Journal
GEOLOGY
Volume 43, Issue 5, Pages 459-462Publisher
GEOLOGICAL SOC AMER, INC
DOI: 10.1130/G36511.1
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Funding
- Massachusetts Institute of Technology NASA Astrobiology Institute node
- National Science Foundation (NSF) Sedimentary Geology and Paleobiology Program [EAR-1148058]
- NSF Graduate Research Fellowship
- Yukon Geological Survey
- Fireweed Helicopters and Canadian Helicopters
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The snowball Earth hypothesis predicts globally synchronous glaciations that persisted on a multimillion year time scale. Geochronological tests of this hypothesis have been limited by a dearth of reliable age constraints bracketing these events on multiple cratons. Here we present four new Re-Os geochronology age constraints on Sturtian (717-660 Ma) and Marinoan (635 Ma termination) glacial deposits from three different paleocontinents. A 752.7 +/- 5.5 Ma age from the base of the Callison Lake Formation in Yukon, Canada, confirms nonglacial sedimentation on the western margin of Laurentia between ca. 753 and 717 Ma. Coupled with a new 727.3 +/- 4.9 Ma age directly below the glacigenic deposits of the Grand Conglomerate on the Congo craton (Africa), these data refute the notion of a global ca. 740 Ma Kaigas glaciation. A 659.0 +/- 4.5 Ma age directly above the Maikhan-Uul diamictite in Mongolia confirms previous constraints on a long duration for the 717-660 Ma Sturtian glacial epoch and a relatively short nonglacial interlude. In addition, we provide the first direct radiometric age constraint for the termination of the Marinoan glaciation in Laurentia with an age of 632.3 +/- 5.9 Ma from the basal Sheepbed Formation of northwest Canada, which is identical, within uncertainty, to U-Pb zircon ages from China, Australia, and Namibia. Together, these data unite Re-Os and U-Pb geochronological constraints and provide a refined temporal framework for Cryogenian Earth history.
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