Coastal Dune Soils in Oregon, USA, Forming Allophane and Gibbsite by Georg H. Grathoff Curt D. Peterson Darren L. Beckstrand Funded by:
Jan 14, 2016
Coastal Dune Soils in Oregon, USA, Forming Allophane and Gibbsite
by
Georg H. GrathoffCurt 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
0 100 200 300 Kilometers
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Dunesheets
Sample Locations#
Figure 1. Study area dune sheets in Oregon, SW Washington and N. California, and context map.Sample locations are where dune characteristics have already been collected by this research group, funding provided by Seagrant and USGS.Bathymetry shows 20 meter contours.
Columbia River
Oregon
Washington
Pac
ific
Oce
an
CLAT
NEHA
PACI
LINC
NEWP
FLOR
COOS
BAND
GOLD
LONG
GRAYNORT
CRESCalifornia
Study Area
Importance of the paleosols
• Influence stability
• Control groundwater chemistry and flow
• Indicate age
“Weeping sands”
0 100 200 300 Kilometers
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N
EW
Dunesheets
Sample Locations#
Figure 1. Study area dune sheets in Oregon, SW Washington and N. California, and context map.Sample locations are where dune characteristics have already been collected by this research group, funding provided by Seagrant and USGS.Bathymetry shows 20 meter contours.
Columbia River
Oregon
Washington
Pac
ific
Oce
an
CLAT
NEHA
PACI
LINC
NEWP
FLOR
COOS
BAND
GOLD
LONG
GRAYNORT
CRESCalifornia
Study Area
Map of TL and 14C dates in ka BP. Core names are in parentheses. (from Beckstrand 2001)
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
Results:Minerals in Dunal Soils
1) Gibbsite: Al(OH)3
2) Allophane/Imogolite: amorphous Al-Silicate
3) Vermiculite and/or chlorite
4) Fe oxides/hydroxides
1) Gibbsite
X-ray Diffraction results
Gibbsite002
Gibbsite110
Gibbsite
5.35 Å 200
2) Allophane replacing tree roots
Seal Rock State Park
Allophane/Imogolite replacing whole pieces of tree
Allophane replacing woodBlue: Allophane
Green: Opal-a
X-ray Diffraction
X-ray Diffraction
XRD data from Wada (1989)
Chemistry
Si:Al ratio
This study (microprobe):1: 1.3 to 1:1.8
Wada (1989):allophane 1:1 to 1:1.5imogolite 1:1.7 to 1:1.8
TGA analysis of tree replacement
Temperature (°C)50 900
Weight loss
Derivative of weight loss
TGA and DTA data forallophane and imogolite(Wada 1989)
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?)