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Paleoenvironmental analysis of Upper Cretaceous Pleasants Sandstone Member (Williams Formation), Santa Ana Mountains, Southern California

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Paleoenvironmental analysis of Upper Cretaceous Pleasants Sandstone Member (Williams Formation), Santa Ana Mountains, Southern California

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Content PALEOENVIRONMENTAL ANALYSIS OF UPPER CRETACEOUS PLEASANTS SANDSTONE MEMBER (WILLIAMS FORMATION), SANTA ANA MOUNTAINS, SOUTHERN CALIFORNIA by Eugene Joseph Enzweiler A Thesis Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE (Geological Sciences) August 1985 UMI Number: EP58749 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 EP58749 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 UNIVERSITY OF SOUTHERN CALIFORNIA THE GRADUATE SCHOOL UNIVERSITY PARK LOS ANGELES. CALIFORNIA 90007 This thesis, written by .Eugene _ Joseph _ Enzwe.iler........... under the direction of his.___Thesis Committee, and approved by all its members, has been pre sented to and accepted by the Dean of The Graduate School, in partial fulfillment of the requirements for the degree of Master of Science Dean D ate July 2, 1985 J6.UM4s/LO ABSTRACT The Williams Formation (Upper Cretaceous; Santa Ana Mountains, southern California) consists of two distinct members, one a medium- to coarse-grained sandstone and conglomeratic unit (Schulz Ranch Sandstone Member), and the other a fine- to medium-grained sandstone unit (Pleasants Sandstone Member). The Pleasants Sandstone Member is the topic of this study, with the focus on strata within Modjeska Grade, Baker Canyon, and Black Star Canyon. Sedimentologic, ichnologic, and paleontologic analysis of the Pleasants support a middle to outer continental shelf paleoenvironmental interpretation. This dominantly fine-grained clayey sandstone member is interbedded with numerous medium- and coarse-grained sandstone deposits that are interpreted as tempestites. The intensity and duration of storm activity determined the thickness of these units, as well as their preservability. The fine-grained clayey sandstones become progressively more dominant towards Black Star Canyon (southeast to northwest). These strata represent sediments deposited via waning storm activity, as well as hemipelagic sedimentation. These rocks exhibit a complete range of biologically- to physically-dominated sedimentologic fabrics, production of which depended upon sedimentation rates, infaunal organism densities, and dissolved oxygen levels. Diagenetic carbon ate concretions are abundant in these strata and are useful in determining the initial sediment fabric of the deposits. These carbonate concretions were formed through the decom position of abundant organic matter (plant and animal) in porous water saturated sediments. Benthic paleocommunities within the fine-grained clayey sandstones are dominated by the infaunal macrofauna Turritella and Ptertrigonia. and the infaunal ichnofauna Helminthoidea. The medium-grained sandstones contained Ophiomorpha and Thaiassinoides trace fossils. A number of escape burrows were also present. Microfossil analyses provide a Campanian-Maastrichtian age for these strata and a paleobathymetric interpretation of upper bathyal depths. The lack of clay minerals, the medium- to coarse-grained texture, rarity of microfossils, primary sedimentary structures (hummocky cross-beds and parallel laminations), transported shell materials, numerous escape burrows, and the thickness of individual units suggest that these sediments were deposited rapidly, via storm activity on a narrow shelf. The majority of this sediment influx came from the vicinity of Modjeska Grade, the study section interpreted as having been in the shallowest part of the Pleasants paleoenvironment. iv DEDICATION To my parents Eugene J. and Helen C. Enzweiler for their continuous, unselfish support and encouragement throughout my life. v ACKNOWLEDGEMENTS I would like to sincerely thank the many individuals who have donated their invaluable assistance during the course of this thesis. First and foremost I would like to give my wholehearted thanks to my thesis advisor, Dr. David J. Bottjer, for guidance and encouragement throughout this scientific undertaking. I am indebted to Drs. Donn S. Gorsline and Barney Pipkin for criticing the text and making helpful suggestions. Dr. Richard L. Squires is thanked for his review and helpful advice. A.A. Almgren and M.V. Filewicz (Unocal) unselfishly provided assistance in performing microfossil analyses. I am grateful to Paul J. Scrivner for his invaluable assistance in photographing my samples and outcrops, and to Victor Santos and Chuck Savarda for their assistance with the LECO gasometric determinations. To my fellow students Mike Bass, Jim Browning, Steve Buck, Mary Droser and Jim Loch, I thank you for making things both educational and entertaining throughout my stay at USC. Thanks goes to Mr. Apple, owner of the Modjeska Grade property for allowing me vi access to outcrops on his land, A very special thanks goes to my uncle Milton E. Rust, my siblings Mark, Mary Ann, Tom, and Barbara, along with Melanie S. Briggs, for their unwavering support throughout this endeavor. Many thanks to Sigma Xi, The Department of Geological Sciences Graduate Student Research Fund at the University of Southern California and the National Science Foundantion (NSF Grant EAR82-13202) for providing partial financial support for this research. CONTENTS ABSTRACT...................................................... ii DEDICATION ................................................. v ACKNOWLEDGMENTS .......................................... vi Ctaptsx pass INTRODUCTION ............................................... 1 GEOLOGIC SETTING .......................................... 9 AGE AND CORRELATION.......................................... 14 METHODS.........................................................17 SEDIMENTOLOGY ............................................... 33 Introduction ............................................ 33 Sandstone Composition: Fine-Grained Sandstones . . . 49 Sandstone Composition: Medium-Grained Sandstone . . 50 Discontinuous Conglomerate Lenses ................... 56 Paleoenvironments of the Pleasants Sandstone Member. 61 Proximality to Shore ................................... 73 Fluctuation of Sea Level.............................. 7 5 Conclusions............................................... 76 TRACE FOSSILS................................................. 77 Introduction ............................................ 77 Traces of the Coarser-Grained Sandstone ............ 82 Traces of the Finer-Grained Sandstone .............. 91 Conclusions............................................... 94 MICROPALEONTOLOGY .......................................... 96 MACROPALEONTOLOGY .......................................... 102 Introduction ............................................ 102 Macrofauna and Macroflora ............................ 102 Mode of Fossil Deposition..............................103 CARBONATE CONCRETIONS ..................................... Ill Introduction ............................................ Ill Concretion Morphologies .............................. 115 Composition of Concretions ............................ 124 Organic Association ................................... 127 Timing of Carbonate Concretions ..................... 133 Conclusions.............................................. 141 PALEOENVIRONMENTAL SUMMARY .............................. 142 Medium-Grained Sandstones ............................ 142 Fine-Grained Sandstones .............................. 144 CONCLUSIONS...................................................146 REFERENCES...................................................148 A. STRATIGRAPHIC SECTION: MODJESKA GRADE ............ 168 B. STRATIGRAPHIC SECTION: BAKER CANYON .............. 17 6 C. STRATIGRAPHIC SECTION: BLACK STAR CANYON .... 185 ix LIST OF FIGURES Eijgj 1. Location map showing field study area and outline of outcrops of Upper Cretaceous strata, Santa Ana Mountains, southern California (modified after Sundberg and Cooper, 1978)........................... 2 2. Generalized stratigraphic columns of Upper Cretaceous strata, Santa Ana Mountains, southern California (modified after Sundberg and Cooper, 1978)................................................... 4 3. Generalized stratigraphic section of the Santa Ana Mountains showing maximum thickness of each formation or member shown (from Schoellhamer, et al., 1981)........................................... 10 4. Location map of exposures measured along Santiago Truck Trail, El Toro Quadrangle, southern Cali fornia (dashed line). Stake numbers are shown on map, these stake number locations are also marked on the corresponding stratigraphic columns in Appendix A, allowing correlation between outcrop location and stratigraphic sections................... 18 5. Location map of exposures measured along Upper Baker Canyon Road, BLack Star Canyon Quadrangle, southern California (dashed line). Shown on the map are numbers indicating outcrop locations which can be correlated with stake numbers on the stratigraphic columns in Appendix B................ 20 x 6. Location map of exposures measured along Edison Power Road, Black Star Canyon Quadrangle, southern California (dashed line)• Stake numbers are shown on map, these stake number locations are also marked on the corresponding columns in Appendix C allowing correlation between outcrop location and stratigraphic sections.................................. 22 7. Location map of microfossil sample sites along Santiago Truck Trail (dashed line). These sample locations are also on the stratigraphic columns in Appendix A, making possible correlation of sample sites and stratigraphic sections.......................25 8. Location map of microfossil sample sites along Upper Baker Canyon Road (dashed line). Sample locations are listed on the map, which can be correlated with sample locations on the corresponding stratigraphic columns in Appendix B. 27 9. Location map of microfossil sample sites along Edison Power Road (dashed line). These sample locations are also listed on the stratigraphic columns in Appendix C, making correlation of sample sites and stratigraphic columns possible. . 29 10. Ideal case, levels of the erosional (a-c) and depositional regime (A-C) should correspond at any point along the proximal-distal gradient of a turbulent event (from Seilacher, 1982)............. 36 11. The proximality gradient most commonly associated with turbidites and inundites. This gradient may also occur in tempestites (from Seilacher, 1982).. 39 12. Sequence of structures in a flood plain deposits of a single flood (Based on McKee, et al., 1967).. 41 13. Schematic representation of turbidite facies model (Bouma Sequence), showing five units each with characteristic sedimentary structures (after Bouma, 1964)........................................... 44 14. The idealized tempestite sequence corresponds closely to the Bouma-sequence, except for the wave-rippled top. Since plane lamination in most cases passes gradually into wave-ripple lamination, wave riples belong to the complete tempestite sequence and are not due to a sub sequent phase of reworking (from Aigner, 1982). . 47 xi 57 59 64 66 69 71 79 83 85 88 92 105 107 116 xii Discontinuous conglomerate lense (shown with arrows) located along the Santiago Truck Trail, MG-15. These are found throughout the Pleasants Sandstone Member....................................... Vertically oriented, complete shell valve (note arrow) within a conglomerate stringer, located at MG-15, along Santiago Truck Trail................... Storm deposit containing edgewise shells located along Santiago Truck Trail, Modjeska Grade, at MG-6 (scale: yellow line equals 1 cm).............. Cross-bedding within a tempestite, located along Modjeska Grade, MG-18................................. Wave ripples (indicated by arrows), near the top of a tempestite, overlain by pelagic deposits. . . Amalgamted storm beds located at MG-18 to MG-19 (indicated by arrows)................................. Environmental significance of trace fossils and their common associations (Seilacher, 1978). . . . Ophiomorpha trace on sandstone bedding plane in Black Star Canyon, BS-5 (scale: red line equals 1 cm)...................................................... Thalassinoides burrow in sandstone strata found along Edison Power Road, Black Star Canyon, BS-5 (note arrow)........................................... Escape burrow in tempestite bed along Santiago Truck Trail, Modjeska Grade, MG-18 (scale: red line equals 1 cm)..................................... Helminthoida traces in concretion slab section, from Baker Canyon, BC-1 (scale: red line equals 1 cm)...................................................... A storm produced shell bed located along Santiago Truck Trail, Modjeska Grade, MG-6................... Possible storm deposit located at BS-25, display disarticulated shells, shell fragments, and mud coated shells.......................................... Ellipsoidal shaped carbonate concretions found within the Pleasants Sandstone Member......... 29. Round shaped carbonate concretion found within the Pleasants Sandstone Member.............................118 30. Rectangular shaped carbonate concretion found within the Pleasants Sandstone Member (field of view equals 1.5 meters)................................120 31. Discontinuous carbonate concretionary beds parallel to beding, formed by coalescing concretions, located at BS-3.......................... 122 32. Highly fragmented, rudimentary carbonate concretions located in the fine-grained sandstones of Baker Canyon......................................... 125 33. Carbonate concretion displaying shell and shell fragments.................................................130 34. Uncrushed fossil material found within a con cretion, indicating an early diagenetic origin. . 134 3 5. The bending of strata around a concretion in the fine-grained clayey sandstone outcrops.............. 137 36. The bending of strata around a concretion found in the medium- to coarse-grained sandstone outcrops (field of view equals 1 meter)........................139 xiii LIST OF TABLES TaJbl££ 1. LECO gasometric determinations of medium- to coarse-grained sandstones (organic carbon to carbon composition percentages)........................51 2. LECO gasometric determinations of fine-grained sandstones (organic carbon to carbonate content percentages).............................................. 54 3. List of identified macrofossils and their locations (X indicates presence) ................... 97 4. LECO gasometric determinations of carbonate con cretions (organic carbon and carbonate compos ition percentages)......................................128 xiv INTRODUCTION This study focuses on the Upper Cretaceous (Upper Campanian) Pleasants Sandstone Member (Williams Formation) in Modjeska Grade, Baker and Black Star Canyons, Santa Ana Mountains, southern California (Fig. 1). Initial studies were performed by E. L. Packard who named the Trabuco Formation in 1916, and W. P. Popenoe who in 1937 used megafossil data to establish the Ladd and Williams Formations along with their present day members. The Upper Cretaceous strata are divided into 3 formations (Packard, 1916 and 1922; Popenoe, 1937, 1941 and 1942; Morton and Miller, 1973) which are in ascending order: the basal Trabuco Formation, the intermediate Ladd Formation (Baker Canyon Conglomerate Member and Holz Shale Member) and the uppermost Williams Formation (Schulz Ranch Sandstone and Pleasants Sandstone Members) (Fig. 2). These are of variable thicknesses, but a composite maximum aggregrate of 2013 m (Trabuco Fm. 173m, Ladd Fm. 1155m, Williams Fm. 685 m) is derived from Schoellhamer et al. (1981). 1 Figure Is Location map showing field study area and the outline of outcrops of Upper Cretaceous strata, Santa Ana Mountains, southern California (modified after Sundberg and Cooper, 1978). 2 BLACK STAR CANYON BAKER CANYON MODJESKA GRADE 3 Figure 2: Generalized stratigraphic columns of Upper Cretaceous strata, Santa Ana Mountains, southern California (modified after Sundberg and Cooper, 1978). 4 m UPPER CRETACEOU, Santonian- Coniacian Turonian Campanian H ) ^ 3 O U < i ) O V V 0 o « — r t The Trabuco Formation is characterized as a dark red, poorly sorted, and poorly stratified, slightly muddy, coarse sandy, polymictic cobble to boulder conglomerate (Sundberg and Cooper, 1978, 1982? Cooper, et al., 1982), The basal member of the Ladd Formation (Baker Canyon Conglomerate Member) is characterized by a greenish gray to brown, medium to coarse sandy, polymictic cobble conglomerate at the base, changing to a ridge forming succession of medium- to thick-bedded and massive, yellow-tan to light brown sandstone at the top as it grades vertically into the upper member (Holz Shale Member) (Sundberg and Cooper, 1978, 1982; Cooper, et al., 1982). This upper member is characterized as a olive brown to tan, bioturbated, very fine sandy mudstone to siltstone with blocky to shaly weathering at the base, while the middle to upper section is darker and consists of poorly laminated, weakly fissile mudstone to silty clay shale containing concretions (Sundberg and Cooper, 1978, 1982? Cooper, et al., 1982). The Williams Formation lies unconformably upon the Ladd Formation (Sundberg and Cooper, 1978, 1982? Cooper, et al., 1982). Its basal member (Schulz Ranch Sandstone Member) is composed of medium to thick beds of fine- to coarse-grained, granular pebbly sandstone with intercalated stringers and thick beds of well-rounded pebbly to cobble conglomerate (Sundberg and Cooper, 1978, 1982; Cooper, et al., 1982). This unit has a 6 gradational contact with the upper member (Pleasants Sandstone Member) which consists of poorly stratified fine to medium sandstones containing concretions and stringers of conglomerates (Sundberg and Cooper, 1978; Schoellhamer et al., 1981). Paleoenvironmental interpretations of these strata follow an overall transgressive-regressive-transgressive sequence (Almgren, 1973, 1982; Sundberg and Cooper, 1978, 1982; Saul, 1982). The specific depositional environments hypothesized for these Cretaceous rocks include alluvial fan (Trabuco Formation) (Cooper and Sundberg, 1978, 1982; Cooper et al., 1982), high-energy near shore, marine (Baker Canyon Comglomerate Member) (Sundberg and Cooper, 1978, 1982; Cooper et al., 1982 Saul, 1982), slope (Holz Shale Member) (Almgren 1973, 1982; Blake and Colburn, 1982; Lee, 1982; Link and Bottjer, 1982; Buck, 1983), high-energy, shallow marine (Schulz Ranch Sandstone Member) and inner- to middle shelf (Pleasants Sandstone Member) (Sundberg and Cooper, 1978, 1982; Cooper et al., 1982; Saul, 1982). The paleoenvironmental interpretation of the Pleasants Member as an inner- to middle shelf deposit interests this author the most. Previous authors (Sandberg and Cooper, 1978 and 1982; Saul, 1982) have based their inner-middle shelfal interpretations on the megafossil data. These 7 studies have been limited in scope and their results have yet to set forth a more complete interpretation. In this author's judgement it is vital to incorporate as many lines of evidence as possible to obtain an accurate paleoenviron mental interpretation. This research project was designed to examine and combine data from the disciplines of paleon tology, ichnology and sedimentology to procure a complete and viable paleoenvironmental interpretation of the Pleasants Member. 8 GEOLOGIC SETTING The Santa Ana Mountains are in the northern part of the Peninsular Range Province. The upper Cretaceous strata in the Santa Ana Mountains are composed of a thick (approxi mately 2013 m.) succession of terrigenous clastic sedimen tary rocks that were deposited in a paralic to bathyal environmental setting. This section was derived from the erosion of the ancestral Santa Ana Mountains and is lying unconformably between rock assemblages of Jurassic-Early Cretaceous and Paleogene ages (Fig. 3). The Bedford Canyon Formation, the oldest unit in the Santa Ana Mountains, is a thick (greater than 5000 m) Triassic (?), Middle to Late Jurassic (Imlay, 1963, 1964? Siberling et al., 1961? Criscione et al., 1978) succession developed mainly as flysch (Moscoso, 1967? Moran, 1973) deposits of a fore-arc or inner arc basin (Buckley, et al., 1975), and is exposed in the overturned limb of a large nappe (Moscoso, 1967) . According to Moscoso (1967) the nappe may have resulted from eastward obduction in Late 9 Figure 3: Generalized stratigraphic section of the Santa Ana Mountains showing maximum thickness of each formation or member shown (from Schoellhamer et al., 1981). 10 < < - J s < n > 6 • ° ^ * >5 \ili/v m e x p l a n a t i o n E x tru s iv e ro c k s Grenitofcd in tru s iv e ro eks C la y * to n e o r shale; si Its to n e S in d ito n s ; s ilty sandstone P s tn ly san d s to n e ; c o n g lo m e ra te S lig h tly m e ta m o rp h o s e d s ilts to n e sn o g re y w e c k e M E T E R S F E E T 3000 — i o-^o V e rtic a l scale 11 Jurassic time. Shallow intrusives cut the Bedford Canyon strata, which are overlain unconformably by extrusive andesitic rocks of the Santiago Peak Volcanics of Late Jurassic age (Fife et al., 1967) to Early Cretaceous (Colburn, 1973). Shortly after the precusor Santiago Peak Volcanics, intrusive rocks of the southern California batholith (Larsen, 1948; Woyski, 1972) were emplaced during early and middle Cretaceous time (Everden and Kistler, 1970; Krummenacher et al., 1975). The intensely deformed Bedford Canyon strata, the andesitic Santiago Peak Volcanics, and the magmatic arc rocks of the southern California batholith make up the basement complex and reflect an orogenic history related to Late Mesozoic subduction (Hill, 1971; Yeats, 1974; Gastil, 1975). The overlying post-orogenic Upper Cretaceous rocks, which compose the lower part of a clastic wedge that is pre-middle Miocene, pre-inception of Los Angeles Basin (Yerkes et al., 1965; Yeats, 1968), contain three forma tions: the basal Trabuco Formation, the middle Ladd Formation and the upper Williams Formation. The overlying Cenozoic (Paleocene) strata, which was first identified by Dickerson (1914) and named the Silverado Formation by Woodring and Popenoe (1945), lies unconformably upon the Williams Formation. This contact represents an episode of deformation, extensive erosion and deep weathering between 12 the deposition of marine Cretaceous rocks and Paleocene rocks. An angular discordance has not been observed, but the Silverado rests on progressively older strata from southwest to northeast (Schoellhamer et al., 1981). 13 AGE AND CORRELATION The age of the Pleasants Sandstone Member has been established by Popenoe (1937 & 1942) based upon macrofossils. Popenoe (1942) assigned the mollusk assemblage in the Pleasants Sandstone Member to the highest faunal division of the Glycermeris veatchii fauna, the Metaplacenticeras pacificum division, the youngest fauna of the Cretaceous in the Santa Ana Mountains. There are numerous mollusks species, but only a few of those that occur abundantly are confined to the division. Lembulus cf. L. striatula. Atria ornatissimus. Leaumen ooides. and an undescribed species of Meekia generally occur no lower in the Santa Ana Mountains.Calve bowersiana is almost completely confined to this division (Schoellhamer et al., 1981). The ammonite Metaplacenticeras pacificum is a common and characteristic fossil that occurs throughout the strata in the Pleasants Sandstone Member. Matsumoto (195 9-1960, v. 2, p. 66) places this ammonite in the upper part of the Campanian Stage, based upon the known stratigraphic range of 14 the genus. Morton (1972) reported fossils of possible Maastrichtian age (?) from the Pleasants Sandstone Member (upper part of the Williams Formation) in the southern part of the outcrop belt. While the Pleasants Sandstone Member is older than the Rosario Formation of El Rosario (Kilmer, 1963; Patterson, 1978; Yeo, 1982; Bottjer and Link, 1984) and the Cabrillo Formation of San Diego (Sliter, 1979; Nilsen & Abbott, 1979 & 1981; Bottjer & Link, 1984), it is probably younger than the Valle Saletral Formation of Baja California, the Pigeon Point Formation of San Mateo Co. (Popenoe et al., 1960), and the Punta Baja Formation of El Rosario (Kilmer, 1963; Patterson, 1978; Yeo, 1982; Bottjer & Link, 1984). Furthermore, based on megafossil (Popenoe, et al., 1960) and microfossil (Almgren, 1973) data from the uppermost Cretaceous strata of the Santa Ana Mountains, the Pleasants Sandstone Member and the middle part of the Jalama Formation of the Western Santa Ynez Mountains (Dailey & Popenoe, 1966; Almgren, 1973; Me Colluch et al., 1979; Browning, 1983), as well as, the upper part of the Chatsworth Formation of the Simi Hills (Saul, 1983; Bottjer & Link, 1984) and the middle section of the Point Loma Formation of Carlsbad and San Diego (Sliter, 1979; Nilsen & Abbott, 1979 & 1981; Bartling & Abbott, 1983) are approximately correlative and are Late Campanian in age (Popenoe et al., 1960; Almgren, 1973). 15 The presence of Metaplacenticeras pacificum aids in correlating the Pleasants Sandstone Member to other formations of relatively the same age, such as: the upper part of Panoche Formation (of Anderson & Pack, 1915? Taff, 1935) of the Diable Range; and the upper part of the Del Valle Formation of the Diablo Range (Popenoe et al.f 1960). 16 METHODS Analysis of the Pleasants Sandstone Member in Baker and Black Star Canyons along with Modjeska Grade was achieved by incorporating both field and laboratory techniques. The stratigraphic columns presented in Appendices A,B, and C represent outline descriptions of stratigraphic data collected from the discontiuous outcrops of the Pleasants Sandstone Member along Santiago Truck Trail, El Toro Quadrangle, California; Upper Baker Canyon Road, Black Star Canyon Quadrangle, California; and Edison Power Road, Black Star Canyon Quadrangle, California (see Figs. 4,5 & 6 respectively). Due to the repetitous nature of the outcrops, a pace-and-compass traverse was originally staked out and the stakes were utilized as reference points for the precise reporting of sample site locations. Geometric calculations based on traverse measurements were used to determine true stratigraphic thickness. Collections of data in the field focused on the gathering of decisive paleontologic, ichnologic and 17 Figure 4: Location map of exposures measured along Santiago Truck Trail, El Toro Quadrangle, southern California (dashed line)• Stake numbers are shown on map, these stake number locations are also marked on the corresponding stratigraphic columns in Appendix A, allowing correlation between outcrop location and stratigraphic sections. 18 19 Figure 5: Location map of exposures measured along Upper Baker Canyon Road, Black Star Canyon Quadrangle, southern California (dashed line)• Shown on the map are numbers indicating outcrop locations which can be correlated with stake numbers on the stratigraphic columns in Appendix B. 20 (1 i u/ V.; f p i j ^ y >.y^ ' " { : ' * * : /J: ^f') §•* :A / A / 7 / v / 7 / 7 ! I / r v A 1 1 I —1 n . / / . ■ / . / ) : M A l l l k y A A I ' A t A : - ^ S W ■ ' "/ N i \ ' n >// /' ' i i \ ’ vV^ ' i f (AM y^iii'V o^/r-j- V t / ' V , t\ 3 v A ‘A v- / y • 1 \\ "V\Omu , ■ £ : J:rrr / / * ' A \ \ * ■ f t ; ;;::..bc-i 7 7; u;r U o ° J i v , 'tr ' — \ ' A A • * X v. ' v v n \ v \ \ v . w 40'co" " •") --s- 21 Figure 6: Location map of exposures measured along Edison Power Road, Black Star Canyon Quadrangle, southern California (dashed line). Stake numbers are shown on map, these stake number locations are also marked on the corresponding columns in Appendix C allowing correlation between outcrop location and stratigraphic sections. 22 sedimentologic information. Most observed macrofossils were collected for identification and analysis. Macrofossil data was collected using Hubco sample bags (12 X 6.5 in.) which were filled with sediments from 1-2 foot deep excavations or from stream cut gullies, along the Santiago Truck Trail, Upper Baker Canyon Road and Edison Power Road (see Figs. 7,8 and 9). Trace fossil analysis in the field concentrated on lateral and vertical variations of traces, intensity of degree of bioturbation, and the interrelationships between traces and associated sedimentologic and paleontologic features. Field observation of sedimentologic data focused on reporting of lateral and vertical textural changes, collection of (50) sandstone hand samples along with (150) concretions for laboratory study. The carbonate concretions, which were unevenly distributed in both the course and fine-grained strata, were randomly collected. Due to the highly weathered and fragmented nature of the strata, analysis of sedimentologic textures and structures were performed in the laboratory. Laboratory examination of concretions and sandstone hand samples was performed utilizing various techniques. Rock samples were serially slabbed in perpendicular planes, thus allowing for three-dimensional study of primary and secondary structures. Polyester boat resin was applied to the friable samples, thus allowing these rocks to be 24 Figure 7: Location map of microfossil sample sites along Santiago Truck Trail (dashed line). These sample locations are also on the stratigraphic columns in Appendix A, making possible correlation of sample sites and stratigraphic sections. 25 26 Figure 8: Location map of microfossil sample sites along Upper Baker Canyon Road (dashed line). Sample locations are listed on the map, which can be correlated with sample locations on the corresponding stratigraphic columns in Appendix B. 27 ^ / • , T-5<S ^ v:' * , \/j,, ■;,r~'A;\, \ u f i r V ^ / r t v A ,". ^ ' V , \ ; \ \ ' \ \ ^ ; | ' j 'g./ , ; ( ^ - Y ( : : i " V n ^ tii® ji\Ofh J - ' ( \ l/;."\ ' ^ J g / i / r ^ J ; ^ t = ^ ^ ' ' rX’ V W 1 / V ^ V1 A' l O ’ - ' / r C r ^ r I j, y ! f • : 5 & X , , / ^ Y W A> ** - 7 ( ’ '>v xVy<, - - > [ • V^l-V\V^v,/OW' , /- r/^ / I u V /yXV 117*40' 00, / 28 Figure 9s Location map of microfossil sample sites along Edison Power Road (dashed line)• These sample locations are also listed on the stratigraphic columns in Appendix C, making correlation of sample sites and stratigraphic columns possible. 29 ' ■ - — , » — " — . ■ ’l ^ - . - ? . : ^B S;42 4 -rf- V H , • c s y - ; ; v W > ' / ; . S , ! / / • - ' . n /■: < £ r »>’.7?v y. . \ r f fc ; - ; < « -;s- — -rx—' -c v . ' ■ • ■ ;<l ^ K \ - ^ 'I ^ \ n i r t \ Vr.\ • A' / . A ■ I /i.vVT ' ^ A r ~ B : s - ^ r^zAy:0; o¥^' w v s ' ’ - ' ' \ ) \ v ^ ~ , r* _ ) , ■ ; -w' I . ^ / « H / m ^ -» ' / i .t 1lf40,30'’ 30 slabbed. After slabbing, several diverse techniques were attempted to enhance the observability of both physical and biogenic structures. Enhancing techniques used in this study included staining of slabbed samples with Alizarian Red, in an effort to accentuate any sedimentologic or biogenic structures where clay minerals were concentrated (after Hamblin, 1962; Buck, 1983); application of a high gloss fast drying lacquer spray on concretions for enhancement of structures (after Buck, 1983); and saturation of sandstones with resin to enhance sedimentary structures and strengthen the rocks. The lacquer spray techniques was found to be the most practical and effective in enhancing both sedimentologic and biogenic structures. Petrographic examinations were performed on approxi mately twenty sandstone and concretion samples, and were utilized for determining the textural relationships and mineral composition within the fine- and coarse-grained rocks. Mineral composition was determined by dividing the thin-section (field of vision under the scope) into 4. equal parts; percent composition of each mineral was then deter mined by how much of this area was filled by each mineral. Results of these analyses are used throughout the text in sedimentologic descriptions of these rocks. Sample loca 31 tions of thin-sections made for this study are marked on the stratigraphic columns in Appendixes AfB and C. Geochemical analyses using x-ray diffraction and LECO gasometric and combustion apparatus were performed to supplement the petrographic studies. The x-ray diffraction studies concentrated on identifying the mineralogic content of sampled sandstones and concretions, especially the clay minerals. The LECO gasometric analyses were used for determination of organic carbon and calcium carbonate content of concretions and their surrounding sandstones. The results of these analyses will be presented and discussed later in this study. 32 SEDIMENTOLOGY INTRODUCTION Turbulent events, such as storm deposits (tempestites), turbidity current deposits (turbidites) and flood deposits (inundites), are probably the most important processes in the deposition of sediments in a marine environment. This idea is not a new one, but has been proposed many times by numerous individuals. Therefore, a wealth of knowledge exists for the recognition of these depositional events and their influence on fossil preservation and position. The effects of turbulent events are very complex, since they suggest sedimentological as well as ecological successions within the depositional unit. Storm deposits, turbidites, and flood deposits have several things in common (Seilacher, 1982): (1) They reflect the start, waning and finish of water turbulence throughout the event by distinctive erosional and depositional structures 33 (Seilacher, 1982). (2) They redistribute the organic and inorganic sediment material along a vertical (bottom to top) and horizontal (shallow to deep) gradient (Seilacher, 1982) . (3) They change the ecological situation for benthic organisms by alternating the consistancy and/or the food content of the bottom for a biologically relevant period after the event (Seilacher, 1982) . It should be noted that although storm deposits, turbidites and flood deposits have similarities, there are several features that can be used to distinguish them from one another. Two such features are the symmetry of proximality gradients, and sequence of sedimentary structures within the turbulent deposits (Aigner, 1982). The agents responsible for turbulent deposits are (1) waves, and (2) currents. These may occur independently, or more likely, in combination, as suggested by Kelling and Mullin (1975) (1) Waves are oscillatory, and therefore responsible for the stirring-up and reworking of bottom sediments in-situ thus resulting in swell lags (Brenner & Davies, 1973). Wave dominated 34 turbulence is more or less stationary, thus lateral sediment transport would be minimal (Brenner & Davies, 1973) . (2) Currents, which may be due to various starting factors (backflow currents, storm surge tides, winds, thermohaline conditions) as well as diverse depositional mechanisms (suspension settling, bottom currents and rip currents), account for lateral transport and deposition of allochthonous sediments (Aigner, 1982). Turbidites and flood deposits are influenced pre dominantly by currents, whereas storm deposits are most influenced by wave action with current transport and deposition playing a lesser role. This fact is best evidenced in proximality gradient symmetry. According to Seilacher (1982), in the ideal case one can assume a symmetrical succession of erosional phases during the increase, and depositional phases during the decrease of the turbulence (Fig. 10). This ideal cycle is most closely emulated by storm deposits, indicating turbulence is wave dominated and more or less stationary. In current dominated turbulence (turbidites and flood deposits) the turbulence peak shifts laterally, therefore the levels of the erosional and depositional phases in any given place will rarely 35 Figure 10: Ideal case, levels of the erosional (a-c) and depositional regime (A-C) should correspond at any point along the proximal-distal gradient of a turbulent event (from Seilacher, 1982)• 36 PROXIMALITY GRADIENTS SYMMETRY A DEPOSITIONAL FACIES B C c EROSIONAL FACIES b a distal proximal 37 correspond (Fig. 11). The sequence of sedimentary structures for tempestites, turbidites and inundites may be quite distinctive, and are discussed below. Inundites include both flood basin and flood plain deposits. Flood basins are the lowest-lying part of a flood plain. They act as settling basins, where fine-grained sediment (silt and clay) settles out. The rate of sedimentation is very slow (generally 1-2 cm/yr) (Reineck & Singh, 1973). Where basins are not well developed or non-existant, deposits accumulate in flood plains. These deposits generally consist of fine sand, silt and clay layers. Sedimentation starts with sand layers, becoming silty upward, containing abundantly developed climbing- ripple and convoluted bedding. The sand and silt layers grade upward into finely laminated clayey sediments, which generally exhibit mud cracks (Fig. 12) (McKee et al., 1967; Reineck & Singh, 1973, 1980). Locally, more than one sequence (coarse to fine) of units is deposited, indicating fluctuations during the flood. Finally, near the surface, concretions (carbonate/ iron) may form in areas of high rates of evaporation (McKee et al., 1967). 38 Figure 11: The proximality gradient most commonly associated with turbidites and inundites. This gradient may also occur in tempestites (from Seilacher, 1982) . 39 PROXIMALITY GRADIENTS SYMMETRY DEPOSITIONAL FACIES A TRANSPORT B C c b EROSIONAL FACIES a distal proximal 40 Figure 12: Sequence of structures in a flood plain deposits of a single flood (Based on McKee et. al.f 1967). 41 MUD LAYER climbing RiPPLE lamination CONVOLUTE BEDDING HORIZONTAL BEDDING (LAMINATED SAND ) LARGE-SCALE CROSS - SE DDi NG (DELTA FORESETS i MUD LAYER CLIMBING R, ; PPlE LAMINATION HORIZONTAL EEDC.NG (LAMINATED sand : OLDER SEDIMENTS 42 Turbidites are the sedimentary deposits of a high- density current flowing down a subaqueous slope. The ideal turbidite sequence, known as the Bouma Sequence (Bouma, 1962), is made up of five units with specific sedimentary structures (Fig. 13) (Bouma, 1962; Reineck and Singh, 1973, 1980) : (1) Basal graded interval; consists of graded bedding and is sandy or gravelly in nature. No other sedimentary structures are present (Reineck and Singh, 1973, 1980). (2) Lower interval of parallel laminations; consists of thick parallel laminae (Reineck and Singh, 1973, 1980). (3) Interval of current ripple lamination; consists of fine sand and silty sediments exhibiting small-current ripple bedding, which may be developed in the form of climbing-ripple laminations. Convolute laminations may be present but are uncommon (Bouma, 1962; Reineck & Singh, 1973). (4) Upper interval of parallel lamination; consists of very fine sandy to silty clay showing a distinct parallel lamination (Reineck & Singh, 1973). (5) Pelitic Interval; consists of clayey 43 Figure 13: Schematic representation of turbidite facies model (Bouma Sequence), showing five units each with characteristic sedimentary structures (after Bouma, 1964). 44 T, Vrrzt o /77» X nyrr rmi T4 T T, T! 45 sediments with no distinct sedimentary structures (Reineck and Singhf 1973). Tempestites are storm-induced, high energy, shelfal deposits. According to Aigner (1982) , the ideal tempestite sequence (Fig. 14) consists of four sedimentary units containing specific structures: (1) Graded bedding; lies on an erosional contact and consists of clastic (gravel to sand) and bioclastic materials which exhibit graded bedding. (2) Plane lamination; consists of fine sand to silty sediments exhibiting parallel laminations. (3) Wave ripple; consists of very fine sand exhibiting wave-ripples. (4) Pelitic division; consists of clayey sediments containing no distinct sedimentary structures. This section will deal primarily in using these and other distinguishing features to demonstrate that the Pleasants Sandstone Member strata were deposited by storms, and not other types of turbulent events. 46 Figure 14: The idealized tempestite sequence corresponds closely to the Bouma-sequence, except for the wave-rippled top. Since plane lamination in most cases passes gradually into wave-ripple lamination, wave ripples belong to the complete tempestite sequence and are not due to a subsequent phrase of reworking, (from Aigner, 1982. 47 IDEAL TEMPESTITE-SEQUENCE + HYDRODYNAMIC INTEPRETATION E E s a s x x s H iwM'tKSESsmm pelitic division L A M IN A R FLO W , very low wave ripples ! LO W E R REGIME ^ "m o derate- low plane lam ination ; U PPER FL O W REGIME ; high ! g ra d e d bedding red ep o s itio n of s u s p e n d e d d e tritu s v e ry high _e r o s j o n a I_ c o n t _ a c_ storm ero sion pelitic b ackg rou nd s e d im e n ta tio n very low SANDSTONE COMPOSITION: FINE-GRAINED SANDSTONES The chemical composition of the fine-grained sandstones was determined using petrographic, x-ray diffraction, and LECO gasometric techniques. Petrographic analysis of the fine-grained sandstones revealed a predominantly clay size matrix (40-55%) containing lesser amounts of detrital quartz, micas, calcite, feldspar, and some organic debris. Detrital quartz, the second most abundant mineral present, constituted between 20-35% of the fine-grained sandstones. The quartz grains are primarily subangular and are imbedded within the clay matrix. Grain size varies slightly, but averages approximately 0.05 mm throughout the sections. A general trend exists indicating a slight decrease in the average grain size up section and from Modjeska Grade to Black Star Canyon (southeast to northwest). The remaining constituents of the sandstones are calcite (1-10%), primarily as a secondary mineral and not detrital; micas (1-15%) predominately biotite with a trace of muscovite; and feldspars (5-10%) which include plagioclase, andesine, orthoclase, and microcline, in decreasing order of relative abundance. X-ray diffraction analysis confirmed clays as the dominant minerals of the fine-grained sandstones, with 49 detrital quartz a fairly distant second, followed by feldspar (plagioclase, andesine, orthoclase, and microcline), calcite, and micas (biotite and muscovite). Although, the actual percentages of these minerals were not readily obtainable using this technique their relative abundances were. Furthermore, the clay peaks observed were not defined well enough for individual identification. The LECO gasometric analysis concentrated on calcium carbonate and organic carbon contents (Table 1). Samples containing bedding planes of organic debris were avoided, since they would bias the organic carbon content. The fine-grained sandstones were found to contain from 4.00 to 9.90% calcium carbonate by weight and 2.75 to 5.70% organic carbon by weight. SANDSTONE COMPOSITION: MEDIUM-GRAINED SANDSTONES The medium-grained sandstones are cleaner than the fine-grained sandstones. This is evident through their chemical compositions, which were determined using x-ray diffraction, petrographic, and LECO gasometric techniques. Petrographic examination of the medium-grained sandstones revealed a predominantly detrital quartz (25-65%) rich rock, with lesser amounts of micas, feldspars, calcite, clays, and organic debris. The detrital quartz grains are primarily 50 Table Is LECO gasometric determinations of medium- to coarse grained sandstones (organic to carbonate composition percentages). 51 LECO GASOMETRIC DETERMINATIONS; Sandstone sample Calcium Organic Site Location: Carbonate Carbon (weight %) (weight %) BS-3B 4.00 5.70 BS-10 9.90 2.75 52 subangular to subrounded, with grain size averaging 0,28 mm., imbedded within a calcite matrix. The remaining constituents of the medium-grained sandstone are the micas (5-15%), primarily biotite; the feldspars (1-10%) which include plagioclase, andesine, and orthoclase, in decreasing order of abundance; and calcite (10-35%) mainly as a secondary mineral acting as a matrix. The medium-grained sandstones are concentrated in the lower third of the stratigraphic sections. X-ray diffraction analysis confirmed detrital quartz as the dominant mineral of the medium-grained sandstones followed by calcite (as the matrix), biotite, plagioclase, andesine, orthoclase, and clays in decreasing order of relative abundance. Although, the actual percentages of the minerals present were not realistically obtainable using this technique, their relative abundances were. Furthermore, the clay peaks observed were not well enough defined for individual identification. The LECO gasometric analysis concentrated on calcium carbonate and organic carbon contents (Table 2). Samples containing bedding planes of organic plant material were avoided, since they could bias determination of the organic content of the rock. The medium-grained sandstones were found to contain from 3.35 to 4.00% organic carbon by weight 53 Table 2: LECO gasometric determinations of fine-grained sandstones (organic carbon and carbonate content percentages). 54 LECQ GASOMETRIC DETERMINATIONS; Sandstone Sample Calcium Organic Site Location: Carbonate: Carbon: (weight %) (weight %) MG—10 1*20 4*00 MG—15—1 1.50 3.35 55 and 1.20 to 1.50% calcium carbonate by weight DISCONTINUOUS CONGLOMERATE LENSES Discontinuous conglomerate lenses (Fig. 15) are found throughout the Pleasants Sandstone Member (Schoellhamer et al., 1981) but mainly concentrate in the lower third of the member. These conglomerate stringers contain clasts that vary greatly in size, from pebble to cobble, are usually poorly cemented and grain supported. The clasts are granitic in composition and subangular to subrounded. These stringers extend 10 to 20 meters laterally but only a few centimeters vertically. Occasionally the stringers contain shell fragments including very common, vertically oriented, complete shell valves (Fig. 16). The shell fragments indicate that the material was transported via waves or current and that they are not in-situ. While the edgewise shells are generally attributed to wave action (Schafer, 1972; Rozanski, 1943; Dionne, 1971; Sanderson and Donovan, 1974), and according to Futterer (1982) accumulate in shallow waters, this orientation may be the result of storm activity. The voids between the clasts making up the conglomerates are usually filled with very fine-grained material which exhibit parallel laminations as well as geopetal fabric. 56 Figure 15: Discontinuous conglomerate lense (shown with arrows) located along the Santiago Truck Trail, MG—15• These are found throughout the Pleasants Sandstone Member. 57 58 Figure 16: Vertically oriented, complete shell valve (note arrow) within a conglomerate stringer, located at MG—15, along Santiago Truck Trail. 59 60 Specht and Brenner (1979) consider fabric like geopetal voids and grain shelter patches as indicative for storm-wave winnowing. PALEOENVIRONMENTS OF THE PLEASANTS SANDSTONE MEMBER The Pleasants Sandstone strata were examined sedimentologically, through the study of very fine-grained clayey sandstones, medium-grained sandstones, and carbonate concretions, to determine their origin of deposition. These strata were analyzed both in hand sample and thin section to define their composition, grain size and sedimentary (primary and secondary) structures. The three stratigraphic sections examined in this study have varying stratigraphic thicknesses; Modjeska Grade (116.5 m), Baker Canyon (140.6 m), and Black Star Canyon (266.0 m). Both Modjeska Grade and Baker Canyon are complete sections. According to Schoellhamer et al. (1981), the Pleasants Sandstone Member has a maximum stratigraphic thickness of 395 meters. This figure seems high, and may in part be due to the fact that the measurements were taken from core samples and therefore did not take into account the repetition of strata caused by faulting. The fine-grained clayey sandstones are the thickest and 61 most abundant strata in each of the three stratigraphic sections. There is a marked decrease in the number and thickness of the coarser-grained sandstones up section and from Modjeska Grade to Black Star Canyon (southeast to northwest), and carbonate concretions also definitely increase in this direction. This decrease in medium-grained sandstone beds and increase in carbonate concretions may be related to the strata's original proximity to shore, and its subsequent effect on sediment porosity. The carbonate concretions which will be discussed extensively in a later Chapter are almost exclusively found in the fine-grained sandstones. SEDIMENTQLOGIC FABRICS; BIOLOGICAL VERSUS PHYSICAL MECHANISMS The sandstone and concretionary strata of the Pleasants Sandstone Member display a wide spectrum of sedimentary fabrics from totally biologically dominated fabrics to entirely physically dominated . The biologically dominated fabrics are most commonly associated with the very fine-grained clayey sandstones and concretions, and exhibit no evidence of physical structures. These rocks display obscure to distinct occurences of abundant Helminthoida and possible Chondrites traces. The greater the degree of bioturbation within these sediments the lesser the degree of 62 trace fossil resolution. There are three possible modes of deposition for these very fine-grained clayey sandstones; turbidity currents, contour currents, and hemipelagic sedimentation from nepheloid flows (Stow and Lovell, 1979). Based on the total absence of both primary structures (i.e. cross-bedding) and textural trends (i.e. graded bedding) (Hesse, 1975) , the slow rate of deposition necessary for total biogenic reworking of the sediments (Howard, 1975), the scarcity of coarser-grained sandstone beds, and the organic carbon content, these deposits are interpreted as hemipelagic particle rain (Griggs et al., 1969; Rupke and Stanley, 1974; and Hesse, 1975). At the opposite end of the spectrum, the physically dominated fabrics occur predominantly in medium-grained sandstones, and more rarely in coarser-grained concretions. These rocks show very little evidence of bioturbation, except for the uncommon escape burrow, but commonly display planar-laminations, shelly beds containing edgewise shells (Fig. 17), concentrations of organic fragments parallel to bedding, graded bedding, occasional hummocky cross-bedding (fig. 18), and wave ripples (in Modjeska Grade). These deposits (sheet sandstones) are interpreted as tempestites that were deposited rapidly enough to prevent bioturbation. This interpretation is based upon the observation that these laminated beds commonly display ordered sequences of 63 Figure 17: Storm deposit containing edgewise shells located along Santiago Truck Trail, Modjeska Grade, at MG—6 (scale: yellow line equals 1 cm). 64 Figure 18: Cross-bedding within a tempestite, located along Modjeska Grade, MG-18. 66 lamination (De Roaf et al., 1977). The transition upward from graded bedding to plane or hummocky cross-stratifica tion (Harms et al., 1975; Wright & Walker, 1980) to climbing wave ripple lamination (Fig. 18) to pelagic deposits suggest waning velocity of oscillatory currents, which are associated with storms, according to the relationships defined by Inman (1957), Allen (1970), Komar and Miller (1975) , Kreisa (1981) , and Aigner (1982) . Reineck and Singh (1972) also suggest that parallel laminations can form when storm-suspended clouds of sediment are deposited in slowly moving water as the storm abates. Intermediate to the two end member fabrics are rocks that exhibit relatively equal amounts of both physical and biogenic structures. These strata display parallel fine-scale planar laminations (1 cm) which were distributed and partially destroyed by the burrowing and grazing activity of deposit feeding organisms. Helminthoida and possible Chondrites traces dominated the bioturbated structures, but also included are occasional Ophiomorpha. This intermediate fabric was associated with outcrops of clayey very fine-grained sandstones. From a distance these structures display planar laminations while up close the laminations are difficult to observe due to extensive bioturbation. This sediment fabric was fairly common in all three stratigraphic sections. This intermediate fabric is 68 Figure 19: Wave ripples (indicated by arrows), near the top of a tempestite, overlain by pelagic deposits. 69 Figure 20: Amalgamated storm beds located at MG-18 to MG-19 (indicated by arrows). 71 72 interpreted to have been deposited as a combination of hemiplegic and or waning storm deposits, where sedimentation rates were too fast for complete biogenic reworking, but at a rate where infaunal organisms could still thrive. These rocks not only display less biogenic reworking than rock with the biologically dominated fabric but also fewer concretions. This fact may be attributed to the lower organic carbon content of these same rocks. PROXIMALITY TO SHORE The Pleasants Sandstone Member strata exhibit a lateral change in rock types from Modjeska Grade to Black Star Canyon. The Modjeska Grade strata (Appendix A) in general are composed of several thick units of medium-grained sandstone, interbedded with fine-grained clayey sandstones. The medium-grained sandstones exhibit an upward gradient of sedimentary structures, and a downward decrease in the degree of bioturbation. The fine-grained clayey sandstones are almost totally bioturbated, but occasionally display a combination of both physical and biogenic structures. Also the Modjeska Grade strata contain several shell or bioclastic beds (tempestites) and occasional to common carbonate concretions. These strata are usually low in organic content. The next study area on the traverse toward Black Star Canyon is Baker Canyon. The Baker Canyon rocks 73 (Appendix B) are comprised of medium-grained sandstones interbedded with fine to very fine-grained clayey sandstones. The medium-grained sandstones are similar to those found in Modjeska Grade outcrops, except not nearly as thick or as common, and they are concentrated in the lower fourth of the section. The very fine-grained materials are higher in organic content, contain a higher percentage of carbonate concretions and display more biogenic reworking than the Modjeska Grade strata. Finally, the strata of Black Star Canyon are composed entirely of fine- to very fine-grained clayey sandstones exhibiting common to abundant carbonate concretions and containing the highest organic carbon content of the three study areas. These same strata are extremely bioturbated throughout and only occasionally display evidence of physical structures. This lateral change displayed within the Pleasants Sandstone Member, while traversing from Modjeska Grade to Black Star Canyon, is expressed by a decrease in bed thickness, grain size, bioclastic content, and a change in sediment type, as well as an increase in cabonate concretions, organic content and degree of bioturbation, and is interpreted as the proximality gradient of storms. Storms are known to exhibit a decrease in their effects towards deeper, offshore bottoms. This obvious relationship has been demonstrated in modern environments (Powers and 74 Kinsman, 1953; Curray, I960, ; Hayes, 1967, ? Reineck & Singh, 1975,). The basinward decrease of storm waves and storm induced currents should be reflected in a lateral succession of bedforms, and should range between proximal and distal end types. According to Aigner (1982), storm beds can be arranged within such a proximality framework; (1) proximal tempestites are relatively thick-bedded, bioclast-dominated and coarse-grained rudites, commonly forming composite and amalgamated beds, (2) distal equivalents are mud-dominated and thinner one-event beds. Therefore, tempestite proximality decreases away from shore, as expressed by a decrease in bed thickness, grain size, bioclastic content, and by a change in sediment type (ie. increase in clay size particles and decrease of sand size particles basinward). FLUCTUATION OF SEA LEVEL The Pleasants Sandstone Member strata exhibit a change in rock types up-section, this change is found in all three study areas. In general, the change consists of upward fining of grain size throughout the section. In Modjeska Grade and Baker Canyon this change is observed as medium-grained sandstones grading upward into fine-grained clayey sandstones. In Black Star Canyon this change is 75 recognized as the upward grading of fine-grained clayey sandstones into very fine-grained clayey sandstones. This decrease in grain size up-section could be interpreted in two ways: (1) a sea level rise; or (2) a change in sediment size due to a change in the source area. According to Saul (1982), a transgression of the late Campanian sea took place during the deposition of the Pleasants Sandstone Member strata. Furthermore, a change in sediment source is not readily explainable. Therefore, the transgressing sea interpretation is not only the simplest but the most viable explanation. c q b q l u s i q e The Pleasants Sandstone Member strata of Modjeska Grade, Baker Canyon, and Black Star Canyon undeniably exhibit evidence of storm activity. The evidence is in the form of thick tempestites and a proximality gradient, as demonstrated by biogenic and sedimentary data. Furthermore, the influence of storm activity is known to be most pronounced on continental shelves, while steadily decreasing offshore. Therefore, the Pleasants Sandstone Member strata of Modjeska Grade, Baker Canyon, and Black Star Canyon contain storm deposits located on the continental shelf, most probably inner to middle shelf. 76 TRACE FOSSILS INTRODUCTION Trace fossils are extremely valuable instruments, in environmental and bathymetric analysis of sedimentary rocks. The reason for this is that trace fossils differ from other fossils in several important aspects: (A) Trace fossil morphology (except for vertebrate and some arthropod tracks) is strongly influenced by the behavioral rather than the anatomical characteristics of the animal. Trace fossils that appear identical may actually be the work of taxonomically unrelated animals. Traces can be useful indicators as long as they express a similar response to the same environmental conditions (Seilacher, 1967). (B) Trace fossils are autochthonous (reworked traces are very rare and easily recognized (Seilacher, 1967)). 