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Three Orosirian basins and associated foreland thrust-fold belts are preserved on the margins of the Slave craton. All three are related to orogenic belts where oceans opened and later closed, uniting new crustal partners. The Great Slave basin differs from the Kilhigok and Coronation basins in ways that have defied explanation. It lacks a passive margin sequence and hosts two discrete igneous suites, separated by large-scale thrusting, that occurred well after the adjacent paleocean had closed. Here we report U–Pb zircon geochronology by chemical abrasion isotope dilution thermal ionization mass spectrometry for a member of each suite to constrain the age and origin of postcollisional thrusting. A widespread pulse of mainly phreatic alkaline volcanism, coeval with renewed foredeep flexure, occurred at 1889.0 ± 0.7 Ma (2σ internal error). A quartz-monzodiorite body, one of a belt-parallel chain of laccoliths that postdate thrusting, was emplaced at 1866.9 ± 0.9 Ma. These ages bracket renewed foredeep sedimentation and thrusting that telescoped major facies zones and was rooted within the basin. The older age is 70 and 30−60 Myr younger than collision in the Thelon and Taltson orogens, respectively. We attribute postcollisional thrusting and foredeep subsidence to "eduction"—the upward and outward ejection of partly subducted crust—and postulate that the top of the ejected wedge was a normal-sense detachment fault projecting beneath the Nonacho basin. We infer that eduction was triggered by slab failure, producing alkaline volcanism, and ended with delamination and laccolith emplacement. Eduction was facilitated by tradewind-driven erosion. Delamination was enabled by crustal transfer to the educted wedge, reducing footwall buoyancy. Slab failure and/or delamination removed the passive margin. [ABSTRACT FROM AUTHOR]

The rotation model for the opening of the Canada Basin of the Arctic Ocean predicts stratigraphic links between the Alaskan North Slope and the Canadian Arctic islands. The Katakturuk Dolomite is a 2080-m-thick Neoproterozoic carbonate succession exposed in the northeastern Brooks Range of Arctic Alaska. These strata have previously been correlated with the pre-723 Ma Shaler Supergroup of the Amundson Basin. Herein we report new composite δ13C profiles and detrital zircon ages that test this connection. We go further and use stratigraphic markers and a compilation of δ13C chemostratigraphy from around the world, tied to U-Pb ages, to derive an age model for deposition of the Katakturuk Dolomite. In particular, we report the identification of ca. 760 Ma detrital zircons in strata underlying the Katakturuk Dolomite. Moreover, a diamictite present at the base of the Katakturuk Dolomite is capped by a dark-colored limestone with peculiar roll-up structures. Chemostratigraphy and lithostratigraphy suggest this is an early-Cryogenian glacial diamictite-cap carbonate couplet and that deposition of the Katakturuk Dolomite spanned much of the late Neoproterozoic. Approximately 500 m above the diamictite, a micropeloidal dolomite, with idiosyncratic textures that are characteristic of basal Ediacaran cap carbonates, such as tubestone stromatolites, giant wave ripples, and decameters of pseudomorphosed former aragonite crystal fans, rests on a silicified surface. Chemostratigraphic correlations also indicate a large increase in sedimentation rate in the upper ∼1 km of the Katakturuk Dolomite and in the overlying lower Nanook Limestone. We suggest that the accompanying increase in accommodation space, along with the presence of two low-angle unconformities within these strata, are the product of late Ediacaran rifting along the southern margin of the North Slope subterrane. There are no strata present in the Amundson Basin that are potentially correlative with the late Neoproterozoic Katakturuk Dolomite, as the Cambrian Saline River Formation rests on the ca. 723 Ma Natkusiak Formation. Detrital zircon geochronology, chemostratigraphic correlations, and the style of sedimentation are inconsistent with both a Canadian Arctic origin of the North Slope subterrane and a simple rotation model for the origin of the Arctic Ocean. If the rotation model is to be retained, the exotic North Slope subterrane must have accreted to northwest Laurentia in the Early to Middle Devonian. [ABSTRACT FROM AUTHOR]

The Neoproterozoic was an era of great environmental and biological change, but a paucity of direct and precise age constraints on strata from this time has prevented the complete integration of these records. We present four high-precision U-Pb ages for Neoproterozoic rocks in northwestern Canada that constrain large perturbations in the carbon cycle, a major diversification and depletion in the microfossil record, and the onset of the Sturtian glaciation. A volcanic tuff interbedded with Sturtian glacial deposits, dated at 716.5 million years ago, is synchronous with the age of the Franklin large igneous province and paleomagnetic poles that pin Laurentia to an equatorial position. Ice was therefore grounded below sea level at very low paleolatitudes, which implies that the Sturtian glaciation was global in extent. [ABSTRACT FROM AUTHOR]

New Ediacaran fossil finds at Sekwi Brook occur in lower shoreface to offshore transition beds at the top of the Blueflower Formation, which are the most shallow-water facies and the youngest strata in which Ediacara-type fossils have been described from the Mackenzie Mountains of NW Canada. Newly discovered Ediacaran body fossils include two new tubular genera: Sekwitubulus annulatus new genus new species was a mm-diameter rigid annulated tube that was rooted to the sea bottom by a holdfast; Annulatubus flexuosus n. gen. n. sp. was a cm-diameter, flexible annulated tube. In conjunction with previously described large attachment discs representing the form-genus Aspidella and a single specimen of the dickinsonid Windermeria, these fossils define an assemblage that differs markedly from the rangeomorph-dominated deeper-water and older assemblages lower in the same section at Sekwi Brook. In contrast, trace fossils show little change upwards through the Blueflower Formation, at least in part reflecting their origin by microbial grazers on mats that formed during low-energy periods in both deep- and shallow-water environments. This implies that the stratigraphic succession of Ediacaran fossils in NW Canada and probably globally represents both evolutionary changes with age and the paleoecology of specific depositional settings. [ABSTRACT FROM PUBLISHER]