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Group Title: Occurrence of plio-pleistocene phosphatized macro-invertebrates from the upper west Florida slope, eastern Gulf of Mexico (FLMNH Bulletin v.42, no.5)
Title: Occurrence of plio-pleistocene phosphatized macro-invertebrates from the upper west Florida slope, eastern Gulf of Mexico
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00099057/00001
 Material Information
Title: Occurrence of plio-pleistocene phosphatized macro-invertebrates from the upper west Florida slope, eastern Gulf of Mexico
Physical Description: p. 219-252 : ill., map ; 23 cm.
Language: English
Creator: Oyen, Craig W
Oyen, Craig W
Donor: unknown ( endowment )
Publisher: Florida Museum of Natural History, University of Florida
Place of Publication: Gainesville FL
Gainesville FL
Publication Date: 2000
Copyright Date: 2000
Subject: Invertebrates, Fossil -- Mexico, Gulf of   ( lcsh )
Paleontology -- Mexico, Gulf of   ( lcsh )
Paleontology -- Pleistocene   ( lcsh )
Paleontology -- Pliocene   ( lcsh )
Genre: bibliography   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
Bibliography: Includes bibliographical references (p. 247-252).
General Note: Bulletin of the Florida Museum of Natural History, volume 42, number 5, pp. 219-252
Statement of Responsibility: Craig W. Oyen ... et al..
 Record Information
Bibliographic ID: UF00099057
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 45142281

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Full Text

of the



Craig W. Oyen, Kendall B. Fountain, Roger W. Portell,
and Guerry H. McClellan

Volume 42 No. 5, pp. 219-252 2000



at irregular intervals. Volumes contain about 300 pages and are not necessarily completed in any one
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Craig W. Oyen1, Kendall B. Fountain2, Roger W. Portell3",
and Guerry H. McClellan2


Numerous phosphatized internal molds of an articulate brachiopod, along with fossils from four other
phyla (Cnidaria, Mollusca, Annelida, and Echinodermata), were collected from several dredge sites in the
Gulf of Mexico. The samples were collected during two cruises aboard the RV Suncoaster in December
1989 and May 1993, approximately 250 km west-southwest of Tampa, Florida. These cruises were not
designed to collect fossils, rather they were aimed at studying the origin of phosphorite nodules and
hardgrounds developing in response to marginal upwelling of the Gulf of Mexico Loop Current along the
western margin of Florida. The invertebrate fossils were collected as part of the phosphorite nodule dredge
hauls and are the focus of this study.
Mineralogical analysis of these internal molds, including a brachiopod and the largest of the three
echinoid specimens, indicates they are composed of francolite, low-magnesium (Mg) calcite, aragonite, and
variable amounts of quartz, which is consistent with nonferruginous nodules recovered from the same areas.
Petrographic examination also identified glaucony and iron-oxyhydroxides (FeOOH) within the phosphatic
molds. The timing of phosphogenesis associated with the fossils and nonferruginous nodules has been
identified as occurring after a late Miocene (Tortonian) sea level lowstand, most likely during Plio-
Pleistocene sea level highstands that favored marginal upwelling over the west Florida slope.
We interpret the paleoecology of the fauna to represent a continental shelf environment of shallower
depth than where the fossils were collected (511-520 m) along the west Florida slope. Though all the taxa
have ranges of depth from which they have been recorded, the best synthesis using all the fossils indicates an
environment of less than several hundred meters depth. It is likely that some transportation of the organisms
occurred after death. Also, significant exposure effects (such as encrusting organisms and borings) are
present on the fossils. Therefore, some mixing of the shallower water and deeper water fauna possibly
occurred prior to their ultimate inclusion within the limestone outcrops on the west Florida slope.


Se colectaron numerosos moldes internos fosfatizados de un braqui6podo articulado provenientes de
diferentes lugares en el Golfo de M6xico, junto a f6siles de cuatro otras phyla (Cnidaria, Mollusca, Annelida
y Equinodermata). Las mustras fueron obtenidas durante dos cruceros a bordo del RV Suncoaster en
Diciembre de 1989 y en Mayo de 1993, aproximadamente 250 km oeste-sudoeste de Tampa, Florida, USA.
Los mencionados viajes de colecta no fueron ideados para colectar f6siles, sino para estudiar el origen de

'Department of Geography and Earth Science, Shippensburg University, 1871 Old Main Drive, Shippensburg, PA 17257.
'Department of Geology, 241 Williamson Hall, University of Florida, Gainesville, FL 32611.
'Florida Museum of Natural History, University of Florida, Gainesville, FL 32611.
corresponding author
Oyen, C.W., K.B. Fountain, R.W. Portell, and G.H. McClellan. 2000. Occurrence of Plio-Pleistocene phos-
phatized macro-invertebrates from the upper west Florida slope, eastern Gulf of Mexico. Bull. Florida Mus.
Nat Hist. 42(5):219-252.


n6dulos de fosforita y el desarrollo de sustratos duros en respuesta al flujo marginal de la corriente del Golfo
de M6xico a lo largo de la costa oeste de Florida. Los f6siles invertebrados fueron colectados como parte del
dragado de n6dulos de fosforita y son el foco de este studio.
AnAlisis mineral6gico de los moldes intemos de un braqui6podo y el mayor de tires especimenes
equin6ideos indica que estan compuestos por francolita, calcita con poco magnesio, aragonita y cantidades
variables de cuarzo, siendo estos resultados consistentes con n6dulos no-ferrugineos recuperados en la misma
area. Examenes petrogrificos tambi6n identificaron glauconita variable (glaucony en el original) y
oxihidr6xidos de hierro en los moldes fosfiticos. Se estim6 que la fosfog6nesis asociada con los f6siles y
n6dulos no-ferrugineos ocurri6 despues del period bajo de las aguas del Mioceno (Tortoniano),
probablemente durante los niveles altos del mar en el Plio-Pleistoceno que favorecieron flujos marginales en
la vertiente oeste de Florida.
Nuestra interpretaci6n paleoecol6gica de la fAuna indica que se trataria de un ambiente en la
plataforma continental a lo largo de la pendiente oeste de Florida menos profundo que los sitios de donde se
colectaron los f6siles (511-520 mts). Si bien las taxa tienen un rango de profundidad conocido, la mejor
sintesis utilizando todos los f6siles indica un ambiente con profundidades menores a cientos de metros. Muy
probablemente ocurri6 cierto grado de transport post mortem de los organismos. Tambi6n, se evidencia en
los f6siles, efectos de exposici6n a organismos incrustantes o penetrantes. Sugerimos que la mezcla de faunas
de aguas poco profundas con faunas de aguas profundas ocurri6 antes de la inclusion de estos organismos
dentro de la matriz limolitica del afloramiento en la pendiente oeste de Florida.


