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.
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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...
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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
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