Citation
The Lithostratigraphy of Nassau County in relation to the superconducting supercollider site investigation ( FGS: Open file report 15 )

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Title:
The Lithostratigraphy of Nassau County in relation to the superconducting supercollider site investigation ( FGS: Open file report 15 )
Series Title:
( FGS: Open file report 15 )
Creator:
Scott, Thomas M
Florida Geological Survey
Place of Publication:
Tallahassee Fla
Publisher:
Florida Geological Survey
Publication Date:
Language:
English
Physical Description:
1 v. (unpaged) : ill., maps ; 28 cm.

Subjects

Subjects / Keywords:
Geology -- Florida -- Nassau County ( lcsh )
Superconducting Super Collider -- Planning ( lcsh )
Nassau County ( local )
City of Ocala ( local )
Greater Orlando ( local )
Alachua County ( local )
Duval County ( local )
City of Jacksonville ( local )
Phosphates ( jstor )
Geology ( jstor )
Geological surveys ( jstor )
Counties ( jstor )
Sediments ( jstor )
Genre:
bibliography ( marcgt )
non-fiction ( marcgt )

Notes

Bibliography:
Includes bibliographical references.
General Note:
Cover title.
Statement of Responsibility:
by Thomas M. Scott.

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
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The author dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law and all related or neighboring legal rights he or she had in the work, to the extent allowable by law.
Resource Identifier:
022028220 ( aleph )
22438903 ( oclc )
AHF9006 ( notis )

Full Text










State of Florida Department of Natural Resources Tom Gardner, Executive Director




Division of Resource Management
Jeremy Craft, Director




Florida Geological Survey
Walt Schmidt, State Geologist and Chief









Open File Report 15 The Lithostratigraphy of Nassau County in Relation
to the Superconducting Supercollider Site Investigation by

Thomas M. Scott


Florida Geological Survey Tallahassee, Florida 1987



































3 1262 04543 6259














LIB RARY




















THE LITHOSTRATIGRAPHY OF NASSAU COUNTY IN RELATION TO THE SUPERCONDUCTING SUPERCOLLIDER SITE INVESTIGATION








BY

Thomas M. Scott Florida Geological Survey







OPEN FILE REPORT NO. 15


1987






The Lithostratigraphy of Nassau County in Relation to the
Superconducting Supercollider Site Investigation INTRODUCTION

The State of Florida is currently conducting the initial site investigation in Nassau County for the proposed superconducting supercollider. Geologic parameters -tayed-a- key-role in the selection of several sites throughout the State. The final selection was made based on geological, environmental and socioeconomic factors with Nassau County being judged the most favorable location (Figure 1).

The Florida Geological Survey provided the initial site proposals

based on the geological data available from Survey publications, personnel and files. The Nassau County site was included based upon the occurrence of a thick confining section above the Floridan aquifer system, the lack of potentially cavernous-carbonates within the confining beds, and the existence of a surficial or shallow aquifer system that produces relatively limited quantities of water. The current Nassau County data base on file at the Florida Geological Survey is limited to lithologic samples from 30 wells (including 2 cores) and geophysical logs of 21 wells. These are listed in the appendicies.


STRUCTURE

Nassau County, the northeastern most county in Florida, lies on the

northern and northwestern flank of the Jacksonville Basin of the Southeast Georgia Embayment (Figure 2). The Jacksonville Basin represents a localized thickening of the stratigraphic section within the Southeast Georgia Embayment. Figure 1 indicates the relationship of the Nassau County area to the other major structural features in Florida.




























































I /
A







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-I


Study area and location of cross-section


Figure 1















0


-JACKSONVILLE


NASSAU NOSE


N


0 50 100 MILES

SCALE


"p


Structures affecting the Hawthorn Group


Figure 2






No faults have been recognized or postulated to occur in the county. Leve (1966.) and Fairchild (1977) suggested the existence of faults in Duval County. If these faults exist, they do not appear to have cut through the Hawthorn Group sediments indicating that they have not been active since at least the late Middle Miocene.


Topography and Geomorphology

The topography of the Nassau County area characteristically consists of higher elevations with greater relief in the western one third of the county and lower elevations and little relief in the remaining area. The western area has elevations of as much as 107 feet above MSL near Boulogne; however, the average elevation in this area ranges from 70 to 80 feet above MSL. The lowlands surrounding the St. Marys River, generally the lowest points in the area, range in elevation from near 50 feet above MSL in the southwest to less than 5 feet above MSL along the northern boundary of the county. The eastern two-thirds of the county average less than 25 feet above MSL with the lowlands generally below 10 feet above MSL.
The topographic quadrangles covering Nassau County include, from west to east: Folkston, Boulogne, Kings Ferry, Kingsland, Toledo, Hillard, Hillard NE, Gross, St. Marys, Fernandina Beach, St. George, Hillard SW, Callahan, Italia, Hedges, Amelia City, McClenny NE, Bryceville, and Di nsmore.
Nassau County lies in the Northern or Proximal Zone of White (1970). The high areas of the western part of the county are part of the Duval Uplands. Most of the remainder of the county falls in the St. Marys Meander Plain. The east coast of Nassau County, the "Sea Islands", are part of the Atlantic Beach Ridges and Barrier Chain (Figure 3).


