HR: 08:15h
AN: GP51A-02 INVITED    [Abstracts]
TI: Reconstructing Past Climates From Thin Loess-Paleosol Sequences - Results From Modern Loessic Soils From the Midwestern United States
AU: * Geiss, C E
EM: christoph.geiss@trincoll.edu
AF: Department of Physics, Trinity College, 300 Summit St., Hartford, CT 06106, United States
AB: Magnetic susceptibility records of loess-paleosol sequences from the Chinese loess plateau and elsewhere have been used successfully to quantify variations in past rainfall by comparing the magnetic properties of magnetically enhanced soil horizons and their respective parent materials. Such an approach may work for thick loess profiles with well separated paleosols, but our experience from modern loessic soils in the Midwestern United States has shown that a straightforward comparison between the magnetic properties (magnetic susceptibility, IRM, ARM etc.) of modern soils and their (assumed) parent material yields unreliable paleoclimate proxies. Such a simple approach works well for well developed, simple soil profiles but breaks down for more complicated soil profiles that may contain recent loess additions, welded paleosols, or redoximorphic features relatively high up in the C-horizon. Our recent rock-magnetic analyses of modern soils from North America (and older studies of Chinese loess) show that the pedogenic magnetic component of these sites is characterized by a narrow range of magnetic properties. This makes it possible to directly estimate the abundance of pedogenically produced magnetite using, for example, magnetic coercivity distributions, ARM/IRM ratios or, in some cases, hysteresis loops. Analysis of over sixty modern loessic soil profiles shows that such estimates can yield reliable climate proxies even if no unaltered parent material is available for comparison.
DE: 1512 Environmental magnetism
DE: 1540 Rock and mineral magnetism
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1865 Soils (0486)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting