stratigraphy of the ohanapecosh formation north of

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Dissertations and Theses Dissertations and Theses

1987

Stratigraphy of the Ohanapecosh Formation north of Stratigraphy of the Ohanapecosh Formation north of

Hamilton Buttes, southcentral Washington Hamilton Buttes, southcentral Washington

Cynthia Marie Stine Portland State University

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AN ABSTRACT OF THE THESIS OF Cynthia Marie Stine for the Master of

Science in Geology presented November 6, 1987.

Title: Stratigraphy of the Ohanapecosh Formation North of

Hamilton Buttes, South-central Washington.

APPROVED BY MEMBERS OF THE THESIS COMMITEE:

Paul E. Hammond

Over 1055 m of early Oligocene andesitic-dacitic volcaniclastic

rocks and minor interbedded andesitic lava flows of the Ohanapecosh

Formation are exposed in a dissected structural high in the southern

Washington Cascade Range, about 22 km southwest of Packwood,

Washington.

The exposed sequence of rocks in the study area are located

approximately 250 m above the base of the Ohanapecosh Formation. A

2

lower sequence of deposits, about 350 m in thickness, are dominated by

primary and reworked lithic lapilli-tuff and epiclastic channelized

volcanic sandstone and conglomerate. These sediments are interpreted

as pyroclastic flows and stream deposits, respectively. The upper

sequence, about 455 m thick is dominated by volcanic diamictites

interpreted as lahars, with minor lithic lapilli-tuff and epiclastic

volcanic sandstone.

These sequences are representative of intermediate source volcanic

facies in an alluvial apron setting. Lithology, sedimentology, and

paleocurrent indicators suggest that the sediments were derived from

explosive volcanoes and the erosion of volcanic highlands located east

and southeast of the study area, along the Oligocene Cascade Arc. The

influx of these volcanic sediments gradually overwhelmed drainages

previously dominated by arkosic sediments from the east.

The Ohanapecosh sequence is folded into a northwest-trending

syncline and intruded by basaltic to andesitic dikes and sills. The

area was uplifted in the Pliocene followed by deep erosional

dissection. A pyroxene andesite lava flow, of Miocene-Pliocene age,

locally filled an ancestral valley.

STRATIGRAPHY OF THE OHANAPECOSH FORMATION

NORTH OF HAMILTON BUTTES, SOUTHCENTRAL WASHINGTON

by

CYNTHIA MARIE STINE

A thesis submitted in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE in

GEOLOGY

Portland State University

1987

TO THE OFFICE OF GRADUATE STUDIES:

The members of the Committee approve the thesis of Cynthia

Marie Stine presented November 6, 1987.

Robert 0. Van Atta

Department of Geology

Bernard Ross, Vice Provost of Graduate Studies

ACKNOWLEDGEMENTS

Several professional geologists and friends were very generous

with their time and offered encouragement when it was most needed.

Thanks go to Ben Lill for being a great field assistant and rescuing me

in the middle of a snow blizzard, Pat Pringle of the U. S. Geological

Survey for his computer graphics and encouragement, Rick Wooten of the

U. S. Forest Service for the use of his reconnaissance data, and Tom

Taylor and Gene Pierson of P. S. U. for knowing how to get things done.

Last but not least, many thanks are due to my parents, friends, and

cohorts for their badly needed sense of humor and support.

Many thanks are also due to the members of my thesis committee

(Drs. Paul E. Hammond, Robert 0. Van Atta, and Ansel G. Johnson) for

their time, assistance, and encouragement.

TABLE OF CONTENTS

PAGE

ACKNOWLEDGEMENTS .................................................... iii

LIST OF TABLES .•........•.........•.............•.................... vi

LIST OF PLATES .....................................................• vii

LIST OF FIGURES ..................................................•. viii

CHAPTER

I INTRODUCTION ....................................•............. 1

II REGIONAL GEOLOGY .........................................•.... 6

Regional stratigraphic framework ........................... 6

Local geologic setting ..............................•..... 10

III STRATIGRAPHY ............................................•.... 13

Terminology of volcaniclastic deposits ...............•.... 13

Outline of li thostratigraphic units ....................... 15

Lithology of the Ohanapecosh Formation ..............••.... 21

IV SEDIMENTARY PETROLOGY ....................................... 35

Field distinction of lithostratigraphic units ............. 35

Methods ..•..................•...............•.•........... 35

Volcanic diamictite ....................................... 36

Lapilli-tuffs ............................................. 38

Volcanic sandstones and conglomerate ................•..... 38

v

Volcanic siltstone .......................•................ 42

V PETROLOGY OF LAVA FLOWS AND INTRUSIONS ...................... 44

Introduction . ............................................. 44

Petrology of lava flows .....•.................•........... 44

Petrology of intrusive rocks ....•................•........ 46

Petrologic type ..............•...........•.....•........•. SO

VI PALEOCURRENTS ............................................... 53

Introduction . ............................................. 53

Methods . .................................................. 53

Discussion ....•........................................... 54

VII STRUCTURAL GEOLOGY .......................................... 59

VIII GENERAL MODEL OF DEPOSITIONAL HISTORY ....................... 61

Introduction ..................•.........•.............•.•. 61

Environment of deposition ......................••......... 64

IX SUMMARY ..................................................... 70

REFERENCES CITED ..................................................... 72

APPENDIX A: POINT COUNT DATA-SEDIMENTARY ROCKS ....................... 76

APPENDIX B: HEAVY MINERALS ........................................... 78

APPENDIX C: POINT COUNT DATA-LAVA FLOWS AND INTRUSIONS ............... 79

APPENDIX D: LOCATION OF MEASURED SECTIONS ............................ 81

TABLE

I

II

III

LIST OF TABLES

PAGE

Summary of lithologies of the Ohanapecosh Formation .............•..................................... 24

Whole rock chemical analysis, volcanic diamictite lithic fragments, Ohanapecosh Formation, Hamilton Buttes area ...................................•.... 37

Whole rock chemical analysis, Ohanapecosh Formation, Hamilton Buttes area .............•.......•...•... 47

LIST OF PLATES

PLATE

I Geologic Map and Cross Sections

II Measured section and sample localities

IN POCKET

IN POCKET

LIST OF FIGURES

FIGURE PAGE

1. Location, Access, and Generalized Geologic Map ................. 3

2. Location and Tectonic Map of Pacific Northwest ................. 7

3. Generalized Geologic Map of the Volcanic Cascade Range ......... 9

4. Classification of Pyroclastic Deposits ...............•........ 14

5. North River Section and Key ..........................••...•... 17

6. Timonium Creek Section .............................•.•........ 19

7. East Wobbly Section ........................................... 20

8. Hamilton Buttes Section ....................................... 22

9. Correlation of Measured Sections ...........................•.. 23

10. Volcanic Diamictite ........................................... 26

11. Generalized Stratigraphic Section of a Lahar .................. 28

12. Lithic Lapilli-tuff ....•...................................... 29

13. Bedded Volcanic Sandstone, Conglomerate, and Siltstone ....••.. 32

14. Location Map of Bishop Mountain Lava Flow ..................... 34

15. Compositional Classification of Some Lithic Fragments in the Volcanic Diamicti te............ . . . . . . . . • . . . . . .........•...... 39

16. Photomicrograph of Elongated Pumice ........................... 40

17. Photomicrograph of an Accretionary Lapilli .................... 41

18. Composition of Sandstones of the Ohanapecosh Format ion . .................................................... 43

19. Plot of Dikes, Sills and Lava Flows ...•......•.......•....•..• 45

ix

20. FeO*/MgO Versus Si02 Diagram .................................. 49

21. AFM Diagram for Analyzed Intrusive Rocks ..........••...••..... 51

22. Plot of Ti Versus Cr .......••.•...............•...•.•....•..•• 52

23. Orientation of Channel Axis .....................•..•..••.••... 55

24. Orientation of Maximum Grain Size Trends •.......•.•....•...... 56

25. Orientation of Wood Fragments ........•...•........••.•..•..... 56

26. Distribution of Paleocurrent Directions ....................... 58

27. Geologic Structure of the Ohanapecosh Formation North of Hamilton Buttes ............................................... 60

28. Schematic Diagram Showing Types and Lateral Extent of Deposits of Varying Volcanic Facies ........................... 62

29. Generalized Cross Section of Volcanic Facies ...............•.• 63

30. Block Diagram of Volcanic Facies Model. ...................•... 68

CHAPTER I

INTRODUCTION

PURPOSE OF STUDY

The lower to middle Ohanapecosh Formation, of late Eocene to

early Oligocene age, is well exposed in an area north of Hamilton

Buttes in south-central Washington. The formation consists of

intercalated medium- to coarse-grained volcanic arenite, lapilli tuff,

conglomerate, diamictite, and minor lava flows. The purpose of the

study is to complete a detailed description of the geology and the

stratigraphy of this area. Volcanic facies, environments of

deposition, and the regional paleogeography were investigated.

METHODS OF INVESTIGATION

Approximately three months were spent in the study area over the

summers of 1985 and 1986. Field work included:

1) geologic mapping at a scale of 1:24,000;

2) measuring of stratigraphic sections with steel tape;

3) recording of all observed paleocurrent indicators;

4) field description and sample collection of sedimentary rocks to define lithofacies, and to compile a representative sandstone suite for petrographic study; and

5) field description and sample collection of intrusive and extrusive volcanic rocks for petrographic study and chemical analysis.

Laboratory work consisted of thin section study of volcanic and

sedimentary rocks, including point counts of selected samples. Heavy

minerals were examined to determine lithology of the sediment source.

Nineteen samples of intrusive rocks, lava flows, and volcanic lithics

2

were analyzed by x-ray fluorescence for major oxides and trace elements

in the laboratory at Washington State University under the supervision

of Dr. Peter Hooper.

LOCATION AND ACCESS

The study area is located in Gifford Pinchot National Forest and

is approximately 22 km south-southeast of Packwood, Washington (Figure

1). Access to the area is provided by USFS (U. S. Forest Service)

roads 22 and 78 which traverse the area. Forest Service side roads

provided additional access. Wobbly Lake and Blue Lake Trails, alpine

meadows, and sparsely vegetated ridges provide easy routes for the

hiker.

Annual precipitation exceeds 165 cm (65 in), and mostly occurs

between November and June. Valley bottoms and valley sides are covered

with thick vegetation. The 1902 Cispus burn afforded excellent

exposures along ridge tops, with access restricted only by steep

terrain.

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SCALE -Figure l· Location, access, and generalized geologic map of area north of Hamilton Buttes, southcentral Washington. U.S. Forest Service secondary roads are shown. Geology from Hammond (1980), Swanson and Clayton (1983), and Winters (1984): Jr, Russell Ranch Formation; Tee, Chambers Creek beds; To, Ohanapecosh Formation; ruled areas, High Cascade volcanic rocks; CCF, projection of Cortright Creek fault.

GEOMORPHOLOGY

The average relief is approximately 950 m. Elk Peak (5551 ft/

1692 m) is the highest point in the map area, and is located on the

eastern margin of the study area.

4

The North Fork Cispus River flows to the west to join the Cispus

River which empties into the Cowlitz River. The U-shaped valley

profiles are indicative of alpine glaciation. In general, tributary

streams follow north-south structural trends and parallel the strike of

the beds. Stream commonly head in cirques. Waterfalls are common.

Landslides, rock slides, and slumps occur in the study area. A

landslide on the west side of Elk Peak blocked the small stream in the

valley below to form Wobbly Lake. Volcanic ash, up to 3 cm thick, from

Mount St. Helen's 1980 eruption, veneers the landscape.

PREVIOUS WORK

The study area had been previously mapped by reconnaissance

techniques. It had been included in the 1:500,000 Geologic Map of

Washington (Hunting and others, 1961) and Hammond's (1980) 1:125,000

map of the southern Washington Cascade Range.

Fisher (1957) worked in the Elbe-Packwood area to the north and

studied the relationships between the upper Eocene Puget Group with the

underlying and overlying volcanic rocks. Winters (1984) mapped an

adjoining area to the east and concentrated on the arkosic sandstones

of the Puget Group which are interstratified with the lower Ohanapecosh

Formation. The Goat Rocks and White Pass area, to the east, has been

5

described by Clayton (1983) and Swanson and Clayton (1983).

The Ohanapecosh Formation was first described in Mount Rainier

National Park by Fiske, Hopson, and Waters (1963) and was believed to

have been supplied with pyroclastic debris from subaqueous eruptions.

Clayton (1983) challenged Fiske and others' (1963) model and proposed

that the Ohanapecosh strata were subaerially deposited in an

environment of low relief. Buckovic (1974) studied the Ohanapecosh and

the interbedded arkosic sediments in the area west of Mount Rainier

National Park. The Ohanapecosh Formation is interpreted to extend as

far south as the Columbia River by Wise (1970).

CHAPTER II

REGIONAL GEOLOGY

REGIONAL STRATIGRAPHIC FRAMEWORK

The deposition of greater than 4575 m (15,000 ft) of Ohanapecosh

volcanic rocks, part of the Western Cascades Group of Hammond (1979,

1980), began in late Eocene time. This igneous activity was the

product of renewed subduction in the middle Eocene of the Farallon

plate by the North American continent in the Pacific Northwest. To

better understand the depositional setting of the Ohanapecosh

Formation, the late Mesozoic and Cenozoic tectonic configuration of

this region is discussed below.

The region between northern California and central Washington is

known as the Columbia Embayment (Wilson and Cox, 1980; Figure 2). The

basement rocks of the embayment are thought to consist of basaltic

seamounts which accreted to the continent during the early Cenozoic.

It is surrounded by a series of metamorphic belts and batholiths of

Paleozoic and Mesozoic age which compose the Klamath Mountain Province,

the Blue Mountain Province, and the North Cascades.

Prior to renewed volcanic activity, which occurred in the late

Cretaceous and continued into the Eocene, a lull in magmatic activity

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Figure 1· Location and tectonic map of Pacific Northwest (modified from Wilson and Cox, 1980).

7

8

occured due to a shallowing of the Farallon plate descent (Dickinson,

1979). This condition allowed arkosic sediments of the Puget Group

derived from an eastern crystalline source to prograde across

southwestern Washington (Gard, 1968, Winters, 1984). Minor episodes of

volcanic activity occurred during this time to produce bimodal

volcanism in the Teanaway and Naches Formations in central Washington

(Tabor and others, 1984) and andesitic volcanism in the Northcraft

Formation in western Washington (Buckovic, 1979).

In the middle Eocene, subduction related volcanic activity

shifted westward from the Challis-Absaroka arc to the Cascade arc

(Snyder and others, 1976). It is believed that this shift was due to

the increased dip of the subducted Farallon plate (Dickinson, 1979).

This was accompanied. by a gradual 70- clockwise rotation of the Coast

Range-Klamath Mountain block (Simpson and Cox, 1977; Heller and Ryburg,

1982).

Andesitic stratovolcanoes developed approximately 40 Ma (Hammond,

verbal communication): lava flows accumulated near vent areas and

volcaniclastic debris was deposited in distal areas. These events

marked the beginning of the deposition of the Western Cascades Group

(Figure 3). Arkosic sedimentation continued during this time but large

volumes of volcanic debris were interstratif ed with the arkosic Puget

Group at the base of the Western Cascades Group. Eventually, arkosic

sediments derived from the east were blocked by the large volume of

volcanic debris being deposited. This volcanic debris buried the

arkosic delta system in southwest Washington. Tuffaceous arkosic

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I I ~ l INTRUSIONS

: I I UPPER MIDDLE

I f"-······ .. ··J LOWER ............ ............

9

Figure]. Generalized geologic map of the volcanic Cascade Range, showing the distribution of the Western Cascade Group, High Cascade Group, and Tertiary granitic intrusions (from Hammond, 1979).

10

sedimentation continued, represented by the Lincoln Creek Formation in

southwestern Washington and the Pittsburg Bluff Formation in

northwestern Oregon (Van Atta, 1971). Deposition of andesitic to

silicic volcaniclastic rocks (Middle and Upper Western Cascades Group

of Hammond, 1980) continued in the Cascade arc. These deposits include

pyroclastic flows, air-fall tuffs, lithic-rich mudflows, lacustrine,

and fluvial deposits.

Regional compressive stress has created two episodes of

deformation, an earlier episode resulting in northwest-trending folds

and a late Cenozoic episode in which westward to southwestward fold

trends, the Yakima fold ridges, were developed. Northwest-trending

high-angle faults developed concurrently with the first episode of

folding (Hammond, 1980).

In middle Miocene time, Columbia River Basalts erupted to the

east of the Cascades, and became locally interstratified with the Upper

Western Cascades Group (Hammond, 1980) where they flowed through the

Cascades. In the last 5 m.y., scattered andesitic to dacitic

stratovolcanoes and abundant basaltic shield volcanoes and cinder cones

formed the High Cascades Group.

LOCAL GEOLOGIC SETTING

Uplift and erosion in the western foothills of the Cascade Range,

near Mount Rainier, have exposed over 7000 m (23,000 ft) of Paleogene

arkosic and volcaniclastic sediments (Buckovic, 1974). The Eocene

Puget Group, the oldest unit, consists of the Carbonado, the

11

Northcraft, and the Spiketon formations. The deposition of the

Carbonado Formation, composed of arkoses, channel sandstones,

siltstones, and minor coal beds was interrupted for a time in the late

Eocene by andesitic volcanism of the Northcraft Formation (Buckovic,

1974). Arkosic sedimentation later resumed to form the Spiketon

Formation. These arkosic sediments were deposited in a prograding

delta system. Paleocurrent data and mineralogy suggest that the

sediments were derived from an eastern crystalline source (Winters,

1984).

Ohanapecosh volcanism initiated in the late Eocene, depositing

great thicknesses of nonmarine volcaniclastic rocks and minor andesitic

lava flows near the vent areas (Fiske and others, 1963). Arkosic

sedimentation continued where westward flowing streams maintained their

courses, producing interstratification of sedimentary beds with

volcanic beds in the basal part of the Ohanapecosh Formation (Winters,

1984).

The study area is located southwest of White Pass and west of the

crest of the Cascade Range in southern Washington (Figure 1). The area

is immediately underlain by strata of the Ohanapecosh Formation. These

are underlain by the Chambers Creek beds, arkosic sediments of middle

Eocene age (Winters, 1984). The Chambers Creek beds or equivalent

strata rest unconformably on the rocks of the Rimrock Lake inlier

(Miller, 1987). The Rimrock Lake inlier, of Jurassic and Cretaceous

age, consists of the Russell Ranch Formation, of deformed carbonaceous

greywackes, argillites, and pillow basalts and the Indian Creek

12

Formation of mafic amphibolites and gneisses.

The Chambers Creek beds are the lowest stratigraphic unit of

arkosic sedimentary rocks exposed just east of the study area. This

informal name was introduced by Winters (1984). The lithology consists

of quartose, micaceous to lithic arkose, siltstone, mudstone, and

sparse interbeds of coal. These arkosic sediments have been correlated

with the Spiketon Formation of Gard (1968) on the basis of lithology

and stratigraphic position. They underlie much of southern Washington

and northwestern Oregon. Paleocurrent data and mineralogy suggest a

crystalline source to the east and transportation across an alluvial

plain (Winters, 1984).

The Ohanapecosh Formation overlies and is interstratified, at its

base, with the Chambers Creek beds. In the study area, it consists

predominantly of volcanic diamictite, pumiceous lapilli tuff, volcanic

conglomerate, sandstones and siltstones, and minor andesitic lava

flows. Small andesitic intrusions occur sporadically. A remnant of an

intracanyon pyroxene andesite lava flow, of Miocene-Pliocene age,

unconformably overlies the volcaniclastic rocks.

Post-depositional deformation created broad northwest trending,

asymmetrical folds. High angle faults parallel this trend. The

Ohanapecosh Formation was subjected to regional alteration to the

zeolite facies of metamorphism and deeply eroded prior to deposition of

the intracanyon andesite lava flow. Pleistocene glacial drift and

landslide deposits overlie the bedrock.

CHAPTER III

STRATIGRAPHY

TERMINOLOGY OF VOLCANICLASTIC DEPOSITS

The term volcaniclastic includes all elastic volcanic material

formed by any process of fragmentation (Fisher, 1961). A pyroclastic

fragment is an "instant" fragment, initially hot, produced directly

from eruptive volcanic processes (Fisher and Schmincke, 1984). The

term epiclastic refers to sediments derived from pre-existing rock

through weathering processes (Fisher and Schmincke, 1984). In this

report, terminology of pyroclastic rocks follows the classification

scheme of Le Bas and Sabine (1980), using modifiers to designate clast

size composition and containing )75% rock fragments and crystals

(Figure 4). Clast size ranges from lapilli to ash. Epiclastic rocks

are named according to grain size as in volcanic conglomerate,

sandstone, and siltstone following the classification of Schmid (1981).

Massive, unsorted, boulder conglomerate is here referred to as

volcanic diamictite, a descriptive but nongenetic term. This term is a

deviation from Le Bas and Sabine's system for mixed pyro-epiclastic

rocks. These sedimentary rocks contain a wide size range of rounded to

subangular clasts in a sand to clay-sized matrix. Volcanic breccia,

pyroclastic breccia

ash ( < 2 mm)

CLASSIFICATION OF LITHIFIED DEPOSITS

lapillistone

blocks lapilli C> 64 mm) (2-64 mm)

crystal-lithic tuf f

rock fragments

tuff

tuf f

CLASSIFICATION O.E' TUFFS

tuff

crystals 75

vitric-crystal tuff

50 75

crystal-vitric tuff

vitric tuff

glass shards & pumice

Figure~· Classification of pyroclastic deposits (after Le Bas and Sabine, 1980).

14

according to Le Bas and Sabine (1980), consists of unsorted, angular

fragments.

15

In the field, volcanic diamictite is easily recognized. Beds are

well lithified, massive, and up to 13 m (45 ft) thick. Lithic

fragments weather out in relief. They are characterized by extreme

poor sorting and subangular to rounded volcanic fragments ranging in

size from boulder to sand-sized clasts, floating in a sand to clay

matrix.

OUTLINE OF LITHOSTRATIGRAPHIC UNITS

Exposures in the study area consist almost entirely of volcanic

strata that have been assigned to the Ohanapecosh Formation of Fiske

and others (1969) on the basis of stratigraphic position and similarity

of the rock types to the type section (Winters, 1984). The exposed

section in the study area is approximately 1055 m thick. The basal 250

m of the formation, consisting primarily of epiclastic rocks and

volcanic diamictite, are exposed outside the northeastern boundary of

the map area on FS Road 22 where it interfingers with the underlying

Chambers Creek beds of Winters (1984). The top of the Ohanapecosh

Formation is not exposed in the study area.

The volcanic strata can be separated into four mappable units as

shown on Plate I. Strata of lapilli-tuff (29%) and interbedded

epiclastic rocks (66%) with minor volcanic diamictite (5%) form what is

designated here as a lower part of the Ohanapecosh Formation,

approximately 350 m thick. Volcanic diamictite (29%) and interbedded

16

epiclastic rocks (53%) with minor pumiceous lapilli-tuff (18%) are

abundant in an upper part, approximately 455 m thick. Intrusions of

basaltic andesite, and a remnant intracanyon lava flow of pyroxene

andesite, are the remaining units. Surficial units include glacial

drift, landslides, and alluvium. Four landslides are shown on the map

(Plate I).

The lower part of the Ohanapecosh Formation consists chiefly of

beds of pumiceous lithic lapilli-tuff and interbedded volcanic

sandstone, and minor volcanic diamictite and lava flows of basaltic

andesite. The lapilli-tuff is characterized by abundant flattened

pumice. The interbeds of volcanic sandstone are rhythmically bedded.

Three lava flows of basaltic to andesitic lava flows are

interstratified in this unit. The best exposures of this part of the

formation occur in three measured sections, the North River section

(Figure 5) along FS Road 22, in the Timonium Creek section (Figure 6)

along FS Road 060, and in the East Wobbly section (Figure 7) along FS

Road 7807. For locations, see Plate II). The base of the Ohanapecosh

Formation is not exposed in the study area although the arkosic

sandstones of the Chambers Creek Beds crop out approximately 2 km map

distance from the axis of the syncline on the eastern limb (on FS Road

22) 250 m below the base of the North River section. The Chambers

Creek Beds do not reappear on the western limb of the syncline at an

equivalent stratigraphic level, indicating the possibility that the

lithologic contact between the Ohanapecosh volcanic strata and the

micaceous, arkosic beds steps up to the east.

KEY TO COLUMNAR SECTIONS

LITHOLOGIES

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18

60

~o

' 40 ~-· .. \ • • A

l:-li-.-: A 61. A ... ~ ......... ..... . ... .. ... ...

.. A A .. A ,_ ...... c '

30 • "" • I~:~ ~ • %

20 r .. '"' ... • ... ·.·~·.'- ... "',..,

10 h A • • • 1 A A ... A • ......... ·.

A A A A 4

....... 4.

:-:""":""':·

EleV=3680

CS12 ._.. Tree Cast

C:S-11

-

HB13

IV

IV

IV

CS2

IV

Figure..§.. Timmonium Creek Section. See page 18 for key.

19

oz

'¥Y¥"\•¥V¥VYV¥ -o ... '¥ 'Y 'Y

01~

oz:

0£

Ot

/i\01.i VArl-(11111 OJ TIIS !-: -: . :-:-:-=J -(,,,, .. _,_ 09

<:C·>>::J

~ OL

21

The upper part of the Ohanapecosh Formation is dominated by thick

intervals of volcanic diamictite, interbedded coarsening upward lithic

lapilli-tuff, and minor normally graded volcanic sandstone. The upper

half of the North River section (Figure S) and the Hamilton Buttes

section (Figure 8) best typifies this sequence. Measured sections of

the Ohanapecosh Formation exposed in the field area were correlated on

the basis of similar lithology, lateral continuity, and projection in

geologic cross-sections (Figure 9).

Dikes and sills of phyric basaltic andesite intrude both map

units. Only the larger units, more than 2 m thick, are shown on the

map.

A pyroxene andesite lava flow, possibly of the High Cascades,

unconformably overlies the Ohanapecosh Formation in the southwestern

portion of the map area. These rocks are columnar jointed and fresh in

appearance.

LITHOLOGY OF THE OHANAPECOSH FORMATION

Introduction

Three major lithologies are recognized in the study area and are

defined on the basis of grain size, sorting, bed thickness, and

sedimentary structures. These characteristics imply different

mechanisms of transport and depositional conditions. A summary of

lithologic characteristics are presented in Table I.

Volcanic Diamictite

Volcanic diamictite is chaotically sorted, massive, and matrix-

270 Elev=5518'

260

250

Jt 240

Elev=5400•

• 230 $.. • ~ • :e

220

210

200

\190 Elev=5260'

HB43

--

90 -180 Elev=5478 -

H~~~A~ 170 80

<~~~~> HB31 • ::>:::r;:::

$.. ·g.·.· .. · .. • ~ )~J~ ~ ~ ~

/160 ... • . ...... ~ 70

150 ~o HB28

('/

140 "50 -

130 40

HB18b

120 30 ID:' .;.o .•• zz:;:;J. I

RB26 ! 110 SlLL 20

100 10

' 0

Figure~· Hamilton Buttes Section. See page 18 for key.

NORTH RIUCR

uo 1·.·.·.·.·.·.,

100 ~

uo

Ito

110

140

/' uo

HO

l)Q

110

~

110

_Y. L

100

TIMONIUM CREEK HftMllTDN llIITES ERST WOBBLY

tO

.~ .... · .. ~:i

~

uo

II

_____ .. ,.,,..._.,..- - '~ --- . ··::: :::

·~1 APPROX. 120 m

l_ . I~

----_ [:\:)

j

Ill

Figure 2· Correlation of measured sections in the Hamilton Buttes area, showing general stratigraphic relationship between upper and lower parts of the Ohanapecosh Formation. Locations of measured sections are shown on Plate II.

I'" 1~1];

JO CIT\.

'" raB ~ .~

Lithology Bed Thicknesses

Volcanic 2-13 • Diamictita

.5-5.

Lapilli- 2-13 • tuff

Bpi- 0,l-4 m elastic rocks

• Discussed in Chapter 8.

TABLE I

Summary of Lithologies of the Ohanapecosh Formation Hamilton Buttes Area

Contacts Grain Size Type of Other Trend Stratification Features

Beae sharp Coarse lapilli Massive, except Non-sorted Top sharp to to cobbles with for croas-bedded aradational a sand to •ud sandy "sole"

matrix layer at base

Cradatioqal Conglo-rate Horizontally Poorly sorted bedded

Base sharp Sand to Massive, Ace retiona ry Top sharp to lapilli nor11111lly graded lapilli gradational

Flattened pumice

Deformed glass shards

Gradational Hudstone to Hassive to Channel conglomerate bedded features

co111111on Top sharp to Predominately Nor111ally gradational coarse sand graded

to pebble Rhythmic stratification

Depositional Processes

Fluid •obilizad debris flow

ffyperconcen-trated flood flow

Pyroclastic flow

Ash flow

Deposition by suspension and traction

Inferred Environment•

Pluvial channel and alluvial plain

Topographic lows to blanket deposits

Shallow lacustrin and fluvial chann

N ~

25

supported (Figure 10). Units are concentrated in the upper part of the

exposed columnar section with excellent examples located throughout the

Hamilton Buttes section.

Lower contacts of the diamictite are sharp. Usually the basal

portion consists of a "sole" layer up to 30 cm thick. This texturally

distinct layer consists of weakly developed cross-bedded, clast

supported coarse sand and gravel. The contacts between the sole layer

and the main body of the unit vary from sharp to gradational over an

interval up to 10 cm thick. The upper contact of the volcanic

diamictite, where exposed, is generally gradational upward into

horizontally bedded conglomerate.

Color ranges from greenish-grey to greyish-olive green and

weathers to light brown to dark yellowish-brown. Units range from 2 m

(6 ft) to 13 m (45 ft) in thickness, the average being 4 m. Beds tend

to be thicker to the south. No bedding is visible. Crude reverse

grading of lithic clasts is common.

Lithics clasts weather out in relief. Their color varies from

red, grey, brown, to green. Clast margins are sharp to indistinct.

They are subangular to rounded and range up to 27.2 cm (10.6 in) in

diameter. The diamictites are polymictic to oligomictic. Specimens

examined in hand sample, in order of decreasing abundance, include

felsic lavas, tuffs, and metamorphic fragments. Volcanic clasts range

from aphanitic to porphyritic; many are amygdaloidal. Petrology of the

lithic clasts is discussed in Chapter 4.

The matrix consists of grains of sand to clay-sized plagioclase

Figure 10. Volcanic diamictite of probable laharic origin. Fine-grained "sole layer" overlain by unsorted, massive deposit. Lithic clasts weather out in relief. Notebook for scale. Photo from Hamilton Buttes measured section.

