Cryogenian of Yukon

Accepted Manuscript Cryogenian of Yukon Francis A. Macdonald, Mark D. Schmitz, Justin V. Strauss, Galen P. Halverson, Timothy M. Gibson, Athena Eyster, Grant Cox, Peter Mamrol, James L. Crowley PII: DOI: Reference:

S0301-9268(17)30121-3 http://dx.doi.org/10.1016/j.precamres.2017.08.015 PRECAM 4862

To appear in:

Precambrian Research

Received Date: Revised Date: Accepted Date:

12 March 2017 21 July 2017 9 August 2017

Please cite this article as: F.A. Macdonald, M.D. Schmitz, J.V. Strauss, G.P. Halverson, T.M. Gibson, A. Eyster, G. Cox, P. Mamrol, J.L. Crowley, Cryogenian of Yukon, Precambrian Research (2017), doi: http://dx.doi.org/ 10.1016/j.precamres.2017.08.015

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Cryogenian of Yukon Francis A. Macdonald1, Mark D. Schmitz2, Justin V. Strauss3, Galen P. Halverson4, Timothy M. Gibson4, Athena Eyster1, Grant Cox5, Peter Mamrol3, and James L. Crowley2 1

Department of Earth and Planetary Science, Harvard University, Cambridge, MA 02138

2

Department of Geosciences, Boise State University, Boise, ID

3

Department of Earth Sciences, Dartmouth College, HB6105 Fairchild Hall, Hanover, NH

03755 4

Department of Earth and Planetary Science, McGill University, Montréal, QC H3A 0E8,

Canada 5

Department of Earth Sciences, University of Adelaide, SA, 5005, Australia

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. 717 Ma. 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. 660 Ma 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 ± 0.2 Ma and demonstrate that syn-sedimentary tectonism resulted in unconformities throughout northwest Laurentia between the end of the Sturtian glaciation at 660 Ma and the end

of the Marinoan glaciation at 635 Ma. These unconformities confound correlations throughout the Cordillera by commonly preserving only one of the two Cryogenian glacial deposits.

1. Introduction The Sturtian glaciation was the first widespread glaciation in over a billion years of Earth’s history (Rooney et al., 2015). Geochronology and paleomagnetic data demonstrate that by 716 Ma ice had encapsulated the Earth all the way to the equator (Macdonald et al., 2010b; Evans and Raub, 2011) in a Snowball Earth glaciation (Hoffman et al., 1998; Kirschvink, 1992) that lasted approximately 57 Myrs (Rooney et al., 2014; Rooney et al., 2015). Strata of the Cryogenian non-glacial interlude were deposited between the Sturtian and Marinoan glaciations and record the earliest biomarker evidence of animals ( Love et al., 2009; Gold et al., 2016) and a putative oxygenation event (Lau et al., 2016). The Cryogenian Period ended with the Marinoan glaciation, which had begun by 639 Ma (Prave et al., 2016) and terminated at 635 Ma (Hoffmann et al., 2004; Calver et al., 2013; Condon et al., 2005). These environmental changes are commonly cast in the backdrop of the break-up of the supercontinent Rodinia and the emplacement of multiple large igneous provinces (Cox et al., 2016). Mechanistic relationships between glaciation, oxygenation, animal evolution, and tectonism remain speculative; however, the application of new Cryogenian age models to global sedimentary successions will facilitate the integration of existing and new datasets into a comprehensive record of paleoenvironmental change. The Yukon territory of northwest Canada is a key locale to probe the relationships between Cryogenian climate, geochemistry and life because it hosts mixed carbonate, siliciclastic, and volcanic successions preserved at a low metamorphic grade, with multiple geochronological constraints (Macdonald et al., 2010b; Rooney et al., 2015) and a rich fossil record (Hofmann et al., 1990; Narbonne and Aitken, 1990; Macdonald et al., 2013b; Strauss et al., 2014a; Carbone et al., 2015). However, because these strata are complicated by early

Neoproterozoic contractional structures (Helmstaedt et al., 1979; Eisbacher, 1981; Thorkelson, 2000), syn-sedimentary Cryogenian to Ediacaran high-angle faults (Young et al., 1979; Eisbacher, 1981, 1985; Jefferson and Parrish, 1989; Young, 1995), and widespread overprinting by the Mesozoic to Cenozoic Cordilleran orogeny (Gabrielse, 1967; Norris, 1997), reconstructing these records requires extensive geological mapping tied to numerous measured stratigraphic sections. In order to decipher these structural and stratigraphic complications, we present new geological mapping, measured stratigraphic sections, U-Pb zircon geochronology, zircon geochemistry, organic carbon isotope, and carbonate carbon and oxygen isotope data from Cryogenian strata in Yukon. These data provide the necessary geological context to further calibrate the Cryogenian record of climate, geochemical, biological, and tectonic change.

2. Geological Setting 2.1. Tectonostratigraphy In the Cordilleran fold-thrust belt of Yukon and Northwest Territories (NWT), Canada, Proterozoic strata are discontinuously exposed in erosional inliers through Phanerozoic strata (Figs. 1–2). Although crystalline basement is not exposed in Yukon, Proterozoic sedimentary successions east of the Mackenzie Mountains in NWT rest unconformably on the ca. 1880–1840 Ma western Bear Province of the Wopmay Orogen (Bowring and Grotzinger, 1992). Despite a lack of outcrops, early Proterozoic arc basement is inferred from positive aeromagnetic anomalies that extend from the NWT through Yukon and into Alaska (Aspler et al., 2003; Pilkington and Saltus, 2009; Crawford et al., 2010). Sedimentary cores drilled into the Fort Simpson anomaly, north of the Mackenzie Mountains in the NWT, intersected granitic basement that was dated with U-Pb on zircon at ca. 1845 Ma (Villeneuve et al., 1991). Near the Yukon-

NWT border, the trend of the Fort Simpson anomaly is offset southwards along the RichardsonHess Fault array (Rohr et al., 2011). This crustal discontinuity separates the Yukon block (Jeletsky, 1962) from the autochthonous Laurentian craton (Fig. 1). The Richardson-Hess Fault Array was active in the Cretaceous to Paleogene (Norris, 1985; Morrow, 1999) and even active today (Hyndman et al., 2005); however, since its Proterozoic inception, it has experienced multiple episodes of reactivation (Eisbacher, 1981; Aitken and McMechan, 1991; Abbott, 1996; Norris, 1997; Crawford et al., 2010; Rohr et al., 2011). Paleomagnetic data from the ca. 717 Ma Mount Harper volcanics in Yukon suggests that the Yukon block rotated ~55° counterclockwise relative to autochthonous Laurentia during the Cryogenian to Ediacaran (Eyster et al., 2016). This movement may have been accommodated along the Snake River Fault and kinematically associated with local transpression near the axis of rotation (Eisbacher, 1981; Thorkelson, 2000) and broad transtension during Windermere Supergroup deposition (Eyster et al., 2016). Proterozoic strata in the Yukon block consist of three unconformity-bounded successions (Young et al., 1979). Sequence A consists of ~1.7-1.2 Ga poly-deformed carbonate and siliciclastic rocks of the Wernecke Supergroup (Delaney, 1981; Furlanetto et al., 2013). Sequence B consists of the ~1.2–0.78 Ga Mackenzie Mountains Supergroup, which is broadly equivalent to the Pinguicula, Hematite Creek, and Fifteenmile groups in Yukon, although there may not be correlatives with the Pinguicula Group in the Northwest Territories (Medig et al., 2016). Sequence C consists of the ~0.78–0.54 Ga Windermere Supergroup and various equivalents in Yukon described herein (Fig. 2). Since its inception (Young et al., 1979), this classification has been refined and subdivided following the recognition of regional unconformities, multiple distinct basin-forming events, and new radioisotopic age constraints

(Jefferson and Parrish, 1989; Macdonald et al., 2010b; Turner et al., 2011; Macdonald et al., 2012; Rooney et al., 2014; Rooney et al., 2015; Baldwin et al., 2016; Milton et al., 2017). Cryogenian and Ediacaran strata of the Windermere Supergroup were deposited in tectonically active basins along the western margin of Laurentia from Alaska to Mexico. The Cryogenian stratigraphy of both northwest Canada and the Basin and Range province of the western United States have been correlated and later subsumed in the Windermere Supergroup (Gabrielse, 1972; Stewart, 1972), which was originally defined in the southern Canadian Rockies (Little, 1960). Although glacigenic strata can be identified in the Windermere Supergroup throughout the Cordillera, formation level correlations are complicated not only by the intrinsic lateral variability of glacial sedimentary facies, but also by prominent syn-sedimentary deformation that resulted in large changes in thickness and overlapping unconformities (Macdonald et al., 2013a). Cryogenian strata are exceptionally well exposed in northwest Canada and contain glacial diamictite, banded iron formation (BIF), and multiple volcanic horizons in mixed carbonatesiliciclastic successions. The most well-known and extensively described Cryogenian strata in northwest Canada are in the Mackenzie Mountains (e.g., Eisbacher, 1978; Yeo, 1981; Hoffman and Halverson, 2011), where Cryogenian glacial deposits of the Rapitan Group overlie the Coates Lake Group, which forms the base of the Windermere Supergroup (Fig. 2). The Coates Lake Group consists of laterally discontinuous mixed siliciclastic, evaporitic, and carbonate units that formed in narrow extensional basins (Jefferson, 1978; Jefferson and Parrish, 1989), that have been correlated with the Mount Harper Group in Yukon (Strauss et al., 2015; Strauss et al., 2014a) and the Chuar-Uinta Mountains-Pahrump (CHUMP) basins of the western United States (Dehler et al., 2005; Dehler et al., 2010; Smith et al., 2015; Dehler et al., 2017).

In the Mackenzie Mountains, the Coates Lake Group is unconformably overlain by the Rapitan Group, which is up to ~1500 m-thick and consists of massive diamictite of the Mount Berg Formation; maroon, stratified diamictite, turbidites, debrite, and iron formation of the Sayunei Formation; and massive diamictite of the Shezal Formation (Eisbacher, 1978; Yeo, 1981). The Mount Berg and Sayunei formations were deposited during active high angle faulting and local folding in fault-bound sub-basins that broadly follow the embayments created during Coates Lake time (Helmstaedt et al., 1979; Eisbacher, 1981; Baldwin et al., 2016). The Rapitan Group formed within two sub-basins, the Mountain River-Redstone River basin of the southern and central Mackenzie Mountains, and the Snake River Basin near the Yukon-NWT border (Baldwin et al., 2016). These sub-basins formed in an extensional or transtensional setting during the ‘Hayhook extensional event’ (Young et al., 1979; Young, 1995). The boundary between the Sayunei Formation and overlying massive diamictite of the Shezal Formation is variably conformable and unconformable, and at some localities BIF clasts derived from the Sayunei Formation occur hundreds of meters of above the base of the Shezal Formation. These observations attest to syn-sedimentary tectonism throughout deposition of the Rapitan Group responsible for generating complex stratigraphic architecture. In the Mackenzie Mountains, the Rapitan Group is overlain by the Cryogenian-Ediacaran Hay Creek Group (Turner et al., 2011), which consists of mixed carbonate and siliciclastic rocks of the Twitya and Keele formations (Day et al., 2004). To the southwest of the Plateau fault (Fig. 1), the Keele Formation and distally-correlative Durkan and Delthore members of the non-glacial portion of the Ice Brook Formation is overlain by the glacigenic Stelfox Member of the Ice Brook Formation (Aitken, 1991a; Hoffman and Halverson, 2011). Northeast of the Plateau thrust fault, the Stelfox Member, is typically absent and the Keele Formation is sharply overlain by the

dolomite of the basal Ediacaran Ravensthroat formation (James et al., 2001; Hoffman and Halverson, 2011. The Ravensthroat formation has also been identified in the Wernecke Mountains and correlated with dolostones in the Coal Creek and Tatonduk inliers of Yukon (Macdonald and Cohen, 2011; Macdonald et al., 2011; Macdonald et al., 2013b). Shale at the base of the Sheepbed Formation was dated with the Re-Os method at 632.0 ± 5.0 Ma (Rooney et al., 2015), confirming correlation between the underlying Ravensthroat formation and ca. 635 Ma basal Ediacaran cap carbonates worldwide (Hoffmann et al., 2004; Condon et al., 2005; Calver et al., 2013). Below we provide descriptions of Cryogenian successions in Yukon, west of the Snake River Fault, as the basis for correlations with the classic Mackenzie Mountains stratigraphy described above. Cryogenian strata of Yukon are predominantly exposed in four inliers: the Tatonduk, Coal Creek, Hart River and Wernecke inliers (Figs. 1 and 2). The Tatonduk inlier extends across the international border into Alaska and outcrops on both sides of the border are described below. Cryogenian strata are also present on the North Slope subterrane of the Arctic Alaska terrane in Alaska and Yukon and in two small inliers in SE Yukon (Pigage, 2009; MacNaughton et al., 2016). However, because the North Slope subterrane is most likely allochthonous (Macdonald et al., 2009; Strauss et al., 2013; Strauss et al., accepted) and little is known about the age and distribution of the basinal facies in the northernmost Snake River Basin (Norris, 1997; Baldwin et al., 2016) and in the Hyland Group of the Selwyn Basin (Gabrielse et al., 1972; Gordey, 1979; Moynihan, 2014), these localities are excluded from this study. Furthermore, because exposures of Cryogenian stratigraphy east of the Snake River Fault along the Yukon-NWT border have been described extensively in previous work (Yeo, 1981, 1984, 1986; Klein and Beukes, 1993; Baldwin et al., 2016), these are only addressed in the discussion.

2.2. Previous geochronological constraints A lower age constraint on the Windermere Supergroup is provided through constraints on the Little Dal basalt in the Mackenzie Mountains, which has been geochemically correlated with a 777.7 +2.5/-1.7 Ma (U-Pb zircon IDTIMS date) quartz diorite plug that intrudes the Mackenzie Mountains Supergroup (Jefferson and Parrish, 1989) and the 780 ± 1.4 Ma Tsezotene-Gunbarrel diabase dikes and sills (Dudás and Lustwerk, 1997). Recently, a 774.9 ± 0.5 Ma (U-Pb zircon IDTIMS date) was obtained directly from the Little Dal basalt (Milton et al., 2017). In the Coppercap Formation of the Coates Lake Group, a Re-Os date of 732.2 ± 3.9 Ma was obtained from organic-rich limestone. The sampled interval is directly above limestone that contains a large negative 13C excursion, which covaries in carbonate and organic 13C (Rooney et al., 2014) and has been correlated with the global Islay excursion (Hoffman et al., 2012; Strauss et al., 2014a). In correlative strata in the Coal Creek inlier (Fig. 2), Re-Os dates of 751.2 ± 5.1 and 739.9 ± 6.1 Ma were obtained from shale near the bottom and top, respectively, of the Callison Lake Formation of the Mount Harper Group (Strauss et al., 2014a; Strauss et al., 2015). The minimum age of the Mount Harper Group is further constrained by a 717.43 ± 0.14 Ma rhyolite flow in the Mount Harper volcanics (U-Pb zircon CA-IDTIMS date; Macdonald et al., 2010b). In the Mackenzie Mountains the age of the Rapitan Group is constrained below by the Re-Os date of 732.2 ± 3.9 Ma in the Coates Lake Group and above by a 662.4 ± 3.9 Ma Re-Os date from organic-rich limestone of the basal Twitya Formation, a Sturtian cap carbonate (Rooney et al., 2014). Additionally, near the border of Yukon and NWT, a detrital zircon CAIDTIMS U-Pb date of 711.34 ± 0.24 Ma was reported from the upper Sayunei Formation (Baldwin et al., 2016). In the Coal Creek inlier, the age of the base of the Rapitan Group is

bracketed by the 717.43 ± 0.14 Ma rhyolite flow in the Mount Harper volcanics and a 716.47 ± 0.24 Ma tuff in the overlying Eagle Creek Formation (U-Pb zircon CA-IDTIMS dates; Macdonald et al., 2010b). Below we provide additional U-Pb zircon CA-IDTIMS dates that refine this constraint.

3. Methods 3.1. Stratigraphy More than 50 stratigraphic sections were measured and logged by the authors between 2008 and 2014 and are synthesized below. The measured sections are divided into thirteen siliciclastic, carbonate, or diagenetic lithofacies (L1-L13) based on composition, texture, bedding style, and sedimentary structures. Lithofacies descriptions are provided in Table 1.

3.2. Carbon and oxygen isotope chemostratigraphy We present 582 new carbonate carbon (δ13Ccarb) and oxygen (δ18Ocarb), and 33 new organic carbon (δ13Corg) isotopic measurements from Cryogenian units in Yukon (data are in Tables S1). Fist- to golf ball-sized hand samples were collected at 0.5–2 m resolution through measured sections for δ13Ccarb and δ18Ocarb chemostratigraphy. Carbonate isotopic results are reported in per mil notation for the ratios 13C/12C and 18O/16O, respectively, relative to the standard VPDB (Vienna-Pee-Dee Belemnite). Carbonate samples were cut perpendicular to bedding with a lapidary saw, polished to reveal internal textures, and carefully microdrilled with 1-3 mm diameter dental drill bits to obtain ~2-10 mg of powder. Care was taken to avoid secondary veins, cements, and siliciclastic components when drilling for isotopic measurements.

Isotopic data were acquired in the Laboratory for Geochemical Oceanography at Harvard University and in the Stable Isotope Laboratory at McGill University. For measurements at Harvard University, carbon and oxygen isotopes ratios were acquired simultaneously on a VG Optima dual inlet isotope ratio mass spectrometer (IRMS) coupled with a VG Isocarb preparation device (Micromass, Milford, MA). Approximately 1 mg of sample powder was reacted in a common, purified phosphoric acid (H3PO4) bath at 90°C. The evolved CO2 was collected cryogenically and analyzed using an in-house reference gas. For measurements at McGill University, measurements were made on a Nu Instruments Perspective dual inlet IRMS coupled to a NuCarb preparation devices (Wrexham, UK). Approximately 50–100 μg of sample powder was reacted with purified phosphoric acid at 70ºC in individual vials, and the evolved CO2 was collected cryogenically and analyzed using the Jackson Dome reference gas, which is calibrated against NBS19 and LSVEC (Kim et al., 2015). For all measurements, the acquired data were calibrated to VPDB using an in-house Cararra Marble standard (CM2). Total analytical errors (1σ) are better than ± 0.1‰ for both δ 13Ccarb and δ18Ocarb based on repeat analysis of standards and samples. Organic carbon (δ13Corg) analyses were performed on large (~10 g) samples to accommodate low total organic carbon (TOC) concentrations. Samples were decalcified with concentrated HCl for 48 hours, buffered back to less acidic pH (pH=5), filtered and dried. The mass of insoluble residue was taken as siliciclastic content and the difference between the original mass and siliciclastic mass is the carbonate content. Homogenized residues were analyzed on a Carlo Erba Elemental Analyzer attached to a ThermoFinnigan Delta V configured in continuous flow mode. Samples and standards were bracketed and each run in duplicate.

These standards have known organic carbon contents and isotope values, and were used to calibrate TOC contents and isotopic compositions.

3.3. Zircon chemistry and U-Pb geochronology Zircon grains were separated from rocks using standard techniques and annealed at 900 °C for 60 hours in a muffle furnace. Grains were mounted in epoxy and polished until their centers were exposed. Cathodoluminescence (CL) images were obtained with a JEOL JSM-1300 scanning electron microscope and Gatan MiniCL. Zircon was analyzed by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) for U-Pb isotope ratios and trace element concentrations. For more precise dates, selected zircon crystals were plucked from the mounts and analyzed via chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-IDTIMS).

3.3.1. LA-ICPMS Zircon was analyzed LA-ICPMS using a ThermoElectron X-Series II quadrupole ICPMS and New Wave Research UP-213 Nd:YAG UV (213 nm) laser ablation system. In-house analytical protocols, standard materials, and data reduction software were used for acquisition and calibration of U-Pb dates and a suite of high field strength elements (HFSE) and rare earth elements (REE). Zircon was ablated with a laser spot of 25 µm wide using fluence and pulse rates of 5 J/cm2 and 10 Hz, respectively, during a 45 second analysis (15 sec gas blank, 30 sec ablation) that excavated a pit ~25 µm deep. Ablated material was carried by a 1.2 L/min He gas stream to the nebulizer flow of the plasma. Quadrupole dwell times were 5 ms for Si and Zr, 200 ms for 49Ti and 207Pb, 80 ms for 206Pb, 40 ms for 202Hg, 204Pb, 208Pb, 232Th, and 238U and 10 ms

for all other HFSE and REE; total sweep duration is 950 ms. Background count rates for each analyte were obtained prior to each spot analysis and subtracted from the raw count rate for each analyte. For concentration calculations, background-subtracted count rates for each analyte were internally normalized to 29Si and calibrated with respect to NIST SRM-610 and -612 glasses as the primary standards. Ablation pits that appear to have intersected glass or mineral inclusions were identified based on Ti and P signal excursions, and associated sweeps were discarded. U-Pb dates from these analyses are considered valid if the U-Pb ratios appear to have been unaffected by the inclusions. Signals at mass 204 were normally indistinguishable from zero following subtraction of mercury backgrounds measured during the gas blank (<200 cps 202Hg), and thus dates are reported without common Pb correction. Rare analyses that appear contaminated by common Pb were rejected based on mass 204 greater than baseline. Crystallization temperatures were calculated from the Ti-in-zircon thermometer (Watson et al., 2006). Because there are no constraints on the activity of TiO2 in the source rocks, a nominal value for high-silica rhyolites of 0.6 was used. All zircon trace element data are reported in supplementary materials Table S2. For U-Pb and 207Pb/206Pb dates, instrumental fractionation of the background-subtracted ratios was corrected and dates were calibrated with respect to interspersed measurements of zircon standards and reference materials. The primary standard Plešovice zircon (Sláma et al., 2008) was used to monitor time-dependent instrumental fractionation based on two analyses for every 10 analyses of unknown zircon. A secondary correction to the 206Pb/238U dates was made based on results from a combination of co-analyzed external zircon standards: Seiland (530 Ma), Zirconia (327 Ma), Temora (417 Ma), and FC1 (1098 Ma). These standards were treated as unknowns and measured once for every 10 analyses of unknown zircon. These results showed a linear age bias of up to several percent that is related to the 206Pb count rate. The secondary

correction is thought to mitigate matrix-dependent variations due to contrasting compositions and ablation characteristics between the Plešovice zircon, other standards, and unknowns. Radiogenic isotope ratio and age error propagation for all analyses includes uncertainty contributions from counting statistics and background subtraction. Uncertainties arising from instrumental calibration are the local standard deviations of the polynomial fits to the interspersed primary standard measurements versus time for the time-dependent, relatively larger U-Pb fractionation factor, and the standard errors of the means of the consistently time-invariant and smaller 207Pb/206Pb fractionation factor. These errors are 1.3-1.9% (2) for 206Pb/238U and 0.5-0.9% (2) for 207Pb/206Pb. While not propagated into the dates reported in supplementary materials Table S3, these errors should be propagated in quadrature into group weighted mean dates.

3.3.2. CA-IDTIMS U-Pb dates were obtained for characterized zircon fragments by the chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-IDTIMS) method (Mattinson, (2005). Annealed zircons were removed from the epoxy mounts for dating based on CL images and LAICPMS data. Individual crystal fragments were partially dissolved (chemically abraded) in 120 l of 29 M HF for 12 hours at 180°C to 200°C in 300 l Teflon PFA microcapsules. The residual grains were rinsed in warm 3.5 M HNO3 in an ultrasonic bath and on a warm hotplate for 60 minutes, then rinsed twice in ultrapure H2O before being reloaded into microcapsules and spiked with the ET535 mixed U-Pb isotope tracer (Condon et al., 2015). Zircon was dissolved in Parr vessels in 120 l of 29 M HF with a trace of 3.5 M HNO3 at 220°C for 48 hours, dried to fluorides, and re-dissolved in 6 M HCl at 180°C overnight. U and Pb were separated from the

zircon matrix using an HCl-based anion-exchange chromatographic procedure (Krough, 1973), eluted together and dried with 2 µl of 0.05 N H3PO4. Pb and U were loaded on a single outgassed Re filament in 5 µl of a silica-gel/phosphoric acid mixture (Gerstenberger and Haase, 1997), and U and Pb isotopic measurements made on a GV Isoprobe-multicollector thermal ionization mass spectrometer equipped with an ion-counting Daly detector. Pb isotopes were measured by peak-jumping all isotopes on the Daly detector for 160 cycles, and externally corrected for mass fractionation based upon other measurements of double Pb spiked (ET2535; (Condon et al., 2015) gravimetric solutions and samples measured during the same time period. Transitory isobaric interferences due to high-molecular weight organics, particularly on 204Pb and 207Pb, disappeared within approximately 30 cycles, while ionization efficiency averaged 104 cps/pg of each Pb isotope. Linearity (to ≥1.4 x 106 cps) and the associated deadtime correction of the Daly detector were monitored by repeated analyses of NBS982. Uranium was analyzed as UO2+ ions in static Faraday mode on 1011 ohm or 1012 ohm resistors for 200-300 cycles, and corrected for isobaric interference of 233U18O16O on 235U16O16O with an 18O/16O of 0.00206. Ionization efficiency averaged 2 x 10 -13 A/ng of each U isotope. U mass fractionation was corrected using the known 233U/235U ratio of the tracer solution. CA-IDTIMS U-Pb dates and uncertainties were calculated using the algorithms of Schmitz and Schoene (2007) and U decay constants recommended by Jaffey and others (1971). 206

Pb/238U ratios and dates were corrected for initial 230Th disequilibrium using a Th/U[magma]

= 3.0 ± 0.3, resulting in an increase in the 206Pb/238U dates of ~0.09 Ma. Up to 0.5 pg of common Pb in analyses was attributed to laboratory blank and subtracted based on the measured laboratory Pb isotopic composition and associated uncertainty; residual common Pb in two grains was subtracted based upon the model Pb isotope evolution model of Stacey and Kramers

(1975) at 717 Ma. U laboratory blanks are estimated at 0.075 pg. All CA-IDTIMS U-Pb isotope ratio and calculated dates are reported in supplementary materials Table S2. Weighted mean 206Pb/238U dates were calculated from equivalent dates (i.e., probability of fit >0.05) using Isoplot 3.0 (Ludwig, 2003). Errors on the weighted mean dates are given as ± x (y) [z], where x is the internal error based on analytical uncertainties only, including counting statistics, subtraction of tracer solution, and blank and initial common Pb subtraction, y includes the tracer calibration uncertainty propagated in quadrature, and z includes the 238U decay constant uncertainty propagated in quadrature. Internal errors should be considered when comparing our dates with 206Pb/238U dates from other laboratories that used the EARTHTIME tracer solution or one that is cross-calibrated using EARTHTIME gravimetric standards. Errors including the uncertainty in the tracer calibration should be considered when comparing our dates with those derived from other geochronological methods using the U-Pb decay scheme (e.g., LA-ICPMS). Errors including uncertainties in the tracer calibration and

238

U decay

constant (Jaffey et al., 1971) should be considered when comparing our dates with those derived from other decay schemes (e.g., 187Re-187Os). Errors for weighted mean dates and dates from individual grains are given at 2 in Table 3 and supplementary materials Table S4.

4. Stratigraphy 4.1. Wernecke inlier The Neoproterozoic stratigraphy of the Wernecke Mountains near Goz Creek was first described by Eisbacher (1981). These preliminary stratigraphic descriptions were incorporated into the regional mapping of Thorkelson et al. (2000; 2005) in the Slats Creek (106D/16), Fairchild Lake (106C/13), and Dolores Creek (106C/14) map areas. These studies demonstrated

that the Cryogenian stratigraphy of the Wernecke inlier display rapid facies changes from north to south that are largely the product of syn-sedimentary faulting. In the northernmost exposures of the map area (Eis Graben; Fig. 3), conglomerate and immature sandstone of the basal Rapitan Group (informally, the Rapitan conglomerate unit) rests unconformably on the Hematite Creek Group (Turner, 2011). The conglomerate unit in section T1408 consists of 460 m of weakly-bedded to massive, rounded to sub-angular, cobble and boulder, clast-supported conglomerate (L3) silty shale (L6) and poorly- to moderately-sorted, gravelly sublitharenite channels (L4), as well as minor matrix-supported, massive diamictite (L1; Fig. 4). This unit thins and become finer-grained ~1000 m to the north and is overlain by over 300 m of massive, matrix-supported, diamictite (L1) with a highly variable clast density, scalyweathering and green-grey calcareous matrix that has been correlated with the Shezal Formation (Eisbacher, 1981). The majority (>90%) of clasts in this unit are dolo-grainstone, though distinct jaspillitic chert clasts, which are possibly derived from the Sayunei Formation, also occur in conglomerate and diamictite facies (Fig. 5A). Both the conglomeratic unit and the massive diamictite of the Shezal Formation are included in the Rapitan Group here. The Shezal Formation is overlain by over 1 km of green-brown siliciclastic strata (L4 and L5) of the Twitya Formation, which forms the base of the Hay Creek Group. In the Wernecke Mountains, the base of the Hay Creek Group does not preserve a clear Sturtian cap carbonate, as is locally present in the Mackenzie Mountains (sensu Rooney et al., 2014), but instead consists of graded beds of sandstone and siltstone with dolostone cements and minor shale. In these northern exposures, the Twitya-Keele transition (e.g., Day et al., 2004) is marked by the appearance of limestone olistoliths that are tens of meters across (Fig. 5B). The olistolith-bearing interval is overlain by approximately 500 m of limestone-dominated strata with minor siliciclastic intervals

that are correlated with the Keele Formation. The steep slopes of this interval precluded measurement, but the top of the Keele Formation in this section is marked by a prominent erosive surface that cuts down into the underlying carbonate with meter-scale relief and is overlain by an 11 m-thick package of interbedded conglomerate and quartz arenite. This conglomeratic interval is sharply overlain by ~50 m of massive matrix-supported diamictite (L1) with yellow carbonate and red siliciclastic matrix and subrounded limestone, dolostone, and sandstone clasts (Fig. 5C). One quartzite clast with well-developed glacial striations was also observed. The diamictite is locally overlain by the Ravensthroat formation, which consists of 8 m of laminated dolostone (L9), and poorly exposed black shale (L6) of the Sheepbed Formation. To the south, Cryogenian strata of the Hay Creek Group variably unconformably overlie the Pinguicula, Hematite Creek, Katherine, and Little Dal groups (Fig. 3). At the Goz A sections, the Katherine Group underlies a tongue of massive brecciated and stromatolitic dolostone (L10 and L11) that we assign to the Mount Profeit dolostone. In more northerly exposures (sections F851 and W8; Fig. 3), the stromatolitic unit is capped with an iron-stained exposure surface and tens of meters of thin-bedded limestone and shale (L6 and L7). To the south (section F1228; Figs. 3, 4), the stromatolitic dolostone is overlain by a green to brown siltstone interval (Fig. 5D), an ~11 m thick stromatolitic dolostone olistolith, and the same iron-stained surface. There, the overlying thinly-bedded limestone and shale interval includes several beds of carbonate clast breccia interpreted as debrites and olistoliths (Fig 5E). This lower carbonate and debris-flow bearing interval is separated by 100-150 m of graded sandstone and siltstone beds and a second olistolith- and debris flow-bearing unit (Figs. 4 and 5F). These strata are overlain by over 500 m of predominately grey-green, normally-graded beds of siltstone and sandstone displaying Bouma B-E cycles with flutes, dewatering structures, and slump folds. We assign all of the Cryogenian

strata above and interfingered with the Mount Profiet dolostone to the Ice Brook Formation (Aitken, 1991a; Aitken, 1991b). The top of the Ice Brook Formation near Goz A is marked by a quartzite clast conglomerate with sulfide mineralization, but diamictite was not observed. The Ice Brook Formation is overlain by dolomite of the Ravensthroat formation and black shale of the Sheepbed Formation. Further south at the Mount Profeit and Goz B sections, nearly all of the Hay Creek Group consists of massive grainstone, recrystallized dolostone, and saddle dolomite (L12 and L13; Vandeginste et al., 2005) with rare windows of exquisitely preserved microbial mounds with clotted fabrics and giant ooids (Fig. 5G). This unit, referred to as the Mount Profeit dolostone (Eisbacher, 1981) is over 500 m-thick and unconformably rests sharply above folded Hematite Creek Group strata and discontinuous wedges of clast-supported conglomerate. This lower conglomerate thickens to over 500 m to the southeast below the Goz B section (Fig. 4 & 5H), and was previously correlated with the Rapitan Group (Eisbacher, 1981). The Mount Profeit dolostone is overlain by ~20 m of conglomerate and sandstone with abundant pyrite, dolomite of the Ravensthroat formation, and black shale of the Sheepbed Formation.

4.2. Hart River inlier The Hart River inlier, located in the southeastern Ogilvie Mountains, hosts Proterozoic strata of the Wernecke, Pinguicula, Fifteenmile, Mount Harper, and Rapitan groups, and units possible equivalent to the Hay Creek Groups (Figs. 1 and 6). The oldest strata exposed in the Hart River inlier comprise mixed siliciclastic and carbonate rocks of the Wernecke Supergroup. The Hart River basalts unconformably overlie the Wernecke Supergroup and are assumed to be extrusive equivalents of the ca. 1380 Ma Hart River sills (Abbott, 1997). The Hart River basalts

are unconformably overlain by ~2.5 km of mixed siliciclastic-carbonate strata of the Pinguicula and Fifteenmile groups (Abbott, 1997; Halverson et al., 2012), which are separated by a prominent angular unconformity (Fig. 6). These units are in turn all unconformably overlain by the ca. 760-740 Ma Callison Lake Formation, which consists of dolostone and minor shale (Strauss et al., 2015). In the Hart River inlier, the Rapitan Group consists of conglomerate, glacial diamictite, mixed carbonate-siliciclastic strata (FL1-L4) and minor breccia (L12) that unconformably overlie the Callison Lake Formation (Figs. 6 and 7; Macdonald et al., 2010). The top of the Rapitan Group is poorly exposed on dip slopes and structurally complicated by Mesozoic thrust faults (Fig. 6). At two localities, poorly exposed siliciclastic units with minor carbonate that overlie the Rapitan Group are tentatively assigned to the Hay Creek Group (Fig. 6). The southernmost of these two exposures is overlain by a massive basalt that was previously mapped as a Neoproterozoic volcanic unit (Abbott, 1997), but we assign this unit to the early Paleozoic Dempster volcanics due to lithologic similarities on other fault slices to the south (Fig. 6). The westernmost measured section of the Rapitan Group (F936, Fig. 6) consists of over 200 m of weakly-bedded diamictite and minor clast-supported conglomerate (Fig. 7). The Rapitan Group overlies rubble breccia (L11) of the Callison Lake Formation. The basal 50 m of the Rapitan Group consists of interbedded maroon siliciclastic matrix and yellow dolomite matrix thin-bedded diamictite (Fig. 8A). Up-section, the Rapitan Group is dominated by more massive crudely-bedded maroon (Fig. 8B) and dark-grey siliciclastic diamictite. Striated clasts are common in the maroon matrix diamictite (Fig. 8C), and the uppermost exposures consist of carbonate-dominated diamictite with localized soft-sediment deformation.

