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Coastal Dune Soils in Oregon, USA, Forming Allophane and Gibbsite by

Coastal Dune Soils in Oregon, USA, Forming Allophane and Gibbsite by. Georg H. Grathoff Curt D. Peterson Darren L. Beckstrand. Funded by:. Objective. Determine the age and mechanism of dune emplacement Determine whether soil/paleosol mineralogy can constrain age of emplacement. Study Area.

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Coastal Dune Soils in Oregon, USA, Forming Allophane and Gibbsite by

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  1. Coastal Dune Soils in Oregon, USA, Forming Allophane and Gibbsiteby Georg H. GrathoffCurt D. Peterson Darren L. Beckstrand Funded by:

  2. Objective • Determine the age and mechanism of dune emplacement • Determine whether soil/paleosol mineralogy can constrain age of emplacement

  3. Study Area

  4. Importance of the paleosols • Influence stability • Control groundwater chemistry and flow • Indicate age

  5. Dunal Paleosols

  6. “Weeping sands”

  7. Study Area

  8. Map of TL and 14C dates in ka BP. Core names are in parentheses. (from Beckstrand 2001)

  9. Eustatic sea level fluctuations and absolute elevations. Chappell and Shackleton (1986) (A), Shackleton (1987) (B), and Bloom and Yonekura (1985) (C). Boxes indicated probable errors of age and height related to curve C. Modified from Pirazzoli (1993). From Beckstrand; 2001

  10. Results:Minerals in Dunal Soils • Gibbsite: Al(OH)3 • Allophane/Imogolite: amorphous Al-Silicate • Vermiculite and/or chlorite • Fe oxides/hydroxides

  11. 1) Gibbsite

  12. X-ray Diffraction results Gibbsite 002 Gibbsite 110 5.35 Å 200 Gibbsite

  13. 2) Allophane replacing tree roots Seal Rock State Park

  14. Allophane/Imogolite replacing whole pieces of tree

  15. X-ray Diffraction Allophane replacing wood Blue: Allophane Green: Opal-a

  16. X-ray Diffraction

  17. XRD data from Wada (1989)

  18. ChemistrySi:Al ratio This study (microprobe): 1: 1.3 to 1:1.8 Wada (1989): allophane 1:1 to 1:1.5 imogolite 1:1.7 to 1:1.8

  19. TGA analysis of tree replacement Derivative of weight loss Weight loss 50 900 Temperature (°C)

  20. TGA and DTA data for allophane and imogolite (Wada 1989)

  21. Conclusion • Gibbsite • forms under highly permeable conditions (change in pH) • Fills cavities not replacing minerals • Allophane/imogolite • Replaces woody material • One phase or two phases • Indication of high Al mobility • Where does the silica go (kinetics?)

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