ABSTRACT
Michael John Kirkland. PETROLOGY AND DIAGENESIS OF SANDSTONES OF THE
BLUEFIELD FORMATION (UPPER MISSISSIPPIAN), SOUTHEAST WEST VIRGINIA.
(Supervising Professor, Dr. Donald W. Neal), Department of Geology,
December, 1985.
The Bluefield Formation comprises interbedded shales, limestones
and sandstones representing deposition transitional between marine
carbonates and shallow marine to deltaic siliclclastics. Bluefield
sandstones vary lithologically from relatively coarse-grained, clean,
and orthoquartzltic (up to 95.0% quartz) to very fine-grained, matrix-
and rock fragment-rich (as low as 41.0% quartz) varieties. In this
study, sandstones are subdivided into two groups: Type 1, which are
very fine-grained and argillaceous; and Type 2, which are
coarse-grained, clean, and quartzitic.
Diagenetic alteration of Type 1 sandstones was dominated by
mechanical compaction. Quartz authigenesis, accompanied by
intergranular pressure solution, was the principal diagenetic process in
Type 2 sands. Minor secondary porosity is present in Type 1 sands.
Type 2 sandstones contain small amounts of both primary and secondary
porosity.
The lower part of the Bluefield Formation consists of marine
limestones, calcareous shales and thin, carbonate-cemented shelf sands
deposited in a shallow marine setting. The Droop Sandstone, located
approximately at the boundary between the upper and lower Bluefield, was
deposited as a prograding barrier island complex. Upper Bluefield
strata were deposited in a prograding delta.
PETROLOGY AND DIAGENESIS OF
SANDSTONES OF THE BLUEFIELD FORMATION (UPPER MISSISSIPPIAN),
SOUTHEAST WEST VIRGINIA
A Thesis Presented to
the Faculty of the Department of Geology
East Carolina University
In Partial Fulfillment
of the Requirements for the Degree
Master of Science in Geology
by
Michael John Kirkland
December, 1985
PETROLOGY AND DIAGENESIS OF
SANDSTONES OF THE BLUEFIELD FORMATION (UPPER MISSISSIPPIAN),
SOUTHEAST WEST VIRGINIA
by
Michael John Kirkland
APPROVED BY:
COMMITEE
CHAIRMAN OF
DEAN OF THE GRADUATE SCHOOL
ACKNOWLEDGEMENTS
Partial funding for this study was provided by a grant-in-aid from
the Sigma Xi Scientific Research Foundation.
I would like to express my thanks to Dr. Donald Neal for his
guidance during the preparation of this thesis. Thanks go also to Dr.
Charles Q. Brown, Dr. Scott Snyder and Dr. Floyd Read for their many
helpful suggestions while serving as committee members.
I particularly wish to express my appreciation to my parents for
their patience, understanding and moral support.
TABLE OF CONTENTS
PAGE
INTRODUCTION 1
PURPOSE 2
LOCATION 2
GEOLOGIC SETTING 2
METHODS 7
SUBDIVISION OF SANDSTONES 11
TYPE 1 SANDSTONES 15
CLASSIFICATION 15
GRAIN SIZE 18
PETROGRAPHY 18
Quartz 18
Rock Fragments 19
Feldspars 20
Carbonate 21
Accessory Minerals 21
Matrix 22
DIAGENESIS OF TYPE 1 SANDSTONES 24
MECHANICAL COMPACTION 24
CARBONATE CEMENTATION 25
IRON MINERALS 29
PRESSURE SOLUTION FEATURES 32
AUTHIGENIC CLAY MINERALS. . 36
TYPE 2 SANDSTONES 37
CLASSIFICATION 37
GRAIN SIZE 37
PETROGRAPHY 39
Quartz 39
Rock Fragments 40
Feldspars 40
Carbonate 41
Accessory Minerals 42
Matrix 43
DIAGENESIS OF TYPE 2 SANDSTONES 44
MECHANICAL COMPACTION 44
POROSITY 45
CARBONATE 47
HEMATITE 50
CLAY MINERALS 52
QUARTZ AUTHIGENESIS 54
Summary 61
STYLOLITES AND FRACTURES 62
DIAGENETIC SEQUENCE 64
EARLY STAGE OF DIAGENESIS 64
MIDDLE STAGE OF DIAGENESIS 66
LATE STAGE OF DIAGENESIS 67
SUMMARY 68
DEPOSITIONAL SETTING 70
GENERAL 70
PROVENANCE 70
PREVIOUS INVESTIGATIONS 72
DEPOSITIONAL ENVIRONMENTS 75
LOWER SANDSTONES 75
DROOP SANDSTONE 78
UPPER SANDSTONES 80
Introduction 80
Indian Mills Sandstone 81
Bradshaw Sandstone 83
Bertha Sandstone 84
Graham Sandstone 86
Clayton Sandstone 87
Summary 88
DISCUSSION 89
Basin Energy 89
Conclusions 91
SUMMARY 93
REFERENCES CITED 95
APPENDIX A: MEASURED SECTIONS 100
General 100
1) Red Sulphur Springs Section 101
2) Buck Section 103
3) Talcott (1) Section 104
4) Marie Section 105
5) Bertha Section 106
6) Big Bend Section 107
7) Pence Springs Section 108
8) Rock Camp Section 109
9) Talcott (2) Section 110
10) Alderson Section Ill
11) Alta Section 112
12) Assurance Section 113
13) Wayside Section 114
14) Greenville Section 115
APPENDIX B: DATA 116
1) POINT COUNT DATA 116
2) GRAIN SIZE DATA 119
LIST OF ILLUSTRATIONS
FIGURES PAGE
1. Location map of study area 3
2. Generalized stratigraphic section for the Upper
Mlssissippian of southeastern West Virginia 4
3. Classification scheme used for Bluefleld Formation
sandstones 10
4. Quartz percentage vs grain size for Bluefield Formation
sandstones 13
5. Classification of Type 1 Bluefleld Formation sandstones
showing all samples 16
6. Classification of outcrops of Bluefield sandstones 17
7. Classification of Type 2 Bluefield Formation sandstones. . . 38
8. Sequence of dlagenetic events 65
9. Upper Mlssissippian (Chesterlan) paleogeography 71
10. Summary of upper Bluefleld sandstone depositional
environments 90
TABLES
1. Sample sites 8
2. Major deltaic depositional environments 82
PLATES
1: Typical development of Type 1 sandstone 14
2: Typical development of Type 2 sandstone 14
3: Carbonate grain with calcite core and dolomite rim in Type 1
sandstone 26
4: Ovoid in lower Bluefield sandstone largely cemented by
quartz 28
5: Euhedral hematite with pyrite core 31
6: "Stylolitic seam" and "solution seam" in Type 1 sandstone. . . 34
7: Primary intergranular porosity in Type 2 sandstone 46
8: Moldlc porosity formed through partial dissolution of
feldspar in Type 2 sandstone 48
9: Carbonate replacement of feldspar 49
10: Carbonate-cemented Type 2 sand 51
11: Authigenic clay surrounding quartz grain and between
quartz grain and its overgrowth 53
12: "Quartz enlargement" vs pressure solution in Type 2
sandstone. 55
13: Grain coatings, Incomplete overgrowths and moldic porosity
in Type 2 sandstone 56
14: Incomplete quartz overgrowth 58
INTRODUCTION
The Bluefield Formation, at the base of the Upper Mississippian
Mauch Chunk Group in West Virginia, is a marginal marine deposit
transitional between the underlying marine Greenbrier Limestone and
overlying shallow marine to deltaic sediments of the upper Mauch Chunk
Group and Pennsylvanian System. The Bluefield Formation is composed of
intercalated sandstone, shale, limestone and minor coal. West Virginia
Geological Survey reports indicate eight prominent sandstone bodies,
some of which are natural gas producers. From oldest to youngest, they
are the Edray, Webster Springs, Droop, Indian Mills, Bradshaw, Bertha,
Graham, and Clayton Sandstones. They vary from greenish-gray to buff,
fine- to very fine-grained, calcareous varieties in the lower part of
the Bluefield to greenish-gray and reddish-brown, fine- to very
fine-grained varieties in its upper parts. The distinctive Droop
Sandstone, located at the transition between upper and lower parts of
the Bluefield Formation, is coarse-grained, white, and cross-bedded.
These sandstones have been briefly described in West Virginia Geological
Survey County Reports (Reger, 1926; Price and Heck, 1939; Price, 1939),
but descriptions are restricted to color, characteristic bedding and
grain size, and thickness. Other references to the Bluefield are found
as part of a general overview of Mississippian stratigraphy (Englund,
1979; Arkle and others, 1979). McColloch (1957), Manspeizer (1958) and
Humphreville (1981) dealt with stratigraphic and paleontological aspects
of the Bluefield Formation. However, detailed studies of the texture,
mineralogy, and diagenetic histories of Bluefield sandstones are
2
lacking.
PURPOSE
An investigation of Bluefield outcrops was undertaken in order to
accomplish the following objectives:
1) determine composition and textures of the sandstones;
2) characterize diagenesis within the sandstones;
3) interpret the depositional environments; and
4) evaluate compositional, textural, and diagenetic changes relative to
depositional environments and stratigraphic position.
LOCATION
The study area encompasses Monroe, Summers, and part of southern
Greenbrier Counties, West Virginia (Fig. 1). It is located within the
Appalachian Plateau physiographic province, a rugged and mountainous
area dissected by numerous streams which have created V-shaped eroslonal
valleys. Maximum relief for the area is 955 meters. The three counties
encompass a total of 4829 square kilometers (Reger, 1926).
GEOLOGIC SETTING
Rocks of the study area crop out in a band of horizontal to gently
northwestwardly dipping strata that form part of a northeast trending
monoclinal structure (Arkle and others, 1979). The Bluefield Formation
is underlain by the Greenbrier Group and is overlain by the Hinton
Formation (Figure 2).
The Greenbrier Group ranges to a maximum thickness of 550 meters in
3
Figure 1. Location map: Summers, Monroe and Greenbrier Counties,
West Virginia showing location of sections (after
Cardwell and others, 1968). The striped area shows the
outcrop of the Bluefield Formation.
4
Figure 2. Generalized stratigraphic section for the Upper
Misslsslpplan of southeastern West Virginia (after Reger,
1926; Arkle and others, 1979).
5
Mercer County, West Virginia, and thins northwestwardly to a minimum of
15 meters. It consists predominantly of cherty, argillaceous, sandy and
oolitic limestone with some interbedded shale (Arkle and others, 1979);
and it was deposited in a shallow open marine setting (Englund, 1979).
The Bluefleld Formation is composed of intercalated gray and green
shale, limestone, and sandstone with minor red shale in its lower part;
and green, gray and red sandstone and shale with minor limestone and
coal in its middle and upper portions (Arkle and others, 1979; Reger,
1926). It reaches its maximum thickness of 400 meters in Mercer County,
West Virginia, and thins to the north and northwest. This is due partly
to stratigraphic convergence and partly to Early Pennsylvanian erosional
truncation. This same thickness trend holds for all Mlssissippian rocks
in the region, but erosion is a factor mainly in the upper part of the
Mlssissippian (Arkle and others, 1979; Youse, 1964). The Bluefleld was
deposited largely under nearshore marine conditions in a shallow, slowly
subsiding basin (Arkle and others, 1979; Englund, 1979; Whisonant and
Scolaro, 1979; Humphreville, 1981). Depositonal environments
represented by Bluefleld strata range from normal marine carbonates to
nearshore muds, sands, and freshwater marshes deposited in a system
Influenced by tidal energy (Whisonant and Scolaro, 1979; Humphreville,
1981).
The Hinton Formation is composed of interbedded red, partly
calcareous shale and siltstone, ferrugenous and calcareous sandstone,
fossil-bearing limestone and minor coal (Arkle and others, 1979). It
represents shallow marine, barrier bar, tidal flat and fresh-water marsh
environments (Craig and Varnes, 1979; Hobday and Horne, 1979; Colton,
6
1970).
The main structural feature in the study area is the St. Clair
thrust fault. It extends from Allegheny County, Virginia southward at
least to Richlands, Virginia (Gwlnn, 1964), and it represents the major
structural boundary separating the gently folded Appalachian Plateau
Province from the more extensively deformed Valley and Ridge Province
(Rogers, 1963).
Another important feature in the area is the Hurricane Ridge
Syncline, described by Reger (1926) in both Mercer and Monroe Counties,
West Virginia, with the St. Clair Fault forming the eastern margin of
the syncline (Fig. 1). McDowell (1982) separated the Hurricane Ridge
Syncline of Reger into the Glen Lyn, Hurricane Ridge, and Caldwell
Synclines. He defined the Glen Lyn as the overturned syncline which
runs parallel and adjacent to the St. Clair Fault. The Hurricane Ridge
Syncline is found in southern Mercer County, West Virginia. The
Caldwell is a broad, open fold extending northward from central Monroe
County, West Virginia (Fig. 1). McDowell considers this to be an
extension of the Caldwell Syncline of Price and Heck (1939). In
addition, Reger (1926) mapped the Abbs Valley Anticline throughout
Mercer and Monroe Counties, West Virginia, but McDowell (1982) stated
that this anticline extends only to Mercer County and is not found in
Monroe County.
Elsewhere in Monroe and Summers Counties, West Virginia, Reger
(1926) named numerous anticlines and synclines, the limbs of which dip
on the order of a few degrees. Folds extending from northern Monroe
County north into Greenbrier County become more more steeply dipping.
7
METHODS
Nineteen sandstone outcrops from 14 localities were measured,
described, and sampled for this study (Fig. 1). They were chosen
according to accessibilty and completeness of section. Samples were
taken to best represent the dominant lithology and any variations in
lithology (Table 1).
Ninety—five thin sections were examined, 82 of which were
point-counted to determine mineralogy by identifying 300 grains along a
traverse normal to bedding. Average grain size was determined by
measuring the apparent long axes of 100 quartz grains per thin section.
Quartz alone was used in order to eliminate bias.
X-ray diffraction analysis (XRD) utilized uncovered thin sections
and whole-rock oriented slides. All thin sections were examined via XRD
to determine the composition of carbonate (where present) and presence
or absence and type of feldspars. This analysis also aided in
determination of clay mineralogy. Twenty samples, selected to best
represent dominant lithologies within Bluefield sandstones, were
crushed, wetted, and allowed to settle on glass slides in order to
enhance basal clay reflections. These oriented slides were used to
further analyze the clay mineralogy.
A modified version of Folk's 1974 sandstone classification scheme
is used for this study. The basic method and format is retained for
those rocks that are relatively clean (matrix less than 10%). Rocks
with more than 10% matrix are treated similarly to Dott's 1964
classification but superimposed on Folk's basic format. For example, a
8
TABLE 1
Section Sandstone Outcrop Sand- Number Number
stone Samples Thin
Type Sections
1-Red Sulpher Clayton la 1 7 2
Springs Graham lb 1 6 2
Bradshaw Ic 1 6 2
Indian Mills Id 1 5 2
2-Buck Clayton 2a 1 10 2
Graham 2b 2 17 10
3-Talcott #1 Clayton 3a 1 9 2
Bertha 3b 1 4 2
4-Marie Bertha 4 mixed 14 7
5-Bertha Bertha 5 mixed 13 6
6-Big Bend Bradshaw 6 mixed 15 8
7-Pence Springs Bradshaw 7 1 6 4
8-Rock. Camp Indian Mills 8 2 14 6
9-Talcott #2 Droop 9 2 15 .8
10-Alderson Droop 10 2 34 8
11-Alta Droop 11 2 22 7
12-Assurance Webster Springs 12 1 7 4
13-Wayside Webster Springs 13 1 11 9
14-Greenville Ed ray? 14 1 4 4
219 95
9
litharenlte under Folk's classification with greater than 10% matrix is
called a llthic wacke (Fig. 3).
10
0
o
Figure 3: Classification scheme used for Bluefield Formation
sandstones (after Dott, 1964 and Folk, 1974).
Q represents quartz, F, feldspar and R, rock
fragments.
11
SUBDIVISION OF SANDSTONES
The sandstones of this study represent the coarser-grained detrital
units of the Bluefield Formation. Based on compositional and textural
criteria, including grain size, petrography, and outcrop development,
they have been divided into two groups, termed Type 1 and Type 2
sandstones.
Outcrops of Type 1 sandstones, the most common type. tend to be
(10 to 20 feet). In outcrop. Type 1 sandstones are generally
green, red, or mixed green and red on fresh surfaces, shaly to flaggy
and occasionally massive, and ripple-marked. Most are shaly towards
their base and have a gradational lower contact. Coarsening upward
sequences are common, the uppermost beds ranging from flaggy to massive
with a sharp upper contact.
Type 2 sandstones, which contain the coarsest-grained detritus
within the Bluefield, occur in thicker exposures (greater than 20 feet)
of its sand members. In outcrop, they are thick-bedded and
coarse-grained and range from flat-bedded to cross-bedded to massive.
Cross-bedding is typically medium- to large-scale and high angle. Both
planar and trough cross-bedding are present. Most Type 2 sandstones are
white to buff in color but may, in part, be greenish or brownish.
Typically, they are composed of coarse-grained, clean sand but may have
shale interbeds or lenses. No fining or coarsening trends are
noticeable in outcrops composed entirely of Type 2 sandstone; however,
fining upward sequences can be recognized in thin section.
Type 2 sandstones are best represented by the Droop Sandstone which
12
provides three of the five outcrops (9, 10, and 11) that are composed
entirely of Type 2 sandstone. Only two other outcrops (2b and 8) are
composed entirely of Type 2 sandstone. These outcrops represent
localized areas of thickening and coarsening within the Graham and
Indian Mills Sandstones, respectively. Three outcrops (4, 5, and 6)
contain both Type 1 and Type 2 sandstone intervals. The basal portion
of outcrop 4 (Bertha Sandstone) is composed of Type 2 sandstone which
fines upward into Type 1 sandstone. Outcrop 5 (Bertha Sandstone)
includes Type 2 sandstone at the top and bottom of the outcrop,- between
which there is Type 1 sandstone. Outcrop 6 (Bradshaw Sandstone) is
composed of intercalated Type 1 and Type 2 sandstones with minor
limestone and shale interbeds.
Figure 4 is a plot of quartz percentage vs grain size for all
samples in this study. The line on the diagram separates Type 1 from
Type 2 sandstones. Type 2 sandstones are coarser-grained and richer in
quartz than Type 1 sandstones. The dividing line was drawn visually and
is somewhat arbitrary, serving primarily for descriptive purposes. Note
that quartz percentage varies dramatically in Type 1 sandstones, whereas
grain size, and not quartz percentage, varies widely in Type 2
sandstones. Other differences are associated with this subdivision.
Type 1 sandstones are generally more mineralogically diverse and are
typically richer in matrix, rock fragments, feldspar, carbonate and
accessory minerals. Type 2 sandstones are richer in quartz, cleaner
(better washed), better sorted, and constituents are better rounded than
Type 1 sandstones. Typical examples of Type 1 and Type 2 sandstones, as
seen in thin section, are shown in Plates 1 and 2, respectively.
13
Figure 4: Quartz percentage vs grain size. Type 2 sandstones are to
the right of the line; Type 1 sandstones are to the left of
the line. Circles indicate multiple samples.
14
Plate 1: Typical development of Type 1 sandstone (crossed nichols,
25x).
Plate 2: Typical development of Type 2 sandstone (crossed nichols,
25x).
15
TYPE 1 SANDSTONES
CLASSIFICATION
Individual samples of Type 1 (fine-grained, impure) sandstones are
plotted on a ternary QFR diagram in Figure 5. Data for this diagram are
listed in Appendix B. Outcrops 4 and 5 of the Bertha Sandstone and
outcrop 6 of the Bradshaw Sandstone contain samples of both Type 1 and
Type 2 sandstone which are plotted on Figures 5 and 7, respectively.
More than half of the samples of Type 1 sandstone are litharenites or
lithlc wackes, which are, in turn, approximately even in number. The
remainder are sublitharenltes or sublithic wackes with the exception of
one quartzarenite. This sample, as well as those that plot at the
quartz-rich end of the sublitharenlte region, is high in either matrix,
carbonate or a combination of both constituents. All but three of the
samples which fall in the sublitharenite/sublithic wacke and
quartzarenite regions are from sandstones in the lower part of the
Bluefield (Webster Springs and Edray Sandstones).
The averages for each outcrop of Type 1 sandstone are plotted in
Figure 6. Most outcrops are lithic wackes or litharenites. Outcrops 13
and 14 (lower Bluefield sandstones), however, plot as sublitharenlte and
sublithic wacke, respectively. The grand mean of Type 1 sandstones
falls near the quartz-rich end of the lithic wacke range. Outcrops 4
and 5 of the Bertha Sandstone and outcrop 6 of the Bradshaw Sandstone
are composed of both Type 1 and Type 2 sandstone. Similar samples from
these outcrops are grouped, averaged and plotted together in Figure 6.
Therefore each of these outcrops is represented by 2 plots, one
16
Quartz
Fragments
Figure 5: Classification of Type 1 Bluefield Formation sandstones
showing all samples. Arenites (less than 10% matrix)
are symbolized as dots. Wack.es (greater than 10% matrix)
are shown with an "x".
17
Quartz
Fragments
Figure 6: Classification of outcrops of Bluefield sandstones.
Numbers refer to outcrops. Arenites (less than 10%
matrix) are symbolized as dots. Wackes (greater than 10%
matrix) are shown with an "x".
18
representing Type 1, and one representing Type 2 components within each
sandstone.
GRAIN SIZE
Type 1 sandstones range from medium silt to very fine sand as
measured in thin section. Calculated grain size averages for all but
one Type 1 sandstone outcrop fall in the coarse silt size range. All
are composed of both silt and sand interbeds. Approximately half
(outcrops 2a, Ic, 7, 12 and 14) are dominated by sand interbeds and the
calculated coarse silt grain size is due to sampling bias. Remaining
Type 1 outcrops (outcrops la, lb, 3b, Id, and 13) are dominated by silt
interbeds and represent siltstone horizons of the sandstones.
Calculated grain size averages for outcrops which contain both Type 1
and Type 2 sandstone interbeds (outcrops 4, 5 and 6) fall in the very
fine sand range; but they contain rocks ranging from coarse silt to fine
sand.
PETROGRAPHY
Quartz
The most abundant detrital constituent in Type 1 sandstones is
quartz. The mean for all samples is 55.8% and the range is from 41.0%
to 71.7%. Grain shape varies from subround to angular and most grains
possess low sphericity. Most grains are monocrystalline with straight
to slightly undulóse extinction. Polycrystalline grains and grains with
strongly undulóse extinction are rare. Quartz grain size is generally
uniform throughout a given sample, but many samples consist of
19
interlayered quartz-rich and phyllosilicate-rich intervals. Most grains
are clear and lack Inclusions. Vacuoles and inclusions (e.g., rutile)
are present in trace amounts.
Rock Fragments
Rock fragments, the second most abundant constituent in Type 1
sandstones, are predominantly metamorphic rock fragments (MRFs). Rock
fragments range from 0.0% to 43.7% and average 21.5%.
MRFs range from 0.0% to 30.0% and average 18.3%. MRFs consist of
slate, phyllite and schist fragments, with phyllite fragments
predominating. They are distinguished from sedimentary rock fragments
(SRFs) by the orientation of clays and/or the large size and parallel
orientation of micas within the fragments. The most abundant mica
within the MRFs is muscovite, followed by biotite, chlorite and
undifferentiated micas. Chlorite schist fragments are present in small
amounts and are distinguished by their color. MRFs are typically
elongate, with their long axes usually greater than those of associated
quartz grains.
SRFs range from 0.0% to 30.7% and average 3.2%. SRFs consist of
shale fragments, rare chert, and very rare siltstone clasts. They are
distinguished from MRFs by lack of orientation of their constituent
clays. Many grains are gradational between MRF and SRF. Some
orientation may occur in SRFs due to extremely low energy during
deposition, or due to diagenetic alteration during lithlfication. Most
SRFs are well-rounded, equant to elongate, and are often somewhat larger
than surrounding quartz grains. Rlp-up clasts are also present. These
20
clasts are often very large relative to other constituents (typically 2
to 3 mm, but up to 1cm in length); they are typically elongate and
highly angular, indicating very short transport distances, and hence are
considered intrabasinal.
Deformation of both MRFs and SRFs is very extensive in some cases.
This feature has been called pseudomatrix (Scholle, 1979). This
phenomenon, plus the fine-grained nature of these samples, makes the
precise differentiation of rock fragments and matrix difficult.
Feldspars
Feldspar percentages, as measured by point count, range from a
trace to 5.3%, and average 1.0%. Feldspar grains are typically equant
to somewhat elongate, and vary from rounded to subangular. Plagioclase
was the only type of feldspar encountered during microscopic
examination. Using the Michel-Levy method to estimate composition,
grains appear to be high sodium plagioclase (oligoclase or perhaps
higher). Uncovered thin sections were examined by X-ray diffractoraetry.
In almost every case, plagioclase is indicated by the X-ray pattern. It
is generally believed that plagioclase must make up at least 5% of a
given sample in order to register on an X-ray pattern (Carroll, 1970).
Point count data may, therefore, underrepresent feldspar. Staining of
selected samples for plagioclase and potassium feldspar yielded negative
results, indicating that no potassium feldspar is present. The stain
for plagioclase requires the presence of calcium in the feldspar
structure, thus high sodlc-low calcic plagioclase does not stain.
Therefore, plagioclase in these samples is considered to be highly
21
sodio. Plagioclase may be overlooked during optical examination due to
lack of twinning, lack of alteration, small size, or Inclusion within
rock fragments.
Alteration of feldspars within Type 1 sandstones is variable. Much
of the feldspar is clear, but some is cloudy due to varying degrees of
alteration, generally kaolinitization. The degree of alteration often
varies widely within a given sample, probably due to compositional
differences or variations in microporosity.
Carbonate
Carbonate occurs in most Type 1 sandstones, ranging from 0.0% to
48.3% among samples, from 0.0% to 20.9% within the individual sandstones
(i.e., the averages for individual sandstones), and averaging 4.0%
overall. Dolomite, the predominant carbonate mineral, appears to be
secondary after calcite. Traces of high-Mg-calclte are present.
Carbonate occurs as large pore-filling, occasionally polkiolitlc grains
and as a granular matrix-like texture. Calcite occurs as large
pore-filling grains while dolomite occurs both as large grains and as a
granular matrix-like texture. Carbonate grains are clear and unaltered
or partly to wholly stained or replaced by hematite.
Accessory Minerals
Accessory minerals found in Type 1 Bluefleld sandstones include
muscovite, biotite, chlorite, hematite, pyrite, zircon, tourmaline,
rutile and opaques. Together they constitute from a trace to 13.3% and
average 3.8% of Type 1 sandstones. The micas (muscovite, biotite, and
22
to a lesser extent chlorite) are the most abundant of these minerals in
most samples. Occasionally, hematite and, more rarely, opaques
predominate. The micas are elongate and usually bent or kinked due to
compaction. They occur as randomly distributed grains, but
coarse-grained micas are often concentrated along bedding planes.
Fine-grained micas associated with MRFs and clay minerals are
concentrated into zones alternating with quartz-rich zones. Hematite is
found as a stain, grain coatings, pore-filling cement, along stylolites,
in association with carbonate as a replacement mineral, as
fracture-fill, and as large subhedral to euhedral crystals which may be
pseudomorphic after pyrite.
Pyrite is found in only a few samples where it forms large euhedral
crystals. In a few samples it is found as shapeless masses, or as
pyrite framboids. In one sample it is found filling circular pores
within a plant fossil. Zircon is ubiquitous in trace amounts. Grains
are typically small, well-rounded and highly spherical to slightly
elongate. A minor fraction is larger, more elongate, and often exhibits
euhedral terminations. Well-rounded, highly spherical, blue and green
pleochrolc tourmaline is present in trace amounts. Some types of
accessory minerals are found concentrated along bedding planes.
Matrix
Matrix material ranges from 0.0% to 28.7% and averages 13.7% of
Type 1 sands. Matrix Includes very fine-grained material (approximately
0.02mm or less) and grains without definite shape. Shapeless material
includes deformed grains, a feature called pseudomatrix (Scholle, 1979).
23
Pseudomatrix occurs during compactional deformation when softer grains,
such as SRFs and low grade MRFs, are squeezed into the interstices
between harder grains such as quartz (Scholle, 1979). Thus, matrix
includes pseudomatrix, detrltal clays, authlgenic clays, and
fine-grained and/or shapeless material. Matrix is often stained by iron
oxide (hematite) which severely hampers differentiation.
24
DIAGENESIS OF TYPE 1 SANDSTONES
Diagenetic alteration of Type 1 (fine-grained) Bluefield sandstones
takes the form of reduction or occlusion of primary porosity through
mechanical compaction, carbonate cementation, hematite cementation, and
pressure solution. Porosity reduction due to growth of authigenic clay
also occurred. Stylolltes are common in these sandstones. Rare
secondary porosity is present in the form of raoldic and fracture
porosity.
MECHANICAL COMPACTION
Mechanical compaction was the most important process in
lithifIcation and occlusion of primary porosity in Type 1 sandstones.
This is evidenced by the distortion of labile fragments (MRFs, SRFs, and
micas), which are typically bent or kinked at one or more points along
their lengths. The compression squeezes portions of the relatively soft
labile grains into the interstices between more rigid grains (largely
quartz), thereby filling pore space and affecting lithlfication. Some
labile grains were so distorted as to obscure their original character,
creating pseudomatrix. Larger grains, particularly the large micas,
appear to have undergone greater amounts of distortion than smaller
grains. Compaction was particularly effective in reducing porosity and
enhancing lithlfication in samples with high percentages of labile
grains. Plagioclase grains also show signs of deformation. Occasional
grains were fractured and separated parallel to twin planes, while
others were kinked at high angles to twin planes.
25
Fractures are common in Type 1 sandstones. Most are oriented
parallel to bedding; but a few are oriented at high angles to bedding,
probably due to overburden stress (i.e., vertically oriented compressive
stress causes horizontal tenslonal strain and fracturing). Fractures
oriented parallel to bedding are most likely caused by release of
overburden stress.
CARBONATE CEMENTATION
Carbonate cementation is common in Type 1 sandstones. It is found
largely as pore-filling cement in clean, quartz-rich samples, but is
also found in oversized pores, randomly distributed "patches" and as
fracture-fill cement.
The pore-filling carbonate cement and the carbonate found in random
patches is mostly dolomite, with lesser amounts of calcite; although in
some samples calcite is more abundant than dolomite. Trace amounts of
high-Mg-calcite are also present. Calcite usually occurs as remnants
within dolomite, suggesting dolomitization of an original calcite cement
(Plate 3). Dolomitization may have occurred due to migration of Mg-rich
fluids derived from diagenesis of clays in associated shales or from
within the sandstones themselves. Permeabilities in calcitic zones,
however, may have been too low to permit infiltration of Mg-rich fluids.
Alternatively, the Mg-bearlng fluids may have become depleted in
magnesium during the course of dolomitization allowing preservation of
some original calcite cement.
In some cases, carbonate appears to replace quartz grains along
their margins. The quartz grains are corroded and embayed at their
26
Plate 3: Carbonate grain with calcite core and dolomite rim in
Type 1 sandstone (crossed nichols, 250x).
27
contacts with the replacing carbonate. Dolomite rhombs sometimes
penetrate quartz grains, suggesting replacement rather than a
solution-precipitation event. Alternatively, quartz overgrowths may
have included the dolomite rhombs. Carbonate also occupies isolated,
oversized pores in many of these sandstones, as well as pores
approximating the average grain size of the sample involved. In these
cases, precipitation of carbonate in pre-existing moldic or
intergranular pores, perhaps with additional replacement of surrounding
grains, may be indicated.
