STRUCTURAL TRANSITION ACROSS THE APPALACHIAN
FOLD FRONT IN NORTH CENTRAL PENNSYLVANIA
by
ROBERT WAYNE DECKER
S.B., Massachusetts Institute of Technology
(1949)
SUBMITTED IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE
at the
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
(1951)
Signature
of
Author...-..........
...
...
...
...
...
...
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Depart en of Geology, January 1, 1951
Certified b ....
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Thesis Sunervisor
Chairman, Departmental Commit ee on Graduate Students
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IRP AIR'
Table of Contents
Abstract...........
page
.
............
..........
.
........
..
1
I Introduction ............................................
5
Location .............................................
5
Problems .............................................
9
Fieldwork.. . . . . . . . . . ..
. . . . . . . . . .10
Bibliography and Library Research...................10
FAcknowledgments...................................1
II Geomorphology.........................................13
Appalachian Plateau.................................13
The Ridge and Valley Province.......................20
Transition Zone.....................................25
III Stratigraphy.........................................32
Ordovician..........................................35
Silurian........................................---.40
Devonian......... .................................. 44
Mississippian..............................................6?
Pennsylvanian...............................- ---..63
Quarternary........................................ 64
IV Sedimentation and Geologic History in Pennsylvania
during Paleozoic Time........................-....
V
Structure..........................................................
......
.......
65
68
Appalachian Plateau............................ ....68
Transition Zone..................................-.
74
The Ridge and Valley Province.......................93
Interpretation....................................98
VI Economic Geology......................................101
Bibliography.............
............-.-------------
106
Map and Sections...........................enclosed in back
Abstract
The Appalachian Fold Front is the boundary between the
plateau structures and the major fold structures of the
Appalachians.
Alabama.
This boundary extends from New York state to
The area concerned in this paper is
a section in
north central Pennsylvania which includes a small rortion
of this Fold Front.
The northeast end of the Nittany Anti-
cline, a major fold of the Ridge and Valley Province, is
separated from the ADalachian Plateau by a four (4) to
eight (8) mile wide strip of highly deformed sediments -the Transition Zone.
Across this zone the raid transition
from the major Appalachian folds to the relatively flatlying rocks of the plateau takes place.
The structural transition is reflected in the Geomorphology
of the area.
The plateau is an unlifted peneplain with a
surface level of about two thousand (2000) feet, highly
dissected by youthful, consequent streams draining southward.
The Ridge and Valley Province, to the southeast, is
made up of long, parallel, evenly-crested ridges separated
by synclinal and anticlinal valleys.
The drainage follows
subsequent courses, and the topography is mature.
Bald
Eagle Mountain, the last of the ridges toward the northwest
in this area, is formed on the upturned, resistant Tuscarora cuartzite (Silurian) on the north limb of the Nittany
Anticline.
ed units, is
The Transition Zone, between the above mentioncharacterized by an irregular, mature topog-
raphy of hills and hollows drained by consecuent streams.
Erosion has proceeded far below the old peneplain surface,
and along the south margin of the zone, the relief has been
truncated by the flood plain of the Susquehanna River.
The
river follows a subsequent course along the aerial outcrop
of Upper Silurian limestones.
Except for Pleistocene and recent alluvium along the major
drainage courses, the entire thesis area is made up of PaLower Ordovician limestones and dolo-
leozoic sediments.
mites are exposed in the core of the Nittany Anticline.
Clastic sediments of the Upper Ordovician and the Silurian
form the north flank of the fold.
The Upper Silurian lime-
stones and the Devonian shales and siltstones outcrop in
the Transition Zone.
The plateau is largely formed on the
relatively flat-lying Pocono sandstone of the Mississipoian.
Some remnants of the Pennsylvanian coal measures occur in
the shallow synclinal basins of the plateau.
This suite of
Paleozoic sediments forms a stratigraphic column over eighteen thousand (18,000) feet thick.
The structure of the plateau is deceptively complex.
The
rocks are relatively flat-lying with a regional dip to the
south, southwest.
Gentle folds, parallel to the main
Appalachian Folds, form long anticlinal and synclinal
trends across the plateau.
A succession of elongate domes
occurs on these anticlines.
They are associated with par-
allel reverse faults.
The fault planes dip steeply north-
west,
and the folds are slightly asymmetric to the south-
eset.
The doming forms an en echelon trend which may be
controlled by both older north-south folds and by a system
of radial stresses developed out from the are of the Fold
Front.
The intensity of the structures increases slightly
with proximity to the Transition Zone.
The TrPnsition Zone
has been subjected to great compressional stresses.
Tight
folds, parallel to the Fold Front, and associated reverse
faults, dipping south or southeast, have resulted from the
yielding to these forces.
The deformation- increases toward
the southwest along the Fold Front and decreases toward the
northwest across the Fold Front.
The joint system indicates
that compression came from the south ten degrees east (SlOE)
at an angle of twenty (20) degrees below the horizontal.
The Nittany Anticline is
the most northwestward fold of the
arcuate Ridge and Valley salient in north central Pennsylvania.
It plunges rapidly at its eastern extremity.
The
fold is very asymmetric toward the northwest.
The cause for the rapid dying-out of the major Ap-,alachian
structures across the narrow Fold Front may be multiDle:
First, the relatively incompetent Devonian section of the
p
Transition Zone may have absorbed much of the stress in
semi-plastic deformation.
Second, there may be a basement
high under the southeast margin of the plateau rather than
under the Nittany Anticline as generally believed.
And
third, a possible set of older north-south folds across
northern Pennsylvania and southern New York state may have
given this area a corrugated strengthening action which
helped to halt the advance of the major Appalachian fold
structures.
The observed structures suggest that the forces involved in
Appalachian Mountain building in this area were largely
tangential compressive forces from the southeast.
They
seem to have effected the veneer of sediments more than the
basement.
Nittany Anticline appears to have been thrust
north, northwestward with great crumpling of the sediments
on its north flank.
The eastern end of the fold acted as a
hinge point for the thrust displacement.
The Nittany Anti-
cline may be overturned or overthrusted at depth in the
thesis area.
The surface trace of such a fault is express-
ed in the intense deformation in the Transition Zone.
Recent doubts concerning the validity of the carbon ratio
theory have opened the area to considerable Detroleum and
natural gas prospecting activity.
Many of the structures
on the southeast margin of the plateau and. even the major
Nittany Anticline, itself, are being tested.
5
I Introduction
Location:
The Appalachian Fold Front is marked by the last major fold
in the Ridge and Valley Province of the Appalachian Mountains toward the north or northwest.
It forms a line which
runs generally northeast-southwest, beginninp in northeastern Pennsylvania and terminating in central Alabama.
The fold front does not die out at these extremities.
At
the northeast limit it becomes obscured by the earlier Taconic mountains, and in Alabama it is covered by the Tertiary overlap of the Mississippian Embayment.
The Analachian Plateaus begin on the northwest side of
this boundary and form a continuous unit.
The plateaus
have different names in the various geographic areas, Appalachian Plateau in Pennsylvania and West Virginia, and
Cumberland Plateau in the South, but there is little
struc-
tural or morphological distinction between these divisions.
The Ridge and Valley Province, on the southeast side of the
fold front, forms a continuous morphological unit from
Pennsylvania to Alabama, but structurally there are more
low angle northwest thrust faults in and south from Virginia.
The line of the fold front can easily be traced on either a
4%
physiographic or aerial geology map of the eastern United
States.
On the physiographic map (figure 1) it is the
boundary between the Appalachian Plateaus and the Ridge and
Valley Province.
On the aerial geology map it can be trac-
ed as the boundary between the large irregular aerial exposures of the same formations (the relatively flat-lying
rocks of the plateau) and the narrow, linear exposures of
many formations (the steeply dipping flanks of the major
folds forming the ridges and valleys).
P. H. Price (bibliography 1) studied this boundary in 1931
and named it
the Appalachian Structural Front.
However,
since this is not the only major structural boundary in the
Appalachians,
Price's name is amended to the Appalachian
Fold Front in this paper.
Price considered the front from
an overall standpoint, and his cornlusions were based on
regional data and observations.
This paper concerns the
detailed structure across the fold front at only one small
section of its more or less one thousand (1000) mile length.
The area is in Lycoming County in north central Pennsylvania,
and surrounds the city of Williamsport.
The Fold Front
forms an are trending about N75E through here, and a valley
four (4)
to eight (8)
miles wide separates the plateau from
the flank of the first major fold.
The area studied (figure 2) was approximately ten (10) miles
-.-----u U
FIGURE
I
SCAL E
30
PHYSICAL
DIVISIONS
OF EA S TERN
U.S
d@J
206
FIGURE
SC A LE
2
t
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RELIEF
-
THESIS
MAP
LOCATION
OF
-
20
,30
PENNSY L VANIA
APPALACHIA N
FOLD FRONT
6 0<
wide across the fold front and twenty-five (25) miles long.
It covers parts of the Williamsport, Trout Run, Warrensville, Milton, Lock Haven, and Waterville fifteen (15) minute cuadrangle topographic maps of Pennsylvania.
Recon-
naissance was made of the general features of the plateau
to the northwest and the major folds to the southeast.
Problems:
The author's first interest in the area was to determine
the continuity or discontinuity of the Oriskany sandstone
where it has been upturned and exposed on the flank of the
first major fold.
The Oriskany is the major natural gas
producing formation in the plateau region, and knowledge of
the variations in its aerial extent is extremely important
to wildcat prospecting.
On tracing the outcrops of the Oriskany sandstone, the complex and highly-deformed structures of the belt between
Bald Eagle Mountain (the flank of the first major fold) and
Allegheny Ridge (the edge of the plateau) were immediately
evident.
This highly deformed zone was not in accord with
the generalized idea of the ridge and valley folds terminating simply into relatively flat-lying beds of the plateau.
Cross sections of the Appalachians have always shown the
underlying beds of the plateau to come up in a simple monocline on the flank of the first major fold.
Instead of
this monocline in the area concerned, there are overturned
.
isoclinal folds and reverse faults of considerable magnitude.
These structures were mapped in considerable detail,
and it
is hoped that this data about the structural transition
across the Appalachian Fold Front will be of some value in
the overall controversy concerning Appalachian Tectonics.
Fieldwork:
Ten (10) weeks of mapping and field study were accomplished
during the summer of 1950.
was traversed by auto.
Every road within the map area
Railroads, all major streams, and
most minor streams were traversed on foot.
Traverses were
plotted directly on topographic maps or aerial photographs,
depending on the necessary detail.
Exposures of complete
sections are non-existent in this area, but partial sections were measured by Brunton compass and pacing.
Bibliography and Laboratory Research:
Library research was done previous to and during the field
work at the facilities of the Massachusetts Institute of
Technology, Cambridge, Massachusetts and in the Pennsylvania Geological Survey Library in Harrisburg, Pennsylvania.
A great deal of information was available on general Appalachian Tectonics, but specific data on the area concerned
was largely limited to the notes on Lycoming County from
the Second Geological Survey of Pennsylvania made in 1880
(bibliography 2).
