Geologic Evolution of Trail Ridge EoMmn

Peat, Northern Florida
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Geologic Evolution of Trail Ridge Eolian 

Heavy-Mineral Sand and Underlying 

Peat, Northern Florida

By ERIC R. FORCE and FREDRICK J. RICH

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1499

The peat underlying ilmenite ore sand is a synchronous fades and 

records the approach of the eolian dune

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1989
DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

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

Library of Congress Cataloging in Publication Data

Force, Eric R.

Geologic evolution of Trail Ridge eolian heavy-mineral sand and underlying peat, northern Florida.

(U.S. Geological Survey professional paper ; 1499) 

Bibliography: p.

Supt. of Docs, no.: I 19.16: 1499

1. Heavy minerals Florida Trail Ridge. 2. Sand Florida Trail Ridge. 3. Peat Florida Trail Ridge. 4. Eolian processes Florida Trail Ridge. 5. Geology Florida Trail Ridge. I. Rich, Fredrick J. II. Title. III. Series. 

QE364.2.H4F67 1989 553.4'6 88-607931

For sale by the Books and Open-File Reports Section, U.S. Geological Survey, 

Federal Center, Box 25425, Denver, CO 80225
CONTENTS

Page

Abstract............................................................................ 1

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

Previous work.................................................................... 2

Nature of the Trail Ridge ilmenite ore sand ............................ 3

Areal distribution and geologic relations........................... 3

Sequence and structure ................................................. 4

Sand morphology and grain size ...................................... 5

Heavy minerals............................................................ 6

Heavy-mineral variation with sedimentary structure .......... 6

	Page

Nature of Trail Ridge Lignitic Peat....................................... 7

General description....................................................... 7

Petrography ................................................................ 8

Palynology................................................................... 9

Age........................................................................... 10

The sand component of Trail Ridge peat.......................... 10

Depositional relation of Trail Ridge peat and sands ................. 14

Paleogeographic reconstruction............................................ 15

Acknowledgments.............................................................. 15

Origin......................................................................... 7 References 15

ILLUSTRATIONS

	Page

FIGURE 1. Location of Trail Ridge shown on a satellite thermal image............................................................................................. 2

2. Cross-sectional profile of Trail Ridge........................................................................................................................... 2

3. Diagrams showing lithologic features, percent leucoxenized ilmenite, and percent Ti02 in altered ilmenite, Trail Ridge ore

	body................................................................................................................................................................ 3

4. Photograph showing humate pseudobedding in Trail Ridge sand...................................................................................... 4

5. Photograph showing Trail Ridge ilmenite ore sand........................................................................................................ 5

6. Circular diagram of azimuths and magnitude of crossbed dip in Trail Ridge ilmenite ore sand .............................................. 5

7. Topographic map showing Trail Ridge localities discussed in the text............................................................................... 6

8. Scanning electron microscope photographs of grains from the Trail Ridge ore sand............................................................. 7

9. Photomicrograph of thin section of Trail Ridge ilmenite ore sand..................................................................................... 8

10. Photograph of laminae alternately rich and poor in heavy minerals .................................................................................. 8

11. Graphs comparing adjacent laminae rich and poor in heavy minerals ................................................................................ 9

12. Graphs showing palynological and maceral constituents of peat in core RTR2 .................................................................... 11

13. Photomicrograph of thin section of sandy lignitic peat from core RTR2............................................................................. 12

14. Scanning electron microscope photograph of sand-bearing lignitic peat sample from core RTR2............................................ 12

15. Graphs showing grain-size distributions of inorganic fraction of sandy Trail Ridge peat from core RTR2................................ 13

16. Scanning electron microscope photographs of sand grains in Trail Ridge peat from core RTR2............................................. 13

17. Photograph showing Holocene coastal transgressive longwall dune near Newcastle, New South Wales, Australia.................... 14

18. Schematic paleogeography of Trail Ridge at the time of dune formation............................................................................ 15

TABLE

TABLE 1. Organic and sand constituents of core samples from Trail Ridge peat.

Page 

..10

ill

GEOLOGIC EVOLUTION OF TRAIL RIDGE EOLIAN HEAVY-MINERAL 

SAND AND UNDERLYING PEAT, NORTHERN FLORIDA

By Eric R. FORCE and Fredrick J. RICH

ABSTRACT

The southern portion of Trail Ridge in Clay County, Fla., has been 

an important domestic source of altered ilmenite, zircon, and other 

minerals since 1949. The ridge as a physiographic feature extends in a 

north-south direction over 160 km and is 1 to 2 km wide. The ore is a 

fine- to medium-grained sand body that extends down from the crest of 

the ridge about 20 m. Average heavy-mineral content is about 4 

percent. Over half of the ilmenite and zircon is contained in thin, dark 

laminae dipping 26° to 41° southwest; these laminae extend deep within 

the ore and outline the slip faces of a great eolian dune complex. The 

subordinate dark laminae differ in heavy mineralogy and grain size 

from the encasing light-colored sand. The dark laminae have a modal 

grain size of 0.2 mm and average about 6 percent heavy minerals, 

among which altered ilmenite, zircon, and rutile predominate. The 

light-colored laminae have a coarser modal grain size of 0.3 mm and 

average only 1 percent heavy minerals, among which the lighter heavy 

minerals staurolite, sillimanite, and tourmaline form half. Grain size 

variables and grain surfaces are appropriate for eolian sand. Overprinted on these original features of the dune are a surficial weathering 

zone over 3 m thick, where tan leucoxene takes the place of black 

altered ilmenite, and several underlying humate-cemented zones that 

probably represent water-table stillstands.

The immediately underlying unit is a lignitic peaty layer 1.5m thick, 

here referred to as peat. The organic fraction is derived entirely from 

freshwater plants. In-place tree stumps have been noted, but the 

predominant component of the peat is fragments of wood and other 

transported plant debris. The peat and its constituents indicate deposition in a swamp environment, and local horizons enriched with 

charcoal and fungal remains indicate periodic subaerial exposure. 

Vegetation varied from open shrub swamp to cypress forest.

The age of the peat has been determined palynologically as postMiocene. Its carbon-14 age is greater than 4.5xl04 years; that is, 

pre-latest Pleistocene.

The upper portion of the peat layer contains admixtures of sand. This 

sand is present as isolated grains embedded in laminated organic 

matrix and is dominantly well rounded and frosted. As a grain 

population, the sand in the peat matches the overlying Trail Ridge ore 

sand in mineralogy and grain morphology but is slightly finer in grain 

size. This sand we regard as an important clue to the history of the 

area. The sand was apparently deposited from aerial suspension, and 

its characteristics were acquired in the adjacent high-energy eolian 

environment. Upward increase of sand in peat records the approach of 

the dune that eventually prograded the swamp. The peat and the

Manuscript approved for publication October 28, 1988.

overlying sand are essentially the same age. Fine sand found in peat 

represents the sand fraction remaining suspended in flow separation at 

the top of the slip face of the dune. Ore represents the traction-load 

fraction. The Trail Ridge dune itself is probably the drainage dam that 

impounded the swamp it later overrode.

