EDIACARAN BIOTA ON BONAVISTA PENINSULA, NEWFOUNDLAND, CANADA

Journal of Paleontology, Jan 2008 by Hofmann, H J, O'Brien, S J, King, A F

ABSTRACT-

Newly found fossils in the Conception and St. John's groups of the Bonavista Peninsula considerably extend the known geographic distribution of the Ediacaran fossils in Newfoundland. They occur in deepwater sediments and are preserved as epireliefs, forming census populations underneath volcanic ash layers throughout a more than 1 km thick turbiditic sequence. The exposed fossiliferous units comprise the Mistaken Point, Trepassey, Fermeuse, and Renews Head formations. The remains are tectonically deformed, with long axes of elliptical discs aligned parallel to cleavage strike; shortening of originally circular bedding surface features is on the order of 30-50% (averaging ~35%).

The assemblage includes Aspidella, Blackbrookia, Bradgatia, Charnia, Charniodiscus, Fractofusus, Hiemalora, and Ivesheadia. These occur throughout the succession, with Aspidella being the most common genus, followed by Charnia and Charniodiscus. Four new taxa are described, with candelabra-like fossils with a Hiemalora-like base referred to Primocandelabrum hiemaloranum n. gen. and sp., bush-like fossils to Parviscopa bonavistensis n. gen. and sp., ladder-like fossils to Hadryniscala avalonica n. gen. and sp., and string-like fossils with basal disc to Hadrynichorde catalinensis n. gen. and sp. The remains also include dubiofossils. The stratigraphic ranges of some taxa on the Bonavista Peninsula are longer than previously reported from the Avalon Peninsula, with Fractofusus spindles present in the Trepassey Formation, Bradgatia, Charnia, Charniodiscus, and Ivesheadia reaching as high as the Fermeuse Formation, and Aspidella extending into the middle of the Renews Head Formation. The spindles in the Trepassey Formation are comparable to those found mainly in the stratigraphically older Briscal Formation on the Avalon Peninsula.

INTRODUCTION

THE DISTINCTIVE and problematic Ediacaran fossils of soft-bodied organisms constitute a prominent marker in the history of the Proterozoic biosphere, and a substantial biologic enigma as well. There is no unanimity as to their affinities. Early interpretations placed forms like those found in Newfoundland in the Kingdom Animalia, principally in the Phylum Cnidaria (e.g., Glaessner, 1959, 1984; Anderson, 1978; Fedonkin, 1981), Others have presented different interpretations. Included among these are attributions to a separate extinct Kingdom, Vendozoa (Seilacher, 1989; later Vendobionta, Seilacher, 1992), xenophyophorean protists (Zhuravlev, 1993, Seilacher et al., 2003), lichens (Retallack, 1994), photosynthetic "metacellular" organisms (McMenamin, 1998), colonies of Prokaryota (Steiner and Reitner, 2001), and fungus-like organisms (Peterson et al., 2003). Ediacaran fossils are now thought to be mostly metazoans. For a comprehensive recent review, see Narbonne (2005).

Discoidal remains of this biota were first recognized in the 19th century in the City of St. John's, Newfoundland and described by Billings (1872) under the name Aspidella terranovica. The black shales in which they were found were subsequently designated the "Aspidella slates" (Murray and Howley, 1881), and the Fermeuse Formation in the more recently constituted St. John's Group (Williams and King, 1979). Even earlier reports, as far back as 1858, treated somewhat similar ring-like structures from the Charnian of England as possible abiogenic concretions (Ford, 1999, p. 230). Aspidella itself remained controversial as a fossil for more than a century (Hofmann, 1971, p. 16). Modern integrative studies finally established its biogenicity convincingly, if not its biological affinities (Gehling et al., 2000). The Ediacaran biota comprises about ten dozen genera (Waggoner, 1999), exhibiting ample variation of morphology based on simple modes of growth that dominated for a period before becoming extinct at the end of the Proterozoic. Nearly three dozen localities are now known worldwide. The most prominent of these also exhibit the greatest diversity, and are situated in South Australia, Namibia, northern Russia, Ukraine, Newfoundland, and northwestern Canada. The age of the Ediacaran biota is constrained to ~635-542 Ma (Condon et al., 2005), and probably between 580-542 Ma.

The assemblages in the different areas are characterized by disparate sedimentary environments and different preservation styles, as well as distinctive biotic compositions (e.g., Narbonne, 1998; Waggoner, 1999; Grazhdankin, 2004). Ediacaran megafossils in northwestern Canada, Australia, and eastern Europe occur typically as hyporeliefs in shallow water siliciclastics, whereas those in Newfoundland, England, and Finnmark are preserved as epireliefs in deepwater sediments, and those in Namibia commonly are transported entities preserved as endoreliefs in storm-generated sandstone. Some forms such as discs are cosmopolitan, whereas others of more complex morphology have more restricted distribution. For analyses of Ediacaran assemblages, see the reviews by Waggoner (1999, 2003) and Grazhdankin (2004). The forms here described from the Bonavista Peninsula conform to what is known from the Avalon Peninsula-preserved on upper bedding surfaces in deep water turbiditic and shallowing-upward pro-deltaic sediments, below ashfall deposits.