-Lj





















ST. MARY'S RIVER


DUVAL UPLAND


GEORGIA


jX ATLANTIC OCEAN




ST. MARYS MEANDER PLAIN



SCALE
o 5 10 15 20 25 Mi 0 8 16 24- 32 40Km


Geomorphology of Nassau County


GEORGIA


Figure 3






L ITHOSTRATIGRAPHY

Thin lithostratigraphic discussion of the supercollider site in Nassau County is limited to the carbonates of the upper part of the underlying Floridan aquifer system, the mixed carbonates and siliciclastics of the intermediate confining system and the sediments of the surficial or shallow aquifer system. This includes the Upper Eocene Ocala Group, the Miocene

Hawthorn Group, the Pliocene Nashua Formation, and the undifferentiated Plio-Pleistocene and Holocene sediments (Figure 4). Total thickness of these sediments ranges from 400 to 500 feet within the county. Construction of the proposed supercollider will most likely occur in the upper 150 feet of this section within the Hawthorn Group.


Ocala Group
The Ocala Group consists of very pure limestones with limited occurrences of thin dolostone near the base of the group. The limestones are

characteristically calcarenitic with varying amounts of carbonate mud in the matrix (grainstone to packstone). The grains are composed of fossil fragments, foraminifera, and biogenic debris. The limestones are generally tan or very light brown to white and range from soft, poorly consolidated to hard, well indurated and recrystallized. The dolostones are hard, generally well indurated, gray to moderate brown and crystalline.

The Ocala Group occurs throughout the county at elevations ranging
from approximately 400 feet below mean sea level (MSL) in the western portion to greater than 500 feet below MSL along the east coast, dipping in a general west to east direction (Leve, 1966) (Figure 4). The thickness of the Ocala Group in this area ranges from approximately 350 feet to greater than 500 feet, thickening from west to east (Leve, 1966). Cooke (1945), Vernon (1951), Herrick and Vorhis (1963), Purl land Vernon (1964) and

Stringfield (1966) provide more information on the Ocala Group. The rela-






































Figure 4 Lithostratigraphic units of the Hawthorn Group
In north Florida






tionship of the Ocala Group to the overlying sediments can be seen in Figures 6 and 7.

The carbonates of the Ocala Group are part of the upper Floridan aquifer system and are capable of producing vast quantities of water. Leve (1q66) indicates flow rates measured in zones of the Ocala Group often exceeded 3,000 gallons per minute. The sediments of the Floridan aquifer system will not be encountered during the construction of the supercollider. The construction activity will be separated from the Floridan aquifer system by as much as 300 feet of low permeability to relatively impermeable sediments of the Hawthorn Group.


Hawthorn Group

The Hawthorn Group sediments represent a dramatic deoosltional change from the carbonates of the Eocene (Oligocene is absent) to the siliciclastic dominated section in the Miocene. The Miocene sediments exhibit tremendous variability both laterally and vertically. In a general sense, the Hawthorn sediments contain more carbonate beds in the lower portion of the section. Carbonates decrease in abundance higher in the section. Research by Scott (1987) in Florida and Huddlestun (1987) in Georgia provides the lithologic framework and formational breakdown of the Hawthorn Group in this area. In ascending order the formations include: the Penney Farms/Parachucla Formations, the Marks Head Formation and the Coosawhatchie Formation including the Charlton Member (Figure 4). These units are recognized in cores (Figure 7). However, in well cuttings it is difficult to seperate the units due to the loss of fine grained sediments and the inclusion of material caving from above. If enough core control is available, cuttings can be utilized in a detailed study. The data pre-













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CLAY HAWTHORN GROUP SAND CALCITE CALCITE CHARLTON MEMBER CALCITE


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PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE
PHOSPHATE PHOSPHATE
PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHAIE
PHOSPHATE

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PHOSPHATE PHOSPHATE PHOSPHATE
PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE PHOSPHATE
PHOSPHATE PHOSPHRT? PHOSPHATE MANO SEASO tOLAITE
PHOSPHATE DOLOMITE PHOSPHATE SOLOAIE




PHOSPHATE OSLOMITS PHOSPHATE DOLOMITE 0OLO1TE CLAY


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CRYSTAL RIVER FORMATION


Reference core for the Charlton Member of the Coosawhatchie Formation, Cassidy #1, Nassau County (Lithologic legend Appendix 8)


........


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sented below on the formations of the Hawthorn Group is excerpted from Scott (08 7) with only minor changes.

Penney Farms/Parachucla Formation

The Penney Farms Formation, introduced by Scott (1987), occurs throughout much of northern Florida as a subsurface unit (Figures 3 and 4). It is the lateral equivalent of the Parachucla Formation in southeastern Georgia as defined by Huddlestun (1987). The facies transition between the Penney Farms and the Parachucla occurs in northern Nassau County and into Charlton and Camden counties, Georgia. As a result, cores taken in Nassau County may contain either Penney Farms or Parachucla. The primary difference between the two units is the amount of carbonate present as discreet beds, with the Penney Farms containing more carbonate.

