DIVERSE VASE-SHAPED MICROFOSSILS IN THE NEOPROTEROZOIC CALLISON LAKE DOLOSTONE, COAL CREEK INLIER, YUKON TERRITORY, CANADA

Vase-shaped microfossils (VSMs) occur in Neoproterozoic sedimentary successions from around the world. Yet, despite the spectacular exposures of Neoproterozoic strata in northwest Canada, they have not been described from this region. Here we report exceptionally preserved new populations of VSMs from the Callison Lake dolostone of the Coal Creek inlier, west-central Yukon. The Callison Lake dolostone was previously mapped with the Fifteenmile Group (unit PF1) due to its stratigraphic position between the Pinguicula and Mount Harper Groups in the Hart River inlier; however, a significant exposure surface and low-angle unconformity separates the Callison Lake dolostone from the underlying Fifteenmile Group in both inliers and indicates that the Callison Lake dolostone is tectono-stratigraphically related to the overlying Mount Harper Group. Recent U-Pb ID-TIMS zircon ages from a tuff interbedded with the Fifteenmile Group and a rhyolite in the upper Mount Harper volcanics bracket the depositional age of the Callison Lake dolostone between 811.51+/-0.25 Ma and 716.47+/-0.24 Ma. Multiple stratigraphic sections through the Callison Lake dolostone reveal two distinct horizons rich in VSMs. A basal 4–75 m thick shale and minor sandstone interval is interbedded with laterally discontinuous stromatolitic dolostone bioherms that host VSMs suspended in organic-rich patches that escaped early diagenetic recrystallization. Medium- to massive-bedded shallow-water platformal dolostone up to 400 m thick overlie the lower clastic interval and gradationally transition into laminated organic-rich black shale and silicified organic-rich mats that host another fossil horizon. This deposit yields abundant and exceptionally preserved specimens of diverse morphologies, sharing multiple species with well-characterized VSM assemblages from the >742+/-7 Ma uppermost Chuar Group, Arizona. The discovery of VSMs in the Callison Lake dolostone adds to a rapidly expanding Neoproterozoic microfossil record in northwestern Canada.