To the east at section F937, only ~110 m of Rapitan Group strata are exposed. Although the top of the section is truncated by a younger thrust fault, internal thinning in tapering stratal geometries is apparent in several units that can be traced further to the east. The upper dark-grey siliciclastic diamictite thins from ~100 m-thick at F938 to only ~10 m-thick at F937 (Fig. 7). At this locality, an additional unit of massive dark-grey siliciclastic diamictite appears within the upper carbonate matrix diamictite at about 75 m above the base of the section (Fig. 7). This diamictite tapers to the east (Fig. 8D) and is underlain by abundant soft-sedimentary folds and plow structures that verge to the north (Fig. 8E). On a separate thrust sheet to the northeast, a ~140 m section of what is interpreted as the Rapitan Group consists predominantly of redeposited carbonate grainstone and rudstone with minor diamictite (F934, J906). Evidence for a glacial influence on this unit is not obvious; however, we tentatively assign it to the Rapitan Group due to lithological similarities and relative stratigraphic position with carbonate matrix conglomerate and diamictite of the Rapitan Group to the southwest. This unit highlights a major map-scale erosional surface that unconformably places the Rapitan Group on the Wernecke Supergroup (Fig. 6).

4.3. Coal Creek inlier The Coal Creek inlier, located in the western Ogilvie Mountains, hosts Proterozoic strata of the Wernecke, Pinguicula, Fifteenmile, Mount Harper, Rapitan, Hay Creek, and ‘Upper’ groups (Figs. 1 and 9). The oldest rocks exposed in the Coal Creek inlier are mixed siliciclastic and carbonate strata of the Wernecke Supergroup. These are unconformably overlain by the Pinguicula, Fifteenmile and Mount Harper groups (Strauss et al., 2014b). The Mount Harper Group consists of the Callison Lake and Seela Pass formations and the overlying Mount Harper

volcanics, which interfinger with the base of the Rapitan Group. In the Coal Creek region, the Rapitan Group consists of the Eagle Creek Formation (Fig. 11), which is formalized herein (Table 2). Two measured sections of the Eagle Creek Formation (formerly the upper Mount Harper formation or PH1; Thompson et al., 1987; Mustard and Roots, 1997; Macdonald et al., 2010b; Macdonald et al., 2011; Strauss et al., 2014b) were previously described by Mustard and Roots (1997) (sections 8 and 9). Additionally, portions of the measured sections described in detail herein were reported by Macdonald et al. (2010b; 2011). The Eagle Creek Formation is overlain by <100 m of poorly exposed siltstone and limestone assigned to the Ediacaran Hay Creek Group. This unit commences with <10 m of dolomite breccia (L11). While a genetic interpretation of this breccia is unclear, it is overlain by a white to buff-colored, finely laminated dolostone with abundant bed-parallel sheet-crack cements (Hoffman and Macdonald, 2010) that shares textural and geochemical similarities with ca. 635 Ma basal Ediacaran cap carbonates in the both Wernecke and Mackenzie mountains and world-wide (Macdonald et al., 2013b). The Mount Harper volcanics are divided into six informal units (A-F) that are defined both stratigraphically and compositionally (Fig. 10; Roots, 1987; Mustard and Roots, 1997; Cox et al., 2013). Members A and B formed a mafic volcanic edifice up to 1200 m-thick, dominated by basaltic flows and breccia, with a transition up-section to more hematitic flows displaying ropey pahoehoe (Fig. 12A) and locally pyroclastic breccia. Members A and B were unevenly eroded and draped by pyroclastic-epiclastic deposits of member C. These deposits thin northward and include tuff-breccia, lapilli tuff, and block-and-ash breccia with basalticintermediate clasts. Where they occur, members D (rhyolite), E (andesite) and F (andesite interfingering with the Eagle Creek Formation) unconformably overlie members A–C (Roots, 1987; Mustard and Roots, 1997). The member D rhyolite is exposed as massive flows in

erosional windows in the southwestern Coal Creek inlier (section F837; Fig. 9). Here we report new dates for two additional rhyolite flows (samples F837A, F837C) within the same section as the flow previously dated at 717.4 ± 0.2 Ma (sample F837B; U-Pb CA-IDTIMS; Macdonald et al., 2010a). Sample F837A is from a columnar jointed rhyolite dome that is overlain by white weathering, green (in fresh exposure), flow-banded rhyolite with feldspar and resorbed quartz phenocrysts (sample F837C), and a maroon to purple flow-banded rhyolite with feldspar and resorbed quartz phenocrysts, and black rhyolite xenoliths (sample F837B). We also report two new dates from rhyolite flows and breccia of Member D that are exposed in the far southwestern portion of the Coal Creek inlier (samples 15PM06 and 15PM08; Figs. 9, 10), which were previously mapped as portions of the early Paleozoic Dempster Volcanics (Roots, 1988). Member E forms cliff exposures of subaerial columnar-jointed and shattered massive flows with ropey pahoehoe textures that prograde over an apron of angular flow shards (‘hydroclastic breccia’) that is extensive atop the older edifice. Epiclastic sedimentary units preserved as erosional outliers in the complex contain abundant clasts derived from members D and E. Member F andesites form pillowed flows, breccias, tuffs and invasive flows that interfinger with and intrude into diamictites of the Rapitan Group. On the south flank of Mount Harper (Figs. 10 and 11), a maroon-colored mudstone with pebble- to cobble dolomite and volcanic lonestones comprises the base of the Eagle Creek Formation. Up-section these strata, which resemble the Sayunei Formation of the Rapitan Group in the Mackenzie Mountains in color, texture, and stratigraphic position (Eisbacher, 1978; Yeo, 1984), are interbedded with volcaniclastic matrix-supported diamictite with volcanic, dolostone, and quartzite clasts, and are overlain by a yellow to grey dolomite matrix-supported diamictite with common bed-penetrating lonestones.

The stratigraphic section at Tango Tarn (F840, F917, F924) is complicated by small-scale faulting (Figs. 11 and 13A). We present a composite measured section that begins with stratified diamictite that rests on volcanic rocks of member B. Our previous study reported a 716.5 ± 0.2 Ma U-Pb CA-IDTIMS zircon age from an ~1 m-thick, green to pink, brecciated tuff (sample F840A) that is directly above stratified diamictite (Macdonald et al., 2010a). The tuff interfingers with a massive to weakly stratified diamictite unit that is >10 m-thick and consists of dolostone and volcanic boulders suspended in a yellow dolomite matrix with lamination-penetrating dropstones. Because section F840 is poorly exposed and fault bounded (Figs. 11 and 13A), additional samples were collected from measured sections of the Eagle Creek Formation that are stratigraphically below F840. A second 0.2 m-thick volcanic tuff (sample F917-1) was collected within matrix-supported diamictite, one meter above the base of the Eagle Creek Formation in section F917 (Fig. 11). The tuff forms a discrete green, porcelaneous layer within a weaklybedded volcaniclastic matrix-supported diamictite (L2) that contains both volcanic and dolomite clasts. The Eagle Creek Formation and Mount Harper volcanics form the top of the ridgeline at Tango Tarn, so the maximum thickness and nature of the upper contact of the Eagle Creek Formation are locally unconstrained. To the northeast at Green Shelter (Fig. 9), units both underlying and overlying the Eagle Creek Formation are locally preserved; thus, despite the lack of complete exposure, this locality is proposed as the type section of the Eagle Creek Formation (Table 2). The type section is a composite of measured sections F918, F919, and F920, which are exposed on a north-facing slope near the headwaters of Eagle Creek (Fig. 9, 11, 13B). This is close to section 8 of Mustard and Roots (1997), which was measured on the other side of the valley to the northwest. At Green Shelter, massive flows of member B of the Mount Harper volcanics are sharply overlain by

volcanic matrix diamictite with sub-rounded cobbles and boulders of dolostone. The lower 60 m consist of varicolored volcanic to siliciclastic matrix diamictite with minor yellow-weathering dolomite matrix and grey limestone matrix diamictite and carbonate clast conglomerate. Softsediment deformation is locally present in the dolomudstone laminations. The upper 50 m consist predominantly of yellow-weathering dolomite matrix diamictite and minor carbonate conglomerate. The upper contact with the Hay Creek Group is covered, but a maximum thickness of the Eagle Creek Formation at Green Shelter of 115 m is obtained by measurement to the first exposure of interbedded blue-grey limestone rhythmite and siltstone of the Hay Creek Group. The upper Hay Creek Group consists of ~12 m of organic-rich black shale overlain by a white dolostone breccia. The top of the Hay Creek Group is marked by a buff-white dolostone that has lithological and geochemical characteristics of the basal Ediacaran Ravensthroat formation and is overlain by a thick black shale succession of the Sheepbed Formation (Macdonald et al., 2013b). Further north, at Mine Camp (Figs. 9 and 11), the Eagle Creek Formation thickens and becomes dominated by yellow-weathering carbonate diamictite and conglomerate (Fig. 12B). A maximum thickness of the Eagle Creek Formation of ~270 m was measured in the northwesternmost exposure (T1401, Fig. 13C), which is the same location of measured section 9 of Mustard and Roots (1997), where Eagle Creek Formation strata were measured to ~290 m. These sections end in a dip slope and lack a top contact. Nonetheless, Mustard and Roots (1997) estimated a maximum thickness of ~400 m for this unit. The lower ~30 m of sections G07, J1011, F1010, and F1013 consist of interbedded dolostone clast diamictite and conglomerate interspersed with several thinly-laminated, ~10-20 cm-thick beds of volcaniclastic siltstone (Fig. 12C), whereas the base of section T1401 comprises ~30 m of thinly-bedded, parallel-laminated,

yellow dolomitic mudstone to grainstone rhythmites (Fig. 12D) with intermittent marly partings (L7), asymmetrical ripples, normally-graded beds and abundant lonestones (Fig. 12E). Upsection, the Eagle Creek Formation is dominated by massive and weakly stratified cobble to boulder diamictite (Fig. 12F) and very poorly-sorted, sub-angular, clast-supported pebble to boulder conglomerate (L1-L3). The principal conglomerate and diamictite facies are intercalated with yellow dolo-rhythmite facies (L7) and thin- to medium-bedded, highly-variable grain-sized grainstone (L9) containing trough cross-beds, normal- and reverse-graded beds, occasional load structures, and abundant bed-penetrating lonestones. At least one thin bed (~0.1 m-thick) of light-blue, crinkly laminated dolomite is present within the Eagle Creek Formation in sections F1010 and F1013 that is interpreted as a microbialaminite (L10). Ice till pellets (Fig. 12G), striated clasts and exotic granite and paragneiss clasts were also identified (Fig. 12H) in exposures at Mine Camp. Mustard and Roots (1997) divided the upper Mount Harper Group into two map units, a green-black volcaniclastic matrix dominated unit PH1 and yellow carbonate matrix dominated unit PH2. However, we do not follow this distinction as these lithofacies are commonly interbedded, thereby limiting their utility as meaningful stratigraphic units. The Eagle Creek Formation generally thickens and the carbonate-matrix facies become more prevalent to the north (Fig. 11). This pattern is exemplified in a series of carbonate-matrix diamictiteconglomerate megasequences in the northernmost T1401 section. These megasequences, originally observed by Mustard and Roots (1997), display an overall increase in clast-to-matrix ratio as they coarsen and thicken upward, with the most prevalent of these occurring from ~0–80 m. Clasts below ~250 m stratigraphic height in section T1401 are exclusively carbonate and chert lithologies, whereas minor purple siltstone clasts appear and pink micritic limestone clasts

become more abundant above ~250 m. This transition coincides with conglomerate facies becoming more clast-dense and channelized. Paleocurrent data from the Eagle Creek Formation indicate flow of the carbonate-dominated facies to the south, whereas the volcaniclastic facies suggest flow north, presumably sourced from the Mount Harper volcanics (Mustard and Roots, 1997).

4.4. Tatonduk inlier The Tatonduk inlier straddles the international border with Alaska and hosts Proterozoic strata of the Pinguicula, Fifteenmile, Rapitan, Hay Creek, and ‘Upper’ groups and the Pleasant Creek volcanics (Figs. 1 and 14). Proterozoic strata along the border were originally referred to as the Tindir Group by Cairnes (1914) and divided into seven map units by Mertie (1930, 1933). The Upper and Lower Tindir Groups were first separated by Payne & Allison (1981), and Young (1982) further subdivided the Upper Tindir Group into five units in ascending stratigraphic order from unit 1 to unit 5: unit 1 consists primarily of mafic volcanic rocks; unit 2, purple mudstone and diamictite, including iron formation; unit 3, massive diamictite; unit 4, platformal dolostone and green to light grey shale; unit 5, grey to black shale and limestone. Macdonald et al. (2011) reassigned the Lower Tindir Group to the Pinguicula and Fifteenmile Groups of the Mackenzie Mountains Supergroup and the Upper Tindir Group to the Rapitan, Hay Creek and ‘Upper’ groups of the Windermere Supergroup (Fig. 2). In this updated stratigraphic framework, unit 1 was renamed the Pleasant Creek volcanics, unit 2 was assigned to the Rapitan Group, unit 3 and the dolomite unit at the base of unit 4 were included in the Hay Creek Group, and the rest of unit 4 and unit 5 were assigned to the ‘Upper’ group (Macdonald et al., 2011).

The ~330 m-thick Pleasant Creek volcanics rest upon a significant disconformity and comprise a series of pillowed and massive basaltic lavas with substantial volcaniclastic breccia (Macdonald et al., 2011). Mafic dikes are pervasive throughout the underlying sedimentary units of the Pinguicula and Fifteenmile groups, but they are not present in units overlying the Pleasant Creek volcanics (Macdonald et al., 2010a). Carbonate clast conglomerate in the upper portion of some Pleasant Creek exposures (Young, 1982) suggest that the basalts may locally interfinger with the overlying strata of the Rapitan Group. Between Pleasant Creek and the Tatonduk River, the Rapitan Group varies in thickness between 0 and >150 m (Fig. 15), but it locally expands to >700 m to the northwest (Young, 1982). The basal contact of the Rapitan Group has not been observed locally; however, volcanic fragments similar in composition to the underlying Pleasant Creek volcanics are common in the lowermost Rapitan strata. In the Tatonduk inlier, the Rapitan Group is chiefly composed of finely laminated and maroon-colored mudstone and siltstone speckled with gravel lonestones (L2). The majority of clasts are dolostone derived from the Fifteenmile Group. These units also contain faceted clasts with striations (Fig. 16A) and bed-penetrating dropstones (Fig. 16B). Along the Tatonduk River and Hard Luck Creek, the Rapitan Group contains prominent ironstone-bearing intervals consisting of hematitic siltstone and minor jaspilite (Figs. 16C and 16D). Paleocurrent analysis from siltstone beds suggests a west-facing margin (present coordinates; Young, 1982). Along Pass Creek, the Hay Creek Group consists of >100 m of planar-bedded, normally graded siltstone and sandstone interbedded with minor dolomitic mudstone (Fig. 16E). These strata are overlain by a poorly-sorted, massive, yellow to brown dolomite-matrix conglomerate with sub-rounded to sub-angular clasts (Fig. 16F) and brown siliciclastic matrix-supported

diamictite, both of which contain jaspilitic chert clasts presumably derived from the underlying Rapitan Group (Fig. 16F). Although there is no definitive evidence for a glacigenic origin of this deposit, this unit is correlative with the unit 3 diamictite in section B of Young (1982), which he interpreted to represent a massive glacigenic debris flow. Further north, near Hard Luck and Pleasant creeks, the lower Hay Creek Group is absent and the Rapitan Group and Pleasant Creek volcanics are unconformably overlain by a white dolomite breccia (L11) and white dolomite with bed parallel ‘sheet-crack’ cements (Fig. 16G) of the Hay Creek Group (Fig. 15). No foreign clasts were noted in the breccia unit, with the exception of some clasts of the Pleasant Creek volcanics near the base.

5. Carbon and Oxygen Isotopic Results Carbonate carbon and oxygen isotope chemostratigraphy was carried out to refine regional and global correlations. In the Goz Creek region of the Wernecke inlier, δ 13Ccarb values from the lower Little Dal Group (F1226) vary from -3.7 to +5.1‰ and δ18Ocarb values range from -5.9 to -11.9‰ (Table S1). Negative δ13Ccarb values are limited to lenticular-shaped cements within siltstone beds. These samples also have the most enriched δ 18Ocarb values (Table S1). Stratigraphically higher, above the overlying conglomerate, δ13Ccarb values from the Mount Profeit dolostone (F853, F854, F1224) are predominantly between 0 and +7.4‰ with an excursion down to -7‰ near the top of the unit (Fig. 4). Carbonate δ 18O values vary between -12 and 0‰. In the lower half of the Mount Profeit dolostone, which is heavily altered by zebra dolomitization (Vandeginste et al., 2005), or saddle dolomite, δ13Ccarb values are relatively monotonous between 0 and +3‰ and δ18Ocarb values are relatively enriched between -4 and 0‰.

Possibly correlative units in the basal Ice Brook Formation that were not effected by zebra dolomitization have δ18Ocarb between -12 and -8‰. Carbonate δ13C values in the Ice Brook Formation (F1228, F851, W8) reach up to +8‰ and negative values as low as -20‰ occur in lenticular-shaped cements. Carbonate δ18O values in the Ice Brook Formation vary from -18 to -1‰. Except for the anomalous values preserved in the cements, no covariance is apparent between δ 13Ccarb and δ18Ocarb, and like the Little Dal Group, the cements with the most negative δ 13Ccarb values also have the most positive δ18Ocarb values. Independent of the extremely negative δ 13Ccarb values from the cements, a large negative δ13Ccarb excursion is preserved in three separate measured sections of the Ice Brook Formation (F1228, F851, W8) in well-bedded limestone rhythmites and ribbonites composed of micrite and calcisiltite, graded beds of ooid grainstone, and debrites (Fig. 4). To test if the δ13Ccarb excursion in the Ice Brook Formation is primary, we also analyzed δ13Corg from section F1228. Organic carbon isotopes also preserved a negative excursion with δ13Corg values varying between -20 and -42‰. This excursion stratigraphically coincides with the δ13Ccarb excursion, and epsilon values (i.e. δ 13Ccarb - δ13Corg) remain between 25 and 33‰. Hence, they broad covariance between carbonate organic carbon suggests that the negative isotopic excursion in the upper Cryogenian interlude stratigraphy is primary. Carbonate carbon and oxygen isotope values from the Ravensthroat formation in Yukon were previously reported by Macdonald and Cohen (2011) and Macdonald et al. (2013). Here we include an additional section from the Eis Graben section in the northernmost exposure of the Goz Creek area (F1427; Fig. 4) to test correlations and confirm whether the underlying diamictite is the Stelfox Member of the Ice Brook Formation. Carbonate δ 13C values from this section vary from -4.7 to -2.5‰ and δ18O vary from -14.4 to -7.8‰ with broad covariance

between the two. We also report δ 13Ccarb and δ18Ocarb data from an additional section of the Ravensthroat formation from the Tatonduk inlier (F843; Fig. 15). These δ 13Ccarb values range from -2 to 0‰ and δ18Ocarb vary from -9 to -5‰.

