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Depositional environments of the Neogene Hungry Valley Formation: Sedimentary response to the initiation of the San Andreas Fault, Ridge Basin, Southern California

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Depositional environments of the Neogene Hungry Valley Formation: Sedimentary response to the initiation of the San Andreas Fault, Ridge Basin, Southern California

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Content DEPOSITIONAL ENVIRONMENTS OF THE NEOGENE HUNGRY VALLEY FORMATION: SEDIMENTARY RESPONSE TO THE INITIATION OF THE SAN ANDREAS FAULT, RIDGE BASIN, SOUTHERN CALIFORNIA by KATHERINE E. NITZBERG A Thesis Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE (Geological Sciences) December 1984 UMI Number: EP58735 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. UMI Dissertation Publishing UMI EP58735 Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 ProQuest UNIVERSITY OF SOUTHERN CALIFORNIA THE GRADUATE SCHOOL UNIVERSITY PARK LOS ANGELES. CALIFORNIA 90007 1 This thesis, written by KcLttier.Liie..L...J\li.tzteir^.................................. under the direction of hex.—Thesis Com m ittee, and approved by a ll its members, has been pre sented to and accepted by the D ean of The Graduate School, in p artia l fu lfillm en t of the requirements fo r the degree of Master of Science Dean D a te..N .9v.emb er _ 2 6 _ 1984 THESIS COMMITTEE Chairman TABLE OF CONTENTS Page ACKNOWLEDGEMENTS............................................... vi ABSTRACT........................................................ vii LIST OF ILLUSTRATIONS.......................................... ix LIST OF TABLES.................................................. xiii INTRODUCTION.................................................... 1 Background and Purpose................................... 1 Geologic Setting.......................................... 6 Location................................................... 7 Previous Investigations.................................. 12 DEPOSITIONAL SYSTEMS........................................... 15 General Description of Study Area....................... 15 Initiation of the San Andreas Fault.................... 18 Sedimentology............................................. 19 Methodology.......................................... 19 Analysis of Fluvial Depositional Systems......... 20 Lithofacies.......................................... 35 Background..................................... 35 Light-Orange Conglomeratic Sandstone........ 38 Description.............................. 38 Environmental Interpretation........... 49 Grayish-Orange Calcareous Sandstone......... 52 Description.............................. 52 Environmental Interpretation........... 56 ii Page Yellow-Brown Massive Mudstone................ 57 Description.............................. 57 Environmental Interpretation........... 60 Yellow-Gray Coarse Conglomerate............. 66 Description.............................. 66 Environmental Interpretation........... 70 Light-Brown Cross-Stratified Calcareous Sandstone................................... 71 Description.............................. 71 Environmental Interpretation........... 77 Calcareous Siltstone.......................... 81 Description.............................. 81 Environmental Interpretation........... 84 Olive-Gray Micaceous Sandstone............... 85 Description.............................. 85 Environmental Interpretation........... 88 Pinkish-Gray Cross-Stratified Sandstone 89 Description.............................. 89 Environmental Interpretation........... 95 Normally Graded Fine Sandstone............... 96 Description.............................. 96 Environmental Interpretation........... 99 Matrix Supported Conglomerate................. 100 Description............................... 100 Environmental Interpretation............ 103 iii Page Coarse Yellowish-Brown Conglomerate......... 106 Description.............................. 106 Environmental Interpretation........... 109 Lithofacies Associations........................... 112 Background (Markov Analysis)................. 112 Hardluck Section.............................. 124 Freeman Section................................ 126 Edison Section................................. 128 Lateral Correlation........................... 129 Discussion........................................... 131 Hardluck Section Depositional Environments.. 133 Freeman Section Depositional Environments... 139 Edison Section Depositional Environments.... 141 Grain Size Analysis...................................... 144 Background........................................... 144 Methodology.......................................... 144 Results.............................................. 145 Discussion........................................... 150 Paleocurrent Analysis.................................... 158 Background........................................... 158 Methodology.......................................... 159 Results.............................................. 159 Discussion........................................... 162 iv Page Petrography............................................... 168 Background........................................... 168 Methodology.......................................... 168 Results.............................................. 169 Discussion...... 174 PALEOMAGNETIC ANALYSIS......................................... 181 Background................................................. 181 Methodology............................................... 181 Results.................................................... 182 Discussion................................................. 187 DIAGENESIS...................................................... 196 Background................................................. 196 Scanning Electron Microscope Study..................... 197 Methodology.......................................... 198 Results.............................................. 198 Discussion........................................... 199 X-ray Diffraction Analysis.............................. 206 Methodology.......................................... 206 Results.............................................. 208 Discussion........................................... 208 GEOLOGIC HISTORY............................................... 213 SUMMARY AND CONCLUSIONS....................................... 223 REFERENCES CITED............................................... 229 APPENDIX........................................................ 236 v ACKNOWLEDGEMENTS I would like to thank the members of my thesis committee, Drs. J. Lawford Anderson, Douglas Burbank and Robert H. Osborne for their helpful suggestions and reviewing this manuscript. Special thanks are extended to Dr. Osborne for his support and guidance throughout this investigation. I would like to acknowledge the field assistance of Pamela Tartaglio, Doug Blatchford, Mark Parmelee, Martha and Frances Nitzberg, Debbie Douglas, and Rob Risley. I would also like to thank Tom Mason and Mike Edelman for discussing my project. Special thanks to the rangers at the Hungry Valley State Park for providing lodging. Dr. Kenneth Verosub of the University of California, Davis graciously ran the paleomagnetic samples for this project. I gratefully acknowledge the financial support from the University of Southern California Geology Department Student Research Fund, Sigma Xi Research Grant and ARCO Exploration Company for defraying laboratory and field expenses. Finally, I wish to thank my husband, my parents and sister for their assistance, support, and understanding throughout this project. ABSTRACT The boundary between the North American and Pacific plates has been dominated by transform faulting during the past 12 million years. Five million years ago, strike-slip movement along the plate margin shifted eastward from the San Gabriel to the San Andreas fault. Before, during, and after this transitional stage, movement along one or both of the faults resulted in the accumulation of strata assigned to the Hungry Valley Formation within the Ridge basin. Eleven lithofacies were identified from the examination of three stratigraphic sections totaling 1700 m in thickness. These lithofacies are based on sedimentary structures using the fluvial classification of Miall (1982) and grain-size analysis. Unlike many fluvial systems, the Hungry Valley Formation fluvial deposits consist entirely of conglomeratic bars and sandwaves with no recognizable clay overbank or floodplain deposits. This coarseness reflects rapidly uplifted highlands surrounding the Ridge basin. A previously described fluvial sedimentary sequence occurs at the base of many channelized fluvial sequences. This structure consists of alternating trough crossbedded conglomerate and sandstone layers which are as much as 1 m high and 2 m wide. The initiation of the present trace of the San Andreas fault is documented by rapid sedimentological changes. Faulting created a new northeastern source of sediment which contributed volcanic vii tuff clasts derived from the Mojave Desert and a change in fluvial environments. A comparison of strata deposited prior to initiation of the San Andreas fault with more recent deposits shows an increase in grain size through time and a change from distal braid bars to more proximal transverse bars. Paleocurrent data indicate that the shift in plate margins did not affect the general southeasterly flow pattern. However, the change in mean grain size and sedimentary structures indicates systematic changes in fluvial environments. A distinctive color change due to variations in the amount of carbonate cement accompanies this change in fluvial environment. During periods when either the San Andreas or San Gabriel fault was active, carbonate cement was deposited; when both faults were active, clay formed the cement. During rapid sedimentation, the carbonate in the system was diluted by clay and unable to cement the sediment. The transition in plate margin from the San Gabriel to the initiation of the San Andreas fault is reflected by a set of subtle sedimentological changes within the strata of the Hungry Valley Formation. LIST OF ILLUSTRATIONS Figure Page 1 Major fault zones of California....................... 2 2 Index map of Ridge basin and major faults............ 4 3 Cross-section of Ridge basin........................... 8 4 Generalized geologic map of Ridge basin.............. 10 5 Location map of study area and three measured stratigraphic sections............................. 16 6 Characters used in drawing stratigraphic sections... 21 7 Columnar section of the Hungry Valley Formation at Hardluck............................................. 23 8 Columnar section of the Hungry Valley Formation at Freeman Canyon...................................... 26 9 Columnar section of the Hungry Valley Formation at Edison .............................................. 28 10 New sedimentary sequence composed of alternating crossbedded sandstone and conglomerate........... 33 11 Braided river depositional models by Miall........... 36 12 Typical exposure of the light-orange conglomeratic sandstone lithofacies as seen in the Edison section.............................................. 39 13 Close-up of the light orange conglomeratic sandstone lithofacies.......................................... 42 ix 14 15 16 17 18 19 20 21 22 23 24 25 26 27 Planar laminated crossbeds............................ Flame structure and bed with concentration of mudstone rip-up clasts............................. Gradational contact at the base of the Hungry Valley Formation.................................... Intensely mottled, yellow-brown massive mudstone lithofacies.......................................... Bioturbation of the yellow-brown massive mudstone lithofacies.......................................... Interbedded layers of yellow-brown massive mudstone and yellow-gray coarse conglomerate lithofacies.. Contact between the two Violin Breccia lithofacies.. Channelized sequence in the light—brown crossbedded calcareous sandstone lithofacies.................. A single channel deposit in the light-brown cross bedded calcareous sandstone lithofacies.......... Fossilized vertebrate bone............................ Bioturbated layer of the calcareous siltstone lithofacies.......................................... Olive-gray micaceous sandstone lithofacies.......... Thin discontinuous channelized sequence of the pinkish-gray cross-stratified sandstone.......... Climbing ripple marks accentuated by heavy mineral laminations.......................................... 28 29 30 31 32 33 34 35 36 37 38 39 40 41 Fining-upward sequence in the normally graded siltstone lithofacies............................ Discontinuous alternating beds of matrix-supported conglomerate and pebbly mudstone in the fore ground............................................. Matrix-supported conglomerate....................... Traction current deposted conglomerate............ Clast-supported conglomerate........................ Cross-sectional view of lithofacies in the Hungry Valley Formation.................................. Transition probability matrix and spider diagram for the Hardluck stratigraphic section......... Transition probability matrix and spider diagram for the Freeman Canyon stratigraphic section...... Transition probability matrix and spider diagram for the Edison stratigraphic section........... Graphs showing variation in moment measure results of each lithofacies.............................. Visher plots of lithofacies......................... Pessega diagram of data from this study........... Rose diagrams of paleocurrent measurements........ Photomicrograph of carbonate-cemented sandstone from lithofacies 5................................ Page 42 Photomicrograph of clay-cemented sandstone from lithofacies 1........................................ 172 43 Ternary diagram of grain composition from lithofacies 1, 2 and 5............................. 177 44. Demagnetization intensity curve of three samples.... 183 45. Ziderveld diagram of the directional behavior of a typical sample during af demagnetization......... 185 46 Virtual geomagnetic pole plots for samples taken along the Edison section........................... 188 47 Virtual geomagnetic pole plots for samples taken along the Freeman section.......................... 190 48 SEM photomicrograph of mixed layer clay (smectite- illite).............................................. 200 49 SEM photomicrograph of pore-lining smectite.......... 202 50 EDX graph from clay sample shown in Figure 48....... 204 51 Graph of XRD output in 20 vs. intensity on clay sample shown in Figure 48.......................... 209 52 Cross-sectional view of the five phases of deposition of the Hungry Valley Formation........ 214 53 Diagrammatic illustration of the environments during deposition of the Hungry Valley Formation............................................ 216 xii LIST OF TABLES Table Page 1 Facies classification from Miall.................. 31 2 List of the eleven lithofacies.................... 115 3 Summary of sedimentological characteristics of each lithofacies................................ 134 4 Average mineralogic composition of 23 thin sections. 175 5 Fisher distribution statistics for the four beds.... 193 xiii INTRODUCTION Background and Purpose The San Andreas fault, the present plate boundary between the North American and Pacific plates, is a major geologic feature in California. The fault extends over 1000 km from the Gulf of California north to Pt. Arena, California (Fig. 1). The location of this plate boundary has progressively shifted eastward. Areas associated with the shifting transform margin have been deformed and offset by this series of north-trending strike-slip faults. Ridge basin in southern California is an example of such a deformed area (Fig. 2). It is a sedimentary basin formed due to deformation along the North American plate margin. During the most recent eastward plate-boundary shift, the Hungry Valley Formation was being deposited in Ridge basin. As the Hungry Valley Formation is located between the old and the new plate boundary, it is an ideal unit to investigate the mechanics and sedimentary response to a change in plate-margin location. In order to gain knowledge of plate-margin shifts, a detailed paleoenvironmental and paleomagnetic examination of the Hungry Valley Formation was undertaken. The five objectives of this study are listed below: 1. Reconstruction of the depositional environments throughout the basin during deposition of the Hungry Valley Formation and the associated Violin Breccia. 2. Reconstruction of the basin drainage patterns through paleocurrent analysis. Figure 1. Major fault zones of California (modified from Strahler, 1977). FAULTS S— San Andreas SG— San Gabriel G-Garlock H-Hayward E-Elainore MC-Malibu Coast Figure 2. Index map of Ridge basin and major faults Location of Figure 3 is outlined with dashes (modified from Link and Osborne, 1978). MOJAVE DESERT LOS ANGELES 30 40 50 60 20 40 80 km 5 3. Determination of sediment-accumulation rates through the use of dating techniques. 4. Determination of the time of initiation of the present San Andreas fault zone and the end of major activity along the San Gabriel fault. 5. Understanding the diagenetic causes for the change in color between the Hungry Valley Formation and all of the older units within Ridge basin. Geologic Setting Ridge basin offers a unique setting to study the shifting of the margin between the North American and Pacific plates. Prior to early Pliocene time (>5.0 mya), the western margin of the North American plate occurred was along the ancestral San Gabriel fault. During the deposition of sediment in Ridge basin, this plate boundary shifted eastward to the presently active trace of the San Andreas fault. The variation in types of sediment deposited in Ridge basin reflect the tectonic changes associated with the change in plate-margin location. The Ridge basin was formed by a double bend in the San Gabriel fault. The bends in the right-slip fault system caused extension to the south and compression to the north. This lead to the creation of a northern mountainous region due to buckling, and stretching with subsequent sinking to the south, which formed the Ridge basin (Crowell, 1952). As the fault continued to move in a right-lateral sense, the basin expanded northward. 6 Ridge basin is a sedimentary wedge-type basin (Crowell, 1974) in the Transverse Ranges of southern California. The sediment within the basin forms a thick section (>12,000 m) documenting a change in environments through time from marine embayment to lake, braided stream and alluvial fan. About 5.5 mya the deep basin filled with sediment so the shallow depression became covered by shallow lakes and streams (Link and Osborne, 1978). During deposition of the Hungry Valley Formation, the active plate margin shifted eastward from the San Gabriel fault with its double bend to the more straight San Andreas trace. The Hungry Valley Formation and the upper part of the Violin Breccia were deposited between the two faults during the transition in the position of this plate margin. Location The Ridge basin is located between Los Angeles and Bakersfield, near the town of Gorman (Fig. 2). The study area is 100 km north of Los Angeles along Interstate 5. Exposures of the Hungry Valley Formation extend from the San Gabriel fault on the west where it interfingers with the Violin Breccia, eastward to the San Andreas fault as shown in Figure 3. The southern limit of this study is of a gradational contact of the Hungry Valley Formation with the underlying Apple Canyon Member of the Ridge Route Formation (Fig. 4). Further north, the Frazier Mountain thrust fault complex overrides the Hungry Valley Formation. 7 Figure 3. Cross-section of Ridge basin (after Link and Osborne, 1978). 8 s w RIDGE BASIN 1 ** • O . o' o O O ' O 'O O 'A ' .0 ' » 'O 0 . • 'o Jo. o . 3 HUNGRY VALLEY FORMATION • • * ' » f - p-» Apple Canyon Sandstone Member Alamos Canyon Slltstone M. — ^ g gU r — nvon ° r0« SS o o O' » ■ * ° * RIDGE ROUTE FORMATION Cerejra Peak Shale M ranchman Flat SS. g jlto Cammn shale M ’ pl»her Spring Sandstone Ranch ShateJJ Marple Canyon Sandstone M SAN - v FRANCISQUITO v FORMATION CASTAIC FORMATION MINT CANYON FORMATION EXPLANATION 1 ^ | Breccia lo Conglomerate | / 1 Sandstone l ^ j Siltstone H Shale (Mudstone) Basement Rocks THICKNESS 17,000 10,000 Meters 3 Km 0 1 2 Miles Horizontal Scale Figure 4 Generalized geologic map of Ridge basin (modified after Link and Osborne, 1978). Explanation CASTAIC FORMATION Me r a HUNGRY VALLEY FORMATION O — [^M m J MODELO FORMATION O Ui O Z m UJ J O <o CL UJ PEACE VALLEY “BEDS' SAN FRANCISQUITO FORMATION _j RIDGE ROUTE “ FORMATION QUARTZ DIORITE GNEISS BASEM'T. ROCKS PRE -TERTIARY \ * Pv I VIOLIN BRECCIA li 4. ft 1 WELL Scale Ph Od Gormon 3 2 km M e Ph Cottoic Mm Gnbnf I. f 0J ’ ’ Mm The Hungry Valley Formation and associated Violin Breccia covers approximately 60 square km which includes sections 5, 6, 7, 8, T.7N., R.18W., sections 3, 4, 10, 11, 12, 13, 14, 15, 24, T.7N., R.19W., sections 18, 19, 20, 21, 28, 29, 30, 31, 32, T.8N., R.18W., and sections 13, 14, 23, 24, 25, 26, T.8N., R.19W.. Part of the Hungry Valley Formation deposited east of the San Andreas fault zone has been displaced southward to an unknown location (Woodburne, 1975). The Hungry Valley Formation and Violin Breccia exposures are on public land managed by Los Padres National Forest, California Department of Parks and Recreation and the U.S. Bureau of Land Management. Accessibility to all areas is good for motorcycle or 4-wheel drive truck. Motorcycle trails cross the entire area providing easy foot travel throughout the study area. Only during certain times of the year are roads passable for 2-wheel drive vehicles. Much of the area was cleared of brush by a fire in 1980 which facilitates hiking and observation of outcrops. Previous Investigations There have been many studies of the structure and tectonics of the San Andreas and the older San Gabriel fault. Eaton (1939) identified the San Andreas fault in Ridge basin. More recent researchers such as Crowell (1952), Woodburne (1975) and Paschall and Off (1961), Ramirez (1983) have studied the amount and types of offset along the faults on both sides of the basin. Controversy still exists as to whether the San Gabriel fault is 12 presently active in this study area. Crowell (1982) defines the last movement along the San Gabriel fault as having occurred at the end of deposition of the Violin Breccia, whereas Weber (1979) considers the fault to be presently active. The regional geology of the Ridge basin was originally mapped by Clements (1937) and Eaton (1939). Research of particular concern to this study is the mapping by Crowell (1950, 1954, 1982). Crowell’s early mapping showed detailed structure and separated the Hungry Valley Formation into 6 members. Later Crowell (1982) remapped the region and divided the Hungry Valley Formation into 3 members plus a separate formation called the Violin Breccia (Fig. 3) The prograding sequence of environments within the Ridge basin has been demonstrated in a series of sedimentological investigations. Other units in the Ridge basin sequences have been described in theses by students at the University of Southern California and University of California, Santa Barbara which are summarized in Link and Osborne (1978) and Crowell and Link (ed., 1982). Sedimentologic studies on the Hungry Valley Formation have been described in a series of recent publications. Crowell (1982) conducted a detailed clast count at 33 sites in the Hungry Valley Formation. Link (1982) measured 22 paleocurrents in this study area. Ramirez (1983) has outlined a possible source area for the clasts in the Hungry Valley Formation near Morango Valley. Paleontologic studies have been performed by David (1945), Axelrod 13 (1982), and Crowell (1982) to aid in environmental and climatic reconstructihn of the Ridge basin. A well-studied faunal zone occurs at the base of the Hungry Valley Formation. The fossils originally were described by Stock in Crowell (1950). Later workers at the California Institute of Technology and Chevron Oil Company located more fossils along the base of the Hungry Valley Formation (personal comm., Downs, 1983). The Kinsey Ranch fauna was named and described by Miller and Downs (1974). The fossils found in this faunal zone are large terrestrial vertebrates assigned to the Hemphillian stage. More precise dating than available from fossils has been carried out on the older portion of Ridge basin. Ensley (1980) developed a magnetic-polarity stratigraphy. This paleomagnetic study dated rocks from the basal Castaic Formation to the top of the Piru Gorge Sandstone Member of the Ridge Route Formation (Fig. 4). With the aid of fossils, Ensley and Verosub (1982), were able to develop a detailed plot showing net sediment accumulation rates. Shale intervals accumulated at a net rate of 3 m/1000 yrs, whereas sandstone intervals accumulated at a net rate of 0.2 m/1000 yrs. This variation is caused by the sand being reworked in environments highly subject to erosion (Smith, 1982). 14 DEPOSITIONAL SYSTEMS General Description of Study Area Three stratigraphic sections were measured to study the variations in sedimentology across the basin (Fig. 5). These sections were chosen for their excellent exposures, vertical continuity and location within the Ridge basin. Each section was measured from the base of the Hungry Valley Formation or the time-synchronous parts of the Violin Breccia to the highest structurally undisturbed stratum. All stratigraphic columns are composite sections measured in stream channels and road cuts. The western measured section named "Hardluck”, was measured along a paved road in Los Padres National Forest which extends from Kinsey Ranch to the Hardluck Campground. This 735—m section is composed of strata assigned to the Violin Breccia and Hungry Valley Formation. Due to flooding during the winter of 1982-1983, many small stream channels were flushed out leaving well-exposed bedrock surfaces. Previously covered portions of the Hardluck section were described using these recent stream exposures. The central measured stratigraphic section is located at the type section described by Crowell (1947). The composite section is 487 m thick and comprises 14 separate measured sections. Individual beds were traced along the eastern crest of Freeman Canyon to measure the complete Freeman section. The base of this stratigraphic sequence is along a dirt road running through Alamo Canyon, the top is the cliff at the northern end of Freeman Canyon. 15 Figure 5 Location map of study area and three measured stratigraphic sections. E t H , s . j x p / S s c - t . 1 , 0 n ■ ■ - ' irj \ Hardluck f l e c t io n rt^cdluclcA,-»"\p!rT-riurj4 Scale LEBEC .AM) BLACK NIT. QUADRANGLES 0 1 mile An eastern section was measured near the San Andreas fault, but far enough west to avoid the shear zone. This stratigraphic section called the "Edison" section is named for the powerline which runs overhead. Most of the section was measured along the service road for the transmission towers. The Edison section parallels Interstate 5 from a small pluton near the Highway 138 exit, to an unnamed valley near the Quail Lake Road exit. Overall the eastern section is 480 m thick. Initiation of the San Andreas Fault The present trace of the San Andreas fault began movement aproximately 5.5 million years ago (Crowell, 1974). Woodburne (1975) recorded the slip rate of the fault from offset of other sedimentary units. However, in the Ridge basin region, no one has determined the exact beginning of movement along the San Andreas fault. Across the gradational contact between the Apple Canyon Sandstone and the Hungry Valley Formation, there is a distinctive change in sedimentology. This change occurs between the last grayish-orange, medium-grained sandstone bed and the first light-orange, conglomeratic sandstone bed. In all three measured sections there are interbeds of finer-grained units which make the recognition of this change more difficult. The change upsection to coarser-grained braided stream deposits and more proximal depositional environments is inferred to indicate a change in the location of the source. In addition, 18 the clasts in the coarser-grained unit show the input of Mojave Desert sediment. During deposition of the older Fisher Springs Member of the Ridge Route Formation, similar Mojave volcanic clasts were brought into the basin (Harper, 1981). An opening on the eastern margin of the basin allowed transport of these clasts into Ridge basin. Subsequently, this opening closed and the northeastern margin became dominated by the Liebre massif. In order for these clasts of similar Mojave volcanoclastic tuffs to be deposited within the Hungry Valley Formation, there must have been a change in the configuration of the northeastern margin. 4 The most likely cause of this change is movement along the San Andreas fault which displaced part of the highlands along the margin. This offset would allow streams from the Mojave Desert to flow across the San Andreas fault and into Ridge basin. If the influx of volcanoclastic clasts is due to movement along the San Andreas, then the base of the first light—orange conglomeratic sandstone indicates the initiation of faulting. Sedimentology Methodology The sedimentologic investigation was conducted from June 1982 to August 1983. Within this period approximately three monthly were spent in the field. Though the Hungry Valley Formation was mapped by Crowell (1947, 1982), the structure is so complex that each section chosen for measuring was first mapped to determine 19 the location of minor faults and folds. The top of each stratigraphic section was chosen at the location of a major structure such as a thrust fault or recumbent fold across which the strata could not be traced. The three sections used in this study were measured by a combination of methods. Where possible, a Jacobs staff with Brunton compass was used (Compton, 1962). In areas of high relief or uneven ground, a Leitz surveying transit, topographic maps, and a Thommen 2000 altimeter were employed. The Jacobs staff method measures true thickness. The surveying technique shows the angle of inclination used for sighting each sedimentary layer. These angles are transformed into apparent thickness using trigonometric methods. Then the apparent thickness is corrected to the true thickness of each bed using Mertie's formula (Kottlowski, 1965, p. 158). The resulting stratigraphic sections are shown in Figures 6, 7, 8 and 9 and described in Appendix A. Analysis of Fluvial Depositional Systems Coarse-grained braided stream deposits have long been considered haphazardly organized deposits (Allen, 1966). In 1977, Miall demonstrated that most braid-bar deposits are actually cyclic. He also was able to develop facies models using modern and ancient braided stream deposits. 20 Figure 6. Characters used in drawing stratigraphic sections. 21 LEGEND TEXTURE 500 m SEDIMENTARY STRUCTURES very c o tr a t conglomerate ► * conglomeratic aandatona • © ♦ o o f t ' O •_ 0 0*0 • o ' C t |° c o* -°o| O • llty sandstone depth above base of Hungry Valley Formatiorv "'^*400m - \ coarse conglomerate aandstone o - ' • » ) ) ) ) } ) ) » ) T j J T T T j j/ lUtVllll1 paleocurrent measurements . n = 4 x = S 8 8 ° W L = 4 8% massive worm burrows horizontal bedding planar crossbeds trough croasbeds ripples 22 Figure 7 Columnar section of the Hungry Valley Formation at Hardluck. 23 HARDLUCK SECTION 200m 3 0 0 m UliU 4 0 0 m n - 9 x=N73 E L= 54% 0m (f M U ))j>) • 100m- n- 10 x — N 5 1 c L -B7% HARDLUCK SECTION - (CONT.) )))))> ( ( ( ( ( ( ) ) ) ) ) 300m (((((«( n = 9 x=N45°W L=40% 200m C((((( ) ) ) ) ) ) x=N 82nE L= 18% 100m )))))) )))))) n - 9 x=N9"E L = 51% « ((((((((( 500m ( ( ( ( ( ( ( ( ) ) ) ) ) ) ) (((((((( n = 13 x=N 4°W L=78% 400m Figure 8* Columnar section of the Hungry Valley Formation at Freeman Canyon. 26 5 * 5 * UJ * n eo 40 o cn <o ^ CO CO— — * © CO © (1 it || — » i ! t! il il II c IX - J c IX - J c |X - J • • • < D W I I I ! I I " V ill X u ! i i i s x § M Y i i h i i r h u m k v ^ h i X V I i l l 5 : j .« • i; ■ i’ - ; • • ' . -i: '»•'»• • • ■ «'. ■ • *■• , ! ■ t ■ ' . J (1 ' . - ' t ■ \* -'.ft: !«'• v •*': * * . • '1 V •.; ■‘ ••'•'ft . * V. •t\*< ' • • o- fie. t-wa f'l tLn m (•Vs UJ « * ® k. « o z ® l i i t I I C (K _l UJ =o * K. O 2 40 l i I I l i c |X -J UJ cto * 4 UJ J* MS f o * ®r 40 1 © 1 ^ 0 C O 2 <o / cs CO K . A * - CO © li 1 ! 1 1 1 1 1 II 11J ' II II II c 4X -J 1 c fx -if C IX ^ x x y x x i l i f * t * . ■ » - ' % * • * * • • * : 9 . f * - . 1 . * . , 1 . 1 - • • : ; - ? t * i . « i * t * * « • i • f t - j • > . ■ : * i . c « « * • • . ; . % • v »' : \ - . .'. • w O & W > H . c r ® H « l i c i x —i UJ Cv 2* ° ^ ^ 2 w ii ii : j C jX -J />. \ f T i r - ) > lisr 5;->..;--v. » • • . t • ; I e - . * ( * . M ... _ i 0 » o -i - » o : .'.-p i -: o/ ; < •«. *«"*.• -r . *r i **.*..•■ *' ‘ - _ c • c • > y ; t 9 \ " V : •. ■;* '.■ ? 5 c® ^ ci a* © os o ® fs* ^ CO ^ CO CD 1! il 1 1 II II II C | X J C IX J • r • /vxv^vvx wv?, 27 54 Figure 9 Columnar section of the Hungry Valley Formation at Edison. 28 EDISON SECTION 400m - vvvw J )}») 0 o 0 0 0 0 o o V^vvv o o o o o o o p O o y b .© o o o o VVV\»A 0 0 o v y o o o o y o o O 0 o o i n«11 x *N31* W L*89% \ • n» 10 x»N52, W L-80% V • n» 10 x • S23* W L * 22% N5 300m- o o o « i > * 3 o a ■ p o o. o V_V,V^ V ^ o ° Q o o o V # o o o o . o- »' V ^ - o o b . f c > . b- ° ** ■ . 4. ■ ■ o . o o p'. O O 3..S ,., V ^ ^ I »)j) \ y y y o o rr-r b-.o o p b o o o p o 0 .A ' v / O 0 . y . O O lA'A'- 9 « o d )))>) o . 6 0 o o o \ v • n «20 x»S 83* W L» 31% • n»10 x • S25*W L *63% \ • n»10 x»S54*E L»60% 200m- 100m- y. uu j> ) ja U l A l JJJJ) ^-4 '-'.la yy • n-11 X-S67 E t-4 7 % T < ■ > o >.uu o o o b • V o . o o o. A o q 9 0 b - i p V . Ob . 3 O y l \ • n» 20 x» S43*E L*39% 't>.b ^ y VV ^44- uuu )))))) < t . 9 t > : < o' . d '. O' b o b. « o o ; V o • O',.' bo o!-b’ . o ’ , o o o . ■o;b o.o.;- 0m- o.O o O O « V / ttttt- vy ' y y 7~T v y muu y jC a ^ • n«24 x»S43*E L»60% I • n» 18 x»S13*W L • 52% This method of analysis of fluvial deposits consists of two phases. Initially one observes the sedimentary structures and grain sizes within individual depositional units. Then all data is used to define lithofacies according to the descriptions shown in Table 1. In this study, one sedimentary sequence commonly found was not classified by Miall (1977). The new sedimentary sequence consists of alternating layers of trough-crossbedded sandstone and conglomerate about 0.5 to 1.0 m thick (Fig. 10). Each of the conglomerate beds fines upward. To be compatible with the Miall classification, the facies "Gt” will be used to designate such trough-crossbedded sandstone and conglomerate sequences. The hydrodynamic cause for this sedimentary sequence was probably similar to the "St" of Miall (1982) except that the flow regime was high enough at times so that the river could carry the large clasts by saltation and deposit them as a braid bar. Since the beds alternate between finer and coarser grain sizes, it is assumed that the competence of the stream varied. These multiple variations during a single depositional phase may be caused by a series of surges and waning stages within one flood. The surges might reflect variations in the time it takes flood waters on different tributary streams to reach the main trunk stream. The second stage in fluvial analysis is to group the observed sedimentary structures into typical sequences. These sequences can then be compared to the six braided-stream models described by 30 Table 1. Facies classification from Miall (1982). 31 F a c i e s C o d e L i t h o f a c i e s S e d i m e n t a r y S t r u c t u r e I n t e r p r e t a t i o n Gms m a s s iv e m a tn x s u p p o r te d g r a v e l n o n e d e b r is flo w d e p o s its Gm m a s s iv e or c ru d e ly b e d d e d g ra v e l h o riz o n ta l b e d d in g , im b ric a tio n lo n g itu d in a l b a rs , la g d e p o s its s ie v e d e p o s its Gt g ra v e l, s tratified tro u g h c ro s s b e d s m in o r c h a n n e l fills Gp g r a v e l s tra tified p la n a r c r o s s b e d s Im g u o id b a r s or d e l ta ic g r o w t h s fr o m o ld e r b a r r e m n a n t s St s a n d , m e d iu m to v c o a r s e m a y b e p e b b ly solitary (th e ta ) or g r o u p e d (pi) tro u g h c ro s s b e d s d u n e s ( lo w e r flo w r e g im e ) Sp s a n d m e d iu m to v c o a rs e , m a y b e p e b b ly solitary (a lp h a ) or g r o u p e d (o m ik ro n ) p la n a r c r o s s b e d s im g u o id . t r a n s v e r s e b a r s s a n d w a v e s ( i o w e r flo w r e g im e ) Sr s a n d v e ry fm e to c o a rse n p p ie m a r k s of an ty p e s n p p le s ( lo w e r flo w r e g im e ) Sh s a n d v ery fm e to v e ry c o a r s e , m a y b e p e b b ly h o riz o n ta l la m in a tio n , p a rtin g or s tre a m in g lin e atio n p la n a r b e d flo w (i a n d u flo w r e g im e ) Si s a n d , fm e low a n g le ( < 1 0 " ) c ro s s b e d s s c o u r fills c r e v a s s e s p la y s , a n t id u n e s Se e ro s io n a ' s c o u rs with in tra c la s ts c ru d e c r o s s b e d d m g s c o u r fills Ss s a n d , fin e to c o a rs e . m a y b e p e b b ly b r o a d s h a llo w s c o u rs in clu d in g e ta c ro ss- stratification SCOUr fills Sse S h e , Spe s a n d a n a lo g o u s to Ss. Sh. Sp e o lia n d e p o s its Ft s a n d . silt, m u d fine la m in a tio n . ve ry s m a i ripp les o v e r b a n k Or w a n in g flo o d d e p o s its Fsc silt m u d la m in a te d to m a s s iv e b a c k s w a m p d e p o s its Fcf m u d m a s s iv e with f r e s h w a te r m o llu s c s b a c k s w a m p p o n d d e p o s its Fm m u d silt m a s s iv e d e s ic c a tio n c ra c k s o v e r b a n k or d r a p e d e p o s its Fr silt m u d ro otlets s e a t e a r t h C c o a i c a r b o n a c e o u s m u d p la n ts m u d fums s w a m p d e p o s its P c a r b o n a te p e d o g e n ic fe a tu re s son 32 Figure 10. New sedimentary sequence composed of alternating crossbedded sandstone and conglomerate. 33 34 Miall (1982) (Fig. 11). The models range from coarse-grained proximal to fine-grained distal fluvial sandstone deposits. In this investigation, the sequences of lithofacies were noted. The typical facies sequence was compared to those described by Miall (1982) for a comparison of environmental models. From the vertical variations in sequences, using a Markov analysis, frequently associated lithofacies were grouped to aid in environmental determination. Lithofacies Background The Hungry Valley Formation and interfingering Violin Breccia have been divided into eleven lithofacies. These individual units vary volumetrically from less than 1 to as much as 30 percent of the total stratigraphic thickness. Most of the lithofacies are found in only 1 or 2 of the measured sections though one lithofacies is prominent in all three sections (Figs. 7, 8, and 9). The units at the base of the Hungry Valley Formation have been included as separate lithofacies to better understand the changes in depositional environment. The eleven lithofacies are: 1) light-orange, conglomeratic sandstone; 2) grayish-orange, calcareous pebbly sandstone; 3) yellow-brown, pebbly mudstone; 4) yellow-gray, coarse conglomerate; 5) light-brown, crossbedded calcareous sandstone; 6) calcareous siltstone; 7) olive-gray, micaceous mudstone; 8) pinkish-gray, cross—stratified sandstone; 9) normally graded siltstone; 10) matrix-supported conglomerate; 35 Figure 11. Braided river depositional models by Miall (1982). .36 Name Environmental setting Main facies Minor facies Trollheim type (G,) proximal rivers (predominantly alluvial fans) subject to debris flows Gms, Gm St, Sp, FI, Fm Scott type (G|.) proximal rivers (including alluvial fans) with stream flows Gm Gp, Gt, Sp, St, Sr, FI, Fm Donjek type distal gravelly rivers Gm, Gt, Gp, S/7, Sr, (G.n) (cyclic deposits) Sf Sp, FI, Fm South Saskatchewan type (S(l) sandy braided rivers (cyclic deposits) Sf Sp, Se, Sr, Sh, Ss. SI. Gm, FI, Fm Platte type (Stl) sandy braided rivers (virtually non cyclic) St, Sp Sh, Sr, Ss, Gm, FI, Fm Bijou Creek type (S.) Ephemeral or perennial rivers subject to flash floods Sh, SI Sp. Sr and 11) coarse, yellowish-brown conglomerate. Depositional environments have been inferred from the size and shape of packets of beds and the sequence of sedimentary structures. Laboratory work was used to refine the depositional environments identified. Light-Orange Conglomeratic Sandstone Description The light-orange conglomeratic sandstone lithofacies consists of grains from clay to clasts as much as 50 cm in diameter with a median grain size of coarse sand. The unit is composed of poorly-sorted, clast-supported conglomerate and interbedded sandstone. The cement is clay which creates a poorly-lithified rock. Some layers are more resistant due to carbonate-cemented beds and concretionary nodules. This light-orange unit is the prominant lithofacies within the Hungry Valley Formation and constitutes 30% of the total thickness measured in all three sections. Using the GSA Rock-Color Chart (1975), this lithofacies is very pale orange (10YR 8/2) and in siltier portions, pale yellowish brown (10 YR 6/2). Cross beds defined by heavy mineral laminae are prominent in the lower part of all three measured sections and are less common in the younger beds of this lithofacies. The light-orange conglomerate lithofacies is composed of discontinuous channelized packages ranging from 1.5 to 53 m wide and 2 to 25 m high (Fig. 12). The variation in thickness and 38 Figure 12. Typical exposure of the light-orange conglomeratic sandstone lithofacies as seen in the Edison section. Each amalgamated bed is composed of channelized sequences. 39 40 width is due more to degree of truncation by later channels than to initial variation in the size of channels, as seen by the number of truncated sequences. Within each channelized sequence, there are from 1 to 10 fining-upward sequences. The erosional base of the channels are convex and asymmetrical. There are two types of bases of these channelized sequences. The most common is a massive conglomerate which fines upward along the edge of the channel. Above the basal massive conglomerate within a channel which is clast supported, the whole channelized sequence fines upward. The less common erosional base of a channel consists of a coarsening-upward sequence. The basal layer is a well-sorted sandstone with heavy-mineral laminations. The sandstone layers follow the shape of the erosional base and are from 2 to 10 cm thick. A sharp contact separates the lower fine-grained sandstone from a massive or trough-crossbedded, clast-supported conglomerate. This basal sequence is followed by many fining-upward sequences which fill in the channel (Fig. 13). Individual channels and whole cliff faces were analyzed using the facies classification of Miall (1978) (Table 1). Most of the sedimentary structures resemble those described by Miall (1982). The trough-crossbedded conglomerate (Gt) in the light-orange conglomeratic sandstone lithofacies often fines and thins up-dip along individual beds (Fig. 10). A generalized channel sequence contains Gm, Gt, St, Sp with Sh or SI as the topmost beds. The internal structure of sand layers are trough-bedded sandstone and 41 Figure 13 Close-up of the light-orange conglomeratic sandstone lithofacies. Note coarsening upward sequence which begins at arrow. 42 43 conglomerate and constitute as much as 80% of the beds in a single channelized sequence. The St layers form groups of beds from 5 to 100 cm thick. Some channels contain superimposed sandstone crossbeds, which give alternating flow directions, for example, a southwest flow direction juxtaposed on southeast flow directions. Clasts within the conglomeratic beds of this lithofacies are subangular to subrounded (Powers, 1953). The pebbles are more angular than the cobbles and range from subangular to angular in shape. It is hard to discern if units are imbricated because of the high degree of sphericity of cobbles and intense weathering. Many of the clasts are weathered tuffs which crush in one's hand; other cobbles have decomposed leaving only a dark stain on the outcrops. Secondary sedimentary structures are more prevalent in the basal part of all three stratigraphic sequences. Deformed heavy—mineral laminated sandstone such as those in Figure 14 occur. Flame structures occur at the base of some light-orange conglomeratic sandstone units, which overlie finer-grained units (Fig. 15). Since there are few mudstone interbeds, loading features are uncommon. The only fossil remains found in this unit are unidentified vertebrate bones. All fossils were disarticulated prior to deposition. The Kinsey Ranch Faunal zone occurs near the base of 44 Figure 14. Planar laminated crossbeds. Heavy mineral concentrations defined crossbeds in the light-orange conglomeratic sandstone lithofacies. Deformation of the upper beds is probable due to liquifaction caused by fault activity. 45 O (mcrtfc.r ) 1 46 Figure 15. Flame structure and bed with concentration of mudstone rip-up clasts. Note coarse grain size of the sandstone beds. Knife is 9 cm long. 47 the Hungry Valley Formation though bones were found higher in the section as well. Environmental Interpretation The light-orange conglomeratic sandstone lithofacies forms laterally persistant amalgamated units. These units are composed of many discontinuous beds within an exposure up to 1 km wide and 50 meters high. Such lateral and vertical continuity of one lithofacies indicates a single depositional environment. On a smaller scale, the beds are very discontinous and channel shaped. This differs from most fluvial environments which consist of interbedded channel, bar, and floodplain deposits (Jackson, 1978). As suggested by Collinson (1978), the river is able to migrate without any limitations when no clay overbank deposits form. In such a case, fluvial sediment would be deposited evenly across the valley. The thick, extensively channelized sequence within the Hungry Valley light-orange sandstone appears to be an ancient analogue of the deposits of the Kosi River which contains no fine-grained overbank deposits (Collinson, 1978). The internal structure of a single channel-shaped sequence varies. A typical facies sequence consists of Gm, St, Sp with Sh or SI at the very top. This sequence of Miall facies follows the Donjek-type model (Fig. 11). Miall (1978) catagorizes the Donjek as a distal gravelly river. The South Saskatchewan model (Miall, 1982) also is similar to the light-orange, conglomeratic sandstone 49 lithofacies. The two models differ in their gravel content; the Donjek has from 10 to 90% gravel, whereas the South Saskatchewan type has less than 10% gravel. In this study, individual channels of the light-orange conglomerate lithofacies vary in the amount of gravel. Some Hungry Valley Formation sequences have less than 10% gravel, whereas most have 10-20% gravel. Miall (1982) considers the Donjek- and South Saskatchewan-type rivers to be part of an assemblage of gradational fluvial environments from medial to distal portions of a fluvial system. Following this classification the light-orange, conglomeratic sandstone lithofacies was deposited by a moderately distal fluvial environment• Since most of the outcrops are well exposed, two-dimensional cliff faces, few three-dimensional features are visible. The length of individual bars and sinuosity of the channels cannot be measured in the field. All available data is from the two-dimensional measurement of vertical sections through the sequences. Sedimentary structures and their sequences are the only data available for determining the types of bars. The intense dissection of the fining-upward sequences indicates a slow rate of fall in flow discharge (Jones, 1977). The sedimentary structures and their order within each channelized sequence indicates changes in the stream discharge. The sequence of trough crossbeds overlain by planar crossbeds is attributed to changes in flow regime (Cant and Walker, 1976). 50 Trough—crossbedded sandstone and conglomerate are formed by dunes with sinuous crestlines migrating downstream. Tabular crossbeds inferred to represent the migration of sandwaves occur stratigraphically above the trough—crossbedded sand. This change is due to a decrease in depth and velocity of the stream (Blatt al., 1980). Sandwaves form in a lower flow regime (flow velocities from 0.5 to 0.7 m/sec) than the larger-scale dune structures (Cant, 1978). Similar ordered sequences of structures and fining-upward sequences are seen in many braided systems. Allen (1983) classifies the sequence shown in this lithofacies as a composite-compound bar sequence. The large variation in structures in each sequence may be attributed to change in sediment supplied to the river and changes in location of major flow channels (Allen, 1983). Rust (1972) classifies the laterally extensive crossbedded layers in recent deposits as transverse bars deposited in the downstream reaches of a river. The sequence of sedimentary structures in this lithofacies follows those typically associated with a point bar model (McGowen and Garner, 1970). Unlike a meandering stream the vertical and lateral facies associations in the Hungry Valley Formation do not include crevasse splays or overbank deposits. Jackson (1978) shows cross-sections of a braided-stream system as being entirely amalgamated channel and bar deposits, similar to the lateral and vertical sequences of this facies in the lower Hungry Valley 51 Formation. In recent braided streams, these point-bar appearing deposits occur as sandflats. The sandflats described by Cant and Walker (1976) form on the tops of large cross-channel bars and grow by accretion onto the top and side of the sandflat. A typical sandflat facies described by Cant and Walker (1976) consists of in-channel trough crossbeds (St) from dunes, overlain by a large set of planar crossbeds (Sp) of the cross channel bar, which is then overlain by smaller scale St, Sp and Sr facies. A second type of sedimentation occurs at sites where a cross-channel bar forms but no sandflat develops. These deposits consist of a large sequence of trough crossbedding with isolated planar crossbedding. Both of these sequences occur in the Hungry Valley Formation. Throughout the light—orange conglomerate lithofacies, there appears to be both sandflat and transverse bar deposits. From the models listed above it is concluded that these transverse bars and sandflats were deposited in the mid to distal reaches of a braided-stream system. Grayish-Orange Calcareous Sandstone Description The grayish-orange, calcareous sandstone lithofacies is part of the Ridge Route Fomation, which occurs stratigraphically below the Hungry Valley Formation. This lithofacies occurs at the gradational contact of the Apple Canyon Sandstone Member of the Ridge Route Formation and the Hungry Valley Formation. The 52 depositional environment of the Apple Canyon Member has been described by Wood (1981). The lithofacies is composed of a range of sand sizes from coarse pebbly sand to medium sand. Overall, the unit is poorly-sorted, though individual crossbeds are moderately well-sorted. The composite beds of sandstone make up channelized sequences from 2 to 4 m thick. Individual channelized packets are from 5 to 75 cm thick and from 50 to 250 cm wide (Fig. 16). The beds within each channel are composed of alternating coarse pebbly sandstone and medium sandstone. There are no fining- or coarsening-upward trends in grain size. The topmost beds in a channel sequence commonly contain larger proportions of heavy minerals than the lower beds. The color of the sandstone beds varies from (10 YR 8/2) very pale orange to (10 YR 7/4) grayish orange (GSA, 1975). The orange color is due to the presence of carbonate cement. This lithofacies is exposed as resistant beds which are moderately lithified. Following the Miall (1982) classification, the grayish-orange, calcareous sandstone lithofacies consists of St, Sp, and FI facies. The channels are discontinuous and have poorly defined erosional bases. The erosional bases are convex upward, containing occasional mudstone rip—up clasts. The upper contact of amalgamated sandstone layers are often finer grained and contain unlined Paleophycus burrows. No secondary sedimentary structures nor vertebrate fossils were found in this lithofacies. 53 Figure 16. Gradational contact at the base of the Hungry Valley Formation. The light—orange sandstone beds are assigned to the Hungry Valley Formation and the grayish-orange, calcareous sandstone beds to the Apple Canyon Sandstone. The cliff is 50 m high. 54 Environmental Interpretation Internal structures of amalgamated beds of the grayish-orange calcareous sandstone lithofacies are typically trough-crossbedded sandstone overlain by minor planar-crossbedded sandstone and low-angle planar-crossbedded, fine sandstone. Following the lithofacies and stream model from Miall (1982), this sequence of St, Sp, FI is similar to the South Saskatchewan type river (Fig. 11). This model is considered a distal fluvial environment compared to the coarser-grained proximal units described elsewhere As compared to other units in the Ridge basin, this lithofacies is a finer—grained fluvial deposit. Channelized sequences in the grayish-orange sandstone lithofacies are thin, ranging from 5 to 75 cm thick and from 50 to 250 cm wide. If only minor erosion at the top of each sequence is assumed, then the water flowing in the channels was shallow. There is no basal lag gravel as seen in most bar complexes (Harms et _al. , 1975). This indicates either a lack of gravel in the system or a low flow regime which was incapable of carrying gravel. Since the source areas are nearby it can be assumed that the low competence of the stream is the cause for the lack of gravel deposition. The grayish-orange sandstone lithofacies is associated with lake and pond deposits described later, so a distal fluvial environment is proposed. The mineralogy of this bed differs from the overlying light-orange sandstone. The grayish-orange sandstone lithofacies 56 contains neither heavy-mineral laminations nor the larger clasts common in the overlying beds. The coarsest material deposited in this lower lithofacies is 5 mm in diameter. Yellow-Brown Massive Mudstone Description The yellow-brown massive mudstone lithofacies was originally described by Crowell (1947) as the brown conglomerate member of the Hungry Valley Formation. Crowell (1982) places it in both the Hungry Valley Formation and the Violin Breccia. The yellow-brown mudstone lithofacies is composed of pebble- to clay-size material with a mean grain size of 0.2 mm sand. The lithofacies is moderately well-sorted and well- indurated. A calcite cement creates well-lithified, but easily eroded outcrops (Fig. 17). Much of this lithofacies is covered with Quaternary terrace material and slopewash, so it is best exposed in stream beds and on steep cliffs. The color of this lithofacies varies depending on its stratigraphic position. The older composite beds are greenish gray (5 GY 6/1) to dark yellowish brown (10 YR 4/2). Higher in the section, the unit is composed of dark yellowish orange (10 YR 6/6) packages. There is a gradational change in color up section from yellow-gray to brown. There are rarely any signs of internal structures in this fine-grained unit. A few of the coarser layers show tabular crossbeds due to the concentration of heavy minerals. These Sp 57 Figure 17. Intensely mottled, yellow-brown, massive mudstone lithofacies. Brunton compass used for scale. 58 structures (Miall, 1976) are discontinuous due to cross-cutting burrows* At gradational contacts reflecting grain size variations within the composite beds, there is evidence of bioturbation. The mixed zone of the two grain sizes shows round tubes 1.5 mm in diameter in the lower bed which are filled with grains the size of the overlying bed and vice versa (Fig. 18). Due to the massive nature of the beds, which may in part be due to bioturbation and trace fossils of Paleophycus, there are no clearly defined boundaries to beds. The interbedded conglomerate of the yellow-gray coarse conglomerate lithofacies is the only indicator of size or shape of the mudstone units. There is no graded bedding in the yellow-brown mudstone lithofacies, though there are more pebble inclusions just above the conglomeratic interbeds than elsewhere in the lithofacies (Fig. 19). The only secondary sedimentary structure within this lithofacies is concretionary nodules and lenses. These more lithified carbonate-cemented zones are extremely well lithified. Some of the nodules contain vertebrate fossils which have been replaced by silica. Environmental Interpretation The yellow-brown massive mudstone lithofacies occurs only on the western side of the Ridge basin within the Violin Breccia. Paleocurrent data from contemporaneous deposits to the east and 60 Figure 18. Bioturbation of the yellow-brown massive mudstone lithofacies. Burrows visible at contacts of different colored beds such as at the base of the hammer head and at the top of the blue handle. Hammer is 28 cm long. 61 62 Figure 19 Interbedded layers of yellow-brown massive mudstone and yellow-gray coarse conglomerate lithofacies. Pen is 14 cm long. 63 L 64 west indicate flow towards this lithofacies. The underlying coarse-grained Violin Breccia indicate flows northwestward towards this finer-grained lithofacies. Interbedded light-orange conglomeratic sandstone lithofacies units from an eastern source indicate a southeastward flow towards this lithofacies. The paleocurrent data suggests a trough along the western margin of the basin similar to that described in studies of older deposits in Ridge basin (Wood, 1981). Since finer—grained material was deposited here, it is assumed that the current velocity decreased enough to allow suspended material to settle out. There are no mudcracks or sedimentary structures preserved to indicate that the lake was ephemeral (Glennie, 1970). But the occurrence of Paleophycus trace fossils means there must have been periods when the lake bed was exposed. Bioturbation has disrupted any internal structures which may have previously existed. Interbedded with the massive yellow-brown mudstone unit are beds of the yellow-gray conglomerate lithofacies. These subaqueous debris flows (Gloppen and Steel, 1981) indicate that there was a body of water into which the mudflows were deposited. The flat base of each conglomeratic layer indicates a non—erosional environment. Similar examples of lakes at the toe of an alluvial fan are described by Brookfield (1980). Since the massive yellow-brown mudstone beds are interbedded with the fluvial light-orange sandstone lithofacies, the lake must have varied in lateral extent. In the measured sections, there 65 are five periods when the lake was enlarged as seen by the yellow-brown mudstone lithofacies deposited between two light- orange sandstone units. No shoreline facies (Link, Osborne and Awramik, 1978) or other characteristic features of a lacustrine environment have been preserved. If a shoreline sequence was ever deposited then each time the lake became smaller, a stream must have eroded away the deposit. Yellow-Gray Coarse Conglomerate Description The yellow-gray, coarse conglomerate lithofacies is part of the Violin Breccia. It is composed of interbedded sandstone and conglomerate. From a distance, the unit appears yellow gray, but it consists of multi-colored beds. The sandstone layers and conglomerate matrix vary from yellowish gray (5 Y 7/2) to between grayish yellow and moderate yellow (5 Y 8/4 to 5 Y 7/6). The conglomerate grain size varies from small pebbles, less than 1 cm in diameter, to cobbles over 50 cm in diameter (Fig. 20). Internally the conglomerates vary from massive to well stratified. The well-stratified layers grade either finer or coarser upsection. The cement is calcite, which forms a moderately well-lithified unit. Composite beds of conglomerate are usually about 1 to 3 m thick. They are lenticular-shaped units from 1-10 m wide; the base is nearly flat with a slight convex-upward shape. Individual beds do not appear to erode into 66 Figure 20. Contact between the two Violin Breccia lithofacies. a) Interbedded yellow-brown pebbly mudstone and yellow-gray coarse conglomerate lithofacies from the lower part of the Hardluck section. Up section is to the right side of both photos. Hammer is 28 cm long. b) Close-up showing normally-graded sequence of the coarse conglomerate lithofacies. Hammer is 28 cm long. 67 L_ 68 other conglomeratic beds more than 0.25 m. Commonly there is a slight undulation in the base with irregularities as much as 5 cm thick. The underlying bed does not show flame structures or other loading features so this irregularity may be caused by either loading or erosion. Based on Miall's classification, a typical sequence of sedimentary facies can be described. The basal unit is usually either Gm or Gms, a massive to horizontally-bedded conglomerate fining up to Sm and Sh layers (Miall, 1982). Within one lens the sequence can repeat or reverse upsection. The thicker, more organized lenses contain a coarsening-upward sequence followed by a fining-upward sequence such as Sh, Gm, Sm, Sh in a 0.5-2.0 m thick section. The thinner, less-organized beds of conglomerate are overlain by sandstone in 1 m wide lenses. Neither type of sequence contains laterally persistant beds within an individual large lens. Thick sandstone to pebbly sandstone interbeds have pronounced internal structures. These beds occur at the top of fining-upward sequences. Heavy minerals accentuate the planar crossbeds. Clasts in the conglomerate beds are rounded to subangular with some imbricated layers. The largest clasts are up to 50 cm in diameter. These poorly-sorted beds contain a range of clast sizes up to 50 cm in diameter. Concretions of well-lithified sandstone and conglomerate are present. They stand out of the outcrops as large bulbous mounds 69 usually along a single horizon. They are often bouden-shaped and cross several beds. Bioturbation and trace fossils are visible in the finer-grained layers. Vertebrate fossils and worm tubes resemble those described by Smith et al. (1982) as being from large Paleophycus also are preserved in this lithofacies. Environmental Interpretation The yellow-gray coarse conglomerate lithofacies is composed of lobe-shaped packets of beds. Individual beds are only distinguishable within some lobes. Composite beds are formed of both ordered traction current deposits and ungraded gravity flow deposits. Fining— and coarsening—upward sequences are present within the traction current deposited layers. The flat bottom on individual, poorly-sorted lobes indicates a lack of erosion by the coarse-grained, matrix—supported material (Brookfield, 1980). The better-sorted traction type flows show as much as 0.5 m of erosion into the bed below. This intertonguing of both gravity and traction current deposits is characteristic of an alluvial fan environment (Bull, 1972). Most of the beds contain sedimentary structures of Gm and Gms facies. Minor sandstone beds of St and Sp facies overly some Gm beds. This sequence of facies fits the Trollheim—type model (Miall, 1982) (Fig. 15). The environmental setting proposed for the Trollheim model is a proximal river on an alluvial fan. Steel and Crowell (1983) describes similar deposits in the lower Violin 70 Breccia. They label the most disorganized debris flow deposits as being from viscous mudflows. The more organized conglomerate lobes which contain a graded sequence of beds are from lower-viscosity debris flows (Gloppen and Steel, 1981). Sandstone beds which overlie the massive conglomerate were deposited by the waning stages of flow. The more organized sandstone beds may have been reworked by later water flow down the alluvial fan (Bull, 1972). Light-Brown Cross-Stratified Calcareous Sandstone Description The light-brown cross-stratified calcareous sandstone lithofacies forms steep cliffs and a badlands topography. This calcite-cemented unit is moderately lithified and more resistant than many of the other lithofacies. The grain size of this lithofacies varies from a sandy matrix to cobbles as much as 30 cm in diameter. The pebble-to-cobble conglomerates are poorly sorted, although individual trough cross—beds are often well sorted. Both the massive and stratified conglomerate beds are clast supported (Fig. 21). All beds within the unit are very discontinuous due to intense channel cutting during deposition. Channels are from 1 to 3 m high and as much as 15 m wide. Individual crossbeds can be traced across a channel (Fig. 22). Most commonly, the base of a channel is a concave-upward surface overlain by a basal lag deposit. The basal conglomerate appears massive and as much as 1 71 Figure 21. Channelized sequence in the light-brown crossbedded calcareous sandstone lithofacies. Seated person is 1 m high. 72 73 Figure 22. A single channel sequence in the light—brown crossbedded calcareous sandstone lithofacies. Person is 1.7 m tall. 74 *' •'? m thick. Less commonly, the material at the base of the sequence is a medium—grained sandstone which has a concave-upward bedding pattern. This means that the basal sandstone beds follow the shape of the erosional base. Above the basal sandstone is a massive to horizontally—stratified cobble conglomerate. Within the normally graded channel filling material, there is at least one fining-upward sequence. These fining upward units are from 0.75 to 1 m thick. The finest-grained silty sandstone beds are often brown colored (5 YR 5/6, light brown) (GSA, 1975). Using the Miall classification (Table 1) to describe these sedimentary structures is difficult. For this study, the conglomerate trough crossbeds were catagorized as the Gt classification (Miall, 1982). The deep, narrow channels contain the following sedimentary structures; Gm, Gt, St, Sp, and SI, or Sh. Larger and wider channels often consist of Gm, and Sp sequences with the Gm layer as much as 25 cm thick. Clasts within the conglomerate layers are subangular to subrounded. There is no well-defined imbrication due to the high degree of sphericity. Some beds contain rip-up clasts of yellow-brown and olive—gray mudstone which are as much as 20 cm in diameter. Most clasts of both mudstone and rock fragments are less than 20 cm in diameter. Concretionary layers are abundant, which commonly follow individual cross—stratified beds. Lenses of concretions also are present in 10—20 cm^ thick areas. A well-preserved undetermined 76 vertebrate bone was found in this lithofacies (Fig. 23). Environmental Intrepretation The light—brown, cross—stratified calcareous sandstone lithofacies has similar sedimentary structures to those described for the light-orange conglomeratic sandstone. Individual composite beds are laterally persistent and continuous for as much as 1 km. Vertical sequences of the light-brown sandstone lithofacies are up to 25 m thick. Like the light-orange sandstone lithofacies, the light-brown unit is composed of channels filled with facies Gm, Gt, St, Sp, and Si or Sh (Miall, 1982). The most prevalent bedding structure is the Gt, trough-bedded sandstone with some conglomerate interbeds. Unlike most fluvial models, there are no interbedded, fine-grained units associated with the channelized sequence of beds. Most of this lithofacies occurs above the last deposit of Violin Breccia and the clay-cemented, light-orange, sandstone lithofacies. This facies is considered to have been deposited in the medial fluvial environment similar to the South Saskatchewan model (Miall, 1982) (Fig. 11). It shows neither proximal nor distal facies qualities and is mostly surrounded by the medial fluvial deposited light-orange conglomeratic sandstone facies. Two types of bottom sequences were described earlier. In the first type, the basal portion of a channel unit consists of a conglomeratic lag deposit overlain by a fining-upward sequence. 77 Figure 23. Fossilized vertebrate bone. Brunton compass for scale. 78 79 The second type consists of one event which cut the channel and deposited a well-sorted sand within the channel. Then a later flood deposited a massive gravel deposit and a fining-upward sequence of sediment. Fluvial environments change so rapidly that there is no way to tell if the initial deposition of sand in the channel happened during a storm prior to the filling of the channel by conglomerate or if the original sequence was deposited long before the second set. The clasts are smaller and the matrix is coarser than the light—orange sandstone lithofacies. This reduction in clast size may have been due to a decrease in flow velocity, a finer-grained source rock, or increased distance from the source. Using the sedimentary structure sequences and bedding shapes, it is concluded that this lithofacies was deposited in much the same environment as the light—orange conglomeratic sandstone lithofacies. Both units are mid-to-distal braided-stream facies. The internal structures suggest a similar environment to the present South Saskatchewan River (Miall, 1982). Sandflat and transverse bar deposits can be seen in the cliff face outcrops. No overbank or floodplain deposits are interbedded with this lithofacies, strengthening the argument for a braided-stream environment (Allen, 1966). 80 Calcareous Siltstone Description The calcareous siltstone lithofacies is part of the Apple Canyon Member of the Ridge Route Formation. It is composed of moderately well-sorted grain sizes ranging from fine-sand to silt size. There is no muddy matrix within this unit, but instead a high percentage of carbonate cement. The sand size grains are subangular to angular (Powers, 1953). Bedding is visible at contacts showing grain-size variation and color changes. At these contacts the rock appears mottled due to mixing of the two units. Burrows below the contact are as much as 1.5 cm in diameter, and are filled with material from the upper unit (Fig. 24). Beds of constant color or grain size vary from 0.5 to 65 m thick with most beds approximately 10 m thick. These beds are laterally persistent, and can be trace for up to 1 km. The calcareous siltstone lithofacies varies in color. Individual packets of this unit also vary; usually the mudstone is browner at the top and base of the packet and greener in the middle. The colors of the mudstone vary from (5 YR 4/4) moderate brown to (5 G 5/2) grayish green. Biogenic structures consist of burrows as much as 1.5 cm in diameter which may be from Paleophycus. The base of some beds are irregular and may be due to loading or liquifaction of the layer below. Ostracodes are visible in thin sections cut from this lithofacies. They are 0.5 mm in diameter and quite prevalent. 81 Figure 24. Bioturbated layer of the calcareous siltstone lithofacies. Beds appear massive due to bioturbation. Paleophycus trace fossils are visible at contact where they are filled with greenish-gray, sandy mudstone. Pencil is 15 mm long. 82 83 Environmental Interpretation The red to green calcareous siltstone lithofacies consists of massive units from 5 to 10 m thick. Each bed is continuous for 0.5 km and may extend farther than the exposures. These thick deposits form during long periods of finer-grained sedimentation and indicate a low-energy, uniform environment. These fine-grained beds result from a low-energy depositional system, not due to the available grain size, since beds surrounding this lithofacies are coarse grained. A lake or overbank environment could have created such a low-energy system. Since the beds are thick and, therefore, assumed to have been deposited continuously for a long period of time, a lake environment is more likely than an overbank environment• The occurrence of Paleophycus trace fossils indicates that the lake was not deep (Smith, et al., 1982). Since the beds are more than 0.5 km wide, the lake must have been broad and shallow. No crossbeds are preserved in the layers to indicate paleoflow directions or depth. Both basal and top contacts of calcareous siltstone beds are sharp. There is minor erosion into the mudstone bed by overlying fluvial channels. Irregularities at the base also are due to loading and bioturbation. Such sharp transitions indicate rapid changes in environment. These rapid changes from carbonate-cemented siltstone to clay-cemented sandstone may be tectonically induced. These multiple lake deposits may be due to 84 local folding and/or basinal subsidence. The sediment was being deposited near the present trace of the San Andreas fault and the presence of these small-scale cycles may be related to eposodic movement along the fault. Olive-Gray Micaceous Sandstone Description This fine, silty sandstone unit is poorly exposed due to its susceptibility to generate mudslides. It is a poorly-indurated, clay-cemented unit. The grain size of this moderately well-sorted unit varies from coarse sand to clay size. Color variations within this unit are common. The base and top of beds are browner than the central part. The top and bottom are grayish red (10 R 4/2) to dusky brown (5 YR 2/2), whereas the center is light olive-gray (5 Y 6/1) to greenish gray (5 GY 6/1) to dark yellowish brown (10 YR 4/2). There are no well-preserved sedimentary structures in this lithofacies. Some beds have concentrations of heavy minerals which are horizontally bedded and form climbing ripples (Fig. 25). Individual beds are from 3 cm to 12 m thick. These beds are horizontally persistent and some can be traced for as much as 0.75 km. The basal contact of the olive—gray massive mudstone beds is horizontal. There is a sharp change in grain size from the underlying lithofacies up to the mudstone unit. Some unlined burrows occur along the base. The upper contact is often cut by 85 Figure 25. Olive-gray micaceous sandstone lithofacies. Note the sharp basal contact and heavy mineral laminations. The bottom bed is light-orange conglomeratic sandstone, whereas the upper beds are part of the olive—gray micaceous mudstone lithofacies. Pen is 25 cm long. 86 channels where the overlying unit is fluvial sandstone. Flame structures and irregularities due to loading cause the upper contact of this lithofacies to be deformed. Environmental Interpretation The olive-gray micaceous sandstone lithofacies occurs only on the far eastern side of the study area, near the San Andreas fault. The ripples and fine grain size indicate a low-energy depositional environment (Blatt ^t^ ad. , 1980). The occurrence of Paleophycus trace fossils suggest that the deposits must have been periodically exposed (Smith, ^t^ ad. , 1982). Since no overbank deposits have been preserved in the thick exposures with the many fluvial lithofacies, it is assumed that no overbank areas existed. These interbedded micaceous mudstone beds are clustered on the far eastern side of the basin rather than being spread throughout the basin as might be expected of overbank deposits. Two beds are exposed in Freeman Canyon, seven along the Edison Rd. section and many more along the freeway frontage road to the east. Hence beds of this lithofacies become more numerous eastward. Two styles of deposits occur in this lithofacies. The thin, 10 cm thick beds are laterally continuous for distances as much as 1 km. Thicker beds are less laterally continuous and more prevalent to the east. The thinner beds are considered lake deposits due to their lateral persistence. Thicker, impersistent 88 beds occur most often near the San Andreas fault zone indicating a potential correlation between fault movement and the depositional environment. Most beds of this lithofacies occur east of and abutt against an anticlinal structure suggesting ponding between the fault and a fold. These micaceous mudstone beds are ponded sediment. Since there are no distinguishing features preserved, no specific quiet-water environment can be proven. Pinkish-Gray Cross-Stratified Sandstone Description The pinkish-gray cross—stratified sandstone lithofacies is poorly exposed in much of the area due to a multitude of landslides. The large amount of clay matrix and cement makes this unit susceptible to sliding. Where clean exposures occur, there is a large variation in grain size and sedimentary structures. Unlike the light-orange conglomeratic sandstone lithofacies, this one is not comprised entirely of channel—shaped deposits. Beds vary from shallow channels to horizontal sheet-like deposits. There also is a large variation in mean grain size between adjacent beds. The largest clasts are 10 cm in diameter (Fig. 26). The cementing agent for this unit is clay which creates a poorly-lithified unit. Some resistent beds occur in this lithofacies due to localized carbonate-cemented concretions. The color of this unit varies from (5 GY 6/1) pinkish gray to (5 YR 8/1) greenish gray. 89 Figure 26. Thin discontinuous channelized sequence of the pinkish—gray, cross-stratified sandstone lithofacies. Scale bar is 1 m long. 90 91 Both the conglomeratic and finer units are moderately well sorted. The conglomerate is clast supported and often massively bedded. Well-developed internal structures are present within this lithofacies. Both channelized and horizontally bedded sequences occur. The channel sequences consist of deposits from 1 to 2 m wide and from 1 pebble to 0.75 m thick. These sequences are relatively flat and show only minor erosion at the base. Many channels are entirely filled with massive conglomerate, Gm facies. The horizontally-stratified layers are normally graded. They contain a basal conglomerate overlain by sandstone and fine silty sandstone. Layers within the fining-upward sequences, and the sequences themselves are laterally impersistant. Individual conglomeratic layers can not be traced more than 2 m. The finer sandstone layers are more persistant and can be traced as much as 30 m along strike. The contact between conglomerate and sandstone beds within most channelized sequence is gradational. Following Miall's (1982) classification a typical sequence consists of Gm, Sp, SI or Sh, Sr (rare) (Table 1). A few trough crossbedded layers are visible within the deeper channels. Ripples occur in the finer grained beds which have concentrations of heavy minerals (Fig. 27). Bioturbated zones also occur in the finer-grained beds creating discontinuous sedimentary structures. 