Geologic controls on the holocene evolution of an open-marine marsh system fronting a shallow-water embayment, Waccasassa Bay, West-Central Florida

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Geologic controls on the holocene evolution of an open-marine marsh system fronting a shallow-water embayment, Waccasassa Bay, West-Central Florida

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Title:
Geologic controls on the holocene evolution of an open-marine marsh system fronting a shallow-water embayment, Waccasassa Bay, West-Central Florida
Creator:
Goodbred, Steven Lee
Place of Publication:
Tampa, Florida
Publisher:
University of South Florida
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Language:
English
Physical Description:
xi, 221 leaves : ill., (some col.) ; 29 cm.

Subjects

Subjects / Keywords:
Salt marshes -- Florida -- Waccasassa Bay ( lcsh )
Coast changes -- Florida -- Waccasassa Bay ( lcsh )
Geology, Stratigraphic -- Holocene ( lcsh )
Dissertations, Academic -- Marine science -- Masters -- USF ( FTS )

Notes

General Note:
Thesis (M.S.)--University of South Florida, 1994. Includes bibliographical references (leaves 172-180).

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University of South Florida
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Universtity of South Florida
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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
020129776 ( ALEPH )
32491627 ( OCLC )
F51-00108 ( USFLDC DOI )
f51.108 ( USFLDC Handle )

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GEOLOGIC CONTROLS ON THE HOLOCENE EVOLUTION OF AN OPENMARINE MARSH SYSTEM FRONTING A SHALLOW-WATER EMBAYMENT: WACCASASSA BAY, WEST-CENTRAL FLORIDA by STEVEN LEE GOODBRED JR. A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Department of Marine Science University of South Florida August 1994 Major Professor : Albert C Hine, Ph. D

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Graduate School University of South Florida Tampa, Florida CERTIFICATE OF APPROVAL Master's Thesis This is to certify that the Master's Thesis of STEVEN LEE GOODBRED, JR. with a major in Geological Oceanography has been approved by the Examining Committee on July 8, 1994 as satisfactory for the thesis requirements for the Master of Science degree Examining Committee: Major Professof: Albert C. ifil{e ( Ph.D. P. Stulli/i, Ph.D. Member: Mark E. Luther, Ph.D.

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ACKNOWLEDGEMENTS I would like to express my gratitude to the many people who contributed to this research and the final production of my thesis. I appreciate the time and effort given by my committee members, Dr. Albert C Hine, Dr. Richard P Stumpf, and Dr. Mark E Luther. Their advice and input helped to greatly improve my research and scientific abilities, and ultimately the final results of the project. I would like to specifically thank Dr. Hine for being my advisor and for all of his help in making my tenure at USF enjoyable and easy-going Special thanks go to all of the people who gave their time to assist me with fieldwork. These same people not only donated their help, but also their blood to the oppressive Waccasassa fly and no-see-urn populations. Among my cohorts, I would especially like to acknowledge the 'marsh group,' Eric Wright, Lynn Leonard, and Wendy Quigley, for their laughs, friendship and innumerable contributions to this project Thanks go to Dr. William Burnett of the Florida State University Department of Oceanography for running the 210Pb analysis and aiding in the interpretation of the results. Beta Analytic, Inc performed all of the radiocarbon dating. Their scientists were helpful with discussing results and interpretations. The Crystal River Nuclear Power Plant was also very helpful in providing much needed weather data for my research. I would also like to acknowledge the U S Geological Survey, Center for Coastal Geology,

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for funding this project and providing me with support to attend meetings and to complete the final stages of my research. My final thanks go to my parents, Pam and Steve Goodbred Sr., who began their contributions to my well-being almost twenty-five years ago. Their love, support, and encouragement have always been there to inspire me. Thank you for giving me the ability to successfully approach so many oflife's pleasures.

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TABLE OF CONTENTS LIST OF TABLE . .... ......... ...... .... ...... ............... .......................... .... ........ ...... .... tv LIST OF FIGURES ...... .... . .......... ....... ...... ..... ..... .... ...... ... ............................ v ABSTRACT... ........ ................. .................. . ......... ....... ... ....... ........ ... .......... .... X 1 INTRODUCTION. ... . ..... .................. ...... ....... .................. ...... .......... .. ........ 1 Objectives . . . . ... . . .. .. . . .. .. . . . .. .. . . .. .. . .. . .. .. . . . . ... . .. . ... .. .. 4 2. GEOLOGIC SETTING... .................. ................ ..... ..... .... . ... ........ ..... ... .... 7 Structure .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . .. .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. 8 Stratigraphy.... ................... ... ...... ...... .... ....... ....... ....................... 12 Geomorphology .. . . .. . . .. . .. .. . .. . . . . .. . .. .. . . .. .. . . . .. .. .. . .. . .. . 15 Holocene Sea Level . .. .. . . .. .. . . . .. . .. . .. .. . .. .. .. .. . .. .. .. .. .. .. .. . . .. 18 3 PHYSICAL SETTING ............................. ........ .............. ................ .. ..... ...... 22 Climate ............. . ..... ... ....... ... ..................... .. ... ........ ... ................... 22 Big Bend Coast . . . . .. . . . . .. . . . .. . . . . .. .. .. . . . .. . .. . .. .. . .. .. .. . . 27 Waccasassa Bay . . .. . . . .. . . .. . .. . . . . .. .. .. . . .. . .. . .. .. .. . ... .. . .. . .. 28 Waccasassa Marshes ..... ......... ... .... ............................. ... ... .... ......... 34 4. METHODS AND MATERIALS ......... .... ............ ... ............. ... .................... 45 High Resolution Seismic Reflection Data .................................... 45 Sidescan Sonar.. .... ............... ... ... ......... ............ .............................. 46 Grab Samples and Probe Rod Tests ... .... .. .. .. ... .. .. .. .. .. .. .. .. .... .. .. .. ... 48 Vibracoring. .... ............ .... ... ...... .......... ......... ..... ..... ..................... 51 Sediment Analysis .. . . .. .. . .. .. .. . .. .. . . . . .. .. .. . .. .. . .. .. .. .. .. . .... . .. 53 Organic Content...... .................... .... . ..... ........... ..... ............. ... 53 Carbonate Content . . . .. .. .. . . .. . .. .. .. . .. .. . . . . ... . . . .. . .. .. . 54 Grain Size Analysis... ....................... ....................... .......... .... 54 RadioIsotopes . . .. . .. . .. . . .. . . .. . .. .. . . . . . . . .. .. . .. .. . .. . .. . ... . .. . .. 55 Carbon (14C) Dating..................................... ............. ............ 55 Lead (210Pb) Dating ... ...................................... ...................... 57 Mineralogical Analysis .. .. .. . . . . .. .. . . . . . . . . .. . .. . .. .. .. . .. .. .. . 58 5. WACCASASSA BAY .................. ...... .... ....... ......... ... ... . ....... . ..... ... . .......... 60 Results ................... ................ ................... .... ............................... 60 Bottom Physiography ................... ............................... ........... 60 1

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Sub bottom Geology .. .. .. .. .. .. .. .. .. .... .. .. .. .. .. .. .. .. .. .. .. .. . .. .. .. 66 Surface Sediments .. .. .. .. .. .. .. .. .. .. .... .. .. .. .. .. .. .. .. .. .. . .. .. .. .. .. .. .. 68 Stratigraphy ... ............................. .... .... ................. .............. .... 76 Discussion .. .. .. .. .. .. .. .. .. .. .. .. .. .. . .... .. .. .. .. .. .. .. .. . .. . .. .. .. .. .. .. .. .. . .. 79 Waccasassa Bay Sediments.................................................... 79 Oyster Reefs .. .. . .. ... .. .. .. .... .. .. .. .. .. .. .. .. .. .. . .. .... . .. . ... .. . .. .... .. 82 6 WACCASASSA MARSHES . .... . .. .. ... .. . .. .. . ... . ...... .. ... ... ... .. .. . .. . .. . .. .. 85 Results ..... ............ . ..... ............... ........ ..... ............ ............ ...... ... ..... 85 Pre-Holocene Facies ... ..... . .............. ..... .... ........... ..... ......... ... 85 Holocene Facies. .. .. . .. .. .. .. . .. .. ... . .. ... . .. . .... . .. . .. ... ... ... .. .. 92 Black, Organic Muds.... ............................... ..... ............... 93 Gray Muds ........ ......... ........... ... ........................................ 98 Green Muds .. .. . .. .. .. .. .. .. .. .. .. .. .... .. .. .. .. .. .. .. .... . .. .. .... . .. 98 Modern Marsh .. .. .. .. .. .. . .. .. .. .. .. ... .. .. .. .... .. .. .. .. .. . .. .. .. .. .. 99 Mineralogy ... ... ......... .............. ........... ........ .................. ...... ... 103 Silts . ... ... . . ... . ... . ... ...... . . .................. ............... ... ... .... 103 Clays ... ...... ......... ......... . ........................... ...... .... .... ......... 109 Sediment and Facies Distribution ......... .... ... ...... ......... ......... 112 Discussion .... .... . ... ........... ....... . ..... ..... ... ......... ... .. .. ... ...... . . . ...... 119 7. HOLOCENE EVOLUTION OF THE WACCASASSA BAY AREA .......... 126 Shoreline Retreat . .................................................... ...... ....... ... ... 127 Source and Transport of Sediment ....................... .. ..................... 132 Environmental Succession and Marsh Development ...... ......... . 134 8 MODERN SYSTEM AND PROCESSES ............ ...... .. .. .......... .. ... .. ............ 138 Results .......... ......... ..... ........... . . . . . .................................... ... ... 138 Discussion .................... ..... .................. . ....... ................ ......... ... 144 9 EFFECTS OF THE MARCH 1993 'STORM OF THE CENTURY' ON THE WACCASASSA BAY SYSTEM ... ... .... .... . .......... ................ . ... ... 151 Results .... ...... ....... ......... . ............... ............. ............ .... : ... ..... ... ...... 151 Discussion ... .................... ..... ...... ...... .. ... ... ........ ........... .... .... ... ... 163 10 CONCLUSIONS ..... ... ...... ..... .... ... ...... ................... ............. .... ... .............. 167 REFERENCES ............ ..... ..... ..... ...... .............. ...... ................... . ... . ............... 172 APPENDICES .. ......... . .... ........... ....... ..... ... ................ .......................... ... ...... 181 APPENDIX 1. CORE LOGS . ............ .... .... .... . ....... .................. 182 APPENDIX 2 PERCENT ORGANIC AND MOISTURE VALUES FROM CORE SEDIMENTS ..... ....... 213 APPENDIX 3 GRAIN SIZE ANALYSIS FROM CORE SEDIMENTS ............................ ....................... 216 11

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APPENDIX 4. PERCENT ORGANIC, CARBONATE, AND SILICICLASTIC VALUES FROM OFFSHORE GRAB SAMPLES .......... ............. 219 APPENDIX 5 GRAIN SIZE ANALYSIS FROM OFFSHORE GRAB SAMPLES . ............... ...... 221 11l

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LIST OF TABLES Table 1. Summary of Radiocarbon D ating Results.. ........ .................... ... . 92 Table 2. Summary of Facies Characteristics of the Waccasassa Marsh Stratigraphy .......................... ..... .............. ............... ... .......... ... .... 100 Table 3 Proposed Depositional/Environmental Setting for Individual Facies .......................... ............... ........... ...... ....................... ...... ..... 121 l V

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LIST OF FIGURES Figure 1. Site and Location Map for the Waccasassa Bay Study Area ....................... ...... .............................................................. 5 Figure 2. Map of the Structural Features of Florida .... .. .. .... .... .. .... .. .. .. 9 Figure 3. Geologic Map of Florida's Surface Units .......................... ........ 11 Figure 4 Stratigraphic Column for the Waccasassa Bay Area .............. 13 Figure 5 Map of Some Geomorphic Features and Marine Terraces of Florida .. .. . .. .... .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 17 Figure 6. Recent Holocene Sea-Level Curve for Florida......................... 21 Figure 7. Average Annual Temperature and Rainfall for Gainesville, Florida... ...... .. ... ............................... ........ ...... ...... 23 Figure 8. Wind Rose Diagrams for Tampa, Florida.................... ............ 25 Figure 9 Path of Hurricanes Striking the Coast from 1885-1990 ......... 26 Figure 10. Physical Map of the Waccasassa Bay Area ............................. 30 Figure 11. Photograph Showing a Typical, Oyster Reef from Waccasassa Bay .. . . . . .. .. . .. . .. .. . . . .. . . .. .. . . . . .. .. . . . .. . .. . .. 31 Figure 12. Coastal Provinces within the Waccasassa Bay Area ...... ........ 33 Figure 13. Photograph Showing the N earsurface Bedrock which Underlies the Forested Upland Zone ...................... ................. 35 Figure 14. Photographs of a Shallow Creek and the Typical Marsh Setting in Waccasassa Bay .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 36 Figure 15. Relative Biomass ofMacrophyte Populations Found along the Big Bend Coast .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 38 v

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Figure 16. Waccasassa River Salinities during 1985 .. .. .. . .. . . . . .. .. . . . 39 figure 17. Photographs of Three Levees of Different Elevation Showing the Change in Flora. .. ... . . . ... . . .. .... .. .... .... . .... .... 40 Figure 18. Two Photographs of the Upland Hammocks Found Across the Waccasassa Marsh Zone ... ...... ... ... .... ....... .... ... .. . ...... ...... 43 Figure 19. Map of Cruise Track for Collection of Seismic Reflection Da'ta .......... ..... ........... ....................... .............. ........... ............... 47 Figure 20. Map of Cruise Track for Collection of Sidescan Sonar Data .. .. ... ... .... ...... ............. ................................. ............... ....... 49 Figure 21. Map of Bottom Grab Sample Sites..... . ............ .. ..... ..... .......... 50 Figure 22 Map ofVibracore Site Distribution .......... ..... .. .......... .... .... .... 52 Figure 23. Cruise Track and Distribution of Bottom Types Mapped from Sidescan Sonar Imaging. ... ....... ... .... ... .. ...... ....... ... ... ... 61 Figure 24. Sidescan Image of Typical Rocky Bottom Found Flooring Much of the Waccasassa Embayment ....... ..... .. ............ .......... 63 Figure 25. Sidescan Image of Typical, Well-Sedimented Bottom . ......... 64 Figure 26 Sidescan Image of Typical Channel-Type Bottom .............. .... 65 Figure 27. Map of the Thickness of Sediment Cover across the Waccasassa Embayment ... .................... .. .. . . .. .. ... .... ... ...... ... 67 Figure 28 Seismic Cruise Track and Areas of Karstic Depression Features Within the Waccasassa Embayment ... ... ..... .... . .. ... 69 Figure 29. Section of Seismic Reflection Data from Waccasassa Bay with Interpretation ... .... .. ... ... ... ... ... .... ....... ... .... ....... ........... ... 70 Figure 30. Map of Percent Mud in Offshore Bottom Grab Samples ........ 71 Figure 31. Map of Percent Siliciclastic Material Measured in the Offsh ore Bottom Grab Samples. .. ..... ... .. .. .. ... .. .. .. ... .. .. .. .. ..... .. 73 Figure 32 Map of Percent Carbonate Values from Offshore Bottom Grab Samples .. . . .. . . .. .. .. ... . . . .. .. .... .. .. . .. ... . .... .. .. ... . . . . 7 4 Figure 33. Locations of Offshore Core Sites and Description of Three Cores. From These Sites ... .... . . .................... ...................... .... 77 Vl

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Figure 34 Photograph of Core 3.7 Showing Shelly, Nearshore Marine Muds Overlying a Preserved Section of Wetland Peats ... ............ ....... . .... .................................... .......... ... ... .... . . 78 Figure 35. Location Map of Cross-Sectional Profiles and Core Sites and Key to Symbols Used in Core Logs .. .. .... ..... .. ... .. ...... ... .. .. 86 Figure 36. Photograph and Core Log of Core 1.3, a Typical Outer Marsh Core From the Lower Marshes Along Rocky Run ..... 88 Figure 37. Photograph and Core Log of Core 6 1 a Core Collected on Top of a Treed Levee Along Bird Creek.... ...... ................. ........ 90 Figure 38. Photograph and Core Log of Core 7 1, a Core Collected About 20 m Into the Marsh From Core 6 1 .. .. .. .. .... .. .. .. .. .. .. .. 94 Figure 39. Log of Core 7 9, a Marsh Core Taken along Lower Kelly Creek ............. . ....... ...... ...... ... ............... ............. . .... ... . ........ ... 96 Figure 40 Log of Core 12 3, a Marsh Core Taken on the Island at the Mouth of the Waccasassa River ........................................ ...... 97 Figure 41. Photograph of a Surface Section of Marsh Sediments Showing the Muddy Marsh Facie s Overlying the Peaty Marsh Faci e s .......................... .... ........... ........ .......................... 102 Figure 42. Photograph and Core Log of Core 3.2, a Core Collected Near the Marsh/Upland Transition Along Crooked Creek ..... 104 Figure 43 Photograph and Core Log of Core 7 3, a Core Collected Near the Marsh/Upland Transition Along Cow Creek .. .. ....... 106 Figure 44. Log of Core 12 5, an Upper Mars h Core from Stafford Island ........................ ........................... .... ... . ... ... ........... . .... .... 108 Figure 45. X-ray Diffractio n Patterns for Two Waccasassa Sediment Samples ................. ..... ........... ............. ....................... ..... ........ 110 Figure 46 X-ray Diffraction Patterns for the Clay-sized Sediment Fraction of Samples Collected Downcore through Core 7 .1 .... 111 Figure 4 7 Map of Sediment Thickness at Core Sites .......... ..................... 113 Figure 48. Core-ba sed Stratigraphic Cross Section of the Marshes Rimming the Embayment ... .... . ... . . .......... .... .... ........... ...... ... 115 Figure 49. Core -based Stratigraphic Cross-Section of Two Transects along the North Arm of the Embayment .............. ............... .... 116 Vll

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Figure 50 Figure 51. Figure 52 Figure 53 Figure 54. Figure 55 Figure 56 Figure 57 Figure 58 Figure 59. Figure 60 Figure 61. Figure 62 Figure 63 Figure 64 Core-based Stratigraphic Cross-section from the Mouth of the Waccasassa River Upstream Toward the Freshwater Transition .... ..... .... .... .......... .. ..... . ... ..... ... ........... .... ... .... . ... 117 Proposed Shoreline Positions for the Late Holocene Transgression ofWaccasassa Bay ..... ..... ................. ..... ... . ... 128 Evolutionary Profiles for the Proposed Development of the Waccasassa Bay System ... . ........ ...... ............ ....... .............. ..... 129 Graph of2IOPb and 137Cs Activity Values for Sediments Collected at Bird Creek near Cores 6.117. 1 ... .... ........... ... ...... . 139 Graph of Suspended Solid Concentration in Bay Water Samples during a Flooding Tidal Cycle . .................. ..... ........ 141 Vertical Profiles of Suspended Solids Con centration at Two Sites in the Waccasassa Bay ............................................ 142 Two-week Recording of Current Velocities and Water Depth from Depew Creek ...................................................... ... 143 Oblique Aerial Photograph of Waccasassa Embayment Showing Suspended Sediment across the Area during a Flooding Tide ...... .................... . . ............... ......................... .... 148 Map of the Distribution of Storm Sedimentation and the Location of Sampling Sites ............................ ... ........ ............ .... 152 Graphs of Wind Speed and Direction for the Month of March 1993 Showing Data from the 'Storm of the Century' ....... .... ............................................................. ...... ... ... 154 Graph of Discharge for the Waccasassa River for the Month of March 1993 Showing Data from the 'Storm of the Century' .......... ....... .................... .......... .... ... ............. ........ ... 155 Photographs Showing Tree Damage and Wrack Deposits Resulting from the 'Storm of the Century' ............. .... .... ........ 156 Two Photographs Showing the Storm Deposit in the Marsh Zone ............ .... ..... ... ...... ....... ... ........ ........ ... ... ..... ..... 159 Two Photographs of the Storm Deposit on Top of the Levees ... ................... ... ...................... ................ ......................... 160 Graph Series of Grain Size Analysis on Storm Sediments at Various S ites .................. .... . ...... ................. ....................... 162 Vlll

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GEOLOGIC CONTROLS ON THE HOLOCENE EVOLUTION OF AN OPEN-MARINE MARSH SYSTEM RIMMING A SHALLOW-WATER EMBAYMENT: WACCASASSA BAY, WEST-CENTRAL FLORIDA by STEVEN LEE GOODBRED, JR. An Abstract Of a thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Department of Marine Science University of South Florida August 1994 Major Professor: Albert C Hine, Ph. D. ix

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Along the west-central coast of Florida lies a 250 km stretch of shoreline, the Big Bend coast, which is dominated by broad, expansive, openmarine marshes. Waccasassa Bay is a wide, open embayment situated in a coastal reentrant along the middle portion of this shoreline. The embayment is rimmed by a healthy marsh system that is similar in appearance to the marshes of the surrounding Big Bend coast. However, the Waccasassa marsh system is unique in this region because it fronts a large, indented coastal embayment. This physiographic feature is suggestive of a sedimentary basin, a potentially important setting along a sediment-poor shoreline Has the Waccasassa embayment influenced the development of the modem marsh system, and might it influence the surrounding marsh systems as sea level continues to rise? A stratigraphic survey of the Waccasassa embayment and surrounding marsh system shows that the area is perched on a flat, shallow carbonate shelf. Bottom sediments are thin or absent across much of the nearshore zone, and the marsh lithosome averages less than 2 meters thick. The sediments are composed of various muds which are unique to the Waccasassa Bay coastal system. The stratigraphy reveals a mid-to-late Holocene evolution for the area, with the embayment being progressively transgressed since about 5,500 years BP. The shallow carbonate bedrock has had a significant influence on the evolution of the Waccasassa system. The embayment is sediment-poor like the surrounding coast, and it should not be considered an accumulating sedimentary basin. The role of the embayment in affecting the region appears to be restricted to the immediate Waccasassa coast. The marshes X

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rimming the bay are different than other systems studied along the Big Bend The stratigraphy is complex and comprised of local clay-rich sedimentary units. The Waccasassa coastal system has evolved under the influence of shallow bedrock and a limited sediment supply like much of the Big Bend coast. Abstract Approved: Major Professor: Albert C. Hine, Ph.D. Professor, Department of Science Date Approved : ---r---t----t---xi

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1 1. INTRODUCTION Coastal wetlands, including salt marshes, delta plains, and estuaries, have long been recognized as vitally productive and critically important environments (Mitsch and Gosselink, 1993) The biological productivity of salt marshes is ranked as one of the highest in the world (Mitsch and Gosselink 1993). In addition to their biological fertility, salt marshes also protect coastal systems by buffering against storm and wave damage and by serving as fllters for upland runoff of nutrients and waste (NOAA, 1991) Despite their recognized importance many marsh systems have already been lost or destroyed through both natural and man-induced processes (Dahl, 1990; Dahl and Johnson, 1991) Unfortunately human effects are taking a toll on the coastlines In marsh systems, past and present coastal engineering projects, such as diking, draining, and dredging, have resulted in significant wetland destruction. Other, more indirect effects of mankind may also be important to the maintenance of existing salt marsh systems. The predicted increase in sea level rise due to the anthropogenic input of C02 into the atmosphere could have grave consequences on coastal systems throughout the (Dolotov; 1992; Hoffman, 1984). The base of scientific knowledge on salt marshes has until recently centered around the biology of these environments. However, as the loss of wildlife communities has been shortly followed by the loss of the entire wetland habitat, interest in the physical and geological processes which

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control the development and maintenance of marshes has increased tremendously. Because of the general lack of previous scientific research, early studies began investigations at the basic levels of evolutionary development and environmental characterization (e.g. Bloom, 1964; Bouma, 1963; Eleuterius, 1972; Frey and Basan, 1985; Redfield, 1972). Nearly twenty-five years after these pioneering studies, expansive, coastal marsh systems such as the pristine, salt marsh shoreline of Florida' s west-central coast remain largely unstudied. 2 Unlike the sandy barrier shorelines typical of the United States' Atlantic and Gulf coasts, Florida's west-central coast is dominated by expansive, open-marine marsh systems. This wetland environment comprises one of the largest stretches of marsh shoreline in North America, extending along 250 km of coast. The area is heavily influenced by a shallow, karstified carbonate basement, freshwater input from numerous springs, and an overall lack of siliciclastic sediments. All of these controls have helped produce a morphologically and ecologically complex shoreline system. Recent studies have already decribed four physiographic environments along the southem portion of the marsh coast; the berm-ridge marsh, marsh peninsulas, marsh archipelago and shelf embayments (Hine and Belknap, 1986; Hine et al 1988). Presently, this study and other ongoing research are looking at the middle and northem portions of the Big Bend coast in an effort to characterize the entire length of this unique shoreline (Garrett et al., 1993; Goodbred and Hine; in review ; Good bred et al. 1993 ; Leonard, 1994 ; Leonard et al. in press a;b ; Raabe and Stumpf, 1993; Wright et al., 1993 a;b). The studies have looked at the geologic history of these coastal systems and the

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controls on their development (Garrett et al. 1993; Goodbred et al. 1993; Wright et al., 1993a;b). The results have provided a basic understanding of the evolution and resulting geology of the modern system. Other studies on the modern Big Bend marsh system have begun to determine the process of marsh deposition and sediment transport along this coast (Leonard, 1994; Leonard et al., in press a;b). 3 In the past, the coastal marsh systems of the Big Bend shoreline had remained relegated to the abundant wildlife and the watermen supported by the coastal production. More recently, however, population growth along this pristine area has caused concern for the well-being of these marshes and the entire coastal system. Censuses show that human population growth rates in the southern half of the region have increased greatly during the past several decades (Knapp, 1978; Whitney, 1981). In order to assess the effects of greater usage by humans, it is necessary to understand the basic underpinnings of the coastal systems. This research needs to be completed before irreparable impacts occur to these systems. The Waccasassa Bay marshes are already protected as a 30,784-acre state preserve. However, this does not preclude impacts to and from surrounding areas. The Crystal River area just to the south of the study area, is being developed and already contrasts sharply with the relatively pristine Waccasassa Bay area. illtimately, a scientific understanding of the coastal system will be required for the proper management and preservation of this region. Such a goal is worthy in respect to this area's importance as a nursery for fishery species, as a buffer against storms and flooding, as an indicator of environmental changes, and as one of the largest-remaining, pristine wetlands in the country.

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4 This particular study focuses on the Waccasassa Bay system along the middle portion of the Big Bend coast (Fig. 1). Waccasassa Bay is a shallow, wide-mouthed, open embayment rimmed by a healthy, expansive salt marsh and wetland system. This area would be classified as a shelf embayment in the scheme ofHine et al. (1988) Prior to this study, the geology of this reentrant-like feature was essentially unknown. The general physiography of the embayment initially suggests that it could be a sedimentary basin containing some significant amount of sediment. Since the majority of the marsh coast is situated in a sediment-poor environment, the potential of Waccasassa Bay as a sediment source is vital to understanding the development and fate of this coastline. Another interest in the Waccasassa Bay area includes the general characteristics of the marsh system, especially because this system fronts a broad, indented feature unlike that found along other portions of the Big Bend coast In the context of the regional Big Bend coast the objectives of this research were to determine the evolution, geology, and modern processes of the Waccasassa Bay system. The results tie back into our evolving view and understanding of the marsh coast, the importance of which has already been expressed Objectives The main objectives of the project follow: 1. Determine the stratigraphy of Waccasassa Bay and the surrounding marsh system. 2. Reconstruct the Quaternary history and development of Waccasassa Bay and the surrounding marsh system.

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shoreline I water body KEi [] oyster reef I bioherm \ Waccasassa Bay Eleven Prong Kilometers 0 1 2 Nautical Miles 0 1 2 0 .':,:;:;t ..:. Withi;cooc'iiee Bay \t .. .... --, .... .. .. -""'':.::) \, .. ,, ... ,). ... "dt =:? 29 00' 83 00' Figure 1. Site and Location Map for the Waccasassa Bay Study Area. 5

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3. Determine the influences of sea level change on the development of Waccasassa Bay and the surrounding marsh system. 6 4 Determine the dominant influences and results of the processes presently operating in Waccasassa Bay and the surrounding marsh system 5 Predict the responses of the Waccasassa Bay system to changes in sea level, and what role it would follow if the rate of sea level rise increases.

