AN ABSTRACT OF THE THESIS OF Erik P. Graven for the degree of Master of Science in Geology presented on October 11. 1990. Title: Structure and Tectonics of the Southern Willamette Valley. Oregon Redacted for Privacy Abstract approved: Dr. bert S. Yeats Surface geology, seismic data, petroleum exploratory well data, and water well data have been used to analyze the structural and tectonic history of the southern Willamette Valley. Tertiary strata beneath the southern Willarnette Valley appear to have had an early Cascade or Clarno volcanic source to the east by the middle Eocene. The Tertiary strata have been deformed into a series of broad north-northeast trending folds and northeast and northwest trending faults which initially developed under east-northeast compression during the middle Eocene and have since been rotated clockwise to their present positions. The cross-cutting pattern of subsurface faults has been complicated by reactivation during the clockwise rotation of Si to its present orientation of north-south. Uplift of the Coast Range prior to emplacement of the Miocene Columbia River Basalt Group (CRBG) produced the gentle east dip of strata beneath the western edge of the Valley and beneath the CRBG in the Salem and Eola Hills. The southern Wilamette Valley is controlled by erosion of the relatively incompetent Eugene Formation following emplacement of the CRBG. Neogene sediments deposited after this degradational event suggest that during the late Miocene to Pliocene, the proto-Willamette River flowed east of the Salem Hills before uplift along the Waldo Hills forced its course to the west. This aggradation appears to have been caused by increased uplift of the Coast Range and/or subsidence of the Willarnette Valley over the slab bend in the subducting Juan de Fuca plate. Degradational and aggradational periods during the Pleistocene appear to have been caused by readjustment of the Willamette River system to new base levels and changes in sediment supply to the valley. Neotectonic features in the valley include: 1) the Owl Creek fault which is at least Pleistocene in age and possibly younger, 2) the Harrisburg anticline, 3) the Turner fault, and 4) deformation in the North Santiam River basin including the Mill Creek fault. With the exception of the Owl Creek fault, the minimum age of these structures is poorly constrained but is at least post-Miocene and possibly younger. Structure and Tectonics of the Southern Willamette Valley, Oregon by Erik P. Graven A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Completed October 11, 1990 Commencement June 1991 APPROVED: Redacted for Privacy Professor of Geology in charge of mjor Redacted for Privacy Head of departn%tç(eology Redacted for Privacy Dean of Graduate Sch Date thesis is presented October 11. 1990 Printed by Erik P. Graven for Erik P. Graven ACKNOWLEDGEMENTS I thank Alan R. Niem and Patricia McDowell for taking the time to serve on my committee and for thoroughly reviewing this thesis. I also thank Robert S. Yeats, not only for his careful reviews of the manuscript, but also for the many hours spent in weekly discussions of the project. His guidance has been invaluable. Discussions with Robert Lilie regarding the interpretation of eophysica1 data were also greatly appreciated. Funding for this research was provided by the National Earthquake Hazards Reduction Program of the U.S. Geological Survey, and by ARCO Oil and Gas. A scholarship was also provided by the Amoco Foundation. Seismic and gravity data were provided by Mobil Oil and ARCO Oil and Gas. Wendy Niem provided drill hole data from the Super Collider Citing Proposal project. Bernie Kleutsch and Marcia Judy-Malsirom of the Oregon Department of Transportation were extremely helpful in providing drill hole and core hole data from throughout the southern Wilamette Valley and in taking time for numerous discussions of unconsolidated sediment stratigraphy in the valley. Jack Meyer of Northwest Natural Gas also provided valuable guidance in the interpretation of well logs and seismic data from the Willamette Valley, and Marvin Beeson always made himself available for questions regarding Columbia River Basalt Group stratigraphy. Plates were drafted by Paula Pius and Linda Hygarth. Numerous figures were drafted by Camela Carstarphen. I also thank Cam for the tremendous amount of physical and emotional support she provided in the latter stages of the project. I thank my parents for their constant emotional support as well as their financial support during times of need. I am also indebted to Nick Enos, and the Crag Rats search- and-rescue team for hauling me, and my broken leg, off Mount Hood, so I could return to defend the thesis. Last, but certainly not least, I thank Ken Werner for all of the following: 1) numerous valuable discussions regarding various aspects of the project, 2) putting up with all the strange noises I made in the office, 3) countless nights at Squirrels discussing the numerous merits of pursuing an M.S., 4) psychological rehabilitation at Lake