Introduction.. ...................................................................................................... 221
A know ledgm ents ....................................... ........................................................................................ 221
G ecological Setting......................................................................................................... ....................... 222
M ethods............................................ .................................................................. 224
Fossil M ineralogy and Petrography............................................................................................................... 224
System atic Paleontology .................................... .................................................................................. 228
Scleractinia, gen. et sp. indet..................................... ............................................................. 228
Tichosina sp ...................... .... ..................................................................................... 229
G astropod, gen. et sp. indet .......................................................... ................................................. 231
O nustus sp.................................... ........................................................................................ 23 1
O streid, gen. et sp. indet ...................................................................................................................... 233
Lucinid, gen. et sp. indet A ................................................................................................................. 234
Lucinid, gen. et sp. indet B .................................................................................................................. 234
A nnelid, gen. et sp. indet ............... ............................................................................................... 235
Pericosmus spp ................... ........................................................................................... 235
B rissid, gen. et sp. indet.............................................................. .................................................. 24 1
Paleoecological Interpretation................ ................................................................................................ 242
Age and Facies Interpretation ........................................................................................ ....... 245
L literature C ited .............................................................................................................................................. 247



Areas of phosphorite formation and accumulation are representative of unique
conditions of paleoenvironment and sedimentation, often in response to global factors
such as sea level fluctuation and plate tectonics (Cook and McElhinny, 1979, Sheldon,
1980). The upper west Florida slope (WFS) is just such a region, possessing
accumulations of ferruginous and nonferruginous phosphorite nodules and hardgrounds
outcropping at water depths of between 450 and 600 m (Fountain and McClellan, in
press). These phosphorites are associated with middle Miocene (12-15 Ma) to Recent
carbonate-rich sediments exposed along the upper WFS in response to Loop Current
winnowing and non-deposition.
Periods of phosphogenesis commonly are associated with increased biological
productivity (Compton et al., 1993). It is not unusual to find a diverse fossil assem-
blage associated with nodular or hardground phosphorites, especially with boring or
encrusting faunas (Soudry and Lewy, 1988). Such is the case on the upper WFS, where
numerous phosphatized fossil molds of invertebrates were recovered during dredging
operations aimed at studying the origin of these phosphorites. The molds collected are
dominated by the brachiopod Tichosina sp. Also present are ahermatypic scleractinian
corals, two species of gastropods (one indeterminate and one Onustus sp.), three
species of bivalves (one ostreid and two lucinids), annelid tubes, and possibly three
species of echinoids (Pericosmus spp. and an unidentifiable brissid).
Interest in the phosphorite deposits found along the upper WFS originated with
the work of Dix et al. (unpublished data) and Mullins et al. (1988b). These groups
were the first to identify phosphatic materials recovered during dredge hauls and
correlate their occurrence to eustatic sea level fluctuations since the mid-Miocene.
Subsequent interest at the University of Florida Department of Geology began when
Dr. A. Hine of the University of South Florida sent a sample to the authors, concerned
with their origin and stratigraphic significance. After careful study of the sample, a
proposal for ship-time with the Florida Institute of Oceanography was submitted and
the first cruise proceeded in December of 1989.


The authors gratefully acknowledge the in-kind service and financial support of the Florida
Institute of Oceanography, the Southeastern Section of the Geological Society of America, the
Division of Sponsored Research of the Graduate School of the University of Florida, and the
Florida Geological Survey. We also acknowledge the crew of the RV Suncoaster for their
assistance with data collection. David Hodell (Department of Geology, University of Florida)
donated several key specimens (UF 101883, UF 101884, and UF 101885) used in our study.
Stephen Donovan (The Natural History Museum, London) and Burt Carter (Department of
Geology and Physics, Georgia Southwestern State University) are thanked for their assistance
with the identification of the fossil echinoids. David Harper (Geological Museum, University of
Copenhagen) and Thomas Stemann (Department of Geography and Geology, University of the


West Indies, Jamaica) assisted with the identification of the brachiopods and corals, respectively.
Richard Petit (North Myrtle Beach, South Carolina) and Harry Lee (Jacksonville, Florida) are
acknowledged for providing gastropod references. Stephen Donovan and Sherwood Wise
(Department of Geological Sciences, Florida State University) kindly reviewed an earlier draft of
this paper. This is University of Florida Contribution to Paleobiology number 506.


Active carbonate sedimentation and erosive conditions controlled by positioning
of the Gulf of Mexico Loop Current have dominated deposition on the continental
slope west of peninsular Florida. The general geology of the upper WFS and the details
of the Neogene stratigraphy have been summarized by Mullins et al. (1987, 1988a, b,
and references therein). The slope forms the edge of a Jurassic-to-Holocene sequence
of marine carbonates intercalated with evaporites, producing a modern carbonate ramp
environment (Doyle and Holmes, 1985). These deposits (more than 5 km thick) record
the isolation of the Florida peninsula from terrigenous sediment input until the early
Miocene (24 Ma), when increased contents of siliciclastic sediments, including quartz
sands, silts, and clays, are recorded in upper WFS sediments (Mullins et al., 1988b).
Prior to this time, the siliciclastic sediment supply from the north (the Appalachians)
was either limited or transported away from the Florida Platform by currents in the
northeast-southwest oriented Gulf Trough and/or Suwannee Strait located in northern
Florida and southern Georgia (Scott, 1992). During the late Oligocene to early
Miocene, renewed uplift of the Appalachians (Stuckey, 1965) led to a replenished
supply of siliciclastics flooding the southeastern North American coastline. This
massive influx of sediments eventually filled the Gulf Trough, permitting siliciclastic
encroachment onto the Florida Platform.
The study area is located south of the DeSoto Canyon, along the continental
shelf-slope transition, in a complicated series of breaks with steps in between (Doyle
and Holmes, 1985). Between the steps, which represent outcrops or reefs, lie gently
sloping areas of unconsolidated carbonate sediments. In this region, the continental
margin forms a distally steepened carbonate ramp with gentle slopes (1 -2) extending
to water depths as great as 2000 m (Uchupi, 1967). Below 2000 m, the sea floor drops
at a sharp angle (20-30*) to the abyssal depths of the Gulf of Mexico basin along the
Florida Escarpment.
West Florida slope phosphorites are oriented approximately north-south along
the upper slope in water depths of 450 to 600 m (Figure 1). In the northern portion of
the study area (OTB8, OTB5, and WFSI), ferruginous and nonferruginous
phosphorites cap lower to middle Miocene shelf-margin carbonates and clays which
form seaward-prograding clinoforms (Mullins et al., 1988b). Sediments located
between local outcrops of these phosphorites are a relatively coarse-grained, winnowed
foraminiferan-sand faces (Mullins et al., 1988a). A basal unconformity underlies the
phosphorites, which is the result of a depositional hiatus of middle Miocene age
(Serravallian; 12-15 Ma). A landward unconformity stratigraphically correlated to the
ferruginous phosphorites is associated with a late Miocene (Tortonian) age eustatic sea


