Effect of Dissolution of the Florida Carbonate Platform on Isostatic Uplift and Relative Sea-Level Change Michael Alan Willett

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2006 Effect of Dissolution of the Florida Carbonate Platform on Isostatic Uplift and Relative Sea-Level Change Michael Alan Willett

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COLLEGE OF ARTS AND SCIENCES

EFFECT OF DISSOLUTION OF THE FLORIDA CARBONATE

PLATFORM ON ISOSTATIC UPLIFT AND RELATIVE SEA-LEVEL

CHANGE

By MICHAEL ALAN WILLETT

A Thesis submitted to the Department of Geological Sciences in partial fulfillment of the requirements for the degree of Master of Science

Degree Awarded: Summer Semester, 2006 The members of the Committee approve the Thesis of Michael Alan Willett defended on April 25, 2006.

______Joseph F. Donoghue Professor Directing Thesis

______Sergio Fagherazzi Committee Member

______Jennifer E. Georgen Committee Member

______Sherwood W. Wise Committee Member

Approved:

______A. Leroy Odom, Chair, Department of Geological Sciences

The Office of Graduate Studies has verified and approved the above named committee members.

This thesis is dedicated to my wife, Claire.

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ACKNOWLEDGMENTS

The author would like to acknowledge and thank the members of his committee, Joseph Donoghue, Jennifer Georgen, Sherwood W. Wise and Sergio Fagherazzi. He would like to also thank the members of the Florida Geological Survey Springs Team and the members of the Florida Geological Survey Oil and Gas Section.

TABLE OF CONTENTS

List of Tables ...... vi List of Figures ...... vii Abstract ...... x

1. INTRODUCTION...... 1 Statement of Problem ...... 1 Classification of Springs...... 6 Karst Processes ...... 8 Isostatic Rebound ...... 12 Isostatic Response to Carbonate Removal by Springs ...... 13 Hypotheses Tested ...... 14 Potential Significance of the Work ...... 14

2. STUDY AREA ...... 15 Introduction ...... 15 Hydrology ...... 20 Sea-level Change and Marine Terraces of Florida...... 28 Geologic Structure ...... 32 Previous Work...... 35

3. METHODS …...... 43 Springs Data Collection...... 43 Field Parameters...... 43 Water Sampling ...... 44 Discharge Measurements ...... 45 Dissolved CaCO3 ...... 47 Borehole Data Collection...... 47 Data Reduction and Isostatic Calculations ...... 50

4. RESULTS ...... 51 Introduction ...... 51 Thickness of Florida Carbonate Sequence ...... 51 Depth to Basement Beneath the Carbonate Platform ...... 54 Carbonate Mass Loss Calculations ...... 55 Calculation A: Florida Platform Dissolution due to Spring Activity ...... 56 Calculation B: Isostatic Uplift with a Single Density Change through the Carbonate Layer...... 58 Calculation C: Isostatic Uplift Results with Density Changes for the Upper (a) and Lower (b) Portions of the Carbonate Layer 61

5. DISCUSSION...... 64 Calculation A Analysis...... 64 Calculation B Analysis...... 64 Calculation C Analysis...... 66 Suggestions for Future Work...... 66

6. CONCLUSIONS...... 68

APPENDIX A. SPRINGS LOCATION AND DATA ...... 72

APPENDIX B. SPRING ALKALINITY AND DISCHARGE GROUPED BY COUNTY AND ZONE ...... 88

APPENDIX C. BOREHOLE DATA SHOWING DEPTHS TO TOP OF BASEMENT AND/OR BOTTOM OF LIMESTONE..... 92

REFERENCES ...... 96 BIOGRAPHICAL SKETCH ...... 103

LIST OF TABLES

Table 1: Spring classification based on discharge...... 7

Table 2: Springs used in this study...... 23

Table 3: Summary data for Florida platform dissolution due to spring activity ...... 59

Table 4: Calculation B - Isostatic uplift results using one density change through the carbonate layer ...... 60

Table 5: Calculation C - Isostatic uplift results using two density changes through the carbonate layer ...... 62

Table 6: Summary results of isostasy calculations ...... 63

Table 7: Summary results of calculations A-C...... 63

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LIST OF FIGURES

Figure 1: Physiographic diagram of the eastern United States ...... 2

Figure 2: The Florida Platform ...... 3

Figure 3: Physiographic regions of Florida ...... 4

Figure 4: LandSat GeoCover satellite image map of Florida ...... 9

Figure 5: Young karst landscape ...... 10

Figure 6: Early stage of karst development ...... 10

Figure 7: Advanced karst areas ...... 11

Figure 8: Detail of advanced stage of karst formation ...... 11

Figure 9a: Geologic map of Florida ...... 16

Figure 9b: Geologic map of the state of Florida – geologic units ...... 17

Figure 9c: Geologic map of the state of Florida – cross section A-A’ .... 18

Figure 9d: Geologic map of the state of Florida – cross section B-B’ .... 19

Figure 10: Karst areas related to first magnitude springs ...... 21

Figure 11: First magnitude springs of Florida ...... 22

Figure 12: Map location of sampled springs ...... 25

Figure 13a: Location of the known offshore springs of Florida ...... 27

Figure 13b: Known offshore springs in the Florida Big Bend Region .... 28

Figure 14: Physiographic diagram of Florida...... 30

Figure 15: Florida Trail Ridge shoreline ...... 31

Figure 16: Florida cross section along the Gulf of Mexico ...... 32

Figure 17: Structural features that affect the Floridan aquifer ...... 34

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Figure 18: East-west cross section through the Peninsular arch...... 35

Figure 19: Elevations of shoreline features of Trail Ridge, Penholoway, and Talbot levels (from Opdyke, 1984) ...... 37

Figure 20: Karst areas and major springs of north-central Florida (from Opdyke, 1984)...... 38

Figure 21: Florida county map, with counties grouped by zones ...... 48

Figure 22: General location of boreholes with depths to basement & depth to base of carbonate sequence ...... 49

Figure 23: Depth to bottom of carbonate sequence (meters)...... 52

Figure 24: East-West cross sections through zones 1-6 ...... 53

Figure 25: Depth to basement (meters)...... 54

Figure 26: Density changes within the carbonate platform...... 65

ABSTRACT

Florida is typically considered to be tectonically stable and representative of global eustatic sea level with little evidence for any anomalous local subsidence or uplift during the late Cenozoic. Sea level during most of that time did not significantly rise above the present level. However, paleoshoreline features near the border of northern Florida and southern Georgia have been found to contain marine fossils of Pleistocene age at elevations of between 42 and 49 m above mean sea level, suggesting that some mechanism of epeirogenic uplift has affected the area. A possible cause of uplift during the late Cenozoic is mass removal from the Florida carbonate platform via karst-related groundwater dissolution.

Calculations carried out as a part of this study, using measurements of dissolved carbonate in Florida’s first- and second-magnitude springs, shows that the karst area of central and north Florida is losing a minimum of 4.8 x 105 m3 /yr of limestone. This carbonate mass loss is equivalent to an approximate thickness of 1 meter of limestone every 160,000 years. The impact of long-term carbonate dissolution and mass loss from the Florida platform has led to isostatic uplift of at least 9 m and as much 58 m since the beginning of the Quaternary (~1.6 Ma). These results were obtained using the measured mass loss rate and calculation of the isostatic response to unloading of the Florida platform. Isostatic uplift due to dissolution of the Florida platform would at least in part explain the occurrence of Plio-Pleistocene marine fossils at elevations significantly higher than sea levels are known to have been during that time.

CHAPTER 1

INTRODUCTION

Statement of Problem The state of Florida sits atop a massive platform of carbonate rocks, which in the southern part of the peninsula is more than 3 km thick (Randazzo, 1997). The carbonate rocks thicken considerably offshore, to as much as 10 km beneath the shelf and inner margin of both the Atlantic and Gulf coasts of Florida (Figure 1). The Florida peninsula is the present-day subaerial portion of the Florida Platform (Figure 2). The Physical geography of the Florida peninsula can be divided into primary regions based on the physical processes responsible for observed landforms. The past marine high stands of sea level have shaped the terrain, while dissolution, running water, waves and wind have eroded the land Cooke (1945). The physiographic regions of the Florida Plateau are based primarily on geologic origin (Figure 3).

The Florida Platform is composed primarily of limestone and dolostone overlying older igneous, metamorphic and sedimentary rocks. The sediments range in age from mid- Mesozoic (200 million years ago, Ma) to Recent. Florida’s aquifer systems developed in Cenozoic sediments ranging in age from latest Paleocene (approx. 55 Ma) to late Pleistocene (Scott, 1992). Fluctuations of sea level and later subaerial exposure have strongly influenced the deposition and character of these sediments. Sedimentation on the Florida Platform has been dominated by carbonate sediment deposition since the mid-Mesozoic. Pulses of siliciclastics sediments have periodically encroached from the north and spread over parts of the platform, temporarily interrupting production and deposition of carbonate sediments (Scott, 1997). Carbonate sediment accumulation beneath the Florida Peninsula varies from almost 600 m in northern Florida to more than 1500 m in south Florida (Scott, 1992).

Figure 1. Physiographic diagram of the eastern United States and the continental margin, showing the extent of the Florida Platform (light blue). (Source: NOAA, 2006a)

Figure 2. The Florida Platform as delineated by the bathymetric contours of the adjacent continental shelf and slope. The shelf break occurs at approximately 200 meters (NOAA, 2006b).

The Florida carbonate platform is karstic, and is subject to high rates of dissolution. Average annual precipitation, in the region of the major springs, ranges from 127 cm in central Florida to 152 cm in the panhandle (Scott et al., 2004). As this precipitated water is transported to either the Gulf of Mexico or the Atlantic Ocean by springs, rivers and seepage, a large mass of dissolved carbonate is removed from the platform each year.

Figure 3. Physiographic regions of Florida showing Trail Ridge, Lake Wales Ridge, and other paleo-shorelines (Schmidt, 1997).

A major issue in past studies of karst processes for Florida’s carbonate platform has been the lack of a comprehensive and detailed data set for the flow rate and chemical composition of freshwater spring discharge. New data sets have recently made it possible to determine a more accurate rate of carbonate dissolution of the Florida carbonate platform. More specifically, a comprehensive water quality data set has been published by the Florida Geological Survey (Scott et al., 2004), for Florida’s first magnitude springs (springs with discharge greater than 100 ft³/sec) and several of Florida’s second magnitude springs (springs with discharge between 10-100 ft³/sec). The author has been part of the data collection effort. Sampling and lab analyses were conducted in accordance with analytical standards as determined by Florida Department of Environmental Protection and are discussed in Chapter 4. These new spring discharge data have made it possible to more accurately quantify the rate of dissolution and consequently the mass of carbonate rock lost over time.

Previous studies analyzing rates of mass reduction due to dissolution of the carbonate platform utilized data sets that were necessarily limited in scope and detail (e.g., Fennell, 1969; Rosenau et al., 1977; Lane, 1986). These studies have also concentrated on measurement of total dissolved solids (TDS) in spring discharge rather than more accurate analyses, such as alkalinity, to determine the annual mass loss of dissolved limestone. In order to avoid the limitations that have restricted previous attempts, this project has focused specifically on total alkalinity as dissolved CaCO3, in order to better determine mass loss of carbonate rock from the Florida platform.

A long-term rate of uplift can be determined using the more accurate rate of dissolution in combination with modeling techniques to calculate isostatic rebound. These techniques are analogous to those used to determine postglacial rebound rates in areas that were under ice sheets during glacial stages. Most previous studies, with one exception, have not attempted to relate the mass loss through carbonate dissolution to isostatic uplift of the platform. The exception is the study by Opdyke et al. (1984). That

study, however, utilized dissolution and discharge data from a relatively small data set. The present study was undertaken in order to achieve a more comprehensive determination of dissolution rates, using a more robust data set, and to approach the issue of isostasy more rigorously.

The primary goal of this project, therefore, was to quantify the effects of isostasy on the Florida platform and to obtain a reliable estimate of the rate of dissolution of the Florida platform using a comprehensive data set for spring discharge. This study posited that if a rigorous determination of isostatic uplift were to indicate that isostasy is a significant component of relative sea level change for the Florida platform shorelines over moderate spans of geologic time (~105 to 106 yr), then these effects should be seen in the present-day elevations of paleo-shorelines. In fact, anomalous uplift and warping of late Cenozoic shorelines of the Florida peninsula have been documented (e.g., Chen, 1965, Hoyt, 1969, Pirkle et al., 1970, Winker and Howard, 1977; Opdyke et al., 1984). Calculations, done as part of this study, will show that these anomalies can be tied to isostatic adjustment due to mass loss from the Florida carbonate platform. These results will have significance in terms of our understanding of the structure of the platform and the history of relative sea-level change in the region.

Classification of Springs The two primary types of springs in Florida are seeps (water-table springs) and karst springs (artesian springs). Seeps are formed as rainwater, percolating downward through permeable sediments, reaches less permeable formations, forcing the water to move laterally. This water may eventually reach the surface in a lower-lying area, often along hillsides, and form a seep. Karst springs are formed when groundwater discharges to the surface through a karst opening. All of Florida’s first magnitude springs, and the great majority of the more than 700 identified springs, are karst springs (Scott et al., 2004)

The classification of a spring is most often based on average discharge of water. Although discharge measurements can be variable over time due to rainfall, drought, recharge or groundwater withdrawal within the recharge area, one discharge measurement is enough to place a spring into one of the eight magnitude categories. Traditionally a new spring assigned a magnitude when it is first described will continue with that magnitude designation even though discharge may change over time. The Florida Geological Survey has suggested that the historical median of flow measurements, which was used in this report for discharge calculations, be utilized in classifying spring magnitude. The flow-based classification, listed below in Table 1, is presented in Scott et al. (2004).

Table 1. Spring classification based on discharge.

Magnitude Average Flow (Discharge) 1 100 cubic feet/second (cfs) or more (64.6 million gallons/day (mgd)) 2 10 to 100 cfs (6.46 to 64.6 mgd) 3 1 to 10 cfs (0.646 to 6.46 mgd) 4 100 gallons/minute (gpm) to 1 cfs (448 gpm) 5 10 to 100 gpm 6 1 to 10 gpm 7 1 pint/minute to 1 gpm 8 less than 1 pint/minute

Karst Processes The development of karst terranes occurs in areas underlain by carbonate rocks, mostly limestone and dolomite. Karst terranes have drainage systems characterized by the formation of sinkholes, springs, caves and disappearing streams. The topography of

karst is usually irregular, due to the solution activity of acidic surface and ground waters (Figure 4).