6. Geochronology Results 6.1. LA-ICPMS zircon geochemistry Spot geochemical analyses on zircon crystals from samples F837A, F837B, and F837C of member D of the Mount Harper volcanics exhibit overlapping and generally restricted ranges of trace element concentrations (Table S3). Tetravalent (Th, U) and pentavalent (Nb, Ta) cations are lower in concentration than the trivalent (REE + Y) cations, resulting in a clustering toward the Y apex of the ternary diagram in Figure 17. Zircon grains from the Mount Harper volcanics have correspondingly low and restricted Th/Y and Nb/U. These characteristics are consistent with the remarkably high Ti-in-zircon temperatures recorded in the Mount Harper volcanics zircons (795-970°C, mean of 900 ± 40°C) in that they suggest crystallization from hightemperature magmas near the zirconium saturation point, erupted prior to significant incompatible trace element enrichment (Rivera et al., 2014; 2016). By contrast, zircon geochemical compositions from samples F917-1 and F840 (A and B are two samples of the same tuff bed) in the Eagle Creek Formation are distinct from those of the Mount Harper volcanics. Eagle Creek Formation volcanics contain zircons with lower Ti-inzircon temperatures (710-917°C, mean of 815 ± 40°C) and associated higher concentrations of incompatible trace elements (Table S3). Niobium, Ta, U and Th concentrations in Eagle Creek Formation zircon are distinctly higher than zircon from the Mount Harper volcanics, resulting in offsets in both ternary and bivariate diagrams (Fig. 17). Correlated with decreasing temperature,

Th/Y and Nb/U ratios are also more variable and higher, mimicking trends seen in other high silica rhyolite zircons (Rivera et al., 2014, 2016).

6.2 CA-IDTIMS U-Pb zircon geochronology Four samples of the Mount Harper volcanics were dated in this study. As highlighted previously, samples 15PM06 and 15PM08 come from newly recognized exposures of the Mount Harper volcanics (member D) in the far southwestern portion of the Coal Creek inlier (Fig. 9). These exposures consist of light grey to brown welded tuff with distinct flow banding and extensive brecciated rhyolite bodies (Fig. 10). Six zircon crystals from sample 15PM08 yielded concordant and equivalent isotope ratios, with a weighted mean 206Pb/238U date of 718.1 ± 0.2(0.4)[0.8] Ma (MSWD=0.98). This result is interpreted as the igneous crystallization age of the zircons, which approximates the eruption and depositional age of the welded tuff within its uncertainties. Five zircon crystals were analyzed from sample 15PM06, of which four yielded concordant and equivalent isotope ratios with a weighted mean 206Pb/238U date of 718.1 ± 0.3(0.5)[0.9] Ma (MSWD=0.42). This result is indistinguishable from the interpreted age of sample 15PM08, attesting to the rapid rock accumulation associated with volcanism in this period. A single grain from sample 15PM06 gave a statistically younger age of 717.3 ± 0.5 Ma, which we attribute to residual Pb loss (Fig. 18). Samples F837A and F837C also yielded relatively abundant, sharply facetted, prismatic and elongate zircon crystals that exhibit predominantly bright, unzoned or planar-zoned internal luminescence patterns with a late CL-dark zone along crystal tips and faces. Of nine crystals from sample F837A analyzed via CA-IDTIMS, the youngest four yielded a weighted mean 206

Pb/238U date of 717.8 ± 0.2(0.4)[0.8] Ma (MSWD=0.64), which is interpreted as

approximating the eruption age of the rhyolite. The other five crystals gave a range of clearly older 206Pb/238U dates from 718.9 to 720.2 Ma (Fig. 18), which may be recycled antecrysts from earlier eruptives. We view it as less likely that these represent inherited cores within grains given the simple zoning patterns and high Ti-in-zircon temperatures presumably near the zirconium saturation temperatures for these magmas. For sample F837C, three crystals combine to yield a weighted mean 206Pb/238U date of 717.7 ± 0.3(0.5)[0.9] Ma (MSWD=0.29), indistinguishable from the interpreted age of sample F837A. A fourth crystal returned a significantly younger date of 716.1 ± 0.5 Ma, which is interpreted as biased by slight Pb loss. From within the Eagle Creek Formation, sample F917-1 contained a sparse population of small, colorless, euhedral prismatic zircon crystals ranging from equant to highly elongate. CL imagery revealed consistently low luminescence crystals with well-developed oscillatory zoning. Rare homogeneously CL-bright cores are overgrown by these oscillatory-zoned, CL-dark domains. Sixteen crystals were selected for CA-IDTIMS on the basis of CL imagery and laser spot analyses. Two crystals with CL-bright cores yielded the oldest 206Pb/238U dates of 717.9 and 717.4 Ma, and are interpreted as containing inherited cores derived from magmas of the Mount Harper volcanics (Fig. 18); these analyses are not considered further. The remaining 14 crystals with consistently low luminescence and oscillatory zoning produced a range of dates from 717.2 to 701.5 Ma; of these the oldest cluster of zircons ranging in age from 717.2 to 716.4 Ma define a weighted mean 206Pb/238U date of 716.9 ± 0.4(0.5)[0.9] Ma (MSWD=1.5). The scatter to younger dates in the rest of the crystals is attributed to Pb-loss. This interpretation is supported by the fact that a chemical abrasion experiment at higher temperature (200°C versus 180°C) consistently produced older dates, including two reproducible fragments of the same grain (z9a and b). Persistent Pb-loss was also noted for sample F840A of the Eagle Creek Formation (Macdonald et

al., 2010b), and may be related to greater degrees of fluid alteration of these tuffs compared to the holocrystalline rhyolites of the underlying Mount Harper volcanics. Nonetheless, the 716.9 Ma cluster of dates is interpreted as a robust estimate of the eruption and depositional age of the F917-1 tuff.

7. Discussion 7.1. Regional correlations 7.1.1. Rapitan Group Our stratigraphic, geochemical, and geochronological data support the correlation of glacial diamictite and conglomerate of the Rapitan Group from the Mackenzie Mountains through Yukon and into Alaska (Fig. 2). At the Eis Graben section in the Wernecke inlier, the lower Rapitan Group consists of fanglomerate and the upper Rapitan Group consists predominantly of green matrix diamictite that Eisbacher (1981) correlated with the Shezal Formation. A conglomerate unit tentatively correlated with the Rapitan Group is preserved in discontinuous wedges that can be followed south, where it is unconformably overlain by the Mount Profeit dolostone (Fig. 4); however, these conglomerates may have formed in part during Twitya time. We follow the correlation of the upper Rapitan Group at Eis Graben with the Shezal Formation and further document syn-depositional faulting and subsequent fan delta progradation (Eisbacher, 1981; 1985). Similarly, in the Hart River inlier, the lower portion of the Rapitan Group is dominated by conglomerate with minor diamictite, which presumably formed during syn-sedimentary faulting. In the Coal Creek inlier, we have formalized the Eagle Creek Formation, which occurs in an identical stratigraphic position to equivalent undifferentiated strata of the Rapitan Group in

the Tatonduk inlier to the west and the Hart River inlier to the east. The Eagle Creek Formation contains interbedded volcanic rocks and fanglomerates, suggestive of syn-sedimentary tectonism. Additionally, the extreme variation in thickness of the Rapitan Group in the Tatonduk inlier appears to be due to an unconformity in the upper Hay Creek Group that cuts out both the lower Hay Creek Group and the Rapitan Group in some sections (Fig. 15). Near the border of Yukon and NWT, a detrital zircon CA-IDTIMS U-Pb date of 711.34 ± 0.24 Ma was reported from the Sayunei Formation and used to argue that Sturtian glacial deposits in the Mackenzie and Ogilvie Mountains are diachronous (Baldwin et al., 2016). This sample was collected from a cross-bedded hematitic siltstone beneath a thin iron formation, which occurs just below the transition from the Sayunei to the Shezal formations (Baldwin et al., 2016). In the measured section from which this sample was collected, ~200 m of Sayunei Formation strata underlie the collection site and the base of the formation is not exposed. Typically, the Sayunei Formation is several hundreds of meters thick and sits above an unconformity of unknown duration, likely related in parts to both glacioeustatic sea level fall and syn-depositional faulting (Eisbacher, 1981, 1985). Thus, the 711.33 ± 0.25 Ma date is simply a maximum depositional age constraint for the top of the Sayunei Formation and base of the Shezal Formation, entirely consistent with our new and published ca. 717 Ma ages at the base of the Rapitan Group in the Ogilvie Mountains.

7.1.2. Hay Creek Group The base of the Hay Creek Group is highly variable throughout northwest Canada. In the Mackenzie Mountains near Mountain River, the basal Twitya cap carbonate rests on the Shezal Formation and has been dated with Re-Os at 662.4 ± 3.9 Ma (Rooney et al., 2014), which is

within error of dates on other Sturtian cap carbonates globally (Rooney et al., 2015). Locally, this cap carbonate marks the base of a glacioeustatic transgressive sequence tract that culminates in a maximum flooding surface of black shale and is overlain by >1 km of graded sandstone and siltstone beds interpreted as turbidites (Rooney et al., 2014). However, elsewhere in the Mackenzie Mountains, the basal transgressive sequence tract is missing, and sandstone of the Twitya Formation rests unconformably on the Rapitan Group (Turner et al., 2011). At the Eis Graben section in the Wernecke inlier, the cap carbonate is absent and shale of the basal Twitya transgression is condensed to <5 m before the appearance of coarse-grained sandstone in graded beds. Further south these units are entirely absent and the Mount Profeit dolostone rests unconformably on the Rapitan Group and underlying units (Figs. 3 & 4). We correlate the lower Mount Profeit dolostone with the Twitya Formation and the upper Mount Profeit dolostone with the Keele Formation and the non-glacial portion of the Ice Brook and Formations (Fig. 4). In the Ogilvie Mountains, in rare windows below the unconformity and breccia of the upper Hay Creek Group, graded beds of siltstone, sandstone, and limestone overlie the Raptian Group. We broadly correlate these units with the Twitya Formation, but emphasize that the lateral variability in these units complicates more precise correlations and is a clear indication that tectonism in this region continued into the Cryogenian glacial interlude. Stratigraphic relationships in the Goz Creek region of the Wernecke inlier indicate that the Mount Profeit dolostone is a dolomitized equivalent of the Keele Formation, and possibly a portion of the upper Twitya Formation. At these locations, δ 13Ccarb values from the Mount Profeit dolostone are predominantly between 0 and +5‰ with an excursion down to -7‰ near the top of the unit (Fig. 4). These platformal strata can be followed to the north where limestone becomes more dominant in the deeper water facies of the Ice Brook Formation. This partitioning between

dolomitic and limestone facies may be due in part to early dolomitization on the platform, but the presence of fabric-destructive zebra (saddle) dolomite suggests that the Mount Profeit dolostone was also affected by late-stage dolomitization (Vandeginste et al., 2005). Inferentially, the deepwater limestone strata were protected from late-stage fluid flow, as they also preserve primary sedimentary fabrics and more δ 13C variability (Fig. 4). Carbonate δ13C values in the Ice Brook Formation reach up to +8‰ and negative values are preserved in authigenic cements that go down to -20‰. The relative homogeneity in the δ13Ccarb in the Mount Profeit dolostone is likely due in part to dolomitization, as is seen in dolomitized Cryogenian sections in Mongolia (Bold et al., 2016). Independent of the extremely negative δ13C values from the authigenic cements, a large negative carbon isotope excursion is present in well-bedded carbonate rhythmites and ribbonites, normally-graded beds of oolitic grainstone, and dolomitic debrites. A primary origin of this excursion is further substantiated by tight covariance between carbonate and organic carbon (Fig. 4). We correlate this excursion locally with the δ 13C excursion at the top of the Mount Profeit dolostone, negative values at the top of the Keele Formation at Eis Graben (Fig. 4), and the global Trezona δ13C excursion (Halverson, 2006; Hoffman and Schrag, 2002; Rose et al., 2012). Although previous studies have shown either no covariance or weak covariance between δ 13Ccarb and δ13Corg through the Trezona anomaly (Swanson-Hysell, 2010), the tight covariance presented herein is consistent with the conclusion of Johnston et al. (2012) that Cryogenian δ13C excursions are primary features. Eisbacher (1981) suggested that the Mount Profeit dolostone was equivalent with the Twitya Formation because the Keele Formation oversteps the Mount Profeit dolostone in the south. However, Eisbacher (1981) was only referring to the upper conglomerate and

Ravensthroat formation (which was formerly included with the Keele Formation). These units also overlie carbonate of the Keele Formation at Eis Graben. Importantly, the nonglacial Ice Brook Formation interfingers with both the Keele Formation at Eis Graben, where the base of the Keele is defined by carbonate olistoliths (Fig. 5b), and the Mount Profeit dolostone just north of Mount Profeit. Thus, we correlate the upper portion of the Mount Profeit Dolostone with the Keele Formation (Fig. 4 and 19a). Further, carbonates in the olistolith bearing strata record extremely enriched δ13Ccarb values (Fig. 4) that can be correlated with the “Keele peak” (Kaufman et al., 1997; Hoffman and Schrag, 2002; Halverson, 2006). In the Wernecke inlier, the Keele Formation, the non-glacial portion of the Ice Brook Formation, and the Mount Profeit dolostone all culminate with ~20 m of conglomerate (Fig. 4). This upper conglomeratic unit may be associated with the Keele lowstand wedge (Day et al., 2004). At Eis Graben, the upper conglomeratic unit is overlain by diamictite that we correlate with the Stelfox Member of the Ice Brook Formation, which is in turn overlain by dolomite of the Ravensthroat formation. Elsewhere in the Wernecke inlier, the Ravensthroat formation sits on the upper conglomeratic unit and no diamictite is preserved. Throughout Yukon, Marinoan glacial deposits are either absent or thin. Along with the diamictite in the Eis Graben locality of the northern Wernecke Mountains (F1427), minor occurrences of the end-Cryogenian diamictite occur in the southern exposures of the Tatonduk inlier. Otherwise the upper Hay Creek Group in Yukon is dominated by dolostone breccia (L11), which appear to include clasts of the Ravensthroat formation. In the Coal Creek and Tatonduk inliers, these dolostone breccias are commonly overlain by thin-bedded dolostones with ‘sheetcrack’ cements that are locally present in the Ravensthroat formation in the Mackenzie Mountains (Hoffman and Halverson, 2011), and globally present above ca. 635 Ma Marinoan

glacial deposits (Hoffman and Macdonald, 2010). Given that these breccias also fill erosional lows, presumably related to end-Cryogenian glaciation, we regard them as latest Cryogenian to basal Ediacaran in age, potentially related to syn-depositional tectonism.

