Stratigraphic framework of a mixed siliciclastic/carbonate inner-shelf sand-ridge system, West-Central, Florida

Stratigraphic framework of a mixed siliciclastic/carbonate inner-shelf sand-ridge system, West-Central, Florida

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Stratigraphic framework of a mixed siliciclastic/carbonate inner-shelf sand-ridge system, West-Central, Florida
Edwards, James H. 1971-
Place of Publication:
Tampa, Florida
University of South Florida
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Physical Description:
ix, 133 leaves : ill. (some col.) ; 29 cm.


Subjects / Keywords:
Geology, Stratigraphic -- Florida -- Gulf Coast ( lcsh )
Rocks, Carbonate ( lcsh )
Continental shelf -- Florida ( lcsh )
Dissertations, Academic -- Marine science -- Masters -- USF ( FTS )


General Note:
Thesis (M.S.)--University of South Florida, 1998. Includes bibliographical references (leaves 93-101).

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Source Institution:
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:
025878959 ( ALEPH )
41463664 ( OCLC )
F51-00025 ( USFLDC DOI )
f51.25 ( USFLDC Handle )

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Graduate School University of South Florida Tampa, Florida Master's Thesis This is to certify that the Master's Thesis of JAMES H. EDWARDS with a major in Marine Science has been approved by the Examining Committee on September 25, 1998 as satisfactory for the thesis requirement for the Master of Science Degree Examining Committee: Major Professor: Albert C. Hine, Ph.D. Gregg R.13rooks, Ph.D. Member: Stanley D. Locker, Ph.D. Member: David C. Twichell, Ph.D.


STRATIGRAPHIC FRAMEWORK OF A MIXED Sll.JCICLASTIC/CARBONA TE INNER-SHELF SAND-RIDGE SYSTEM WEST-CENTRAL FLORIDA by JAMES H. EDWARDS A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Department of Marine Science University of South Florida December 1998 Major Professor: Albert C. Hine, Ph.D


DEDICATION I would like to dedicate this thesis to my parents. They are truly the best role models, friends and parents a son could ever have and none of this could have been possible without their love and support. They stressed the importance of education throughout my life and this thesis is a direct result of it. Thanks mom and dad, I love you.


ACKNOWLEGDEMENTS I would like to thank my committee members Dr. Albert C. Hine, Dr. Stanley D. Locker, Dr. Gregg R. Brooks and Dr. David C. Twichell for the many years of guidance and insight through the years. They are great mentors as well as friends. Particularly, I would like to thank my major advisor Dr. Hine for giving me the opportunity and steering me in the right direction when things looked dim, Dr. Locker for an enormous amount of help and technical support, Dr. Brooks for his long term commitment to my education beginning back at Eckerd College; and Dr. Twichell for his comments and suggestions. I would also like to extend my gratitude to the United States Geological Survey for funding my research through the West-Central Florida Coastal Studies Project and Florida Atlantic University for the use of the area's chirp sonar data. Finally, I would like to thank all of my friends that assisted me with the study. I appreciate the help. Sorry I could not list everyone's name.


TABLE OF CONTENTS LIST OF TABLES ............................................................................ iii LIST OF FIGURES .......................................................................... iv ABSTRACT ................................................................................... vii 1. INTRODUCTION ......................................................................... 2. PREVIOUS INVESTIGATIONS ....................................................... 6 Sand-Ridge Characteristic .......................................................... 6 Regional Setting Characteristics of Sand-Ridge Fields ........... .... 6 Sand-Ridge Dimensions .................................................. 7 Sand-Ridge Morphology ................................................... 9 Sediment Character ........................................................ 9 Sand-Ridge Provinces .............................................................. 11 Inner Shelf Sand Ridges ................................................... 11 Middle Shelf Sand Ridges ................................................. 15 Tidal Sand Ridges ........................................................... l8 Carbonate Sand Ridges ..................................................... 19 Ancient Sand Ridges .............................................. ......... 19 Previous Sand-Ridge Investigations in Study Area............................ 20 Sea Level. ............................................................................. 24 3. METHODS ................................................................................. 26 Geophysical Data Collection ....................................................... 26 High-Resolution Seismic Reflection Profiling .......................... 26 Chirp Sub-Bottom Profiles ................................................ 27 Side-Scan Sonar ............................................................. 27 Sediment Data Collection ............................................................ 29 Vibracores .................................................................... 29 Sediment Analyses ................................................................... 29 Grain Size Analyses ........................................................ 29 Percent Calcium Carbonate ................................................ 30 Mineralogy ................................................................... 31 Dating ......................................................................... 31 Pretreatment. ........................................................ 31 Analysis ............................................................. 32 Reported Dates ..................................................... 32 4. RESULTS .................................................................................. 34 Vibracore Analyses .................................................................. 34 Pre-Holocene Sedimentary Facies .................................................. 34


Limestone Gravel Facies ................................................... 34 Blue-Gray Clay Facies ................................ ....... .............. 39 Holocene Sedimentary Facies ...................................................... 39 Organic-Rich Mud Facies ......... ......................................... 39 Muddy-Sand Facies ......................................................... 44 Shelly Facies ................................................................. 44 Siliciclastic/Carbonate Sand Facies . ..................................... 47 Fine Sand Facies ........................................... ................ 51 Dating Analyses ...................................................................... 51 Side-Scan Sonar Analyses .......................................................... 54 Sand Ridge Distribution and Morphology ............................... 54 Side-Scan Sonar Mosaic Time Series ..................................... 55 Distribution ................................................. ................. 57 Sub-bottom Analyses ............................................. ... ................ 57 5. DISCUSSION ............................................................................. 69 Depositonal Environments of the Seven Sedimentary Facies ................... 69 Limestone Gravel Facies ....... .. ...... .... .. ............................. 69 Blue-Gray Clay Facies ..................................................... 69 Organic-Rich Mud Facies ........... ....................................... 71 Muddy-Sand Facies ........................................................ 71 Shelly Sand Facies ............................................. .. ........... 73 Mixed Siliciclastic/Carbonate Sand Facies ............................... 74 Fine Quartz S and Facies .................................................... 75 Inner Shelf Evolution ....................................................... 76 Modell ............................................................. 76 Model2 .............................................................. 81 Sand-Ridge Evolution ............................................................... 81 Mobility and Stability ................................................................ 85 6. CONCLUSION ............................................................................ 90 7. REFERENCES ............................................................................ 93 APPENDICES ................................................................................ 102 Appendix 1 ............................................................................ 103 Appendix 2 .......................................................... ............. .. .. 124 Appendix 3 ............................................................................ 128 11


Table 1 Table 2. Table 3. LIST OF TABLES Characteristics of continental shelves where sand ridges are present.. ...... 8 Table displaying the average standard deviation, mean grain size, percent calcium carbonate, and percent mud for all the samples of sediment taken from each of the seven different facies ............................ 37 Results from Beta Analytic Inc ................................................................. 53 iii


Figure 1. Figure 2 Figure 3 Figure 4 Figure 5 Figure 6. Figure 7 Figure 8. Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. LIST OF FIGURES Study area offshore west-central, Florida ... .............. .... ..... .. ...... ..... . .......... 3 Illustration displaying the deposition and erosion created by a perturbance on the seafloor . .... ....... .......... ... ............ . . . .......... ... . ......... . 1 0 Displays the diachronous nature of a ravinement surface .... ........... .......... 12 A model for sand ridge evolution as a function of shoreface retreat and sand ridge migration rates ............ .... ..... ........................ .... ........... .... 14 Evolutionary sequence ofhow a sand ridge develops from a combination of inlet migration and sea level rise ......... .... .... ............... ... 16 This model displays the overstepped barrier theory ..... ................. . . . ...... 17 Riggs and O'Connor generalized cross section of the sand ridges off the coast oflndian Rocks Beach, Fl.. .... ........ ... ...... .......... ... . . ...... . . 22 Simplified model of the sand ridges and the underlying facies of the ridges in the study area ..... ... . ............. ....... ... .............. ........... .... ............ 23 Sea -level curve compiled from west Florida data ... . . ... ... ....... ............ 25 Harrison s side-scan sonar mosaic with the 21 vibracore locations extracted for this study plotted with white circles .......... ... ........... ..... ... .. 35 February, 1998 side-scan sonar mosaic blow up with 1 2 ofthe 21 vibracore locations .... ......... .... ...... ....................... ....... . .... ... . .............. .... 36 Picture oflimestone gravel facies being altered to a blue-gray clay from vibracore IRB-96-27 . ...... .............. ........ ... . . ................ .... .... ... 38 Picture ofblue-gray clay facies primarily composed of the mineral paly gors kite underlying a muddy-sand facies from vibracore IR.B-96-28 . ..... . . ............ ........... ... ............. ............ .... .... ........ ... ....... . 40 IV


Figure 14. Figure 15. Figure 16. Figure 17 Figure 18. Figure 19. Figure 20. Figure 21. Figure 22. Figure 23 Figure 24. Figure 25 Fiugre 26. Figure 27. Figure 28. Figure 29 Figure 30. Blue-gray clay sample 122-124 em from vibracore IRB-96-9(2) ............ .41 Blackened grains from sample 122-124 em of vibracore IRB96-9(2) ........ .......................................................................... ................... 42 Picture of organic-rich mud facies from vibracore IRB-96-35 ................. .43 Picture of burrowed muddy-sand facies from vibracore IRB-96-35 ........ .45 Picure of shelly sand facies underlying a siliciclastic/carbonate facies from vibracore IRB-96-9(2) ........................................................... 46 Blackened grains from sample 115-117 em ofvibracore IRB-96-35 ....... .48 Scanning electron microscope photograph of two most common forams; A) Archais angulatus, B) Broekina orbitolitoides ...... ................ .49 Picture of mixed siliciclastic/carbonate facies that makes up the majority of the sand ridges from vibracore IRB-96-11.. ........................... 50 Picture of fine quartz sand facies from vibracore IRB-96-33 ... ................ 52 Blow up of the trough of a sand ridge field displaying the 4th order bedforms with approximately a 80 em wavelength ................... ............. 56 Side-scan sonar mosaic collected in February of 1998 ............................ 58 Harrison's mosaic of 1995 . ..... . .... .... ........ ........................... .............. 59 Harrison's side-scan sonar mosaic of 1995 with overlapping outlines of February 1998's mosaic ..... .................... . ..... ..... . .............. .............. 60 Harrison s Indian Rocks Beach mosaic of 1995 showing vibracore locations in transitional zone of the inner shelf.. ....................... .............. 61 Chirp sonar interpretation indicating sand ridges are approximately 2-3 meters in relief with an intermittent reflector defining the base of the sand ridge unit. ......... .............................................................. ........... 62 High-resolution seismic profile displaying multiple sand ridges with reliefs of approximately 3 meters .................................. ........................ 63 Display vibracores IR.B-96-8 and IR.B-96-9(2) superimposed upon corresponding chirp sonar profile .... ............................ ........................... 64 v


Figure 31. Figure 32. Figure 33. Figure 34. Figure 35 Figure 36 Figure 37. Figure 38. Figure 39. Display vibracores IRB-96-1 0 and IRB-96-1 1 superimposed upon corresponding chirp sonar profile ....................... .... ................................ 65 Displays vibracore description IRB-96-23 superimposed upon corresponding chirp sonar profile ................ ...... ...... ... ........................... . 66 Displays vibracore IRB-96-35 superimposed upon corresponding chirp sonar profile .. ... ........... .... .... .... . . ........ ....... ...... ............ .... ............... 67 Represents an idealized stratigraphic model and the patterns assigned to each of the sediments on the inner shelf of west-central Florida ........ ........ ............ ....... ... ............................................ 70 Sea level curve compiled from west Florida data from Suwannee River (Wright, 1995), Wacassassa Bay (Goodbred, 1994 ), and the Ten Thousand Islands (Scholl et al., 1969) ....................................................... 72 Schematic of the evoutionary stages of the inner shelf through the Holocene ...... .......... . . ........... ...... ............ ...... ...... ... .... ....... .... .... ... ............. 77 Schematic of preservation of the muddy-sand core ......... .......................... 80 Schematic of the evoutionary stages of the inner shelf through the Holocene ..... . ........ ...... ......... ............ ... ......... ............... ........... ....... .......... 82 Schematic of sand-ridge migration ................. ...... ..................... ............ 87 vi


STRATIGRAPHIC FRAMEWORK OF A MIXED SllJCICLASTIC/CARBONA TE INNER-SHELF SAND-RIDGE SYSTEM, WEST -CENTRAL FLORIDA by JAMES H. EDWARDS 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 December 1998 Major Professor: Albert C. Hine, Ph.D. VII


The west-central Florida inner shelf has recently been the focus of extensive high resolution seismic, side scan sonar and vibracore surveys. The various surveys have identified that the bedrock of the inner shelf is dominated by a Cenozoic limestone with karst topography. Superimposed on the bedrock is a thin sediment veneer of mixed siliciclastics and carbonates. The sediment cover is commonly sequestered into linear sand ridges obliquely oriented to the shoreline, possessing relief from 1-4 meters and widths from 1 00-300 meters. Twenty-one vibracores extracted from a sand ridge field on the inner shelf of west central Florida have identified seven different lithofacies, five Holocene and two pre Holocene, within the sand ridges. The vibracores' stratigraphy represents the evolution of the sand ridges and inner shelf through the Holocene transgression, demonstrating a shift from a low energy possibly back-barrier depositional environment to an open marine regime. The major sand ridge facies consists of sediments deposited in the nearshore open marine environment. It appears to be a mixture of siliciclastic/carbonate sands with intermittent lenses of shelly sand. Other common facies identified from top to bottom include a muddy-sand interpreted as a paleo-seagrass bed, an organic-rich mud marsh deposit, a blue-gray clay interpreted to be a diagenetic alteration of the underlying limestone bedrock and a limestone gravel which is considered to be fragments of the underlying bedrock. Genesis of the sand ridges appear to be a result of the present day hydraulic regime. AMS dating suggests sand ridge fom1ation initiated approximately 1,580 YBP when sea level was 1-2 meters below present. It is inferred that storm induced flow in combination Vlll


with sea-level rise and shoreface erosion have carved and sequestered the siliciclastic/carbonate sands into these linear features. Abstract Approved:-------------,-------:----..,----------:-:----::::-::--=-Major Professor: Albert C. Hine, Ph.D. Professor, Department of MariJe Date Approved: q } l Cf? IX


1. INTRODUCTION Some of the most prominent features on continental shelves around the world can be observed with detailed bathymetric maps. Bathymetric highs and lows aligned in a ridge/swale topography are commonly identified as sand ridges. Sand ridges are topographic features that evolve from a complex array of hydrodynamic forces (Swift et al., 1972; Duane et al., 1972). The hydrodynamic forces carve these features into long sub-parallel ridge and swale features which usually are aligned obliquely across the regional trend of the depth contours and converge with the shoreline at an angle (Swift et al., 1972). Sand ridges described in the geological literature exist in various dimensions and have world-wide distribution. They are most commonly found on low-gradient continental shelves with an established flow direction. Multiple studies have shown that sand ridges align themselves obliquely to the flow direction and generally exhibit an asymmetric cross section (Duane et al., 1972; Swift et al., 1972; Kenyon et al., 1981; Huthnance, 1973; 1982a; 1982b). Ridges have been described throughout the east coast of the United States, Argentina, and Brazil margins (Moody, 1964; Smith, 1969; Duane et al., 1972; Swift et al., 1972; McKinney et al., 1974; Stubblefield et al., 1975; 1984; Swift and Field, 1981; Figueiredo et al., 1981; Figueiredo, 1984; Swift and Niedoroda, 1985; Tillman, 1985; McBride and Moslow, 1991; Rine et al., 1991; Snedden et al., 1994). In addition to these shelf environments, sand-ridge morphologies have been described in tide-dominated regions as well. Tidal sand ridges are described in the North Sea, Gulf of Korea, and the Quicksand's of southwest Florida (Smith, 1969; Caston, 1


1972; Johnson et al., 1981; Kenyon et al., 1981; Shinn et al., 1990; Collins et al., 1995). Furthermore, sand ridges consisting of entirely carbonate derived sediments have been identified. In the northern Bahamas, Hine, Wilber, and Neuman (1981) observed five varieties of carbonate sand bodies. They suggested that the classification of the contrasting sand bodies is a result of the different types of the host carbonate bank margins. Sand ridges in the United States are not just limited to the Atlantic margin. Bathymetric maps from Florida's west coast, as early as 1879, have displayed a ridge and swale topography identified as sand ridges (Hyne and Goodell, 1967; Winston et al., 1968; Riggs and O'Connor, 1974; Herbert, 1985; Davis and Klay, 1989; Locker and Doyle, 1992; Harrison et al., 1995; Locker et al., 1995; Wright, 1995; Harrison, 1996). This study focuses on a sand-ridge field identified on the inner shelf of west-central Florida (Winston et al., 1968; Riggs and O'Connor, 1974; Harrison et al., 1995; Locker et al., 1995; Harrison, 1996a; Harrison, 1996b)(Figure 1 ). Sand ridge studies on the inner shelf of west-central Florida is a relatively new area of focus. The first work was centered around side-scan sonar, swath beam bathymetry and high-resolution seismic studies (Harrison, 1995; 1996a; 1996b ). This study will focus on the sand ridges stratigraphy and sedimentation and what this can infer about the history of the depositional environments. Harrison et al. (1995) and Locker et al. (1995) were the first to acoustically image the ridges with high-resolution side-scan sonar. They identified the topographic features to be a field of sub-linear sand ridges oriented NW-SE, trending obliquely with respect to the shoreline Using bottom sampling and high-resolution seismic profiles, Locker et al. (1995) inferred that the ridges have up to three meters in relief, consisting of a mixture of siliciclastic and carbonate sand-sized sediments. There are various theories described in the literature about the genesis of linear sand ridges. To develop models, scientists have focused their attention on large modem ridge systems such as the United States Atlantic margin and the tidal ridges of the North Sea. 2


8250' 8240' Figure 1. Study area offshore Sand Key, Florida Notice within the study area the bathymetric highs (shaded) in a NW -SE orientation. 3


With limited research, Figueiredo (1984) described that the ridges off west-central Florida share similar morphologies to the ridges on the east coast of the U.S. continental shelf with exception of being an order of magnitude smaller. In light of this, Figueiredo ( 1984) suggested the Pinellas County ridges may share similar evolutions. Therefore, the variety of hypotheses generated for the origin of the US east coast ridges in the literature will be investigated as possible analogs. Riggs and O'Connor (1974) briefly considered the genesis of the Pinellas County ridges. They identified this ridge and swale topography as a series of remnant inlets or recurved spits of a transgressing barrier island. An additional theory proposed for the origination of the ridges was the possibility of relic hurricane deposits (Winston eta!., 1968). It is evident from a broad range of interpretations a thorough study is required. The importance of this study relies on the fact it is very detailed and incorporates numerous data acquisition techniques. The study couples remotely sensed data (high resolution seismic, chirp sonar, side-scan sonar) with ground truthing data via vibracores. Using these methods, a detailed stratigraphic model can be produced integrating a variety of vertical scales from centimeters to meters. Application for this study can be utilized for the recognition and of similar features in the geologic record. Several elongate marine originated sandstones have been compared to modem submarine sand ridges (Figueiredo, 1984). The results are also applicable to determine if the sand ridge field is a viable beach re-nourishment borrow area. Sand ridges preserved in the rock record have also attracted oil companies attention because of the potential oil and natural gas reservoirs they provide (Walker, 1985; Tillman et al., 1985; Nummedal et al., 1993). The main contribution of the sand ridge study will be to clarify various enigmas of sand-ridge development, evolution, and sedimentary character by creating an accurate stratigraphic model. In addition, the study has valu e in interpretin g th e history and development of the inner shelf of west-central Florida 4


The main objectives of the study are as follow: 1) Identify the sedimentary facies present. 2) Interpret the depositional environment of the identified sedimentary facies. 3) Develop a detailed stratigraphic model for the inner shelf of west-central Florida 4) Reconstruct the evolution of the sand ridges and inner shelf of west-central Florida. 5) Determine the mobility and stability of the sand ridges. 5


2. PREVIOUS INVESTIGATIONS In 1919, the United States Navy developed the first sounding system for depth measurements called the "Hayes sonic depth finder". It wasn't until 1939 the system was modified enough to collect continuous measurements that permitted charts to be published with depth contours. Veatch and Smith (1939) took full advantage of this to interpret bottom topography of the United States Atlantic shelf and slope. They identified a series of sand ridges off the New Jersey coast. Since then, a number of submarine sand ridges have been identified, varying in dimensions, and existing in many different environments These investigations have derived a wide range of evolutionary theories. The purpose of this previous works section is to synthesize the major morphological and textural characteristics of the different sand ridges and the evolutionary theories developed. Sand-Ridge Characteristics Regional Setting Characteristics of Sand-Ridge Fields Sand-ridge fields located on inner continental shelves generally share similar characteristics such as gradient, shelf break depth tidal range, wave direction and sediment input (Figuieredo, 1984). In addition, sand ridges are almost always associated with barrier islands. Barrier islands generally occur on coastlines of trailing margins, with a wide, gently deepening shelf, and a broad, low-lying coastal plains (Glaeser, 1978). The average shelf gradient for sand ridge fields is 1:1245 with an average shelf break of 100m 6


(Table 1 ). Sand ridges are commonly situated in areas where there is little sand contribution from rivers. On the United States Atlantic and Gulf of Mexico coasts, estuaries trap most in excess of 90% of the sediment (Shepard, 1960; Meade et al., 1975). Also, they are commonly associated in regions with tidal ranges of micro (0-1 m) to low mesotidal (1-2m), and regions that have a wave approach oblique to the shoreline (Figueiredo, 1984). Sand-Ridge Dimensions Sand ridges are elongate wave-like sand bodies found on inner continental shelves that exhibit many different sizes (Figueiredo, 1984). Sand ridges are defined as large scale bedforms with spacings of 1 to 5 km and reach up to 10 m in height (Swift, 1984 ). Sand ridges influenced by open marine processes of the inner and middle continental shelf generally have re lief of up to 10m, spacings of 6 to 8 km, widths of 2-4 km, and lengths of up to 50 km. The ridges generally occur in 3 to 45 m of water depth (Figueiredo, 1984). Tidal submarin e sand rid ges describ ed by Off (1963), have reliefs of 8 to 30m, lengths of 8 to 64 km, and spacings between 2 and 10 km. In the carbonate realm, Ball (1967) describes a sand belt ornamented with bars and ripples of varying size. He describ es the lar gest features as ridges with relief up to ten f ee t and spacings as great as 2000 feet. In the Bahamas, asymmetrical sand waves have been identified superimposed on a sand wedge. They are 1 to 4 min height and 100 to 400 met ers in spacing (Hine et al., 1981 ). Sand ridges have been identified in the geo logical rock record as well. For example, Winn et al. (1983) described elongated sandstones in the Powder River Basin, Wyoming that display relief from 15 -20 m, widths of 3 km and lengths from 10-12 km. 7


Region Long Island, NY New Jersey Delaware Maryland Clearwater, Fl Apalachicola, Fl Pensacola, Fl Depth Shelfbreak (m) 120 120 80 80 80 80 80 Laguna Madre, Tx 60 South Brazil 150 Argentina 150 Shelf Width (km) 170 150 130 100 160 120 20 50 150 200 Shelf Slope 0.04 0.04 0.03 0 03 0.02 0.03 0.04 0 06 0.05 0.04 Shelf Gradient 1:1,416 1:1,250 1:1,625 1:1,250 1:2,000 1:1,500 1:2,500 1:8,340 1:1,000 1:1,334 Table 1. Characteristics of continental shelves where sand ridges are present. Data is from nautical charts from United States, Brazil, and Argentina. (Modified from Figueiredo, 1984) 8


Sand-Ridge Morphology Sand ridges often display asymmetrical cross sections. Sand ridges that have developed from a continuous flow direction tend to have gently sloping up-current flanks and steeper down-current flanks. The ridges generally orient themselves obliquely to the prevailing flow direction for possible reasons discussed later (Caston, 1972; Duane et al., 1972; Swift et al., 1972; Huthnance, 1973, 1982a, 1982b; Kenyon et al., 1981; Collins et al., 1995;). The ridges can be attached or detached to the shoreface, when attached the ridges intersect the shoreline at approximately 35 degrees (Figueiredo, 1984 ). Sediment Character Sand ridges exposed to a prevailing flow direction, commonly have surficial sediment variability. Texturally, the coarsest sediment tends to be located on the up-current flank while it fines towards the down-current flank (Figure 2) (Swift and Field, 1981). In contrast, Swift et al. (1972) describes a helical flow model where the flow lines converge and are directed downward towards the trough between two ridges and subsequently rise up the flanks. This process is believed to erode the trough leaving a coarse lag and cause fine sediment to be deposited on the crests. In the subsurface, sand ridges vary a number of ways, too. Stubblefield et al., (1984) describes fining upward sequences, coarsening-upward sequences, and homogeneous sequences all within various sand ridges. He postulates the origin of the sequences are the result of migrating sand ridges Rine (1986) describes the sedimentary facies of a series of sand ridges on the middle shelf of New Jersey. He recognizes three facies: (1) non-fossiliferous mud and poorly sorted sand at the base of the ridges, (2) shell rich mud and sand, and (3) upper ridge sand Within the stratigraphy of the west-central Florida's ridges there exists a basal gravel which is interpreted by Harrison ( 1996) to be a ravinement surface. This is commonly seen in other ridges around the globe as well as vibracores extracted locally 9


GRAIN SIZE Figure 2. IIIustration displaying the deposition and erosion created by a perturbance on the sea floor. The ridge experiences maximum bottom shear stress on the up current flank while the down-current flank experiences negative shear stress. This results in a positive shear stress gradient (modified from Swift and Field, 1981). 10


within the study area. Many ridge studies describe a continuous subsurface reflector identified as the "R reflector". This reflector is interpreted to be a gravel Jag remnant left behind from a shoreface erosion processes in conjunction with a transgressing sea level (Figure 3). It is interpreted to be the contact between the Pleistocene and Holocene (Swift eta!., 1972; McClennen, 1973; Kneble and Spiker, 1977; Knebel et a!., 1979; Stubblefield and Rine, 1981; Figueiredo, 1984). Brooks eta!. (1996) also reports shell layers of various thicknesses located in vibracores from the west-central Florida inner shelf that may represent either a channel lag or ravinement surface. Sand-Ridge Provinces For discussion purposes, sand ridges are divided into five main categories: (1) inner shelf, (2) middle shelf, (3) tidal, (4) carbonate, (5) and ancient. Inner Shelf Sand Ridges In the beginning, Veatch and Smith (1939) identified a se1ies of ridges from continuous bathymetric data on the shelf of New Jersey. They interpreted them as being a succession of barrier-island remnants formed as a result of a transgressing sea. Later in 1960, Shepard interpreted the sand ridges as a drowned barrier-island system. Many other interpretations developed. Off (1963) inferred that the 1idges were the products of the reworking of glacial material by tidal currents. Uchupi (1968) suggested that the sand ridges were the result of intense stonm reworking the sediments and claimed that the ridges remained inactive between stom1s. McKinney and Friedman (1970) predicted that the submarine sand ridges were the result of stream interfluves at a prior sea-level low stand. Moody (1964) proposed a mobile sand ridge. He witnessed a shift in the sand ridges after a storm had passed in 1962 and concluded that the sand ridges were a product of the modern hydraulic regime. In addition, Moody stated that the ridges would grow from 1 1


A. B c Barrier isochrons Ravinement surface Beach Haven Ridge Model ------------Inner Shelf Sand Ridge Ravinement Surface Washover Fans & Storm Channels Storm Sands Lagoon Muds Low-Stand Surface Figure 3. Displays the diachronous nature of a ravinement surface. (A) When sea level is at position 1, modem coastal processes develop offshore bars, barrier island and back-barrier strata. When sea level has risen to position 2 the shoreline moves landward, the ravinement process truncates the original barrier island structure but overlies and preserves the backbarrier facies. New inner shelf morphologies form at sea level 2 that are younger than the underlying back-barrier facies but are contemporary with sediments at S I. (B) Generalization of the chronostratigraphic surfaces crossing a ravainment surface in a transgressive environment. (C) Beach Haven Ridge Model displaying a sequence resulting from a transgressive environment. The low-stand surface is the sequence boundary and is overlain by mud infilling an abandoned tidal channel. Later interbedded washover deposits increase as the barrier island approaches. Subsequently, the barrier migrates landward and the island's structures were removed by a retreating shoreface and replaced with a ravinement surface. The surface then develops an inner-shelf sand ridge (Nummedal and Swift, 1987). 12


offshore to onshore with the retreat of the shoreline The ideas of Moody aided others, such as the development of the shoreface retreat model. This model suggests that the ridges are a result of coastal storm currents in conjunction with helical flow during a period of shoreface retreat. This requires the sand ridges to prograde offshore to onshore at a rate controlled by coastal retreat (Figure 4)(Duane et al., 1972; Swift et al., 1972; Swift, 1976). Another theory presented was the shear wave model (Stubblefield and McGrail, 1979; 1980). This was based on satellite data displaying the transportation of turbid water. This model shows how a ridge grows from onshore to offshore without any changes in sea level unlike the shoreface retreat models Duane et al. (1972) categorized the inner shelf sand bodies into two groups. The shoals can be arcuate (inlet and cape associated) or linear. Linear shoals can be divided up into shoreface connected or isolated. These shoals generally form a angle less than 35 degrees with the coastline opening northward regardless of the littoral transport direction. Seismic reflection profiles display the two types of shoals to be plano-convex exhibiting some internal bedding structures superimposed on a featureless stratal layer. The sediment sequestered by the sand ridges is nearly all siliciclastic sand except the ridges south of Cape Kennedy, Florida where carbonate skeletal grains becomes an important constituent. Sediments are generally well sorted, medium-grained sand and similar to adjacent beaches in sedimentology. Inner shelf shoreface connected ridges are presently undergoing modification by storm currents and waves They appear to be presently forming in response to the interaction of wind and wave-generated bottom currents during winter storms. These ridges are in a wide range of evolutionary states. They are in the process of elongating and eventually becoming isolated from the shoreface as a result of barrier-island retreat. Therefore, the isolated ridges are interpreted to be relict shoreface attached ridges that have been detached during the Holocene transgression. The ridges are maintained by helical 13


Sand Ridge Evolution PRESENT PRESENTLY ACTIVE ;SEGMENT / ioooer ..... :... ......................... ... ... < . t COASTAL HElHEAT . RAT,. I Km/1000 YR .. c-.. . 0 .-:--.., ''1-,. .. .,., .":--, RIDGE MIGRATION RATE :;r I Krn/1000 YR Figure 4. A model for sand ridge evolution as a function of shoreface retreat and sand ridge migration rates Rates are described to be approximately 1 km/1000 years (Swift, 1976) 1 4


flow currents induced from storms that aggrade the crests of the ridges and scour the troughs leaving a gravel lag (Duane et al., 1972; Swift et al., 1972). Figueiredo (1984), McBride and Moslow (1991), and Snedden et al. (1994) support a model that suggests that the ridges may initially develop on a bulge created from an ebb tidal delta. This is seen stratigraphically by Snedden et al. (1994) with vibracores. Vibracores indicate deltaic sand overlied by an open-marine sediment. This requires barrier-island retreat as a result of sea level rise in conjunction with a migrating inlet that supplied the sand to account for the oblique orientation with respect to the shoreline (Figure 5). Huthnance's (1982) model for the aggradation of shelf sands upon a perturbance also suggests this idea. Middle Shelf Sand Ridges Middle shelf sand ridges have been described off the coast of New Jersey (Stubblefield, 1984). These ridges have been interpreted as drowned barrier islands with modern ridges being formed on top. This is tem1ed the "overstepped banier" theory (Figure 6). The term is used to indicate a barrier island that has been left behind on the continental shelf after sea level has transgressed. The theory was developed as a result of the ridges parallel orientation with respect to the shoreline and their seaward inclined reflectors. The reflectors are interpreted as aggradation and progradation of the barrier (Swift et al., 1972; McKinney et al., 1974; Stubblefield et al., 1980; Stubblefield et al., 1983a,b). Another set of ridges have been described on middle shelf of New Jersey (Stubblefield, 1984). These are interpreted to be shoreface connected ridges like the ones existing on the inner shelf. It is interpreted that there was a series of pauses in sea level that permitted shoreline features to develop and become preserved. These are believed to be attached to a paleo-shoreface. 15


1. Barrier Island Coast ..... __________ .., ..... ....__..... ... ___ ....... _..-._.---. lO.m._.... ___ -t 2. Inlet Opens 5. Inlet Closed 1--...... -. ..-.. . '--3. Inlet Migrates .. ; : ::.; 1 ..------1 Barrier Migratior ln-.. Ridge Figure 5. Evolutionary se quence of how a sand ridge develops from a combination of inlet migration and sea level rise. (McBride and Moslow, 1991) 16


_____ .. __ ,..---------._.--"';;--Bottom Topography .,. ...... ""' .. Previous Bl.",ttom Topography Sea Level Time 1 Sea Level Time 2 Sea Level Time 3 fW{J Barrier Sands Muds Substrate Figure 6. This model displays the overstepped barrier theory. At sea-level time 1, the sediment supply is abundant enough to maintain it's position during sea-level rise. At sea-level time 2, sedimentation can not keep up and the barrier island is eventually over-stepped and partially preserved. At sea-level time 3, the preserved portion acts as a nucleus upon which mid shelf sediments accumulate (Stubblefield et al., 1984 ). 17


