Cryptic disc structures resembling ediacaran discoidal fossils from the lower Silurian Hellefjord Schist, Arctic Norway

• Published in: PLOS ONE
• Main Authors: Kirkland, Chris, Macgabhann, B., Kirkland, B., Daly, J.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Public Library of Science 2016
• Subjects: Arctic; Holdfast; Norway
• Online Access: https://hdl.handle.net/20.500.11937/19994; https://doi.org/10.1371/journal.pone.0164071

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. © 2016 Kirkland et al.