AN ABS'i
C OF TidE
IS OF
Stephen W. Little for the degree of Master of Science in
Geoloay presented on June 11, 1986.
Title: Stratigraphy, Petrology,
Gable Creek
Formation,
and Provenance of the Cretaceous
Wheeler County, Oregon
Abstract approved:
The Mitchell inlier in r:orth-central Oregon contains the largest
exposure of Cretaceous marine sediaentary rocks in this
Nearly
region.
9,000 ft of Albian-Cencmanian rocks are exposed along the flanks of the
Mitchell
anticline.
Permian(?)
The Cretacews section rests unoonformably on
metal wdinertarrocks and is unocnformably overlain by Tert-
iary volcanic rocks. The Cretaceous rocks have previously been divided
into the Hudspeth and Gable Creek Formations.
The Hudspeth Formation
consists of thick sequences of hemipelagic mudstone that contain
subordinate siltstones and thin beds of turbiditic sandstone.
Gable Creek Formation is cx
The
osed of rumieroas isolated sequences of
coarse conglanerate, pebbly sandstone, and sandstone.
This study con-
centrates on the stratigraphy and petrologic oaqposition of the Gable
Creek oonxjlomerates.
The Gable Creek cor lacerates are ccmposed of a heterogeneous
assemblage of volcanic
of s
rocks,
chert, plutoniic rocks, and lesser amounts
and metamorphic rocks.
The petrologic ociposition of
the conglomerates can be accurately reflected by means of pebble count
analysis.
Pebble counts provide a valuable tool for quantifying con-
glomerate composition and documenting compositional variations within
the 70-square-finale Cretaceous outcrop area. Cluster analysis of the
data confirms the presence of two major conglomerate
pebble count
petrofacies within the inlier.
The striking compositional
contrasts
between the two petrofacies may be due to primary differences in
sediment composition or secondary, post-depositional changes.
Statis-
tical correlation values reveal that conglomerate oonposition is fairly
uniform within each of the two petrofacies.
Petrologic composition
also remains nearly constant within each of the major conglomerate
units but exhibits random variations upward through the stratigraphic
section.
The Cretaceous rocks at Mitchell were deposited in a deep marine
basin sometimes referred to as the Ochoco
cacmm., 1985).
Basin (Odiorne, written
The Ochooo Basin may have extended into southwestern
Oregon where Cretaceous rocks of the Hornbrook Formation are exposed.
Several small Cretaceous inliers in central Oregon represent nonmarine
and shallow
marine environments of deposition that flanked the basin
margins.
This study supports the interpretation of the Cretaceous rocks at
Mitchell
as submarine turbidites as suggested by KLeinhans (1984).
The Gable Creek rocks were deposited in submarine channels by various
sediment gravity flow processes in a base-of-slope or proximal fan
setting. The Gable Creek units are arranged into thinning- and
fining-upward sequences that may be the result of progressive channel
abanxlornaerit.
The correlative Hudspeth rocks are interpreted as sub-
marine levee, overbank, and interchannel deposits associated with
the Gable Creek channels.
The geometry of the Cretaceous rocks is
defined by a series of stacked
channel-levee--interchannel
sequences.
Paleocurrent data fraon the Cretaceous section yield a dominant
southwesterly direction of sediment transport and a subordinate
northwesterly trend.
Variations in paleocurrent orientation may re-
flect several directions of sediment input, overbank deposition, and
channel abandormient.
The Gable Creek conglomerates have source areas
located to the southeast, east, and northeast, of Mitchell within the
Late Paleozoic and Early Mesozic accreted terranes in eastern Oregon.
The provenance of the congla rates is widespread and includes the
island arc rocks of the seven Devils Group, rocks of the dismembered
oceanic crustal terrane, forearc strata of the John Day inlier, and the
Jurassic plutons in no:
Oregon. A previously uxx ascribed
tuffaceous unit within the Gable Creek Formation probably marks a
short-lived
areas.
episode of
mid-Cretaceous volcanic activity in the source
STRATIGRAPHY, PETROLOGY AND PROVENANCE OF THE CRETACEOUS
GABLE CREEK FOFd +.TION, WHEELER COUNTY, OREGON
by
Stephen W. Little
A =IS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Master of Science
Completed June 11, 1986
C.o
x ncement June 1987
sociate Professor of Geology ,' n ;age of major
Dean of Gradu
School
Date thesis is presented
June 11, 1986
TABLE OF CONTENTS
INTRODUCTION
location
Previous Work
Purpose
BACKGROUND
1
1
i
4
5
Geologic Setting
Structure
Regional Extent of Cretaceous Rocks
5
Pre-Cretaceous Rocks in Eastern Oregon
8
STRATIGRAPHY
Cretaceous Rocks at Mitchell
6
7
12
12
Outcrop Area
12
Terminology
Hudspeth Formation
Gable Creek Formation
12
12
17
Sedimentary Structures
Cretaceous Tuff Unit
Structural Behavior
Facies Relationships
Other Cretaceous Conglomerates in Central Oregon
20
23
27
27
28
METHODS OF INVESTIGATION
Pebble Counts
Field Identification
Petrographic Analysis
Data Processing
32
32
34
35
36
CONGLOMERATE PE
LOGY
Plutonic Rocks
Volcanic Rocks
37
37
Sedimentary Rocks
Metamorphic Rocks
40
44
46
RESULTS
Pebble Counts
Correlation Matrix
Sampling Technique Study
Coayipositional Variability Study
Cluster Analysis
Vertical Variation of Ccatiposition
Ccanparison With Other Cretaceous Conglomerates
Paleocurrents
49
DISCUSSION
79
49
49
54
56
57
67
69
73
Provenance
79
Tectonics and Basin Origin
84
Subsidence, Sea Level Changes, and Sedimentation
Petrologic Evolution
Cretaceous Paleogeography
Facies Models
OONCLUSIONS
REFERENCES CITED
APPENDICES
86
88
89
91
99
102
LIST OF FIGURES
Figure
1.
2.
3.
4.
5.
Page
location map showing distribution of cretaceous
sedimentary rocks in central and eastern Oregon.
Matrix-supported pebbly mudstone within the
Hudspeth Formation.
16
Typical outcrop of Gable Creek conglomerate
located near Mitchell, Oregon.
19
Conglomerate rip-up clast near the base of a
thick conglomerate bed.
22
Large vortex-type flute cast on the base of a
pebble conglomerate bed overlying mudstone.
6.
7.
8.
9.
24
Derxlrograms resulting from cluster analysis of
the pebble count data.
59
Ternary plot of chert, volcanic, and plutonic
clast percentages at each sample site.
62
Hoodoo-like Gable Creek conglomerate outcrops
along Girds Creek.
64
Light-colored, clay-rich clasts in conglomerate
outcrop.
10.
2
65
Bar graph showing ratio of chert, volcanic, and
plutonic clasts in the stratigraphic section located south of the Mitchell fault.
69
11.
Ternary plot of data fran Figure 10.
70
12.
Rose diagram of paleocurrent data collected from
the Cretaceous sequence at Mitchell.
76
13.
Schematic representation of geometry of the
Cretaceous deposits at Mitchell.
97
LIST OF TABLES
Table
Page
1.
Lithologic categories used for pebble counts
35
2.
Sample format for tabulated pebble count results.
50
3.
Correlation values between the Michell locality
and all other sample sites.
53
4.
Results of sampling technique ccq arison.
55
5.
Correlation values between several Cretaceous
inliers in central Oregon and the Gable Creek
conglcmnerates at Mitchell.
72
Appendix
A.
Modal analysis results frau plutonic rock clasts.
B.
Tabulated pebble count results listed by sample
C.
D.
108
number.
109
Mean values of pebble count results at each
sample site.
127
Correlation matrix of all pebble count sample
sites.
130
The writer would like
individuals
who have made a contribution
appreciation
University
to express his gratitude to the many
to this
I extend my
to the members of the Geology Department at Oregon State
especially my major professor, Dr. E. M. Taylor, for his
suggestions and support both during and after
tion.
study.
Appreciation
is also extended to
Dr.
the field
investiga-
R. D. Lawrence for his
help and ideas during the field season and to W.H. Taubeneck for his
helpful discussions afterward. Special thanks
to
L.C. Kleinhans for
assistance and stimulating discussions in the field.
I am especially grateful to my
wife,
Carrie, for her unwavering
support without which this project would not have been possible.
STRATIGRAPHY, PETROLOGY AND PROVENANCE OF THE CRETACEOUS
GABLE CREEK FORM TION, WHEELER COt]NTY,OREGON
INTRODUCTION
Location
More than 70 square miles of Cretaceous sedimentary rocks are
exposed near the town of
Mitchell in
north-central Oregon
(Figure 1).
The Cretaceous outcrop area is located in the southern half
Mitchell
of the
quadrangle in Wheeler County. U.S. Highway 26 traverses
the area in an east-west direction and is joined
at Mitchell.
by State Highway 207
Numerous unpaved roads of varying quality transect the
area and provide access to most of the Cretaceous exposures.
The landscape around Mitchell is hilly and semi-arid with
juniper,
and grasses dominating the natural vegetation.
sagebrush,
The soil layer
is thin
lations restricted
and poorly developed
to the valleys
valleys support cultivated
with the thickest aocumx-
and along streams.
Many of the
fields of alfalfa and grass hay.
larger drainages in the area contain small
streams that
The
form tribu-
taries to the John Day River which passes through the northern part of
the
quadrangle.
The climate in this region
swnmrs with occasional thunderstorms
is characterized by hot
that deliver
tion of short duration and by cold winters with
intense precipita-
light rain
or snow.
Previous Work
The first published account of Cretaceous rocks in the Mitchell
area was by Gabb in
1868.
Merriam (1901) described the geology of the
2
f!
t
ohn
1\1
T
S
;
P4
us,
aft p irk
14t
6
nty---.
S po , s t,
0
,
Frail
lie
14,
to n
X13
r
-Al nc
I MITCHELL
T
Is
2 BEARWAY MEADOWS
3 FOPPIANO CREEK
4 WATERMAN FLAT
5 MOUNTAIN CREEK
6 ANTONE
7 GOOSE ROCK
B BIG BASIN
9 ALDRICH MOUNTAIN
10 BULL RUN
-- --- !
-
t
-rk
n n bay
nyon
d
' Strawb ry Mt..
v
a
I
\
I
II RICCO RANCH
i
12 BATTLE CREEK
13 DEXTER RANCH
14 TUNNEL CREEK
IS ROUND CREEK
i
16 BERNARD RANCH
t.
ac
!
to
(Or
Fossil B ds
John
a
to
5
0
10
5
15
20
miles
Figure 1. Iocation map showing distribution of Cretaceous sedimentary
rocks in central and eastern Oregon (after Oles, 1973).
3
John Day basin and noted the presence of marine Cretaceous rocks south
of the basin.
Fossil determinations were made by Packard (1928, 1929)
and Anderson (1938, 1958) and the rocks were assigned an Albian-Cenomanian age.
A statuary of this earlier work can be found in Popenoe
and others (1960).
Re=Maisance geologic mapping was performed by Hodge (1932).
Graduate students from Oregon State University have mapped most of the
Cretaceous rocks as part of thesis dissertations (Bowers, 1952; Swarbrick, 1953; Bedford, 1954; Howard, 1955).
McKnight (1964) described
the stratigraphy and proposed a turbidite origin for the thin sandstone interbeds in the dark, laminated mudstone unit.
Wilkinson and
Oles (1968) divided the Cretaceous section into two intertonguing
formations and discussed their paleoenvirormnents.
The predominantly
mudstone and siltstone units were designated as the Hudspeth Formation
while the
lensing conglomerate and sandstone units were assigned to
the Gable Creek Formation.
Wilkinson and Oles proposed a fluvial-del-
taic origin for the conglomerates and suggested episodic or possibly
cyclic changes between marine and continental sedimentation to produce
the intertonguing deposits.
The most detailed geologic map of the
quadrangle was published by Oles and Enlows (1971).
Jarman (1973)
concentrated on the clay mineralogy and sedimentary petrology of the
Hudspeth Formation. A paleogeographic reinterpretation by Kleinhans
and others (1984) suggested that the conglomerate units were deposited
within a submarine turbidite system.
was based on facies
associations,
eontologic data.
This deeper water interpretation
sedimentary structures, and
4
Pose
The emphasis of this study is on the stratigraphy and conglomerate petrology of the Cretaceous Gable Creek Formation.
The clast
composition of the conglomerates has been previously not. by several
workers but no systematic approach to quantify compositional changes
throughout the entire outcrop
area has been attempted.
The purpose of
the study is to identify the lateral and vertical variations in conglomerate petrology in order to relate composition to stratigraphic
position. It is hoped that this information might make detailed
stratigraphic correlations possible. Such correlation would help
unravel some of the structural complexities that characterize the
Cretaceous section.
In addition, paleocurrent trends are analyzed and
attempts are made to identify the provenance of the various conglom-
erate clast types.
5
BACXMRO JND
Geologic Settina
The rock units in the Mitchell area range in age from Permian
to Tertiary and represent a variety of marine and terrestrial environments.
The oldest exposed basement rocks are Permian metasedi-
ments consisting primarily of chert, phyllite, and crystalline limestone.
The Permian age determination is based on poorly preserved
fusulinids collected from recrystallized limestones that resemble
Early Permian forms found in the Coyote Butte Formation located 45
miles southeast of Mitchell. The metased merits near Mitchell contain
lawsonite blueschists that yielded a radiometric age of 220 m.y. B.P.
(Hotz and others, 1977).
In
addition, the cherts in this unit contai
radiolarians of undetermined age that closely resemble common Triassic
forms (Lawrence, oral came.,
1986).
Thus the Permian age for this
unit is questionable and the rocks can only be regarded as pre-Late
Triassic.
Overlying the basement rocks with angular unconformity is the
basal member of the Hudspeth Formation composed of a transgressive
marine sandstone and pebbly
conglomerate.
This basal unit grades up-
ward into the dark mudstones and siltstones of the Main Mudstone mem-
ber.
Succeeding this thick unit, eleven tongues of the conglomeratic
Gable Creek Formation interfinger with a similar number of Hudspeth
tongues (Wilkinson and tiles,
1968).
The conglomerate units contain
sandstone lenses and grade transitionally upward into the next overlying mudstone tongue.
in this manner,
the exposed Cretaceous marine
6
sedimentary rocks comprise a stratigraphic section approximately 9,000
feet thick.
The Cretaceous rocks are unconformably overlain by Tertiary volcanic rocks of the Clarno Group, the John Day
River
Group,
and the Rattlesnake
Formation.
canic units include lava flows, mudflow
Formation,
These terrestrial vol-
deposits,
ments, ignimbrite, and local intrusions.
the Columbia
tuffaceous sedi-
All of the major Tertiary
units are separated by angular unconformnities that attest to the
tectonic instability of the region. The Tertiary rocks are, in turn,
unconformably overlain by Quaternary pediments, alluvial fans, and
colluvium.
Structure
The major structural features in the Mitchell area include broad
northeast-southwest-trending folds represented by the Sutton Mountain
syncline and the doubly-plunging Mitchell anticline. The Cretaceous
sequence is exposed along the flanks of the breached Mitchell anticline.
The axial region exposes the thick Hudspeth mudstone unit and
is cut by numerous faults and small intrusions.
The principal fault in the area is the east-rest trending
Mitchell fault that offsets the axis of the Mitchell anticline.
The
Mitchell fault exhibits right-lateral displacement along with a poorly
constrained eoaponent of vertical offset.
In some areas, the Mitchell
fault juxtaposes the Cretaceous strata against volcanic rocks of the
Eocene Clarno Formation indicating a post-Eooene age of fault movement.
Taylor
(1981)
suggested that a stress regime of northwest-
southeast coampression during early Oligocene time could have produced
the Mitchell fault. A similar stress regime was probably responsible
7
for the comipressional event that created the Mitchell anticline during
the latest Cretaceous and early Tertiary times. A more recent folding
event of similar orientation is reflected in the Miocene basalts of
the Sutton Mountain syncline.
In addition to these large-scale structures, numerous smaller
faults, folds, and intrusions add to the structural complexity of the
area.
Regional Extent of Cretaceous Rocks
The Mitchell inlier represents the largest exposure of Cretaceous
Several other small, scattered
sedimentary rocks in eastern Oregon.
inliers of Cretaceous strata are present to the south and east of
Mitchell (Figure 1).
occurrences
These isolated
suggest that signifi-
cant accumulations of Cretaceous sediments may be preserved beneath
the cover of Tertiary volcanic rocks.
In southwestern Oregon, Cretaceous sedimentary rocks are more
widespread.
Lower Cretaceous rocks of the Days Creek Formation crop
out near the coast in Curry County (Peck, 1961).
ation consists of marine sandstone,
ate.
siltstone,
The Days Creek Form-
and minor conglomer-
The Upper Cretaceous Hornbrook Formation crops out along the
northeastern flank of the Flamath Mountains in Jackson County, southern Oregon and Siskiyou County, northern California.
The Hornbrook
Formation consists of about 1,200 m of nonmarine and marine clastic
rocks (Nilsen, 1984).
outcrops of Hornbrook strata extend for about
80 km in a narrow, northwest-trending belt.
In north-central California, Upper Cretaceous fore-arc strata of
the Great Valley sequence are exposed along the western edge of the
8
Similar rocks of Jurassic to
San Joaquin Valley (Ingersoll, 1979).
late Cretaceous
age are preserved
in the Methow Trough of northern
Washington and southern British Columbia (Tennyson and Cole, 1978).
Upper cretaceous sediments of the Nanaimo Trough
are exposed on
The thick sequence of sandstone,
Vancouver Island, British Columbia.
shale, and conglomerate in the Nanaimo Group is also interpreted as
forearc basin deposits (Muller and Jeletsky, 1970).
During the Cretaceous Period, the
western Cordillera became
nearly continuous from Alaska to Mexico and prevented the Pacific
ocean from entering the continental interior (Williams and Stelck,
1975).
Periodic uplifts along the Cordillera
caused large
quantities
of clastic materials to be shed westward into the Pacific ocean and
eastward into the interior.
By late Albian time, the western interior
was occupied by a shallow, epicratonic sea that connected the Artic
Ocean with the Gulf of Mexico.
Along the western margin of this Cret-
aceous seaway thick wedges of coarse sediment prograded eastward into
the basin.
local
regressions, caused by this progradation, produced
interfingering deposits
of coarse
grained basinal sediments.
fan-delta clastics and the fine-
On the
western side
of the Cordillera,
deep forearc basins formed along the continental margin and it was in
such a basin that the Cretaceous rocks at Mitchell were formed.
Pre-Cretaceous Rocks in Eastern Orecxon
The extremely heterogeneous composition of the Gable Creek
conglomerates suggests that the source area for these
widespread and geologically diverse.
sediments was
Much of the source
area is un-
doubtedly buried at present beneath the younger volcanic cover.
The
9
isolated exposures of pre-Cretaceous rocks provide clues to the nature
of potential source areas of the Gable Creek Formation.
Within the Blue Mountains province of eastern Oregon, pre-Tertiary rocks are exposed in a number of erosional inhere surrounded by
Tertiary volcanic rocks. These older rocks are mostly contained
within the several tectonostratigraphic terranes that have been
identified in this region (Brooks and Vallier, 1978; Dickinson, 1979;
Brooks,
1978).
All of these terranes are metamorphosed to varying
degrees and are locally intruded by late Mesozoic granitic plutons.
Devonian through Cretaceous rocks are
present,
but most of the rocks
range from Permian to Jurassic in age.
Pre-Late Triassic rocks exposed near Mitchell and further to the
east represent a mixed assemblage of rocks with oceanic crustal
affinities (Vallier and others,
1977).
The largest exposure of these
rocks is the ophiolitic Canyon Mountain Complex located south of the
town of John Day.
The Canyon Mountain Complex is Late Permian to
Middle Jurassic in age and consists largely of quartz diorite, albite
granite (plagiogranite), and ultramafic rocks including serpentinite,
peridotite, and
pyroxenite.
Included in this terrane are the Permian
to Triassic rocks of the Elkhorn Ridge Argillite and the Burnt River
Schist located in the Baker quadrangle (Gilluly, 1937).
The Elkhorn
Ridge Argillite is composed of interlayered chert, argillite, tuff,
basalt, and minor amounts of limestone and conglomerate.
River Schist is mostly quartz phyllite,
litic quartzite,
and marble.
greenschist,
The Burnt
greenstone, phyl-
The Burnt River Schist is more highly
deformed and may represent the older of the two units (Gilluly,
1937).
10
A pre-Tertiary volcanic arc terrane is exposed in Hells Canyon of
the Snake River near oxbow, and northward in the Wallowa Mountains.
This assemblage is commonly referred to as the Seven Devils Group and
consists of metamorphosed basalt
(greenstone),
andesite, dacite, and
rhyolite flows and volcaniclastic rocks (Vallier, 1977).
These
Permian and Triassic rocks are overlain by Upper Triassic and lower
Jurassic carbonate and clastic sedimentary rocks. A similar assem-
blage of rocks is present further south along the Snake River near
Huntington, Oregon.
A thick sucession of Triassic through Cretaceous clastic strata
is exposed in the John Day inlier and eastward to the Snake River.
The entire sequence is more than 15,000 m thick and is dominantly
ca posed of voicaniclastic
sandstone,
turbiditic
graywacke,
siltstone,
and shale, along with minor volcanic components (Dickinson and Thayer,
1978).
The largely volcaniclastic Triassic and Jurassic sucession is
unconformably overlain by Cretaceous sandstone and conglomerate
similar to the Gable Creek Formation located near Mitchell.
South of the John Day
inlier,
approximately 20 square miles of
Paleozoic rocks are exposed near the small town of Suplee (Merriam
and Berthiaume, 1943).
The Paleozoic sequence is more than 3,000 feet
thick and is divided into the Coffee Creek Formation and the Spotted
Ridge Formation.
limestone,
The Mississippian Coffee Creek Formation consists of
marl, and calcareous
sandstone.
The overlying Spotted
Ridge Formation is Pennsylvanian in age and is composed of bedded
cheat,
mudstone, sandstone,
and conglomerate. The poorly sorted con-
glcmerate unit contains boulders of diorite and dacite that reach a
maximum diameter of two feet.
11
Plutonic rocks in eastern Oregon can be divided into Middle
Triassic to Early Jurassic and Late Jurassic to Early Cretaceous
episodes of
plutonism.
The quartz diorite and albite granite at
Sparta in the Pine Quadrangle is characteristic of the earlier event.
The later episode of plutonisn is represented by quartz diorite,
granodiorite,
and tonalite in the Bald Mountain and Wallowa Batholiths
(Taubeneck, 1957).
The older granitic rocks are metamorphosed and
sheared whereas the younger rocks are undeformed (Gilluly, 1937).
In
western Idaho, the granite and granodiorite of the Idaho Batholith is
mostly Late Cretaceous in age and is probably younger than the Mid-
Cretaceous deposits at Mitchell.
12
cretaceous Rocks at Mitchell
Outcrop Area
The Cretaceous outcrop area in the vicinity of Mitchell, Oregon
extends for more than 22 miles along strike in a northeast-southwest
direction (Plate
1).
The maximum width of the outcrop belt on the
north side of the Mitchell fault is about 5 miles. South of the
Mitchell fault, the outcrop area is about 12 miles wide. Two small
outliers of Cretaceous rocks are present along the lower portion of
Bridge Creek and at Bearway
Meadows,
respectively. The best exposures
of Cretaceous strata occur on the gently dipping southeast limb of the
Mitchell
anticline.
Structural dips range from near horizontal to a
maxiimnn of 70 degrees, the latter being represented by a fault-steep-
ened conglomerate unit in the SE 1/4, Sec. 21, T. 11 S., R. 21 E.
Terminology
The terms mudstone, siltstone, and sandstone are used here as
textural designations referring to the V*xrhmrth classification of
sedimentary-rock grain size.
The division between mudstone and
siltstone is made at 50% silt-sized
particles.
Pebbly sandstone and
pebbly mudstone are rocks in the respective size ranges which contain
less than 50% pebble-sized clasts.
The term conglomerate refers to a
sedimentary rock containing 50% or more of grains larger than sand
size. Textural terms including pebble conglomerate and cobble conglomerate are used to emphasize the dominant size range of the clasts.
Hudspeth Formation
The Hudspeth Formation is, in
part,
older than the Gable Creek
13
Formation and directly overlies the metasedimentary basement ccuplex
with sharp angular
unconformity.
The basal unit of the Hudspeth
Formation is best exposed near the head of Meyers Canyon in the SW
1/4, NE 1/4, Sec. 13, T. 11 S., R. 21 E., where it consists of a
sandstone and conglomerate unit approximately 75 feet thick.
At the contact with the underlying basement rocks, the sandstone
is a medium-grained lithic arenite that is pinkish orange in color due
to abundant limonite staining. Sandstone grains are mostly angular
and dominantly cmnposed of quartz, feldspar, mica, chert, quartzite,
microlitic volcanic fragments, and
fragments,
phyllite.
Fossil wood and plant
up to several inches long, are locally abundant in the
sandstone.
The basal sandstone is overlain by a thin conglomerate bed com-
posed mainly of subroundeed pebbles of chart, quartzite, and volcanic
and metamorphic rocks.
The matrix of this clast-supported conglomer-
ate is sandy and the cementing agent is calcite. The conglomerate bed
is several feet thick and exhibits grading with one to two inch
pebbles at the base fining upward into a pebbly sandstone.
Within the basal member at Meyers Canyon, there is a thin bed of
light-colored
sandstone.
In thin
section,
the rack is seen to be
silicified and many of the framework grains are replaced by crypto-
crystalline silica with the exception of quartz and quartzite grains.
The matrix has also been similarly replaced and the rock exhibits no
reaction to hydrochloric acid. This distinctive sandstone bed is exposed in a small saddle in the center of Sec. 13, T. 11 S., R. 21 E.
The basal Hudspeth member is also exposed on the southwest flank
of Tony Butte in Green
Hollow.
At this
location,
a thin sandstone
14
bed rests unconformably on the basement rocks and contains pelecypod
shells and angular fragments of the underlying rock. Unlike the
stratigraphic sequence at Meyers Canyon, the sandstone here is
abruptly succeeded by a thick, coarser-grained conglomerate unit.
The Tony Butte conglomerate differs markedly from the conglomer-
ate at the Meyers Canyon exposure in both texture and composition. At
Tony Butte,
the conglomerate consists of large, well rounded pebbles
and does not grade upward into pebbly sandstone.
Whereas the Meyers
Canyon conglomerate is almost wholly composed of chert, quartzite,
volcanic rocks, and metamorphic rocks, the Tony Butte unit contains
plutonic and sedimentary clasts, less chert, and is richer in mafic
volcanic clasts.
The lowermost Hudspeth unit is depositionally overlain by a thick
mudstone unit referred to as the Main Mudstone member (Wilkinson and
Oles,
1968).
This unit is more than 3,000 feet thick and consists of
dark green to gray mudstone with subordinate amounts of siltstcne and
sandstone.
The Main Mudstone member is thickest near the head of
Meyers Canyon and appears to thin northward toward Tony Butte where
the section is reduced by about 1,000 feet (McKnight, 1964).
mudstones contain varying amounts of
composed of quartz, feldspar,
(Jarman, 1973).
inated.
silt-
The
and sand-sized particles
mica, chlorite, and glauconite pellets
Fresh exposures show the mudstone to be thinly lam-
Spheroidal weathering is typical and the naadstone breaks
into angular chips.
Calcareous concretions are found throughout the mudstone unit and
range in size from several inches to more than two feet in diameter.
The concretions commonly contain ammonite fossils which may function
15
as nuclei.
Septarian concretions occur less commonly and exhibit a
network of calcite-filled cracks 2-10 nn wide. Ammonites are the most
coon fossils but
pelecypods,
crab
claws,
belemnite rostra, and fish
teeth have also been found in the mudstone.
In the upper portion of the Main Mudstone member, thin sandstone
beds are rhythmically interbedded with the mudstone.
The sandstone
beds are 1 to 3 feet thick and are manly graded near the base.
The
basal contacts with the underlying mudstone are sharp and may exhibit
sole markings such as groove and flute casts. The upper sandstone
contacts are gradational with the overlying mudstones.
Amalgamation
of the sandstone beds is omm on where the intervening mudstone layer
has been scoured away prior to deposition of the next sandstone
layer.
The thin sandstone beds of graywacke conosition within the Hud-
speth Formation are interpreted as turbidity deposits (McKnight, 1964;
Kleinhans and
others, 1984).
Consistent with this interpretation is
the observation that many of the sandstone beds contain all or part
of the subdivisions of the classic Bouma
sequence.
In addition,
transported shallow water pelecypod fossils including Trigonia sp. and
Inoceramus sp. can be found within the sandstones.
Several pebbly mudstone units are locally present within the
Hudspeth Formation (Figure
thin,
restricted,
2).
and laterally
In general, the pebbly mudstones are
discontinuous.
These unbedded dep-
osits are matrix supported with poorly sorted pebbles suspended in
mudstone.
The pebbly mudstones are interpreted as chaotic submarine
slump and debris flow deposits as described by Crowell (1957).
A deep marine origin for the Hudspeth Formation is supported by
16
1i1L
71
o
i
.a
r
I
U,
L-
Matrix-supported pebbly ffixlstone within the Hudspeth
Formation (photo courtesy of L.C. IQeinhans).
Figure 2.
17
the presence of ammonites and benthonic foraminifera in the dark
mudstones and the paucity of a typical shallow marine fauna.
The
finely laminated nature of the mudstones indicate a lack of bioturbation or reworking by wave action (Wilkinson and Oles, 1968).
Water depths determined from benthonic foraminifera collected frcan the
mudstones suggest a neritic to upper bathyal environment of deposition
(Kleinhans and
others,
1984).
The conglomerate units of the Gable Creek Formation are also interpreted as having been deposited in a marine environment.
The pres-
ence of gastropod and pelecypod fossils and the intimate relationship
of the Gable Creek units with the Hudspeth iroudstneto
interpretation.
s support this
The applicability of the turbidite classification
scheme as outlined by Nhitti and Ricci Iucchi (1972, 1975) led Klein-
hans
(1984)
to regard the Gable Creek rocks as part of a submarine
turbidite system.
The conglomerates also exhibit several fabrics and
levels of organization cited by Walker (1978) as evidence of resedimented marine deposits.
Gable Creek Formation
The Gable Creek Formation is the designation given to the
numerous conglomerate and sandstone units that interfinger with the
fine-grained rocks of the Hudspeth Formation.
The base of the Gable
Creek Formation is taken to be the first occurrence of conglomerate
overlying the Main Mudstone member of the Hudspeth Formation.
Wilkinson and Oles
Main Mudstone.
(1968)
In all,
mapped eleven Gable Creek tongues above the
The stratigraphic secession is idealized because a
corn lete section is not present along any single transect. The most
camplete Gable Creek section is exposed south of the Mitchell fault
18
where the conglomerates crop out along the southeast limb of the
Mitchell anticline.
In outcrop, the resistant Gable Creek Formation forms prominant
hogback ridges and steep cliffs.
Conglomerate outcrops can be easily
recognized from a distance by their massive, rounded shape and dark
brown color punctuated by thin, light colored sandstone lenses (Figure
3).
One exception to this generalization is the rusty brawn and pin-
nacle-like hoodoos of conglomerate that crop out along Girds Creek
in the northern part of the inlier.
The conglomerates are generally
medium to thickly bedded with individual beds ranging from one to
several meters.
Thick bedding is exemplified by normally graded beds
up to 8 m that represent a single depositional event.
Distinct
bedding is sometimes difficult to recognize in the more disorganized,
unstratified horizons.
Basal contacts of the conglomerates are invariably sharp and
usually manifest distinctive scour and fill features.
Undulatory con-
tacts and the presence of maudstone rip-ups near the base of the con-
glomerate beds attest to the erosional power of these currents during
deposition.
ubitquitous.
Grading is common in the conglomerates, but by no means
The overall tendency is toward normal grading but both
reverse grading and doubly graded beds are locally prevalent.
The
Gable Creek units demonstrate an overall fining-upward trend with
thick basal conglomerates passing upward into pebbly sandstone and
sandstone.
The upper contacts are gradational, with sandstone and siltstone
transitional between the conglomerates and the mudstone of the next
overlying Hudspeth tongue.
19
w
Y
G
}
N..K
aN
Figure 3. Typical outcrops of Gable Creek conglomerate located near
Mitchell, Oregon.
I
ti
20
The conglomerate fabric is best described as clast supported,
although matrix-supported pebbly sandstones are present in the upper
portions of some units.
Sorting is highly variable but generally poor
and clasts range in size from pebbles to boulders.
Pebble canglom-
erates are most abundant followed by lesser quantities of cobble-sized
material.
The maximum grain sizes recorded are on the order of two to
four feet in diameter.
Thin boulder beds are present at the base of
some units but boulders are also randomly scattered among the smaller
clasts.
The boulder beds are laterally discontinuous and probably
represent unusually coarse, localized channel fill.
Roundness is high among conglomerate clasts and tends to increase
with increasing grain size.
Angularity is much higher among the
interbedded sandstone grains as compared to the conglomerate clasts.
The sandy conglomerate matrix is similar in composition to the lithic
arenites in the sandstone lenses and calcite is the main cementing
agent thtout.
Sedimentary Structures
The Gable Creek conglomerates and sandstones display a wide variety of primary sedimentary structures.
Scour and fill features and
grading, mentioned above, are probably the most abundant types.
Planar stratification, manifested by the parallel alignment of elongate clasts, is often helpful in accentuating bedding in the conglomerates.
Pebble imbrication is cannon, specifically as A-axis imbrica-
tion, in which the long axes of clasts are in parallel alignment and
dip in the same direction.
Under unidirectional flow conditions,
pebbles will preferentially became oriented with their long axes
dipping upstream against the direction of flow (Potter and Pettijohn,
21
1977).
The dip angle
of imbrication observed in the Gable Creek
conglomerates ranges from 10 to 25 degrees.
Rip-up clasts composed of the underlying mudstones and sandstones
are present near the base of many Gable Creek
generally
than three
elongate and range
feet.
in length
units.
The rip-ups are
from several inches to more
Mudstone rip-ups are coamnonly oriented with the
elongated direction
parallel
to bedding and, in one location, a
distinct imbrication of these rip-ups was noted. The less resistant
mudstones comprising the rip-ups weather out of the conglomerate
leaving hollow molds to mark
their
former
presence.
In one instance,
a conglomerate rip-up, derived from an underlying bed, was found
within a coarser conglomerate bed (Figure
4).
This relationship
suggests that some of the congloanerates became semilithified and
coherent prior to deposition of the next bed.
Thin layers of 7mastone
may have accumulated on top of the conglomerate beds but were sub-
sequently scoured away during deposition of the next conglomerate.
Cross stratification is present on a variety of scales
sandstones and conglomerates.
within the
Most cross bedding is low angle and
ranges from planar to trough shaped.
Foreset strata are more easily
recognized within the sandstone beds than in the accompanying conglom-
erates.
Ripple marks are locally present within some sandstone beds
and are mostly symmetrical
in shape.
Primary current lineations and
parting lineations can be found along bedding planes in the Gable
Creek sandstones.
Sole markings are found only where a coarse
sediment overlies a fines-grained bed.
In a typical Gable Creek
sucession,
sandstones overlie conglomerates and thus, lack sole
markings.
Large flute casts
have,
however, been observed on the base
22
I.
_4
r
-
. I
I. % 3
0
4
..
Y
lV
t
-
o
b
1
Q
!
LL
jr 4
C
,. .
L
tI
Figure 4.
eo
.
r.
.
x
.
eI
_r-.
ba
Is
,
i
o
R, S
'L
+r
Conglomerate rip-up clast near the base
g1a rte bed (photo courtesy of L.C.
fleinhans).
of a thick can-
23
of conglomerate beds where they rest directly upon mudstone or
siltstone (Figure 5). Flute casts occur much more frequently in the
turbiditic sandstones of the Hudspeth Formation.
Soft-sediment deformation structures are cannon throughout the
Cretaceous section.
Convoluted bedding, slump features, and load
casts are present within the Hudspeth Formation while flame structures
and clastic dikes occur within the Gable Creek Formation.
Cretaceous Tuff Unit
A previously undescribed tuffaceous unit is preserved in several
locations on the north side of the Mitchell fault. The tuff is
present in the lower portion of the Gable Creek Formation as a thin,
dicontinuous unit within a typical conglomerate and sandstone sequence.
The best exposures of the tuff are along Monroe Creek in the
NW 1/4, NE 1/4, Sec. 16, T. 11 S., R. 22 E., and on the south side of
Meyers Canyon in the NE 1/4, SW 1/4, Sec. 14, T. 11 S., R. 21 E.
At the Monroe Creek locality, the sequence' begins with a basal
conglomerate and grades upward into sandstone which is conformably
overlain by about 10 m of tuffaceous
sediments.
The tuff unit strikes
generally northeast and can be traced in this direction over the
divide and into Payne Creek and upper Girds Creek.
The unit is offset
by several small faults and appears to thicken and became coarser
grained to the northeast (Taylor, oral communication, 1985).
In outcrop the tuff is medium bedded and distinctively lighter
in color than the neighboring
sandstones.
Upon closer inspection, the
rock is seen to contain green, angular clasts from 3-10 mm in size.
These clasts have been indentified as flattened pumice fragments
replaced by green celadonite.
The rock is very fine grained but a few
24
tt
0
- r':wfy r
r--
L
')
t
' 16
Jff,
,..1
i
t%
e
I, ?
t
14,
00
9'
i+
e..
t,;s'i
i
wry:
Figure 5. Large vortex-type flute cast on the base of a pebble
conglomerate bed overlying mudstone (current moved right to left).
25
small crystals are visible. The rock is soft, but not friable, and
appears to be cemented
In thin
section,
shards, pumice
by silica.
the rock is seen to be mainly composed of glass
fragments,
and a few angular crystal fragments.
The
glass shards composing the groundmass are broken and commonly altered.
The shards show signs of compaction and are probably cemented by
silica derived
from
diagenesis of the
tuff.
The small crystals, up to
1.0 mm., are composed of broken fragments of quartz and feldspar.
lithic fragments of volcanic rocks and chert are also present.
tuff does not exhibit significant
dilution by the
Rare
The
type of sediments
normally associated with the other Gable creek units.
South of Meyers
Canyon,
the tuff unit is preserved within a sim-
ilar Gable Creek sequence of conglomerate and sandstone.
The unit
strikes northward and can be traced over the hill into Meyers Canyon.
North of Meyers Canyon, the tuff is difficult to find, partially due
to structural complications, but small exposures have been reported in
Sec. 11, T. 11 S., R. 21 E. (Taylor, oral
communication,
1985). The
outcrops in the Meyers Canyon area are light gray in color and the
unit exhibits bedding about 1 to 2 feet
along bedding planes and splits into
The
rock fractures
flat, slightly
crumbly slabs.
thick.
Some of the beds are graded and the pumice fragments are largest near
the base and fine progressively upward.
The mode of occurrence suggests that the tuff unit is a channelized deposit
within
the Gable Creek Formation.
The tuff is
conformable within the sequence and exhibits grading in both a
vertical and lateral sense. The unit appears to become progressively
finer grained toward the southwest, which corresponds to the average
26
paleoslope direction for the Gable Creek Formation determined by
Wilkinson and Oles (1968).
These relations are compatible with a
submarine turbidite mode of deposition for the tuff unit.
The thin and stratigraphically restricted nature of the tuff indicates a short-lived episode of nearby active volcanism during the
middle Cretaceous.
The tuff appears to be confined to submarine
channels which suggests that it originated as a terrestrial air-fall
or ash-flow deposit and was subsequently transported into the basin by
fluvial processes.
The absence of the tuffaceous deposits in the
interchannel, mudstone-dominated
areas indicates
not occur directly over the water surface.
that airfall did
This brief episode of
pyroclastic activity mist have temporarily dominated the landscape and
innudated the streams, thereby producing relatively undiluted deposits
of this material within the nearby basin.
volcanic
ash are preserved
Relatively pure deposits of
in this manner in the modern-day Astoria
Fan off the coast of Oregon and Washington (Nelson and Nilsen, 1974).
it is not known whether the restricted extent of the tuff is
due to depositional controls, subsequent erosion, or the lack of good
exposures.
The absence of this unit south of the Mitchell fault may
indicate that the tuff was not deposited basinwide.
Most likely, the
tuff was deposited only within the submarine channels that were active
at this particular time.
The low stratigraphic position of the tuff
unit within the Gable Creek Formation suggests that it was deposited
during an early stage in the development of this submarine turbidite
system.
If the entire system prograded through time in the direction
of the paleoslope, then we might expect to find the tuff unit only in
the more proximal areas.
27
structural Behavior
The tightly cemented conglomerates constitute rigid rock masses
that respond in a brittle manner to tectonic disruption.
Numerous
faults cut the Cretaceous section and conglomerates are commonly
juxtaposed against
water
mudstones.
Fault zones are delineated by ground-
calcareous crusts, and gouge zones.
seepage,
Where conglomer-
ates have been faulted against one another, the clasts commonly
exhibit polished
surfaces,
silicification.
Large-scale slickensides and calcite veins commonly
healed fractures, iron oxide coatings, and
mark the major fault zones within the conglomerates.
Facies Relationships
Facies relationships within the Gable Creek Formation are highly
variable and undergo rapid lateral
transitions.
Grain size, sorting,
grading, and stratification can change drastically within a
distance
of several feet. Beds exhibiting a high degree of organization such
as grading,
stratification, and imbrication can yield abruptly, in any
direction, to
unorganized,
chaotic deposits.
Likewise,
conglomerates
and sandstones pass laterally into mudstone and siltstone with
rela-
tively abrupt transitions along or across strike. For this reason,
individual Gable Creek tongues cannot be characterized by a particular
grain size distribution, degree of sorting, or level of organization.
The representation of the Gable Creek Formation as
discrete,
continu-
ous tongues is difficult to verify because of rapid lensing, lateral
pinchouts,
and facies
transitions.
hampered in part by structural
The lack of stratigraphic control,
cxunplications,
makes long-distance cor-
relations within the Gable Creek Formation extremely difficult.
The geometric and stratigraphic relationships between Gable
28
Creek and Hudspeth rocks have led this writer to regard the conglom-
erate and sandstone units as coarse, channelized deposits rather than
sheet-like
tongues.
The presence of coarse, channelized clastics
encased within thick, hemipelagic mudstones is suggestive of turbidity
deposits (Walker, 1978; Normark,
1978;
Mutti and Ricci
Iucchi,
1975).
Other Cretaceous Conxrlamerates in Central Oreclon
Several isolated exposures of Cretaceous connglanerates were
also visited during the field investigation in order to make ccuiparisons with the Gable Creek Formation at
Mitchell.
Most of these
Cretaceous rocks have not been formally subdivided but are generally
correlative with the rocks at Mitchell. Pebble counts were performed
at each of the localities and the stratigraphic relations of the conglomerates were
noted.
Limited paleocurrent data was also collected
at scene of these sites. The Cretaceous outcrops visited are located
to the south and east of Mitchell as shown in Figure 1.
Mountain Creek
This exposure is located approximately 25 miles east of Mitchell
along Mountain Creek in the northwest portion of T. 12 S., R. 25 E.
The Cretaceous rocks are exposed in a roadcut along U.S. Hwy 26 at
milepost 92.
The outcrop is limited to a small area about 75 feet
wide and 30 feet high.
The stratigraphy at the Mountain Creek eqxmme is characterized
by a basal conglomerate overlain by sandstones that contain thin madstone
interbeds.
The basal ccrxjlcanerate bed is about five feet thick
and is mainly composed of small rounded pebbles.
The conglomerate is
well sorted although mudstone rip-up clasts are cannon near the base
29
of the
bed.
The overlying sandstones are medium bedded lithic
arenites that exhibit weakly developed cross beds.
Intercalated with
the sandstones are beds of dark mudstone less than two feet thick.
No
underlying basement rocks are exposed and the Cretaceous sequence is
unconformably overlain by Tertiary volcanic rocks.
In overall
appearance,
the rocks at Mountain Creek are similar to
the Cretaceous deposits at Mitchell.
The major difference is the fine
grained nature of the conglomerates at Mountain Creek.
The presence
of dark mudstone at Mountain Creek may indicate that these deposits
are also marine in
origin.
No fossils were encountered at the
Mountain Creek locality although the mudstones were not sampled for
microfossils.
Due to the limited exposure provided by the roadcut,
determination of paleocurrent directions was not possible.
Goose Rock
These Cretaceous outcrops are located along the John Day River in
the southwest portion of T. 11 S., R. 24 E. The Goose Rock exposure
is located just north of the visitor center for the Sheep Rock unit of
the John Day Fossil Beds National Monument.
The Cretaceous outcrop
area is about 0.5 miles wide and extends for several miles in an east-
west direction.
The sequence at Goose Rock is characterized by more than 300
feet of conglomerates
and subordinate sandstones
(Coleman, 1949).
The massive conglomerates form sheer cliffs several hundred feet high
along the John Day
River.
erates as
lenses and
pinching
Sandstones are present within the conglomthin interbeds.
The sandstones are
highly cross-stratified and the orientation of the foresets can be
used to measure paleocurrent direction.
30
The Cretaceous sedimentary rocks at Goose Rock are interpreted by
the writer to have been deposited in a nornnarine setting.
marine deposits at
Mitchell,
Unlike the
dark mudstones are wholly absent at Goose
No marine fossils were encountered in either the conglomerate
Rock.
or sandstone.
This paucity of fossils makes accurate determination of
the age of these strata
difficult.
The abundance of well developed
cross bedding in the sandstones at Goose Rock may be more indicative
of fluvial rather than marine
two feet
long,
processes.
Large woody fragments, up to
are present within the conglomerates and are also
suggestive of a nornnarine environment of deposition.
Antone
Cretaceous sedimentary rocks crop out in the Antone Ranch area
near Spanish Peak in the northeast portion of T. 13 S., R. 24 E.
outcrop area can be divided into two geographic parts.
The
Only the
larger western portion of the Cretaceous outcrop area was visited
during this
investigation.
about 700 m of
conglomerate,
The exposed Cretaceous section consists of
sandstone, and siltstone (Dobell, 1948).
Pebble conglomerate beds dominate the stratigraphy at Antone
Ranch.
Thin sandstone interbeds display limited cross stratification.
At higher stratigraphic levels and topographic
elevations,
cessions of sandstone and siltstone are present.
thick suc-
These upper sand-
stones are medium bedded lithic arenites and contain abundant fossils
of the thick-shelled pelecypod Triaonia sp. and well preserved leaf
imprints.
Current lineations along bedding planes in the sandstones
provide paleocurrent
orientations.
The Cretaceous deposits at Antone
are interpreted to represent a nearshore shallow marine environment
of
deposition.
Evidence supporting this interpretation includes the
31
lack of
dark,
laminated mudstones and the presence of abundant shallow
marine fossils.
The well sorted, fossiliferous sandstones may indi-
cate deposition on a shallow marine shelf.
Bernard Ranch
Cretaceous sedimentary rocks crop out near the small town of
Suplee in the east half of T. 17 S., R 25 E. These rocks are assigned
to the Bernard Formation and are, in
part,
slightly younger than the
Cretaceous deposits at Mitchell (Dickinson and Vigrass, 1965).
The
Bernard Formation is part of the Mesozoic John Day inlier and rests
unconformably on Upper Jurassic turbidites (Dickinson and Thayer,
1978).
The Cretaceous rocks are best exposed to the northwest of Suplee,
along the main road to Paulina. Approximately 500 m of gently dipping
conglomerates and sandstones crop out along the highway and in the
adjacent foothills. The clast-supported conglomerates are made up of
rounded pebbles and small cobbles.
overlain by pebbly
sandstones.
The conglomerates are commonly
Much of the sandstone is highly fos-
siliferous and contains shallow marine pelecypods and woody fragmerits.
The strata probably represent a shallow marine environment,
perhaps on a submerged delta
margin.
No paleocurrent data were
collected here and none is documented in the literature.
32
METHODS OF INVESTIGATION
Pebble Counts
The detailed petrologic data needed for this investigation
were obtained by performing numerous pebble counts throughout the
inlier.
Each of the major Gable Creek units was sampled as well as
several other Cretaceous conglcaaaerate exposures in central Oregon.
More than 15,000 conglomerate clasts were identified for pebble
counting purposes during the field season.
The sampling technique used for the pebble counts was designed
to hopefully provide random, representative samples that could be
analyzed statistically.
Each pebble count for a specific conglomerate
unit consisted of several equal-sized sub-samples of 100 clasts.
Most
of the counts contain five such sub-samples for a total of 500 clasts.
A few of the less extensive conglomerate units were pebble counted for
300 clasts only.
Due to the heterogeneous nature of the conglomer-
ates, a sample size of 500 is probably desirable in order to obtain a
representative sample of clast types.
A pebble count of this size can
be feasibly performed during the course of a typical field day.
The clasts for each pebble count sample were collected from the
extensive talus deposits along the base of the steep conglomerate
. Along
a randomly selected traverse, 100 pebbles were col-
lected without regard to physical appearance.
Clasts smaller than
about one inch or larger than six inches in diameter were generally
not collected.
Each of the sub-samples were taken at varying dis-
tances from each other and the entire pebble count was usually spread
33
out over a length of 1/4 to 1/2 mile along strike.
Clasts were collected from the talus rather than directly from
the outcrop for several reasons.
The high degree of induration of the
conglomerate outcrops prevent them from being easily dissected and
identification of clasts within the outcrop is difficult.
Pebbles can
be rapidly collected from the talus piles with little chance of confusion between Gable Creek clasts and rock fragments of a different
origin.
Secondly, samples derived from one distinct area or horizon
of the outcrop may not be representative of the unit as a whole.
The
talus piles contain clasts derived from all parts of the cliff-forming
outcrops and should provide a more representative sample.
Outcrop
sampling is limited to the base of the outcrops which could introduce
bias if composition is controlled by grain size or depositional pro-
cesses.
Several previous graduate students have made limited pebble
counts in various parts of the inlier.
Swarbrick (1953) made the
most extensive pebble counts and identified about 1200 pebbles collected from several outcrops.
The samples were taken from definite
areas one square foot in size.
This technique would result in samples
of varying
size
depending on the grain
specific sample site.
size
of the clasts at the
Howard (1955) identified conglomerate clasts,
collected from talus piles at randomly chosen localities.
Other
workers, including Bedford (1954) and McKnight (1964), made pebble
counts but did not specify their sampling technique.
Both the outcrop and the talus were sampled at one locality
in order to identify potential differences in pebble count results due
to sampling technique.
This test was conducted on the extensive con-
34
glomerate outcrops above the town of Mitchell along the north side
of the highway.
Paired samples were taken at three separate locali-
ties with each pair consisting of one outcrop sample and one talus
.sample.
The results of this experiment are suimnarized in the results
section of the text.
Field Identification
All conglomerate clasts sampled during pebble counting were
identified in the field with a handlens and by using a hardness test
and hydrochloric
acid as
needed.
Many of the clasts are moderately
weathered and must be broken several times to obtain a reasonably
fresh surface. A small percentage of the pebble count samples could
not be accurately identified in the field and were recorded under a
category for unidentified
clasts.
The first week in the field was spent examining conglomerate
clasts in order to became familiar with the many lithologies represented in the conglomerates.
Identification of the more ambiguous
clasts was made with the assistance of o amnittee members Dr. E. M.
Taylor and Dr. R. D. Lawrence. A list of lithologic categories was
decided upon in order to accurately document the conglomerate petrology determined by the pebble counts.
These categories needed to be
specific enough to provide resolution of subtle c rrpositional changes
yet they must encompass the entire range of rock types present. A
total of 20 lithologic categories were selected and used in each of
the pebble
counts
(Table 1).
35
Table
1.
Lithologic
categories used for pebble counts.
Volcanic
Plutonic
Sedimentary
Metamorphic
trachyte
granite
conglomerate
metaquartzite
rhyolite
QFM phanerite
sandstone
phyllite
mafic volc.
gabbro
siltstone
schist
tuff
aplite
limestone
metaplutonic
vein qtz.
chert
gneiss
argillite
A few of the categories are somewhat generalized and include a
range of ccanpositions rather than one distinct lithology.
category labeled mafic
basaltic
volcanics,
andesite, basalt,
for
instance,
and metavolcanic
The
includes andesite,
greenstone.