The sand embedded in peat is also an important clue to the weathering history of Trail Ridge heavy minerals, as entombment in peat 

probably arrested oxidation. The presence of leucoxene, and other 

features of the mineral assemblage, shows that the minerals were 

already weathered at deposition. This evidence is in accord with 

grain-surface features and grain-size-density relations. Thus, mineral 

alteration at Trail Ridge occurred in two stages, one before and one 

after deposition.

Trail Ridge apparently represents a coast-parallel transgressive 

dune complex, analogous to younger dunes elsewhere that have become 

completely decoupled from parental shorelines. The Trail Ridge body 

was probably composite, made up of individual parabolic dunes, each 

migrating southwestward. The base of the Trail Ridge body was 

probably originally higher at the southern end than at the northern 

end.

INTRODUCTION

Trail Ridge is a linear north-south-trending ridge 

about 1 to 2 km wide, which extends at least 160 km from 

northeastern Florida to southeastern Georgia. It is about 

65 km inland from the coast, and its crest increases in 

elevation from about 46 m (150 ft) in the north to as much 

as 77 m (252 ft) in the south. Because the ridge typically 

stands tens of meters above adjacent areas and impounds 

the Okefenokee Swamp, it is one of the most conspicuous 

linear landforms in the coastal plain of the Southeastern 

States (fig. 1). A profile is shown in figure 2.

The ridge is composed of a sorted fine-grained to 

medium-grained quartzose sand body up to 20 m thick. In 

a 29-km portion of its length in Florida, the sand 

throughout its thickness averages about 4 percent heavy 

minerals, 1 predominantly altered ilmenite, and lesser 

zircon, rutile, and aluminosilicates. This sand is, or was

1 All listed mineral percentages are by weight, unless otherwise specified.
GEOLOGIC EVOLUTION OF TRAIL RIDGE, NORTHERN FLORIDA

FIGURE 1. Location of Trail Ridge shown on a satellite thermal

image.

20 KILOMETERS

FIGURE 2. Approximate cross-sectional profile of Trail Ridge, with 

vertical exaggeration of 200. Shaded bodies are heavy-mineral sands. 

Line of section A-A' is shown in figure 1.

before mining, probably the most valuable single 

resource of titanium minerals in the United States.

Since 1949, E.I. Du Pont de Nemours and Company 

has mined this body in Clay County, Fla. Exploration 

holes and cores in this area have shown that the central 

to western portions of the south end of the Trail Ridge

sand body rest on about 1.5 m of lignitic peat that 

typically contains large wood fragments. In this paper 

we examine the relation between the lignitic peat and the 

overlying sand body (henceforth referred to as ilmenite 

ore sand) to clarify their original paleogeographic relation and their origin.

PREVIOUS WORK

The earliest geologic descriptions of Trail Ridge were 

entirely geomorphic. Cooke (1925, 1939) envisioned the 

ridge as a large Pleistocene marine sand spit that was 

attached to a mainland near Jesup, Ga. (Cooke, 1925, 

plate Xb). Cooke believed that the sand body possibly 

was tilted northward after deposition and that the sand 

was partly eolian in origin. MacNeil (1950) extended this 

view to include the Okefenokee Swamp as a former 

lagoon behind a Trail Ridge marine shoreline and bar.

By the mid 1940's, Florida was the site of several small 

heavy-mineral mining operations. Discovery of economic 

heavy minerals at Trail Ridge coincided with the first 

descriptions of its sands. Spencer (1948) reported on a 

U.S. Bureau of Mines drilling program on Trail Ridge 

that encountered valuable deposits of altered ilmenite, 

zircon, and rutile in sand containing 3 to 10 percent heavy 

minerals to depths of over 10 m. A heavy-mineral 

assemblage of altered ilmenite, zircon, rutile, staurolite, 

tourmaline, sillimanite, kyanite, corundum, monazite, 

and spinel was described, as was the nature of ilmenite 

alteration. Credit for the discovery is shared by Spencer's team and the Du Pont company, under J.L. Gillson. 

Thoenen and Warne (1949) extended the drilling investigations along and adjacent to Trail Ridge by using the 

newly developed jet drill.

The Trail Ridge mine was opened by Du Pont near the 

southern end of the ridge in 1949. At first the plant was 

operated by Humphrey Gold Corporation. The operation 

was described in several mining journals in the early 

1950's. The most thorough such description, by Carpenter and others (1953), was the first to describe the 

humate-cemented "hardpan" in the ilmenite ore sand and 

the woody peat layer underlying it. They found wood 

fragments, up to 5 cm in diameter, and pinecones in this 

peat layer. They reported the thickness of the peat to be 

about 1.5 m and that of the overlying ilmenite ore sand to 

be up to 20 m. Average heavy-mineral grade was listed 

as 4 percent.

Recognition by Creitz and McVay (1948) that Trail 

Ridge ilmenite is altered to an iron-deficient, less-dense 

compound containing microcrystalline rutile, and by 

Cannon (1950) that the heaviest ilmenite alteration at 

Trail Ridge occurs above the present water table, 

spawned many worldwide comparative studies from 1954
NATURE OF THE TRAIL RIDGE ILMENITE ORE SAND

DEPTH PERCENT OF TiO2

,.,, m IN ALTERED ILMENITE (M) (FT)

0 10 20 30 40 50 60 70 80 90 _ 50 60

PERCENT OF 

LEUCOXENIZED ILMENITE

0- -0

-5

70 80 90

2-

-10

4-

6-

8-

-15

-20

-25

L 30

I I

FIGURE 3. Leucoxene zonation in the Trail Ridge ore body. Percent leucoxenized ilmenite is calculated as a moving average from E.C. Pirkle 

and Yoho (1970, cores TR 1 and 2); Ti02 in altered ilmenite is from Temple (1966).

to 1966 of ilmenite alteration in sand matrix. Of these 

studies, the one by Temple (1966) is most concerned with 

Trail Ridge per se. Garnar (1972) showed the chemical 

alteration path for Trail Ridge ilmenite.

The papers by E.C. Pirkle and Yoho (1970) and E.C. 

Pirkle and others (1970) constitute the first thorough 

descriptions of the deposit and emphasize the vertical 

sequence shown in two cores. They present the first 

records of (1) the remarkably consistent grain size of the 

deposit, the median value being about 0.3 mm, (2) 

sedimentary structures and other original depositional 

features in the ore sand, and (3) configuration of the base 

of the ore body and the relation of ore sand to peats and 

other underlying lithologies. The "Trail Ridge Sequence" 

of these authors consists of the ore sand and underlying 

peat. Figure 3 shows their data on leucoxene zonation 

within the ore body. They hypothesized that the ore sand 

was deposited in a complex of beach ridges and associated eolian dunes.