77 (C) One organism may be responsible for several trace fossils, therefore the chances for preservation of any one trace is significantly higher than for the producer itself (Seilacher, 1967) . Seilacher (1963, 1964, 1967) concluded that six distinct and important trace fossil communities (ichnocoenoses) are recognized in aquatic sediments. Based on these ichno coenoses, models were constructed (Seilacher, 1967, 1978) for determining the paleobathymetry and paleoenvironment (Fig. 21) of trace fossil bearing strata. All too often geologists are concerned with only the paleontological and not the sedimentological significance of trace fossils. This is a grave oversight, because lebensspuren are considered as sedimentary structures (Howard, 1975). These structures, although biologically formed, often supply evidence of sedimentological conditions that might otherwise not be available through examination of only physically produced sedimentary structures. The activites of the animals responsible for the lebensspuren are regarded as (1) processes that may form new, or destroy preexisting, fabrics or structures; (2) mechanisms for sediment concentration, reworking,or modification; and (3) devices for determining rates of 78 Figure 21: Environmental significance of trace fossils and their common associations (Seilacher, 1978). 79 A 8 r S S al oscai p » p p lc s POSStL* D ^ t o c » n r m o i* ^H»coot 3 T flC H !C « » U J I tr » O A U f » : » CO**OSTie**U3. » n L C » C t » 3T f » t * C 1T C 5 »Mtrocnw*Ltiu« Tw»l»SS>WO»Df S. r»u?'*N* mTMfto^oo tn»r«$ ZOOPMYCOJ * EOOtCT TON O t D M IM f A lO P H o c T fm u ti S C O l'C H (M F A H D f » t* 0 » co**»o»w *pM f H C LM IN TM O IO A DICT tO O O il * f ►CSTCS » »T» 80 sediment deposition or erosion (Howard, 1975). Because almost every environment is inhabited by some type of organism, it follows that during sediment deposition a conflict exists, between physical and biological processes, to dominate the sedimentary structures. The end result of this contest depends on the conditions of the environment, including such things as physical energy, rates of deposition, grain size, organic content of the sediment, and the density, adaptation, and variety of organisms present. This interrelationship between biogenic activity and physical processes has been repeatedly shown through precise studies of beach to offshore facies (Moore and Scruton, 1957; Reineck and Singh, 1971: Howard and Reineck, 1972? Howard, 1975). In a very general way these detailed studies revealed that a decrease in wave or current activity (which generally occurs from beach to off-shore) is correlative with an increase in bioturbation. It should be stressed that this relationship is dependant on environmental conditions, and will change as these conditions vary. Therefore, in paleobathymetric and paleoenvironmental reconstructions, trace fossils become very important since they can provide both sedimentological (as sedimentary 81 structures) and paleontological (as fossils) data. Trace fossils, used in this manner, can furnish valuable information regarding: (1) general depositional processes; (2) episodes of local deposition and erosion; (3) characteristics of currents, substrate consistency, and in some instances, causes of sediment sorting; and (4) ichnocoenoses (Seilacher, 1967, 1978). The trace fossils (ichnofauna) in this study were examined in two parts; (1) ichnofauna of the coarse-grained sandstone strata, and (2) ichnofauna of the fine-grained clayey sandstone strata. All three canyons were closely scrutinized for interrelationships within and between the ichnofaunas of each strata type. TRACES OF THE COARSER-GRAINED SANDSTONE The ichnofauna of the coarse-grained strata in all three canyons (Modjeska Grade, Baker and Black Star) is dominated by Ophiomorpha(Fig. 22) and uncommon Thaiassinoides traces (Fig. 23) . The pellet-lined Ophiomorpha burrows are round in cross-section and vary in size from 0.5 to 4.5 cm in diameter. The rarer unlined Thaiassinoides burrows are circular and range in size from 0.6 to 1.0 cm in diameter. Both burrow types are usually observed as endichnial traces (after Martinsson, 1970) or endogenic traces (after 82 Figure 22: OpJllQEifixpJbs trace on sandstone bedding plane in Black Star Canyon, BS-5 (scale: red line equals 1 cm) . 83 34 Figure 23: ThalasBlnoldes burrow in sandstone strata found along Edison Power Road, Black Star Canyon, BS-5 (note arrow). 85 Chamberlain, 1971). Lebensspuren observed as epichnial ridges, (after Martinsson, 1970), found principally on con cretions, are uncommon, but no epichnial grooves were ever found. The morphologies of the lebensspuren were quite simple ranging from straight to sinuous Y-shaped branching tubes. There appear to be no vertical or lateral trends in trace composition or morphology. According to Frey and Howard (1970) the presence of Ophiomorpha and Thalassinoides traces in the same stratum indicates that at the time of burrowing the original deposits were reasonably cohesive, but regionally variable. Escape burrows, vertically oriented tubes which originate deep within a single stratum, are evidence of rapid deposition and are fairly common in the coarser-grained strata (Fig. 24). The escape structures can be distinguished from other vertically oriented tubes by the presence of backfilling "nested cone" structures having the apex pointed downward. Callianassid and Glyphioid (suspension-feeding thalassinoid shnimp) are considered the producers of Ophiomorpha and Thalassinoides traces (Sellwood, 1971? Bromley and Asgaard, 1972; Frey, 1978). These lebensspuren are regarded as dwelling structures and were initially thought of as reliable indicators of shallow water, 87 Figure 24: Escape burrow in tempestite bed along Santiago Truck Trail, Modjeska Grade, MG-18 (scale: red line equals 1 cm). 88 89 high-energy marine environments (Seilacherf 1967). Recently, though, Ophiomorpha and Thalassinoides lebensspuren have also been reported from several high-energy, deep-marine depositional environments (Crimes, 1977; Bottjer, 1981; Buck, 1983). The most probable explanation for the wide depth range of these traces is that similar environmental conditions (e.g. high current activity, relatively low organic contents, and sandy substrates) were present in both high-energy environments. Therefore, the presence of Ophiomorpha and Thalassinoides seems, at least, to imply a high-energy environment of deposition for these strata. The dominance of pellet lined, horizontally oriented traces in endichnial position located near the top of the strata suggest that these traces represent post-depositional colonization of these sandy substrates. The low quantity and diversity of lebensspuren in the sandy substrate might indicate that the habitats present were inhospitable to the burrowing shrimp, either because the sediments were too coarse-grained, erosional forces were too extreme, sedimentation rates were too high, organic content too low, or a combination of the above. The presence of numerous escape burrows gives some insight into this problem, since they indicate rapid sedimentation rates. Also, the compositional studies of the coarser-grained sandstone 90 strata indicate a low organic content in these strata. TRACES OF THE FINER-GRAINED SANDSTONE The finer-grained sandstone strata in this study always exhibit some degree of bioturbation. Quite commonly the bioturbation is so intense, particularly near the top of any single stratum, that the primary physical structures are obliterated. In such intensely bioturbated strata individual lebensspuren are difficult to identify. The traces found within the carbonate concretionary beds are well preserved and quite easily identified. The ichnofauna of the fine-grained clayey sandstone strata within (Modjeska Grade, Baker and Black Star Canyons) the study area is dominated by abundant Helminthoida (Fig. 25). These lebensspuren are usually round in cross-section and vary in size from 1.0 to 2.0 mm in diameter and can be followed for up to 3 cm . The burrows are most commonly observed as endichnial traces (after Martinsson, 1970) within both concretions and surrounding beds. Commonly the lebensspuren are observed on concretions as epichnial ridges, but no epichnial grooves were ever found. The morphology of these are, quite simply, tightly packed meanders or spiral patterns that don't touch or cross one- another. Richter (1928) demonstrated that these patterns 91 Figure 25: Helminthoida traces in concretion slab section, from Baker Canyon, BC-1 (scale: red line equals 1 cm) . 92 originated as the two dimensional trace of a sediment-eating organism, grazing on thin detritus-rich organic layers of sediment, that attempted to "graze" an area with maximum efficiency. Such trails, although extremely dense, very rarely cross over earlier formed parts of the same trace. This feeding (grazing) method is attributed to a series of behavioral characteristics of the organisms responsible for the lebensspuren. These characteristics are: (l)phobo- taxis, (2) thigmotaxis, (3) strophotaxis. Furthermore, there appear to be no vertical or lateral trends in trace composition or morphology. The true origin of Helminthoida is not known, but these traces may possibly have been produced by gastropods (Seilacher, 1953a) and/or sediment ingesting polychaetes (Heezen and Hollister, 1971). These lebensspuren are regarded as grazing structures and are associated with the following environmental conditions; muddy substrate, relatively high organic contents, and low current activity. Therefore, the presence of Helminthoida seems to imply a low-energy environment of deposition for these strata (Seilacher, 1967a; Macstoay, 1967; Crimes, 1973). CONCLUSION Although none of the lebensspuren observed in these 94 strata are diagnostic of a specific depositional environment (water depth), their presence does indicate a changing environment, from one of high energy to low energy. This is a cyclic environmental change, such as would be seen in tempestite deposits, and is compatible with a continental shelf or upper slope paleoenvironmental interpretation, particularly the shelf, because it is most susceptible to the effects of storm activity. 95 MICRO PAL EON TOL OG Y The purpose of microfossil analysis of the Pleasants Sandstone Member was to acquire biostratigraphic and paleobathymetric information which could be used to complement the other geologic analysis performed in this study. Samples for microfossil data were collected from fine-grained sandstone outcrops along Santiago Truck Trail, Upper Baker Canyon Road, and Edison Power Road (see Figs. 7, 8, 9). A. A. Almgren and M. V. Filewicz (Union Oil Company of California) performed all of the analyses (identification and interpretations) on the foraminifera and calcareous nannoplankton. To this author*s knowledge this is the first information ever collected or published on the microfossils of the Pleasants Sandstone Member. Taxonomic lists corresponding to these samples are represented in Table 3. Only four samples were found barren of both foraminifera and calcareous nannofossils. These were the three samples collected from the fine-grained sandstones 96 Table 3 List of identified microfossils and their locations (X indicates presence). 97 MICROFOSSIL IDENTIFICATION TABLE Sample Site Locations: Taxonomic List: Foraminifera: Bathysiphon vitta Gaudryina foeda Haplophragmoides cf. G_. eggeri Haplophragmoides cf. G_. excavata Haplophragmoides sp. Silicosigmoilina sp. Trochammina bagginaformis Trochammina sp. Trochammina subvesicularis CO 1 —1 1 1 CN VO 1 —1 VO p- 00 o iH a \ I CM ■ CN ■ 1 i —1 1 i —1 1 CN 1 CN 1 CN 1 CN I CN B CO 1 CO 1 i —1 1 CN 1 03 03 03 1 03 1 03 1 03 1 03 1 03 1 03 1 03 1 03 1 03 1 03 1 u 1 u P Q P Q P Q P Q P Q P Q P Q P Q P Q P Q P Q P Q P Q P Q P Q X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X Bathysiphon sp. Cibicides sp. Cribrostomoides sp Frondicularia sp. Thalmannamina sp. x x x x x x x VO 00 near the base of the member, along Upper Baker Canyon Road. These sandstone beds were somewhat cleaner (lower percentage of clay minerals) than the other samples collected. Of the remaining samples none contained calcareous nannofossils. Unfortunately, diagnostic calcareous foraminifera, which are necessary for definite age and paleobathymetric determinations, were also absent. However, generalizations are given based on the common agglutinated and much rarer calcareous foraminifera tests found. The Pleasants Sandstone Member strata of Black Star Canyon are characterized by the occurence of common agglutinated foraminifera including species of the genera Bathysiphon, Haplophramoides. Trochammina. Gaudryina and Silicosigmoilina. The age of thes strata, based primarily on the morphologic type of Haplophragmoides sp. present, is Late Cretaceous, probably Campanian-Maastrichtian undiffentiated. The paleobathymetric determination, using the Sliter-Baker Model, of the same strata is based on the common occurence of Haplophragmoides sp. and the persistent occurence of Bathysiphon vitta. and is considered upper bathyal in water depth. The Baker Canyon strata are similar in age and relative paleobathymetry to the Black 99 Star Canyon strata, but contain no Trochammina sp. The general assemblages of foraminifera, and particularly the Trochammina species present in these samples (Black Star Canyon) are similar to those present in the upper part of the Holz Shale as exposed on the Silverado Truck Trail and in Williams Canyon (A.A. Almgren, 1984, pers. comm.). At these localities the upper part of the bathyal Holz Shale is apparently transitional with the overlying megafossil beds at the top of the section, which are placed in the basal part of the Schulz Member of the Williams Formation by Colburn and McKeown (1982). The foraminifera assemblage found within these rocks (Holz Shale) is assigned to the F-2 Zone of P. P. Goudkoff's (1945) foraminiferal zonation. The presence of Haplophragmoides eageri. a species characteristic of the F-l or F-2 Zone, support a similar correlation for the Black Star and Baker Canyon strata. The presence of abundant agglutinated foraminifera, the rare occurence of calcareous foraminifera and the total absence of calcareous nannofossils, suggest that dissolution processes played an important role in selective preservation of the microfauna. According to Douglas (1982), selective preservation could create foraminiferal assemblages that appear to be of brackish-water depths when 1 0 0 in reality they are deep-water. Therefore, the microfauna of the Pleasants Sandstone (in Black Star and Baker Canyons) are very difficult to accurately interpret. Almgren (1984, pers. comm.) suggests that these strata may have been deposited in waters of upper bathyal depths. 1 0 1 MACROPAL EONTOLG Y INTRODUCTION The macrofauna and macroflora of the Pleasants Sandstone Member in Modjeska Grade, Baker Canyon, and Black Star Canyon are characterized by abundant Turritella chicoensis pescaderoensis> Ptertrigonia evansana. Cymbophora popenoei. and Metaplacenticeras cf. H. pacificum. This chapter will be discussed in two parts: 1) generic makeup, 2) mode of fossil deposition. MACROFAUNA AND MACROFLORA Cymbophora popenoei and Metaplacenticeras cf. pacificum are most common in the lower part of the Pleasants Sandstone Member and indicate a shallow shelf environment. According to Saul (1982), the strata of the lower Pleasants Sandstone Member have yielded the most diverse Late Cretaceous fauna from the Santa Ana Mountains. The fauna is predominantly of North Pacific affinities, but contain 1 0 2 fossils of possible Tethyan origins. This fauna is essentially similar to the mid-Campanian, upper Holz Shale Member, shallow shelf fauna. Its slight increase in diversity may suggest somewhat shallower water or even a Late Cretaceous warming trend. The upper Pleasants Sandstone Member strata are characterized by Turritella chicoenosis pescaderoensis and Ptertriaonia evansana. This fauna is less diverse than the lower part of the member, and indicates a moderate depth shelfal environment (Saul, 1982). This fauna is similar in generic makeup to the late Turonian and mid-Campanian moderate depth shelf faunas of the lower Holz Shale Member (Saul, 1982). The macroflora of the Pleasants Sandstone Member is composed of fragmented unidentifiable fossils. Unfortunately, even if the fossils were recognizable, the science of Cretaceous paleobotany is not well enough developed to provide useful paleoecologic or biostratigraphic information. MODE QE EQBSIL DEPOSITION The majority of the fossils (fauna and flora) are found within discontinuous concretionary beds. These concretions, as will be discussed in the succeeding chapter, formed 103 around the fossil debris during diagenesis. It is these same fossil bearing concretions that will shed some light on what depositional mechanisms placed the original fossil materials here in the first place. The macrofauna of the Pleasants Member appears to have been transported, as evidenced by the biogenic features of these thick shell beds. One such bed, in Modjeska Grade (Fig. 26), exhibits disarticulated shell valves, prefered orientations, infiltration fabrics, and mudcoated shells. Another such bed (Fig. 16) displays shells on edge, intraclasts, and geopetal fabric. A third such example is found in Black Star Canyon (Fig. 27) this bed displays a diverse conglomerate of fossils showing preferred orientation, disarticulated shells, shell fragments, and mudcoated shells. According to Kreisa and Bambach (1982), strata that exhibit such features as preferred orientation, infiltration fabrics, intraclasts, and mudcoated shells are best interpreted as storm beds. Plant fragments in these strata of the Pleasants are relatively common and include one small leaf found in Modjeska Grade. The organic remains are preserved as carbonized compressions, concentrated along bedding planes of concretions. Such concentrations are much more frequently observed in outcrops of the fine-grained strata. 104 Figure 26: A storm produced shell bed located along Santiago Truck Trail, Modjeska Grade, MG Figure 27: Possible storm deposit located at BS-25, displays disarticulated shells, shell fragments, and mud coated shells. 107 106 The abundance of plant material preserved in this section implies that sedimentation rates were at least intermittently rapid, and that reducing conditions may have existed during deposition of these strata. The rapid deposition of these strata are thought to be associated with storm activity. Alternate mechanisms for implacement of organic debris include the slow settling of waterlogged fragments in the water column, and dilute turbidity currents. This author believes that these alternative mechanisms contributed little if any organic material to the strata, but that storm activity was the primary source of terrestrial organic matter. The majority of all fossil material within the Pleasants Sandstone Member is found within discontinuous concretionary beds that are parallel to bedding. These concretions are formed around the fossil debris which was concentrated in bands by storm activity. According to Bouma, et al. (1963) the accumulation of thick shell beds is the direct product of storm activity. The influence of storms is not just limited to stratification and sedimentary features. Storms also modify the fossil record through bias in preservation of body fossils, fossil associations (paleocommunities) and trace faunas (Kreisa and Bambach, 1982). Therefore, although the fossils cannot be relied upon, as tools, to reconstruct the paleocommunities of the Pleasants Sandstone 109 Member, they are able to provide undeniable proof of storm activity, and the importance it played in the formation of these strata. 110 CARBONATE CONCRETIONS INTRODUCTION The presence of carbonate concretions is quite common in sedimentary rocks. Concretions often contain well preserved fossils? thus concretion formation is very closely associ ated with organic compounds. This idea is one which has been recognized and studied extensively. There is a basic problem with this association, the result of bacterial decomposition in sediments is the lowering of pH brought about by the release, to solution, of bacteriogenic C02 (Berner, 1966). This process is known to produce various organic acids such as carbonic acid (Berner, 1968, 1969), which should inhibit the precipitation of carbonate minerals, necessary for carbonate concretion formation, not enhance it. This problem was resolved by a series of experimental studies (Berner, 1968, 1969) which showed during the early stages of decomposition a marked increase 1 1 1 in the pH (alkalinity) of water directly surrounding decaying organic debris. There are several bacterial processes which may result in a rise in alkalinity and bring about the precipitation of calcium. The two most important ones, which occur during the early stages of organic matter decomposition, are: (1) the reduction of dissolved sulfate to form hydrogen sulfide, and (2) the decarboxylation and deamination of amino acids to form ammonia and amines (Thimann, 1963). Berner (1968) demonstrated that the rise in alkalinity was directly due to the release of ammonia and other bases to solution. The loss of nitrogen compounds during the early stages of decay has also been observed in experimental studies of decaying phytoplankton (Krause, 1959) and in modern sediments (Emery, 1960). Berner (1968) suggests that ammonia, besides raising pH, also reacts with bacterially generated C02 to form dissolved carbonate and bicarbonate ions: CO 2 + NH3 +H20 -----> NH4 + HC03 CO2 + 2NH3 + H20 ---> 2NH4 + C03 Because of the increase in pH, the formation of high concentrations of carbonate ions, and the loss of calcium from solution, precipitation of calcium carbonate was anticipated, but never discovered. Instead, the formation of Ca-salts, or soapy fatty acids in the carbon range 1 1 2 14C-18C, called adipocere, was observed (Berner, 1968, 1969). Adipocere, according to Sondheimer, et al. (1966), forms concretion-like structures around decomposing oganic matter. Calcium may be precipitated, in the form of calcium carbonate, from adipocere during the later stages of decomposition if there is increased diagenesis (Berner, 1968) . Concretions are usually thought of as the result of early diagenesis (Weeks, 1953; Pantin, 1958; Gabinet, 1974; Hudson, 1978; Gantier, 1982), although concretions formed much later in a sediment's diagenetic history have also been reported (Pantin, 1958; Raiswell, 1971). To eliminate some of the uncertainty in determining the time of concretion formation, Pantin (1958) devised a relative time scale that classifies three major periods of concretionary growth. This classification includes: (1) syngenetic growth, formation of concretions on the sea-bed at the time of deposition of the confining sediment; (2) diagenetic growth, formation of concretions (probably within a few thousand years) after burial in uncompacted sediment; (3) epigenetic growth, formation of concretions in compacted and consolidated sediments. Obviously, these age divisions are extensive and concretions within a single age division may still develop 113 at different times. However, concretions within a single age division share some similarities which includes: the bending of strata around concretions (diagenetic; Tomkeiff, 1927; Weeks, 1953, 1957); crushed fossils within concretions (syngenetic or diagenetic; Weeks, 1953); the presence of boring or encrusting traces on concretion surfaces (syn genetic or diagenetic: Pantin, 1958); non-compacted trace fossils within concretions (syngenetic or diagenetic; Dickson and Barber, 1976); concretions containing cone- in-cone structures, which are only associated with uncon solidated sediment (diagenetic; woodland, 1964); radical increase of compaction of laminae within a concretion (diagenetic or epigenetic; Raiswell, 1971); the presence of septarian structures associated with uncompacted water-laden sediments (syngenetic or diagenetic; Lippman, 1955; Raiswell, 1971); concretions overgrowing certain deposi- tional and post-depositional structures (syngenetic or diagenetic; Crimes, 1966); and carbon and oxygen composi tions indicating concretions formed in direct contact with seawater (syngenetic; Gautier, 1982). Usually it is necessary to utilize as many characteristics as possible, since many of the above criteria apply to one or more of Pantin's (1958) time divisions. These criteria where possible will be used in this study to determine the relative formation time of Pleasants Sandstone Member 114 concretions. CONCRETION MORPHOLOGIES The Pleasants Sandstone Member contains numerous carbonate concretions, randomly distributed, within its strata. These are most commonly oriented parallel to bedding and cover a wide range of shapes and sizes. The represented shapes (Figs. 28, 29 & 30) are ellipsoidal sphere, round sphere, and rectangular or blocky. The ellipsoidal sphere is by far the most common (75%), with rectangular (23%) and round spheres (2%) comprising the remainder. The dimensions of these concretions vary considerably and range from 5 cm to 2 m in diameter (average 0.5 m), and from 5 cm to 1 m in thickness (average 0.3 m). These diagenetic features quite commonly coalesce together, in small groups, along the same stratigraphic horizon to form discontinuous carbonate beds (Fig. 31). Buck (1983), recognized similar coalesced concretionary beds in the Holz Shale Member of the Santa Ana Mountains. Close examination of these beds reveals the contacts between the coalescing concretions; these contacts are much more visible in weathered outcrops than fresh ones. Concretions of the Pleasants Sandstone Member are 115 Figure 28: Ellipsoidal shaped carbonate concretions found within the Pleasants Sandstone Member. 116 L 117 Figure 29: Round shaped carbonate concretion found within the Pleasants Sandstone Member. 118 Figure 30: Rectangular shaped carbonate concretion found within the Pleasants Sandstone Member (field of view equals 1.5 meters). 120 Figure 31: Discontinuous carbonate concretionary beds parallel to beddingr formed by coalescing concretions, located at BS-3. 122 123 generally well-cemented carbonate nodules, which are dis tinct from the surrounding strata. Many of the concretions are surrounded by a weathering rind, indicating their ex posure to the elements. The thicker the rind the greater the degree of weathering. Most concretions in the Pleasants Sandstone Member are predominately well-cemented nodules exhibiting distinct boundaries that partition them from the surrounding strata. In addition to these concretions, some of the strata contain numerous rudimentary (juvenile) concretions which are highly fragmented spheres (Fig. 3 2) showing vague concentric layers. Although these nodules are more resistant than the enclosing strata, their relatively poor cementation account for their high degree of fragmentation and poorly defined boundaries. The diagenesis of these rudimentary concretions appears to have been interrupted and left incompleted, but the cause is unknown. COMPOSITION OF CONCRETIONS Chemical composition of the Pleasants Sandstone Member concretions was determined by using x-ray diffraction, petrographic and LECO gasometric techniques. Petrographic analysis (thin-section) of the concretions revealed a predominately clay sized sediment with varying amounts 1 24 Figure 32: Highly fragmented, rudimentary carbonate concretions located in the fine-grained sandstones of Baker Canyon. 125 126 (trace to 10%) of detrital quartz grains (silt size) and abundant calcite cement. Detrital plagioclase feldspar and calcite grains were absent. The majority of the quartz grains are surrounded by calcite cement. X-ray diffraction analysis was performed on seventeen concretion samples. The samples are dominated by calcite (the primary component), with quartz a distant second. Also observed were small amounts of plagioclase feldspar, biotite and muscovite. In addition, numerous clay peaks were observed but were not defined well enough for identification of specific clays. LECO gasometric analysis, performed on the same seventeen samples, concentrated on the determination of organic carbon and carbonate carbon content (Table 4). Samples containing bedding planes of organic debris were avoided, since they could bias the organic determinations. The concretion samples contained organic carbon contents ranging from 0.7%- 22.8%, averaging 8.4%. The carbonate carbon contents of these same concretions displayed a range of 14.9% to 57.45%, averaging 34.2%. ORGANIC ASSOCIATION The carbonate concretions examined from the Pleasants Sandstone Member commonly contain shells or shell fragments (Fig. 33); these shells may occur within and/or cover the exterior of the concretion. In rare occurrences, well- 127 Table 4 LECO gasometric determinations of carbonate concretions (organic carbon and carbonate composition percentages). 128 LECO GASOMETRIC DETERMINATIONS: Concretion Sample Calcium Organic :e Location: Carbonate: (weight %) Carbon: (weight %) BS-3 29.20 22. 80 BS-4 16.40 12.20 BS-9 14.90 11.95 BS-24 54.10 6.20 BS-26 41.50 8.85 BS-27 41.30 6.05 BS-28 31.10 16.25 BS-29 57.45 12.65 BS-31 55.05 4.00 MG—1 26.35 5.20 MG-2 23.85 1.35 MG-2-1 34.80 5.55 MG-7 33.00 10.45 MG-8 35.30 .70 MG-14 31. 80 8.60 MG-16 22.15 8.00 MG—18=1 33.50 2.75 129 Figure 33: Carbonate concretions displaying shell and/or shell fragments. 130 preserved ammonites were found within the concretions. These organic remains probably acted as nuclei or catalysts for carbonate precipitation during initial concretion formation. Many of the concretions examined lack a carbonate nucleus, but contain high concentrations of organic (plant) debris. The plant fragments were concentrated along bedding planes of concretionary beds, indicating that the plant debris was directly associated with the formation of con cretions. Buck (1983) also noted similar associations in the Holz Shale Member. Quite commonly concretions lack an apparent nucleus (i.e. plant), but exhibit abundant bio- turbate structures. These structures due to their high organic content and the permeability of associated sedi ments, may act as nuclei for concretionary growth. Therefore, based upon this common association of organic matter with the carbonate concretions, it seems quite feasible that decay processes played an important part in their formation. Still, the uncommon observation of organic debris (plant) and shell material in the non-concretionary strata indicates that other factors must have also been involved. 132 TIMING OF CARBONATE CONCRETIONS The carbonate concretions of the Pleasants Sandstone are hypothesized to be of an early diagenetic origin (syngenetic or diagenetic), which is suported by several lines of evi dence. Body and trace fossils show little or no compaction (Figs. 34, 25), supporting an early diagenetic origin (Weeks, 1953; Dickson and Barber, 1976). Another line of evidence supporting the early diagenetic origin of these calcareous concretions is the lack of radial deformation of laminae within these concretions. According to Raiswell (1971), concretions which form over a sub stantial period of time display an increase in the pinching of laminae near the edges due to greater compaction with time. In the Pleasants Sandstone Member concretions, it is the absence of this pinching of laminae which indicates that diagenesis occured either before any significant compaction took place, or that concretionary formation happened so quickly that no time differences in the compaction of the sediments is observable. The former appears correct, based on observations of uncrushed fossils and non-compacted trace fossils within these same concretions. All of the above characteristics suggest either a syngenetic or diagenetic age. 133 Figure 34: Uncrushed fossil material found within a concretion, indicating and early diagenetic origin. 134 The deformation or bending of strata around the Pleasants Sandstone Member concretions is another obser vation supporting the early diagenetic origin of these calcareous nodules. The bending of strata around these concretions is quite common in both fine- (Fig. 35) and coarse-grained (Fig. 36) sandstone beds. This deformation suggest that concretion formation occurred before lith- ification of the surrounding strata (Weeks, 1953; Raiswell, 1971). This characteristic is suggestive of only a dia genetic age and precludes a syngenetic origin. Another line of evidence that excludes a syngenetic origin for these concretions is the total absence of borings and encrusting fossil upon them. The presence of uncrushed fossils, non-compaced trace fossils, and the lack of radial increase of compaction of laminae is suggestive of either a syngenetic or diagenetic origin. However, the total lack of borings and encrusting fossils, and the bending of strata around these concretions, clearly suggest a diagenetic age for these nodules. Since the two later characteristics are more limited in their time of origin (formation) and can occur only during the diagenetic growth period it can be assumed the Pleasants Sandstone concretions formed during this time period. 136 Figure 35: The bending of strata around a concretion in the fine-grained clayey sandstone outcrops. 137 'JVM 138 Figure 36: The bending of strata around a concretion found in the medium- to coarse-grained sandstone outcrops (field of view equals 1 meter). 139 140 CONCLUSIONS The very fine-grained sandstone strata of the Pleasants Sandstone Member in Modjeska Grade, Baker and Black Star Canyons have abundant carbonate concretions. These dia genetic features contain varying amounts of inorganic (as calcite) and organic carbon, and occur in a variety of shapes and sizes, but the most common are elliptical spheres that are oriented parallel to bedding. The genesis of these nodules seems to be the result of bacterial decomposition of organic matter in a highly-reducing environment. All lines of evidence for timing of concretion formation indicate an early diagenetic origin. These concretions most probably formed in water-saturated sediments, characterized by high porosity and low permeability. The information from this chapter along with succeeding data, will culminate to give a clearer picture of the depositional environments of the Pleasants Sandstone Member. 141 PALEOENVIRONMENTAL SUMMARY The strata of the Pleasants Sandstone Member, based on paleontologic, sedimentologic and ichnologic analyses, strongly support a inner to outer continental shelf paleoenvironmental interpretation. Evidence includes the existence of faunas normally associated with shallow to moderate depth shelf environments, as well as highly bioturbated fine-grained sediments with no sedimentary structures, indicative of quiet waters. This chapter will discuss the Pleasants Sandstone Member strata as two seperate units; the medium-grained sandstones and the fine-grained clayey sandstones. MEMUUtfiBAIHED S & m S T Q N E S The medium- to coarse-grained deposits of the Pleasants Sandstone Member are generally physically-dominated, and exhibit numerous sedimentary structures. These structures, geopetal fabric and tempestite sequences, are indicative of storm activity. 142 The ichnological information contained within these medium- to coarse-grained sandstones is characterized by numerous escape burrows, along with truncated Qphiomorpha and Thalassinoides burrows (Fig. 23). The escape burrows, produced by animals trying to dig themselves out of deep overlying sediment, indicate rapid deposition. The truncated Qphiomorpha and Thalassinoides traces indicate degrading or erosional processes have taken place, such as during the generation of a storm. Macropaleontologic evidence is scarce in these strata. This may be in part due to dissolution of the carbonate shells. Another possibility is that the shell material was reworked and transported seaward by subsequent storm activity. Of the few macro fossils found, all were disarticulated or fragmented and many were deposited edgewise, indicating storm transport. Microfossil data in these medium-to coarse-grained deposits are non-existant, all the samples examined were barren of formainifera and calcareous nannoplankton. This is most probably due to dissolution of the tests. Therefore, by compiling all the above evidence, it appears most likely that these medium- to coarse-grained sandstones were storm-generated. Furthermore, since storm activity is most prevalent on the continental shelf, it is safe to suggest a continental shelf paleoenvironmental interpretation for these deposits. 14 3 FINE-GRAINED CLAYEY SANDSTONES The fine-grained, clayey, sandstone units of the Pleasants Sandstone Member generally exhibit biologically dominated fabrics. The majority of the sedimentological evidence available for these strata was obtained through examination of their concretions (early diagenetic). These concretions display planar laminations. These primary sedimentary structures could be interpreted as originating from hemipelagic sedimentation or from deposition of storm-suspended clouds as the storm abates. Ichnological evidence for the fine-grained strata is characterized by the abundance of Helminthoida. These infaunal traces are grazing structures that inhabit quiet, low-energy environments. The macrofossil fauna is charac terized by Cymbophora and Turritella and suggests a shallow to moderate depth, mid-continental shelf paleoenvironmental interpretation. This however is suspect, since the vast majority of these fossils appear to have been transported. The microfossil fauna of these fine-grained strata is characterized by Bathysiphon. Haplophraqmoides. Trochammina. Gaudryina and Silicosiamoilina. This fauna indicates a paleobathymetric interpretation of upper bathyal depths. Therefore, the most probable paleoenvironmental inter 144 pretation for the Pleasants Sandstone Member*s fine-grained clayey sandstone strata is outer continental shelf to possibly upper continental slope. A lateral examination of the Pleasants Sandstone Member strata discloses that grain-size and bed thickness decrease progressively from Modjeska Grade to Black Star Canyon. This information along with previous interpretations of the Pleasants strata suggest that the Late Cretaceous continen tal shelf was probably narrow. According to Nilsen (1978), the Cretaceous Pacific Coast of North America was most likely very similar to the modern coast. Finally, the strata of the Pleasants Sandstone Member were deposited in a Late Cretaceous transgressing sea. This interpretation is based upon the previously stated paleo environmental and paleobathymetric interpretations of the fine- and medium-grained Pleasants strata, and is reinforced by the near continuous upward decrease in grain-size, of the strata throughout the member. 145 CONCLUSIONS The field and laboratory analysis performed on the sedimentology, petrology, ichnology, micro- and macropale- ontogy for this study most strongly support the paleoenvi ronmental interpretation of periodic storm activity on a narrow continental shelf, for the Pleasants Sandstone Member. Tempestites, escape burrows (trace fossils), macrofauna and the lack of turbidite sedimentary sequences are important indicators of shelf deposition. The gradual decrease in grain size progressively upsection indicates a period of possible transgression (marine). The decrease in grain size from Modjeska Grade to Baker Canyon to Black Star Canyon, along the same stratigraphic horizon demonstrates a proximality gradient, which is commonly associated with storm activity. Previous studies of the Pleasants Sandstone Member have been limited in both scope and number, and resulted in a paleoenviromental interpretation of a inner to middle con tinental shelf deposition. In completing a much more com 146 prehensive study of the sedimentology, paleontology, and ichnology of outcrops in Modjeska Grade, Baker Canyon and Black Star Canyon, the author hopes to have helped clarify not only the environment of deposition, but also the method of deposition of these strata. 147 REFERENCES Aigner, T., 1982, Calcareous tempestites? Storm-dominated stratification in Upper Muscheckalk Limestones: in Cyclic and Event Stratification (ed. by Einsele/Seilacher) Springer,1982, p. 180-198. Allen,J.R.L.,1970, Physical processes of sedimentation: an Introduction, (eds. G. Allen and Unwin) London,1970,p.248 Almgren, A.A., 1973 Upper Cretaceous foraminifera in southern California, in Cretaceous Stratigraphy of the Santa Monica Mountains and Simi Hills, southern California: Pacific Section, Soc. Econ. Paleontologists Mineralogists, Field Trip Guidebook, p. 31-44. 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Surv. Prof. Paper 420-A, p. A1-A57• 167 Appendix A STRATIGRAPHIC SECTIONS Stratigraphic sections of Pleasants Sandstone Member outcrops along Santiago Truck Trail, Modjeska Grade, Santa Ana Mountains, southern California. 168 KEY VERY FINE- to FINE-GRAINED SANDSTONE • « « • • • • • 1____f--a---■ MEDIUM- to COARSE-GRAINED SANDSTONE PEBBLY SANDSTONE PEBBLE CONGLOMERATE (STRINGER) O CARBONATE CONCRETION jOOCoo CONCRETIONARY BED (COALESCING) O O O CONCRETIONARY BED (UNCOALESCED) RUDIMENTARY CONCRETION 1 69 VERTICAL SCALE lm m=microfossil sample t=thin-section sample g=Leco gasometric sample MG-8=stake location Outcrop of massive (blocky), medium-grained sandstones dis playing weak parallel lamina tions, these laminations are accentuated by biotite and black carbonaceous (plant) fragments. The sandstone strata have a fresh color of moderate yellowish brown (10YR5/4) weathering to moderate brown (5YR4/4). The strata also contains numerous carbonate con cretions with a fresh color of light gray (N7) to medium gray (N6). Concretions up to lm in diameter are found near the base of this unit, they decrease in size upsection. Near the top of the section there is 1.5m of fine-grained sandstone that is very crumbly, and has a fresh color of medium yellowish brown (10YR5/4). This strata contains numerous concretions, fresh color light gray (N7) to medium light gray (N6), averaging 0.3m in diameter. The fine-grained strata is overlain by a thin layer of medium-grained sandstone beds. 170 9 * • • COVERED Overall, the strata of this unit display a fining upward sequence of both the sandstone grain size and concretion dia meter size. The concretions also contain bedding planes of organic fragments that form planes of weakness in the strata. Dominantly fine-grained sand stone outcrops with scattered carbonate concretions and medium- grained sandstone beds. The car bonate concretion beds are 0.3 m thick with a fresh color of light gray (N7) and medium light gray (N6). The concretions displayed planar laminations, but no trace fossils were found. The concre tions did display concentrations of black carbonaceous fragments and body fossils, along bedding planes, as well as displaying a small log. The medium-grained sandstone displayed a fresh color of grayish orange (10YR7/4) to dark yellowish orange (10YR6/6) 171 and range in thickness from 0.5 to 1.0 m. These sandstones were void of trace and body fossils, but displayed planar laminations and were blocky or massive. The fine-grained sandstones, in the upper 1/2 of this unit, are highly fragmented displaying no physical structures. These strata have a fresh color of light bluish gray (5B7/1) and very light gray (N7) intermingled with beds colored grayish orange (10YR7/4) and dark yellowish orange (10YR6/6) giving these beds a marbled appearance. The fine-grained sandstones in the lower half display some degree of physical structures (planar laminations) and are colored grayish orange (10YR7/4). These fine-grained strata contain no identifiable trace fossils although the beds are highly bioturbated. 172 This unit is made up of 3 fine-grained sandstone strata interbedded with A medium-grained sandstone beds. The uppermost fine-grained strata is approx imately 4 m thick, and is grayish orange (10YR7/4) in color. These strata exhibit no primary sedi mentary structures but do contain numerous rudimentary concretions, no identifiable traces or body fossils were found. The upper most medium-grained sandstone is approximately 2 m thick with a fresh color of grayish orange (10YR7/4) to dark yellowish orange (10YR6/6). These strata display planar laminations and a occasional Ophiomorpha trace. The next two fine-grained sand stones are highly fragmented strata exhibiting some degree of primary sedimentary structures (parallel laminations) although the beds are heavily bioturbated. These strata are approximately 6 and 14 m thick respectively. The thick beds are slightly blockier near the top than the rest of this fine-grained strata. The beds are dark yellowish orange (10YR6/6) to very light gray (N8), also these strata contain numerous concretions. These con cretions (5B7/1) range from 0.5 to 1.0 m in diameter, and several fossils were found within them, including two ammonites. The 7 m thick medium-grained sandstone strata located between MG-15 and MG-16 are dark yellow ish orange (10YR6/6) in color, weathering to moderate reddish brown (10YR4/6) and light brown (5YR5/6), interbedded with light 173 bluish gray sandstones (5B7/1) weathering to light gray (N7). Within this strata is a conglo merate lense, containing clasts varying in size from 1 to 6 cm. in diameter. Found within this stringer were several vertically oriented fossil valves along with geopetal fabric. This strata is interpreted as a tempestite. The lower two medium-grained sandstone beds are dark yellow ish orange (10YR6/6) in color, and display parallel laminations. These beds also contain a few concretions, and Ophiomorpha an burrows. The lower two fine-grained sandstone beds are highly frag mented concretion ((N7) & (N6)) bearing strata. These strata have a fresh color of primarily light bluish gray (5B7/1) inter mingled with light brown (5YR 5/6), giving this strata a marbled appearence. The beds are totally bioturbated although the traces are not identifiable. The under surface of the lowest bed has ripple marks on them. 174 20 15 10 m The basal 21 m of the Pleas ants is composed of fine- and medium-grained interbedded sand stones. At the base are two 1 m thick medium-grained sandstones (10YR7/4), the upper one is well bedded, the lower poorly bedded, no traces, body fossils or con cretions are found within these beds. The fine-grained beds of this unit are heavily bioturbated with a fresh color of light bluish gray (5B7/1). These strata con tain several concretions along with a thin pebbly conglomerate lense. The clasts making up these stringers are igneous in origin and are 1 to 3 cm. in diameter. The top of this unit is com posed of a 6 m thick medium- grained amalgamated sandstone bed. This strata has a fresh color of grayish orange (10YR7/4) and contains several concretions (10YR7/4). These concretions range in size from 0.5 to 1.0 m in diameter. The sandstone also contains several escape burrows, along with Ophiomorpha and burrows. Parallel laminations are the most predom inant primary sedimentary structures in both the sandstone and concretions. At the top of the bed are wave or current ripple marks. This amalgamated sandstone strata in interpreted as tempestite deposits. 1 7 5 Appendix B Stratigraphic Sections Stratigraphic sections of the Pleasants Sandstone Member outcrops along Upper Baker Canyon Road, Baker Canyon, Santa Ana Mountains, southern California. 176 VERTICAL SCALE lm m=microfossil sample t=thin-section sample g=Leco gasometric sample BC-8=stake location m 1.40 177 140 m 135- 130- o o O dl> r— : 125- - ./ The outcrops of strata from BC-0 to BC—11 are composed pri marily of very fine-grained sand stones. These sandstones are fresh colored light bluish gray (5B7/1) to light gray (N7), and weather to grayish orange (10YR7/4) and grayish orange pink (5YR7/2). These beds display an extremely high degree of biotur- bation, as evidenced by cross- sections of their concretions. The strata also, are extremely fragmented giving these beds a mushy appearance/ particularly near the top. The concretions within these strata are found in discontinuous beds. They rarely contain body fossils or display primary sedimentary structures, but they do display a healthy population of . The concretions are light gray (N7) to light bluish gray (5B7/1) in color and range in size from 0.5 to 1.0 meters in diameter. 120 17 8 These outcrops consists of fine-grained sandstones, saturat ed with rudimentary concretions. These concretions are light bluish gray (5B7/1) in the center and dark yellowish orange (10YR6/6) on the outside. No body fossils, traces or primary sedimentary structures were noted in these rocks. 100 o 9 5 90- CTP From stake BC-17 to BC-26 the strata are fine-grained sand stones. These beds are more consolidated at the top of this unit and become increasingly more fragmented downward. The sand stones are primarily dark yellow ish orange (10YR6/6) and grayish orange (10YR7/4), but a few beds are light gray (N7). A few con cretions are found throughout these rocks. The nodules are light (N7) contain no body fossils nor do they display primary sedi mentary structures, but they do contain Helmithoida traces. 85' 80 180 80 COVERED m 7 5' 70- These outcrops consists of fine-grained sandstones, saturated with rudimentary concretions. These rudimentary concretions are light bluish gray (5B7/1) in the center and dark yelowish orange (10YR6/6) on the outside. No body or trace fossils, or primary sedi mentary structures were located in these rocks. "TALUS" 65 60 (&J c ® 181 Blocky fine-grained sandstones make-up the strata within BC-45 to BC-54. The beds are medium light gray (N6) to medium bluish gray (5B5/1). These beds are blocky and not as friable as the previ ously discussed units above them, also these rocks display traces of planar laminations. Within these strata are numerous carbonate concretions and rudimentary con cretions, both of these features are the same color as the sand stones. The nodules have quite a range in size, from 0.3 to 1.5 m in diameter. Many of these con cretions contain numerous body fossil fragments, mainly those nearer the base of this unit. Most of these fossils are non- identifiable, but some turritella, ostrea, and ptertrigonia were recognized. 182 Fine-grained, highly frag mented, crumbly sandstones con stitute the beds found within stake locations BC-54 thru BC-61. The strata are medium light gray (N6) to medium bluish gray (5B5/1). These beds are not blocky like those of the previous unit, but are very crumbly due to the high degree of fragmentation (maybe poor cementation or in creased weathering). Within these strata are numerous carbonate nodules and rudimentary features, both of these concretions are the same color as the sandstone beds. The nodules have quite a range of sizes from 0.3 to 1.25 m in diameter. Many of these con cretions contain body fossil fragments. The fossils have been identified as ptertrigonia, turritella and ostrea. These beds also have been bioturbated, obscuring most of the primary sedimentary structures. Faint planar laminations have been noticed occasionallly. The traces responsible for the bioturbation are not readily identified, but appear to be Helminthoida. 20 COVERED 15- "TALUS" COVERED 5- "TALUS" COVERED These outcrops are medium- grained sandstones over- and underlain by fine-grained sand stones. The sandstone beds are fresh colored grayish orange (10YR7/4) and display planar lam inations. No megafossils, or concretions were found. A few Ophiomorpha were found in the medium-grained sandstones, these strata were interpreted as possible tempestite deposits. The finer strata were heavily biotur bated and showed only faint lamin ations. These strata contained a few carbonate concretions, fresh colored light gray (N7). 184 APPENDIX C STRATIGRAPHIC SECTION Stratigraphic section of outcrops of Sandstone Member along Edison Power Road Santa Ana Mountains, southern California the Pleasants Black Star Canyon, 185 VERTICAL SCALE lm m=microfossil sample t=thin-section sample g=Leco gasometric sample BS-8=stake location 270 265 The top of this member is composed of fine-grained clayey, highly fragmented, sandstone (5B6/1), and is overlain uncon- formably by the Silverado Form ation. 260 186 260 255- COVERED 250- m 245 ' 240 240 235* 230- Outcrop of highly fragmented, bioturbated, fine-grained clayey sandstones. These sandstone strata are fresh colored light bluish gray (5B7/1) and medium gray (N5/5). The beds have a marbled appearance and display no primary sedimentary structures. This strata contains many small faults that may account for its marbled appearance. Trace fossils, that appear to be Ophiomorpha are present near the top of the unit, and although the strata are extremely bioturbated it is impossible to positively identify the traces responsible. 225, 220 188 220 215 m 210- CM m 200 189 > The outcrops from BS-2 to BS-4 are fine-grained, clayey, highly fragmented, bioturbated sand stones. These sandstones are fresh colored light gray (N7) to light bluish gray (5B7/1), but weather to grayish orange (10YR7/4) and light brown (5YR6/4). Numerous faults traverse through this unit, though they are to small to map. In many places these faults give the strata a very crumbly and disoriented appearance. The fine grained strata are thinly laminated and contain bedding planes of carbonaceous fragments, which account for their high organic content. Many of these rocks are partially covered with a calcite coating. No macrofossils were found in these strata. These sandstones also contain many coalescing concretion beds and individual concretions. The carbonate concretions have fresh colors of light gray (N7) to light bluish gray (5B7/1), and weather to grayish orange (10YR7/4) and light brown (5YR6/4). Concretion size varies considerably, ranging in diameter from 0.3 to 1.5 m . The majority of the concretions have an ellipsoidal shape, and most are found in coalescing beds. These beds are known to extend 10 to 13 m in length, and are parallel to bedding. The nodules are normally accentuated by black carbonaceous 190 180 175. fragments. These fragments are concentrated along bedding planes. The origin of these black carbon aceous fragments is postulated as being plant material (terrestri al?) . Furthermore, all of these carbonate concretions exhibit some degree of bioturbation (moderate to high levels). The predominant trace fossil found within these nodules are Helminthoida. A rare Ophiomorpha was also found. Macrofossils are rare in these concretions, only a broken valve and a possible ammonite shell fragment were found. 170- c z c > 165- 160 191 160 155 m 150 g 145 140 CD The outcrops from BS-4 to BS-7 are fine-grained,- clayey, highly fragmented, bioturbated sand stones. These sandstones are fresh colored light gray (N7) to light bluish gray (5B7/1), these weather to grayish orange (10YR7/4) and light brown (5YR6/4). The fine-grained beds are thinly laminated and contain bedding planes of carbonaceous materials. Many of these rocks are coated with a calcium deposit. Many faults cut thru these beds, making them very crumbly. The sandstone beds also contain numerous coalescing concretionary beds. The carbonate concretions have fresh colors of light gray (N7) and light bluish gray (5B7/1), weathering to grayish orange 192 140 m 13 5- (10YR7/4) and light brown (5YR6/4). Concretion size varies, ranging in diameter from 0.5 to 1.5 m . The majority of the concretions are ellipsoidal in shape, and are found in coalescing beds. These beds are known to extend 10 to 15 m in lenght, and are parallel to bedding. The nodules are normally accentuated by carbonaceous material. These fragments are concentrated along bedding planes. Furthermore, all of these carbonate concretions exhibit some degree of bioturba- tion (usually high). The trace fossil found is Helminthoida> no other traces are found. Macro fossils are non-existant. 130- 125- 120 193 120 COVERED m 125 - 110 • 105. 100 The strata that outcrops from BS-24 to BS-27 are fresh colored light gray (N7) to light bluish gray (5B7/1), and weather to yellowish orange (10YR7/6) and light brown (5YR5/6). At the top of this unit the strata are extremely fragmented, appearing very crumbly, and similar to BS-3 and BS-13• These upper strata, of this unit, contain a few concretions. The concretions are fresh colored light gray (N7) to light bluish gray (5B7/1). The concretions occasionally contain ammonite shells, but more commonly 194 bivalve shells. The shape of these concretions is round, usually 10 to 25 cm in diameter, and they occur individually not in beds (coalescing). The rest of this unit contains numerous coalescing concretionary beds. The beds are made-up of ellipsoidal concretions that range in size (diameter) from 0.3 to 1.0 m . These concretions are very fossiliferous, containing T U x x jL f£ lla , P ts x iL r lg s u ls , Cymbophora and ammonites. There are also several rudimentary concretion beds within these strata. The fine-grained sandstone of the rest of this unit is highly fragmented, but not nearly as much as the upper part. Also the sandstone strata, or the lower and middle part of this unit, display faint planar laminations from a distance. Two medium-grained sandstone beds, ranging from 15 to 30 cm thick, are located in the middle part of this unit. These beds contain no concretions or fossils. The beds are located at BS-25-1. The lower part of this unit contains fewer concretions than the middle section. Also, at the base of this section is a fault. 195 COVERED 60 196 55- 50“ 45- m g 00 CM I COVERED 40 40 •trt ♦ i t > » i 35 - 30 - g 25 -f 20 1 The outcrops from BS-28 to BS-31 are heavily bioturbated, extremely fragmented, fine-grained sandstones. They are light gray (N7) to light bluish gray (5B7/1) in color, weathering to yellowish orange (10YR7/6) and light brown (5YR5/6). These strata contain no carbonate concretions, although the rocks are high in calcium carbonate content. The organic carbon content is also relatively high near the top of this unit but decrease greatly downsection (Table 1). No megafossils were found in these strata, and the trace fossils responsible for the bioturbation of these sediments were not identifiable. These 198 strata do exhibit primary sedimentary structures, in the form of very faint planar laminations. These beds are extremely faulted, with fairly large faults at both the top and base of this unit. There are also numerous small faults which cut thru these beds. These faults give this unit a very very crumbly, extrmely fragmented and mushy appearance. Small calcite veins slice through these rocks along the fault zones. 199

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Asset Metadata

Creator Enzweiler, Eugene Joseph (author)

Core Title Paleoenvironmental analysis of Upper Cretaceous Pleasants Sandstone Member (Williams Formation), Santa Ana Mountains, Southern California

Degree Master of Science

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-c30-123713

Unique identifier UC11225401

Identifier usctheses-c30-123713 (legacy record id)

Legacy Identifier EP58749.pdf

Dmrecord 123713

Document Type Thesis

Rights Enzweiler, Eugene Joseph

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