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‘(HESIt

This is to certify that the
thesis entitled
LATE PALE OZOIC CRUSTAL COMPOSITION AND DYNAMICS
IN THE SOUTHEASTERN UNITED STATES

presented by

Mary Walter Davis

has been accepted towards fulfillment
of the requirements for

Ph. D. degree in GGOlOgV

 

Major professor

0-7639

 

 

 

 

 

 

ABSTRACT

LATE PALEOZOIC CRUSTAL COMPOSITION AND DYNAMICS
IN THE SOUTHEASTERN UNITED STATES

By

Mary Walter Davis

The Appalachian province has been the site of tectonic
activity throughout the Paleozoic. This activity was a
prelude to the rifting which occurred along the continental
margin in the late Paleozoic or early Mesozoic.

Each of these tectonic events included the uplift of
crustal material, and the erosion and deposition of this
material into nearby sedimentary basins. Determination of
the petrologic character, location, and orientation of these
uplifts should limit the range of theoretical models invoked
to explain the rifting of continental masses.

Although the roots of many of these uplifts are pre-
served in the Piedmont and Blue Ridge, much of the infor—
mation about these uplifts is avaliable only through
petrologic and stratigraphic analysis of the sediments
derived from them. The investigation described in this
paper was designed to thus determine the petrology and

tectonic history of a mid-Carboniferous uplift of the

 

 

Mary Walter Davis

central Appalachian region.

The minerals and rock fragments present in the mid-
Carboniferous sediments of the West Virginia and Virginia
coal field indicate that these sediments were derived from
a source terrane which included low and medium grade meta—
morphic rocks, unmetamorphosed sediments, and intrusive and
extrusive magmatic rocks. The distinct vertical composition-
al zonation of these sediments suggests the progressive
erosion of a single source terrane following a major epi-
sode of uplift and magmatic emplacement. This terrane
consisted of a batholithic complex surrounded by low and
medium grade metamorphics, and capped by a sedimentary-
volcanic cover. The limited vertical and lateral extent of
batholith—derived detritus in the sediments suggests that
this magmatic complex was relatively thin, and was nearly
completely removed by erosion. The source terrane was one
of three Carboniferous source terranes located along the
eastern margin of the continent, and oriented at high angles

to the present Appalachian trend.

 

 

 

LATE PALEOZOIC CRUSTAL COMPOSITION AND DYNAMICS

IN THE SOUTHEASTERN UNITED STATES

By

Mary Walter Davis

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Geology

1972

 

 

ACKNOWLEDGMENTS

My sincere thanks go to Robert Ehrlich, not only for
his assistance with this project, but for his friendship
and encouragement through the years.

John Ferm of the University of South Carolina was
instrumental in obtaining the core samples, and served as
field advisor. His interest and encouragement have been
invaluable.

This study would not have been possible without the
cores provided by Consolidation Coal Company, and by
(other firms which wish to remain anonymous. I am especially
ggrateful to Nick Spanos, Jack Vonfeld, Gene Highlander,
.Iim Yates, Chuck Mills, Jarrette Estep, George Denton, Fred
IAllison, George Billings and Doug Prebble.

Carl Steinfurth of Michigan State University provided
exurberant assistance during most of the field work. Field
tirne was also contributed by David Carpenter and Guy
Paxigett of the University of South Carolina, who sometimes
negglected their own work to help with mine. The West
Vil?ginia Geologic and Economic Survey provided financial
aSSistance for part of the field work.

I would particularly like to thank the members of my

COUHnittee--Thomas A. Vogel, Robert L. Anstey, James Fisher,

ii

iii
and Sam B. Upchurch--for their assistance. The students
and faculty of the Geology Department have provided a
pleasant atmosphere and a good deal of moral support.

It is hardly possible to summarize my gratitude to
my parents, Norman and Esther Walter, in a few brief
sentences. However, in connection with this research, I
must at least thank them for providing a base of operations
for the field work, and feeding many a hungry geologist
I have brought their way.

Of the many teachers who have helped and encouraged
rne, Esten Davis, J. Attison McClanahan, and Bennett T.

ESandefur deserve special mention and thanks.

 

 

 

TABLE OF CONTENTS

Page

LIST OF TABLES . . . . . . . . . . . . . vi
LIST OF FIGURES . . . . . . . . . . . . . vii
INTRODUCTION 0 O O O O O O O O O O O O O l
Pocahontas Coal Field . . . . . . . . . 3
LOCAL GEOLOGY O O O O O O O O O O O O O 5
£3AMPLING AND ANALYTICAL TECHNIQUES . . . . . . 7
iPETROLOGY . . . . . . . . . . . . . . . 11
Minerals . . . . . . . . . . ll
Quartz o o o o o o o o o o o o 0 ll
Feldspars . . . . . . . . . . . . l3

Micas . . . . . . . . . . . . 17

Rock Fragments. . . . . . . . . . . 21

Low Grade Metamorphic Fragments . . . 21
Sedimentary Fragments . . . . . . . 21
Plutonic Fragments . . . . . . . . 21
Volcanic Fragments . . . . . . . . 24

smary O O O O O O O O O O O O 224-
COMPOSITIONAL VARIATION . . . . . . 26
Ubiquitous Components . . . . . . . 26
Restricted Components . . . . . . . 26
Petrologic Assemblages . . . . . . . . . 28
Sedimentary—Volcanic . . . . . . . . 28
Low-Medium Metamorphic. . . . . . . 28

Medium Metamorphic-Migmatitic . . . . . 29

Plutonic . . . . . . . . . . . . 29
Variation Within Cores . . . . . . . . . 29

Bear Wallow . . . . . . . . . . . 3O

Erbacon . . . . . . . . . . . . 35

iv

 

 

Ameagle and Kopperston Mtn. . .
Welch . . . . . . . . .
Summary. . . . . . . . .

Composition at Other Sample Locations

Big Ugly . . . . . . . .
Charleston. . . . . . . .
Mt. Alto O O O O O O O 0

Variation Through the Sample Array .
INTERPRETATION OF COMPOSITIONAL VARIATION
Drainage and Deposition. . . . .
Source Terranes . . . . . . .
Discussion of Models.
Class A. . .
Class B. . .

Class C. . . . .
Class D. . . . .

O O O O O
O 0 O O O
O
0

Summary . . . . . . . . .
LOCATION OF SOURCE TERRANE . . . . .
LATE PALEOZOIC CRUSTAL DYNAMICS. . .

Locations of Source Terranes . . .

Petrology of Source Terranes . . .

Paleotectonics. . . . . .
CONCLUSIONS . . . . . . . . .
LIST OF REFERENCES . . . . . . . .
APPENDIX A. . . . . . . . . . .
APPEMNX B. . . . . . . .

 

Table

Ala.

Alb.

A2.

A3.

LIST OF TABLES

Bear Wallow #1: grain size and composition
data . . . . . . . .

Bear Wallow #2: grain size and composition
data . . . . . . . . .

Erbacon: grain size and composition data .

Big Ugly: grain size and composition data .

vi

Page

81

82
83
8A

 

 

Figure

la.

lb.

2a.

2b.

2c.

2d.

3a.

3b.

5a.

5b.

LIST OF FIGURES

Page
Geographic locations of core and outcrop
samples . . . . . . . . . . . . . . 8
Stratigraphic locations of core and outcrop
samples relative to major coal horizons. Cross-
section is along line AA' of Figure 1a . . . . 9
Photographs of mineral components: quartz.
100 X magnification . . . . . . . . . .12

Photographs of mineral components: plagioclase.
100 X magnification . . . . . . . . . .14

Photographs of mineral components: K—feldspar.
100 X magnification . . . . . . . . . .18

Photographs of mineral components: micas.
100 X magnification . . . . . . . . . .20

Photographs of rock fragment components:
sedimentary and volcanic fragments. 100 X
magnification . . . . . . . . . . . .22

Photographs of rock fragment components:
metamorphic and plutonic fragments. 100 X
magnification . . . . . . . . . . . .23

Petrologic assemblages . . . . . . . . .27

Bear Wallow: distribution of feldspar varieties

in cores #1 and #2. Depths in feet are shown to

the left of solid vertical lines; horizontal

bars to the right of solid vertical lines

indicate positions of samples . . . . . . .31

Bear Wallow #1: variation of grain size and

quartz content with depth. Grain size is in phi
units; quartz deviations are based on least

squares regression line shown in Appendix A,

Figure A1. . . . . . . . . . . . . .32

vii

 

 

Figure

5c.

6a.

6b.

9a.

9b.

10.

ll.

12.

138“

13b.
13c.

13d.

Viii

Bear Wallow #2: variation of grain size and
quartz content with depth, illustrated as in
Figure 5b. . . . . . . . . . . .

Erbacon: distribution of feldspar varieties.
Depths in core and positions of samples illus-
trated as in Figure 5a . . . . . . . .

Erbacon: variation of grain size and quartz
content with depth. Grain size is in phi units;
quartz deviations are based on least squares
regression line shown in Appendix A, Figure A2

Ameagle: distribution of feldspar varieties.
Depths in core and positions of samples illus-
trated as in Figure 5a; lithologic legend as in
Figure 6a. . . . . . . . . . . . .

Welch: distribution of feldspar varieties.
Depths in core and positions of samples illus-
trated as in Figure 5a; lithologic legend as in
Figure 6a. . . . . . . . . . . . .

Big Ugly: distribution of feldspar varieties.
Depths in core and positions of samples illus-
trated as in Figure 5a; lithologic legen
(incomplete) as in Figure 6a . . . . .

Big Ugly: variation of grain size and quartz
content with depth. Grain size is in phi units;
quartz deviations are based on least squares
regression line shown in Appendix A, Figure A3

Compositional zonation of West Virginia coal
field sediments. . . . . . . . . . .

Possible source terrane models. Lithologic
legend as in Figure 10 . . . . . . . .

Possible combinations of source terrane models
with drainage-deposition models, and resultant
sediment compositional zonation . . . . .

Development of Model A—l through time. Time I
is oldest; Time IV is youngest. . . .

Development of Model A-2 through time . . .
Development of Model B through time . . .

Development of Model C through time . .

Page

- 33

.36

. 37

. 38

, AO

. 43

.44

.46

. 51

. 56
. 57

 

 

Figure
130 .
14.

Al.

A2.

A3.

AA.

ix

Development of Model D through time . . .

Late Paleozoic tectonic patterns of the
southeastern United States . . . . . .

Bear Wallow: least squares regression relation

between quartz + feldspar content and grain

size. Core #1 shown by circles; core #2 shown

by squares . . . . . . . . . . .

Erbacon: least squares regression relation
between quartz + feldspar content and grain
size . . . . . . . . . .

Big Ugly: least squares regression relation
between quartz + feldspar content and grain
size . . . . . . . . . . . .

Relation between mica composition and

stratigraphic distance above red and green shale
facies (expressed as geographical distance from

Bear Wallow . . . . . . . . . . .

Page

 

 

 

INTRODUCTION

The Appalachian province, which extends from the
Maritime provinces of Canada south to Alabama, was the
site of tectonic activity throughout the Paleozoic. Each
tectonic event included the uplift of crustal material,
and the erosion and deposition of this material into
nearby sedimentary basins. This pairing of uplifts and
adjacent basins continued at least to the late Paleozoic
or early Mesozoic, when rifting occurred along the
continental margin.

This tectonic activity was a prelude, then, to the
major orogenic events affecting this portion of the conti-
nent; late Paleozoic uplifts, in particular, may have been
directly related to the rifting process. Thus determina—
tion of the petrologic character, location, and orienta—
tion of these uplifts should limit the range of theoreti—
cal models invoked to explain the rifting of continental
masses.

Although the roots of many of these uplifts are
preserved in the Piedmont and Blue Ridge, much of the
information about these uplifts is available only through
petrologic and stratigraphic analysis of the sediments

derived from them. The locations and gross geometry of

 

these uplifts can sometimes be outlined by sediment dis-
persal patterns. The composition of detrital sediments
provides information regarding the proximity and petro—
logic character of the uplands, their internal structure,
and the extent of uplift. Such information, as a whole,
should also clarify the tectonic style of this region, and
determine whether these orogenic regions of the Piedmont
were periodically remobilized, or were uplifted and eroded
in a single episode.

Some of these techniques of reconstructing tectonic
history from sediment analysis have been successfully
applied in the late Paleozoic sediments of the Appalachian
region. Devonian sediments of the Catskill complex (Allen
and Friend, 1968) contain volcanic rock fragments and other
shallow crustal material consistent with the erosion of
newly uplifted terranes. Analysis of the compositional
variation of mid—Carboniferous sediments in the Black
Warrior basin of Alabama (Ehrlich, 1965; Davis and Ehrlich,
1972) demonstrated that they were eroded and transported
northward from an east—west trending Ouachita structure;
the roughly north—south trending Appalachian structure was
not an active source of sediment in this area at this
time.

In the central Appalachian region, the depositional
history and dispersal patterns of the Carboniferous sedi—
ments of the Pocahontas coal field of West Virginia and

Virginia indicate that they were derived from a localized

 

source oriented at high angles to the present Appalachian
trend. The investigation described in this paper was
designed to determine the petrology and tectonic history

of this source terrane.

Pocahontas Coal Field

One of the major depositional basins of the Carboni-
ferous is the Pocahontas coal field region of West Virginia
and Virginia. The basin contains graywacke sandstones, which
are associated with coals, dark silts and shales, and
orthoquartzitic sandstones; this sedimentary sequence
seldom exceeds 3,000 feet in thickness throughout the
basin. In the northwestern part of the basin this thick—
ness encompasses strata ranging from Chester to Mononga—
hela in age; but in the southeastern portion, this entire
thickness is included in the lower Pottsville Pocahontas
Group (White, 1903). The sandstone composition, and the
rapid thinning of the sediments away from the basin,
therefore indicate the rapid deposition of material eroded
from a nearby source terrane; thus these sediments record
a major orogenic event.

Although these sediments have attracted a good deal
cxf attention, because of their economic resources, most
exeologic investigations have concerned mapping, resolu-
tjxon of stratigraphic relations, and other problems related
tC> coal quality and production. Little petrologic work has

beeni done. However, preliminary examination had shown that

 

 

4

these sediments contain a great variety of minerals and
rock fragments which should enable description, in some
detail, of the source terrane petrology. In addition,
evidence that these sediments were derived from a small
source terrane suggests that it might be possible to relate
large scale variation in sediment composition to the
internal compositional geometry of the source terrane.

Thus this investigation of the Pocahontas coal field
region has several objectives. One is the determination of
the variety of rock types present in the source. Another is
the development of models for the internal structure of the
source terrane, and the tectonic, erosional, and deposi—
tional history of the uplift and its derived sediments. A
third goal is the synthesis of these results with those of
other workers to produce a reconstruction of the late
Paleozoic tectonic history of the southeastern United

States.

 

 

 

LOCAL GEOLOGY

The coal field region of West Virginia and Virginia
is bounded on the east and south by the Appalachian fold
belt, and to the northwest by the broad Cincinnati arch.
Although the southeastern portion of the coal field
sediment has been involved in the folding, most of it is
exposed in the relatively flat—lying strata of the Appa—
lachian plateau.

The sediments of interest here are the coal measures,
which contain coarse sandstones (sometimes conglomeratic),
siltstones, dark shales, and coals. These sediments are
underlain by an assemblage of red, green, and gray shales,
with minor amounts of sandstone and limestone; this litho-
logic assemblage (Mauch Chunk and Greenbrier) was used as
a lower datum for sampling. It has been assigned to the
Mississippian, and the overlying coal measures to the
Pennsylvanian; but recent work in eastern Kentucky (Ferm,
et al., 1971) has demonstrated that the red shale and
Llimestone assemblage is simply the offshore facies of the
filuvial—deltaic coal measures.

The coal measures themselves are divided into strati—
g1?aphic units first described by White (1903). Analysis

Of' the depositional environments of these sediments (Ferm,

 

 

6

1971; Ferm and Cavaroc, 1968; Englund, 1972) has demon-

strated the presence of several distinctive synchronous

environments which transect the traditional litho-strat—
graphic units. The present study establishes a composi—

tional zonation within these sediments which cross-cuts

both the traditional stratigraphic units and the deposi—
tional units, thus providing a third framework within

which these sediments may be described.

 

 

 

SAMPLING AND ANALYTICAL TECHNIQUES

Sampling was directed towards sandstones and conglo-

 

merates, since the maximum variety of detrital components
occurs in coarse—grained sediments. Samples were taken
primarily from the sandstones of six continuous cores
ranging from 800 to 2,000 feet in length. Outcrops near
the core locations served to extend the vertical sections;
other outcrop samples were taken in areas where cores were
not available. These outcrop samples were collected only
from recently exposed outcrops, since exposure to sub-
aerial weathering quickly destroys or alters many minerals
and rock fragments.

The sample array covers all of the major facies in
the basin and incorporates a number of well-known coal beds.
The geographic and stratigraphic locations of the samples
are shown in Figures 1a and lb.

Compositional data was largely obtained from about
150 thin sections cut perpendicular to the bedding of the
samples; additional rock chips and powdered samples were
used for staining and X-ray analysis.

Most routine microscope work was done on the flat
stage. Quantitative compositional data was based, in most

cases, on 100 point counts per thin section; grain size

7

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estimates were based on measurements of the apparent long
axes of ten quartz (or feldspar) grains located along the
point count traverses.

Determination of plagioclase composition and twin
types was based on the 5-axis universal stage methods
described by Emmons (1943); some plagioclase and K—feldspar
compositions were determined with the electron microprobe.
The presence of K-feldspar was detected, in some cases, by
staining of rock chips and thin sections according to the
method of Bailey and Stevens (1960), and K-feldspar struc—
tural state was determined by X—ray diffraction analysis
(Wright and Stewart, 1968). Diffraction techniques (Borg
and Smith, 1968) were of little use in the determination
of plagioclase composition due to the wide range of compo-

sitions present in these samples.

PETROLOGY

The samples contain a wide variety of minerals and
rock fragments derived from igneous, metamorphic and
sedimentary rocks (Figures 2 and 3). Although some of these
detrital components, like quartz, are not distinctive of
any particular rock type, many of them can only be derived
from a limited range of source rocks. Thus an examination
of the petrology of these sediments can lead to a descrip—
tion of the variety of rock types present in the source

terrane.

Minerals

Quartz

The quartz in these sediments (Figure 2a) ranges from
unstrained through polycrystalline to highly sheared and
foliated. Clouds or trains of small inclusions are common;
occasional grains show vermicular chlorite or rutile inclu-
sions. Some of the quartz exhibits Bohm lamellae, which are
generally indicative of a metamorphic origin (Hietanen,
1938). Although there have been attempts to relate quartz
extinction types to petrogenesis, the only conclusion that
Can be drawn is that the highly sheared types are most

likely derived from metamorphic rocks (Blatt, 1967).

ll

 

 

 

l2

‘\

 

 

Figure 2a.-—Photographs of mineral components: quartz.
100 X magnification.

 

 

 

l3

Feldspars

 

The feldspars in these sediments include members of
the plagioclase series, and several varieties of potassium
feldspar. The twinning, composition and structural state of
the feldspars are influenced by their petrogenetic environ—
ment; thus these minerals are valuable in outlining the
petrology of their source rocks.

Plagioclase composition. The compositions of the

 

plagioclases in these sediments range from high sodium
albite to about Anuo. This compositional range may well
reflect the range in the rocks of the source terrane. How—
ever, since chemical instability of the plagioclases
increases with increasing calcium content, it may be that
more calcic plagioclase was present in the source, but has
been destroyed by weathering and transport.

The high sodium untwinned albite is a distinctive
mineral of low grade metamorphic rocks (Winkler, 1967).
The more calcic plagioclase occurs at higher grades of
metamorphism, but there is no direct correlation between
calcium content and metamorphic grade (Cannon, 1966). Such
plagioclase may also be derived from the entire spectrum of
igneous rocks; compositions in the albite to andesine
range occur in granites and granodiorites.

Plagioclase twinning. The plagioclase twin varieties

 

include untwinned grains, and both simple (such as albite)
and complex (such as Carlsbad-albite) twin types (Figure

2b). The process of transport tends to increase the number

 

 

 

l4

   

       

    

TW/A/A/E ZOMED

Figure 2b.——Photographs of mineral components: plagioclase.
100 X magnification.

 

15

of untwinned grains by breaking down twinned grains
(Pittman, 1969); thus inferences about the source area are
based solely on the variety of twin types present, not on
their relative proportions.

Untwinned plagioclase is often abundant in metamorphic
rocks. As noted above, untwinned albite is characteristic
of low grade metamorphism, but absence of twinning is a
feature common to all grades.

Plagioclase twinning occurs in several types:
"normal”, of which albite is a common type; ”parallel”,
of which Carlsbad, acline and pericline are common; and
"complex”, with Carlsbad—albite the most common form. The
normal and parallel twin types are sometimes referred to as
simple twins. This leads to some confusion of terminology;
the term ”simple” in this context refers to the nature of
the twin law. The term is also used to refer to twins with
only two individuals; thus a grain with albite twinning
follows a simple twin law, but the twinning may be either
simple or multiple. The term ”simple” will be used here
only in reference to the twin laws.

A genetic classification of twin types was suggested
by Vance (1961). Growth (primary) twins form during crys-
tallization from a melt, whereas deformation (secondary)
twins form in response to post-crystallization pressure in
faither magmatic or metamorphic rocks. However, Vance‘s
<3riteria for recognition of growth twins really depend upon

the presence of zoning, which is not common in these

 

16

sedimentary feldspars.

A more useful classification, which is based on the
optical-crystallographic nature of the twin laws, is that
of Turner (1951) and Gorai (1951). They pointed out that
the complex twins are confined to magmatic rocks, and Carls-
bad twins are usually magmatic; the other simple twins may
occur in either metamorphic or igneous rocks. Thus the
presence of complexly twinned plagioclase in these sediments
is a firm indication of a magmatic petrogenetic environment
in the source.

Plagioclase Zoning. Some of the plagioclase in the

 

Pocahontas sediments is compositionally zoned, although
this type is not common in these sediments. The scarcity of
zoned plagioclase may be due to their destruction by weath-
ering, since even in fresh samples of igneous material the
cores of zoned plagioclase are often extensively serici-
tized.

Oscillatory zoned plagioclase occurs in volcanic or
shallow intrusive igneous rocks (Vance, 1965). It occurs
only rarely in metamorphic rocks, and in most such cases
appears to be relict zoning which originally formed in a
nhagmatic environment. The presence of such zoned plagio-
Clxase in these sediments thus carries an important line of

eViidence, for it indicates that at least some of the magma-
‘tiJ: material was shallowly emplaced.

Potassium Feldspar. The sediments contain both twinned

 

aJICi'U.‘ntwinned varieties, both of which are sometimes

 

 

l7

perthitic (Figure 2c). The non—perthitic K-feldspar,
particularly that with microcline twinning, is distinctive
of low and medium grade metamorphic rocks with a high
potassium content, such as metamorphosed arkoses or gray-
wackes, or potassium—rich shales and siltstones (Winkler,
1967).

The perthitic intergrowths of plagioclase in K—feld—
spar can be classified as replacement or exsolution types.
The replacement types are characterized by a large propor—
tion of plagioclase to K-feldspar, and by the arrangement
of the plagioclase in large, irregularly shaped veins and
patches. The exsolution perthites contain a much smaller
amount of plagioclase, which occurs in crystallographi-
cally aligned blebs or stringers.

Replacement perthites are formed by the replacement of
K—feldspar by sodium-bearing vapor or by liquid plagio—
clase (Higazy, 1949; Hutchinson, 1956). An alternative
theory for their formation (Robertson, 1959) is the replace—
ment of plagioclase by K-bearing vapors or solutions.

The exsolution perthites result either from post—
crystallization unmixing of the two feldspar phases (Tuttle,
1952) or from their simultaneous crystallization (Hogan,
et al., 1971). Both types of perthites are characteristic
of magmatic rocks.

The micas found in these sediments include the potas-

sium mica muscovite, and the iron—bearing micas chlorite

 

 

 

 

l8

 

M/Eeoc / '
p59 7/—// 75 @579 74/99/72:

Figure 2c.——Photographs of mineral components: K—feldspar.
100 X magnification.

 

 

 

 

 

l9

and biotite. These are illustrated in Figure 2d.

Muscovite. This is the most common mica in these

 

sediments, and occurs in large, single-crystal flakes.
This mineral is stable under a wide range of temperature
and pressure conditions, and occurs in many potassium—
bearing igneous and metamorphic rocks; thus its presence
in these sediments carries little information.

Chlorite. Chlorite usually occurs in these sediments

 

in small, irregular chunks. This mineral is not abundant
in igneous rocks, but is considered the diagnostic mineral
reflecting the onset of metamorphism. It is stable at low
grade (greenschist) conditions (Winkler, 1967); thus the
presence of chlorite indicates metamorphic rocks of this
grade in the source terrane.

Biotite. The biotite content in these sediments is
quite variable. Where it occurs in more than minor amounts,
it is present in large books, or in coarse aggregates in
combination with chlorite. The petrogenesis of this mineral
is rather ambiguous, since it occurs in a variety of igneous
and metamorphic rock types. However, under metamorphic
conditions, biotite replaces chlorite at medium grade
(amphibolite) conditions (Winkler, 1967). The mutual asso-
ciation of chlorite and biotite in coarse fragments seems

to indicate a metamorphic origin for this biotite.

2O

 

(HA [9/75
Figure 2d.-—Photographs of mineral components: micas.
100 X magnification.

 

 

21

Rock Fragments

 

Rock fragments are a major constituent of these sedi-
ments, and provide additional information about the rock
types of the source terrane. Metamorphic fragments are the
most abundant, but volcanic, plutonic, and sedimentary
fragments (Dicksenson, 1970) also occur. These are illus-
trated in Figures 3a and 3b.

Low Grade Metamorphic Fragments

These fragments are characterized by a high percent—
age of mica and a foliated texture (Figure 3b). They
generally contain muscovite or chlorite, with varying
amounts of quartz or feldspar. Some fragments contain much
organic material, and are probably only slightly metamor-
phosed shales and siltstones.

Sedimentary Fragments

 

The only fragments of this type usually seen in thin
section are shale and limestone fragments (Figure 3a).
These types, as well as siltstone and sandstone fragments,
also occur as pebbles. It may be that some material identi—
fied as ”polycrystalline quartz” in thin section is really
sedimentary debris.

Plutonic Fragments

 

These are compositionally similar to the metamorphic
fragments, but mica is much less abundant and the texture
is equigranular (Figure 3b). Some of these fragments may
be meta-sandstones, but the presence of granite pebbles in

a few localities confirms the presence of magmatic rocks

 

22

       
  

SE mam EV

 
  

"a0 ’1
rut , .

l/OL CAM/C

Figure 3a.-—Photographs of rock fragment components
sedimentary and volcanic fragments. 100 X

magnification.

 

23

 

p4 are/we

Figure 3b.——Fhotographs of rock fragment components:
metamorphic and plutonic fragments. 100 X
magnification.

 

 

24

in the source.

Volcanic Fragments

 

These fragments are fine-grained; some are aphanitic,
while others contain phenocrysts of quartz or feldspar or
show devitrification textures (Figure 3a). Some silicified
fragments occur as pebbles (and may be mistaken for chert

pebbles in the field).

Summary

The minerals and rock fragments of the Pocahontas
coal field sediments were derived from a heterogeneous
source terrane composed of several rock types. These in-
clude low to medium grade metamorphics, unmetamorphosed
sediments, and extrusive and intrusive magmatic rocks.