Subsequent geologic publications on Trail Ridge have 

continued to be almost entirely by the Pirkle family and 

their colleagues. E.C. Pirkle and others (1971) 

described an additional core through Trail Ridge, adjacent to the Florida-Georgia line. F.L. Pirkle (1975) 

compared grain sizes, heavy-mineral suites, and grain 

shapes among Trail Ridge sands and proposed possible 

source regions. E.C. Pirkle and others (1977) described 

the portion of the Trail Ridge deposit northwest of 

Highway 301 in Florida. F.L. Pirkle and Czel (1983) 

reported marine fossils of probable Pleistocene age at 

elevations of 39 to 49 m (130 to 160 feet) in sands just 

west of and stratigraphically above a Georgia segment of

the ridge. W.A. Pirkle and E.C. Pirkle (1984) and F.L. 

Pirkle (1984) summarized the evidence for a beach-ridge 

origin of Trail Ridge, the latter paper concluding that 

some grain-size characteristics of the deposit are consistent only with an eolian origin.

The most recent published work is by the authors. 

Rich (1985) described the palynology of the peat bed, and 

Force and Garnar (1985) described eolian crossbedding of 

the ilmenite ore sand.

NATURE OF THE TRAIL RIDGE ILMENITE ORE

SAND

AREAL DISTRIBUTION AND GEOLOGIC RELATIONS

The nature of the sand composing Trail Ridge is well 

documented only in the portion having high heavymineral contents, which is at the southern end of the 

body, in Clay and Bradford Counties, Fla. Even there 

the areal distribution and geologic relations of the sand 

body are not adequately reported in the literature. Most 

of our knowledge comes from descriptions of the ilmenite 

ore sand in profile, in substantial part from four cored 

drill holes. The mining operations only rarely expose the 

main part of the ore body. Unpublished company 

reports, to which we have limited access, constitute the 

largest body of information that can be used to define the 

geometry of this sand body.

At the southern end of the ridge near Starke, Fla., the 

central and perhaps western parts of the sand body are 

underlain by lignitic peat. The nature of the contact is a
GEOLOGIC EVOLUTION OF TRAIL RIDGE, NORTHERN FLORIDA

FIGURE 4. Humate pseudobedding in Trail Ridge sand, photographed in wall of dredge pond, in interval 1.6 to 2.6 m below land

surface.

major focus of this paper. The contact surface apparently 

dips about 3 m/km (15 feet per mile) to the westsouthwest (E.G. Pirkle and Yoho, 1970, fig. 3). Underlying the peat are the "post-Hawthorn elastics" of E.G. 

Pirkle and others (1970), consisting in part of marine 

clay. North of this area, the sand body is underlain by 

fine-grained sands and (or) clays that locally contain 

wood (root?) fragments and show mineralogical indications of subaerial weathering (E.G. Pirkle and others, 

1977).

The ilmenite ore sand extends from this subhorizontal 

base to the ground surface. Thus the ore is thickest 

where the elevation of the ridge is greatest (fig. 2). 

Maximum thickness is about 20 m.

SEQUENCE AND STRUCTURE

The ore is more or less homogeneous except for a 

rootlet-mottled leached zone extending down 2 to 3 m 

from the ground surface and grading downward into a 

variably indurated humate-cemented zone. Humate 

induration increases irregularly downward to a hardpan 

that can make a hammer ring. Several humate-indurated 

horizons occur in some localities, to as much as 6.5 m

below the land surface, forming pseudobedding (figs. 4, 

5) overprinted on weathered sand. This humate cement 

must represent precipitation at the present and former 

water tables. Below 6.5 m, humate cementation is weak.

The surficial leached zone and the upper part of the 

humate-cemented zone coincide approximately with the 

interval in which leucoxene is enriched at the expense of 

less-altered ilmenite (fig. 3).

Force and Garnar (1985) reported that the weakly 

cemented ilmenite ore sand underlying the humatecemented zone shows high-angle eolian crossbedding 

outlined by heavy-mineral laminae dipping southwest at 

26° to 41° (fig. 6). This underlying zone was exposed 

during a 1984 lowering of the dredge pond level at the 

Trail Ridge mine (figs. 5,7). A 1968 lowering had also 

exposed such crossbeds (E.G. Pirkle and Yoho, 1970, fig. 

6; Force and Garnar, 1985, fig. 2), and a core shows the 

crossbeds from a deeper interval (E.G. Pirkle and 

others, 1970, p. 39, PTR1). These three localities represent a relatively small area (fig. 7), so it is not yet 

possible to define the areal extent of eolian deposits. All 

three localities are in the area where the sand body is 

underlain by peat.
FIGURE 5. Trail Ridge ilmenite ore sand exposed in 1984. The 

basal interval (about 0.9 m thick) is eolian sand with southwestdipping crossbeds, overprinted by thin humate-cemented zones. 

Overlying lithologies are weakly cemented sand with crossbedding still visible (0.6 m thick), massive resistant humatecemented sand (1.2 m thick), and at the top a rootlet-mottled 

bleached zone (the remainder). Location is shown on map in 

figure 7.

SAND MORPHOLOGY AND GRAIN SIZE

The ilmenite ore sand is remarkably homogeneous in 

the four profiles that have been described from cores 

(E.G. Pirkle and Yoho, 1970; E.G. Pirkle and others, 

1970, 1977). This homogeneity is understandable in the 

context of an eolian origin and deposition on steep slip 

faces. Median grain size of the sand ranges only from 0.24 

to 0.38 mm, and the distribution of median grain size 

values within the sand body appears random.

Skewness values for grain-size distribution of the 

sands have never been published. Our calculations 

(based on samples of E.G. Pirkle and Yoho, 1970; E.G. 

Pirkle and others 1970,1977) show the sands that are low 

in postdepositional clay give positive values, consistent 

with Friedman's (1961) conclusions for eolian sand.

FIGURE 6. Stereographic projection of azimuths and magnitude 

of crossbed dip in Trail Ridge ilmenite ore sand.

These positive values persist to the base of the ilmenite 

ore sand.

Grain sorting by size is good. Sorting coefficients listed 

by E.G. Pirkle and Yoho (1970) for the ilmenite ore sand 

in the two southern drill holes range only from 1.16 to 

1.32, again with irregular vertical distribution. 2 There is 

no apparent relation to median grain size. These sorting 

coefficients indicate the sands to be well sorted, in the 

terminology of Trask (1932).

The sands are well rounded also, though this description has never been rigorously quantified. However, 

F.L. Pirkle (1975) presents average axial ratios of intermediate and maximum axes of zircon and aluminosilicates from one size fraction of sands from three of the 

drill holes. This measure of sphericity ranges from 0.64 

to 0.68.

Quartz sand grains from the Trail Ridge ilmenite ore 

sand are somewhat frosted, and grains of altered 

ilmenite show a polish. Figure 8 shows scanning electron 

microscope photographs of quartz and ilmenite, collected 

in 1984 from a crossbedded sand exposed below the 

lowest humate hardpan layer. The surfaces are analogous to those described elsewhere for eolian sands (for 

example, Krinsley and Margolis, 1971).

