740 Ma vase-shaped microfossils from Yukon, Canada: Implications for Neoproterozoic chronology and biostratigraphy

Biostratigraphy underpins the Phanerozoic time scale, but its application to pre-Ediacaran strata has remained limited because Proterozoic taxa commonly have long or unknown stratigraphic ranges, poorly understood taphonomic constraints, and/or inadequate geochronological context. Here we report the discovery of abundant vase-shaped microfossils from the Callison Lake dolostone of the Coal Creek inlier (Yukon, Canada) that highlight the potential for biostratigraphic correlation of Neoproterozoic successions using species-level assemblage zones of limited duration. The fossiliferous horizon, dated here by Re-Os geochronology at 739.9 ± 6.1 Ma, shares multiple species-level taxa with a well-characterized assemblage from the Chuar Group of the Grand Canyon (Arizona, USA), dated by U-Pb on zircon from an interbedded tuff at 742 ± 6 Ma. The overlapping age and species assemblages from these two deposits suggest biostratigraphic utility, at least within Neoproterozoic basins of Laurentia, and perhaps globally. The new Re-Os age also confirms the timing of the Islay δCcarbonate anomaly in northwestern Canada, which predates the onset of the Sturtian glaciation by >15 m.y. Together these data provide global calibration of sedimentary, paleontological, and geochemical records on the eve of profound environmental and evolutionary change. GEOLOGY, August 2014; v. 42; no. 8; p. 659–662; Data Repository item 2014244 | doi:10.1130/G35736.1 | Published online 9 June 2014 © 2014 eological Society of America. For permission to copy, contact Copyright Permissions, GSA, or [email protected]. Fi ft ee nm ile G ro up M ou nt H ar pe r G p. Gibben Fm. Chandindu Reefal Assemblage Craggy Dolostone Callison Lake dolostone Mount Harper conglomerate Mount Harper volcanics Rapitan Group Hay Creek Group Upper Group 716.47±0.2 Ma Coal Creek Inlier, Ogilvie Mountains, Yukon Conglomerate Sandstone Shale Dolostone Basalt/Rhyolite Evaporite Diamictite U-Pb Age Re-Os Age Cover VSM Nodular Chert Intraclasts Fine lamination Exposure surface Stromatolite/Microbial 811.51±0.1 Ma 717.43±0.1 Ma