Age and Diagenesis of the Upper Floridan Aquifer 

and the Intermediate Aquifer System in 

Southwestern Florida 

U.S. GEOLOGICAL SURVEY BULLETIN 2122 
AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY 

Instructions on ordering publications of the U.S. Geological Survey, along with prices of the last offerings, are given in the currentyear issues of the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological Survey publications released prior to the current year are listed in the most recent annual "Price and Availability List." Publications that may be listed in 

various U.S. Geological Survey catalogs (see back inside cover) but not listed in the most recent annual "Price and Availability List" may 

be no longer available. 

Order U.S. Geological Survey publications by mail or over the counter from the offices given below. 

BY MAIL 

Books 

Professional Papers, Bulletins, Water-Supply Papers, Techniques of Water-Resources Investigations, Circulars, publications 

of general interest (such as leaflets, pamphlets, booklets), single 

copies of Earthquakes & Volcanoes, Preliminary Determination of 

Epicenters, and some miscellaneous reports, including some of the 

foregoing series that have gone out of print at the Superintendent 

of Documents, are obtainable by mail from 

U.S. Geological Survey, Information Services 

Box 25286, Federal Center, Denver, CO 80225 

Subscriptions to periodicals (Earthquakes & Volcanoes and 

Preliminary Determination of Epicenters) can be obtained ONLY 

from the 

Superintendent of Documents 

Government Printing Office 

Washington, DC 20402 

(Check or money order must be payable to Superintendent of 

Documents.) 

Maps 

For maps, address mail orders to 

U.S. Geological Survey, Information Services 

Box 25286, Federal Center, Denver, CO 80225 

Residents of Alaska may order maps from 

U.S. Geological Survey, Earth Science Information Center 

101 Twelfth Ave. - Box 12 

Fairbanks, AK 99701 

OVER THE COUNTER 

Books and Maps 

Books and maps of the U.S. Geological Survey are available 

over the counter at the following U.S. Geological Survey offices, 

all of which are authorized agents of the Superintendent of 

Documents: 

• ANCHORAGE, Alaska-Rm. 101,4230 University Dr. 

• LAKEWOOD, Colorado-Federal Center, Bldg. 810 

• MENLO PARK, California-Bldg. 3, Rm. 3128, 345 

Middlefield Rd. 

• RESTON, Virginia-USGS National Center, Rm. 1 C402, 

12201 Sunrise Valley Dr. 

• SALT LAKE CITY, Utah-Federal Bldg., Rm. 8105, 125 

South State St. 

• SPOKANE, Washington-U.S. Post Office Bldg., Rm. 135, 

West 904 Riverside Ave. 

• WASHINGTON, D.C.-Main Interior Bldg., Rm. 2650, 18th 

and C Sts., NW. 

Maps Only 

Maps may be purchased over the counter at the following 

U.S. Geological Survey offices: 

• FAIRBANKS, Alaska-New Federal Bldg., 101 Twelfth 

Ave. 

• ROLLA, Missouri-1400 Independence Rd. 

• STENNIS SPACE CENTER, Mississippi-Bldg. 3101 
Age and Diagenesis of the Upper Floridan Aquifer 

and the Intermediate Aquifer System in 

Southwestern Florida 

By Lucy McCartan, Suzanne D. Weedman, G. Lynn Wingard, and Lucy E. Edwards, 

U.S. Geological Survey, and Peter J. Sugarman and Mark D. Feigenson, Rutgers 

University, and Marc L. Buursink and Julie C. Libarkin, U.S. Geological Survey 

U.S. GEOLOGICAL SURVEY BULLETIN 2122 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1995 
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary 

U.S. GEOLOGICAL SURVEY 

GORDON P. EATON, Director 

For sale by U.S. Geological Survey, Information Services 

Box 25286, Federal Center, Denver, CO 80225 

Any use of trade, product, or firm names in this publication is for descriptive purposes only and 

does not imply endorsement by the U.S. Government. 

Published in the Eastern Region, Reston, Va. 

Manuscript approved for publication Aprill, 1993. 

Library of Congress Cataloging in Publication Data 

Age and diagenesis of the upper Floridan aquifer and the intermediate aquifer system in 

southwestern Florida I by Lucy McCartan ... [ et al.]. 

p. em.- (U.S. Geological Survey bulletin; 2122) 

Includes bibliographical references (p. - ). 

Supt. of Docs. no.: 119.3 

I. Floridan Aquifer. 2. Groundwater-Florida. I. McCartan, Lucy. II. Series. 

QE75.B9 no. 2122 

[GB1199.3.F6] 

557.3 s--dc20 

[551.49'09759] 

95-7177 

CIP 
CONTENTS 

Abstract .......................................................................................................................... . 

Introduction..................................................................................................................... 1 

Acknowledgments................................................................................................... 2 

Geologic Framework .. .... . . . . . . . . . . . ..... . . . . . . . . . .... . . . . . . . . . . . . . ... . . . . . . . . . . . . . .. ...... . . . . . . . . . ...... . . . .. . . . . ..... . 2 

Hydrogeologic Framework............................................................................................. 4 

Field and Laboratory Methods........................................................................................ 4 

Results............................................................................................................................. 6 

87 Sr/86Sr and Paleontologic Age Estimates .. .. ...... .. .. .. .. ...... .... .. .. .. .... ...... .. .. .. .. .... .. .. 6 

Lithology and Mineralogy .. . . . . . . . . . . ..... . . . . . . . . . . . . . ..... . . . . . . . . . . ............... .... ..... . . . . . . . . . .... . . . . 13 

Diagenesis . . . .. .. .. . . . . . . . . . . .. .. . .. .. . . . . . . . . .. .. . . . . . . . . . . . . . .. .. .. . . . . . . . . . .. .. .. . .. . . . . . . . . .. .. .. .. . . . . ... . . . . .. .. . . . . 16 

Modem Ground-water Chemistry........................................................................... 17 

Discussion . . . . . . . . . .. .... . . . . . . .. . . ..... . . .. . . . . . . . . .. .... . . . . . . . . . . . . . . .... . . . . . . . . . . .. ..... .. . . . . . . . ................... .... . . . . 17 

Age of the Deposits................................................................................................. 17 

Geophysical Logs ..................................................................................................... 18 

Regional Diagenetic Alteration............................................................................... 18 

Sources of Diagenetic Waters ................................................................... :..... 19 

Rocks and Water Chemistry of the Intermediate Aquifer System .. .. .. .. .. .... .. .. 20 

Rocks and Water Chemistry of the Upper Floridan Aquifer........................... 20 

Conclusions..................................................................................................................... 22 

References Cited .... . . . . . . . .. .. ..... . . . . . . . . . . . .... .. . . . . . . . . . .. . ...... . . . . . . . . . . ... .. . . . . . . . . . . . .................... ... . . . . . 22 

FIGURES 

1. Map showing the location of boreholes in southwest Florida........................................................................................ 2 

2. Generalized east-west transects of cores 

A. Cross section A-A', northern transect....................................................................................................................... 8 

B. Cross section B-B', southern transect...................................................................................................................... 9 

3. Plane-polarized-light optical photomicrographs of diagenetic textures 

A. W-16782, 70.2 m..................................................................................................................................................... 10 

B. W-16814, 193.1 m ................................................................................................................................................... 10 

C. W-11946, 57.1 m..................................................................................................................................................... 10 

D. W-12050, 182.9 m................................................................................................................................................... 10 

E. W-16814, 122.6 m................................................................................................................................................... 10 

F. W-17000, 126.4 m.................................................................................................................................................... 10 

G. W-11946, 32.6 m..................................................................................................................................................... 11 

H. W-16784, 84.8 m..................................................................................................................................................... 11 

4. SEM images of selected sample chips 

A. W-17000, 156.8 m................................................................................................................................................... 12 

B. W-11946, 32.6 m..................................................................................................................................................... 12 

C. W-16784, 91.3 m..................................................................................................................................................... 12 

D. W-16814, 61.0 m..................................................................................................................................................... 12 

E. W-16814, 82.9 m..................................................................................................................................................... 12 

F. Walton, 80.2 m ......................................................................................................................................................... 12 

5. Distribution of magnesian minerals in cores 

A. Transect A-A' from figure 1 ..................................................................................................................................... 14 

B. Transect B-B' from figure 1 .... .. .. . .. .. .. ................. ................... ...... .. .. .. .. .. .. .. ...... .. .. .. .. ................ ........ .... .. .. ........ ...... .. 14 

m 
IV CONTENTS 

6. Maps of flow regimes and water chemistry of aquifer systems 

A. Intermediate aquifer system; saturation with respect to calcite . . . . . . . . . . . . . . . . . . . . ..... .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....... ........ 21 

B. Intermediate aquifer system; saturation with respect to dolomite . . . . . . . . . . . . . . . . ........... .... .. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ... . . ........ 21 

C. Upper Floridan aquifer system; saturation with respect to calcite........................................................................... 21 

D. Upper Floridan aquifer system; saturation with respect to dolomite....................................................................... 21 

TABLES 

1. Core locations and sample information.......................................................................................................................... 5 

2. 87 Sr/86Sr age estimates................................................................................................................................................... 6 

3. Mineralogy of the South Venice core (W -16814) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . ............ .................................... .. . . . . . .. ... 7 

4. Petrographic observations of diagenetic alteration processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............ .............................................. 13 

5. Water chemistry of the intermediate aquifer system and Upper Floridan aquifer, west-central Florida....................... 15 
Age and Diagenesis of the Upper Floridan Aquifer and the 

Intermediate Aquifer System in Southwestern Florida 

By Lucy McCartan, Suzanne D. Weedman, G. Lynn Wingard, and Lucy E. Edwards, 

U.S. Geological Survey, and Peter J. Sugarman and Mark D. Feigenson, Rutgers University, and 

Marc L. Buursink and Julie C. Libarkin, U.S. Geological Survey 

ABSTRACT 

The age and diagenetic alteration of strata that constitute the Upper Floridan aquifer and intermediate aquifer 

system in southwestern Florida are assessed on the basis of 

samples ~aken from 12 cores and 1 set of cuttings from the 

upper 300 meters. Data were integrated from hand sample 

analysis; optical and scanning electron microscopy; and Xray, isotopic, and paleontologic analyses. Diagenetic history 

is analyzed within a framework of past sea-level oscillations 

and modem ground-water chemistry. Both age and diagenetic data are integrated for a better understanding of a 

genetic stratigraphic framework of the aquifer and aquifer 

system. 

Mollusk species and dinocyst assemblage distributions 

and 87Sr/86Sr values indicate that the "Suwannee" Limestone is early Oligocene and the Hawthorn Group ranges 

from late (possibly early) Oligocene to Pliocene. Within the 

Hawthorn Group, the Arcadia Formation ranges from late 

(possibly early) Oligocene to middle to earliest late 

Miocene; its Nocatee Member is late Oligocene and its 

Tampa Member ranges from late Oligocene to early 

Miocene; and the Peace River Formation is Pliocene. 

Diagenetic textures indicate that much of the alteration was 

early but that a magnesium mineral diagenetic facies characterized by dolomite, palygorskite, and sepiolite cross-cuts 

stratigraphy and may obscure stratigraphic correlations. 

Dolomite textures indicate a complex, multigenerational 

history; high saturation indices for dolomite in the modem 

Upper Floridan aquifer ground water suggest that modem 

dolomite precipitation, though volumetrically small, may be 

occurring. 

Age data reported here indicate extensive deposition in 

the study area during the late Oligocene, conventionally 

thought to be a time of subaerial exposure and nondeposition across much of the Florida platform, and an unconformity of ~10 m.y. between the Arcadia and Peace River 

Formations. The age data establish a framework that will 

help delineate a genetic stratigraphy based on depositional 

units rather than nongenetic lithostratigraphy. Diagenetic 

analysis indicates that most of the magnesium in the carbonates and clays may have been introduced prior to the establishment of the modem ground-water regime and that the 

magnesium-rich diagenetic facies cross-cuts stratigraphy 

and obscures stratigraphic correlations. 

INTRODUCTION 

The carbonates and siliciclastics of the Tertiary System 

of the Florida platform host the fresh ground-water supply 

for the region in three aquifer systems: the Floridan, the 

intermediate, and the surficial. Currently, this interval is 

subdivided into lithostratigraphic units on the basis of lithologic properties. Some of those lithologic properties, however, may include diagenetic (postdepositional) alteration, 

which can obscure stratigraphic boundary identification. 

Additionally, the ages of the lithostratigraphic units are not 

well constrained, and their boundaries may cross regional 

unconformities. The long-range objective of our study in 

southern Florida is to identify and map depositional, unconformity-bounded units in the subsurface, instead of nongenetic lithostratigraphic units; our focus is on the section that 

constitutes the upper portion of the Upper Floridan aquifer 

and the intermediate aquifer system. Delineating this 

genetic stratigraphy will enhance our ability to calibrate 

hydrologic models of the ground-water systems of Florida, 

as well as our understanding of part of the depositional history of the Florida platform. In addition, a genetic stratigraphy will provide the necessary geologic framework to 

predict hydrologic properties of aquifer rocks in areas that 

are sparsely drilled. 

The results presented in this paper document our initial 

steps toward a genetic stratigraphy and include constraints 

on the age and correlation of subsurface strata and an 

assessment of their diagenetic alteration. Three independent 

time indicators are used: 87 SrJ86Sr composition of shells, 

the distribution of mollusks species, and the distribution of 

dinocyst assemblages. Diagenetic alteration is examined 

petrographically with the scanning electron microscope 

(SEM) and by X-ray diffraction (XRD) and is compared 

with modem ground-water chemistry. This comparison 
2 AGE AND DIAGENESIS OF THE UPPER FLORIDAN AQUIFER IN SW. FLA. 

MANATEE HARDEE ' HIGHLANDS 

I +37 

i 

34 +35 

+ I 

/ 

< 

/OKEECHOBEE 

/ 

,.. ... s&H'io -. ' I 33 +O Sebring W-15166 , 31 W-16784 +j2 W-11946""' ... ,._,,-J ·"· \ .I ,, ,t-" + 30 .. ,. 29 

..-A +27 + · · --~~ + ··-··-··-··-··-··-+·+·· ! ' ,...._A, 

SARASOTA 2: 25 B+ ~J·- -~-~~~~~·-··-··-··-··-·+t:z-1 W-17000 

·.'-....... ) 

\ 

9, 11 I 

I 

Walton L..·-··-··-··-1 

S&H4~ W-15636 .,._: 8 "!~ _ .. _ .. _.....,, 1 

0 Arcadia 

W-15303 + 8' 

· S&H5 r W-12050 

, • % -.w-16182 I 

\vt-15168 : 

V'w-16814 s&~2 •0 south Venice;··-··-··-··-1 • ...!: 

.......... "-'>,... i' 

··-··--·~;~£!~~~~-5!~-- .. -··-··-··-··-··-··- CHARLOTTE GLADES 

0 10 20 30 MILES 

FLORIDA ~----~~--~----~---------~ 

Sarasota 

30' X 60' 

quadrangle 

quadrangle 

0 

• 

10 

Core site 

20 30 KILOMETERS 

EXPLANATION 

S&H Swancar and Hutchinson 

+ Water chemistry • .._..,. Cross section 

Figure 1. Map showing the location of boreholes in southwest Florida; cuttings only were examined from site W-15636. Cross sections 

A-A' and B-B' are discussed in the text and are shown in figures 2A and 2B; Sarasota and Arcadia quadrangles are outlined in bold lines and 

indicated on index map, lower left. 

allows identification of relict diagenetic features that 

formed in different water chemistries in the past and 

enhances our understanding of the freshwater diagenetic 

environment in the aquifer system. 

ACKNOWLEDGMENTS 

We thank the USGS reviewers, Gregory Gohn and 

Carol Wicks, as well as Thomas Scott (Florida Geological 

Survey) and an anonymous reviewer, for helpful suggestions and corrections; Steven Van Valkenberg and David 

Mason, USGS, for the XRD data; and the geologists, 

hydrologists, and drillers of the Florida Geological Survey 

and Southwest Florida Water Management District for samples, lithologic and geophysical logs, and wide-ranging discussions of ongoing stratigraphic research. Laboratory time 

and equipment for the strontium isotope analyses were contributed by Kenneth Miller (Rutgers University). Niel 

Plummer and Eric Prestemon (USGS) selected the previously unpublished water-chemistry records used in this 

study and analyzed them with WATEQF. Warren Allmon 

(Paleontological Research Institute, Ithaca, NY) suggested 

the use of turritellids and made some of the initial identifications; he and Lauck Ward (Virginia Museum of Natural 

History), Joseph Hazel (Louisiana State University), and 

David Webb, Roger Portell, Gary Jones, and Gary Morgan 

(Florida Museum of Natural History) helped clarify the current thinking on the ages and correlations of the Oligocene 

and Miocene units. Our age estimates for each unit are not 

necessarily the views of our colleagues. Anthony Randazzo 

(University of Florida) and Ruth Deike (USGS) discussed 

postdepositional alteration effects with us. We also thank 

the staff at Archbold Biological Station for their hospitality 

and support of our investigations. 