85030'W 85000'W

1200 1000 800 600 400
1400 \

1600 OTB8

o --- OTB5 27o00'N


- . 26030'N

v 0 ,I* M
,- ... :--?." .', '1%'E



\ 200m--
0 100 200kn

850W 80W
Figure 1. Location of the study area on the upper west Florida slope illustrating the bathymetric
characteristics of the shelf-slope transition and the location of the dredge sites (OTB8, OTB5,
and WFS1) employed in this study.


level lowstand beginning at 10.2 Ma (Mullins et al., 1987). Post-late Miocene
sedimentation was dominated by the vertical accumulation of pelagic sediments,
resulting in the development of a gently-dipping aggradational ramp that has withstood
Quaternary environmental fluctuations (Gardulski et al., 1991). It is from these
overlying late Miocene to Holocene sediments that the phosphatized invertebrate fossil
molds were collected.
Oceanic circulation in the eastern Gulf of Mexico is dominated by clockwise flow
of the Loop Current, which enters the Gulf through the Straits of Yucatan as the
Caribbean Current and exits via the Straits of Florida as the Florida Current (Mullins et
al., 1988b). The Loop Current presently extends to the sea floor and has produced a
swath of winnowed foraminiferal sand at 400 to 600 m depth, reportedly inhibiting off-
platform transport of shallow-water grains (Mullins et al., 1987; Gardulski et al.,
1991). Upwelling occurs along the margin of the Loop Current in association with
eddies that commonly break away from the current and migrate either westward or
eastward over the outer shelf of west Florida (Elliot, 1982), enhancing primary
production (Jones, 1973).


Phosphatized internal molds of fossil invertebrates from five phyla (Cnidaria,
Brachiopoda, Mollusca, Annelida, and Echinodermata) were collected during two
cruises aboard the RV Suncoaster in December 1989 and May 1993, approximately
250 km west-southwest of Tampa, Florida (Figure 1). The corals, brachiopods,
mollusks, annelids, and two echinoid fossils were recovered by dredge hauls in the
northern portion of the study area (OTB8 and OTB5) during the 1989 cruise, while the
third and largest echinoid fossil (Pericosmus sp.) was collected during the 1993 cruise,
south of the previous locations (WFS1). Representative specimens of these fossils are
deposited in the Invertebrate Paleontology Division, Florida Museum of Natural
History (FLMNH), University of Florida, Gainesville, Florida (collection acronym UF).
In order to define the timing of phosphatization, and thereby estimate the age of
the invertebrate fauna, mineralogical and petrographic analyses were performed to
correlate the fossils to phosphorite nodule data compiled by Fountain and McClellan
(in press). Mineralogy was determined by X-ray diffraction (XRD) using a Philips
Electronics Instruments x-ray diffractometer with Cu Kot radiation operated at 40 KV
and 30 mA, with a step size and time constant of 0.02 and I second. Petrographic
analysis of thin sections using polarized light microscopy (PLM) was performed using
an Olympus Model BHS System binocular petrographic microscope.


X-ray diffraction analyses performed on one brachiopod specimen uncatalogedd;
Tichosina sp.) from the OTB5 dredge site and one fragment of echinoid (UF 66566;



Figure 2. XRD diffractograms of phosphatic fossil molds of echinoid (UF 66566 Pericosmus
sp.) from dredge site WFS1 and brachiopod uncatalogedd; Tichosina sp.) from dredge site
OTB5, both from the upper west Florida slope.

Pericosmus sp.) collected from the WFS1 dredge site indicate francolite (carbonate
fluorapatite) as the principal apatite mineral, along with low-Mg calcite and aragonite
(Figure 2). Quartz, an indicator of detrital flux to WFS sediments, was present only in
the echinoid specimen. The presence of aragonite and the lack of high-Mg calcite in
these samples permits their correlation to the BI nonferruginous nodule lithotype
identified by Fountain and McClellan (in press).
Petrographically, the fossil molds are phosphatic biomicrite with allochems of
fragmented or nonfragmented planktic (globigerinids, globorotalids, and Orbulina sp.)
and benthic foraminifera. Additionally, echinoid fragments and gastropods, with
granular and test infilling glaucony and detrital quartz in a micrite and francolite
matrix, are present (Figure 3). As also observed in the BI nodules (Fountain and
McClellan, in press), iron-oxyhydroxide (FeOOH) exhibits variable enrichment,
replacing micrite, francolite, and glaucony, as well as replacing and/or infilling matrix
and foraminiferal tests. Glaucony and FeOOH were not detected by XRD due to their
low abundance (glaucony) and X-ray amorphous nature (FeOOH).




Figure 3. (A, B) Photomicrographs of phosphatic fossil mold of Tichosina sp. (scale bars in PLM photomicrographs = 0.5 mm). (A) Phosphatic
biomicrite mold recovered from OTB5 illustrating the abundance of fragmented and nonfragmented foraminiferal tests, as well as echinoid fragments
(arrow) in a matrix dominated by francolite and micrite. Note the glaucony grain (G) possessing minor FeOOH alteration along the edges. (B)
Example of a mold possessing greater FeOOH enrichment (arrows) at the expense of matrix and allochems. Note more advanced FeOOH alteration of
glaucony grain (G).



Phylum CNIDARIA Hatschek
Class ANTHOZOA Ehrenberg
Scleractinia, gen. et sp. indet.
(Figure 4A, B)

Material-Two partial internal molds of coralla (UF 57742 and UF 97924).
Both dredged from approximately 511 m, December 19, 1989, at OTB5 (270 O1'N,
84 56'W) (UF locality 3784).
Discussion-The coral specimens were incompletely and imperfectly preserved.
Preliminary identifications were not attempted given the large number of ahermatypic
corals known from the Western Atlantic and Gulf of Mexico. See Cairns (1979) for a
discussion of the Recent deep-water ahermatypic scleractinia of the Western Atlantic
and Gulf of Mexico.

A 4k B

Figure 4. (A-C) Examples of phosphatized fossil invertebrates from the upper WFS dredge site
OTB5. (A, B) Partial internal molds of coralla from ahermatypic corals gen. et sp. indet. (left
specimen UF 97924; right specimen UF 57742). (C) Internal mold of annelid tube gen. et sp.
indet. (UF 70554) on the left portion of phosphorite nodule. All specimens are at natural size


Phylum BRACHIOPODA Dumeril
Genus Tichosina Cooper
Tichosina sp.
(Figure 5)

Material-One hundred seventeen internal molds, UF 57741, UF 57744, UF
57746, UF 70551, UF 70552, UF 90721, UF 90723, UF 90726, and UF 101882,
dredged from approximately 511 m, December 19, 1989, at OTB5 (27 01'N, 84
56'W) (UF locality 3784).
Measurements-Biometric values all in millimeters (mm). UF# = Florida
Museum of Natural History lot number; SLPV = sagittal length of pedicle valve; SLBV
= sagittal length of brachial valve; MWI = maximum width; THCK = maximum
thickness of articulated valve pair.

70551a 31.5 27.6 28.7 16.6
70551b 40.1 34.9 34.5 22.3
90721 34.1 29.8 30.9 19.4
90726a 39.4 35.6 34.5 23.7
90726b 41.0 36.9 36.0 22.5
90726c 31.3 27.8 28.5 17.3
90726d 33.1 29.4 26.9 13.5
90726e 37.1 32.2 29.5 23.7

Discussion-Identification of internal molds of brachiopods can be very difficult.
However, the fossil brachiopods from the upper WFS are exceptionally well preserved.
Morphologically, the specimens appear to represent the large, smooth-shelled,
terebratulid genus Tichosina. The placement of our specimens in this genus was based
on their general shape, size, and modified anterior commissure (Figure 5).
The stratigraphic range of Tichosina in the Caribbean is Eocene through Recent.
In Cuba, Cooper (1979) reported the genus as occurring in the Eocene Taguasco
Formation and the Miocene Yumuri Limestone. He also reported occurrences in the
Eocene of Trinidad and the upper Oligocene of Antigua. In Jamaica, Tichosina is
known from the lower Miocene Montpelier Formation and the lower Pleistocene Man-
chioneal Formation (Harper et al., 1995, 1997). In the Dominican Republic, Logan
(1987) reported the genus from the Miocene Gurabo Formation and the Pliocene Mao
Formation. Harper and Donovan (in press) have also reported middle Pleistocene
Tichosina from Barbados.










Figure 5. (A-H) Internal molds of two phosphatized Tichosina sp. (both UF 70551) from upper
WFS dredge site OTB5. (A-D) Dorsal, ventral, anterior, and side view of one specimen. (E-H)
Dorsal, ventral, anterior, and side view of second specimen. All specimens at natural size (Ix).



Tichosina fossils have not previously been recorded from Florida. However, the
known Cenozoic brachiopod taxa from Florida include the inarticulates Discradisca
aldrichi (Gardner, 1928) from the middle Miocene Shoal River Formation and D.
lugubris (Conrad, 1834) from the Pliocene Tamiami Formation, Jackson Bluff
Formation, and Pinecrest Beds and the Plio-Pleistocene Caloosahatchee Formation.
Additionally, Portell and Oyen (1997) and Campbell et al. (1997) reported Glottidia
inexpectans Olsson, 1914, from the Pliocene Tamiami Formation and the Bone Valley
Member of the Peace River Formation. Articulate brachiopods recorded from Florida
include Terebratulina lachryma (Morton, 1833) from the upper Eocene Crystal River
Formation (see Toulmin, 1977 and references therein), and Terebratula sp. and Argy-
rotheca schucherti Dall, 1903, both from the upper Pliocene Jackson Bluff Formation.
Today Tichosina occurs throughout the Caribbean and Gulf of Mexico, and
exhibits extreme morphological variation (Cooper, 1977).

Phylum MOLLUSCA Cuvier
Gastropod, gen. et sp. indet.
(Figure 6A)

Material-One internal mold embedded in slab (UF 70553) dredged from
approximately 511 m, December 19, 1989, at OTB5 (27 01'N, 84 56'W) (UF
locality 3784).
Measurements-Maximum length = 19.5 mm and maximum width = 8.5 mm.
Discussion-The poor preservation of this specimen does not permit a confident
generic or familial assignment.

Family XENOPHORIDAE Philippi
Genus Onustus Swainson
Onustus sp.
(Figure 6B)

Material-Partial internal mold consisting of four whorls (UF 101884) dredged
from approximately 511 m depth, December 19, 1989, at OTB5 (27 01 Ol'N, 84 56'W)
(UF locality 3784).
Measurements-Maximum width of incomplete internal mold = 53.4 mm and
maximum height of incomplete internal mold = 28.1 mm.
Discussion-The family Xenophoridae is remarkable for its habit of attaching
foreign objects, such as shells, pebbles, and corals, to the exterior of its shell. Today,
three species are known to exist in the Western Atlantic and Gulf of Mexico. These are
Xenophora conchyliophora (Born, 1780), Onustus caribaeus (Petit de la Saussaye,
1857), and Onustus longleyi (Bartsch, 1931).





' m
*'* *.^.^i
' '^
' ** '^i
_ *"***iuk.

Figure 6. (A-E) Additional examples of phosphatized fossil invertebrates from the upper WFS
dredge site OTB5. (A) Internal mold of gastropod gen. et sp. indet. in phosphorite nodule (UF
70553). (B) Incomplete internal mold of gastropod Onustus sp. (UF 101884). (C) Internal mold
of single ostreid valve (UF 70559). (D) Internal mold of lucinid gen. et sp. indet. A. (UF 97925).
(E) Internal mold of lucinid gen. et sp. indet. B (UF 101883). All specimens at natural size (lx).


