Molecular preservation of 1.88 Ga Gunflint organic microfossils as a function of temperature and mineralogy
Julien Alleon, Sylvain Bernard, Corentin Le Guillou, Johanna Marin-Carbonne, Sylvain Pont, Olivier Beyssac, Kevin D. McKeegan & François Robert
AffiliationsContributionsCorresponding author
Nature Communications 7, Article number: 11977 doi:10.1038/ncomms11977
Received 14 August 2015 Accepted 18 May 2016 Published 17 June 2016
a) Photomicrograph of spheroidal organic microfossils from the Schreiber Beach chert and (b) corresponding Raman map showing the distribution of organic carbon. Red lines indicate the location of the cross-sections shown in c,d. Scale bars, 5 μm. (c,d) FIB–SEM images of cross-sections of the microfossils shown in a, illustrating that Gunflint spheroidal microfossils can be more or less permineralized by silica or filled by organics (which appear dark) and micrometric mineral phases (which appear bright). Scale bars, 5 μm.
Abstract
Abstract• Introduction• Results• Discussion• Methods• Additional information• References• Acknowledgements• Author information
The significant degradation that fossilized biomolecules may experience during burial makes it challenging to assess the biogenicity of organic microstructures in ancient rocks. Here we investigate the molecular signatures of 1.88 Ga Gunflint organic microfossils as a function of their diagenetic history. Synchrotron-based XANES data collected in situ on individual microfossils, at the submicrometre scale, are compared with data collected on modern microorganisms. Despite diagenetic temperatures of ~150–170 °C deduced from Raman data, the molecular signatures of some Gunflint organic microfossils have been exceptionally well preserved. Remarkably, amide groups derived from protein compounds can still be detected. We also demonstrate that an additional increase of diagenetic temperature of only 50 °C and the nanoscale association with carbonate minerals have significantly altered the molecular signatures of Gunflint organic microfossils from other localities. Altogether, the present study provides key insights for eventually decoding the earliest fossil record.
Subject terms: Earth sciences Palaeontology Geology and geophysics
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