Letter abstract
Nature Geoscience 1, 782 - 786 (2008)
Published online: 19 October 2008 | doi:10.1038/ngeo335
Subject Categories: Biogeochemistry | Geomagnetism, palaeomagnetism and core processes
Putative greigite magnetofossils from the Pliocene epoch
Iuliana Vasiliev1, Christine Franke1, Johannes D. Meeldijk2, Mark J. Dekkers1, Cor G. Langereis1 & Wout Krijgsman1
Magnetotactic bacteria produce chains of magnetite1, 2 and/or greigite3, 4, 5 crystals within their cell bodies called magnetosomes that are permanently magnetized6. They use these magnets to navigate along geomagnetic field lines to reach their preferred habitat7. Greigite magnetosomes have been well documented in modern sedimentary environments, but their identification in the fossil record remains controversial. Here we use transmission electron microscopy, electron diffraction patterns and rockmagnetic analyses to assess the origins of nanometre-scale greigite crystals found in Pliocene claystones from the Carpathian foredeep of Romania. We find that, like modern magnetosomal greigite grains, the crystals are single domain8, with few crystallographic defects and an overall shape consistent with an intracellular origin. We suggest these crystals are magnetosomal in origin, which would place them among the oldest greigite magnetofossils identified so far. The crystals also carry a primary magnetic signal, which has remained stable since its acquisition 5.3–2.6 million years ago. We suggest that greigite magnetofossils could therefore provide reliable records of ancient geomagnetic field variations, and that they could also be used as a proxy to assess palaeoenvironmental conditions in low-oxygen sedimentary environments.
- Paleomagnetic Laboratory 'Fort Hoofddijk', Department of Earth Sciences, Utrecht University, Budapestlaan 17, 3584 CD, Utrecht, The Netherlands
- Department of Chemistry, Utrecht University, Sorbonnelaan 16, 3545 CA Utrecht, The Netherlands
Correspondence to: Iuliana Vasiliev1 e-mail: vasiliev@geo.uu.nl
Correspondence to: Christine Franke1 Current address: Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS-UVSQ, Campus du CNRS, Bat. 12, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France
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