The formation of karst primarily involves the chemical weathering and erosion of 2+ carbonate rocks (CaCO3), thereby removing rock mass (Ca ) through solution activity.

Rain falling through the atmosphere becomes weakly acidic (2 HCO3) as carbon dioxide and nitrogen gasses dissolve in it (H2O + CO2). This water becomes more acidic when it comes in contact with decaying matter in the soil. As this slightly acidic water slowly passes through limestone beds, solution features begin to form (Sinclair and Stewart, 1985; Lane, 1986) (Figure 5). The general chemical equation describing carbonate dissolution is:

2+ CaCO3 + H2O + CO2 ---> Ca + 2 HCO3

During early stages, groundwater percolates through limestone along joints, fractures and bedding planes (Figure 6). The acidic water will in time extend these zones of weakness in the limestone. Caverns are created and enlarged by solution activity at and below the water table, resulting in the collapse or subsidence of surficial sediments.

As the stage of karst formation advances, well-developed interconnected passages, known as conduits, form an underground drainage system in the limestone, which captures much of the former surface drainage (Figure 7). Springs occur when this underground water is discharged at the land surface or seafloor. Sinkholes can result from the collapse of overlying rock or sediment as the conduits continue to form and enlarge. Portions of the original land surface may be lowered by erosion, dissolution of limestone and subsequent collapse of overburden. Normal surface drainage systems may begin to be transformed into dry or disappearing stream systems. Eventually, in the advanced stage of karst, all of the surface drainage may be diverted underground.

Figure 4. Landsat GeoCover 2000 satellite image map demonstrating the prevalence and distribution of karst-related features on the Florida platform. The large water-filled karst features, such as sinkholes and lakes formed by dissolution, show up here as irregular to semi-circular dark blue to almost black areas (Source: geology.com, 2005).

Figure 5. Young karst landscape showing underlying limestone beds and sandy overburden with normal surface drainage. The beginning of dissolution can be seen within the limestone below the stream (Lane, 1986).

Figure 6. Early stages of karst development showing the beginning of carbonate dissolution caused by infiltrating acidic ground water. Preferential dissolution can be seen along joints, fractures and bedding planes (Lane, 1986).

Figure 7. Advanced karst area, showing preferential dissolution along fractures, faults, bedding planes and the water table. Secondary formations such as subsidence sinkholes over a buried-infilled sinkhole and a solution pipe/fracture fill can also be seen (U.S. Geological Survey, 2000).

Figure 8. Detail of advanced stage of karst formation showing extensive solution activity along joints, fractures and bedding planes. Widespread development of conduits leading to cave, cavern and sinkhole formation can be seen (Lane, 1986).

Isostatic Rebound Isostasy is a term used to refer to the state of gravitational equilibrium between the Earth’s lithosphere and asthenosphere, such that the lithospheric regions "float" at an elevation which depends on their thickness and density. It also explains how a large change in regional mass distribution can affect the interaction between the lithosphere and the asthenosphere. When large amounts of mass, in the form of sediment, ice or water, are deposited on a particular area, the immense weight of the new mass may cause the lithosphere to subside. Similarly, when large amounts of material are removed from a region, through erosion, dissolution, or removal of ice or water, the land surface may rise to compensate. When a region of the lithosphere is no longer subject to vertical compensation forces, it is said to be in isostatic equilibrium (Peltier, 1978, Peltier, 1980, Douglas and Peltier, 2002).

Isostasy explains the vertical distribution of elevations on the Earth's crust. There are two end-member hypotheses used to explore isostatic processes. Airy (1855) proposed that the density of the crust is everywhere the same and the thickness of crustal material varies. For example, higher mountains are compensated by deeper roots. Pratt (1855) hypothesized that the density of the crust varies, allowing the base of the crust to be at the same depth everywhere. Sections of crust with high mountains, therefore, would be less dense than areas where there are lowlands. In practice, both mechanisms are at work (Hutchinson, 2004).

Isostatic rebound (sometimes called continental rebound, post-glacial rebound or isostatic adjustment) is the rise of land masses that were depressed by a large load of ice, water or sediment through a process known as isostatic depression. As a specific example, ice loading during the Quaternary glaciations has affected northern Europe, especially Scotland, Scandinavia, Siberia, as well as the glaciated regions of Canada and the United States. As weight is removed, the load on the lithosphere and asthenosphere is reduced and the surface rebounds back towards equilibrium levels.

This is a similar effect to that which can be seen by observing the loading and unloading of a large cargo ship.

Isostatic Response to Carbonate Removal by Springs. The removal of carbonates as a result of dissolution should have a similar isostatic effect as that of rebound following glacial melting. Numerous studies have been conducted on the effects of post-glacial rebound or glacial isostasy (e.g., Morner, 1971, Peltier et al., 1978, Newman et al., 1980, Sigmundsson, 1991). These studies show that there is a rebound of the earth’s surface after the massive ice sheets have receeded. Similarily a rebound effect could be expected in the study area after large masses of carbonate sediment are removed from the upper sediment layers via the dissolution action of springs and groundwater. Calculation of the response of the Florida platform to this unloading via dissolution can be approached using methods that are similar to those used for quantifying glacial rebound, as will be illustrated in this study.

Hypotheses Tested This study used a newly available data set for Florida’s springs to examine the effect of carbonate dissolution on the carbonate platform and the potential isostatic effects of the mass removal over time. Two hypotheses were examined in carrying out this investigation.

The first hypothesis is that unloading of Florida’s carbonate platform via long-term subsurface dissolution of the carbonate bedrock, and consequent isostatic uplift of the platform surface, has had a measurable effect on the long-term rate of relative sea-level change, with the greatest uplift expected in the regions of greatest karst activity.

The second hypothesis is that the anomalous uplift and warping of the late Cenozoic shorelines of Florida and the Southeastern United States may be explained, at least in part, by karst dissolution and subsequent isostatic adjustment.

Potential Significance of the Work Florida is typically considered to be tectonically stable and representative of global eustatic sea level. The peninsula is far from any tectonically active areas, and little evidence exists for any anomalous subsidence or uplift during the Quaternary. However, beach ridges near the border of northern Florida and southern Georgia have been found to contain marine fossils of Pleistocene age at elevations of between 42 and 49 m above mean sea level (Opdyke et al., 1984), suggesting that some mechanism of geologic uplift has affected the area.

In the past, the effect on relative sea-level change due to isostatic response to regional dissolution of carbonate bedrock has not been considered significant. Utilization of the present data set may help to answer the question as to the significance of carbonate dissolution and the magnitude of the resultant uplift of the surface. The results of this project could be of benefit to researchers interested in the mechanisms of long-term sea level change and in the rates of carbonate dissolution in karstic environments.

CHAPTER 2

STUDY AREA

Introduction The Florida peninsula is the subaerial eastern portion of the Florida Platform, which forms a wide, relatively flat geologic feature between the Gulf of Mexico and the Atlantic Ocean. The Florida Platform, as delineated by the 200 m bathymetric contour, is more than 483 km wide and measures nearly 650 km north to south. It extends more than 240 km westward under the Gulf of Mexico offshore from Tampa, and more than 113 km under the Atlantic Ocean from Jacksonville. The width of the present-day subaerial Florida peninsula is less than one half that of the total platform (Scott et al., 2004).

The Florida Platform is composed of a thick sequence of variably permeable carbonate sediments, limestone and dolostone, which lie on older sedimentary, igneous and metamorphic rocks. The carbonate sediments may exceed 1500 m in the southern part of the state and are overlain by a thinner sequence of sand, silt and clay, with variable amounts of limestone and shell (Scott, 1992). The carbonate rocks, predominantly limestone, occur at or very near the surface in portions of the west-central and north- central peninsula and in the central panhandle. Carbonate outcrops are common. Away from these areas, the overlying sand, silt and clay sequences become thicker. The generalized stratigraphy for the upper parts of the platform can be found in Figures 9 a- d.

Figure 9a. Geologic Map of Florida, showing geologic units statewide (Scott et al., 2000). Abbreviations for geologic units are described in Fig. 9b.

Figure 9b. Geologic Map of the State of Florida, showing geologic units for Figure 9a (Scott et al., 2000).

Figure 9c. Geologic Map of the State of Florida, showing cross section A-A’ , from Figure 9a, through the panhandle to the eastern coast of the state. Geological units can be seen for the upper 200 meters of the stratigraphic column (Scott et al., 2000)

Figure 9d. Geologic Map of the State of Florida, showing cross section B-B’ of Figure 8a, running through the center of the state from north to south. Geological units can be seen for the upper 200 meters of the stratigraphic column (Scott et al., 2000).

Hydrology Within this thick sequence of permeable carbonate sediments lies the Floridan aquifer system (FAS) (Miller, 1986; Berndt et al., 1998). In some areas the FAS is overlain by the intermediate aquifer system and confining unit (IAS), which consists of carbonates, sand, silt and clay. The surficial aquifer system (SAS) overlies the IAS, or the FAS where the IAS is absent, and is composed of sand, shell and some carbonate (Scott et al., 2004). Increased permeability of the sediments, due to dissolution of portions of the limestone, forms karst features and conduits that may terminate in springs. Karst distribution throughout the state is documented in Sinclair and Lewis (1985).

Florida’s first- and second-magnitude springs occur in areas where carbonate rocks are at or near the surface. Such areas are usually designated karst plains, karst hills or karst hills and valleys (Figure 10) and are generally concentrated in the central panhandle and northern two-thirds of the state. The central panhandle and northern two-thirds of the state are also the locations where the Florida Geological Survey’s recent comprehensive spring study was focused, as described below. Numerous springs are known to flow from vents beneath rivers and many more are thought to exist. Hornsby and Ceryak (1998) identified many newly recognized springs that occur in the channels of the Suwannee and Santa Fe Rivers. Table 2 lists all of Florida’s major springs, as employed in this study, with first magnitude springs (Figure 11) highlighted (Scott et al., 2002). The 93 springs used for this study represent the predominate portion of the spring discharge flowing from the Florida platform. The dataset was confined to these 93 sites, due to the limited number of springs for which both discharge and alkalinity measurement data were available. The springs that were used in this study are also shown in Figure 12.

Figure 10. Karst areas related to first magnitude springs occur in areas where karst features are common. These are areas where the potentiometric surface of the Floridan aquifer system is high enough and surface elevations are low enough to allow ground water to flow at the surface (Scott et al., 2002).

Figure 11. Location of the first magnitude springs of Florida. The localities shown include individual springs, spring groups and river rises (Scott et al., 2002).

Table 2. Springs used in this study. Florida’s major springs are listed by county, showing location and discharge. First-magnitude springs are shown on boldface.

Spring name County Latitude Longitude Mean discharge (ft³/s) Hornsby Alachua 29 51 01.2794 82 35 35.5244 113.4 Poe Alachua 29 49 32.5768 82 38 56.3023 63.3 Treehouse Alachua 29 51 17.5898 82 36 10.3569 223 Gainer Springs Grp Bay 30 25 39.6228 85 32 45.8285 160.5 Chassahowitzka Springs Grp Citrus 28 2 55.8651 82 34 34.3325 137.5 Citrus Blue Citrus 28 58 09.6016 82 18 52.3435 16 Homosassa Springs Grp Citrus 28 47 56.6673 82 35 18.6909 105.8 Kings Bay Springs Grp Citrus 28 52 54.1917 82 35 42.1758 975 Green Cove Clay 29 59 36.2416 81 40 40.4776 3.4 Columbia Spring Columbia 29 51 14.7992 82 36 43.0317 39.5 Ichetucknee Springs Grp Columbia 29 59 03.10 82 45 42.73 191.6 Santa Fe Spring Columbia 29 56 05.2957 82 31 49.5135 99 Copper Spring Dixie 29 36 50.4507 82 58 25.8905 22.2 Guarto Spring Dixie 29 46 47.2688 82 56 23.8495 10 Devil's Ear Spring Gilchrist 29 50 07.2562 82 41 47.7618 206.6 Gilchrist Blue Gilchrist 29 49 47.6409 82 40 58.2654 75.2 Ginnie Springs Gilchrist 29 50 10.8213 82 42 00.4370 52 Hart Spring Gilchrist 29 40 32.6669 82 57 06.1608 71.7 Otter Spring Gilchrist 29 38 41.2880 82 56 33.9097 10 Rock Bluff Spring Gilchrist 29.47 56.7024 82 55 07.1057 33 Sun Spring Gilchrist 29 42 17.0527 82 56 00.6980 20.8 Gator Spring Hernando 28 26 02.7547 82 39 05.6134 0.36 Little Spring Hernando 28 30 48.4708 82 34 51.6997 8.4 Magnolia Spring Hernando 28 26 01.9335 82 39 08.9563 6.9 Salt Spring Hernando 28 32 46.7491 82 37 08.2751 31.4 Weeki Wachee Hernando 28 31 01.8859 82 34 23.3983 168.5 Buckhorn Hillsborough 27 53 21.8108 82 18 09.7969 13.3 Lithia Spring Major Hillsborough 27 51 58.6018 82 13 53.2939 30.5 Sulphur Spring Hillsborough 28 01 16.0814 82 27 05.8857 43.7 Holmes Blue Holmes 30 51 06.0345 85 53 09.0475 13.3 Ponce de Leon Holmes 30 43 16.3259 85 55 50.4658 16.6 Baltzell Spring Jackson 30 49 50.1600 85 14 03.8400 60.8 Black Spring Jackson 30 41 55.4030 85 17 40.0758 62.4 Blue Hole Spring Jackson 30 49 12.5235 85 14 41.6227 28.8 Double Spring Jackson 30 42 13.6800 85 18 11.1600 37.5 Gadsen Spring Jackson 30 42 12.0868 85 17 18.4226 15.4 Jackson Blue Spring Jackson 30 47 25.8536 85 08 24.3181 165.6 Mill Pond Spring Jackson 30 42 13.3200 85 18 27.0000 28.2 Springboard Jackson 30 42 26.6400 85 18 23.7600 25.7