92 Figure 27. Climbing ripple marks accentuated by heavy mineral laminations. Knife is 9 cm long. 93 Clasts in the conglomeratic beds are predominantly potassium feldspar-rich igneous rocks from 5 to 20 cm in diameter. Distinctive tuffaceous clasts of light-greenish gray, pale red, grayish-pink and pale blue are present. Within the finer siltstone beds, white nodules of carbonate material from 1 to 2 cm in diameter have formed. These nodules may be altered animal tests or concretions. Concretions and bioturbated zones are the only secondary sedimentary structures observed. No vertebrate fossils were found in this lithofacies. Environmental Interpretation The pinkish gray cross-stratified sandstone lithofacies is composed of normally graded, discontinuously bedded, traction-current deposits. The erosional bases of beds are shallow, concave-upward surfaces indicating a low degree of erosion by overlying units. The internal structure is highly variable, such as clast-supported, conglomerate-filled channel and horizontal sheet-like deposits of fine sandstone. A typical Miall (1982) facies sequence consists of Gm, Sp, Sr and SI or Sh. This fits the Platte River-type model (Miall, 1982) (Fig. 11). Linguoid and longitudinal bars are typically the fluvial deposits of the Platte River model (Miall, 1982). Ripples occur in the topmost beds of some sequence and often contain large numbers of heavy-mineral 95 laminations. This indicates a decreasing-energy system (Cant and Walker, 1976). Most of the channels sequences are less than 1 m thick indicating a shallow fluvial system. The lack of trough-crossbedded sand also indicates a shallow water environment in which dunes were unable to form (Miall, 1982). Normally-Graded Fine Sandstone Description This normally-graded fine sandstone lithofacies composes less than 1% of the measured thickness in all three sections. The fine sandstone beds are from 30 to 150 cm thick and can be traced less than 2 m along strike. The length of individual beds may be longer than the exposures (Fig. 28). Unlike most of the lithofacies in the siliciclastic basin, there are only a few coarse-grained beds. The mean grain size is 0.2 mm in diameter (fine sand). The color of this fine sandstone varies from (10 YR 5/4), yellowish brown to (10 YR 7/4) grayish orange. Heavy-mineral laminations make some beds darker. Internal structures are rare due to intense bioturbation. Disrupted planar-crossbedded heavy-mineral laminations indicate some primary sedimentary structures originally were present. Each bed consists of a fining—upward sequence with the finest bed a claystone; above the finest bed there is a slight reverse grading 96 Figure 28. Fining-upward sequence in the normally-graded siltstone lithofacies. Sequence begins at lower left corner; white bed on the right is overlying this sequence with a sharp basal contact. Orange field notebook is 18 cm long. 97 98 prior to deposition of the coarser-grained overlying bed* Secondary sedimentary structures have formed at the top of the packets. Since the normally-graded fine sandstone lithofacies is always covered by the light-orange cross-stratified sandstone, flame structures occur in the siltstone beds. The top contact is erosional and irregular due to loading caused by deposition of the overlying sandstone. Environmental Interpretation The beds of normally-graded fine sandstone are not traceable for long distances and may only fill single channel sequences. This finer-grained unit must be deposited in a lower-energy environment than the coarser sediment (Friedman and Sanders, 1978). Bioturbation along the top of each sequence also provides evidence of a low-energy and shallow—water environment. These channel-filling deposits may have been deposited far more often than is preserved in the rock record. Many mud rip-up clasts within the light-orange conglomeratic sandstone lithofacies may have been eroded from similar deposits. The Ridge basin is a coarse-grained siliciclastic basin. What may form as a fine-grained abandoned channel fill in a finer-grained system actually may be a coarser-grained siltstone in this setting, since the mean grain size here is larger than in other modeled systems. This lithofacies is correlated with channel—filling sediment after abandonment described by Jackson (1976). This finer unit is only preserved where it was deposited 99 as a thick sequence prior to subsequent erosion. The irregular top of the bed indicates that the next influx of fluvial sand caused much of the siltstone and mudstone to be eroded away. In some cases it is expected that whole sequences of this lithofacies were eroded away, leaving only rip-up clast concentrations in layers of the light—orange coarse conglomerate lithofacies. Matrix-Supported Conglomerate Description The matrix-supported conglomerate lithofacies consists of interbedded light-brown pebble conglomerate and yellowish-brown cobble conglomerate. In outcrop, this lithofacies appears as alternating bands of fine— and coarse-grained conglomerate. Each layer is about 2 m thick. This alternating sequence occurs about 6 times, each layer is traceable for as much as 0.5 km. At a smaller scale, the individual coarse conglomerate layers actually are composite sequences of many lobe-shaped deposits. The finer conglomerate has no internal structure nor any shape of bedding. Slopewash covers the surface of many of the finer-grained beds because of the large amount of silty matrix. The coarser conglomerate beds contain matrix-supported clasts as much as 10 cm in diameter. The lobe-shaped beds have flat bases with no sign of erosion into the underlying bed (Fig. 29). There is a slight thinning on the edges of the beds causing them to be a flattened lobe shape. All contacts around the coarser conglomerate lobes are sharp with no lateral grading. Interbeds 100 Figure 29. Discontinuous alternating beds of matrix- supported conglomerate and pebbly mudstone in the foreground. Bushes in the foreground are about 0.5 m in diameter. 101 102 of the finer, pebble-conglomerate fill the spaces between individual lobes and form the alternating layers within the six sequences. The clast composition of the cobble conglomerate is approximately 60% granitic and metaquartzite and 40% gneiss. Clasts are subangular to subrounded. No imbrication or well developed grading is apparent in individual lobes (Fig. 30). Following Miall’s classification (1982), this lithofacies consists of Gms and Sm facies. All beds are massive and difficult to distinguish from one another. The cementing agent is clay except along concretionary layers. The concretion—rich beds are cemented by calcium carbonate and form well—indurated zones. Cobble conglomerate lobes are more resistent to erosion than the pebbly mudstone layers. This variation in erosion rates causes the alternating re-entrants and prominent cliffs typical of this lithofacies. Environmental Interpretation The matrix—supported conglomerate lithofacies is composed of multiple lobe-shaped deposits which coalesce to form resistent outcrops. The conglomerate is poorly sorted as is the matrix, forming a polymodal, matrix—supported conglomerate (Harms et al., 1975). Each lobe is ungraded and unstratified indicating a debris—flow mode of depositon (Hooke, 1967). Debris flows form at the apex of most fans indicating a proximal source for this 103 Figure 30. Matrix supported conglomerate. View of one of the coarse-grained beds in Figure 29. Hammer is 26 cm long 104 lithofacies (Bull, 1972). There is no internal structure in any of these lobes. According to Mial.1 (1982), this lithofacies is made up of Gms, massive gravel debris-flow deposits. The cyclicity of this lithofacies indicates periods of debris flow activity alternated with finer-grained mudflow deposition. Two small-scale cycles suggest shifting of active lobes. Debris flows were deposited during activity on each lobe. Coarse Yellowish-Brown Conglomerate Description The coarse yellowish brown conglomerate lithofacies consists of interbedded coarse conglomerate and coarse sandstone. Clast size varies from 3 to 30 cm in diameter. These poorly-sorted cobbles are subangular to subrounded with a high sphericity. Internal stratification is visible only on a large scale in the conglomerate beds. Some clast-supported conglomerate beds show minor fining-upward sequences though many appear poorly sorted throughout. Individual beds are lens shaped with a nearly flat base. The beds are as much as 1.5m thick and 10 m wide. The erosional base is always concave upward with less than 50 cm of erosion into the layer below (Fig. 31). Sandstone beds occur only at the top of channelized sequences which fine upward. Not many of the channel sequences contain sandstone layers either due to erosion or non—deposition. The sandstone beds often have heavy-mineral laminae which accentuate 106 Figure 31. Traction current deposited conglomerate. The sandstone interbeds show sedimentary structures. Car is 2 m wide. 107 108 their internal structure. Sedimentary structures visible in the sandstone portions consist of planar and low-angle planar crossbeds (Sp, SI), Minor trough-crossbedded sandstone layers occur at the base of some sequences. A typical sequence in the finer beds is St, Sp, and either SI or Sh, The grain size of the sandstone portions is the same size as the matrix in the conglomeratic beds. Classifying the overall unit according to Miall (1982) yields a typical sequence of Gm, Gms, Sp, and SI (Fig. 32). Nearly 75% of each bed consists of gravel (Gm) the other 25% is coarse sand with planar and low-angle crossbeds (Sp, SI) . The composition of clasts changes gradually up section. The base contains 40% gneiss, whereas the top contains 18% gneiss. Up section there is an increase in amount of granitic rock fragments and hematite stained, well-lithified sandstone clasts. No fossils were found in this lithofacies. Imbrication was not visible due to the high degree of sphericity of most clasts. Environmental Interpretation Like the yellow-gray conglomerate lithofacies, the yellowish-brown conglomerate lithofacies is composed of both traction and debris—flow beds. Both types of sedimentation occurred as intertonging lobes. Bull (1972) considers the occurrence of both methods of deposition to be indicative of an alluvial-fan deposit. 109 Figure 32. Clast—supported conglomerate. Compare this clast—supported conglomerate with the matrix—supported conglomerate shown in Figure 30. Hammer is 26 cm long. 110 Ill The clast—supported, moderately—sorted lobes consist of a fining-upward sequence. The uppermost beds in each sequence are planar and trough cross-stratified sandy beds. These traction deposits may have been slightly reworked by water flowing down the fan. Many sequences have had the top beds eroded away indicating that the overlying deposits were moderately erosive. Lobes of matrix-supported conglomerate are poorly sorted and unstratified. They appear to be from low-viscosity debris flows as the matrix is only a small portion of the deposits which show a fining upward trend (Gloppen and Steel, 1981). Typical sedimentary facies for the lithofacies are and Gm overlain by Sp and St. This fits the Trollheim model of Miall (1982), which is considered a proximal alluvial-fan environment (Fig. 11). Some of the overlying sandstone layers may have been deposited as stream flood deposits (Brookfield, 1980). Lithofacies Associations Background The sequence of lithofacies for each measured stratigraphic section are studied to determine trends in vertical associations (Fig. 33). Then all three measured sections are pooled to determine if there are any lateral lithofacies trends. For simplification the name of each lithofacies is represented by a number (Table 2). 112 m Figure 33. Cross-sectional view of lithofacies in the Hungry Valley Formation. Location of stratigraphic sections shown in Figure 5. 113 Hardluck South 500m n 400 Freeman Edison 3 0 0 - 200- 100- * ; North o oooo; o 0 Q Q o ' r, ° ° O \0 O O O ^ 0 O Q ran / / 7 7 7 W / . (km ) Lithofacies □ °o° S_o Table 2. List of the eleven lithofacies. 115 1 2 3 4 5 6 7 8 9 10 11 Lithofacies Name Light-Orange Congomeratic Sandstone Grayish-Orange Carbonate Pebbly Sandstone Yellow-Brown Pebbly Mudstone Yellow-Gray Coarse Conglomerate Light—Brown Cross—Stratified Calcareous Sandstone Calcareous Siltstone Olive—Gray Massive Mudstone Pinkish-Gray Cross-Stratified Sandstone Normally Graded Fine Sandstone Matrix Supported Conglomerate Coarse Yellowish—Brown Conglomerate Fluvial strata are often cyclic due to large- and small-scale cyclic depositional processes. The small-scale cyclic events occur as lateral migration of a single channel or variation in seasonal rainfall rates. On a larger scale, cycles are caused by sedimentation (Davis, 1973). The results of such an analysis indicate which environments are closely associated and which occur as isolated events. The results of a Markov chain analysis allow one to determine the most probable lithofacies to follow any given lithofacies, which helps to define cyclic sedimentation patterns. An embedded Markov chain method is the one used in this study. It was chosen because a constant sediment—accumulation rate could not be assumed within all lithofacies nor across the basin. In the embedded method, transitions between lithofacies are used to form a transition probability matrix. Thin beds and thick beds are counted equally in the embedded Markov transition-probability matrix. One transition-probability matrix was constructed for each stratigraphic section (Figs. 34, 35, 36). A similar method is employed by Miall (1982) on individual facies in a core. The analysis for this study is done on a larger scale, because the cycles on the facies changes were observed and recorded in the field. The sedimentary characteristics for each lithofacies are discussed in the preceeding set of descriptions. 117 Figure 34. Transition probability matrix and spider diagram for the Hardluck stratigraphic section. 118 Hard! lick 1 2 3 4 5 6 7 8 1 0 0 0.71 0 0 0 0.29 0 2 0 0 1.00 0 0 0 0 0 3 0.03 0.03 0 0.94 0 0 0 0 4 0 0 1.00 0 0 0 0 0 5 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 7 0.50 0 0 0 0.50 0 0 0 8 0 0 0 0 0 0 0 0 4 alluvial fan '0.94 / / 7 ^ 0.29 • , ^ 0.03 3 lake-------------- ^ stream ^ lake 0.50 0-71 o .e j 5 stream stream Figure 35. Transition probability matrix and spider diagram for the Freeman Canyon stratigraphic section. 120 Freeman 6 pond 1 2 3 4 5 6 7 8 9 10 11 1 0 0 0.10 0 0.20 0.60 0 0.10 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0 1.00 0 0 0 4 0 0 0 0 0 0 0 0 0 0 0 5 0.33 0 0 0 0 0 0 0.67 0 0 0 6 1.00 0 0 0 0 0 0 0 0 0 0 7 0 0 0 0 0 0 0 0 0 0 0 8 0.29 0 0 0 0.14 0 0 0 0 0.57 0 9 0 0 0 0 0 0 0 0 0 0 0 10 0 0 0 0 0 0 0 0.80 0 0 0.20 11 0 0 0 0 0 0 0 0 0 0 0 11 alluvial fan 0.2 3 take 0.1 0.6 1.0 ~ w stream 10 debris flow 0 .8' 0.57 0.29 0.1 stream stream 0.67 121 Figure 36. Transition probability matrix and spider diagram for the Edison stratigraphic section. 122 Edison 1 2 3 4 5 6 7 8 9 1 0 0 0 0 0 0 0.36 0 0.64 2 0 0 0 0 0 0 1.00 0 0 3 0 0 0 0 0 0 0 0 0 4 0 0 0 0 0 0 0 0 0 5 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0 7 0.82 0.18 0 0 0 0 0 0 0 8 0 0 0 0 0 0 0 0 0 9 0.86 0 0 0 0 0 0.14 0 0 stream 0.82 0.36 lake 0.86 0.64 0.14 1.0 0. ^ ^stream overbank 123 Hardluck Section The western measured section, Hardluck, is composed of six lithofacies (Fig. 34). The lower part of the section consists of the Violin Breccia, which is represented by lithofacies 3 and 4 the yellow-brown pebbly mudstone and yellow-gray coarse conglomerate respectively. From the tally matrix (Fig. 34), it is shown that there are many transitions from lithofacies 3 to 4 and from 4 to 3. The basal Violin Breccia is predominantly composed of the yellow-gray coarse conglomerate lithofacies (4) with alternating thin beds of lithofacies 3. There is a gradational change upsection from a large volume of lithofacies 4 to a majority of the beds being lithofacies 3. The uppermost part of the Violin Breccia is predominantly composed of lithofacies 3 mudstone with minor units of lithofacies 4. In the upper part of the Violin Breccia, thin beds of Apple Canyon Sandstone interfinger with the Violin Breccia (Fig. 33). At the top of the last appearance of the Apple Canyon Sandstone (lithofacies 2), is an amalgamated sandstone bed of the Hungry Valley Formation (lithofacies 1). The contact between these two formations at this location is a distinct erosional surface which is in contrast to the gradational contacts seen in other parts of the basin. The uppermost Violin Breccia interfingers with the Hungry Valley Formation in the middle of the measured section. This gradational transition from Violin Breccia to the Hungry Valley 124 Formation is shown on the Markov transition probability matrix as multiple transitions between lithofacies 1 and 3. The transition occurs ten times. This set of alternating beds can be traced along strike for nearly 1 km without any variation in thickness. The top half of the Hardluck section is within the Hungry Valley Formation. As mentioned previously, the light-orange sandstone amalgamated beds of lithofacies 1 are laterally and vertically persistant. Within the light-orange conglomeratic sandstone lithofacies, there are only two interbeds of another lithofacies. The olive-gray micaceous mudstone (lithofacies 7) occurs once within the light-orange sandstone sequence and as the overlying bed. Above the second occurrence of lithofacies 7 is a thick, laterally continuous section of lithofacies 5. Lithofacies 5, a light-brown cross-stratificd calcareous sandstone, contains no interbeds of other lithofacies within the section measured. Therefore on the transition probability matrix, the sequence of lithofacies 5 is represented by only 50% probability transition, though it volumetrically forms a major part of the stratigraphic sequence. One major cyclic pattern of bedding was found using the embedded Markov chain analysis on the Hardluck section. This is the persistant transitions of lithofacies from 3 to 4 and 4 to 3. Minor alternations also occur between lithofacies 1 and 3. The common transition between lithofacies 3 and 4 of the Violin Breccia suggests that these lithofacies are environmentally related deposits. Almost all transitions to 3 are from 4 and all 125 transitions to lithofacies 4 are from lithofacies 3. The thick sequences of lithofacies 1 and 5 formed without many interbeds in the Hardluck section, indicating no cyclicity on this scale within the western Hungry Valley Formation. Freeman Section The results of a Markov analysis of the central measured section are shown in Figure 35. Eight of the eleven lithofacies occur in this measured section. The Markov tally matrix indicates that a majority of the transitions occur between lithofacies 1 and 6. This sequence of alternating units occurs at the base of the measured section (Fig. 33). Lithofacies 1 is the light-orange conglomeratic sandstone of the Hungry Valley Formation, whereas lithofacies 6 represents the calcareous siltstone of the Apple Canyon Member of the Ridge Route Formation. This alternating set of beds of lithofacies 1 and 6 represents the interfingering of both formations at the base of the Hungry Valley Formation. In the middle of the Freeman section, the light—orange conglomeratic sandstone lithofacies (1) predominates. As in the Hardluck section, this lithofacies forms thick sequences with few interbeds. Two mudstone beds of lithofacies 6 are the only interbeds in the oldest sequence of light-orange sandstone beds (lithofacies 1). Above the sandstone beds of lithofacies 1 lies a sequence of beds composed of lithofacies 5 and 8. Lithofacies 5, a light- 126 brown cross-stratified calcareous sandstone overlies the light—orange sandstone (lithofacies 1). The light—brown sandstone (5) forms a thin bed which in turn is overlain by lithofacies 8. The pinkish-gray cross-stratified sandstone (lithofacies 8) composes a large portion of the Freeman section (Fig. 33). Within the large sequence of lithofacies 8 there are two amalgamated beds of lithofacies 1 and 5 sandstone. Near the top of lithofacies 8, a yellow-brown mudstone layer similar to lithofacies 3 is exposed• The top of lithofacies 8 grades into the fine portion of lithofacies 10. There is gradational change from predominantly traction to debris-flow transport mechanisms which marks the alter-nation between variation from lithofacies 8 and lithofacies 10. Coarse-grained lithofacies 10 and 11 occur at the top of the Freeman measured section. There is a sharp contact between the matrix-supported conglomerate of lithofacies 10 and the clast-supported conglomerate of lithofacies 11. This transition is from debris-flow deposited conglomerate to interbedded debris-flow and traction-current deposited conglomerates. There are many variations shown on the Markov transition probability matrix for Freeman Canyon. As described above, a majority of these changes occur in the basal transition phase. The rest are singular occurrences scattered amongst the lithofacies. Therefore, the only highly probable transition in 127 lithofacies along the Freeman section occurs at the basal contact of the Hungry Valley Formation which is interbedded with the Ridge Route Formation. Edison Section The Edison stratigraphic section was measured on the eastern side of Ridge basin. The Edison Markov tally matrix indicates three prominant associated lithofacies (Fig. 36). The light-orange conglomeratic sandstone lithofacies (1) was deposited with numerous interbeds of both lithofacies 7 and 9. The most common transition is between lithofacies 1 and lithofacies 7. Lithofacies 7 is composed of olive-gray micaceous mudstone beds. These olive—gray mudstone beds are interbedded with both the Apple Canyon Sandstone of lithofacies 2 and the light—orange sandstone of lithofacies 1. The basal part of the Edison section consists of alternating units of lithofacies 2 and 7. Up section, lithofacies 1 sandstone assigned to the Hungry Valley Formation occurs interbedded with the olive-gray mudstone of lithofacies 7. Both lithofacies form laterally continuous outcrops which can be traced along strike for over 0.5 km. The upper part of the section is primarily composed of vertically continuous light-orange sandstone packets of lithofacies 1. The only variation throughout the upper section involves thin interbeds of normally-graded siltstone from lithofacies 9. Some of the siltstone interbeds contain mudstone layers which have been classified as lithofacies 7. 128 The two cyclic processes of sedimentation are separated, one occurs in the lower part of the stratigraphic sequence and the other near the top. The initial cycle of lithofacies 7 interbedded with sandstone of lithofacies 1 and 2 rarely occur after the initiation of lithofacies 9 interbeds in the lithofacies 1 sandstone. This indicates that the environment of deposition changed over time from a site of deposition of laterally continuous mudstone beds (lithofacies 7) to the deposition of discontinuous fine sandstone beds (lithofacies 9). The sandstone beds of lithofacies 1 do not change up section, though the types of interbeds changed from laterally continuous mudstone to normally graded sandstone. Lateral Correlation Correlation of the three measured sections is difficult. Lithofacies which occur in one measured section are not necessarily found in the next section, making lateral correlation impossible. No marker beds are continuous across the basin other than the basal contact of the Hungry Valley Formation. Altered, nearly pure glass, ash beds are present on the eastern side of Ridge basin, but can only be traced a short distance due to minor faulting and erosion. Since the only marker bed is the base of the Hungry Valley Formation, this contact is used for correlation. It is assumed to be at least parisochronous due to the change in clasts and cement-type. The base of the Hungry Valley Formation is a 129 gradational contact in the Hardluck and Freeman measured sections. The first occurrence of light-orange conglomeratic sandstone is the correlated horizon used here. Crowell (1950) describes the contact at the base of the Hungry Valley Formation as occurring higher in the stratigraphic section. The three sections when placed together do not show any major changes across the basin. Minor changes occur in each section at different thicknesses above the base of the light—orange sandstone (lithofacies 1) (Fig. 33). The cause of this inability to correlate from one side of the basin to the other is due to the major influence of local tectonic variation and the discontinuous nature of braided stream deposits. The San Gabriel fault and the associated Violin Breccia influenced the deposition of strata assigned to the Hungry Valley Formation along the western margin. The sedimentologic processes in Freeman and Edison sections were not directly influenced by the deposition associated with the western margin. Thus cyclic and major changes along the Hardluck section were not observed in the other two sections. Lithofacies 10 and 11 found in the Freeman section, are not exposed in either of the other two sections nor are clasts derived from these lithofacies found in the Hardluck section. This indicates a localized depositional system from a separate source or separate drainage network not connected to the rest of the basin. 130 Pi scussion The purpose of the Markov transition matrix is to find cycles in sedimentation and to determine associated lithofacies to aid in interpretation of the depositional environment. The transition-probability matrices in Figures 34, 35 and 36 indicate the probability of each transition within each of the three measured sections. Four major sets of transitions were determined from the analysis. The common transition in the Hardluck section is between the fine-grained and coarse conglomerate lithofacies of the Violin Breccia (Fig. 33). From field observations it has been determined that the conglomeratic lithofacies 4 represents alluvial deposits, whereas the lithofacies 3 represents lacustrine deposits. Frequent alternations between alluvial-fan and lacustrine deposits indicate that the alluvial-fan toe was immediately adjacent to the lake. The transitions probably are due to shifting lobes on a fan—delta which periodically deposited sediment into the lake. In the central section, the major transition occurs at the contact between the Apple Canyon Sandstone Member of the Ridge Route Formation and the Hungry Valley Formation (Fig. 33). It has been shown that the Apple Canyon beds of lithofacies 6 are lake deposits. These lake deposits alternate with beds of lithofacies 1, the fluvial sand of the Hungry Valley Formation. The alternating beds of lake and stream sediment with no shoreline or delta deposits indicate that the lake was shallow and ephemeral. 131 Numerous braided streams prograded over the lake and then were covered hy later lake deposits. The transition-probability matrix for the Edison section indicates two sets of transitions. The initial one consists of alternating beds of lithofacies 2 and 7 which change to 1 and 7 at the base of the Hungry Valley Formation (Fig. 33). The transitions between 2 and 7 represent the changes from braided-stream to lake or pond deposits. This is the same set of environments as the transitions between 1 and 7, except lithofacies 1 is more proximal braided-stream deposits than lithofacies 2. Upsection there are no lithofacies 7 interbeds, and instead lithofacies 1 is interbedded with lithofacies 9. According to field observations, lithofacies 9 is an abandoned channel-fill deposit. Therefore the interbeds of lithofacies 9 within the braided-stream deposits of lithofacies 1, indicate that channels were abandoned long enough to allow for infilling and then not eroded away by the next braided stream flowing over the area. The rapid change from ponds to abandoned channel fill as interbeds also indicates a change in local topography so that ponding was no longer possible. The Markov transition-probability matrix aided in refining the depositional environments. A better understanding of changes between environments is possible by estimating the frequency of transitions between associated lithofacies. Many of the 132 lithofacies in this study showed no cyclic variation on a lithofacies scale indicating a constant environment during deposition. The lithofacies are summarized in Table 3. For clarity in summarizing the results, the data has been broken down into the three stratigraphic sequences. Hardluck Section Depositional Environments The sediment in Hardluck section is assigned to both the Violin Breccia and Hungry Valley Formation. Volumetrically the most prevalent units are coarse debris-flow and traction—current deposits of an alluvial fan and coarse sandstone braided bar sequences. A Markov analysis indentifies the main transitions are between lithofacies 3 and 4 with some transition between lithofacies 1, 5 and 7 (Fig. 34). The oldest lithofacies exposed is the yellow—gray coarse conglomerate lithofacies 4 which was deposited on an alluvial fan. The interbedded finer units of lithofacies 3 represent lake deposits. The interfingering of the lake and coarse alluvial-fan deposits indicates that the western edge of Ridge basin was a lake into which an alluvial fan complex associated with the San Gabriel fault scarp deposited material. Since the lake beds deposits are so intensely bioturbated, no sedimentary structures are preserved to aid in determining water depth. The Paleophycus trace fossils in beds of lithofacies 3 and the fact that overlying debris-flow deposits have only minor erosional bases, suggests that the lake 133 Table 3, Summary of sedimentological characteristics of each lithofacies. 134 Lithofacies Lithology Bed thickness Lower boundary Miall Associated facies Environment Light-orange Conglom eratic Sandstone 1.5-53 m erosional G m , St, Sp, ShorSl 2, 3, 5, 6, 7, 8, 9 Lithofacies 2 Grayish-orange Carbonate Pebbly Sandstone 2-4 m erosional St, Sp, FI 3, 7 Transverse bar and sand- Linguoid and longitudi- wave braided stream nal bar, braided stream deposits , deposits Lithofacies Li thology Interbedded sandstone Fine sandy siltstone and cobble conglomerate Bed thickness Lower boundary Miall Associated facies Envi ronment 1-3 m 0.5-65 m erosional depositional G m , Gt, St, Sp, SI or S h massive 1, 7, 8 1, 2 Transverse bar and sand- Sag ponds wave braided stream deposits 3 4 Yellow-brown Pebbly Mudstone 0.5-2 m depositional 1, 2, 4, 8 Shallow, ephemeral lake 7 Fine s ilty sandstone 0.03-12 m depositional massive G m 1. 2, 5, 9 Shallow ephemeral lake Yellow-gray Coarse Conglomerate 1-3 m erosional G m , S m , S h 3 Traction and debris flow from medial a llu via l fan 8 Interbedded fine sand stone and clast supported conglomerate 0.05-0.75 m erosional Sp, SI or Sh, Sr (rare) 1, 3, 5, 10 Linguoid and longitudi nal braided stream deposits (Lithofacies Continued) Lithofacies Lithology Bed thickness Lower boundary Miall Associated facies Environment 9 Normally Graded Fine Sandstone 0.3-1.5 m gradational S p 1, 7 Abandoned channel f i l l in braided stream 10 1 1 Matrix supported Coarse Yellowish-brown conglomerate Conglomerate 2 m >1.5 m depositional erosional G m s, S m G m , G m s, St, Sp, SI 8, 11 10 Debris flew from proxi- Traction and debris flows mal a llu via l fan from medial a llu v ia l fan was very shallow. Upsection there is an increasing number of lake deposits along with fewer and thinner beds of coarse conglomerate. The uppermost beds of the coarse-grained lithofacies 4 are all matrix-supported conglomerate. Beds downsection contain more traction-current deposits, and the base of the measured section is composed predominantly of traction-current deposits of lithofacies 4. The increased quantity of lake deposits upsection shows that there was a decreasing amount of coarse-grained material supplied to the western alluvial—fan complex, which reduced the area of the fan. This smaller fan provided space for a lake to form and enlarge westward. Older units studied by Wood (1981), Smith (1982), and Link (1982) describe the axis of the basin to be along the western margin of the basin. The occurrence of a lake supports this idea during Hungry Valley deposition and shows that until the end of movement on the San Gabriel fault, there was a trough of low relief (the basinal axis) along the west side. Since the amount of coarse material in the Violin Breccia decreases over time, either the supply of debris was decreasing or the lobes shifted. Nowhere in the basin are remains of coarse alluvial—fan deposits in the upper portion of the Violin Breccia, so it is assumed that the decrease in alluvial-fan deposits is due to a decreased supply of debris. The vertical movement on the San Gabriel fault was decreasing as the fault became less active. This would have allowed the steep scarp to erode, creating less 137 material for deposition into Ridge basin. With the end of fault movement, there would have been the loss of source, and the end of deposition of coarse alluvial-fan deposits of the Violin Breccia. The uppermost lake deposits interfinger with the fluvial sand of the Apple Canyon Member and Hungry Valley Formation (lithofacies 2 and 1). This indicates an increase in sediment input from across the basin as shown by paleocurrents or a decrease in lake size due to a change in basin shape or water input. Since the lake and fluvial beds are interbedded either an increase in volume of fluvial sediment or decrease in water supply are possible causes. Changes in basin configuration would produce more permanent changes in sedimentary environments. An increase in the rate of supply of the Hungry Valley fluvial sand due to tectonics is chosen as the cause of environmental changes. The last intermittent lake deposit coincides with the initiation of a continuous deposit of lithofacies 5, the carbonate-cemented fluvial sandstone. The fluvial sand in the middle and upper parts of the measured section are classified as lithofacies 1 and 5. Following the Miall classification, these two units are similar to the Donjek and South Saskatchewan models which are medial to distal fluvial facies. Deposition along the western section indicates three separate periods of deposition (Fig. 33). The initial one consists of alluvial fans bounded by a lake on the east. The next phase indicates fluvial deposits interfingering with the lake on its 138 eastern side. This was followed by a third phase of entirely fluvial deposition derived from the eastern sources flowing toward the western margin of Ridge basin. Freeman Section Depositional Environments The Freeman Canyon section of the Hungry Valley Formation is represented by eight lithofacies. The basal depositional environment is lacustrine and is followed by fluvial and then alluvial—fan deposits in a prograding sequence. The Apple Canyon Member occurs at the base of the measured section. The environment characterized by this lithofacies (2) is a shallow lake. No deltaic or shoreline deposits have been preserved to indicate a major change in relief or basinal configuration. Wave ripples defined by heavy-mineral laminae are preserved to indicate deposition above wave base. Therefore the lake was probably quite shallow. The alteration of fluvial and lacustrine deposits indicates that minor lowering of lake-level would result in fluvial progradation. At the top of this alternating zone, the fluvial beds are thicker and the lake beds much thinner, which shows that the influx of coarse sediment was filling in the basin, so there was no depression in which to form a lake. The lake deposits along the western margin are coarser-grained than those in the central section. This difference in grain size may be due to different locations within the lake, the western margin was closer to a coarse source. The 139 variation in grain size may be because the deposits are from two separate lakes with different hydrodynamic regimes. According to sedimentary structures, sediment was deposited by two fluvial environments in the central section of Ridge basin. The older fluvial deposits are coarse-grained, braided—stream deposits of transverse bar and sandflats. The younger deposits consist of finer-grained, more-distal linguoid and longitudinal bars . The youngest unit in the Freeman section consists of coarse-grained beds of lithofacies 10 and 11 (Fig. 33). These deposits produce a coarsening—upward progradational sequence of an alluvial-fan environment. Traction-current deposits are present within individual lobes, however, a decrease in traction-deposits occurs upsection. There is an increase in thickness and coarseness upsection of the coarse-grained alluvial-fan lithofacies. The basal beds of the alluvial-fan sequence are alternating pebbly mudstone layers and matrix—supported conglomerate. The conglomeratic lobes are discontinuous, although they are concentrated in bands which from a distance look like beds. These debris-flow deposits are overlain by a sequence of conglomerate which is predominantly of traction-current origin. The change from fluvial traction-current deposits to debris-flow and back to dominantly traction deposits indicates that changes occurred in the source area for the fans. Debris-flow deposits 140 are most commonly found in the apex of a fan, while the interbedded traction and debris-flow deposits form along the mid-fan (Bull, 1972). This alluvial fan was derived from Frazier Mountain according to the clast composition and previous studies by Crowell (1952). The uplift of Frazier Mountain was caused by the Frazier Mountain thrust fault located at the northwest corner of Ridge basin (Fig. 4). Since the alluvial fan deposits show a progradational sequence of deposits, the mountain must have risen rapidly and then eroded back. Such a sequence of events would cause proximal debris-flow deposits to be deposited on top of fluvial sediments. Then as the mountain wore back, the deposition of more distal facies would occur at the same location. Overall, the sequence in the Freeman section is progradational. The base of the section is lacustrine deposits overlain by fluvial deposits which in turn prograde into alluvial-fan environments. Edison Section Depositional Environments The eastern section is composed of four lithofacies. The Apple Canyon Sandstone Member occurs at the base of this section and is overlain by the Hungry Valley Formation. The contact between the two units is quite sharp compared to that seen in the Freeman section. 141 Three sets of lithofacies have been along identified the Edison section. Lithofacies 2, the carbonate-cemented sandstone of the Apple Canyon member, is the main rock type of the basal Edison section. It forms laterally continuous beds which are interbedded with lithofacies 7 mudstone. There is nearly an equal thickness of beds of the mudstone and the sandstone. Both types of beds are thinner than the ones exposed in the Freeman section. This may be because the lake, which deposited lithofacies 7, had a higher sedimentation rate near the Freeman section. The difference in bed thickness may be due to different locations around the lake. For example, if there were higher sedimentation rates along the margin of a lake, then the Edison exposures may have been toward the center of the lake whose western margin was located near Freeman Canyon. Beds of the Hungry Valley sandstone occur stratigraphically above the alternating lake sediment and Apple Canyon fluvial sandstone. These amalgamated Hungry Valley Formation sandstone beds are thicker than the Apple Canyon beds and contain coarser clasts. The olive—gray mudstone beds of lithofacies 7 are less frequent and thinner upsection. The sequence upsection is progradational from the fine fluvial Apple Canyon to the coarser Hungry Valley Formation. The third sequence in the Edison Road section shows a change in the character of interbeds. The light-orange sandstone has a constant grain size distribution and clast types, but the olive—gray, fine-grained beds of lithofacies 7 no longer occur. 142 The interbeds between white sandstone are brown siltstone with a graded base of lithofacies 9. The siltstone is conformable at the base with the white sandstone of lithofacies 1 and has an erosional top. The overlying light-orange sandstone beds often contain rip—up clasts of the siltstone interbeds. This sequence of alternating beds of lithofacies 1 and 9 is considered to be a period during which sediment—filled channels were abandoned, and finer overbank material was deposited. In order to preserve such a deposit, there must have been a decreased rate of channel migration. Thick overbank deposits had to form prior to new channel formation at a given location, otherwise the fine unit would be completely removed by renewed channel erosion. This decreased rate of channel migration may have been due to a decrease in source material or water and/or basin configuration. As these overbank deposits have not been observed in the other two measured sections, the eastern margin of Ridge basin may have been raised above the western side and had fewer streams flowing southward so that large quantities of overbank material were able to settle out and not be eroded away. The three types of environments along the Edison section show a change from lacustrine to fluvial environments. The basal part of the section shows alternating lake and stream deposits. Up-section the stream deposits become more proximal and the lakes more ephemeral. The third section contains no lake deposits and 143 is entirely composed of stream and overbank deposits. This change in environments are caused by changes in basin configuration due to tectonics. Grain-Size Analysis Background Eleven lithofacies were identified through field observations. To determine if the eleven divisions were deposited by different hydraulic regimes a grain-size analysis of most lithofacies was completed. Grain-size analysis has been used to indicate the depositional environment, as well as to show the textural difference between lithofacies (Pessega, 1957, Visher, 1972, and Friedman, 1967). Methodology Grain-size analysis of 41 samples was conducted to assist in defining separate lithofacies. Samples of 100 grams were disaggregated and wet sieved over a 4 phi screen. The clay—cemented samples were disaggregated in cold water. Calcium carbonate—cemented samples were disaggregrated by soaking in a solution of 10% HC1 and then wet sieving. All samples were dried in an oven at 100°C for 30 minutes after being sieved. The wet sieving and then drying procedure removed the clays, allowing grains to be mechanically sieved without a clay coating and making the grain size measurements more accurate. After drying, each sample was dry sieved for 15 minutes on a Fisher-Wheeler sieve 144 shaker. The set of sieves ranged from -2.0 phi to 4.0 phi in a 0.5 phi interval. The resulting grain-size distribution data was analyzed using statistical and graphical methods. Graphically the plots of data from this study were compared to those of Visher (1969), Friedman (1967), and Passega (1957). Results The grain-size distribution data is separated into the previously identified eleven lithofacies for discussion (Table 3). Grains from -2.5 phi to 4.0 phi size fractions are the only material analyzed from each lithofacies. Therefore, measurements from the conglomerate units show only the distribution of the sandy matrix. The range of moment measures for each lithofacies is shown in Figure 37. Samples grouped into lithofacies 1 have a mean grain size of 0.7 phi and a standard deviation of 1.4 to 1.8 phi. All measured samples are positively skewed. Lithofacies 2 has a mean grain size of 2.25 phi and a standard deviation of 0.7 to 1.6 phi. A comparison of lithofacies 1 and 2 samples indicates that lithofacies 2 is finer grained and better sorted than lithofacies 1. Lithofacies 1 is poorly sorted, whereas lithofacies 2 is moderately sorted (Friedman, 1962). The third lithofacies, the yellow-brown pebbly mudstone yields a mean grain size of 2.25 phi with a standard deviation of 145 Figure 37. Graphs showing variation in moment measure results of each lithofacies. The three moment measures are mean phi, standard deviation and skewness. 146 ekewneee o o o 01 * m CD <0 o ro W * u» 0) - « j CD (0 -P - "J etandard deviation mean (phi) -% m o * 1.41 phi. This is similar to the distribution of the Apple Canyon Sandstone (lithofacies 2) and is better sorted than lithofacies 1. Both lithofacies 2 and 3 have positively and negatively skewed samples. Sandstone beds and conglomerate matrix within lithofacies 4 were analyzed. These beds have a mean grain size ranging from 0.1 to 0.9 phi and a standard deviation of 1.5 phi. The sand of lithofacies 4 is poorly sorted compared to the other lithofacies and consists of a range of grain sizes. Lithofacies 5 has a slightly coarser grain size distribution than lithofacies 1 with a mean grain size of 0.5 phi and a standard deviation of 2.0 phi. It is a very poorly-sorted unit (Friedman and Sanders, 1978), which is positively skewed to the same degree as lithofacies 1. Lithofacies 6, mudstone beds within the Apple Canyon Member of the Ridge Route Formation, is a fine-grained unit. The mean grain size is 0.1 phi with a 1.2 phi standard deviation. This unit is moderately sorted (Friedman, 1962), and much finer grained than the previously mentioned units. The plot of all samples from lithofacies 6 show that they are negatively skewed. Lithofacies 7 samples plot with a wide variation in all three moment measures. The mean grain size varies from 1.0 phi to 4.0 phi and a standard deviation from 0.3 to 1.5 phi. Most of the samples are negatively skewed, but one shows positive skewness. The range in standard deviation shows some samples are very well 148 sorted, whereas others are poorly sorted. Lithofacies 8 is fine grained with a mean grain size of 2.5 phi. The standard deviation is similar to that of lithofacies 2 and 6, 1.25 phi, which is moderately sorted (Friedman and Sanders, 1978). Like lithofacies 6, lithofacies 8 is negatively skewed. The samples from lithofacies 9 are slightly coarser than lithofacies 6 and 8, but finer grained than the sandstone beds of lithofacies 1 and 5. The mean grain size of lithofacies 9 is 2.5 phi. It is a poorly-sorted unit as shown by a standard deviation 1.75 phi (Friedman, 1962). All samples from lithofacies 9 are negatively skewed. The coarse conglomerate of lithofacies 10 was analyzed using only the matrix and pebble-size clasts. The matrix of lithofacies 10 is moderately coarse grained xzith a mean grain size of 1.0 phi. As is expected in a matrix-supported conglomerate, the matrix is poorly sorted with a standard deviation of 1.7 to 2.0 phi. The samples are evenly divided between positive and negative skewness. There is a large overlap of moment-measure values between lithofacies. From grain-size analysis alone, these eleven lithofacies are not separable. Three groups are indicated by standard deviation values and can not be separated further using mean or skewness (Fig. 37). From standard deviation values alone, lithofacies 5 and 10 show high values (2 phi), lithofacies 1, 3, 4, 9 are intermediate with 1.6-1.8 phi and lithofacies 2, 6, 7 and 8 have lower standard deviations than the rest. 149 Discussion Moment measures from the grain—size analysis are not distinctly different for each of the eleven lithofacies. In order to analyze the grain size distributions and distinguish environments, three commonly used methods of analysis were attempted. The first method follows that outlined by Visher (1969). The grain-size distribution of individual samples is plotted on log probability paper (Fig. 38). According to Visher (1972), the plot of fluvial deposits is distinctive with inflection points separating saltated and suspended sediment at 2.75 to 3.5 phi respectively. Data from this study does not follow the model shown by Visher (1972). Since the sediment in lithofacies 1 and 5 is so coarse-grained, a distinctive inflection point commonly occurs at a grain size coarser than 3 phi. Within the lithofacies whose sedimentary structures suggest fluvial deposition, there is a large variation in location of inflection points. Some plots show 3 or more inflection points whose sedimentological significance have not been described by Visher. These multiple inflection points may be a sign that more than one fluvial population is being sampled. For example, the washing out or later addition of fines may change the shape of the grain-size log probability plot. Another possiblity is that the flow energy in this study is higher than those sampled by Visher. Streams with a higher flow regime carry larger particles in suspension (Blatt, et al., 1980). Streams with high flow regime would plot 150 Figure 38. Visher plots of lithofacies. a) Visher, 1972 b) Hungry Valley Fm. Fluvial c) Hungry Valley Fm. Alluvial Fan d) Hungry Valley Fm. Lacustrine 151 99.99 99.8 98 Vish«rCI972) Fluvial 90 70 50 30 0 4 Fluvial HtHafaeias 1 ----- 2----- 5 ----------- • ----- phi 99.99 9 9 .8 98 90 70 30 0.1 -2-1 0 I 3 phi Alluvial Fan WtfeufaciM 4 ------ 1 0 ------ Lacuttrine ttth ffacits 3 ------------- 6 ____ 7 ------------- 9 ----------- 09. 99, 99.8 98 90 70 50 30 2 1 2 3 4 PM 99.99) 99.8 98 90 70 50 30 2 I 0 I 2 3 153 with an inflection point moved to a coarser grain size on a Visher diagram. Comparison of the grain-size distributions from this study and the idealized model shows a different proportion of grain sizes. Samples measured in this study have more fine and coarse material and less medium sand—sized particles than Visher's (1972). Friedman (1961) uses bivariate plots to designate separate depositional environments. Since there is such a wide range of moment-measure values within a specific lithofacies, the environmental groupings in this study are ambiguous (Fig. 37). In his original data analysis, Friedman (1967) chose not to include coarse-grained fluvial deposits, because they were both positively and negatively skewed. In this study, the light-orange and light—brown Hungry Valley Formation sandstone beds of lithofacies 1 and 5 are positively skewed, whereas fluvial sediment from lithofacies 2, 7, 8 show both positive and negative skewness. With such a high degree of variation in the moment measures, these bivariate plots were not helpful in distinguishing separate environments such as stream deposits from lake sediments. A third commonly used method of analyzing grain size data for environmental recognition is from a Pessega diagram (Pessega, 1962). There are many different Pessega diagrams in the literature (Pessega, 1957; Blatt jit_ al_. , 1980; Bull, 1972), which 154 all look similar at first glance. The "s"-shaped portion, the field in which the fluvial-derived sediment should plot, is located at different values for different studies (Pessega, 1964, 1957). The Pessega plot used by Bull (1972) for recent alluvial fans correlates well with data from this study. Samples of lithofacies 1 have the same M parameter as Bull (1972) and a coarser C-size fraction (Fig. 39). The finer-grained lithofacies such as lithofacies 6 and 8 plot in undesignated fields of the Pessega diagrams. These anomalous points are due to the pebble clasts found in the Hungry Valley mudstone units (Fig. 25). The coarsest one percent by weight of a mudstone may reflect the minor volume of pebbles in the deposit. Such deposits with a minor coarse fraction change the location of the point on the Pessega diagram considerably. With modification of the location of the fluvial field by Bull (1972), the Pessega diagram can be used to aid in environment determination. Mudflow and stream channel deposits are separable from lacustrine deposits by means of this plot. The textural analysis using the Pessega diagram in conjunction with field observations helps to identify the depositional environments of the many lithofacies within the Hungry Valley Formation and Violin Breccia. The grain-size distributions for each of the lithofacies helps to determine their different environments of deposition. Of the three methods used for interpretation, only the Pessega and 155 Figure 39. Pessega diagram of data from this study. C is the grain size of the coarsest 1% and M is the median grain size. Unlabeled fields are not defined by Bull (1972). 156 C (m icrons) 10,000 00 A ^*0' XyX XXA 1000 ■ X braldsd strtant A alluvial fan 1 0 0 100 10,000 1000 M (microns) Visher plots were useful. The data was too scattered to use the bi-variate plots described by Friedman (1967). Results from the Visher diagram indicate that the mean grain size of the lacustrine deposits is smaller than that of the alluvial-fan lithofacies. There is a large variation in mean grain sizes of different fluvial deposits (Fig. 38). The more proximal units have a mean grain size of —1.0 phi while the distal lithofacies have values down to 3.0 phi. The Pessega diagram from Bull (1972) shows differences in location of points for different grain size (Fig. 39). The proximal fluvial samples have the coarsest median grain size, while the more distal fluvial, alluvial-fan, and lacustrine samples have a lower M values. None of the samples fall in their proper field because of the coarseness of the one percentile portion. Paleocurrent Analysis Background Paleocurrents from the non-bioturbated lithofacies were measured to gain better understanding of the sediment dispersal system associated with deposition of the Hungry Valley Formation. The overall pattern of current directions aids in defining the shape of the basin and the direction of flow during deposition of the Hungry Valley Formation. Changes in paleocurrent directions over time is one of the best indicators of changes in basin morphology and sources. 158 Methodology Over 350 paleocurrent measurements were taken in the three measured sections for this study. All measurements were from unidirectional structures, trough, and planar crossbeds. Since the formations are poorly lithified, the only three-dimensional exposures of crossbeds available for measuring are irregularites in the sheer cliffs. No bedding surfaces are exposed sufficiently to aid in measuring trough axes of the trough crossbeds. Both planar and trough crossbeds have been measured wherever a three dimensional view was exposed. Each field measurement was converted to original horizontality using a Wulf net, as outlined by Potter and Pettijohn (1977, p. 371). Graphical representation of the paleocurrent data is shown in the form of rose diagrams for each amalgamated bed (Fig. 40). The rose diagrams and vector means and consistency varies for each amalgamated bed were constructed following the method described in Potter and Petti;john (1977, p. 375-376). Re s ul t s Rose diagrams of the paleocurrent data show a high degree of dispersion. In a fluvial environment, a high degree of variation is to be expected (McLean and Jerzykiewicz, 1978). Fluvial deposits within channels bend around obstructions such as bars and islands. At any spot along the river, the deposits may be 159 Figure 40. Rose diagrams of paleocurrent measurements. Data are summarized from the Violin Breccia and the Hungry Valley Formation along the Hardluck, Freeman and Edison stratigraphic sections. 