A wildcat well was drilled to the Oriskany at Hyner, Pennsylvania during the summer of 1950.
This well is on the
plateau but only fifteen (15) miles from the fold front.
Until the drilling of this well,
the nearest subsurface
stratigraphic data in the area was more than thirty-five
(35) miles from the fold front.
Samples from the Hyner
well were made available to the author.
These cuttings
were examined with a binocular microscope,
and a well log
was assembled.
Acknowledgements:
Thanks are due to all the members of the Geology Department
at the Massachusetts Institute of Technology for the background training which made this study possible.
Special
thanks are due to Dr. W. L. Whitehead, who originally approved the thesis area and followed the progress of the
work.
Edward G. Dobrick, Geologist, and W. L. Effinger, Explor-
ation Superintendent,
both with the Williamsport Office of
the California Company, deserve great thanks for their help
in suggesting and focusing thought on some of the main topics in this thesis.
Also, it was through their effort that
samples from the Hyner well were available to the author.
Thanks to D. I. Hecker, T. D. Hinkleman, F. C. Hayes, and
my wife, whose interest and assistance were most helpful.
II Geomorphology
Represented within a radius of ten (10) miles of Williamsport, Pennsylvania,
are three (3)
distinct physiographic
units (figures 3 and 4): A. The Appalachian Plpteau in the
north bounded by the flank of the Allegheny Ridge; B. The
Ridge and Valley Province in the south bounded by Bald
Eagle Mountain; and C. The belt of irregular topography six
(6)
to eight (8)
miles wide between the above units.
This
belt, hereafter described as the Transition Zone, contains
the valley of the Susquehanna River.
The features of these three (3) zones are quite distinct
and, therefore, are treated separately.
Appalachian Plateau:
Seven (7) miles north of Williamsport the plateau begins
abruptly on the top of Allegheny Ridge (figure 5).
This
ridge or escarpment forms the southeast flank of the entire
plateau and. runs more or less continuously along the entire
fold front in Pennsylvania.
north of Williamsport is
The face of Allegheny Ridge
in some places steeper than thirty
(30) degrees and has a relief of about nine hundred (900)
feet.
It is formed on the relatively flat-lying and re-
sistant Pocono sandstone (Mississippian), which also caps
the top of the plateau in much of this area.
The surface elevation of the plateau averages from seven-
FIGURES
3 AND
4
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- -
- -
- - -
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-
C.
-
-
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E
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FL 11-
-
(
-
-
- ----
Figure 5.
Looking north across the transition zone toward Allegheny
Ridge.
The gap in the ridge marks the gorge out into the
Appalachian Plateau by Lycoming Creek.
miles northwest of Williamsport-.
Photo taken six (6)
teen hundred (1700) feet to two thousand (2000) feet and reEvidence of
presents an old peneplain surface (figure 6).
this is well established by the truncation of the formations involved in the minor synclines and anticlines farther north on the plateau.
Continental glaciation covered
the surface, but left little evidence except some scattered
boulders from the nearby formations and drainage disruptions expressed by swamps and ponds.
Glaciation extended
over the Transition Zone but left no evidences on Bald
Eagle Mountain.
It
is probable that this area was very
near the southern margin of the ice sheet and, therefore,
shows poor evidence of the features generally associated
with continental glaciation.
Drainage of the plateau is entirely north to south in this
area.
Three (3) major streams, Pine Creek, Lycoming Creek,
and Loyalsock Creek flow out of the plateau in Lycoming
County.
These streams and their tributaries have cut gor-
ges up to one thousand (1000) feet deep.
The gorges are
steep and V-shaped, and the divides between the streams are
wide and flat.
The dendritic nature of the drainage pat-
tern and the relatively homogeneous rocks, through which
they have cut, indicate consequent streams.
In some places
the stream courses are so serpentine in nature as to suggest incisement from an earlier meandering stage.
ent erosional stage of the plateau is youthful.
The presThis is
due in part to both relatively recent uplift of the entire
Figure 6.
Looking southwest from Hyner View across the summit peneplain of the Appalachian Plateau.
The river gorge is cut
over eleven hundred (1100) feet into the plateau.
'9
area and disruption of drainage by glaciation.
The major
streams named above have nearly reached the temporary base
level formed by the elevation of the Susouehanna River into
which they drain.
For this reason they have developed nar-
row flood plains on the valley floors.
Some gravel strewn
terraces are evident on or just above these flood plains.
They may be interpreted as either evidence of intermittent
uplift, or more likely, as terraces formed by the stream
elevations during the receding stage of the last glaciation.
Two (2) anticlinal valleys occur on the plateau in northern
Lycoming County where the minor folding has exposed the
softer Catskill formation (Devonian), underlying the Pocono
sandstone.
These might better be described as shallow,
elliptically-shaped bowls or basins rather than valleys.
The higher surface of the plateau proper forms a rim of
ridges around the basins.
The major axis of the ellipse
inside this rim is about ten (10) miles long in an eastwest direction.
bowls.
Several small streams head into these
The Catskill formation forms a good soil, and the
many farm fields in these shallow basins make excellent
contrast to the dense second growth forest, which everywhere characterizes the plateau surface formed on the Pocono sandstone.
The plateau area of Lycoming County may be summed up as an
-
-
uplifted peneplain with a surface level of about two thousend (2000)
feet, highly dissected by youthful, conseauent
streams draining southward.
The Ridge and Valley Province:
Bald Eagle Mountain (figure 7) is formed from a resistant
Silurian sandstone, which rises at a steep angle on the
north flank of the first major fold in the Ridge and Valley
Province of the Appalachians.
This major fold, known as
the Nittany Anticline, is continuous for over one hundred
(100) miles to the southwest.
Near Williamsport the axis
swings in an east-west direction, and about twelve (12)
miles to the east it
plunges rapidly.
Bald Eagle Mountain
and North White Deer Ridge, formed by the outcrop of the
same resistant formations on the south flank of the anticline, join due to this eastward plunging and disappear
under the overlying formations near Muncy, Pennsylvania
(figure 8).
The Susquehanna River, following a subsequent
course along the aerial outcrop of the Keyser and Tonoloway limestones (Silurian), swings around this nose of the
mountain.
The ridge mountains formed on the flanks of these major Appalachian Folds are long, even-created, and straight (figure 9).
row.
Their sides are steep and the summits flat but narIn many places they are cut by watergaps and windgaps.
All the summit elevations are nearly the same, averaging
Figure 7.
South from the Susquehanna River at Jersey Shore, Bald
Eagle Mountain marks the boundary of the Ridge and Valley
Province.
Note the watergap cutting the ridge near the
center of the photo.
Figure 8.
Bald Eagle Mountain represents the north limb of a major
anticlinal fold.
This fold plunges to the east, and the
mountain, therefore, dies out in this direction.
Photo
taken from a hill just west of Montoursville, looking
southeast.
?.3
Figure 9.
To the southwest, Bald Eagle Mountain continues for over
one hundred (100) miles as an even-created ridge.
The ir-
regular breaks are caused by wind and water gaps.
Photo
taken three (3) miles west of Williamsport.
about two thousand (2000) feet.
This surface corresponds
to the peneplained surface of the plateau toward the northwest.
Bald Eagle Mountain is a tyoical examDle of these ridge
mountains.
South of Williamsport the mountain rises sharp-
ly, and the summit at two thousand (2000) feet has a total
relief of fifteen hundred (1500) feet above the river valley.
Here the summit flat is auite broad due to the junc-
tion of the north and south limb ridges of the Nittany
Anticline.
A few miles west at Nippenose Valley the limbs are six (6)
miles apart, and the valley lies in the breach of the anticline.
The floor of this valley is formed on an exposed
window of Beekmantown limestones and dolomites (Ordovician).
Sink holes and disappearing drainage exemplify the Karst
Topography in this valley.
Antes Creek drains this valley
to the north through a watergap in Bald Eagle Mountain.
The mountain at this point is actually two (2)
parallel
ridges one (1) mile apart,
separated by a shallow depress-
ion called Morgan Valley.
The north ridge is formed on the
Tuscarora cuartzite (Silurian) and the other on the Oswego
sandstone (Ordovician).
The depression corresponds to the
exposure of the Juniata shale (Ordovician).
east of the Antes Creek watergap,
Two (2)
miles
a windgap two hundred and
fifty (250) feet deep cuts across the ridges of Bald Eagle
Mountain.
Stream piracy by a tributary of Antes Creek,
which worked headward up Morgan Valley, captured the stream
which originally cut the gap.
Minor streams are consequent to the topography in this area,
but major drainage courses are generally subseauent to the
It is this erosion by subsequent drain-
underlying strata.
age which has produced the ridge and valley topography,
which characterizes the area.
The ridges not only stand
out in bold relief in contrast to the synclinal and breached
anticlinal valleys but also present a strong vegetational
contrast.
Bald Eagle Mountain,
like most of the ridges,
is
covered with a dense second growth forest, while the valleys to either side are largely cultivated.
Summing up, the Ridge and Valley Province is made up of
long, parallel, evenly-crested ridges separated by synclinal and anticlinal valleys.
subseauent courses,
The major drainage follows
and the topography is mature.
The area
just south of Williamsport is a typically developed section
of this province with ths ridges predominating over the
valleys.
Transition Zone:
The belt between the Appalachian Plateau and the Ridge and
Valley Province cannot be related to either of these physiographic units.
Considering the entire Appalachians, this
transition zone is not of great enough aerial extent to
warrent a description as a regional physiographic province.
However, this belt has a six (6) to eight (8) mile width in
the very center of the area described in this paper, and
therefore, deserves equal description.
The southern portion of this transition zone just to the
north of Bald Eagle Mountain is
occupied by the flood plain
of the Susquehanna River (figure 10).
The river flows east
and closely follows the aerial outcrop of the Silurian
limestones.
The flood plain is two (2) to three (3)
miles
wide and the river, generally about one quarter (1/4) of a
mile wide,
meanders from one side of it
to the other.
The
city of Williamsport and most of the other population centers in the area are built on this flood plain.
The remainder q' the Transition Zone, approximately six (6)
miles wide, except north of Jersey Shore where it is only
four (4) miles wide, is characterized by a very irregular
topography consisting of rolling hills and narrow twisting
hollows (figure 11).
Relief averages between three hundred
(300) and five hundred (500) feet, the hill tops seldom
over twelve hundred (1200) feet in elevation, with the separating hollows at seven hundred (700) to eight hundred
(800) feet.
The streams follow consequent dendritic pat-
terns and flow generally to the south.
Some eastward and
Figure 10.
This composite picture views a one hundred and eighty (180)
degree arc from west through north to easti.
Taken from
Bald Eagle Mountain three (3) miles southeast of Williams-
port,
it
shows the Susquehanna River and its flood plain
in the foreground.
The irregular topography of the Trans-
ition Zone, and Allegheny Ridge on the horizon appear in
the background.
Figure 11.
Looking west along the irregular, rolling topography of the
Transition Zone.
The horizon is formed by Bald Eagle Moun-
tain on the left and by Allegheny Ridge on the right.
Photo taken four (4) miles northeast of Jersey Shore.
westward flowing streams form tributaries to the main
streams (Pine Creek, Lycoming Creek, and Loyalsock Creek),
These main streams
which flow south out of the plateau.
have developed flood plains up to a mile wide where they
cross the Transition Zone.
The belt of irregular topography is
(4) miles in width
reduced to only four
just to the north of Jersey Shore, fif-
teen (15) miles west of Williamsport.
Short Mountain (fig-
ure 12), an outlier of Pocono sandstone (Mississippian)
south of Allegheny Ridge, causes this shortening.
A sharp
synclinal fold accounts for the presence of the Pocono to
the south of its exposure on Allegheny Ridge.
The boundary
between plateau and transition zone in the remainder of the
area is formed by this ridge.
The two thousand (2000) foot peneplain surface, which is
evident both to the north and south, has been completely
destroyed in the Transition Zone.
Greater erosion of the
relatively softer Devonian rocks in this belt is apparently
responsible.
zone.
Glacial activity was also present in this
Sorted and unsorted till makes up the west bank of
Loyalsock Creek just north of the U. S. Highway 220 bridge
near Montoursville.
In general, the Transition Zone is characterized by an irregular, mature topography of hills and hollows drained by
3a
Figure 12.
Taken from the same location as Figure 11, but looking
north.
The east end of Short Mountain shows at the left,
and Allegheny Ridge appears in the distance.
conseouent streams.
Erosion has proceeded far below the
old peneplain surface, and along the south margin of the
zone, the relief has been truncated by the flood plain of
the Susquehanna River.
The river follows a subsequent
course along the aerial outcrop of limestone formations.
.
I-I
- L - -
nl _
ow
III Stratigraphy
The entire thesis area, in fact, the entire region of the
Appalachian Plateau and Ridge and Valley Province in northern Pennsylvania, is composed of Paleozoic sediments (figures 13, 14, and 15).
On the plateau just north of Williamsport, sandstone of the
Mississippian System forms the bed rock.
Farther to the
north in some of the shallow synclinals on the plateau remnants of the Pennsylvanian System occur on the higher elevations.
Low relief monadnocks on the surface of the old
plateau peneplain are generally made up of Pottsville conglomerate, the basal member of the Pennsylvanian.
Outcroppings in the Transition Zone belong entirely to the
Devonian System, except along the Susquehanna River flood
olain which follows the limestone and shale formations of
the Upper Silurian.
Between Montoursville and Jersey Shore
the flood plain overlaps and covers the outcrops of the
Oriskany group and other formations of the Lower Devonian.
On the north flank of Bald Eagle Mountain, the Clinton
formation (Silurian) outcrops.
talus from the summit ridge.
It is largely concealed by
The two (2) parallel creste
of the mountain are made up of the Tuscarora quartzite
ridge to the north and the lower ridge of Oswego sandstone
to the south.
These ridges are separated by a shallow
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BEEKMANTOWN
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GENERALIZED
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FIGURE
13
LYCOMING
SECTION
COUNTY,
PENNSYLVANIA
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FIGURE
15
depression formed on the outcrop of the Juniata shale.
The Tuscarora is
the basal member of the Silurian, and the
Juniata and Oswego are Upper Ordovician.
Underlying the Oswego sandstone is the Reedsville shale,
the Trenton limestone, and the Beekmantown group.
These
Lower Ordovician limestone and dolomites form the floor of
the breached Nittany Anticline.
The Ordovician and Silur-
ian formations are repeated in reverse order toward the
south across the other limb of the fold.
In the following portion of this paper each of these systems will be briefly described.
The section exposures of
wnny formations are concealed or poorly exposed in the vicinity of Williamsport.
For this reason the general
stratigrpahic column is built up from measured sections and
well logs (especially the Devonian)
in and adjoining the
thesis area, and from well established sections in northern
and central Pennsylvania projected and extrapolated into
the area.
Ordovician:
Limestones and dolomites of the Lower Ordovician Beekmantown group are exposed in the breached anticlinal valleys
--
Moscuito Valley and Nippenose Valley --
Eagle Mountain.
south of Bald
The group has never been differentiated at
these exposures, but thirty (30)
miles to the southwest at
3(0
Bellefonte the same section has been studied by Swartz (bibliography 3) and Butts (bibliography 4).
Butts (bibliog-
raphy 5) has also studied this Ordovician section in the
Huntingdon - Hollidaysburg quadrangle, seventy (70) miles
southwest of Nicpenose Valley.
Both of these above mention-
ed sections are excosed in the center of the Nittany Anticline in much the same manner as the undifferentiated sections in Mosquito and Nippenose Valleys.
The Beekmantown group of the Huntingdon - Hollidaysburg
auadrangle is represented by the Mines dolomite, the Larke
dolomite the Nittany dolomite, the Axemann limestone, and
the Bellefonte dolomite.
Mines dolomite --
This formation is two hundred and
fifty (250) feet in thickness and contains abundant
chert of all sizes un to one (1)
foot in diameter.
It
is generally gray in color, but in some places characteristic oolite grains make It very dark colored.
Larke dolomite --
In character this formation is com-
oosed of thick-bedded, crystalline, blue dolomite.
The lower part is thin-bedded with some siliceous
material.
Thickness totals two hundred and fifty
(250) feet.
Nittany dolomite --
two (2) feet thick.
This dolomite is in layers up to
The bottom one hundred (100) feet
is thin-bedded and shaley.
Coarse chert occurs in the
middle oart and to a lesser degree throughout.
ness is
Thick-
one thousand (1000) feet.
Axemann limestone
This formation consists of a
--
thin-bedded, fossiliferous, blue limestone one hundred
and fifty (150) feet in thickness.
Bellefonte dolomite --
gray, and crystalline.
The dolomite is
thick-bedded,
It is cherty throughout but
more so in the middle and lower parts. Thickness totals
about one thousand (1000) feet.
A disconformity at this point separates the Beekmantown
from the Carlin limestone of the Chazyan group, a thinbedded, dark gray limestone one hundred and eighty (180)
feet thick at the Huntingdon - Hollidaysburg exposure.
Marshall Kay (bibliography 6) believes this is divisible
into the Hatter and Benner limestones at Bellefonte on the
basis of fossil content.
The relationship of the Chazyan
group, including its conformable or unconformable relationship to the underlying Beekmantown and the overlying Black
River and Trenton groups,
is not clear.
However,
the
thickness of the group does not greatly exceed four hundred
(400) feet in the Bellefonte area with the inclusion of the
formations under auestion.
The Black River group of the Middle Ordovician consists in
the Huntingdon - Hollidaysburg area of two (2)
formations.
The Lowville, one hundred and eighty (180) feet thick, is a
thick-bedded, dark, fine-grained limestone forming the lower unit.
The Rodman limestone, only thirty (30) feet thick,
of a gray, granular nature, forms the upper unit.
Three
hundred and fifty (350) feet of thin-bedded, dark gray to
black, non-granular Trenton limestone makes up the remainder of the Middle Ordovician.
The ReedSville shale, the Oswego sandstone, and the Juniata
formation, from the bottom to the top, make up the Upper
Ordovician.
In the Huntingdon - Hollidaysburg area the
Reedsville shale is black at the base, olive green in the
middle and contains limestone bands in the top.
thousand (1000) feet thick.
It is one
The gray, medium-grained,
thick-bedded Oswego sandstone is eight hundred (800) feet
thick.
The red shales and finely cross-bedded sandstones
of the Juniata formation are eight hundred and fifty (850)
feet thick.
At Bellefonte, Pennsylvania, thirty (30) miles southwest of
the thesis area, the same Ordovician section is exposed.
Some increases in thickness over the Huntingdon-
Holli-
daysburg section are noted, but with the exception of the
addition of the Stonehenge limestone, the same formations
are present.
The Beekmantown group shows the greatest
increase in thickness.
The Stonehenge limestone, near the
base, adds a six hundred and thirty (630) foot thick formation of medium-bedded, blue limestone to the section.
Kay (bibliography 6) has also placed the lower part of the
Reedsville shale at Bellefonte into the Trenton group under
the name of the Antes Gao shale.
Swartz believes that
Bellefonte was the locus of greatest deposition during the
Beekmantown Stage (bibliography 3, p. 1560).
If this is
true, then the formations of the Lower Ordovician will
again thin to the northeast.
Nippenose Valley in the thesis area; Bellefonte, thirty
(30) miles southwest; have in common an Ordovician section
exposed in the core of the Nittany Anticline.
They lie in
a line which paralleled the major axis of the Appalachian
Geosyncline.
It seems reasonable, therefore, that known
sections near Bellefonte and in the Huntingdon - Hollidaysburg area can be extrapolated with reasonable accuracy into
the Nippenose Valley section.
an attempt to do this.
The following tabulation is
The accuracy of this method will be
known in the near future, for the California Company is
drilling a sub-Trenton test well in Nippenose Valley.
When
correlation of the well log is established, it should not
be too difficult to measure the entire exposed and sub-surface sections of Ordovician in the valley.
-44o
Upper Ordovician
HuntingdonHollidaysburg
Bellefonte
Nippenose Val.
Juniata
850'
1000'
1200'
Oswego
800'
800'
700'
Reedsville
1000'
1000'
1000'
Trenton
350'
600'
550'
Black River group
210'
250'
200'
180'
400'
300'
Bellefonte
1000'
1500-2200'
1200'
Atemann
150'
360'
300'
Nittany
1000'
1200'
1000'
Stonehenge
0
630'
200'
Larke
250'
0
Mines
250'
200'
Middle Ordovician
Lower Ordovician
Chazyan group
Beekmantown group
100'
Silurian:
The Silurian System is represented in the Lock Haven, Wil-.
liamsport, and Milton quadrangles by the following group
and formations (from the older to younger): The Tuscarora
quartzite, the Clinton shale, and the Cayuga group which
includes the McKenzie formation,
the Wills Creek and
Bloomsburg shales, and the Tonoloway and Keyser limestones.
There has been considerable argument as to whether the
Keyser is uppermost Silurian or the base of the Devonian
(bibliography 7).
However, the two (2) systems are con-
formable in north central Pennsylvania, and any pigeonholing within pure time boundaries is probably arbitrary.
The Silurian System also appears to be conformable with the
underlying Ordovician System in this area.
The Tuscarora quartzite forms the resistant core of the
limbs of the Nittany Anticline.
formed by its outcrop.
Bald Eagle Mountain is
The Clinton shale outcrops on the
north flank of the mountain but is largely covered by talus
material from the Tuscarora quartzite of the summit ridge.
Recent alluvium in the flood plain of the Susauehanna River
at the base of Bald Eagle Mountain conceals the outcrops of
most of the Cayuga group.
For full descriptions of the
concealed formations it is again necessary to refer to better exposures in Huntingdon - Hollidaysburg quadrangle (bibliography 5).
The Tuscarora auartzite is a white to reddish-gray sandstone.
The texture is irregular and varies from conglom-
eratic to a fine-grained, tightly-cemented ortho-quartzite.
It weathers into irregular blocks and boulders.
Many of
these are rough cubes caused by fracture along a rectangular joint system.
The surface of the weathered blocks is
often pitted where holes are left from the weathering out
of Debbles and nodules.
Accumulations of these weathered
blocks on the flanks of Bald Eagle Mountain are very conspicuous due to their lack of vegetation.
The Oswego sand-
stone also forms these weathered rocks heaps.
They are
known to the local residents as "The Devil's Cabbage Patches".
The Tuscarora is nearly vertical in the Mosouito Val-
ley gap southwest of Williamsport.
Its thickness is about
five hundred (500) feet.
The Clinton shale is exposed at a few small outcrops in the
gaps of Bald Eagle Mountain.
It extends along the entire
north flank of the mountain but is largely covered by thick
soil and talus from the ridge.
At its exposures it
brown-green to brown-red, thin-bedded, soft shale.
is
a
The
Clinton formation contains thin beds of sedimentary iron
ore, which were at one time mined at various places along
the Fold Front southwest from Williamsport.
No beds of
iron ore are apparent in the Clinton shale in Lycoming
County, but it is probable that they do occur in the concealed section.
Total thickness is in the order of nine
hundred (900) feet.
The McKenzie formation at the base of Cayuga group has been
noted by Butts (bibliography 5, p. 54) along Bald Eagle
Mountain two (2) miles southeast of Lock Haven.
This is
only ten (10) miles west of the thesis area.
It is made up
of a thin-bedded limestone with numerous shale partings.
Thickness is about two hundred and fifty (250) feet.
The Bloomsburg shale is a red shale with some sandy red
members.
The Swartzes (bibliography 8, p. 659) have pro-
posed that it represents a non-marine red bed facies which
thickens to the east until it makes up the entire Cayuga
group in eastern Pennsylvania.
In the vicinity of Williams-
port it is probably less than two hundred (200) feet thick.
Overlying the Bloomsburg formation is the Wills Creek shale.
This shale is not exposed.
Its thickness at other outcrops
along the mountain front is generally about four hundred
(400) feet.
The Susquehanna River follows the aerial outcrop of the
Tonoloway and Keyser limestones through most of the thesis
area.
At Jersey Shore the limestone in the river bed,
of the south river bridge, is probably the Tonoloway.
is a thin-bedded, dense, dark-colored limestone.
east
It
The sec-
tion is not at all complete, but the thickness is probably
about four hundred (400) feet.
Swartz (bibliography 7, p.
75 - 80) describes Keyser outcrops in Mifflin, Northumberland, and Perry Counties as thin-bedded, dense limestones.
These counties bracket Lycoming County, and the general
thickness observed for the Keyser in those counties --
one
w
hundred and eighty (180) feet --
should apply in Lycoming
County.
Devonian:
In Lycoming County the belt between the north bank of the
Susquehanna River and the Allegheny Ridge is formed almost
entirely on the outcrop of Devonian rocks.
East of Mon-
toursville the Oriskany group outcrop is considerably north
of the river, and it is evident, therefore, that a wedge of
Upper Silurian rocks outcrops on the north bank.
The Helderberg group forms the base of the Devonian.
In
north central Pennsylvania it is made up of three (3) formations: the Coeymans limestone, the New Scotland limestone,
and the Mandata shale (bibliography 7, p. 51).
The only
full exposure in the thesis area is about three-eights (3/ 8
of a mile south of the U. S. Highway ?20 bridge over Pine
Creek just west of Jersey Shore.
Here the Helderberg group
is exposed as the core of a sharp anticlinal fold on the
east bank of Pine Creek and in the road cut and cuarry one
hundred (100) yards east of the creek.
If the buff, thick-
bedded limestone is the Keyser, then the Coeymans and New
Scotland limestones together are approximately thirty-five
(35) feet thick.
The Silurian-Devonian contact is sharp
but irregular and probably represents a disconformity.
interval, which should contain the Mandata shale, was
The
)
Nk
A
4s
covered for seventy-five (75) feet, and the next exposure
was the shaly Shriver chert of the Oriskany group.
The Oriskany group is made up of the Shriver formation and
the Ridgeley sandstone (bibliography 7, p. 97).
This sand-
stone formation of the group is commonly called the Oriskany sandstone and is
that name.
It
often referred to in this paper by
is well exposed at three (3)
the thesis area.
localities in
At Jersey Shore it is exposed at the same
locality as the Helderberg mentioned above.
The Shriver
formation here seems to be mostly a dark, thin-laminated
shale.
Most of it
is
concealed, but the interval between
contacts is about seventy-five (75) feet.
The Ridgeley
sandstone is tan-colored and fine-grained with a Saccharoidal texture.
The grains are cemented by calcite, but
porosity is not destroyed.
feet thick at this noint.
kany group is
The sandstone is ninety (90)
East of Williamsport, the Oris-
exposed on the north side of U. S. Highway
220 on the hill just west of Loyalsock Creek (figure 16).
Here the sandstone formation is extremely hard and durable,
and its outcrop is the resistant strata which forms the
hill.
Microscopic examination shows the grains to be
tightly cemented.
The grains are faceted by authigenic
ouertz, and this silica cement has reduced the porosity to
almost nil.
The sand is practically pure silica except for
forty-five-one-thousandth percent (0.045%) iron.
This iron
Figure 16.
The auarry in the sandstone of the Oriskany group on the
north side of U. S. Highway 220 just west of Loyalsock
Creek.
The beds in the background are nearly horizontal
and are so durable that blasting is necessary before removal.
Photo was taken looking west.
'41
content is too high to allow use of the material for glass
sand.
The Lycoming Silica Sand Company does quarry the
sand for foundry work and for traction sand for the railroad.
The top contact and an indeterminable amount of the
The remaining
Ridgeley has been removed by erosion here.
formation is
over fifty (50)
feet thick.
poorly exposed on the hill side.
about one hundred (100)
The Shriver is
The interval here is
feet.
The absence of outcrops of the Oriskany group in the eighteen (18) mile interval between the above mentioned exposures has previously been interpreted by Garrett (bibliography 9, p. 837) and others as an interuption in sedimentation of the Oriskany in this interval.
The thickness of
the Ridgeley sandstone at each end of this interval makes
this seem unlikely.
It is more probable that the outcrop
is buried beneath the flood plain of the Susquehanna River.
The outcrop just west of Montoursville probably escaped
truncation by the river because of its silica cementation
and resulting durability.
Evidence to support the conclu-
sion that the Oriskany is present beneath the river flood
plain is available from water well samples.
At the Stewart
Artificial Ice Company in Williamsport a two hundred and
forty-four (244) foot water well encountered "white sandstone" beneath "black, flinty limestone" (bibliography 10s,
p. 146).
This is probably the Ridgeley sandstone which
underlies the Onondaga limestone and shale.
East of Montoursville, two (2) miles from the outcrop on
the hill just west of Loyalsock Creek, the Oriskany shows
little relief.
The Ridgeley is again auarried here by the
Lycoming Silica Sand Company (figure 17).
However, the
nature of the sand is completely changed.
It is very
loosely cemented by calcite and can be mined directly with
a power shovel (figure 18).
Microscopic examination shows
the grains to be sub-angular and frosted.
Porosity and
permeability are high, and any water in the bottom of the
pit forms a quick sand.
At the upper contact of the Rid-
geley, the contact with the Onondaga formation, a four (4)
foot zone of the sandstone is tightly cemented with limonite (figure 19).
feet thick.
Here, the Ridgeley sandstone is sixty (60)
A cherty limestone at the base probably be-
longs to the Shriver formation, which is
so largely con-
cealed that its thickness is uncertain.
The only constant
feature of the Oriskany at all the locations was the abundance of fossil brachiopods (figure 20) and the purity of
the auartz sand.
The lateral variation in the extent and porosity of the
sandstone formation of the Oriskany is of major interest.
This formation produces immense volumes of natural gas in
the plateau area to the north and northwest.
Many dry
holes have been drilled on favorable structure, which
41
Figure 17.
Looking east into the Lycoming Silica Sand Company's cuarry
east of Montoursville.
The light buff formation is the
Ridgeley sandstone of the Oriskany group.
The overlying,
dark gray formation is the Onondaga limestone and shale.
so
Figure 18.
Photo taken in the quarry shown in Figure 17.
The Oriskany
sandstone is so uncemented here that new exposures wash
into erosion pillars within a few weeks.
SA
Figure 19.
The contact of the Ridgeley (Oriskany) sandstone, below,
and the Onondaga limestone and shale, above.
A four (4)
foot bed of hard sandstone cemented with limonite is formed
at the top of the Ridgeley.
This is the "cap rock" of the
Oriskany sandstone in the plateau areas where it produces
natural gas.
Photo taken in the ouarry east of Montours-
ville (figure 17).
Figure 20.
A plan view of a bedding surface in the Ridgeley (Oriskany)
sandstone.
dant.
ision.
Casts of fossil brachiopods are extremely abun-
Note pencil in lower right corner for size comparPhoto taken in quarry shown in Figure 16.
w
encountered either no Oriskany sandstone or tightly cemented sandstone which contained no gas or connate water.
The
no sand area has been fairly well delineated (bibliography
11, p. 309), but the changes in porosity are more complex.
Lateral variations in the primary sorting and the secondary
cementation are rapid and of considerable magnitude.
Screen Analyses of Oriskany Sandstone
Retained on Sieve
%Fine Grain
6
0.0
0.0
12
0.0
0.0
20
0.4
0.5
30
0.9
2.8
40
3.0
16.6
50
15.1
45.6
70
32.0
2702
100
3409
4.6
140
11.4
1.6
200
1.7
0.7
270
0.3
0.1
Pan
0.3
0.1
Coarse Grain
The above screen analyses are of samples from the two (2)
cuarries of the Lycoming Silica Sand Company.
They are two
(2) miles apart, the fine grade from the quarry east of
54
Montoursville and the coarse grade from the hard, highlycemented sandstone on the hill just west of Loyalsock Creek
on the north side of U. S. Highway 220.
It should be noted
that the coarse grade sand. shows the best sorting and from
this point would presumably have the greatest porosity.
However, the cementation of the coarse sand has been so
complete that the reverse is true, and the fine grade sand,
which originally was less porous, is now many times more
porous than the cemented coarse grade.
It is possible that
the originally poorer porosity of the fine grade material
prevented the cementation from taking place.
The remaining section of the Devonian, which outcrops in
the Transition Zone, is poorly exposed.
Intense structur-
al deformation makes correlation of the occasional outcrops
almoqt impossible.
For this reason the aerial geology map
(figure 14) shows the section undifferentiated.
Continuous
stratigraphic detail of the Upper and Middle Devonian is
not obtainable from the highly deformed Transition Zone.
Fortunately the California Company generously loaned the
author samples from a drilling well at Hyner, Pennsylvania.
This well is in the plateau area twenty (20) miles north of
the Transition Zone.
It is the closest test to the margin
of the plateau that has been drilled in this area.
It pen-
etrated a horizontal section of most of the Upper and Middle Devonian and provides much more reliable data than
attempting to integrate partial sections in the Transition
Zone.
Samples were collected from almost every bailer run
on the well.
The resulting seven hundred and thirty (730)
samples were examined by the author under a 23X binocular
microscope and tested with dilute hydrochloric acid.
A
great many of the samples show monotonous repetition, and a
summary of the examination seems sufficient for this paper.
For convenience sake, the Oriskany to Catskill interval of
the Lower to Upper Devonian will be described in reverse
order to the older through younger procedure used in this
chapter.
they will be described as they occur in
That is,
the well from top to bottom.
Well Sample Record (Summary)
Harmon #1
Shaw and Smith et al.
Clinton County, Pennsylvania, Chapman Township
Renovo East Quadrangle: One mile south of latitude fortyone degrees twenty minutes; one half mile west of longitude
seventy-seven degrees thirty-three minutes thirty seconds
Elevation: 640'
Still drilling: November 15, 1950
Total depth: 6488'
Deepest formation: Oriskany
Result: Shallow gas in small volume from sands in the Chemung formation.
No gas or water in the first fifteen (15)
5'6
feet of the Oriskany
Catskill formation: 0
Samples 0 -
0.1
-
654'
-
506 missing; 506
-
545 angular quartz sand
0.3 mm, calcareous cement, 10 - 301 buff to red
argillaceous material, limonite stains; 545 - 654 gray
to brown calcareous siltstone, 631
-
654 10 - 20% red
argillaceous material
Chemung formation: 654
-
2975'
Mainly gray argillaceous siltstone; mica present but
not plentiful; calcareous cement throughout; shell
fragments at several intervals; sub-angular quartz sand
0.1 - 0.5 mm present from 20 - 80% at intervals 722
735, 838 -
-
843, 871 - 902, 992 - 998, 1073 - 1081,
1287 - 1301,
1476 - 1507,
1566 - 1587; limonite stains
common; pyrite at 2710 - 2717, 2719 - 2727, 2772 -
2782, 2865 - 2873; from 2680 very fine gray sandstone
0 -
60%
Trimmers Rock formation: 2975 - 4400'
50
-
70% fine, gray sandstone; 30
-
50% gray argilla-
ceous siltstone; some mica; more or less calcareous
throughout; limonite stains present at occasional
intervals but less common than in Chemung; calcite
fragments at 3616 - 3668; pyrite at 3977 - 3987, 4058
4071,
-
4149 - 4159, 4181 - 4191; dark, gray, silty,
micaceous shale becomes more plentiful around 4200,
this alternates with siltstone for dominent constituent until 4462 where siltstone becomes less than 50%
and generally remains so
Brallier formation: 4400 - 5200'
Gray siltstone and dark, gray, silty, micaceous shale
in varying quantity with the proportion averaqing
about 301 siltstone and 70% shale; shale irregularly
laminated about o.2 mm apart; pyrite at 4482
4513 - 4523, 4545 - 4562,
4802 - 4823,
4840
-
-
4495,
4851,
4937 - 4950; calcareous cement present but not so
strongly as in Chemung and Trimmers Rock; from 5200 5300 the silt decreases, the calcium carbonate increases and the color of the shale becomes darker gray
Harell shale: 5200 -
5420'
Dark gray, silty, micaceous shale; with increasing
depth silt decreases, calcium carbonate increases,
color becomes very dark gray to gray black; pyrite at
5374 -
5393; 5393 - 5413 dark gray to brown calcareous
mudstone
.5%
Tully limestone: 5420 -
5590'
5413 - 5427 very calcareous, gray, silty shale; 5427 5435 fine-grain, light gray limestone 60%, 40% dark
gray shale; 5435 - 5451 fine-grain impure limestone
with silt, shale, and pyrite; 5451 - 5457 fine-grain
limestone with silt and shale, 50% limonite and pyrite; 5457 - 5505 dense gray limestone with minor pyrite and limonite; 5505 - 5537 silty, argillaceous impure gray limestone; 5537 - 5562 light gray,
argilla-
ceous, limestone, brown mud residue with acid; 5562 5594 calcareous,
argillaceous,
gray siltstone
Hamilton - Marcellus shale: 5590 - 6420'
5590 -
5733 gray, silty, micaceous shale; 5733 - 6247
dark gray, micaceous shale; 6249 - 6420 very dark gray
to gray black, micaceous shale; pyrite at 5637 - 5651,
6054 -
6064, 6132 -
6140, 6210 -
6220, 6240 -
6420;
pyrite very abundant at 6240 - 6247; calcite fragments
at 6100 - 6112, 6140
Onondaga formation: 6420
-
-
6146, 6305 - 6420
6475'
6420 - 6422 dark gray, calcareous shale, much fine pyrite and limonite, calcite fragments; 6422 - 6429 40%
very calcareous, dark gray shale, 40% red-brown, fine
59
sand and clay aggregate, 20% pyrite, calcite, and limonite; 6429 - 6439 calcareous,
dark gray shale 70%,
20% red-brown clay and sand aggregate, pyrite,
and
calcite; 6439 - 6451 sample missing; 6451 - 6464 fine,
light gray limestone 40 -
60%, dark gray shale 20 -
40%, red-brown clay and sand aggregate 0 - 20%, pyrite and calcite fragments; 6464 - 6470 fine, light
gray limestone 40%, dark gray shale 20%, red-brown
clay and sand aggregate 20%, fine, white sandstone,
pyrite, and calcite fragments; 6470 - 6473 dark gray,
calcareous shale, pyrite, limonite, and some 0.5 mm
rounded, frosted quartz sand grains
Oriskany (Ridgeley) sandstone: 6475' - ?
6475 - 6487.5 approximately 50 drill runs to make this
penetration, extremely hard drilling; frosted,
sub-
angular to rounded ouartz sand grains 0.1 - 1mm up
to 40% of a sample; with calcareous,
gray shale, 1i-
monite, calcite fragments, pyrite, and a blue-green
mineral (smitheonite ?)
The boundaries between the Catskill, Chemung, Trimmers Rock,
Brallier, and Harell are arbitrary.
clearly defined.
They have never been
In fact, the very division of these units
represents the confusion in Appalachian Stratigraphy, which
has resulted from the establishment of the time rock units
of the paleontologist.
All these above formations are in
reality transitional into each other and represent a part
or a facies equivalent within a single genetic rock unit.
To conform with the present division of these units, the
boundaries were arbitrarily established as follows: The
base of the Catskill is marked by the lowest stratigraphic
red bed; the Chemung becomes Trimmers Rock when the fine
sandstone content consistently exceeds fifty (50) percent;
the Brallier begins when the shale exceeds the siltstone;
and the Harell is marked by the next decrease in the silt
content.
Only a small portion of the Catskill formation or facies is
represented in the Hyner well.
The Catskill is the contin-
ental equivalent of the Chemung and consists of red and
green sandstones, siltstones and shales in irregular and
rapidly changing order.
cross-bedded.
In many places it is complexly
The Catskill thins to the northwest in the
plateau area, but from the Chemung contact along Loyalsock
Creek near Loyalsockville, the calculated interval is about
twenty-six hundred (2600) feet to the Pocono sandstone
(Mississippian).
This contact is again arbitrarily placed
at the beginning of the red color in the beds.
The exposed
section of steeply dipping beds is eight hundred and seventy-two (872) feet of stratigraphic interval.
From north
to south along the creek the exposures are as follows:
red, silty shale and fine sandstone
78'
concealed
97'
red, silty shale
13'
gray shale and siltstone
65'
red sandstone
5'
gray and red, silty shale
9'
red siltstone (with hematite)
3'
red and gray, silty shale
29'
gray, silty shale and fine sandstone
67'
brown shale and fine sandstone
19'
7'
gray sand.stone
gray to brown, silty shale
15'
concealed
79'
brown, silty shale and fine, gray sandstone
15'
red and gray, silty shale
53'
fine,
gray sandstone
red and gray,
silty shale
fine, gray sandstone
gray,
silty shale
fine,
gray sandstone
gray,
silty shale
7'
37'
18'
30'
2'
49'
red, silty shale
6'
fine, gray sandstone
5'
red and gray, silty shale
gray,
3'
silty shale
10'
red and brown siltstone
18'
Top of Chemung
gray,
silty shale
133'
872'
The remainder of the Catskill appears from sporadic outcrops to become more sandy and cross-bedded higher in the
facies.
A green, flaggy, cross-bedded sandstone marks the
top of the Catskill (bibliography 7, p. 301), and this can
be seen in several of the smaller ravines which work back
into the plateau from the gorge of Loyalsock Creek.
Mississippian:
This system is exposed on the margin of the Appalachian
Plateau and in the gorges cut into the plateau by the major
drainage streams --
sock Creek.
Pine Creek, Lycoming Creek, and Loyal-
In Lycoming County the entire system is rep-
resented by only two (2) formations --
the Pocono sandstone
and the Mauch Chunk shale.
The change from the red beds of the Catskill to the coarse
gray to brown Pocono sandstone is quite rapid.
There is no
visible evidence that the contact is disconformable as
Willard (bibliography 7, p. 256) believes it is in north-
The sandstone var-
western and northeastern Pennsylvania.
ies irregularly from coarse and massive to fine-grained
sandstone of a flaggy nature.
In many places it shows
cross-beds up to ten (10) feet long.
occur in the sandstone.
Small lenses of coal
In most areas of the plateau the
Pocono is sufficiently flat-lying to measure the thickness
by elevation difference of the top and the bottom.
This
thickness is about eight hundred (800) feet along the Allegheny Ridge in Lycoming County.
The Mauch Chunk shale is made up of irregularly bedded red
and green shale.
The shale is soft and earthy and weathers
readily into a red soil.
Outcrops are rare, but the red
soil found near the top of the Pocono sandstone is characteristic.
The top of the Mauch Chunk is truncated by a
disconformity,
and it
varies in thickness from zero (0)
about one hundred (100) feet.
to
The Loyahanna limestone for-
mation of the Mississippian is not present.
In northwest-
ern Pennsylvania this formation occurs between the Pocono
and the Mauch Chunk.
Whether this absence represents a
hiatus or a facies change is uncertain.
Pennsylvanian:
Monadnocks and shallow truncated structural basins on the
plateau peneplain contain the only remnants of the Pennsylvanian System.
Most of the Pennsylvanian formations,
which at one time blanketed the entire area, have been
(4
stripped off by erosion.
in the thesis area.
Two (2)
of these remnants occur
One is south of Loyalsock Creek where
this stream flows west and the other west of Lycoming Creek
near the south margin of the plateau.
They both contain
the Pottsville formation and part of the Allegheny formation.
The Pottsville formation is a coarse, gray sandstone which
is conglomeratic at the base.
The conglomerate contains
many cuartz oebbles up to one-half (1/2) inch in diameter.
The entire formation is only about one hundred (100) feet
thick.
The Allegheny formation is made up of shales and sands with
interbedded coal seams.
to be commerical,
The coal is sufficiently developed
and one (1)
seam is mined and stripped
near Hoaglands Run in the Allegheny remnant west of Lycoming Creek.
Quarternary:
The flood plain of the Susquehanna River and the valley
floors of the major streams in the area have a mantle of
glacial and recent stream gravels.
At one time the main
channel of the river must have been much deeper.
Recent
tests for a new bridge across the river show the quarternary sand and gravels to be greater than eighty (80) feet
thick.
IV Sedimentation and Geologic History in Pennsylvania
during Paleozoic Time
To completely describe this complex and controversial subject would require exhausting study and a paper of much
greater length than this entire thesis.
However, the high
points can be briefly noted, and they add greatly to the
attempt to understand the history of deposition and deformation of this area.
Pre-Cambrian igneous and sedimentary rocks from undetermined sources make up the basement rocks of the Atlantic Coast
of the United States.
This series was uplifted, and a
trough was formed on their inner margin between this uplifted hinterland and the Cincinnati Arch,
the foreland.
Coarse clastic sediments filled the geosyncline trough on
its eastern flank, and limestones formed in the central
area of the basin during the later phases.
Several trans-
gressions and regressions of the sea complicated the deposition, but generally the result to Middle Ordovician Time
was a thick accumulation of Cambro-Ordovician limestones
overlying, especially in the east, a thick section of Cambrian conglomerates, sandstones, and shales.
The total
thickness of these early Paleozoic clastics is widely disputed because the age of much of the Piedmont metamorphics
(040
is
undetermined.
The Upper Ordovician sediments give testimony to activity
in the foreland and probably shallower seas.
The Oswego
sandstone seems to indicate a source from the northwest, as
its thickness decreases to the southeast.
Lower Silurian
As
clastics fall into this same cycle of sedimentation.
more stable conditions and deeper seas return in Upper
Silurian Time, deposition of limestone again took place.
By Devonian Time the sea had regressed to a smaller area.
The expansion of the sea early in this period is marked by
the Oriskany sandstone.
Renewed activity in the bordering
land-masses supplied the clastic sediments.
The Taconic
disturbance in the east supplied a tremendous amount of
clastic continental sediments which formed the Catskill
delta.
This facies occupies the entire Hamilton - Chemung
interval in the Catskill Mountains.
By the Carboniferous Period the sea had migrated westward
into Ohio,
and in Pennsylvania non-marine deposition sup-
plied from the east continued.
Rapidly alterating condi-
tions of activity in the hinterland to the southeast, and
advances and retreats of the sea from the west, marked the
great coal formation stage in Pennsylvania.
sandstone,
Coals,
shale,
and limestone occur in repeated and rapid se-
quence in the Allegheny formation.
Permian deposition migrated still farther westward and is
represented only in the southwestern corner of Pennsylvania.
Major uplift and deformation during the final stage of the
Appalachian Orogeny brought the end to the Appalachian Geosyncline.
In summary the Appalachian Geosyncline is marked by a progressive shift of the axis of maximum deposition from the
east or southeast toward the northwest during Paleozoic
Time.
The orogenic movements of the hinterland also mi-
grated in this direction.
It is a possibility that much of
the later Paleozoic sediments are derived from earlier Cambrian and Ordovician sediments laid down on the eastern
margin of the early position of the Geosyncline and later
incorporated and uplifted in the hinterland as the Tectonic
deformations progressed toward the northwest.
V Structure
Appalachian Plateau:
North of the Fold Front in northern Pennsylvania the relatively flat-lying rocks of the plateau have been warped into gentle,
Cathcart --
undulating folds (figure 21 --
bibliograrhy 12).
modified from
The axes of the folds are
sinuous, but in general closely parallel the axes of the
major folds of the Ridge and Valley Province.
This north-
east-southwest lineation is the most prominent structural
generlaity of the entire Apnalachians.
tral Pennsylvania the fold system is
convex side toward the northwest.
In north and cen-
slightly arcuate,
the
The minor folds of the
plateau show on the map as long continuous folds, some of
them over one hundred and fifty (150) miles in length.
Cathcart (bibliography 12, p. 7) has calculated the amplitude of some of these folds.
They vary from one thousand
(1000) to three thousand (3000) feet between the synclinal
axis and the next anticlinal axis.
The trend is for the
amplitude to increase with closer proximity to the Fold
Front, but there are definite exceptions.
These exceptions
are the intermediate folds, like the Slate Run Anticline,
which have only relatively small --
two (2) to five (5)
miles --
horizontal displacement from the adjoining syn-
clines.
Therefore,
the actual trend is for the dips to in-
crease with proximity to the Fold Front.
The fold amplitude
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FIGURE
22
10
is the function of these dips times the horizontal displacement between the synclinal axis and the anticlinal axis,
and when this horizontal displacement remains approximately
the same, the fold amplitude reflects the trend.
The dips of the fold flanks in the plateau vary from one
(1) to five (5) degrees except the folds very close to the
Transition Zone and Fold Front, where dips up to twenty (20)
degrees are not uncommon.
Faulting is sometimes expressed
at the surface by sudden increase in dip, but these steeper
dips are not widespread.
The dips on the south flank are
in general steeper than those of the north flank of the
anticlines.
This indicates asymmetry toward the southeast
or plunge of the axial surface of the fold toward the northwest.
Many wells drilled to the Oriskany on these plateau
folds seem to bear this out.
great.
This asymmetry is not very
Dips of one (1) to three (3)
degrees on the north-
west flank of an anticline are generally contrasted with
dips of three (3) to five (5) degrees on the southeast
flank.
In theory, this would call for a two hundred (200)
to three hundred (300) foot offset of the crest of the
anticline toward the northwest at a depth of five thousand
(5000) feet.
Regional dip toward the southwest would ac-
count for part of this asymmetry, but even correcting for
this, Sherril (bibliography 13, p. 417) finds the southeast
flank dips exceed the northwest flank dips by one point
three times (1.3X).
The magnitude of the asymmetry is small,
but the southeast direction is noteworthy.
Almost all other
asymmetrical structural features in the Transition Zone and
the Ridge and Valley Province are in the reverse direction.
According to Cathcart's map, the anticlinal folds of the
plateau show a succession of domes and intervening saddles.
These domes vary from only one (1) to as many as seven (7)
on an anticline.
Maximum closure on these domes is about
four hundred (400) feet at the Oriskany top horizon.
The
arrangement of these domes and saddles seems to indicate
the trend of a possible series of cross folds aligned
north-south to northwest-southeast.
Cathcart (bibliography
12, p. 7) believes this cross folding to be part of a system
of radial stresses developed out from the arcuate salient
of the major folds in the Ridge and Valley Province.
is good evidence to support this.
There
First, the arrangement
of the possible cross folds seems to be more or less radial
in nature, perpendicular to the tangent of the northeastsouthwest fold which it crosses.
Second, Foose (bibliog-
raphy 14) reports a cross synclinal structure near Lock
Haven, Pennsylvania, which crosses the Nittany Anticline
and continues into the plateau area to the northwest.
This
cross syncline forms the southwest closure to the structure
in Nippenose Valley where the California Company has recently been testing the petroleum possibilities.
Torrey
(bibliography 15, p. 968), on the other hand, believes the
cross folding to be older than the major northeast-southwest Appalachian folds.
He accounts for the bends in the
more recent fold axes as the intersections of the two (2)
fold systems.
Hamilton (bibliography 16, p. 1585) also
supports this view, stating that the coarse Oriskany sand
was deposited on the highs of old north-south folds formed
from the Taconic disturbance.
The author believes the sys-
tem of cross folds is complex enough that it
may be due in
part to both older folding and to deformation by rotational
stresses.
These latter stresses would be resultant from the
interaction of the northwestward comnressive force from the
arcuste fold front salient and the southward resistive forces from the corrugation effect of the older north-south
folds.
This resultant force would be a westward shear and
would tend to produce en echelon folds striking northwest.
Faulting is
nearly parallel to the folds, and from subsur-
face data (bibliography 17) the faulting is most intense at
the high points on the domes of the anticlines.
These
faults parallel the elongate axes of the domes and are generally high-angle, reverse faults dipping northwest.
The
down-thrown side is on the southeast, or Ps in the cse of
the Tioga field, there is a down-thrown graben along the
axis of the dome.
depth.
The fault displacement increases with
A displacement of several hundred feet at the
Oriskany top horizon may die out almost completely and be
expressed at the surface as a few scattered, anomalous,
steep dips.
It is not clear whether faulting is resultant
from doming or vice versa.
The faults may be due to the
swelling of the more plastic shales or perhaps salt beds in
the Silurian System (the southern limit of the Salina formation under the plateau is not known) underneath the domes.
Then, again, the southeast asymmetric folds may be due to
drag along deep-seated, reverse faults dipping northwest.
The origin and reverse nature, contrasted to major Appalechian asymmetry,
of these phenomena will be further dis-
cussed under the "interpretation" heading later in this
chapter.
The regional dip in the plateau area of northern Pennsylvania is south, southwest.
with this regional dip.
The anticlines plunge southwest
However,
the Upper Devonian thick-
ens to the south and east, and northeastward plunging or
closure along an anticline may be pronounced at depth and
not noticeable at the surface.
The plateau in this region has a deceptively complex structure for an area that at first appearance is made up of
nearly horizontal strata.
The regional dip to the south,
southwest with superimposed, gentle folds parallel to the
main Appalachian folds; the possible older north-south
folds which may have controlled the formation of the en
echelon anticlines and domes; the associated parallel reverse faulting; the southeast asymmetry of the folds and
faults; and the general increase in structural intensity
with depth are all factors which contribute to the complex
and economically imnortant structure of the Appalachian
Plateau in northern Pennsylvania.
Transition Zone:
The deformation in the Transition Zone near Williamsport,
Pennsylvania has been so intense that the structure cannot
be mapped in perfect detail.
If the soil cover were less
and the exposures more complete, this could be done.
Even
so, it would. take a great deal of small scale mapping.
Nevertheless, the data available on the mao and sections
(figures 14 and 22) is sufficient to substantiate certain
conclusions to the nature and extent of the deforming forces and the resultant structures.
Intense folding is the most obvious structural feature in
the Transition Zone.
The axes of these folds closely par-
allel the Fold Front, but they are not continuous for any
great length.
Instead, they plunge or split, and each cross
section of the zone presents an entirely new arrangement.
Section AA' shows three (3)
anticlines.
The first and se-
cond from the north are accurately located, but the fold in
the Upper Silurian rocks underneath the river flood plain
is inferred.
fold --
There is good evidence to support this latter
first, the width of the outcrop area; and second,
intense multiple folds can be seen in this band farther
west.
Proceeding farther west, the number and intensity of the
folds increase.
In section BB' there are three (3)
anti-
clines before the river flood plain and an unknown number
of tight folds under that area.
In section CC' the number
of anticlinal folds between the flood plain and the plateau
increases to five (5).
This occurs in a shorter horizontal
distance than in the other sections because of the decreased width of the Transitional Zone here.
The tight folds,
exposing cores off Upper Silurian limestone in the quarries
on the east bank of Pine Creek one and one-half (11/2)
miles north of the river, are very asymmetrical toward the
north, northwest.
The plunge of the axial surface is about
twenty-five (25) degrees south (figure 23).