GEOLOGIC FRAMEWORK 

The study area (fig. 1) is underlain by a sequence of 

sediment and rocks several kilometers thick, ranging in age 

from Mesozoic to Holocene; most of the sequence was 
GEOLOGIC FRAMEWORK 3 

deposited in nearshore, relatively shallow marine environments (Mansfield, 1937; Petuch, 1982; Tedford and Hunter, 

1984; Webb, 1990; and Jones and others, 1991). The upper 

300-450 m of this sequence, which includes rocks of 

Eocene to Pliocene and Pleistocene age, is the subject of 

this report; we focus on Oligocene and Miocene deposits. 

The complex distribution patterns of the lithofacies in 

the study area are the consequence of paleoshoreline migration and the convergence of coastlines along the Atlantic 

and the Gulf of Mexico. Shoreline migration has been 

attributed to eustatic sea-level oscillations (Haq and others, 

1987; Dowsett and Cronin, 1990; Krantz, 1991; McCartan 

and others, 1991; Muhs and others, 1992), tectonic uplift (to 

the north, beneath the Ocala arch; inferred from distribution 

of Oligocene and Miocene rocks; Puri and others, 1967; 

Gohn, 1988) and subsidence (to the south; Herrick and 

Vorhis, 1963), and subsidence due to dissolution of carbonate rocks (Beck and Sinclair, 1986). The position and configuration of the Florida peninsula also has increased the 

complexity of the deposits, particularly during and since the 

late Oligocene. Longshore currents sweep siliciclastic sediment southward from river mouths in northern Florida and 

Georgia along both sides of the peninsula (Martens, 1928; 

McCartan and Owens, 1991); in the study area they interfinger with locally produced carbonates and phosphates. 

In this paper, we use the lithostratigraphy of the Florida Geological Survey proposed by Scott (1988) as a frame 

of reference. Scott (1988) subdivided the section we have 

examined into the Ocala Group, the "Suwannee" Limestone, and the Hawthorn Group (Arcadia and Peace River 

Formations). The Ocala Group consists largely of very 

porous limestone, thought to be late Eocene, that forms 

much of the Floridan aquifer system; it was first described 

by Dall and Harris (1892) near Ocala in Marion County, 

Fla., and is subdivided into a locally dolomitized, lower 

grainstone and an upper packstone/wackestone, typically 

containing large foraminifers (Miller, 1986). The Ocala 

Group includes the Crystal River and Williston Formations; 

few of the cores examined in this study penetrate the Ocala. 

Overlying the Ocala Group in the study area is a white 

to cream, vuggy molluscan and foraminiferal limestone that 

Scott (1988) refers to as the "Suwannee" Limestone with 

some uncertainty. Over the years, the age of the Suwannee 

Limestone has alternately been placed in either the early, 

the late, or the entire Oligocene. The Suwannee Limestone 

was originally named by Cooke and Mansfield (1936) for 

exposures along the Suwannee River from Ellaville to near 

White Springs, in northern Florida; they stated that the 

Suwannee "unconformably overlies white limestone containing Vicksburg (Oligocene) fossils" (Cooke and Mansfield, 1936, p. 71), implying that the Suwannee is 

Vicksburgian age or younger. In the present day, Vicksburgian is restricted to the early Oligocene, but in 1936 the term 

"Vicksburg Group" was used by the U.S. Geological Survey 

(USGS) to refer to all Oligocene deposits in the gulf coast 

region (MacNeil, 1944, p. 1313). Further confusion 

occurred when MacNeil (1944) revised the concept of the 

Vicksburg by restricting its use to deposits of middle Oligocene age; in his abstract and throughout his paper, he 

places the Suwannee Limestone in the upper Oligocene, 

overlying deposits of the Vicksburg Group. In an easily 

overlooked footnote, however, MacNeil concluded that the 

Suwannee may be equivalent in age to the Marianna Limestone and Byram Formation, Vicksburg Group (subsequent 

studies, for example MacNeil and Dockery, 1984, indicate 

an early Oligocene age), as well as the late Oligocene 

Chickasawhay Limestone (MacNeil, 1944, p. 1313-1314, 

footnote 3). The confusion about whether the Suwannee 

Limestone is late or early Oligocene or whether .it spans the 

Oligocene continues to this day (see, for example, AAPG, 

1988). We agree with Scott (1988): in the study area, the 

limestone, which commonly has been identified as the 

Suwannee, may not be correlative with the Suwannee Limestone from the type area. Until a correlation can be demonstrated, or a new assignment made, we will retain Scott's 

usage of Suwannee in quotation marks. 

The Hawthorn Formation was raised to group status by 

Scott (1988) and includes the Arcadia and Peace River Formations. The Arcadia Formation encompasses the carbonates and associated siliciclastics overlying the "Suwannee" 

Limestone and is thought to be early early to late early 

Miocene (Scott, 1988); the type section is in core W-12050 

(DeSoto County). The Arcadia Formation comprises limestones and dolomites with different amounts of quartz sand, 

clay, and phosphate grains and in places is subdivided into 

two members, the Nocatee and the Tampa; the remainder is 

referred to as undifferentiated Arcadia Formation. The 

Nocatee Member, named by Scott (1988), is primarily a 

siliciclastic unit, which comprises quartz sand and clays, 

with some carbonates and locally abundant phosphate sand 

and fine gravel, and which occurs at, or near, the base of the 

Arcadia Formation. The Tampa Member, above or laterally 

adjacent to the Nocatee Member, is a limestone with different amounts of quartz sand, dolomite, and clays and is distinguished from other Hawthorn Group carbonates by 

having less than 3 percent phosphate grains. Scott (1988) 

reduced the Tampa Formation as used by King and Wright 

(1979) to member status on the basis of its limited spatial 

extent and suggests that the Tampa Member may straddle 

the Oligocene-Miocene boundary (Paul Huddelstun, Georgia Geological Survey, personal communication 1984, in 

Scott, 1988). The Tampa Member in its type area at Tampa 

and at other places around Tampa Bay (Ballast Point and 

Six Mile Creek, Tampa Bay, Fla.; Dall and Harris, 1892) 

differs in appearance from the Tampa Member elsewhere; 

therefore, a reference core (W-15166) in Manatee County 

has been proposed (Scott, 1988). 

Disconformably overlying the Arcadia Formation, in 

the uppermost Hawthorn Group, is the poorly indurated, 

siliciclastic Peace River Formation (upper Miocene, accord-
4 AGE AND DIAGENESIS OF THE UPPER FLORIDAN AQUIFER IN SW. FLA. 

ing to Scott, 1988). The Peace River Formation consists of 

interbedded quartz sand, clay, and carbonates ( <33 percent) 

as well as minor amounts of chert. The Bone Valley Formation (Altschuler and others, 1964 ), a clastic unit of pebbleto cobble-sized phosphate clasts in a matrix of quartz and 

phosphate sand and clay, originally described by Matson 

and Clapp (1909) as the Bone Valley gravels, is now considered a member within the Peace River Formation (Scott, 

1988) and is not differentiated in this report. 

Joyner and Sutcliffe (1976) identified a clay bed (5-7 

m thick) at the base of the overlying Tamiami Formation 

(Pliocene) in central and southwestern Sarasota County. 

They informally referred to this bed as the Venice clay 

(Joyner and Sutcliffe, 1976; Sutcliffe and Thompson, 1983). 

Because of the informal nature of the stratigraphic name 

and the lack of a rigorous description, some uncertainty persists in stratigraphic placement of this clay bed, and in 

whether several similar clay beds may be present. Lynn 

Barr (USGS, oral communication, 1993) mapped the extent 

of a clay unit (referred to in the field as the "Venice clay") 

as a confining layer near the top of the intermediate aquifer 

system. 

Deposits stratigraphically younger than ~he Hawthorn 

Group are composed of thin, overlapping sheets and lenses 

of sand and mud, with local concentrations of shells and 

phosphatic gravel of late Pliocene and Pleistocene age 

(Jones and others, 1991; McCartan and others, 1991). A few 

remnants of lower Pliocene deposits are known near the 

gulf coast (Jones and others, 1991), and Holocene swamp 

and eolian deposits have been recognized in patches at the 

surface (Watts, 1980; McCartan and Rubin, 1991). These 

deposits form the surficial aquifer system, and in this report, 

we do not differentiate among them. 

The complex diagenetic history of Tertiary rocks in 

west-central Florida has been noted and discussed by Randazzo and Zachos (1984), Randazzo and Cook (1987), 

Budd and others (1993), and Jones and others (1993). Budd 

and Jones and their colleagues focus on calcite diagenesis in 

the "Suwannee" Limestone in approximately the same 

study area as ours. Our study includes younger strata and 

places a greater emphasis on dolomite and fibrous magnesian clays, palygorskite and sepiolite, whose coincidence in 

these rocks has been noted previously (Randazzo and 

Zachos, 1984; McCartan and others, 1992). The postdepositional roles of magnesium and silica, critical in the formation of sepiolite and palygorskite, have been discussed by 

Callen (1984), Singer and Galan (1984), and Weaver 

(1984). 

HYDROGEOLOGIC FRAMEWORK 

Three major aquifer systems occur in the study area, 

and the rocks containing these aquifer systems have been 

classified into formal hydrogeologic units (Southeastern 

Geological Society 1986); however, it is important to note 

that the boundaries of the hydrologic systems do not coincide with either lithostratigraphic or chronostratigraphic 

boundaries. The unconfined surficial aquifer system is 

found over most of the State and consists of unconsolidated 

to weakly consolidated siliciclastic deposits. The deeper 

intermediate aquifer system is found throughout the study 

area and consists of anastomosing, permeable siliciclastic 

and carbonate deposits with subregional, clayey upper confining units, and other local zones of low permeability 

(Duerr and others, 1988). The Floridan aquifer system is 

typically divided into upper and lower parts; our study does 

not extend to the base of the Upper Floridan aquifer, so the 

term "Upper Floridan aquifer" in this report refers to the 

upper part of that aquifer. The Upper Floridan aquifer consists mainly of limestones and dolomites that underlie the 

intermediate aquifer system in the study area, and has been 

studied as part of the USGS's Regional Aquifer System 

Assessment project by Ryder (1985), Miller (1986), Bush 

and Johnston (1988), Johnston and Bush (1988), Meyer 

(1989), and Sprinkle (1989). The configuration of the top of 

the Upper Floridan aquifer has been mapped in the study 

area by Buono and Rutledge (1979) and the thickness of the 

intermediate aquifer system has been mapped by Buono and 

others (1979). The hydrogeochemistry of Florida has been 

investigated further by Hanshaw and others (1971), Plummer (1975), Wigley and Plummer (1976), Hanshaw and 

Back (1979), Katz (1992), and Swancar and Hutchinson (in 

press). 

FIELD AND LABORATORY METHODS 

Subsurface samples from 10 cores and from 1 set of 

cuttings, stored at the Florida Geological Survey, Tallahassee, and also from 1 core at the USGS, Reston, Va., were 

examined for age determinations, mineralogy, and petrography; geophysical logs were obtained from 9 of those cores 

from the USGS and the Southwest Florida Water Management District (table 1). 

87Sr/86Sr analyses were performed at Rutgers University on 16 mollusk shells and 1 foraminifer from the top 200 

m in the study area. Original aragonite or calcite, or slightly 

recrystallized calcite, shells were cleaned, crushed, and dissolved in a solution of 1.5 N HCl. Ion exchange (Hart and 

Brooks, 197 4) was used to separate strontium for analysis 

on a mass spectrometer, with an intrarun precision on this 

instrument of ±0.000008 and an interrun variability of about 

0.000026 to 0.000030 (Miller and others, 1991). The 

National Bureau of Standards strontium sample ratio at Rutgers University is 0. 710252 (2 cr standard deviation is 

0.000026; n=35) normalized to 86srJ88sr of 0.1194 (Miller 

and others, 1991). Numerical ages were estimated using the 

regression equations of Miller and others (1988, 1991), 

Hodell and others (1991), and Oslick and others (1992, 
FIELD AND LABORATORY METHODS 5 

Table 1. Core locations and sample information 

[Dino=Dinocysts; Moll=Mollusks; Sr=Strontium isotope dating; Xrd=X-ray diffraction; Ts=Microscope and SEM; Litho=Lithologic logs; Geophy=Geophysical logs; *Cuttings only] 

Elevation Core Length Latitude Latitude Core County Dino Moll Sr XRD Ts Litho Geophy (m) (ft) (m) (ft) North West 

W-15166 .................... 2 8 193 634 Manatee 27°25'10" 82°34'57" X X 

W-16784 .................... 21 70 331 1088 Manatee 27°28'30" 82°12'45" 31 11 X X 

W-11946 .................... 20 67 143 470 Hardee 27°27'50" 81°41'45" 2 32 3 X 

W-17000 .................... 26 85 398 1304 Highlands 27°23'10" 81 °27'15" 2 52 12 X X 

W-15168 .................... 4 14 199 654 Sarasota 27°08'08" 82°27'05" 2 5 X X 

Walton site (USGS) .... 5 16 92 304 Sarasota 27°11'43" 82°24'03" 2 39 2 X X 

W-15636* .................. 5 15 276 906 Sarasota 27°09'19" 82°23'42" X X 

W-16782 .................... 3 11 177 580 Sarasota 27°08'04" 82°21'05" 5 63 13 X X 

W-16814 .................... 4 13 213 701 Sarasota 27°02'40" 82°23'57" 3 7 2 86 12 X X 

W-15303 .................... 7 22 436 1430 DeSoto 27°10'26" 82°49'30" 3 24 X X 

W-12050 .................... 19 62 183 600 DeSoto 27°10'00" 81°43'11" 1 4 28 5 X 

W-16578 .................... 13 41 345 1133 DeSoto 27°02'25" 81 °44'33" 3 X 

1994); stage boundaries are based on the time scale of Berggren and others (1985). 

Dinocysts were separated from fine-grained unlithified 

samples in hydrochloric and hydrofluoric acids, and their 

occurrences were compared to published range data for the 

individual taxa. Emphasis was placed on ranges in the midAtlantic region (Stover, 1977; Edwards, 1986, 1991; Verteuil and Norris, 1992), but worldwide compilations also 

were used (Williams and Bujak, 1985; Haq and others, 

1987; Powell, 1992). Mollusks were analyzed primarily 

from internal and external molds or from latex casts of the 

molds. The large size of many of the preserved mollusks, 

relative to the core diameter, limits the investigation to time 

ranges of individual species rather than assemblages. 

Within the core studied, Turritella species are relatively 

abundant, easily identifiable and well preserved, even as 

molds or casts; are fairly widespread geographically; and 

appear to have evolved rapidly. These characteristics make 

the turritellids good biostratigraphic indicators. 

Samples for XRD were prepared from whole-rock subsamples or from the fraction finer than 2 micrometers that 

was concentrated by centrifuge-separation (Soller and 

Owens, 1991). Although these methods do not produce 

identical peak heights (intensities}-because the first inhibits parallel orientation of planar and fibrous minerals 

whereas the second enhances orientation-several duplicate 

test runs produced comparable results. Untreated centrifuge 

samples that exhibited approximately IS-nanometer peaks 

were treated with ethylene glycol; a peak shift to approximately 17 nanometers indicates illite/smectite mixed-layer 

clay, whereas dioctahedral vermiculite peaks do not shift 

with this treatment. Minerals were identified by matching 

one or more major peaks with published standards (Joint 

Commission on Powder Diffraction Standards, 1974, 1981). 

Geophysical logs are available for 9 of the 12 boreholes from the Southwest Florida Water Management District and the USGS. Logs from five of the nine boreholes 

have been included in various previously published reports, 

but four are presented here for the first time: Walton, W16782, and W-16814 were logged by the USGS, and W17000 was logged by Southwest Florida Water Management District. The primary use of geophysical logs in southem Florida is as a tool for correlation of boreholes with and 

without cores. The electric logs, single point (SP) and resistivity (Res), were run prior to casing the holes and natural 

gamma radiation logs were run after the hole was cased. 

