Stratigraphy, structure and phosphate deposits of the Pungo River formation of North Carolina

              North Carolina
'-
STRA
PHOSPHATE DEPOSITS OF THE
PUNGO RIVER FORMATION
OF NORTH CAROLINA
James A. Miller
BULLETIN 87
1982
NORTH CAROLINA DEPARTMENT OF NATURAL RESOURCES
AND COMMUNITY DEVELOPMENT
1
DIVISION OF LAND RESOURCES - GEOLOGICAL SURVEY SECTION
Digitized by the Internet Archive
in 2013
http://archive.org/details/stratigraphystru1982mill
STRATIGRAPHY, STRUCTURE AND
PHOSPHATE DEPOSITS OF THE
PUNGO RIVER FORMATION OF
NORTH CAROLINA
by
James A. Miller
Abstract
CONTENTS
Page
1
Introduction 1
Purpose and scope 1
Method of study 1
Previous work 3
Acknowledgments 3
Stratigraphy 4
Regional setting 4
Pungo River Formation 5
Definition 5
Lithology 7
Carbonate rocks 8
Argillaceous rocks 8
Arenaceous rocks 8
Facies distribution 9
Phosphate 10
Microfauna 11
Structure 12
Marine phosphorites 15
Lithologic associations 15
Chemical environment 16
Theories of origin 16
Origin of the Pungo River phosphorite 17
Conclusions 19
References 20
Explanatory note 1 — Base map numbering system 23
Appendix A— Stratigraphic and lithologic data for wells used on maps and cross sections 23
LIST OF ILLUSTRATIONS
Page
Figure 1. Map showing extent of the Pungo River Formation in eastern North Carolina 2
2. Correlation chart of the Tertiary Formations of North Carolina, Virginia, and Maryland 4
3. Type core of the Pungo River Formation, showing adjusted top of unit 6
4. Sedimentary structures in selected cores from the Pungo River Formation in Beaufort County,
North Carolina 7
5. Percentage triangle showing distribution of data points in a three-component system and
percentage breakdown used 9
6. Location of structural features, extent of high concentrations of phosphate, and location of lines
of section shown on figure 7 13
7. Diagrammatic cross sections showing structural conditions in the basin of phosphate deposition 14
8. Idealized cross section of a phosphorite basin, showing downdropping on the downbasin side
of a hinge line 18
9. Idealized cross section of a phosphorite basin, showing downdropping on the upbasin side
of a hinge line 18
10. Cross section of the Phosphoria Formation showing relation of phosphorite and hinge line 19
Table 1. Generalized stratigraphic column of the Tertiary rocks of North Carolina 5
2. Percentage categories used on lithof acies map and example of each 10
PLATES
(all plates in pocket)
1
.
Base map showing location of data points and lines of cross section.
2. Map showing structure contours on the base of the Pungo River Formation in North Carolina.
3. Map showing structure contours on the top of the Pungo River Formation in North Carolina.
4. Isopach and lithofacies map of the Pungo River Formation in North Carolina.
5-10. Geologic cross sections along line:
5. A-A' from well BER-P-6, Bertie County, to well CUR-OT-1, Currituck County.
6. B-B' from well BEA-OT-6, Beaufort County, to well DA-OT-3, Dare County.
7. C-C from well BEA-T-18, Beaufort County, to well DA-OT-7, Dare County.
8. D-D' from well BEA-C-40, Beaufort County, to well HY-T-15, Hyde County.
9. E-E' from well CR-T-20, Craven County, to well CAR-OT-7, Carteret County.
10. F-F' from well WA5-OT-10, Washington County, to well CAR-OT-6, Carteret County.
in
STRATIGRAPHY, STRUCTURE AND PHOSPHATE DEPOSITS OF THE
PUNGO RIVER FORMATION OF NORTH CAROLINA
By
James A. Miller1
ABSTRACT
Borehole data from subsurface early and middle Mio-cene
rocks of North Carolina show that the phosphatic
sand, clay, and limestone comprising this part of the sec-tion
can all be assigned to the Pungo River Formation.
The definition of the top of the formation is revised in
the type core and the surrounding area to conform with
lithologic and paleontologic criteria used to define the
unit elsewhere.
Structural, isopach, and lithofacies maps of the for-mation
show that north-trending flexure zones (hinge
lines) and northeast-trending noses and troughs have
greatly affected sediment distribution and thickness in
the Pungo River. These structural features, particularly
the hinge lines, were a major influence in determining
where primary phosphate was formed and concentrated.
Foraminifera recovered from the formation are in part
time-diagnostic and in part facies-controlled, and they in-dicate
that most of the formation was deposited in a
slightly restricted, shallow shelf environment of normal
salinity. Abundant diatom remains indicate that Pungo
River seawater was rich in silicia and in nutrients,
thought to have been provided by upwelling deep ocean
waters.
The rock suite, which includes high concentrations of
phosphate, and the structural setting of the Pungo River
Formation are similar to those associated with numerous
other primary phosphorite occurrences. Deposition of
such phosphorites appears to be influenced primarily by
physical (structural) conditions on the sea floor, and sec-ondarily
by biologic activity and current distribution.
INTRODUCTION
Purpose and Scope
During the course of a regional study of the strat-igraphy,
structure, and permeability distribution of the
subsurface sediments of the Atlantic Coastal Plain from
North Carolina to Long Island, N.Y. (Brown, Miller, and
Swain, 1972), structural lineaments were delineated
which have a direct effect on the distribution, composi-tion,
and texture of coastal plain sediments. These linea-ments
are thought to represent either flexures in the
basement surface or deep-seated faults which die out up-ward.
They are expressed in the blanket of coastal plain
sediments as areas of thickening, thinning, or absence of
stratigraphic units. The trend of these features is north-south,
northeast-southwest,; and northwest-southeast.
'U.S. Geological Survey, Atlanta, Ga.
Maps made during the regional study indicated that
the occurrence of phosphatic sediments in rocks of early
and middle Miocene age was influenced by structural ele-ments.
Large scale, more detailed maps constructed
subsequently for the present study confirm and empha-size
this relation of phosphate to structure.
The early and middle Miocene rocks of North Carolina
offer a unique opportunity for the study of the strati-graphic
and structural associations of marine, pelletal,
sand-sized sedimentary phosphate (hereinafter referred to
as "primary" phosphate, to distinguish it from pebble-sized
or other reworked phosphate). Rarely are primary
phosphorite deposits found in such a relatively un-disturbed
state, from both an erosional and a deforma-tional
standpoint. Therefore, it is of interest to (1) de-scribe
these rocks in detail over an area large enough to
establish their position in the basin of deposition, (2)
show that Pungo River rock types and facies distribution
result from deposition in a normal marine, primary phos-phorite
basin, and (3) to compare primary phosphorite
desposits elsewhere, so that a common stratigraphic and
structural setting favorable for phosphorite deposition
can be identified.
Previous studies of the Pungo River Formation have
been confined mostly to Beaufort County, where the
phosphate contained in these strata attains maximum
concentration and thickness, and where it is nearest the
surface. This paper presents the results of a study of the
attitude and configuration, lithologic variations, and
structural relationships of the rocks of the entire early
and middle Miocene section, throughout their extent in
North Carolina as shown on figure 1. The heavy line on
the figure indicates the westward limit of the main body
of early and middle Miocene rocks. The isolated patches
in Beaufort, Jones, and Onslow Counties represent ero-sional
remnants or outliers.
Method of Study
Data used in the study were obtained from 241 bore-holes
of various kinds, whose locations are shown on
plate 1. Of these data points, 119 were used in the con-struction
of a lithofacies map. The only wells used for
lithofacies determinations were those for which either
core, or a combination of cuttings and geophysical logs,
was available. Appendix A (p. 23 ) lists the type of data
available at each control point, along with the thickness,
lithology, and altitude of the top and base of the Pungo
River Formation as determined at that point.
Detailed lithologic descriptions were made for cores
7tr 77° 76°
_J
33°
10 10 20 30 40
Miles
_-/"" ^V
36°
35'
34°
33<
78° 77° 76°
Figure 1. Extent of the Pungo River Formation (patterned) in eastern North Carolina.
and for cuttings recovered from water and test wells in the
study area, and lithologic breaks were adjusted, where
necessary, to match breaks on borehole geophysical logs of
the same wells. Distinctive log patterns were recognized
that are characteristic of Pungo River rocks, and these pat-terns
were used to define the boundaries of the unit in areas
where geophysical logs but no samples were available. The
mineralogy of the clays from the type core of the Pungo
River Formation was determined by X-ray diffraction
analysis.
Microfossil suites were obtained from cuttings and
from cores by floating washed and sieved samples in car-bon
tetrachloride. Certain foraminifera which have been
found to be stratigraphic markers for the Pungo River
Formation were used to augment the lithologic and geo-physical
boundaries selected.
Maps showing the top, base, thickness, and facies vari-ations
of the Pungo River Formation were prepared,
using the equal-spacing method for most of the contour-ing,
in order that the resulting maps might be as objective
as possible. Structure sections were constructed using
wells judged to best illustrate the lithologic variations and
the structural setting of the unit.
From an analysis of facies distribution and structure,
generalizations were made concerning the mode of origin
of the phosphate-rich strata within the unit. A literature
search showed that similar lithologic associations and
similar structural conditions exist in other primary phos-phate
deposits.
Previous Work
Brown (1958) first described and delineated phosphatic
sediments from the subsurface of Beaufort County, N.C.,
and correlated them with the middle Miocene Calvert
Formation of Maryland on the basis of their benthonic
foraminifera.
Kimrey (1964) proposed the name Pungo River Forma-tion
for the middle Miocene rocks of North Carolina and
selected the core from a hole in Beaufort County as the
type section, since the unit does not crop out. He fol-lowed
this work with a detailed paper (Kimrey, 1965)
which presented lithologic descriptions of cores and illus-trated
characteristic gamma-ray log patterns of the for-mation
in Beaufort County.
Gibson (1967) discussed the planktonic and benthonic
foraminifera of the Pungo River Formation in detail, and
concluded that most of the unit was deposited in 100 to
200 meters of water. This study was based on exposures
of the formation in a test pit at the Texas Gulf Sulphur
Company's Lee Creek mine, near Aurora in Beaufort
County.
Rooney and Kerr (1967) conducted chemical, X-ray,
and other tests to determine the phosphate and clay
mineralogy of the formation. Their study, which was also
confined to the Lee Creek mine, disclosed the presence of
clinoptilolite in the clay fraction of the phosphatic beds.
They believed this zeolite formed by alteration of vol-canic
detritus, and suggested that phosphate deposition
coincided with pyroclastic activity.
Cathcart (1968) presented a brief discussion of the
Pungo River Formation in a generalized paper on Atlan-tic
Coastal Plain phosphorites. He proposed a similar
origin for phosphates from Florida through North Caro-lina.
Scarborough and Riggs (1980) described the extent and
character of four informal units within the Pungo River
and thought the lower three were deposited during a
major transgression while the upper was laid down dur-ing
a regressive phase.
Riggs and others (1980) discussed cyclic patterns of
sedimentation in the Pungo River and suggested the
cycles were controlled by third-order global eustatic sea
level fluctuations. The formation has been traced off-shore
into Onslow Bay (Lewis and others, 1980) where it
shows several despositional sequences that may also
correspond to third-order sea level cycles (S. W. P.
Snyder and others, 1980).
Kartrosh and Snyder (1980) studied the benthonic
foraminifera of the Pungo River and concluded, as had
Gibson in 1967, that the unit was deposited in an inner to
middle shelf environment. S. W. Snyder and others
(1980) thought that faunal and sedimentary characteris-tics
of the formation showed the phosphate in its lower
part formed in situ, while that of the upper part was de-rived
from reworking.
Gibson (1980), in a regional study of Miocene paleo-environments,
thought that both the Calvert Formation
of Maryland and the phosphatic, diatomaceous Miocene
strata of North Carolina were deposited in part during
early Miocene time.
Miller (1980) compared the rock types and structural
setting of the Pungo River Formation to those of the
Hawthorn Formation in north Florida, and concluded
that structure on the Miocene basin floor was largely re-sponsible
for the deposition and concentration of primary
phosphate in both units.
Acknowledgments
This paper is based largely on a Ph.D. dissertation sub-mitted
to the University of North Carolina at Chapel Hill
in 1971. That study was done under the direction of
Walter H. Wheeler, whose guidance, encouragement, and
comments are deeply appreciated.
Appreciation is also expressed to P. M. Brown, for-merly
of the U.S. Geological Survey, who placed on open
file the cuttings, core, and geophysical logs used in com-piling
the report, and who gave generously of his time
and experience in discussing various aspects of the study;
to S. G. Conrad, State Geologist of North Carolina, for
making available certain cores and unpublished borehole
geophysical data for examination; to J. M. Hird of Texas
Gulf Sulphur Companv for permission to visit and sam-ple
the Lee Creek pit; to the late J. L. Weaver of Wayne
Thomas, Inc., Tampa, for information concerning the
phosphate deposits of the Mediterranean and Sechura.
Peru, areas, and for the benefit of his thinking on the
origin of sedimentary phosphate; and to J. O. Kimrey.
U.S. Geological Survey, and V. E. McKelvey, former di-rector
of the U.S. Geological Survey, for their critical re-view
of the manuscript.
STRATIGRAPHY
Regional Setting
Rocks of early and middle Miocene age extend from
North Carolina northward into Virginia and Maryland,
where they comprise the lower part of the Chesapeake
Group. In North Carolina, these rocks are represented by
the Pungo River Formation, which has been correlated
with the Calvert Formation of Maryland and Virginia by
Brown (1958) on the basis of benthonic foraminifera and
by Gibson (1967, 1980) on the basis of mollusks and
foraminifera. These correlations are here accepted as
valid, and the stratigraphic position of the unit is shown
on figure 2.
The Pungo River Formation unconformably overlies
rocks of Paleocene, Eocene (Sabine and Claiborne equiva-lents),
and Oligocene age. The approximate up-dip limits
of pre-Miocene units which underlie the Pungo River
Formation are shown on the structural map of the base of
the formation (plate 2). Pungo River rocks are almost
everywhere overlain by the Yorktown Formation of Plio-cene
age. Very locally, in parts of Hertford and Gates
Counties, the Eastover Formation of late Miocene age
overlies the Pungo River. The unconformity developed
on the top of the Pungo River is not as pronounced as
the unconformity at its base.
An abbreviated lithologic description of the Tertiary
rocks of North Carolina, arranged in stratigraphic order,
is given in table 1.
Closely spaced well control shows that basal Pungo
River sediments fill shallow channels developed in under-lying
formations at many places. Where the underlying
unit is a limestone, such as the Castle Hayne Formation
of Eocene age or the River Bend Formation of Oligocene
age, a gently undulating surface was developed before
Pungo River deposition occurred. On parts of this sur-face,
the permeable limestones have been partially or
completely replaced by phosphate, creating a dark-colored
"rind" that extends to a depth of 2 to 12 inches
below the top of the limestone. This hardened, dense,
phosphatized surface was referred to by Gibson (1967) as
the "welded zone." Such replacement of limestone by
phosphate is restricted to areas where phosphatic sands
immediately overlie limestone; in areas where clay is in
contact with the underlying limestone, no such phos-phate
enrichment has occurred, and the limestone is pre-
SERIES
MIOCENE
MARYLAND VIRGINIA
North
NORTH CAROLINA
South
Calvert
Formation
Plum Point Marl
Member
Pect 8n
Fairhaven Diatomaceous humphreysii
Earth Member ^
Pungo River Formation
Figure 2. Correlation chart of the Tertiary formations of North Carolina, Virginia, and Maryland. (Modified from
Ward and Black welder, 1980, and Gibson, 1967).
Personal communication, L. W. Ward, 1982.
-
01
J*:
co
>
-5
3
u 3
(J UJ
Formation Subsurface L i t h o 1 o g y
01
C
Vu
0»
io
York town
Blue-gray marl, shell hash, gray
calcareous clay. Minor, gray,
fine-grained sand, white, sandy
shell limestone. Trace amounts
of phosphate and glauconite.
01
O-Cl
V
a
-a
i
o>
s
o —
>o
U
3
X.
«J
B <
Eastover Fine-grained, well sorted,
greenish-blue shelly sand. Thin
and local in North Carolina.
Oi
c
01
2
Pungo
River
Brown phosphatic sand, gray to
green diatomaceous clay, gray
calcareous clay, gray to green
dolomitic limestone. Minor, gray,
shell limestone, white chalk,
dolomite.
Absent in North Carolina
01
c
u
a
Oi
-J
n
bo
Ih
3
>
Belgrade Gray to brown highly shelly
sands with clay lenses and
laminae prominent.
M
River
Bend
Cream, tan, gray, and white shell
limestone; algal in part. Massive,
well-indurated, commonly
recrystallized.
a.
a.
CO
u Absent in North Carolina
c
o
UJ
c
1
u
Castle
Hayne
White, light-gray, and cream
colored, massive shell limestone,
well indurated, usually
recrystallized, and sandy. Traces
of glauconite, pyrite and
phosphate. Dolomitized in part.
01
0*
15
n
Unnamed,
Subsurface
only
Dark-gray to greenish-gray
slightly glauconitic sand, clayey
sand and sandy clay. Minor dark-brown
dolomite.
01
c
o
c
-a
i
Beaufort
Dark-green to dark gray-green
highly glauconitic sand, clayey
sand, and sandy clay. Minor,
dark-brown dolomite. Locally,
gray to black siliceous mudstone
and intercalated sandstone.
served either as an indurated shell limestone or (rarely) as
a soft, white calcareous clay which is the result of
weathering in pre-Miocene time. Phosphatization of the
carbonate rock is thought to be due to the downward
percolation of ground water which became enriched in
phosphate as it passed slowly through the low-permeability
Pungo River section.
The lowermost beds of the overlying Yorktown For-mation
of Pliocene age may occupy small channels cut
into the top of the Pungo River Formation. The channels
are only a few feet deep, and are blanketed, along with
the higher areas between them, with well-rounded peb-ble-
sized (5-15 mm) particles of quartz and phosphate,
mixed with coarse-grained sand and abundant phospha-tized
fish and animal remains. These coarse materials
form a basal conglomerate which was derived from the
reworking of Pungo River sediments by the erosive
action of a transgressive Yorktown sea. The configura-tion
of the top of the Pungo River Formation is shown on
plate 3.
PUNGO RIVER FORMATION
Definition
The name, Pungo River Formation, was first applied
by Kimrey (1964) to phosphatic sediments of middle
Miocene age in the subsurface of eastern North Carolina.
Since the formation does not crop out, Kimrey selected
the core from a test hole located at 76°34'59"W,
35°35'58"N, in northeastern Beaufort County, as the
type section. This hole is well BEA-C-14 of the present
report. 1 The unit was defined (Kimrey, 1964, p. 195) as
consisting of "interbedded phosphatic sands, silts and
clays, diatomaceous clays, and phosphatic and non-phosphatic
limestones." The lithology and geophysical
expression of the type core are shown on figure 3.
Kimrey's description of the formation was based upon
the lithologic variations that he observed in Beaufort
County, but the present study shows that this general-ized
description applies to Pungo River-age rocks
throughout eastern North Carolina. In addition to the
rock types mentioned above, beds of shell hash (unin-durated
to poorly indurated coquina) are found in the
upper part of the formation in wells located in Pamlico
Sound (well DA-OT-7, Section C-C; well HY-OT-14)
and locally, chalk is found in the middle part of the unit
(well HY-OT-12. Section C-C). The chalk contains
numerous brown spots identified as algal remains by A.
Winslow, Humble Oil Company (personal comm., 1968).
Although much limestone is found in the Pungo River
Formation, many of the rocks referred to as "limestones"
Table 1. Generalized lithologic descriptions of
Tertiary rocks in the subsurface of the
North Carolina Coastal Plain.
'In the well numbering system used herein, the first two or three let-ters
of the well designation are the abbreviation of the county where the
well is located (BEA = Beaufort Co.), the letters between hyphens indi-cate
the type of well (C = core hole); and the number is sequential within
the county (14 = 14th well in Beaufort County from which data. were ob-tained).
by Kimrey (1964) are actually dolomitic limestones and
dolomites.
Kimrey's type core was examined during the course of
this study. The core showed that fine-grained, greenish-brown
phosphatic sand, interbedded with thin layers of
green clay, lies above the massive clay unit which Kimrey
designated as the top of the Pungo River Formation.
These clayey phosphatic sands were placed in the York-town
Formation by Kimrey, and their phosphate content
(4 to 5 percent P2 5 ) was attributed to reworking of
Pungo River phosphate by a transgressing Yorktown sea.
The present study revealed no evidence of reworking in
either the quartz or the phosphate fractions of the clayey
sand. Samples of beds above Kimrey's contact were proc-essed
for microfauna and yielded foraminifera which are
elsewhere confined to the Pungo River Formation. Dif-fractograph
patterns of the clays in samples above and
below Kimrey's contact are identical, further indicating
that no break in deposition is present.
Accordingly, the top of the Pungo River Formation is
herein placed at a depth of 194 feet below land surface in
the type core section, rather than at 224 feet below land
surface as shown by Kimrey. Six other wells (BEA-P-17,
BEA-T-20, BEA-P-21, HY-T-3, HY-T-7, HY-T-10) in
the vicinity of the type core hole show this same (higher)
lithologic, paleontologic, and geophysical log top for the
formation. The revision of the type core section is shown
by the solid horizontal line and by the extended, offset
lithologic column on figure 3.
The top of the Pungo River Formation is defined in
this report as the highest occurrence of any one or any
combination of the following^
1. Primary (sand-sized, spheroidal to ovate, oolitic to
sub-oolitic in form) phosphate.
2. Light-green clay that may be either diatomaceous or
non-diatomaceous.
3. The abundant occurrence of any one or any combi-nation
of the following foraminifera:
a. Uvigerina calvertensis Cushman
b. Siphogenerina lamellata Cushman
c. Spiroplectamina mississippiensis (Cushman)
d. Cibicides concentricus (Cushman)
e. Fursenkoina miocenica (Cushman and Ponton)
Feet
200-
280L
Electric log
(resistivity curve)
Natural Gamma-ray log Feet
240
J 280
Clay
Phosphatic sand
Phosphatic dolomitic limestone
Top of Pungo River Formation as revised in this report
Datum is land surface (Elevation 10 feet)
Figure 3. Type core of the Pungo River Formation, showing adjusted top of unit (solid
line). Kimrey's top is shown by the heavy dashed line. (Modified from Kimrey,
1964).
f. Robulus americanus (Cushman) var. spinosus
(Cushman)
These foraminifera are considered to be restricted,
in North Carolina at least, to the Pungo River For-mation.
4. Relatively high radioactivity, as recorded by natural
gamma-ray logs, that is nearly continuous through-out
the formation. The logs illustrated on geologic
cross sections A-A' through F-F' (plates 5 through
10) are considered to be good examples of natural
gamma-ray log patterns from the Pungo River For-mation.
The base of the Pungo River Formation is defined as
the highest occurrence of arenaceous limestone or glau-conitic
sand, or of the highest persistent occurrence of
pre-Pungo River fossils. Where geophysical control alone
is available, an extremely low natural gamma-ray log ex-pression
characterizes the base of the unit, as shown on
the cross sections.
The Pungo River Formation is found in the subsurface
from approximately longitude 77°00'W eastward to the
North Carolina coastline (fig. 1). In Carteret and Jones
Counties, the formation occurs slightly to the west of this
parallel. Erosional remnants are present in Washington,
Onslow, and Jones Counties, to the west of the main
body of the formation. Pungo River rocks have been
identified in submarine outcrop in Onslow Bay, off the
southeastern North Carolina coast (F. M. Swain, personal
comm., 1969; Lewis and others, 1980). The formation
ranges in thickness from a feather edge along the line
representing its up-dip limit to a maximum measured
thickness of 969 feet in well DA-OT-8. The maximum
contoured thickness is about 1000 feet near Cape Hat-teras.
Lithology
The Pungo River Formation is composed chiefly of
two rock types: light-green, low-density, diatomaceous,
illitic to montmorillonitic clay; and fine- to medium-grained,
clear, angular to subangular quartz sand con-taining
varying amounts of greenish-brown clay and fine
to medium-grained light to dark-brown phosphate. The
phosphate and clay impart a brown color to practically all
the sands in the unit. Fine crystalline light olive-green
dolomite and dolomitic limestone are common as thin (1
to 3 feet) intercalations; rarely they are as thick as 10
feet. Beds of white to light-gray molluscan limestone,
pale-green to gray to white calcareous clay, shell hash,
and white chalk are less common Pungo River rocks.
Minor amounts of phosphate occur in all these rock
types, including the diatomaceous clays. Cross sections
A-A' through F-F' (plates 5 through 10) show the vertical
and lateral relationships of these interbedded lithologies.
Bedding in all Pungo River rock types is thick to very
thjck. Both in cores and in the exposure of the Pungo
River Formation in the Lee Creek mine near Aurora, rock
types are commonly vertically consistent for 5 to 15 feet,
and any lamination or thin interbedding is the exception,
rather than the rule.
Locally, some clay beds show rounded channels and
tubes that are filled with medium- to coarse-grained sand
and collophane (fig. 4A) or thin laminations and lenses of
fine-grained phosphatic sand (fig. 4B). The tubes and
channels appear to be animal burrows, indicating that the
clays were deposited in a moderately shallow-water en-vironment.
The lenticular fine-sand lenses were probably
formed by local current action, which piled up the sand
as ripples on clay substrate. These current ripples can be
found vertically throughout the Pungo River Formation.
The ripples, the water-polishing evident on most of the
quartz in the formation, and the oolitic to sub-oolitic
form of the phosphate grains in the unit all show that
bottom currents were active throughout the time of
Pungo River deposition. These currents are thought to be
in part responsible for the accumulation of high concen-trations
of phosphate in the formation.
Bituminous material is present in many Pungo River
clays, as evidenced by a fetid odor given off by fresh
cores when broken. This material is usually present only
in trace amounts, but is rarely concentrated enough to
209'9"
Coarse
Phosphatic
Sand
2I0'4"
Core from well BEA-C-33
Elev.=3'
Figure 4. a. Blebs and stringers of coarse phos-phatic
sand, interpreted as animal bur-rows,
in a clay matrix.
205'6"
Fine
Phosphatic
Sand
205
Core from well BEA-C-52
Elev. = 4'
Figure 4.b. Lenticular laminations of sand, inter-preted
as poorly developed current rip-ples,
in a silty clay matrix.
Figure 4. Sedimentary structures in selected cores
from the Pungo River Formation in Beau-fort
County, North Carolina. Depths are
in feet below land surface. Not to scale.
show fluorescence in the standard carbon tetrachloride
test for hydrocarbons. A commercial mud logging com-pany
has reported a show of methane gas (OWLCO,
written comm., 1970) near the base of the unit in an oil
test well drilled on Roanoke Island (well DA-OT-3, Sec-tion
B-B). Glass shards have been reported from the
Pungo River Formation (Rooney and Kerr, 1967) but
none were observed during the current study.
Carbonate Rocks. Carbonate rocks in the Pungo
River Formation are chiefly fine to medium crystalline,
well-indurated, grayish olive (110 Y 4/2 on NRC rock
color chart) to light gray (N 7) dolomitic limestones and
dolomites. Dolomitic rocks occur both as thin inter-calations
in the clay beds of the formation and as thick to
very thick beds which are often laterally continuous for
several miles. Although they are found at several levels in
the Pungo River section, they are more common in the
middle and lower two-thirds of the formation. Dolomitic
rocks are restricted chiefly to an area of high phosphate
concentration in Beaufort' and Pamlico Counties. Tex-turally,
they consist of a mosaic of rhombic crystals, with
rare shell imprints and trace amounts of phosphate and
fine quartz sand. Occasionally, dolomitic pebbles occur in
the coarse fraction of some sandy beds. Isolated dolomite
rhombs are common in the diatomaceous clays of the for-mation.
The Pungo River dolomites appear to have
formed mostly by replacement of limestone, brought
about by an influx of magnesium-rich water. The origi-nal
limestones probably formed in a low to moderate
energy environment.
Biostromal limestones in the unit are of two types:
molluscan and bryozoan. Both types are light-gray to
white, thickly to very thickly bedded, and slightly sandy.
The molluscan limestones are well indurated, consist of
whole to broken fossil material in a matrix of fine crystal-line
limestone, and are confined to the lower one-third of
the Pungo River in an area extending from eastern Car-teret
County to Cape Hatteras. The bryozoan limestones,
called "coquina" by Kimrey (1965), are unindurated to
poorly indurated and occur in the uppermost part of the
formation in Hyde, Dare, and the eastern part of Beau-fort
Counties. Both types of limestone formed in high
energy environments in an area which received little clas-tic
input. They carry a diversified microfauna which is
usually highly recrystallized.
Chalk occurs in the middle part of the formation in
eastern Hyde County (well HY-OT-12, Section C-C).
The chalk is tan to white, soft, massive, highly friable,
and is composed chiefly of foraminiferal tests and car-bonate
flour. Small brown spots in the chalk may repre-sent
the remains of planktonic algae (A. Winslow, per-sonal
comm., 1968). This chalk reflects a low-energy,
deep-water environment of deposition.
Argillaceous Rocks. Both diatomaceous and cal-careous
clays occur in the Pungo River Formation. Both
types consist predominantly of illite and mixed-layer
montmorillonite-illite. Trace amounts of chlorite and of
clinoptilolite, a zeolite mineral, are present in all clays
analyzed from the formation, including those which oc-cur
as minor fractions of phosphatic sands. The zeolite is
more prominent in the phosphate-rich beds of the Pungo
River than in the clays. Clinoptilolite was thought by
Rooney and Kerr (1967) and Gibson (1967) to indicate
volcanic action during Pungo River time, since it com-monly
forms from the devitrification of rhyolitic ash.
However, clinoptilolite has been reported from recent
continental shelf sediments off Mexico (D'Anglejan,
1967), where it occurs as a defrital mineral in nearshore
clays and silts, and has apparently been derived from on-shore
Tertiary volcanics. The literature records no exten-sive
volcanic activity on land in the Atlantic border re-gion
during Pungo River time, and no submarine source
is known. The writer agrees with Cathcart (1968) who
concluded that the small amount of clinoptilolite in the
Pungo River Formation is coincidental.
The diatomaceous clays of the Pungo River Formation
occur in the upper to middle parts of the unit, are light-weight,
grayish yellow-green (5GY 7/2), thickly to very
thickly bedded, and show no lamination other than oc-casional
light-colored bands which mark unusually high
concentrations of disc-shaped diatoms. Radiolaria and
foraminifera are abundant in these clays, and they con-tain
traces of phosphate, in pelletal form or as phospha-tized
fish scales and small vertebrae. Diatomaceous clays
comprise the bulk of the formation in the northern and
eastern parts of the study area, and compose most of the
sediments represented by the shale symbol on the litho-facies
map (plate 4). They are also prominent in Beaufort,
Hyde, and Pamlico Counties, and represent a low-energy
environment of deposition. The low density of these
clays is attributed to their high diatom content.
The calcareous clays of the formation are light gray to
white, medium- to thick-bedded, and comprise only a
small portion of the unit. They are areally restricted and
are generally located laterally adjacent to carbonate-rich
areas. Locally they are semi-indurated by carbonate
cement. Fine-grained quartz and phosphate are minor
constituents. The calcareous clays, if unindurated, yield
the most prolific microfaunas found in the Pungo River
Formation. They were deposited in an environment tran-sitional
between a relatively high-energy carbonate en-vironment
and a low-energy clay environment.
Classic supply for both types of clay was low to mod-erate,
with biologic sedimentation equal to or exceeding
clastic deposition, especially in the diatomaceous clays.
Diatom concentrations of up to 90 percent of the total
sample have been noted (Kimrey, 1965).
Arenaceous Rocks. The sands of the Pungo River
Formation are fine- to medium-grained (1/8 to 1/2 mm),
very thickly bedded, well to moderately well sorted, and
consist of mixtures of angular to subrounded, clear,
water-polished quartz sand, brown to olive clay, and
varying amounts of black and brown phosphate pellets.
Color of the sands varies from dusky yellowish-brown
(10 YR 2/2) to olive gray (5 Y 3/2), and is governed by
the amount of clay and phosphate present. Outside the
area of high phosphate concentration shown on figure 6,
phosphate pellets usually account for less than 10 to 15
percent of the overall composition of the sands. Inside
this "high-grade" area, however, phosphate grains make
up as much as 50 to 60 percent of the .bulk composition
of the rock- The P2 5 content of the sands varies directly
with the amount of phosphate mineral present (Kimrey,
1965) and ranges from 2.5 to 18 percent of the total sam-ple.
The higher phosphate percentages generally coincide
with the thicker sand accumulations.
Phosphatic sands are found at several levels in the
Pungo River section, and are interbedded with dia-tomaceous
clays, calcareous clays, dolomites, and dolo-mitic
limestones. A phosphatic sand 2 to 10 feet thick,
locally calcareous and indurated, occurs at the base of the
Pungo River Formation throughout much of the area of
study. In the area of high phosphate concentration, phos-phatic
sands recur roughly one-third of the way up the
section and again at, or just below, the top of the forma-tion.
In general, the phosphatic sands that are in the up-per
part of the section show higher P2Os contents than
those in the lower part.
Disseminated grayish-olive (10 Y 4/2) to olive-gray (5
Y 3/2) clays and silty clays occur in the sands, usually as
traces, but rarely in amounts of up to 20 percent. Garnet,
phosphatized remains of marine animals, and rhombic
calcite and dolomite which occur both as aggregates and
as isolated grains, are found in trace amounts in the sand.
Very few identifiable foraminifera can be recovered
from the phosphatic sands due to replacement of the cal-careous
foraminiferal tests by phosphate. Such replace-ment,
occurring either penecontemporaneously or epi-genetically,
has also altered the siliceous skeletons of dia-toms
and radiolaria found in the sands, but the form of
the original siliceous animals is generally recognizable.
The environment of deposition of the phosphatic
sands is interpreted as a shallow shelf, open marine en-vironment
with a low to moderate clastic supply. The de-gree
of sorting of the sands and the water-polishing de-veloped
on the quartz fraction indicate bottom currents
were active. The scarcity of clay in these rocks is at-tributed
to winnowing by the bottom currents. A current
velocity of 10 cm/sec or slightly greater would be neces-sary
to transport or agitate, these fine to medium-grained
sands. Currents of sufficient velocity exist in the modern
ocean at depths of 500 meters and less.
Facies Distribution
Plate 4 is an isopach map of the Pungo River Forma-tion,
and was constructed chiefly from the actual meas-ured
thickness of the formation at well control points. In
areas of sparse control — e.g., Tyrrell County, south-western
Pamlico Sound — the thickness of the unit was
estimated by computing the difference in elevation of the
contoured top and base of the unit at selected points.
Superimposed on this isopach map is a plot of the
lithofacies variations in the formation. In constructing
this map, major emphasis was placed on control points
for which cuttings or core and both electric and natural
gamma-ray logs were available. In up-dip areas and in
areas of rapid horizontal facies change, supplementary
wells with less complete data were used to delineate pat-terned
areas more accurately.
The lithofacies map is based on percentage composi-tion
of the formation at a given well point. Sand, clay,
and carbonate components of the unit, whose lithologic
character and variations are described above, were chosen
as end members. Phosphate pellets were included with
sand, since they are predominantly sand-sized. At each
well point, the thickness of these three components was
measured, either directly, from core or indirectly, from
geophysical logs interpreted with the aid of lithologic
descriptions. These thicknesses were then expressed as
percentages of the total thickness of the formation at that
point. Appendix A (p. 23) contains the thickness and
percentage data for each of the 119 well points used to
construct the lithofacies map.
Following these calculations, percentage breakdowns
were selected which were judged to best portray overall
lithologic variations and relative down-basin and up-basin
directions at the map scale used. Figure 5 is a per-centage
triangle which shows the distribution of the 119
well points in this three-component system, the per-centage
breakdowns used, and the pattern chosen to
represent each breakdown on the lithofacies map. Per-centage
contours of each end member were drawn on
work maps and these maps were then combined to pro-duce
the finished lithofacies map. In some places, there
may be a considerable change in rock type between wide-ly
scattered wells. Interpolation has been made between
such control points, and an intermediate facies may be
mapped between them even though there are few wells
CARBONATE
I00A0
Clay Percentage
EXPLANATION
SAND
i = Data Point
Figure 5. Percentage triangle showing distribution of
data points in a three-component system and
percentage breakdown used on lithofacies
map.
that actually penetrate the in-between rock type. The
percentage categories selected as meaningful are shown
on table 2, along with a well which is an example of each
category and which is illustrated on a cross section.
Gravels and beds of shell hash (unindurated coquina)
are included in the "sand" categories. These materials,
along with sand-sized materials, represent high- to
moderate-energy environments of deposition. Limestone
(both biostromal and chalk), dolomite, and dolomitic
limestone are included in the carbonate categories.
Locales high in carbonate indicate areas in which chemi-cal
deposition, as well as clastic deposition, was active.
Biostromal molluscan and bryozoan limestones are
judged to represent areas of high energy but low clastic
input. High-energy rock types occur either in up-basin
areas or on structural highs.
The high-clay areas represent low-energy environ-ments
of deposition and indicate either a down-basin,
deep water area or a depositional site with relatively low
clastic supply.
Phosphate-rich areas are not delineated on the litho-facies
map, but they coincide in general with areas rich in
quartz sand. The phosphate represents a locale in which
chemical precipitation was active along with clastic
deposition.
Category Well
Cross
Section
Plate
Number
Sand 75 %-l 00% CR-T-23 E-E' 9
Clay 75%-100% CUR-OT-1 A-A' 5
Carbonate 75%-100% CR-T-20 E-E' 9
Sand 50%-75% BEA-T-53 D-D' 8
Clay 50%-75% PAS-T-3 A-A' 5
Carbonate 50%-75%
Roughly equal mixture of
end members
HY-T-15
BEA-C-4
D-D'
F-F'
4
10
Table 2. Percentage Categories used on lithofacies map
and example of each.
Phosphate
Phosphate pellets occur in all rock types found in the
Pungo River Formation, but they are found in high
concentrations only in the sands of the unit. Practically
all of the pellets are fine to medium sand-sized (1/8 to
1/2 mm) and spheroidal to prolate spheroidal to rod-shaped.
Most of the pellets are moderate brown (5 YR
3/4) to dusky brown (5 YR 2/2), but light gray (N 7) to
black (N 1) particles are prominent. Analyses by Rooney
and Kerr (1967) showed the darker pellets have a higher
content of organic carbon, iron oxide, or glauconite.
Combinations of these compounds account for the color
variations observed. Rooney and Kerr also demonstrated
that the phosphate mineral is very fine-grained franco-lite,
a carbonate apatite. X-ray diffraction patterns ob-tained
by the author from phosphatic clays in the unit
support this finding.
The francolite pellets have a smooth, shiny surface for
the most part and they occasionally show concentric sur-face
markings, especially on the more spheroidal grains.
No concentric inner structure was observed in any of ap-proximately
300 spheroidal to sub-spheroidal grains
broken for study. A rough zoning inside the grains,
similar to that illustrated by Rooney and Kerr (1967,
plate 2) and attributed by D'Anglejan (1967) to zonal
staining by diffuse organic matter, is a common feature
but is not confined to spheroidal grains. Quartz and glau-conite
nucleii were recorded in a few grains by Rooney
and Kerr, but the present study revealed only dense
phosphate at the center of broken grains. An oolitic
origin, in the classic sense, thus appears precluded for the
pellets.
Phosphatized organic remains found with the pellets
include diatoms, radiolaria, foraminifera, vertebrae and
other bones, shark and ray teeth, and fish skin and
scales. The teeth, bone material, and anomalous irregular
black masses of phosphate thought by Gibson (1967) to
represent internal molds of gastropods and pelecypods,
occur in the coarser fraction ( 2 mm) of the sediments.
Disc-shaped planoconvex to doubly convex pellets are
thought to represent pinfish teeth (A. Winslow, personal
comm., 1968). A fecal origin for some of the rod-shaped
pellets is indicated by their high diatom and radiolarian
content.
Pebble-sized (up to 8 cm) particles of dolomitic lime-stone
and of phosphate-cemented pellets and/or shell
material occur in phosphatic beds of the Pungo River and
indicate that some reworking of the phosphatic sediments
has taken place. The high degree of sorting of the pelletal
francolite and associated quartz, the rounding of many of
the rod-shaped francolite pellets, and the rounded and
water-polished appearance of the quartz fraction also in-dicate
some reworking within the basin of deposition.
These features are attributed to the action of bottom cur-rents,
possibly storm-generated, in an area of slow sedi-ment
accumulation.
Trace amounts of uranium and thorium are incor-porated
in the francolite lattice, probably as finely dis-persed
oxides. The presence of these radioactive elements
produces an easily recognizable pattern on natural
gamma-ray logs (cross-sections A-A' through F-F') in
which the intensity of the gamma radiation is directly
proportional to the P2Os content of the sediment (Kim-rey,
1965). This characteristic high-radiation expression
on the natural gamma-ray log has been utilized in phos-phate
exploration in North Carolina and elsewhere with
excellent results in the case of primary deposits. Where
phosphatic sediments have undergone extensive re-working,
as in the Bone Valley Formation of Florida,
leaching has removed or redistributed much of the radio-active
material, and natural gamma logs are inconclusive
as to the presence of phosphate (Altschulter and others,
1964).
Some workers (Watkins, 1942; Ames, 1959, Degens,
1965; Malde, 1959; Pevear, 1966, 1967) have attributed
the origin of sedimentary phosphate largely or entirely to
10
the replacement of calcite by phosphate. There is no evi-dence
for carbonate replacement in the Pungo River For-mation,
other than the phosphatization of foraminifera.
The dolomites, dolomitic limestones, and limestones of
the unit commonly show francolite pellets in sharp con-tact
with an enclosing mosaic of microcrystalline to
coarse crystalline carbonate. In some of the clastic beds,
isolated euhedral dolomite and calcite rhombs occur in di-rect
contact with francolite pellets. None of the cal-careous
beds in the unit show more than trace amounts
of phosphate (Kimrey, 1965). A calcite replacement
origin would concentrate francolite in the calcareous
strata and the contacts between francolite and calcite
grains would tend to be irregular rather than sharp. Of
course, as shown by laboratory experiments and by field
evidence, this type replacement can, and does, occur. In
the study area the Castle Hayne Formation, underlying
the Pungo River sediments, has locally been partially
phosphatized. Hard, dense, black phosphate marks the
top of the Castle Hayne in many places and extends sev-eral
inches downward into the limestone, replacing it.
This replacement, however, is attributed to solution of
francolite from phosphatic Pungo River beds, and subse-quent
redeposition of phosphate in the permeable lime-stone
by downward-percolating ground water. The
aragonitic structure of the carbonate in the shell material
of the Castle Hayne and in foraminiferal tests which oc-cur
sparsely in the Pungo River phosphatic sands is
probably more susceptible to replacement than the rhom-bic
structure of calcite or dolomite.
Evidence for a primary, or first-cycle, origin for the
sand-sized, pelletal francolite of the Pungo River Forma-tion
includes the following:
1. The chemical composition and the fresh, unleached
appearance of the majority of the pellets indicate
primary deposition. Most phosphate that forms in a
marine environment is composed of francolite. The
uranium content of the pellets would be much
lower than observed if they had undergone ex-posure
and leaching.
2. The clay mineralogy of the phosphatic beds and
their associated sediments indicates normal marine
deposition. If extensive reworking had occurred,
illite concentration in the clays would be higher
than observed. During reworking, prolonged ex-posure
of montmorillonitic clays to seawater would
allow more potassium fixation in the montmoril-lonite
lattice. Consequently, more montmorillonite
would be altered to illite.
3. Altered, but recognizable, shallow-water, open
marine fauna are present in the phosphatic beds.
4. The quartz and francolite of the phosphatic sedi-ments
both exhibit a polished appearance. This is
' thought to result from gentle attrition such as
would be expected from bottom current action. The
francolite does not show the effects of any ex-tensive
transportation (such as would occur during
reworking).
5. No recognizable rock fragments or fauna from older
units have been found in the Pungo River Forma-tion.
The easily erodable nature of the older Coastal
Plain rocks suggest that this would be the case if the
Pungo River deposits were of secondary origin.
6. No known source for the phosphate exists in the
older sedimentary strata in the area. Trace amounts
of phosphate occur in the Eocene Castle Hayne For-mation,
but the grain size of this material is much
larger (4 to 20 mm) than that of the phosphate of
the Pungo River Formation.
The occurrence of well-rounded, water-polished quartz
and fine- to medium-sand-sized particles of francolite, as
well as the appearance and mineralogy of the francolite, in-dicate
deposition in a moderately-shallow inner shelf envi-ronment.
Storm or bottom currents in the basin of deposi-tion
are responsible for the sedimentary structures developed
in the phosphate-rich areas, for winnowing of clay-sized
material from the phosphatic sands, and for the minor re-working
shown by both quartz and francolite.
Microfauna
Benthonic foraminifera which are restricted to the
Pungo River Formation in North Carolina are listed
above (p. 6). Gibson (1967, p. 637) listed a suite of
planktonic foraminifera that indicate a middle Miocene
age (planktonic zone N. 9) for beds near the top of the
formation. Brown (1958) and Gibson (1967) thought that
the Pungo River Formation might be in part older than
middle Miocene. Recent work (Gibson, 1980) has con-firmed
that part of the formation is of early Miocene age.
Both planktonic and benthonic foraminifera are more
common in the calcareous and diatomaceous clays of the
formation; few identifiable fossils can be recovered from
the phosphatic sands of the unit.
The foraminiferal assemblages from the Pungo River
Formation in the Texas Gulf Sulphur Company's Lee
Creek mine indicate deposition in an open marine, shal-low
shelf environment, of normal salinity (Gibson, 1967).
The fauna indicates a water depth of 100 to 150 meters,
with temperatures ranging from cool to cool-temperate.
Benthonic foraminiferal suites from wells in other areas
in North Carolina suggest a cold-water or other adverse
environment, as they are characterized by few species but
large numbers of individuals. The observed fauna could
have resulted from a nearshore, southward-flowing cool
current, similar to the present-day Labrador Current, that
apparently extended as far south as North Carolina in
middle Miocene time.
The abundance of radiolarian and diatom tests in clays
and sands of the formation show that the marine waters
were enriched in silica (Taliaferro, 1933). Abundant dia-toms
indicate a rich nutrient supply, such as would be
supplied by upwelling water (Brongersma-Sanders,
1948). Phosphate and nitrogen concentrations are the
limiting chemical factors on diatom abundance, and both
elements would occur in greater than normal concentra-tions
in an area of upwelling. The radiolaria in the Pungo
11
River sediments are diagnostic of nothing other than a
marine environment.
Smith (1968) reported on phosphatic and siliceous
shales of middle or late Miocene age in California. The
foraminiferal assemblages of these shales and their high
diatom content are paralleled by faunas found in the
Pungo River Formation. From the benthonic foramini-fera,
Smith interpreted a water depth of 150 feet as the
probable environment for the deposition of phosphate.
D'Anglejan (1967) found a foraminiferal assemblage in
recent phosphatic sediments off Mexico which is very
similar to that of the Pungo River. D'Anglejan's samples
came from water depths of 100 meters and less.
During the present study, microfaunal float slides were
examined for 49 wells (see Appendix A), in an attempt to
zone the Pungo River Formation by means of benthonic
foraminifera. The attempt was made to try to determine
which parts of the formation are missing on structurally
high features in the study area. Core holes were used
where possible in order to obtain more representative
faunas. No zoning could be established, since the same
faunas were found to recur at successive depths down-hole.
The foraminifera selected were found to be facies
influenced. As expected, argillaceous sediments yielded
better faunas. Gibson's (1967) contention that the dia-tomaceous
clays of the unit carry few foraminifera was
not borne out by this stuy. Those examined yielded a rich
foraminiferal fauna.
. The following generalizations emerge from study of
the selected wells:
1. Cibicides con-:tntricus (Cushman) and Uvigernia
calvertensis Cushman are the most widespread spe-cies,
both horizontally and vertically, in the Pungo
River Formation. The two species occur simul-taneously
in large concentrations at two or more
horizons in the unit, and prefer an argillaceous to
arenaceous-argillaceous substrate.
2. Siphogenerina lamellata Cushman is associated with
diatomaceous to calcareous clays, and occurs in pro-fusion
whenever found. The species is more promi-nent
in deeper-water environments, but substrate,
rather than depth, apparently controls its occur-rence.
3. Fursenkoina miocenica (Cushman and Ponton),
along with Bolwina calvertensis Dorsey, and other
species of Bolwina occurs immediately adjacent to
phosphatic sands, either vertically or laterally. The
most prolific occurences are just east of the area of
high phosphate concentration in Beaufort and Pam-lico
Counties.
4. Robulus americanus (Cushman) var. spinosus
(Cushman) is restricted to deeper-water environ-ments,
and occurs in argillaceous sediments.
5. Spiroplectammina mississippiensis (Cushman) is
found only in carbonate rocks or in calcareous
clays.
6. Large species of Oolina, Marginulina and Poly-morphina
occur in calcareous clays near limestone-rich
areas.
STRUCTURE
The classic concept of the structure of the Atlantic
Coastal Plain is that of a monocline dipping gently to the
southeast. Superimposed on this wedge of sediment are
large-scale noses and troughs, the axes of which strike
northwest-southeast and plunge to the southeast. Exam-ples
of these features are the Cape Fear Arch, the Nor-mandy
Arch, and the intervening Salisbury Embayment.
The Pungo River Formation «does not conform to such a
structural framework. This study shows that Pungo
River sediments in North Carolina were deposited in a
basin which generally trends east-northeast and plunges
to the east (plate 4).
Brown, Miller, and Swain (1972) identified structural
lineaments along the Atlantic Coast which trend, in order
of importance, northeast-southwest, north-south, and
northwest-southeast. The north-south lineaments were
interpreted as zones of flexure which were more active
during certain periods of geologic time than others. The
timing and relative magnitude of activity along these
zones has had a profound effect on the distribution,
lithology, and thickness of the overlying blanket of
Coastal Plain sediments. The flexures are expressed in the
sedimentary column by marked thickening of strati-graphic
units in a down-basin direction when one of
these features is crossed. Change in the basement slope
may be associated with these flexures, or they may form
as a type of growth fault. They are thought to represent
"hinge lines'' which mark the upward dying-out of a
fault in the manner proposed by Weeks (1952).
The western limit of the Pungo River Formation, as
presently preserved, generally coincides with one of these
north-south trending lineaments which was active as a
flexure during Pungo River time (compare figures 1 and
6). This lineament is a major hinge line that affects
underlying units as well as the Pungo River Formation,
and originates as a basement feature (Prouty, 1946;
Spangler, 1950). Outliers of Pungo River to the west of
the hinge line, in Onslow, Jones, and Beaufort Counties,
show that the lineament was crossed by the middle Mio-cene
sea. These outliers consist of molluscan limestone
and coarse-grained sand, both indicative of shallow water
conditions west of the lineament. East of the major hinge
line, a steepening in the slope of the floor of the Pungo
River basin created a bottom which shallowed rapidly
westward. The abrupt shallowing of water and the re-sultant
restriction of circulation, aided by smaller struc-tures
tangential to the flexure zone, were critical factors
in determining the site of accumulation of phosphatic
sediments. The location of the major hinge line and tan-gential
structures is shown on figure 6.
Plate 2 is a structural map whose contours represent
the base of the Pungo River Formation. As mentioned
previously, the Pungo River unconformably overlies sev-eral
older units which range in age from Paleocene
through Oligocene. Accordingly, this map represents a
composite of the tops of these units. Approximate updip
limits of the older rocks are shown by various broken
lines on plate 2. The pre-Miocene units become progres-
12
78°
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77 c
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--?-"[" "H NORTHAMPTON GAJES ^
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36°
/
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HALIFAX ^ /_-
FRANKLIN/ /
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'JOHNSTON /
hertfArd'y" r^9 \ '^o^eA
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35 c
34°
—$—^ Axis of Positive Feature
^ > Axis of Negative Feature
10 10 20 30 40
Miles
II
Hinge Line
A A'
Line of Section
|
|
High Phosphate Area
kj
36
35°
34 <
33°
78° 77° 76<
Figure 6. Location of structural features, extent of high concentrations of phos-phate
(shaded), and location of lines of section shown on Figure 7.
13
sively younger in a general southeast direction. The pre-
Pungo River surface generally strikes north and dips east.
West of the -350 foot contour, the minor irregularities on
the surface are in part real, because of erosion in an up-dip
direction, and in part apparent because of the greater
density of well control in the western half of the con-toured
area. Significant features on this map include:
1. A prominent nose whose axis strikes and plunges
northeast from western Carteret County toward
Pamlico Sound, and dies out beneath the Sound.
2. More subtle, less extensive positive features in
north-central Beaufort County and in central Cho-wan
County, subparallel to and north of the promi-nent
nose. The Beaufort County nose was the more
important influence on phosphate concentration.
3. Intervening northeast-striking and plunging
troughs between the high areas.
4. A steepening of slope along a north-south line lo-cated
roughly at longitude 76°15'W. This line is in-terpreted
as a second zone of flexure, or hinge line,
paralleling the major (westernmost) one.
Plate 3 is a structural map whose contours represent
the top of the Pungo River Formation. The effect of
erosion is more pronounced on this map than on plate 2,
especially to the west of the -300 foot contour. The top
of the unit strikes generally north and dips east. The con-tours
show an alternating series of noses and troughs of
various sizes, all of which trend either northeast or east.
The most pronounced features on this map are:
1. A nose whose axis trends eastward and extends
along the south shore of Albemarle Sound.
2. A prominent northeast-trending nose whose axis
extends from the Morehead City area almost com-pletely
across Pamlico Sound. This nose is located
just north of, and roughly parallel to, Core Banks.
3. An intervening northeast-trending low, extending
from Lake Mattamuskeet through the Manteo area,
and bifurcated by a local nose just north of Lake
Mattamuskeet.
Plate 4 is an isopach and lithofacies map of the Pungo
River Formation. In addition to the facies distribution
discussed above (p. 9), this map shows the following sig-nificant
features:
1. A "thin" area, or structural high extending from
Washington County through northern Dare
County. This area is generally high in sand, and
was probably a site where high energy conditions
existed.
2. A second "thin" area extending northeastward
through Carteret County, also coinciding with a
high-sand facies.
3. An intervening "thick"area, or structural basin, in
eastern Beaufort and Pamlico Counties, trending
east to northeast. This basin contains sediments
which are, for the most part, highly phosphatic
sands, but it also has local areas high in clay and
carbonate rocks.
4. A change in the rate of thickening of the formation
along a line that extends southward from roughly
the center of Lake Mattamuskeet. To the west of
this line, the formation is relatively thin and sandy.
To the east, its thickness and clay content increase
rapidly, indicating a deeper water environment.
This thickening is in response to flexure along the
easternmost hinge line mentioned above.
The structural model which emerges from these three
maps is one of a partly restricted basin with a shelved
edge, bordered on the north and south by structurally
positive features. The trends of the flexure zones (hinge
lines) and the axes of the positive and negative structural
features are shown in figure 6.
The combination of these structural features produced
a relatively flat sea floor in southeastern Beaufort
County, bordered to the east and west by steeper ramp-like
slopes, and to the north and south by positive struc-tures.
All these structural features apparently were pres-ent
throughout Pungo River time, for an isopach map of
the formation (plate 4) shows both of the hinge lines ex-pressed
as a basinward increase in the rate of thickening
of the unit, and shows the positive structures as areas
where the formation is thin.
The Carteret County area was structurally high pre-ceding
(plate 2), during (plate 4), and following (plate 3)
deposition of the Pungo River Formation. The structural
high parallel with Albemarle Sound and the basin be-
Figure 7. a. East-West cross-section across the basin of
phosphate deposition.
EXPLANATION
Coorse sand
and gravel
Phosphatic
sand
Carbonate Diatomaceous
clay
Figure 7.b. North-South cross-section across the basin of
phosphate deposition.
Figure 7. Diagrammatic cross-sections showing structural
conditions in the basin of phosphate deposition.
Location of cross-section lines is shown on Fig. 6.
Vertical exaggeration x50.
14
tween the two highs were not in existence until Pungo
River time (compare plates 2 and 3). The north-trending
flexure zones, or hinge lines, are pre-Miocene features
which were active before and during early and middle
Miocene time.
The location of high concentrations of pelletal, sand-sized
(primary) phosphate deposits (fig. 6) with respect to
the structural features outlined above shows that the
structurally-produced basin-bottom topography was a
prominent, perhaps dominant, factor determining where
phosphate was deposited and concentrated. Diagram-matic
cross sections of the basin of phosphate accumula-tion,
idealized and simplified, are shown on figure 7. The
relationship of rock type to structural position is striking.
Molluscan limestones and coarse elastics occur on the
structural highs, while the intervening lows were the sites
of fine clastic and chemical (phosphorite) sedimentation.
MARINE PHOSPHORITES
The geochemical cycle of phosphorous is complex, as
are the lithologic associations of marine phosphorites.
Precipitation of phosphate minerals from ocean water is a
delicate mechanism, and the scarcity of marine phos-phorite
in the geologic column shows that conditions
favorable for its deposition are rarely met. Ocean cur-rents,
physical-chemical and biochemical conditions, and
clastic supply are factors that must reach a certain bal-ance
before phosphate can form and be concentrated.
The structural setting of a phosphorite basin influences
all these factors.
As pointed out by Bentor (1980), there have been, and
continue to be, differences of opinion concerning the
exact mechanism and environment of deposition neces-sary
for formation of marine phosphorites. These dif-ferences
exist partly because our knowledge of the phos-phorous
cycle in the ocean is incomplete and partly be-cause
phosphorites forming in the modern ocean are not
completely analogous with those formed in the geologic
past. Modern phosphorites appear to result from re-actions,
in a reducing marine environment, between
organic-rich bottom sediments and phosphate-rich inter-stitial
waters. Phosphate minerals apparently form within
the bottom sediments. Biologic activity serves to concen-trate
the phosphorous, both in near-surface ocean waters
and within the sediment-water mixture on the ocean
floor. Modern phosphorites form in water depths of 60
to 400 meters. Upwelling currents are thought to re-plenish
the supply of phosphorous to near-surface
waters, where organisms constantly remove and concen-trate
the phosphorous by their life processes. As the
organisms perish, settle to the ocean floor, and partially
or completely decompose, the phosphorous content of
both bottom waters and ocean-floor sediment is greatly
increased.
It is probable that ancient pelletal phosphorites, such
as those discussed in this paper, formed above the sedi-ment-
water interface in contrast to modern phosphorites.
Riggs (1979a) postulated that a colloidal phosphorous-rich
gel just above the sediment-water interface was con-solidated
into pellets by the digestive action of organisms,
and these pellets were subsequently concentrated by bot-tom
currents. In the author's opinion, gentle bottom cur-rent
action alone could be responsible for both the forma-tion
and concentration of pellets from such a gel.
Lithologic Associations
A characteristic suite of sediments is associated with
marine phosphorites, and recognition of this suite pro-vides
a useful exploration tool (McKelvey, 1963; Shel-don,
1964a). The Phosphoria Formation of Idaho and
Wyoming is one of the better-known examples of phos-phorite-
associated rock types and facies relationships
(Mansfield, 1927; McKelvey and others, 1959). A typical
sequence, listed by McKelvey (1967) and going from
down-basin toward shallow water, consists of: dark-colored
carbonaceous shale; phosphatic shale, phos-phorite,
and dolomite; chert and several facies of car-bonate
rock; and, in areas of arid climate, saline deposits
and red to light-colored sandstone or shale. The vertical
sequence varies, depending on whether deposition is as-sociated
with marine transgression or with regression,
and is characterized by complex interbedding. Similar
rock types and sequences have been described by the
British Sulphur Corporation (1961) from numerous
phosphorite deposits throughout the world. Paleolatitude,
in part, determines the development of black shale and of
carbonate (McKelvey, 1963) and has been correlated with
phosphate occurrence (Sheldon, 1964b).
Volcanic debris, in the form of glass shards, zeolites, or
high-temperature feldspars, is a common trace con-stituent
of phosphorites and their associated rocks (Gul-brandsen,
I960; D'Anglejan, 19e>7) and has been con-sidered
by some workers to represent contemporaneous
volcanic activity. Others (D'Anglejan, 19o7) attribute
such debris to the erosion of older subaerial volcanic
rocks in the vicinity of the basin of phosphate deposi-tion.
Most marine phosphorites and associated rocks were
deposited in shallow water (Kazakov, 1937; Bushinski,
1964; Gibson, 1967), in a depth range between 50 and
200 meters; and phosphate deposition is influenced bv
the upwelling of cold, nutrient-rich marine water.
Pevear's (196e>) hypothesis of deposition in an estuarine
environment, in the case of appreciable concentrations of
phosphate, is not borne out by field evidence. The con-sensus
of most workers is that most phosphorites are de-posited
in a restricted shallow shelf or platform environ-ment.
The diatomaceous clays and phosphatic sands in the
Pungo River Formation in North Carolina are part oi a
suite of rocks deposited in an area oi upwelling nutrient-rich
marine water. Carbonaceous shale has not been
found in the Pungo River, possibly because circulation in
the deep-water portion of the basin of deposition was
relatively unrestricted. It is also possible that the increase
in the amount of organic material accompanying upwell-ing
was not great enough to produce enough dead or-ganisms
to form carbonaceous mud. In Walvis Bay. on
15
the west coast of Africa, modern upwelling causes mass
mortality in planktonic and nektonic organisms, but the
argillaceous bottom sediments found there are green
rather than black muds (Brongersma-Sanders, 1948). Al-though
diatoms and radiolaria are locally abundant in the
Pungo River, chert— so prominent in many other phos-phorite
provinces— is absent, as it is also in other eastern
United States phosphorite provinces (McKelvey, 1967, p.
D12).
Chemical Environment
Judging from the suite of sediments associated with
phosphorites, pelletal (primary) phosphate deposition is
favored by seawater enriched in silica, fluorine, calcium
phosphate, and calcium carbonate. The high silica con-tent
of the water has been attributed (Taliferro, 1933;
Gibson, 1967) to submarine volcanic activity. It appears
to the author that enrichment in silica can more reason-ably
be attributed simply to silica fixation in the shells of
plankton. Subsequent solution of the siliceous tests may
or may not occur, depending upon the pH of waters that
pass through the siliceous sediment after deposition. If
the pH of such waters is greater than 9 (Cook, 1970),
chert would be expected to form, leaving few radiolarian
or diatom remains. The siliceous planktonic tests in the
Pungo River Formation are preserved in an unaltered
state, showing that the rocks of this unit were never af-fected
by pore waters with a high pH.
Mansfield (1940) thought the high fluorine content of
phosphorites was indicative of volcanic activity. How-ever,
McKelvey and others (1953) showed that the
concentration of fluorine in normal seawater is sufficient
to account for the amount of this element found in the
phosphate lattice. While it is true that an increase in the
flourine content of marine waters (such as would be asso-ciated
with volcanism) can cause apatite precipitation,
several other chemical changes can produce the same re-sult
(Gulbrandsen, 1969). The author has seen no definite
evidence of volcanic activity in the Pungo River Forma-tion.
Precipitation of calcium carbonate and of calcium
phosphate are controlled by pH (Kazakov, 1937; Krum-bein
and Garrels, 1952; Gulbrandsen, 1969). Phosphate
precipitates at a relatively low pH (7.0 to 7.5), while cal-cite
requires a pH of 7.8 or higher to form in appreciable
amounts. From a solution saturated with respect to both
calcite and phosphate, coprecipitation will occur with a
rise in pH, or with evaporation of seawater. Calcite pre-cipitation
will predominate because of the lower absolute
solubility of calcium phosphate with respect to calcite
(Krumbein and Garrels, 1952). In a restricted basin, how-ever,
conditions favor removal of calcium as phosphate,
as long as the pH is relatively low. Restricted circulation
which gives rise to a negative Eh, is indicated by the
presence of organic matter in phosphorites. Modern
phosphate forms in a reducing environment (Bentor,
1980). However, Krumbein and Garrels (1952) found
both calcium carbonate and calcium phosphate to be
independent of Eh.
In summary, the geochemistry of marine phosphorites
and associated rocks indicates deposition in a somewhat
restricted, slightly euxinic, shallow-water basin with
either constant or periodic access to the open sea. This
access and the resultant replenishment of seawater is nec-essary
to acount for the amount of silica, calcite, and
phosphate observed in the field. A low clastic supply and
the predominance of chemical sedimentation is also borne
out by field evidence.
Since these conditions are not unusual in shallow seas,
either modern or ancient, why then is marine phosphorite
not more common in the geologic column? Riggs (1979b)
suggests that an increase in exhalative hydrothermal
activity associated with an increase of tectonism at plate
boundaries, along transform faults, etc., could account
for increased concentrations of phosphorous, fluorine,
and silica in seawater. However, samples at some hydro-thermal
vents show little phosphorous. Cook and
McElhinney (1979) believe that marine phosphorites
form during late stages of plate separation and therefore
are not directly connected with tectonism. The author be-lieves
that there have been changes in the concentration
of phosphorous in seawater at various times in the geo-logic
past. Sheldon (1980) pointed out that phosphorite
deposition has not been constant throughout geologic
time, but rather that major "episodes of phosphogenesis"
have occurred periodically. Sheldon's hypothesis, which
seems reasonable to the author, is that the phosphorous
content of the deep ocean builds up slowly and is "with-drawn,"
primarily by upwelling, at times when the deep-ocean
circulation system changes, perhaps in response to
climatic change. The Miocene Epoch represents one such
episode of phosphorite formation.
Theories of Origin
Several hypotheses have been used to explain the
origin of marine phosphorites. No single hypothesis ap-plies
to all deposits because field evidence shows that
marine apatite may form in different environments and
may undergo various diagenetic changes, and/or enrich-ment
by reworking. Reviews of the historical develop-ment
of thought on the origin of phosphorite deposits are
given by Gulbrandsen (1969), Bentor (1980), and Shel-don
(1980); the interested reader is referred to these
papers and their extensive lists of references. Sheldon
(1980) placed hypotheses on the origin of marine phos-phorite
into three categories: (1) special or catastrophic
events (e.g., fluorine influx of Mansfield, 1940); (2)
action of directly-related land and sea processes in a near-shore
environment (e.g., estuarine deposits of Bushinski,
1964; Pevear, 1966); (3) processes related to upwelling
marine waters. This third process, in some form, is the
most widely advocated, particularly for sand-sized pel-letal
phosphate deposits such as those described from the
Pungo River Formation.
Kazakov, in 1937, postulated that ancient marine
phosphorites formed from physical-chemical reactions.
These involved primarily the loss of CO; and an increase
in pH, resulting from a temperature rise as cold, deep
16
ocean waters rose toward the surface in areas of upwell-ing.
The rising water becomes super-saturated first with
respect to calcite, then calcium phosphate, and direct
chemical precipitation supposedly occurred. Although
much of the mechanism proposed by Kazakov has now
been refuted, most current investigators agree that up-welling
is an important factor in the formation of both
ancient and modern phosphorites.
Practically all marine phosphorites, ancient and mod-ern,
are associated with organic matter. While we do not
know, at present, the exact role that organisms play in
the accumulation of a phosphate deposit, we know that
phosphorous is a major component in the hard parts of
vertebrates and invertebrates, and it is present in lesser
amounts in their soft parts and in plants as well. The life
processes of marine plants and animals concentrate phos-phorous
from seawater. Upon their death and decompo-sition,
this phosphorous is released to solution and can be
concentrated to form marine apatite, given the proper
chemical environment.
From the observed intimate association of marine life
with phosphorite in the Pungo River Formation, it ap-pears
likely that organic processes influenced phos-phorite
deposition in this unit. Abundant planktonic and
nektonic life is indicated both by the extremely high dia-tom
and radiolarian population in the clays associated
with the phosphatic sands and by the abundance of fish
and diatom remains in the sands themselves. Due to
phosphatization of benthonic life forms in the phosphatic
sands, it is difficult to assess the relative importance of
bottom-dwelling organisms. The fact that their remains
occur, even in subordinate amounts, indicates that
anaerobic bottom conditions did not exist continuously
during the time of phosphate deposition.
Upwelling marine waters appear to be a reasonable
source of supply for the phosphorous and other nutrients
that trigger the high organic activity favorable for the
formation and concentration of primary (pelletal, sand-sized)
phosphate. The upwelling waters do not have to
originate at great depths, nor do they need to have phos-phorous
concentrations greatly in excess of those in
normal seawater (Bentor, 1980). All that is apparently
necessary is a steady supply of nutrients to replenish
those depleted from near-surface waters by organic activ-ity.
The configuration of the ocean bottom has a direct and
important effect on the location of upwelling and on the
site of phosphate accumulation. A gently shelving bot-tom
configuration provides a slope along which rising
cool waters may be directed to shallow depths. As tem-perature
and pH increase with decrease in water depth, a
thin, sheet-like deposit of phosphate may be laid down
on such a slope. Kazakov (1937) recognized such a de-posit
in the Permian rocks of the Ural Mountains of Rus-sia,,
and it greatly influenced his thinking concerning
phosphate deposition. Sheets of phosphorite, however,
are unlikely to attain either the thickness or the concen-tration
necessary to make a deposit of economic interest.
Further concentration of the phosphate must take place.
Restricted circulation in the shallower parts of the
basin of deposition promotes the chemical and/or bio-chemical
precipitation and subsequent concentration of
phosphatic material. One place such restriction is at-tained
is in structural or erosional depressions on the sea
floor. Erosional features are usually of limited areal ex-tent;
consequently, the amount of phosphorite in such
features would likely be insignificant, and their
boundaries and trends could be identified only by de-tailed
exploration. Structural lows, on the other hand, are
large, relatively easily recognized, and their position can
often ue predicted if the tectonic history of the basin is
known.
Such a structural basin (fig. 7) is the site of accumula-tion
of the high-grade phosphatic sands of the Pungo
River Formation. Similar basins containing comparable
rock suites are the sites of accumulation of significant
amounts of marine phosphorites in Australia (Keyser and
McLeod, 1968), in Egypt (Youssef, 1965), in Iran
(Notholt, 1968), in Israel (Bentor, 1953), in parts of Rus-sia
(Anonymous, 1968), in Syria (Omara, 1965), and in
Iraq, Jordan, Lebanon, and the Algerian-Tunisian Basin
(British Sulphur Corp., 1961). Published isopach maps of
the Hawthorn Formation in northeast Florida (Freas,
1968), the Phosphoria Formation in the western United
States (Partridge, 1958), and structural (Youngquist,
1958) and isopach maps (Cheney and others, 1979) of the
Sechura phosphate deposits in Peru show that phos-phatic
sediments in these areas occupy structural posi-tions
similar to the situation found in North Carolina.
That is, the phosphorite is found in shallow marine
basins with relatively flat floors, which are located adja-cent
to structural highs and which have steeply sloping
floors on their seaward sides.
ORIGIN OF THE PUNGO RIVER
PHOSPHORITES
The phosphorites of the Pungo River Formation were
deposited in a restricted marine basin which had open
seaward access to a southward-flowing cool-water cur-rent.
Structural features that produced this restriction
were: (1) north-south trending hinge lines which bor-dered
the basin of phosphate deposition to the east and to
the west, and (2) east to northeast-trending structural
noses which formed the northern and southern bound-aries
of the basin (fig. 6).
The depth of water in the area of phosphate accumula-tion,
as interpreted from foraminifera, was about 100 to
200 meters. The clastic sedimentation rate was low to
moderate, and phosphate deposition probably took place
slowly. Abundant life was present, chiefly as planktonic
and nektonic forms. The rare remains of normal marine
benthos show that the bottom waters were periodically
non-toxic. The pH of these waters varied from near 7.0
to more than 7.8, as shown by the deposition of both
phosphate and calcite.
Currents upwelling from the deep ocean were the
source of supply of the phosphate and carbonate in the
17
Pungo River Formation. These currents were directed up-ward
by a steeply sloping sea floor, whose basinward tilt
was produced by flexure along a north-south trending
hinge line. Ascending waters, by decrease in the partial
pressure of C02 with decreasing depth, became enriched
in calcium phosphate until deposition of a thin blanket of
this material occurred on the steep slope. The phosphate
is thought to have accumulated in a colloidal form, and
was probably disseminated, in part, in the interstices of
arenaceous to argillaceous bottom sediments.
At the head of the steep seaward slope, the ascending
waters crossed the hinge line and spilled over into a rela-tively
flat shelf-like platform. This platform was tran-sected
by a series of small-scale noses and troughs whose
axes lay nearly normal to the hinge line. On this undula-tory
surface, colloidal phosphate was deposited in the
troughs, and carbonates were deposited on the high
areas.
Planktonic organisms, chiefly diatoms and radiolaria,
flourished in the waters of the trough areas and also in
the deeper waters east of the hinge line as a result of the
abundant nutrient supply afforded by the upwelling
waters. Upon death, these organisms settled to the sea
floor, where the remains of their protoplasm served as
the nucleii around which the colloidal phosphate ac-cumulated.
Active storm or bottom currents in the trough
areas aided in this concentration and produced the sub-oolitic
form of the phosphate pellets, as well as the
polished surface texture exhibited by both the phosphate
and its associated sand-sized quartz.
The general facies progression of sediments in the
Pungo River Formation, from shallow water basinward,
is: carbonate rocks; interbedded carbonates and phos-phatic
sands; phosphatic sands; interbedded phosphatic
sands and diatomaceous clays; and finally, diatomaceous
clays and chalky to algal limestones. The complex inter-bedding
of these rock types indicates that there were
fluctuations in water depth in the basin of deposition as a
result of a series of minor transgressions and regressions.