The carbonates are variably quartz sandy, phosphatic, clayey dolostones. Sand content is variable to the point that the sediment may become a dolomitic sand. Phosphate grains may comprise twenty-five (25) percent or more with an average of approximately five (5) to ten (10) percent. Clay percentages are generally minor [below five (5) percent] but often increase in the dolostones of the upper portion of the formation. The dolostones are medium gray to pale yellowish brown. They are generally moderately to well indurated and finely to coarsely crystalline in the lower part. The dolostones of the upper portion are generally less indurated. Thicker, more massive beds predominate in the lower zone while thinner beds are most common in the upper section. Mollusk molds are common in the dolostones, particularly in the more coarsely crystalline

type.

Zones of intraclasts are common in the hard, finer grained dolostones of the lower part of the Penney Farms. The intraclasts are composed of dolostone that is essentially the same as the enclosing matrix. The







intraclasts are recognizable due to a rim of phosphate replacement along the edges of the clasts. Edges of the clasts vary from angular to subrounded indicating very little to no transport of the fragments. They also may 'e bored, indiating at.'least a semi-lithified state prior to being redeposi ted.

Limestone, in the basal portion of the Penney Farms Formation, occurs sporadically. When it does occur, it is generally dolomitic, quartz sandy and phosphatic.

The quartz sands are fine to coarse grained, moderately to poorly

sorted, variably phosphatic, dolo.mitic, silty and clayey. The phosphate grain content varies considerably, sometimes to the point of being classified as phosphorite sand [fifty (50) percent or greater phosphate grains]. In general, however, the phosphate grain content averages between five (5) and ten (10) percent. The sands are typically olive gray or grayish olive to medium light gray. Clay content varies considerably in the sands.

Clay beds in the Penney Farms Formation are typically quartz sandy,

phosphatic, silty and dolomitic. The proportions of the accessory minerals vary from nearly zero to more than fifty (50) percent. Nearly pure clay beds are uncommon. Dolomite is very common in the clays, often being the most abundant accessory mineral. Olive gray and grayish olive green colors generally predominate, but colors may range into the lighter shades. Smectite typically dominates the clay mineralogy of this unit, with palygorskite, illite and sepiolite also present. X-ray analyses by Hetrick and Friddell (1984) indicate that palygorskite may become predominant over smectite in some samples. Reik (1982) indicated that palygorskite dominates in the lower part of the Penney Farms while smectite dominated in the upper portion in Clay County. Other minor mineralogic constituents include







-mica, K-feldspar and opal-ct. Clinoptilolite has been identified ih a few sampl es.

When abundant silt-sized, unconsolidated dolomite occurs, difficulty arises in.determining whether the actual rock type is a very dolomitic clay or a very clayey dolostone. Insoluble residue analysis is the only accu-. rate method of determining the clay and dolostone contents. Rough analysis indicates that, in general, the lighter the color of the sediment, *the higher the dolomite content. This method was employed:for determining the sediment type in these situations.
The clastic beds of the Penney Farms Formation are lithologicaly very similar to those in the Parachucla Formation in southeastern Georgia (Huddlestun, 1987). As the Penney Farms Formation begins to lose its carbonate units northward and northwestward into Georgia, the chapacteristic lithologies are no longer apparent and the formation can no longer be identified as the Penney Farms. These sediments in Georgia are included in the Parachucla Formation (Huddlestun, 1987).

The Penney Farms Formation unconformably overlies limestones of the Upper Eocene Ocala Group in Nassau County. The unconformity is very apparent due to the drastically different lithologies of a pure limestone below to a sandy, phosphatic dolostone or dolomitic, clayey phosphatic sand above. The Marks Head Formation unconformably overlies the Penney Farms Formation throughout Nassau County.

The overlying Marks Head Formation consists of interbedded fuller's earth type clays, sands and dolostones which are generally lighter colored than the sediments of the Penney* Farms. The top of the Penney Farms is placed at the break between the lighter colored sediments of the Marks Head and the darker colored sands and clays of the upper part of the Penney







Farms. Occasionally, a rubble zone marks the break between the Marks Head and the Penney Farms formations. When it occurs, the rubble consists of clasts of phosphatized carbonate. The relationship of the Penney Farms Formation io the underlying and overlying sediments can be seen in the cross section (Figures 5 and 6).

The Penney Farms Formation of the Hawthorn Group occurs as a subsurface unit in Nassau County. The top of the Penney Farms Formation ranges in cores from -333 feet MSL in Carter #1, W-14619, Duval County to +80 feet MSL in Devils Millhopper #1, W-14641, Alachua County. In Nassau County,

the top of the Penney Farms Formation occurs at approximately -250 feet MSL in the northwestern area to an estimated -350 feet MSL in the southeastern to eastern area (Figure 8). The Penney Farms Formation dips in a general easterly to southeasterly direction in Nassau County toward the Jacksonville

Basin with an average dip of 4 feet per mile. Locally, both the direction and angle of dip may vary.

The Penney Farms Formation varies in thickness from zero on the crests of the Ocala Platform and Sanford High (Figure 2) to more than 155 feet in Carter #1, W-14619, Duval County in the Jacksonville Basin (Figure 2). The total thickness of this unit was not determined in this core as the core terminated in the Penney Farms Formation after penetrating 155 feet. This author estimates that the base of the Penney Farms should occur near.-575 feet MSL based on nearby water wells. This suggests that approximately 230 feet of the unit should be present in the deepest portion of the Jacksonville Basin. The observed thickness of the Penney Farms in Cassidy #1, W-13815, Nassau County is 150 feet (Figure 9).

The Hawthorn Group sediments of northern Florida yield very few

datable fossils or fossil assemblages. Diagenetic overprinting on the










































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Figure 8


Top of Penney Farms Formation (shaded area indicates undifferentiated Hawthorn Group)









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sediments has obliterated the vast majority of fossils leaving mainly molds and casts. Diatom and mollusk molds are the most frequently encountered fossil remains. Nt the present time, a date has been obtained from the Cassidy 4I core, 14-13815, Nassau County in the interval from -370 to -375 MSL. The sediment, a calca.reous, quartz sandy clay, contained benthic and planktonic foraminifera, ostracods, spicules.(sponge?-), echinoid fragments and hryozoans. The planktonic foraminifera indicate an Aquitanian, upper Zone 41.4 or lower 1.5.of Bl-ow (1969)) for this interval (Huddlestun, personal communication, 1983).
The Penney Farms Formation of the Hawthorn Group is older than the

commonly accepted age for the Hawthorn Formation as described by Purl and

Vernon (1964). Purl and Vernon used a Middle Miocene age only for their Hawthorn Formation. This has been the accepted age for the Hawthorn Formation by the Florida Geological Survey for sometime. Armstrong and Wise (1985) suggested a latest Oligocene age for the base of the Hawthorn in southeastern Florida. The data presented here indicate this should further

be revised.
The carbonate section of the Penney Farms Formation has often been referred to as the basal Hawthorn dolostone in northern Florida. The gamma-ray signature is quite distinctive, consisting of a number of very high counts per second (cps) peaks (see section on gamma ray logs).


Marks Head Formation
Huddlestun (1987) reintroduced the Marks Head Formation in Georgia and

included it as part of the Hawthorn Group. The Marks Head Formation is extended into northern Florida as the middle unit of the Hawthorn Group. The lithologic similarities between the Marks Head Formation in southeast Georgia and in north Florida warrants the use of the same nomenclature.








The Marks Head Formation in Florida consists of interbedded sands,

clays and dolostones throughout its extent. Carbonate beds are more common in the Marks Head Formation in Florida than in Georgia; the proportion of carbonate, both as a rock type and an accessory (matrix) mineral, gradually increases into Florida. This unit is the most lithologically variable formation of the Hawthorn Group in north Florida. Miller (1978) defined his

Unit D (equivalent to the Marks Head Formation) in the Osceola National Forest in Columbia and Baker counties, Florida as-being."complexly interbedded shell limestone, clay, clayey sand and fine grained sandstone."

The carbonate portion of the Marks Head Formation is typically dolostone; limestone is uncommon but does occur sporadically as is the case throughout the Hawthorn Group. The Marks Head dolostones are generally quartz sandy, phosphatic and clayey. The dolostones vary in induration from poorly consolidated to well indurated. The induration varies in inverse relationship to the amount of clay present within the sediment. Phosphate grains normally comprise up to five (5) percent; however occasional beds may contain significantly higher percentages. Quartz sand content varies from less than 5 percent to greater than 50 percent where it grades into a dolomite cemented quartz sand. The dolostones range from yellowish gray to olive gray in color. Crystallinity varies from micro-to very finely crystalline with occasional more coarsely crystalline zones. Molds of mollusk shells are often present.

The occurrence of limestone within the Marks Head Formation in Florida is quite rare. The majority of the "limestone" reported from this part of the section by other workers is actually dolostone. The limestone that does occur is characteristically dolomitic, quartz sandy, phosphatic, clayey, and fine grained.







The quartz sands from the Marks Head Formation are generally fine to nediu grained (occasionally coarse grained), dolomitic, silty, clayey and phosphatic. The dolomite, silt and clay contents are highly variable and gradational with the other lithologies. Phosphate grains are usually present in amounts ranging from one (1) to five (5) percent; however, phosphate percentages may range considerably higher in thin and localized beds. The quartz sands are typically light gray to olive gray in color. Induration varies from .poor .to moderate..

Clay beds are quite common in the Marks Head Formation, occasionally comprising a large portion of the section. The clays are quartz sandy, silty, dolomitic and phosphatic. As is the case in the underlying Penney

Farms Formation, the Marks Head clays contain highly variable percentages of accessory minerals; relatively pure clays do occur but are not common. The clays range from greenish gray to olive gray in color and are typically lighter colored than the clays of the underlying unit.
Phosphate grains are present virtually throughout the Marks Head Formation. They characteristically occur asbrown to black, sand-sized grains scattered throughout the sediments. The phosphate grains are rounded and often in the same size range as the associated quartz sands. Phosphate* pebbles occur rarely.