The SP logging instrument was not available for W-16814. 

Electric logging was performed in three increments at W16782, between drilling and setting casings, to obtain as 

complete records as possible. On electric logs, electrical 

conductivity (for SP) and resistance values increase to the 

right, and natural gamma radiation values increase to the 

right on gamma logs. In all logs, the geophysical signature, 

which is the frequency and amplitude of spikes, was a characteristic used in correlation of rock units. Of the three 

types of logs, gamma logs are considered potentially the 

most useful for tracking lithologic boundaries, so individual 

gamma spikes and groups of spikes were compared with 

lithologic contacts discerned in the cores. 

Blue-dyed, epoxy-impregnated thin sections from 58 

samples were examined with a petrographic microscope, 

and selected sample chips and polished thin sections were 

examined with the SEM. All thin sections were dyed with 

Alizarine red S to differentiate calcite from dolomite 

(method of Friedman, 1959). 

Unpublished water-chemistry data were obtained from 

19 water samples taken from 18 wells (within the study 

area) that are open in the stratigraphic and hydrologic 
6 AGE AND DIAGENESIS OF THE UPPER FLORIDAN AQUIFER IN SW. FLA. 

Table 2. 87Sr/86Sr age estimates1 

Core 

Depth 87srj86sr Age 

(m) (ft) (Ma) Epoch 

W-12050 .......................... 25.0--26.5 82.0-87.0 0.708980±6 5.1 Pliocene 

W-17000 .......................... 95.4 313.0 0.708730±7 16.7 

W-15636 .......................... 88.4-89.9 290.0--295.0 0.708595±13 18.9 

W-12050 .......................... 57.3 188.0 0.708534±10 19.7 Miocene 

W-12050 .......................... 87.1 286.0 0.708379±4 22.3 

W-15166 .......................... 87.3 286.4 0.708342±8 22.9 

W-17000 .......................... 114.0 374.0 0.708216±9 25.3 

W-16782 .......................... 70.1 230.0 0.708192±6 26.0 

W-16782 .......................... 79.2 260.0 0.708182±6 26.3 

W-16814 .......................... 118.4 388.5 0.708166±5 26.8 

W-16782 .......................... 96.6 317.1 0.708163±8 26.8 Late Oligocene 

W-16782 .......................... 94.7 310.8 0.708153±6 27.1 

W-15168 .......................... 116.3 381.5 0.708127±5 27.9 

W-11946 .......................... 55.3 181.5 0.708101±18 28.6 

W-16814 .......................... 200.9 659.0 0.708042±5 30.3 

W-12050 .......................... 178.6 586.0 0.707927±8 33.6 Early Oligocene 

W-11946 .......................... 140.2 460.0 0.707853±8 35.8 

1 Regression curves for age estimates: Pliocene, Hodell and others. 1991: Miocene, Miller and others, 1991: Oslick and others, 1992, 

1994: Oligocene, Miller and others, 1988. Time scale for all regression curves from Berggren and others, 1985. 

intervals of interest. Saturation indices (SI) for calcite and 

ordered dolomite were calculated at the USGS, National 

Center, using a slightly modified version of the WATEQF 

program of Plummer and others ( 1978) (Niel Plummer and 

Eric Prestemon, USGS, written communication, 1993). 

These data were supplemented by similar SI data from 

seven wells reported by Swancar and Hutchinson (in press). 

WATEQF input requirements for a large number of ions and 

<30 percent error in charge balance eliminated more than 

2,500 of the chemical analyses available. The SI for a water 

sample with respect to a given mineral is defined as the 

following: 

S/=log [IAP/Ksp] 

where lAP is the measured ion activity product and Ksp is 

the calculated solubility product at equilibrium for the dissolution reaction of interest. An SI value of 0±0.5 is considered equal to 0, meaning that the water is exactly saturated 

with a given dissolved mineral species; Sl<-0.5 indicates 

undersaturation and that the mineral is susceptible to dissolution; Sl>0.5 indicates supersaturation and, from a thermodynamic point of view, that precipitation of the mineral is 

possible (Stumm and Morgan, 1981). 

RESULTS 

The contributions of this study are age estimates 

for subsurface lithostratigraphic units and a regional 

understanding of diagenetic history. Strontium isotope and 

paleontologic age estimates for rocks in the upper 266 m in 

the study area constrain the time of deposition of the lithostratigraphic units of Scott ( 1988). Through investigation of 

mineralogy and texture, we differentiate primary and diagenetic features, and we use modem water chemistry to identify relict diagenetic alteration. Strontium isotopic age 

estimates are given in table 2; lithostratigraphy is shown for 

all cores in two cross-sections in figures 2A and 2B; XRD 

mineralogy is given for W-16814 in table 3; the effects of 

diagenetic processes observed in selected thin sections are 

illustrated in figures 3 and 4 and are summarized for all 

samples in table 4; the distribution of diagenetic magnesium-rich minerals (from XRD data) is shown in figures SA 

and 58; and modem ground-water chemistry and SI analyses are given in table 5. 

87SRf86SR AND PALEONTOLOGIC AGE 

ESTIMATES 

The 87 Sr/86Sr values of shell samples from the top 200 

m in the study area indicate numerical age estimates that 

range from 5.1 Main the Peace River Formation to 36.1 Ma 

in the "Suwannee" Limestone (table 2). The locations of the 

molluscan and dinocyst samples and the samples used in the 

strontium analysis are indicated on the cross-sections (figs. 

2A and 2B). 

The core at W-16814 provides our best integration of 

isotopic and paleontologic data (fig. 2B). Analysis of 
RESULTS 7 

Table 3. Mineralogy of the South Venice core (W-16814). Minerals identified by X-ray diffraction 

[liS, illite smectite mixed-layer clay; Se, sepiolite; P, palygorskite; I, illite; K, kaolinite;?, possible occurrence; T, trace:./, mineral present;,/,/, dominant 

XRD peak@, prepared with amyl acetate; cristobalite (opal-CT) is present at 57.2 m; L, light phase; D, dark phase. Empty cells mean mineral not detected. 

Depth in meters below surface.] 

Depth liS Se 

0.3.............. 92 

1................. 100 

1.5.............. 100 

2.7 ............ .. 

4.4.............. 100 

p 

? 

K 

8 

T 

T 

Q c 

./ ./ 

././ 

./ 

T 

4.7.............. T 53 47 ./ 

5.2@ ........ .. 

5.9 ............ .. 

6.6.............. 85 

7.0.............. 89 

7.2 ............. . 

7.5.............. 100 

8.1.............. 90 

12.2.............. 89 

14.5.............. 85 T 

18.6.............. 82 

21.7 .............. 51 42 

22.1.............. 46 43 

10 

14 

17 

7 

11 

24.7.............. 45 36 T 18 

25.9@ ......... . 

28.7@ ......... . 

30.2.............. 46 54 

31.9@ .......... T 

34.9@ .......... T 

37.8.............. 35 31 26 8 

38.3.............. 39 

40.6.............. 53 

42.5@ ........ .. 

45.1@ ........ .. 

47.5 ............. . 

48.5@ ......... . 

50.3@ ........ .. 

51.3@ ........ .. 

55.1@ ......... . 

55.7@ ......... . 

61.0@ ........ .. 

67.3@ ........ .. 

69.5L@ ....... . 

69.50@ ..... .. 

73.2@ ......... . 

79.3@ ......... . 

25 25 11 

16 23 8 

T 

32 68 

23 77 

T 

T 

100 

24 76 

T 

100 

T 

100 

100 

25 75 

82.9@ .......... 56 44 

87.6.............. 22 33 36 9 

././ 

100 

15 ./ 

11 

10 

T 

./ 

./ 

./ 

./ 

./ 

./ 

./ 

./ 

T 

./ 

./ 

./ 

./ 

./ 

./ 

? 

./ 

T 

? 

./ 

T 

./ 

./ 

././ 

./ 

./ 

D 

./ 

./ 

T 

././ 

././ 

./ 

././ 

././ 

./ 

././ 

././ 

././ 

././ 

././ 

././ 

././ 

././ 

././ 

././ 

././ 

././ 

././ 

././ 

./ 

Depth liS Se p 

88.9 .......... . 15 22 52 11 

90.9 ......... .. 31 63 6 

92.8 .......... . ? 36 61 3 

93.9@ ...... . 

97.9@ ..... .. 

101.9@ ...... . 

106.0@ ...... . T 

108.0@ ...... . 

109.3@ ..... .. 

112.1@ ..... .. 

112.9@ ...... . 

113.8 .......... . 100 

118.5@ ..... .. 

121.6@ ...... . T 

125.7@ ..... .. 

136.7@ ....... ? 

139.0@ ...... . 34 66 

142.6L ....... .. 100 T 

142.60 ....... . 100 T 

146.4@ ...... . 

149.7@ ...... . T 

152.1@ ...... . 

157.3@ ...... . T 

164.2@ ..... .. 

170.2@ ...... . 

173.9@ ...... . 75 25 

174.5@ ...... . 64 36 

179.6@ ...... . 72 28 

182.2@ ...... . T 

183.8@ ...... . 57 43 

184.9@ ...... . 72 28 

188.0@ ...... . 51 49 

190.3@ ...... . 82 18 

193.1@ ...... . 

194.2L@ .... . 65 35 

194.20@ ... . 68 32 

198.0@ ...... . 

201.0@ ...... . T 

202.1@ ...... . 

203.2@ ...... . 100 

205.3@ ...... . 

206.5@ ...... . 

212.3@ ..... .. 

K Q 

./ 

./ 

./ 

./ 

./ 

c D 

./ 

./ 

././ 

././ T 

././ 

././ T 

./ 

T ././ 

././ 

./ ./ ./ 

././ 

././ 

./ ././ 

./ ././ 

././ ./ 

././ ./ 

./ ./ ? 

./ 

./ 

./ 

./ 

./ 

././ 

./ 

./ 

? 

././ 

./ ./ ./ 

././ 

././ 

././ T 

./ ./ ./ 

./ ./ ./ ./ 

./ 

./ 

./ 

./ 

./ 

././ 

././ 

./ 

././ 

././ 

? 

././ 

./ 

./ ./ ./ ./ 

./ ./ ./ ./ 

./ 

./ 

./ 

./ 

./ 

T 

././ 

././ 

././ 

././ 

././ 

././ 
00 

Elevation 

Meters Feet A W-17000 A' 

251100 

W-16784 \At .unA~ 

W-15166 

0 Sea level • ~ '- ~::::::::~:::::! P \ ~ ~ _ \ ~ 1 

~ EXPLANATION ~ 100 ~ ~ ~ '----. A-..1:.. 1n.. J:;r:;:I1 \ 1:::::::::::::::::~ I I for figure 2 A and B Z 

0 D Quartz sand 0 

50--1 ~- t ~r'?- p ~JI?\ m p ~ I~ Siltand(or)clay > 0 P ·:·:·:·:~·:·:-:· P 6:J limestone tr1 

200 ......... " u. f1 ~ calcite-cemented sandstone ~ 

E:ZJ Dolomite 5!3 P J ~ ~ I TA~nna I / f-rl-rLl '- '\los (.':::::::.] ... ..$ 1 \. I ~ Dolomite-cemented sandstone ~ 

300 P Phosphate ~ 

~ < ~\ V E5:5l \~ -i" ~? I & Chert :I: 

100--1 ~ \ ~ / ~ ~ ./- I J xx Breccia tr1 

~ Burrowed surface g 

p ~ m l.:iamma eOs ~ ~ f 1 p ' I SP v Self potential ~ .... 400 ~ - / :?,:'D = 14:! m RES Resistivity :::0 

TO Total depth shown graphically fl 

(TO) Total depth greater than shown ~ 

150 --1_ t:r:::r=1 I FI;I;=l / !I;I;I.. .. I 1 1 .........._ Extent ofthe Arcadia Formation S 

500 !=;I;II $ ~ Ocala Group 1-r-r'i r ~ > 

z 

> 

Age indicator § 

600 Ea::l ( b:!:d / --Gamma SP Res I Md Miocene dinocyst ~ 

oMd Middle Oligocene dinocyst :::0 

PPd Pliocene or Pleistocene Pecten z Mt Miocene Turritella tZl 

700 ~ I MuOt Miocene or upper Oligocene Turritella ~ 

MOt Miocene or Oligocene Turritella fl 

Ot Oligocene Turritel/a ?>" 

eOt Early Oligocene Turritel/a 

800 t::r::!:r:!:l I ct p Oligocene and younger pelecypod 

Ps Pliocene strontium ratio 

Ms Miocene strontium ratio 

(TO • 331 m) I lOs Late Oligocene strontium ratio 

A eOs Early Oligocene strontium ratio 
Elevation 

Meters Feet 

10 50 

0 Sea level 

100 

50 

200 

300 

100 

400 

150 500 

600 

700 

800 

900 

B 

B 

W-15168 W-16814 

Gamma 

TO= 213m 

W-15636 

es 

W-16782 

"Suwannee" Limestone 

Ocala Group 

B' 

W-12050 

W.16578 

l IMP p 

p 

p 

p 

p 

p 

p 

p 

p 

p 

p 

(TO= 345m) 

Figure 2. Generalized east-west transects of cores showing lithology, geophysical logs, and age indicators. (A) Cross section A- A', northern transect; (B) cross section B-B', southem transect; symbols used in cross sections are indicated on key. 

~ VJ 

~ >-3 

VJ 

\0 
10 AGE AND DIAGENESIS OF THE UPPER FLORIDAN AQUIFER IN SW. FLA. 

0.5mm 0.5mm 

0.5mm 0.5mm 

1 mm 

Figure 3. See caption on facing page. 
RESULTS 11 

0.5mm 

Figure 3. Plane-polarized-light optical photomicrographs of 

diagenetic textures. (A) W-16782, 70.2 m, micritized foraminifer 

with intraparticle calcite cement (arrow) in porosity (p). (B) W16814, 193.1 m, blocky calcite cement predates shell dissolution 

and nearly fills primary porosity over geopetal infilling of 

leached bivalve, matrix is micrite. (C) W-11946, 57.1 m, mollusk moldic porosity (p) is partially filled with postdissolution 

blocky calcite (arrow); dark micrite matrix holds quartz (white) 

and phosphate (speckled) grains; small dolomite rhombs occur in 

this sample but are not visible in this view. (D) W-12050, 182.9 

m, echinoid spine and fragments (arrows) with syntaxial calcite 

overgrowths into interparticle porosity (p ); fine calcite rim 

cement coats other grains. (£) W-16814, 122.6 m, fossil moldic 

porosity (p), (probably a benthic foraminifer) lined with limpid 

(inclusion-free) dolomite (arrow), matrix is brown dolomicrite, 

white grains are fine quartz sand. (F) W -17000, 126.4 m, sandy 

dinocyst assemblages from three depths indicates the following ages: (1) 24.9 m, middle Miocene, or slightly 

younger; (2) 38.1 m, early to middle Miocene; (3) 187.8-

187.9 m, latest early Oligocene or earliest late Oligocene 

(the Globoratalia opima opima zone). The shallowest 

dinocyst assemblage indicates that the beds referred to in 

the field as the "Venice clay" (L. Barr, oral communication), 

is middle Miocene or slightly younger and is a part of the 

Arcadia Formation. Molluscan data from W-16814 indicate 

that the Oligocene-Miocene boundary may be crossed 

between 97.7 and 102.7 m depth. Turritella cf. T. tarponensis Mansfield, 1937, found at 97.7 m, and Turritella aff. T. 

pagodaeformis Heilprin, 1887, found at 97.8 m, resemble 

species generally considered to be early Miocene (Heilprin, 

1887; Mansfield, 1937). Turritella cf. T. tampae Heilprin, 

1887, was found from 100.6 to 101.5 m; T. tampae has long 

been considered early Miocene on the basis of its occurrence in the interval now designated the Tampa Member of 

the Arcadia Formation (Heilprin, 1887; Dall, 1892; Mansfield, 1937; Cooke, 1945), but a revision in age of the 

Tampa Member considered herein would lower the range of 

Turritella tampae into the late Oligocene (this agrees with 

the observations of Ward, 1992, p. 119-120). Turritella cf. 

dolostone with partially filled molds of two echinoderm plates 

and other fossils, dolomite infilling at arrows is in optical continuity, but the echinoid has dissolved leaving a dolmicritic, 

microporosity filling of the original shell; white grains are quartz 

sand and silt; gray areas are dyed porosity-filling epoxy (p). (G) 

W-11946, 32.6 m, dyed epoxy-impregnated (forms gray background) claystone of palygorskite (confirmed by XRD) with 

floating etched dolomite (ed) rhombs; grains are quartz (white) 

and concentrically layered phosphate grains (speckled); dolomite 

rhombs show several etched layers (arrow, lower right). (H) W16784, 84.8 m, dolomicrite with leached phosphate grains (Ph, 

right arrow) that are white in the middle and dark around the 

margins, dyed porosity-filling epoxy is gray (p), matrix retains 

shape of the original phosphate clast; white botryoidal silica 

coats void surface (S, left arrow). 

