CALIFORNIA STATE UNIVERSITY, NORTHRIDGE DEPOSITIONAL ENVIRONMENTS OF THE EOCENE THROUGH OLIGOCENE SESPE FORMATION IN THE NORTHERN SIMI VALLEY AREA VENTURA COUNTY, SOUTHERN CALIFORNIA A thesis submitted in partial satisfaction of the requirements for the degree of Master of Science in Geology by Gary Edward Taylor May 1984 The Thesis of Gary Edward Taylor is approved: D£7. I v'a'K P. Col burn Dr. A. Eugeqe Fritsche Dr. Richard t. Squ-fres, Ct;ommittee- Chairman California State University, Northridge ii CONTENTS Page ABSTRACT vii INTRODUCTION 1 PREVIOUS WORK 4 AGE 5 METHODS 5 STRATIGRAPHY 9 MEASURED SECTIONS 10 SEDIMENTATION RATE 12 ACKNOWLEDGEMENTS 13 DESCRIPTION AND DEPOSITIONAL ENVIRONMENTS 14 SANDY BRAIDED-RIVER DEPOSITS 14 BRAIDED-RIVER SANDSTONE LITHOSOMES 16 BRAIDED-RIVER CONGLOMERATE LITHOSOMES 24 BRAIDED-RIVER MUDROCK LITHOSOMES 28 DISCUSSION OF BRAIDED-RIVER DEPOSITS 29 MEANDERING-RIVER FLOODBASIN DEPOSITS 30 MEANDERING-RIVER SANDSTONE LITHOSOMES 31 MEANDERING-RIVER CLAYSTONE LITHOSOMES 35 MEANDERING-RIVER CONGLOMERATE LITHOSOME 38 DISCUSSION OF MEANDERING-RIVER FLOODBASIN DEPOSITS 39 iii Page LOWER-DELTA PLAIN DEPOSITS 42 LOWER-DELTA PLAIN FINE SANDSTONE LITHOSOME 42 LOWER-DELTA PLAIN CLAYSTONE LITHOSOME 46 LOWER-DELTA PLAIN, MEDIUM TO COARSE SANDSTONE LITHOSOME 47 DISCUSSION OF LOWER-DELTA PLAIN DEPOSITS 48 PALEOCURRENTS AND PALEOCLIMATE 50 PALEOCURRENTS 50 PALEOCLIMATE 50 PROVENANCE 53 DESCRIPTION 53 DISCUSSION 55 PALEOGEOGRAPHY 59 LOWER DEPOSITIONAL PHASE 59 MIDDLE DEPOSITIONAL PHASE 61 UPPER DEPOSITIONAL PHASE 61 SESPE/VAQUEROS TRANSITION PHASE 65 REFERENCES CITED 67 iv LIST OF ILLUSTRATIONS Figure Page 1. Index map of the Simi Valley area 2 2. Generalized stratigraphic section of Simi Valley area 3 3. Explanation for stratigraphic sections of the Sespe Formation north of Simi Valley 7 4. Measured sections of the Sespe Formation north of Simi Valley 8 5. Generalized stratigraphic relationships of the Sespe Formation north of Simi Valley 11 6. Stratigraphic position of the Sespe/Vaqueros transition north of Simi Valley 13 7. Sketch of Lenticular Conglomerate Lithosome 22 8. Photo of Parallel and Low-Angle Cross-Bedded Lithosome 22 9. Photo of Lenticular Conglomerate Lithosome 25 10. Photo of Stratified Pebble-Cobble Conglomerate Lithosome 27 11. Photo of typical fining upward sandstone/claystone sequences of the middle member 30 12. Photo of botryoidal, fibrous-calcite concretion 34 13. Photo of claystone intraclasts within Bedded Sandstone Lithosome 36 14. Photo of Lenticular Sandy Claystone Lithosome 38 15. Photo of Matrix-Supported Pebble-Cobble Conglomerate Lithosome near Canada de la Brea fault 40 16. Photo of calcareous rhizomorph in Mottled Rhizomorph-Bearing Claystone Lithosome 47 17. Paleocurrent rose diagrams from lower and upper members 51 18. Composite stratigraphic section of the Sespe Formation showing stratigraphic position of depositional phases 60 v Figure Page 19. Diagrammatic paleogeographic reconstruction of the Sespe Formation north of Simi Valley 62 20. Diagrammatic paleogeographic reconstruction of the lower and middle depsoitional phases 64 21. Diagrammatic paleogeographic reconstruction of the upper and Sespe/Vaqueros transition depositional phases 66 Table Page 1. Vertebrate megafossils of the Sespe Formation north of Simi Valley 6 2. Comparison of calculated stratigraphic thicknesses of the members of the Sespe Formation 11 3. Distinguishing characteristics of the lithosomes seen in the Sespe Formation north of Simi Valley 15 4. Petrology of lower member samples 17 5. Petrology of upper member samples 18 6. Heavy mineral analysis of samples from the lower and middle members 19 7. Clast counts from the lower and upper members 25 8. Petrology of middle member samples 32 9. Heavy mineral analysis of samples from the middle member 33 10. Clast count from one locality in the middle member 40 11. Petrology of Sespe/Vaqueros transition samples 43 12. Heavy mineral analysis of samples from the Sespe/Vaqueros transition 44 13. Comparison of compositional assembleges of the Sespe Formation 54 Geologic Map In pocket vi ABSTRACT DEPOSITIONAL ENVIRONMENTS OF THE EOCENE THROUGH OLIGOCENE SESPE FORMATION IN THE NORTHERN SIMI VALLEY AREA VENTURA COUNTY, SOUTHERN CALIFORNIA by Gary Edward Taylor Master of Science in Geology The nonmarine Sespe Formation (early late Eocene through late Oligocene age) is well exposed in a northward-dipping, homoclinal sequence of strata north of the Simi anticline, northern Simi Valley, Ventura County, California. Three members and one transitional zone were recognized in the formation. The lower member and lower three-fourths of the upper member represent sandy braided-river deposits. Braided-bar deposits consist of parallel, low-angle, and trough cross