As reported by Ponder (1983) and Kreipl and Alf (1999), X conchyliophora has
a geographic range from North Carolina south to Brazil and from the Gulf of California
to the Gulf of Panama. It averages 47 mm in diameter at its base (excluding foreign
attachments) and is known to attach considerable rubble, shells, and shell fragments to
nearly its entire shell surface. Onustus caribaeus has a geographic range from Florida
to Brazil and averages 60 mm in diameter at its base (excluding foreign attachments).
Onustus longleyi occurs from North Carolina to Barbados and averages 130 mm in
diameter at its base (excluding foreign attachments). The latter two species are deeper
water taxa that attach far fewer foreign objects to their shell than does the typically
shallower water X conchyliophora (see Abbott [ 1974], Clench and Aguayo [1943],
Ponder [1983], and Kreipl and Alf [1999] for further discussion of modem taxa).
Comparisons were made of the incomplete internal mold (UF 101884) to the
three above-mentioned Recent species and all Florida fossil species of Xenophoridae
housed in the Invertebrate Paleontology Division (IP) of the Florida Museum of
Natural History (FLMNH). The entire collection of fossil X. conchyliophora from the
Plio-Pleistocene shell beds were considerably smaller than the phosphatized
incomplete internal mold. Similarly, the early Miocene species Xenophora textilina
Dall, 1892 from the Chipola Formation was also considerably smaller. Only one
specimen of Xenophora sp. (UF 9000) in the IP collection even approached the
estimated total base width for the upper WFS Florida slope specimen. It is a nearly
complete internal mold from the early Oligocene Suwannee Limestone. However, all
the examined fossil species exhibited angled ("stair-stepped") rather than smooth,
sloping, whorls as seen in UF 101884. The only specimens exhibiting such smooth,
sloping whorls were the two Recent, deeper water taxa, 0. caribaeus and 0. longleyi.
Therefore, due to the overall large size of the four whorls of the incomplete
internal mold and the smooth slope of the mold's whorls (with few and only minor
impressions of foreign attachments), we concluded that this specimen represents a
member of the genus Onustus, a typically deep-water taxon. However, because the
critical characters that could further facilitate identification of this specimen, such as
the presence of an umbilicus, the shape of the aperture, and the presence of a cape or
palatal extension were not preserved, specific taxonomic identification was not attemp-
ted. The only other known fossil occurrence of Onustus from the Gulf of Mexico or
Western Atlantic is from Miocene deposits of the Dominican Republic (Ponder, 1983).

Class BIVALVIA Linnaeus
Order OSTREOIDA F6russac
Family OSTREIDAE Rafinesque
Ostreid, gen. et sp. indet.
(Figure 6C)

Material-One internal mold of a single valve (UF 70559) dredged from
approximately 511 m, December 19, 1989, at OTB5 (270 Ol'N, 84 56'W) (UF
locality 3784).
Measurements-Maximum length = 50.3 mm and maximum width = 34.0 mm.


Discussion-Based on its size and shape, the single, bored, worm tube-
incrusted valve infilling most closely resembles the genus Ostreola or Conradostrea.
However, because of its unexceptional preservation, the size and shape of the
impression of the muscle scar is not visible on the internal mold, or is any other
landmark such as the impression of marginal crenulations.

Order VENEROIDA H. and A. Adams
Family LUCINIDAE Fleming
Lucinid, gen. et sp. indet. A
(Figure 6D)

Material-Five internal molds of paired valves and one internal mold of a
single valve (UF 70557), two internal molds of paired valves (UF 90722 and UF
97925). All dredged from approximately 511 m, December 19, 1989, at OTB5 (270
01'N, 840 56'W) (UF locality 3784).
Measurements-Maximum length = 34.6 mm, maximum width = 36.7 mm, and
maximum internal mold thickness (paired valves) = 15.3 mm (UF 97925).
Discussion-All specimens appear to represent a single taxon. The outlines of
the internal molds are ovate, with the most complete specimens having umbos that are
centrally located and moderately projecting above the body of the mold. The molds
exhibit moderate compression representative of the original paired valves, but with no
visible impressions of shell sculpture, ventral margin crenulation, muscle scars, or
hinge teeth. However, on several specimens in UF lot 70557, the slight impression of
the pallial line is visible. All molds show varying degrees of borings which obscure
internal mold detail. There is a tremendous diversity among lucinids; however, it
appears that these specimens are most closely allied to either the genus Linga or
Lucina, based on comparisons to fossil and Recent collections at the FLMNH.
Unfortunately, as with most other mollusks collected from OTB5, poor preservation
precludes a more confident identification.

Lucinid, gen. et sp. indet. B
(Figure 6E)

Material-One internal mold (UF 101883) dredged from approximately 511 m,
December 19, 1989, at OTB5 (27 01'N, 84 56'W) (UF locality 3784).
Measurements-Maximum length = 43.4 mm, maximum width = 43.7 mm, and
maximum internal mold thickness (paired valves) = 21.2 mm.
Discussion-The single internal mold of paired valves is subcircular in outline
and moderately compressed. The umbo is slightly off-center and projecting above the
body of the mold. As with most of the mollusks from the upper WFS, a high degree of
boring is evident. No impressions of the shell sculpture, ventral margin crenulation, or
hinge teeth are visible. However, the strong impression of the pallial line and the faint
impressions of the muscle scars are visible. Comparisons to all species of Lucinidae


housed in the Malacology Division of the FLMNH reveal that this specimen is most
closely allied to the genus Lucina. However, further identification is not possible.

Phylum ANNELIDA Lamarck
Annelid, gen. et sp. indet.
(Figure 4C)

Material-Sixteen phosphorite nodules with internal molds of worm tubes
attached, UF 57745, UF 70554, UF 70556, UF90724, and UF 90725, dredged from
approximately 511 m, December 19, 1989, at OTB5 (27 01'N, 84 56'W) (UF
locality 3784).
Discussion-The poor preservation of these internal molds does not permit a
generic or familial assignment. Worm tubes and internal molds of worm tubes are very
common in Florida rocks of Eocene to Pleistocene age. However, very little has been
published as to their identities.

Genus Pericosmus L. Agassiz
Pericosmus spp.
(Figures 7 and 8)

Material-One partial, phosphatized test with nearly complete internal mold
(UF 101885) dredged from approximately 511 m, December 19, 1989, at OTB5 (27
Ol'N, 84 56'W) (UF locality 3784). One internal mold of test (UF 66566) dredged
from approximately 520 m, May 4, 1993, at WFSI (26 56.29'N, 84 55.75'W) (UF
locality 3810).
Description-One fossil, UF 101885, test outline is subcircular, with maximum
width slightly anterior of ambitus. Specimen somewhat compressed at apical system,
although overall shape is not distorted significantly. Unfortunately, this compaction and
the remnant sediment cemented to the surface has inhibited identification of apical
system morphology. Periproct and peristome are nearly intact and largely unaffected by
diagenesis or fragmentation. Peristome has elevated labrum, and is located slightly
anterior of the test center and distinctly posterior of the anterior sulcus termination on
adoral surface. Anterior sulcus is modestly developed and approximately half as deep
as wide. Adoral surface is generally flat while aboral surface originally was dome-
shaped (though presently collapsed). Test margins are broadly rounded. The anterior
half of both adoral and aboral surfaces show well-preserved molds of tubercles, both
large and small, and relict plate sutures are visible in various areas of the specimen.
Ambulacrum I and IV petals are partially preserved, with pore-pairs present. Petals are
closed, lanceolate, and terminate approximately midway between former apical system
and ambitus.