T. bowenae Mansfield, 1937, was found at 103.0 m; T. 

bowenae is typical of the Suwannee Limestone (Mansfield, 

1937). A Trigoniocardia sp. from 118.4 m brackets that 

sample as Oligocene or younger (Keen, 1969). The most 

definitive mollusk was Turritella caelatura Conrad, 1848, 

found in samples from 197.9 to 200.9 m; this species has 

been reported only from the lower Oligocene (Vicksburgian) Mint Springs Formation of Mississippi (MacNeil and 

Dockery, 1984). The paleontologic samples analyzed at W16814 agree with the 87Sr/86Sr age estimates of 30.3 Ma 

(early Oligocene) for samples from 200.9 m and 26.8 Ma 

(late Oligocene) for samples from 118.4 m. 

Dinocyst assemblage data from the core at W -15168 

indicate an early to middle Miocene age for samples from 

both 18.3 m and 21.6 m; samples from 14.8 m and 20.1 min 

the Walton core also indicate an early to middle Miocene 

age. The molluscan species Turritella cf. T. tampae Heilprin, 1887, was found at 69.2 min the core at W-16782; at 

69 m the 87Srj86Sr age estimate is 26.0 Ma (late Oligocene), 

an age that is consistent with the revised range for Turritella 

tampae. In the core at W-16578, Turritella cf. T. tampae 

Heilprin, 1887, was found at 99.1 m, and Turritella cf. T. 

bowenae Mansfield, 1937, was found at 100.6 m. The 
12 AGE AND DIAGENESIS OF THE UPPER FLORIDAN AQUIFER IN SW. FLA. 

100 ~m 

Figure 4. SEM images of selected sample chips. (A) W-17000, 

156.8 m, micritized foraminifer; sample is all calcite. (B) W11946, 32.6 m, dolomite rhomb with zoned etching and fibrous 

palygorskite. (C) W-16784, 91.3 m, dolomite (d) with etched 

outer surface in a palygorskite matrix. (D) W-16814, 61.0 m, 

10 ~m 

intergrown dolomite rhombs with etched centers, no clays 

present. (E) W-16814, 82.9 m, dolomite rhombs (not etched) and 

fibrous palygorskite. (F) Walton, 80.2 m, opal-CT lepispheres 

resting on an etched phosphate grain not on image. 
RESULTS 13 

Table 4. Petrographic observations of diagenetic alteration processes 

[l=shell micritization; 2=shell dissolution; 3=equant calcite cement; 4=calcite overgrowths on echinoid pieces; 5=dolomite; 6=dolomite replacement of, or 

overgrowths on, echinoid pieces; 7=etched dolomite; 8=phosphate grain dissolution; 9=amorphous silica cement] 

Sample 2 3 4 5 6 7 8 9 

W-11946 

32.6 ........... X X X X X X X 

57.1 ........... X X X X X 

140.3 ........... X X X 

W-12050 

64.1 ........... X X X X 

92.7 ........... X X X 

135.4 ........... X X X X 

162.0 ........... X X X X X 

182.9 ........... X X X X 

Walton 

27.5 ........... X X X X X 

80.2 ........... X X 

W-17000 

88.8 ........... X X 

94.6 ........... X X X X X X 

117.8 ............ X X X 

123.0 ........... X X X X 

126.5 ........... X X X X X X 

146.2 ........... X X X X 

156.8 ........... X X X X 

168.7 ........... X X X X 

175.7 ........... X X X X 

194.7 ........... X X X X 

210.4 ........... X 

W-16782 

30.6 ........... X X X X 

39.0 ........... X X X X X 

57.3 ........... X X X X X 

70.2 ........... X X X X 

74.9 ........... X X 

87.6 ........... X X 

occurrence of Turritella cf. T. tampae and T. cf. T. bowenae 

within a few meters of each other was seen at W -16814 as 

well as at W-16578 and may prove to be a significant biostratigraphic marker. Turritella cf. T. halensis Dall, 1917, 

was found at 270.4 min W-16578 and at 70.7 m, 73.2 m, 

and 87.5 m in W-15303. Dall (1917) found Turritella 

halensis at Hale landing on the Flint River, Georgia; the age 

of these deposits has been placed from early Oligocene to 

early Miocene (Dall, 1917; Cooke, 1935; Cooke, 1959). 

Mansfield identified Turritella cf. T. halensis from the 

Suwannee Limestone near the type area. 

Sample 2 3 4 5 6 7 8 9 

W -16782-continued 

97.7 ............ X X X 

108.1 ............ X X 

122.6 ............ X 

126.3 ............ X 

154.3 ............ X 

171.7 ............ X X X 

176.4 ............ X 

W-16784 

52.5 ............ X X X 

62.7 ............ X 

84.8 ............ X X X X X X 

91.3 ............ X X 

95.6 ............ X X X 

103.2 ............ X X X X 

114.1 ............ X X X 

121.1.. .......... X X X 

216.1.. .......... X X X X 

265.0 ............ X X 

321.5 ............ X 

W-16814 

24.9 ............ X X X X 

61.0 ............ X X X X 

69.5 ............ X X X X X 

73.2 ............ X X X 

82.9 ............ X X X 

106.0 ............ X X X 

122.6 ............ X X X X 

136.6 ............ X X X 

146.4 ............ X X 

149.7 ............ X X X X 

157.3 ............ X 

193.1.. .......... X X X X 

LITHOLOGY AND MINERALOGY 

The cores examined are characterized by carbonate 

sequences that span several tens of meters, and interbedded 

carbonates and siliciclastics from less than a meter to tens 

of meters thick (figs. 2A and 2B). The limestones are mainly 

mudstones, wackestones, and packstones (classification of 

Dunham, 1962), commonly with phosphatic minerals 

(mainly hydroxyfluorapatite, collectively called "phosphate" in this paper), and quartz sand and silt. Many locally 

dolomitized limestones retain the original limestone 
14 

A 

8 

AGE AND DIAGENESIS OF THE UPPER FLORIDAN AQUIFER IN SW. FLA. 

West 

Sea 

level 

50 

100 

~ 150 

Q) 

-

Q) 

~ 200 

250 

300 

350 

West 

Sea 

level 

50 

100 

~ 150 

Q) 

-

Q) 

~ 200 

250 

300 

350 

EXPLANATION 

I Dolomite 

D Palygorskite/sepiolite 

Aquifer system boundary 

Palygorskite/sepiolite data 

unavailable 

"Suwannee" Limestone 

EXPLANATION 

I Dolomite 

0 Palygorskite/sepiolite 

Aquifer system boundary 

Palygorskite/sepiolite 

data unavailable 

Mineralogical data 

unavailable 

Avon Park Formation 

W-17000 East 

Avon Park 

Formation 

Intermediate 

aquifer 

system 

Upper Floridan 

aquifer (of the 

Floridan aquifer 

system) 

East 

D 

Intermediate 

aquifer 

system 

Upper Floridan 

aquifer (of the 

Floridan aquifer 

system) 
RESULTS 15 

Table 5. Water chemistry of the intermediate aquifer system and Upper Floridan aquifer, west-central Florida 

[m=meter; ppm=parts per million; IAS=intermediate aquifer system; LIA=lower intermediate aquifer; UIA=upper intermediate aquifer; UFA=Upper 

Floridan aquifer] 

Open Interval Saturation index 

Stratigraphic units3 

Name County Latitude Longitude Elevation Depth Field1 Mg++j Cl- Aquifer2 (Scott, 1988) 

North West (m) (m) pH ca++ (ppm) Calcite Dolomite 

ID 01 (TRG WELL TB3) .. DeSoto 27°15'12" 81°34'47" 27.5 28-92 8.20 0.316 148.0 lAS Arcadia ................ 0.989 1.839 

ID 02 (TRG WELL TB 1) .. De Soto 27°15'20" 81°39'42" 26.2 32-90 8.00 0.686 94.0 lAS Arcadia ................ 0.432 1.065 

ID 07 (GOLDEN "Suwannee"-

RAINBOW) .................. Manatee 27°18'02" 82°06'27" 22.6 153-467 7.60 0.428 17.0 UFA Avon Park (?) .. 0.373 0.735 

ID 08 (M.J. RANCH) ........ Manatee 27°18'12" 82°11'12" 16.8 153-244 7.50 0.362 11.0 UFA "Suwannee"-

Ocala(?) ......... 0.310 0.530 

ID 09 (ROMP 22) .............. Sarasota 27°18'13" 82°20'13" 10.7 72-83 7.55 0.627 150.0 L lA Arcadia ................ 0.245 0.640 

ID 11 (ROMP 22) .............. Sarasota 27°18'13" 82°20'13" 10.7 28-38 7.31 0.394 73.0 U IA Arcadia ................ 0.130 0.196 

ID 12 (AMOCO 1) ............ DeSoto 27°20'15" 81°39'29" 28.7 44-87 7.60 0.562 67.0 lAS Arcadia ................ --o.061 -0.015 

ID 24 (VERNA #7) ........... Sarasota 27°23'06" 82°18'27" 23.2 44-146 8.10 0.551 13.0 IAS-UFA(?) Arcadia ................ 0.712 1.525 

ID 25 (VERNA #19) ......... Sarasota 27°23'07" 82°17'18" 25.0 43-140 7.80 0.750 35.0 IAS-UFA(?) Arcadia-

"Suwannee" (?) 0.332 0.866 

ID 27 (VERNA 1A) .......... Manatee 27°23'56" 82°18'13" 25.0 126--146 7.30 0.500 10.0 IAS-UFA(?) Arcadia ................ --Q.065 --o.082 

ID 29 (COCA COLA) ....... Highlands 27°24'08" 82°23'25" 38.4 167-182 7.79 0.680 16.0 UFA "Suwannee" ......... 0.052 0.319 

ID 30 (PARKS D. WELL) Manatee 27°24'23" 82°05'19" 24.4 61-403 7.70 0.444 54.0 IAS-UFA Arcadia-Avon 

Park(?) ........... 0.427 0.882 

ID 31 (MANLEY FARMS) Manatee 27°26'43" 82°18'19" 24.7 61-305 7.20 0.569 13.0 IAS-UFA Arcadia-Ocala..... --o.087 0.074 

ID 32 (ROMP 032-2) ........ Manatee 27°28'14" 82°03'48" 31.7 171-183 8.80 0.524 20.0UFA "Suwannee" ......... 0.471 1.034 

ID 33 .................................. Highlands 27°29'20" 81°26'03" 40.3 171-430 8.30 0.325 6.4 UFA "Suwannee"-

Avon Park ....... 0.021 --o.079 

ID 34....... ... .. .. .... ... .. .. ..... .. .. Hardee 27°32'05" 81°49'20" 28.1 19-70 7.40 0.466 12.0 lAS Arcadia................ --o.372 --o.751 

ID 35 .................................. Hardee 27°32'12" 81 °37'22" 22.9 60-329 7.40 0.445 4.0 IAS-UFA Arcadia-Avon 

Park ................. --o.645 -1.259 

ID 36 .................................. Hardee 27°35'07" 81°44'47" 30.8 17-33 8.10 0.666 8.0 lAS Arcadia ................ 0.414 0.979 

ID 37 (AVON PARK) ........ Highlands 27°35'27" 81°31'08" 46.7 153-458 7.60 0.270 9.1 IAS-UFA Arcadia-Avon 

Park(?) . .. ......... --o.539 -1.299 

The following data are from Swancar and Hutchinson (in press): 

S&H1 (ROMP TR 3-1) .... Charlotte 26°56'38" 82°13'07" 2.1 183-189 7.48 0.718 410.0 UFA "Suwannee" ......... 0.098 0.437 

S&H2 (ROMP 10) ............. Charlotte 27°01'52" 82°00'28" 6.1 181-280 7.53 0.650 180.0 UFA "Suwannee" ......... 0.076 0.349 

S&H3 ................................. DeSoto 27°02'56" 8}047'28" 10.7 214-275 7.70 0.560 340.0 UFA "Suwannee" ......... 0.211 0.580 

S&H4 (ROMP TR 5-2) .... Sarasota 27°09'19" 82°23'42" 4.6 156--214 7.10 0.292 44.0UFA "Suwannee" ......... 0.188 0.234 

S&H5 (ROMP 16) ............. DeSoto 27°11'15" 81°46'27" 18.3 231-287 8.60 0.575 39.0 UFA "Suwannee" ......... 0.995 2.157 

S&H6 (ROMP 26) ............. De Soto 27°17'57" 81 °49'30" 22.9 177-403 7.45 0.520 14.0 UFA "Suwannee"-

Avon Park ...... 0.166 0.472 

S&H 10 (Zolfo Springs 1). Hardee 27°29'44" 81°47'40" 19.8 107-305 7.45 0.478 17.0 UFA "Suwannee"-

Avon Park ....... 0.082 0.252 

1 Lab pH used for S&H1, S&H2, S&H6, S&H 10. 

2 Aquifer penetrated is estimated from Buono and Rutledge, 1979. 

3 Stratigraphic unit penetrated is estimated from data in Scott (1988, and written communication, 1993) and Johnson (1986); Arcadia, Arcadia Formation; "Suwannee," 

"Suwannee" Limestone; Avon Park, Avon Park Limestone; Ocala, Ocala Group. 

~ Figure 5. Distribution of magnesian minerals in cores. 

Approximate depth intervals of the intermediate aquifer system 

and the Upper Floridan aquifer of the Floridan aquifer system 

are indicated on the right. Dolomite occurrence, detected 

within at least 5 m vertically by XRD, is indicated on the left of 

cores; sepiolite and palygorskite occurrences are shown on the 

right of cores. (A) Transect A-A' from figure 1; (B) transect BB' from figure 1; PR, Peace River Formation; T, Tampa Member of the Arcadia Formation. Magnesian minerals are more 

abundant and are found in more of the section to the west and 

south. 

textures at the macroscopic scale and, in some places, relatively unaltered shell material still exists. 

Limestone and dolomite grade vertically and, we 

assume, laterally in the study area into quartz sandstone and 

mudstone. The mudstone is composed mainly of quartz silt, 

illite-swectite mixed layer clay, illite, and the fibrous magnesian clays, sepiolite and palygorskite, and forms beds that 

are a few centimeters to tens of centimeters thick. In addition, magnesian clays form a significant component of the 

fine-grained carbonate rocks (see table 4). 
16 AGE AND DIAGENESIS OF THE UPPER FLORIDAN AQUIFER IN SW. FLA. 

Quartz sandstone with variable amounts of phosphate 

grains is cemented by calcite or dolomite and is present in 

zones as thick as 60 m (W-16782). Quartz sand that is 

poorly consolidated or unconsolidated or sandstone that is 

cemented by silica is found mainly in beds less than 0.3 m 

thick. Silica-cemented quartz sand generally is accompanied by phosphate grains and a small proportion of detrital 

carbonate grains. Feldspar is a minor component of most 

sandstones. 

Phosphate is present primarily as shiny sand-size 

grains or small black, brown, tan, and off-white pebbles; a 

small portion is present as cement in hardgrounds. The 

grains include phosphatic bone fragments and teeth, phosphatized fossil invertebrate fragments, phosphate-cemented 

quartz sandstone, and phosphate-cemented sandstone and 

siltstone composed mainly of detrital carbonate grains. Thin 

sections reveal concentric structures in the phosphate 

grains. 

Brecciated zones a few centimeters to over 30 em thick 

with veinlike interstitial fillings were observed singly or in 

groups of several beds on the order of a meter apart vertically. These zones are especially notable in the Arcadia Formation. The broken bed lithologies and angular clasts are 

siliciclastic mudstone, limestone, or dolomite, and the interstitial filling is detrital quartz and phosphate silt, limestone, 

or dolomite. In some of the brecciated zones, patches and 

stringers of black to tan chert are evident. The chert has 

replaced carbonate and siliciclastic clay and, in places, has 

filled voids caused by dissolution of carbonates. Chert also 

occurs as thin beds (0.1-2 em thick) and irregular patches in 

nonbrecciated rock. 

