The stratigraphical context of the Ediacaran biota of eastern Newfoundland

• Main Author: Matthews, Jack
• Other Authors: Brasier, Martin
• Published: University of Oxford 2015
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.730549

Detailed geological mapping and improved understanding of the geological evolution of the siliciclastic late Ediacaran rocks of the Mistaken Point Ecological Reserve (MPER) and the Catalina Dome, both of Newfoundland, provide a new framework for improved lithostratigraphic subdivision of the successions. The lithostratigraphic correlation of the Catalina Dome with the succession at MPER is found to be incorrect, prompting the erection of the Trinity Bay North Group to classify the rocks of the Catalina Dome. U-Pb (zircon) ages from the successions provide essential temporal constraints on the rise and fall of the Ediacara biota, and show that the Catalina Dome sections are up to 5 Myr older than previously thought. Both the MPER and Catalina Dome successions show an early fossil assemblage characterised by the presence of Trepassia and Vinlandia ; a taxonomic radiation ~575 Ma; the emergence of evidence for animals ~565 Ma; and the sudden disappearance of most forms within post-565 Ma slumped slope deposits. These points provide the basis of discussion around the potential for a biostratigraphy for the Ediacaran of Avalonia, and support the 'Ediacaran Explosion' hypothesis. Previous research using sedimentary strucutres and geochemical proxies to assign a nonmarine deposition environment to the MPER and Catalina Dome sections is found to be flawed and without merit. There is no evidence for shallow marine or sub-aerial depositional environments. All known Avalonian rangeomorphs are found in deep-marine facies. The environmental controls on the stratigraphic distribution of taxa remain poorly constrained. Analysis of tuffites within MPER suggests they were deposited by ashy turbidity currents, rather than as ash-falls. This prompts caution when using these tuffites for geochronological analysis, and requires the re-evaluation of the traditional taphonomic model for rangeomorph fossilisation. 'Post-fossilisation processes' are shown to bias fossil census studies, most notably through differing mechanisms of tuffite weathering and erosion. The impacts on palaeoecological studies, and geoconservation efforts are considered. The geoconservation legislative frameworks for Newfoundland and England are compared and contrasted, and recommendations made.