HR: 08:45h
AN: GP41A-04 INVITED     [PDF]
TI: Organic Matter and Wind Strength: the {\it Two} Workhorses Shaping Magnetic Susceptibility Fluctuations in Loess Deposits of Central Alaska
AU: Lagroix, F
EM: lagr0012@umn.edu
AF: University of Minnesota, Departement of Geology and Geophysics, 108 Pillsbury Hall 310 Pillsbury Dr. SE, Minneapolis, MN 55455 United States
AU: * Banerjee, S K
EM: banerjee@umn.edu
AF: University of Minnesota, Departement of Geology and Geophysics, 108 Pillsbury Hall 310 Pillsbury Dr. SE, Minneapolis, MN 55455 United States
AB: The Holocene soils at Halfway House (HH) and Gold Hill Steps (GHS) in Central Alaska are poorly developed, comprising only of an A-horizon, where organic matter is concentrated at the top and decreases with depth. The contact between the A-horizon and the underlying parent material (C-horizon) is smeared across an interval of oxidized parent material (Cox-horizon). We have focused on the Holocene soil and the underlying parent material because: 1) the enhanced magnetic susceptibility of the Holocene soil's A-horizon is in disagreement with the Alaskan-type end-member model; and 2) maghemitization occurs both as a pedogenic process in the soil and a diagenetic process in the parent material. The pedogenic in-situ formation of maghemite in the soil and the diagenetic maghemitization of (titano)magnetite particles at depth below the soil drive the magnetic susceptibility profile to increase and decrease, respectively. Our results suggest that these processes alone can explain the apparent discrepancy between the magnetic susceptibility high measured in active developing soils and the magnetic susceptibility low measured in inactive buried soils of Central Alaska. We do not dismiss the possibility that other diagenetic processes might occur, e.g., delayed reduction, iron dissolution in buried soils, but these other diagenetic processes appear to occur homogeneously and hence causing no apparent relative evolution of the susceptibility profile.
DE: 1512 Environmental magnetism
DE: 1615 Biogeochemical processes (4805)
DE: 3344 Paleoclimatology
DE: 5109 Magnetic and electrical properties
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting