Rate of solution of limestone in the karst terrane of Florida

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Rate of solution of limestone in the karst terrane of Florida
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Florida Water Resources Research Center Publication Number 6
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Brooks, H. K.
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Gainesville, Fla.
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Notes

Abstract:
Data are presented and examples cited to explain the rate and pattern of development of the solution features in the karst terrane of Florida. The overall rate of erosion is 1.5 inches per 1,000 years; the rate varies considerably depending upon the quantity and composition of the runoff influx. The early stages of the cycle have developed under artesian conditions with limited entry of surface water. Relatively low primary porosity and permeability have resulted in the circulation and solution being fracture controlled. Subsequent development and channeling of surface runoff into the aquifer results in solution of deep sink holes, extensive caverns and the development of lake basins and prairies. Circulation of the nearly saturated water through the rock from pore to pore away from the solution cavities has resulted in high secondary porosity and permeability. In the open limestone plain under water table conditions solution is concentrated in the upper phreatic zone but not because of shallow lines of flow. With this theoretical model of the development of the porosity, permeability, and cavities in the Floridan aquifer the fracture traces evident on aerial photographs can be used to obtain the quantity and quality of water desired.

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PUBLICATION NO. 6


RATE OF SOLUTION OF LIMESTONE
IN THE
KARST TERRANE OF FLORIDA

by

H. K. Brooks
Associate Professor of Geology
University of Florida


























RATE OF SOLUTION OF LIMESTONE
IN THE
KARST TERRANE OF FLORIDA

by

H. K. Brooks
Associate Professor of Geology
University of Florida


PUBLICATION NO. 6





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RATE OF SOLUTIOMi OF LIlIES'fONiE
1i THE
KARST TEF'PJUIE OF FLORIDA

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PULiLICATIuC, NO. 6

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TABLE OF CONTENTS



Page


ABSTRACT ------------------------------------------------- ii

PROJECT SUMMAR--Y ------------------------------------------- 1

APPINTRODUCATION IN DEVELOPING WATER RE-------------------SOU--------------- 2

AREA OF STUDY ------------------------------------------ 4

CLIMATE ------------------------------------------------- 6

RATE OF SOLUTION ---------------------------------------- 6

GEOMORPHOLOGY -------------------------------------------- 7

PATTERNS OF SOLUTION ------------------------------------ 9

APPLICATION IN DEVELOPING WATER RESOURCES --------------- 13

LITERATURE CITED ----------------------------------------15












Abstract


RATE OF SOLUTION OF LIMESTONE IN THE KARST TERRANE OF FLORIDA


Data are presented and examples cited to explain the rate and J
pattern of development of the solution features in the karst terrane of
Florida. The overall rate of erosion is 1.5 inches per 1,000 years; the
rate varies considerably depending upon the quantity and composition of
the runoff influx, The early stages of the cycle have developed under
artesian conditions with limited entry of surface water. Relatively low
primary porosity and permeability have resulted in the circulation and
solution being fracture controlled. Subsequent development and channeling
of surface runoff into the aquifer results in solution of deep sink holes,
extensive caverns and the development of lake basins and prairies.
Circulation of the nearly saturated water through the rock from pore to
pore away from the solution cavities has resulted in high secondary
porosity and permeability. In the open limestone plain under water table
conditions solution is concentrated in the upper phreatic zone but not
because of shallow lines of flow. With this theoretical model of the
development of the porosity, permeability, and cavities in the Floridan
aquifer the fracture traces evident on aerial photographs can be used to
obtain the quantity and quality of water desired.





I-
Brooks, H. K.
RATE OF SOLUTION OF LIMESTONE IN THE KARST TERRANE OF FLORIDA
Completion Report to Office of Water Resources Research, Department of
the Interior, September 1967, Washington, D.C. 20240
KEYWORDS: aerial photography/ aquifer/ artesian system/ caverns/ cavities/
erosion/ Floridan aquifer/ fracture traces*/ limestone plain/ karst
terrane*/ permeability/ porosity/ water quality and water storage/ stream
erosion*/ runoff/ sinkholes*/ water table.










PROJECT SUMMARY


Research on the rate of solution of limestone in the karst
terrane of Florida was undertaken with the financial support of the Office
of Water Resources Research to obtain quantitative data on the rate that
mineral matter was being dissolved and removed by ground water. The
objective in obtaining this data was to provide basic scientific infor-
mation on the development of the karst landscape and the solution features
in the limestone aquifer system. More data and empirical field observa-
tions have been obtained than can be synthesized and reported herein.

Not only has the original objective been achieved, but evidence
bearing on the origin and evolution of secondary porosity, permeability
and cavity development in the limestone aquifer has been obtained. Much
additional information on the changes of climate and sea level have been
obtained as a result of examination of the sediments in the lakes, springs,
and rivers. This work on the paleo-hydrological conditions is being
completed with the financial support of the Graduate School, University
of Florida, The Florida State Museum and Silver Springs, Incorporated.

The research procedure has involved chemical studies of the
surface and ground water throughout the karst area of northern peninsular
Florida. One complete analysis of rain water was obtained. Hydrological
information on surface and ground water has been synthesized. This study
on the rate of solution was based upon the premise that if the quantity
of water circulating through the rock can be determined and the chemical
composition before and after analyzed, it is possible to calculate the
rate at which rock materials per unit area of land are being removed in
solution. These quantitative results have been supported by extensive
field observations on the stratigraphy, structure, and landscape. The
nature and pattern of the solution features accessible to exploration both
above and below the water table were examined.

The results of the study show that the overall rate of solution
in the karst terrane of Florida is about 1.5 inches per 1,000 years. In
areas of influx of surface streams it was 2.0 inches whereas under open
water table conditions, with complete sub-surface runoff, it was 1.2 inches
per 1,000 years. In the high land area with few sink holes the rate of
solution was determined to be insignificant. This information is signif-
icant in interpreting the pattern and history of development in the karst
terranes as well as the secondary development of porosity, permeability,
and solution cavities in the limestone aquifer. Flow is not concentrated
at the water table as has been proposed. The solution that does occur in
the upper phreatic zone in the limestone plain, where water table conditions
S exist, is not due to the shallow lines of flow, but rather because the run-
off reacts rapidly with the limestone. In the initial and mature stages of



1


.2i


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development of the karst terrane the limestone aquifer was under artesian
conditions. This resulted in channeling and localization of solution in
sinks, and extensive deep caverns, and in the development of lake basins
and prairies.

Several papers will ultimately be submitted for publication
based entirely or in part on data obtained in this research. A paper on
the rate of solution in the karst terrane of Florida is being prepared
which is similar to this completion report, but with tables, graphs, and
maps. Additional papers are now in the process of being prepared on the
marls in the springs and rivers and on the consolidation of the Neogene
clastic sediments.

Publications that have resulted from this project thus far are:

:.!*, H. K., 1966, Geological history of the Suwannee River:
Southeastern Geological Society, Guidebook of the 12th Ann. Field Con-
ference, p. 37-45.

Teleki, P. G., 1966, Differentiation of materials formerly
assigned to the Alachua Formation. Unpublished M.S. thesis. University
of Florida, 102 p.



INTRODUCTION


Limestone terranes are notable because of the large percentage
of runoff transmitted as ground water through the rocks. In large part
this hydrological characteristic of karst areas and the underlying lime-
stone or dolomite aquifer system is the result of solution, both cavity
and interstitial. Only a small proportion of the transmissibility is due
to the primary depositional characteristics of the carbonate rocks, the
porosity and permeability, or the results of tectonic activity. This
study of the rate and pattern of limestone solution in the karst region
of the Suwannee River of Florida was undertaken to provide basic scientific
data on an area of active erosion. Quantitative information has been
hitherto unavailable.

The study of the rate of solution of rock materials in the
Suwannee and Waccasassa River watersheds was based upon the premise that
if the water entering and leaving a unit area were balanced and the
chemical composition before and after determined, then it would be pos-
sible to calculate the rate at which rock materials per unit area of
land was being removed in solution.

Meteorological data and the runoff in different portions of the
watershed are unbalanced because of differences in percentage of surface
and subsurface runoff, but for the total hydrological units, the Suwannee
and the Waccasassa, a water balance exists. From runoff and chemical data

2


At.. .. -










it has been calculated that the rate of solution is one cubic foot of rock
material (largely as CaCO3) per one square foot of land per 8,000 years. In
lake basin, prairie, and sink areas where surface waters are channeled
locally into the aquifer and where the large volume of surface water first
comes in contact with the aquifer, the rate is increased many fold.
Localization of solution has resulted in many peculiarities in the karst
landscape of Florida.

The overall rate of solution resulting in a degradation of the
land is averagely one foot per 8,000 years, or 1.5 inches per 1,000 years.
The average rate of terrestrial erosion by all processes in the United
J States is 2.4 inches per 1,000 years (Judson and Ritter., 1964)1.

Carbonate deposits in general have low syngenetic porosity
and peiea-bi lity. Eoigenetic changes due to compaction, cementation
or recrystallization further reduce the capability of the rock to hold
and transmit fluids. Limestone aquifers of high transmissibility have
developed this characteristic through removal of rock materials by
meteoric water circulating through the rock from pore to pore in strati-
graphically controlled zones or along fractures.

Development of the solution features of a limestone aquifer is
a slow terrestrial process resulting from circulation of runoff through
the rocks. The nature and patterns of solution are determined by the
lithology of the rock, stratigraphic relationships, structural relation-
ships, climate, and the stage in the geomorphic cycle. Florida is unique
* in many of these characteristics, thus it is a mistake to indiscriminately
apply to Florida the concepts developed in the well known karst terranes
of Yugoslavia, Kentucky, Indiana, and Jamaica. The Floridan aquifer in
the area of this study is 500 feet thick or more; it is relatively porous
and fractures from jointing and faulting are not detectable in fresh
exposures. Most significantly, much of the solution occurs under artesian,
not water table, conditions.

In this completion report not all of the aspects of research on
the Suwannee River watershed will be discussed. The lithology, strati-
graphy and structure have been summarized elsewhere (Cooke, 1945; Vernon,
1951; Pirkle, 1956; Brooks, 1966). In a paper on the origin and hydrology
of the lake basins of north central peninsular Florida by Pirkle and
Brooks (1959) the stages of karst development have been summarized.
* Recently : :ks (1966) reviewed the geological history of the Ocala Arch
and discussed the origin and history of the Suwannee River.

Much quantitative information has been collected in the course of
this study that will be published as tables and graphs. At this time only
the essential results of the research on the rates and patterns of solution
will be presented.





See reference list attached.


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AREA OF STUDY


The Suwannee River watershed of north peninsular Florida and
south Georgia (See Figure 1) is an ideal area to study karst development.
Different portions of the watershed are stratigraphically distinct and
are in different stages of development in the fluviatile and karst
geomorphic cycles. The headwaters of all the tributaries originate in
upland areas 120 feet or more above sea level. These highlands, the
Tifton Uplands and high terraces of Georgia and the Central Highlands of
Florida, are directly underlain by sands and clays of Miocene and Pliocene
age. The limestone aquifer occurs at a depth of 80 feet or more. The
Floridan aquifer in the area of study is predominantly Ocala Limestone of
late Eocene age, but in the northern portion of the area the Suwannee
S Limes oe of Oligocene age is present,

The Suwannee River originates in the Okeefenokee Swamp at an
elevation of about 120 feet above sea level. The swamp is in an old
Pliocene strath developed by an ancestral Suwannee River that originally
flowed northeasterly to the Atlantic Ocean off the Ocala Arch (Brooks, 1966).
The main trunk of the river now flows southwesterly in the old strath to
near White Springs, Florida where it descends through a series of rapids
and then turns abruptly to the northwest. Here it flows in an entrenched
meandering valley cut into limestone of Eocene and Oligocene age. This
segment of the river borders the northeastern margin of the Ocala Arch and
appears to be structurally controlled. After receiving the waters of the
Alapaha and Withlacoochee Rivers northeast and north of Ellaville, Florida
the Suwannee turns south and meanders in a broad valley across a limestone
plain developed upon the Ocala Arch. South of Branford, Florida it re-
ceives the waters of the Santa Fe River and then turns to the southwest
and flows to the Gulf of Mexico. Enormous quantities of ground water run-
off are discharged into the Suwannee River through springs along its
course in the limestone terrane. It is this hydrological characteristic
of the river that made this study of the amount of mineral transport in
solution meaningful.

Periodic samples for chemical analysis were taken at the gaging
stations shown in Figure 1. The stations at Pinetta, Statenville, White
Springs and High Springs essentially conform to the boundaries of the water-
shed between the highlands with a high percentage of surface runoff and the
limestone plain where surface runoff, for the most part, is nonexistent.
Surface water leaving the area of study was last monitored at the gaging
station near Wilcox, Florida.

To provide information on the development of the limestone plain
west and southwest of Gainesville, Florida samples were analyzed which were
taken at the gaging station on the Waccasassa River south of Otter Creek
and near Gulf Hammock.

The Suwannee River transports virtually no clastic sediments.
Its cumulative detrital load for the last 10,000 years is a portion of
the small amount of Recent sand and mud at its mouth. All of the sands
in the dunes and islands, from Horseshoe Beach to the Cedar Keys origi-
nated in an earlier cycle of erosion. These islands and dunes are


I 4


























































Figure 1


. .









paleodunes that presently are partially drowned by marine water. They
originated before the post-glacial rise of sea level.



CLIMATE


f For this report the meteorological records of the recording
stations at Lake City, Cross City, and Gainesville were used. The
climate is warm temperate with a mean annual temperature of 690 F. The
rainfall in the area fluctuates about a mean of 51.8 inches per year
(Butson, 1962). The calculated rate of evapo-transpiration is 39.7
inches which c es with the 40 inches reported for Jacksonville.
rTus, the mean annual precipitation available for runoff is essentially
one foo:.



RATE OF SOLUTION


Final calculation of the rate of limestone solution cannot be
made at this time due to the inaccessibility of stream flow data from
the U.S. Geological Survey. Therefore only preliminary results are
summarized herein. Tables, graphs and basic calculations will be in-
: eluded in the paper prepared for publication.

A water balance does exist in the Suwannee River drainage area
as a whole. Gaging stations at the margin of the highlands show a de-
ficiency of water because stream flow is largely surface and perched water
runoff. It is also true that the divides between the surface and sub-
surface areas of drainage do not always completely coincide. However,
when all the segments of the watershed are integrated, there is re-
markable agreement between the amount of water being discharged at Wilcox
and the amount of runoff calculated from meteorological data.

Two hundred and five tons of mineral matter per square mile of
watershed per year is transported in the water of the Suwannee River at
Wilcox. This is equivalent to degradation of the landscape by 1.5 inches
per 1,000 years.

To check the above rate of erosion, calculations were made in a
strip one mile wide directly down the slope of the peizometric surface in
the area of subsurface drainage west of Gainesville. Data used for these
calculations were determined from the analysis of 66 selected wells,
typical surface water, and rain water. These data have been compiled as
maps and tables and will be submitted for publication separately.

In the sinks and prairies south and west of Gainesville, where
surface water runoff from relatively large areas enters the ground, the
rate of solution is 262 tons per square mile per year. At the points of
entry it is probably many times this amount. In the limestone plain

6










where solution is due to direct infiltration of the excess of one foot
of precipitation over evapo-transpiration, the rate of solution is about
172 tons per square mile per year. These rates agree remarkably well
with the overall rate calculated for the Suwannee River. They indicate
that the most active karst development is in the areas of influx of
surface runoff.

In the flatwoods of the Central Highlands very little water in-
filtrates downward to the aquifer. The rate of solution here is insig-
nificant except in the vicinity of the few open collapsed sinkholes which
have developed. The sinks, largely incipient, and ponds that do exist in
the flatlands are the net result of downward percolation and solution.
There is substantial removal of rock materials by solution in the lime-
stone pLbIn duea solely to downward and lateral movement of excess pre-
.cipitation, but here the water movement is not being channeled.

Figure 2 summarizes the physiographic and hydrologic conditions
discussed above.



GEOMORPHOLOGY


In the northwestern portion of peninsular Florida in the area
of this study two physiographic divisions are recognized, the Central
Highlands and a Limestone Plain (Cooke, 1945). The portion of the Central
Highlands discussed herein is a poorly dissected plain that lies between
120 and 180 feet elevation, MSL. There are a few open sinkholes.
Mostly the solution features are incipient sinks in the form of small
circular cypress ponds. The reason for this is that an aquifuge tens
of feet thick, the "Hawthorne Formation", (including both Miocene and
Pliocene sands and clays) overlies the Floridan aquifer. At the western
margin of the highlands there may be a relatively abrupt erosional scarp
but in most places there is a belt four to ten miles wide that is
maturely dissected by sinkholes and collapsed cavern development. The
hills are capped by outliers of the insoluble rock material of the aquifuge
of the high flatlands to the east. The limestone plain is a subdued
. erosional feature with only a few remnant outliers. Its inner portion
has an elevation of between 90 and 100 feet, MSL. In the Suwannee River
valley and the coastal areas the plain generally dips one foot per mile.

The portion of the limestone plain above 90 feet appears to be
a karst peneplain graded to a base level, the sea, during an early Pleisto-
cene interglacial interval of long duration. The level of the plain has
been lowered somewhat through subsequent solution but extensive sink and
cavern development has not occurred in the rejuvenated cycles. Large
lake basins and prairies are developing in the area of the limestone plain
adjacent to the highlands. The present base level of erosion of these
basins appear-s to be the water table (Pirkle and Brook-s, 1959).

A study of aerial photographs reveals that the texture of the


7

















4


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I



I



SFLORIDA KARST
GCAI CSNIIEA TO rANIN sRINoS
-: j ,~~.0, L,N CS.-













;Figure 2















8


MIN .I










iLni i-. .:.minated by sinkholes, lakes and cypress ponds which have a distinct
S Ii-.ci..n. The fabric of the landscape has a distinct northeast-southwest
. .-,..i ..-st-shoutheast trend. Maps of the caverns in peninsular Florida
S !-r. c'.. f-les of the Florida Speological Society in Gainesville also show
r...:.:ers of the caverns to be similarly oriented. This preferential
S .i'z cia : prevails in spite of the fact that the limestone is not the
T i.-'. nse impervious rock typical of fracture controlled karst features.
TI- I *:.an aquifer, for the most part, is only partially lithified. It
S-i! r icively high permeability, and fracture systems cannot be detected
7 _---h rock in quarries except where solution features have developed.
-l: r :a here can be no doubt that a fracture system is controlling the
-r karst development.

The limestone plain has been referred to by-many (Cooke, 1945;
: 5)0; Brodkorb, 1959) as a plain of marine planation. Pirkle
d E'.r:. (1959) have shown that the plain developed as the ultimate
.o -. 3 karst cycle of erosion just as the present water table is
S:r'.ir- -. the base level for the solution in Orange Lake, Payne's Prairie
Si;-,. i .-. Prairie.

Phe limestone terrane on the Ocala Arch has had a long history
..f .c development. This is proven by the many sink holes and cavern
I i.: containing the remains of terrestrial land vertebrates of Late
I :.* ne-Lower Miocene age, Middle Miocene age, Early and Middle Pliocene
:, TJ Pleistocene age (Patton, 1967; Webb, 1967). Pirkle (1956) and
.re r,-.:-rLcly Brooks (1966) have interpreted the stratigraphic and tectonic
..:c* :- the Ocala Arch. There are buried limestone hills in the area
-:.:h ari eastward from Crystal River to Brooksville. The sediment covering
[t[-Li] .irl]ier karst landscape appears to be Upper Miocene in age (Teleki, 1966).
Ir i i'-:.; .ible that some portions of the Arch were covered by a late Pliocene
c --n. of -ea level that rose to 120 to 140 feet higher than present sea level,
_i _, -zt marine deposits to prove this have not been found. The axis of
IhL Acch i.as probably undergoing active karst development during most of
F lio -.e cime, but the erosional plain at 90 to 100 feet elevation is obviously
[.; *-*r 'l -ri ene.

A spring throat filling of marls and freshwater snail shells was
in::*, ,::.ed in the quarrying operations at Haile, north of Newberry. Mixed
-.i*h -1.e 3oring fauna were a few Chione cancellata, a typical Pleistocene
,ari'r .:.n. Evidence from elsewhere (Brooks, 1966 and Conklin, 1966) indi-
-c r:'.-: the 90 foot stand of sea level to which the karst plain is graded
f1 L t ts Laterglacial Pleistocene: Aftonian.



PATTERNS OF SOLUTION


Sinkhole and cavern development in Florida conforms to the
S.- _--stem within-the limes-tone, inci-pient and-inconspicuous as




9










,' these fractures may be. There is more to the pattern of development than
S this. There is the problem of the depth at which active solution occurs
and the influence of geographic variations due to stratigraphic, physio-
graphic and hydrologic conditions. There is also the added complication
of distinguishing the relic karst features from paleohydrological conditions.

The area of this study can be separated into three basic
categories: (1) a limestone plain of nearly complete direct sub-surface
runoff, (2) a highland area in which an aquifuge overlies the limestone
artesian system resulting in considerable surface runoff, and (3) an area
between the two in which a large volume of surface runoff from the highlands
is discharged onto the limestone in sinks, lake basins, and prairies. As
proved in chis research, the rate of erosion in the limestone plain is 172
tons per square mile per year; whereas the rate in the lake-sink area is
ac least 262 tons per square mile per year. In the highland area underlain
by the aquifuge, the amount of rock material removed in solution is rela-
tively insignificant.

Many sinkholes and caverns in Florida extend to considerable
depth. It is common for water well drills to intersect chambers at 300
* or more feet below present sea level. Much evidence has been presented
from work on other limestone terranes (Davis, 1930, Bretz, 1942) confirming
that the most active solution occurs at or near the water table. String-
field and LeGrand (1966) have attributed the deep solution features in
Florida to more active circulation of the ground water during lower
Pleistocene stands of sea level. They conclude that "The rough zonation
of cavities is thought to be related to lower positions of Pleistocene
sea level and to corresponding lower positions of water level in the lime-
stone," and not to stratigraphic control.

Sea-level has been 350 feet or more lower during continental
glacial stages. It is also true that the sinks, springs, and underwater
caverns, i.e., Wakulla, Hornsby and Silver Springs, provide evidence of
being dry to levels of 160 feet or more below the present sea level.
White (1958) believed that changes in sea level would have little or no
effect upon the water table or the piezametric surface. As he reasoned
the lowering would merely extend the land seaward at essentially the same
slope as the present land area. This is true for the shallower portions
of the limestone terrane extending into the Gulf of Mexico. However, there
is no doubt that the lakes, prairies, sinks, and springs of peninsular
Florida were dry during continental glacial stages.

Large quantities of water flow through the Floridan aquifer. In
an artesian system the water may be channeled downward or upward several
hundred feet. Jordan (1950) has argued that this is the cause of the
deeper cavities in the limestone terrane of Florida; however, he neglects
to mention that deep cavities also exist in the limestone plain where water
table conditions prevail.









Ground water from some wells 800 feet or more into the Floridan
aquifer are not completely saturated with calcium carbonate (Back, 1963).
This chemical evidence proves that deep circulation and solution are occurring
at the present time.

Water samples from sixty-six selected wells representative of the
different stratigraphic, geomorphic, and hydrological conditions were ana-
lyzed to provide chemical data relative to the rate and pattern of rock
solution. pH readings were taken on the fresh sample in the field with a
Beckman model N2 meter. This data has been prepared in map form and will
be published.

From the study of the composition and pH of the ground water in
the Floridan aquifer it became apparent that chemical equilibrium was
approached very quickly by reaction with the limestone. For example, in
wells in fracture zones where large amounts of acid surface waters (pH 4.4 -
5.6) were flowing directly into the limestone aquifer, it was rare to find
water that had a pH of less than 7.2 and total dissolved solids of less than
100 ppm. The majority of the well water samples had a pH of 7.6 and 150 to
180 ppm of total dissolved solids, most of which was as CaCO3. In the areas
where the largest amounts of surface water were infiltrating the aquifer, it
was not uncommon to find total dissolved solids from 250 to over 320 ppm.
This super concentration must be due to the increased reactivity of the
organic acids in the surface waters with the limestone.

Shallow wells in the limestone plain typically have 150 to 180 ppm
of total dissolved solids. Even the water being discharged into the Suwannee
River from the aquifer has only 190 to 230 ppm of total dissolved solids
(Ferguson, Lingham, Love, and Vernon, 1947). Much of this spring water must
travel great distances through the limestone; some as much as 40 to 45 miles
S and to depths of 400 feet or more.

Davis (1930), Bretz (1942), and Stringfield and LeGrand (1966)
have concluded that limestone solution is concentrated in the upper portion of
the phreatic zone. Rhodes and Sinacori (1941) have argued that in a homogenous
aquifer, the initial flow occurs at both great and shallow depths but that
solution and increased flow becomes more pronounced in the upper zone be-
S cause of the shorter flow lines. Progressive increase in flow in the upper
phreatic zone is believed to produce master conduits and cause eventual
diminution of flow and solution at depth. This argument appears to be valid
for many karst terranes, but in Florida it is complicated by the fact that
the early solution history is under artesian conditions. It also does not
appear to apply to the open limestone plain where water table conditions exist.
In the large areas being drained by sub-surface runoff, flow of water 300 to
400 feet vertically is of no significance in the many miles the water per-
colated from its point of entry to its point of discharge.

In the Pliocene-Pleistocene-Recent history of karst development
in north peninsular Florida the limestone originally was completely over-
lain by 80 feet or more of sands and clays acting as an aquifuge. In the
early stages of development of the landscape and the-aquifer, sub-surface
runoff was channeled through sink holes that breached the impermeable clays.

11


1110'll Mm"M -*, PlaT.










{ h; orientation of the solution features proves that the initial circulation
;f water through the rock was controlled by a fracture system.

The high permeability of the Ocala limestone and the Floridan
.uifer, in general, can be proved to be largely a secondary feature as the
re-sult f selective solution of the fine-rock matrix, particularly the
y r.-onite. A definite mineralogical distinction has been achieved between
the two CaCO3 minerals calcite and aragonite. Only calcite fossil and
mineral particles have prevailed in rock subjected to circulation of
meteoric water.

Solution of the limestone is largely localized where runoff first
S c.es in contact with the limestone. The amount of solution is largely

runoff from large areas is channeled underground through sinks, lakes, and
prairies the rate of solution may be rapid.

With the aid of SCUBA gear the author has explored every accessible,
sinkhole, spring and underwater cavern in Florida. In the sinkholes the
lateral chambers are joint controlled. They rapidly narrow and close away
from the central chamber. The springs have a similar pattern and appear to
be converted sinkholes that have changed functions due to changing hydro-
logical conditions. The springs are certainly not the result of solution
J by the mineral-charged water they are now discharging. In this respect
Jordan (1950) was wrong, but he was correct in attributing much of the deep
cavity solution to channeling of water in an artesian system.

There are some chambers and cavities in the karst terrane of
Florida that do extend for several miles. For example, the Santa Fe River
northeast of High Springs enters a sinkhole and emerges three miles farther
down the valley through another vertical passage, probably a former sink-
hole. The general area of the Santa Fe River near High Springs is riddled
with extensive underwater caverns. There are vast chambers that have never
been completely explored in the Hornsby Sink-Springs cavern complex that
extend downward over 200 feet.

All of the known extensive underground caverns in Florida have a
relationship to present or former surface drainage systems. South and west
of Gainesville is an extensive fracture zone known to be riddled with caverns
(Brooks, 1966). There are two surface streams that originate from surface
runoff in the high flatlands that discharge into sinkholes in this zone.
They are Prairie Creek (from Hatchet Creek and Newnan's Lake) that discharges
into the Floridan aquifer south of Gainesville in Payne's Prairie at Alachua
Sink, and Hogtown Creek that discharges into the Floridan aquifer west of
Gainesville in Hogtown Prairie and Sink. No doubt the deep sinkholes
and extensive cavern systems that have developed are the result of such
channeled and localized flow of large volumes of acid surface water into
the aquifer system. From Gainesville it is over twenty miles to the point
of nearest discharge from the aquifer. There is no evidence of an integrated
system of -solution caverns. Thus-it is -concluded that as the ground water-
approaches saturation it leaves the cavities that have been dissolved and
flows through the integranular pores in the limestone.

12









Solution may take place just below the water table as Davis (1930)
and Bretz (1942) have postulated. Observations in caverns and deep quarries
in the limestone plain of northwestern peninsular Florida show a pattern of
chambers, both incipient and developed, in relationship to the present and
past stands of the water table.

Solution is occurring in the limestone plain away from the points
of entry of surface streams into the sinkholes, lakes, and prairies. West
of Gainesville and throughout much of the limestone plain of the Suwannee
River watershed all of the runoff is as ground water. This water that is
infiltrating directly into the ground is dissolving limestone to the amount
of 170 to 220 ppm of total dissolved solids as it flows through the rock,
resulting in an erosional rate of 172 tons of rock material per square mile
-er year. No doubt the runoff water obtains its mineral load very quickly.
i: may be this instead of the subsequent lines of flow that determines the
development of solution features in the upper phreatic zone under water
table conditions.



APPLICATION IN DEVELOPING WATER FL.n7URCES


It has often been assumed that the high yield characteristics
of the Floridan limestone aquifer were due to a high primary porosity and
permeability (Palmer, 1965). In the area of outcrop the rocks do, for the
most part, have a high porosity and permeability, especially the Ocala
Limestone. Porosity ranges from 20 to 55 per cent and permeability from
0.02 to 1.55 darcies on representative specimens. Most wells produce
directly from the rock and not from joint controlled cavities so typical
of other limestone terranes (Lattman and Parizek, 1962).

In the early history of circulation in the area of recharge, solu-
tion is controlled by fracture systems. This can be due only to a relatively
Z low original transmissibility of the carbonate rock. As the landscape and
underlying hydrological system has evolved, circulation of meteoric water
directly through the rock from pore to pore away from the fracture zones
has resulted in a high secondary porosity and permeability. It is now
recognized that in areas of artesian conditions and incipient karst develop-
ment in Florida, higher yield wells and well fields can be developed only in
fracture zones. In the areas of more mature karst landscape with extensive
cavern development these zones should be avoided because of the poorer
quality of water due to color and pollution (from the surface water) and
higher mineral content, especially calcium and iron. In these areas and in
the open karst plain under water table conditions the aquifer system has
developed a high secondary porosity and permeability and copious yield can
be obtained directly from the rock.

Lattman and Parizek (1962) have called attention to the relation-
ship between fracture traces and the occurrence of ground water in carbonate
rocks. These traces can readily be detected on aeriarIphotographs. It is

13









recommended that more use be made of this valuable tool to obtain the quality
and quantity of ground water desired in developing the water resources of the
Floridan aquifer.



























































i14
-0 :









LITERATURE CITED


Back, William, 1963, Premiminary results of a study of calcium carbonate
saturation of ground water in central Florida: Bull. Intern. Assoc.
Sci. Hydrology, v. 8, p. 43-51.

Bretz, J. H., 1942, Vadose and phreatic features of limestone caverns:
Jour. Geology, v. 50, p. 675-811.

Brooks, H. K., 1966, Geological history of the Suwannee River: South-
eastern Geological Soc., guidebook 13th Ann. Field Conference, p. 37-45.

Brodkorb, W. P., 1957, The Pleistocene avifauna of Arredondo, Florida: Fla.
State Museum-, Biol. Sci. Bull., v. 4, p- 269-291.

Butson, Keith, 1962, Climates of the states, Florida: U.S. Dept. of
Commerce, Weather Bureau, Climatography of the United States No. 60-8.

Conklin, C. V., 1967, The foraminifera fauna in the Plio-Pleistocene strata
of south Florida: Graduate School, Univ. of Fla. Thesis for M.S. degree,
84 p.

Cooke, C. W., 1945, Geology of Florida: Bull. Florida Geological Survey,
v. 29, 339 p.

Davis, W. M., 1930, Origin of limestone caverns: Geol. Soc. American, Bull.,
v. 41, p. 457-628.

Ferguson, G. E., C. W. Lingham, S. K. Love and R. 0. Vernon, 1947, Springs
of Florida: Bull. Florida Geol. Survey, v. 31, 96 p.

Jordan, R. H., 1950, An interpretation of Floridan karst: Jour. Geology,
v. 58, p. 261-268.

Judson, Sheldon and D. F. Ritter, 1964, Rates of regional denudation in the
United States: Jour. Geophysical Research, v. 69, p. 3395-3401.

Lattman, L. H. and R. R. Parizek, 1962, Relationship between fracture traces
and the occurrence of ground water in carbonate rocks: Jour. Hydrology,
v. 2, p. 73-91.

MacNeil, F. S., 1949, Pleistocene shore lines in Florida and Georgia: U. S.
Geol. Survey, Prof. Paper 221-F, p. 95-106.

Palmer, A. N., 1965, The occurrence of ground water in limestone: Compass,
v. 42, p. 246-255.

Patton, T. H., 1967, Oligocene and Miocene vertebrates from central Florida:
Southeastern Geol. Soc., 13th Field Trip, p. 3-9.


15


*^^"'^^i^'as^^ Tli^^^ !"T'!1! ;; I ^^^^^^^^^










Pirkle, E. C., 1956, The Hawthorne and Alachua formations of Alachua County,
Florida: Florida Acad. Sci., Quart. Jour., v. 19, p. 197-240.

