Timothy William Auch. PALEOECOLOGY OF MIDDLE PLEISTOCENE ESTUARINE
DEPOSITS IN SOUTHERN BEAUFORT COUNTY, NORTH CAROLINA. (Under the
direction of Dr. Scott W. Snyder) East Carolina University, Department
of Geology, November 1987.
Pleistocene deposits exposed in the Lee Creek mine near Aurora,
and penetrated by coring in southern Beaufort County, North Carolina
consist of unfossiliferous muds overlain by fossiliferous sands and
sandy muds. Co-occurrence of the bivalves Argopecten solarioides and
Anadara ovalis in shelly deposits indicates a middle Pleistocene age
(molluscan zone 2 of Blackwelder [1981b]) which postdates the James
City Formation and predates the Flanner Beach Formation (between 0.5
and 0.2 ma).
The "shell bed" is a condensed bed, more specifically a sifted
deposit, for which detailed community reconstruction is impossible.
The "oyster bed" is a paleo-channel deposit that is partially situ
and partially condensed. Each of these "beds" contains fossils derived
from a distinctive community (or communities), the precise nature of
which has been masked to produce time-averaged fossil associations.
Molluscan associations include: 1) Mulinia lateralis, which
characterizes fossiliferous muddy sands and shell "pavements"; 2)
Mulinia lateralis-Nuculana acuta, found in fossiliferous sandy muds; 3)
Crassostrea virginica-Corbula swiftiana, limited to muddy, sandy oyster
banks. Foraminiferal associations include: 1) Elphidium excavatum
forma clavata-E. limatulum, found with molluscan Association 1; 2)
Elphidium excavatum formae clavata and selseyensis, which occurs with
molluscan Associations 2 and 3. All associations indicate deposition
within a barrier-built estuarine ecosystem.
Within the estuarine ecosystem, each deposit represents a specific
environment. Fossiliferous muddy sands (molluscan Association 1,
foraminiferal Association 1) represent subtidal deposits along the
margins of a back-barrier lagoon or estuary mouth. Included shell
"pavements" were deposited in the intertidal zone along sandy shoals.
Fossiliferous sandy muds (molluscan Association 2, foraminiferal
Association 2) accumulated in quieter, perhaps slightly deeper portions
of a sound or estuary mouth. Muddy, sandy oyster banks (molluscan
Association 3, foraminiferal Association 2) represent subtidal to
intertidal deposits within a tidal creek or protected mainland
embayment. Underlying unfossiliferous muds represent organic-rich,
carbonate-poor channel muds of the estuary mouth and inner sound.
Vertical juxtaposition of these deposits requires lateral
migration of the appropriate depositional environments. Although the
entire sequence is associated with marine transgression, the
relationships of strata observed during this study may have been
produced either in direct response to an advancing shoreline or by
lateral migration of environments parallel to it.
PALEOECOLOGY OF
MIDDLE PLEISTOCENE ESTUARINE DEPOSITS
IN SOUTHERN BEAUFORT COUNTY, NORTH CAROLINA
A Thesis
Presented to
the Faculty of the Department of Geology
East Carolina University
In Partial Fulfillment
of the Requirements for the Degree
Master of Science in Geology
by
Timothy William Auch
November 1987
PALEOECOLOGY OF
MIDDLE PLEISTOCENE ESTUARINE DEPOSITS
IN SOUTHERN BEAUFORT COUNTY, NORTH CAROLINA
by
Timothy William Auch
APPROVED BY:
DIRECTOR OF THESIS
Dr. Scott W. Snyaer
COMMITTEE MEMBER
COMMITTEE MEMBER
COMMITTEE MEMBER mJL
Dr. William Miller, III
CHAIRMAN OF THE DEPi^TMENT OF-CEOLOGY
Dr. Carles Q. Brown
DEAN OF THE GRADUATE SCHOOL
ili
ACKNOWLEDGMENTS
Acknowledgments go, first and foremost, to my parents, Stephen and
Toni Auch. I neither would have started nor finished this program
without their encouragement and support. Great thanks go to my thesis
director Dr. Scott W. Snyder, who supplied much needed comment and
direction, listened objectively to my thoughts and ideas, and, most
importantly, laughed at my jokes. Thanks also go to the members of ray
thesis committee. Dr. William Miller, III, Dr. Lee J. Otte and Dr.
Stanley R. Riggs. Their editorial comments strengthened the thesis. 1
will fondly remember the cast of characters at East Carolina,
especially those who attained the pinnacle of panache and the climax of
clubdom; those who were members of the illustrious "lunch bunch". Life
was never too dull.
iv
TABLE OF CONTENTS
TITLE PAGE i
SIGNATURE PAGE ii
ACKNOWLEDGMENTS iii
LIST OF ILLUSTRATIONS AND TABLES vii
INTRODUCTION 1
GEOLOGIC SETTING 4
PREVIOUS WORK 9
Terrace Formations and Escarpments 9
Formations 13
Morphostratigraphic Units 20
METHODS OF STUDY 22
FIELD OBSERVATIONS 27
Locality 31
Locality 2_ 34
Locality _3 34
Locality ^ 37
SEDIMENTS 40
STRATIGRAPHY 46
TAPHONOMY 53
Taphonomic Observations 55
"Shell Bed" 55
"Oyster Bed" 59
DEFINITION OF FOSSILIFEROUS ASSOCIATIONS 60
PALEOECOLOGICAL INTERPRETATIONS 64
Introduction 64
Species Distribution 66
Diversity 70
Molluscan Associations 72
Mulinia lateralis Association 72
Mulinia lateralis-Nuculana acuta Association 82
Crassostrea virginica-Corbula sviftiana Association... 88
Foraminiferal Associations 94
Elphidium excavatum forma clavata-Elphidium limatulum
Association 94
Elphidium excavatum formae clavata and selseyensis
Association 100
DEPOSITIONAL ENVIRONMENT 104
Modem Pamlico Sound 104
Pleistocene Deposits 107
SUMMARY 113
ANNOTATED FAUNAL LIST 116
Introduction 116
Foraminifera 117
Bivalves 130
Gastropods 154
REFERENCES 169
APPENDIX A: COMPLETE FAUNAL LIST 179
APPENDIX B: RELATIVE ABUNDANCES OF IDENTIFIED FORAMINIFERA 182
APPENDIX C: RELATIVE ABUNDANCES OF IDENTIFIED MOLLUSKS 184
APPENDIX D: STATISTICAL COUNTS OF THE SAND FRACTION
vil
LIST OF ILLUSTRATIONS AMD TABLES
FIGURE 1: MAP SHOWING LOCATION OF STUDY AREA 2
FIGURE 2: CROSS-SECTION OF SEDIMENTARY FORMATIONS 5
FIGURE 3: MAP OF STRUCTURAL AND TOPOGRAPHIC FEATURES 7
FIGURE A: TABLE OF PLEISTOCENE STRATIGRAPHY IN N.C 10
FIGURE 5: CHART OF EVOLUTION OF PLEISTOCENE TERRACE FORMATIONS... 12
FIGURE 6: MAP OF THE SUFFOLK SCARP 14
FIGURE 7: CORRELATION CHART OF PLIOCENE AND PLEISTOCENE DEPOSITS. 17
FIGURE 8: MAP OF DRILL HOLES 55-80, 59-80 AND 68-30 23
FIGURE 9: STRATIGRAPHIC COLUMNS FOR LOCALITIES 1-4 28
FIGURE 10: MAP VIEW OF MINING BLOCKS, LEE CREEK MINE 30
PLATE 1: PHOTOS OF THE "SHELL BED" 32
PLATE 2: PHOTOS OF THE "OYSTER BED" 35
TABLE 1: PERCENT MUD-SAND-GRAVEL FOR EACH SAMPLE 40
FIGURE llA-C: DIAGRAMS OF WEIGHT PERCENTS OF SEDIMENTS 41
TABLE 2: AVERAGE SAND GRAIN SIZES FOR EACH SAMPLE 44
FIGURE 12: SCHEMATIC CROSS-SECTION OF ESTUARINE DEPOSITS 48
FIGURE 13A-C: CUMULATIVE FREQUENCY DIAGRAM OF SPECIES FOR
MOLLUSCAN ASSOCIATION 1 73
TABLE 3: LIFE HABIT AND HABITAT OF SPECIES FROM MOLLUSCAN
ASSOCIATION 1 76
TABLE 4: PERCENT ABUNDANCES OF SPECIES FROM MOLLUSCAN
ASSOCIATION 1 77
TABLE 5: LIFE HABIT AND HABITAT OF SPECIES FROM MOLLUSCAN
ASSOCIATION 2 33
vili
FIGURE 14: PERCENT ABUNDANCES OF SPECIES FROM MOLLUSCAN
ASSOCIATION 2 84
TABLE 6: DIVERSITY AND EQUITABILITY INDICIES 87
TABLE 7: LIFE HABIT AND HABITAT OF SPECIES FROM MOLLUSCAN
ASSOCIATION 3 89
FIGURE 15: PERCENT ABUNDANCES OF SPECIES FROM MOLLUSCAN
ASSOCIATION 3 90
FIGURE 16A-C: CUÎ-1MULATIVE FREQUENCY DIAGRAMS OF SPECIES FROM
FORAMINIFERAL ASSOCIATION 1 95
TABLE 8A-B: PERCENT ABUNDANCES OF SPECIES FROM FORAMINIFERAL
ASSOCIATIONS 1 AND 2 98
FIGURE 17A-B: CUl'iMULATIVE FREQUENCY DIAGRAMS OF SPECIES FROM
FORAMINIFERAL ASSOCIATION 2 102
PLATE 3: SEM PHOTOGRAPHS OF ELPHIDIUM SPECIES 126
PLATE 4: SEM PHOTOGRAPHS OF AMMONIA AND BUCCELLA SPECIES 128
INTRODUCTION
Pleistocene deposits in the east-central portion of the North
Carolina Coastal Plain are generally poorly exposed. However, a
Pleistocene section is well exposed at the Lee Creek Mine of Texasgulf,
Inc. located near Aurora in Beaufort County. This exposure consists of
fluvial-estuarine sands and clays, and two fossiliferous deposits. One
deposit is a thin (approximately 1 ra) bed consisting of slightly muddy,
highly fossiliferous sands that unconformably overlie muds and are
unconformably overlain by unfossiliferous, iron-stained sands. This
"shell bed" is exposed throughout much of the mine. The other deposit
occurs as a channel cut filled with highly fossiliferous mud, which is
unconformably underlain and overlain by a darker, unfossiliferous mud.
The entire depositional package of muds, fossiliferous sands and muds,
and sands unconformably overlies the James City Formation (or Croatan
Formation) and extends upwards, terminating at the top of the exposure.
According to Gibson (1983), the age of the Croatan Formation is late
Pliocene to early Pleistocene. This interpretation suggests that the
age of the "shell bed" and shelly channel-fill deposits is middle
Pleistocene.
The study area is located in southern Beaufort County. It is
bounded to the north by the Pamlico River and extends southward to the
county line (Fig. 1). Samples used in this study were obtained from
exposures of the shell bed and channel-fill deposits in Lee Creek Mine,
and from cores drilled into the coastal plain subsurface. . Cores
yielded samples with faunas and sediments similar to those of the two
2
Figure 1. Map showing location of the study area in the
of CoastalNorth Carolina. Plain
fossiliferous deposits exposed in Lee Creek Mine.
The objective of this study is to provide paleoecologic and
stratigraphic information useful in interpreting Pleistocene deposits
of the North Carolina Coastal Plain. Initial focus is placed on: 1)
the composition of the deposits, and 2) the stratigraphic relationships
that exist between these deposits and other Pleistocene deposits found
along the North Carolina Coastal Plain. What follows is a
paleoecological study emphasizing 1) taxonomic identification of macro-
and microfauna (mollusks and foraminifera), 2) characterization of
species' habits and habitats, 3) taphonomy of the fossiliferous beds
and the quality of preservation, 4) analysis of species distributions,
5) means of accumulation and preservation of fossiliferous deposits,
and 6) analysis of the depositional environment.
GEOLOGIC SETTING
The eastern portion of the North Carolina Coastal Plain is low,
generally broad, borders the Atlantic Ocean and slopes gently seaward.
It is composed of a seaward-thickening wedge of strata that dates back
to the Cretaceous Period. The exposed coastal plain represents
recently emerged sea floor. Repeated cycles of submergence and
emergence controlled the extensive build-up of coastal deposits.
The North Carolina Coastal Plain is a portion of a larger coastal
plain that stretches from New Jersey to Texas and slopes east-southeast
from the fall line at its western edge. The North Carolina Coastal
Plain is drained by numerous rivers that flow into estuaries as they
near the coast. The largest of these estuaries are the Albemarle and
Pamlico Sounds, and the Pamlico and Neuse Rivers; all of which occur
north of Cape Lookout (Fig. 1). Subsurface deposits of the North
Carolina Coastal Plain include the Cretaceous Black Creek and Pee Dee
Formations, the Paleocene Beaufort Formation, the Eocene Castle Hayne
Limestone, the Miocene Pungo River Formation, and the Pliocene Yorktown
Formation (Fig. 2). Lying stratigraphically above these formations is
a thin veneer of Plio-Pleistocene and Holocene deposits.
Pleistocene deposits in North Carolina are composed of fluvial,
estuarine and marine deposits. Distribution of these deposits is
related both to the tectonic framework of the Atlantic Coastal Plain
and to variations in Pleistocene climatic conditions. Cenozoic and
Pleistocene sediments lap onto the flank of the Carolina Platform,
which is a block of pre-Jurassic continental crust extending from
5
Figure 2. Cross-section of sedimentary formations in Beaufort County
(after Mauger, 1979; from U. S. Army Corps of Engineers, 1977)
Georgia to Virginia (Klitgord and Behrendt, 1979). Associated with the
Carolina Platform is the Mid-Carolina Platform High (Hine and Riggs,
1986). Originally recognized as the Cape Fear Arch by Stephenson
(1923), the Mid-Carolina Platform High is not a distinct anticlinal
structure; rather it represents the topographically highest portion of
the Platform. Tertiary sequences were subsequently deposited around
the axis of this paleotopographic high (Fig. 3). Another positive
feature associated with the Carolina Platform is the Cape Lookout High
(Fig. 3). This paleotopographic high was created by sediment drift
resulting from wandering of the ancestral Gulf Stream during the
Oligocène (Snyder, 1982). The Cape Lookout High controlled subsequent
Miocene deposition, although the controlling influence lessened
significantly after Miocene sedimentation essentially buried the
feature (Hine and Riggs, 1986). Deposition during the Pleistocene
occurred primarily north of Cape Lookout on the flank of the Carolina
Platform. Greatest thicknesses of Pleistocene sediments accumulated in
the Albemarle Embayment, located between Cape Lookout and the Norfolk
Arch (Gibson, 1967) (Fig. 3).
Distribution of Pleistocene sediments was also affected by glacio-
eustatic sea level fluctuations. As glaciers developed, sea level
dropped, exposing areas where sediment had previously accumulated. A
period of non-deposition and erosion followed. As the climate warmed
and glaciers melted, sea level rose, and a period of deposition
followed. Glacial and interglacial climatic variations, coupled with
the structural/topographic character of the North Carolina Coastal
7
Figure 3. Map of structural and topographie features that have
influenced coastal deposition during the Cenozoic and
Pleistocene (Gibson, 1967; Snj'der, 1982; Hine and Riggs,
1986).
8
Plain, contributed to stratigraphic complexities found within
Pleistocene and Holocene deposits.
PREVIOUS WORK
Historically, interpretation of Pleistocene deposits of the North
Carolina Coastal Plain has been marked by controversy, owing in part to
the complexity of sediment patterns but also to the use of varying
interpretive schemes that are difficult to reconcile with one another.
It is against the resulting background of bewildering terminology that
the Pleistocene fossiliferous sequences in Beaufort County must be
stratigraphically interpreted. Reference to Figure A will help to
clarify the following summary, which is offered not as a solution to
stratigraphic problems but as evidence for the complexity of such
problems.
Several interpretive schemes have been used to describe
Pleistocene depositional sequences. These schemes include the concepts
of terrace formations, escarpments and morphostratigraphic units, as
well as the attempt to define Pleistocene exposures as formations.
Each scheme offers a slightly different explanation of the depositional
history of the coastal plain and, often times, supplies stratigraphic
interpretations that are in conflict with other schemes. Therefore,
any attempt to correlate the depositional members of one scheme to
another is speculative.
Terrace Formations and Escarpments
Shattuck (1901, 1906) first described a terrace formation in his
works concerning the Maryland Coastal Plain. He considered the terrace
formation a thinly-veneered plain composed of marine sediments that
10
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Figure U® Historical account of Pleistocene stratigraphy in
North Carolina. Note: NETJSE RIVER and PAMLICO RIVER
in Miller (1985) refer to bodies of water, not deposits.
terminates landward (or westward) at a wave-cut scarp. He believed the
"terrace" to be underlain by and coextensive with stratigraphic unit(s)
forming its profile. Both the stratigraphic unit(s) and morphologic
surface were given the same name. Stephenson (1912) used the terrace
formation concept to define the general "stair-step" or terraced
topography of the North Carolina Coastal Plain. Stephenson's terrace
formations, set apart by a series of erosional scarps, not only include
surficials, but also contain the underlying deposits, which he
considered to be Pleistocene.
Listed below and shown in Figure 5 are Stephenson's (1912) five
Pleistocene terrace formations:
Pamlico +0 to +25 ft. MSL
Chowan +25 to +50 ft. MSL
Wicomico +50 to +110 ft. MSL
Sunderland +110 to +160 ft. MSL
Coharie +160 to +235 ft. MSL
With the exception of one locality in the Chowan Formation, the Pamlico
was thought to be the only formation that contained marine fossils.
Stephenson equated the Chowan and Pamlico Formations with Shattuck's
Talbot Formation, a Maryland Coastal Plain deposit described in 1906
(Fig. 5). Cooke (1931) dropped Stephenson's Chowan Formation and
replaced it with the Talbot Formation. Richards (1950) related Cooke's
Horry Clay (1937), which is a cypress-bearing peaty clay exposed at
Myrtle Beach, S. C., back to Holmes' (1885) description of a similar
clay deposit near Flanner Beach, N. C. Richards considered the
deposits correlative, referring to both as the Horry Clay, and
continued to recognize Stephenson-'s-Pamlico Formation, but placed it
above the Horry Clay. Richards also noted exposures of Cooke's (1931)
12
Figure 5 Chart showing the evolution of Pleistocene terrace-formation
terminology.
13
Talbot Formation along the Chowan River, although he did not believe it
was exposed along the Meuse River.
Many references have been made to the escarpments that separate
Stephenson's terrace formations. Greatest controversy surrounds the
north-south trending scarp separating the upper Chowan surface (Talbot
msu) from the lower Pamlico surface (Pamlico msu) (Figs. 4 and 6).
Many names have been applied to this scarp, although the existence of
the feature is not in question. What Stephenson (1912) termed the
Pamlico escarpment was referred to by Richards (1950) as the Pamlico
shoreline occurring at +25 feet MSL and extending south from the
Pamlico to the Meuse River. The Suffolk Scarp was named by Wentworth
(1930) for a feature in southeastern Virginia and was later correlated
with the Pamlico escarpment by Flint (1940). Mixon and Pilkey (1976)
did not believe the Suffolk Scarp of Virginia and the Pamlico
escarpment were formed at the same time. They renamed Stephenson's
Pamlico escarpment the Grantsboro Shoreline. Daniels (1977) and Miller
(1985) did not agree with Mixon and Pilkey's interpretation and called
this erosionad feature the Suffolk Scarp. The crest of the Suffolk
Scarp has been referred to as both the Arapahoe Barrier by DuBar and
others (1974), and the Minnesott Ridge, which is composed of the
Minnesott Sand, by Daniels and others (1972).
Formations
In an attempt to define and correlate Pleistocene exposures, many
workers did not adhere to original terrace formation nomenclature and
adopted formational names based upon litho- and biostratigraphic data.
Figure 6. Map of the Suffolk Scarp. The Pamlico msu runs eastward
from the toe of tne scarp, while the Talbot msu is situated
to the west (Daniels et.al., 1972; Mixon and Pilkey, 1976),
These newly-named formations often contained several lithologies, which
led to later disagreement and further division of formations into other
formations, members and separate units of sands and clays.
Dali (1892) proposed the name "Croatan beds" for all exposures
along the Neuse Estuary near Croatan. Although he described both
sediments and molluscan fauna, he did not formally designate a type-
section. Mansfield (1928) stated that Dali's Croatan molluscan
assemblages contain mixtures of both Pliocene and Pleistocene species;
so, he divided the unit into two parts, applying the name "Croatan" to
Pliocene deposits and "Chowan" to overlying Pleistocene deposits. In
1936, Mansfield and MacNeil collected samples from an exposure along
the southern bank of the Neuse River, 2 miles south of James City,
North Carolina. Mansfield (1936) placed the lower 15 feet of this
exposure within his "Croatan" and the overlying deposits in his
"Chowan". MacNeil (1938) proposed the same 15-foot section as the
type-section for the Croatan Formation. DuBar, Solliday and Howard
(1974) believed that the beds to which Mansfield assigned the names
"Croatan" and "Chov^ran" represent a singular fossiliferous Pleistocene
unit containing reworked Pliocene fossils.
DuBar (1959, 1962) discussed the ages and stratigraphic
relationships between the Croatan and Waccamaw Formations, suggesting
that they are correlative Plio-Pleistocene units. DuBar and Solliday
(1963) suppressed the name "Croatan" and replaced it with "James City".
They also rejected the Pamlico Formation of Stephenson (1912), and
referred to the deposits which overlie the James City Formation as the
16
Planner Beach Formation. Their Planner Beach includes parts of the
former Pamlico and Chowan Formations, as defined by Stephenson and
Mansfield, and the cypress-bearing Horry Clay. DuBar and Howard (1969)
discussed the paleoecology of the type James City Formation, which they
maintained was late Pliocene to Pleistocene.
Fallaw and Wheeler (1969) continued usage of Croatan Formation for
deposits previously referred to as James City, at the same time
rejecting the name Planner Beach because this formation contains
numerous distinct lithologies. They reintroduced the Horry Clay,
placed all marine fossiliferous deposits found above the Horry Clay
within the Neuse Formation and delineated surficial, unfossiliferous
sands as a separate unnamed late Pleistocene formation. In 1974,
DuBar and others rejected Fallaw and Wheeler's proposals, retained the
names "James City" and "Planner Beach" and placed unnamed surficial
sands west of the Arapahoe Barrier into the "Cherry Point unit".
Gibson (1983) described upper Pliocene to lower middle Pleistocene
deposits in eastern North Carolina. His description included the
"Yorktown Formation" in southeastern Virginia and northeastern North
Carolina, the Croatan and James City Formations in east central North
Carolina, and the Waccamaw Formation in southeastern North Carolina and
northeastern South Carolina (Fig. 7). Gibson equated the Croatan and
Waccamaw Formations with his "Yorktown Formation", which he viewed as
the undifferentiated late Pliocene-early Pleistocene top of the
Yorktown Formation. He believed the "Croatan" and "James City" to be
correlative. Gibson's solution to past nomenclatural controversy was
to suggest that the name "Croatan" be reserved for deposits in the Lee
17
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Figure 7. Correlation of Pliocene and Pleistocene deposits in
southeast Virginia, North Carolina and northeast South
Carolina.
18
Creek Mine and the name "James City" be used for deposits that crop out
along the Neuse River. Hazel (1983) studied the ostracodes of the
Yorktown and Croatan Formations exposed at Lee Creek Mine. On the
basis of faunal differences, he divided the Croatan into upper and
lower parts, correlating the upper part with the Plio-Pleistocene
Waccamaw Formation and the lower part with the Pliocene Bear Bluff
Formation (Fig. 7).
Blackwelder (1981a) proposed the Chowan River Formation for marine
and estuarine deposits of late Pliocene age exposed along the Chowan
River in North Carolina (at least partially equivalent to Gibson's
"Yorktown Formation"). He divided this formation into the Edenhouse
Member and overlying Colerain Beach Member (Fig. 7). Blackwelder
suggested the name Croatan Formation be dropped and proposed that the
Croatan be separated into the lower Chowan River Formation and
overlying James City Formation on the basis of changes in lithology and
fauna. I agree with this interpretation because the name "Croatan" is
confusing. "Croatan" originally referred to Dali's (1892) "Croatan
beds". These beds were later sub-divided into two parts by Mansfield
(1936), the lower part being named the "Croatan Formation". Thus,
conflicting stratigraphic meanings for the name "Croatan" exist. Usage
of the "James City Formation" in place of the "Croatan Formation" is
less confusing and makes better stratigraphic sense.
Mixon and Pilkey (1976) divided the Planner Beach Formation into
three informal members. These include, from base to top, the Beard
Creek member, Arapahoe Sand member and Newport Sand member. The Beard
19
Creek member is composed of the cypress-bearing peaty clay deposit (the
Horry Clay of other workers) and overlying estuarine and marine
fossiliferous muddy sands. The other two members are interpreted to be
barrier sands and are laterally equivalent. Mixon and Pilkey also
named the "Core Creek sand" for fossiliferous and non-fossiliferous
sands that underlie the surface of Bayboro and Core Creek plains east
of the Minnesott Ridge. Also named were late Pleistocene deposits that
either impinged upon or overlay the Core Creek sand. Mixon and Pilkey
regarded the "Small Sequence" of Daniels and others (1972) as an
invalid geologic unit and did not attempt to assign any deposits to
either the Talbot or Pamlico msu.
Based on lithology, Miller (1985) formally named four members
within the Planner Beach Formation, including the Arapahoe Sand,
Newport Sand and Beard Creek members of Mixon and Pilkey (1976), and a
fourth member called the Smith Gut. Miller also studied exposures of
two brackish estuarine sequences found along the Pamlico River, 16 km
southeast of Washington. He called these sequences the Hills Point and
Mauls Point Members, and stated that they are roughly time equivalent
with the Planner Beach Formation. The Hills Point Member grades into a
different facies that Miller referred to as the unnamed member.
Susman and Heron (1979) described three lithologies in Pleistocene
and Holocene deposits at Shackleford Banks. They applied the name Core
Creek sand (Mixon and Pilkey, 1976) to a fossiliferous sandy
Pleistocene deposit and placed overlying Holocene deposits within the
Diamond City Clay and Outer Banks Sand.
Snyder and Katrosh (1979) examined an exposure of marginal marine
Pleistocene sediments at Fountain Quarry in Pitt County. Using
macrofauna and microfauna, they estimated the age of the unit as early
Pleistocene but did not feel that correlation with the Croatan or James
City could be conclusively demonstrated. Other unnamed units of
Pleistocene age were discussed by Belt and others (1983) in a
description of coastal marine and estuarine sequences in Lee Creek
Mine. Two sequences in particular, the "mottled unit" and the "peaty
clay", might be lateral equivalents of the "shell bed" and the mud unit
of this study. Belt and others proposed that the difficulties
surrounding identification of Pleistocene deposits in Lee Creek Mine
and within the North Carolina Coastal Plain are related to erosion of
previously deposited sediments and subsequent redeposition over the top
of a partially or entirely eroded depositional surface, as well as to
lateral changes in the composition of time-equivalent units.
Morphostratigraphic Units
Daniels and others (1972) expanded upon Stephenson's work, using
the term "morphostratigraphic unit" (msu) to describe the Pleistocene
deposits of the North Carolina Coastal Plain. A morphostratigraphic
unit is identified primarily from the surface form it displays. Frye
and Willman (1960, p. 37) stated that a morphostratigraphic unit "may
or may not be distinctive lithologically from contiguous units; it may
or may not transgress time through its extent". Daniels and others
preferred msu to terrace or formation because the msu, by definition,
incorporated both the surficial deposits of a terrace and the deposits
(or formations) which lie directly beneath the surface.
21
In their treatment of Stephenson's work, Daniels and others (1972)
recognized Stephenson's terraces and escarpments, but believed that
there is little evidence at this time to prove whether or not a new
formation begins at the toe of each scarp. The only difference
between the terrace formation concept of Stephenson and the msu of
Daniels and others is the interpreted topographic extent of each.
Whereas Stephenson's terraces extend past escarpments up major rivers
and estuaries, enwrapping unsubmerged portions of the previous terrace,
Daniels and others place all surfaces and deposits found behind each
escarpment within each respective msu.
Daniels and others (1972) informally named the Croatan Formation
(including the James City Formation) the Small Sequence, and created
the Talbot msu and the Pamlico msu. Included v\rithin the Talbot msu are
the Flanner Beach Formation of DuBar and Solliday (1963) and the Neuse
Formation of Fallaw and Wheeler (1959), and included within the Pamlico
msu are the Minnesott Sand of the Minnesott Ridge (Arapahoe Barrier of
DuBar and Solliday, 1963) and surficial sediments east of the Suffolk
Scarp. Daniels and others (1983) did not extend the Pamlico msu up the
Neuse River Estuary to include exposures of the cypress-bearing peaty
clay and overlying deposits as they had previously done with the
Pamilco Formation, but they stated that the Pamlico msu may overlie a
portion of the Talbot msu east of the Suffolk Scarp.
METHODS OF STUDY
Field Techniques
Samples of fossiliferous Pleistocene deposits were collected from
five localities v/ithin the study area. Localities 1 through 4 are
situated in Lee Creek Mine. Field observations, including the bed
thickness, textural characteristics, sediment-structures and facies
relationships, v/ere noted at each locality. Bulk samples of
approximately 0.25 cubic meters were collected from Localities 1
through 3. Sampling v/as initiated at the base of the bed. Samples at
all localities are numbered sequentially from bottom to top of the bed
(see stratigraphic columns in Fig. 9 for position of sampling
intervals). Four samples were taken from Locality 1, three from
Locality 2, and one from Locality 3. Locality 4 best exhibited the
stratigraphic relationships among the "shell bed", the mud unit and
the "oyster bed". To aid in taxonomic identification of macrofossils,
well-preserved specimens were collected from float debris.
Core samples from drill holes 55-30, 59-80 and 68-80 were
provided by Texasgulf, Inc. (Fig. 8). Whereas Hole 59-80 yielded no
evidence of the Pleistocene fossiliferous deposits. Hole 68-30 produced
three core samples and riole 55-80 produced one. The stratigraphic
position of these core samples relative to the underlying James City
Formation indicated that they might be correlative with the Pleistocene
fossiliferous deposits exposed at Lee Creek Mine.
Analytical Techniques
23
Figure 8e Map showing position of drill holes relative to
Lee Creek Mine#
Bulk samples and core samples (not including sample 3 of Hole 68-
30) were each divided into two small-volume samples (about 120 ml) and
one large sample. One small-volume sample was used to calculate
gravel-sand-mud percentages and the other was archived. Analysis of
gravel-sand-mud percentages began by weighing the dry samples. Weighed
samples were soaked in a dilute sodium hexametaphosphate (Galgón)
solution for at least seven days and then wet sieved. Gravel and sand
percentages were based on the dry weight of size fractions trapped on
U.S. Standard Sieves #10 (gravel—2 mm) and #230 (sand—.00625 mm).
Because the muds were washed away, mud percentages were calculated by
subtracting weights of sand and gravel from total-sample v/eight.
Large samples were soaked and sieved in the same manner as small-
volume samples used for gravel-sand-rnud calculations. The gravel- and
sand-sized fractions Virere retained and dried. To facilitate
macrofaunal identification, the gravel fractions were split into
workable sizes such that a minimum of 300 v/hole or partially fragmented
individuals could be counted. The left and right valves of each
bivalve species were isolated and tallied. The highest valve total was
considered to be the number of individuals per species. Gastropods and
barnacles være grouped by species and counted. Relative abundances of
species were calculated for each sample. The fact that some of these
organisms might not be indigenous v/as taken into consideration,
although it appears that all identified organisms are autochthonous
(see taphonomy section).
Each sand fraction sample \ias split into two sub-samples. The
larger sub-sample, used for miicrofaunal analysis, was soaked in a
dilute sodium hexametaphosphate solution for at least 24 hours,
breaking up residual clays that were later rinsed from sand-sized
particles trapped on a U.S. Standard Sieve i!-230. After air drying,
each sieved sub-sample was floated in carbon tetrachloride. Because
many of the raicrofossils did not float the first time, two to three
floats v/ere necessary. Floated concentrates of microfossils were then
split, using a microsplitter, and spread out onto a grid-marked picking
tray. Specimens resting in the squares of the grid were picked in an
orderly fashion (i.e., square by square) until at least 300 individuals
had been collected. Individuals were identified to species level under
a binocular microscope using published descriptions, figures and plates
[Copeland (1964), Schnitker (1971), and A.A.L. Miller and others
(1982)].
Relative abundances of molluscan and foraminiferal species were
calculated for each sample, as was the Shannon-V/iener Information
Function, using the Checklist program for the Apple II microcomputer.
The Shannon-Wiener Information Function is a measure of species
diversity and is written as:
I-Î(S) = -^P In p ,
i i
where p equals the relative abundance (expressed as a decimal value)
i
of a given species.
The smaller sub-sample was used for sediment description of the
sand fraction. Each sub-sample was spread onto a grid-marked picking
tray. Grains that rested on grid lines were counted in an orderly
fashion until at least 100 grains were tallied. Using the binocular
microscope, composition, grain size and degree of angularity were
determined for counted grains. No microfaunal analysis v/as performed
for sample 3 of Hole 63-80 because the sediment was inadvertently
washed away prior to this study.
FIELD OBSERVATIONS
Two fossiliferous deposits, each representing a distinct
depositional environment, are exposed in the shallow subsurface at the
Lee Creek Mine. These two deposits are referred to as the "shell bed"
and the "oyster bed". The stratigraphic relationships of these
fossiliferous deposits are shown in Figure 9. Sample localities in the
mine are represented in Figure 10. The "shell bed" was sampled at
Localities 1 and 2 along the north and south walls of Mine-block 10,
and examined at Locality 4 in Mine-block 18. Samples were taken to
provide maximum stratigraphic coverage and to ensure that all
faunal/textural components at each locality were examined. The "shell
bed" is composed of slightly muddy, fine quartz sand and contains a
variety and abundance of molluscan species numerically dominated by
Mulinia lateralis. The "shell bed" in Mine-blocks 10 and 18 lies 3 to
5 m above the James City Formation. The lateral extent of the "shell
bed" (traced using core-hole data supplied by Texasgulf) will be
discussed later.
The "oyster bed" at Locality 3 (Mine-block 11) is a small
channel-cut exposed along the westernmost mining face adjacent to
Porter Creek (Fig. 10). One bulk sample was taken at this locality.
Another "oyster bed" is exposed at Locality 4 in Mine-block 18.
Deposits at both localities are composed of highly fossiliferous mud
numerically dominated by Crassostrea virginica. Although the James
City Formation is not exposed at Locality 3, it is present below the
oyster bed at Locality 4. The channel deposits are bounded vertically
28
Figure 9.
Stratigraphic columns of middle Pleistocene estuarine deposits
exposed in Lee Creek Mine. Approximate location of each sampling
locality is shown in Figure 10. Sampling intervals are indicated by a
dash and the corresponding sample number. Columns exhibit interpreted
stratigraphic relationships existing betv/een the "shell bed", the
"oyster bed" and the mud unit. Lying unconformably below this
estuarine sequence is the James City Formation. The contact is
inferred because it was covered by spoil. Unconformably overlying the
"shell bed" at Localities 1, 2 and 4, and the mud unit at Locality 3 is
an unfossiliferous iron-stained sand. Zero meters represents the mine
surface and not MSL. There is no horizontal scale.
Symbols
- sand
- mud
\^\ - Argopecten
1.5SI - Crassostrea
1 - Mulinia
(TTôl - Cyrtopleura
- other mollusks
- burrows
Locality 1 Locality 2 Locality 4 Locality 3
30
Figure 10, lîap view of mining blocks in Lee Creek Mine, Localities
l-U are marked within corresponding blocks.
and laterally by a homogeneous mud.
Locality
The lower contact of the "shell bed" is at the base of an
accumulation of large mollusks, including Argopecten solarioides,
Busycon carica, Cyrtopleura costata, Dinocardium robustum, Ensis
directus. Mercenaria mercenaria and Polinices duplicatas, and can be
traced in Plates la and lb. This interval is 10 to 20 cm thick.
Although larger mollusks appear to be abundant at first glance, smaller
mollusks are more numerous. Above the molluscan "pavement", the "shell
bed" is less-densely fossiliferous and contains mostly small gastropods
and disarticulated bivalves. The less-densely fossiliferous interval
becomes shellier up-section. The transition is marked by the
appearance of burrowing and reclining mollusks, some of which
(Cyrtopleura costata, Dosinia discus and Raeta plicatella) are in life
position. The uppermost portion of the bed contains abundant smaller
forms and terminates at a sharp contact. The entire deposit is
predominated by Mulinia lateralis and is 88 cm thick. Underlying the
Mulinia-dominated "shell bed" is a partially bioturbated, dark gray mud
(the mud unit). Plate 2b shows the iron-stained, mottled texture that
is typically present at the top of the mud unit. Overlying the "shell
bed" is an unconsolidated, unfossiliferous, iron-stained sand. Both
the mud unit and overlying sand are in sharp contact with the "shell-
bed". Plate la is a panoramic view representing a typical exposure of
the "shell bed".
32
PLATE 1
la) Panoramic view of the "shell bed" at Locality 1. The dark
geometric shapes near the center of the photograph represent areas
where samples were extracted. Exposures at Localities 2 and 4
display similar lateral and vertical continuity.
lb) Profile of the "shell bed" at Locality 1. Note the accumulation
of larger mollusks (referred to as the shell "pavement") at the
base of the bed. Exposures of the "shell bed" at Localities 2 and
4 are texturally similar.
33
34
2Locality
The lower contact of the "shell bed" is a series of shelly lenses
composed of slightly muddy, Mulinia-dominated sands that extend
downward into a mud similar in composition to the mud at Locality 1.
These lenses are 2 to 10 cm in length and represent either filled
burrows or erosiona! scours later filled by deposition of the "shell
bed". Mulinia-dominated sands extend upward 10 to 13 cm from the
contact to the abrupt appearance of a 13 to 16 cm-thick accumulation of
large mollusks. This concentration is nearly identical to the
"pavement" at Locality 1, differing only in its stratigraphic postion
within the bed. Large mollusks common to this interval include
Argopecten solarioides, Busycon carica, Dinocardium robustum, Ensis
directus and Mercenaria mercenaria. Cyrtopleura costata, Dosinia
discus and Raeta plicatella were found in life positions near the top
of this interval. Lying above the shell "pavement" is an interval of
Mulinia-rich sand some 50 to 55 cm thick that terminates at a sharp
contact. The "shell bed" is overlain by unconsolidated,
unfossiliferous, iron-stained sands identical to the sands at Locality
1. The entire "shell bed" is predominated by M. lateralis and measures
83 cm thick.
3Locality
The "oyster-bed" at Locality 3 is a channel cut filled with highly
fossiliferous dark-gray mud. Plate 2b shows the texture typically
associated with the muddy fossiliferous bed. The channel is cut into a
dark gray mud, slightly lighter in color than the channel mud. Above
35
PLATE 2
2a) View of the "oyster bed" at Locality 3. It is a paleochannel seen
in the center of the photograph.
2b) Photograph showing a Crassostrea-rich fossiliferous deposit and
underlying unit with mottled texture. The mottled texture was
created by bioturbation and is typically present at the top of
the mud unit.
36
the channel deposits are unfossiliferous, iron-stained sands. Both
underlying and overlying deposits are similar in composition to those
at Localities 1, 2 and 4, and appear to continue laterally between
sampling localities. The channel deposit is 84 to 93 cm thick at the
center and 13 to 16 m wide, one edge of the channel being covered by
spoil (Plate 2a). The most common mollusk is Crassostrea virginica.
Individual oysters near the sides of the channel are articulated and
encrusted, suggesting that they are close to or actually in life
position, whereas those in the center of the channel are disarticulated
and often broken, suggesting an up-channel or down-channel source.
Locality ^
Both the "shell bed" and "oyster bed" are exposed at Locality 4.
Deposits include a slightly muddy sand that becomes progressively
muddier as it grades upward into the "oyster bed", which, in turn, is
overlain by a burrowed dark gray mud. Unconformably resting upon this
interval is the Mulinia-rich "shell bed". The "shell bed" is overlain
by unfossiliferous, iron-stained sands.
Along the gradational contact between the "oyster bed" and
the slightly muddy sands, the moderately deep-burrowing bivalve Mya
arenaria (Linné) is present and is usually in life position. The
"oyster bed", unlike the channel cut at Locality 3, appears to
represent a lengthwise view of the channel. Its thickness ranges from
a few cm to nearly 1 meter. The most common mollusk is Crassostrea
virginica. Other species include Anadara transversa, Anomia simplex,
Corbula contracta and Corbula swiftiana, Cyrtopleura costata,
Mercenaria mercenaria, Noetia ponderosa and Polinices duplicatus.
Above the "oyster bed" is a burrowed, slightly fossilferous dark
gray mud 1 to 1.75 m thick. The burrows probably represent the work of
crustaceans and annelids. In some rare instances, the bivalve
Cyrtopleura costata penetrated the mud and is found resting at the base
of its burrow. Nearly every burrow is filled with the Mulinia sand
from the bed above. Burrowing activity is present throughout the mud,
but is most prevalent toward the top. Also present in the mud unit are
stringers composed of molluscan and barnacle hash. These highly
fragmented accumulations are just a few mm thick and appear to have
been introduced from shallower molluscan-rich areas by unusually strong
water currents generated by a storm.
The mud unit grades upward into the "shell bed". It is difficult
to pinpoint where the mud ends and the Mulinia bed begins because the
contact is obscured by intensive burrowing. Although Mulinia lateralis
is predominant, many other species of mollusks are present. Several
individuals of Panopea sp. occur at the base of the Mulinia bed.
Panopea's burrow initially extends downv/ards in a vertical fashion but
then slopes abruptly until the burrow and bivalve are nearly
horizontal. This burrow morphology is either a result of its inability
to penetrate the underlying mud, or is a deformational feature created
as the bed was condensed.
Near the base of the "shell bed" is an accumulation of larger
species present wherever the bed is exposed. The fauna associated with
the shell "pavement" is identical to faunas identified at Localities 1
39
and 2. Cyrtopleura costata is commonly found in life position and is
generally restricted to a zone just above the shell "pavement". It is
not clear why C_^ costata is restricted to this zone. Perhaps it
burrowed through the muddy sands but could not penetrate the shell
"pavement". Disarticulated valves of C_^ costata are present within the
"pavement". Above the shell "pavement" are sparsely fossiliferous
muddy sands that become progressively shellier toward the top of the
bed. Larger forms such as Dosinia discus, Mercenaria mercenaria and
Raeta plicatella occur in life position. The top of the bed is marked
by the appearance of Ensis directus. The valves of this moderately
deep burrower are oriented horizontally and are often broken.
SEDIMENTS
Deposits are composed of varying proportions of mud, sand and
gravel. The gravel fraction is composed solely of calcareous shell
material. Sands are predominatly quartz with minor amounts of
calcareous material and phosphate. Muds are made up of silts and
clays. Table 1 and Figure 11 a-e show mud-sand-gravel percentages for
each sample.
TABLE 1
C7
/o 7/'O % Corresponding
Mud Sand Gravel Faunal Associations
Locality 1
sample 4 11.6 70.3 13.1
sample 3 10.2 86.9 2.9
sample 2 11.1 81.0 7.9
sample 1 10.7 80.6 8.7
Foraminiferal and
Locality 2 Molluscan Association
sample 3 10.2 81.9 7.9 ^ 1
sample 2 8.7 80.9 10.4
sample 1 12.4 83.4 4.2
Hole 68-30
sample 1 17.8 69.7 12.5
sample 2 13.5 73.3 13.2
Hole 55-80
sample 1 60.0 36.3 3.7 Molluscan Association
I?t'Í z9.
Locality 3
sample 1 22.8 15.3 61.9 Molluscan Association
7f Z>
(Foraminiferal
Association # 2 is
associated with
both samples)
41
HOLE 6S-80
PERCENT OF SEDIMENT
20 40 60 80
SAMPLE
Figure 11, parts a-e.
Cummulative frequency diagrams exhbiting wei^t percentages for
sediment size fractions in each sample.
42
PERCENT OF SEDIMENT
4
3
UJ
a.
LOCALITY 2<CO 2
1
b
PERCENT OF SEDIMENT
20 40 60 80
_l I I l_
c
PERCENT OF SEDIMENT
LOCALITY 3
Sample 1
PERCENT OF SEDIMENT
HOLE 55-80
Sample 1
e
OJ
Mud-sand-gravel percentages from Hole 55-80 and Locality 3 are markedly
different than samples from Localities 1 and 2 and Hole 68-80.
Changes in sediment texture are reflected by and correspond to
fossiliferous associations.
The sand fraction is largely quartz grains and skeletal material.
Grain sizes range from coarse to very fine sand. In most cases, quartz
is predominant; but sample 1, Locality 3 has a co-dominance quartz and
skeletal material. Other components include small gastropods and
bivalves such as Acteocina canaliculata, Mulinia lateralis, Caecum
pulchellum (Stimpson) and Parvilucina multilineata, foraminifera,
ostracodes, glauconite, phosphate grains and magnetite. See Appendix
D for statistical counts.
Table 2 summarizes grain sizes, as determined by microscopic
inspection of the sand fraction for each sample.
Table 2
Locality 1 sample 4 very fine to medium ;
sample 3 fine to very fine
sample 2 fine to very fine
sample 1 very fine to fine
Locality 2 sample 3 very fine to fine
sample 2 very fine to fine
sample 1 very fine to fine
Hole 68-80 sample 2 fine to very fine
sample 1 very fine to fine
Hole 55-80 sample 1 very fine to fine
Locality 3 sample 1 very fine to fine
45
Fine to very fine sands found along the modern North Carolina
coast most commonly occur in estuarine, sound and back-barrier
environments and rarely extend into inlets or the shallow shelf
(Ingram, 1968). The amount of mud versus sand is a product of
vegetation (a baffling agent), coastal morphology and, ultimately, the
distance from an inlet and proximity to the center of a sound or the
back-side of a barrier island. Sites further away from an inlet and
closer to the center of a sound, back-barrier lagoon or estuary have
finer grain size (Ingram, 1968; Peterson and Peterson, 1979). This
results in a gradational accumulation of muds, sandy muds, muddy sands
and clean sands, representing deposition in response to lower and
higher energy regimes (Ingram, 1968). In addition to the effects of
hydrualic energy, biologic effects like bioturbation and accumulation
of fecal pellets, and the effect of local topography, including
proximity to river mouths, are important in determining what sediment
patterns will be preserved (Knox, 1986).
STRATIGRAPHY
Stratigraphers in the past have attempted to correlate Pleistocene
coastal plain sequences on the basis of similar lithologies.
Widespread correlation of deposits was also based on the depositional
time-frame determined by interpretation of scarps and terraces between
scarps. Correlation has proved difficult because Pleistocene deposits
are inconsistently exposed and represent many episodes of deposition,
subsequent erosion and redeposition. It is evident from difficulties
associated with the stratigraphic interpretation of Pleistocene coastal
sequences that the depositional history is more complex than simple
scarp-terrace correlation. Furthermore, correlation of deposits that
are similar in composition and are intermittently exposed across the
coastal plain and beneath the terrace surface is a simplification of
the regional stratigraphic history. What was or is considered to be a
single, laterally extensive, time-equivalent deposit, might actually
represent a multi-depositional event.
Middle Pleistocene deposits exposed in Lee Creek Mine are
thought to have been deposited during episodes of rising sea level.
Although barriers responsible for the development of a sound or
estuary must have migrated landward, the whole barrier system was not
superimposed on the entire coastal plain. Present sea level need only
rise a few meters to flood portions of the coastal plain, allowing
barriers to migrate toward but never reach newly flooded portions.
The depositional sequence exposed at Localities 1-4 is made up of
"oyster beds", a mud unit and the "shell bed". Irregularly exposed
oyster banks and channels occur stratigraphically below the "shell
bed"; they overlie fine to medium sands at Locality 4 and cut into a
mud unit at Locality 3. The mud unit and the "shell bed" were
encountered at every locality in Lee Creek Mine (except for Locality 3
where the "shell bed" was missing) and appear to persist laterally
throughout much of the mine. The mud unit underlies the "shell-bed"
and is separated from it by an abrupt contact. The "shell bed" caps
the sequence, which probably resulted from the lateral migration of
depositional environments during the late-early to middle Pleistocene.
Figure 12 is a schematic section showing the stratigraphic
relationships within this sequence in Lee Creek Mine.
This particular depositional sequence is not the only post-James
City Pleistocene sequence in the mine. Belt and others (1983)
recognized several Pleistocene coastal marine and estuarine sequences
in Lee Creek Mine, two of which (the mottled unit and the peaty clay)
are probably lateral equivalents of the "shell bed" and the mud unit.
Roberts (1981) noted what appears to be the mud unit ("M" for mud) and
the "shell bed" (the "light gray shelly sand"). Samples from a netv/ork
of cores, drilled from 1973 to 1979, revealed regions where these
deposits were either eroded away or never deposited. Data from cores
recovered between 1983 and 1985, made available by Texasgulf, also
document variable thickness and lateral pinch-outs of the "shell bed"
(referred to by mine personnel as the Mulinia bed) within the mine.
Holes 55-80, 59-80 and 68-80 were drilled in Beaufort County by
Texasgulf. Hole 59-80 did not yield any evidence of the "shell bed".
48
Figure 12.
Schematic stratigraphie cross-section of middle Pleistocene
estuarine deposits in Lee Creek Mine. The "oyster bed" has cut into
the mud unit. The "shell bed" caps the sequence. Undifferentiated
iron-stained sands overlie the "shell bed". The nature of the contact
between the mud unit and the James City Formation is unknown. Channel
width is 15 m.
s
- sand
- mud
- Argopecten
- Crassostrea
- Mulinia
- Cyrtopleura
- other mollusks
- burrows
JAMES CITY FORMATION
4
50
whereas Hole 68-80, samples 1 and 2 yielded Mulinia-dominated sands and
sample 3 yielded an oyster-dominated calcareous gravel. Sample 1
represents stratigraphic top. Hole 55-80 yielded a Mulinia-dominated
sandy mud. Although these deposits have lithologies and faunas similar
to deposits exposed at Localities 1-4, relationships among individual
units are not always similar (e.g., oyster gravels both underlying and
overlying a Mulinia-rich zone). Because of the limited sampling base
in southern Beaufort County, correlation with the exposed fossiliferous
deposits in the mine remains tentative.
Middle to late Pleistocene deposits in the North Carolina Coastal
Plain are an accumulation of marine and estuarine environmental
components that exhibit compositional changes over relatively short
distances and are not easily traceable (Belt, Frey and Gamble, 1983).
Further complexity is generated when successive events of regional
submergence and emergence are superimposed upon portions of the coastal
plain, altering previously deposited sequences. Although the pattern
of middle to late Pleistocene estuarine deposition has been rendered
complex and is now difficult to recognize, correlation of deposits and
sequences is possible and can be facilitated by: 1) increasing the
sampling base, especially across inter-estuary divides, 2) using
seismic stratigraphy, 3) better understanding the processes that are
responsible for the accumulation and erosion of deposits, and 4) more
thoughtful investigation of taphonomic and sedimentologic features
within fossil beds and other deposits.
The precise age of the estuarine depositional sequence exposed at
Localities 1-4 in Lee Creek Mine is difficult to determine. It can be
assumed, however, considering this sequence unconmformably overlies the
early Pleistocene James City Formation, that it is no older than late-
early Pleistocene and that it is not part of the James City Formation,
unless it represents the last gasp of the James City depositional cycle
(W. Miller, III, pers. comm.)- Based on the co-occurrence of the
extinct bivalve Argopecten solarioides and the extant bivalve Anadara
ovalis, and the fact that ^ solarioides does not appear to be reworked
into the "shell bed", these deposits are no older than molluscan zone
M2 (Blackwelder, 1981b). This zone includes the Canepatch Formation
of DuBar (1974). These deposits are not as young as the Socastee
Formation of DuBar (1974) or as the deposits at Flanner Beach (with the
possible exception of the Smith Gut Member) (L.W. Ward, pers. comm.;
Blackwelder, 1981b). According to Blackwelder (1981b), Argopecten
solarioides makes its last appearance in M2, whereas Anadara ovalis
makes its first appearance in zone M2 and marks the lower boundary of
the Myrtlean Substage of the Longian Stage. Thus, estuarine deposits
exposed in Lee Creek Mine are apparently restricted to the middle
Pleistocene (0.5 to 0.2 my). Amino acid racemization performed on
Mulinia lateralis valves from the Flanner Beach Formation and the
"shell bed" in Lee Creek Mine also suggest that the "shell bed" is
older than the Flanner Beach Formation. The Flanner Beach Formation
yielded a date of 0.2 my (McCarten and others, 1982), whereas the
"shell bed" produced an age of 0.4-0.5 my (L. York, pers. comm.).
Because of possible age discrepancies and the lack of sampling
control, correlation of estuarine Pleistocene deposits at Lee Creek
52
with other deposits such as the Shirley and Tabb Formations exposed in
southeastern Virginia, the Planner Beach Formation exposed along the
Neuse River, and the Canepatch Formation in South Carolina is not
advisable. Even correlation with similar deposits in Holes 55-80 and
68-80 is not unequivocal. However, it is highly probable that these
other middle to late (?) Pleistocene deposits accumulated under similar
environmental conditions and in much the same manner as the estuarine
deposits exposed in Lee Creek Mine.
TAPHONOMY
Understanding and interpreting taphonomic processes responsible
for the accumulation of a fossiliferous deposit is essential to
paleoecology• Whereas paleoecology is concerned with the period of
time between the birth and death of an organism, taphonomy exam.ines the
post-mortem history of organisms and attempts reconstruction of the
depositional and post-depositional history.
Because the fossiliferous component of deposits examined for this
study is numerically dominated by mollusks, the taphonomic
characteristics of molluscan species were examined. Characteristics
evaluated include the number of individuals found in life position, the
number of articulated and disarticulated valves, and the taphonomic
condition of the individual [e.g., borings, encrusting organisms, and
degree of fragmentation and abrasion (Pilkey and others, 1969a,
1959b)]. Other factors used to interpret taphonomy include sorting or
size frequency of the fossils, the fabric or orientation, and the
spatial distribution pattern within the deposit (HcCall and Tevesz,
1903).
Also important to taphonomy is whether or not the fossiliferous
deposit represents an endemic community or an allochthonous
accumulation of transported individuals. Attempts to reconstruct
communities, depositional environments and the post-mortem depositional
history of fossil accumulations depend upon what is preserved and
whether or not the preserved fauna lived together.
There are many post-mortem physical and biological processes that
54
are capable of erasing evidence of community boundaries. These
processes include mixing by waves and currents, bioturbation and
burrowing, and stratigraphic condensation (Kidwell and Jablonski,
1983; McCall and Tevesz, 1983). Stratigraphic condensation is the
process of accumulating a relatively thin, shell-rich stratigraphic
deposit either under conditions of increased hardpart production or
reduced net sedimentation, or a combination of both (Kidwell and
Aigner, 1985; Kidwell and Jablonski, 1983). Low net sedimentation
rates favor the formation of fossiliferous concentrations, allowing
for the continuous accumulation of shell material. Condensation occurs
because the rate of hardpart accumulation exceeds the rate of
sedimentation (Kidv;ell, 1986).
Processes that modify the rate of sedimentation include sediment
starvation, sediment bypassing and erosionad truncation (Kidwell and
Jablonski, 1983). Sediment starvation and sediment bypassing are
products of omission or lack of sedimentation (Kidwell, 1936).
Sediment starvation refers to little or no sediment influx, whereas
sediment bypassing connotes retainment of the sediment load, either in
suspension or in a migrating bedform (Kidwell and Jablonski, 1933;
Kidwell, 1906). Erosiona! truncation generates hardpart concentrations
by winnowing away the fine matrix and leaving a lag of heavier skeletal
material at the sediment-water interface, or by hydraulic reworking of
the sediment matrix and hardparts, leading to local redeposition of
hardparts (Kidwell, 1986). Aggradation of a condensed deposit involves
any or all of these dynamic accumulatory processes. The condensed
55
shell bed can range in a temporal and spatial scale from a simple thin
accumulation of shells to a transgressive-regressive sequence composed
of a series of condensed beds. Although condensed shell beds are
characterized by a general lack of community structure, it is possible
for preserved faunas v/ithin condensed beds to reflect the environment
of deposition if preserved components are interpreted as "in place" or
as an association of ecologically compatible taxa.
Taphonomic Observations
"Shell Bed" Deposit
The "shell bed" represents a sifted deposit. Valiela (1984)
defined a sifted deposit as a condensed bed of fossils and sediment
representing all that was deposited during a specific amount of time,
assuming no hiatuses and no significant lateral transport. The sifting
or mixing action is a direct product of physical and biological
disturbances. In this case, disturbances refer to the continuing post-
mortem processes that act upon accumulated shell and sediment, rather
than the physical and biological phenomena that affect the distribution
of species (see Paleoecologic Interpretations—Species Distribution).
Physical disturbances are caused by wind-generated wave and water
currents, and, to a lesser degree, tidal currents, that mix sediment
and fauna under conditions of minimal sediment input. Biological
disturbances are produced by burrowing and bioturbation. These types
of disturbances are common in rnicrotidal estuarine or back-barrier
sound environments (Knox, 1935).
The fauna of the "shell bed" represents a "disturbed
56
neighborhood", which is a physically mixed association of ecologically
compatible species falling intermediately between an in-place
community and a transported accumulation of allochthonous individuals
(Scott, 1970). The disturbed condition results from the processes that
create a sifted deposit. Although the molluscan fauna in the "shell
bed" consists of a mixture of estuarine and marine species that are
ecologically compatible, reconstruction of community structure is not
possible because physical and biological disturbances have mixed and
condensed the fossiliferous components. The preserved hardparts within
the "shell bed" probably represent a time-averaged fossiliferous
association containing some species that never lived together and
interacted, and other species that did.
The "shell-bed" is composed of whole or nearly whole individuals
and skeletal fragments of broken mollusks, barnacles, echinoderms and
crabs. Nearly every bivalve in every sample is disarticulated. The
disarticulated condition of the valves, the well-preserved nature of
identifiable individuals and the autochthonous state of the "shell bed"
suggest in situ winnowing rather than transport. Energies capable of
winnowing are common in marginal-marine sound and back-barrier lagoonal
environments (Pickett and Ingram, 1969; Duane, 1963). Many bivalve and
gastropod individuals are fractured or broken due to predation, to
post-mortem events such as reworking and physical compaction of the
sequence, and to breakage during the sampling process.
The "shell bed" is characterized by the dense concentration of
skeletal material consisting mostly of valves and fragments of Mulinia
lateralis. The ability of ^ lateralis to rapidly proliferate has been
57
documented by many workers, (Levinton, 1970; Boesch and others, 1976;
and Rhodes and others, 1978). Reproductive activity of this fecund
species can add thousands of individuals to the substrate in a single
season (Boesch, 1976). If this localized phenomenon recurs over a
relatively long period of time under conditions of minimal sediment
input, a condensed fossil bed will be produced. It is possible that
dewatering could have contributed to condensing the "shell bed".
However, the large percentage of sand suggests that dewatering was a
minor factor. Condensation accomplished by winnowing and aggradation
seems much more plausible considering the composition of sediment and
the influence of currents and wind-driven waves associated with shallow
estuaries and marginal marine environments (Duane, 1963). Because
primary sediment structures such as cross-beds, interbeds of muds and
sands and burrow structures are not visible, neither the duration nor
intermittency of the condensation processes that affected the "shell
bed" are evident. The general lack of primary sediment structures
could be attributed to bioturbation or winnowing, wherein primary
structures are obliterated through the homogenization of the sediment.
The presence of the deep-burrowing bivalve Panopea sp.,
articulated but not in life position, is good evidence for the effects
of condensation. This deep borrower normally inhabits a muddy,
sparsely fossiliferous substrate unlike the substrate in which it is
preserved within the "shell bed" (Abbott, 1974; Andrews, 1977). It is
likely that an accumulation of muddy sediments from 12 to 36 inches
thick (Abbott, 1974) was present before the "shell bed" was deposited.
58
As the process of condensation progressed, fines were winnowed away and
the valves were exhumed, then buried by coarser sediments and skeletal
material, leaving the valves intact but allowing for subsequent
slumping from a vertical to a horizontal orientation. Specimens of
Panopea sp. occur stratigraphically below the shell "pavement".
Cyrtopleura costata is a deep-burrowing bivalve that penetrates
some 12 to 18 inches into muddy and muddy sand substrates (Andrews,
1977). It occurs in life position (with the lengthwise axis of both
valves oriented vertically) near the top of the shell "pavement",
occasionally in life position within the underlying mud unit, and as a
disarticulated member of the shell "pavement". Each of these
occurrences probably represents a different period in the depositional
history of the "shell bed". Individuals that burrowed into the
underlying mud apparently did so prior to the formation of the shell
"pavement", as their burrow structures terminate at the lower contact
of the "shell bed" and do not continue upward through the shell
"pavement". It is possible but improbable that these individuals
burrowed through openings or gaps in the "pavement" sometime after its
deposition. Disarticulated C_^ costata valves associated with the
"pavement" must also have existed prior to its formation. Condensing
processes exhumed, disarticulated and incorporated the valves into the
"pavement". Individuals in life position just above the "pavement"
apparently burrowed sometime after the formation of the "pavement" and
were unable to penetrate it.
59
"Oyster-Bed" Deposit
The "oyster bed" has many whole or nearly whole mollusks, as well
as abundant skeletal fragments dominated by pieces of Crassostrea. It
is characterized by a dense concentration of skeletal material which
accumulated as a channel-fill deposit. Crassostrea valves exhibit
varying states of preservation. Some broken and disarticulated valves
were transported some distance, either from an upstream source, the
channel margins or a tidally-influenced downstream setting. Others
were probably rolled around at this site and subjected to chemical
dissolution. Unbroken, articulated valves were most likely deposited
near or in life position along the sides of the channel as the oyster
banks grew laterally. The "oyster bed" appears to represent a
fossiliferous accummulation that has been somewhat condensed as the
channel was filled.
DEFINITION OF FOSSILIFEROUS ASSOCIATIONS
An association is "a group of organisms derived from a single
community" (Kauffman and Scott, 1976, p. 19). Community is defined as
a grouping of spatially-related benthic organisms that regularly recur
and interact, or are at least a part of each other's biological
environment (Tenore, 1972; Boucot, 1931). The "shell bed" and the
"oyster bed" are considered fossiliferous associations, defined as
accumulations of ecologically compatible taxa that possibly originated
from a single community (Kauffman and Scott, 1976; Hiller, 1982). The
term "fossiliferous association" is used with the understanding that
the components of more than one community might be preserved. Benthic
community structure has been obliterated by the mixing and condensing
of hardparts and cannot be deciphered.
Three molluscan and two foraminiferal associations were identified
in samples from Localities 1-3, Hole 63-80 and Hole 55-80. Molluscan
associations include the Mulinia lateralis Association, Mulinia
lateralis-Nuculana acuta Association and Crassostrea virginica-Corbula
swiftiana Association. Foraminiferal associations include the
Elphidium excavatum forma clavata-Elphidium limatulum Association and
Elphidium excavatum forma clavata-forma selseyensis Association. Each
association corresponds to a certain group of sampled deposits. Only
species making up more than 1% of the fauna are used in defining
associations.
61
Molluscan Fossiliferous Associations
Mulinia lateralis Association
This association occurs in samples 1-4, Locality 1; samples 1 -
3, Locality 2; and samples 1 and 2, Hole 68-80. Mulinia lateralis is
the predominant species, never making up less than 72% and averaging
82% of the molluscan fauna. Other numerically important species
include Acteocina canaliculata. Corbula contracta. Corbula swiftiana.
Ensis directus, Parvilucina multilineata, Polinices duplicatus and
Tellina agilis. Larger forms such as Argopecten solarioides, Busycon
carica, Cyrtopleura costata, Dinocardium robustum, Dosinia discus,
Mercenaria mercenaria and Raeta plicatella, though not numerically
abundant, are generally found in a distinct zone (the shell "pavement")
rather than sparsely distributed throughout the bed.
Mulinia lateralis-Nuculana acuta Association
This association occurs in sample 1, Hole 55-80. Mulinia
lateralis, the predominant species, makes up 68.9% of the molluscan
fauna. The deposit feeders Nuculana acuta and, to a lesser degree,
Nucula próxima are moderately abundant, together making up 16.3% of the
fauna. Acteocina canaliculata, Anachis avara, Anadara transversa,
Mitrella gardnerae escarinata, Nassarius acutus and Odostomia (now
called Boonea) impressa are less abundant but characteristic members of
this association.
Crassostrea virginica-Corbula swiftiana Association
This association occurs in sample 1, Locality 3 and sample 3, Hole
68-80. Crassostrea virginica and Corbula swiftiana are predominant.
Crassostrea virginica composes 37.1% of sample 1, Locality 3 and 16.7%
of sample 3, Hole 68-80, whereas Corbula swiftiana makes up 34.7% of
sample 1, Locality 3 and 44.4 % of sample 3, Hole 68-30. Other
numerically important species include Acteocina canaliculata, Anomia
simplex, Mulinia lateralis, Nassarius vibex and Seila adamsi. Piadora
cayenensis makes up more than 1% of the fauna in sample 3, Hole 68-80,
and Noetia ponderosa attains a similar abundance in sample 1, Locality
3.
Foraminiferal Fossiliferous Associations
Elphidium excavatum forma clavata-Elphidium limatulum Association
This association occurs in samples 1-4, Locality 1; samples 1 -
3, Locality 2 and samples 1 and 2, Hole 68-80. ^ excavatum forma
clavata and ^ limatulum are equally abundant and together average 50%
of the fauna. Forma clavata ranges between 17.4 and 50.8% of the
foraminiferal fauna, averaging 30,9%; and E. limatulum ranges between
2.0 and 34.6%, averaging 21.9%. Other numerically abundant species are
Elphidium excavatum forma selseyensis and Ammonia beccarii formae
sobrina and tepida. Elphidium galvestonense forma mexicanum, Elphidium
poeyanum and Buccella inusitata are of lesser importance.
Elphidium excavatum formae clavata and selseyensis Association
This association occurs in sample 1, Locality 3 and sample 1, Hole
55-80 (sample 3, Hole 68-80 did not yield any data). ^ excavatum
formae clavata and selseyensis are predominant. Forma clavata composes
58,2% of sample 1, Locality 3 and 48.7% of sample 1, Hole 55-80;
whereas forma selseyensis makes up 14.2% of sample 1, Locality 3 and
sample 1, Hole 55-80. Other numerically abundant species include
Ammonia beccarii forinae sobrina and tepida and Elphidium poeyanum.
PALEOECOLOGICAL lUTERPRETATIONS
Introduction
Lawrence (1971) described three methods of reciprocation pair
analysis and the benefits of their usage in paleoecologic studies.
Coaction pair analysis involves the study of how organisms affect one
another, reaction pair analysis deals with how organisms affect the
abiotic environment and action pair analysis examines the effect of the
abiotic environment upon organisms. Lawrence also defined three levels
of validity related to paleoecologic work. The first or optimum level
is reconstruction based entirely upon direct evidence within the
ancient deposit, the second level is reconstruction based upon direct
observation of the ancient deposit supplemented by evidence from the
recent and the third level is based on the direct transfer of recent
data to the ancient system. Coaction and reaction pair analyses
correspond to levels 1 and 2, whereas action pair analysis corresponds
to level 3. Studies based solely on direct transfer of recent data to
the ancient system are not complete without consideration of life
orientation patterns and adaptive form in the ancient setting.
Action pair analysis is based on three assumptions: 1) the
distribution of organisms is controlled by a finite number of external
parameters (e.g., temperature, salinity and water currents); 2) an
ordering or hierarchy of controlling external parameters exists; and 3)
ancient organisms had the same biological responses and indicate the
same environment as do modern equivalents. With increase in the age of
an assemblage, it becomes increasingly difficult to draw inferences
65
from modern examples and apply them to the ancient settings. Although
paleoecologic inferences based on these assumptions might be less
authoritative than those made from direct comparison, valid
paleoecologic interpretations can be generated by: 1) concentrating on
numerically dominant species, 2) examining the ecological
characteristics of each dominant species (life habit, salinity range,
habitat, etc.), and 3) determining if species are ecologically
compatible. Action pair analysis appears particularly appropriate for
deposits as young as Pleistocene.
Fifty-five species of mollusks and 3Ó species of foraminifera were
identified, and individuals within each zone were counted. Five
additional species of mollusks were identified in the field but were
not encountered in the statistical count. Also found were barnacles
(some whole) and fragments of echinoids and decapod crustaceans.
Vviith the exception of one pectinid, every molluscan and foraminiferal
species identified is extant. Ecological tolerances of extant species
were collected through a literature search and are summarized in the
annotated faunal lists.
The aim of this paleoecologic study is to reconstruct the general
environmental setting for each fossiliferous deposit based on the
preserved molluscan and foraminiferal faunas. Although precise
definition of the ancient community (or communities) is not possible,
interpretation of the environmental setting can be accomplished by: 1)
focusing on the predominant species of each fossiliferous association
and on any supplementary members that might provide useful insight, 2)
66
noting recurrences of molluscan and foraminiferal species within
samples, and 3) assessing whether fossiliferous components are
ecologically compatible.
Determination of predominant species was facilitated by the use of
tables and cummulative frequency diagrams, which record the relative
abundances of those species that constitute at least 1% of the fauna.
There are statistical reasons for avoiding rare taxa. Results from a
study conducted by Koch (1987) on the effect of sample size on the
measured distribution patterns of species show that if a particular
exposure is first sampled and then resampled, as many as 25% of the
species identified in the first sample will not be found in the second,
even if the samples are of the same size. There is even greater
discrepancy if the samples are of different sizes. Additionally, most
species are rare and occur infrequently (Buzas and others, 1982), so
that variations in the abundance and distribution of fossiliferous
components might occur as a result of infrequent and fluctuating
appearances of rare taxa.
Species Distribution
The distribution of benthic species in environments within modern
barrier-built estuarine ecosystems can result from disturbances, patch
dynamics, vagaries in larval dispersal and settlement, adult-larval
predation, pre-emptive and interference competition, and zonation in
response to salinity gradients. Interaction of the same phenomena
probably affected the distribution of species within the Pleistocene
"shell bed" and the "oyster bed". Although it is unknown to what
extent these phenomena operated, a brief discussion of each should
shed some light on the distributional interactions in the respective
paleocommunity or paleocommunities.
Disturbances are physical fluctuations or destructive events that
either create open spaces by disrupting the substrate and killing many
or all of the existing inhabitants, or adversely affect the community
by inhibiting the growth and colonization of some species (Denslow,
1985; Pickett and V/hite, 1985). Open spaces in marine invertebrate
communities can result from the operation of internal, periodic and
chronic biological disturbances, such as disruption of the substrate by
predators (e.g., rays, fish, crabs and large mollusks); or from the
occurrence of outside, periodic or acute disturbances, such as storms
(Pickett and V/hite, 1935). Changes in the availability of resources,
the effect of adult-larval predation, and the death of some species
caused by the resuspension of detritus by deposit-feeding sediment
reworkers (i.e., Trophic-Group Amensialism; Rhoads and others, 1970)
are also important in the disruption of communities (Denslow, 1935).
Other examples of disturbances include fluctuations in salinity and
temperature, space limitations, shallow waters easily influenced by
wind tides and storms, changes in pH, and oxygen depletion (Levinton,
1970, 1974; Rhoads and others, 1973; Peterson and Peterson, 1979).
Most disturbances produce patchy effects that are manifested as faunal
successions or as random differences in community composition (Pickett
and White, 1985). Because disturbances are the sources of multiple
levels of environmental heterogeneity, it is possible that high
frequency of disturbance enhances heterogeneity within the community by
68
excluding some species and allowing others to colonize (Denslow, 1985;
Pickett and White, 1985). Of course, the effect of disturbances are
ultimately related to the state of the community before the
disturbance, and the ability of the community population to respond to
the disturbance (Pickett and V/hite, 1985).
Because uniform dispersion of benthic marine organisms over
extensive areas is uncommon, patches develop (Connell, 1963). Patch
distributions result from the fruitful reproductive nature of
opportunistic species or from the heterogeneity of a habitat (Boucot,
1981). A patch is a changing, dynamic unit that implies a discrete
spatial pattern with no size constraint, and suggests a relationship of
one patch to another in space and to the uninhabited or less inhabited
matrix (Pickett and White, 1985). Interactions betv/een frequency of
disturbance, rate of resource supply, and the dispersal, settlement and
extinction of larvae are largely responsible for the faunal composition
of individual patches (Denslow, 1905; Knox, 1986).
Vagaries in larval recruitment are largely responsible for
fluctuations in species composition within soft-bottom communities
(Dayton, 1984; Denslow, 1985; Knox, 1936). Factors such as larval
settlement and emigration, species composition of the larval rain,
early mortality of new recruits, physical instability of the substrate
inhibiting settlement, fluctuations in wind, currents, turbulence,
silt, nutrients and predators, larval tolerance of salinities, and
seasonality of larval recruitment all have an impact upon the
composition of species within communities (Tenore, 1972; Boesch, 1976,
1977; Gray, 1981; Woodin, 1983; Underwood and Denley, 1984; Denslow,
1985). The relationship between disturbance-created patches and the
composition of the colonizing species is also important in shaping the
distribution of benthic marine organisms (Denslow, 1985).
Competition is of lesser importance in the distribution of species
in soft-bottom environments, although interference competition, that is
the ingestion of larvae by adults, and pre-emptive competition, that is
the prior exploitation of space not allowing for settlement of larvae,
appear to be influential (Petersen, 1980; Underwood and Denley, 1984;
Knox, 1986). Knox (1986) noted that certain trophic groups have
affinities toward the larvae of other trophic groups. For example, the
larvae of small polychaetes and deposit feeders are filtrated by
suspension feeders, placing competitive pressures on the potentially
ingestible organisms and forcing them to settle elsewhere (Petersen,
1980; Knox, 1986). A predominance of suspension feeders in an area
might literally "eat up the competition". It is also possible for
first arrivals to prevent the invasion of other species, unless the
later arrivals are capable of outcompeting the early arrivals
(Underwood and Denley, 1984).
Benthic species are generally distributed in the form of a
continuum, where there are no discrete boundaries (Gray, 1981; Knox,
1936). Variations in salinity appear to control the distribution of
benthic species found in waters of restricted marine circulation such
as those in barrier-built estuaries, lagoons and river estuaries
(Valentine, 1983). Although each species has an optimum somewhere
along the continuum, its spatial distribution may not always follov/ the
same pattern (Gray, 1981; Knox, 1986). So, it appears that spatial
distribution of benthic species within a barrier-built estuarine
ecosystem is contingent first on the existing salinity gradient, and
then on the physical and biological phenomena responsible for
fluctuations in species composition.
Diversity
The diversity of a community seems to be a balance between
competitive exclusion within the community and the prevention of this
tendency by physical and biological disturbances (Valiela, 1984).
Connell (1978) believes it is possible to correlate high and low
diversity with the frequency and magnitude of environmental stress,
especially in environments that are characterized by physical and
biologic fluctuations. Diversity is apparently maximized in
environments where the frequency of disturbance is low enough to allow
recruits with reproductive abilities inferior to those of opportunistic
species to colonize, and high enough to prevent the exclusion of
competitively inferior species by more efficient competitors (Connell,
1973; Gray, 1981). Disturbances can either inhibit the process of
competitive elimination, or remove inhabitants that competitively
exclude potential recruits (Connell, 1978). Extremes of disturbance,
such as catastrophic disturbances that create large areas of open space
or minor disturbances that open up small spaces, provide opportunities
for those few species that either are adapted for traveling great
distances before settling, or are tolerant of nearby resident
competitors and natural enemies. Intermediate openings seem to afford
71
species the greatest opportunity for settlement and colonization
(Connell, 1978).
Diversity and equitability were determined both for mollusks and
foraminifera using the Shannon-Wiener Information Function. Calculated
indices consider only the shelly-fossil diversity, providing an overall
assessment of what was preserved. The Shannon-Wiener Information
Function measures compound diversity, which is a function of the number
of species and the apportionment of individuals among the species,
Equitability indices measure hov; evenly abundances are distributed.
Diversity indices neither reflect the diversity of the original
comiiiunity, nor represent a specific type of environment (Gray, 1931).
The calculated diversity of fossiliferous deposits can vary with
sample size. According to Koch (1937), if larger and larger samples
are taken, the diversity of the faunal component will increase. This
increase in diversity is related to the increased probability of
finding rare taxa and to the inclusion of several different organisms
from different habitats (Valiela, 193A). Caution should be exercised
Vv'hen drav/ing any conclusions from calculated diversity indices for
fossilferous deposits.
72
Molluscan Associations 1, 2_ and ^
1. Mulinia lateralis Association
This molluscan association occurs in all samples from Localities 1
and 2, and in samples 1 and 2 of Hole 68-80. Species richness ranges
from 17 to 23. Ten species have relative abundances of 1 % or more.
These ten species and their respective life habits are listed in Table
3, and their abundances are displayed in cumulative frequency diagrams
(Figs. 13a-c), in Table 4 and in Appendix C. Note: Sample 3, Hole 68-
80 in Figure 13c represents molluscan Association 3.
Mulinia lateralis is the predominant member of this association.
It is found in a variety of shallow water, marginal marine environments
along the United States Atlantic Coast, but it proliferates in
polyhaline to ultrahaline waters (15 to 40 ppt.) associated with muddy
and/or fine-grained sandy substrates where most other suspension
feeding mollusks are unable to thrive or never become established
(Levinton and Bambach, 1970). The small size (approximately two cm)
and thin, moderately inflated, unornamented shell not only give Mulinia
less bulk density and greater stability in soft substrates, but also
facilitate rapid burrowing (Levinton and Bambach, 1970; Stanley, 1970).
Adult specimens of Mulinia are well adaptated to muddy-silty and
fine sandy substrates, but juveniles are not. Juveniles have smaller
siphon diameters, smaller gill surface areas and smaller, less-inflated
valves; thus, they are more prone to clogging and eventual death
(Levinton and Bambach, 1970). Large accumulations of dead valves occur
in Narragansett Bay, Rhode Island (Stickney and Stringer, 1957),.Long
Island Sound (Saunders, 1956), along the pro-delta slope and mouth of
73
L1(POFMECARoAUCLllIFuETNYsNAkTs)
31dlN VS
Figure 13, parts a~e.
