Presumed magnetic biosignatures observed in magnetite derived from abiotic reductive alteration of nanogoethite |
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| Authors: | Jessica L Till Yohan Guyodo France Lagroix Guillaume Morin Nicolas Menguy Georges Ona-Nguema |
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| Institution: | 1. Institut de minéralogie, de physique des matériaux et de cosmochimie (IMPMC), Sorbonne Universités–UMPC, CNRS UMR 7590, Muséum national d’histoire naturelle, IRD UMR 206, 4, place Jussieu, 75005 Paris, France;2. Institut de physique du globe de Paris, Sorbonne Paris Cité, université Paris-Diderot, UMR 7154 CNRS, 1, rue Jussieu, 75005 Paris, France;3. Institute of Earth Sciences, University of Iceland, Askja, 7, Sturlugata, 101 Reykjavik, Iceland |
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| Abstract: | The oriented chains of nanoscale Fe-oxide particles produced by magnetotactic bacteria are a striking example of biomineralization. Several distinguishing features of magnetite particles that comprise bacterial magnetosomes have been proposed to collectively constitute a biosignature of magnetotactic bacteria (Thomas-Keprta et al., 2001). These features include high crystallinity, chemical purity, a single-domain magnetic structure, well-defined crystal morphology, and arrangement of particles in chain structures. Here, we show that magnetite derived from the inorganic breakdown of nanocrystalline goethite exhibits magnetic properties and morphologies remarkably similar to those of biogenic magnetite from magnetosomes. During heating in reducing conditions, oriented nanogoethite aggregates undergo dehydroxylation and transform into stoichiometric magnetite. We demonstrate that highly crystalline single-domain magnetite with euhedral grain morphologies produced abiogenically from goethite meets several of the biogenicity criteria commonly used for the identi?cation of magnetofossils. Furthermore, the suboxic conditions necessary for magnetofossil preservation in sediments are conducive to the reductive alteration of nanogoethite, as well as the preservation of detrital magnetite originally formed from goethite. The findings of this study have potential implications for the identification of biogenic magnetite, particularly in older sediments where diagenesis commonly disrupts the chain structure of magnetosomes. Our results indicate that isolated magnetofossils cannot be positively distinguished from inorganic magnetite on the basis of their magnetic properties and morphology, and that intact chain structures remain the only reliable distinguishing feature of fossil magnetosomes. |
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| Keywords: | Magnetite Magnetosomes Inorganic alteration Nano-goethite Magnetism-based biosignature |
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