Table 2. Continued Wacissa Springs Grp Jefferson 30 20 22.1257 83 59 30.3968 392.7 Allen Mill Pond Lafayette 30 09 46.2278 83 14 35.0558 12 Lafayette Blue Lafayette 30 07 33.0033 83 13 34.0802 80.2 Mearson Spring Lafayette 30 02 28.8360 83 01 30.1013 50.9 Owens Spring Lafayette 30 02 45.3929 83 02 28.0692 70.6 Ruth Spring Lafayette 29 59 44.7815 82 58 36.5027 13 Troy Spring Lafayette 30 00 21.6939 82 59 51.0091 153.8 Turtle Spring Lafayette 29 50 50.6147 82 53 25.0299 27.6 Alexander Spring Lake 29 04 52.6830 81 34 33.1809 118.2 Apopka Spring Lake 28 33 59.7652 81 40 50.4077 34.3 Bugg Spring Lake 28 45 07.1522 81 54 05.4622 10.9 Horn Spring Leon 30 19 08.8888 84 07 43.4472 21.5 Natural Bridge Spring Leon 30 17 06.6647 84 08 49.6413 113.5 Fanning Spring Levy 29 35 15.3220 82 56 07.0956 97 Levy Blue Spring Levy 29 27 02.6863 82 41 56.2789 5.3 Manatee Spring Levy 29 29 22.012 82 58 36.7387 178.4 Madison Blue Madison 30 28 49.5687 83 14 39.7076 102.9 Suwanachoochee Madison 30 23 12.0174 83 10 18.3592 36.6 Fern Hammock Marion 29 11 00.8638 81 42 29.5013 13.9 Juniper Springs Marion 29 11 01.3417 81 42 44.6809 11.4 Orange Spring Marion 29 30 38.3422 81 56 38.6596 4.6 Rainbow Springs Grp Marion 29 06 08.9133 82 26 14.8792 741.5 Salt Springs Marion 29 21 02.3573 81 43 58.0520 74.8 Silver Glen Marion 29 14 45.0382 81 38 36.5011 111.8 Silver Springs Grp Marion 29 12 58.3421 82 03 09.4724 799 Rock Springs Orange 28 45 23.2034 81 30 06.2450 59.6 Wekiwa Spring Orange 28 42 42.7915 81 27 37.5151 68.5 Crystal Springs Pasco 28 10 55.9231 82 11 06.5308 60 Beecher Spring Putnam 29 26 55.1680 81 38 48.7060 10.7 Warm Mineral Sarasota 27 03 35.6450 82 15 35.8339 9.2 Sanlando Springs Seminole 28 41 19.3237 81 23 43.0666 19.8 Starbucks Spring Seminole 28 41 49.2478 81 23 28.2154 14.5 Fenney Spring Sumter 28 47 41.9913 82 02 17.2106 33.9 Gum Springs Main Sumter 28 57 31.3980 82 13 53.4932 9.9 Branford Spring Suwannee 29 57 17.5253 82 55 42.718 17 Ellaville Spring Suwannee 30 23 04.0780 83 10 21.0183 48 Falmouth Spring Suwannee 30 21 40.187 83 08 05.9703 183.6 Little River Spring Suwannee 29 59 48.7105 82 57 58.7433 84.7 Running Springs Suwannee 30 06 16.0708 83 06 57.3230 29.6 Suwannee Springs Suwannee 30 23 40.1198 82 56 04.3355 23.2 Telford Springs Suwannee 30 06 25.3782 83 09 56.6611 38.3 DeLeon Springs Volusia 29 08 03.4081 81 21 45.8942 27.2 Volusia Blue Volusia 28 56 50.9415 81 20 22.5182 157 Newport Spring Wakulla 30 12 45.7014 84 10 42.5628 6.2 Sheppard Spring Wakulla 30 07 31.0799 84 17 07.8000 5

Table 2. Continued Spring Creek Spring Grp Wakulla 30 04 48.6372 84 19 47.3099 1153 Wakulla Spring Wakulla 30 14 06.6438 84 18 09.2145 375 Morrison Spring Walton 30 39 28.3808 85 54 14.1776 78.9 Beckton Spring Washington 30 38 55.1291 85 41 37.1869 30.1 Brunson Landing Washington 30 36 33.2239 85 45 30.8900 4.4 Cypress Spring Washington 30 39 31.4862 85 41 03.7401 89.5 Washington Blue (Choctawhatchee) Washington 30 30 47.7322 85 50 49.8677 39.8 Washington Blue Spring (Ecofina) Washington 30 27 10.1610 85 31 49.3276 11.5 Williford Spring Washington 30 26 22.3864 85 32 51.2922 29.7

Figure 12. Map location of the 93 sampled springs used for this study (Source: R. Meegan, Florida Geol. Survey).

Offshore or submarine springs are also known to exist off Florida’s Gulf of Mexico and Atlantic coastlines. These springs can most often be found along the Gulf coastline north of Tampa and west of the Ochlocknee River south of Tallahassee. Currently, little is known about the offshore springs with the exception of the Spring Creek Group (see Figures 13a and 13b) (Scott et al., 2004), which is the largest spring group in Florida; it has an average daily discharge of more than one billion gallons of water per day (Rosenau et al., 1977). Water quality data collected from submarine springs indicates that the water is often brackish. Figure 13a shows the location of the known offshore springs of Florida, as depicted in Rosenau et al’s (1977) revision of the original publication (Ferguson et al. 1947). Figure 13b depicts the locations of more recently discovered offshore springs in the Florida Big Bend Region south of Tallahassee (Scott et al., 2004), as well as those listed in Rosenau et al. (1977) for this area.

Florida’s “Boulder Zone” (Vernon, 1970; Puri and Winston, 1974; Lane, 1986; Meyer, 1989) is one of the most dramatic examples of karst dissolution in Florida. The Boulder Zone is a deeply buried (500 to 2,500 m below the surface) cavernous zone of extremely high groundwater transmissivity (2.8 x 105 m²/day) developed in the Paleocene and Lower Eocene section of southern Florida (Randazzo, 1997). The term “Boulder Zone” originated from drillers, who described drilling in this area as similar to drilling into a pile of boulders. When a large cavity is encountered during drilling, rock fragments are often formed as a result of the collapse of the cavity roof or wall. These rock fragments can form man-made boulders as they move about the drill stem.

In some parts of the state karst dissolution has resulted in extremely large (up to 45 m in diameter) cave systems, which have been mapped for several kilometers. These cave systems are conduits for some of the larger springs found in the study area. Personal records and dive logs show that many of the mapped cave systems tend to fall within two general categories: 20-30 m and 75-90 m below land surface.

Figure 13a. Location of Florida’s offshore springs. Florida's known submarine springs -- all issuing from limestone orifices -- are most numerous along the northwest Gulf (Rosenau et al., 1977).

Figure 13b. Known offshore springs in the Florida Big Bend Region. The springs shown here are on Florida’s Gulf of Mexico coast, south of Tallahassee, which is located near the top left center of the map. Recently mapped locations of submarine springs in this area are depicted in addition to those shown in Figure 13a (Scott et al., 2004).

Sea-Level Change and Marine Terraces of Florida Florida’s landforms show the dominant effect of marine forces in shaping the land surface. During periods when the sea covered the Florida Platform, erosion and deposition associated with shallow marine currents shaped the shallow seabed. Extensive flat plains, that were shallow floors and scarps representing coastlines, were cut into the uplands and were left behind when ancient seas receded. Coastal ridges and highlands were formed by ocean currents eroding away sediments or windborne sand building coastal dunes and beach ridges (Figures 14-15). These features continue

to be modified by erosional and depositional forces acting on the subaerial part of the modern Florida Platform.

The highest and oldest of the relict shoreline features is the Trail Ridge shoreline near the border of northeastern Florida and southeastern Georgia (Figure 15). Trail Ridge is an elongated sand ridge that was formed by sediments from the southeastern coastal plain and southern Appalachians. These sediments were reworked and reshaped by subsequent sea-level fluctuations and associated near-shore, coast-parallel currents (Schmidt, 1997). The industrial minerals rutile and ilmenite, which are sources of the titanium metal used in the spacecraft operated at Cape Canaveral on Florida's east coast, are mined from some of the ridges. As a paleo-shoreline, Trail Ridge can be assumed to have been originally horizontal. In the present day, the Trail Ridge shoreline elevation varies from approximately 35 m in south-central Florida to approximately 60 m in north Florida (Opdyke et al., 1984).

The present-day elevation of the older marine terraces of Florida and the Southeast is considered anomalous. The basis for this conclusion is the fact a region’s sea level history is a product of tectonic uplift or subsidence and global eustatic change. The Florida platform has been tectonically stable during most of the late Cenozoic, and so uplift or subsidence can be considered negligible during that period. Furthermore, global sea level has not reached much above the present level during the entire period since the Plio-Pleistocene (Shackleton and Opdyke, 1976). So it might be expected that elevated shorelines, representing relative high-stands of the sea, should be close to present sea level. Florida’s oldest shorelines are elevated many tens of meters, implying some anomalous forces at work. These issues will be discussed in detail in Chapter 4.

Figure 14. Physiographic diagram of Florida showing prominent north-south trending systems of elongated coastal dunes and beach ridges. It is shown in more detail below in Figure 15. Physiographic units are identified in Figure 3. (Source: U.S. Geological Survey, 2000a).

Figure 15. Portion of the Florida peninsula, showing the Florida Trail Ridge shoreline. The figure is a close up of the northeastern corner of Figure 14, showing the Plio- Pleistocene Trail Ridge elevated shoreline. The paleo-shoreline physiographic units are shown in Figure 3 as the Trail Ridge, Mount Dora Ridge and Lake Wales Ridge. (Source: U.S. Geological Survey, 2000b).

Geologic Structure of the Florida Platform The basic shape of the sedimentary sequence underlying the northern Florida platform is that of a tilted wedge that slopes and thickens southward from southern Georgia (Figure 16). Superimposed on this sedimentary sequence are arches and embayments, which have developed on regional structural features.

Figure 16. Florida cross-section along the coastal area of the northern Gulf of Mexico. Clastic and carbonate formations are shown to a depth of approximately 270 meters (Source: F. Rupert, Florida Geol. Survey).

In local areas, fault systems cut all or part of the sedimentary rocks. Some of the more prominent structural features are shown in Figure17. The large positive (convex) and negative (concave) features have affected the distribution and configuration of sediments over long periods of geologic time. Some of the smaller faults were active structures for only a relatively brief period of time and their effects have generally been small.

The Peninsular Arch (Figures 17 and 18) has been the dominant influence on sedimentation in the north-central portion of the study area. Its northwest-trending shape has affected sedimentation in a manner similar to an upwarp produced by compressional tectonics. The Ocala “uplift” (Figure 17) was produced through sedimentary processes, due either to an anomalous buildup of middle Eocene carbonate sediments (Winston, 1976) or differential compaction of middle Eocene carbonate material shortly after deposition (Miller, 1986). Negative features which have been depositional centers since at least Early Cretaceous time (Miller, 1986) flank the Peninsular arch (Figure 17) on three sides.

In the South Florida basin a thick sequence of platform carbonates was deposited south and west of the arch. The Southeast Georgia or Savannah embayment (Figure 17) to the northeast represents a shallow east- to northeast-plunging syncline that subsided at a moderate rate. The Southeast Georgia embayment is a depositional area of Lower Cretaceous clastics, followed by Late Cretaceous and early Cenozoic carbonate rocks, which were then succeeded by Late Cenozoic clastic rocks. The Southwest Georgia, or Apalachicola embayment, (Figure 17) is a shallow southwest-plunging syncline, lying northwest of the Peninsular arch, composed of mostly clastic rocks deposited since Late Jurassic time.

Figure 17. Major structural features of the southeastern U.S. The large positive and negative features shown here have affected the distribution and configuration of sediments over long periods of geologic time. The Peninsular arch in the north-central portion of the state is the dominant influence on sedimentation in the northern Florida study area (Miller, 1986).

Figure 18. East-west cross-section through the Peninsular Arch (see Figure 17). The depth to the bottom of the carbonate sequence and top of basement rock can be seen (Source: F. Rupert, Florida Geol. Survey).

Previous Work Several previous studies have employed measurement of dissolved carbonates in spring discharge to estimate the rate of carbonate platform removal (Sellards, 1909; Fennell, 1969; Rosenau, 1977; Sinclair, 1982; Opdyke et al., 1984; Lane, 1986). The calculated rates of removal vary widely (Lane, 1986). Specifically, estimates of removal rate (in terms of an equivalent thickness of carbonate rock removed per year) range from as low as 1.3 cm/yr (for Rainbow Springs; Fennell, 1969) to as high as 17.8 cm/yr (for the springs of the Tampa area; Sinclair, 1982). These calculations are dependent on knowing the springs’ karst drainage basin area, which includes both surface and underground drainage systems, as well as assumed rock properties, such as density (Lane, 1986).

In one of the more quantitative studies of dissolution losses from the Florida Platform, Opdyke et al. (1984) noted the occurrence of marine fossils of Pleistocene age in beach ridges near the border of northern Florida and Southern Georgia at elevations between 42 and 49 m above mean sea level. Opdyke et al. (1984) also noted that there was no evidence of massive glacial melt that would have been needed to raise sea levels to such elevations. They concluded that the northeastern region of Florida must have been uplifted epeirogenically during the Pleistocene. Based on published measurements of dissolved solids from Florida’s springs, Opdyke et al. (1984) calculated that the karst area is losing a minimum of 1.2 million m³/yr of limestone through spring flow, the equivalent thickness of 1 m of limestone removed every 38,000 yr. They calculated that this loss has led to an isostatic uplift of the north-central part of the Florida peninsula of at least 36 m during the Quaternary time, which they said is in approximate agreement with the observed elevation of the highest Pleistocene marine terraces of Florida, at about 50 meters (Figure 19). Opdyke et al. (1984) concluded that this isostatic uplift is the mechanism that is at least in part responsible for the elevation differences for paleo- shorelines in the karstic areas of north Florida, particularly the Trail Ridge (Figures 3 and 15), the highest and oldest (Plio-Pleistocene) relict shoreline in this region (Hoyt, 1969; Winker and Howard, 1977).

