Cryogenian of Yukon

Abstract

Cryogenian strata of the Windermere Supergroup were deposited in tectonically active basins throughout the North American Cordillera from Alaska to Mexico. The Windermere Supergroup of Yukon, Canada, hosts key geochronological constraints on the start of the Cryogenian Period and the onset of the Sturtian Snowball Earth glaciation at ca. 717Ma. A 57-million-year duration for the Sturtian glaciation has been suggested by correlations of the glacigenic Rapitan Group in Yukon with equivalent strata in the Mackenzie Mountains of Northwest Territories, where it is overlain by organic-rich argillaceous carbonate of the ca. 660Ma Twitya Formation; however, syn-depositional faulting and large lateral facies variation complicate these stratigraphic correlations. Here we describe Cryogenian strata of the northern Wernecke Mountains, Yukon, where correlations with the Rapitan and Hay Creek groups of the Mackenzie Mountains have been previously established. These units are then traced south across Cryogenian structures to the southern Wernecke Mountains and west through the Hart River inlier to the Coal Creek and Tatonduk inliers of the Ogilvie Mountains in order to construct a new regional stratigraphic framework. The Coal Creek inlier preserves volcanic rocks in the Mount Harper Group and the Eagle Creek Formation of the Rapitan Group, for which we provide new U-Pb CA-IDTIMS zircon ages. We further formalize the glacigenic Cryogenian Eagle Creek Formation. Together, the new correlations and geochronological data allow us to more precisely integrate geological data from northwest Canada with the rest of the Cordillera and beyond. Particularly, these data refine the onset of the Sturtian glaciation in northwestern Canada to between 716.9±0.4 and 717.4±0.2Ma and demonstrate that syn-sedimentary tectonism resulted in unconformities throughout northwest Laurentia between the end of the Sturtian glaciation at 660Ma and the end of the Marinoan glaciation at 635Ma. These unconformities confound correlations throughout the Cordillera by commonly preserving only one of the two Cryogenian glacial deposits.