CALIFORNIA STATE UNIVERSITY, NORTHRIDGE

~ i

LOWER PALEOGENE GEOLOGY OF THE SIMI VALLEY AREA, VENTURA COUNTY, CALIFORNIA

A thesis submitted in partial satisfaction of the requirements for the degree of Master of Science in Geology by Jonathan David Parker

t '-

January, 1985 The Thesis of Jonathan David Parker is approved:

t)ll.v fvan P. Colburn

Dr. A. E~gene Fritsche

California State University, Northridge

ii ACKNOWLEDGEMENTS

I would like to thank R. L. Squires for his help and encouragement throughout all aspects of this study. His

support and geologic insight have been invaluable to this ., study. Many others have also been very helpful throughout this project. A. E. Fritsche reviewed the manuscript and focused my attention on many important aspects of these strata which were crucial to environmental analysis. I. P. Colburn shared much of his knowledge of Paleocene strata throughout the area. M. v. Filewicz and H. Heitman of Union Oil Company shared their knowledge of the micropaleontology of these strata. L. Ames typed the manuscript, and D. Dow of Getty Oil Company drafted the geologic map. Many property owners allowed access to their proper-

ty. They include the Sage Ranches, the Lang Ranch Com- pany, the Brandeis-Bardin Institute, and the s. P. Milling Company. In particular 0. Sage of the Sage Ranches, M. Harris, J. Varble, D. Dolder, and Lydia of the Brandeis- Bardin Institute, J. Kenyon, L. Edmonson, and Mr. Vinson of s. P. Milling, and L. Cheney of the Lang Ranch Company ,. were very helpful. ' I would also like to thank my parents. Without their love and support this project never would have been

completed.

iii TABLE OF CONTENTS

List of Illustrations •••••••••••••••••••••••••••••••• v Abstract ••••• ...... viii Introduction •••••••••••••••••••••••••••••••••••••• 1 Location and Purpose ••••••••••••• ...... 1 Previous Work •••••• ...... 2 Nomenclature •••••••••••• ...... 5 Age •• •••••••••••••••••••••••• ...... 7 Geologic Setting.. • •• ...... 8 Procedure ••••••••• ...... 9 Structure ••••••• ...... 18 Folds •••• ...... 18 Faults ••••• ...... 18 Stratigraphy and Depositional Environments •••••••• 21 Western Deposits ••••••• ...... 21 Simi Conglomerate...... 21 Description ••• ...... 21 Interpretation •••••••••••••••••••••••• 27 Las Virgenes Sandstone ••••••••••••••••••• 30 Description ••••••••••••• ...... 30 Interpretation ••••••••• 34 Santa Susana formation •••••••••••••••••• 38 Description •••••••• ...... 38 Interpretation...... 45 Eastern Deposits ••••••••••••••• .. . 48 Simi Conglomerate...... 48 Description •••• ...... 48 Interpretation ••••••• ...... 59 Santa Susana formation...... 63 Description •••••••••••• . .. 63 Interpretation •• ...... 68 Petrography ••••• ...... 73 Sandstone...... 73 Mudrock ••• ...... 76 Interpretation of Sandstone and Mudrock •• 76 Paleocurrents •••••••••••••••••••••••••••••••••••••••• 78 Provenance ••••• ...... 80 Paleogeography...... 82 References...... 89

iv LIST OF ILLUSTRATIONS

FIGURE

1. Index map showing the location of the study area...... 1 2. Stratigraphic nomenclature of Paleocene through lower Eocene strata, Simi Valley area...... 3 3. Explanation of symbols used in stratigraphic sections ••••••••••••••••••••••• 10 4. Stratigraphic sections A and c •....•.••.•..•. 11 5. Portions of stratigraphic sections A Cleft) and C {right) ••••••••••••••••••••••••• 12

6. Stratigraphic section B, measured through the western Simi Conglomerate and the Las Virgenes Sandstone ••••••••••••••••••••••••••• 13

7. Stratigraphic sections D and E ••••••••••••••• 14

8. Detailed stratigraphic section of the upper tongue of Simi Conglomerate in Poison Oak Canyon •••••••••••••••••••••••••••• 15

9. Notation applied to parts of Bouma sequences •••••••••••••••••••••••••••••••••••• 17

10. Facies classification for deep water clastics after Mutti and Ricci Lucchi (1972) •••••••••• 10

11. The western Simi Conglomerate and the Las Virgenes Sandstone near the head of Las Virgenes Canyon, looking west •••••••••••••••• 22

12. The western Simi Conglomerate - Chatsworth Formation contact near Montgomery Canyon ••••• 23

13. Thick, poorly bedded conglomerate in the western Simi Conglomerate •••••••••••••••••••• 24

14. Sandy claystone at the upper contact of the western Simi Conglomerate near the head of Bus Canyon ••••••••••••••••••••••••••• 27

15. Cross laminations in the Las Virgenes Sandstone near Bus Canyon •••••••••••••••••••• 32

v LIST OF ILLUSTRATIONS

FIGURE

16. Bioturbated fine sandstone in the lower western Santa Susana formation in Bus C:ctll~()ll...... 40

17. Conglomerate and sandstone Cat 1160 m on section A) present in the western Santa Susana formation in Bus Canyon ••••••••••••••• 44 18. Contorted mudrock in the western Santa Susana formation in Bus Canyon ••••••••••••••• 44 19. Distribution of deposits throughout the study area based on measured sections and map contacts ••••••••••••••••••••••••••••••••• 50 20. View of the eastern Simi Conglomerate as exposed on the north flank of Poison Oak Canyon...... 51 21. Densely bioturbated fine sandstone within the eastern Simi Conglomerate in Runkle Canyon. . . . • . • . . • . • . • ...... • . . . . . • . . . • . 55

22. Partial Bouma sequences in the eastern Simi Conglomerate in Runkle Canyon •••••••••••••••• 56 23. Lenses of conglomerate and sandstone in the eastern Simi Conglomerate near the head of Meier Canyon ••••••••••••••••••••••••••••••••• 57 24. Comparison of western {A) and eastern {B) Simi Conglomerate •••••••••••••••••••••••••••• 62

25. This series of photographs records the upward transition from Facies A through Facies G in the upper tongue of the Simi Conglomerate and the overlying Santa Susana formation in Poison Oak Canyon ••••••••••••••• 65 26. Lowermost Facies A conglomerate and sandstone near the mouth of Meier C:allye>n ••••••••••••••••••••••••••••••••••••••• 68

27. Fossiliferous concretionary sandstone lens near Runkle Canyon •••••••••••••••••••••• 70

vi ~1 '

LIST OF ILLUSTRATIONS

FIGURE 28. Sandstone composition of samples from the Simi Conglomerate, Las Virgenes Sandstone, and Santa Susana formation ••••••••••••••••••• 75

29. Paleocurrent patterns of the Simi Conglomerate, Las Virgenes Sandstone, and Santa Susana formation in the Simi Valley area •••••••••••••.••••••••••••••••••••.•••••• 78

30. Simplified paleogeographic model for the Simi Valley area during late Paleocene time •••••.•••••.•••••••••.••••••••• 86

TABLE

1. Clast characteristics of the Simi Conglomerate, western deposits ••••••••••••••• 25

2. Clast characteristics of conglomerate within the Santa Susana formation, western deposits ••••••••••••••••••••••••••••• 43 3. Clast characteristics of the Simi Conglomerate, eastern deposits ••••••••••••••• 58 4. Clast characteristics of conglomerate within the Santa Susana formation, eastern deposits ••••••••••••••••••••••••••••• 69 5. Sandstone characteristics of the Simi Conglomerate, Las Virgenes Sandstone, and Santa Susana formation ••••••••••••••••••• 74

PLATE

1. Geology of a portion of the Simi Valley area, Ventura County, California •••••••• in Pocket

vii ABSTRACT

LOWER PALEOGENE GEOLOGY OF THE SIMI VALLEY AREA, VENTURA COUNTY, CALIFORNIA by Jonathan David Parker Master of Science in Geology

The Simi Conglomerate, Las Virgenes Sandstone, and Santa Susana formation, of early Paleocene through early Eocene age, represent nonmarine through deep-marine depo­ sitional environments. The distribution of types of en­ vironments is, in part, confined by the Runkle Canyon fault. Strata west of the fault are referred to as "western" deposits. The Simi Conglomerate, present at the base of the sequence, consists mostly of poorly bedded, clast-supported conglomerate and subordinate sand­ stone. These rocks are interpreted as gravelly and sandy braided-river deposits on an alluvial plain. The over­ lying Las Virgenes Sandstone, present only west of the Runkle Canyon fault, consists of variable amounts of sand­ stone, mudrock, and granule conglomerate, and is inter-

viii preted as representing sandy braided-river, meandering­

stream, and nearshore-marine deposits. The western Santa

Susana formation reflects deposition in a deepening marine environment. The lower portion of the formation consists of sandstone and siltstone and represents

transition zone to offshore and shelf deposits. The upper portion consists mostly of mudrock with subordinate

amounts of interbedded sandstone and lenses of con­

glomerate and represents slope deposition. The uppermost

part of the formation may represent shelf deposition. Strata east of the Runkle Canyon fault are referred to as "eastern" deposits. Nonmarine environments and the Las Virgenes Sandstone are not recognized on this side of

the fault. The eastern Simi Conglomerate consists of conglomerate with subordinate sandstone and mudrock and

represents submarine canyon or channel fill and inner-fan deposits. The eastern Santa Susana formation is composed of mudrock with local tongues of sandstone and conglomerate and represents slope and inner-fan deposits.

Clast types and durability indicate a complex source terrane, which consisted of granitic, metamorphic, and volcanic bedrock and quartzite-rich conglomerate deposits. The Santiago Peak Volcanics and quartzite terranes in Sonora, Mexico may have been sources in part.

ix INTRODUCTION

LOCATION AND PURPOSE The Simi Conglomerate, Las Virgenes Sandstone and. Santa Susana formation comprise one of the best exposures of Paleocene through lower Eocene strata in California.· These formations are part of an Upper Cretaceous through Pleistocene section in the hills flanking Simi Valley, eastern Ventura County (Fig. 1). Virtually all of the study area is on private property, beyond locked gates, where a network of ranch and fire roads makes outcrops readily accessible. The Simi Valley Paleocene section has been the focus of numerous geologic investigations since 1914. Early

SANTA SUSANA MTNS.

1:l=====:::::::srkm-----'5 miles /' N 'SANTA MONICA MOUNTAINS

Figure 1. Index map showing the location of the study area.

1 2 studies were concerned largely with the diverse molluscan fauna of the Santa Susana formation and correlation of the

Simi section with northern California strata. Most subse­ quent work has focused mainly on the microfauna present in mudrock of the Santa Susana formation. Sedimentologic studies have been few and most have concentrated on only portions of these deposits, both areally and stratigraphi­ cally.

The purpose of this report is to 1) show the distri­ bution of the Simi Conglomerate, Las Virgenes Sandstone, and Santa Susana formation in the Simi Valley area, 2) describe the general lithologic character of these forma-_ tions, and 3) present an environmental framework for depo­ sition of these strata.

PREVIOUS WORK Waring (1914, 1917) published the first detailed description of Cretaceous and lower Tertiary strata in the Simi Valley area. Based on molluscan faunal content, he correlated the Simi rocks with the Chico, Martinez, and

Tejon Formations farther to the north (Fig. 2). Kew ( 1924) , in a discussion of the geology and oil resources of Los Angeles and Ventura Counties, mapped and described lower Tertiary strata in the Simi Valley area. He subdivided the strata into the Chico, Martinez, Meganos, and Tejon formations in ascending order (Fig. 2).