Geophysical logs are presented here for the first time 

for four boreholes (Walton, W-16782, W-16814, and W17000) (figs. 2A and 2B). 

DIAGENESIS 

Nine diagenetic processes are tracked in thin sections 

to determine the timing and regional extent of diagenetic 

alteration of the rocks in the study area: ( 1) shell micritization, (2) shell dissolution, (3) precipitation of equant or 

blocky calcite cement in pore spaces, ( 4) syntaxial calcite 

overgrowths on echinoderm fragments, (5) precipitation of 

dolomite as a replacement of calcite or in pore spaces, ( 6) 

syntaxial dolomite replacement of echinoderm fragments 

and overgrowths, (7) partial dissolution of dolomite rhombohedra, (8) partial dissolution of phosphate grains, and (9) 

precipitation of amorphous silica in pore linings with local 

alteration to opal-CT and quartz (figs. 3 and 4; table 4). 

Shell micritization is one of the earliest diagenetic processes that affects the skeletal grains in the carbonates 

examined (figs. 3A and 4A); the shell structure is destroyed, 

but the shell shape is preserved. Micritization is observed in 

foraminifers, bryozoans, and red algae and is rare in echinoids and oysters. An early blocky calcite cement fonns a 

thin rind on grain and fossil surfaces in many samples, filling primary porosity in foraminifer chambers and articulated pelecypods (fig. 3B). This generation of calcite 

cement predates shell dissolution. Moldic porosity, the consequence of the dissolution of aragonitic and calcareous 

shells, also is common in most of the carbonates examined 

(fig. 3B), especially of the aragonitic mollusks and some 

soritid foraminifers. Dissolution of bryozoans, other foraminifers, ostracodes, calcitic molluscs (oysters and pectens), and red algae is less common; dissolution of 

echinoderm fragments is very rare. In many samples, a second generation of blocky calcite cement grows on the void 

surfaces (that is, on the cemented matrix material that 

packed around the fossil), rarely filling the void completely 

(fig. 3C). Syntaxial overgrowths of calcite are common on 

echinoid fragments, especially in packstones and grainstones, and extend into intergranular pore space and, in 

some cases, into nearby fossil molds (fig. 3D), indicating 

postdissolution precipitation. Shell micritization, shell dissolution, equant calcite cement, and calcite overgrowths on 

echinoderm fragments are observed at all depths in the 

cores examined and show no preferred depth or regional 

distribution (table 4). 

Dolomite occurs as pore-lining crystals (figs. 3£ and 

3F), as etched and nonetched rhombohedra (figs. 3G, 4B, 

4C, 4£, and 4F), as a replacement of calcareous fossils (red 

algae, foraminifers, bryozoans, and echinoderms) (see 

replaced echinoderm in fig. 3£), as syntaxial overgrowths 

on dolomitized echinoderm fragments, and as dolomicrite 

(fig. 3H). Dolomite is observed in three leached conditions: 

leached centers of rhombs (figs. 4£), leached zones (figs. 

3G and 4B), and etched surfaces (fig. 4C). Etched dolomite 

is observed only within the upper 95.8 m in the study area 

(table 4). 

Detrital phosphate grains are common constituents of 

both the siliciclastic and carbonate rocks examined. In most 

cases, several concentric zones that differ in color or texture 

can be seen in each grain (fig. 3G), indicating multiple generations of phosphate precipitation. Phosphate coatings are 

observed on fossil fragments, quartz grains, and cementing 

horizons or groups of grains. In a few samples, phosphate 

grains show evidence of leaching (fig. 3H); most examples 

are in the upper part of the undifferentiated Arcadia Formation, except at W-12050 and W-11946 where phosphate 

dissolution is observed in the Tampa Member. Most occurrences of amorphous silica, observed at the thin section 

scale, are associated with leached phosphate grains in the 

upper part of the undifferentiated Arcadia Formation (table 

4); however, occurrences are observed at W-17000 in the 

lower part of the undifferentiated Arcadia Formation and at 

W -16814 at the same stratigraphic horizon. Alteration of 

amorphous silica to opal-CT can be detected by XRD and 

observed only at the SEM scale, where it exhibits a fibrous 
DISCUSSION 17 

and bladed spheroidal habit (fig. 4G); these lepispheres 

were found only as cavity linings. 

Dolomite, palygorskite, and sepiolite are all magnesium-rich minerals and have very similar spatial distributions in the cores examined, as indicated by XRD analysis 

(figs. SA and 5B). Also, palygorskite and sepiolite typically 

occur with dolomite (figs. 3C, 3D, and 3F). These two magnesian silicate minerals are wispy and fibrous, and encase 

both etched and nonetched dolomite rhombs. At site W16814, the most southwesterly as well as the most pervasively dolomitized core in the study area, the limestones and 

siliciclastics are dolomitized down to 203 m (see fig. 5B). 

All three minerals are more pervasive and extend through a 

greater stratigraphic interval in the southern and western 

parts of the study area than in the north and east. In the 

intermediate aquifer system, magnesian minerals are common along both cross-sections, but their occurrence 

declines toward the east. In the Upper Floridan aquifer, 

magnesian minerals occur near the top of the aquifer in the 

central and western portion of the southern cross-section 

only and are nearly absent in the northern cross-section. 

MODERN GROUND-WATER CHEMISTRY 

Modem ground-water analyses from the files of the 

USGS, Tampa, from 18 wells are analyzed by WATEQF for 

calculation of SI values with respect to calcite and dolomite 

(Plummer and others, 1978) and combined with published 

data from 7 other wells (Swancar and Hutchinson, 1992; 

WATEQF was also used in their study) (table 5). Included in 

the table are well locations, elevation of wellhead, open 

depth interval below the land surface, stratigraphic interval 

sampled, assumed regional aquifer sampled, chloride content, magnesium-calcium ratios, field pH, and SI values for 

calcite and ordered dolomite. In the study, in general, wells 

open to the Hawthorn Group are in the intermediate aquifer 

system, and wells open to the "Suwannee" Limestone and 

Ocala Group are in the Upper Floridan aquifer, with some 

exceptions. 

The pH of the ground water is greater than 7.0 at all 

sites, a finding that indicates that reaction with the carbonate rocks has raised the pH from meteoric water values that 

are typically near 5.5. Most water samples are saturated 

with respect to calcite, indicated by a SI value within the 

interval -0.5 to +0.5. Exceptions are at sites 35 and 37, 

where the ground water is undersaturated, and sites 1 and 24 

and site S&H5 (Swancar and Hutchinson, in press), where 

the ground water is slightly supersaturated with respect to 

calcite. Ground water is supersaturated with respect to dolomite at sites 1, 2, 7, 9, 24, 25, 30, 32, 36, S&H3, and S&H5 

and undersaturated at sites 34, 35, and 37. 

DISCUSSION 

AGE OF THE DEPOSITS 

Chronostratigraphic information is critical to this study 

because of the lateral variation and vertical repetition of 

rock and sediment types within the subsurface of the study 

area. Biostratigraphic and isotopic data were gathered independently from lithostratigraphic data and from each other. 

This integrated method allows independent verification of 

published age ranges of mollusks, which are frequently tied 

to the strata in which they occur rather than to other primary 

chronostratigraphic indicators. The mollusks and dinocysts 

were initially identified, and ages were assigned based on 

reports in the published literature; the biostratigraphic data 

were integrated with age estimates based on 87 SrJ86Sr 

values. 

We note that good agreement exists between the biostratigraphic and isotopic ages despite the differences in time 

resolution. In general, the time estimates based on the strontium isotopic composition of unaltered shells are our best 

numerical time indicators, but they have an error of at least 

±1.5 m.y. This error is based on our assessment of the scatter of data reported in Miller and others ( 1991 ). Error in 

assigning age estimates to fossil ranges is more difficult to 

assess. Dinocyst assemblage data have a greater time resolution than individual species ranges of mollusks because 

dinocysts evolve more rapidly than mollusks and because 

assemblages, in general, have narrower time ranges than 

individual species. In the two places where fossils used for 

biostratigraphy and for isotopic dating were found close 

together (W-16814 at 200.9 m, and W-16782 at 69.2-70.1 

m) (figs. 2A and 2B), the ages estimates corroborate each 

other. It is significant also that multiple age indicators in 

single cores are in correct sequence with one exception (W16782 at 94.7 m and 96.7 m); that is, the numerical ages 

increase with depth. Therefore, we infer that the isotopic 

ages reflect the time of deposition of the strata from which 

the samples were taken, but we recognize that our data are 

sparse and require further corroboration from more closely 

spaced samples in individual cores. 

Age indicators provide us with a new basis for examination of the lithostratigraphy. The 87 Sr/86Sr analyses from 

the "Suwannee" Limestone in W-11946 and W-12050 support an early Oligocene age for the "Suwannee" Limestone. 

At the base of W -16814, both an early Oligocene strontium 

date and an early Oligocene Turritella at were found at 

::?.00.9 m, a few meters above the top of the "Suwannee" 

Limestone but within the lower undifferentiated part of the 

Arcadia Formation (T.M. Scott, written communication, 

1993). An early Oligocene age for the Arcadia Formation is 

anomalous and may be due to pervasive dolomitization in 

this core that has obscured the lithostratigraphic contact 

between the "Suwannee" Limestone and the Arcadia 

Formation. 
18 AGE AND DIAGENESIS OF THE UPPER FLORIDAN AQUIFER IN SW. FLA. 

The age indicators within the Arcadia Formation range 

from early Oligocene to middle, or earliest late, Miocene. 

For purposes of this discussion, the Arcadia can be broken 

into four parts: a lower undifferentiated part, the Nocatee 

Member, the Tampa Member, and an upper undifferentiated 

part. Age indicators found in the lower part of the undifferentiated Arcadia are early to late Oligocene (30.3 to 26.8 

Ma); age indicators within the Nocatee Member are late 

Oligocene (27 .1 to 26.3 Ma); age indicators within the 

Tampa Member range from late Oligocene to middle 

Miocene (27.9 to 18.9 Ma); and age indicators within the 

upper part of the undifferentiated Arcadia Formation range 

from late Oligocene to middle Miocene (28.6 to 16.7 Ma). 

Overlapping age ranges of the Tampa and Nocatee Members with the undifferentiated Arcadia Formation support 

Scott's (1988) assertion that the Arcadia Formation is composed of several coeval lithofacies, at least at this time 

resolution. 

We think it is significant that tens of meters of rock are 

late Oligocene in age in southern Florida. Although the 

rocks in the study area have not been rigorously dated in the 

past, the assumption often has been made that because of 

the regional low sea-level stand thought to occur during late 

Oligocene time (for example, Haq and others, 1987), the 

duration of the unconformity between the "Suwannee" 

Limestone and the Hawthorn Group spanned the late Oligocene, from about 30 to 25 Ma. 

87 Sr/86Sr from a mollusk very near the top of the Peace 

River Formation at W-12050 yields an age of 5.1 Ma. This 

age is nearly 10 m.y. younger than the shallowest age indicator within the underlying Arcadia Formation and, if correct, expands the duration of deposition of the Hawthorn 

Group sediments, as they are now defined, to approximately 

25 m.y. No definitive late Miocene fauna are observed or 

reported in the cores examined nor are there any numerical 

ages from strontium isotopic analyses between 6 and 

16 Ma. 

As more numerical and biostratigraphic information 

becomes available for several of the cores, it may be possible to delineate depositional units separated by shorter term 

local and longer term regional hiatuses. Mapping of 

regional hiatuses or unconformities will clarify some of the 

complex lithostratigraphic relationships. 

GEOPHYSICAL LOGS 

Geophysical logs, singly or in groups, are widely used 

for correlating lithologic contacts among boreholes in south 

Florida, particularly where cores are not available. Electric 

logs are particularly sensitive to porosity of rocks and composition of pore fluid; gamma logs reflect detrital or diagenetic concentrations of radioactive isotopes (Levine, 1988; 

Weinberg, 1991). In the study area, thick zones of relatively 

pure carbonates ("Suwannee" Limestone and Ocala Group) 

give a flat gamma signature, whereas alternating siliciclastics and carbonates in the Hawthorn Group give an irregular, spiky signature. In the new logs from W-17000, three·of 

the four lithostratigraphic contacts coincide with notable 

changes in geophysical signature in all three logs, and the 

fourth contact, at the top of the Arcadia Formation, is just 

above a change in the gamma log. 

REGIONAL DIAGENETIC ALTERATION 

The processes observed in thin sections indicate in 

many samples that the strata have been alternately saturated 

with a range of water chemistries, such that calcite or dolomite can precipitate in sites where calcareous fossils were 

previously leached. Also, many samples showed evidence 

for multiple generations of calcite or dolomite. Several of 

the processes documented are attributed to early marine and 

meteoric processes, are observed in nearly all rocks examined, and show no regional distribution, such as shell micritization by boring marine algae and perhaps boring sponges, 

as well (Bathurst, 1964) (figs. 3A and 4A). Meteoric water 

entering the aquifer systems in recharge areas typically has 

a pH in the 5--6 range and low total dissolved solids; therefore, it has the capacity to dissolve aquifer minerals and 

enhance porosity and permeability (Sprinkle, 1989). Consequently, with a sea-level drop and exposure to meteoric 

waters, all carbonate materials near the ground surface, 

especially the aragonitic mollusks, are susceptible to dissolution, and high-Mg calcite shells (echinoids, foraminifers, 

and red algae) are converted to low-Mg calcite, often with 

no loss of the details in shell structure (James and 

Choquette, 1983). Blocky calcite cements both pre- and 

postdate shell leaching and are generally attributed to 

precipitation from fresh water, with some exceptions (Folk, 

1974; Moore, 1989) (fig. 3C). The precipitation of syntaxial 

calcite overgrowths on echinoderm fragments, common at 

depths greater than 70 m in the study area, has been attributed to both shallow-marine phreatic diagenesis (Fiichtbauer, 1969) and to meteoric phreatic diagenesis (James and 

Choquette, 1984). 

Textural evidence supports a diagenetic origin for 

much of the dolomite as either the replacement of micrite 

and calcareous fossils or as precipitation in moldic porosity. 

Dolomite precipitation in carbonate and siliciclastic rocks 

of Florida and the Caribbean has been attributed by several 

authors to a mixing-zone process (Hanshaw and others, 

1971; Land, 1973; Folk, 1974; Folk and Land, 1975; Randazzo and Hickey, 1978; Morrow, 1982a, b). The mixingzone hypothesis states that the precipitation of slow-growing and well-formed, limpid rhombohedra of dolomite is 

facilitated in water chemistries with Mg/Ca ratios near 1 

and low ionic activity-conditions that are achieved with 

very dilute sea water in the subsurface mixing zone (Folk 

and Land, 1975). Commonly, water in the mixing zone is 
DISCUSSION 19 

saturated with respect to dolomite and undersaturated with 

respect to calcite, but the difference and magnitude of saturation indices of both minerals vary with calcium and magnesium concentrations and with C02 content (Wigley and 

Plummer, 1976). A case has been made, however, for dolomite precipitation from water that is closer in composition 

to sea water (Land, 1985; Cander, 1991). In both hypotheses, the source of magnesium is ultimately sea water; however, they differ in the timing and hydrology of the 

dolomitization process. 

Etched dolomite has been interpreted as a product of 

mixing-zone precipitation followed by meteoric dissolution 

of the more soluble, nonstoichiometric dolomite in the core 

(Randazzo and Cook, 1987). Evidence of dolomite replacement of calcite in our samples includes the growth of dolomite rhombs around calcite grains, dolomite rhombs 

floating in a calcite micrite matrix, and the replacement of 

fossils that were originally magnesian calcite, such as echinoderm fragments (fig. 3£) and red algae. 

The regional and depth distribution of the diagenetic 

processes shown in table 4 reflects the source and residence 

time of exposure to waters of different chemistries: meteoric water, marine water, and evolved formation water from 

both meteoric and marine sources. Early marine diagenetic 

features (micritization of shells and echinoderm fragment 

overgrowths) and meteoric diagenetic features (shell dissolution, equant calcite cement precipitation, and perhaps further growth of echinoderm fragment overgrowths) are 

present at nearly all depths in the sampled cores in both 

transects shown in figures 2A and 2B. Dolomite rhomb 

etching, in contrast, is observed only in the upper 96 m of 

cores examined, suggesting a surface-down process of dissolution from meteoric water. Whole dolomite rhombs 

observed at greater depths in the cores may be either healed 

or may never have been leached. 

Age indicators for the entire section suggest at least 

one large regional unconformity may be at the contact 

between the Arcadia and Peace River Formations. The 

duration of the unrecorded interval may be as great as 

10 m.y. This long period of exposure could have been 

responsible for the leaching of dolomite rhombs in the 

upper 96 m as well as the extremely leached condition of 

some phosphate grains within the Arcadia (fig. 3H). 

.The diagenetic features that we are attributing to either 

marine or a mixed marine and meteoric water processes 

(that is, the precipitation of limpid dolomite and dolomite 

replacement of echinoderm overgrowths and perhaps precipitation of magnesian clays) have an asymmetric spatial 

distribution that cross-cuts stratigraphy: they are more pervasive and stratigraphically more extensive in the southern 

transect and in the western parts of both transects (figs. SA 

and 5B). Limpid dolomite is observed down to the base of 

the Arcadia Formation in all cores examined in thin section 

and by SEM in the southern transect (W-16814, W-16782, 

and W-12050) but diminishes in depth and stratigraphic 

range, as defined by age indicator or lithostratigraphy, to the 

north and east. 

SOURCES OF DIAGENETIC WATERS 

Palygorskite and sepiolite are diagenetic minerals on 

the basis of their common association with dolomite and 

their delicate branching form (fig. 4B). Although the magnesian clays may have formed by direct precipitation from 

pore fluids at least in part (Callen, 1984; Esteoule-Choux, 

1984 ), it is unlikely that they formed in a sabkhalike environment; they are not found precipitating with carbonates in 

modem sabkhas such as Coorong, Australia (Callen, 1984). 

Much of the clay was probably formed by addition of magnesium to illite/smectite clay (Weaver, 1984). 

The large volume of diagenetic dolomite, palygorskite, 

and sepiolite, in the study area requires a significant source 

of magnesium. The largest source of nearby magnesium is 

the sea water of the Gulf of Mexico and the Atlantic Ocean. 

Water-quality data (table 5) show that both the intermediate 

aquifer system and the Upper Floridan aquifer, in the depths 

studied, are saturated with waters that have low chloride 

concentrations (< 150 parts per million, except in the far 

southern part of the study area) and low Mg/Ca ratios 

(<0.75), characteristic of fresh water. Therefore, none of the 

open intervals in wells for which we have water-quality data 

is currently in the coastal mixing zone or in saline ground 

water. The most reasonable mechanism for introducing 

magnesium into aquifer rocks is raising the sea level. 

Sea level has risen eustatically as much as 30.5-40 m 

above modem sea level since the Miocene (Dowsett and 

Cronin, 1990), and for at least 10 periods during the last 16 

m. y., sea level has been higher than at present. The highest 

sea level over this time span was probably during the period 

between 4 and 3 Ma (Webb and others, 1984). These high 

stands have been documented on the Atlantic Coastal Plain 

and in Florida by dating the marine deposits and in some 

cases by estimating the depth of water and the total uplift 

since deposition (Dowsett and Cronin, 1990; Krantz, 1991; 

McCartan and others, 1991). Maximum lowstands (drawdowns below modem sea level) since the middle Miocene, 

based mainly on evidence from o18o and on the distribution 

of vertebrates, were as low as -20 to -60 m (Wardlaw and 

Quinn, 1991), or possibly -100 to-175m (Pitman, 1978; 

Haq and others, 1987; for better fit with data from Florida, 

see Prentice and Matthews, 1988; Quinn and Matthews, 

1990; and Krantz, 1991 ). 

Another source of reactive fluids is upwelling water 

from the lower part of the Floridan aquifer system, which 

contains high concentrations of dissolved solids from contact with evaporite beds (Simms, 1984). That source seems 

unlikely, however, for the rocks of the intermediate aquifer 

system (primarily the Hawthorn Group) because the 

"Suwannee" Limestone, theoretically in the pathway of 
20 AGE AND DIAGENESIS OF THE UPPER FLORIDAN AQUIFER IN SW. FLA. 

upwelling saline waters in the study area, has very little 

dolomite. 

Magnesium and silica also can be derived through the 

dissolution of siliceous fossils, detrital clays (Altschuler and 

others, 1963; Weaver, 1984), and possibly volcanic ash. 

Diatoms and radiolarians are now rare in the study area 

rocks, but they are locally abundant in correlative units in 

northern Florida (Scott, 1983), South Carolina (Abbott and 

Andrews, 1979), Maryland (Andrews, 1988), and New Jersey (Andrews, 1987) and may have provided a source of silica. In the Yucatan peninsula of Mexico, sepiolite and 

palygorskite are alteration products of volcanic ash (Isphording, 1984), which also may have been present in Florida; 

volcanic debris is present in Oligocene and Miocene units 

in Mississippi and the Virgin Islands (May, 197 4; Lidz, 

1984). 

ROCKS AND WATER CHEMISTRY OF THE INTERMEDIATE 

AQUIFER SYSTEM 

The intermediate aquifer system is locally confined by 

marine clays and carbonates of the Hawthorn Group and 

comprises a vertically and horizontally anastomosing network of limestone, dolomite, clay, phosphatic clayey quartz 

sand, and calcite-cemented quartz sand. These lithologic 

facies have a wide range of hydraulic conductivities and 

consequently, an unpredictable hydraulic character (Duerr 

and others, 1988) that has a significant component of vertical recharge within the study area (Ryder, 1985). 

Seven of the wells listed in table 5 are open only in the 

intermediate aquifer system: 1, 2, 9, 11, 12, 34, and 36; 

three others, 24, 25, and 27, are open mainly in the intermediate aquifer system. Well locations, approximate flow 

paths (from potentiometric map of Mularoni, 1992), and SI 

values of the ground water with respect to calcite and dolomite are shown in figures 6A and 6B. Core locations from 

which mineralogical data are available are indicated. 

In general, ground-water flow is from the northeast to 

.the southwest from two potentiometric highs just north of 

Hardee and Manatee Counties. Water from sites 1 and 24 is 

supersaturated with respect to both calcite and dolomite. 

Water from sites 2, 9, 25, and 36 is supersaturated with 

respect to dolomite (though saturated with respect to calcite) and yields three zones where ground water is saturated 

with respect to dolomite: eastern De Soto County, along the 

border between Sarasota County and Manatee County, and 

at well 36 in northern Hardee County. Dolomite is very 

common in the rocks that constitute the intermediate aquifer 

system; however, nearly all dolomite observed in that 

aquifer is etched dolomite (table 4), strongly suggesting that 

the etched surfaces on dolomite rhombs are relict dissolution features and that the dolomite was probably not precipitated from modem ground water. In fact, etched dolomite is 

observed only within the intermediate aquifer system and 

no deeper. The one negative SI calculated from data from 

site 34, where the well is open from 19 to 62 m depth, suggests rapid infiltration by meteoric water, perhaps by way of 

sinkholes or other connections with the surficial aquifer. 

The flow directions indicated in figure 6B suggest that 

rocks that form the intermediate aquifer system from cores 

at W-12050, W-16782, Walton, W-16814, and W-11946 

are now in ground water that is supersaturated with respect 

to dolomite. Samples of the Hawthorn Group from the eastem cores, W-17000, W-12050, and W-11946, however, 

have much less dolomite than the cores examined from the 

same stratigraphic units further west (figs. 3A and 3B). Very 

little dolomite was detected in samples from W-12050, just 

down-flow from sites 1 and 2, where ground water has 

dolomite saturation indices of 1.839 and 1.065, respectively, 

also suggesting that dolomite may not be precipitating there 

now despite supersaturation. 

ROCKS AND WATER CHEMISTRY OF THE UPPER FLORIDAN 

AQUIFER 

The rocks of the Upper Floridan aquifer are mainly 

limestone and dolomite (Ocala Group, "Suwannee" Limestone, and some strata in the lower part of the Hawthorn 

Group in the western part of the study area). Fifteen wells in 

the study area are open in the upper portion of the Upper 

Floridan aquifer: Swancar and Hutchinson's (in press) sites 

(S&H) 1, 2, 3, 4, 5, and 6; and our sites 7, 8, 29, 30, 31, 32, 

33, 35, and 3T (table 5). The locations and SI values with 

respect to calcite and dolomite for these sites are shown in 

figures 6C and 6D. Core locations from which thin sections 

were made are indicated; sites S&H3 and our sites 29, 33, 

and perhaps 37, are in adjacent ground-water basins and are 

not considered in this discussion. 

Ground water, with the exception of that at site 35, is 

saturated with respect to calcite; note that site 35 is close to 

site 34, in the overlying intermediate aquifer system, and 

has an anomalously negative SI value for calcite. The water 

chemistry is consistent with the observation that pore-filling, equant calcite cement is common down to depths of 

more than 213 m in the upper portion of the Floridan aquifer system. Pore-filling calcite examined with SEM is 

smooth and unetched (fig. 4A). Analysis of trace elements 

and stable isotopes of calcite cements in the Upper Floridan 

aquifer, however, strongly suggests that they were precipitated very early and are probably not from modem water 

(Budd and others, 1993). 

The saturation indices for dolomite in all wells through 

the Upper Floridan aquifer, except sites 35 and 37, indicate 

saturation or supersaturation (fig. 6D). The highest values 

occur in a zone from southeastern Manatee County to central De Soto County; however, the most abundant dolomite 

observed in XRD data and in thin sections examined is in 

the west at W -16782, and W -16814, where SI values are 
DISCUSSION 21 

INTERMEDIATE AQUIFER SYSTEM FLOW PATHS 

Saturation indices for calcite 

lMAN.ATEE I I HARDEE --:-:-hHiGHLANDS ~ '\ .; 0 414 (36) 

""\)~""" _/ W-16784) (34J W-11~46 \~ --- • -0372 • 

'::-\- -0.065(27)+ .W-17000 

SARASOTA o 712 (24) + + 0.332 (25) 1J ( +O.T30/0.245 

A 

't\ 1) 

"~ Wa~to: 

~ W-16782 

DESOTO -0.061 

I 

! 

·w-12o5o 

\ W-1681r-4 ---I...----------··--~----- \~ 

Saturation indices for dolomite 

~.f'"MANATEE / 'HARDEE + 1 !HIGHLANDS e::t '\ /0.979 (36) 

,,r=.._., _/ .W-16784) (34/ W-119;46 .....-- -0751 • ' 0 -0.082 (27) + : \------++0.866(25) j .W-17000 

SARASOTA 1.525 (24) ----i 

~ I +0.196/0.640 DESOTO -0.015 (12t 

( ) + 1.839 (1) 

Walton 1.065 (2) +, • .W-15303 1 

• W-12050 

8 10 20 30 40 MILES 

10 20 30 40 KILOMETERS 

Figure 6. Maps of flow regimes and water chemistry of aquifer 

systems. (A) Flow paths within the intermediate aquifer system and 

saturated indices (SI) of ground water with respect to calcite; (B) 

Flow paths within the intermediate aquifer system and SI of 

ground water with respect to dolomite; (C) Flow paths within the 

Upper Floridan aquifer and SI of ground water with respect to calcite; and (D) Flow paths within the Upper Floridan aquifer and SI 

near saturation. Dolomite distribution was detected by XRD 

at core site W-15303 (fig. 1). 

Saturation indices often are tracked along groundwater flow paths constrained by potentiometric contours 

(Plummer, 1977; McCartan and others, 1992). Rising SI 

values along a flow path are interpreted as either continued 

dissolution along that path or mixing with water of a different chemistry. A rapid decline along a flow path in SI values 

indicates precipitation of the mineral in question. A similar 

line of reasoning can be applied to the data set for dolomite 

in the study area. If the generalized flow paths are correct, 

ground water appears to enter study area at or below 

saturation with respect to dolomite, to increase in SI values 

within the central part of the study area, and then to drop 

back down to near saturation near S&H4 in the southwest. 

UPPER FLORIDAN AQUIFER FLOW PATHS 

Saturation indices for calcite 

\ 

I HIGHLANDS -0.539 (37) + \ 

W-16784 -0.645 (35) + l + 0.021 (33) 

W-11946• ~ ~ 0.052 (29) 

.~ 

• + 0.471 (32) 

+ 0.074 (31) + 0.427 (30) 

\--SA_R_A_S-OT_A_I 

W-17000 0

·

310 (8

)+ DESOTO 0.166(S&H6) 

1 0.373 (7) + 

Walton---- 0.995 (S&H 5) + ! 

. 0.188~ W-16782 • W-15303 • W-12051° 

(S&H 4) • (S&H 2) 

\ • W-16814 0.076 0.211 (S&H 3) 

r '"" ._. + ·-+ .. ---.. --.. ··- _,. .. --'" 

c 

"(._ ~ 0.098 (S&H 1) 

·:.:~:-~ 

Saturation indices for dolomite 

JMANATEE HARDEE 1 HIGHLANDS ?:i:! -1.299 (37) + \ 

'\',<!3-v. W-16784 -1.259 (35) + l + -0.079 (33) 

\~ • + 1.034 (32) • '+ 0.319 (29) 

~:' +0.074(31) +0.882(30) W-11946 

\1 \"SARASOTA--·1 : ·w-n';;: ~\' 1

°· 530 (

8

)+ .fOE SOTO + 0.472 (S&H6) 

"' 0.735(7) i ~'\ 2.157(S&H5) + 4\. .walton ----l 

(sJJ~f .W-16782 ! •W-15303 • W- 1205~ 

\\W-16814 I )~~~ ) +0.5~~~----~-

;.. + 0.437 (S&H 1) 

D ,.,_~ 

of ground water with respect to ordered dolomite. Flow paths for 

the intermediate aquifer system are approximated from the potentiometric map of Mularoni (1992); flow paths for the Upper Floridan aquifer are approximated from potentiometric map in 

(Johnston and others 1980). Water chemistry from Swancar and 

Hutchinson (in press) indicated in table 5. 

The increase followed by decrease of SI for both minerals 

along the flow path suggests dissolution followed by precipitation, especially of dolomite. The distribution of dolomite within the upper portions of the Upper Floridan aquifer 

shown in figures 3A and 3B shows that dolomite does not 

become abundant along the cross-section from east to west 

until site W-15303, a short distance "down-flow" from the 

highest SI values for ground water with respect to dolomite. 

This observation raises the possibility that dolomite could 

be precipitating today from modem water approximately in 

the zone of upward leakage of the Upper Floridan aquifer in 

southwest Florida (Ryder, 1985), noted also by an increase 

in magnesium and calcium (table 5). 

In summary, most waters in both the intermediate aquifer system and the upper part of the Upper Floridan aquifer 
22 AGE AND DIAGENESIS OF THE UPPER FLORIDAN AQUIFER IN SW. FLA. 

are saturated with respect to calcite and dolomite. Rocks 

examined show evidence for numerous episodes of precipitation and dissolution of both minerals as well as dissolution of aragonite shells, strongly suggesting that many 

diagenetic alterations, especially dissolution of calcareous 

fossils and dolomite rhomb surfaces, are relicts of past 

water chemistries. The etched nature of dolomite in the 

intermediate aquifer system cQ ... existing with water near saturation with respect to dolomite suggests that the dolomite 

there is relict also. We think that this diagenetic history is 

best explained by repeated alternation of meteoric and 

marine water that occurs with sea-level oscillations, and 

magnesium-rich mineral diagenetic facies reflects the 

cumulative residence time of marine or mixed waters in the 

aquifer rocks. Also, in the western part of the study area, 

especially in the core at W-16814 where we have fairly 

good age and X-ray diffraction data, dolomitization is very 

extensive and may have obscured the lithostratigraphic contact between the "Suwannee" Limestone and the Arcadia 

Formation. Within the upper portions of the Upper Floridan 

aquifer, dolomite distribution coincides with declining SI 

values along presumed flow paths, and the possibility exists 

of volumetrically small amounts of modem dolomite precipitation. The multigenerational nature of much of the 

dolomite suggests a complex precipitation history; if dolomite precipitation is going on today, it is probably a small 

addition to dolomite precipitated at an earlier time. 

CONCLUSIONS 

Age indicators in the "Suwannee" Limestone in the 

study area are all early Oligocene. Because of the uncertainty of the age of the type section of the Suwannee 

Limestone as defined by Cooke and Mansfield (1936) and 

the lack of rigorous correlation between the rocks of the 

type section and the study area, we retain the usage of 

"Suwannee" in quotation marks as suggested by Scott 

( 1988). The Hawthorn Group, previously reported to be 

Miocene, is shown to range in age from late (possibly early) 

Oligocene to Pliocene on the basis of strontium isotopic 

ratios, mollusks, and dinocyst assemblage distributions. 