Carbonate "patches" on the order of 0.5mm in diameter occur within
the lower Bluefield sands. These are typically ovoid in shape,
resembling the cross-section of a small bivalve. The ovoid may be
completely cemented by large calcite crystals, but the central portion
is usually cemented by megaquartz (coarse-grained authigenlc quartz).
hematite, and/or calcite wl th dolomite surrounding the ovoid and
decreasing in abundance away from it. Organic matter is often
intermixed with the surrounding dolomite. These features are
interpreted as follows: an original articulated fossil preserved pore
space within the fossil; later the original shell material was mobilized
and/or recrystallzed and dolomltized; the central cavity was then
cemented by calcite, quartz, and/or hematite (Plate 4).
Carbonate also fills fractures. Unlike other carbonate found in
Type 1 Bluefield sandstones, the fracture-fill carbonate is composed
entirely of calcite. This indicates that a second carbonate cementation
phase occurred after dolomitization. Pore space is sometimes present
between fracture-fill cement and walls of the fracture, indicating that
28
Plate 4: Ovoid in lower Bluefield sandstone largely cemented by
quartz (crossed nichols, 63x).
29
reactivation of the fracture occurred after cementation, that leaching
of the cement occurred, or that spreading of the fractures occurred
during the thin section process. Generally, the calcite shows no sign
of corrosion, suggesting that the pore space associated with the
fracturing is due to reactivation or is a thin-section artifact. Other
fractures are devoid of cement because they were not originally cemented
or any original cement was totally leached out.
IRON MINERALS
Iron oxide (hematite) is present in Type 1 sandstones as 1) a stain
and disseminated fine particles, 2) a replacement of carbonate, 3) large
euhedral crystals, and 4) fracture-fill. Iron oxide in Bluefield
Formation occurs as a stain and disseminated fine particles in red sands
which are intercalated, often finely, with green sands. The color
difference reflects the oxidation state of the iron. Chlorite is partly
responsible for the coloration of the green sandstones. The degree of
staining and abundance of iron oxide varies widely, possibly due to
permeability differences. Hematite mixed with matrix and strongly
strained labile fragments often make differentiation of these components
difficult or impossible. Small disseminated grains of hematite are
present in association with the hematite stain.
Calcite and dolomite were both subject to replacement by iron
oxide, ranging from staining along cleavage traces to total replacement.
The occurrence and degree of replacement often varies greatly over small
distances, perhaps indicating an advanced stage of lithification at the
time of hematitization. Scholle (1979) notes that hematitizatlon may
30
occur late in diagenesis. Small-scale permeability differences may have
been the controlling factor in replacement.
Hematite also occurs as subhedral to euhedral crystals up to 0.25mm
in diameter. In a few samples of green Type 1 sandstones, pyrite also
occurs as large euhedral crystals of approximately the same size and
shape. A few of these crystals have a pyrite core and a hematite rim
(Plate 5). Hematite is probably pseudomorphic after pyrite. The large
size and euhedral shape of the pyrite crystals indicates diagenetic
origin. Pyrite also occurs in other forms in Type 1 sandstones.
Some of the fractures present in Type 1 Bluefield sandstones are
cemented by hematite. Often surrounding the hematite-filled fractures
are "halos" of hematite stain and cement caused by lateral migration
from the fracture through pore space and along microfractures. Scholle
(1979) points out that fracturing infers extensive lithification, so
this hematite phase was emplaced in a relatively late stage of
diagenesis and possibly after exposure.
The source of the hematite is problematical. Hematite cementation
is generally attributed to intrastratal solution of iron-bearing
minerals (Blatt, Middleton, and Murrey, 1980; Walker, 1974, 1977).
Iron-bearing minerals, such as pyroxenes and amphiboles, are lacking in
both red and green Type 1 sandstones, although some magnetite may be
present in the opaque accessory mineral fraction. The dearth of
iron-bearing minerals in both red and green Type 1 sandstones suggests
that they were not present at the time of deposition. Hence, the iron
oxide probably originated from sources other than constituent
iron-bearing minerals, possibly from iron-bearing fluids produced by
31
Plate 5 Euhedral hematite with pyrite core (crossed nichols, 250x)
32
solution of iron-bearing minerals in associated shales or by diagenesis
of clay minerals in associated shales or within the sandstones
themselves. Oxidation of pyrite may have contributed minor amounts of
iron to the system.
PRESSURE SOLUTION FEATURES
When pressure from overburden or tectonism exceeds hydrostatic pore
pressure, solution may occur. Two types of pressure solution features
occur within Type 1 Bluefield sandstones; intergranular pressure
solution and stylolites. Intergranular pressure solution involves
mutual dissolution and interpenetration between individual grains; the
solution surface generally does not extend into adjacent grains.
Stylolites are much larger-scale features in which a solution surface
extends across many grains. Intergranular pressure solution tends to
occur prior to extensive lithification when stresses are concentrated at
grain-to-grain contacts. After extensive lithification, stresses are
more evenly distributed throughout the rock and dissolution, if it
occurs, will tend to proceed along the larger scale more continuous
stylolitic surfaces (Heald, 1956). However, stylolites have been known
to occur prior to extensive llthification (Heald, 1959).
In samples that are relatively free of ductile material, such as
rock fragments and matrix, and where carbonate cementation did not
occur, intergranular pressure solution between quartz grains essentially
occluded porosity. Where pressure solution occurred, quartz-to-quartz
contacts are generally straight or curved, and a few are sutured. Such
grain-to-grain contacts are characteristic of pressure solution (Heald,
33
1956). Sprunt and Nur (1977), in experimental studies on pressure
solution, found that porosity loss (degree of pressure solution)
increases with increased surface area; hence, finer grains are more
susceptible to pressure solution. The fine grain size of Type 1
sandstones would have made them susceptible to pressure solution.
Epitaxial quartz overgrowths, identified by thin "dust rims" present
between the detrital core of the grain and its overgrowth, can be
observed on some grains in samples that have undergone pressure
solution. Straight, smooth and sutured contacts are characteristic of,
but, not diagnostic of pressure solution; they may also be caused by
simple epitaxial quartz cementation unrelated to pressure solution
(Sibley and Blatt, 1976; Slppel, 1968). Therefore, quartz cementation
unrelated to pressure solution may have been in part responsible for
porosity occlusion in these areas.
Stylolltes or solution features which are not restricted to
contacts between individual grains are common in Type 1 Bluefield
sandstones. Most stylolltes reported in the literature are relatively
large scale features that, according to Wanless (1979), "have a
cross-section resembling the trace of a stylus on a chart recorder",
with "relief along stylolite surfaces anywhere from less than 1 mm to
tens of centimeters". Stylolltes in Type 1 sands are of a smaller scale
and lack the vertical relief referred to by Wanless. Stylolitic
development occurs in Type 1 sands in two forms: 1) as "stylolitic
seams" where solution has taken place along a distinct surface, and 2)
as "solution seams" where solution has taken place not along a distinct
surface but throughout a "broad vertical section" (Plate 6).
34
Plate 6: "Stylolltíc seam" and "solution seam" in Type 1 sandstone
(crossed nichols, 25x).
35
"Stylolitic seams" are identified by concentrations of insoluble
materials such as clay, heavy minerals and/or organic material along the
solution surface (Heald, 1955). "Stylolitic seams" in Type 1 sands are
generally marked by clay and organic matter. These seams often
bifurcate into "swarms" of smaller seams similar to the anastomosing
swarms described by Wanless (1979). "Stylolitic seams" occur most
commonly in matrix-rich samples and at the contacts between matrix-rich
and matrix-poor intervals within samples. The concentration of the
"stylolitic seams" in these intervals is due to differences in
resistance to compressive stress between matrix-rich and matrix-poor
intervals (i.e., solution will tend to occur in Intervals less resistant
to stress). The matrix-rich intervals are less resistant than the
carbonate or quartz cemented matrix-poor intervals. These seams have
frequently been stained by hematite which suggests that "stylolitic
seams" may have served as conduits for migrating fluids during
diagenesis. Also, some fractures are lined with residues of insoluble
materials. Apparently, fracturing occurred preferentially along
stylolites.
As with "stylolitic seams", insoluble materials are concentrated
within "solution seams". These seams sometimes display vertical offsets
which were apparently caused by differential movement resulting from
continued compressional stress after or during solution. The vertical
offsets frequently have hematite seams parallel to their lengths
(perpendicular to bedding and parallel to overburden stress direction).
Small scale dislocations must have developed allowing infiltration of
the hematite
36
AUTHIGENIC CLAY MINERALS
Authigenic clays are clearly indicated in only one sample where
kaolinite, perhaps mixed with minor amounts of silica and/or chlorite,
cements part of a fracture. Elsewhere, growth of authigenic clays
probably occurred but, because of the combined effects of compactional
deformation, hematite staining and the presence of detrital clays,
identification of authigenic clays is impossible in Type 1 sandstones.
37
TYPE 2 SANDSTONES
CLASSIFICATION
Individual samples of Type 2 sandstones are plotted on a ternary
QFR diagram (Figure 7). Data for this diagram are listed in Appendix B.
Twenty-four samples plot as quartzarenites, two as quartz wackes, 11 as
sublitharenltes, and two as sublithic wackes. The two quartz wackes may
be so classified because hematite was so thoroughly intermixed with
other matrix material that it calculated as matrix. All sublitharenltes
are from the mid portion of the Bluefield (outcrops 4 of the Bertha
Sandstone, 6 of the Bradshaw Sandstone, 8 of the Indian Mills Sandstone,
and 9 of the Droop Sandstone). Feldspar percentages are much higher in
outcrops 8 and 9 than in other Type 2 sandstones. Outcrops 4, 5 and 6
are composed of both Type 1 and Type 2 sandstone interbeds. Samples of
Type 2 sandstone from these outcrops are also plotted on Figure 7.
Figure 6 plots the average of each outcrop. Three outcrops (2b of
the Graham Sandstone, and 10 and 11 of the Droop Sandstone) plot as
quartzarenites, whereas 5 outcrops (4 and 5 of the Bertha Sandstone, 6
of the Bradshaw Sandstone, 8 of the Indian Mills Sandstone, and 9 of the
Droop Sandstone) plot as sublitharenltes. The grand mean for Type 2
sandstones plots at the quartz-rich end of the sublitharenite region.
GRAIN SIZE
Grain size in Type 2 Bluefield sandstones ranges from 0.083mm to
0.281mm. Within individual samples, grain size is relatively uniform.
The mean for the Droop Sandstone (outcrops 9, 10, and 11) is 0.181mm.
38
Quartz
Fragments
Figure 7: Classification of Type 2 Bluefield sandstones. Arenites
(less than 10% matrix) are symbolized as dots. Wackes
(greater than 10% matrix) are shown with an "x". Circles
indicate multiple samples.
39
The mean for the Graham sandstone at Buck (outcrop 2b) is 0.255mm,
marking the coarsest-grained detrital sediment found within the
Bluefield during this study. The mean for the Indian Mills Sandstone at
Rock Camp (outcrop 8) is 0.118mm. Grain size for Type 2 interbeds
within outcrops composed of both Type 1 and Type 2 sand interbeds are;
0.103mm in outcrop 4 , 0.176mm in outcrop 5, and 0.092mm in outcrop 6;
but they contain rocks ranging from coarse silt to fine sand. Quartz
overgrowths and/or pressure solution obscures original detrital grain
size in most samples.
PETROGRAPHY
Quartz
Quartz, the most abundant detrital constituent in Type 2 Bluefield
sands, ranges in abundnce from 54.3% to 95.7% and averages 83.8%.
Quartz overgrowths and/or pressure solution usually obscure original
detrital grain shape. Where grain coats or dust rims outline the
detrital grain, grains are rounded to very well rounded and moderately
to highly spherical. Extinction is typically straight to slightly
undulóse. Monocrystalline grains predominate, but polycrystalline
grains and grains with strongly undulóse extinction are present. The
quartz is clear but vacuoles are common. Inclusions, such as rutile,
are rare. Some grains have subparallel lines of vacuoles known as Boehm
lamellae. It is unclear if such lamellae in the Bluefield sands are
caused by stress in the diagenetic environment or are inherited from an
earlier depositional cycle.
40
Rock Fragments
Rock fragments compose from 0.0% to 15.7% and average 6.4% of Type
2 sandstones. Metamorphic rock fragments (MRFs) include phyllite,
schist and quartzite fragments. Shale and chert fragments compose the
sedimentary rock fragments (SRFs).
MRFs constitute from 0.0% to 14.7% and average 4.0% of Type 2
sandstones. Phyllitic and schistose grains, the predominant MRFs, are
typically well rounded and slightly elongate in the B-axis direction of
their constituent micas. Muscovite and lesser amounts of biotite
compose the bulk of these micas. Rarer quartzose MRFs are well-rounded
and spherical and consist of either stretched or equant subgrains.
SRFs range from 0.0% to 6.0% and average 1.7% of Type 2 sandstones.
Clay-shale and chert fragments are present in approximately equal
amounts. Clay-shale fragments, which lack orientation of their
constituent clays, are usually well-rounded, except where they have
undergone extensive deformation. Some larger fragments are elongate and
angular, reflecting short transport distances and suggesting
intrabasinal origin. Well-rounded, highly spherical chert grains are
present in small amounts.
Feldspars
Feldspars, although a minor constituent, occur in all but two
outcrops (10 and 11 of the Droop Sandstone) of Type 2 sandstones. They
range in abundance from 0.0% to 2.0% and average 0.3%.
In outcrops 8 and 9 (Indian Mills and Droop Sandstone,
41
respectively) the feldspar, which averages 0.6%, appears to be a
plagioclase, although It is untwinned and staining attempts were
unsuccessful. Where unaltered, feldspar grains are equant and somewhat
angular and exhibit cleavage. They are clear except along cleavage
planes which are dark due to alteration. Typically, grains are
partially dissolved. Dissolution appears to have started along cleavage
traces and progressed inward, dividing grains into equant to elongate
subgrains. The degree of this dissolution is variable within any given
sample. While some grains are unaffected, moldlc porosity is caused by
total dissolution of other grains. The majority of the porosity in
outcrops 8 and 9 originates in this way. Moldic porosity in outcrops 10
and 11 may be due to complete dissolution of a similar grain type.
Twinned plagioclase is present in trace to minor amounts in Type 2
interbeds in outcrops 4, 5 (Bertha Sandstone) and 6 (Bradshaw
Sandstone), as well as in the more argillaceous samples of outcrop 8
(Indian Mills Sandstone). Trace amounts of feldspars occur in the
carbonate-cemented basal part of outcrop 2b (Graham Sandstone). These
feldspars have been extensively replaced by the carbonate, making
accurate identification of the type of feldspar impossible.
Carbonate
Carbonate occurs in only one Type 2 sandstone. It occurs
abundantly in the lower part of outcrop 2b (Graham Sandstone) where it
constitutes as much as 44.7% of one sample. In outcrop 2b, carbonate
averages 8.8%. The carbonate is poiklolitic, iron-stained and heavily
twinned. As in Type 1 sandstones, dolomite, as well as calcite, is
42
present; and, similarly, it is probably secondary after calcite. Rock
fragments, micas, and to a lesser extent quartz have been extensively
replaced by the carbonate.
Accessory Minerals
Accessory minerals include detrital muscovite, biotite, zircon,
tourmaline, rutile and opaques, as well as authigenic hematite and/or
llmonite and clays. Together they range in abundance from a trace to
1.5% and average 0.4%. Muscovite, the most abundant accessory mineral,
is ubiquitous in Type 2 sandstones in minor to trace amounts. It occurs
as discrete flakes of variable size which are sometimes bent or kinked
due to compressional deformation. Biotite is present in trace amounts
in a few Type 2 sandstones.
Zircon is also ubiquitous in trace to minor amounts and is by far
the most abundant heavy mineral. Most grains are well-rounded, but a
few are subhedral to euhedral. Large, well-rounded, highly spherical
opaques are present in trace amounts. A few very well-rounded, highly
spherical, pleochrolc tourmaline grains were found. Opaques, zircon,
and other accessory minerals are concentrated along stylolites.
Iron oxide is present as pore-filling cement, fracture-fill, stain
on grain coatings, and disseminated granular material. Trace amounts of
authigenic clay form booklets and flakes lining and filling pores, and
lining graln-to-grain contacts. Clay flakes are typically oriented
randomly or parallel to grain surfaces, but, rarely are oriented normal
to these surfaces. Clays are sometimes stained by iron oxide.
