Stuart Gilder: Estimating relative paleointensity from remanence anisotropy
Channel: Institute for Rock Magnetism
Date: 2021-06-02

12th Institute for Rock Magnetism

Session 1: Anisotropy and Applications
Conveners: France Lagroix (IPGP) & Suzanne McEnroe (NTNU)

Title: Estimating relative paleointensity from remanence anisotropy

Authors: Stuart Gilder (1) Kuang He (1,3) Michael Wack (1) Josef Jezek (2)

Institutions:
(1) Ludwig Maximilians Universität, Munich, Germany
(2) Charles University, Prague, Czech Republic
(3) Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China

Abstract:
It is important to understand how sediments acquire remanent magnetizations and to better assess the quality of relative paleointensity data derived from sediments. We present redeposition experiments of sediments deposited in controlled magnetic fields to observe the changes in magnetic anisotropy as a function of applied field strength going from near Earth-like values to almost full saturation. Relative paleointensity values followed a very well defined power law through the entire range of applied field intensities. Magnetic remanence fabrics evolved from oblate with maximum anisotropy axes in the sedimentary plane at low field strengths to prolate with maximum anisotropy axes parallel to the applied field direction at high fields. Anisotropy of magnetic susceptibility also evolved with field strength, but in a much less coherent manner than anisotropy of magnetic remanence. The experiments used well-characterized, natural sediments containing single domain magnetite, which made it possible to numerically model the data. The model matches the field dependency of both relative paleointensity and magnetic fabric development using a simple assumption that a large proportion (∼80%) of the remanence carriers in the sediments are unable to align with the magnetic field while a small fraction are free to align. Anisotropy of magnetic remanence thus holds promise to improve and assess relative paleointensity estimates and helps improve theoretical treatment of magnetic recording in sediments. Our presentation will also discuss some of the factors/protocols that should be considered when carrying out anisotropy of magnetic remanence experiments.