bedded, medium to coarse lithic arkose and cross-bedded pebble conglomerate. Structureless and graded lithic arkose and structureless, silty claystone represent overbank-sheetflood and braided-river floodplain deposits. Migrating, primary channel-fill deposits consist of intraclast-bearing sandstone vii and clast supported, pebble-cobble conglomerate. Anabranch channel- lag deposits are represented by discontinuous, stratified pebble- cobble conglomerate beds. Climbing-ripple laminated, carbonaceous, mudstone indicates braided-river swamp (pond) deposits. The middle member consists predominantly of cyclical sandstone and claystone with lesser amounts of conglomerate and represents meandering-river floodbasin deposits. Structureless and graded, medium to coarse lithic arkose and mottled, structureless, claystone represent overbank-sheetflood and suspension deposits. Crevasse-splay deposits consist of cross-bedded, intraclast-bearing, medium to coarse lithic arkose and lenticular sandy claystone beds. Rare matrix- supported pebble-cobble conglomerate represents meandering channel- fill deposits. The upper one-fourth of the upper member (Sespe/Vaqueros transition) represents lower-delta-plain deposits that are gradational ,.., with overlying wave-dominated delta-front deposits of the Vaqueros Formation. Parallel-bedded, medium to coarse, intraclast-bearing lithic arkose represents distributary channel-fill deposits. Laminated well-sorted fine arkose occurs near the top of the formation and represents foreshore deposits. Mottled, rhizomorph-bearing claystone occurs near the top of the formation and represents salt-marsh deposits. The provenance appears to be primarily from reworked Paleogene formations which crop out in the Simi Hills area. Less dominant and more distant mafic and high-rank metamorphic source areas may have originated from the southern San Gabriel Mountains. In addition, the viii rare occurrence of anorthosite clasts in the upper member may indicate a northern San Gabriel Mountains source. The Sespe Formation north of Simi Valley represents a south­ eastward-transgressive fluvial to deltaic sequence, which is indicated by four depositional phases. The lower phase represents a braided­ river floodplain which onlapped onto a pre-Sespe erosion surface in the Simi Valley area. The middle phase consists of meandering-river floodbasin deposits resulting from infilling of a stable depositional basin. The upper phase consists of northwesterly-flowing braided­ river deposits which, based on stratigraphic position, were deposited in a upper-delta plain environment. The Sespe/Vaqueros transition phase represents lower-delta plain deposits which moved into the area by continued southeastward transgression of the "Vaqueros shoreline". ix INTRODUCTION The nonmarine Sespe Formation in northern Simi Valley, Ventura County, California (Fig. 1; Geologic Map in pocket) is well exposed in a broad, homoclinal sequence of strata that crops out between the Simi Valley and the southern flank of Big Mountain. The formation is of particular economic interest in the Simi Valley area because it is the major oil-producing horizon in the Simi, Canada de la Brea (C.D.L.B.). and Big Mountain oil fields. The scope of this paper is to describe, in detail, the Sespe sedimentary deposits and to determine their depositional environments by the use of modern stratigraphic analysis techniques. Based on a study of detailed measured sections as well as on a lateral tracing of beds in a 38 km 2 area, the following depositional environments are recognized: 1) sandy braided river, 2) meandering-river floodbasin, and 3) lower delta plain. Early workers did not discuss depositional environments of the formation, and they obtained stratigraphic thicknesses from ortho­ graphic projections, cross sections, and/or well logs. Later workers discussed only the generalized depositional environments of the formation in the Simi Valley area. The Sespe Formation attains a maximum thickness of 1,656 m, which comprises approximately one-fourth of the entire thickness of the Cenozoic section found in the Simi Valley area (Fig. 2). 1 Rl'ler Piru ··-··. .../··· "'ountaln •.• --···-· Fillmore~ \Cl --···-c••'···- ... - Cl\0 Newhall .. 0 ~>Jdl• ~ 0 oak .. ~\::1 Sa171 :l s \ s~s "'ountaln \ a,., [·:· ·sruar· AREA'.(.:pll \ - 1+~~~-i~/.:\:/;::: ~·····'''' Valley ,,. '~-' 0 Chatsworth sun I ...J r Canoga Park 0 Reaeda I o ~it c,.,. 'c N sa,,il 'Monica Mountains 0 5 10 Miles 0 5 10 20 34° Point Dume Kilometers 119° 118.30' Figure 1. Index map of Simi Valley and vicinity. N 3 SERIES/ SYSTEM Sub series ,:G:.:R.:.:A:;P:-;H:.:I:.::C~L.::O:;G;.-____=.:..::..:..:.:::..:::=...:.....:::....:==:!:::!!.....!.!.!;~~:.!:..::::...._ _____, .,; Up . Ill ~ c Gi ~.-. II NONMARINE SANDSTONE