Pre-Mazama Pedogenesis in Post-Outburst Flood Sediments, Columbia Plateau Brett R. Lenz1, Herman Gentry2, Aaron Kuntz1, Danielle L. Clingman3 1. PUD No. 2 of Grant County, WA; 2. Gentry Consulting, Ellensburg, WA; 3. Columbia Geotechnical Associates Inc., Redmond, WA The shallow subsurface of the Scabland region of the Columbia Plateau in central Washington State, displays abrupt changes in depositional environments and sedimentation rates recorded in Pleistocene and early Holocene pedogenic sequences. Depositional environment change occurred rapidly as a result of catastrophic flood sedimentation, the source of eolian and alluvial parent material. Cross-Scabland flooding ceased between 12.1 and 12.8 KBP, while catastrophic floods that were restricted to the Columbia River channel post-date the fall of Glacier Peak tephra (11.2 KBP). Pedogenesis into these flood deposits and thin L1 loess at numerous Scabland locations consists of two soil-forming periods. The lower soil, termed the Bishop Paleosol, is characterized by a well-developed A horizon and a relatively thin Bw or Bt horizon, depending on the local environment. The age of this soil is constrained by its relative position between Mt. St. Helens Set S (12.8±60KBP) and Glacier Peak tephras. Separating the soils at several locations is a post-Glacier Peak tephra period of eolian deposition which may reflect dispersement of outburst flood sediments restricted to the Columbia River Valley during the Younger Dryas cooling period. The second period of pedogenesis postdates deposition of Glacier Peak tephra and pre-dates Mazama (7.7KBP) tephra deposition. This soil, termed the Badger Mountain paleosol is characterized by multiple, stacked buried A (Ab) horizons and welldeveloped cambic (Bw) horizons and argillic (Bt) horizons which may qualify as Natric soils. These strong B horizons overprint the deepest buried A horizons and the Bishop paleosol in some exposures. The cap of the Badger Mountain soil is characterized by a zone of extremely welldeveloped cicada burrowing up to 1m thick, indicating a shift to arid conditions between 7.7 and 11.2KBP. Bishop Paleosol The Bishop paleosol (Lenz 2004) is a terminal Pleistocene age soil that is present west of the Palouse Subregion to the Cascade foothills. The Bishop paleosol is often characterized by a well-developed A horizon and relatively thin Cambic (Bw) or Argillic (Bt) horizons, depending on the depositional environment. The age of this soil is constrained by its relative position between Mt. St. Helens Set S (12.8±60KBP) and Glacier Peak tephras. While no upper-Pleistocene correlate soils are known in the well-studied Palouse subregion of the Plateau, other examples of regional paleosols exist. The upper Pleistocene Rock Creek soil of Davis (2001) appears to correlate well with the Bishop paleosol, and several examples of Bishop-age soils are recorded in the western portion of the Columbia Plateau, on the Yakima Firing Center (Gough, Galm and Nials 2001) although they are treated as local pedogenic phenomena rather than regional-scale soils. Figure 3. Preliminary Distribution Area of the Bishop and Badger Mountain Paleosols Our present understanding of the distribution of the Bishop and Badger Mountain Paleosols is limited to areas we have observed at project sites and in road-cuts while passing through the Scabland. Not every exposure includes both paleosols; the degree of soil preservation is controlled by the sedimentary environment. Present observations suggest that sandy alluvial soils and soils with a generally coarse base are less likely to preserve the Bishop soil. Similarly, alluvial and some hillslope environments are poor environments for Badger Mountain preservation. Both paleosols are pervasive throughout the Scabland and may extend beyond the present mapping area where they are likely correlated to other regional paleosols. Background This work is an