title: Low-oxygen waters limited habitable space for early animals.
abstract: The oceans at the start of the Neoproterozoic Era (1,000-541 million years ago, Ma) were dominantly anoxic, but may have become progressively oxygenated, coincident with the rise of animal life. However, the control that oxygen exerted on the development of early animal ecosystems remains unclear, as previous research has focussed on the identification of fully anoxic or oxic conditions, rather than intermediate redox levels. Here we report anomalous cerium enrichments preserved in carbonate rocks across bathymetric basin transects from nine localities of the Nama Group, Namibia (∼550-541 Ma). In combination with Fe-based redox proxies, these data suggest that low-oxygen conditions occurred in a narrow zone between well-oxygenated surface waters and fully anoxic deep waters. Although abundant in well-oxygenated environments, early skeletal animals did not occupy oxygen impoverished regions of the shelf, demonstrating that oxygen availability (probably >10 μM) was a key requirement for the development of early animal-based ecosystems.
authors.affiliation: Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK.
authors.forename: R
authors.identifier: http://orcid.org/0000-0003-2843-7741
authors.initials: R
authors.lastname: Tostevin
authors.affiliation: School of GeoSciences, The University of Edinburgh, James Hutton Road, Edinburgh EH9 3FE, UK.
authors.forename: R A
authors.initials: RA
authors.lastname: Wood
authors.affiliation: Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK.
authors.forename: G A
authors.initials: GA
authors.lastname: Shields
authors.affiliation: School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK.
authors.forename: S W
authors.initials: SW
authors.lastname: Poulton
authors.affiliation: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK.
authors.forename: R
authors.initials: R
authors.lastname: Guilbaud
authors.affiliation: School of GeoSciences, The University of Edinburgh, James Hutton Road, Edinburgh EH9 3FE, UK.
authors.forename: F
authors.initials: F
authors.lastname: Bowyer
authors.affiliation: School of GeoSciences, The University of Edinburgh, James Hutton Road, Edinburgh EH9 3FE, UK.
authors.forename: A M
authors.initials: AM
authors.lastname: Penny
authors.affiliation: Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK.
authors.forename: T
authors.initials: T
authors.lastname: He
authors.affiliation: School of GeoSciences, The University of Edinburgh, James Hutton Road, Edinburgh EH9 3FE, UK.
authors.forename: A
authors.initials: A
authors.lastname: Curtis
authors.affiliation: Geological Survey of Namibia, Private Bag 13297, Windhoek, Namibia.
authors.forename: K H
authors.initials: KH
authors.lastname: Hoffmann
authors.affiliation: School of GeoSciences, The University of Edinburgh, James Hutton Road, Edinburgh EH9 3FE, UK.|Department of Chemistry, University of Otago, Dunedin 9054, New Zealand.
authors.forename: M O
authors.initials: MO
authors.lastname: Clarkson