Cryptic Disc Structures Resembling Ediacaran Discoidal Fossils from the Lower Silurian Hellefjord Schist, Arctic Norway

• Published in: PLOS ONE
• Main Authors: Kirkland, Christopher L, MacGabhann, Breandan, Kirkland, Brian, Daly, Stephen
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: G Geography (General); Arctic; Norway; Holdfast
• Online Access: http://repository.edgehill.ac.uk/8379/; http://repository.edgehill.ac.uk/8379/1/journal.pone.0164071.PDF; http://journals.plos.org/plosone/article? id=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.