East of here,
on the southeast bank of the Susquehanna River at the Jersey
Shore bridge, the asymmetry is in the reverse direction
(figure 24).
This also seems to be the case on the south
flank of the hill one-half (1/2) mile east of Loyalsock
Creek and one (1) mile north of the river (figure 25).
A-
symmetry of the folds is toward the north, northwest in the
northern part of the Transition Zone.
But approaching the
16'
Figure 23.
A close asymmetric fold in the Keyser limestone (Silurian)
in a quarry on the east bank of Pine Creek one and one-half
(11/2) miles north of the river. Photo taken looking east.
Figure 24.
Upper Silurian limestone on the east bank of the Susquehanna River at the Jersey Shore bridge.
The fold is over-
turned to the south (right side of photo).
4
I
Figure 25.
Asymmetric fold (expression of minor reverse fault ?) in
the Helderberg limestones on the south flank of a hill onehalf (1/2) mile west of Loyalsock Creek and one (1) mile
north of the river.
Photo taken looking east.
1i
river flood plain and the north limb of Nittany Anticline,
the folds become smaller and tighter, and the asymmetry is
often reversed.
This does not seem to merit any great sig-
nificance for the intense folds are of such a plastic nature (figure 26 and 27) that the causal stresse were not
transmitted sufficiently well to maintain any symmetry pattern.
The significant conclusion demonstrated by the in-
tense folding is that this zone not only underwent tremendous compressional forces, but also that it yielded to these
forces to a great extent.
The rapidity with which the de-
formation decreases to the north, northwest in the folds of
the Transition Zone shows that the transmission of the stress
was poor; that the force was applied from the south, southeast; and that much of this force was absorbed in the deformetion and shortening of the Devonian and Upper Silurian rocks in this zone.
Most of the dips in the Transition Zone are northward.
This is to be expected for the amplitude of the Nittany
Anticline is over twenty thousand (20,000) feet, and even
without the intense deformation, there would be a sizable
monocline on its north flank.
Most of the idealized cross
sections of the Appalachians show the Transition Zone as
such a monocline.
Faulting is also well expressed in the Transition Zone.
Reverse faults are by far the most common.
They are always
Figure 26.
Intense folding on east side of Pine Creek Valleys, two and
one-half (21/ 2 ) miles north of the river.
looking east.
Photo taken
Figure 27.
Complex, semi-plastic folding in shale quarry north of the
end of Market Street in Williamsport.
The width of the
area in the photo is about twelve (12) feet.
east.
Taken looking
associated with folding, and it
is
not possible to deter-
mine whether they are a cause or result of the folding.
The displacements are not too great, since in most cases
the intense folding has absorbed most of the slip (figures
28 and 29).
These faults are easily spotted in the major
stream cuts and along road and railroad cuts paralleling
the stream valleys (figure 30).
At least one (1)
major re-
verse fault, but probably not the same fault, crosses each
major stream spanning the Transition Zone.
Along Lycoming
Creek the steep dips just at the edge of the plateau indiWhether the faults are
cate a second fault in that valley.
continuous or in some en echelon arrangement is not determinable because of the soil cover.
There is little or no
topographic expression of these faults, since the foot wall
and hanging wall are equslly resistant to erosion.
On the
map they are shown in en echelon arrangement, for it seems
probable that the strike of the faults would parallel the
bedding and folding in the area rather than swing across
the compressive lineation.
Other minor reverse faults are
present which are associated with the tight folds, especially along Pine Creek,
but they indicated only very small
fault displacement and were not included on the map.
Most
of the reverse faults are up-thrown on the south side with
the fault plane dipping to the south.
The angle of the
plane is not determinable for any distance.
Small reverse
15
Figure 28.
Intense folding accompanying reverse fault near Quenshukeny
Creek two (2) miles north of the river.
Photo taken on the
west side of the creek valley looking west.
14
Figure 29.
Folding associated with reverse faulting on the road one
(1) mile south of Balls Mills.
Photo taken looking west.
s
Figure 30.
Reverse fault exposed in a railroad out on east side of
Pine Creek Valley three (3) miles north of the river.
Photo taken looking east.
faults in the opposite direction are suggested in some of
the folds which are asymmetrical to the south, southeast
(figures 24 and 25).
The presence of reverse faults is a-
gain conclusive evidence to the fact that this area was
subjected and yielded to great compressive stresses.
A
conjugate set of minor reverse faults in a shale quarry
just north of the end of Market Street in Williamsport i1lustrates a peculiar expression of these stresses.
Here,
two (2) reverse faults of opposite direction intersect, and
a pie-shaped wedge has been pushed up between the faults
(figure 31).
disturbed.
The strata below the intersection are not
This seems to imply that here the tangential
compression was greater along the top beds than in the lower ones.
The south dipping reverse faults also support the
possibility that the Nittany Antieline is overturned or
overthrusted at depth in this area.
This will be discussed
further in the next section concerning the structure of the
Ridge and Valley Province.
Minor normal faulting is evident at two (2) places along
the cut of the railroad parallel to Pine Creek (figure 32).
These two (2) faults strike approximately east-west and dip
sixty (60) degrees to the north.
The displacement is very
small, but some drag folding is developed up to six (6)
feet on either side of the fault.
Normal faults striking
north-south would be expected to accompany the structural
Figure 31.
Intersecting minor reverse faults in the shale quarry north
of the end of Market Street in Williamsport.
Notice the
upthrown pie-shaped segment and the undisturbed beds below.
Photo taken looking east.
Figure 32.
Minor normal fault and drag folds on the east side of Pine
Creek Valley, two and one-half (21/2) miles north of the
river.
Photo taken looking east.
fabric of this zone.
However, if these are present, the
lack of east-west cuts into the bed rock effectively hide
their presence.
The jointing system in the Transition Zone is well developed.
The system is three (3) directional, but at many local-
ities, depending on the rock characteristics,
only one (1)
or two (2) of the directions are present (figure 33).
The
following localities are representative of the jointing at
several scattered localities in the Transition Zone:
Oriskany sandstone in the quarry on the hill just west of
Loyalsock Creek on the north side of U. S. Highway 220 (figure 34)
#1
Strike NlOE, Dip 80E
#2
Strike NBOW, Dip 703
Helderberg limestone at the west end of hill mentioned above
#1
Strike N2OE,
#2
Strike N80W, Dip 73S
Dip 77E
Onondaga limestone in the quarry one (1) mile east of Monto-ursville
#1
Strike N70E,
Dip 60S
#2
Strike N40W, Dip 70S
Shale ouarry north of the end of Market Street in Williamsport, Pennsylvania
Figure 33.
Jointing in relatively flat-lying beds in the shale quarry
north of the end of Market Street in Williamsport, Pennsylvania.
Notice the change of the joint pattern in the dif-
ferent beds.
Photo taken looking southeast.
Figure 34.
Jointing in the Ridgeley (Oriskany) sandstone in the quarry
on the hill one-half (1/2) mile east of Loyalsook Creek on
the north side of U. S. Highway 220.
west.
Photo taken looking
#1
Strike N20W, Dip 85E
#2
Strike N5E, Dip 85E
#3
Strike N55W, Dip 75SW
Quarry just north of highway at Linden, Pennsylvania
Dip 75E
#1
Strike N30W,
#2
Strike N60E, Dip 75S
Plotting these joints on a stereonet leads to the interesting fact that all the joints intersect in a linear zone.
This line plunges about sixty-five (65) degrees to the
south ten degrees east (SlOE).
Assuming that a simple com-
pressional stress caused the joint system, and further assuming shear to be maximum at forty-five (45) degrees to
the compressive force, the joint pattern can be readily interpreted.
The compressive stress must have impinged on
the area from south ten degrees east (SlOE) at an angle of
twenty (20) degrees above the horizontal.
That is, the de-
forming force in the Transition Zone was mainly a tangential compression toward the north with a smaller component
of upward force.
The joints striking from north twenty de-
grees west (N2OW) to north sixty degrees west (N60W) and
dipping steeply would be tension joints and the others
shear joints.
This analysis is hypothetical, but the assumptions are valid,
and the interpretation so closely parallels the implications
crI
of the fold pattern that the results, to the author at
least, are significant.
The Transition Zone along the Appalachian Fold Front near
Williamsport,
Pennsylvania can be summarized as follows:
The intense deformation in the Devonian and Upper Silurian
rocks, expressed in folding and reverse faulting, which becomes less intense toward the north and toward the east
along the Fold Front, indicates strong compressional forces
from the south, southeast; and rapid absorption of these
forces by the incompetency and shortening of the section.
The joint system supports these indications and demonstrates that the compressional force was largely tangential
with a small upward component.
The intensity of the stress-
es seems to have been greater toward the west and southwest
in the direction of the center of the arcuate salient of
Nittany Anticline.
The Ridge and Valley Province:
This area of large major folds is
one of the most striking
phenomena in the entire subject of Appalachian structure.
Many publications and controversial theories have resulted
from the study of the origin and mechanics of Appalachian
folding.
For the purpose of this paper, the only generali-
ties of the province which are important are the northeastsouthwest lineation of the folds, and that asymmetry and
overthrusting, when present, are always toward the northwest.
Nittany Anticline is the last major fold in the Ridge and
Valley Province toward the northwest in central Pennsylvania.
It
w-hich,
is
the outermost are of the major fold salient
from the Tectonic Map of the United States (bibliog-
raphy 18),
appears to swing into the major structural sad-
dle between the Adirondack Uplift and the Findlay Arch.
From near Its eastern extremity, where the Tuscarora quartzite plunges beneath the present surface, the amplitude of
Nittany Anticline increases toward the west and southwest
until it is well over twenty-five thousand (25,000) feet.
North and south from Nippenose Valley the ridges of Tuscarora auartzite, forming the flanks of the fold, are six (6)
miles apart.
This separation becomes even greater toward
the southwest.
Dios on the north flank are steeper than
those on the south flank (figure 22).
The intensity of
this asymmetry varies from place to plsce along the Fold
Front.
East of Williansport the north limb of Tuscarora
quartzite dips north at forty-five (45) degrees.
Following
Bald Eagle Mountain westward, the dip of the Tuscarora increases rapidly until it is nearly vertical in the gap from
Mosquito Valley.
The dip decreases farther west, and in
gap of Antes Creek it
is
again forty-five (45)
degrees.
Much farther southwest, past the center of the arc, between
Port Matilda and Altoona, Pennsylvania, the Nittany Antialine is slightly overturned to the northwest; and a northward overthrust fault has been mapped on the northwest
flrnk of the fold (bibliography 18).
In the vicinity of
Williamsport the dips on Bald Eagle Mountain (the north
flank of the Nittany Anticline) all increase with decreasing elevation on the side of the fold.
That is,
there is
no indication above the present erosional level of the
flank dips becoming less, as they eventually must 9t some
depth, to join their equivalent gentle dips beneath the
tateau.
The joint pattern in the north limb of the Nittany Anticline near Williamsport falls into the same system as that
in the Transition Zone.
