HR: 17:00h
AN: GP34A-05 INVITED     [Abstracts]
TI: Magnetic fabrics elucidate past climatic and environmental conditions
AU: * Lagroix, F
EM: lagr0012@umn.edu
AF: CNRS-Intitut de Physique du Globe de Paris, 4, place Jussieu, Paris, 75252 France
AU: Banerjee, S K
EM: banerjee@umn.edu
AF: Institute for Rock Magnetism - University of Minnesota, 108 Pillsbury Hall 310 Pillsbury Drive, Minneapolis, MN 55455 United States
AB: Loess and paleosol deposits, worldwide, have provided an important medium from which paleoclimatic conditions and paleoenvironments could be reconstructed. Within the field of environmental magnetism, the most fruitful data have been time series of various common magnetic parameters, such as, but not exclusively, bulk susceptibility and its frequency dependence, magnetic coercivity, remanent magnetizations and coercivity of remanence. Until some recent efforts by others in China and Siberia and our own in Alaska, the potential of the anisotropy of magnetic susceptibility (AMS) had been underestimated. In non-lithified poorly consolidated sediments offering very little textural differentiation, as is the case in Central Alaskan loess deposits, AMS is an indispensable tool. Loess intervals having undergone post-depositional deformations cannot provide reliable paleoclimatic data yet environmental conditions leading to the preserved deformations inferred from their magnetic fabrics do impose chronological constraints. Furthermore, loess intervals preserving magnetic fabrics of aeolian deposition enable the reconstruction of relative time series of paleowind directions from their magnetic lineations. These relative time series provide additional chronological constraints and suggest a paleoclimate glacial - interglacial cycle control over surface air circulation in Central Alaska. Other common environmental magnetic parameters as well as geochemical data could not identify post-depositional deformations or paleowind directions in the loess deposit studied herein. This underscores the resolving power magnetic anisotropy has and can have in non-lithified poorly consolidated sediments.
DE: 1512 Environmental magnetism
DE: 1518 Magnetic fabrics and anisotropy
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting