HR: 09:45h
AN: GP21C-08    [Abstracts]
TI: Discrete element modeling of post depositional remanent magnetization acquisition: first results.
AU: * Heslop, D
EM: dheslop@uni-bremen.de
AF: Research Center Ocean Margins (RCOM), Am Fallturm 1, Bremen, 28359 Germany
AU: Witt, A
EM: witt@tzi.de
AF: University of Bremen Department of Geosciences, Klagenfurter Str., Bremen, 28359 Germany
AU: von Dobeneck, T
EM: dobeneck@uni-bremen.de
AF: Research Center Ocean Margins (RCOM), Am Fallturm 1, Bremen, 28359 Germany
AU: Huhn, K
EM: khuhn@uni-bremen.de
AF: Research Center Ocean Margins (RCOM), Am Fallturm 1, Bremen, 28359 Germany
AU: Fabian, K
EM: karl.fabian@uni-bremen.de
AF: University of Bremen Department of Geosciences, Klagenfurter Str., Bremen, 28359 Germany
AU: Bleil, U
EM: bleil@uni-bremen.de
AF: University of Bremen Department of Geosciences, Klagenfurter Str., Bremen, 28359 Germany
AB: Marine and limnic sediments continuously record temporal changes in both the direction and intensity of the earth's magnetic field. Up to now, because of the underlying processes' complexity, there exists only empirical information and no physical theory describing the mode of post-depositional remanent magnetization (PDRM) acquisition. Using a discrete element model, we simulate the behaviour of sediment particle deposition and subsequent compaction from colloidal suspensions. A collection of two-dimensional models considering particle size distribution, particle shape, compaction, the external magnetic field, gravity, Brownian motion, van der Waals forces and bioturbation is used to investigate the theoretical background of PDRM acquisition. In particular, the controlling factors of particle alignment and fixation are studied. Employing Debye's theory of rotational Brownian motion, we will show that thermal fluctuations have a negligible effect upon the efficiency of the PDRM acquisition mechanism. In systems of deposited particles, the PDRM is found to lock gradually as compaction increases. The compaction required to fix the magnetic particles is primarily dependant on particle size distribution, shape and the external magnetic field. The packing structure of the sediment is strongly controlled by van der Waals forces and as such particle-particle electrostatic interactions play an important role in determining the position at which a particle is fixed and thus the PDRM intensity. Once the PDRM is formed, we investigate the effects of bioturbation. Bacterial scale reworking is accounted for by performing a two dimensional random walk through the sediment with a high-energy particle. The combination of different model results representing different stages of depositional processes will be demonstrated by a series of animations while numerical details of the model will be presented in an associated poster. Investigating the model outcome, we hope to obtain a detailed insight into the activation processes governing the dynamics of PDRM intensity.
DE: 1512 Environmental magnetism
DE: 1521 Paleointensity
DE: 1540 Rock and mineral magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting