In the West Eugene Wetlands and the Willamette Valley Is Weathered and Redeposited Ash from Mount Mazama

Production services provided by: Bureau of Land Management National Operations Center Information and Publishing Services Section P.O. Box 25047 Denver, CO 80225 Suggested citation: Baitis, K.E., G.J. Retallack, and M.E. James. 2015. Gray Clay (Malpass Clay) in the West Eugene Wetlands and the Willamette Valley is Weathered and Redeposited Ash from Mount Mazama. U.S. Department of the Interior, Bureau of Land Management, National Operations Center, Denver, CO. BLM/OC/ST-15/006+7100 GRAY CLAY (MALPASS CLAY) IN THE WEST EUGENE WETLANDS AND THE WILLAMETTE VALLEY IS WEATHERED AND REDEPOSITED ASH FROM MOUNT MAZAMA Gray Clay (Malpass Clay) in the West Eugene Wetlands and the Willamette Valley is Weathered and Redeposited Ash from Mount Mazama Authors: Karin E. Baitis, Bureau of Land Management (retired), Eugene District Office, Springfield, Oregon Gregory J. Retallack, University of Oregon, Department of Geological Sciences, Eugene, Oregon Michael E. James, James Geoenvironmental Services, Eugene, Oregon JUNE 2015 TECHNICAL NOTE 447 i GRAY CLAY (MALPASS CLAY) IN THE WEST EUGENE WETLANDS AND THE WILLAMETTE VALLEY IS WEATHERED AND REDEPOSITED ASH FROM MOUNT MAZAMA Acknowledgments The outcome of this study results from a decade element values by neutron activation. Countless of support from many people and partners and others in the community spent time discussing funding from the Bureau of Land Management. and reviewing data and providing office space for Data were collected through cooperative storing samples and conducting work. In addition efforts during the course of this project and to those previously mentioned, the authors would in partnership with the Long Tom Watershed like to personally thank William C. Sidle of the U.S. Council. Numerous people freely performed Environmental Protection Agency National Risk lab work and data interpretation. Professor Paul Management Research Laboratory; Mike Remboldt Engelking of the University of Oregon Chemistry of KA Engineering; Mark Reed, Paul Wallace, Ewart Department conducted soil profile conductivity Baldwin, Nate Sheldon, and John Donovan of the with ion chromatography. Professor Erwin University of Oregon Department of Geological Schutfort of the Oregon State University Radiation Sciences; and Herb Huddleston of the Oregon State Center conducted C-14 radiometric, tephra, University Crop and Soil Science Department. and pedological analyses and calculated trace ii TECHNICAL NOTE 447 GRAY CLAY (MALPASS CLAY) IN THE WEST EUGENE WETLANDS AND THE WILLAMETTE VALLEY IS WEATHERED AND REDEPOSITED ASH FROM MOUNT MAZAMA Table of Contents Abstract......................................................................iv Introduction..................................................................1 Geologic Setting of Malpass Clay and Dayton Soil..............................2 Materials and Methods .......................................................4 Stratigraphic Position of the Gray Clay in the West Eugene Wetlands . .5 Chromatography .............................................................7 Vertic Soil and Gilgai Relief....................................................8 X-Ray Diffraction . .9 Transmission Electron Microscope EDX Analyses..............................11 Transmission Electron Microscope Images....................................13 Mineralogy of Gray Clay Unit.................................................13 Radiometric Ages............................................................15 Palynology . 16 Conclusions . .17 References . 19 TECHNICAL NOTE 447 iii GRAY CLAY (MALPASS CLAY) IN THE WEST EUGENE WETLANDS AND THE WILLAMETTE VALLEY IS WEATHERED AND REDEPOSITED ASH FROM MOUNT MAZAMA Abstract The climactic eruption of Mount Mazama the missing ash from Mount Mazama. Over time approximately 7,600 years ago distributed airfall and weathering, the ash has transformed into a tuff throughout what is now eastern and offshore smectitic gray imogolite and clay. Analysis of this Oregon. This distinctive tephrostratigraphic widespread gray clay provided a radiocarbon date marker had been thought to be absent across the of 6,850 ± 70 years before present. Radiometric Willamette Valley. X-ray diffraction, examination of dating of the clay provided the ages of 7,987 ± 102, pyrogenic mineral suites, and new high-resolution 8,451 ± 57, and 8,540 ± 48 years before present. radiometric dating (40AR/39AR) of Malpass clay These dates are comparable with that of the from tuffaceous marker beds suggest that it is climactic eruption of Mount Mazama. iv TECHNICAL NOTE 447 GRAY CLAY (MALPASS CLAY) IN THE WEST EUGENE WETLANDS AND THE WILLAMETTE VALLEY IS WEATHERED AND REDEPOSITED ASH FROM MOUNT MAZAMA Introduction Malpass clay is a widespread gray clay originating The caldera-forming eruption of Mount Mazama from the Holocene and found today in the approximately 7,600 years ago created Crater Willamette Valley in Oregon (Figure 1). Theories of Lake, which is about 85 miles (136 km) southeast its origin vary from the idea that the clay came from of Eugene and the southern end of the Willamette weathering in place (Nikiforoff and Drosdoff 1943), Valley (Figure 1). Most ash from Mount Mazama from erosion from the Coast Range mountains was borne eastward by prevailing winds from (Parsons and Balster 1965, 1966; Balster and Parsons the Cascades onto desert soils and playa lakes of 1968, 1969), from deposition of the Missoula floods eastern Oregon, southeastern Washington, and roughly 12,500 years ago (Gelderman and Parsons northwestern Nevada (Crandell and Mullineaux 1972; Roberts 1984), or from a separate windblown 1978; Kittleman 1973; Matz 1991; Mehringer et deposit (Glasmann et al. 1980; O’Connor et al. 2001). al. 1977; Sarna-Wojcicki et al. 1981). However, This technical note presents evidence that the pumiceous Mazama ash also has been identified unusual composition of Malpass clay and a suite of in lake deposits of western Oregon (Williams 1942; rhyodacitic minerals in other soils and sediments Kittleman 1973; O’Connor et al. 2001; Worona are derived from Mount Mazama volcanic ash, and Whitlock 1995) and in offshore marine cores which has weathered in place and redeposited from (Goldfinger et al. 2003). Early studies of the volume surrounding hillslopes (Norgren 1962; Glenn 1965; of ash issued from Mount Mazama, calculated by James and Baitis 2003). Williams and Goles (1968), theorized that more magma erupted than had been mapped. The authors of these studies explained the discrepancy with subterranean withdrawal of magma. This tech note proposes that some of the missing tephra was deposited into the Willamette Valley and weathered into Malpass clay and the Greenback Member of the Willamette Formation. An airfall ash deposit into the Willamette Valley Lincoln • 0 City would have required a wind from the south or southeast, sending the ash north and west. .J 3~ 0l : Mazama ash is 0.35-0.47 in (0.9-1.2 cm) thick in S::: 25 : submarine canyons of offshore Oregon (Goldfinger ~Ill l:: et al. 2003); 0.39 in (1 cm) thick in Little Lake in the '1:l • ~g Oregon Coast Range (Worona and Whitlock 1995); c f: Figure 1. Isopachs (cm) of Malpass clay in the Willamette Valley (solid lines, representing approximate thickness) (James and Baitis 2003) compared with isopachs of Mazama ash (broken lines) (Matz 1991). In addition, 0.35- 0.47 in (0.9-1.2 cm) of Mazama ash have been found at three locations in OREGON deep sea cores of the Oregon continental slope (Goldfinger et al. 2003), and 0.39 in (1 cm) of Mazama ash has been found in Little Lake in the Oregon Coast Range (Worona and Whitlock 1995). TECHNICAL NOTE 447 1 GRAY CLAY (MALPASS CLAY) IN THE WEST EUGENE WETLANDS AND THE WILLAMETTE VALLEY IS WEATHERED AND REDEPOSITED ASH FROM MOUNT MAZAMA and 3.9 in (10 cm) or more thick west of the eastern shot out from the displaced bulge. Finally, a large Willamette Valley (Matz 1991). Malpass clay fills in Plinian column of gray ash shot 11 miles (18 km) the intervening country, where fresh Mazama ash into the atmosphere. Five subsequent vertical has not been found. Malpass clay in the Willamette eruptions trailed off to the east at high elevation. Valley is an order of magnitude thicker than the Much of the column collapsed back on the volcano, predicted 0.4-4 in (1-10 cm) between the Cascades distributing ash radially around the mountain; and Coast Range and was likely redeposited by the ash redistributed later by landslides and rivers wind and water into local depressions. (Lipman and Mullineaux 1981). On May 25, 1980, winds sent airborne ash north and west to the On May 18, 1980, the volcanic eruption of Mount coastal Washington towns of Grays Harbor, Oakville, St. Helens south of Seattle, Washington, showed and Hoquiam. Oakville received 0.75 in (1.9 cm) similar ash distribution in the Pacific Northwest. (Kliem et al. 2005). During this timeframe, Bureau The eruption began with a collapsing bulge of of Land Management (BLM) (retired) soil scientist the volcano and a mudflow. Then a pyroclastic Karin Baitis observed 0.25-0.5 in (0.64-1.27 cm) of blast of mountain debris and hot volcanic gases very fine, gray-colored ash at Hoquiam. Geologic Setting of Malpass Clay and Dayton Soil Stiff, gray and olive brown clays overlying Holocene The West Eugene Wetlands in the southern alluvial deposits, paleosols, and Missoula flood Willamette Valley rest above impervious gray silts in western Oregon’s Willamette Valley have Malpass clay, which is 59 in (150 cm) thick, with been called Dayton soils or the Malpass

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