Mineralogically, the Marks Head Formation clays contain palygorskite, sepiolite, smectite and illite; kaolinite is present only in the weathered

section (Hettrick and Friddell, 1984). Hettrick and Friddell (1984) indicated that palygorskite is often the dominant clay mineral in this unit; smectite is the second most abundant clay mineral. Smectite becomes the most abundant clay mineral when palygorskite content decreases. Other

minor mineralogic constituents include mica, opal-ct and feldsoar. Huddlestun (in press) reports the occurrence of zeolite in the Marks Head








Formation.

The Marks Head Formation is underlain disconformably throughout Nassau County by the Penney Farms Formation. The upper part of the Penney Farms Formation consists predominantly of darker, olive gray colored sands and clays with occasional dolostone beds. The base of the Marks Head Formation Is placed at the contact between the darker colored sands and clays of the upper Penney Farms and the generally lighter oloredi more complexly interbedded sands, clays and dolostone of the Marks Head. Occasionally, the contact is marked by a rubble zone containing phosphatized carbonate clasts but the unconformity is often difficult to recognize. The Coosawhatchie Formation disconformably overlies the Marks Head Forma-tion throughout Nassau County. The Coosawhatchie-Marks Head contact is generally placed at the top of the first hard carbonate bed or light colored clay unit below the darker colored clayey, dolomitic, quartz sands and dolostones of the basal Coosawhatchie Formation. Occasionally, the contact.appears gradational in a sequence of dolostone and interbedded sands. In this case the top of the Marks Head is placed at the uppermost hard dolostone bed in the interbedded sequence. A rubble bed sometimes marks the unconformity. The relationship of the Marks Head Formation to the underlying and overlying units is graphically illustrated in Figures 6 and 7.

The Marks Head Formation of the Hawthorn Group occurs as a subsurface unit in Nassau County. The top of the Marks Head Formation in the subsurface varies from -260 feet MSL in Carter #1, W-14619, Duval County to +114 feet MSL in Devil's Millhopper #1 W-14641 in Alachua County. The top of the Marks Head in Nassau County varies from -100 feet MSL in the southwestern most corner to -250 feet MSL on the east coast (Figure 10).


















A


Top of the Marks Hea&.Formation (shaded area indicates undifferentiated Hawthorn Group)


Figure 10


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The Marks Head Formation in Nassau County dips to the northeast and east with an average dip of 4 feet per mile. The direction and angle of dip may vary locally.

The thickness of the Marks Head Formation varies from zero on the crest of the Ocala and Sanford highs to 130 feet in the core N.L. #1, W-12360, Bradford County. In northwestern Nassau County, it is 80 feet thick (Figure 11).

Datable.fossil assemblages, within the Marks Head Formation have not been found in north Florida. The only fossils noted were scattered molds of mollusk shells and occasional diatom molds. Lithologic correlation between these sediments and those in Georgia, where fossiliferous sediments are found, indicates that the Marks Head Formation is late Early Miocene (Burdigalian) age (Huddlestun, personal communication, 1983). Planktonic foraminifera in Georgia indicate Zone N.6 or early N.7 of Blow (1969).

As is the case for the Penney Farms Formation, the Marks Head Formation is older than the previously accepted age for the "Hawthorn Formation" in Florida as interpreted by Cooke .(1945) and Puri and Vernon (1964). Cooke (1945) and Purl and Vernon (1964) suggested a strictly Middle Miocene age for their "Hawthorn Formation".


Coosawhatchie Formation

The Coosawhatchie Formation of the Hawthorn Group .is used the upper

unit of the group in much of north Florida. Huddlestun (1987) proposed the Coosawhatchie as a formal lithostratigraphic unit in Georgia. It extends into north Florida with only minor lithologic changes (Scott, 1987).

The Coosawhatchie Formation in Florida consists of quartz sands, dolostones and clays. Characteristically, clayey, sandy to very sandy dolo-













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LEGEND
0 cal jiDs
a CUTTI*NGS N R A'JCO
LIMITS DI HIM THORN ;Aou)t)P












1 0 L K.. .




Figure 12 Top of Coosawhatchie Formation (shaded area indicates undifferentiated Hawthorn Group)



















0


'AA D '.S ON.
~ LC





A'i
I -.; t '


1 -. C 1


ICHRIsST


t "% A M,.
un . ", o.,o.,tL Fl L Aj L E,, .1, /,R


SCALE



SCAME N CI 50. FEET : 0 20o 40 MILE,


LEGEND
0 CORES HI 9IA NID

CUTTING8
XA MITS OF HAWTHORN GROUP


P A S rC






HILS0100


.-6









I -100


-I i~

N


FOigure 12 Top of Coosawhatchie Formation (shaded area
indicates undifferentiated Hawthorn qroup)


V L U IS A M IN~l LEI


n ..1_. 5 ,~ N-- G E



n .


SRO#






stone and dolomitic, clayey sands are the most common lithologies in the unper part. In the lower part, the quartz sands and clays predominate with interbedded dolostones.

The quartz sands are dolomitic, clayey and phosphatic. The sand grains are fine to medium grained, poorly to moderately sorted, and subangular to subrounded. The proportions of accessory materials vary greatly. The sands grade into the dolostones and clays in many instances. Phosphate content is quite variable ranging from a trace to more than 20 percent. Clay content varies from less than 5 percent to greater than 30 percent. The sands are often lighter colored in the upper part where there is more carbonate in the matrix and darker in the lower part. Colors range from greenish gray and light gray to olive gray. Induration is generally poor.