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7 2. GEOLOGIC SE'ITING The modem geologic system of the Florida platform can be considered a mixed, siliciclastic-dominated environment supporting relatively flat and low lying features. The present-day processes involved with these configurations are affected b y the shallow underlying carbonate bedrock. The deposition of this immense thickness of rock has dominated Florida geology for over 100 million years, from the early Cretaceous until the late Paleogene (Chen, 1965). The dominance continued until the introduction of continental siliciclastics during the early Miocene This influx of sediment drastically altered Florida' s carbonate system into the mixed siliciclastic-carbonate environment found today (McKinney 1984). Although the Florida platform is tectonically stable, remnant structural features exhibit significant control on the modem topography and sediment distribution of the region ( Riggs, 1979) With relatively little siliciclastic material being introduced to the system since at least the Pliocene, many of the sedimentary deposits of the past 5 million years have undergone periods of reworking and redistribution. As a result of the reworking, the pre. sent stratigraphy of the thin, unconsolidated veneer of Neogene material is disjunct and complex across much of the Florida platform ( Scott 1992)

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8 Structure Three major structural features have influenced the development of central Florida's physiography: the Peninsular Arch, the Ocala High, and the Suwannee Straits (Fig 2). The Peninsular Arch is a northwest-trending, anticlinal structure extending from southeastern Georgia through southern Florida and into the Great Bahamas platform (Applin, 1951) This subsurface feature is believed to originate in the metamorphic Paleozoic basement rock which unconformably underlies the thick Mesozoic/Paleogene carbonate sequences (Vernon, 1951) The Peninsular Arch largely controlled the Mesozoic sedimentation of carbonates along the Florida peninsula (Riggs, 1979), but was ultimately covered by the deposition of those rocks (Klitgord et al., 1984). Contemporaneous and post-deposition regional movements during the late Mesozoic and Paleogene resulted in the folding of the carbonate sediments overlying this basement structure (Carr and Alverson 1959; Purl and Vernon, 1964;), an event possibly related to the formation of the Ocala High (Vernon, 1951). The Ocala High is a northwest trending anticlinal feature paralleling the west side of the Peninsular Arch. It was frrst described as a late Oligocene/early Miocene flexure by Vernon (1951). The origin of the Ocala High is still unclear, but its age and development is not associated with the Peninsular Arch (Chen 1965). Recent studies have suggested that its formation is associated with Paleogene fracturing/faulting resulting from Mesozoic rifting (Klitgord et al., 1984). Other theories propose that the Ocala High is a sedimentary feature related to an anomolous buildup of Eocene

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t JJ 0 km 100 200 Figure 2 Map ofthe Structural Features of Florida (after Chen, 1965) The study area is located along the west side of the Ocala High. 9

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carbonates (Winston, 1976) or the differential compaction of Eocene carbonates following deposition (Miller, 1986). 10 The Ocala High dominates the geology in the northwest portion of peninsular Florida. It is expressed by the oldest surface exposure of carbonate rocks in the state, revealing the middle Eocene rocks of the Avon Park Formation near to the study area (Fig. 3). Exposure of these less resistant rocks along Florida's west-central coast may be responsible for the large coastal reentrant comprising the Big Bend shoreline (White, 1958). Dissolution of these older rocks by the freshwater springs associated with the Ocala High (White, 1958) is another process which may be related this coastal reentrant. Opdyke et al. ( 1984) suggested that large amounts of carbonate rock have been removed from this region through freshwater dissolution. They conclude that the removal of this material has resulted in crustal unloading and isostatic uplift. They propose that the freshwater flow can remove an equivalent of one meter of surficial limestone every 38,000 years and that this process has led to an epeirogenic uplift of 36-41m. The occurrence of this uplift event is partially supported by the anomalous elevations of Plio-Pleistocene shorelines in northern Florida (Winker and Howard, 1977). During the Mesozoic/early Paleogene an active marine seaway separated the carbonate system of the Florida platform from the siliciclastic system of the North American craton (Dall and Harris, 1892; Hull, 1962; Chen, 1965; Applin and Applin, 1967; McKinney, 1984; Popenoe et al., 1987). This feature has been alternately referred to as the Suwannee Straits or Channel, or the Gulf Trough. The seaway marked the northern extent of carbonate production, and this boundary steadily migrated to the northwest

PAGE 26

post-Miocene Miocene t upper Eocene }J middle Eocene Okm 100 200 Figure 3 Geologic Map of Florida's Surface Units (after Chen, 1965) The study area is dominantly underlain by upper Eocene carbonates, but the middle Eocene Avon Park Fm. also o utcrops locally within the area. 11

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12 from the late Cretaceous until late Eocene (Chen, 1965). To the benefit and maintenance of carbonate production on the platform, continental siliciclastics were prevented from entering the system by this seaway (McKinney, 1984). However, by the late Oligocene the seaway had infilled or otherwise become inactive (Chen, 1965; McKinney, 1984; Popenoe et al., 1987). This closure resulted in the influx of siliciclastic sediments onto the Florida platform and the essential shutdown of carbonate sediment production (McKinney, 1984). As a result of this alteration in sediment regime, the Neogene environment became a mixed, siliciclastic-dominated system. Stratigraphy The lithic stratigraphy of Florida is dominated by Mesozoic/Paleogene carbonates unconformably underlain by a lower Paleozoic basement. These underlying metamorphic rocks are part of a continental crust mass (Applin, 1951). The overlying carbonates are up to several kilometers thick and are dominantly composed of various shallow marine material (Hine, in press). The sequence begins in the late Jurassic (Klitgord et al., 1984) when the Florida Platform was part of an extensive carbonate 'gigaplatform' extending along the Atlantic and Gulf coasts from the modem Caribbean to Canada (Poag, 1991). Carbonate deposition on the Florida platform continued until the closure of the Suwannee seaway in the middle Paleogene (McKinney, 1984) Once the carbonate system had shut down, sedimentation was

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SYSTEM SERIES FORMATION Holocene ----Quaternary Undifferentiated Pleistocene Sands and Clays ------Pliocene Miocene Tertiary Oligocene Eocene ?Alachua Fm? Ocala Group Avon Park Fm. Figure 4. Stratigraphic Column for the Waccasassa Bay Are a (after Crane, 1986). 13

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14 dominated by siliciclastic and authigenic material associated with longshore transport and nearshore upwelling (Riggs, 1979) The near-surface stratigraphy of the Big Bend coast begins with the middle Eocene Avon Park Formation (Fig. 4). This tan-to-brown dolomite is frequently interbedded with limestones and dolomitic limestones containing varying amounts of peat, lignite, and plant remains (Miller, 1986; Vernon, 1951) In the study area, the top of the unit varies from surface outcrops to 45 m deep, with total thickness ranging from 250-350 m (Rupert, 1988). The Avon Park rock is mined near the town of Gulf Hammock, 10 km east of Waccasassa Bay, for use as concrete aggregate, soil conditioner, and as a filler in bituminous mixes (Lane et al., 1988). The Ocala Group unconformably overlies the Avon Park Formation everywhere in the study area except where it pinches out against Avon Park surface outcrops (Vernon, 1951) The Ocala Group consists of three members; in ascending order, the Inglis, Williston, and Crystal River members. These units are distinguished by their fossil assemblages and were originally considered to be three distinct formations, but they have since been classified as biozones (Randazzo, 1982). The strata grade from the gray fossiliferous limestone and dolomitic limestone of the Inglis and lower Williston units into the abundantly fossiliferous, chalky limestones of the upper Williston and Crystal River units (Rupert, 1988). The thickness of the Ocala Group averages 35 m, except again where it thins around the Avon Park outcrops The depth of the Ocala Group is generally less than 15 m, but its surface is highly karstified and surface outcrops are common A series of unlithified sandy sediments unconformably overlie the Ocala Group in the study area. The poorly understood Alachua Formation is

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15 the earliest of these strata. Many ideas on the origin and age of the Alachua Formation have been put forth (Cooke, 1945; Purl and Vernon, 1964; Scott, 1988), but the variability of the sediments makes a coherent model difficult to support. Based on vertebrate fossils the formation has been given the broad age range of Miocene to Pleistocene. The succession of these fossil assemblages supports the thought that the formation is a series of time transgressive, reworked deposits (Rupert, 1988). Scott (1988) considers the formation to be weathered and perhaps reworked material originating from the Hawthorn Group Overlying the Alachua Formation are a series of undifferentiated Plio Pleistocene siliciclastics, generally less than 6 m thick. In places up to several meters of Holocene quartz sands, muds, and marls cap the Plio Pleistocene sediments. In general the post-Miocene stratigraphy of the Big Bend coast and nearby upland remain undefined. Most of the deposits exist as only thin, discontinuous veneers scattered upon the underlying bedrock. The lack of widely traceable sequences and the variability of these sequences seem to preclude a coherent stratigraphic model at this time. Geomorphology Early studies have divided Florida into three main, geomorphic regions; the northern or proximal zone, the central or mid-peninsular zone, and southern or distal zone (Fig. 5). The study area and the entire Big Bend coast fall within the central zone White (1970) further divided the central zone into the central highlands and the coastal lowlands, which flank the

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16 former on both sides (Fig. 5). The highland areas are characterized by sandy, shore-parallel ridges locally separated by topographic lows. The coastal lowlands are characterized by flat, poorly-drained areas of thin sediment cover, much of which forms wetland environments. In general the geomorphology of the entire region is dominated by relatively flat, low-lying features formed since the Miocene by repeated sea level fluctuations. These sea level fluctutions are represented by a series of Plio-Pleistocene marine terraces and shorelines which have been mapped across the state (Fig. 5; Matson and Sanford, 1913; Cooke, 1945; Healy, 1975). The Brooksville Ridge and other similar features associated with the central highlands have developed in response to the highest stages of these Pleistocene fluctuations (White, 1958). These ridge and valley systems are composed of large sand bodies that are likely remnant beach ridges or barrier islands (Winker and Howard, 1977). The elevation of the Brooksville Ridge ranges from 20 to 75 m above sea level. The thick sequence of sands comprising this feature may have developed at the 33 m Pleistocene sea level highstand associated with the Wicomico shoreline (Knapp, 1978). The Gulf coastal lowlands are situated to the west of the Brooksville Ridge and highlands province This low, flat geomorphic region comprises the whole of the Big Bend marsh coast, an environment which typifies the lowland system. Inland of the coastal marshes are freshwater swamps, river valley lowlands, and a series of low, Pleistocene marine terraces (Fig. 5). The Pamlico terrace (elev. 2-13m above m.s. l.) is occupied by a 4-5.5 m thickness of clayey sands called the Waccasassa Flats (Vernon, 1951; White, 1970). This area hosts the majority of the Waccasassa River drainage basin. Situated below the Pamlico terrace is the more obscure Silver Bluff terrace,

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17 Central or Mid-peninsu lar K E Y Zone H igh lands r egion (Wh it e, 1 970) Brooksville R idge Big B end coasta l r eentrant and mar sh system t Pa m lico terrace 2 5 -7.5 m S i lver Bluff terrace N 0 .3-3. 3 m Southe rn o r Di stal Zone Okm 100 200 Figure 5. Map of Some Geomorphic Features and Marine Terraces of Florida (after White, 1 970 and Heal y 1975)

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elevation 0 3-3 m above mean sea level. This feature is associated with the delineation of the coastal marsh belt of the Big Bend shoreline and is comprised of a thin veneer of Quaternary marine sediments (Rupert, 1988). 18 In addition to the influence of fluctuating sea level, karstification of the shallow limestone basement has exhibited a strong control on the development and distribution of regional geomorphology. White (1958) describes the extensive lake-filled plains of Florida in association with the more permeable sands of the highland areas. In this environment the sands allow for the subterranean flow of surface water, and therefore, the dissolution of the limestone and development of karstic collapse features. In lowland areas the environment is often swampy, indicating the presence of impermeable clayey sediments which preclude the surface formation of extensive karst lakes. A more recent study of two karst-controlled water bodies in central Florida showed that the morphology of surface karst features reflect in which stratigraphic zone subterranean dissolution had taken place (Evans et al., 1994). Steep, narrow shafts formed through the dissolution of Miocene carbonates, large-scale collapse sinkholes were associated with the catastrophic collapse of subterranean caverns, and broad solution valleys developed by the dissolution of Paleogene carbonates. These features locally affect the morphology of the modern coastal system (Hine et al., 1988).

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19 Holocene Sea Level Sea-level fluctuations are one of the main controls on shoreline development and coastal/shelf stratigraphy (Fletcher and Wehmiller, 1992). During the Pleistocene, numerous glacially-driven fluctuations were responsible for forming the majority of surface features found across the Florida platform (Hays et al., 1976) Sea levels through this period fluctuated wildy in response to shifts in the volume of continental ice (Williams, 1988). The most widely accepted theory is that these changes in the cryosphere were largely driven by variations in planetary insolation which result from orbital pertubations called Milankovitch cycles (Hays et al., 1976). More recently, Holocene sea level has been characterized by a continuous, but variable, rise in water level (Fairbanks, 1989). Florida is situated in a largely inactive tectonic setting, and so changes in relative sea level are assumed to be eustatic in origin This stability allows for greater precision and accuracy in developing a local sea level curve Since such a curve ideally represents only eustatic changes, it should presumably reflect global sea level history as well Scholl and others have developed a Holocene sea level curve for Florida using a series of radiocarbon dates from mangrove peats, and some shells and carbonate muds (Fig. 6; Scholl, 1964; Scholl and Stuiver; 1967; Scholl et al. 1969) The findings of more recent studies have generally supported Scholl's original curve (e.g Wanless, 1982 ; Hine et al 1988; Parkinson, 1989) and as a result it has remained largely unchanged The first record of sea level effects near the modem coast of Florida occur at about 7,000BP, when sea level was approximately 6 m below present

PAGE 35

20 (Scholl et al., 1969). From about 5,000BP until3, 500BP, sea level had risen steadily at a rate of approximately 13 em per century (Fig. 6) However at that time there appears to have been a decrease in the rate of rise, slowing to about 4 em per century up until the present (Scholl et al., 1969) The development and progradation of many coastal environments at about 3,500 BP has been attributed to this slow down (Evans et al. 1985; Hine et al. 1988; Parkinson, 1989 ; Stapor et al. 1991). In contrast to the smooth curve of Scholl et al. (1969), some authors have presented late Holocene sea-level curves which show episodic, short-period fluctuations during this period (Fairbridge 1984 ; Most recently, data compiled from U.S coastal tide gauges has provided sea level fluctations for the much of this century (Hicks et al., 1983) The tide gauge records at Cedar Key FL (15 km to the west of Waccasassa Bay) have shown a rise of 8 2 em for the period of 1914 to 1980. This is equivalent to a rise of 12.2 em per century, a rate closer to that of the middle Holocene than during the past 3,500 years.

PAGE 36

present 1 0 o> 2.0 _Q) a.>-..0('11 Q) 3 0 V)Vl .... a.>c Q)Q) 4 0 EE 5 0 5000 4000 3000 2000 14C-years ago A -MATERIAL DATED 1. terrestrial gastropod 2 detrital organic material 3. detrital organic material 4 detrital organic material 5 charred wood 6 freshwater peats 7 detrital wood fragme nt s 8 wood fragment (beneath oyster reef ) 9 wetland peat 21 .. 1000 Figure 6 Recent Holocene Sea-level Curve for Florida (after Scholl, 1969). Radiocarbon dates from this study (A) are included along the curve.

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22 3. PHYSICAL SE'ITING Climate Central Florida lies within the transition zone from the subtropical climate of south Florida to the temperate climate of the Panhandle. The region is characterized by hot, humid summers with an average July/August temperature of 30C, and relatively warm, dry winters with an average January/February temperature of 15C (Hoenstine and Lane, 1991) The yearly average temperature is 22 C (Fig. 7). Annual rainfall in central Florida averages approximately 150 em, although considerable yearly variation has produced a range of 75-215 em. The summer months yield the most precipitation, largely as a result of brief, intense, and abundant daily thundershowers (Fig. 7). The winter season is drier and typically warm and sunny. However, the winter weather pattern is affected by longer-period cold fronts sweeping down from the midwest, often bringing rain, cooler temperatures, and increased winds (Wolfe, 1990). The rainfall associated with Florida storms can be intense. The Florida record for 24-hour precipitation is held by Yankeetown, located only 10 km to the south of the Waccasassa Bay study area. From September 5-6, 1950 this town received 98 em of rainfall (Knapp, 1978 ) The wind patterns of central Florida are divided between relatively weak south/southeast winds and stronger, more periodic northerly winds.

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32 (/) ::I '(ii 24 Qi () 0 16 ::I ; .... Q) 0. 8 E Q) 1-0 25 20 (/) .... Q) -Q) 15 E ;:; c Q) t..') (ij 10 c n; a: 5 0 -------Average -21 1 oc c al J ..c <1.> u.. ..c Cl> u.. '-al '->c. al <{ c ::J J c ::J J ::J J C> c. ::J Cl> <{ U) C> c. :J Cl> <{ U) -(.) 0 -(.) 0 > 0 z > 0 z (.) <1.> 0 (.) <1.> 0 Figure 7. Average Annual Temperature and Rainfall for Gainesville, Florida. Data period is 1953-1988 (from Hoenstine and Lane, 1991) 23

PAGE 39

24 Seasonal windroses from Tampa (nearest data site) show that the southerly winds driven by the westem side of the Bermuda high-pressure cell dominate in the warmer spring and summer months (Fig. 8). The prevailing fall and winter winds blow from the north/northeast in association with the passage of cold fronts. Thunderstorms can locally control the speed and direction of winds and can produce strong, gusty winds for short periods. Overall, the annual resultant wind vector in the study area is from the north, largely because of the higher wind speeds following the winter fronts (Wolfe, 1990) Storms, including thunderstorms, hurricanes, and extratropical events, are a significant part of Florida's weather patterns. Thunderstorms are the most abundant type of storm to occur in the study area, being most active during the warm, humid summer months. In contrast, hurricanes are the most infrequent type of storm to the effect the Big Bend coast (Fig. 9). These periodic events often move into the Gulf of Mexico where they can affect the study area through winds, waves, and surge waters. Although they are not common, the strength and intensity of hurricanes and tropical storms make them a potentially serious threat to the marsh coast. Damage caused by these events can result from not only the severe winds ( > 120 kmh-1), but from the sometimes large storm surges as well Winter fronts and extratropical storms are generally not as powerful as the tropical systems, but they occur more frequently along the Big Bend coast Up to one front per week may come through during the winter months, with eight to ten strong events occurring during this period CHine and Belknap, 1986). Very powerful, extratropical storms have infrequently occurred in the region, producing winds and storm surge levels similar to those of a hurricane (see Modem. System and Processes chapter)

PAGE 40

40 N N Spring (March-May) Summer (June-August) 0 N N Fall (September-November) Winter (December-February) Figure 8 Wind Ros e Diagrams for Tampa, Florida Data collected 1959-1979 (after Fernald, 1981). 25

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TAYLOR PATHS OF HURRICANES STRIKING THE COAST 1885-1990 Figure 9 Path of Hurricanes Striking the Coast from 1885-1990 (after Wolfe, 1990) Note that this figure only shows major hurricanes moving onshore of the area. Many more hurricanes and tropical storms not shown on this figure have also variably affected the region 26

PAGE 42

27 Big Bend Coast The Big Bend coast is a 250 km long stretch of shoreline comprised of expansive, open-marine salt marshes (Fig 5). This marsh coastline has evolved in a low-energy and sediment-starved setting. The coastal environment is a slightly tide-dominated system, with a mean annual wave height of approximately 30 em and an average spring tidal range of approximately 90 em (Hine and Belknap, 1986) Wave energy along this coast is reduced largely because of the wide, shallow continental shelf, which precludes or dampens large sea swells from reaching the shoreline. The shelf is approximately 200 km wide and has a low gradient of 1:3,000-6,000 off the Big Bend coast The astronomical tides along this shoreline are mixed diurnal/semidiurnal tides. The regime varies between one and two tidal cycles per day, with one tide generally being higher than the other during semediurnal cycles. The small tidal range, shallow water, and storm events of this region lead to wind-driven tides, either setups or drawdowns, which are often greater in magnitude than the astronomical tides. This effect results in actual water levels commonly varying from those of the predicted tides In general the marsh coastline is set in a sediment-starved regime, with only a thin veneer of siliciclastic sediments overlying the shallow carbonates basement. One reason for this absence of coastal material is the lack of fluvial sediment input. The only major point source of sediment discharge along the Big Bend coast is the Suwannee River, located 30 km to the northwest of Waccasassa Bay. The headwaters of the Suwannee lay in the Okefenokee Swamp of southern Georgia Discharge averages 300 m3s-1,

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28 the second highest rate in Florida (Meadows et al., 1991). Despite the size of the river, it presently transports relatively small amounts of suspended and bedload material (Meadows et al., 1991). The Suwannee River is not, however, typical of freshwater discharge along the Big Bend coast. Rather, this shoreline system is characterized by a series of short spring-fed rivers which are concentrated along the southern portion of the region (Rosenau et al., 1977). The waters in these rivers are typically crystal clear and have little to no suspended sediment load. The rivers are supported by large and abundant artesian springs associated with the Floridan Aquifer (Wetterhall, 1965). There are also a large number of smaller, unmapped springs which discharge along the entire region. The great magnitude of freshwater discharge along this coast has produced locally intense dissolution of the carbonate bedrock This development of a complex karst topography has resulted a diverse, bedrock-controlled coastal morphology (Hine et al., 1988). Waccasassa Bay Waccasassa Bay is a broad, open and shallow embayment flanked by the Cedar Key promontory to the west and the Eleven Prong high to the south (Fig. 1) The dimensions of the bay are approximately 10 km wide by 10 km long. The average depth in the embayment is 1.2 mat mean low water, with a deeper central channel (3-6m below m.l.w.) trending southwest away from the Waccasassa River about 4 km offshore A large majority of the basin is covered by a shallow flats area with depths of less than one meter at

PAGE 44

29 m.l .w. (Fig. 10). Near the shore-edge this shallow bottom shoals to fonn subtidal mud flats which are exposed only at extreme low tides. The flats broaden near the head of the embayment and are nearly continuous from the mouth of Depew Creek south to Williams Creek (Fig. 1). Offshore of Waccasassa Bay, a break in slope marks the boundary of the low-gradient, shallow shelf area upon which the modern system is situated. This increase in the nearshore slope corresponds approximately to the 1.8 m isobath (Fig. 10 ) where the gradient changes from about 1:2,500 to 1:1,250 This broad, shallow area above the 1.8 m isobath might be considered to be one nearshore zone, referred to here as the Waccasassa shelf. Near the center of the bay lies a series of large, transverse and inactive, subtidal oyster (Crassostrea virginica) biohenns. These features are situated at the head of the offshore central channel and mark the edge of the broad flats area (Fig. 10). A smaller series of active, intertidal oyster reefs extend from the offshore biohenns shoreward to the mouth of the Waccasassa River (Fig. 11). Small, patchy oyster reefs are also situated throughout the embayment along the marsh edge. The Waccasassa River is the only major po int source of freshwater within the embayment, lying directly at the head of the bay. This small, 35 km long river has a 2,425 km2 drainage basin and an average discharge of 8.5 m 3 s 1 ( Meadows e t al., 1991 ) Two major tributaries join the river, the Wekiva River and Otter Cree k. Spring-water disch arge within the river basin is dominated by the second-magnitude (3-30 m 3s-1) Blue and Wekiva Springs, which feed the Waccasa ssa and Wekiva Ri v ers, respectively ( M e adows e t al., 1991)

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water depth l::o:,::;:_-J 0 -1 8 m 1.8-3. 6 m -> 3.6 m / . . ,. '-,/ } .. environment E3 salt marsh E:3 upland -oyster reef/bioherm Figure 10. Physical Map of the Waccasassa Bay Area. 30 ...

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31 Figure 11. Photograph Showing a Typical Oyster Reef from Waccasassa Bay. The photo was taken near the mouth of the Waccasassa River at low tide

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32 One kilometer upstream of the river mouth, Cow Creek forms a confluence with the Waccasassa River. This small creek and its spring-fed tributary, Ten Mile Creek (1 m3s-1), contribute a variable amount of freshwater to the system. Numerous creeks are also situated along the margins ofWaccasassa Bay. The flow in most of these creeks is entirely tidal, however, several have a small freshwater discharge fed by sinkholes located in the headwaters area. There are also many, unmapped artesian springs, both in the upland and offshore, which flow from the shallow limestone of the area (Rupert, 1988) Surrounding the rim of the Waccasassa Bay reentrant are several distinct coastal provinces (Fig 12). Along the westem edge of area is a short stretch of coastline characterized by exposed, karstified bedrock covered with isolated patches of marsh. This environment is similar to the marsh archipelago coast defined by Hine and Belknap (1986) along the southem Big Bend coast. East of the archipelago lies the Waccasassa coastal province (described in Waccasassa Marshes chapter). The southem extent of the Waccasassa province is bound by a shallow-bedrock high which supports a mangrove/marsh headland. This is the Eleven Prong promontory (Fig. 1), a coastal environment that generally appears to follow the definition of a marsh peninsula; a marsh headland feature composed of peninsulas and detached islands controlled by rocky high areas (Hine and Belknap, 1986) The southernmost . extent of the regional reentrant is the Withlacoochee Bay area (Fig. 1) which can be characterized as a shelf embayment after Hine and Belknap (1986). This environment is a microtidal, low-wave energy, freshwater-influenced, shallow-water depositional basin.

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-.::. .:::.. _,:::'_<._ :: ____ __, ........... :; :: ;. 29 o8' marsh archipelago .. : waccasassa., 2-oast .. ':: . . .. . : .;,.,., ... .: marsh peninsula shelf embayment 33 ( / .... ./ ...... .. .. .;.'0: -: .... : :.: : . : 83 00 Figure 12. Coastal Provinces within the Waccasassa Bay Area. Defmed by this study and Hine and Belknap (1986)

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34 Waccasassa Marshes The salt marshes of the study area are 0 7-1.5 km wide and cover a region of approximately 70 km2 rimming the Waccasassa embayment. The morphology of these wetlands is characterized by broad, expansive marsh zones with relatively fine-scaled creek drainage and well-developed levees. Along the backside of the marsh zone, this environment quickly grades into the forested upland. This setting is characterized by dense tree cover and nearsurface bedrock The bedrock shoals from the marsh zone up to nearly a surface exposure in the upland area (Fig. 13). The creeks are generally shallow, meandering features which often show a dendritic pattern of gullies and rivulets at the headwaters. These small creeks are usually controlled by their exposed bedrock channel bottoms (Fig. 14) Several larger creeks (e.g. Bird Creek) in the northeast corner of the embayment are deeper, up to 3m. These creeks drain sinkhole features located at their headwaters; freshwater discharge from the springs may be related to the development of the deeper creeks The ecology of the wetlands area is dominated by Juncus roemerianius (black needlerush), the typical marsh plant in the region. J roemerianius commonly forms expansive, monotypic stands and becomes mixed with other vegetation only along the fringes of the marsh or near the freshwater transition (Fig 14). Another important plant in the marsh zone is Spartina alterniflora (smooth cordgrass). This plant commonly edges the J. roemerianus marsh along the shoreline and waterways where it acts as an early colonizer and substrate stabilizer. Other plants commonly found in the

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Figure 13. Photograph Showing the Nearsurface Bedrock which Underlies the Forested Upland Zone. This picture was taken along the upper Waccasassa River near the top of the map in Figure 1. 35

PAGE 51

36 Figure 14. Photographs of a Shallow Creek and the Typical Marsh Setting in Waccasassa Bay. [A] Rocky Run, a typical bedrock-controlled creek Note outcropping carbonate rock. [B] View of the broad, expansive, monotypic stands of Juncus roemerianus which dominate the Waccasassa marshes. Picture taken looking north across the marshes.