Nelson (1925) studied the fauna and stratigraphy of 3

Waring Kew Nelson Lalmlng Stipp Mallory Sage Zinsmeister 1914,1817 1824 1925 1840,1843 1843 1959 1973 1974 This Paper w E w E E E w E w E

Tejon Meganoa Tejon Tl Tl Tl Tl Tl

Oomengine ! ~ - Meganoa Tea I

not diiCUIIed

I I

Martinez

I Martinez/ I Martinez Martinez marine Martinez Tss Burro Tss Tss I Tss undllf. Sandstone member - Tlv Tlv -- Martinez ~ y ~ Tsc Tsc Tsc Tsc Tsc

Chico Chico Chico Chico Chico Chico Chico Chico Kc

Figure 2. Stratigraphic nomenclature of Paleocene through lower Eocene strata, Simi Valley area. W(west) and E (east) refer to nomenclature changes with respect to the Burro Flats and Runkle Canyon faults. Kc = Chatsworth Formation, Tsc = Simi Conglomerate, Tlv = Las Virgenes Sandstone, Tss = Santa Susana formation and Tl=Llajas Formation. the "Martinez" in detail in the Simi Hills. He further refined the previous nomenclature schemes by raising the "Martinez" to group status and subdividing the encompassed strata into the Simi Conglomerate, Las Virgenes Sandstone,

Martinez marine member, and Santa Susana Formation (Fig. 2). Variations on this nomenclatural scheme are used in most published literature to date.

Several workers have included the lower Tertiary of the Simi Valley area in discussions of California biostrati- graphy. Clark and Vokes (1936) incorporated Nelson's (1925) 4 work in a summary of informal molluscan biostratigraphy of the Pacific Coast states. Laiming (1940a, 1940b, 1943) established a provisional biostratigraphic zonation based on benthic foraminifers from several sections throughout California, including one from the north side of Simi Valley. Browning (1951) and Grier (1953) described the foraminifer content of samples collected by Mallory from the Simi Con­ glomerate, "Martinez", and "Santa Susana Formation" in Poison Oak Canyon. Mallory (1959) later integrated their results in a regional review of California lower Tertiary biostratigraphy. Sullivan (1965) included the fauna from Mallory's samples in a discussion of nannoplankton biostrati­ graphy of California. Schmidt (1970) included a section from Poison Oak Canyon in a discussion of lower Tertiary planktonic foraminifer biostratigraphy. Poore (1976) com­ pared the microfauna of several sections throughout Califor­ nia and correlated calcareous nannoplankton zones and ben­ thonic foraminifer stages. Several unpublished u.C.L.A. Master's theses deal with various portions of Upper Cretaceous and lower Tertiary geology in the Simi Valley area (Conrad, 1949; Fantozzi, 1955; Levorsen, 1947; Macrvor, 1955; Seiden, 1972). It is difficult to correlate between these works, however, because of differing stratigraphic unit designations. Sage (1973} discussed the sedimentology and deposi­ tional environments of several southern California Paleo­ cene localities, including the Simi Hills, and interpreted 5

Paleocene geography. His work in the Simi Hills concen­ trated mostly on the Simi Conglomerate and Las Virgenes

Sandstone and did not include geologic mapping. He later (Sage, 1975) published a discussion of the sedimentology, depositional environments, related tectonics, and paleogeo­ graphy of Upper Cretaceous and Paleocene strata in the

Simi Hills. Zinsmeister (1974, 1983a) described in detail Paleocene molluscan biostratigraphy of the Simi Hills. He correlated the Simi fauna with the European middle Thanetian Stage and the Gulf Coast upper Midwayian or lower Sabinian Stage. Janes (1976) discussed the geology and micropaleon­ tology of the "Santa Susana Shale" in the hills flanking eastern Simi Valley and Finch (1980) discussed the micro­ fauna of a portion of the "Santa Susana Formation" in Bus Canyon, central Simi Hills.

NOMENCLATURE Several nomenclatural schemes have been applied to the strata between the Chatsworth Formation and the Llajas Formation (Fig. 2). No two workers have agreed on what to call the various units or where to place contacts. This is probably the result of the presence of rapid lateral­ facies changes in conjunction with specific workers study­ ing only portions of the area. Some workers may also have been attempting to define chronostratigraphic units rather 6 than lithostratigraphic units (i.e., Kew, 1924; Nelson, 1925; Fantozzi, 1955).

Most published works have followed the terminology of

Nelson (1925), with considerable differences as to where to place contacts. Nelson's (1925) terminology also will be followed in this report with exception of the term "Martinez marine member". Nelson uses this term to des- cribe strata above the Las Virgenes Sandstone and the Simi·

Conglomerate east of the Runkle Canyon fault and below his

"Santa Susana Formation n and "Domengine Formation II. Be­ cause the term "Martinez" already refers to a provincial molluscan faunal stage (Clark and Vokes, 1936; Weaver and others, 1944) and refers to a formation which cannot be lithologically correlated with the Simi strata, its usage is discontinued in this report. Instead, the term "Santa

Susana formation" is used informally to describe all strata above the Las Virgenes Sandstone and the eastern Simi Con­ glomerate and below the Llajas Formation (Fig. 2). Be­ cause of informal usage, formation is not capitalized.

11 Strictly speaking the term Santa Susana II should be abandoned rather than redefined, but it is believed that the addition of yet another term without formal definition would be more confusing. The "Santa Susana Formation", as mapped by Nelson (1925), is not a well-defined strati­ graphic unit. However, the lithology described for the

"Santa Susana Formation" can be recognized in strata

Nelson (1925) called the "Martinez marine member", perhaps 7 in part justifying the expanded usage. The strata between the Chatsworth and Llajas Formations would best be des­ cribed by a single formation, with the names now in use reduced to member status, but such changes are beyond the scope of this report.

The most recent studies of the fauna of the Las Virgenes Sandstone and Santa Susana formation reveal an early Paleocene through early Eocene age (Filewicz and

Hill, 1983; Heitman, 1983; Saul, 1983). Based on the pre­ sence of Turritella peninsularis guaylei, Saul (1983) ten­ tatively correlated the oldest Tertiary strata in the Simi Hills to the Danian Stage, which is of early Paleocene age. Filewicz and Hill (1983) reported that the youngest calcareous nannofossil assemblage present in the Santa Susana formation represents the Discoaster diastypus Zone, which is early Eocene in age. Heitman (1983) correlated the Santa Susana formation to the Standard Planktonic P4, P5, and early P6 Zones, which are late Paleocene in age. Early workers correlated the Las Virgenes Sandstone and Santa Susana formation to the Eocene (Waring, 1914, 1917; Kew, 1919, 1924; Clark, 1921; Nelson, 1925; Clark and Vokes, 1936; Laiming, 1940a, 1940b, 1943). Subsequent workers (Browning, 1952; Grier, 1953; Fantozzi, 1955; Sulli­ van, 1965; Janes, 197 6; Mount, 197 6; Poore, 197 6; Zinsmeister,

1974, 1975, 1977, 1983a, 1983b; Finch, 1980) studied por- 8

tions of the Las Virgenes Sandstone and Santa Susana forma­ tion, and their age determinations fall within the range delimited by Filewicz and Hill (1983) and Saul (1983).

GEOLOGIC SETTING The study area is within the Ventura Basin as defined by Bailey and Jahns (1954). The basin, a subunit within the Transverse Ranges Province, is bounded by the Santa

Ynez and Topatopa Mountains to the north, the San Gabriel fault to the east, the Santa Monica Mountains to the south, and extends into the Santa Barbara Channel to the west. It is characterized by several anticlinal highlands and synclinal valleys, including the Simi Valley, in conjunc­ tion with thrust and reverse faults (Bailey and Jahns,

1954). Rocks within the study area form the limbs of a westward-plunging syncline expressed topographically by the Simi Valley. The Simi Conglomerate, Las Virgenes Sandstone, and Santa Susana formation are part of a thick Upper Creta­ ceous through Tertiary section consisting of both marine and nonmarine rocks. The middle Campanian to lower Mae­ strichtian Chatsworth Formation (Colburn and others, 1981) underlies the Simi Conglomerate throughout the study area. The Chatsworth consists of over 1,800 m of sandstone with minor mudstone and conglomerate deposited in a sand-rich deep-sea fan complex (Link, 1981). Conglomerate, sand­ stone, and siltstone of the upper lower through middle 9

Eocene Llaj as Formation dis conformably overlie the Santa Susana formation (Squires, 1981, 1983, 1984). The Llajas

Formation reflects a retrogradational sequence consisting of coastal alluvial-fan deposits through outer-shelf and slope deposits and progradation back to shallow-marine deposits (Squires, 1981, 1983, 1984).

PROCEDURE Field work included geologic mapping, measurement of stratigraphic sections, description of 1 i thologic units, and measurement of paleocurrent data. Geologic mapping was undertaken on enlarged u.s. G. s. topographic maps and transfered to portions of the Calabasas, Santa Susana, and Thousand Oaks 7.5-minute quadrangles (1:24,000). The strata were subdivided into units based solely on litho­ logic characteristics. Five stratigraphic sections were measured by means of Jacob staff and Brunton compass (Pl. 1). Sections are generally in canyons or along roadcuts where strata are well exposed. Section localities were chosen so the full variability of strata present in the study area would be represented. Clast counts were undertaken during the measur­ ing of sections and keyed to them. At least fifty contig-

uous clasts were counted per station and normalized to 100%. Samples for micropaleontologic analysis and thin­ section study were also collected and keyed to the sec-

tiona. 10

An explanation of the symbols used on the sections is provided in Figure 3. Figures 4, 5, 6, 7, and 8 graphi- cally represent the strata. Sections A, c, and E are com- plete sections measured from the top of the Chatsworth

Formation to the base of the Llajas Formation. Section D

is nearly complete with only 125 to 150 m missing due to cover. Section B was measured only through the Simi Con- glomerate and Las Virgenes Sandstone. Select portions of some of the sections are shown at a larger scale to high- light features important to environmental interpretation (Figs. 5 and 8).

Paleocurrent directions were deduced from clast imbri- cation. An average of 35 attitudes were recorded per sta-

MVF- e microfossil sample locality SH-23 rock sample locality Figure 3. Explanation of symbols used in strati- graphic sections. 11

Llajas Fm. -- disconformlty Llajas Fm. - dlsconformlty

1200 1200

1100 1100

fault?

1000

SH-30

800 Santa Susana fm. Santa Susana fm.

MVF-20

SH-24

600 SH-23

SH-22

500 500 .y MVF-19 <10 "'-" . 400 dil MVF-18 qJ SH-29

300 300

MVF-17 200 SH-28

SH-27 Simi Conglomerate

Sandstone 100 i~~~~t= Las Virgenes 100 ~~SH-26 SH-25 Simi Conglomerate l - unconformity - 0 -- unconformity -­ Chatsworth Fm. meters Chatsworth Fm.

SECTION A SECTION C

Figure 4. Stratigraphic sections A and c. Section A represents western deposits and C eastern deposits. See Plate 1 for the locations of traverses. 12

Santa Susana fm.

contorted mudrock

y . . (/jj marine body and I . ....:_:, · . trace fossils

Bouma sequence s channel deposits 100

Las Virgenes Sandstone Simi Conglomerate . . .

overbank deposits

bioturbated fine sandstone

sandy claystone 0

0

Simi Conglomerate 0 0

0 150 - unconformity- 0 +--_.:_..--:---..-' 0 meters Chatsworth Fm. meters

Figure 5. Portions of stratigraphic sections A (left) and C (right). Note the fining-upward cycles in the Las Virgenes Sandstone. Note also the presence of macro­ fossils and bur rows near the top of the unit. The upper western Santa Susana formation contains conglomerate and contorted mudrock. Burrows and Bouma sequences are present in the eastern Simi Conglomerate. 13

.. ~ ·· :] Santa Susana fm.

