Petrology and Sedimentation of Cretaceous and Eocene Rocks in the Medford-Ashland Region, Southwestern Oregon

AN ABSTRACT OF THE THESIS OF

Brian Keith McKnight of the Doctor of Philosophy (Name) (Degree) in Geology presented on ,u 1 ,IT76 (Major) (Date)

Title: Petrology and Sedimentation of Cretaceous and Eocene Rocks in

the Medford-Ashland Region. Southwestern Oregon

Abstract approved: Redacted for privacy Harold E. Enlows

Late Cretaceous and late Eocene rocks over 12,000feet thick are exposed in Bear Valley between the Klamath and Cascade Mountains.Detailed field and laboratory examinations of these rocks were undertaken todeter- mine the conditions under which they were formed.

Late Cretaceous rocks of the predominantly marineHornbrook Formation consist of 1,000 feet of sandstone overlain by 3,000 feetof mudstone.

Fossils indicate a Cenomanian to late Turonian orpossibly Maestrichian age. The Cretaceous sandstones are arkosic to feldspathicarenities and wackes. The basal sandstones strongly reflect the local bedrocklithology.

Higher in the formation, the local bedrock has nocontrol over the mineral

composition. A gradual change from a plutonic source to ametasedimentary

and metavolcanic source is suggested by the verticalchange in mineralogy

of the sandstones. Animal borings, ripple marks, cross-bedding,and

other sedimentary structures as well as the shallow waterfauna suggest

that these sandstones were deposited on the continentalshelf. Above the

300 foot thick basal sandstone unit, shale and thin coal seamssuggest

temporary paralic sedimentation after the initial transgression. A

deepening of the sedimentary basin or an increase in the distancefrom the source of the sediment is indicated by the overlying 3,000feet of mudstone. The mudstone has numerous sandstone interbeds and is locally richly fossiliferous. Sedimentary structures and a progressive decrease in the age of the basal sandstone unit from north to south suggestthat the Hornbrook Formation was deposited in a sea which trangressedtoward the southwest.

Overlying the Cretaceous Hornbrook Formation are nearly8,500 feet of late Eocene sedimentary rocks referred to in this reportinformally as the Payne Cliffs Formation. The Payne Cliffs Formation is composed primarily of sandstone with lesser amounts of conglomerate,shale, tuffaceous sedimentary rock, and coal. A progressive change in the composition of the sandstone from the base to the top of theformation suggests a change from the metamorphic and plutonic sourcerocks of the

Klamath Mountains to volcanic source recies of the earlyCascade Range.

Most of the Payne Cliffs Formation, with itsebundant cress-bedding, cut-and-fill structures, and silicified logs, is clearly theresult of sedimentation by northward flowing streams. The elastic material was deposited in the Medford-Ashland area, at that time anextensive lowland

situated between the rising highlands of the Klamathand Cascade provinces

and draining toward the Pacific coastal plain 60 to 100miles to the north

and northwest. Small lakes and swamps locally received organicand

tuffaceous sediments. A subtropical flora flourished leaving manyplant

remains, especially in the tuffaceous beds. PETROLOGY AND SEDIMENTATION OF CRETACEOUSAND EOCENE ROCKS IN THE MEDFORD-ASHLAND REGION, SOUTHWESTERN OREGON

BRIAN KEITH MCKNIGHT

A THESIS

submitted to

OREGON STATE UNIVERSITY

in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY

June, 1971 APPROVED:

Redacted for privacy

MajcfProfessor and Head of Department of Geology in charge of major

Redacted for privacy

Dean of Graduate School

Date thesis is presented Lam. ()) 70

Typed by Pamela Spaulding ACKNOWLEDGEMENTS

The writer wishes to express his appreciation to the many individuals that have made a contribution to this study. To Dr. Harold E. Enlows, my major professor, a very special thank you is extended. I also wish to acknowledge Drs. John V. Byrne, David A.

Bostwick, and Keith F. Oles, who reviewed the manuscript and added constructive criticism. Dr. Paul T. Robinson aided in interpreting the x-ray data. His helpful dis- cussions during the early part of the investigation are appreciated. Dr. David L. Jones, of the United States

Geological Survey, identified fossil material collected during the field investigation. Financial support for laboratory expenses was provided through a grant from The Society of the Sigma

Xi. The geology departments at Oregon State University and Wisconsin State University-Oshkosh assisted me in many ways. The able secretarial assistance of Pamela

Spaulding has been invaluable.

I would also like to thank my wife for her help during the preparation of this manuscript and for her encouragement, understanding, and patience. TABLE OF CONTENTS

I. Introduction 1

Regional Geology 1 Previous Workers 6

II. Hornbrook Formation 8 Stratigraphy and Age Relationships 8 Sedimentary Structures 19

Cross-bedding 19 Ripple Marks 21 Sole Markings 23 Parting Lineation 25 Shale Clasts 25 Cut-and-Fill 27 Miscellaneous Structures 29

Directional Studies 32 Petrology 37

Sandstones 39 Siltstones, Mudstones, and Shales 56 Conglomerate 58 X-Ray Analyses 60

Provenance 64 Probable Transport Direction 64 Mineralogy of Source Area 66 Mineralogical Maturity 70 Environment of Deposition 71 Tectonics, Relief and Climate 76 78 III. Payne Cliffs Formation Stratigraphy and Age Relationships 78 Sedimentary Structures 87

Bedding 87 Cut-and-Fill 88 Graded Bedding 90 Imbrication 91 TABLE OF CONTENTS (Continued)

Directional Studies 91 Petrology 94

Sandstones 95 Conglomerate 117 Tuff 120 X-Ray Analyses 121

Transport Direction 124

Composition of Source Rocks 125

Mineralogical Maturity 128 Environment of Deposition 129 Tectonics, Relief and Climate 133

IV. Summary of Geologic History 136

V. Bibliography 141

VI. Appendices 148

Appendix A 148 Appendix B 157 Appendix C 163 Appendix D 173 LIST OF ILLUSTRATIONS

Figure Page

1 Index map 2

2 View of general topography 3

3 Stratigraphic column of Hornbrook Formation 9

4 Basal sandstone of Hornbrook Formation overlying Ashland granite 15

5 Pinch-out of shale lens 15

6 Abundant pelecypod shells in sandstone 17

7 Interbedded shale and mudstone 17

8 Hornbrook Formation mudstone 20

9 Interbedded shale and mudstone 20

10 Cross-bedded sandstone 22

11 Current ripple cross lamination 22

12 Current ripple marks 24

13 Load casts from Hornbrook Formation 24

14 Parting lineation in sandstone 26

15 Rounded shale clast in sandstone 26

16 Abundant shale clasts in sandstone 28

17 Burrowing in Cretaceous sand 28

18 Animal trails on bedding plane 30

19 Flame structures 30

20 Sandstone dike 33

21 Current rose of foreset beds 35 LIST OF ILLUSTRATIONS (Continued)

Figure Page

22 Fabric diagram of cross-bedding 36

23 Modal analyses of Cretaceous arenites 47

24 Modal analyses of Cretaceous wackes 48

25 Photomicrograph showing biotite crinkled by compaction 51

26 Photomicrograph showing biotite expanded by calcite crystallization 53

27 Photomicrograph showing replacement of plagioclase by calcite 53

28 Photomicrograph showing siderite- ankerite rimming calcite 57

29 Vertical variation of six minerals in Hornbrook Formation rocks 69

30 Sketch of Payne Cliffs Formation roadcut 80

31 Stratigraphic column of a conglomerate unit 81

32 Interfingering sandstone and conglomerate 84

33 Large boulder in conglomerate bed 84

34 View of the Payne Cliffs 85

35 View of the Van Dike Cliffs 85

36 Honeycomb weathering pattern in sandstone 86

37 Fossil plant fragments in sandstone 86

38 Cross-bedding in Payne Cliffs Formation 89 LIST OF ILLUSTRATIONS (Continued)

Figure Page

39 Cross-bedding in Payne Cliffs Formation 89

40 Current rose of foreset beds 93

41 Photomicrograph of sandstone 98

42 Photomicrograph of volcanic grains 98

43 Photomicrograph of volcanic grains 103

44 Photomicrograph of feldspar partially replaced by calcite 103

45 Modal analyses of Late Eocene arenites 107

46 Modal analyses of Late Eocene wackes 108

47 Modal analyses of Late Eocene sandstones 109

48 Photomicrograph of biotite in sandstone 111

49 Photomicrograph of grains replaced by biotite 114

50 Photomicrograph of grains replaced by chlorite 114

51 Photomicrograph of authigenic chlorite 116

52 Photomicrograph of authigenic chlorite and a zeolite 116

53 Vertical variation of six minerals in Payne Cliffs Formation rocks 127 LIST OF ILLUSTRATIONS(Continued)

Page Table 11 1 Cretaceous fossils in auartz 41 2 Extinction and inclusions rocks 42 3 Plagioclase in Cretaceous 49 4 Textural features ofCretaceous rocks Pebble composition ofCretaceous 5 59 rocks 61 6 X-ray data of Cretaceousrocks 97 7 Extinction and inclusionsin quartz Textural features of LateEocene 8 110 rocks . Pebble composition ofLate Eocene 9 118 rocks 122 10 X-ray data of Late Eocenerocks types .... 128 11 Vertical change of sandstone

Plate vicinity .. In Pocket 1 Geologic map of Medford and PETROLOGY AND SEDIMENTATION OF CRETACEOUS AND EOCENE ROCKS IN THE MEDFORD-ASHLAND REGION, SOUTHWESTERN OREGON

INTRODUCTION

Regional Geology

The primary study area is within a broad valley situated between the Klamath Mountains to the west and the Cascade Mountains to the east (Figure 1); the towns of Medford and Ashland, Jackson County, Oregon, are in this valley. It is within the U. S. Geological Survey 15-minute Medford, Ashland, Lakecreek, and Talent topographic quadrangles. Additional studies were made to the north in the 15-minute Trail, Gold Hill, and Wimer topographic quadrangles.

The rocks under investigation rise approximately one to two hundred feet up the west flank of the valley and several hundred feet up the east flank (Figure 2).

They are relatively unresistant marine Cretaceous and nonmarine Eocene strata. These rocks lie between two physiographic and structural provinces, the Mesozoic Klamath Mts. and the Cenozoic Cascade Mts. (Figure 1).

These provinces are separated in age by at least 75 million years. Rocks immediately underlying those investigated and extending farther to the west as part of the Klamath esaia =MP

CO / I- / 1 I ).- 1 W I- / I W / I CDi I 1 Z --/ // i 2 I c7J/ CO / Q 1 -J Q/ Z I I I

-J>/ I CC 1 / l / v I.- 1 I / I I i Z I I I \ 1- I / ) / / 0 / CO / I, Z r II 1 r Or to 1 /1 C.) I/11 0 / If I Q / /(/ / /z. CO v. I i IL 1 1 , I .... (..)

4- co., t Vt" X. l -44. Medford \ Ashland\ .0100 WIND _--1 ...... =MD4.0011 Figure 1. Index map of research area. This shows how the rocks being investigated occupy a position between the Klamath Mountains and the Cascade Mountains. 3

Figure 2. A general view of Bear Valley looking north and taken just above the city of Ashland. The Cretaceous rocks underlie most of the area in the foreground and the Eocene rocks occupy the rest of the valley and the lower one-half of the hills in the background. 4

Mountains are the Late Triassic Applegate Group and Late

Jurassic to Early Cretaceous intrusives.The Applegate

Group consists of metavolcanic, metasedimentary, and gneissic rocks in that order of abundance, but in the

Medford quadrangle, metasedimentary rocks predominate. According to Wells (1956), these are lens-shaped bodies

of chert, quartzite, argillite, and marble. The large lithologic variation is accompanied by a wide range in

degree of metamorphism. Folding is described by most

persons working in the area as severe and complex. Where attitudes can be measured, beds dip steeply to the

southwest. The major structural trend of the Klamath

Mountains is northeast. Ultramafic bodies parallel to this structural trend are common in the Klamaths, and

are most abundant along the western halfof the range. The largest intrusive within the area is a

batholith, which forms Mt. Ashland, at 7,553 feet the

highest point in the Klamath Mountains. The batholith

is exposed over an area of approximately 180 square

miles. Associated with it and probably connected at

depth are numerous small stocks. Rock types are predominantly diorite, quartz diorite, and granodiorite,

with lesser amounts of granite. Coarse-grained gabbroic

dikes cut both the Applegate Group and younger

intrusives. Bodies of serpentine up to 6 squaremiles 5

in areal extent are present in the Medford quadrangle.

Parent rock ranges from dunite to peridotite but is mostly altered to serpentine minerals.

An occurrence of schists of unknown age but older than the Applegate Group occur approximately 20 miles southwest of Ashland. Because rocks with a

lithology similar to these are found only a few miles

away overlain by sedimentary rocks containing known

Silurian fossils, these schists are presumed to be

Silurian or older in age. Two rocktypes predominate:

quartz-epidote-chlorite schist and quartz-graphite

schist.

Overlying the rocks under investigation are

Tertiary volcanic rocks and sediments derived from the

volcanic constituents.Water-deposited tuffs and

tuffaceous conglomerates of the overlying Late Eocene

Colestin Formation appear to grade upward from the

Eocene sandstones in the northern part of the area, but

overlie them unconformably in the southern part. A few

thin interbedded flows are present in this,formation.

Above this is the Oligocene Roxy Formation, which consists predominantly of vesicular to scoriaceous

basalt flows. Locally, volcanic breccias and tuffs make

up part of the Roxy Formation. 6

Previous Workers

Numerous people have contributed to the present state of knowledge about southwestern Oregon geology in general and the Medford-Ashland region in particular.

Individual contributions will be cited at the appropriate place in the text.

Worthy of special recognition for his diligent work in this part of Oregon is Francis G. Wells, who has published articles and geologic maps pertaining to this region over a period of several decades. His geologic map of the Medford quadrangle, first published in 1939 and revised in 1956, has been particularly beneficial to this study. F. M. Anderson has also contributed much to the knowledge of the stratigraphic age relationships in southwest Oregon and northern California by his many publications on paleontology and stratigraphy (1895,

1902, 1931, 1937, 1938, 1941, 1942, 1943, 1958). Diller's early contributions (1890, 1893, 1907a, 1907b) have significantly helped many later studies. In 1956, Peck, Imlay, and Popenoe described and named the Cretaceous rocks immediately south of the thesis area in Siskiyou County, California. The authors included the Cretaceous strata of the Medford-Ashland 7 region, Oregon, in this report and considered them as part of their newly named Hornbrook Formation. 8

HORNBROOK FORMATION

Stratigraphy and Abe Relationships

The Upper Cretaceous sedimentary rocks in the

Medford-Ashland area of southwestern Oregon and the

Hornbrook area of northern California have generally been referred to as the Chico Group although they are approximately 150 miles north of the Chico type locality.

Until Muller and Schenck published their standard of the

Cretaceous System in 1943, it was common practice

(Anderson, 1931, 1938, 1941, 1942; Louderback, 1905;

Diller, 1907, and others) to include all California and

Oregon rocks of Upper Cretaceous age within the Chico "series." In 1956, these rocks were given formational status by Peck, Imlay, and Popenoe and were named the

Hornbrook Formation for the excellent exposures just south of the thesis area near Hornbrook, California.

At the type locality, the Hornbrook Formation consists of five sandstone units with an aggregate thickness of 1,545 feet, minor interbedded siltstones and conglomerates, and an upper mudstone unit 1,128 feet thick (Peck, et. al., 1956; see Figure 3). At the type section, the Upper Cretaceous rocks are Cenomanian,

Turonian, Coniacian, and Campanian in age according to

Peck, et. al. (1956). Santonian rocks were not 9

...... , ....., ....., ....., ...... --s. ---,--

...... e......

...... - es..

e...- ...-- VI (1128') Mudstone with sandstone

...... ,...... -,-

......

...... -

/1 ....."...... ,

e-s- ,......

.....,...... --

...."-

.-.- __ V (311') Sandstone with siltstone

. . .

..-. IV (372') Siltstone with sandstone

--- ...- ...... -

e . . . III (134') Sandstone ...... II (286') Sandstone . .

. . . . .

...... I (442') Sandstone with conglomerate j2.4. ..'''SE

'77., .... '.../( t... // , - tt e , i..., .... e

Figure 3. A graphic stratigraphic sectionof the Hornbrook Formation at the type area preparedfrom the written descriptions presented by Peck,Imlay, and Popenoe (1956). 10 recognized by the above authors and may be represented by a disconformity. Jones, in an abstract (1959), listed the lowermost beds at the type section as upper Turonian rather than Cenomanian, and the uppermost beds as possibly Maestrichtian in age. Furthermore, Cenomanian fossils in the Medford-Jacksonville region make the Cretaceous section there older than the type section at Hornbrook, California.

Peck, et. al. (1956) state that the Cretaceous rocks near Ashland are only 600 feet thick contrasted with a thickness of more than 2,600 feet at the type locality, and nothing younger than Coniacian is recognized. McKnight, in this report, recognizes that the Cretaceous rocks are over 3,000 feet thick in the

Ashland area and contain fossils identified by Jones as

Cenomanian and a few that are possibly Maestrichtian in age. Species identified by Jones are listed in Table 1. Construction for a new four lane highway south of

Ashland temporarily exposed shale near the base of the

Cretaceous section. This shale contains identifiable

Turonian fauna. Although Anderson (1958) reported

Cenomanian fossils just north of Ashland, Jones (in

Popenoe, et. al., 1960) states that no fossils older than Turonian are present in the Hornbrook Formation south of Dark Hollow, near Medford. The base of the 11

Table 1. Eight collections of Upper Cretaceous fossils from the Ashland area, southwestern Oregon, were identified by Dr. D. L. Jones, United States Geological Survey. Locations of these collections are given on the geologic map.

FL-1. NE 1/4 SW 1/4 sec. 31, T. 39 S., R.2 E., Ashland quadrangle. Subprionocyclus normalis (Anderson) Gaudryceras sp. Inoceramus sp. Scalarites sp. Age: late Turonian

FL-2. NW 1/4 SW 1/4 sec. 12, T. 39 S., R. 1 E., Ashland quadrangle. Indeter. fragment of a large ammonite.

FL-3. NE 1/4 NW 1/4 sec. 5, T. 39 S., R. 1 E., Ashland quadrangle. Indeter. ammonite fragments.

FL-4. SE 1/4 NW 1/4 sec. 13, T. 39 S., R. 1 E. Desmophyllites siskiyouensis Anderson Age: late Campanian or early Maestrichtian

FL-5. NE 1/4 SW 1/4 NW 1/4 sec. 11, T. 39 S., R. 1 E., Ashland quadrangle. Perilomya? sp. Tellina? sp.

FL-6. SE 1/4 SW 1/4 sec. 24, T. 39 S., R. 1 E., Ashland quadrangle. Tragodesmoceras ashlandicum (Anderson) Protocardium Age: Turonian

FL-7. NE 1/4 SW 1/4 sec. 12, T. 39 S., R. 1 E. Baculites cf. B. inornatus Meek Age: Campanian

FL-8. SE 1/4 SW 1/4 sec. 1, T. 38 S., R.2 W. Medford quadrangle. Subprionocyclus normalis (Anderson) Scalarites sp. Age: late Turonian 12

Hornbrook Formation is upper Turonian at Hornbrook,

California (Jones, 1959), Turonian (possible middle Turonian-Jones, personal communication) south of

Ashland, Cenomanian (Popenoe, et. al., 1960) at Dark

Hollow, nine miles north of Ashland, and Albian (Jones,

1960) at Grave Creek, approximately 30 miles north of

Ashland. Therefore, the Hornbrook Formation is progressively younger from north to south.

The primary objective of this study is to interpret the geological history and environmental factors under which the rocks formed. To accomplish this, particular attention was paid to the petrography and petrology of the rocks. In addition, field mapping and measurements of stratigraphic sections were carried out. This work resulted in a composite stratigraphic column that is presented in Appendix A. Four stratigraphic units were recognized in the

Cretaceous Hornbrook Formation in the Ashland area.

Eleven partial stratigraphic sections were measured, but at no one locality were exposures good enough to measure all four units as part of a continuous traverse. The best exposed location for each of these units is used in compiling the composite stratigraphic section. These units will be referred to in the text by their map designations: Khs (Khsi, Khs2, and Khs3 where 13

differentiated) for the lower sandstone units and Khm for the upper mudstone unit.

Khs1, the lowermost unit of the Hornbrook

Formation in the Medford-Ashland region, is approximately

360 feet thick. The base is exposed at three localities.