Pirkle, E. C., and H. K. Brooks, 1959, Origin and hydrology of Orange Lake,
Santa Fe Lake, and Levys Prairie Lakes of North-Central peninsular
Florida: Jour. Geology, v. 67, p. 302-316.

Rhodes, Roger and M. N. Sinacori, 1941, Pattern of ground-water flow and
solution: Jour. Geology, v. 49, p. 785-794.

Stringfield, V. T. and H. E. LeGrand, 1966, Hydrology of limestone terranes
in the Coastal Plain of the Southeastern United States: Geological
Soc, America, Sp. P. 93, 46 p.

aiaeki, ? G.P 1966, Differentiation of materials formerly assigned to the
Alachua Formation: Graduate School, Univ. of Fla., Thesis for M. S.
degree, 102 p.

Vernon, R. 0., 1951, Geology of Citrus and Levy Counties, Florida: Bull.
Florida Geol. Survey, v. 33, 256 p.

Webb, S. D., 1967, Pliocene terrestrial deposits of peninsular Florida:
Southeastern Geol. Soc., guide book, 13th Field Trip, p. 11-15.

White, W. A., 1958, Some geomorphic features of central peninsular Florida:
Bull. Florida Geol. Survey, v. 41, 92 p.




























16
6 1




Full Text

PAGE 1

PUBLICATION NO. 6 RATE OF SOLUTION OF LIMESTONE IN THE KARST TERRANE OF FLORIDA by H. K. Brooks Associate Professor of Geology University of Florida

PAGE 2

RATE OF SOLUTION OF LIMESTONE IN THE KARST TERRANE OF FLORIDA by H. K. Brooks Associate Professor of Geology of Florida PUBLICATION NO. 6

PAGE 3

RATE OF SOLUTION OF LIMESTONE IN THE KARST TERRANE OF FLORIDA by H. K. Brooks Associate Professor of Geology University of Florida PUBLICATION NO. 6

PAGE 4

I TABLE OF CONTENTS Page ABSTRACT ii PROJECT SUMMARY -----------------------------------------1 INTRODUCTION AREA OF STUDY 2 4 CLIMATE 6 RATE OF SOLUTION --------------------____________________ 6 GEOMORPHOLOGY ____________________________________________ 7 PATTERNS OF SOLUTION ------------------------------------9 APPLICATION IN DEVELOPING WATER RESOURCES _____ 13 LITERATURE CITED ____ ------------------------------------15 i

PAGE 5

Abstract RATE OF SOLUTION OF LIMESTONE IN THE.KARST TERRANE OF FLORIDA Data are presented and examples cited to explain the rate and pattern of development of the solution features in the karst terrane of Florida. The overall rate of erosion is 1.5 inches per 1,000 years; the rate varies considerably depending upon the quantity and composition of the runoff influx, The early stages of the cycle have deveJ..oped under artesian conditions I"ith limited entry of surface water. Relatively low primary porosity and permeability have resulted in the circulation and solution being fracture controlled. Subsequent development and channeling of surface runoff into the aquifer results in solution of deep sink holes, extensive caverns and the development of lake basins and prairies. Circulation of the nearly saturated water through the rock from pore to pore away from the solution cavities has resulted in high secondary porosity and permeability. In the open limestone plain under water table conditions solution is concentrated in the upper phreatic zone but not because of shallow lines of flow. With this theoretical model of the development of the porosity, permeability, and cavities in the Floridan aquifer the fracture traces evident on aerial photographs can be used to obtain the quantity and quality of water desired. Brooks, H. K. RATE OF SOLUTION OF LIMESTONE IN THE KARST TERRANE OF FLORIDA Completion Report to Office of Water Resources Research, Department of the Interior, September 1967, Washington, D.C. 20240 KEYWORDS: aerial photography/ aquifer/ artesian system/ caverns/ cavities/ erosionl Floridan aquifer/ fracture traces*/ limestone p1ain/ karst terrane*/ permeability/ porosity/ water quality and water storage/. stream erosion*/ runoff/ sinkho1es*/ water table. ii

PAGE 6

I i i I PROJECT SUMMARY Research on the rate of solution of limestone in the karst terrane of Florida was undertaken with the financial support of the Office of Water Resources Research to obtain quantitative data on the rate that mineral matter was being dissolved and removed by ground water. The objective in obtaining this data was to provide basic scientific information on the development of the karst landscape and the solution features in the limestone aquifer system. More data and empirical field observations have been obtained than can be synthesized and reported herein. No t oD.ly has the original obj ective been achieved, but evidence bearing on 1::[le origin and evolution of secondary porosity) permeability and cavity development in the limestone aquifer has been obtained. Much additional information on the changes of climate and sea level have been obtained as a result of examination of the sediments in the lakes, springs, and rivers. This work on the paleo-hydrological conditions is being completed "lith the financial support of the Graduate School, University of Florida, The Florida State Museum and Silver Springs, Incorporated. The research procedure has involved chemical studies of the surface and ground water throughout the karst area of northern peninsular Florida. One complete analysis of rain water was obtained. Hydrological information on surface and ground water has been synthesized. This study on the rate of solution was based upon the premise that if the quantity of water circulating through the rock can be determined and the chemical composition before and after analyzed, it is possible to calculate the rate at \vhich rock materials per unit area of land are being removed in solution. These quantitative results have been supported by extensive field observations on the stratigraphy, structure, and landscape. The nature and pattern of the solution features accessible to exploration both above and below the water table were examined. The results of the study show that the overall rate of solution in the karst terrane of Florida is about 1.5 inches per 1,000 years. In areas of influx of surface streams it was 2.0 inches whereas under open 'i.;rater table conditions, with complete sub-surface runoff, it was 1.2 inches per 1,000 years, In the high land area with few sink holes the rate of solution was determined to be insignificant. This information is significant in interpreting the pattern and history of development in the karst terranes as well as the secondary development of porosity, permeability, and solution cavities in the limestone aquifer. Flow is not concentrated at the water table as has been proposed. The solution that does occur in the upper phreatic zone in the limestone plain, where water table conditions exist, is not due to the shallow lines of flow, but rather because the runoff reacts rapidly with the limestone. In the initial and mature stages of 1

PAGE 7

development of the karst terrane the limestone aquifer was under artesian conditions. This resulted in channeling and localization of solution in sinks, and extensive deep caverns, and in the development: of lake basins and prairies. Several papers will ultimately be submitted for publication based entirely or in part on data obtained in this research. A paper on the rate of solution in the karst terrane of Florida is being prepared which is similar to this completion report, but with tables, graphs, and maps. Additional papers are now in the process of being prepared on the marls in the springs and rivers and on the consolidation of the Neogene clastic sediments. Publications that have resulted from th:is project thus far are: Brooks, H. K., 1966, Geological history of the Suwannee River: Southeastern Geological Society, Guidebook of the 12th Ann. Field Conference, p. 37-45. Teleki, P. G., 1966, Differentiation. of materials formerly assigned to the Alachua Formation. Unpublished M.S. thesis. University of Florida, 102 p. INTRODUCTION Limestone terranes are notable because of the large percentage of runoff transmitted as ground water through the rocks. In large part this hydrological characteristic of karst areas and the underlying limestone or dolomite aquifer system is the result of solution, both cavity and interstitiaL Only a small proportion of the transmissibility is due to the primary depositional characteristics of the carbonate rocks, the porosity and permeability, or the results of tectonic activity. This study of the rate and pattern of limestone solution in the karst region of the Suwannee River of Florida was undertaken to provide basic scientific data on an area of active erosion. Quantitative information has been hitherto unavailable. The study of the rate of solution of rock materials in the Smvannee and Waccasassa River watersheds was based upon the premise that if the water entering and leaving a unit area were balanced and the chemical composition before and after determined, then it would be possible to calculate the rate at which rock materials per unit area of land was being removed in solution. Meteorological data and the runoff in different portions of the watershed are unbalanced because of differences in percentage of surface and subsurface runoff, but for the total hydrological units, the Suwannee and the Waccasassa, a water balance exists. From runoff and chemical data 2 ________________________ IBI