26

feldspar and lithic fragments. Color ranges from greyish green to

redish brown.

27

Associated with this lithologic unit are plane bedded, poorly

sorted, clast-supported pebble conglomerate with a coarse-grained sand

matrix. Bed thickness ranges from 0.5 to 6.0 m and are normally

graded. Color ranges from yellowish brown to dark reddish brown.

These beds generally overlie a bed of volcanic diamictite and grade

upward into indistinct low-angle, trough cross-bedded coarse-grained

sandstone.

The volcanic diamictite with its associated "sole" layer, are

interpreted herein as lahars, similar to fluid-mobilized debris flows

described by Scott (1985; Figure 11). The clast-supported gravel

conglomerate represents hyperconcentrated flood-flow deposits described

by Scott (1985) and Smith (1986). These hyperconcentrated flood-flow

sedimentary beds were high discharge flows intermediate in the

sediment/water ratio between stream flow and debris flow.

Lapilli-tuff

Pumiceous lithic lapilli-tuf f occurs throughout the exposed

section of the Ohanapecosh Formation (Figure 12). This lithology is

best exposed in the lower North River, Timonium Creek, and Hamilton

Buttes sections. These deposits are laterally extensive and are

characterized in outcrop by crude columnar jointing, coarse, angular to

subrounded lithic fragments, and abundant pumice which weathers out

preferentially, producing a pitted surface. Weathered outcrops are

light brown to moderate yellowish brown; fresh surfaces are pale green

.... -... •· .. • • • • • •••

• • • • t• -. ' . ' . . . ' .. ' . . ·,·. •. • • t ... ,· .... • • ... •· t • .. .£ , •• ... ~ ' .... • • ••• ~ .. ··~·· 41 ....... ... -·· .. ... • • •· •..,. ~ IGB -·•·''., f ~ .... ,., ...... : .. . ..... . . ..• ·='·· : •. •• •• •: ••• •• •. • .. · Sole Layer

Figure 11· Generalized stratigraphic section of a laharflood plain facies. Igb, inversly graded bedding (after Scott, 1985).

28

Figure Jl. Lithic lapilli-tuff. Note massive bedding, columnar jointing, and sharp upper contact in the lower unit. Photo from the Hamilton Buttes section.

29

30

to greyish green. Upper and lower contacts of beds of lapilli-tuff are

generally sharp. Thickness of units ranges from 2 to 13 m. Beds are

generally massive, poorly sorted, and are normally graded. Structure

ranges from weakly eutaxitic to massive.

Units are usually oligomictic; fragments are composed chiefly of

andesite. Clast size is rarely larger than 3 cm; the average size is 2

cm. Pumice is abundant, has been plastically deformed, flattened, and

often displays a subparallel alignment with bedding planes. Locally

pumice fragments wrap around lithic fragments.

In thin section, euhedral as well as broken plagioclase crystals

and relict glass shards are common in the matrix. Glass shards are

deformed indicating slight compaction in some units. This evidence

suggests that these deposits were deposited hot, have not been

reworked, and are primary. These deposits are interpreted as

pyroclastic-flow or ash-flow deposits.

Epiclastic Sedimentary Rocks

Epiclastic sedimentary rocks in the study area consist of medium

to very coarse-grained volcanic sandstone, volcanic pebble

conglomerate, and minor volcanic siltstone. These deposits are present

throughout the investigated stratigraphic section and are commonly

associated with the more resistant lapilli-tuff and volcanic

diamictite. These rocks are well exposed in the East Wobbly, and the

lower Timonium Creek sections. They form interbeds in all sections.

These beds consist almost entirely of volcanic rock fragments of

andesite and vesicular basalt. Clasts range from subangular to

31

subrounded and are poorly sorted.

Volcanic sandstones vary from massive to medium to thickly

bedded, with bed thickness ranging from 0.1 to 4.0 m (Figure 13). Beds

are normally graded and some display rhythmic stratification with a

basal conglomerate followed by an upward fining sequence. Pebbles are

concentrated in lenses 2-8 cm thick, which are scattered throughout the

sandstone. Low-angle trough crossbedding occurs in some beds. Lower

contacts of the beds, when associated with coarse-grained rocks, are

generally gradational over a 10 cm interval; the upper contact is

generally sharp. Broad, shallow scour and fill channels are common in

the sandstone beds.

The conglomerate consists of subrounded, clast-supported, gravel

sized volcanic lithic fragments. Long axis of clasts display a

preferred orientation and are locally imbricated. Beds grade upward

into finer-grained low angle, trough cross-bedded sandstones.

Greyish-green to greyish-blue green siltstone and mudstone

commonly occur interbedded with the sandstone. They are thinly to

medium bedded, and normally graded. Fine laminations are locally

visible. Intact leaf fossils were found in these beds. Many covered

intervals probably consist of these fine-grained deposits.

Age of the columnar section

Age of the Ohanapecosh Formation in the study area, is not well

constrained. The lithostratigraphic boundary between the underlying

arkosic sedimentary rocks of the Spiketon Formation of Gard (1968) and

the younger volcanic rocks of the Ohanapecosh Formation is regionally

Figure 11· Bedded volcanic sandstone, conglomerate, and siltstone. Hammer for scale (length is 40 cm). Photo from the East Wobbly section.

32

33

time-synchronous (Winters, 1984). Potassium-argon dates throughout the

region, at this stratigraphic horizon, range from 42 to 39 million

years before present. The mapped stratigraphic sequence of the

Ohanapecosh Formation lies approximately 250 m above this boundary.

Age of the upper part of the Ohanapecosh Formation in the mapped

sequence is based on a tenative correlation with a stratigraphically

higher basaltic-andesite lava flow located at Bishop Mountain

approximately 10 km (6.2 mi) to the west of the study area (Figure 14).

A potassium-argon date of 30.1 + 2.2 m.y. was reported by Phillips and

others (1986). The mapped stratigraphic sequence in the Hamilton

Buttes area is probably early to middle Oligocene in age, about 42 to

30 m.y. before present.

• •

.. .. "' .. ..

,. -·

To

. ..

. • • • • • .. ' .. •,to .. " •

•

• • ,

Figure 14. Location map showing the study area and the site of age-dated Bishop Mountain lava flow.

34

CHAPTER IV

SEDIMENTARY PETROGRAPHY

FIELD DISTINCTION OF LITHOSTRATIGRAPHIC UNITS

The lithofacies are readily distinguishable in the field on the

basis of grain size, clast roundness, sorting, and color. Lithic

lapilli-tuff and coarse volcanic sandstone and conglomerate may appear

similar but the tuff can be recognized by the abundance of wispy

looking pumice and the oligomictic composition. By contrast, the

volcanic sandstone and conglomerate display clasts of mixed

lithologies, are better sorted, and have less matrix.

Volcanic diamictite are distinguished from the lithic lapilli

tuff by their light brown to dark yellowish-brown color. The volcanic

diamictite lithic clasts are cobble sized, weather out in relief, and

are nonsorted.

METHODS

Thin sections of tuffs, conglomerates, sandstones, and siltstones

were examined under the petrographic microscope. A modal analysis was

carried out on 9 of the least altered, representative samples.

Textures were examined in all samples.

Eleven categories of lithic fragments and minerals were

designated for point counting. These categories include quartz,

feldspar, metamorphic rock fragments, microlitic volcanic rock

fragments, tuffaceous volcanic rock fragments, pumice, unknown rock

fragments, phyllosilicates, glass shards, pyroboles, and other

authigenic minerals. Results are listed in Appendix A.

36

In addition, sandstone heavy mineral grain mounts were examined

to determine the provenance of the sediments. Samples were crushed and

wet sieved. The 80 to 150 Tyler ASTM mesh fraction was used. The

heavy minerals were gravity separated using TBE (tetrabromoethane,

Spec. gravity=2.96 at 20° C) and mounted in epoxy.

Six lithic clasts from volcanic diamictite beds were sent to Dr.

Peter Hooper, Department of Geology, Washington State University, for

x-ray fluorescence (XRF) whole rock geochemical analysis. The analyses

are reported in Table II.

VOLCANIC DIAMICTITE

Volcanic diamictite forms resistant beds with lithic clasts

weathering out in relief. Thin sections of the diamictite were not

examined due to the difficulty in obtaining a representative sample.

However, hand samples and thin sections of lithic clasts within the

beds were examined in order to characterize the source material. They

are subangular to rounded, and some have indistinct resorbed margins

due to alteration. Samples include andesite, dacite, andesitic tuffs,

and metamorphic fragments. Whole rock geochemical analysis are

37

TABLE II

Whole Rock Geochemistry - Volcanic Diamictite Lithic Fragments

(l) Sample .!!2.:. HB22A HBLl HBL2 HBL3 HBL4 HBL5

Major Element Weight ! Si0 2 71.09 69.72 72.25 68.19 72.15 72.68

Al203 14.53 14.31 13.87 14.16 14.09 13.32

Ti02 .430 • 770 .707 1.213 .774 .609

Fe2o3 4.32 5.41 5.41 5.27 3.14 4.32

HnO .094 .133 .083 .140 .063 .044

CaO 6.83 1.56 1.98 4.56 2.49 1.53

HgO .86 .76 .39 l.49 .76 .14

IC 20 .53 2.79 .54 .74 2.91 3.03

Na20 .61 4.19 5.48 3.76 3.31 4.0

PzOs .005 .173 .154 3.610 .192 .140

Trace Element Jll!m_

Ni 16 8 8 15 16 16

Cr 4 10 2

Sc 28 26 29 31 23 24

v 47 42 29 162 64 40

Ba 351 770 146 82 392 841

Rb 18 56 13 13 so 55

Sr 1114 142 120 210 182 128

Zr 334 350 352 94 307 371

y 51 55 45 29 45 41

Nb 17 24 24 6 20 23

Ga 13 16 17 15 17 13

Cu 7 30 24 10

Zn 104 122 106 65 36 91 ------ ---- ----- ------- ---- ----100% 100% 100% 100% 100% 100%

(1) Sample locations given in Plate II.

38

reported in Table II. Of the silicic clasts selected 67% were dacite

and 33% were rhyolite (Figure 15).

LAPILLI TUFFS

Lithic clasts consist chiefly of pilotaxitic andesitic lava flow

fragments (28-40%) and flattened pumice (10-15%). Plagioclase

framework grains in the matrix are euhedral and commonly broken.

Anorthite content of plagioclase in the lithic fragments and in the

framework ranges from An20 to An45. Relic glass shards (.5-4.5%) are

common in a matrix (35-45%) consisting chiefly of authogenic clay,

chlorite, zeolite, and calcite. Delicate glass shards are not broken as

is commonly seen in water-laid tuffs. Welding features include

plastically deformed shards, elongated pumice with length to width

ratios of 3:1 (Figure 16). Margins of pumice fragments are deformed

around crystals and rock fragments. One example of accretionary

lapilli was observed (Figure 17). This evidence supports

interpretations of pyroclastic flow origin of the lapilli-tuffs.

VOLCANIC SANDSTONE AND CONGLOMERATE

Volcanic arenite is olive grey to olive brown in color, poorly

sorted, subangular, and composed almost entirely of volcanic lithic

fragments in a clay matrix. Outcrops reveal low-angle trough

crossbedding to massive, normal graded beds and commonly contain pebble

trains.

These rocks are composed predominantly of angular to subrounded

14

12

~ - 10 • 0

N

:.: a + 0

N

~ 6

4

2

39

Rhyolite

Basalt Basaltic: l Andesi t e jAnd esi t e Dac:i te

41 45 52 57 65 68 77

Figure J2. Compositional classification of some lithic fragments in the volcanic diamictites. Classification scheme after La Bas and others (1986).

40

Figure 1..§.. Photomicrograph of elongated pumice; magnification

20X.

Figure lZ· Photomicrograph of an accretionary lapilli; magnification 20X.

41

42

microlitic and tuffaceous volcanic rock fragments (40-65%), and

euhedral to subhedral feldspar grains (3-8%), in a clay and chlorite

matrix (29-39%). Results of modal analyses are shown in Appendix A.

Data obtained by point counting the sandstone samples are plotted in

Figure 18. All samples are composed of clasts derived from a magmatic

arc.

Crystals and lithic fragments in the sandstones appear to have

been derived from pyroclastic sources. Most lithic fragments are

hydrothermally altered (contain zeolites) and display weathering rinds.

Some are red in color due to iron oxidation. Anorthite content of the

plagioclase could not be determined due to extensive replacement of the

crystals by clay.

Heavy mineral separations were made from three sandstone samples.

One sample of sandstone was collected from the middle of the Timonium

Creek section and two were collected from the top of the Hamilton

Buttes section. The list of heavy minerals and their relative

abundances are given in Appendix B. Sample locations are shown in

Plate II. The heavy mineral assemblage, consist chiefly of magnetite,

oxyhornblende, hypersthene, and apatite. Biotite occurs in trace

amounts only in the stratigraphically lowest sample.

SILTSTONE

Siltstone and mudstone, the least abundant rock type in the

stratigraphic section, are altered and consist chiefly of smectite,

chlorite, and iron oxides. The fine-grained rocks were not point

counted.

Continental Block

I I

Q

Provenance•

I r- '-----/ I ''

\.I I '...._

' I ' \ ' ' ' ', '

Magmatic Arc Provenances \ ' I

FI ''> A /• Jtlfk \ L

43

Figure 18. Composition of sandstones of the Ohanapecosh Formation. Fields relate to Dickinson and Suczek (1979); sandstone suites derived from different types of provenances. End member components of the ternary diagram are Q-quartz and chert, F-feldspar crystals, and L-lithic fragments. All samples from the Ohanapecosh Formation near Hamilton Buttes appear to have been derived from a magmatic arc provenance.

CHAPTER V

PETROLOGY OF LAVA FLOWS AND INTRUSIONS

INTRODUCTION

The exposed stratigraphic section of the Ohanapecosh

Formation north of Hamilton Buttes includes a few lava flows and is cut

by north-trending dikes and tabular sheet-like sills. These rocks are

concentrated but not found exclusively in the lower member.

Chemical analyses of selected samples are tabulated in Table III;

sample sites are shown on Plate II. Modal analyses are listed in

Appendix C.

PETROLOGY OF THE LAVA FLOWS

Four lava flows crop out near the base of the Ohanapecosh

Formation in the study area. Rocks were identified in the field as

phyric andesite. Their exposed thicknesses range from 4 to 10 m.

Weathered surfaces range from brown to greyish brown; fresh rock is

black to brown. Geochemistry and field relations suggest that the four

outcrops represent three lava flows.

The lava flows are classified as basaltic andesite and andesite

(Figure 19). Silica contents in the lava flows range from 68 to 72%

14

12

~ i 10

0 N

~ 8 + 0

N .. z 6

4

2 •

Basalt

41 45

A A

• •

• a-.ltic: Andesi t • jAnd esi t •

52 57 65

SI02 Wt%

Rhyoll te

D•cite

68 n

Figure 19. Plot of dikes and sills (closed triangles) and lava flows (open triangles) of the Ohanapecosh Formation in the volcanic rock classification scheme of La Bas and others, 1986.

45

(Table III). They plot close to the tholeiite-calcalkaline boundary

(Figure 20).

46

Four thin sections of the lava flow samples were examined; all

are phyric with a pilotaxitic groundmass. Phenocrysts consist of 20 to

40% labradorite (An50-64) and approximately 5% augite. The groundmass

ranges from 40 to 65% labradorite (An50-57), 0 to 9% augite, and 1 to

5% magnetite. The rocks are altered from their original mineralogy and

contain up to 30% secondary chlorite, 20 to 30% clay minerals, and

veinlets of calcite and zeolites.

PETROLOGY OF INTRUSIVE ROCKS

Most dikes and sills, are located in the lower member of the

exposed Ohanapecosh Formation. Weathered surfaces of the intrusive

rocks range from light brown to dark brown. They are grey to black on

a fresh surface, dense to slightly vesicular, and were identified in

the field as phyric andesite. Analyses of the intrusions range from

50.1 to 64.5 percent weight silica (Table III). They range from basalt

to andesite in composition (Figure 19) and plot close to the tholeiite

calcalkaline boundary (Figure 20).

Samples examined petrographically are phyric. Modal analysis

(Appendix C) show that phenocrysts range from 25 to 40 percent

labradorite (An51-60) and 0-5 percent augite. Microlites display a

subparallel alignment and range from 10-65 percent laths of andesine to

labradorite (An46-57), 0 to 5 percent ophitic to subophitic augite, and

0 to 5 percent magnetite. All rocks have been altered and contain 10

47

Table III

Whole Rock Chemical Analysis, Ohanapecosh Formation, Hamilton Buttes area

Lava~ (1)

Sample .!!2..:.. CS-11 EEW-7 EW-7 WW-8

Major Element Weight.!

Si02 56.62 54.05 54.01 56.05

Al 203 16.59 17.45 17.70 16.95

TiOz 1.287 1.440 1.455 1.315

Fe203 9.72 10.06 10.57 9.38

HnO .135 .223 .208 .150

CaO 7.30 8.34 7.76 9.04

HgO 4.73 4.18 3.68 4.09

I 20 .92 .66 .74 .44

Na20 2.37 3.23 3.50 2.27

Pz05 .208 .244 .245 .187

Trace Element .!!£!!!.

Ni 31 21 31 22

Cr 41 65 52 19

Sc 35 37 40 35

v 207 274 255 220

Ba 176 172 216 138

Rb 24 12 14 11

Sr 250 256 243 376

Zr 217 208 211 175

y 34 37 39 27

Nb 11 13 12 9

Ga 23 23 20 17

Cu 101 102 108 129

Zn 90 93 93 87 ------ ------ ---- ----

100% 100% 100% 100%


48

Intrusions-Whole rock chemical analysis, Ohanapecosh Formation

Sample .!!2..:.. (1) HB-26 EEW-9 NR-SA NR-11 NR-14 TC-4 WW-2 WW-7

Major Element Weight!

Si02 53.80 53.39 64.46 56.29 54.81 57.57 49.62 59.79

Alz03 18.65 17.83 14.74 16.95 17.86 15.82 20.35 15.74

Ti02 1.372 1.637 1.199 1.538 1.548 1.570 1.133 1.285

Fe2o3 9.28 10.52 7 .11 9.71 10.01 10.33 10.12 10.49

MnO .142 .150 .120 .142 .162 .164 .177 .122

CaO 7.98 9.15 6.68 8.02 8.89 7.41 11.64 6.06

MgO 3.71 3.34 2.04 3.21 2.85 2.77 4.09 3.38

I2::> .91 1.12 .26 .99 .83 1.11 .35 .24

Na20 3.87 2.47 3.10 2.79 2.67 2.86 2.30 2.55

Pz05 .156 .255 .192 .224 .256 .263 .117 .222

Trace Element .21!!!

Ni 19 20 18 17 15 15 16 22

Cr 32 39 39 38 1 15 19 47

Sc 34 39 31 37 38 37 41 39

v 265 262 206 228 190 244 238 207

Ba 192 318 158 247 206 288 145 184

Rb 22 28 4 29 22 18 8 4

Sr 341 195 201 246 254 282 260 224

Zr 132 205 184 199 195 226 80 212

y 24 37 30 35 39 44 23 27

Nb 6 12 11 12 12 14 2 11

Ga 23 23 17 23 23 20 21 19

Cu 121 92 93 68 118 73 86 54

Zn 76 104 so 90 96 107 65 73 ----- ----- ---- ----- ----- ------ ----- -----100% 100% 100% 100% 100% 100% 100% 100%


5.0

.. ,, 4.0

3-'.

3.0

* F.O/Mg 2.S

2.0

1.!5

1.0

0-' 0.0

e =5C) " 60 ~ 70 ~

smvt.'5

* Total iron recalculated to Fe2+.

Figure 20. A plot of FeO*/MgO versus Si02 in Miyashiro's (1974) diagram. Open diamonds, lava flows; closed diamonds, dikes and sills.

49

to 30 percent secondary chlorite, 20 to 30 percent clay minerals, and

variable amounts of calcite veining and zeolites.

PETROLOGIC TYPE

so

Rocks of the Western Cascade Group can be divided geochemically

into two stratigraphic sequences. Lower Western Cascade rocks in

southern Washington (Hammond, 1980) and early Western Cascade rocks of

Oregon (Priest and others, 1983) have a basaltic to andesitic

composition which display an iron-rich tholeiitic geochemical trend.

The upper or middle to late Western Cascade rocks are more silicic and

are intermediate calc-alkalic.

The intrusive rocks and lava flows in the study area, when major

oxide geochemistry is compared to published data on Western Cascade

rocks (Priest and others, 1983; Garcia, 1978), clearly fall into the

Early Western Cascade tholeiitic trend of Priest and others (1983;

Figure 21). The intrusive rocks in the study area fall into the

island-arc tholeiite field in a Ti versus Cr diagram (Figure 22).

Ohanapecosh Formation

(Garcia, 1978)

NA20 +K20

FEO

Early Western Cascade

t hol • ilt i c lavas

(Priest, 1983)

Moo

Figure 21. AFM diagram for analyzed intrusive rocks (closed triangles) and lava flows (open triangles) from the Ohanapecosh Formation north of Hamilton Buttes (after diagram prepared by Winters, 1984).

51

c::::=:i:: 1 ~., r-r

' ' I• C"I

Ti ppm • ~ ;II~

~ ,.

~ . I

1 .-....A

OF1~

IAE l"llo.

"Ill ~

I"' I'll!"

1 l I 1M .

0.1 1.0 10.0 100.0 1000.0 10000.0

Cr ppm

Figure 22. Plot of Ti versus Cr (after Pearse, 1975) distinguishes ocean floor basalts (OFB) from younger island-arc tholeiites (IAB). Analyzed samples from the study area fall into the island-arc tholeiitic field. Open diamonds, lava flows; closed diamonds, dikes and sills.

52

CHAPTER VI

PALEOCURRENTS

INTRODUCTION

Trends in maximum grain size in the volcanic diamictite and

orientation of channel features within the volcanic sediments in the

Ohanapecosh Formation, north of Hamilton Buttes, indicate southwestward

paleoflow in the lower part of the section, changing to a northwestward

direction in the upper part. These trends generally agree with the

data of Winters (1984). His data from the underlying Chambers Creek

beds and the lowermost Ohanapecosh indicate a westward to southwestward

paleoflow.

METHODS

Grain size in debris flows beyond the flanks of the volcano has

been shown to decrease with distance from the source (Sharp and Nobles,

1953; Cameron and Pringle, 1986; Scott, 1985). Maximum grain-size

measurements were taken from an individual volcanic diamictite bed over

a 2 square meter area. Grain size of the 10 largest lithic fragments

was recorded and the mean calculated. A second and usually a third

measurement was taken from the same bed up to 2.4 km distant from the

54

first measurement. Measurements were taken from fourteen volcanic

diamictite beds. The best exposures of continuous beds occur along

strike and roughly perpendicular to strike in the upper Ohanapecosh

part as exposed in the Hamilton Buttes section.

Bearings of primary sedimentary features, such as channel axis

and the long axis of oriented wood fragments, were recorded along with

the local strike and dip. Most data were collected in the lower

Ohanapecosh section. Direction of cross-bedding is indistinct and was

not measured.

Bedding dips in the study area are generally less than 15°, so

tilt adjustment corrections were not necessary. Results of

measurements are displayed in a series of diagrams (Figures 23-25).

The length of each class interval is proportional to the percentage of

readings recorded. In a rose diagram showing the maximum grain size

a . measurements, a 90 class interval was used due to the lack of three

dimensional exposure of the bed. Current direction was assigned to the

appropriate compass quadrant. Actual direction is approximate.

DISCUSSION

Channel axis orientations, measured primarily from beds in the

lower section of the Ohanapecosh Formation, indicate a southwestward

paleoflow with a vector mean of 235° (Figure 23a). Maximum grain size

data is displayed in Figure 24. Due to the large class interval and

standard deviation, a vector mean cannot be defined. Flow direction

may be in any direction within the northwest quadrangle. Five channel

23a. Lower To map unit channel axes orientation n=26 vector mean=55•,235• class interval=l0° tt"=40

55

~

23b. Upper To map unit channel orientations n=6 vector mean=109• ,289° class interval=l0°

0--.25

23c. Combined upper and lower map unit channel axes orientations n=32

o a vector mean=67 ,247 class interval=to• 0-=35

Figure 23. Orientation of channel axes.

n=13 class interval=90° 0--=1 04°

Figure 24. Orientation of maximum grain size trends.

Vector mean=145° ,325° class interval=10° 0"'=68°

Figure 25. Orientation of wood fragments throughout the Ohanapecosh sections.

56

57

axis orientations were measured in the upper unit (Figure 23b). Their

0 vector mean is 289 . In addition, volcanic diamictite beds in the

southern portion of the study area undergo a f acies change to

epiclastic sedimentary beds to the north. Figure 23c shows combined

channel axis orientations in both upper and lower units to give a

vector mean current direction of 247~.

The long axis of oriented wood fragments are shown in Figure 25.

Four of the eight bearings were taken from the same bed, strongly

biasing the results. The remaining four have scattered orientations.

This data indicates that the paleof low direction in the upper

part of the stratigraphic section is closer to due west than to due

north. Data suggest a change of paleoflow direction from west to

northwest upward in the section. Figure 26 shows the distribution of

measured paleocurrent directions in the study area.

CHAPTER VII

STRUCTURAL GEOLOGY

Folds and Faults

The major structure in the area is a broad, slightly

assymetrical, northwest trending syncline, herein named the Hamilton

Buttes syncline. Its flanks dip 15° to 55°, the eastern flank being

the steeper. Its axis plunges shallowly, about 5°, to the north

(Plate I, Figure 27). The eastern limb is part of the Johnson Creek

anticline (Winters, 1984). The hinge line trends Nl5°W, and is located

just west of Wobbly Creek valley. North-trending faults are common in

this region of the Cascade Range, but no evidence of faulting was

observed in the study area.

Intrusions

Basalt to andesite dikes and sills intrude the lower part of the

Ohanapecosh Formation. Two nearly vertical dikes are located less than

.4 km (.25 mi) apart on FS Road 22. A third dike is located on FS Road

78. They strike N23°W to N30°W and dip vertically. Exposed contacts

are non-sheared suggesting that intrusions occurred after folding.

CHAPTER VIII

GENERAL MODEL OF DEPOSITIONAL HISTORY

INTRODUCTION

Volcaniclastic facies models in a non-marine setting, relating

deposits to distance from source, have been described by Vessel and

Davies (1981), Swanson (1966), Fisher and Schminke (1984), Cas and

Wright (1986) and Bestland (1985). Progressive changes can be seen in

volcanic sediments with increasing distance from the source (Figures 28

and 29). Near-source facies (Fisher and Schminke, 1984) or volcanic

core f acies and proximal volcaniclastic facies of Vessel and Davies

(1981) are characterized by lava flows, pyroclastic flows, and airfall

deposits. Intermediate-source facies (Fisher and Schminke, 1984) or

medial volcaniclastic facies of Vessel and Davies (1981) consists of

volcanic diamictite, interpreted as debris flows, conglomerates and

coarse sandstones, deposits from pyroclastic flows, and minor lava

flows. These coarse-grained deposits are poorly sorted and accumulate

in aprons which ring the volcanic cone. Distant-source facies (Fisher

and Schminke, 1984), or distal volcaniclastic facies of Vessel and

Davies (1981) are dominated by braided or meandering stream deposits of

coarse sands and conglomerate with thin air-fall beds. Any facies

Tye

Tye

~

G;]~ ...)t--

~

.:,L._ ~

~

luck lid.tes

OCEAN

VOLCANIC CORE FACIES

< ! s \ PROXIMAL VOLCANIC

FACIES

~MEDIAL ... 1: :· \· · ·) I~ VOLCANIC

· ·. / FACIES

.::,t_

.::L-

.::,t_

(lll1rial F111)

~

~

DISTAL VOLCANIC

FACIES lSi11111 + lr1iff4

cUIHI,, 11"4 usil ltl4 'UlstliM)

_j/_.

::it-

~

~DELTA

Figure 28. Schematic diagram of a non-marine, fore-arc area between an active cone and the sea, showing types and lateral extent of deposits of varying volcanic f acies (after Vessel and Davies, 1981).

62

/Volcanic ? Core Faciu

l \~~1 ~ ,~ ,)

I

, Proximal '(?~ Volaniclastic

t.\ Facies Medial

Volcaniclastic Facies

Distal Vol cniclastic Facies Offshore

L = A. '-II E'~§1 Glowing Anluche 51:. ·.". Fl . I C"- --• an 1ric . . rt..b . R • · .• ~ uta a.anas , • .. -· o +in: ris ow ·. .

Figure 29. Generalized cross section of volcanic facies (after Vessel and Davies, 1981).

63

model relating to distance from source uses relative terms. Absolute

distances can not be defined (Fisher and Schminke, 1984).

ENVIRONMENT OF DEPOSITION

Summary

64

Lithology and sedimentary characteristics of the deposits in the

study area fall into the intermediate source f acies of Fisher and

Schmincke (1984) or the medial facies of Vessel and Davies (1981).

These deposits form an alluvial apron beyond the flanks of the volcano.

Evidence of this type include the scarcity of fine-grained deposits,

lateral continuity of beds, and narrow, thin channel deposits. Lateral

continuity of deposits indicates that deposition occurred on a nearly

flat surface forming bajada-like accumulations.

Volcanic Diamictite

Volcanic diamictite beds are interpreted as lahars (Table I).

Lahars consist of fluid mobilized debris associated with

stratovolcanoes. They originate on the flanks of the volcano and may

travel tens of kilometers from the volcanic source. They form fans

that coalesce or form broad individual lobes on lowland areas. On low

slopes (7-10°), the base of the flow is non-erosive (Fisher and

Schminke, 1984). They commonly form during late stages of an eruption

when loose pyroclastic flow or airfall deposits become water soaked.

The basal sole layer forms during the rising and peak stages of

flow in response to shear concentrated at the flow boundary. It is the

"ball bearing bed" of Scott (1985). The sole layers in the study area

65

are Type 1, as described by Scott (1985), which are typical of flood

plain facies lahars (Figure 11). They characteristically comprise 10-

20% of the thickness of the lahar, rarely show compaction features, and

lack large dispersed clasts. The main body of the lahar has a sharp

lower contact; and commonly grades upward into horizontally bedded

conglomerate. These conglomerates represent hyperconcentrated stream

flow, a transition phase from debris flow to stream flow.

Hyperconcertrated stream flow results from the dilution of the debris

flow by streamflow (Scott, 1985). The cross-bedded sandstone

represents the reestablishment of normal stream flow.

Lapilli-tuf f

Lapilli-tuf f consists of normally graded pumice-rich angular

lithic clasts in an ash matrix (Table I). The abundance and angularity

of pumice suggests that many of these deposits are primary and

originated as pyroclastic flow and airfall deposits. Beyond the flanks

of volcanoes, pyroclastic flows spread out in fan-like lobes, mantling

the topography.

Epiclastic Sedimentary Rocks

Volcanic conglomerate, sandstone, and siltstone (Table I), and

are found throughout the exposed section. The conglomerate and

sandstone were deposited by traction currents in fluvial paleochannels

and sheet flood processes and represent the reworking of easily

erodible pyroclastic materials. The subrounded to angular lithic

fragments and rapidly changing channels suggest rapid aggradation of

the stream channels.

Siltstone and mudstone were deposited by fine-grained materials

settling out of suspension in shallow lakes and as overbank deposits.

The massive to laminated intervals, in the Hamilton Buttes measured

section, consist of graded beds and contain a few intact leaf fossils

which imply near-shore deposition.

Subaerial versus Subaqueous Deposition

66

Fiske (1963) argued that much of the Ohanapecosh Formation was

deposited by subaqueous debris flows off the flanks of volcanoes. For

evidence, he cites 1) lateral continuity of individual volcaniclastic

beds; 2) widespread nature of the formation; 3) and the absence of

fluvial deposits. However, these characteristics do not unequivocally

establish that the Ohanapecosh strata were deposited subaqueously.

This evidence simply indicates the wide-spread extent of the deposits

on a low relief surface. Evidence for subaerial deposition in the

study area includes 1) presence of accretionary lapilli, which would

not remain intact if they had settled through water or during transport

in a turbidity flow; 2) partially welded tuffs and bent glass shards

implying hot plastic deformation; 3) terrestial fossils (leaf, wood

fragments, tree trunk) but no aquatic fossils; 4) interbedded fluvial

sandstones at the base of the formation; S) scour-and-fill channel

features; and 6) lack of pillowed lavas.

Paleogeography

Each map unit in the Ohanapecosh Formation in the study area

represents a different depositional process. The lower part of the

67

Ohanapecosh Formation consists of reworked volcaniclastic deposits,

including channel-fill, pyroclastic flow and air-fall deposits, and

minor lava flows. These deposits are a product of volcanism to the

east of the study area. As volcanic eruptions grew more energetic or

produced more ejecta, pre-existing distributary channels became

overwhelmed with large volumes of volcanic debris. These streams

rapidly aggraded and shifted channels frequently producing volcanic

apron deposits. Scarce fine-grained deposits occur in areas that were

poorly drained.

Early Ohanapecosh sedimentation was coeval with Chambers Creek

sedimentation as evidenced by their interf ingering relationship exposed

to the east of the study area along FS Road 22. Drainages transporting

arkosic sediments from the east were overwhelmed with volcanic debris.

The upper part of the Ohanapecosh Formation is characterized by

abundant volcaniclastic debris flows, volcanic sandstone and siltstone,

and pyroclastic flow and air-fall deposits. Lahars originated in

volcanic source areas to the southeast. They flowed in preexisting

drainages incorporating soil and lithic material from the valley walls.

Well beyond the flank of the volcano, they formed lobate deposits

creating coarse volcaniclastic apron fans in the study area (Figure

30). Lahars grade upward into horizontally bedded conglomerate with no

distinct bedding plane separating them. This fining-upward sequence

implies that the conglomerate were deposited by the same event as the

lahars. Away from the source area, the debris flows were diluted by

stream flow and graded upward into hyperconcentrated flood flow and

Vd

I'

\ \

' ' ....

"'=7Epi

NO SCALE

Figure 30. Block diagram of volcanic facies model for Hamilton Buttes area. Epi: epiclastic sedimentary rocks; Vd: volcanic diamictite; Lt: lapilli-tuff; Lava: lava flow.

68

normal stream flow deposits (Fisher and Schminke, 1984; Harrison and

Fritz, 1982; Pierson and Scott, 1982).

69

CHAPTER IX

SUMMARY

Over 1055 m of andesitic-dacitic volcaniclastic rocks and minor

interbedded andesitic lava flows of the Ohanapecosh Formation are

exposed in a dissected structural high at Hamilton Buttes, about 22 km

southwest of Packwood, Washington. This sequence of rocks are between

42 and 30 m.y. old or approximately late Eocene to early Oligocene in

age.

Three lithologies are distinguished here in the volcaniclastic

strata. Volcanic diamictite is interpreted as lahars. Beds consist of

angular to rounded, pebble to sand sized lithic clasts, ranging in

composition from andesite to rhyolite, in a crystal-lithic mud matrix.

They form well indurated, massive, non-sorted beds 2 to 13 m thick.

Pumiceous lithic lapilli-tuff are primary deposits of pyroclastic

flow origin. They are characterized by 1 to 13 m thick beds of angular

to subrounded lithic fragments, flattened pumice, and glass shards.

Volcanic conglomerate, sandstone, and siltstone represents

reworking of volcanic debris. The coarse-grained deposits were

deposited by aggrading, rapidly changing streams. Siltstone intervals

represent overbank and lacustrine deposits.

Strata in this part of the Ohanapecosh Formation were deposited

71

in an alluvial apron environment. Sediments were derived from

explosive volcanic deposits and the erosion of volcanic highlands whose

drainages were located to the east and southeast of the study area, as

shown by current direction structures. At the time of deposition, the

study area was a low-lying alluvial plain.

The Ohanapecosh Formation and the underlying arkosic Chambers

Creek Beds of Winters (1984) were subsequently folded, producing the

north-plunging syncline in the Hamilton Buttes area. Post-deformation

sills and dikes of tholeiitic basalt to andesite intrude the sequence.

Uplift and erosional dissection in the Miocene and Pliocene

followed deformation. These events preceeded the outpouring of a calc

alkaline pyroxene andesite lava flow along an ancestral valley.

REFERENCES CITED

Bestland, E. A., 1985, Stratigraphy and sedimentology of the Oligocene Colestin Formation, Siskiyou Pass area, southern Oregon: Unpub. M.S. Thesis, Eugene, University of Oregon, 149 pp.

Buckovic, W. A., 1974, Cenozoic stratigraphy and structure of a portion of the west Mount Rainier area, Pierce County, Washington: Unpub. M.S. Thesis, Seattle, Univ. of Washington, 123 pp.

-----, 1979, The Eocene deltaic system of west-central Washington: in Armentrout, J.M., and others, ed., Cenozoic paleogeography of the western United States, Pacific Coast Paleogeography Symposium 3: Pacific Section Soc. Econ. Paleon. Miner., p. 147-163.

Cameron, K. A., and Pringle, P. T., 1986, Post-glacial lahars of the Sandy River basin, Mount Hood, Oregon: Northwest Science, v. 60, no. 4, p. 225-237.

Cas, R. A. F., and Wright, J. V., 1987, Volcanic Successions: Modern and Ancient: London, England, Allen and Unwin, 528 p.

Clayton, G. A., 1983, Geology of the White Pass area southcentral Cascade Range, Washington: Unpub. M.S. Thesis, Seattle, Univ. of Washington, 212 pp.

Dickinson, W.R., 1970, Interpreting detrital modes of greywacke and arkose: Journ. Sed. Petrol., v. 40, p. 695-707.

-----, 1979, Cenozoic plate tectonic setting of the Cordilleran region in the United States, in Armentrout, J. M., ed., Cenozoic paleogeography of the Western United States, Pacific Coast Paleography Symposium 3: Pacific Section Soc. Econ. Paleon. Miner., p. 1-13.

Dickinson, W.R., and Suczek, C. A., 1979, Plate tectonics and sandstone compositions: American Association of Petroleum Geologists Bulletin, v. 63, p. 2164-2182.

Fisher, R. V., 1957, Stratigraphy Df the Puget Group and Keechelus Series in the Elbe-Packwood Area of Southwest Washington: Unpub. Ph.D. Dissertation, Seattle, Univ. of Washington, 153 pp.

-----, 1961, Stratigraphy of the Ashford area, southern Cascades, Washington: Geological Society of America Bulletin, v. 53, no. 1, p. 30-54.

Fisher, R. V., and Schminke, H.-U., 1984, Pyroclastic Rocks: Springer-Verlag, New York, N. Y., 472 pp.

Fiske, R. S., 1963, Subaqueous Pyroclastic Flows in the Ohanapecosh Formation, Washington: Geological Society of America Bulletin, v. 74, p. 391-406

-----, 1969, Recognition and Significance of Pumice in Marine Pyroclastic Rocks: Geological Society of America Bulletin, v. 80, p. 1-8.

Fiske, R. S., Hopson, C. A., and Waters, A. C., 1963, Geology of Mount Rainier National Park, Washington: U. S. Geological Survey Prof. Paper, n 444, 93 pp.

Garcia, M. 0., 1978, Criteria for the identification of ancient volcanic arcs: Earth Science Review, v. 14, p. 147-165.

Gard, L. M., 1968, Bedrock geology of the Lake Tapps quadrangle, Pierce County, Washington: U. S. Geological Survey Professional Paper 388-B, 33 pp.

Hammond, P. E., 1979, A Tectonic model for evolution of the Cascade Range, in Armentrout, J.M., ed., Cenozoic paloegraphy of the western United States, Pacific Coast Paleography Symposium 3: Pacific Section Soc. Econ. Paleon. Miner., p. 219-237.

-----, 1980, Reconnaissance geologic map and cross sections of southern Washington Cascade Range: Portland, Oregon: Publications of the Department of Earth Sciences, Portland State University, 31 pp.

Harrison, S., and Fritz, W.J., 1982, Depositional features of March 1982 Mount Saint Helens sediment Flows: Nature, v. 299, p. 720-722.

Heller, P. L., and Ryburg, P. T., 1983, Sedimentary record of subduction to f orearc transition in the rotated Eocene basin of western Oregon: Geology, v. 11, p. 380-383.

73

Hunting, M. T., Bennet, W. A.G., Livingston, V. E., Jr., and Moen, W. S., 1961, Geologic Map of Washington, 1:500,000: Washington Division of Mines and Geology.

Irvine, T. N., and Baragar, W.R. A., 1971, A guide to the chemical classification of the common volcanic rocks: Canadian Journal of Earth Sciences, v. 8, no. 5, p, 523-548.

Le Bas, M. J., Le Maitre, R. W., Streckeisen, A., and Zanettin, B., 1986, A chemical classification of volcanic rocks based on the total alkali-silica diagram: Journal of Petrology, v. 27, part 3, p. 745-750.