The presence of sedimentary and volcanic rocks in the
source is inferred from the presence of fragments of these
lithologies in the sediments. Low grade metamorphic rocks
supplied albite, chlorite, and low grade metamorphic
fragments; medium grade rocks supplied more calcic plagio-
clase and biotite. Both grades probably contributed non-
perthitic microcline to these sediments. The presence of
magmatic rock types in the source is indicated by the
presence of zoned and complexly twinned plagioclase in the
sediments. Although some of these may be volcanic in origin,
the presence of perthitic K-feldspar and coarse—grained
granitic pebbles assures the presence of intrusive igneous

material in the source.

 

 

25

This variety of source terrane lithologies is similar
to that seen today in the Blue Ridge and Piedmont. How-
ever, knowledge of this variety of rock types does not, in
itself, allow description of the internal structure of the
source terrane. This detrital assemblage could be produced
by simultaneous erosion of these lithologic types from a
heterogeneous, previously uplifted terrane which has been
remobilized, or by progressive erosion through a vertical
lithologic sequence of a previously inactive area. This
question will be partially resolved in the following
discussion of sediment compositional variation; the result

will clarify the deformational history of the Piedmont.

 

COMPOSITIONAL VARIATION

The detrital components discussed above are not
distributed uniformly through the sample array; they fall
into several associations, which are illustrated in Figure
4. This variation might be attributed to a number of
factors, ranging from simple variation in grain size to
variation in the type of material being supplied from the

source terrane.

Ubiquitous Components

 

Each sample generally contains plagioclase, musco—
vite, chlorite, quartz, and volcanic and low grade metamor-
phic rock fragments. These components are present through-
out the sample array, and reflect the erosion of volcanic,
low grade metamorphic, and intrusive magmatic rocks. This
assemblage acts as an ever present background, upon which
variations in the distributions of the other components

are superimposed.

Restricted Components

 

The components which do not occur in all samples
(Figure 4, center column) include microcline, perthitic

K—feldspars, large books of biotite, and sedimentary rock

26

 

27

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28

fragments. Volcanic fragments, although they constitute
part of the background assemblage, are most abundant when
found with the sedimentary fragments. These variably
distributed components, when combined with the background
components, constitute distinct petrologic assemblages;
each of these can only be derived from a limited set of

source rocks.

Petrologic Assemblages

 

Sedimentary—Volcanic

 

 

The sedimentary-volcanic assemblage contains the
background components, an enhanced abundance of volcanic
fragments, and sedimentary fragments. Since volcanic rocks
form at the earth's surface, and unmetamorphosed sediments
are most likely to occur at the surface, this assemblage 1
reflects the erosion of surficial or shallow crustal
material.

Low—Medium Metamorphic

 

This assemblage contains non—perthitic microcline, 1
which is characteristic of metamorphic rocks with a high
potassium content. Since the background assemblage also
contains material eroded from metamorphic source rocks,
the difference between these two assemblages is largely
one of bulk composition. The potassium-poor background
metamorphic material may have been derived from rather basic

metavolcanics, or potassium-poor metasediments.

 

29

Medium Metamorphic-Migmatitic

This assemblage is characterized by abundant coarse-
grained biotite, biotite-chlorite aggregates, and non—
perthitic untwinned K-feldspar. As noted above, biotite
may be igneous in origin; but the intimate association with
chlorite suggests a metamorphic origin. The amount of
biotite present is from 5% to 15% of the total rock; taking
into account the enhancement in quartz in sediments, the
material which produced these sediments probably contained
30% to 50% biotite. This high biotite content would be
most likely in metamorphic rather than magmatic rocks. The
K—feldspar associated with this biotite indicates the
presence of some magmatic material in the source rocks.
Plutonic

The plutonic assemblage contains perthitic K-feldspar,
which is characteristic of intrusive magmatic environments.
This assemblage usually occurs, in these sediments, in
combination with the microcline-bearing low-medium meta—
morphic assemblage; this probably reflects the commonly
observed close association of these two petrogenetic

environments in the source.

Variation Within Cores

 

The distribution of the petrologic assemblages through
the sample array can be established by examining their

distribution in individual cores.

 

 

 

 

30

Bear Wallow

 

The core samples were taken from two cores spanning
about the same stratigraphic interval; outcrop samples
collected between Bear Wallow and Princeton (within twenty
miles of the cores) served to extend the vertical section
down to the red and green shale facies.

The variation in feldspar varieties with depth is
shown in Figure 5a. In both cores, plagioclase, which is a
member of the background assemblage, occurs throughout the
section. Microcline and perthitic K—feldspars, which charac—
terize the low-medium metamorphic and plutonic assemblages,
occur only in the upper portions of the cores. Outcrop
samples (stratigraphically equivalent to and below the base
of the cores) contain plagioclase and abundant sedimentary
and volcanic rock fragments; thus these rocks contain the
sedimentary-volcanic assemblage.

The effect of grain size upon this compositional
variation is negligible. First, since samples were initially
restricted to the sandstones, grain size variation is
minimal. Secondly, most of the assemblages are defined on
the presence or absence of certain detrital components, not
on their abundance. Thus grain size could only affect the
distribution of these assemblages if grain size fell below
the minimum stable size for these components. Thirdly,
inspection of the grain size variation (Figures 5b and 5c)
in comparison with the compositional variation shows no

correlative trends. That is, the sandstones containing the

 

 

31

 

BEAR WALLOW --1 .-2
I o' 3I
! .5: 2|
2; C
0
500 ;|
I
. I . |
El
3. I
2I 0
g z:
5 fl 3
5 a
3 ° '5
. .l _.
1000 8 3
'3 E
.3
a I
1500

 

Figure 5a.--Bear Wallow: distribution of feldspar
varieties in cores #1 and #2. Depths in feet
are shown to the left of solid vertical lines;
horizontal bars to the right of solid vertical
lines indicate positions of samples.

 

32

BEAR WALLOW --1

 

 

Grain Size Quartz Dovlatlons
3 2 1 0 10 0 10
11, I I .L 1 l J I l I l
0 00 00 - .. + +4,
00 .9.
4.

Figure 5b.-—Bear Wallow #1: variation of grain size and
quartz content with depth. Grain size is in
phi units; quartz deviations are based on
least squares regression line shown in
Appendix A, Figure Al.

 

 

33

BEAR WALLOW "2

 

 

Grain Slze Quartz Dovlatlono
3 2 1 0 r0 0’ 10
I I I I I L 1 I 4 I
00 ++
.00 -- — +
0 +
O O -— +
0 +
0 +

Figure 5c.--Bear Wallow #2: variation of grain size and
quartz content with depth, illustrated as
in Figure 5b.

 

 

34

background assemblage do not have a significantly different
grain size than those containing the metamorphic and
plutonic assemblages.

The effect of depositional environment upon composi-
tion must also be considered, since sands of the same grain
size may be either orthoquartzites or graywackes, depending
upon the depositional environment. The first step in
assessing the effect of the environment is distinguishing
between quartz—rich and quartz-poor sands of the same grain
size; this is done by finding the least squares regression
relation between quartz + feldspar content and grain size
(Ehrlich, 1965; Davis and Ehrlich, 1972). This relation,
for the Bear Wallow cores, is shown in Appendix A in Figure
Al. Data points falling above the line are relatively
quartz-rich for their grain size; those falling below the
line are quartz-poor. The deviation of the observed quartz
content from the expected quartz content (for the same
grain size) may be expressed as a positive or negative
number; these deviations are shown graphically in Figures
5b and 5c. As with grain size, there is no correlative
trend between quartz deviations and the compositional
variation.

To summarize, the sequence of assemblages observed at
this sample locality goes upwards from sedimentary—vol-
canic, through the background assemblage, to the combined
low—medium metamorphic and plutonic assemblage; this

variation is not due to variation in grain size or

 

35

depositional environment. Thus the sequence apparently
reflects variation in the type of material being supplied
from the source terrane.

Erbacon

This section is based on a core which extends 1,300
feet from the surface down to the red and green shale
facies. Compositional variation within this core is shown
on Figure 6a.

Plagioclase occurs throughout the core, but micro-
cline is found only in the upper portion. Perthites are
not present; thus this core contains the potassium—bearing
metamorphic assemblage found in the Bear Wallow cores, but
not the plutonic assemblage. Volcanic fragments and some
sedimentary fragments occur in the lower part of the core.
The sequence is similar to that found in the Bear Wallow
cores, except that the uppermost K—feldspar assemblage is
only metamorphic, rather than metamorphic and magmatic.

As in the Bear Wallow cores, there is no apparent
relation between grain size variation and the distribution
of microcline (Figure 6b). Although the quartz deviations
show a definite vertical pattern, the microcline-bearing
zone includes both quartz-rich and quartz-poor portions of
the core. Thus the compositional variation is not controlled

by either grain size or depositional environment.

Ameagle and Kopperston Mtn.

 

This section consists of a core which includes 2,000

feet of section upwards from the red shale facies, and

 

36

 

 

ERBACON
:
g:
3|
0 0|
a h
2 2|
o 2
2 l
a
500 2 I
a
1000
LEGEND
Sandstone
Slltetone Coal
__ :___ Shale
_-_-- Shale --Red&Green

   

Figure 6a.-—Erbacon: distribution of feldspar
varieties. Depths in core and positions
of samples illustrated as in Figure 5a.

 

 

37

 

 

ERBACON
Grain Size Quartz Deviations
3 2 1 0 10 Q 10
I l I J l I l J 1 I J
.0 ++
. +
e e - +
O O -’ —- _ +
0 +
e +
0 +
0 +
0 +
e e e + 4. +

Figure 6b.--Erbacon: variation of grain size and
quartz content with depth. Grain size
is in phi units; quartz deviations
are based on least squares regression
line shown in Appendix A, Figure A2.

 

 

 

38

500 —

'—-t—.

 

I.
'I

l‘:'
l"
M

I \ll
1 I
.1!

! lll‘l
I
l
l

I
17!!

e—o—a

3 .
' I
. l '
I

1000

Plagioclase

 

'1 £5 ()‘() IIIIIIIIIIIIIIII

d-‘l—

2000 3.81 E

Figure 7.--Ameagle: distribution of feldspar
varieties. Depths in core and positions
of samples illustrated as in Figure 5a;
lithologic legend as in Figure 6a.

 

 

39

several hundred feet of section above this taken from
outcrops on Kopperston Mtn. The lower part of the core
contains the orthoquartzitic barrier beach facies.

The core is composed entirely of the background
assemblage, which contains plagioclase as the feldspar
variety (Figure 7). (The absence of the sedimentary-
volcanic assemblage at the base of this core may be due to
the orthoquartzitic nature of the sandstones.) Samples
from Kopperston Mtn., however, contain some microcline
and perthitic K-feldspar, and thus belong to the same
petrologic assemblage found in the top of the Bear Wallow
cores. like the Bear Wallow cores, then, this section
shows a vertical sequence from the background assemblage
upwards into the metamorphic and plutonic assemblages.

Welch

 

This location includes a core which extends upwards
from the red and green shale facies for about 1,000 feet;
the upper 700 feet of this section is taken from outcrops
a few miles away. Most of the core samples contain extensive
calcite cement, which replaces some feldspars and rock
fragments; thus quantitative grain size and compositional
data were not obtained.

The distribution of compositional assemblages in this
section is shown on Figure 8. Like the Bear Wallow cores,
the background zone is replaced upwards by the potassium
feldspar metamorphic and plutonic assemblage; but in this

section the background assemblage reappears in the upper

 

 

40

.—~—.——.

5C”) .1::::

~—- _._.__

 

O
2
E I I
E” I
‘t l
1000 I
Elzl
E'EI
3';
SH
II
I
1500 I I

 

’——--

Figure 8.—-Welch: distribution of feldspar varieties.
Depths in core and positions of samples
illustrated as in Figure 5a; lithologic
legend as in Figure 6a.

 

 

41

part of the section. The extensive calcite replacement in
the core makes it impossible to say whether the sedimentary-
volcanic components are truly absent here, or if they have
been diagenetically destroyed. Although complete grain
size and compositional data are not available, it appears,
by analogy with the other cores, that the compositional
variation is not controlled by grain size or depositional
environment.
Summary

The four vertical sections described above each contain
a definite zonation of petrologic assemblages. Each of these
presents essentially the same record—-an upward succession
of material produced at increasing depth in the crust. Two
cores contain a complete sequence from the sedimentary—
volcanic assemblage through the background (volcanic and
metamorphic) assemblage, and into the K-feldspar low-
medium metamorphic and plutonic assemblages. (The other
two sections lack the sedimentary-volcanic assemblage at
the base; this may be due to destruction of these relatively
soft fragments by a barrier-beach depositional environment,
or by weathering and diagenesis.) Thus the record indicates,
to a first approximation, progressive denudation of a
source terrane rather than erosion of a compositionally

heterogeneous uplift.

 

 

 

42

Composition at Other Sample Locations

The remaining core and outcrop locations each show
little vertical compositional variation. One of these, a
core, encompasses the same stratigraphic interval as those
previously described, and provides evidence of lateral
changes in compositional facies. The outcrop samples occupy
a stratigraphically higher portion of the section, and are
compositionally different from any of the core samples.
Big Ugly

This section is contained in an 850 foot core (Figures

 

9a and 9b). The entire section is in the metamorphic-
plutonic assemblage which contains perthites and non-
perthitic microcline; in that respect it resembles the
upper portions of the Bear Wallow, Welch, and Ameagle-
Kopperston Mtn. sections. The perthites here are usually
of the exsolution type, in contrast to the replacement
type which is most abundant in the Bear Wallow samples.

Charleston

 

These are outcrop samples, taken over a small area
but with little vertical control. The assemblage here is
the biotite—rich, non—perthitic K—feldspar assemblage
attributed to the erosion of a largely medium grade meta-
morphic terrane. These samples also contain large, coarse-
grained micaceous aggregates of chlorite, biotite and musco-
vite. Some samples collected in this area by other workers
contain small amounts of microcline, which characterizes

the low-medium metamorphic assemblage; so it appears that

 

 

43

BIG UGLY

 

Perthite

Plagioclase

500

Microcline

 

Figure 9a.-—Big Ugly: distribution of feldspar varieties.
Depths in core and positions of samples
illustrated as in Figure 5a; lithologic
legend (incomplete) as in Figure 6a.

 

 

44

 

 

BIG UGLY
Grain Size Quartz Deviations
3 2 1 0 1C) (I it)
0 +
0 +

o +
0 +

0 +
Q .Q — t

0 0 + +

Figure 9b.—-Big Ugly: variation of grain size and quartz
content with depth. Grain size is in phi
units; quartz deviations are based on least
squares regression line shown in Appendix
A, Figure A3.

 

45

the Charleston area marks a transition between the meta—
morphic and plutonic zones and the uppermost medium meta-
morphic..migmatitic zone.
Mt. Alto

These outcrop samples contain the same biotite-rich
K-feldspar assemblage as in the Charleston samples, but
biotite is more abundant. (The increase in the amount of
biotite relative to the other micas through the sample

array is shown in Appendix A, Figure A4.)

Variation Through the Sample Array

 

The distribution of the petrologic assemblages through
the sedimentary volume can be portrayed on a regional
cross-section, drawn by projecting all sample locations into
the AA' plane of Figure 1a. This section, which is shown
in Figure 10, shows the sample locations and the distri-
bution of the petrologic assemblages discussed above.

The most prominant feature on the cross-section is a
large wedge of plutonic and low-medium metamorphic detritus
which includes major portions of the Bear Wallow, Welch,
and Big Ugly cores, and pinches out northwards. Below this
wedge is a zone of sedimentary, volcanic and metamorphic
detritus, which becomes more K-rich in the Erbacon core.
Above the plutonic material, at Charleston and Mt. Alto,
the medium grade metamorphic and migmatitic assemblage
occurs.

Thus the large scale compositional pattern reflects

 

46

 

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47

the variation, through time, in material supplied by the
source terrane; this variation is also apparent in indivi-
dual core sections. The Charleston and Mt. Alto samples
demonstrate the influx, at a still later time, of material

derived from a higher-grade metamorphic terrane.

 

 

INTERPRETATION OF COMPOSITIONAL VARIATION

The data presented thus far have demonstrated the
presence of metamorphic rocks, unmetamorphosed sediments,
and intrusive and extrusive magmatic rocks in the source
terrane of the West Virginia Carboniferous sediments. It
has also been shown that the distinctive petrologic assem-
blages resulting from the erosion of these different rock
types have been preserved in the large scale compositional
variation in the resulting sediments.

Perhaps the most simple conclusion is that, if this
pattern were inverted, the vertical and lateral composi-
tional variations would mirror those of the source terrane.
That is, the sediment compositional pattern is a result of
progressive denudation of a source terrane in which the
major rock types occur in a vertical sequence. However, the
possible effects of uplift, erosion, and depositional
processes must be taken into consideration.

In order to arrive at some acceptable models for the
tectonic and depositional history of the area, a wide range
of source terrane—erosion—deposition interactions was
systematically evaluated. There are a number of combina—
tions of source terrane geometries with drainage and

depositional histories which could produce a compositional

1+8

 

49

zonation in the resulting sediments. However, many of
these zonations would be inconsistent with that observed
in the West Virginia sediments; models which produce such
patterns may be discarded forthwith. In addition, some of
those which produce acceptable compositional zonations are
unrealistic in terms of their source terrane geometry and

their tectonic, drainage, and depositional history.

Drainage and Deposition

 

The drainage and depositional patterns through time

 

are classified here into two general categories, constant
and variable. "Constant” patterns are those in which drain-
age is established and maintained in more or less the same
position through time. Although there will be some migration
of depositional centers, particularly of deltaic lobes,

this will not be on a scale large enough to produce the
regional sediment compositional patterns. Under this type

of system, the sediment compositional pattern will be, in
inverted order, the same pattern as in that portion of the
source terrane which is immediately upstream.

"Variable" drainage and depositional patterns are
those in which major shifts in drainage patterns or deposi-
tional centers occur through time. These would be of such
magnitude, for example, that rock types occurring in
vertical sequence in the source would be deposited as

lateral equivalents in the sediments.

 

SO

Source Terranes

 

These two basic types of drainage—depositional
histories can act upon a number of source terrane geome-
tries, of which four general types are considered here
(Figure ll). The first two types (A and B) involve a single
primary uplift of the source terrane. The latter two (C and
D) are more complex, and require several episodes of uplift,
erosion, and rejuvenation.

The two models of Class A have the major rock types

restricted to generally horizontal layers. The sedimentary-

 

volcanic cover occurs at the surface, and is underlain by
low to medium grade metamorphics, which rest upon the zone
of magmatic emplacement. This source terrane model is
similar to that proposed by Hamilton and Myers (1967) for
the Boulder batholith in particular, and for other batho—
liths in general. The only difference between models A-l
and A—2 is the lateral extent of the magmatic zone; that is,
A—l represents uplift of the central portion of the batho—
lith, whereas A-2 represents uplift of the marginal portion.
The compositional geometries shown by these models
could also be produced by a more complex history involving
uplift, erosion of material down to the low-medium metamor-
phic zone, and deposition of sediment on the eroded
surface. Such a model would also require some volcanism
associated with the second uplift to account for the asso-
ciation of volcanic detritus, in the sediments, with sedi-

mentary fragments.

 

 

 

51

 

Sou rco Terran. Models

 

 

 

 

 

 

 

 

 

 

Figure ll.--Possible source terrane models. Lithologic
legend as in Figure 10.

 

52

The B model presents the major rock types in the same
sequence as the A models, except that the sequence is
lateral rather than vertical. This model could be formed
by doming and partial erosion of the sort of batholithic
terrane shown in model A—l.

The C model involves successive uplifts of small
terranes consisting of the major rock types. This model is
somewhat similar in appearance to the B model in that the
greatest variation in rock type is lateral rather than
vertical; however, the history of uplift is more complex.

The D model is also a possible derivative of the A-l
model; the terrane has undergone an episode of uplift and
erosion, followed by deposition of the sedimentary cover

(unconformably) on the old erosional surface.

Discussion of Models

 

Figure 12 illustrates potential combinations of these
source terranes and drainage patterns. The sediment compo-
sitional zonations resulting from these combinations are
also shown; those which are inconsistent with the observed
compositional zonation are rejected as unacceptable. The
five models which remain are acceptable to a first approxi-
mation; these are illustrated, in time sequence, in Figure
13. However, consideration of these models in more detail
allows further reduction in the number of acceptable

possibilities.

 

 

 

 

53

Drainage-Deposition
Models

Constant Variable

llnaccentanle ”BENIN

A-1 A ~~

Axgxnxtl’rx

~ ~
A‘2 * m A
A A. I. “ i Y t * X. K
~ ~ ~ x i x x A
3 ~m~~~~~~ -~~~~~A "J‘Jtl
0
'0
° unaccenlanlu Incanlanla
E r
0
:1 B
N
h
h
3
° “MW"HMB
0
LI
:3 “w ‘x
O C N ”0' x x
m ~~~ x x