Interbedding is particularly complex in the area of high
phosphate concentration shown on figure 6.
The hinge lines that bound the high-phosphate basin
to the east and west appear to have been the primary
control in Pungo River phosphate deposition. Figure 8
hypothesizes downdropping of the ocean floor on the
basinward side of the west hinge line (labelled "active"
on the figure) steepening the seaward tilt of the relatively
flat area shown between the two hinge lines on the fig-ure.
Downdropping can take place on the basinward side
of either of the hinge lines shown, but figure 8 hypo-thesizes
movement only east of the up-basin or major
one. The easternmost, or down-basin, hinge line, labeled
"passive" on figure 8, appears to have moved concur-rently
with the major hinge line. This movement, how-ever,
is apparent, not real, and results from the geometry
of the figure. Because downdropping is in the form of
flexure, rather than fault-block movement on the sea
floor, shallow water conditions are created up-basin, and
coarse elastics and molluscan limestones are deposited
Phosphatic Sand
\~~Z-I
[
Diatomaceous Clay
|
I
,
I
\ Carbonate
Figure 8. Idealized cross section of a phosphorite basin,
showing downdropping on the downbasin side
of an active hinge line causing regression.
there. Phosphatic sands and diatomaceous clays are de-posited
in progressively deeper water. Primary phosphate
deposition occurs in the area of the easternmost hinge
line and just basinward of it. The entire effect is that of
regression.
Figure 9 shows the result if movement along the major
hinge line is the opposite of that described above— that is,
if the sea floor on the up-basin side of the "active" hinge
line is downdropped with respect to that on the down-basin
side. The area between the two hinge lines becomes
relatively flat, rather than having a tilt as shown on fig-ure
8. Primary phosphate accumulates over much of this
flat area. Recall that, regardless of which configuration
the major hinge line assumes, the basin between the
hinge lines is bounded to the north and south by struc-tural
highs that serve to restrict circulation and thereby
enhance phosphate concentration. In the structual con-figuration
shown on figure 9, diatomaceous clay, that
forms in a relatively deep-water environment, is found
shoreward of the down-basin or "passive" hinge line.
The entire effect is that of transgression, with deeper-water
facies occupying positions in the basin that were
receiving shallow-water deposits when the relative move-ment
along the hinge line was in the opposite sense. The
W
Active
•Hinge
Line
Passive I
Hinge i
Line |
Figure 9. Idealized cross section of a phosphorite basin,
showing downdropping on the upbasin side of
an active hinge line causing transgression.
18
sea may extend across the up-basin ("active") hinge line,
as shown on figure 9. Such a transgression accounts for
the outliers of Pungo River sediments west of the main
body of the Formation.
If the relative downward movement of the sea floor on
opposite sides of the "active" hinge line alternates, cyclic
transgression and regression result. Relative down-dropping
on the seaward side of the hinge line (fig. 8)
produces regression: transgression results from relative
downdropping of the up-basin side (fig. 9). If the reader
mentally combines, alternately, the situation shown on
these two figures, the result is to produce the cycles of
transgression and regression summarized by the facies
distribution on figure 7— that represents the general
three-dimensional distribution of rock types observed in
the Pungo River Formation.
The relationship between a hinge line and primary
phosphate deposition can be seen in certain other main
phosphorite deposits. Figure 10, taken from McKelvey
and others (1959), is a generalized cross section showing
facies distribution in the Phosphoria Formation and re-lated
rocks in the phosphate field of the western United
States. The abrupt westward steepening of the basin
floor is thought to represent a hinge line, in the approxi-mate
location as added to McKelvey's figure. Most of the
phosphate in the Phosphoria Formation is found in the
area of flexure of the basin floor or just seaward of it— in
a similar structural position to that occupied by the
Pungo River phosphate. Like the Pungo River deposits,
the phosphate of the Phosphoria Formation is chiefly pri-mary
phosphate. Figure 10 shows cyclic repetition of
rock types similar to those described from the Pungo
River Formation, except that the siliceous rocks of the
Phosphoria are largely chert while those of the Pungo
River are diatomaceous clays. The cycles of deposition,
the distribution of carbonates, argillaceous rocks, and
phosphatic sediments are in the same position, with re-spect
to the hinge line, as those in the Pungo River
Formation. The effect of, and the behavior of, the Phos-phoria
hinge line parallels that of the major Pungo River
hinge line.
CONCLUSIONS
From an analysis of lithologic, paleontologic, geo-physical,
and stratigraphic data, the following con-clusions
are drawn concerning the Pungo River Forma-tion:
1. All the early and middle Miocene rocks of North
Carolina fall within the range of rock types designated by
Kimrey (1964) as belonging to the Pungo River Forma-tion.
2. The top of the formation in the type core hole is 30
feet higher than the top proposed by Kimrey. The micro-
Southern
Idaho
Southeastern
Wyoming
Tfc----A-T-~ •
Phosphorite and
mudstone
Greenish grey
shale
C hugwoter Fm .
23
Red beds
Figure 10. Cross section of the Phosphoria formation showing relation of phosphorite and hinge line (modified
from McKelvey and others, 1959).
19
faunal and lithologic characteristics of this additional
30-foot section are identical with those of the upper part
of the Pungo River Formation.
3. The foraminifera recovered from the formation are
in part time-diagnostic and in part facies-controlled.
4. The relatively high natural radioactivity of the
phosphate in the formation produces a distinctive natural
gamma-ray log pattern, which can be used to identify the
unit in areas where lithologic control is lacking.
5. Most of the phosphate in the formation is primary,
and is the result of a combination of upwelling waters
and biologic activity.
6. The formation contains a rock suite which is typical
of that found with many other primary sedimentary
phosphorites. Lithologic, faunal, and geochemical criteria
show that the formation was deposited in a slightly re-stricted,
shallow-shelf marine environment of normal
salinity.
7. Structural features on the floor of the Pungo River
sea greatly affected sediment distribution in general, and
phosphate distribution in particular.
8. There is little evidence for a volcanic source of
either the phosphorous or the silica in the formation.
9. Upwelling deep-ocean waters were probably the
source of the Pungo River phosphate.
10. Steep sea-floor slopes, and the relatively flat areas at
their heads, both produced by movement along hinge
lines, were the main sites of primary Pungo River phos-phate
deposition.
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Lewis, D. W., Riggs, S. R., Snyder, S. W., and Waters, V.
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in Onslow Bay, continental shelf, North Carolina:
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355 p.
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1953, The Permian phosphorite deposits of the western
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de phosphates de chaux: 19th International
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section 11.
McKelvey, V. E., Williams, J. S., Sheldon, R. P. Cressman,
C. R., Cheney, T. M., and Swanson, R. W., 1959, The
Phosphoria, Park City and Shedhorn Formations in the
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Miller, J. A., 1980, Structural and sedimentary setting of
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States, Schedule and Abstracts, p. 11 (abstract).
Notholt, A. J. G., 1968, The stratigraphical and
geographical distribution of phosphate deposits in the
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on sources of mineral raw materials for the fertilizer in-dustry
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Omara, S., 1965, Phosphatic deposits in Syria and Safaga
District, Egypt: Economic Geology, v. 60, p. 214-227.
Partridge, J. F., Jr., 1958, Oil occurrence in Permian,
Pennsylvanian, and Mississippian rocks, Big Horn
Basin, Wyoming, p. 293-306 in Weeks, L. G., editor,
Habitat of oil — A symposium: Tulsa, Oklahoma,
American Association of Petroleum Geologists, 1364 p.
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21
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-
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22
EXPLANATORY NOTE 1
Base Map Numbering System
Borehole data points are located on the base map (plate
1) and are numbered consecutively from left to right and
from north to south within a county. The letter prefix
which precedes each well number indicates what type
well the control point represents. These designations,
which are used both on the base map and in the well
tables (Appendix A), are:
A — Auger Hole
C — Core Hole
OT - Oil Test Well
P - Producing Water Well
T — Test Hole, no coring
Due to space limitations, the county abbreviations
used in listing the wells in Appendix A were not used on
the base map. These abbreviations are:
Beaufort- BEA
Bertie - BER
Camden — CAM
Carteret- CAR
Chowan — CHO
Craven — CR
Currituck -CUR
Dare -DA
Gates — GA
Hertford -HE
Hyde-HY
Jones -JON
Martin -MAR
Onslow -ON
Pamlico -PAM
Pasquotank — PAS
Perquimans — PER
Pitt -PI
Washington — WAS
APPENDIX A
Stratigraphic and lithologic data for wells in the
Pungo River Formation and associated rocks
Well number: County prefixes are abbreviations, usually
the first two to three letters in the county
name. Letter preceding number shows
well type: A, auger hole; C, core hole;
OT, oil test; P, producing water well; T,
test well, no coring. Number is sequential
within a county.
Owner: Geophysical logs from wells listed as
"Kimrey's" were published in reduced
form by Kimrey (1965). The original, full
scale logs were used in preparation of this
report.
Location: Latitude figures are listed first, followed
by longitude.
Elevation: In feet above Mean Sea Level; m.p., meas-uring
point.
Middle All tops, thicknesses, and elevations are
Miocene data: given in feet; top and base figures are
given in feet below Mean Sea Level.
Underlying PBe — Paleocene, Beaufort Formation
formation: ESab - Rocks of Sabine Age
ECh — Eocene, Castle Hayne Formation
Ol — Rocks of Oligocene Age
Lithology: Components are expressed in feet of
thickness of each, and as a percentage of
the total formation.
Type of E — Electric Log
control: G - Gamma Log
L — Lithologic Log
P — Paleontologic Information
23
Appendix A. Stratigraphic and lithologic data for wells in the Pungo River Formation and associated rocks.
Well
Number
Owner Location Eleva-tion
Middle Miocene
Top Base Thick-
(MSL) (MSL) ness
Under
lying
fm.
Pur goRiver Lith slogy
County S
Th.
and
% Th
Clay
%
Carl
Th.
jonate
%
Type of
Control
BEA-C-1 USGS, C7-63 35°41'50'
76°39'35'
11 165 211 46 Ech 31 67 8 17 7 16 EGLP
BEA-C-2 USGS, C5-o3 35°41T5
76°45T0'
20 128 150 22 Ech 9 41 9 41 4 18 EGL
BEA-C-3 USGS, C6-63 35°39'45'
76°40'50'
12 164 204 40 Ech 30 75 10
1
25 EGLP
BEA-C-4 USGS, C8-63 35°39'15'
76°36'15'
8 196 232 36 Ech 14 39 10 28 12 33 EGLP
BEA-OT-5 Coastal Plains,
West Dismal #1
35°39'00'
76°48'10'
35 105 115 10 Ech EL
BEA-OT-6 Coastal Plains,
H.M. Jackson #1
35°38'15'
7b°5lT5'
40 65 90 25 Ech EL
BEA-T-7 Washington, TW
#1, 1963
35°36'45
77°08'15'
25 20 27 7 Ech 7 100 E
BEA-C-8 USGS, C9-63 35°36'40'
75°51'50'
40 78 91 13 Ech 3 38 3 24 5 38 EGL
BEA-T-9 USGS, Swindell
Test Well
35°36'45'
76°41'55'
12 118 176 58 Ech 31 53 27 47 EGLP
BEA-OT-10 Coastal Plains,
Z. Ratcliff #1
35°35'45'
7o°48'10'
15 110 135 25 Ech EL
BEA-C-11 USGS, C4-03 35°35'20'
7o°47'30'
16 10« 137 28 Ech 14 50 22 8 28 EGL
BEA-P-12 Kimrey's
PI-6-G
35°35'10'
76°45'45'
17 119 146 27 Ech G
BEA-P-13 Kimrey's
PA-13 G
35°36'05'
76°40'20'
8 le>6 220 54 Ech G
BEA-C-14 USGS, C7-62 35°35'58' 10 183 2o4 81 Ech 47 58 21 20 13 16 EGLP
H
u.
BEA-P-15
(Type Pungo River)
Kimrey's
76°34'59'
35°34'55' 27 81 109 28 Ech G
PI-7-G 76°50'35'
BEA-OT-lo Coastal Plains, 35°33'45' 23 91 140 49 Ech EL
<
UJ
CO
Rodman #2 76°45'35'
BEA-P-17 Kimrey's
BE-4-G
35°34'10'
76°31T2'
4 181 >100 G
BEA-T-18 Washington, TW 35°33'20' 25 ABSENT ELP
#2, 1«63 77°01'25'
BEA-P-lo Kimrey's
PA-20-G
35°33'40'
7o°42'00'
10 130 178 48 Ech G
BEA-T-20 NCWRD, Belhaven
Test Well
35°33'20'
76°37'20'
3 142 229 87 Ech G
BEA-P-21 Kimrey's
BE-7-G
35°33'20'
76°35'30'
4 152 257 105 Ech G
BEA-P-22 Kimrey's
PI-18-G
35°32'45'
76°51'45
25 65 85 20 Ech G
BEA-OT-23 Coastal Plains,
Rodman #1
35°32'45'
76°46'45'
16 "9 146 47 Ech EL
BEA-P-24 Kimrey's 35°32'05' 33 00 > 8 G
BEA-C-25
BU-2-G
USGS, C2-o2
76°56'15'
35°32'15'
76°49'55'
16 80 >33 EGL
BEA-P-20 Kimrey's
PA-25-G
35°32'20'
7o°43'45'
11 109 175 06 Ech G
BEA-C-27 USGS, C4-62 35°32'20' 6 128 101 63 Ech 45 71 8 13 10 lo EGL
BEA-C-28 TGS-NCP, #7
76°41'15'
35°30'30' m . p
.
ABSENT EGLP
77°01'20' 7
BEA-C-20 USGS, ClO-63 35°30'15'
76°57'30'
10 38 44 6 Ech 100 EGL
BEA-P-30 Kimrey's
BU-9-G
35°30'15'
7o°55'50'
lo 42 52 10 Ech G
BEA-P-31 Kimrey's
PI-33-G
35°30'20'
76°49'25'
17 75 108 33 Ech G
24
Appendix A. Stratigraphic and lithologic data for wells in the Pungo River Formation and associated rocks.
Well
Number
Owner Location Eleva-tion
Middle Miocene
Top Base Thick-
(MSL) (MSL) ness
Under
lying
fm.
Pun go River Lith<Dlogy
County Sand
Th. %
Clay
Th. %
Carbonate
Th. %
Type of
Control
BEA-P-32 Kimrey's 35°30'15' 12 104 162 58 Ech G
BEA-C-33
PA-33-G
USGS, C8-62
76°44'20'
35°30'30' 3 147 237 00 Ech 68 76 18 20 4 4 ECLP
76°38'20'
BEA-P-34 Kimrey's 35°29'15' 18 66 98 32 Ech G
BEA-C-35
BA-4-G
TGS-NCP, #2
76°52T5'
35°29'00' m.p. ABSENT EGLP
76°59'28' 6
BEA-P-36 Kimrey's
BB-3-G
35°28'50'
76°55'55'
4 40 48 8 Ech G
BEA-T-37 NCWRD, B
Test Well
ath 35°29'05'
76°47'30'
15 80 127 47 Ech 32 68 15 32 EGLP
BEA-P-38 Kimrey's
RA-7-G
35°29'00'
76°38'10'
9 143 231 88 Ech G
BEA-C-39 USGS, C5-(52 35°28'25'
76°40'47'
6 138 >67 EGL
BEA-C-40 TGS-NCP, #1 35°27'37' m.p. ABSENT EGLP
76°57'32' 6
BEA-P-41 Kimrey's
BA-13-G
35°27'00'
76°49'55'
17 59 109 50 Ech G
BEA-P-42 Kimrey's
RA-17-G
35°27'50' 7 129 189 bO Ech G
BEA-C-43 TGS-NCP, #3 35°26'41'
76°54'10'
m.p.
6
53 08 15 Ech 6 40 9 60 EGL
BEA-T-44 Kimrey's
BA-16-GR
35°2o'15'
76°47'30'
8 82 138 56 Ech EG
H BEA-C-45 USGS, Cll -62 35°2o'00' 3 149 253 104 Ech 64 62 35 34 5 4 EGL
BEA-P-46 Kimrey's
76°37'25'
35°25'00' 12 42 56 14 Ech G
<
LU
PQ
BEA-P-47
BB-6-G
Kimrey's
76°57'00'
35°25'50' 35 53 69 16 Ech G
BEA-C-48
BB-5-G
FMC, E-l
76°53'50'
35°24'30' m.p. 102 185 83 Ech G
76°42'00'
BEA-P-49 Kimrey's
BB-10-G
35°23'45'
76°56'50'
30 44 50 6 Ech G
BEA-T-50 Kimrey's
BA-19-GR
35°24'05'
76°50'00'
10 72 114 42 Ech G
BEA-C-51 USGS, C9-62 35°24'20' 12 155 229 74 Ech 50 67 2 3 22 30 EGL
BEA-C-52 USGS, ClO -62
76°38'50'
35°23'45' 4 150 >119 Ech EGL
BEA-T-53 NCWRD, L
Creek TW
ee
76°36'10'
35°22'45'
76°46'05'
10 80 142 62 Ech 37 o0 10 16 15 24 EGL
BEA-P-54 Kimrey's
BB-ll-G
35°22'50'
76°59'25'
30 26 34 8 Ech G
BEA-T-55 Kimrey's
AU-8-GR
35°21T5'
76°52T5'
30 73 101 28 Ech EG
BEA-T-56 Kimrey's
AU-2-GR
35°22'25'
76°49'30'
13 73 125 52 Ech EG
BEA-T-57 Kimrey's
SC-5-GR
35°20'47'
76°43'00'
5 90 197 107 Ech EG
BEA-P-58 Kimrey's
Ed-2-G
35°20'30'
76°58'45'
30 38 46 8 Ech G
f
BEA-T-59 Kimrey's
AU-14-GR
35°20'10'
76°49'50'
14 78 >52 EG
BEA-T-60 Kimrey's
AU-12-GR
35°20'15'
76°46'55'
11 Ol 159 08 Ech EG
BEA-C-61 USGS, Cll -63 35°lo'45'
76°40'00'
3 113 253 140 Ech 52 37 58 41 30 j n EGLP
25
Appendix A. Stratigraphic and lithologic data for wells in the Pungo River Formation and associated rocks.
Well Owner Location Eleva-
Middle M
Top Base
ocene
Thick-
Under
lying
Pungo River Lith Dlogy
County s and Clay Carbonate Type of
Number tion (MSL) (MSL) ness fm. Th. % Th. % Th. % Control
BEA-T-62 Kimrey's
AU-20-GR
35'
76
>19'25'
>51'50'
15 57 115 58 Ech EG
BEA-T-63 Kimrey's
SC-ll-GR
35
76
5 19'40'
>43'30'
Q 99 206 107 Ech EG
BEA-P-64 Kimrey's
ED-9-C
35
76
'19'10'
5 54'00'
32 50 92 42 Ech
1
G
BEA-T-65 Aurora Test
Well
35
76
>18'10'
> 47'20'
10 94 170 76 Ech 30 40 30 40 16 20 EGLP
BEA-P-66 Kimrey's
ED-ll-G
35
76
>17'45'
'53T5'
37 53 107 54 Ech G
H BEA-P-67 Kimrey's 35 J 18'10' 9 99 217 118 Ech G
u.
SC-13-G 76 5 44'35'
BEA-T-68 Kimrey's 35 >17'15' q 107 >114 EG
D SC-16-GR 76 '42'45'
<
|
i
]
BEA-P-69 Kimrey's 35 >18'35' 4 128 268 140 Ech G
CO SC-12-G 76 >39'05'
BEA-T-70 Kimrey's
AU-43-GR
35
76
>17'00'
5 51'35'
55 66 131 65 Ech EG
BEA-C-71 USGS, C13-63 35
7b
>16'45'
>40'00'
3 113 253 140 Ech 52 37 58 41 30 22 EGLP
BEA-P-72 Kimrey's
AU-49-G
35
76
'16'35'
5 49'00'
14 7b 162 86 Ech G
BEA-P-73 Kimrey's
AU-56-G
35
76
'16'00'
>46'45'
b 90 190 100 Ech G
BEA-C-74 USGS, C12-63 35
76
'13'SO'
> 46'50'
12 99 198 99 Ech 52 53 32 32 15 15 EGLP
BER-P-1 Town of 36 c 13'30' 35 ABSENT E
Aulander 76''46'36'
BER-P-2 C.L. Watford,
Trap
36'
76 c
'13'10'
51'30'
DO 46 61 15 PBe GLP
BER-P-3 R.L. Perry,
Goose Pond
36'
76'
'11'40'
46'30'
70 88 121 33 PBe 8 24 25 76 EGL
uu BER-P-4 Graham Pierce 3b' lO'OO' 05 93 126 33 ESab 8 24 25 76 G
H 76 c 46'35'
uu BER-P-5 Town of 36''07'SO' 95 ABSENT E
DQ Lewiston 77 c 10'15'
BER-P-6 White's
Crossroads
36 c
76 c
'08'15'
51'45'
45 94 116 2 PBe G
BER-P-8 Town of 35 c 59'40' 46 ABSENT E
Windsor 76 c 57'00'
BER-P-8 Avoca Farms,
Merry Hill
35'
76'
58'20'
'43'10'
15 152 157 5 Ech 5 EGLP
2
uu
Q CAM-OT-1 E.F. Blair, 36 c 24'40' m.p. 3o0 525 165 Ech 15 9 150 91 EGLP
<u
Weyerhauser #1 76 c 10'30' 16
CAR-OT-1 Carolina Pet.,
D.L. Phillips #1
34'
76'
'58'50'
'39'00'
m.p.
12
116 238 122 01 ELP
H CAR-OT-2 Carolina Pet., 34''58'45' m.p. 114 229 115 01 ELP
uu
J. Wallace #1 76''38'00' 13
uu
H
<
U
CAR-C-3 C-194 34''ss'so' 5 95 194 PQ 01 56 57 38 38 5 5 EGLP
76'! 36'40'
CAR-OT-4 Carolina Pet., 34''57'05' m.p. 118 227 109 ol EL
G. Carraway #1 76'! 38'30' 16
CAR-C-5 C-193 34'
76<
'55'30'
>38'50'
5 95 167 72 01 52 72 20 28 GLP
26
Appendix A. Stratigraphic and lithologic data for wells in the Pungo River Formation and associated rocks.
Well Owner Lo cation Eleva
Middle M
Top Base
ocene
Thick-
Under
lying
Pur goRiver Lith ology
County S and Clay Carb onate Type of
Number tion (MSL) (MSL) ness fm. Th. % Th % Th. % Control
CAR-OT-6 Coastal Plains,
G.P. Yeatman #1
34'
76'
>54'30"
>37'30"
m.p,
20
108 178 70 01 ELP
CAR-OT-7 Coastal Plains,
Bayland Corp. #1
34'
76'
> 53'55"
>22'00'
m.p.
18
214 304 90 01 61 68 19 21 10 11 ELP
CAR-C-8 C-191 34"
76'
>49'20"
>52'55"
30 17 36 19 01 15 79 4 21 LP
CAR-C-9 C-190 34'
76'
'48'00"
>45'4o"
15 58 127 69 ol 54 73 15 27 EGLP
CAR-C-10 C-198 34'
76'
>47'25"
>33'30"
5 124 263 139 ol 42 31 45 32 52 37 GLP
CAR-P-11 Town of
Newport
34'
76'
>47T0"
>51'30"
20 40 56 16 01 11 69 5 31 GL
CAR-C-12 C-192 34'>47'00" 10 84 202 118 ol 70 59 25 21 23 20 EGLP
H 76'>37'35"
CAR-C-13 C-179 34''45'45" 30 1 24 23 ol 19 83 4 GLP
UJ
77 c>04'25"
CAR-T-14 C-175 34'•45'40" 35 19 39 20 ol 13 65 7 35 GL
es 76'>55'45"
<U
CAR-C-15 C-195 34'>46'25" 15 45 116 71 ol 46 65 10 14 15 21 EGLP
76'•45'55"
CAR-OT-16 F.M. Karston, 34''45'40" m.p. 45 116 71 ol ELP
Laughton #1 76'> 43'30" 19
CAR-C-17 C-178 34'
77 (
>44'00"
>03'25"
30 14 30 16 ol 11 69 5 31 GLP
CAR-OT-18 Coastal Plains, 34'•43'50" m.p. 128 252 124 ol 49 39 47 38 28 23 ELP
Huntley-Davis #1 76'>34'30" 20
CAR-P-19 Sea Hawk Motel 34<
76'
'41'50"
>43'50"
15 104 179 75 ol E
CAR-T-20 Ft. Macon Test
Well
34'
76'
>41'40"
>41'00"
10 103 176 73 ol 42 57 31 43 EGL
CAR-P-21 Cape Lookout
USCG Station
34'
76'
! 36'00"
'32'20"
6 183 336 153 01 GP
CHO-T-1 USGS, Gliden
Test Well
36'
76'
>19'00"
>37'15"
36 181 216 35 PBe 26 84 5 16 GLP
CHO-P-2 Isaac Bryan 36<
76'
'17'50"
'37'35"
28 183 224 41 PBe G
CHO-P-3 W.T. Byrum 36'
76'
'16'00"
'37'30"
27 183 217 34 PBe 10 29 24 71 G
CHO-P-4 IB. Hollowell 36'
76'
'13'32"
>39'25"
31 163 203 40 ESab 11 27 29 73 G
CHO-P-5 J.I. Boyce 36'13'10" 48 184 224 40 ESab 22 55 18 45 G
76'>36'40"
z CHO-P-6 J.R. Peele 36 >11'20" 23 125 155 30 ESab 9 30 21 70 G
<
Iu
76 >42'25"
CHO-T-7 USGS, Valhalla 36 5 08'30" 34 146 187 41 ESab 14 34 27 66 EGLP
Test Well 76 5 39'15"
CHO-P-8 C.H. Small 35 3 05'15' 22 156 170 14 ESab 14 100 G
76 D 39'45"
CHO-P-9 Town of
Edenton
36'
76'
5 04'15"
'35'55"
15 169 189 20 Ech 20 100 G
CHO-P-10 Austin Company 36'
76
> 03'40"
'34'15"
14 214 228 14 Ech 14 100 G
f
CHO-P-11 C.L. Parker 36
76
>04'15"
5 31'30"
14 243 252 Ech 100 G
CHO-P-12 USDI, Fish
Hatchery
36
76
'03'30"
5 38'40"
15 167 183 16 Ech lo 100 EGL
CHO-T-13 USGS, Air Base
Test Well
36
76
'Ol'lS"
> 33'45"
15 201 213 12 Ech 12 100 EGL
27
Appendix A. Stratigraphic and lithologic data for wells in the Pungo River Formation and associated rocks.
Well Owner Location Eleva-
Middle Miocene
Top Base Thick-
Under
lying
Pur goRiver Lithology
County s and Clay Carbonate Type of
Number tion (MSL) (MSL) ness fm. Th. % Th % Th. % Control
CR-T-1 USGS, Wilmar
Test well
35°23'15'
77°10'15
50 ABSENT EGLP
CR-A-2 USGS, A48-62 35°17'45'
76°57'05'
40 ABSENT LP
CR-A-3 USGS, A46-62 35°17'00'
77°00T5'
35 45 70 25 01
I
LP
CR-P-4 Kimrey's
ED-15-G
35°16'25'
76°58'10'
25 43 53 10 01 G
CR-A-5 USGS, A47-62 35°15'20'
77°00'40'
30 ABSENT LP
CR-A-6 USGS, A51-62 35°15'30'
76°54'20'
45 25 77 52 01 LP
CR-A-7 USGS, A49-&2 35°14'30'
76°59'00'
25 ABSENT LP
CR-T-8 USGS, Street's
Ferry TW
35°12'40'
77°09'10'
23 ABSENT EGP
CR-A-9 USGS, A50-62 35°12'15'
77°02'00'
35 ABSENT LP
CR-A-10 USGS, A52-62 35°12'45'
76°57'05'
25 ABSENT LP
CR-A-11 USGS, A5-63 35°12'00'
76°59T5'
35 3 >2 LP
CR-A-12 USGS, A55-62 36°10'15'
76°00'15'
25 ABSENT LP
2
UJ
CR-T-13 USGS, New Bern 35°08'15' 27 ABSENT GLP
Test Well 77°06'20'
><
04
CR-A-14 USGS, A53-62 35°07'30' 15 ABSENT LP
76°59'40'
U CR-T-15
CR-T-16
CR-T-17
USGS, Fields
C-187
Weyerhauser,
Test Well #3
35°06'30'
77°08'50'
35°00'20'
77°04'00'
34°57'00'
77°02'25'
30
20
37
ABSENT
ABSENT
ABSENT
EGL
GLP
EG
CR-P-18 Cherry Point,
MEMQ
34°5oT0'
76°53'30'
25 43 97 54 ol 21 39 33 61 G
CR-C-19 C-197 34°56'45'
76°40'50'
10 71 125 54 ol 32 59 22 41 GLP
CR-T-20 Weyerhauser,
Test Well #2
34°55'40'
77°05'15'
38 >6 18 24 ol 4 17 20 83 ELP
CR-T-21 C-186 34°55'35'
77°00'30'
35 15 40 25 ol 10 40 10 40 5 20 LP
CR-T-22 C-184 34°54'25
77°0e'05'
30 ABSENT GLP
CR-T-23 C-188 34°54'30'
76°48'00'
28 46 121 75 ol 66 88 9 12 LP
CR-C-24 C-196 34°54'45'
76°43'45'
15 66 llo 50 ol 44 88 5 10 1 2 GLP
CR-C-25 C-180 34°51'40'
77°03'10'
30 4 21 17 ol 12 71 5 2 Q GLP
CR-A-26 USGS, A66-62 34°52'15'
76°51'25'
20 55 85 30 ol LP
CR-OT-27 Great Lakes,
C. Bryan #1
34°50'55'
76°57'45'
m. p
.
41
29 83 54 ol 54 100 ELP
CR-T-28 C-189 34°50'50'
7b°47'00'
18 40 98 58 ol 53 92 5 8 EGLP
28
Appendix A. Stratigraphic and lithologic data for wells in the Pungo River Formation and associated rocks.
Well Owner Location Eleva-
Middle Miocene
Top Base Thick-
Under
lying
Pungo River Lithology
County S ,ui d C ay Carbonate Type of
Number tion (MSL) (MSL) ness fm. Th. % Th. % Th. % Control
u CUR-OT-1 E.F. Blair, 36 c 18'10" m.p. 561 750 189 Ech 20 11 169 89 EGLP
H Twiford #1 70 c 55'30" 12
GL CUR-OT-2 Rapp Oil Co., 36 c 06'45" m.p. 838 >273 Ech EG
Kellogg #1 76 c 50'50" 17
u
DA-OT-1 Mobile Oil. Co.,
State Lease #1
35'
75'
>59'55"
>52'00"
m.p.
24
396 866 470 Ech 16 3 417 89 37 8 EGLP
DA-OT-2 Rapp Oil Co.,
Ethridge #1
35'
75'
, 56'00"
>41'35"
m.p.
26
558 1036 478 01 EG
DA-OT-3 E.F. Blair,
M. Collins #1
35<
75'
, 53'00"
>40'15"
m.p.
13
621 1076 455 01 389 85 66 15 EGLP
UJ DA-OT-4 E.F. Blair, 35'>51'50" m.p. 522 807 285 Ech 157 57 118 41 10 2 EGLP
6& <
D
W. Va. P&P #1 75'>55'30" 11
DA-OT-5 Std. Oil of NJ 35'»42'12" m.p. e.oo 1251 552 01 120 22 432 78 ELP
N.C. Esso #2 76'>35'54" 21
DA-OT-6 Rapp Oil Co.,
L. Twiford #1
35'
75'
>42'00"
>46'36"
m.p.
13
582 079 397 01 61 15 33o 85 EGL
DA-OT-7 Mobil Oil Co.,
State Lease #2
35'
75'
>26'20"
>34'35"
m.p.
24
350 1301 942 01 511 54 180 19 251 27 EGLP
DA-OT-8 Std. Oil of NJ
Hatteras Lt. #1
35'
75'
>42'12"
'35'54'
m.p.
25
391 1360 969 01 707 73 50 5 212 22 ELP
GA-T-1 C-164 36'
76'
'31 '00'
'45'10'
55 115 135 20 PBe 14 70 6 30 GL
GA-P-2 Kittrell Farm 3 b
76
'31'30'
'36'00"
42 17o 222 46 PBe 4o 100 G
UJ
GA-P-3 Holly Grove 36 '30'35' 41 221 261 40 PBe 40 100 G
Texaco 76 '34'20'
< GA-P-4 Buckland School 36 '28'30" 25 121 154 33 PBe G
76 '45'50'
GA-P-5 Town of Roduco 36 '27'45' 30 8^ 120 31 PBe 26 84 5 16 GLP
76 '48'35'
GA-T-o C-165 36
76
'2o'15'
'50'40'
25 55 93 38 PBe 17 45 20 53 1 2 LP
GA-T-7 Prison Farm 3d
7o
'25'35'
>43'25'
30 129 158 29 PBe 29 100 GL
HE-P-1 [?,] Como, N.C 36 '28'55' 30 ABSENT G
77 '00'50'
HE-P-2 Town of Winton 36 '23'45' 30 ABSENT G
76 '55'30'
u. HE-P-3 Ahoskie Prison 36 '19'25' 55 ABSENT EL
Farm 77 '01'15'
UJ
X HE-P-4 L. Basemore 36 '10'15' 25 89 108 19 PBe 10 53 o 47 GL
76 '50'10'
HE-T-5 C-161 3d 'ls^s' 65 ABSENT L
77 '01'30'
29
Appendix A. Stratigraphic and lithologic data for wells in the Pungo River Formation and associated rocks.
Well
Number
Owner Location Eleva
tion
Middle Miocene
Top Base Thick-
(MSL) (MSL) ness
Under
lying
fm.
Pungo River Lithology
County S
Th.
and
%
Clay
Th. %
Carb
Th.
onate
%
Type of
Control
HY-C-1 C-204 35°39'00"
76°18'30"
5 415 >44 GP
HY-C-2 Nash Core Hole 35°37'30"
76°21'45"
7 360 425 65 Ech 37 57 15 23 13 20 L
HY-T-3 Upchurch, Test
Hole #1
35°33T0"
76°25'30"
12 234 382 148 Ech 45 30 103
'
70 EGLP
HY-OT-4 Coastal Plains,
Ballance #1
35°33'50"
76°09'00"
10 360 630 270 Ech 90 33 30 12 150 55 LP
HY-OT-5 Coastal Plains,
J.L. Simmons #1
35°32'00"
76°18'00"
5 285 485 200 Ech LP
HY-OT-6 Coastal Plains,
Holton #1
35°32'50"
7b°13'20"
5 320 565 245 Ech 30 12 200 82 15 6 LP
HY-T-7 W.E. Bishop, 35°29'50" 5 241 370 129 Ech 74 57 53 41 2 2 GL
UJ TGS Test Well 76°27T0"
D
>-
X
HY-OT-8 Coastal Plains, 35°2Q'20" 5 315 480 lb5 Ech 27 16 125 76 13 8 LP
J.L. Simmons #2 76°19'00"
HY-T-9 Upchurch, Test
Hole #2
35°28'35"
76°21'30"
6 289 >170 LP
HY-C-10 C-203 35°28'05"
76°26'25"
5 230 373 143 Ech 81 57 48 43 GLP
HY-OT-11 Coastal Plains,
Swindell #1
35°27T5"
76°14'55"
5 3«0 590 200 Ech 20 10 170 85 10 5 LP
HY-OT-12 E.F. Blair,
O. Ballance #1
35°27'25"
76°01'50"
m.p.
10
478 762 284 01 60 21 163 57 61 22 EGLP
HY-T-13 FMC, Asparagus
Point Test Well
35°26'30"
76°32'40"
5 185 >100 EGLP
HY-OT-14 Mobile Oil Co.,
State Lease #3
35°18'25"
75°49'45"
m.p.
24
301 995 694 01 399 58 60 8 235 34 EGLP
HY-T-15 Ocracoke, NPS
Test Well
35°04'30"
76°00'05"
5 384 755 371 Ol 65 17 122 33 184 50 GP
JON-P-1 Oak Grove NAF 35°01'45" 25 ABSENT L
77°15'00"
ION-A-2 USGS, A57-62 35°01'50" 20 ABSENT LP
77°06'20"
UJ
Z
JON-T-3 Maysville Test 34°54'35" 35 ABSENT EL
Well 77°13'30"
JON-T-4 C-183 34°53'35" 30 >10 >1 9 ol 1 11 8 8Q LP
*~^ 77°09'25"
JON-C-5 C-182 34°49'00" 25 ABSENT L
77°10'55"
JON-C-6 C-181 34°48'35"
77°05'25"
25 11 25 14 ol 4 29 10 71 GLP
MAR-P-1 Williamston, 35°51'20" 60 ABSENT EL
Church Street 77°03'50"
2
H
Cs5
MAR-A-2 Cherry Well,
James ville
35°49'20"
76°51'45"
35 85 100 15 Ech 15 100 LP
MAR-A-3 USGS, A24 35°48'20" 35 ABSENT LP
< 76°59'55"
2 MAR-A-4 USGS, A30 35°47'le>"
76°54'00"
30 47 67 20 Ech P
MAR-A-5 USGS, All 35°45'45" 35 ABSENT LP
7°55'40"
30
Appendix A. Stratigraphic and lithologic data for wells in the Pungo River Formation and associated rocks.
Well Owner Location Eleva
Middle Miocene
Top Base Thick-
Under
lying
Pur go River Lith ology
County s and C ay Carbonate Type of
Number tion (MSL) (MSL) ness fm. Th. % Th. % Th. % Control
z
MAR-A-6 USGS, A25 35 5 43'35' 30 ABSENT LP
76 >57'45'
H
<
MAR-T-7 USGS, T2-61 35 >42'35' 36 60 69 9 Ech 9 100 EL
76 5 52'30'
£ MAR-A-8 USGS, A26 35
76
5 41T5'
>59'10'
40 15 30 15 Ech LP
ON-OT-1 E.T. Burton, 34 >51'45' m.p. ABSENT EL
B.P. Seay #2 77 >24'45' 32
ON-T-2 Jacksonville, 34 >48'25' 30 >22 >13 9 01 9 100 EL
TW #2 (1957) 77 5 27T0'
ON-T-3 Jacksonville, 34'>47'10' 25 ABSENT EL
U1
Z TW #2 (1962) 77 <'28'15'
ON-T-4 Jacksonville, 34'>47'10' 30 ABSENT E
TW #1 (1957) 77 <>25'40'
ON-T-5 Bear Island, 34'>40'45' 15 ABSEr LP
N.C. Park Ser. 77 <>06'45'
PAM-T-1 Potter Test
Well, TGS
35'
76'
'le>'35'
'32'20'
5 215 338 123 Ech 65 52 60 48 GLP
PAM-C-2 Davidson, D7 35'
76'
>13'30'
>56'30'
25 50 76 26 Ech LP
PAM-T-3 TGS, Test Well
#69
35'
76'
'13'00'
>51'30'
35 65 134 69 Ech EG
PAM-P-4 Clyde Jones 35'
76'
>12'05'
'38'15'
10 152 >32 G
PAM-T-5 Upchurch, Jones
Island Test
35'
76'
'12'05'
5 31'40'
2 212 >38 G
PAM-C-6 Davidson, Dl 35
76"
J 10'55'
'ss^o'
35 50 69 19 Ech 15 79 4 21 LP
PAM-P-7 T. Bennett 35''10'05' 20 74 183 109 Ech 35 32 48 44 26 24 G
76''50'10'
y~ PAM-C-8 Davidson, D2 35'5 09'50' 30 68 96 28 Ech 17 61 9 32 2 7 LP
76''SS'IS'
2 PAM-C-9 Alpine, Hole 35''08'55' 3 122 235 113 Ech 43 38 45 40 25 22 L < #3 76''42'15'
PAM-P-10 Cheverolet Co.,
Bayboro
35'
76'
'08'20'
J 46'40'
15 76 179 103 Ech G
PAM-C-11 Alpine, Hole
#1
35'
7b'
'OS'IO'
, 44'40'
5 91 187 96 Ech 36 38 10 10 50 52 L
PAM-C-12 Taylor Lbr. Co.
Hole #1
35'
76'
'07'25'
, 42'05'
5 119 227 108 Ech GL
PAM-C-13 P-200 35'
76'
'06'SO'
) 37'45'
5 106 >104 GLP
PAM-P-14 E. Edwards 35'
76
>05'55'
'42'45'
10 102 210 108 Ech 74 08 18 17 16 15 GLP
PAM-OT-15 Carolina Pet., 35 '05T0' m.p. 110 212 102 01 EL
Linley #1 76 J 42'00' 16
PAM-OT-1 6 Carolina Pet.,
Plywood #1
35
76
5 05T5'
5 40'35'
m.p.
17
142 234 92 01 50 53 42 47 EL
31
Appendix A. Stratigraphic and lithologic data for wells in the Pungo River Formation and associated rocks.
Well Owner Location Eleva-
Middle M
Top Base
ocene
Thick-
Under
lying
Pur go River Lith ology
County Sand C ay Carbonate Type of
Number tion (MSL) (MSL) ness fm. Th. % Th. % Th. % Control
PAM-OT-17 Carolina Pet., 35 c 04'35' m.p. 155 260 105 01 65 62 25 24 15 14 ELP
Pulpwood #1 76 c 39'00" 12
PAM-T-18 Town of
Arapahoe
35 c
76 c
02'50"
48'00"
20 71 138 b7 Ech G
PAM-C-19 P-201 35 c 03'15' 6 96 226 130 01 109 77 30 , 21 3 2 GLP
y 76 c 41/15"
<
Cm
PAM-C-20 Alpine, Hole 35' 02'10' 5 100 223 114 01 41 36 63 55 10 9 L
#7 76 c 40'25'
PAM-C-21 C-199 34 c 58'35" 25 51 119 68 01 41 60 27 40 GLP
76 c 49'30'
PAM-C-22 Alpine, Hole
#6
34 c
76 c
58'30"
47'10'
6 41 130 80 01 46 52 32 36 11 12 L
Z PAS-T-1 R.F. Hewitt, 3b c 2 7 '00' 15 205 325 30 Ech 25 83 5 17 G
< Test Well 76 c 27'15'
o
o
PAS-T-2 USGS, Tl-62 36' 26'15' 14 306 346 40 Ech 13 32 27 68 EGLP
76 c 24'45'
PAS-T-3 USGS, T2-62 36' 12'00' 10 410 456 46 Ech 12 26 34 74 EL
IT) <
C«
76 c 14'05'
PER-P-1 N. Riddick 36<
7o<
'21'00'
> 27'00'
15 270 323 53 PBe 22 41 31 50 G
z<
o
PER-P-2 C. Chappel 36<>17'30' 51 205 251 46 PBe 18 41 28 50 G
76 ) 33'20'
PER-P-3 J. Winslow 36 5 15'00' 15 243 291 48 Ech G
76 '2915'
PER-P-4 F. Winslow 36 5 13'50' 5 247 295 48 Ech 16 33 32 67 G
76 '29'40'
PER-P-5 T. Harrell 3b
76
'll'SO'
'34'30'
15 201 248 47 ESab 24 51 23 49 G
PER-P-6 Town of
Hertford
36
76
'11'25'
J 28'30'
15 249 293 44 Ech q 20 35 80 E
PI-P-1 VOA, Blackjack 35 >30'05' 45 ABSENT EL
t- 77 3 14'00'
WAS-T-1 WA-1 35
76
3 5e.'15'
5 38'15'
10 169 190 21 Ech 5 24 16 76 GLP
WAS-T-2 W-206 35
76
5 5b'15'
5 35'55'
10 180 208 22 Ech 22 100 GLP
WAS-T-3 WA-4 35
76
3 55'50'
5 29'35'
10 225 268 43 Ech 7 16 32 74 4 10 GLP
Zo
u
WAS-T-4 WA-3 35 5 54'30' 12 233 253 20 Ech G
76 3 32'20'
WAS-T-5 WA-7 35 >53'30