CuTiirmilative frequency diagrams for Localities 1 and 2, and Hole
68-80 snowing relative abundances of species from molluscan
Association 1. Hole 68-80, sample 3 in Figure 11c represents
species from molluscan Association 3*
LOCALITY 2 PERCENT OF FAUNA (Mollusks)
20 40 60 80
SAMPLE
'va
HOLE 68-80 PERCENT OF FAUNA (Mollusks)
20 40 60 80
SAMPLE
Ln
Table 3
species type habit trophic type
Acteocina canaliculata G epifaunal carnivore
Corbula contracta B infaunal sf
Corbula swiftiana B infaunal sf
Ensis directus B infaunal sf
Mulinia lateralis B infaunal sf
Nassarius trivattatus G epifaunal carniv./scaven
Nuculana~acuta B infaunal df
Parvilucina multilineata B infaunal sf
Polinices duplicatas G epifauna carnivore
Tellina agilis B infaunal df /sf
{G—gastropod B—bivalve df—deposit feeder sf—suspension feeder}
(Sources: Abbott, 1974; Andrews, 1977)
CO r—i CO o CO o in I—i CM
TELLINA AGILIS CM tM CM 1—H 1—1 CM 1—i o
to CO CO CM o CO \D CO
• •
POLINICES DUPLICATUS o CM I—1 o 1—i iH O I—i
CM O m r—1 CTi CJ^ MJ- o^
PARVILUCINA MULTILINEATA CO CO CM <r (N 1—i O 1—i
1 1 1 1 1 1 1 1
NUCULANA ACUTA 1 j 1 1 j 1 CM 11 1 1 1
1—i CM r—1 o I—i 00
NASSARIUS TRIVATTATUS O o O r—t o O I—i CM o
00 »—i 1—i o O o
MULINIA LATERALIS in f-H <r CM m00 00 00 00 00 00 00
00 LO m 00 o m vO
ENSIS DIRECTUS o f-H <r O CM i—i O CM o
CM CO 00 'd’ O 00 CO CM CO
CORBULA SWIFTIANA CM CO CM O CM O O I—I
CO CO O in 'd- o
CORBULA CONTRACTA o r—i rH I—t o 1—i I—i o I—i
O in CO m CM
ACTEOCINA CANALICULATA o o CM CM o CO CM CM ini-H
r—l CM CO -d- r—1 CM CO 1—1 CM
?j J h4 ?J ?J
è Pi Pi CLi & Pi & O oS X X 00 00
CO CO CO CO CO CO CO 1
CO 00
f—I r—i CM CM CM VO vO
• w w
u u u u o u c; hJ hJ
o o o o o o o o o
hJ hJ K-J H-I J zc PS
Table h • Relative percent abundances of species from
molluscan Association 1,
78
the Mississippi Delta (Parker, 1956), near the mouth of the Pamlico
River Estuary (Tenore, 1972), and in the lower York Estuary adjacent to
southern Chesapeake Bay (Boesch and others, 1976). Levinton and
Bambach (1970) studied bivalve mortality patterns of Yoldia limatula,
Nucula próxima and Mulinia lateralis. Dead juvenile valves of ^
lateralis greatly outnumber dead adult valves, suggesting that it has a
high juvenile mortality rate.
Mulinia lateralis is an opportunistic species characterized by the
capacity to rapidly increase its population when the opportunity arises
(Levinton and Bambach, 1970). The ability to rapidly increase
population size stems from its potential for year-round gameteogenesis
(two to three generations per year), very short generation length (tv/o
months), rapid sexual maturation, early age of first production and
longevity of two to three years (Levinton, 1974; Valiela, 1934). These
reproductive properties are characteristic of an "r-strategist"
(MacArthur and Wilson, 1967), whose adaptability to a v/ide range of
environmental conditions allov/s it to inhabit a variety of marginal-
marine environments (Boesch and others, 1976; Dodd and Stanton, 1931;
Valiela, 1984).
Rhoads and others (1973) showed there was a temporal pattern to
the recolonization of recently disturbed or altered substrates on the
floor of Long Island Sound. In many cases, the first mollusk to
reappear follov/ing a disturbance was lateralis. It often reinvaded
just a few days after the disturbance and reached peak abundance within
a year. The appearance of other mollusks follows initial colonization
by Mulinia, but it can take several years before a more diverse
population replaces the initial colonizers (Rhoads and others, 1973).
Boesch and others (1976) studied modern populations of
macrobenthic fauna in the lower York Estuary adjacent to southern
Chesapeake Bay. Samples taken from 1960 to 1965 and from 1971 to 1975
exhibit the irruptive nature of ^ lateralis. Proliferation of
populations peaked in 1961, 1963 and 1971. The largest irruption
occurred in 1961 and was due to larval recruitment during November and
December, and April and May. The dense population of Mulinia vras
virtually eliminated by July due to near-bottom turbidity created by
deposit-feeding polycheates reworking the fine sand and silty
substrate. A similar silting effect could be initiated by the
increased production of fecal material from thousands of Mulinia
individuals, causing the mass mortality of juvenile members because of
their inability to cope with excess fecal matter (Knox, 1986).
Seasonality of larval recruitment was documented by Tenore (1972)
in his study of macrobenthos in the Pamlico River Estuary. Mulinia
spawns in the spring and fall, v/hereas other benthic species spav/n only
in spring or only in fall. The seasonality of recruitment of Mulinia
and other recurring benthic species, coupled v;ith the seasonal invasion
of marine (stenohaline) species into the Pamlico River Estuary, adds to
the complexity of the faunal composition and serves to mask the
character of the existing community. This phenomenon fits into the
realm of community response, defined by Miller (1986, p. 100) as
"short-term changes in the composition and structure of communities
resulting from allogenic environmental fluctuations, not leading to
80
complete replacement of one community".
It is evident that the temporal abundance of Mulinia lateralis
tends to fluctuate widely in the term of one to ten years (Boesch and
others, 1976; McCall and Tevesz, 1933). If an environment undergoes
repeated or chronic instances of physical or biological disturbance,
enough to kill off the large majority of juvenile members of
lateralis, it is possible to form large concentrations of shells that
are numerically dominated by juveniles (Rhoads and others, 1978;
Levinton and Bambach, 1970). High juvenile mortality coupled v;ith
irregular success in colonization is responsible for locally abundant
patches of dead Mulinia valves and limited species richness of
associated shallovvr bottom communities (Levinton and Bambach, 1970).
The mixing and condensing of such patches through time could produce a
relatively thin, fossiliferous accumulation that exhibits little or no
variation in faunal composition, sedimentary matrix or internal
structure (Kidwell and Jablonski, 19S3). If preserved, these
transient accumulations can appear in the fossil record as a condensed
deposit (Levinton and Bambach, 1970; Kidwell and Jablonski, 1983;
McCall and Tevesz, 1983).
Except for sample 1, Hole 68-80, relative abundances of M^
lateralis are similar among samples of Association 1. The relative
abundance of 72% in sample 1 is lower than the 82% overall average for
Mulinia, and it is accompanied by a slight increase in the percentage
of mud and the only appearance of Nuculana acuta, a deposit feeder.
Perhaps small changes in grain size are responsible for lowering the
81
percentage of lateralis, but a comparable increase in mud content in
sample 2, Hole 68-80 is accompanied by higher abundance of Mulinia.
This variablity in relative percent is minor and probably reflects the
effects of time-averaging through condensation and the physical and
biological phenomena that determine fluctuations in species
distribution.
Three episodes of turnover and abundance changes among other
species occur at Localities 1 and 2. One is the replacement of Corbula
sv/iftiana by Corbula contracta. At Locality 1 (Fig. 13a) C^ contracta
first appears in sample 2 and completely replaces C_^ swiftiana in
sample 3, whereas at Locality 2 (Fig. 13b) the same replacement occurs
in sample 2. Another change is the first appearance of the predatory
gastropods Acteocina canaliculata and Polinices duplicatas, which occur
upward from sample 2 at Localities 1 and 2 (Figs. 13a S b). The third
change involves the limited occurrence Ensis directus. This elongated
borrower is present only in samples 2 and 3 at Locality 1 (Fig. 13a),
and at Locality 2 (Fig. 13b) it occurs only in samples 1 and 2. These
faunal changes are probably related to physical and chemical variations
typically associated with estuarine environments, but might also
reflect vagaries in larval recruitment or inconsistencies in species
distribution not captured by sampling (LeFurgey, 1976 ; Duane, 1963;
Levinton, 1970, 1974; Levinton and Bambach, 1970; Dayton, 1984;
Denslow, 1985; Knox, 1986; Koch, 1987).
The molluscan "pavement" present at Localities 1 and 2 (previously
discussed in field observations) is a thin (10 to 20 cm) accumulation
of large molluscan species. At the base of the "pavement" lie mostly
82
disarticulated valves of Aroppecten solarioides and an occasional
grouping of Panopea sp. Interspersed above the base of the "pavement"
are Busycon carica, Cyrtopleura costata, Dinocardium robustum, Dosinia
discus, Ensis directus, Mercenaria mercenaria and Polinices duplicatas.
Although these species are not numerically abundant, they represent a
large share of the molluscan biomass and reflect a slight difference in
environmental conditions. Since all "pavement" species are sand flat
dwellers most commonly found in sound, bay and back-barrier
environments, the "pavement" may represent a tidal flat community or a
condensed intertidal-shallow subtidal faunal association different in
composition from the rest of the "shell bed". The "pavement" may also
reflect variability in the condensing process that produced an
extremely condensed portion as compared to the rest of the "shell bed".
2. Mulinia lateralis-Nuculana acuta Association
This molluscan association occurs only in sample 1 of Hole 55-80.
Associations 1 and 2 are both numerically dominated by Mulinia
lateralis and contain many of the same species. The presence of
deposit-feeding bivalves in Association 2 distinguishes it from
Association 1. Unlike Association 1, which occurs in a muddy sand.
Association 2 is found in a sandy mud (36.3% sand and 60.0% mud) that
is characterized by the common occurrence of two deposit-feeding
bivalves, Nucula próxima and Nuculana acuta. Of the 23 molluscan
species identified in Association 2, nine have relative abundances of
1% or more (Table 5, Fig. 14, Appendix C).
Nucula próxima and Nuculana acuta are most commonly found in muddy
83
Table 5
species type habit trophic type
Acteocina canaliculata G epifaunal carnivore
Anachis avara G epifaunal carnivore
Anadara transversa B infaunal sf
Mitrella gardnerae
escarinata G epifaunal carnivore
Mulinia lateralis B infaunal sf
Nassarius acutus G epifaunal carniv,/scaven.
Nucula próxima B infaunal df
Nuculana acuta B infaunal df
Odostomia impressa G epibiont parasite
{G—gastropod B—bivalve df—deposit feeder sf—suspension feeder}
(Sources: Abbott, 1974; Andrews, 1977)
84
ODOSTOMIA IMPRESSA
NUCULANA ACUTA 'd*
NUCULA PROXIMA
NASSARIUS ACUTUS
(Molluikt MULINIA LATERALISFAUNA MITRELLA GARDNERAE ESCARINATAOPERCFENT ANADARA TRANSVERSA
ANACHIS AVARA
ACTEOCINA CANALICULATA 6315H85O.-.720189L0E
HOLE 55-80
Sample
Figure lii» Table and cummulative frequency diagram for sample 1,
Hole 55-80 shoiring relative percent abundances of species
from molluscan Association 2*
environments where organic detritus is abundant and sediment
resuspension results from either the vigorous feeding action of these
bivalves at the sediment-water interface or the periodic influence of
waves and water currents (Levinton and Bambach, 1970; Knox, 1986). The
feeding activity of numerous deposit-feeding individuals can place
great amounts of mud into suspension at or near the sediment-water
interface. This tends to clog the filtering apparatus of suspension-
feeding bivalves living at the sediment-water interface, thereby
limiting their numbers and distributional ranges (Levinton and Bambach,
1970). Mulinia lateralis, however, is unusual among suspension-feeding
bivalves because it is capable of withstanding the high content of silt
and clay in muddy sediments (Levinton, 1970). Mulinia is primarily
equipped for filtering phytoplankton out of water, but is capable of
feeding on organic detritus that is resuspended from muddy bottom
sediments (Levinton, 1974). Flexibility in feeding habit coupled with
its low bulk density and small size enables Mulinia to proliferate at
the surface of muddy environments where other suspension feeders cannot
survive (Levinton, 1974).
The sandy mud conditions that existed during the deposition of
Assemblage 2 favored the proliferation of the suspension feeder Mulinia
lateralis, while supporting a modest population of deposit feeders.
Mulinia lateralis constitutes nearly 70% of the molluscan population,
whereas Nuculana acuta and Nucula próxima make up 14.6% and 1.7%,
respectively. Predominance of Mulinia might be attributed to: 1) an
insufficient detrital food supply for deposit feeders due to the fact
86
that 30% of preserved sediments are inorganic sands (Gray, 1981), 2)
competition between deposit feeders and Mulinia for settling sites
(Petersen, 1979; Valiela, 1984; Knox, 1986), 3) ingestion of deposit
feeder larvae by Mulinia and other suspension feeders (Petersen, 1979;
Gray, 1981; Knox, 1986), and 4) stabilization of the muddy substrate by
tube-dwelling polychaetes (Levinton, 1970). The limited numbers of
Nuculana acuta and Nucula próxima probably could not extensively rework
the sandy mud substrate, thus leaving it stable enough for
colonization by Mulinia.
With the exception of Acteocina canaliculata, the gastropod
species found in Association 2 (Fig. 14) differ from those found in
Association 1. Anachis avara, Mitrella gardnerae escarinata, Nassarius
acutus and Odostomia impressa are not found in Association 1. The
differences between associations possibly reflect changes in prey-
predator relationships in response to changes in the physical
environment, such as water currents, salinities, living space,
sediment composition and sedimentation rate (Levinton, 1970, 1974;
Peterson and Peterson, 1979; Rhoads and others, 1978). Differences
could also be related to fluctuations in species composition caused by
vagaries in larval recruitment or by sample-size effects, v\?here the
spatial distributional range of rare or uncommon species is wider than
the sampled interval (see Koch, 1987).
Calculated diversity values for molluscan Associations 1 and 2
range from 0.70 to 1.26 (Table 6). These low values reflect an uneven
apportionment of individuals among species, namely the predominance of
Mulinia lateralis. Calculated equitability values, which range from
Molluscan Diversity and Equitability Values
Number of Number of Shannon-Weiner Equitabi
Sample Specimens Species Diversity
LOG. 1 SMPL 1 1201 29 0.79 0.08
LOG. 1 SMPL 2 797 28 0.98 0.10
LOG. 1 SMPL 3 979 28 1.16 0.11
LOG. 1 SMPL 4 1617 21 0.70 0.10
LOG. 2 SMPL 1 459 19 0.76 0.11
LOG. 2 SMPL 2 512 25 0.98 0.11
LOG. 2 SMPL 3 668 20 0.81 0.11
HOLE 68-80 1 475 27 1.22 0.13
HOLE 68-80 2 628 17 0.74 0.12
HOLE 55-80 1 418 23 1.26 0.15
HOLE 68-80 3 126 13 1.83 0.48
LOG. 3 SMPL 1 248 15 1.73 0.38
Foraminferal Diversity and Equitability Values
Number of Number of Shannon-Weiner Equitability
Sample Specimens Species Diversity
LOG. 1 SMPL 1 306 17 2.03 0.45
LOG. 1 SMPL 2 312 15 1.93 0.46
LOG. 1 SMPL 3 301 15 1.72 0.37
LOG. 1 SMPL 4 307 20 2.07 0.39
LOG. 2 SMPL 1 321 16 1.95 0.44
LOG. 2 SMPL 2 316 20 2.03 0.38
LOG. 2 SMPL 3 300 13 1.92 0.53
HOLE 68-80 1 307 12 1.19 0.27
HOLE 68-80 2 319 15 1.91 0.45
HOLE 55-80 1 308 5 0.99 0.54
LOG. 3 SMPL 1 316 20 1.39 0.36
Table 6. Diversity and equitability index values for mollusks
and foraminifera.
88
0.08 to 0.15 on a scale of 0.00 to 1.00, also reflect the predominance
of lateralis. The predominance of Mulinia is related to its own
opportunistic capabilities in an environment characterized by frequent
physical and biological fluctuations and disturbances. When the
opportunity arose, Mulinia simply out-produced the competition and,
once established, inhibited the settlement of other species. It is
likely that the time between disturbances was not long enough to allow
for competitors to proliferate.
3. Crassostrea virginica-Corbula swiftiana Association
Association 3 is numerically dominated by the bivalves Crassostrea
virginica and Corbula swiftiana. Although Mulinia lateralis is
present, it accounts for less than 3% of the fauna. Sample 1 from
Locality 3 and sample 3 from Hole 68-80 yielded a total of 13 and 15
molluscan species, respectively. Eleven of these species had relative
abundances of 1% or more (Table 7, Fig. 15, Appendix C).
Crasssostrea virginica is an encruster that requires a firm
substrate such as sand, firm mud or clay. Unsuitable substrates
include shifting sands and soft mud (Bahr and Lanier, 1981).
Crassostrea inhabits the intertidal to subtidal zone in marsh-
estuarine ecosystems v/here water currents or wave energies are below a
threshold level that allows for spat settling, initial attachment,
growth and development of an oyster bank (Bahr and Lanier, 1981). If
energies are too low, fine sediments settle out, clogging valves and
preventing the growth of the bank. Thus, a minimum current velocity is
required to limit accumulation of fine sediments, bring in adequate
Table 7
species type habit trophic type
Acteocina canaliculata G epifaunal carnivore
Anachis avara G epifaunal carnivore
Anadara transversa B infaunal sf
Anemia simplex B epifaunal sf
Corbula contracta B infaunal sf
Corbula swiftiana B infaunal sf
Crassostrea viroinica B epifaunal sf
Piadora cayenensis G epifaunal herbivore
Mulinia lateralis B infaunal sf
Nassarius vibex G epifaunal carniv./scaven
Noetia ponderosa B infaunal sf
PyroQcythara plicosa G epifaunal carnivore
Seila adamsi G epifaunal herbivore
{G—gastropod B—bivalve df—deposit feeder sf—suspension feeder}
(Sources: Abbott, 1974; Andrews, 1977)
CM CM
SEILA ADAMSI ro CO
^ ro
• •
PYRGOCYTHARA PLICOSA¡ O
1—i
^ 00
NOETIA ponderosa! <r o
NASSARIUS VIBEXi iH CO
00
MULINIA LATERALISi CM r—1
VÛ
DIADORA CAYENENSIS! O r-t
(MollusKa rHCRASSOSTREA VIRGINICa! ysOro .HFA CORBULA SWIFTIANaIO ro ^PERUCFENNAT 00CORBULA contracta! O -H
CM O
ANOMIA simplex! uO <?
<? I
•
ANADARA TRANSVERSA! ICM j
I \0
ANACHIS avara! II rH
I
CM 00
ACTEOCINA CANALICULATa! I—(
rH ro
J
eu o
LOCALITY 3 S 00
œ I
00
ro v£>
Sample
• w
U hJ
o o
hJ 33
Figure 15. Cununulative frequency diagram for sample 1, Locality 3»
and table for sample 3» Hole 68-80 and sample 1, locality
3 showing relative percent abundances of species from
molluscan Association 3»
91
amounts of suspended food (phytoplankton) and wash wastes away
(Galtsoff, 1964). The continuous renewal of seawater necessary to
sustain the bank is brought about by the ebb and flood of the tidal
cycle (Galtsoff, 1964). Banks of Crassostrea can exist wherever there
is a hard surface, vvrhich is usually near the flanks of channels.
Oysters generally grow in a direction perpendicular to tidal currents
to maximize efficiency of waste removal and nutrient replenishment
(Bahr and Lanier, 1981). Although oyster banks are sometimes found in
the subtidal zone, their distribution is apparently limited by
increased predation, fouling and shell destruction by boring sponges
(mainly Cliona) (Bahr and Lanier, 1981).
Corbula swiftiana is a shallow borrower that requires a soft,
sandy or muddy sand substrate. -It can inhabit both the intertidal and
subtidal zone, but would not likely proliferate in the middle to upper
intertidal region because of: 1) Crassostrea inhabiting potential
settling spots, or 2) vagaries in larval settlement and survival
brought about by water currents or predation (Petersen, 1980; Dayton,
1984; Denslow, 1985; Knox; 1986). Although areas of high current
energy are not conducive for most suspension feeding mollusks. Corbula
is an exception because it can anchor itself to the substrate by byssal
threads (Boucot, 1981). Thus, Corbula can inhabit areas of low current
energy, as well as areas where current energy is higher but not high
enough to disrupt its normal burrowing and feeding activities. The
numerical abundance of Cj_ swiftiana in Association 3 is probably
related to its adaptability.
92
Although Association 3 is dominated by the biomass of Crassostrea
virginica, it is co-dominated in numerical abundance by Crassostrea
virginica and Corbula swiftiana. The coexistence of these suspension
feeders in a tidal channel environment is best explained by their
respective substrate preferences. Crassostrea virginica encrusts
wherever a substrate or surface is stable enough to support it.
Corbula swiftiana, incapable of living on the surface of oysters, most
likely inhabited interstices within the oyster bank and the low
intertidal to subtidal zone below the base of the bank.
Species unique to Association 3 include Piadora cayenensis, Noetia
ponderosa, Pyrgocythara plicosa and Seila adamsi. Although
Pyrgocythara plicosa is the only species actually found in association
with modern oyster beds (Andrews, 1977), all species mentioned are
capable of living in intertidal and subtidal environments of tidal
channels. Herbivores such as ^ cayenensis and S_^ adamsi might feed
upon algae that accumulated on the shells of oysters. Noetia ponderosa
is able to attach itself by means of a byssus in areas where currents
are moderately strong, as in tidal channels (Stanley, 1970). Although
the "oyster bed" deposits may be partially condensed and time-averaged.
Association 3 appears to represent a single oyster-bank community.
Calculated diversity values for molluscan Association 3 range
from 1.73 to 1.83, and calculated equitability values range from 0.38
to 0.48 (Table 6). These low to moderate values reflect slightly more
even apportionment of individuals among species as compared to
Associations 1 and 2. The numerical dominance of two species
(Corbula swiftiana and Crassostrea virginica) in Association 3, as
compared to one species (Mulinia lateralis) in Associations 1 and 2, is
largely responsible for the increase in equitability and compound
diversity values.
94
Foraminiferal Associations ^ and _2
1. Elphidium excavatum forma clavata-Elphidium limatulum Association
The association occurs in all samples from Localities 1 and 2 and
from Hole 68-80. The number of foraminiferal species identified per
sample varied from 12 to 20. Samples yielded a total of eight species
having relative abundances above 1% (Figs. 16a-c, Table 8a).
Elphidium excavatum forma clavata and limatulum generally
predominate samples from Localities 1 and 2. The one exception is
sample 3 of Locality 2, where ^ excavatum forma selseyensis is more
abundant than forma clavata. E. limatulum is markedly less abundant in
samples 1 and 2 from Hole 68-80 (from an average of 26.5% in Localities
1 and 2 to 2% in sample 1, Hole 68-80). Abundances of ^ excavatum
formae clavata and selseyensis decrease upward in Hole 68-80 (forma
selseyensis dropping nearly 30%). Ammonia beccarii formae sobrina and
tepida show a corresponding increase in abundance.
Elphidium excavatum formae clavata and selseyensis typically occur
in marginal-marine environments, including barrier-built estuaries.
Many studies of nearshore Atlantic benthic foraminifera list ^
excavatum or ^ clavata (equivalent to ^ excavatum f. clavata and
quite possibly forma selseyensis of this study) among the taxa most
frequently encountered. Although it occurs southward to southern
Florida, forma clavata is most abundant in temperate to arctic waters,
where it is the predominant member of nearshore faunas. Feyling-
Hanssen (1972) and A.A.L. Hiller et. al. (1982) found abundant forma
clavata in arctic to sub-arctic waters and abundant forma selseyensis
in sub-arctic to temperate waters. Schnitker (1971) noted the
95
L1POF(E)iCfARAoCmarUenLEFITNYTA
31dlN VS
Figure 16, parts a-c.
Cuinmilative frequency diagrams for Localities 1 and 2, aind Hole
68-80 showing relative abundances of species from foraminiferal
Association 1.
SAMPLE
VO
o^
HOLE 68 80 PERCENT OF FAUNA (Foraminifera)
20 40 60 80
—1— I I I
2-
E. «xcavatum
SAMPLE
c
98
R
tr"
hd w
SC
M Tl
o Z
M M Pi
c o r*
M TJ
G Z
a 2 M
> o 2 §
n M M 2 o
< X G O z
m 2 z M
c/3 > M >
H < w >
w O > X G
K f z H n W G G
r" PI G > G w o
?v sc z 2 < O n
sc M c/3 > n n >
M o w H n > z
o M • G z z M
M i-h 2 z M M
c • C/3 > M
2 Dn Hh Hh
r 2 z • M h-h •
T) M W c/3 z •
o X R C~) G G
W M Hi z CO H o
Hi H n w > M W G
G z < H Z z
*Zt r c/3 > > M M
c G G M H H o z
S 2 cn > > > >
LOG. 1 SMPL 1 2.3 28.8 6.5 9.2 25.2 6.2 5.6 10.8
LOG. 1 SMPL 2 1.9 20.2 2.2 11.2 33.3 4.2 15.1 7.1
LOG. 1 SMPL 3 1.7 34.6 7.0 12.6 31.6 1.0 5.6 3.0
LOG. 1 SMPL 4 2.3 26.1 9.4 9.8 29.0 3.3 4.6 6.2
LOG. 2 SMPL 1 1.9 19.6 2.8 18.1 28.0 1.9 13.7 10.0
LOG. 2 SMPL 2 3.5 28.5 4.4 17.1 23.7 2.5 9.8 3.8
LOG. 2 SMPL 3 4.0 27.4 7.0 26.1 17.4 6.0 6.0 2.0
HOLE 68-80 1 1.6 2.0 0.3 37.5 50.8 1.0 1.6 3.9
HOLE 68-80 2 1.6 10.3 8.5 7.8 39.2 0.9 13.2 13.2
w
z
G
z
M G
o z
1—1 z
z z
s M
o !<
H M j < o
X G o z
B n z z M> M >
< M >
> X G
w H n G m
z G > M n
z s < n n
z > n - >
I-H I-h H > z
a • G z M
M z M M
G G M
s w i-h i-h
z • i-h •
TJ G •
o m n G
M Hi z H o
m > w w
> z < z z
Z G > M M
M H c z
G > > >
LOG. 3 SMPL 1 2. 8 14. 2 58. 2 10.1 9
HOLE 55-80 1 1. 0 43. 5 48. 7 2.9 3
Table 8a-b. Relative percent abundances of species from
foraminiferal Associations 1 and 2.