43
Matrix
Matrix material ranges from a trace to 17.3% and averages 4.7%.
Matrix includes fine-grained phyllosilicate material, clay minerals,
very fine-grained mineral particles, and iron oxide. Clays and iron
oxide are included because they are often intermixed and cannot be
differentiated. Hence, matrix includes grain coats and pore-filling
clay and iron oxide.
44
DIAGENESIS OF TYPE 2 SANDSTONES
Dtagenetic alteration of Type 2 (coarse-grained, clean) sandstones
includes porosity reduction due to mechanical compaction, quartz
cementation, intergranular pressure solution, and minor amounts of
calclte cementation and growth of authigenic clays. Other diagenetic
processes include stylolitization, fracturing, and precipitation of iron
oxides. Most porosity in these sands is primary, but some secondary
porosity was produced by dissolution of feldspars and by fracturing.
MECHANICAL COMPACTION
Mechanical compaction is evidenced by deformation of labile
fragments (MRFs, SRFs, and micas). MRFs and micas are typically bent or
kinked at one or more points. This deformation squeezes parts of the
grains into surrounding pore space, contributing in a minor way to
llthlfication by cementing adjacent grains together. Occasionally,
localized compression of micas caused separation along cleavage planes.
Pore space between cleavage planes was later filled by quartz cement.
Clays of SRFs lack orientation and show no evidence of internal
deformation as do the MRFs. Rather, portions of the relatively soft
SRFs are "injected" into the interstices between more rigid surrounding
grains (i.e., quartz).
The degree of deformation of labile fragments, particularly MRFs,
varies widely both between samples and within samples. Some variation
is attributable to the type or orientation of the fragment involved.
MRFs with finer-grained micas underwent more deformation than those with
45
coarser-grained micas. Deformation also varies widely between
compositionally similar MRFs, because of variation in their orientation
in the timing of cementation. Early cemented intervals undergo less
mechanical compaction and preserve the Integrity of the labile
fragments. Uncemented intervals undergo more mechanical compaction
causing more deformation of the labile grains.
POROSITY
Type 2 sandstones are not highly porous, yet both primary and
secondary porosity are present. All Type 2 sandstones contain some
porosity, with the exception of outcrop 2b (Graham Sandstone) in which
porosity is totally occluded.
Primary intergranular porosity occurs only in clean, coarse-grained
samples. There are minor amounts in all outcrops of the Droop Sandstone
and in outcrop 8 (Indian Mills Sandstone). Intergranular pores are
highly angular, often three-sided, and result from incomplete pore
closure by quartz overgrowths (Plate 7). No evidence was found for a
precursor cement. Hence, intergranular porosity in these sections is
considered to be reduced primary porosity.
With the exception of outcrop 2b, moldic porosity occurs in all
Type 2 sandstones, but it is most common in the clean, coarse-grained
samples. It is particularly abundant in the Droop Sandstone and in
outcrop 8 (Indian Mills Sandstone). In outcrops 10 and 11 (Droop
Sandstone), moldic pores are void and offer no evidence of the dissolved
grain. In outcrops 8 and 9 (Indian Mills and Droop Sandstones) a single
grain type (untwinned plagioclase) has undergone dissolution and is
46
Plate 7 Primary intergranular porosity in Type 2 sandstone
(crossed nichols, 250x).
47
responsible for moldic porosity. Dissolution proceeded from grain
margins and cleavage traces. Undissolved portions of these plagioclase
grains remain clear and unaltered. The same grain type may have been
responsible for moldic porosity in outcrops 10 and 11 (Plate 8).
Porosity associated with fracturing is present in a few Type 2
sandstones. Fracturing occurred only in relatively Impure, fine-grained
samples, but it is abundant where present. Overall, fracture porosity
constitutes a minor proportion of the porosity in Type 2 sands. Most
fractures contain no cement, and lack of remnant patches of cement
within them suggests they were never cemented and probably formed late
in the dlagenetic history of these rocks. One fractured sample contains
quartz cement.
CARBONATE
Carbonate occurs in only one Type 2 sandstone (the basal part of
outcrop 2b, Graham Sandstone). The carbonate is composed of both
calclte and dolomite. It is poikllotopic, iron-stained, and heavily
twinned; and it replaces, in part or completely, all observed grain
types. It was particularly effective in replacing rock fragments,
micas, and feldspars, which frequently appear as "skeletal" grains in
which the original nature of the grain is barely preserved (Plate 9).
While feldspars occur in the carbonate-cemented basal part of outcrop
2b, its upper part contains no feldspar. Although the feldspars are
extensively replaced, the carbonate cement in the base of the outcrop
prevented feldspar dissolution during quartz diagenesis. This suggests
that carbonate cementation was early (l.e., the carbonate cement
48
Plate 8 Moldíc porosity formed through partial dissolution of
feldspar in Type 2 sandstone (crossed nichols, 250x).
49
Plate 9 Carbonate replacement of feldspar (crossed nichols 160x)
50
prevented dissolution of the feldspars which apparently occurred in the
upper part of the outcrop).
Quartz also underwent replacement by the carbonate. Replacement
proceeded from the margins of the grains, as evidenced by irregular
grain boundries where carbonate-filled embayments penetrate quartz
(Plate 10). The quartz grains are also replaced along internal linear
zones of weakness, perhaps along pre-existing vacuole trains.
Replacement of quartz was extensive in some cases. Quartz "shards",
apparently remnants of an extensively replaced quartz grain, are found
floating in the carbonate. Alternatively, such cases may represent the
remnants of an originally quartz-rich rock fragment where carbonate
selectively replaced other constituents.
Most quartz grains are surrounded by "halos" of unstained,
untwlnned carbonate (Plate 10). Where quartz grains have been partially
replaced internally by carbonate, that carbonate is also untwlnned and
unstained. At least two possibilities exist for the formation of these
"halos": 1) a two-stage replacement of quartz by carbonate in which a
second phase of replacement produced the "halos" after twinning and
staining of the early carbonate; 2) grain rotation accompanied by
recrystallization of carbonate adjacent to quartz grains.
HEMATITE
Hematite occurs in Type 2 sandstones as a stain, as finely
disseminated grains, and as pore-filling cement. Hematite stains clay
minerals and to a lesser extent micaceous rock fragments. All three
types of hematite occur together, suggesting only one phase of
51
Plate 10: Carbonate-cemented Type 2 sand. Note marginal
replacement of quartz by carbonate; clear carbonate"halo"
around quartz grain in lower left of photo and; partial
replacement of feldspar in lower right of photo (crossed
nichols, 63x).
52
hematitizatlon. Hematite fills both primary and secondary porosity.
Secondary porosity in Type 2 sands shows no evidence of reduction and,
therefore, probably occurred relatively late in diagenesis. Early
formed secondary porosity would have been at least partly occluded by
mechanical compaction or quartz cementation. Because hematite infills
secondary porosity, hematitizatlon must have occurred late in
diagenesis, possibly at outcrop.
CLAY MINERALS
Clay minerals in Type 2 Bluefleld sands occur as discrete flakes
and coatings around quartz grains, as inclusions within authigenic
quartz, and rarely as pore-filling material. The clay is composed
largely of illite but may contain some kaolinite. Clays are sometimes
stained by iron oxide, making accurate optical identification difficult
or impossible. Clay minerals in Type 2 sandstones may be both detrital
and authigenic. Authigenic clays are generally distinguished from
detrital clays by their distinctive morphologies. However, the combined
effects of mechanical compaction, quartz cementation and pressure
solution can make distinction between authigenic or detrital origins
impossible. In a few cases, it is possible to identify the origin of
the clay. For instance, clay grain coatings between the detrital cores
of quartz grains probably developed prior to deposition. Clays are
sometimes clearly authigenic, as where kaolinite booklets are found
filling pores and where clays are oriented perpendicular to quartz grain
boundaries (Plate 11). But, the precise origin of clays could not be
routinely determined
53
Plate 11: Authigenlc clay surrounding quartz grain and between
quartz grain and its overgrowth (crossed nlchols, 160x).
54
QUARTZ AUTHIGENESIS
The most important processes in porosity reduction and
lithificatlon of Type 2 Bluefield sandstones were quartz cementation
resulting from pressure solution and "quartz enlargement" (quartz
cementation unrelated to pressure solution). Together, these two
processes significantly reduced and sometimes occluded primary porosity
(Plate 12).
Both "quartz enlargement" and intergranular pressure solution are
relatively early diagenetic events. "Quartz enlargement" requires pore
space into which overgrowths can expand and so must precede extensive
lithification. Lithification also hinders pressure solution by
distributing stresses more evenly throughout the rock, rather than at
the grain-to-grain contacts where intergranular pressure solution occurs
(Heald, 1956).
An important factor in controlling which of these two processes
occur is the presence and thickness of clay coatings on detrltal quartz
grains (Plate 13). Clay coatings inhibit the formation of quartz
overgrowths by blocking nucléation sites on the surfaces of quartz
grains (Heald and Larese, 1974). Grain coatings of sufficient thickness
(thick enough to prevent diffusion across the coating?) will prevent
"quartz enlargement" and preserve primary porosity. Where such coatings
are lacking or Incomplete, nucléation sites are available and quartz
overgrowths will form, provided that silica is available and that
conditions are otherwise favorable for quartz growth (Heald and Larese,
1974). Where clay coatings are absent, overgrowths totally surround
55
Plate 12: "Quartz enlargement" vs pressure solution in Type 2
sandstone. Area in top of photo dominated by "quartz
enlargrment. Bottom part of photo shows pressure solution
(crossed nichols, 25x).
56
Plate 13; Grain coatings, incomplete overgrowths and moldic
porosity in Type 2 sandstone (plain light, 25x).
57
detrítal grains and most grain-to-grain contacts are between
overgrowths. Where grain coatings are incomplete, "irregular
overgrowths" are formed (Heald, and Larese, 1974) because localization
of nucléation sites causes restriction of the overgrowths. A given
detrital grain may possess a well developed overgrowth along part of the
grain, but the overgrowth may be absent along other parts of the grain
(Plate 14). Detrital grain-to-overgrowth contacts become common (i.e.,
overgrowths from one grain often are in contact with detrital cores of
adjacent grains on which clay coatings prevented overgrowth formation).
Where grain coatings are thin or absent, epitaxial quartz
overgrowth formation ("quartz enlargement") was the dominant process by
which Type 2 sandstones were cemented. Epitaxial overgrowths are
identified by "dust rims" between detrital cores and the overgrowths, or
by variations in other characteristics between the detrital cores and
their overgrowths. For example, overgrowths typically contain fewer
inclusions (except for clays) than the detrital cores, which contain
vacuole trains and other linear features that terminate against
overgrowths. Overgrowths in Type 2 sands are largely "irregular
overgrowths". Contacts between clay-coated detrital cores and
overgrowths of adjacent grains are common in these intervals. These
contacts are fairly weak and sands cemented in this manner are often
friable (Heald and Larese, 1974). The friable nature of the Droop
Sandstone is likely due to cementation in this fashion.
While "quartz enlargement" was the dominant cementation process in
intervals where grain coatings are thin, evidence of pressure solution
is rarely lacking. Most grain-to-grain contacts are smooth or straight.
58
Plate 14: Incomplete quartz overgrowth (crossed nichols 63x)
59
but the interpenetration of detrital cores, marked by sutured contacts,
suggests that some pressure solution occurred. Cementation by
overgrowths was apparently incomplete when overburden (?) pressure
Initiated pressure solution. In Intervals with thin grain coatings,
pressure solution was relatively minor and contributed little cement to
the system.
Where grain coatings are complete and of sufficient thickness,
quartz enlargement is Inhibited and primary porosity is often preserved.
When overburden or tectonic stress becomes great enough, solution may
occur. Pressure solution involves solution at graln-to-grain contacts.
Dissolved silica migrates along grain boundaries and is precipitated in
areas of lower stress (l.e., within adjacent pore space). When pressure
solution occurs in sands that lack grain coatings (clean sands), a water
layer adsorbed at the margin of the grain is the only migration path
available to dissolved silica. Clay coatings tend to enhance pressure
solution by providing a wider diffusion path for the silica. The silica
migrates either between the clay coating and the detrital grain or
between the clay layers (Weyl, 1959). During the latter process, clay
may become incorporated within the authigenic quartz as inclusions.
Sometimes such inclusions are oriented parallel to prism planes within
the authigenic quartz, creating a feature termed "polygonal-grid" quartz
(Heald and Larese, 1974).
In intervals where clay coatings are relatively thick.
Intergranular pressure solution was the dominant lithification process.
Compared to Intervals cemented mostly by "quartz enlargement", pressure
solution intervals contain more detrital core-to-detrital core contacts.
60
more sutured contacts, and fewer and smaller overgrowths identifiable by
dust rims. Solution is most easily Identified at detrital
core-to-detrital core contacts, but it also probably occurred between
overgrowths and detrital cores, and between adjacent overgrowths.
Grain coatings in Type 2 sandstones may cover both a detrital grain
and its overgrowth, indicating that silica diffused mainly between the
clay coating and detrital grain. As quartz precipitated on the detrital
grain, the clay coating "migrated" away from it, leaving the overgrowth
between the detrital grain and the clay coating. More commonly, clay
flakes are included within the authigenic quartz. Most clay inclusions
within authigenic quartz in Type 2 Bluefield sands are oriented
randomly. "Polygonal-grid" quartz is present but not common.
Most of the authigenic quartz formed by pressure solution in Type 2
Bluefield sandstones formed epitaxially. Some authigenic quartz is not
in optical continuity with any observed grain, but this authigenic
quartz may be epitaxial on grains outside the plane of the thin section.
Grain size tends to be smaller in zones with extensive pressure
solution than in zones cemented by "quartz enlargement". These zones
are small in scale and may vary within a single thin section. Early
formed overgrowths tend to increase grain size, while pressure solution
has less effect on grain size; and so grain size difference may reflect
authigenesis. Alternatively, the grain size difference may be
depositional in nature. Sprunt and Nur (1977) found that degree of
pressure solution increases with decreased grain size, and so intervals
of finer grain size would have been more susceptible to pressure
solution. A combination of these two factors may be responsible for the
61
observed correlation between grain size and method of lithification.
Clay coatings of sufficient thickness will inhibit pressure
solution by cushioning the effects of overburden pressure and reducing
stress at graln-to-grain contacts. The thickness at which clay coatings
cease promoting and begin inhibiting pressure solution has not been
documented (Sibley, 1975; Sibley and Blatt, 1976). In a few samples of
Type 2 sandstones grain coatings were apparently of sufficient thickness
to prevent pressure solution.
Summary
Type 2 Bluefield sandstones were cemented by both "quartz
enlargement" and intergranular pressure solution. Most Intervals show
the effects of both processes, and all gradations between cementation
totally by "quartz enlargement" and totally by pressure solution can be
observed.
Clay coatings (largely illite) on detrital grains are almost
ubiquitous in Type 2 sands, but they vary in thickness. The thickness
of clay coatings correlates with changes in dlagenetic processes within
the sands.
"Quartz enlargement" began before pressure solution where
nucléation sites were available for quartz growth. In intervals with
relatively thick and complete clay coatings "quartz enlargement" was
inhibited. Increased overburden stress later in diagenesis initiated
solution at grain-to-graln contacts (intergranular pressure solution).
Pressure solution, aided by the presence of clay coatings, produced
additional free silica for quartz authlgenesis, which completed
62
cementation of Type 2 sandstones.
STYLOLITES AND FRACTURES
Stylolites occur in only a few of the Type 2 sandstones sampled.
They are characterized by concentrations of insoluble materials such as
clay minerals, heavy minerals, and organic matter along the stylolitic
surface. Most stylolites occur in the more argillaceous samples of Type
2 sandstone, and most are oriented parallel to bedding. They were
probably caused by overburden pressure. Fracturing later, occurred
preferentially along these stylolites. One sample, taken from the base
of outcrop 9 (Droop Sandstone), contains stylolites which are oriented
normal to bedding. These were caused by directed stress, possibly
associated with folding and thrust faulting in the region, in the
horizontal plane.