Figure 7. (A-E) Partial phosphatized test and internal mold of Pericosmus sp. (UF 101885) from
upper WFS dredge site OTB5. (A) Aboral view. (B13) Adoral view. (C) Anterior view with
peristome visible. (D) Posterior view with outline of periproct visible. (E) Lateral view. All
specimens are at natural size (Ix).


The second fossil, UF 66566, test outline subcircular to subpentagonal, with
maximum test width located distinctly anterior of ambitus. All surfaces of this internal
mold have been bored extensively, but the general shape of the test is preserved.
Adoral surface relatively flat, with test margins broadly curved or rounded, and a gently
domed aboral surface with a slight peak at the approximate apical system location. No
ambulacra, plate sutures, tubercles, or other morphological traits are visible on the
mold surfaces. Anterior sulcus is small to moderate in size, with sulcus length subequal
in dimension to sulcus width. Peristome visible on adoral surface, positioned distinctly
anterior of test center and near the posterior margin of sulcus. Peristome slightly
curved and ovate, with elevated labrum. Periproct not preserved.
Measurements-UF 101885 specimen: maximum test length = 47.3 mm,
maximum test width = 51.0 mm, anterior sulcus maximum length = 4.3 mm, anterior
sulcus maximum width = 10.8 mm, peristome position (anterior peristome margin to
anterior test margin) = 14.9 mm, UF 66566 specimen: maximum test length = 97.8
mm, maximum test width = 93.2 mm, anterior sulcus maximum length = 12.3 mm,
anterior sulcus maximum width = 14.0 mm, peristome position (anterior peristome
margin to anterior test margin) = 19.6 mm.
Discussion-The UF 101885 specimen has undergone phosphatization, but it is
apparent that the anterior portion of the test is intact, while only the posterior portion is
exclusively an internal mold of phosphatized carbonate sediment. Some
micromorphology is visible, such as tubercles and pore-pairs (see description), and
overall preservation is the best of the echinoids collected along the upper WFS.
Surface borings and epibionts are present, and are located principally on the aboral
surface. The only significant preservational effect that limits complete description of
the specimen is the slight compaction and collapse of the apical system. Original
skeletal composition of echinoids is high magnesium (4-16% Mg+2) calcite, which is
relatively stable chemically (Sprinkle and Kier, 1987). Therefore, it is typically
uncommon to find fossil echinoid tests completely dissolved or replaced during the
preservation process. According to Donovan (pers. comm., 1999), some taxa do seem
to be prone to this kind of preservation (e.g., Brissus spp. in the Pleistocene of
Barbados, Oligo-Miocene in Jamaica, and Miocene in the Cayman Islands). In Florida,
several species of Miocene brissids are only preserved as molds; one example is
Lovenia clarki (Lambert, 1924) from the Chattahoochee Formation.
Preservation quality of the second Pericosmus specimen (UF 66566) is better
than that of the brissid (UF 57743; see below), but it is a more poorly preserved
internal mold than the other Pericosmus sp. fossil (UF 101885). Therefore, relatively
few diagnostic morphological characteristics could be described. However, in addition
to the traits of test length, width, and height, the shape and position of the peristome are
evident. The aboral surface of UF 66566 (Figure 8A) is imperfectly preserved and
bored, but adorally (Figure 8C) the mold provides a generally good surface for
examination. Since the peristome shape and position commonly are used to aid in
taxonomic descriptions, this specimen can be identified (tentatively) to generic level.
Based on these discernable characteristics, our best placement for this specimen is also
within the genus Pericosmus.



it t -
'1. -.*' .^ .' 4 **)l t .


'-'Vt-. (

Figure 8. (A-C) Phosphatized internal mold of test from Pericosmus sp. (UF 66566) from upper
WFS dredge site WFSI. (A) Aboral view. (B) Anterior view with peristome visible. (C) Adoral
view. All specimens are at natural size (Ix).


Comparison of the two Pericosmus specimens from different upper WFS
localities indicates morphological differences exist between them, which supports
identifying them as two distinct taxa. The position of the peristome relative to both the
test center and the anterior test margin is different between the specimens. In the better
preserved Pericosmus sp. (UF 101885) the peristome is more centrally located,
whereas in the other Pericosmus sp. (UF 66566) the peristome is distinctly positioned
much nearer the anterior portion of the test Further, the anterior sulcus length-to-width
ratio for Pericosmus sp. (UF 101885) is approximately 0.40, whereas for the second
Pericosmus sp. (UF 66566) the ratio is approximately 0.88. Nowhere in the literature
referring to species of Pericosmus is a size range of over 50 mm listed for any species
of the genus. The two upper WFS specimens, herein called Pericosmus spp., differ by
slightly more than 50 mm in test length. Assuming these specimens are adults, this is
not a trivial variation in size and would likely indicate two different taxa. Specific
identification of these specimens will be difficult, if not impossible (particularly for UF
66566), but we believe there is a real morphological difference between the specimens
and have tentatively identified them as unique varieties of the genus for this study,
based on the characteristics listed above.
Both fossil and extant species of Pericosmus are known from the Caribbean as
well as from other parts of the world. Only three countries in the Caribbean and the
Gulf of Mexico region, Cuba, Costa Rica, and Venezuela, have fossil records of this
genus. Most of the taxa were originally reported and described by Sinchez Roig from
the Eocene through Miocene of Cuba (see Kier and Lawson, 1978, p. 102-103, for
taxonomic listing, stratigraphic ages, and associated references), though several were
synonymized or transferred to other genera later by Kier (1984). The five Cuban fossil
species considered valid by Kier (1984) were the Eocene Pericosmus atolladosae
(Sanchez Roig, 1951) and the four Oligocene-Miocene species, P. aguayoi (Sanchez
Roig, 1949), P. blanquizalensis Sanchez Roig, 1952, P. camagueyanus SAnchez Roig,
1949, and P. mortenseni (Sanchez Roig, 1952). It should be noted, however, that Kier
expressed concern regarding the validity of all the species attributed to Pericosmus in
Cuba, since the samples were relatively poorly preserved and had only subtle
morphologic variation as the basis for specific differentiation.
Kier also included two additional taxa from the Caribbean and Gulf of Mexico
region in his monograph; P. israelskyi Durham, 1961, from the Miocene of Costa Rica
and P. stehlini Jeannet, 1928, from the Miocene of Venezuela. Kier (1984, p. 9) was
cautious regarding the Venezuelan species, however, noting its strong similarity to P.
camagueyanus of Cuba, which he believed may warrant future synonymy. A potential
Caribbean record from Jamaica was reported by Donovan (1993), with a tentative
generic identification of Paleopneusles sp. or Pericosmus sp. However, Donovan and
Embden (1996) identified this Pleistocene echinoid from the Manchioneal Formation
as Paleopneustes cristatus A. Agassiz, 1873, rather than a species of Pericosmus,
thereby eliminating any Jamaican fossil records of the genus.
Other fossil records of Pericosmus have been reported from localities including
eastern Africa, Madagascar, Italy, Japan, and the Philippines (Kier and Lawson, 1978).
In addition to these regions, several fossil taxa are known from New Zealand and