A~
~~~lx¥
~~ (at!

IV

D

N

~
~ A. I» g: 1‘} I
~ ~ ~ [It A y

(\-

‘\

 

Figure l2.-—Possible combinations of source terrane

models with drainage—deposition models, and
resultant sediment compositional zonation.

 

 

Class A

54

Since both of these models are variants of the same

batholithic source terrane model, the major point of diff-

erence between them is their drainage-depositional history.

Model A—l requires some
in order to concentrate
southern portion of the
has a constant drainage

depositional history of

shifting of the depositional centers
the magmatic detritus into the
sediment volume, whereas model A-2
pattern. The knowledge of the

these sediments is not detailed

enough at present to choose between these two models; thus

we must regard both as equally acceptable.

It would probably not be possible to determine whether

these terranes had been previously uplifted and eroded.

Since the postulated erosional depth in the previous

episode is only through the original sedimentary cover,

material produced by this erosion would not be distinctive

enough to detect in the

Class B

sedimentary record.

This model requires a series of rather drastic

changes of the drainage

and depositional patterns to pro-

duce the sedimentary compositional zonation. This appears

almost too fortuitous to be acceptable.

The drainage-depositional pattern proposed by this

model requires deposition of a considerable volume of

sediment laterally equivalent to the volume of sediment

considered here. If subsidence were uniform throughout the

basin, then we would expect to find these lateral

 

55

 

.pmowQSoz we >H oSHB mpmooao mfl
H mafia .msflp gmsosnp H|< Hobo: wo onEmoao>oQII.wma masmfim

 

 

 

 

 

 

 

 

 

 

 

56

.oEHp
. smsos
Sp m
|< am
60: mo onSQOH
o>oml
{pma m
sswa
.m

 

 

 

 

 

 

 

 

 

   

57

 

.maflp gwsossp m

 

 

 

 

 

Hoooz no pso8moao>omuu.oma osswflm

 

 

 

 

 

58

equivalents to be equally thick, coarse-grained, and dirty;
however, the sediments of the basin thin to the north and
south, so the required volume of sediment is not present.
This implies that the model is simply incorrect, or that
subsidence was not uniform throughout the basin. In the
latter case, sediment not deposited directly into the basin
would be bypassed and carried farther from the source.

This model would also imply--if it forms by doming of
a batholithic terrane—~some prior erosion which exposed the
present surface. The eroded material would contain debris
of all the major rock types. However, the sediments (Missi-
ssippian) which contain this detritus are rather fine—
grained, with some limestones. Therefore the initial stages
of uplift (if the model is correct) would have been rather
slow; the original character of the metamorphic and magmatic
detritus would have been obscured by time spent in the soil
profile, in transport, or in the depositional environment
before burial.
Class C

This model involves the uplift and erosion of several
source terranes, in succession, to produce the sedimentary
compositional pattern. The principal objection to this
model is that sediments were apparently dispersed radially
outward from a small terrane (Ferm, 1971) perhaps only 100
miles across; this is comparable in size to many of the
smallest active uplifts today. Thus it seems unlikely that

four such distinct uplifts would occur in such a small area.

 

 

59

.oaap chOMSp o Hobo: no pCoEmoaobomln.©ma osswfim

 

 

 

 

 

 

 

 

 

 

60

Class D

This model requires a complex tectonic history and a
variable drainage—depositional history. As discussed above,
the A-l and A—2 models could also have had such a tectonic
history, but their drainage—depositional histories would be
simpler. As with the A models, the evidence is not suffi-
cient at present to determine whether or not the proposed
depositional history is acceptable.

If this terrane had been previously uplifted and
eroded, there should be some evidence in the older Paleozoic
(or Precambrian) sedimentary record, since magmatic and
metamorphic detritus would have been eroded. Thus this
aspect of this model may be tested as the petrology of
these older sediments is known in more detail.

This model would also imply, as does model B, some
bypassing of sediment through the basin, and its deposition
farther from the source. It seems unlikely that this
bypassing would selectively remove some detrital components,
whilst leaving others behind to produce the compositional

zonation.

Summary
Of the ten original models proposed in Figure 12,
five were rejected immediately because the sediment compo-
sitional zonation they produced was inconsistent with that
observed in the Pocahontas sediments. However, the sequence

of events required to produce the five acceptable patterns

 

 

61

 

.osflp swsongp m Hoooz mo psoegoam>omuu.oma osswflm

 

 

 

 

 

 

 

 

 

 

 

62

is not equally likely in all five cases.

Three of the five models represent source terranes
which are similar to the batholith model of Hamilton and
Myers (1967). Two of these (A—1 and A—2) are vertically
stratified; the other (B) is laterally stratified. The two
remaining models involve the rejuvenation of a previously
uplifted terrane (Model D) or a sequence of small uplifts
in various portions of a compositionally heterogeneous
terrane (Model C).

The latter two models are considered to be unlikely.
The distinct uplift model (C) appears to involve too much
localized tectonic activity for a source terrane of the
size postulated. Model D, which involves erosion through
an unconformable sedimentary cover into metamorphic and
magmatic material, could only be accepted if we assume
bypassing of some of the eroded material through the basin.
However, since the compositional zonation is based on the
presence or absence of detrital components, rather than
their relative abundance, it would seem fortuitous that the
bypassing could be so efficient as to "censor” the deposi-
tional record and thus produce the observed zonation.

Of the batholithic models, Model B is also acceptable
only if the bypassing mechanism is sufficient to create
the compositional zones. Thus it, too, seems an unlikely
possibility.

Therefore, on the basis of these arguments, the

author inclines toward a source terrane based on some

 

 

63

variant of the Hamilton and Myers batholithic model.

If the batholithic model is correct, then at least one
region of the Piedmont, which was previously tectonically
stable, underwent a major episode of uplift shortly before
and during the Carboniferous. Emplacement of magmatic
material may have been associated with this tectonic event,
or may have occurred earlier. Hamilton and Myers (1967)
suggest that many batholiths are emplaced in connection
with tectonic activity, and are eroded during the same

tectonic episode. Portions of the Piedmont do contain mag-

 

matic material which was formed at about this time (Fulla~
gar, 1971); hence the association of magmatic emplacement
with this Carboniferous uplift is a possibility.

Although the Piedmont contains magmatic intrusions
of several ages, it may not be possible to find the speci-
fic terrane which contributed to the Pocahontas sediments.
The sediment composition variation apparently reflects
erosional removal of a batholithic terrane, so the only
remnants of this terrane may be sub—batholithic metamor-
phic material. No doubt a major portion of the information
regarding the development of the Piedmont cannot be found
in the Piedmont itself, but must be extracted from the

sedimentary record.

 

LOCATION OF SOURCE TERRANE

Analysis of sediment dispersal patterns (Ferm, 1971)
has suggested location of the source terrane in Virginia
or North Carolina, with sediments being shed radially
northwest, west, and southwest. The extent of the source
terrane, as measured along the present Appalachian trend,
was probably less than 150 miles. Thus the terrane was
either a small, ovoid terrane like the Black Hills, or
was simply the western end of a linear trend such as the
Ouachitas.

The coincidence of the Cape Fear arch with the
postulated location of the source terrane suggests that
it may be a remnant of a linear terrane. The Appalachian
folds bend in this region, with their trend changing from
northeast in Alabama and Tennessee to nearly north in
Virginia and West Virginia. This could be due to inter—
ference during folding from a large, roughly east—west
linear structure. Thus, the evidence suggests a linear
structure nearly perpendicular to the present continental
margin. If this is true, then it should be possible to
find the equivalent "matching” Carboniferous structure
in Europe or North Africa; such investigations, in turn,

should lead to a reconstruction of the pre—drift tectonic

6A

 

 

65

pattern of Pangaea.

Comparison of the Pocahontas sediments with those of
the Black Warrior basin permits a more precise estimation
of the location of the source terrane. In the Black Warrior
sediments, the location of the source, and the variation in
quartz content (corrected for grain size) with distance from
the source, are known. The fluvial sediments (of the equi—
valent low-medium metamorphic assemblage) at Bear Wallow
are equivalent in quartz content to those about 100 miles
from the source in the Black Warrior; thus the nearest
portion of the Pocahontas source terrane was about this
distance from Bear Wallow. This would place the westernmost
end of this linear structure in south-central Virginia,

just east of the North Carolina—Tennessee border.

 

   

LATE PALEOZOIC CRUSTAL DYNAMICS

The petrologic and tectonic character of a small
portion of the late Paleozoic crust in eastern North Amer—
ica has been described. These results, when combined with
those of other workers in the region, permit a general re-

construction of the eastern continental margin during this

 

time. This reconstruction is based on two major lines of
evidence: the locations of source terranes which were

active at that time, and their petrologic character.

Locations of Source Terranes

 

The source terrane of the West Virginia Carbonifer—
ous sediments was a linear terrane in the Virginia-North
Carolina region, oriented perpendicular to the present
continental margin.

Another major Carboniferous detrital basin in the
southeastern United States is the Black Warrior basin of
Alabama and Mississippi. Ehrlich (1964) demonstrated, on
the basis of sediment composition variation within the
barrier beach facies, that the source of these sediments
lay to the south, and was part of the Ouachita structural
trend. Thus, this source was a linear, roughly east-west

structure, definitely pre-dating any tectonic activity

66

 

Ill v, [A

67

along Appalachian trends in this region.

A similar east-west structure may have existed in the
Pennsylvania—New Jersey-New York area, supplying sediment
to the anthracite coal basin. Aside from the sedimentolo-
gical evidence for a source terrane, the Appalachian
structures are strongly curved in this region (as they are
in the area of the West Virginia source terrane); and there
is some geophysical evidence (Drake, et al., 1963) for an
east—west fault zone in the area of the proposed source

structure.

Petrology of Source Terranes

The sediments of the Black Warrior basin (Davis and
Ehrlich, 1972) contain abundant volcanic and low grade
metamorphic fragments, but lack the suite of abundant pla-
gioclase and K—feldspar so common in the West Virginia
sediments. Either the source terrane for these sediments
did not contain much intrusive magmatic material, or
erosion never out deeply enough into the terrane to expose
magmatic material. In either case, the presence of volcanic
and low grade metamorphic material implies that this
terrane, like that of the West Virginia sediments, was
newly uplifted in the late Paleozoic.

Preliminary work in the anthracite basin sediments
shows the presence of volcanic and metamorphic fragments
and a variety of feldspars. It thus appears that the

terrane for these sediments was also a newly activated

 

68

uplift during the Carboniferous.

Paleotectonics

 

The paleogeography of the southeastern United States
in Carboniferous time is shown on Figure 14. This pattern
is only one of a set of tectonic patterns which existed
through the Paleozoic; the distribution of Devonian high-
lands and basins, for example, is rather different. Thus
the Paleozoic tectonic history of this portion of the
continent is really a mosaic of short-lived, localized
uplifts.

The occurrence of rifting during the late Paleozoic
or early Mesozoic suggests that the tectonic pattern of
the Carboniferous (and perhaps earlier periods) may have
been directly related to the rifting process. In that case,