outcome of several previous studies (Lenz et al., 2002, 2004a,b, 2006, 2007) and the culmination of several years of independent research by the primary author. Our study sites were selected during research-based field mapping operations and at the request of landowners to augment a variety of resource surveys. To complete the study we described representative pedons, sampled more than one kilometer of excavated trenches and pits and examined several dozen road cuts across central Washington State. When trenching or excavation were not feasible we used a bucket auger to recover sediment samples. We recovered all sediment and soil samples using standard field methods (Compton, 1985; Soil Survey Staff, 1995). At select sites, samples were taken for micromorphology, radiocarbon, tephrochronology and particle size determination. McDonald and Busacca (1992) describe an early to middle Holocene paleosol, the Sand Hills Coulee soil, among numerous others, in the Palouse subregion of the Columbia Plateau. Together the soils these authors present are recorded as loess soils, and they have distinct properties that are best expressed in a loess parent material. We have logged similar soils in a nonloess scabland setting that are correlative in time to the Sand Hills Coulee soil—but we have also recognized an upper-Pleistocene paleosol that is apparently not present in the Palouse sub-region, but that is a very prominent feature in a variety of depositional settings at the close of the Pleistocene in other portions of the Columbia Plateau. When considered in light of other regional soils, together, the soils record details of post-glacial climate change over a relatively broad area. Figure 1. Typical Exposures of Bishop Paleosol with Slightly Elevated Chroma in Ab and Bwb Horizons. Note Redox in Underlying Outburst Flood Sediment. Bishop and Badger Mountain Paleosols Badger Mountain Paleosol The Badger Mountain paleosol post-dates deposition of Glacier Peak tephra and pre-dates Mazama (7.7KBP) tephra. It is characterized by multiple, stacked buried A (Ab) horizons, Cambic horizons and well developed Argillic horizons. It includes prominent carbonate filaments in the Bk horizon and cicada cementation in a zone up to 1.5m thick, with carbonate cementation in many exposures. Typically the Bk horizon has 2030% cemented cicada casts, with some exposures as much as 90%. Multiple argillic horizons which underlie the Ab horizon of the Badger Mountain paleosol represent natric conditions (Figure 5). Skeletans are on many of the ped faces underlying the Badger Mountain Ab horizon in settings where the dispersion of clay occurred. These B horizons overprint the Bishop paleosol in some exposures on colluvial slopes and at the base of local depositional basins. In every instance the Badger Mountain paleosol immediately underlies the Mazama tephra, and in some locations the relationship is disconformable, suggesting a significant change in climate just prior to eruption of Mt. Mazama. Disconformities typically exist in open depositional settings such as broad plains that were subject to deflation. Figure 5. Example of strongly developed Natric soil horizon in Exposure of Badger Mountain Soil, East Wenatchee, Douglas County, Washington. Carbonate Development and Cicada Burrowing Two ubiquitous features of the Badger Mountain paleosol are formation of 1-3 cm. cylindrical cicada nodules and carbonate development. Busacca et al. (2002) present an explanation for development of cicada burrows in loess paleosols of the Palouse. The authors suggest that cicada burrowing occurs in the A and upper cambic horizon of the soil column. Cementation of the cicada burrows takes place at some point following aggradation of the land surface or a major decrease in soil moisture. O’Geen (1998) found that Cicada nymphs feed solely from shrub host plants, principally sagebrush, providing an excellent understanding of the early Holocene paleoenvironment. Paleosol Formed into Outburst Flood Cap The Bishop Paleosol was first recognized at the David Bishop Ranch, on the Babcock Bench in Grant County, Washington. The Bishop Ranch lies on a structural bedrock bench capped by Pleistocene outburst flood sediment, patches of lithosol and post-flood eolian sediment. A dark Ab horizon has formed at the contact of the scoured basalt with overlying sediment whose parent material is comprised of reworked outburst flood sands. On recognizing a buried A horizon there, Lenz and Gentry examined several central Washington roadcuts presented in previous studies by Quaternary scientists (Fryxell 1965, Moody 1976, Mullineaux et al. 1978). The subtle change in chroma that suggests soil formation is not often visible in weathered soil profiles, but once the faces of the roadcuts were exposed, we immediately recognized the characteristic Ab and Bw horizons. The relative stratigraphic position, forming into the cap of the outburst flood deposits helped us understand the timing of the paleosol. Subsequently, we have recognized the Bishop paleosol forming into stable surfaces between UpperPleistocene outburst flood events. Figure 2 provides an example of Bishop soil expressed between layers of Glacier Peak tephra in an Upper Pleistocene alluvial fan. Figure 2. Buried Ab Horizons of Bishop Paleosol in an Alluvial Fan Setting. Alternating Horizons of Buried Glacier Peak Tephra Bracket the Paleosol. POSTER TEMPLATES BY: www.PosterPresentations.com Paleosol Distribution Age and Paleoenvironmental Context Mud Lake Years BP 7,000 Bonaparte Goose Lake Simpsons Creston Fen Flat Meadows W/D C/M W/D D. Pine Disconformity Grass Sage Steppe D. Pine Artemesia Steppe Figure 4. East Wenatchee Section Displaying Bishop and Saddle Mountain Paleosols Figure 6. Example of Carbonate Formation in Exposure of Badger Mountain Soil in a Sandy Eolian Deposit, near East Wenatchee, Douglas County, Washington. Big Meadows Hager Pond W/D D. Pine Grass Steppe W/D W/D D. Pine Grass Steppe Williams Lake Fen 9,000 Some D. Pine Artemesia Steppe Some D. Pine 10,000 C/M Steppe Tundra Grass D. Pine Sage Steppe C/M Steppe Tundra Some Pine/ Spruce Steppe/ Grass Tundra C/M H. Pine Sage Sage Steppe Tundra Sage/Grass Tundra Steppe Younger Dryas Deposition Columbia River Valley Floods Fir, Spruce C/M 12,000 Bishop Paleosol Sage/ Grass Steppe 10,000 C/M 11,000 Some H. Pine 9,000 C/M Some H. Pine C/M Mazama 7,000 8,000 C/M C/M D.and H.Pine Tephrochronology Pre-Mazama Grassland/ Degradation Shrub Steppe Badger Mountain Paleosol W/D Alluvial Sequence W/D D. Pine Fir, Spruce Sage Steppe/ Pine Mt. St. Helens Set J 11,000 Glacier Peak Mt. St. Helens Set J Some H. Pine 12,000 Mt. St. Helens Set S End of CrossScabland Outburst Flooding 13,000 13,000 Figure 8. Stratigraphic and Paleoecologic Correlation Chart Displaying the Relationship Between Palynologic Reconstruction, Outburst Flood and Alluvial Chronologies, Tephrochronology and Pedology (paleoecology based on Galm et al. 1991). The age of both paleosols is constrained by relative stratigraphic position of air-fall tephra and direct radiocarbon dates on bone (Bishop) and charcoal (Badger Mountain). The Bishop paleosol formed at some point just prior to deposition of Mt. St. Helens Set S tephra (12.8KBP) and is capped by Mt. St. Helens Set J (~11.1-11.6KBP) and Glacier Peak tephra (11.2KBP) in most exposures. The Badger Mountain Paleosol formed after deposition of Glacier Peak tephra and prior to deposition of Mazama tephra (7.7KBP). A discontinuity is commonly present at the interface of the Mazama tephra with the Badger Mountain paleosol. In all cases, the Badger Mountain paleosol is buried by Mazama tephra, a stratigraphic relationship which supports a relatively late shift to altithermal conditions, as suggested by regional pollen records which indicate a warmer and drier climatic regime based on the expansion of xeric plant species and an increase in sagebrush and grass communities during this period of time (Mehringer 1985; Wigand 1989). The Bishop and Badger Mountain paleosols are separated by a nonloess eolian depositional event that is coeval in time with the Younger Dryas cooling episode. It is possible that post-Glacier Peak outburst flood events that were restricted to the Columbia River trench produced an abundance of new parent material which could be transported into the uplands of the Scabland. The relatively cool, dry climate of the Younger Dryas precluded soil formation into the eolian material until the close of Younger Dryas during Badger Mountain time. Contact information Figure 7. Example of Cicada Burrowing in Exposure of Badger Mountain Soil on a FineGrained Colluvial Slope, Beezley Hills, Chelan County, Washington. D. Pine Arid Steppe/ Sage Disconformity 8,000 Waits Lake AGGRADATION Abstract Brett R. Lenz 16541 REDMOND WAY STE. 244C REDMOND WA 980524482 MOBILE: 509.933.3081 OFFICE: 425.256.2402 EMAIL: brettlenz@gmail.com 

PRE-MAZAMA PEDOGENESIS RECORDED IN POST-OUTBURST... 1 of 1 https://gsa.confex.com/gsa/2007AM/finalprogram/abstract_132548.htm 2007 GSA Denver Annual Meeting (28�31 October 2007) Paper No. 27-30 Presentation Time: 8:00 AM-12:00 PM PRE-MAZAMA PEDOGENESIS RECORDED IN POST-OUTBURST FLOOD GEOLOGIC DEPOSITS OF THE SCABLAND, COLUMBIA PLATEAU, WASHINGTON LENZ, Brett R., 17503 NE 138th Street, Redmond, WA 98052, brettlenz@gmail.com, GENTRY, Herman, Kittitas, WA 98926, KUNTZ, Aaron, PO Box 878, Ephrata, WA 98823, and CLINGMAN, Danielle L., Geoarchaeological Research, 904 E. 2nd Avenue, Ellensburg, WA 98926 The shallow subsurface of the Scabland region of the Columbia Plateau in central Washington State, displays abrupt change in mode of deposition and sedimentation rates recorded in Pleistocene and early Holocene pedogenic sequences. Local depositional environment change occurred rapidly as a result of catastrophic flood sedimentation, the source of eolian and alluvial parent materials. Cross-Scabland flooding ceased between 12.8 and 12.1 KBP, while catastrophic floods that were restricted to the Columbia River valley post-date the fall of Glacier Peak tephra (11.2 KBP). Pedogenesis into these flood deposits and thin L1 loess at numerous Scabland locations is recorded in two soil-forming periods. The lower soil, termed the Bishop Paleosol, is characterized by a well-developed A horizon and relatively thin Cambic (Bw) or Argillic (Bt) horizons, depending on the depositional environment. The age of this soil is constrained by its relative position between Mt. St. Helens Set S (12.8�60KBP) and Glacier Peak tephras. Separating the two soils at several locations is a post-Glacier Peak tephra period of eolian deposition which may reflect disbursement of Columbia River Valley outburst flood sediments during the Younger Dryas cooling period. The second period of pedogenesis post-dates deposition of Glacier Peak tephra and pre-dates Mazama (7.7KBP) tephra deposition. This soil, termed the Badger Mountain paleosol, is characterized by multiple, stacked buried A (Ab) horizons, Cambic horizons and well developed Argillic horizons which may qualify as Natric soils. These strong B horizons overprint the deepest buried A horizons and the Bishop paleosol in some exposures. The cap of the Badger Mountain soil is characterized by a zone of extremely welldeveloped cicada burrowing up to 1m thick, indicating a shift to arid conditions after 11.2KBP. 2007 GSA Denver Annual Meeting (28�31 October 2007) General Information for this Meeting Session No. 27--Booth# 137 Quaternary Geology/Geomorphology (Posters) Colorado Convention Center: Exhibit Hall E/F 8:00 AM-12:00 PM, Sunday, 28 October 2007 Geological Society of America Abstracts with Programs, Vol. 39, No. 6, p. 82 © Copyright 2007 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions. 1/10/2019, 10:44 AM