Winker and Howard (1977) addressed the assumption of absolute tectonic stability on the southern Atlantic coastal plain during Pleistocene time. This assumption has influenced most previous attempts to map, name, and correlate relict shorelines and surficial deposits, also referred to as terraces, on the southern Atlantic coastal plain. Their study was the first to correlate terraces throughout the region independently of that assumption. They correlated three shoreline sequences that are well preserved, permitting paleogeographic reconstructions. A combination of published and direct geomorphic evidence suggested that to Winker and Howard (1977) all three shoreline sequences have been deformed. Winker and Howard (1997) concluded that vertical warping continued through Pleistocene time.

Figure 19. Elevation of shoreline features of Trail Ridge, Penholoway, and Talbot terraces, as modified from Winker and Howard (1977). Penholoway terrace is equivalent to Winker and Howard’s Effingham Sequence, and Talbot terrace is equivalent to their Chatham Sequence. (Opdyke et al., 1984)

The previously mentioned study by Opdyke et al. (1984) represents the only previous attempt to relate the warping of the paleo-shorelines of the Florida platform to differential isostatic uplift resulting from dissolution of the underlying carbonate rock. The present investigation has revisited their methods and recalculated the results using a more robust and extensive data set, and has redone the calculations to include a more complex basement scenario, as will be described in a later chapter. Opdyke et al. (1984) employed 3 methods to arrive at their estimates for the effect of carbonate dissolution on the Florida platform. In their first method, in which they determined a mass loss rate of dissolved limestone, they calculated an average daily spring discharge for the platform (1.87 x 107 m³) and estimated the minimum amount of limestone lost through spring flow (1.2 x 106 m3/yr) by using dissolved solids data presented by Rosenau and Faulkner (1975), Rosenau et al. (1977), and Slack and Rosenau (1979). Opdyke et al. (1984) applied this calculation to the “karst areas” (Figure 20), the area of which they gave as 4.6 x 1010 m². The result was an estimate

for the annual loss of limestone, which they expressed as being the surface equivalent thickness loss of 2.6 x 10-5 m/m², or a 1 m equivalent thickness loss of limestone every 38,000 yr.

Figure 20. Karst areas, major springs and major paleo-shoreline features of north- central Florida. Paleo-shoreline complexes are labeled PBI (Penholoway Barrier Islands), TBI (Talbot Barrier Islands), and PABI (Pamlico Barrier Islands) (Opdyke et al., 1984).

Opdyke et al.’s (1984) second approach calculated the isostatic response to mass loss. Using the mass loss rate of 1 m of the surface equivalent thickness of limestone lost

every 38,000 years as described above, they postulated that isostatic uplift would compensate the mass lost due to erosion by raising higher-density mass at depth across a compensation surface. By assuming an original density of 2.2 g/cm³ for the limestone layer and an effective density contrast of 0.2 g/cm³ across the compensation depth, Opdyke et al. (1984) concluded that a corresponding simple isostatic uplift of 1 m every 41,000 years would result, based on Equation 1:

(Eqn.1)

M (ρ0) = Ur (ρ0 + ρn)

Where: M = Mass loss rate of 1 m of the surface equivalent thickness of limestone

ρ0 = Original bulk density of unaltered carbonate rock

Ur = Uplift rate

ρn = Density contrast between unaltered and altered carbonate

Opdyke et al.’s (1984) uplift calculation, using the above equation, is as follows:

(1 m /38,000 yr) (2.2 g/cm³) = Ur (2.2 g/cm³ + 0.2 g/cm³)

Ur = I m /41,000 yr

Stating that surface erosion was probably negligible, Opdyke et al. (1984) extrapolated this uplift rate throughout the Quaternary (approx. 1.6 Ma) to arrive at an approximation of 36 m of Quaternary isostatic uplift. They noted that, based on paleo-shoreline investigations (Winker and Howard, 1977), this is the approximate magnitude of uplift observed for the north-central Florida area, based on a warping of the early Pleistocene shorelines by approximately 50 meters.

Opdyke et al. (1984) took an alternate approach to determine net isostatic uplift for their third calculation. First, they used an estimated density change of 2.2 g/cm³ to 2.0 g/cm³ for the original upper 500 m thickness of carbonate rock as a result of Pleistocene subsurface erosion, i.e., dissolution (Oglesby et al., 1973). Next, they assumed a density of 1.95 g/cm³ for the highly karstified rock raised above the base level (Wicker and Smith, 1978). Finally, by using a density contrast of 0.2 g/cm³ at the depth of compensation and an assumed surficial erosion loss of 10 m since the mid-Pleistocene, Opdyke et al. (1984) used a simple balanced equation (Eqn. 2) (e.g., Turcotte and Schubert, 1982), to estimate an isostatic uplift, U, of 51 m, as shown below. This results in a net change in surface elevation of U – 10 m (surficial erosion), or 41 m.

(Eqn. 2)

ρ0Tk = ρB(Tk – U) + ρ0U + ρA(U – E) + (ρ0 – ρB) U

Where:

ρ0 = Original bulk density of unaltered carbonate rock

Tk = Thickness of the carbonate sequence

ρB = Bulk density of carbonate platform after karst dissolution

ρA = Bulk density of the portion of the carbonate platform raised above the original platform surface. E = Erosion of the surface of the platform, estimated U = Uplift, or change in surface elevation of the platform

Opdyke et al.’s (1984) uplift calculation, using the above equation, is as follows:

(2.2 g/cm3) (500m) = (2.0 g/cm3) (500m – U) + (2.2 g/cm3) U + (1.95 g/cm3) (U – 10 m) + (0.2 g/cm3) U U = 50.9 m

where: (1) 1st term before the equality: original mass of the upper block, i.e., original density x carbonate thickness. (2) 1st term after the equality: new mass of upper block remaining below the original surface, i.e., density below original surface x (carbonate thickness – U). (3) 2nd term after the equality: mass replacing the uplifted part of the original block, i.e., original density x U. (4) 3rd term after the equality: mass of upper block raised above the original surface (minus erosion), i.e., density above original surface x (U - surficial erosion). (5) 4th term after the equality: mass difference from flexure at compensation depth, i.e., density contrast x U.

Opdyke et al. (1984) pointed out that the calculations do not incorporate strain rates or time lags in response to an uncompensated unloading of the crust. Updated modeling techniques have been developed since Opdyke et al’s (1984) initial calculations were made. In addition to approaching the problem as an isostatic balance calculation dealing with vertical columns in an Airy model, it is beneficial to also examine the calculations from the point of plate flexure. In this way the model could treat the plate as a continuous mass instead of a series of vertical columns.

Opdyke et al. (1984) also noted that, when averaging through time, it should be understood that the present rate will not be the rate as averaged over the Pleistocene, due to varying rainfall and groundwater levels in Florida, in response to the increases and decreases in the volume of the ice caps. Additionally, during glacial maxima, the lowering of sea level would also have an effect on water tables in the Floridan Aquifer. Global sea level fell by as much as 120 meters during the glacial advances of the Quaternary (Bard et al., 1990). By lowering sea level by as much as 120 meters, and

groundwater levels by some large but lesser amount, the subsurface erosion would penetrate deeper into the carbonate section, also causing the area impacted by erosion to widen.

CHAPTER 3

METHODS

Spring Data Collection Samples and/or data were collected from over 400 springs by the Florida Springs research team members of the Florida Geological Survey. The author was part of the group which collected and analyzed some of the data. These data were published in Scott et al. (2004), and are shown in Appendix A .The 93 springs used for this project and their locations are listed in Chapter 2, Table 1, and are shown in Figure 12. The locations of the first magnitude springs can also be found in Figure 11. The methodology used by the FGS Springs team for newly collected springs data (Scott et al., 2002) is summarized below.

Field Parameters. Standard FDEP sampling protocols were followed for each sampling event (Morse et al., 2001). Temperature, dissolved oxygen, specific conductance, and pH were measured in the field, using Hydrolab Quanta, YSI data sonde (model no. 6920) and YSI data logger (model no. 6100). Instruments were calibrated twice daily, before and after sampling events. For quality assurance purposes, field reference standards were analyzed every five to ten samples and ten equipment blanks were submitted to the FDEP Bureau of Laboratories throughout the sampling period.

To begin each spring sampling event, two stainless steel weights were attached to polyethylene tubing (3/8" O.D. x 0.062" wall) which was then lowered into the spring vent opening, ensuring the intake line was not influenced by surrounding surface water. Masterflex tubing was attached to the other end, run through a Master Flex E/S portable

peristaltic pump (model no. 07571-00), and the discharge line was then fed directly into a closed-system flow chamber.

The data sonde was inserted into the flow chamber and water was pumped through with a constant flow rate between 0.25 and 1 gallon/minute. No purge was required because springs are considered to be already purged. The field parameter values for temperature, dissolved oxygen, specific conductance, and pH were recorded after the field meter displayed a stable reading (approximately 10 minutes). The flow chamber was removed and sampling was conducted directly from the freshly cut masterflex discharge line.

Two exceptions to this sampling method occurred at Wakulla Spring (Wakulla County) and Homosassa Springs (Citrus County). Both springs have pre-set pipes running down into the cave systems where the spring vents are located. In the case of Homosassa Springs, tubes from the three vents converge at an outlet box with three valves inside, one for each vent. Sampling was conducted from these valves. At Wakulla Spring, the pipe runs to a pump on shore from which sampling is conducted. The sampling system was designed and operated by Northwest Florida Water Management District (NWFWMD) (Wakulla Spring) and Southwest Florida Water Management District (SWFWMD) (Homosassa Springs). Each tube was purged for 10 minutes as there is typically a quantity of water remaining in tubes from the last sampling effort. FDEP standard operating procedures for water quality sampling were then applied. Springs used for this project and their locations are listed in Table 2 and are shown in Figures 11 and 12.

Water Sampling. Seven bottles and three whirlpacks were filled with water from the sampled spring vents and analyzed by the FDEP Bureau of Laboratories. Analytical procedures followed U.S. Environmental Protection Agency methods or standard methods in accordance with the Florida Administrative Code (F.A.C.), and with FDEP (2004b). This document lists specific procedures for sampling at springs, which may

not be directly addressed in FDEP (2002). All bottles were pre-rinsed with sample water prior to filling. Four bottles and three whirlpacks were filled with unfiltered water samples. A GWV high capacity in-line filter (0.45 µm) was attached to the microflex tubing and the remaining three bottles were filled with filtered water samples. Whirlpacks were placed on ice immediately after filling. Bottles for filtered and unfiltered nutrients were preserved with sulfuric acid followed by acidification of bottles for filtered and unfiltered metals using nitric acid. pH litmus paper was used to confirm acidity of pH less than or equal to 2. All water samples were placed on ice and delivered to the FDEP Bureau of Laboratories within 24 hours. Tubing and filters were discarded after each sampling event. Tidally influenced springs were sampled at low tide to minimize the influence of salt water on the water-quality samples.

Discharge Measurement. Where available, discharge data were obtained from the Water Management Districts, U.S. Geological Survey (USGS), and published sources. Methodology for each discharge measurement technique is described below. Some discharge measurements given in Scott et al. (2002) for first order magnitude springs contain flow data collected between September and November of 2001 and reflect drought-influenced conditions. These measurements were used in combination with historical data (Rosenau et al. 1977) when determining average discharge rates

used for calculating dissolved CaCO3. The FGS Springs Team employed the discharge measurement methodology of Buchanan and Sommers (1969) and the DEP standard methods (FDEP, 2002) for discharge measurement.

The U.S. Geological Survey’s Tallahassee district office operates continuous recording gauges on Fanning and Manatee Springs (Levy County). Discharge rates are calculated using continuous data for gauge height and stream velocity. The most recent discharge measurement used to define the flow rate at each spring was used in this investigation. Discharge for the Devil's Ear Spring (Gilchrist County) complex was measured by FDEP using an Acoustic Doppler Current Profiler (ADCP). ADCP measurements were

performed following the guidelines established in the most current ADCP manuals by RD Instruments. ADCP measurements included 5 cross-sectional traverses of the outlet stream. The discharge values from each traverse were summed and a mean was calculated to determine the net discharge.

Recording gauges, operated by NWFWMD, are located on Econfina Creek above and below the Gainer Springs (Bay County) complex. Readings were recorded at ten- minute intervals. The difference in discharge between the two recorder stations, incorporating an eleven-hour lag to travel the approximate six miles between each station, was calculated as the Gainer Springs Group flow. An average discharge rate for the day of sampling was calculated.

The NWFWMD operates a submerged flow meter within the cave system of Wakulla Springs (Wakulla County) main vent. The meter was brought to the surface monthly and discharge measurements were calculated from the velocity data. The most current reading was included in this report.

The discharge for Kings Bay Group (Citrus County) was obtained from a publication prepared by the SWFWMD (Jones et al., 1998) in connection with the ambient groundwater quality-monitoring program.

Provisional discharge data for Chassahowitzka (Citrus County), Homosassa (Citrus County), and Weeki Wachee (Hernando County) springs were obtained from the U.S. Geological Survey, Tampa office. Mean discharge per day was calculated using physical discharge measurements at the springs, the stage and nearby groundwater well water elevations. The measurements control the mean discharge equation and are compiled over the water year. Discharge rates of the remaining nineteen first magnitude springs were measured using Price-AA and Pygmy current meters by the Suwannee River Water Management District (SRWMD) (Alapaha Rise, Lafayette Blue, Madison Blue, Columbia, Falmouth, Hornsby, Ichetucknee, Santa Fe Spring, Tree

House, Troy), the USGS Orlando office (Alexander, Rainbow, Silver Glen, Silver Springs, Volusia Blue), and by the FGS (Holton Creek, Jackson Blue, Nutall Rise, St. Marks). Refer to Figure 11 and Table 1 for spring locations. Vertical-axis meter discharge measurements were conducted at intervals across the spring channel such that no partial section contained more than 5 percent of the flow from the spring (Buchanan and Sommers, 1969). At least 20 sectional readings were obtained per spring. When water depth was less than 0.8 m (2.5 ft), one velocity measurement was recorded at six-tenths of total depth. For water depths greater than 0.8 m (2.5 ft.), the two-point method (velocity measurements at two-tenths and eight-tenths of total depth) was used primarily for velocity measurement in a partial section. The discharge values for each partial section were summed to obtain the total discharge measurement.

Dissolved CaCO3. Alkalinity measurements were carried out by the FDEP labs on the water samples collected from each spring site. The results were reported as dissolved CaCO3. To avoid the limitations of past attempts to quantify dissolution of the Florida carbonate platform, this project employed recently compiled data and focused specifically on total alkalinity as dissolved CaCO3. These data were combined with the best available discharge measurement for individual springs to determine the mass of dissolved carbonate removed from the platform by each spring annually.

