HR: 17:30h
AN: GP34A-07 [Abstracts]
TI: Oxygen isotopes as biogenic criteria for nanocrystal of magnetite?
AU: faivre, d
EM: faivre@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4, place Jussieu, case 89, Paris, F75252
France
AU: Agrinier, P
EM: agrinier@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4, place Jussieu, case 89, Paris, F75252
France
AU: Menguy, N
EM: menguy@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4, place Jussieu, case 89, Paris, F75252
France
AU: Guyot, F
EM: guyot@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4, place Jussieu, case 89, Paris, F75252
France
AU: * Zuddas, P
EM: zuddas@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4, place Jussieu, case 89, Paris, F75252
France
AU: * Zuddas, P
EM: zuddas@ipgp.jussieu.fr
AF: PEPS Universite Claude Bernard -Lyon1, campus la Doua, Villerbanne, F69245
France
AB:
Recent geochemical investigations have shown that physical and chemical properties of nanometer-sized objects do
significantly differ from those of millimeter- and micrometer- sized particles. In sediments and sedimentary rocks, magnetite
crystals of nanometer size are often neogenic. They can be formed either by a biogenic process or by inorganic reactions.
It is therefore of primary importance to understand how magnetite nanocrystals can be formed to define quantitative tools to
differentiate biotic from abiotic processes for paleoenvironmental reconstructions.
A series of carefully controlled laboratory experiments was carried out to calibrate the oxygen isotopic fractionation
between abiotitc nano-magnetites and water at low temperature. We found a 2% progressive increase in the magnetite-water
oxygen isotope fractionation factor between 5 and 70 ø C. Our results stand in contrast to previous experimental data on the
oxygen isotope composition of biogenic magnetite nanoparticles in which the fractionation factor was found to decrease with
increasing temperature.
We propose that this different dependence can be used to determine the abiotic/biotic contribution to the remanent
magnetization of sediments if the temperature of formation is known.
DE: 1503 Archeomagnetism
DE: 1505 Biomagnetism
DE: 1512 Environmental magnetism
DE: 1540 Rock and mineral magnetism
DE: 1600 GLOBAL CHANGE (New category)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting