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Sedimentary Petrology of Some Tertiary Formations, Upper Nehalem River Basin, Oregon

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Sedimentary Petrology of Some Tertiary Formations, Upper Nehalem River Basin, Oregon AN ABSTRACT OF THE THESIS OF ROBERT OTIS VAN ATTA for the DOCTOR. OF PHILOSOPHY (Name of student) (Degree) in Geology presented onaitcl(g,25/://917/ (Major) Title: SEDIMENTARY PETROLOGY OF SOME TERTIARY FORMATIONS. UPPER NEHALEM RIVER BASIN, OREGON Abstract approved: Redacted for privacy /I- Harold E. Enlows The southern half of the upper Nehalem River basin contains the most complete section of lower to middle Tertiary marinesedi- mentary and volcanic rocks in northern Oregon.Determination of stratigraphic relationships of six formations, and their depositional environments and provenance is the chief objective of this paper. More than 75 percent of the sedimentary rocks comprisingthe Cowlitz, Keasey, Pittsburg Bluff and Scappoose Formations istuffa- ceous arkosic sandy mudstone and siltstone.Much of this has been incorrectly called "shale" in the past.Goble Volcanics, consisting of basaltic lava, breccia, dikes and irregular bodies areinterbedded with and intruded into the late Eocene lowermost CowlitzFormation, made up of immature volcanic siltstone and lithic arkose.Con- glomerate is locally associated with the volcanics. The lithologic identity between the mudstone and muddy volcanic arenite of the uppermost 1,500 feet of the Cowlitz and the lowermost Keasey Formations as previously mapped indicates that they should both be called lower Keasey.The sandy mudstone of the Pittsburg Bluff Formation is easily distinguished from the lithic ar- kose with minor siltstone of the overlying Scappoose Formation. Smectitic clays present in nearly all rocks were formed diagenetically from volcanic detritus.Kaolin is restricted to the mudstone of the uppermost Cowlitz Formation.The lithologic similarity of the four sedimentary units is so pronounced that it is recommended that they be combined to form the Nehalem Group. The Columbia River Group overlies the sedimentary rocks un- conformably in the eastern part of the area.It once had wide distri- bution, as shown by lateritic soil, remnant patches of basalt, and feeder dikes. The sediments accumulated in an environment which changed from shallow marine, flanking volcanic islands, in the late Eocene, to shallow shelf and delta during the Oligocene.Besideslocal vol- canic sources of these sediments, there were volcanic sources to the east and plutonic igneous and metamorphic sources in the northern Rocky Mountains. Sedimentary Petrology of Some Tertiary Formations, Upper Nehalem River Basin, Oregon by Robert Otis Van Atta A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy June 1971 APPRO VED: Redacted for privacy AssociateI. / Professor and Acting Chairman Department of Geology in charge of major Redacted for privacy Dean of Graduate School Date thesis is presented (L/ALc.),i) Typed by Barbara Glenn for Robert Otis Van Atta ACKNOWLEDGEMENTS The writer is deeply indebted to many persons who contributed in so many ways to the completion of this work.The late Dr. W. D. Wilkinson was especially helpful in the beginning of the study and the initial encouragement of Dr. Ira S. Allison is appreciated.Dr. Harold E. En lows supervised the research, accompanied the writer in the field and critically read the manuscript.Dr. Keith F. Oles, Dr. John V. Byrne and Dr. John Eliot Allen all read the manuscript and made valuable suggestions.Dr. Gilbert T. Benson also critically read a portion of the manuscript and aided in interpretation of structure. The following geologists visited the area of study in the company of the writer and contributed valuable discussions: Dr. Jon C. Cum- mings, Dr. Keith F. Oles, Dr. Paul Howell, Dr. Paul E. Hammond, Raymond C. Corcoran, and Dr. Richard E. Thorns, who also made a number of helpful suggestions concerning Lower Tertiary bio- stratigraphy. Discussions and correspondence with Dr. Ewart M. Baldwin, Dr. Parke D. Snavely, Jr., Robert J. Deaconand Herbert G. Schlicker are greatly appreciated.Dr. Jerry L. Glenn contributed valuable assistance in the interpretation of X-ray diffractogra.ms of clay minerals and Dr. Moyle E. Harward read the clay mineralogy section of the manuscript and offered a number of helpful criticisms. During the course of the research many of my students assisted me in some of the routine work, contributing mucheffort and, at times, important suggestions.G. William Avolio and Frances L. Olson helped with some of the clay mineral separations and X-ray diffraction.Michael Moran, Donald W. Baggs and G. William Avolio assisted in the field on several occasions. Heavy mineral separa- tions were very ably done by Linda M. Barry and Frances L. Olson, who also did the thin section analyses