PAGE 8

it has been calculated that the rate of solution is one cubic foot of rock material (largely as CaC0 3 ) per one square foot of land per 8,000 years. In lake basin, prairie, and sink areas where surface waters are channeled locally into the aquifer and where the large volume of surface water first comes in contact with the aquifer, the rate is increased many fold. Localization of solution has resulted in many peculiarities in the karst landscape of Florida. The overall rate of solution resulting in a degradation of the land is averagely one foot per 8,000 years, or 1.5 inches per 1,000 years. Th:e average rate of terrestriq.l erosion by all processes in the United States is 2.4 inches per 1,000 years (Judson and Ritter., 1964)1. Carbonate deposits in general have low syngenetic porosity and perrnedbility. Epigenetic changes due to compaction, cementation or recrystallization further reduce the capability of the rock to hold and transmit fluids. Limestone aquifers of high transmissibility have developed this characteristic through removal of rock materials by meteoric water circulating through the rock from pore to pore in stratigraphically controlled zones or along fractures. Development of the solution features of a limestone aquifer is a slow terrestrial process resulting from circulation of runoff through the rocks. The nature and patterns of solution are determined by the lithology of the rock, stratigraphic relationships, structural relationships, climate, and the stage in the geomorphic cycle. Florida is unique in many of these characteristics, thus it is a mistake to indiscriminately apply to Florida the concepts developed in the well known karst terranes of Yugoslavia, Kentucky, Indiana, and Jamaica. The Floridan aquifer in the area of this study is 500 feet thick or more; it is relatively porous and fractures from jointing and faulting are not detectable in fresh exposures. Most significantly, much of the solution occurs under arteSian, not water table, conditions. In this completion report not all of the aspects of research on the Suwannee River watershed will be discussed. The lithology, stratigraphy and structure have been summarized elsewhere (Cooke, 1945; Vernon, 1951; Pirkle, 1956; Brooks, 1966). In a paper on the origin and hydrology of the lake basins of north central peninsular Florida by Pirkle and Brooks (1959) the stages of karst development have been summarized. Recently Brooks (1966) reviewed the geological history of the Ocala Arch and discussed the origin and history of the Suwannee River. Much quantitative information has been collected in the course of this study that will be published as tables and graphs. At this time only the essential results of the research on the rates and patterns of solution will be presented. lSee reference list attached. 3

PAGE 9

I AREA OF STUDY The Suwannee River watershed of north peninsular Florida and south Georgia (See Figure 1) is an ideal area to study karst development. Different portions of the watershed are stratigraphically distinct and are in different stages of development in the fluviatile and karst geomorphic cycles. The headwaters of all the tributaries originate in upland areas 120 feet or more above sea level. These highlands, the Tifton Uplands and high terraces of Georgia and the Central Highlands of Florida, are directly underlain by sands and clays of Miocene and Pliocene age. The limestone aquifer occurs at a depth of 80 feet. or more. The Floridan aquifer in the area of study is predominantly Ocala Limestone of lete Eocene age, but in the northern portion the area the Suwannee Limestone of Oligocene age is present The Suwannee River originates in the Okeefenokee Swamp at an elevation of about 120 feet above sea level. The swamp is in an old Pliocene strath developed by an ancestral Suwannee River that originally flowed northeasterly to the Atlantic Ocean off the Ocala Arch (Brooks, 1966). The main trunk of the river now flows southwesterly in the old strath to near White Springs, Florida where it descends through a series of rapids and then turns abruptly to the northwest. Here it flows in an entrenched meandering valley cut into limestone of Eocene and Oligocene age. This segment of the river borders the northeastern margin of the Ocala Arch and appears to be structurally controlled. After receiving the waters of the Alapaha and Withlacoochee Rivers northeast and north of Ellaville, Florida the Suwannee turns south and meanders in a broad valley across a limestone plain developed upon the Ocala Arch. South of Branford, Florida it receives the waters of the Santa Fe River and then turns to the southwest and flows to the Gulf of Mexico. Enormous quantities of ground water runoff are discharged into the Suwannee River through springs along its course in the limestone terrane. It is this hydrological characteristic of the river that made this study of the amount of mineral transport in solution meaningful. Periodic samples for chemical analysis were taken at the gaging stations shown in Figure 1. The stations at Pinetta, Statenville, White Springs and High Springs essentially conform to the boundaries of the watershed between the highlands with a high percentage of surface runoff and the limestone plain where surface runoff, for the most part, is nonexistant. Surface water leaving the area of study was last monitored at the gaging station near Wilcox, Florida. To provide information on the development of the limestone plain west and southwest of Gainesville, Florida samples were analyzed which were taken at the gaging station on the Waccasassa River south of Otter Creek and near Gulf Hammock. The Suwannee River transports virtually no clastic sediments. Its cummulative detrital load for the last 10,000 years is a portion of the small amount of Recent sand and mud at its mouth. All of the sands in the dunes and islands, from Horseshoe Beach to the Cedar Keys originated in an earlier cycle of erosion. These islands and dunes are 4

PAGE 10

o ....... Figure 1 5 Waccasassa River Watersheds Conlou, tint. repr.sent the pielOometrJe lurtoe. of the qrQvndwat.r in feet above SICIIVa-1 sampling stations eiti" acal. In mU ..

PAGE 11

paleodunes that presently are partially drowned by marine water. They originated before the post-glacial rise of sea level. e:r..IMATE For this report the records of the recording stations at Lake City, Cross City, and Gainesville were used. The climate is warm temperate with a mean annual temperature of 690 F. The rainfall in the area fluctuates about a mean of inches per year (Butson, 1962), The calculated rate of evapo-transpiration is 39.7 inches which compares with the 40 inches reported for Jacksonville. To.us, the mean annual precipitation available for runoff is essentially one foot. RATE OF SOLUTION Final calculation of the rate of limestone solution cannot be made at this time due to the inaccessibility of stream flow data from the U.S. Geological Survey. Therefore only preliminary results are summarized herein. Tables, graphs and basic calculations will be included in the paper prepared for publication. A water balance does exist in the Suwannee River drainage area as a whole. Gaging stations at the margin of the highlands show a deficiency of water because stream flow is largely surface and perched water runoff. It is also true that the divides between the surface and subsurface areas of drainage do not always completely coincide. However, when all the segments of the watershed are integrated, there is remarkable agreement between the amount of water being discharged at Wilcox and the amount of runoff calculated from meteorological data. Two hundred and five tons of mineral matter per square mile of watershed per year is transported in the water of the Suwannee River at Wilcox. This is equivalent to degradation of the landscape by.5 inches per 1,000 years. To check the above rate of erosion, calculations were made in a strip one mile wide directly down the slope of the peizometric surface in the area of subsurface drainage west of Gainesville. Data used for these calculations were determined from the analysis of 66 selected wells, typical surface water, and rain water. These data have been compiled as maps and tables and will be submitted for publication separately. In the sinks and prairies south and west of Gainesville, where sur f acewater-X:uno:H--rrom-reraE:fveTy-Tar-ge--areas enters-fn-e:-gr6und-;Efie rate of solution is 262 tons per square mile per year. At the points of entry it is probably many times this amount. In the limestone plain 6

PAGE 12

where solution is due to direct infiltration of the excess of one foot of precipit:ation over evapo-transpiration, the rate of solution is about 172 tons per square mile per year. These rates agree remarkably well "ith the overall rate calculated for the Suwannee River. They indicate that the most active karst development is in the areas of influx of surface runoff. In the flatwoods of the Central Highlands very little water infiltrates downward to the aquifer. The rate of solution here is insignificant except in the vicinity of the few open collapsed sinkholes which have developed. The sinks, largely incipient, and ponds that do exist in the flatlands are the net result of downward percolation and solution. 'luere is substantial removal of rock materials by solution in the lime stone pldl.n soleLy to c1m'7nward and lateral movement of excess pre cipitation, but here the water movement is not being channeled. Figure 2 summarizes the physiographic and hydrologic conditions discussed above. GEOMORPHOLOGY In the northwestern portion of peninsular Florida in the area of this study two physiographic divisions are recognized, the Central Highlands and a Limestone Plain (Cooke, 1945). The portion of the Central Highlands discussed herein is a poorly dissected plain that lies between 120 and 180 feet elevation, MSL. There are a few open sinkholes. l>lostly the solution features are incipient sinks in the form of small circular cypress ponds. The reason for this is that an aquifuge tens of feet thick, the "Hawthorne Formation", (including both Miocene and Pliocene sands and clays) overlies the Floridan aquifer. At the western margin of the highlands there may be a relatively abrupt erosional scarp but in most places there is a belt four to ten miles wide that is maturely dissected by sinkholes and collapsed cavern development. The hills are capped by outliers of the insoluble rock material of the aquifuge of the high flatlands to the east. The limestone plain is a subdued erosional feature with only a few remnant outliers. Its inner portion has an elevation of between 90 and 100 feet, MSL. In the Suwannee River valley and the coastal areas the plain generally dips one foot per mile. The portion of the limestone plain above 90 feet appears to be a karst peneplain graded to a base level, the sea, during an early Pleistocene interglacial interval of long duration. The level of the plain has been lowered somewhat through subsequent solution but extensive sink and cavern development has not occurred in the rejuvenated cycles. Large lake basins and prairies are developing in the area of the limestone plain adjacent to the highlands. The present base level of erosion of these be the water table-{P-irkle andBrooks, 195-9). A study of aerial photographs reveals that the texture of the 7