2 Our calculations from E.C.Pirkle and Yoho (1970) data give a range of 1.23 to 

1.35. Apparently their values are for sand fractions, free of postdepositional 

matrix.
GEOLOGIC EVOLUTION OF TRAIL RIDGE, NORTHERN FLORIDA

29°55'

CONTOUR INTERVAL 10 FEET

0 1 KILOMETER

FIGURE 7. Part of the Starke quadrangle map (1949 edition) illustrating Trail Ridge localities discussed in the text. PTR localities refer to 

E.G. Pirkle and Yoho (1970); RTR localities refer to Rich (1985).

HEAVY MINERALS

The heavy-mineral content of the ilmenite ore sand 

varies widely even in the interval samples analyzed by 

E.G. Pirkle and Yoho (1970) and E.G. Pirkle and others 

(1970, 1977). The reported heavy-mineral content ranges 

from less than 1 percent to 16.29 percent (in tetrabromoethane). Variation is high even within a single core. 

Among the drill holes, average heavy-mineral content of

the body varies from 6 percent toward the south to 3 

percent to the north.

Average percentages of the altered ilmenite and leucoxene in the heavy-mineral assemblage have been published by E.G. Pirkle and Yoho (1970) and E.G. Pirkle 

and others (1970, 1977). These minerals together range 

from 47 to 64 percent in the northern part of the body and 

from 16 to 67 percent toward the south. Values below 

about 50 percent are mostly restricted to the uppermost 

parts of the ilmenite ore sand; that is, the same zone in 

which leucoxene has formed at the expense of lessaltered ilmenite. 3

The remainder of the heavy (p>2.85) suite at Trail 

Ridge consists on the average of about 15 percent zircon, 

2 to 3 percent rutile, 15 percent staurolite, 3 percent 

kyanite, 5 to 6 percent sillimanite, 5 percent tourmaline, 

and minor amounts of spinel, corundum, and monazite 

(from Spencer, 1948). The grain sizes of various heavymineral species from commercial concentrates are given 

by Garnar (1980). The median size for altered ilmenite is 

about 0.15 mm and for zircon about 0.10 mm. Staurolite 

is coarser than either (Garnar, 1980, fig. 8).

HEAVY-MINERAL VARIATION WITH SEDIMENTARY 

STRUCTURE

Force and Garnar (1985) found that high-angle eolian 

crossbeds are outlined by laminae up to 1 cm in thickness 

that are enriched in heavy minerals (and preferentially 

cemented by iron-organic compounds; see fig. 9). Intervening light-colored sands are coarser (about 0.3 mm) 

than the dark layers (about 0.2 mm). The light-colored 

sands in one layer contained 1.0 percent heavy minerals, 

of which only 36 percent was titanium minerals and 15 

percent was zircon. This light-colored layer has high 

proportions of the lighter heavy minerals staurolite (24 

percent), tourmaline (13 percent), and aluminosilicates 

(13 percent). As can be seen in figure 9, these are present 

as relatively coarse grains.

An adjacent layer of dark-colored sand contained 6.3 

percent heavy minerals. The light mineral quartz, as well 

as the heavy minerals, is finer in these layers, although 

some coarser quartz is present (fig. 9). The heavymineral assemblage in the dark layer is dominated by 

titanium minerals (54 percent) and zircon (28 percent); 

staurolite, tourmaline, and aluminosilicates are each less 

than 10 percent of the heavy-mineral assemblage.

3 The nature of altered ilmenite at Trail Ridge needs some explanation here. 

Below the surficial leucoxene zone, altered ilmenite consists of a microcrystalline 

aggregate of pseudorutile and other less-abundant phases (Temple, 1966) with 

little ilmenite detectable to X-ray diffraction. The Ti02 contents of these 

aggregates average about 65 percent. Magnetic and density properties and color 

are still enough like ilmenite that the name ilmenite has customarily been 

retained.
NATURE OF TRAIL RIDGE LIGNITIC PEAT

FIGURE 8. Scanning electron microscope photographs of grains from the Trail Ridge ore sand. A, Quartz. B, Ilmenite. The structure of this

grain suggests a concentric weathering zonation developed prior to deposition.

For this study, the grain-size distributions of mineral 

fractions in adjacent light-colored and dark-colored laminae were determined for us by Jeanette (Hilbish) Thomas. The sampled laminae are shown in figure 10, and 

the results in figure 11. The light-colored lamina contained 0.6 percent heavy (p>2.85) minerals, whereas the 

dark-colored one contained 12.3 percent. The modal 

grain sizes of each are similar to those analyzed by Force 

and Garnar (1985). In the dark-colored layer the modal 

grain size of both light-mineral and heavy-mineral fractions are 0.5 to 0.75 c}> finer than in the adjacent lightcolored layer. In each layer, the heavy minerals are 0.5 

to 0.75 c}> finer than the light minerals. The dark lamina 

contains a heavy-mineral assemblage having a much 

higher percentage of the densest heavy minerals, 

ilmenite and zircon (78 percent); the light-colored layer 

contains an assemblage dominated by sillimanite, staurolite, and tourmaline (55 percent). In the dark-colored 

bands, the size distribution of individual heavy-mineral 

species is a sensitive function of mineral density, with the 

median size of sillimanite (p =3.25) almost 1 $ coarser 

than that of zircon (p=4.6). Figure 11 suggests that 

ilmenite (p=4.7 if fresh) behaved during deposition like a 

mineral having specific gravity of 4.0 to 4.6 and hence 

must have already lost density by leaching. Leucoxene 

apparently had its present specific gravity of about 4.0 at 

deposition.

Our calculations, assuming that these layers are typical and that dark layers constitute 10 percent of the

deposit, indicate that 50 to 75 percent of the titanium 

minerals of the deposit, and 55 to 90 percent of its zircon, 

are contained in these thin, dark laminae. The dark 

layers contain only 10 percent of the tourmaline of the 

deposit, however, and comparably low percentages of 

other minerals of intermediate density.

ORIGIN

The Trail Ridge ilmenite ore sand in the area where it 

is best known is clearly eolian. Steep slip faces dip 

southwest; dune migration must therefore have been in 

this direction.

The separation of grains by size into laminae richer and 

poorer in heavy minerals suggests that the grains are 

entrainment equivalents (in the sense of Slingerland, 

1977). However, this equivalence probably was not 

established on the slip face, where the laminae formed, 

but on the windward side of the dune, where sorting 

power is great. Heavy-mineral-enriched material may 

have been supplied from the windward side in daily 

pulses (as in Hunter and Richmond, 1986).

NATURE OF TRAIL RIDGE LIGNITIC PEAT

GENERAL DESCRIPTION

The lower stratigraphic unit of the Trail Ridge 

sequence is referred to as peaty or sapropelic sediment
GEOLOGIC EVOLUTION OF TRAIL RIDGE, NORTHERN FLORIDA

FIGURE 9. Photomicrograph of thin section of Trail Ridge ilmenite 

ore sand, from impregnated box core taken toward base of the 

sequence shown in figure 5. Orientation is right-side-up. Field of 

view is 6 mm; plane light. Note dark iron-organic cement in 

heavy-mineral lamina.

by E.G. Pirkle and Yoho (1970) and is described as 

containing over 92 percent woody substances in a mat 1.5 

m thick. We find that Trail Ridge peat when dried is 

medium brown in color and has recognizable woody 

fragments in an amorphous organic matrix, which was 

deformed by compaction into a fissile to blockyfracturing mat. A laminated appearance is imparted by 

flattened and reoriented woody fragments. The considerable variation in peat structure includes unconsolidated peaty sand and solid plugs of wood.