Tahoe, and 5) simply being a fantastic friend through it all. TABLE OF CONTENTS Page INTRODUCTION 1 AREA OF STUDY 2 PREVIOUS WORK 2 TIME SCALE USED 4 METHODS AND DATA BASE 5 SURFACE BEDROCK COMPILATION 5 SUBSURFACE BEDROCK INTERPRETATION Petroleum Exploratory Wells 5 Seismic Reflection Profiles 7 Gravity Data 13 SUBSURFACE UNCONSOLIDATED SEDIMENT INTERPRETATION Water Wells 1 3 Engineering Drill Holes 14 REGIONAL TECTONIC HISTORY 15 STRATIGRAPHY 21 BEDROCK Siletz River Volcanics 21 Tyee Formation 26 Yam/zill Formation 32 Spencer For,nation 35 Fisher Formation 37 Eugene Formation 41 Little Butte Volcanics 42 Scotts Mills Formation 46 Molalla Formation 48 Columbia River Basalt Group 49 Sardine Formation 52 Snow Peak Volcanics 53 Intrusive Rocks 54 UNCONSOLIDATED SEDIMENTS Unnamed Fluvial Sediments 55 High Terrace Gravels 62 Rowland For,nation 64 Willamette Formation 65 STRUCTURE 68 REGIONAL STRUCTURE 68 SURFACE FAULTS 69 SUBSURFACE FAULTS 73 Owl Creek Fault 74 Oak Creek Fault 77 Pierce Creek Fault 77 Ridgeway Butte Fault 79 Calapooia River Fault 80 Lebanon Fault 81 Beaver Creek Fault 82 East Albany Fault 83 Mill Creek Fault 83 SURFACE FOLDS 86 SUBSURFACE FOLDS 87 DISCUSSION 96 CONCLUSIONS 109 REFERENCES CITED 110 LIST OF FIGURES Figure Tectonic and physiographic provinces map of western Oregon and Washington 3 Reference map showing petroleum exploratory well and engineering core hole control in the southern Willamette Valley 6 Reference map showing the location of seismic control 8 Synthetic seismogram of M&P Farms well (right) and a section of seismic line3neartheM&PFarmswell 10 Synthetic seismogram from Porter 1 well (left) and a section of seismic line 10 near the Porter 1 well 11 Velocity profile applied to seismic line 10 12 Northeast Pacific plate geometry at 65, 48, 37, and 16 Ma 16 Tectonic rotation of Tertiary rocks, grouped by age 18 Schematic model of dextral shear rotation along western North America (Beck, 1980) 18 Orientation of stress at 22, 18-12, and 3.5-0 Ma, inferred from dike and vein data in the Western Cascades, latitudes 43-44° 20 Comparative stratigraphic correlation chart for western Oregon 22 Deep seismic reflection profile (Oregon 1) from western Oregon recorded byCOCORPin 1984 24 A) Location map of seismic reflection profile Oregon 1, and B) Cross section of Oregon 1 as interpreted by Keach (1986) 25 Electric log correlation section for wells along cross section A-A' 27 Electric log correlation section for wells along cross section B-B' 28 Electric log correlation section for wells along cross section C-C' 29 Electric log correlation section for wells along cross section D-D' 30 Generalized isopach map of "Miller sand" member of the Yamhil Fm. constrained by petroleum exploratory wells 34 Section of electric log from Merrill 1 well showing contact between mudstone of the upper Spencer Formation (Ems) and overlying sandstone and siltstone of the Eugene Formation (OEm) 38 Section of electric log from Hickey 9-12 well showing contact between volcanics within the Spencer Formation (EVS) and overlying sandstone and siltstone of the Eugene Formation (OEm) 39 Subcrop map of southern Wilamette Valley showing the eastern extent of the Eugene Formation (OEm), the Miocene-Oligocene volcanics (MOv) and the Scous Mills Formation (MOs) 45 Late Oligocene paleogeography of western Oregon and Washington 47 Stratigraphic nomenclature, age, and magnetic polarity for the Columbia River Basalt Group, as revised by Swanson et al. (1979) and modified by Beeson et al. (1985) 50 Distribution maps of CRBG units in western Oregon and Washington 51 Graphic log of DH13-88 drilled on the southeast side of Corvallis 57 Graphic log of DH14-90 drilled near Mill Creek on the southern edge of the Waldo Hills 58 Structure contour map of the base of the Rowland Formation including subcrop map of the underlying unnamed fluvial sediments 59 Shallow structural cross section H-H' controlled by water wells, engineering bore holes, and petroleum exploratory wells, showing Neogene and probable Pleistocene displacement along the Owl Creek fault, and the relationship between the overbank and channel facies of the proto-Wiilameue River 60 Schematic Neogene and Quaternary stratigraphic history of the southern Willameue Valley 63 Comparative stratigraphic nomenclature chart for Quaternary and Neogene units in the southern Willamette Valley 66 Structure map of the southern Willameue Valley 70 Seismic line 3 (unmigrated) across Owl Creek fault 75 Western part of seismic line 7 (unmigrated) across Oak Creek fault 78 Western part of seismic line 1 (unmigrated) across East Albany fault 84 Residual gravity anomaly map of the southern Willamene Valley showing the filtered complete Bouguer gravity with wavelengths50 km 85 Western part of seismic line 10 near the Porter 1 well showing a broad anticline 88 Correlation of mud logs from the Cindy 1 and Merle 1 wells 91 Structural cross section through Henschell 17-34, Miller 1, and Wolverton 13-31 wells 92 A) General longitudinal profile along the present Willamette River.