120 250 .y . ·r .· '--'--'--· -

110 240 • --

. - 100 230 -.. 90 220-J••··~ ·.~

80

Las Virgenes 70 200t~~~~~ Sandstone Simi Conglomerate ·~~ . ·.~ 60 190 -;- .- . .. --..:.. 0 •••• ./// .. . 50 180 .. __:_.:_:_ .·. -' '--~ ...... 170 ~ . · .·· ·.·: ·-:-:.:.(<. 30 160- . . . . : .. . :) · ~· . . ·· · : ·. : : : : ·. ·. :j . . · ·. . 20 150-. 0 0 0 o= oOoo~ 0000.:=:? oo 0 0 0 0 0 0 v 0 0 0 0 Simi Conglomerate 10 140 c 0 0 0 0 0

0 0 ~ 0 0 0 • "------4 n 0 o o o 0 -- unconformity --­ ~130~-o~ __o __ ~ --o~ meters Chatsworth Fm.

SECTION 8

Figure 6. Stratigraphic section B, measured through the western Simi Conglomerate and the Las Virgenes Sand­ stone. See Plate 1 for the location of traverse. 14

covered

Llajas Fm. disconformity 1200

1100 MVF-16 MVF-14

SH-21 1000

900 Santa Susana fm.

MVF-13

800 SH-18

Santa Susana fm.

700

MVF-11 600 600

SH- 19

500 covered 500 MVF-10 MVF-9 SH-17 MVF-8 0 0 0 0 0 upper tongue Simi Conglomerate 0 MVF-7 400 400 SH-14 MVF-6 MVF-5 MVF-4 300 300 MVF-3 MVF-2 MVF-1 SH-13 Simi Conglomerate lower tongue Simi Conglomerate 200 200 SH-12 MVF-1a

100 Simi Conglomerate

MVF-1 b

0 - unconformity --­ meters Chatsworth Fm.

SECTION D SECTION E

Figure 7. Stratigraphic sections D and E. Both sec­ tions represent eastern deposits. The locations of tra- verses are on Plate 1. 15

717m to base Llajas

490

Facies C

Facies E ?

480 Facies B

.·~ -.....c-.-~ 430 .. J

~ . . Facies D 470 . J

~\

•• • 0 ··· --~

Facies A ~\. . .

0 Q 0 • • •• 0 0 0 0 . " · ) 420 .... C) 0

0 :~. ·\ 0 . . . . . ·I 460 \.__\..... ' ... ·. ·. - ~ . ·-\

. · ~\. .

.-~-~\· ·. - .-.- ..

410

:JIII!!:... :J ...· ·_j meters 408m above base Simi Conglomerate

Figure 8. Detailed stratigraphic section of the upper tongue of Simi Conglomerate in Poison Oak Canyon. See Figure 7 for the location within section E. 16 tion from tabular-shaped clasts. These attitudes were then corrected for bedding dip using a computer program. The notation commonly used in the literature for Bouma sequences will be followed in this report (Fig. 9) and the facies schemes developed by Mutti and Ricci Lucchi (1972) for deep-water deposits will be applied where appropriate (Fig. 10). 17

Bouma (1962) Divisions Notation " " . . : " .

lnterturbidite Te

-. Upper parallel laminae Td

. · ~ -~ Ripples, wavy or Tc ~ convoluted laminae Plane parallel laminae Tb ...... 4 • • • • :

• • • •• •• • • 0 • . • . 0 • # •• •

••• • • : 0 Massive and/or graded Ta • • • • 0

•• 0 ......

Figure 9. Notation applied to parts of Bouma se- quences.

FACIES A coarse sandstone and conglomerate. Thick irregular locally amalgamated beds.

FACI&S B Medil.liYrfine to coarse sandstone. Thick lenticular beds with p:1rallel or undulating current laminae.

FACIES C Medium to fine sandstone with minor shale. Bouma se­ quences commom and beds laterally continuous.

FACIES D Fine to very fine sandstone, siltstone, and shale hav­ ing marked lateral continuity. Base-missing Bouma se­ quences corrrrnon.

FACIES E Similar to D except higher sand-shale ratios and thin­ ner irregular beds.

FACI&S F Chaotic deposits resulting from mass movanent down­ slope.

FACI&S G Shale and marl with indistinct or poorly developed even pa.rallel laminae.

Figure 10. Facies classificat ion for deep water clas­ tics after Mutti and Ricci Lucchi (1972). STRUCTURE

Geologic structure within the study area is simple, consisting of a major fault system, a major fold, and minor faults. Folding reflects the north-south compression indicated by several folds and faults throughout the central Ventura Basin (Bailey and Jahns, 1954), and all but one minor fault are left-separation faults.

FOLDS Except for the northernmost edge of the study area the rocks investigated in this report are part of an open syncline which is expressed topographically by the Simi

Valley. Rocks within the Simi Hills comprise the southern limb of this syncline and rocks northeast of Simi Valley form the northern limb. Computer analysis (Griffis and others, 1983) of bedding attitudes indicates the axis of the syncline plunges 28°, N60°W. The hinge trace is covered in the study area. At the northern edge of the study area, strata are folded into an anticline which also plunges northwestward (Pl. 1). This folding may reflect drag along the Simi fault, which is present just north of the study area.

FAULTS One large-displacement fault system is present within the study area. Due to its proximity to Burro Flats (Pl. 1),

18 19 ~1 '

it is herein informally named the Burro Flats fault. The fault trends generally N85°W and locally consists of several subparallel faults. Because the fault surface is not well exposed, the steepness of the fault cannot be accurately determined. General map patterns, however, suggest that in its present configuration it is steeply dipping. Displacement of the Simi Conglomerate indicates 2.4 km of left separation. The fault is difficult to map west of truncated Simi Conglomerate near Runkle Canyon (Pl. 1) because it juxtaposes similar, generally covered, mudrock of the Santa Susana formation. Evidence indicat­ ing that the fault extends beyond this point includes local­ ly exposed sheared and deformed zones within the mudrock and drag folding of strata in the proximity of the fault. Deformed zones were observed as far west as Bus Canyon

(Pl. 1) •

The Burro Flats fault displaces a fault of minor structural consequence but of great significance to strati­ graphic relationships. The southern portion of this fault is south of Burro Flats, and the northern portion is west of Runkle Canyon (Pl. 1). This fault is herein informally named the Runkle Canyon fault. Both portions of the fault trend generally Nl0°W, nearly perpendicular to bedding.

Poor exposures again preclude an accurate determination of the attitude of the fault plane, but map patterns suggest it also is steeply dipping. Evidence indicating that the northern and southern faults were once the same fault 20 include: 1) similar displacement of lithologic units, approximately 600 m of left separation, and 2) removal of separation across the Burro Flats fault, using the base of the Simi Conglomerate as a datum, nearly juxtaposes both portions of the Runkle Canyon fault (Pl. 1). Dramatic stratigraphic changes are present across the Runkle Canyon fault. As will be shown later, several depo­ sitional environments are represented only on the western side of the Runkle Canyon fault. Because of these changes, strata west of the Runkle Canyon fault will be referred to as the "western" portion of their respective formations and strata east of it the "eastern" portion of their respec­ tive formations. Minor faults include a left-separation fault south of Long Canyon and a right-separation fault near Meier Canyon (Pl. 1). Both these faults resulted in minor strike separa­ tion of less than 100 m. STRATIGRAPHY AND DEPOSITIONAL ENVIRONMENTS

The Simi Conglomerate, Las Virgenes Sandstone, and Santa Susana formation represent, as do many Tertiary

strata in California, a wide range of depositional envi­

ronments in a relatively complex intertonguing relation­ ship. Environments of deposition within the study area

range from nonmarine to deep marine.

WESTERN DEPOSITS

Western deposits are present only west of the Runkle Canyon fault. These rocks are best exposed in Bus Canyon (Pl. 1, Fig. 4) and are interpreted to be braided-river,

soil, meandering-stream, nonmarine to marine-transition,

shelf, slope, and deep-marine deposits.

SIMI CONGLOMERATE

Description The western Simi Conglomerate is present above the

Chatsworth Formation west of the Runkle Canyon fault (Pl. 1). Thickness ranges from 150m near Las Virgenes Canyon to 28 m near the head of Bus Canyon. At the extreme west­ ern end of the study area, the unit thins to a few meters. Generally the unit thins westward, but variations in thick­ ness were also observed near Bus Canyon. The rocks are

commonly well exposed in incised east-west trending ridges

(Fig. 11).

21 22

Figure 11. The western Simi Conglomerate and the Las Virgenes Sandstone near the head of Las Virgenes Canyon, looking west. The lower contact of the Simi Conglomerate is rarely well exposed. Where seen, it consists of a sharp scoured contact between sandstone and mudrock of the Chatsworth Formation and pebble and cobble conglomerate of the Simi Conglomerate (Fig. 12). The contact is considered an uncon- formity due to its erosional character and the abrupt change in depositional environment from deep-sea fan to nonmarine braided-river (see Interpretation). The upper contact of the Simi Conglomerate with the Las Virgenes Sandstone is generally sharp and conformable. It consists of a sharp lithologic change from cobble and pebble conglomerate to coarse sandstone. 23

Figure 12. The western Simi Conglomerate - Chats­ worth Formation contact near Montgomery Canyon. Erosional channel is approximately 1 m deep. Staff is 1.4 m long. The western Simi Conglomerate contains 75% to 100% conglomerate, 0% to 20% sandstone, and 0% to 5% mudrock. Conglomerate occurs as very poorly bedded sequences tens of meters in thickness (Fig. 13) and as thin lenses and stringers in sandstone bodies. Sandstone occurs in lenses up to 10 m in thickness, and mudrock consists of discontin- uous bodies reaching 9 m in thickness. Sandstone and mud- rock are most common near the base of the unit. Both sharp and gradational contacts are present between these rock types. Conglomerate characteristics are listed in Table 1. Most clasts are pebble to cobble size, well rounded, and 24

Figure 13. Thick, poorly bedded conglomerate in the western Simi Conglomerate. This exposure is on the north­ ern wall of Lone Oak Canyon. Sandstone lenses are 1 to 2 m in thickness. equant to tabular in shape. Quartz i te clasts are very resistant, are commonly banded and cross banded, and locally exhibit percussion marks. Volcanic clasts are also general- ly resistant. Metamorphic and granitic clasts are common- ly very weathered, in places so much so they resemble sand- stone matrix. Rare sedimentary clasts consist of poorly resistant mudrock intraclasts. Marked increase in the percentage of any one of these clast types can take place locally. Concavo-convex and long contacts were observed locally. Body and trace fossils were not found. Sedimen- tary structures within the conglomerate are limited to horizontal and inclined stratifica tion and channeling. 25

TABLE 1. CLAST CHARACTERISTICS OF THE WESTERN SIMI CONGLOMERATE

Localities (Plate 1) Bus Canyon Las Virgenes Canyon A B

Composition* of clasts (%} Granitic 40 32 36 Volcanic 24 24 15 Metamorphic (excluding quartzite) 10 27 28 Quartzite 22 16 20 Mudrock 4 1 1 Clast size (ern) Range 0.2-30 0.2-20 0.2-50 Average 5 5 6 Packing Clast-clast A A A Clast-matrix R R R Internal fabric Imbricate c c c Lacking c c c Stratification Horizontal R R R Inclined R R R Unstratified A A A Grading Normal R Inverse Nongraded A A A

*Granitic includes granite, granodiorite, quartz-monzonite, and quartz­ monzodiorite. Volcanic is predominantly porphyritic andesite. Meta­ morphic (excluding quartzite) is predominantly biotite gniess. Abbreviations: A-Abundant, C-Cornmon, R-Rare, --Not Observed. 26

Sandstone is present as matrix in the conglomerate and in discontinuous lenses up to 10 m in thickness (Fig.

13}. An average sandstone is poorly sorted, silty, medium to coarse grained, submature, and a micaceous arkose (see

Petrography and Fig. 28}. Color ranges from very pale orange

(Fig. 14). The claystone is unique to both typical Simi Conglomerate and Las Virgenes Sandstone deposits and is arbitrarily included with the Simi Conglomerate for des- criptive purposes. The sand component of the claystone consists of fine- to medium-grained quartz and comprises 10% to 20% of the rock. The claystone is very poorly in- durated and no sedimentary structures or fossils were seen.

Interpretation The western Simi Conglomerate is interpreted as rep­ resenting a braided-river deposit on an alluvial plain.

Figure 14. Sandy claystone at the upper contact of the western Simi Conglomerate near the head of Bus Canyon. Staff is 1.5 m long. 28

The thick conglomerate sequences represent stacked bar deposits of a proximal gravelly braided river, and the discontinuous sandstone lenses represent cutoff-channel fills or bar-edge sand wedges. Thicker sandstone units may represent development of bars composed primarily of sand or more distal sandy braided-river deposits. Very fine sandstone and variegated siltstone was deposited dur­ ing waning floods on top of bars or in overbank areas. The sandy claystone represents a Paleocene soil deposit. The above conclusions are based on similarities be­ tween the Simi strata and modern sediments whose environ­ ments and depositional models have been discussed by Smith (1974), Rust (1978), Miall (1978), Cant (1978) and Birke­

land (1974). A modern analog for deposition of the con­ glomeratic western Simi Conglomerate is found along the Kicking Horse River, British Columbia. Smith (1974) studied bar formation and sediment distribution in a 6.4- km-long, braided-outwash plain near the upper reaches of the river. Trenching revealed that the main deposit of the river is clast-supported, structureless to crudely horizontally-bedded gravel, which is commonly imbricate. Although a variety of bedforms are present and specific grain-size distributions result during initial formation of bars, subsequent erosion and deposition alter these characteristics. Other deposits present include coarse­ grained trough and planar cross-bedded sand, rippled sand and silt, and laminated silt. These characteristics are 29 all present in the western Simi Conglomerate.

The thicker and more laterally persistent sandstone deposits that occur in the Simi Conglomerate may represent more distal sand-dominated braided-river deposits. Cant

(1978) discussed various facies present in modern and ancient sandy braided-river deposits. Facies present in­ clude (1) poorly defined trough cross-bedded coarse sand­ stone, ( 2) well defined trough cross-bedded rnedi urn sand­ stone, (3) planar cross-bedded units, and (4} ripple­ bedded sandstone interbedded with variable amounts of mud­ rock. Mudrock intraclasts may be present in any of these facies. With the exception of planar cross-bedded units, these types of deposits are present in the sand-rich por­ tion of the western Simi Conglomerate.

Conglomerate deposits present in the Simi Conglomer­ ate are also very similar to those present in the Scott­ type depositional model described by Miall (1978) and the equivalent GII facies assemblage described by Rust (1978}.

Their models consist primarily of structureless to crudely­ bedded, clast-supported gravel, which is commonly imbricate, and subordinate amounts of planar and trough cross-bedded sand. Planar and trough cross-bedded gravel, rippled sand, and laminated to structureless silt and mud may also be present in minor amounts. The GII assemblage reflects facies present in the proximal reaches of the Donjek river,

Yukon, Canada, and is proposed by Rust (1978) as a general 30 model for proximal braided river and alluvial plain deposi­ tion. As will be discussed later (see Simi Conglomerate, Eastern Deposits), the structures discussed above are not in themselves environmentally unique to nonmarine depos­ its. The conformable stratigraphic position of the western Simi Conglomerate below soil and meandering stream depos­ its (see below), however, strongly indicates a nonmarine origin for the western Simi Conglomerate.

The quartz-bearing claystone which is locally present at the upper contact of the Simi Conglomerate is inter­ preted as representing an ancient soil. Modern soils are subdivided into horizons based on various characteristics. The B horizon is considered by Birkeland (197 4) as "the most important horizon for recognizing buried soils". This horizon (specifically the oxic B horizon) is highly weathered and consists of clay and quartz grains (Birke­ land, 1974). Other silicate minerals have been altered. The quartz-bearing claystone, locally present at the upper contact of the western Simi Conglomerate, has all the char­ acteristics of an oxic B horizon.

LAS VIRGENES SANDSTONE

Description

The Las Virgenes Sandstone is present only west of the Runkle Canyon fault. Measured thickness ranges from 100 to 195 m (Figs. 4 and 6), although the formation 31 thins considerably to the west. Generally the unit is tabular shaped. Exposure of the rocks on brushy slopes ranges from good to poor (Fig. 11).

The lower contact of the Las Virgenes Sandstone with the Simi Conglomerate, as discussed previously, is general­ ly sharp and conformable and consists of a distinct grain size change. The upper contact with the Santa Susana forma­ tion is locally sharp, but commonly gradational. West of Oak Canyon (Pl. 1) the contact is difficult to map due to its gradational character and to cover. Where sharp, the contact consists of a distinct lithologic break from medium and coarse sandstone to mudrock of the Santa Susana. Where gradational, the contact is placed at a fossiliferous pebbly sandstone horizon. Based on map locations, these contacts follow Nelson's (1925) original intent for the contacts of the Las Virgenes Sandstone.

At Bus Canyon, the formation can be subdivided into a somewhat arbitrary lower and upper unit. The lower unit is 100 m in thickness and consists of approximately 7 5% sandstone, 20% siltstone, and 5% granule and pebble con­ glomerate. Sandstone and conglomerate are present in fining­ upward sequences which average 3 m in thickness. Silt­ stone and very fine sandstone intervals up to 20 m, but more commonly 5 m in thickness, are present between the fining-upward sequences.

A typical fining-upward sequence has a sharp basal contact overlain by pebble conglomerate and poorly-sorted 32 coarse sandstone that is 0.5 to 1.5 m in thickness. These lithologies grade upward through moderately sorted medium sandstone 1 to 2 m in thickness to fine sandstone 0.5 to 1 m in thickness. Compositionally the sandstone is sub- mature micaceous arkose with biotite and chlorite content ranging up to 10%. Grains are subrounded to angular. Color ranges from very pale orange (lOYR 8/2) to grayish orange

Figure 15. Cross laminations in the Las Virgenes Sandstone near Bus Canyon. The black layers are concen­ trations of biotite. The gravel is alluvium. Pencil is 14 em long. 33 faces are commonly defined by high concentrations of bio­ tite. Locally the sequences are stacked and reach 15 rn in thickness.

The uppermost medium and coarse sandstone package differs from the typical sequence discussed. Although fining-upward intervals which locally exhibit the described sedimentary structures are present, bedding and cross bedding commonly are absent. Burrows, external molds of marine bivalves, and carbonized wood fragments are common locally. Some strata are well sorted.

The sandstone packages grade upward to siltstone and very fine sandstone sequences. These rocks are highly fractured and no sedimentary structures were observed. Commonly the rocks are medium dark gray (N4) to olive gray (5Y 4/1). Local variegated sections are present. Colors in these intervals include dusky red (5R 3/4), grayish olive

The individual lithologic elements present in the Bus

Canyon section are not always present at other localities, nor are they present in the same distribution or thickness. Near Las Virgenes Canyon (Fig. 6), the sandy claystone at the basal contact is absent, siltstone occurs in much thin­ ner sequences, and distinct fining-upward sequences are not as apparent. The fossiliferous pebbly sandstone at the upper contact is also missing. The lower third of the unit consists of medium to coarse sandstone. Poorly de­ veloped trough cross bedding is common. The middle third of the unit consists of interbedded sandstone and mudrock.

Ripple-laminated sandstone is common. Some beds reach 0.5 m in thickness but most average 0.2 m. The upper third of the unit resembles the lower third and consists of coarse and medium sandstone which is crudely trough cross bedded.

Poorly developed fining-upward sequences are also present.

The uppermost 5 m of the formation consists of coarse sand­ stone which is locally pebbly and rarely burrowed, but does not contain macrofossils. It resembles the uppermost sandstone of the lower unit in Bus Canyon.

Interpretation

The Las Virgenes Sandstone marks a transition from nonmarine to marine deposits where fluvial and marine pro- 35 cesses interacted to form a complex intertonguing of deposits. The lower unit at Bus Canyon is interpreted as a meandering-stream deposit. The fining-upward sequences are interpreted as channel-lag and point-bar deposits and the interbedded fine sandstone and siltstone as floodplain deposits. The medium and coarse sandstone package at the top of the unit was deposited by fluvial processes but altered by marine interaction. Wave activity may have led to better sorted horizons, and burrowing destroyed bedding character­ istics locally. Reineck and Singh (1980) suggest fluvial and marine deposits in close stratigraphic position indi­ cate deposition in a coastal plain - delta association.

The above interpretation is based on comparison of the Bus Canyon strata with a fluvial model discussed by Allen (1970). Allen (1970) proposed a quantitative model for fluviatile sedimentation following the study of several cyclothems within the Old Red Sandstone in Britain and North America. A fluvial origin for the rocks was docu­ mented (Allen, 1970) by comparison with several modern analogs. A composite cyclothem consists of six major facies arranged in a fining-upward cycle. Five of these facies are present in fining-upward sequences in the lower unit at Bus Canyon. The deposits common to both the rocks and the model include: 1) conglomerate, commonly with an ero­ sional base, 2) cross-bedded sandstone, mainly large-scale tabular and trough cross bedding, 3) flat-bedded sand- 36 stone, 4) cross-laminated sandstone, and 5) siltstone.

The conglomerate is interpreted as representing channel lag, the sandstone facies as representing point-bar depo­ sits, and the siltstone as representing levee, overbank, and floodplain deposits (Allen, 1970; Collinson, 1978; Reineck and Singh, 1980). The thickness of a fining­ upward cycle may represent channel depth (Reineck and Singh, 1980), suggesting channels in the Bus Canyon section aver­ aged 3 m in depth.

The upper unit of the Las Virgenes Sandstone at Bus

Canyon is interpreted as being a nearshore-marine deposit along a low-energy coast based on the stratigraphic posi­ tion of the unit between nonmarine and transition zone to offshore deposits (see Santa Susana formation). Both shore­ face and foreshore deposits probably are represented by this unit. In comparison to intermediate and high-energy analogs (Howard and Reineck, 1972, 1981), the only sedimento­ logic characteristic indicating a shoreface/foreshore inter­ pretation is the pebble and marine-fossil hash horizons, which represent storm lag (Kumar and Sanders, 1976). Sedi­ mentary structures, including cross-bedding and ripple lamination, which are abundant in modern shoreface and foreshore deposits (Kumar and Sanders, 1976; Davis, 1978; Howard and Reineck, 1972, 1981) are not seen at Bus Canyon.

The lack of these structures is probably the result of bioturbation. A significant number of burrowing organisms are reported in nearshore environments, but the result of 37 their activity is outweighed by constant wave and current effects (Howard and Reineck, 1981}. However, in a low-energy environment, biogenic activity may overcome any reorgani­ zation of sediment (Elliot, 1978}. Because sedimentary structures are rare in the marine portion of the Las

Virgenes Sandstone and bioturbation is common, a low-energy environment is postulated.

The section at Las Virgenes Canyon is interpreted as representing deposition by a sandy braided river. The lower and upper third of the unit reflects major channel deposition, whereas the middle third of the unit reflects minor channel and overbank deposition. The burrows

(Ophiomorpha?} near the top of the unit are the first evi- dence of the transgressing sea. This interpretation is based on comparison of the Simi strata with a facies model developed by Cant <1978) following a study of the South

Saskatchewan River and the Devonian Battery Point Forma­ tion.