Borehole Data Collection The borehole data set contains data from 47 deep boreholes that have been drilled in the study area. These data were obtained from published sources (Jordan, 1949; Barnett, 1975; Brown, 1978). This data set, consisting of borehole name, location, depth to bottom of carbonate sequence and depth to top of bedrock, is found in Appendix C. Not all of these parameters were available for all of the boreholes. Rather than considering each of the 38 counties as a separate region, the lack of completeness of the data set was compensated for by dividing the study area into nine “zones” in order to determine regional averages (Figure 21). Zones boundaries were determined by location of borehole, size of the area and density of springs in that area. The general

location of the borehole, along with the depths to basement and depth to the base of the carbonate sequence, can be seen on the map in Figure 22.

Figure 21. Florida county map (U.S. Census Bureau, 2006), with counties grouped into nine zones, as described in text.

Figure 22. General location of borehole, showing depth to basement (DB) and depth to the base of the carbonate sequence (DL). Dark lines delineate the nine zones, as depicted in Figure 21. Data extracted from Appendix C.

Data Reduction and Isostatic Calculations Spring location, discharge and alkalinity data were collected from current and historical sources (Rosenau, 1977, Scott et al., 2002, and Scott et al., 2004). These data sets were checked for completeness with raw data obtained by the author from the FGS Springs Team and are compiled in Appendix A. Data from Appendix A were then filtered to produce the 93 springs used for this study. This subset represents the springs for which there is sufficient discharge and geochemical data to enable using them for quantitative analysis. This data set is shown in Appendix B and Table 1. This information is also compiled and summarized in Appendix C.

Initial calculations of mass dissolution from the Florida platform due to dissolution, and the resulting isostatic uplift due to the unloading, were carried out using the new springs database and the stratigraphic data obtained from boreholes. An initial calculation was performed using original Opdyke et al. (1984) data set and the new data set in order to compare results using the two sets. More refined calculations were then carried out with the new data set, using different assumptions regarding density variation with depth. Details of the calculations and their results are given in Chapter 4.

CHAPTER 4

RESULTS

Introduction Historical springs data were collected and merged with current data produced by the FGS Springs Project for 93 springs. The decision as to which springs to use was decided in part by the amount of information available for each spring. Generally, the required data was discharge and alkalinity as CaCO3. Although alkalinity is not a direct measure of dissolved limestone, it was used because it is a more accurate measure than total dissolved solids (TDS), which has been used in past estimates of carbonate loss from the Florida platform. There are many factors which can influence groundwater chemistry. Upchurch (1992) listed the following factors, among others: surface conditions at the site of recharge, soil type in the recharge area, flow path in the aquifer, mixing of other waters in the system and aquifer microbiology. Taking these factors into consideration, it was determined that alkalinity measurements would be used as the best representative of carbonate rock dissolution. A summary of the springs data that has resulted from the new springs data set will be presented later in this chapter.

Thickness of Florida Platform Carbonate Sequence Based on a compilation of the available borehole measurements, the thickness of the carbonate sequence of the Florida platform, within the study area, ranges from approximately 625 meters in Bay County to approximately 1500 meters in Volusia County (see Figure 22 and Appendix C). Thicknesses were measured from the land surface to the bottom of the carbonate sequence. The average results for each of the nine zones can be seen in Figures 23 and 24. An east-west cross-section across the

northern part of the study area, based on the zone-averaged well data, is shown in Figure 18.

Figure 23. Depth to bottom of carbonate sequence (meters). Data extracted from Appendix C. Dark lines delineate the nine zones, as depicted in Figure 21. Approximate location of boreholes is shown in Figure 22.

Representative Boreholes for Zones 1-6

500

-500

-1000

-1500

-2000

-2500 Elevation (m) Elevation -3000

-3500

-4000

-4500 km 48 114 198 275 352 412 Surface 39 11 20 20 45 34 Carbonate Bottom -586 -1181 -1099 -1025 -920 -1028 Top of Basement -3464 -4273 -3219 -1524 -958 -1036

W E

Figure 24. East-west cross section through Zones 1-6. The x-axis represents the distance (km) from the western edge of Zone 1 to the midpoint of each of the zones. Borehole data extracted from Appendix C. Approximate location of boreholes is shown in Figure 22.

Depth to Basement Beneath the Carbonate Platform The term “basement” is usually used to describe an underlying crystalline complex which is overlain unconformably by sedimentary strata. In this study the sedimentary strata represent the carbonate platform. In more general terms, basement refers to those rocks under any pronounced unconformity, below which the lithology of the rocks is poorly known (Smith and Lord, 1997). Depth to the top of the basement was measured from the land surface and an average was assigned to each zone. The results of these measurements are shown in Figures 24 and 25.

Figure 25. Depth to basement (meters). Data extracted from Appendix C. Approximate location of boreholes is shown in Figure 22.

Carbonate Mass Loss Calculations Calculation of the effect of carbonate mass loss from the Florida platform was carried in several steps. Initial calculations were carried out in order to replicate methods employed by Opdyke et al. (1984) (Eqn. 1) as outlined earlier in Chapter 2. These results will be discussed first.

Calculation A: Florida Platform Dissolution Due to Spring Activity. Average mean spring discharge and average alkalinity for each of the 93 springs used were determined using data presented in Rosenau et al. (1977), Scott et al. (2002) and Scott et al. (2004). These data can be found in Appendix A and the relevant data are summarized in Appendix B. Alkalinity was employed instead of total dissolved solids (TDS) because it better reflects the mass of carbonate rock being removed from the Florida platform through dissolution. This information (discharge in m³/day x alkalinity in mg/L) was employed to determine a carbonate dissolution rate in metric tons per year and was patterned after the method utilized by Opdyke et al. (1984). This value was converted to m³/yr by assuming an average bulk density of 2.2 g/cm³. An example calculation using the average values from Zones 4-8 are given below is given in Eqn. 3.

(Eqn. 3)

C = (D x Ak) / ρ0

Where:

C = Carbonate dissolution rate D = Spring discharge

Ak = Alkalinity as CaCO3

ρ0 = Original bulk density of unaltered carbonate rock

Using the above equation, the calculation for Zones 4-8 is as follows:

3.6 x 105 m3/yr = (1.62 x 107 m³/day x 133.9 mg/L) / (2.2 g/cm3) or, equivalently

7.92 x 105 tonne/yr = (1.88 x 105 L/sec x 133.9 mg/L) / (2.2 g/cm3)

In other words, Zones 4-8, which are nearly equivalent in area to Opdyke et al.’s (1984) karst region (see Fig. 21), undergo a loss of 3.6 x 105 m3/yr of carbonate due to karst dissolution. In order to determine an equivalent thickness of limestone lost (m/yr), the limestone dissolution rate (m³/yr, shown in Eqn. 3) was divided by the surface area (m²) of the area being investigated, as taken from Table 3. The calculation is shown in Eqn. 4. (Eqn. 4)

S = C / A

Where: S = Surfical equivalent thickness of limestone lost C = Carbonate dissolution rate A = Area

Using the above equation, the calculation for Zones 4-8 is as follows:

7.33 x 10-6 m/yr = 3.6 x 105 m3/yr / 4.91 x 1010 m2

That is, an equivalent thickness of 7.33 x 10-6 mm is lost annually from the Zone 4-8 region due to karst dissolution. Using this result the time required to dissolve the

equivalent of 1 m thickness of limestone can be determined by taking the inverse of the above value (yr/m). The result is 136,497 yr/m.

To determine the amount of time in years for 1 m of isostatic uplift to occur, the time to dissolve 1m of limestone (136,497 yr) was divided by (original density/density below compensation depth). An original bulk carbonate density of 2.2 g/cm³ was assumed. Density below the compensation depth was estimated to be 2.4 g/cm³. Finally, to arrive at the amount of uplift (m) since the beginning of the Quaternary (~1.6 Ma), 1.6 million was divided by the time required for 1m of isostatic uplift. The calculation is shown for Zones 4-8 in Eqn. 5 below.

(Eqn. 5)

Tu = Td / (ρ0 / ρd)

Where:

Tu = Time for 1 m of isostatic uplift

Td = Time to dissolve 1 m of carbonate rock

ρ0 = Original bulk density of unaltered carbonate rock

ρd = Density below compensation depth

Using the above equation, the calculation for Zones 4-8 is as follows:

148,906 yr = 136,497 yr / (2.2 g/cm3 / 2.4 g/cm3)

The result of these calculations indicates that approximately 149,000 yr is required to produce an isostatic uplift of 1 meter due to karst dissolution. Finally, the amount of uplift that has occurred since the beginning of the Quaternary (~1.6 Ma) is shown in Eqn. 6 below:

(Eqn. 6)

UQ = Te / Tu

Where:

UQ = Amount of uplift since the Quaternary (~ 1.6 Ma)

Te = Elapsed time

Tu = Time for 1 m of isostatic uplift

Using the above equation, the calculation for Zones 4-8 is as follows:

11 m = 1.6 x 106 yr / 148,906 yr/m

In other words, using this method, about 11 meters of uplift is calculated to have occurred during the Quaternary. These calculations, (Eqns. 1-6), were carried out for each of the nine zones separately, and again for zones 1-9 combined, and finally for zones 4-8 combined. The results of these calculations are shown in Table 3. Using an original density of 2.2 g/cm3 and a density below compensation depth of 2.4 g/cm3, these results show, among other things, the time required to dissolve the surface equivalent thickness of 1 meter of limestone is approximately 135,000 years for zones 4-8.

Calculation B: Isostatic Uplift with a Single Density Change through the Carbonate Layer. Opdyke et al. (1984) also took an alternate, more refined, approach for calculating the net uplift of the Florida platform since Plio-Pleistocene time (see Eqn. 2 above). For the current project these calculations were redone for each of the nine zones, using the new springs data sets and the published borehole data. The results of the more refined calculations are shown in Table 4.

Table 3. Summary data for Florida platform dissolution rate due to spring activity

Carbonate Carbonate dissolution dissolution Zone Area Area Discharge Discharge Discharge Alkalinity rate rate (sq. mi.) (m²) (ft³/sec) (L/sec) (m³/day) (mg/L) (tonne/yr) (m³/yr) 4-8 18,969 4.91E+10 6,622.3 187,522.7 1.62E+07 133.9 7.92E+05 3.60E+05 1-9 29,898 7.74E+10 9,379.4 265,593.9 2.29E+07 126.5 1.06E+06 4.82E+05 1 3,376 8.74E+09 474.3 13,430.7 1.16E+06 86.8 3.68E+04 1.67E+04 2 3,311 8.58E+09 424.4 12,017.7 1.04E+06 113.3 4.29E+04 1.95E+04 3 2,809 7.28E+09 1,674.2 47,408.1 4.10E+06 132.7 1.98E+05 9.02E+04 4 3,996 1.03E+10 972.5 27,538.1 2.38E+06 163.9 1.42E+05 6.47E+04 5 3,337 8.64E+09 1,623.5 45,972.4 3.97E+06 148.8 2.16E+05 9.81E+04 6 2,610 6.76E+09 14.1 399.3 3.45E+04 96.8 1.22E+03 5.54E+02 7 4,856 1.26E+10 1,929.4 54,634.5 4.72E+06 131.1 2.26E+05 1.03E+05 8 4,169 1.08E+10 2,082.8 58,978.3 5.10E+06 95.8 1.78E+05 8.10E+04 9 1,433 3.71E+09 184.2 5,216.0 4.51E+05 116.6 1.92E+04 8.72E+03 Opdyke et al. (1984) data: 4.60E+10 1.87E+07 1.20E+06

Amount of Uplift Surface Equivalent Time for 1m Since Plio- Thickness of Limestone Time to Dissolve 1m of Isostatic Pleistocene Zone Lost of Limestone Uplift (~1.6 Ma)

(m/m²)/yr (yr) (yr) (m) 4-8 7.33E-06 136,497 148,906 11 1-9 6.22E-06 160,787 175,404 9 1 1.91E-06 523,237 570,804 3 2 2.28E-06 439,362 479,304 3 3 1.24E-05 80,676 88,010 18 4 6.25E-06 159,965 174,508 9 5 1.13E-05 88,139 96,152 17 6 8.20E-08 12,201,548 13,310,779 0 7 8.16E-06 122,496 133,632 12 8 7.50E-06 133,318 145,437 11 9 2.35E-06 425,574 464,263 3 Opdyke et al. (1984) data: 2.61E-05 38333 41,818 38

Table 4. Calculation B – Isostatic Uplift Results Using One Density Change Through the Carbonate Section

Zone ρ0 T ρB B ρA E U

(g/cm³) (meters) (g/cm³) (g/cm³) (meters) (meters)

1 2.2 625 2 1.95 10 61

2 2.2 1192 2 1.95 10 110

3 2.2 1119 2 1.95 10 104

4 2.2 1045 2 1.95 10 97

5 2.2 965 2 1.95 10 90

6 2.2 1062 2 1.95 10 99

7 2.2 945 2 1.95 10 89

8 2.2 1004 2 1.95 10 94

9 2.2 1509 2 1.95 10 137

Opdyke et 2.2 500 2 1.95 10 51 al.

Where:

ρ0 = Original bulk density of unaltered carbonate rock T = Thickness of the carbonate sequence

ρB = Bulk density of carbonate platform after karst dissolution

Calculation C: Isostatic Uplift Results with Two Density Changes Through the Carbonate Layer. An alternative approach to Calculation B was then carried out using the new data sets, to explore the effects of different patterns and magnitudes of dissolution-driven density changes throughout the carbonate column. In Calculation C, the total carbonate thickness was sub-divided into an upper and lower region and individual isostatic calculations (Eqn. 2) were applied to each. The upper region consisted of the upper 200 m of carbonate rock and was assigned a density change of 2.4 g/cm³ (original bulk density before dissolution) to 2.2 g/cm³ (density after dissolution) . A bulk density of 2.4 g/cm³ was assigned to represent an average density for the carbonate platform using data presented in Dobrin and Savit (1988). This is the region where the greatest amount of karst activity would occur. The lower carbonate region consisted of the total thickness of carbonates minus the 200 m assigned to the upper region. For the lower region an estimated density change of 2.4 g/cm³ to 2.35 g/cm³ (representing the density of the clastics beneath the carbonate platform) was assigned. This method was used to allow for a more varied density change throughout the total carbonate thickness and to allow for differences in the amount of karstification that could be expected between the upper and lower sections of the stratigraphic column. A density change from 2.2 g/cm3 to 1.95 g/cm³ was used for the highly karstified portion of the upper carbonate layer, some of which would have been raised above the original surface level. The complete results for these calculations are given in Table 5 and summarized in Table 6. These results show a net change in elevation of between 47-91 meters. The average net change with two density changes for zones 4-8 is 66 meters, compared to 51 meters with a single density change as calculated by Opdyke et al. (1984). The results for Calculations A-C are summarized in Table 7.

Table 5. Calculation C – Isostatic Results Using Two Density Changes Through the Carbonate Section

Zone T ρ0 ρB B ρC ρA E U (g/cm³) (g/cm³) (g/cm³) (g/cm³) (meters) (meters)

1 625 2.4 2.2 2.35 1.95 10 47

2 1192 2.4 2.2 2.35 1.95 10 75

3 1119 2.4 2.2 2.35 1.95 10 72

4 1045 2.4 2.2 2.35 1.95 10 68

5 965 2.4 2.2 2.35 1.95 10 64

6 1062 2.4 2.2 2.35 1.95 10 69

7 945 2.4 2.2 2.35 1.95 10 63

8 1004 2.4 2.2 2.35 1.95 10 66

9 1509 2.4 2.2 2.35 1.95 10 91

T = Thickness of the carbonate sequence

ρ0 = Original bulk density of unaltered carbonate rock

ρB = Bulk density of carbonate platform after karst dissolution

ρC = Bulk density of the underlying clastic rocks.

ρA = Bulk density of the portion of the carbonate platform raised above the original platform surface. E = Erosion of the surface of the platform, estimated U = Uplift

Table 6. Summary Results from Tables 4 & 5

Change in Change in Net change Net change in Mean elevation elevation in elevation elevation depth to Mean depth for upper for lower using one using two bottom of to top of carbonate carbonate density densities Zone carbonates basement layer layer (Table 4) (Table 5) (meters) (meters) (meters) (meters) (meters) (meters) 1 625 3503 26 21 61 47 2 1192 4284 26 50 110 75 3 1119 3239 26 46 104 72 4 1045 1544 26 42 97 68 5 965 1003 26 38 90 64 6 1062 1070 26 43 99 69 7 945 1577 26 37 89 63 8 1004 1953 26 40 94 66 9 1509 1798 26 65 137 91 Opdyke et al. (1984) 500 51

Table 7. Summary Results of Calculations A – C.

Zone Calculation A: Amount of Calculation B: Amount Calculation C: Amount uplift since Plio-Pleistocene of uplift with a single of uplift with two (~1.6 ma) density change density changes

(meters) (meters) (meters)

1 3 61 47 2 3 110 75 3 18 104 72 4 9 97 68 5 17 90 64 6 0 99 69 7 12 89 63 8 11 94 66 9 3 137 91 4-8 11 94 (avg) 66 (avg) 1-9 9 98 (avg) 68 (avg) Opdyke data 38 51 n/a

CHAPTER 5

DISCUSSION

Calculation A Analysis Using an original density of 2.2 g/cm3 and a density below compensation depth of 2.4 g/cm3, these results show, among other things, the time required to dissolve the surface equivalent thickness of 1 meter of limestone is approximately 135,000 years for zones 4-8. This may be compared to Opdyke et al’s (1984) estimate of approximately 38,000 years. The results also produce 11 m of uplift since Plio-Pleistocene time (~1.6 Ma) for zone 4-8 compared to Opdyke et al’s estimate of 38 m of uplift for the equivalent area over that time span. The differences between the two results is due primarily to the higher values for spring discharge and mass loss assumed by Opdyke et al. (1984), as opposed to those determined using the newer springs data set.

Calculation B Analysis These results differ from those presented in Opdyke et al. (1984) due in part to the differences in the estimate of thickness of the carbonate sequence. Opdyke et al. (1984) based their calculation on only the upper 500 meters of carbonates while in this study the results for Calculation B were for the total thickness of carbonates, as given by the borehole data (Appendix C). Opdyke et al. (1984) found the total uplift to be 51 m, for a net uplift of 41 m (51 m total uplift – 10 m of estimated surface erosion). Using the new data set, the total uplift varies from 61 m to 137 m among the 9 zones, averaging 98 m. For zones 4-8, the area that equates to Opdyke et al.’s area, the mean total uplift is 94 m. Using the same assumption of 10 m of surface erosion, the net uplift is 84 m. This is approximately twice the value determined by Opdyke at al. (1984). The density changes, which were used in Calculation B (one density change for the carbonate platform), are shown diagrammatically in Figure 26. The densities assigned

for this calculation were chosen so comparisons could be made with results obtained by Opdyke et al. (1984).

Figure 26. Diagrammatic sketch of density changes within the carbonate platform. Density changes as a result of dissolution are shown based on the parameters used for Calculations B and C, as described in the text. In Calculation B, the platform is considered as a single block (blue). For Calculation C, the platform is divided into an upper (yellow) and a lower (orange) block. In both cases, the mass raised above the original surface is the highly karstified uppermost part of the platform that has been uplifted (light blue). The mass below the platform represents the underlying clastic sedimentary rocks.

Calculation C Analysis The density changes, which were used in Calculation C (two density changes for the carbonate platform), are shown diagrammatically in Figure 26. The densities assigned for this calculation were chosen to be more representative of the bulk densities for carbonates and the underlying clastics than those used by Opdyke et al. (1984). The results for this calculation differ from those presented in Opdyke et al. (1984) due to differences in the densities used as well as the difference in the method the carbonate platform was divided. Opdyke et al. (1984) based their calculation on only a single density change for the upper 500 meters of carbonates while in this study the results for Calculation C reflect separate calculations for the upper 200 m and the total thickness of carbonates minus 200 m. Using the new data set, the total uplift varies from 47 m to 91 m among the 9 zones, averaging 68 m. For zones 4-8, the area which equates to Opdyke et al.’s area, the mean total uplift is 66 m. Using the same assumption of 10 m of surface erosion, the net uplift is 56 m.

Suggestions for Future Work Although this report utilizes data sets not presented in previous work, additional data would allow for even more rigorous isostasy calculations to be performed. These additional data sets would include:

1) Additional spring discharge and alkalinity measurements to cover more of the 733 springs listed by the FGS, i.e., more second and third magnitude springs, 2) Data from more deep boreholes to eliminate the need to “zone” the study area, 3) Better defined and more specific deep borehole logs to aide in defining carbonate thickness and depth to basement, 4) More accurate and better defined long term rates of surficial erosion, 5) Laboratory-determined rock densities, to more accurately determine density contrasts between the upper and lower blocks of carbonates, and 6) Estimates to determine the effects of carbonate dissolution as a result of submarine groundwater discharge (SGD) and mass loss from rivers. Knowledge

of the quantity and dissolved composition of SGD is only beginning to be understood. This is potentially a significant contributor to carbonate mass loss from the Florida platform and, if reliably measured, would increase the magnitude of the results reported herein.

Incorporation of these additional data into the study would allow better-constrained calculations. Future work should incorporate such data as they become available.

CHAPTER 6

CONCLUSIONS

This study was undertaken for the purpose of making a more comprehensive determination of dissolution rates by use of a more robust Florida springs data set and to approach the issue of isostasy more rigorously than in past studies. The primary goal of this project was to quantify the potential effects of isostasy on the Florida platform and then determine if these effects should be evident in the elevations of paleo- shorelines. An analysis of the data presented in this study shows that the impact of long-term carbonate dissolution and mass loss from the Florida platform, and the resulting isostatic rebound, may be significant in explaining anomalous elevations in the Plio-PleistoceneTrail Ridge shoreline of north-central Florida and other remnant shoreline features.

The loss of carbonate rock mass through karst dissolution appears to be in part responsible for the uplift and anomalous warping of the paleo-shorelines. Because the Florida carbonate platform is karstic, it is subject to high rates of dissolution and mass removal to the ocean each year. Dissolution of the carbonate platform is best reflected in the dissolved bicarbonate content of Florida’s groundwater, as measured in spring discharge. The lack of a comprehensive and detailed date set for the flux and chemical composition of freshwater spring discharge has been a major issue in past studies of karst processes for Florida’s carbonate platform. New comprehensive water quality data have made it possible to determine a more accurate rate of carbonate dissolution of the Florida carbonate platform. Using the more accurate rate of dissolution in combination with modeling techniques analogous to those used to determine postglacial rebound, one can calculate a long-term rate of isostatic uplift.

The database for this project consisted of two primary types. The first was the springs data set. That set includes data collected from historical sources, plus original data collected as part of the Florida Geological Survey springs project, which was completed in 2004. The springs database comprised information on discharge and alkalinity from 93 first-magnitude (discharge greater than 100 ft3/sec), and second-magnitude (discharge between 10-100 ft3/sec) springs. For each spring, discharge and alkalinity data were combined to determine mass dissolution rates.

The second data set comprised data from 47 deep boreholes that were drilled in the study area. These data were obtained from published sources. This database consists of well name, location and depth to bottom of carbonate sequence and depth to top of bedrock. This database provided thickness and lithologic data for calculating isostatic uplift of the Florida platform. Not all of the parameters were available for all of the boreholes. Rather than considering each of the 38 karst-affected counties as a separate region, the incomplete nature of the data set was compensated for by dividing the study area into nine regions

Carbonate mass removal calculations, using average spring discharge and alkalinity measurements, were carried out for the entire karst-affected region of Florida. Calculations were done for each of the nine zones individually, for zones 1-9 combined, and finally for zones 4-8 combined. Zone 4-8 represented a comparable study area to that used by Opdyke et al. (1984) in their earlier calculations of isostatic uplift. This investigation’s results show that using Opdyke et al.’s (1984) methods, the time required to dissolve the surface equivalent thickness of 1 meter of limestone to be approximately 135,000 years. This is significantly longer than the estimates of Opdyke et al (1984) of approximately 38,000 years. The new data set also results in an uplift of 11 m of uplift since the Plio-Pleistocene (~ 1.6 Ma) for zones 4-8, compared to Opdyke et al’s (1984) estimate of 38 m. The amounts of uplift due to mass carbonate loss for zones 1-9 individually were between 3-18 m. Uplift calculations for the entire study area combined yielded 9 m of uplift since the Plio-Pleistocene. The large difference between the

results from Opdyke et al. (1984) and those calculated for this study is due primarily to the differences in the basic data sets available and the use of the more conservative alkalinity measurement rather than the less precise TDS measurement. The present comprehensive springs data set reveals a significantly smaller dissolution mass loss per year from the Florida platform than the earlier investigation. To a lesser degree, the difference in the discharge values for some of the springs, due in part to drought conditions during the period that measurements were taken for the present springs data set, also contributed to the difference in the results.

Isostatic uplift due to unloading of the carbonate platform, as a result of changes in density, was calculated by using two different approaches. The first approach, shown in Fig. 26 as Calculation B, used a single density change for the entire thickness of the platform. Results range from 61-137 m of uplift for zones 1-9 individually and 94 m of uplift for an average of zones 4-8. This compares with a result of 51 m of uplift for Opdyke et al. (1984). Results differ between the two studies due to the differences in the thickness used for the carbonate sequence. Opdyke et al. (1984) based their calculation on the upper 500 meters of the platform while in this study the results were determined by using the total thickness of carbonates, as evidenced by the borehole data. Calculations for the total thickness were done to determine a maximum amount of isostatic uplift possible as a result of carbonate dissolution within the area of study.

The second approach to the calculation, using two density changes for the carbonate platform, was also used to quantify isostatic uplift. This approach is shown as Calculation C in Fig. 26. The total carbonate thickness was subdivided into an upper and lower region and individual calculations, like those for a single density change, were applied to each. The upper region consisted of the upper 200 m of carbonate rock and was assigned a density of 2.2 g/cm³. This is the region where the greatest amount of karst activity could be assumed to take place. The lower carbonate region consisted of the total thickness of carbonates minus the 200 m assigned to the upper region. For the lower region an estimated density of 2.4 g/cm³ was assigned. The underlying clastic

sedimentary rocks were assigned a density of 2.35 g/cm3. This method was selected in order to allow for a more complex and realistic density change throughout the total carbonate section and to allow for differences in the amount of karstification that might be expected between the two regions. A density change from 2.2 g/cm3 to 1.95 g/cm³ was used for the highly karstified portion of the upper carbonate layer, some of which would have been raised above the original surface level. The results of these calculations show a net change in elevation of between 47-91 meters, depending on the zone. The average net change in elevation with two density changes for zones 4-8 is 66 meters, compared to 51 meters uplift with a single density change as calculated by Opdyke et al. (1984).

The results of the analysis presented herein may be of value in improving the understanding of the late Cenozoic geologic history of Florida. Mass removal, due to the dissolution of carbonates, led to isostatic adjustment and the anomalous uplift of paleo- shorelines. The degree of uplift was a function of the intensity of karstification, varying north-to south along the peninsula. Future investigation into this process, in conjunction with improved dating of paleo-shoreline deposits, may further refine our understanding of relative sea-level change in the region.

