title: The 2.1 Ga old Francevillian biota: biogenicity, taphonomy and biodiversity.
abstract: The Paleoproterozoic Era witnessed crucial steps in the evolution of Earth's surface environments following the first appreciable rise of free atmospheric oxygen concentrations ∼2.3 to 2.1 Ga ago, and concomitant shallow ocean oxygenation. While most sedimentary successions deposited during this time interval have experienced thermal overprinting from burial diagenesis and metamorphism, the ca. 2.1 Ga black shales of the Francevillian B Formation (FB2) cropping out in southeastern Gabon have not. The Francevillian Formation contains centimeter-sized structures interpreted as organized and spatially discrete populations of colonial organisms living in an oxygenated marine ecosystem. Here, new material from the FB2 black shales is presented and analyzed to further explore its biogenicity and taphonomy. Our extended record comprises variably sized, shaped, and structured pyritized macrofossils of lobate, elongated, and rod-shaped morphologies as well as abundant non-pyritized disk-shaped macrofossils and organic-walled acritarchs. Combined microtomography, geochemistry, and sedimentary analysis suggest a biota fossilized during early diagenesis. The emergence of this biota follows a rise in atmospheric oxygen, which is consistent with the idea that surface oxygenation allowed the evolution and ecological expansion of complex megascopic life.
authors: Institut IC2MP, UMR 7285 CNRS-INSU, Université de Poitiers, Poitiers, France.
authors: Abderrazak
authors: A
authors: El Albani
authors: Department of Palaeozoology and Nordic Center for Earth Evolution, Swedish Museum of Natural History, Stockholm, Sweden.
authors: Stefan
authors: S
authors: Bengtson
authors: Nordic Center for Earth Evolution, Odense M, Denmark.
authors: Donald E
authors: DE
authors: Canfield
authors: Laboratoire Géosystèmes, UMR 8217 CNRS, Université Lille 1, Villeneuve d'Ascq, France.
authors: Armelle
authors: A
authors: Riboulleau
authors: Centre de Recherches Pétrographiques et Géochimiques, CNRS UMR 7358, Vandoeuvre-lès-Nancy, France.
authors: Claire
authors: C
authors: Rollion Bard
authors: Département Géosciences, Université de Poitiers, Poitiers, France; Département de Préhistoire, UMR 7194 CNRS, Muséum National d'Histoire Naturelle, Paris, France.
authors: Roberto
authors: R
authors: Macchiarelli
authors: Institut IC2MP, UMR 7285 CNRS-INSU, Université de Poitiers, Poitiers, France.
authors: Lauriss
authors: L
authors: Ngombi Pemba
authors: Department of Palaeozoology and Nordic Center for Earth Evolution, Swedish Museum of Natural History, Stockholm, Sweden; Nordic Center for Earth Evolution, Odense M, Denmark.
authors: Emma
authors: E
authors: Hammarlund
authors: Institut IC2MP, UMR 7285 CNRS-INSU, Université de Poitiers, Poitiers, France.
authors: Alain
authors: A
authors: Meunier
authors: Institut IC2MP, UMR 7285 CNRS-INSU, Université de Poitiers, Poitiers, France.
authors: Idalina
authors: I
authors: Moubiya Mouele
authors: IMPMC, Sorbonne Universités, UMR 7590, MNHN - UPMC - IRD UMR 206, Paris, France.
authors: Karim
authors: K
authors: Benzerara
authors: IMPMC, Sorbonne Universités, UMR 7590, MNHN - UPMC - IRD UMR 206, Paris, France.
authors: Sylvain
authors: S
authors: Bernard
authors: Département Géosciences, UMR 6118, Université de Rennes, Rennes, France.
authors: Philippe
authors: P
authors: Boulvais
authors: Centre de Recherches Pétrographiques et Géochimiques, CNRS UMR 7358, Vandoeuvre-lès-Nancy, France.
authors: Marc
authors: M
authors: Chaussidon
authors: Laboratoire Géosystèmes, UMR 8217 CNRS, Université Lille 1, Villeneuve d'Ascq, France.
authors: Christian
authors: C
authors: Cesari
authors: Institut IC2MP, UMR 7285 CNRS-INSU, Université de Poitiers, Poitiers, France.
authors: Claude
authors: C
authors: Fontaine
authors: Stockholm University, Department of Geological Sciences, SE-106 91, Stockhom, Sweden.
authors: Ernest
authors: E
authors: Chi-Fru
authors: Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, 18100 Armilla, Granada, Spain.
authors: Juan Manuel
authors: JM
authors: Garcia Ruiz
authors: Laboratoire d'Hydrologie et de Géochimie de Strasbourg, UMR 7517 CNRS, Strasbourg, France.
authors: François
authors: F
authors: Gauthier-Lafaye
authors: Société Etudes Recherches Matériaux, CRI Biopole, Poitiers, France.
authors: Arnaud
authors: A
authors: Mazurier
authors: Département Géosciences, UMR 6118, Université de Rennes, Rennes, France.
authors: Anne Catherine
authors: AC
authors: Pierson-Wickmann
authors: IFREMER, Department of Physical Resources and Deep-Sea Ecosystems Technopôle Brest-Iroise, Plouzané, France.
authors: Olivier
authors: O
authors: Rouxel
authors: Laboratoire Géosystèmes, UMR 8217 CNRS, Université Lille 1, Villeneuve d'Ascq, France.
authors: Alain
authors: A
authors: Trentesaux
authors: Laboratoire Géosystèmes, UMR 8217 CNRS, Université Lille 1, Villeneuve d'Ascq, France.
authors: Marco
authors: M
authors: Vecoli
authors: Marum Center for Marine Environmental Sciences, Bremen, Germany.
authors: Gerard J M
authors: GJ
authors: Versteegh
authors: Agence Nationale des Parcs Nationaux, BP. 20379, Libreville, Gabon.
authors: Lee
authors: L
authors: White
authors: Laboratory for Isotope Geology and Nordic Center for Earth Evolution, Swedish Museum of Natural History, Stockholm, Sweden.
authors: Martin
authors: M
authors: Whitehouse
authors: Department of Earth Sciences, University of California, Riverside, Riverside, California, United States of America.
authors: Andrey
authors: A
authors: Bekker
mesh_terms: D044822:Biodiversity; D005075:Biological Evolution; D005580:Fossils; D005681:Gabon; D000069497:Origin of Life; D010802:Phylogeny