Age indicators in the strata suggest the following ages: the 

Arcadia Formation ranges in age from late (possibly early) 

Oligocene to middle or earliest late Miocene; the Nocatee 

Member of the Arcadia Formation is late Oligocene; the 

Tampa Member of the Arcadia Formation ranges in age 

from late Oligocene to early Miocene; the Peace River Formation is Pliocene. Extensive carbonate deposition appears 

to have taken place in the study area during the late Oligocene, conventionally thought to be a time of subaerial 

exposure and nondeposition across much of the Florida 

platform. 

Much of the diagenetic alteration of the aquifer rocks 

is early. Early calcite cementation of micrite matrix and 

internal porosity has preserved the shapes of leached fossils. 

Some dolomite cement preserves the shape of early leached 

aragonitic fossils. Dissolution of calcite and dolomite is 

consistent with dissolution from meteoric water. Modem 

aquifer water of meteoric origin, however, is saturated with 

respect to these two minerals. Therefore, dissolution must 

have occurred soon after deposition when the rocks were at 

very shallow depths where the ground water pH is closer to 

that of rain water. 

A magnesium-rich diagenetic facies characterized by 

dolomite, palygorskite, and sepiolite cross-cuts stratigraphy 

and may obscure stratigraphic boundaries. The magnesium 

minerals are more pervasive and extend through a greater 

stratigraphic interval in the western part of the study area. 

This distribution forms a diagenetic facies and may be due 

to the longer cumulative residence time of sea water near 

the coast during past sea-level fluctuations. Much of this 

dolomite has textures that suggest multiple generations and 

was probably precipitated prior to the establishment of the 

modem ground-water regime. High saturation indices for 

dolomite in the modem Upper Floridan aquifer water suggest, however, that some dolomite precipitation may be 

occurring now. 

We recognize that data presented here are sparse and 

allow only tentative age determinations. They are sufficient, 

however, to indicate a need for a reassessment of subsurface 

stratigraphy. The next phase of this project uses the same 

integrated approach outlined here but with more closely 

spaced samples to delineate more accurately the depositional and diagenetic facies of the Upper Floridan aquifer 

and intermediate aquifer system of southern Florida. 

REFERENCES CITED 

Abbott, W.H., and Andrews, G.W., 1979, Middle Miocene marine 

diatoms from the Hawthorn Formation within the Ridgeland 

Trough, South Carolina and Georgia: Micropaleontology, 

v. 25, p. 225-271. 

Altschuler, Z.S., Cathcart, J.B., and Young, E.J., 1964, Geology 

and geochemistry of the Bone Valley Formation and its phosphate deposits, west central Florida: Geological Society of 

America Annual Meeting Guidebook, field trip no. 6, 68 p. 

Altschuler, Z.S., Dwornik, E.J., and Kramer, H., 1963, Transformation of montmorillonite to kaolinite during weathering: 

Science, v. 141, p. 148-152. 

American Association of Petroleum Geologists, 1988, Correlation 

of the Gulf Coast region (F.A. Lindberg, ed.,): Tulsa, Okla., 1 

folded sheet in jacket. (Correlation of Stratigraphic Units of 

North America (COSUNA) Project.) 

Andrews, G.W., 1987, Miocene marine diatoms from the Kirkwood Formation, Atlantic County, New Jersey: U.S. Geological Survey Bulletin 1769, 14 p. 

---1988, A revised marine diatom zonation for Miocene strata 

of the southeastern United States: U.S. Geological Survey 

Professional Paper 1481, 29 p. 
REFERENCES CITED 23 

Bathurst, R.G.E., 1964, The replacement of aragonite by calcite in 

the molluscan shell, in Imbrie, J., and N.D. Newell, eds., 

Approaches to paleoecology: New York, Wiley, p. 357-376. 

Beck, B.F., and Sinclair, W.C., 1986, Sinkholes in Florida: an 

introduction: Sinkhole Research Institute Report 85-86-4, 

College of Engineering, University of Central Florida in 

cooperation with U.S. Geological Survey, Orlando. 

Berggren, W.A., Kent, D.V., Flynn, J.J., and Van Couvering, J.A., 

1985, Cenozoic geochronology: Geological Society of America Bulletin,v. 96, p. 1407-1418. 

Budd, D.A., Hammes, U., a.'ld Vacher, H.L., 1993, Calcite cementation in the upper Floridan aquifer: a modem example for 

confined-aquifer cementation models?: Geology, v. 21, 

p. 33-36. 

Buono, A., and Rutledge, A.T., 1979, Configuration of the top of 

the Floridan aquifer, Southwest Florida Water Management 

District and adjacent areas: U.S. Geological Survey 

Water-Resources Investigations Open-File Report 78-34, 1 

sheet. 

Buono, A., Spechler, R.M., Barr, G.L., and Wolansky, R.M., 1979, 

Generalized thickness of the confining unit overlying the 

Floridan aquifer, Southwest Florida Water Management District: U.S. Geological Survey Open-File Report 79-1171, 

1 sheet. 

Bush, P.W., and Johnston, R.H., 1988, Ground-water hydraulics, 

regional flow, and ground-water development of the Floridan 

aquifer system and in parts of Georgia, South Carolina, and 

Alabama: U.S. Geological Survey Professional Paper 

1403-C. 

Callen, R.A., 1984, Clays of the palygorskite-sepiolite group: 

Depositional environment, age and distribution, in Singer, A., 

and Galan, E., eds., Palygorskite-sepiolite, occurrences, genesis and uses: Developments in sedimentology 37: Amsterdam, Elsevier, p. 1-37. 

Cander, H.S., 1991, Dolomitization and water-rock interaction in 

the middle Eocene Avon Park Formation, Floridan aquifer: 

University of Texas, Austin, unpublished Ph.D. dissertation, 

172 p. 

Conrad, T.A., 1848, Observations on the Eocene formation, and 

descriptions of one hundred and five new fossils of that 

period, from the vicinity of Vicksburg, Mississippi; with an 

appendix: Academy of Natural Sciences of Philadelphia Journal, 2nd ser., v. 1, pt. 2, p. 111-134,4 plates. 

Cooke, C.W., 1935, Notes on the Vicksburg Group: Bulletin ofthe 

American Association of Petroleum Geologists, v. 19, n. 8, 

p. 1162-1172. 

---1945, Geology of Florida: Florida Geological Survey Bulletin, n. 29, p. 1-339. 

---1959, Cenozoic echinoids of eastern United States: U.S. 

Geological Survey Professional Paper 321, 106 p. 

Cooke, C.W., and Mansfield, W.C., 1936, Suwannee Limestone of 

Florida: Proceedings of the Geological Society of America 

for 1935, p. 71-72. 

Dall, W.H., 1892, Contributions to the Tertiary fauna of Florida: 

Transactions of the Wagner Free Institute of Science of Philadelphia, v. 3, pt. 2, p. 309. 

---1917, A contribution to the invertebrate fauna of the Oligocene beds of Flint River, Georgia: Proceedings of the U.S. 

National Museum, v. 51, n. 2162, p. 487-524, 6 plates. 

Dall, W.H., and Harris, G.D., 1892, Correlation papers-Neocene: 

U.S. Geological Survey Bulletin 84, 349 p. 

Dowsett, H.J., and Cronin, T.M., 1990, High eustatic sea level during the middle Pliocene: Evidence from the southeastern U.S. 

Atlantic Coastal Plain: Geology, v. 18, p. 435-438. 

Duerr, A.D., Hunn, J.D., Lewelling, B.R., and Trommer, J.T., 

1988, Geohydrology and 1985 water withdrawals of the aquifer systems in southwest Florida, with emphasis on the intermediate aquifer system: U.S. Geological Survey WaterResources Investigations Report 87-4529, 115 p. 

Dunham, R.J., 1962, Classification of carbonate rocks according 

to depositional texture, in Ham, W.E., ed., Classification of 

carbonate rocks: American Association of Petroleum Geologists Memoir 1, p. 108-122. 

Edwards, L.E., 1986, late Cenozoic dinoflagellate cysts from 

South Carolina, U.S.A., in Wrenn, J.H., Duffield, S.L., and 

Stein, R.A., eds., Papers from the First Symposium on Neogene Dinoflagellate Cyst Biostratigraphy: American Association of Stratigraphic Palynologists Contributions series 17, 

p. 47-58. 

---1991, Neogene and Pleistocene dinocysts of the Charleston, South Carolina, region, in Studies related to the Charleston, South Carolina, earthquake of 1886-Neogene and 

Quaternary lithostratigraphy and biostratigraphy: U.S. Geological Survey Professional Paper 1367-E, p. El-E9. 

Esteoule-Choux, J., 1984, Palygorskite in the Tertiary deposits of 

the Armorican massif, in Singer, A., and Galan, E., eds., 

Palygorskite-sepiolite, occurrences, genesis and uses: 

Developments in sedimentology 37, Amsterdam, Elsevier, 

p. 75-86. 

Folk, R.L., 1974, The natural history of crystalline calcium carbonate: effect of magnesium content and salinity: Journal of 

Sedimentary Petrology, v. 44, p. 40-53. 

Folk, R.L., and Land, L.S., 1975, Mg/Ca ratio and salinity: two 

controls overcrystallization of dolomite: American Association of Petroleum Geologists Bulletin, v. 59, p. 60--68. 

Friedman, G.M., 1959, Identification of carbonate minerals by 

staining methods: Journal of Sedimentary Petrology, v. 29, 

p. 87-97. 

Fiichtbauer, H., ed., 1969, Lithification of carbonate cements: Sedimentology, v. 12, 327 p. 

Gohn, G.S., 1988, Late Mesozoic and early Cenozoic geology of 

the Atlantic Coastal Plain: North Carolina to Florida, in 

Sheridan, R.E., and Grow, J.A., eds, The geology of North 

America, vols. 1-2, The Atlantic Continental margin: Geological Society of America, p. 107-130. 

Hanshaw, B.B., and Back, W., 1979, Major geochemical processes 

in the evolution of carbonate aquifer systems: Journal of 

Geology, v. 43, p. 287-312. 

Hanshaw, B.B., Back, W., and Deike, R.G., 1971, A geochemical 

hypothesis for dolomitization by groundwater: Economic 

Geology, v. 66, p. 710-724. 

Haq, B.U., Hardenbol, Jan, and Vail, P.R., 1987, Chronology of 

fluctuating sea levels since the Triassic: Science, v. 235, 

p.1156-1167. 

Hart, S.R., and Brooks, C., 1974, Clinopyroxene-matrix partitioning of K, Rb, Cs, and Ba: Geochemica et Cosmochimica 

Acta, v. 38, p. 1799-1806. 

Heilprin, A., 1887, Explorations on the west coast of Florida and 

in the Okeechobee wilderness: Transactions of the Wagner 
24 AGE AND DIAGENESIS OF THE UPPER FLORIDAN AQUIFER IN SW. FLA. 

Free Institute of Science of Philadelphia, v. 1, 134 p., 

18 plates. 

Herrick, S.M., and Vorhis, R.C., 1963, Subsurface geology of the 

Georgia coastal plain: Georgia Department of Mines, Mining 

and Geology Information Circular 25, 67p. 

Rodell, D.A., Mueller, P.A., and Garrido, J.R., 1991, Variations in 

the strontium isotope composition of seawater during the 

Neogene: Geology, v. 19, p. 24-27. 

Isphording, W.C., 1984, The clays of Yucatan, Mexico: a contrast 

in genesis, in Singer, A., and Galan, E., eds., Palygorskitesepiolite, occurrences, genesis and uses: Amsterdam, 

Elsevier, p. 59-73. 

James, N.P., and Choquette, P.W., 1983, Diagenesis 5. 

Limestones-introduction: Geoscience Canada, v. 10, no. 4, 

p. 162-180. 

---1984, Diagenesis 9. Limestones-the meteoric environment: Geoscience Canada, v. 11, no. 4, p. 161-194. 

Johnson, R.A., compiler, 1986, Shallow stratigraphic core tests on 

file at the Florida Geological Survey: Florida Geological Survey Information Circular No. 103, 431 p. 

Johnston, R.H., and Bush, P.W., 1988, Summary of the hydrology 

of the Floridan aquifer system in Florida and parts of Georgia, South Carolina, and Alabama: U.S. Geological Survey 

Professional Paper 1403-A, 24 p. 

Johnston, R.H., Krause, R.E., Meyer, F.W., Ryder, P.D., Tibbals, 

C.H., and Hunn, J.D., 1980, Estimated potentiometic surface 

of the Tertiary limestone aquifer system, southeastern United 

States, May 1980, U.S. Geological Survey Open-File Report 

80--406, 1 sheet. 

Joint Commission on Powder Diffraction Standards, 1974, 

Selected powder diffraction data for minerals, (1st ed.), 

Swarthmore, Pa., 833 p. 

---1981, Selected powder diffraction data for minerals, (supplement 1 ), Swarthmore, Pa., 463 p. 

Jones, D.S., MacFadden, B.J., Webb, S.D., Mueller, P.A., Rodell, 

D.A., and Cronin,T.A., 1991, Integrated geochronology of a 

classic Pliocene fossils site in Florida: Linking marine 

and terrestrial biochronologies: Journal of Geology, v. 99, 

p. 637-648. 

Jones, I.C., Vacher, H.L., and Budd, D.A., 1993, Transport of calcium, magnesium, and S04 in the Floridan aquifer, 

west-central Florida: Implications to cementation rates: Journal of Hydrology, v. 143, p. 455-480. 

Joyner, B.F., and Sutcliffe, H. Jr., 1976, Water resources of the 

Myakka River Basin area, southwest Florida: U.S. Geological 

Survey Water-Resources Investigations Report 76-58, 87 p. 

Katz, B.G., 1992, Hydrochemistry of the upper Floridan aquifer, 

Florida: U.S. Geological Survey Water-Resources Investigations Report 91-4196, 37 p. 

Keen, M., 1969, Superfamily Cardiacea, in Moore, R.C., ed., Treatise on invertebrate paleontology, part N, v. 2, Mollusca 6, 

Bivalvia, p. N583-N594. 

King, K.C., and Wright, R., 1979, Revision of the Tampa Formation, west central Florida: Transactions, Gulf Coast Association of Geological Societies, v. 29 p. 257-262. 

Krantz, D.E., 1991, A chronology of Pliocene sea-level fluctuations: The U.S. middle Atlantic Coastal Plain record: Quaternary Science Reviews, v. 10, p. 163-174. 

Land, L.S., 1973, Contemporaneous dolomitization of Middle 

Pleistocene reefs by meteoric water, N. Jamaica: Bulletin of 

Marine Science, v. 23, p. 64-92. 

---1985, The origin of massive dolomite: Journal of Geological Education, v.33, p. 112-125. 

Levine, B.R., 1988, Uranium isotope survey of the groundwater 

system in Lee County, Florida: Florida State University, Tallahassee, Fla., unpublished Masters thesis, 251 p. 

Lidz, B.H., 1984, Neogene sea-level change and emergence, St. 

Croix, Virgin Islands: Evidence from basinal carbonate accumulations: Geological Society of America Bulletin, v. 95, 

p. 1268-1279. 

MacNeil, F.S., 1944, Oligocene stratigraphy of southeastern 

United States: American Association Petroleum Geologists 

Bulletin, v. 28, n. 9, p. 1313-1354. 

MacNeil, F.S., and Dockery, D.T., 1984, Lower Oligocene gastropoda, scaphopoda, and cephlopoda of the Vicksburg Group 

in Mississippi: Mississippi Geological Survey, Bulletin, n. 

124, p. 51-52, plate 12. 

Mansfield, W.C., 1937, Mollusks of the Tampa and Suwannee 

Limestones of Florida: Florida Geological Survey, Bulletin, 

n. 15, 334 p. 

Martens, J.H.C., 1928, Beach sands between Charleston, South 

Carolina, and Miami, Florida: Geological Society of America 

Bulletin, v. 46, p. 1563-1596. 

Matson, G.C., and Clapp, F.G., 1909, A preliminary report of the 

geology of Florida with special reference to the stratigraphy: 

Florida Geological Survey 2nd Annual Report, p. 25-173. 

May, J.H., 1974, Wayne County geology and mineral resources: 

Mississippi Geological, Economic and Topographical Survey 

Bulletin 117, 293 p. 

McCartan, L., Duerr, A.D., and Hawkins, R.M., 1992, Magnesium-rich clay minerals in Tertiary carbonate rocks of southwestern Florida, in Gohn, G.S., ed., Proceedings of the 1988 

U.S. Geological Survey Workshop on the geology and geohydrology of the Atlantic Coastal Plain: U.S. Geological Survey 

Circular 1059, p. 121-128. 

McCartan, L., Muhs, D.R., Allmon, W., Portel, R., and Wingard, 

G.L., 1991, Ages of shorelines at the southern end of Lake 

Wales Ridge, Fla. [abs]: Program and abstracts, research conference on Quaternary coastal evolution, SEPM (Society for 

Sedimentary Geology) and IGCP Project 274, p. 66-67. 

McCartan, L., and Owens, J.P., 1991, Detrital heavy minerals in 

surficial sand of the Florida peninsula: Research conference 

on Quaternary coastal evolution field guidebook, SEPM 

(Society for Sedimentary Geology) and IGCP Project 274, 

p. 91-95. 

McCartan, L., and Rubin, M., 1991, Wet-dry cycles in southcentral Florida in last 26,000 years [abs.]: Geological Society 

of America Abstracts with Programs, v. 23, p. 99. 

Meyer, F.W., 1989, Hydrogeology, ground-water movement, and 

subsurface storage in the Floridan aquifer system in southern 

Florida: U.S. Geological Survey Professional Paper 1403--G, 

59p. 

Miller, J.A., 1986, Hydrogeologic framework of the Floridan aquifer system in Florida and in parts of Georgia, Alabama, and 

South Carolina: U.S. Geological Survey Professional Paper 

1403-B, 91 pages and 28 plates. 

Miller, K.G., Feigenson, M.D., Kent, D.V., and Olsson, R.K., 

1988, Upper Eocene to Oligocene isotope (87Srf86Sr, () 180, 
REFERENCES CITED 25 

813C) standard section, Deep Sea Drilling Project site 522: 

Paleoceanography, v. 3, p. 223-233. 

Miller, K.G., Feigenson, M.D., Wright, J.D., and Clement, B.M., 

1991, Miocene isotope reference section, Deep Sea Drilling 

Project site 608: An evaluation of isotope and biostratigraphic 

resolution: Paleoceanography, v. 6, p. 33-52. 

Moore, C.H., 1989, Carbonate diagenesis and porosity: Developments in sedimentology 46, Amsterdam, Elsevier, 338 p. 

Morrow, D.W., 1982a, Diagenesis 1. Dolomite-Part 1: The chemistry of dolomitization and dolomite precipitation: Geoscience Canada, v. 9, p. 5-13. 

---1982b, Diagenesis 2. Dolomite-Part 2: Dolomitization 

models and ancient dolostones: Geoscience Canada, v. 9, 

p. 95-107. 

Muhs, D.R., Szabo, B.J., McCartan, L., Maat, P.B., Bush, C.A., 

and Halley, R.B., 1992, Uranium-series age estimates of corals from Quaternary marine sediments of southern Florida, in 

Scott, T.M., and Allmon, W.D., eds., Plio-Pleistocene stratigraphy and paleontology of southern Florida: Florida Geological Survey Special Publication, p. 41-49. 

Mularoni, R.A., 1992, Potentiometric surface of the upper Florida 

1988, The lithostratigraphy of the Hawthorn Group 

(Miocene) of Florida: Florida Geological Survey Bulletin 59, 

148 p. 

Oslick, J.S., Miller, K.G., and Feigenson, M.D., 1992, Lower to 

middle Miocene 87Sr/86Sr reference section: Ocean Drilling 

Program hole 747 A: EOS, Transactions of the American 

Geophysical Union, v. 14, (supplement), p. 171-172. 

Oslick, J.S., Miller, K.G., Feigenson, M.D., and Wright, J.D., 

1994, Oligocene-Miocene strontium isotopes: Stratigraphic 

revisions and correlations to an inferred glacioeustatic record: 

Paleoceanography, v. 9, p. 427-443. 

Petuch, E.J., 1982, Notes on the molluscan paleoecology of the 

Pinecrest Beds at Sarasota, Florida, with the description of 

Pyruella, a stratigraphically important new genus (Gastropoda: Melogenidae): Proceedings Academy Natural Sciences of Philadelphia, v. 134, p. 12-30. 

Pitman, W.C., III, 1978, Relationship between eustacy and stratigraphic sequences of passive margins: Geological Society of 

America Bulletin, v. 89, p. 1389-1403. 

Plummer, L.N., 1975, Mixing of sea water with calcium carbonate 

ground water: Geological Society of America Memoir 142, 

p. 219-236. 

---1977, Defining reactions and mass transfer in part of the 

Floridan aquifer: Water Resources Research, v. 13, p. 801-

812. 

Plummer, L.N., Jones, B.F., and Truesdell, A.H., 1978, 

WAtEQF-A FORTRAN IV version of WATEQ, a computer 

program for calculating chemical equilibrium of natural 

waters (rev.): U.S. Geological Survey Water-Resources Investigations 76-13, 63 p. 

Powell, A.J., ed., 1992, A stratigraphic index of dinoflagellate 

cysts: British Micropalaeontological Society Publication 

Series, Chapman and Hall, London, 290 p. 

Prentice, M.L., and Matthews, R.K., 1988, Cenozoic ice volume 

history: Development of a composite oxygen isotope record: 

Geology, v. 16, p. 963-966. 

Puri, H.S., Yon, J.W., Jr., and Oglesby, W.R., 1967, Geology of 

Dixie and Gilchrist Counties, Florida: Florida Division of 

Geology Bulletin 49, 155 p. 

Quinn, T.M., and Matthews, R.K., 1990, Post-Miocene diagenetic 

and eustatic history of Enewetak Atoll: Model and data comparison, Geology, v. 18, p. 942-945. 

Randazzo, A.F., and Cook, D.J., 1987, Characterization of dolomitic rocks from the coastal mixing zone of the Floridan 

Aquifer, U.S.A.: Sedimentary Geology, v. 54, p. 169-192. 

Randazzo, A.F., and Hickey, E.W., 1978, Dolomitization in the 

Floridan aquifer: American Journal of Science, v. 278, 

p. 1177-1184. 

Randazzo, A.F., and Zachos, L.G., 1984, Classification and 

description of dolomitic fabrics of rocks from the Floridan 

aquifer, U.S.A.: Sedimentary Geology, v. 37, p. 151-162. 

Ryder, P.D., 1985, Hydrology of the Floridan aquifer system in 

west-central Florida: U.S. Geological Survey Professional 

Paper 1403-F, 63 p. 

Scott, T.M., 1983, The Hawthorn Formation of northeast Florida: 

Part I-the geology of the Hawthorn Formation of northeast 

Florida; Florida Bureau of Geology, Report of Investigation 

94, p. 1-43. 

---1988, The lithostratigraphy of the Hawthorn Group 

(Miocene) of Florida: Florida Geological Survey Bulletin 59, 

148 p. 

Simms, M., 1984, Dolomitization by groundwater-flow systems in 

carbonate platforms: Transactions-Gulf Coast Association 

of Geological Societies, v. 34, p. 411-420. 

Singer, A., and Galan, E., eds., 1984, Palygorskite-sepiolite, 

occurrences, genesis, and uses: Developments in sedimentology 37, Amsterdam, Elsevier, 352 p. 

Soller, D.R., and Owens, J.P., 1991, The use of mineralogic techniques as relative age indicators for weathering profiles 

on the Atlantic Coastal Plain, USA: Geoderma, v. 51, 

p. 111-131. 

Southeastern Geological Society, 1986, Hydrogeological units of 

Florida: Florida Geological Survey, Special Publication 28, 

9p. 

Sprinkle, C.L., 1989, Geochemistry of the Floridan aquifer system 

in Florida and in parts of Georgia, South Carolina, and 

Alabama: U.S. Geological Survey Professional Paper 1403-I, 

109p. 

Stover, L.E., 1977, Oligocene and early Miocene dinoflagellates 

from Atlantic Corehole 5/5B, Blake Plateau: American Association of Stratigraphic Palynologists Contributions series 

5A, p. 66-89. 

Stumm, W., and Morgan, J.J., 1981, Aquatic chemistry, (2nd ed.): 

New York, Wiley, 780 p. 

Sutcliffe, H., Jr., and Thompson, T.H., 1983, Occurrence and use 

of ground water in the Venice-Englewood area, Sarasota and 

Charlotte Counties, Florida: U.S. Geological Survey 

Open-File Report 8'2-700, 59 p. 

Swancar, A., and Hutchinson, C.B., in press, Chemical and isotopic composition and potential for contamination of water in 

the"Upper Floridan aquifer, west-central, Florida, 1986-89: 

U.S. Geological Survey Water-Supply Paper 2409. 

Tedford, R.H., and Hunter, M.E., 1984, Miocene marinenonmarine correlations, Atlantic and Gulf Coastal Plains, 
26 AGE AND DIAGENESIS OF THE UPPER FLORIDAN AQUIFER IN SW. FLA. 

north America: Palaeogeography, Palaeoclimatology, Palaeoecology v. 47, p. 129-151. 

Verteuil, L. de, and Norris, G., 1992, Miocene protoperidinacean 

dinoflagellate cysts from the Maryland and Virginia coastal 

plain, in Head, M.J., and Wrenn, J.H., eds., Neogene and 

Quaternary dinoflagellate cysts and acritarchs: Salt Lake 

City, American Association of Stratigraphic Palynologists 

Foundation, p. 391-430. 

Ward, L.W., 1992, Molluscan biostratigraphy of the Miocene, middle Atlantic Coastal Plain of North America: Virginia 

Museum of Natural History, Memoir no. 2, 159 p. 

Wardlaw, B.R., and Quinn, T.M., 1991, The record of Pliocene 

sea-level change at Enewetak Atoll: Quaternary Science, 

V. 10, p. 247-258. 

Watts, W.A., 1980, The late Quaternary vegetation history of the 

southeastern United States: Annual Review of Ecology and 

Systematics, v. 11, p. 387-409. 

Weaver, C.E., 1984, Origin and geologic implications of the 

palygorskite deposits of S.E. United States, in Singer, A., and 

Galan, E., eds, Palygorskite-sepiolite, occurrences, genesis, 

and uses: Developments in Sedimentology 37, Amsterdam, 

Elsevier, p. 39-58. 

Webb, P.N., Harwood, D.M., McKelvey, B.C., Mercer, J.H., and 

Stott, L.D., 1984, Cenozoic marine sedimentation and 

ice-volume variation on the East Antarctic craton: Geology, 

v. 12, p. 287-291. 

Webb, S.D., 1990, Historical biogeography, in Myers, R.L., and 

Ewel, J.J., Ecosystems of Florida, Orlando, Fla., University 

of Central Florida Press, p. 70-100. 

Weinberg, J.M., 1991, Evidence for valence of groundwater 

234uf238U A.R.'s [activity ratios], and uranium distribution in 

sediments, Lee County, Florida: Florida State University, Tallahassee, Fla., unpublished masters thesis, 146 p. 

Wigley, T.M.L., and Plummer, L.N., 1976, Mixing of carbonate 

waters: Geochimica et Cosmochimica Acta, v. 40, 

p. 989-995. 

Williams, G.L., and Bujak, J.P., 1985, Mesozoic and Cenozoic 

dinoflagellates, in Bolli, H.M., Saunders, J.P., and PerchNielsen, K., eds., Plankton stratigraphy, Cambridge, Cambridge University Press, p. 847-864. 


SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS 

Periodicals 

Earthquakes & Volcanoes (issued bimonthly). 

Preliminary Determination of Epicenters (issued monthly). 

Technical Books and Reports 

Professional Papers are mainly comprehensive scientific 

reports of wide and lasting interest and importance to professional 

scientists and engineers. Included are reports on the results of 

resource studies and of topographic, hydrologic, and geologic 

investigations. They also include collections of related papers 

addressing different aspects of a single scientific topic. 

Bulletins contain significant data and interpretations that are 

of lasting scientific interest but are generally more limited in scope 

or geographic coverage than Professional Papers. They include the 

results of resource studies and of geologic and topographic investigations, as well as collections of short papers related to a specific 

topic. 

Water-Supply Papers are comprehensive reports that present 

significant interpretive results of hydrologic investigations of wide 

interest to professional geologists, hydrologists, and engineers. 

The series covers investigations in all phases of hydrology, including hydrogeology, availability of water, quality of water, and use of 

water. 

Circulars present administrative information or important 

scientific information of wide popular interest in a format designed 

for distribution at no cost to the public. Information is usually of 

short-term interest. 

Water-Resources Investigations Reports are papers of an 

interpretive nature made available to the public outside the formal 

USGS publications series. Copies are reproduced on request unlike 

formal USGS publications, and they are also available for public 

inspection at depositories indicated in USGS catalogs. 

Open-File Reports include unpublished manuscript reports, 

maps, and other material that are made available for public consultation at depositories. They are a nonpermanent form of publication that may be cited in other publications as sources of 

information. 

Maps 

Geologic Quadrangle Maps are multicolor geologic maps 

on topographic bases in 7.5- or 15-minute quadrangle formats 

(scales mainly 1 :24,000 or 1 :62,500) showing bedrock, surficial, 

or engineering geology. Maps generally include brief texts; some 

maps include structure and columnar sections only. 

Geophysical Investigations Maps are on topographic or 

planimetric bases at various scales; they show results of surveys 

using geophysical techniques, such as gravity, magnetic, seismic, 

or radioactivity, which reflect subsurface structures that are of economic or geologic significance. Many maps include correlations 

with the geology. 

Miscellaneous Investigations Series Maps are on planimetric or topographic bases of regular and irregular areas at various 

scales; they present a wide variety of format and subject matter. 

The series also includes 7 .5-minute quadrangle photogeologic 

maps on planimetric bases that show geology as interpreted from 

aerial photographs. Series also includes maps of Mars and the 

Moon. 

Coal Investigations Maps are geologic maps on topographic 

or planimetric bases at various scales showing bedrock or surficial 

geology, stratigraphy, and structural relations in certain coalresource areas. 

Oil and Gas Investigations Charts show stratigraphic information for certain oil and gas fields and other areas having petroleum potential. 

Miscellaneous Field Studies Maps are multicolor or blackand-white maps on topographic or planimetric bases for quadrangle or irregular areas at various scales. Pre-1971 maps show bedrock geology in relation to specific mining or mineral-deposit 

problems; post-1971 maps are primarily black-and-white maps on 

various subjects such as environmental studies or wilderness mineral investigations. 

Hydrologic Investigations Atlases are multicolored or 

black-and-white maps on topographic or planimetric bases presenting a wide range of geohydrologic data of both regular and 

irregular areas; principal scale is 1 :24,000, and regional studies are 

at 1:250,000 scale or smaller. 

Catalogs 

Permanent catalogs, as well as some others, giving comprehensive listings of U.S. Geological Survey publications are available under the conditions indicated below from the U.S. 

Geological Survey, Information Services, Box 25286, Federal 

Center, Denver, CO 80225. (See latest Price and Availability List.) 

"Publications of the Geological Survey, 1879-1961" may 

be purchased by mail and over the counter in paperback book form 

and as a set of microfiche. 

"Publications of the Geological Survey, 1962-1970" may 

be purchased by mail and over the counter in paperback book fonn 

and as a set of microfiche. 

"Publications of the U.S. Geological Survey, 1971-1981" 

may be purchased by mail and over the counter in paperback book 

form (two volumes, publications listing and index) and as a set of 

microfiche. 

Supplements for 1982, 1983, 1984, 1985, 1986, and for subsequent years since the last permanent catalog may be purchased 

by mail and over the counter in paperback book form. 

State catalogs, "List of U.S. Geological Survey Geologic: 

and Water-Supply Reports and Maps For (State)," may be purchased by mail and over the counter in paperback booklet form 

only. 

"Price and Availability List of U.S. Geological Survey 

Publications," issued annually, is available free of charge in 

paperback booklet form only. 

Selected copies of a monthly catalog "New Publications of 

the U.S. Geological Survey" are available free of charge by mail 

or may be obtained over the counter in paperback booklet form 

only. Those wishing a free subscription to the monthly catalog 

"New Publications of the U.S. Geological Survey" should write to 

the U.S. Geological Survey, 582 National Center, Reston, VA 

22092. 

Note-Prices of Government publications listed in older catalogs, announcements, and publications may be incorrect. Therefore, the prices charged may differ from the prices in catalogs, 

announcements, and publications.