward the center to a 

maximum depth of approximately 24 feet (7 m). In 

the southern part, shoals project from the western 

shore well into the bay. A tidal delta extends into the 

sound from Ocracoke Inlet (fig. 32).

Hydrology. Average fresh-water inflow to the 

southern part of the sound from the Neuse and Pamlico Rivers is 290 m3 /sec. Salinities at the mouths of 

these rivers is most often between 10 and 15 parts per 

thousand. To the north, inflow to Albemarle Sound

from the Roanoke and Chowan Rivers averages 380 

mVsec. Some of this fresh water enters Pamlico Sound 

and reduces the salinity near Roanoke Island to a 

minimum of about 3 parts per thousand in the spring. 

Salinities at the inlets are generally between 26 and 33 

parts per thousand. Currents within the sound are controlled mostly by wind and are generally less than 0.5 

knot (25 cm/sec). Velocities are as much as about 2 

knots (100 cm/sec) in the inlets. Water is slightly 

acidic in the western part of the sound adjacent to 

swamps and becomes slightly alkaline to the east.

SEDIMENT TEXTURE

Bottom. Fine sand covers most of the bottom. Toward the central deep area of the northern basin, silt 

becomes abundant; whereas in the southern part, the 

finer sediments are confined mostly to the channels that 

extend into the bay from the river mouths. Medium 

sand covers most shoals and extends basinward from 

inlets as tidal-channel deltas and from the barrier

FIGUEE 32. Bathymetry (in feet) of Pamlico Sound, N.C. 

(from Pickett, 1965).

FIGURE 33. Texture of bottom sediments in Pamlico 

Sound, N.C. (from Pickett, 1965).
AREA SUMMARIES 23

islands as washover fans (fig. 33).

Subbottom. No quantitative data are available. 

Cores were taken to a maximum depth of 1 foot (0.3 

m). Sediments seem to be fairly homogeneous to that 

depth in the central part of the bay and near river 

mouths.

SEDIMENT COMPOSITION

Organic carbon. Concentrations shown by the 

shaded areas in figure 34 are based on analyses by the 

Walkely-Black (in Jackson, 1958) method. The discrete values presented were obtained with the Leco gas 

analyzer. Both methods reveal a general increase in 

carbon concentration toward the center of the northern 

part of the bay and toward the axes of the drowned 

Neuse and Pamlico River channels where the finer 

sediment is concentrated. Most of the organic material

is apparently due to indigenous biologic activity, although some peat evidently underlies a thin veneer of 

sand at the southern end of the bay.

Mineralogy. The sand fraction is mostly composed 

of quartz. Kaolinite content decreases to the east with 

increasing distance from the river source areas, whereas illite content increases. Chlorite and a trace of 

montmorillonite are also present. Heavy minerals 

make up about 1 percent of the coarse fraction and 

include ilmenite, epidote, garnet, and hornblende. 

Fifty percent of the opaque fraction consists of ilmenite. Garnet content decreases westward from its 

apparent source, the barrier islands.

Calcium carbonate. Highest concentrations of calcium carbonate, mostly shell detritus, are associated 

with the fine sediments in the northern basin and near 

the river mouths, and with the medium sands of tidalchannel deltas at inlets (fig. 35).

FIGURE 34. Oxidizable organic matter and organic carbon 

content of bottom sediments in Pamlico Sound, N.C. 

Oxidizable organic matter data are from Pickett (1965) ; 

organic carbon data are from Hathaway (1971).

FIGURE 35. Calcium carbonate content of bottom sediments in Pamlico Sound, N.C. (from Pickett, 1965).
24 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

REFERENCES

Bue (1970), Duane (1962), Hathaway (1971), 

Pickett (1965), Pickett and Ingram (1969), Koelofs 

and Bumpus (1954), Williams and others (1967), 

Wilson (1967).

CORE SOUND, NORTH CAROLINA 

SETTING

Geology. Core Sound is flanked by sand and clay 

of Pleistocene and Holocene age which overlie the unexposed Yorktown Formation of Miocene age. Core 

Banks, a series of post-Pleistocene barrier islands, isolate the sound from the Atlantic Ocean.

Bathymetry. Many shoals are present around the 

margin and in the central area of the bay (fig. 36). 

Mean depth is between 3 and 4 feet (0.9-1.2 m) and 

the maximum depth is 11 feet (3.3 m).

Hydrology. Brackish water in the sound is probably derived mostly from Pamlico Sound immediately 

to the north. Salinities range from about 25 parts per 

thousand north of Cedar Island to 35 parts per thousand near the southern margin of the area shown in 

figure 36. Tidal range is 0 to 3 feet (0.9 m), depending 

on wind conditions. Currents in the inlets may attain 

1 knot (50 cm/sec), but water motion within the bay 

is generally sluggish.

SEDIMENT TEXTURE

Bottom. Texture of bottom sediments was evaluated by mechanical analysis and microscopic examination of samples. Most of the bottom is covered by fine 

sand. Medium sand is only abundant near the barrier 

island and on some shoals near the shore margin. Silt 

is concentrated only in the deepest parts of the bay 

center and in the protected mouths of creeks (fig. 37).

SEDIMENT COMPOSITION

Mineralogy. Light minerals in the sand fraction 

consist mostly of quartz with a trace of feldspar. 

Heavy minerals, mostly magnetite and zircon, make up 

less than 1 percent of the sand. Carbonate concentrations range from less than 3 percent near the barrier 

islands to 12 percent south of Cedar Island where 

shells and shell debris are most abundant (fig. 38).

REFERENCE

Skean (1959).

NEWPORT RIVER ESTUARY, NORTH CAROLINA

SETTING

Geology. Quaternary sand and clay of the Atlantic 

Coastal Plain are exposed in cliffs 5 to 15 feet (1.5- 

4.5 m) high around much of the Newport River Estuary.

FIGURE 36. Bathymetry (in feet) of Core Sound, N.C. (from Skean, 1959).
AREA SUMMARIES 25

EXPLANATION

KffffS MEDIUM SAND

FINE SAND

SILT

FIGURE 37. Texture of bottom sediments in Core Sound, N.C. (from Skean, 1959).

FIGURE 38. Calcium carbonate content (in percent) of bottom sediments in Core Sound, N.C.

(from Skean, 1959).
26 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

Bathymetry. West of Core Creek most of the flat 

estuary bottom is less than 6 feet (1.8 m) deep. East 

and south of Core Creek the bathymetry is complicated by natural and dredged channels, which reach a 

maximum depth of about 18 feet (5.4 m). Shallow 

water covers oyster and mussel reefs near the head of 

the estuary (fig. 39).

Hydrology. No data are apparently available on 

the inflow of fresh water from the Newport River or 

from the many small creeks to the estuary. Salinity in 

the bay is reported to range from about 24 to 35 parts 

per thousand. Tidal ranges are between 2 and 3 feet 

(0.6-0.9 m), and maximum tidal currents through 

Beaufort Inlet are about 1 knot (50 cm/sec). Water 

circulation in the bay is often dominated by windgenerated currents.

SEDIMENT TEXTURE

Bottom. Texture was evaluated by mechanical 

analysis and by microscopic examination. Most of the 

bottom is covered by fine sand. In the upper estuary, 

clayey silt in the center grades shoreward into silty 

sand around the margins (fig. 40). Material greater 

than 2 mm in diameter is composed almost entirely of 

shell fragments.

SEDIMENT COMPOSITION

Mineralogy. The light minerals of the sand fraction consist of quartz (94 percent), plagioclase (3 percent), and orthoclase (3 percent). Heavy minerals account for less than 1 percent of the sand fraction and 

consist mostly of ilmenite, rutile, and zircon. Illite and 

chlorite are the most abundant clay minerals. Calcium 

carbonate is present in concentrations of less than 5 

percent throughout most of the estuary, except in 

oyster and mussel shoals where values are locally high 

(fig. 41).

REFERENCE

Johnson (1959).

BOGUE SOUND, NORTH CAROLINA

SETTING

Geology. Quaternary sediments mantle the adjacent Atlantic Coastal Plain north of Bogue Sound. 

A single barrier island isolates the sound from the Atlantic Ocean to the south.

Bathymetry. Depths in the shallow lagoon average 

2 to 3 feet (0.6-0.9 m). Deepest natural areas, excluding the two inlets, reach 12 to 16 feet (3.6-4.5 m). The

-34° 45'

76°45'

I

FIGURE 39. Bathymetry (in feet) of Newport River Estuary, N.C. (from Johnson, 1959).
AREA SUMMARIES 27

-34° 45'

EXPLANATION

EvffvSI MEDIUM SAND 

FINE SAND 

CLAYEY SILT

76e 45'

I

FIGURE 40. Texture of bottom sediments in Newport River Estuary, N.C. Modified from

Johnson (1959).

-34°45

76°45'

I

FIGURE 41. Calcium carbonate content (in percent) of bottom sediments in Newport River 

Estuary, N.C. (from Johnson, 1959).

460-197 O - 72 - 5
28 CHARACTERISTICS OF ESTUARINE SEDIMENTS EST THE U.S.

Intracoastal Waterway, which is dredged to a depth 

of 15 feet (4.5 m), extends along the northern margin 

of the sound and is flanked by piles of dredge spoil, 

which often break the surface (fig. 42).

Hydrology. Fresh-water drainage from the two 

principal rivers in the area moves mostly out to sea 

through the inlets at each end of the sound. Salinities 

in the sound therefore are generally between 31 and 

33 parts per thousand, although values as high as 36 

parts per thousand have been recorded from shallow 

areas during dry periods when local runoff is low. 

Diurnal tides have a range of 1 to 3.5 feet (0.3-1.1 m), 

but wind under certain conditions may cause the water 

level to vary by as much as 5 or 6 feet (1.5-1.8 m). 

Tidal currents in the sound are generally less than 

0.5 knot (25 cm/sec), but velocities in the inlets may 

be as high as 3 knots (150 cm/sec).

SEDIMENT TEXTURE

Bottom. Most sediment at the few locations sampled consists of fine sand (fig. 43). Medium sand is accumulating only near Beaufort Inlet. Sediment 

coarsens slightly toward the center of the bay, which 

is less well protected from wave action. Over most of 

the sound, clay constitutes less than 5 percent of the 

total sediment; only in a few local areas along the 

margins does clay content exceed 15 percent (fig. 44).

SEDIMENT COMPOSITION

Organic matter (sample analyses by the WalkelyBlack (in Jackson, 1958) technique). Concentrations of oxidizable organic matter are generally less 

than 0.5 percent in midbay. In the small estuaries 

along the northern margin of the sound, values close 

to 3 percent have been measured (fig. 45).

Mineralogy. Quartz dominates the sand fraction. 

Clay-sized components in order of relative abundance 

consist of quartz, kaolinite, illite, mixed-layer clays, 

montmorillonite, and a small amount of chlorite.

REFERENCES

Batten (1962), Brett (1963), Daniels and Owen 

(1968).

CHARLESTON HARBOR, SOUTH CAROLINA

SETTING

Geology. Sediments exposed on the Atlantic Coastal Plain in the area of Charleston Harbor are Quaternary in age. Most terrigenous detritus deposited in 

the harbor itself was eroded locally until the Santee 

River was diverted about 40 nautical miles (74 km) 

north of Charleston into the Cooper River in 1942. 

Fine sediment is now being transported by the Santee-Cooper system into the estuary from the upper 

Coastal Plain and the Piedmont.

Bathymetry. Although natural deep areas of the 

harbor still exist, the large inflow of the Cooper River 

since 1942 has resulted in rapid shoaling, which has 

required continuous dredging. The bathymetry of 

much of the harbor bottom is therefore due to the manmade effects of dredging and dumping of spoil (fig. 

46).

Hydrology. The tidal Wando and Ashley Rivers 

contribute little fresh water to the estuary except from 

local runoff. Discharge from the Santee-Cooper system is regulated at about 425 m3 /sec by the Pinopolis 

Dam at Moultrie Reservoir, approximately 22 miles 

(35 km) north of Charleston. The limit of salt-water 

intrusion in the Cooper River is about 20 miles (37

FIGURE 42. Bathymetry (in feet) of Bogue Sound, N.C. (from Brett, 1963).
AREA SUMMARIES 29

FIGURE 43. Median diameter (in millimeters) of bottom sediments in Bogue Sound, N.C. (from Brett, 1963).

FIGURE 44. Clay content (in percent) of bottom sediments in Bogue Sound, N.C. (from Brett, 1963).

FIGURE 45. Oxidizable organic matter content (in percent) of bottom sediments in Bogue Sound, N.C. (from Brett, 1963).
30 CHARACTERISTICS OF ESTUARINE SEDIMENTS EST THE U.S.

FIGURE 46. Bathymetry (in feet) of Charleston Harbor, S.C. 

(from U.S.C. & G.S. Chart 470).

km) upstream from the jetties at the harbor mouth. 

Greatest dilution of salt water occurs on the western 

side of the estuary. The mean tidal range measured 

between Drum Island and Shutes Folly Island is 5.1 

feet (1.5 m). Maximum current velocities under normal conditions are 2.5 to 3.0 knots (125-150 cm/sec).

SEDIMENT TEXTURE

Bottom. Clay, presently accumulating in the channels, forms most of the shoals. Much of this material

EXPLANATION

SAMPLE LOCALITY 

SHOWING MEDIAN 

DIAMETER(mm)

FIGURE 47. Median diameter of discrete sediment samples 

(from U.S. Army, Corps of Engineers, 1954) and distribution of shoals composed mostly of clay (from U.S. Army, 

Corps of Engineers, 1966) in Charleston Harbor, S.C., 

and on the continental shelf outside the harbor.

may have been dredged previously. Areas of shoal formation as of 1966 are shown in figure 47. Where 

river-transported fine detritus is not accumulating, 

such as near the estuary mouth, the sediment is mostly 

sand.

SEDIMENT COMPOSITION

Organic carbon (values obtained with a Beckmann
AREA SUMMARIES 31

FIGURE 48. Organic carbon content of bottom sediments in 

Charleston Harbor, S.C. (from U.S. Federal Water Pollution Control Administration, 1966).

gas analyzer). Owing to the abundance of raw sewage presently being dumped into the estuary and to 

the changing pattern of fine sediment deposition, organic carbon concentrations probably change rapidly 

on the bottom. North of Charleston Harbor area 

values are less than 0.1 percent in sediments of the 

Cooper River. Adjacent to and downstream of the 

city, values are generally between 3 and 5 percent, although a maximum of almost 14 percent was recorded.

High concentrations in the Ashley River are probably 

due mostly to the introduction of untreated industrial 

wastes, whereas those in the Cooper River area are 

due mostly to raw sewage (fig. 48).

Mineralogy. Bottom sediments are composed principally of quartz, feldspar, and layered silicates. The 

sand fraction, mostly quartz and feldspar, is probably 

being transported into the estuary mainly from the 

continental shelf. Silt and clay principally composed 

of kaolinite, montmorillonite, and illite are being 

brought in mainly by the Santee-Cooper River system. 

Kaolinite/montmorillonite ratios of about 1, which 

occur in the western part of the estuary, apparently 

reflect well-mixed sediments of both Piedmont and 

Coastal Plain origin. An average ratio of 0.7 in the 

eastern area reflects a predominance of Coastal Plain 

material. Heavy minerals range from 1 to 7 percent by 

weight of the total assemblage but are most commonly 

less than 3 percent. The most abundant of these 

hornblende, ilmenite, and epidote are probably carried into the estuary from the continental shelf.

Color. Reddish-tan sediments in the Cooper River 

grade into gray and black soupy muds in the harbor 

that contain sewage, petroleum, and industrial waste 

products. These pollutants have constituted as much 

as 30 or 40 percent of the fine sediments which have 

accumulated over the last 20 years.

REFERENCES

U.S. Federal Water Pollution Control Administration (1966), Neiheisel and Weaver (1967), U.S. Army 

Corps of Engineers (1954, 1966).

BISCAYNE BAY, FLORIDA

SETTING

Geology. Quaternary deposits are exposed around 

Biscayne Bay. With the exception of a thin stratum 

that contains quartz sand (Pamlico Sand), these deposits are primarly carbonate. The Key Largo Limestone of Pleistocene age forms most of the keys and 

shoals which isolate the bay from the Atlantic Ocean. 

A thick section of Tertiary and Cretaceous rocks, also 

mostly carbonate, underlies the younger sediments.

Bathymetry. Water depths in most of the bay are 

less than 12 feet (3.6 m). A complex series of shoals 

(Featherbed Bank) oriented roughly east-west divides 

the bay into two parts. Slopes in both areas dip uniformly from the western shore toward the middle of 

the basin, but a complex of banks forms the northeast 

margin. Topography is more uniform on the southeast 

flank. The maximum depth in the bay (21 feet or 6.4 

m) is in a channel south of Key Biscayne (fig. 49).
32 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

EX PL AN A TI ON K'M vM-J^^^§§^"^^^a| 

C3 COARSE SAND

FIGURE 49. Bathymetry (in feet) of Biscayne Bay, Fla. 

(from Bush, 1958).

FIGURE 50. Texture of bottom sediments in Biscayne 

Bay, Fla. Modified from Bush (1958).

Hydrology. Fresh-water inflow is derived mainly 

from the Miami and Little Rivers, the Tamiami 

Canal, and other dredged canals which lie mostly 

northwest of the bay. Salinities range from about 3 

parts per thousand at the mouth of the Miami River, 

north of the map area, to 39 parts per thousand at 

Featherbed Bank. Tidal range is only 2 to 2.5 feet 

(0.6-0.7" m), but wind and rainfall often obscure normal tidal fluctuations. In the channels, currents may 

attain velocities of 2 knots (100 cm/sec) at flood tide 

and 3 knots (150 cm/sec) at ebb tide.

SEDIMENT TEXTURE

Bottom. Fine sand is most abundant in the northern part of the bay and medium to coarse sand predominates in the southern part (fig. 50). The size distribution, however, is bimodal due to the presence of

two constituents namely, well-sorted quartz sand (fig. 

51) and fragments of detritus composed of calcium 

carbonate (fig. 52). Silt deposits are located in two 

areas, southeast ol Biscayne Island and west of Ragged Keys.

SEDIMENT COMPOSITION

Mineralogy. Fine quartz sand (fig. 51), probably 

derived mostly from the Pamlico Sand, and fragments of calcium carbonate (fig. 52), derived from 

indigenous organisms (principally the calcareous alga 

Halimeda], make up most of the sediment. Heavy 

minerals, mainly epidote, constitute less than 0.1 percent of the sediment. Clay minerals are rare.