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37 marsh zone include Distichlis spicata (marsh spike grass) on the levees and drier areas and Cladium jamaicense (sawgrass) at the freshwater transitions In general the marshes of the Big Bend coast do not show the high/low marsh zonation typical of Atlantic coastal marshes (Frey and Basan, 1985). This characteristic is largely a result of the low tidal amplitude along the coast (Hine and Belknap, 1986). Salinity is one of the dominant factors controlling the distribution of these wetland plants (Eleuterius, 1980; Fig 15), and with them the characteristics of the depositional environment. Salinity gradients along the lower Waccasassa River range from a mean of 2%o approximately 6.5 km upstream from the mouth to 15%o at 3.5 km upstream from the mouth (Fig. 16). Within this gradient range along the river, J. roemerianus remains the dominant, and nearly singular, type of marsh vegetation. In zones of lowered salinity levels and inundation period, the plant community changes to that of a more upland environment One such zone is the elevated bankside levees that are a common feature along many of the creeks in the area. These levees are colonized by Sabal palmetto (sabal palm) and Juniperus silicicola (southern red cedar) on the higher levees (Fig. 17 A), by various semi-halophytic upland species such as Baccharis halimifolia and Iva frutescens along the middle elevation levees (Fig. 17B), and by the high saltmarsh plant, Distichlis spicata along the lowest levees (Fig 17C). The distribution of these plants suggests that the levees are higher and better developed towards the head of the Waccasassa embayment Field observation and the presence of these plants also indicate that these levees are not flooded during normal tidal fluctuations. Along the Big Bend coast,

PAGE 53

(j) )> r z m 11 JJ < > m (j) I Cladium jamaicense G> . . Sagittaria lancifolia Scirpus olneyi Spartina patens Spartina cynosuroides Juncus roemerianus Spartina alterniflora Figure 15 Relative Biomass ofMacrophyte Populations Found along the Big Bend Coast ( from Stout, 1984). 38

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Surlace B dtom 1 5Yoo Kil o meters 5 0 s_ B 10%o 5 B 5%o s B 2%o Figure 16. Waccasassa River Salinities during 1985 Shown are the locations of mean, surface and bottom, high-tide isohaline positions (from Dixon, 1986) C..:l c.o

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40 Figure 17 Photographs of Three Levees of Different Elevation Showing the Change in Flora. [A] The highest and best developed levees are near the head of the embayment along the Waccasassa River and its tributaries. Here the stand of trees, sabal palms (Sabal palmetto) and southern red cedar (Junipe ru s silicicola ) are typical of these high levees [B] Away from the treed banks the lower, but still well-developed levees are found along the tidal creeks off Waccasassa Bay. This photo was taken along Depew Creek.

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41 Figure 17. (Continued). [C] Photograph of a low levee along the bay margin west of the mouth of Depew Creek. This levee is colonized by the high saltmarsh plant, Distichlis spicata Also note the distinct plant zonation at this site. Spartina alterinifora is the flooded plant along the lower terrace, where it is commonly found. A thin edge of Juncus roemerianus separates the S. altemiflora and the D spicata Along the backside of the levee the elevation drops and the vegetation changes to the expansive, monotypic J roemerianus marsh.

PAGE 57

the wide extent and development of these levees are unique to the Waccasassa Bay area. 42 Elevated hammock zones are also scattered throughout the middle and upper portions of the marsh (Fig. 18) These areas are dominantly colonized by S. palmetto, J silicicola, and Quercus virginiana (live oak). The hammocks develop on areas of nearsurface limestone outcrops where lenses of fresh groundwater can be maintained (Hine and Belknap, 1986). The limestone outcrops associated with the hammocks are also sometimes the site of small freshwater springs. On the north-central portion of the Waccasassa marshes is a large hammock called Salt Island (Fig. 1). This site was named for a large solution feature in the center of the hammock which supports a saltwater spring.

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43 Figure 18. Two Photographs of the Upland Hammocks Found Across the Waccasassa Marsh Zone. [A] The scattered, elevated hammocks stand out as tree islands amongst the J roemerianus grasses of the marsh.

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45 4. METHODS AND MATERIALS This study is largely structured around stratigraphic information used to determine the history and controls on the development of the region. Following this approach, the methods employed in the research incorporate general and broad-scale rec onnaissance methods . These include vibracoring, probe rod tests, surface samples of the marsh and grab samples from the bay. Other technique s include the use of two water-based remote-sensing systems, high resolution seismic refl e ction and sidescan sonar imagery. The latitude and longitude of the sampl e site s and cruis e tracks w e r e d etermine d using portable GPS ( Global Positionin g S ys t e m ) instruments tied to the North American Datum ( NAD '83 ) High Resolution Seismic Reflection Data An ORE GEOPULSE seismic profiling system was use d to investigate the sub bottom geology of the Waccasassa Basin. This system involves the transmiss i o n of a s ound pulse downward thro u g h the water column into the subs urface s e dim ents and underlying bedrock. Portions of this sound pulse are refl e cted back t o the surface by changes in the acoustic impe denc e of the transfe r m edium. These differences r epre s ent lithological changes in the subsurface and the r e f o r e c orre spond to distinc t f a cies and

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46 structure within the stratigraphy. The return signal is collected through a hydrophone and is translated by a receiving system into a paper-recorded subbottom profile Depth of the various sub bottom reflectors is based upon the two-way travel time of the sound pulse. The maximum depth of penetration varies with the frequency and strength of the sound signal, the depth of water, and the subsurface lithology. The ORE system was used with a 105J acoustic source and sampled at a frequency of 700-3000 Hz to maximize both resolution and penetration. However, the shallow-water of Waccasassa Bay and the thin sediment cover reduced the seismic profiling conditions to less than ideal. The benefits of this remote-sensing system allowed for the coverage of a large portion of the study area. Over 120 km of seismic profiling were gathered across the embayment (Fig. 19). The system was deployed from a 23' Boston Whaler towed at a speed of about 5 knots Information targeted for collection included the thickness of the nearshore sediment cover, the bottom topography, and the topography of the underlying bedrock Other features of interest were bedrock karst, sediment infilling, and paleo-river channels. Sidescan Sonar Sidescan sonar is another water-based acoustic system designed to provide a map view of the seafloor (Johnson and Helferty, 1990). Like the seismic system, the sidescan sonar employs the transmission of an acoustic

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29 08' 29 04' 47 : . '! ,J": .. ..... : \; .. ,. .. _ / (// .. If? V'...".# ,.. . . \ \ l.. ",! J j : <<'.. /'V/ . . v ;; w J. ) \ l l ... \ !: r i' /' (" , J : ', .:=,< !J:::4.y.1t< _..:. / _r . .. /'-. :-;; .. ,, ... ;, ( t ... -.:: .: :. .. --::. .. :: i'' . :'.:'.'.\ :.: ; ' : ........ -:-==-=: .... { ...;. I''' .... <" Kilometers 0 2 / .... / ,/ I l ,' ,__ .... 1 ... < .... ;..,..,v., <.;. ,< '..: .. :'. . .. .. : .. I.'; ,&-.,., ""}''.{ ; .: .. \ .. .. ,.. . ... 29 00' ____ / / ' 83 00' Figure 19 Map of Cruise Track for Collection of Seismic Reflection Data.

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48 pulse and reproduces an image based on the strength and return time of the incoming signal. The sound pulse is emitted at a broad angle from two 'windows' on either side of a towfish and can cover a swath of 50 meters or more. The sound pulse is run at a high frequency for maximum resolution and is not strong enough for penetration into the sediment, thereby providing an image of only the immediate seafloor. Approximately 120 km of sidescan profiles were collected for the project using an EG&G Model 260 Image Correcting system with a 100kHz Model272 towfish (Fig 20) The unit was deployed from the bow of a 23' Boston Whaler and towed at a speed of about 5 knots. This data was used to determine characteristics such as bottom roughness and type (i.e sand, shell, rock), extent of seafloor vegetation, and location of bedforms and oyster reefs/bioherms. Grab Samples and Probe Rod Tests Grab sampling and probe rod tests were used to delineate the remotesensing data gathered with the high resolution seismic and sidescan sonar systems. This type of ground-truthing is necessary to strengthen and support the characteristics recognized with the other techniques. An array of 35 grab samples (Fig 21) and 45 probe rod tests were taken across Waccasassa Bay in conjuction with the path of the seismic and sidescan profiles. The grab samples were collected using a small VanVeen-type sampler, and sediments and biological samples were preserved in whirl-pack bags. In the lab the grab samples were analyzed for grainsize, organic content, percentage of carbonate

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' ',( ... \ .. ,' ;,) / ... \ -::-:::::' i ,,_ c ....... / . .. (: ., I :..... / /" ..... . .. .--....... . (. : : .... / / Kilom ete rs 0 1 2 / / :.._ ... ........ / . . / \ ..... ---....... .... ...... ( ' Figure 20. Map of Cruise Track for Collection of Sidescan Sonar Data. 49

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50 / Kilometers 0 1 2 Figure 21. Map of Bottom Grab Sample Sites.

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51 material, and mineralogy. These techniques are discussed in the following Methods sections. The probe rod tests consisted of simply driving a 4 m long 15 mm stainless steel rod into the sediment until striking bedrock The water depth and the thickness of sediment cover was recorded in this fashion Vibracoring Coring is an important method for gathering continuous, undisturbed stratigraphic sequences. This information is invaluable in determining the sea level history and development of a system. Specifically, the data collected from these cores can provide a time-transgressive record of the depositional environments at any fixed place in the study area. Fortunately, a method of coring, known as vibracoring (Lanesky et al 1979 ) is an inexpensive and versatile system for coring in the nearshore and coastal zone Vibracoring uses a concrete vibrator driven by a portable 5 h p. gasoline engine to shake a thin-walled ( 2mm), 7 em diameter, aluminum irrigation tube up to 9 minto unlithified sediments. The sediments immediately surrounding the aluminum tubing become liquified because of the vibration transmitted along the tube, allowing the weight of the tube and vibrato r head to drive the core into the sediment. Once penetration has ceased, the core was capped to create a vacuum and, in the case of the short cores taken in this area, was removed by hand using a rabbit-ear clamp A total of 35 vibracores were collected throughout the study area (Fig 22). Five cores were taken in the coastal zone to determine the nearshore

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52 .' :-I) + ,., 3 6 2 9 0 -04' ..-JI__ e_l-r __ :_i-lo_m_1_e_te_r_: ____ __ rr .... 82 56' Figure 22. Map ofVibracore Site Distribution.

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stratigraphy. The remaining 26 cores were taken in the marsh and upland habitats. The cores were cut open in the lab and then photographed, described, and subsampled. Moisture, organic, and carbonate content were immediately measured from the subsamples. At a later date the core was again subsampled and analyzed for grainsize and mineralogy These methods are described in the succeeding Methods sections. Sediment Analysis Organic Content 53 Samples of a known volume (12 cm3) were extracted from the cores at various depth intervals and placed into ceramic crucibles These sampes were weighed and dried for 48 hours at 90 C. The dried samples were then weighed again after cooling in a dessication chamber containing Drierite (CaS04 } This step allows for the measurement of water content and the determination ofbulk density. The dried sediments were then combusted in an electric muffie furnace at 450 C for 4 hours (Dawes 1981). This temperature is below the temperature at which carbonate material combusts (550 C) Following combustion, the samples were allowed to cool in the dessication chamber. The percent of ash-free organic material was calculated by measuring the weight loss from the original dried sample. The results are reported as percent ashed dry weight.

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54 Percent organic values are a useful tool in characterizing and comparing different facies since the measurements can reflect changes in the depositional environment ( Cohen and Spackman, 1972) For example, the extent of marine influence on a marsh system is often reflected in the organic carbon values, usually decreasing with increased salinity. Carbonate Content Once the organic content analysis was complete, the ashed sediments were placed in small beakers and treated with successive dilute hydrochloric acid (10% HCl) baths. This method removes the calcium carbonate (CaCOg) from the sediments by dissolution with the acid bath. When no visible reaction occurred with the introduction of more acid, the process was considered complete. The samples were then washed with deionized water to remove salts produced by the acid-base reaction. Marine salts in the grab sample sediments had been removed prior to organic combustion. The clean samples were dried and weigh e d to determine the percent weight of carbonate material. Because of the abundance of carbonate-producing organisms in the nearshore zone of Waccasassa Bay, this measurement provides another indication of marine influence on the depositional marsh system.

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55 Grain Size Analysis Grain size analysis was performed on the majority of the vibracores and grab samples. The cores were sampled at varinus intervals to get measurements from each facies. The sample preparation took a significant amount of time and began with either bleach (5.25% NaOCl) or hydrogen peroxide (20% H202) washings (Anderson, 1961 [bleach] ; Starkey et al., 1984 [peroxide]). These solutions were used to remove organic material, with the more reactive peroxide being used only on samples with greater than 15 % organic values. Mter the reaction had visibly ceased the samples were decanted with the use of a centrifuge. The cleaned sediments were then wet sieved through a stainless mesh sieve separating the sample into sand and mud fractions. The sands were then dried and weighed. The mud fraction was washed into a 600 ml or 1000 ml beaker and filled with deionized water. From 0.5 to 1 grams of Calgon ({NaP03h3 x Na20) were added as a deflocculating agent. For further deflocculation of the samples, they were placed in an ultrasound bath for 10 to 20 minutes just prior to being poured into 1000 ml graduated cylinders. The final grain size measurements were made using standard pipette analysis after the methods of Folk (1980). Four 25 ml aliquots were taken to determine the grain sizes of 40 60 80 and 100 {lJl). The samples were finally dried in tared 50 ml beakers and then weighed. The weight value for calgon in the sample was subtracted and the percent weight for each phi size was then determined.

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56 Radio-Isotopes Carbon (14C) Dating Radiocarbon dating techniques were employed in order to established a chronology for the development of the Waccasassa Bay area and the deposition of the stratigraphy ( Arnold and Libby, 1949). This dating method is based on the radioactive decay of the carbon isotope 14C, which has a half life of 5570 years. This isotope is largely produced by the collision of incoming cosmic particles with atmospheric carbon atoms (Montgomery and Montgomery, 1939) Other more recent sources of 1 4 C include the testing of nuclear devices and large scale burning of fossil fuels In addition to the recent fluctuations of the radiocarbon reservoir resulting from anthropogenic inputs, natural fluctuations have also occurred due to variation in the amount of incoming galactic radiation. As a result of these fluctuations, there is an error involved with reporting uncalibrated radiocarbon ages (Beta Analytic Inc. calibrating methods) Therefore, all14C dates are provided with both the uncalibrated radiocarbon age and the calibrated age range for the sample. The uncalibrated ages have been adjusted according to the results of ol3 /12C measurements, which reflect the resevoir source of the carbon. The calibrated value is reported as a calendar date. The correction for this value considers the variation in the radiocarbon resevoir and is based upon extensive known-age tree ring dating (Stuiver and Polach, 1977) Because of its basis on live trees, this calibrated conversion extends to only 7,200 BP and

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57 dates beyond this age have not undergone the dendra-calibration. All of the dating and results were prepared by Beta Analytic Inc. of Miami, FL. A total of eleven dates were been obtained from various types of material, including marine shells, freshwater peats, charred and detrital wood, and an intertidal gastropod (see Table 1 for a summary of results). Lead (210Pb) Dating In order to determine the approximate rate of sedimentation in the marshes of Waccasassa Bay, 2IOPb radiometric analysis was performed on marsh core sediments ( Robbins and Edgington 1975) 21Pb is a radioisotope that is part of the 238Uranium decay series and has a halflife of 22 3 years. It is essentially the daughter product of the gaseous radioisotope 222Rn (T112 = 3 84 days), but there is a series of quick intermediate step between these two species The premise of the technique is that the short-lived, gaseous 222Rn atom rapidly decays to 210Pb, whence this new nuclide can no longer remain airborn and settles onto the land surface (Sharma et al 1987). The lead atom is then scavenged to the sediments and is buried at a concentration determined by the rate of fallout and the rate of sedimentation. An assumption with this technique is that planetary uranium decay is relatively constant, and therefore so is the fallout of the 21opb isotope. With this assumption the rate of sedimentation can be determined by measuring the activity of the 2IOPb radionuclide per unit depth. The interpretation of 2lOPb profiles can be hindered by several factors. One significant problem with this method in the Florida marshes is

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58 bioturbation caused by abundant burrowing organisms and plant root and rhizome propagation. Another problem is the ability of various sediment types to scavenge the radionuclide. Fine-grained materials (i.e clays) have more surface area for sequestering 210Pb particles, and therefore changes in sediment grain size can effect the decay profile. To aid in extracting these effects, the analysis of another radionuclide, 137Cesium, provides a comparison profile (Sharma et al., 1987) A telltale feature for the 137Cs profile is a peak in activity levels concurring with the height of nuclear bomb testing in the early 1960's. Like 210Pb, the 137Cs profile is affected by bioturbation, but analysis of the two distinct profiles allows for a relative determination on mixing rates (Sharma et al., 1987). One core series, taken at a site near the head of Wacc asassa Bay, was analyzed by beta-counting techniques for the determination of accretion rates. The analysis was performed and interpreted by Dr. William Burnett of the Florida St. University, Department of Oceanography. Mineralogical Analysis The mineralogy of the sediments within the Waccasassa Bay area was determined by x-ray diffraction CXRD) techniques (Moore and Reynolds, 1989). This method employs the fact that minerals have a unique diffrative signature based on their individual crystal structure. A SCINT AG XDS2000 diffractometer was used for the mineral analysis. A beam of x-rays is aimed at a low angle across a slide containing a dried and powdered sample of the material. On the opposite side of the source is an x-ray detector which

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59 measures the arriving activity The analysis was run at a range of 2-40 2 which encompasses the activities of most minerals. The results are presented by graphing activity versus 2 Patterns in the spacing and intensity of the activity peaks are used to determine the minerals present in the sample, each pattern being unique to a particular mineral structure (Moore and Reynolds, 1989). Final identifications by comparing the results with published mineral diffraction patterns (JCPDS, 1988)

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60 5. WACCASASSA BAY Previous work within Crystal River bay, a shelf embayment to the south of the study area, showed that it could be considered a sedimentary basin (Hine et al., 1988). The surficial physiography of Waccasassa Bay also suggest that it may be a sedimentary basin containing a considerable thickness of material. Results Bottom Physiography The bottom physiography ofWaccasassa Bay was determined using . sidescan sonar techniques to map the bottom character of the embayment. The distribution of rocky zones, sediment sheets, channels, and oyster grounds can all be recognized from this data (Fig 23). These four bottom types are characteristic of the majority of the embayment. In general, the bottom reflections show some expression of bedrock character throughout the bay, with the intensity of the acoustic reflector being dependant upon the thickness of sediment cover Areas of open rocky bottom are concentrated on

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29 00' 61 ; _.,. ;, l. (;"/" / ., _., _., I .. \ :: --" : I .1' {-...._ -'. ,_. . <'(;'.? {'<>k:.;.. . .. / . y .; . :,;;._ .. .. ::;: .;_ ....... ) -: .... ... . ./ ............... / ) /:: : .... .. . Kilometer s 0 1 2 "' .. . ..... ........ / ... .:.f.<. r ..__ ..... .J;\<, , .. : .... ., .... : .. = :,;o,.,. ...-::::... "'' : well-sedimented bottom exposed rock bottom thin sediment cover channel; bedforms g oyster reef; bioherm 83 00' Figure 23. Cruise Track and Distribution of Bottom Types Mapped from Sidescan Sonar Imaging

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62 the outer shelf zone, particularly along the edges of the deep central channel. This might be a result of flooding tidal currents sweeping sediment off this shallow margin. The rock exposures can be recognized from the sidescan data by strong, scattered, semi-circular r eflectors ranging in size from 2 m to 20m across (Fig. 24) As the sediment cover increases the bedrock reflectors become weaker and more widely spaced, usually grading into an open, soft bottom. The sediment covered areas are restricted to the upper portions of the embayment inside of the Waccasassa Reefs and locally within the deeper central offshore area (Fig 23). The character of the sedimented bottom image is light-colored with no strong reflectors (Fig 25) Sediments in the upper bay cover the majority of this shallow region The appearance of the sidescan record for this zone is light-colored with a gentle mottling (Fig. 25). The mottling probably represents shells or small surfac e irregularities. The sidescan image of the sedimented bottom in the offshore areas have a slightly higher reflectivity, suggesting a harder bottom In fact, grab samples from the offshore channel sediments are composed of coarse, gravel-sized shell and skeletal fragments with low mud content. The sidescan of this sediment type is similar to that of softer bottom in the upper bay, but the record is darker with better defined mottling. The channel zones can be recognized by the narrow width of the sedimented bottom and by the usual presence of bedforms (Fig 26). These channels are generally situated in low areas between higher rocky bottoms and are 50-150m wide The spacing of the bedforms within the channels is in the range of megaripples, about 1-3 m Their form varies from slightly cuspate to sinuous.' The size and shape of these bedforms are indicative of a

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0 10 20 30 40 50 meters Figure 24. Sidescan Image of Typical Rocky Bottom Found Flooring Much of the Waccasassa Embayment. Note the high reflectivity of the hard carbonate rock 63

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... ;."::_ : ..... :A: ,::-: > ... ; .;:J_. ;_;:.,1;t'-;.. . .. : : ;: ..... t !'' .. : .. ; . }.(:.: ... . : ..... ,. , 0 10 20 30 meters ;. .;:.. ... < , , ; : ,.,;. 40 50 r ,, _,l<(,_: .;>: : t : ; ' Figure 25. Sidescan Image of Typical, Well-sedimented Bottom. Note in this image the lack of the hard reflectors like those seen in the rocky bottom sample of Figure 24. 64

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0 10 20 meters 30 40 : Figure 26. Sidescan Image of Typical Channel-type Bottom. Note the bank where the bottom drops off from a rocky ledge down into the channel with sediment and megaripple bedforms. 65

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66 middle-strength flow regime with associated water velocities of 70-150 cmsec-1 (Boothroyd, 1985) The locations of most of the channel-type bottom reflectors properly correspond to the long, deep channel-like features delineated by bottom bathymetry contours (Fig 23) The other major bottom type recorded from Waccasassa Bay is the oyster ground, including the outer bioherms and the inner reefs. This reflector type is strong and chaotic like the exposed rock bottom, but in contrast it displayed a continuous, well-developed front along the edge of the oyster bed The oyster reefs also appeared abruptly adjacent to the open, soft-sediment bottoms The distribution of this bottom type was found to occur specifically where reefs are mapped on NOAA coastal charts. No unmapped oyster grounds were located during the data collection Subbottom Geology Probe rod tests across the embayment have shown that this broad, expansive feature is not truly a basin, but rather a largely exposed, shallow, flooded limestone shelf. Sediment cover within the bay is thin to absent; in general there is less than 1.0 m of material with large areas of exposed bedrock bottom (Fig. 27) The thickest sequences of material occur within small dissolution holes(< 3m deep) out in the bay or on top of the oyster reefs near the head of the embayment. High-resolution seismic reflection data was collected across the Waccasassa embayment to determine the distribution and thickness of sediments and the subbottom topography (Fig. 19). However, in this shallow-

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+<5 .. ... \ ./ / ............ ,.,. / K i l ome t ers +<5 +<5 ;"-./ -'+<5 / > 100 em 67 Figure 27 Map of the Thickness of Sediment Cover across the Waccasassa Embayment.

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68 water, shallow-bedrock environment, the use of probe rods for site tests of sediment thickness proved to be more useful and accurate. The vertical resolution of the seismic record was hindered by the very shallow water. This problem affected the data by resulting in the superposition of the bubble pulse and direct arrival signals over the bottom/nearbottom reflectors The vertical resolution of the record was not suitable for interpreting shallow reflectors The only features with enough relief to be recognized in the seismic profiles were bedrock karst and deeper subbottom reflectors. The dissolution holes are scattered throughout the embayment and appear to be distributed in loose clusters of karstic topography (Figs 28-29) The relief of the dissolution holes is low, ranging from 1-3m deep Measurements from oblique cross-sections show diameters of approximately 5-50 m.. Beneath the surficial stratigraphy, a traceable subbottom reflector r e vealed the presence of a channel-shaped feature within the bedrock basement. Threedimensional correlation of the cross-section profiles indicates that this feature is linear in nature, roughly trending north (Fig 28) The depression is 2-4 km wide and is up to 15 m deep Surface Sediments Sedimentary analysis of bottom grab samples shows that the majority of sediments found within the nearshore consist of clean-to-muddy, shelly sands. The sand-sized fraction comprises 50 % or more of these sediments by weight, with variable amounts of muds and gravel ( Fig. 30). The mud

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... . ...... ... ... ...... ...... ; ' . ... <.:.1 / .... .. Kilometers 0 .... I . /; ; : cruise track locationof Figure 29 \ ' I"J'7A areas of karst topography depth 1-3 meters approximate location of subbottom 'ch annel' 69 Figure 28. Seismic Cruise Track and Areas of Karstic Depression Features Within the Waccasassa Embayment. The karst features are shallow (1-3m) dissolution holes which appear to be grouped in loose fields scattered across the embayment

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Ul Q) !!! >. CIS == -Ul Q) E :;::: 24 \ \ I 100m I 0 Q) 12 > CIS ..... >. CIS == I 0 24 .. lill ; .:.-J .. > '-; .. :. : ( . ... ,._ . . . . Quaternary sediments; infilled karst topography Eocene carbonate bedrock; internal reflector possibly represents Avon Park Fm/Ocala Group contact 18 I 100m I 0 3 6 9 12 15 18 I a. Q) '0 I a. Q) '0 Figure 29 Section of Seismic Reflection Data from Waccasassa Bay with Interpretation. Location shown in Figure 28 This particular section shows a karst field, but the majority of the embayment looks more like the right portion of the figure, with little or no sediment cover. 0

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. .. ..... -... ::: (.: ::(i / +13 M ud inte rv als: 1:;:>::@<1 < 6 % o::::J 6 12% CJ 1 2-2 4 % t'Z2l > 2 4 % Figure 30 Map of Percent Mud in Offshore Bottom Grab Samples. Note the high value s n ear the shore-edge and the rapid d e crease moving off shore. 71

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72 fraction decreases with distance from the shore-edge, particularly along the outer central channel where tidal currents may sweep away the fine-grained sediment. The gravel fraction is most abundant near oyster reefs and other more shelly areas. The siliciclastic component of the nearshore sediments comprises 366% of the material by weight, with most measurements falling between 25% and 50% (Fig. 31). The values increased toward the shoreline and dropped drastically near oyster reefs and in the offshore channel. The values are generally very low when compared to other Gulf and Atlantic coastal systems (Davis, 1985), indicating that this is certainly a mixed, if not dominantly carbonate, system. The mineralogy of the siliciclastics shows a large quantity of silt-to-fine sand sized quartz and a suite of mixed clays No heavy minerals or phosphates were found in the samples. A general characteristic of the nearshore sediments along the Big Bend marsh coast is a predominance of biogenic carbonate material (Hine and Belknap, 1986) This proved to be true within the Waccasassa embayment where carbonate sediments comprise at least 50% of the material by weight (Fig 32) Near the oyster reefs and other biologically active the carbonate content values reach well over two-thirds by weight. The majority of these carbonate sediments are composed of sandto-gravel sized shell hash, with variable amounts of microfauna} and skeletal material. The dominance of biogenic sediments in Waccasassa Bay thereby expresses the importance of carbonate-producing fauna to this coast. The most abundant and obvious of these organisms is the american oyster (Crassostrea virginica) which grows in estuarine waters all along the Big Bend coast. The oyster forms large reefs or bars, around which an entire

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73 '' ... >.I .. ... J: .. /-.. .. : ... : , . -.. .. ./ ;.! .: . . (;;.;.. ..... f ) ... , t' 1o._ I ":.J 't j j .o;:'o..yl r l ... :.:. ) .. ;' Y / .\ t ... r... f. ... .... r" .... .., ... ; '>'1-::: f.<;!,; '> :;! ,,..: 7-'1<$. .. / . : ;: ... ."' ( .. '>:.=-..... 1 "'0 I ; { ; \ j,"i/{ I ,.., ... .:>.. I .. .: ' , .......... : u . ,. ... "... ) ' . \ t . . . ) .h " .. : < .. ..4 J J : !;., ; "'/vr''' ,, ,1 : .:::: : : :. : .<" ::.: .. 57 . : ., : . ')!)\.} ';> .. q?!?. ( <-. \. . .... f. ........ \:::/:,. :!!.yr.., ? /. < "'-''-";'; .. '> .. c 0 '' ) ."' ....... .o:. ::.:::::.. ;:. ?./ .. \ . \.,.,.:,..., ... ., ...... .: .. . ... . > ... ......... .......... ....... .. .. ; ... "' ...... .... .::) : .. . .... ,. ... ... ... '": .. :(. -;: : ,.: i . ( . :=: ..... >. .. Kilometers 83 00 Sj!jcjc!astjc intervals : <10% 1 0-30 % 1-:::':::'}''. : j 30 -50 % c=J >50% Figure 31 Map of Percent Siliciclastic Material Measured in the Offshore Bottom Grab Samples Note the increasing values near the shore-edge

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./ u:.. , . -. ... ... / .. ......... \ _ . .. ..... ' ........ ..... --....... >', ? .... -., .. ': ... -;..,,_ : :.::. . .-:-: :'.:>. : ; .::: .: .. ,.> K il o m ete r s / : .': .... .'.>: ':::_: .. ., 74 0 2 ) o carb ? nate values ..... ,>: '? ,. 29 .. ... .. .__ .. .. ___ .. _ ' __ 83 00' Carbonat e i n terv als: c=:J < 4 0 I ,, I 40-6 0 M?:m:::::M 6 08 0 >80 Figure 32. Map of Percent Carbonate Values from Offshore Bottom Grab Samples. Note that the values increase in an offshore direction and locally around the oyster reefs.

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75 community of organisms has evolved. Of the 248 species of animals found in association with the oyster reefs, no less than 50 produce carbonate shells or tests (Gorzelany, 1986) In addition to the oyster, the associated faunal assemblage includes several species of mussel (Mytilidae spp.), another type of oyster (Ostreola equestris), and other bivalve mollusks which produce a considerable amount of shell material. In general the carbonate content increases near oyster reefs/bioherms due to the productivity of these organisms and the abundance of associated fauna: In other areas of the embayment, echinoderms (Phylum Echino dermata) form an important biological sediment component, particularly in regions of thin sediment cover or exposed hard bottom. Among the echino derms, brittle stars (Class Ophiuroidea), sand dollars (Order Clypeasteroida), and sea urchins (Order Ciduroida) are all commonly found in these areas. Their tests are the most common carbonate fragments found within the marsh stratigraphy and are also commonly preserved within the carbonate bedrock (Fischer, 1951). Another type of organism found in areas of thin to absent sediment cover are sponges (Phylum Porifera). These animals yield SJ?lall and abundant calcareous or siliceous spicules which support their internal structure. Sponge spicules were commonly found to occur in sediments collected throughout the embayment Around deeper portions of exposed hard bottom, skeletal fragments from encrusting and branching bryozoans (Bryozoa spp.) also form locally important sediment sources. Two bottom grab samples of nearly pure bryozoan skeletal material were collecied in the deep channel at the southwest edge of the embayment.

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76 Stratigraphy The lack of a significant quantity of nearshore sediments precluded the need for an extensive offshore stratigraphic survey. However, the presence of infilled karst topography and oyster reef sequences required an investigation of these local features. A total of five vibracores were taken offshore where considerable sediment thicknesses could be located (Fig. 33). These include cores at four oyster reef sites (cores 7 5, 3 .1, 3.5, and 3.6) and one infilled sinkhole (core 3.7). The thickness of sediment at these sites ranges from 1.22.0 m, with water depths from l.03.5m. The stratigraphy of the oyster reef sites is simple, being comprised of one to two facies (Fig. 33). The top unit of the reef cores invariably consists of a 1.0-1.5 m thickness of variably muddy, abundantly shelly sediment typical of the oyster reef environment. This facies unconformably overlies a thin, pre-Holocene, gray clayey-sand deposit, or in some cases li es directly on the limestone bedrock (Fig. 33) A reddi s h, grainy wood fragment, probably cedar or cypress, was collected from the base of core 3.1 at a depth of approximately 3m below m.s.l. Radiocarbon analysis of this wood produced a corrected age date of 5310 80 BP (see Table 1 for a summary of 14C-dating results) Core 3.7 was taken from an infilled karst feature about 18 km offshore in a water depth of 3.5 m (Fig. 34). The uppe r unit of the core consists of 60 em of gray-brown, shelly, muddy sands capped by a thin shell lag ( Fig. 33). This unit grades into 45 em of shelly, oyster reef sequence similar to that seen in the reef cores. The surprise in this core was an organic-rich peat layer which is unconformably situated beneath the nearshore marine

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'E a. Q) "0 brown-gray (SY 311), shelly muds (SYR 211) organic rich peats (mangrove ?) infilled bottom of karst feature: brown muds and limestone boulders greenish-gray (SGY dry sandy mud; no shells; pre-Holocene shell mud IKEYI sand organic sediment carbonate rock Figure 33. Locations of Offshore Core Sites and Description of Three Cores From These Sites. Note the modern, shelly, nearshore sediment sequences overlying older, preserved facies, including a wetland peat from far offshore (Core 3 7) 77

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78 Figure 34. Photograph of Core 3.7 Showing Shelly, Nearshore Marine Muds Overlying a Preserved Section of Wetland Peats This core was taken in a karst feature offshore of the Waccasassa R e efs ( location in Figure 29). C ore log shown in Figure 33 The core box is 1 m long marked by 5 em increments.

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79 sediments. A radiocarbon date on the top portion of this material gave an age date of 5860 70 yrs. BP. This unit is 45 em thick and is underlain by a basal, limestone-clast infilling of the karst feature. Discussion Waccasassa Bay Sediments A general map of the sediment distribution shows the localized portions of the embayment which contain material (Fig. 27). Offshore of the Waccasassa shelf, sediments have accumulated in the deeper waters of that zone. This offshore region of Waccasassa Bay may be the local sediment basin. The presence of unlithified material here can be misleading, however, since these sediments are characterized by a high-carbonate and a low mud content. As such, the sediments largely consist of locally-produced biogenic material. The lack of fine-grained materi al in the area suggests that water currents there are strong enough to preclude the deposition of such sediments. Another factor resulting in the low siliciclastic content may be the distance from the shoreline; terrestrially-derived muds might not be transported that far into the Waccasassa embayment. The thickness of sediments in the central portion of Waccasassa Bay are associated with the formerly productive Waccasassa Reef oyster grounds (Fig. 27). Like the deep offshore area these sediments have high carbonate content (Fig. 32). However, higher mud and siliciclastic contents (Figs 30-31)

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80 are indicative of the environmental change occurring at this margin. This area is situated along the edge of the shallow-water Waccasassa shelf where the reefs have developed on the bank of the margin (Fig. 10). The muds and quartz sands found within this area suggest the trapping of this material by the oyster reefs within the inter-bioherm lows (Ririe and Belknap, 1986). The thickest and broadest area of sediment accumulation in Waccasassa Bay is near the head of the embayment (Fig. 27). These sediments contain the highest percentage of muds and siliciclastic material (Figs. 30-31). The influence of the marsh and upland areas is expressed by this change in sediment characteristics. The shallow-water area in the upper bay appears to be a local sediment basin for material moving near to and within the adjacent marsh system. The material may be temporarily stored in this region, where the greater depth of underlying rock allows for sediment accumulation. This lower basement near the head of the Waccasassa River may be associated with carbonate dissolution due to fresh and saltwater mixing (Hine and Belknap, 1986). In general, there appears to be three areas of sediment accumulation within the Waccasassa Bay. The offshore contains a em thickness of nearly pure, biogenic material produced by bryozoans, sponges, and mollusks. Across the embayment are local areas of sediment associated with oyster-reef production. These productive communities are found from the Waccasassa shelf margin up to the mouth of the Waccasassa River At the head of the embayment is the largest, thickest extent of material (up to 350 em thick). This is also the only area of significant siliciclastic content. The remote sensing data ( sidescan sonar and seismic reflection) concurs with the grab sample and prode rod data, showing tha t the sediment

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81 thickness is thin to absent across much of the shallow shelf zone (Figs. 24, 29). The seismic data also revealed several patches of sediment infilling shallow karst features in the offshore area (Figs. 28-29). These local features appear to be potential preservation sites for transgressed facies. The discovery of a preserved unit of wetland peats in one of these depressions (Fig 34) supports the model of transgression for the Gulf coast and provides a basic timing for the shoreline retreat (see Holocene Evolution of Waccasassa Bay Area). Since the nearshore zone of Waccasassa Bay is shallow and largely floored by clean-swept bedrock, such preservation is a unique occurrence and perhaps restricted to karst features. Although there are local karst features, the seismic data supports the conclusion that Waccasassa Bay is largely floored by a relatively even surfaced, shallow bedrock. However, a series of shelf embayment environments south of the study area contrast with the Waccasassa embayment. The smaller, southern shelf embayments are characterized by high-relief (up to 4 m), heavily karstified bedrock and high, spring-fed, freshwater discharge (4-26m3/sec) (Hine et al., 1988). The karst features in these embayments have formed along patterned fracture within the bedrock (Hine et al 1988) and developed through dissolution caused by mixing-zone undersaturation (Plummer, 1975). In Waccasassa Bay, the absence of significant spring discharge may be responsible for the lack of high relief karst topography. Ultimately, the differences in bedrock topography between these sites has strongly affected the nearshore stratigraphy. Whereas the Waccasassa embayment is characterized by an even-surfaced, exposed bedrock bottom, the southern embayments contained 2-3 m of sandy

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82 nearshore sediments and preserved marsh peats overlying highly karstified carbonate bedrock (Hine et al, 1988) Within the subbottom carbonate rock of the Waccasassa embayment, the seismic data revealed a broad, channel-shaped feature in the bedrock (Fig. 28). This depression may have been a shallow channel preserved during the deposition of the shallow-water carbonates. The change in lithology represented by this reflector might correlate with the contact between the middle Eocene Avon Park Formation and the overlying late Eocene Ocala Group limestone. illtimately, the subbottom feature may have influenced the long-term, Neogene evolution of the embayment. With reference to channel preservation, an early geologic study of Levy and Citrus Cos proposed the possibility that the Suwannee River at one time occupied the Waccasassa lowlands (Vernon, 1951). However, in view of the absence of any large, buried post-Pliocene channel within the Waccasassa embayment, there is no evidence that this event occurred. The forementioned channel preserved within the Eocene bedrock is too old to represent the paleo-Suwannee River Oyster Reefs Oyster reefs and their associated community are not only important as a source of biogenic sediment, but these features can influence nearshore circulation and serve as paleoenvironmental indicators as well C Hine and Belknap, 1986). The american oyster (Crassostrea virginica) is a marine/estuarine organism, preferring salinities of 10-30%o and an optimal water temperature of 25 C (FDNR, 1971). Along the Big Bend coast, reefs

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83 typically fonn from 5 5 km offshore up to the shore-edge and are usually in association with nearby freshwater discharge. In this region the elevation of oyster reefs generally centers around the middle portion of the tidal zone; this zone is situated between the critically long periods of subaerial exposure which occur higher elevations and the siltation and predation problems which begin at the lower intertidal and subtidal zones (Wolfe, 1990). In Waccasassa Bay oyster reefs are found from the outer reaches of the bay shelf shoreward to the marsh edge. The smallest reefs are those growing along the shore-edge or within the lower reaches of tidal marsh creeks The growth and development of these incipient features may be limited by siltation processes associated with decreased flow conditions at the creek mouth. It is common to see reefs in this type of environment becoming colonized by marsh grasses, usually Spartina alt e rniflora The abundance of sediment and little freshwater discharge of the shallow creeks appear to be factors limiting their growth. At the head of the embayment are an extensive group of patchy reefs which have developed at the mouth of the Waccasassa River (Fig. 11) This well-flushed, freshwater-influenced environment provides an ideal habitat for reef growth, although these young reefs have not yet evolved into the linear features characteristic of mature reef development (Hine and Belknap, 1986) The present growth and position of these reefs at the mouth of the river makes them a potential nearshore marker. Moving offshore of the mouth there is a disjunct series oflinear reefs growing in the open bay. Although these reefs are presently" intertidal, there are very few live oysters growing on the surface of the reef. Most of the surface material consists of loose shell valves from small oysters and other reef fauna. These nearshore reefs may

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84 be an intermediate step between the young, healthy reefs at the mouth of the Waccasassa River and the large, inactive reefs offshore The outer series of reefs, collectively called the Waccasassa Reefs, are comprised of three linear, subtidal bars each over 2 km in length. These reefs do not support any growing oysters. The linear bioherms are separated into shorter lengths by the presence of intra-bioherm channels. These channels can be seen in aerial photographs and show small, well-developed ebb and flood tidal deltas. It is suggested by the delta features that the bioherms have an effect on tidal flow in the embayment. The bioherms are situated normal to the deep central channel which lies just seaward of them, a potentially effective position for flow disruption. The reefs within Waccasassa Bay show several trends indicative of a step-wise retreat with sea level rise and shoreline transgression. First, the reefs/bioherms become larger and more linear offshore, indicating that they are more mature and most likely older. Second, the present activity of growing oysters decreases rapidly away from the river mouth, ending with inactive, non-producing bioherms well offshore This supports the observation (Hine and Belknap, 1986) that the reefs require freshwater influence for growth and development, and that the offshore oyster bioherms must have actively evolved near a freshwater source (i.e. a paleo-Waccasassa River mouth). Finally, the depth of the reefs/bioherms increases in an offshore direction. The nearshore reefs are intertidal, while the outermost bioherms and several smaller bioherms just landward are subtidal at a depth of 1-2m below m.l. w The ecology of the oyster indicates that these presently inactive, offshore bioherms developed in the intertidal zone at a lower stage of sea level.

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85 6. WACCASASSA MARSHES The sediments of the Waccasassa marshes contain a stratigraphic record of the environment change and development which has led to the evolution of the present setting. Changes in the grain size, color, organic content and other characteristics of the sediments suggests varying depositional environments and thereby provide an understanding of the processes operating at that time. Correlation of the recognized units across the area help to determine the extent of that environment. By assembling the sediment characteristics and facies changes, a model for the methods and timing of the development of the Waccasassa marshes can be produced. Results Pre-Holocene Facies A variable and undifferentiated unit of sandy sediments are unconformably situated on top of the carbonate bedrock. The units often contain clasts and fragments of the bedrock The sediments unconformably lie beneath the younger facies which comprise the majority of the stratigraphy. The basal sediments are characterized by significantly greater

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29 12' 29 10' 29 08' 29 06' 82 52' 82 50' 82 48' 82 46' KEY TO CORE SKETCHES Qsand 1-I mud rE2i5J carbonate I* 1( I echinoid test l mollusk shell gastropod shell organic sediment [ill upland roots r;:::-, large woody Is\< s \l plant Figure 35 Location Map of Cross-sectional Profiles and Core Sites and Key to Symbols Used in Core Logs. 86

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87 sand content than the overlying units, with percent weight values of 15-60% (Fig. 36A) The sediment classification varies from a sandy mud to a muddy sand. Another distinguishing feature is the common presence of echinoderm fragments (Fig 37 A). The tests are from both clypeasteroids (sand dollars) and ciduroids (urchins ) two organisms typical of shallow, marine environments such as that found in the modern Waccasassa embayment. The color of the sediments varies from a light tan-gray (6Y 7/1) (Fig 37B) to a darker gray (N4) commonly mottled with orange (lOYR 6/8) (Fig. 36B). These colors appeared to represent two distinct units. Only one basal unit was normally found in a core, but on one occurrence both units were found with the tan-gray sediment underlying the mottle-orange gray sediment (Fig. 37). Two radiocarbon dates from echinoderm fragments contained in these basal units were obtained ( Table 1). These shells were collected near the bedrock basement in two cores at a depth of 90 em and 120 em; they provided dates of 29 ,600-2,300 BP and greater than 4 7,400 BP, respectively The dates may not be entirely reliable as there may have been some alteration of the shell material. However, the preservation of fragile test ornamentation suggests that the shells have not been heavily encrusted or abraded. The dates are reliable enough to conclude that the units are pre.: Holocene and are not part of the modern stratigraphy.

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elevation: -ZOcm msl Ocm 25 50 75 100 125 150 175 200 % organic grain size CORE 1 3 surface veg eta tion : (J uncus roemer ianu s) C1l c: C1l g 0 I olive-gray (5Y 4 / 1) muds with fibrous prant material grayish-green (5GY 3 /2) muds brown i sh-black (5YR 211) muds with detrital organics minor unconformity 0 I med. gray (N3) sandy clay c. dry, olive-gray (5Y 4 /1) muds mottled with dk yellowish-orange (1 oYR 6/6) major unconformity C1l c: C1l u 0 w Figure 36. Photograph and Core Log of Core 1.3 a Typical Outer Marsh Core From the Low e r Marshes Along Rocky Run. [A] Core log showing sediment d esc riptions organic content, grain size and a sketch of the core. Symbol key in Figure 35. 88

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Figure 36. (Continued). [B] Photograph showing the sequence of pre Holocene and Holocene sediments comprising the Waccasassa stratigraphy. Note thin, modern marsh horizon, gradational facies contacts, and color differences. The core box is 1 m long and marked in 5 em increments, and the top of the core begins in the upper left corner. 89

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CORE 6.1 surface vegetation : t rees (Junj>erus siliciro/a) I IS&bal CH!/meUo / dry black (SY 2.5f2) soil dry dk. gray-brown (1 OYR 312), sandy, soily, clay lt. yellowish-brown (2 .5Y 6 / 4) muds (oxidized green muds) grayish-green (1 OGY 512) muds
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91 Figure 37 (Continued). [B] Photograph showing the stratigraphy underlying the creek bank levees. Note the intense color changes and diverse stratigraphy. The relative length of this core is greater than normal because of the deepening of the bedrock along the large Bird Creek. The core box is 1 m l ong and marked in 5 em increments, and the top of the core begins in the upper left corner.

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Table 1. Summary of Radiocarbon Dating Results. DEPTH ELEVATION CORE I in CORE around MSL (em) (em) FACIES MATERIAL COUNT METHOD C14 AGE uncalibrated (years BP) C13/C12 C13-adjusted AGE DENDROPDB stnd norm to -25/ mi l C13 CALIBRATED AGE %o (years BP) (95% p r obability) ....... ...... -........... .. --.-..... ....................... .. ......... .. .......... .......... .. .. ................... ......................... .. ..... -.................. .. ......... .. .... ................... ......................... ................... .. .. ....... .. .......... ............ .. .. ................... ........................... .. ........................... .. .... .. .. ........ ..................... 2?. ............ ................... .................................. .. .................. .. ............... ......................... .. .. ...................... :!.:.?. ............................ .. .......................................................................... ........ .............. .. .. _!op ..... ....... .. .......... ............ .. ...................................................................................... -...................................................................... .. ..... ... ................ _______ ......... ............ .. .. .. -...... .. ........... .......... .. .. ..................................... -.................................. ............. -........................................................ -...... .. ....... ? :?. ................... 1..!.?. ... -...... -........ .......... .... ........................ .......................... ............. . ?.2 ............ ....... :?..?.:g .......................... .. ............................ .. ........ 6.1 242 -142 basal black muds detrital wood radi ometric 3,960 9 0 ........ 1..:3 .................... ............................. ............... ............. .. ......... ....... .. .. .............. ....................... ............... .................................................. (undifferentiated pre-Holocene) (extended) ....... ................... .... ... -........... :?.9_ ...... ............. ................. .................. ... ?. .. ...................... .... ........... -.. .. .... ___ ............................... ... .............. (undifferentiated pre-Holocene) ....... ................ .. .............. ...... ............ -.. ... .. .. ...................... ........................ ...... ...... .. .. .......... ......... :?..?.:.! ............................ ?.2.!g .. .. ....................... .. .. ...... 3.7 105 -305 beneath oyster reef peat radiometric 5 ,910 70 -28. 0 5 ,860 70 6,530-6,900 BP > t-.:1

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93 Holocene Facies Black, Organic Muds. Along the northem rim of the Waccasassa embayment, a wet, blackish, and muddy unit overlies the top of the sandy, pre-Holocene sediments. These sediments can be recognized by their dark color (7.5YR 2/1) (Figs. 37B, 38B) and an organic carbon content greater than the overlying sediments. These values range from 8-25% ashed dry weight, numbers noticeably higher than the 4-6% of the overlying unit (Figs. 36A, 38A-40). Unlike the upper core facies, the organic fraction is not composed of tough, tubular roots, but rather of soft, degraded material suggestive of fleshy plants. The thickness of the unit is generally about 20 em, although it is as thick as 80 em on the two cores at Bird Creek. The sediments are soft and wet to the touch, suggesting a fine-grained unit. Grain size analysis shows that the sediments are silty clays of similar composition to the overlying facies (Figs. 38, 40). However, sand is present in some samples overlying older coarse-grained units (Fig. 39). Detrital wood fragments were commonly found within the unit (Fig 37B); four radiocarbon dates were obtained from this material (Table 1). Two samples from from a levee core (6.1) bounded the upper and lower contacts of the unit, giving age dates of 1,870 -70 BP and 3,960-90 BP, respectively (Fig. 37A) One sample taken near the base of the unit in another core provided an age date of 2,840-90 BP. The fourth date of 2,730-90 BP was given by a sample of charred wood near the top of the unit (Fig. 40). The constancy of these dates indicates that this unit is correlative between cores

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elevation : -80cmmsl Ocm 0 CORE 7 1 surfa ce vege tation: (Juncus roemerianus) 94 dk gray-brown {10YR 3/2) muds with f i brous plant material 25 50 75 100 125 150 175 200 grain s i ze olive-gray (5Y 5 / 2) muds (oxidized green muds) green-gray (5G 5/1) muds dk. gray (7.5Y 3/1) muds black (2 .5Y 2 .511) muds with detri ta l organics Figure 38. Photograph and Core Log of Core 7 1, a Core Collected Ab out 20 m Into the Marsh From Core 6 .1. [A] Core lo g s h owing sediment descriptions, organic content, grain size and a sketch of the core. Symbol key in Figure 35.

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95 Figure 38. (Continued). [B] Photograph showing the sequence of preHolocene and Holocene sediments comprising the Waccasassa stratigraphy. Note thin, mod ern marsh horizon, gradational facies contacts, and color differences. The core box is 1 m long and marked in 5 em increments, and the top of the core begins in the upper left corner.

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elevation : -60c m msl Ocm 25 50 75 100 125 150 175 CORE 7.9 surface vegetation : 0 grain size %organic dk. gray-brown (10YR 3 / 2) muds with fibrous plant material dk. green-gray (sG 4 / 1) muds dk gray (5Y 4 / 1) muds Figure 39. Log of Core 7 9, a Marsh Core Taken along Lower Kelly Creek. Shown are sediment descriptions organic content, grain size, and a sketch. Symbol key in Figure 35. 96

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elevation : -60cm msl Ocm 25 50 75 100 125 150 175 grain size %organic CORE 12.3 surface vegetation: (Juncus roemerjanusl dk. gray-brown muds olive-gray (5Y 5/2) muds (oxidized green muds) green-gray (5G 5/1) muds dk. gray (5Y 4/1) muds Figure 40. Log of Core 12.3, a Marsh Core Taken on the Island at the Mouth of the Waccasassa River. Shown are sediment descriptions, organic content, grain size, and a sketch. Symbol key in Figure 35. 97

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98 Gray Muds. One of the most widespread units is a moist, dark gray (2 5Y 4/1) mud (Figs 36B, 38B) This unit forms the lowest Holocene unit everywhere except in those areas underlain with the black, organic muds. Thickness of the unit ranges from 30-70 em. The typical organic values are 410% ashed dry weight (Figs 36A, 38A, & 39-40). These mid-range values are characteristic of the gray mud facies and are consistently less than the overlying unit (Figs 36A, 38A, & 39-40). The unit occasionally contains plant roots similar to those of the upper marsh facies, but fleshy, degraded root material is much more common The gray mud facies appears to be intermediate between the blac k muds and the overlying green mud unit in both color (Figs. 37B, 38B) and organic content ( Figs. 38B, 40) Sponge spicules, foraminifera and diatoms were found in this unit using a standard light microscope and mark the first appearance of marine-derived material within the Holocene sequence. The base of the gray muds along the northwest arm of the Waccasa ssa marshes contain fragments of a thinshelled mollusk and some gastropod she lls ( Fig. 39) Green Muds. The green mud is another widespread facies located throughout the lower marshes of the Waccas assa area where it overlies the gray mud unit. This facies is characterized by its unique green color (5G 4/1-5G 5 / 2 ) and low organic value s ( 2 5 % ) Thickness measurements range from 20 em to 80 em. The contact betwe e n this green unit and underlying gray mud is consistently gradational, indicating a slow transition of environmental change. Common roots like thos e of the m odern marsh horizon are found in the green mud unit, but some may originate from plants within the modern marsh unit. In several freshly split cores from the head of the embayment

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99 the upper portion of the green mud unit was oxidized to a tan-gray (5Y 5/2) color. In the lab the exposed green clay took several weeks to oxidize to this tan color A small gastropod shell from the green mud unit was radiocarbon dated at an age of 1,170-60 BP (Table 1; Fig. 37 A). This very fragile, paperthin shell was that of a unidentified species commonly seen on the modern marsh surface. Modern Marsh. The modern marsh horizon in the Waccasassa area is characterized by two very different facies Despite the surface expression of a widespread, nearly homogeneous J uncus roemerianus marsh, the depositional environment across this region varies considerably. This variation is largely reflected by the organic and siliciclastic content of the facies (Table 2). The thin muddy marsh is distributed across the outer marshes where there is significant influence of tidal waters and marine processes. The unit is characterized by its medium brown color (10YR 3/2), muddy appearance, organic matrix, and small thickness (Figs. 36, 38-40). The marsh unit extends to a depth of only 10-30 em, averaging approximately 15 em before quickly grading into the green mud unit. The organic values of the facies range from 12-24% ashed dry weight (Figs. 36, 38-39). In some places this brown, muddy marsh type is found overlying the darker, watery marsh sediments of the upper marsh zone (Fig. 41) The peaty inner marsh facies is found in the upper wetland zone where there is considerable freshwater influence and away from the higher energy processes near the shore-edge The peaty inner marsh is organic-rich (25-

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Table 2. Summary of the Facies Characteristics of the Waccasassa Marsh Stratigraphy. FACIES DISTRIBUTION FACIES AGE/PERIOD CONTACT OF DEPOSITION continuous across the outer rapid, but gradational Muddy Marsh modern marsh system contact with underlying -500BP to present green muds facies marsh zone near upland sharp contact with Peaty Marsh transition, and upstream commonly underlying -2,000BP to present along the Waccasassa River pre-Holocene muds and tributaries continuous beneath nearly rapid, gradational contact with Green Muds the entire extent of the muddy overlying muddy marsh; -1,200BP to -500BP marsh facies, disappears toward very slow and gradational upland along outer edges of area with underlying gray mud facies continuous across entire study rapid, gradational contact where Gray Muds area, except upstream along the muddy marsh overlies; very slow -2,500BP to -500BP Waccasassa River and tributaries gradational contact with overlying green mud and underlying black mud facies nearly continuous around the sharp to rapid and gradational Black Muds head of the embayment and along contact with overlying gray mud -4,000BP to -l,BOOBP the outer marsh zone of the north facies; sharp, unconformable contact arm of the embayement with underlying basal facies. Pre-Holocene nearly continuous across entire sharp, unconformable contact with pre-Holocene Basal Muds study area underlying Eocene bedrock and ? -125,000BP? overlying gray or black mud facies (Continued on next page) f-' 0 0

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Table 2. (Continued). FACIES COLOR THICKNESS ORGANICS MOISTURE SHELLS GRAIN SIZE (tyPe & % wt ) ( % wt. ) medium gray refractory roots and marsh clam, some silty clays to Muddy Marsh to yellowish 10-30cm rhizomes ; detritus 40-75% gastropods & clayey silts brown 12-25% abundant microfossils dark gray-brown abundant roots and no shells; some silty clays to Peaty Marsh to black 50-150cm rhizomes and detritus 75-90 % marine microfossils cla y ey silts fonning organic matrix 25 60 % light to medium little detritus ; absent some gastropods ; silty clays to Green Muds grayish green; 15-90cm to common Juncus 30-60 % abundant marine clayey s ilts oxidizes to med roots; 2-5% microfossils tan-brown medium to detrital organics; generally none ; some silty clays to Gray Muds dark gray 30-120cm absent to sparse 40-70% thin-shell mollusks at clayey silts or gray-brown Juncus roots; some base of facies along fleshy root material outer north ann; somecommon microfossils dark gray/brown detrital organics ; no shells ; none to silty cla y s to Black Muds to black 19 90cm common fleshy root 55-90% few marine clayey silts material ; common wood microfossils fragments; Pre-Holocene light to dark absent to some detrital absent to common sandy muds to Basal Muds gray or 10-llOcm organics ; common 20-50% echinoderm tests; muddy sands gray-brown woodyroots ; 0-7% abundant microfossils 0

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102 Figure 41. Photograph of a Surface Section of Marsh Sediments Showing the Muddy Marsh Facies Overlying the Peaty Marsh Facies The sample location is in the vicinity of Williams Creek, approximately 0 5 km away from the shoreface and tidal creeks. The top of the pen is pointed upward on the sample, and the facies transition occurs at the base of the pen cap. Note the mucky appearance of the upper unit in contrast to the reddish, dense organic matrix of the lower unit.

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103 60%) (Figs 42A, 43A, &44; Table 2) and has a nearly black color (2. 5Y 2.5/1) (Figs 42B, 43B). In this habitat the dominant J. roemerianus is commonly intermixed with the less salt tolerant Cladium jamaicense indicating a lower salinity environment. The thickness is generally greater than the muddy marsh, commonly reaching 1 m and ranging up to 1.5 m (Figs. 42A 43A, & 44) The deposits are watery and contain little siliciclastic material, making them distinct from the muddy outer marsh (Table 2). Mineralogy The mineral composition of these sediments represents a potential for further defining the different facies, expecting that the variation in color would be reflected in the mineralogy of the clay fraction. A series of downcore samples (7.1, 7.8, 7.9, 7.10, and 12.6) were analyzed for their mineral content to determine the exact characteristics of these variable sediments. The sandsized fraction of the samples were not analysed by x -ray diffraction. Microscope viewing showed that the sand fraction is composed almost entirely of fine to-very fine quartz grains with occasional shell hash and carbonate bedrock fragments. Silts. Like the sand-sized fraction the silts are composed largely of quartz grains. All other silt-sized minerals present in the samples are exceedingly sparse. These secondary minerals are all carbonates and include aragonite, calcite, dolomite, and an uncommon and unusual mineral,

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elevation: -50cm msl Ocm 25 50 75 100 125 150 175 Figure 42. 0 .. I I I %organic CORE 3 2 surface vegetat i on : (Juncus roemer i anus) / (Cfad jum jamajcense) 60 Cll c: Cll u 0 0 I wet, clean, black (N1) peats minor unconformity 0 0 I I Q. dk. gray (2.5Y 4 / 1) muds with olive-yellow (2 .5Y s/s) mottling carbonate rock fragments associated with mottl i ng 104 0 0 I I Cll .... similar to overlying unit except sediments are dry and stiff Q. major unconformity Cll c: Cll 8 w Photograph and Core Log of Core 3 2, a Core Collected Near the Marsh/Upland Transition Along Crooked Creek. [A] Core log showing sediment descriptions organic content, and a sketch of the core Symbol key in Figure 35

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105 Figure 42. (Continued) [B] Photograph of core 3.2 showing the thick sequence of black, peaty marsh sediments overlying gray, pre Holocene muds. The core box is 1 m long and marked in 5 em increments, and the top of the core begins in the upper left corner.

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elevation : -50cm msl Ocm 25 50 75 100 125 150 175 CORE7. 3 surface vegetation : (Juncus roemerianus) I ( Ciadjum jama ic ensel 106 0 50 0 % 50 100 ........ grain size % organ i cs mucky, dk gray-brown muds with f1brous plant material med brown, compacted peaty material similar to above but with more muds dk. brown-gray sandy muds to muddy sands Figure 43. Photograph and Core Log of Core 7 .3, a Core Collected Near the Marsh/Upland Transition Along Cow Creek. [A] Core log showing s ediment descriptions organic content, and a sketch of the core. Symbol key in Figure 35

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107 Figure 43 [B] Photograph of core 7 3 showing the thick sequence of black peaty marsh sediments overlying pre-Holocene muds. The core box is 1 m long and marked in 5 em increments, and the top of the core begins in the upper left comer.

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elevat i on : -ZOcm msl Ocm 25 50 75 100 125 0 I % organics 60 0 % 50 CORE 12 5 surface vegetation : (Juncus roemerianusl 108 dk. brown muddy peats wet, clean, dk. brown peats Figure 44. Log of Core 12 5, an Upper Marsh Core from Stafford Island. Provides sediment descriptions, organic con tent, grain size, and a sketch. Symbol key in Figure 35.

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109 weddelite (CaC204 2 H20) (Fig 45) The aragonite and calcite come from a suite of biogenic River revealed a deposit of dolomite sediment worthy of note. Below a thin upper unit of dark, bottom river muds was a 1.2 m thick sequence of clean, huffy (lOYR 8/2) silts Mineralogical analysis showed this material to be comprised of nearly pure ferroan dolomite (Ca (Mg .61Fe.33) (Fig. 45). Clays. The clay mineralogy of the Waccasassa marsh sediments is comprised of a complex suite of species containing three dominant mineral forms These three clay minerals show little variation in their relative abundance across the study area. The x-ray diffraction analyses shows that there are no major mineralogical distinctions between the stratigraphic facies nor across the extent of the Waccasassa marshes. A down core series of diffraction patterns from core 7.1 shows this general absence ofvariability (Fig. 46) The dominant clay mineral in the marsh sediments was identified as a randomordered, mixed-layer illite/smectite, with 50% or more illite. This conclusion is based upon the shift in diffraction peaks after saturation with ethylene glycol (Moore and Reynolds, 1989). This clay produces a strong low angle reflection at ad-spacing of 12 6-15.1 A The low angle peak is supported by smaller peaks around d=4.9 A and d=3. 1 A (Fig 46) This illite/smectite clay ,is present in all of the marsh samples in the study area. When collected from a centrifuged clay sample, i t tends to be concentrated towards the top of the sample This portion of the sample has a characteristic greasy feel and appearance.

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A. A 17.66 8.838 5 .90 1 4.436 3 .559 2.976 2.561 2.252 2050 I I I I I I I 100% >.t: 1025 1-50 CD C/) a.. (.) :E 0 B. 3150 1575 C/) a.. (.) 0 A -I 029 5 10 I 2s I I 15 20 30 35 I I I CALCIUM OXALATE HYDRATE I WEDDELITE, SYN I . c 2 Ca 0 2 H 0 4 2 A 17 .66 8.838 5.901 4.436 3 .559 2.976 2.561 I I I I I I I """ 1 l 029 5 I I I I I I 10 15 20 25 30 35 I I CALCIUM MAGNESIUM IRON CARBONATE I DOLOMITE, FERROAN 4 0 0 2.252 100% ;... 0 40 I l I II I I Ca (Mg .67 Fe .33) (C03) 2 Figure 45. X-ray Diffraction Patterns for Two Waccasassa Sediment Samples. These samples are shown with the corresponding pattern card for the dominant mineral. [A] River bottom sample from north of Stafford Island. This pattern shows a small clay peak at 15 The remainder of the peaks correspond to the mineral weddelite. [B] Sample from core 12.6 (river core) at 55 em. This sample is composed of nearly pure ferroan dolomite 110

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A 17.66 8.838 5.901 4.436 3 .559 ill ita/smectite kaolinite 10 wedde lite I illite / smectite 15 20 kaolinite 25 2.976 quartz 30 VC 7.1 Clay-fraction at Depths of (in order of p osition): bottom of core --96 em gray organic muds 76 em g ray/gr een tra nsition 66 em base of green m uds 36 em -t op of green muds 1 6 em green / marsh trans ition top of core --7 em modern marsh horizon 2.561 2 252 ka o l i nite? 35 40 Figure 46. X-ray Diffraction Patterns for the Clay-sized Sediment Fraction of Samples Collected Downcore through Core 7.1. Note the similarity of the mineral assemblages between the different facies 111

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112 Kaolinite is the second most abundant clay in the marsh sediments. This mineral is recognized by well-defined peaks at d=7 .2 A. and 3 6 A., and a smaller peak at d=2.4 A.. These peaks are not affected by glycolation and therefore show no shift in spacing after treatment (Moore and Reynolds, 1989; Fig. 46) . Like the illite/smectite clay, kaolinite is present in all samples from the study area. It also appears to concentrate in the upper portion of the centrifuged clay samples. The third clay mineral is present in much lower quantities than the preceding two species Its presence can only be detected by collecting a bottom sample of the centrifuged clays or occasionally by glycolating an upper sample. The exact identity of the mineral has not been determined, but it appears to be from the chlorite group Its dominant peaks occur at d = 14.2 A., 7.1 A. and 4 8 A.. The difficulty in characterizing this mineral is that these peaks are generally overshadowed by those of the more dominant illite/smectite and kaolinite minerals. When the peaks are isolated they prove to correspond to either chlorite or vermiculite, but the presence of the other clays makes further tests inconclusive. Sediment and Facies Distribution Sediment thickness across the marsh zone ranges from less than 1 m near the marsh-upland transition to about 1.75 mat the shore-edge (Fig 47). Core length and probe rod tests at the core sites indicate that the underlying bedrock forms a flat, even subsurface with little karstification or variation in

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i .......... ,., / \. .... \... ..i 82 48' ..... ...... ' --; --Figure 4 7. Map of Sediment Thickness at Core Sites. Note the general thinning toward the upland transition. The thickest sediments (>250 em) are from cores taken on levees where the bedrock deepens near the creek bed. 113

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114 elevation, except immediately at the creek banks ( Fig. 4 7). When located surface irregularities of the bedrock were found to have slight depth increases (<50 em) and were local in extent (<1m diameter). Core 3.4 was taken in such a hole and only showed a difference from nearby cores in having thicker sequence of pre-Holocene sediments (log in Appendix). The even-surfaced bedrock underlying the Waccasassa marshes contrasts sharply with the shelf embayment marshes to the south where abundant karst features are 2-3 m in relief. The stratigraphy of the Waccasassa marshes is relatively continuous, allowing the upper facies to be correlated over a widespread portion of the study area (Figs ; 48-50) Three main sediment sequences are found within the marsh zone The first is a series of undifferentiated pre-Holocene basal sandy units which are preserved discontinuously under more modern sediments. The second sequence is a series of Holocene-age, silty clay units comprising the upper stratigraphy of the shoreward marshes around the lower Waccasassa River and along the rim of the embayment. The third sequence is a modern, wet, organic-rich marsh sequence found along the inland and freshwater-influenced zones An important note must be made concerning the stratigraphic correlations presented here, because many cores were collected from similar geologic settings. Since the majority of core sites were located within fifty meters of a creek edge or shoreline margin, the stratigraphic cross-sections may show slightly biased correlations To judge the potential bias, several small trenches were dug along a transect leading 0 5 km into the marsh near the Williams Creek site ( Fig 35; core 7 .2). This transect revealed that the shore-edge stratigraphy could be traced a way from the bay margin to a point

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w eiN s core numberL.9 .LJ 7.6 7.1 g_j_ 12d core 7.2 -number 100cm above msl -Ocm 60cm m above msl .. 1 o .., .-: .. .:: .. .:-.::.-::.: ... :.:.-:.::;;;:;:;:.-::: .. _:. ..................... ... ... r 1 o -E 50 () Q) ctS 100 ctS () :e Q) > 150 200 8881 modem, muddy marsh leveesoil green muds gray muds D wet, organic-rich marsh organic, blackish muds undifferentiated pre-Holocene sandy muds major unconformity minor unconformity graded contact Figure 48. Core-Based Stratigraphic Cross-Section of the Marshes Rimming the Embayment. Locations shown in Figure 35. Note the correlation of facies across the study area and the similarity of the general stratigraphy within the cores 50 -E () Q)
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North ...... South LQ -core number gacm _elevation above msl North ..... South major unconformity minor unconformity .,....______ graded contact muddy marsh Eli] green muds I :::::::::::::::::I:J gray muds organic, blackish muds D undifferentiated pre Holocene sandy muds e Q) 100 Figure 49. Core-based Stratigraphic Cross section of Two Transects along the North Arm of the Embayment. Locations shown in Figure 30. Note the stratigraphic similarity of the cross-sections and the pinching out of the black and green mud facies toward the upland transition. Also note the shallowing of the bedrock toward the upland. 116

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$4 N/W._.E/SW4 NE/S 4 ..,. N core number 12 3 L.1 2...1 7.11 M 12.5 3 3 3 2 core number 100cm elevation ___ .. above :' v .M"-10 'E 50 (]) 'E "ffi () (/) (]) "ffi () "ffi 100 () 100 'E (]) > 200 major unconformity minor unconformity ......,_.__ graded contact 15 0 leveesoil 200 modem l!!l;!.;l t h h muddy marsh B!1l we orgamc-nc mars [::.:-,:::.:.:-) green muds organic black ish muds mrrm o undifferentiated liliiliW gray muds . pre-Holocene sandy muds Figure 50 Core-Based Stratigraphic Cross Section from the Mouth of the Waccasassa River Upstream toward the Freshwater Transition. Location of cross-section shown in Figure 35. Note the distribution of the black mud facies near the mouth of the river, and also the transition from the muddy, outer facies to the upstream brackish marshes <1l () 'E (]) > ....... ....... -.1

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118 approximately 0.4 km into the marsh. At this distance from the bay margin, the shore-edge stratigraphy graded into the organic-rich marsh stratigraphy (Fig. 41), a transition similar to that represented in the river-parallel cross section (Fig 50) Therefore, it should be recognized that the correlations made in Figures 48-50 have been made on a large scale and that there could be some local, intercore variation not represented in the cross-sections A shore-parallel, outer marsh cross-section does show the broad lateral extent of all of the facies (Fig 48). It is apparent that the stratigraphy of the Waccasassa Bay area is generally correlative. The black, organic mud facies is dominantly located near the head and north rim of the embayment (Fig. 48) It is localized along the outer margin, not extending far inland (Figs 4950). The gray and green Holocene mud facies are the most extensive Holocene, pre-modern facies. They are found a c ross the embayment marshes and extend inland a considerable distance (Figs 48-50 ) The green and gray facies everywhere thin or eventually disappear toward the upland transition (Fig 49) Similarly, a stratigraphic profile along the Waccasassa River shows the pinching out of the green and gray Holocene mud facies away from the bay margin (Fig. 50). The thin, modern, muddy marsh horiz on caps the Holocene sequence over the m ajority of the area (Figs 48-50). Its extent is expressed by the expansive, monotypic stands of Junc us roemerianus marsh. The thicker, peaty marsh horizon is restricted the wetland areas most distant from the bay margin. The cross-section of river valley stratigraphy shows the appearance and extent of this facies along the middle Waccasassa River and creek tributaries (Fig. 50 )

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119 Discussion Probe rod tests and core lengths suggest that modern marsh sediments are perched on a relatively smooth bedrock surface (Fig. 47). These bedrock qualities are also found in the carbonate rock flooring Waccasassa Bay, indicating that the marsh has d e veloped upon a portion of this bedrock shelf. Again, this Waccasassa bedrock surface contrasts sharply with the high-relief karst found underlying the marshes rimming the southern Big Bend shelf embayments (Hine e t al ., 1988 ) The shall o wing of the bedrock along the backside of the Waccasassa marsh zone may represent a pinning point for the marshes. In general, though, the shallow underlying bedrock limits the available space for sediment accumulati o n and exhibits control on the thin stratigraphic sequences which charac teriz e the Waccasassa area. The shore-parallel lower marsh cross-section shows the broad lateral extent of the Holocene mud facies (Fig 48). The characteristic green and gray mud units can be traced from the far western arm of the Waccasassa embayment around to the Eleven Prong promontory The extent of these unique margin deposits d elineates the area here defined as the Waccasassa coastal province (Fig 12). The western edge of this province is bound by a marsh archipelago setting, and the s outhern extent of the Waccasassa province is bound by a marsh peninsula, as defmed by Hine and Belknap (1986 ) In the southern area cores 6.3, 6.4, and 6 5 (Fig. 22; logs in Appendix 1), collected on a transect along Eleven Prong, revealed that the sediments and stratigraphy there were unlike those found in the Wac casassa province The sediments were generally all dark colored sandy, and more organic rich than the Waccasassa sediments Thi s area appears t o have ev olved in a

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120 different manner or under diff erent controls than the Waccasassa marshes, and so the Eleven Prong coastal wetlands are considered to be a separate Overlying the bedrock nearly everywhere beneath the modern marsh zone are a variable series of pre-Holocene basal units (Figs 48-50). These sediments comprise a thin, remnant veneer of material representing a former environment. Within these sediments, the presence of nearshore marine shells suggests that the sediments were deposited in a shallow-water marine environment ( Figs 37A, 38 & 40). The higher sand content may also indicate deposition in a higher-energy environment or a perhaps a source no longer available to today' s sys t e m For comparison, sandy, shelly muds like those of the pre-Holocene facies are found in the modern nearshore zone of Waccasassa Bay (Fig 34 ; upper unit). This similarity suggests that the pre Holocene sediments were d e posit e d in a shallow-marine environment during a period of higher sea level. The timing of this deposition is not certain, but the age may be tied to the Stag e 5 e hig h stand at about 12 0 ,000 BP. Current data indicates that this was the most recent period of sea lev el above the present ( Kendall and Lerche, 1988 ) The black, organic mud faci e s appears to represent a fr eshwater wetland environment ( Table 3 ) Wood fragments and the soft fleshy type of organics present in this unit support this general type of setting (Figs. 37, 40) The detrital wood indicates tha t there were trees within the environment, but the apparent absence of woody roots makes a simple wooded system suspect. The pre s e nc e of less refrac t o ry, flesh y plant material hints at the presence of freshwater we tland plants such as arrowhead ( Sagittaria spp. ) pickerelweed ( P ente daria codata ) and blue iris (Iris ve r sic o lo r ) ( Fig.

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Table 3. Summary of the Proposed Depositional and Environmental Settings for Each Stratigraphic Facies. FACIES NAME Muddy, Marsh Peaty Marsh Green Muds Gray Muds Black Muds Undifferentiated Basal Muds PROPOSED DEPOSITIONAL ENVIRONMENT modern marsh setting; densely vegetated, middle to high, intertidal saltmarsh; dominant siliciclastic deposition modern marsh setting; densely vegetated, middle to low, intertidal brackish marsh; accretion largely through organic production. late Holocene environment; loosely vegetated, middle to high, intertidal saltmarsh; higher energy environment with high accretion rates, active deposition. ?perhaps a salt pan setting with siliciclastic deposition but little organic production/deposition? late Holocene environment; vegetated, low to middle, partly tidal brackish wetland, with fleshy plants producing labile organics; a transitional setting, increasing marine influence (fresh --> salt water) over period offacies deposition. Holocene environment; well vegetated, low-lying, freshwater swamp with both treed and herbaceous areas; low accretion rates and high organic production, but herbaceous organics labile and degraded. Pre-Holocene environment; subtidal, shallow marine setting with variably abundant shell-producing organisms; modern inner shelf of Florida an analogous environment. 121

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122 15) A mixed wooded/herbaceous, freshwater swamp or wetlands might be envisaged for the environmental setting in which these sediments accumulated. A similar environment exists landward of the marsh zone at the present. The gray mud facies is continuous and widespread within the Waccasassa area (Figs. 48-50). The depositional environment of this facies, however, is not clear. The unit does not contain any woody material, indicating that the trees associated with the underlying unit were no longer present at the time of deposition The general lack of preserved roots or peats does not suggest a marsh environment, or at least a dense, healthy one The absence of shells in most of the unit precludes a shallow, subtidal flat environment. One distinct indication of the setting, however, is the appearance of sponges spicules in the gray facies. This marine material represents the first detectable influence of rising sea level on the area. It might be considered that the gray mud facies represents the effects of marine waters intruding into the fresh swamps associated with the underlying black muds. The gray muds appear to have been deposited during the transition from a freshwater, swampy environment to a more marine-influenced, brackish setting (Table 3). Like the associated gray mud unit, the exact depositional environment of the green clay is difficult to determine. The universal absence of marinemacrofauna! shell material in the sediments makes a lower tidal or subtidal environment unlikely (Figs. 36A, 38A-40). This is also supported by the fact that the top of the unit is higher than the present elevation of mean sea level (Figs 36A-38A, 39-40) The very low organics make an intertidal marsh environment also difficult to imagine (Figs. 36A, 38A-40). However, the very

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123 fragile shell of a gastropod commonly seen on the modern marsh surface is found within the green muds facies, supporting deposition in an upper intertidal environment (Fig. 37 A). The abundant marine biogenic material (e.g. sponge spicules, foraminifera, and diatoms) within the unit indicates the continued and perhaps increasing influence of the marine environment (Table 2) Juncus roemerianus (needlerush) roots and other more refractory root material are consistently found in the green mud facies, though not in great abundance. A thin, high saltmarsh habitat are generally consistent with the characteristics of this unit. The overall absence of detrital organics within these sediments is a curious feature of the facies and does not readily suggest a typical coastal wetland environment (Table 3). Another characteristic of this unit, unique within the Waccasassa sediments, is the distinct green color. The source of the color is not known, but the small amount of chlorite type clay detected within the sediment could be responsible. The depositional environment of the modern marsh facies is readily apparent through observation The thin, muddy marsh unit is presently accumulating in a marine-influenced, dense saltmarsh environment characterized by deposition of both organic material and siliciclastic sediments (Table 3). This setting is represented by the broad, monotypic J. roemerianus stands found across the outer marsh zone (Fig 14B) Toward the upland transition and upstream along the Waccasassa River, the muddy marsh facies is replaced by a wet, peaty facies (Fig. 50). The flora of the latter habitat supports the growth of Cladium jamaicense (saw grass) amongst the J. roemerianus plants, indicating that the wet, peaty marsh facies represents a brackish environment ( Fig. 15) Thus the transition between these two modern marsh facies marks the change from a fresh or

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124 brackish setting to a more saltwater-dominated environment. In addition, the high-moisture, high-organic peaty facies does not have the considerable content of inorganic sediments found in the muddy marsh facies (Table 2). This reduced siliciclastic content suggests that the depositional environment of the peaty facies is further from the source of material and/or is in a lower energy setting. The mineralogy of these sediments is not discussed with the individual facies because the mineral assemblages are the same for the entire stratigraphic sequence (Fig. 46). Due to this similarity in mineralogy, the stratigraphic facies within the Waccasassa marshes are largely characterized by their unique colors and different type and content of organic material (Table 2) Although the mineralogical data cannot be used to distinguish individual facies, it does indicate that these varied units were all derived from the same source of material. The presence of marine-derived material within the gray, green, and muddy marsh facies suggest that the sediments were transported from a nearshore marine source (Table 2). A sediment source from the embayment rather than the river is further supported by decrease in siliciclastic content away from the bay margin (i.e. toward the peaty marsh transition) Further support for a nearshore sediment supply is the presence of weddelite in several nearsurface marsh samples (Fig. 45A). This mineral is formed subtidally in conjunction with the oxidative degradation of organic matter, often within the guts of benthic macro-organisms (Van Vleet, pers. comm .). Therefore, the presence ofweddelite on the marsh surface is indicative of the importation of subtidal sediments. Although this mineral was found in both nearshore and river grab samples, the apparent dominance

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125 of marine sediments in the marsh stratigraphy suggests that the source of the weddelite is the nearshore zone In addition, the absence of dolomite within the marsh stratigraphy indicates that the upriver supply of dolosilts (Fig. 45B; core 12.6) is not being transported downstream to the marshes. This finding again shows the apparent lack of fluvial sediment transport by the Waccasassa River, and thus provides further support that the marsh sediments are derived from an offshore source.

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126 7. HOLOCENE EVOLUTION OF THE WACCASASSA BAY AREA In the Holocene, rising sea level has driven a considerable marine transgression across the west Florida shelf. During the latter half of this period, sea-level rise exhibited a large control on the evolution of the modem coastal systems of Florida More specifically the variation in the rates of rise has closely affected the development of several different coastal environments now found along the Gulf shoreline (Evans et al 1985 [barriers] ; Hine et al. 1988 [salt marsh]; Parkinson, 1989 [mangroves]) Regionally, the shallow-to-exposed bedrock basement of the Big Bend coast added an additional control on the evolution of this diverse marsh system. The low regional gradient (1: 3,000 6,000 ) of this flat carbonate shelf makes the area susceptible to rapid and considerable inundation CHine and Belknap, 1986) In addition to the topographic control of the bedrock, the general lack of sediment cover has also influenced the evolution of the Big Bend coastal system. Repeated marine transgressions have kept much of the shallow Florida platform devoid of significant sediment cover. This general absence of sediment exhibits an additional and critical control on the evolution of Florida's marsh coast The influences of sea-level rise, bedrock topography, and sediment cover must all be considered when reconstructing the history of the Waccasassa embayment and the development of the modem marsh system.

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127 Shoreline Retreat At 5,500 BP sea level was 3.5-4.5 m below present (Fig 6; Scholl et al., 1969). This period appears to mark the start of marine influence on the modern Waccasassa Bay area. This marine elevation also corresponds to the general bedrock depth just offshore of the modern shallow-water platform of Waccasassa Bay. Given that the study area is presently covered by only a thin veneer of sediment, it might be assumed that conditions were similar during the middle Holocene. With only a thin covering of sediment, an approximate shoreline can be drawn along the depth of bedrock at that particular sea level. Figure 51 shows a hypothetical shoreline position based on this assumption. A 5,860 BP radiocarbon date of wetland peats in this vicinity supports the general shoreline position suggested here ( Fig. 52A). From 5,500 BP to 3,500 BP sea level rose approximately 2.5 m at a rate of about 13 em per century. During this period sea level topped the edge of the elevated carbonate ramp upon which the modern system is perched (corresponds to the 1 8 m isobath in Figure 10) It is probable that at this point the shoreline began to transgress more rapidly across this very low gradient shelf(Fig. 51). However, the nature and t iming ofthis retreat is not known. A possible scenario is that the shelf area was covered with a thin ( < 1 m) veneer of pre-Holocene sediment like that underlying the modern marsh system. This facies commonly contains small, woody roots, suggesting that the area was colonized by upland plants (Fig. 37B) Saltwater intrusion may have destabilized this terrestrial system expediting shoreline retreat. As the transgression progi-essed, nearshore processes swept away the thin sediment

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128 14C -1 780 BP : _) ,; <' / 14C3 960 BP m:.CS f 29 04' water depth ITIITITI 0 -1 .8 m .. r a 1 > 3.6 m F i gure 51 Proposed Shoreline Positions for the Late Holocene Trans gression of Waccasassa Bay Break in slope shown in Figure 53 corresponds to the 1 8 m isobath. Note the sites of the radiocarbon dates used in Figure 52

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A upland ; live oak coastal wetlands ; ?vegetation? B 5,500 BP herbaceous fresh swamp; sawgrasslbu lrush ( Cladium jatreic enseiScirp u s spp. ) low saltmarsh; need le rush 3,500 BP oyster reef / bioherm undifferentiated KEY I:R.lJJ pre-Holo ce ne sediments Eocene carbonate rock 81 peat coastal marsh fresh swamp facies Om 4 6 upland; live oak 129 ( Quercus Figure 52. Evolutionary Profiles for the Proposed Development of the Waccasassa Bay System. Profiles correspond to the shoreline positions in Figure 52 [A] This early stage shows an upland forest growing across the wide shelf which today is flooded to form the Waccasassa embayment. The lower sea level is below the shelf edge, and the coastline is perhaps colonized by mangroves. [B] Sea level has topped the edge of the Waccasassa shelf and begun to rapidly transgress the low-gradient plane. The upland forest has di e d off and been r eplace d by a low, unstable marsh. A freshwater swamp is established at the upland transition.

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c D brackish marsh; sawgrass (Ciadium ;.maioenM) 2 4 130 jOC 5 860BFj 2,000 BP 6 saltmarsh ; brackish mars h; needlerush sawgrass (June us roemerianus) (CiadOJm jamaioenM) 4 6 modern KEY oyster reef / bioherm r-:-:-1 undifferentiated pre-Holocene sediments m Eocene carbonate rock m peat saltmarsh facies 0 green mud facies E] gray mud facies fresh/brackish marsh facies fresh swamp facies Figure 52. (Continued). [C] The Waccasassa shoreline has continued to transgress and the habitat zones have migrated landward. The slowing of sea level rise has also resulted in slowed transgression and a more vertical accretion A higher, healthier marsh system is beginning to develop. [D] As sea level becomes increasingly steady, the coastal system fully develops. Vertical accretion is a dominant process, while shoreline retreat has ceased.

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131 cover, leaving only remnant patches preserved within karst features (Figs 33 & 52B). At 3,500-3,200 BP, the rate of sea level rise decreases to about 3.5 em per century (Scholl et al 1969 ; Robbins, 1984) This slowdown has been implicated in the growth and development of the modem coastal systems of Florida's Gulf coast (Evans et al., 1985; Hine et al., 1988 ; Parkinson, 1989; Stapor et al., 1991) In the Waccasassa system the slowdown would have been important in reducing the impact of marine inundation, and perhaps in slowing the transgression. If shoreline retreat did slow, then vertical accretion processes would benefit from the increased stability. Conditions would have been suitable for the development of an incipient coastal marsh system (Fig. 52C) Establishment of oyster reefs would also be encouraged by the slowed sea level rise and greater constancy of shoreline position (Fig. 52C) Perhaps between 3,000 BP and 2,000 BP a coastal system similar to that of today would have evolv e d in a position just seaward of the present coast (Fig 51). The environment would have consisted of a shore-edge salt marsh backed by freshwater marsh and swamp (Fig 52C) The elevation of sea level would have raised the water tabl e initiating the establishment of the swampy upland. In fact, the preservation of such a facies is found within the marsh stratigraphy at the head of the embayment (Figs. 37-40,48, & 50). Radiocarbon dates from the black mud facies bound the period of deposition from an early date of 4,000 BP until the most recent date of 1,900 BP. Around 2 500-2,000 BP the deposit ion of marine-derived sediments succeeded the freshwater environment within the modem stratigraphy. This change in setting indicates the continued transgression of the shoreline and

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132 the increasing influence of the marine environment. This also marks the initial period of deposition for the gray mud facies (Table 2) Subsequently, around 1,500-1,000 BP (Table 2), deposition of the gray unit was slowly replaced by the green muds along the shore edge and adjacent (within 500 m) marsh zone An important consideration during the past 2,500 years, though, is the continued decrease in the rate of sea level rise during (Scholl et al., 1969) This slowing of sea level rise represents a waning of the tendency for the coastal system to transgress. In the terms of coastal processes, vertical accretion processes may have begun to outpace shoreline retreat at this time. Such a transition may be represented by the gradual change from deposition of the gray muds to the green muds (Fig 48) At about 500 BP the green and gray muds were everywhere replaced by the development of the modern muddy marsh horizon (Table 2 ; Figs. 48-50 ; 52D) This most recent facies change appears to represent the establishment of the modern marsh vegetation and stabilization of the shoreline. Source and Transport of Sediment As a shoreline transgresses an area, sediments are eroded from the shoreface and nearshore zone by marine processes (Bruun, 1962). The fate of such sediments is important to the development of a marsh system, where vertical accretion is required to avoid inundation. This has been particularly true in the sediment-poor Waccasassa Bay system. This region has no fluvial sediment supply, and the offshore zone is at most covered by a only thin

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133 veneer of material (Fig. 27) Thus, the transport and distribution of the limited sediment supply is critical to the evolution of the Waccasassa coastal system. Ultimately, it is the landward transport of sediments which is required to establish and maintain a healthy marsh in this area. This process does appear to be active in the Waccasassa system and is expressed in the marsh stratigraphy. The sediments overlying the freshwater or basal units contain marine microfossils indicating that they were derived from a marine source. These microfossils include benthic forminifera, diatoms, sponge spicules, and urchin spines Thus, it can be assumed by the presence of such indicators that the vertical accretion of this stratigraphy was driven by the reworking of the sediments within the nearshore zone followed by transport into and deposition upon the marsh surface. The source of these nearshore sediments is also a point of concern. Modem sediment cover in the Waccasassa area is thin to absent from the offshore zone up through the upland forests This regional paucity of sediment suggests that there was also little sediment covering the bay shelf during the period of transgression Where then did the sediment comprising the modem stratigraphy come from? As the transgression moved across the embayment, sediments were continually swept off the shelf and pushed toward the retreating shoreline As sea level rise slowed, this material began to increasingly accrete verti cally rather than being horizontally transported. So the sediment supply has evolved through the removal of a thin veneer from a large area and the deposition of the reworked material over relatively smaller area (Fig. ?2A-D).

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134 The lack of sediment in an offshore direction shows that there has been little movement of eroded material that way and supports a model of landward transport and accumulation. In addition, the sediment thickness within the embayment is greatest at the head of the bay, where such material might be expected to accumulate. The bedrock surface is deepest in this area, and so it can accomodate the accumulation of shoreward-transported material (Fig. 27). Mineralogically, the similarity of pre-Holocene basal sediments and the modern muds proves that they are comprised of the same material (Fig. 46) By that same means, the presence of marine-derived material, such as weddelite and marine microfossils, in the recent stratigraphy supports that these sediments were reworked in a subtidal environment. These characteristics support the evolutionary model that a thin veneer of preHolocene sediments covering the Waccasassa shelf was transgressed and reworked and that these sediments were ultimately transported shoreward and deposited at the present shoreline. Environmental Succession and Marsh Development The base unit of organic-rich, black muds appears to have been deposited in a freshwater swamp habitat (Table 3). Bounding dates show that the unit was deposited under slow accretion rates ( -0.4-0.8 mmyrl). These sediments do not contain marine-derived material (Table 2). The unit is distributed across the northern arm of the embayment (Figs. 48-50), where an extensive forested swamp presently exists just landward of the modern marsh.

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135 The overlying facies, the organic gray muds, is the first widely spread unit to be deposited. This stratigraphic change appears to represent the transition from fresh to saltwater influence (Table 3) Marine microfossils first appear in this unit, indicating such a transition (Table 2). The actual depositional environment is not clear, however Thin-walled mollusk shells at the base of this unit in cores from the west end of the bay suggest that this area may have initially transgressed before accreting verti_ cally (Figs. 48-49) There are no such shells in the unit across the rest of the area. Plant remains in the unit indicate that the environment was vegetated, but the gray color and lack of peaty material are not indicative of a healthy marsh habitat. The environment may have been a tidal flat with scattered, poorlyestablished vegetation (Table 3) The gray muds everywhere slowly grade into the much cleaner, light colored green muds (Table 2 ) The depositi o n of this unit might represent the fmal change from a transgression-dominated system to that of a vertically accreting system. The sediments contain abundant marine-derived material, and they are generally devoid of organic material ( Table 2 ) This lack of organics and the absence of any marine she lls sugge s t that unit may have been deposited in a nearly supratidal environment (Table 3). In addition, the top of unit is above the elevation of modem sea level, thereby making deposition in an "intertidal mud flat environment unlikely If deposition had occurred in a lower mid-tidal environment, then the sediments should have collected more organic material. A possible scenario is that the gradation from the gray muds to the clean green muds represents an increase in vertical accretion rates and the heightening of the surface in relation to sea level.

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136 The green muds are capped by 10-20 centimeters of modern, muddy marsh sediments (Figs. 36, 38-40) The thickness of the unit indicates that the dense, healthy stand of Juncus roemerianus covering the marsh is a relatively recent development. The reason for this rapid change is not known. Does it merely represent an intense vegetative colonization of the area, or is the change a reflection of varying processes? The theory is presented here that this recent establishment of salt marsh environment across the area is a function of the stability of the region. The healthy, present-day salt marsh signifies the final stage of development in the approximate 5,000-year evolution of this coastal system. The record of this evolution is currently preserved in the layers and associations of the sedimentary units contained within the coastal stratigraphy. Upstream of the Waccasassa River mouth occurs a lateral transition from muddy salt marsh sediments to watery, organic-rich brackish marshes (Fig. 50). This environmental change is driven by the lowering of salinity levels as a function of distance from the bay and increasing river influence. Isolated from the active depositional processes operating at the shoreface, this area became flooded due to the ponding of river water behind the elevated shore-edge Essentially removed from the shoreface and the area of sediment deposition, the result was a local fresh to brackish-water environment where organic accretion heavily outpaced inorganic sediment accumulation. As sea level has continued to rise, saltwater influence has extended inland along the river. The effect of the salt intrusion can be seen in upstream, lateral migration of the brackish marsh facies (Fig 50). In core 3.4, the green mud facies and muddy salt marsh overlie a former brackishwater peat (Fig 50). This facies juxtaposition shows that since the initial

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137 establishment of a brackish marsh facies (in core 3.4), that the brackish/salt marsh transition has migrated landward. This retreat represents the continued rise of sea level and its influence on the evolving coastal system. The position of the modern transition between salt and brackish marsh must lie between cores 3.4 and 12 5 (Fig 35). This stretch of marsh also corresponds to the length of river where the mean salinity level drops to 10%o (Fig. 16). Such a low salinity level is in the range of more fresh/brackish plant species (Fig 15).

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138 8. MODERN SYSTEM AND PROCESSES The Waccasassa coastal marsh system has developed during a period of rising seas, in a sediment-poor region, and along a low-gradient bedrock plain susceptible to rapid inundation. Thus, the formation of this system was largely a function of the small, limited sediment supply and the processes controlling its distribution. The measurement of marsh accretion rates, bay water suspended sediment concentrations, and tidal creek water velocities have given a general, qualitative understanding of the processes operating in the Waccasassa system and controlling sediment transport and distribution. Results A large sediment core was collected from the marsh about 10 m away from the site of core 7.1 along Bird Creek. This core was sampled at one and two centimeter intervals and selected depths were analyzed for 210Pb and 137Cs activity. The results have provided an averaged accretion rate of 2 1 mmyrl for deposition over approximately the past 100 years (Fig. 53) Sea level rise has been determined to have been approximately 1.2 mmyr1 over the past 80 years (Hicks et al., 1983). The accretion rate for this core provides a maximum rate over the measure d period because of the effects of bioturbation. A minimum rate could be as low as 1.3 mmyr1 or about equal

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-E u 0.01 0 1 activity ( dpm/g) 1.0 10 100 0 / s = 0 .2 05 0 035 cmyr1 / / / 10 / s = 0.131 0.035 cmyr 1 depth of bioturbat i on ..c 20 -0. Q) "C 30 / / + Excess Pb-21 0 Excess Pb-21 0 not used 0 in regress ion analysis -<>-Cs-137 Figure 53 Graph of210Pb and 137Cs Activity Values for Sediments Collected at Bird Creek near Cores 6 117 .1. The measured rate of accumulation (s) is derived from the slope of the 210Pb exponential line. Solid line corresponds to normal regression dashed line represents a minimum rate corrected for bioturbation effects. 139

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140 to rate of current rate of sea level rise. The actual rate is likely between the two values given here. On February 10, 1994 water samples were collected from the area of Williams Creek (Fig. 1). These samples were measured for suspended solid concentrations to look at floodstage sediment transport in Waccasassa tidal creek. The results show very high, water-column sediment concentrations (>70 mgl-1) during slack water over a shallow flats area (Fig. 54). Measurements from inside the creek mouth during the floodstage show that suspended l oad concentrations dropped significantly, but still ranged from 1030 mgl-1 (Fig. 54). Other water samples collected from the study area include two vertical profile series from sites in the open bay (Fig. 55). This data shows horizontal and vertical variation in suspended sediment concentrations during the floodstage in the nearshore and offshore areas of Waccasassa Bay. Values ranged from 12-30 mgl-1 at the inshore site, dropping to 8 -1 0 mgl-1 in the offshore zone. The general trends showed suspended solid concentrations increasing with depth and toward the shoreline. A two-week deployment of an 84 current meter with a pressure sensor provided tidal current velo cities and water depth for that period (March 1226, 1994). The data was collected from Depew Creek, one of the deeper creeks located along the inner, north arm of the embayment (Fig. 1). The current velocities ranged from 0-38 cmsec-1 and showed peak flood velocities consistently higher than the corresponding peak ebb value (Fig 56A). However, the ebb cycles appear to be longer in duration than the flood cycles (Fig. 56A). The water depth data shows a varied tidal range of20-100 em

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-"0:::::::: -0> oE en'-"" "'c Q). o "0-Q)a.C C/)Q) ::Ju cnc 0 (.) 80 60 40 inside Williams Creek 20 shallow flats outside 0 I of creek mouth I I I I I I I I 10:26 10:45 11 :05 11 :25 12:05 time 12:25 12:45 13:05 15:20 Figure 54. Graph of Suspended Solid Concentration in Bay Water Samples during a Flooding Tidal Cycle Early samples were collected outside of the creek mouth over a shallow flats area. Later samples were collected from the channel inside the creek mouth. Note the high concentrations over the shallow flats area resulting from wind-induced resuspension. ....... .......

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29 12' 29 08' 29" 04' 29 oo I 8 3 oo I ......... E (.) -..c ... c.. Q) "'0 0 50 125 175 I I I I 5 10 tf If I I I I II I I I I I I I I I I I 8 2J 56' I J I 15 10 82 52' 20 concentration (mg/1) 82 48' 30 \ \ 0 50 125 175 40 ......... E (.) -..c ... c.. Q) "'0 Figure 55 Vertical Profiles of Suspended Solids Concentration at Two Sites in the Wac casassa Bay. Samples collected on a flooding tide. Note the increase in concentrations toward the head of the emb ayment and with greater d epth in the water column 142

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...-... (.) Q) E (.) -"'C Q) Q) c.. (/) .--.. E -.c ....... c.. Q) "'C 143 30-201 0 -W't/ J lA I l I h \ w 0 ? ? 1.5 1.0 0.5 0 3/12/94 v v A nN v y v v 3/19/94 3/26/94 Figure 56. Two-week Recording of Current Velocities and Water Depth from Depew Creek. [A] Water velocity. Black bars denote tidal cycles, with the first peak corresponding to the flood stage. Note the higher peak velocities of the flood stage and the longer duration of the ebb stage. [B] Depth. The mixed semi-diurnal and nearly diurnal tides The greatest tidal range here shows an amplitude of about 1.0 m.

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during the two-week period (Fig. 56B). The change from semi-diurnal to nearly diurnal tides can also be seen in this data (Fig. 56B). Discussion 144 A primary indicator of the health and fate of a marsh system is the sediment accumulation rate versus the rate of rising sea level. For a marsh surface to remain vegetated and stable, the period of inundation, a function of elevation, must remain within the toleranc e of the plants. Therefore as sea level rises, so too must the marsh surface In the Waccasassa system, the analysis of 210Pb radiodecay within the upper marsh stratigraphy has provided an accretion rate for the marshes with which to compare to observed sea level rise. The results of this analysis show an accretion rate between 1.3-2 1 mmyr1 over the past one hundred years ( Fig. 53 ) This compares to a sea-level rise of 1.2 mmyr1 during approximately the same period determined from tide-gauge data at Cedar Key, Florida ( Hicks et al. 1983). Apparently, the marshes are accreting at a rate near to or above that of relative sea level rise, implying that sedimentation processes are actively maintaining the marsh surface elevation 210Pb data from other nearby marsh systems support the Waccasassa results, providing accretion rates of 2.6 mmyrl for the coastal marshes to the south of the study area (Crystal River, Florida; unpublished data) and 2 0-2.6 mmyr1 for the marshes to the north (Suwannee River, Florida; Wright et al 1993 ) Based upon the accumulation rate given by the Waccasassa 2 1 0Pb-dating analysis, the age of

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the modern marsh horizon (muddy marsh facies) in this area could range from about 500 years to as young as 75 years. 145 The marsh surface seems to be receiving a sufficient quantity of sediment to maintain the integrity of the system. Where then, is this material arriving from, and what is its source? The two potential sources in this estuarine system are fluvial and offshore sediments. The widespread presence of marine biogenic material (i.e. sponge spicules, foraminifera, urchin spines) within the upper stratigraphy of the marshes indicates the strong influence of offshore sediments (Table 2). However, this does not preclude the presence of fluvial material as a sedimentary component. The general character of the Waccasassa River, though, suggests that there is comparatively little sediment being transported by riverine processes. The river is slow-moving, has a small discharge, and largely drains broad, flat freshwater swamps. Such conditions are not those associated with significant sediment transport. It appears that the sediments comprising the marsh stratigraphy and those presently being d e posited on the marsh surface are arriving from a seaward source. As discussed in the previous chapter, this material has apparently been derived from the erosion and nearshore reworking of a former, thin veneer of pre-Holoc ene sandy muds overlying the bedrock. It has also been shown that there is not an extensive distribution of these nearshore sediments (Fig. 23). The main l ocat ion of significant sediment thickness appears to be restricted to the head of the embayment ( Fig. 27). These data suggest that the net transport directi o n of the nearshore material is landward. However, the pro cesses controlling the distribution of these

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146 sediments have not been studied. Longshore currents resulting from coastal onshore sea-breezes could be one driving mechanism. Another possibility is the dominance of flood-stage tidal currents moving sediment to the head of the embayment. This may occur during the flood-stage when currents are focused within the deeper central channel, the higher velocity waters sweeping sediment up onto the shallow shelf area. During the ebb-stage, the flow of water would be spread across the width of the embayment, resulting in increased cross-sectional area and reduced tidal velocities, perhaps causing decreased transport competency Thus far it has been suggested that nearshore sediments located at the head of the embayment are being transported and deposited on the marsh surface What then might be the processes responsible for the resuspension of these nearshore sediments and their subsequent transport into the marsh system? During a relatively calm day (Feb 10, 1994) sediment resuspension was observed in response to light winds blowing across a shallow flats area during slack low water. The measured suspended sediment concentration of these waters was high (Fig. 54), indicating that this may be one process active in the entrainment of nearshore sediments into the water column (Leonard et al in press). In deeper waters, larger, wind-driven waves may act in a similar fashion, resuspending material across the outer portions of the embayment. Although sediment is being deposited in the marsh system, the net vector movement of nearshore material is not known. However, it appears by the distribution of nearshore sediments, the initial suspended solid concentration data, and the marsh accretion measurements, that it is probably in a landward direction Field observations and aerial photographs

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147 have shown that there can be significant sediment entrainment and transport during the flood stage (Figs. 54-55, & 57). In addition, these field observations were made on a calm day, suggesting that normal flood-stage tidal currents are fast enough to cause sediment resuspension in the open bay. Other results also indicate that the system is flood dominated Preliminary water velocity data from Depew Creek show that peak flow values generally occur during the flood stage (Fig. 55A), suggesting greater competency during this period. The high silt content within the marsh sediments could reflect transpo_rt. of such material by the higher flood velocities (Figs. 36A, 38A-40) Although the peak velocities are lower, the duration of the ebb cycle is longer than the floodstage, suggesting that there could be a net export of material over the entire tidal cycle However, marsh surface accumulation might occur through the settling of coarser-grained material (i.e. silts) imported on faster flood waters, while finer-grained material may actually be exported. If this process was occurring, it could explain the 1:1 or greater ratio of silt:clay-sized particles comprising the Waccasassa marsh sediments (Figs. 36A, 38A-40) Again, the indications of sediment transport direction are not conclusive, but the net movement does appear to be landward. A general process model might be that nearshore bottom sediments are resuspended at low water stage by winds and waves moving across shallow flats areas. Once entrained within the water column, the material is then transported onto the marsh surface by the subsequently incoming tidal flood waters. Although the data and observations are limited none of these phenomena were observed in conjunction with ebb conditions.

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148 Figure 57. Oblique Aerial Photograph of Waccasassa Embayment Showing Suspended Sediment across the Area during a Flooding Tide. Photo taken at 11 : 30 on March 10 1992 during a flooding tide. Note the flow disruption caused by the subtidal Waccasassa Reef bioherms.

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149 The determination of a positive marsh surface accretion rate has already been discussed earlier in this chapter. In addition to the conclusions of the 21Pb data, the morphology of the area also offers supportive indications of active sedimentation across the system. The well developed levee system is one such indicator. First, the facies underlying the surface levee sediments are stratigraphically identical to that underlying the modern marsh muds (Fig 37) This evidence shows that the levees are recently developed features rather than remnant elevated banks. So there must be an active process responsible for the levee formation, and accretion rates are assumed to be higher along these banks in order for them to develop Second, the l evees are most notably distributed around the head of the embayment. This suggests that accretion processes are more active in this area. In addition, the el evation of the lev ees appears to increase towards the head of the embayment, also suggesting greater accretion rates. This increase in elevation is characterize d by the pr9gression of the dominant flora from the most salt-tolerant of the lev ee species, Distichlus spicata and Salicomia sp., to Iva frut escens and Baccharis halimifoli a, and finally to the salt-intolerant species, Sabal palmetto and Juniperus silicicola.(Fig. 17 ) This floral zonation results from the d ecreasing inundation period along the more elevated levees and their subsequent reduction of saltwater influence. It appears from the distribution and elevation of these levees that sedimentation is actively occurring as a result of surface inundation, and that this process increases towards the apex of the embayment. The elevation of the better-developed levees within the Waccasassa system is above highest high water. These levees are n ot flooded during normal tidal cycles, and so their d eve l opment and accr e tion cannot be

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150 explained by this process. Therefore, in order to flood the levees and deposit sediment, wind-induced tidal fluctations are needed Such events are usually tied to the numerous storm systems and fronts which strike this coast during the year (the following chapter discusses the effects of one, severe event occurring in March 1993).

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9. EFFECTS OF THE MARCH 1993 'STORM OF THE CENTURY' ON THE WACCASASSA BAY SYSTEM 151 The effects of the "Storm of the Century" represent the general influence that storms have on this coast. Albeit, this especially powerful storm presents unique circumstances, but the general results of the event suggest that the processes are at least representative of smaller storms and normal daily processes. ffitimate ly, the effects of this event and the common occurrence of storm conditions along this coast indicate that storms may be the dominant process affecting the Big Bend coastal marsh systems. Results On March 12-13 199 3 the passage of a severe extra tropical storm, dubbed as the "Storm of the Century," resulted in the d eposition of stormsuspended sediments along portions of the Big Bend marsh coastline. Sedimentation on the marshes rimming Waccasassa Bay was widespread and considerable (Fig. 58). Surge waters over 3m in height delivered d eposit thicknesses of up to 12 em on top of the river l evees. Storm sedimentation was visible several hundred meters from the creek banks into the marsh interior. The tanto-gray storm lay e r was comprised of mixed clays, silt-to fine sand sized quartz, and marine biogenic sediments, similar to thos e of the

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Figure 58 Map of the Distribution of Storm Sedimentation and the Location of Sampling Sites. The black line shows the approximate distribution of the sediments based upon site visits Storm-induced sedimentation occurred across the entire outer marsh zone within the Waccasassa area. These sediments thinned and disappeared towards the uplands and along the outer reaches of the embayment. 152

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underlying marsh sediments. In general, the storm had a large, and dominantly positive effect on the Waccasassa system. 153 The strength of the storm was certainly expressed by the severe weather associated with it. Along the Big Bend coast, sustained gale-force winds, tornadoes, and coastal flooding were the most damaging forces of the storm. Wind gusts to 85 knots were recorded at Cedar Key, Florida, and the Crystal River Nuclear Power Plant recorded sustained winds over 50 knots for a period of 8 hours, with gusts reaching 80 knots (Fig. 59 A). The winds blew from the west, directly onshore along the Big Bend coast (Fig. 59B). Severe storm surges were associated with these strong winds. Water levels along the coast ranged from 2-3.5 m above m.s.l., moving up to 3 km inland and further along waterways (NOAA, 1993). The U S Geological Survey gauging station on the Waccasassa River recorded a peak flood flow of -525 m3sec-1 at 10 : 00AM on March 13. This flow is over 25 times greater than during normal astronomical tides (Fig. 60). The most obvious effects of the storm were fallen trees, defoliation, and detrital wrack lines at the upland transition and in the high marsh. The spring foliage of many coastal and hammock trees was damaged or destroyed by the salt spray and wind bum from the cold temperatures and strong winds. Many trees were also snapped or uprooted by gusting winds (Fig 61A) Large wrack deposits were distributed throughout the area, pinning against the upland forest, hammocks, leveea, and creek meanders. The wrack-covered areas were large (over 5000 m2) and consisted almost entirely of dead Juncus roemerianus stalks deposited up to one meter in thickness (Fig 61B)

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A. WIND SPEED: MARCH, 1993 Crystal River Nudear Power Plant data 20 averaged hourly winds of >30 knots for a 16 hour period 40 l 15 en 30 g E g 10 Q) > 5 5 10 15 20 25 date (March) B WIND SPEED AND DIRECTION: MARCH, 1993 X= "Storm of the Century" data points + = data points for rest of month oo -10 30 Figure 59. Graphs of Wind Speed and Direction for the Month of March 1993 Showing Data from the 'Storm of the Century' [A] Hourly wind speed data from Crystal River, FL, 10 km south of Waccasassa Bay Note the intensity and duration of the sustainded winds. [B] Hourly-averaged wind directions from Crystal River Note the grouping of the 'Storm of the Century' data points at high-velocity values in the western quadrant. 154

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155 WACCASASSA RIVER DISCHARGE: MARCH, 1993 -..... u Q.) 50 USGS Water Resources Data E Q.) e> co -50 .c (.) (/) "'C -100 -500 storm surge floodwater discharge -25 times norma l flow 1 5 10 15 20 25 30 date (March) Figure 60 Graph of Discharge for the Waccasassa River for the Month of March 1993 Showing Data from the 'Stann of the Century'. Note the tremendous floodwaters resulting from storm surge, and the subsequent disruption of the daily tide signal for over 10 days after the event.

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156 Figure 61. Photographs Showing Tree Damage and Wrack Deposits Resulting from the 'Storm of the Century'. [A] Uprooted and defoliated trees along the river levee. Winds and cold weather killed many of the trees which help stabilize the levee systems. [B] Dense, widespread detrital wrack covered many areas where it collected up to 1 m thick. The majority of the material is comprised of dead June us stalks.

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157 Figure 61. (Continued). [C] The dense wrack cover killed back the marsh grasses in these areas, leaving open mud-flat environments once the wrack degraded or washed away Abundant new shoots show that marsh plants are rapidly recolonizing these areas.

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158 Along the shoreline there was little to no erosion or alteration resulting from the stonn. The high stonn surge flooded the shore-edge early during the event and prevented wave cutting along the shoreface. The shore-edge was also stabilized by the root mat of well established Spartina alterniflora and J. roemerianus marsh plants (Day et al., 1973). Marsh surface erosion was limited by the cohesive nature of the muds (Mehta, 1982; Reed, 1988) and because across-marsh flow was baffled by the thick J. roemerianus canopy (Leonard et al., in press). The most significant result of the stonn was the widespread deposition of nearshore sediments onto the marsh surface. A variably thick, tan-to-gray deposit was distributed from the outer shores of the embayment to several kilometers upstream along the Waccasassa River (Fig. 58, 62-63). Measurable deposition on thE! marsh surface was found up to several hundred meters from the creek banks and shore-edge. The layer was thickest on top of the levees and thinned with distance into the marsh. A maximum thickness of 12 em was found on a river levee 4 km upstream from the mouth of the Waccasassa River (Fig. 63-64). The grain-size distribution of the storm sediments varied between sites, particularly along the transects (Fig 64). In general the sediments were coarser near the head of the embayment and fined away from the levees and creek banks. The sand-sized fraction ranged up to 60% dry weight on the river levees, while .the clay fraction reached over 60% dry weight only 100m into the marsh (Fig. 64C). The coarser sediments were dominantly well sorted, very fine quartz sands. Silts composed of quartz and biogenic sediments comprised at least 15% dry weight and not more than 50% dry weight. The percentage of organic material was generally less than 5% ash

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159 Figure 62. Two Photographs Showing the Storm Deposit in the Marsh Zone. The gray and tan layers are the storm sediments overlying the normal muddy marsh unit. The thin, tan, top layer represents an oxidized layer over the reduced gray sediments. These samples are typical of the deposit approximately 50 m away from the creek or levee.

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160 Figure 63. Two Photographs of the Storm Deposit on Top of the Levees. [A] This photo shows the thickest sample of the storm deposit found in the area. It was taken along the river levee 100m downstream from Stafford Island ( Fig. 1). Note the layering with alternating deposits of clean, tan sediments and darker organic-rich laminations.

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161 Figure 63. (Continued). [B] This photo shows the well-developed desiccation cracks which commonly developed in areas where the deposit dried quickly. The sample was taken about 0 5 km downstream from the preceding photo. Note the separation of the layers along specific planes, and the collection of foliage debris on top of the clean, storm sediments.

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A. WEST PASS CORE E 0-2 0 g 2-4 "'C .c a. 4-6 Cl) "'C cumulative weight% 0 10 20 30 40 50 60 70 80 CJ%sand B!o/osilt ll%clay B. DEPEW CREEK CORE [Jo/osand Q%silt l!ll%clay top portion of storm layer lower portion of storm layer underlying marsh sedjment C. WACCASASSA RIVER TRANSECT 1 0 1 distance from river (m) D %sand m %silt II %clay 162 Figure 64 Graph Series of Grain Size Analysis on Storm Sediments at Various Sites. The locations are shown in Figure 52. [A] & [B] Vertical grain size profiles. The similarity in grain size between the lower portion of the storm layer and the underlying marsh sediments can be seen in this graph. Note the inversion of coarser sediments on the top of the layer. [C] Horizontal grain size and thickness variation. This graphs shows expected thinning and fining trends expected with distance from the creek bank.

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163 dry weight, except for samples from the top of the river levees where values increased to 25-30% ash dry weight. The mineralogy of the storm sediments consisted of clays, silt and fine sand-sized quartz, dolomite, and marine biogenic material. The clay fraction was comprised of kaolinite and mixed-layer illite/smectite; the same clays found within the underlying facies. The clays were gray (N6) colored under reducing conditions and readily oxidized to a yellowish brown (10YR 5/6) color. The coarser material was dominated by fme quartz, with lesser amounts of molluskan shell hash. Other significant components included dolomite, benthic microfauna, siliceous sponge spicules, and aragonite. The presence of these constituents indicates the nearshore marine source of these sediments. Layering was common within the deposit at the levee sites, with laminations ranging from 1-7 mm thick. The individual layers were separated by planes of clean, coarser sediments or organic layers. The layering only occurred on the major levees where there was an absence of a ground canopy. The exposure of this open-ground area to waves and surge pulses may be related to the local occurrence of these laminations. In addition to the laminations, the levee deposits showed classically well-developed desiccation cracks (Fig. 63B) Discussion Overall, the response of the Waccasassa Bay system and Florida's Big Bend marsh coast in general was unique for several reasons. First, the lack

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164 of shoreline erosion and the occurrence of surface accretion represents the largely positive response of a coastal system to a powerful storm producing hurricane-force winds and a 2-3 5 m storm surge (Fig. 59-60) Secondly, the layer of storm-suspended sediments deposited along Waccasassa Bay and other areas represent a significant contribution to the accumulation of marsh sediments in the face of a rising sea level. Thirdly, the storm deposit itself represents a potentially preservable record of this catastrophic event. In the present regime of a coastal marsh system and rising sea level, the sediment introduced to the Waccasassa marshes must be helpful in keeping the them paced with sea level rise. Whether periodic events like the Storm of the Century contribute greatly to the marsh accretion rates is uncertain, but the effect of up to 2 em of accumulation during one event must at least be a considerable aid in maintaining marsh surface elevation. From a depositional point of view, the "Storm of the Century" might be considered a 'storm of the decade' since it delivered approximately 10 years worth of deposition based on the average accumulation rate (Fig. 53). In actuality, though, the storm layer probably represents much more than 10 years of accretion. The storm deposit in the Waccasassa Bay marshes was still easily recognizable one year after the event. However, the layer is becoming increasingly mottled and disturbed by fiddler crab ( Uca pugnax) burrows and plant root and rhizome propagation. On the levees some of the sediment has been lost, presumably removed or reworked by rainwater. Forecasting over the next 10 to 30 years it appears that bioturbation by burrowing organisms and eventually through root and rhizome propagation will destroy the integrity of the layer. This active bioturbation is apparent in the 21Pb core

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165 profile (Fig. 53) and in the fact that there are no other storm layers preserved in the modem stratigraphy. In some areas there may be enough contrast in grain size to preserve a diffuse storm signature (Fig. 64), but not likely one that can be visibly detected. On a long-term, regional scale there is little chance of preservation. The extremely low-gradient of the Florida platform and the shallow bedrock basement of the Waccasassa basin leave little accommodation space for sediment accumulation and preservation. The nearshore zone of Waccasassa Bay is already covered by only a thin to absent veneer of mainly reworked sediment (Fig. 27). Given the prediction of continued sea level rise it is most probable that the present day marsh system will ultimately transgress with little preservation of the modem coastal environment. However, depositional events such as this help to preserve the health and integrity of the marsh system, and in doing so may play a role slowing the transgression. From this viewpoint, storms could be considered to be agents that retard erosion and coastal drowning rather than promoting these effects The effects of this storm on the Waccasassa marsh systems may be indicative of the general importance of storm processes in marsh development and maintenance. Other studies have also suggested that storm-induced sedimentation is an important and sometimes dominant form of deposition in coastal marsh systems (Stumpf, 1983; Baumann et al., 1984). Research on the deteriorating wetlands of the Mississippi Delta and northem Gulf of Mexico have shown that hurricane-induced deposition has been a significant process in maintaining sedimentation rates along this rapidly subsiding coastline (Conner et al., 1988 ; Rejmanek et al 1988) Several studies have also implicated storms as the source of short-period pulses in sedimentation

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166 rates along the barrier-fronted marsh systems of the Atlantic coast (Stumpf, 1983; Stevenson et al., 1988) Despite the recent attention, however, the role of storms in coastal marsh deposition is still evolving. Results have shown that storms can be detrimental to these system as often as they are beneficial (Stevenson et al., 1988; Reed, 1989). Storms of the magnitude of the March 1993 event have only infrequently struck the southwest-oriented Big Bend coastline. As such this can be considered an unusual event, but the overall transport processes and pattern of sedimentation do suggest that storm events and perhaps daily processes may also operate in a similar fashion. Ultimately, whether this event and its effects are the exception or the rule, they are certainly a notable occurrence along this low-energy, sediment-poor coastline

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167 10. SUMMARY AND CONCLUSIONS In general the results of this investigation have given a broad, holistic understanding of the development, composition, and modem processes of this previously unstudied coastal system. By the conclusion of the research, the Waccasassa Bay area had proven to be an almost wholly different system than originally anticipated. It is certainly distinct from the coastal provinces to the north and south of the area, and may be unique to the entire Big Bend marsh shoreline 1. Waccasassa Bay and nearshore sediments The Waccasassa embayment proved to be a largely exposed, shallow-water, carbonate shelf with little to no sediment cover The initial suggestion was that this broad, basin-like feature might contain some significant thickness of sediment representing a source of material for the sediment-poor Big Bend coastline. This has not proven to be the case, and as such it should be considered a partially drowned, bedrock plain. The sediments that are contained.within the nearshore zone are dominantly composed of biogenic carbonate material, ranging from silt to gravel-sized shell hash, skeletal grains, and test fragments. Sidescan, seismic reflection, and probe rod data show that sediment cover is thin ( < 50 em) to absent over the broad, outer, and shallow portions of the bay. Thicker sequences are found locally in the deep offshore channels and at the head of the embayment. Sediments are also contained

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within large, shallow karst features which are located in widely scattered, loose fields across the embayment. 168 2. Waccasassa marsh stratigraphy. Like the offshore region, the stratigraphy of the expansive marsh system rimming the Waccasassa embayment is thin. Sediment thicknesses range from 1.5-2.0 meters along the outer marshes and shallow to one meter or less in the upper marshes. The indication is that the marshes are perched on a portion of the same broad, flat carbonate shelf which comprises the embayment. The sediments are composed of a series of mud units, with nearly equivalent proportions of clay and silt-sized material. The basal unit, when present, is comprised of variable pre-Holocene sandy muds containing quartz silts, marine biogenic material, and mixed-layer illite/smectite, kaolinite, and a chlorite-group clay. The overlying sequence of Holocene sediments is nearly identical in mineralogy to these older units and can be separated into five distinct facies. The facies in order of decreasing age are: (1) a black, organic-rich mud; (2) a gray, organic mud; (3) a clean, green mud; (4) a wet, blackish, organic-rich fresh/brackish marsh; (5) and a brown, muddy salt marsh. The depositional environment for all of these units in not certain, but they represent the transition from a forested, freshwater habitat through to the salt and brackish environment of the present-day system. The Waccasassa marshes are unique along the Big Bend coast, and among salt marshes in general, because the 'typical' marsh horizon across most the area is only 10-30 em thick, suggesting only recent formation of this habitat. 3 Evolution of the modem Waccasassa Bay system The preservation of a pre-Holocene, shelly facies beneath the modem marsh stratigraphy indicates that at some previous period, likely the Stage 5E highstand at

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169 about 120,000 BP, the area was transgressed and existed as a shallow-water, nearshore environment. Beyond that, there is no record or preservation of material from any time period until the middle Holocene. The first record of marine influence on the Waccasassa Bay area during the Holocene occurs around 5,500 BP. This date is recognized by the preservation of a wetland peat found within a karst feature in the offshore zone of the embayment. From this point it appears that the broad, exposed shelf of the modern bay was steadily trangressed by rising sea level. This coastal inundation gradually changed from one dominated by shoreline-retreat processes to one dominated by vertical accretion. It is this latter stage that has been responsible for the ultimate development of the healthy marsh systems found today. During the transgression period, the thin veneer of pre-Holocene shelly, muds covering the carbonate shelf was eroded, reworked, and transported in a shoreward direction This material was deposited on the evolving marsh surface by coastal transport processes. During approximately the past 2,000 years, the area has undergone the final stage of development, with the accumulation of eroded material comprising a sediment supply large enough to maintain the marsh system. 4. The modern Waccasassa Bay system and processes The results of this objective are largely qualitative conclusions based upon the distribution of sediments and preliminary measurements. Aerial photographs and suspended solid measurements from the bay suggest that there is an intensification of floodstage tidal currents across the embayment and perhaps specifically along the deeper central channels. This information and the distribution of nearshore sediments at the head of the embayment indicate that material is likely being transported in a landward direction and

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170 accumulating at the apex of Waccasassa Bay. A portion of this sediment is derived from the limited sediment supply within the bay, but this source may be augmented by an unknown source more seaward of the area. The presence of levees and the distribution of sediments deposited during a storm event indicate that there is more active sedimentation occurring at the head of the embayment. This phenomenon supports the idea that nearshore processes are controlling the distribution of sediments in the bay and in the marsh. Wind-induced resuspension may be an active process across the shallow sediment flats found across much of the upper bay during lower tides. Normal daily processes appear to have sufficient energy to affect sediment deposition and distribution in the Waccasassa Bay. Imprinted upon this daily signature is a strong, and perhaps dominant, storm signature. Results of a large storm in March 1993 suggest that storm and heavy wind events can significantly eff e ct, and sometimes benefit, the Waccasassa Bay marsh system through the reworking and deposition oflarge quantities of sediment. 5. The future of the Waccasassa Bay system The lack of fine sediments in Waccasassa Bay preclude the embayment as a current sediment source for the marsh coast in general, and probabl y for the local system as well. A significant transgression has already occurred during the past 5,000 years, and although the present system appears to be stable there is little material with which to maintain it. Accretion rate data suggest that the marsh systems of the project area are accreting at a rate just above that of sea level rise. With the absence of significant quantities of fluvial material and nearshore siliciclastics there is not the means with which the marsh system can ultimately maintain its elevation above sea level. If the sediment

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171 supply decreases, the sea level rates increase it is probable that the Waccasassa Bay system would transgress to a more landward position until it reaches another point of stability. At the present, however, the system appears to be both healthy and stable

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172 REFERENCES Applin, P.L., (1951), Preliminary report on buried pre-Mesozoic rocks in Florida and adjacent states : U.S. Geological Survey Circulation 91, 20 pp. Applin, P L., and Applin, E.R., (1967), The Gulf series in the subsurface in northern Florida and southern Georgia : U S Geological Survey Professional Paper 524. Anderson, J.U. (1961), An improved pretreatment for minerlogical analysis of samples containing organic matter: Proceedings of the lOth National Conference on Clays and Clay Minerals, Austin, Texas, pp 380-388. Arnold, J R and Libby, W.F., (1949), Age determinations by radiocarbon content: checks with samples of known age : Science, 110, pp. 678-680. Baumann, R H., Day Jr., J.W., and Miller C A., ( 1984), Mississippi deltaic wetland survival: sedimentation versus coastal submergence : Science, 224,pp. 1093-1095. Bloom, A L., (1964) Peat accumulation and compaction in a Connecticut coastal marsh: Journal of Sedimentary Petrology, 34, pp. 599-603. Boothroyd, J C ., (1985), Tidal inlets and tidal deltas in Davis, R.A., Jr., ed. Coastal sedimentary environments : New York, pp. 445532 Bouma, A H., (1963), A graphic presentation of the facies model of salt marsh deposits: Sedimentology, 2, pp 122-129 . Bruun, P (1962), Sea level rise as a cause of shoreline erosion: Journal of Waterways and Harbors Division American Society of Civil Engineering Proceedings, 88, pp. 117-130 Carr, W J and Alverson, D C (1959), Stratigraphy of middle Tertiary rocks in part of west-central Florida: U S Geological Survey Bulletin, pp. 1160 Chen, C.S., (1965), The regional lithostratigraphi c analysis of Paleocene and Eocene rocks of Florida: Florida Geological Survey Bulletin 45, 105 p

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173 Cohen, A.D and Spackman, W., (1972), Methods in peat petrology and their application to reconstruction of paleoenvironments : Geological Society of America Bulletin; 83, pp. 129-142 Conner, W.H., Baumann, R.H Day, Jr., J.W. and Randall, J.M. (1988), Influence of hurricanes on coastal systems along the northern Gulf of Mexico a review: Wetlands Ecology Management. Cooke, C W., (1945), Geology of Florida : Florida Geological Survey Bulletin 29, pp. 339. Crane, J.J., (1986), An investigation of the geology, hydrology, and hydrochemistry of the Lower Suwannee River Basin Florida Geological Survey Open File Report 96, 205 pp. Dahl, T.E., (1990), Wetlands losses in the United States, 1780's to 1980's: Washingtion D.C, U S. Fish & Wildlife Service, 21 p Dahl, T.E., and Johnson, C E., (1991), Wetlands status and trends in the conterminous United States mid-1970's to mid-1980's : Washington, D.C., U S. Fish & Wildlife Service, 28 p Dall, W H and Harris, G.D., (1892), Correlation papersNeocene: U.S Geological Survey Bulletin 84, 107 p Davis, R A Jr., (1985), Beach and nearshore zone, in Davis, R A., Jr., ed., Coastal sedimentary environments: New York, Springer-Verlag, pp. 379444. Dawes, C .J., (1981), Marine botany : New York, John Wiley & Sons, 628 p Day, J.W., Smith, W.G Wagner, P R., and Stowe, W C., (1973), Community Structure and Carbon Budget of a Salt Marsh and Shallow Bay Estuarine System in Louisiana : Publ. LSU-SG-72-04, Lousiana St. Univ., Center Wetland Res., Baton Rouge, LA, 79 p. Dixon, L K : (1986), Water Chemistry, Vol. 1 ofSouthwest Florida Water Management District: A data collection program for selected coastal estuaries in Hernando, Citrus, and Levy Counties, Florida, Brooksville, 259 p Dolotov, Y.S., (1992), Possible types of coastal evolution associated with the expected rise of the world's sea level caused by the Greenhouse Effect : Journal of Coastal Research, 8, pp. 719-726. Eleuterius, L N., (1972), The marshes of Mississippi : Castanea, 37, pp. 153168.

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174 Eleuterius, L.N., (1980), Tidal marsh plants -an illustrated guide to the tidal marsh plants of Mississippi and adjacent states: Mississippi-Alabama Sea Grant Consortium, Publication MASGP 77-039, 131 p. Evans, M.W., Hine, A. C., Belknap, D F., and Davis, R.A, Jr., (1985), Bedrock controls on barrier island development: west-central Florida coast: Marine Geology, 63, pp. 263-283. Evans, M.W., Snyder, S.W., and Hine, A.C., (1994), High-resolution seismic expression of karst evolution within the upper Floridan aquifer system: Crooked Lake, Polk County, Florida: Journal of Sedimentary Research, B64(2), pp. 232-244. Fairbanks, R.G., (1989), A 17,000-year glacio-eustatic sea level record: Influence of glacial melting rates on the Younger Dryas event and deep ocean circulation: Nature, 3421, pp. 637-642. Fernald, E.A., ed., (1981), Atlas of Florida: Florida State University Foundation, Tallahassee, 276 p. Fischer, A. G., (1951), The echinoid fauna of the Inglis Member, Moody's Branch Formation : Florida Geological Survey Bulletin 34 (Part II), 112 p. Fletcher, C H., III, and Wehmiller, J.F. eds., (1992), Quaternary coasts of the United States : marine and lacustrine systems: SEPM Special Publication 48,450 p. Florida Department of Natural Resources, (1971), A preliminary invesitgation: the effect of elevated temperature on the American oyster, Crassostrea virginica (Gmelin): Florida Department of Natural Resources Marine Research Laboratory Professional Paper Belies 15. Folk, R L (1980), Petrology of sedimentary rocks: Austin Texas, Hemphill Publishing Company, 185 p. Frey, R.W., and Basan, P.B., (1985), Coastal salt marshes, in Davis, R.A., Jr. ed., Coastal sedimentary environments: New York, Springer-Verlag, pp. 225-302. Garrett, C., Hertler, H., Hoenstine, R and Highley, B., (1993), Holocene sedimentation and coastal wetlands response to rising sea level at the Aucilla River mouth, a low energy coast in the Big Bend area of Florida, in 0., ed., Coastal Zone '93.

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175 Goodbred, S L and Hine, A. C., in review, Coastal stonn deposition along west-central Florida's marsh shoreline; effects of the 1993 "Stonn of the Century": Geology. Goodbred, S.L., Hine, A.C., and Stumpf, R P., (1993), Bedrock control on the development of a thin, sediment-starved coastal marsh system: Waccasassa Bay, Florida : Biennial Estuarine Resear c h Federation International Meeting, Abstracts with Program, Hilton Head, SC Hays, J D., Imbrie, J., and Shackleton, N.J., (1976), Variations in the Earth's orbit: pacemaker of the Ice Ages : Science 194, p 1121-1132 Healy, H G., (1975), Terraces and shorelines of Florida : Florida Bureau of Geology Map Series 71. Hicks, S D., Debaugh, H A., Jr., and Hickman, L.E., (1983), Sea level variations for the United States 1855-1980: Rockville Maryland, National Ocean Survey, 170 p. Hine, A C ., in press, Geological oceanography of the Florida platform, in Randazzo, A.F and Jones, D S. eds Geology of Florida Hine, A. C., and Belknap, D.F., (1986), Recent geological history and modern sedimentary processes of the Pasco, Hernando and Citrus County coastline : west central Florida : Gainseville, Florida, Florida Sea Grant Report 79, 166 p Hine, A C Belknap, D.F Hutton, J G., Osking, E B., and Evans, M.W., (1988), Recent geological history and modem sedimentary processes along an incipient, low-energy, epicontinental-sea coastline: northwest Florida : Journal of Sedimentary Petrology, 58, pp. 567-579. Hoenstirie, R.W., and Lane, E., (1991), Environmental geology and hydrogeology of the Gainesville area, Florida : Florida Geological Survey Special Publ. 33, 70 p Hoffman, J S (1984 ), Estimates in future sea level rise, in Barth, M.C., and Titus, J.G., eds. Greenhouse Effect and sea level rise: New York, Van Nostrand Reinold, pp. 79-103 Hull, J.P.D. (1962), Cretaceous Suwannee Strait, Georgia and Florida : American Association of Petroleum Geologists Memoir 36, pp. 118-122. JCPDS International Centre for Diffraction Data, (1988), Powder diffraction file : Inorganic phases : Swarthmore, PA, International Centre for Diffraction Data, 784 p

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176 Johnson, H.P., and Helferty, M., (1990), The geological interpretation of sidescan sonar: Reviews of Geophysics, 28(4), pp. 357-380. Kendall, C.G.St C., and Lerche, I., (1988) Rise and fall of eustacy, in Sea level changes: an integrated approach: Tulsa, OK, SEPM Foundation, Inc pp. 3-18. Klitgord, K.D., Popenoe, P., and Schouten, H., (1984), Florida: a Jurassic transform plate boundary: Journal of Geophysical Research, 89, pp. 7753-7772. Knapp, M.S., (1978), Environmental geology series : Gainesville sheet : Florida Bureau of Geology Map Series 79. Lane, E., Hoenstine, R.W., Yon, J W., and Spencer, S.M (1988), Mineral resources of Levy County, Florida Florida Geological Survey Map Series 116 Lanesky, D.E Logan, B .W., Brown, R.G and Hine, A. C (1979), A new approach to portable vibracoring underwater and on land: Journal of Sedimentary Petrology, 49, pp. 654-657. Leonard, L.A., (1994), Environmental and physical factors controlling sediment transport and deposition in microtidal marsh systems : implications for marsh stability : unpublished Ph.D. dissertation, Department of Marine Science, University of South Florida. Leonard, L A Hine, A. C., and Luther, M.E., in press, Suspended sediment transport and deposition processes in a Juncus roemerianus marsh, west-central Florida: Journal Coastal Research. Leonard, L.A., Hine, A C and Luther, M.E., and Stumpf, R.P., in press, Sediment transport processes in a west-central Florida open marine marsh tidal creek; the role of tides and extra-tropical storms: Coastal and Estuarine Science Matson, G.C., and Sanford, S., (1913), Geology and ground waters of Florida: U S Geological Survey Water-Supply Paper 319. McKinney, M L., (1984), Suwannee channel of the Paleogene coastal plain: support for the Carbonate suppression model of basin formation: Geology, 12, pp. 343-345. Meadows, P.E., Martin, J.B. and Mixson, P.R., eds., (1991), Water resources data for Florida, Water Year 1991: U.S. Geological Survey Water-Data Report FL-91-;4, 182 p

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177 Mehta, A.J Parchure, T.M., Dixit, J G., and Ariathurai, R., (1982), Resuspension potential of deposited cohesive sediment beds, in Kennedy, V., ed. E s tuarine Comparisons : Academic Press, New York pp. 591-609 Miller, J A., (1986), Hydrogeologic framework of the Floridan aquifer system in Florida and parts of Georgia, Alabama and South Carolina: United States Geological Survey Professional Paper 1403-B 91 pp. Mitsch, W.J. and Gosselink J G., (1993), Wetlands : New York, Van Nostrand Reinhold, 722 pp. Montgomery, C G., and Montgomery, D.D., (1939), The intensity of neutrons of thermal energy in the atmosphere at sea level: Physics Review, 56, pp. 10-12. Moore, D M., and Reynolds, R C Jr. (1989 ) X ray diffraction and the identification and analy s is of clay mine rals : Oxford University Press, New York, 332 p National Oceanic and Atmospheric Administration National Climatic Data Center, (1993 ) The Big One!May 14, 1993 update: Ashville, NC. National Oceanic and Atmospheric Administration, National Welands Inventory, Field, D.W Reyer, A.J., Genovese P .V., and Shearer, B D (1991), Coastal wetlands ofthe Unit e d States : U.S. Government Printing Ofllce, Washington, D .C. Opdyke, N D Spangler, D.P ., Smith, D.L., Jones, D S and Lingquist, R C., ( 1984 ) Origin of the epeirogenic uplift of PliocenePleistocene beach ridges in Florida and the development of the Florida karst: Geology 12, pp. 226-228 Parkinson, R W., (1989) Decelerating Holocene sea-level rise and its influence on southwest Florida coastal evolution : a transgressive/ regressive stratigraphy: Journal of Sedimentary Petrology, 59(6) pp. 960-972. Plummer, L N (1975 ) Mixing of sea water with calcium carbonate ground water: Geological Society of America Memoir 142, pp. 219-236 Poag, C W., (1991) Rise and demise of the Bahama-Grand Banks gigaplatform northern margin of the Jurassic proto-Atlantic seaway: Marine Geology, 102, pp. 63-130 Popenoe, P., Henry, V.J and Idris F M., (1987) Gulf Trough-the Atlantic connection : Geology, 15 pp. 327-332.

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180 White, W.A., (1958), Some geomorphic features of central peninsular Florida: Florida Geological Survey Bulletin 41, 92 p. White,. W A (1970), Geomorphology of the Florida peninsula: Florida Geological Survey, Bulletin 51, 164 p. Whitney, E., (1981), North Suncoast growth rate in past decade leads state: St. Petersburg Times, Business section, March 8, 1981, p 14D. Williams D.F., (1988), Evidence and agaipst sealevel changes from the stable isotopic record of the Cenezoic : in Sea-level changes : an integrated approach : Tulsa, OK, SEPM Inc., pp. 31-36 Winker, C.D., and Howard, J D., (1977), Plio-Pleistocene paleogeography of the Florida Gulf Coast interpreted from relict shorelines : Transactions -Gulf Coast Association of Geological Societies, 27, pp 409-420 Winston, G.O ., (1976), Florida s Ocala Uplift is not an uplift : American Association of Petroleum Geologists Bulletin, 60, pp. 992-994. Wolfe, S.H. ed., (1990), An ecological characterization of the Florida Spring Coast: Pithlaschascotee to Waccasassa Rivers : U.S Fish & Wildlife Service, Biological Report 90(21) 323 p. Wright, E.E., Hine, A. C and Stumpf, R P., (1993) Analysis of shoreline stability of the Suwannee River marsh system, west-central Florida: Biennial Estuarine Research Federation International Meeting, Abstracts with Program, Hilton Head, SC. Wright, E.E., Hine, A.C and Stumpf, R.P., (1993), Development of the Suwannee River marsh system, west-central Florida : American Society for Limnology and Oceanography I Society for Wetland Scientists Meeting, Abstracts with Program, Edmonton, Canada.

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APPENDIX 1 CORE LOGS 29 12' .... 29 08' KEY TO CORE SKETCHES sand f-.:1 mud I* ec h inoid tes t mollusk shell gastropod shell 82 52' organic sed i ment [1JJ u pland roots r-i>=i1 large, woody marsh plant 1 82

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APPENDIX 1. (Continued) elevation: -70cm msl Ocm 25 50 75 100 CORE 1.1 surface vegetation: (Juncus roemerianusl rii--:W--=--""%'1 %organic grain size: %sand. sitl. clay S:9, S:68, C:23 Iiron concretions 8:27, S:50, C:23 Q) c Q) (,) 0 0 I olive-gray muds with fibrous plant material olive-black muds minor unconformity Q) c dry, dusky yellow S:37, S:39, C:24 sandy muds c.. 183

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APPENDIX 1. (Continued) elevation: -ZOcm msl Ocm 25 50 75 100 125 0 25 %organic CORE 1.2 Cll c: Cll dusky yellowish brown (1 oYR 212) muds with f i brous plant material lt. olive-gray (sY 5 / 2) muds withdk. yellowish orange (1 oY 6/6) mottling g o soupy, olive-gray (SY 3 / 2) muds I 1-1-.......... ----f minor unconformity ....,..,...,.,_, ...... r _1 4c 29 6008P olive-gray, sandy muds g (echinoderm) 0 :I,= lt. olive-gray (SY 6 / 1 ) sandy muds a. 184

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APPENDIX 1. (Continued) elevation : -ZOcm msl Ocm 25 50 75 100 125 150 175 200 CORE 1.3 surface vegetation: (Juncus roemerjaausl 0 15 0% 50 100 %organic grain size <1l c <1l g 0 I olive-Qray (SY 411 l m.uds with fibrou-s prant matenal grayish-green (sGY 3/2) muds brownish-black (sYR 211) muds with detrital organics minor unconformity med. gray (N3) sandy clay 0 0 I I dry, olive-gray (sY 411) muds mottled with dk. yellowish-orange (1 oYR 6/6) major unconformity <1l c <1l g w 185

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APPENDIX 1. (Continued) e leva t ion: -50cm msl Ocm 25 50 75 100 1 25 150 175 0 .. I % org anic CORE 3 2 surface vegetation: (Juncus roemerianus)l (Ciad ium jamaicense) 60 wet clean black (N 1 ) peats dk gray (2.5Y 4/1) muds with olive-yellow (2 5Y 6 /S) mottling carb o nate rock fragments associated with mottling 0 0 I a. similar to over lying un i t except sed iments are dry and stiff major un con f o rmity Q) c Q) g UJ 186

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187 APPENDIX 1. (Continued) elevation : -60cm msl Ocm 25 50 75 100 125 0 50 %organic CORE 3.3 C1l c: C1l 0 I wet, clean, black (2.5Y 2 5 / 1) peats minor unconformity C1l c: C1l g 0 I brown-gray, sandy muds a.

