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Electronic Theses, Treatises and Dissertations
The Graduate School
2006
Effect of Dissolution of the Florida
Carbonate Platform on Isostatic Uplift and
Relative Sea-Level Change
Michael Alan Willett
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THE FLORIDA STATE UNIVERSITY
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.
ii
This thesis is dedicated to my wife, Claire.
iii
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.
iv
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
v
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
vi
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
vii
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
viii
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
ix
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.
x
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 midMesozoic (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).
1
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)
2
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.
3
Figure 3. Physiographic regions of Florida showing Trail Ridge, Lake Wales Ridge, and
other paleo-shorelines (Schmidt, 1997).
4
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
5
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)
6
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
7
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
carbonate rocks (CaCO3), thereby removing rock mass (Ca2+) 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:
CaCO3 + H2O + CO2 ---> Ca2+ + 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.
8
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).
9
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).
10
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).
11
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.
12
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.
13
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.
14
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 northcentral 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 ad.
15
Figure 9a. Geologic Map of Florida, showing geologic units statewide (Scott et al.,
2000). Abbreviations for geologic units are described in Fig. 9b.
16
Figure 9b. Geologic Map of the State of Florida, showing geologic units for Figure 9a
(Scott et al., 2000).
17
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)
18
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).
19
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.
20
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).
21
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).
22
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
Hornsby
Poe
Treehouse
Gainer Springs Grp
Chassahowitzka Springs Grp
Citrus Blue
Homosassa Springs Grp
Kings Bay Springs Grp
Green Cove
Columbia Spring
Ichetucknee Springs Grp
Santa Fe Spring
Copper Spring
Guarto Spring
Devil's Ear Spring
Gilchrist Blue
Ginnie Springs
Hart Spring
Otter Spring
Rock Bluff Spring
Sun Spring
Gator Spring
Little Spring
Magnolia Spring
Salt Spring
Weeki Wachee
Buckhorn
Lithia Spring Major
Sulphur Spring
Holmes Blue
Ponce de Leon
Baltzell Spring
Black Spring
Blue Hole Spring
Double Spring
Gadsen Spring
Jackson Blue Spring
Mill Pond Spring
Springboard
County
Latitude
Longitude
Mean
discharge
(ft³/s)
Alachua
Alachua
Alachua
Bay
Citrus
Citrus
Citrus
Citrus
Clay
Columbia
Columbia
Columbia
Dixie
Dixie
Gilchrist
Gilchrist
Gilchrist
Gilchrist
Gilchrist
Gilchrist
Gilchrist
Hernando
Hernando
Hernando
Hernando
Hernando
Hillsborough
Hillsborough
Hillsborough
Holmes
Holmes
Jackson
Jackson
Jackson
Jackson
Jackson
Jackson
Jackson
Jackson
29 51 01.2794
29 49 32.5768
29 51 17.5898
30 25 39.6228
28 2 55.8651
28 58 09.6016
28 47 56.6673
28 52 54.1917
29 59 36.2416
29 51 14.7992
29 59 03.10
29 56 05.2957
29 36 50.4507
29 46 47.2688
29 50 07.2562
29 49 47.6409
29 50 10.8213
29 40 32.6669
29 38 41.2880
29.47 56.7024
29 42 17.0527
28 26 02.7547
28 30 48.4708
28 26 01.9335
28 32 46.7491
28 31 01.8859
27 53 21.8108
27 51 58.6018
28 01 16.0814
30 51 06.0345
30 43 16.3259
30 49 50.1600
30 41 55.4030
30 49 12.5235
30 42 13.6800
30 42 12.0868
30 47 25.8536
30 42 13.3200
30 42 26.6400
82 35 35.5244
82 38 56.3023
82 36 10.3569
85 32 45.8285
82 34 34.3325
82 18 52.3435
82 35 18.6909
82 35 42.1758
81 40 40.4776
82 36 43.0317
82 45 42.73
82 31 49.5135
82 58 25.8905
82 56 23.8495
82 41 47.7618
82 40 58.2654
82 42 00.4370
82 57 06.1608
82 56 33.9097
82 55 07.1057
82 56 00.6980
82 39 05.6134
82 34 51.6997
82 39 08.9563
82 37 08.2751
82 34 23.3983
82 18 09.7969
82 13 53.2939
82 27 05.8857
85 53 09.0475
85 55 50.4658
85 14 03.8400
85 17 40.0758
85 14 41.6227
85 18 11.1600
85 17 18.4226
85 08 24.3181
85 18 27.0000
85 18 23.7600
113.4
63.3
223
160.5
137.5
16
105.8
975
3.4
39.5
191.6
99
22.2
10
206.6
75.2
52
71.7
10
33
20.8
0.36
8.4
6.9
31.4
168.5
13.3
30.5
43.7
13.3
16.6
60.8
62.4
28.8
37.5
15.4
165.6
28.2
25.7
23
Table 2. Continued
Wacissa Springs Grp
Allen Mill Pond
Lafayette Blue
Mearson Spring
Owens Spring
Ruth Spring
Troy Spring
Turtle Spring
Alexander Spring
Apopka Spring
Bugg Spring
Horn Spring
Natural Bridge Spring
Fanning Spring
Levy Blue Spring
Manatee Spring
Madison Blue
Suwanachoochee
Fern Hammock
Juniper Springs
Orange Spring
Rainbow Springs Grp
Salt Springs
Silver Glen
Silver Springs Grp
Rock Springs
Wekiwa Spring
Crystal Springs
Beecher Spring
Warm Mineral
Sanlando Springs
Starbucks Spring
Fenney Spring
Gum Springs Main
Branford Spring
Ellaville Spring
Falmouth Spring
Little River Spring
Running Springs
Suwannee Springs
Telford Springs
DeLeon Springs
Volusia Blue
Newport Spring
Sheppard Spring
Jefferson
Lafayette
Lafayette
Lafayette
Lafayette
Lafayette
Lafayette
Lafayette
Lake
Lake
Lake
Leon
Leon
Levy
Levy
Levy
Madison
Madison
Marion
Marion
Marion
Marion
Marion
Marion
Marion
Orange
Orange
Pasco
Putnam
Sarasota
Seminole
Seminole
Sumter
Sumter
Suwannee
Suwannee
Suwannee
Suwannee
Suwannee
Suwannee
Suwannee
Volusia
Volusia
Wakulla
Wakulla
24
30 20 22.1257
30 09 46.2278
30 07 33.0033
30 02 28.8360
30 02 45.3929
29 59 44.7815
30 00 21.6939
29 50 50.6147
29 04 52.6830
28 33 59.7652
28 45 07.1522
30 19 08.8888
30 17 06.6647
29 35 15.3220
29 27 02.6863
29 29 22.012
30 28 49.5687
30 23 12.0174
29 11 00.8638
29 11 01.3417
29 30 38.3422
29 06 08.9133
29 21 02.3573
29 14 45.0382
29 12 58.3421
28 45 23.2034
28 42 42.7915
28 10 55.9231
29 26 55.1680
27 03 35.6450
28 41 19.3237
28 41 49.2478
28 47 41.9913
28 57 31.3980
29 57 17.5253
30 23 04.0780
30 21 40.187
29 59 48.7105
30 06 16.0708
30 23 40.1198
30 06 25.3782
29 08 03.4081
28 56 50.9415
30 12 45.7014
30 07 31.0799
83 59 30.3968
83 14 35.0558
83 13 34.0802
83 01 30.1013
83 02 28.0692
82 58 36.5027
82 59 51.0091
82 53 25.0299
81 34 33.1809
81 40 50.4077
81 54 05.4622
84 07 43.4472
84 08 49.6413
82 56 07.0956
82 41 56.2789
82 58 36.7387
83 14 39.7076
83 10 18.3592
81 42 29.5013
81 42 44.6809
81 56 38.6596
82 26 14.8792
81 43 58.0520
81 38 36.5011
82 03 09.4724
81 30 06.2450
81 27 37.5151
82 11 06.5308
81 38 48.7060
82 15 35.8339
81 23 43.0666
81 23 28.2154
82 02 17.2106
82 13 53.4932
82 55 42.718
83 10 21.0183
83 08 05.9703
82 57 58.7433
83 06 57.3230
82 56 04.3355
83 09 56.6611
81 21 45.8942
81 20 22.5182
84 10 42.5628
84 17 07.8000
392.7
12
80.2
50.9
70.6
13
153.8
27.6
118.2
34.3
10.9
21.5
113.5
97
5.3
178.4
102.9
36.6
13.9
11.4
4.6
741.5
74.8
111.8
799
59.6
68.5
60
10.7
9.2
19.8
14.5
33.9
9.9
17
48
183.6
84.7
29.6
23.2
38.3
27.2
157
6.2
5
Table 2. Continued
Spring Creek Spring Grp
Wakulla Spring
Morrison Spring
Beckton Spring
Brunson Landing
Cypress Spring
Washington Blue (Choctawhatchee)
Washington Blue Spring (Ecofina)
Williford Spring
Wakulla
Wakulla
Walton
Washington
Washington
Washington
Washington
Washington
Washington
30 04 48.6372
30 14 06.6438
30 39 28.3808
30 38 55.1291
30 36 33.2239
30 39 31.4862
30 30 47.7322
30 27 10.1610
30 26 22.3864
84 19 47.3099
84 18 09.2145
85 54 14.1776
85 41 37.1869
85 45 30.8900
85 41 03.7401
85 50 49.8677
85 31 49.3276
85 32 51.2922
1153
375
78.9
30.1
4.4
89.5
39.8
11.5
29.7
Figure 12. Map location of the 93 sampled springs used for this study (Source: R.
Meegan, Florida Geol. Survey).
25
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.
26
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).
27
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
28
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.
29
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).
30
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 PlioPleistocene 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).
31
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).
32
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.
33
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).
34
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).
35
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 paleoshorelines 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.
36
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
37
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 northcentral 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
38
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.
39
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
40
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
41
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.
42
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
43
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
44
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
45
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 tenminute 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
46
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
47
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.
48
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.
49
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.
50
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
51
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.
52
Representative Boreholes for Zones 1-6
500
0
-500
Elevation (m)
-1000
-1500
-2000
-2500
-3000
-3500
-4000
km
-4500
48
114
198
275
352
39
11
20
20
45
34
Carbonate Bottom
-586
-1181
-1099
-1025
-920
-1028
Top of Basement
-3464
-4273
-3219
-1524
-958
-1036
Surface
W
412
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.
53
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.
54
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
55
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
56
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:
57
(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.
58
Table 3. Summary data for Florida platform dissolution rate due to spring
activity
Zone
Area
(sq. mi.)