REFERENCES 

Bush (1958), Wanless (1969).
AREA SUMMARIES 33

FIGURE 51. Quartz content (in percent) of bottom 

sediment in Biscayne Bay, Fla. (from Bush, 1958).

FIGURE 52. ^auuuin caroonate content (in percent) of 

bottom sediments in Biscayne Bay, Fla. (from Bush, 

1958).

FLORIDA BAY, FLORIDA

SETTING

Geology. Florida Bay is bounded on the north by 

coastal fresh- and brackish-water swamps of the Everglades and on the southeast by the Florida Keys which 

consist of elevated Pleistocene coral reefs (Key Largo 

Limestone). In the bay the Miami Oolite (Pleistocene) 

underlies unconsolidated Holocene sediments that 

range in thickness from a few inches where water 

depth is greatest to approximately 5 or 6 feet (1.5- 

1.8 m) where mud banks are present (fig. 53).

Bathymetry. The bottom slopes gently from a 

depth of approximately 3 feet (1 m) in the northeastern part of the bay to about 8 or 10 feet (2.4-3 m) 

along the western margin. Average water depth is 

roughly 6 feet (1.8 m), except where tidal currents

have cut channels into bedrock to depths as great as 

15 feet (4.5 m). Many mud banks are exposed during 

periods of low water (fig. 53).

Hydrology. Fresh-water inflow from the Everglades to the bay increases near the end of the rainy 

season, which lasts usually from June to December. 

Maximum dilution therefore occurs between December 

and February, when salinities may be as low as 10 

parts per thousand in the northern part of the bay. 

During the dry months of the year, salinities throughout the whole bay average 35^0 parts per thousand, 

but in local restricted areas values as high as 70 parts 

per thousand have been recorded. The mixed semidiurnal tides have a range at Cape Sable of almost 3 

feet (1m); but in the interior of the bay, tidal range 

is less than 1 foot (0.3 m). Currents, often mainly the
34 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

GRASS-COVERED MUD BANKS 

(WATER DEPTH LESS THAN 2 Ft DEEP)

FIGURE 53. Bathymetry (in feet) of Florida Bay, Fla. (from Ginsburg, 1956).

result of wind, are greatest in the passes where they 

reach 3 to 4 knots (150-200 cm/sec). Throughout most 

of the bay, however, current velocities are less than a 

few tenths of a knot.

SEDIMENT TEXTURE

Bottom. The average texture of most bottom sediments throughout the bay is rather uniform, though 

grain size may vary greatly in small areas. The average median diameter of bottom sediments in the eastern part of the bay is 0.025 mm, and in the western 

part, 0.028 mm. On the exposed edges of banks, sediment is generally sand; but throughout most of the 

deep areas and on protected parts of the banks, silt 

and clay predominate. Average sediments on the mud 

banks in the western bay are 70 percent silt and clay 

(less than 0.062 mm diameter) and 30 percent sand.

Subbottom. Sediment texture below the bottom to a 

depth of 4 feet (1.2 m) differs little from that on the 

surface; silt and clay (less than 0.062 mm diameter) 

range from slightly over 50 percent to 100 percent.

SEDIMENT COMPOSITION

Organic carbon. Average values for organic carbon 

at the bottom are 2.1 percent in the western part and 

3.5 percent in the eastern part, but concentrations as 

high as 30 percent have been recorded from cores 

taken where plant detritus is particularly abundant. 

Below the upper few inches of oxidized sediment, an 

H2S odor is notable in most sediments.

Mineralogy. The sediment consists of approximately 90 percent carbonate particles, and the remainder is mostly quartz, opaline sponge spicules, and 

organic matter. Average estimates of the carbonate 

mineralogy of bottom sediments in the western and 

eastern parts of the bay, respectively, are: aragonite, 

59-67 percent; high-magnesium calcite (4-19 percent 

MgCO3 ), 19-37 percent; low-magnesium calcite, 14-17 

percent. The coarse fraction consists almost entirely 

of mollusk shells, foraminifer tests, and detrital 

quartz. Dolomite is present in low concentrations (less 

than 5 percent) as discrete particles smaller than 0.062
AREA SUMMARIES 35

mm. Physical properties, mineralogy, and chemistry 

of Florida Bay sediments are summarized in table 2.

TABLE 2. Physical, mineral, and chemical characteristics of 

sediments in Florida Bay, Fla.

[Modified from Scholl (1966). Values are given as weight percent except as otherwise

indicated]

Sediment characteristic

Western Florida Bay Eastern Florida Bay 

Average Range Average Range

Mass properties and grain-size distribution

Mass properties:

Water content (dry weight basis)... 71.5 ......_.

Porosity (volume percent).......... 65.9 -...._..

Grain density (g/cc).--------------- 2.71 ._._.-._

Bulk density (g/cc)----------------- 1.58 .____.__

Grain-size distribution:

Median diameter (mm)............. .028 _.___._.

Trask sorting coefficient............ 6.81 ...-....--...-.

0.125-mm diam sand...................................... 51

0.062-mm diamsand................ 30 1-52...

0.062-0.001-mm diam silt-clay....... 48 9-70 ..-

<0.001-mm diam subclay..--------- 22 5-50 ...

0.025

15-90

Carbonate mineralogy

Subsurface and surface sediments:

Surface sediments:

Low-Mg calcite _ ................

-. 59

97

-. 14

-. 59

-. 26

.. 15

35-77 3-54

1-29

41-70

10-47

10-20

46

37

17

67

19

16

20-78

0-51

4-80

40-100

0-39

0-44

General sediment chemistry

Ca/Mg.................................. 25 6-41

ST/C&X103 ---.------------------------ 8.7 6.3-11.7

St............ .-...--.----.-...-.

Mg._......................................................__.

Mn............................................. .............

Ba....................._.........--_...-..-.._....._...-_.....

Calcareous minerals....-------.---__--- 87 81-90

Noncalcareous minerals_..-...-..-... 9 8-13 

Organic matter.---...-.-.........--.... 4 2-6

Organic carbon......................... 2.1 1.3-3.7

Organic nitrogen_..................... .15 .29- .09

Organic carbon/organic nitrogen........ 17 13-26

0.42 0.20 -0.64

1.4 .06-4.1

. 006 . 0005- . 04

. 002 .001 - . 004

6.2

3.5

.1

27.5

REFERENCES

Fleece (1962), Ginsburg (1956, 1964), Lloyd (1964), 

Scholl (1966), Stehli and Hower (1961), Taft (1962), 

Taft and Harbaugh (1964).

WHITEWATER BAY, FLORIDA

SETTING

Geology. Southwestern Florida is characterized by 

a stable flat limestone surface of late Cenozoic age. 

Bedrock in White water Bay, the Miami Oolite (Pleistocene), underlies 2 to 3 feet (0.6-0.9 m) of unconsolidated sediment composed of peat and calcareous shell 

debris. Structure contours on the top of the bedrock 

are shown in figure 54. Mangrove islands are abundant 

throughout the bay, which is flanked on the northeast by 

mangrove forests and the Everglades and on the southwest by marshes which form part of Cape Sable.

Bathymetry. The floor of the bay is flat and averages 4 to 5 feet (1.2-1.5 m) in depth. In channels between mangrove islands, currents have scoured into 

bedrock to depths of 6 feet (1.8 m).

FIGUKE 54. Structure contours (in feet below sea level) on 

the bedrock surface (Miami Oolite) in Whitewater Bay, Fla. 

(from Scholl, 1964, and Spackman and other, 1964).

FIGURE 55. Ratios of sand to silt for the calcium carbonate 

and quartz fractions of bottom sediments in Whitewater 

Bay, Fla. Modified from Scholl (1963).
36 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

FIGURE 56. Organic carbon content (in percent) of bottom 

sediments in Whitewater Bay, Fla. (from Scholl, 1963).

Hydrology. Four rivers drain into the bay from 

the Everglades swamp. Kunoff fluctuates seasonally. 

Salinity in the bay ranges from about 1 part per 

thousand when runoff is greatest to hypersaline conditions (40 parts per thousand) during extended periods 

of low rainfall. Maximum values during normal dry 

periods seldom exceed 37 parts per thousand. Water 

circulation in the bay is roughly counterclockwise and 

generally is sluggish (less than 0.5 knot or 25 cm/sec).

SEDIMENT TEXTURE

Bottom. No map of the overall size distribution of 

the sediments is available. Near the entrance to the 

bay, bottom sediment is approximately 0.5 mm in 

median diameter. Within the bay, particle size is controlled primarily by the amount of coarse shell debris 

present and varies greatly over short distances. Particle-size ratios for the quartz and calcium carbonate 

fractions are shown in figure 55. Quartz is present 

mostly as clay and silt. Both ratios indicate a great 

abundance of fine material within the bay; in contrast, 

sediments on the shelf nearby contain somewhat 

coarser material.

SEDIMENT COMPOSITION

Organic carbon (samples analyzed by the Allisson 

(1935) method). Organic carbon is most abundant 

near the center of the bay (18 percent) (fig. 56). Even 

higher concentrations, however, occur adjacent to mangrove islands where peat is exposed. Most of this organic material is derived from autochthonous plant 

debris and sessile algae. Values in bottom sediment of 

the adjacent continental shelf are about 1 percent.

Mineralogy. The sediment is composed mainly of 

aragonite, calcite, and quartz. Detrital dolomite and 

authigenic pyrite are also present. Carbonates, which 

are 60 percent aragonite, make up 65 percent of the 

total sediment, and quartz constitutes 5 to 10 percent.

REFERENCES

School (1963, 1964), Spackman, Scholl, and Taft 

(1964).

GULLIVAN BAY, FLORIDA

SETTING

Geology. Surface sediments that cover the low 

topography of the Florida Peninsula in the area of 

Gullivan Bay consist of fine, unconsolidated marsh 

and swamp deposits; these are underlain by the Tamiami Formation (Miocene). The Ten Thousand Islands on the eastern margin of the bay are sand bars 

made up mostly of shell fragments which are now 

covered by mangrove forests. The bay is a reentrant 

on the coastline and is probably structurally controlled. Bay sediments apparently are derived mostly 

from shoals offshore, swamps and marshes onshore, 

and eroded Pleistocene terraces.

Bathymetry. The bottom slopes gently away from 

shore at a gradient of about 1.5 feet per mile to a 

maximum depth of about 21 feet (6.3 m) on the western side of the bay. A series of curved en echelon 

shoals lie offshore (fig. 57).

Hydrology. Many small ungaged streams drain 

the swampy terrain adjacent to the bay. Gradients 

are so low, however, that most water movement is due 

to tidal action. The mixed semidiurnal tides have an 

approximate range of 2.5 to 3.5 feet (0.7-1.0 m). Tidal 

currents in the open bay flow in a counterclockwise direction.

SEDIMENT TEXTURE

Bottom. The noncarbonate detritus of the bottom 

sediment consists mostly of very fine to fine sand 

which is distributed over most of the bay center. Silt 

is abundant adjacent to the Ten Thousand Islands and 

in a few offshore areas (fig. 58).

SEDIMENT COMPOSITION

Organic carbon (method of analysis not given). 

Concentrations of organic carbon on the shelf are 

generally less than 1 percent. In channel sediments 

between the islands, values range from 1 to 4 percent; 

in the lagoon behind the mangrove islands, from 4 to
AREA SUMMARIES 37

EXPLANATION 

MEDIUM SAND 

FINE-VERY FINE SAND 

SILT

FIGURE 57. Bathymetry (in feet) of Gullivan Bay, Fla. 

(from Holmes and Evans, 1963).

8 percent, and near the islands where plant detritus is 

most abundant values are as high as 24 percent.

Mineralogy. Quartz is abundant in the sand fraction. Heavy minerals, which generally constitute less 

than 0.4 percent of the sediment, are mostly sillimanite 

and zircon, followed in abundance by staurolite, kyanite, rutile, tourmaline, and phosphate. Illite and 

minor amounts of montmorillonite and kaolinite are 

the most abundant clay minerals in the bay. Illite predominates on the shelf and on shoals; kaolinite, associated with some montmorillonite and illite, is most

FIGURE 58. Texture of bottom sediments (carbonate-free) 

in Gullivan Bay, Fla. Modified from Holmes and Evans 

(1963).

abundant in the mangrove swamps. Highest carbonate 

concentrations (60-80 percent) occur locally along the 

outer fringes of the islands due to the erosion of cemented carbonate shell debris; similar high concentrations are found on oyster bars. In most of the area, 

however, carbonate concentration generally ranges 

from 10 to 40 percent (fig. 59).

REFERENCE 

Holmes and Evans (1963).
38 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

FIGURE 59. Calcium carbonate content (in percent) of 

bottom sediments in Gullivan Bay, Fla. (from Holmes and 

Evans, 1963).

PORT CHARLOTTE HARBOR, FLORIDA

SETTING

Geology. The area surrounding Port Charlotte 

Harbor is underlain by post-Eocene limestone and 

dolomite and minor amounts of clay, quartz sand, and 

phosphate. A series of barrier islands that are broken 

by narrow inlets separates the bay from the Gulf of 

Mexico. The average thickness of Holocene sediments 

within the bay is about 10 feet (3m).

Bathymetry. Most of the harbor is less than 12 feet 

(3.6 m) deep. Broad, shallow, sandy grass flats less 

than 6 feet (1.8 m) deep surround the bay margins; 

depths then increase gradually toward the channels in 

midbay. The maximum depth (51 feet or 15 m) occurs in Boca Grande Pass (fig. 60).

Hydrology. Based on limited data the average total 

fresh-water inflow from the three principal rivers 

the Myakka, Peace, and Caloosahatchie is about 

50 m3 /sec. Salinity ranges from 34 to 36 parts per 

thousand near the inlets to about 13 to 18 parts per 

thousand at the river mouths. Mean tidal range at the 

San Carlos Bay entrance is 2.5 feet (0.8 m) and at 

Boca Grande Pass, 1.7 feet (0.5 m). Maximum tidal 

current velocities in these two inlets range from 0.9 to 

2.2 knots (45-110 cm/sec).

FIGURE 60. Bathymetry (in feet) of Port Charlotte 

Harbor, Fla. (from Huang and Goodell, 1967).
AREA SUMMARIES' 39

SEDIMENT TEXTURE

Bottom. Based on the mean diameter, most sediment on the bottom of the bay is very fine to fine sand; 

only a few samples are composed of silt and clay. 

Medium to coarse sand is abundant north of Pine Island in the channel that extends into the bay from 

Boca Grande Pass (fig. 61).

SEDIMENT COMPOSITION

Organic carbon (samples analyzed by the Coleman 

gas analyzer). Most sediment in the bay contains 0.1 

to 1.0 percent organic carbon. The highest value (3.1 

percent), among more than 200 measurements, was 

found in a sample collected between the mouths of

the Myakka and Peace Rivers; Most other samples that 

contained more than 1 percent organic carbon were 

collected in areas protected from wave and current 

action (fig. 62).

Mineralogy. Most sediment in the bay consists of 

quartz and carbonates. The carbonates include lowmagnesium calcite, aragonite, and dolomite. Mollusk 

shells and shell fragments are the major carbonate 

source. The carbonate concentration ranges from less 

than 1 percent in sediments of the river bottoms to 94 

percent in those of tidal channels, where shell detritus 

makes up most of the coarse sediment (fig. 63). Phosphate minerals range in abundance from 0 to 9 percent, but most samples contain less than 2.5 percent.

BOCA 

GJfANOE 

PASS ^

-26-40'

Kilometers

Nautical Miles 

EXPLANATION

EZ3VERYCOARSE-COARSE SAN

E3 MEDIUM SAND

I '.. 1 FINE-VERY FINE SAND

ti±3 SILT a CLAY 10'

FIGURE 61. Texture of bottom sediments in Port 

Charlotte Harbor, Fla. Based on data presented by 

Huang (1966).

FIGURE 62. Organic carbon content in bottom sediments 

of Port Charlotte Harbor, Fla. Based on data presented 

by Huang (1966).
40 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

FIGURE 63. Calcium carbonate content (in percent) of 

bottom sediments in Port Charlotte Harbor, Fla. 

Modified from Huang (1966).

Heavy minerals are notably sparse. Layered silicates 

include montmorillonite, kaolinite, illite, attapulgite, 

and mixed-layer clays. Kaolinite seems to be concentrated in deep parts of the bay, whereas illite is more 

abundant near the harbor mouth.

REFERENCES 

Huang (1966), Huang and Goodell (1967).

TAMPA BAY, FLORIDA

SETTING

Geology. Pliocene and Miocene marl, limestone, 

and sand underlie more recent deposits around the 

margin of Tampa Bay. Unconsolidated Pleistocene

and Holocene sediments in the bay are generally 40 to 

50 feet (12-15 m) thick but in channels are as much 

as 100 feet (30 m) thick.

Bathymetry. Shallow sand flats around the bay 

margins are generally less than 6 feet (1.8 m) deep 

and slope gradually into channels near the axis of the 

bay; the channels generally are more than 18 feet 

(5.4 m) deep. The rather smooth topography has been 

greatly altered in much of the bay by dredging and 

spoil disposal (fig. 64).

Hydrology. Discharge from the rivers on the eastern side of the bay is very low. Salinities average 36 

parts per thousand at the bay mouth, 26 parts per 

thousand at the head of Old Tampa Bay, 21 parts per 

thousand in upper Hillsboro Bay, and 22 to 28 parts 

per thousand along the eastern shore of Tampa Bay. 

Tidal range is about 1.5 feet (0.45 m) and tidal currents are generally less than 1 knot (50 cm/sec), except in restricted channels where currents are nearly 

2 knots (100 cm/sec). Waters draining the mangrove 

swamps on the shoreline are acidic.

FIGURE 64. Bathymetry (in feet) of Tampa Bay, Fla. (from 

U.S.C. & G.S. Chart 587).
AREA SUMMARIES 41

SEDIMENT TEXTURE

Bottom. Sand-sized detritus is widespread throughout the estuary. Silt is abundant only in Hillsboro 

Bay. Coarsest material occurs in channels where tidal 

velocities are highest (fig. 65).

Subbottom. The sediment size distribution is rather 

homogeneous to a depth of approximately 2 feet (0.6 

m), probably due to burrowing by abundant benthic 

organisms.

SEDIMENT COMPOSITION

Mineralogy. In the shallow flats around the periphery of the bay the sediment is composed of an 

almost pure, fine quartz sand. On the slopes and in the 

channels, abundant fragments of mollusk shells account for most of the calcium carbonate in the sediments (fig. 66) and for the coarse texture. Heavy 

minerals consist mostly of kyanite, staurolite, and 

sillimanite. Some fluorapatite and cellophane are also 

present. Clay minerals, including kaolinite and montmorillonite, are present but rare.