The dolostones of the Coosawhatchle Formation are quartz sandy, clayey .and phosphatic. The percentages of quartz sand and clay vary widely and may be as much as 50 percent in transitional zones. Phosphate is quite

variable also, but is generally less than 10 percent. The dolostones are micro-to finely crystalline, poorly to moderately indurated and occasionally contain nolds of fossils. They range in color from light gray and greenish gray to light olive gray. The dolostones of the upper part appear to become more calcareous in the Jacksonville Basin.

The clays in the Coosawhatchie Formation are typically quartz sandy, silty, dolomitic and phosphatic. The clays are light olive gray to olive gray. Clay beds are most common in the lower member (Scott, 1983). The clay mineralogy Is dominated by smectite (Hettrick and Friddell, 1984). The clay beds often contain diatoms (Hoenstine, 1984).

The phosphate grains present in the Coosawhatchie Formation are nor?nally amber colored to brown or black; lighter colors occur near the land







surface. The phosphate grains are usually well rounded and in the same size range as the associated quartz sands. Coarser phosphate sands and phosphate pebbles or rubble are not common but are present.

The Coosawhatchie Formation disconformably overlies the Marks Head Formation but the disconformity is often not readily apparent. It is, however, recognized biostratigraphically in Georgia (Huddlestun, personal communication, 1983). The contact often occurs in a thin gradational sequence of interbedded sands and dolostones. Occasionally, the contact is marked by a rubble bed.

The Coosawhatchie is overlain by undifferentiated Plio-Pleistocene deposits in most of northern Florida. In much of Nassau County, the Coosawhatchie is overlain disconformably by the Pliocene Nashua Formation. The relationship of the Coosawhatchie to the underlying and overlying units is indicated in Figures 6 and 7.

The Coosawhatchie Formation occurs throughout much of north Florida. The top of the Coosawhatchie ranges from -93 feet MSL in Bostwick #1, W-14477, Putnam County to +168 feet MSL in Devils Millhopper #1, W-14641, Alachua County. In Nassau County, the top of the Coosawhatchie ranges from near sea level in the southwestern corner edge to greater than -50 feet MSL along the east coast (Figure 12). It attains a maximum thickness in Florida (including the Charlton Member) of 222 feet in Carter #1, W-14619, Duval County (Figure 13). Huddlestun (1987) indicates that the Coosawhatchie attains a maximum thickness of 284 feet in the southeast Georgia Embayment in Georgia. The Coosawhatchie Formation dips in a northeasterly to easterly direction in Nassau County. The average dip is approximately 4

feet per mile. The angle and direction of dip is variable throughout the region.












"A 1255
.. o 100












LEGEND ,--- -4 : .E.-. NOLE7 50

MIOAONS













A i 1"~ '1 So FS E o ,rT








'- I''




Figure 13 Isopach of Coosawhatchte Formation (shaded area
indicates undifferentiated Hawthorn Group)





The Coosawhatchie Formation is not known to occur over the Ocala and Sanford highs or in the immediately surrounding areas. This is thought to be due primarily to erosion; nondeposition may also have played a role. The Coosawhatchie extends from Georgia southward into central Florida.

Huddlestun (1987) suggests a Middle Miocene (Early Serravallian age) for the Coosawhatchie Formation based on planktonic foraminifera. Huddlestun placed it in Zone N.11 of Blow (1969). Hoenstine (1984) studied diatoms from a few selected cores through the Hawthorn. He recognized a Middle Miocene assemblage in Florida sediments assigned in this paper to the Coosawhatchie Formation in northeastern Florida.

The Coosawhatchie Formation is widespread in northern Florida and throughout most of this area the Coosawhatchie is the uppermost Hawthorn sediment encountered. In limited areas, it is shallow enough to be exposed in some foundation excavations. The Coosawhatchie Formation in the Jacksonville Basin contains a lower clay bed of variable thickness. This clay bed correlates with the Berryville Clay Member of the Coosawhatchie Formation in southeastern Georgia.


Charlton Member Of The Coosawhatchie Formation

Huddlestun (1987) redefined the "Charlton Formation" of Veatch and Stephenson (1911) as a formal member of the Coosawhatchie Formation in Georgia. He found that the Charlton Member is a lithofacies of the upper part of the Coosawhatchie in south Georgia and north Florida. Huddlestun (1987) discussed the reference localities in some detail. A reference section for the Charlton Member of the Coosawhatchie Formation in Florida is the Cassidy #1 core, W-13815, Nassau County (NWV4, NWI4, Sec. 32, T3N, R24E). The surface elevation is 80 feet MSL. The Charlton Member occurs from +3





feet MSL to -43 feet MSL.
The Charlton Member characteristically consists of interbedded carbonates and clays. It is less sandy than the upper part of the Coosawhatchie, into which it grades. It is typically low in sand and phosphate (Huddlestun, 1987). Huddlestun (1987) states that the clay component is often very conspicuous in the cores. This has been found to be true in Florida also.