understanding these tectonic events should clarify our

understanding of the rifting of continents.

 

 

69

   
 
 
   

LEGEND

 
 

" Uplift

z Sediment Transport
Direct ion

 

 

 

Figure 14.-—Late Paleozoic tectonic patterns of the
southeastern United States.

 

 

 

CONCLUSIONS

The Carboniferous sediments of the West Virginia coal

 

field region were derived from a small source terrane in
the Virginia-North Carolina area. The range of detrital
components present in these sediments indicates that rock

types present in the source included sediments, volcanics,

 

shallow intrusives, and low and medium grade metamorphics.
The distinct vertical compositional zonation of these
sediments suggests progressive denudation of a single source
terrane, rather than simultaneous erosion of several
terranes with differing lithologies; thus these sediments
were produced by erosion following a major tectonic event.
On the whole, the large scale horizontal and vertical
variations in sediment composition reflect a complex
response to the composition and geometry of the source
terrane, and the history of erosion, transport, and depo—
sition. Although the data are not precise enough to pro-
duce a unique genetic solution, only a few models are
acceptable. All of these must include a relatively thin
zone of plutonic material, since the plutonic detritus in
the sediments is bounded both vertically and laterally by
metamorphic detritus; this conclusion supports the model

proposed by Hamilton and Myers (1967) for batholiths as

70

 

 

71

thin crustal features.

The presence of plutonic and metamorphic material in
the present—day Blue Ridge and Piedmont suggests that some
remnants of this source terrane might still be preserved.
However, the fact that these rock types are now exposed at
the earth's surface means that considerable erosion of more
shallow crustal material has taken place; the only evidence
for the nature of this material lies in the eroded sedi-
ments.

Stratigraphic and petrologic analysis of sediments

 

derived from other Carboniferous source terranes in east-
ern North America indicates the presence of at least three
major source terranes: one for the anthracite coal basin,
the one discussed in this paper, and one for the Black
Warrior basin. These were roughly linear, and oriented
perpendicular to the present Appalachian trend. Each of
these terranes contained metamorphic and magmatic material
formed at shallow levels of the crust, and represented a
primary episode of tectonic activity.

Similar types of analysis in Europe and northern
Africa should prove valuable in locating any correspond—
ing matching terranes in those continents. Although these
structures, and many other Paleozoic source terranes, may
have been obscured or partially destroyed by subsequent
tectonic activity, their presence should be recorded in the
sediments derived from them. Thus the approach outlined in

this study may be applied to the analysis of other terranes,

 

 

72

and should ultimately lead to a detailed reconstruction

of the Paleozoic tectonic history of Pangaea.

 

 

 

 

LIST OF REFERENCES

 

 

LIST OF REFERENCES

Allen, J. R. L. and Friend, P. F. Deposition of the
Catskill facies, Appalachian region: with notes on
some other Old Red Sandstone basins: Geological
Society of America Special Paper 106, p. 21-74, 1968.

Bailey, E. M. and Stevens, R. E. Selective staining of
K-feldspar and plagioclase on rock slabs and thin
sections: American Mineralogist, Vol. 45, p. 1020-
1025, 1960.

Blatt, H. Original characteristics of clastic quartz
grains: Journal of Sedimentary Petrology, Vol. 37,

p. 401-424, 1967.

Borg, I. Y. and Smith, D. K. Calculated powder patterns:
I. Five plagioclases: American Mineralogist, Vol. 53,

p. 1709-1723, 1968.

Cannon, R. T. Plagioclase zoning and twinning in relation
to the metamorphic history of some amphibolites and
granulites: American Journal of Science, Vol. 264,

p. 526-542, 1966.

Davis, M. W. and Ehrlich, R. Late Paleozoic crustal compo—
sition and dynamics in the southeastern United States:
Geological Society of America Special Paper, in press,

1972.

Dickinson, W. R. Interpreting detrital modes of graywacke
and arkose: Journal of Sedimentary Petrology, Vol. 40,

pr 695-707: 1970'
Drake, C. L., Heirtzler, J. and Hirshman, J. Magnetic

anomalies off eastern North America: Journal of
Geophysical Research, Vol. 68, p. 5259—5275, 1963.

73

 

 

 

74

Ehrlich, H. Evidence on relative ages of the Appalachian
and Ouachita structural trends: Geological Society
of America Special Paper 82, p. 299, 1964.

Ehrlich, R. Quartz content-grain size relationship and
location of source terrane: American Association of
Pegroleum Geologists Bulletin, Vol. 49, Pt. 1, p. 399,
19 5.

Emmons, R. C. The universal stage: Geological Society of
America Memoir 8, 205 p., 1943.

Englund, K. J. Sandstone distribution patterns in the
Pocahontas Formation of southwest Virginia and southern
West Virginia: Geological Society of America Special
Paper, in press, 1972.

Ferm, J. C. Carboniferous paleogeography and continental
drift: Compte Rendu 7e Congres Intern. Strat., Geol.
Carbonif., Krefeld, in press, 1971.

 

Ferm, J. C. and Cavaroc, V. V. A nonmarine sedimentary
model for the Allegheny rocks of West Virginia:
Geological Society of America Special Paper 106,

p. 1-19, 1968.

Ferm, J. 0., Horne, J. C., Swinchatt, J. P. and Whaley,
P. W. Carboniferous depositional environments in
northeastern Kentucky: Guidebook for annual spring
field conference, Geological Society of Kentucky, 1971.

Fullagar, P. D. Age and origin of plutonic intrusions in
the Piedmont of the southeastern Appalachians:
Geolo ical Society of America Bulletin, Vol. 82,

p. 28 5—2862, 1971.

Gorai, M. Petrological studies on plagioclase twins:
American Mineralogist, Vol. 36, p. 884-901, 1951.

Hamilton, W. and Myers, W. B. The nature of batholiths:
United States Geological Survey Professional Paper
554-0, 30 p., 1967.

Hietanen, A. On the petrology of Finnish quartzites:
Government Press, Helsinki, 1938.

Higazy, R. A. Petrogenesis of perthite pegmatites in the
Black Hills, South Dakota: Journal of Geology, Vol.
57, p. 555-581, 1949-

 

75

Hogan, L. M., Kraft, R. W. and Lemkey, F. D. Eutectic
grains: in_Advances in Materials Research, Vol. 5,
Wiley-Interscience, 499 p., 1971.

Hutchinson, R. M. Structure and petrology of Enchanted Rock
batholith, Llano and Gillespie Counties, Texas:
Geological Society of America Bulletin, Vol. 67,

p. 763—806, 1956.

Pittman, E. D. Destruction of plagioclase twins by stream
transport: Journal of Sedimentary Petrology, Vol. 39,
p. 1432—1437, 1969.

Robertson, F. Perthite formed by reorganization of albite
from plagioclase during potash feldspar metasomatism:
American Mineralogist, Vol. 44, p. 603—619, 1959.

Turner, F. J. Observations on twin laws commonly exhibited
by plagioclase in metamorphic rocks: American Mineralo—
gist, V01. 36, p. 581—589, 1951.

 

Tuttle, O. F. Origin of the contrasting mineralogy of
extrusive and plutonic salic rocks: Journal of Geology,
V01. 60, p. 106-124, 1952.

Vance, J. A. Polysynthetic twinning in plagioclase:
American Mineralogist, Vol. 46, p. 1097—1110, ,961.

Vance, J. A. Zoning in igneous plagioclase: Journal of
Geology, Vol. 73, p. 636-651, 1965.

White, I. C. West Virginia Geological Survey, Volume II,
1903.

Winkler, H. G. F. Petrogenesis of metamorphic rocks:
Springer-Verlag New York, Inc., 237 p., 1967.

Wright, T. L. and Stewart, D. B. X-ray and optical study
of alkali feldspar: Parts I and II: American Mineralo—
gist, v61. 53, p. 38-104, 1968.

 

 

APPENDIX A

 

APPENDIX A

Graphs and Data Tables

 

 

 

 

77

1M

IIHII WIlllHl

 

 

O a .0
F a: I
L. I
H I
2 z .
-
.3 . ..II
I&— ° .
0
~ 2
N
: I
‘
=
ear ‘3' _.
“'-‘ x=185 ¢
' 7:671
=: I>=:#12 4
r'-'.72

a 2 1
liralll Slze, I

Figure A1.——Bear Wallow: least squares regression
relation between quartz + feldspar content
and grain size. Core #1 shown by circles;
core #2 shown by squares.

 

 

 

 

a
a
[MIMI
a
a O
C . O
I a ..
?" ea»
0

L. . II
a . . I
" r~
'- I
z .
u.
0U :3

‘- I I .
N .o
2."
- O
: a

“a i: 1.52 ¢

7:721.
2 b=-15.9
r-.78

3 2 1
train SlzeJ

Figure A2.--Erbacon: least squares regression
relation between quartz + feldspar content
and grain size.

 

 

 

 

79

 

e
:2
[Hi lllill
e
63
=
S 6° :
g:
a
a I I
a a .
u f‘
E . '
lb
on
= O
N ‘9 .
Z
a O
=
= O
a -
“’ x=1.65¢
7: 68 'I.
a: b== -9.6€5
"

.78

H
II

3 2 l
liraln sun, I

Figure A3.--Big Ugly: least squares regression
relation between quartz + feldspar content
and grain size.

 

 

80

 

.Azoaaoz seem 809% oocmpmflo Hooflnmosmoow
we commosmxov moflosn oamsm soosw one nos o>ono ooqppmflo
ofismphwfipmnpm one Coflpflmomsoo some newspop coepmaomui.:< onsmflm

Io:!.30..I3 boom So: oocouaa
our om cc 0

0V

ennoosnw + ONIONS + Oillolfl

OS'
Oiliolfl

07'

 

09'

 

 

81

Table Ala.-—Bear Wallow #1: grain size and composition data.

 

 

EEEEIE. §l§2. 222322. Femspar 922212.
3156 .82 67 22 11
3158 1.58 60 10 30
3159 1.65 65 5 3O
3160a 1.55 74 6 2o
3160b 1.99 73 4 23
3161a 2.05 59 3 38
3161b 2.51 62 2 36
3162 1.76 64 3 33
3163 1.39 63 2 35
3164a 2.56 52 3 45
3164b 2.62 65 O 35
3165 2.51 67 5 28
3166 2.36 62 1 37

 

 

82

Table Alb.--Bear Wallow #2: grain size and composition data.

 

 

222222. §222. 922222 Feldspar 922222.
3167a 1.63 66 11 23
3167b 1.78 59 13 28
3168a 1.34 60 13 27
3168b 1.58 68 12 20
3169 1.48 59 6 35
3170 1.11 66 1 33
3171 1.72 74 1 25
3172 2.52 45 1 54
3173 1.34 60 6 34
3174 3.20 45 0 55
3175 3.10 44 2 54
3176 1.38 64 3 33
3177 1.53 63 4 33
3178 1.51 77 2 21
3179 1.30 64 2 34

 

83

Table A2.-—Erbacon: grain size and composition data.

 

 

 

Sampl§_ s1§§_ Quartz Feldspar Others
E-13-6 .90 8o 4 16
E-13—5 1.28 67 4 29
E—l3—4 1.32 73 5 22
E-13-2 1.39 7O 5 25
E-11-6 2.08 68 0 32
E-ll-4 1.37 82 2 16
E-ll-3 1.08 73 3 24
E-lO-l 1.14 76 0 24
E- 9—1 1.92 48 6 46
E- 8-2 2.55 54 5 41
r- 7-2 1.71 52 5 43
E- 7-1 1.60 56 2 42
r- 6-3 1.62 61 5 34
E- 6-2' 1.57 73 0 27
r- 6-2 1.41 70 2 28
M- 6—1 1.76 59 1 40
E— 5-1 1.16 82 1 17
E- 4—3 2.89 59 0 41
E— 4—1 1.20 78 0 22
E- 3-1 1.03 81 1 18
E- 2-2 1.39 78 0 22
E- 1—2 1.98 66 o 34
E— l-Ia 1.19 84 1 15
E- l-lb .71 89 0 11

 

84

Table A3.--Big Ugly: grain size and composition data.

 

 

 

Sample Size 822322. Feldspar Others
CH—7-2 .84 73 5 22
CH—7—l 1.08 66 2 32
CH-6-3 1.03 79 5 16
CH—6-2 .96 76 3 21
CH-6-l 1.49 72 0 28
CH-5-2 1.70 67 5 28
CH—5—l 1.49 59 8 33
CH-4—3 1.10 64 11 25
CH-4-2 1.07 54 7 39
CH-4-l 1.45 60 11 29
CH—3—3 2.43 57 3 40
CH-3-2 2.76 48 4 48
CH—3—1 1.86 58 2 40
CH-2—3 .96 75 5 20
CH-2—2 1.64 62 8 30
CH-2-l 3.90 54 0 44
CH-l—l 2.22 51 3 46

 

APPENDIX B

 

APPENDIX B

Sample Locations

 

Cores

 

The cores described in this study were generously
supplied by several coal and gas firms in the coal field

region. Some of these cores were drilled during explora-

 

tion programs which are still in progress, so I do not
feel at liberty to reveal their precise locations.

The towns of Bear Wallow, Erbacon, Ameagle, and Welch
are located near the core sites, and may be found on most
road maps of West Virginia and Virginia. The Big Ugly core
was named for the Big Ugly Public Hunting Area, which is
located near the town of Leets, West Virginia.

Outcrops

 

Bear Wallow. Outcrop samples were taken from several

 

locations. Samples identified as ”Jacob's Fork” were
collected along Virginia Route 16, between the towns of
Bishop and Jacob's Fork. Samples identified as ”Pocahontas”
were taken from outcrops along Virginia Route 644, between
Pocahontas, Virginia and Bramwell, West Virginia. Samples
identified as ”Princeton” were collected on Interstate 77

south of Princeton, West Virginia.

 

 

 

86

nggh, Outcrop samples associated with the Welch core
are named as ”Sewell”, after the coal of that name which is
stripped from the hilltops near Welch. They were collected
along West Virginia Route 16, from the top of Indian Ridge
down to the junction of that road with U. S. 3oute 52, and
along Route 52 down into the town of Welch.

Kopperston Mtn. These samples were collected along

 

West Virginia Route 85, on the high ridge above the town
of Kopperston.

Charleston. There are three localities represented in

 

this set of samples. Location I is north of Charleston, on

a short spur road which links the south end of Interstate 77
with U. S. Route 21. Location II was a graded hillside

(now overgrown) on West Virginia Route 62 between Cross
Lanes and Rock Branch. Location 111 is on Interstate 64,
between the Nitro and Institute exits.

Mt. Alto. These samples were collected along West

 

Virginia Route 2, between the towns of Mt. Alto and

Millwood.

 

 

 

 

 

 

 

 

 

              

 

 

 

 

 

 

 

 

 

 

 

  
   

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