Australia. Henderson (1975) described three new Cenozoic Pericosmus taxa from
New Zealand and reported the occurrence of two previously described species;
therefore New Zealand represents the only area equal to Cuba in fossil species
diversity of the genus. The taxa and ages are: P. crawfordi (Hutton, 1873), Oligocene-
Miocene; P. borraeus Henderson, 1975, Miocene; P. scaevus Henderson, 1975,
Miocene; P. annosus Henderson, 1975, Eocene; and a taxon tentatively identified by
Henderson as Pericosmus? altus (Hutton, 1873), age uncertain but estimated to be
Oligocene. Henderson (1975, pp. 56-57) also noted that, until his work, two valid
species of Pericosmus, (i.e., P. compressus [Duncan, 1877] and P. maccoyi Gregory,
1890) were present in southeastern Australia. Following closer examination,
Henderson determined that both P. compressus and P. maccoyi only represent slight
morphological variations of P. crawfordi, and thus are synonyms of the New Zealand
species. Therefore, only five fossil species of Pericosmus are known from the New
Zealand and Australia region.
One point of significance regarding our Pericosmus spp. fossils is their age. All
the Cuban species were found in Eocene through Miocene age strata. The Venezuelan
and Costa Rican species both were collected from the Miocene. Therefore, our
specimens represent the youngest fossils of Pericosmus in the Caribbean and Gulf of
Mexico. In addition, only one other record of a Pliocene species (i.e., P. schencki
Israelsky, 1933, from the Malumbang Formation, Philippine Islands) has been
published. In another complication of stratigraphic ranges, Israelsky (1933, p. 301)
noted in his paper that the age of the Malumbang Formation was uncertain because all
taxa but one were extant, so he believed the Malumbang may be younger than
Pliocene. Rocks collected from the dredge sites along the upper WFS are broadly
identified as Plio-Pleistocene age (Fountain and McClellan, in press), and therefore our
work may allow a biostratigraphic range extension of the genus. Furthermore, if our
identification is correct, this represents the first report of fossil Pericosmus from the
United States.

Brissid, gen. et sp. indet.
(Figure 9)

Material-One internal mold of a test (UF 57743) dredged from approximately
511 m, December 19, 1989, at OTB8 (27 05'N, 84 57'W) (UF locality 3811).
Measurements-Maximum internal mold length =33.5 mm, maximum internal
mold width = 30.8 mm, maximum internal mold height = 21.1 mm.
Discussion-Of the three echinoids recovered from the upper WFS Florida
slope, this specimen is the most poorly preserved. However, the general test length,
width, and height can be distinguished, as well as the slight sulcus along ambulacrum
III (Figure 9A-C). The relative proportions of these morphologic characteristics as a
reflection of the overall shape suggest a strong affinity to the family Brissidae.


A ..B' C

Figure 9. (A-C) Phosphatized internal mold of test from unidentified brissid (UF 57743) from
upper WFS dredge locality OTB8. (A) Aboral view. (B) Adoral view. (C) Lateral view. All
specimens are at natural size (Ix).

The stratigraphic range of brissids extends from the Cretaceous through the
Recent (Kier and Lawson, 1978; Smith, 1984), and species of this family are present in
Tertiary rocks of North America and the Greater Antilles. Numerous species of
brissids have been reported from Cuba in Eocene through Miocene strata (Sinchez
Roig, 1953; Kier, 1984), and one species of brissid has been reported from the
Pliocene of the Dominican Republic (Kier, 1992). In Jamaica, Donovan (1993) also
reported a variety of brissid species in selected units ranging in age from Eocene
through Miocene and the Pleistocene. Extant species of the family are present in the
marine realm of the Gulf of Mexico, Caribbean, and Western Atlantic, as well as most
other major oceans of the world.


Specimens collected from three localities (OTB8, OTB5, and WFSI) along the
west Florida slope were examined in the course of this study. Locality OTB5 contained
the most taxa, including molds of corals, brachiopods, mollusks, annelids, and one
echinoid (Pericosmus sp.). Locality OTB8 produced a single brissid echinoid, and at
locality WFSI another echinoid (Pericosmus sp.) was collected.
Due to the poor preservation of most of the above-mentioned specimens, and
therefore the inability to identify the taxa more specifically, paleoecologic
interpretation is rather difficult, although worthwhile. Additionally, we realize that even
though the preservation is similar at all three localities, the environmental settings for
all three sites may have been different. Therefore, the following provides only the most
basic interpretation of the paleoecology.
Present-day articulate brachiopods are always marine and benthic, and there is no
reason to suppose that fossil species, particularly in the Tertiary, were otherwise
(Logan, 1987). In the Caribbean, extant species of Tichosina range to 1000 m depth,
but rarely are found at depths of less than 100 m (Cooper, 1977). Therefore, the