7.2. Tectonostratigraphy The map relationships, nature of sedimentation, and the stratigraphic correlations documented above suggest that Cryogenian units in the Yukon were deposited during the generation of significant topography. In the Wernecke inlier, a major structural high developed in latest Tonian to Cryogenian time coincident with the development of contractional structures in the Corn Creek orogeny (Thorkelson et al., 2005), which folded strata of the Mackenzie Mountains Supergroup. These structures are unconformably overlain by diamictite and conglomerate of the Rapitan Group and the Mount Profeit dolostone (Figs. 3 and 4). Carbon isotope chemostratigraphy through the youngest folded strata, which were deposited in a relatively deepwater environment, preserve a profile that rises from ~ -2 to +5‰ (Fig. 4), consistent with correlations with the Stone Knife Formation (formerly Basinal assemblage) of the lower Little Dal Group (Halverson, 2006; Long and Turner, 2013). Assuming deformation occurred after deposition of the Little Dal Group, which formed between ca. 900-790 Ma ( Macdonald et al., 2010b, 2012; van Acken et al., 2013), Corn Creek folding occurred sometime after ca. 790 Ma but before or during deposition of the ca. 717-660 Ma Rapitan Group. The Corn Creek faults consist of two sets that appear to be syn-kinematic: north-south striking, west-vergent, thrust faults and east-west striking high-angle faults. The high-angle faults have predominantly right-lateral displacement and appear to be tear faults accommodating the thrusting of structurally deeper units in the northern portion of the map area (Fig. 3), consistent

with left-lateral wrenching (Wilcox et al., 1973; Christie-Blick and Levy, 1989) and counterclockwise rotation of the Yukon block relative to autochthonous Laurentia (Eyster et al., 2016). This fault system evolved into an extensional to transtensional regime during Rapitan to early Hay Creek deposition with the opening of the Snake River Basin (Baldwin et al., 2016). The Corn Creek structures are unconformably overlain by fanglomerate wedges that taper to the north off of east-west high-angle faults at Eis Graben and to the south off of east-west high-angle faults at Mt. Profeit (Figs. 3 and 19a). The termination of the Shezal Formation along the synsedimentary normal fault on southern margin of Eis Graben suggests that this structure is a relict fragment of the northwestern boundary of the Snake River Basin during Rapitan time (Fig. 19a). Taken together, the data presented here suggest that down-to-the-northeast faults stepped back to the southwest during Twitya and Keele time creating a trough that accommodated the olistolithbearing, non-glacial portion of the Ice Brook Formation (Figs. 4 and 19a). A paleo-high on the footwall progressed from northeast to southwest, culminating with the upper Mt. Profeit dolostone, which was the source of redeposited carbonate preserved in the Ice Brook Formation (Eisbacher, 1981). This trough was filled during the Keele low-stand (Day et al., 2004), resulting in deposition of the coarse wedge of conglomerate at the top of the Mt. Profeit dolostone, which can be followed through the top of the Ice Brook Formation in the trough to the top of the Keele Formation at Eis Graben (Fig. 4). During the Marinoan glaciation, additional space was created in the northeast towards the Snake River Basin, accommodating the Stelfox Member of the Ice Brook Formation (Fig. 19a). A similar tectono-stratigraphic history of pre-Cryogenian transtension, syn-Rapitan extension, and a syn-Hay Creek basin reorganization is recorded in the other Proterozoic inliers in the Ogilvie Mountains. Narrow, left lateral strike-slip basins were created during deposition of

the Mount Harper Group (Strauss et al., 2015), which possibly persisted through deposition of the Eagle Creek Formation (Fig. 19b). It is not clear if this motion continued during deposition of the lower Hay Creek Group in the Ogilvie Mountains because much of the lower Hay Creek Group is cut out beneath sedimentary breccias (L11) of the upper Hay Creek Group. We attribute the breccias below and within the basal Ediacaran cap carbonates throughout the Yukon to extensive subaerial exposure associated with a combination of glacioeustatic sea level fall and local tectonic uplift (Fig. 19b), potentially related to glacio-isotstatic uplift. That is, although there was certainly a major regression during the Marinoan glaciation, rapid facies changes in the Hay Creek Group, and profound unconformities below the breccias are also suggestive of syndepositional faulting. Although this episode of ‘Hayhook extension’ resulted in local basin formation in the Wernecke inlier, where there is abundant evidence of syn-sedimentary faulting, including massive olistostromes, we expect that paleo-highs were also generated elsewhere in the Yukon. If these structures formed during the ~55° counterclockwise rotation of the Yukon block (Eyster et al., 2016), local transtension near the Snake River Fault associated with the opening of the northern Snake River Basin may have resulted in local transpression in the Ogilvie Mountains. Cryogenian basin formation and unconformities in the Yukon described here have been previously noted in part by Eisbacher (1981) and are broadly equivalent to the ‘Hayhook extensional event’ described in the NWT (Young et al., 1979; Aitken, 1991a; Young, 1995; Turner, 2011). In both the Yukon and the NWT, the earliest manifestation of Hayhook extension (transtension?) occurred in the Tonian period, with basin formation and deposition of the correlative Coates Lake and Mount Harper groups between ca. 775 and 717 Ma (Jefferson and Parrish, 1989; Strauss et al., 2015). Faulting continued in the Yukon during deposition of the

Rapitan Group, between 717 and 660 Ma, as has been previosly described in the NWT (Eisbacher, 1985). Here we have further documented unconformities in the Yukon that developed during the early portion of the post-660 Ma Cryogenian non-glacial interlude; these are broadly equivalent to unconformities previously described at the base of the Twitya Formation in the Mackenzie Mountains (Turner et al., 2011). We have also better constrained the timing of syn-sedimentary tectonism and the emplacement of olistoliths in the Wernecke Mountains by demonstrating synchroneity with the “Keele peak” and Trezona δ13Ccarb excursion (Kaufman et al., 1997; Hoffman and Schrag, 2002; Halverson, 2006), which can be correlated with the non-glacial portion of the Ice Brook Formation (Aitken, 1991a; Aitken, 1991b). In the western Yukon, syn-sedimentary faulting continued through the Marinoan glaciation, and potentially into basal Ediacaran strata. Thus, topography developed throughout the Cryogenian in the NWT and Yukon in at least four distinct events, and perhaps continually, that were manifested in a series of overlapping unconformities. An appreciation of the profound effects of syn-depositional tectonism on the stratigraphic framework provides important context for any attempt at interpreting the dynamic Cryogenian depositional environments of the Yukon.

7.3. Depositional environments 7.3.1. Glacigenic facies Glacially-influenced facies from this study consist of massive- and thin-bedded matrixsupported diamictite (L1 and L2) that are commonly interbedded with conglomerate, sandstone/grainstone, siltstone, shale (L3-L6) and various allochems (L7-L10). A glacigenic origin for the diamictite facies (L1 and L2) is inferred for matrix-supported deposits with multiple clast lithologies, but confirmed where striated clasts, dropstones within hemipelagic

facies, ice till pellets and/or plow structures are preserved. These diamicite facies are very poorly-sorted, with sub-rounded to sub-angular boulder- to gravel-sized clasts of the underlying units and a highly variable clast to matrix ratio. The massive diamictite facies (L1) are commonly associated with shear fabrics, soft-sedimentary folding, and scour surfaces and are interpreted to have formed as lodgement tills, till tongues, and glacigenic debris redeposited by gravity-driven mass wasting downslope from the ice grounding line (Evans et al., 2006). The stratified diamictite facies (L2) are commonly normally-graded with lamination-penetrating lonestone clasts and are interpreted as either melt-out till or till that was periodically reworked by currents during oscillating grounding-line conditions (Domack and Hoffman, 2011). The glacigenic diamictites are commonly interbedded with clast-supported conglomeratic facies (L3) that are preserved in wedge-shaped geometries and inferred to have been deposited primarily by gravity driven processes on submarine fan deltas, as well as mudstone and grainstone rhythmites that, based on associations with glacigenic facies (L1 and L2), likely record ice-distal turbidites. Conglomerate beds that exhibit channel-form basal geometries and multiple generations of erosion and channel-fill, such as above ~260 m in section T1401 (Eagle Creek Formation), are interpreted to record either fluvial or submarine channel proglacial deposits resulting from increased meltwater flux on glacial out-wash fans during global deglaciation (Lønne, 1995). Glacigenic facies (L1 and L2) that contain dropstones and striated clasts have been found in all four of the Proterozoicinliers in Yukon. As described above, the bounding units and existing geochronological constraints suggest these are dominantly Sturtian (ca. 717-660 Ma in age), with rare occurrences of Marinoan glacigenic deposits at Eis Graben in the Wernecke inlier and at Pass Creek in the Tatonduk inlier. Commonly, the Marinoan glaciation in the Yukon is represented by exposure surfaces and rubble breccia (L11). The Sturtian and Marinoan glacial

horizons are separated by mixed carbonate-siliciclastic strata (L3-L13) of the Hay Creek Group that were deposited in a variety of environments that reflect rapidly changing basin configurations related to ongoing rotation of the Yukon block.

7.3.2. Rapitan Group In the northernmost exposures of the map area (Eis Graben; Fig. 3), ~460 m of conglomerate and immature sandstone of the Rapitan Group are interbedded with matrixsupported diamictite and rest below massive diamictite of the Shezal Formation (Eisbacher, 1981). We correlate this conglomerate with >500 m of conglomerate that rests below the Mount Profeit dolostone south of Mount Profeit (Fig. 4). The position of the conglomeratic unit below the Shezal Formation, and the presence of jaspillitic chert clasts, presumably derived from the Sayunei Formation, suggests that the conglomerate was deposited during or after deposition of the Sayunei Formation. These fanglomerates are interpreted to have formed by gravity flow processes on prograding submarine to subglacial fan deltas adjacent active fault scarps. The conglomerates indicate that considerable local topography was generated along the ancestral Snake River fault during deposition of the Sayunei Formation in the Snake River Basin (Baldwin et al., 2016). This syn-Rapitan tectonism may have contributed to the development of a restricted or silled glaciomarine basin, which has been invoked as a necessary condition for the deposition of iron formation during the Sturtian glaciation (Ashkenazy et al., 2013; Baldwin et al., 2016). In both the Coal Creek and Hart River inliers of Yukon, glacial lithofacies of the Rapitan Group and Equivalent Eagle Creek Formation preserve evidence for deposition near an ice grounding line in the form of massive lodgment tills, till sheets, and till tongues with glacial plow structures, internal shear structures, and soft-sediment deformation. In the Hart River

inlier, thick accumulations of massive diamictite with laterally tapering stratal geometries on the scale of 102–103 m are interpreted to represent lodgement tills deposited along the ice grounding line. Other glacial lithofacies of the Rapitan Group preserve evidence for distal depositional settings with respect to an ice grounding line, in the form of graded turbidite rhythmites and hemipelagites with interbedded glacigenic debris flows and abundant bed-penetrating dropstones that are interpreted as ice rafted debris, along with less common ice till pellets and striated clasts. Importantly, it is difficult to discern if these deposits were formed in a sub-ice shelf environment or in an open water environment distal to a receding ice margin. Although the numerous dropstones in the Rapitan Group and a microbialaminated dolostone bed in the Eagle Creek Formation may suggest ice breakup and at least a temporary open water environment, elaborate modern sub-ice microbial mat communities and stromatolites have been described in Antarctic subglacial lakes (Mackey et al., 2015; Sumner et al., 2016). The generation of dropstones does not necessarily imply glacial termination, but rather, the presence of dynamic ice that flows, which is predicted throughout the Snowball state (Goodman and Pierrehumbert, 2003). The regional distribution of clast and matrix composition within the Rapitan Group, as well as paleoflow measurements (Mustard and Roots, 1997) and soft sediment deformation vergence in massive diamictite facies, indicate that yellow- to grey-weathering carbonate matrix conglomerates were sourced from active fault scarps to the north and that siliciclastic and volcanic facies were sourced from glacial erosion of the MHVC along the Harper fault to the south (Mustard and Roots, 1997). Although we have not identified the original northern fault scarps, the coarse-grained nature of these deposits implies proximal sedimentation. In the Tatonduk inlier, iron-bearing stratified diamictite (L2) has previously been correlated with the Sayunei Formation of the Rapitan Group (Young, 1982; Klein and Beukes,

1993) . Due to the lack of lateral exposure, it is unclear if this isolated iron formation formed in a separate tectonically active sub-basin. The predominance of stratified diamictite in the Tatonduk inlier suggests a relatively deep-water sedimentary environment relative to the ice grounding line at the other inliers.

7.3.3. Hay Creek Group Cryogenian carbonate lithofacies in the Wernecke inlier include platformal dolostones of the Mount Profeit dolostone and clastic carbonates of the Ice Brook Formation that were reworked and redeposited from underlying strata. The Mount Profeit dolostone preserves exquisite giant ooids, microbial mounds with clotted fabrics, and stromatolites in places; however, detailed facies analysis is precluded by extensive zebra dolomitization (saddle dolomite; L13), which obliterates primary depositional features (Vandeginste et al., 2005). Carbonate strata of the Ice Brook Formation in the Wernecke Mountains consist of both limestone and dolostone that was derived from the Mount Profeit dolostone to the south and Keele Formation to the north. The Ice Brook Formation includes carbonate-clast breccias interpreted as debris flows and olistoliths that are hundreds of meters across and locally associated with slump folds, suggestive of local slope failure and the development of mass transport complexes. Excluding the debris flows, carbonate strata of the Ice Brook Formation consist predominantly of normally-graded lime mudstone and calcisiltite with occasional redeposited ooids, all of which are consistent with derivation from the Mount Profeit carbonate platform (Fig. 19). Eisbacher (1981) measured slump folds verging to the northeast in the Ice Brook Formation, which he interpreted to reflect a paleo-high near Mount Profeit.

Siliciclastic strata of the Ice Brook Formation preserve hundreds of meters of normallygraded beds displaying Bouma B-E cycles with flutes, dewatering structures, and slump folds. These units are interpreted to record the development of a deep, narrow, turbidite-dominated intra-platformal sub-basin that funneled sediment southeast to the Selwyn Basin. In contrast to the northeast vergence of the slump flows, flute casts within the turbidites record southeast paleoflow (Eisbacher, 1981). We agree with Eisbacher (1981) that the Mount Profeit dolostone likely formed on a paleo-high creating a local northeast-deeping slope orthogonal to a broader northwest-southeast oriented (present coordinates), narrow, intra-platformal sub-basin. We suggest this local topography was generated as a pull-apart basin (Burchfiel and Stewart, 1966) during sinistral displacement and counterclockwise rotation. Marinoan age (ca. 645-635 Ma) glacial lithofacies in Yukon are limited to a wedge of massive diamictite at the Eis Graben locality in the Wernecke Mountains and conglomerate and diamictite at the Pass Creek locality in the Tatonduk inlier that consist of weakly-bedded and graded massive till. The Eis Graben deposits are interpreted to have formed along the grounding line as a lodgement till, whereas the abundant graded beds interbedded with massive diamictite at Pass Creek suggest these formed as glacigenic debris flows (Young, 1982). Elsewhere in Yukon, evidence for the younger Marinoan glaciation is represented by prominent exposure surfaces and massive breccias and evidence of extensive erosion and subaerial exposure including abundant dolomite and silica cements. We attribute this surface to a combination of regional uplift related to the Cryogenian counterclockwise block rotation of the Yukon (Eyster et al., 2016), glacioeustatic sea-level fall, and subsequent glacio-isostatic rebound. The Marinoan cement-dominated breccias are overlain by dolomite of the Ravensthroat formation and black shale of the Sheepbed Formation, which together are interpreted to record a significant basal

Ediacaran glacioeustatic transgression (James et al., 2001; Hoffman and Halverson, 2011; Macdonald et al., 2013b).

7.4 Geochronology and timing of the Sturtian glaciation in Yukon The geochronology presented reinforces the conclusion that the Sturtian glaciation, as recorded in Yukon, began between 717.5 and 716.5 Ma (Macdonald et al., 2010). Previously it was unclear if zircon crystals in the syn-Eagle Creek Formation tuffs (possibly equivalent with Mount Harper volcanics member F) were inherited from members D and E of the Mount Harper volcanics and variably biased by residual Pb-loss, leaving open the timing of glaciation as possibly younger than 716.5 Ma. Here we demonstrate that the pre- and syn-glacial eruptions are distinct both in chemistry, as manifested in zircon thermometry and chemical compositions (Fig. 17), and time (Table 3). High-temperature, low incompatible trace element compositions for zircon from members D and E of the Mount Harper volcanics are consistent with whole rock geochemistry and hot, anhydrous rhyolite eruptives within a bimodal volcanic suite (Mustard and Roots, 1997; Cox et al., 2013). Recent work on high-silica rhyolites of the Yellowstone Volcanic Field illustrates the fidelity with which zircon compositions can record the progressive cooling and differentiation of a magma body (Fig. 17; Rivera et al., 2016). The restricted and high range of crystallization temperatures for the Mount Harper volcanics suggests that these rhyolites were arrested in their liquid line of descent by eruption. By contrast, the tuffs in the Eagle Creek Formation record distinctly more evolved, lower temperature zircon compositions, and are certainly not inherited or reworked grains from the underlying Mount Harper volcanics (Fig. 17). The contrasting maximum crystallization temperatures of the Mount Harper and Eagle Creek

zircons suggest somewhat different primary magma compositions and zirconium saturation temperatures for the two eruptive suites. Experiments with chemical abrasion also lend confidence to the interpretation of the oldest cluster of dates in both Eagle Creek Formation tuffs (716.5 ± 0.2 Ma in sample F840A, and 716.9 ± 0.4 Ma in sample F917-1) as representing the eruption and depositional age of those strata. Higher chemical abrasion temperatures yield more reproducibly older and more concordant ages. New work thus affirms the results of Macdonald et al. (2010b) in reproducing via independent samples the younger ages (716.5 to 716.9 Ma) for the Eagle Creek Formation tuffs versus older ages for the Mount Harper volcanics (717.4 to 718.1 Ma). Furthermore, the identification of subaerial textures in member E of the Mount Harper volcanics, above the dated flows (Figs. 10 and 11), supports our interpretation that the new and old ages from Member D predate the glacial onset. Although it is possible that glaciation had already begun and was manifested in a subaerial exposure surface before the growth of local ice sheets, we find no local evidence for glaciation prior to 717 Ma. A 717 Ma onset for the Sturtian glaciation is consistent with current geochronological constraints from the oldest glacial deposits in the Windermere Supergroup elsewhere in the Cordillera. The 711.34 ± 0.24 Ma date (CA-IDTIMS U-Pb zircon) from the Sayunei Formation in the Mackenzie Mountains is from a detrital sample hundreds of meters above the base of the Rapitan Group (Baldwin et al., 2016) and occurs below the Rapitan iron formation. Whereas this age provides a useful maximum constraint on the timing of iron formation deposition, it does not provide new constraints on the timing of Rapitan glaciation. At Gataga Mountain, in northern British Columbia, the Gataga Volcanics are interbedded with glacial diamictite, and have been dated between 696.2 ± 0.2 and 690.1 ± 0.2 Ma (CA-IDTIMS U-Pb zircon; (Eyster et al., 2017;

Ferri et al., 1999), providing synglacial constraints. A maximum age constraint on the diamictite at Gataga Mountain is provided by a 735.8 ± 0.6 Ma date (CA-IDTIMS U-Pb detrital zircon) from an underlying sandstone unit with herringbone cross-stratification and mud-cracks interpreted to represent non-glacial conditions (Eyster et al., 2017). In Idaho, Keeley et al. (2013) report a maximum depositional age of 685.5 ± 0.4 Ma for a volcaniclastic diamictite with cobble-sized clasts within the ‘lower diamictite’ unit of the Scout Mountain Member of the Pocatello Formation in southeastern Idaho. More recently, Isakson et al. (2016) reported the first true pyroclastic depositional ages of ~697 Ma for pyroclastic ash flow tuffs also preserved within the lower diamictite unit at Scout Mountain. Taken together these ages suggest that the lower diamictite of the Pocatello Formation records the latter portion of the Sturtian glaciation; the base of the Pocatello Formation is fault-bounded and thus correlative strata to the basal Sturtian in Yukon are apparently missing from these Idaho successions. A ca. 717 Ma onset for the Sturtian glaciation is also consistent with current geochronological constraints from South China (Lan et al., 2014; 2015), Arabia (Bowring et al., 2007), and Arctic Alaska (Cox et al., 2015). That is, we find no evidence of glaciation globally prior to 717 Ma (Rooney et al., 2015). The more precise ages presented herein facilitate future studies that explore the cause of the onset of the Sturtian glaciation and possible links to other changes in the Earth system, such as the emplacement of the Franklin large igneous province (LIP). Current age constraints on the Franklin LIP are too coarse to distinguish if the onset of the Sturtian glaciation lags by millions of years, more consistent with the basalt- weathering hypotheses (Godderis et al., 2003; Rooney et al., 2014; Cox et al., 2016), or is precisely coincident, which is more consistent with an increase in planetary albedo resulting from the emission of sulfur aerosols to the stratosphere during multi-year to decadal fire fountain

eruptions (Macdonald and Wordsworth, 2017). Future geochronology on the Franklin LIP should be able to distinguish between these hypotheses.