PAGE 13

flORIDA KARST GAINESVILLE TO __ U.ll.l J 11.0" ll)l;['5 fAHhlN S'RIHGS Figure 2

PAGE 14

land is dominated by sinkholes, lakes and cypress ponds which have a distinct lineation. The fabric of the landscape has a distinct northeast-southwest and northwest-shoutheast trend. Maps of the caverns in peninsular Florida in the files of the Florida Speological Society in Gainesville also show the chambers of the caverns to be similarly oriented. This preferential orientation prevails in spite of the fact that the limestone is not the tVDical dense impervious rock typical of fracture controlled karst features. Floridan aquifer, for the most part, is only partially lithified. It has a relatively high permeability, and fracture systems cannot be detected in the fresh rock in quarries except where solution features have developed. However, there can be no doubt that a fracture system is controlling the pattern of karst development. 'rhe limestone plain has been referred to by many (Cooke, 1945; l'!adieil, 1950; Brodkorb, 1959) as a plain of marine planation. Pirkle and Brooks, (1959) have shown that the plain developed as the ultimate stage in a karst cycle of erosion just as the present water table is serving as the base level for the solution in Orange Lake, Payne's Prairie and Hogtown Prairie. The limestone terrane on the Ocala Arch has had a long history of karst development. This is proven by the many sink holes and cavern fillings containing the remains of terrestrial land vertebrates of Late Oligocene-Lower Miocene age, Middle Miocene age, Early and Middle Pliocene age, and Pleistocene age (Patton, 1967; Webb, 1967). Pirkle (1956) and more recently Brooks (1966) have interpreted the stratigraphic and tectonic history of the Ocala Arch. There are buried limestone hills in the area south and eastward from Crystal River to Brooksville. The sediment covering this earlier karst landscape appears to be Upper Miocene in age (Teleki, 1966). It is possible that some portions of the Arch were covered by a late Pliocene stand of sea level that rose to 120 to 140 feet higher than present sea level, but as yet marine deposits to prove this have not been found. The axis of the Arch was probably undergoing active karst development during most of Pliocene time, but the erosional plain at 90 to 100 feet elevation is obviously post-Pliocene. A spring throat filling of marls and freshwater snail shells was encountered in the quarrying operations at Haile, north of Newberry. Mixed ,
PAGE 15

these fractures may be. There is more to the pattern of development than this. There is the problem of the depth at which active solution occurs and the influence of geographic variations due to stratigraphic, physiographic and conditions. There is also the added complication of distinguishing the relic karst features from pa1eohydro1ogica1 conditions. The area of this study can be separated into three basic categories: (1) a limest.one plain of nearly complete direct sub-surface runoff, (2) a highland area in which an aquifuge overlies the limestone artesian system resulting in considerable surface.runoff, and (3) an area between the two in which a large volume of surface runoff from the highlands is disch2rged onto the limestone in sinks, lake basins, and prairies. As proved ie, this research, the rate of erosion in the limestone plain is 172 tons }J,:::r .>cluare mile per year; whereas the rate in the lake-sink area is at least '262 tons per square mile per year. In the highland area underlain by the aquifuge, the amount of rock material removed in solution is relatively insignificant. Many sinkholes and caverns in Florida extend to considerable depth. It is COlILTUon for ';vater well drills to intersect chambers at 300 or more feet below present sea level. Much evidence has been presented from work on other limestone terranes (Davis, 1930, Bretz, 1942) confirming that the most active solution occurs at or near the water table. String field and LeGrand (1966) have attributed the deep solution features in Florida to more active circulation of the ground water during lower Pleistocene stands of sea level. They conclude that "The rough zonation of cavities is thought to be related to lower positions of Pleistocene sea level and to corresponding lower positions of water level in the limestone," and not to stratigraphic control. Sea-level has been 350 feet or more lower during continental glacial stages. It is also true that the sinks, springs, and underwater caverns, i.e., Wakulla, Hornsby and Silver Springs, provide evidence of being dry to levels of 160 feet or more below the present sea level. hnite (1958) believed that changes in sea level would have little or no effect upon the water table or the piezametric surface. As he reasoned the lowering would merely extend the land seaward at essentially the same slope as the present land area. This is true for the shallower portions of the limestone terrane extending into the Gulf of Mexico. However, there is no doubt that the lakes, prairies, sinks, and springs of peninsular Florida were dry during continental glacial stages. Large quantities of water flow through the Floridan aquifer. In an artesian system the water may be channeled downward or upward several hundred feet. Jordan (1950) has argued that this is the cause of the deeper cavities in the limestone terrane of Florida; however, he neglects to mention that deep cavities also exist in the limestone plain where water table conditions prevail. 10

PAGE 16

I Ground water from some wells 800 feet or more into the Floridan aquifer are not completely saturated with calcium carbonate (Back, 1963). This chemical evidence proves that deep circulation and solution are occurring at the present time. Water samples from sixty-six selected wells representative of the different stratigraphic, geomorphic, and hydrological conditions were analyzed to provide chemical data relative to the rate and pattern of rock solution. pH readings were taken on the fresh sample in the field with a Beckman model N2 meter. This data has been prepared in map form and will be published. From the study of the composition and pH of the ground water in the Floridan aquifer it became apparent that chemical equilibrium was approached very quickly by reaction with the limestone. For example, in wells in fracture zones where large amounts at acid surface waters (pH 4.4 -5.6) were flowing directly into the limestone aquifer, it was rare to find water that had a pH of less than 7.2 and total dissolved solids of less than 100 ppm. The majority of the well water samples had a pH of 7.6 and 150 to 180 ppm of total dissolved solids, most of which was as CaC03 In the areas where the largest amounts of surface water were infiltrating the aquifer, it was not uncommon to find total dissolved solids from 250 to over 320 ppm. This super concentration must be due to the increased reactivity of the organic acids in the surface waters with the limestone. Shallow wells in the limestone plain typically have 150 to 180 ppm of total dissolved solids. Even the water being discharged into the. Suwannee River from the aquifer has only 190 to 230 ppm of total dissolved solids (Ferguson, Lingham, Love, and Vernon, 1947). Much of this spring water must travel great distances through the limestone; some as much as 40 to 45 miles and to depths of 400 feet or more. Davis (1930), Bretz (1942), and Stringfield and LeGrand (1966) have concluded that limestone solution is concentrated in the upper portion of the phreatic zone. Rhodes and Sinacori (1941) have argued that in a homogenous aquifer, the initial flow occurs at both great and shallow depths but that solution and increased flow becomes more pronounced in the upper zone be-cause of the shorter flow lines. Progressive increase in flow in the upper phreatic zone is believed to produce master conduits and cause eventual diminution of flow and solution at depth. This argument appears to be vali4 for many karst terranes, but in Florida it is complicated by the fact that the early solution history is under artesian conditions. It also does not appear to apply to the open limestone plain where water table conditions exist. In the large areas being drained by sub-surface runoff, flow of water 300 to 400 feet vertically is of no significance in the many miles the water percolated from its point of entry to its point of discharge. In the Pliocene-Pleistocene-Recent history of karst development in north peninsular Florida the limestone originally was completely over-lain by 80 feet or more of sands and clays acting as an aquifuge. In the of developme-rrc-o-r-t:tIe--randscape and-the "'. runoff was channeled through sink holes that breached the impermeable clays. 11