Five miles south of Ashland, near the Siskiyou Lodge, the

unit lies directly over Ashland Granite (Figure 4). Here

it strongly reflects the nature of the underlying

material; it is a light-colored arkosic sandstone with numerous incorporated granitic fragments.A second

exposure of this unit is in the northeast corner of the

city of Ashland where it also lies directly over Ashland

granite. However, here it consists of limestone that grades upward into sandy limestone and finally to

calcareous sandstone. The limestone is composed of

abundant shell fragments cemented with sparry calcite. A

third exposure of the base of Khsl is near Jacksonville, where the unit overlies meta-sedimentary rocks of the

Applegate group. Fragments of the underlying rocks are

present but not abundant. A few ten's of feet above the

base, the Cretaceous rocks everywhere take on similar

characteristics and do not appear to be influenced by

the pre-Cretaceous rocks that lie directly beneath. Although there are local variations, a few

generalizations can be made about the lower unit of the Hornbrook Formation. Very noticeable upon first examination is its well-bedded nature. Most individual beds are less than three feet thick and average approximately one foot to one and one-half feet thick. Individual beds can be traced throughout the distance of the outcrop in most cases, some up to several hundred feet. Minor shale beds and lenses (Figure 5) up to one foot thick and fine pebbly conglomerate beds up to several feet thick are interbedded with the sandstone.

Infrequent cross-bedding and ripple marks have been observed.

Minerals visible in the sandstone include mica, quartz, feldspar, and chlorite. The micas are especially noticeable because of the sheen they impart to freshly separated bedding planes.

Fossils are numerous along a few bedding planes.

Most are pelecypods, but some gastropods and cephalopods are included. Fossils are usually observed as internal casts on the top surface of the bed, but original shell material (or calcite replacement of original shell material) on the under surface of the overlying bed are also present. Convex side upward is the most frequent position of pelecypods found along bedding planes. Layers and lenses of very fossiliferous sandstone

(Figure 6) may have the shells more randomly oriented. 15

Figure 4. Resistant calcareous sandstone of the Hornbrook Formation overlies badly decomposed Ashland granite. Granitic pebbles and cobbles are incorporated in the arkosic sandstone. A red to red-brown soil is produced by weathering of the Cretaceous sandstones.

Figure 5. Shale lens pinches out to the north. Sandstone here is thicker bedded than average for this lower part of the Cretaceous section (Khs1). 16

These shells for the most part belong to the genus

Trigonia.

Khs is well-exposed in the southern part of 2 the mapped area but is not recognized elsewhere. The unit consists of approximately 75 feet of interbedded mudstone, shale, siltstone, and sandstone (Figure 7). Large concretions were present near the top of the unit

at two exposures but were absent at a third.

The lithology of Khs3 is perhaps the most

interesting in the Cretaceous section. Although

predominantly a sandstone, the unit has considerable

lithologic variation. Features observed in this unit

suggest that it represents a transition from a true marine environment to marginal marine to nonmarine.

Although no clear-cut line may be drawn to separate this

unit, differences in lithology do allow a general three-

fold division that will be used in the text for

convenience, and these divisions will be designated

Khs3a, Khs3b, and Khs3c.

Unit Khs3a consists predominantly of olive to

greenish tone sandstone. It is a thick-bedded unit

whose beds average 5-6 feet and reach a maximum thickness

of approximately 11 feet. Weathering brings out fine

laminations not visible on a fresh surface. Concretions from six inches to six feet in diameter are particularly 17

46)Ck4

Figure 6. The orientation of these pelecypod shells is equally distributed betweenconcave upward and convex upward. Most shells belong to the genus Trigonia. Hornbrook formation sandstone (Khs1).

Figure 7. Typical of Khs2 is the high proportion of shale and mudstone and the concretionary nature of much of the sandstone. 18

striking. These concretions are nearly spherical and are seen only on the weathered surface. On a fresh break they are indistinguishable from the enclosing matrix, and features such as laminations and cross-laminations

follow through from concretion to matrix. Fossils of this unit include pelecypods, ammonites, and animal borings.

Unit Khs3b is characterized by its variation in

lithology. It consists of approximately 70 percent

sandstone and lesser amounts of siltstone, shale, coal,

and conglomerate. Thin-bedded sandstone, finely laminated with wavy bedding planes, convolutions, and

flame structures, is common. Small black to brown carbonaceous plant fragments are scattered throughout

the unit.

Unit Khs3c consists primarily of thick-bedded

vari-colored sandstone and minor amounts of interbedded

conglomerate. Color is light olive gray to grayish

orange. Weathering shows finer laminations and small

scale cross-bedding in some thick beds. This unit

contains the only planar type cross-bedding observed in

the Hornbrook Formation. No fossils or other evidence

to indicate a marine origin was observed in these rocks.

The fourth unit, Khm, is a thick marine

sequence of grayish mudstone and numerous butthin 19 interbeds of fine-grained greenish gray sandstone.

Although locally the rock is fissile and would best be called a shale, the mudstone unit is generally characterized by an irregular to subconchoidal fracure pattern (Figure 8). Numerous concretions, the larger ones somewhat flattened, are found in both the mudstone and shale. Fossils, especially ammonites, have been found in some of these concretions.

Animal borings, wood fragments, ammonites, pelecypods, and gastropods are present in this uppermost unit and some attest to the marine origin of this unit. Sandstone interbeds are extremely abundant in the upper 241 feet of this unit (Figure 9). At one measured section, 107 feet of strata contained 138 separate sandstone and mudstone beds, averaging approximately nine inches per bed.

Sedimentary Structures

Cross-bedding

Cross stratification (terminology after Potter and Pettijohn, 1963, p. 69-72) is the most abundant one- way directional structure in the Cretaceous sandstones.

Although cross-bedding is the most abundant sedimentary structure, it is not present everywhere. Many of the 20

Figure 8. Mudstone from the uppermost unit (Khm). An irregular fracture is typicalof these rocks.

Figure 9. The upper part of the thick mudstone unit (Khm) consists ofmany thin sandstone beds interbedded with the mudstone. 21 Cretaceous rocks are characterized by well-defined

parallel bedding. In respect to size, there appears to

be a wide variation between cross-beddedsets.

Thicknesses range from less thanone inch to over three

feet, lengths from 4 inches to 15 feet. Where exposures are good enough to see the cross-bedded unit in three

dimensions, almost all show troughtype cross-bedding.

Clear-cut examples of planar cross-beddingare rare. There appears to be a relationship between the

thickness of the sandstone beds and the size ofthe

cross-bedded sets. Thin sheet-type sand bodies usually contain very small cross-beds, and thick sandstone bodies contain cross-beds ofa much larger scale

(Figures 10 and 11). Regardless of the size of the beds, the size of the cross-bedded unit, the shape of the trough, or the inclination of the foresets, foreset beds were always concave in the down-current direction.

Ripple Marks

The most common cross-lamination present in the thinner sandstone beds is the type that would be called current ripple cross-lamination (Figure 11).

Although cross-bedding is an internal characteristic and ripple marks a surface phenomena, both are largely the result of the migration of sand waves at the water- 22

Figure 10. Larger scale cross-bedding characteristic of the thick-bedded sandstone units. Hammer gives scale. Hornbrook Formation sandstone (Khs3).

Figure 11. Current ripple cross lamination. Note the somewhat irregular bottom surface of the sandstone bed. Pencil gives scale. Hornbrook Formation (Khm). 23 sediment interface. The example in Figure 11 shows this relationship between cross-lamination and current ripples.

Ripple marks occur locally in the lower part of the Cretaceous section. These are most prominent in thin-bedded sandstone and shale sequences. Most have wave lengths averaging 18-20 cm. and amplitudes of less than 2 cm. The Ripple Index ranges from 9 to 12.

Crests are typically straight (Figure 12); interference ripple marks are rare. Most ripple marks are the result of unidirectional currents, but because of the low amplitude, it is often very difficult to distinguish the asymmetry.

Sole Markings

Sole markings are rare in the Cretaceous sequence. One specimen of a flute cast was found near the uppermost part of the Hornbrook Formation. Load casts are more abundant than flute casts but still are rare in the Cretaceous sequence. They are best seen where fine-grained sandstone is interbedded with shale, especially near the top of the formation.

Most load casts are small, extending less than 2 inches into the underlying shale, and are usually no more than

2 or 3 inches in diameter. Evidence of orientation by 214

Figure 12. Current ripples with a low amplitude and fairly high ripple index. Current direction from left to right. Hornbrook Formation (Khsi).

Figure 13. Load casts showing slight orientation as a result of downslopemovement. Hornbrook Formation (Khm). 25 down-slope flow was observed inone of the load cast specimens (Figure 13).

Parting Lineation

Parallel step-like partings (Figure 14) present on some thin-bedded flaggy sandstones common to theupper part of the formation are similar to those described by

Crowell (1955, p. 1361)as parting lineation and by

McBride and Yeakel (1963,p. 780) as parting-step lineation. This is an internal feature of the sandstone and according to Yeakel (1959) is apparently governed by the fabric. The lineation is parallel to current direction but is not unidirectional.

Shale Clasts

Small clasts of angular to sub-rounded shale within the sandstone beds of the lower 300 feet of

Cretaceous rocks (Figures 15 and 16) showa very strong orientation parallel to the bedding planes of thicker sandstones. Undisturbed thin laminae within the mudstone clasts and marked rounding of some clasts indicate that the shale had attained at least a limited degree of competency before erosion and redeposition. 26

Figure 14. Parting lineation in flaggy thin- bedded Cretaceous rocks. Pencil gives scale. Hornbrook Formation (Khm).

Figure 15. Shale clast approximately 4 inches long that shows some rounding of the corners. The a and b axes of the shale clast are parallel to the bedding plane. Hornbrook Formation (Khs1). 27

Cut-and-fill

Cut-and-fill structures, although not abundant, are present throughout the Cretaceoussection. A relationship exists between the coarseness of the detrital material, the thickness of the bedding, and the scale of the cut-and-fill features. Small-scale cut-and-fill structures are associated with fine-grained sandstone that is interbedded with shale and silty mudstone. The irregular lower surfaces of the sandstone beds represent a scour- filled surface on the shale substratum. Close examination shows truncation of horizontally deposited shale laminae, indicating that these are truescour-fill rather than ripple-marked surfaces covered withsand.

These small but locally abundant scours have amaximum depth of several centimeters and channelwidths of

30-40 cm. Much less common are larger scalefeatures present in thick-bedded sandstone unitsand in conglomerate. In sandstone, the deepest cut observed was about 18 inches, but in theconglomerate cuts up to

8 feet deep and 30 feet wide are present. 28

Figure 16. Abundant shale clasts within thinly laminated sandstone near the base of the Cretaceous sequence (Khsi).

Figure 17. Intensive burrowing in Cretaceous sand is well preserved in this specimen (Khm). 29 Miscellaneous Structures

Animal Burrows and Trails. Sand-filled burrows and worm trails on bedding planesare locally prominent.

Figure 17 showsan example of intensive burrowing.

Close examination of the burrow fillingsshows that they are filled with neither the mudstone surrounding the

burrow nor the overlying sandstone butrather by clay-

rich sandstone thatappears intermediate between the two. It is coarse-grained like the overlying material

but darker gray in color. This suggests the possibility

that organic material and fine mudhave been incorporated in the sand, possibly by passingthrough the intestinal track of the organism.

Another occurrence shows trails on the bedding plane (Figure 18) thatcan be traced into the sand bed

itself. Again, the filling appears to be like the

surrounding sand but witha considerable admixture of organic mud.

Flame Structures. These features were found in abundance at only one locality in the thesisarea--an excavation for a new reservoir, two miles south of

Medford on Dark Hollow Road. The flames are small

(Figure 19) and are associated with cross-beddedglauco- nitic sandstone that is interbedded with fineshales. 30

Figure 18. Small trails on the bedding plane can be traced into the bed itself. The darker color appears to be the result ofa higher organic-rich clay content. Hornbrook Formation (Khm).

Figure 19. Flame structures in the Cretaceous sandstone from Dark Hollow. Abundant ammonites and glauconite are both present at this locality. 31

Imbrication. A very weak imbrication is present within the Cretaceous conglomeratesfound near the village of Jacksonville and alongInterstate 5 one and one-half miles southeast of Ashland. Most of the gravel is too nearly spherical to developa well-defined imbrication, but where the sand matrix isa little more abundant, and the pebbles less spherical, the imbrication becomesmore easily discernible.

Sandstone Dikes. The presence of sandstone dikes in the Cretaceous deposits of the Medford-Ashland region is a phenomena that is interesting but ofsomewhat questionable interpretive significance. Sandstone dikes are not rare in Cretaceous rocks of the west coast. An extensive paper on such dikes occurring in northern

California was presented by Diller (1890), and the structural interpretation of sandstone dikes insome of the northern California rockswas reported by Peterson

(1966).

Sandstone dikes in the Hornbrook Formation are mostly small, ranging from 3/4 inch to 3 inchesacross.

At Dark Hollow, southwest of Jacksonville, theoccurrence of sandstone dikes are muchmore striking. Although the dikes in this region are fairly large, with a.maximum width of two feet, theyare exposed only in road cuts and 32 small excavations, hence cannot be traced laterally.A complex dike from this region is seen in Fugure 20. Here, the clastic dike intrudes interbedded mudstones and siltstones of the upper part of the Hornbrook

Formation. Upon close examination of this dike, there appeared to be a faint alignment of the micaceous minerals parallel to the dike's sides. Slabs of this material were observed under the binocular microscope and a parallel alignment was observed. A thin section of the dike material showed numerous fractured grains and biotite books that appeared to be somewhat shredded.

Directional Studies

Many sedimentary structures reflect the direction of water movement at the sediment interface.

Cross-bedding, ripple marks, flute casts, imbrication, flame structures, and parting lineation are among these.

Wherever possible, measurements reflecting current direction or directions were recorded for their possible paleoslope and source-direction implications. Of all these structures only cross-bedding was abundant enough for any regional interpretation.

At each outcrop an average direction for foreset orientation was obtained. This may have involved from one to several individual measurements. The present 33

Figure 20. A complex sandstone dike intruding Upper Cretaceous siltstone and shale in the vicinity of Dark Hollow. 34 orientation of the cross-bedded unit and the dip and

strike of the beds were recorded and later the readings were corrected to horizontal with the aid of a stereo

net.

A current rose showing cross-bedding in 38

different outcrops is presented in Figure 21. The same

data are seen in Figure 22, which is a fabric diagram

representing poles normal to the foreset beds. This

diagram has the advantage of representing the

inclination of the foreset beds as well as the

direction.

Cross-bedding has long been used as a criterion

for distinguishing top from bottom of beds in complexly

folded areas. Because cross-stratification is a

response to the direction of current flow, it is also

valuable in determining local sediment transport

directions of local sediment. Although it is generally

accepted that cross-bedding can indicate the local

transport direction, there is some question that it

accurately represents regional sediment transport

directions. However, studies by Potter (1955, Fig. 17), Siever and Potter (1956, Fig. 3), Pelletier (1958), and

others provide evidence for assuming that cross - bedding

over a large area does reflect regional paleoslope. 35

N 30 30

60 60

30 30 S

Figure 21. Current rose representing cross- bedding measurements of 38 Cretaceous outcrops. 36

Figure 22. Fabric diagram with poles normal to foreset beds plotted for 38 Cretaceous outcrops. 37

Accepting cross-bedding asan indication of sediment transport and paleoslope, it wouldappear that the main direction of sediment transport and the paleoslope for the Cretaceous rocks of the Medford-Ashland region is toward the northeast. This is in agreement with the suggestion by Jones (1960) that theLate Cretaceous seas transgressed southward in the vicinity of Hornbrook, California, justacross the Oregon border. Two occurrences of asymmetrical ripple marks and one cross-bed oriented 180 degrees to the dominant foreset bedding direction must havesome other explanation. A tidal current capable of moving sand and producing current ripples isone possibility.

Petrology

The main objective of the petrographic study was to find criteria that would allow interpretations relating to the provenance, history of transport, environment of deposition, and post-depositional changes that have taken place. To do this, objective observations and quantitative information of maximum interpretational significance were stressed. In this paper, the mineralogy and textural relationships have been given the most careful attention. 38

Modal analyses of 80 thin sections from

Cretaceous rocks were made by point counter using 500 counts per slide. Thirty-three samples were selected for x-ray analyses of the clay content of the mudstones and shales as well as the clay fraction of the sandstones.

A heavy mineral study had been planned but was discontinued when it was found that the amount of intrastratal solution of heavy minerals was very significant over a large part of the study area. This became evident when concretions were disaggregated and the heavy minerals were compared with heavy minerals from the more porous surrounding sandstones.

In the study of the sandstones, emphasis was placed on trying to distinguish between original detrital matrix and later introduced clay and other fine- grained components. Framework components were plotted on triangular diagrams and classified according to

Gilbert's classification of sandstones (in Williams,

Turner and Gilbert, 1955). For the finer-grained rocks, the classification by Ingram (1953) is followed. Median diameter averages were obtained with the aid of a micrometer eyepiece. Roundness and sphericity are estimates using the visual estimate scale.of Krumbein and Sloss (1963, p. 111) as a guide. 39 Sandstones

Composition. Modal analyses for 80 selected

samples are given in Appendix B. Note that the framework

constituents are listed separately from the matrixand cement.

Quartz is the most abundant mineral in the

framework, averaging 27 percent of the rock. This does

not include polygranular varieties of quartz suchas

chert or quartzite. Quartz grain characteristics were observed by making a single traverse through each of the

80 thin sections and noting thetype of grain, the degree of undulatory extinction, and type of inclusion in each

grain of quartz along this traverse. The results are

presented in Table 2. Over 50 percent of the quartz grains show some degree of undulatory extinction,

although only about 12 percentare strongly undulatory. Over 30 percent of the quartz showed sharp extinction and no evidence of strain.

Inclusions were present in all quartz grains observed. Seventy-four percent of the grains observed contained only irregular inclusions, by far the most abundant type. These globular inclusions appear to be mostly gaseous or fluid vacuoles. The larger ones may be arranged in rows or randomly distributed; smaller 40

ones are commonly arranged along planar surfaces. High magnification shows theyare identical to the larger

globules in form butare too small to allow their composition to be determined.

Regular inclusions are a distant second in

abundance. Zircon, apatite, quartz, feldspar, biotite, actinolite, and epidoteare present, but no one mineral

is dominant. Acicular inclusions are less than halfas

abundant as regular inclusions, makingup only 7.5

percent of the grains counted. Although a great

variation exists in the number of inclusionsper grain, no grain was found to be completely inclusionless.

Feldspar, averaging 15 percent of the rock, is

the second most abundant framework constituent. This

includes all varieties of feldspar; plagioclase ismore

abundant than orthoclase, and microcline israre except

in a very few samples. In all instances where there are

appreciable amounts of microcline, the Cretaceous

sandstone lies directly over granitic intrusive rocks; thus, the source for these microcline-rich arkosic

sandstones appears to be very local.

Where possible, the composition of the

plagioclase feldspar was determined. If the grain was properly oriented, the A-Normal method was used; some

feldspars were determined by their refractive indices, Extinction Single Sing le Single Semi-composite Composite Composite slightly strongly straight to straightto strongly TOTAL Inclusions straight undulatory undulatory slightly undul.slightly undul.,undulatory Regular

4.5 9.8 1.5 0.5 1.7 0.2 17.7 a . Aciculor .

1.4 4.6 0.3 0.0 0.9 0.3 7.5

Globular 8 Dusty Trails . 25.0 30.1 6.7 1.5 8.0 2.8 74.1 C/*

Inclusionless

. , TOTAL 30.9 44.5 8.5 2.0 10.6 3.3

Table 2. Inclusions and extinction types forquartz grains were determined and the results are presented here as percentages. 42 others estimated by their extinction angles in sections normal to (010). Plagioclase ranged from albite to high labradorite or bytownite, but the sodic plagioclases were predominant. Estimates of the amounts of the various plagioclases are given in Table 3.

Table 3. Estimated percentages of the various types of plagioclases present in the Cretaceous rocks.

PLAGIOCLASE ESTIMATED PERCENT

Albite 5

Oligoclase 42

Andesine 40

Labradorite 12

Bytownite 1

Anorthite 0

The state of preservation of the feldspars is not consistant. Both clear, limpid, unaltered feldspar and cloudy to very highly-altered, almost unrecognizable feldspar are commonly present in the same sample.

Potash feldspars alter to either sericite or kaolinite.

Plagioclase alters to clay, sericite, calcite, epidote, quartz, and albite. Alteration is most pronounced along the cleavage planes but proceeds through the rest of the grains in advanced cases of alteration. Some plagioclase 43 grains are more highly altered near the center of the grain than near the rim. It is very difficult to differentiate between many of the fine-grained rock fragments, but it is important to do so because they have a strong influence on later interpretations. The less stable grains, which include metavolcanic rock fragments, slaty rock fragments, chlorite, and biotite, together make up approximately 13-14 percent of the rock. This includes framework grains only--chlorite matrix and cement are listed separately. Of these, the metavolcanic rock fragments are the most abundant, averaging 6 percent. These grains are altered, difficult to identify, and may include a few grains of basic, non-volcanic constituents that are so similar that they could not be differentiated.

Some grains show phenocrysts, some ghosts of phenocrysts, and others are so altered that they show only a fine mixture of chlorite, epidote, plagioclase, and carbonate, making positive identification virtually impossible. Low- to medium-grade metamorphic rock fragments are much easier to recognize in thin section than grains of the igneous or metamorphic rocks discussed above.

Included in this group are slate, phyllite, and fine- grained schist fragments. Most consist primarily of quartz and mica, and are in the size-range of a phyllite 44

or fine-grained schist. A very distinct variety of schist was noted, consistingof graphite and quartz; it

is not abundant but doesoccur throughout the Cretaceous rocks.

