Out of rock: A new look at the morphological and geochemical preservation of microfossils from the 3.46 Gyr-old Strelley Pool Formation

Frédéric Delarue (1, 2) , Francois Robert (1) , Sylvie Derenne (2) , Romain Tartèse , Clément Jauvion (3, 1) , Sylvain Bernard (1) , Sylvain Pont (1) , Adriana Gonzalez-Cano (1) , Rémi Duhamel (1) , Kenichiro Sugitani

1 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie
2 METIS - Milieux Environnementaux, Transferts et Interactions dans les hydrosystèmes et les Sols
3 CR2P - Centre de Recherche en Paléontologie - Paris

The biogenicity of most of the putative Archean organic-walled microfossils discussed in the literature remains debated. Here, we report morphological and geochemical characterizations of an assemblage of microfossils isolated from the 3.46 Gyr-old Strelley Pool Formation (Western Australia), thereby providing a new set of data on the oldest authentic microfossils on Earth. Isolated microstructures/microfossils were studied by combining scanning electron microscopy imaging and elemental analyses, Raman spectroscopy and nanoscale secondary ion mass spectrometry (NanoSIMS). We identified four morphological types, namely filaments, films, spheroids and lenses. A minority of spheroids, films and lenses exhibits a continuous wall cell surface and high N concentrations and substantial P contents (as suggested by 31 P − / 12 C 2 − ionic ratios), i.e. exceptionally high morphological and geochemical preservation levels. In addition to the detection of P within microfossil walls, P was also found within micrometric patches in lenses exhibiting a fusiform shape. These patches may be remains of polyphosphate granules possibly formed during sporulation, suggesting, in turn, that cellular organization appeared as soon as 3.46 Gyr ago.

Domaines: Planète et Univers [physics]

Frédéric Delarue, Francois Robert, Sylvie Derenne, Romain Tartèse, Clément Jauvion, et al.. Out of rock: A new look at the morphological and geochemical preservation of microfossils from the 3.46 Gyr-old Strelley Pool Formation. Precambrian Research, 2020, ⟨10.1016/j.precamres.2019.105472⟩. ⟨hal-03021289⟩