The peat layer marks the lower limit of the ilmenite 

ore sand, and the buried stumps and branches in it are a 

mining nuisance. E.G. Pirkle and others (1977) note in 

passing that some of these stumps are in growth position. 

Pine cones were noted by Carpenter and others (1953).

Our samples of this organic layer, which we shall refer 

to as Trail Ridge peat, come from two cores of sediment. 

They were acquired through a joint drilling project 

managed by E.I. Du Pont de Nemours and Company and 

the Florida Bureau of Geology. The cores are referred to

FIGURE 10. Laminae alternately rich and poor in heavy minerals, 

below humate-cemented material (at top of photograph) at locality of figure 5. (See fig. 7 for location.) Sample of heavymineral-rich laminae analyzed for figure 11 is shown by arrow. 

The heavy-mineral-poor laminae of figure 11 immediately overlie 

it. Field of view is 0.8 m.

as RTR1 and RTR2 and come from the area of the Trail 

Ridge ore body in Clay County, Fla. (fig. 7).

PETROGRAPHY

Rich and others (1978) showed that Trail Ridge peat is 

actually intermediate between peat and lignite in character. The light color of palynomorphs, pronounced solubility of the sediment in alkali, and certain ultravioletemission spectral characteristics support its designation 

as a peat. On the other hand, the morphology of petrographic constituents (for example, the fact that samples 

can be polished), the huminite reflectance, and other 

ultraviolet-emission spectral properties indicate that the 

sediment is a lignite.

Microscopic analysis of 22 polished pellets of Trail 

Ridge peat is summarized in table 1 and shown with
NATURE OF TRAIL RIDGE LIGNITIC PEAT

LIGHT BAND DARK BAND

60

50

40

O 30

40

30

20

10

0

100

-J 80

cc

 11

Z LU

i p GO

LL <

O -3

Z ^ 40

20

0

MESH 0 

MM 0

0.6% Heavy minerals 

(shaded)

60

50

40

O 30

10

37% llmenite

and zircon

(shaded)

50

40

30

20

EXPLANATION

 Staurolite 23%

 Sillimanite 19%

 - llmenite 33%

- Zircon 4%

30 45 70 120 200 325

.60 .35 .21 .125 .075 .044

1 234

0

100

80

2 60

40

20

0

MESH 0 

MM 0

1 I I I

12.3% Heavy minerals 

(shaded)

78% llmenite and zircon 

(shaded)

EXPLANATION 

 Staurolite 13%

 Sillimanite 13%

- - llmenite 55%

- - Zircon 22%

 Leucoxene

30 45 70 120 200 325

.60 .35 .21 .125 .075 .044

1 234

FIGURE 11. Comparison of adjacent laminae rich and poor in heavy minerals. The upper graphs show histograms of the whole sample, the middle 

graphs show histograms of the heavy-mineral fraction, and the bottom graph shows cumulative curves for individual heavy-mineral species. 

Analyses by Jeanette (Hilbish) Thomas.

palynologic information in figure 12. The dominant constituent in all samples is detrital particles of various 

degraded humic materials (humodetrinite). Other constituents (defined in table 1) are textinite, ulminite, and 

gelinite. Local horizons of charcoal (fusinite) and fungal 

remains are present. Dominance by humodetrinite (fig. 

13) suggests an analogy with highly degraded shrub 

peats of the modern Okefenokee Swamp (Rich, 1979; 

Cohen and others, 1984).

PALYNOLOGY

Pollen and spores in the Trail Ridge peat were studied 

by Rich (1985). Stratigraphic trends in microflora for

core RTR2 are shown in figure 12 for comparison with 

petrographic constituents. In most samples, the dominant microflora is of the shrubs and small trees, especially holly (Ilex), wax myrtle/bayberry (Myrica), ti-ti 

(Cyrilla), hazel (Corylus) and loblolly bay (Gordonia), 

and herbaceous forms such as sedges (Cyperaceae), ferns 

(Osmunda), and moss (Sphagnum). All of these forms 

are consistent with or diagnostic of a freshwater origin, 

and some suggest standing water.

A stratigraphically lower zone of peat in RTR1 contains more abundant cypress (Taxodium) pollen and 

pollen of shrubby forms consistent with a bald cypress 

swamp community. Ti-ti (Cyrilla) shows a peak in the
10 GEOLOGIC EVOLUTION OF TRAIL RIDGE, NORTHERN FLORIDA

TABLE I. Organic and sand constituents of core samples from Trail Ridge peat

[n.d. = no data; locations of cores are shown in figure 7J

Ulminite. Biochemically and (or) geochemically gelified tissues having little cell

structure remaining.

Humodetrinite. Detrital plant fragments and bits of gelified plant tissue.

Gelinites. A broad range of structureless organic materials derived exclusively

by precipitation of colloidal humic suspensions within cell cavities and interparticulate spaces.

Other huminites. A variety of morphologically dissimilar organic substances,

generally derived from colloidal humic suspensions (for example, corpohuminite). 

Includes textinite (coalified cell walls).

Fusinite. Charred tissues, usually having well-preserved cell structure. 

Other inertinites. Highly oxidized byproducts of biochemical and geochemical 

alteration, as well as fungal remains and minute fragments of charcoal. 

Liptinites. Resins, waxes, spores and pollen, algae, and plant cuticles. 

Textinite. See Other huminites.

Sampled interval 

(m depth) Ulminite

Macerals, expressed as volume percent of organic matter1

Humodetrinite Gelinites Other huminites Fusinite Other inertinites Liptinites

Sand, expressed as approximate 

volume percent of peat2

Ash, expressed as weight 

percent dry basis

Core RTR1

15.6 ...........

15.7 ...........

15.8 ...........

16.0 ...........

16.2 ...........

16.3 ...........

16.5 ...........

16.6 ...........

16.7-17.4. ......

17.4-17.5. ......

...... 30.4

...... 63.3

...... 22.0

...... 13.0

...... 19.7

...... 15.5

...... 8.7

...... n.d.

...... 13.8

...... 44.9

54.3

16.3

64.2

74.5

58.8

71.1

83.7

n.d.

77.8

44 0

1.6

2.1

.8

1.3

2.0

2.5

1.0

n.d.

.7

.5

4.5

2.5

4.0

2.0

2.6

5.1

2.8

n.d.

4.5

5.2

2.8

4.8

1.2

1.3

8.2

1.8

.0

n.d.

.4

.5

4.0

6.8

3.3

5.8

6.7

2.8

2.2

n.d.

1.5

2.5

2.4

4.2

4.5

2.1

2.0

1.2

1.6

n.d.

1.3

2.4

n.d.

n.d.

n.d.

n.d.

4 percent

n.d.

30.7

4.3

4.7

4.9

36.3

14.0

4.5

39.0

65-89

33.0

Core RTR2

16.7-16.9. ......