Tidal Sand Ridges In 1968 Houbolt identified a series of tidal sand ridges in the North Sea. These are among the most extensively studied tidal ridges and maybe used as an analog for many of the linear sand banks or tidal sand ridges on continental shelves around the world. It was not until 1982 that Huthnance developed a model of genesis for these ridges. Huthnance describes how the ridges are slightly oblique to the tidal current directions and proposed a model of how the ridges could evolve from irregular bottom topography. He suggested that linear sand banks can form as a result of tidal currents generating vorticity and advection in flow over a small isolated hump. In contrast, Collins et al. (1995) described that the topography of a sea bed may not be necessary for the genesis of sand ridges. He shows flat and featureless sub bottom images from the Broken Bank in the North Sea underlying sand ridges Collins et al. (1995) states that the initial stage of sand bank growth cannot be inferred from the underlying deposits and claims that the early stages of development is controlled hydrodymamically without the requirement of a perturbation on the sea floor as Huthnance (1982a) claims. Collins et al. (1995) manifests how helical flow may initiate ridge development with a featureless host ground in the beginning. For the maintenance and further growth of the rid ge, a clockwise circulation of water and sand from the ebb and flow tides converging at the crest line appear to be the dominant process. These tidal s a nd ridg e s generally occur in re g ions with a tidal range greater than 3 m and current speeds within a range of 51 to 257 em per second (Figueiredo, 1984) The majority of the tidal-current derived ridges align themselves obliquely to the peak tidal flow, as much as 20 degrees in a anti clockwise offset. Ninety five percent of the tidal sand ridges align themselves in an anti-clockwise fashion, generally between 7 and 15 degrees but can range from 0 to 20 degrees. This suggests that the oblique orientation is driven by Coriolis forces (Kenyon et al. 1981 ) Most linear s a nd rid ge s are asymmetric in cross-section, with their steep face or lee slope reaching a maximum angle of 6 degree to the horizontal (Collins e t al., 1995). Cores fro m the rid g e sys te m find that th e ridge 18


sediment consists of glacial, fluvial, and deltaic sand that has been reworked during the Holocene transgression. These ridges also display an erosive gravel lag interpreted to be the contact between the Pleistocene and Holocene (Walker, 1985). Carbonate Sand Ridges Sand bodies dominated by carbonate grains can also accumulate on the sea floor. Ball (1967) states that for a given topographic setting, water acts in a similar manner regardless of the carbonate or terrigenous sedimentary nature. In the Bahamas Hine, Wilber, and Neuman ( 1981) observed 5 varieties of carbonate sand bodies. They suggested that the classification of the contrasting sand bodies are a result of the different types of host carbonate bank margins. The 5 margins, each with their own sedimentary characteristics, are: (1) windward open; (2) windward protected; (3) leeward open; (4) leeward protected; and (5) tide dominated. The diversity is suggested to be related to the level, duration, and magnitude of the physical energy flux across the edges of the platform. In areas of strong tidal currents due to basin shape, windward and leeward margin effects are reduced and tidal currents become the dominating factor in the modification of the these sand bodies. Ancient Sand Ridges Numerous sand ridges have been preserved and recognized in the geologic rock record. Elongate marine sandstones could be possible analogs for modem submarine sand ridges. These ancient ridges intrigued oil companies due to the potential petroleum reservoir they provide. Understanding the setting where sand ridges are formed, the physical factors involved in the formation and the resulting morphology caused focus on continental shelf sand ridge studies. Sandstones from the Frontier Fom1ation, Spearhead Ranch Field, Powder River Basin, Wyoming are compared to modem sand ridges (Tillman and Almon, 1979; Winn et 19


al., 1983). Tillman and Almon ( 1979) recognized a sequence of environments in the Frontier Formation. They described a transition of depositional environments all within the Frontier Formation: lagoon, beach, sand ridge, and open marine. Winn et al. (1983) only recognized the sand ridge facies and open marine deposition in this Formation. Tillman (1985) furthered his research and developed some general trends of these sand ridge deposits. He noted that they all : 1) have coarsening-upward sequences, 2) are coarser grained than the respective shoreline deposits, 3) are encased in shale, 4) are linear and 5) vary in thickness from 1 to 25 m. Some other elongate sandstone investigations that are compared with the US Atlantic sand ridges include Boyles and Scott (1982) who studied Duffy Mountain Sandstone Member of Mancos Shale, Rice (1983) who studied the Medicine Hat Sandstone and the Mosby Sandstone Member of the Belle Fourche Shale, and the Shannon and Sussex Sandstone Members of the Cody Shale which was studied by Tillman and Martinsen (1979), and Hobson et al. (1982). Previous Sand Ridge Investigations in Study Area Acoustic surveys have shown the inner continental shelf of west-central Florida to be dominated by a Cenozoic limestone bedrock which hosts a mixed siliciclastic/carbonate sediment veneer. The bedrock surface has antecedent topography consisting of: (1) pits, depressions, ledges from em's to several m s of relief and widtMength's from em's to 100's m, to (2) broad rises, flat bedrock plain s and sh e lf vall e ys (Hin e, 1996 ; Locker et al., 1995a; 1995b; 1996) The sed i ment veneer i s composed of a mixed siliciclastic/carbonate sand (Gould and Steward 1956; Ginsburg and James, 1974; Doyle and Sparks, 1980; Davis et al., 1992 Lo cker et al., 1995a; 199 5b; Brooks et a l., 1996). The carbonate sands and gravels are predominately derived from fragments of mollusks, benthic forams, sponge spicules, rock s a rthropods, a lgae, bryzoans, and echinoids in 20


descending order (Doyle et al., 1995). The siliciclastic sands are primarily quartz and terrigenous in origin from the Appalachian Mountains. These sediments commonly take the form of submarine sand-ridges. A literature review reveals that conflicting origination theories exist for sand ridges on the inner shelf of west-central Florida. Riggs and O'Connor (1974) concluded that the ridges were 2-7 feet in height and several hundred feet in width with an oblique trend relative to the present barrier beach. They suggested that the ridges consist of a clean, well sorted, fine-grained quartz sand and shelly sand, This overlies an internal core of undisturbed lagoonal muddy sand perched on a uncorroded carbonate rock surface. The ridge sand is generally of the same composition and character as the sand and shell of the barrier islands and passes. They demonstrated the rock swales having dramatic biological corrosion and erosion grading into the uncorroded surface protected by the ridge sediments (Figure 7). About 20 years later, the ridges were mapped with a side-scansonar and high resolution seismic profiling techniques. These studies revealed that the ridges are presently 1-4m in height and exist from the toe of the shoreface to more than 25 km seaward (Locker et al., 1995a; Harrison et al., 1995; Harrison, 1996a; 1996b). Harrison (1996b) concluded that the ridges are not relic features but have developed during the Holocene transgression. Three vibracores were described as having four facies overlying the limestone bedrock. From top to bottom: sand ridge facies; tan sand and shell facies; organic silt facies; and non-fossiliferous carbonate facies All were considered to be deposited in the open-marine environment expect for the organic silt facies which was considered to be a back-barrier deposit. Also noted was a basal gravel that resided between the sand ridge facies and the tan sand and shell facies (Figure 8). AMS radiocarbon dates suggest the formation of the ridges began approximately 1 ,60 0 YBP. Harrison (1996b) postulates from his data that the ridges are in equilibrium with the modern hydraulic regime and that the 21


Figure 7. Riggs and O'Connor generalize cross section of the sand ridges off the coast of Indian Rocks Beach, Fl. Note the muddy-sand core under the sand ridge and the eroded bedrock converting to an uncorroded limestone surface beneath the ridge. They interpret these sand ridges to be a series of remnant inlets or recurved spits of a transgressing barrier island. (Modified from Riggs and O'Connor, 1974) 22


lkm Present Sc.1 Lev<' I [ill! Sand Ridgl' Facit'S } Basal Gr;wcl/ 11nd Undtrlyinr, 0 tv! -H 1 , Surfncl! pen .umc ' CJ Tan S .md an, Shell I' ;lcit s Organic Sill Fades -----Pre-Transgressive H()loc:enc Miocene Limestone [kdro.:k Figure 8. Simplified model of the sand ridges and the underlying facies of the ridges in the study area. Harrison describes a pitted limestone bedrock hosting a pre-trangressive lagoonal facies. Overlying the lagoonal facies is an open marine tan sand which is capped with an erosional surface. The erosional surface or basal gravel is at the base of the sand ridge facies. (Harrison, 1996) 23


underlying bedrock exerts no control over the positioning or orientation of the ridges. The sand ridges off the west-central Florida coast are morphologically similar to those of the intensely studied US Atlantic margin. The major difference is that they are an order of magnitude smaller and are in an environment of lower shelf gradient and energy. In light of this, Figueiredo (1984) suggested that the Gulf Coast ridges share similar evolutionary histories and require a detailed stratigraphic investigation. Sea Level Sea level throughout the Pleistocene has undergone many fluctuations and is one of the main controls on shelf development (Fletcher and Wehmiller, 1992). Sea-level fluctuations are the result of changes in the amount of continental ice (Williams, 1988). The most widely accepted theory for ice cover changes results from orbital forcing which varies the planetary insolation. These are called Milankovich cycles (Imbrie et al., 1992). Glacial and interglacial stages have been well documented throughout the Pleistocene. The last high stand or interglacial above present day sea level was during oxygen isotope stage 5e, approximately 125,000 ya. Sea level reached approximately 6 m above present day. The last low stand or glacial interval, was documented at approximately 18,000 ya approximately 121 m below present sea level. Since the low stand, sea level has risen to present day's but at different rates Sea level is suggested to have risen rapidly until-5,000 BP, then leveled off at a steady yet slower rate (Fairbanks, 1989). Scholl et al. (1969) also presents a sea level rise for the last 5,000 BP. They suggest a rise of 0.09 crn/yr before 3,500 BP, decelerating to 0.06 cm/yr from 3,500 to 1,700 BP, and lastly slowing again to 0.03 crn/yr after 1,700 BP. For purposes of this study Wright's (1995) sea-level curve compiled from Suwannee River data will be used. This is because of the high resolution it offers for this particular time range and it's close proximity to the study area (Figure 9). 24


1 2 3 -E -4 c:: 0 ';::: 5 co > Q) iii 6 7 8 9 14C(5568 half-life) years (BP) 9000 yr<> vrl v 0 'IV <> 0 I V Suwannee River above 0 I T Suwannee River below r j <> Wacassassa Bay Above i 0 Ten Thousand lsi. above I Ten Thousand Is!. be!owj i-smooth curve i uneven curve "-----------........ ____ ......... __ ___ Figure 9. Sea-level curve compiled from west Florida data. Suwannee River (Wright, 1995), Wacassassa Bay (Goodbred, 1994), and the Ten Thousand Islands (Scholl et al., 1969) data displays a sea level rise with a deceleration at approximately 4,000 YBP. (modified from Harrison, 1996b) 25


3. METHODS The methods for this study incorporated a number of sampling methods. The study integrates broad scale, remotely-sensed reconnaissance surveys with tightly-spaced vibracores. Some of the geophysical methods utilized to infer distribution, stratigraphy, and geologic framework include seismic profiling, side-scan sonar and chirp sonar. Vibracores were collected for ground truthing and stratigraphic purposes. The latitude and longitude of the cruise tracks and sampling sites were determined with a Differential Global Positioning System (DGPS). For purposes of correlation, timing, and origin of the different sedimentary facies, lab analyses were completed including grain size, percent calcium carbonate, radiometric dating, and x-ray diffraction. Geophysical Data Collection High-Resolution Seismic Reflection Profiling Seismic profiling is a method to acoustically image the subsurface. It consists of a sled sound source and hydrophone array towed at the surface of the water. A sound pulse is transmitted through the water column and into the subsurface. As the sound pulse moves through the sediments some of the energy is reflected back to the surface by changes in the acoustic impedance of the transfer medium. The array of hydrophones detect the reflected pulses, convert the pulses into electrical pulses and is recoreded on a computer for post-processing The depth of the numerous sub-bottom reflectors is based upon the two way travel time of the seismic pulse (Sheriff, 1989). 26


Several seismic surveys in the vicinity of the study area were completed. These were completed utilizing the RN Bellows, July 10-15, 1994 and the RN Suncoaster, October 12-13, 1994. These studies utilized a Elics Delph2 system for data collection and post processing, a Huntec Sea Otter "boomer" and a ITI hydrophone streamer Acquisition parameters for the studies utilized a shooting interval of 400 ms with output power levels up to 1000 Joules. Post-processing was completed with various automatic gain controls (AGC), a low and high pass filter from approximately 1000 to 3000 Hz, a horizontal stacking setting of three shots and a swell filter. Chirp Sub-Bottom Profiles A chirp sub-bottom profiling sy s tem was used in this study to provide an additional high-resolution perspective between the lower frequency seismic profiling and the higher frequency side scan sonar. This was completed with an EG&G chirp syst e m on June 1st and 2nd of 1996. Chirp sonar is different from the conventional seismic pulse systems in that it transmits a band of FM pulses with a range of 200Hz to 30kHz (Schock and LeBlanc, 1990). Using a band width of such, in theory, allows for resolution of strata as fine as 5 em. For this study this resolution was not attained, although there is evidence in the data of internal stratigraphy within the ridge Side-Scan Sonar Side-scan sonar is another acoustic imaging technique used in seafloor mapping. It consists of a towfish that has two transdu c ers which emit sound pulses at a ngles from the towfish. The sound travels to the seafloor wh e r e the pulse is e ither absorbed or reflect e d by the sediment matrix. The amount of backscatter is then measured also by the transducers and an image is produced based on the strength and return time of the incoming signal. Side-scan sonar differs from seismic pro f iling in that the frequen c y is much high e r (100kHz) and only penetrates a few centimeters into the subsurface It maps the surficial 27


geology rather than the subsurface. The strength of the backscatter is a function of the textural sediment properties and topography. Fine sands and muds attenuate the sound and in tum have a weak backscatter measured by the transducer whereas rocks, gravels, hardgrounds and sea grasses all produce strong acoustic returns. For images presesented in this study, sands or a low-backscatter medium appears to be white or light shades of gray and a high-backscatter seafloor such as a hardground outcrop produce gray to black shades (Fish and Carr, 1990). The system used for the study was an EG&G model 272-TD dual frequency (100/500 kHz) towfish and a Delph Sonar for Windows, version 1.34, used in conjunction with Trimble Hydro navigation software. The study was conducted during the month February, 1998, on the RN Suncoaster. The total area of the mosaic is approximately 2 km2 and was post-processed using the Delph Sonar and Delph Map software for Windows. The study area also contains two larger mosaics collected previously by Harrison in 1994 and 1995 on the RN Bull Boat, a 22ft. Sea Hawk. The first mosaic collected in 1994 is approximately 45 km2 and runs from the shoreline to approximately 8 km gulfward. The second mosaic partially overlaps the first and is approximately 14 km2 Harrison used the overlay to observe any mobility or reorientation of the sand ridges that may have taken place over a years time. Each of these two data sets were post-processed by Harrison on a UNIX system with a Woods Hole Image Processing System Software (WHIPS) package. Navigation was by DGPS. Additional side-scan sonar data also exist within the study area. An October 12-13, 1994 sand survey was completed for the US army CORPS of Engineers for purposes of determining the extent of the sand ridges and if the sequestered sand could be a potential beach re-nourishment source. In conjunction with the side-scan sonar, an Elics Delph2 seismic system and an underway surface sediment sampler was utilized. Navigation was also by DGPS. 28


Sediment Data Collection Vibracores Vibracoring is a valuable method for extracting a continuous, relatively undisturbed stratigraphic sequence for ridge development studies. Twenty-one vibracores were collected from July 24th-August 2, 1996 off the coast of Sand Key, FL for the purpose of studying ridge stratigraphy. The vibracoring was conducted on board the USGS's research vessel the RN G.K. Gilbert using a Branford R5000 flange-mount vibrating head system driven by compressed air. This was mounted on an aluminum I beam supported by a stainless steel frame and maneuvered by a six ton Hyatt crane. Cores were collected in 6m (20ft) long, 7.6 em (3in) diameter aluminum irrigation barrels with brass core catchers fastened by rivets at the base to maximize recovery Penetration was measured by markings on the side of the core barrels and by a penetrometer that was attached to the vibracore head Navigation was by a Trimble NavGraphic GPS receiver used in conjunction with a Trimble NavBeacon to obtain real time DGPS broadcasts from Egmont Key, FL. The vibracores were split, described, photographed at approximately 30 em segments and sub-sampled at approximately 10 em intervals. One hundred and eighty-five samples were extracted for further analyses. Sediment Analyses Grain Size Analysis Sub-samples were extracted from the cores to represent each of the facies present. Grain-size analysis and percent calcium carbonate were completed on the 185 samples taken from the cores. The analysis began by dividing each sub-sample into four representative samples by cone and quartering techniques. The samples weighed 29


approximately 20 grams. Two of the four were archived and the other two continued through the analyses, one for grain size and the other for %CaC03. The grain size division was first rinsed and decanted twice to remove any of the salts present. Next, 10 ml of a 5% sodium metaphosphate solution was added to the sample as a dispersent. Following this, the samples were wet sieved at 4 phi (0.063mm) to separate the sand fraction from the silt and clay fractions. Samples, both sand and mud, were then dried in an oven at approximately 40 Celsius and weighed to determine the weight percents. The final step of the grain-size analysis consisted of dry sieving the sand fraction and weighing each individual grain size separation. This was completed using multiple sieves. Sieves of sizes -1.0 phi (2.0mm), 0.0 phi (1.0 mm), 1.0 phi (0.5 mm), 2.0 phi (0.25 mm), 3.0 phi (0.125 mm), and 4.0 phi were used To obtain mean and standard deviation calculations, Folk's method of moments was used (1980). This is a computational (not graphical) method of obtaining values. It involves every phi division whereas graphical methods only use a few selected percentage lines This provides a much truer value. Subsequently, a cluster analyses was completed to group the sub-samples into different categories of sedimentary facies. The cluster analyses used was an add in program to Excel called Xlstat, which used the mean grain size, standard deviation and percent calcium carbonate calculations from each of the samples for categorization (F AHMY, 1998). Percent Calcium Carbonate The percent calcium carbonate analysis consisted of taking the pre-weighed samples from the original cone and quartering and leaching the calcium carbonate from it via a 10% Hydrochloric acid bath. When no more visible reaction occurred with the introduction of more acid, the process was considered complete. The samples were then rinsed, decanted, dried at approximately 40" Celsius, and weighed to determine the weight percent of CaC03. 30


Mineralogy X-ray diffraction (XRD) techniques using a SCINTAG XDS-2000 x-ray diffractometer were completed on representative samples of shelly and blue-gray clay facies. A continuous scan from 2-40. was conducted with the diffractometer because this range encompasses most of the common minerals of sedimentary material. The diffraction patterns were identified by using the published diffraction patterns (JCPDS, 1988). To prepare a sample, they were first washed in a bleach bath to remove any organic material then dried. The dried sample was then crushed into a fine powder using a mortar and pestle, spread over a glass slide and run through the XRD process. Dating To provide the chronology of stratigraphic development, six samples were dated by Beta Analytic Inc. in Miami, FL. Two organic-rich sediment samples and four samples consisting of the foraminifera species Archais angulatus and Broekina/Parasorities orbitoloidies were used. Forams were identified using Bock et al., c. 1970; Poag, 1981 and Cottey, 1987. Organic-rich sediments were dated via radiocarbon techniques and foraminifera samples were dated via Accelerator Mass Spectrometry (AMS). Pre-treatment. Approximately 40 mg of foraminifera species per sample were sent for AMS evaluation. The individual forams were selected carefully under a binocular microscope to insure that the foram was intact and unabraded. Broken or abraded forams were discarded because of the possibility of transport. The unscathed forams were then washed in a 10% sodium metaphosphate solution, rinsed several times and lastly placed in a sonic bath for five minutes to completely remove any silts or clays that may of been adhering to the tests. No pre-treatments took place at Beta Analytic Inc. 31