The category
labeled Q4-F+M phanerite is used for plutonic rocks that are dominantly
made up of quartz, plagioclase, and mafic minerals.
This ca nposition
corresponds to a range of lithologies including quartz
monzodiorite, and granodiorite.
diorite,
quartz
The metaplutonic category includes
recrystallized igneous rocks that have a remnant, yet recognizable
phaneritic texture but does not include gneiss of unknown protolith.
Petrographic Analysis
Thin sections were made from most of the ommnon clast types in
order to determine the mineralogic identities.
The plutonic rock
samples were point counted using a calibrated microscope stage to
36
determine the different suites of granitic rocks present. The percent
abundance of minerals in the other samples was visually estimated
using a chart prepared for this purpose by Terry and Chilingar (1955).
The hand samples for thin section analysis were collected mainly
from
the talus piles and occasionally from the outcrop. The clasts
selected as petrographic hand samples ranged in size from three inches
to one foot in
diameter.
It was found that the larger clasts were
more likely to contain relatively fresh rock.
collected throughout the
pebble
inlier,
The clasts were
mostly at localities sampled during
It is believed that the clasts selected for petro-
counting.
graphic analysis are representative of the lithologies recorded in the
pebble counts.
Data Processing
The results of the pebble counts were tabulated and processed
using the Lotus 1-2-3 System (TM) software program on the IBM--PC
microc- m!puter.
The Lotus 1-2-3 program was found to be extremely
efficient for organizing and manipulating large quantities of numerical data making possible in-depth data analysis that would be
prohibitive if performed by hand.
Regression analysis was performed
on the IBM--PC/AT microcomputer using the Statgraphics (TM) program.
Cluster analysis of the data was performed on a VAX 11/730 cuter
using the SAS
(TM)
Version 5.03 statistics software program.
37
CDNGIDNERATE PETROLOGY
The conglomerates of the Gable Creek Formation contain a wide
variety of rock types.
The diverse lithologies that carnprise the
conglomerates represent a wide range of geologic
processes and
settings as well as a considerable span of geologic time.
were derived at varying
distances
The clasts
from the basin and have been
subjected to different rates of weathering, erosion, and transport.
Some of the clasts have probably been involved in several cycles of
transport and deposition.
Whatever distances of space or time init-
ially separated the original rock units, their remnants were brought
together during the middle Cretaceous to form the polymitic conglomer-
ates
of the Gable Creek Formation.
Numerous species of igneous rocks are represented in the conglomerates along with several types of sedimentary and metamorphic rocks.
Some of these lithologies are common throughout the deposits while
others are quite rare.
The clast types encountered during this in-
vestigation are described in the following section.
Plutonic Rocks
All plutonic rocks discussed here are classified according to the
nomenclature of Streckeisen (1976).
rocks are presented in Appendix A.
mineral
The modal analysis data for these
The precise determination of some
species, especially the mafic conponents, is difficult due to
the degree of weathering affecting the plutonic rock clasts.
Quartz Diorite/
nzodiorite
Quartz diorite and quartz monzodiorite are common among the
plutonic rock clasts. A typical sample of this rock type is medium
38
grained with a subhedral, granular texture.
On a weathered surface,
equant and relatively unaltered quartz grains are conspicuous and give
the rock a distinctive, mottled appearance.
In thin section the rock
is seen to be rich in plagioclase with subordinate amounts of quartz,
potassium feldspar, and mafic minerals.
about 10% to 15%.
Quartz content ranges from
The dominant mafic component is hornblende which
constitutes about 15% of the rock and is cxmanonly altered to chlorite,
epidote, and iron oxides.
Granodiorite
Rocks of this c cu osition are also ccmunan and may represent a
more siliceous member of the previously mentioned suite.
In hand
sample they are similar in appearance to the quartz diorites.
The
maximum quartz content is about 35% and the granodiorites are slightly
richer in potassium feldspar.
Plagioclase is present as both sub-
hedral laths in the groundmass and larger, unzoned crystals.
Plagio-
clase is generally more altered than the potassium feldspar and is
partially replaced by sericite, epidote, carbonate, and chlorite.
Mafic ccunponents are represented by severely altered hornblende and
biotite crystals which ccnprise about 10% of the rock.
Quartz Monzogabbro
Rocks that were considered to be gabbroic in the field were
petrographically determined to be closer in ccupositon to a quartz
monzogabbro.
In hand sample, these rocks are finer grained and darker
in color than the granodiorites.
The color index is about 30% and the
mafic minerals, now replaced by chlorite and iron oxides, were
probably pyroxenes.
Quartz does not exceed 7% of the rock.
Plagio-
clase crystals are ccunly zoned and the potassium feldspar is
39
perthitic
and contains micrographic intergrowths of quartz.
Granite
The granite clasts are fine to medium grained, pinkish gray,
and have a granular
texture.
This lithology
tends to form well
rounded, extremely resistant and durable clasts.
reaches about 35% and potassium feldspar
plagioclase.
grain
Most of the crystals
boundaries.
Quartz content
is slightly
dominant over
are anhedral and have curved
Hornblende and biotite are the sole primary mafic
minerals and constitute about 10% of the
include chlorite, epidote, sericite,
Secondary minerals
rock.
hematite,
carbonate, and clays.
AAplite
'These leucocratic clasts are richer in quartz and potassium
feldspar and contain smaller amounts of mafic minerals
granites.
The aplites are mostly fine
and have a
subhedral,
the rock.
quartz, the latter
The dominant minerals are
of which may exceed 40% of
Plagioclase is minor and the sole mafic mineral
which generally
Quartz
grained, whitish to pinkish,
granular texture.
potassium feldspar and
than the
is biotite,
constitutes less than 5% of the rock.
Alk-Feld Syenite
This rock is fine to medium grained, pinkish gray, and has an
anhedral,
granular texture.
Potassium feldspar is the dominant
mineral and is present as orthoclase and microcline.
does not exceed 15% and plagioclase, present as
minor.
Quartz content
albite, is very
Hornblende and chlorite form about 10% of the
rock.
Accessory
minerals include small grains of acicular apatite and anhedral
magnetite.
40
Pyroxenite
This is a previously undescribed lithology in the conglomerate
and only one of these clasts was encountered during the field season.
The hand sample was highly weathered, slightly
crmmbly,
and was not
thin sectioned for petrographic analysis. On the fresher surfaces,
this ultramafic rock is seen to be dark greenish in color and coarse
grained. The rock has a simple mineralogy and appears to be almost
wholly composed of
clinopyroxene.
The euhedral-to-subhedral pyroxenes
form stubby, randomly oriented prisms.
Volcanic Rocks
Volcanic
lithologies,
abundant clast
rock types is
type within
present,
smmied together, represent the most
the
conglomerates. A diversity
including
porphyritic
volcanic breocias, and welded tuffs.
In
volcanic
rocks are
difficult
to classify
and aphyric flow rocks,
addition,
ics and low-grade metavolcanic rocks are not
of volcanic
silicified volcanSome of these
uncommon.
by petrographic
techniques
due to their fly fine-grained nature or high degree of alteration.
Identification of the volcanic lithologies
the Streckeisen
(1979)
attempts
to follow
classification system whenever possible.
Porphyritic-aphanitic rocks are mostly classified based on the type
and proportion of their phenocrysts.
Rhyolite Pozphyy
These rocks are variable in appearance but most are
dark
gray, sometimes pinkish,
quartz and potassium
feldspar.
light to
and exhibit distinctive phenocrysts of
A few of the samples are flow banded.
41
The clear quartz phenocrysts are euhedral to subhedral and range in
size from 2 to 5 mm.
smaller, mostly
Phenocrysts of potassium feldspar are somewhat
subhedral,
and are manly
pinkish.
Subordinate
plagioclase phenocrysts are greenish white and a small amount of
biotite is visible in same of the hand samples.
In thin section the
phenocrysts are surrounded by a grour mass of microcystalline quartz
and potassium feldspar along with patches of epidote and scaly chlor-
ite. Evidence of an originally glassy groundmass is present in a
few of the samples
examined.
Small phenocrysts of plagioclase com-
prise about 5% of the rock and are partially altered to sericite,
chlorite, and carbonate.
Biotite appears to be the sole mafic
camponent and does not exceed 5% of the rock.
Trachyte Porphyry
A typical hand sample of this rock is pinkish gray and contains
pink feldspar phenocrysts up to 4 mm in size.
Smaller phenocrysts of
mafic minerals are less abundant but also present.
The groundmass is
composed mainly of small potassium feldspars along with rare plagio-
clase crystals, disseminated
quartz.
magnetite,
and possibly a small amount of
Mafic minerals generally constitute less than 5% of the rock
and are completely replaced by chlorite and iron oxides.
Latite Porphvrv
This medium gray rock has a glemeropozphyritic texture with clots
of light-colored feldspar phenocrysts and visible crystals of pyrite.
In thin
section,
the phenocrysts are seen to consist of subequal
amounts of plagioclase and potassium
feldspar.
The groundmass is com-
posed of denitrified glass, spherulites, cryptocrystalline quartz, and
disseminated grains of mafic and opaque minerals.
Hornblende and
42
biotite together comprise 5 to 10% of the rock. Secondary minerals
include
pyrite, limonite, sericite, chlorite,
and carbonate.
Andesite Porthvrv
These rocks are dark greenish gray with phenocrysts of white
feldspar and green mafic minerals set in an aphanitic groundmass.
Feldspar phenocrysts range in size from 1 to 4 mm and are mostly
composed of plagioclase which is ocmanonly zoned.
Approximately 15% of
the rock is made up of mafic components represented by hornblende and
lesser amounts of
of
plagioclase,
pyroxene,
biotite.
The holocrystalline grouncbmass is composed
lesser potasium
disseminated
feldspar,
magnetite,
altered mafics which may be
and is lacking in visible quartz.
Basalt
A variety of rocks of basaltic composition is present in the
conglomerates.
They are dark gray to black and generally have a thick
weathering rind of a rusty brown hue. Most of these rocks are aphan-
itic, but some are porphyritic and others are glassy.
Plagioclase is
the dominant, if not exclusive feldspar and is cxmmonly zoned.
In
same porphyritic samples the plagioclase phenocrysts exhibit a sub-
parallel alignment indicative of flow orientation. The mafic minerals
are pyroxenes, but due to their high degree of alteration, cannot be
further
subdivided.
No olivine was recongnizable in any of the
basalts. The hypocrystalline basalts contain microlites of plagioclase and pyroxene in a groin mass of tachylitic glass,
disseminated iron
oxides.
chlorite, and
A few of the samples are slightly vesicular
and contain amygdules of chalcedony.
Greenstone
These low-grade metavolcanic rocks are similar to the basalts in
43
appearance but have a distinct dark green color.
Most of the
greenstones are aphanitic but a few contain phenocrysts of greenish
plagioclase.
In thin section they have a texture similar to the
basalts but appear much more altered.
cloudy in
appearance.
The plagioclase is dirty and
Pyroxenes are almost wholly altered to
chlorite. The groundmass is mostly replaced by chlorite, epidote,
granular sphene, and minor carbonate.
Volcanic Breccia
These fragmental rocks are multicolored in shades of gray,
green, and
purple.
The rock is couposed of angular to similar
clasts that range in size from a few millimeters to several centimeters.
Supporting the clasts is a fine grained greenish matrix con-
taining visible pyrite crystals. In thin section the clasts can be
identified as aphanitic and microporphyritic volcanic rock fragments.
Some of the rock fragments appear to be silicified or replaced by
microcrystalline quartz. Void spaces are filled with secondary
silica. The matrix is largely composed of chlorite, epidote, limonite, and minor pyrite.
Welded Tuff
These crystal-lithic tuffs are greenish gray and contain small
crystals and angular rock fragments set in a fine grained matrix.
The
crystals consist of shattered plagioclase and potassium feldspar along
with broken and commonly embayed quartz grains.
generally less than 1 mm in size.
size,
The crystals are
Lithic fragments, up to 5 mm in
are composed of glassy volcanics and microporphyries containing
quartz, feldspar,
and altered mafic
minerals.
The matrix exhibits a
relict eutaxitic texture and is now represented by devitrified shads,
44
pherulites,
cryptocrystalline quartz, and carbonate.
Sedimentary Rocks
The most prom rant sedimentary clasts, excluding chert, are
siliciclastic rocks that range in texture from siltstone to pebble
conglomerate.
The clastic rocks discussed here are named according to
the classification scheme of Dott (1964). Textural terms used refer
to the Wentworth
(1922)
scale of grain size.
Laminated Siltstone
This distinctive rock consists of alternating light and dark
colored laminations of silt-sized material.
individual laminae
are generally less than 1 an thick and boundaries between them are
sharp.
Grain size does not differ significantly among the laminae
although in a few samples the light-colored horizons are composed of
fine quartzose sand. Small-scale sedimentary structures including
cross lamination and soft sediment deformation features such as ball
and pillow structures are visible in some of the samples.
The rock is
well indurated and probably cemented by silica.
Lithic Wacke
These fine grained sandstone clasts are medium gray and commonly
exhibit faint laminations of darker material. The framework grains
consist of quartz,
possibly organic
feldspar,
material.
chert, lithic
fragments,
and opaque,
The lithic grains appear to be aphanitic
volcanic rock fragments and the quartz grains are monocrystalline.
The matrix comprises about 20% of the rock and is dominantly cant osed
of clays and iron
oxide,
which also serve as the cementing agents.
The weak stratification is defined by layers richer in clay minerals.
45
Overall, sorting is poor and most grains are subangular.
Lithic Arenite
These poorly sorted, indurated sandstones are medium gray and are
caqxSed of medium to coarse sand and scattered, rounded pebbles.
Lithic grains comprise about 90% of the rock and consist of chert,
aphyric volcanics, schistose metamorphic rocks, and shale fragments.
A few of the sedimentary lithic grains contain uniserial for minifera
fossils.
The remainder of the framework grains are monocrystalline
quartz and subordinate feldspars.
Most grains are subangular to sub-
rounded and matrix materials are all but absent.
Cementing agents
include silica, hematite, and minor amounts of carbonate.
Sub-lithic Arenite
These calcareous sandstone clasts are present within the conglcxn-
erates as
large, spherical concretions that are light brown in color.
The interior of the concretions are dark gray and carrnnonly contain
thick-shelled pelecypod fossils. irk grains consist of quartz,
feldspar, mica, and lithic fragments.
monocrystalline
grains
Quartz is present as both
and sutured, polycrystalline
include muscovite, biotite, and chlorite.
grains. Micas
Lithic grains are composed
of chest, aphanitic volcanic rocks, slate, and shale.
The well-sorted
framework grains are surrounded by, and nearly suspended in the abundant carbonate cement.
Minor matrix materials include clays and iron
oxide.
Arenite
These indurated sandstone clasts are
have a vitreous
appearance.
monocrystalline quartz grains
light to meidium
gray and
More than 90% of the rock is cm1posed of
that are slightly
sheared, sutured, and
46
exhibit strong undulatory
consist of chert,
muscovite.
The remainder of the grains
plagioclase, microcline,
and trace amounts of
Matrix materials are absent but many of the grains have
thin rims of iron-stained
well
extinction.
sorted,
clay.
The rock is fine to medium grained,
and cemented by small amounts of silica.
These rocks
grade directly into metaquartzites.
Pebble Conglomerate
Highly indurated clasts of pebble conglomerate are present within
the conglomerate units. These second cycle conglomerate clasts are
corn osed of tightly packed, rounded pebbles and minor amounts of sandy
matrix.
The pebbles are dominantly couposed of chert and aphanitic
volcanic rock fragments. The rock is cemented by silica and exhibits
no reaction to hydrochloric acid.
Chest
Rounded clasts of gray-to-black chert are extremely common within
the
conglomerates.
The chest is slightly recrystallized and cut by
numerous intersecting veins of lighter-colored chalcedony.
Poorly
preserved radiolarian fossils are visible within some of the samples.
Limestone
Cobble- to small boulder-sized clasts of gray limestone are
occassionally encountered within the conglomerate. No skeletal grains
or other allochems are visible in the hand samples. These limestones
are classified as unfossiliferous micrites according to the system of
Folk (1968).
The limestones show no signs of recrystallization or
sparry void fillings.
Metamorphic Rocks
Several types of metamorphic clasts are present in the conglcmer-
47
ates although they are much less conmion than the igneous and sedimen-
tary
clasts.
These rocks appear to be the products of low to medium
grade regional metamorphism and include such lithologies as phyllite,
schist,
marble,
and metaplutonic rocks. Metavolcanic greenstone and
metaquartzite were mentioned previously and the remaining lithologies
are descibed here in general terms only.
Phyllite
This
quartz-
and mica-rich
sheen on the fresher surfaces.
phyllite
is dark gray and has a slight
The rock displays a slaty cleavage and
has a hackly fracture which makes it appear rough and splintery in
hand sample.
The phyllite is highly weathered and forms subangular,
crumbly, clasts. The phyllite clasts are recognizable both in outcrop
and among the talus but may be under represented in the talus due to
their low potential for weathering intact. One rounded clast was
encountered in which the
phyllite
was partially surrounded
vein quartz that protected the less resistant
decanposition.
In overall
phyllite
appearance, the phyllite
by milky
from physical
clasts are indis-
tinguishable from the pre-Cretaceous phyllites of the metasedimentary
basement rocks exposed in the Mitchell area.
Schist
Only a few samples of
this light
encountered during the field
gray, schistose rock were
investigation.
The rock is dominantly
composed of quartz and muscovite and has a well
developed, medium-
grained schistosity.e schist is moderately weathered and some of
the mica has altered to clay. This rock tends to form somewhat flattened and
elongate,
subrounded clasts.
48
Marble
This dense and massive rock is light to medium gray and coarsely
crystalline.
The original depositional fabric of the rock has been
obliterated by recrystallization and no fossils or skeletal
visible.
grains are
Light colored veins of calcite cut through the rock.
The
marble forms well rounded, resistant clasts that reach a size of more
than one foot in diameter.
This rock is similar in appearance to the
recrystallized limestones that crop out among the basement rocks in
Meyers Canyon.
Metaplutonic Rocks
These rocks differ in appearance from the other plutonic clasts
in that the minerals have begun to segregate into distinct bands.
Quartz is present as irregular blebs that form stringers throughout
the rock.
The quartz pods are made up of elongate, sutured, and
highly strained crystals.
The quartz crystals
show signs of crushing
along the margins, but are highly drawn out in a parallel fasion within the stringers.
The quartz seams cut across the original plutonic
fabric and the feldspar crystals
are ccnn my broken.
Mafic
minerals
are canpletely altered to chlorite and iron oxide but may have originally been pyroxenes.
The c
nposition of this rock is probably
similar to a metagabbro or meta-quartz diorite.
49
RESULTS
Pebble Counts
Pebble counts were performed on a total of 36 conglomerate locali-
ties, 32 of which are within the Mitchell inlier (Plate 1). The tabulated results of these pebble counts are listed by sample number in
The results are organized into a standard format as shown
Appendix B.
in Table 2.
Each sub-sample is tallied separately and an average
abundance and standard deviation is calculated for each lithologic
category.
Since each sub-sample consists of 100 observations, the
values for each lithology also represent percentages of the total.
The totals recorded at the bottom of the data sheet include the total
abundance of plutonic and volcanic clasts and the ratio between the two
values.
The pebble count tally sheets can be used visually to compare
conglomerate compositions between two or more sample sites.
It is
difficult to make an eyeball comparison of more than a few sites without further treatment of the pebble count data. The columns containing
the average abundances of each clast type provide the input data for
statistical investigations including cluster analysis and regression
analysis.
The values of the averages for each pebble count are listed
by site in Appendix C.
Correlation Matrix
Comparison of
conglomerate composition
between two sites can
be made using a statistical measure known as the Correlation Coefficient.
This statistical technique
is analagous
to plotting the pebble
50
Table
2.
Sample format for tabulated pebble vaunt results.
SAMPLE: Mitchell (M-18)
LOCATION: SW 1/4, Sec. 36, T. 11 S., R. 21 E. (near Mitchell)
lithology sample I sample 2 sample 3 sample 4 sample 5 average
quartzite
4
chert
vein qtz.
QFM phan.
12
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
maf. vol.
tuff
1
12
5
3
14
0
15
3
2
1
11
15
14
1
2
12
13
13
1
1.02
1.47
0.63
1.10
0.80
0.89
0.49
0.49
4
4
6
4
3
3
2
1
0
1
0
1
1
1
0
1
0
0
27
25
5
24
0
0
24
23
6
S
26
8
27
23
25.20
1.60
0
0
25
0
0
1
0-.20
0
0.00
0.40
0.00
1
2
1
0
0.80
0.75
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0.20
0.00
0.00
0.00
0.00
0.00
0.40
0.00
0.00
0.00
0.00
0.00
6
27
0
0
0
0
0
gneiss
0
0
0
0
0
0
0
0
unknown
4
5
6
5
6
100
100
23
54
0.43
100
20
57
100
22
53
0.42
100
total P
total V
P/V ratio
std. dev.
1
conglom.
sandstone
siltstone
argillite
limestone
phyllite
schist
total
2.60
13.20
1.00
13.00
4.60
2.00
0.60
0.40
25.00
19
60
0.32
0
0.35
19
58
0.33
6.00
100.00
20.60
56.40
0.37
1.41
1.10
51
count results from a pair of sites against each other on a Cartesian
The correlation coefficient (r) is a measure of how closely the
graph.
scatter distribution of the data points approximate a linear relationship.
Correlation is the ratio of the covariance of two variables to
the product of their standard deviations
(Davis,
1973).
Since the cor-
relation coefficient is a ratio, it is a unitless value that ranges
from +1 to -1.
A correlation of +1 indicates a perfect linear rela-
tionship between two variables while a value of zero indicates a lack
of any linear relationship.
Negative correlation values indicate that
one variable changes inversely with respect to the other.
A correlation matrix contains the r-values for each possible
pair of
variables.
The resulting correlation matrix of the 36 con-
glomerate sample sites appears in Appendix D.
For any particular
site, the highest and lowest correlation values among all other sites
can be found by reading across the raw.
The sample sites corresponding
to each value are given at the top of the columns.
The correlation matrix can be used to determine which sites are
similar
to,
or unlike each other in terms of conglomerate composi-
tion. This information provides useful constraints for the interpretation of field observations and other statistical results.
For example,
the conglomerate exposures represented by the sample sites labeled
Meyersl and Meyers2 are located on either side of a major drainage
known as Meyers Canyon.
two sample sites were
From among several adjacent exposures, these
thought to be
based on field relations.
parts of the same conglomerate unit
The correlation matrix shows a correlation
value of 0.98 which is taken to represent a high degree of composition-
al similarity between the two sites. Thus, the correlation data sup-
52
port the interpretation that is based on field
instance,
evidence.
In another
it was concluded that the conglomerates at the sample sites
labeled Mitchell and Hoodoos were significantly unlike both in cmTposi-
tion and
A low correlation value of 0.30 for the pair con-
appearance.
firms this observation.
At the outset of the
study,
it was hoped that pebble count data
might make stratigraphic correlations possible within the Gable
Correlation across the Mitchell fault would help
Creek conglomerates.
constrain the magnitude of displacement across this structure.
It is
known that the Mitchell fault has right-lateral displacement of roughly
3.5 miles based on the offset of the Mitchell anticline and the belt of
intrusions that delineate its axis. Based on this evidence and approximate stratigraphic
position,
it was thought that the conglomerate unit
exposed at Mitchell on the north side of the fault might correlate with
a conglomerate unit in the vicinity of Black Butte on the south side.
Both sites are located fairly low in the section on the southeast limb
of the anticline.
The correlation values of the Mitchell site with all other Gable
Creek sites are listed in decreasing order in Table 3.
If a r-value
of 0.95 and above is arbitrarily taken as a meaningful correlation,
then almost one half of the sites fit this
criteria.
Knowledge of the
stratigraphy and structural relations can be used to eliminate many of
these possible
correlations.
Sites that are located on the sage side
of the fault or on the opposite limb of the anticline can be dismissed
as not
possible.
Similarly,
than Mitchell can be
sites that are much higher in the section
eliminated.
main, including Spetch Rim, Black
Only four possible correlation reButte,
'Ihcenpson Cr., and White Butte
53
Table 3. Oorrelaticn values between the Mitchell locality and all
other sample sites listed in descending order.
Mitchell
SITE
1.00
Mitchell
0.99
UpMonroe
NelsonCr
0.99
0.99
Thomp.2
0.99
Monroe2
Thomp.1
0.98
Courthse
0.98
0.98
Spetch
0.98
JohnsonCr
Marshall
0.98
WhButte
0.97
Thomp.3
0.97
0.97
Meyers2
0.97
Meyersl
0.97
UpGirds
0.96
BlkButte
0.95
GordyFlat
0.94
Bernard
UpSable
0.94
Rip-Up
0.91
0.89
Radiotow.
0.88
Webers
Monroel
0.87
0.87
MudCreek
0.87
Narrows
0.83
BridgeCr
0.75
TonyButte
0.66
Antone
0.65
SheepCyn
0.63
Goose
0.60
E.Doolitt
0.51
SheepCmp
0.40
MtnCreek
0.38
CherryRch
0.35
UpSheep
0.30
Hoodoos
54
in order of increasing stratigraphic level.
Correlation of the
Mitchell site with these units, especially 'Ihorqson Cr., would approximately equal the amount of estimated lateral displacement across the
fault.
Thus,
this part of the section on the south side of the fault
seems to compositionally match the Mitchell site. Although the stat-
istical data do not provide a unique solution in this
case,
the tech-
nique could lead to further, more refined correlations within the
Gable Creek Formation.
Sampling Technique Study
A ccmyparison of sampling methods for pebble counting purposes was
undertaken at the conglomerate outcrops near the town of Mitchell in
the SW 1/4, Sec. 36, T. 11 S., R. 21 E. The purpose of the experiment
was to canpare pebble count results derived frcr<n sampling both the
outcrop and the talus at the same location.
The comparison consisted
of three paired samples taken at three sites approximately 100 in apart.
Each pair consisted of one outcrop sample of 100 clasts and one talus
sample of. the same size.
The outcrop was sampled along a transect at
chest height and only pebbles larger than about 2 an were identified.
The talus piles were sampled for clasts of similar size along random
traverses.
The pebble count results from the two sampling techniques are
presented in Table 4.
The results are not significantly different and
a definite pattern of influence due to sampling method is not apparent.
The average abundance columns show that quartzite is more abundant in
the talus samples whereas chert is more abundant in outcrop samples.
No ready explanation is offered for these relationships.
It might be
55
Table 4. Results of saDpliN technique vaiiparison.
Mitchell Locality: Outcrop vs. Talus sampling method
Outcrop 3 AVG Tal. AVG Otcp.
lithology Talus 1 Outcrop 1 Talus 2 Outcrop 2 Talus 3
1.67
3.33
1
3
1
3
3
4
quartzite
15.33
12.33
15
11
17
14
14
12
chart
1.67
0.67
2
1
1
2
0
1
vein qtz.
14.00
13.00
14
12
15
15
13
12
OFM phan.
4.33
4.33
4
5
4
4
4
5
granite
1.67
2.33
2
3
1
3
2
1
gabbro
0.67
0.33
1
0
0
1
1
0
aplite
0.00
0.67
0
1
0
0
0
1
metaplut.
25.67
25.33
28
24
24
25
25
27
trachyte
5.67
8
6
4
5.67
5
5
6
rhyolite
22.33
26.00
23
27
21
24
23
27
mef. vol.
0.00
0.00
0
0
0
0
0
0
tuff
conglom.
sandstone
0
0
0
0
0
0
0
2
1
0
0
0
0
0
0
1
1
phyllite
0
0
0
0
0
0
0
0
schist
gneiss
0
0
0
0
0
unknown
4
6
5
100
100
19
20
siltstone
argillite
limestone
total
total P
total V
P/V ratio
60
0.32
0
0
53
0.38
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0.00
0.00
1.00
0.00
0.67
0.33
0.00
0.00
0.00
0.00
0.00
5.00-
0.00
0.00
0.00
0.00
0.00
6.00
0
0
7
6
5
100
23
54
100
100
20
100
100.00
100.00
21
53
57
55
0.43
0.40
0.35
0.38
20.67
57.00
0.36
20.67
53.67
0.39
21
56
expected that the most durable lithologies would be over represented
in talus samples while the least resistant lithologies would be under
represented using this
technique.
For example, clastic sedimentary
rocks might not weather out of the outcrop intact to the degree that
igneous clast would.
Similarly,
fine grained volcanic lithologies
might be more abundant in the talus piles than more coarsely crystal-
line plutonic lithologies due to the differences in weathering poten-
tial of the two rock
types.
This relationship may be reflected by the
results in the totals for the two methods. Total average abundance of
volcanic clasts is
slightly
higher in the talus samples and the ratio
of total plutonic to volcanic clasts reflects this difference.
The similarity of the results from the two sampling
methods
can be demonstrated statistically by means of the calculated co
tion
coefficient.
The average abundance data yield an r-value of 0.98
which clearly indicates a high degree of correlation between the two
sets of
results.
Thus, sampling technique does not seem to produce
significantly different pebble count results.
Compositional Variability Study
A study of the variability of conglomerate composition was
undertaken to test the validity of the assumption that petrologic
composition does not change significantly within a single conglomerate
unit.
The prominant conglomerate unit that extends for nearly three
miles along the west side of Thompson Cr. from the SE 1/4 of Sec. 32,
T. 11 S. R. 21 E. to the SE 1/4 of Sec. 12, T. 12 S., R. 20 E. was
selected for this study.
This particular unit was selected for its
good exposure, lack of structural complications, and laterally continu-
57
ous nature.
The study consisted of three pebble counts of 500 clasts each made
in three locations along this unit.
The locations were selected to
maximize the distance between adjacent sample sites.
are numbered 1 through 3 from north to south.
The sample sites
At each site the indi-
vidual sub-samples of one hundred clasts each were collected within 100
m of each other along strike.
The results of the pebble counts show a high degree of consistency
with one
another.
The correlation values between sites range from 0.96
to 0.98 with an average value of
0.97.
There is a slightly higher de-
gree of correlation among adjacent sample sites than there is between
the two sites at either end of the study area. This indicates that
there may be a slight but prc ably insignificant variation in conglomerate ctposition within this extensive Gable creek unit.
It is thought that omrpositional variablility is likewise minor
within the other conglomerate units located throughout the inlier.
Compositional consistency within any one unit would facilitate ca orison between pairs of conglomerate units to determine their degree of
similarity.
The average correlation value of 0.97 derived from this
study of a single unit can be used as a reference guide when comparing
two geographically separated Gable Creek units.
Cluster Analysis
Cluster analysis was performed on the pebble count data in
order to classify the various Gable Creek conglomerate units into
groups of similar cosition. Cluster analysis places the observations into more or less homogeneous groups, in a manner so that the
58
relation between groups is revealed (Davis, 1973).
Several clustering
techniques were used that differ only in the method of calculating the
distances between clusters.
The raw data consisted of the pebble count
averages for each conglomerate unit sampled (Appendix B).
The resulting dendrograms for two clustering techniques known as
Ward's minim= variance method and the average linkage method are shown
in Figure 6.
A third clustering technique, known as the centroid
method produced almost identical results as the average linkage method
and will not be discussed.
The derrdrograms or tree diagrams plot the
sample sites against the measure of distance used to form the clusters.
At any given distance, the number and coposition of the
clusters is graphically shown.
distance
are more
Clusters formed at a large measure of
significantly different than clusters formed at
progressively smaller distances.
The dendrogram resulting from the Ward's method shows that two
major clusters are formed almost immediately at a large measure of
distance.
This implies that there are two distinctly different
compositional groups of conglomerates within the Gable Creek Formation.
The Gable Creek sites labeled Hoodoos, Cherry Ranch, Sheep Flat,
Sheep Camp, Upper Sheep, Tony Butte, and East Doolittle are composi-
tionally different from the rest of the conglomerates in the Mitchell
area.
Of the other Cretaceous conglomerates sampled, the Goose Rock,
Antone, and Mountain Creek sites fall into this same cluster.
At a
smaller cluster distance, the Goose Rock, Antone, and East Doolittle
sites form a separate sub-cluster.
Only the Bernard Ranch site
clusters with the other, larger Gable Creek group.
The average linkage method shows a similar segregation of the data
59
(a)
Webers
Narrows
MudCreek
UpGirds
Thomp.1
UpGable
BlkButte
Rip-Up
Monroel
Radiotow
a
446
BridgeCr
Thomp.3
Meyers1
Meyers2
Marshall
a
Gordy
NelsonCr
Johnson
Monroe2
Thomp.2
Mitchell
WhButte
Upmonroe
Spetch
Courthse
Bernard
SheepCyn
SheepCmp
MtnCreek
UpSheep
Hoodoos
Cherry
TonyBut
Goose
E.Doolit
An tone
4----------------4-------- -------------------------+
0.6
0.5
0.4
0.3
0.2
0.1
0
Distance Between Clusters
Figure 6. Deridrograms resulting from cluster analysis of the pebble
count data using (a) Ward's minima variance method and (b) average
linkage method.
60
SheepCyn
SheepCmp
MtnCreek
UpSheep
Hoodoos
Cherry
Webers
Narrows
MudCreek
Radiotow
BridgeCr
Rip-Up
Monroel
WhButte
Gordy
NelsonCr
Johnson
Meyers2
Thomp.3
Meyersl
Monroe2
Thomp.2
Mitchell
Marshall
UpMonroe
Spetch
Courthse
UpGirds
Thomp.1
UpGable
BlkButte
Bernard
TonyBut
Goose
E.Doolit
Antone
+------+------+------+------+------+------+-------------+
1.6
1.4
1.2
1.0
0.8
0.6
Distance Between Clusters
Figure 6.
(Continued).
0.4
0.2
0
61
with a Gable Creek cluster of
Hoodoos,
Cherry Ranch, Sheep Flat, Sheep
Using this method, the
Camp, and Upper Sheep being formed immediately.
Tony Butte and East Doolittle sites are grouped with the larger of the
two clusters but segregate out at a slightly smaller distance.
At
progressively smaller measures of distance, the average linkage method
forms more clusters than the Ward's method.
These numerous clusters
represent further subdivisions of the data but probably do not reflect
significant compositional differences.
The clusters formed by the
average linkage method are also apparent on a ternary plot of chert,
volcanic,
and platonic clast abundance at each of the sample sites
(Figure 7).
The two major clusters formed from the Gable Creek data can be
interpreted as distinct conglomerate
petrofacies.
The two petro-
facies are, in general terms, represented by the cosition of the
Mitchell and Hoodoos sites
respectively.
The Mitchell type petrofacies
is hereby designated as Facies 1 and the Hoodoos type petrofacies will
be called Facies 2 for convenience.
Facies 1
This petrofacies encompasses a majority of the Mitchell sites and
can be regarded as the most typical Gable Creek conglomerate co posi-
tion. It is not restricted to a particular stratigraphic level within
the Gable Creek Formation and is especially representative of the sites
located on the south side of the Mitchell
rate
petrology,
fault.
In terms of conglome-
this facies is characterized by relatively low amounts
of chert and rhyolite and moderately high amounts of plutonic and mafic
volcanic lithologies.
62
CHERT
PLUTONIC
VOLCANIC
Figure 7. Terns y plot of chert, volcanic, and plutonic clast
percentage at each Gable Creek sample site.
63
Facies 2
The petrologic composition of this petrofacies is represented by
abundant chert and rhyolite and low amounts of plutonic and mafic
volcanic
lithologies.
typical Gable Creek
These rocks differ in appearance from,the more
conglomerates.
The outcrops are deeply weathered,
crmmbly, and heavily iron stained as exemplified by the hoodoos along
Girds Creek (Figure 8).
The individual clasts are also highly altered
and there is an abundance of
white,
powdery, clay-rich clasts
(Figure 9).
In contrast to Facies 1, this petrofacies appears to be restricted
in both a geographic and stratigraphic sense.
The sample sites that
comprise this facies are all located on the northwest limb of the
Mitchell anticline on the north side of the Mitchell fault.
These
sites generally seem to be stratigraphically equivalent but structural
complications prevent determination of their exact level.
A major
high-angle fault has been identified that externs for at least eight
miles in a northeast direction from the SE 1/4 of Sec. 21, T. 11 N,
R. 21 E., to the NW 1/4 of
comm.,
1985).
Sec.
3, T. 11 S., R. 22 E (Taylor, oral
The Facies 2 sites are located on the downthrown,
northwest side of this
structure.
The magnitude of vertical displace-
ment along the fault is unknown but may be considerable.
The relation-
ship of the Facies 2 rocks to the fault is unclear but may indicate
that they were down-dropped from a much higher stratigraphic level.
The relationship between the two distinct petrofacies within
the Gable Creek Formation is not well
understood.
Facies 2 rocks
nay reflect a distinct change in provenance or a significant influx of
I
04
1
s
f.
kr
e
5
e
.,A--
v
I
l
d
A
-
1.
i -it
cry
a e Creek
ree con 1om erato out
8 . Hoo d oo-like Gable
Creek in the northern part of the inlier.
F'figure
a lo
I
Gisd s
_ 1.
p
Ln
.o
66
previously unexposed rocks in the source areas.
material in the Facies 2 rocks may record an
ism in the
source areas.
The abundant volcanic
episode of
active volcan-
A large influx of silicic volcanic material
might temporarily dominate the system and control the type of sediments
that were delivered to the basin.
Likewise, a shift in the major
drainage patterns could introduce a significant change in sediment
composition.
Another possibility is that the Facies 1 and
Facies 2 rocks were
originally similar in composition but have been subjected to different
degrees and rates of weathering and post-depositional alteration.
The
deeply weathered condition of the conglomerate at the Hoodoos locality
may indicate that this part of the Cretaceous section was exposed at
the surface for a long period of time prior to deposition of the over-
lying Clarno rocks.
Although the straigraphic level of the Facies 2
rocks is unclear due to the possibility of major vertical displacements, these rocks may have occupied a position high in the section.
The climate of eastern Oregon during Clarno time was humid and subtropical (Manchester, 1981).
High rates of chemical
deccaposition in this
climatic regime could have severely altered all but the most stable
types of clasts.
This phenomenon would explain the high percentages of
chert and silicic volcanics present in Facies 2 rocks.
The light
colored, clay rich clasts observed in the outcrops may be the altered
reuiants of the less stable lithologies that were originally
present.
A different possible explanation is that Facies 2 sediments
were subjected to intense weathering before arriving at their final
site of deposition. A shift in
major drainage
patterns could have left
these unconsolidated materials subaerially exposed for a considerable
67
period at sane stage of their transportation history.
Perhaps these
sediments underwent several episodes of reworking before being intro-
duced into the
basin.
Under these conditions of both physical and
chemical weathering, only the most resistant lithologies would survive
the complete cycle.
Vertical Variation of Composition
One of the purposes of the study was to document compositional
variations within the Gable Creek
conglomerates.
Lateral variations
appear to be small within a single unit but can change drastically
between major conglomerate units.
It is also important to investigate
the possibility of vertical variations throughout the section. Sig-
nificant compositional changes with increasing stratigraphic level
might indicate progressive changes in
provenance,
drainage configur-
ation, or the erosion of previously covered rocks in the source areas.
The stratigraphic section on the south side of the Mitchell fault
was chosen for this investigation because it is the most complete Gable
Creek section and is relatively free of structural complications.
The
section is located on the southeast limb of the anticline and extends
eastward from Spetch Rim which rests directly on the
member to Johnson
Cr.
in } dstone
at the uppermost exposure of the section.
A
total of ten major conglomerate units, each separated by mudstone
units, comprise this section.
Since the conglomerates are dominantly composed of
chest,
pluton-
ic, and volcanic rocks, the abundance of these three clast types should
provide a indication of vertical compositional changes. A plot of the
abundances of these clast species at each stratigraphic level is shown
68
in Figure 10.
All three species of clasts exhibit fluctuations in
abundance upward throughout the section but are not significantly
different at the top of the section canpared to the
base.
Plutonic
clasts show the least amount of variability and volcanics have the
greatest fluctuations which is not surprising since they are the most
abundant clast type as a whole.
One apparent relationship is that
plutonic and volcanic clasts vary inversely with respect to one an-
other.
As volcanic content
increases,
corresponding decrease and vice versa.
plutonic abundance shows a
Chert abundance merely reflects
changes in the sum total of the igneous clasts.
A plot of the ten sample sites on a ternary diagram does not show
any definite trend of compositional change (Figure 11).
All of the
sites group together in a small field which reflects their cxositional similarities as part of the fairly hamogeneous Facies 1 rocks.
Increased chert abundance is apparent at levels 5 and 6 and volcanic
clasts are most abundant at stratigraphic levels 7 and 9.
whole,
it appears that the vertical variability of o
On the
lcmerate
composition is more or less random in this part of the Gable Creek
section.
Comparison with Other cretaceous Conglomerates
The conglomerates within the several Cretaceous inliers in central Oregon can be coq:)ositionally cm pared to the Gable Creek rocks by
means of the pebble count data.
Similarities or differences in con-
glomerate petrology might provide important clues to the location of
source areas and provenance of the clasts.
The statistical correla-
tion values discussed above can be used to care the different sites
69
Composition vs. Stratiaraphic Level
e
4
5
6
7
9
B
10
Stratigraphic Level
Chert
PIUtO nits
T
Volcanics
10. Bar graph showing ratio of diert, volcanic, and plutonic
clasts in the stratigraphic section located south of the Mitchell
Figure
fault.
70
level
CHERT
10
unit
Johnson Cr.
9
Radio Tower
8
Nelson Cr.
7
White Butte
6
Weber Rch.
5
Mud Creek
4
Gable Cr.
3
Thompson Cr.
2
Black Butte
1
Spetch Rim
VOLCANIC
PLUTONIC
Figure 11.
Ternary plot of data fr n Figure lo.
71
to the conglomerates at
Mitchell.
The correlation values for the four
non-Mitchell sites compared to the Gable Creek sites are listed in
decreasing order in Table 5.
A value of 0.95 is arbitrarily chosen as
the lower limit of a good correlation.
Bernard Ranch
The Bernard Formation conglomerates are most similar to the
Gable Creek sites at Spetch Rim,
Monroe Cr.
Courthouse,
White
Butte,
and Upper
Although the Bernard Formation is slightly younger than the
Gable Creek Formation (Dickinson,
1978),
it is interesting to note that
these rocks most closely match the Spetch Rim and Courthouse sites
which are stratigraphically low in the Gable Creek section.
The can-
position of the Bernard conglomerate is more similar to the Facies 1
rocks at Mitchell as shown by the low correlation values among Facies 2
sites.
Goose Rock
The Goose Rock conglomerates are closest in carnposition to the
Gable Creek sites Tony Butte and E. Doolittle as well as the Antone
Ranch conglomerates.
The two Gable Creek sites mentioned above are
included in Facies 2 but are slightly anomalous in their moderate
amounts of chert and high abundance of trachyte and rhyolite clasts.
The Tony Butte conglomerate was included in the Basal Member of the
Hudspeth Formation which is slightly older than the Gable Creek
Formation (Wilkinson and Oles,
1968).
The age of the Cretaceous Goose
Rock deposits is not sufficiently known to permit any speculations of
age correlations with the Cretaceous section at Mitchell.
Antone Ranch
The Antone Ranch conglomerates also correlate with the Tony
Oorrelation values between several cretaceous inliers in
central Oregon and the Gable Creek conglomerates at Mitchell.
Table 5.
SITE
Spetch
Courthse
WhButte
UpMonroe
Meyers2
NelsonCr
Mitchell
Thomp.2
MonroeZ
Meyersl
Rip-Up
Marshall
GordyFlat
JohnsonCr
Thomp.1
Thomp.3
UpGirds
Monroel
B1kButte
Radiotow.
UpGable
BridgeCr
Narrows
Webers
TonyButte
MudCreek
Antone
Goose
E.Doolitt
SheepCyn
SheepCmp
MtnCreek
CherryRch
UpSheep
Hoodoos
Bernard
0.98
0.97
0.96
0.96
0.94
0.94
0.94
0.94
0.94
0.93
0.92
0.91
0.91
0.90
0.90
0.90
0.89
0.88
0.85
0.84
0.81
0.79
0.77
0.77
0.77
0.74
0.74
0.65
0.S8
0.56
0.42
0.32
0.29
0.27
0.22
SITE
TonyButte
E.Doolitt
Antone
BridgeCr
Monroe!
SheepCmp
Rip-Up
UpSheep
Radiotow.
SheepCyn
Meyersl
CherryRch
MtnCreek
Narrows
Meyers2
Hoodoos
MudCreek
Thomp.3
Webers
Marshall
Spetch
UpMonroe
Monroe2
GordyFlat
Courthse
Thomp.2
WhButte
BlkButte
Bernard
NelsonCr
Mitchell
UpGirds
Thomp.l
JohnsonCr
UpGable
Goose
0.98
SITE
(intone
0.76
0.75
0.74
0.73
0.70
0.70
0.69
0.69
TonyButte
Goose
Rip-Up
E.Doolltt
BridgeCr
Monroel
Meyers2
Meyersl
Radiotow.
Courthse
Spetch
UpMonroe
Marshall
Bernard
Thomp.3
Monroe2
SheepCyn
WhButte
GordyFlat
SheepCmp
Narrows
Thomp.2
NelsonCr
MudCreek
0.97
0.96
0.86
0.86
0.86
0.96
0.80
0.80
0.77
0.75
0.75
0.75
0.74
0.74
0.74
0.72
0.72
0.71
0.71
0.69
0.69
0.68
0.67
0.67
0.68
Mitchell
0.66
0.66
0.65
0.65
0.65
0.63
0.63
0.62
0.61
0.60
0.49
Webers
JohnsonCr
MtnCreek
UpSheep
CherryRch
BlkButte
Thomp.1
UpSirds
Hoodoos
Up6abl
0.65
0.65
0.64
0.64
0.63
0.62
0.96
0.96
0.92
0.84
0.83
0.83
0.82
0.82
0.82
0.79
0.79
0.79
0.78
0.78
0.77
0.61
0.60
0.57
0.46
SITE
CherryRch
UpSheep
SheepCmp
Hoodoos
SheepCyn
E.Doolltt
Goose
BridgeCr
MudCreek
TonyButte
Narrows
Webers
Antone
Meyersl
Thomp.3
Radiotow.
BlkButte
Marshall
Meyers2
Monroel
Rip-Up
UpGirds
Monroe2
UpGable
Thomp.2
Spetch
GordyFlat
UpMonroe
Thomp.l
NelsonCr
Mitchell
Courthse
JohnsonCr
WhButte
Bernard
MtnCreek
0.98
0.96
0.96
0.95
0.92
0.81
0.79
0.77
0.74
0.73
0.73
0.72
0.64
0.59
0.59
0.58
0.56
0.52
0.51
0.50
0.49
0.48
0.45
0.44
0.44
0.43
0.43
0.43
0.42
0.40
0.40
0.38
0.35
0.33
0.32
73
Butte and Goose Rock samples.
The Antone rocks do not appear to have
a greater affinity to either Facies 1 or Facies 2 rocks at Mitchell.
Both the Mitchell
Antone.
and Hoodoos sites have low correlation values with
The most obvious relationship is the close similarity of
Antone and Goose Rock con ositions.
had very similar
This suggests that both deposits
source areas although the Antone deposits are shallow
marine in origin and the Goose Rock conglomerates are interpreted as
normarine deposits.
Mountain Creek
The conglomerates exposed at the Mountain Creek locality are
most similar to the Facies 2 rocks, especially the Cherry Ranch, Upper
Sheep, and Sheep Camp sites.
However, the Mountain Creek conglomerate
is much finer grained than the typical Gable Creek conglomerate and it
is not known to what
degree
cc uposition is controlled by grain size.
The Mountain Creek conglomerate is not particularly similar in
appear-
ance to the Facies 2 outcrops but the exposure is extremely limited at
this locality.
Neither the age or stratigraphy of the Mountain Creek
exposure is well known.
Paleocurrents
A limited amount of paleocurrent
data was collected
Gable Creek and Hudspeth Formations (Plate 2).
from both the
Some of the field data
was collected in conjunction with L. C. Kleinhans.
The purpose of the
paleocur ent investigation was to determine the regional paleoslope,
sediment dispersal pattern, and to help define channel geometry.
An
exhaustive or statistically valid sampling program was not attempted.
A total of 40 paleocurrent observations were recorded, mostly from the
74
Gable Creek Formation.
A variety of both unidirectional and bidirec-
tional indicators were utilized.
Unidirectional Indicators
Emphasis was placed on collecting data that provide a unique
measurement of flow direction.
Several sedimentary structures of this
type were utilized including pebble imbrication, flute casts,
bedding.
iance
and cross
Pebble imbrication provides directional readings of low var-
because pebble and cobble-sized material is only moved under
high flow conditions.
Currents tend to migrate and meander least dur-
ing high energy flow (Rust, 1975).
Care
must be taken during measure-
ment, however, to find exposures that provide a three-dimensional view
of the imbrication geometry.
Sole markings such as flute casts are typically associated with
turbidity currents and liquified flow (Miall, 1984).
Flute casts re-
sult from scouring of the underlying sediments by turbulent currents
and eddies that commonly have a corkscrew or vortex sense of motion.
Most of the flutes were found on the base of the thin sandstone
turbidites within the Hudspeth Formation although
ed within the Gable Creek conglomerates.
a few were encounter-
When measuring flutes, the
overturned sandstone slabs must be restored to their oringinal bedding
positions before recording the flute orientation.
Bidirectional Indicators
Sedimentary structures such as primary current lineations,
parting lin eati ons, and groove casts provide only a line
with two possible solutions that differ by 180 degrees.
tio s must
be used in
of movement
These cbserva-
conjunction with directional structures or other
supporting data to determine paleocurrent orientation.
Current linea-
75
tions and parting lineations form under plane bed flow regimes and
also yield readings of low variance.
These structures are common along
bedding planes within the Gable Creek sandstones.
Groove casts form
under similar conditions as flutes and may result from pebbles or other
objects being dragged along the sediment surface.
As with flute casts,
the beds must be properly replaced before measuring any of these
structures.
Paleocurrent Orientation
The parent data were plotted in the form of a rose diagram
as shown in Figure 12.
degrees azimuth.
The data are placed into modal classes of 30
Correction of the data for structural dip in excess
of 20 degrees was made on an equal area stereonet.
Shallower dip
angles produce an error of less than 3 degrees and can be ignored
(Potter and Pettijohn, 1977).
The unidirectional data indicate a southward direction of movement
with a point estimate of the average orientation of S. 45 W.
most proninant direction of flow is S. 15 W.
The next
The rest of the data
range from northwest and northeast to nearly due east.
The bidirec-
tional data likewise support this configuration but also emphasize a
northwest-southeast component of flow.
The overall dominant south-
westerly flow direction is taken as the average or regional paleoslope
orientation. Wilkinson and Oles (1968) measured foresets in the conglomerates and arrived at a similar conclusion.
The strike and geo-
metry of the conglomerate units agree with this interpretation and
indicate that the submarine canyons or channels in which these sedi-
ments were deposited were approximately parallel to the dip of the
paleoslope.
76
Figure 12.
Ruse diagram of paleocurrent data
Cretaceous sequence at Mitchell.
collected
from the
77
The subordinate pattern of paleocurrent directions may have sev-
eral
explanations.
Current eddies, changing flow regime, and local
obstructions could account for these
Paleocurrent orienta-
variations.
tions at high angles to the regional paleoslope could result from overbank deposition, breaching of submarine levees, and channel abandon-
Finally, it is possible that the paleocurrent indicators possess
ment.
some degree of unreliability.
There appears to be a relationship between paleocurrents and
stratigraphic position suggesting that sediment dispersal patterns
change through
time.
and imbrication,
The northwesterly
indicators,
may
including flutes
were recorded in the lower portion of the Cretaceous
section (Plate 2). Flute casts within the upper part of the Main Mudstone member led McKnight
(1964)
to support a paleoslope direction
of N. 10-15 W. with source areas presumably located to the south of
Mitchell.
There is a distinct possibility that there was sediment
input from both sides or several directions within this restricted
basin.
However,
sediment composition does not differ markedly with
paleocurrent direction.
The dominant southwesterly indicators are mostly from the middle
and upper parts of the section and suggest that the major shelf or
basin margin lay to the northeast of Mitchell.
In
contrast,
the east-
erly paleocurrent measurements were recorded in the Johnson Creek
area at the assumed top of the exposed Cretaceous section.
Submarine
channels have a tendency to become oriented parallel to the basin axis
through time (Griggs and Kulm,
1970).
In the northern hemisphere the
channels turn to the left due to the Coriolus effect.
The gradual
shift of the paleocurrents to an easterly direction in the uppermost
78
Gable Creek Formation may reflect this tendency.
On the other hand,
the apparent
relationship
graphic level
may be coincidental and solely due to the random proces-
between paleocurrent
direction
and strati-
ses mentioned previously.
Cretaceous Inliers in Central Oregon
Of the four exposures of cretaceous conglomerates sampled for
pebble counts, limited paleocurrent data was collected
Goose Rock and Antone Ranch
only at the
The highly cross bedded
localities.
sandstones at Goose Rock yield an average paleocurrent direction of
southwest which is similar
interesting
to note that
to the Mitchell
paleocurrent data.
It is
the Antone Ranch exposure is located approxi-
mately S. 45 degrees W. of Goose Rock and lies
directly in line with
the paleocurrent data collected at Goose Rock.
At the Antone Ranch
locality, paleocurrents measured from foreset
Higher in the stratigraphic section, current lineations in the fossiliferous sandstones
sandstone beds were oriented N. 20 degrees W.
yielded an average line of movement oriented N. 65 W.-S. 65
in conjunction with the
ection of
transport.
foresets, probably
E. which,
indicates a northwest dir-
Although perhaps coincidental, the Mitchell
inlier is located approximately N. 70 W. of Antone Ranch which
may
indicate sediment transport from the Antone area towards deeper water
at
Mitchell.
the Mitchell
The Antone rocks occuppied a shallow shelf that flanked
basin or was part of another separate basin.
79
DISCUSSION
Provenance
The polymict Gable creek
conglomerates were derived from wide-
spread and geologically diverse source areas.
Undoubtedly, much
of these pre--Cretaceous rocks are now hidden beneath the cover of
Cenozoic lavas.
Partly for this reason, little is known about the late
Paleozoic and Early Mesozoic geologic history of central and eastern
Oregon.
The region has been very tectonically active since at least
the Early Mesozoic as evidenced by the several accreted terranes and
numerous widespread unconformities between the younger rock units.
Coarse conglomeratic deposits are the legacy of tectonic unrest in the
geologic past.
Presumably,
the Gable Creek Formation represents one of
the major episodes of tectonic instability that characterizes the
region.
The pre-Cretaceous geology of the region can be summarized
as a diverse rock assemblage of oceanic affinity
including submarine
volcanics rocks, ultramafic rocks, and a variety of marine sedimentary and metasedimentary rocks.
Scene of these older rocks are intruded
by Jurassic plutons which scan workers believe mark the final accretion
and consolidation of the oceanic and island-arc terranes with the North
American continent (Dickinson and
Thayer, 1978).
A collage of these
older rocks was subjected to a deformational event that created
the tectonic highlands from which the Gable creek sediments were shed.
Several exposures of older rocks were visited during the field
season but much of the information on other localities is taken from
descriptions in the published literature. In most cases, the exact
80
provenance of the conglomerate clasts cannot be determined but compatible source areas that probably are representative of the unexposed
rocks can be identified.
exclusively located, the
Since the actual source
areas cannot be
provenance data can be used to elucidate the
regional paleogeography and drainage patterns in a general sense only.
Plutonic Clasts
Many of the plutonic rocks present in the conglomerates have
counterparts
in eastern
Oregon.
For example, the quartz diorite and
granodiorite clasts that are common at Mitchell are microscopically
indistinguishable
from rocks in the Wallowa and Bald Mountain batho-
liths located to the northeast (Taubeneck, 1959).
Several of the ap-
lite clasts from Mitchell are similar in mineralogy to rocks in these
Jurassic plutons as described by Taubeneck (1957).
The gabbroic
clasts encountered in the conglomerates have similar counterparts in
the Early Mesozoic Sparta Complex east of Baker.
The metasanatized
Sparta granite was described by Gilluly (1933) as medium grained,
sheared, and invaded by blebs and veinlets of bluish quartz.
clasts matching this description are present at Mitchell.
diorites described by Hamilton (1963) in the Riggins
Plutonic
Meta-quartz
Group of eastern
Oregon and western Idaho may be similar to the metaplutonic clasts at
Mitchell.
The single pyroxenite clast encountered in the conglomerate is
identical in appearance to the ultramafic rocks of the Canyon Mountain
Complex located approximately 60 miles
east of
ic Canyon Mountain Cat lex is the largest
Mitchell.
of several
ultramafic ex-
posures in eastern Oregon that are included in the dis
crust terrane of Brooks and Vallier (1978).
The ophiolit-
nbered oceanic
These rocks are probably
81
rare in the conglomerates due to their unstable mineralogy and potential for rapid weathering.
It is difficult to find counterparts to the pinkish granites and
K-spar granites found at Mitchell.
At first glance, these rocks would
appear to be of continental rather than oceanic affinity.
The granite
clasts could be derived from the craton but the larger batholiths in
Idaho and western Montana are late Cretaceous in age and too young to
be represented at Mitchell.
Small silicic plutons in eastern Oregon,
now covered, could have provided a source for these rocks.
The gran-
ites are fine grained with few mafic components and could represent
aplites or late stage intrusions in a composite pluton of less silicic
composition overall.
Thus, many of the plutonic clasts at Mitchell are similar in
ition to Jurassic plutons in eastern Oregon.
Some of the
plutonic clasts are too altered or metamorphosed to be Jurassic rocks
and may represent Late Paleozoic plutons such as the Sparta Complex.
Others are more silicic than exposed plutons in eastern Oregon suggesting more silicic magmatism either earlier in Oregon or futher to the
east on the continent.
Volcanic Clasts
Volcanic igneous rocks are the single most abundant clast type in
the Gable Creek conglomerates and there is no paucity of these materials among the older rocks in eastern Oregon.
The oceanic crustal com-
ponents and the island-arc rocks of the Seven Devils, Wallowa, and
Juniper Cuddy Mountains provide an abundant source for the basalt,
greenstone, volcanic breccia, and ash-flow tuff clasts present at
Mitchell.
These volcanic lithologies are widespread among the older
82
rocks exposed in eastern Oregon and western Idaho and the provenance of
similar clasts in the conglomerates cannot be further pinpointed.
The pre-Cretaceous rocks of the John Day inlier also contain minor
volcanic components including lava flows and ash-flow tuffs (Dickinson,
1979).
The Aldrich Mountains Group in the northern half of the inlier
contains thin andesitic flows that could have provided a source for the
volcanic clasts of intermediate composition at Mitchell.
A source of silicic volcanic rocks is present near Hells Canyon of
the Snake River.
Small bodies of rhyolite and silicic porphyries in-
trude Permian volcanic
1976).
rocks
in the Red Ledge mining dristrict (Long,
Rhyolite clasts in the conglomerates are similar in appearance
to rocks of the Red Ledge intrusions (Field, oral ccmnm., 1986).
There
are probably numerous similar intrusions in the area that are not exposed at the present.
Within the surrounding Permian rocks, minor
amounts of dacite, latite, and rhyolite are present and have undergone
lower greenschist facies metamorphism.
Thus, compatible source areas for most of the volcanic clasts
present at Mitchell are located in eastern Oregon and western Idaho.
Many of the volcanic conglomerate clasts, especially the mafic lithologies, are highly weathered and replaced with abundant chlorite.
The
abundance of silicic volcanic clasts at Mitchell may be, in part, due
to the durable and resistant nature of these lithologies.
Sedimentary Clasts
A variety of sedimentary clasts are present in the conglomerates
and are interpreted
as marine
in origin.
Radiolarians are visible in
some of the chert grains and foraminifera have been identified in a
few lithic sandstone samples.
The majority of the sedimentary clasts
83
probably have direct counterparts in the Mesozoic clastic terrane of
Dickinson and Thayer
(1978)
in eastern
Turbiditic deposits of
Oregon.
mudstones, lithic arenites, and wackes are common in the John Day inlier.
Thin
the Vester
layers of chert pebble
Formation in this
area.
are present within
conglomerate
The Laycock Formation is
cmqx)sed
of graywacke and laminated siltstone that is similar in appearance to
clasts found
at Mitchell.
Near Suplee, Oregon, the Pennslyvanian
Spotted Ridge
contains a variety of marine sedimentary rocks including
Formation
pebbly cheat
sandstones and carbonaceous sandstones that resemble clasts present in
the Cretaceous conglomerates.
The underlying Coffee Creek Formation
Fossiliferous lime-
contains limestones and calcareous sandstones.
stones are present above the volcanic rocks in the Seven Devils
Mountains and in parts of
clasts found
at Mitchell
the John Day
inlier.
Most of the limestone
are unfossiliferous micrites. Abundant
sources of chert are present in the widespread oceanic crustal terrane
and the Elkhorn
Ridge Argillite
near
Baker, Oregon.
Chert clasts in
the Gable Creek conglomerates are very similar in appearance to the
cherts in the basement rocks exposed in Meyers
Canyon,
near Mitchell.
Quartzite clasts are present in all of the Cretaceous conglomerates
sampled.
These metaquartzites would appear to be cratonic in
origin although
River Schist
minor amounts of quartzite are present
of eastern Oregon
(Gillily,
bles and small boulders are present as
1937).
alluvial
within the Burnt
Rounded quartzite cob-
deposits near the
Bernard Ranch locality suggesting a source of quartzite somewhere in
the Blue
Mountains.
tinental
margin or western interior is also possible.
A source of quartzite from the Early Mesozoic con-
84
Metamorphic Clasts
Several types of metamorphic clasts are present in the conglcmner-
ates including phyllite, marble, schist, and gneiss.
Both phyllite and
marble are amt in the basement rocks exposed in the Mitchell inlier and are very similar to clasts found in the conglomerates.
lites are also exposed at Muddy Ranch northwest of Mitchell.
phyl-
Presum-
ably much more extensive areas of these rocks were exposed during the
Cretaceous Period.
The other metamorphic lithologies may have been derived from areas
further to the east.
The Burnt River Schist in the Baker Quadrangle is
composed of quartz phyllite and a variety of schistose rocks.
Gneissic
rocks are reported from near Oxbow, Oregon along the Snake River
(Brooks and Vallier, 1967). Only a few banded gniess
clasts were en-
countered in the Gable Creek conglomerates which might imply that their
source was quite distant.
Tectonics and Basin Origin
The Cretaceous marine rocks in central Oregon are interpreted as
forearc basin deposits by Dickinson (1979) but the trench geometry,
subduction polarity, and location of the associated magmatic arc are
not known.
The Cretaceous strata at Mitchell and the earlier Mesozoic
marine rocks in the John Day inlier rest unconformably on oceanic metasediaw.ntary basement rocks which probably represent an uplifted and
eroded subduction co plex.
Blueschist and ophiolitic rocks are present
near Mitchell and in the Blue Mountains respectively, and are indicative of active subduction prior to the Cretaceous.
85
Central Oregon was tectonically active throughout the Mesozoic but
the plate motions and configurations are not well known.
plate regime
was one of
The overall
of an eastern
northeastward convergence
plate with the North American plate (Coney, 1972).
Pacific
This oblique plate
convergence, which resulted in the accretion of numerous allochthonous
terranes,
was accarnpanied
by northward translation and c1oc,Jaaise rot-
ations (Silver and Smith, 1983).
The forearc basin in central Oregon,
commonly referred to as the Ochoco
Basin, formed
along the Mesozoic
continental margin during this regime, possibly as a result of rifting
or pull-apart motions.
The size and the shape of the cretaceous forearc basin is unknown
but one possible
scenario
connects the Cretaceous forearc strata of the
the Great Valley Sequence in California and the Methow Trough in Washington with central Oregon to form a long, linear belt.
The Ochoco
Basin extends at least as far east as the John Day area and as far
south
as the Suplee-Izee area
and presumably farther.
Cretaceous
strata were penetrated in four wildcat wells drilled to the south of
Mitchell and foraminiferal assemblages indicate deposition at outer
neritic to bathyal depths (Thaupson and others, 1984).
Nilsen (1984)
suggested that the Ochoco Basin was originally connected to the basin
in which the Hornbrook Formation was deposited and was bounded by the
Klamath Mountains to the south.
are located in both the
eastern
Blueschists of similar Triassic age
Klamaths and near Mitchell.
Given the
tectonic complexity of the region, however, it is questionable how long
this larger linear
basin
would remain intact.
The possibility of sev-
eral smaller, segmented forearc basins of complex geometry cannot be
ruled out.
86
Subsidence,
Sea Level Chances, and Sedimentation
The Cretaceous rocks at Mitchell were deposited into a rapidly
subsiding basin.
overlain
Shallow water transgressive deposits
by mudstones and siltstones deposited
are abruptly
at neritic
to upper
Large volumes of coarse clastics derived from
bathyal depths.
source areas were poured into the
basin.
uplifted
This material probably accum-
ulated in the shallow shelf areas and was later transported into deeper water.
In this manner, the
resediment.
de
conglomerates and sand-
stones of the Gable Creek Formation were deposited at depth and contain
transported shallow water fauna and terrigenous material.
ous rocks
at Mitchell
The Cretace-
show no evidence of shallow water deposition or
shoaling anywhere in the exposed section.
Sedimentation rates were high in the basin but are
difficult to
determine because the youngest age of the deposits is not known.
The
Main Mudstone member of the Hudspeth Formation, about 3,000 feet
thick, is Early Albian at
(McKnight, 1964).
the base and
Late Albian at the top
The Main Mudstone member was probably deposited at
an average rate of about 10 cm per thousand years which is high for
normal hemipelagic sedimentation (Kennett,
1982).
The Gable Creek
Formation is Late Albian at the base and is Cenamanian or younger in
the upper part. Sedimentation rates for the conglomerate and sandstone
units are
much
less uniform but average rates of deposition may have
been on the order of 20 to 30 cm per thousand years.
The entire Cret-
aceous sequence preserved at Mitchell was probably deposited in the
span of 10 to 15 million years.
The Cretaceous Period was overall a time of transgressions of the
87
seas onto the continents and the Ochoco Basin was presumably flooded
during one of these relative rises in sea level. Many workers believe
that the Cretaceous transgressions were global in extent and resulted
from volume increases of the mid-oceanic ridge system due to rapid
spreading (Schlanger and others, 1981).
The western Cordillera was
tectonically unstable during this period and the effects of eustatic
sea level changes can either be amplified or attenuated by the local
tectonic regime. Relative changes in sea level can result from eu-
static
changes,
local
tectonics, subsidence,
sediment aggradation, or a
combination of these factors.
Deposition of the thick Hudspeth mudstone sequence was probably
dated by subsidence along with a eustatic rise in sea level.
global sea level curves of Vail and others
(1977)
The
show a relative rise
throughout the Albian stage. The rising sea level permitted the depo-
sition of laminated mudstones and siltstones in deep water while the
coarser clastic input was trapped on the adjacent shelf areas.
A
major change in the depositional style occurred in the late Albian or
Early Cena avian when coarse sediments of the Gable Creek Formation
bypassed the shelf and were dumped, into deeper water. The global Vail
curves show a distinct regression in the Early Cenomanian that may
correspond to this
event.
A relative low stand of the sea might expose
the shelf region and favor the erosion and formation of submarine canyons or
channels.
The submarine canyons would incise the shelf margin
funnel
large volumes of coarse, un-
consolidated sediments into deep water.
Continued subsidence of the
by means of headward erosion and
basin acoamodated these resedimented materials and maintained their
deep water site of final deposition.
88
Thus, in a general sense, the global sea level curves of Vail and
others (1977) correlate in both timing and polarity to the relative sea
level changes inferred from the sedimentary deposits in the Ochoco
Basin.
Rapid spreading along the mid-oceanic ridge system would result
in both transgression and accelerated plate motion.
Rapid convergence
of an oceanic plate with the continent would create the active subduction regime in which the cretaceous rocks are interpreted to have formed.
Local tectonics must have influenced the basin also but it is
difficult to distinguish between ecstatic and tectonic
causes of rela-
tive changes in sea level recorded in the rock record.
Petrologic Evolution
The petrologic composition of both the Hudspeth and Gable Creek
Formations is similar in that they represent a suite of eugeosynclinal
rocks.
The Hudspeth sediments contain more basement derived material
including chest and metasedimentary rocks.
The Gable Creek sediments
are richer in plutonic detritus which may indicate the progressive
unroofing of plutons
in the source areas.
The most striking lateral cositional variations within the
Gable Creek Formation are the two distinct petrofacies described
previously.
Within each petrofacies, however, the petrologic composi-
tion is fairly uniform.
Variability within a single conglomerate unit
is also low, indicating a lack of lateral compositional changes due to
depositional or other controls.
C¢nposition does not appear to be
strongly affected by clast size, shape, or grading.
Vertical compositional changes are present within the conglomerate
sequence but do not follow any definite trend or pattern.
The relative
89
proportions of certain
clast types fluctuate
between adjacent strati-
increases or decreases upward
graphic levels but do not exhibit net
not reveal significant increases
through the
section.
in plutonic
content upward through the conglomerate section as mention-
This
study did
ed by some previous workers
(McKnight, 1964;
Wilkinson and Oles, 1968).
Neither does chert or mafic volcanic content appreciably decrease as
might be expected if there was a progressive reduction of oceanic
crustal materials
source areas.
in the
Perhaps the lack of distinct
vertical carr ositional changes within
the conglomerates is due to their resedimented origin or the short span
of geologic
time in which
they were
deposited.
Mixing and reworking of
the unconsolidated gravels on the shelf might have eliminated
ary differences in sediment composition.
ments during deposition
by turbidity
Further mixing of the sedi-
or other gravity processes would
the uniformly heterogenous nature of the conglomerates.
result in
It is this lack
of consistent
vertical
change that makes stratigraphic
correlations based on conglomerate petrology
Mitchell
any prim-
difficult within the
inlier.
Cretaceous Paleoaeoararhv
The regional setting of central Oregon in the cretaceous was characterized by a deep reentrant of the Pacific Ocean surrounded by up-
lifted highlands. This major forearc basin developed in Early Albian
time and persisted to at least the Caupanian (Thcnpson and others,
1984).
The size of the basin is questionable but it may have extended
to southwestern Oregon or possibly further.
flanked by the Klamath mountains on the
The basin was probably
southwest,
the rising Idaho
90
Batholith to the east, and the Blue Mountains on the northeast (Nilsen,
1984).
Provenance of the Gable Creek conglomerates indicates that tectonic highlands representing major source areas were located to the
east, southeast, and northeast of Mitchell.
Paleocurrent data from
Hudspeth and lower Gable Creek rocks suggest the possibility of a sediment source to the southeast during the early stages of basin development.
late Albian to Cencamanian strata yield paleocurrent indicators
directed southwest which may indicate a change in source areas or
drainage configuration.
It should be remembered that paleocurrent data
from the resedimented deposits at Mitchell reflect the direction in
which the sediments were transported within the basin and not necessarily the direction from which source materials were delivered to the
basin.
Another paleogeographic uncertainty is that microplate rota-
tions may have influenced the present distribution of the Cretaceous
inliers.
Clockwise rotations of up to 60 degrees have been recorded
from Jurassic plutons in eastern Oregon and evidence from the Eocene
Clarno Formation indicates that most of this rotation occurred prior to
50 million years ago (Wilson and Cox, 1980).
The sequence at Mitchell is the only surface exposure of deep
water Cretaceous sediments in central Oregon although similar rocks
were encountered in the subsurface to the south of Mitchell.
The
smaller Cretaceous inliers at Goose Rock, Antone Ranch, and Bernard
Ranch record deposition in terrestrial and nearshore marine environments.
The strata at Goose Rock were probably deposited in a major
fluvial system and were located near the eastern margin of the basin.
The shallow marine deposits at the Antone and Bernard exposures were
91
presumably situated on a narrow shelf flanking the deeper parts of the
basin.
These sediments may have prograded across the shelf and enter-
ed the submarine canyon system near Mitchell during the Late Albian as
suggested by IQeinhans
Thus, major river systems draining
(1984).
tectonic highlands may have fed shallow marginal deltas which in turn
fed an extensive submarine turbidite system within the Ochoco Basin.
Facies Models
The turbidite facies association scheme as outlined by Mutti and
Ricci Lucchi
(1972)
is commonly used to infer specific environments
within a submarine fan
system.
The turbidite facies are actually the
result of various depositional processes that are c coon in, but not
restricted to, particular submarine fan environments. Turbidity currents are one of several types of sediment gravity flow processes
including debris flows, grain flows, liquified flows, and fluidized
flows (Nardin and others, 1979). All of these processes are active in
forming deep sea
deposits.
The term turbidite is used loosely to des-
cribe rocks that should correctly be referred to as sediment gravity
flow deposits.
The applicability of the turbidite facies A-G of Mutti and Ricci
Iucchi
(1972)
by Ineinhans
to the Cretaceous rocks at Mitchell was used as evidence
(1984)
to infer a deep water origin for these deposits.
Recognition of common turbidite facies associations led to the identification of various submarine fan
environments.
However, a fanlike
geometry of these deposits based on channel morphology and sediment
dispersal patterns has yet to be
documented.
Several
factors,
includ-
ing the restricted size of the basin may be responsible for the lack of
92
a well developed fan shape.
Until evidence of fan development is
presented, the Cretaceous deposits at Mitchell must tenatively be re-
garded only as part of a submarine turbidite system.
Many of the turbidite facies divisions are well represented
at Mitchell.
Particularly useful in describing the Gable creek
units are Facies A, consisting of thick beds of coarse conglomerate and pebbly sandstone, and Facies B, characterized by coarse-
to medium-grained sandstone in thick or massive beds.
Turbidite
Facies C and D are represented by the thin sandstone layers interbedded
with mudstone in the upper Hudspeth units.
Facies F consists of
chaotic slide and slump deposits and includes the pebbly mudstone units
that are indicative of mass transport processes.
Facies G consists of
fine-grained hemipelagic sediments and is best represented by the thick
Main Mudstone member of the Hudspeth Formation.
The thick deposits of coarse Facies A conglomerates within the
Gable Creek Formation suggest deposition in the proximal part of a
sukamarine turbidite system.
The coarse conglomerates probably occup-
pied a submarine canyon on the lower continental slope or a channel
system on the inner part of a submarine fan.
These two environments
can be difficult to distinguish because they are both sites of extensive hemipelagic sedimentation and sediment gravity flow deposits.
Several factors including slope stability, sediment texture, and
sediment thickness can aid in the recognition of these environments
(McGregor and Bennett, 1977).
Choatically bedded slump and slide
deposits are particularly common in slope envirorm*nts due to the
gradient and inherent sediment weakness.
These Facies F deposits
are also present in fan environments but are relatively minor.
93
Gravity flow deposits on the slope caarmonly consist of massive boulder-
bearing conglomerates that are sheetlike or confined to relatively
narrow, straight
In a typical fan sequence these deposits
channels.
consist of sandstones arranged into
quences and form in
broader,
thinning-
and fining-upward se-
meandering channels.
In addition, fan and
continental rise sediments are usually thicker than coeval slope
deposits.
The coarse-grained Gable Creek deposits are highly channelized and
arranged in
thinning-
and fining-upward sequences defined by thick
basal conglomerates overlain by pebbly sandstone,
stone,
respectively.
sandstone, and mud-
This type of conglomerate sequence was interpret-
ed by Walker (1977) to be the result of progressive channel abandonment
on a submarine fan.
Although the conglomerates are prominent in the
section, they may represent unusual, oversized flows that plugged the
channel base and caused the diversion of the normal sediment flows into
other
channels.
Once the channel bases became plugged, the coarser
con onents of subsequent flows were diverted and only sand was deposit-
ed in the former channel. Eventually, even the sand was diverted as a
result of complete channel abandorment until only hemipelagic sediment-
ation occurred in the old channel. This interpretation is compatible
with the observed sequence of Facies A,B,G within the channelized Gable
Creek deposits.
In a submarine fan
setting,
leveed valleys cmwnly occur at the
bases of submarine canyons (Howell and Normark,
1982).
A typical val-
ley complex contains numerous open channels and associated levee
deposits.
The coarse material is restricted to channels and deposition
of fine-grained sediments takes place on the levees and in inierchannel
94
areas.
Overbank deposition results in the formation of thin sandstone
interbeds within the thicker, interchannel mudstones (Normark, 1974).
Modern submarine fan channels have well developed levees built by
overbank deposition but levee deposits are rarely documented in ancient
submarine fans.
This discrepancy may result from the fact that most
levees are much larger than a typical outcrop and therefore are not
easily recognized.
The fine-grained deposits that encase ancient fan
channels may actually be large levee systems (gam and others,
1985).
Several facies models have been developed to describe resedimented
conglomerates in turbidite systems (Walker, 1975, 1977).
The descrip-
tive features that form the basis of the models are clast fabric,
stratification, and graded bedding. The inverse-to-normally graded
model is characterized by the presence of both inverse and normal
grading, and the
absence
of stratification.
The graded-stratified
model is recognized by the absence of inverse grading and the presence
of normal grading and stratification.
Most examples of this model ex-
hibit a preferred clast fabric consisting of A-axis imbrication. A
third model, the disorganized-bed model, is characterized by a lack
of grading, stratification, or a preferred fabric.
Walker attributes
the models to depositional processes or events that may correspond to
specific regions of a submarine fan system.
The disorganized-bed model may result from rapid deposition of
grain flows on steep slopes in the proximal parts of the fan system.
The inverse-to-normally graded model may form on less steep slopes
downstream from the disorganized-bed model.
Reverse grading may result
from dispersive pressure within a grain-supported
flow
and normal grad-
95
ing implies deposition from suspension (Bagnold,
stratified
model suggests direct deposition
rolling on
the bed, possibly
The graded-
1954).
from suspension without
due to turbidity currents.
model may be characteristic of deposition
This last
on the flatter
the midfan region. Thus, these models may grade
slopes in
into one an-
laterally
other as the slope angle decreases from the most proximal
to the more
medial portions of a submarine fan envirornuent.
All three
of the models proposed by Walker
(1975)
are present
within the Gable Creek conglomerates in varying degrees.
The disor-
ganized-bed model is probably dominant at Mitchell with the graded-
stratified model next most
conglomerates,
tion.
=mmuon.
Within the
graded-stratified
planar stratification is more co mnon than is imbrica-
The inverse-to-normally
graded model is also represented but is
subordinate to the other two types of
organization.
Conglomerate
or-
ganization is highly variable at Mitchell and can change abruptly
within a single outcrop. Well organized beds may.pass in a lateral or
vertical
direction into chaotic, unordered beds.
It is
difficult
to define a well developed trend or transition
among levels of conglomerate organization
organization
is highly variable,
within the inlier.
Although
it does appear that the unorganized
bed model is possibly more prevalent in the northern part of the
inlier. Graded-stratified beds are present throughout the exposure but
are slightly more corm n in the southern half of the inlier. The
abundance of disorganized-bed conglomerates suggests deposition prim-
arily from grain flow and liquified flow processes which are characteristic
of steeper slopes (Nardin and others, 1979).
relationship
is the observation
that chaotic
In support of this
Facies F deposits are also
96
dominant in the northern portions of the inlier.
Higher levels of or-
ganization in the southern part of the inlier suggest deposition on
slightly flatter slopes.
This transition, observed within the extent
of the inlier, may indicate a progressive lateral change from proximal
to slightly more distal environments in a submarine turbidite system.
The direction in which this inferred reduction in slope occurs generally corresponds to the interpreted paleoslope direction.
The geometry and sedimentology of the Gable Creek units indicate
the presence of numerous channels filled with coarse-grained sediments.
The mudstones, siltstones, and turbiditic sandstones of the
Hudspeth Formation are interpreted as conteaporaneous overbank and
interchannel. deposits associated with the Gable Creek units.
The
thinning- and fining-upward. sequences within each Gable Creek unit may
indicate progressive channel abandonment and diversion of coarse-grained sediments into new channels.
This mechanism would result in the
superposition of numerous channel-levee-interchannel systems through
time.
Thus, the conglomerate and sandstone filled channels at Mitchell
are encased in their associated fine-grained deposits (Figure 13).
Therefore, if the upper Hudspeth units are actually lateral equivalents
of the Gable Creek units, it may not be necessary or desirable to separate the rocks into two distinct formations.
Turbidite facies associations within the inlier support the interpretation of the Cretaceous deposits as part of a submarine turbidite system.
The middle and upper parts of the Cretaceous section
represent a channelized system consisting of Gable Creek units and
turbiditic Hudspeth units.
The abundance of Facies A deposits in the
Gable Creek Formation indicates deposition in a proximal or inner fan
97
Creek Fm.
—
—
——
Fm
7
Main Mudstorie
member
Figure 13. Schematic representation
deposits in the Mitchell inlier.
of the
gecznetry of the
98
environment.
The superposition of this upper sequence on the Main
Mudstone member may be the result of progradation of proximal turbidity
deposits across distal turbidites or hemipelagic deposits.
Conglomerate fabric relationships also suggest a proximal depositional environment, probably near the base of a submarine canyon or
apex of a fan.
The lack of a fanlike morphology for these deposits may
be due to their proximal position within the system where channels
tend to have a parallel rather than radial arrangement.
The transition
in levels of conglomerate organization from north to south within the
inlier may indicate a reduction of primary slope angle in this direction.
The coarse-grained nature of the Gable Creek sediments suggests
that only the more proximal part of this submarine system
the Mitchell inlier.
Equivalent distal parts of the
is exposed in
turbidite system
were presumably deposited to the south of Mitchell but were not preserved or are presently unexposed.
Although many facies models have been developed to aid in the
recognition of ancient submarine turbidite and fan environments, they
must be used with caution.
Turbidite
facies
mechanisms rather than specific envirornnents.
represent depositional
Models developed for
ancient submarine fans are not always supported by observations from
modern fans.
The models based on conglomerate fabric are mostly des-
criptive in nature
and do not necessarily have genetic implications.
Facies modeling is a valuable tool but no limited set of models will
acocenodate
all the observations from every ancient
example.
variables exist within depositional systems and existing
must be modified and adapted to fit each new example.
Many
facies models
99
CONCLUSIONS
1.
The heterogeneous Gable Creek conglomerates are composed of
an assemblage of volcanic rock fragments, chert, plutonic, sedimentary,
and metamorphic rock fragments in order of decreasing abundance.
2.
Lateral compositional variability is low within each of the major
conglomerate units and petrologic composition remains nearly constant
along strike.
3.
The petrologic composition of the conglomerate units can be
quantified by performing pebble counts of 500 clasts each.
Pebble
count samples collected from the outcrop and talus piles respectively,
yield nearly identical results.
4.
Vertical compositional variations are present within the Gable
Creek sequence but do not define any obvious trend or pattern of petrologic change upward through the stratigraphic section.
The lack of
significant vertical change may be due to sediment mixing and reworking
or the short span of time in which the conglomerates were deposited.
5.
Cluster analysis of the pebble count data supports the field ob-
servation of two distinct petrofacies present within the conglomerate
outcrop area.
The contrasting petrology of the Facies 2 rocks may be
due to primary compositional differences or secondary weathering and
alteration.
6.
Statistical correlation values show that conglomerate composition
is fairly uniform among separated units within the same petrofacies.
Correlation values are useful in identifying conglomerate units of high
compositional similarity and possible stratigraphic equivalence.
7.
Of the Cretaceous inliers studied in central Oregon, the conglom-
erates at the Bernard Ranch and Mountain Creek localities have conposi-
100
tional similarities to the Facies 1 and Facies 2 conglomerates at
The Goose Rock and Antone Ranch conglomer-
Mitchell, respectively.
ates are mutually similar in caqposition but do not have
strong compositional affinities
facies at
8.
of the conglomerate petro-
to either
Mitchell.
Paleocurrent data from the Cretaceous
dominant southwesterly
divergent
particularly
direction
rocks at Mitchell
of sediment transport.
reflect a
Subordinate
paleocurrent patterns may represent multiple directions of
sediment input, channel migration, overbank deposition, or channel
abandorm ent.
9.
The polymict Gable Creek conglomerates have source areas within
the several accreted terranes in central and eastern Oregon. A large
proportion of the Gable Creek sediments were derived from rocks analogous to, if not part
of, the
Seven Devils Group, the
John Day inlier
rocks, the oceanic crustal terrane, and Jurassic plutons in eastern
Oregon.
A previously
undescribed tuff unit within the lower part of
the Gable Creek section
nearby volcanic
10.
probably
records
a
short-lived episode of
activity.
The Ochoco Basin formed in a forearc setting along the Mesozoic
continental
margin during a regime of oblique, northeastward plate
convergence.
11.
The Cretaceous sediments of the
into a
deep, rapidly
Mitchell
inlier were deposited
subsiding basin. The fine-grained sediments
carnprising the lower part of the sequence probably accumulated during a
relative rise in sea level in Early Albian time. The coarse Gable
Creek sediments were deposited following a brief lowering of sea level
in the late Albian or Early
Ceaaanian stage.
101
The Ochoco basin may have originally extended into southwestern
12.
Oregon and was flanked by highlands on the
northeast.
ifornia,
southwest,
east, and
Upper Cretaceous forearc strata located in northern Cal-
Washington,
and southern British Columbia accumulated in
forearc basins similar, and possibly connected, to the Ochoco Basin.
The Cretaceous rocks at Mitchell are interpreted as submarine
13.
turbidity deposits based on outcrop geometry, sedimentology, sedimentary
structures,
and facies associations.
The Gable Creek Formation
represents coarse channelized sediments deposited in a proximal base-
of-slope or inner submarine fan environment.
siltstones,
The Hudspeth mudstones,
and turbiditic sandstones represent
levee,
overbank, and
interchannel deposits associated with the Gable Creek submarine chan-
nels.
The channelized and laterally discontinuous nature of the
conglomerates makes stratigraphic correlations within the Gable Creek
Formation difficult.
14.
The stratigraphic relationship between the two Cretaceous forma-
tions at Mitchell is not a simple, intertonguing geometry, but rather a
sequence of stacked channel-levee-interchannel systems.
102
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APPENDICES
SAMPLE
MI-1
MI-2
HF-I
JC-1
JC-2
RT-1
FZ-2
MI-S
MB-1
MB-2
SP-1
RT-4
KG-S
------------------------------------------------------------ --------------------------------------------------------------
Quartz
22
IS
16
6
60
28
34
35
29
30
32
Pleploclese
16
64
Be
48
7
17
20
39
47
34
36
K-Peldspar
5l
7
8
24
27
37
37
16
10
17
16
52
14
Hornblende
2
4
8
7
0
2
S
3
6
10
2
0
2
Blotite
0
0
0
2
2
3
0
0
0
0
8
4
3
Chlorite
4
6
6
8
2
6
2
2
S
4
3
3
5
Sericite
2
1
0
1
0
2
0
1
1
1
1
1
1
Epidote
0
0
1
0
0
1
0
2
0
1
0
0
0
Opaque
2
1
1
3
1
2
1
t
2
1
1
2
1
Other
1
2
0
1
1
2
1
1
0
2
1
2
0
MI-i
MI-2
HF-I
JC-1
JC-2
RT-I
FZ-2
Appendix A.
Granite
Qtz. Monzodiorite
Qtz. Monzodiorite
Qtz. Monzopabbro
Aplite
Granite
Granite
MI-5
MB-1
MB-2
SP-1
RT-4
KG-5
Granodiorite
Granodiorite
Granodiorite
Granodiorite
K-spar Granite
Meta-Granodiorite
Modal analysis results fran plutonic rock Blasts.
30
36
38
109
Tabulated pebble count results listed by sample number
(locations shown on, Plate 1).
Appendix B.
Courthse (M-1)
SAMPLE
LOCATION: SE 1/4, Sec. 21, T. 12 S., R. 20 E. (Courthouse Rock)
lithology sample 1 sample 2 sample 3 sample 4 sample 5 average
quartzite
chert
vein qtz.
QFM phan.
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
maf. vol.
tuff
conglom.
sandstone
0
0
10
17
2
2
0
6
14
S
3
2
8
13
5
4
0
12
0
1
0
30
0
29
0
32
2
6
4
24
24
0
0
20
0
0
1
0
0
std. dev.
0.00
13.00
1.33
0.00
2.94
0.94
11.67
5.33
3.00
0.67
2.62
0.47
0.82
0.47
0.00
0.00
30.33
4.00
22.67
1.25
1.63
1.89
0.00
0.00
0.00
0.00
1
1
2
1.33
0.47
siltstone
argillite
0
0
0
2
1
limestone
0
0.00
0.82
0.00
phyllite
0
0
3
0
0.00
2.00
0.00
1
1
schist
1
0
0
gneiss
1
0
0
0.67
0.33
0.33
0.47
0.47
0.47
unknown
4
2
4
100
100
100
100.00
23
56
17
20.67
59
22
56
0.41
0.29
0.39
0.36
total
total P
total V
P/V ratio
SAMPLE E.Doolitt (M-2)
LOCATION: NW 1/4, Sec.
3, T. 12 S.,
57.00
.
20 E.
(E.
Doolittle Flat)
lithology sample 1 sample 2 sample 3 sample 4 sample 5 average std.dev.
4
2
2.60
0.80
2
2
3
quartzite
4.41
1.10
1.33
1.10
2
1
granite
4
3
0
5
3
gabbro
0
1
0
0
1
1
1
1
1
0
0
2
1
0
21
22
24
26
27
24
28
25.60
2.73
rhyolite
0
28
28
29.40
1.00
2.80
3.00
0.40
0.80
0.60
4
2
1
tuff
6
0
0
0
0
conglom.
sandstone
0
0
0
0
0
0
0
0
1
1
0
0
2
1
0
0
0
0
0
0
gneiss
0
0
24.60
3.40
0.00
0.00
0.00
0.60
0.60
0.00
0.00
0.00
0.00
2.15
maf. vol.
23
4
0
0
0
unknown
4
4
total
total P
total V
100
7
chert
vein qtz.
23
36
29
0
1
phan.
OFM
aplite
metaplut.
trachyte
siltstone
argillite
limestone
phyllite
schist
P/V ratio
0
0
0
32
3
3
1
27
1
3
4
1
0
0
0
0
0
0
0
0
0
0
0
5
4
6
100
100
100
100
6
11
6
8
0
60
49
52
52
55
0.12
0.12
0.21
0.12
0.15
100.00
7.60
53.60
0.14
0.49
0.40
0.80
1.74
0.00
0.00
0.00
0.49
0.80
0.00
0.00
0.00
0.00
110
SAMPLE: Spetch (M-3)
LOCATION: NE 1/4, Sec. 12,
lithology
T. 12 S., R. 20 E. (Spetch Rim)
sample 1 sample 2 sample 3 sample 4 sample 5 average std. dev.
quartzite
0
2
1
1.80
0.82
chart
vein qtz.
QFM phan.
granite
gabbro
17
15
0
9
13.67
3.40
1
1.00
0.82
5
9.67
4.11
6
9
8
10
0
2
1
8.00
1.00
1.63
0.82
aplite
metaplut.
trachyte
rhyolite
maf. vol.
1
1
0
0.67
0.47
4
2
0
2.00
1.63
23
33
8
27.33
4.19
2.83
4.90
0.00
0.00
0.82
0.00
tuff
conglom.
sandstone
siltstone
argillite
limestone
phyllite
schist
2
15
0
26
8
28
0
0
2
1
3
6.00
22.00
0.00
0.00
2.00
0
0
0
0
0
0.00
0
2
22
0
16
0
0
1
0
0
0
3
1.33
1.25
0
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
gneiss
0
0
0
0
unknown
5
3
5
100
26
47
100
100
100.00
22
57
16
62
21.33
55.33
0.55
0.39
0.26
0.40
total
total P
total V
P/V ratio
0
0
SAMPLE: BlkButte (M-4)
LOCATION: SW 1/4,
Sec. 31,
T. 11 S.,
R. 21
E.
(near Black Butte)
lithology sample I sample 2 sample 3 sample 4 sample S average std. dev.
4
2.06
3.40
2
1
7
3
quartzite
1.74
chart
vein Qtz.
20
OFM phan.
granite
gabbro
aplite
12
4
3
0
1
18
21
1
1
16
5
13
6
3
0
0
20
0
0
2
14
18
0
15
6
2
5
0
16
5
4
18.60
1.00
0.63
14.00
4.60
1.41
1.50
4.00
0.00
0.00
0.89
0.00
0.00
metaplut.
0
0
trachyte
rhyolite
maf. vol.
12
18
0
0
23
14
17.40
11
5
5
9
10
8.00
24
0
27
0
25
21
18
23.00
3.98
2.53
3.16
0
0
0.00
0.00
1
0
0
0
2
1
sandstone
siltstone
argillite
limestone
phyllite
1
1
2
0
1
0.80
1.90
0.75
0.63
0
0
0
0
0
0
0
0
0
0
0
0
0
schist
gneiss
0
0
0
0
0
0
0
0
0
0
0
0
0
0.00
0.00
0.00
0.00
0.00
0.00
unknown
4
3
4
5
0
5
0.00
0.00
0.00
0.00
0.00
0.00
100
100
47
25
50
0.40
0.50
100
22
53
0.42
100
19
tuft
conglom.
total
total P
total V
P/V ratio
0
0
0
22
50
0.44
100
2S
42
0.60
100.00
'
22.60
48.40
0.47
111
SAMPLE: Thomp.1 (M-5)
LOCATION: NW 1/4, Sec. 5, T. 12 S.,
R. 21
(W. Thompson Cr.)
E.
lithology sample 1 sample 2 sample 3 sample 4 sample 5 average std. dev.
quartzite
chart
vein qtz.
OFM phan.
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
mef. vol.
tuff
conglom.
5
2
3.00
2
16
13
3
15
1
1
10
8
0
10
1
5
3
9
4
2
4
2
3
0
0
0
23
0
0
23
0
18
0
25
2
24
7
9
9
11
10
27
28
0
32
31
0
0
0
3
14
0
12
3
4
0
1
it
0
0
0
0
0
0
0
0
0
0
0
gneiss
0
0
0
0
unknown
4
6
S
4
25
0
0
0
0
0
0
0
0
0
S
100
20
57
0.35
100
100
100
100
13
17
15
60
0.22
59
0.29
67
18
59
0.22
0.31
0
2
1
1
limestone
0
0
0
0
phyllite
schist
sandstone
siltstone
argillite
total
total P
total V
P/V ratio
0
0
0
0
1
0
0
0
0
0
SAMPLE: Thomp.2 (M-6)
LOCATION: SW 1/4, Sec. 6, T. 12 S.,
R. 21
chart
vein qtz.
OFM phen.
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
maf. vol.
tuff
conglom.
sandstone
siltstone
argillite
limestone
phyllite
schist
0
18
1
1
2.42
1.33
28.60
0.00
0.60
0.40
0.00
0.00
0.00
0.00
0.00
0.00
2.58
0.00
0.80
0.49
0.00
0.00
0.00
0.00
0.00
0.00
100.00
16.60
60.40
0.20
0.00
0.60
0.00
0.80
21
7
26
26
25.60
7.60
26.00
2.65
1.96
1.10
0.00
0.00
0.20
0.20
0.80
0.00
0.08
0.00
0.00
0.00
0.00
0.40
0.40
0.40
0.00
0.00
0.00
0.00
6
3
1
2
0
0
0
2
1
25
29
11
5
26
0
27
7
27
0
0
0
0
0
1
1
15
1
13
4
8
0
1
27
0
0
0
0
1
1
0
1
1
0
0
0
0
e
0
0
0
0
0
0
0
1
22.60
9.20
1
S
0
0
0.89
0.08
0.80
0
0
4
0
24
0
0
0
0
1.33
3.00
0.00
0.60
0
0
0
0
gneiss
0
e
0
0
0
unknown
3
3
4
4
4
100
100
100
lee
10e
17
21
18
22
SS
0.40
18
19.20
60
0.30
59.20
total
total P
total V
P/V ratio
60
0.28
60
0.35
0
61
0.30
1.33
0.98
1.85
0.63
1.50
0.75
1.02
15
S
2
11
3.20
1.20
14.60
1.00
12.40
4.80
1.40
13
1
0.49
4 sample S average std. dev.
3
14
13
0
12
11
1.72
0.40
9.80
(W. Thompson Cr.)
E.
lithology sample I sample 2 sample 3 sample
quartzite
1.10
13.80
0
0
100.00
0.33
112
SAMPLE: Thomp.3 (M-7)
LOCATION: SW 1/4, Sec. 7, T. 12 S.,
R. 21 E. (W. Thompson Cr.)
lithology sample 1 sample 2 sample 3 sample 4 sample S average std. dev.
0.80
0
2
1.40
2
2
1
quartzite
chart
vein
qtz.
QFM phan.
23
19
2
1
12
4
granite
gabbro
1
apllte
0
metaplut.
2
trachyte
rhyolite
17
8
mat. vol.
23
tuff
21
19
17
0
2
1
13
5
2
0
3
9
9
10
5
0
S
1
6
2
0
0
0
2
5
1
21
9
19
25
26
24
8
4
6
22
23
0
0
0
0
0
0
24
0
1
0
1
0
1
0
0
0
siltstone
0
0
2
0
1
2
limestone
0
0
phyllite
0
0
0
0
0
0
schist
0
0
4
0
0
4
0
0
5
100
100
48
100
23
49
0.40
0.47
conglom.
sandstone
ergillite
gneiss
unknown
total
total P
total V
19
P/V ratio
1
1
0
0
0
0
0
0
0
4
S
100
19
55
100
20
53
0.29
0.38
0.35
16
SAMPLE: UpSable (M-B)
LOCATION:
NW
1/4, See.
5, T. 12 S.,
0
54
19.80
1.20
10.60
5.00
1.20
0.00
2.60
22.60
7.00
22.20
2.04
0.75
1.62
0.63
0.75
0.00
1.36
3.26
1.79
0.00
0.20
0.80
0.00
1.00
0.00
0.00
0.00
0.00
0.00
0.40
0.75
0.00
0.63
0.00
0.00
0.00
0.00
1.72
100.00
19.40
51.80
0.38
R. 21 E. (E. Gable Cr.)
lithology sample 1 sample 2 sample 3 sample 4 sample 5 average std. dev.
quartzite
chart
vein qtz.
QFM phan.
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
mat. vol.
tuff
conglom.
sandstone
siltstone
3
13
1
3
2
2
2.20
0.75
15
16
22
15
2
2
1
1
0
16.20
1.20
3.06
0.75
14
13
16
15
4
3
2
2
6
4
7
0
0
0
0
0
5
0
0
5
0
17
21
13
11
10
27
S
6
33
0
3
0
0
0
0
28
0
0
0
0
0
0
0
argillite
1
1
limestone
0
0
0
schist
0
0
0
0
0
0
0
gneiss
0
0
unknown
3
0
3
100
20
58
0.34
phyllite
total
total P
total V
P/V ratio
100
24
54
0.44
34
0
1
0
0
0
0
0
14.40
1.02
0.89
0
0
3.08
5.40
0.00
0.00
16
7
31
15.60
7.00
30.60
3.44
2.45
2.73
0
0
0.00
0.20
0.20
0.00
0.60
0.00
0.00
0.00
0.00
0.00
0.40
0.40
0.00
0.49
0.00
0.00
0.00
0.00
14
4
1
0
1
0
0
0
0
0
4
0
100
25
52
100
0.48
0.46
100
23
54
0.43
3
22
48
4
100.00
22.80
S3.20
0.43
1.02
0.00
0.00
113
SAMPLE: MudCreek (M-9)
LOCATION: NE 1/4, Sec. 4, T. 12 S., R. 21 E.
lithology sample 1 sample 2 sample 3 sample 4 sample 5 average std. day.
1.60
3.20
3
2
1
5
5
quartzite
3.92
chart
vein qtz.
QFM phan.
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
mef. vol.
tuff
eonglom.
sandstone
siltstone
argillite
limestone
phyllite
schist
30
29
23
21
2
7
0
14
0
2
12
21
0
13
1
3
3
4
2
3
0
4
0
0
0
16
7
15
13
23
0
0
0
18
13
0
0
0
0
0
3
12
2
6
2
0
0
0
16
12
15
14
10
19
0
0
0
1
1
0
0
0
0
0
0
0
0
0
0
gneiss
i
unknown
4
0
4
total
total P
total V
100
1
P/V ratio
22
0
2
0
0
0
0
0
0
0
0
lithology
quartzite
chart
vein qtz.
QFM phan.
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
maf. vol.
0
0
2
2.42
1.02
1.17
0.60
0.00
0.80
0.00
15.40
11.60
19.60
2.80
3.14
0.00
0.00
0.40
0.80
0.80
0.75
0.00
0.00
0.00
0.00
0.00
0.20
0.00
0.00
0.00
0.00
0.00
0.40
0
7
5
4
100
100
100.00
19
51
19
51
0.37
0.37
18.40
46.60
0.40
12
100
20
45
41
100
22
45
0.27
0.49
0.49
1/4, Sec.
20
0.98
11.60
2.40
3.80
0
0
0
0
SAMPLE: Webers (M-10)
LOCATION: SW
0
24.80
0.80
4, T. 12 S.,
0
0
1.96
R. 21 E. (near Weber Ranch)
sample 1 sample 2 sample 3 sample 4 sample 5 average std.dev.
5
5
3
2
4
23
23
25
19
1
2
2
2
6
6
8
7
14
2
6
2
2
5
2
0
0
2
1
3
3
0
21
2
13
3
0
0
12
17
15
14
17
11
11
20
0
0
19
0
0
23
0
0
15
19
3.80
22.20
1.17
1.80
9.60
4.00
3.40
2.04
0.40
3.Z6
1.67
1.36
0.60
0.40
0.80
0.80
13
8
21
14.60
12.00
20.40
2.06
2.68
1.50
0
0
0.00
0.00
0.00
0.00
5
0
0
tuff
0
conglom.
0
sandstone
siltstone
argillite
limestone
phyllite
schist
3
1
3
2
3
2.40
0.80
0
0
0
0
0
1
1
1
1
0.00
0.40
0
0
0
0.00
0.80
0
0.20
0.40
0
0
0
0.00
0.00
0
1
0
0
0
0.00
0.00
gneiss
0
0
0
0
0
0
0
1
0
0.20
0.40
unknown
5
2
3
3
5
100
100
100
100.00
14
19
100
20
100
16
21
46
52
0.27
44
51
42
18.00
47.00
0.43
0.39
0.50
0.39
total
total P
total V
P/V ratio
0.35
114
SAMPLE: WhButte (M-11)
LOCATION: SW 1/4, See. 9, T. 12 S., R. 21 E.
(near White Butte)
lithology sample 1 sample 2 sample 3 sample
quartzite
chart
vein qtz.
QFM phan.
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
maf. vol.
4 sample S average std. day.
0.75
4
3.20
1.17
9.80
9
11
3
3
8
3
4
11
1
2
1
0
6
8
10
9
7
7
2
0
7
2
6
2
S
3
4
4
0
0
27
0
0
34
0
0
29
0
0
30
9
7
6
8
28
0
0
0
31
7
2
10
5.80
1.02
1.41
1.17
2.60
0.00
0.00
0.80
0.00
0.00
30.20
7.40
25.20
2.32
1.02
2.04
0.00
0.20
0.00
8.40
1.40
8.00
26
26
0
0
22
0
24
tuff
conglom
sandstone
siltstone
argillite
limestone
phyllite
schist
gneiss
unknown
0
0
0
1
1
2
0
3
1
1.40
1.02
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0.00
0.00
0.00
0.00
0.00
0.00
6
3
0
5
0
0
0.00
0.00
0.00
0.80
0.00
0.00
S
5
100
100
100
17
18
100
17
100
i5
64
62
0.27
0.29
total
total P
total V
P/V ratio
0
0
0
0.23
0
0
0
0
0
59
0.29
63
SAMPLE: NelsonCr (M-12)
LOCATION: NE 1/4, Sec. 2, T. 12 S.