16.9 ...........

17.1 ...........

17.3 ...........

17.4-17.6. ......

17.6-17.8. ......

17.8-18.0. ......

18.0-18.3. ......

18.4 ...........

18.5 ...........

18.7 ...........

18.8 ...........

...... 38.6

...... 19.8

...... 27.1

...... 14.5

...... 11.0

...... 17.3

...... 4.6

...... 10.0

...... 12.4

...... n.d

...... 16.6

...... 27.4

52.1

69.8

62.6

66.0

75.1

6Q Q

79.8

77.6

76.0

n.d.

74.6

65.9

1.9

1.4

.9

3.0

2.6

1.7

2.7

4 9

3.0

n.d.

1.8

1.0

3.4

2.5

3.8

4.2

6.5

6.3

2.2

1 9

1.3

n.d.

2.4

2.7

0.1

q

.3

4.6

1.4

i ^

3.6

q o

3.2

n.d.

2.0

.1

2.0

2.6

3.0

5.6

2.9

9 1

5.9

2.6

3.2

n.d.

1.2

2.0

1.9

3.0

2.3

2.1

.5

1.4

1.2

.7

.9

n.d.

1.4

.9

n.d.

n.d.

n.d.

<.l

n.d.

n.d.

<.l

<.l

<.l

<.l

47.8

57.2

78.2

32.1

7.1

4.8

8.8

6.1

8.4

8.6

4.9

5.0

1 Maceral abundance was determined by 1,000-point counts of polished pellets in reflected white light.

2 Sand abundance was determined in thin section by use of visual comparison charts.

uppermost part of both cores. Oak (Quercus) and pine 

(Pinus), although common constituents, are less abundant than in modern swamps of the same region.

Palynology of many samples is closely related to 

petrography (fig. 12). The pollen was apparently produced by a local flora, as some of these pollen are known 

to have restricted dispersal patterns (Rich and Spackman, 1977). Analogous correlations have been found 

elsewhere by Teichmuller (1958), Corvinus and Cohen 

(1979), and others.

AGE

Palynology by Rich (1985) established only a postMiocene age for the peat. Some relative-abundance evidence suggested a Pliocene rather than a Pleistocene 

age, but control by environmental change could not be 

ruled out for this evidence.

Two samples of lignitic peat from core RTR2 were 

analyzed for 14C. Both samples, taken from the upper 

peat between 16.76 to 17.09 m of depth, proved to be 

"dead," indicating an age greater than 45,000 years B.P.

(Meyer Rubin, USGS, written commun., 1985). Thus the 

peat is not of latest Pleistocene or Holocene age. The 

stratigraphic relations described below suggest that the 

overlying ilmenite ore sands, likewise, are of postMiocene, pre-latest Pleistocene age.

THE SAND COMPONENT OF TRAIL RIDGE PEAT

Toward the top of the peat body, several narrow 

intervals of Trail Ridge PTR cores (fig. 7) have been 

aptly described as sandy peat (E.G. Pirkle and others, 

1970, p. 50). We studied this sandy peat in thin section, 

as a separated bulk sample, and via analysis for ash 

content and chemistry. The 12 thin sections, representing most of the peat thickness in the two RTR cores (fig. 

7), show that the uppermost peat layers characteristically contain about 1 percent or more of sand (table 1) 

that is dominantly well rounded, especially the coarser 

grains (fig. 13). The entire heavy-mineral suite of the 

overlying Trail Ridge ore body is present. Underlying 

peats most commonly contain little sand or more angular 

sand poor in heavy minerals. Ash values (table 1) partly
NATURE OF TRAIL RIDGE LIGNITIC PEAT 11

Taxodium

PERCENT 0 10

Corylus

0 10

Ilex

0 10

No Data

Cyrilla Myrica

0 20 40 0 10 20 30 40 50

J I I I

No Data No Data

Ulminite Humodetrinite

PERCENT 0 20 40 0 20 40 60

I I I I I I I I I I I

Gelinite

80 0 1 2 3450

I I I I I I L

Textinite

246

I I I I I

FIGURE 12. Palynological (top) and maceral (bottom) constituents of peat in core RTR2. Palynofloral constituents are expressed 

as a percentage of total microflora (from Rich, 1985). Maceral constituents are expressed as a percentage of total macerals.

reflect the distribution of sand; ash from this peat 

commonly contains 1 to 2 percent Ti02 and 0.1 to 0.4 

percent zirconium (Jesse Yeakel, written commun., 

1980).

Figures 13 and 14 show that rounded sand grains in the 

upper peat are isolated and disseminated and embedded 

in laminated organic matrix, with deformed organic 

material draped around the grains. The organic matrix of
12 GEOLOGIC EVOLUTION OF TRAIL RIDGE, NORTHERN FLORIDA

FIGURE 13. Thin-section photomicrograph of exceptionally sandy 

lignitic peat from core RTR2, 17.09-m depth. Field of view is 6 

mm; plane light. Sand is imbedded in an organic matrix of 

humodetrinite.

this upper sandy peat and peaty sand is dominated by 

humodetrinite (table 1) with admixed charcoal and (or) 

fungal remains, suggesting subaerial exposure of the 

peat during sand accumulation. It appears unlikely that 

the sand represents either traction-load detritus or material reworked from the overlying sand mass after deposition; in the former case the sand would be bedded, and 

in the latter case the sand would occupy veins. In either 

case, the sand grains would be in contact.

We were able to separate 1.1 g of sand from the RTR2 

sample and subjected it to one of the most rigorous 

textural and mineralogic analyses possible for a sample of 

this size. Figure 15A shows the grain-size distribution of 

the sand. The modal grain size is about 0.2 mm, sorting 

is rather poor, and a fine tail is present in the grain-size 

population. Skewness is probably slightly positive. Compared to the overlying Trail Ridge ilmenite ore sand(fig. 

11), there is a great deal of overlap in grain-size distriFIGURE 14. Scanning electron microscope photograph of sandbearing lignitic peat sample from core RTR2, 16.76 to 16.99 m. 

Note the isolation of sand grains in an organic matrix of plant 

fragments.

bution, but modal grain size of sand in peat is finer and 

sorting is poorer.

Heavy-mineral content of this sand is 6.7 percent, 

slightly higher than in the overlying ilmenite ore sand. 

Heavy minerals show a modal grain size slightly finer 

than that of light minerals (fig. 155).

The mineralogy of the sand in peat compares closely 

with that of overlying ilmenite ore sand. The light 

fraction of the sand is over 99 percent quartz. No 

feldspar was identified. The heavy minerals are dominated by ilmenite (46.5 percent by volume), zircon (16 

percent), staurolite (8.5 percent), and sillimanite+ 

kyanite (7.5 percent) (fig. 15). Minor but characteristic 

constituents are tan or gray leucoxene (5 percent), rutile 

(4 percent), tourmaline (2 percent), and monazite, spinel, 

corundum, and garnet (all less than 1 percent). Size 

distributions of the heavy minerals (fig. 15C) are apparently a function of mineral density and are related to each 

other much as in the overlying ilmenite ore sand.