Kilometers

5 (0 

I_______I

Nautical Miles

(TTJJVERY COARSE-COARSE SAND 

*+"* |::!-|MEDIUM SAND

frfrJFINE SAND 

H1|VERY FINE SAND 

|!!J SILT 

I

FIGURE 65. Texture of bottom sediments in Tampa Bay, Fla. 

Modified from Goodell and Gorsline (1961).

FIGURE 66. Calcium carbonate content (in percent) of 

bottom sediments in Tampa Bay, Fla. (from Goodell and 

Gorsline, 1961).

REFERENCES 

Goodell and Gorsline (1961), Walton (1964).

APALACHICOLA BAY, FLORIDA

SETTING

Geology. The lowlands adjacent to the northern 

part of the Apalachicola Bay complex are composed 

of unconsolidated deltaic material deposited on Pleistocene and Pliocene strata by the Apalachicola River. 

Post-glacial barrier islands form the southeastern 

margin of the bay complex. Sediment presently accumulating in the bay overlies Tertiary limestone and 

marl that are exposed in the scoured channels of West 

Pass and Indian Pass.

Bathymetry. The bottom dips gently seaward from 

depths of about 2 feet (0.6 m) at the mouth of the 

Apalachicola River to 7 feet (2.1 m) before shoaling 

abruptly at the barrier islands. In the western part of 

the area (St. Vincent Sound), shallow oyster bars are 

exposed at low tide. To the east, St. George Bay is 

partly isolated from Apalachicola Bay by a north-
42 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

trending bar. The bottom in St. George Bay is hummocky with numerous depressions and shoals. Current 

scour maintains the depth of West Pass at approximately 54 feet (16 m). Hurricanes have significantly 

and periodically altered the bottom and the configuration of the barrier islands (fig. 67).

Hydrology. Fresh-water inflow to the area is derived principally from the Apalachicola River. The 

mean flow at Chattahootchee, 80 km upriver from the 

bay, is approximately 600 m3 /sec. Generally, salinity 

increases from 5 parts per thousand near the river 

mouth to 30 parts per thousand in the passes. The maximum tidal range is about 3 feet (0.9 m) and averages

1.5-2 feet (0.5-0.6 m). Wind, however, may move the 

water in the shallow bays sufficiently to mask the normal tidal cycle. Current velocities are a function of 

river discharge, tides, and wind direction. Velocities 

in the bay seldom exceed 1 knot (50 cm/sec) but in 

West and Indian Passes, velocities may reach 5-6 

knots (250-300 cm/sec).

SEDIMENT TEXTURE

Bottom,. Much of the fine sediment transported by 

the Apalachicola River is deposited in Apalachicola 

Bay and in the eastern half of St. Vincent Sound. 

Sand accumulating along the bay margins grades into 

silt and clay in the deep central area (fig. 68). Silt

FIGURE 67. Bathymetry (in feet) in Apalachicola Bay, Fla. (from Kofoed and Gorsline, 1963).

CAPE SAN BLAS

EXPLANATION

r.l VERY COARSE SAND

C'VJ COARSE 8 MEDIUM SAND

Eg=3 FINE 8 VERY FINE SAND

^ SILT

^3 CLAY

85°20' 

I

CAPE ST GEORGE

Nau lical Miles

85°

29°40' 

FIGURE 68. Texture of bottom sediments in Apalachicola Bay, Fla. Modified from Kofoed and Gorsline (1963).
AREA SUMMARIES 43

predominates where depths are greater than 6 feet 

(1.8m).

SEDIMENT COMPOSITION

Organic carbon, Values of organic carbon throughout the bay complex generally range from 1 to 2 percent. Around the margins and on topographic highs, 

however, concentrations are generally less than 0.5 

percent. Most of the organic matter is probably derived from indigenous plants and animals. Low values 

occur in shallow depths where organic matter is apparently oxidized rapidly (fig. 69).

Mineralogy. Most of the sand consists of quartz 

mixed with shell debris. Among the layered silicates, 

kaolinite predominates over much lesser amounts of 

illite, chlorite, and montmorillonite. Heavy minerals, 

which are uniformly distributed throughout the area, 

seldom exceed 1 percent of the sediment. Glauconite is 

common as small pellets in clay.

Carbonates. Carbonates, which consist mostly of 

oyster shells, range from about 10 to 40 percent of the 

total sediment but only exceed 20 percent in shoal areas 

and around the bay margins (fig. 70).

29-40 

CAPE SAN BLAS

CAPE ST GEORGE

Nau tical miles

20' 85°

FIGURE 69. Organic carbon content (in percent) of bottom sediments in Apalachicola Bay, Fla. (from Kofoed and Gorsline,

1963).

29°40 

CAPE ST GEORGE

Nau tical miles

20' 85°

FIGURE 70. Calcium carbonate content (in percent) of bottom sediments in Apalachicola Bay, Fla. (from Kofoed and Gorsline,

1963).

460-197 O - 72 - 7
44 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

REFERENCES 

Gorsline (1963), Kofoed and Gorsline (1963).

ST. JOSEPH BAY, FLORIDA

SETTING

Geology. St. Joseph Bay is underlain by a series of 

Pleistocene terraces which have been partly covered by 

Holocene fluvial deposits. No outcrops of consolidated 

sedimentary rocks have been found in the immediate 

area of the bay, but to the west, limestone of possible 

Miocene age is exposed on the bottom in 100 feet (30 

m) of water. A postglacial spit isolates the bay from 

the Gulf of Mexico. Fine to medium sand, which has 

been swept by longshore currents from the mouth of

the Apalachicola River, is presently accumulating in 

the bay.

Bathymetry. Gentle bottom slopes on the eastern 

side of the bay contrast sharply with the steep gradients on the western side. The bottom has an average 

depth of 21 feet (6.3 m) and a maximum depth of 40 

feet (12 m). The physiography of the bottom has 

changed little since the first bathymetric chart of the 

area was constructed in 1841 (fig. 71).

Hydrology. Aside from local runoff, fresh-water 

inflow is limited to discharge from a papermill into 

the lagoon through a canal at a rate of 1.3 m3 /sec 

(fig. Yl). Salinity measurements in surface waters 

range from 16 parts per thousand near the canal en85°20'

ST. JOSEPH SPIT.

EXPLANATION

im VERY COARSE-

^-^ COARSE SAND

E3 MEDIUM SAND

E-Sa FINE-VERY FINE SAND

fc-^3 SILT

E3 CLAY

40 

FIGURE 71. Bathymetry (in feet) of St. Joseph Bay, Fla. 

(from Stewart and Gorsline, 1962).

FIGTJEE 72. Texture of bottom sediments in St. Joseph Bay, 

Fla. Modified from Stewart and Gorsline (1962).
AREA SUMMARIES 45

trance to 33.5 parts per thousand throughout most of 

the area. Below a depth of 5 feet (1.5 m) salinity 

values are similar to those in the open gulf. Tidal current velocities attain a maximum of about 1.5 knots 

(75 cm/sec) at the tip of St. Joseph spit. Within the 

bay a counterclockwise gyre has been established. Current movement diminishes rapidly with depth, however, so that reducing conditions exist at the bottom 

in the deepest areas.

SEDIMENT TEXTURE

Bottom. Fine sand is presently being deposited at 

the northern end and around the margin of the bay. 

Very little clay or silt is being transported into the

area. The gradation from sand around the bay margin 

to clayey silt and clay toward the center reflects two 

periods of sedimentation rather than textural response 

to present hydrodynamic or bathymetric conditions. 

Silty clay under the bay is exposed only in the deepest 

areas. Coarse material on the southeastern side of the 

bay consists mostly of shell debris (fig. 72).

Subbottom. Only a few cores were taken, the 

longest of which was 46 cm in total length. Silt and 

clay increase with depth in the core and reach a maximum of 50 percent by weight at 40 cm. The finer sediment is interpreted to be relict from a period preceding the present cycle of sand and silt deposition. The

85°20'

ST. JOSEPH SPI

FIGURE 73. Organic carbon content (in percent) of bottom 

sediments in St. Joseph Bay, Fla. (from Stewart and 

Gorsline, 1962).

FIGURE 74. Calcium carbonate content (in percent) of 

bottom sediments in St. Joseph Bay, Fla. (from Stewart and 

Gorsline, 1962).
46 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.Su

contact between the exposed relict clay and the encroaching sand and silt has been identified by divers 

where it crops out in the deepest part of the bay at a 

water depth of 37 feet (11.1 m).

SEDIMENT COMPOSITION

Organic carbon. Concentrations of organic carbon 

generally increase from less than 0.5 percent around 

the bay margin to high values of 4.5 percent in the 

deep central area. High concentrations (6.5 percent) 

in rather coarse sediments near the canal mouth are 

probably due mostly to effluent from the papermill 

(fig. 73).

Mineralogy. Layered silicates are most abundant 

(approximately 50 percent) in bottom sediments of the 

central part of the bay where fine detritus apparently 

was deposited by a former distributary of the Apalachicola River; kaolinite is more abundant than either 

montmorillonite or illite. Most of the fine sand being 

swept into the bay by longshore currents consists of 

quartz. Heavy minerals the most abundant of which 

are ilmenite, staurolite, and kyanite make up a maximum of 1 percent of the sediment and average about 

0.3 percent.

Calcium carbonate. Carbonates in the bay are primarily biogenic. In the absence of a significant amount 

of quartz, the silt fraction consists mostly of foraminifer and ostracode tests and fragments of shell detritus. 

The highest values of calcium carbonate in the bay 

are from an extensive bank of shell detritus composed 

mainly of mollusk shells (fig. 74).

REFERENCE 

Stewart and Gorsline (1962).

PENSACOLA BAY, FLORIDA

SETTING

Geology. The Pensacola Bay system, including 

Pensacola Bay, East Bay, Blackwater Bay, Escambia 

Bay, and Santa Rosa Sound, lies on the Gulf Coastal 

Plain. Holocene sediments are underlain by Tertiary 

sand, silt, and limestone and by Pleistocene terrace deposits. Only the Citronelle Formation (Pliocene) 

crops out in the area. Santa Rosa Island isolates the 

bay complex from the Gulf of Mexico.

Bathymetry. Most of Escambia, Blackwater, and 

East Bays are covered by only 6 to 12 feet (1.8-3.6 m) 

of water (fig. 75). Depths in north-central Pensacola

FIGURE 75. Bathymetry (in feet) of the Pensacola Bay system, Florida (from Horvath, 1968).
AREA .SUMMARIES 47

Bay are between 18 and 25 feet (5.4 7.5 m) and increase to the south where maximum depths are between 30 and 40 feet (9-12 m). Santa Rosa Sound is 

over 18 feet (5.4 m) deep at the western end and 

shallows to the east to about 6 feet (2m).

Hydrology. Fresh-water inflow to the bay averages 

about 250 m3 /sec, 75 percent of which is carried by 

the Escambia River. Available measurements of salinity taken at Santa Rosa Island ranged from 5.5 

to 35.0 parts per thousand. The mean tidal range in 

Pensacola Bay is 1.3 feet (0.4 m) and at the bay entrance 1.1 feet (0.3 m). Northerly winds often lower 

the water level by approximately 1.5 feet (0.5 m), and 

hurricanes have raised the level as much as 9 feet 

(2.7 m). Tidal current velocities are greatest at the 

bay entrance and reach 2 to 2.5 knots (100-125 cm/ 

sec) during ebb tide and 1.7 knots (85 cm/sec) at flood 

tide.

SEDIMENT TEXTURE

Bottom. The mean grain size of sediments in the 

bay complex ranges from coarse sand to clay. Sediment becomes finer with distance north of the barrier 

island. Most sand is therefore located in Santa Rosa 

Sound and in the lower part of Pensacola Bay. Sand

predominates around most of the bay margin and 

grades into silt and clay in deeper water (fig. 76).

Sufobottom. Borings for the four bridges which 

cross different parts of the bay system have penetrated 

to a depth of about 140 feet (42 m). Gray fine to black 

silty sand is most abundant to a depth at 50 to 60 

feet (15-18 m) below which the sediment ranges from 

silty clay to silty sand.

SEDIMENT COMPOSITION

Mineralogy. Sand on Santa Rosa Island consists of 

quartz (99 percent) and such heavy minerals as staurolite, rutile, ilmenite, and kyanite. In the bay sediments, 

minerals such as quartz, muscovite, albite, and amphiboles have been identified by X-ray diffraction methods. The clay minerals consist of montmorillonite, 

kaolinite, illite, chlorite, and mixed-layer clays. Calcium carbonate makes up about 3 percent of the sediment ; average concentrations are lowest in Santa Rosa 

Sound (1.3 percent) and increase to the west to almost 

5 percent in Escambia and Pensacola Bays.

REFERENCE

Horvath (1968).

FIGTJKE 76. Texture of bottom sediments in the Pensacola Bay system, Florida (from Horvath, 1968).

460-197 O - 72 - 6
48 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

MOBILE BAY, ALABAMA

SETTING

Geology. The drainage basins of rivers flowing into 

Mobile Bay are underlain by sedimentary, igneous, 

and metamorphic rocks of Precambrian to Holocene 

age. Locally, Pleistocene and Holocene alluvium overlies Tertiary clay (Miocene?). Sand, gravel, and clay 

of the Citronelle Formation (Pliocene) crop out on 

the adjacent Coastal Plain. The shape of the bay is 

apparently controlled in part by a graben.

Bathymetry. Most of the flat-floored bay is 10-12 

feet (3.0-3.6 m) deep. Shelves 2-6 feet (0.6-1.8 m) 

deep and about 1 mile (1-2 km) wide surround most 

of the bay and drop off abruptly to the deeper bottom (fig. 77). Ship channels are maintained at a width 

of about 400 feet (120 m) and a depth of 40 feet (12 

m). The pass between Mobile Point and Dauphin Island is approximately 50 feet (15 m) deep. The bay 

has shoaled an average of almost 2 feet (0.6 m) in the 

last 100 years.

Hydrology. Mean fresh-water inflow (1,700 m3/ 

sec) to the bay from the Mobile Eiver system is about 

equally contributed by the Alabama and Tombigbee 

Rivers. (The Tensaw River is a distributary of the 

Alabama River.) Flow is lowest between September 

and November and greatest between January and May. 

The maximum discharge, measured during a flood, was 

14,000 ni3 /sec. Suspended sediment transported to the

FIGURE 77. Bathymetry (in feet) of Mobile Bay, Ala. (from FIGURE 78. Texture of bottom sediments in Mobile Bay, Ala. 

Ryan, 1969). (from Ryan, 1969).
AREA .SUMMARIES 49

bay has averaged about 4.7 X106 tons per year. Mean 

tidal range is 1.0 foot (0.3 m) at the lower end of the 

bay and 1.5 feet (0.4 m)" at the upper end. Winds, 

however, are responsible for greater variations. Hurricanes, for example, have caused the water level to rise 

about 10 feet (3m) above and fall about 10 feet (3m) 

below mean sea level. Tidal currents average 1.4 knots 

(70 cm/sec), but maxima of 3 knots (150 cm/sec) 

have been measured at the bay entrance. During periods of high discharge the salinity may drop to less 

than 5 parts per thousand throughout most of the bay; 

during periods of low discharge values of 30 parts per 

thousand at the bottom may extend almost to the head 

of the bay. The ship channel has allowed the salt 

wedge to penetrate the whole length of the bay.

SEDIMENT TEXTURE

Bottom. Most of the bottom of the lower bay, which 

is generally deeper than 6 feet (2 m), is covered with 

clay or silty clay (fig. 78). These sediments grade 

northward into sandy silt and sand. The finest sediments, concentrated on the eastern side of the estuary, 

are probably deposited mostly from bottom currents 

during flood tide. Sand covers almost all the shallow 

shelf around the bay margin.

SEDIMENT COMPOSITION

Mineralogy. Kaolinite and montmorillonite dominate the fine sediments. Kaolinite is more abundant at 

the bottom, but montmorillonite content increases with

depth below the bottom. Illite and chlorite are minor 

and variable constituents. Most sediment contains less 

than 4 percent carbonate except on or near oyster 

reefs. Carbonate detritus consists mostly of gravelsized fragments of pelecypod shells.

REFERENCE

Kyan (1969).

MISSISSIPPI SOUND, MISSISSIPPI AND ALABAMA

Geology. Quaternary deltaic sands and clays border 

Mississippi Sound to the north. Five barrier islands 

and the broad inlets between them form the southern 

margin. The islands are made up mostly of medium 

sand, commonly in dunes that are 40 to 50 feet (12-15 

m) thick and overlie 10 feet (3m) of gray clay.

Bathymetry. Most of the northern half of the 

sound is less than 10 feet (3m) deep; in the southern 

part, depths average 15 to 20 feet (4.5-6 m). Inlet 

channels near and between barrier islands range from 

25 to 50 feet (7.5-15 m) in depth. Shoals consist of 

sand bars or oyster reefs (fig. 79).

Hydrology. Among the many streams and rivers 

contributing fresh water to the sound the most important are the Pearl, Pascagoula, and Biloxi. The 

Pearl and Biloxi which flow into the spund at its western and eastern ends are not within the area shown 

by the figures. Total average fresh-water inflow from 

the three rivers is 1,600 m3 /sec. Salinities range from 

zero near river mouths to 30 parts Der thousand in the

FIGURE 79. Bathymetry (in feet) of Mississippi Sound, Miss, and Ala. (from Upshaw and others, 1966).
50 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

open sound. Normal tidal ranges are less than 2 feet grade into very fine to fine sand toward the margins.

(0.6 m), and currents are most often less than 1 knot ^ear the barrier islands and along the northern mar-

(50 cm/sec). SEmMENT TEXTURE gin west of Pascagoula, sands are medium to coarse.

Bottom.-Sn.t and clay (carbonate-free), which are East of Pascagoula fine sand, silt, and clay are being

most abundant in the deep central part of the sound, deposited along the mainland shore (fig. 80).

GULF OF MEXICO

89°00' 

I

EXPLANATION

ES3 MEDIUM-COARSE SAND 

K&* FINE-VERY FINE SAND

EE3 SILT a CLAY

WA SAND-SILT-CLAY

45 

I

I____I____i___I____I 

Kilometers

Nautical Miles

30' 

I

FIGURE 80. Texture of bottom sediments in Mississippi Sound, Miss, and Ala. Modified from Upshaw, Creath, and Brooks

(1966).

FIGURE 81. Organic carbon content (in percent) of bottom sediments in Mississippi Sound, Miss, and Ala. Data from W M.

Sackett and R. R. Thompson (in Upshaw and others, 1966).
AREA SUMMARIES 51

FIGURE 82. Calcium carbonate content in bottom sediments of Mississippi Sound, Miss, and Ala. (from Upshaw and others,

1966).