99
predominance of clavata in nearshore waters just north of Cape
Hatteras. The environmental conditions indicated by Association 1
probably represent a temperate climate similar to that along the modern
Atlantic coast north of Cape Hatteras. Kraft and Margules (1971) noted
several foraminiferal assemblages in Indian River Lagoon, Delaware.
One such assemblage was the Elphidium clavata-Ammonia beccarii
Assemblage, which is associated with the central region of the lagoon,
and which is comparable with foraminiferal Associations 1 and 2 of this
study.
The terms "nearshore" and "marginal-marine" are used here to
indicate a broad region extending from the estuary across the inner
shelf. The abundances of Elphidium and Ammonia, coupled with the
uncommon occurrence of open-shetf dwellers such as Bolivina, Rosalina
and Quinqueloculina, and the complete absence of planktonic individuals
suggest an estuarine depositional environment.
Elphidium limatulum is another nearshore species, present in the
inner to mid-shelf off Wrightsville Beach, North Carolina (Workman,
1981). The co-occurrence of ^ excavatum forma clavata and ^
limatulum has not been linked to any specific nearshore environment,
although abrupt changes in the relative abundance of ^ limatulum and
E. excavatum formae clavata and selseyensis in Hole 68-80 might be
related to fluctuations in food source, competition for food and space,
and slight changes in sediment composition (Kraft and Margules, 1971).
Elphidium excavatum forma selseyensis and Ammonia beccarii formae
sobrina and tepida are secondary in abundance and also suggest
marginal-marine environments. Elphidium galvestonense forma mexicanum,
E » poeyanum and Buccella inusitada are tertiary members of the
association. Elphidium galvestonense forma mexicanum is usually
associated with warmer marginal-marine and estuarine conditions, while
E. poeyanum and ^ inusitada are most commonly found in open-marine
environments.
Calculated diversity values for foraminiferal Association 1 range
from 1.19 to 2.07, and calculated equitability values range from 0.27
to 0.53 (Table 6). With the exception of values from Hole 68-80,
sample 1, diversity and equitability values are moderate and reflect a
soméwhat even apportionment of individuals among species. The lower
diversity and equitability values from Hole 68-80, sample 1 correspond
to a pronounced drop in the relative abundance of Elphidium limatulum,
accompanied by increased abundances of Elphidium excavatum formae
clavada and selseyensis. Although species richness is greater for
molluscan Associations 1 and 2, diversity values for foraminiferal
Association 1 are higher because of more even apportionment of
individuals among the species (mollusks being numerically dominated by
Mulinia). The lesser magnitude in dominance is probably related to
differences in reproductive and life habits between marginal-marine
mollusks and foraminifera. It is not known if any numerically dominant
foraminifera possess opportunistic reproductive capabilities.
2. Elphidium excavatum formae clavada and selseyensis Association
This association occurs only at Locality 3 and in Hole 55-80. In
comparison to Association 1, the species richness drops significantly.
Five foraminiferal species were identified in sample 1, Hole 55-80 and
11 were identified in sample 1, Locality 3. Seven species had relative
abundances of 1% or more, but only five were present in both samples
(Figs. 17a-b, Table 8b). Elphidium limatulum, which averaged 22% of
Association 1, is absent from Association 2.
Elphidium excavatum formae clavata and selseyensis are the
predominant members of Association 2. Forma clavata maintains high
abundance (48-58%), whereas forma selseyensis is abundant in sample 1,
Hole 55-80 (44%) but accounts for only 14% of the fauna in sample 1,
Locality 3. Ammonia beccarii formae sobrina and tepida increase in
abundance to compensate the decrease of forma selseyensis. The
decreased abundance of forma selseyensis may result from the two
samples representing different environments. Sample 1, Locality 3 is
interpreted as a tidal creek or stream, whereas sample 1, Hole 55-80
represents quiet-water, subtidal conditions of a sound or back-barrier
lagoon. Some individuals in the tidal creek setting may have
experienced post-mortem transport, but the lack of abrasion and the
preservation of fine detail suggest that most were indigenous. These
depositional environments, though differing with respect to energy
level, both occur v/ithin the estuarine setting.
Common in Association 1 but conspicuously absent from Association
2 is Elphidium limatulum. Its disappearance may be due to changes in
water temperature (from warm temperate to cool temperate, similar to
modern changes around Cape Hatteras) or to fluctuations in food supply,
salinity and competition associated with subtle changes in the
depositional environment (Workman, 1981; Kraft and Margules, 1971).
102
()iMOFPAnamoEreURCFNENAT
CQ n
HOLE 55-80
LOCALITY 3
Sample 1
Sample 1
Figure 17a-b. Cummulative frequency diagrams for a) sample 1,
Locality 3 and b) sample 1, Hole 55-80 showing
relative percent abundances of species from
foraminiferaJ. Association 2.
103
Also absent from Assemblage 2 are Buccella inusitata and Elphidium
galvestonense forma mexicanum. The absence of these taxa may indicate
more restricted environmental conditions, possibly related to increased
physical and chemical stress such as turbulence, increased mud content
and changes in salinity.
No agglutinated foraminifera were identified in any sample.
Agglutinated taxa are common in modern marginal-marine environments
such as brackish streams, estuaries and sounds (LeFurgey, 1976).
Because agglutinated tests are composed of organically-cemented
detrital grains, they are fragile and disintegrate easily. It is
likely that agglutinated foraminifera were once members of this
fossiliferous association. Their absence is probably due to
preferential destruction.
Calculated diversity values for foraminiferal Association 2 range
from 0.99 to 1.39, and calculated equitability values range from 0.36
to 0.54 (Table 6). These values reflect less even apportionment of
individuals among species than in Association 1. Low diversity (0.99)
and moderate equitability (.54) correspond to low species richness (5).
Because only two of the five species identified are abundant,
equitability values reflect the ratio between these two species.
Greater species richness coupled with just one numerically dominant
species lowers equitability. Low to moderate diversity values for both
molluscan and foraminiferal associations reflect the dominance of just
a few marginal-marine benthic species, indicating an estuarine rather
than open shelf environment.
DEPOSITIONAL ENVIRONMENT
Post-James City Formation, middle Pleistocene shelly deposits
exposed in Lee Creek Mine probably accumulated in a barrier-built
estuarine environment similar to modern-day Pamlico Sound. This
paleoenvironmental assessment is based upon the knov/n ecology of extant
representatives of foraminifera and raollusks, sediment composition of
the deposits, and present-day regional topography. Pleistocene
deposits in Beaufort County can best be interpreted in light of what is
known about the modern Pamlico Sound.
Modern Pamlico Sound
Pritchard (1967) defined an estuary as "a semi-enclosed coastal
body of vi/ater which has a free connection with the open sea and within
which sea water is measurably diluted with fresh v/ater derived from
land drainage". Schubel (1971) summarized Pritchard's (1967)
classification of estuaries, discussing the drowned river valley, the
bar-built estuary, fjords and estuaries produced by tectonic processes.
Pamlico Sound is interpreted to be a bar-built estuary because it 1)
was produced by the formation of barrier islands across reentrants
along the coast, 2) receives freshwater drainage from the mainland, and
3) is connected to the open sea by inlets (Schubel, 1971).
Modern Pamlico Sound is a large, shallow basin that has a maximum
depth of eight meters. Currents in the sound are generally weak,
dependent upon prevailing wind direction and velocity, and generally
unaffected by tidal fluctuation. The fair-weather tidal range in the
105
sound is estiraated at five cm but increases to nearly one meter near
barrier island inlets (Roelofs and Burapus, 1953; Duane, 1963).
Agitation by wind prevents any extreme thermal or saline stratification
within the sound, although the deepest parts of the sound are
infrequently mixed and remain oxygen poor (Duane, 1963; Pickett and
Ingram, 1969).
Salinities within modern Pamlico Sound vary from 15 to 19 ppt.
near the mouths of the Pamlico and Meuse Rivers, and from 29 to 31 ppt.
adjacent to inlets (Pickett and Ingram, 1969; Tenore, 1972). Rivers
and creeks drain directly into the sound, adding fresh or brackish
water and supplying fine-grained silts and clays (Pickett and Ingram,
1969). Salinities in a barrier-built estuarine system fluctuate
seasonally and geographically because of variations in runoff, seasonal
variability in rainfall and evaporation, proximity to inlets and
variable wind direction (Duane, 1963). Connecting sounds also affect
the salinity; some, such as Bogue Sound, contribute to higher
salinities and others, like the Croatan Sound, dilute salinity (Duane,
1963).
Sediments in modern Pamlico Sound vary from fine silts and clays
in the central deeps to silty, fine to medium, clean quartz sands along
the margins (Duane, 1963; Pickett and Ingram, 1969). The supply of
sediment to Pamlico Sound is low. Moderate amounts of silts and clays
carried into the sound through drowned river estuaries and by erosion
of headland marshes are deposited in baffled areas or deeper parts of
the sound. Fine to medium quartz sands are dispersed and deposited in
the vicinity of inlets as flood-tide deltas, are washed over barrier
islands by storm activity, or are wind blown off the barriers. Because
of the relatively low influx of new sediments, sedimentation occurs
primarily through 1) reworking and redistribution of sediments on the
sound floor and along its margins, and 2) erosion from Pleistocene
headlands (Duane, 1963; Kraft, 1979),
Foraminifera and mollusks show some zonation in modern Pamlico
Sound, apparently in response to salinity levels, sediment types, water
depth and oxygen levels. A good example of foraminiferal zonation
within the sound is exhibited by agglutinated and calcareous types.
Agglutinated foraminifera are more prevalent in the brackish waters of
drowned river estuaries, whereas calcareous foraminifera increase in
abundance tov/ard more normal marine salinities near the inlets (Duane,
1963; LeFurgey, 1976). Mollusks also exhibit zonation, increasing in
diversity towards more normal marine salinities (Tenore, 1972; Boesch,
1977).
Barrier islands are géomorphologie sand bodies that form if the
shelf slope is not too steep and if there is adequate sediment
available. The barriers enclosing modern Pamlico Sound are breached
by numerous inlets, where sediments are reworked and redistributed by
wave action and tidal flow to form flood-tidal deltas. As inlets close
or migrate, flood-tidal deltas are abandoned and stabilized by
vegetation to become part of the barrier (Fisher, 1962). North
Carolina barriers are partially composed of old stabilized flood-tidal
deltas and overwash fans on which marshes build into the sound
(Fisher, 1962; Kraft and others, 1979).
107
Barrier islands migrate landward in response to rising sea level.
Barrier migration proceeds as a result of erosion on the shoreface, and
development of flood-tide deltas, overwash fans and marsh grov/th on the
backside (Pilkey and others, 1978). Episodes of storm overwash deposit
lobes or fans of beach sand over the barrier and into the sound,
providing a surface for nev/ marsh grov/th. As the barrier island
migrates, continued erosion at the shoreface by v/ave action truncates
buried back-barrier marsh, lagoonal and estuarine deposits and balances
soundward growth (Pilkey, Neal and Pilkey, 1978; Kraft and others,
1979; Dolan and Lins, 1936).
Studies of Holocene barrier deposits include those of Susman and
Heron (1979) on Shackleford Banks and Moslovi/ and Heron (1979) on Core
Banks. The succession of barrier to marsh to lagoonal systems in
vertical sequences of Holocene deposits along the beachface and in
cores suggests landward migration of barrier islands (Kraft and others,
1979; Pilkey and others, 1978; ^!oslo^^í and Heron, 1979; Susman and
Heron, 1979).
Pleistocene Deposits
Pierce and Colquhoun (1970) and Mixon and Pilkey (1976)
interpreted deposits beneath present-day barriers, as well as several
sand deposits on the Pamlico msu (east of the Suffolk Scarp) as
Pleistocene barrier complexes. Pierce and Colquhoun (1970) stated that
many of the modern barrier systems on the North Carolina coast are made
up of older barrier deposits that have been reworked and modified since
the late Pleistocene (at least post-Jarnes City Pm.). Mixon and Pilkey
108
(1976) recognized the Atlantic and Newport Sands as relict Pleistocene
barrier deposits. Other barrier deposits might also have been
deposited during the Pleistocene but have been rendered unrecognizable
by erosional processes as barrier islands migrated across the terrace
and over the crest of a scarp (Pierce and Colquhoun, 1970).
The fossiliferous associations of the "shell bed" and "oyster bed"
suggest the type of estuarine conditions associated with a modern
barrier-built estuary such as the Pamlico Sound. Predominant members
of molluscan and foraminiferal Association 1 (associated with the
"shell-bed") include Mulinia lateralis, Elphidium excavatum forma
clavata and Elphidium limatulum. When found in abundance, all indicate
estuarine and back-barrier estuarine environments. Predominant members
of molluscan Association 3 (associated with the "oyster bed") include
Crassostrea virginica and Corbula swiftiana. Crassostrea virginica
inhabits intertidal creeks and small bays found in estuaries. Corbula
swiftiana probably inhabited subtidal environments. Predominant
members of molluscan Association 2 (associated with the muddy facies of
the "shell bed") include Mulinia lateralis and Nuculana acuta.
Although Nuculana acuta inhabits muddy offshore environments, it also
occurs in muddy estuarine environments. Hence, its presence is
consistent with the estuarine setting suggested by the predominance of
Mulinia. Predominant members of foraminiferal Association 2
(associated with both the "oyster bed" and the Mulinia-rich sandy mud)
are Elphidium excavatum formae clavata and selseyensis, both indicators
of estuarine environments. These Pleistocene faunas suggest that
salinities were similar to those of modern-day Pamlico Sound. Salinity
109
does effectively limit faunal types and their populations in modern
estuaries (Tenore, 1972; Boesch, 1976, 1977).
The estuarine ecosystem is composed of many environments. Abrupt
lateral variations in biotic and abiotic factors cause fluctuations in
foraminiferal and raolluscan abundances, variations in lithology, and
patchy community structure v/ithin these environments (LeFurgey, 1976).
Considering the salinity range inferred from tolerances of extant
species, the sediment composition and geographic location of
Pleistocene estuarine deposits in Lee Creek Mine, and the local
topography of the Pamlico River-Pamlico Sound region, deposits examined
in this study should compare with some modern sedimentary environments
of Pamlico Sound and Pamlico River Estuary.
Pickett and Ingram (1969) identified 11 environments in Pamlico
Sound based on the geographic distribution of sediment types. The mud
unit below the "shell bed" compares best with their "lagoon near river
mouth" environment, which is the elongate, deep, mud-filled channel
located at the mouth of the Pamlico River. The channel mud' deposit
extends from the narrowest part of the mouth six km towards the center
of the sound in water depths of six to eight meters. Salinities near
the mouth of the Pamlico River are usually around 18 ppt. (Tenore,
1972). Fine-grained muds and fecal pellets accumulate in this
sedimentary environment, which is characterized by a general lack of
calcareous material. The lithology of the Pleistocene mud unit
suggests deposition in a sedimentary environment similar to the mouth
of the modern Pamilco River Estuary.
lio
The "shell-bed" compares closely with what Pickett and Ingram call
the "lagoonal margin", which includes margins of the Pamlico Sound
where wave and current energy is able to winnow away a moderate amount
of mud. The sound margin is generally less than three meters in depth.
Salinities of 19 to 22 ppt. characterize the western side, whereas
values of 22 to 29 ppt. occur near inlets. Sediments along the margins
consist of fine sands on the eastern side behind the barriers and
silty fine sands on the western side and near marshes. The calcareous
component varies from less than 1 to 8 weight percent and is composed
largely of mollusks. Macrobenthos in modern Pamlico Sound and near the
mouth of Pamlico River Estuary include some of the taxa, such as
Acteocina, Mercenaria, Mulinia, and Tagelus, identified in the
fossiliferous Pleistocene deposits. The fauna observed does not
correspond exactly with the modern fauna. Fossiliferous associations
represent time-averaged faunas that include some species which may
never have lived together or interacted, whereas modern macrobenthic
faunas reflect an instant in time and represent a small portion of what
might eventually be preserved. Effects other than small-scale physical
and biologic interactions probably contributed to fluctuations in
faunal composition. For example, the opening and closing of inlets
likely provided access for different groups of taxa and permitted
colonization by benthic species tolerant of different salinities.
The shell "pavement" within the "shell bed" and the Mulinia-rich
sandy mud of Hole 55-30 were also deposited along the "lagoonal
margin", but each represents a distinct facies. The presence and
abundance of sand flat dwellers in the shell "pavement" reflects an
Ill
intertidal setting, perhaps a shoal adjacent to the mouth of an
estuary, tidal creek or small bay. The Mulinia-rich sandy mud of Hole
55-80 suggests quieter water associated with deeper parts of the sound
margin.
The "oyster bed" loosely correlates with v;hat Pickett and Ingram
call the "protected mainland embayment", which refers to small
estuarine bays and tidal creeks. Salinities range betv;een 19 and 29
ppt., depending upon the proximity of bays and creeks to inlets.
Sediments are composed of muds and sands, accumulations of v/hich are
dependent upon baffling agents, current energy and the growth of the
oyster bank. Although the tidal range in Pamlico Sound is small, a
tidal current is generated that, depending on the width and depth of
the channel or bay, is at least swift enough to bathe the oysters in
nutrient-rich waters and carry away wastes.
The distribution of tidal creeks in the Pleistocene depositional
record exhibits the transient nature of these shell-rich bodies.
Pleistocene "oyster-bed" deposits exposed in Lee Creek iiine both cut
into and underlie the unfossiliierous mud unit. Oyster-rich deposits
underlie "shell bed"-type deposits in Hole 68-30. The geometries of
"oyster bed" exposures in Lee Creek ¡line vary from the cross-section of
a channel at Locality 3, to either an oblique longitudinal viev/ of a
channel or the cross-section of a small embayment at Locality 4.
To account for the deposition of this entire paleo-estuarine
sequence, a relative rise in sea level is required. As Pleistocene
seas transgressed and flooded portions of the coastal plain.
112
deposition accompanied landward migration of sound and barrier systems,
lateral migration of environments within a back-barrier estuarine
ecosystem, or a combination of both. The "shell bed", "oyster beds"
and Linfossiliferous mud unit may, therefore, represent a succession of
1) laterally migrating environments near the mouth of a drovmed river
estuary, or 2) landward migrating environments directly reflecting a
rising sea. Unfortunately, the stratigraphic relationships among these
estuarine deposits does not prove either scenario.
SUMMARY
1. The unfossiliferous mud unit, "shell bed" and intermittently
occurring "oyster beds" that underlie and are present within the mud
unit represent estuarine deposits that accumulated during the middle
Pleistocene.
2. The "shell bed" is composed of a slightly muddy, shelly, fine
to very fine quartz sand. The "oyster bed" is composed of slightly
sandy mud. Both deposits are densely fossiliferous.
3. The stratigraphic position of the deposits and the
occurrence of" biostratigraphic indicators within the "shell bed"
suggest a middle Pleistocene age. Co-occurrence of the bivalves
Argopecten solarioides and Anadara ovalis, which do not appear to be
reworked, constrain the "shell bed" to Blackwelder's (1981b) Molluscan
Zone 2, indicating that the "shell bed" might be time-equivalent with
the Canepatch Formation. The sequence in Lee Creek Mine is younger
than the James City Formation but older than the Flanner Beach
Formation.
4. Correlation of core samples from Holes 68-80 and 55-80 with
fossiliferous deposits exposed in Lee Creek Mine is tentative. More
complete sampling is necessary before correlation can be verified.
5. The "shell bed" represents a condensed bed containing a time-
averaged fossiliferous association which is numerically dominated by
the bivalve Mulinia lateralis and by the foraminifera Elphidium
excavatum forma clavata and Elphidium limatulum. Predominance of these
species indicates an estuarine environment of deposition.
114
6. The "oyster bed" represents a paleo-channel deposit at Locality
3, and either a paleo-channel or small embayment at Locality 4. The
"oyster bed" contains a partially condensed fossilferous association
numerically dominated by the bivalves Crassostrea virginica and Corbula
swlftiana, and by the foraminifera Elphidium excavatum formae clavata
and selseyensis. The predominance of these species indicates an
estuarine environment of deposition.
7. Hole 55-80, sample 1 contains fossiliferous sandy mud
characterized by numerical dominance of the bivalve Mulinia lateralis,
abundant Nuculana acuta, and predominance of the foraminifera Elphidium
excavatum formae clavata and selseyensis. The abundance of these
species indicates an estuarine environment. The greater percentage of
mud suggests a quieter-water setting than that indicated for the "shell
bed".
8. The "shell-bed" and the "oyster bed" were deposited in a
barrier-built estuarine system that compares closely to modern
sedimentary environments near the mouth of the Pamlico River Estuary
and in the Pamilco Sound.
9. Physical and biological fluctuations and disturbances, which
characterize modern back-barrier estuaries, affected the distribution
of species, created and maintained patches of benthic organisms,
regulated the intermittent colonization of Mulinia, and contributed to
the mixing and condensation of these fossiliferous Pleistocene
deposits.
10. Fluctuations in species composition within sampled intervals
115
are attributable to the combined effects of limited sample size and
sample density, the wide-spread spatial occurrence of rare taxa,
salinity gradients, physical and biological phenomena that alter
community structure or interfere with recruitment, and time-averaging
of communities through condensation.
11. The sequence exposed in Lee Creek Mine accumulated as
depositional environments migrated laterally within the back-barrier
system. Deposition either occurred in direct response to marine
transgression and the invasion of estuarine waters onto the coastal
plain, resulted from lateral migration of environments parallel to
shore, or involved a combination of the two processes.
ANNOTATED FAUNAL LIST
Thirteen species and sub-species of benthic foraminifera.
species of bivalves and 23 species of gastropods are lis
alphabetically by genus within their respective taxonomic groupings.
Foraminifera listed are present in nearly every sample, maintaining an
average relative abundance of over 1.0% for all samples. A morphologic
description and a brief discussion of geographic distribution is
included for each species and subspecies of foraminifera. All
identified species of bivalves and gastropods are listed. Description
of geographic range, habit and habitat is included for each molluscan
species, focusing primarily on environmental tolerances and substrate
type. Comments concerning abundances of certain species are placed at
the end of each discussion. A complete faunal list is found in the
appendices.
117
FORAMINIFERA
Genus: AMMONIA Brunnich, 1772
Ammonia beccarii (Linne)
Nautilus beccarii LINNE, 1758, Systema Naturae, ed. 10, v. 1, Stockholm,
p. 710.
forma sobrina Shupack
PI. 4, fig. A-C
Ammonia sobrina SHUPACK, 1934, Some foraminifera from western Long
Island Sound and Mew York Harbor: Am. Hus. [Nat. Hist. Novitates
737].
forma tepida Cushman
PI. 4, fig. D-F
Ammonia tepida CUSHMAN, 1926, Recent foraminifera from Porto Rico
(sic): Carnegie Inst. Washington Pub. 344, p. 75-34.
The bioconvex formae sobrina and tepida, recognized by Schnitker
(1974) as ecophenotypes of ^ beccarii, are identified by the presence
or absence of a calcified plug found v;ithin the umbilical region.
According to Schnitker, forma sobrina has a calcified umbilical plug, 7
to 9 chambers in the final whorl and is slightly larger than forma
tepida, which lacks a plug and has only 6 to 7 chambers in the final
whorl. Because the size and number of chambers vary from this
pattern, it is best to identify these formae by umbilical
characteristics.
Distribution: Ammonia beccarii occurs along the eastern coast of North
America from the mouth of the St. Lawrence Seaway to the Florida
118
Keys (Culver and Buzas, 1980). This species typically inhabits
nearshore to marginal marine environments, though it has been
identified at depths up to 2000 meters. Ammonia beccarii is
commonly found in shallow shelf waters off the coast of North
Carolina (Schnitker, 1971) and is abundant in Beaufort Inlet
(Akers, 1971). Todd (1979) listed Ammonia beccarii forma
tepida as a common inner- to middle-shelf dweller near 0nslov>i Bay,
North Carolina; Charleston, South Carolina; and Jacksonville,
Florida.
Comments: A_^ beccarii forma sobrina and forma tepida are present in
every sample.
Genus: BUCCELLA Andersen, 1952
Buccella frigida (Cushman)
PI. 4, fig. G-I
Pulvinulina frigida CUSHMAN, 1922, Results of the Hudson Bay
expedition, 1920: I, The Foraminifera. Contr. Can. Biol., no. 9,
p. 144.
Buccella hannai (Phleger and Parker)
PI. 4, fig. J-L
Eponides hannai PHLEGER and PARKER, 1951, Ecology of foraminifera,
northwest Gulf of Mexico: Geol. Soc. Amer. Mem. 46, p. 21, pi. 10,
figs. 11-14.
Buccella inusitata Andersen
PI. 4, fig. M-O
Buccella inusitata ANDERSEN, 1952, Buccella, a new genus of the rotalid
foraminifera: Jour. Wash. Acad. Sci., v. 42, no. 5, p. 148, figs.
10, 11.
The genus Buccella v/as described by Andersen (1952) as a bioconvex
form which develops pustules concealing the umbilical region and a good
portion of the sutures on the umbilical side of the test. Species of
Buccella closely resemble one another and are not easily identified.
Buccella frigida has 4 to 6 chambers in the last whorl, a rounded
margin and an abundance of pustulose material on the umbilical side.
Unlike Buccella frigida, B. inusitata exhibits o to 9 chambers in the
last whorl, less development of pustulose material on the umbilical
side, a more acute margin and a small, imperforate band about the
periphery. Buccella hannai differs from frigida and inusitata in
having 7 to 9 distinctly lobate chambers in the last whorl, lacking an
imperforate peripheral margin and exhibiting a highly conical spiral
side.
Distribution: Buccella frigida is a temperate to cooler water
species found from the Chesapeake Bay northward through Long
Island Sound to Nova Scotia. This species largely inhabits
coastal, marginal marine v/aters, though it can be found at depths
of 200 to 2000 meters (Culver and Buzas, 1930). Buccella hannai
is an abundant species inhabiting the inner part of the
continental shelf near Onslov/ Bay, North Carolina; Charleston,
South Carolina; and Jacksonville, Florida. Its dominance
increases towards the middle shelf and shelf-slope break (Todd,
1979). Buccella hannai has also been recorded at depths of less
120
than 100 meters in the northv/est region of the Gulf of Mexico
(Andersen, 1952). Buccella inusitata has been reported off the
Washington Coast (Andersen, 1952).
Genus: ELPHIDIUÎ'l de Montfort, 1808
Elphidium compressulum Copeland
PI. 3, fig. 0-P
Elphidium compressulum COPELAND, 1964, Eocene and Miocene forarninifera
from two localities in Duplin County, North Carolina: Bull. Amer.
Paleontology, v. 47, no. 215, p. 262, pi. 37.
Elphidium compressulum is characterized by its thin, strongly
compressed, planispiral test, depressed umbilicus and coarsely
perforate hyaline wall. This species has 9 to 12 chambers in the final
whorl; chambers are flattened in the earliest portions and become
slightly inflated in the latter chambers. The sutures are distinct and
radial having short, broad retral processes (Copeland, 1964).
Elphidium excavatum (Terquem)
forma clavata Cushman
PI. 3, fig. A-B
Elphidium incertum (Williamson) var. clavatum CUSHMAN, 1930, The
forarninifera of the Atlantic Ocean, pt. 7: Nonionidae,
Camerinidae, Peneroplidae, and Alveolinellidae: U.S. Nat. Mus.
Bull., no. 104, pt.7, p. 20, pi. 7, figs. lOa-b.
forma lidoensis Cushman
121
PI. 3, fig. E-F
Elphidium lidoense CUSHMAN, 1936, Some new species of Elphidium and
related genera: Cushman Lab. Foram. Res., Contr., v. 12, pt. 4, p.
86, pi. 15, fig. 6.
forma selseyensis (Heron-Alien and Earland)
Pi. 3, fig. C-D
Polystomella striatopunctata (Fichtel and Moll) var. selseyensis HERON-
ALLEN and EARLAND, 1911, On the recent and fossil foraminifera of
the shore-sands of Selsey Bill, Sussex, VIII: Roy. Micr. Soc.
Jour., p. 448.
The species Elphidium excavatum is represented by five sub-species
or formae named by A.A.L. Miller (1932). Three of the five formae v/ere
identified from my material. These formae are characterized by
planispiral, involute coiling, a perforate test and 9 to 11 chambers in
the final whorl. Differences among formae involve varying degrees of
peripheral, umbilical and sutural development. Forma clavata is
recognized by a rounded periphery, the occurrence of an umbilicus boss
(or bosses), an imperforate (complete or incomplete) collar surrounding
the umbilicus and narrow sutures having several, sometimes incomplete
sutural bridges. Forma lidoensis is characterized by wide, depressed
sutures which distictly broaden towards the umbilicus and have few, if
any, poorly-developed sutural bridges. It has a less-rounded periphery
than forma clavata and a large, depressed umbilicus sometimes filled
with papillae. Forma selseyensis is characterized by wide, depressed
sutures that either slightly broaden or remain consistent towards the
umbilicus, a less-rounded periphery than forma clavata and slightly
inflated chambers in the latter portion of the final whorl, Unlike
forma clavata, forma selseyensis has minor development of sutural
bridges and a slightly depressed rather than flattened umbilicus.
Distribution: Elphidium excavatum forma clavata is the most abundant
form in cold v/aters of normal to reduced salinities along the
North Atlantic Coast from Long Island Sound to Newfoundland
(A.A.L. Miller, 1982). Feyling-Hanssen (1972) described forma
clavata as largely an arctic and sub-arctic inhabitant found at
moderate depths, but pointed out that it can occur in boreal and
warmer waters. Schnitker (1971) calls Blphidium clavata (=
Elphidium excavatum forma clavata) the most predominant benthic
foraminifer in nearshore and central shelf environments north of
Cape Hatteras. This forma shows some spotty predominance south of
the cape.
Elphidium excavatum forma selseyensis occurs in subarctic to
temperate, shallow, nearshore waters under estuarine influence
(A.A.L. Miller, 1982). Feyling-Hanssen (1972) found forma
selseyensis in boreal waters along intertidal margins.
Elphidium excavatum forma lidoensis occurs in shallow,
subtidal estuarine environments where highest temperatures reach
more than 20 degrees C (warm to temperate waters) (A.A.L. Miller,
1982). Feyling-Hanssen (1972) found forma lidoensis in regions
warmer than boreal.
Culver and Buzas (1980) noted the common occurrence of
Elphidium excavatum from just north of Cape Hatteras to N’ova
123
Scotia. This species is typically a coastal dweller, although it
is found at depths of 200 to greater than 2000 meters. These
authors did not differentiate the formae of excavatum.
Comments: ^ excavatum forma clavata and forma selseyensis are present
in every sample.
Elphidium galvestonense Kornfeld
forma mexicanum Kornfeld
PI. 3, fig. K-L
Elphidium mexicanum KORNFELD, 1931, Recent littoral foraminifera from
Texas and Louisiana: Contr. Dept. Geol., Stanford Univ., v. 1, p.
269-476.
Elphidium galvestonense forma mexicanum is a planispiral form v/ith
a finely perforate test, sub-rounded periphery and 9 to 11 chambers in
the final whorl. The sutures are narrow and slightly depressed
exhibiting 6 to 9 delicate, well-formed sutural bridges. The umbilical
region is slightly raised and is engulfed by a large umbilical plug.
Distribution: Elphidium galvestonense forma mexicanum. inhabits
shallow estuarine waters, such as those of San Antonio Bay in the
Gulf of Mexico (Poag, 1978).
Elphidium gunteri Cole
forma typicum Poag
PI. 3, fig. I-J
Elphidium gunteri Cole forma typicum POAG, 1978, Paired foraminiferal
ecophenotypes in Gulf Coast Estuaries: ecological and
124
paleoecological implications: Trans. Gulf Coast Assoc, of Geol.
Soc., V. 18, p. 402, pi. 2.
Elphidium gunteri forma typicum is a planispiral form having a
coarsely perforate test, slightly lobate periphery and 12 to 15
chambers in the final whorl. The sutures are wide, distinctly
depressed and contain numerous thick, well-defined sutural bridges.
The umbilical region is flat and often develops several small bosses or
papillae.
Distribution: Akers (1971) noted the occurrence and numerical dominance
of Elphidium gunteri near Beaufort, North Carolina in shallow
(approximately 11 meters) open marine v/aters and in Beaufort
Inlet. Byrum (1973) refers to Elphidium gunteri as a warm
temperate to sub-tropical individual inhabiting shallow waters.
Elphidium limatulum Copeland
PI. 3, fig. G-H
Elphidium limatulum COPELAIID, 1964, Eocene and Miocene foraminifera
from two localities in Duplin County, North Carolina: Bull. Amer.
Paleontology, v. 47, no. 215, p. 263, pi. 37, figs. 5a-b.
Elphidium limatulum is a planispiral form with a broadly rounded
periphery, depressed umbilicus filled v/ith clear granular material and
a finely perforate glossy white test. The 9 to 11 chambers in the last
whorl are separated by distinctly depressed sutures having ó to 7 well-
developed sutural bridges. Elphidium limatulum differs from Elphidium
galvestonense forma mexicanum by its depressed umbilical region, lack
125
of a large umbilical plug and broadly rounded rather than acute
periphery.
Distribution: Elphidium limatulum is found in assemblages living within
the nearshore environment off Wilmington, North Carolina (Workman,
1981).
Elphidium poeyanum (Orbigny)
PI. 3, fig. M-N
Polystomella poeyana ORBIGNY, 1039, Foraminiferes: in de la Sagra,
Histoire Physique, Politique et Naturelle de I'lle de Cubana, p.
55, pl. 6, figs. 25, 26.
Elphidium poeyanum is a planispiral forra having a broadly rounded
periphery, depressed umbilical region and a coarsely perforate hyaline
test. The 9 to 10 inflated chambers in the last whorl are separated by
slightly depressed sutures having 5 to 7 distinct sutural bridges.
Distribution: Elphidium poeyanum is commonly found in the shallow
waters of the West Indies (the type locality) (Cushman, 1939
referenced by Mauger, 1978).
Comments: E. poeyanum is present in every sample.
PLATE 3
Elphidium species
(all scale bars represent 100 micrometers)
Figure :
A-B. Elphidium excavatum (Terquem) forma clavata Cushman
A. Side view
B. Edge view
C-D. Elphidium excavatum (Terquem) forma selseyensis (Heron-Alien
C. Side view & Earland)
D. Edge view
E-F. Elphidium excavatum (Terquem) forma lidoensis Cushman
E. Side view
F. Edge view
G-H. Elphidium limatulum Copeland
G. Side view
H. Edge view
1—1 1 Elphidium gunteri Cole forma typicum Poag
I. Side view
J. Edge view
K-L. Elphidium galvestonense Kornfeld forma mexicanum Kornfeld
K. Side view
L. Edge view
M-N. Elphidium poeyanum (d'Orbigny)
M. Side view
N. Edge view
0-P. Elphidium compressulum Copeland
O. Side vievi^
P. Edge view
127
PLATE 4
Ammonia and Buccella species
(all scale bars represent 100 micrometers)
Figure:
y
A-C. Ammonia beccarii (Linne) forma sobrina Shupack
A. Umbilical view
B. Edge view
C. Spiral view
y
D-F. Ammonia beccarii (Linne) forma tepida Cushman
D. Umbilical view
E. Edge view
F. Spiral view
G-I. Buccella frigida (Cushman)
G. Umbilical view
H. Edge view
I. Spiral view
J-L. Buccella inusitata Andersen
J. Umbilical view
K. Edge view
L. Spiral view
M-0. Buccella hannai (Phleger and Parker)
M. Umbilical view
N. Edge view
O. Spiral view
129
MOLLUSKS
Bivalves
ABRA Lamarck, 1818
Abra aequalis Say
Abra aequalis SAY, 1822, An account of some of the marine shells of the
United States: Journal of the Academy Natural Sciences
Philadelphia, v. 2, 1st ser., p. 307.
Range: Delaware to Florida, Texas; Gulf of Campeche; Yucatan; West
Indies; Surinam; northeastern and eastern Brazil.
Habit: Abra aequalis is an infaunal suspension feeder tolerant of
stenohaline conditions (Andrews, 1977). Bird (1970) referred to this
species as a burrowing, selective deposit feeder.
Habitat: Abra aequalis is a characteristic inhabitant of medium
sandy to muddy substrates in the Newport River Estuary, located near
Cape Lookout N.C. It is most abundant in the near-mouth and midreach
regions of the estuary (Bird, 1970). Andrews (1977) commonly found
A. aequalis in open bays, inlet-influenced areas and along the lower
shore face of the Texas Gulf Coast, living in sandy muds and clays.
Parker (1956) noted this bivalve in sandy silts, silty clays and sands
of upper sound, inlet and shallo\\f shelf environments near barrier
islands in the east Mississippi Delta region. aequalis has been
reported in Bogue Sound and in open waters stretching from Cape Lookout
to Southport, N. C., living in 3 to 140.meters of water (Porter, 1974
referenced by Gay, 1980).
131
ANADARA Gray, 1847
Anadara ovalis (Bruguiere)
Lunarca ovalis Bruguiere, 1787, Encyclopédie Méthodique, v, 1, no. 1,
p. lio.
Range: Cape Cod to West Indies, Gulf States; Costa Rica; Brazilian
Coast to Rocha, Uruguay.
Habit: Anadara ovalis is a semi-infaunal (lives partially within
the substrate and partially exposed with the flattened posterior margin
horizontal to and slightly above the sediment surface) suspension
feeder tolerant of stenohaline conditions (Stanley, 1970; Andrews,
1977). All species of Anadara are sluggish burrowers and employ a weak
byssus as an anchor in shifting, generally sandy substrates (Gay,
1980).
Habitat: Anadara ovalis prefers predominantly sandy substrates of
protected subtidal areas where currents are moderately strong and
silt/clay content is low; but it is tolerant of a variety of habitats
(Stanley, 1970). Sandy substrates are often unstable, shifting with
current flow. Andrews (1977) found ovalis in estuary inlets and
offshore regions of the Texas Gulf Coast.
Anadara transversa (Say)
Area transversa SAY, 1822, An account of some of the marine shells
of the United States: Journal of the Academy of Natural Sciences
Philadelphia, v. 2, 1st ser., p. 269.
Range: South of Cape Cod to Florida, Texas to Carmen and Campeche,
132
Mexico and in the Gulf of Campeche; Bermuda.
Habit: Anadara transversa is a semi-infaunal suspension feeder and
is similar in life habit to Anadara ovalis, feeding with siphons at,
near or above the sediment surface. ^ transversa is tolerant of
stenohaline conditions (Andrews, 1977).
Habitat: Both Anadara transversa and ovalis are found in the
midreaches of the Newport River Estuary and increase in abundance
towards near-mouth and shallow shelf regions (Bird, 1970). Anadara
transversa has a noted association with Spisula, Tellina, Dosinia,
Ensis and Nucula (Bird, 1970 referenced by Gay, 1980). This species
occurs within inlet-influenced areas and on the lower shoreface and
shallow shelf of the Texas Gulf Coast, living in or on rocks, shells,
sand and rubble (Andrews, 1977). Parker (1956) found A. transversa in
upper sound, inlet and shallow shelf environments within the east
Mississippi Delta region. Sediment type appears to influence the
distribution of this bivalve. ^ transversa is uncommon in sediments
with more than 5 % silt-clay v;hile its distribution is positively
correlated with that of medium to coarse sand (Driscoll and Brandon,
1973 referenced by Gay, 1930).
ANOHIA Linné", 1758
Anomia simplex Orbigny
Anomia simplex ORBIGNY, 1845, Mollusques: Jn de la Sagra, Histoire
Physique, Politique et Naturelle de I'lle de Cuba, v. 2, p. 367,
pi. 38, figs. 31-33.
133
Range: Eastern United States; Bermuda; Gulf of Mexico; Gulf of
Campeche; Quintata Roo; VJest Indies to Brazil; Surinam.
Habit: Anomia simplex is a byssate, closely attached epifaunal
supension feeder tolerant of euryhaline conditions (Andrews, 1977). It
attaches its flattened right valve to a hard surface such as rocks or
oyster shells by means of a stout, calcified byssus growing in such a
manner as to prevent the overlapping of the object of attachment
(Andrews, 1977; Stanley, 1970). The right valve often remains cemented
to its substrate.
Habitat: Anomia simplex attaches to pebbles, cobbles and shell
material on the substrate, seldom attaching to broad, rocky surfaces.
It is restricted to shallow subtidal environments with moderate current
flow (Stanley, 1970). This bivalve is found in estuaries nearer to
freshwater sources than to the open shelf along the Texas Gulf Coast
(Andrews, 1977). Bird commonly found A. simplex in midreach and near-
mouth regions of the Newport River Estuary and noted its occurrence in
shallow, open ocean environments adjacent to the estuary.
Comments: ^ simplex reaches maximum abundance in sample 1,
Locality 3 and sample 3, Hole 68-30.
ARGOPECTEN Monterosato, 1899
Argopecten solarioides (Heilprin)
Pecten solarioides Heilprin, 1887, The Miocene mollusca of the
state of New Jersey: Academy of the Natural Sciences Philadelphia,
Procedings, 3rd ser., v. 17, p. 397-405.
Range: Argopecten gibbus (Linne)— Bermuda; eastern U.S., Gulf of
134
Mexico; Campeche Bank; VJest Indies. Argopecten irradians (Lamarck)—
Cape Cod to New Jersey. A. irradians concentricus (Say)— Maryland to
western Florida and Louisiana. ^ irradians amplicostatus (Dali)—
Louisiana to Mexico. [The above species are extant and closely related
to the extinct species eboreus (Conrad) and ^ solarioides
(Heilprin)].
Habit: Argopecten gibbus is a free-living epifaunal suspension
feeder tolerant of stenohaline conditions (Andrews, 1977). It spends
most of its life reclining on the substrate but, if disturbed, is able
to swim short distances by shooting several pulsating jets of water
from its siphons, which are oriented tov\iards the hingement. Argopecten
irradians is tolerant of slightly lower salinities (euryhaline), but is
otherwise identical in life habit to ^ gibbus. A. gibbus is also
slightly less inflated and larger (Andrews, 1977; Rehder, 1981).
Habitat: Argopecten gibbus is found on sandy substrates associated
with estuary inlets and the open marine intermediate shelf along the
Texas Gulf Coast (Andrews, 1977). Bird (1970) noted v\fhat he called
Aequipecten gibbus in fine to very fine sands associated with open
marine and, less commonly, estuarine environments near Beaufort, N.C.
A. gibbus is com.mercially fished offshore east of Cape Lookout and
southwest of Beaufort Inlet at depths of 100 feet (Porter and Tyler,
1981).
Porter and Tyler (1981) stated that Argopecten irradians lives
only in sounds and estuaries found along the North Carolina coast.
Kirby-Smith and Gray (1973) noted the occurrence of the sub-species ^
135
irradians concentricus on mud fiat, sand flat, and eel grass
environments in Bogue Sound, Beaufort Inlet and the Newport River
Estuary and in dredge samples from Bogue Sound and trawl material from
the Newport River Estuary. The sub-species irradians amplicostatus
inhabits bays and open lagoons along the Texas Gulf Coast, and is often
found reclining in grass beds or algae (Andrews, 1977).
Comments: ^ solarioides is present only in sample 1, Locality 1
and sample 2, Locality 2.
CORBULA Bruguiere, 1797
Corbula contracta Say
Corbula contracta SAY, 1822, An account of some of the marine shells of
the United States: Journal of the Academy Natural Science
Philadelphia, v. 2, 1st ser., p. 312.
Range: Cape Cod to Florida, Texas; Gulf of Campeche; VJest Indies;
Brazil.
Habit: Corbula contracta is an infaunal suspension feeder tolerant
of euryhaline conditions (Andrews, 1977). The inflated nature of
Corbula's valves helps to increase buoyancy at the sediment-water
interface so that the siphons do not clog (Stanley, 1970). All
Corbulas maintain a rather sedentary life habit, buried just beneath
the surface of muddy sands and gravel, often attached to stones or hard
surfaces by byssal threads (Redder, 1931).
Habitat: Corbula contracta inhabits clayey to sandy substrates in
open sound, estuary inlet and shallow shelf environments along the
136
Texas Gulf Coast (Andrev^rs, 1977). Bird (1970) commonly found this
species in medium to very fine sands of near-mouth and midreach
portions of the Newport River Estuary and in shallow shelf environments
adjacent to the estuary. C. contracta is also present in Upper Breton
and Chandeleur Sounds in the east Mississippi Delta region (Parker,
1956).
Comments: Though C. contracta is present in every sample, it never
constitutes more than l.ó % of any sample.
Corbula swiftiana C.B. Adams
Corbula swiftiana C.B. ADAMS, 1852, Contributions to Conchology, v. 12,
p. 236.
Range: Massachusetts to eastern Florida, Texas; West Indies;
Brazil to Argentina.
Habit: Corbula swiftiana is an infaunal suspension feeder tolerant
of euryhaline conditions (Andrews, 1977). C. swiftiana differs from C_^
contracta by valve sculpture; C_^ contracta has many strong, well-
developed concentric lines while C_^ svjiftiana exhibits fewer, weakly-
developed, irregular concentric lines. C_^ caribaea Orbigny is a
synonym of C. swiftiana (Andrews, 1977).
Habitat: Corbula swiftiana inhabits sands and muddy sands in
estuary and inlet-influenced areas and open bay margins along the Texas
Gulf Coast; and it is the most common species of Corbula along that
coast (Andrews, 1977). This species is also found off the U.S.
Atlantic Coast in v/aters 6 to 450 fathoms deep (Abbott, 1974).
Comments: C_^ swiftiana is present in every sample except sample
137
1, Hole 55-80. It reaches maximum abundance in sample 1, Locality 3
and sample 3, Hole 68-80.
CRASSOSTREA Sacco, 1897
Crassostrea virginica (Gmelin)
Ostrea virginica GMELIN, 1791, Carol! a Linne systema naturae per régna
tria naturae, 13 th ed., v. 1, pt. 6, p. 3336.
Range: Gulf of St. Lawrence to Gulf of Mexico; Yucatan; West
Indies.
Habit: Crassostrea virginica is an epifaunal suspension feeder
which cements to rocks and shell debris and is tolerant of euryhaline
conditions (Andrews, 1977). Although many beds of C. virginica grow in
waters greater than 25 ppt. salinity, juveniles develop best at 17.5
ppt. This species is the most ubiquitous oyster on the Atlantic Coast
due largely to its ability to withstand repeated exposure to freezing
temperatures (Stenzel, 1971). Its northernmost range is limited by
its reproductive capabilities. Because C_^ virginica cannot propagate
in waters less than 20 C, it must inhabit regions where summer climate
allows for just such an increase in water temperature (Stenzel, 1971).
C. virginica attaches to rocks and mangroves and forms fringe, string
and patch reefs (Stenzel, 1971).
Habitat: Crassostrea virginica lives in brackish bays, open bays,
lower ends of bays with tidal influence, bay margin shoal waters, grass
flats, shallow bay margins with dense grass and estuaries along the
Texas Gulf Coast (Andrews, 1977). This oyster inhabits restricted bays
and estuaries where salinity ranges from 10 to 29 ppt. and is found in
138
intertidal areas of sounds and estuaries along the North Carolina
Coast (v/ells, 1961 referenced by Gay, 1980; Porter and Tyler, 1981).
C. virginica largely inhabits areas where waves and currents are too
weak to initiate shifting of the sands but too strong to allow for the
accumulation of muds (Stenzel, 1971).
Comments: Cj_ virginica reaches maximum abundance in sample 1,
Locality 3 and sample 3, Hole 68-80.
CYRTOPLEURA Tryon, 1862
Cyrtopleura costata (Linne)
Barnea costata LINNE, 1758, Systema Naturae per régna tria naturae. Vol
1, Regnum animale, 10th ed., Stockholm, p. 669.
Range: Massachusetts to Florida, Texas; Mexico; West Indies.
Habit: Cyrtopleura costata is an infaunal suspension feeder which
burrows into sandy to clayey substrates to a depth of nearly 2 feet.
This species is tolerant of euryhaline conditions, but is susceptible
to changes in salinity for it is much too large to withdraw its soft
parts into its shell. The two valves act as a drill bit when burrowing
into the substrate (Andrews, 1977). C. costata can move up and down in
its burrow (Abbott, 1974).
Habitat: Cyrtopleura costata inhabits sandy and clayey substrates
found in estuary inlets, bays, inlet-influenced areas and open bay
margins along the Texas Gulf Coast (Andrews, 1977). Porter and Tyler
(1981) noted the occurrence of this bivalve in shallow offshore and
estuarine environments burrowing into muds or clays. Parker (1956)
139
found C_^ costata living in sands and silty clays of upper sound, inlet
and shallow shelf environments within the east Mississippi Delta
region.
Comments: C. costata is present only in samples 1 and 2, Locality
1 and sample 2, Locality 2.
DINOCARDIUî'I Dali, 1900
Dinocardium robustum (Lightfoot)
Laevicardium robustum LIGHTFOOT, 1736, A catalogue of the Portland
Museum, London, p. 53.
Range: Virginia to Florida, Gulf States; Mexico; Bahamas.
Habit: Dinocardium robustum is an infaunal suspension feeder
tolerant of stenohaline conditions (Andrews, 1977). ^ robustum is
similar in life habit to the sub-species Dinocardium robustum
vanhyningi. This sub-species is a large and rapid burrower having the
ability to extract itself from burial by quickly straightening its bent
foot, literally leaping from the sediment surface (Stanley, 1970).
Habitat: Dinocardium robustum is found in estuarine, bay or
lagoonal and lov\?er shoreface regions along the Texas Gulf Coast, though
it seems to prefer the sandy substrates of inlet-influenced and
shoreline areas (Andrews, 1977). Gay (1930) noted an abundance of D^^
robustum valves on the beach along Emerald Island H. C. and has seen
live individuals on shallow sand bars exposed at low tide around Bogue
Inlet. Kirby-Smith and Gray (1973) found this species on sand flats in
the Newport River Estuary, Bogue Sound and Beaufort Inlet.
DIPLODONTA Bronn, 1831
Diplodonta punctata (Say)
Taras punctatus SAY, 1322, from Abbott, 1974, American Seashells, 2nd
0claj 323*
Range: North Carolina to Florida; Bermuda; Brazil.
Habit: Diplodonta punctata is an infaunal suspension feeder
tolerant of euryhaline conditions (Andrews, 1977).
Habitat: Diplodonta punctata lives in sandy muds found in open
bays, bay margins and shoal waters bordering bays, and in grass flats
associated with estuarine environments along the Texas Gulf Coast
(Andrews, 1977). It occurs in muddy sands and gravels at depths of less
the one meter in Kingston Harbour, Jamaica (Allen, 1958 referenced by
Gay, 1980). Stanley (1970) noted ^ punctata in poorly-sorted
carbonate sand in areas covered with eel grass. This species inhabits
midreach and near-mouth regions of the Newport River Estuary and
shallow shelf areas adjacent to the estuary (Bird, 1970).
DIVARICELLA von Martens, 1380
Divaricella quadrisulcata (Orbigny)
Lucina quadrisulcata ORBIGNY, 1842, Mollusques: ini Histoire physique,
politique, et naturelle de I'lle de Cuba, p. 294, pi. 27, figs.
34-35.
Range: Massachusettes to southern half of Florida; West Indies;
Brazil.
Habit: Divaricella quadrisulcata is an infaunal, slow-burrowing
141
suspension feeder tolerant of stenohaline conditions (Andrews, 1977).
This species uses its divaricate ornamentation and smooth, pronounced
rocking motion to cut or saw its way into sandy substrates to a depth
of nearly 20 centimeters (deep for a lucinid) (Stanley, 1970).
Habitat: Divaricella quadrisulcata is found in medium to very fine
sands of both the shallow, open marine environment and near-mouth to
midreach region of the Newport River Estuary. It occurs most
frequently in the shallow, open marine environment (Bird, 1970).