The Reedsville shale on the north
side of Mosquito Valley shows good jointing in two (2) directions (figure 35).
fl
Strike N5E,
#2
Strike N80E,
Dip 85E
Dip 65S
The Tuscarora quartzite south of Mountain Beach in South
Tilliamsoort has three (3) joint directions.
#1
Strike N-S,
Dip 70W
#2
Strike N70E,
Dip 70E
#3
Strike N55W,
Dip 60SW
Since these joints seem to be part of the same system as
*1i.
Figure 35.
Jointing in the Reedsville shale on the north side of
Mosquito Valley.
into the picture.
The bedding dips away to the right and
Photo taken looking northwest.
those in the Transition Zone, their interpretation is likewise the same.
The northward asymmetry of Nittany Anticline and the indication that the north flank dits will increase or even
overturn with depth before they begin their reversal toward
the gentle dips of the plateau, suggest that the Nittany
Anticline in this area may be overturned or overthrusted at
depth.
The intense compressional deformation and reverse
faulting in the Transition Zone support this conclusion.
Many of these Transition Zone structures may be semi-plastic exDressions of the surface trace of a possible low
angle thrust plane beneath the Nittany Arch.
Even the re-
gional structure seems to support this conclusion.
The en-
tire Nittany Anticline forms a bow-like are convex to the
northwest.
The east end of the fold plunges into relative-
ly less disturbed strata, but toward the west and southwest,
as the arc approaches its center point, the amplitude of
the fold increases and the comnressional deformation in
front of the north flank of the fold increases.
Even far-
ther southwest there is a known northwest overthrust (bibliography 18) in front of the north flank.
The indications
from this data seem to be that the plunging east end of the
Nittany Anticline acted as a hinge point; and the fold was
thrust north, northwestward with increasing displacement
toward the southwest to at least, and perhaps beyond, the
1.
center of the arc.
The displacement along such a thrust plane may have been
entirely taken up by the asymmetry of the fold in the vicinity of Williamsport.
It
seems likely, however, that if
such is the case, the north limb of Nittany Anticline will
be found overturned at deoth.
Interpretation:
The task of integrating the conclusions derived from the
structures found along the Fold Front in north central
Pennsylvania belongs to geologists with wide experience in
regional areas of the Appalachians and with mature views of
the mechanics involved.
The author certainly does not pur-
port to be included with the few capable of doing this.
However, it is almost impossible to work in an area without
attempting to fit the local findings into some picture of
the regional fabric.
For this reason, the following re-
gional interpretations are presented.
The forces involved in causing the major folds of the Appalachians seem to be primarily tangential.
They seem to
have mainly affected the veneer of Paleozoic sediments,
causing buckling and folding associated with low angle
overthrusting.
school
Ps
This is in agreement with the "thin skinned"
Rodgers (bibliography 19, p. 1653) has classified
it. Some recent studies of the magnetic profiles across
the Fold Front in north central Pennsylvania support this
view.
They indicate that there is no concordance between
the basement and the surface configuration of Nittany Anticline (bibliography 20, p. 1756).
The tangential forces involved seem to have been applied
from the southeast, and they have caused three (3) arcuate
salients (the northern, middle, and southern Appalachians)
all convex toward the northwest.
The areas of least ad-
vancement of the structural deformation toward the northwest, that is, the ends of the middle arc, correspond to
the Adirondack Uplift and the Cincinnati Arch.
The impli-
cation is that here the positive basement areas blocked the
advance of the deformation.
The reason for the rapid dying-out of the major folds and
faults across the narrow Fold Front and Transition Zone is
probably multiple.
Price (bibliography 1) believes this is
due to the absorption of much of the stress in the deformation of the relatively incompetent Devonian section on the
northwest flank of the Ridge and Valley Province.
This
boundary corresponds closely to the axis of greatest known
Devonian sedimentation in the Appalachian Geosyncline.
The
rapid decrease in major structures may also be due to a
basement high under the southeast edge of the Appalachian
Plateau.
This possible high is suggested by the magnetic
too
survey of the Clearfield - Philipsburg area in Pennsylvania
(bibliography 20, p. 1757).
In north central Pennsylvania,
the sudden structural transition may also be due in part to
the corrugated strengthening action given to the plateau by
a possible set of older north-south folds across northern
Pennsylvania and southern New York state.
It is probable that eventual solution of the controversial
subject of the origin and mechanics of Appalachian Structure will be dependent on widespread geophysical work -magnetic, gravimetric, and seismic --
to delineate the base-
ment configuration and its association to surface structures.
Nevertheless, there is still much to be done in the
way of surface structural mapping in the Appalachians, and
it is an area of such intense and varigated structural phenomena as to offer interesting challenge to even the most
experienced student of structural geology.
tI
VI Economic Geology
The southeast margin of the Appalachian Plateau has long
been avoided as a likely petroleum and natural gas prospecting area.
This was due, in most part, to the carbon ratio
theory of David White and others which indicated that no
gas and oil would be found in areas where the coal had been
metamorphosed to a fairly high ratio of fixed carbon.
How-
ever, a recent discovery of major natural gas production
from the Oriskany sand in Leidy Township,
Clinton County,
Pennsylvania, has increased the growing doubt of the validity of the carbon ratio limitation.
For this reason, Cogan
House and Rose Valley anticlines on the south margin of the
plateau in the thesis area, and even some of the folds in
the Transition Zone, have recently been leased for oil and
gas rights and will probably be tested in the near future.
The Cabot Company of Boston has already started a test well
on the Cogan House structure.
In connection with plateau
gas production from the Oriskany sand, a very interesting
side point can be noted.
The rock pressure in the gas
pools when they are first discovered increases with proximity of the pool to the Fold Front.
This is in part due
to the deeper burial of the Oriskany on the south margin of
the plateau, but calculating the hydrostatic pressures at
the producing depth, the ratio of hydrostatic head to rock
pressure decreases to the south.
In southern New York
101.
state the discovery rock pressures were slightly under the
hydrostatic head.
about ecual.
In northern Pennsylvanian they were
At the East Fork - Wharton Field, thirty-five
(35) miles south of the state line, the rock pressure was
about one and one-half (11/2) times the hydrostatic head.
And at the Leidy Field in Clinton County, the nearest production of Oriskany gas to the Fold Front in north central
Pennsylvania, the discovery rock pressure was forty-two
hundred (4200) pounds per scuare inch.
This is almost
double the hydrostatic head which would develop at the
fifty-five hundred (5500) foot depth when the sand is encountered.
These very high rock pressures make drilling
with cable tools hazardous,
and blow outs and one (1)
se-
vere fire have resulted (figure 36).
Coal and clay are present in considerable quantity in the
besins of the Allegheny formation in the plateau synclines.
Some of this coal is mined and stripped from the small
Pennsylvanian remnant just west of Lycoming Creek on the
south margin of the plateau.
Oriskany sand is quarried in the Transition Zone for abrasive and foundry purposes.
Some Helderberg limestone has
also been quarried in this zone for ballast rock or burned
for agricultural purposes.
The Mansfield Iron Ore (a hematite rich bed near the base
103
Figure 36.
Remains of the drill rig of the Dorcie Calhoun #2 well in
Leidy Township, Clinton County, Pennsylvania.
The well
caught fire when it blew in and the thirty million
(30,000,000) cubic foot per day open flow of natural gas
burned for seventy-two (72) hours before it was extinguished
and the well finally capped.
104
of the Catskill formation) and the sedimentary iron ores in
the Clinton formation are present in the thesis area.
These have been mined in the past but are not economical at
the present time.
Silica brick can be produced from the Tuscarora ouartzite.
This industry has been developed near Port Matilda, farther
southwest along the Fold Front.
The California Company has recently shown great interest in
the petroleum possibilities of the Cambro-Ordovician limestones exposed in the core of the Nittany Anticline.
A
well is now being drilled into these limestones on the
structural dome in Nippenose Valley.
If any commerical
production results from this exploration program,
it may
well prove to be the most valuable product of the entire
region.
Regardless of the proved and potential economic value of
the mineral wealth in north central Pennsylvania, the area
has a wealth of stratigraphic and structural examples which
can seldom,
one another.
if
ever, be seen in such close relationship to
ins
Figure 37.
Cable tool rig at the Harmon #1 well near Hyner, Pennsylvania.
This is typical of the standard tool rigs used in
the plateau area of northern Pennsylvania to prospect for
gas and oil.
Rotary tools cannot be economically operated
because of the hard formations.
E
m
to(
Bibliography
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Geol.,
vol.
39,
pp. 24 - 44, 1934
2. Sherwood, A., The Geology of Lycoming and Sullivan Counties: Pa. 2nd Geol. Sur., 1880
3. Swartz, Frank M., Trenton and Sub-Trenton of Outcrop
Areas in New York, Pennsylvania, and Maryland: Bull. Amer.
Assn. Petrol. Geol., vol. 32, pp. 1493 - 1595, 1948
4. Butts, C. and Moore, E. S.,
Geology and Mineral Resources
of the Bellefonte Quadrangle, Pennsylvania; U. S. Geol. Sur.
Bull, 855, 1936
5. Butts, Charles, Hollidaysburg . Huntingdon: U. S. Geol.
Sur. Folio 227, 1946
6. Kay, Marshall, Middle Ordovician of Central Pennsylvania:
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8. Swartz, C. K. and F. M., Early Silurian Formations of
Southeastern Pennsylvania: Geol. Soc. Amer. Bull., vol.
42, 1931
9.
Garrett,
S. G., Oriskany Gas Fields of Pennsylvania and
ton
New York: Bull. Amer.
Assn. Petrol.
Geol.,
vol. 15, p. 837,
1931
10. Lohman, S. W., Ground Water in North Central Pennsyland Geol.
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Sur. of Pa.,
Bull. W 6,
1939
11. Finn, F. H., Geology and Occurrence of Natural Gas in
Oriskany Sandstone in Pennsylvania and New York: Bull.
Amer. Assn. Petrol. Geol., vol. 33, pp. 303 - 335, 1949
12. Cathcart, S. H., Geologic Structures in the Plateaus
Region of Northern Pennsylvania: Topo. and Geol. Sur. of
Pa., Bull.
108, 1934
13. Sherrill, R. E., Some Problems of Appalachian Structure: Bull. Amer. Assn. Petrol. Geol., vol. 25, pp. 416 423, 1941
14. Foose, Richard M., A Cross Synclinal Structure near
Lock Haven,
Pennsylvania: Proc. Pa. Acad. Sci.,
vol. 14,
pp. 64 - 69, 1940
15. Torrey, P. D., Gas Fields of New York and Pennsylvania:
Sym.,
Amer.
Assn. Petrol. Geol.,
Natural Gas, pp. 949 -
987
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S. H., Oriskany Exploration in Pennsylvania
and New York: Bull. Amer. Assn. Petrol. Geol.,
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Middle and Southern Appalachians: Bull. Amer. Assn. Petrol.
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20. Joesting, Keller and King, Geologic Implications of
Aeromagnetic Survey of Clearfield - Philipsburg Area, Pennsylvania: Bull. Amer. Petrol. Geol., vol. 33, pp. 1747 1766, 1949