160 Edison n = 1 42 San M h Fault L = 25% GORMAN Freeman n = 98 L 1 3 1 % Dry Creek Hardiuck n : 36 L =14% i mile Violin Breccia n r 52 L ^ 47% 161 produced by water flowing as much as 90° away from the trunk stream direction (Williams and Rust, 1969). High and Picard (1974) demonstrate that planar and trough crossbeds differ in their degree of accuracy for use in determining paleocurrent directions. Planar crossbeds give a unimodal direction of flow which may be oriented as much as 50° away from the main channel direction (McGowen and Garner, 1970). Trough crossbeds, if measured along the axis yield a ±25° dispersion around the true channel direction (High and Picard, 1974). Observed paleocurrent directions were measured on limbs of trough crossbeds, yielding a bimodal distribution. According to De Celles et al. (1983), if more than 15 measurements are taken, the paleoflow direction can be determined within ±25° of the correct value using measurements on the limbs of trough crossbeds. To reduce the error, as many measurements as possible were taken on each bed or unit. Discussion The three measured sections show mean vectors which vary in paleoflow directions (Figs. 7, 8 and 9). Looking at these changes within an individual stratigraphic section and across the basin provides information concerning the drainage pattern during deposition of the Hungry Valley Formation. Variations (<30°) in vector means were ignored due to the large dispersion expected in fluvial and alluvial-fan depositional environments (Williams and 162 Rust, 1969). Over 100 paleocurrent measurements in the western section were derived from 8 beds. Two distinct directions of flow are indicated from the paleocurrent data. The lower part of the Hardluck section consisting of Violin Breccia, has a mean vector of N.22°E. This flow direction is perpendicular to the San Gabriel fault scarp, from which the unit was derived. The slight variation in vector means (<30°) observed in adjacent beds is attributed to the radiating flow pattern of streams off an alluvial fan (Figs. 7, 8 and 9). The second direction of flow is associated with the light-orange and light-brown sandstone beds assigned to the Hungry Valley Formation. The vector mean of these beds indicates a S.77°E. direction of transport. This eastward flow direction suggests that the streams flowed nearly parallel to the San Gabriel fault. Therefore the basin gradient must have sloped down toward the southeast. Previous studies indicate that prior to deposition of the Hungry Valley Formation, the basin axis was along the western side of Ridge basin (Hollywood, 1981; Smith, 1982). Paleocurrent results from the Hardluck section indicate that this trough may have continued to exist throughout deposition of the Hungry Valley Formation. Measurements on western beds deposited after cessation of the San Gabriel fault also indicate a S.77°E. direction of 163 paleoflow. Thirteen separate amalgamated beds were measured in Freeman Canyon section. The 98 paleocurrent measurements throughout the section can be grouped into three separate directions according to stratigraphic position. The oldest set is at the gradational contact between the Apple Canyon Sandstone Member and the Hungry Valley Formation which indicates a S.5°W. flow direction (Fig. 8). Upsection the paleocurrent direction gradually shifts from south to southeast to east. Even younger beds in the Freeman Canyon stratigraphic section yield N.65°E. paleocurrent directions. This apparent shift from southwest to northeast paleoflow directions indicates at least a local and perhaps a basinwide change in morphology. Freeman Canyon is presently near the center of the crosssection of the basin. Yet during deposition of the Hungry Valley Formation, the axis of the basin was further west. Older units in the Ridge basin indicate that the deepest part of the basin was on the far western side (Crowell, 1952). This observed shift in paleocurrent directions in the Hungry Valley Formation may indicate a change in basin configuration causing a shift of the depositional axis perhaps due to local folding. A shift in the depositional axis may have been caused by warping of the basin from the west to the east in response to movement on the San Andreas fault or from infilling of the western side of the basin. Another possibility is that the change in drainage direction 164 in the Freeman Canyon measurements may be due to local variations in the basin topography due to folding or faulting. There is evidence of anticlinal folding during deposition of the Hungry Valley Formation along the Edison section. The granitic cored anticline at the base of the Edison section shows on-lapped Hungry Valley sediments indicating that folding occurred during sedimentation. Such folding could have created topographic obstructions in the older drainage network. New channels would form around an tiplifted area; in the measured sequence these diverted streams may have flowed eastward. The youngest beds in the Freeman stratigraphic section constitute the third set of paleocurrent directions. The measurements are all quite consistent, indicating a N.75°W. flow direction. This direction is nearly perpendicular to Frazier Mt. which is probably the source of the clasts. Therefore Frazier Mt. either was not the source of this alluvial—fan deposit, or else the data was obtained from the west side of lobes on the alluvial fan. Since the clasts match those presently exposed in the Frazier Mt. thrust, it is assumed that the anomalous vectorial directions are due to the high variability of paleocurrent directions on an alluvial—fan surface. Another cause for the unexpected flow direction is that most of the measurements were taken on planar crossbedded structures which can be oriented as much as 50° away from the main flow direction (McGowen, and Garner, 1970). 165 The Edison section contains 142 measured paleocurrent directions. The older beds in the section indicate a consistent S.43°E. flow direction. The younger beds show a S.25°W. paleocurrent pattern. This variation in flow direction may be due to changes in the basin configuration or simply from folding of the granitic-cored anticline located at the base of the section. Since the only correlative horizon in the three measured sections is the base of the Hungry Valley Formation, it was used as a datum for comparing paleoflow directions in different parts of the basin. By comparing paleocurrent results across the basin at such a single time horizon, a better understanding of the basin shape is possible. The eastern stratigraphic section and the central one are a short distance apart, yet the direction of stream flow is quite different in these two observed sections. Further upsection the mean vectors indicate convergent flow from the two locations. Streams along the Freeman section flowed westward while streams along Edison section flowed eastward (Figs. 8 and 9). Both sets of paleocurrents have a southward component of flow indicating that the basin outlet was to the southwest. There are two possible causes for this convergent flow. One possibility is that local irregularities in the basin topography formed a low area between the observed sections, creating a tributary drainage system. The other plausible cause is a shift in the basin axis due to major folding or uplift along the western margin. 166 The western exposures of the Hungry Valley Formation consistently produce paleocurrent data indicating that the streams flowed southeast parallel to the San Gabriel fault (Fig. 40). Therefore, there was a gradient sloping continuously southeastward. This proves that the changes in flow direction along the other two observed sections was caused by local tectonics, since the streams on the western side of the basin remained unchanged after cessation of the San Gabriel fault. Paleocurrent data from the three measured sections shows only minor changes in stream flow directions. These changes are attributed to local changes in basin-floor gradient, since there are no systematic shifts in all three sections. The environments previously described are predominantly fluvial and alluvial fan with minor lacustrine deposits; therefore, it can be assumed that the topography was relatively flat. The lack of overbank deposits in the fluvial lithofacies also indicates the the basin floor was uniformly covered by braided streams and bars. With the use of environment recognition of the onlapped beds along an anticline and paleocurrent data, it is shown that there was minor local folding and ponding of sediments but overall, Ridge basin was nearly a flat fluvial plain with a slight gradient southward, towards the San Gabriel fault during deposition of the Hungry Valley Formation. 167 Petrography Background A petrographic analysis of the sandstone beds within the study area was conducted to determine the cause of color change among lithofacies and to determine the source of the sediment. Provenance studies and clast counts of the Hungry Valley Formation have been conducted by Crowell (1982) and Ramirez (1983). Herein a thin-section analysis was directed toward the description of the sand- and silt-size fraction and cements. Such an analysis helped to explain the sudden color and grain—size change at the contact between the Hungry Valley Formation and the Apple Canyon Sandstone. It helped to identify changes in source on opposite sides of the basin. These changes may be caused by local tectonic activity which, in turn, may be linked to movement on the San Andreas fault. Methodology Twenty-three thin sections from four of the lithofacies were analyzed. A modified Glagolev-Chayes method was chosen for point-counting grains (Galehouse, 1971). Since the sample contained coarse sand- to pebble-size grains, a constant increment of 2 ram was chosen; many grains were counted more than once. Rock samples used for thin sectioning are poorly lithified making it difficult to prepare thin sections. Many grains were plucked out in the mounting process, which yields an 168 unrealistically high percentage of porosity. Therefore, pore spaces were not counted in the thin section analysis. The compositions were calculated from 350 point counts on each thin section. Samples from the eastern side of the basin are shown in the Edison section counts, whereas western samples are from the Hardluck section. Each thin section was leached by hydrofluoric acid which etches all feldspars. Then a sodium cobalti-nitrate stain was applied to half of each thin section to stain the potassium-rich feldspars. The plagioclase grains appear distinctive, because they are altering to clay. Many grains are so highly altered that they can only be determined to be plagioclase by the alignment of clays along the old twinning planes. Results Three distinct colors of sandstone are exposed in the study area. The Apple Canyon Sandstone of lithofacies 2 is a yellowish color while the directly overlying sandstone of the Hungry Valley Formation lithofacies 1 is light-orange. From thin-section analysis, it was determined that the yellowish sandstone is carbonate cemented (Fig. 41), whereas the light-orange one is clay cemented. The light-brown sandstone of lithofacies 5 occurs in the upper part of the stratigraphic sections. The color for this unit is derived from the carbonate and hematite cementing agents (Fig. 42). 169 Figure 41 • Photomicrograph of carbonate-cemented sandstone from lithofacies 5. 170 i TV T\ Figure 42. Photomicrograph of clay—cemented sandstone from lithofacies 1. 172 173 The grain composition of the thin sections is summarized in Table 4. The average sample consists of 40% quartz, 37% lithic fragments and 23% feldspar. Most of the rock fragments are granodiorite and gneiss with minor volcanoclastic and siltstone. The thin sections from the western side of the basin contain higher quantities of gneissic rock fragments than those from the eastern side of the basin. The eastern samples contain a high percentage of granodioritic rock fragments. Discussion Since the samples analyzed are of coarse sand to pebble size, they are coarser than the grain size used by most authors for petrographic analysis (Okada, 1971). The ternary diagram showing relative percentages of quartz + chert, feldspar, and lithic fragments is intended for visual comparison of this data, and cannot be compared directly with any classification based on medium sand size grains (Fig. 43). From this petrographic study, the grain composition suggests that the sandstone is relatively immature. The presence of 23% feldspar grains indicates only minor weathering prior to deposition (Mack, 1978). A high percentage of lithic fragments, 37%, is partially a function of the grain size analyzed. Both the types and ratios of rock fragments reflect the major ultimate source terrain on either side of the basin. The metamorphic source rock is dominantly exposed on the western side of Ridge basin along the San Gabriel fault. The highest percentage of 174 Table 4. Average mineralogic composition of 23 thin sections. 175 Surmary o f P etrog raph ic Data Western Side Minerals Observed P o ly c ry s ta llin e q u artz 3 grains P o ly c ry s ta llin e q uartz 2 -3 grains Non-undulose q u artz Undulose q uartz K-spar P lag io cla se Metamorphic rock fragment P lu to n ic rock fragm ent V olcanic rock fragm ent Sedimentary rock fragment Mica Hornblende Sphene Hemati te Chert Clay C a lc ite Clay Cemented Range % Mean % <1-6 5 0 -5 0-2 15-25 3-15 9-20 11-36 1-12 0 -3 0 -3 0 -3 0 -< l 0 0 -< l 0 5-12 0 5 1.5 20 11 15 25 8 1 1 1 <1 0 <1 0 11 0 Carbonate Cemented Range % Mean % 0 -4 1 < 1-2 1 0 0 2-19 11 5-17 11 6-16 10 27-36 31 1-15 8 0 -< l <1 0 -< l 1 0-6 2 0-2 1 0 0 0 -< l <1 0 0 0-1 0 2 15-26 21 Eastern Side Clay Cemented Range I Mean X 3-12 6 1-5 0-2 13-30 4-15 9-22 0 -< l 10-44 0-2 0-3 0-8 0 -< l 0-2 0-2 0 -3 1-19 0 3 <1 25 9 13 <1 29 <1 <1 2 <1 <1 <1 <1 8 0 176 Figure 43. Ternary diagram of grain composition from lithofacies 1, 2 and 5. Outlined region shows cluster of eastern samples. Grains are coarse sand to pebble size. 177 Qu«rt2 + Ch*rt X •••t»rn ttmplts O vsttsrn • •mpfes 178 gneissic rock fragments is found in those samples from the western side of the basin. Plutonic rock fragments are the dominant lithic fragment in the samples from the eastern side of the basin. This correlates well with the occurrence of a small pluton in the core of several anticlines and the Liebre Mountain massif on the eastern margin of the basin. A large percentage of the clasts in both sets of samples are volcanic tuff. Yet there are almost no sand-size volcanic grains in the thin sections. This may indicate that the volcanic source is so local that transportation occurs faster than they can weather into sand-size particles or that the volcanic clasts may weather directly into clay and plagioclase grains and would, therefore, be counted as their constituents rather than as rock fragments. The lack of sedimentary rock fragments indicates that the older sediment which fills Ridge basin is not being recycled to form the Hungry Valley Formation. The only clasts of sedimentary rocks exposed in the study area are found in the youngest conglomerate beds of the Freeman Canyon section of lithofacies 11. The two types of cements, clay and carbonate, appear to be mutually exclusive in most samples. One sample which is from a carbonate-cemented concretionary layer within the clay-cemented portion, shows both cements together. Individual grains of this sample are surrounded by a clay layer though the pore spaces have been filled by calcite cement. This indicates that the clay is the initial cementing agent and the calcite filled in the pore 179 space later. If the samples which show either clay or carbonate cement in thin section formed similar to the concretionary layer, then clay should be present in all samples. Since carbonate has such high birefringence, any clay present would be obscured from view by the later infilling of carbonate. A second indicator that the clay cement must have formed prior to the carbonate is that if the pores of a rock were once filled completely with carbonate cement, leaching of the cement must occur before a second cement can be deposited. It would be very difficult to dissolve all of the carbonate prior to deposition of the clay cement in the samples which appear completely clay cemented. Therefore the order of cementing from thin-section analysis is: deposition of authigenic clay followed by pore filling of carbonate cement in some of the samples. A more detailed analysis of the cementing agents and their diagenetic causes is discussed later. 180 PALEOMAGNETIC ANALYSIS Background The paleomagnetic stratigraphy of the Hungry Valley Formation was studied to form detailed correlative horizons across the basin. Such magnetostratigraphic units are helpful in determining sedimentation rates and give better control of sedimentary response to changes in tectonics. Methodology A pilot study was performed on two of the three measured sections used for the sedimentologic study. Samples were taken at 30-m intervals to study the strength of the magnetic signal and for a fold test (Irving, 1964). A total of 10 samples were taken from each section. Each sample was removed from the cliff by cutting away at the rock face with a pen knife and file to form a pedestal the size of the sample box. The box was then placed over the sample, the orientation and tilt of each box were accurately measured. One drop of General Electric Glyptal 1276 Lacquer cement was added to the sample in the box to cement the rock for analysis and shipment. A second set of 16 samples were taken from one stratigraphic section. Four beds between layers which appeared to be reversely magnetized were chosen. Each individual bed was sampled four times to test for consistency. This test was conducted to determine the variability within one layer and the continuity of a magnetically reversed section. These additional samples were treated similarly 181 to the initial set of twenty samples. In the laboratory, the direction and intensity of natural remnant magnetism (NRM) of all twenty samples were analyzed. The NRM intensities vary from 0.7 x 10~5 to 0.2 x 10~3 emu Alternating-field (af) demagnetization studies were conducted on each sample. This was done in a stepwise fashion in 50 OE intervals from 50 to 400 OE and in 100 OE steps from 400 to 1000 OE. Results Most samples analyzed show an exponential decay in intensity intially and after about 200 OE remained constant up to 1000 OE of af demagnetization (Fig. 44). A few samples gained intensity initially and then decayed to a constant value in a 300 OE field. The directional behavior exhibited by samples during af treatment was investigated with the use of Ziderveld diagrams (Irving, 1964) (Fig. 45). These diagrams are orthogonal projections of the magnetic vector onto 3 separate horizontal planes. Each horizontal projection shows the orientation of the magnetic vector following each demagnetization, so that variations in the magnetic vector can be traced through the demagnetization process. 182 Figure 44. Demagnetization intensity curve of three samples. 183 J/Jmax .0 0.5 0.0 1000 500 0 (OE) Demagnetization 184 Figure 45. Ziderveld diagram of the directional behavior of a typical sample during af demagnetization. 185 Vertical LOO Vertical i o North o o m o o o Discussion Many magnetostratigraphic studies determine the polarity of the sample using the direction of the Mean Dipole Field (MDF) (MacFadden, 1977). This was not done in this study because the initial decay of the sample is rapidly followed by a long period of slow decay. Instead, the 600 0E level of demagnetization results were analyzed. A virtual geomagnetic pole (VGP) for each sample was computed. A VGP is the apparent position of the paleopole based on 1) the inclination and declination of a magnetic site at a specific spot on the earth's surface and 2) the assumption of an axial dipole field. It was assumed that no tectonic rotation has occurred because Ensley (1980) studied older sediment in the Ridge basin and found no evidence of rotation. The VGP latitude for each sample is plotted in Figures 46 and 47. On the right-hand side of each figure the samples have been assigned to one of three catagories. Sample which have normal polarity must plot between +60° and -90° at 600 OE. Intermediate samples are all samples between -60° and +60° at 600 OE. Reverse polority sample plot between -60° and -90° at 600 OE. Samples which vary more than 20° in latitude between 200 OE and 600 OE are indicated by an arrow. Most such samples are becoming more southerly in VGP during af demagnetization. Such cases indicate a large overprint with possibly a negative detrital 187 Figure 46. Virtual geomagnetic pole plots for samples taken along the Edison section. Points with arrows have over 20° of variation between 200 OE and 600 OE. 188 sz 9 Edison Section *5 f O Virtual Geomagnetic Pole jc a Latitude m 9 C O 0 - 9 0 C ) 90 • 400m - • • • • • • • mmm 30 0 - # • • • • • • 2 0 0 — # • • 100 - # # 4-# # 189 Figure 47. Virtual geomagnetic pole plots for samples taken along the Freeman section. Points with arrows have over 20° of variation between 200 OE and 600 OE. 190 O ft a Freeman Section Virtual Geomagnetic Pole Latitude c s k . o - 9 0 90 30 0m — 150 - 0 - 191 remanant magnetism (DRM). For this study, they are classified as intermediate samples because they plot in the central latitudes. The four sets of repetitive samples from an individual bed are plotted in Figures 46 and 47. The four VGP results are plotted together on one line. One set appears quite consistent, though the other three vary up to 120 degrees. A Fisher precision parameter was calculated for each bed (McElhinny, 1973). The results are shown in Table 5. The 095 value indicates a large angle of dispersion of data from within a single bed. This suggests that the reliability of all other data with only one sample per site may be poor. The mean grain size of the sediment tested is medium to coarse sand, which is coarser than the sediment usually studied. The pebbles and lithic clasts in some samples may have added a large component of viscous remanent magnetism (VRM). Another cause of the high degree of variation of samples from within one horizon is the presence of hematite. Large flat concentrations of hematite are visible in thin section. These concentrations, form coatings on some clasts in sample FC-8. Other samples likely contain hematite as well, because the NRM values do not decrease the 200 to 600 OE field, which is common in magnetite-bearing sediments (Fig. 44). The presence of hematite in this unit may not indicate a single depositional event. Since the sediment is coarse-grained, loosely packed, fluvial deposits and poorly lithified, the beds 192 Table 5 Fisher distribution statistics for the four beds. Each bed contains four samples. Data is accepted with an 0195 less than 30°. 193 Fisher Distribution Ka a95 91-94 A 6.94 37.6 96-99 B 1.87 156.6 6-9 D 3.85 54.2 1-4 C 3.27 60.6 194 may have been submerged within the water table for long periods of time (throughout a series of reversals). Hematite would therefore have been able to form over a long time period. Thermal demagnetization may remove some of this hematite overprint, but the collected samples were too friable for such testing. In order to refine the magnetostratigraphy of the Hungry Valley Formation, a detailed sampling procedure and thermal demagnetization must be conducted. With the af demagnetization procedure outlined herein, the data is unreliable and quite low in intensity. 195 DIAGENESIS Background There is a sharp change in sandstone color from brownish-beige to light—orange at the base of the Hungry Valley Formation. This color change coincides with a change in cement type and grain size. The lower part of the Hungry Valley consists of clay—cemented, conglomeratic sandstone. The uppermost Apple Canyon Sandstone beds are grayish—orange, finer grained, carbonate—cemented sandstone. The youngest part of the Hungry Valley Formation is called the conglomeratic member in the Freeman Canyon section and the upper member in the Hardluck section by Crowell (1982). Both of these members are carbonate—cemented sandstone and conglomerate. The Hardluck section has a sharp contact between lithofacies 1 which is clay—cemented sandstone and lithofacies 5 at the top of the section which is a carbonate—cemented sandstone. The grain size and sedimentary structures are the same in each of the lithofacies, the only difference is in cementing agent and color. The second carbonate—cemented unit in the younger part of the Hungry Valley Formation is the upper member, which is assigned to lithofacies 10 and 11 at the top of the Freeman Canyon section. These beds overlie the clay-cemented sandstone of lithofacies 1, and are a prograding alluvial-fan sequence. There is a major diagenetic change at the contact between cement types. The carbonate cemented beds are muddy, matrix-supported conglomerate 196 from debris—flow deposits, whereas the underlying clay—cemented beds are traction-current deposited sand. A diagenetic study of the units on either side of these two sets of contacts was undertaken to determine the cause of the sharp changes in cementing agents and to determine better the types of cementing material. Since the base of the clay-cemented, light—orange sandstone beds in the Hungry Valley Formation may coincide with the initiation of movement on the San Andreas fault and the base of the lithofacies 5 carbonate-cemented sandstone along the Hardluck section may coincide with the end of movement on the San Gabriel fault, a tectonic cause for the cement changes was assumed. Several types of studies were conducted to determine the types and history of cementation in the study area. Petrographic work described in a previous chapter determined that there were different types of cement present in different parts of the stratigraphic sections. Scanning electron microscope, energy dispersive x-ray analysis, and x-ray diffraction analysis were utilized to determine more accurately what cementing agents were present. Scanning Electron Microscope Study From thin—section analysis, it appeared that either clay or carbonate cement was present. Only in carbonate concretions within the clay—cemented regions were both clay and carbonate cement visible in one thin section. A scanning electron 197 microscope (SEM) was used to determine if there were any clays in the carbonate cemented rocks and, if so, what types. Samples from the clay-cemented beds also were studied to determine the types of clays and whether they are detrital or authigenic clays. Methodology The USC Engineering Department scanning electron microscope was run at 20kv. Each sample was plated with gold prior to analysis to increase the conductivity of the sample. Photographs of some common clays from each sample were taken at 500x to 50,000x magnification using a Polaroid camera attached to the microscope. To determine the chemical composition of individual grains of clay, an EDX system mounted on the scanning electron microscope was used. Through an energy dispersive x-ray analysis, the elements are separated. In interpreting the EDX results from the samples, the two gold peaks must be ignored, because they are due to the coating procedure. Results The three samples analyzed which appeared to be carbonate cemented in thin section were shown to contain small quantities (<1%) of clay from the SEM analysis. These clays are both pore filling and thin coatings on some grains. All of the clays are authigenic as determined by the clay structure (Walker et al., 1978). The most common clay is in the smectite family and forms 198 clusters of clay particles which are unordered (Figs, 48a and 48b). Some of the clays contain illite as seen by the rough surface of each platelet, and are therefore classified as a mixed layer clay (J. Welton, personal comm,, 1983), Four samples from the clay—cemented unit were analyzed. These show more frequent occurrences of clay than the carbonate-cemented ones. Most of the clay occurs as thin coatings on the surface of grains and in pores. Less often, the clays occur as clusters within a pore. Again all clays are authigenic with similar morphology to the previous group (Figs. 49a and 49b). All clays seen are from the smectite category. EDX data was collected for each sample which was photographed. A typical elemental plot of a clay is shown in Figure 50. The clay composition was abnormally low in magnesium and very high in iron. This large input of iron may be primary or from a later alteration of the clay (J. Welton, personal comm., 1983). Discussion The occurrence of similar authigenic clays in both the carbonate- and clay-cemented units indicates that clay was the earlier cementing agent. If the carbonate cement were first, then there would be no pore walls on which the clay may grow and there would be the complex problem of how to remove the carbonate completely from the clay-cemented region. 