7.5. Recommendations for a Cryogenian Global Boundary Stratotype Section and Point Here we present a type section for the Eagle Creek Formation (Figs. 9, 11 and 13A; Table 2) and propose three potential locations for the Cryogenian Global Stratotype Section and Point (GSSP) in Yukon. The Coal Creek inlier is a suitable location for the basal Cryogenian GSSP because it contains important fossil assemblages and Re-Os geochronological constraints in the underlying Callison Lake Formation (Strauss et al., 2014a), the global Islay negative carbon isotope excursion (Strauss et al., 2014a), paleomagnetic constraints (Eyster et al., 2016), and the most robust geochronological framework of any early Cryogenian succession (Macdonald et al., 2010; this paper). Relative to most of Yukon, the Coal Creek inlier is accessible with a short, ~30 minute helicopter ride from Dawson, Yukon, which can be reached by commercial airline from Vancouver, Canada. Three candidate GSSPs are the Tango Tarn section (Figs. 9, 11 and 13A), the Green Shelter section (Figs. 9, 11 and 13B), and the northwestern Mine Camp section (Figs. 9, 11 and 13C). Although the geochronological constraints are from the Tango Tarn section, exposure is largely on a cliff face that is complicated by faults, and the section does not have a stratigraphic top. The Green Shelter section has both a top and a bottom, lacks tectonic complications, and is relatively easy to traverse; however, a drawback of this section is the lack of continuous exposure. The northwestern Mine Camp section (T1401) is the thickest and best exposed, but it also does not have a stratigraphic top and facies represent one endmember dominated by dolostone-matrix conglomerate and diamictite with no volcanic influence. Although the volcanic units that underlie the Eagle Creek Formation preclude many types of

sedimentary geochemical and micropaleontological measurements that could be made in sedimentary strata, they are ideally suited for geochronological and paleomagnetic studies, which are two criteria for defining the base of the Cryogenian with the onset of the first appearance of low-latitude glacial deposits.

8. Conclusion Cryogenian strata in Yukon, Canada, host key geochronological constraints on the start of the Cryogenian Period and the onset of the Sturtian Snowball Earth glaciation at ca. 717 Ma. Geological data presented herein substantiate regional correlations of the Rapitan Group throughout Yukon and into the Mackenzie Mountains of NWT; however, glacial facies and correlations are greatly complicated by syn-sedimentary Tonian–Ediacaran tectonism in northwestern Canada. We also present five new U-Pb CA-IDTIMS zircon dates that refine the onset of the Sturtian glaciation in northwestern Canada to between 716.9 ± 0.4 and 717.4 ± 0.2 Ma. Because of the importance of these ages for defining the base of the Cryogenian Period, we propose a GSSP at the base of the Eagle Creek Formation at the Green Shelter section in the Coal Creek inlier of the Ogilvie Mountains, Yukon, Canada.

FIGURES Figure 1. Location map of Proterozoic inliers in northwestern Canada adapted from Strauss et al. (2015). N.W.T.–Northwest Territories.

Figure 2. Schematic lithostratigraphic correlation of Cryogenian and bounding strata in Yukon, Canada. Cryo.–Cryogenian; H.C.–Hay Creek Group; Rap.–Rapitan; P.C.–Pleasant Creek

volcanics; E.C.–Eagle Creek Formation; Fm–Formation; L.D.–Little Dal Group; MMSG– Mackenzie Mountains Supergroup; Cu-cap–Copper Cap Formation; Thund.–Thundercloud Formation; T.S.–Ten Stone Formation; S.S.–Snail Spring Formation. Geochronology from Jefferson and Parrish (1989), Macdonald et al. (2010), Strauss et al. (2014a), Rooney et al. (2014; 2015), Baldwin et al., (2016), Milton et al. (2017), and this paper.

Figure 3. Geology of the Goz Creek region of the Wernecke Mountains, eastern Yukon. Mapping based on previous work by Thorkelson (2000) and Thorkelson et al. (2005) with updates from the authors over the summers of 2008-2014. Stratigraphic sections discussed in the text and plotted on Figure 4 are depicted as red lines with accompanying section numbers.

Figure 4. Cryogenian stratigraphy of the Goz Creek region of the Wernecke Mountains, eastern Yukon, along with proposed correlations, supported by mapping, sedimentological analyses, and chemostratigraphy. Locations of measured sections shown in Figure 3. Note that diamictite matrix lithology is used for width in the stratigraphic columns. Carbonate lithofacies of the Keele Formation are undifferentiated.

Figure 5. Selected photographs of Cryogenian lithofacies from the Goz Creek region of the Wernecke Mountains, eastern Yukon. A) Conglomerate of the lower Rapitan Group at 85 m in section T1408 at Eis Graben, which contains jaspelitic chert clasts possibly derived from the Sayunei Formation. Mechanical pencil for scale. B) Carbonate olistoliths at the Twitya-Keele transition at Eis Graben, below section F1427. C) Massive diamictite of the Stelfox Member, Ice Brook Formation at Eis Graben (F1427). D) Distal tongue of Mount Profeit dolostone overlain

by olistolith bearing Ice Brook Formation, looking north from section F1228, geologist circled in red for scale. E) Olistoliths at the base of the Ice Brook Formation (F1228), geologist for scale. F) Fault repitiation of lower Mount Profeit dolostone and Ice Brook Formation looking north at sections F851 and W8 with giant olistolith near top of section F851. G) Redeposited giant ooids and coated grains near the base of the Ice Brook Formation (F1228), Canadian dollar for scale. H) Cliff of >500 m of brown-weathering Rapitan (?) conglomerate overlain with the Mount Profeit dolostone (F853 and F854), and dolomite of the basal Ediacaran Ravensthroat formation (F855), looking southeast from near Mount Profeit.

Figure 6. Geology of the Hart River inlier, central Ogilvie Mountains, Yukon, modified from Strauss et al. (2015). Thick lines are fault contacts, thin lines are depositional contacts, and dashed lines are inferred. Stratigraphic sections discussed in the text and plotted on Figure 7 are depicted as red lines with accompanying section numbers.

Figure 7. Cryogenian stratigraphy of the Hart River inlier, central Ogilvie Mountains, Yukon. Locations of measured sections shown in Figure 6. Note that diamictite matrix lithology is used for width in the stratigraphic column.

Figure 8. Selected photographs of Cryogenian stratigraphy in the Hart River inlier, central Ogilvie Mountains, Yukon. A) Interbedded maroon siliciclastic matrix diamictite and yellow dolomite matrix diamictite of the Rapitan Group looking west along cliff-face of section F936, m stick for scale; B) Rapitan Group maroon siliciclastic matrix diamictite with a clast of dolostone (F936), Canadian quarter for scale; C) Striated clast in the Rapitan Group (F936), Canadian

quarter for scale; D) Tapering wedge of dark grey massive diamictite facies of the Rapitan Group, outlined with dashed line, looking east from section F936, geologist circled for scale; E) North-verging glacial plow structure (F936), outlined with dashed line, looking southeast, geologist for scale.

Figure 9. Geology of the Coal Creek inlier, western Ogilvie Mountains, Yukon, after Strauss et al. (2014b) and references therein. Thick lines are fault contacts, thin lines are depositional contacts, and dashed lines are inferred. Stratigraphic sections discussed in the text and plotted on Figures 10 and 11 are depicted as red lines with accompanying section numbers that are plotted east-west along the A-A’ cross-section and north-south along the B-B’ cross-section, respectively.

Figure 10. Volcanic stratigraphy of the Mount Harper volcanics and Rapitan Group in the Coal Creek inlier of Yukon. Locations of measured sections shown in Figure 9 along the A-A’ crosssection.

Figure 11. Cryogenian stratigraphy of the Coal Creek inlier, Yukon. Locations of measured sections shown in Figure 9 along the B-B’ cross-section. Note that diamictite matrix lithology is used for width in the stratigraphic columns.

Figure 12. Selected photographs of Cryogenian lithofacies in the Coal Creek inlier of the Western Ogilvie Mountains, Yukon. A) Pahoehoe textures in Member B of the Mount Harper volcanics at Mount Harper; B) Clast-supported, normally-graded beds of conglomerate (F3) from

section T1401 of the Eagle Creek Formation, mechanical pencil for scale; C) Green laminated volcaniclastic siltstone facies interbedded with carbonate conglomerate of the Eagle Creek Formation at Mine Camp (F1013), hammer for scale; D) Graded beds of grainstone (facies F9) within the Eagle Creek Formation, from 30.5 m in section T1401, mechanical pencil for scale; E) Bed-penetrating dolomite clast dropstone in laminated shale at 27 m in section T1401 of the Eagle Creek Formation; F) Massive dolomite boulder clast dominated diamictite of the Eagle Creek Formation at Mine Camp (F1010), geologist for scale; G) Ice pellet in stratified diamictite facies of the Eagle Creek Formation at Mine Camp (F1013), Canadian quarter for scale; F) Striated quartzite clast at Mine Camp (F1013), Canadian quarter for scale.

Figure 13. Photos of key sections of the Eagle Creek Formation in the Coal Creek inlier. Blue lines are faults, white lines are contacts, and red lines are measured stratigraphic sections. A) Tango Tarn looking northwest at sections F840, F917, and F924. B) Composite type section of the Eagle Creek Formation (F918-F920) and proposed GSSP looking southwest. Locations of measured sections shown in Figure 9 with stratigraphic log in Figure 11. C) Mine Camp looking north at section T1401.

Figure 14. Geology of the Tatonduk inlier, western Ogilvie Mountains, Yukon and Alaska. Mapping based on compilation by van Kooten (1997) with updates from the authors over the summers of 2007-2013. Stratigraphic sections discussed in the text and plotted on Figure 15 are depicted as red lines with accompanying section numbers that are plotted north-south along the A-A’ cross-section. Thin grey lines mark internal stratigraphic contacts.

Figure 15. Cryogenian stratigraphy of the Tatonduk inlier, western Ogilvie Mountains, Yukon and Alaska. Locations of measured sections shown in Figure 13. Note that diamictite matrix lithology is used for width in the stratigraphic columns. 15–Fifteenmile Group; PCV–Pleasant Creek volcanics; HC–Hay Creek Group.

Figure 16. Selected photographs of Cryogenian stratigraphy in the Tatonduk inlier. A) Striated clast from the Rapitan Group at the Tatonduk River section, U.S. quarter for scale; B) Dropstone in hematitic siltstone of the Rapitan Group from Tatonduk River section, pocketknife for scale; C) Tatonduk River section of the Rapitan Group, backpack for scale, looking downstream to the west at the north bank; D) Rapitan Group at Hard Luck Creek (T702) with boulder-sized clasts weathering out and ironstone on dipslope; E) Normally-graded siliciclastic beds and minor carbonate of Hay Creek Group at Pass Creek (T710), geologist for scale; F) Conglomerate of Hay Creek Group at Pass Creek (T710) with ironstone clasts of Rapitan Group; G) Dolomite of the basal Ediacaran Ravensthroat formation with sheetcrack cements near the international border (T708).

Figure 17. Zircon geochemistry from Mount Harper volcanic (F837A, F837B, F837C) and Eagle Creek Formation (F917-1, F840A, F840B) tuff samples. Illustrated for reference are zircon compositions from the Huckleberry Ridge and Mesa Falls Tuffs of the Yellowstone Volcanic Field, which exhibit consistent down-temperature differentiation trends from zirconium saturation through to eutectoid crystallization and eruption (Rivera et al., 2016).

Figure 18. Concordia diagrams illustrating U-Pb CA-IDTIMS zircon dates from samples 15PM06, 15PM-08, F837A, F837C, and F917-1. Sample locations are shown in Figure 9. Stratigraphic position of samples shown in Figures 10 and 11.

Figure 19. A) Schematic north-south cross-section of the Wernecke inlier between Mount Profeit and Eis Graben, restored to the 635 Ma surface at the base of the Ravensthroat formation with a gentle slope towards the Snake River Basin. B) Schematic north-south cross-section of the Coal Creek inlier between Bald Hill and Mine Camp, restored to the 635 Ma surface at the base of the Ravensthroat formation. Dips on faults are largely inferred due to common later reactivation.

TABLES Table 1. Lithofacies description Table 2. Formalization of the Eagle Creek Formation Table 3. Summary of U-Pb zircon ages

SUPPLEMENTARY MATERIALS Table S1. Geochemistry data tables Table S2. LA-ICPMS trace element concentrations in zircon Table S3. LA-ICPMS U-Pb isotope ratios and apparent ages in zircon Table S4. CA-IDTIMS U-Pb isotope ratios and apparent ages in zircon

ACKNOWLEDGMENTS

This contribution is dedicated to Dr. Charlie Roots, a dear friend, colleague, and constant life inspiration. We acknowledge financial support through National Science Foundation grants EAR-1148499 and EAR-1148058 (Sedimentary Geology and Paleobiology), NASA NAI MIT Node, and the Yukon Geological Survey (YGS). Maurice Colpron accompanied JVS, PM, and JC to collect the 2015 Mount Harper sample suites, and the YGS is thanked for their encouragement and logistical support. JVS and PM thank the Undergraduate Advising and Research (UGAR) Program and the Department of Earth Sciences at Dartmouth College for financial support. We thank Dan Schrag for use of the Harvard University Laboratory for Geochemical Oceanography, and Dave Johnston, Lyle Nelson, and Eben Hodgin for help with geochemical measurements. We thank Trevor Petach, Andrey Bekker, Sierra Petersen, Emmy Smith, Marcus Kunzmann, Malcom Hodgskiss, Sarah Wördle, and Viv Cumming for help in the field.

REFERENCES CITED Abbott, G., Implications of probable late Proteorozoic dextral strike-slip movement on the Snake River fault, in Proceedings Slave-Northern Cordillera Lithosphere Experiment, Lithoprobe Report #501996. -, 1997, Geology of the Upper Hart River Area, Eastern Ogilvie Mountains, Yukon Territory (116A/10, 116A/11): Exploration and Geological Services Division, Yukon Region, Bulletin 9, p. 1-76. Aitken, J. D., 1991a, The Ice Brook Formation and Post-Rapitan, Late Proterozoic glaciation, Mackenzie Mountains, Northwest Territories: Geological Survey of Canada Bulletin, v. 404, p. 1-43. Aitken, J. D., 1991b, Two late Proterozoic glaciations, Mackenzie Mountains, northwestern Canada: Geology, v. 19, no. 5, p. 445-448. Aitken, J. D., and McMechan, M. E., 1991, Middle Proterozoic assemblages, Chapter 5, in Gabrielse, H., and Yorath, C. J., eds., Geology of the Cordilleran Orogen in Canada, Volume 4, Geological Survey of Canada, p. 97-124. Ashkenazy, Y., Gildor, H., Losch, M., Macdonald, F. A., Schrag, D. P., and Tziperman, E., 2013, Dynamics of a Snowball Earth ocean: Nature, v. 495, no. 7439, p. 90-93.

