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Deep-Water Ediacaran Fossils from Northwestern Canada: Taphonomy, Ecology, and Evolution

Published online by Cambridge University Press:  15 October 2015

Guy M. Narbonne
Affiliation:
Department of Geological Sciences and Geological Engineering, Queen's University, Kingston, ON, K7L 3N6, Canada, Research Associate, School of Geosciences, Monash University, Melbourne, Victoria, 3800 Australia
Marc Laflamme
Affiliation:
Department of Chemical and Physical Sciences, University of Toronto Mississauga, 3359 Mississauga Road N., Mississauga, ON, L5L 1C6, Canada
Peter W. Trusler
Affiliation:
Research Associate, School of Geosciences, Monash University, Melbourne, Victoria, 3800 Australia
Robert W. Dalrymple
Affiliation:
Department of Geological Sciences and Geological Engineering, Queen's University, Kingston, ON, K7L 3N6, Canada,
Carolyn Greentree
Affiliation:
Research Associate, School of Geosciences, Monash University, Melbourne, Victoria, 3800 Australia

Abstract

Impressions of soft-bodied Ediacaran megafossils are common in deep-water slope deposits of the June beds at Sekwi Brook in the Mackenzie Mountains of NW Canada. Two taphonomic assemblages can be recognized. Soles of turbidite beds contain numerous impressions of simple (Aspidella) and tentaculate (Hiemalora, Eoporpita) discs. A specimen of the frond Primocandelabrum is attached to an Aspidella-like holdfast, but most holdfast discs lack any impressions of the leafy fronds to which they were attached, reflecting Fermeuse-style preservation of the basal level of the community. Epifaunal fronds (Beothukis, Charnia, Charniodiscus) and benthic recliners (Fractofusus) were most commonly preserved intrastratally on horizontal parting surfaces within turbidite and contourite beds, reflecting a deep-water example of Nama-style preservation of higher levels in the community. A well-preserved specimen of Namalia significantly extends the known age and environmental range of erniettomorphs into deep-water aphotic settings. Infaunal bilaterian burrows are absent from the June beds despite favorable beds for their preservation. The June beds assemblage is broadly similar in age and environment to deep-water Avalonian assemblages in Newfoundland and England, and like them contains mainly rangeomorph and arboreomorph fossils and apparently lacks dickinsoniomorphs and other clades typical of younger and shallower Ediacaran assemblages. Fossil data presently available imply that the classically deep- and shallow-water taxa of the Ediacara biota had different evolutionary origins and histories, with sessile rangeomorphs and arboreomorphs appearing in deep-water settings approximately 580 million years ago and spreading into shallow-water settings by 555 Ma but dickinsoniomorphs and other iconic clades restricted to shallow-water settings from their first known appearance at 555 Ma until their disappearance prior to the end of the Ediacaran.

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Type
Research Article
Copyright
Copyright © The Paleontological Society 

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