Quartz overgrowth formation and stylolitization tend to occur in
mutually exclusive samples of Type 2 sandstones, stylolites in
argillaceous samples and quartz overgrowths in "cleaner" samples.
Therefore, no cross-cutting relationships were observed and relative
timing of these two events could not be determined.
All fractures observed in Type 2 sandstones are oriented parallel
to bedding, and were probably caused by release of overburden pressure.
Fractures which occurred along pre-existing stylolite surfaces may have
been opened during the thin section process. Most of the fractures
contain no cement and were probably never cemented. This suggests that
fracturing occurred late in the dlagenetic history of these rocks.
One fracture set was cemented by quartz This indicates that
63
either a second generation of quartz authigenesis followed quartz
cementation, or free quartz which remained in the system after primary
porosity reduction cemented this fracture.
64
DIAGENETIC SEQUENCE
Dlagenesis within Bluefield sandstones can be separated into early,
middle and late stages. The sequence discussed below refers to both
Type 1 and Type 2 sandstones except where noted. Diagenetic events are
summarized in Figure 8.
EARLY STAGE OF DIAGENESIS
Early diagenetic events include mechanical compaction and formation
of authigenic pyrite, clay minerals (largely illite), calcite, and
hematite. The first minerals to form were pyrite and calcite. Calcite
probably formed from carbonate present at or near the sediment-water
interface. Some early formed calcite was subsequently dolomltized.
Detrital quartz grains and other grain types were partially replaced by
calcite. Evidence from the base of outcrop 2b (Graham Sandstone), where
calcite authigenesis prevented dissolution of feldspars, suggests that
this replacement occurred early. Oxidation of some of the pyrite to
hematite occurred and, probably concurrently, some calcite and dolomite
were also partly replaced by hematite.
Authigenic illite formed grain coatings (of variable completeness
and thickness) on quartz grains in Type 2 sandstones. Some of these
grain coatings may be predeposltional. The fact that they were
"involved or mobilized" during quartz authigenesis, a process which
occurred in the middle stage, suggests that they formed early. Illite
probably formed in Type 1 sandstones as well. This illite, as well as
other authigenic clay minerals, is mixed with detrital clays.
DIAGENETIC DIAGENETIC STAGE
EVENT early middle late
HEMATITE ?? ??
AUTHIGENESIS
CLAY MINERAL ?? —
AUTHIGENESIS
CALCITE “ ??
AUTHIGENESIS
DOLOMITIZATION
MECHANICAL ? ? ?
COMPACTION
QUARTZ —
AUTHIÇENESIS
INTERGRANULAR
PRESSURE SOLUTION
FRACTURING
STYLOLITIZATION 1 1 1 1
PYRITE
AUTHIGENESIS
Figure 8. Sequence of dlagenetic events
66
Mechanical compaction, especially through deformation of labile
fragments, begins only after shallow burial (Blatt and others, 1980).
Compaction began early and continued throughout the early stage of
diagenesis.
MIDDLE STAGE OF DIAGENESIS
The middle stage of diagenesis is characterized by formation of
quartz overgrowths and stylolites, and by Intergranular pressure
solution. Free silica began to precipitate as epitaxial overgrowths on
quartz grains, a process particularly important in Type 2 sandstones.
Mechanical compaction during the early stage of diagenesis in Type 1
sandstones prevented significant quartz authigenesls by occluding
primary porosity. Later, as overburden pressure increased,
intergranular pressure solution began. This process, aided by the
presence of clay coatings on detrital grains, released additional silica
which precipitated as epitaxial overgrowths and randomly oriented
pore-filling cement.
Stylolitization may occur prior to. during, or after quartz
cementation within sandstones. In fact. it may be an important
contributor of silica when it occurs before or during cementation
(Heald, 1959). Stylolites occur most frequently in the more
fine-grained and argillaceous components of the Bluefield sandstones,
which contain only minor amounts of authigenlc quartz. Therefore,
cross-cutting relationships could not be observed. Stylolitization is
placed in the middle stage of diagenesis based on its relationship with
fractures. Fracturing occurred preferentially along stylolites during
67
the late stage of diagenesis. Stylolitization clearly preceded
fracturing and is considered to be a middle stage event.
LATE STAGE OF DIAGENESIS
The late stage of diagenesis includes events which occurred after
extensive lithification of Bluefield sandstones. Important events
include fracturing; the infilling of many fractures by authigenic
quartz, calcite, hematite and clay minerals; and the formation of moldic
porosity by dissolution of feldspars.
Fracturing typically occurs after extensive lithification, when
repacking at the graln-to-grain level can no longer close the fractures.
Stylolites served as preferred sites for fracturing, suggesting that
fracturing occurred relatively late in the diagenetic sequence.
Bluefield sandstones were fractured both parallel and at high angles to
bedding. Fractures at high angles to bedding were probably formed at
depth by overburden pressure, and may have occurred in either the middle
or late stage of diagenesis. Fractures parallel to bedding probably
occurred late in response to release of overburden pressure. Many of
these fractures were later cemented by calcite, hematite, quartz, or
clay minerals. Only one of these mineral phases is usually present in
any given fracture, and so relative timing of these events could not be
determined. One fracture contains both calcite and clay minerals. The
calcite appears somewhat corroded, which possibly indicates that calcite
authigenesls preceded clay mineral authigenesis. Variation in pore
fluid chemistry may have been responsible for variations in cement type.
Feldspar dissolution produced secondary moldic porosity during this
68
diagenetíc stage, particularly in Type 2 sandstones. Moldic pores
contain no quartz cement. Had this porosity been produced before or
during quartz authigenesis, the pores would have been at least partly
Infilled by quartz cement. Feldspar dissolution must, therefore, have
occurred after quartz authigenesis (i.e., in the late stage of
diagenesis). Occasionally pores are partially cemented by hematite, but
otherwise they contain no late stage cement, suggesting that late-stage
quartz, calclte and clay mineral authigenesis preceded feldspar
dissolution and, possibly, hematite authigenesis. Hematite authigenesis
either postdated or co-occurred with feldspar dissolution.
SUMMARY
The most important diagenetic events in Bluefield sandstones were
mechanical compaction and quartz cementation. During the early stage of
diagenesis, mechanical compaction was the dominant diagenetic process in
the Type 1 sandstones which contain large percentages of ductile grains.
At the end of the early stage of diagenesis, lithification was
essentially complete and primary porosity essentially occluded in Type 1
sandstones. At the beginning of the middle stage of diagenesis,
significant primary porosity remained in Type 2 sandstones. Large
amounts of silica available to the system initiated formation of quartz
overgrowths. Continued burial during the middle stage of diagenesis
induced intergranular pressure solution. This released additional
silica, further promoting quartz authigenesis and completing
lithification of Type 2 sands. Late stage diagenetic events include
minor secondary porosity formed through fracturing. feldspar
69
dissolution, and partial infilling of secondary porosity by various
authigenic minerals.
70
DEPOSITIONAL SETTING
GENERAL
During the late Mlsslssipplan the study area was located
approximately 5 to 10 degrees south of the paleoequator (Humphrevllle,
1981; Scotese and others, 1979; Bambach and others, 1980; deWitt and
McGrew, 1979). Figure 9 is a map adapted from deWitt and McGrew (1979)
showing generalized Chesterian paleogeography. To the east, Appalachia
was developing as an Andean-type mountain chain (Scotese and others,
1979). Uplift to the east caused large volumes of detritus to be
deposited in the area (Bambach and others, 1979; deWitt and McGrew,
1979). These sediments were deposited in a shallow, slowly subsiding
basin which occupied southeastern West Virginia during this time
(Scotese and others, 1979).
PROVENANCE
Metamorphic rock fragments (MRFs), such as slate and phyllite
fragments, are very abundant in Bluefield sandstones. Slate, phyllite
and chlorite-bearing MRFs suggests erosion of a low-grade metamorphic
source. Higher metamorphic grade fragments, such as biotite and
coarser-grained (schistose) fragments, are also present. This suggests
that source rocks were composed of multiple metamorphic facies or that
multiple sources contributed sediments to the area.
Minor quantities of sedimentary rock fragments are present. These
are primarily claystone clasts and a few siltstone clasts. Although
they may represent erosion of a sedimentary source, they are most likely
71
Figure 9 : Upper Mississippian (Chesterian) paleogeography (after
Craig and Varnes, 1979). Shaded area represents marine
conditions. Darkened area indicates study area.
72
Intrabasinal. No rock fragments clearly indicative of a plutonic source
were found.
PREVIOUS INTERPRETATIONS
Whisonant and Scolaro (1980) interpreted a stratigraphic section
from the middle part of the Bluefield Formation in Mercer County, West
Virginia as a nearshore deposit. Inferred environments included shallow
subtidal, lower intertidal, middle intertidal, and higher intertidal.
The section was found to be regressive in nature.
Humphreville (1981) investigated the stratigraphy and paleoecology
of the Bluefield Formation in Mercer County, West Virginia and Tazewell
County, Virginia. The lower Bluefield, composed primarily of
argillaceous wackestones, was interpreted to represent deposition during
the waning periods of storm events. The upper Bluefield, composed of
olive-green and maroon mudstones lacking both marine and terrestrial
fossils, was interpreted to represent deposition as a prograding muddy
shoreline or in a muddy marsh setting. Humphreville interpreted the
Indian Mills Sandstone, a coarse quartzose sandstone between the upper
and lower Bluefield, as a crevasse splay and stated that it is the only
one of Reger's (1926) members still recognized. Interbedded clays and
coals are interpreted as terrestrial swamp deposits. In summary, he
stated that the formation represents a shallow water, muddy environment
with tidal flats, crevasse splay sands, and muddy shoreline and swamp
deposits.
Swires (1972) studied sediments of the Mauch Chunk Group in the
Hurricane Ridge Syncline in Mercer, Monroe, and Summers Counties, West
73
Virginia. He interpreted the lower Bluefield as open marine deposits
which grade upward into "deltaic/fluvial" and lagoonal sediments. He,
like Humphreville (1981), recognized only the Indian Mills Sandstone as
a member within the Bluefield. He Intrepreted the Indian Mills as a
"deltaic/fluvial" deposit.
McColloch (1957) studied the Bluefield Formation in Mercer, Monroe,
Summers, and southern Greenbrier Counties, West Virginia. He noted that
the basal Bluefield is predominantly marine limestone and shale with
minor terrestrial sandstones and shales, and that the upper Bluefield is
predominated by terrestrial shales and sandstones with minor marine and
freshwater limestones. Unlike Swires and Humphreville, McColloch places
the Droop Sandstone of Reger (1926) at the boundary between the lower
and upper Bluefield.
McColloch claimed that the limestones of the lower Bluefield can be
traced throughout the study area, but that the marine limestones of the
upper Bluefield, including the Raines Corner and Bertha Limestones of
Reger (1926), lens out or undergo facies changes north of Pence Springs
(sample site 12 of this report). He also noted that the Bluefield is
thinnest at Pence Springs and thickens both to the north and south from
there. He reported deltaic deposits to the north in his Clintonvllle
section, while his southern sections (not specifically designated but
certainly south of Pence Springs) were deposited in marine conditions.
Otherwise, he referred to upper Bluefield deposition as "terrestrial".
Manspeizer (1958) studied the Bluefield Formation in Greenbrier and
Pocahontas Counties, West Virginia. He interpreted those units below
the Droop Sandstone to be largely of marine origin (Lillydale, Glenray,
74
Reynolds, and Ada members of Reger), with minor lagoonal (Bickett Shale)
and "transitional-littoral" deposits (Webster Springs Sandstone). Units
above the Droop were interpreted variously as transitional-deltaic,
littoral, and lagoonal deposits within an overall deltaic setting. The
Droop was interpreted as a beach (littoral) sand. Manspeizer recognized
a delta distributary north of Droop Mountain in Pocahontas County. He
noted that the Droop Sandstone thickens toward the north, reaching its
maximum thickness at Droop Mountain, north of which it undergoes facies
changes. He stated that north-flowing currents piled up Droop sediments
against the delta producing the increased thickness.
75
DEPOSITIONAL ENVIRONMENTS
LOWER SANDSTONES
Lower Bluefield sandstones include the Webster Springs and Edray as
named by Reger (1926). These sands are most prominant north of the
study area and attempts to trace them into the area are tenuous at best.
Lower sandstones of this study are best thought of as sands which occur
at horizons similar to those of the named sandstones to the north and
not necessarily contiguous units.
Three outcrops were sampled in the lower part of the Bluefield
Formation. Two of the outcrops sampled (outcrops S and J) were first
described by Reger (1926) who assigned them to the Webster Springs
Sandstone. The third outcrop sampled (outcrop R) was located lower in
the Bluefield and may be the equivalent of the Edray sandstone of Reger
(1926). All three outcrops consisted of Type 1 sandstone.
Outcrop S consists of calcareous, very fine-grained sand which
shows no grain size sequence. It ranges from greenish-brown to buff,
cross-bedded sand in its lower part to green, flaggy and ripple-marked
sand in its upper part. Quartz percentage is low (mean = 61.7%). Rock
fragment percentage is relatively high (mean = 21.2%).
Outcrop J is composed of 3 units of Type 1 sandstone which are
intercalated with yellow-brown calcareous shale. The coarse-grained
units are variously brown, greenish-brown or gray and massive to
ripple-marked. Grain size in the "coarse-grained" units ranges from
coarse silt to very fine sand. The mean grain size falls in the coarse
silt range. Quartz percentage is low (mean = 56.1%). Rock fragment
76
percentage is highly variable, ranging from a trace to 30.0% and
averaging 10.6%. Carbonate percentage ranges from a trace to 48.3%.
Stratigraphic evidence suggests that the Webster Springs Sandstone
is encased in marine deposits. The Webster Springs Sandstone (outcrops
S and J) is underlain by the marine Glenray Limestone. The overlying
Bickett Shale contains a red zone, but also contains interbedded
limestones, particularly in its upper portion where it grades upward
into the marine Reynolds Limestone (Reger, 1926; McColloch, 1957). The
Bickett is sandy at its base.
This sequence suggests that a "pulse" of clastic sedimentation
occurred in what was otherwise a basin dominated by carbonate
deposition. This influx of elastics temporarily displaced carbonate
deposition. Resumption of carbonate deposition is recorded by the
transition of the top of the Bickett Shale into the overlying Reynolds
Limestone. Moreover, while the Webster Springs is massive at outcrop S,
it interfingers with apparent marine shales at outcrop J. This suggests
that the Webster Springs was deposited under marine conditions.
Similar sands, particularly in the Cretaceous of Texas and the
Rocky Mountain region, have been interpreted as "shelf ridge sands"
(Swift and Rice, 1984). These sands are formed by winnowing of sandy
shales (muds) largely by storm induced currents (Swift and Rice, 1984).
Ripple-marks, cross-bedding and horizontal bedding are the most common
sedimentary structures in these sands (Swift and Rice, 1984). They are
also the most common structures in the Webster Springs Sandstone. Most
documented shelf sands are, however, more extensively cross-bedded and
somewhat coarser-grained and better sorted than outcrops of the Webster
77
Springs observed in this study. Grain size is in part a function of the
grain size of available sediment; i.e., grain size in the Webster
Springs may include the coarsest materials that were available. Size
and kind of bedform (especially cross-bedding) are a function of the
energy of the depositional environment. The difference in bedforms,
finer grain size, and poorer sorting suggests that basin energy, and
more precisely the size and intensity of storms, was higher in the
Cretaceous examples than in the Appalachian basin when the lower
Bluefield was being deposited.
The Webster Springs Sandstone probably developed through winnowing
of the muds of the lower Bluefield shale and represents shelf sand ridge
deposition. Most shelf sand ridges are linear features. Outcrop S is
relatively thick, coarse-grained and massive and probably was deposited
near the axis of a sand ridge. Outcrop J, which is interbedded with
marine shales, probably represents deposition along the lateral margin
of a ridge. Such intercalation of sands with shale or mud is common at
the margins of shelf sand ridges (Swift and Rice, 1984).
Outcrop R (Edray Sandstone?) is calcareous, ripple-marked and very
fine-grained. Grain size ranges from coarse silt to very fine-grained
sand and averages 0.046mm. Quartz percentage is low (mean = 65.6%).
Rock fragment and matrix percentages are high (averages of 14.6% and
13.5%, respectively). Like outcrops J and S, outcrop R is surrounded by
marine sediments. Processes that formed outcrop R were probably similar
to those that formed outcrops J and S. Outcrop R, therefore, is
interpreted as a shelf sand ridge. The fine grain size and lack of
cross-bedding suggests that outcrop R was deposited at the distal margin
78
of a sand ridge.
DROOP SANDSTONE
The Droop Is a Type 2 sandstone. It is sheet-like in geometry,
clean, and coarse-grained, and it lies at the transition between the
upper and lower parts of the Bluefield Formation.
Grain size within the Droop ranges from 0.09mm to 0.34mm and
averages 0.19mm (fine sand). Grain size fines upward; however, quartz
authigenesis obscures original detrital grain size and so this trend may
not be significant. Quartz percentage is high (88.3%). Rock fragment
and matrix percentages are low (combined mean = 7.2%).
The Droop overlies fossillferous marine shales (Talcott Shale) and
is overlain by a sequence of shales (Raines Corner and Possumtrot) which
include coal horizons (Reger, 1926). The overlying shales are highly
variable in ,appearance. They may be gray, blue-green, black or olive
and occasionally red in color. They Include carbonaceous material as
well as pyrite, siderite and carbonate nodules. Both plant and marine
fossils have been reported. Sandstone Interbeds and lenses are also
found (Reger, 1926; McColloch, 1957). These shales would appear to be
estuarine and/or lagoonal deposits associated with marsh environments.
The Droop appears to be a nearshore coastal sand.
The upper part of the Droop is typically horizontally stratified or
exhibits low angle cross-bedding, and it is sometimes ripple-marked.
The upper contact is gradational. The lower part is extensively
cross-bedded. Most of the cross-bedding is trough cross-bedding, but
tabular planar cross-bedding is present at some exposures. A relatively
79
narrow zone, sometimes present just above the lower contact, is
horizontally stratified or massive. The lower contact is erosional.
The clean, well-sorted, coarse-grained, quartz-rich
(orthoquartzitic) lithology of the Droop is characteristic of barrier
island and strand plain deposits (Galloway and Hobday, 1983; Balazs and
Klein, 1972). Strand plain and barrier island models, as summarized by
McCubbin (1983), show a general beach to offshore trend consisting of 4
environments: 1) horizontally stratified beach deposits; 2) cross-bedded
upper shoreface deposits; 3) horizontally stratified lower shoreface
deposits and; 4) offshore deposits. The contact between the beach and
upper shoreface is sharp. The contact between the upper shore-face and
lower shoreface is gradational. The lower shoreface grades into and is
interbedded with the off-shore environment (McCubbin, 1982; Galloway and
Hobday, 1983). Beach and upper shoreface deposits are present in the
middle and upper portions of the Droop. However, the lower contact of
the Droop Sandstone is erosional and its basal portion is cross-bedded,
unlike the horizontally stratified and gradational lower portion
described in these models.
Tidal inlet deposits, which are associated with barrier islands,
have erosional lower contacts and are characterized by extensive
high-angle cross-bedding (McCubbin, 1982; Galloway and Hobday, 1983).
Lateral migration results in replacement of the normal beach to offshore
sequence by cross-bedded tidal inlet sands. Continued migration allows
reestablishment of beach and upper shoreface environments which then
overlie the tidal inlet deposits. Large proportions of the barrier
island may be comprised of tidal inlet deposits as a result of this
80
process. The vertical progradational sequence thus formed consists of a
lower cross-bedded zone with a scoured base overlain by a horizontally
stratified zone (Galloway and Hobday, 1983). This is very similar to
the sequence observed in the Droop.
The Droop was deposited as a barrier island complex and consists
primarily of tidal inlet and beach deposits. The lower, cross-bedded
zone represents tidal inlet deposition. The upper, horizontally
stratified zone of the Droop represents beach (foreshore) deposition,
but may also contain washover fan and/or flood tidal delta deposits.
Cross—bedded upper shoreface environments would accompany
re-establishment of the beach environment after tidal inlet migration
(Galloway and Hobday, 1983). Therefore, upper shoreface deposits are
probably present between in the middle part of the Droop.
No dune deposits were identified. Dickenson and others (1972)
noted that such deposits would likely be destroyed during reworking. In
addition. the low offshore slope of the basin would have been conducive
to barrier island formation provided a source of sand existed. The
sheet-like geometry of the Droop is due to the progradation of the
barrier island.
UPPER SANDSTONES
Introduction
Clastic Mississlppian strata in southeast West Virginia are
considered to be deltaic in origin (deWitt and McGrew, 1979; Craig and
Varnes, 1979). The upper Bluefield consists of interbedded red, green
and variegated shales (many of which are fossiliferous) with thin silts
81
and sands. The sands are highly variable in lithology but most commonly
are fine-grained and impure. Several sands were named by Reger (1926).
More recent workers (Manspeizer, 1957; McColloch, 1958) have noted that
upper Bluefield sandstones are highly localized and cannot be traced
laterally for any significant distance. This pattern of discontinuous
sandstone distribution is common in deltaic settings, particularly in
those that are dominated by fine-grained sediments. Intercalated with
the shales, silts and sands are thin marine and nonmarine limestones,
coals and dark gray to black shales (Reger, 1926; McColloch, 1957;
Manspeizer, 1958). The close association of these lithologies is also
diagnostic of deltaic deposition (Visher and others, 1975).
Environments of deposition in a deltaic setting include shelf,
prodelta, distal bar (also known as delta platform and delta front), and
distributary mouth bar in the lower delta plane (subaqueous delta).
Environments in the upper delta plane (subaerial delta) include natural
levee (overbank splay), distributary channel, beach, interdistributary
bay, crevasse splay (bay fill), marsh, and lacustrine delta fill.
Barrier islands are sometimes formed at the distal margins of deltaic
lobes (Coleman, 1981). Major deltaic depositional environments are
summarized in Table 2.
INDIAN MILLS SANDSTONE
Outcrop 8 (Indian Mills Sandstone) is composed of intercalated
sandstone and shale. The sandstones are composed entirely of Type 2
sandstone. Four sand units are present. The lowermost sand, which
coarsens upward, is 2.6 meters thick, slightly shaly at its base and
82
TABLE 2
MAJOR DELTAIC DEPOSITIONAL ENVIRONMENTS
INTERDIS- Shales and silts; lenticular laminations;
TRIBUTARY scattered macro and micro brackish water fauna.
BAY:
CREVASSE Coarsens upward from shales to sands; sands
SPLAY: usually poorly sorted and contain 70-80% quartz;
sands contain small-scale cross-beds; sequence
may be repeated several times.
DISTRIBUTARY Sand fining upward into clays or, sands with one or
CHANNEL more fining upward sequences; cross-bedding
common; usually scoured lower contact.
NATURAL Alternating thin sand, silt, and shale; sands
LEVEE : and silts have poor lateral continuity; sands
often well sorted; base of sands usually
gradational; ripple marked.
BEACH: Clean, medium sorted sand with transported
organics.
DISTRIBU- Sands and silts with small scale cross-bedding
TARY MOUTH and high mica content; coarsens upward ;
BAR:
DISTAL BAR: Coarsening upward sequence of alternating sand,
silt and shale laminations; sand and silt become
more abundant near top; ripple marks common;
faunal content decreases upward.
PRODELTA: Finely laminated shale with scattered shells;
faunal content decreases upward; grain size
increases upward; silt-sand laminations become
thicker upward.
TIDALLY PRO- Coarsening upward sand with scoured base.
DUCED SHELF
SANDS
SHELF : Marine shales or sediments Indigenous to
receiving basin.
(after Coleman, 1981)
83
massive in its upper part, and is composed of very fine-grained
(0.08-0.09 mm), moderately clean sand. The lower middle sand is 2
meters thick, cross-bedded, and massive. It is composed of clean,
fine-grained (0.14mm) sand which shows no grain size trend. The upper 2
sands are each approximately 0.5 meter thick, massive and are composed
of very fine- to fine grained sand. These sands are interpreted as
distributary mouth bar sands. The outcrop represents stacking of
multiple bars which interfinger with prodelta clays.
Outcrop Id consists of intercalated shale, silt and sand.
Individual laminae are on the order of 2 to 4 cm thick. Maximum grain
size is very fine-grained sand. Shale and silt decrease in abundance
upward. Quartz percentage is low. Rock fragment and matrix percentages
are high. The coarsening upward trend and overall lithology of this
unit closely approximates that of distal bars.
BRADSHAW SANDSTONE
Outcrop Ic consists of finely intercalated sand, silt and shale
with most laminae on the order of 2 to 4 cm in thickness. Grain size in
the coarse-grained laminae ranges from coarse silt to very fine-grained
sand. Shale and silt abundance decreases upward. Quartz percentage is
relatively low. Rock fragment and matrix percentages are high. This
deposit resembles the coarsening upward sequence of distal bar deposits.
The intercalation of sand, silt and shale and overall lithology are
typical of distal bar deposits.
Outcrop 6 is composed of 2 coarsening upward sequences. The upper
sequence grades from fine-grained, matrix-rich (Type 1) sandstone at its
84
base to massive, coarse-grained, clean (Type 2) sandstone in its upper
portion. Grain size ranges from coarse silt (0.04mm) in the Type 1 sand
in the lower part of the sequence to very fine sand (0.097mm) in the
upper part of the sequence.
The lower sequence grades from shale at its base to Type 1 sand in
its middle part to Type 2 sand in its upper part. Grain size ranges
from very coarse silt (0.06mm) in the Type 1 sand to very fine sand
(0.08mm) in the Type 2 sand.
The lithology and grain size trend of the upper sequence are
characteristic of distributary mouth bar deposits. The lithology of the
lower sequence is intermediate between upper distal bar and distributary
mouth bar deposits. The upper sequence is interpreted as a distributary
mouth bar. The lower sequence may represent upper distal bar deposition
or deposition in the distal portion of a distributary mouth bar.
Outcrop 7 is a coarsening upward sequence from shale and silt at
the base to fine-grained (Type 1) massive sandstone at the top. The
outcrop is 3.05 meters thick. The upper contact is sharp and the
sequence is overlain by green, fosslliferous shale. The overall
sequence is similar to that of the distributary mouth bar, but the
outcrop is thinner and more fine-grained than typical distributary mouth
bar deposits. Outcrop 7 probably represents the distal portion of a
distributary mouth bar.
BERTHA SANDSTONE
Outcrop 5 is composed of 2 strata of Type 2 (coarse-grained)
sandstone located at the top and bottom of the outcrop. The Type 2 sand
85
at the base of the outcrop Is coarse-grained, contains abundant clay
matrix, and is poorly sorted. Where clay matrix is absent, the sand is
cemented by carbonate. The Type 2 sand at the top of the outcrop is
coarse-grained, very clean, well-sorted and quartz cemented. The
central portion of the outcrop is composed of intercalated calcareous
Type 1 sand (very fine-grained, impure), silt and shale.
The central portion of the outcrop was largely covered and could
not be examined closely. Its general lithology (intercalated sand, silt
and shale) can be found in a variety of deltaic environments and so the
origin of the sand could not be determined precisely. However, the
upper sand provides helpful Information. Its white color and very
clean, coarse-grained (medium sand) lithology is rare in the upper
Bluefield. Moreover, it is very thin (0.5m) unlike most coarse-grained
sands in the deltaic environment. This sand is interpreted as a beach
sand developed through reworking of sediments. Deposits of the central
part of the outcrop were deposited in relatively shallow water proximal
to the beach.
Outcrop 4 consists of 4 separate parts. The upper three parts are
coarsening upward sequences which range from 2.3 to 3 meters in
thickness. These are shaly at their base and coarsen up to massive
sand. The sands in the upper sequences are fine-grained (Type 1 sand)
and matrix-rich.
The lowermost part of outcrop 4 is a fining upward sequence. It is
composed of 2 meters of Type 2 (coarse-grained, clean) sandstone at its
base which fines upward into silts and shales. The lower contact is
sharp and undulatory (scoured).
86
The scoured base and coarse-grained lithology of the base of the
lowermost part of outcrop 4 suggests a distributary channel. The
channel was abandoned, allowing infilling by finer grained materials.
Establishment of an interdistributary bay above the distributary channel
resulted in later deposition of crevasse splay deposits represented by
the upper sequences of outcrop 4.
Outcrop 3b consists of intercalated shale, silt and sand.
Individual beds are on the order of 2 to 4 cm thick. Maximum grain size
is very fine-grained sand. Shale and silt beds decrease in abundance
upward. Quartz percentage is low. Rock fragment and matrix percentages
are high.
This outcrop is lithologically similar to distal bar deposits. The
red color of the outcrop suggests that it was subject to subaerial
exposure. Such exposure is characteristic of subaerial natural levee
deposits. Outcrop 3b is Interpreted to be a natural levee deposit.
GRAHAM SANDSTONE
Outcrop 2b, a Type 2 sandstone, is white in color, coarse-grained
(medium sand), very clean, well-sorted and quartz-cemented. It is
extensively cross-bedded but also contains planar bedding. Crossbedding
is generally high angle and unidirectional. Most cross-bedding is
planar tabular but accretion bedding and trough cross-bedding are also
present. Scour surfaces are present within the sand.
Outcrop 2b is interpreted as a braided stream deposit. Trough
cross-bedding probably represents channel deposition, while scour
surfaces record lateral channel migration. Planar tabular cross-bedding
87
and lateral accretion bedding record downstream bar migration, while
planar beds indicate upper flow regime conditions, probably along bar
crests. A complex assemblage of these types of bedforms and deposits is
characteristic of braided channel deposits (Galloway and Horne, 1983;
McCubbin, 1982; Coleman and Prior, 1982).
Channel and bar migration within braided channels produces fining
upward sequences. Repeated channel and bar migration commonly truncates
the earlier sequence, resulting in multiple but often incomplete fining
upward sequences (Galloway and Horne, 1983; McCubbin, 1982; Coleman and
Prior, 1982). In thin section, outcrop 2b shows two fining upward
sequences, perhaps recording channel and bar migration. However,
extensive quartz cementation obscures original detrital grain size and
so these trends may not be significant.
Outcrop lb is composed of Interbedded shale, silt and sand.
Individual laminae are on the order of 2 to 4 cm thick. Maximum grain
size is very fine-grained sand. Grain size distribution is uniform.
Quartz percentage is low. Rock fragment and matrix percentages are
high. The unit is calcareous and overlies calcareous and fossiliferous
shale. This unit resembles the lower parts of crevasse splay deposits.
The absence of a coarser sand, usually found at the top of these units,
suggests that outcrop lb was formed at the distal margin of a crevasse
splay.
CLAYTON SANDSTONE
Outcrops la, 3a, and 2a of the Clayton Sandstone are coarsening
upward sequences. The outcrops consist of shaly to flaggy sandstone and
88
silt at their bases and coarsen up into massive sandstone. The main
sand units range from 1.8 to 4.9 meters in thickness. Sand units on the
order of Im thick or less are associated with the main sand bodies.
Ripple marks and small scale cross-bedding are commonly present. The
sands contain abundant matrix. Grain size in the sands ranges from
coarse silt to very fine sand.
Associated with the sands are green, black and red shales, some of
which are calcareous and/or fossiliferous, and yellow unfossiliferous
limestones. Most of these units are interdistributary bay deposits.
Some of these may have been subject to restricted or semirestricted
conditions.
Grain size trends and lithologies are similar to those of crevasse
splays. Associated sediments are typical of those of interdistributary
bays. Therefore, these sands are interpreted as crevasse splays.
Summary
Sandstone depositional environments within the upper Bluefield
reflect a shift from subaqueous delta deposition in the lower part of
the upper Bluefield to subaerial delta deposition in the uppermost
Bluefield. Sandstones of the lower part of the upper Bluefield (Indian
Mills to Bertha Sandstones) consist largely of distal bar and
distributary mouth bar deposits. Uppermost Bluefield sandstones (Bertha
to Clayton Sandstones) consist largely of crevasse splay and
distributary channel deposits. The upper Bluefield, therefore, is a
progradational deltaic sequence with subaerial delta deposits prograding
over subaqueous deposits.
89
Interpreted depositlonal environments of upper Bluefield sandstones
are summarized in Figure 10. Note that subaerial delta deposits are
found as low as the Bertha Sandstone in the northwestern part of the
study area but only as low as the Graham Sandstone in the southeastern
part of the study area. This indicates that progradation proceeded from
northeast to southwest across the study area.
DISCUSSION
Basin Energy
DeWitt and McGrew (1979) suggest that conditions in southeast West
Virginia may have shifted from high to lower energy during lower
Bluefled time due to "shoaling of the sea and restriction of wave energy
along the front of the growing Mauch Chunk-Pennington delta complex in
mid-Chester time". Most deposits of the Bluefield Formation below the
Droop indicate low energy conditions.
Whisonant and Scolaro (1980) studied a stratigraphic section from
the middle part of the Bluefield Formation in Mercer County, West
Virginia. Primarily on the basis of paleocurrent data, the section was
interpreted as having been deposited in a nearshore, tide-dominated
environment. No specific tidal range was suggested for the section,
however they suggested that tidal currents were oriented north-south.
Lower Bluefield shelf sands in the study area are finer-grained
than sands deposited in similarly reported environments. Swift and Rice
(1984) note that such shelf sands are generally not formed by fair
weather processes (currents) but rather by large storms (hurricanes).
Most documented shelf sands from the Cretaceous mid-continent area
SOUTHWEST NORTHEAST
SECTIONS 1 5 2 12 6 A lA 8 13 3 9 7 10 11
CLAYTON
SANDSTONE CUVASU cacvASsi CAfTASSt
SPLAT SPUT SPUT
SUBAERIAL
GRAHAM
SANDSTONE CtCVASSI D&AIOCD
SPLAT OtAIOfCL
DELTAIC
BERTHA cuvast
SPUT
SANDSTONE DtACI êmà LCVCt
DtSTBIS*
OTAKT
ounitL
BRADSHAW
OISTUD* DISTUA-
SANDSTONE DISTAL bTAAT UTAtT
lAD N0L*IV SUBAQUEOUSncvn
AAA la
INDIAN DELTAIC
OlSTtlB*
MILLS DISTAL VTAITAAl HDtmi
SANDSTONE AAH
DROOP
SANDSTONE AAJUliei lAJlAUt AAAAIEA
tSUlfD ISLAND ISLAND COASTAL
LOWER
SANDSTONES tmj SMLP SMtir
un SAAD SAAO SHELF
Figure 10: Bluefield sandstone depositional environments
VO
o
91
referred to by Swift and Rice (1984) are from the north-south trending,
east-facing shelf and, therefore, were subject to hurricanes. During
the Late Mississippian the Appalachian basin was a south and west facing
basin and so storm intensities may have been lower than those of the
east-facing Cretaceous shelf (i.e., they would not have been subject to
the direct impact of hurricanes). The finer-grained nature of the lower
Bluefield sandstones, therefore, does not necessarily indicate that
normal (fair weather) energy conditions were low.
The coarse-grained, clean, cross-bedded lithology of the Droop
Sandstone suggests that basin energy was high at least through
deposition of the middle Bluefield. Both wave and current energy were
probably important contributors. The preponderence of shales and
fine-grained, impure lithology of the sandstones in the upper Bluefield
suggests that basin energy was low (deWitt and McGrew, 1979). Deltaic
sands in high energy environments are typically thicker, cleaner and
more laterally extensive than those found in the upper Bluefield.
Conclusions
The Droop Sandstone was likely deposited as a barrier island
complex fronting a delta complex as it prograded over the lower
Bluefield shelf sediments. The delta was deposited into esturine and/or
lagoonal environments which were protected by the barrier island
complex. Basin energy was largely absorbed by the barrier island
complex. Wave and tidal energy were lower in the back barrier area
allowlng less winnowing of fines and less concentration of
coarse-grained materials resulting in the largely fine-grained shaly
92
nature of upper Bluefleld sands. Coarse-grained, clean (orthoquartzite)
sands in the uppermost part of the Bluefield were produced by fluvial
processes (subaerial delta).
93
SUMMARY
The Bluefield Formation represents deposition transitional between
the marine Greenbrier Limestone below and the shallow marine to deltaic
upper Mauch Chunk sediments above. Most lower Bluefield units are
laterally continuous and readily identifiable. Upper Bluefield units
are laterally discontinuous. The Droop Sandstone, located at the
transition between the lower and upper Bluefield, is a sheet-like,
coarse, white, cross-bedded unit of distinctive lithology
(orthoquartzite) which can serve as a marker unit separating the upper
and lower Bluefield in the study area. Sandstones within the Bluefield
range from greenish-gray to buff, fine-grained, calcareous varieties in
the lower part to greenish-gray and reddish-brown, fine- to very
fine-grained or, rarely, coarse, white, cross-bedded varieties in its
upper part.
Bluefield sandstones fall into two groups. Types 1 and 2. Type 1
sands are thin, fine-grained, ripple-marked, and coarsen upward in
outcrop. Quartz abundance is low, averaging 55.8%, and they are rich in
rock fragments and matrix. Type 2 sands are relatively thick,
coarse-grained, well-sorted and cross-bedded and are quartz-rich
(averaging 83.8%).
Diagenetic alteration of Type 1 sands was dominated by mechanical
compaction. Other diagenetic events include carbonate, quartz, pyrite,
hematite and clay mineral authigenesis, intergranular pressure solution,
stylolitization and fracturing. All primary porosity was occluded in
Type 1 sandstones. Minor secondary moldic and fracture porosity is
94
present.
Quartz authigenesis, accompanied by intergranular pressure solution
and stylolitization, was the principal diagenetic process in Type 2
sandstones. Quartz authigenesis did not totally occlude primary
intergranular porosity. Secondary moldic porosity was formed by the
solution of feldspars (moldic porosity) and by fracturing. Carbonate
and clay mineral authigenesis and mechanical compaction also occurred in
Type 2 sandstones.
Lower Bluefield units consist of marine limestone, calcareous shale
and thin carbonate-cemented shelf sands deposited in a shallow marine
setting. The Droop Sandstone was deposited as a prograding barrier
island complex. Uplift of a largely metamorphic source to the east of
the study area caused large volumes of detritus to be eroded and
transported to the area. Upper Bluefield units reflect encroachment
into the area of prograding deltaic environments in which red and green
shales and sandstones, minor coals and limestones were deposited.
Sandstones found within the upper Bluefield include distal bar,
distributary mouth bar, beach, crevasse splay, natural levee and
distributary channel deposits.
95
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100
APPENDIX A;
MEASURED SECTIONS
GENERAL
Named units in the Bluefield are largely those of Reger (1926).
More recent workers have found that most of the units named by Reger,
particularly in the upper part of the Bluefield, cannot be traced
laterally for significant distances. Manspeizer (1958) and McColloch
(1957) combined many of these units into various "intervals". For
example, the Bertha Sandstone, Limestone, and Shale were combined into
the "Bertha Interval". These "intervals" generally can be traced
laterally and can be identified at most outcrops of the Bluefield
Formation, whereas its individual components (Bertha sandstone, Bertha
Limestone etc.) cannot be so identified. The names given to the
sandstones by Reger (1926) are used in this report. Most sample sites
chosen in this study were those identified by Reger (1926).
101
RED SULPHUR SPRINGS SECTION
Location
This section begins just north of the town of Ballard in Monroe
County, West Virginia, and continues, in descending stratigraphic
order, northward to Red Sulphur Springs along state road 12. Reger
(1926) measured this section along a road (which is no longer in use)
parallel to state road 12.
Unit Lithologies
Outcrop la - Clayton Sandstone Thickness Total
(meters)
Sandstone, reddish-brown to greenish-brown, 3.66 6.15
fine-grained, massive to ripple-marked,
slightly flaggy in parts, becomes shaly at
top; upper contact sharp to narrowly
transitional
Shale, green, partly covered 0.91 2.49
Sandstone, green, fine-grained, massive 0.76 1.58
Shale, covered 0.36 0.82
Sandstone, green, fine-grained, flaggy to 0.46 0.46
shaly, ripple-marked; plant fossils present;
lower contact sharp with underlying shales
Outcrop lb - Graham Sandstone Thickness Total
(meters)
Sandstone, green, very fine-grained, shaly, 2.90 2.90
becomes more shaly in center of section,
ripple-marked; upper contact covered, lower
contact narrowly transitional; underlying
shales are sandy and fosslliferous
102
Outcrop le - Bradshaw Sandstone Thickness Total
(meters)
Sandstone, green, fine-grained, massive in 1.49 3.93
upper and lower parts, shaly to flaggy and
ripple-marked in center; upper contact covered
Sandstone, green, fine-grained, shaly to 2.44 2.44
flaggy, ripple-marked; lower contact covered
Outcrop Id - Indian Mills Sandstone Thickness Total
(meters)
Sandstone, green, fine-grained, shaly at 1.52 3.78
bottom, grades upward into massive sandstone
at top; upper contact covered
Sandstone, green, fine- to very fine-grained, 2.26 2.26
lower 1.83 meters shaly to very shaly and ripple-
marked, upper 0.43 meters massive; lower contact
transitional with underlying shales
103
BUCK SECTION
Location
The village of Buck is located in Summers County, West Virginia,
on county road 14. The Clayton and Graham Sandstones are exposed in
the vicinity of Buck and are included in this section. The Clayton
Sandstone is found on the north side of county road 14, 1.5 miles west
of Buck. Reger (1926) described this outcrop as "25 feet thick and
shaly". The Graham Sandstone is found in the bed of Wolf Creek just
east of Buck on the south side of county road 14. Reger described
this outcrop as "coarse, massive" and "30 to 40 feet thick".
Unit Lithologies
Outcrop 2a - Clayton Sandstone Thickness Total
(meters)
Sandstone, reddish-brown, fine-grained, 4.48 7.16
massive, medium-bedded, ripple-marked; minor
shale lenses present; upper part becomes
shaly and grades into overlying red shales
Shale, red 1.22 2.28
Limestone, yellow 0.15 1.06
Sandstone, reddish-brown, fine-grained, 0.91 0.91
massive; sharp bounding contacts; underlying
units consist of red shales
Outcrop 2b - Graham Sandstone Thickness Total
(meters)
Sandstone (orthoquartzite), medium- to coarse- 14.02 14.02
grained, white to buff; uppermost portion
horizontally bedded, middle portion
extensively cross-bedded; cross-beds are large
scale (up to 2 feet) and generally high-angle
(up to 25 degrees), and are apparently
unidirectional; planar cross-bedding most
abundant; lowermost portion is calcareous and
cross-bedded and contains lenses and lobes of
non-calcareous orthoquartzite
104
TALCOTT #1 SECTION
Location
This is the Talcott Section of Reger (1926) and is located just
east of the town of Talcott in Summers County, West Virginia, on state
road 12. It begins just north of the eastern portal of Big Bend
Tunnel and continues, in descending stratigraphic order, northeast
toward Talcott.
Unit Lithologies
Outcrop 3a - Clayton Sandstone Thickness Total
(meters)
Sandstone, reddish-brown, fine-grained, 1.83 7.61
massive becoming flaggy at top; upper contact
sharp to narrowly transitional with overlying
red shales
Shale, green 0.91 5.78
Sandstone, green, massive 0.15 4.87
Shale, green, calcareous, fossiliferous 0.15 4.72
Shale, reddish-brown 1.22 4.57
Sandstone, reddish-brown, fine-grained, upper 3.35 3.35
two thirds massive, lower third shaly to very
shaly; lower contact narrowly transitional
with underlying yellow limestone and gray
calcareous shale
Outcrop 3b - Bertha Sandstone Thickness Total
(meters)
Sandstone, reddish-brown, fine-grained, 2.44 2.44
ripple-marked; lower shaly part coarsens
upward to flaggy upper part; upper and lower
contacts covered
105
MARIE SECTION
Location
This outcrop is located southeast of the village of Marie in
Monroe County, West Virginia, on county road 19. Reger (1926)
described the outcrop as "shaly at top, massive at base" and 30 feet
thick.
Unit Lithology
Outcrop 4 - Bertha Sandstone Thickness Total
(meters)
Sandstone, green, fine-grained, shale at base 2.74 11.58
grading up to massive sandstone in upper part;
upper contact sharp with overlying shales
Sandstone, green, fine-grained, shaly at base, 1.16 8.84
grades up to flaggy sandstone
Shale, dark gray 0.82 7.68
Shale, green, upper 0.38 meters consists of 1.68 6.86
green, flaggy to massive sandstone
Sandstone, green, fine- to very fine-grained, 1.37 5.18
upper and lower portions shaly, center part
flaggy to massive
Shale, green; mostly covered 1.83 3.81
Sandstone, brown becoming greenish toward 1.98 1.98
upper part, fine- to medium-grained, massive;
more massive at base and fines upward; shaly
zone in center; lower contact sharp and wavy
with underlying shales and yellow limestone
106
BERTHA SECTION
Location
Reger (1926) first described this section on what is now county
road 33 near the village of Bertha in Summers County, West Virginia.
Bertha is now covered by water of the Bluestone Reservoir. The
outcrop is located on county road 33 west of its juncture with county
road 14/2 and west of and below the Bluestone Conference Center. This
is the type section for the Bertha Sandstone. Reger (1926) described
the outcrop as being "shaly and 45 feet thick".
Unit Lithology
Outcrop 5 - Bertha Sandstone Thickness Total
(meters)
Sandstone, white to buff with iron stains, 0.30 10.81
medium to coarse-grained, massive; sharp
bounding contacts; overlain by shales
Shale, green, mostly covered 0.76 10.51
Sandstone, green, fine-grained, massive and 5.33 9.75
ripple-marked; calcareous; intercalated with
green shale, most of which is covered
Sandstone, green, fine-grained, flaggy to 0.61 4.42
shaly
Sandstone, green, fine- to medium-grained, 0.46 3.81
cross-bedded
Sandstone, green, fine-grained, shaly to 0.91 3.35
flaggy; intercalated with green shale
Sandstone, green to dark gray, fine- to very 1.92 2.44
fine-grained, very shaly; coarsens upward from
lower shaly part into coarser upper part
Sandstone, greenish-brown, medium-grained, 0.52 0.52
massive; calcareous; underlying shales are
covered
BIG BEND SECTION
Location
This outcrop is located in Summers County, West Virginia, just
east of the mouth of Spruce Run, and just northeast of the juncture of
state road 12 and county road 29, on the southeast side of county road
29. Reger (1926) described this outcrop as shaly and 50 feet thick.
Unit Lithology
Outcrop 6 - Bradshaw Sandstone Thickness Total
(meters)
Sandstone, green, fine- to medium-grained, 2.44 10.81
massive with minor shale lenses; upper contact
and overlying sediments eroded
Sandstone, green, fine-grained, very shaly at 2.71 8.37
base coarsening upward into flaggy sandstone
Sandstone, gray, fine- to medium-grained; 1.46 5.66
cross-bedding present and especially prominant
in upper part; ripple-marks also common
Shale, dark green to dark gray, fisile 0.27 4.20
Sandstone, greenish-brown, fine-grained, with 1.34 3.93
shaly portion in center
Sandstone, green, fine-grained, shaly to 1.22 2.59
flaggy; partly covered
Sandstone, gray to green to brown, fine- 1.37 1.37
grained, ripple-marked; contains brown
carbonate interbeds, lower contact is sharp;
underlying shales are green, gray and red and
nodular and contain coal seams
108
PENCE SPRINGS SECTION
Location
This outcrop is located in Summers County, West Virginia, on
county road 3/18 just northeast of the juncture of county road 3/18
and state road 12. This locality is the Pence Springs Section of
Reger (1926). Reger described the Bradshaw Sandstone here as being
green, hard and 10 feet thick.
Unit Lithology
Outcrop 7 - Bradshaw Sqandstone Thickness Total
(meters)
Sandstone, green, fine-grained, massive, 1.22 3.05
ripple-marked; minor shale lenses; upper
contact sharp with overlying green,
calcareous, fossiliferous shale
Sandstone, green, fine-grained, shaly to 1.83 1.83
flaggy; contains one thin massive sand layer;
lower contact transitional with underlying
green, black and gray shales
109
ROCK CAMP SECTION
Location
This outcrop is located in Monroe County, West Virginia, on the
north side of U.S. Route 219, approximately 0.1 miles north of the
junction of U.S. Route 219 and county road 29 at the town of Rock
Camp. Reger (1926) described this outcrop as "gray, coarse, massive,
and hard".
Unit Lithology
Outcrop 8 - Indian Mills Sandstone Thickness Total
(meters)
Sandstone, green, fine-grained, massive; sharp 0.46 7.71
bounding contacts; overlying rocks are covered
Shale, green, largely covered 0.67 7.25
Sandstone, green, fine-grained, massive; sharp 0.61 6.58
bounding contacts
Shale, green, sandy; largely covered 0.64 5.97
Covered 1.28 5.33
Sandstone, green, fine-grained; low angle 1.52 4.05
cross-bedding; becomes shaly in center; sharp
bounding contacts
Shale, green, partly covered; coal seam at top 1.01 2.53
Sandstone, green shaly at base coarsening 1.52 1.52
upward into fine-grained sand; sharp lower
contact; underlying sediments are shale with
thin sand stringers
lio
TALCOTT #2 SECTION
Location
This outcrop is located in Summers County, West Virginia, just
southeast of the town of Talcott, on the south side of county road
15/2 approximately 0.25 miles east of the juncture of county roads 17
and 15/2. The outcrop was measured along a private road which ascends
Wind Creek Mountain.
Unit Lithology
Outcrop 9 - Droop Sandstone Thickness Total
(meters)
Sandstone (orthoquartzite), white to buff, 21.34 21.34
weathers buff to brown; medium-grained,
friable; lower part characterized by abundant
high angle (up to 25 degrees), large-scale
(up to 2 feet), trough and minor planar
cross-bedding; upper part characterized by
low-angle, small-scale cross-bedding,
horizontal bedding and minor ripple-marks;
lower contact sharp and undulatory with
underlying greenish-brown, calcareous, highly
fossiliferous shale
Ill
ALDERSON SECTION
Location
This outcrop is located in Monroe County, West Virginia,
southwest of the town of Alderson on the north side of county road 1
approximately 0.3 miles east of the juncture of county road 1 and
state road 3. Reger (1926) noted that the exposure "makes a great
white cliff 80 feet thick".
Unit Lithology
Outcrop 10 - Droop Sandstone Thickness Total
(meters)
Covered; includes Droop float 3.66 24.54
Sandstone (orthoquartzite), white to buff, 20.88 20.88
weathers buff to brown; medium-grained,
friable; lower part characterized by abundant
high angle (up to 25 degrees), large-scale
(up to 2 feet), trough and minor planar
cross-bedding; upper part characterized by
low angle, small-scale, cross-bedding,
horizontal bedding and minor ripple-marks;
upper contact covered, lower contact sharp
and wavy
112
ALTA SECTION
Location
This outcrop is located in Greenbrier County, West Virginia, on
the southeast side of U.S. Route 60, just northeast of the bridge
which spans Interstate 64, and 1.5 miles northwest of the town of
Alta. Price and Heck (1939) described this outcrop as white, massive,
cross-bedded and 50 feet thick.
Unit Lithology
Outcrop 11 - Droop Sandstone Thickness Total
(meters)
Sandstone (orthoquartzite), white to buff, 13.72 13.72
weathers buff to brown; medium-grained,
friable; lower part characterized by abundant
high angle (up to 25 degrees), large-scale
(up to 2 feet), trough and minor planar
cross-bedding; upper part characterized by
low angle, small-scale cross-bedding,
horizontal bedding and minor ripple-marks;
upper and lower contacts covered
113
ASSURANCE SECTION
Location
This outcrop is located in Monroe County, West Virginia,
approximately 2 miles south of the town of Greenville, on the north
side of county road 25/4. Reger (1926) described this outcrop as
"being massive but having some green shale in the upper portion, the
entire thickness being 35 feet".
Unit Lithology
Outcrop 12 - Webster Springs Sandstone Thickness Total
(meters)
Sandstone, green, shaly to flaggy, ripple- 1.22 7.32
marked; upper contact covered
Sandstone, greenish-brown, shaly, ripple- 2.44 6.1
marked; thin shale seam at top
Sandstone, greenish-brown, fine-grained, 1.68 3.66
medium-bedded to flaggy; contains a few shale
lenses; cross-bedded at base, fines upward
Sandstone, greenish-brown to buff, cross- 1.98 1.98
bedded; lower contact covered
114
WAYSIDE SECTION
Location
This outcrop Is located In Monroe County, West Virginia, on the
north side of county road 7 approximately 2 miles northeast of the
village of Wayside. Reger (1926) described this outcrop as "15 feet
thick, calcareous and shaly".
Unit Lithology
Outcrop 13 - Webster Springs Sandstone Thickness Total
(meters)
Sandstone, partly gray and calcareous and 1.75 10.37
partly greenish-brown; fine-grained, massive
at top becoming shaly at base; upper and lower
contacts sharp; overlying sediments largely
calcareous shales
Shale, yellow, calcareous 2.29 8.62
Sandstone, greenish-brown, fine-grained, 0.23 6.33
massive
Shale, yellow, calcareous 3.66 6.10
Sandstone, greenish-brown, fine-grained, 2.44 2.44
upper part massive, lower part massive to
slightly shaly, central part shaly; ripple-
marks present In shaly part; upper contact
with shale sharp; lower contact covered
115
GREENVILLE SECTION
Location
Approximately 2 miles west of the town of Greenville in Monroe
County, West Virginia, a road cut on the north side of state road 122
exposes a sandstone in the lower part of the Bluefield Formation.
This sandstone may be equivalent to the Edray Sandstone of Reger
(1926).
Unit Lithology
Outcrop 14 - Edray Sandstone Thickness Total
(meters)
Sandstone, green, very fine-grained, very 4.22 6.86
shaly to flaggy; calcareous; upper contact
gradational; overlain by shale
Sandstone, gray, very fine-grained, ripple- 2.44 2.44
marked; calcareous; lower contact covered
116
APPENDIX Bl:
POINT COUNT DATA
Type 1 Sandstones
Sample Quartz MRFs SRFs Matrix Feld- Pore Carbon- Other
Number spar Space ate
Ka8 56.0 27.0 1.3 6.0 3.7 0.0 0.3 5.7
Ka2 46.7 17.3 16.7 19.3 T 0.0 0.0 T
Avg. 51.3 22.2 9.0 12.6 1.8 0.0 0.1 2.8
Fll 49.0 18.0 T 26.0 1.0 0.0 0.0 6.0
F6 64.7 16.0 T 15.0 1.3 0.0 0.0 3.0
Avg. 56.8 17.0 T 20.5 1.1 0.0 0.0 4.5
B3 59.0 23.7 T 10.3 T 0.0 0.0 7.0
B7c 43.3 21.0 T 28.7 T 0.0 0.0 7.0
Avg. 51.1 22.4 T 19.5 T 0.0 0.0 7.0
Kbl 46.3 23.0 6.3 18.3 0.7 0.0 1.3 4.1
Kb2 51.3 25.0 0.3 ?? 13.0 0.3 1.0 5.7 3.4
Avg. 48.8 24.0 3.3 15.6 0.5 0.5 3.5 3.8
L3 46.0 25.3 T 19.3 1.3 0.3 0.0 7.8
LI 60.7 19.7 T 10.3 T 1.0 0.0 8.3
Avg. 53.3 22.5 T 14.8 0.6 0.6 0.0 8.0
Ke6 48.0 10.7 9.7 19.3 3.7 0.0 6.0 2.6
Ke4 65.3 18.3 T 11.7 1.3 0.3 0.0 3.1
Avg. 56.6 14.5 4.8 15.5 2.5 0.1 3.0 2.8
V4 67.7 19.3 1.0 2.7 1.0 0.0 4.7 3.6
V6 58.7 20.7 1.3 7.3 1.0 0.7 5.7 4.6
V8 42.3 13.0 30.7 6.7 0.3 0.0 2.7 4.3
Avg. 56.2 17.7 11.0 5.6 0.8 0.2 4.4 4.2
Kc5 45.7 2.0 17.0 26.3 T 0.7 4.3 4.0
Kc2 56.3 22.3 0.7 19.0 1.0 0.0 0.0 0.7
Avg. 51.0 12.1 8.8 22.6 0.5 0.3 2.2 2.3
S7 58.3 13.3 T 7.3 0.3 0.0 15.7 5.1
S3 66.0 24.3 0.3 2.7 3.0 0.0 2.3 1.4
S2 62.3 25.0 0.3 5.0 1.3 7 ? 6.1
SI 60.3 21.0 0.7 9.7 5.3 0.3 2.3 0.4
Avg. 61.7 20.9 0.3 6.2 2.5 0.1 5.1 3.2
117
J5 41.0 T 0.0 7.0 2.0 0.0 47.7 2.3
J4 50.0 0.3 0.0 0.0 0.3 ? 48.3 1.0
J3 71.7 7.3 0.0 16.7 T 0.7 0.0 3.6
J2b 71.0 4.7 0.0 2.3 1.0 0.0 18.0 3.0
Ja4 51.0 23.0 7.0 6.3 0.7 1.7 8.3 2.0
Ja3b 58.0 6.7 0.0 13.7 T 0.0 20.0 1.6
Ja2 49.7 25.0 0.0 8.0 T 0.0 4.0 13.3
Avg. 56.1 9.6 1.0 7.7 0.6 0.3 20.9 3.8
R4 67.7 7.0 0.7 18.7 0.7 0.3 2.3 2.6
R3 62.0 18.7 0.0 14.3 0.7 0.0 2.3 2.0
R1 67.0 16.7 0.7 7.6 1.3 0.0 5.3 1.4
Avg. 65.6 14.1 0.5 13.5 0.9 0.1 3.3 2.0
Type 2 Sandstones
Cla 90.3 2.3 0.7 4.0 0.3 1.7 0.0 . 0.7
C3 79.7 T T 17.3 T 3.0 0.0 T
C4 87.3 1.3 T 6.0 0.3 5.0 0.0 T
C5 85.0 1.3 6.0 3.3 T 4.3 0.0 T
C9 72.0 7.3 2.3 13.0 1.0 3.7 0.0 0.7
CIO 75.0 10.3 3.3 8.3 0.3 1.3 0.0 1.3
Avg. 81.6 3.8 2.0 8.6 0.8 3.2 0.0 0.4
D2 93.0 0.7 2.0 0.7 0.3 3.3 0.0 T
D3cl 95.7 1.3 T 0.7 0.0 2.3 0.0 T
D6 95.7 T T 0.3 0.0 4.0 0.0 T
D9 95.3 T 0.0 1.7 0.0 2.7 0.3 0.3
D20 86.0 T 0.0 8.7 0.0 5.0 0.3 T
D18 72.3 T T 3.7 0.0 4.3 19.7 T
D17 54.3 0.3 T T 0.7 0.0 44.7 T
D16 92.3 0.7 0.3 T 0.0 1.0 5.7 T
Avg. 85.6 0.4 0.3 2.0 0.1 2.8 8.8 T
M16 76.3 7.7 3.0 9.0 0.3 3.7 0.0 T
MU 78.7 1.0 1.3 15.0 0.3 2.7 0.0 1.0
MIO 84.0 7.0 2.0 1.3 T 4.7 0.0 1.0
M7 80.0 0.3 1.3 10.0 0.7 7.0 0.0 0.7
M5b 89.7 3.0 1.3 1.7 1.0 3.0 0.0 0.3
M4 87.3 2.3 0.7 2.3 2.0 5.0 0.0 0.3
M3 79.7 9.3 T 5.3 0.7 5.0 0.0 T
Avg. 82.2 4.4 1.4 6.4 0.7 4.4 0.0 0.5
DB67 87.0 T 3.0 5.0 0.0 5.0 0.0 T
DB49 87.3 T 4.3 8.0 0.0 T 0.0 T
DB35 94.3 0.7 T 0.3 0.0 4.3 0.0 0.3
DB20 89.7 3.0 1.0 1.7 0.0 4.7 0.0 T
DB12 87.7 2.3 0.3 1.7 0.0 8.0 0.0 T
DBl 94.0 0.3 T 2.0 0.0 3.7 0.0 T
Avg. 90.0 1.0 1.4 3.1 0.0 4.3 0.0 0.1
118
DD40 89.3 T 2.3 5.0 0.0 3.3 0.0 T
DD26 93.7 1.7 1.7 0.7 0.0 2.3 0.0 T
DD20 94.7 T 2.7 1.3 0.0 1.3 0.0 T
DD8 94.3 0.7 T 0.3 0.0 4.3 0.0 0.3
DD4 91.0 1.3 T 2.3 0.0 5.3 0.0 T
Avg. 92.6 0.7 1.3 1.9 0.0 3.3 0.0 0.1
Mixed Type 1 and Type 2 Sandstones
116 61.3 24.3 0.7 8.7 0.7 1.0 0.0 3.3
114 64.0 13.3 T 21.7 T T T 1.0
17 68.3 4.3 4.0 20.7 0.3 T 0.0 2.3
16 78.3 7.0 3.0 9.7 0.7 1.3 0.0 T
14 87.0 T 2.0 3.0 T 5.3 0.0 0.7
Avg. 71.8 9.8 1.9 12.8 0.3 1.5 T 1.5
A19b 55.3 26.3 4.0 10.7 T 0.3 T 3.3
A16 61.3 23.7 0.7 12.0 0.7 T 0.0 1.7
A13 86.0 5.7 1.4 5.5 T T 0.0 1.5
All 80.3 11.0 4.7 2.7 T T 0.0 1.3
A8 56.0 30.0 T 9.3 1.7 0.3 T 2.7
A2 78.0 14.7 1.0 2.0 0.3 2.7 0.0 1.3
Avg. 70.3 18.2 1.9 6.7 0.4 0.6 T 1.9
H13 92.3 0.7 3.3 2.3 0.0 1.0 0.0 0.3
HU 55.3 21.7 3.0 14.7 0.7 1.3 T 3.3
H7 48.3 18.3 0.3 8.7 0.7 0.0 22.0 1.7
H4 49.3 24.3 5.3 6.7 1.0 0.3 11.0 2.0
H3 52.0 11.3 1.0 10.7 T T 21.7 3.3
HI 56.3 14.7 1.0 9.3 0.7 2.7 15.0 0.3
Avg. 58.9 15.2 2.3 8.7 0.5 0.9 11.6 1.8
APPENDIX B2
GRAIN SIZE DATA
Sandstone Sample Mean long
Number axis diameter
(in mm)
Clayton Ka8 .07
ka2 .0441
Fll .043
F6 .038
B3 .042
B7c .081
Graham Kbl .05
Kb2 .0626
D2 .256
D3cl .2225
D6 .2669
D9 .2757
D20 .2505
D18 .2191
D17 .2808
D16 .2693
Bertha H13 .2023
H9 .0503
H7 .0577
H4 .0781
H3 .0470
HI .1504
116 .0594
114 .0557
17 .0645
16 .0847
15 .0954
14 .1281
L3 .0474
LI .0328
Bradshaw Ke6 .0764
Ke4 .0456
V4 .0688
V5 .0636
V6 .0657
V8 .0378
120
A19b .0464
A17 .0357
A16 .0559
A13 .0826
A8 .0551
A7 .0652
A2 .0974
Indian Mills Kc5 .0366
Kc2 .0562
Cla .1198
C3 .1347
C4 .1419
C5 .1391
C9 .0933
CIO .0783
Droop M16 .0923
Mil .1131
MIO .1095
M7 .153
M5b .1512
M4 .1553
M3 .1608
DB67 .1824
DB49 .204
DB35 .2093
DB20 .2403
DB12 .1516
DBl .3426
DD40 .19
DD26 .209
DD20 .24
DD8 .1872
DD4 .2115
Webster J5 .0494
Springs J4 .0478
J3 .0590
J2b .0528
JA4 .0628
JA3a .0419
JA3b .0392
JA2 .0309
S7 .0645
S3 .0768
S2 .0694
SI .0647
Edray R4 .0390
R3 .0371
R1 .0615