Aspler, L. B., Pilkington, M., and Miles, W. F., 2003, Interpretations of Precambrian basement based on recent aeromagnetic data, Mackenzie Valley, Northwest Territories: Geological Survey of Canada, Current Research, p. C2. Baldwin, G. J., Turner, E. C., and Kamber, B. S., 2016, Tectonic controls on distribution and stratigraphy of the Cryogenian Rapitan iron formation, northwestern Canada: Precambrian Research, v. 278, p. 303-322. Bold, U., Smith, E. F., Rooney, A. D., Buchwaldt, R., Ramazani, J., Dudás, F. Ö., Crowley, J. L., Schrag, D. P., and Macdonald, F. A., 2016, Neoproterozoic stratigraphy of the Zavkhan Terrane of Mongolia: The backbone for Cryogenian and early Ediacaran chemostratigraphic records: American Journal of Science, v. 316, no. 1, p. 1-63. Bowring, S. A., and Grotzinger, J. P., 1992, Implications of new chronostratigraphy for tectonic evolution of Wopmay Orogen, northwest Canadian Shield: American Journal of Science, v. 292, no. 1, p. 1-20. Bowring, S. A., Grotzinger, J. P., Condon, D. J., Ramezani, J., and Newall, M., 2007, Geochronologic constraints on the chronostratigraphic framework of the Neoproterozoic Huqf Supergroup, Sultanate of Oman: American Journal of Science, v. 307, p. 10971145. Burchfiel, B., and Stewart, J., 1966, “Pull-apart” origin of the central segment of Death Valley, California: Geological Society of America Bulletin, v. 77, no. 4, p. 439-442. Cairnes, D. D., 1914, The Yukon-Alaska international boundary between Porcupine and Yukon Rivers: Geological Survey of Canada Memoir 67, v. Map 140-A. Calver, C., Crowley, J., Wingate, M., Evans, D., Raub, T., and Schmitz, M., 2013, Globally synchronous Marinoan deglaciation indicated by U-Pb geochronology of the Cottons Breccia, Tasmania, Australia: Geology, v. 41, no. 10, p. 1127-1130. Carbone, C., Narbonne, G., Macdonald, F. A., and Boag, T., 2015, New Ediacaran fossils from the uppermost Blueflower Formation, NW Canada: Disentangling biostratigraphy and paleoecology: Journal of Paleontology, v. 89, no. 02, p. 281-291. Christie-Blick, N., and Levy, M., 1989, In search of a late Proterozoic eustatic curve, in Stearn, C. W., ed., Abstracts with Programs, Geological Association of Canada, Volume 14, p. 99. Condon, D., Schoene, B., McLean, N., Bowring, S., and Parrish, R., 2015, Metrology and traceability of U–Pb isotope dilution geochronology (EARTHTIME Tracer Calibration Part I): Geochimica et Cosmochimica Acta, v. 164, p. 464-480. Condon, D. J., Zhu, M., Bowring, S. A., Wang, W., Yang, A., and Jin, Y., 2005, U-Pb ages from the Neoproterozoic Doushanto Formation, China: Science, v. 308, p. 95-98. Cox, G. M., Halverson, G. P., Stevenson, R. S., Vokaty, M., Poririer, A., Kunzmann, M., Li, Z.X., Dudas, F. O., Strauss, J. V., and Macdonald, F. A., 2016, A Basalt Weathering Trigger for Snowball Earth: Earth and Planetary Science Letters, v. 446, p. 89-99. Cox, G. M., Roots, C. F., Halverson, G. P., Minarik, W. G., Macdonald, F. A., and HubertTheou, L., 2013, Mount Harper Volcanic Complex, Ogilvie Mountains: A far-flung occurrence of the Franklin Igneous Event, in MacFarlane, K. E., Nordling, M. G., and Sack, P. J., eds., Yukon Exploration and Geology 2012: Whitehorse, Yukon, Yukon Geological Survey, p. 19-36. Cox, G. M., Strauss, J. V., Halverson, G. P., Schmitz, M. D., McClelland, W. C., Stevenson, R. S., and Macdonald, F. A., 2015, Kikiktat Volcanics of Arctic Alaska – Melting of

harzburgitic mantle associated with the Franklin Large Igneous Province: Lithosphere, v. L435-1. Crawford, B. L., Betts, P. G., and Aillères, L., 2010, An aeromagnetic approach to revealing buried basement structures and their role in the Proterozoic evolution of the Wernecke Inlier, Yukon Territory, Canada: Tectonophysics, v. 490, no. 1, p. 28-46. Day, E. S., James, N. P., Narbonne, G. M., and Dalrymple, R. W., 2004, A sedimentary prelude to Marinoan glaciation, Cryogenian (Middle Neoproterozoic) Keele Formation, Mackenzie Mountains, northwestern Canada: Precambrian Research, v. 133, p. 223-247. Dehler, C., Gehrels, G., Porter, S., Heizler, M., Karlstrom, K., Cox, G., Crossey, L., and Timmons, M., 2017, Synthesis of the 780–740 Ma Chuar, Uinta Mountain, and Pahrump (ChUMP) groups, western USA: Implications for Laurentia-wide cratonic marine basins: Geological Society of America Bulletin, v. 129, no. 5-6, p. 607-624. Dehler, C. M., Elrick, M. B., Bloch, J. D., Crossey, L. J., Karlstrom, K. E., and DesMarais, D. J., 2005, High-resolution d13C stratigraphy of the Chuar Group (ca. 770-742 Ma), Grand Canyon: Implications for mid-Neoproterozoic climate change: Geological Society of America Bulletin, v. 117, p. 32-45. Dehler, C. M., Fanning, C. M., Link, P. K., Kingsbury, E. M., and Rybczynski, D., 2010, Maximum depositional age and provenance of the Uinta Mountain Group and Big Cottonwood Formation, northern Utah: Paleogeography of rifting western Laurentia: Geological Society of America Bulletin, v. 122, no. 9/10, p. 1686-1699. Delaney, G. D., 1981, The mid-Proterozoic Wernecke Supergroup, Wernecke Mountains, Yukon Territory, in Campbell, F. H. A., ed., Proterozoic basins of Canada: Ottawa, Geological Survey of Canada Paper 81-10, p. 1-23. Dudás, F. O., and Lustwerk, R. L., 1997, Geochemistry of the Little Dal basalts: continental toleites from the Mackenzie Mountains, Northwest Territories, Canada: Canadian Journal of Earth Sciences, v. 34, p. 50-58. Eisbacher, G. H., 1978, Redefinition and subdivision of the Rapitan Group, Mackenzie Mountains: Geological Survey of Canada Paper 77-35, p. 1-21. -, 1981, Sedimentary tectonics and glacial record in the Windermere Supergroup, Mackenzie Mountains, northwestern Canada: Geological Survey of Canada Paper 80-27, p. 1-40. -, 1985, Late Proterozoic rifting, glacial sedimentation, and sedimentary cycles in the light of Windermere deposition, western Canada: Palaeogeography Palaeoclimatology Palaeoecology, v. 51, p. 231-254. Evans, D., Phillips, E., Hiemstra, J., and Auton, C., 2006, Subglacial till: formation, sedimentary characteristics and classification: Earth-Science Reviews, v. 78, no. 1, p. 115-176. Evans, D. A. D., and Raub, T. D., 2011, Neoproterozoic glacial palaeolatitudes: a global update, in Arnaud, E., Halverson, G. P., and Shields-Zhou, G., eds., The Geological Record of Neoproterozoic Glaciations, Volume 36: London, Geological Society of London, p. 93112. Eyster, A. E., Ferri, F., Schmitz, M. D., and Macdonald, F. A., 2017, One diamictite and two rifts: Stratigraphy and geochronology of the Gataga Volcanics of northern British Columbia: American Journal of Science, v. XXX, p. XXX-XXX. Eyster, A. E., Fu, R. R., Strauss, J. V., Weiss, B. P., Roots, C. F., Halverson, G. P., Evans, D. A., and Macdonald, F. A., 2016, Paleomagnetic evidence for a large rotation of the Yukon block relative to Laurentia: Implications for a low-latitude Sturtian glaciation and the breakup of Rodinia: GSA Bulletin, p. B31425. 31421.

Ferri, F., Rees, C., Nelson, J., and Legun, A., 1999, Geology and mineral deposits of the northern Kechika Trough between Gataga River and the 60th parallel, British Columbia, Ministry of Energy and Mines, Energy and Minerals Division, Geological Survey Branch, Bulletin. Furlanetto, F., Thorkelson, D. J., Gibson, H. D., Marshall, D. D., Rainbird, R. H., Davis, W. J., Crowley, J. L., and Vervoort, J. D., 2013, Late Paleoproterozoic terrane accretion in northwestern Canada and the case for circum-Columbian orogenesis: Precambrian Research, v. 224, p. 512-528. Gabrielse, H., 1967, Tectonic evolution of the northern Canadian Cordillera: Canadian Journal of Earth Sciences, v. 4, no. 2, p. 271-298. Gabrielse, H., 1972, Younger Precambrian of the Canadian Cordillera: American Journal of Science, v. 272, p. 521-536. Gabrielse, H., Blusson, S. L., and Roddick, J. A., 1972, Geology of Flat River, Glacier Lake, and Wrigley Lake map-areas, District of Mackenzie and Yukon Territory, Dept. of Energy, Mines, and Resources, v. 366. Gerstenberger, H., and Haase, G., 1997, A highly effective emitter substance for mass spectrometric Pb isotope ration determinations: Chemical Geology, v. 136, p. 309-312. Godderis, Y., Donnadieu, Y., Nedelec, A., Dupre, B., Dessert, C., Grard, A., Ramstein, G., and Francois, L. M., 2003, The Sturtian 'snowball' glaciation: fire and ice: Earth and Planetary Science Letters, v. 6648, p. 1-12. Gold, D. A., Grabenstatter, J., de Mendoza, A., Riesgo, A., Ruiz-Trillo, I., and Summons, R. E., 2016, Sterol and genomic analyses validate the sponge biomarker hypothesis: Proceedings of the National Academy of Sciences, v. 113, no. 10, p. 2684-2689. Goodman, J. C., and Pierrehumbert, R. T., 2003, Glacial flow of floating marine ice in “Snowball Earth”: Journal of Geophysical Research: Oceans, v. 108, no. C10. Gordey, S., 1979, Stratigraphy of southeastern Selwyn Basin in the Summit Lake area, Yukon Territory and Northwest Territories: Current Research, Part A, Geological Survey of Canada, Paper, p. 13-16. Halverson, G. P., 2006, A Neoproterozoic chronology, in Xiao, S., and Kaufman, A. J., eds., Neoproterozoic Geobiology and Paleobiology, Volume Topics in Geobiology 27: New York, NY, Springer, p. 231-271. Halverson, G. P., Macdonald, F. A., Strauss, J. V., Smith, E. F., and Cox, G. M., 2012, Updated definition and correlation of the lower Fifteenmile Group in the central and eastern Ogilvie Mountains: Yukon Exploration Geology, v. XX. Helmstaedt, H., Eisbacher, G. H., and McGregor, J. A., 1979, Copper mineralization near an intra-Rapitan unconformity, Nite copper prospect, Mackenzie Mountains, Northwest Territories, Canada: Canadian Journal of Earth Sciences, v. 16, p. 50-59. Hoffman, P. F., and Halverson, G. P., 2011, Neoproterozoic glacial record in the Mackenzie Mountains, northern Canadian Cordillera, in Arnaud, E., Halverson, G. P., and ShieldsZhou, G., eds., The Geological Record of Neoproterozoic Glaciations, Volume 36: London, The Geological Society, p. 397-412. Hoffman, P. F., Halverson, G. P., Domack, E. W., Maloof, A. C., Swanson-Hysell, N. L., and Cox, G. M., 2012, Cryogenian glaciations on the southern tropical paleomargin of Laurentia (NE Svalbard and East Greenland), and a primary origin for the upper Russøya (Islay) carbon isotope excursion: Precambrian Research, v. 206, p. 137-158.

Hoffman, P. F., Kaufman, A. J., Halverson, G. P., and Schrag, D. P., 1998, A Neoproterozoic Snowball Earth: Science, v. 281, p. 1342-1346. Hoffman, P. F., and Macdonald, F. A., 2010, Sheet-crack cements and early regression in Marinoan (635 Ma) cap dolostones: Regional benchmarks of vanishing ice-sheets?: Earth and Planetary Science Letters, v. 300, p. 374-384. Hoffman, P. F., and Schrag, D. P., 2002, The snowball Earth hypothesis; testing the limits of global change: Terra Nova, v. 14, no. 3, p. 129-155. Hoffmann, K. H., Condon, D. J., Bowring, S. A., and Crowley, J. L., 2004, U-Pb zircon date from the Neoproterozoic Ghaub Formation, Namibia: Constraints on Marinoan glaciation: Geology, v. 32, p. 817-820. Hofmann, H. J., Narbonne, G. M., and Aitken, J. D., 1990, Ediacaran remains from intertillite beds in northwestern Canada: Geology, v. 18, p. 1199-1202. Hyndman, R. D., Flück, P., Mazzotti, S., Lewis, T. J., Ristau, J., and Leonard, L., 2005, Current tectonics of the northern Canadian Cordillera: Canadian Journal of Earth Sciences, v. 42, no. 6, p. 1117-1136. Isakson, V. H., Schmitz, M. D., Dehler, C. D., Macdonald, F. A., and Yonkee, W. A., 2016, Revised age constraints for Cryogenian glacial deposits in the Pocatello Formation, southeastern Idaho: Abstracts with Programs - Geological Society of America, v. 48, no. 6, p. 28-25. Jaffey, A. H., Flynn, K. F., Glendenin, L. E., Bentley, W. C., and Essling, A. M., 1971, Precision measurements of half-lives and specific activities of 235U and 238U: Physical Review C, v. 4, p. 1889-1906. James, N. P., Narbonne, G. M., and Kyser, T. K., 2001, Late Neoproterozoic cap carbonates; Mackenzie Mountains, northwestern Canada; precipitation and global glacial meltdown: Canadian Journal of Earth Sciences, v. 38, no. 8, p. 1229-1262. Jefferson, C. W., 1978, The Upper Proterozoic Redstone Copper Belt, Mackenzie Mountains, Northwest Territories [Ph.D: University of Western Onterio, 445 p. Jefferson, C. W., and Parrish, R., 1989, Late Proterozoic stratigraphy, U-Pb zircon ages and rift tectonics, Mackenzie Mountains, northwestern Canada: Canadian Journal of Earth Sciences, v. 26, p. 1784-1801. Jeletsky, J. A., 1962, Pre-Cretaceous Richardson Mountains Trough--its place in the tectonic framework of Arctic Canada and its bearing on some geosynclinal concepts: Transactions of the Royal Society of Canada, v. 56, p. 55-84. Johnston, D. T., Macdonald, F. A., Gill, B., Hoffman, P. F., and Schrag, D. P., 2012, Uncovering the Neoproterozoic carbon cycle: Nature, v. 483, no. 7389, p. 320-323. Kaufman, A. J., Knoll, A. H., and Narbonne, G. M., 1997, Isotopes, ice ages, and terminal Proterozoic Earth history: Proceedings of the National Academy of Sciences, v. 95, p. 6600-6605. Kim, S.-T., Coplen, T. B., and Horita, J., 2015, Normalization of stable isotope data for carbonate minerals: Implementation of IUPAC guidelines: Geochimica et Cosmochimica Acta, v. 158, p. 276-289. Kirschvink, J. L., 1992, Late Proterozoic low-latitude global glaciation: the snowball earth, in Schopf, J. W., and Klein, C., eds., The Proterozoic Biosphere: Cambridge, Cambridge University Press, p. 51-52. Klein, C., and Beukes, N. J., 1993, Sedimentology and geochemistry of the glaciogenic late Proterozoic Rapitan iron-formation in Canada: Economic Geology, v. 84, p. 1733-1774.

Krough, T. E., 1973, A low contamination method for hydrothermal decompostion of zircon and extraction of U and Pb for isotopic age determination: Geochmica et Cosmochimica Acta, v. 37, p. 485-494. Lan, Z., Li, X., Zhu, M., Chen, Z.-Q., Zhang, Q., Li, Q., Lu, D., Liu, Y., and Tang, G., 2014, A rapid and synchronous initiation of the wide spread Cryogenian glaciations: Precambrian Research, v. 255, p. 401-411. Lan, Z., Li, X.-H., Zhang, Q., and Li, Q.-L., 2015, Global synchronous initiation of the 2nd episode of Sturtian glaciation: SIMS zircon U–Pb and O isotope evidence from the Jiangkou Group, South China: Precambrian Research, v. 267, p. 28-38. Lau, K. V., Macdonald, F. A., Maher, K., and Payne, J. L., 2016, Uranium isotope evidence for temporary ocean oxygenation in the aftermath of the Sturtian Snowball Earth: Earth and Planetary Science Letters, v. 458, p. 282-292. Little, H. W., 1960, Nelson map-area, west half, British Columbia, Natural Resources Canada. Long, D., and Turner, E., 2013, Formal definition of the Neoproterozoic Mackenzie Mountains Supergroup (Northwest Territories), and formal stratigraphic nomenclature for terrigenous clastic units of the Katherine Group, Geological Survey of Canada. Lønne, I., 1995, Sedimentary facies and depositional architecture of ice-contact glaciomarine systems: Sedimentary Geology, v. 98, no. 1, p. 13-43. Love, G. D., Grosjean, E., Stalvies, C., Fike, D. A., Grotzinger, J. P., Bradley, A. S., Kelly, A. E., Bhatia, M., Meredith, W., Snape, C. E., Bowring, S. A., Condon, D. J., and Summons, R. E., 2009, Fossil steroids record the appearance of Demospongiae during the Cryogenian period: Nature, v. 457, p. 718-722. Ludwig, K. R., 2003, User’s manual for Isoplot 3.00: a geochronological toolkit for Microsoft Excel: Berkeley Geochronology Center Special Publication, v. 4, p. 1-70. Macdonald, F. A., and Cohen, P. A., 2011, The Upper Tindir Group, east-central Alaska, in E., A., Halverson, G. P., and Shields, G., eds., The geological record of Neoproterozoic glaciations: London, Geological Society of London. Macdonald, F. A., Cohen, P. A., Dudás, F. O., and Schrag, D. P., 2010a, Early Neoproterozoic scale microfossils in the Lower Tindir Group of Alaska and the Yukon Territory: Geology, v. 38, p. 143-146. Macdonald, F. A., Halverson, G. P., Strauss, J. V., Smith, E. F., Cox, G., Sperling, E. A., and Roots, C. F., 2012, Early Neoproterozoic Basin Formation in Yukon, Canada: Implications for the make-up and break-up of Rodinia: Geoscience Canada, v. 39, no. 2. Macdonald, F. A., McClelland, W. C., Schrag, D. P., and Macdonald, W. P., 2009, Neoproterozoic glaciation on a carbonate platform margin in Arctic Alaska and the origin of the North Slope subterrane: Geological Society of America Bulletin, v. 121, p. 448473. Macdonald, F. A., Prave, A. R., Petterson, R., Smith, E. F., Pruss, S. B., Oates, K., Waechter, F., Trotzuk, D., and Fallick, A. E., 2013a, The Laurentian record of Neoproterozoic glaciation, tectonism, and eukaryotic evolution in Death Valley, California: Geological Society of America Bulletin, v. 125, no. 7-8, p. 1203-1223. Macdonald, F. A., Schmitz, M. D., Crowley, J. L., Roots, C. F., Jones, D. S., Maloof, A. C., Strauss, J. V., Cohen, P. A., Johnston, D. T., and Schrag, D. P., 2010b, Calibrating the Cryogenian: Science, v. 327, p. 1241-1243. Macdonald, F. A., Smith, E. F., Strauss, J. V., Cox, G. M., Halverson, G. P., and Roots, C. F., 2011, Neoproterozoic and early Paleozoic correlations in the western Ogilvie Moutnains,