Fine, polygranular quartz isa troublesome constituent to identify forthose working in the

Cretaceous rocks. Some grains are clearly chert, others unmistakably silicified volcanicrock fragments, and others show characteristics similarto both but with no clear-cut criteria to differentiate betweenthem.

Because of this,many decisions made during the point count were arbitrary but basedon the author's experience in these types of rocks. Criteria used to distinguish the volcanic fragments fromthe chert include the presence of angular-shapedareas of slightly differing compositionor texture, interpreted to be relics of former phenocrysts, andthe presence of leucoxene impurities in the rock. A fairly high titanium content is not unusual in volcanicrocks but is not common in fine-grained sedimentary rocks.

Biotite is present in almost all of the

Cretaceous rocks. Although it averages only 3.6 percent, it occurs in amountsup to 11 percent and in 25 of the

80 thin sections itoccurs in excess of 5 percent of the sample. It occurs both as thin, long flakes, commonly 45 bent by compaction, and as thicker biotite books. As noted in the discussion on authigenesis, the books are often expanded by calcite grains growing between cleavage flakes and wedging the biotite apart. Bleaching of the biotite and partial alteration to chlorite are common.

Apatite, zircon (with pleochroic halos), quartz, and magnetite inclusions were noted in the biotite. Bending and distortion of biotite flakes caught between equi- dimensional quartz and feldspar grains indicates

compaction in these Cretaceous sandstones.

Eighty percent of all grains counted as opaque

oxides were magnetite, although several other minerals were represented, including: ilmenite, chromite,

leucoxene, limonite, and hematite. The presence of

titanium and chromium in opaque grains was detected

chemically, but ilmenite and chromite were not

distinguished from magnetite in routing petrographic

analysis. All of the above are grouped together as

opaque oxides.

Summary of Framework Constituents. According

to Gilbert's classification of sandstones (in Williams,

Turner and Gilbert, 1954, p. 292-293), twenty-four

samples would be classified as wackes and fifty-five as

arenites. The framework of the two main classes is 46

essentially the same. Therefore, the only real

difference is that some have more clay in the matrix

than the rest. Framework percentages plotted on a

triangular diagram are given for the arenites in

Figure 23 and for the wackes in Figure 24. Both figures show that the rocks group strongly around the arkosic and feldspathic parts of the diagram. Only 15 percent of the rocks sampled fall outside those two classes.

Those that do fall outside the arkosic or feldspathic areas have a higher percentage of rock fragments and a

lower percentage of feldspar.

Textural Features. Several textural aspects were noted in each thin section. These are summarized

in Table 4. From this, it can be seen that most sand-

stones show fair to good sorting, have a low porosity, and exhibit some compaction. For the most part, those showing poor sorting are wackes. The low porosity is the result of three major factors: the clay matrix of the wackes, high compaction in many of the sandstones, and the presence of large amounts of calcite cement in other sandstones.

The roundness factor of .335 (subangular-

subrounded) indicates a textural immaturity of the

sandstone. 147

Quartz

Feld. + Granitic Fine-grained Rock Fragments Rock Fragments

Figure 23. Modal analyses of 58 Cretaceous arenite samples. 48

Quartz

Feld. + Granitic Fine-grained Rock Fragments Rock Fragments

Figure 24. Modal analyses of 24 Cretaceous wacke samples. 49

Table 4. Numerical values for roundness and sphericity are based on the chart for visual estimates in Krumbein and Sloss (1963, p. 111).

Median Diameter .329 Medium-grained Sandstone

Roundness .335 Subangular - Subrounded

Sphericity .529

30% Low Compaction Compaction 31% Moderate Compaction 39% Marked Compaction

64% Low Porosity Porosity 14% Moderate Porosity 22% High Porosity

25% Poorly-Sorted Sorting 42% Fairly Well-Sorted 33% Well-Sorted

Lithification, Diagenesis, and Authigensis. Diagenesis, as used in this paper, includes all processes taking place from the time a sediment is deposited to the time of metamorphism. This usage is somewhat broader than that preferred by some workers. Authigenic minerals as used here include all new minerals, recrystallized minerals, and crystal overgrowths formed between the time of sedimentation and the onset of metamorphism. Since rocks in this study are nowhere metamorphosed, all changes that have occurred in them come under the heading of diagenesis and authigenesis. Lithification is used to 50 include all processes that tend to form an indurated rock from a loose, unconsolidated sediment. Lithification of the Cretaceous rocks is the result of both compaction, with or without amatrix, and cementation. The degree of compaction varies within the formation but is generally greater in the lowerhalf.

Evidence of a high degree of compaction is primarily the presence of highly-deformed and brokenbiotite flakes

(Figure 25). In addition, broken edges of weakgrains and sharp corners of quartz and feldsparprotruding into weaker chlorite and schistose rock fragments attestto the degree of compaction. Visual estimates of compaction, using the degree of biotite deformation as anindicator, show approximately a 15-20 percent reductionin total volume of the sandstones and a much greaterpercentage if the siltstones and mudstones are considered. Cementation is an important process oflithi- fication in the Cretaceous rocks. The types of cement are varied and arediscussed in decreasing order of abundance: calcite, quartz, chlorite,ankerite-siderite, and iron oxides. Calcite is the most widespread of thecements, and in places the proportion of cement toframework is very large. In fact, at the base of theformation in the northeast corner of the city of Ashland,it grades from a 52 limestone to a calcite-cemented sandstone. At other locations, the proportion of cement is so large that the grains seem to "float" in the calcite cement. This is often attributed to recrystallization of the detrital carbonate, but Waldschmidt (1941) attributes it to the forcing apart of detrital grains by growth of carbonate cement. Not all of the Cretaceous sandstones are cemented with calcite, and some have only sparse, patchy cement with compaction a more important lithifying agent. Remarkable examples of calcite cement forming between cleavage planes and wedging the crystals apart can be seen in these rocks. This is especially true of biotite books, which may be expanded several times their normal thickness (Figure 26). This replacement by calcite occurs first along cleavages, fractures, and grain boundries, then proceeds into the solid portion of the grain. Some grains are very deeply embayed by the calcite. In some cases it only attacks the more unstable grains such as the metavolcanic or slaty rock fragments; in other cases, deep embayment of quartz and feldspar

(Figure 27) are common. This replacement is not random, however, as it attacks mafic volcanic rock fragments, metamorphic rock fragments, feldspars, biotite, and quartz in a decreasing order of intensity. Most calcite cement is the type that would be called sparrycalcite 53

Figure 26. Crystallization of calcite along cleavage planes of this biotite book has resulted in expansion of the biotite by about one-third its original thickness. This is most typical of the lower sandstone beds (Khs1).

Figure 27. Calcite replacement of plagioclase feldspar. Most replacement shows some systematic arrangement, usually along cleavages or fractures. From the Hornbrook Formation sandstone (Khs3). 54 by Folk (1965), although threeoccurrences of micritic cement were noted. One section displayed a predominance of micritic cement but with scattered patches of fine- grained sparry calcite.

Three varieties of quartz cement are found in the Cretaceous rocks. The most abundant variety and the earliest formed are overgrowths of the detrital quartz grains. These are generally very small but locally are an important cementing agent. Micro- crystalline quartz is not uncommon in the same rocks that contain the quartz overgrowths. Wherever the two varieties of quartz are found together, the microcrystalline quartz was always emplaced later. Coarsely crystalline quartz cement that is not part of an overgrowth has been observed but is infrequent. Chlorite is ubiquitous in the Cretaceous rocks.

It occurs as detrital grains in the framework, as part of a fine detrital matrix, and as chlorite cement. As an authigenic cement, it forms fibrous fringes normal to the detrital grain boundries, especially in the void spaces. The centers of some of these fibrous chlorite- lined voids are filled with either microcrystalline chlorite or randomly-oriented fibers of the same size as those rimming the void. The fibers of chlorite extend part-way into many of the detrital grains. 55

Ankerite-siderite as a cementing agent is relatively rare and generally is found only as rims on calcite cement. Unlike the calcite, this cement is often in small euhedral rhombs. Its shape, higher refractive index, and darker color distinguish it from calcite.

Iron oxide is a comparatively minor constituent.

Where it does occur, it forms a thin rim around the detrital grains or the carbonate cement. Locally, it is associated with one of the iron-bearing carbonates, and may be an oxidized carbonate.

Paragenesis of the Cements. The paragenesis of the cements is difficult to determine, and often the evidence is contradictory. Difficulties arise because of the various interpretations that are possible from the same observation. Also, because of the patchy distribution of much of the cement, it is not common to find two cements in contact with one another. By piecing together the available evidence, the order of cementation has been determined as carefully as possible.

Where quartz overgrowths are present, they appear earlier than the other cements, except perhaps for a thin, dusty, iron-oxide coating. Sparry calcite, where found as patchy cement in rocks containing quartz 56

overgrowths, is later in developmentthan the quartz.

Chlorite is definitely laterthan either the quartz

overgrowths or the calcitecement in most rocks but is

earlier than calcite ina few others. Rocks rich in chlorite cement alsoappear to have numerous mafic

volcanic or metavolcanic rockfragments in different states of alteration. It seems probable that these rock fragments providedmost of the ions to form the authigenic chlorite. Ankerite-siderite rims calcite cement and at firstappears earlier than the chlorite.

However, it also coats the insideof the voids if not completely filled by calcite. This may represent an alteration of the calcite by iron-magnesianbearing solutions migrating along grain boundriesand through voids (Figure 28). Iron oxide may be either early, as seen by dusty coatings on detrital grains beforeover- growths occur, or late, probablyas an oxidation product of sideritic cement.

Siltstones, Mudstones, and Shales

The petrography of the argillaceous rockswas not studied in detail. Three thin-sections were point counted to give an indication of the amount andtype of framework present. Modal analyses from these three thin sections show: 18% quartz, 10% feldspar, 7% lithic 57

Figure 28. Calcite cement is rimmed with siderite-ankerite and the void in the center is filled with a clay mineral. Appreciable alteration of unstable rock fragments is evident and may have provided the ions to form the iron-bearing carbonate rather than calcite. 58 fragments, 2% chlorite, and 56% fine-grained clay-sized matrix.

The composition of the matrix will be discussed in the x-ray analyses section.

Conglomerate

The conglomerates occur near the bottom of the stratigraphic section. The bedrock lithology has a marked influence on the pebble types present in the conglomerate, as seen in Table 5. Samples number 1 and

2 are from the southern part of the thesis area, where sandstone directly overlies granitic rocks. This is reflected in the pebble composition, especially in the basal zone (sample no. 1) that has 18.6 percent granitic rock fragments. Samples 4 and 5 are taken from the north part of the area, where Cretaceous rocks overlie metavolcanic and metasedimentary rocks. Here the granitic pebbles constitute only 2.3 and 2.0 percent of the sample. Locality no.3 is intermediate between the other two areas, but is somewhat closer to the granitic terrain.

Differentiating between chert and silicified volcanic rocks presents a major difficulty and must be done with care. If there are feldspar phenocrysts present and they have not been altered too greatly by 59

silicification, identificationis easy. Commonly, only ghosts or weak outlines showinga slightly different color remain of the phenocryst.

Table 5. Lithologic types determinedby pebble count. At least 300 pebbles foreach count were broken and identified with the aidof a binocular microscope. Several major pebble typeswere sectioned as a check on the identification.

#1 #2 #3 #4 #5

Metavolcanic Mafic (inc. Diabase) 4.3 8.6 6.6 9.6 11.3 Intermediate 9.6 12.6 12.3 14.6 11.3 Femic 20.3 24.0 25.0 22.6 27.6 Metasedimentary Quartzite 4.6 8.6 6.3 13.6 12.0 Argillite 1.0 3.3 0.6 2.3 3.0 Metawacke 2.0 3.2 0.6 3.0 2.0 Schist 0.0 0.6 1.0 4.3 3.6 Chert 29.6 26.6 27.1 21.3 20.3 Granitic 18.6 7.3 14.6 2.0 2.3 Vein Quartz 4.6 2.6 1.3 4.0 4.3 Unknown 5.3 2.6 4.6 2.6 2.3 #1 Base of Section at Neil Creek #2 200' above base at Neil Creek #3 Base of Section in Ashland #4 Base of Section at Jacksonville #5 350' above base at Jacksonville

Mafic rock pebblesare weathered to a much greater degree than the intermediate and acidicfragments. They weather to avery soft pebble but still retain the felty texture of the original minerals.

The quartzite was not ofone particular variety but included red, pink, white, andgrey specimens. 60

X-Ray Analyses

Thirty-three Cretaceous rocks were selected for x-ray analyses of their clay content. Oriented samples of the clay fraction were prepared on glass slides. All samples were run a full 44 degrees 2 g. Samples with a

14 X peak were treated with ethylene glycol and rerun.

Direct saturation with glycol proved to disrupt the orientation, so the "vapor pressure" method described by

Brunton (1955) was employed. Samples were then heated at 550°C for one hour and rerun approximately 15 degrees

2 O. Methods and interpretations of the resulting patterns were based on the techniques described by

Weaver (1956). The tabulated results are presented in

Table 6. For the most part, this clay represents the fine matrix present in the sandstones. However, in some cases, what was being identified by the x-ray analysis proved to be the weathered products of some framework constituents--notably the feldspars. In rocks that were highly arkosic and somewhat porous the feldspars were strongly altered to kaolinite. Thin sections of the

same rocks show little or no fine clay matrix, but do

show quite advanced stages of kaolinization and some

sericitization of the feldspars. Very commonly the feldspar grain is barely recognizable as a result of the 61 Table 6. X-ray analyses of the Cretaceous rocks. Large X's represent moderate to strong peaks and small x's represent smaller peaks.

H EOCENE 0 43 1 0 P r) I% ROCKS H 4114 za .1 X >-4 0 H .-1 H < f=4 1-4 Z.--3

M-7-11-4 X X M-8-1-2 x X M-8-5-1 X K-7-8-6 X K-7-15-4 X x K-7-18-2 X K-7-18-3 X K-7-18-6 X K-7-20-1 X x x K-7-20-2 X X K-9-8-1 X x X M-7-2-lb x X M-7-11-3 X M-7-20-3 X X M-7-21-1 x X X K-8-19-5c x X K-8-20-5 X X K-8-20-7 X X K-8-20-11 X X M-7-1-4 X M-7-1-7 X M-7-23-2 X X M-8-5-2 X M-8-12-4 X M-8-12-8 X X K-8-19-1 x X K-8-19-6 X X K-8-20-3 X X K-9-8-4 x X K-9-8-6 X K-9-20-3 X X K-9-24-1 X x X K-9-25-1 X x X 62 advanced state of alteration. Because the evidence indicates that much if not most of the kaolinite is an alteration product, care must be used in interpreting the results.

Potter and Glass (1958, p. 40), in a study of

Pennsylvania sandstones, found that when interbedded shales and sandstones were examined for their clay mineralogy, the sandstones generally contained more kaolinite and less mica, mixed-lattice clays, and chlorite than their associated shales. This was attributed to post-depositional alteration, most of which took place in the more permeable sandstone. The

Cretaceous sandstones of the Hornbrook Formation appear to have been altered in a similar manner.

Chlorite is present in several samples. Thin section studies show that part of it is present as a matrix, part as an authigenic chlorite cement, and part as framework grains. One sample (M-7-11-3) that showed appreciable chlorite on the x-ray pattern is an arenite with essentially no chlorite in the matrix. There are a few grains of chlorite in the framework, but most of it occurs as an authigenic replacement of the pelecypod shells.

Montmorillonite is not one of the most abundant clays but is more abundant in all mudstones and 63 in those sandstones thathave a high proportion of clay matrix. This probably more closelyrepresents the original detrital clay thandoes either the chlorite or kaolinite.

Illite is the most abundant clay present,as might be expected of Cretaceous marinerocks. If we discount the kaolinite that is believedto be the weathered product of the detrital feldspars,illite is more than twice as abundant as the next clay.Twenty- seven of the 33 samples showed thepresence of illite, and 16 had illite asa major constituent. That some of the illite might also bea sericitic alteration of the feldspars must be acknowledged. However, in thin section this does notappear to be nearly as important as the kaolinite alteration.

Mixed-layer clays are common in the Cretaceous rocks but are quantitatively important in onlytwo samples. The techniques used in this investigation were not sophisticated enough to determine precisely the nature of the mixed-layer clay structure. However, both an illite-chlorite-montmorillonite and a chlorite- montmorillonite mixtureare believed to be present. Because these occur along with regular clay minerals, interpretation of thex-ray patterns is difficult. 64

Provenance

In interpreting the provenance of sedimentary rocks, the source area, the composition of that area, and the tectonic and climatic conditions existing at the time of sedimentation are all important aspects.

Probable Transport Direction

The paucity of oriented sole features in the

Cretaceous rocks and the essentially "vertical" aspect of the sampling means that most of the burden of a transport direction indicator falls on cross-bedding and ripple marks. The cross-bedding results, presented earlier in Figure 21, show that the foreset beds dip toward the northeast, indicating a source somewhere to the southwest. This would indicate the source as the Klamath Mountains of southwestern Oregon and northwestern California. It was suggested by Jones (1960) that the sea transgressed southward in the vicinity of

Hornbrook, just south of the California-Oregon border.

He also suggests that the seas transgressed northeastward in the vicinity of Redding, California, against an uplifted Klamath highland. Further evidence for this Late Cretaceous Klamath highland is furnished by

Ojakangas (1968) from paleocurrent studies of the 65

Cretaceous strata of the Sacramento Valley, California. Ojakangas found strong southward-trending directional measurements, and from these he concluded that the

Klamath Mountains were a positive landmass at that time. From his work in the southwest Oregon coastal region,

Koch (1966) reported that the Early Cretaceous sea transgressed eastward against an uplifted Klamath

Mountain province.

No sedimentary rocks earlier than Late

Cretaceous are present near Ashland to permit determination of how long this highland was exposed. The Cretaceous sequence marks a transgression of the

Late Cretaceous sea onto the Klamath highland. However, as early as Late Jurassic, paleocurrent trends south of the Klamath Mountains indicate an uplift of at least part of the Klamath Mountains.

Mineralogical evidence supporting this transport direction includes the presence of glaucophane in the sandstones near Jacksonville, Oregon. Glaucophane is best known from the Franciscan Formation of the central and northern California Coast Range. However, it is also present along the southern Oregon coast where it occurs as glaucophane schist in the Colebrooke Formation (Koch,

1966). Less distinctive than glaucophane but perhaps of some significance is the presence of quartz-graphite 66 schist in many of the Cretaceous samples. Whereas this may occur in many places in a deformed belt such as the

Klamath Mountains, one locality is known for an abundance of this lithologic type. Approximately 20 miles southwest of Ashland is an exposure of quartz- graphite schists. If the grains present in the Cretaceous rocks are from this source, it means the exposed Klamath highland was only a few miles from the basin of sedimentation. Considering the immaturity of the sandstones, this would not seem unreasonable to the author.

Mineralogy of Source Area

Determining the nature of the source rocks may be an important aid in identifying the source area. The mineralogy of the Cretaceous sandstones and associated conglomerates indicate more than one type of source rock.

There is evidence of acid igneous rocks, low- to high- rank metamorphic rocks, and reworked sedimentary rocks.

Also, there is a clear indication that the source rocks were not the same throughout the period of Upper

Cretaceous sedimentation.

Several minerals such as biotite, quartz and hornblende may indicate more than one source-rock type.

Others, such as microcline and granitic rock fragments, 67

are fairly certain indicators ofone distinct source-

rock type--acid igneous rocks. Chert in these rocks is

believed to be primarilyof sedimentary origin; slaty

rock fragments and metavolcanicrock fragments are of metamorphic origin. All of the above lithologic types

are found in the Cretaceous rocks andare used as provenance indicators.

The presence of such constituentsas granitic

rock fragments, microcline,and orthoclase indicate a

plutonic source for at leastpart of the sediments.

Pettijohn (1957,p. 290) uses feldspar/rock fragment

ratios as a provenance indicator. If feldspar is greater

than rock fragments, he considers itprimarily a plutonic source. If feldspar is less than rock fragments,

the source is consideredto be composed primarily of

supracrustal rocks. Feldspar/rock fragment ratios of

the Cretaceous rocks leadto interesting conclusions.

The lower part of the sectionshows that feldspar is more abundant than rock fragments, thusa plutonic source is indicated. The upper part of the Cretaceous section

shows rock fragmentsmore abundant than feldspar, hence a supracrustal source is indicated. This would seem to indicate an exposed highland of plutonicrocks initially supplying sediment for the Cretaceous basin. Gradually, this plutonic sourcewas either removed by erosion or 68

covered by the Cretaceoussea, thus removing it as the major source of sediment. Since it is doubtful thata newly rising granite plutonwould be completely removed by erosion and since graniticrocks presently underlie Cretaceous sedimentary rocks,the latter explanation is more plausible.

In Figure 29, the abundance of sixprovenance- indicator typesare plotted to show the vertical variation. The three lower graphs, of orthoclase, granitic rock fragments, and biotiteshow a progressive decrease toward the top of thestratigraphic section. The top line on the graph showsthree types definitely indicating supracrustal rocks: chert, slaty rock fragments, volcanic and metavolcanicrock fragments. All three of these provenance indicators increasetoward the top of the section. This increase supports the evidence of the feldspar/rock fragment ratios inthat it indicates a change from a plutonic source for the lower part of the

Cretaceous section toa supracrustal source for the upper part.

The type of quartz is also a usefulprovenance indicator. In an earlier section (Table 2), the types of inclusions found in quartzare presented. This, along with the type of extinction and thepresence of rounded overgrowths, indicated that plutonic, metamorphic, and 0 10% 0 10% 0 10% Chert .Slaty Rock Volcanic and Fragments Metavolcanic Rock Fragments

0 10% 0 10% 0 10% K-feldspar Granitic Rock Biotite Fragments

Figure 29. Plots showing the vertical variation of six minerals of the Hornbrook Formation. The lower, middle, and upper third of the formation is represented by each column. 70

sedimentary sources contributed sedimentsto the

Cretaceous rocks. However, the plutonic and metamorphic

sources were quite equally divided, but the sedimentary source was minor.

Mineralogical Maturity

The Cretaceous rocks are mostlya mixture of

arkosic and feldspathic wackes and arenites. As such, they are considered immature sediments, with the

arkoses more immature mineralogically than the

feldspathic sandstones and the wackesmore immature texturally than the arenite8.

An appropriate index of maturity for sandstones of this type, which contain both supracrustal rock fragments and feldspar, is the ratio of quartz plus chert/feldspar plus rock fragments. The average index computed for the Cretaceous rocks is 1.3. These can be compared with averages of different rock types given by

Pettijohn (1957, p. 509). According to his table, an average arkose is 1.1, an average graywacke 1.2, and an average lithic sandstone 2.3. Because the ratio index number increases with mineralogic maturity, it is apparent that the Hornbrook sandstones are slightly more mature than the average arkose. This is expected, 71 because the Cretaceous rocks include the more mature feldspathic sandstones as well as arkoses.

Environment of Deposition

Whereas mineralogical maturity is primarily the end product of provenance, tectonics, relief, and climate, textural maturity is primarily the result of the depositional environment.

When dealing with depositional environments, we must consider both the physical and chemical environment.

Main factors comprising the physical environment are current velocity, water depth, and fluidity. Eh, pH, and temperature are the major factors of the chemical environment.

The basal unit of the Cretaceous section is better exposed than any of the other units. Therefore, a much better indication of the environment of deposition should be expected from this unit than from the others.

Evidence indicating that Unit 1 was deposited in a rough- water environment rather than in quiet water include the presence of conglomerate, pebbles and cobbles in the sandstone beds, moderate sorting of the sandstone, ripple marks and cross bedding (although both uncommon), and that the thinly-laminated sandstone beds that commonly contain pebble-size mudstone clasts strung along certain 72 lamina. Also, the orientation of strongly concavo-convex pelecypod shells show that the current was strong enough to move them about. An exception to the orientation of pelecypod shells is found locally where there is a complete lack of orientation displayed by the pelecypod

Trigonia. These shells are found in pods, lenses, and irregular beds of sand (Figure 5) and appear to have been swept into the area and deposited in a completely unoriented manner. Because of the heavy ornamentation, the heavy wall structure and irregular shape, perhaps shells of Trigonia do not easily assume an oriented position even where the current action may be considerable. It is believed that the Trigonia shells, along with the sand, were swept in rapidly and deposited over a short period of time. Because of the sand matrix, orientation of the shells would be that much more difficult.

Many of the sandstone beds that appear massive or structureless have fine laminations that can be traced laterally for a considerable distance. There are no disturbances such as cross-bedding or ripple marks, and the beds are almost devoid of fossils. Incorporated in these laminations are mudstone clasts many. times larger than the sand grains. Therefore, the current energy was strong enough to transport mud clasts along 73 the bottom but was not strong enough to produce cross- bedding and ripple marks. This may seem somewhat anomalous. Flume studies show that this type of lamination, along with an absence of ripple marks, can occur in unidirectionally-deposited sediments only when there is a high regime and the sand moves as a

"sheet flow". It cannot be assumed that these same conditions prevailed during the deposition of these thinly-laminated sandstones, but it would explain the laminations, the lack of benthonic organisms and the lack of accompanying ripple marks. The non-laminated sandstone beds may be the result of flow regime, different rate of sediment supply, or perhaps to conditions favoring a larger benthonic population to disturb any original laminations. Although it is difficult to establish the exact conditions prevailing at the time of sedimentation, it is clear that conditions changed rapidly. Although the flow regime may have been high, there is evidence that the environment was not extremely rigorous. The high percentage of mica, the presence of a chlorite and clay matrix, the fact that the sandstones exhibit only fair sorting, and the lack of abundant cross beds indicate this is probably not a beach or bar type of deposit. Also, a close look at the highly ornamented shells of Trigonia shows that there is 74 no evidence of prolonged abrasion as might be expected in a beach environment.

There appears to be no clear-cut evidenceto establish the depth of water duringthe time of sedimentation. Evidence for extremely shallow or extremely deep sedimentation, however, is lacking. A beach environment has been discounted previously. The absence of graded bedding, rhythmically beddedsandstone and shale, the lack of sole marking generallyattributed to turbidity currents, and the local abundanceof numerous benthonic organisms generally not considered deep-water dwelling all suggest that this isnot an extremely deep-water deposit. The observed evidence suggests that these sedimentary rocksare probably typical neritic deposits inwaters from a few 10's to a few 100's of feet in depth.

Depositional environment temperatures of most marine rocks, lacking indications of carbonateor evaporate deposition or glacial conditions, are probably not too significant, although there isa decrease in temperature with depth of sedimentation. The pH of normal marine water is approximately 7.8. Unless micro- environments is considered, these rocks giveevery indication of being normal marine in character. In some thin beds of sandstone and in mudstone units where the 75 organic concentrations are high, reducing conditions did exist. In these beds, authigenic pyrite is not uncommon.

Most of the discussion thus far has dealt with the lower sandstone unit of the Hornbrook Formation. In the overlying unit, which is a thin sequence of mudstones, shales, siltstones, and sandstones, the poor exposures do not yield sufficient evidence for distinguishing the depositional environment. It is not yet understood whether these finer-grained rocks represent a deepening

of the basin or represent a more quiet water environment

such as a lagoon or both. The high organic content plus

the nature of the overlying rocks (Khs3) might suggest

that a lagoon is not an unreasonable assumption.

Immediately above the second unit (Khs2) is a thick

sandstone unit (Khs) that has marine fossils at the 3 base. Higher in the third unit (Khs3), the lack of

fossils, the nature of the cross-bedding, and the

addition of conglomerates to the section indicate shallower water and perhaps even nonmarine conditions.

Coal seams in the section also suggest that conditions have fluctuated from normal marine to a transitional

environment.

The thick upper mudstone unit (Khm) .with its

numerous interbedded fossiliferous sandstonesand

siltstones is clearly a marine deposit. This unit 76 probably represents a deepening of the sedimentary basin. It also could be argued that it represents a filling in of the basin with the source supplying only finer-grained materials. Probably the best evidence for water depth is obtained from benthonic fauna studies, especially of the Foraminifera. A foraminiferal study of these units may in the future shed more light on the water depth and other environmental conditions.

Tectonics, Relief, and Climate

The tectonics, relief, and climate are major controlling factors determining the composition of the sediment. For this reason, a look at the mineral composition should shed light on all three factors.

Feldspar is used here as the key mineral for interpretations. The feldspar grains show a wide range in their degree of alteration. Clear, limpid feldspar grains as well as grains so cloudy they are barely recognizable as a feldspar are present in the Hornbrook formation. Also, the average grain size of the feldspar is close to that of quartz, even in poorly sorted sandstones. Neither quartz nor feldspar grains are more than subrounded. The textural features of the feldspar indicate that the source area is close by. According to Krynine (1942), a mixture of fresh and weathered 77 feldspar indicates a humid climate with high relief where streams are capable of cutting through the deeply- weathered mantle and eroding the fresh bedrock. To expose the granitic rocks that supply fresh feldspar to produce arkosic rocks, either major block faulting or orogenic uplifts must be considered. The Cretaceous

Hornbrook Formation rocks are not thick wedge-shaped deposits classically associated with block faulting.

They were most likely derived from a rising orogenic belt in the area of the present Klamath Mountains. 78 PAYNE CLIFFS FORMATION

Stratigraphy and Abe Relationships

Tertiary sedimentary rocks that directly overlie Cretaceous strata in the Medford-Ashland region have been mapped as the Umpqua Formation by Wells (1939,

1956) and are referred toas nonmarine sedimentary rocks on the more recently published geologicmap of western Oregon (1961). Approximately thirteen square miles of marine strata included in the Umpqua Formation by Wells (1956) are now known to contain Late Cretaceous ammonites (D. L. Jones, personal communication). Marine rocks younger than Cretaceous have not been recognized by the author. The name Umpqua Formation should not be used for the nonmarine strata of this area because they have not been correlated with the Early Eocene Umpqua

Formation to the northwest. Furthermore, current evidence indicates they are not correlative. Well- preserved fossil leaves from Tertiary beds discovered just south of Ashland have been identified by Brown (1956) as Late Eocene.

Late Eocene rocks in the Medford-Ashland area that lie above the Cretaceous Hornbrook Formation and below the Late Eocene Colestin Formation or the Early

Oligocene Roxy Formation will be referred to informally 79

as the Payne Cliffs Formation. This name will be used because of the goodexposures of the upper part of the

section in the vicinityof the Payne Cliffs.

Numerous short sections ofthe formation were measured and described inorder to compile the composite

stratigraphic column givenin Appendix C. At no one

locality wereexposures adequate to describea complete

section. Although this is essentiallya vertical

sequence study with little opportunityfor the recognition of changes inlateral variations, some major trends in grain-sizedistributions within sandstone and conglomerateunits were recorded, aswere some thickness variations withinthe conglomerate units. Approximately 8,500 feet ofthe Late Eocene

Payne Cliffs Formationare present in the Medford-

Ashland area. This thick sequence is composedmostly of sandstone, with lesseramounts of conglomerate and very minor amounts of tuff. The lower half of the section lies in Bear Valley,and exposures are scarce. Highway cuts provide the best opportunityto view freshly exposed rocks, and a detailed examinationof well-exposed areas was undertaken. One such exposed section, at the eastern edge of the village of Phoenix,was described and measured and the resultsare given in Figures 30 and 31.

Photographs showing the freshnessof the exposure and a HWY

Figure 30. This detailed sketch shows the intertonguing nature and general characteristics of the lowermost conglomerate of the Payne Cliffs Formation at one locality. This exposure is the result of a recent excavation for the construction of Interstate 5 at Phoenix, Oregon, and thus is very fresh. Approximately one-fourth of this outcrop is sandstone, the rest conglomerate. Beds A through V correspond to the lettering of individual beds on the detailed columnar section (Figure 31). 81 N.Avv1/4, o0 Cont. bottom next page. 0 O 0 0' O 0 O 00 O 0 O 00 O 0 O 0 0 Sandstone: grayish green (5G 6/1), 0 fresh; dusky yellow (5Y 6/4), weathered; medium- to coarse-grained; sorting fair P 0 to good; quartz, biotite, feldspar, mafic minerals; clay or chlorite H coating masks many grains; calcareous 0 0 0 0 and noncalcareous zones; in thin O 0 0 section: sandstone grains subangular; 0 0 0 sorting fair; calcite occurs as 0 0 0 F scattered patches of cement and as O o O 0 0 E partial or complete replacement of O o detrital grains; a chlorite matrix in 0 0 0 D some beds probably accounts for the OO 0 0 0 greenish color of the rock; clay matrix 0 0 0 also present in some sections; grains O 0 0 tightly compacted; total amount of O 0 0 cement and matrix small. O0 0 0 00 O 0 0 0 0 0 O 0 o O 0 0 O 0 0 O 0 0

Cretaceous mudstone

Vert. Scale 1" = 20'

Figure 31. Detailed stratigraphic section of part of the lowermost conglomerate of the Payne Cliffs Formation. Stratigraphic relationships of these bedscan better be seen in the preceeding figure. Beds are lettered to correspond to those of Figure 30. 82

Conglomerate with sandstone. This particular outcrop consists of 74 percent conglomerate and 26 percent sandstone. The somewhat lighter colored sandstone occurs as thin beds, lenses, and as fingers extending into the conglomerate. Most sandstone beds thin or pinch out within the outcrop 0 0o (Figure ). The southern half of the 00 exposure is fresh and undisturbed. O D0 0 The northern half is partially covered and more highly weathered, especially a0 along fractures and faults. o o O 0 O 0 0 Conglomerate: grayish-green (5G 5/2) O 0 to dark grayish green (SGY 4/1), fresh; moderate brown (5YR 4/4) to moderate O 0 yellowish brown (10YR 5/4), weathered; o o most pebbles are between 1 inch and 3 O 0 inches in diameter; numerous scattered 00 cobbles and boulders; largest boulder, oo0 which appears to be Cretaceous sand- O 0 stone, is 18 inches in diameter and 5 0 0 inches thick; conglomerate fairly well- O 0 sorted within any one zone, but O 00 vertical and lateral changes in pebble T size are common; most pebbles are well- 0 0 rounded; no evidence of imbrication; O0 S pebbles show a high degree of R O 0 0 sphericity; most common pebble types O 0 Q are quartz, intermediate to acidic volcanic rocks, sandstone, chert, O 0 0 quartzite, metavolcanic and jasper; O o O o 0 pebbles are set in a noncalcareous to slightly calcareous matrix of sand 0 0 o 0 0 grains; sand in the matrix essentially O 0 0 same as in sandstone beds described 0 0 previously. o 0 0 O 0 O 0 0 83

detail of the conglomerate are shown in Figures 32 and

33.

Overlying the lower pebble and boulder-rich beds of the Payne Cliffs Formation are approximately 2000 feet

of sandstone with lesser amounts of conglomerate, pebbly

sandstone, tuff, and mudstone. A few thin coal seams correlative to these sandstones are present in the

southern part of the mapped area. A conglomerate lens overlies the thick sandstone beds. This conglomerate

is poorly exposed but appears to be much like the basal unit, although it contains more cross-bedding and fewer

sandstone tongues. Above this is another thick sequence of sandstone and pebbly sandstone beds with minor conglomerate. This sequence has several ridge-forming units. Spectacular cliffs such as the Payne Cliffs (Figure 34) and Van Dike Cliffs (Figure 35) are held up by resistant sandstone and pebbly sandstone beds. The added resistance of these cliff-forming beds can usually be traced to an increase in the amount of cement or a lower porosity resulting from a greater abundance of clay-sized matrix than in adjacent beds. Silicified logs up to 18 inches in diameter were found protruding from the cliffs. A honeycomb-like weathered surface

(Figure 36) is common along the cliff face. Present, 814

Figure 32. Sandstone beds of the lowermost Payne Cliffs Formation interfingering with the more abundant conglomerate. Outcrop is part of a roadcut near Phoenix, Oregon.

Figure 33. A detail of the lowermost Eocene conglomerate. The large sandstone boulder is indistinguishable from certain Cretaceous sandstones lower in the section. 85

Figure 34. The Payne Cliffs as viewed from the west. Both sandstone and conglomerate are present, but sandstone is predominant.

Figure 35. The Van Dike Cliffs are stratigraphically higher in the section than the Payne Cliffs. Lithologically, they are very similar. Figure 36. Weathering has Figure 37. Fossil plant produced this honeycomb-like fragments found near Payne pattern in the sandstone at Cliffs. Van Dike Cliffs. 87 but much less common, are plant fragments on the underside of some sandstone bedding planes (Figure 37). In the southern and central parts of the

Medford-Ashland region, the Payne Cliffs Formation is overlain by volcanic rocks of the Early Oligocene Roxy

Formation. Here, the Roxy Formation consists of

interbedded volcanic flows, blocky flow breccias, and water-laid pyroclastic rocks. Further to the north,

the Payne Cliffs Formation forms a gradational contact with the dominantly water-laid volcanic sedimentary

rocks of the Colestin Formation of Late Eocene age.

Sedimentary Structures

Bedding

The Eocene rocks are characteristically very

thick-bedded. Bedding features are best observed where

the sandstones and conglomerates stand as massive cliffs,

such as the Payne Cliffs in the central part of the mapped area (Figure 34) and the Van Dike Cliffs a little

to the south (Figure 35). Lateral continuity of

individual beds and common cross-bedding are important

features to be noted in these rocks. Individual beds or sedimentation units can be traced as far as one-half

mile. The most outstanding sedimentary structure present 88 is the persistent and widespread cross-bedding found within some units. There is a wide variation in the scale and type of cross-bedding. The thickness of the sedimentation unit ranges from a few inches to over thirty feet. Cross-bedding, where the sedimentation unit is small, generally has foreset beds that are less than an inch thick and only a few inches in length.

Larger sedimentation units may, however, have foreset beds greater than 2 feet thick and a few tens of feet

long. Regardless of the scale, both tangential and non-

tangential types of cross-bedding occur in the same outcrop, although the tangential variety is much more

common (Figures 38 and 39).

Cut-and-Fill

Cut-and-fill structures resulting from the

infilling of erosional channels are present, but their

abundance varies greatly from one part of the section

to another. The structures are most commonly observed

in the conglomerate units, which locally have numerous

lensing sandstone beds. Less conspicious but just as

abundant are channels cut into sandstone and infilled

with sandstone of the same grain size. A scattering 89

Figure 38. Cross-bedding typical of the Payne Cliffs Formation isseen here near the lower part of the section.

Figure 39. Stratigraphically lower by afew feet than the above photo, cross-beddinghere takes on a very different character. 90

of pebbles in one body commonly is the most obvious

indication of a channel.

High turbulence and velocity are indicated by

channels cut into the beds of conglomerate.

Conglomerate, pebble sandstone, or sandstone commonly

backfill these channels. Cross-bedding within the

channel fill shows a general northernly direction of dip

for the foresets. However, limited measurements, because

of poor exposures and the wide variation in the direction

of foreset dips, leave any interpretation based on these measurements inconclusive.

Graded Bedding

Graded bedding is not particularly common in

the Eocene rocks but is more apparent where there are

'marked vertical changes in grain size. Graded bedding

occurs in the sandstones, pebbly sandstones, and

conglomerates. These rocks very commonly intergrade

into one another. Normal grading, with a decrease in grain size

upward, is the most prevalent, but reverse grading and

even double grading are also represented. Double grading within a single depositional unit maybe either

of two varieties, of which the first variety is only

slightly more common: 1) from finer material at the 91 base grading upward to coarser and then back to finer at the top again, and 2) coarse at the base grading up to a finer center and then back to coarser at the top. It is important to note there appears to be no appreciable change in sorting along with the grading.

Imbrication

Imbricate structure has been observed only locally in the Payne Cliffs Formation. Where imbrication does exist it is weakly developed. This may be in part due to the high degree of sphericity of the pebbles and cobbles. At only three localities was the imbrication well-enough developed to measure the dip of the a-axis.

Average inclination of the pebbles is about 12-15 degrees. According to Potter and Pettijohn (1963, p. 35), inclination angles are generally between10 and

30 degrees, so the Eocene rocks show angles corresponding to the lower end of the range.

Where imbrication was observed, it supported

directional interpretations based on cross-bedding measurements.

Directional Studies

Directional interpretations are based almost

entirely on observations of cross-bedding, although 92 directions suggested by imbricationsupport those of cross-bedding wherever imbrication ispresent. Methods of measuring cross-beddingwere described previously, along with a brief discussion of thesignificance of cross-bedding as an indicator of regionalpaleoslope. A current rose showing the plots of 41 different outcrops is presented in Figure 40. An average of several compass readings for eachoutcrop was used to make the diagram. Although the variation or scatter appears quite large, a northnortheast slope direction is indicated. If this diagram is compared with the rose diagram for the Cretaceous rocks, two differences are evident. The Eocene cross-bedding shows a greater variation and a more northernly trend. The first difference, that of the greater variation, issomewhat surprising because Pryor (1960, Table 4) found in his studies of Cretaceous rocks in the Mississippi Embayment that the standard deviation for cross-bedding in marine rocks averaged 11to 12 degrees higher than fluvial-deltaic deposits. Potter and Pettijohn (1963,

Table 4-2) compiled directional data from nine marine and twenty fluvial-deltaic units and found similar standard deviations (standard deviations between 63 and

78 degrees for fluvial-deltaic compared withbetween 78 and 89 degrees for marine). 93

30 30

60 60

30 30 S

Figure 40. Current rose representing cross-bedding measurements of foresets at 41 Eocene outcrops. This diagram indicates a peleoslope to the northnortheast. Compare this with the current rose for the Cretaceous rocks, Figure 21. 94 The reason the cross-bedding variance of the thesis rocks is inconsistent with the average is not

clear. The Cretaceous outcrops are much more restricted

in areal extent than are the Eocene rocks, and it might be expected that increasing the areal extent would result in a more variable transport direction as

indicated by cross-bedding. This seems to be true in a study by Potter and Pryor (1961) where the variation was found to be much greater if they sampled several watersheds rather than just one. Also, if part of the

Eocene rocks were deposited by tributaries (or distributaries) of a main river system, the variation would most likely be greater.

Regardless of the amount of the variation or the cause of the variation, the general interpretation of the paleoslope (sloping to the northnortheast) is not altered.

Petrology

Objectives cited for the petrographic study of the Cretaceous rocks also apply to the rocks of the Payne Cliffs Formation. These objectives are to find criteria relating to the provenance, history of transport, environment of deposition, and post- depositional changes. Mineralogy and textural 95 relationships have been given the most careful attention.

A total of 180 samples from the Payne Cliffs

Formation were examined and ninety thin sections were prepared and studied. Sixty-three sandstone sections were selected for point counting. Tuff and conglomerate samples were also examined but not point counted. Examination of pebbles in the thin sections of conglomerate helped significantly in identifying some of the sand-sized rock fragments present in the sandstone. Thirty-seven samples of sandstone, tuff, and tuffaceous sandstone were selected for x-ray analysis of their clay content.

Techniques of sample preparation, x-ray studies, and point counting are identical to those described

earlier for the Cretaceous rocks.

Sandstones

Modal analyses of the 63 sandstones selected

for point counting are given in Appendix D. Note that

the framework is listed separately from the matrix and

cement.

Quartz is the most abundant framework

constituent. Although most of the quartz grains are subangular to subrounded, display sharp extinction and 96 have only a few inclusions, the number of quartz varieties is great. A few well-rounded grains and some rounded overgrowths were observed but are rare.

Undulatory extinction is slightly more common than sharp extinction. A few multigranular quartz grains that are exceptionally clear with sharp straight boundary contacts appear to be low-temperature vein quartz.

Rounded but irregularly shaped quartz grains of presumed volcanic origin appear toward the top of the section. These may or may not show a resorption hole or cavity in the central part of the grain. Inclusions were studied by making a single traverse through all sections and describing the type of inclusion in each quartz grain encountered. The type of extinction was also recorded for each quartz grain. Results are tabulated in Table 7. Dusty trails and globular inclusions are by far the most abundant; acicular and regular inclusions are approximately equal in abundance but account for only a small percentage of the total number of inclusions.

Volcanic rock fragments are second in abundance (Figure 41). Varieties identified include olivine-bearing basalt, basalt, andesite, dacite, rhyolite, and tuff. Of these, andesite is the most abundant. Extinction Single Single Single Semi-composite Composite Composite slightly strongly straight to straightto Inclusions strongly TOTAL straight undulatory undulatory,slightly undul.slightly Regular undul. undulatory

3.5 5.5 0.6 0.4 1.0 0.8 11.8

. Aciculor .

4.3 4.7 1.2 0.0 0.8 0.0 11.0

Globulara Dusty Trails . 25.7 30.3 6.1 3.9 6.7 3.1 0 75.8

inclusionless

1.5 0.0 0.0 0.2 0.0 0.0 1.7

TOTAL 35.0 40.5 7.9 4.5 8.5 3.9

Table 7. Inclusions and extinction types forquartz grains were determined and the results are presentedas percentages. 98

Figure 41. An Eocene sandstone with several volcanic grains, quartz, feldspar, biotite, muscovite, and calcite cement.

Figure 42. The euhedral to subhedral outlines of plagioclase are seen in these mafic volcanic grains. The large clear grain is quartz. 99

Andesites are generally porphyritic with phenocrysts of plagioclase feldspar, hornblende, augite, biotite or hypersthene. These phenocrysts are set in a pilotaxitic matrix of oligoclase-andesine and microfelsite. Plagioclase phenocrysts appear to be more calcic than the plagioclase in the matrix. In only a few grains were accurate An contents determined, and these showed the phenocrysts to be close to the andesine- labradorite border while the matrix grains were generallyAn40 or less. Plagioclase phenocrysts may be strongly zoned but many show weak or no zoning. Phenocrysts (Figure 42) most commonly are subhedral to euhedral in outline. Hornblende is the most abundant mafic phenocryst and is usually the variety lamprobolite

(oxyhornblende) with its characteristic red-brown color, high birefringence, and magnetite rims. Hornblende crystals are typically euhedral as are outlines of former hornblende crystals that have been completely

altered to chlorite. Augite is found as a phenocryst in a few andesite grains; it usually shows signs of

resorption. Biotite is dark brown to reddish brown and like hornblende may be partially replaced orrimmed with iron oxide. 100

Basalt fragments are not as abundant as andesite and are almost always much more highly altered. Chlorite, iron oxide, epidote and calcite are common alteration products. Zeolites are present but are not common.

Dacite(?) and rhyolite are present in small amounts. Some grains identified as dacite may actually be quartz latite or rhyodacite, since they were identified by the presence of quartz and plagioclase phenocrysts. Any K-feldspar in the matrix would not have been detected. Common to both dacites and rhyolites are resorbed quartz phenocrysts. The embayments caused by resorption are filled with a very fine-textured matrix. The matrix is too fine-grained to positively identify, but quartz, feldspar, clay biotite and glass appear to be present. Biotite and muscovite are present in these silicic volcanic rock fragments, although neither is abundant.

Both silicic and basic tuffs are present in

these rocks. The silicic tuffs are generally vitric and appear clear, yellow-brown, or patchy with both

light and dark areas present (Figure 43). They are almost black under crossed nicols. The basic.tuffs are much darker in color, commonly are more highly altered, and generally contain considerably more crystalline 101 material than the silicic tuffs. Some are so dark and highly altered that identification is uncertain. Shards and ghost outlines of shardsare present in the tuffs, but these are much more evident in the silicic varieties.

Taken together, the feldspars are slightlymore abundant than volcanic rock fragments, but plagioclase, the major feldspar, is less abundant than the rock fragments. Several varieties of feldspar are present, and in decreasing order of abundance theyare: sodic to intermediate plagioclase (oligoclase-andesine), orthoclase, microcline, sodic plagioclase (albite), sanidine, and calcic plagioclase.

Most of the plagioclase ranges from Ann to An45; progressive zonation is present but not abundant; oscillatory zoning is present butrare.

Alteration has progressed to an advanced state in some plagioclase grains but is absent insome clear, limpid grains. All intermediate degrees of alteration can be found. Vacuolization, giving an extremely cloudy appearance to the rock, is the most common alteration.

Kaolinitization also gives a somewhat turbid appearance to the grains. Unlike sericitic alteration, kaolinite penetrates throughout the sample and is not aligned according to any crystalographic direction.

Sericitization (or illitization) is common in small 102 amounts. Sericite is most oftenseen as flat crystals

aligned parallel to thecleavage traces. In the most

advanced, but rare, stages ofalteration, it penetrates

throughout the grain withouta preferred orientation

after the fashion of kaolinite. Some grains of plagio-

clase are partially altered to epidote. Replacement of feldspar by calcite iscommon, the replacement starting along cleavages or fractures and progressinginward

(Figure 44). Sometimes whole grains have been replaced by this process.

Orthoclase is less abundant in most samples than intermediate plagioclase. The orthoclase generally has a cloudy appearance, very few grainsare really fresh.

Alteration of the K-feldspars is much thesame as described earlier for the plagioclase. Vacuolization, kaolinitization, sericitization, andreplacement by calcite have all been observed. In general, there appears to be more vacuols and kaolinite in the K- feldspar than the plagioclase. Microcline is scattered throughout the Eocene rocks in small quantities, but nowhere is it abundant. It generally appears much fresher than the orthoclase in thesame rock and commonly appears fresher than much of the plagioclase.. Figure 43. A tuff fragment with hematite borders is seen among quartz, feldspar and badly altered volcanic fragments.

Figure 44. A large, somewhat indistinct feldspar fragment (f) with large areas replaced by calcite (c). 104

Minor amounts of albite or sodic oligoclase is present. Plagioclase feldspar more calcic than An50 and sanidine feldspar were recognized.

Granitic rock fragments composed of K-feldspar,

Na-rich plagioclase, and quartz are found throughout the

Eocene section. Hornblende or biotite are sometimes present. A few fragments are composed of three or more minerals, but most are composed of only two. It is esimated that orthoclase is approximately twice as abundant in these lithic fragments as Na-plagioclase, and microcline is relatively rare. Myrmekitic, micrographic, and perthitic intergrowths were observed in a few grains.

All multigranular quartz grains with moderately- to strongly-sutured boundries were point counted as quartzite grains. A marked elongation of some crystals within the quartzite suggest the possibility that these were derived from quartz schists rather than quartzites.

Chert grains were more troublesome to identify than other constituents of these rocks. Some of the chert is easily identified, but there is a gradation between clear, clean chert and cherty-appearing silicified volcanic rock fragments. Ghost outlines. of former phenocrysts and the presence of leucoxene were used as indicators of a volcanic source. However, not all grains 105 are clearly volcanic or sedimentary, and therefore the possibility of an error in identification exists.

The micas are very common with biotite more abundant than muscovite. Both very fresh and slightly weathered biotite is present; the weathered biotite is either bleached or partially altered to chlorite. The

freshest biotite is a rich, dark brown color and is generally seen as thick books rather than as thin flakes.

Muscovite always appears fresh. Neither biotite nor muscovite have many inclusions. Grains counted as slaty rock fragments include

slates, phyllites, and fine-grained schists. Of these, phyllite fragments are the most abundant. No sure way of differentiating between shale and slate has been

determined; therefore, any shale with well-oriented mica

fragments was counted with the slate. Any error in

classification is minor, because these grains

constituted only a small percentage of the slaty rock

fragments. Quartz and mica are overwhelmingly the most

abundant constituents, and carbonaceous matter, iron oxide, epidote, pyrite and chlorite are present in

smaller quantities.

Summary of Framework Constituents. According to Gilbert's classification of sandstones (in Williams, 106 Turner and Gilbert, 1955, p. 292-293), 55 of the samples point counted would be classified as arenites and eight as wackes (Figures 45 and 46 respectively). Of the arenites, 24 are arkosic arenites, 22are lithic arenites, 5 are volcanic arenites, and 1 is a subfeldspathic lithic arenite. All eight wackes are lithic wackes according to this classification.

Of particular interest is the progressive change in sandstone composition from the lower to the upper part of the Payne Cliffs Formation. This change can be seen in Figure 47. The lower part of the formation consists primarily of arkosic rocks, the central part is more evenly divided between arkosic and lithic sandstones, and the upper part of the section is mostly lithic sandstones. The lithic fragments of these rocks are predominantly volcanic rock fragments and those particularly rich in lithic fragments could appropriately be called volcanic sandstones.

Textural Features. A summary of the textural features displayed by rocks of the Payne Cliffs

Formation is presented in Table 8. From this chart, it can be seen that these are medium-grained sandstones, slightly coarser than the underlying Cretaceous sandstones. The major textural differences between 107

Quartz

Feldspar + Granitic Fine-grained Rock Fragments Rock Fragments

Figure 45. Modal analyses of 51 samples ofarenite of the Payne CliffsFormation have been recalculated and plottedon this triangular diagram. 108

Quartz

Feldspar + Granitic Fine-grained Rock Fragments Rock Fragments

Figure 46. Modal analyses of 8 samples of wacke of the Payne Cliffs Formation that have been recalculated and plotted on this triangular diagram. 109

Quartz

Feldspar Granitic Fine-grained Rock Fragments Rock Fragments

Figure 47. All samples from the Payne Cliffs Formation are plotted on this triangular diagram to show the change in composition upward in the section. Open circles (o) are from the lower part of the section, half-filled circles (o) from the middle part, and filled circles (o) from the upper part. 110

these sandstones and those of the Hornbrook formation

that they show a significantly lesser degree of

compaction and a much greater degree of porosity.

Crinkling of biotite books, so common in the Cretaceous section, is less marked in these sandstones (Figure 48).

The lower porosity in these sandstones is partially the result of a lesser degree of compaction and partially

the result of smaller amounts of cement filling the pore spaces. The degree of compaction is greater near the bottom of the section and is accompanied by a corresponding decrease in porosity.

Table 8. Numerical values for roundness and sphericity are based on the chart for visual estimates in Krumbein and Sloss (1963, p. 111).

Median Diameter .405 Medium-grained sandstone

Roundness .333 Subangular - subrounded

Sphericity .51

81% Low Compaction Compaction 15% Moderate Compaction 4% Marked Compaction

18% Low Porosity Porosity 14% Moderate Porosity 68% High Porosity

28% Poorly Sorted Sorting 63% Fairly Well-Sorted 9% Well Sorted 111

Figure 48. Biotite in the sandstone of the Payne Cliffs Formation is somewhat bent as a result of compaction, but is not crinkled to the extent of that found in the Hornbrook Formation. 112

Subangular to subrounded grains indicatea

textural immaturity of the sandstones. Roundness

increases with an increase in mediandiameter. Values

for sphericity also increase withan increase in median diameter.

Lithification, Diagenesis and Authigenesis.

Rocks of the Payne Cliffs Formation in the Medford-

Ashland area do not showas great a degree of

lithification as displayed by the underlyingCretaceous Hornbrook Formation. Much of the section would be considered "friable" sandstone, and weathered surfaces

can be dug into quite readily with a pick.This results from two factors: the rocks show signs of only

limited compaction, and the amount ofcement present is much less than in the Cretaceous rocks. The rocks have a high porosity except where calcite cement is abundant. The porosity decreases with depth of burial, but the decrease is not marked.

The major cementing agents in the Payne Cliffs

Formation are, in decreasing order of abundance, calcite, clay, chlorite, and quartz. Locally, minor amounts of iron oxide and zeolite are cementing agents.

All calcite cement in these rocks is sparry calcite. It occurs as a sparse patchy cement in most 113 rocks but is extremely abundant in others. The great abundance of calcite in some specimens brings the average amount of calcite up to a higher figure than that for either clay or chlorite. In reality, it is probably not as important a cementing agent as the others when considering the formation as a whole. Calcite occurs as random small patches or it may poikilitically inclose several detritalgrains.

It commonly replaces other constituents, notably volcanic rock fragments, hornblende, feldspar and quartz (Figure 49). The replacement of feldspar is similar to that shown in Figure 26 for the rocks of the Hornbrook Formation. Calcite was not observed to expand books of biotite in the Payne Cliffs Formation as it was in the Hornbrook Formation.

Clay and chlorite cement will be discussed here as one, because the mode of occurrence of the two appear to be the same. To a very limited degree they occur as detrital matrix constituents, butmostly they occur as authigenic cement. Types recognized include montmorillonite, nontronite, chlorite, and more rarely

kaolinite. Nontronite and chlorite are the most

abundant clay-like cementing agents. Montmor.illonite

is less abundant but occurs in numerous samples,

whereas kaolinite is rare as a cement. 114

Figure 49. Calcite cement (c) has partially replaced many of the detrital particles. The gray mineral showing a prominant cleavage (z) is a zeolite. Payne Cliffs Formation sandstone.

Figure 50. The space between grain boundries has been replaced by chlorite. The three detrital grains are plagioclase, quartz, and andesite. Payne Cliffs Formation sandstone. 115

The authigenic nature of most of these cements can be well established. Fibrous clay and chlorite is typically oriented normal to the grain boundries

(Figure 50) and commonly penetrates into detrital grains. If pore space remains after the fibrous cement forms, the space may be filled later with randomly oriented clay or chlorite of the same variety as the fibrous cement on the grains, with another clay mineral, quartz, or zeolite, or it may remain open as a void

(Figures 51 and 52). Some clay minerals are more randomly oriented than those described above.

Quartz cement is minor, but traces are scattered throughout the Eocene rocks. Most quartz cement occurs as overgrowths on detrital quartz grains; minor microcrystalline quartz has been observed. Locally, iron oxide is abundant enough to be considered as a cement. Where it occurs, it is always the last cement formed, coats most grain boundries, and partially or completely fills voids. Zeolites are abundant as a cement in two

samples only. Optical data was inconclusive, but heulandite and possibly stilbite and chabazite are

thought to be present. 116

Figure 51. Authigenic chlorite cement with quartz filling the central cavity. Payne Cliffs Formation sandstone.

Figure 52. Authigenic chlorite rims the detrital grains and the central part is entirely filled with a zeolite mineral. Payne Cliffs Formation sandstone. 117

Conglomerate

Conglomerate beds, common throughout the Payne

Cliffs section, show a wide variation in thickness and lateral continuity. Near the base of the formation, a thick, coarse conglomerate appears nearly continuous, whereas lens-shaped beds are more common higher in the formation. Cross-bedding and channeling are the only structures common to these beds; imbrication is present but rare.

Pebble counts were made at numerous localities.

Averages for these pebble counts are given for the lower, middle and upper parts of the formation so that vertical changes may be seen. No lateral variation was found in the composition of the pebbles. However, in a northernly direction, conglomerate is less abundant, beds less thick, and average pebble sizes smaller.

A summary of the pebble counts is presented in

Table 9. Volcanic rocks are the most numerous group. Most pebbles listed under the heading of femic volcanic rocks are rhyolites, a few are trachytes, and some others are not precisely determined. All pebbles counted as intermediate volcanic rocks are thought to be andesite in composition, many of which are badly weathered and difficult to identify.The greatest error Table 9. Pebble percentages averaged for the Payne Cliffs Formation. This data based on counts of 200 pebbles at 16 different locations for a total of3200 counts.

BASE OF EOCENE MIDDLE OF EOCENE TOP OF EOCENE

Femic Volcanic Fragments 13.0% 11.5% 12.5%

Intermediate Vol. Fragments 14.0% 26.0% 36.5%

Mafic Volcanic Fragments 5.0% 10.5% 14.0%

Silicified Volcanics 6.5% 4.0% 1.5%

Quartzite 26.0% 26.5% 24.5%

Chert 6.0% 7.0% 5.0%

Jasper 0.0% 1.5% 2.0%

Vein Quartz 1.5% 3.0% 1.0%

Granite 5.5% 2.5% 0.5%

Schistose Rock Fragments 4.0% 0.0% 1.0%

Sandstone 3.0% 1.0% 0.0%

Greenstone 3.5% 0.0% 0.0%

Unknown plus Others 12.0% 2.5% 4.5%

1-4 100.0% 100.0% 100.0% co 119 in pebble identifications is probably in these weathered andesite pebbles. Mafic volcanic fragments at many localities are also badly weathered and difficult to identify. Some pebbles appear to be chert upon first examination, but a closer study may show ghost outlines of former phenocrysts or crystals. Persistence of rectangular feldspar crystals is not uncommon. These were all classified as silicified volcanics in the tabulation of the pebble counts.

Quartzite is abundantly represented in all the conglomerates of the Payne Cliffs Formation. The wide range of colors include white, light gray, dark gray, blue-gray, pink, purple, light green and orange-red.

The apparent degree of metamorphism varies considerably.

It is interesting to note that quartzite pebbles do not decrease upward in the section to a noticeable degree.

This is probably the result of the durability of quartzite, rather than the abundance of quartzite in the source area compared with other rocks.

Granitic and schistose rock fragments are not abundant anywhere in the formation, but do show a marked decrease upward. Unidentifiable pebbles are much more abundant in the lower part of the formation. It is believed by the author that many are metasedimentary and other types of metamorphic rock that are very

tuff is altered to kaolinite. Crystals of quartz, 120 susceptible to weathering. They do not show the same textures or relic phenocrysts that badly weathered volcanic rocks show, but they do show the tendency to break in a preferred direction.

Cobble and even boulder conglomerates are common at the base of the formation, but above that pebble conglomerate is most common. An occasional cobble or boulder can be found within the pebble conglomerates high in the section but these are rare.

The largest boulder measured is approximately 53 centimeters in the longest dimension (Figure 33), but the average diameter of the conglomerate clasts is between five and eight centimeters.

Tuff

Volcanic tuff is found throughout the Payne

Cliffs Formation in small amounts but is thicker bedded and more abundant in the upper one-half of the section. Most tuff beds are thin (6 inches or less) and finely laminated. The thickest bed encountered is about four and one-half feet thick, and the only place it is exposed is near an intrusion, where it was oxidized to a bright red color and hardened to a brick-like consistency. Most of the vitric part of the tuff is altered to kaolinite. Crystals of quartz, 121 muscovite, Na-plagioclase and biotite, in decreasing order of abundance, make up about 25 percent of the tuff, and hematite makes up about 5 percent. X-ray analysis of two tuff samples from this bed, one red and rich in iron oxide (M-7-13-5), the other white

(M-7-15-7), show that kaolinite is the only clay mineral present.

X-ray Analyses

Thirty-seven rock samples were selected for

X-ray analysis of their clay content. Although most were sandstones, four tuffs and the matrix from two conglomerates were also included. All samples were run a full 44 degrees 2 G. Samples with a 14 7 peak were treated with ethylene glycol and rerun. Samples were then heated at 550°C for one hour and rerun approximately 15 degrees 2 G. The results of these analyses are presented in

Table 10. The clay represents clay cement or matrix present between detrital sand grains. Alteration products of some detrital framework grains, especially the unstable volcanic constituents, undoubtedly contributed clays that are included in the analyses.

The three most abundant clays are montmorillonite, kaolinite, and chlorite. Where these 122

Table 10. X-ray analyses of rock samples from the Payne Cliffs Formation. Large X's represent moderate to strong peaks and small x'srepresent smaller peaks.