Area
Discharge
Discharge
(m²)
(ft³/sec)
Discharge
Alkalinity
Carbonate
dissolution
rate
(mg/L)
(tonne/yr)
(L/sec)
(m³/day)
4-8
1-9
18,969
29,898
4.91E+10
7.74E+10
6,622.3
9,379.4
187,522.7
265,593.9
1.62E+07
2.29E+07
1
3,376
8.74E+09
474.3
13,430.7
2
3,311
8.58E+09
424.4
12,017.7
3
2,809
7.28E+09
1,674.2
4
3,996
1.03E+10
5
3,337
6
2,610
7
8
Carbonate
dissolution
rate
(m³/yr)
133.9
126.5
7.92E+05
1.06E+06
3.60E+05
4.82E+05
1.16E+06
86.8
3.68E+04
1.67E+04
1.04E+06
113.3
4.29E+04
1.95E+04
47,408.1
4.10E+06
132.7
1.98E+05
9.02E+04
972.5
27,538.1
2.38E+06
163.9
1.42E+05
6.47E+04
8.64E+09
1,623.5
45,972.4
3.97E+06
148.8
2.16E+05
9.81E+04
6.76E+09
14.1
399.3
3.45E+04
96.8
1.22E+03
5.54E+02
4,856
1.26E+10
1,929.4
54,634.5
4.72E+06
131.1
2.26E+05
1.03E+05
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
Opdyke et al.
(1984) data:
3.71E+09
184.2
5,216.0
4.51E+05
116.6
1.92E+04
8.72E+03
Zone
1.87E+07
4.60E+10
Surface Equivalent
Thickness of Limestone
Lost
(m/m²)/yr
1.20E+06
Time to Dissolve 1m
of Limestone
Time for 1m
of Isostatic
Uplift
Amount of Uplift
Since PlioPleistocene
(~1.6 Ma)
(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
Opdyke et
al. (1984)
data:
2.35E-06
425,574
464,263
3
2.61E-05
38333
59
41,818
38
Table 4. Calculation B – Isostatic Uplift Results Using One Density Change
Through the Carbonate Section
Zone
T
E
U
ρ0
ρB
ρA
B
(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
al.
2.2
500
2
1.95
10
51
Where:
ρ0 = Original bulk density of unaltered carbonate rock
T = 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
60
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.
61
Table 5. Calculation C – Isostatic Results Using Two Density Changes Through
the Carbonate Section
Zone
T
E
U
ρ0
ρB
ρC
ρA
(meters)
(g/cm³) (g/cm³)
(g/cm³) (g/cm³)
(meters)
B
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
62
Table 6. Summary Results from Tables 4 & 5
1
2
3
4
5
6
7
8
9
Mean
depth to
bottom of
carbonates
(meters)
625
1192
1119
1045
965
1062
945
1004
1509
Opdyke et
al. (1984)
500
Zone
Mean depth
to top of
basement
(meters)
3503
4284
3239
1544
1003
1070
1577
1953
1798
Change in
elevation
for upper
carbonate
layer
(meters)
26
26
26
26
26
26
26
26
26
Change in
elevation
for lower
carbonate
layer
(meters)
21
50
46
42
38
43
37
40
65
Net change
in elevation
using one
density
(Table 4)
(meters)
61
110
104
97
90
99
89
94
137
Net change in
elevation
using two
densities
(Table 5)
(meters)
47
75
72
68
64
69
63
66
91
51
Table 7. Summary Results of Calculations A – C.
Zone
1
2
3
4
5
6
7
8
9
4-8
1-9
Opdyke data
Calculation A: Amount of
uplift since Plio-Pleistocene
(~1.6 ma)
Calculation B: Amount
of uplift with a single
density change
Calculation C: Amount
of uplift with two
density changes
(meters)
(meters)
(meters)
3
3
18
9
17
0
12
11
3
11
9
38
61
110
104
97
90
99
89
94
137
94 (avg)
98 (avg)
51
47
75
72
68
64
69
63
66
91
66 (avg)
68 (avg)
n/a
63
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
64
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.
65
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
66
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.
67
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 paleoshorelines. 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.
68
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
69
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
70
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 paleoshorelines. 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.
71
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)
72
Spring
County
Hornsby
Alachua
Latitude
Longitude
29 51 01.2794
82 35 35.5244
Avg
Poe
130
163
Alachua
29 49 32.5768
82 38 56.3023
170
179
Alachua
29 51 17.5898
82 36 10.3569
56
250
76
86.5
75.1
31.2
84
75.3
39.2
91.7
93.1
50.59
6.1
63.3
Date
April 19, 1972
April 19, 1975
September 16,
2001
February 19, 1917
January 31, 1929
March 14, 1932
December 13,
1941
July 22, 1946
May 2, 1956
October 17, 1972
April 18, 1972
May 26, 1997
May 14, 2002
2001
406
39.9
223
May 26, 1998
October 30, 2001
Bay
30 25 39.6228
85 32 45.8285
49.3
52.3
58.3
58
54.5
1962
1972
2001
2002
162
159
128.2
192.8
160.5
May 15, 1905
January 30, 1963
October 14, 2002
January 5, 2004
Citrus
28 2 55.8651
140
1970
138.5
82 34 34.3325
140
140
130
152
154
142.7
1971
1972
1975
2001
2002
1930-1972
(81
measurements)
October 15, 2001
140
146
1975
2002
Springs Grp
Avg
Citrus Blue
Spring
1972
2001
56
Avg
Chassahowitzka
Discharge
(ft³/s)
14.1
113.4
174.5
Avg
Gainer
Springs Grp
1972
2001
146.5
Avg
Treehouse
Alkalinity
(mg/L)
Date
Citrus
28 58 09.6016
82 18 52.3435
73
53
137.5
11.1
17.7
19.6
15.1
March 15, 1932
March 7, 1961
June 19, 1961
May 25, 1972
Avg
Homosassa
143
Citrus
Springs Grp
Citrus
Green Cove
Spring
Clay
October 16, 2002
106
1931-1974
(90
measurements)
June 23, 1905
28 47 56.6673
110
1956
82 35 18.6909
110
115
115
115
113
1966
1972
2001
2002
105
107
106
2001
2002
79
86
1972
2003
5.4
4.4
4.3
2.7
2.7
3.5
3
1.4
3.4
February 12, 1929
April 18, 1946
November 4, 1950
June 18, 1954
April 25, 1956
October 19, 1960
March 8, 1972
January 8, 2003
Avg
Kings Bay
Springs Grp
Avg
16.3
16
28 52 54.1917
82 35 42.1758
29 59 36.2416
81 40 40.4776
Avg
87
105.8
975
1965-1977
975
82.5
Columbia Spring
Avg
Columbia
29 51 14.7992
82 36 43.0317
54
54
2001
39.5
39.5
November 1, 2001
Ichetucknee
Springs Grp
Columbia
29 59 03.10
82 45 42.73
140
149.3
147.5
145.6
1975
2001
2002
197.2
186
May 17, 1946
October 3, 2001
107
2001
150
48
99
June 1, 1998
November 1, 2001
May 12, 1932
November 18,
1960
November 11,
1975
September 22,
1997
July 16, 2002
Avg
Santa Fe Spring
Columbia
29 56 05.2957
82 31 49.5135
Avg
Copper Spring
191.6
107
Dixie
29 36 50.4507
200
1975
18.8
82 58 25.8905
201
2002
31.9
25.4
Avg
Guarto Spring
20.7
14.2
22.2
201
Dixie
29 46 47.2688
153
74
1973
12.4
May 12, 1932
82 56 23.8495
183
2002
3.41
12
12.8
9.33
10
March 19, 1962
November 2, 1972
July 21, 1997
July 16, 2002
175
172
173.5
2001
2002
206.6
September 5, 2001
Avg
168
Devil's Ear
Spring
Avg
Gilchrist
29 50 07.2562
82 41 47.7618
Gilchrist Blue
Spring
Avg
Gilchrist
29 49 47.6409
82 40 58.2654
148
173
160.5
1975
2002
70.4
80
75.2
Ginnie Springs
Gilchrist
29 50 10.8213
82 42 00.4370
159
2002
45.8
58.2
52
April 28, 1975
November 4, 1997
1972
2002
40
62.1
58.6
58.6
March 14, 1932
May 12, 1932
July 24, 1946
April 27, 1956
November 23,
1960
November 1, 1972
June 26, 1997
Avg
Hart Spring
159
Gilchrist
29 40 32.6669
82 57 06.1608
Avg
Otter Spring
Gilchrist
29 38 41.2880
82 56 33.9097
152
79.4
51.3
71.7
160
209
1972
2002
Gilchrist
29.47 56.7024
82 55 07.1057
120
129
1972
2002
42.1
25
23.8
40.3
39.3
27.6
33
124.5
Gilchrist
5
5.5
16.1
21.2
2.3
10
184.5
Avg
Sun Spring
170
191
180.5
Avg
Rock Bluff
Spring
206.6
29 42 17.0527
120
1972
27.6
82 56 00.6980
166
2002
31.2
75
March 14, 1932
May 12, 1932
November 1, 1972
September 19,
1997
July 16, 2002
December 8, 1942
April 19, 1956
April 28, 1956
November 23,
1960
November 2, 1973
July 17, 1997
November 2, 1972
September 19,
1997
Avg
143
3.5
20.8
July 16, 2002
January 7, 2003
Gator Spring
Avg
Hernando
28 26 02.7547
82 39 05.6134
115
115
2003
0.36
0.36
Little Spring
Hernando
28 30 48.4708
160
1962
7.8
82 34 51.6997
130
130
140
140
1964
1965
2003
14.7
2.7
110
110
1964
1965
11
7.9
112
112
9.1
9.4
10
Avg
Magnolia Spring
Hernando
28 26 01.9335
82 39 08.9563
Avg
Salt Spring
8.4
1
0.2
6.9
110.7
Hernando
28 32 46.7491
82 37 08.2751
130
129
1965
2002
24.7
38.9
28.4
31.9
Avg
Weeki Wachee
Spring
28 31 01.8859
130
1964
82 34 23.3983
130
140
147
149.3
139.26
1969
1974
2001
2002
Avg
Buckhorn
176
161
April 30, 1964
July 24, 1964
September 13,
1964
February 4, 1965
August 5, 1965
December 12,
1972
January 7, 2003
January 18, 1961
December 8, 1965
June 30, 1966
December 14,
1972
December 11,
1975
1988-1989
1917-1974
(364
measurements)
October 18, 2001
168.5
Hillsborough
27 53 21.8108
82 18 09.7969
110
100
122
110.7
1966
1972
2002
10.9
15
14
13.3
June 2, 1966
June 5, 1972
June 14, 1905
Hillsborough
27 51 58.6018
100
1968
30.5
avg given in
Avg
Lithia Spring
31.2
33
31.4
129.5
Hernando
December 15,
1972
December 11,
1975
March 5, 2003
76
Bulletin 66
Major
82 13 53.2939
Avg
Sulphur Spring
Hillsborough
28 01 16.0814
82 27 05.8857
Avg
110
121
110.3
1972
2002
120
130
140
170
140.0
1956
1966
1972
2002
30.5
44
38.9
15 yr mean
1999
43.7
Holmes Blue
Avg
Holmes
30 51 06.0345
85 53 09.0475
102
102
2002
13.3
13.3
December 3, 2002
Ponce de Leon
Spring
Holmes
30 43 16.3259
85 55 50.4658
100
107
1972
2002
20.7
18.1
18.8
8.6
16.6
May 20, 1942
December 9, 1946
April 19, 1972
June 28, 2002
1973
2002
72.8
48.8
60.8
73.2
51.6
62.4
August 16, 1973
March 22, 2002
Avg
103.5
Baltzell Spring
Jackson
30 49 50.1600
85 14 03.8400
Avg
Black Spring
Jackson
30 41 55.4030
85 17 40.0758
Blue Hole
Spring
Avg
Jackson
30 49 12.5235
85 14 41.6227
130
118
124
1973
2002
56.8
0.7
28.8
August 8, 1973
June 28, 2002
Double Spring
Jackson
30 42 13.6800
85 18 11.1600
120
121
120.5
1973
2002
37.5
July 17, 1973
Avg
Gadsen Spring
Spring
1973
2002
July 18, 1973
May 23, 2002
37.5
Jackson
30 42 12.0868
85 17 18.4226
120
125
122.5
1973
2002
18
12.8
15.4
July 18, 1973
May 23, 2002
Jackson
30 47 25.8536
98
1972
134
85 08 24.3181
109
118
2001
2002
56
265
January 24, 1929
December 22,
1934
May 20, 1942
November 15,
1946
January 30, 1947
March 6, 1973
December 17,
Avg
Jackson Blue
120
127
123.5
90
89
89.5
178
178
287
61
77
2001
Avg
Mill Pond Spring
108.3
165.6
Jackson
30 42 13.3200
85 18 27.0000
97
120
108.5
1973
2002
33.2
23.2
28.2
July 18, 1973
May 22, 2002
Springboard
Spring
Avg
Jackson
30 42 26.6400
85 18 23.7600
120
99
109.5
1973
2002
17.4
34
25.7
July 18, 1973
May 22, 2002
Wacissa
Springs Grp
Jefferson
30 20 22.1257
83 59 30.3968
135
147.5
1960
2001
280
605
293
392.7
October 12, 1972
April 17, 1973
October 2, 2001
Avg
Avg
Allen Mill Pond
141.3
Lafayette
Spring
30 09 46.2278
170
1973
21.8
83 14 35.0558
194
2002
11.2
2.9
12
1973
2001
92.8
102
45.9
80.2
1975
2002
50.6
62.1
Avg
Lafayette Blue
Spring
182
Lafayette
30 07 33.0033
83 13 34.0802
170
200
Avg
Mearson Spring
185
Lafayette
30 02 28.8360
83 01 30.1013
Avg
Owens Spring
Lafayette
30 02 45.3929
83 02 28.0692
150
163
156.5
1973
2002
51.2
90
70.6
Lafayette
29 59 44.7815
82 58 36.5027
150
167
158.5
1973
2002
11.5
14.4
13
Lafayette
30 00 21.6939
150
1960
149
82 59 51.0091
150
1973
161
Avg
Troy Spring
68.5
22.5
50.9
158.2
Avg
Ruth Spring
150
167
78
November 26,
1973
September 23,
1997
July 9, 2002
November 23,
1973
June 24, 1998
October 24, 2001
May 14, 1927
December 3, 1975
September 15,
1997
August 14, 2002
September 10,
1973
June 2, 1998
November 14,
1973
June 24, 1997
July 17, 1942
November 26,
1960
163
163
Avg
Turtle Spring
148
205
106
153.8
May 28, 1963
October 16, 1973
October 30, 2001
November 3, 1972
September 22,
1997
July 17, 2002
156.5
Lafayette
29 50 50.6147
150
1972
40.8
82 53 25.0299
216
2002
36.4
5.7
27.6
1972
2001
2002
112
124
162
74.5
131
101
136
Avg
Alexander
Spring
2001
2002
183
Lake
29 04 52.6830
81 34 33.1809
120
82
82
124
124
146
114
109
103
Avg
Apopka Spring
Lake
28 33 59.7652
81 40 50.4077
Avg
Bugg Spring
94.2
118.2
94.7
65
80
1972
2002
24.7
34.3
72.5
Lake
28 45 07.1522
81 54 05.4622
120
120
126
79
28.6
35
1946
1972
2002
17.6
10.3
18.6
12.4
10.8
10.2
8.5
11.4
8.1
8.6
9.1
10.7
February 12, 1931
February 7, 1933
April 13, 1935
October 15, 1935
December 3, 1935
April 2, 1946
April 23, 1956
November 16,
1960
June 8, 1960
April 25, 1967
June 22, 1967
July 2, 1969
April 19, 1972
September 12,
2001
May 4, 1971
Mean 1971-1999
(22
measurements)
Annual mean 2001
1946
1956
1960
1967
1972
1985
1990
1991
1992
1993
1994
1995
Avg
Horn Spring
122
110
125
117.5
1972
2002
28.8
14.2
21.5
Leon
30 17 06.6647
84 08 49.6413
110
125
1972
2002
115
132
97
79
106
151.9
113.5
May 19, 1942
May 14, 1946
December 5, 1960
May 15, 1963
October 6, 1971
April 25, 2002
170
160
1956
1972
109
79.2
193
193
2001
2002
137
64
October 25, 1930
March 14, 1932
December 17,
1942
May 1, 1956
November 18,
1960
March 27, 1963
April 25, 1972
July 31, 1973
October 24, 2001
117.5
Levy
29 35 15.3220
82 56 07.0956
Avg
Levy Blue
111
83.4
98.7
139
51.5
97
179
Levy
Spring
29 27 02.6863
110
2002
8.9
82 41 56.2789
Avg
Manatee Spring
November 12,
1971
February 20, 2002
30 19 08.8888
84 07 43.4472
Avg
Fanning Spring
1996
1997
1998
1999
2000
Leon
Avg
Natural Bridge
Spring
11.7
8.6
11.7
9
8.5
10.9
1.7
5.3
110
Levy
29 29 22.012
180
1956
149
82 58 36.7387
170
198
199
1972
2001
2002
218
137
110
238
145
220
80
Avg for 1917-1974
(56
measurements)
December 17,
2002
March 14, 1932
December 17,
1942
July 24, 1946
April 27, 1956
November 18,
1960
May 28, 1963
April 19, 1972
Avg
Madison Blue
Spring
186.8
Madison
30 28 49.5687
83 14 39.7076
Avg
Suwanachoochee
Spring
30 23 12.0174
83 10 18.3592
Fern Hammock
75
77.8
122
123
2001
2002
141
113
139
71.4
102.9
1973
2002
40.8
18.3
51.6
35.5
36.6
156
Marion
Spring
March 16, 1932
April 24, 1956
November 15,
1960
May 28, 1963
November 6, 1973
October 23, 2001
1960
1973
160
152
Avg
April 25, 1972
July 31, 1973
October 23, 2001
120
120
121.3
Madison
210
203
154
178.4
29 11 00.8638
43
1972
15.5
81 42 29.5013
46
2002
16.8
15.6
17.6
11.6
17.7
12.7
13.6
11
13
10.9
Avg
Juniper Springs
10.6
13.9
44.5
Marion
29 11 01.3417
40
1972
8.9
81 42 44.6809
48
2002
15.7
13.1
12.8
14.1
81
November 6, 1931
March 16, 1932
November 8, 1973
September 24,
1997
December 16,
1935
1936 (5
measurements)
March 11, 1937
April 4, 1946
April 23, 1956
November 15,
1960
April 19, 1972
1985 (4
measurements)
1990 (6
measurements)
1995 (4
measurements)
2000 (5
measurements)
2001 (4
measurements)
April 13, 1935
December 16,
1935
1936 (4
measurements)
March 11, 1937
April 11, 1946
9.7
13.6
10.1
12.2
9.1
12
8.8
Avg
Orange Spring
Marion
29 30 38.3422
81 56 38.6596
120
129
124.5
1972
2003
7.6
1.5
4.6
Marion
29 06 08.9133
82 26 14.8792
53
116.3
116.4
95.2
1974
2001
2002
763
634
67
2002
Avg
Rainbow
Springs Grp
Avg
Salt Springs
8.2
11.4
44
Marion
29 21 02.3573
81 43 58.0520
87.3
81.4
69.6
78.7
79.9
88.2
107
91.9
77.1
88.5
70.2
73.4
74.8
67
82
September 11,
1972
January 8, 2003
1965-1974
October 23, 2001
741.5
92.5
73.3
61.8
Avg
April 23, 1956
November 5, 1960
April 19, 1972
1985 (5
measurements)
1990 (6
measurements)
1995 (4
measurements)
2000 (5
measurements)
2001 (4
measurements)
76.4
74.8
February 9, 1929
September 8, 1930
1931 (5
measurements)
March 3, 1932
February 7, 1933
1935 (3
measurements)
April 4, 1946
April 24, 1956
November 16,
1961
June 8, 1966
April 25, 1967
April 20, 1972
1985 (5
measurements)
1990 (6
measurements)
1995 (4
measurements)
2000 (5
measurements)
2001 (4
measurements)
Silver Glen
Marion
Springs
29 14 45.0382
69
1972
81 38 36.5011
69
2001
69.7
69.2
2002
109
111.8
29 12 58.3421
170
1972
820
82 03 09.4724
162.3
168
166.8
2001
2002
556
28 45 23.2034
86
1971
81 30 06.2450
95
90.5
2002
28 42 42.7915
98
1971
81 27 37.5151
130
114
2002
140
135
154
143
1968
1972
2002
Avg
Silver
Marion
Major
Avg
Rock Springs
Orange
Avg
Wekiwa Spring
Orange
Avg
Crystal Springs
Pasco
28 10 55.9231
82 11 06.5308
Avg
Beecher Spring
Spring
Avg
60
27 03 35.6450
130
1962
9.7
82 15 35.8339
130
131
130.3
1972
2003
28 41 19.3237
100
1972
81 23 43.0666
145
122.5
2002
28 41 49.2478
100
1972
81 23 28.2154
127
113.5
2002
83
Mean 1932-2000
(239
measurements)
Avg 1923-1974
60
Sarasota
Seminole
Mean 1931-2000
(249
measurements)
68.5
12.4
9
10.7
Avg
Starbucks
68.5
1972
2002
Seminole
Avg 1932-1974
November 15,
2001
59.6
92
130
111
Avg
Sanlando
Springs
59.6
29 26 55.1680
81 38 48.7060
Spring
1931-1972
(11
measurements)
September 13,
2001
799
Putnam
Avg
Warm Mineral
112
4.2
9.2
19.8
November 23,
1960
April 20, 1972
Avg 1942-1974
(10
measurements)
March 4, 2003
Mean 1941-2000
(115
measurements)
19.8
14.5
14.5
Mean 1944-2000
(109
measurements)
Fenney Spring
Sumter
28 47 41.9913
82 02 17.2106
110
132
Avg
Gum Springs
Main
Avg
Branford Spring
28 57 31.3980
82 13 53.4932
110
129
119.5
1972
2002
11.1
8.6
9.9
March 15, 1932
1999 avg
Suwannee
29 57 17.5253
82 55 42.718
150
198
1972
2002
12.4
8.9
8.5
May 15, 1927
March 15, 1932
April 26, 1956
November 17,
1960
November 3, 1972
July 21, 1997
July 10, 2002
29.8
29.2
24.5
5.6
17
174
Suwannee
30 23 04.0780
170
1973
41.2
83 10 21.0183
171
2002
27.9
82
40.7
48
1973
2001
167
220
365
59.6
157
170.5
Suwannee
30 21 40.187
83 08 05.9703
170
187
183
159
Avg
Little River
Spring
158
183.6
178.5
Suwannee
29 59 48.7105
160
1973
84.4
82 57 58.7433
163
161.5
2002
84.9
84.7
30 06 16.0708
160
1973
37
Avg
Running Springs
July 26, 1946
April 26, 1956
November 22,
1960
March 16, 1972
Sumter
Avg
Falmouth Spring
21.6
4.7
95.5
13.9
33.9
121
Avg
Ellaville Spring
1972
2002
Suwannee
84
December 9, 1942
November 16,
1960
November 8, 1973
June 2, 1998
1908
1913
February 10, 1933
December 9, 1942
July 22, 1946
November 16,
1960
November 15,
1973
November 13,
2001
November 27,
1973
September 19,
1997
November 27,
1973
83 06 57.3230
Avg
Suwannee
Springs
2002
22.4
29.5
29.6
July 30, 1997
July 9, 2002
23.4
Avg 1906-1973
(52
measurements)
June 24, 1997
164.5
Suwannee
30 23 40.1198
140
1966
82 56 04.3355
150
149
146.3
1973
2002
30 06 25.3782
170
1973
35.1
83 09 56.6611
171
2002
28
48.2
Avg
Telford Springs
169
Suwannee
14.1
23.2
53.5
33.8
Avg
DeLeon Springs
170.5
Volusia
29 08 03.4081
100
1972
81 21 45.8942
121
110.5
2002
28 56 50.9415
105
1960
81 20 22.5182
121
1972
142
122.7
2001
87
157
Avg
Volusia Blue
Volusia
Spring
Avg
Newport Spring
31.2
38.3
27.2
162
30 12 45.7014
84 10 42.5628
170
184
177
1972
2003
8.2
4.2
6.2
Sheppard Spring
Avg
Wakulla
30 07 31.0799
84 17 07.8000
143
143
2002
5
5
Spring Creek
Springs Grp
Wakulla
30 04 48.6372
84 19 47.3099
110
67
125.5
100.8
1972
1973
2001
2000
307
130
146
1972
2001
Avg
Wakulla Spring
Wakulla
30 14 06.6438
84 18 09.2145
85
Mean 1929-2000
(244
measurements)
27.2
Wakulla
Avg
May 14, 1927
December 12,
1941
May 29, 1942
November 17,
1960
November 21,
1973
September 17,
1997
1932-1974 avg
(360
measurements)
November 24,
2001
March 2, 1972
February 20, 2003
November 25,
2002
May 30, 1974
November 1, 1996
1153
390
128.9
1907-1974
September 27,
2001
Avg
Morrison Spring
Walton
144.3
140.1
2002
110
114
1972
2002
121
89
54.9
62.2
67.2
78.9
May 27, 1942
December 9, 1946
November 5, 1963
April 19, 1972
September 6, 2002
1972
2002
49.5
33.2
23.4
25.7
30.6
26.2
22.1
30.1
May 26, 1942
June 6, 1972
October 21, 1987
October 20, 2000
October 25, 2001
June 10, 2002
May 15, 2003
2003
5.9
2.8
4.4
May 21, 2003
June 5, 2003
1972
2002
85
70
102
79
83
88
104
93.3
101
89.5
May 26, 1942
June 6, 1972
June 28, 1987
May 24, 1994
October 20, 2000
October 25, 2001
December 9, 2002
June 5, 2002
May 15, 2003
1975
2002
36
32
October 15, 1941
May 26, 1942
December 16,
1946
June 7, 1972
September 4, 2002
30 39 28.3808
85 54 14.1776
Avg
Beckton Spring
112
Washington
30 38 55.1291
85 41 37.1869
110
108
Avg
109
Brunson Landing
Spring
Avg
Washington
Cypress Spring
Washington
30 36 33.2239
85 45 30.8900
107
107
30 39 31.4862
85 41 03.7401
94
106
Avg
Washington Blue
Spring
375
100
Washington
30 30 47.7322
85 50 49.8677
60
68
(Choctawhatchee)
Avg
Washington Blue
Spring
(Econfina)
51
44
35.8
39.8
64
Washington
30 27 10.1610
52
1962
12.3
85 31 49.3276
49
55
1975
2002
10.8
12.7
11.1
86
April 10, 1962
September 11,
1962
January 29, 1963
May 28, 1963
Avg
Williford Spring
Avg
12.6
14.2
7
11.5
52
Washington
30 26 22.3864
85 32 51.2922
62
65
63.5
87
1972
2002
31.1
32.3
31.9
31.2
26.4
25.5
29.7
August 28, 1963
May 16, 1972
June 13, 2002
September 11,
1962
January 31, 1963
May 29, 1963
August 27, 1963
May 15, 1972
June 13, 2002
APPENDIX B
SPRINGS ALKALINITY AND DISCHARGE
GROUPED BY COUNTY AND ZONE
A Compilation of Data From
Appendix A
88
Spring
Zone 1
Gainer Springs Grp
Holmes Blue Spring
Ponce de Leon
Morrison Spring
Beckton Spring
Brunson Landing Spring
Cypress Spring
Washington Blue Spring
(Choctawhatchee)
Washington Blue Spring (Ecofina)
Williford Spring
Zone 2
Baltzell Spring
Black Spring
Blue Hole Spring
Double Spring
Gadsen Spring
Jackson Blue Spring
Mill Pond Spring
Springboard Spring
Zone 3
Natural Bridge Spring
Horn Spring
Newport Spring
Sheppard Spring
Spring Creek Springs Grp
Wakulla Spring
Zone 4
Copper Spring
Guarto Spring
Wacissa Springs Grp
Allen Mill Pond Spring
Lafayette Blue Spring
Mearson Spring
Owens Spring
County
Alkalinity
(mg/L)
Alkalinity
Avg
(mg/L)
Discharge
(ft³/s)
Bay
Holmes
Holmes
Walton
Washington
Washington
Washington
54.5
102.0
103.5
112.0
109.0
107.0
100.0
160.5
13.3
16.6
78.9
30.1
4.4
89.5
Washington
Washington
Washington
64.0
52.0
63.5
86.8
39.8
11.5
29.7
474.3
474.3
113.3
60.8
62.4
28.8
37.5
15.4
165.6
28.2
25.7
424.4
424.4
132.7
113.5
21.5
6.2
5.0
1153.0
375.0
1674.2
1674.2
Jackson
Jackson
Jackson
Jackson
Jackson
Jackson
Jackson
Jackson
123.5
89.5
124.0
120.5
122.5
108.3
108.5
109.5
Leon
Leon
Wakulla
Wakulla
Wakulla
Wakulla
117.5
117.5
177.0
143.0
100.8
140.1
Dixie
Dixie
Jefferson
Lafayette
Lafayette
Lafayette
Lafayette
201.0
168.0
141.3
182.0
185.0
158.2
156.5
89
22.2
10.0
392.7
12.0
80.2
50.9
70.6
Ruth Spring
Troy Spring
Turtle Spring
Madison Blue Spring
Suwanachoochee Spring
Zone 5
Hornsby
Poe
Treehouse
Columbia Spring
Ichetucknee Springs Grp
Santa Fe Spring
Devil's Ear Spring
Gilchrist Blue Spring
Ginnie Springs
Hart Spring
Otter Spring
Rock Bluff Spring
Sun Spring
Branford Spring
Ellaville Spring
Falmouth Spring
Little River Spring
Running Springs
Suwannee Springs
Telford Springs
Zone 6
Green Cove Spring
Beecher Spring
Zone 7
Chassahowitzka Springs Grp
Citrus Blue Spring
Homosassa Springs Grp
Kings Bay Springs Grp
Gator Spring
Little Spring
Magnolia Spring
Salt Spring
Weeki Wachee Spring
Buckhorn
Lithia Spring Major
Sulphur Spring
Fanning Spring
Lafayette
Lafayette
Lafayette
Madison
Madison
158.5
156.5
183.0
121.3
156.0
Alachua
Alachua
Alachua
Columbia
Columbia
Columbia
Gilchrist
Gilchrist
Gilchrist
Gilchrist
Gilchrist
Gilchrist
Gilchrist
Suwannee
Suwannee
Suwannee
Suwannee
Suwannee
Suwannee
Suwannee
Clay
Putnam
163.9
13.0
153.8
27.6
102.9
36.6
972.5
972.5
148.8
113.4
63.3
223.0
39.5
191.6
99.0
206.6
75.2
52.0
71.7
10.0
33.0
20.8
17.0
48.0
183.6
84.7
29.6
23.2
38.3
1623.5
1623.5
96.8
3.4
10.7
14.1
14.1
146.5
174.5
56.0
54.0
145.6
107.0
173.5
160.5
159.0
180.5
184.5
124.5
143.0
174.0
170.5
178.5
161.5
164.5
146.3
170.5
82.5
111.0
Citrus
Citrus
Citrus
Citrus
Hernando
Hernando
Hernando
Hernando
Hernando
Hillsborough
Hillsborough
Hillsborough
Levy
90
142.7
143.0
113.0
106.0
115.0
140.0
110.7
129.5
139.3
110.7
110.3
140.0
179.0
137.5
16.0
105.8
975.0
0.4
8.4
6.9
31.4
168.5
13.3
30.5
43.7
97.0
Levy Blue Spring
Manatee Spring
Crystal Springs
Fenney Spring
Gum Springs Main
Zone 8
Alexander Spring
Apopka Spring
Bugg Spring
Fern Hammock Springs
Juniper Springs
Orange Spring
Rainbow Springs Grp
Salt Springs
Silver Glen Springs
Silver Springs Grp
Rock Springs
Wekiwa Spring
Sanlando Springs
Starbucks Spring
Zone 9
DeLeon Springs
Volusia Blue Spring
Levy
Levy
Pasco
Sumter
Sumter
110.0
186.8
143.0
121.0
119.5
Lake
Lake
Lake
Marion
Marion
Marion
Marion
Marion
Marion
Marion
Orange
Orange
Seminole
Seminole
131.1
5.3
178.4
60.0
33.9
9.9
1929.4
1929.4
95.8
118.2
34.3
10.9
13.9
11.4
4.6
741.5
74.8
111.8
799.0
59.6
68.5
19.8
14.5
2082.8
2082.8
116.6
27.2
157.0
184.2
184.2
94.7
72.5
122.0
44.5
44.0
124.5
95.2
67.0
69.2
166.8
90.5
114.0
122.5
113.5
Volusia
Volusia
110.5
122.7
Avg/Total
126.5
91
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)
92
93
94
95
96
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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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