0
0
0
15
66
0.23
100.00
16.40
62.80
0.26
R. 21 E. (E. Nelson Cr.)
lithology sample 1 sample 2 sample 3 sample 4 sample 5 average std. day.
0.75
1.80
2
1
1
2
3
quartzite
chart
vein qtz.
13
14
9
13
13
2
1
1
2
2
QFM phan.
13
5
5
14
11
7
4
6
4
0
0
0
0
22
14
10
granite
6
gabbro
6
8
6
aplite
metaplut.
trachyte
rhyolite
maf. vol.
tuff
conglom.
sandstone
0
0
25
3
20
0
4
1
siltstone
0
limestone
0
0
0
argillite
phyllite
0
0
22
6
21
0
1
3
0
0
0
1
0
21
8
23
5
25
6
19
25
0
0
0
2
4
1
1
3
0
0
5
0
0
0
0
0
0
0
0
0
0
0
0
0
schist
0
gneiss
0
0
0
0
unknown
3
6
5
5
6
total
total P
total V
100
26
48
100
24
100
27
48
100
49
100
24
54
0.54
0.49
0.44
0.S6
0.37
P/V ratio
0
0
0
19
52
12.40
1.60
12.40
6.00
5.40
0.20
0.00
22.60
5.60
22.00
0.00
1.80
3.20
0.00
0.00
0.00
0.00
0.00
0.00
100.00
24.00
50.20
0.48
1.74
0.49
1.62
1.41
0.80
0.40
0.00
1.36
1.62
2.53
0.00
1.17
1.33
0.00
0.00
0.00
0.00
0.00
0.00
115
SAMPLE: RadiotoJ (M-13)
Sec. 2,
LOCATION: SE 1/4,
lithology
quartzite
chart
vein qtz.
QFM phan.
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
mat. vol.
(Radiotower ridge)
T. 21 S., R. 21 E.
sample 1 sample 2 sample 3 sample 4 sample 5 average std. day.
3
2
1
11
17
19
1
1
7
8
7
3
7
2
2
6
8
1
3
6
2
0
0
0
0
0
0
16
tuff
conglom.
0
0
0
0
sandstone
siltstone
argillite
limestone
phyllite
schist
2
24
27
0
27
18
17
16
0
0.75
2.65
0.80
0.49
2.33
1.67
0.00
0.00
0.00
0.00
15
18
23.40
17.80
16.80
3.20
4.83
2.64
0
0.00
0.00
0.80
1.00
0.80
0.75
0.63
0.75
0.00
0.00
0.00
0.00
0.00
16
2
0
26
13
21
2.20
15.60
1.60
7.40
4.60
3.00
3
2
15
17
13
0
1
8
5
3
0
0
22
1
2
1
1
1
0
1
0
0
0
1
0
2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
gneiss
0
0
0
0
0
0
0.00
0.00
0.00
0.00
0.00
unknown
4
6
5
4
6
5.00
total
total P
total V
100
100
100
100
100
1@
13
17
i6
67
60
0.22
19
51
57
0.30
55
0.29
100.00
15.00
58.00
0.27
P/V ratio
0.15
SAMPLE: Johnson (M-14)
LOCATION: NE 1/4, Sec.
0.37
T. 21
7,
S.,
R. 22
E.
1
0
0
0
(E. Johnson Cr.)
lithology sample 1 sample 2 sample 3 sample 4 sample
quartzite
chart
vein qtz.
QFM phan.
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
mat. vol.
tuft
conglom.
sandstone
siltstone
argillite
2
2
3
10
3
12
0
4
13
12
2
11
1
0
1
0
0
26
4
23
0
25
1
1
11
S average std. day.
0.75
1.80
1
1
9
2
15
2
6
7
5
0
0
23
0
7
27
0
0
23
8
22
0
0
2
0
2
0
5
3
4
3
0
1
1
4
2
0
0
1
1
0
0
1
16
0
7
1
16
4
18
0
26
S
23
0
4
2
1
0
0
limestone
0
0
schist
8
0
0
0
gneiss
0
0
0
0
0
0
unknown
5
5
5
4
0
3
total
total P
total V
100
23
53
100
100
17
18
59
53
100
24
45
100
22
54
0.43
0.29
0.34
0.53
0.41
phyllite
P/V ratio
0
0
@
11.00
1.80
14.00
0.80
5.80
0.20
0.00
24.60
5.60
22.60
0.00
2.60
3.20
1.00
0.60
0.00
0.00
0.00
0.00
100.00
20.80
52.80
0.40
1.41
0.75
2.10
0.75
1.17
0.40
0.00
1.36
1.62
2.87
0.00
1.74
0.75
0.63
0.49
0.00
0.00
0.00
0.00
116
SAMPLE: Monroel (M-15)
LOCATION: NW 1/4, Sec. 16, T. 11 S.,
R. 22 E.
(lower
Monroe Cr.)
lithology sample 1 sample 2 sample 3 sample 4 sample 5 average std. dev.
9.33
1.25
9
8
11
quartzite
chart
vein qtz.
QFM phan.
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
maf. vol.
tuff
conglom.
sandstone
siltstone
argillite
limestone
phyllite
schist
gneiss
unknown
total
total P
total V
P/V ratio
14
0
18
0
17
0
lithology
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
m4f. vol.
0.00
1.70
0.00
1
2
1
1.33
6
4
5
1
0
0.47
0.82
0.47
0
0
0
0
5.00
0.33
0
33
0
12
19
0
2
0
0
0
32
13
16
0
0
0
0
31
0.00
0.00
0.00
0.00
32.00
0.82
11
12.00
0.82
20
0
18.33
1.70
0.00
0.00
1
1.00
0.82
0
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0
0
0
0
0
0
0
0
0
0
0
0
0
4
4
0
5
100
100
100
100.00
8
6
6
64
0.13
61
62
0.10
0.10
6.67
62.33
0.11
0
0
SAMPLE: Monroe2 (M-16)
LOCATION: NE 1/4, Sec. 16, T. 11 S.,
quartzite
chart
vein qtz.
QFM phan.
16.33
R. 22 E. (lower Monroe Cr.)
sample 1 sample 2 sample 3 sample 4 sample S average std. dev.
1
1.33
0.47
15
0
13
17
0
8
16
16.00
0.82
1
2
6
3
6
0
3
0
0.47
2.05
1.70
1.25
0
25
0
4
0
0
0.33
10.33
3.67
4.33
0.00
0.00
0.00
0.00
29
26
26.67
1.70
7
25
5
26
0
0
0.94
0.82
0.00
0.00
0.00
2
1
10
conglom.
1
1
1
sandstone
0
0
1
0
0
6.33
26.00
0.00
1.00
0.00
0
0.33
0.47
argillite
0
0
limestone
0
0
0
0
phyIlite
schist
0
0
0
0
0
gneiss
0
0
0
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
unknown
3
4
4
100
100
100
21
17
17
18.33
57
0.37
60
60
0.28
59.00
tuff
siltstone
total
total P
total V
P/V ratio
7
0.28
27
0
0
100.00
0.31
117
SAMPLE: UpMonroe (M-17)
LOCATION: NW 1/4, Sec. 22, T. 11 S.,
R. 22
E.
(
upper Monroe Cr.)
lithology sample 1 sample 2 sample 3 sample
quartzite
chart
vein qtz.
QFM phan.
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
mef. vol.
tuff
conglom.
sandstone
siltstone
argillite
limestone
phyllite
schist
gneiss
unknown
total
total P
total V
P/V ratio
1
13
2
1
12
16
1
1
8
2
14
7
2
1
1
0
25
2
1
19
8
4 sample 5-average std. dev.
1.40
0.49
2
15
13.60
1.62
12
0.40
2
1.20
1
3.83
11
12.40
10
6
6.20
1.17
5
1
5
1
1
2
1.60
0.49
0
0
28
0
0
0.40
0.49
1
0
30
0.60
0.80
27.60
7.60
1.62
1.36
21.60
0.00
0.00
0.80
0.00
0.00
0.00
0.00
0.00
0.00
2.58
0.00
0.00
0.98
0.00
0.00
0.00
0.00
0.00
0.00
23
0
0
28
7
26
0
0
2
2
0
0
0
0
0
0
S
0
0
0
0
0
0
S
100
30
100
26
51
0.59
.27
7
20
6
20
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
4
0
10
0
0
0
8
19
0
0
0
0
0
0
6
5
100
100
100
100.00
17
61
19
21.20
54
14
61
57
0.48
0.23
0.28
0.33
56.80
0.38
SAMPLE: Mitchell (M-18)
LOCATION: SW 1/4, Sec. 36, T. 11 S., R. 21
E.
(near Mitchell)
lithology sample l sample 2 sample 3 sample 4 sample S average std. dev.
quartzite
chart
vein qtz.
QFM phan.
4
3
3
2
1
2.60
1.02
12
14
11
15
14
13.20
1.47
1
0
1
1
15
4
3
12
2
13
6
13
4
1.00
13.00
2
`1
0.63
1.10
0.80
0.89
0.49
0.49
12
granite
5
gabbro
1
aplite
metaplut.
trachyte
rhyolite
m8f. vol.
tuff
conglom.
0
1
27
6
27
0
1
0
25
0
5
24
0
0
siltstone
0
0
0
ergillite
0
limestone
0
phyllite
0
schist
sandstone
1
0
0
0
0
0
gneiss
0
0
unknown
4
5
100
100
19
23
total
total P
total V
P/V ratio
4
3
0
1
24
6
27
0
0
2
0
0
0
0
0
8
6
60
54
100
20
57
0.32
0.43
0.35
1
0
23
S
25
0
1
0
26
8
23
1
1
0
0
0
1
0
0
0
0
0
0
0
5
100
22
S3
0.42
0
0
0
0
6
100
19
58
0.33
4.60
2.00
0.60
0.40
25.00
6.00
25.20
0.20
0.00
0.80
0.20
0.08
0.00
0.00
0.00
0.00
100.00
20.60
S6.40
0.37
1.41
1.10
1.60
0.40
0.00
0.75
0.40
0.00
0.00
0.00
0.00
0.00
118
SAMPLE: Marshall (M-19)
LOCATION: NW 1/4, See. 33,
lithology
quartzite
chert
vein qtz.
QFM phan.
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
mat. vol.
T. 11 S., R. 22 E. (E. Marshall Butte)
sample 1 sample 2 sample 3 sample 4 sample 5 average std. dev.
3
15
2
12
3
17
3
17
3
2
18
2
11
11
10
3
0
1
1
4
2
1
. 4
2
1
2
1
0
0
2
1
14
1
14
0
1
28
10
22
0
0
26
9
1
23
5
25
0
0
2
2.20
16.20
2.20
11.60
2.20
1.60
1.00
0.75
1.47
0.75
1.36
1.17
1.36
0.89
0.60
0.49
25.20
9.00
22.40
2.10
0
0.00
0.00
0.00
0.00
0
1
25
24
11
10
21
1.72
1.50
1
21
0
0
0
0
0.20
1
1
1
2
1.40
0
0
0
0
2
1
1
0.80
0
0
0
0
0
0
0.40
0.49
0.75
0
gneiss
0
0
0
0
0
0
0
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
unknown
3
3
4
3
4
100
19
60
100
100
100
100
100.00
16
17
17
16
17.00
58
0.28
57
0.30
S5
0.32
53
0.32
56.60
0.30
23
sandstone
slltstone
argillite
limestone
phyllite
schist
0
0
0
0
2
tuff
conglom.
total
total P
total V
P/V ratio
0
0
0
0
0
8.29
SAMPLE: Up6irds (M-20)
LOCATION: NW 1/4, Sec. 13, T. 11 S., R. 22 E. (upper Girds Cr.)
lithology sample 1 sample'2 sample 3 sample 4 sample 5 average std. dev.
0.00
1.00
1
1
1
quartzite
chart
vein qtz.
QFM phan.
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
met. vol.
tuff
conglom.
sandstone
siltstone
argillite
20
12
16
1
11
2
11
10
8
5
2
1
2
1
1
0
1
1
1
1
19
10
20
29
28
0
0
0
0
0
0
1
1
2
0
23
8
28
0
1
10
0
0
2
0
16.00
1.33
10.67
5.00
1.33
0.67
3.27
0.47
0.47
2.45
0.47
0.47
1.00
0.00
20.67
9.33
28.33
1.70
0.94
0.47
0.00
0.00
0.00
0.00
0.00
0.00
1.33
0.67
0.47
0.94
0.00
0.00
0.00
0.00
0.00
8.00
0.00
0.00
limestone
0
0
phyllite
schist
0
0
0
0
0
0
0
gneiss
0
0
0
unknown
2
3
3
total
total P
total V
100
100
100
100.00
22
19
15
59
0.37
58
0.33
58
0.26
18.67
58.33
0.32
P/V ratio
119
SAMPLE: Narrows (M-21)
LOCATION: SE 1/4, Sec. 21, T. 11 S., R. 21
lithology
E.
(N. Narrows)
sample 1 sample 2 sample 3 sample 4 sample S average std. dev.
9
5
6
6
4
22
0
7
20
25
0
20
29
2
11
11
2
9
4
5
0
0
21
12
19
0
5
5
8
0
15
10
11
conglom.
0
0
sandstone
siltstone
argillite
limestone
phyllite
schist
gneiss
unknown
0
1
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
@
0
5
4
5
6
6
i@0
100
100
21
19
52
48
0.44
44
100
19
47
100
12
0.43
0.40
quartzite
chart
vein qtz.
OFM phan.
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
mat. vol.
tuff
total
total P
total V
P/V ratio
1
0.23
1
23
0
3
0
0
14
19
6.00
23.20
1.67
3.43
0.89
2.04
5
5
0
0
2
1.00
10.20
4.20
4
3.60
1.17
1.50
0
0
0.00
0.00
0.00
0.00
18
12
17
14
12
14
15.80
12.00
18.40
3.43
1.26
2.94
0
0
0
0
0.00
0.00
0.20
0.00
0.00
0.20
0.00
0.00
0.00
0.00
0.00
0
0
0
0
13
0
0
0
0
0
0
0
0
19
40
0.48
@.4@
0.00
0.00
0.40
0.00
0.00
0.00
100.00
18.00
46.20
8.40
RipUp (M-22)
SAMPLE:
LOCATION: SE 1/4, Sec. 21, T. 11 S., R. 21
E.
(Rip-up Gulch)
lithology sample 1 sample 2 sample 3 sample 4 sample 5 average
3
14
2
15
2
1
0
6
7
6
5
0
7
5
1
2
quartzite
chart
vein qtz.
5
14
0
3
16
3
14
2
OFM phan.
6
granite
4
6
4
gabbro
0
1
1
1
1
0
0
33
aplite
metaplut.
trachyte
rhyolite
met. vol.
tuff
0
35
10
20
0
32
i5
16
0
14
14
0
0
0
32
16
18
0
0
0
0
31
13
19
0
0
0.98
0.80
0.89
0.40
1.10
0.49
0.63
0.00
1.36
2.06
17.40
2.15
0.00
0.00
0.80
0.00
0.00
0.00
6.00
0.00
0.00
0.00
0.00
0.75
0.00
0.00
0.00
0.00
0.00
0.00
schist
0
0
0
0
0
0
0
0
gneiss
0
0
0
0
0
0
0
0
unknown
5
4
0
0
0
0
0
5
100
100
100
100
100
11
12
12
14
65
0.17
63
0.19
14
61
66
63
100.00
12.60
63.60
0.23
0.18
0.22
0.20
conglom.
sandstone
siltstone
argillite
limestone
phyllite
total
total P
total V
P/V ratio
0
1
1
2
0
0
0
0
0
0
0
3
0
0
0
0
0
0
std. dev.
3.20
14.60
1.00
6.20
5.00
0.40
1.00
0.00
32.60
13.60
4
120
SAMPLE: BridgeCr (M-23)
LOCATION: SE 1/4, Sec.
13, T. 11 S., R. 21 E. (lower Bridge Cr.)
lithology sample 1 sample 2 sample 3 sample 4 sample S average std. dev.
Quartzite
chart
vein qtz.
OFM phan.
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
4
5
3
29
27
0
4
1
23
0
3
3
1
3
6
0
0
2
0
1
0
17
15
0
0
0
23
33
15
14
maf. vol.
21
1
1
12
12
0
conglom.
sandstone
0
0
0
2
2
0
0
0
tuff
siltstona
0
0
limestone
0
schist
0
0
gneiss
argillite
1
0
0
0
0
0
0
0
0
unknown
6
4
6
total
total P
total V
100
5
100
100
8
10
54
53
57
0.09
0.15
0.18
phyllite
P/V ratio
0
0
SAMPLE: Meyersl (M-24)
LOCATION: SW 1/4, Sec.
14, T. 11 S.,
4.00
26.33
0.33
3.33
3.33
1.00
0.00
0.00
24.33
14.00
15.67
0.67
0.00
1.67
0.00
0.00
0.00
0.00
0.00
0.00
0.82
2.49
0.47
0.47
2.05
0.82
0.00
0.00
6.60
1.41
3.86
0.47
0.00
0.47
0.00
0.00
0.00
0.00
0.00
0.00
100.00
7.67
54.67
0.14
R. 21 E. (5. Meyers Canyon)
lithology sample 1 sample 2 sample 3 sample 4 sample 5 average std. dev.
Quartzite
chart
vein qtz.
OFM phan.
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
maf. vol.
1
3
18
2
2.00
0.82
1.25
0.47
1.70
11
7
8
19.33
0.67
8.67
4
6
5
5.00
0.82
3
3
2
2.67
0.47
0
0
27
0
0
0
0
26
0.00
0.00
0.00
0.00
25.67
7.33
21.33
1.25
0.94
0
0.00
0.00
0.00
0.00
2
2
1
1.67
0.47
1
1.00
0
0
0.00
0.82
0.00
0
0
0
0.33'
0.47
0.00
0.00
0.00
0.00
0.00
0.00
21
1
8
17
1
24
6
24
0
0
19
0
8
23
0
tuff
conglom.
0
sandstone
2
argillite
limestone
0
0
0
phyllite
schist
0
0
gneiss
0
0
0
0
unknown
5
3
0
5
100
100
100
100.00
18
16
15
S2
54
57
16.33
54.33
0.35
0.30
0.26
0.30
siltstone
total
total P
total V
P/V ratio
0
1
3.09
121
SAMPLE: Meyers2 (M-25)
LOCATION: NW 1/4, See. 14, T.
11 S.,
R. 21
E.
(Meyers Canyon)
lithology sample 1 sample 2 sample 3 sample 4 sample S average std. dev.
0.47
2
2.67
3
3
quartzite
chart
vein qtz.
QFM phan.
Granite
gabbro
aplite
meteplut.
trachyte
13
0
14
6
4
0
0
19
20
1
1
7
8
4
6
3
2
1
0
maf. vol.
8
18
20
0
0
0
0
conglom.
sandstone
0
1
siltstone
0
0
1
schist
0
0
0
0
0
0
5
0
limestone
0
0
0
tuft
argillite
phyllite
11
0
25
7
23
0
0
0
0
8
0
4
gneiss
0
unknown
5
total
total P
total V
100
24
55
100
100
15
16
57
55
0.44
0.26
0.29
P/V ratio
0.67
9.67
5.33
3.00
0.33
0.00
26.67
8.67
20.33
0.00
0.00
0.33
0.33
0.00
0.00
0.00
0.00
0.00
0
29
0
26
rhyolite
17.33
3.09
0.47
3.09
0.94
0.82
0.47
0.00
1.70
1.70
2.05
0.00
0.00
0.47
0.47
0.00
0.00
0.00
0.00
0.00
100.00
18.33
55.67
0.33
SAMPLE: SheepCmp (M-26)
LOCATION: SE 1/4, Sec. 7, T. 11 S., R. 21 E. (near Sheep Camp)
lithology sample 1 sample 2 sample
quartzite
chart
vein qtz.
QFM phan.
granite
gabbro
aplite
1
0
0.80
0.75
45
48
49.20
2
1
2
3
1
1.80
2.48
0.75
3
5
10
9
7
1
2
1
1
6.80
1.40
0.80
1.00
0.00
2.56
0.49
0.75
0.63
0.00
50
0
1
0
trachyte
rhyolite
10
19
8
0
0
1
0
1
2
1
1
0
0
0
14
8
13
14
3
14
14
15
12
13.20
1.72
13.40
3.56
5
2.42
0
7
0
0
6.60
0
0
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
siltstone
0
0
argillite
0
limestone
0
phyllite
0
schist
gneiss
0
8
unknown
5
conglom.
sandstone
total
total P
total V
P/V ratio
2
2
0
0
10
0
0
0
0
0
0
0
0
0
tuft
sample 4 sample 5 average std. dev.
51
2
mataplut.
maf. vol.
3
0
52
1
0
0
0
0
0
0
0
0
0
0
6
3
6
5
100
100
100
100
100
100.00
5
8
13
12
12
10.00
37
0.14
32
30
0.43
33
34
33.20
0.36
0.35
0.31
0.25
0
0
0
0
0
0
0
0
0
0
0
0
122
SAMPLE: SheepCyn (M-27)
LOCATION: W 1/2. Sec. 7,
T. 11 S., R. 21 E.
lithology sample 1 sample 2 sample 3 sample 4 sample S average std. dev.
0.75
0.80
2
0
1
1
0
quartzite
0
44.20
2.40
7.80
2.00
0.80
3.66
1.02
1.47
0.63
0.49
0
0.40
0.49
0
0.00
0.00
15
S
17
16.00
6.20
13.60
1.41
0
0
0
0.00
0.00
0.00
0.00
50
43
46
43
39
vein qtz.
1
2
3
QFM phan.
7
2
6
2
0
7
1
9
2
4
10
1
1
1
1
0
0
0
0
16
17
10
10
0
0
14
chart
granite
3
gebbro
aplite
metaplut.
trachyte
rhyolite
maf. vol.
1
tuff
conglom.
sandstone
siltstone
argillite
limestone
phyllite
schist
gneiss
unknown
total
total P
total V
P/V ratio
0
0
18
3
7
15
12
8
0
0
0
6
14
0
2
2.32
2.42
1
2
0
2
1
1.20
0.76
0
0
0
0
0
0
0
0
0
0
0.00
0.00
0
0
0
0
0
@.00
0
0
0
0
0
0
0
0
0
5
0
0.00
0.00
0.00
4
0
0
6
0
0
0
0.00
0.00
0.00
0.00
0.00
0.00
100
100
100
9
12
12
33
0.33
38
100
10
37
100
11
34
0.24
0.27
0.35
37
0.32
4
5
100.00
10.80
35.80
0.30
SAMPLE: UpSheep (M-28)
LOCATION:
SW 1/4, Sec. 6, T. 11 S., R. 22 E.
lithology sample 1 sample 2 sample 3 sample 4 sample 5 average
std. dev.
0
1
2
1.00
0.82
63
55
54
57.33
1
1
2
1.33
4.03
0.47
0
0
0
0
0
0.00
0.00
granite
1
0.33
0.47
gabbro
0
2
0
aplite
1
1
1
0
0.67
1.00
0.00
0.94
0.00
0.00
11.00
23.67
2.45
2.87
0.00
0.00
0.00
0.00
0.00
0.00
0.33
0.47
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.08
0.00
0.00
Quartzite
chart
vein ptz.
QFM phan.
metaplut.
0
0
trachyte
rhyolite
11
14
8
20
0
0
0
24
0
0
0
0
0
0
27
0
0
0
0
0
0
0
0
0
0
0
0
0
0
maf. vol.
tuff
conglom.
sandstone
siltstone
1
gneiss
0
0
0
0
0
0
unknown
3
2
5
total
total P
total V
100
argillite
limestone
phyllite
schist
P/V ratio
100.00
100
100
1
3
2
2.00
31
38
35
34.67
0.03
0.08
0.06
0.06
123
SAMPLE: TonyButte (M-29)
LOCATION: NE 1/4, Sec. 3, T.
11 S.,
R. 22
E.
(near Green Hollow)
lithology sample 1 sample 2 sample 3 sample .4 sample S average std. dev.
1.70
2.67
2
1
5
quartzite
chart
29
vein qtz.
31
0
1
QFM phan.
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
mat. vol.
tuft
conglom.
sandstone
siltstone
argillite
limestone
phyllite
schist
2
3
1
3
0
0
1
1
0
39
0
31
12
7
0
12
8
0
25
2
0
4
0
0
0
28.33
1.00
2.49
0.82
1.00
3.33
0.33
0.33
0.82
0.47
0.47
0.47
0.00
0.00
11
35.33
13.33
8.67
3.30
1.89
1.70
0
0
0.00
0.00
0.00
0.00
0.67
0.67
0.47
0.94
36
16
0
0
1
0
1
2
0
0
0
0
0.00
0.00
1
0.33
0.47
0
0
0
0
0
0.00
0.00
0.00
0.00
0.00
0.00
0
0
0
0
gneiss
0
0
0
unknown
5
4
3
100
100
100
100.00
7
4
4
50
0.14
59
63
5.00
57.33
0.07
0.06
0.09
total
total P
total V
P/V ratio
SAMPLE: Cherry (M-30)
LOCATION:
SW
1/4,
Sec. 34,
T. 10 S., R. 22 E. (near Cherry Ranch)
lithology sample 1 sample 2 sample 3 sample 4 sample 5 average std. dev.
0.47
2
2
1.67
54
57
57
56.00
1.41
vein
4
1
4
0
4
2
4.00
1.00
granite
2
1
0
gabbro
1
0
1.00
0.33
0
0
0
0.00
0.82
0.82
0.47
1
0
0
0.33
0.33
0.47
0.47
9.00
0.82
16.67
1.25
0.82
0.00
0.00
0.00
0.82
0.00
0.00
0.00
Quartzite
chart
qtz.
QFM phan.
aplite
meteplut.
trachyte
rhyolite
mat. vol.
tuft
conglom.
sandstone
siltstone
argillite
limestone
phyllite
1
1
9
10
15
I8
8
17
5
0
0
3
4
0
0
0
0
0
0
0
0
0
0
1
0
0
0
4.00
0.00
0.00
0.00
1.00
0.00
0.00
0.00
1
0
0.33
8.47
0
0
0.00
0.00
0
2
8
0
gneiss
0
0
0
unknown
6
4
3
100
100
100
schist
total
total
P
total V
P/V ratio
5
29
0.17
3
100.00
3.00
31
29
29.67
0.03
0.10
0.10
1
124
SAMPLE: Moodoos (M-31)
Sec. 32, T. 10 S., R. 22
LOCATION: SE 1/4,
E.
(along Girds Cr.)
lithology sample 1 sample 2 sample 3 sample 4 sample S overage std. dev.
0.63
3
3.00
4
3
3
2
quartzite
chart
0
53.80
1.40
0.00
3.71
1.20
0.00
2
2.00
0.63
0
0.00
0.00
1
1
0.80
0.40
0
0
0
0.00
0.00
6
8
6
28
26
0
6.20
25.80
0.20
1.33
3.71
0.40
0.60
0.00
0.80
0.00
0.20
0.60
0.40
0.49
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
51
2
0
50
0
0
1
2
0
0
0
1
0
1
0
0
4
31
7
20
52
60
vein qtz.
0
2
56
3
QFM phan.
0
0
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
maf. vol.
3
2
0
0
0
tuff
conglom.
sandstone
2
0
0
0
0
0
24
0
0
0
0
siltstone
argillite
limestone
phyllite
schist
gneiss
unknown
0
1
1
0
0
0
0
0
0
0
0
0
0
8
S
5
0
0
0
4
100
100
4
2
37
0.11
27
0.07
30
0.07
total
total P
total V
P/V ratio
0
1
0
0
0
0
1
0
0
1
1
0
0
0
0
0
0
0
7
6
100
180
2
3
37
100
3
33
100.00
2.80
32.80
0.08
0.09
0.08
0
0
SAMPLE: GordyFlat (M-32)
LOCATION: SE 1/4, Sec. 23, T. 10 S., R. 22 E. (Gordy Flat)
lithology
quartzite
sample 1 sample 2 sample 3 sample 4 sample S average std. dev.
4
14
3.67
14.33
0.47
1.25
0
3
4
0
5
0.00
0.00
2
4
1
1
3
0
1
1
3
4
13
16
0
granite
2
3
gabbro
chart
vein qtz.
QFM phan.
aplite
metaplut.
trachyte
rhyolite
maf. vol.
tuff
2
0
28
3.33
1.25
3.00
3.00
0.82
0.82
0.67
0.67
28.33
9.67
0.47
0.47
2.05
1.70
28.00
0.00
0.00
0.00
0.00
1.00
0.00
0.00
0.00
0.00
1.41
26
ailtstone
31
9
30
0
0
0
0
argillite
1
1
1
limestone
0
0
phyllite
schist
gneiss
0
0
0
unknown
4
0
0
0
5
0
0
0
100
100
100
9
13
10
10.67
70
61
0.21
67
66.00
0.16
conglom.
sandstone
total
total P
total V
P/V ratio
0.13
8
27
0
0
0
0
12
27
0
0
0
0
0
4
0.15
100.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
125
SAMPLE: Antone
LOCATION: NE 1/4 of T. 13 S., R. 24
lithology
quartzite
chart
vein qtz.
QFM phan.
granite
gabbro
Oregon)
Ranch,
sample 1 sample 2 sample 3 sample 4 sample 5 average std.dev.
1.41
2
2.00
30.00
1.20
0
0.60
0.49
8
4.40
2.06
0
0
0
44
7
0.00
0.00
0.00
0.00
0.00
0.00
46.00
8.00
1
2
4
0
3
28
31
0
30
34
27
1
1
0
3
1
1
1
2
4
0
0
0
0
0
49
0
47
8
0
0
0
43
8
5
0
0
0
47
8
2
aplite
meteplut.
trachyte
rhyolite
maf. vol.
E. (Antone
2
1
1
0
1
1.00
2.19
0.63
0.63
0
0
0
0
0
0
0
0
0
0
0.00
0.00
0.00
0.00
9
tuff
conglom.
sandstone
2.45
0.75
1
1
2
2
3
1.80
0.75
siltatone
argillite
0
0
0
0
0.00
0.00
1
2
1
1.40
1.02
limestone
0
0
phyllite
gneiss
0
0
0
0
0
schist
0
0
0
0
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
unknown
4
3
0
0
0
0
3
0
0
0
2
4
total
total P
total V
100
3
Be
100
100
100
6
8
56
100
5
52
55
52
0.05
0.05
0.10
0.11
0.15
P/V ratio
0
0
5
3
SAMPLE: Bernard
LOCATION:
East half
of T. 17
S., R. 24
E.
0
0
100.00
5.00
55.00
0.09
(Bernard Ranch)
lithology sample 1 sample 2 sample 3 sample 4 sample 5 average std. dev.
quartzite
3
2
1
1
2
14
9
11
vein qtz.
0
1
9
0
1
10
0
phan.
12
8
9
12
chart
QFM
granite.
gabbro
aplite
11
4
3
0
6
13
13
8
15
4
2
2
3
1
1
2
0
0
30
3
0
29
21
22
0
0
1
0
trachyte
25
3
0
31
maf. vol.
3
19
20
metaplut.
rhyolite
32
4
0
0
0
conglom.
0
3
22
0
0
sandstone
0
1
4
2
2
2
2
1
1
1
0
0
0
0
1
0
0
0
0
0
0
0
3
tuff
siltstone
argillite
limestone
S
1
0
0
0
unknown
0
4
0
0
0
0
2
4
total
total P
total V
100
30
47
100
26
56
100
24
57
100
54
100
26
55
0.64
0.46
0.42
0.48
0.47
phyllite
schist
gneiss
P/V ratio
0
0
26
0
0
1.80
10.60
0.40
8.60
12.80
3.00
2.00
0.00
29.40
3.60
20.80
0.00
0.20
1.80
1.40
0.40
0.00
0.00.
0.00
0.00
3
100.00
26.40
53.80
0.50
0.75
1.85
0.49
1.96
1.33
0.09
0.89
0.00
2.42
0.80
1.17
0.00
0.40
1.33
0.49
0.49
0.00
0.00
0.00
0.00
126
SAMPLE: Goose
LOCATION: SW 1/4 of T.
lithology
S., R. 24
11
E.
(Goose Rock)
sample 1 sample 2 sample 3 sample 4 sample 5 average std.dev.
quartzite
3
2
3
1
3
2.40
0.80
chart
vein qtz.
QFM phan.
granite
gabbro
aplite
31
0
37
28
38
34
33.60
3.72
1
1
1
0
0
0
0
0
0.60
0.00
0.49
0.00
3
4
4
2
3.20
0.75
0
0
0
0
0
metaplut.
0
36
14
0
0
37
0
0
trachyte
rhyolite
maf. vol.
0.00
0.00
0.00
33.80
15.60
2.20
2.32
1.02
0.75
1
0
0
0
0
0
0
0
0.00
0.00
0.00
0.00
1
1
0.80
0.75
2
2
2
2.60
0.80
2
1
2
3
0
1
1.20
0.75
0
0
0
0
8
0
0
0
0
0
0
0
0
0
0
0
0
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
4
4
4
5
100
100
100
100
100
100.00
3
4
4
2
52
49
56
50
3
51
3.20
51.60
0.06
0.08
0.07
0.04
0.06
0.06
sandstone
siltstone
argillite
limestone
phyllite
schist
2
4
gneiss
0
3
total P
total V
P/V ratio
0.00
0.00
0.00
0
0
0
2
0
total
0
32
17
0
0
0
33
16
2
tuff
conglom.
unknown
0
31
15
3
0
3
0
0
0
SAMPLE: MtnCreek
LOCATION: NW 1/4 of T. 12 S.,
16
3
R. 25 E. (Mountain Creek)
lithology sample i sample 2 sample 3 sample 4 sample S average std. dev.
Quartzite
chart
vein
1
0
1
54
46
49
0.67
49.67
0.47
3.30
13.00
1.00
2.16
0.00
qtz.
12
16
11
OFM phan.
1
1
1
granite
1
1
2
1.33
0.47
gabbro
0
0
0
0
metaplut.
0
0
0
0
8.00
0.00
0.00
0.00
0.00
0.00
9
15
12
16
11
maf. vol.
10.67
15.00
1.25
14
3
6
4.67
1.25
tuff
conglom.
0
5
0
0
0
0
0.00
0.00
0.00
0.00
1
0.67
0.47
0
0.00
0.00
0.00
0.00
0.80
0.00
0.00
0.00
0.00
0.00
0.00
0.00
aplita
trachyte
rhyolite
sandstone
0
1
siltstone
ergillite
0
limestone
0
phyllite
0
schist
0
0
0
0
gneiss
0
0
0
0
0
0
unknown
3
3
4
100
100
100
100.00
2
2
27
33
3
31
2.33
30.33
0.07
0.06
0.10
0.08
total
total P
total V
P/V ratio
0
0
0
0
0
0
0.82
127
Mean values of pebble count results at each sale site.
AMerylix C.
Lith.
quartzite
Courthse
0.00
chart
vein qtz
QFM phan
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
maf. vol.
13.00
1.33
11.67
5.33
3.00
0.67
0.00
30.33
4.00
22.67
conglom
0.00
0.00
sandstone
1.33
siltstone
argillite
limestone
phyllite
schist
0.00
2.00
0.00
tuff
gneiss
Lith.
quartzite
chart
vein qtz
OFM phan
granite
gabbro
aplite
0.67
0.33
0.33
0.40
trachyte
14.60
12.00
20.40
maf. vol.
tuff
conglom
sandstone
siltstone
argillite
limestone
phyllite
schist
gneiss
Gordy
Cherry
UpSheep
3.20
14.60
1.00
6.20
5.00
0.40
1.00
0.00
32.60
13.60
3.67
14.33
1.67
56.00
1.00
0.00
4.00
1.33
3.33
1.00
0.00
3.00
3.00
1.00
0.33
0.33
0.67
0.67
0.67
0.33
17.40
0.00
0.00
0.80
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
2.40
0.00
0.80
0.20
0.00
0.00
0.23
57.33
28.33
0.33
9.00
1.00
0.00
11.00
9.67
16.67
23.67
28.00
0.00
0.00
0.00
0.00
1.00
0.00
0.00
4.00
0.00
0.00
0.00
1.00
0.00
0.00
0.00
0.00
0.33
0.00
0.00
0.00
0.00
0.00
0.33
0.00
0.00
0.00
0.00
0.00
0.00
UpGirds MtnCreek
1.00
16.00
1.33
10.67
5.00
0.67
49.67
13.00
1.00
1.33
1.33
0.67
1.00
0.00
0.00
0.00
20.67
9.33
28.33
10.67
15.00
4.67
0.00
0.00
0.00
1.33
0.67
0.00
0.00
0.00
0.00
0.00
0.00
0.67
0.00
0.00
0.00
0.00
0.00
0.00
WhButte BridgeCr Monroel Monroe2 TonyBut
1.50
2.67
4.00
9.50
3.20
16:00
28.33
16.00
26.33
9.80
0.00
1.00
0.00
0.33
1.40
10.50
1.00
1.50
3.33
8.00
4.00
3.33
5.00
3.33
5.80
4.50
0.33
0.50
1.00
2.60
0.00
0.33
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
35.33
32.50
27.00
24.33
30.20
22.60
6.00
13.33
12.50
14.30
7.40
5.60
8.67
25.50
17.50
15.67
25.20
22.00
0.00
0.00
0.00
0.67
0.00
0.00
0.00
1.00
1.00
0.00
0.20
1.80
0.67
0.00
0.00
1.57
1.40
3.20
0.67
0.00
0.50
0.00
0.00
0.00
0.00
0.00
0.30
0.00
0.00
0.00
0.33
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.33
0.00
0.00
0.00
0.00
0.03
0.30
0.00
0.00
0.00
0.00
0.00
0.00
0.30
Webers NelsonCr
1.80
3.80
12.40
22.20
1.60
1.80
9.60
12.40
6.00
4.00
5.40
3.40
0.20
0.60
metaplut.
rhyolite
RipUp
128
Appendix C (Omt. )
Lith.
quartzite
Courthse
0.00
RipUp
3.20
chart
vein qtz
OFM phan
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
maf. vol.
tuff
13.00
1.33
11.67
5.33
3.00
0.67
0.00
30.33
4.00
22.67
0.00
14.60
conglom
0.00
sandstone
siltstone
argillite
0.00
1.33
2.00
limestone
0.00
phyllite
schist
0.67
0.33
gneiss
0.33
Lith.
quartzite
chart
vein qt:
OFM phan
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
mar. vol.
tuff
conglon
sandstone
siltstone
argillite
limestone
phyllite
schist
gneiss
1.00
6.20
5.00
0.40
1.00
0.00
32.60
13.60
17.40
0.00
0.00
0.80
0.00
0.00
0.00
0.00
0.00
0.00
Webers NelsonCr
1.80
3.80
Cherry
UpSheep
3.67
14.33
1.67
56.00
1.00
57.33
0.00
4.00
1.33
3.33
1.00
0.00
10.67
1.00
3.00
3.00
1.00
0.33
0.33
0.67
0.67
0.67
0.33
0.33
5.00
1.33
0.67
1.00
1.33
0.00
0.00
0.00
28.33
9.00
1.00
0.00
11.00
20.67
10.67
9.67
16.67
23.67
9.33
15.00
28.00
0.00
0.00
0.00
0.00
1.00
0.00
0.00
4.00
0.00
0.00
0.00
28.33
4.67
0.00
0.00
0.00
1.33
0.67
0.00
0.00
0.33
0.00
0.00
0.00
0.00
0.00
0.33
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.67
0.00
0.00
0.00
0.00
0.00
0.00
1.00
0.00
0.00
0.00
0.00
0.00
0.00
WhButte BridgeCr
4.00
3.20
26.33
9.80
0.33
1.40
Monroel
Monroe2
7onyBut
9.50
1.50
16.00
2.67
28.33
0.00
8.00
5.80
2.60
3.33
3.33
1.00
1.50
10.50
1.00
1.00
5.00
0.50
0.00
0.00
0.00
0.00
0.00
0.00
4.00
4.50
0.00
3.33
0.33
0.33
24.33
14.00
15.67
0.67
32.50
12.50
17.50
0.00
0.00
1.00
16.00
0.00
1.80
9.60
12.40
1.60
12.40
4.00
6.00
3.40
0.60
5.40
0.20
0.40
0.00
14.60
12.00
20.40
22.60
5.60
22.00
30.20
7.40
0.00
0.00
0.00
0.00
2.40
1.80
3.20
1.40
1.57
0.00
0.00
0.80
0.20
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.23
0.00
0.00
0.00
0.30
0.00
0.00
0.00
0.00
0.03
0.00
0.00
0.00
22.20
UpGirds MtnCreek
1.00
0.67
49.67
16.00
1.33
13.00
Gordy
25.210
0.0
0.00
0.00
27.00
6.00
25.50
35.33
13.33
8.67
0.00
1.00
0.00
0.00
0.00
0.50
0.67
0.67
0.00
0.00
0.00
0.33
0.00
0.00
0.00
0.00
0.00
0.20
129
Lith.
quartzite
chart
vein qtz
QFM phan
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
maf. vol.
tuff
conglom
Meyers2
2.00
3.00
19.50
16.00
1.20
14.40
1.00
9.00
5.00
3.00
0.00
0.00
0.50
1.40
1.00
1.00
0.80
10.50
5.00
3.50
0.50
0.00
0.00
13.00
2.00
0.00
0.80
0.00
4.60
2.00
0.60
0.40
9.67
8.00
11.60
2.40
1.00
0.67
2.00
3.80
0.60
0.00
25.50
27.50
6.20
25.00
7.00
20.50
0.00
0.00
2.00
1.00
0.00
0.50
0.00
0.00
0.00
9.50
19.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
25.80
0.20
0.60
0.00
0.20
0.60
0.00
0.00
0.00
0.00
0.00
6.20
27.33
6.00
15.40
11.60
22.00
0.00
0.00
2.00
0.00
1.33
0.00
0.00
0.00
0.00
19.60
0.00
0.40
3.00
5.40
0.00
0.00
15.60
7.00
30.60
0.00
0.20
0.20
siltstone
argillite
limestone
phyllite
schist
0.00
0.60
0.00
0.00
0.00
0.00
Lith.
BlkButte
3.40
chart
18.60
1.00
14.00
quartzite
vein qtz
QFM phan
granite
gabbro
aplite
metaplut.
trachyte
rhyolite
maf. vol.
tuff
conglom
sandstone
siltstone
argillite
limestone
phyllite
schist
gneiss
Spetch MudCreek
Meyersl
sandstone
gneiss
Hoodoos Mitchell
3.00
2.60
UpSable
2.20
16.20
4.60
4.00
0.00
0.00
17.40
8.00
23.00
0.00
0.80
1.00
0.00
0.00
0.00
0.00
0.00
0.00
53.80
13.20
25.20
0.20
0.00
0.80
0.20
0.00
0.00
0.00
0.00
0.00
1.00
3.20
13.67
24.80
0.80
0.00
0.00
0.00
0.00
0.00
0.20
130
Appendix D. Correlation matrix of all pebble Daunt sample sites
(location of sites given on Plate 1 and in Appendix B).
Correlation Matrix
Bernard
Bernard
Goose
Marshall
Antone
Thomp.3
Thomp.1
Thomp.2
E.Doolitt
UpMonroe
SheepCmp
SheepCyn
JohnsonCr
Radiotow.
Narrows
BikEutte
MudCreek
Webers
NelsonCr
WhButte
BridgeCr
Monroel
Monroe2
TonyButte
Spetch
Courthse
Rip-Up
GordyFlat
CherryRch
UpSheep
UpGirds
MtnCreek
UpGable
Meyersl
Meyers2
Hoodoos
Mitchell
1.00
0.65
0.91
0.74
0.90
R-squared values for Gable Creel: conglomerate units
Goose Marshall
0.65
0.91
1.00
0.73
0.73
1.00
0.96
0.74
0.75
0.98
0.61
0.97
Antone
0.74
0.96
0.74
Thomp.3
0.90
Thomp.1
0.90
Thomp.2
0.94
0.75
0.61
0.66
0.98
0.74
0.97
0.61
1.00
0.96
1.00
0.99
0.99
0.68
0.99
0.99
E.Dool:ttUpMonroe
0.58
0.96
0.71
0.96
0.94
0.66
0.99
0.68
0.98
0.58
0.96
0.42
0.56
0.96
0.70
0.83
0.82
0.71
0.98
0.61
0.72
0.86
0.75
0.72
0.97
0.69
0.69
0.61
0.96
0.52
0.72
0.80
0.65
0.90
0.60
0.96
0.65
0.93
0.96
0.84
0.77
0.82
0.78
0.94
0.91
0.77
0.91
0.91
0.64
0.99
0.54
0.67
0.97
0.91
0.E9
0.94
0.89
0.89
0.71
O.E6
0.72
0.61
0.64
1.00
0.67
0.84
0.80
0.57
0.86
0.81
0.85
0.65
0.96
0.94
0.91
0.92
0.96
0.65
0.96
0.79
0.92
0.90
0.88
0.94
0.84
0.69
0.90
0.98
0.89
0.90
0.98
0.97
0.65
0.88
0.79
0.77
0.53
0.61
0.91
0.80
0.86
0.87
0.98
0.98
0.86
0.90
0.99
0.65
0.98
0.77
0.98
0.97
0.92
0.98
0.70
0.69
0.83
0.83
0.97
0.97
0.94
0.77
0.93
0.82
0.95
0.98
0.6E
0.99
0.91
0.69
0.79
0.96
0.49
0.27
0.89
0.32
0.81
0.93
0.94
0.22
0.94
0.82
0.62
0.79
0.49
0.79
0.79
0.77
0.63
0.47
0.97
0.52
0.92
0.98
0.99
0.43
0.98
0.94
0.90
0.97
0.41
0.38
0.99
0.82
0.26
0.42
0.39
0.60
0.64
0.97
0.59
0.99
0.42
0.98
0.46
0.80
0.80
0.57
0.66
0.93
0.99
0.97
0.50
0.97
0.96
0.95
0.95
0.34
0.29
0.61
0.81
0.66
0.81
0.66
0.62
0.81
0.51
0.75
0.76
0.83
0.60
0.99
0.95
0.95
0.29
0.72
0.97
0.75
0.75
0.86
0.71
0.63
0.64
0.96
0.89
0.91
0.97
0.96
0.85
0.87
0.98
0.73
0.66
0.76
0.74
0.63
0.97
0.94
0.95
0.96
0.93
0.92
0.88
0.98
0.84
0.97
0.95
0.91
0.94
0.58
0.56
0.96
0.74
0.77
0.94
0.62
0.67
0.65
0.67
0.71
0.86
0.90
0.97
1.00
0.74
0.61
0.86
0.96
1.00
0.44
0.94
0.97
0.97
0.34
0.99
0.98
0.75
0.97
0.96
0.99
0.E7
1.00
0.54
0.67
0.96
0.92
0.87
0.41
0.39
0.9E
0.43
0.89
0.97
0.99
0'34
0.99
131
Bernard
Goose
Marshall
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0.85
0.74
0.77
0.84
0.90
0 42
0.56
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0.82
0.72
0.72
0.60
0.82
0.77
0.96
0.65
0.94
0.77
0.91
0.80
0.93
0.91
0.65
0.67
0.79
0.66
0.97
0 66
0.60
0.70
0.96
0.97
0.56
0.96
0.46
0.60
1.00
0.87
0.91
0.91
0.86
0.92
0.66
0.70
0.87
1.00
0.82
0.87
0.83
0.91
0 67
0.78
0.93
0.89
0.83
0.89
0.84
0.89
0 79
0.84
0.91
0 51
0.86
0.65
0.98
0 . 42
0.56
0.96.
0.89
0.90
83
0 57
0.87
0.65
0.70
0.81
0.66
0.63
0.65
0.64
0.93
0.90
0.70
0.92
0.67
0.79
0.72
0.86
0.65
0.79
0.83
0.98
0.72
0.94
0.97
0.89
0.92
0.33
0.30
0.93
0.35
0.92
0.94
0.95
0.24
0.98
0.94
0.93
0.91
0.88
0.90
0.88
0.96
0.92
0.57
0.59
0.90
0.59
0.82
0.93
0.95
0.55
0.89
0 83
0 61
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0 . 69
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0.62
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0.67
0.65
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0.95
0.97
0.91
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0.69
0.94
0.89
0.65
0.96
0.62
0.97
0.96
0.76
0.91
0.67
0.93
0.89
0.89
0.96
0.89
0.90
0.81
0.67
0.82
0.87
0.53
0.66
0.94
0.67
0.78
0.93
0.79
0.86
0.83
0.89
0.84
0.77
0.87
0.79
0.86
0.84
0.91
1.00
0.96
0.99
0.89
0.96
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0.96
0.89
0.99
0.91
0.98
0.89
0.99
0.87
0.96
0.97
0.96
1.00
0.99
0.87
0.99
0.87
0.81
0.94
0.83
0.88
0.82
0.85
0.82
0.84
0.56
0.74
0.72
0.91
0.73
0.89
0.93
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0.96
0.89
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0.81
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0.74
0.92
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0.85
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0.55
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0.82
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0.75
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0.70
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0.69
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0.38
0.38
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0.85
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Bernard
Goose
Marshall
Antone
Thcrnp. 3
Thonp.1
Thorip.2
E.Doolitt
UpMonroe
SheepCmp
SheepCyn
JohnsonCr
Radictow.
Narrows
B1kButte
MudCreek
Webe,
NelsonCr
WhButte
SridgeCr
Monroel
Monroe2
TonyButte
Spetch
Courthse
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UpSheep
UpGirds
MtnCreek
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M ev er s 1
Me y ersl
Hocdoos
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CherryRch UpSheep
0.27
0 29
0.82
0.79
0.47
0.49
0.64
0 62
0.55
0.58
0.38
0.41
0.39
0.42
UpGirds MtnCreek Upuable
33
0.86
0.39
0.97
0.89
0.30
0.59
0.72
0.52
0.72
0.69
0.35
0.89
0.62
0.97
0.60
0.97
0.99
0.98
0.62
0.96
0.57
0.70
0.94
0.90
0.91
0.97
0.91
0.93
0.96
0.32
0.79
0.52
0.54
0.59
0.42
0.44
0.81
0.43
0.96
0.92
0.35
0.56
0.73
0.56
0.74
0.72
0.40
0.30
0.28
0.94
0.33
77
0 49
0.77
0.50
0.41
0.73
0.38
0.33
0.49
0.40
0.99
1.00
0.43
0.96
0.38
0.55
0.49
0.99
0.35
0.55
0.84
0.97
0.73
0.95
0.93
0.88
0.95
0.46
0.43
1.00
0.48
0.97
0.95
0.94
0.40
0.98
0.77
0.50
0.45
0.73
0.43
0.36
0.49
0.43
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0.95
0.48
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0.44
0.59
0.51
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0.53
0.56
0.38
0.31
0.49
0.92
0.46
0.93
0.56
0.94
0.51
0.89
0.54
0.67
0.92
0.82
0.89
0.97
0.90
0.92
0.93
0.87
0.77
0.73
0.93
0.61
0.88
0.97
0.77
0.39
0.43
0.38
0.97
0.44
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0.98
0.35
0.94
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0.2 4
0.93
0.63
0.77
0.78
0.79
0.98
0.43
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0.66
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0.80
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0.34
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0.51
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0.62
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0.72
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0.94
0.99
0.56
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0.93
0.87
0.70
0.91
0.93
0.96
0.49
0.94
0.95
0.87
0.70
0.89
0.92
0.88
0.57
0.90
0.93
0.99
0.30
0.95
0.95
0.97
0.23
0.96
0.55
0.83
0.73
0.92
0.93
0.87
0.46
0.94
0.92
0.99
0.36
0.98
0.98
0.75
0.63
0.88
0.88
0.98
0.33
0.97
0.97
0.38
0.27
0.97
0.96
0.91
0.43
0.97
0.94
0.95
0.35
0.95
0.95
0.38
0.98
0.50
0.57
0.35
0.99
0.49
0.55
0.97
0.40
0.94
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0.40
0.95
0.51
0.55
0.94
0.35
0.68
0.90
0.97
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0.44
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