199 Figure 48. SEM photomicrograph of mixed layer clay (smectite-illite). a) at 2000x b) at 5000x 200 0 i x mictons 2 0 1 Figure 49. SEM photomicrograph of pore-lining smectite. a) at 500x b) at lOOOx 202 lO m icrons 203 Figure 50. EDX graph from clay sample shown in Figure 48. 204 SiK« AuMo. FeKx. AuLa There is no evidence of detrital clay as one would expect in a recent traction current deposit. This indicates that the detrital clay probably was eroded away by groundwater flowing through the sediment, then later, authienic clays precipitated. The large amount of iron present in the clays may be the cause of the scatter in the paleomagnetic data. The iron associated with the clays was deposited either with the authigenic clays or as a later alteration product. In either case, the magnetic domain iron atoms would have aligned with the magnetic pole at a later time than the pole location present when the sediment was deposited. Therefore, the paleomagnetic results would give erroneous directions and a high degree of scatter if the atoms were placed in a lattice already present. The fine-grained, clay-rich beds are sometimes red in an outcrop of Hungry Valley sandstone. These beds contain the iron-rich clays which create the red color. X-ray Diffraction Analysis To determine the relative quantities and types of clays seen under the scanning electron microscope, an x—ray diffraction (XRD) study was conducted. Such an analysis semi-quantitatively determines the different types of clays present. Methodology Clay-size particles were separated from rock samples by a two-step process. First a 100 gram sample was placed in a beaker 206 of deionized water in an ultrasonic cleaning device. Such vibration disaggregated the particles without crushing any grains. Then the sample was poured into a 1000 ml settling tube filled with 10% calgon for dispersion. Samples were stirred with a rod until all of the material was in suspension. Then it was allowed to settle for seven hours. After seven hours the material in suspension in the top 30 cm of water was less than 8 phi in diameter (Folk, 1980). The clay-size material was removed from the settling tube using a siphon and then separated by centrifuge. The water and clay portion was placed on a porous ceramic tile using an eye dropper. This method was used to give a random orientation of clay particles (Fleischer, 1970). An internal standard of silicon was used to calibrate each run. In addition, silicon on a ceramic plate was analyzed to determine the amount of background signal produced by the ceramic plate. X—ray diffraction analyses were made on a Norelco wide-angle goniometer. Copper K-alpha radiation was measured from a scintillation detector at 40 kv and 30 ma from 20 of 5° to 30°. The graphs of intensity of K-alpha versus the 29 angle were analyzed to determine the mineral associated with each peak. This was done by visual comparison between the graphs and those shown in Carroll (1972) and Thorez (1982). 207 Results Two major peaks were visible in all 6 samples (Fig. 51). These peaks occur at a d-spacing of 17 A and near 10 A. They correspond to the (001) face of montmorillonite or smectite and the (001) face of illite respectively. A third peak visible in 3 samples at about 7 A which corresponds with the (001) face of kaolinite. Quartz and feldspar peaks occurred between 4 A and 3 A. Since the relative area under a peak is not a true indicator of relative quantity, the area under the curve at a specific d-spacing must be multiplied by a constant of proportionality for each clay (Pipkin, 1965). The ratio of area for a given volume of clay is : mont/illite 1:5 mont/kaolinite 1:5 kaolinite/illite 1:1 Through these calculations, it was shown that the majority of the clay is from the smectite family with less illite and in some cases minor kaolinite. The composition ranges from 60% smectite with 40% illite to 45% smectite with 45% illite and 10% kaolinite. Discussion The x-ray diffraction analyses of 6 samples from the Violin Breccia and Hungry Valley Formation indicate that all samples have similar quantities and types of clays. The amounts of smectite 208 Figure 51. Graph of XRD output in 20 vs. intensity on clay sample shown in Figure 48. 209 illitt 5 I I qutrtz fiM ifir and illite vary only slightly among samples. The major change is the presence or absence of kaolinite. In the EDX photographs (Figs. 48 and 49), the clays vary in type and morphology. Some of the illite peak on the XRD graphs is due to mixed-layer clays, which contain both illite and smectite. Therefore the XRD data without the SEM photomicrograph, is not as informative. Another example is that the EDX analysis of individual platelets of clay within two samples differ in aluminum and calcium content. Yet on the XRD graph the whole sample analysis indicates that the samples are identical. The cause of cement variations can be determined from the combination of scanning electron microscope and x-ray diffraction studies. The SEM photomicrographs indicate that all of the clay present is authigenic. No detrital clay was found. In the carbonate-cemented beds, the same types of clay are visible only in smaller quantities. The difference between the carbonate- and the clay—cemented beds is the lack of carbonate and larger volume of clay in the clay-cemented beds. Changes in groundwater conditions or climate are two possible causes. Yet, the lower contact between the clay and carbonate cement is interbedded and alternates too quickly. In the lower part of the Hungry Valley Formation, the carbonate-cemented units are fine grained, whereas the clay-cemented beds are coarser-grained. But in the upper portion of the Hardluck section, the grain size of the clay—cemented sandstone is the same. Apparently grain size is independent of the cause of variations in cementing agents. 211 In a smaller scale study, Davies (1967) found alternating beds of friable and calcareous sandstone. These variations in cementing agent were attributed to variations in sedimentation rate. The calcareous-cemented strata were deposited at a slower rate than the friable clay-cemented sandstone. During periods of high sedimentation, the carbonate material present was diluted by the large input of detritus. In the Hungry Valley Formation, similar reasoning can be used to explain the variation in cements. During periods when either the San Andreas fault or the San Gabriel fault was active, the sediment deposited is carbonate cemented. During the period when both faults were active, the unit is clay cemented. The volume of sediment coming into the basin while the two faults were active was probably much larger then the amount when only one fault was active. The increase in sediment input would be attributed to uplift of highlands along the fault scarp. The changes in cementing material may be a result of changes in basinal tectonics. When the basin was bounded by active faults and a new source, there were very high rates of uplift and sedimentation diluting the carbonate in the system. During periods of moderate tectonism, the sedimentation rate was slower and carbonate material was precipitated in a sufficient quantity to cement the rocks. The reduced amount of detritus made it possible for the carbonate to cement the rock because it forms a larger percentage of the rock. The carbonate remained constant throughout deposition of the Hungry Valley Formation, but the rate of flux of detritus varied with tectonic changes. 212 GEOLOGIC HISTORY The complex history of deposition of the Hungry Valley Formation is divided into five episodes for ease of description. The sediments deposited during each phase are depicted in Figure 52. Data from field observation, laboratory work and Markov analyses have been synthesized to form this history. The initial period described is prior to deposition of the Hungry Valley Formation. The Apple Canyon Sandstone Member of the Ridge Route Formation and the Violin Breccia were being deposited. Along the active San Gabriel fault, alluvial-fan deposits were being shed into a shallow lake (Fig. 53). This lake extended from one margin of the basin to the other. The northern boundary was comprised of alluvial fans and fluvial deposits shed off the Liebre massif. During some dry periods, the lake level dropped allowing distal braided streams to cover the lacustrine sediment. This created an interbedded sequence of lake deposits and medium sand beds cemented by carbonate. The second phase begins with the initiation of movement on the San Andreas fault. The Liebre massif no longer extended along the whole northern margin of the basin. A fluvial system contributed sediment through an opening which linked Ridge basin with the Mojave desert. Adding Volcanoclastic clasts and coarser grained material which was deposited by more proximal, braided streams. Transverse-bar and sandflat deposits characterize these braided-stream deposits. 213 Figure 52. Cross-sectional view of the five phases of deposition of the Hungry Valley Formation. 214 215 Hardluck South 500m Freeman Edison North \ ° °no 0 o ° o v° o ° O 0 o v . ° o 0 o \0 O O O \ O n O v O O o o o o / o° o00°o°' o 0 ° ° 0 ° / o o ' 0 0 srj 30 0- 200- i i r r r r m m * Llthofacles □ 3&4 6 ^37 V n O 8 9 10411 Figure 53. Diagrammatic illustration of the environments during deposition of the Hungry Valley Formation. a. Prior to initiation of San Andreas fault b. At initiation of San Andreas fault c. After end of movement on San Gabriel fault 216 ! 217 I I t 218 Along the northern margin of the basin, the fluvial deposits are interbedded with fine-grained, shallow-lake deposits. Closer to the San Andreas fault, the interbeds became more common. Therefore, these are likely to have been pond deposits related to folding along the San Andreas. The center of the basin contains interbeds of shallow lake deposits similar to those between the Apple Canyon stream deposits. The lake deposits became thinner and less laterally continuous with time, indicating fewer periods of lake formation. The southern margin along the San Gabriel fault still has alluvial-fan deposits draping the fault. There was an increase in fine-grained interbeds of mudstone which represent a shallow lake environment. Both the coarse-and fine-grained units interfinger with the light-orange sandstone of the Hungry Valley Formation. The third phase is marked by the end of lakes in the central section of the basin. The northern region continued to be proximal braided streams with small interbedded pond deposits. The central region contains finer-grained, more distal braided stream deposits. Linguoid bars and longitudinal bars became the common type of deposit. On the southern margin, the Violin Breccia became much finer-grained and is composed of nearly 80% lake deposits and 20% subaqueous debris flows off the fault scarp. The area of lake was reduced, which allowed more braided streams to prograde. Since there are distal fluvial facies between the proximal 220 streams along the north and south margins, some local topographic feature must have changed the flow pattern. A higher region similar to that drawn in Figure 53 must have obstructed flow from the center of the basin southward toward the margin. The fourth phase occurred at the end of deposition of the Violin Breccia. This also signifies the end of major movement along the San Gabriel fault. At this time, there are changes in sedimentologic style across the whole basin. The northern margin contained no more pond deposits and instead the proximal braided-stream sediment is interbedded with a few fine-grained, abandoned channel deposits. The central region becames coarser-grained and contained more proximal braided-stream sediment with one lake deposit. The southern margin no longer contained lake or alluvial-fan environments. The area was completely covered by proximal braided streams. These fluvial deposits are light-brown and cemented by carbonate. This change from light—orange, clay—cemented stream deposits to the light-brown, carbonate-cemented stream deposits occurs at the top of the Violin Breccia. The type of braided-stream deposits do not change at this contact, only the cement does. The fifth and final phase studied occurs at the contact between the upper and lower members of the Hungry Valley Formation (Crowell, 1982). The upper member is exposed only in the central part of the basin. It consists of a layer of matrix—supported 221 conglomerate derived from debris flows. These flows are proximal alluvial-fan deposits formed during the uplift of Frazier Mountain (Fig. 53). Overlying the debris-flow are interbedded traction and debris-flow deposits from a medial fan environment. The change from proximal to medial fan environments indicates rapid uplift of Frazier Mountain followed by erosion of the fan causing the apex to recede. Since the sediment south of the alluvial-fan complex show no change with the growth of the fan, the fan must have come after deposition of the strata juxtaposed against it. The alluvial-fan complex must have eroded a channel into the fluvial system. The youngest part of the studied sections, therefore is alluvial-fan complex derived from Frazier Mountain. 222 SUMMARY AND CONCLUSIONS The Hungry Valley Formation in Ridge basin was studied to analyze the sedimentary response to Pliocene shifts in the position between the North American and Pacific plate margin. Through a variety of measurements and observations, five main objectives of this study have been addressed. The first objective was to determine the depositonal environments of the Hungry Valley Formation and the Violin Breccia. This was done through detailed measuring of three stratigraphic sections along the west, central, and east side of the basin. From the field observations of sedimentary structures, grain size and bed configuration, eleven lithofacies were identified. Each of the lithofacies was assigned to a given environment using Miall's (1982) fluvial models. Lithofacies associations were determined by a Markov analysis for each stratigraphic sequence. Petrographic studies of thin sections helped to differentiate sediment from the east and west sides of the basin. From the field observations and lab results, it was determined that the basin became more shallow through time (Fig. 53). The lowermost beds along all three sections are interbedded fluvial and lacustrine deposits. Younger beds are purely fluvial, braided—bar sequences with no fine-grained overbank or floodplain deposits. The younger beds along the east and west margins of the basin are fluvial deposits, whereas the center of the basin is coarse-grained alluvial-fan deposits of debris flow and traction 223 current origin (Fig. 51). The second objective was to reconstruct the fluvial pattern using paleocurrent data. Over 100 measurements were taken along each of the three measured sections. Local changes through time were observed in individual stratigraphic sequences but no large-scale changes were identified. The Violin Breccia shows a N.45°E. flow direction off the fault scarp as postulated by Crowell (1947). All of the fluvial sandstone beds of the Hungry Valley Formation indicate flow in a southeasterly direction throughout the study area (Fig. 40). This indicates that the basin was nearly flat with a slight slope down to the south. The coarse alluvial fan deposits at the top of the central measured section indicate an eastward drainage direction. This may be due to sampling error by collecting data from one lobe rather than across the whole alluvial-fan sequence. The third objective of this study was to determine sediment-accumulation rates within the Hungry Valley Formation. A paleomagnetic study was attempted to create a detailed set of horizons with dates which could be correlated across the basin. This study was not feasible because of the high iron content in the authigenic clays and the coarse grain size of the beds. Ash beds occur on the eastern side of the basin, but do not extend sufficiently far into the basin to be a reliable horizon for dating. The only method found for deducing sediment-accumulation rates is through an estimation of bed thickness and age. The base of the Hungry Valley Formation is 5.5 mya by the Kinsey Ranch 224 faunal zone (Ensley, 1980). The Hungry Valley Formation is overlain by Pleistocene terraces, so the unit is between 5.5 and 2.5 my old. The Hungry Valley Formation has been measured by Crowell (1982) to be 1400 m thick. Therefore, the sediment-accumulation rate is at least 0.47 m/1000 yrs. Ensley and Verosub (1982) found the sandstone beds in the lower part of Ridge basin to have a sediment-accumulation rate of 0.2 m/1000 yrs and the shale beds at 3 m/1000 yrs. From these calculations, it appears that the sediment-accumulation rate of the Hungry Valley Formation was higher than the older sandstone beds in Ridge basin. The fourth objective of this study was to determine the time of initiation of movement on the San Andreas fault and the time when the San Gabriel fault became inactive. The initiation of the San Andreas fault is placed at the first appearance of light-orange, clay-cemented sandstone beds of the Hungry Valley Formation. This occurs lower in the section than where Crowell (1952) places the contact between the Ridge Route and Hungry Valley Formation. These white sandstone beds at the base of the Hungry Valley Formation are coarser-grained and contain abundant purple volcanic clasts from the Mojave Desert. This rapid change in grain size from the finer-grained Apple Canyon sandstone to the coarse Hungry Valley sandstone and the occurrence of new clast types is due to the influx of material from a new nearby source. The initiation of movement along the San Andreas Fault, on the eastern side of the basin, caused folding and the formation of 225 ponds. Anticlines with a granitic core formed at the start of deposition of the light-orange Hungry Valley sandstone beds as seen by the truncation of bedding against the pluton. Fine-grained mudstone of lithofacies 5 occurs in increasing quantities to the east. These fine-grained lake deposits do not occur in the center or western side of the basin, but only exist near the pluton-cored anticline which may have caused the collection of water in tectonically controlled low areas to the east. These beds are discontinuous in some areas indicating local topographic variations. Paleocurrent data from the Hungry Valley Formation indicate the streams flowed southward across the area presently occupied by the San Andreas fault. Older units in the basin have paleocurrent directions showing flow off the east and west margins and then flowing southeast along the axis (Link, 1982). The continuous southerly flow direction and change in clast composition of the Hungry Valley Formation deposits shows that the source was not from the basin margins but had to come from across the San Andreas fault in the Mojave desert. The cessation of the San Gabriel fault occurred near the end of deposition of the Violin Breccia (Crowell, 1982). Paleocurrent directions indicate that large amounts of material came from the west to form the Violin Breccia. The overlying beds of the Hungry Valley Formation have paleocurrents which suggest they were derived from the northeast. The last paleocurrents show that sediment was derived from the San Gabriel fault scarp 226 end with the termination of the Violin Breccia. The lower part of the Hungry Valley Formation is interbedded with lake deposits assigned to the Violin Breccia. The top of the Violin Breccia contains the last lacustrine deposits along the western margin of Ridge basin. This suggests that the west side of the basin stopped sinking due to oblique slip on the San Gabriel fault, so that there was no low area for a lake to form. Through the diagenetic study, it was inferred that carbonate-cemented sandstone formed during periods of slower sediment accumulation. The Hungry Valley Formation beds which directly overlie the youngest bed of Violin Breccia are the first carbonate-cemented layer in the Hungry Valley Formation. This indicates that as soon as the San Gabriel fault became inactive there was a decrease in sediment derived from the scarp and the rate of sedimentation slowed enough to form large quantities of carbonate—cemented sediment. The fifth objective was to determine the diagenetic cause of the color change between the older sand bodies in Ridge basin and the Hungry Valley Formation. The difference in color is due to the type of cement present. In the grayish—orange beds, carbonate acts as the cementing agent, whereas in the light-orange beds, clays are the cement. Both the carbonate—and clay—cemented beds contain smectite and minor mixed-layer clays of illite-smectite. These clays occur as pore lining and pore filling material. The carbonate-cemented rocks have less authigenic clay and contain 227 large quantities of carbonate material easily seen in thin section. The difference between the beds which are clay cemented and those with carbonate may be the sedimentation rate. Beds which were deposited quickly have diluted the carbonate in the system so there is only a small amount present for cement. Whereas beds which are carbonate cemented were deposited slowly allowing carbonate cement to precipitate. The sedimentary changes associated with shifting major faults between the Pacific and North American plates is reflected by subtle sedimentologic changes. The most visible change is in the color of the beds. Sandstone units deposited prior to the initiation of the San Andreas fault are grayish-orange, whereas the later beds are light-orange. This is due to the quantity of carbonate cement present in those strata which, in turn, is affected by the sedimentation rate. When both the San Andreas and the San Gabriel fault were active, more sediment was carried into the basin and this influx diluted the carbonate material. The basin configuration changed due to the shift of the plate margin. 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Okada, H., 1971, Classification of sandstone: analysis and proposal: Jour. Geology, v. 79, p. 509-525. Paschall, R. H., and Off, T., 1961, Dip-slip versus strike-slip movement on the San Gabriel fault, southern California: Am. Assoc. Petroleum Geologists Bull., v. 45, p. 1941-1956. Pessega, R., 1957, Texture as characteristic of clastic deposition: Am. Assoc. Pet. Geologist Bull., v. 41, p. 1952-1984. ________, 1962, Problem of comparing ancient with recent sedimentary deposits: Am. Assoc. Petroleum Geologists Bull., v. 46, p. 114—118. , 1964, Grain size representation by C M patterns as a geological tool: Jour. Sed. Petrology, v. 34, p. 830-847. Pipkin, B. W., 1965, The clay mineralogy of Roosevelt Lake - a trap for fine-grained sediments in east—central Arizona: Journ. Arizona Acad. Sci., v. 3, p. 151—158. Potter, P. E., and Pettijohn, F. J., 1977, Paleocurrents and basin analysis: New York, Springer-Verlag , 425p. Powers, M. C., 1953, A new roundness scale of sedimentary particles: Jour. Sed. Petrology, v. 23, p. 117-119. Ramirez, V. R. , 1983, Hungry Valley Formation: evidence for 220 kilometers of posts Miocene offset of the San Andreas fault, in D. W. Anderson and M. J. Rymer, ed., Tectonics and sedimentation along faults of the San Andreas system, Soc. of Economic Paleontologists and Mineralogists, p. 33-44. Rust, B. R., 1972, Pebble orientation in fluviatile sediments: Jour. Sed. Petrology, v. 42, p. 384-388. _______ , 1978, Depositional models for braided alluvium: Can. Soc. Pet. Geol., Mem. 5, p. 605-625. 234 Smith, P. R., 1982, Sedimentology and paleolimnology of the Mio—Pliocene Peace Valley Formation, Ridge basin, central Trans-verse Range, California (unpub. M.S. thesis): Univ. Southern California, 230p. , Harper, A. S., and Wood, M. F., 1982, Non-marine trace fossils in the Mio-Pliocene Ridge Basin Group, southern California, in_, Crowell, J. C., and Link, M. H. , eds., Geologic history of Ridge basin, southern California: Soc. Econ. Paleontologists and Mineralogists, Pacific Section, p. 2 53-258. Steel, R. J., and J. C. Crowell, 1983, Facies of the Violin Breccia, Ridge basin [abs.]: Am. Assoc. Petroleum Geologists 58th Annual Meeting, Pacific Section, p. 138. Strahler, A. N., 1977, Principles of Physical Geology: Harper and Row Publishers, New York, 131p. Thorez, J., 1982, Phyllosilicates and clay minerals: a laboratory handbook for their x-ray diffraction analysis: Lelotte, Dison, Belgium, 579p. Visher, G. S., 1962, Grain size distributions and depositional processes: Jour. Sed. Petrology, v. 39, p. 1074-1106. , 1972, Physical characteristics of fluvial deposits; in, J. K. Rigby and W. K. Hambling eds., Recognition of ancient sedimentary environments, Soc. Econonmic Paleontologists and Mineralogists, Special Pub. No. 16, p. 84-97. Walker, T. R., Waugh, B., and Grone, A. J., 1978, Diagenesis in first—cycle desert alluvium of Cenozoic ages, southwestern United States and northwestern Mexico: Geol. Soc. Am. Bull., v. 89, p. 19-32. Weber, F. H., Jr., 1979, Geologic and geomorphic investigations of the San Gabriel Fault zone, Los Angeles and Ventura Counties: Final Techn. Rept., U.S. Geological Survey, Contract No. 14-08-0001-16600, modif. 1, 78p. Williams, P. F., and Rust, B. R., 1969, The sedimentology of a braided river: Jour. Sed. Petrology, v. 39, p. 649-679. Wood, M. F., 1981, Depositional environments of the Apple Canyon Sandstone, Ridge basin, central Transverse Range, California (unpub. M.S. thesis): Univ. Southern California, 266p. Woodburne, M. 0., 1975, Cenozoic stratigraphy of the Transverse Ranges and adjacent areas, southern California: Geol. Soc. America Spec. Paper 162, 91p. 235 APPENDIX 236 SECTION A The western measured section called the Hardluck section is described below. The Violin Breccia, Ridge Route Formation and the Hungry Valley Formation are all exposed within this 1000 meters. The section was measured along a paved road and in the stream bed of the nearby unnamed creek. This composite section was measured in section 13, T. 7N., R. 19W. Here the beds vary in strike from N40W to N80W and dip about 40°N. Measurements in this section begin at the first roadcut north of Piru Creek. The top of the section is located at the top of the pass near the boundary of the Los Padres National Forest and the California State Park. Hungry Valley Formation: Thickness (meters) A—24. Sandstone. Light-brown colored, carbonate cement. Poorly sorted and very coarse in some areas. Forms channelized sequences up to 2 m high with planar and trough crossbeds. Sequences are normally graded above a basal lag gravel.................... 140 A—23. Mudstone, grayish green to olive-gray colored. No well preserved sedimentary structures due to bioturbation. Some heavy mineral laminations are visible. Beds are horizontally persistant and of constant thickness........................ 