APPENDIX A

SPRINGS LOCATION AND DATA

Data extracted from

Springs of Florida Florida Geological Survey Bulletin No. 31, Revised (Rosenau et al., 1977)

First Magnitude Springs of Florida Florida Geological Survey Open File Report No. 85 (Scott et al., 2002)

Springs of Florida Florida Geological Survey Bulletin No. 66 (Scott et al., 2004)

Latitude Alkalinity Discharge Spring County Longitude (mg/L) Date (ft³/s) Date

Hornsby Alachua 29 51 01.2794 130 1972 250 April 19, 1972 82 35 35.5244 163 2001 76 April 19, 1975 September 16, 14.1 2001 Avg 146.5 113.4

Poe Alachua 29 49 32.5768 170 1972 86.5 February 19, 1917 82 38 56.3023 179 2001 75.1 January 31, 1929 31.2 March 14, 1932 December 13, 84 1941 75.3 July 22, 1946 39.2 May 2, 1956 91.7 October 17, 1972 93.1 April 18, 1972 50.59 May 26, 1997 6.1 May 14, 2002 Avg 174.5 63.3

Treehouse Alachua 29 51 17.5898 56 2001 406 May 26, 1998 82 36 10.3569 39.9 October 30, 2001 Avg 56 223

Gainer Bay 30 25 39.6228 49.3 1962 162 May 15, 1905 Springs Grp 85 32 45.8285 52.3 1972 159 January 30, 1963 58.3 2001 128.2 October 14, 2002 58 2002 192.8 January 5, 2004 Avg 54.5 160.5

Chassahowitzka Citrus 28 2 55.8651 140 1970 138.5 1930-1972 (81 Springs Grp 82 34 34.3325 140 1971 measurements) 140 1972 53 October 15, 2001 130 1975 152 2001 154 2002 Avg 142.7 137.5

Citrus Blue Citrus 28 58 09.6016 140 1975 11.1 March 15, 1932 Spring 82 18 52.3435 146 2002 17.7 March 7, 1961 19.6 June 19, 1961 15.1 May 25, 1972

16.3 October 16, 2002 Avg 143 16

Homosassa Citrus 28 47 56.6673 110 1956 106 1931-1974 (90 Springs Grp 82 35 18.6909 110 1966 measurements) 115 1972 87 June 23, 1905 115 2001 115 2002 Avg 113 105.8

Kings Bay Citrus 28 52 54.1917 105 2001 975 1965-1977 Springs Grp 82 35 42.1758 107 2002 Avg 106 975

Green Cove Clay 29 59 36.2416 79 1972 5.4 February 12, 1929 Spring 81 40 40.4776 86 2003 4.4 April 18, 1946 4.3 November 4, 1950 2.7 June 18, 1954 2.7 April 25, 1956 3.5 October 19, 1960 3 March 8, 1972 1.4 January 8, 2003 Avg 82.5 3.4

Columbia Spring Columbia 29 51 14.7992 54 2001 39.5 November 1, 2001 Avg 82 36 43.0317 54 39.5

Ichetucknee Columbia 29 59 03.10 140 1975 197.2 May 17, 1946 Springs Grp 82 45 42.73 149.3 2001 186 October 3, 2001 147.5 2002 Avg 145.6 191.6

Santa Fe Spring Columbia 29 56 05.2957 107 2001 150 June 1, 1998 82 31 49.5135 48 November 1, 2001 Avg 107 99

Copper Spring Dixie 29 36 50.4507 200 1975 18.8 May 12, 1932 November 18, 82 58 25.8905 201 2002 31.9 1960 November 11, 25.4 1975 September 22, 20.7 1997 14.2 July 16, 2002 Avg 201 22.2

Guarto Spring Dixie 29 46 47.2688 153 1973 12.4 May 12, 1932

82 56 23.8495 183 2002 3.41 March 19, 1962 12 November 2, 1972 12.8 July 21, 1997 9.33 July 16, 2002 Avg 168 10

Devil's Ear Gilchrist 29 50 07.2562 175 2001 206.6 September 5, 2001 Spring 82 41 47.7618 172 2002 Avg 173.5 206.6

Gilchrist Blue Gilchrist 29 49 47.6409 148 1975 70.4 Spring 82 40 58.2654 173 2002 80 Avg 160.5 75.2

Ginnie Springs Gilchrist 29 50 10.8213 159 2002 45.8 April 28, 1975 82 42 00.4370 58.2 November 4, 1997 Avg 159 52

Hart Spring Gilchrist 29 40 32.6669 170 1972 40 March 14, 1932 82 57 06.1608 191 2002 62.1 May 12, 1932 58.6 July 24, 1946 58.6 April 27, 1956 November 23, 152 1960 79.4 November 1, 1972 51.3 June 26, 1997 Avg 180.5 71.7

Otter Spring Gilchrist 29 38 41.2880 160 1972 5 March 14, 1932 82 56 33.9097 209 2002 5.5 May 12, 1932 16.1 November 1, 1972 September 19, 21.2 1997 2.3 July 16, 2002 Avg 184.5 10

Rock Bluff Gilchrist 29.47 56.7024 120 1972 42.1 December 8, 1942 Spring 82 55 07.1057 129 2002 25 April 19, 1956 23.8 April 28, 1956 November 23, 40.3 1960 39.3 November 2, 1973 27.6 July 17, 1997 Avg 124.5 33

Sun Spring Gilchrist 29 42 17.0527 120 1972 27.6 November 2, 1972 September 19, 82 56 00.6980 166 2002 31.2 1997

3.5 July 16, 2002 Avg 143 20.8

Gator Spring Hernando 28 26 02.7547 115 2003 0.36 January 7, 2003 Avg 82 39 05.6134 115 0.36

December 15, Little Spring Hernando 28 30 48.4708 160 1962 7.8 1972 December 11, 82 34 51.6997 130 1964 14.7 1975 130 1965 2.7 March 5, 2003 140 2003 Avg 140 8.4

Magnolia Spring Hernando 28 26 01.9335 110 1964 11 April 30, 1964 82 39 08.9563 110 1965 7.9 July 24, 1964 September 13, 112 112 9.1 1964 9.4 February 4, 1965 10 August 5, 1965 December 12, 1 1972 0.2 January 7, 2003 Avg 110.7 6.9

Salt Spring Hernando 28 32 46.7491 130 1965 24.7 January 18, 1961 82 37 08.2751 129 2002 38.9 December 8, 1965 28.4 June 30, 1966 December 14, 31.9 1972 December 11, 31.2 1975 33 1988-1989 Avg 129.5 31.4

Weeki Wachee Hernando 28 31 01.8859 130 1964 176 1917-1974 (364 Spring 82 34 23.3983 130 1969 measurements) 140 1974 161 October 18, 2001 147 2001 149.3 2002 Avg 139.26 168.5

Buckhorn Hillsborough 27 53 21.8108 110 1966 10.9 June 2, 1966 82 18 09.7969 100 1972 15 June 5, 1972 122 2002 14 June 14, 1905 Avg 110.7 13.3

Lithia Spring Hillsborough 27 51 58.6018 100 1968 30.5 avg given in

Bulletin 66 Major 82 13 53.2939 110 1972 121 2002 Avg 110.3 30.5

Sulphur Spring Hillsborough 28 01 16.0814 120 1956 44 15 yr mean 82 27 05.8857 130 1966 38.9 1999 140 1972 170 2002 Avg 140.0 43.7

Holmes Blue Holmes 30 51 06.0345 102 2002 13.3 December 3, 2002 Avg 85 53 09.0475 102 13.3

Ponce de Leon Holmes 30 43 16.3259 100 1972 20.7 May 20, 1942 Spring 85 55 50.4658 107 2002 18.1 December 9, 1946 18.8 April 19, 1972 8.6 June 28, 2002 Avg 103.5 16.6

Baltzell Spring Jackson 30 49 50.1600 120 1973 72.8 August 16, 1973 85 14 03.8400 127 2002 48.8 March 22, 2002 Avg 123.5 60.8 Black Spring Jackson 30 41 55.4030 90 1973 73.2 July 18, 1973 85 17 40.0758 89 2002 51.6 May 23, 2002 89.5 62.4

Blue Hole Jackson 30 49 12.5235 130 1973 56.8 August 8, 1973 Spring 85 14 41.6227 118 2002 0.7 June 28, 2002 Avg 124 28.8

Double Spring Jackson 30 42 13.6800 120 1973 37.5 July 17, 1973 85 18 11.1600 121 2002 Avg 120.5 37.5

Gadsen Spring Jackson 30 42 12.0868 120 1973 18 July 18, 1973 85 17 18.4226 125 2002 12.8 May 23, 2002 Avg 122.5 15.4

Jackson Blue Jackson 30 47 25.8536 98 1972 134 January 24, 1929 December 22, Spring 85 08 24.3181 109 2001 56 1934 118 2002 265 May 20, 1942 November 15, 178 1946 178 January 30, 1947 287 March 6, 1973 61 December 17,

2001 Avg 108.3 165.6

Mill Pond Spring Jackson 30 42 13.3200 97 1973 33.2 July 18, 1973 85 18 27.0000 120 2002 23.2 May 22, 2002 Avg 108.5 28.2

Springboard Jackson 30 42 26.6400 120 1973 17.4 July 18, 1973 Spring 85 18 23.7600 99 2002 34 May 22, 2002 Avg 109.5 25.7

Wacissa Jefferson 30 20 22.1257 135 1960 280 October 12, 1972 Springs Grp 83 59 30.3968 147.5 2001 605 April 17, 1973 293 October 2, 2001 Avg 141.3 392.7

November 26, Allen Mill Pond Lafayette 30 09 46.2278 170 1973 21.8 1973 September 23, Spring 83 14 35.0558 194 2002 11.2 1997 2.9 July 9, 2002 Avg 182 12

November 23, Lafayette Blue Lafayette 30 07 33.0033 170 1973 92.8 1973 Spring 83 13 34.0802 200 2001 102 June 24, 1998 45.9 October 24, 2001 Avg 185 80.2

Mearson Spring Lafayette 30 02 28.8360 150 1975 50.6 May 14, 1927 83 01 30.1013 167 2002 62.1 December 3, 1975 September 15, 68.5 1997 22.5 August 14, 2002 Avg 158.2 50.9

September 10, Owens Spring Lafayette 30 02 45.3929 150 1973 51.2 1973 83 02 28.0692 163 2002 90 June 2, 1998 Avg 156.5 70.6

November 14, Ruth Spring Lafayette 29 59 44.7815 150 1973 11.5 1973 82 58 36.5027 167 2002 14.4 June 24, 1997 Avg 158.5 13

Troy Spring Lafayette 30 00 21.6939 150 1960 149 July 17, 1942 November 26, 82 59 51.0091 150 1973 161 1960

163 2001 148 May 28, 1963 163 2002 205 October 16, 1973 106 October 30, 2001 Avg 156.5 153.8

Turtle Spring Lafayette 29 50 50.6147 150 1972 40.8 November 3, 1972 September 22, 82 53 25.0299 216 2002 36.4 1997 5.7 July 17, 2002 Avg 183 27.6

Alexander Lake 29 04 52.6830 120 1972 112 February 12, 1931 Spring 81 34 33.1809 82 2001 124 February 7, 1933 82 2002 162 April 13, 1935 74.5 October 15, 1935 131 December 3, 1935 101 April 2, 1946 136 April 23, 1956 November 16, 124 1960 124 June 8, 1960 146 April 25, 1967 114 June 22, 1967 109 July 2, 1969 103 April 19, 1972 September 12, 94.2 2001 Avg 94.7 118.2

Apopka Spring Lake 28 33 59.7652 65 1972 28.6 May 4, 1971 81 40 50.4077 80 2002 35 Mean 1971-1999 (22 measurements) 24.7 Annual mean 2001 Avg 72.5 34.3

Bugg Spring Lake 28 45 07.1522 120 1946 17.6 1946 81 54 05.4622 120 1972 10.3 1956 126 2002 18.6 1960 12.4 1967 10.8 1972 10.2 1985 8.5 1990 11.4 1991 8.1 1992 8.6 1993 9.1 1994 10.7 1995

11.7 1996 8.6 1997 11.7 1998 9 1999 8.5 2000 Avg 122 10.9

November 12, Horn Spring Leon 30 19 08.8888 110 1972 28.8 1971 84 07 43.4472 125 2002 14.2 February 20, 2002 Avg 117.5 21.5

Natural Bridge Leon 30 17 06.6647 110 1972 115 May 19, 1942 Spring 84 08 49.6413 125 2002 132 May 14, 1946 97 December 5, 1960 79 May 15, 1963 106 October 6, 1971 151.9 April 25, 2002 Avg 117.5 113.5

Fanning Spring Levy 29 35 15.3220 170 1956 109 October 25, 1930 82 56 07.0956 160 1972 79.2 March 14, 1932 December 17, 193 2001 137 1942 193 2002 64 May 1, 1956 November 18, 111 1960 83.4 March 27, 1963 98.7 April 25, 1972 139 July 31, 1973 51.5 October 24, 2001 Avg 179 97

Levy Blue Levy 29 27 02.6863 110 2002 8.9 Avg for 1917-1974 (56 Spring 82 41 56.2789 measurements) December 17, 1.7 2002 Avg 110 5.3

Manatee Spring Levy 29 29 22.012 180 1956 149 March 14, 1932 December 17, 82 58 36.7387 170 1972 218 1942 198 2001 137 July 24, 1946 199 2002 110 April 27, 1956 November 18, 238 1960 145 May 28, 1963 220 April 19, 1972

210 April 25, 1972 203 July 31, 1973 154 October 23, 2001 Avg 186.8 178.4

Madison Blue Madison 30 28 49.5687 120 1960 75 March 16, 1932 Spring 83 14 39.7076 120 1973 77.8 April 24, 1956 November 15, 122 2001 141 1960 123 2002 113 May 28, 1963 139 November 6, 1973 71.4 October 23, 2001 Avg 121.3 102.9

Suwana- choochee Madison 30 23 12.0174 160 1973 40.8 November 6, 1931 Spring 83 10 18.3592 152 2002 18.3 March 16, 1932 51.6 November 8, 1973 September 24, 35.5 1997 Avg 156 36.6

December 16, Fern Hammock Marion 29 11 00.8638 43 1972 15.5 1935 1936 (5 Spring 81 42 29.5013 46 2002 16.8 measurements) 15.6 March 11, 1937 17.6 April 4, 1946 11.6 April 23, 1956 November 15, 17.7 1960 12.7 April 19, 1972 1985 (4 13.6 measurements) 1990 (6 11 measurements) 1995 (4 13 measurements) 2000 (5 10.9 measurements) 2001 (4 10.6 measurements) Avg 44.5 13.9

Juniper Springs Marion 29 11 01.3417 40 1972 8.9 April 13, 1935 December 16, 81 42 44.6809 48 2002 15.7 1935 1936 (4 13.1 measurements) 12.8 March 11, 1937 14.1 April 11, 1946

9.7 April 23, 1956 13.6 November 5, 1960 10.1 April 19, 1972 1985 (5 12.2 measurements) 1990 (6 9.1 measurements) 1995 (4 12 measurements) 2000 (5 8.8 measurements) 2001 (4 8.2 measurements) Avg 44 11.4

September 11, Orange Spring Marion 29 30 38.3422 120 1972 7.6 1972 81 56 38.6596 129 2003 1.5 January 8, 2003 Avg 124.5 4.6

Rainbow Marion 29 06 08.9133 53 1974 763 1965-1974 Springs Grp 82 26 14.8792 116.3 2001 634 October 23, 2001 116.4 2002 Avg 95.2 741.5

Salt Springs Marion 29 21 02.3573 67 2002 87.3 February 9, 1929 81 43 58.0520 81.4 September 8, 1930 1931 (5 92.5 measurements) 73.3 March 3, 1932 61.8 February 7, 1933 1935 (3 69.6 measurements) 78.7 April 4, 1946 79.9 April 24, 1956 November 16, 88.2 1961 107 June 8, 1966 91.9 April 25, 1967 77.1 April 20, 1972 1985 (5 88.5 measurements) 1990 (6 70.2 measurements) 1995 (4 73.4 measurements) 2000 (5 74.8 measurements) 2001 (4 76.4 measurements) Avg 67 74.8

Silver Glen Marion 29 14 45.0382 69 1972 112 1931-1972 (11 Springs 81 38 36.5011 69 2001 measurements) September 13, 69.7 2002 109 2001 Avg 69.2 111.8

Silver Marion 29 12 58.3421 170 1972 820 Avg 1932-1974 November 15, Major 82 03 09.4724 162.3 2001 556 2001 168 2002 Avg 166.8 799

Rock Springs Orange 28 45 23.2034 86 1971 59.6 Mean 1931-2000 (249 81 30 06.2450 95 2002 measurements) Avg 90.5 59.6

Wekiwa Spring Orange 28 42 42.7915 98 1971 68.5 Mean 1932-2000 (239 81 27 37.5151 130 2002 measurements) Avg 114 68.5

Crystal Springs Pasco 28 10 55.9231 140 1968 60 Avg 1923-1974 82 11 06.5308 135 1972 154 2002 Avg 143 60

November 23, Beecher Spring Putnam 29 26 55.1680 92 1972 12.4 1960 81 38 48.7060 130 2002 9 April 20, 1972 Avg 111 10.7

Warm Mineral Sarasota 27 03 35.6450 130 1962 9.7 Avg 1942-1974 (10 Spring 82 15 35.8339 130 1972 measurements) 131 2003 4.2 March 4, 2003 Avg 130.3 9.2

Sanlando Springs Seminole 28 41 19.3237 100 1972 19.8 Mean 1941-2000 (115 81 23 43.0666 145 2002 measurements) Avg 122.5 19.8

Starbucks Seminole 28 41 49.2478 100 1972 14.5 Mean 1944-2000 (109 Spring 81 23 28.2154 127 2002 measurements) Avg 113.5 14.5

Fenney Spring Sumter 28 47 41.9913 110 1972 21.6 July 26, 1946 82 02 17.2106 132 2002 4.7 April 26, 1956 November 22, 95.5 1960 13.9 March 16, 1972 Avg 121 33.9

Gum Springs Sumter 28 57 31.3980 110 1972 11.1 March 15, 1932 Main 82 13 53.4932 129 2002 8.6 1999 avg Avg 119.5 9.9

Branford Spring Suwannee 29 57 17.5253 150 1972 12.4 May 15, 1927 82 55 42.718 198 2002 8.9 March 15, 1932 8.5 April 26, 1956 November 17, 29.8 1960 29.2 November 3, 1972 24.5 July 21, 1997 5.6 July 10, 2002 Avg 174 17

Ellaville Spring Suwannee 30 23 04.0780 170 1973 41.2 December 9, 1942 November 16, 83 10 21.0183 171 2002 27.9 1960 82 November 8, 1973 40.7 June 2, 1998 Avg 170.5 48

Falmouth Spring Suwannee 30 21 40.187 170 1973 167 1908 83 08 05.9703 187 2001 220 1913 365 February 10, 1933 59.6 December 9, 1942 157 July 22, 1946 November 16, 183 1960 November 15, 159 1973 November 13, 158 2001 Avg 178.5 183.6

Little River November 27, Spring Suwannee 29 59 48.7105 160 1973 84.4 1973 September 19, 82 57 58.7433 163 2002 84.9 1997 Avg 161.5 84.7

November 27, Running Springs Suwannee 30 06 16.0708 160 1973 37 1973

83 06 57.3230 169 2002 22.4 July 30, 1997 29.5 July 9, 2002 Avg 164.5 29.6

Suwannee Springs Suwannee 30 23 40.1198 140 1966 23.4 Avg 1906-1973 (52 82 56 04.3355 150 1973 measurements) 149 2002 14.1 June 24, 1997 Avg 146.3 23.2

Telford Springs Suwannee 30 06 25.3782 170 1973 35.1 May 14, 1927 December 12, 83 09 56.6611 171 2002 28 1941 48.2 May 29, 1942 November 17, 53.5 1960 November 21, 33.8 1973 September 17, 31.2 1997 Avg 170.5 38.3

DeLeon Springs Volusia 29 08 03.4081 100 1972 27.2 Mean 1929-2000 (244 81 21 45.8942 121 2002 measurements) Avg 110.5 27.2

Volusia Blue Volusia 28 56 50.9415 105 1960 162 1932-1974 avg (360 Spring 81 20 22.5182 121 1972 measurements) November 24, 142 2001 87 2001 Avg 122.7 157

Newport Spring Wakulla 30 12 45.7014 170 1972 8.2 March 2, 1972 84 10 42.5628 184 2003 4.2 February 20, 2003 Avg 177 6.2

November 25, Sheppard Spring Wakulla 30 07 31.0799 143 2002 5 2002 Avg 84 17 07.8000 143 5

Spring Creek Wakulla 30 04 48.6372 110 1972 2000 May 30, 1974 Springs Grp 84 19 47.3099 67 1973 307 November 1, 1996 125.5 2001 Avg 100.8 1153

Wakulla Spring Wakulla 30 14 06.6438 130 1972 390 1907-1974 84 18 09.2145 146 2001 128.9 September 27,

2001 144.3 2002 Avg 140.1 375

Morrison Spring Walton 30 39 28.3808 110 1972 121 May 27, 1942 85 54 14.1776 114 2002 89 December 9, 1946 54.9 November 5, 1963 62.2 April 19, 1972 67.2 September 6, 2002 Avg 112 78.9

Beckton Spring Washington 30 38 55.1291 110 1972 49.5 May 26, 1942 85 41 37.1869 108 2002 33.2 June 6, 1972 23.4 October 21, 1987 25.7 October 20, 2000 30.6 October 25, 2001 26.2 June 10, 2002 22.1 May 15, 2003 Avg 109 30.1

Brunson Landing Washington 30 36 33.2239 107 2003 5.9 May 21, 2003 Spring 85 45 30.8900 2.8 June 5, 2003 Avg 107 4.4

Cypress Spring Washington 30 39 31.4862 94 1972 85 May 26, 1942 85 41 03.7401 106 2002 70 June 6, 1972 102 June 28, 1987 79 May 24, 1994 83 October 20, 2000 88 October 25, 2001 104 December 9, 2002 93.3 June 5, 2002 101 May 15, 2003 Avg 100 89.5

Washington Blue Washington 30 30 47.7322 60 1975 36 October 15, 1941 Spring 85 50 49.8677 68 2002 32 May 26, 1942 December 16, (Choctawhatchee) 51 1946 44 June 7, 1972 35.8 September 4, 2002 Avg 64 39.8

Washington Blue Washington 30 27 10.1610 52 1962 12.3 April 10, 1962 September 11, Spring 85 31 49.3276 49 1975 10.8 1962 (Econfina) 55 2002 12.7 January 29, 1963 11.1 May 28, 1963

12.6 August 28, 1963 14.2 May 16, 1972 7 June 13, 2002 Avg 52 11.5

September 11, Williford Spring Washington 30 26 22.3864 62 1972 31.1 1962 85 32 51.2922 65 2002 32.3 January 31, 1963 31.9 May 29, 1963 31.2 August 27, 1963 26.4 May 15, 1972 25.5 June 13, 2002 Avg 63.5 29.7

APPENDIX B

SPRINGS ALKALINITY AND DISCHARGE GROUPED BY COUNTY AND ZONE

A Compilation of Data From Appendix A

Alkalinity Spring County Alkalinity Avg Discharge (mg/L) (mg/L) (ft³/s) Zone 1 Gainer Springs Grp Bay 54.5 160.5 Holmes Blue Spring Holmes 102.0 13.3 Ponce de Leon Holmes 103.5 16.6 Morrison Spring Walton 112.0 78.9 Beckton Spring Washington 109.0 30.1 Brunson Landing Spring Washington 107.0 4.4 Cypress Spring Washington 100.0 89.5 Washington Blue Spring (Choctawhatchee) Washington 64.0 39.8 Washington Blue Spring (Ecofina) Washington 52.0 11.5 Williford Spring Washington 63.5 29.7 86.8 474.3 474.3 Zone 2 Baltzell Spring Jackson 123.5 60.8 Black Spring Jackson 89.5 62.4 Blue Hole Spring Jackson 124.0 28.8 Double Spring Jackson 120.5 37.5 Gadsen Spring Jackson 122.5 15.4 Jackson Blue Spring Jackson 108.3 165.6 Mill Pond Spring Jackson 108.5 28.2 Springboard Spring Jackson 109.5 25.7 113.3 424.4 424.4 Zone 3 Natural Bridge Spring Leon 117.5 113.5 Horn Spring Leon 117.5 21.5 Newport Spring Wakulla 177.0 6.2 Sheppard Spring Wakulla 143.0 5.0 Spring Creek Springs Grp Wakulla 100.8 1153.0 Wakulla Spring Wakulla 140.1 375.0 132.7 1674.2 1674.2 Zone 4 Copper Spring Dixie 201.0 22.2 Guarto Spring Dixie 168.0 10.0 Wacissa Springs Grp Jefferson 141.3 392.7 Allen Mill Pond Spring Lafayette 182.0 12.0 Lafayette Blue Spring Lafayette 185.0 80.2 Mearson Spring Lafayette 158.2 50.9 Owens Spring Lafayette 156.5 70.6

Ruth Spring Lafayette 158.5 13.0 Troy Spring Lafayette 156.5 153.8 Turtle Spring Lafayette 183.0 27.6 Madison Blue Spring Madison 121.3 102.9 Suwanachoochee Spring Madison 156.0 36.6 163.9 972.5 972.5 Zone 5 Hornsby Alachua 146.5 113.4 Poe Alachua 174.5 63.3 Treehouse Alachua 56.0 223.0 Columbia Spring Columbia 54.0 39.5 Ichetucknee Springs Grp Columbia 145.6 191.6 Santa Fe Spring Columbia 107.0 99.0 Devil's Ear Spring Gilchrist 173.5 206.6 Gilchrist Blue Spring Gilchrist 160.5 75.2 Ginnie Springs Gilchrist 159.0 52.0 Hart Spring Gilchrist 180.5 71.7 Otter Spring Gilchrist 184.5 10.0 Rock Bluff Spring Gilchrist 124.5 33.0 Sun Spring Gilchrist 143.0 20.8 Branford Spring Suwannee 174.0 17.0 Ellaville Spring Suwannee 170.5 48.0 Falmouth Spring Suwannee 178.5 183.6 Little River Spring Suwannee 161.5 84.7 Running Springs Suwannee 164.5 29.6 Suwannee Springs Suwannee 146.3 23.2 Telford Springs Suwannee 170.5 38.3 148.8 1623.5 1623.5 Zone 6 Green Cove Spring Clay 82.5 3.4 Beecher Spring Putnam 111.0 10.7 96.8 14.1 14.1 Zone 7 Chassahowitzka Springs Grp Citrus 142.7 137.5 Citrus Blue Spring Citrus 143.0 16.0 Homosassa Springs Grp Citrus 113.0 105.8 Kings Bay Springs Grp Citrus 106.0 975.0 Gator Spring Hernando 115.0 0.4 Little Spring Hernando 140.0 8.4 Magnolia Spring Hernando 110.7 6.9 Salt Spring Hernando 129.5 31.4 Weeki Wachee Spring Hernando 139.3 168.5 Buckhorn Hillsborough 110.7 13.3 Lithia Spring Major Hillsborough 110.3 30.5 Sulphur Spring Hillsborough 140.0 43.7 Fanning Spring Levy 179.0 97.0

Levy Blue Spring Levy 110.0 5.3 Manatee Spring Levy 186.8 178.4 Crystal Springs Pasco 143.0 60.0 Fenney Spring Sumter 121.0 33.9 Gum Springs Main Sumter 119.5 9.9 131.1 1929.4 1929.4 Zone 8 Alexander Spring Lake 94.7 118.2 Apopka Spring Lake 72.5 34.3 Bugg Spring Lake 122.0 10.9 Fern Hammock Springs Marion 44.5 13.9 Juniper Springs Marion 44.0 11.4 Orange Spring Marion 124.5 4.6 Rainbow Springs Grp Marion 95.2 741.5 Salt Springs Marion 67.0 74.8 Silver Glen Springs Marion 69.2 111.8 Silver Springs Grp Marion 166.8 799.0 Rock Springs Orange 90.5 59.6 Wekiwa Spring Orange 114.0 68.5 Sanlando Springs Seminole 122.5 19.8 Starbucks Spring Seminole 113.5 14.5 95.8 2082.8 2082.8

Zone 9 DeLeon Springs Volusia 110.5 27.2 Volusia Blue Spring Volusia 122.7 157.0 116.6 184.2 184.2

Avg/Total 126.5 9379.4

APPENDIX C

BOREHOLE DATA SHOWING DEPTHS TO TOP OF BASEMENT AND/OR BOTTOM OF LIMESTONE

Legend:

Barnett (1975) Jordan et al. (1949) Brown (1978)

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BIOGRAPHICAL SKETCH

Michael Alan Willett was born in Decatur, Alabama, attended elementary and junior high school in Albertville, Alabama and graduated high school from Northwest Georgia High School in Trenton, Georgia. Following graduation he entered the U.S. Army and served with the 1st Ranger Battalion at Ft. Stewart, Georgia. After leaving active duty he served in the National Guard with the 19th SFGA, 20th SFGA and 122nd LRSU while attending school. He received a Bachelor of Science degree in political science/public administration from the University of Tennessee at Chattanooga and a Bachelor of Science degree in geology, with a minor in biology, from Georgia Southwestern University. He completed his Master of Science degree in geological sciences, concentration on coastal geology, from Florida State University under the direction of Dr. Joseph Donoghue. He currently resides in Cairo, Georgia with his wife, Claire.

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