Archean; Strelley Pool Formation; biomorphs; microfossils; spheroids; Ecology, Evolution, Behavior and Systematics; Environmental Science (all); Earth and Planetary Sciences (all); General Earth and Planetary Sciences; General Environmental Science
Abstract :
[en] The morphogenesis of most carbonaceous microstructures that resemble microfossils in Archean (4-2.5 Ga old) rocks remains debated. The associated carbonaceous matter may even-in some cases-derive from abiotic organic molecules. Mineral growths associated with organic matter migration may mimic microbial cells, some anatomical features, and known microfossils-in particular those with simple spheroid shapes. Here, spheroid microstructures from a chert of the ca. 3.4 Ga Strelley Pool Formation (SPF) of the Pilbara Craton (Western Australia) were imaged and analyzed with a combination of high-resolution in situ techniques. This provides new insights into carbonaceous matter distributions and their relationships with the crystallographic textures of associated quartz. Thus, we describe five new types of spheroids and discuss their morphogenesis. In at least three types of microstructures, wall coalescence argues for migration of carbonaceous matter onto abiotic siliceous spherulites or diffusion in poorly crystalline silica. The nanoparticulate walls of these coalescent structures often cut across multiple quartz crystals, consistent with migration in/on silica prior to quartz recrystallization. Sub-continuous walls lying at quartz boundaries occur in some coalescent vesicles. This weakens the "continuous carbonaceous wall" criterion proposed to support cellular inferences. In contrast, some clustered spheroids display wrinkled sub-continuous double walls, and a large sphere shows a thick sub-continuous wall with pustules and depressions. These features appear consistent with post-mortem cell alteration, although abiotic morphogenesis remains difficult to rule out. We compared these siliceous and carbonaceous microstructures to coalescent pyritic spheroids from the same sample, which likely formed as "colloidal" structures in hydrothermal context. The pyrites display a smaller size and only limited carbonaceous coatings, arguing that they could not have acted as precursors to siliceous spheroids. This study revealed new textural features arguing for abiotic morphogenesis of some Archean spheroids. The absence of these features in distinct types of spheroids leaves open the microfossil hypothesis in the same rock. Distinction of such characteristics could help addressing further the origin of other candidate microfossils. This study calls for similar investigations of metamorphosed microfossiliferous rocks and of the products of in vitro growth of cell-mimicking structures in presence of organics and silica.
Disciplines :
Earth sciences & physical geography
Author, co-author :
Coutant, Maxime ; Université de Liège - ULiège > Astrobiology ; Univ. Lille, CNRS, Univ. Littoral Côte d'Opale, UMR 8187, LOG - Laboratoire d'Océanologie et de Géosciences, Lille, France
Lepot, Kevin; Univ. Lille, CNRS, Univ. Littoral Côte d'Opale, UMR 8187, LOG - Laboratoire d'Océanologie et de Géosciences, Lille, France ; Institut Universitaire de France (IUF), France
Fadel, Alexandre ; UMR 8207 - UMET - Unité Matériaux et Transformations, Univ. Lille, CNRS, INRAE, Centrale Lille, Lille, France
Addad, Ahmed; UMR 8207 - UMET - Unité Matériaux et Transformations, Univ. Lille, CNRS, INRAE, Centrale Lille, Lille, France
Richard, Elodie ; Univ. Lille, CNRS, INSERM, CHU Lille, Institut Pasteur de Lille, US 41 - UAR 2014 - PLBS, Lille, France
Troadec, David; Univ. Lille, CNRS, Centrale Lille, Junia, Univ. Polytechnique Hauts-de-France, UMR 8520 - IEMN - Institut d'Electronique de Microélectronique et de Nanotechnologie, Lille, France
Ventalon, Sandra; Univ. Lille, CNRS, Univ. Littoral Côte d'Opale, UMR 8187, LOG - Laboratoire d'Océanologie et de Géosciences, Lille, France
Sugitani, Kenichiro ; Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan
ANR - Agence Nationale de la Recherche [FR] CNRS - Centre National de la Recherche Scientifique [FR] F.R.S.-FNRS - Fonds de la Recherche Scientifique [BE]
Funding text :
Financial support for this project was provided by the Agence Nationale de la Recherche, France (ANR M6fossils: ANR‐15‐CE31‐0003‐01 to K.L.), and Région Hauts de France (project Vison‐AIRR iM4 to K.L.). Preliminary analyses were carried using financial support of FRS‐FNRS FRFC Grant no. 2.4558.09F (E.J.J.), CNRS‐INSU (Program INTERRVIE – K.L.) and FNRS (K.L.). Support also comes from ULiege‐UR Astrobiology (M.C. scholarship), M.C. is a FRIA grantee of the Fonds de la Recherche Scientifique – FNRS and FNRS PDR 35284099 “Life in coastal Archean Environments” (E.J.J). The authors thank x anonymous reviewers for their constructive comments.For SEM analyses and training we thank Philippe Recourt (LOG, U. Lille). We thank the UMS2014/US41 PLBS‐ BICeL Campus CS Facility for access to instruments and technical advice (CLSM microscopy). Jian Wang (Canadian Light Source) is thanked for help with STXM analyses. The Canadian Light Source is thanked for access to beamline 10ID‐1. The Chevreul Institute is thanked for its help in the development of this work through the ARCHI‐CM projectsupported by the “Ministère de l'Enseignement Supérieur de la Recherche et de l'Innovation, the region “Hauts‐de‐France,” the ERDF program of the European Union and the “Métropole Européenne de Lille.” FIB work was partly supported by the French RENATECH network.
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