Approximately 300 grams per sample of organic-rich sediment were sent for radiometric techniques. Beta Analytic Inc. performed acid washes on the sediment. This involves crushing the chunks and dispersing the sediment prior to application of the hydrochloric acid to remove any carbonates. Chemical concentrations, temperatures, exposure times, and number of repetitions, were applied accordingly with the uniqueness of each sample (Stuiver et al., 1993; Talma et al., 1993; Vogel et al., 1993) Analysis. AMS dates were derived by reducing the sample to graphite (100%) carbon and running the graphite through an accelerator-mass-spectrometer. 13C/2C ratios were calculated relative to a PDB-1 (Pee Dee Belomnite) international standard, for fractionation (Stuiver et al., 1993; Talma et al., 1993; Vogel et al., 1993). Materials measured by the radiometric technique were analyzed by synthesizing sample carbon to benzene (92%), measuring for 14C content in a scintillation spectrometer, and then calculating a radiocarbon age. For the two samples of organic-rich sediment a 13C/2C ration of -25 was assumed based on the values typical of this material type (Stuiver et al., 1993; Talma et al., 1993; Vogel et al., 1993). Reported Dates. The dates reported are the conventional 14C age and calendar years based on the radioactive decay of 14C, which has a half life of 5,568 years (Libby, 1955). Calibrations of radiocarbon age determinations are applied to convert BP results to calendar years. The short-term difference between the two is caused by fluctuations in the heliomagnetic modulation of the galactic cosmic radiation and, recently, large-scale burning fossil fuels and nuclear device testing Geomagnetic variations are the probable cause of longer term differences. The parameters used for the con-ections have been obtained through precise analyses of hundreds of samples taken from known-age tree rings of oak, sequoia, and fir 32


up to 7,200 BP. The parameters for older samples, up to 22,000 BP have been inferred from other evidence. This is the Pretoria Calibration procedure that uses splines through the tree-ring data as calibration curves. This eliminates the statistical scatter of the actual data points (Stuiver et al., 1993; Talma et al., 1993; Vogel et al., 1993). 33


4. RESULTS Vibracore Analyses Within the vibracores, 7 different sedimentary facies have been identified, 2 deposited in the pre Holocene and 5 in the Holocene (Figure IO,ll)(Table 2). From bottom to top: (1) limestone gravel facies, (2) blue gray clay facies, (3) organic rich mud facies, (4) muddy-sand facies, (5) shelly facies, (6) mixed siliciclastic/carbonate sand facies, and the fine quartz sand. Pre-Holocene Sedimentary Facies Limestone Gravel Facies If present, this facies is always at the base of the vibracore. It contains lithoclasts of carbonate, gravei to cobble in size, and appears to be fragments of the underlying limestone bedrock (Figure 12) It is only present in core IRB 96-27 where the base of the core consists of a cobble sized limestone ma ss and in core IRB-96-34 where some limestone gravel was located in the core catch er. Ther e appears to be no fauna associated with this facies 34


Figure 10. Harrison's side-scan sonar mosaic with the 21 vibracores extracted for this study plotted with white circles. Low backscatter (light gray to white) corresponds to the topographic highs and high backscatter (darker grays) corresponds to the gravel and rock of the topographic lows. All vibracore labels exclude IRB-96-xx. 35


27 56.300 INDIAN ROCKS BEACH MOSAIC FEBRUARY, 1998 82 54.300 82 54.100 8253.900 500 meters 82 53.700 Figure 11. February, 1998 side-scan sonar mosaic blow up with 12 of the 21 vibracore locations. Low backscatter (light gray to white) corresponds to sands of the topographic highs and high backscatter (darker grays) corresponds to the gravels and rock of the topographic lows.


Quantitative Sediment Analysis Results Sedimentary Facies Std. Dev. Mean (phi) Phi % CaC0 3 %Mud Fine Sand 1.1 2.4 14. 3 .2 Siliciclastic/Carbonate 1.0 2.3 25. 0 .6 Shelly Facies 1.6 .9 59. 9 1 1 Muddy-sand 1.5 2.9 20. 9 19.8 Organic-rich Mud 1.2 3.9 17. 2 57.1 81 ue-gray clay 1.4 2.8 11.2 20.4 Limestone Gravel no grain size data Adjacent Beach Sample 1 1 2.4 17. 9 .3 Table 2. Table displaying the average standard deviation, mean grainsize, per cent calcium carbonate, and percent mud for all the samples of sediment taken from each of the seven different facies Then an adjacent beach sample is shown for comparison. 37


1 em 30 em Blue-gray clay alteration Carbonate Lithoclasts Core catcher Figure 12 Picture of limestone gravel facies being altered to a blue-gray clay from vibracore IRB-96 27. 38


lllue-Gray Clay Facies This facies consists of a highly compacted sediment that is primarily made up of the mineral palygorskite ((Mg,Al)2Si4010(0H)-4H20)(Figure 13,14) In the literature, palygorskite is commonly associated with the Hawthorne Group. The clay commonly contains some sand-sized blackened grains and quartz and is considered to be poorly sorted. X-ray diffraction patterns display the blackened grains to be either calcium carbonate or carbonate fluorapatite (francolite) (Ca5(P04MF))(Figure 15). The facies is found at the base of a few of the cores, IRB-96-8, IRB-96-9(2), IRB-96-11, IRB-96-27, and IRB-96-28 and impedes any penetration of the vibracore. The mean grain size, standard deviation, %calcium carbonate, and %mud averaged for all of the sub-samples of this facies is 2.8 phi, 1.4, 11. 2 % and 20.4% respectively (Table 2). It is characterized as a clay even though the mean grain size of the samples are 2.80 phi because the majority of the sample is clay sized. Within this facies are lithoclasts of calcium carbonate and lenses of quartz sand. Occasionally these get incorporated into the analyses and effect the calculations greatly. Since it is a weight percent all it takes is one or two gravel sized lithoclasts to skew the grain size results. The effect of these sand lenses and lithoclasts is seen in the high standard deviation that determines the facies as poorly sorted according to Folk (1980) Thert appears to be no fauna associated with this facies. Holocene Sedimentary Facies Organic-Rich Mud Facies This facies is dominated with a dark brown to black organic rich mud but also has some sand-sized grains and macrofauna present (Figure 16) It is located at the base of two vibracores cores, IRB 96-23 and IRB -9635, in bed thicknesses of lO's of centimeters and is considered to be moderately to poorly sorted. The mean grain size, standard deviation, % calcium carbonate, and % mud averaged for all of the sub samples of this facies is 3.9 39


1 em 30 em Muddy-sand facies Carbonate lithoclast Blue-gray clay facies Figure 13. Picture of blue -gray clay facies primarily composed of the mineral palygorskite underlying a muddy sand facies from vibracore IRB 96 28. 40


100 90 80 -70 0 > 60 -en c: 50 G) c: 40 30 20 1 0 0 X-Ray Diffraction Pattern Palygorskite peak Primary Ca lcite p7 5 10 15 20 25 30 35 Angle (Degrees) Figure 14. Blue-gray clay sample 122-124 em from vibracore IRB-969(2). The x-ray diffraction analysis was run only on the clay fraction of the sample. The pattern illustrates that the sample is primarily composed of the mineral palygorskite with minor amounts of quartz and calcite. 41 40


X-Ray Diffraction Pattern 90 80 7 0 (/!. >. 60 -tn c: 50 Q) c: 4 0 3 0 20 1 0 Calcite Francolite Quartz 5 1 0 15 20 25 3 0 35 A n gle ( D e grees ) Figure 15. Blackened grains from sample 122-124 em of vibracore IRB-96-9(2). X-ray diffraction pattern illustrates the blackened grains are primarily composed of the minerals calcite and francolite 42 4 0


1 em 30 em Mixed siliciclastic/ rbonate sand lenses punctostriatus Core catcher Figure 16 Picture of organic-rich mud facies from vibracore IRB 96-35 4 3


phi, 1.2, 17.2% and 57.1% respectively (Table 2). There appears to be no microfauna associated with this facies but does contain minor amounts of the gastropods Truncatella caribaeensis and Acteon punctostriatus. Two dates have been acquired utilizing standard radiometric techniques. Muddy-Sand Facies This facies consists primarily of quartz sand with minimal shell similar to the open marine quartz sand but lacks the grayish color because of its olive tinge (Figure 17). The olive hue is attributed to the slightly greater mud content. This facies appears in various thicknesses from <1 em to IO's of em and is only found in cores IRB-96-8, IRB-96-9(2), IRB-96-11, IRB-96-23, IRB-96-27, IRB-96-28, and IRB-96-35. The mean grain size, standard deviation, % calcium carbonate, and % mud averaged for all the sub-samples of this facies is 2.9 phi, 1.5, 20.9% and 19.8% respectively (Table 2). It is commonly seen grading into a much more compacted, viscous muddier sand. The wide range of grain sizes is indicated in the poorly sorted standard deviation value. The facies contains some root structures and the dominant foraminifera species present is Broekina orbitolitoides but in minimal amounts. Shelly Facies This facies consists of high percentages of shell fragments, whole shells, blackened grains, quartz sand, mud, and forams (Figure 18). The sediment has a wide range of grain size (muds to gravels) and therefore in considered poorly sorted as the high standard deviation value concurs. This type of facies can occur throughout the core but most commonly occurs beneath or within the open marine quartz sand facies. This facies can range from a centimeter to tens of centimeters in thickness and can impede penetration of the vibracore. This particular facies is also located in the troughs of the sand ridges in the form of ripples The reworked shell fragments and whole shell are of a variety of sizes 44


1 c 30 em Figure 17. Picture of burrowed muddy-s a nd facies from vibracore IRB 9635 45 Burrows Root Structures Burrows Broekina orbitolitodes


1 30 em S ili ciclast i c / Carbon a t e S h e ll Facies S h ell f ragm e nts a nd B l acke n e d gr a in s C hione cancellata Figure 18. Picture o f shelly sand fa cies u nderly ing a s iliciclastic/carbonate facies from vibra c ore IRB 96-9( 2 ) 46


(sand to gravel) and predominately appear to be of molluscan origin. The blackened grains are also several sizes and X-ray diffraction patterns display that they can be either calcium carbonate or carbonate fluorapatite (francolite) (Figure 19). The mean grain size, standard deviation, % calcium carbonate, and % mud averaged for all the sub-samples of this facies are .9 phi, 1.6, 59.9%, and 1.1% respectively (Table 2). An accelerated mass spectrometry date has been acquired within this sedimentary facies that was thought to represent the base of the sand ridge. The dominant foraminifera species present is Archais angulatus with minor amounts of Broekina orbitolitoides (Figure 20) Various amounts of open marine mollusks are present with the majority being Chione cancellata. Mixed Siliciclastic/Carbonate Sand Facies This facies consists of relatively clean, moderately sorted, fine to medium grained quartz sand with some whole shell and shell fragments (Figure 21). This is the most common facies identified. It constitutes the majority of the ridge sediment and is located in 19 of the 21 vibracores: IRB-96-5, IRB-96-8, IRB-96-9(2), IRB-96-10(2), IRB-96-11, IRB-96-12, IRB-96-13, IRB-96-14, IRB-96-23, IRB-96-26, IRB-96-31, IRB-96-33, IRB-96-34, IRB-96-35, IRB-96-39, IRB-96-40, IRB-96-42, IRB-96-50, IRB-96-51. The vibracores contain stacked units of coarsening upward, fining upward and homogeneous sediments ranging from 1 O's of centimeters to meters in thickness. The mean grain size, standard deviation,% calcium carbonate,% mud averaged for all the sub samples of this facies are 2.3 phi, 1 0, 25.0%, .6% respectively (Table 2). 47


X-Ray Diffraction Pattern 90 80 -70 eft. >-60 -en c 50 C1) c 40 30 20 1 0 Calcite Fr an c o lite 5 1 0 1 5 20 2 5 30 35 Angle (Degrees) Figure 19. Blackened grains from sample 115-117 em ofvibracore IRB-96-35. X-ray diffraction pattern illustrates the blackened grains a re primarily composed of the minerals calcite and francolite. 48 4 0


A B Figure 20. Scanning electron microscope photograph of two most common forams; A) Arclzais angulatus, B) Broekina orbitolitoides. 49


1 30 em Blackened Grains and Shell Fragments cancellata Figure 21 Picture of mixed siliciclastic / carbonate facies that makes up the majority of the sand ridge s from vibracore IRB 96 -11 5 0


The dominant foraminifera species present is Archais angulatus with minor amounts of Broekina orbitolitoides species. The shell fragments appear to be of molluscan origin with the majority of the whole shells being Chione cancellata. Fine Quartz Sand Facies This facies consists of a very clean, light gray to white, moderately sorted, fine to medium grained quartz sand with some carbonate material in the form of shell fragments (Figure 22). It only occurs in two cores, IRB-96-31 and IRB-96-33, which are located in the toe of the shoreface (Figure 11) The mean grain size, standard deviation, % calcium carbonate, % mud averaged for all the sub-samples of this facies is very similar to that of the siliciclastic/carbonate sand facies and are 2.4 phi, 1.1, 14.3%, .2% respectively (Table 2). There appears to be no microfauna associated with the facies such as the Archais angulatus and Broekina orbitolitoides seen in most other facies. The shell fragments appear to be of molluscan origin. Quantitatively, the sands appear to be of very similar compositions to the adjacent beach sand. The adjacent beach sample collected from Sand Key's beach yielded a mean phi of 2.4 phi, a standard deviation of 1.1, a calcium carbonate percentage of 17.9, and a mud percentage of .3 (Table 2) Dating Analyses Six sub-samples from the vibracores were sent off for dating purposes, 2 radiocarbon and 4 accelerator mass spectrometry. The dates are presented as conventional dates (YBP)(Table 3). The bulk radiocarbon results are as follows: sediment sample 200245 em from vibracore IRB-96-23 yielded a date of7,960 +/60 and sediment sample 190213 em from vibracore IRB-96-35 yielded a date of9,880 +/120. The accelerator mass spectrometry results are as follows: foram sample 102-108 em from vibracore IRB-96-9(2) yielded a date of 1,580 +/50, foram sample 93-98 em from vibracore IRB-96-35 yielded a 51


30 em Fine Quartz Sands Shell Fragments and Blackened Grains Figure 22. Picture of fine quartz sand facie s from vibracore IRB-96 33. 5 2


Radiocarbon and Accelerated Mass Spectrometry Results Facies Siliclastic/ Carbonate Sand Muddy-sand Organic-rich mud Sample Material Dated/ Dating Method IRB-96-9(2) Forams/ 102-108 em AMS IRB-96-35 Forams/ 93-98 em AMS IRB-96-11 Forams/ 221-228 em AMS IRB-96 35 Forams/ 150-155 em AMS IRB-96-23 Bulk Carbon/ 200-245 em Radiocarbon IRB-96-35 Bulk Carbon/ 190-213 em Radiocarbon Date 1,580 +1-50 1,260 +160 2,890 +150 3 ,480 +150 7,960 +160 Depth Below Sea Level Approx. (m) 7.9 m 6 8m 7.0 m 7.4 m 9.2 m 9 ,880 +1-120 7.8 m Table 3. Results from Beta Analytic Inc. AMS dates utilized forams Archais angulatus and Broekina orbitolitoides. Radiocarbon dates utilized the bulk carbon from an organic-rich mud located at the base of two vibracores. 53


date of 1,260 +/60, foram sample 221-228 em from vibracore IRB-96-11 yielded a date of 2,890 +/-50, foram sample 150-155 em from vibracore IRB-96-35 yielded a date of 3,480 +/50. Side-Scan Sonar Analysis Sand Ridge Distribution and Morphology Side-scan sonar imagery c ollected in February, 1998 has shown an overview of the morphology of the sand-ridgefield of Indian Rocks Beach. The resulting mosaic uses a 256 gray scale range with the white to gray shades or low backscatter representing the fine to medium grained sands that compose the bathymetric highs and the dark gray to black tones or high backscatter corresponding to the coarse grained shell hash, limestone gravel or hardground exposures. These predominantly make up the troughs of the ridges The light and dark bands of backscatter (ridge/swale topography) making up the sand ridges (siliciclastic/carbonate) have a NW-SE orientation with respect to the shoreline (Figure 11). The sand ridges exist in various dimensions. Harrison (1996) describes a hierarchy of bedforms (1 s\ 2"d, 3rd and 4th order) in the study area that cot>Jesce to create a larger ridge system. Harrison ( 1996) synthesiz ed several works to create a classification system that this study will adhere to First order bedforn1s are the largest of the bedforms existing in this study area and are described as having spacings greater than 1.0 km. These are considered sand ridges by Swift (1984). Second order bedforms are also relatively large scale bedforms, 40-300 min spacing. The s e are classified as sand waves by Jackson (1975). Third order bedforms are also considered sand waves by Boothroyd (1985) and possess spacings of 10-40 m. Finally fourth order bedforn1s or ripples/m ega ripples exhibit spacings of< 10.0 m (Boothroyd, 1985 ) All four classifications are present in the study area and can be resolved with I 00 kHz side-scan sonar. 54


Figure 23 displays the 4lh order bedforms, <10.0 m in spacing, which by definition are considered ripples/megaripples (Boothroyd, 1985) These bedforms in the study area are generally 80 em in spacing and have a north-south orientation. The ripples are only seen in the troughs between the ridges and consist of coarse sands, shell hash, and limestone gravels. Wave oscillatory motions probably are responsible for the development of these bedforms. These bedforms can be resolved with the 100kHz side-scan sonar only if the sonar's tracklines are running parallel with the bedforms, in this case north-south. The side-scan sonar system emits a sound pulse out at angles to the sea floor where the sound is either absorbed or reflected by the sediment matrix. The reflected sound is called backscatter and is received by the transducers of the towfish. Either differences in relief or texture on the sea floor are necessary for the towfish to receive backscatter. As a result of the ripples not possessing surficial sediment texture variations or possessing texture variations beyond the resolution capabilities of the side-scan sonar, only the differences in relief can be detected Therefore, parallel tracklines with respect to the strike of the ridge are required. These tracklines can detect relief differences because the sound pulse emitted will reflect off the flanks of the bedforms unlike tracklines running normal to the trend of the bedforms. For tracklines trending normal, the emitted sound pulse does not have the flanks of the bedfom1s to reflect off of and small scale bedforms such as these can go undetected. S i de-Scan Sonar Mosaic Time Series The hi e rarchy of bedforms in this study a rea w ere first im a ged by Harrison (1996b). With two overlapping mosaics collected eight months apart and many navigation corrections, he illustrated a south-west shift of the 1st and 2"d order bedforms of approximately five met e rs (aft e r n a vigation corr ec tion). Two ye ar s lat e r, this study also collected side-scan data within this area. Again, the bedforms appear to shift 55


Ut 0'1 27 INDIAN ROCKS BEACH MOSAIC FEBRUARY, 1998 82 54.500 500 meters 82 54.300 82 54.100 8253.700 Figure 23. Blow up of sand ridge trough displaying the 4th order bedfonns with approximately a 80 em wavelength. The bedfonns are composed of a coarse shelly sand.


south-west (Figures 24,25,26). Third order bedform mobility is difficult to discern and 4th order bedforms certainly would not be identifiable between mosaics. In addition, 4th order bedforms are not resolved in Harrison's mosaics. Distribution The sand ridges of west-central Florida begin approximately two km offshore and extend to distances greater than 25 km (Harrison, 1996b) Vibracores have determined that the sand ridges are isolated and not shoreface attached. Vibracores used in conjunction with sub-bottom profiling have shown the inner shelf to go through a transition where the sand ridges attenuate and the bedrock begins to rise. The data suggest there is a zone where there is a thin to no sediment veneer, an area with a relatively shallow limestone bedrock. This inner shelf region most commonly possess sediments such as blue-gray clay and limestone gravel all very shallow within the sediments. This is seen in vibracores IRB96-27 and IRB-96-28 and suggests a shallow limestone bedrock (Figure 27). All vibracores west of this zone posses a mixed siliciclastic/carbonate sand sequestered in the form of sand ridges. East of the zone, the vibracores are composed of finer sands of the shoreface. Sub-bottom Analysis Chirp sonar and high-resolution seismic data have displayed the sand ridges to be approximately three meters in relief, 200 300 meters in width, and have a relatively symmetric cross-sectional profile. An intermittent refle ctor is common and marks the base of the sand ridge unit (Figures 28 and 29). This is seen throughout the study area and is usually an unpredictable surface because of its karst-type characteristics. The reflector has been correlated with various facies transitions within the vibracores (Figur es 30,31 ,32,33). Most commonly it defines the boundary between the Cenozoic lim esto ne bedrock or the blue-gray clay with the Holocene sediment deposits such as a thick lags of shelly sand, 57


....... ....... : . 82 54300 82 54.100 82 53.900 82 53.700 500 Figure 24. Side-scan sonar mosaic collected in February of 1998. White outl i nes signify the contact between sand and coarse shell hash/limestone outcrops


27 56.500 27 56.400 27 56.300 82 54.300 82 54.100 82 53.900 82 53.700 5 0 0 Figure 25. Harrison's mosaic of 1995. White outlines are the same as in figure 24, georeferenced and overlying Harrison's mosaic. Displays approximately a 20 meter south-west shift that appears to be a sur veying artifact.


