Holocene loess deposition and soil formation as competing processes, Matanuska Valley, southern Alaska

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Holocene loess deposition and soil formation as
competing processes, Matanuska Valley, southern
Alaska

• Presented By Jason Windingstad

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Adapted from a publication by

• Daniel R. Muhs, John P. McGeehin, Jossh Beann,
  and Eric Fisher

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Objectives

• Identify loess sedimentation as a competing
  factor against soil formation
• Show that loess sedimentation was episodic during
  the Holocene
• Show increased soil development with distance
  from Loess source through chemical and physical
  data

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Introduction

• Loess is the most widely distributed sediment of
  Quaternary age in Alaska (Pewe, 1975)
• Loess-paleosol sequences represent an important
  record of climate change during the Quaternary

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Distribution of Loess in Alaska
D.R. Muhs et al. / Quaternary Research 61 (2004)
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Active Loess Deposition, Matanuska Valley
Photo by Warren Huff.
Taken from tvl1.geo.uc.edu/ ice/Image/propro/32.h
tml
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Geographic Setting

• Glacial drift and loess mantled trough
• MAP 393mm
• APE 466mm
• MAT 1.9 degrees C
• Spruce-dominated boreal forest
• Knik and Matanuska Glaciers still active
• Summer winds 3.9-5.7 m/s
• Winter winds 3.3-4.0 m/s

D.R. Muhs et al. / Quaternary Research 61 (2004)
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Loess Deposition and Soil Formation in the
Matanuska Valley

• Previous studies in the mid-continent of North
  America, show the degree of soil development in
  loess derived soils increases as a function of
  distance downwind from the source area. (Ruhe,
  1969)
• Soils in the Matanuska Valley near the source
  area are classified as Entisols or Inceptisols
  while soils at more distal localities are
  Spodosols.

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Spodosols

• White Earths
• Humid boreal climatic zones
• Typically coarse textured parent materials
• O,A,E,Bs(Bh or Bhs) horizons
• Podzolization primary pedogenic process
• Fully developed Spodosols have formed within 300
  yrs in SE Alaska
• (Buol et al., 2003)

cropandsoil.oregonstate.edu/.../ slides.html
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Inceptisol

• Weakly expressed profile features
• A, Bw, C horizons
• Develop in a variety of climates
• Common soil in areas of high relief and on
  younger land forms
• (Boul et al., 2003)

cropandsoil.oregonstate.edu/.../ slides.html
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Purpose of Study

• Determine when episodes of loess deposition began
  during the Holocene
• Explore the relationship between loess deposition
  and soil development in an active eolian
  environment.
• Identify loess deposition and soil formation as a
  competing process

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Methods

• Loess sections were described from river cut
  banks, road cuts, and hand dug pits
• Charcoal and wood fragments were radiocarbon
  dated by accelerator mass spectrometry
• Soil and Sediment was sampled by horizon for
  particle size, bulk mineralogy, and geochemistry
• Semiquantitative mineralogy was determined by
  X-ray diffractometry
• Concentrations of select major elements of bulk
  soil samples were determined by energy-dispersive
  X-ray fluorescence

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Stratigraphy and Sedimentology
D.R. Muhs et al. / Quaternary Research 61 (2004)
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Particle Size vs. Distance From Source
D.R. Muhs et al. / Quaternary Research 61 (2004)
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Loess Thickness vs. Distance From Source
D.R. Muhs et al. / Quaternary Research 61 (2004)
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Chemical Weathering

• Optical examination along with X-ray diffraction
  analysis indicate that the dominant minerals of
  the coarse silt fraction in the unaltered Loess
  are quartz, plagioclase, mica, chlorite, and
  hornblende (K-feldspar is also present in small
  amounts)
• Plagioclase, mica, chlorite, and hornblende
  undergo rapid alteration under low pH conditions
  with sufficient precipitation

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Mobile-to-Immobile Elemental Ratios

• Previous studies by Muhs et al., 2001 indicate
  that certain major elemental ratios in
  loess-derived soils of the Mississippi River
  Valley give useful proxies for mineral depletions
  and thus the degree of chemical weathering that
  has taken place.
• The elemental ratios in the Matanuska valley
  soils should show a similar trend

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Titanium as an Immobile Element

• Immobile elements are residually enriched in
  comparison to the more mobile elements released
  from soluble mineral phases in leached zones of a
  soil profile (Stiles et al., 2003).
• Ti and Zr are commonly considered immobile due to
  the insoluble nature of the minerals they are
  concentrated in e.g. zircon ZrSiO4 and
  rutile/anatase TiO2 (Stiles et al., 2003)

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Elemental Ratios for Matanuska Valley Loess
D.R. Muhs et al. / Quaternary Research 61 (2004)
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Translocation of Fe vs. Distance From Source

• Through the process of Podzolization Fe, Al, and
  organic matter under low pH conditions and the
  presence of chelates migrate from O,A and E
  horizons into B horizons.
• Total Fe2O3 should increase in B horizons with
  distance from the source

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Fe2O3
D.R. Muhs et al. / Quaternary Research 61 (2004)
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Pedogenic Pathway
D.R. Muhs et al. / Quaternary Research 61 (2004)
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Conclusions

• Radiocarbon dating suggests loess accumulation
  began after 6500 C14 yr B.P.
• Loess sedimentation was episodic during Holocene
• Stratigraphic complexity is at a maximum at
  intermediate distances from the source
• Textures change drastically with distance from
  the source area
• Mobile elements decrease in surface horizons with
  distance
• Systematic increases in chemical weathering and
  Spodosol formation over the Holocene time scale
  are unexpected results

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References

• Muhs, D.R., J.P. McGeehin, J. Beann, and E.
  Fisher. 2004. Holocene loess deposition and soil
  formation as competing processes, Matanuska
  Valley, southern Alaska. Quaternary Research
  61265-276.
• Pewe, T.L., 1975. Quaternary Geology of Alaska.
  U.S. Geological Survey Professional Paper, 835.
• Muhs, D.R., Bettis III, E.A., Been, J., McGeehin,
  J., 2001b. Impact of climate and parent material
  on chemical weathering in loess-derived soils of
  the Mississippi River Valley. Soil Science
  Society of America Journal 65, 17611777.
• Ruhe, R.V., 1969a. Application of pedology to
  Quaternary research. In Pawluk, S. (Ed.),
  Pedology and Quaternary Research. National
  Research Council of Canada and University of
  Alberta, Edmonton, pp. 1 23.
• Buol, S. W., R. J. Southard, R. C. Graham, and P.
  A. McDaniel. 2003. Soil Genesis and
  Classification, 4th ed. Iowa State Univ. Press,
  Ames.
• Stiles, C.A., C. I. Mora, and S. G. Driese. 2003.
  Pedogenic processes and domain boundaries in a
  Vertisol climosequence evidence from titanium
  and zirconium distribution and morphology.
  Geoderma 116 279-299.