As discussed earlier, facies that develop in the South

Saskatchewan River include (1} poorly defined trough cross­ bedded coarse sand, ( 2} well defined trough cross-bedded medium sand, (3} planar cross-bedded units, and (4) ripple­ laminated sandstone with variable amounts of mud (Cant, 1978}. Large sinuous-crested dunes that floor major chan­ nels deposit coarse-grained trough cross-bedded sand, and small dunes in minor channels deposit better defined trough cross beds (Cant, 1978}. Planar cross beds result from 38

deposition of sand waves in channel margins and on sand

flats. Interbedded rippled sand and mud are deposited at

the tops of sand flats and in overbank areas (Cant, 1978).

With the exception of well developed planar cross bedding, the Las Virgenes Sandstone is very similar to deposits of the South Saskatchewan River. Braided- and meandering-stream deposits can be very similar, and in some cases nearly identical (Rust, 1978). The two represent artificial boundaries in a continuum of river deposits (Collinson, 1978). Cant (1978) suggests one of the preservable differences between the two is a thicker floodplain deposit in meandering systems. The pre­ sence of thick siltstone and fine sandstone sequences in the Bus Canyon deposits is the major difference between these and the Las Virgenes Canyon strata. Because of the gradational nature of meandering and braided streams, it is perhaps not surprising to find them in close proximity

in the Las Virgenes Sandstone.

SANTA SUSANA FORMATION Description The western Santa Susana formation overlies the Las Virgenes Sandstone west of the Runkle Canyon fault. The thickness of the formation in Bus Canyon is 1,030 m (Fig.

4). The formation may thin to the west based on map con­ tacts from Squires (1983) • Property access was denied west of Montgomery Canyon so the formation could not be 39 studied in this area. Exposure of strata is generally good in canyon bottoms and poor on slopes and hills.

The lower contact with the Las Virgenes Sandstone, as described above, is commonly gradational, although locally it can be sharp. The upper contact with the Llajas Forma­ tion is a parallel unconformity (Squires, 1981, 1983, 1984). It consists of a distinct lithologic break through­ out most of the study area. Pebble and cobble conglomer­ ate of the Llajas overlie sandstone and siltstone of the Santa Susana. Just west of the Runkle Canyon fault, the contact is less distinct because the basal Llajas is most­ ly sandstone and contains very little conglomerate.

The western Santa Susana can be subdivided into a lower and upper unit throughout the study area. The con­ tact between these units is marked by a lithologic change from densely bioturbated, fossiliferous, very fine and fine sandstone to poorly fossiliferous, interbedded mud- rock and sandstone. The contact is distinct where not covered and is mappable throughout the western study area

(Pl. 1) ~ The contact is present at 610 m on Section A (Fig. 4). The lower unit is 390 m in thickness in Bus Canyon and is tabular shaped. It consists of 80% to 90% very fine and fine sandstone and 10% to 20% siltstone. Silt­ stone generally is confined to the lower 100 m of the unit. Contacts between these lithologies are gradational.

The sandstone is very fine to fine calcitic, subma- ~~ -- ·------

40 ture to mature arkose. Color ranges from light gray (N7) to yellowish gray (5Y 7/2). It is typically bioturbated, so bedding character is tics commonly are destroyed (Fig. 16). Ichnogenera include Arenicolites and vertical Ophio- rnorpha. Pockets and intervals of parallel laminae are also present. Macrofossils, including Turri tell a and Veneri- cardia, are present both as well preserved complete indi- viduals and in concentrated pockets where the fossils are fragmental and abraded. Siltstone is poorly fossiliferous, pervasively frac- tured, and medium dark gray (N6). Sedimentary structures including bedding were not observed. Fossiliferous concre- -

Figure 16. Bioturbated fine sandstone in the lower western Santa Susana in Bus Canyon. Pencil is 14 ern long. 41

tionary sandstone beds and pebbly sandstone beds contain­

ing shell hash are present locally. These beds are up to

1 m in thickness.

The thickness of the upper unit in Bus Canyon is 640

m. The unit appears to be tabular in shape although thin­

ning west of Montgomery Canyon may take place, leading to a wedge shape. The unit consists of 70% mudrock, 20% sand-

stone, and 10% pebble and cobble conglomerate. Mudrock and subordinate sandstone are interbedded throughout the

unit and conglomerate, with associated sandstone and mud­

rock, is limited to two horizons (Fig. 4). Sandstone and mudrock associated with conglomerate differ from the major­

ity of these lithologies and will be discussed in conjunc­

tion with the conglomerate. Mudrock includes siltstone and mudstone which range

in color from medium gray (NS) to light gray CN7). The

rocks are pervasively fractured, commonly conchoidally,

and do not seem laminated. Sandstone, generally fine to medium calcitic, imma­

ture to submature arkose, is present in beds averaging 20 em in thickness. These beds are commonly concretionary

and may contain partial Bouma sequences including Ted and

Tbcd. Contacts with mudrock vary from sharp to gradational

and are nonparallel and undulatory. At the top of the unit, near Bus Canyon, macrofossils (including Venericardia)

are present in 2 to 3 m of sandstone. 42

Characteristics of the conglomerate are listed in Table 2. With the exception of composition, this conglomer­

ate is very similar to the Simi Conglomerate. Clasts are

pebble to cobble size, tabular to equant, and well rounded.

The percentage of volcanic clasts is significantly larger, from an average of 21% in the Simi Conglomerate to 44% in the Santa Susana, and quartzite clasts are much less abundant. Granitic clasts tend to be more mafic as well.

Both lenses and laterally continuous beds are present. Sedimentary structures include channeling and rare normal

grading. Sandstone associated with conglomerate is present as matrix, in discontinuous lenses (Fig. 17), and over­ lying the first horizon of conglomerate. Sedimentary struc­

tures within the lenses of sandstone include normal grading and trough cross bedding. The sandstone overlying the stratigraphically lowest conglomerate horizon, at 1000 m

on Figure 6, contains contorted mudrock layers and rare

pebbles and cobbles supported by sandstone (Fig. 18). At the top of this sequence, the sandstone is locally graded

and laminated. Vertical burrows are also present. Siltstone overlying both conglomerate horizons is

locally laminated and ranges in color from medium gray

(N5) to light gray (N7). Although macrofossils are rare in the upper unit, a rich microfauna is reported by Finch <1980). He studied

the fauna present between the two conglomerate horizons in Bus Canyon (Fig. 4) and interpreted paleodepth to range 43

TABLE 2. CLAST CHARACTERISTICS OF CONGLOMERATE WITHIN THE WESTERN SANTA SUSANA FORMATION

Locality (Plate 1) Bus Canyon

Composition* of clasts (%) Granitic 30 Volcanic 44 Metamorphic (excluding quartzite) 20 Quartzite 4 Mudrock 2 Clast size (an) Range 0.2-30 Average 5 Packing Clast-clast A Clast-matrix R Internal fabric Imbricate c Lacking c Stratification Horizontal R Inclined Unstratified A Grading Normal R Inverse Nongraded A

*Granitic includes granite, granodiorite, quartz-monzonite, and quartz­ monzodiorite. Volcanic is predominantly porphyritic andesite. Meta­ morphic

Figure 17. Conglomerate and sandstone (at 1160 m on section A) present in the western Santa Susana formation in Bus Canyon. Outcrop is approximately 15 m thick.

Figure 18. Contorted mudrock in the western Santa Susana formation in Bus Canyon. See Figure 7 for the strati­ graphic position of these deposits. Hammer is 28 em long. 45 from upper continental slope at the base of the section to outer continental shelf upsection. Filewicz and Heitman (personal communication, 1983) suggest this fauna may indi­ cate deposition took place at bathyal depths.

Interpretation The lower unit of the western Santa Susana formation is interpreted as representing transition zone and off­ shore to shelf sedimentation. Modern deposits in the transition zone consist of bioturbated horizons alternat­ ing with parallel laminated horizons (Kumar and Sanders, 1976; Howard and Reineck, 1981). Offshore and shelf de­ posits are densely bioturbated with only remnant parallel laminae present (Reineck and Singh, 1980; Howard and Reineck, 1981). Shells and shell fragments occur in iso­ lated pods and lenses and burrows are commonly filled with sediment (Howard and Reineck, 1981). These characteristics are present throughout most of the lower unit except in siltstone horizons which are pervasively fractured. Gold­ ring and Bridges (1973) and Squires (1981, 1983, 1984) interpret ancient deposits that are similar to the lower unit of the western Santa Susana formation as transition zone and shelf deposits also. Stratigraphic position, paleobathymetric interpreta­ tion, and assemblages of facies indicate the upper unit of the western Santa Susana represents deposition in a slope setting. The interbedded mudrock and sandstone of the 46 upper unit reflects overbank deposition in association with submarine-channel deposits. Some of the mudrock prob­ ably also resulted from hemipelagic deposition. These conclusions are based on similarities of this portion of the Santa Susana to Facies E and G of Mutti and Ricci Lucchi <1972) (Fig. 10). Facies E is restricted to depo­ sition in middle- ~o inner-fan and slope environments, and facies G is common in slope environments (Mutti and Ricci

Lucchi, 1972~ Walker and Mutti, 1973).

The conglomerate present in the upper unit represents

Facies A simply because of its coarse nature. Walker and Mutti <1973) subdivided Facies A into subtypes based on grain size and the presence or absence of sedimentary structure or fabric. The disorganized subtype contains no structure or fabric and the organized subtype does. Based on these criteria, both disorganized and organized conglom­ erate are present in Bus Canyon. Walker (1975, 1978) later refined the organized conglomerate subtype by further dividing it into specific models. Graded bedding, either normal or inverse, is present in all models proposed for organized conglomerate. In much of the conglomerate in Bus Canyon, however, specific graded units could not be identified, yet imbrication is common. Walker's (197 5, 1978) refined classification, therefore, cannot be applied.

Kelling and Holroyd (1978) proposed another classifi­ cation for deep-sea conglomerate. Variables include organi­ zation, in the same sense as Walker's (1975, 1978) model, 47 and lateral continuity of individual conglomerate beds.

The latter characteristic differentiates channel and non­ channeled types, both of which are present in the western

Santa Susana. The laterally persistent, nonchannelized type is more common, however. These subtypes of Facies A have been interpreted as representing specific environ­ ments, such as fan apex or inner fan, but because no single subtype is dominant these interpretations are not applied to the western Santa Susana conglomerate deposits.

The contorted mudrock and pebbly sandstone represent

Facies F (Fig. 10). The rare pebbles and cobbles in the sandstone suggest rapid deposition, perhaps due to a change in gradient.

The facies represented in the upper unit of the west­ ern Santa Susana, specifically A, E, F, and G, occur in the slope association discussed by Mutti and Ricci Lucchi

(1972, as translated by Nilsen, 1978). However, the rela­ tive abundance of the facies represented varies consider­ ably. Differences between the association and the rocks include: 1) Facies E is more abundant in the Santa Susana relative to Facies G, 2) Facies F constitutes only a small part of the western Santa Susana and 3) although lenticu­ lar beds occur within Facies A of the western Santa Susana, overall unit geometry of Facies A is sheetlike. The causes of these differences are unknown. They may reflect differ­ ent shelf-slope-basin relationships, including paleoslope and sediment supply, or tectonic activity and regime. 48

The uppermost few meters of this unit, just below the

Llajas Formation, consists of siltstone or sandstone with rare macrofossils, including Venericardia. These beds may reflect uplift prior to deposition of the nonmarine basal Llajas conglomerate.

