DEEP-WATER FIRST OCCURRENCES OF EDIACARA-TYPE FOSSILS ALONG A SHELF-TO-SLOPE TRANSECT IN THE WERNECKE MOUNTAINS, YUKON, CANADA

Ediacara-type macrofossils appear as early as ~579 Ma in deep-water slope facies of the Avalon Terrane of Newfoundland, but remain notably absent from shallow shelf environments worldwide until ca. 560-555 Ma. Our ability to assess whether this deep-water origination is a genuine reflection of evolutionary succession, an artifact of an incomplete stratigraphic record, or a bathymetrically controlled biotope is fundamentally limited by a lack of geochronological constraints and detailed shelf-to-slope transects within global Ediacaran basins.

 The Ediacaran ‘upper group’ in the Wernecke Mountains of NW Canada represents an ideal shelf-to-slope depositional system to understand the spatiotemporal and environmental context of Ediacara-type organisms’ first occurrences. Recent mapping and chemostratigraphic studies have established a new stratigraphic framework for the Rackla region of the southern Wernecke Mountains, which enables shelfal strata from the well-studied Goz Creek area to be directly traced into lower slope deposits. The presence of the global Shuram carbon isotope excursion (CIE) provides a robust regional and global time marker that links these two regions.

 Preliminary paleontological investigation has found that while slope deposits of the Nadaleen Formation (formerly ‘June beds’, below Shuram CIE) in the Rackla Belt record Ediacara-type macrofossils, none are found in coeval shelfal strata at Goz Creek. Ediacara-type fossils on the shelf are only found above the Shuram CIE in the Blueflower Formation. Critically, this is the first time the presence/absence of Ediacara-type fossils within a single basin has been observed with stratigraphic control on both shallow- and deep-water environments. Iron-based redox geochemistry of the fossiliferous Nadaleen Formation slope deposits from the Rackla belt record an oxic signature, in contrast to generally anoxic settings in coeval slope strata at Sekwi Brook in the central Mackenzie Mountains. These data demonstrate significant biostratigraphic and redox heterogeneity within the Ediacaran sedimentary succession of NW Canada, highlighting the potential for further multidisciplinary studies to yield important information regarding the environmental and evolutionary context of Ediacaran biotic assemblages.