The carbonates of the Charlton Member are often dolostones but range

into limestone. They are slightly sandy, slightly phosphatic to nonphosphatic and clayey. They often contain abundant molds of fossil mollusks. The dolostones are finely crystalline, light olive gray and ooorly to moderately indurated. The limestones are characteristically very

fine grained, slightly sandy, clayey, ooorly to moderately indurated, and yellowish gray.

The clays are dolomitic to calcareous, with poor to moderate induration, silty, and light gray to greenish gray. The clay minerals present include smectite, palygorskite, illite and kaolinite (Hettrick and Friddell, 1984).

The Charlton Member both overlies and interfingers laterally with the upper portion of the undifferentiated Coosawhatchie Formation. The Charlton is simply a distinct facies of the upper Coosawhatchie. It is overlain by the sediments discussed as overlying the Coosawhatchie Formation. The upper contact is unconformable.

Sediments assigned to the Charlton occur at Brooks Sink (SWI/4, SWI/4, Sec. 12, TS, R2OE, Bradford County) at an elevation of +145 feet MSL. The highest elevation for the top of the Charlton in a core was in Wainwright 41, W-14283, Bradford County where it occurred at +109 feet MSL. The deepest that the top of the Charlton Member was found is in Carter #1,





W-14619, Duval County where it is -38 feet MSL. The top is very near MSL to Nassau County (Figure 14).

The Charlton Member of the Coosawhatchie Formation reaches its maximum recognized thickness in Florida in Cassidy #1, W-13815, Nassau County, where it is 70 feet thick (Figure 7 and 15). It is very spotty in its occurrence.

The Charlton Member, as originally defined by Veatch and Stephenson

(1911), was considered Pliocene. Huddlestun (1987) postulates that, based on his observations of the molluscan fauna and the lithostratigraphy of the unit, it i-s Middle Miocene (Seravallian) in age.

Nashua Formation

The Nashua Marl of Matson and Clapp (1909) was reintroduced by

Huddlestun (1987) as the Nashua Formation. The name Nashua Marl had been abandoned by Cooke and Mossom (1929) who replaced it with the Caloosahatchee

Marl, a presumed south Florida equivalent. The Florida Geological Survey, in following the recommendation of Huddlestun (1987), utilizes the Nashua Formation in northern Florida for the shelly sands, clays and some coquina. In Florida, the Nashua is primarily shelly sands and clay. Data on the extent of the Nashua and it's thickness in northern Florida is limited. Huddlestun (1987) indicates that the Nashua underlies most of Nassau County. The Florida Geological Survey core hole Cassidy #1, W-13815 in west-central Nassau County, encountered the Nashua at 27.5 feet above MSL with a thickness of approximately 50 feet.
Lithologically, the Nashua contains fine to medium quartz sands with varying percentages of calcilutite, clay and shell. The occurrence of shell, both whole and fragmented, occasionally becomes the dominant lithologic component. Colors range from light gray to light olive gray.























































SCALe a -20 FT
0 20 40 MILS

LEGENO
a CUTTINGS
,4--UMITS OF HAWTHORN GROUP


Figure 14


Top of the Charlton Member (dashed line indicates extent of Charlton)




























































LEGEND
CORES
a CUTTINGS
AXVJ'4 IUMITS OF HAWTHORN GROUP


Figure 15


Isopach of the Charlton Member (dashed line indicates extent of Charlton)






Plio-Pleistocene Undifferentiated and lolocene Sediments

The Plio-Pleistocene undifferentiated sediments mantle the Nassau
County area with a blanket of fine to medium quartz sands. These sediments contain variable amounts of heavy minerals, silt, clay, iron staining and organic matter. Data on the thickness of these sediments is very limited, however, a thickness of 52.5 feet is recognized in W-13815. Holocene sediments occur along the modern coastline and in association with the present day rivers and streams.


HAWTHORN GROUP GAMMA-RAY LOG INTERPRETATION
Gamma-ray logs are of particular importance to the Investigator

studying the complex section of the Hawthorn Group. The gamma-ray activity in the Hawthorn Group sediments is generally significantly higher than subJacent or supraJacent formations, thus allowing the delineation of this unit. Also, since thee sediments are often partially or entirely cased off during well construction, the ability of gamma-ray probe to obtain information through casing is most important. In the course of this study gamma-ray logs were the only geophysical logs used. For a discussion of resistivity logs of the Hawthorn Group sediments see Johnson (1984).

The Hawthorn Group of northern Florida consists of a complex sequence of clastics and carbonates containing varying percentages of uraniumbearing phosphate minerals. The resultant gamma-ray log shows widely varying peak Intensities (Figure 16). The patterns of peaks are similar throughout much of the area from Duval County west to western Hamilton County and from Nassau County south to southern Putnam County. The Hawthorn thins and the gamma-ray signature changes somewhat south of Putnam County in Marion, Lake and northwestern Orange counties. This is due to











CLAY COUNTY
W-14219
FEET
FEETUNDIFFE RENTIAT ED




..-IoI



-'-COOS AWHATCH IE




-200- MARKS HEAD
-200 Fm.








-300
--' PENNEY

~FARMS Fm.




