Constraining the depositional history of the Neoproterozoic Shaler Supergroup, Amundsen Basin, NW Canada: Rhenium-osmium dating of black shales from the Wynniatt and Boot Inlet Formations

• Black shales from the Neoproterozoic Shaler Supergroup yield Re–Os ages between 761 ± 41 Ma and 892 ± 13 Ma.
• Cryogenian–Tonian chronology is further refined by using these absolute ages as anchor points for chronostratigraphy.
• Initial 187Os/188Os reflects strong continental input to seawater, reflecting supercontinent growth prior to global glaciations.

New Re–Os ages from black shales of the Neoproterozoic Shaler Supergroup from the Minto Inlier, Victoria Island, Arctic Canada, constrain the late Tonian to early Cryogenian depositional history of the Amundsen Basin. The Re–Os ages of 761 ± 41 Ma and 848 ± 49 Ma for the Wynniatt Fm., and 892 ± 13 Ma for the Boot Inlet Fm., along with recently reported U-Pb ages, provide anchor points for correlation of stable isotope stratigraphy, most notably the Bitter Springs isotopic anomaly within the Wynniatt Fm. across the Tonian–Cryogenian transition in NW Canada. These data suggest that deposition of lower units of the Shaler Supergroup began earlier than previously estimated. Initial 187Os/188Os for all three sample suites is around 0.6, lower than modern seawater, but significantly higher than unradiogenic Archean/Paleoproterozoic seawater composition, supporting a Proterozoic transition from mantle-dominated Os input into the global ocean towards a crust-dominated flux.