Stanley (1970) noted this bivalve on exposed intertidal flats composed
of fine to very fine sand. Stanley also stated that ^ quadrisulcata
is not as strongly restricted to grassy bottoms as most Caribbean
lucinids. ^ quadrisulcata has been reported south of Bogue Inlet in
Bogue and Core Sounds in 1 to 18 meters of water and around Cape
Lookout in 0.5 to 12 meters of v/ater (Porter, 1974 referenced by Gay,
1980).
DOSINIA Scopoli, 1777
Dosinia discus Reeve
Dosinia discus REEVE, 1850, Conchologia iconica, London, v. 6, pi. 2.
Range: Virginia to Florida, Gulf States; Mexico; Bahamas.
Habit: Dosinia discus is an infaunal suspension feeder tolerant of
stenohaline conditions (Andrews, 1977). Stanley (1970) noted that the
life habit and habitat of ^ discus are similar to Dosinia elegans
Conrad. Both species are rapid burrowers which live 2.5 to 8
cm beneath the sediment surface. These two species differ only by the
number of exterior valve ridges. Dosinia elegans has nearly 25 ridges
142
per inch while D. discus has 45 to 50 (Porter and Tyler, 1981).
Habitat: Dosinia ele^ans (similar in habitat to ^ discus)
inhabits clean, medium to coarse sands of moderately exposed sand flats
and areas scoured by tidal currents (Stanley, 1970). Andrews (1977)
found Dosinia discus in lower shoreface to shallow shelf areas
extending up into estuary inlets along the Texas Gulf Coast. Dosinia
discus is commonly found along well-drained, protected sandy beaches in
the Newport River Estuary and in near-mouth and shallow open ocean
environments adjacent to the estuary (Norton, 1947 and Bird, 1970
referenced by Gay, 1980).
ENSIS Schumacher, 1817
Ensis directus Conrad
Ensis directus CONRAD, 1343, from Abbott, 1974, American Seashells,
2nd ed. p. 494.
Range: Labrador to South Carolina and Florida.
Habit: Ensis directus is an infaunal, moderately deep-burrowing
suspension feeder tolerant of stenohaline conditions (Bird, 1970).
This individual makes use of its smooth, streamlined shape to burrow
rapidly into the substrate. If disturbed, it can quickly retreat into
its burrow. ^ directus can also move at the sediment surface by
periodically straightening its foot or expelling a jet of water
posteriorly, creating either a leaping or a swimming motion (Stanley,
1970).
Habitat: Ensis directus is generally restricted to lov»r intertidal
143
and shallow subtidal settings, living in cohesive fine sands and muddy
sands (Stanley, 1970). Stanley noted this species' greatest abundances
in areas swept by moderately strong currents, including tidal channel
margins and exposed sand flats. ^ directus is a sand flat dweller
v^rhich occurs in the Newport River Estuary, Bogue Sound and Beaufort
Inlet. Abbott (1974) observed this bivalve on sand flats associated
with New England coastal environments.
Comments: E. directus is present in every sample except sample 1,
Locality 3 and sample 3, Hole 68-80.
MERCENARIA Schumacher, 1817
Mercenaria mercenaria (Linné)
Venus mercenaria LINNE, 1758, from Abbott, 1974, American Seashells,
2nd ed., p. 523.
Range: Gulf of St. Lawrence to Florida and Gulf of Mexico.
Habit: Mercenaria mercenaria is an infaunal, moderately rapid
burrowing suspension feeder tolerant of stenohaline conditions. When
fully buried, this species lives only 2 centimeters belov/ the sediment
surface (Stanley, 1970).
Habitat: Mercenaria mercenaria is present throughout the Newport
River Estuary and associated shallow shelf environments, living in
medium sands to muddy sands and sandy muds (Bird, 1970). Stanley
(1970) found this bivalve living in the sands and muddy sands of
intertidal and shallow subtidal environments. Kirby-Smith and Gray
(1973) regard M. mercenaria as a sand and mud flat dweller which occurs
in Bogue Sound and Beaufort Inlet.
144
MULINIA Gray, 1837
Mulinia lateralis (Say)
Mactra lateralis Say, 1822, An account of some of the marine shells
of the United States; Journal of the Academy of Natural Sciences
Philadelphia, v. 2, 1st ser., p. 309.
Range: Maine to northern Florida, Texas; Gulf of Campeche;
Yucatan.
Habit: Mulinia lateralis is an infaunal, moderately rapid
burrowing suspension feeder tolerant of euryhaline conditions (Stanley,
1970; Andrews, 1977). It is an opportunistic species characterized by
short generation time and rapid population growth. lateralis
invades a community if conditions such as salinity, space, temperature,
predation and food availability allow for its proliferation (Levington,
1970).
Habitat: Mulinia lateralis occurs in clays and sands within middle
estuary, sound, inlet and adjacent shallow shelf regions along the
Texas Gulf Coast (Andrews, 1977). Stanley (1970) calls lateralis
"a lagoonal species which can tolerate a wide range of salinités and
substrata, but is not generally found in shifting sands". Bird (1970)
found this species throughout the Nev/port River Estuary, but it
occurred most commonly in medium-grained sands and muds in near-mouth
and rnidreach areas of the estuary. Porter and Tyler (1981) mention
that this bivalve is generally found in estuarine waters saltier than
those which contain Rangia cuneata (Sowerby), a brackish-water bivalve.
145
Parker (1956) found H, lateralis in delta front, lower and upper sound,
inlet and shallow shelf environments v/ithin the east Mississippi Delta
region, though it seemed to be most abundant in lower sound and pro-
delta slope areas.
Comments: lateralis is present in every sample, predominating
in all but two samples (sample 1, Locality 3 and sample 3, Hole 68-80)
v;ith an average relative abundance of 30.7 %.
MYSELLA Angas, 1877
Mysella planulata (Stimpson)
Mysella planulata (Stimpson), 1851, Shells of Nev/ England, p. 17.
Range: Greenland to Texas; West Indies.
Habit: Mysella planulata is an epifaunal suspension feeder
tolerant of euryhaline conditions. This bivalve attaches itself to
pilings, buoys and grasses (Andrews, 1977). M_^ planulata is a
commensal bivalve, often found living on the abdomen of marine
arthropods. It is capable of crawling with its foot, much like a
gastropod (Andrews, 1977).
Habitat: Mysella planulata is found living in medium to very fine
sands of the Newport River Estuary and adjacent shallov^; shelf areas
(Bird, 1970). This species occurs south-southeast of Beaufort Inlet at
depths up to 63 meters and inhabits muddy, very fine sands found in
northeast Long Island Sound (Porter, 1974 and Franz, 1976 referenced
by Gay, 1980).
NOETIA Gray, 1340
146
Noetia ponderosa (Say)
Arca ponderosa SAY, 1822, An account of some of the marine shells of
the United States: Journal of the Academy of Natural Sciences
Philadelphia, v. 2, 1st ser., p. 267.
Range: Virginia to Key V/est, Gulf of Mexico.
Habit: Noetia ponderosa is an infaunal suspension feeder tolerant
of euryhaline conditions (Andrews, 1977).
Habitat: Noetia ponderosa inhabits sandy substrates near estuary
inlets and the shoreface of beaches along the Texas Gulf Goast
(Andrevvfs, 1977). This species is a common shallow water sand dweller
found along the U. S. Atlantic Coast and has been dredged from the
bottom of Bogue Sound (Abbott, 1974; Kirby-Smith and Gray, 1973).
NUCULA Lamarck, 1799
Nucula próxima Say
Nucula próxima SAY, 1822, An account of some of the marine shells of
the United States: Journal of the Academy of Natural Sciences
Philadelphia, v. 2, 1st ser., p. 270.
Range: Nova Scotia to Florida and Texas; Bermuda.
Habit: Nucula próxima is an infaunal, moderately rapid burrowing
deposit feeder tolerant of euryhaline conditions (Stanley, 1970;
Andrews, 1977). This species moves slowly and sporadically while
feeding and shows a marked tendency to migrate toward areas of current
flow (Stanley, 1970).
Habitat: Nucula próxima prefers muddy substrates and sheltered
147
subtidal conditions (Stanley, 1970). Gay (1980) stated that a
relationship exists between the distribution of this species and the
silt/clay content of the substrate, with the greatest abundances of
próxima in sediments having a silt/clay content of 35% or more. This
small bivalve inhabits the poorly sorted fine to very fine sands found
in the near-mouth and midreach regions of the Newport River Estuary
(Bird, 1970). Andrews (1977) noted that _N^ próxima prefers clayey
sands and is commonly found near estuary inlets along the Texas Gulf
Coast. Parker (1956) placed this species in his deep shelf assemblage
which is adjacent to the east Mississippi Delta region, ranging from 13
to 50 fathoms.
Comments: próxima is present only in sample 1, Hole 55-80 and
sample 2, Hole 68-30.
NUCULAHA Link, 1807
Nuculana acuta Conrad
Muculana acuta CONRAD, 1832, American Marine Conchology, Philadelphia,
p. 32, pi. 6, fig. 1.
Range: Cape Cod to Texas and West Indies; Carmen and Campeche,
Mexico; Gulf of Campeche and Campeche Bank.
Habit: Nuculana acuta is an infaunal deposit feeder tolerant of
stenohaline conditions (Andrews, 1977).
Habitat: Nuculana acuta is found in sandy mud beyond low tide
within estuary inlets and shallovi^ shelf regions along the Texas Gulf
Coast (Andrews, 1977). This species inhabits the near-mouth region of
the Newport River Estuary and adjacent shallow open ocean environments
148
(Bird, 1970).
Comments: acuta is present only in sample 1, Hole 55-80 and
sample 1, Hole 68-80.
PANDORA Bruguiere, 1797
Pandora trilineata Say
Pandora trilineata SAY, 1822, An account of some of the marine shells
of the United States: Journal of the Academy of Natural Science
Philadelphia, v. 2, 1st ser., p. 261.
Range: North Carolina to Florida and Texas.
Habit: Pandora trilineata is an infaunal suspension feeder
tolerant of stenohaline conditions (Andrews, 1977). P. trilineata is
similar in life habit to Pandora gouldiana (Dali), a slow borrower
which can be easily dislodged from its burrow. Once dislodged, it lies
on its side until it is able to burrov/ again (Stanley, 1970).
Habitat: Pandora trilineata is found along the Texas Gulf Coast in
inlet areas, open sound and lagoon centers and in shallow shelf areas
living in clayey sediments and sandy substrates (Andrev/s, 1977). This
flattened bivalve occurs in medium to very fine sands of the near-mouth
and midreach regions of the Newport River Estuary and shallow shelf
environments adjacent to the estuary (Bird, 1970). ^ trilineata is
present in shallow shelf and upper and lower sound areas of the east
Mississippi Delta, but its greatest abundances occur v\/ithin inlets
(Parker, 1956). P. gouldiana prefers coarse substrates not exceeding
10 percent gravel or mud content and areas swept by moderately strong
149
currents (Stanley, 1970),
PARVILUCINA Dali, 1901
Parvilucina multilineata (Tuomey and Holmes)
Lucina multilineata TUOMEY and HOLMES, 1856, Pleiocene (sic) Fossils
South Carolina, p. 61.
Range: North Carolina to both sides of Florida, Texas; Yucatan;
Quintana Roo; eastern and southern Brazil.
Habit; Parvilucina multilineata is an infaunal suspension feeder
tolerant of stenohaline conditions (Andrews, 1977). This small lucinid
has relatively long siphons (Rehder, 1981). The longer siphon length
might reflect adaptation for added protection and/or a modified feeding
habit useful in muddier environments, where it is able to place its
siphons above the sediment surface.
Habitat: Parvilucina multilineata inhabits medium to very fine
sands o.f shallow shelf, inlet and estuary environments near Beaufort,
N.C. This small bivalve occurs south-southeast of Cape Hatteras dov/n
to Beaufort Inlet, and in Bogue Sound (Porter, 1974 referenced by Gay,
1980). Assemblages dominated by this species suggest a high degree of
ecological stress, such as low food supply, stagnant conditions and
large fluctuations in temperature and salinity (Stanley, 1970; Allen,
1953 and Jackson, 1973 referenced by Gay, 1930).
Comments: P. multilineata is present in all samples except sample
1, Locality 3, sample 1, Hole 55-80 and sample 3, Hole 63-80.
RAETA Gray, 1853
150
Raeta plicatella (Lamarck)
Labiosa plicatella LAMARCK, 1813, Histoire naturelle des animaux sans
vertebres, Paris, v. 5, p. 470.
Range: North Carolina to Florida, Texas and Mexico; Uest Indies.
Habit: Raeta plicatella is an epifaunal suspension feeder which
reclines upon sandy substrates and is tolerant of stenohaline
conditions (Andrews, 1977).
Habitat: Raeta plicatella inhabits the sandy bottoms of the outer
surf zone along the Texas Gulf Coast, commonly occurring on the lov/er
shoreface (Andrev/s, 1977). Parker (1956) found Labiosa (Raeta)
plicatella on the shallow shelf adjacent to barrier islands in the east
Mississippi Delta region.
TAGELUS Gray, 1847
Tagelus plebeius (Lightfoot)
Tagelus plebeius (Lightfoot), 1786, A catalogue of the Portland Museum,
London, pp. 42, 101, 156.
Range: Cape Cod to southern Florida; V/est Indies; Surinam;
Brazilian Coast to Bahia; Blanca, Argentina.
Habit: Tagelus plebeius is an infaunal suspension feeder tolerant
of euryhaline conditions (Andrews, 1977). This bivalve burrows slowly
into silty fine to very fine sand to depths of 25 to 45 cm. It is
able to move up and down in its burrow in order to feed and protect
itself (Stanley, 1970).
Habitat: Tagelus plebeius is an intertidal species that prefers
151
moderately sheltered conditions and substrates consisting of muddy
sands (Stanley, 1970). It is commonly found living along margins of
bays and estuaries and in enclosed lagoons (Stanley, 1970; Andrev/s,
1977). gibbus (Solander) (= plebeius) occurs in fine to very
fine sands within the Nev/port River Estuary and adjacent open ocean
areas (Bird, 1970). T. plebeius commonly inhabits sandy mud and m.uddy
sand flats in Bogue Sound and Beaufort Inlet (Kirby-Smith and Gray,
1973).
TELLINA Linne, 1753
Tellina aequistriata Say
Tellina aequistriata SAY, 1824, Journal of the Academy of Natural
Sciences Philadelphia, v. 4, 1st ser., p. 145, pi. 10, fig. 7.
Range: North Carolina to both sides of Florida, Texas; Campeche
Bank; Yucatan; West Indies; Brazilian Coast to Bahia.
Habit: Tellina aequistriata is an infaunal deposit/suspension
feeder tolerant of stenohaline conditions (Andrews, 1977; Rehder,
19S1).
Habitat: Tellina aequistriata occurs in sands and muddy sands on
the lower shoreface and shallov/ shelf regions along the Texas Gulf
Coast (Andrews, 1977).
Tellina agilis Stimpson
Tellina agilis STIMPSON, 1857, from Abbott, 1974, American Seashells,
2nd ed., p. 500.
Range: Gulf of St. Lawrence to Georgia (Tellina texana Dali, which
152
is probably an ecophenotype of agilis, extends further south to
Texas and Cuba).
Habit: Tellina avilis is very similar to T_^ texana, vvhich is an
infaunal deposit and sometimes suspension feeder/scavenger tolerant of
lower salinities than other tellins (euryhaline) (Andrews, 1977). Like
all tellins, agilis employs the use of one short siphon for
discharge and one long siphon for feeding, scouring the surface for
food much like a vacuum hose (Rehder, 1981).
Habitat: Tellina agilis inhabits eel grass beds associated v/ith the
Newport River Estuary, Bogue Sound and Beaufort Inlet (Kirby-Smith and
Gray, 1973). It is found in sands, muddy sands and sandy muds within
estuaries and bay centers along the Texas Gulf Coast (Andrev/s, 1977).
Abbott (1974) noted the common occurrence of T. texana on sandy bottoms
of shallow coastal environments along the southern Atlantic Coast from
the low tide mark to 25 fathoms. TL_ texana has been collected by
trawlers in Onslow Bay, N.C. and was found in deep shelf environments
off barrier islands in the east Mississippi Delta region (Kirby-Smith
and Gray, 1973; Parker, 1956).
Comments: I\_ agilis is present in every sample except sample 1,
Locality 3 and sample 3, Hole 63-30.
Tellina alternada Say
Tellina alternada SAY, 1822, An account of some of the marine shells of
the United States: Journal of the Academy of Natural Sciences
Philadelphia, v. 2, 1st ser., p. 275.
Range: North Carolina to Florida, Gulf States; Yucatan; Costa
153
Rica; West Indies; southern Brazil.
Habit: Tellina alternata is an infaunal suspension feeder tolerant
of stenohaline conditions (Andrews, 1977). This species burrows
rapidly into fine, muddy sands (Stanley, 1970).
Habitat: Tellina alternata is generally restricted to muddy,
subtidal substrates in protected bay and lagoonal environments
(Stanley, 1970). Andrews (1977) found this species living in sands and
muddy sands within bay margins, inlets and shallov/ shelf regions along
the Texas Gulf Coast, while Bird (1970) noted its occurrence in near-
mouth and adjacent shallow shelf regions of the Newport River Estuary.
T. alternata is a sand flat dweller found in Bogue Sound and Beaufort
Inlet (Kirby-Smith and Gray, 1973).
YOLDIA Moller, 1842
Yoldia sapotilla (Gould)
Leda sapotilla Gould, 1841, from Abbott, 1974, American Seashells,
2nd ed., p. 417.
Range: Arctic Seas to North Carolina.
Habit: Yoldia sapotilla is an.infaunal deposit feeder similar to
Yoldia limatula (Say), which burrows rapidly into muddy substrates to a
depth of 1 to 2 centimeters, feeding only v;hen completely buried
(Abbott, 1974; Stanley, 1970).
Habitat: Yoldia sapotilla is commonly dredged off the New England
Coast in waters 4 to 45 fathoms deep (Abbott, 1974).
154
Gastropods
ACTEOCINA Gray, 1847
Acteocina canaliculata (Say)
Retusa canaliculata SAY, 1826, Journal of the Academy of Natural
Sciences Philadelphia, v. 5, 1st ser., p. 211.
Range: Nova Scotia to Florida and Texas; West Indies and Surinam.
Habit: Acteocina canaliculata is a tiny epifaunal carnivore
tolerant of euryhaline conditions (Andrews, 1977). This species feeds
on worms, mollusks and other sand-dwelling invertebrates (Rehder,
1981).
Habitat: Acteocina canaliculata inhabits the sandy substrates of
estuary inlets, bays, sounds and shallow shelf environments found along
the Texas Gulf Coast and east Mississippi Delta region (Andrews, 1977;
Parker, 1956). Bird (1970) noted this species living in medium to very
fine-grained sands and muds in the Newport River Estuary, N.C. and in
adjacent shallow shelf areas. A_^ canaliculata is abundant on mud flats
near mouths of rivers or large bays (Rehder, 1981).
Comments: A. canaliculata is present in every sample.
ANACHIS H. Sc A. Adams, 1853
Anachis avara (Say)
Columbella avara (Say), 1322, from Abbott, 1974, American Seashells,
2nd ed., p. 195.
Range: Massachusetts Bay to east Florida and Texas; Brazil.
Habit: Anachis avara is an epifaunal carnivore tolerant of
155
euryhaline conditions (Andrews, 1977).
Habitat: ^ avara is typically found on grassy sand flats in
sounds, inlet and shallow shelf areas (Porter and Tyler, 1981). This
species is wide ranging and is commonly seen on mud flats, pilings,
jetties and seawalls in the Newport River Estuary, Bogue Sound and
Beaufort Inlet. It has also been collected from trawlers in Onslow Bay
(Kirby-Smith and Gray, 1973).
BUSYCON Roding, 1798
Busycon caricum (Graelin)
Busycon caricum (Gmelin), 1791, from Emerson and Jacobson, 1975, The
American Museum of Natural History Guide to Shells, p. 143-144,
pi. XXIII, 3.
Range: South shore of Cape Cod to Cape Canaveral, Florida.
Habit: Busycon caricum is similar to ^ canaliculatum (Linne),
which is an epifaunal carnivore tolerant of stenohaline conditions
(Andrews, 1977). ^ caricum is a major predator of bivalves such as
Mercenaria, Ostrea and Crassostrea (Porter and Tyler, 1931; . Abbott,
1974).
Habitat: Busycon caricum is commonly found within sounds, inlets
and shallow offshore waters along the North Carolina Coast (Porter and
Tyler, 1981). Rehder (1981) noted this species on sand in waters 3 to
12 feet deep. He often found them cast up on beaches after storms and
buried in sand flats exposed by low tides. B^ caricum inhabits sand
flats in Newport River Estuary, Bogue Sound and Beaufort Inlet and v/as
156
also identifioú in Onslov; Bay (Kirby-Smith and Gray, 1973).
BRACHYCYTHARA Woodring, 1928
Brachycythara galae dominia Olsson, Harbison, Fargo and Pillsbry
Brachycythara galae dominia OLSSON, HARBISON, FARGO and PILLSBRY, 1953,
Pliocene mollusca of southern Florida: Academy of the Natural
Sciences Philadelphia, Monographs, no. 8, p. 339, pi. 20, fig.
6.
In the past, members of the genus Brachycythara have been assigned
to the genus Mangelia Risso, 1826, which is a predator living along the
Atlantic Coast in shallow waters (Abbott, 1974).
CREPIDULA Lamarck, 1799
Crepidula fornicata (Linne)
Crepidula fornicata (Linne), 1758, Systema Naturae per régna tria
naturae. Vol 1, Regnum animale, 10th ed, Stockholm, p. 1257.
Range: Canada to Florida and Texas; Yucatan; introduced to
California and England.
Habit: Crepidula fornicata is a sedentary epifaunal suspension
feeder tolerant of euryhaline conditions (Andrev/s, 1977). This species
clings to a hard surface, usually rocks and shells (especially dead
Oliva shells), and individuals are often found piled on top of one
another (Andrews, 1977).
Habitat: C. fornicata is found in estuaries, bays, sounds, inlets
and waters of the shallow shelf along Texas Gulf and North Carolina
Coasts and in the east Mississippi Delta region (Andrews, 1977; Bird,
157
1970; Parker, 1956). This species inhabits intertidal mud flats and
eel grass beds within Bogue Sound and Beaufort Inlet (Kirby-Sraith and
Gray, 1973).
Crepidula plana Say
Crepidula plana SAY, 1822, An account of some of the marine shells of
the United States: Journal of the Academy of Natural Sciences
Philadelphia, v. 2, 1st ser., p. 226.
Range: Bermuda; Canada to Florida, Gulf States, Texas; Gulf of
Mexico to Quintana Roo; rare in the West Indies; Surinam; Brazil.
Habit: C_^ plana is a sedentary epifaunal suspension feeder
tolerant of euryhaline conditions (Andrews, 1977). Unlike
fornicata, this species is not as particular in its selection of a site
of attachment, and as a result the shape of the shell can vary
(Andrews, 1977). C. plana is more flattened than C. fornicata and does
not stack with the same frequency (Abbott, 1974).
Habitat: Crepidula plana is found in estuaries, bays, sounds,
inlets and waters of the shallow shelf along the Texas Gulf and North
Carolina Coasts and in the east Mississippi Delta region (Andrews,
1977; Bird, 1970; Parker, 1956). It inhabits the intertidal mud and
sand flats within Bogue Sound and Beaufort Inlet and has been dredged
from Onslow Bay (Kirby-Smith and Gray, 1973).
DIODORA Gray, 1821
Piadora cayenensis Lamarck
Piadora cayenensis LAMARCK, 1822, Histoire Naturelle des animaux sans
158
vertebres, Paris, v. 6, p. 12.
Range: Maryland to southern half of Florida, Texas; Bermuda; Gulf
of Mexico to Quintana Roo.
Habit: Piadora cayenensis is a semi-attached epifaunal
grazer/scraper tolerant of stenohaline conditions. This species is
normally found on hard surfaces and grasses, scraping and digesting
surface accumulations of algae (Andrews, 1977).
Habitat: D. cayenensis inhabits intertidal to moderately deep
waters found in estuary inlets and shallow shelf environments along the
Texas Gulf and North Carolina Coasts (Andrews, 1977; Porter and Tyler,
1931).
Comments: ^ cayenensis is present only in sample 1, Locality 3
and sample 3, Hole 68-80.
EPITONIUId Roding, 1798
Epitonium angulatum Say
Epitonium angulatum SAY, 1831, American Conchology, New Harmony,
Indiana, School Press, v. 3, pi. 27.
Range: Long Island to Florida, Texas; Bermuda; Brazil.
Habit: Epitonium angulatum is an epifaunal carnivore tolerant of
stenohaline conditions (Andrews, 1977). It feeds upon sea anemones and
corals. Costae of this species are usually in alignment v\iith those on
the whorl above, fused at their points of contact and angulated at the
shoulder or joint of fusion.
Habitat: E. angulatum inhabits sandy substrates in estuary
inlets and shallow shelf areas along the Texas Gulf Coast (Andrews,
159
1977). Bird (1970) noted this species living in fine to very fine
sands associated with the raidreach and near-mouth regions of the
Newport River Estuary and in sound and shallow shelf environments
adjacent to the estuary. ^ angulatum has also been dredged from Bogue
Sound (Kirby-Smith and Gray, 1973).
Epitonium rupicola Kurtz
Epitonium rupicola KURTZ, 1860, Catalogue of recent marine shells found
on the coasts of North and South Carolina, Portland, Maine, p. 7.
Range: Massachusetts to Florida and west to Texas.
Habit: Epitonium rupicola is an epifaunal carnivore tolerant of
stenohaline conditions (Andrev/s, 1977). ^ rupicola has more costae
per whorl (12 to 18) than E. angulatum (9 to 10).
Habitat: ^ rupicola inhabits sandy substrates within estuary
inlets and shallow shelf areas along the Texas Gulf Coast and is often
found with other species of Epitonium (Andrev;s, 1977). This species
commonly occurs off the Atlantic Coast in waters up to 20 fathoms deep
(Abbott, 1974).
MITRELLA Risso, 1826
Mitrella gardnerae escarinata Olsson, Harbison, Fargo and Pillsbry
Mitrella gardnerae escarinata OLSSON, HARBISON, FARGO and PILLSBRY,
1953, Pliocene mollusca of southern Florida: Academy of the Natural
Sciences Philadelphia, Monographs, no. 8, p. 236, pi. 38, fig. 3.
Range: Probably similar to Mitrella lunata (Say): Massachusetts to
Florida, Texas; Bermuda; Carmen and Campeche, Mexico; Gulf of Campeche;
160
Yucatan; West Indies; Surinam; north and northeast Brazil.
Habit: Mitrella ^ardnerae escarinata is similar to lunata,
which is an epifaunal herbivore/carnivore tolerant of euryhaline
conditions. M. lunata feeds upon algae (Andrews, 1977).
Habitat: Mitrella lunata is found on high-salinity shell reefs
and grass flats lying just below the low tide mark in estuaries, sounds
and inlets along the Texas Gulf Coast (Andrews, 1977). Bird (1970)
noted lunata in midreach and near-mouth regions of the Newport River
Estuary.
NASSARIUS Dumeril, 1806
Nassarius acutus Say
Nassarius acutus SAY, 1322, An account of some of the marine shells of
the United States: Journal of the Academy of Natural Sciences
Philadelphia, v. 2, 1st ser., p. 234.
Range: Western coast of Florida to Texas.
Habit: Nassarius acutus is a semi-infaunal scavenger/carnivore
tolerant of stenohaline conditions. It can bury into the substrate for
a period of time to feed and forage. acutus is attracted by light
and the scent of decaying flesh and feeds upon other mollusks, mollusk
egg capsules and organic debris (Andrev/s, 1977). It is characterized
by well-developed, coarsely beaded ribs v/hich are stronger and more
pointed than the ribs of trivattatus or vibex.
Habitat: acutus inhabits sandy substrates within open lagoon,
inlet and shallow shore environments along the Texas Gulf Coast
161
(Andrev/s, 1977). This species commonly occurs throughout delta front,
lower and upper sound, inlet and shallow shelf areas of the east
Mississippi Delta region (Parker, 1956). Parker also states that
acutus is often found in association with Mulinia lateralis.
Nassarius trivattatus Say
Nassarius trivattatus SAY, 1822, from Abbott, 1974, American Seashells,
2nd ed., 224.
Range: Newfoundland to northeastern Florida.
Habit: Nassarius trivattatus is a semi-infaunal
scavenger/carnivore similar in life habit and habitat to other species
of Nassarius. N. trivattatus is similar in appearance to acutus,
but is not so strongly ornamented.
Habitat: trivattatus inhabits shallow shelf and beach areas
along the Atlantic Coast in waters up to 45 fathoms deep and is common
to Massachusetts coastal environments (Abbott, 1974). This species is
often found on intertidal sand flats (Rehder, 1981).
Nassarius vibex Say
Nassarius vibex SAY, 1322, An account of some of the marine shells of
the United States: Journal of the Academy of Natural Sciences
Philadelphia, v. 2, 1st ser., p. 234.
Range: Cape Cod to Florida, Gulf States; Costa Rica; West Indies;
Brazil.
Habit: M. vibex is a semi-infaunal scavenger/carnivore tolerant of
euryhaline conditions (Andrews, 1977). N. vibex has poorly developed,
coarsely-beaded ribs and, unlike N. acutus or N. trivattatus, exhibits
162
an enlarged parietal shield which overlaps onto the surface of the last
whorl.
îiabitat: ^ vibex commonly inhabits mud and sand flats found in
bays, sounds and inlet areas along the Texas Gulf Coast (Andrews,
1977). Bird (1970) found this species living in fine sands and muds
Vifithin the midreaches of the Newport River Estuary and Parker (1956)
noted its occurrence in the upper sound areas of the east Mississippi
Delta.
ODOSTOMIA Fleming, 1817
Odostomia impressa Say
Odostomia impressa SAY, 1322, An account of some of the marine shells
of the United States: Journal of the Academy of Natural Sciences
Philadelphia, v. 2, 1st ser., p. 244.
Range: Massachusetts Bay to Gulf of Mexico; Gulf of Campeche.
Habit: Odostomia impressa is an epifaunal ectoparisite tolerant of
euryhaline conditions. This species generally feeds upon Crassostrea
virginica, but will also feed on Diastoma, Crepidula, polychaete worms
and oyster drills (Andre\>?s, 1977).
Habitat: 0. impressa inhabits oyster reefs found in estuarine and
shallow shelf environments along the Texas Gulf Coast (Andrev\is, 1977).
Bird (1970) identified it in medium sands and muds in the Newport River
Estuary and in near-mouth and shallow shelf areas adjacent to the
estuary.
Comments: Odostomia impressa is synonymous with Boonea impressa.
163
OLIVA Bruguière, 1789
Oliva sayana Ravenel
Oliva sayana RAVENEL, 1834, Catalogue of recent shells, p. 19.
Range: North Carolina to Florida, Gulf States; 'Nest Indies;
Brazil.
Habit: Oliva sayana is an infaunal carnivore/scavenger tolerant of
stenohaline conditions. This species is a nocturnal predator which
plows just under the surface of sandy substrates in search of prey
(Andrews, 1977).
Habitat: 0^ sayana inhabits inlets and offshore areas along the
Texas Gulf and North Carolina coasts (Andrews, 1977; Porter and Tyler,
1931). Tills gastropod is a sand flat dv/eller and is often found among
trawl debris collected in Onslow Bay, N.C.
OLIVELLA Swainson, 1813
Olivella mutica Say
Olivella mutica SAY, 1822, from Abbott, 1974, American Seashells, 2nd
ed., p. 234.
Range: North Carolina to Bahamas.
Habit: Olivella mutica is an infaunal carnivore tolerant of
stenohaline conditions (Andrews, 1977). This species burrows into
surfaces of sandy substrates in search of prey (Bird, 1970).
Habitat: 0_^ mutica inhabits medium to very fine sands in the
Newport River Estuary and near-mouth and shallow shelf areas adjacent
to the estuary (Bird, 1970). Porter and Tyler (1901) note the
164
occurrence of this species in sounds and inlets along the coast of
North Carolina.
POLINICES Montfort, 1810
Polinices duplicatus Say
Polinices duplicatus SAY, 1822, Journal of the Academy of Natural
Sciences Philadelphia, v.2, 1st ser., p. 247.
Range: Cape Cod to Florida and Gulf States.
Habit: Polinices duplicatus is an infaunal carnivore tolerant of
stenohaline conditions (Andrews, 1977). This species plows through the
sand in search of other mollusks. Once finding its prey, P. duplicatus
wraps its foot around the victim and initiates the slow process of
drilling a neat, round hole through the exoskeleton into the mantle
cavity. After penetrating the mantle, the predator inserts its
proboscis and rasps out the soft parts with its radula. ^ duplicatus
will not feed unless buried (Andrews, 1977).
Habitat: ^ duplicatus occurs in sandy substrates in estuary
inlets and shallow shelf areas along the Texas Gulf Coast (Andrews,
1977). It commonly inhabits the sandy shore and shallow shelf regions
of the North Carolina Coast (Porter and Tyler, 1931).
Comments: duplicatus is present in every sample except sample
1, Locality 3 and sample 3, Mole 68-30. Because it is impossible to
distinguish between the juvenile members of ^ duplicatus and tiny
Natica pusilla Say, many individuals identified as ^ duplicatus in
this study might instead represent Natica pusilla.
165
PYRGOCYTHARA Woodring, 1928
Pyrgocythara plicosa (C.B. Adams, 1850)
Mangelia plicosa C.B. ADAMS, 1850, Contributions to Conchology, v. 4,
p. 54.
Range: Cape Cod to western Florida, Texas.
Habit: Pyrgocythara plicosa is an epifaunal carnivore tolerant of
euryhaline conditions (Andrews, 1977).
Habitat: Pyrgocythara plicosa commonly inhabits the grassy and
muddy bottoms of shallov/, hypersaline lagoons along the Texas Gulf
Coast. It is often found in association with oyster beds (Andrews,
1977). Bird (1970) noted this carnivore in fine to very fine sands in
the Newport River Estuary and in shallow shelf areas adjacent to the
estuary.
Comments: ^ plicosa is present only in sample 1, Locality 3 and
sample 3, Hole 63-30.
SEILA A. Adams, 1861
Seila adamsi H.C. Lea
Seila adamsi H.C. LEA, 1845, Transactions of the American Philosophical
Society, V. 2, no. 9, p. 42.
Range: Massachusetts to Florida, Texas; Bermuda; Carmen and Campeche,
Mexico; Gulf of Campeche, Campeche Bank, Yucatan; Costa Rica; West
Indies; Brazil.
Habit: Seila adamsi is an epifaunal herbivore tolerant of
euryhaline conditions. This species feeds upon algae under broken
166
shells (Andrev;s, 1977).
Habitat: ^ adamsi inhabits grass flats and muds and sands in
hypersaline bays and inlets along the Texas Gulf Coast (Andrews, 1977).
Bird (1970) found this gastropod in medium to very fine sands in the
midreaches of the Newport River Estuary and in near-mouth and shallov;
shelf regions adjacent to the estuary.
Comments: Sj_ adamsi is present only in sample 1, Locality 3 and
sample 3, Hole 68-80.
TEIMOSTOHA H. & A. Adams, 1854
Teinostoma cryptospira Verrill
Rotella cryptospira (Verrill), 1844, from Abbott, 1974, American
Seashells, 2nd ed., 89.
Range: North Carolina to West Indies.
Habit: Tiny Teinostoma cryptospira is similar to ^ biscaynensis
(Pilsbry and McGinty), which is a deposit feeder tolerant of euryhaline
conditions (Andrews, 1977).
Habitat: T. cryptospira is found off the coast in waters 30 to 150
fathoms deep (Abbott, 1974). T. biscaynensis inhabits sands and rubble
in inlet and shoreface areas along the Texas Gulf Coast (Andrews,
1977).
TEREBRA Bruguiere, 1792
Terebra dislocata Say
Terebra dislocata SAY, 1822, An account of some of the marine shells of
the United States: Journal of the Academy of Natural Sciences
167
Philadelphia, v, 2, 1st ser., p. 235.
Range: Maryland to Florida, Texas; West Indies; Brazil.
Habit: Terebra dislocaba is an infaunal carnivore tolerant of
stenohaline conditions. It's venomous radula is particularly effective
for predation (Andrews, 1977).
Habitat: T. dislocaba inhabits sandy substrates in estuary inlets
and shallow shelf areas along the Texas Gulf Coast and is a common sand
flat dv/eller in the coastal waters of North Carolina (Andrews, 1977;
Porter and Tyler, 1981).
TUR30NILLA Risso, 1826
Turbonilla interrupta Totten
Turbonilla interrupta TOTTEN, 1835, American Journal of Science, v. 1,
(28), p. 352.
Range: Maine to West Indies; Texas; Carmen and Campeche, Mexico;
Gulf of Campeche; Yucatan; Brazil.
Habit: Turbonilla interrupta is an epifaunal ectoparasite tolerant
of euryhaline conditions. This gastropod lives attached to the tissue
of its host (Andrews, 1977).
Habitat: interrupta is found in inlets and along the shores of
the Texas Gulf Coast and is an inhabitant of the Newport River Estuary
and near-mouth and shallow shelf areas adjacent to the estuary
(Andrews, 1977; Bird, 1970).
ZEBINA H. n0£ A. Adams
168
Zebina browniana (Orbigny)
Rissoina brovmiana ORBIGNY, 1842, Mollusques: R. de la Sagra,
Histoire physique, politique, et naturelle de I'lle de Cuba,
V. 2, p. 28.
Range: Bermuda; North Carolina to Gulf of Mexico, Texas to
Quintana Roo; Costa Rica; V/est Indies.
Habit: Zebina browniana is a tiny epifaunal deposit feeder
tolerant of euryhaline conditions (Andrews, 1977).
Habitat: browniana is comraoly found beyond the littoral zone
under shells and debris on grassy bottoms associated with estuary
inlets and shallow shelf environments along the Texas Gulf Coast
(Andrews, 1977).
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APPENDIX A
COMPLETE FAUNAL LIST
SPECIES LIST
Mollusks
Bivalves Gastropods
Abra aequalis Acteocina canaliculata
Anadara ovalis Anachis avara
Anadara transversa Brachycythara galae dominia
Anomia simplex Busycon carica
Argopecten solarioides Busycon candelabrum
Corbula contracta Caecum pulchellum
Corbula swiftiana Crepidula fornicaba
Crassostrea virginica Crepidula plana
Cyrtopleura costata Piadora cayenensis
Dinocardium robustum Epitonium angulatum
Diplodonta punctata Epitonium humphreysi
Pivaricella quadrilsulcata Epitonium rupicola
Dosinia discus Eupleura caudata
Ensis directus Mitrella gardnerae escarinata
Macrocallista nimbosa Nassarius acutus
Mercenaria mercenaria Nassarius trivattatus
Mulinia lateralis Nassarius vibex
Mysella planulata Odostomia impressa
Mya arenaria Oliva littorata
Noetia ponderosa Oliva sayana
Nucula próxima Oliva sp.
Nuculana acuta Olivella mutica
Pandora trilineata Polinices duplicatas
Panopea sp. Pyrgocythara plicosa
Parvilucina multilineata Seila adamsi
Raeta plicatella Sinum perspectivum
Tagelus plebeius Teinostoma cryptospira
Tellina aequistriata Terebra dislocaba
Tellina agilis Turbonilla interrupta
Tellina alternata Zebina browniana
Yoldia sapotilla
Foraminifera
Ammonia beccarii forma sobrina
Ammonia beccarii forma tepida
Ammonia beccarii sp.
Bolivina paula
Bolivina sp.
Buccella frigida
Buccella hannai
Buccella inusitata
Buliminella elegantissima
Elphidium compressulum
Elphidium excavatum forma alba
Elphidium excavatum forma clavata
Elphidium excavatum forma lidoensis
Elphidium excavatum forma selseyensis
Elphidium galvesonense forma mexicanum
Elphidium gunteri forma typicum
Elphidium limatulum
Elphidium poeyanum
Epinoides tumldulus
Epistominella exigua
Epistominella sp.
Florilus sp.
Fursenkoina pontoni
Globocassidulina crassa
Guttulina pulchella
Guttulina sp.
Hanzawaia concéntrica
Nonion tidburyensis
Nonion sp.
Nonionella miocenica
Parafissurina bidens
Quinqueloculina jugosa
Quinqueloculina seminula
Rosalina floridana
Rosalina floridensis
Rosalina globularia
Crustaceans
Balanus sp.
182
APPENDIX B
RELATIVE ABUNDANCES OF IDENTIFIED FORAMINIFERA
(In Percent)
HDL HOLE O ? C C C O :i T r f-
r- r
c r
r r* r~ II
r: n r L’n n n n nn r r. r n O n
1-^
II n II
E r ? f- n I 1 n n fl f ) f 1 r-'II IIm m m
•.^í KJ *0 M - - « - II II
O i-J FJ FJ •>« M »O' II II
CD œ L^cncncncDcncncn O' O' NICO II II
I 3 3 2 3 œ3 3 LU3 in tn tn rn rn (0 rn CO rn II1 1 1 3 7 3 3 3 3 3 3 II
m rr m T T 1' •n T' ?n II
r r" r- r" II
“ - “ ’.J ‘J Í» II- rj - II - - - C4 FJ “ A ?JJ FJ -
f r.iF. VMiJi.in II.
fj J» ^ ^J — N- II UITCCMF-I î ÇOFjf-'1 rjM
CI •c r: O' LJ 'si II
0-0- r CD ; cn >0 '.-j ?sj < ?: II II
II U <1 «c i-j c- cc O »J C - œ II
II ' I NO I OF .-, r ijM r rn.iL'I-, I'
: II II f.iF-1; CMf I I tefidm
11 i^i U C' O' >c <^4 en en en U
4 II II
II FO O' <1 - œ Nj O' O' — O' II
II F r 1 r ijM I riEL L « £:: 1 OMm II
II II ONIm DFCCwFII -.F'.
II II
II II
II II
II F»"-! rriMirjcL l • II
II I'.'INm T'hHLm
c I'
II
I^J II
II «"L o»;-1L.u :? ' r II.
II l< l'.'irjM -r.
II II
It II
II
•'r-F N* o I Ni* f^ rirj 7 orj i II
II F:’ r i_L M rt-1 1 ;.M
c : to - O - C - II
II
C' Ui U >c Vj O' O' II
i. J Ni.ti JfiM i:C'^ II?
i II D IJ C >: r LL n umniím I- O O c c - II
II
II C4 • • 14 ‘JJ • • U Í.4 c II
II IT TUL 1 Nh PULC HEl L m II
C II : : II L- Il I CEL L M I rJU - I T mT Mc - O FO - tJ - O' II
II
1^. C' en >0 '?J IJ FJ II
II
II C’l.i r ri.iL I fJ*4 II FUI':: cellm z.r-.
II
II
II II
II II
II HMN.rMWM I H OOrJCF NTC I r.H : II RIJL I f1 I NELLh EL r dont 1 I Mm
11 Q. II
II II
II ? • LJ O C4 • O' 'JJ II
II II
It NONIi.lN .F'. : : II r l'iMF' C-E SCUL IJ HII c O O - II
II II
• •
11 1:4 >c O' 'g Nj O' C II
II
II NON I ori 1 1 DFii.li^ YErj : I i il r. E ; : T: M T M T1 IM L I nu E r J M Í
II II
II II
II LJ t4 II
II II
II rjorj I t.triELLH m i occu I Ci II E . EXCnUtiTIJM hLEîM
II II
II
II
il
II r mPmF I oO'.iC' I riM f' I DFN^ . J en en K) F.) F,1 LJ L4 M E EXi'h'.'FîTIJM CLh'.’‘'4Th
II Jl m If -s; ',4 m • 4 |f
II
II tj CD •sJ FJ NJ O' LJ FJ
II
II O' I I NO'.IF LOCUL I tin Jl.'i.-C' 'r.FI '.4 F.1 M F : ' C M 14 r IJ M E L “r. F V E N I. I •?.
•Ni 'Nj (4 Ih SJ m 47 M I-* 47
II
II CD CJl en FJ I-» N» CD CF tJ IJ
II
11 0" I rjouLL C'C'-iL I fiM CCn I rjULFi • F ch'-'E : ToriENi.E me:-: i • htjijm
II m • •nJ 4k FJ 47 •sJ Fl CF
II
II Ln LJ •F' 4» CD 4k 1^' IJ en
II
II iî'Ui.HLlNH rLOPIDHlJH > E CUNTC'T TVFICUM
II t M • O c“ Q
II
C' >.'J C/J '.4 II O c^ Ll <yi • \3'
II
il c n--.HL I rjrt FLO^' I riErrj I s • FJ Fl M= FJ FJ FJ E U I M M T IJ I. U M
t.7 • Vj m -n (*• 4k fp
UJ C en 0- O' FJ CD
UN 1 DF riT l K I Ml :L L-•
esT
(^uaojaj uj)
s^ísmiow aaidiiNaai ao saoNvamav aMivian
0 xiQNaddv
T T T I r r r r r r* r r
n fi r 3 O r n n a n p D
1“ r r- n n n r 1 n n n
m m m m
v< I j tj to N- •*»
i> fh r> if|
LU tr m in ifi ir in in in rn
1 "K ?7 T ; T ?Í
C£ CD CP Tl T' T! Tl *n
— I 2 2r r 1- ?7 2 rr r- •* X II? • : ? n 2 n 2 c 2 p C‘ ii
' ;
t 1 > • p r 2,? r 2 ; ' nJ fo ;irr r- m m II
Vi ro rj rj to* to- to* to* II
rr vj fv r Ch r* IVrp CP rnvf p CT Mill I fj ' tl.1 1 '•! I • •
•-* »0 ir. CP cr cr». f n- 1 ^ f T cn cn cn cn cn fD in rr ll1 1 2 1 3 T T II
r-1
r> T Tl Tl T* T- •0 CD œ T T».fr 1^. m fT T*- — T II
- •- ñ 1“ P P P r- '*? 11
? M K l_ L- H , ,rjn^ H 1 M Vi Tj *- U rj - Xk 1.^ rj - li
X> t j II•
II
• • •
» • • • riw ^MC- 1 2M ,
r. Hi;:l 1 1 1
2 2 II
'
Vi “? • • rs • ll• • CP NJ to* • ro to* ro W ro II
Xk w • » LH » IIto* II
Xk rn • .i to* r.j f.l
riM'i i.nC KJ1 1 I f. T r.)c- I 2- II'.'H T 1
M mTIJT.M w -2 r-. IICP SJ to* FJ cn w A L" rn O' CK It
CD KJ 2' O' Xk to* rj to* NJ ll• • • • II
to* • • to* •
• riMT •:.Me .Tl'
• •
iLi-v uinr:-: II
03 2- 2' ItO' • • 2- » to* t •• • kto• NJ Ln to* II
vj O' to* A II
II
•*.
ri'urriM Torinr.*:? it.m tl
V' • II
• • ro II
CP • II
* • • II
• 2' 2' to* r-J • »M' M'. IILM pr'-i'i: 2 1^': I 7-Mm 2 Q II
?2/ *-• II»
• • W KJ ro A • • KJ to* ro C'i rj II
Nj II
« • • • tl
2
fit.ic Lfl
» • • •
ULuriH Mijl.l Tm <71' 2’ 2 II
fO « IIC' A ro ro • • ro * to* to* • II
Nj 0 II
• * • • ll
1 if ir 1 OM ] H 1 MP-I-T *.'.M tl
• ll
ro II
• II
M
rs r-. .to".
1 ll r un 1.11 I mc-htH
•2 2 IIDD Xk <1 M A O' f J Xk rj II
»0 f ’ II
• • • • • II nr
* ,*• r.iMn• I rj 1 H• ? t
Ml I'.i'i '-.t-r. MfiM
• 2 •“ II
• rj to* • • • to* • ll
•
to* II
II IrM-.Vi.-iirj
2- CmCJi-• *• • *
'•L 1 Q II
II II
• hJ • KJ • • • • 1'
•
-* 11 II
II
ML 1 ' T.l. L M riMT 1 Cl.
4» N) CD Ln ^ >4 O W A CD
m, (.i II I'
II II r i-iMPt.iL M 1 r 1 1 pfiM
^
II l-J C M t'J II
II r-Ml.tiOf^M TfcILiTJfHTH II*
O O O I' U 10 CD O ^ CD (/J M II
II
rj • f-J f'J II C'-'M-:. '.n-LT c rp ,JO' I• C r-G III
r I L UC 1 rJH mult I L I flEl^T ?: II
N- r j C--J J* Oi
o *0 Í» - c.n o ro
^1 T' I ni IL roc-rj j i :mT ^
II Fi'lL I ri 1 CE’:- DÜÍ-L ICmT IJ^
*- ij II
II
0 UJ Vi cn Nj II II' • • • ' •
II • '?
ii T Hm» M F'LI'.:m:.h
II ? • KJ CD • • KJ • to* II
|i
• • » II
• • • • •
II t'HE Tm f L I C m Î f.l I O'!? I.. 1!
II II• ' • • * » • • •
II rj tj II
II
II II
II ?Î.E 1 Lh hTimM I ll
II 0 It•
II II
II II• •
II ll• • •
ll ThGELEH. PlEEîEIUC 2 p. c 2 II
II II» •
II r-;
to* Xk to* to* ro II
II II
II 11
It T E. 1 nij ^ T OMh r pyr TO i.p I 2 I'
Xk tl
Ii
1'
rr L L I riM HEOI.I J . TP I H th 1!
II
11
tl
• • II
*
TELL I fin 2' 2
« •
MO 1L. 1 p c 2 Ô' 2 2' 11
to - ho r j 10 - IIKJ • to* 0* M k»» Ni C'i II
yi C' Vi C' Vi ^ Oj 11
• C KJ 2 2 to*T E L L r rj M M L 1 E p rj T KJH 2H ?2. II
II
• O' (.n IJ • 'sJ O' 2,' CD cn ID 11
It
1'
TE Ü I CLOUhT h II
C C’ O C C‘ c II
C^ * l- J cn ^ ly
II f- r-1 1 oti 1 i.iM 11.1 M
TIiCTiOtil LLm 1 NTEPPi.'PTf
I'
ll
11 M‘ K i'L Un»; I M Ml c-r t 1 I
'M- N' iijrj I fii 11 i L'l uhl 'i.
ll M 1 T i.-i I M Omi rifiC‘'-Mr E mp I fiM 1
:iLi 11 H r 11
Ç8T zrp! 1 tJM DK outi j MfiM
APPENDIX D
STATISTICAL COUNTS OF THE SAND FRACTION
Sand Fraction Mineralolgy
(out of 100 grains for each sample)
Locality 1, sample 1
Grain size Quartz Shell Material Phosphate Magnetite
coarse 1
medium 21
fine 55 1 1 1
very fine 15 3 2 1
Locality 1, sample 2
Grain size Quartz Shell Material Phosphate Magnetite
medium 10 1
fine 54 1 1
very fine 23 7 2 1
Locality 1, sample 3
Grain size Quartz Shell Material Phosphate Magnetite
medium 3
fine 53
very fine 32 8 2 2
Locality 1, sample 4
Grain size Quartz Shell Material Phosphate
fine 36
very fine 58 4 2
Locality 2, sample 1
Grain size Quartz Shell Material Phosphate Magnetite
coarse 1
medium 7
fine 31
very fine 54 4 2 1
Locality 2, sample 2
Grain size Quartz Shell Material Phosphate Magnetite
medium 2
fine 36 2
188
very fine 54 4 1 1
Locality 2, sample 3
Grain size Quartz Shell Material Phosphate Glauconite
medium 2
fine 33
very fine 60 1 3 1
Hole 68-80, sample 1
Grain size Quartz Shell Material Phos. Magn. Mica
fine 43 4
very fine 45 4 1 2 1
Hole 68-80, sample 2
Grain size Quartz Shell Material Phosphate
coarse 1
fine 29 4
very fine 56 9 1
Hole 55-80, sample 1
Grain size Quartz Shell Material Phos, Magn. Glauc.
medium 1
fine 32 4 1
very fine 48 9 2 2 1
Locality 3, sample 1
Grain size Quartz Shell Material Phosphate Glauconite
coarse 1
medium 1
fine 18 10
very fine 36 35 1 1