of the basalts involved inthis study and typed the initial copy of the manuscript. Mavis D.Hensley and Margaret C. Lewis also assisted with some of the typing. Ronald L. Jackson and Donald W. Baggs did the drafting on diagrams and Steven A. Pedersen helped with some of the photography inthe field.Several other students assisted in minor but essential waysin the sample preparation and granulometric analyses.The patience and understanding of all my colleagues and students during the course of this study is greatly appreciated. Barbara Glenn typed the manuscript and kindly assisted in some of the final organization of the thesis.Thomas R. Bess ler did all of the photographic printing of the illustrations. The deepest appreciation is due my wife, Lucki, whotyped the rough draft and gave unstinting support and encouragement throughout the entire study, taking upon herself many additional responsibilities in order to make my work possible. My daughter, Sue, and my son, Steve, both ably assisted me in some of the field work and my son, Walt, aided me in other ways. To all of the above and to others who also contributed but are not mentioned, I express my sincerest thanks. TABLE OF CONTENTS Page INTRODUCTION Area of Study 3 Physiography 8 Previous Work 11 STRATIGRAPHY, GROSS LITHOLOGY AND STRUCTURE 15 General Discussion 15 Structure 18 Cowlitz Formation 19 Siltstone Member 20 Goble Volcanics Member 21 Sandstone Member 42 Primary Structures 46 Methods of Study 46 Results 48 Mudstone Member 50 Keasey Formation 54 Lower Member 56 Primary Structure 56 Middle Member 58 Upper Member 61 Pittsburg Bluff Formation 64 Scappoose Formation 72 Columbia River Group 77 PETROLOGY 86 Methods 86 Sampling 86 Sample Preparation 87 Mineral Separation 91 Light Minerals 91 Heavy Minerals 94 Description of Minerals 96 Rock Classification and Nomenclature 113 Sandstones 117 Texture 130 Mineral and Rock Components 133 Feldspar 133 TABLE OF CONTENTS (continued) Page Quartz 137 Volcanic Glass 138 Rock Fragments 139 Mineralogic Maturity 140 Heavy Minerals 143 Mudrocks 150 Textural and Mineralogical Classification 150 Mineral and Rock Components 151 Feldspar 151 Quartz 152 Volcanic Glass and Rock Fragments 153 Mineralogical Maturity 157 Heavy Minerals 158 Opaque Minerals 160 Authigenic Minerals 161 Clay Mineralogy 162 Methods 162 Inter stratified (Mixed- layer) Clay Minerals 166 Smectite 169 Kaolin 173 Mica (Illite?) 177 Chlorite 178 Non-clay Minerals in Clay-size Fraction 178 Origin of the Zeolites 179 Summary of Mineralogy of the Clay-size Fraction 182 SEDIMENTATION 183 CONCLUSIONS 190 BIBLIOGRAPHY 199 APPENDIX A Nehalem River Section 205 APPENDIX B Size Analysis of Disaggregated Samples 212 APPENDIX C Mineralogical and Textural Maturity of Sandstones and Siltstones 217 Mineralogy of Sand and Coarse Silt 221 TABLE OF CONTENTS (continued) page APPENDIX D Thin Section Analyses of Basaltic Rocks 242 APPENDIX E Clay Mineralogy of Selected Samples 243 LIST OF TABLES Table Page 1 Summary of Size Parameters 131 2 Criteria for Determination of Textural Maturity 132 3 Frequency Percentage of Feldspar Types 137 4 Frequency Percentage of Various Types of Quartz 138 5 Frequency Percentage of Glass and Rock Types 141 6 Pettijohn's Maturity Indices for Different Types of Clastic Rocks 142 7 Frequency Percentage of Abundance Rank of Heavy Minerals 145 8 Frequency Percentage of Hornblende Types 146 9 Frequency Percentage of Apatite Types 147 10 Frequency Percentage of Zircon Types 149 11 Frequency Percentage of Glauconite 162 12 Criteria for Identification of Clay Minerals 167 13 Size Analysis of Disaggregated Samples 212 14 Mineralogic and Textural Maturity of Sandstones and Siltstones 217 15 Mineralogy of Sand and Coarse Silt 221 16, Thin Section Analyses of Basalts 242 17 Clay Mineralogy of Selected Samples 243 LIST OF FIGURES Figure Page I Index map showing location of upper Nehalem River basin 4 2 Upper Nehalem River valley, looking southeast from Rocky Point 9 3 Nehalem River, looking along the strike of a resistant calcareous pebbly sandstone bed, upper mudstone member, Cowlitz Formation 9 4 Correlation chart of Tertiary formations of northwestern Oregon and adjacent regions 17 5 Pebble conglomerate, lower Cowlitz Formation with included blocks and slabs of basalt of Goble Volcanics 23 6 Zeolitized basalt block in pebble conglomerate, lower Cowlitz Formation 23 7 Basalt in pebble conglomerate, lower Cowlitz Formation 24 8 Boulders in conglomerate overlying basaltic sill 26 9 Conglomerate sliver included in basaltic sill 26 10 Fan jointing in basalt intrusion (Goble Volcanics) with overlying siltstone, sandstone member, Cowlitz Formation 27 11 Laminated mudstone inclusion in basalt 31 12 Basalt pillow with palagonitic glass "rind" 31 13 Basalt pillows with included lathinated mudstone 32 14 Inclusions of sandy mudstone in basalt of
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