Tichosina from the upper WFS, as well as most other brachiopod genera, are typically
poor depth range indicators.
Today, three living species of Xenophoridae are known to exist in the Western
Atlantic and Gulf of Mexico, Xenophora conchyliophora, Onustus caribaeus, and
Onustus longleyi. According to Ponder (1983) and Kreipl and Alf (1999), X.
conchyliophora, is mostly a shallow-water species. Onustus caribaeus is typically
found at depths greater than 100 m (down to 640 m). Onustus longleyi occurs at
depths between 180 and 695 m. As stated above, the single, incomplete, phosphatized
mold of Onustus sp. from the upper WFS exhibits the characters of the two deeper
water taxa mentioned above. We are thus confident that this specimen represents a
deep-water taxon; however, without better-preserved material, refinement of a
paleobathymetric interpretation is not possible.
The ecological regime inhabited by extant brissids around Florida and the
Caribbean includes a range of substrate grain-sizes from mud to coarse sands, and
water depth ranges from 0-3200 m (Serafy, 1979; Hendler et al., 1995). Unfortunately,
information regarding life habits of extant paleopneustids is not as easy to obtain. No
living Pericosmus has been observed in its habitat (Kier, 1984), so only indirect
interpretations can be made for both the fossil and modern taxa. Related taxa, the
schizasterids, found in the same geographic region of the Caribbean and Florida inhabit
a substrate grain-size range similar to the brissids noted above and have been reported
from depths ranging from 0-1750 m (Serafy, 1979; Hendler et al., 1995).
Extant species of Pericosmus are restricted to the Indo-West Pacific region
(Mortensen, 1951; Henderson, 1975; Kier, 1984). All species of the family
Paleopneustidae are tropical inhabitants of present seas with the exception of two taxa,
one of which is P. cordatus Mortensen, 1950. This species is found in Japanese seas
from Sagami Bay to southwestern Kyushu at depths of 80-200 m (Imaoka et al., 1990,
p. 125). Henderson proposed that even though all species in the family inhabit deeper
water (70-800 m), temperature appears to control their geographic distribution, so it is
likely the tropical-derived waters of the Kuroshio Current sustains the echinoids and
other warm water taxa in areas of southern Japan. McNamara (1984) described and
reported a single living species, P. porphyrocardius, as occurring along the continental
slope of Australia at water depths of 309-420 m. Kier (1984) suggested the Cuban
fossil species inhabited tropical waters greater than 100 m, based on the fact that
modern taxa normally live at depths of 200-500 m, with the shallowest taxa at 18-70
m. Kier also examined the morphological characteristics of the Cuban fossils, and on
this basis determined they likely burrowed deep enough infaunally to at least have the
dorsal portion of the test covered.
Therefore, based on the limitation of taxonomic resolution for the Florida
echinoids, we generalize that they likely inhabited a shallow water depth of less than
several hundred meters when living. Furthermore, the variety of brissids in the Carib-
bean and Florida and paleopneustids in the Indo-Pacific are infaunal (Mortensen, 1951;
Hendler et al., 1995), burrowing a few cm under the sediment-water interface to as
much as 10 cm deep. Using modern taxa as environmental indicator guides, we feel it
is likely the Pericosmus species reported herein occupied a similar habitat when alive.


O / Turbulent Water

CL /Quiet Water MODEL
Jw 1 Assemblages \\

Exposure Effects

Figure 10. Hypothetical models for fossil assemblage formation. Relationship between duration
of exposure of fossils on sea floor and the potential distance of transport of fossils (prior to
ultimate burial and incorporation into the rock record) will control assignment of specimens to
one of the three models plotted in figure (from Johnson, 1960).

Using the information known about modem species of brissids and schizasterids,
we suggest that the echinoids dredged from the upper WFS inhabited an environment
similar to that described in the above paragraph. The preservation of the fossil
assemblage can be interpreted using fossil assemblage models designed by Johnson
(1960). In Johnson's models, an assemblage of fossils can reflect the environmental
conditions affecting that assemblage. These include characteristics regarding the
relative distance of transport of individual organisms prior to burial and incorporation
into the sediment, as well as factors reflecting the amount of exposure on the surface of
the sea floor any organisms' remains had prior to burial. An illustration of the
relationship between the three fossil assemblage types, and the variation of
transportation and exposure effects on the fossil remains, is provided in Figure 10.
Examples of features found on fossils that can reflect the degree of transport or
exposure on the sea floor include (but are not limited to): density of fossils, size-
frequency distribution, fragmentation, surface condition of fossils, chemical and
mineralogical composition, orientation, and sediment structure and texture (see
Johnson, 1960, for complete discussion of important factors).
Although the fossils in this paper all were collected indirectly via dredging, some
generalizations can be made regarding the style of fossil assemblage that is present at
the collection localities. The best interpretation for these fossils would be as
representatives of Model II assemblages. Since the echinoids probably were shallow,


infaunal inhabitants (as were some of the mollusks), it is likely they died within the
substrate and had at least limited shelter from transportation (from their death site to a
new assemblage site), except in unusually high sea-floor scour conditions. The fossils
do, however, show some evidence of exposure effects. Exposure effects include
features such as epibiont encrustation and borings by other biologic entities. The fossils
collected along the upper WFS tend to show extensive borings (see figures 7A, 8).
Encrusting organisms, such as bryozoans and annelids, can be found on some of the
fossils, reflecting exposure to the sediment-water interface on the sea floor prior to
burial. Therefore, the moderate presence of exposure effects and the limited presence
of transportation effects on the fossils collected tend to support our interpretation of the
fossils as part of a Model II assemblage.


Sediments capping ferruginous phosphorite nodules recovered from the northern
portion of the study area (OTB8, OTB5, and WFS ) correspond to sequence I of
Mullins et al. (1988b), which, in turn, correlates to Vail supercycle TB2 (10.2 Ma)
through supercycle TB3 (late-middle Miocene to Holocene) (Haq et al., 1987).
Accumulation of ferruginous phosphorites predates subsequent invertebrate
fossilization, as well as the development of the BI nonferruginous nodules with which
they are associated (Fountain and McClellan, in press; Fountain et al., in prep). Based
on a model proposed for the WFS which favors sea level highstand conditions during
phosphogenesis (Fountain and McClellan, in press), formation of both phosphatic
fossil molds and BI nonferruginous nodules most likely would have occurred during
the Plio-Pleistocene (Fountain et al., in prep.).
This interpretation is supported by the age of incorporated planktonic
foraminifera. Globorotalia truncatulinoides, Globorotalia inflata, Globorotalia
menardii, Globorotalia tosaensis, and Globigerinoides ruber are found within
nonferruginous phosphorite in the northern portion of the study area and constrain the
age of the phosphatic sediment to the Plio-Pleistocene (Dix et al., unpublished data).
Thus, the macrofauna must have been present during the Plio-Pleistocene, with
phosphatization occurring during subsequent sea level highstands.
Sea level highstands associated with Vail supercycle TB3 third order cycles 3.4
through 3.9 (Haq et al., 1987) would have created conditions favorable to francolite
and glaucony crystallization, preserving the invertebrate macrofauna present within
WFS sediments. It seems likely that the fauna inhabited the area during either
transgressive or regressive episodes, which would have favored shallower water
depths. The presence of epifaunal and infaunal species tends to suggest increased
current velocities generated by a seaward deflection of the Loop Current associated
with a lowering of sea level. Subsequent burial associated with increased sea level and
a reduction in current velocity would have favored later preservation and
phosphatization of the macrofauna (Figure I1).


Figure 11. (A, B) Proposed diagenetic model for fossilization of the upper west Florida slope
invertebrate macrofauna. (A) Macrofauna most likely inhabited the upper slope during
transgressive or regressive sea level episodes. (B) Phosphatic molds are formed during episodes
of phosphogenesis associated with sea level highstands and increased Co. fluxes to WFS
sediments. Cog oxidation releases phosphorous (P) to surrounding pore waters, increasing
concentrations to levels required for francolite crystallization.



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