Grain shapes and surface characteristics of the sand 

grains are also similar to those of the ilmenite ore sand 

(fig. 16). Rounding and sphericity are moderate to 

superb. The sand grains are frosted and show microscopic impact and abrasion features suggestive of an 

eolian origin. (See Krinsley and Margolis, 1971.)
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SIZE DISTRIBUTION OF MINERAL SPECIES, 

IN WEIGHT PERCENT (CUMULATIVE CURVE)

HEAVY MINERALS, 

IN WEIGHT PERCENT

WEIGHT OF SAMPLE, 

IN GRAMS

O ^ _,

o. ffi

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14 GEOLOGIC EVOLUTION OF TRAIL RIDGE, NORTHERN FLORIDA

FIGURE 17. Holocene coastal transgressive longwall dune near Newcastle, New South Wales, Australia, taken from the landward 

side. This dune, an economic heavy-mineral deposit, has migrated away from the coast but remains parallel to it and now rests in 

part on Holocene peats (Thorn and others, 1981).

Certainly the sand did not acquire these features in the 

depositional environment, a swamp. The distribution of 

sand suggests that the transport agent that moved it 

there apparently did so in some form of suspension, not 

as bed load. In a swamp, the appropriate form of 

suspension transport is eolian. An eolian origin for the 

sand component of peat is an additional tie to the 

overlying ilmenite ore sand, which is independently 

known to be eolian.

DEPOSITIONAL RELATION OF TRAIL RIDGE 

PEAT AND SANDS

The Trail Ridge ilmenite ore sand represents a large 

southwest-migrating eolian dune complex. Trail Ridge 

peat represents a freshwater swamp, originally formed 

west of the dune but later overridden by it. The sand 

component of the upper peat was deposited from aerial 

suspension and acquired its characteristics in the adjacent eolian environment. The sand serves as a sensitive 

recorder of the approach of the dune; it represents the 

finer fraction that remained in suspension during eolian 

flow separation at the top of the slip face of the dune. The

ilmenite ore sand represents the fraction that moved 

down the slip face as traction load. Thus the peat and the 

ilmenite ore sand are essentially the same age.

The existence of a large active dune, probably littlevegetated, upwind of the swamp explains the scarcity of 

pine and oak pollen in the peat. The portions of the 

swamp nearest the dune were largely subaerially 

exposed and vegetated partly by ti-ti. Some other portions of the swamp were subaqueous, as indicated by 

some of the palynoflora of the peat.

Oxidation is the first stage of ilmenite alteration 

(Temple, 1966) and is important in the weathering alteration of other minerals also. Thus the sand entombed in 

reducing peat should serve also as a recorder of the 

original composition of ilmenite and other minerals supplied to the dune before postdepositional weathering. 

The presence of leucoxene and the absence or trace 

amounts of labile constituents such as feldspar show that 

the dune was supplied by a sand already highly weathered. This observation is consistent with the previously 

discussed surface polish and grain-size-density characteristics in the ore sand. Since postdepositional weathering at Trail Ridge is already well established, a two-stage 

weathering history is implied.
PALEOGEOGRAPHIC RECONSTRUCTION 15

FIGURE 18. Schematic paleogeography of Trail Ridge at the time of 

dune formation.

Eolian dunes very commonly block natural drainage 

channels, and it seems likely that the active Trail Ridge 

dune thus impounded the swamp represented by Trail 

Ridge peat. In the same way, the inactive Trail Ridge 

landforrn now impounds the modern Okefenokee Swamp.

No evidence of marine influence in deposition of the 

Trail Ridge sequence has ever been encountered. All 

observed sands are eolian, and all observed sheltered 

deposits were deposited in fresh water. Marine fossils 

collected by F.L. Pirkle and Czel (1983) were thought by 

them to postdate Trail Ridge deposition.

PALEOGEOGRAPHIC RECONSTRUCTION

The lack of marine facies coeval with Trail Ridge 

deposition suggests that the Trail Ridge dune had 

become decoupled from parent shoreline facies and 

moved inland while remaining roughly parallel to shore, 

similar *o the formation of transgressive longwall dunes 

of eastern Australia (Thorn and others, 1981). These

bodies, of both Pleistocene and Holocene age, are similarly decoupled from parallel coeval shorelines and rest in 

part on marsh and swamp deposits (fig. 17). An eolian 

body as large as Trail Ridge would probably have been 

composite, composed of individual transgressive parabolic dunes oriented according to prevailing wind direction (fig. 18), analogous to Pleistocene dunes of the 

southern Queensland coast (Ward, 1977, 1978; Thompson 

and Ward, 1975) that are even larger than Trail Ridge. 

Many of the Australian transgressive dunes are also 

heavy-mineral ore bodies (McKellar, 1975).

Transgressive dunes may move inland considerable 

distances and climb onto irregular surfaces well above 

coeval sea levels (Australia Hesp, 1986; Short, 1987; 

Brazil Bigarella, 1972). Our conception of paleogeography at the time of formation of the Trail Ridge dune is 

shown in figure 18. The transgressive dune moved west, 

roughly parallel to the coast, but migrated by successive 

accretions of parabolic dunes moving upslope toward the 

southwest, thus forming slip facies oriented as shown in 

figure 6.

ACKNOWLEDGMENTS

The authors would like to thank E.I. Du Pont de 

Nemours Company and the Florida Bureau of Geology 

for help in the field and with core acquisition and T.E. 

Garnar and Fred Pirkle for useful advice. Jesse Yeakel of 

Exxon Corporation and William Spackman of Pennsylvania State University provided thin sections and petrographic data. John Evans (USGS, Reston) took the 

scanning electron microscope photographs. Jeanette 

(Hilbish) Thomas generated the data for figure 11. Meyer 

Rubin (USGS) provided the radiometric dates on peat. 

The Department of Geology and Geological Engineering 

at South Dakota School of Mines and Technology is 

acknowledged for extending support to F.J. Rich.

REFERENCES

Bigarella, J.J., 1972, Eolian environments: their characteristics, recognition, and importance: Society Economic Paleontologists and 

Mineralogists Special Publication 16, p. 12-62.

Cannon, H.B., 1950, Economic minerals in the beach sands of the 

Southeastern United States, in Snyder, F.G., ed., Symposium on 

mineral resources of the Southeastern United States: University 

Tennessee Press, p. 202-210.

Carpenter, J.H., Detweiler, J.C., Gillson, J.T., Weichel, E.G., and 

Wood, J.P., 1953, Mining and concentration of ilmenite and 

associated minerals at Trail Ridge, Fla.: Mining Engineering, 

August, p. 1-7.

Cohen, A.D., Andejko, M.J., Spackman, W., and Corvinus, D.A., 

1984, Peat deposits of the Okefenokee Swamp, in Cohen, A.D., 

ed., The Okefenokee Swamp: Wetlands Surveys, Los Alamos.

Cooke, C.W., 1925, The coastal plain, in Physical geography of 

Georgia: Georgia Geological Survey Bulletin 42, p. 19-57.
16 GEOLOGIC EVOLUTION OF TRAIL RIDGE, NORTHERN FLORIDA

 1939, Scenery of Florida interpreted by a geologist: Florida 

Department Conservation Geological Bulletin 17, 118 p.