SEDIMENT COMPOSITION

Organic carbon (samples analyzed spectrographically). In the open sound, silts and clays generally 

contain less than 1.5 percent organic carbon and sands, 

less than 1 percent. Highest concentrations of between 

2 and 4 percent were measured in samples collected 

near shore in the small bays at Biloxi and Pascagoula 

(fig. 81).

Mineralogy. Carbonates in the sound, consisting 

mostly of shell debris, generally constitute 10 to 15 

percent of the fine sediments and less than 10 percent 

of sands (fig. 82). In average coastal beach or dune 

sands, heavy-mineral concentrations range from 2 to 6 

percent; in order of abundance these include staurolite, kyanite, tourmaline, ilmenite, magnetite, limonitehematite, leucoxene, zircon, rutile, sillimanite, and 

andalusite. Light minerals accumulating in the sound 

consist mostly of quartz and potassium feldspar. The 

most abundant clay minerals are kaolinite, illite, and 

montmorillonite; chlorite is rare.

REFERENCES

Foxworth and others (1962), Ludwick (1964), and 

Upshaw, death, and Brooks (1966).

BRETON AND CHANDELEUR SOUNDS, LOUISIANA

SETTING

Geology. Most of the submerged area of both 

Breton and Chandeleur Sounds is an abandoned distributary of the Mississippi Kiver Delta which, because

of erosion by the sea, compaction of Holocene unconsolidated sediments and regional subsidence is now 

being ~ covered by «' marine sediments. The sounds are

flanked on the west by brackish and salt marshes of 

the Mississippi Delta and on the east by a series of 

barrier islands that consist of well-sorted medium sand 

deposits as much as 35 feet (11 m) thick. In the 

sounds, Holocene marine sediments range in thickness 

from a few inches to several feet and overlie marsh 

and fluviatile deposits of the abandoned delta.

Bathymetry. The bottom slopes gently from west 

to east and reaches depths of between 12 and 18 feet 

(4-5 m) near the barrier islands (fig. 83).

Hydrology. Fresh-water inflow to the sound is derived mostly from the swamps and bayous of the delta 

and from the Mississippi River. Salinities vary 

roughly between 15-30 parts per thousand depending 

on season, wind direction, and runoff. Tidal ranges are 

less than 2 feet (0.6 m). The velocity of the current 

which flows northward between Breton Island and the 

delta at about 0.5 and 1.0 knot (25-50 cm/sec) is in 

part controlled by the wind.

SEDIMENT TEXTURE

Bottom. The bottom of both sounds is covered 

mostly with very fine sand. Coarser average textures 

are primarily due to the presence of shells and shell 

debris. Silt and clay derived from erosion of deltaic 

material is being deposited along the western margin 

of the bay and in a tongue along the western margin
52 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

FIGURE 83. Bathymetry (in feet) of Breton and Chandeleur 

Sounds, La. (from Treadwell, 1955).

FIGURE 85. Total organic matter (in percent) in bottom 

sediments in Breton and Chandeleur Sounds, La. (from 

Treadwell, 1955).

FIGURE 84. Texture of bottom sediments in Breton and 

Chandeleur Sounds, La. Modified from Treadwell (1955).

FIGURE 86. Shell content (in percent) of bottom sediments in 

Breton and Chandeleur Sounds, La. Modified from Treadwell (1955).
AREA SUMMARIES 53

of the barrier islands, where fine suspended detritus 

carried by the Mississippi River is evidently being deposited. The texture of much of the bottom sediments 

results from the mixing of old subdelta deposits and 

contemporary marine sediments (fig. 84).

Subbottom. Cores taken in Chandeleur Sound contain an upper 7-foot (2.1 m) section of silty clay an'd 

silty sand which overlies approximately 33 feet (10 m) 

of clay and silty clay.

SEDIMENT COMPOSITION

Organic matter (dry weight loss after boiling sample in 10 percent H2O2 ). Concentrations of organic 

matter on the bottom are very low; they range from 

less than 1 percent in the central area to 2 or 3 percent 

near marshland borders (fig. 85).

Mineralogy. Sand along the northwest margin of 

the sound consists mostly of quartz and feldspar and 

contains some rock fragments, amphiboles, pyroxenes, 

epidote, ilmenite, and biotite. Principal clay minerals 

are montmorillonite and illite, plus lesser amounts of 

kaolinite and chlorite. Heavy minerals constitute less 

than 0.5 percent of the sediment in the sounds and consist of an assemblage of mostly hornblende and pyroxene and small amounts of epidote and garnet. Carbonates are generally sparse (less than 2 percent), except 

in the south-central part of Chandeleur Sound where 

shells and shell fragments make up roughly 50 percent of the sediment (fig. 86).

REFERENCES

Scruton (1956, 1960), Shepard (1960), Treadwell 

(1955), Van Andel and Poole (1960).

BARATARIA BAY, LOUISIANA

SETTING

Geology. Barataria Bay is on the southwest side of 

the postglacial delta built by the Mississippi River. 

Several barrier islands isolate the bay from the Gulf 

of Mexico.

Bathymetry. Most depths in the shallow bay are 

less than 6 feet (2 m). A channel which is about 18 

feet (5.4 m) deep extends into the central bay from 

Barataria Pass which is 165 feet (50 m) deep (fig. 87).

Hydrology. Fresh-water inflow from an ungaged 

canal, which joins the Mississippi River near New 

Orleans, is probably very small. The tidal range in the 

bay is less than 2 feet (0.6 m).

SEDIMENT TEXTURE

Bottom. Most of the bottom is covered by very fine 

sand. Only near Pass Justin and Pass Abel is fine sand 

predominant. Silt is most abundant in shallow protected areas around islands (fig. 88).

FIGURE 87. Bathymetry (in feet) of Barataria Bay, La. 

(from Krumbein and Caldwell, 1939).

EXPLANATION

O3 FINE SAND 29°I5 

VERY FINE SAND 

SILT

FIGURE 88. Texture of bottom sediments in Barataria Bay, 

La. Modified from Krumbein and Aberdeen (1937)
54 CHARACTERISTICS OF ESTTJARINE SEDIMENTS IN THE TT.Su

GULF OF 

MEX/CO

Nautical Miles

EXPLANATION 

% ORGANIC CARBON

 i

1=1 0. 0.5 

E3 0.5-1.0

E23 1 0-1.5

K3 1 5-2.0

a >2.o 89°55'

FIGURE 89. Organic carbon content of bottom sediments in 

Barataria Bay, La. (from Krumbein and Caldwell, 1939).

FIGURE 90. Calcium carbonate content (in percent) of 

bottom sediments in Barataria Bay, La. (from Caldwell, 

1940).

SEDIMENT COMPOSITION

Organic carbon (samples analyzed by the Popoff 

(1927) method). Most sediment in the bay contains 

less than 2.5 percent organic carbon. Highest values 

occur in silt deposits (fig. 89).

Mineralogy, Calcium carbonate concentrations generally range from 5 to 20 percent. Rare higher values 

are confined to areas surrounding small islands and to 

areas near oyster reefs. Most of the carbonate is concentrated in the finest sediments (fig. 90).

Heavy minerals throughout most of the bay make 

up 0.8 to 1.6 percent of the sand fraction. A few higher 

values occur in channels or passes.

REFERENCES

Caldwell (1940), Klovan (1966), Krumbein and 

Aberdeen (1937), Krumbein and Caldwell (1939), 

Scruton (1960).

SABINE LAKE, TEXAS AND LOUISIANA

SETTING

Geology. Sabine Lake is entirely within the Gulf 

Coastal Plain and is isolated from the Gulf of Mexico 

by a broad expanse of sand made up mostly of beach 

ridges (cheniers).

Bathymetry. The bottom dips gently from the 

northwest margin of the lake and more steeply on the 

southeast margin to a maximum depth of approximately 8 feet (2.4 m). Spoil due to dredging has 

formed a narrow island along the western margin of 

the lake (fig. 91).

Hydrology. The Sabine and Neches Rivers account 

for most of the fresh-water inflow to the lake. At gaging stations, approximately 25 nautical miles (46 km) 

north of the lake, average flow rate of the two rivers 

totals 430 m3 /sec.

SEDIMENT TEXTURE

Bottom. Most sediment on the lake bottom consists 

of fine sandy or clayey silt and very fine sand; however, near the mouths of the Neches and Sabine Rivers, 

fine sand is abundant (fig. 92). Sorting is generally 

poor in the finest material and improves in the sand. 

The silty muds, which contain abundant plant material, especially in the marshy areas around the eastern 

margin, are light to dark gray. The sands are mostly 

light gray.

Subbottom. Cores as much as 8 feet (2.4 m) long 

were recovered from the lake bottom; these consisted 

of a mixture of silt and clay. Gray to greenish-gray 

Pleistocene clay was penetrated by one core (depth 

was not given). Plant detritus is abundant below the 

bottom.
AREA SUMMARIES 55

2 9° 50' 

FINE SANO 

F53 VERY FINE SAND 

El SILT

FIGURE 91. Bathymetry (in feet) of Sabine Lake, Tex. and 

La. (from Kane, 1966).

FIGURE 92. Texture of bottom sediments in Sabine Lake, 

Tex. and La. (from Kane, 1966).

SEDIMENT COMPOSITION

Mineralogy. Quartz constitutes approximately 70 

percent and potassium feldspar 20 percent of the sand 

fraction. Plagioclase feldspar and chert make up most 

of the remainder. Opaque minerals account for 39-56 

percent of the heavy-mineral fraction, which makes 

up about 2-6 percent of the sediments, and zircon, 

tourmaline, monazite, hornblende, and apatite make up 

most of the remainder. Carbonates, consisting mostly 

of oyster and clam shells, make up as much as 20 percent of the total sediment.

REFERENCES 

Kane (1963, 1964, 1966).

TRINITY RIVER DELTA AND UPPER TRINITY 

BAY, TEXAS

SETTING

Geology. The Trinity River Delta has grown outward from the eastern side of the Trinity River alluvial valley, isolating part of Trinity Bay and forming Lake Anahuac. Upper Pleistocene deltaic sediments deposited by the Trinity and Brazos Rivers form 

bluffs around the upper bay.

Bathymetry. The upper bay has a flat floor and 

gentle slopes dip southwest toward the central area 

where the maximum depth is approximately 10 feet 

(3m) (fig. 93).
56 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

FIGURE 93. Bathymetry (in feet) of Trinity River Delta and 

Upper Trinity Bay, Tex. (from McEwen, 1963). Dashed 

contours enclose areas exposed at mean low water.

FIGURE 94. Texture of bottom sediments in Upper Trinity 

Bay, Tex. Modified from McEwen (1963).

Hydrology. Fresh-water discharge by the Trinity 

River averages approximately 240 m3 /sec at a gage 

about 40 nautical miles (74 km) upstream from the 

delta. Salinity of the bay is mostly a function of discharge of the Trinity River. Values range from 0 to 

15 parts per thousand during periods of normal runoff. 

Bottom salinities commonly are 2 to 5 parts per thousand greater than those at the surface. Dredging has 

resulted in salt-water encroachment into the Trinity 

River above Anahuac. Mean tidal range in the bay is 

about 1 foot (0.3 m), but water-level fluctuation 

caused by wind is common, and hurricanes have resulted in tidal ranges of 14 feet (4.2 m). The average 

silt load of the river is about 0.7 part per thousand 

(5.5 million tons per year).

SEDIMENT TEXTURE

Bottom. Silty clay covers most of the bottom in the 

central-upper part of Trinity Bay except around the

margins where sand derived from the Pleistocene 

bluffs predominates. The submerged delta front consists mostly of fine to medium sand which grades bayward into clay. Channels are filled with sediments 

ranging from cross-laminated sands to silty clays. On 

the surface of the subaerial delta, natural levees and 

marsh deposits consist mostly of sand and silty clays 

(fig. 94).

Subbottom. Silty and sandy clays exposed at the 

surface of the subaerial delta and levees are underlain 

by delta-front deposits consisting mostly of fine to 

very fine sands which become finer in texture with increasing depth. Shells are abundant near the base of 

these sections and decrease upward. Wood is locally 

abundant. Underlying prodelta sediments consist of 

Pleistocene fine to medium sand and overlying darkgray shelly sand, silt, and clay. Some of the sediment 

under Lake Anahuac is composed of black clay and 

peat (fig. 95).
AREA SUMMARIES 57

EXPLANATION

E3 SILT CLAY CI] VERY FINE-FINE SAND 

3 CLAYEY SAND £3 PRODELTA DEPOSITS

FIGURE 95. Map and cross sections showing sediment texture 

of the Trinity River Delta, Tex. Modified from McEwen 

(1963).

SEDIMENT COMPOSITION

Mineralogy. Predominant clay minerals in the bay 

area are kaolinite and montmorillonite, plus lesser 

amounts of illite. Clay carried by the Trinity Eiver 

consists mostly of montmorillonite. For example, clay 

minerals in the sample taken from a Trinity River 

point bar consisted of 61 percent montmorillonite, 23 

percent kaolinite, and 16 percent illite. Some Pleistocene deposits that contribute detritus to the margins 

of the bay consist of 39 percent montmorillonite, 48 

percent kaolinite, and 13 percent illite.

Bay sediments contain as much as 25 percent calcium carbonate, mostly as shell debris.

BRAZOS RIVER DELTA, TEXAS

SETTING

Geology. The Brazos drainage basin cuts rocks 

ranging in age from Paleozoic to Holocene. The delta 

lies on Quaternary deltaic sands and clays of the Gulf 

Coastal Plain. After the river was diverted in 1929 to 

its present channel, it built a delta which by 1952 extended nearly 2 nautical miles (3.6 km) into the gulf 

from the former shoreline. By 1964 the delta had been 

cut back and spread westward apparently by storms 

and prevailing longshore currents (figs. 96, 97).

Hydrology. At Richmond, 100 miles (185 km) upstream from its mouth, the average flow rate of the 

Brazos is approximately 200 m3 /sec. During the flood 

of 1930, the maximum flow rate measured at the mouth 

was about 2,000 m3 /sec. The river carries a suspended 

load averaging 4.5 parts per thousand which is the 

highest of any Texas river flowing into the gulf. The 

bedload consists of medium to fine sand 35-40 miles 

(65-74 km) upstream from the gulf and grades into 

silt near the river mouth.

REFERENCE

McEwen (1963).

FIGURE 96. Brazos River Delta, Tex., in 1964. Based on 

U.S.C. & G.S. Chart 887. Dotted line shows limit of 

marsh at mean low water. Dashed line shows approximate isobath, in feet.
58 CHARACTEEISTICS OF ESTUARINE SEDIMENTS IN THE U.Si.

Nautical Miles

24' 

J_

9 5° 22'

I

SEA 

LEVEL

W-14 W-5 W-13 W-2 E-6 E-2 E-8 E-13 E-19

325

EXPLANATION

E3 WATER

EZ3 SAND

S SILT

E3 CLAY

FIGURE 97. Texture of delta, bottom, and subbottom sediments 

of the Brazos River Delta, Tex., in 1952. Modified from Odem 

(1953). »E-2, indicates location and number of core.

SEDIMENT TEXTURE

Bottom. The distribution of various sediment sizes 

observed in 1952 is doubtless significantly different 

from that present today, for the delta has since 

changed both in size and shape (figs. 96 ,97). The sediment distribution shown in figure 96 has been inferred 

from only a few samples. Fine sand is most abundant 

along the original shoreline and along the beaches at

the seaward margin of the delta and on the bottom of 

most inlets. Silt covers most of the lagoon bottoms and 

the surfaces of the normally exposed marshy areas between the river channel and the lagoons (fig. 96).

Subbottom. Data from sediment cores 2-4 feet 

(0.6-1.2 m) long are shown for each major physiographic province of the delta (fig. 96). Interlayered 

silt and sand reflect changes in the position of the 

delta margin and channels with time.

SEDIMENT COMPOSITION

Mineralogy. Heavy minerals on the beaches include 

ilmenite, magnetite, zircon, garnet, and tourmaline and 

lesser amounts of epidote, staurolite, monazite, rutile, 

green hornblende, and spinel. The light fraction consists mostly of quartz and muscovite.

REFERENCE

Odem (1953).

MATAGORDA BAY, TEXAS

SETTING

Geology. Flat-lying Quaternary sand and clay deposits crop out, commonly in bluffs 5 to 8 feet (1.5- 

2.4 m) high, around the landward margin of Matagorda Bay. A postglacial barrier spit and island, the 

Matagorda Peninsula, separates the bay from the Gulf 

of Mexico. Holocene sediments at least as thick as 80 

feet (24 m) overlie a channeled Pleistocene surface 

in the bay.

Bathymetry. The rather smooth bottom of the bay 

averages approximately 11 to 12 feet (3.3-3.6 m) in 

depth and reaches a maximum depth of about 15 feet 

(4.5 m). The main inlet into the bay from the gulf, 

Pass Cavallo, is 42 feet (12.6 m) deep. The only other 

inlet, Green's Bayou, is less than 6 feet (1.8 m) deep. 

Shell reefs are common and extend bayward from 

several promontories (fig. 98).

Hydrology. Most fresh-water inflow comes from 

the Lavaca River which enters Matagorda Bay at its 

western end via Lavaca Bay. The river's average flow 

rate is approximately 20 m3 /sec; its maximum is about 

70 m3 /sec, and its minimum is about 1 m3/sec. Flow 

from the many small streams draining into the bay 

has been estimated at 18 m3/sec. During summer and 

fall, evaporation generally exceeds runoff and precipitation; this results in salinities of approximately 36 to

FIGURE 98 (right, top). Bathymetry (in feet) of Matagorda 

Bay, Tex. (from Fagg, 1957).

FIGURE 99 (right, bottom). Texture of bottom sediments in 

Matagorda Bay, Tex. (from Shenton, 1957).
AREA SUMMARIES 59

96°32' 96°26' 96" 14'

96°26 96-22' 9618'

SAND, SILT,CLAY 

SAND, SILT.CLAY, SHELL 

SAND,SHELL,SILT.CLAY, 

E3 REEF
60 CHARACTERISTICS OF ESTUARINE SEDIMENTS EST THE U.S.

37 parts per thousand in the bay. During winter and 

spring, however, values are generally less than 30 

parts per thousand. The tidal range is less than 2 feet 

(0.6 m), but storms may cause extreme changes in 

water level. At maximum flood tide, current velocities 

of 2 knots (100 cm/sec) through Pass Cavallo have 

been observed. Within the bay, however, current velocities due to tides are very small.

