title: Cryptic Disc Structures Resembling Ediacaran Discoidal Fossils from the Lower Silurian Hellefjord Schist, Arctic Norway.
abstract: The Hellefjord Schist, a volcaniclastic psammite-pelite formation in the Caledonides of Arctic Norway contains discoidal impressions and apparent tube casts that share morphological and taphonomic similarities to Neoproterozoic stem-holdfast forms. U-Pb zircon geochronology on the host metasediment indicates it was deposited between 437 ± 2 and 439 ± 3 Ma, but also indicates that an inferred basal conglomerate to this formation must be part of an older stratigraphic element, as it is cross-cut by a 546 ± 4 Ma pegmatite. These results confirm that the Hellefjord Schist is separated from underlying older Proterozoic rocks by a thrust. It has previously been argued that the Cambrian Substrate Revolution destroyed the ecological niches that the Neoproterozoic frond-holdfasts organisms occupied. However, the discovery of these fossils in Silurian rocks demonstrates that the environment and substrate must have been similar enough to Neoproterozoic settings that frond-holdfast bodyplans were still ecologically viable some hundred million years later.
authors: Department of Applied Geology, (Centre for Exploration Targeting - Curtin Node and Core to Crust Fluid Centre), Curtin University, Perth, Australia.
authors: Christopher L
authors: http://orcid.org/0000-0003-3367-8961
authors: CL
authors: Kirkland
authors: Department of Geography, Edge Hill University, Ormskirk, Lancashire, England.
authors: Breandán A
authors: BA
authors: MacGabhann
authors: Independent Researcher, Coleraine, N. Ireland.
authors: Brian L
authors: BL
authors: Kirkland
authors: UCD School of Earth Sciences and UCD Earth Institute, University College Dublin, Dublin, Ireland.
authors: J Stephen
authors: JS
authors: Daly
mesh_terms: D000818:Animals; D005580:Fossils; D009664:Norway; D010163:Paleontology; D055110:Radiometric Dating; D017640:Silicates / Q000737:chemistry; D018707:Volcanic Eruptions; D015040:Zirconium / Q000737:chemistry
chemical_list: D017640:Silicates; C003784:zircon; D015040:Zirconium