-400


~OCALA1 GROUP


Ioo C PS 260






Figure 16 Gamma ray log, Jennings #1, W-14219, Clay County






both erosional removal of the upper sediments and less deposition in the are' between the Ocala Uplift and the Sanford High.

4 typical gamma-ray log from the'north Florida area (Figure 16) consists of five generalized zones. This gamma-ray signature is generally present in north Florida. However, the pattern may show significant variation in the intensities of peaks and thicknesses of peak groups. Formatlonal correlation with the gamma-ray signiture is relatively consistent. The upper, high intensity zone and part of the subjacent lower intensity zone correlate with the Coosawhatchie Formation. The Marks Head Formation correlates with part of the low intensity zone, the underlying higher intensity zone, and the upper portion of the second low intensity zone. The Penney Farms Formation incorporates the remainder of this low intensity zone and the basal, high to very high intensity zone. The underlying Ocala Group has significantly lower generalized signatures than the sediments of the Hawthorn Group. The formational correlations with the gamma-ray signature are shown in Figure 15. The upper and lower boundaries of the Hawthorn Group are generally easily picked on the gamma-ray logs. However, caution must be exercised in making formational identifications based solely on the signatures.











TABLE 1. GEOLOGISTS LOGS/CUTTINGS NASSAU COUNTY


Location
(T.R.Sec)


Wel 1 #


El evation


Depth


4N, 24E, 19, SE4 3N, 28E, 14 Ft. Clinch/Amelia Is. 3N, 28E, 24 3N, 28E, 24 3M, 28E, 30, NE4 3N, 28E, 24, NE4 5N, 24E, 27 30-43-10/81-37-50 2N, 27E, 42, SW4 Hilliard Fernandina Beach Hilliard 2N, 28E (Fer. Bch) 3N, 24E, 9, SW4 4N, 23E, 26 3N, 27E, 50 2N, 28E, 22 2N, 28E, 39 2N, 28E, 39 3N, 27E, 50 2N, 27E, 44 3N, 24E, 22, NW4 4N, 23E, 27, NE4


99' 15' 5' 15' 11'
20' 25' 10'
5' 37'


55'

70'
95' 40'

10' 10'


80' 60'


4,824'
900' 800' 750' 1,060' 2,130' 1,205'
60' 45' 905' 821' 1201' 700' 1200' 803'
98'
990' 1016' 95'
700'
580'(?)
624' 490' 905'


Geol. Log


336 371 391 343 670
890
2918 1030 1026 2964
3586 4310 4875 6265 6532 10482 10715 11100 12315 12317 13074 13563 13815 15662


Yes
Drillers
Yes Partial
Yes Yes
Drillers
Yes
Drillers Drillers
Yes
Drillers Drillers Drillers
Yes Core
Yes
Drillers
Yes Yes

Drillers
Core


p








GEOPHYSICAL LOGS NASSAU COUNTY


Geol. Loq #


Location (T.R.Sec)


Elevation


I Ft. Below LSD.


I Charl.


Coosa. M!. Head P. Farms Ocala


3N, 28E, 30
- elect. only
An N


Ft. Clinch 543 10 3N, 28E, 24 40 Caliper only 12 3N, 28E, 35
3N, 24E, 32 (core) 80 Same as #9
SE Callahan 26 Fernan. Bch. CCA9 32 Same as #5
Fernan. Bch
(Test Well) 3 CCA #6 4 CCA #10 17 2N, 28E, 5 11 4N, 23E, 27 60 2N, 28E, Gulf Coarse ? 3N, 28E, 24 11 3N, 28E, 23 9 2N, 25E, 29 20


90
47?


-- 107 77 123


77 75?

82?


119


119
74

98 129 118
111 113?
50


228? 223?

308?
252

170?


302?


298?
304? 310? 308?


360
384

366 332

258
387


380
380
394 357 359 366
373 390 237


529 536

545 482

421 535


546 532 558 533 307
540 547
545 388


*These are located west of Amelia Island; remainder are located in or near Fernandina Beach.


20.1


295


404


560


5 6
7 8
9
*10
*11
12 13
14

15 16
17
*18 19
20 21
*22


TABLE 2.






200 190 180 _170 _160

ISO




130 120

Ito


100

90 80 70 60

so


T 'T
., T.' ., ...












ffa
-, _" -,--_.,









_ -- .,- _. -.- -. .,_ ,-," P.. .' P- . .I ,
'T .' "-T.' T..'.' 'T..'.


quartz sand clayey quartz sand calcareous quartz sand dolomitic quartz sand clay

.sandy clay calcareous clay dolomitic clay shell bed dolomite clayey dolomite sandy dolomite calcareous dolomite limestone sandy limestone clayey limestone dolomitic limestone phosphorite chert

silt

no sample


Appendix B








BIBLIOGRAPHY/SELECTED REFERENCES


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Cathcart, J. B., and Young, E.
J., 1964, Geology and geochemistry of the Bone
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Assefa, G., 1969, Mineralogy and petrology of
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Badiozamani, K., 1973, The Dorag dolomization model
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Banks, J. R., and Hunter, M. E., 1973, Post-Tampa,
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1967, Miocene-Pliocene problems of
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Gremillion, L. R., 1965, The origin of attapulgite
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