Iron minerals within specific microfossil morphospecies of the 1.88 Ga Gunflint Formation.
Problematic microfossils dominate the palaeontological record between the Great Oxidation Event 2.4 billion years ago (Ga) and the last Palaeoproterozoic iron formations, deposited 500-600 million years later. These fossils are often associated with iron-rich sedimentary rocks, but their affinities, metabolism, and, hence, their contributions to Earth surface oxidation and Fe deposition remain unknown. Here we show that specific microfossil populations of the 1.88 Ga Gunflint Iron Formation contain Fe-silicate and Fe-carbonate nanocrystal concentrations in cell interiors. Fe minerals are absent in/on all organically preserved cell walls. These features are consistent with in vivo intracellular Fe biomineralization, with subsequent in situ recrystallization, but contrast with known patterns of post-mortem Fe mineralization. The Gunflint populations that display relatively large cells (thick-walled spheres, filament-forming rods) and intra-microfossil Fe minerals are consistent with oxygenic photosynthesizers but not with other Fe-mineralizing microorganisms studied so far. Fe biomineralization may have protected oxygenic photosynthesizers against Fe2+toxicity during the Palaeoproterozoic.
Laboratoire d'Océanologie et de Géosciences, Université de Lille, CNRS UMR8187, Cité Scientifique, SN5, 59655 Villeneuve d'Ascq, France.|Paléobiogéologie, Paléobotanique &Paléopalynologie, UR Geology, Département de Géologie, Université de Liège, 14 Allée du 6 Août B18, Quartier Agora, 4000 Liège, Belgium.
Kevin
0000-0003-0556-0405
K
Lepot
Unité Matériaux et Transformations, Université de Lille, CNRS UMR8207, Cité Scientifique C6, 59655 Villeneuve d'Ascq, France.
Ahmed
A
Addad
Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, Massachusetts 02138, USA.
Andrew H
AH
Knoll
Canadian Light Source Inc., University of Saskatchewan, 44 Innovation Boulevard, Saskatoon, Saskatchewan, Canada S7N 2V3.
Jian
J
Wang
Institut d'Electronique, de Micro-électronique et de Nanotechnologie, CNRS UMR8520, Avenue Poincaré, 59655 Villeneuve d'Ascq, France.
David
D
Troadec
Electron Microscopy for Material Science, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium.
Armand
A
Béché
Paléobiogéologie, Paléobotanique &Paléopalynologie, UR Geology, Département de Géologie, Université de Liège, 14 Allée du 6 Août B18, Quartier Agora, 4000 Liège, Belgium.
Emmanuelle J
EJ
Javaux
D005580:Fossils; D019015:Geologic Sediments / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D017348:Microscopy, Electron, Scanning Transmission; D008903:Minerals / Q000737:chemistry*; D009864:Ontario; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D010163:Paleontology; D010788:Photosynthesis
D008903:Minerals; D007501:Iron; D010100:Oxygen