2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 7
Presentation Time: 9:30 AM


HOFMANN, Hans J., Dept. of Earth and Planetary Sciences, and Redpath Museum, McGill University, 3450 University St, Montreal, QC H3A 2A7, Canada, O'BRIEN, Sean J., Geological Survey of Newfoundland,  Newfoundland and Labrador Department of Natural Resources, St. John's, NF A1B 4J6, Canada and KING, Arthur F., Dept. of Earth Sciences, Memorial University of Newfoundland, St. John's, NF A1B 3X5, Canada, hofmann@eps.mcgill.ca

Since the discovery of the Ediacaran biota on the eastern Bonavista Peninsula in 2003, more than 20 new occurrences identified during the past two field seasons have augmented the data on the biotal composition, stratigraphic ranges, and geographic distribution of taxa. The fossils occur as biocoenoses under abundant laminae and thin beds of volcanic ash, within a minimum 1 km thick succession of deep-water basin and slope turbiditic sediments (upper part of the Conception Group) and overlying basinal, pro-delta and delta front facies showing major coarsening-upward cycles (St. John's Group). The Bonavista fossil assemblage comprises many forms known from the Charnian of the British Isles and the Avalon Peninsula, including Aspidella, Bradgatia, Charnia, Charniodiscus, Hiemalora, Ivesheadia, and, possibly, Blackbrookia, as well as informally named forms referred to as spindles, strings, brush-like fossils, and rare ladder-like bodies. Other genera present on the Avalon Peninsula, such as Triforillonia and Thectardis, have not been recognized to date on the Bonavista Peninsula, but may yet reveal themselves as mapping continues, given that the lithostratigraphic sequence and facies correspond closely to that of southeastern Newfoundland.

New discoveries in 2005 demonstrate that the ranges of Bradgatia, Charnia, Charniodiscus, Ivesheadia, and spindles are considerably longer than reported from the Avalon Peninsula, extending upward at least 300 m into the Fermeuse Formation, essentially amalgamating the two separate Mistaken Point and Fermeuse assemblages provisionally recognized earlier by those working on the Avalon sequence.

Some rare specimens of Hiemalora at levels in the Mistaken Point and Fermeuse formations are attached to stems and fronds, indicating that the characteristic radial processes, often branching distally, are more likely to be root-like structures than tentacles. Specimens can attain decimetric size, with a central disc diameter up to 7.5 cm, and overall dimensions (including the processes) as much as 16 cm.