27 56.500 27 56.400 82 54.500 82 54.300 82 54.100 82 53.900 82 53.71HJ 500 meters Figure 26. Harrison's side-scan sonar mosaic of 1995 with overlapping outlines of February 1998's mosaic. Blow up displays similar geometries of small scale features between the two mosaics through time. This suggests the overall south-west shift seen is an artifact. If migration distances were true, morphologies of small-scale features should be unrecognizable from mosaic to mosaic.


27 57' 00" 27 56'()()" 27 53'()()" t 11111111111 N 1 km Transition Zone where ridge/swale topography attenuates Figure 27. Harrison's Indian Rocks Beach mosaic of 1995 showing vibracore locations in transitional zone of the inner shelf. Sand ridges attenuate and the shoreface begins in this zone. Ridge/swale topography of the side-scan sonar data also loses definition in this region. 61


Chirp Sonar Profile Figure 28. Chirp sonar interpretation indicating sand ridges are approximately 2-3 meters in relief with a intermittent reflector defining the base of the sand ridge unit. Base of the sand ridge unit generally can be defined lithologically by a coarse shell lag although muds and clays are common.


10m High-Resolution Seismic Profile Figure 29. High-resolution seimic profile displaying multiple sand ridges with reliefs of approximately 3 meters. Intermittent reflector defines the base of the sand ridge unit.


1m-IRB-96-8 Sand P Jl -Shelly Sand -Muddy-Sand 0 -Organic-rich Mud t::::J ... : Clay 100 meters IRB-96-9(2) Figure 30. Displays vibracores IRB-96-8 and IRB-96-9(2) superimposed upon corresponding chirp sonar profile. Notice the intermittent reflector aligning with a major facie change within the vibracores.


.5m-IRB-96-1 0 IRB-96-11 1:: : j-Siliciclastic/Carbonate Sand ;,j -Shelly Sand j; I:] -Muddy-Sand r:.:'.:I Organic-rich Mud -Blue-gray Clay (\'\':. 199 m et ers -1m -2m Figure 31. Displays vibracores IRB-96-1 0 and IRB-96-11 superimposed upon corresponding chirp sonar profile. Notice the intermittent reflector aligning with a major facie change within vibracores.


0\ 0\ 1m 2 m IRB-96-23 Seafloor 100 m hd -Siliciclast i c/Carbonate Sand pJ -Shelly Sand p::'::j-organi c-rich Mud Figure 32. Displays vibracore IRB-96-23 superimposed upon corresponding chirp sonar profile. Notice the intermittent reflector aligning with a major facie change within vibracore and the limestone depression hosting the organic-rich mud. -7 m 10m


1m 2m IRB-96-35 b d -Siliciclastic/Carbonate Sand H -Shelly Sand -Muddy-Sand E < ..;j-Organic-ri ch 100m Figure 33. Displays vibracore IRB-95-35 superimposed upon correspond i ng chirp sonar profile. Notice the intermittent reflector aligning with a major facie change within vibracore and the limestone depression hosting the organic-rich mud, similar to IRB-96-23. 7 m 1 0 m


muddy sand or organicrich mud deposits. This particular reflector shallows and changes slope from offshore to onshore providing a bedrock terrace (1-1.5 m of relief) in the study area for the barrier island to aggrade upon, preventing land wards migration of the barrier island (Evans et al., 1985). 68


5. DISCUSSION Depositional Environments of the Seven Sedimentary Facies Seven sedimentary facies have been described from the 21 vibracores collected in the study area. The vibracores have revealed the sedimentary units to be discontinuous and patchy throughout the inner shelf. An idealized stratigraphic model has been developed to display the relationships between the seven different sedimentary facies. The base of all the sedimentary facies are the limestone lithoclasts The lithoclasts are occasionally overlain with a blue-gray clay facies followed by an organic-rich mud facies, a muddy sand facies, a shelly facies, siliciclastic/carbonate sand, and finally a fine quartz beach sand facies (Figure 34). The idealized model is a transgressive sequence illustrating a landward migration of depositional environments. Limestone Gravel Facies The limestone gravel facies was discovered in two of the vibracores and was always at the very base of the vibracore usually in the core catcher (Figure 12). The facies alway causes coring refusal and is interpreted to be fragments of the underlying limestone surface. It occasionally grades into the blue-gray clay facies. Blue-Gray Clay Facies In 5 of the 21 vibracores a blue gray clay is found at the base The facies lies directly over the limestone bedrock and contains some limestone lithoclasts and blackened grains (Figure 13) The highly compacted sediment is primarily composed of the mineral 69


"'0 c: "' V) QJ c: u:: >. "' 0 >. 3 0 em 30cm C) I QJ :::1 iii I I I "'0 c: "' I V) QJ .... "' c: 0 ..0 .... "' 30cm u ....... u p C/) "' u ;g V5 Figure 34. Represents an idea li zed stratigraphic model and the patt erns ass i g ned to each of the sediments on the i n ner shelf of west -cen tra l Flori da. 7 0


palygorskite according to X-ray diffraction patterns (Figure 14). This type of facies has been reported in the literature to be affiliated with the Hawthorn Group and is interpreted to be a diagentic alteration of the underlying limestone bedrock. Above this facies is a distinct contact representing a depositional hiatus. Organic-Rich Mud Facies The organic-rich mud facies is only present in two of the 21 vibracores. It is located at the base of the two vi bra cores and radiocarbon dates of 7,960 and 9,880 YBP have been acquired (Table 3). These dates place the facies being deposited at approximately sea level if Wright's (1995) sea level is extrapolated back in time (Figure 35). The organic nature and marsh gastropods (Truncatella caribaeensis and Acteon punctostriatus) present suggest the facies to be deposited in a marsh-type environment. The reason the facies is only seen in two of the vibracores is because preservation of the organics is only possible if a shelter is provided by a negative relief bedrock feature. The only two vibracores the facies is present in are located in limestone depressions according to chirp sonar data. The topographic low protects the mud from the erosive properties of the shoreface during the Holocene transgression (Figures 32 and 33). Muddy-Sand Facies Riggs and O'Connor (1974) describe this facies to be a lagoonal sediment that is about 10 feet thick under the barrier island, and thins and deepens seaward from 1/4 to 1 1/2 miles offshore where it laps onto the Miocene rock surface. They describe a very muddy-sand unit that contains abundant plant fragments that grades into a very peaty sediment at the base, a facies that contains brackish water fauna. Therefore, they interpret the entire facies to be a back-barrier deposit. This study suggests two possible depositional environments. The relic root structures and burrowing evidence (Figure 17) both suggest that the facies accumulated in a 71


14c(5568 half-life) years (BP) 9000 1 I I 2 I E I 3 E I 8 I I Vl '71 N --. 4 E Q\ iit N ..c: a. Cll c Vl _I Vll 5 I d; I Q\ Q\ 6 :::I =I e.: I e.: I e.: I e:l 7 I 8 9 Core ID Sub-sample Depth below Conventional Sealevel Date IRB-96-9(2) 102-108cm 7.9 1,580 +I-50 IRB-96-11 221-228cm 7.0 2,890 +I-50 IRB-96-23 200-245cm 9.2 7,960 +l-60 IRB-96-35 93-98cm 6.8 1,260 +l-60 IRB-96-35 150-155cm 7.4 3,480 +I-50 IRB-96-35 190-213cm 7.8 9,880 +1-120 Figure 35. Sea level curve compiled from west Florida data from Suwannee River (Wright, 1995), Wacassassa Bay (Goodbred, 1994), and the Ten Thousand Islands (Scholl eta!., 1969) The data displays a sea l evel rise with a dece leration at approximately 4 ,000 YBP. Radiocarbon and accelerator mass spectrometry dates from this s tudy are labeled with dashed lines displaying the approximate depth below sea l evel at the time of deposition. 72


sea-grass bed, but the geographic locations of the deposit can differ with respect to the barrier island. It is inferred the muddy-sand was either deposited in the back-barrier or nearshore regions in approximately five meters of water depth (Figure 35). The ambiguity is a result of sea grasses existing in high-energy environments can produce a relatively low-energy sedimentary signature, such as a back-barrier region (Hine et al., 1986). This makes paleogeographic reconstruction difficult. Hine et al. (1986) describes this situation just north of the study area. Offshore of Anclote Key, FL between 1957 and 1967, an extensive seagrass community in the nearshore died off leaving behind a facies that is difficult to discern from a lagoonal/back-barrier facies. Fortunately, such an episodic event was documented which opens the door for additional interpretations. Above this facies both gradual transitions and distinct contacts have been noted to occur with the shelly facies or mixed siliciclastic/carbonate sand facies. Shelly Sand Facies The shelly facies is primarily composed of shell fragments and whole shell (Figure 18). It is interpreted that the majority of the shell is reworked from the sand ridges and adjacent trough. Other common constituents are blackened grains and limestone gravel. These appear to be eroded out of the underlying limestone bedrock. X-ray diffraction depict the black grains to be either calcium carbonate or carbonate fluorapatite (francolite) (Figure 19). This facies can be deposited under a variety of environmental conditions; all open marine deposits. First, the thinner shell hash lenses located throughout the vibracores may represent high-energy storm events that rework and deposit coarse material. Secondly, the thin marine shell lenses could represent the base of a migrating bedforms. Coarse shelly sediments are present in the troughs in between the sand ridges. These sediments could be the source of the basal gravel seen in the vibracores for the siliciclastic/carbonate sands to migrate upon. Lastly, the more apparent thick layers that tend to occur at the base of the 73


open marine siliciclastic/carbonate sand facies and may represent a ravinement surface. This is an erosive lag of coarse sediment that is left behind from shoreface erosion as the barrier island retreats during a sea-level rise (Figuereido, 1984; Swift et al., 1984; Rine et al., 1991). This is a common feature on the U.S. Atlantic coast's sand ridges and may play a role in this study area's ridges. The siliciclastic/carbonate sand facies and the shelly facies can also be interpreted as one combined open marine facies. Throughout the vibracores, stacked units of open marine sand facies are separated by various thicknesses of marine shell facies layers. It is a possibility that the inter-bedding of the two facies can represent different stages of sand ridge growth. The theory implies that the sand ridge growth stage is represented by the siliciclastic/carbonate sand deposition and non-depositional periods are represented by a coarse shell lag. Perhaps the energy conditions of the environment change or the influx/outflux of sands to the ridge field changes to create such a pattern. Mixed Siliciclastic/Carbonate Sand Facies The mixed siliciclastic/carbonate sand facies is an open marine deposit and is the most common of all the facies. It occupies the tops of all the vibracores with exception to the four located closest to the beach. Vibracores used in conjunction with seismic profiles show the facies to range in thickness from 1 O's of centimeters to up to four meters. This sediment forms a thin veneer over the inner-shelf and is commonly sequestered into obliquely oriented, linear submarine sand ridges. An AMS date of 1,580 +/-50 YBP acquired from the base of this facies indicates that sand ridges are a very recent development in the Holocene and deposited in approximately seven meters of water depth (Figure 35). This open marine sand makes up the majority of the sand rid g es. Within the vibracores of the sand ridges, stacked units of fining upward sands, coarsening upward sands and homogeneous sands are pres e nt. The stacked units are usually separated by 74


coarse shelly layers. The. open marine facies can be superimposed on any of the other six facies but most commonly overlies the muddy-sand or coarse shell layers. Previous studies have described these types of graded bedding characteristics (fining upward or fining downward) to be common amongst migrating bedforms (Moody, 1964; Swift and Field, 1981; Stubblefield and Swift; 1981 ). One interpretation is that the stacked units of the open marine facies are individual migrating bedforms There maybe some evidence of migration and this strata feature could be the result of coaslescing bedforms. Fine Quartz Sand Facies The fine quartz sand facies is only located in two vibracores very close to the beach. It is very similar to the offshore siliciclastic/carbonate sand seen sequestered in the sand ridges but is clearly a different unit. Grainsize data quantifies their differences as well as visually they appear different. The fine sand facies has a much cleaner appearance to it and lacks the darker gray colors. It has a whitish color, very similar to the adjacent beach sand and one interpretation is that it is a shoreface deposit. Therefore the two (shoreface and adjacent beach sand) were compared with grain size and percent calcium carbonate methods. What was considered the shoreface yielded a 2.4 mean phi, 1.1 standard deviation, 14.3% CaC03 and .2% mud values. This was very similar to the 2.4 phi, 1.1 standard deviation, 17.9% CaC03 and .3% mud values calculated from the beach sample collected from Sand Key beach (Table 2). Therefore the two facies are considered to be the same. They represent a sedimentary facies that is very dynamic, always mobile, and constantly exchanging with the beaches. An additional interpretation could be that the sand collected here are exotic, derived from a beach re-nourishment in or near the study area. Some of the beaches in the proximity have und e rgone re nourishments and sediments from this could skew grain-size results. 75


Inner Shelf Evolution The inner shelf of west-central Florida as well as continental shelves throughout the world have experienced many rises and falls of sea level during the Pleistocene (Fletcher and Wehmiller, 1992). The sediments re c overed in the vibracores is not a continuous sediment record back to the limestone bedrock but the vibracores do have good representation of the latest accumulation from the most recent Holocene transgression. The next few paragraphs are going to describe the evolution of the inner shelf by interpreting the depositional history of e a ch of the sedimentary facies displ a yed in the vibracores. The interpretation will give a basic idea of how the inner shelf evolved from the oldest of bedrock to the most recent active pan of the sand ridge. Two models of inner shelf evolution are discussed Model one describe s the barrier island aggradation method and model two describes the barrier island mi g r a tion method. Figure 36 demonstrates a simple schematic of Model one's sequence of evolutionary events through time. Model 1 The Cenozoic limestone bedrock is the underlying foundation of the modem sedimentary facies. It possesses a karst topo g r a phy with v a rious pits, v a lleys and depressions and is commonly diagen etic ally a ltered to a bluegra y clay c omposed of the mineral palygorskite. This is the top of a major sequ e nce boundary. It is these n e gativ e relief features of the bedrock that host the org a nic-rich se diment. This is the oldest Holocene s e diment a ffiliated with the sand rid ges but still millions of ye ar s young e r than the bedrock and blue gray cl ay. Brook s (199 8 ) h as d a t e d this limestone bedrock a nd the blue-gray clay to Miocene in age. Only two of the twenty one vibracores extracted bear this organic rich facies. The two org a nic-ri c h f a cies h ave been d a ted to 7 960 and 9,880 YBP which put s sea l e vel a p prox im ately 8 to 10 m e t e r s below p r ese n t d a y sea l e v e l if you extrapolate Wright's sea le v el curve from 199 5 (Figur e 35) The depth of thi s facies is 7 6


