HR: 13:40h
AN: GP33E-01 [Abstracts]
TI: Constraints on the Acquisition of Magnetization in Fine-Grained Sediments Derived from Redeposition Experiments
AU: Carter-Stiglitz, B
EM: brian Carter-Stiglitz
AU: * Valet, J
EM: valet@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4, Place Jussieu, 75252, Paris, France
AU: LeGoff, M
EM: legoff@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4, Place Jussieu, 75252, Paris, France
AB:
Despite many attempts, the transfer function between the remanent magnetization of sediments measured in
laboratory and the characteristics of the geomagnetic field coeval with the magnetization remains poorly
documented. We performed redeposition experiments using carbonate-rich (ODP site 851) and clay-rich (ODP
site 854) sediments. The originality of our approach was to use a dilute solution of gelatin which gels below
20°C, thereby allowing to measure the amount of magnetization acquired at different water concentrations which
is linked to mechanical blocking of the magnetic grains. We observed two critical results:
-1) the efficiency of DRM decreases with increasing sediment concentration (c) and is zero when it reaches 50%.
-2) post-depositional remanent magnetization (pDRM) is important below a concentration of 50%.
We compared the original NRM/ARM values of natural magnetization with those obtained during the redeposition
experiments. The intersection of the NRM/ARM values measured in the original sediment with the value of
redeposition was obtained for a concentration of 44 percent at site 851. We infer that the DRM was acquired at
this site for 44 percent concentration of sediment and that pDRM was significant within the depth interval going
from 44 to 56 percent of sediment. If the concentration profile for the uppermost sediment were known at site 851,
we could define the filter function. In contrast, almost all magnetization was "locked-in" with a concentration of 50
percent at site 854 which is dominated by clay-rich sediment. Finally, the dependence of DRM efficiency on c
suggests that changes in the thickness of the sediment layer which is homogenized could change DRM efficiency.
DE: 1540 Rock and mineral magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting