CALIFORNIA STATE UNIVERSITY NORTHRIDGE STRATIGRAPHY AND DEPOSITIONAL ENVIRONMENTS OF THE VAQUEROS FORMATION, CENTRAL SANTA MONICA MOUNTAINS, CALIFORNIA A thesis submitted in partial satisfaction of the requirements for the degree of Master of Science in Geology by Juli G. Oborne January, 1987 is approved: Dr. A.~ritsche (CSUN), Chair California State University, Northridge ii To Mark and Alex whose constant encouragement, love, and impending arrival made this possible iii _, . ACKNOWLEDGMENTS I would like to thank my thesis chairman, Dr. Eugene Fritsche for all his help and guidance throughout the project. I am appreciative of the participation of Dr. Frank Kilmer in ·this study. Special thanks goes to Dr. Richard Squires for critically reading the thesis and making helpful comments. Dr. Eugene Fritsche also aided in the macrofossil identification. Dr. Judith Smith, U. S. Geological Survey, provided assistance in macrofossil iden­ tifications and also provided many helpful suggestions. I would like to thank Jeff Kennedy, of the Minerals Manage­ ment Service, for first introducing me to the area. A very special thanks go to all of my field assis­ tants, Mark Oborne, Steve Anderson, and Mike Blundell. These people were kind enough to offer their time, coopera­ tion, and much encouragement to help complete the field portion of this study. I would like to thank Hark Oborne and Barbara Henschel for all of their help with the typing of the thesis. I am especially grateful for the continual moral support and encouragement given to me by my husband and parents. iv r . TABLE OF CONTENTS Page Abstract............................................ xi In trod uc tion. 1 Purpose and Location.............................. 1 Previous Work..................................... 4 Geologic Setting.................................. 5 Stratigraphy.................................... 5 Age and Correlation...... 11 StruGture. 12 Lithosome Descriptions and Process Interpretations.. 22 Methods........................................... 22 Introduction to Lithosomes........................ 23 Lithosome Descriptions and Interpretations........ 25 Parallel-Laminated Siltstone (A)................ 25 Description................................... 25 Interpretation.. • . • . 2 7 Parallel-Laminated Fine-Grained Sandstone (B)... 28 Description................................... 28 Interpretation................................ 30- Structureless Fine-Grained Sandstone (C)........ 32 Description................................... 32 Interpretation...... • . 33 Cross-Bedded Sandstone (D)...................... 34 Description................................... 34 Interpretation. • . 39 v Page Parallel-Laminated Coarse-Grained Sandstone (E). 39 Description ...........·........................ 39 Interpretatign.. • . 41 Structureless Coarse-Grained Sandstone (F)...... 42 Description................................... 42 Interpretation... • . 43 Bioturbated Fine-Grained Sandstone (G).......... 44 Description . ............................ -·... 44 Inter pretatign..... • . • . 47 Parallel-Laminated Medium-Grained Sandstone (H). 48 ])escript ion .... ............ ~ . • . 48 In terpreta ti0n..... • . 49 Interbedded Red-and-Green Siltstone (I)......... 50 Description. Cl................................. 50 Interpretation.. 52 Paleogeographic Interpretation...................... 53 Paleoenvironmental Analysis....................... 53 Introduction. • . • . 53 Offshore/Prodelta Environments.................. 56 Transition Zone Environments.................... 58 Shoreface/Delta-Front Environments.............. 59 Distributary Mouth Bar Environments............. 61 Foreshore Environments.......................... 62 Backshore Environments.......................... 63 Lower Delta-Plain Environments.................. 65 vi Page Upper Delta~Plain Environments.................. 66 Paleocurrent Analysis............................. 69 Provenance. • . 7 2 Paleogeographic Map and Conclusions............... 76 References ....... 83 Appendix............................................ 92 vii LIST OF ILLUSTRATIONS Figure Page 1. Map showing the study area in the central Santa Monica Mountains...................... 2 2. Map of the central Santa Monica Mountains showing Vaqueros Formation outcrops......... 3 3. Summary of the stratigraphic nomenclature used by previous workers in the Santa Monica Mountains................................... 6 4. Composite vertical diagram of the sedimen- tary rock units of the central Santa Monica Mountains ................................... 7 5. Age correlation chart for the Vaqueros Formation in the central Santa Monica Mountains................................... 13 6. Approximate location of the "detachment surfaces" in the central Santa Monica Mountains ................................... 2-1 7. Photograph of swales and cross bedding in the fine-grained, cross-bedded sub- lithesome (D)............................... 37 8. Photograph of the bioturbation in the b~oturbated, fine-grained sandstone lithesome (G)............................... 46 9. Lateral facies diagram of the Vaqueros Formation in the study area ................. 54 viii Page 10. Study area interpreted epositional environ- ments and associated lithosomes............. 57 11. Paleocurrent data from the Vaqueros Formation in the central Santa Monica Mountains................................... 71 12. Ternary diagrams showing the composition of the sandstones in the Vaqueros Formation.... 73 13. Pre-rotation geometry in southern California about late Ol~gocene time................... 77 14. Possible orientations of the shoreline during the deposition of the Vaqueros Formation in the Santa Monica Mountains ..... 78 15. Paleogeographic map ..................•...... 80 Table Page 1. List of macrofossils collected from the Vaqueros Formation by the United States (;eological Survey. • . 15 2. List of microfossils collected from the Vaqueros Formation by the United States (;eological Survey........................... 19 ix Plate 1. Measured stratigraphic columns of the Vaqueros Formation, central Santa Monica Mountains, California ........•.••....... (in pocket) 2. Petrology of sandstone samples collected during this study from the Vaqueros Formation .....•.......................•. (in pocket) X p ' ABSTRACT STRATIGRAPHY AND DEPOSITIONAL ENVIRONMENTS OF THE VAQUEROS FORMATION, CENTRAL SANTA MONICA MOUNTAINS, CALIFORNIA by Juli G. Oborne Master of Science in Geology The Vaqueros Formation along the southern flank of the central Santa Monica Mountains is a sequence of lower upper Oligocene through lower middle Miocene sandstone and siltstone that records a rapid transgression due to rising sea level and a subsequent progradation of a deltaic system. Study of these rocks reveals nine lithosome units that are process controlled. The lithosomes, from lower to upper, include: a parallel-laminated siltstone (A); parallel-laminated, fine-grained sandstone (B): structure­ less, fine-grained sandstone (C); cross-bedded sandstone (D); parallel-laminated, coarse-grained sandstone (E); structureless, coarse-grained sandstone (F); bioturbated, xi <1 ' fine-grained sandstone (G); parallel-laminated, medium- grained sandstone (H); and interbedded red-and-green siltstone (I). Provenance and paleocurrent data are scarce, but source terrains that contributed high-grade metamorphic and reworked sedimentary clastic material to the study area are indicated. The river that supplied sediment probably flowed from a northern or eastern direction. There are two possible orientations of the shoreline: one that trended north-south and another that trended east-west. A river- dominated deltaic depositional system existed in the east­ ern portion of the study area, whereas wave-dominated deposition along an erosional coastline took place in the western region. The western stratigraphic sections - San Nicholas Canyon, Encinal Canyon, and Latigo Canyon contain strictly marine environments from offshore to backshore. A large amount of sediment from increasing tectonics caused the shoreline to prograde and the rocks generally reflect a shallowing upward from the bottom to the top of the strati­ graphic sections. The eastern sections Corral Canyon, Puerco Canyon, Malibu Canyon, and Piuma Road - contain rocks which also reflect a general shallowing upward, however, this is due to the progradation of a River- dominated deltaic system. The inferred environments deter- mined from these rocks are prodelta, delta front, and xii lower and upper delta plain. Although it is difficult to distinguish between the two, the deltaic and marine strandline deposits probably interfinger with each other between Corral and Latigo Canyons. During the early late Oligocene there was a rapid transgression of the sea. In the west, offshore and shoreface sediment of the Vaqueros was deposited unconfor- mably on the nonmarine Sespe Formation. At the same time, deltaic deposits of the Vaqueros and fluvial deposits of the Sespe were interfingering in the east. The greatest extension of the transgression was just east of the Puerco Canyon section. Continued subsidence and deposition al- lowed a thick section of sand to accumulate. Although sea levels continued to rise, the delta prograded due to the high sedimentation rate. After the early medial Miocene, uplift was followed by erosion and the Topanga Canyon For­ mation was deposited unconformably onto much of the Vaqueros. xiii INTRODUCTION PURPOSE AND LOCATION The purpose of this thesis is to examine