8 Inner Shelf Evolution MODE L 1 Muddy-Sand Organicich Mud 2km Sea Grasses Sea Level 2 Approximately 4,000YBP 1Om L imestone edroc k Mu ddy-Sand OrganicR ich Mud 2km c Barrier I sland Sea Level3 Present Muddy-Sand Organic Rich Mud 2km Figure 36. Schematic of the evolutionary stages of the inner shelf through the Holocene. It is suggested that the nearshore was originally a protected low-lying marsh coast environment (A) that gradually shifted with sea-level rise. The rise caused an increase in the environment's energy, sea grasses to retreat, erosion of the muddy sand deposit, and invasion of shelf sand via longshore currents. The eroded mud deposit and shelf sand began to be sequestered into sand ridge structures (B) Eventually the inner shelf was modified to the open -marine environment seen today (C). 77


approximately nine meters below present day sea level. Therefore, at the time of deposition, sea level was within +/-a meter. This suggests a very broad low-lying coastal plain that produces much organic material, probably a marsh-type environment. Presence of common marsh gastropods Truncatella caribaeensis and Acteon punctostriatus also lean towards a marsh-like environment (Perry, 1955). Sea level was slowly transgressing across the shelf and reworking/oxygenating the exposed organics while the sheltered sediments in the bedrock lows remain relatively undisturbed. Overlying the organic-rich sediment is a muddy-sand facies that contains root structures but lacks the marsh gastropods AMS dates place deposition of this facies in approximately five meters of water depth (Figure 35). This suggests that sea-level continued to rise causing the coastline to retreat and patchy sea-grass beds to develop. The seagrass beds bound the finer sediments and prevented some of the erosive processes of the transgressing sea. The muddy-sand facies displays a graded bedding characteristic. There appears to be a gradual transition shown in the vibracores from a more mud-rich sediment to a less muddier sand. This is evidence of a transgressing sea probably invading with open marine sands brought in by longshore currents and the reworking of Plio-Pleistocene deposits. The continuing transgression probably increased the energy of the environment imposing shoreface erosion and stressed the sea-grasses beyond adequate living conditions and the beds began to die off. Three methods of seagrass mortality that may pertain to this study have been postulated by Hine et al. (1986) from a Anclote Key study, which are as follows: 1) physical destruction by storms; 2) infection by pathogens; and 3) sea urchin overgrazing. Eventually the sea -g rasses died off completely and liberated thousands of years of muddy-sand bound by the seagrass root structures. The sand-sized sediments were now free to be incorporated into bars, barrier islands, sand ridges, etc. while the mud sized sediments probably r ema ined in suspension until they were deposited offshore in a lower energy regime. 78


Davis and Kuhn (1985) explain a similar situation seen within cores from Anclote Key. They describe extensive sub-tidal grass flats, to supratidal mangrove swamp and salt marsh environments present from approximately 4,400 to 2,000 years ago offshore of Anclote Key. Around this time, they explain that the outer fringe of the mangrove swamp was experiencing wave activity but not enough to develop a beach. As wave action increased with a rising sea level, this type of environment was out of equilibrium and the sand that was bound up by the seagrass rhizomes was liberated. When sea level reached the break in slope cf the limestone bedrock terrace, a concentration of sand and shell accumulated as a subtidal shoal. Continued wave action and sea-level rise caused aggragation of the shoal until it became a barrier island. Subsequently, environments typical of a barrier island system developed including beaches, dunes and mangrove covered overwash fans (Davis and Kuhn, 1985). This idea concurs with Evans et al.(l985). He infers that a growth stage of the barrier island was initiated by a late Holocene slow down in sea level and an increase in sediment supply as sea level reached the bedrock terrace of west-central Florida. The sand ridges begin to develop in the shoreface, growing vertically to up to four meters consisting of a mixed siliciclastic/carbonate sand. The sand were derived from longshore currents and the reworking of Plio-Pleitocene deposits. AMS dates of approximately 1,500 years ago were calculated at the base of the sand ridge and place their initiation in approximately six to seven meters of water depth (Figure 35). The sand ridges overlie what is left of the muddy-sand facies and protect the sediments from the erosive properties of the open-marine environment. This preserves the core of muddy-sand under the sand ridges and leaves the part of the facies not protected by the sand ridges exposed causing the muddy-sand facies to be eroded away at the flanks and troughs of the sand ridges. Eventually leaving only the muddy-sand cores beneath the sand ridges (Figure 37). 79


Ridge troughs undergoing erosional San Ridge San Ridge Muddy-sand Muddy-sand Coarse Shelly Sand Figure 37. Schematic of preservation of the muddy-sand core. It is sug gested that the sand ridge shelters the muddy-sand from open marine con ditions and preserves it. This is because of the sand ridges limited mobility. In the troughs and flanks of the sand ridges the muddy-sand get winnowed away while the main muddy sand core is protected. 80


It is suggested by this theory that the barrier island aggraded at or at least close to its present position which is supported by Davis and Kuhn (1985) and Evar.s et al. (1985). The muddy-sand and organic-rich mud appear to be deposited in a protected marine environment but, as mentioned before, these facies can be confused with a back-barrier deposit. Therefore model two was developed. Model 2 Within the vibracores some minor evidence exists of a transgressing barrier island. Coarse lags of sediment are common in between the muddy-sand and siliciclastic/carbonate facies that may represent a ravinement surface left behind as the barrier island transgresses. This suggests a barrier island was present greater than six km seaward from the present barrier island approximately 10,000 years ago. Riggs and O'Connor (1974) work also supports this. Figure 38 demonstrates a simple schematic of the sequence of evolutionary events time of the barrier migration model. Sand Ridge Evolution Data have shown that the sand-ridgefield of west-central Florida coast is a very complex system, with many similarities and contrasts to the sand ridges of the U.S. Atlantic margins Therefore, many of the sandridge evolution theories for the U.S. Atlantic margin will be investigated for possible comparisons but can not be completely translated from one environment to another because of the few contrasting characteristics. Some comparisons include similar orientations to the shoreline, locations on the inner shelf and asymmetric smficial sediment grain size patterns. The sand ridges of west central Florida and their Atlantic counterparts all trend obliquely to the shoreline at approximately 30-35, generally open towards the dominant wave train and posses coarser 81


A Inner Shelf Evolution MODEL2 Ravinement Surface ? Sea Level Appro xim 8,000YB P Barrier I sland Ravinement 1 8 Sea Grasses S an d Rid g e s S u r face? l Sea Level 2 Approximately 4,000 YBP Lim e st one ed rock Muddy-Sand 2km c Sea Levcl3 Present M u ddy-Sand Limesto n e B edroc Organic Rich Mud 2km 10m Figure 38. S chematic of the evolutionary stages of the inner shelf through t he H ol o cene I t is suggested that a barrier island existed offshore (A) and migrated acr o ss t h e shelf wit h sea-level rise (B). The barrier is l and migrated until it reached a b edrock terrace that prevent additional landward migration a n d developed into the coastline seen today (C). 8 2


sediments on the up-current flank than the down-current flank. Although the grain size gradient is a much more gradual transition on the crests of west-central Florida's sand ridges than that of the Atlantic margin, there still appears to be similarities. Contrasts between the sand-ridge systems include dimensions and cross sectional shape. U.S. Atlantic ridges are generally an order of magnitude larger in every aspect and have a steeper slope on the up-current flank than the down-ctment flank. The majority of sand ridges in the Sand Key region tend to have symmetric cross sections according to subbottom profiling data, although there are asymmetric exceptions (Figures 28 and 29). Both systems are located in areas that are considered swf zones during major storms and both posses characteristics of wave-built bars as a result of these storms, but ridge genesis canner be completely explained by this. The main reason is because of the subparallel orientation to wave train. Wave ori ginate d bars are typically nonnal to the wave approach (Sonu eta!., 1967) and this is not true is these situations. Other genesis theories must be considered. Shoreface, nearshore and offshore ridges constitute a sequence of evolutionary stages (Swift and Fi e ld, 1 ). Swift and Field postulate that the changing characteristics of the sand ridges with respect to the location on the shelf are a result of the changing hydraulic regime associated with sea-level rise. Therefore, shoreface sand ridges have been interpreted to r e pr e sent the initial stages of evo lution durin g the Holocene transgression (Swift and Field, 1981 ). An attractive analogy would be Swift eta!. (1972 ) and Duane eta!. (1972). They developed a model of ridge growth model as a result of shoreface retreat. The model suggests that th e ridges are a result of coastal stom1 c urrenrs in conjun ctio n with h e lical flow during a period of shoreface retreat. The morphology, sedimenrary character and current meter data from the inner shelfs sand rid ges of west-central Florida indicate that fluid motion associated with storms can play a major role, but other factors a lso come into play too. Harrison (1996b) concluded that bottom flow recorded in a current-meter survey


of the study area was generally a bi-directional flow. The prevailing flow observed was slightly skewed NNE-SSW. Interestingly, only during intense stom1 events was the critical threshold velocities reached to induce fine-grained sediment transport and the dominant direction during these events was in a southerly direction. This concurs with the slightly asymmetric grain-size pattern displaying a coarser northern than southern ridge flank and south-west migration behaviors The obliqur nature of the sand ridges still remains a mystery. Swift and Fie'ld (1981) suggest thatthe oblique nature of the ridges may be due to the rapid intensification of wave orbital velocity as the breaker zone of the inner shelf is approached. Therefore, the transporting flow component would be more efficient near the beach than further offshore. Consequently, sand ridges closer to the nearshore would migrate faster than offshore. In addition, a second reason for faster migration is that the sand-ridgecrest is shallower inshore than offshore and as a result will constrict and accelerate the flow Bottom flow data in Harrison's study only included a current meter in the trough and adjacent ridge well offshore. The study did not sample current data throughout the inner shelf. In addition, the sampling rate of HaiTi son's current meters were relatively low compared to orbital wave motions too. Therefore, this intensified nearshore flow is completely speculative The current intensification would also cause sand ridges to curve along the strike and this is not a characteristic seen. If the evolutionary sequence mentioned above for the sand ridges were true the growth of the ridges would be from offshore to onshore with sea-level rise. The farther offshore, the more mature the sand ridge. Therefore, radiometric dating techniques should display older dat es farther offshor e at facie boundari es The four acce l e rated mass spectrometry dates acquired (Table 3) prove to be inconclusive. Two dates acquired from the base of the sand rid ge units (siliciclastic /c arbonate faci e s) in two diffe r e nt vibracores displayed an age dat e opposite of wh a t was expect e d Vibracore IRB-96-35, 2/3 of a km farther offshore than vibracore IRB-96-9(2), displayed 84


a date approximately 300 years younger. On the other hand, two dates acquired from the base of the muddy-sand facies display age dates of what would be expected of sand ridges growing forn1 offsrore to onshore with the Holocene transgression. A vibracore (IRB-9635) approximately 1 km farther offshore than another (IRB-96-11) displayed an age approximately 500 years older. The data collected leads to the speculative conclusion that inner shelf sand ridges are sequestered by hydrodynamic processes acting during storm events. The general bi directional flow described by Harrison (1996b) never reached the critical threshold velocities of major sediment transport. This bi -di rectional flow could possibly modify the ridges slightly but the storn1s that exceed the critical threshold flow velocities probably do the majority of the sand ridge erosion/deposition. In summation, the coastline appems to be retreating in response to Holocene sea level rise. As a result, the shoreline rec edes, the water level deepens over the sand ridges, and the sand ridges undergo a series of maturation stages of elongation and growth due to the different hydraulic regimes presented by the deepening water. The study area's sand ridges are considered to be in the initial srages of the evolutionary sequence and are undergoing modern modification primarily by storm generated currents. Mobility and Stability Submarine sand ridges occur on the inner shelf of Sand Key in various shapes and sizes. Illustrated in the data is a hierarchy of sand ridges (ls\ 2"d, 3rd, and 4th order). All scales of sand ridges described are not relic features, but appear to be active under today's hydraulic regime. Harrison (1996b) displ ayed overlapping side scan sonar mosaics in the study area spaced in time approximately eig ht months apart as mentioned in the results. The mosaics indicate a five meter south-west shift of the sand ridges. Side-scan sonar data collected and 85


georeferenced in February 1998 of the same area also illustrates a south-west shift in the sand ridges; a shift of approximately the same magnitude (Figures 24 and 25). Although, this large of a shift is believed to be an artifact of the sampling technique. Comparative studies of the three overlapping mosaics have been examined. It is suggested that the hydraulic conditiom: presently acting on the sand ridges on a yearly time scale have minimal effects on the 151 and 2"d orders but do impact the smaller 3'd and 4th orders. It appears that the smaller scale features and the flanks of the larger order ridges are continuously getting reshaped and reorganized, but at a magnitude not great enough to imply large-scale ridge migration. Many morphologic features easily discernible with the eye in the mosaic maintain similar geometries from mosaic to mosaic which suggests the shift in the ridge mass through time is an artifact. Geometries of small-scale features should not be preserved if relatively large-scale ridge migration is active. The small-scale features would not be recognizable from the first mosaic in 1995 to the last mosaic in 1998 (Figure 26). Therefore, it appears that the submarine sand ridges are fairly stable under present hydraulic conditions only with minor amounts of sand reorganization. In addition, sedimentary facies analyses of vibracores suggest that the sand ridges have been fairly stable. Preserved within the sand ridges are cores of muddy-sands with paleo-seagrass bed evidence (root structures and burrows) (Figure 17). This sedimentary facies has been radiocarbon dated at 2 to 3 thousand years before present. If large scale migration were occurring at the rates displayed in the data the muddy-sand would of been exposed to open marine conditions, out of equilibrium and reworked (Edwards, 1996)(Figure 39). Furthermore, mature biological communities (sponges and soft corals) live within the swales of the ridges that also suggest a stable ridge system. If five meters of migration per year was true, biological communities would be buried often and would not have the time to develop to such an extent. These biological communities corrode and bioerode the exposed bedrock. Riggs and O'Connor (1974) suggest if the sand ridges did not migrate, 86

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Time 1 away Time 2 Coarse Shelly Sand Left Behind Time 3 Demise of Muddy -sand ______....__ Figure 39. Schematic of sand ridge migration. It is suggested that if the ridge is migrating the muddy-sand core would get exposed to open marine conditions, get reworked, suspended, and not be preserved leaving a shelly sand vaneer behind. 87

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a unaltered limestone bedrock should exist beneath the protective sand ridge (Figure 7). The data for this study proves to be inconclusive. The sub-bottom data shows a karst-type bedrock but not enough to infer that it hosts a buried biological community as a result of sand ridge migration. In addition, little to no evidence of hardbottom communities exist within the vibracores. Coarse sand on the up-current flank and fining of the sand on the down-current flank is characteristic of migrating bedfonns (Swift and Field, 1981 ). Harrison ( 1996b) completed surficial sediment analyses and found a slightly asymmetrical surficial grain-size distribution of the sand ridge which suggests a possible mobile sand 1idge. Harrison's (1996b), grain-size survey showed the sand ridges mainly posses a coarse siliciclastic/carbonate shell hash with limestone fragments in the troughs and finer siliciclastic/carbonate sand on the crests. The crest of the ridge itself, did consist of a slightly coarser sediment on the up-current than down current flank but was not discernible enough to imply ridge migration. The combination of vibracore and side-scan data implies that the sand ridges on a year to year basis ar.! stationary and that the majmity of the south-west shift manifested in the overlapping mosaics must be an artifact. It is possible that first and second order bedforms are presently migrating, but, at very small distances beyond the resolution capabilities of the side-scan sonar Third and fourth order bedfmms appear to be active but are definitely too fine a scale to predict migration behaviors with this methodology. Perhaps a yearly time scale is too small to see significant mobility differences and continuous side -sc an coverage over many decades can resolve migration behaviors better. Sand ridges of the U S. Atlantic margin are said to migrate approximately 1 km/1000 years (Swift and Field, 1981). Perhaps west -c entral Flmida's ridges have a slightly slower migration rate and effects have not yet been seen because of the immaturity of the sand ridges. Until the n a vigation used with the remotely sensed data collection methods 88

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are more precise or the sand ridge migration distances are greater than the error of the DGPS the questions of mobility will remain. 89

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6. CONCLUSION Vibracore and remotely sensed data shows the surface of the inner shelf of west central Florida to be characterized by obliquely oriented, linear sand ridges composed of a mixed siliciclastic/carbonate sediment. The sand ridges extend from two to greater than 25 km offshore and are considered to be unattached to the shoreface. The sand ridges are a large part of the inner shelf of west-central Florida and are a result of the dynamic hydraulic processes of inner shelf. An understanding of them can provide a better understanding of the coastal processes that modified or is modifying the inner shelf. Listed below are the conclusions of the study. 1) The vibracores display seven different sedimentary facies. An idealized stratigraphic model relating the facies shows the underlying base unit to be a Cenozoic limestone bedrock, a unit with karst-type characteristics. Although the karst-type topography does not impact the location of the sand ridges, it does impact the sedimentary facies within. It appears that the antecedent limestone bedrock does play a role in the preservation of the organic-rich mud facies. Only two of the 21 vibracores extracted possess this facies and both occur over a negative-relief feature in the bedrock. The depressions shelter these from shoreface erosion processes from sea-level rise. From the base up, overlying the bedrock is a blue-gray clay facies determined to be a diagenetic alteration of the limestone bedrock. Continuing, an organic-rich mud facies deposited in a marsh environment lies beneath a muddy-sand facies with root evidence. This facies has been interpreted to be a paleo-seagrass bed in a protected marine 90

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environment. Commonly a shelly facies overlies the muddy-sand and is considered to be deposited under a couple of different regimes. Small lenses of this facies are determined to represent storm layers while larger units are considered to be the base of migrating bedforms or the erosive lag of a ravinement surface. The last two facies (siliciclastic/carbonate sand and fine quartz sand) are the most recent deposits The mixed sand is deposited in open marine environment and makes up the majority of the sand ridge's sediment. The fine quartz sand facies is considered to be part of the shoreface and deposited under surf zone conditions or possibly a exotic sediment derived from a beach re-nourisment. 2) The idealized stratigraphic model forms a transgressive sequence with a landward migration of depositional environments. Radiocarbon dates (7,960 and 9,880 YBP) show the organic-rich facies to be deposited in the early Holocene at approximately sea-level. Accelerator mass spectrometry dates (2,890 and 3,480 YBP) from forams suggest that the muddy-sand facies, above the organic-rich unit, was deposited as a seagrass bed in approximately three to four meters of water depth. Finally, the modem ridge system dates (1,260 and 1,580 YBP) show the sand ridges are recent features that were deposited under modem hydraulic conditions. The dates and stratigraphic relationship between the seven sedimentary facies represents a classic transgressive sequence. 3) The sand ridges of the inner shelf of west -c entral Florida are morphologically similar to that of the intensely studied U.S Atlantic margins. The only major difference is that west-central Florida's are an order of magnitude smaller In light of this and current meter data collected in the study area by Harrison (1996), a similar evolutionary theory is suggested. Current-meter data displayed that only during storm events were the currents strong enough to reach the critical threshold velocity that would mobilize sand ridge 91

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sediment. It is then inferred that the sand ridges of Sand Key are a result of storm activity that continuously carves and sequesters the sand into a ridge formation. This process combined coastal retreat as se1l: level rises causes the ridge to elongate and to grow from offshore to onshore into the features seen today. 4) The sand ridges described are not relic features but appear to be active under the modern hydraulic regime. Evidence exists for both mobile and immobile ridge behaviors. Overlapping time-series mosaic, asymmetric surface sediment textures and a southerly storm flow are supporting evidence for migrating sand ridges. On the other hand, data displaying a inner-core of muddy-sand, similar geometries of small-scale sand bodies from mosaic to mosaic, a symmetric ridge cross section, and a mature live bottom community residing in the troughs leans to a more stable, immobile feature. The study suggests that large scale south-west shifts displayed in the mosaic time-series must be an artifact or of a lesser magnitude 92

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7. REFERENCES Ball, M.M., (1967), Carbonate Sand Bodies of Florida and the Bahamas: Journal of Sedimentary Petrology, 37, pp. 556-591. BaiTell, J., (1912), Criteria for the recognition of ancient delta deposits: GSA Bulletin, v 23, p.377-446. Bock, W.D., Lynts, G.W., Smith, S., Wright, R Hay, W.W., Jones, J.I., (c 1970), A symposium of recent south Florida foraminifera: Miami Geological Survey, Memoir 1. Boothroyd, J.C., (1985) Tidallnlets and Tidal Deltas, in: Davis, R.A., Jr., ed., Coastal Sedimentary Environments : New York, Springer-Verlag, New York, pp. 445525. Brooks, G .R., Doyle, L.J (1995), Characteristics of sediments on the inner west Florida shelf (Part A): US Geological Survey Open File Report 95-840. Brooks, G.R., Locker, S.D Gelfenbaum, G., DeWitt, N.T., (1995b), Nearshore sedimentary facies and distribution patterns off west-central Florida: Abstracts with Program First SEPM Congress on Sedimentary Geology, St. Petersburg Beach, FL. Brooks, G.R., Doyle, L.J DeWitt N.T., (1996), Analyses of the sedimentary parameters, carbonate mineralogy and constituents of vi bra-cores and surface samples taken from the inner west Florid continental shelf: US Geological Survey Open File Report 97-51. Brooks, G.R., Doyle,L.J., (199X) Boyles, M.J., Scott, A.J. (1982) A model for migration shelf-bar sandstones in Upper Mancos Shale (Campani a n), northwestern Colorado: AAPG Bulletin, v. 66, p. 491-508. Caston, V .D.N., (1972) Linear s and banks in the southern North sea: Sedimentology, v. 18, p. 63-78. Chen, C.S., (1965), The regional lithostratigraphic analysis of Paleocene and Eocene rocks of Florida: Florida Geological Survey Geological Bulletin No. 45, p. 105. Collins, M.B., Shimwell, S.J Gao, S., Powell, H Hewitson C., Taylor, J.A., (1995), Water and sediment movement in the vicinity of linear sandbanks: The Norfolk Banks, southem North Sea: Marine Geology, 123, pp. 125-142. 93

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. R.A Kl a y, J M ., ( 1989 ), Origin a nd development of Quaternary terngenous mner shelf sequences, southwest Florida: Transactions-Gulf Coast Assoc iation of Geological Societies, 39, p. 34!-347. Davis, R.A., Kuhn, B.J., (1985), Origin and development of Anclote Key, westpeninsular Florida: Marine Geology, 63, pp. 153-171. Davis, R.A., Hine, A.C., Shinn E.A., (1992), Holocene Coastal Development on the Florida Peninsula, in Fletcher, C.H. III and Wehmiller, J.F., eds., Soc. Econ. Paleont .. Min., Special Publication No. 48, Quaternary coasts of the U S.: Marine and Lacustrine Systems, pp. 193-212. Doyle, L.J., Brooks, G.R., Lee, E., (1995), Characteristics of Sediments on the Inner West Florida Shelf: US Geological Survey Open File Report 95-840. Doyle, L.J., Sparks, T.N., ( 1980), Sediment of the Mississippi, Alabama, and Florida (MAFLA) continental shelf: Journal of Sedirnentary Petrolog y, 50, No. 3, p 905 -916. Duane, D.B. Field M.E., Meisburger, E.P., Swift D.J.P., Williams, S.J., (1972), Linear shoals on the Atlantic Inner Continental Shelf, Florida to Long Island, in Swift, D.J.P., Duane, D. B., and Pilkey O.I -I., eds., Shelf Sedime nt Transport: Process and Pattern: Dowden Hutchinson and Ross, Stroudsburg P ennsy lvania. Edwards, J.H ., Hin e, A.C., Locker, S.D., Harrison, S. E ., Brooks, G.R., Twichell, D., (1996), Stratigraphy of west-central Florida's inner shelf sand Iidges: US Geological Survey Open File Report 97-51. Evans,tv:.w., Hine, A C., Belkn ap, D.F., D avis, R.A., (1985), Bedrock controls on barrier island development: west-central Florida coast: Marine Geology, 63, pp. 263-283. FAHMY, Thierry, (1998), ww\v.x l Fairbanks, R.G. (1989) A 17 ,000-year glacio-eustatic sea level record: Influence of glacial m elting rates on th e Younger Dryas event and deep-ocean circulation: Nature, 3421' pp. 637-642. Figueiredo, A.G.D., J r., Swift, D.J .P., Stubblefield, W.L., Clarke, T .L., (1981), Sand ridges on the inner Atlantic shelf of North America: morphometri c comparisons with Huthnance stability model : Ceo-Marine L e tters v. 1, p 187-191. Figue iredo, A.G.D., Jr. (198 4), Submarine san? . development, New Jers e y, USA: unpublished Ph.D. Dissertation, Uni vers ity of Miami, 409 pp. Fish, J.P. Carr, H.A., ( 1990) Sound Underwater Im ages: A g uid e to the generation and interpretation of side scan sonar data: Orleans, MA, Lower Cape Publishing, 189, p. F l ectc h e r C.l-1., Ill and Wehmiller, J .F., eds., (1992), Quaternary coasts of the Unite d Stat es: marine and l acustrine systems: SEPM Sp ecial Publi cation 48, 450p. 94

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Folk, R.L., (1980), Petrology of sedimentary rocks: Austin Texas Hemphill Publishing Company, 185, p. ' Ginsburg, R.N., James, N.P (1974), Holocene Carbonate Sediments of Continental Shelves, in Burk, C.A., Drake, C.L., eds., Geology of Continental Margins: Springer-Verlag, New York. Glaesser, J.D., (1978), Global distribution of barrier islands in terms of tectonic setting: Journal of Geology, v 86, p. 283-297 Goodbred, S L., (1994), Geologic controls on the Holocene evolution of an open marine system fronting a shallow-water embayment: Waccasassa Bay, West Central Florida: Unpublished Master's Thesis, Marine Science Department University of South Florida, 221 p. Gould, H.R., Stewart, R.H., (1956), Continental t enace sediments in the northeastern Gulf of Mexico: Soc. con. Paleont .. Min., Special Publication No. 3, pp. 219. Harrison, S.E., Locker, S.D., Hine, A.C., Twichell, D.C., (1995), Morphlogy and evolution of a siliciclastic sand ridge field over a carbonate bedrock substrate, Indian Rocks Beach, Florida: Abstracts with Program, First SEPM Congress on Sedimentary Geology, St.. Pete Beach, FL, I, p 66. Harrison, S.E., (1996a) Mophology and evolution of a Holocene carbonate/silicilastic sand ridge field, west-central Florida inner shelf: US Geological Survey Open File Report 97-51. Harrison, S.E., (1996b), Morphology and evolution of a Holocene carbonate/siliciclastic sand ridge field West-central Florida inner shelf: Unpubl. M.S. Thesis, Department of Marine Science, Univ e rsity of South Florida Herbert, J.A., (1985), High-resolution seismic stratigraphy of the inner west Florida shelf west of Tampa B a y, Evidence f r o a Miocene kar s t valley system: Unpubl. M.S. Thesis, Department of Marine Science, University of South Florida. Hine, A.C., Wilber, R.J. Neum a n A C., (1981) Carbonate Sand Bodies Along Contrasting Shallow Bank Mar g ins Facing Open Seaways in Nm1hem Bahamas: AAPG Bulletin, pp. 261-290. Hine, A C., Davis, R.A., Belknap, D:F., (1987), Depositional response to seagrass mortality along a low-energy, b a rrier-i s land coa st: we s t-central Florida: Journal of Sedimentary Petrology v. 57, pp. 4314 39. Hine, A.C. Belknap, D.F., (1986), Recent Geological History and Modem Sedimentary Processes of the P a sco, H e rnando, and Citms County Coastline: West Central Florida: Florida Sea Grant, Report Number 79. Hine, A.C., Locker S.D. Harri s on, S .E (1995), Lin k ages b e tween the barrier island/tidal inl e t coa s tal sys tem and the inne r c o ntin enta l sh elf off F lorida's west central shoreline: US Geolo g ical Survey Open File Report 95 840. 95

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Hine, A.C., Edwards, J.H., Locker, S.D., Harrison, S.E., Twichell, D., (1996), West Florida inner shelf provinces--Links to present coastal system, to modern shelf processes, and to the geologic past: US Geological Survey Open File Report 97-51. Hobson, J.P., Jr., Fowler, M.L., Beaumont, E.A., (1982), Depositional and statistical exploration models Upper Cretaceous offshore sandstone complex, Sussex Member, House Creek Field, Wyoming : AAPG Bulletin., p. 689-707. Huthnance, J .M. (1973), Tidal current asymmetries over the Norfolk sandbanks:Estuarine and Coastal Marine Science, I, p. 89-99. Huthnance, J.M., (1982a), On one mechanism forming linear sand banks: Estuarine, Coastal and Shelf Science, 14, p. 79-99 Huthnance, J.M., (1982b), On the formation of sand banks of finite extent: Estuarine, Coastal, and Shelf Science 15, pp. 277-299 Hyne, J.J Goodell, H.G., (1967), Origin of the sediments and submarine geomorphology of the inner continental shelf off Choctawhatchee Bay, Florida: Marine Geology, 5, pp. 299-313. Imbrie, J ., et al., (1992), On the structure and origin of major glaciation cycles: 1. Linear responses to Milankovitch forcing: Paleoceanography, v. 7, n. 6, p. 701-738. Jackson, R G ., II, ( 1975), Hierarchical attributes and unifying model of bedforms composed of cohesion less material and produced by shearing flow: Geological Society of America Bulletin, 86, pp. 1523-1533 JCPDS Internation Centre For Diffraction Data, (1988), Powder Diffraction File: Inorganic Phases, Internation Centre For Diffraction: Swarthmore, PA, 784p. Johnson, M.A Stride, A.H., Belderson, R.H., Kenyon, N.H., (1981), Predicted sand-wave formation and decay on a large offshore tidal-current sand sheet, in Nio, S.D, Shuttenhelm,R.T.E., and Van Weering, T.C.E.,eds., Holocene Marine Sedimentation in the North Sea Basin : International Association of Sedimentologists Special Publication 5, pp. 247-256. Kenyon, N .H., Belderson R.H. Strid e, A.H., Johnson, M.A., (1981), Offshore tidal sand-banks as indicators of net sand transport and as potential deposits, in Nio, S.D, Shuttenhelm, R T .E., and Van \Veering, T.C.E., eds Holocene Marine Sedimentation in the North Sea Basin: International Association of Sedimentologists Special Publication 5, pp. 257-268 Knebel, H.J., and Spiker, E. C., (1977), Thickness and age of surfiCial sand sheet, Baltimore Canyon trough areas: AAPG Bulletin, 61, pp 861-871. Knebel, H.J., Wood, S.A ., Sp iker, E .C., (1979), Hudson River : evidence for extensive migration on the exposed continenta l shelf during Pleistocene time: Geology, 7' pp. 254-258 Libby, W.F., (1955), Radioactive Dating: University of Chicago Press, Chicago, 11, 175 p. 96

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. McGrail, D.W., (1979), Ridge and swale topography revisited: multiple workmg hypothe sis in action: EOS Trans. Amer. Geophysical Union, V. 60, p. 285. Stubblefield, W.L., McGrail, D.W., (1980), Lateral shear waves as formative mechanism for nearshore and ridges : in 26 Congres Geologique International, Paris, Abstract, v. 11, section 6, p. 545. Stubblefield W.L., Rine, J.M., (1981 ), Analysis of high-resolution reflection seismic (3.5 kHz) survey of nearshore and midshelf ridges on New Jersey shelf: Atlantic shelf coring project cruise, 1979: in Tillman, R.W., Rine, J.M., Siemers, C.T., Stubblefield, W.L., Swift, D.J.P., eds., Atlantic shelf coring project: Data Report on 1979 Cruise: Cities Service Company, Research Report 102 Stubblefield, W.L., McGrail, D.W., D.G., (1983), Development of middle continental shelf sand ridges: New Jersey: AAPG Bulletin, v. 67, p 817-830. Stubblefield, W L., McGrail, D W ., Kersey, D.G ., (1983), Recognition of Transgressive and Post-Transgressive Sand Ridges on the New Jersey Continental Shelf, in Tillman, R.W., and Seimers, C.T. eds., Siliciclastic Shelf Sediments: Society of Economic Paleontologists and Mineralogists, Special Publication 34. Stuvier, M ., Long, A., Ora R.S. Devine, J.M ., (1993), Calibration-1993, Radiocarbon 35 ( 1 ). Swift, D.J.P. Kofoed, J .W., Saulsbury, F P., Sears, P., (1972), Holocene evolution of the shelf surface, central and southern Atlantic shelf of North America, in Swift, D.J. P., Duane, D. B., and Pilkey, O .H., eds ., Shelf Sediment Transport: Process and Pattern: Dowden, Hutchinson and Ros s, Stroudsburg, P en nsylvania Swift, D.J (1976) Coastal Sedimentation, in S wift, D.J .. and Stanley, D J., eds., Marine Sediment Transport and Environmental Management: Wiley Intersience Publication. Swift, D.J.P. Field, M.E., (I 9X 1 ), Evolution of a classic sand ridge field: Maryland sector, Norht Ame rican inn e r shelf: Sediment ology 28, pp. 461-482. Swift, D.J.P., McKinney T.F. Stahl, L., (198 4), Reco g nition of Transgressive and Post-Transgressive Sand Ridges on the New Jersey Continental Shelf: Discussion, in Tillman, R.W., and Seimers, C.T., eds., Siliciclastic Shelf Sediments : Society of Economic Paleontolo g ists and Mineralo gists, Special Publication 34. Swift, D.J P Rice, D O. (19R4), Sand bodi es on muddy shelves : a model for sedimentation on the Western Interior North A me1ic a, in Tillman, R.W., and Seimers, C T., eds., Siliciclastic Sh e l f Sediments: Soci e t y of Economic Paleontologists and Mineralogists Special Publication 34. Swift, D.J.P., Niediroda A.W., ( 1 985), Fluid and sediment dynamics on the continental shelves, in Tillman R.W Sv.:ift, D.J.P. W alke r, R.G ., eds., Shelf Sands and Sandstone Reservoir s: SEPM s hort course 1 3, pp 47 1 34. T a lma l\.S., Vogel J. C. ( I Sl93), A simplified approach to Calibrating C14 d a t e s, Radiocarbon 35(2), p317-322 99

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Winston, D., Riggs, S R O'Connor, M.P., Breuninger, R.H., (1968), Geological evaluation of coastal petroleum company's offshore lease from the Honeymoon Island area south to Blind Pass, Pinellas County Florida: Open report, Coastal Petroleum Company, Tallahassee, Fla., p 116. Wright, E.E., (1995), Sedimentation and stratigraphy of the Suwannee river marsh coastline: Unpubl. Ph. D. Dissertation, Department of Marine Science, Unversity of South Florida. Wright, L.D., Boon, J.D., Kim, S.C., List, J.H., (1991) Modes of cross-shore sediment transport on the shoreface of the Middle Atlantic Bight: Marine Geology, 96, pp. 19-51. !01

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Appendices 102

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0 w West-Central Florida Coastal Studies Project Vibracore Description Core Identification: IRB-96-5 Water Depth: 5.8m Latitude: 27 56.276 Longitude: 82 54.051 -

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...,. : . . .... . 50 ___ : Open marine sediments with a sharp contact at the base bet ween the open marine san d s and blue-gray clay West-Central Florida Coastal Studies Project Vibracore Description Core Identification: IRB-96-8 Water Depth : 6.5m Latitude: 27b 56.371 Longitude: 82 54.223 0 0 ::l o. ::l c: 0 0. '-'

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II USGS "ECKERD ,..,.,..,.,.,.,""'""""""' COLLEGE West-Central Florida Coastal Studies Project Vibracore Description Core Identification: IRB-96-9{2) Water Depth: 6.9m Latitude: 27 56.37 4 Longitude: 82 54.118 'n' 0 ::s o ::s c e

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...... 0 0\ .EUSGS ECKERD COLLEGE West-Central Florida Coastal Studies Project Vibracore Description Core Identification: IRB-96-10 Water Depth : 5.8m Latitude: 27 56.378 Longitude: 82 54.927 i I .C .. ,_J . !.
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0 -..) EUSGS ECKERD COLLEGE : 0 : : : : : 1 : : : : : ..... 1 :::::: l : J ; ..... 1 j .. l 1"'"1 50 l ... ..... ( t<:l i : ; : : : i Open marine sands ::::: l gradually fining into a 100 :::::; muddy-sand until a a : : : : : l sharp contact is made :::: : i between the muddy -,::;: : j sand and the blue-gray .' 1 clay 'I:::::, : : : : : :::::: i 160 .. r .. _;;;;; .......... .. 200 ... ::::: l : -.: :: ;j r; .. : .. : _-j West-Central Florida Coastal Studies Project Vibracore Description Core Identification: IRB-96-11 Water Depth: -sm i Siliciclastic/-..... : :! Carbonate Sand : tl 11 l l .. ;--:_ -221-228 em dated at .. . . 8 .9.0+/.cS.O .YBP ......... . "-" "-'"-' ... '-' ......... X ......

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. West-Central Coastal Studies Project Vibracore Description Core Identification: IRB-96-12 Water Depth: 6.3m Latitude: 27 56.026 Longitude: 82 53.723 ......... (') 0 :::I o. :::I c::: 0.. '-"

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s Gs .. : ECKERD COLLEGE West-Central Coastal Studies Project Vibracore Description Core Identification: IRB-96-13 Water Depth: 6.0m Latitude: 27 56.010 Longitude: 82 53.710

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-0 . . U __ ........................................ ...... . West-Central Florida Coastal Studies Project Vibracore Description Core Identification: IRB-96-14 Water Depth: 6.0m Latitude: 27 56.051 Longitude: 82 53.602

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West-Central Florida Coastal Studies Project Vibracore Description Core Identification: IRB-96-23 Water Depth: 7 .2m Latitude: 27 56.481 Longitude: 82 54.316

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West-Central Florida Coastal Studies Project Vibracore Description Core Identification: IRB-96-26 Water Depth: 6.3m Latitude: 27 56.379 Longitude: 82 54.494 ..... ......... ("') 0 ::l .... ::l c 0. '--'

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.. . ECKERD COLLEGE 50 100 Olive colored muddy sand Poorly sorted mixture of mud and shell Blue-gray clay with brown steaks and black ooooc>Ci sand sized particles 20 em of solid limestone West-Central Florida Coastal Studies Project Vibracore Description Core Identification: IRB-96-27 Water Depth: 6.3m Latitude: 27 53.764 Longitude: 82 52 .247 c i a y --------------------------I : .................................... . ..... ... .. .. .. ." . .... J... .. ..... i ..... : ..... l.. : ... t ... : .. .< ..:....JL-.:....L...:....t.:..L.L:..L:..JC.l. ---------------______..1

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West-Central Florida Coastal Studies Project Vibracore Description Core Identification: IRB-96-28 Water Depth: 6 6m Latitude: 27 55.188 Longitude: 82 51.419 ........ ("') 0 ::l ::r. ::l c:: 0 0.. .........,

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. . ECKERD COLLEGE West-Central Florida Coastal Studies Project V i bracore Descrip ti on Core Ident i ficat i on : IRB-96-31 Wate r Depth: 6 .0m Latit ude : 27 5 4 .5 84 Long itude: 8 2 52.590 [ ............ ................ 0 ; o .. whitish i n color t hat .. mHEHH!gradc s into a mixture of sand and shell 50 frag m e nts. >00 Jilt____ -_ ,......:..,._t._, __ _, __ J I. .,r .. ... 1 !; Fine Quartz Sand I : Jj I c ;ljt I I t :!:,' : lit I ,,,, I til r l I ljl I l f l ; 1!1 : rir : .: I : : I t : :!, : _: ..... L .;,,.;_,.:_, ,!.._', .. l... :._J_:._jLLJ.:.t:.J.;, l .'.! : t ;' .. ...... .... ..... .... M._ .. _. ..... -.................... . -() 0 ::s c. ::s c: 0 0.. ........

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.. ECKERD '11Jf6ll!f COLLEGE ,,::f ... .. r .,,, West-Central Florida Coastal Studies Project Vibracore Description Core Identification: IRB-96-33 Water Depth: 3m Latitude: 27 53.775 Longitude: 82 51.040 r: ... l!.; .. [ .................... .. ... .. I 0 0 -50 100 clean quartz sand, in color Lhat into a mixture of uartz sand and shell Base again fines wilh some olive-colored veins of muddy sediment .......

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-EUSGS ECKERD COLLEGE West-Central Florida Coastal Studies Project Vibracore Description Core Identification: IRB-96-34 Water Depth: 6.0m Latitude: 27 56.010 Longitude: 82 53.710 L:l,; __ 1. ... ............ 0 0 1::: : : r .. _. ................ ...... ............ ................ % .......... .... .... Ulholades ................... Poorly sorted mixture of u:..:..:...j quartz sand and :::: : ; shells( whole and j v.: : fragments) .. 50 ... ; ::::: : 0 0 1TJ ; ; ; ; : j Cobble of limestone at . L: : ............................. .. r;-rTf '! l:l c b s I; ................................. II !J!, .... _______ I Shelly Sand I ; I ...................................... ... --------j ! SiliciclasLic/ : i : CarbonaLc Sand til t:l "' ,f, til =.i .L.I-'.J..U.J.dl .... ...... ...... ................. ............................ "" ,__. '()" 0 :::::1 ::t. :::::1 c: 0 0.. ..........

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West-Central Florida Coastal Studies Project Vibracore Description Core Identification: IRB-96-35 Water Depth: 5.9m Latitude: 27 56.342 Longitude: 82 54.519 ................ .. :::1.

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West-Central Florida Coastal Studies Project Vibracore Description Core Identification: IRB-96-39 Water Depth: 5.8m Latitude: 27 56.487 Longitude: 82 54.976 I' I' j I i I : I I I' j' Shelly Sand SiliciclasLic/ CarbonaLc Sand '-----------' i j Shelly Sand i ---------------........... : Siliciclaslic/ i Carbonalc Sand l .... .............. .. ___ Shelly Sand

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West-Central Florida Coastal Studies Project Vibracore Description Core Identification: IRB-96-40 Water Depth : 5 .8m Latitude : 27 56.569 Longitude : 82 54. 310 O '::: ::;::r' ---------: ,T : Siliciclastic/ l : I : Carbonate Sand j Fair! y homogeneous marine sediments so ---.-,-;--..,-, i with a lag of coarse s h ell \:::::; hash l : ::: : -i : : : : : t ....... ....... i . .. . i .... 1 00 ::::: t < ....... : t ..... ( . ............ : . ............ . ...................... ___ ._., ... LLL.!..L! .. .i.Li.!.L! .. U .. : ..... . ... L. .. : ..... : ..... IL ... ... L .J. . .. I..J.. i. J '()' 0 ::l o. ::l t: 0.. ..........

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N N West-Central Florida Coastal Studies Project Vibracore Description Core Identification: IRB-96-50 Water Depth: 5.8m Latitude: 27 56.367 Longitude: 82 53.883 ...-.. (") 0 ::I .... ::I c 0. '-'

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tv w i&USGS ECKERD COLLEGE H,1 : ... \:::;: 1 Fairly well sorted open 50 .. : : : : : : marine quartz sand with 1 ; ; ; : ; some sea grass evidence l : : ; : at the lOp :-:: -:: = 1::::: West-Central Florida Coastal Studies Project Vibracore Description Core Identification: IR. B-96-51 Water Depth: 5.9m Latitude: 27 56.338 Longitude: 82 53.839 I l l 100 + .......................... ............. ._.i.......i.......L-l.. .... .. .l ... l. .... ..... l.. ......

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Appendix 2. X-Ray Diffraction Pattern 90 80 -70 '#. >60 rn c 50 G) -c 40 30 20 10 Palygorskite peak P Q Primary Calcite rtmary uartz k peak "" /pea Secondary peaks I l J 5 10 1 5 20 25 30 35 Angle (Degrees) Blue-gray clay sample 154-156 em from vibracore IRB-95-8. The x-ray diffraction analysis was run only on the clay fraction of the sample. The pattern illustrates that the sample is primarily composed of the mineral palygorskite with minor amounts of quartz and calcite. 124 40

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Appendix 2. (continued) X-Ray Diffraction Pattern 90 80 -70 eft > 60 -t/) c: 50 G) c: 40 30 20 10 0 Primary Calcite Secondary peaks t 5 10 15 20 25 30 35 Angle (Degrees) Blue-gray clay sample 93-95 em from vibracore IRB-95-27. The x-ray diffraction analysis was run only on the clay fraction of the sample. The pattern illustrates that the sample is primarily composed of the mineral palygorskite with minor amounts of quartz and calcite. 125 40

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Appendix 2. (continued) X-Ray Diffraction Pattern 90 80 7 0 eft >-60 UJ c: 50 C1) c: 4 0 3 0 20 1 0 Palygorsk i te peak Pr i mary Calcite p/ 5 1 0 15 2 0 25 3 0 3 5 Angle ( Degrees) Blue-gray clay sample 229-231 em from vibracore IRB-95-11. The x-ray diffraction analysis was run only on the clay fraction of the sample. The pattern illustrates that the sample is primarily composed of the mineral palygorskite with minor amounts of quartz and calcite. 126 4 0

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Appendix 2. (continued) X-Ray Diffraction Pattern 90 80 7 0 "#. >-60 t/) c:: 50 Cl) c:: 4 0 30 2 0 1 0 Palygorskite peak Primary Calcite peak 5 1 0 1 5 20 25 3 0 3 5 Angle ( Degrees ) Blue-gray clay sample 114-116 em from vibracore IRB-95-28. The x-ray diffraction analysis was run only on the clay fraction of the sample. The pattern illustrates that the sample is primarily composed of the mineral palygorskite with minor amounts of quartz and calcite. 127 4 0

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Appendix 3. Grainsize Analysis Results Core ld Sediment Samp. Standard Mean %Calcium IRB-96-( ) Range (em) Deviation Phi Carbonate 5 3-5 1.47 1.1 0 51.86 5 20-22 1.13 1.95 42.58 5 64-66 2.01 0.61 64.22 8 3-5 0.82 2.88 17.81 8 48-50 2.00 1.51 33.42 8 78-80 0.97 2.63 20.65 8 107-109 1.64 1.56 26.71 8 131-133 1.07 2.61 4.84 8 154-156 1.80 1.11 21.76 9 3-5 0.99 2.36 21.34 9 28-30 1.74 1.04 31.83 9 78-80 1.81 2.02 28.84 9 122-124 0.89 2.82 2.01 1 0 2-4 1.01 1.84 44.02 10 35-37 0.74 2.46 32.66 10 72-74 1.15 2.26 19.72 11 3-5 0.87 1.47 44.21 1 1 26-28 0.79 2.50 18.58 11 102-104 1.75 1.27 45.50 11 162-164 1.53 2.14 29.24 11 208-210 1.24 2.40 22.01 11 229-231 0.92 2.75 5.27 12 0-2 0.65 2.67 16.57 12 10-12 0.65 2.75 14.98 12 20-22 0.74 2.61 18.27 12 30-32 1.01 2.30 22.56 12 40-42 0.74 2.64 15.88 12 50-52 0.66 2.64 14.48 12 60-62 0.70 2.70 15.20 12 70-72 0.80 2.75 19.73 12 80-82 0.81 2.70 17.48 12 90-92 0.83 2.69 19.84 12 100-102 0.95 2.51 19.39 12 110-112 0.88 2.46 24.80 128

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Appendix 3. (continued) Core ld Sediment Samp. Standard Mean %Calcium IRB-96-( ) Range (em) Deviation ptj Carbonate 13 0-2 0.67 2.65 17.89 13 10-12 0 .82 2.54 19.79 13 20-22 0.79 2.60 22.26 13 30-32 0.71 2.72 16.72 13 40-42 0.69 2. 71 13.61 13 50-52 0.65 2.62 17.19 13 60-62 0.89 2.37 24.05 13 70-72 0.94 2.65 24.69 13 80-82 0.95 2.44 24.02 13 90-92 0 .78 2.67 21.70 13 100-102 1.04 2 .37 29.02 13 110-112 1. 11 2.35 27.09 13 120-122 0 .80 2.74 23.17 13 130-132 0 .86 2.77 25.45 13 140-142 0 .78 2.63 27.01 13 152-154 0.76 2 .59 24.93 13 158-160 0.83 2.72 24.34 14 0-2 0.62 2.51 14.58 14 10-12 1 .09 1.44 8.20 14 20-22 1 .19 2.25 23.29 14 28-30 1.51 0 .83 22. 51 14 46-48 0.87 2 41 18.41 23 1-3 0 .73 2.96 14.86 23 20-22 1.57 2.33 34. 51 23 40-42 1.12 2.94 24.82 23 60-62 1 .38 2.52 32.87 23 80-82 1 .01 3 .19 20.70 23 100-102 1.05 3 .14 19.59 23 120-122 1.40 2.63 28.57 23 134-136 1 .46 2 .69 21.99 23 144-146 1.53 3.23 28.42 23 154-156 1.42 3 .67 39.50 23 164-166 1.66 3 .35 38.43 23 174-176 1.45 3 .93 27.53 129

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Appendix 3. (continued) Core ld Sediment Samp. Standard M e a n %Calcium IRB-96-{ ) Range (em) Deviation Phi Carbonate 23 184-186 1.41 3 .29 25.78 23 198-200 1 .24 4 .21 11.53 23 208-210 0 9 9 4 5 9 23.92 23 218-220 0.67 4 .80 23.39 2 3 228-230 0.46 4 .87 34.26 2 3 241-243 0 .56 4 .82 31.94 26 1-3 0 .85 1 7 1 46.38 26 20-30 1 .08 1 .56 52.79 2 6 40-42 1 01 1 .89 3 9 .58 26 60-62 0 .91 1 .99 29.62 2 6 80-82 1 .34 1.11 63.04 26 88-90 1.48 0 .76 63.46 26 95-97 0 .89 1 .98 40.75 26 115-117 0.91 2.42 30.47 26 127-129 0 .76 2 .54 24.92 26 145-147 0.77 2 .78 22.76 26 165-167 0 .86 2.85 21 .76 27 1-3 1 .85 3 .17 24.33 2 7 15-17 1 .73 2 .84 1.79 27 25-27 1.99 0 .76 49.29 2 7 53-55 1.77 2 .96 1 0 .00 27 63-65 1.61 3 .14 15. 6 5 27 80-82 1.21 3 .16 10.93 27 93-95 1 .36 2 .78 7.07 2 7 104-106 1 .60 3 31 11.19 28 68 1 .98 1 7 5 4 .55 28 22-24 1 31 2 .90 8 .94 28 64-66 1 .73 3 .02 16. 21 28 114-116 2.89 3 .03 32.72 31 1-3 0.48 2 .50 7.52 31 20-22 0 .53 2.46 6.53 31 35-37 0 .63 2.47 8 .03 31 44-46 0 .88 2 .27 19.65 130

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Appendix 3. (continued) Core ld Sediment Samp. Standard Mean %Calcium IRB-96-( ) Range (em) Deviation Phi Carbonate 31 55-57 1.76 1.26 37.74 31 68-70 1.00 2.22 17.08 31 84-86 1.69 1.60 31.74 31 97-99 1.51 1. 76 31.74 33 1-3 1.12 2.07 23.85 33 20-22 1 .38 2 .08 21.10 33 40-42 1.47 1.74 35.47 33 60-62 1 .82 1 .16 48.13 33 68-70 1 .87 1.45 40.47 33 80-82 1. 71 2.09 21.19 33 90-92 1 .24 2.54 12.42 33 100-102 1 .31 2.56 13.35 34 0-2 0 98 2.30 29.47 34 10-12 0 .80 2 .33 24.40 34 20-22 1 .95 0 .09 73.54 34 30-32 1.78 1.57 41.39 34 40-42 2.11 0 .83 49.41 34 50-52 1.72 1 .43 43.88 34 60-62 1 .54 1 .50 37.43 34 70-72 1 .29 1 .86 27.50 34 80-82 1.18 2.33 24.41 34 88-90 2 .24 1 .29 41.94 35 1-3 0.73 2.61 21.89 35 25-27 0 .64 2 .64 18.23 35 40-42 0 .88 2 .57 25.35 35 50-52 1.65 0 .15 75.47 35 64-66 0.97 2 .32 32.62 35 75-77 1.27 1.55 52.89 35 84-86 1.55 0.84 63.97 35 95-97 1 .84 0 .69 44.70 35 105-107 1.26 2 .23 33.25 35 115-117 2.01 0 .24 56.82 35 125-127 1 .06 2 .51 20.76 131

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Appendix 3. (continued) Core ld Sediment Samp. Standard Mean %Calcium IRB-96-( ) Range (em) Deviation ptj Carbonate 35 140-142 1 .23 2 .28 24.58 35 153-155 1.08 2.48 16.71 35 163-165 1 .59 2 91 13.32 35 175-177 1.67 2.86 15.90 35 185-187 1.44 3 .69 11.33 35 195-197 1.32 4.10 7.80 35 209-211 1.25 4.21 6.93 39 0-2 0.82 1. 72 50.54 39 14-16 0.88 2.03 42.55 39 22-24 1.48 0 .14 74.96 39 32-34 1. 61 1.50 41.80 39 44-46 0 81 2 .13 38.96 39 54-56 0.73 2.33 28.08 39 64-66 0 .66 2 .38 24.06 39 76-78 1.63 0.63 68.88 39 86-88 1 .29 1 .64 48.92 39 96-98 0 .82 2 .54 28.20 39 106-108 0 .92 2.44 30.90 39 116-118 0.97 2 .55 23.68 39 122-124 2 .20 0.72 64.01 39 132-134 1 .98 0 .33 71 .65 40 1-3 0 .98 2 .15 30.09 40 10-12 1 .14 2 .22 27.57 40 20-22 0 .61 2 .54 17. 51 40 30-32 0 .76 2 .52 18.37 40 45-47 1 .53 0. 71 73.06 40 53-55 0 .76 2 .52 24. 51 40 63-65 0 .75 2.47 24.93 40 73-75 0.74 2.55 22.02 40 83-85 0 .84 2 .40 24.86 40 93-95 0 .74 2.61 22.87 40 103-105 0 .84 2 .54 30.15 42 1 3 1.12 2 .03 23.99 132

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Appendix 3. (continued) Core ld Sediment Samp. Standard Mean %Calcium IRB-96-( ) Range (em) Deviation Phi Carbonate 42 10-12 0 .93 2.41 25.68 42 20-22 0 .73 2 .45 22.46 42 30-32 0 .78 2.52 27.82 42 40-42 1 .37 2.26 27.25 42 50-52 0 .77 2 .52 24. 31 42 60-62 0.76 2.46 24.69 42 79-81 1.69 0 .97 51 .02 42 90-92 0 .97 2 31 28.72 42 100-102 0 .99 2.47 32.32 42 110-112 0 .95 2 .46 29.38 42 120-122 1 01 2.41 30.33 50 1-3 0 .66 2 .58 7.11 50 20-22 0.85 1 91 28.76 50 76-78 1 .13 2 .26 26.28 51 1-3 0 .72 2 .34 17.14 51 40-42 0 .89 2 .22 16.98 51 65-67 1 .21 1 .97 23.31 5 1 104-106 0 71 2 .65 15.31 Beach Sample N / A 1 .09 2.4 17.88 133


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