SEDIMENT TEXTURE

Bottom. In water depths exceeding 9 feet (2.7 m) 

most of the bottom is covered by silt and clay. Sand, 

which is present around the southwestern and northwestern shores, grades bayward into a mixture of sand, 

silt, and clay. Sand also is abundant in Pass Cavallo. 

Shell debris, which occurs in patches, is most abundant 

near promontories. The sand is usually well sorted except where shells and shell debris are abundant; but 

finer sediments, silt and clay, are poorly to very poorly 

sorted. Keefs are associated with a mixture of sediment 

types (fig. 99).

Subbottom. Cores have been recovered along a traverse bisecting the long axis of the bay. The texture of 

the Holocene subbottom varies slightly with depth 

from silty clay to sandy, clayey silt (Fagg, 1957, figs. 

3-8).

SEDIMENT COMPOSITION

Mineralogy. Quartz predominates in the coarse 

fraction of the sediments, but mica, magnetite, glauconite, and pyrite are also common. Carbonates composed mostly of foraminifer tests and mollusk shells 

and shell fragments are locally abundant.

REFERENCES

Fagg (1957), Shenton (1957), Weiser and Armstrong (undated).

SAN ANTONIO BAY, TEXAS 

SETTING

Geology. San Antonio Bay is flanked on the northwest and west by a Pleistocene barrier island and to 

the north by Quaternary delta and flood-plain alluvium. Matagorda Island, a postglacial barrier island, separates the bay from the Gulf of Mexico.

Bathymetry. The delta of the Guadalupe Eiver 

divides the head of the bay (fig. 100) into two parts 

which are mostly less than 4 feet (1.2 m) deep. Water 

depth increases southward to approximately 6 feet 

(1.8 m), except where oyster beds form shoals. Mesquite Bay, to the west, is mostly less than 5 feet (1.5 

m) deep.

Hydrology. Fresh-water inflow is derived mostly 

from the Guadalupe-San Antonio River system which

FIGURE 100. Bathymetry (in feet) of San Antonio Bay, 

Tex. (from Shepard and Moore, 1955).

enters the bay through Mission Lake. The average rate 

of flow in this system, measured approximately 30 

nautical miles (55 km) north of the bay head, is about 

60 m3 /sec. During spring floods, salinities in waters 

throughout most of the bay may be only a few parts 

per thousand. During dry periods in late summer, 

values may range from 14 parts per thousand at the 

bay head to 40 parts per thousand in the shallow restricted waters of Mesquite Bay. The tidal range is 

only about 1 to 2 feet (0.3-0.6 m) and winds are responsible for most fluctuations of water level. Currents are generally less than 1 knot (50 cm/sec).

SEDIMENT TEXTURE

Bottom. Silty clay covers most of the bottom of the 

central bay. A north-south trending oyster reef di-
AREA SUMMARIES 61

FIGURE 101. Texture of bottom sediments in San Antonio 

Bay, Tex. (from Shepard and Moore, 1955).

vides the lower bay into two areas of different texture. 

West of the reef, silty clay is most abundant; east of 

it, silty sand and a mixture of sand-silt-clay predominate. Sand, silty sand, and clayey sand are most common along the margins of the lower bay (fig. 101).

Subbottom. Sediments recovered from holes drilled 

along the axis of the bay consist mostly of silty clay 

and oyster shells. Only near the barrier island is sand 

abundant in the upper 20 feet (6 m) of the section 

(Shepard and Moore, 1960, fig. 18).

SEDIMENT COMPOSITION

Organic carbon (samples analyzed by the Krogh 

and Keys (1934) technique). Concentrations of organic carbon are 2-3 precent in the silts and clays of

FIGURE 102. Calcium carbonate content (in percent) of 

bottom sediments in San Antonio Bay, Tex. (from 

Shepard and Moore, 1955).

the upper bay and are less than 1 percent in sands of 

the lower bay.

Mineralogy. The coarse fraction of the sediments 

consists mostly of quartz, plagioclase feldspar, and 

potassium feldspar. Heavy minerals make up less than 

1 percent of the sediment and include such stable 

minerals as tourmaline, garnet, zircon, and rutile. 

Most staurolite occurs in sediments near the Guadalupe 

delta; hornblende is most concentrated near Matagorda Island.

In the fine fraction, montmorillonite, chlorite, and 

illite are equally abundant in the lower bay. In the 

upper bay, however, montmorillonite predominates. 

Calcium carbonate ranges from almost 40 percent in
62 CHARACTERISTICS OF ESTUARINE SEDIMENTS EST THE U.S.

oyster reefs to about 5 percent around sandy margins 

(fig. 102).

REFERENCES

Shepard and Moore (1955, 1960).

ARANSAS BAY, TEXAS

SETTING

Geology. Aransas Bay is flanked to the northwest 

by a Pleistocene barrier island and is isolated on the 

southeast from the Gulf of Mexico by a postglacial 

barrier island consisting of dunes and washover fans 

as much as 50 feet (15 m) thick.

Bathymetry. Depths increase rapidly from the bay 

margin toward the rather flat floor of the bay (fig. 

103). A northwest-trending reef divides the bay into 

two parts. Maximum depth in the southwestern part is 

approximately 13 feet (4 m) ; maximum depth in the 

northeastern part is only about 7 feet (2.1 m).

Hydrology. Fresh-water inflow directly into the 

bay is negligible. Most fresh water is derived from 

adjacent connecting bays and causes a mean salinity 

in the bay waters of about 12 parts per thousand. The 

tidal range is only 1 to 2 feet (0.3-0.6 m), but storm 

winds cause water-level variations of 4 to 5 feet (1.2- 

1.5 m). At Aransas Pass, current velocities may exceed 1 knot (50 cm/sec) depending on wind direction 

and velocity.

SEDIMENT TEXTURE

Bottom. Clayey or silty sand is abundant around 

the margin of the southwestern part of the bay, but 

silty clay predominates over most of the bottom. Sand 

along the southeastern shore is derived mostly from 

the barrier island. In the northeastern section of the 

bay, silty sand is most abundant (fig. 104).

Subbottom. Size analyses of sediment samples 

taken from one core recovered in the bay indicate that

C t£S3 CLAYEY-SILTY SAND

FIGURE 103. Bathymetry (in feet) of Aransas Bay, Tex. 

(from Shepard and Moore, 1955).

FIGURE 104. Texture of bottom sediments in Aransas Bay, 

Tex. Modified from Shepard and Moore (1955).
AREA SUMMARIES 63

the coarser fraction increases at approximately 60 cm 

below the bottom.

SEDIMENT COMPOSITION

Organic carbon (samples analyzed by the Krogh and 

Keys (1934) technique). Concentrations of organic 

carbon are generally slightly in excess of 1 percent in 

the fine sediments at the center of the bay and are less 

than 1 percent elsewhere.

Mineralogy. In the coarse fraction (>62 microns), 

light minerals are present in the following proportions: quartz, 65 percent; plagioclase feldspar, 22 percent; and potassium feldspar, 12 percent. Heavy minerals amount to less than 1 percent of the total sediment.

In the fine fraction, montmorillonite, chlorite, and 

illite are present in roughly equal proportions. Carbonates, which generally make up less than 20 percent

FIGURE 105. Calcium carbonate content (in percent) of 

bottom sediments in Aransas Bay, Tex. (from Shepard and 

Moore, 1955).

of the total sediment, consist mostly of shells of 

foraminifers and lesser amounts of ostracode, echinoid, 

and mollusk shells (fig. 105).

REFERENCES

LeBlanc and Hodgson (1961), Shepard and Moore 

(1955, 1960).

LACUNA MADRE, TEXAS

SETTING

Geology. Upper Quaternary sediments on the mainland adjacent to Laguna Madre consist mostly of 

clayey sands. A barrier island (Padre Island), built 

during the postglacial rise in sea level, forms the eastern margin. The island has periodically been cut by 

narrow inlets, and in the lagoon, deltas and washover 

fans are common. Sand flats (Saltillo flats), built up 

by landward movement of sediment from the barrier 

island, divide the bay into northern and southern parts.

Bathymetry. The bottom of the shallow lagoon 

slopes evenly from exposed sand flats on the eastern 

side to a few deep (8 feet or 2.4 m) elongate basins 

close to the western margin (fig. 106). The Intracoastal Waterway channel is maintained along the 

western side at an approximate depth of 9 to 12 feet 

(2.T-3.6 m).

Hydrology. No major streams drain into the lagoon, and evaporation generally exceeds precipitation 

and local runoff. In the northern bay, salinities are directly related to abundance of rainfall and generally 

range from 30 to 80 parts per thousand. Waters in the 

southern area, which is nearer the Brazos Santiago 

Pass, have salinities more typical of the open gulf. 

Celestial tides may vary by 12 to 18 inches (0.3-0.5 m) 

in spring and fall, but diurnal tides are absent in the 

lagoon. Extreme winds, however, cause variations in 

water level of 3 to 4 feet (0.9-1.2 m). Most water circulation is controlled by wind. Velocities at Brazos 

Santiago Pass are generally less than 1 knot (50 cm/ 

sec). Water is often turbid because strong winds, 

which blow from the southeast at 9 to 14 miles per 

hour (14-23 km/hr) during seven months of the year, 

generate waves that stir up the bottom sediments in 

the shallow bay.

SEDIMENT TEXTURE

Bottom. On the eastern side of the lagoon most 

sediment consists of very fine well-coated quartz sand 

derived from the barrier island by normal windgenerated wave action and by storm-wave washover. 

Clayey and silty sand increases in abundance in the 

narrow deeper areas close to the western shore (fig. 

108).

460-197 O - 72 - 4
64 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

FIGURE 106. Bathymetry (in feet) of Laguna 

Madre, Tex. (from Rusnak, 1960). Dashed 

contour indicates area exposed at mean low 

tide.

Subbottom. The general distribution of sediment 

to a depth of approximately 20 feet (6m) at mean 

low water (M.L.W.) along points A, B, and C of figure 

108 is shown in figure 107.

SEDIMENT COMPOSITION

Organic matter (data based on dry weight loss after 

digestion with H2O2 ). The highest concentrations of 

organic matter (6 to 7 percent) occur in algal mat 

deposits which occur in shoal areas; but throughout 

most of the sandy bay, values are less than 1 percent.

Mineralogy. Quartz constitutes 90 percent, feldspar less than 10 percent, and chert 1 to 5 percent, of 

the terrigenous fraction. The northern area contains a

138VSI 1UO

t

22 o o

 a

I1

a

2

oo 

o

O 

73

a

Io

I 

l-l

O

oIH

ta
AREA SUMMARIES 65

FIGURE 108. Texture of bottom sediments in 

Laguna Madre, Tex. Modified from Rusnak 

(1960). Points A, B, and C lie along the 

sections shown in figure 107.

FIGURE 109. Calcium carbonate content (in 

percent) of the fine fraction «62 microns) of 

bottom sediments in Laguna Madre, Tex. 

(from Rusnak, 1960).

suite of heavy minerals including tourmaline, zircon, 

kyanite, and staurolite derived mostly from local outcrops of Pleistocene sediment. South of the barrier 

flats the heavy-mineral suite consists mainly of green 

hornblende, pyroxene (augite), epidote, and basaltic 

hornblende and is apparently derived from erosion 

and shoreward drift of Pleistocene Kio Grande delta 

material that is exposed along the shore and occurs 

near shore on the gulf bottom. The distribution of carbonate in the fine sediment fraction (< 62 microns) is 

shown in figure 109. Fine-grained well-sorted oolites 

are most abundant on the wave-exposed shores of the 

northern lagoon and decline rapidly in abundance with 

distance from the shoreline.

REFERENCES 

Breuer (1957), Kusnak (1960), Simmons (1957).

BAFFIN BAY, TEXAS

SETTING

Geology. Upper Pleistocene to Holocene dune sand 

is widespread south of Baffin Bay. The Beaumont 

clay (Pleistocene), part of the Nueces Kiver deltaic 

plain, forms bluffs along the northern margin. The bay 

opens into Laguna Madre which is isolated from the 

Gulf of Mexico by Padre Island.

Bathymetry. Numerous shoals border the bay and 

restrict the water circulation, particularly where the 

shoals extend bayward from promontories (fig. 110).
66 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

FIGURE 110. Bathymetry (in feet) of Baffin Bay, Tex. (from Rusnak, 1960). Stippled areas are shoals.

EXPLANATION

E3 SAND

SILTY-CLAYEY SAND 

E3 CLAY

^MI^^^^Mr^ &' ' ' V.-^.- 

^YOD^^|BK^v"-( .-Vtvvtv^V:

I N F IE R NILiar^T-T^: ' > ' . '\-\^C-"\*-Ji

mf^f'.^^^iS

FIGURE 111. Texture of bottom sediments in Baffin Bay, Tex. Modified from Rusnak (1960).
AREA SUMMARIES 67

From the shoals, water deepens rapidly to the basin 

floor where depths exceed 6 feet (1.8 m).

Hydrology. Runoff into the bay from a few streams 

is intermittent and salinity generally varies inversely 

with rainfall. Salinity from 1951 to 1953 ranged from 

a low of 1.4 parts per thousand to a high of 75 parts 

per thousand with a mean of approximately 52 parts 

per thousand. Lunar tides are negligible and have a 

range of only 12 to 18 inches (0.3-0.5 m) in spring 

and fall. Strong winds, however, result in considerable 

exchange of water between Baffin Bay and Laguna 

Madre and cause significant changes in water level. 

Wind-generated waves and currents are sufficiently 

strong over shoal areas at the entrances to Baffin and 

Alazan Bays to cause scour.

SEDIMENT TEXTURE

Bottom. The margins of the bay are covered mostly 

with fine sand (fig. 111). Most coarser components 

comprise pelecypod shells and shell fragments. Very 

fine sand, silt, and clay predominate in the central area 

of the bay where water depths are in excess of 5 feet 

(1.5 m).

SEDIMENT COMPOSITION

Organic carbon. Measurements of organic carbon in 

the bay average approximately 1.5 percent. An H2 S 

odor is common in the sediments.

Mineralogy. Noncarbonates consist mostly of 

quartz plus minor feldspar and chert. Quartz sands 

are most widespread in Alazan Bay but are common 

around the entire bay margin. Based on limited data, 

the black silty clay accumulating in the deep central 

part of the bay consists mostly of quartz and illite 

plus minor amounts of montmorillonite, kaolinite, or 

chlorite. Carbonates, including shells and shell debris, 

and oolites which are abundant along wave-washed 

basins and as coatings on silicate grains constitute a 

mean of 35 percent of the sediment.

REFERENCES 

Breuer (1957), Dalrymple (1964), Rusnak (1960).

SAN FRANCISCO BAY, CALIFORNIA 

SETTING

Geology. The San Francisco Bay complex, which 

includes Suisun Bay, San Pablo Bay, and central and 

south San Francisco Bay, lies in a structural valley 

between the Santa Cruz Mountains on the west and 

the Diablo Mountains on the east. The faulted synclinal depression which probably began to form in late 

Pliocene time is surrounded by rocks ranging in age 

from Late Jurassic to Holocene. Sediments adjacent to 

the bay and those overlying bedrock (Franciscan Formation of Late Jurassic to Late Cretaceous age) in the 

bay consist mostly of Pleistocene sand, silt, and clay as 

much as 300 feet (90 m) thick. Estimates of the sedimentation rate of unconsolidated bay sediments are 

between 1 and 7 feet (0.3-2.3 m) per thousand years.

Bathymetry. Approximately 70 percent of the bottom of the bay complex is less than 18 feet (5.4 m) 

deep and 80 percent is less than 30 feet (9m) deep. 

Tidal flats surround most of the bay complex (fig. 

112). Maximum depths in channels in the middle of 

the northern part of San Francisco Bay are about 80 

feet (24 m). South of Dumbarton Bridge maximum 

depths are approximately 50 feet (15 m), but at mean 

lower low water average depths are less than 6 feet 

(2 m). At the Golden Gate Bridge the water depth is 

about 380 feet (114m).

Hydrology. The San Joaquin and Sacramento 

Rivers carry over 70 percent of the average freshwater inflow (800 m8 /sec) to the bay. Runoff is greatest during the winter and spring. The Sacramento 

River transports most (70 percent) of the suspended 

sediment entering the bay; the San Joaquin accounts 

for 13 percent, and smaller rivers and creeks account 

for the remainder. The mean tidal range varies from 

about 4 feet (1.2 m) at Antioch to 8.5 feet (2.6 m) at 

Calaveras Point. The average salinity of the whole bay 

complex is about 27 parts per thousand. Values in 

Suisun Bay range from zero at the east end to 27 parts

FIGURE 112. Bathymetry of the San Francisco Bay system, 

California (from TJ.S.C. & G.S. Charts 5531-5534).
68 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

EXPLANATION

C3 COARSE SAND 

ESS MEDIUM SAND 

E53 VERY FINE-FINE SAND

SILT 

E3 CLAY

ROCK

FIGURE 113. Texture of bottom sediments in the San 

Francisco Bay system, California. Data in Suisun Bay are 

generalized from Reese (1965) and Slater (1965); in San 

Pablo Bay, from Trask (1953) and Storrs and others (1963); 

in Richardson Bay, from Means (1965); in central San 

Francisco Bay, from Trask (1953) and Gram (1966); in 

south San Francisco Bay, from Conomos (1963); and west 

of the Golden Gate Bridge, from Schatz (1963).

per thousand at the west end. Average salinity at Dumbarton Bridge is 28 parts per thousand. Maximum 

currents at ebb and flood tide in central San Francisco 

Bay are about 2 knots (100 cm/sec). Ebb currents in 

Carquinez Strait are significantly stronger and reach 

4 knots (200 cm/sec).

SEDIMENT TEXTURE

Bottom. Sediment carried into the bay (mostly by 

the Sacramento River) is composed of approximately 

60 percent clay, 30 percent silt, and 10 percent fine 

sand. Sediment texture on the bottom of San Pablo 

Bay varies with seasonal changes in suspended load. 

Silt and clay, for example, cover the bottom in winter 

and spring as a result of high runoff. In summer much 

of the fine material is stirred into suspension by windgenerated waves and transported to shallow protected 

areas where wave and current energy is not sufficient to 

keep the material in suspension.

Detailed maps of bottom sediment texture are available for Suisun Bay, Richardson Bay, and south San 

Francisco Bay. For central San Francisco and San 

Pablo Bays, sediment texture has been inferred from

FIGURE 114. Organic carbon content (in percent) of bottom 

sediments in the San Francisco Bay system, California. 

Data in Suisun Bay generalized from Reese (1965) and 

Slater (1965); in Richardson Bay, from Means (1965); and 

in south San Francisco Bay, from Conomos (1963).

descriptive data compiled by Trask (1953) and from 

analyses of samples collected repeatedly at only a few 

locations (Storrs and others, 1963).

In the northern parts of the bay complex, fine to 

medium sand generally covers channel bottoms; silt 

and clay is widespread in the shallow areas and tidal 

flats. Bedrock surrounded by gravel and coarse sand is 

exposed over a considerable area of the bottom in central San Francisco Bay. Throughout south San Francisco Bay, silt and clay predominate (fig. 113).

SEDIMENT COMPOSITION

Organic carbon. Analyses were carried out by the 

Carbon Determinator No. 30003 (commercial unit 

manufactured by the H. W. Diedrich Company) and 

by the Allisson (1935) technique.

Measurements of organic carbon in Suisun, San 

Pablo, Richardson, and south San Francisco Bays are 

shown in figure 114. Most values are less than 2 percent organic carbon in silts and clays and less than 1 

percent in sands. At a few localities in Suisun Bay, 

concentrations in peat are as high as 17 percent (not 

shown). Although industrial contaminants are 

abundant throughout the bay they do not seem to be
AREA SUMMARIES 69

reflected by the available measurements of organic 

carbon in the sediments. Concentrations in south San 

Francisco Bay and San Pablo Bay vary little with 

season. Some measurements taken in Suisun Bay, 

however, range from 3.4 percent in September to 1.2 

percent in March.

Mineralogy. In Suisun Bay, light minerals that 

make up as much as 90 percent of the sand fraction 

consist of 51 percent quartz, 31 percent plagioclase 

feldspar, 5 percent potassium feldspar, and 13 percent rock fragments. Heavy minerals make up 0 to 19 

percent of the sand fraction (highest values occur in 

main channels, lowest values near shore) and consist 

mainly of biotite, magnetite, hornblende, and garnet. 

The average clay-mineral composition in Suisun Bay 

sediment according to Slater (1965) is 47 percent 

montmorillonite, 35 percent chlorite, and 18 percent 

vermiculite; according to Keese (1965), however, the 

clay minerals consist of 34 percent kaolinite, 39 percent illite, 14 percent montmorillonite, and 13 percent vermiculite.

In central San Francisco Bay, pebbles and cobbles 

are composed mostly of chert, serpentine, and graywacke. In the sand fraction, quartz and plagioclase 

predominate over potassium feldspar which generally 

constitutes less than 10 percent of the assemblage. 

Heavy minerals (13 percent of the sand fraction) 

consist mostly of serpentine, glauconitic material, chlorite, and various amphiboles and pyroxenes. Montmorillonite and kaolinite are the most abundant clay 

minerals.

In south San Francisco Bay, quartz, feldspar, and 

rock fragments are present in a ratio of 2:1:1 and 

quartz, plagioclase feldspar, and potassium feldspar 

are present in a ratio of 6.5:2.5:1. Heavy minerals, 

which roughly range in concentration from 3 to 30 

percent, consist mostly of magnetite, ilmenite, serpentine, and tremolite-actinolite. Clay minerals are present as montmorillonite-chlorite-illite in the ratio of 

3:1:1.

Carbonates are sparse throughout most of the bay 

and seldom exceed 4 percent of the total sediment except in a few areas where shell banks are present.

REFERENCES

Conomos (1963), Goldman (1967), Gram (1966), 

Harris, Feuerstein, and Pearson (1961), Krone 

(1966), McCarty and others (1962), Means (1965), 

Mitchell (1963), Porterfield, Hawley, and Dunnam 

(1961), Keese (1965), Schatz (1963), Slater, (1965), 

Smith (1965), Storrs, Selleck, and Pearson (1963), 

Trask (1953), Treasher (1963).

YAQUINA BAY, OREGON

SETTING

Geology. Yaquina Bay is located on the western 

flank of the central Oregon Coast Kange. The drainage system is superimposed on a Tertiary volcanic 

complex of lava flows, tuffs, and breccias. Along the 

southern margin of the bay close to the shoreline, migrating dunes cover parts of Pleistocene marine terraces.

Bathymetry. The central channel of the bay from 

the mouth to Oneatta Point is 20 to 30 feet (6-9 m) 

deep. It is flanked on both sides by shallow broad 

tidal flats. The bottom topography has been altered 

significantly by the construction of jetties at the bay 

mouth and by dredging (fig. 115).

Hydrology. Average rate of fresh-water inflow 

from the Yaquina Kiver was measured in February 

1965 at 17 m3 /sec and in August 1965 at 1 m3/sec. 

Normal marine salinities at the mouth grade into 

fresh water at the head of the estuary. The water is 

partly mixed in winter and spring and well mixed 

in summer and fall. Mixed semidiurnal tides have an 

average range of 5.5 feet (1.7 m). Maximum tidal 

current velocities near the entrance are in excess of 

2 knots (100 cm/sec). Maximum ebb current velocities 

slightly exceed those of maximum flood currents.

SEDIMENT TEXTURE

Bottom. From the mouth of the estuary to Oneatta 

Point, sediments in the channel are composed of fine 

to medium sand. Sandy silt covers the bottom in King 

Slough and on tidal flats at Sally's Bend. Between 

Coquille Point and Oneatta Point medium to fine sand 

in the central channel grades into poorly sorted silty 

sand and sandy silt at the margins (fig. 116).

SEDIMENT COMPOSITION

Organic carbon (samples analyzed by the Curl 

(1962) technique). Highest concentrations of organic carbon (as much as 2.7 percent) occur in sediments that accumulate in sloughs or on tidal flats in 

quiet shallow water. The two values that were measured in well-sorted channel sediments are less than 

0.2 percent (fig. 117).

Mineralogy. The distribution of minerals in the 

bay sediments is due to two main sediment-source 

areas. For approximately 1.5 nautical miles (2.8 km) 

up the estuary from the mouth, migrating dunes derived from Pleistocene terrace sands, nearby beach deposits, and near-shore marine deposits contribute sediment to the estuary. This source material is of sub-
70 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE TT.SL

 44°36'

FIGURE 115. Bathymetry (in feet) of Yaquina Bay, Oreg. (from Kulm and Byrne, 1966).

arkosic composition (quartz-feldspar ratio generally 

less than 1) and contains heavy minerals such as 

pyroxene, hypersthene, and diopside in concentrations as high as 15 percent. Upstream above Oneatta 

Point, sediment composition is due to river-transported detritus, which is more arkosic (quartz-feldspar ratio less than 1) than the source material downstream, and has a heavy-mineral suite consisting 

mostly of biotite, muscovite, hematite, and limonite. 

Yellow sand grains composed mostly of weathered 

feldspars, cherts, and volcanic rock fragments are 

most abundant (10 percent) in sediments along the 

Pacific shoreline and in the channel at the mouth of 

the estuary. In the estuarine sediments the concentration of these grains declines to zero in the area of 

Oneatta Point. The mineralogy of sands accumulating 

on tidal flats at Sally's Bend reflects the fluviatile 

source whereas that of sediments accumulating on the 

southern margin of the bay is controlled mostly by 

material contributed by wind from contiguous dunes. 

Carbonates. One to seven percent of the sand fraction consists of molluscan shell fragments and foraminiferal tests. The high carbonate concentrations in 

river channel depressions and tidal flats decrease toward the bay margins (fig. 118).

REFERENCES 

Kulm and Byrne (1966, 1967).

WILLAPA BAY, WASHINGTON

SETTING

Geology. Willapa Bay is located in an area of 

folded sedimentary rocks west of the Coast Ranges. 

Lower Miocene tuff, agglomerate and lava crop out 

at the northeastern end of the bay. To the south, 

middle Miocene sandstone overlies Oligocene shale 

and sandstone exposed in a syncline. Long Beach 

Peninsula, a Holocene spit, protects much of the bay 

from the open ocean.

Bathymetry. Fifty-five percent of the bay is intertidal, and smooth flat topography predominates in 

water less than 18 feet (5.4 m) deep. Steep-sided 

channels occupy the midbay. Only the Willapa River 

channel is dredged. Tidal scour is apparently re-
AREA SUMMARIES 71

EXPLANATION

 44°36'

FINE AND MEDIUM SAND 

SILTY SAND 

CLAYEY SAND

SANDY SILT

SAND-SILT-CLAY

FIGURE 116. Texture of bottom sediments in Yaquina Bay, Oreg. Modified from Kulm and Byrne

(1966).

FIGURE 117. Organic carbon content (in percent) of bottom sediments in Yaquina Bay, Oreg. (from 

Kulm and Byrne, 1966). Dot in triangle shows measurement of channel sediments; other measurements were in sloughs or on tidal flats.
72 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

FIGURE 118. Calcium carbonate content (in percent) of bottom sediments Yaquina Bay, Oreg.

(from Kulm and Byrne, 1966).

sponsible for maintaining the depth of 97 feet (30 m) 

at the bay entrance (fig. 119).

Hydrology. The average rate of total fresh-water 

inflow from the Willapa, Nemah, Naselle, and North 

Rivers is roughly 100-150 m3/sec. Mixed tidal ranges 

vary from 8.1 feet (2.5 m) at the bay entrance to 

10.2 feet (3.1 m) at Nahcotta. Maximum currents at 

the bay mouth average approximately 2.5 knots (125 

cm/sec) but may attain 4 to 6 knots (200-300 cm/ 

sec) at ebb tide.

SEDIMENT TEXTURE

Bottom. Fine sand covers most of the bottom. Silt 

seems to be most abundant near river mouths and on 

tidal flats. With few exceptions, coarsest material is 

restricted to narroAv channels (fig. 120).

SEDIMENT COMPOSITION

Organic carbon (sample analyses by the Leco gas 

analyzer). Measurements were made on samples collected mostly from the margins of the bay. Concentrations are inversely related to grain size (fig. 121). 

Most organic carbon, therefore, is accumulating with 

silt and clay near river mouths and on tidal flats 

(fig. 122).

Mineralogy. Quartz predominates in the lightmineral fraction, which also contains a small percentage of unaltered plagioclase feldspar. Opaque 

minerals consist mostly of magnetite, plus small quantities of ilmenite and rutile. Among the heavy minerals, orthopyroxenes and amphiboles are most abundant. Pumice is present in most samples. No data are 

available on the concentrations of layered silicates.

REFERENCE

Andrews (1965).

GRAYS HARBOR, WASHINGTON

SETTING

Geology. Grays Harbor lies immediately south of 

the Olympic Mountains in a hilly region where elevations seldom exceed 600 feet (180 m). The oldest rocks 

exposed in the area are Tertiary. Unconsolidated to 

partly consolidated Pliocene sand and gravel crop out 

in bluffs at Point New and on the eastern side of 

South Bay. Oligocene and Pliocene marine shaly sandstone and Pleistocene deposits are exposed around the 

inner harbor. Holocene terraces lie on marine sands on 

the western margin of the outer harbor.
AREA SUMMARIES 73

FIGURE 119. Bathymetry (in feet) of Willapa Bay, Wash, 

(from Andrews, 1965).

FIGURE 120. Texture of bottom sediments in Willapa Bay, 

Wash. Based on data of Andrews (1965).

Bathymetry. Only 40 percent of the harbor lies 

below mean lower low water. The remainder consists 

of tidal flats. Although channels depths reach about 80 

feet (24 m), the bottom is generally shallower than 

25 feet (7.5 m). Between 1933 and 1961 the harbor 

became shallower at an average rate of approximately 

1 cm/year. Only North Bay and the channel entrance 

appear to have been eroded during that time. Spoil 

from the dredging of channels has been dumped in 

the harbor entrance (fig. 123).

Hydrology. The Chehalis River system accounts 

for about 80 percent of the fresh-water drainage into 

the harbor. The mean flow rate of the river in 1954 

was approximately 280 m3/sec. In winter fresh water 

at the head of the harbor grades into Pacific Ocean 

water that has salinities of 30 to 31 parts per thousand at the harbor entrance. In summer when runoff 

is at a minimum, salinities may reach 16 to 23 parts 

per thousand near the mouth of the Chehalis River. 

Tides are of the mixed type. The mean tidal range in-
74 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

3.0

o

QQ 

<t

22.0

<fc

o 

k. 1.0

EXPLANATION 

O TIDAL FLAT 

 ~&H-OW MEAN LOWER LOW WATER

0.500 0.250 0.125 0.062 0.034 

ME A N GRAIN SIZE (mm)

0.016 0.008

FIGURE 121. Relation of organic carbon content to mean 

grain size of bottom sediments in Willapa Bay, Wash, 

(from Andrews, 1965).

creases from 6.9 feet (2.1 m) at the harbor entrance to 

7.8 feet (2.4 m) at the harbor head. Tidal currents 

are generally about 2.5 knots (125 cm/sec) but maximum velocities of 5 knots (250 cm/sec) occur during 

spring tides. Current velocities do not change appreicably with depth. Ocean swells in the outer harbor 

generally do not exceed about 3 feet (0.9 m) in height.

SEDIMENT TEXTURE

Bottom. Coarse sand is limited to the channel at 

the harbor entrance. Fine to very fine sand covers 

most of the bottom in the outer harbor, much of North 

Bay and northern South Bay, and the western parts 

of the channels of the inner harbor. Poorly sorted 

sandy silt is present along the shore of North Bay 

and on tidal flats nearest the mouth of the Chehalis 

River (fig. 124) ; it is also present (not shown in fig. 

124) along the shore of South Bay.

SEDIMENT COMPOSITION

Organic carbon (samples analyzed by the Allisson 

(1935) technique). Only a few analyses are available. In North Bay, sand contains 0.01 to 0.9 percent 

organic carbon, and silt contains approximately 0.9 

to 2.0 percent. Insufficient data are available to evaluate the effects of industries located near the head of 

the harbor on the carbon concentration (fig. 125).

Mineralogy. The coarse fraction of the sediment 

consists mostly of rock fragments, minerals, wood, and 

mud galls. Heavy minerals, constituting less than 1 

percent to 16.5 percent of the total sediment, include 

50 percent rock fragments, 35 percent hypersthene, 

8 percent olivine, 7 percent hornblende, and minor 

amounts of garnet, chlorite, and corundum (fig. 126). 

No information is available on the composition of the 

clay minerals.

FIGURE 122. Organic carbon content (in percent) of bottom 

sediments in Willapa Bay, Wash, (from Andrews, 1965).

REFERENCES

Milliman (1963), Washington [State] University 

Department of Oceanography (1955).

BELLINGHAM BAY, WASHINGTON

SETTING

Geology. East of Bellingham Bay glacial debris, 

Eocene sedimentary rocks, and metamorphic rocks are 

exposed on steep hillsides. Lowlands at the northern 

and southern ends are covered by marine silt and clay
AREA SUMMARIES 75

FIGURE 123. Bathymetry (in feet) of Grays Harbor, Wash, (from Milliman, (1963).

EXPLANATION 

E3 COARSE SAND 

E3 MEDIUM SAND 

EH FINE SAND 

ED VERY FINE SAND 

S3 SANDY SILT 

5

Nautical Milts

FIGURE 124. Texture of bottom sediments in Grays Harbor, Wash. Modified from Milliman (1963).
76 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

FIGURE 125. Organic carbon content (in percent) of bottom sediments in Grays Harbor, Wash, (from

Milliman, 1963).

Nautical Miles

FIGURE 126. Heavy-mineral content (in percent) of bottom sediments in Grays Harbor, Wash, (from

Milliman, 1963).
AREA SUMMARIES 77

and glacial detritus. The islands, separating the bay 

from Puget Sound to the west are composed mostly of 

metamorphic rocks. Total thickness of imconsolidated 

sediment in the bay is not known, but bedrock was encountered at 245 feet (75 m) in a water well drilled 

at Marietta.

Bathymetry. Most of the bay (fig. 127) is less than 

100 feet (30 m) deep. The deepest area, between 

Eliza and Vendovi Islands, reaches 335 feet (102 m). 

In the southern part of the bay, depths are less than 

60 feet (18 m), except for a depression northwest of 

Samish Island which is 192 feet (59 m) deep.

Hydrology. Approximately 75 percent of the fresh 

water flowing into the Bellingham-Samish Bay drainage basin is derived from the Nooksack River, which 

flows at a mean rate of approximately 100 m3/sec, and 

the Samish River, which flows at roughly 7 m3 /sec. In 

winter when runoff is greatest, water at the mouth of 

the Nooksack River is fresh. Normal salinities (29 

parts per thousand) are generally present south of a 

line between Point Francis and Post Point. In late

summer when runoff is lowest, salinities near 29 parts 

per thousand are present throughout the bay. The 

mean diurnal tidal range in the bay is 8.6 feet (2.6 

m). Except in passages between islands, current ve: 

locities are generally less than 0.6 knots (30 cm/sec).

SEDIMENT TEXTURE

Bottom. Sediments in the bay have been divided 

into three textural provinces: well-sorted medium 

sand, which makes up the deltas at each end of the 

bay; clayey silt, which covers most of the central part 

of the bay; and well-sorted gravel (median diameter 

about 24 mm), which has accumulated on the sill 

between Point Francis and Eliza Island (fig. 128).

Subbottom. Cores collected at each end of the bay 

within the area covered by silt were megascopically 

homogeneous to a depth of 36 feet (11 m).

SEDIMENT COMPOSITION

Organic carbon. No quantitative data are available. 

Wood fragments derived from a papermill are abundant in the bottom sediments. Within a 4-mile radius

PAPER MILL

EXPLANATION

E3 GRAVEL

E3 MEDIUM SAND

fe?3 CLAYEY SILT

TRANSITION SEDIMENTS

FIGURE 127. Bathymetry (in feet) of Bellingham Bay, Wash, 

(from Sternberg, 1967).

FIGURE 128. Texture of bottom sediments in Bellingham 

Bay, Wash, (from Sternberg, 1967).
78 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

FIGURE 129. Wood fragment content (in percent) of the 

coarse fraction (>62 microns) of bottom sediments in 

Bellingham Bay, Wash, (from Sternberg, 1967). Coarse 

fraction constitutes about 2 percent of the total sample.

FIGURE 130. Shell (dashed line) and Foraminifera (solid line) 

content (in percent) of the coarse fraction (>62 microns) 

of bottom sediments in Bellingham Bay, Wash, (from 

Sternberg, 1967). Coarse fraction constitutes about 2 percent of the total sample.

of the pulp mill, wood concentrations in the coarse 

fraction, which is about 2 percent of the total sample, 

decline from 70 to about 20 percent (fig. 129). Concentration of wood fragments within the coarse fraction also decreases with depth below the bottom; near 

the mill, for example, values of 70 percent at the surface decline to 5 percent at a depth of 3 feet (1m). 