Corvinus, D.A., and Cohen, A.D., 1979, Petrographic characteristics 

of carbonaceous sediments from the Snuggedy Swamp of South 

Carolina tabs.]: 9th International Congress Carboniferous Stratigraphy and Geology, Urbana, Abstracts, p. 45.

Creitz, E.E., and McVay, T.N., 1948, A study of opaque minerals in 

Trail Ridge, Florida, dune sands: American Institute Mining 

Metallurgical Engineers Technical Publication 2426, 7 p.

Force, E.R., and Garnar, T.E., 1985, High-angle aeolian crossbedding 

at Trail Ridge, Florida: Industrial Minerals, August, p. 55-59.

Friedman, G.M., 1961, Distinction between dune, beach, and river 

sands from their textural characteristics: Journal Sedimentary 

Petrology, v. 31, p. 514.

Garnar, T.E., Jr., 1972, Economic geology of Florida heavy mineral 

deposits: Florida Bureau of Geology Special Publication 17, p. 

17-21.

 1980, Heavy minerals industry of North America, in, Coope, 

B.M., ed., Proceedings of the 4th Industrial Minerals International 

Congress Industrial Minerals, London, p. 29-42.

Hesp, P.A., 1986, A review of Australian coastal vegetated dune 

evolution, dynamics, geomorphology, and internal structures 

[abs.]: 12th International Sedimentological Congress (Canberra) 

Abstracts, p. 139-140.

Hunter, R.E., and Richmond, B.M., 1986, Daily cycles in coastal dunes 

[abs.]: 12th International Sedimentological Congress (Canberra) 

Abstracts, p. 147-148.

Krinsley, D.H., and Margolis, S.V., 1971, Surface grain texture, in 

Carver, R.E., ed., Procedures in sedimentary petrology: New 

York, Wiley-Interscience, p. 151-180.

MacNeil, F.S., 1950, Pleistocene shore lines in Florida and Georgia: 

U.S. Geological Survey Professional Paper 221-F, p. 95-108.

McKellar, J.B., 1975, The eastern Australia rutile province: Australasian Institute Mining Metallurgy Monograph 5, p. 1055-1061.

Pirkle, E.G., Pirkle, W.A., and Yoho, H.H., 1974, The Green Cove 

Springs and Boulougne heavy-mineral sand deposits of Florida: 

Economic Geology, v. 67, p. 1129-1137.

 1977, The Highland heavy-mineral sand deposit on Trail Ridge

in northern peninsular Florida: Florida Bureau of Geology Report

Investigation 84, 50 p. 

Pirkle, E.G., and Yoho, W.H., 1970, The heavy mineral ore body of

Trail Ridge, Florida: Economic Geology, v. 65, p. 17-30. 

Pirkle, E.G., Yoho, W.H., and Hendry, C.W., 1970, Ancient sea level

stands in Florida: Florida Bureau of Geology, Geological Bulletin

52, 61 p.

 1971, North Florida setting for fifteenth field conference, 

Southeastern Geological Society: Geological Review of Some 

North Florida Mineral Resources, Southeastern Geological Society, Tallahassee, p. 1-15.

Pirkle, F.L., 1975, Evaluation of possible source regions of Trail Ridge 

sands: Southeastern Geology, v. 17, p. 93-114.

 1984, Environment of deposition of Trail Ridge sediments as 

determined from factor analysis, in Cohen, A.D., ed., The 

Okefenokee Swamp: Los Alamos, Wetlands Surveys, p. 629-650.

Pirkle, F.L., and Czel, L.J., 1983, Marine fossils from region of Trail 

Ridge, a Georgia-Florida landform: Southeastern Geology, v. 24, 

p. 31-38.

Pirkle, W.A., and Pirkle, E.G., 1984, Physiographic features and field 

relations of Trail Ridge in northern Florida and southeastern 

Georgia, in Cohen, A.D., ed., The Okefenokee Swamp: Los 

Alamos, Wetlands Surveys, p. 613-628.

Rich, F.J., 1979, The origin and development of tree islands in the 

Okefenokee Swamp, as determined by peat petrography and 

pollen stratigraphy: unpublished Ph. D. dissertation, the Pennsylvania State University, 301 p.

 1985, Palynology and paleoecology of a lignitic peat from Trail 

Ridge, Florida: Florida Bureau of Geology Information Circular 

100, 15 p.

Rich, F.J., and Spackman, W., 1977, A comparison of modern and 

ancient pollen: sedimentation around tree islands in the Okefenokee Swamp [abs.]: American Association Stratigraphic Palynology, 10th Annual Meeting, p. 25.

Rich, F.J., Yeakel, J.D., and Gutzler, R.Q., 1978, Trail Ridge buried 

peat: its significance as a coalification intermediate [abs.]: Geological Society America Abstracts with Programs, v. 10, no. 7, p. 478.

Short, A.D., 1987, Modes, timing and volume of Holocene cross-shore 

and aeolian sediment transport, southern Australia, in Kraus, 

N.C., ed., Coastal sediments '87: New York, N.Y., American 

Society of Civil Engineers, v. 2, p. 1925-1937.

Slingerland, R.L., 1977, The effects of entrainment on the hydraulic 

equivalence relationships of light and heavy minerals in sands: 

Journal Sedimentary Petrology, v. 47, p. 753-770.

Spencer, R.V., 1948, Titanium minerals in Trail Ridge, Fla.: U.S. 

Bureau of Mines Report of Investigations 4208, 21 p.

Teichmuller, M., 1958, Rekonstruktion verschiedner Moortypen des 

Hauptflozes der niederheinischer Braunkohle: Fortschrift Geologie Rheinland und Westfalen, v. 2, p. 599-612.

Temple, A.K., 1966, Alteration of ilmenite: Economic Geology, v. 61, p. 

695-714.

Thoenen, J.R., and Warne, J.D., 1949, Titanium minerals in central 

and northeastern Florida: U.S. Bureau of Mines Report of Investigations 4515, 62 p.

Thorn, E.G., Bowman, G.M., and Roy, P.S., 1981, Late Quaternary 

evolution of coastal sand barriers, Port Stephens-Myall Lakes 

area, central New South Wales: Quaternary Research, v. 15, p. 

345-364.

Thompson, C.H., and Ward, W.T., 1975, Soil landscapes of North 

Stradbroke Island: Proceedings Royal Society Queensland, v. 86, 

p. 9-14.

Trask, P.O., 1932, Origin and environment of source sediments of 

petroleum: Houston, Tex., Gulf Publishing Co., 323 p.

Ward, W.T., 1977, Sand movement on Fraser Island: a response to 

changing climates: University Queensland, Occasional Papers in 

Anthropology no. 8, p. 113-126.

 1978, Notes on the origin of Stradbroke Island: University 

Queensland Geologic Department Papers, v. 8, p. 97-104.
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.

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of geohydrologic data of both regular and irregular areas; principal scale 

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