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Published November 18, 2008 | Supplemental Material + Published + Updated
Journal Article Open

Gigantism in unique biogenic magnetite at the Paleocene-Eocene Thermal Maximum


We report the discovery of exceptionally large biogenic magnetite crystals in clay-rich sediments spanning the Paleocene-Eocene Thermal Maximum (PETM) in a borehole at Ancora, New Jersey. Aside from previously-described abundant bacterial magnetofossils, electron microscopy reveals novel spearhead-like and spindle-like magnetite up to 4 μm long and hexaoctahedral prisms up to 1.4 μm long. Similar to magnetite produced by magnetotactic bacteria, these single-crystal particles exhibit chemical composition, lattice perfection, and oxygen isotopes consistent with an aquatic origin. Electron holography indicates single-domain magnetization despite their large crystal size. We suggest that the development of a thick suboxic zone with high iron bioavailability – a product of dramatic changes in weathering and sedimentation patterns driven by severe global warming – drove diversification of magnetite-forming organisms, likely including eukaryotes.

Additional Information

© 2008 by The National Academy of Sciences of the USA. Edited by James Zachos, University of California, Santa Cruz, CA, and accepted by the Editorial Board August 29, 2008 (received for review April 15, 2008). # This article is a PNAS Direct Submission. J.Z. is a guest editor invited by the Editorial Board. Published online before print October 20, 2008, doi: 10.1073/pnas.0803634105 We gratefully acknowledge comments from Boswell Wing, Adam Maloof, Nicholas Swanson-Hysell, and Harunur Rashid and technical assistance from Jeannie Mui. We are grateful to the editor and three anonymous reviewers for their constructive comments, which improved the final version of the manuscript. This work was supported by grants from the Natural Science and Engineering Research Council of Canada and the Fonds Québécois de la Recherche sur la Nature et les Technologies to the Centre for Biorecognition and Biosensors (H.V.) and the NASA Exobiology program (J.L.K.). Samples were provided by the Ocean Drilling Program, which is sponsored by the U.S. National Science Foundation and by participating countries under management of Joint Oceanographic Institutions, Inc. Author contributions: D.S. and H.V. designed research; D.S., J.-L.G.-K., T.-D.W., I.R., S.K.S., U.L., and H.V. performed research; D.S., T.D.R., R.E.K., I.R., A.V.S., S.M.T., R.H., J.L.K., and H.V. analyzed data; and D.S., T.D.R., R.E.K., S.M.T., J.L.K., and H.V. wrote the paper. The authors declare no conflict of interest. This article contains supporting information online at www.pnas.org/cgi/content/full/0803634105/DCSupplemental.

Attached Files

Published - SCHUpnas08.pdf

Supplemental Material - SCHUpnas08movie.mov

Supplemental Material - SCHUpnas08supp.pdf

Updated - Schumann2008_magnetofossils_postprint.pdf


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