Hydrogen sulfide in surface sediments was noted only 

in samples collected near the paper mill and near the 

sewer outfall of the city of Bellingham. Below the 

bottom, H2S odor was noted at various depths in core 

samples in the north-central part of the bay.

Calcium carbonate. Pelecypod shell fragments constitute 0-23 percent and foraminifer tests make up 

0-6 percent of the coarse fraction of the bottom sediments (fig. 130).

REFERENCES

Collias and others (1966), Sternberg (1967).

PUGET SOUND, WASHINGTON

SETTING

Geology.^ Puget Sound lies between the Coast 

Range and the Cascade Mountain Range and consists 

of a system of glacially modified drowned channels. 

Bluffs surrounding much of the bay are composed 

mostly of glacial deposits and range in height from 

50 to 500 feet (15-150 m). The present sedimentation 

rate in the bay is approximately 0.6 mm/year; more 

than half the material deposited is detritus derived 

from shoreline erosion.

Bathymetry. In the northern part of the sound the 

bottom has steep sides; midchannel depths are generally about 600 feet (180 m) below sea level and 

reach a maximum of 900 feet (275 m) near Seattle 

(fig. 131). To the south, depths are generally about 

300 feet (90 m) and maximum depths are roughly 

550 feet (170 m).
AREA SUMMARIES 79

FIGURE 131. Bathymetry (in feet) of Puget Sound, Wash, 

(from Wang, 1955).

FIGURE 132. Texture of bottom sediments in Puget Sound, 

Wash, (from Wang, 1955).

Hydrology. The mean total fresh-water inflow to 

the sound has been estimated at 1,100 m3 /sec; monthly 

extremes range from a minimum of 400 m3/sec to a 

maximum of 10,000 m3 /sec. Surface-water salinities 

vary from less than 27.5 parts per thousand in April 

and May to 30 parts per thousand in fall. Vigorous 

vertical mixing results in fairly uniform salinities at 

all depths in the southern part of the sound. Mixed 

tides measured at Seattle have mean and diurnal 

ranges, respectively, of 7.5 feet (2.3 m) and 11.3 feet 

(3.4 m). The maximum range of spring tides rarely 

exceeds 16 feet (4.9 m). Current velocities are highest 

in constricted channels where they may attain velocities of 7.2 knots (360 cm/sec). Elsewhere velocities 

are generally less than 1 knot (50 cm/sec).

SEDIMENT TEXTURE

Bottom. Clay, silt, and fine sand cover approximately two-thirds of the bottom of the sound. Sand 

is most abundant in shallow water near shore, in tidal 

channels, on deltas, and on slopes; it covers about a 

sixth of the bottom. In the remaining area exposed 

rock, gravel, and mixtures of rock, gravel, and sand 

cover bottoms of tidal channels, banks, and slopes. 

Sediments are finer grained and more poorly sorted 

with increasing water depth. Basin mud in deep water
80 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

is finer grained than estuary and delta mud in shallow 

water (fig. 132).

SEDIMENT COMPOSITION

Carbonates. Calcium carbonate occurs mostly as 

shell fragments and Foraminifera tests; concentrations generally range from 2 to 12 percent. In channels and shelf sands, carbonate concentrations are 0 

to 28 percent; in basin muds, 8 to 16 percent.

REFERENCES

Washington [State] University Department of

Oceanography (1953, 1954), Wang (1955).

NISQUALLY RIVER DELTA, PUGET SOUND, 

WASHINGTON

SETTING

Geology. A broad plain that is composed of glacial 

detritus and has an irregular kame and kettle topography extends inland from Nisqually River Delta. 

Approximately 40 nautical miles (74 km) upstream 

the gradient of the river increases from 14 feet per 

mile (2.8 m/km) to 99 feet per mile (20.2 m/km), 

which further increases on the slopes of Mount 

Rainier to the toe of the Nisqually Glacier. Much of 

the detritus transported by the Nisqually River is 

eroded from that volcano.

Bathymetry. The flat topset surface of the delta

extends for approximately 0.5 mile (0.9 km) seaward 

of the su-baeria1! delta (fig. 133). The foreset slope 

forms a uniform arc that is about 3.2 miles (5.9 km) 

long. The gradient of the foreset slope ranges from 

20° at the northeast corner to 7° in the center. Seaward of the delta in Nisqually Reach, the maximum 

depth is approximately 240 feet (73 m).

Hydrology. The mean flow rate of the Nisqually 

River is approximately 57 m3/sec and attains a maximum of approximately 670 m3/sec. Flooding is common in winter. Salinity measurements near the delta 

front show highest dilution by river water in the upper 16 to 33 feet (5-10 m) of the water column. Tides 

in Puget Sound are of a mixed type with large differences between successive heights of low water. The 

mean tidal range at Nisqually Reach is 9.6 feet (2.9 

m). Maximum tidal current velocities at the surface 

are 2 knots (100 cm/sec) at ebb and 1 knot (50 cm/ 

sec) at flood.

SEDIMENT TEXTURE

Bottom. Sediment textures range from coarse silt 

to medium sand over most of the delta. Clay is notably 

sparse. Moderately sorted, fine to medium sand occurs 

in the Nisqually River distributary channels. East and 

west of the channels, most sediment is composed of 

coarse silt and fine sand. Well-sorted medium sand 

covers the bottom of Nisqually Reach (figs. 134, 135).

Subbottom. Cores were collected to a maximum

FIGURE 133. Bathymetry (in feet) of Nisqually Delta and Nisqually Reach, Wash, (from Brundage, 1960).
AREA SUMMARIES 81

depth below the bottom of approximately 3 feet (0.9 dance at depth decreases toward the delta front. Sand

m). Silt becomes predominant with depth on the sub- is most abundant at depth in cores from the river

aerial delta front near McAllister Creek, but its abun- channel and seaward of the delta.

FIGURE 134. Sand (>62 microns) content (in percent) in bottom sediments of Nisqually Reach, Wash. 

(from Brundage, 1960). Dashed line shows approximate location of delta front.

FIGURE 135. Medium sand (0.25-0.5 mm) content (in percent) of bottom sediments in Nisqually Reach,

Wash, (from Brundage, 1960).
82 CHARACTERISTICS OF ESTUARINE SEDIMENTS EXT THE U.S.

SEDIMENT COMPOSITION

Mineralogy. In the coarse fraction, porphyritic 

rock fragments and gray to white pumice are common. Abundant minerals include quartz, magnetite, 

and pyroxene. Wood and plant tissue make up less 

than 2 percent of the coarse fraction of the sediment.

REFERENCE

Brundage (1960).

DEEP INLET, ALASKA

SETTING

Geology. The long U-shaped bay, 5 nautical miles 

(9 km) southeast of Sitka, Alaska, on Baranof Island, is a classic example of a fjord formed primarily 

by glacial action during the Pleistocene Epoch. Bedrock underlying Deep Inlet is probably composed 

mostly of graywacke, volcanic rocks, and dark-gray 

slate of Cretaceous and probable Jurassic age.

Bathymetry. The precipitous slopes of the valley 

on each side of the inlet extend beneath the water to a 

maximum depth of 330 feet (100 m). At the head of 

the fjord, slopes are more gentle. At the mouth, a sill 

rises to within 84 feet (26 m) of the surface (fig. 

136).

Hydrology. The volume of fresh-water runoff into 

the bay is unknown. Salinity values range from 16 to 

32 parts per thousand. Tidal ranges at nearby Sitka

are approximately 8 feet (2.4 m). No direct measurements of tidal current velocities are available. Dissolved oxygen ranges from 7.1 milligram-atoms per 

liter at the surface to 0.01 milligram-atoms per liter 

near the bottom in the deepest areas.

SEDIMENT TEXTURE

Bottom. Poorly sorted gravel and sand covers most 

near-shore areas and the sill at the mouth of the bay. 

Silt, clay, and minor amounts of plant debris and 

shell and rock fragments cover the bottom of the central bay. Fine sand mixed with abundant plant debris 

and rock fragments has accumulated near the head of 

the inlet (fig. 137).

Subbottom. Texture, determined in nine short 

gravity cores (1.5 feet or 0.5 m long), coarsens with 

depth only along the margins of the fjord. Cores 

from midbay showed little change in grain size downward to the limit of core penetration.

SEDIMENT COMPOSITION

Organic carbon (samples analyzed by the Allisson 

(1935) technique). Concentrations of organic carbon range from less than 1 percent to almost 12 percent. Values generally increase toward the basin center but are higher on the moderately gentle southwest 

slope. H2S was noted in samples that have high organic carbon concentrations. As no industries or towns 

contribute effluents to the inlet, most of the carbon is

FIGURE 136. Bathymetry (in feet) of Deep Inlet, Alaska (from Andersen, 1962).
AREA SUMMARIES 83

derived from indigenous organisms and allochthonous near the head of the estuary. Keducing conditions in

material carried into the estuary by runoff. Plant the water below the depth of the sill probably account

debris composed mostly of tree bark is most abundant for the high values in the basin center (fig. 138).

EXPLANATION

I* -I VERY COARSE SAND

L*'l COARSE SAND

ESD MEDIUM SAND

EZ3 FINE-VERY FINE SAND

E3 SILT

FIGURE 137. Texture of bottom sediments in Deep Inlet, Alaska. Modified from Andersen (1962).

FIGURE 138. Organic carbon content (in percent) in bottom sediments of Deep Inlet, Alaska (from Andersen,

1962).
84 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

FIGURE 139. Calcium carbonate content (in percent) of bottom sediments in Deep Inlet, Alaska (from

Andersen, 1962).

Mineralogy. Medium sand and gravel deposits are 

mostly of graywacke composition; these sediments 

contain quartz, feldspar, biotite, and rock fragments 

in a dark aphanitic matrix. Fine material is composed of quartz and low concentrations of feldspar 

and biotite. Volcanic ash (medium sand) is abundant 

in sediments at the head of the estuary and on the bay 

slope of the sill at the mouth.

Carbonates. High carbonate values (as much as 

40 percent) shown in figure 139 are due mostly to 

concentrations of pelecypod shell debris. Highest concentrations occur in local near-shore areas and on the 

sill at the mouth of the inlet. A few gastropod shells 

and echinoid spines are also present. Foraminifera 

tests account for less than 1 percent of the sediments.

REFERENCE

Andersen (1962).

SUMMARY OF THE CHARACTERISTICS OF SEDIMENTS IN ESTUARIES AND ESTUARINE ZONES 

OF THE UNITED STATES

The distribution and composition of contemporary 

sediments in estuaries and estuarine zones result from 

the complex relations between the geology and hydrology of the coastal region. The rate and amount of 

sediment erosion and deposition determine the evolution of the shape and character of the shoreline. Summaries of the processes involved, in areas both inside 

and outside the United States, have been presented by 

Emery and Stevenson (1957), Shepard and Moore 

(1960), Emery (1967), Postma (1967), Gorsline 

(1967), Pritchard (1967), and Eeineck (1967).

SETTING

GEOLOGY AND BATHYMETRY

The approximate shape and maximum depth of 

most estuaries, lagoons, and embayments on the coast 

of the United States were initially established during 

the period of lowered sea level associated with the last 

Pleistocene glaciation. Differences in width and depth 

of river valleys at that time were related to the type 

of sediment or bedrock over which the rivers flowed 

and to the volume and rate of river runoff. During 

and after the subsequent rise in sea level (11,000- 

3,000 years ago), marine processes became dominant 

in the drowned embayments. The degree to which 

estuaries and embayments have currently evolved toward extinction that is, complete infilling by sediments has been determined mostly by the volume of 

detritus transported into these areas by rivers and by 

the consequent development of offshore bars, spits, and 

islands across bay mouths. The most notable changes 

have taken place where unconsolidated sediments exposed on wide, gently dipping coastal plains have been
SUMMARY 85

eroded rather rapidly and deposited in the estuarine 

zones or on broad continental shelves (Emery, 1967). 

Least notable changes have occurred where coastal 

plains and continental shelves are narrow or consist 

mostly of resistant rock.

The glaciated coast of the Northeastern United 

States is characterized by low relief and exposures of 

crystalline or sedimentary rocks covered by thin 

patchy deposits of glacial detritus. Erosion of these 

resistant rocks is slow, and little suspended sediment 

has been carried by rivers to the coast. The roughly 

triangular shape that was acquired at the end of the 

postglacial rise in sea level by many of the estuaries 

in the region has therefore been preserved. These estuaries are generally narrow and deep. Narragansett 

Bay, for example, which fills a drowned valley cut 

into Paleozoic consolidated sedimentary rocks, is more 

than 150 feet (45 m) deep. Glacial scour is probably 

in part responsible for the more than 500-foot (150 m) 

depth of Penobscot Bay, which is underlain and bordered by metamorphic and igneous rocks. In some 

areas where glacial detritus is most abundant, the 

general shape of large deep embayments, such as 

Buzzards Bay (140 feet or 42 m deep) and Cape Cod 

Bay (220 feet or 66 m deep), has been modified only 

slightly by postglacial processes; however, many small 

bays, such as Nantucket Bay (30 feet or 9 m deep) 

and Moriches Bay (8 feet or 2.4 m deep), that have 

shorelines composed of glacial detritus have almost 

been isolated from the open sea by the postglacial formation of spits or barrier islands.

South of New York the character of the coastline 

changes. Offshore bars, spits, and barrier islands are 

common, whereas to the north they are present mainly 

where glacial detritus is most abundant (Cape Cod, 

Nantucket, Long Island). The change is due mostly to 

the transition from the New England shore, where 

resistant igneous and metamorphic rocks are exposed, 

to the shore of the Middle Atlantic States, where the 

broad Atlantic Coastal Plain is covered by relatively 

unconsolidated sediments. Coastal Plain deposits 

mainly Quaternary and Tertiary sand, silt, and clay 

have been rather rapidly eroded by rivers, and the 

detritus has been carried to and deposited in the estuaries and bays or on the continental shelf. Where 

marine currents and waves have concentrated the 

sediments on the continental shelf into spits, bars, and 

barrier islands that parallel the coast, many drowned 

river valleys have been partly isolated from the open 

sea. The original triangular shape of many bays in 

this area has also been modified by building of deltas 

at the head, by erosion of the banks by waves, and by 

transport of sediments from the shelf into the estuaries. Only the largest estuaries south of New York, 

Chesapeake Bay and Delaware Bay, are still deep and 

have not been partly cut off from the sea by barrier 

islands. Albemarle Sound, which has maintained its 

triangular shape, no longer has any direct connection 

with the open sea, and its neighbor to the south, Pamlico Sound, has been reshaped by postglacial formation of the extensive barrier island chain, the Outer 

Banks.

On the shores of the Southeastern States many estuaries have been completely filled with sediment and 

rivers such as the Altamaha in Georgia meander 

through extensive salt marshes to the sea.

The southern part of the Florida Peninsula, however, is far from the source of terrigenous sediment 

which has filled many estuaries to the north. Erosion 

of the low-lying terrain, consisting mostly of limestone, is slight and provides scant terrigenous detritus 

to the many bays and estuaries. Therefore, most infilling has been derived from local material and biogenie detritus formed in situ in the bays or on the 

continental shelf. Most bays have been partly isolated 

from the open sea by carbonate banks (Biscayne 

Bay), reefs (Florida Bay), or mangrove swamps 

(Whitewater Bay). On the Florida west coast, terrigenous detritus which enters the northern Gulf of O

Mexico from rivers becomes sufficiently abundant between Port Charlotte Harbor and Tampa Bay to significantly influence the composition of bay sediments.

Along the shores of the gulf coast an extensive 

series of barrier spits and islands extends from Apalachicola Bay to the Laguna Madre. Rivers flowing to 

the coast not only drain the broad Gulf Coastal Plain 

but much of the interior of the United States. The 

chain of barrier islands, formed mostly because of the 

abundance of available sedimentary material, is broken 

only where deltas have filled estuaries and have overridden the continental shelf (Mississippi River Delta, 

Brazos River Delta). In estuaries where the triangular drowned river valleys have been filled with sediment, the long axis now parallels the coastline (Apalachicola Bay, Mississippi Sound, Matagorda Bay, Laguna Madre). Others, such as San Antonio Bay or 

Baffin Bay, which still have a rough triangular outline, have not evolved as far.

Few large estuaries indent the rugged California 

Coast Ranges. The San Francisco Bay complex, which 

owes its origin partly to mountain-building processes, 

is deep only at the mouth (380 feet or 114 m), but 

abundant sediment derived from the Coast Ranges 

and the Sierra Nevada has reduced depths generally 

to less than 20 feet (6m) and formed widespread 

tidal flats. To the north along the coasts of Oregon
86 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

and southern Washington, an abundant supply of 

sediment has nearly filled several estuaries, and wide 

tidal flats are common (Yaquina Bay, Willapa Bay, 

and Grays Harbor). In northern Washington and 

Alaska, however, sediment supply has been inadequate 

to fill many glacially scoured estuaries such as Puget 

Sound, Bellingham Bay, or Deep Inlet, Alaska, and 

great depths (about 1,000 feet or 330 m) are still 

present.

In summary, estuaries are common on the Atlantic 

and gulf coasts, are sparse along the California coast, 

and are more abundant in the Northwestern States 

and Alaska. The estuaries and embayments are deepest 

on the extreme northwestern and northeastern coasts. 

Most of the bays and estuaries located on the broad 

Atlantic and Gulf Coastal Plains have for the most 

part been filled with sediment and are generally less 

than 50 feet (15 m) deep.

HYDROLOGY

Within the geologic framework of the coastal region, 

the hydrologic regime determines the extent and rate 

that erosion and deposition will modify the shoreline. 

The size of the coastal river valleys during the time 

of lowered sea level was, therefore, determined in part 

by the character of rivers flowing into the ocean. Subsequent erosion during the rise in sea level was related 

as well to the vigor of the waves, currents and tides. 

After the sea reached its present level; sediment deposition in the bays was limited by the fresh-water inflow at the head, by tidal exchange of sea water 

through the bay mouth, and by wave erosion of the 

contiguous shorelines. The amount of mixing of salt 

and fresh water has influenced the amount and kind of 

biotic activity in the bay and hence the sediment texture and composition.

In the Northeastern and Middle Atlantic States, 

fresh-water inflow to the major estuaries is fairly 

large. For example. Penobscot Bay receives an average 

of 470 m3/sec; New York Harbor, 7403/sec; and 

Chesapeake Bay, 2,000 m3/sec. The suspended load of 

these rivers is low, however, due mainly to the erosional resistance of the terrain over which they flow.

On the southeastern coast north of Florida, the only 

estuary included in this report, Charleston Harbor, 

receives about 400 m3/sec from the Santee-Cooper 

Kiver system. The flow is regulated by the Pinopolis 

Dam. Although little suspended sediment is carried 

from the reservoir, the high flow rate (due to the diverted flow of the Santee River) has caused severe 

erosion of the river and estuary banks and has resulted in extensive shoaling in the channels. In southern Florida, flow rates into most of the shallow bays 

are difficult to estimate because of the swampy terrain.

Along the gulf coast, average fresh-water inflow to 

the areas included in this study varies widely. In the 

eastern gulf, average values range from less than 1.3 

m3/sec in St. Joseph Bay to about 1,700 m3/sec in 

Mobile Bay. (Mississippi River flow to its delta averages 18,000 m3/sec.) There are a few rather high 

values west of the Mississippi Delta (Brazos River 

Delta, Sabine Lake, and Trinity River Delta), but 

most receive less than 100 m3/sec of fresh water. All 

the rivers, however, often carry large suspended loads 

which account in part for the shallow depths of most 

bays in the region and for the formation of large 

deltas (Brazos River Delta and Mississippi Delta).

On the Pacific coast north of San Francisco, average fresh-water inflow is generally high as much as 

1,100 m3/sec in Puget Sound.

The salinity distribution in most embayments is a 

function of the amount of fresh-water inflow and the 

salt-water circulation. During periods of greatest runoff average salinities of a few parts per thousand may 

extend throughout an entire bay (Albemarle Sound). 

In dry periods, however, water of almost normal 

oceanic salinity may extend well up the rivers at bay 

heads (Trinity Bay). In arid regions or in lagoons 

receiving little runoff, evaporation may result in 

supersaline conditions. In Baffin Bay, Texas, for example, salinities are as high as 75 parts per thousand. 

The salinity distribution is largely responsible for 

variations in the distrbuton of shellfish that have produced significant banks of shells and shell detritus in 

such estuaries as San Antonio, Matagorda, and St. 

Joseph Bays..

The water circulation in the estuarine zone is an important control on the distribution, composition, and 

texture of the bottom sediments. Tides are not only 

important as the driving mechanism for most horizontal water motion, but the magnitude of their vertical range has an important effect on sediment distribution as well. Diurnal tides of large vertical range are 

limited to the northern Atlantic coast (mostly north of 

Cape Cod) and to the Pacific coast. In Penobscot Bay, 

Boston Harbor, and Cape Cod Bay the tidal range is 

about 9 feet (2.7 m); in San Francisco Bay, about 6 

to 8 feet (1.8 to 2.4 m); and in Puget Sound, about 

7 to 11 feet (2.1 to 3.3 m). In the Middle Atlantic 

States, values are generally 1 to 3 feet (0.3 to 0.9 m), 

and on the gulf coast they are mostly less than 1.5 

feet (0.4 m).

The effects of large tidal ranges are manifold. Currents in restricted channels may scour the bottom and 

allow little sediment to accumulate. Where the sediment supply to the estuary is rather large, as in San 

Francisco Bay, the large tidal range results in the
SUMMARY 87

transportation of silt and clay, during flood tide, from 

the channels into the shallow marginal areas where 

tidal flats are then formed. This process has been 

summarized by Postma (1967) for estuaries in the 

Dutch Wadden Sea.

On the gulf coast the tidal range of only 1 to 2 feet 

results in strong currents only in the narrow passes 

between barrier islands and spits. Inlet deltas on the 

bay bottoms indicate, however, that considerable sediment exchange takes place between the estuary and 

the continental shelf.

Exceptional tides caused by storms often have more 

influence on sediment distribution than normal diurnal 

tides or tidal currents. Hurricane-generated tides that 

exceed 10 feet on the gulf coast have periodically 

transported great quantities of sand into the estuaries 

from the continental shelf and from the barrier islands. In areas subject to many storms, such as Cape 

Hatteras (east of Pamlico Sound), waves often cross 

the barrier island and carry sand into estuaries to 

form washover fans.

In summary, the hydrologic regime not only was 

important in shaping the initial form of the present 

coastline through erosion, but it continues to modify 

the shape of the bays and the sediment texture and 

composition. The most rapid changes occur where 

rivers and marine currents supply large quantities of 

sediment from the continent and continental shelf to 

the estuaries.

SEDIMENT TEXTURE

Regional differences in the processes that affect 

sediment distribution in estuaries have been discussed. 

The sediment texture on the bottom indicates the response of the component particles to these processes.

In simplest terms, coarsest sediment accumulates in 

bays and estuaries where energy levels are high, and 

finer sediments, such as silt and clay, accumulate 

where energy levels are low. The mean or median 

grain diameter of most bottom sediments accumulating in areas cited in this study ranges from that of 

clay to that of gravel; rarely, however, is material 

coarser than sand (>2 mm) volumetrically significant.

Deep estuaries in the Northeastern States, such as 

Penobscot Bay, receive little suspended sediment from 

rivers. Tidal ranges are large and wave energy at the 

shoreline is commonly great. Clay, therefore, is most 

abundant in deep areas in the upper estuary and 

grades seaward into silt and sand near the bay mouth.

In deep embayments such as Cape Cod Bay and 

Buzzards Bay, sand and gravel at the margins give 

way with depth to silt and clay despite the predominance of sand in the glacial debris that is the 

source of most of the sediments. Even in the bar-built

estuaries and lagoons such as Moriches and Nantucket 

Bays, which also derive most of their sediment from 

glacial detritus, silt and clay are accumulating in the 

deepest areas.

The differences in the distribution of sediment texture under various physical conditions is apparent in 

three estuaries of the Middle Atlantic States Chesapeake Bay, Pamlico Sound, and Bogue Sound. In 

Chesapeake Bay, a large deep estuary that has abundant fresh-water inflow, silt and clay are widespread 

in the deep central area, and fine to medium sand predominates around the margin. Pamlico Sound, a large 

but rather shallow bar-built estuary south of Chesapeake Bay, contains a preponderance of sand; silt is 

concentrated only in the bay center and in drowned 

river channels. The widespread distribution of sand 

in Pamlico Sound is due mostly to washover fans, 

inlet deltas, and the winnowing action of waves on 

the rather shallow bottom. Bogue Sound, south of 

Pamlico Sound, receives very little fresh-water inflow 

and most of the shallow bottom is subject to wave action. As very little fine suspended matter is transported to Bogue Sound by rivers, the bottom is almost 

entirely covered by sand.

Of the estuaries on the southeastern Atlantic coast, 

Charleston Harbor is significant mainly because the 

present sediment distribution is due to the diversion of 

the Santee River into the Charleston estuary. Two 

important changes occurred when the estuary started 

recieving the greatly increased inflow of fresh water: 

first, the banks of both river and estuary were eroded 

rapidly and much fine sediment was contributed at the 

head of the harbor; and second, the stronger flow apparently set up a two-layer circulation system that resulted in transport of sand into the harbor from the 

continental shelf. Much spoil derived from extensive 

dredging- has flowed back into the system. Silt and 

clay, therefore, cover most of the bottom in the upper 

harbor, and fine to medium sand is abundant near the 

mouth.

In bays along the coast of Florida, fine sediment 

is most abundant in swampy areas (Whitewater Bay) 

or where carbonates are precipitating directly from 

sea water (Florida Bay). Little silt and clay is carried from the peninsula or from the continental shelf 

into such shallow estuaries as Biscayne Bay and Port 

Charlotte Harbor, and fine to medium sand is therefore predominant.

The depositional environments of the northern gulf 

coast are sufficiently uniform to produce a broadly 

similar distribution of sediment textures in most bays. 

Virtually all the estuaries are partly barred from the 

open gulf by spits or barrier islands. Abundant sus-
88 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.S.

pended sediment is transported to most bays in the 

area, which therefore have an average depth of less than 

10 feet (3 m). In this low-energy marine environment, 

tidal ranges are less than 1.5 feet and winds and 

waves, except during hurricanes, are usually moderate. Due to the abundant sediment supply from the 

rivers and to the absence of strong currents, silt and 

clay cover most of the central areas of bay bottoms. 

Sand is abundant only near the bay margins where 

waves and currents are most vigorous. From Apalachicola Bay to Mississippi Sound, this pattern of sediment distribution is uniform.

Around the Mississippi Delta, however, the sediment pattern changes. The inactive parts of the delta 

are presently subsiding and the fine delta deposits 

around the perimeter are being covered by marine 

sediments. In Chandeleur and Breton Sounds, sand is 

abundant over much of the deepest area and grades 

shoreward into silt and clay, which are characteristic 

of recent delta sediments. A similar pattern in Barataria Bay has been attributed to scouring by strong 

tidal currents.

West of the Mississippi Delta Matagorda, Aransas, and San Antonio Bays all have silt and clay concentrated in the central region. Sand is most common 

around the margins and oyster reefs are also abundant. 

Recent dredging has been extensive in all these bays 

and the textural pattern has doubtless been altered 

since the studies used in this report were made. Baffin 

Bay and Laguna Madre are unique in that arid conditions prevail most of the year. Sand blown from the 

barrier island by the prevailing winds has separated 

Laguna Madre into two parts; windblown material 

therefore is a very important component of the sediments filling this lagoon.

The contrast between the low-energy environment 

of the gulf coast and the high-energy environment of 

the Pacific coast has been described by Gorsline 

(1967). This difference is reflected in the pattern of 

sediment distribution in the estuaries. In San Francisco Bay, for example, fine sand is most common in 

the channels; silt and clay are distributed around the 

margins in shallow water and on tidal flats. Similar 

patterns are present in Yaquina and Willapa Bays. 

These patterns apparently are in part due to the large 

diurnal tidal range which permits fine material to be 

carried during flood tide over the tidal flats where it 

is deposited in shallow water where wave motion is 

restricted. Most fine material deposited 011 the tidal flats 

in the west coast estuaries is probably derived from

river detritus rather than from offshore deposits, as is 

the case in the Dutch Wadden Sea (Postma, 1967).

In estuaries on the Washington coast the textural 

distribution is similar to that in Penobscot Bay, 

Maine. In Grays Harbor, for example, silt and clay 

at the head of the estuary grade seaward into sand. In 

Puget Sound, bedrock is commonly exposed at the 

bottom.

In summary, the distribution of sediment texture at 

the bottoms of estuaries, bays, and lagoons along the 

United States Coast is determined by the complex relations between geology, hydrology, and bathymetry. 

In estuaries of the northeast and northwest that receive a small influx of suspended sediment, clay near 

the bay heads grades seaward into sand. Where suspended load is greater and tidal range large, as on 

the California and Oregon coasts, sand is most abundant in the channels and fine materials accumulates in 

the shallow marginal areas and on tidal flats. On the 

gulf coast where sediment supply is large and energy 

low, the finest sediments are most abundant in the 

central areas of the bays and grade shoreward into 

fine and medium sands. Sands in the barred estuaries 

are mostly derived from shore erosion, from the offshore barrier bar, and from the continental shelf.

SEDIMENT COMPOSITION

The bottom sediments in the coastal region consist 

of a mixture of mineral particles eroded from the 

continents, bio'genic debris derived from indigenous 

organisms, and various human and industrial waste 

products. Inorganic terrigenous detritus, except in a 

few areas, account for most of the sediment which has 

accumulated. Biogenic debris, particularly pelecypod 

shells (mainly clam and oyster), are locally abundant 

in many areas. The shells only become dominant constituents of the sediments, however, where terrigenous 

components are almost entirely lacking as in southern 

Florida. Many of man's influences on sedimentation 

in estuaries have been described in reports by Meade 

(1969a, 1969b, 1972). Organic carbon is the only component discussed in this report which may give an 

indication of the volume of pollutants retained by 

estuarine sediments.

ORGANIC CARBON

The concentration of organic carbon in the sediments represents about half the total organic matter 

present and consists of natural plant and animal remains and of pollutants. Silt and clay generally contain the highest concentrations of finely divided organic matter. The inverse relationship between sediment grain size and organic matter concentration was
SUMMARY 89

recognized by Trask (1932). Areas where organic 

matter will accumulate can therefore be predicted, 

with some degree of accuracy, by knowing the distribution of sediment texture on the bottom.

In most areas where pollutants are sparse the organic carbon concentration seldom exceeds 5 percent 

and is most commonly less than 3 percent. Concentrations, for example, in clays of Penobscot Bay, Pamlico 

Sound, Mississippi Sound, Baffin Bay, and Willapa 

Bay are less than 4 percent. Concentrations in sands 

of these same bays are generally less than 1 percent. 

In some unpolluted areas, however, high values exist 

because of special conditions. The clays of Deep Inlet, 

Alaska, for example, contain concentrations as high 

as 11 percent. This deep fjord has a sill at the mouth 

which inhibits circulation of deep water and results 

in anaerobic bottom conditions. In estuaries that have 

swampy or peaty bottoms, such as Whitewater Bay, 

Fla., values as high as 20 percent are due mostly to 

plant detritus. Some local values of as much as 20 or 

30 percent are occasionally recorded from bottom samples recovered from restricted peat deposits (Albemarle Sound).

Systematic measurements of organic carbon in sediments of estuaries near major population centers are 

sparse. In New York Harbor, for example, few measurements are available. And in the San Francisco Bay 

complex, measurements are only available in Suisun 

Bay and in part of south San Francisco Bay. Comprehensive studies have been carried out, however, in 

Boston and Charleston Harbors where pollutants 

mostly composed of sewage are abundant. Concentrations of organic carbon in these areas are as high as 

15 percent. In Chesapeake Bay, the few available organic carbon values increase toward the head of the 

estuary and reach 7 percent where finely divided coal 

is known to be abundant in the sediments. Some 

thorough studies were made of organic matter in bottom sediments of several small bays. The results give 

us an indication of the amount of pollutants that can 

be retained in the sediments under different conditions. 

In Moriches Bay, Long Island, for example, values 

of total organic matter are as high as 28 percent and 

are mostly due to the extensive duck farms operated 

in the small drowned river valleys on the north side 

of the bay. In St. Joseph Bay, Fla., which presently is 

receiving very little sediment influx, organic carbon is 

abundant in the deepest area and in sand on the bay 

margin near a small canal that carries effluents to the 

bay from a paper plant. The supply of pollutants has 

evidently been sufficiently great to override the effects 

of normal winnowing action which removes most fine 

terrigenous detritus.

MINERALOGY

Most bottom sediments in the estuarine zone contain 

only a few species of minerals. Much of the sediment 

is derived from the coastal plains and the continental 

shelf and therefore has undergone a previous cycle of 

erosion and deposition. Furthermore, many minerals 

that have poor resistance to weathering are destroyed 

before reaching the estuarine environment.

In the bottom sediments of most estuaries reviewed 

in this report, the minerals in the sand fraction (>62 

microns) that have a specific gravity of less than 2.8 

consist mostly of quartz (50-95 percent) and feldspar 

(0-30 percent). Highest concentrations of quartz are 

present in reworked glacial material (Nantucket Bay, 

90 percent) and in shallow estuaries such as Bogue 

Sound where abrasive wave action evidently is particularly strong and has worn down and removed less 

mechanically resistant minerals. Even in Biscayne 

Bay, which is bordered and underlain by carbonate 

rocks, the coarse fraction of the sediments contains 

abundant quartz derived from a thin quartz-bearing 

stratum. Plagioclase and orthoclase feldspar are abundant and in some places exceed quartz content in sediments of bays along the Pacific coast where the Coast 

Ranges and the Sierra Nevada contribute igneous rock 

fragments (Grays Harbor, Yaquina Bay).

The composition of the heavy minerals (specific 

gravities greater than 2.8) in bottom sediments is related to the source of the sediment and to the amount 

of abrasion which the particles have undergone prior 

to deposition. On the Atlantic and gulf coasts, concentrations are generally less than 3 percent. In Nantucket Bay the reworked glacial detritus contains only 

ilmenite and magnetite. In the Middle Atlantic States 

(Chesapeake Bay), hornblende, garnet, and hypersthene are abundant. Along the eastern gulf coast, 

metamorphic minerals that probably were derived 

mostly from the southern Appalachians predominate. 

Along the western gulf coast (San Antonio Bay), 

tourmaline, garnet, and zircon are most common. On 

the Pacific coast, high heavy-mineral percentages (as 

much as 18 percent) reflect the proximity of mafic 

source rocks (Grays Harbor, Yaquina Bay, and San 

Francisco Bay). In San Francisco Bay, biotite, magnetite, hornblende, and garnet are abundant; to the 

north in Grays Harbor, rock fragments are followed 

in abundance by hypersthene, olivine, and hornblende.

Clay minerals commonly constitute over 90 percent 

of the fine fraction. The relative abundance of the 

specific clay minerals varies with the source region 

supplying the estuarine area and with the type of 

weathering which the source rocks have undergone. 

From Penobscot Bay to Chesapeake Bay, for example,
90 CHARACTERISTICS OF ESTUARINE SEDIMENTS IN THE U.Su

illite and chlorite are the most abundant clay minerals. These minerals probably are mostly derived 

from the continental shelf and slope and are being 

transported into the estuaries by bottom currents 

(Hathaway, 1972). Kaolinite, derived mostly from 

the crystalline Piedmont region, is most abundant in 

east coast bays south of Chesapeake Bay and predominates over illite, montmorillonite, and mixed-layer 

clays. Kaolinite abundance is greatest (80 percent of 

the fine fraction) in Albemarle Sound. The Apalachicola River contributes a similar clay-mineral assemblage to fine sediments in several eastern gulf coast 

bays. The Mississippi River and other rivers in the 

western gulf transport a preponderance of montmorillonite, which is reflected in the composition of the fine 

sediments in most bays between the Mississippi Delta 

and Laguna Madre. On the Pacific coast where volcanic rocks are abundant, montmorillonite is also more 

abundant than illite, kaolinite, or chlorite.

Calcium carbonate concentrations in bay sediments 

reach a maximum of about 90 percent. In most areas, 

highest concentrations are principally due to abundant 

molluscan shells and shell fragments. On the Atlantic 

coast some local high values (40 percent) are due to 

mussel and oyster banks (New York Harbor). In the 

gulf coast estuaries, such as San Antonio Bay, Matagorda Bay, and St. Joseph Bay, values are as high as 

40 to 80 percent in reefs and shell banks but are generally less than 20 percent. In the estuaries of the 

Northwestern States, such as Puget Sound and Bellingham Bay, maximum carbonate concentrations are 

20 to 30 percent. Only the bays along the coast of 

southern Florida contain widespread concentrations 

exceeding 50 percent. In Biscayne Bay, carbonate contents as high as 80 percent consist of fragments of 

calcareous algae; in Florida Bay, carbonates make up 

as much as 90 percent of the sediment and generally 

consist of 50-70 percent aragonite, 20-30 percent highmagnesium calcite, and 10-20 percent low-magnesium 

calcite.

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