EASTERN DEPOSITS

Eastern deposits are present east of the Runkle Canyon fault (Pl. 1). Sections were measured in these rocks near Runkle Canyon, east of Meier Canyon, and in Poison Oak

Canyon (Pl. 1, Figs. 4 and 7). Several subenvironments related to slope and deep-sea fan deposition are represent­ ed by eastern deposits.

SIMI CONGLOMERATE

Description The eastern Simi Conglomerate overlies the Chatsworth Formation east of the Runkle Canyon fault. The thickness of the eastern Simi Conglomerate is extremely variable

(Fig. 19). For example, east of Meier Canyon it is 440 m in thickness, whereas at the head of Meier Canyon it is less than 30 m in thickness. The formation exhibits a complex shape due to its intertonguing relationship with the overlying Santa Susana formation (Fig. 19). The rocks are well exposed on south- and east-facing cliffs and slopes (Fig. 20).

The lower contact commonly is poorly exposed. General- ,c.. 1,0

Figure 19. Distribution of deposits throughout the study area based on measured sections and map contacts. This figure represents outcrop patterns after removal of folding. Large-scale incisement of the Chatsworth Formation was not documented in the field. + . ,:;., ...... _.-~·'·· -~~~~BIJI!I!iiiliiii11!1I~jliiW'iii~11&i~fa~ltili!j~!~~~lliltifii~ii~t~~l~t~ti~i~;

·····--·········-····-·················--·------···-·-- E

··-:zue • ';N SECTION LOCALITY + t t arrows Indicate north o.;v.·. ;&:·Lr._.. --:· Tt f. .:.aSf"''lMtC?'.-~ .• :!i:~!'.."":Ji•• Sect/of!~~·.-;r:::'!.·Plr-•~•u . ·lllllf~--~~- ;,;.~~!:'!:b~:•:n.t!:J¥.1

i- c -0 c>­

l11 0 51

Eastern Simi Conglomerate

Chatsworth Formation

Figure 20. View of the eastern Simi Conglomerate as exposed on the north flank of Poison Oak Canyon. Mudrock interbeds to the south and east indicate deposition took place at bathyal depths. Turbidites of the Chatsworth Formation are exposed at the base of the section. Expo­ sure is approximately 170 m from base to top. ly it is defined by a distinct lithologic change from sand- stone and mudstone of the Chatsworth Formation to pebble and cobble conglomerate of the Simi Conglomerate. Incise- ment of channels, with 1 to 2 m of relief, is present local- ly, which suggests the contact is erosional. No angular dis- 52 cordance between the Chatsworth Formation and Simi Conglomer­ ate was documented. A change in provenance (see Proven­ ance) and source-area sediment characteristics suggest the erosion surface is an unconformity. A hiatus between the unfossiliferous Simi Conglomerate and Chatsworth Forma­ tion cannot at this time be proven unequivocably, however. Lower contact relationships may be further compl i­ cated southeast of Meier Canyon. A tongue of sandstone within the Simi Conglomerate which extends eastward from the northern portion of the Runkle Canyon fault (Pl. 1) contains partial Bouma sequences (Parker, 1983) (Figs. 4 and 5). At the head of Meier Canyon the conglomerate tongue below this sandstone tongue pinches out (Pl. 1,

Fig. 19). If the sandstone tongue continues eastward from the point where the lower conglomerate pinches out, then sandstone with partial Bouma sequences associated with deposition of the eastern Simi Conglomerate would overlie sandstone deposited in the sand-rich deep-sea fan complex (Link, 1981) of the Chatsworth Formation. This is apparent­ ly the case. Southeast of Meier Canyon, a mappable contact strati­ graphically below the lithologically defined contact be­ tween the Chatsworth Formation and Simi Conglomerate local­ ly contains granitic boulders up to 1 m in diameter (Pl.

1). Boulders this size are not seen elsewhere in the Chats­ worth Formation (Colburn, personal communication, 1983), but they are present at the base of the Simi Conglomerate 53 east and west of the area in question. This "boulder bed" extends eastward along strike from the point where the lower conglomerate tongue pinches out to a point where the

Simi Conglomerate thickens appreciably (Pl. 1, Fig. 19).

It is possible that the boulders represent lag resulting from scouring of the Chatsworth surface prior to or concur­ rent with deposition of the eastern Simi Conglomerate, and the sandstone present above this bed is the eastward exten- sion of the sandstone tongue within the Simi Conglomerate.

The sandstone above the "boulder bed" should be consi- dered a part of the Chatsworth Formation because it is indistinguishable, within the limits of field observations, from sandstone below the "boulder bed". If the "boulder bed" does mark the contact between sandstone associated with the Simi Conglomerate and sandstone of the Chatsworth

Formation, and an unconformity is present between the two

' formations elsewhere, then the Chatsworth Formation would contain an intraformational unconformity and would, in part, be Paleocene in age. This would require that the

Chatsworth-Simi Conglomerate contact be conformable above the "boulder bed". Micropaleontologic study in this area would be of great help in confirming the nature of the contact.

The upper contact of the Simi Conglomerate with the

Santa Susana formation is sharp except in the vicinity of

Poison Oak Canyon. Here the upper contacts of two tongues

(Pl. 1, Figs. 9 and 19) of Simi' Conglomerate are grada- 54 tional. The tongues grade upward from conglomerate to sandstone and finally to interbedded sandstone and mud­ rock. Somewhat arbitrary contacts were chosen within the sandstone sequences that would hopefully be most useful in defining both lithologic and environmental boundaries and would also produce viable cartographic units. Where the upper contact is sharp, it consists of an abrupt litho­ logic change from cobble conglomerate to mudrock and fine sandstone. The eastern Simi Conglomerate can be subdivided into three cartographic units. The conglomerate and sandstone tongues at the head of Runkle Canyon (Pl. 1, Fig. 19), which were discussed previously, comprise two of the units and the rest of the formation comprises the third. The lower conglomerate tongue in Runkle Canyon is lithological­ ly similar to the upper conglomerate, therefore the two will be treated as one with regard to description and in­ terpretation. The sandstone tongue at Runkle Canyon (Pl. 1, Fig. 19) is 60 m in thickness in Runkle Canyon and consists of 85% sandstone, 10% mudrock, and 5% granule and pebble con­ glomerate (Fig. 5). Mudrock and conglomerate are restrict­ ed to the upper half of the unit. The lower half of the tongue consists of plane-parallel laminated, coarse to medium sandstone which is interbedded with bioturbated fine sandstone (Fig. 21). Normal grading is common in the coarser fraction. The upper half of the tongue consists 55

Figure 21. Densely bioturbated fine sandstone within the eastern Simi Conglomerate in Runkle Canyon. See Figure 7 for the stratigraphic position of these strata. Pencil is 14 em long. of several stacked partial Bouma sequences (Fig. 22). Ta consists of a scoured basal contact, commonly injected by mudrock flame structures, overlain by pebble to granule conglomerate which grades upward to coarse sandstone. Tb is medium to coarse sandstone that is plane-parallel lamin- ated, and Tc is fine to medium ripple- and convolute- laminated sandstone. Td is plane-parallel laminated fine sandstone and siltstone. Tab divisions locally contain abundant mudrock rip-up clasts. At the top of the tongue is 10 m of interbedded very fine sandstone and mudrock. Gypsum commonly fills fractures in this interval. 56

Ta

Tb & Tc

Tb

Ta

Tb

Ta

Td-­ Tc-­ Tb--

Ta--

Figure 22. Partial Bouma sequences in the eastern Simi Conglomerate in Runkle Canyon. See Figure 7 for the stratigraphic position of these strata. Hammer is 28. ern long. With the exception of the described sandstone tongue, the eastern Simi Conglomerate generally consists of 60% to 90% conglomerate, 10% to 40% sandstone, and up to 5% mud- rock. Conglomerate is present in very poorly bedded se- quences tens of meters in thickness and as lenses within sandstone bodies. Sandstone is present in discontinuous 57 lenses throughout the formation (Fig. 23 ) and mudrock is present in local tabular units. Essentially, the conglomerate is very similar to the western conglomerate. Eastern conglomerate is generally poorly sorted and clasts are well rounded and pebble to cobble size. Table 3 summarizes conglomerate character- istics. A major difference between the western and east- ern conglomerate is the presence of fossiliferous mudrock clasts in the upper eastern Simi Conglomerate tongue in Poison Oak Canyon. Macrofossils include Turritella peninsularis which is late Paleocene in age (Saul, 1983). Also Zinsmeister (1983 ) reports the presence of macro-

Figure 23. Lenses of conglomerate and sandstone in the eastern Simi Conglomerate near the head of Meier Canyon. Staff is 1.5 rn long. 58

TABLE 3. CLAST CHARACTERISTICS OF THE EASTERN SIMI CONGLOMERATE.

Localities (Plate 1) Runkle Brandeis Poison Oak canyon A B C D

Comp:>sition* of clasts (%) Granitic 32 36 32 36 28 36 Volcanic 8 4 20 20 20 52 Metamorphic 36 28 20 16 24 4 (excluding quartzite)

Quartzite 16 24 20 20 12 4 Hudrock 8 8 8 8 16 4 Clast size (em)

Range 0.2-300 0.2-40 0~2- 0.2- 0.2- 0.2- 20 70 30 50

Average 5 5 4 5 4 5 Packing Clast-clast A A A A A A Clast-matrix R R R R c Internal fabric Imbricate c c R c c c Lacking c c c c R c Stratification Horizontal R R c R R c Inclined R R R Unstr:atified A A A A A A Grading Normal R R c R R Inverse R Nongraded A A A A A A

*Granitic includes granite, granodiorite, quartz-monzonite, and quartz­ monzodiorite. Volcanic is predominantly porphyritic andesite. Meta­ morphic (excluding quartzite) is predominantly biotite gniess. Abbreviations: A-Abqndant, C-common, R-Ra.re, --Not Observed. 59 fossils in the uppermost Simi Conglomerate near Meier Canyon. Sedimentary structures include scour and fill and horizontal stratification. Imbrication is common. Normal­ ly graded sequences are present locally. Sandstone occurs both as discrete lenses and as ma­ trix for conglomerate. Typically, the sandstone is a poor­ ly sorted, medium to coarse, submature, micaceous arkose. Limonite and hematite staining is common. Concave-convex and long contacts between grains are also common. Sedimen­ tary structures include trough cross bedding, fining­ upward sequences, horizontal, convolute, and ripple lamina­ tion, and scour and fill. Pebble lenses 2 to 3 em in thick­ ness are common. Horizontal Ophiomorpha, Thalassinoides, and carbonized wood are present locally. Mudrock includes siltstone and mudstone, and occurrence is limited to local tabular-shaped units and to rip-up clasts in conglomerate and sandstone units. Typically the mudrock is pervasively fractured and light gray (N7). East of the study area, near the head of Blind Canyon, a siltstone interval con­ tains microfossils indicative of bathyal depths (Colburn, personal communication, 1983).