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APPENDIX 1. (Continued) elevation : -80cm msl Ocm 25 50 75 100 125 150 CORE3.4 surface vegetation : Juncus roemerianus o.---_.....:2=-:;5 188 dk. gray (5Y 3 / 1) muds with fibrous plant material dk. g r een-gray (SGY 4 / 1) muds black ( 1oYR 211 ) muds olive-g r ay (SY 3 /1) sandy muds lt. olive (sY 6 / 3) sandy muds

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APPENDIX 1. (Continued) elevation: -10cm msl Ocm 25 50 75 100 125 surface : oyster reef CORE 3.6 Q) c Q) u 0 0 I oyster and shell material with dk. green-gray (SG 4/1} mud matrix similar to overlying unit but less mud and shens oriented horizontally gray-orange (1 oYR 7/4) silts Q) g 0 I I 0. 189

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APPENDIX 1. (Continued) elevation: -200cm msl Ocm 25 50 75 100 125 150 175 200 CORE 3 7 surface : shelly muds clean shell lag olive-gray (5Y 3 /1) muds oyster and shell material with olive-gray (5Y 3 / 1) mud matrix brown-black (5YR 211) organic-rich muds carbonate rocks with brown black (5YR 211) mud infill 190

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APPENDIX 1. (Continued) CORE 6 1 surfa c e vegetat ion : ele vation : trees (Juniperus silicico/a) I (Sabat oalmettol 25 50 75 dry, black (SY 2 5/2) soil dry, elk. gr:ay-brown (10YR 3/2), sandy so1ly, clay Jt. yellowish brown (2 .5Y 6 / 4) muds (oxidized green muds) grayish-green (10GY 5/2) muds 1"C1 1 70BP (terre s trial ga s tr opod) 100 125 root cast m ois t dali< gray (SY 4 /1) muds dense, black (SY 2.5/1) clays with detrital organics Jt. gray (SY 7 / 1) sandy muds 191

PAGE 207

192 APPENDIX 1. (Continued) elevation : -ZOcm msl Ocm 25 50 75 100 125 150 CORE 6.2 0 I surf ac e vegetat ion: (Juncu s ro e meri an us) I fC/adjum J a m aic e nse / 20 %or ganic black ( 10YR 211), organic-rich sands mo ist, dk brown (10Y R 212) muddy sands moist, gray-brown (2 5 Y 5 / 2) silty sands lt. olive-br o wn (2 5Y 5 / 4 ) sandy muds with yellow (2 5 Y 7 /6) mottling wet dk gray-brown ( 2 5Y 4 /2) silty sands lt. oli ve-brown (2 .5Y 5 /6) s i lty san9s

PAGE 208

APPENDIX 1. (Continued) elev ation: -50cm msl Ocm 25 50 75 100 30 %organics CORE 6.3 dk. gray-brown{1 oYR 3 / 2) rooty organ i c-rich muds 0 0 :r: minor unconformity (1) c (1) g 0 :r: dk gray { 10YR 311) sandy muds a. lt. gray {1 oYR 6/1 ), friable carbonate rock 193

PAGE 209

APPENDIX 1. (Continued) elevation : -BOcm msl Ocm 25 50 75 100 125 150 175 0 40 ---I I % organics 194 CORE6.4 mucky, dk gray-brown {10YR3/2) muds with fibrous plant material <1> c black (10YR 211), dense, organic-rich muds g dk gray (SY 3 / 1), layered silty, sandy clays minor unconformity wet, dk gray muddy sands <1> g 0 I I a. lt. gray (sY 7 / 1) sandy muds

PAGE 210

APPENDIX 1. (Continued) elevation: -ZOcm msl Ocm 25 50 75 100 %organics CORE 6.5 dk. gray-brown (10YR 3/2} rooty, organic-rich muds dk. gray (1oY 4 / 1} muds with iron concretions wet, dk. gray (5Y 3/1} muds 195

PAGE 211

196 APPENDIX 1. (Continued) elevation : -80crn msl Ocm 25 50 75 100 125 150 175 200 CORE 7.1 surface vegetation: (Juncus roemedanusl 100 grain size dk. gray-brown (1oYR 3/2) muds with fibrous plant material olive-gray (5Y 5 /2) muds (oxidized green muds} green-gray (5G 5 /1) muds dk gray (7.5Y 3 / 1) muds black (2 .5Y 2.5/1) muds with detrital organics

PAGE 212

APPENDIX 1. (Continued) elevation : -?Ocm msl Ocm 25 50 75 100 125 175 0 CORE 7.2 surface vegetation: (Juncus roemer i anusl grain size : 20 %sand. sitt. clay __..... ,...............,,_ ........ S : 3 S:59, C:38 dk. gray-brown {1 ovR 3 / 2) muds with fibrous plant material olive-brown {2.5Y 4 / 3) muds (oxid i zed green clay) S:2 S : 59 C : 4o dk. green-gray (5G 411) muds % organ i cs dk. gray (5 Y 4 / 1) muds lt. brown-gray (SY Z / 1) muds and fractured carbonate rock 197

PAGE 213

198 APPENDIX 1. (Continued) elevation : -50cm msl Ocm 25 50 75 100 125 150 175 0 %organics CORE 7.3 surface vegetation : (June us roemerianus) I (C/adjum jamajcense) grain size med. brown, compacted peaty material similar to above, but with more muds dk. brown-gray sandy muqs to muddy sands

PAGE 214

APPENDIX 1. (Continued) e l evation: -ZOcm ms l Ocm 25 50 75 100 CORE7.4 dk. brown, peaty marsh sediments dk brown, muddy marsh sedimsnts dk gray-brown muddy sands 199

PAGE 215

APPENDIX 1. (Continued) elevation : -Ocm msl Ocm 25 50 75 100 125 150 175 200 surface : oyster reef CORE 7 5 oyster and shell material with pale brown (1 oYR 6 / 3) mud matrix oyster and shell material with dk. gray-brown (10YR 4 / 2) mud matrix oyster and shell material with gray black (N2) mud matrix dry, lt. gray (sY 7 /1) sandy muds 200

PAGE 216

APPENDIX 1 (Continued) elevation : -90cm msl Ocm 25 50 75 100 125 150 175 200 225 0 30 CORE 7 6 gra i n size : % sand. silt. clay dk yellow-brown (10YR 412) muds 201 dk green-gray (SG 411) muds dk gray (2 5Y 3 / 1) muds lt. brown-gray (1 ovA 6 / 2) sandy muas

PAGE 217

APPENDIX 1. (Continued) elevation: -ZOcm msl Ocm 25 50 75 100 CORE 7.7 surfa ce vegetat i on: (Juncus roemedanusl %organic ...---.II-..IL.,-, grain size : %sand. silt. clay S:1, s:s9, C: 40 olive black (SY 211) muds with f i brous plant material !iron concreti ons S : 1 S:57, C : 42 dk. gray (SY 4/1) muds S :6, s:s4, C :41 with fibrous plant material dk gray muds 202

PAGE 218

203 APPENDIX 1. (Continued) elevation: -50cm msl Ocm CORE 7.8 surface vegetat i on: (June us roemerianus) I (C!adiurn jamajcense / grain s i ze : %sa nd. clay .,.,.J.-.1.-............. s :s. S : 67 c:2a olive-black (5Y 211) muds with fibrous plant material 25 wet, dk. gray (sY 411) muds 50 75 100 S :28, S :47, C:26 minor unconfor mity with fibrous plant material rock fragements with dry dk. yellow-orange (1 oYR 6 /6) S:42 S : 32, C :26 mud matrix

PAGE 219

APPENDIX 1. (Continued) elevation: -60cm msl Ocm 25 50 75 100 125 150 175 CORE 7.9 surface vegetation : 0 grain size %organic dk gray-brown (1oYR 3/2) muds with fibrous plant material dk. green-gray (5G 4 / 1) muds dk gray (5Y 411) muds 204

PAGE 220

APPENDIX 1. (Continued) elevation : 60cm rnsl Ocm 25 50 75 100 0 50 % organic CORE 7.10 grain size : %sa nd s jtt. clay S :1, S : 57 C :41 S: 1 S : 58 C :41 S : 1 S : 59 C : 40 S : 1, S : 57 C : 42 S : 6, S :5 3 C:41 205 fibrous plant material with dk. gray {1 oYR 3 / 1) muds wet, compact peats with dk. gray (sY 4 / 1) muds S:10 S:53, C:37 black (10YR 211) organic-rich muds

PAGE 221

APPENDIX 1. (Continued) elevation : -ZOcmmsl Ocm 25 50 75 100 125 150 175 0 CORE 7.11 surface vegetation : (Juncus roemer i anu s ) 30 grain size : %sand. sjlt. clay S:Z, S:59, C :34 brown-gray (SYR 4) muds with fibrous plant material lt. brown-gray (10Y 6 / 2 ) muds (oxidized green muds) green-gray (SG 6 / 1) muds dk. gray (2 5Y 3/1) muds 206

PAGE 222

APPENDIX 1. (Continued) elevation: -80cm msl Ocm 25 50 75 100 125 150 0 30 %organics CORE 12.1 sur1ace vegetation: fDisticblls grain size : %san d. sitt. clay S:4 5 : 58, C:38 sand layer, storm? b l ack (5Y 2 5/1) muds with fibrous plant material dk gray (5Y 3/1) muds S:1 1, S :53, C : 35 0 :r: minor unconformity Cll :"7 _;;:;;';_-: dk. gray (5Y 3/1) sandy muds 0 5 :40,5:37, C:23 .. - c. 207

PAGE 223

APPENDIX 1. (Continued) elevation : -20cm msl Ocm 25 50 75 100 125 150 CORE 12.2 surface: jntertjdal flat dk. green-gray (SG 411) muds graded contact dk. gray (N3) muds med gray (N4) sandy muds 208

PAGE 224

APPENDIX 1. (Continued) elevation : -60cm msl Ocm 25 50 75 100 125 150 175 grain size %organic CORE 12.3 surface vegetation : (Juncus roemerianusl dk. gray-brown muds olive-gray (5Y 5/ 2) muds (oxidized green muds) green-gray ( 5G 5 /1) muds dk. gray (5Y 4 / 1) muds 209

PAGE 225

APPENDIX 1. (Continued) elevation : -BOcm msl Ocm 25 50 75 0 40 %organics CORE12.4 CD c CD 0 0 I wet black peats wet, black muds with fibrous plant material moist dk. brown-gray muds with detrital organ1cs F=5:-..,..,<=w=::-.l minor unconformity CD c CD g dk brown-black sandy muds 0 I a, 0.. 210

PAGE 226

APPENDIX 1. (Continued) elevation : -ZOcm rnsl Ocm 25 50 75 100 125 0 60 0 % 50 %organi cs CORE 12.5 surfa ce vegetation: (Juncus roemerianus) 211 dk. brown muddy peats wet, clean, dk brown peats

PAGE 227

APPENDIX 1. (Continued) elevation: 10cm msl Ocm 25 50 75 100 125 150 surface: river bank -.----......_ - -_-_ ..... ---. --. CORE 12 6 olive-black (5Y 211) sandy muds olive-gray (5Y 4 / 1) muds pale orange (10YR S / 2) silts (dolosilts) dk. yellow-orange (1 oYR 6/6) sandy muds 212

PAGE 228

APPENDIX 2. PERCENT ORGANIC AND MOISTURE VALUES FROM CORE SEDIMENTS. depth Core 1.1 Core 1.2 Core 1.3 Core 3.2 Core 3.3 Core 3.4 Core 6.2 Core 6.3 em %wt. %wt. %wt. %wt. %wt. %wt. %wt. %wt. %wt. %wt. %wt. %wt. %wt. %wt. %wt. %wt. org. moist org. moist org. moist org moist org. moist org. moist moist org moist 16.9 69.9 11.1 59.8 7.0 50.5 7.9 51.8 5 16. 7 64.8 24.0 74.7 11.9 61. 6 61. 9 88. 5 38.4 81.2 18 .0 68.5 16. 9 69. 6 10 15.5 65.4 19.3 72.5 9 2 57 5 2 6 34. 5 13. 3 61. 5 15 68. 6 13 8 67.4 5 1 47 7 22.2 74. 6 20 15.4 67.9 13 3 66.5 5 1 49. 3 53. 9 84. 4 47. 4 82.1 2.1 28. 9 23. 4 72.2 25 10. 4 58. 1 11. 4 66.0 3 1 42. 6 13 1 59.6 30 17 7 67. 4 3 .6 48.7 2.0 32. 5 29. 3 78. 1 35 6.8 58. 7 5 2 60. 6 36. 4 82. 5 42. 3 86. 3 8 8 59. 1 40 6 5 63.0 0 8 21. 2 4 6 41.4 45 6 4 64. 0 2 9 45. 8 50 7 1 58. 8 4.0 58.1 1 2 7 61. 2 14 6 68.6 7.6 56. 3 0 9 21 8 3.5 35. 4 55 4.9 58.5 60 4.3 53.0 4.3 54.9 1.2 28.0 4.3 40. 4 65 4.1 55. 5 9 6 55 9 14 7 68 5 11.3 60.5 70 6 3 50. 3 5.0 55. 8 1 5 29.7 7 1 55. 3 75 5.4 58 6 5 6 62. 7 8.0 50. 1 80 6 0 61.2 4 8 47. 7 2.4 26.2 1 .6 29.6 8.0 46. 3 85 4.0 51.0 90 3 8 31.8 6.0 61. 0 7.5 64. 0 4.0 40.0 0 9 22. 0 95 2 8 24. 2 100 6 2 34.0 0 6 18. 6 105 7 9 64. 6 3 6 40 1 4 0 37.1 110 3.4 32. 9 2 5 22. 6 0 7 18 7 115 120 6 1 53.2 1 7 27. 9 0 8 23. 1 125 130 2 9 33 7 0 6 22. 4 135 6 8 55. 8 140 0 3 20. 2 145 0.6 17 7 150 3.7 45. 8 155 2 7 29.6 160 165 1 7 26.1 170 1 0 24. 4 175 180 1 6 23.3 185 190 195 4.9 23. 7 200 205 213

PAGE 229

214 APPENDIX 2. (Continued) depth Core 6.4 Core 6.5 Core 7.1 Core 7 2 Core 7.3 Core 7 6 Core 7 7 Core 7 8 em %wt. % wt. % wt. % wt. %wt. %wt. %wt. %wt. % wt. %wt. %wt. %wt. %wt. %wt. %wt. %wt. org. moist org. moist org. moi s t org. moist. org. moist org. moist org moist Q!K. moist 30. 6 76 9 18.8 69 5 9.7 51. 0 13 3 60. 4 34 0 82.7 12.3 n 2 13 3 76.7 5 32. 0 n 6 15 4 63. 7 15 8 82. 4 13. 9 79. 6 10 0 0 79.0 20. 5 71. 6 8 1 48. 4 10 8 57 7 45. 9 86. 2 13 7 79. 6 15 29. 6 79. 9 4 5 56 1 17 1 82. 9 17 5 81 3 20 30. 5 80.8 23.3 70. 5 3 4 35. 0 43. 3 84 3 10.8 78. 3 25 31. 4 80.9 3 7 56. 3 17 5 83. 1 13 2 79. 7 30 32. 5 81.2 2 6 35. 3 40. 0 85. 2 7 2 80. 6 35 34. 0 82. 1 15 6 69. 2 16 4 83. 3 6 9 71. 6 40 32. 1 81. 5 2 7 35. 9 6 7 60. 5 32 4 81. 2 8 6 78. 9 45 33. 0 80. 2 14 7 83. 3 3 1 61. 5 50 27. 9 79. 1 18 0 67. 9 3 0 39 1 14 8 63. 9 9 8 78.7 55 31 6 79. 8 2 6 52 6 60 27. 4 78. 9 42. 7 82. 7 11. 1 81. 0 13 6 81. 4 2 1 51. 7 65 25. 5 78. 4 15 7 64. 6 70 30. 2 n.o 3 4 47 5 5 6 57 5 45. 2 82.2 11. 2 81. 8 75 17 7 72. 2 1 9 48. 8 1 6 51. 7 80 11. 1 62. 1 6 0 53 8 27. 7 75.9 11. 8 8 2. 1 85 10. 6 62. 1 7 1 62. 6 90 7 9 54. 4 6 9 55 0 22. 6 76.5 8.7 n o 5 7 60. 8 95 2.7 39. 1 100 1.9 30. 2 6 8 63.0 18 4 69.7 6 4 79.2 105 110 2 4 25. 9 17 5 65.8 19 0 66.2 7.9 76.5 115 120 1 6 25. 8 5 8 56. 1 1 5 22. 6 5 5 70. 4 125 130 1 2 27.9 16 7 69. 5 7 7 53. 5 5 9 75.0 135 1 4 24. 7 140 14 1 43. 6 4 6 69. 5 145 1 4 24. 1 150 30.0 70.0 2 0 30.2 4 0 68. 9 155 160 0 9 19.3 26. 3 87. 2 165 1 4 25. 3 170 27. 0 73. 4 6 9 66. 0 175 180 3 6 60. 7 185 13 1 56.0 190 195 200 6 5 49. 8 205 3 .0 54. 9

PAGE 230

215 APPENDIX 2. (Continued) depth Core 7.9 Core7.10 Core7.11 Core 12 .1 Core 12.2 Core 12. Core 12.5 em %wt. %wt. %wt. %wt. %wt. %wt. %wt. %wt. %wt. %wt. %wt. %wt. % wt. %wt. org. moist org. moist ora:. lmoiat ora:. ora:. hnoiat ora:. hnoiat org. moist 20. 7 85. 6 11.4 59 0 22.9 70. 5 5.2 39.2 22 2 75. 4 27.5 76. 1 5 24. 3 85. 0 43 2 90 1 10 17.0 81. 8 38.5 88. 8 8 9 50.4 23.3 72. 0 2 5 30.8 33.0 78.9 37. 2 79.0 15 15.6 79.8 20 31. 4 89.8 4 4 44. 1 27. 7 76.5 2 0 31.1 28.0 78. 0 33. 8 77. 6 25 5 4 74. 5 34. 3 79. 1 30 31. 9 88. 0 31.2 78. 6 20.5 79 6 29.6 80. 3 35 5.0 75.2 4 6 52 5 2.0 33.7 55.3 78.9 40 19.7 88. 9 23 4 76. 8 16 9 78.9 43.1 84.5 45 5.2 74. 9 50 17.9 71 6 1.8 30. 3 17.5 77.9 33. 8 55 5.4 78. 0 14.6 84. 4 3 7 51.6 60 14.5 70.0 17.0 76.4 44. 0 84.1 65 6.2 77.5 2 1 35. 3 70 17. 6 85. 2 11. 4 68. 0 17.6 76.3 36.5 81. 1 75 9 4 78.5 3.7 51. 9 80 8 8 64. 4 2.3 37.9 17.5 74.9 25. 4 77.4 85 8.4 74 7 19.5 84.9 90 6 1 59 3 13.7 74. 7 18.0 74.9 95 5 8 64. 5 6 7 60. 0 2 5 39.3 100 21.8 87. 0 8 3 58 .5 19.0 75.4 105 4.1 62 8 110 2 5 42 7 3.0 46. 1 3 .4 50.4 115 3 8 68. 1 23.6 85. 4 8 5 59 6 120 3 4 50. 6 11.4 65.9 125 4.3 67.4 5 .5 48.6 130 17.9 84. 6 16.4 51. 1 135 2 .3 59. 5 11.4 58. 8 140 8 4 55. 0 10.3 63. 0 145 2 8 63. 4 17 4 81 2 150 30.6 74.1 155 5.7 66.6 160 11. 8 75. 1 6.7 48. 9 165 14 4 78. 3 170 14.7 69 4 175 180 185 190 195 200 17.8 68 8 205 210 215 220 225 230 13. 7 62. 3 235 240 245 250 5 .2 44 1 255 260 265 270 : 2 1 28.4

PAGE 231

216 APPENDIX 3. GRAIN SIZE ANALYSIS FROM CORE SEDIMENTS. Core 1.1 Core 1.3 Core 7.1 Core 7.2 Core7.3 depth sand silt clay sand silt clay sand silt clay sand silt clay sand silt clay 0 10 4 59. 3 30. 3 5 9 4 67. 5 23. 2 14. 1 56.1 29. 9 12 4 61. 9 25. 7 1 9 61. 7 36. 3 6 8 55. 6 37. 6 10 47 1 40. 6 12 3 15 39. 9 44 0 16 1 20 2.9 59. 1 38. 1 25 40. 2 43. 2 16 5 11.0 52. 7 36. 2 30 23. 1 52. 2 24 7 35 32. 1 45. 6 22. 4 40 1 3 59. 9 38. 7 45 30. 2 47.9 21. 8 50 26. 9 50. 1 23.1 38. 9 39. 9 21.2 55 23. 6 51.6 24. 9 60 11. 9 55. 4 32. 7 1 9 58. 7 39. 5 65 27. 4 49. 4 23. 2 70 75 17.2 52.2 30.6 31 6 38. 4 30. 0 80 85 13 .8 52.0 34. 2 29. 8 39. 5 30. 7 90 4 9 53. 4 41. 7 95 37. 1 39. 0 23. 8 8 5 46. 9 44. 6 100 46.2 30. 1 23. 7 105 12.5 51 1 36. 5 110 21.0 44. 3 34.8 115 7 5 54. 6 37. 9 120 20. 9 43.1 36. 0 125 130 74.5 14 6 11. 0 135 4 8 54. 5 40. 7 140 145 5 2 53. 0 41.8 150 155 14 3 49. 3 36. 4 160 51 0 28.2 20. 8 165 170 175 26. 2 42. 1 31 7 180 185 190

PAGE 232

217 APPENDIX 3. (Continued) Core7. 6 Core7.7 Core7.8 Core 7.9 Core 7.10 d epth sand silt clay sand silt clay sand silt clay sand silt clay sand silt 0 5 1 0 59. 1 39. 9 4.9 66. 8 28.3 2 0 58. 2 39.8 1 3 57.4 41. 3 10 15 20 1.2 57.3 41. 5 1 3 57. 5 41. 2 25 3.2 61. 6 35.2 30 2 9 57. 7 39. 5 35 40 5 6 53.8 40.5 27.5 46. 8 25. 7 1 1 58. 6 40. 3 45 50 1 6 58. 6 39.8 55 5.8 53 8 40. 4 60 65 70 1 4 60.5 38. 2 42 0 31. 8 26.2 1 .0 57. 3 41.6 75 2 2 55. 4 42.5 80 82. 9 9 8 7 3 85 90 95 100 37 3 37.1 25.6 105 110 6.0 53. 3 40. 7 115 2 5 64. 9 32.6 120 28.8 42. 0 29.2 12 5 130 135 140 145 54 8 28. 0 17.2 150 9 7 53. 4 36. 9 155 160 165 40. 5 36.5 23 .1 170 175 180 185 190 24. 1 51. 2 24 7

PAGE 233

218 APPENDIX 3. (Continued) depth Core 7 .ll Core 12.1 Core 12. 3 Core 12. 5 (em) .sand silt clay sand silt clay sand silt c l ay sand silt clay 0 5 7 3 59.1 33.6 1 6 59 6 38. 8 58. 1 27. 6 14 3 10 15 3 9 61. 3 35.6 20 25 46.2 33. 1 20. 7 30 12. 6 58.1 29.3 35 40 45 50 47 5 32.6 19.9 55 3 8 61. 1 35. 3 60 11.2 53.2 35. 6 65 7 0 75 45. 6 33.5 21.0 17.4 54. 7 28.0 80 85 90 1 7 59. 2 39.2 95 10 0 16 .8 48. 8 34.4 43 7 33.3 23.0 105 110 1 9 53.7 44.5 115 3 4 59. 9 36. 8 120 125 130 36. 0 36. 2 27. 7 135 140 31 4 39. 9 28. 7 145 15 0 155 160 165 170 175 180 185 190

PAGE 234

APPENDIX 4. PERCENT ORGANIC, CARBONATE, AND SILICICLASTIC VALVES FROM OFFSHORE GRAB SAMPLES ...... ( .. ; ....... ...... l : .. (> : .. Kilomete rs 0 1 2 219

PAGE 235

220 APPENDIX 4. (Continued) SAMPLE % % % ORGANICS CARBONATE SILICICLASTIC 12-19 2.54 56 8 40.7 6-2 1.91 31. 8 66 3 12-15 2 03 78.0 19.9 6-6 7.57 14.3 78.1 6-5 10 92 37.0 52.1 1(}-A 2 .38 72 1 25 5 12-9A 3.71 39.7 56.6 12-518 5 85 58 9 35 2 12--42 2 56 50 8 46 7 12-32 2 72 69 0 28 3 12-13 1 55 38.2 60 2 12-14 2 19 88.5 9 3 12-25 2 05 63.8 34 2 6-1 2 62 56 .2 41. 2 12-9C 2 62 36 2 61. 2 12-12 1 .8 8 64 2 34 0 12-11 4 06 47.9 48 0 12-9 2 89 48 6 48 5 6-9 14 19 18.0 67. 8 12-10 2 .25 67. 2 30 5 6-3 2 23 82.7 15 1 12--49 2 23 69.4 28.3 1 C}-31 3.14 94 6 2 3 1(}-30 1 .96 88 7 9.3 1(}-25 2.27 46 7 51. 0 6-4 2 08 67.7 30.2 1 C}-31 3.49 93. 0 3 5 1(}-8 1 79 73. 4 24.9 12-51A 13 47 50.0 36 5

PAGE 236

APPENDIX 5. GRAIN SIZE ANALYSIS FROM OFFSHORE GRAB SAMPLES. SAMPLE# %CLAY %SILT %MUD %SAND %GRAVEL 12-19 7.8 3.8 11.6 74.4 14 6-2 6 5 2 8 9 3 88.5 2 2 12-15 2 4 1.4 3 9 85.7 10. 4 6-6 10. 5 6 2 16. 7 83.3 0 6-5 23. 2 25. 7 48.9 51.1 0 10-A 2 5 1 .8 4.3 91.5 4 1 12-9A 6 8 9 9 16.7 83.3 0 12-518 15. 8 11 .2 27 69.6 3.4 12-42 7 3 4 9 12. 1 87. 9 0 12-32 3 6 2.4 6 91 3 2.7 12-13 4 3 1 7 6 93.6 0 4 12-14 0 3 0 0 3 91.6 8.1 12-25 3 8 2 5 6.3 93. 1 0 6 6-1 11.2 0 11 .2 85. 8 2 9 12-9C 5.4 8 13.5 81 5 5.1 12-12 5.4 1.5 6 9 77. 9 15.3 12-11 10. 1 7 6 17. 6 82.4 0 12-9 7 7 5 6 13. 3 83. 2 3 5 6-9 7.6 14.8 22.4 77.6 0 12-10 5.1 3 1 8 2 82. 7 9.1 12-49 7 3 6 3 13. 6 54. 6 31.8 10-31 2 8 1 3.8 67 29. 2 10-30 2 6 0 5 3.2 84 12.9 10-25 6 8 3 9.8 84. 9 5 3 6-4 5 5 1 10. 1 64. 5 25. 4 10-8 5 2 1 6 6 8 92. 5 0 7 12 51 A 32. 9 25.4 58. 3 41 7 0 221


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