1 A—22. Sandstone. Channel—shaped sequences typically 1 m thick and up to 10 m wide. Internal bedding is mostly trough crossbeds overlain by planar and low angle crossbeds. Heavy mineral laminations accentuate internal structures in the finer grained beds........ 185 237 Silt stone, massive since no well preserved sedimentary structures due to bioturbation. Color varies from grayish green to olive- gray. Beds are horizontally persistant and of constant thickness. Secondary sedimentary structures such as loading features are seen at the top of some beds.. Sandstone. Channel-shaped sequences approxi mately 1 m thick and up to 8 m wide. Internal bedding is mostly trough crossbeds with some planar and low angle crossbeds. Normally graded channel sequences are yellow- gray colored................................... Siltstone and mudstone. Color varies from grayish green to olive-gray. No well preserved sedimentary structures due to bioturbation. Beds are horizontally persistant and of constant thickness....... Sandstone, wide, flat channel-shaped sequences composed of trough crossbeds with some planar and low angle crossbeds. Heavy mineral laminations in the upper finer grained beds. Each channel sequence is normally graded, yellow-gray colored.......................... Pebbly mudstone with minor conglomerate lenses. Carbonate cemented units composed of massive beds of mudstone with lobes about 15 cm thick and 1 m wide............................ Sandstone. Channel-shaped sequences each 50 cm - 1 m thick, and up to 2 m wide. Internal bedding is mostly trough crossbeds with some planar and low angle crossbeds. Heavy mineral laminations in the finer grained beds. Normally graded channel sequences..................................... Pebbly mudstone with pebble conglomerate interbeds. Carbonate cemented units composed of massive beds of yellow-brown mudstone with up to 1 m thick lobes of conglomerate...... A-14. Sandstone. Channel-shaped sequences typically 3 m thick and up to 25 m wide. Internal bedding is mostly trough crossbedded sandstone and conglomerate with some high angle planar crossbeds. Heavy mineral laminations in the finer grained beds at top of sequences. Each channel sequence is normally graded, yellow-gray colored, with basal rip-up clasts.............. 38 A-13. Pebbly mudstone with conglomerate; 90% mudstone, 10% matrix and clastsupported conglomerates. Carbonate cemented units composed of massive beds of mudstone with up to 0.5 m thick lobes of grayish-orange conglomerate.................................. 6 A-12. Sandstone. Channel-shaped sequences typically 3 m thick and greater than 15 m wide. Internal bedding is mostly trough crossbeds with some planar and low angle crossbeds. Heavy mineral laminations at top of channel sequences. Each channel sequence is normally graded, yellow-gray colored, with vertebrate fossils................................. 3 A-ll. Pebbly mudstone with conglomerate; 80% mudstone, 20% matrix and clastsupported conglomerates. Carbonate cemented beds composed of massive units of mudstone with up to 0.5 m thick lobes of conglomerate. Whole unit is grayish-orange and poorly exposed except in stream channel............ 2 A-10. Sandstone. 3 m thick and up to 25 m wide channel-shaped sequences Internal bedding is mostly trough crossbeds with some planar and low angle crossbeds. Heavy mineral laminations in the finer grained beds. Channel sequences are normally graded, yellow-gray colored, with rip-up clasts at base.................. 8 A—9. Pebbly mudstone with thin conglomerate interbeds. Carbonate cemented layers composed of bioturbated beds of grayish-orange mudstone with up to 1 m thick lobes of conglomerate.......... 20 239 A-8. Sandstone. Channel-shaped sequences 0.5 - 3 m thick and up to 25 m wide. Sedimentary structures of trough crossbeds with some planar and low angle crossbeds. Each channel sequence is normally graded with yellow-gray color........... 6 A—7. Pebbly mudstone with conglomerate; Carbonate cemented units composed of massive beds of mudstone with up to 1 m thick lobes of grayish-orange conglomerate................ 13 A-6. Sandstone. Channel-shaped sequences typically 3 m thick and up to 25 m wide. Internal bedding is mostly trough crossbeds with some planar and low angle crossbeds. Heavy mineral laminations in the finer grained beds. Each channel sequence is normally graded and yellow-gray colored......... 1_ Total thickness ....... 482 Violin Breccia and Ridge Route Formation A-5. Pebbly sandstone, well sorted, grayish-orange color, channel shaped sequences with both trough and planar crossbeds................. 1 A-4. Pebbly mudstone with conglomerate; 80% mudstone, 20% matrix and clast supported conglomerates. Carbonate cemented units composed of massive beds of mudstone with up to 1 m thick lobes of conglomerate. Whole unit is grayish-orange and poorly exposed.. 146 A-3. Pebbly mudstone Conglomerate and interbedded lobes of conglomerate up to 0.5 m thick. Mudstone is massive with trace fossils preserved at contacts. Conglomerate and mudstone vary from greenish-gray to dark yellow-brown in color..................... 9 A-2. Pebbly sandstone, well sorted, light-orange to grayish-orange color, channel shaped sequences with both trough and planar crossbeds, heavy mineral laminations in the finer beds..................... ....... ...... 240 A-l. Conglomerate and pebbly mudstone. Interbedded lobe shaped units up to 3 m thick. Mudstone is massive with trace fossils preserved at contacts. Conglomerate and mudstone vary from greenish-gray to dark yellow-brown in color.................. 368 Total thickness............... 525 SECTION B Freeman Canyon in the center of the present exposures of the Hungry Valley Formation, is the location of this measured section. Crowell (1982) considers this to be the type section for the Hungry Valley Formation. The composite section described below was measured along the east side of the crest of Freeman Canyon. The base of the sequence was chosen at the first appearance of light-orange sandstone near the base of the Hungry Valley Formation. The upper limit of this sequence is a cliff at the head of Freeman Canyon which is complexly folded. This section is located in sec. 24, T. 8N., R. 19W., sec. 19, 30, 31, T. 8N., R. 18W. and sec. 5, 6, 8, 17, T. 7N., R. 18W. The strike of this measured section varies due to small folds but is mostly N20W with a 20°W dip. With such a low dip angle, individual beds are traceable for long distances. Hungry Valley Formation: Thickness (meters) B-26. Coarse conglomerate, clast supported with a fining upward trend. Matrix is sandstone with planar crossbeds. Overall unit is orangish-brown. Conglomerate beds form large lobe shaped and trough shaped deposits up to 1.5 m high and 10 m wide..................... 32 241 Sandstone and siltstone. Sandstone is medium grained with channel—shaped sequences. Many beds are horizontally bedded and laterally continuous. Internally, the channelized portions are composed of massive and planar crossbeds commonly above a basal gravel deposit........................................ Conglomerate and pebbly mudstone. Interbedded massive mudstone and matrix supported cobble conglomerates. Conglomerates form lobe shaped deposits 0.5 m thick and 10 m wide. They are concentrated in 5 m thick pockets which alternate with 5 m thick layers of pebbly mudstone............................. . Sandstone and siltstone. Sandstone is medium grained with channelized sequences 2 to 50 m wide and 0.5 to 3 m thick. Many beds are horizontally bedded and laterally continuous. Internally, the channelized portions are composed of massive and planar crossbeds. Ripples and heavy mineral concentrated beds occur in the siltstone layers............... Siltstone and mudstone. Red—brown colored. No well preserved sedimentary structures due to bioturbation. Unit is horizontally persistant and of constant thickness....... Sandstone. Normally—graded, channel—shaped sequences 1 to 3 m thick and up to 15 m wide. Internal bedding is mostly trough crossbeds with some planar and low-angle crossbeds. Heavy mineral laminations in the finer grained beds.................................. Sandstone. Light-brown colored, carbonate cement. Poorly sorted and very coarse at base of normally graded sequences. Forms channelized sequences up to 2 m thick with planar and trough crossbeds................. Sandstone. Channel-shaped sequences containing trough crossbeds with some planar and low-angle crossbeds. Each channel sequence is normally graded, yellow—gray colored, 1 to 3 m thick and up to 25 m wide...... ,....... Sandstone and siltstone. Medium sandstone contains variable sized channel sequences. Many beds are horizontally bedded and laterally continuous for > 50 m. Internally, the channelized portions are composed of massive and planar crossbeds. Ripples and heavy mineral concentrated beds occur in the siltstone layers ......................... Sandstone. Channel-shaped, light-orange sequences 3 m thick and up to 25 m wide. Internal structures are trough crossbeds with some planar and low-angle crossbeds. Heavy mineral laminations in the finer grained beds Sandstone. Light-brown colored, carbonate cement. Poorly sorted and very coarse in some areas. Forms channelized sequences up to 2 m high with planar and trough crossbeds. Sequences are normally graded above a basal lag gravel................................ . Sandstone. Normally graded, light-orange channel-shaped sequences typically 1 to 3 m thick and up to 25 m wide. Internal bedding is mostly trough crossbeds with some planar and low-angle crossbeds. Heavy mineral laminations in the finer grained beds. Vertebrate fossils found.............. Siltstone and mudstone. Color varies from grayish green to red—brown. No well preserved sedimentary structures due to bioturbation. Beds are horizontally persistant and of constant thickness. Ostracodes visible in thin section......... Sandstone. Channel—shaped sequences 3 m thick and up to 25 m wide. Internal bedding is mostly trough crossbeds with some planar and low angle crossbeds. Heavy mineral laminations in the finer grained beds........................................ Siltstone and mudstone. Massive bedded due to bioturbation. Secondary sedimentary structures such as loading features are seen at the top of some beds...................... B-ll. Sandstone. Normally graded, channel-shaped sequences consisting of trough crossbeds with some planar and low angle crossbeds. Heavy mineral laminations in the finer grained beds. Each channel sequence is normally graded, 1 to 3 m thick and up to 20 m wide. 3 B-10. Siltstone. and mudstone. Color varies from grayish green to red-brown. No well preserved sedimentary structures due to bioturbation, paleophycus trace fossils visible along contacts. Beds are horizontally persistant and of constant thickness.................... I B—9. Sandstone. Channel—shaped normally graded sequences 1 to 3 m thick and up to 25 m wide. Internal bedding is mostly trough crossbeds with some planar and low-angle crossbeds... 12 B-8. Siltstone and mudstone. Color varies from grayish green to olive-gray. No well preserved sedimentary structures due to bioturbation. Some heavy mineral laminations are visible. Beds are horizontally persistant and of constant thickness. Secondary sedimentary structures such as loading features are seen at the top of some beds ...... 7 B—7. Sandstone. Channel—shaped sequences made up of trough crossbeds with some planar and low-angle crossbeds. Heavy mineral laminations in the finer grained beds. The normally graded light-orange beds are clay cemented ........ 15 B-6. Siltstone and mudstone. Color varies from grayish green to light-brown. No well preserved sedimentary structures due to bioturbation. Some heavy mineral laminations are visible. Secondary sedimentary structures such as loading features are seen at the top of some beds ........... 36 B-5. Sandstone. Channel-shaped light orange sequences 3 m thick and up to 25 m wide. Internal bedding is trough crossbeds with some planar and low-angle crossbeds. Mud rip-up clasts at base of some channel sequences.................. ................... 15 244 B-4. Siltstone and mudstone. Color varies from grayish green to light-brown. No well preserved sedimentary structures due to bioturbation. Carbonate cemented.......... 13 B—3. Sandstone. Channel—shaped sequences typically 3 m thick and up to 25 m wide. Internal bedding is mostly trough crossbeds with some planar and low-angle crossbeds. Heavy mineral laminations in the finer grained beds. ................................ 9 B-2. Siltstone and mudstone. Color varies from grayish green to light-brown. No well preserved sedimentary structures due to bioturbation. Beds are horizontally persistant and of constant thickness. Ostracodes visible in thin section......... 4 B-l• Sandstone. Light-orange channel-shaped sequences 1 to 3 m thick and up to 25 m wide. Internal bedding is mostly trough crossbeds with some planar and low-angle crossbeds. Heavy—mineral laminations in the finer grained beds............. 4 Total thickness........ 488 SECTION C The easternmost measured section is located west of Interstate 5. Exposures were measured along an abandoned road and under the Southern California Edison powerlines. Portions of the stratigraphic sequence were not exposed in the roadcuts, so some of the section was described from rock in the canyon below. Beds generally strike east-west with a 45°N dip. This stratigraphic sequence begins at the fault contact with a pluton and extends upward to a recumbant fold. The measurements were taken in sec. 29, T. 8N., R. 18W. 245 Hungry Valley Formation: Thickness (meters) C-49. Siltstone and mudstone. Color varies from grayish green to light-gray. No well preserved sedimentary structures due to bioturbation. Some heavy-mineral laminations are visible. Beds are horizontally persistent and of constant thickness. Secondary sedimentary structures, such as loading features, are seen at the top of some beds......................... 11 C-48. Sandstone, channel-shaped sequences up to 1 m thick and 10 m wide. Internal bedding is mostly trough crossbeds with some planar and low-angle crossbeds. Heavy-mineral laminations in the finer grained beds..................... 25 C-47. Sandstone and siltstone. Yellowish-brown to grayish orange, normally graded beds. Intensely bioturbated so it appears massive bedded with loading features at the upper contact........................................ 4 C—46. Sandstone. Channel-shaped sequences containing 3 trough crossbeds with some planar and low-angle crossbeds. Heavy mineral laminations in the finer grained beds at the top of channel sequences..................... 6 C-45. Covered........................................... 58 C-44. Sandstone, channel-shaped sequences typically 1 to 1.5 m thick and up to 10 m wide. Internal bedding is mostly trough crossbeds with some planar and low angle crossbeds. Each channel sequence fines upward and is light-orange colored ...... 12 C-43. Sandstone and siltstone. Yellowish-brown to grayish orange, normally graded beds. Loading features at the upper contact and gradational at lower contact .......... 2 C-42. Sandstone, channel-shaped sequences with loading features at base. Internal bedding is mostly trough crossbeds with some planar and low-angle crossbeds. Heavy mineral laminations in the topmost fine grained beds 246 C-41. Sandstone and siltstone. Yellowish-brown to grayish orange, normally graded beds with a gradational basal contact.................... <1 C-40. Sandstone, channel—shaped sequences basal beds are coarse conglomerate. Internal bedding is mostly trough crossbeds with some planar and low-angle crossbeds. Each channel sequence is normally graded, light-orange colored, with volcanic clasts......................... 1 C-39. Sandstone and siltstone. Yellowish-brown to grayish orange, normally graded beds. Loading features at the upper contact and a gradational lower contact................. <1 C-38. Sandstone, channel-shaped fining upward sequences 0.5 to 1 m thick and up to 10 m wide. Internal bedding is mostly trough crossbeds with some planar and low-angle crossbeds. Heavy mineral laminations in the finer grained beds............................ 26 C-37. Siltstone and mudstone. Color varies from grayish green to olive-gray. No well preserved sedimentary structures due to bioturbation. Beds are horizontally persistant and of constant thickness. Secondary sedimentary structures such as loading features are seen at the top of selected beds........ <1 C-36. Sandstone. Internal structures consist of trough crossbeds with some planar and low-angle crossbeds. Heavy mineral laminations in the finer grained beds at the top of some fining upward sequences........ I C-35. Sandstone and siltstone. Yellowish-brown to grayish orange, normally graded beds. The upper contact contains loading features while the lower contact is gradational <1 C-34. Sandstone, channel-shaped sequences with trough planar and low-angle crossbeds. Heavy mineral laminations in the finer grained beds 22 247 C-33. C-32. C-31. C-30. C-29. C-28. C-27. C-26. Siltstone and mudstone. Grayish green colored at top and bottom with red-brown. No well preserved sedimentary structures due to bioturbation. Some heavy mineral laminations are visible. Secondary sedimentary structures such as loading features are seen at the top of some beds...................... 1 Sandstone. Light-orange colored channel-shaped sequences. The internal bedding is mostly trough crossbeds with some planar and low-angle crossbeds. Each channel sequence is normally graded with heave mineral laminations in the finer beds.............. 29 Covered............ 76 Siltstone and mudstone. No well preserved sedimentary structures due to bioturbation. Secondary sedimentary structures such as loading features are seen at the top of the sequence layers ................. 5 Sandstone and siltstone. Yellowish-brown to grayish orange, normally graded beds. Bioturbated so now is massive bedded with loading features at the upper contact. Impersistant beds are in gradational contact with beds below............................ 1 Sandstone. Channel-shaped sequences 0.5 tO 1 m thick and up to 15 m wide. A typical channel is filled with trough crossbeds as well as some planar and low-angle crossbeds. Each channel sequence is normally graded, light-orange colored arkosic sandstone 15 Siltstone and mudstone. Grayish green to olive-gray colored. No well preserved sedimentary structures, due to bioturbation. The bed is horizontally persistant and of constant thickness....... 1 Sandstone, channel-shaped sequences with trough crossbeds and some planar and low-angle crossbeds. Heavy mineral laminations in the finer grained beds..................... 17 248 C-25. C-24. C-2 3. C-22. C-21. C-20. Siltstone and mudstone. Color varies from grayish green to red-brown in center. Some heavy mineral laminations are visible. Beds are horizontally persistant and of constant thickness. Secondary sedimentary structures such as loading features are seen at the top of sequence................... 1 Sandstone, channel-shaped sequences with basal rip-up clasts. Internal bedding is mostly trough crossbeds with some planar and low-angle crossbeds. Each channel sequence is normally graded, light-orange colored, with vertebrate fossils ............... 16 Siltstone and mudstone. Color varies from grayish green to olive-gray. No well preserved sedimentary structures due to bioturbation. Beds are horizontally persistant and of constant thickness. Secondary sedimentary structures such as loading features are seen at the topmost bed................. 2 Sandstone, channel-shaped fining upward sequences. Internal bedding is mostly trough crossbeds with some planar and low-angle crossbeds. Heavy mineral laminations in the finer grained beds.................. 4 Sandstone and siltstone. Yellowish—brown to grayish orange, normally graded beds. Bioturbated so now is massive bedded with loading features at the upper contact. Impersistant beds which have a gradational lower contact............................. 1 Sandstone, channel-shaped sequences typically 1 to 2 m thick and up to 10 m wide. Internal bedding is mostly trough crossbeds with some planar and low-angle crossbeds. Heavy mineral laminations in the finer grained beds grained beds............... 18 Siltstone and mudstone. Color varies from grayish green to red-brown. No well preserved sedimentary structures due to bioturbation. Finer grained in central portion. Beds are horizontally persistant and of constant thickness.................... 4 249 C-17. C-16. C-15. C-14. Sandstone, channel-shaped fining upward sequences 1 m thick and up to 5 ra wide. Internal bedding is mostly trough crossbeds with some planar and low-angle crossbeds. Heavy mineral laminations in the upper finer grained beds.................................. 10 Siltstone and mudstone. Grayish green at contact and yellow-brown in center portion. Beds are horizontally persistant and of constant thickness. Secondary sedimentary structures such as loading features are seen at the top of some beds...................... <1 Sandstone, channel-shaped sequences up to 1 m thick and 10 m wide. Internal bedding is mostly trough crossbeds with some planar and low-angle crossbeds. Heavy mineral laminations in the finer grained beds at top of normally graded sequences................ 12 Siltstone and mudstone. Color varies from grayish green to yellow-brown. No well preserved sedimentary structures due to bioturbation. Sharp contact at top and base. Beds are horizontally persistant and of constant thickness............................ <1 Sandstone, channel-shaped sequences. Internal bedding is mostly trough crossbeds with some planar and low-angle crossbeds. Each bed is 3—10 cm thick. Heavy mineral laminations in the finer grained beds. Each channel sequence is normally graded yellow-gray colored sandstone.......................... 10 Siltstone and mudstone. Beds are horizontally persistant and of constant thickness. Color varies from grayish green to olive-gray. No well preserved sedimentary structures due to bioturbation. Some heavy mineral laminations are visible. Secondary sedimentary structures such as loading features are seen at the top of some beds........ 4 250 C-ll. C-10. C-9. Sandstone, channel—shaped sequences typically 1 to 3 m thick and 3 to 10 m wide. Internal bedding is mostly trough crossbeds with some planar and low-angle crossbeds. Heavy mineral laminations in the finer grained beds. Each channel sequence is normally graded, red-brown to yellow-gray colored... 22 Siltstone and mudstone. Color varies from grayish green to olive-gray. Due to bioturbation there are no well preserved secimentary structures. Some heavy mineral laminations are visible. Beds are horizontally persistant and of constant thickness. Secondary sedimentary structures such as loading features are seen at the top of some beds....... 2 Sandstone, channel-shaped sequences typically 3 m thick and up to 25 m wide. The basal layer is heavy mineral laminated fine sand overlain by trough crossbeds with some planar and low-angle crossbeds. Each channel sequence is reversely graded then normally graded above.................................. <1 Siltstone and mudstone. Color varies from dark yellow-brown to olive-gray. No well preserved sedimentary structures due to intense bioturbation. Beds are horizontally persistant (up to 0.5 km wide) and of constant thickness............................ 2 Sandstone, channel-shaped sequences typically 1 to 3 m thick and 3 to 15 m wide. Trough crossbeds are overlain by planar and low- angle crossbeds. Heavy-mineral laminations are visible in the finer grained beds..... 23 Total thickness............... 447 251 Ridge Route Formation: C—7. Siltstone and mudstone. Color varies from dusky brown to olive-gray. No well-preserved sedimentary structures due to bioturbation. Some heavy-mineral laminations are visible. Beds are horizontally persistent and of constant thickness. Secondary sedimentary structures, such as loading features, are seen at the top of some beds................ 2 C-6. Pebbly sandstone, well-sorted, light-orange to grayish-orange color. Channel-shaped sequences are normally graded with both trough and planar crossbeds.......... 6 C—5. Siltstone and mudstone. Yellowish—brown to olive-gray colored. No well-preserved sedimentary structures due to bioturbation. Some heavy-mineral laminations are visible. Horizontally persistent beds are constant thickness with some loading features....... <1 C-4. Pebbly sandstone, well-sorted, light-orange to grayish-orange color, channel-shaped sequences with both trough and planar crossbeds, heavy-mineral laminations in the finer beds....... 7 C-3. Siltstone and mudstone. Color varies from grayish green to olive-gray. No well preserved sedimentary structures due to bioturbation. Beds are horizontally persistant and of constant thickness...... 12 C-2. Pebbly sandstone, well-sorted, light-orange to grayish—orange color, channel—shaped sequences with both trough and planar crossbeds, heavy-mineral laminations in the finer beds......... 1 252 Siltstone and mudstone. Color varies from grayish green to olive-gray. No well preserved sedimentary structures due to bioturbation. Some heavy-mineral laminations are visible. Beds are horizontally persistent and of constant thickness. Secondary sedimentary structures such as loading features are seen at the top of some beds...................................... Total thickness

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Engineering properties of Southern California borderland sediments

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Geology and economic significance of Pleistocene channel and terrace deposits on the San Diego mainland shelf, California

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Foraminiferal trends and paleo-oceanography in Late Pleistocene-recent cores, Tanner Basin, California

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Stratigraphy and sedimentary petrology of the Moss Back Member of the Late Triassic Chinle Formation, north Temple Wash - San Rafael Desert area, Emery County, Utah

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Clast-contact conglomerates in submarine canyons: Possible subaqueous sieve deposits

Asset Metadata

Creator Nitzberg, Katherine E (author)

Core Title Depositional environments of the Neogene Hungry Valley Formation: Sedimentary response to the initiation of the San Andreas Fault, Ridge Basin, Southern California

Degree Master of Science

Degree Program Geological Sciences

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag OAI-PMH Harvest,Sedimentary Geology

Language English

Contributor Digitized by ProQuest (provenance)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c30-121717

Unique identifier UC11225392

Identifier usctheses-c30-121717 (legacy record id)

Legacy Identifier EP58735.pdf

Dmrecord 121717

Document Type Thesis

Rights Nitzberg, Katherine E.

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA