T164 Magnetostratigraphy of Critical Intervals in Earth History: Contributions to Geochronology, Geobiology, Paleogeography, and Global Change

Tuesday, 24 October 2006
1:30 PM - 5:30 PM

ASSESSING THE SOURCE OF MAGNETIZATION IN SEDIMENTS WITH ROCK MAGNETISM AND FERROMAGNETIC RESONANCE SPECTROSCOPY

Paper number: T164-6
Program: Technical Sessions
Time: 2:50 PM – 3:10 PM

Authors

Abstract

Magnetic carriers in sediments originate from a number of different sources, among them detrital input, biologically-induced mineralization of fine particles, and the controlled precipitation of magnetite or greigite by magnetotactic bacteria. Knowledge of the composition of the magnetic carriers in sediments provides insights into the origin of sedimentary paleomagnetism as well as the depositional environment and diagenetic history. Magnetic minerals precipitated by magnetotactic bacteria are also magnetofossils, which potentially provide insight into ancient microbial ecosystems.

Rock magnetism and ferromagnetic resonance spectroscopy (FMR) can be used to analyze the magnetic composition of sediments at a bulk level. Magnetization properties particularly serve as a means for assessing crystal size distribution. FMR provides a mechanism for surveying the distribution of internal fields within a sample, and thus of investigating the degree of homogeneity and nature of crystal arrangement and elongation within a sample, traits which are particularly characteristic of the magnetotactic bacteria. Measurements of modern and ancient sediments suggest that FMR can distinguish sediments with magnetic mineralogy dominated by magnetite produced by magnetotactic bacteria from those with magnetic mineralogy dominated by detrital input or biologically-induced mineralization.