EOCENE ROCKS E41-1 ArX 1-1 41 41 a x >-1 -1 H < H Z 1-1

M-7-8-2 X X M-7-13-2 X M-7-13-5 X M-7-13-6 X X X M-7-15-7 X M-7-15-8 X M-7-25-4 X M-8-11-6 X X M-8-11-7 X M-8-18-1 X K-6-28-4 X K-7-6-3 X K-7-6-6 X K-7-9-4 X K-7-19-2 X K-8-16-9 X K-9-10-2 X K-9-11-8 X X K-9-11-17 X K-9-13-2 X K-9-14-1 X K-9-14-4 X K-9-16-3 X K-7-7-3 X K-9-26-1 X M-7-8-1 X M-7-15-1 X M-7-15-5 X X M-8-20-4 X K-6-28-3 X K-7-7-1 X K-9-11-22 x X K-9-13-1 X K-9-13-6 X K-9-13-7 X K-9-14-9 X K-8-11-2 X 123 clays are present, they are dominant over illite or mixed-layer clays, and in twenty out of the forty samples containing these clays, they are the only clay present. Of the thirty-three Cretaceous rock analyses, only three samples have only one clay present. Unlike the Cretaceous rocks, illite and mixed-layer clays always accompany other clays in rocks of the Payne

Cliffs Formation and should be considered minor constituents.

Petrographic studies were made to determine how the different types of clays occurred. It was hoped that the type of clay present and the manner in which it occurred would lead to some general conclusions regarding the origin of the clays.

Chlorite nearly always occurs as a cementing agent in the sandstones. As described earlier, it often is arranged normal to the grain surfaces, penetrating the grain on one side and projecting out into a void on the other. In most rocks with abundant chlorite cement, there also is an abundance of highly- altered detrital rock fragments. It is believed by the author that most chlorite is authigenic and is derived from mafic-mineral bearing volcanic rock fragments or from basic volcanic glass. 124

Montmorillonite also is primarily authigenic and occurs in much the same manner as chlorite. Except for the high birefringence of the nontronite, it would be easily mistaken for chlorite because its color and mode of occurrence is essentially the same.

Several samples of tuffaceous sandstone and tuff from one area contain kaolinite as the only clay present. Three samples were obtained from beds near an intrusion and have been highly oxidized. The alteration of the tuffaceous material may have been the result of close contact with the intrusion. The kaolinite-bearing sandstones are quite porous, which may have facilitated thorough leaching and the formation of kaolinite. Illite is uncommon in these Eocene rocks.

Mixed-layer clays are more abundant, but strong peaks were observed in only four of the thirty-seven samples. The exact composition of the mixed-layer clays was not determined.

Transport Direction

Interpretations of transport direction are based primarily on cross-bedding with imbrication used where possible. Although the cross-bedding results, presented in Figure 40, show more scatter than do those 125 for the Cretaceous rocks, a definite northerly trend is indicated.

The Late Eocene sea apparently reached a position approximately 60 to 100 miles to the north and northwest (Snavely and Wagner, 1963; Dott, 1964)of the Medford-Ashland region. This paleogeographic interpretation would place the area of investigation during the Late Eocene between the coastal plain and the rising highlands of both the Klamath and Cascade

Mountains. Assuming the correctness of the interpretations of these authors, the regional paleoslope would clearly be in a northerly direction. Data collected during this investigation corroboratesthis interpretation.

Composition of Source Rocks

Several different rock types contributed material to the Payne Cliffs Formation. Volcanic rocks are represented by femic,intermediate, and mafic types. Slaty and schistose rocks show that a metamorphic source was available, and femicplutonic rocks found in minor amounts through theformation show that a plutonic source was also available. Sedimentary sources were also contributors, buttheir importance is difficult to establish. 126

A mineralogical study provides evidence that the source rocks changed during Late Eocene time. As seen in Figure 53, granitic rock ,fragments and biotite decrease upward in the section. The biotite in the upper part of the formation is less altered than near the base, which suggests an increase in younger, fresher volcanic-derived biotite. Slaty rock fragments also show a steady progressive decrease as do chert and

K-feldspar, although their decrease is not as distinct. The most striking change takes place in the volcanic rock fragments which show an increase from less than

10 percent at the base to over 27 percent in the upper one-third of the formation (Figure 53).

Pettijohn's use of feldspar/rock fragments ratio (1957, p. 290) is modified here to include granitic rock fragments as well as feldspar to indicate a plutonic source rather than a supracrustal source.

In the lower third of the formation, this index is 1.93, which indicates a strong plutonic source. In the middle third of the section, supracrustal rock fragments are more abundant than feldspar and granitic rock fragments, and the index is down to .86. This has dropped further to .60 for the upper third of the section. 127

Chert Slaty rock Volcanic rock fragments fragments

0 10% 0 10% 0 10 20%

K -Feldspar Granitic rock Biotite fragments

0 10% 0 10% 0 10%

Figure 53. Plots showing the vertical variation of six minerals. The lower, middle, and upper one-third of the Payne Cliffs Formation is represented by each column. 128

This change in composition is reflected in the types of sandstones present. Table 11 shows how the arkosic sandstones at the base give way to lithic sandstones higher in the section.

Table 11. These figures show a striking and progressive change in composition between the lower, middle, and upper part of the payne Cliffs Formation. Most lithic fragments in the upper part of the formation are volcanic.

Lower Middle Upper

Arkosic ss. 93% 55% 14%

Lithic ss. 7% 45% 86%

The type of quartz present can also be used as a provenance indicator, and information on quartz grains has already been presented (Table 7). Igneous and metamorphic sources are both indicated, but metamorphic sources are definitely minor.

Mineralogical Maturity

The Late Eocene rocks are arkosic and lithic sandstones, mostly arenites but they include a few wackes. The wackes are more immature texturally than the arenites, but both the arkoses and lithic sandstones are immature compositionally. 129 Quartz plus chert plus quartzite to feldspar plus rock fragments ratios have been computed as an index of maturity. The average quartz plus chert plus quartzite to feldspar plus rock fragments ratio for the

Eocene rocks is 1:1.4. This can be compared with averages given by Pettijohn (1957, p. 509). This comparison shows that the Eocene sandstones have a ratio between that for the arkosic sandstones and the lithic sandstones although the ratio is closer to that of the lithic sandstones. This means the Payne Cliffs

Formation rocks are only slightly more mature than the average lithic sandstone.

Environment of Deposition

A fluvial environment of deposition is indicated for most of the beds of the Payne Cliffs

Formation in the Medford-Ashland region. Cut and fill structures, cross-bedding, and other sedimentary features described earlier, as well as the logs and abundant plant debris, are compatible with such an environment. A paluvial or lacustrine environment must be called on to explain the thinly and continuously laminated tuffs, the shale lenses, and the coal seams. A major problem appears to be how an accumulation of several thousands of feet of sands and gravels 130

could occur with no more than a few ten's of feet of shale, tuff, and coal in a typical fluvial environment.

There is a lack of finer-grained floodplain deposits

characteristic of many aggrading streams. If one

envisions a stream that drainsa highland area and flows

out to a coastal plain, there must be some point at which this stream is depositing onlycoarse elastics and

flushing finer material toward the sea. With down- warping of the sedimentary basin and concurrent upwarping

and upbuilding of the source area, it is conceivable that this zone of coarse clastic deposition in the stream's

profile could remain in one geographic position for a

long period of time and could build up thick deposits of coarse elastics.

Also worthy of some consideration would be a

braided stream system. This is attractive in that it leaves essentially no floodplain deposits as the entire

floodplain is constantly being reworked by the rapid shifting of the river's course. Braided streams occur

today mainly in arid or arctic climates where vegetation is sparse. In order to occur in a subtropical climate

such as that during the Eocene of Oregon, a great supply

of sediments would probably be necessary. In India, the

Kosi River, which originates in the vicinity of Mt.

Everest, emerges from the mountains onto a broad plain. 131 It forms a flat cone with a gradient from .0009 to .0002

(Leopold, Wolman and Miller, 1964). The river is

braided over the entire 130 mile length of the cone, and it has moved laterally some 70 miles during the past

two centuries. According to Leopold, et. al., it has been known to shift as much as 12 miles laterally

during a single season. The Kosi River is not flowing

through a tropical area, but rainfall there is between

60 and 80 inches annually and vegetation is abundant.

Braided streams also develop along some of the coastal regions in Alaska where rainfall and vegetation are

both abundant, although annual temperatures are much

too cool to be considered subtropical. There, the

great supply of glacially-derived material appears to

be responsible. In western Oregon, a strongly downwarped basin developed during Early Eocene time, as

evidenced by the thick accumulation of submarine volcanics and sediments of the Umpqua and Tyee

Formations. Uplift of the Klamath Mountains was necessary to supply these sediments (Snavely and Wagner,

1963), and the volcanic rocks of the present Cascade

Mountains were being built up providing an additional

source. From this, it appears there was sufficient available source material to consider the possibility of a braided stream. 132

In addition to the fluvial sands and gravels, finer clastics were deposited in the Late Eocene Payne Cliffs Formation. The main coal seams are found along the formation's strike and, although no seam continues far laterally, many appear to occupy approximately the same stratigraphic position. The development of swamps for the accumulation of the coal and shale was not continuous throughout the deposition of the Payne Cliffs

Formation but was apparently widespread at certain times. Local lakes developed where white, buff, and pastel green and pink tuffs were deposited.

Do the environments discussed above fit into a regional picture, and are they compatible with other information known about the Eocene of southwestern Oregon? Fluvial processes and coarse clastic sediments were dominant in the Medford-Ashland region during Late

Eocene time. Northwest 20 to 30 miles, in Sam's Valley, the deposits are generally finer-grained, with less conglomerate and more shale. This is at least 50 miles from the Late Eocene shoreline as proposed by Dott

(1964), Williams (1962), Baldwin (1965), and Snavely and

Wagner (1963). So we have a system of fluvial sedimentation with the sediments becoming finer-grained toward the shoreline. 133 Tectonics, Relief and Climate

The Late Eocene rocks of the Payne Cliffs

Formation are arkosic near the base of the formation and become richer in volcanic detritus toward the top.

This requires a source of feldspar to produce the arkose

and conditions favorable for its survival. Conditions favorable for the preservation of feldspar-rich

sediments include arid or arctic climates that inhibit

the chemical breakdown of feldsparor a steep relief to promote rapid weathering and deposition (Krynine, 1941,

1950). Furthermore, Krynine (1942) states that where all of the feldspar is weathered, slow erosion is

indicated, but that a mixture of fresh and weathered

feldspar indicates a warm humid climate and steep relief.

The Late Eocene rocks in the Medford-Ashland area do contain a mixture of fresh and weathered

feldspars. They do not, however, fit the simple picture of post-orogenic arkosic sedimentation as proposed by

Krynine (1941, 1942, 1943, 1950, 1951) in that they

contain a high proportion of volcanic constituents.

This will probably not appreciably alter the overall

interpretation, as volcanic activity is often associated with active tectonism. 134

From fossil evidence, Chaney (1948) has concluded that most of Oregon during the Eocene was subtropical, but that from Ashland northward into the

Willamette Valley, the climate was more nearly tropical.

He has suggested a lagoonal or low floodplain environment for much of the flora found in this region.

The Early Tertiary, through the Oligocene, was considerably warmer world wide than today (Schwartzback, 1963, p. 164-180), a conclusion based on both faunal and floral evidence. Through a different approach using oxygen isotopes, Bowen (1966, p. 179-189) has found essentially the same conditions. Thus, it appears, the climate was warm and humidduring this Epoch, so steep relief must have accompanied it to preserve the unstable feldspars. Krynine (1942) has pointed out that to have steep relief, it is not necessary to have high elevations or rugged mountainous topography. The uplifts and volcanic centers could be close to the site of deposition and thereby produce steep gradients for the streams. The large amounts of volcanic fragments do not significantly alter this picture. They appear simply as an addition of volcanic constituents to an arkosic source, and the volume of these volcanic constituents increased through time. A logical interpretation then appears to be that 135 these Late Eocene beds are derived from a steep source area with a moist warm climate. 136

SUMMARY OF GEOLOGIC HISTORY

The Cretaceous and Eocene rocks of the Medford-

Ashland region are nestled between two physiographic and geologic provinces, the Klamath Mountains to the west and the Cascade Mountains to the east, and therefore must reflect the history of each. The Klamath province is the older of the two both physiographically and geologically, having its origins somewhere in the early Paleozoic. The birth of the Cascade Mountains did not begin until Eocene time; thus their influence on the rocks in Bear Valley was felt much later than was the influence of the Klamaths.

Because the Klamath province is the older of the two, its influence will be evaluated first. This region has been tectonically active throughout the

Paleozoic, Mesozoic, and Cenozoic. Its deformational history has been well-documented during the Mesozoic.

According to Dott (1965) the most probable age for the major orogenesis lies between 141 and 145 million years ago. This would indicate this region fits the classic concept of the Nevadan Orogeny, although this concept for California and Western Oregon rocks has fallen into ill repute during the past few years (Dott, 1965). From the rocks exposed and studied in the Klamaths, the 137 major sedimentation and plutonism, as well as diastrophism, appear to be Mesozoic.

During the Cretaceous, crustal movements were widespread and numerous, but were accompanied by little volcanism. According to Hinds (1933) and Williams (1962), few periods were less active volcanically than the Cretaceous of western Oregon and northwestern

California. Because of the metamorphism accompanying the Middle Mesozoic orogenies, and the lack of syn- and post-orogenic volcanism before the Late Cretaceous transgression, volcanic fragments supplied to the

Cretaceous rocks were essentially all metavolcanic. During the Cretaceous, the Klamath Mountains were alternately a highland supplying sediments to the

surrounding basins, a site of marine deposition, and a

zone of orogenesis. The warm climate and rapid chemical weathering produced much clay, which along with fresh

and weathered feldspar, was supplied to the sedimentary

basins of Oregon and California. Evidence shows that the Cretaceous seas that transgressed on the Klamath Mountains came from the north against the northern part

of the highland and from the south against the southern

part of the highland. The lowermost units of these

transgressive deposits, strongly reflecting the

lithology of the underlying rocks, are veryarkosic over 138 the plutons and lithicover the metasedimentary and

metavolcanic basementcomplex. Local bedrock types became less important higherin the formation as mixing occurred whilethe sediments were being

transported greater distances. Shelf-type deposits dominate the lower bedsof the formation. Reefs formed locallyon higher bedrock surfaces, producing small limestone pods. That transgression was not continuous is indicated bythe lagoonal and non-marine sediments overlying the basalshelf sediments. Later, the basin either deepenedor the source was much further away, during which timea few thousand feet of silty muds and sandswere deposited. A Middle to Late Cretaceous diastrophism occurred approximately along the line ofthe present

Oregon coast (Dott, 1965), but there isno evidence that diastrophism extended inlandas far as the

Medford-Ashland region. Uplift of the Klamath Mountains and retreat of the Late Cretaceoussea marked the last time that theoceans penetrated as far as the Medford- Ashland area.

Latest Cretaceous and Early Eocenewere times of stability and erosion in theMedford-Ashland region. By Late Eocene time, basinsto the north and northwest 139

were downwarped receiving sedimentsthat make up the Umpqua and Tyee Formations.

During the Eocene, anotherevent occurred

which had an importantinfluence on all of western

Oregon--the birth of theCascade Mountains. During the Eocene, the Cascadeswere seemingly a disconnected

chain of volcanoes ratherthan a continuous range.

Bear Valley changed froman area of erosion to an area

of deposition by LateEocene time. Material was brought in from the KlamathMountains to the west and southwest

and from the Cascade Mountainsto the east and

southeast. Abundant fresh volcanic material fromthe

Cascades was mixed with themore arkosic sediments from the Klamath province, and thepercentage of the volcanic detritus increased through time.

It is known that the Eocenewas a time of very mild climate with abundantvegetation (Chaney, 1948),

but the exact paleogeographicsetting is not known for

Bear Valley during theEocene. It probably was a broad

valley that was the site of transportationof much

clastic material from the surroundinghighlands to the Late Eocene ocean approximately100 miles to the northwest. Although some shale and coal are present, most of the thick Late Eocenesequence is comprised of

sandstone and conglomerate.The circumstances that led 140 to the deposition of several thousands of feet of coarse clastics and only one or two hundred feet of fine material is unknown.

Subsequent to the deposition of the Eocene rocks, uplift of the Klamath Mountains resulted in tilting of the Cretaceous and Eocene beds to the northeast, resulting in an average dip of 13 degrees. A slight angular discordance may be present between the

Cretaceous Hornbrook Formation and the Eocene Payne

Cliffs Formation, but if present it is probably less than five degrees. 141

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APPENDIX A

Composite stratigraphic column for the Cretaceous Hornbrook Formation 149

Composite stratigraphic column of the Hornbrook Formation in the Medford-Ashland Region, southwestern Oregon.

EXPLANATION FOR SECTION

0 0 Conglomerate o0

Sandstone

Mudstone

Silty or sandy mudstone

Shale

Coal bed Add Break in section used when continuing 50' with normal scale would be unwieldy.

Concretions

Igneous rocks

Scale 1" = 20' (Cont. on bottom of next page) 150

Sandstone: dark greenish gray (5GY 4/1), fresh; moderate brown (5YR 4/4), weathered; medium- to coarse-grained; sorting fair; detrital grains masked by green matrix; abundant mica flakes on most bedding planes; central part has heavy mineral bands (up to 30% magnetite); slightly calcareous; scattered small concavo-convex pelecypod shells on bedding plane, oriented with convex side up; most sandstone thinly bedded (less than 6") but beds may be up to 4 feet thick; some beds show fine laminations, others are structureless. A few small concretions are present.

. Muddy sandstone: dark gray (N3), fresh; moderate yellowish brown (10YR 5/4), weathered; quartz grains visible in dark clay matrix; carbonaceous fragments extremely abundant; slightly calcareous; thin (1-3 inch) beds break with a hackly fracture like a typical mudstone; abundant pyrite altering to limonite and gypsum crystals.

Sandstone and conglomeratic sandstone: white (N9) to bluish-white (5B 9/1), fresh, dark yellowish orange (10YR 6/6), weathered; coarse to very coarse sand, Z CO. . ammo 1 numerous pebbles and scattered cobbles near base; sand grains angular to subrounded, pebbles and cobbles subrounded to well-rounded; quartz, feldspar, mica,, lithic fragments, hornblende; cobbles mostly quartzite, chert, or granitic rock fragments; patchy calcareous cement; feldspar visibly altering to chalky- white clay; beds average 2-3 feet thick, some finer laminations present, but not prominent; pyrite mineralization along high-angle to vertical fractures; upper 18 feet somewhat finer grained, but pebbles still present; beds average 1-2 feet thick.

Biotite-rich Quartz Monzonite (Cont. on bottom of next page) 151

Sandstone with minor shale: sandstone greenish gray (5G 6/1), fresh; moderate yellow brown (10YR 5/4), weathered; medium-grained sand; sorting fair; quartz, feldspar, chlorite biotite; cement moderately calcareous, patchy; sorting fair; medium thick- bedded (2-4 feet), average, 8-10' beds present; some beds appear structureless, others thinly laminated with lamina 1/4 to 1/2 inch apart; pelecypod and sub- orginate gastropod shells abundanton bedding planes; lenses of pelecypod- rich sands (primarily Trigonia) 1 foot thick by 25' long; certain horizons appear to have several of these lenses pinching out and reappearing along the 300' of sandstone exposed along strike; ripple marks with a high ripple index present but not abundant; shale parting up to 6 inches thick and muddy sandstone beds up to 2 feet thick interbedded with the sandstone; the shale dark gray (N3), fissile, and carbonaceous. (Cont. on bottom ofnext page) 152

Sandstone: pale olive (10Y 6/2), fresh; medium olivegray (5Y 4/2), weathered; quartz, feldspar, biotite, carbonaceous fragments, olive-green clay-like matrix; moderately calcareous; beds 5-6 feet thick;some beds have lamina 2-4mm apart that is accentuated by weathering; minoramounts of shale and conglomerateare interbedded with the sandstone; shalebeds 2-6 inches thick have flamestructures; a few thin (1-3 inch) conglomerate beds with pebbles 1/4 to 1/2 inch in diameter; prominent concretions froma few inches up to 6 feet in diameter;on a fresh break, they blend in with the matrix; are prominent when weathered; sandstone in the concretions is medium dark gray (N3), fresh; brownishblack (5Y 2/1), weathered; fine-to medium- grained; faint beddingseen within some concretions; fossils in this unit include pelecypods, ammonites, and animal borings.

