Marine Osmium Source Transitioned From Mantle in Archean to Continents in the Proterozoic

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

Authors:

1. David van Acken (a)
2. Danielle Thomson (b)
3. Robert H. Rainbird (c)
4. Robert A. Creaser (a)

Affiliations:

a. University of Alberta, Dept. of Earth and Atmospheric Sciences, 1-26 ESB, Edmonton, AB, Canada T6G 2E3

b. Carleton University, Dept. of Earth Science, 1125 Colonel By Drive, Ottawa, ON, Canada K1S 5B6

c. Geological Survey of Canada, 601 Booth Street, Ottawa, ON, Canada K1A 0E8

Abstract:

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.