Le Bas, M. J., and Sabine, D. A., 1980, Progress in 1979 on nomenclature of pyroclastic materials: Geological Magazine, v. 117, p. 389-391.

Miller, R. B., 1987, The Rimrock Lake Inlier and its implications for the basement of the Columbia Embayment: Abstract, American Geophysical Union, 34th Annual Meeting, Sept. 2-4, 1987, Pacific Northwest Section, Olympia, Washington, Evergreen State College.

Miyashiro, A., 1974, Volcanic rock series in island arcs and continental margins: Amer.Journ. of Science, v. 274, p.321-355.

Pearce, J. A., 1975, Basalt geochemistry used to investigate past tectonic environment on Cypress: Tectonophysics, v. 25, p. 41-67.

Phillips, W. M., Korosec, M.A., Schasse, H. W., Anderson, J. L., and Hagan, R. A., 1986, K-Ar ages of volcanic rocks in southwest Washington: Isocron/west, v. 47, p. 18-24.

Pierson, T. C., and Scott, K. M., 1982, Downstream dilution of a lahar: Transition from debris flow to hyperconcentrated flow: Water Resources Research, v. 21, no. 10, p. 1511-1524.

Priest, G. R., Woller, N. M., and Black, G., 1983, Overview of the geology of the central Oregon Cascade Range: in Priest, G. R., and Vogt,B. F., eds., Geology and Geothermal resources of the central Oregon Cascades Range, Oregon Dept. of Geol. and Min. Ind. Special Paper 15, p. 3-28.

Schmid, R., 1981, Descriptive Nomenclature and Classification of Pyroclastic Deposits and Fragments: Recommendations of the IUGS Subcommission on the Systematics of Igneous Rocks: Geology, v. 9, p. 41-43.

74

Scott, K. M., 1985, Lahars and lahar-runout flows in the ToutleCowlitz River system, Mount St. Helens, Washington-origins, behavior, and sedimentology: U. S. Geological Survey OpenFile Report 85-500, 202 pp.

Simpson, R. W., and Cox, A., 1977, Paleomagnetic evidence for tectonic rotation of the Oregon Coast Range: Geology, v. 5, p. 585-589.

Sharp, R. P., and Nobles, L. H., 1953, Mudflows of 1941 at Wrightwood, southern California: Geological Society of America Bulletin 64, p. 547-560.

Smith, G. A., 1986, Coarse-grained nonmarine volcaniclastic sediment: Terminology and depositional process: Geological Society of America Bulletin, v. 97, p. 1-10.

Snyder, W. S., Dickinson, W. K., and Silberman, M. L., 1976, Tectonic implications of time-space patterns of Cenozoic magmatism in the western United States: Earth and Planetry Science Letters, v. 81, p. 3253-3258.

Swanson, D. A., 1966, Tieton volcano, a Miocene eruptive center in the southern Cascade Mountains, Washington: Geological Society of America Bulletin, v. 77, p. 1293-1314.

Swanson, D. A., and Clayton, G. A., 1983, Generalized geologic map of the Goat Rocks Wilderness and Roadless Areas (6036, Parts A, C, and D), Lewis and Yakima Counties, Washington: U. S. Geological Survey Open-File Report 83-357.

Tabor, R. W., Frizzell, V. A., Vance, J. A., and Naeser, C. W., 1984, Ages and stratigraphy of lower and middle Tertiary sedimentary and volcanic rocks of the central Cascades, Washington: application to the tectonic history of the Striaght Creek Fault: Geological Society of America Bulletin, v. 95, p. 26-44.

Van Atta, R. 0., 1971, Sedimentary petrology of some Tertiary formations, upper Nehalem River basin, Oregon: Ph. D. Thesis, Corvallis, Oregon State University, 245 pp.

Vessel, R. K., Davies, D. K., 1981, Nonmarine Sedimentation in an Active Fore Arc Basin: Society of Economic Paleotologists and Mineralogists, Special Publication No. 31, p. 31-45.

Wilson, D, and Cox, A., 1980, Paleomagnetic evidence for tectonic rotation of Jurassic plutons in the Blue Mountains, Eastern Oregon: Journal of Geophysical Research, v. 85, p. 3681-3689.

75

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~--~~--

Winters, W. J., 1984, Stratigraphy and sedimentology of paleogene arkosic and volcanoclastic strata, Johnson Creek - Chambers Creek area, southern Cascade Range, Washington: Unpub. M.S. Thesis, Portland State Univ., 163 pp.

Wise, W. S., 1970, Cenozoic volcanism in the Cascade Mountains of southern Washington: Washington Division of Mines and Geology Bulletin, v. 60, 45 pp.

76

APPENDIX A

POINT COUNT DATA

(1) Catagories used in point counts:

qtz: quartz and chert.

pc: plagioclase feldspar: often altered or replaced by sericite, calcite, albite, zeolites, or clay minerals; slides were not Stained to differentiate feldspars, so as not to mask the lithic fragments; all feldspar was counted as plagioclase.

MRF: foliated and non-foliated metamorphic rock fragment: composed of quartz and mica.

mVRF: microlitic volcanic rock fragment: microlites and phenocrysts of plagioclase feldspar in a subodinate f erromagnesian groundmass; trachytic to felted texture; intermediate to mafic composition.

tVRF: tuffaceous volcanic rock fragment.

pum: pumice

unk: unknown rock fragment: highly altered rock fragment of unknown affinity.

Phyllo: biotite and muscovite; does not include authogenic chlorite.

pyroboles: pyroxenes and amphiboles.

auth: other authigenic minerals: includes clay minerals, chlorite, zeolites, and calcite.

glass shards: glass shards and relic glass shards.

footnotes: 1) categories modified from Frizzell (1979a, p. 104-106).

78

POINT COUNT DATA - Volcanic Sandstones

(1) (2) (1) (2) (3) (3)

sample no. CS-2 NR-12 CS-12 NR-7 HB-28 HB-18b

points counted 1000 1000 1000 1000 1000 1000

Qtz 17 22 - 13 - 10

pc 78 48 33 71 61 66

MRF - - 10

mVRF 395 520 628 609 429 357

tVRF 5 7 17

pum 5 42 2 28 156 136

unk 11 3 1 19 12 5

phyllo 1 - 1 4 3

pyroboles 102 14 15 38 - 32

au th 385 331 293 218 294 349

glass shards - 13 - - 15 45

1) Timonium Creek Section 2) North River Section 3) Hamilton Buttes Section Sample sites are shown in Figures 5, 6, 8, and in Plate II.

APPENDIX B

HEAVY MINERALS

Abundance was visually estimated using the following abundance classes:

F flood - > 50% VA very abundant - 20-50% A abundant - 10-20% C common - 5-10% P present - 1-5% T trace - < 1%

In addition, magnetite, the most abundant heavy mineral in all samples, was removed prior to mounting so as not to mask the other mineral grains.

sample no.

common hornblende

oxyhornblende

orthopyroxene (hypersthene)

apatite

zircon

biotite

enstatite

opaques/rock fragments

1) Timonium Creek Section 2) Hamilton Buttes Section

(1) HB-13

A

p

VA

-

T

T

p

VA

Sample locations given in Plate II.

(2) HB-31

A

p

VA

T

VA

(2) HB-43

A

A

T

VA

APPENDIX C

MODAL ANALYSIS OF LAVA FLOWS AND INTRUSIVE ROCKS

LAVA FLOWS (1) (2)

sample no. WW-8 CS-11 EW-7

phenocryst %

plag 41 38 24

pyroxene 5 25 5

groundmass %

plag 49 32 61

pyroxene 3 2 9

magnetite 2 3 1

glass

vu gs

total % 100 100 100

alteration %

smectite 25 20 20

zeolites 10

chlorite - 5 30

calcite 2 5

1) Timonium Creek Section 2) East Wobbly Section Sample locations given in Plate II.

81

INTRUSIVE ROCKS (1) (2) (1)

sample no. WW-7 NR-11 HB-26 WW-2 NR-5A

phenocryst %

plag 32 27 29 41 30

pyroxene 4 3 2 5 2

groundmass %

plag 9 63 61 39 27

pyroxene - 1 10 7

magnetite - 5 5 3 1

glass 49 - - - 40

vugs 10

total % 100 100 100 100 100

alteration %

smectite 20 20 15 3 20

zeolites 10 - 3 20 3

chlorite 10 15 10 5

1) North River Section 2) Hamilton Buttes Section Sample locations shown in Plate II.

APPENDIX D

LOCATIONS OF MEASURED SECTIONS

(see Plate II for general locations)

Timonium Creek Measured Section: base is located at the first exposure of two meters of an olive-grey pumiceous lithic lapilli tuff in the first drainage before the blocked end of USFS Road 060, §3.7 mi (§6 km) from the intersection with USFS Road 78; this bed forms the base of the waterfall and grades up into bedded volcanic sandstone; elevation §3680 ft (§1122 m).

top is located at the top of 4 m of bedded coarse volcanic sandstone overlying 12 m of basaltic andesite on USFS Road 060, §.9 mi (1.5 km) from the junction of USFS Road 78 and 060; elevation §3550 ft (1082.3 m).

Hamilton Buttes Measured Section: base is located at the base of a prominent 4 m bed of brown volcanic diamictite, §.1 mi (.16 km) north of the intersection of USFS Road and the unmarked road to Mud Lake; elevation §4930 ft (1503 m).

top is located at the top of a resistant ridge forming brown volcanic diamictite 1.4 mi N25W from the same intersection; elevation §5518 ft (1682 m).

North Cispus Measured Section: base is located at the base of a 9 m section of bedded angular lithic lapilli tuff overlain by massive lithic lapilli tuff 10 yards west of mile marker 9 on USFS Road 22; elevation §2655 ft (809.5 m)

top is located at the top of a 2 m massive crystal lithic lapilli tuff followed by an extensive covered section 1.1 mi SW of St. Michael Creek on USFS Road 22; elevation §3250 ft (991 m).

East Wobbly Measured Section: base is located at the base of a brown zeolitized lithic lapilli tuff .5 mi (.8 km) west of the intersection of USFS

Road 7807 and an unmarked road leading north to Wobbly Lake Trail; elevation §4440 ft (§1354 m).

top is located at the top of 3 m of graded sandstone beds 1.15 mi from the same intersection; elevation §4660 ft (§1421 m).

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stratigraphy of the ohanapecosh formation north of

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