Shale and mudstone: olive gray (5Y 5/1), fresh; moderate brown (5YR 3/4), weathered; mudstone breaks with irregular ,..... fracture; silt content high in mudstone units; mudstones showed only weak / stratification. Some shale close to "paper" shales, most pronounced incenter of unit; lower one-third of unit contains approximately 20% thin (2-3 inch) sandstone interbeds. Near top of unit is a 4 foot thick bed of medium-grained sandstone; flattened calcareous concretions, several inches to 2 feet acrossare present in the mudstone. .," ti /ON* (Cont. on bottom of next page) 153

Sandstone, siltstone, shale,coal, and conglomerate: the central part of Unit 3, at the location describedhere, has a great variation in lithology. Whether this variation continues along strike is unknown. Sandstone greenish- gray (5GY 6/1), fresh; olive-gray (5Y 5/1), weathered; fine-grainedto medium-grained; sorting fair; thinly laminated, some wavy bedding planes; convolutions near base of some beds. Mudstone beds range from thin partings up to ten inches. Some contain wavy lenses of siltstone and fine-grained sandstone. Several coal beds up to 1-1/2 inches thick present. Conglomerate and pebbly sandstoneoccur near the lower part of this unit; pebbles of the conglomerate do not exceed 1-1/2 inches, and they average approximately 3/4 inch in diameter; sandstone approximately 70 percent of section.

Add 84' (Cont. on bottom of next page) 154

Sandstone: greenish-gray (SOY 6/1) to light olive-gray (5Y 6/1), fresh; grayish-orange (10YR 7/4) to grayish orange pink (5YR 7/2), weathered; fine- to medium-grained; sorting good in some beds, fair in others; sorting of pebbles in conglomerate beds and lenses good to very good; quartz, feldspar, mica, plant fragments; calcareous cement in some beds, patchy calcareous to noncalcareous in others; fresh outcrops show thick-bedded sandstone; badly- weathered outcrops generally show thin- Add bedded sandstone; weathering of the thin 164' laminations may produce this thinly- bedded appearance. Numerous dark concretions stand out in contrast against the lighter colored sandstone. Concretions are less than one foot in diameter; bedding can be seen continuing through some concretions; cross-bedding locally abundant; most show concave foresets that terminate into partially- truncated bottomset beds; two localities show planer to convex surfaces on the foreset beds; thin shale (3-4 inches) and thicker conglomerate (up to 4 feet) beds occur with the sandstone; shale lumps present on some bedding planes; conglomerate pebbles range from 1/2 inch to 2 inches; pebbles are well-sorted within any one bed. (Cont. on bottom ofnext page) 155

Mudstone with numerous sandstoneinter- beds. Mudstone: light olive gray (5Y 5/2)to grayish black (N2), fresh;moderate yellowish brown (10YR 5/4)to dark yellowish brown (10YR 4/2),weathered; small carbonaceous fragmentsup to 3 mm long common; abundant fine muscoviteand biotite grainsseen with the hand lens; rare quartz sand grains; rest of rock is clay-like matrix; noncalcareous;locally, mica abundant enough to givesheen to rock in direct sunlight; mudstoneappears massive but parallel alignment ofplaty constituents produces a laminated appearance; rocks generally do not break readily parallel to this direction; fracture irregular or subconchoidal; locally, rock is fissile and wouldbest be called shale; flattened concretions up to 5 inches thick and 16 inches in diameter and round concretionsup to 8 inches in diametercommon; some concretions septarian; concretionsmay or may not contain fossils; thin sandstone dikes less than 2 inches wide present in southern part ofarea, and sandstone dikes up to 2 feet widepresent in northern part; animal borings,wood fragments, carbonaceous fragments, pelecypods, gastropods, foraminifera, and ammonites in the mudstone unit

Sandstone: dark greenish gray (5GY 4/1), fresh; dusky yellow (5Y 6/4),weathered; fine or very fine-grained; micaflakes and carbonaceous fragments visable; sorting fair; moderately calcareous; beds less than 4 feet, average 2-3 inches; beds often show finer lamina (1-2mm); convolutions, animal borings, low-angle cross-bedding, flame structures, andwavy bedding planes. O 0c, 0 0a (Cont. on bottom of next page) 156 C,0a O Eocene conglomerate 00 00 0 C>

Interbedded mudstone andsandstone: the upper 241 feet of the mudstone unit has numerous sandstone and siltstone interbeds; the mudstone similarto that described for underlying beds,except for a greater amount of carbonaceous debris; fissile enough locallyto be called a shale; lower 107 feet of section has 138 separate sandstoneand mudstone beds, givingaverage thickness of 9 inches per bed; theupper 134 feet of section notas well-exposed but has a higher percentage of silt and sand, and beds average just 5 inches thick; sandstone olive gray (5Y 4/1) to dark greenish gray (5GY 4/1), fresh; dusky yellow (5Y 6/4), weathered; fine- grained; abundant mica and plant fragments; moderately calcareous; thinly laminated, load casts, low angle cross-bedding, ripple marks, parting lineation, animal borings, and worm trails; fossils include ammonites, pelecypods, gastropods, and foraminifera.

Add 2435' 157

APPENDIX B

Modal analyses of the

Hornbrook Formation Sandstones CO1 I I I i I s 1/40 $ 1/40I , i x1/40I x I x I ';'C I s I i V1 V,- .1 COsO1 soI spI I I I 1/40 1/40 1/401 I *--.11 SA:."TLE 1.- -. N)- I N) CO1 CO1 04ICO CO1 COI ) N) N) I N) V I NO. .r.- I V Os VI ( i- b.-.o0I oI 1--.o I o I (...)oI 4 V1... MINERAL 32.0 6.4 31.6 2.0 34.8 3.2 N 36.0 1.8 35.6 2.0 32.4 2.4 12.4 0.4 31.6 5.2 32.0 5.2 16.4 3.0 N.NV 16.8 3.8 i-Ch 16.0 5.6I's.) 26.6 8.4 VI 34.0 8.8 11.234.0 38.812.0 OrthoclaseQuartz 12.8 0.40.8 T 12.4 6.01.0 T 0.24.40.4 - 0.86.61.6 - 6.8 --- 0.6 1.0 - 10.6 2.8 - - 16.0 T- 15.2 7.2 - 3.27.0 - 3.81.4 - 1.68.4ts.V- 7.6 - 0.48.4 7.2 T- 14.0 0.2 T ChertMicroclinePlagioclase 2.8 1.8 1.8 III 2.0 1.6 1.05.2 11.2 1.2 1.21.2 3.2 2.06.4 5.64.4 5.0 - 0.80.4 1.23.6 7.44.0 5.06.8 10.2 7.6 1.44.84.0 4.22.0 - 9.62.8 T 3.21.6 T Slatyletavol.Gran. Rx. Rx.Frag. 0.86.8 T 1.0 -T 0.24.4 - 5.21.4 - 0.85.2 0.29.2 - 1.2 T 1.2 T 0.64.4 - 0.84.2 - 2.80.2 2.4 T 6.8 -- 0.40.61.63.2 0.88.81.2 T HornblendeMuscoviteBiotiteQuartzite n 0.42.2 -TT 1.6 - 1.0 T 0.8 T 0.4 T 0.8 - 1.6 T 1.2 T 0.4 T 0.2 - T 2.4 T 0.2 1.2 3.6 T OpaqueEpidote Oxides H..._: 1.2 4.4 11.8 12.0 - - 0.2 T 4.0 4.2 4.8 6.8 - 6.4 - 4.0 - 2.4 Chlorite ,-.. T- - T------1.0 -T 0.41.4 - -TT T 0.2 T -T 0.2 -T Garnet-SphenePyritePyrexene > -T -OD -T -T ------T - -T - -T -T - - FossilTcur:Rutile-Zircon aline Frag. -T 6.8 -T 2.8 -T 4.6 -T -T- 16.8 1.8 - -T -T -T 15.2 - 20.0 - 6.8 - 21.4 1.28.4 0.4TTOtlier7.6 T 4.83.2 4.01.2 QuartzChlorite - - - - - 13.6 ------T Dol-Sider-AnkerSericite ./.n 28.8 0.40.8 24.4 2.4 - 29.2 0.89.2 10.2 0.29.2 16.4 8.8 - 0.2 - 76.0 7.2 - 28.0 0.21.6 27.8 1.02.4 34.2 0.2 - 27.6 2.0 - 40.8 0.6 - 2.20.86.2 10.4 0.64.0 17.6 0.80.4 0.68.0 - OtherClayCalcite ,-, 43 ...4 -4 ,-1T . 1 03 1 03 CO T V03 V La 1I coV1--.II TTcoII co I coII co-4I coVI co sI co1-.-I t.)-4o IV4.4 I34./., I LoN3 sI oIV03 I ts3 I --.03I SAMPLE NO. t-. T1I I I I o - .O 03I In L.) mIV 7T1IV I t...) La N3 I--. C.9 La MINERAL 31.211.2 10.424.6 0 3.09.6 r 1.47.2r 40.6 7.0 r 48.3 6.5 -;- 37.4 6.2 r 37.0 8.0 -I 34.0 9.0 32.6 38.0 28.4 38.0 30.8 P. 23.2 20.0 Quartz 11.8 1.01.8 10.6 0.61.6 3.21.0 0.80.21.6 3.05.01.0 3.03.7 - 7.05.26.4 6.05.83.2 4.05.43.0 8.67.62.8 T 11.8 1.26.4 T 11.6 3.04.6 - 12.8 0.45.6 T 10.0 2.45.6 T 12.0 0.82.81.2 16.0 2.03.6 T MicroclineChertPlagioclaseOrthoclase 4.28.91.0 12.2 7.01.6 13.4 4.2 - 10.8 4.0 - 7.22.0 - 8.1 -T 16.0 0.4 - 13.0 T- 11.0 T- 6.07.42.0 1.06.01.4 12.6 8.41.8 4.80.8 T 5.26.41.6 3.26.02.0 4.46.0 T Metavol.SlatyGran. Rx. Rx. Frag. 9.0 -T 7.82.8 - 0.8 -T T-T 1.2 0.40.2 -- 0.20.43.4 T- 0.4 T 1.010.42.21.0 1.6 - 0.21.8 - 11.2 0.21.8 0.40.8 T 0.8 -T 4.41.2 - BiotiteQuartzite 3.4 0.2 4.09.2 5.24.2 T- - T- 0.8 - T- 0.2 - T- T- T- 0.2 - -- 0.60.8 HornblendeMuscovite ,-3Cl)n 0.83.4 1.41.0 12.4 2.2 28.2 2.0 0.20.6 0.2 - -T -T -T 2.44.0 2.0 - 0.2 - 2.4 - 1.4 - 0.84.8 2.81.2 OpaqueEpidote Oxides ,tC-'..) T- T------PyroxeneChlorite HI-4 T T- 1.0 T 1.0 T- -T -T -T -T 0.4 - T T- - T- -T -T T- GarnetPyrite - Sphene crln T- 2.1 -T - T-T ------0.4 - --T -T 2.2 -T 0.2 -T 1.2 - -T -T FossilTourmalineRutile- Frag.Zircon p 4.0 - 10.4 - 18.8 - 16.8 -T 0.26.0 - 8.9 - -T 6.0 T- 6.2 T- - 6.6 - - 6.4 - - - - SericiteQuartzChloriteOther n 0.57.8 - 0.35.4 - 15.2 1.0 - 16.0 0.6 - 25.0 0.4 - 20.3 1.0 -T 15.2 0.22.0 - 21.8 1.8 -T 24.2 2.0 -- 21.4 0.8 - 13.4 0.2 -- 18.2 5.41.6 - 12.0 3.4 -- 31.2 0.22.6 - 42.0 0.4 - 34.8 2.2 - OtherClayCalciteDol-Sider-Anker Hm X-..18s X 1e -4XI-.1e X,-I Xp-I ,-.1I X I I-.1 x--1 1 z t.-1 x--1 1 4)X 1 X(..1V"1 Xt..34)1 X%01 Xt....)%/:,1 SAMPLE .0 Vp- V V V V 0-. t.4 1 L.) NO. 1 1.4.-.1 NJ--.1 )-+--.11 CM1 .P(7%1 -ON11 1.4I.-.1 I"..-1 1CT 1 VI1".1 0% l.r1 .P, l....) 1,..) MINERAL 35.4 6.23.8t....I1 33.0 4.66.0 22.413.8 2.2 33.415.0 6.2 34.810.6 2.8 lii 10.033.412.6 41.012.4 4.6-. 13.619.0 2.6 11.410.828.8 - 36.0 4.89.0 57.0 8.89.2 31.615.4 8.0 15.212.829.8 1111 36.213.014.0 34.410.411.6 32.611.8 PlagioclaseOrthoclaseQuartz 11111111 - -T 0.8 - -T 0.8 - 1.0 T 0.6 1.0 0.2 - 1.0 - 3.0 - 5.2 - 5.8 5.4 2.2 T 3.0 T Microcline 2.60.2 - 2.85.6 T 5.24.4 T 0.64.83.6 6.08.0 - 0.26.03.8 T 0.46.22.2 T 2.87.0 - 15.4 3.6 T 2.06.4 - 21.6 0.2 - 0.83.09.0 T 2.42.06.8 T 8.02.0 T 2.66.8 T 2.40.68.2 - Metavol.SlatyGran.Chert Rx. Rx. Frag. 4.6 - 7.2 - 3.4 T 2.81.2 8.4 - 10.0 0.6 0.65.0 5.01.0 5.2 T 9.2 - 0.20.8 -. 13.4 0.6 11.2 0.4 6.8 T 5.0 - 6.0 T BiotiteQuartzite -- T- 4.4 - 0.2 - -T 0.6 - 0.2 ------TT -- 1.0 - -T MuscoviteHornblende mt--3n'>. 4.02.25.2 4.83.26.4 1.81.6 3.83.05.0 2.01.01.6 0.21.0 T 1.2 T 2.21.0 T 5.84.03.2 7.63.01.8 0.2 -T 4.23.21.0 0.64.62.6 3.81.2 T 2.83.01.0 4.23.21.0 ChloriteOpaqueEpidote Oxides C-)1 - - - - -. - 00- OP- - - 40. - III/- Mb. NO- NW- Pyroxene 5-1,-3 T0.6 - - .. - Garnet-SphenePyrite iT...: 5.8 -TTTTTT-T0.2TTTTTT- - - - -T -T - 2.0 - - T- - - T- - --TRutile-Zircon 0.8 - TourmalineFossil Frag. m 5.0 6.8 12.0 5.0 5.0 T 2.2 4.4 3.2 - 6.2 2.6 -T- 5.8 3.8 4.0 Chlorite - -TTT-TT------0.6 - - 6.0 - -T 2.6 4.4 7.6 2.0 T Quartz n1:5, 1.0 3.0TTTTTTTTTTTTTTOther 3.4 0.6 - - - - T - OW MD- MP- 1.0 OD Sericite ------17.8 4.61.0 0.86.88.2 48.0 0.2 - 0.21.01.2 0.43.01.41.2 10.6 3.8 12.4 1.01.6 T 50.0 0.4 - 0.63.00.21.2 2.6 - 0.2 - 0.41.2 - 15.8 -- 0.83.2 - 10.4 1.6 - 12.8 0.2 - OtherClayCalciteDol-Sider-Anker HZ 1 I coI co 1 xco1 %CI1 ,-.1 1 --.1 X 1 +4 1 1 ..../ ....1 1 ....1 i-.IV1 r-.tU 1-.NJ1 U' 1 .P. 1 V1 Nf1 1`..) 1I COV1 1 V1 5--.xco1 I--.1 I-,co 1 VDvD1 CO-.11 1 SAMPLE NO. 41.6 L..)6.4 29.6 N., I 47.6 I-. 38.2 i-+ 26.2 .P, 28.6 NJ 6.4...) 14.6 NJ 46.6 ;-.f 41.0 ----I 45.2 t-ON 13.8 Ul 14.6 La 4.0 N.3 23.4 N 32.4 W Quartz MINERAL 10.8 1.4 4.48.4 T 12.4 1.25.6 0.48.07.0 2.44.83.0 7.02.0 - 15.8 3.2 - 0.22.60.8 - 9.22.2 T 0.89.05.2 10.8 8.4 T 5.00.2 T 4.6 TT 2.80.4 - 15.0 5.2 - 20.0 8.6 T MicroclinePlagioclaseOrthoclase 7.64.8 T 8.80.41.6 4.02.81.6 10.810.2 2.2 2.27.40.2 - 1.07.63.6 11.0 -TT 4.02.2 2.00.61.2 1.61.8 - 1.02.4 T 3.0 - 2.8 T- 3.8 - 7.05.2 T 13.2 5.00.6 Metavol.Gran.Chert Rx. Rx. Frag. 2.01.4 1.61.4 - 0.81.21.6 2.02.24.2 4.21.0 - 0.82.2 2.0 T 0.4 -- 3.81.8 - 5.2 -- 6.4 - 0.4 - 2.6 - - 3.81.2 - 7.02.64.6 QuartziteSlaty Rx. Frag. 4.00.4 - 0.81.6 0.40.4 - 0.21.2 T- 0.2 T- 14.2 T- -T- 1.65.20.2 0.41.4 T 2.4 - 2.60.2 -- 1.4 - - HornblendeMuscoviteBiotite >cnn 0.41.6 - 0.43.6 T 4.00.4 - 0.60.2 - -T 1.8 -T 4.0 TT -T 1.4 - 3.61.2 Vf 0.81.81.0 0.6 TT 0.80.2 1.2 - 1.80.61.0 0.60.40.8 - ChloriteOpaqueEpidote Oxides ,fnH1-1 -T- -T -T- -T - T- 1.0 - - 0.4 - TT T- - T -T T- T- PyritePyroxene nH1-1 T- T- - - 12.8 -T TT - -- -T T- - 33.4 - 27.0 - 38.2 - --TRutile-Zircon - TourmalineGarnet- Sphene mrm 6.05.2 -T --T 3.64.0 - 10.8 1.4 - 0.4 - -T -T -T 22.0 1.8- T 4.21.0 T 3.4 T - - -T -T 2.20.2 - ChloriteOtherFossil Frag. - - - - 0.4 ------0.2 - - SericiteQuartz n-t7,1 1.62.8 T 36.8 0.8 T 8.4 -- 0.20.4 - 34.8 0.6 - 42.4 0.4 - 42.2 0.2 T 75.2 - -T 17.2 3.03.0 16.0 1.81.0 40.2 1.0 - 44.0 0.4 - 50.4 0.8 -- 34.0 0.2 - 1.01.8 -- OtherClayCalciteDol-Sider-AnkerE1 Hz 1 ,:*X --.4X I x I N I PCI X I X I N I cox 1 cox I cox I XcoI I O`1,t)II I.-.mI 1I I-.Crsm1I N.)...,1 03-4I 1.4i....coI VIcoI mI I 1-+ I I 1--. 1 m1 SAMPLE NO. N IDLA) a)0(...1N 03 0I-I N I 1 NI o-....N1-.I ,-.NI--.I i--.NI 1-NI OsN1 t.nN1-. 1 MINERAL 17.638.2 8.4 16.020.0 3.6 32.6 7.62.8 22.8 4.42.8 30.8 7.22.4 24.013.6 35.4 6.4F 24.8 6.4 40.4 2.4 cl, 30.1 5.2 to 11.234.8 0 41.2 8.0-J 14.4 2.0 17.8 3.2 OrthoclaseQuartz 6.01.4 T 2.0 T 2.08.6 - 3.2 - 2.86.4 T 21.2 8.0 T 10.0 4.42.0 11.2 2.46.4 11.2 -- 3.22.47.6 - 11.2 3.64.12.0 3.22.80.88.0 3.62.00.86.0 10.0 7.44.0 T MicroclineGran.ChertPlagioclase Rx. Frag. 4.24.21.88.0 4.44.41.26.0 1.02.26.07.4 2.40.8 T- 2.06.87.2 T 6.42.49.0 T 10.8 4.44.01.6 14.8 2.86.0 0.81.4 - 0.81.65.2 3.21.63.6 2.06.8 T 0.40.44.4 17.8 5.24.0 QuartziteMetavol.Slaty Rx. Rx. Frag. 1.40.2 - 0.8 T 1.0 - -T 2.4 - 1.6 - - 1.2 - 0.4 - 2.4 -- 1.2 - 0.44.8 - 4.01.2 - 1.0 -- HornblendeMuscoviteBiotite f)n 0.81.6 2.80.61.2 2.44.00.2 2.0 -T 3.2 -T 0.80.20.8 4.80.82.0 3.62.01.8 3.25.20.8 2.01.41.2 3.20.81.2 0.42.0 T 0.40.81.4 -T ChloriteOpaqueEpidote Oxides ronH1-1 T- T- T- -T - T- T- T- 1- 0.2 - 0.8 - - - - PyritePyroxene HP;J.. MD ODT MD- T 111 - 0.2 T - T - - -T - - Garnet-Sphene F. - -T- -T 4.8 -- -T 5.0 -T 2.8 -- 2.4 - -T 1.0 - 0.8 - -- - 22.2 2.8 - OtherFossilTourmalineRutile-Zircon Frag. m 2.4 - - - - -= 6.4 T 0.44.8 - 10.0 -T 28.8 2.2 - - 8.43.2 - 6.81.6 - 3.6 - SericiteQuartzChlorite 2.20.81.8 34.8 4.2 - 21.4 0.8 - 39.014.8 1.0 28.0 0.8 - 0.4 -- 0.25.2 - 2.0 0.6 -- 1,61.6 -T 34.4 1,4 -- 0.41,1 -- 12.0 0.8 - 58.4 0.2 -- 0.81.8 - OtherClayCalciteDol-Sider-Ankerr7 Hz,m 163

APPENDIX C

Composite stratigraph. column for the

Late Eocene Payne Cliffs Formation 1614

Composite stratigraphic column of the Payne Cliffs Formation.

