Holocene loess deposition and soil formation as competing processes, Matanuska Valley, southern Alaska Presented By: Jason Windingstad

Adapted from a publication by: Daniel R. Muhs, John P. McGeehin, Jossh Beann, and Eric Fisher

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

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

Distribution of Loess in Alaska D.R. Muhs et al. / Quaternary Research 61 (2004)

Active Loess Deposition, Matanuska Valley Photo by Warren Huff. Taken from: tvl1.geo.uc.edu/ ice/Image/propro/32.htmltvl1.geo.uc.edu/ ice/Image/propro/32.html

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 m/s Winter winds m/s D.R. Muhs et al. / Quaternary Research 61 (2004)

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.

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

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

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

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

Stratigraphy and Sedimentology D.R. Muhs et al. / Quaternary Research 61 (2004)

Particle Size vs. Distance From Source D.R. Muhs et al. / Quaternary Research 61 (2004)

Loess Thickness vs. Distance From Source D.R. Muhs et al. / Quaternary Research 61 (2004)

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

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

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)

Elemental Ratios for Matanuska Valley Loess D.R. Muhs et al. / Quaternary Research 61 (2004)

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

Fe2O3% D.R. Muhs et al. / Quaternary Research 61 (2004)

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

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

References Muhs, D.R., J.P. McGeehin, J. Beann, and E. Fisher Holocene loess deposition and soil formation as competing processes, Matanuska Valley, southern Alaska. Quaternary Research 61: Pe´we´, T.L., 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, 1761–1777. 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 Soil Genesis and Classification, 4 th ed. Iowa State Univ. Press, Ames. Stiles, C.A., C. I. Mora, and S. G. Driese Pedogenic processes and domain boundaries in a Vertisol climosequence: evidence from titanium and zirconium distribution and morphology. Geoderma 116: