Chronology, Lithology and Paleoenvironmental Interpretations of the Penultimate Ice-Sheet Advance into the Puget Lowland, Washington State Kathy Goetz Troost A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Washington 2016 Reading Committee: Derek Booth, Chair Michael Brown Estella Leopold Program Authorized to Offer Degree: Earth and Space Sciences ©Copyright 2016 Kathy Goetz Troost Page 2 of 239 University of Washington Abstract Chronology, Lithology and Paleoenvironmental Interpretations of the Penultimate Ice-Sheet Advance into the Puget Lowland, WA Kathy Goetz Troost Chair of Supervisory Committee: Dr. Derek B. Booth Earth and Spaces Sciences Stratigraphic nomenclature and chronology has been a problem for geologists seeking to understand the Quaternary history of the Puget Lowland of Washington State for over one hundred years. Accurate identification of deposits, and accurate age assignments for those deposits, can help us to better understand the paleoclimate of the region, the physical characteristics of deposits encountered during infrastructure projects, the timing of tectonic deformation and recent seismicity, and our geological history. Each of these has profound consequences on our daily lives. In this dissertation I have established a stratigraphic framework for the last million years of geologic history in the Puget Lowland, based on global climate patterns, abundant new absolute dates, and detailed mapping that synthesizes my work and the work of others over the last century. Two decades of detailed field mapping, absolute and relative dating, and analyses have identified new geologic units and clarified and expanded our understanding of many others that had been Page 3 of 239 previously identified but imprecisely described or understood. The techniques I have made use of include luminescence dating, paleomagnetic correlations, radiocarbon dating, fission-track and Ar/Ar dating, palynology, macrofossil identification, provenance, and field-measured sections. My data suggest that the Vashon stade (representing the regional advance of the Marine Isotope Stage 2 ice sheet) ended quite abruptly, nearly simultaneously in the north and south Lowland. The prior MIS 4 ice sheet advance, named the “Possession glaciation,” was of similar extent to that of the Vashon stade, extending to within about 25 km of the Vashon limit. MIS 4 fine- grained glacial deposits are abundant in the Puget Lowland. The Whidbey Formation (MIS 5) and Double Bluff Drift (MIS 6), previously recognized only north of Seattle, have now been newly identified in the southern Puget Lowland, over 60 km from their type section on Whidbey Island. Newly identified stratigraphic units include deposits from the MIS 7 interglacial period, informally named the “Hamm Creek formation” for 200-ka pumice deposits in Seattle; deposits from the MIS 8 glacial period, collectively named the “Defiance drift”; and the “Gig Harbor gravel,” which may be part of MIS 8 or even older. In addition, reversely magnetized deposits, assumed to be older than 780 ka based on limiting luminescence ages, have been identified in multiple locations along the Tacoma and Gig Harbor coastline. Many unconformities exist in the Pleistocene record of the Puget Lowland, making stratigraphic correlation difficult even with absolute dating. Each time-stratigraphic unit is an unconformity- bounded sequence with widely distributed but discontinuous deposits. Glaciotectonic and tectonic discontinuities further confound correlations. With diligence and knowledge, however, we can continue to improve our geologic understanding. Society’s future economic progress and human well-being in the Puget Lowland region depends in large measure on our ability to predict and plan for global climate changes, geologic hazards, and the complexity of the ground beneath Page 4 of 239 us. Understanding the relatively recent geologic history of the region, of which this dissertation is a contribution, is a necessary step in that process. Page 5 of 239 Acknowledgements This dissertation and the two decades of my professional life that it represents would not have been possible without the support of a number of people. I thank the following for their support, be it financial, professional, or emotional. First I must thank my PhD committee for their tireless hours of reading, editing, technical assistance, expertise, and encouraging conversations: Derek Booth, Mike Brown, and Estella Leopold. And I thank my GSR Marina Alberti for her support. Derek and I spent hundreds of days in the field discussing everything about the Quaternary geology of the Pacific Northwest; he with binoculars and me with a handlens. Thank you, Derek, for your unselfish support, mentoring, and the great geology! At the USGS I thank: Ray Wells, Shannon Mahan, Tom Pratt, Ralph Haugerud, Jon Hagstrum, Craig Weaver, Brian Sherrod, Andrei Sarna-Wojicki, Robert Fleck, and the many others who offered collaboration and support. Working with all of you has been inspiring. At the UW I thank the faculty and chairs of the Earth and Space Sciences Department for their support of me and my lengthy process. Worthy of particular note for their constant support and encouragement are chair Bruce Nelson, and former chairs Robert Winglee and Mike Brown, Eric Cheney (the consummate field geologist), Liz Nesbitt, and the late Richard Stewart. And at the other UW, I thank Brian Mahoney. At the WDNR-DGER, the Washington Geological Survey, I thank Tim Walsh for inspiring conversations about the Pleistocene of the Puget Lowland and the geology of Washington. I also Page 6 of 239 owe a debt of gratitude to the super mappers Michael Polenz, Joe Dragovich, Trevor Contreras, and Josh Logan. My geo buddies in the professional realm deserve huge thanks: Rich Borden, Stan Dodd, Curtis Koger, Bill Laprade, David McCormack, Jim Miller, Mark Molinari, Jenny Saltonstall, Matthew von der Ahe, Aaron Wisher, Ann Youberg, and many more. I enjoy our friendship and collegiality. I look forward to many more years of collaborations and great geology. Most importantly, I thank my family for without them, this dissertation and my career would not have happened. Dan and Lindsay, you have been my biggest supporters and are my greatest joys. Thank you for all of your help and encouragement in getting this document done (GSD). Lastly, Roger, thank you for being my rock, my foundation, and soul mate. Thank you for your countless hours of graphics and document work, your long days and late nights, and for taking care of me through this entire process. I dedicate this dissertation to Roger, Dan, and Lindsay! Page 7 of 239 Table of Contents Chapter 1 - Introduction ............................................................................................................... 15 1.1 Significance ........................................................................................................................ 15 1.2 Research Goals ................................................................................................................... 16 1.3 Funding ............................................................................................................................... 18 1.4 Geographic Setting ............................................................................................................. 19 1.5 Geologic Setting ................................................................................................................. 20 1.6 Glacial Setting ..................................................................................................................... 21 1.7 Tectonic Setting .................................................................................................................. 22 Chapter 2 - Summary of Geochronological Studies in the Puget Lowland ................................. 25 2.1 History of Stratigraphic Efforts .......................................................................................... 25 2.2 Problems with the early correlations of Quaternary deposits ............................................. 29 2.3 Review of Existing Data ..................................................................................................... 34 2.4 Summary of the History of Nomenclature and Evolution of Pleistocene Nomenclature in the Puget Lowland .............................................................................................................. 37 2.5 Definitions of the Whidbey interglaciation and the Olympia nonglacial interval .............. 45 2.6 Age of Volcanic Events ...................................................................................................... 47 Chapter 3 - Methods of New Data Acquisition ............................................................................ 49 3.1 Methods of new data acquisition ........................................................................................ 49 3.2 Field Mapping ..................................................................................................................... 50 3.3 Chronological Methods ....................................................................................................... 52 3.3.1 Radiocarbon Dating .................................................................................................... 54 3.3.2 Optically Stimulated Luminescence Dating ............................................................... 55 Page 8 of 239