EXPLANATION FOR SECTION

V V Volcanic rocks \./ V

Sandstone

0 0 Conglomerate 0°0)

Shale, sandy shale

Tuff

Igneous rocks

Scale 1" = 200' 165 (Cont. on bottom of next page)

Sandstone: yellowish gray (5 Y 8/1) to light olive gray (5 Y 6/1), fresh; dusky yellow to dark yellowish orange (10 YR 6/6), weathered; coarse- to very coarse-grained; sorting fair; quartz, feldspar, biotite, muscovite, mafic grains; mostly noncalcareous; some patchy calcareous cement; individual beds are several feet thick; some units strongly cross-bedded; large, angular mudstone clasts up to 11 inches long numerous locally; small tongues of conglomerate present in the sandstone.

Conglomerate with interbedded sandstone: grayish green (5 G 5/2) to dark grayish green (5 GY 4/1), fresh; dusky yellow (5 Y 6/4) to moderate brown (5 YR 4/4), weathered; pebbles and cobbles typical but scattered boulders present at most localities; quartz, acid to basic volcanic rocks, sandstone, quartzite, chert, and metavolcanic pebbles; sand matrix may be sparse or more abundant than the pebbles; lenses, and beds that interfinger with the conglomerate are common; the sandstone is medium- to coarse-grained; sorting fair to good; quartz, feldspar, biotite, rock fragments, and mafic minerals; clay or chlorite matrix important locally; calcareous cement patchy. A detailed description of this unit is given in Figures 30 and 31.

Cretaceous Hornbrook Formation 166 (Cont. on bottom of next page)

Sandstone: poorly exposed and deeply weathered; greenish-gray (5 G 6/1), fresh; dusky yellow (5 Y 6/4), weathered; medium- to coarse-grained, pebbly layers and scattered pebbles and cobbles common; sand grains subangular to subrounded; noncalcareous to only slightly calcareous, concretions O 0 very calcareous; quartz, feldspar, biotite abundant; muscovite, hematite and rock fragments visible; clay-rich matrix; angular clasts of mudstone up to 18 inches long, 5 inches thick near base of unit; bedding poorly defined; some indication of large-scale cross- bedding; numerous conglomerate lenses are found throughout this unit; pebbles of quartzite, volcanic rocks, quartz, sandstone, and chert are the most abundant.

o0 0 ° O 0 0 Conglomerate: deeply weathered; no O 0 recent excavations to expose fresh o 0 rock; moderate brown (5 YR 4/4), fresh; to moderate yellowish brown (10 YR 5/4), O 0 0 weathered; well-sorted within any one O 0 bed; may range from 1/4 inch pebbles to 0 0 0 boulders; lateral and vertical changes O 0 0 in grain size evident within numerous O 00 outcrops; composition essentially the Oo I 0 same as conglomerate unit described o below.

0 o

o o 167 (Cont. on bottom of next page)

Sandstone: poorly exposed and deeply weathered; greenish-gray (5 G 6/1), fresh; dusky yellow (5 Y 6/4), weathered; medium- to coarse-grained, pebbly layers and scattered pebbles and cobbles common; sand grains subangular to subrounded; noncalcareous to only slightly calcareous, concretions very calcareous; quartz, feldspar, biotite abundant; muscovite, hematite and rock fragments visible; clay-rich matrix; angular clasts of mudstone; bedding poorly defined; numerous conglomerate lenses are found throughout this unit; pebbles of quartzite, volcanic rocks, quartz, sandstone, and chert are the most abundant. 0 0

Qf 168 (Cont. on bottom of next page)

Conglomerate with interbedded sandstone: conglomerate dusky yellow green (5 GY 5/2), fresh; dusky yellow 0 (5 Y 6/4), weathered; fine pebbles conglomerate to boulder conglomerate; 0 0 largest boulders 11-13 inches in 0 0 diameter; clasts average 2-4 inches in O 0 diameter; basic, intermediate and 0 0 acidic volcanics, quartzite, chert, 0 silicified volcanics, granite, 00 calcareous sandstone, and jasper present; sorting fair to poor. Sand- stone matrix is mostly yellowish gray (5 Y 7/2), fresh; moderate brown (5 YR 4/4) or dusky yellow (5 Y 6/4), weathered; fine to coarse-grained; quartz, feldspar, rock fragments, o0 o 00 biotite; subangular to subrounded; 0 only locally calcareous; patches with cleavage showing optical continuity O0 0 0 0 0 0 several inches across locally; bedding 0 0 0 in this unit typically very thick; O 0 0 large-scale cross-bedding found locally; unit 6 somewhat more resistant than underlying sandstone, therefore a slight ridge formed.

Sandstone: as described on previous page. \N"."4", 169 e0 (Cont.on bottom of next page) 0

Sandstone with pebbly sandstone, shale, and coal: sandstone yellowish gray 4) (5 Y 8/1) to light olive gray (5 Y 6/1), fresh; dusky yellow (5 Y 6/4) to dark yellowish orange (10 YR 6/6), weathered; medium to very coarse grains predominate;angular to subrounded; quartz, feldspar, biotite, muscovite, and rock fragments abundant; lithification primarily by compaction and fine matrix; mostly noncalcareous, some carbonate cement;bedding units commonly 10 to 20 feet thick; large- scale cross-bedding persistent in some units; cross-bedding planar to slightly concave; calcareous concretionslocally abundant; carbonized plant debris on underside of some sandstone bedding planes. Shale medium dark gray (N 4) to olive gray (5 Y 4/1); silty locally; poorly exposed but contains coal fragments of poor quality at two localities. 170 (Cont. on bottom of next page)

Sandstone with pebbly sandstone, conglomerate, and tuff interbeds: Sandstone; yellowish gray (5 Y 8/1) to light olive gray (5 Y6/1), fresh; dusky yellow (5 Y 6/4) to dark yellowish orange (10 YR 6/6), weathered; medium to very coarse grains predominate; angular to subrounded; quartz, feldspar, biotite,muscovite, and rock fragments abundant; lithification primarily by compaction and fine matrix; mostly noncalcareous but some potely carbonate cement; a honey comb-like weathering phenomena very common in thesesandstone; spotted sandstone with round,light- colored spots averaging 1centimeter across locally abundant;bedding units commonly 10 to 20 feet thick;large- scale cross-bedding persistantin some units; cross-bedding planar toslightly concave; calcareousconcretions locally abundant; silicified logs up to18 inches in diameter weathering from cliffs; carbonized plant debrisfound on underside of somesandstone bedding planes. Conglomerate: matrix of sand as described above;pebbles, cobbles and boulders primarilyquartzite and volcanic rocks; minor chert andjasper also present. Tuff: white to buff, thinly laminated; no unit wasfound to be more than 9 feet thick. 171 (Cont. on bottom of next page)

Sandstone with pebbly sandstone, conglomerate, and tuff interbeds: Sandstone: yellowish gray (5 Y 8/1) to light olive gray (5 Y 6/1), fresh; dusky yellow (5 Y 6/4) to dark yellowish orange (10 YR 6/6), weathered; medium to very coarse grains predominate; angular to subrounded; quartz, feldspar, biotite, muscovite, and rock fragments abundant; lithification primarily by compaction and fine matrix; mostly noncalcareous but some potely carbonate cement; a 0 0 honey comb-like weathering phenomena very common in these sandstone; spotted sandstone with round, light- colored spots averaging 1 centimeter across locally abundant; beddingunits commonly 10 to 20 feet thick; large- scale cross-bedding persistent in some units; cross-bedding planar to slightly concave; calcareous concretionslocally abundant; silicified logs up to 18 inches in diameter weathering from cliffs; carbonized plant debris found on underside of some sandstonebedding planes. Conglomerate: matrix of sand as described above; pebbles,cobbles and boulders primarily quartzite and 00 volcanic rocks; minor chert and jasper also present. Tuff: white to buff, thinly laminated; no unit was found to be more than 9 feet thick. 172

V V V V V V V V V' V V V V Younger volcanic flow rocks, breccias, V V and volcanic-derived sedimentary rocks of the Colestin and Roxy Formations. VV. v V' V V V VV V V V

Sandstone with conglomerate beds as described on the previous page; locally much more tuffaceous than underlying sandstone. 173

APPENDIX D

Modal analyses of the

Payne Cliffs Formation Sandstones -4 I tv-4 I Iv-4 I tv-.4 I Iv.4 I na-4I oo....1I -..03I 1-.03I CO1-.I I-.CO I -.00I V,....I I-...4a VI-.. 1 -.4 I NO. fTfTVfffffTTTffsAmpLEL.)-4N I to03 to--4a toasa 4.to a to(.4a ,-I 031-..1 I-toI I-A.4".I is.)I-. I-.1--.I to I 1.0toI P.)to a toi--. MINERAL 37.0 5.2 35.2 4.2 38.0 5.0 34.8 5.0 35.0 5.6 37.2 5.0 30.0 3.0 24.0 2.8 20.8 2.0 18.6 4.0 29.2 4.4 10.4 1.6 30.4 4.8 12.4 T 21.8 3.6 30.2 4.4 OrthoclaseQuartz 24.4 4.02.6 T 22.8 2.82.0 T 20.8 4.02.0 T 24.2 3.11.4 - 25.0 0.25.01.0 24.2 4.22.4 T 24.614.2 0.8 T 18.6 0.83.2 - 21.4 0.40.81.2 4.09.9 - 28.8 2.41.6 - 12.4 6.80.4 25.6 4.60.86.4 2.46.83.0 - 0.65.29.8 - 13.6 5.40.8 T Gran.ChertMicroclinePlagioclase Rx. Frag. 5.02.05.61.0 3.02.02.65.8 4.22.61.4 T 2.02.46.4 2.22.64.0 2.05.81.4 4.0 T- 32.0 T- 34.0 1.6 - 13.6 0.61.2 4.87.6 - 10.223.6 - 2.21.88.6 26.225.4 0.4 2.63.81.2 2.65.21.2 QuartziteSlatyVolcanic Rx. Rx. Frag. 1.0 - T- -T 6.2 T- 2.45.4 - 4.61.2 - 0.26.41.8 T -T 0.4 T- 0.21.2 - 0.8 - 1.6 - 3.6 - -T 0.24.6 - 0.24.8 - MuscoviteHornblendeBiotite w.rn 1.4 1.21.0 -T 1.41.0 T 1.8 T 1.4 T 0.81.0 0.8 -T T 0.4 0.43.2 - 0.81.8 -T 1.41.0 - 1.21.0 - OpaqueEpidote Oxides n.1JH 3.4 3.2 T 0.2 0.8 2.0 - - - PyroxeneChlorite HI-4 ------T-- - -- 0.2 - -T - - - -T T- Garnet-SphenePyrite wmrn 1.6 - T- 1.2 - 3.2 - T- 2.6 - 2.2 - - 7.61.4 - --T-T-TTRutile-Zircon5.6 0.8 - 4.04.8 - T- 1.8 - 4.8 - 4.2 T- ChloriteOtherFossilTourmaline Frag. TTTTTTT1.0T 1.0 T - T 1.0 2.0 - - - - 1.2 - - - - QuartzSericite m-,.c- 4.2 - 14.4 - 17.2 - 7.6 - 7.4 - 3.2 - -- 5.2 - 3.7 - 43.0 - - - 1.8 - 13.8 - 39.6 - .- CalciteDol-Sider-Anker5i Hz TTTTTTT5.0TT- - T T - 1.8 1.8 - 0,8 - 3.2_0.4 3.20.8 2.6 - 3.63.6 T- 1.4 T OtherClay .4 T (3,x 's x f T f oof fCO V x x TCO CO SAMPLE LA0%1I t..)as-4$ IVC)coI CON-) I l..)'01--.I L.)1-+'0I -4I-.I Loai--4I vt--.I I)1- I I--.N3 I Vl..)VI N.)V I N.)0%V I 1-(...)I 4)P-1 I NO. MINERAL 39.2 4.4 16.4 2.8 18.8 -4.0 39.2 .P` 4.8 29.6 N.)6.0 40.8 i-.. 5.2 30.8 P2.80 31.2 3.20 27.2 2.4N.)0 26.1 IV 3.0 17.6 2.0P-. 24.6 3.6 20.0 3.0 28.2 3.2 38.6 7.60% 28.0 7.4VI OrthoclaseQuartz 16.8 1.2 - 13.6 3.0III- 12.8 0.80.8 14.8 -.80.2 - 12.0 1.21.6 - 11.6 2.01.2 T 15.8 3.00.2 T 15.6 3.20.4 - 2.08.9 T- 10.0 1.21.8 - 19.2 0.40.2 - 23.6 4.01.0 - 14.6 2.60.2 - 19.4 2.81.0 - 25.2 4.8 T 20.2 6.43.4 T MicroclineGran.ChertPlagioclase Rx. Frag. 12.4 2.8 - 48.0 1.6 - 42.4 2.8 - 22.8 0.80.4 20.4 0.21.6 24.8 1.2 - 25.4 T- 25.6 - 36.2 1.2 - 25.2 5.01.6 42.4 2.00.4 22.4 2.43.0 22.0 2.41.4 22.6 TT 2.05.03.4 T 12.2 3.81.4 QuartziteSlatyVolcanic Rx. Rx.Frag. 2.42.04.8 0.20.4 - 0.81.2 - 0.82.02.8 1.6 - 1.6 -- 0.6 T- 0.20.8 - T- 0.60.8 - 0.21.6 - 4.8 T 0.64.0 T 0.65.6 T 2.2 - 4.6 -T HornblendeMuscoviteBiotite cn>rn 0.40.2 - 1.21.4 T 1.2 T 0.20.4 - 0.4 - 1.2 T 0.81.6 0.81.6 0.41.2 T- 0.4 T 0.81.0 T 1.0 -T- 0.81.4 - 1.21.41.8 - 0.24.63.8 - OpaqueEpidoteChlorite Oxides c>roH 0.2 - -- - -T T- - T- -T- - - - T- -T -T - T- Rutile-ZirconGarnetPyritePyroxene - Sphene mrnH-3 1.4 T- 0.88.0 ....- 5.2 - 1.8 - - T- 4.0 - 0.42.0 -- 3.4 -_ 0.8 - T-T 0.8 - T- T- 3.4 - - OtherFossilTourmalineChlorite Frag. - 0.2 - 1.2 - 1.2 1.8 - 2.0 - -- 0.43.6 - 11.0 - 1.1 - - QuartzSericite 53mn 8.01,2 - 0.4 - 0.48.8 - 8.8 - 24.0 - 9.0 - - 14.4 -- 10.0 5.0 - 15.6 3.44.2 - 13.0 - 0.6 T- 28.0 T- - 0.8 T 1.0 OtherDol-Sider-AnkerClayCalcite Hz '7. I I .oI 8 X,c31 X,o1 X--/ 1 .o1I 4:, 1 xqz. 1 g::.1 x,o1 .o1 x-41 xco 1I xoo 8I 1" 1 Z 1 Zs..11 sAmpLE .p.-I-.I P%s--*I -F--I .0I xcr,1--.I xas I ON I xON 0%I xCr,.I I.-,.P. I CO I ONV.)I t...34L...)t--.$ V(4I 1-+1,...)1 NO. MINERAL VN.) I-, rNID Nr Qs rl/1 -4 rL4 rN rH rH 31.8 r 15.2 32.0 Nr 36.4 r Quartz 36.819.6 0.22.0 21.625.6 6.0 - 36.215.2 3.6 - 32.2 0.87.85.0 18.012.4 3.1 - 14.417.6 2.2 - 26.816.0 0.63.2 29.215.2 3.6 - 18.019.2 2.4 . 20.411.2 4.0 - 35.218.6 8.8 - 27.4 9.65.6 - 19.2 0.40.8 9.61.2 9.22.4 - 20.0 3.2 - MicroclinePlagioclaseOrthoclase 19.8 1.21.0 22.0 1.0 T 11.6 4.81.0 2.64.87.0 32.- 0.8 - 32.8 0.8 - 26.4 0.8 -T 24.4 0.8 T 19.4 2.4 - 25.6 5.61.6 1.4 T- 5.62.8 - 15.4 3.60.4 31.2 0.40.8 21.2 0.8 - 22.2 4.01.6 VolcanicGran.Chert Rx. Rx. Frag. 2.4 T- 8.80.81.6 2.02.4 -- 2.42.8 T- 2.44.82.0 0.44.81.6 5.61.2 - 2.43.2 1.61.4 4.63.6 -T 6.41.4 - 5.21.0 - 0.23.22.2 0.20.4 T 0.22.00.8 4.8 -_ BiotiteQuartziteSlaty Rx. Frag. T- 2.0 T - - 1.0 T 2.01.4 0.4 0.8 - 0.80.61.2 - - 2.4 - 0.4 T- 0.2 - 0.2 T- 0.2 - MuscoviteHornblende 1-3Q 0.62.21.6 1.8 T 2.61.4 3.80.2 T 0.61.2 0.60.21.6 2.20.81.0 0.60.4 1.61.4 0.60.8 - 2.45.2 - 2.6 T- 1.0 T 0.84.0 T 0.8 T 0.2 - ChloriteOpaqueEpidote Oxides nHPJro ------Pyroxene )--.1.-.3 ------Pyrite t--, 0.81.0.4-T -- - - -T -T- - -T- - -- - 0.4 T 0.2 -T T-- 0.2 T -T- TourmalineRutile-ZirconGarnet-Sphene mn 1.2 - 0.22. 5.0 - - 1.6 T- T- - - -- 2.4 - 1.8 -T -T 0.21.8 - 0.6 - T- 0.81.4 - ChloriteOtherFossil Frag. 4.0 - 0.: 2.0 - 1.0 T 4W- 7.6 - - 2.4 - 0.6 ------T Quartz n ,, -_ - -M - - - - - 16.2 - -- - - Dol-Sider-AnkerRiSericite m,-3 2.62.4 - 3.21.14 - 2.0 -T 28.2 -T 11.6 5.6 - 0.86.4 T 4.87.6 - 11.2 T 14.2 T- 8.44.61.2 --- 5.24.60.8 23.6 6.87.2 10.0 1.0 - 28.8 2.4 - 15.214.4 - 2.81.0 OtherClayCalcite z PCi s 1 s i s a t 1o 1e t oI i 1 x 1o X i 0 0 0% s o% e SAMPLE 0 0 0 0 0 0 0 0 t...-1 I-.o. cfl).... t ,-.0- 8 .0-s I-.P- t I-. 1-s 1-.s 1-.s s isa 1 to 1 NO. m --.1 .o -co cy. -P.P.%.n le .p. NP1ZwP.L.0loll -.1 Cnw -.Pw I--.w IV MINERAL 21.6 17.6 10.4 13.2 22.2 26.4 28.4 38.0 36.4 22.8 25.2 23.2 5.2 32.4 OrthoclaseQuartz 13.6 2.8 -T 12.8 3.2 - 5.62.0 T- 0.80.4 T- 13.0 3.4 T- 11.0 3.41.4 T 10.8 0.42.41.6 21.2 1.81.2 T 12.8 0.85.2 - 11.6 0.44.0 - 16.4 0.22.4 - 19.2 1.2 T 3.24.41.2 MicroclinePlagioclaseChert 27.6 3.80.81.2 35.6 5.21.6 13.6 0.4 T- 12.6 0.80.2 - T- 20.6 0.21.0 T 22.8 0.80.2 T 23.4 2.61.21.0 20.6 25.64.01.62.4 2.81.4 - 14.8 0.81.21.6 34.0 1.01.6 T 13.6 4.02.80.8 VolcanicQuartziteSlatyGran. Rx.Rx. Frag. 2.0 2.4 6.2 6.8 1.8 1.4 0.2 0.8 - 2.0 1.6 2.81.6 0.8 0.21.6 Biotite t.-. 3.2 T 2.01.2 T 0.6 - 1.8 - 6.8 T- 0.4 - 0.2 - - -T 0.2 - 0.4 0.8 T T- MuscoviteEpidoteHornblende nm,-3> 1.2 1.2 0.4 - 1.4 T 1.8 T 2.41.8 Oxides .1:1 0.81.6 - 0.4 - 0.2 -- 1.2 - -T - - - 0.8 -TTTOpaque-T- 0.8 - - - - PyroxenePyriteChlorite lq T-_ -T- -T ------T- T- -T -T - - TourmalineRutile-ZirconGarnet-Sphene mFr:H 4.42.8 - 1.8 - 7.2 T- 0.85.2 - -T T- 0.8 - - - - 0.2 - T-- -T OtherFossilChlorite Frag. 1.6 - 2.8 - -T -T - -T 0.4 ------0.2 - 0.2 - SericiteQuartz o=7;1 5.63.2 -- 7.25.2 - 50.4 2.4 - 48.4 4.4 - 30.618.2TTTTT0.8-- 13.013.4 - 12.8 - 2.61.8 4.09.6 28.8- -- 30.0 - 12.4 -T 12.418.0 - OtherCalciteDol-Sider-AnkerClay HzRI