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The orientation of the solution features proves that the initial circulation of .,.;ater through the rock was controlled by a fracture system. The high permeability of the Ocala limestone and the Floridan .:(;U ifer, in general, can be proved to be largely a secondary feature as the I-L:sult of selective solution of the fine-rock matrix, particularly the .iLlgonite. A definite mineralogical distinction has been achieved between the two CaC03 minerals calcite and aragonite. Only calcite fossil and :rineral particles have prevailed in rock subjected to circulation of r::eteoric water. Solution of the limestone is largely localized i-lhere runoff first Ul contact '>lith the limestone, The amOUf1.t of solution is largely llpon the quant:i.ty of ,vater entering the aquifer. At points l.rhere runoff from large areas is channeled underground through sinks, lakes, and prairies the rate of solution may be rapid. With the aid of SCUBA gear the author has explored every accessible' sinkhole, spring and underwater cavern in Florida. In the sinkholes the lateral chambers are j oint controlled. They rapidly narrol-' and close alvay from the central chamber. The springs have a similar pattern and appear to be converted sinkholes that have changed functions due to changing hydrological conditions. The springs are certainly not the result of solution by the mineral-charged water they are now discharging. In this respect Jordan (1950) was wrong, but he was correct in attributing much of the deep cav:i.ty solution to channeling of water in an artesian system. There are some chambers and cavities in the karst terrane of Flor:i.da that do extend for several miles. For example, the Santa Fe River northeast of High Springs enters a sinkhole and emerges three miles farther do,vu the valley through another vertical passage, probably a former sinkhole. The general area of the Santa Fe River near High Springs is riddled \v:i.th extens:i.ve underwater caverns. There are vast chambers that have never been completely explored in the Hornsby Sink-Springs cavern complex that extend dowmvard over 200 feet. All of the known extensive underground caverns in Florida have a relat:i.onship to present or former surface drainage systems. South and west of Gainesville is an extensive fracture zone known to be riddled with caverns (Brooks, 1966). There are two surface streams that originate from surface runoff in the high flatlands that discharge into sinkholes in this zone. They are ?rairie Creek (from Hatchet Creek and Newnan's Lake) that discharges :i.nto the Floridan aquifer south of Gainesville in Payne's Prairie at Alachua Sink, and Rogtown Creek that discharges into the Floridan aquifer west of Gainesville in Hogtown Prairie and S:i.nk. No doubt the deep sinkholes and extensive cavern systems that have developed are the result of such channeled and localized flow of large volumes of acid surface water into the aquifer system. From Gainesville it is over twenty miles to the point of nearest discharge from the aquifer. There is no evidence of an integrated of solut-i-oItcaverns.-Thus it i-s-concluded that as tbe ground-w-ater approaches saturation it leaves the cav:i.ties that have been dissolved and flows through the integranular pores in the limestone. 12 a iiii!II

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Solution may take place just below the water table as Davis (1930) and Bretz (1942) have postulated. Observations in caverns and deep quarries in the limestone plain of northwestern peninsular Florida show a pattern of chambers, both incipient and developed, in relationship to the present and Dast stands of the water table. Solution is occurring in the limestone plain away from the points of entry of surface streams into the sinkholes, lakes, and prairies. West of Gainesville and throughout much of the limestone plain of the Suwannee River watershed all of the runoff is as ground water. This 1;vater that is infiltrating directly into the ground is dissolving limestone to the amount of 170 to 220 ppm of total dissolved solids as it flows through the rock, resulting in an erosional rate of 172 tons of rock material per square mile :12r doubt the runoff \,mter obtains its mineral load very quickly. l:t: may be tilis instead of the subsequent lines of tIm" that determines the development of solution features in the upper phreatic zone under water table conditions. APPLICATION IN DEVELOPING HATER RESOURCES It has often been assumed that the high yield characteristics of the Floridan limestone aquifer were due to a high primary porosity and permeability (Palmer, 1965). In the area of outcrop the rocks do, for the illost part, have a high porosity and permeability, especially the Ocala Limestone. Porosity ranges from 20 to 55 per cent and permeability from 0.02 to 1.55 darc:les on representative specimens. Most wells produce directly from the rock and not from joint controlled cavities so typical of other limestone terranes (Lattman and Parizek, 1962). In the early history of circulation in the area of recharge, solution is controlled by fracture systems. This can be due only to a relatively 10,,7 original transmissibility of the carbonate rock. As the landscape and underlying hydrological system has evolved, circulation of meteoric water directly through the rock from pore to pore away from the fracture zones has resulted in a high secondary porosity and permeability. It is now recognized that in areas of artesian conditions and incipient karst development in Florida, higher yield wells and well fields can be developed only in fracture zones. In the areas of more mature karst landscape with extensive cavern development these zones should be avoided because of the poorer quality of water due to color and pollution (from the surface water) and higher mineral content, especially calcium and iron. In these areas and in the open karst plain under water table conditions the aquifer system has developed a high secondary porosity and permeability and copious yield can be obtained directly from the rock. Lattman and Parizek (1962) have called attention to the relation between fracture traces and the occurrence of ground water in carbonate rocks. These traces can readily be aetectedon aeri-al pnbtographs-;It -is 13

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I -------rrecommended that more use be made of this valuable tool to obtain the quality and quantity of ground water desired in developing the water resources of the Floridan aquifer. 14

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I I LITERATURE CITED Back, William, 1963, Premiminary results of a study satur&tion of ground water in central Florida: Sci. Hydrology, v. 8, p. 43-51. of calcium carbonate Bull. Intern. Assoc. Bretz, J. R., 1942, Vadose and phreatic features of limestone caverns: Jour. Geology, v. 50, p. 675-811. Brooks, H. K., 1966, Geological history of the Suwannee River: South eastern Geological Soc., guidebook 13th Ann. Field Conference, p. 37-45. 3rodkorb, ;0, P., 1957, The Pleistocene avifauna of Arredondo, Florida: Fla. State HUSE'.Uill, BioI. ScL BulL, v. If, 269-291. Butson, Keith, 1962, Climates of the states, Florida: U.S. Dept. of COImnerce, Weather Bureau, Climatography of the United States No. 60-8. Conklin, C. V., 1967, The foraminifera fauna in the Plio-Pleistocene strata of south Florida: Graduate School, Univ. of Fla. Thesis for H.S. degree, 84 p. Cooke, C. W., 1945, Geology of Florida: Bull. Florida Geological Survey, v. 29, 339 p. Davis, W. M., 1930, Origin of limestone caverns: Geo1. Soc. American, Bull., v. 41, p. 457-628. Ferguson, G. E., C. W. Lingham, S. K. Love and R. O. Vernon, 1947, Springs of Florida: Bull. Florida Geol. Survey, v. 31, 96 p. Jordan, R. R., 1950, An interpretation of Floridan karst: Jour. Geology, v. 58, p. 261-268. Judson, Sheldon and D. F. Ritter, 1964, Rates of regional denudation in the United States: Jour. Geophysical Research, v. 69, p. 3395-3401. Lattman, L. R. and R. R. Parizek, 1962, Relationship betlreen fracture traces and the occurrence of ground water in carbonate rocks: Jour. Hydrology, v. 2, p. 73-91. MacNeil, F. S., 1949, Pleistocene shore lines in Florida and Georgia: U. S. Geol. Survey, Prof. Paper 221-F, p. 95-106. Palmer, A. N., 1965, The occurrence of ground water in limestone: Compass, v. 42, p. 246-255. Patton, T. R., 1967, Oligocene and Miocene vertebrates from central Florida: Southeastern Geol. Soc., 13th Field Trip! p. __ 3-9. 15

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-Pirkle, E. C., 1956, The Hawthorne and Alachua formations of Alachua County, Florida: Florida Acad. Sci., Quart. Jour., v. p. 197-240 Pirkle, E. C., and H. K. Brooks, 1959, Origin and hydrology of Orange Lake, Santa Fe Lake, and Levys Prairie Lakes of North-Central peninsular Florida: Jour. Geology, v. 67, p. 302-316. Rhodes, Roger and M. N. Sinacori, 1941, Pattern of ground-water flow and solution: Jour. Geology, v. 49, p. 785-794. Stringfield. V. T. and H. E. LeGrand, 1966, Hydrology of limestone terranes in the Coastal Plain of the Southeastern United States: Geological Soc.. A'11eric.a; Sp. P. 93, 46 p Teleki, P. G., 1966, Differentiation of materials formerly assigned to the Alachua Formation: Graduate School, Univ. of Fla., Thesis for M. S. degree, 102 p. Vernon, R. 0., 1951, Geology of Citrus and Levy Counties, Florida: Bull. Florida Geol. Survey, v. 33, 256 p. Webb, S. D., 1967, Pliocene terrestrial deposits of peninsular Florida: Southeastern Geol. Soc., guide book, 13th Field Trip, p. 11-15. \ihite, W. A., 1958, Some geomorphic features of central peninsular Florida: Bull. Florida Geol. Survey, v. 41, 92 p. 16 r I I I I r r ;,-