Interpretation Similarities to facies associations discussed by Mutti and Ricci Lucchi (1972, as translated by Nilsen, 1978) and the microfossil paleobathymetric evidence discussed above indicate the eastern Simi Conglomerate was deposited in 60

submarine canyon or channel and inner-fan environments. The sandstone tongue near Runkle Canyon contains excellent and nearly complete Bouma sequences (Fig. 22) which indi­ cate deposition by turbidity currents (Bouma, 1962). The strata in this tongue represent Facies C (Fig. 5). For­ aminifers in mudrock beds in Poison Oak Canyon indicate deposition took place at bathyal depths, however, the bur­ rowed sandstone near the base of the tongue is remarkably similar to bioturbated sandstone present in "shelf" de­ posits of the lower western Santa Susana (see Figs. 16 and 21) • Perhaps the westernmost eastern Simi Conglomerate was deposited near the head of a submarine canyon at shelf depths. The conglomerate portion of the eastern Simi Conglomer­ ate represents Facies A (Fig. 10) because of its coarse nature. Portions of the unit can be described by using Walker and Mutti's (1973) and/or Kelling and Holroyd's (1978) models. Disorganized, organized, channeled, and nonchanneled conglomerate types are all present to some extent. However, much of the unit is perhaps best de­ scribed by using the proximal braided-river models of Miall (1978) and Rust (1978). The lithofacies common to both the models and most of the Simi Conglomerate is struc­ tureless to crudely developed, parallel-bedded conglomerate, the clasts of which are commonly imbricated. The "fluvial" appearance of the conglomerate has understandably led workers to interpret the eastern Simi Conglomerate as a braided- 61 river or alluvial-fan deposit (Sage, 19737 Zinsmeister,

1974). Some of the similarities between the nonmarine and marine deposits of the Simi Conglomerate are shown in

Figure 24.

The mechanism resulting in deposition of proximal braided rivers (i.e., traction currents) (Miall, 1978), differs from the debris-flow and grain-flow mechanisms suggested for emplacement of marine conglomerate (Walker, 19747 Middleton and Hampton, 19767 Clifton, 1981). It is interpreted that tractive processes may have significantly altered the conglomerate after initial deposition, as Middleton and Hampton (1976) suggest can occur.

Winn and Dott (1977) describe deep-water conglomerate deposits in the Upper Cretaceous Cerro Torro Formation of southern Chile that also do not fit established models.

This conglomerate contains many characteristics attributed to traction processes including large-scale dunes and well sorted beds that contain imbricated clasts. Winn and Dott

<1977) suggest this conglomerate was deposited by debris flows or other turbulent flows and later reworked by low­ density turbidity currents. Throughout most of the eastern portion of the study area, and below the two tongues of conglomerate near Poison Oak Canyon, the Simi Conglomerate is associated with only strata that are interpreted as representing Facies G and subordinate E of the overlying Santa Susana formation. Except for the lack of chaotic-slump deposits (i.e., 62

Figure 24. Comparison of western (A) and eastern (B) Simi Conglomerate. The western Simi Conglomerate, as ex­ posed on the north wall of Lone Oak Canyon, was deposited in a gravelley braided river. The eastern Simi Conglomer­ ate, as seen near the head of Meier Canyon, was deposited in a submarine canyon. Sandstone lenses in A are 0. 5 to 1.5 m thick. Staff in B is 1.5 m long. 63

Facies F) this association of facies is similar to that

ascribed to slope deposits by Mutti and Ricci Lucchi {1972, translated by Nilsen, 1978). The Simi Conglomerate repre­ sents submarine-canyon fill within this environment.

In the northeastern portion of the study area the upper two tongues of Simi Conglomerate grade upward into

sandstone, followed by interbedded sandstone and mudrock (Fig. 25). This upward transition reflects a change from Facies A deposits to B, then to c. The Santa Susana for­ mation which encloses these two tongues of the Simi Con­

glomerate consists of deposits which represent facies E and G. This assemblage of facies (A, B, and C of the Simi

Conglomerate, enclosed by E and G of the Santa Susana for­ mation) indicates deposition in an inner-fan environment (Mutti and Ricci Lucchi, 1972, as translated by Nilsen, 1978; Walker and Mutti, 1973). Heitman (1983) reports

bathyal foraminiferal assemblages from this section.

SANTA SUSANA FORMATION

Description

The eastern Santa Susana formation overlies the Simi Conglomerate east of the Runkle Canyon fault. Near Runkle

Canyon the formation is 925 m in thickness and in Poison Oak Canyon it is 933 m in thickness. This thickness ex­ cludes 117 m of strata assigned to the two tongues of Simi

Conglomerate present in Poison Oak Canyon. Thickness of

the complete sequence, including the two tongues, is 1050 Figure 25. This series of photographs records the upward transition from Facies A through Facies G in the upper tongue of the Simi Conglomerate and the overlying Santa Susana formation in Poison Oak Canyon. See Figure 10 for the stratigraphic position of these strata. Staff is 1.5 m long, hammer is 28 em long, and coin is 2.4 em in diameter. The exposure in B is approximately 20 m thick. 65 Facies C r1f

.. Facies A & B

Bouma sequence In Facies C ...

• 68

Figure 26. Lowermost Facies A conglomerate and sand­ stone near the mouth of Meier Canyon. This unit pinches out rapidly to the west (Pl. 1). The outcrop is approx­ imately 10 m thick. West of the section, they grade into interbedded mudrock and sandstone intervals. A typical tongue consists of fine to medium, calcitic, submature arkose. Macrofossils, present in concentrated layers within concretionary sand- stone, are abundant (Fig. 27). Both incomplete abraded specimens and complete well preserved specimens are pre- sent.

Interpretation Most of the eastern Santa Susana formation consists of mudrock which is locally interbedded with sandstone 69

TABLE 4. CLAST CHARACTERISTICS OF CONGLOMERATE WITHIN THE EASTERN SANTA SUSANA FORMATION

Localities {Plate 1) Brandeis A B

COmposition* of clasts {%) Granitic 36 36 Volcanic 32 12 Metamoq:hic {excluding quartzite) 24 20 Quartzite 4 16 Mudrock 4 16 Clast size (an) Range 0.2-20 0.2-50 Average 4 4 Packing Clast-clast A A Clast-matrix c c Internal fabric Imbricate c c Lacking c c Stratification Horizontal R R Inclined R R Unstratified c c Grading Normal c R Inverse Nongraded A A

*Granitic includes granite, granodiorite, quartz-roonzonite, and quartz­ roonzodiorite. Volcanic is predominantly :porphyritic andesite. Meta­ morphic {excluding quartzite) is predominantly biotite gniess. Abbreviations: A-Abundant, c-cornmon, ~Rare, -- Not Observed. . ------~~~~-~~.

70

Figure 27. Fossiliferous concretionary sandstone lens near Runkle Canyon. Zinsmeister (1974, 1983a, 1983b) considers this fauna indicative of shelf depths. Pencil is 14 ern long. (Fig. 19). These rocks are interpreted as representing Facies G, E, and possibly D (Fig. 10). Facies E is asso­ ciated with the upper tongues of the Simi Conglomerate near Poison Oak Canyon, and in conjunction with these tong- ues, represent inner-fan deposits

in this area. Foraminiferal data indicate deposition at middle-bathyal depths near the base of the formation followed by a shoaling event to upper- bathyal depths ap­ proximately 400 rn below the base of the Llajas Formation (Heitman, 1983). A deepening event followed, with depo- 71

sition resuming at middle-bathyal depths, followed in turn by another shoaling to outer-shelf depths near the top of formation (Heitman, 1983). The interbedded conglomerate and sandstone present near the top of the formation near Meier Canyon (Pl. 1, Fig. 19) represent Facies A, B, and c. Facies A includes sandstone intervals up to 10 m in thickness which are not common in the rest of the study area. This facies usually consists of conglomerate. These rocks are interpreted as being the coarse portion of inner-fan and perhaps slope deposits based on similarities to the slope and inner-fan associations of Mutti and Ricci Lucchi (1972, as trans­ lated by Nilsen, 1978), although Facies F is lacking in the Simi rocks. The depositional environment of the fossiliferous sandstone tongues near Runkle Canyon is uncertain. Defini­ tive sedimentary structures were not observed. The di­ verse macrofauna is considered indicative of shallow-water environments by Zinsmeister (1974, 1983). The shallow water fauna and the lack of sedimentary structures suggest these tongues were deposited in a shelf environment. This produces a paradox because the tongues overlie and inter­ finger with rocks that are considered deep-marine deposits (Fig. 19), and a microfossil sample collected between the tongues contains a fauna characteristic of middle-bathyal depths (Heitman, written communication, 1983). A large percentage of the microfauna from the sample consists of 72 p ' displaced shelf species (Heitman, written communication, 1983), and perhaps the macrofauna is displaced. These strata may instead have been deposited at shallower depths in response to the first shoaling event described by Heit­ man (1983). The uppermost 100 m of the formation in Poison Oak Canyon consists of fine to medium sandstone which contains macrofossils, including Turritella, and burrows. Turritella is indigenous in subtidal to shelf environments (Merriam, 1941; Keen, 1971; Keen and Coan, 1974; Squires, 1984). The presence of a shallow-water fauna in bur rowed sandstone which is locally laminated suggests these beds are also shelf deposits . These beds may record uplift prior to deposition of the non­ marine basal Llajas conglomerate. This conclusion is also reached by Heitman (1983}. PETROGRAPHY

Seventeen thin sections from samples in the Simi con­

glomerate, Las Virgenes Sandstone, and Santa Susana for­

mation were studied to determine compositional and tex­ tural properties of sandstone and mudrock as an aid to the

interpretation of source area and depositional environ­ ments. Eight of the sections are sandstone, five are silt­ stone, three are mudstone, and one is a sandy claystone. Figures 4 and 7 show the stratigraphic locations of the samples studied.

SANDSTONE

Sandstone characteristics are listed in Table 5. No general textural or compositional trends related to the

formation the samples represent were noted. Mean sand- stone composition is quartz, 54%; feldspar, 45%; and rock

fragments, 1%; and compositional range is quartz, 46% to 76%; feldspar, 24% to 76%; and rock fragments, 0% to 6%.

With the exception of SH-22, a subarkose, all samples are arkose (Fig. 28). Biotite and chlorite are abundant in

all samples, ranging from 6% to 37%. Recognized cements

include calcite and limonite. Abundant single and common composite quartz varieties are present. Most grains exhibit straight to slightly

undulose extinction; strong undulose extinction is rare. Vacuoles and inclusions are also rare. Orthoclase is the

73 TABLE 5. SANDSTONE CHARACTERISTICS OF THE SIMI CONGLOMERATE, LAS VIRGENES SANDSTONE, AND SANTA SUSANA FO~\TION

Sample Composition Texture 2 No. % Grains %Cement % 9 % F %RF Cement (l) Size Sorting Roundness ( ) SH-12x 74 26 54 46 0 calcite Fine Mod. Sa SH-13* 80 20 47 76 0 Limonite Med.- R:>or Sa Coarse

SH-14x 95 5 64 36 0 Limonite Very Good Sa Fine

SH-17* 100 0 46 48 6 Nr Med. Mod. R

SH-21x 57 43 46 54 0 calcite Fine Mod. Sa-Sr

SH-22x 40 60 76 24 0 calcite Fine Mod. Sa-Sr

SH-26+ 100 0 56 44 0 Nr Med. .MXI. Sr SH-27+ 100 0 64 36 0 Nr Fine- R:>or Sa-Sr Med.

stratigraphic unit: * Simi Conglomerate, + Las Virgenes sandstone, x santa Susana formation. (1) Nr=Not recognized (2) Sa=Subangular, Sr=Subrounded, R=Rounded.

'-.1 ~ 75

Q

SH-14 and 27

F 3:1 R

Figure 28. Sandstone composition of samples from the Simi Conglomerate, Las Virgenes Sandstone, and Santa Susana formation. See Figures 4, 6 and 7, for the stratigraphic position of the samples. Specific characteristics of the samples are listed in Table 5. most common feldspar, followed in decreasing abundance by plagioclase, microcline, and perthite. Both unaltered and altered feldspars are present, some of the same species. Rock fragments are granitic, gneissic, and volcanic. Only volcanic grains are included in the % RF (Table 5) as recom- mended by Folk (1980). Pyrite is present in samples SH-17 and SH-21. Sample 76

SH-22 contains molluscan shell fragments. Limonite and hematite staining is common to many of the samples. Sandstone grain size ranges from very fine to very coarse. Grains are typically subangular and samples gener­ ally are moderately sorted. Most samples are submature. Abundant long and concavo-convex contacts are present in samples SH-12, SH-13, SH-14, SH-17, SH-26. All samples have little or no observed porosity.

MUD ROCK Mudrock thin sections include five siltstone, three mudstone, and one medium-sandy claystone. Silt particles, except in the claystone as noted below, are composed of quartz and subordinate orthoclase, plagioclase, chlorite, and biotite. Pyrite is present in sample SH-24 and glauco­ nite? is present in sample SH-29. Most grains are sub­ rounded. Many of the mudrock samples contain pellets, foraminifers, or shell fragments. Most are also cemented with calcite. The medium sandy claystone, SH-25, consists of 10% subrounded to subangular sand grains composed ex­ clusively of quartz and 90% clay. This sample is neither calcitic nor fossiliferous.

INTERPRETATION OF SANDSTONE AND MUDROCK PETROGRAPHY In the samples studied both unaltered and altered subangular feldspar grains are present in conjunction with subangular quartz grains of the same size. Folk (1980) 77 suggests a combination of these grain types and weathering characteristics indicates a humid climate and high relief in a source area. Quartz types are equivocal, but the presence of unaltered feldspars and abundant micas indi­ cate a nearby granitic and metamorphic source. The angular­ ity of the grains suggests short to moderate transport distances. Calcite cement is common and suggests deposition in alkaline conditions. The presence of pyrite in some of these rocks indicates they were deposited under reducing conditions. Limonite and hematite are common but may reflect diagenetic changes common to iron minerals. PALEOCURRENTS

Paleocurrents were determined from measurement of 387

imbricate clasts at 10 stations throughout the study area

(Fig. 29). Vector mean for all clasts measured is N6°E. Vector means for individual stations range from N69°w,

These results are in general agreement with paleocurrent directions reported by Janes (1976) in the

upper tongues of the Simi Conglomerate in Poison Oak Canyon,

6'

Total Clasts Meascred

51' 1·

1 km

10 CLA S T S ~ "'"""' "' "'

CLASTSC~ f~EO

Figure 29. Paleocurrent patterns of the Simi Con­ glomerate, Las Virgenes Sandstone, and Santa Susana for­ mation in the Simi Valley area. The wide scatter of data precludes an accurate determination of paleoshoreline trend. The data may indicate a region to the south (ESE to WSW) was a source area. The diagrams show inferred current direction. Tsc = Simi Conglomerate, Tlv = Las Vir­ genes Sandstone, and Tss = Santa Susana formation.

78 79 but differ somewhat from those reported by Sage (1973) throughout the Simi Conglomerate. The two stations which represent the braided-river environment of the western Simi Conglomerate show east­ northeast transport. The marine conglomerate of the Santa Susana and eastern Simi Conglomerate reflect a wide range of transport directions from west to east. Channels in both braided-river and marine environments can show a wide range of current directions (Nilsen, 1977 ~ Smith, 197 4) , so perhaps most significant is that few clasts indicate a southward current flow. The lack of clasts indicating a southward current flow may indicate a region to the south (ESE to WSW) supplied sediment to a depositional basin in the north (ENE to WNW), during Paleocene time (Fig. 29}. This con­ clusion is somewhat speculative, however, due to the wide scatter of data. This general paleocurrent trend is in agreement with trends reported for the Chatsworth Forma­ tion (Trembly and Kraemer, 1981}. Kamerling and Luyendyk (1979), based on paleomagnetic studies, suggest clockwise rotation of up to 81 degrees may have taken place in the Santa Monica Mountains region after Miocene time. Removal of this rotation would result in a source area to the east (NNE to SSE) with the depositional basin in the west (NNW to SSW}. PROVENANCE

Clast composition indicates sedimentary, volcanic, igneous, and metamorphic rocks were present in the source area. Most granitic and metamorphic clasts are very deeply weathered, locally resembling sandstone matrix. This low durability suggests first cycle de­ position from a nearby source. Volcanic clasts are generally more resistant and are well rounded. Deeply weathered clasts were also observed. They may be the product of more than one cycle of deposition. Quartzite clasts are very durable and well rounded, which suggests that they are at least second cycle. A complex source terrane consisting of exposed granitic, metamorphic, and perhaps volcanic bedrock and quartzite-rich sedimentary deposits is indicated. As previously discussed, the presence of unaltered and altered subangular feldspars in conjunction with sub­ angular quartz grains of the same size in sandstone sam­ ples indicates a humid climate and high relief in the source area. Unaltered feldspar and abundant mica suggest a nearby granitic and metamorphic source. The angularity of the grains suggest relatively short transport. Colburn and others (1981) subdivided southern Cali­ fornia into bedrock provinces to aid in determining the source terrane of Chatsworth Formation conglomerate. The Peninsular Ranges province, specifically the Santiago Peak

80 81

Volcanics, is the only local source for andesitic and daci­ tic volcanic clasts, which are common in the Simi Conglom­ erate and Santa Susana formation. Argillite, present in the Peninsular Ranges province and the Chatsworth Forma­ tion is not present, however, in the Paleocene rocks. This may be the result of low durability of this rock type or changes in bedrock types exposed in the source area. The volcanic clasts in the Simi Conglomerate and Santa Susana formation suggest the Peninsular Ranges rocks may have been, at least in part, a source for sediments. Quartzite, common in the Simi Conglomerate and Santa Susana formation, is not present in any of the southern California provinces (Colburn and others, 1981). Merriam (1979) suggests a source of supermature orthoquarzite in northwest Sonora, Mexico, for southern California Paleo­ cene conglomerate deposits. Perhaps prior to movement on the San Andreas fault, this source and the Peninsular Ranges province were juxtaposed, leading to the complex assemblage of clasts present in ~he Simi Conglomerate and Santa Susana formation. PALEOGEOGRAPHY

The Simi Conglomerate, Las Virgenes Sandstone, and Santa Susana formation, of early Paleocene through ear­ ly Eocene age, reflect a wide range of depositional environments. The distribution of these environments is confined by the Runkle Canyon fault. Western deposits, present west of the fault (Pl. 1) , represent a complete retrogradational (transgressive) sequence followed by possible progradational (regressive) deposition. The Simi Conglomerate, present at the base of this sequence, is interpreted as gravelly and sandy braided-river deposits on an alluvial plain. The overlying Las Virgenes Sand­ stone, present only west of the Runkle Canyon fault, in­ cludes sandy braided-river, meandering-stream, and near­ shore-marine deposits. The western Santa Susana reflects deposition in a deepening marine environment, which in­ cluded transition zone to offshore, she~f, and slope en­ vironments. The uppermost part of the formation may repre­ sent shelf sedimentation prior to deposition of the basal nonmarine Llajas Formation. Eastern deposits are present east of the Runkle Can­ yon fault. Nonmarine deposits are not recognized on this side of the fault. The eastern Simi Conglomerate is inter­ preted as representing submarine canyon or channel fill and inner-fan deposits. Foraminiferal assemblages in in­ ter£ inger ing mudrock of the Santa Susana formation near

82 83

Poison Oak Canyon indicate deposition took place at bathyal depths, whereas trace fossils indicate deposition may have in places been at shelf depths. The eastern Santa Susana formation is interpreted as representing the fine-grained part of slope and inner-fan deposits with the eastern Simi Conglomerate as the coarse counterpart. Sandstone and conglomerate, present in tongues near the top of the Santa Susana, are interpreted also as represent­ ing the coarse portion of inner-fan deposits. These rocks represent the only introduction of coarse clastics near the top of the formation which are stratigraphically equi­ valent to mudrock containing bathyal foraminiferal assem­ blages (Fig. 19). This introduction of coarse sediment occurs above the thickest portion of easten Simi Conglomer­ ate and begins stratigraphically at approximately the same level as the first shoaling event described by Heitman (1983) in the Poison Oak Canyon area. Vail and Hardenbol ( 1979) suggested periods of low sea level are times of increased submarine canyon and fan sedimentation. River sediment can be transported closer to the heads of sub­ marine canyons rather than being trapped in drowned river valleys. The shoaling event described by Heitman (1983) may have resulted in a resurgence of coarse-sediment depo­ sition in this part of the basin. This reoccurrence most probably would occur at the focal point of past deposi­ tion. This is apparently the case because the conglomer­ ate of the upper Santa Susana overlies the thickest por- 84 tion of the eastern Simi Conglomerate (Fig. 19), which would presumably be the focal point of deposition. The bioturbated fossiliferous sandstone present at the top of the eastern Santa Susana formation and in tongues near Runkle Canyon most likely represents deposition at shelf depths. A shelf environment at the top of the eastern Santa Susana is consistent with the shoaling near the top of the formation discussed by Heitman (1983). The nature of the Runkle Canyon fault is uncertain. Left separation is only 600 m, yet the fault brings non­ marine and marine deposits, which are at the same strati­ graphic horizon, within close proximity. Based on paleo­ current data, the marine rocks were most likely deposited east-northeast to west-northwest of the nonmarine rocks. This suggests a larger component of actual slip was in a right-lateral sense. The fault plane is steeply dipping and is nearly perpendicular to formational contacts. The fact that the fault is steeply dipping today, (and prob­ ably was in the past, because of its nearly perpendicular relationship to strata) suggests it is not a low-angle thrust fault. This model assumes the nonmarine

Figure 30. Simplified paleogeographic model for the Simi Valley area during late Paleocene time. A repre­ sents P4 time, B represents PS time, and C represents late PS and early P6 time. Kc = Chatsworth Formation, Tsc = Simi Conglomerate, Tlv = Las Virgenes Sandstone, and Tss = Santa Susana formation. I BRA/0£0 R/1/ERS BRAIOEIJ R/1/ERS C"AA"nv BRA/OElJ ~ I

I 1BHAIIJEZJI Hllei'S I I I

Kc and basement Kc and basement

Western Deposits Western Deposits

SLOPE

Eastern Deposits Eastern Deposits A. B. c .

• 86

Sf/ELF

SLOIF

Kc and basement

Western Deposits

IPOsits

• 87 ' .

All three diagrams depict deposition during late Paleocene time, so planktonic foraminiferal zones (after Stainforth and others, 1975) are used to refine the times that each diagram represents. These times, P4 through P6, are approx­ imations based on interpretations by Heitman <1983) for strata in Poison Oak Canyon and represent deposi t!ion of the strata seen in outcrop, not time-transgressive equiva­ lents. Most of the strata seen in outcrop are shown on the northward face of each block. Figure 30A represents deposition during P4 time. All of the western Simi Conglomerate and most of the eastern Simi Conglomerate that is seen in outcrop has been deposit­ ed and the Las Virgenes Sandstone and eastern Santa Susana are being deposited. Figure 3 OB represents deposition during early PS time. Eastern sedimentation is limited to mud and silt deposited by low density turbidity currents. In the western region mud and sand of the lower western Santa Susana is being deposited at shelf depths. Figure 30C represents deposition during later PS and early P6 time. Eastern deposition is still limited to mud and silt except during times of shoaling, when deposition of coarse clastics resumes locally. Western deposition now consists of predominantly slope mud and submarine-canyon or inner­ fan gravel and sand. Following the time depicted in Figure 30C, regional shoaling takes place and shelf sediments are deposited. Erosion which took place prior to basal Llajas deposition (late early Eocene) removed all but remnants of 88 these shelf deposits and any shallow-marine or nonmarine deposits that may have resulted from this shoaling. Some time after deposition of the Llajas Formation, right-lateral movement along the Runkle Canyon fault jux­ taposed western and eastern deposits, as shown on the north­ ward faces of Figure 30C, into the configuration present today. REFERENCES

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