Yukon, in MacFarlane, K. E., Weston, L. H., and Relf, C., eds., Yukon Exploration and Geology 2010: Whitehorse, Yukon Geological Survey, p. 161-182. Macdonald, F. A., Strauss, J. V., Sperling, E. A., Halverson, G. P., Narbonne, G. M., Johnston, D. T., Kunzmann, M., Schrag, D. P., and Higgins, J. A., 2013b, The stratigraphic relationship between the Shuram carbon isotope excursion, the oxygenation of Neoproterozoic oceans, and the first appearance of the Ediacara biota and bilaterian trace fossils in northwestern Canada: Chemical Geology, v. 362, p. 250-272. Macdonald, F. A., and Wordsworth, R., 2017, Initiation of Snowball Earth with volcanic sulfur aerosols: Journal of Geophysical Research, v. XXX, p. XXX-XXX. MacNaughton, R. B., Pigage, L. C., and Allen, T. L., 2016, Sedimentology and regional significance of the ‘argillite unit’, a probable Cryogenian map unit in southeast Yukon, Canada: Geological Journal. Mattinson, J. M., 2005, Zircon U-Pb chemical abrasion ("CA-TIMS") method: combined annealing and multi-step partial dissolution analysis for improved precision and accuracy of zircon ages: Chemical Geology, v. 220, p. 47-66. Medig, K., Turner, E., Thorkelson, D., and Rainbird, R., 2016, Rifting of Columbia to form a deep-water siliciclastic to carbonate succession: The Mesoproterozoic Pinguicula Group of northern Yukon, Canada: Precambrian Research, v. 278, p. 179-206. Mertie, J. B., 1930, Geology of the Eagle-Circle district, Alaska: U.S. Geological Survey Bulletin, v. 816, p. 121-122. -, 1933, The Tatonduk-Nation district, Alaska: U. S. Geological Survey Bulletin, v. 836-E, p. 345-454. Milton, J. E., Hickey, K. A., Gleeson, S. A., and Friedman, R. M., 2017, New U-Pb constraints on the age of the Little Dal Basalts and Gunbarrel-related volcanism in Rodinia: Precambrian Research, v. 296, p. 168-180. Morrow, D. W., 1999, Lower Paleozoic stratigraphy of northern Yukon Territory and northerwestern District of Mackenzie: Geological Survey of Canada Bulletin, v. 538. Moynihan, D. P., Stratigraphic relationships between the Windermere Supergroup and Hyland Group in the Rackla belt of east-central Yukon: Implications for the age of Selwyn Basin and formation of the Laurentian passive margin, in Proceedings 2014 GSA Annual Meeting in Vancouver, British Columbia2014. Mustard, P. S., and Roots, C. F., 1997, Rift-related volcanism, sedimentation, and tectonic setting of the Mount Harper Group, Ogilvie Mountains, Yukon Territory: Geological Survey of Canada Bulletin, v. 492, p. 0-92. Narbonne, G. M., and Aitken, J. D., 1990, Ediacaran fossils from the Sekwi Brook area, Mackenzie Mountains, northwest Canada: Palaentology, v. 33, no. 4, p. 945-980. Norris, D., 1985, Eastern Cordilleran foldbelt of northern Canada: its structural geometry and hydrocarbon potential: AAPG Bulletin, v. 69, no. 5, p. 788-808. Norris, D. K., 1997, Geology and mineral and hydrocarbon potential of northern Yukon Territory and northwestern District of Mackenzie, Ottawa, Geological Survey of Canada, Geological Survey of Canada, Bulletin 422, 397 p.: Payne, M. W., and Allison, C. W. A., 1981, Paleozoic continental-margin sedimentation in eastcentral Alaska: Geology, v. 9, p. 274-279. Pigage, L. C., 2009, Bedrock geology of NTS 95C/5 (Pool Creek) and NTS 95D/8 map sheets, southeast Yukon: Yukon Geological Survey Bulletin 16, p. 1-150.

Pilkington, M., and Saltus, R. W., 2009, The Mackenzie River magnetic anomaly, Yukon and Northwest Territories, Canada—Evidence for Early Proterozoic magmatic arc crust at the edge of the North American craton: Tectonophysics, v. 478, no. 1, p. 78-86. Prave, A. R., Condon, D., Hoffmann, K.-H., Tapster, S., and Fallick, A. E., 2016, Duration and nature of the end-Cryogenian (Marinoan) glaciation: Geology, v. 44, no. 8, p. 631-634. Rohr, K. M., Lane, L. S., and MacLean, B. C., 2011, Subsurface compressional structures and facies transitions imaged by seismic reflection data, eastern margin of Richardson Trough, Peel Plateau, Yukon: Bulletin of Canadian Petroleum Geology, v. 59, no. 2, p. 131-146. Rooney, A. D., Macdonald, F. A., Strauss, J. V., Dudas, F. O., Hallman, C., and Selby, D., 2014, Re-Os geochronology and coupled Os-Sr isotope constraints on the Sturtian snowball Earth: Proceedings of the National Academy of Science, v. 1073, p. 1-6. Rooney, A. D., Strauss, J. V., Brandon, A. D., and Macdonald, F. A., 2015, A Cryogenian Chronology: Two long-lasting, synchronous Neoproterozoic Snowball Earth glaciations: Geology, v. 43, no. 5, p. 459-462. Roots, C. F., 1987, Regional tectonic setting and evolution of the Late Proterozoic Mount Harper volcanic complex, Ogilvie Mountains, Yukon [Ph.D.: Carleton University, 219 p. Rose, C. V., Swanson-Hysell, N. L., Husson, J. M., Poppick, L. N., Cottle, J. M., Schoene, B., and Maloof, A. C., 2012, Constraints on the origin and relative timing of the Trezona δ< sup> 13 C anomaly below the end-Cryogenian glaciation: Earth and Planetary Science Letters, v. 319, p. 241-250. Schmitz, M. D., and Schoene, B., 2007, Derivation of isotope ratios, errors and error correlations for U-Pb geochronology using 205Pb-235U-(233U)-spiked isotope dilution thermal ionization mass spectrometric data: Geochemistry, Geophysics, Geosystems v. 8, p. Q08006. Sláma, J., Košler, J., Condon, D. J., Crowley, J. L., Gerdes, A., Hanchar, J. M., Horstwood, M. S., Morris, G. A., Nasdala, L., and Norberg, N., 2008, Plešovice zircon—a new natural reference material for U–Pb and Hf isotopic microanalysis: Chemical Geology, v. 249, no. 1, p. 1-35. Smith, E. F., Macdonald, F. A., Crowley, J. L., Hodgin, E. B., and Schrag, D. P., 2015, Tectonostratigraphic evolution of the c. 780–730 Ma Beck Spring Dolomite: Basin Formation in the core of Rodinia: Geological Society, London, Special Publications, v. 424, p. SP424. 426. Stewart, J. H., 1972, Initial deposits in the Cordilleran geosyncline: Evidence of a late Precambrian (< 850 my) continental separation: Geological Society of America Bulletin, v. 83, no. 5, p. 1345-1360. Strauss, J. V., Macdonald, F. A., Halverson, G. P., Tosca, N., Schrag, D. P., and Knoll, A., 2015, Stratigraphic evolution of the Neoproterozoic Callison Lake Formation: Linking the break-up of Rodinia to the Islay carbon isotope excursion: American Journal of Science, v. 315, p. 881-944. Strauss, J. V., Macdonald, F. A., and McClelland, W. C., submitted, Pre-Mississippian stratigraphy and provenance of the North Slope subterrane of Arctic Alaska I: Platformal rocks of the northeastern Brooks Range and their significance in circum-Arctic evolution: Geological Society of America Special Papers.

Strauss, J. V., Macdonald, F. A., Taylor, J. F., Repetski, J. E., and McClelland, W. C., 2013, Laurentian origin for the North Slope of Alaska: Implications for the tectonic evolution of the Arctic: Lithosphere, v. 5, no. 5, p. 477-482. Strauss, J. V., Rooney, A. D., Macdonald, F. A., Brandon, A. D., and Knoll, A. H., 2014a, 740 Ma vase-shaped microfossils from Yukon, Canada: Implications for Neoproterozoic chronology and biostratigraphy: Geology, p. G35736. 35731. Strauss, J. V., Roots, C. F., Macdonald, F. A., Halverson, G. P., Eyster, A. E., and Colpron, M., 2014b, Geological map of the Coal Creek Inlier, Ogilvie Mountains (NTS 116B/10-15 and 116C/9,16) (1:100,000 scale): Yukon Geological Survey, Open File, v. 2014-15. Swanson-Hysell, N. L., Rose, C.V., Calmet, C.C., Halverson, G.P., Hurtgen, M.T., Maloof, A.C., 2010, Cryogenian glaciation and the onset of carbon-isotope decoupling: Science, v. 328, p. 608-611. Thompson, R. I., Mercier, B., and Roots, C. F., 1987, Extension and its influence on Canadian Cordilleran passive-margin evolution, in Coward, M. P., Dewey, J. F., and Hancock, P. L., eds., Continental Extensional Tectonics, Volume 28: London, Geological Society Special Publication, p. 409-417. Thorkelson, D. J., 2000, Geology and mineral occurences of the Slats Creek, Fairchild Lake and "Dolores Creek" areas, Wernecke Mountains, Yukon Territory (106D/16, 106C/13, 106C/14): Exploration and Geological Services Division, Yukon Region, Bulletin 10. Thorkelson, D. J., Abbott, G. J., Mortensen, J. K., Creaser, R. A., Villeneuve, M. E., McNicoll, V. J., and Layer, P. W., 2005, Early and Middle Proterozoic evolution of Yukon, Canada: Canadian Journal of Earth Sciences, v. 42, p. 1045-1071. Turner, E. C., 2011, Stratigraphy of the Mackenzie Mountains supergroup in the Wernecke Mountains, Yukon, in MacFarlane, K. E., Weston, L. H., and Relf, C., eds., Yukon Exploration and Geology 2010: Whitehorse, Yukon, Yukon Geological Survey, p. 207231. Turner, E. C., Roots, C. F., MacNaughton, R. B., Long, D. G. F., Fischer, B. J., Gordey, S. P., Martel, E., and Pope, M. C., 2011, Chapter 3. Stratigraphy, in Martel, E., Turner, E. C., and Fischer, B. J., eds., Geology of the central Mackenzie Mountains of the northern Canadian Cordillera, Sekwi Mountain (105P), Mount Eduni (106A), and northwestern Wrigley Lake (95M) map-areas, Northwest Territories, Volume 1: Yellowknife, NWT Geoscience Office, p. 31-192. van Acken, D., Thomson, D., Rainbird, R. H., and Creaser, R. A., 2013, 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: Precambrian Research, v. 236, p. 124-131. Vandeginste, V., Swennen, R., Gleeson, S. A., Ellam, R. M., Osadetz, K., and Roure, F., 2005, Zebra dolomitization as a result of focused fluid flow in the Rocky Mountains Fold and Thrust Belt, Canada: Sedimentology, v. 52, p. 1067-1095. Villeneuve, M., Thériault, R., and Ross, G., 1991, U-Pb ages and Sm-Nd signature of two subsurface granites from the Fort Simpson magnetic high, northwest Canada: Canadian Journal of Earth Sciences, v. 28, no. 7, p. 1003-1008. Watson, E., Wark, D., and Thomas, J., 2006, Crystallization thermometers for zircon and rutile: Contributions to Mineralogy and Petrology, v. 151, no. 4, p. 413-433. Wilcox, R. E., Harding, T. t., and Seely, D., 1973, Basic wrench tectonics: Aapg Bulletin, v. 57, no. 1, p. 74-96.

Yeo, G. M., 1981, The Late Proterozoic Rapitan glaciation in the northern Cordillera, in Campbell, F. H. A., ed., Proterozoic Basins of Canada, Volume Geological Survey of Canada Paper, 81-10, p. 25-46. -, 1984, The Rapitan Group: relevance to the global association of Late Proterozoic glaciation and iron-formation [Ph.D. Thesis: University of Western Ontario, 521 p. -, 1986, Iron-formation in the late Proterozoic Rapitan Group, yukon and Northwest Territories, in Morin, J. A., ed., Mineral Deposits of Northern Cordillera, Volume 37, Canadian Institute of Mining and Metallurgy Special Volume, p. 142-153. Young, G. M., 1982, The late Proterozoic Tindir Group, east-central Alaska; Evolution of a continental margin: Geological Society of America Bulletin, v. 93, p. 759-783. Young, G. M., 1995, Are Neoproterozoic glacial deposits preserved on the margins of Laurentia related to the fragmentation of two supercontinents?: Geology, v. 23, p. 153-156. Young, G. M., Jefferson, C. W., Delaney, G. D., and Yeo, G. M., 1979, Middle and late Proterozoic evolution of the northern Canadian Cordillera and Shield: Geology, v. 7, p. 125-128.

Table 1.

Bedding Style/Structures

Depositional Environment

Distribution

L1: Massive diamictite

Very poorly sorted shale to sandstone and yelllowweathering carbonate grainstone matrix with subrounded to sub-angular boulder- to gravel-sized clasts of underlying units. Clast/matrix ratio highly variable.

Massive to thickly bedded, matrix supported. Shear fabrics, softsedimentary folding, concretions, scours

Lodgement tills, till tounges, and glacigenic debris flows formed above or near the ice grounding line

Rapitan Group, Eagle Creek Formation, minor occurences in Hay Creek Group

L2: Stratified diamictite

Very poorly sorted shale to sandstone and yellowweathering carbonate grainstone matrix with rare lonestones. Sub-rounded to sub-angular boulder- to gravel-sized clasts of underlying units. Clast/matrix ratio highly variable.

Fine laminated to medium bedded, matrix supported with occassional clast supported horizons. Normally graded with lamination-penetrating lonestone clasts

Glacigenic debris flows and hemipelagic deposits with ice rafted debris formed below ice grounding line or in ice marginal setting

Rapitan Group, Eagle Creek Formation

L3: Conglomerate

Dark gray and yellowweathering silt to sand and carbonate grainstone matrix. Rounded to sub-angular gravel to boulder carbonate, quartzite, volcanic and minor siltstone clasts

Massive to medium bedded and clast supported. Coarsening up ~100 m thick megasequences. Weakly normal and reverse graded with imbrication. Clast imbrication and ripple crosslaminae indicate broadly south directed paleoflow

Prograding submarine to subglacial fan deltas; deposition by sediment gravity flow off of active fault scarp; also includes debris flows and olistoliths of the Durkan Member of the Ice Brook Formation

Rapitan Group, Eagle Creek Formation, Hay Creek Group, Durkan Member

L4: Sandstone

Fine- to coarse-grained siliciclastic and volcaniclastic (quartz, feldspar, lithic fragments)

Thin to massive. Both normally graded, planar and ripple cross laminated with loaded bases

Bouma AE and BE turbidites are most common, but more complete Bouma sequences also occur

Rapitan and Hay Creek groups

L5: Siltstone

Volcaniclastic (quartz, feldspar, lithic fragments)

Thin to medium, commonly graded between shale and finesandstone. Grading from shale to fine sandstone, ripple cross-lamination.

Turbidites with convolute bedding formed by soft sedimentary deformation

Rapitan and Hay Creek groups

L6: Shale

Green, gray and black colored, occasionally calcareous or silty.

Thin. Suspension lamination.

Background suspension settling and waning turbidite flow

Rapitan and Hay Creek groups

Lithofacies

Composition

Clastic Facies:

Carbonate Facies:

L7: Rhythmite

Grey to dark grey and yellow-weathering micrite & calcisiltite with occasional lonestones

Flat-parallel, fine laminated to thinly bedded. Normal grading and suspension lamination.

L8: Ribbonite

Grey to dark grey micrite, calcisiltite, minor matrix supported peloids and ooids

Wavy to nodular, thin to medium bedded. Lowangle cross-lamination and normal grading.

In Mt. Profeit Dolostone, constrained to transgressive horizons associated with relatively low-energy deposition; in Rapitan Group and Durkan Member includes suspension settling during waning turbidite flow Carbonate turbidites with nodular and convolute bedding formed by soft sedimentary deformation and differential compaction

Eagle Creek Formation, Mt. Profeit Dolostone, Durkan Member

Durkan Member

L9: Grainstone (includes wackestone and packestone)

Grey to light grey and yellow-weathering dolograinstone and minor limestone grainstone composed of peloids, ooids, and chips of microbialite. Occassional lonestones.

L10: Stromatolitic dolostone

Light grey stromatolitic doloboundstone; close association with stromatolite-rich intraclast wackestone and grainstone; commonly silicified and massively recrystallized

L11: Breccia

Grey to white dolostone breccia; commonly silicified with angular clasts of dolostone; clasts range from sand- to boulder-sized with ubiquitous cement

L12: Recrystallized dolostone

Light grey to white sucrosic dolostone with fabricdestructive diagenetic recrystallization; occasional oolitic ghosts

L13: Saddle dolomite

Light grey to white dolostone dominated by fabric-destructive diagenetic cement

Thin to thickly bedded and massive to finely laminated. Occasional trough cross-bedding, low-angle cross-bedding, and planar bedding or normal grading, but typically massive and crudely stratified. Centimeter- to meterthick stromatolitic structures; forms laterally-linked, low relief, and domal to highinheritance columnar structures; minor clotty thrombolitic structures Massive and generally thick-bedded; crude stratification with clear horizons indicating subaerial exposure and karst development Medium- to thick-bedded and massive; crude stratification and commonly impossible to determine precursor facies; abundant secondary isopachus, drusy, and botryoidal cements Massive obliteration of precursor sedimentary facies and replacement with saddle cements with a 'zebra' texture

High-energy sub-tidal deposition associated with tidal sand bars and/or migrating barrier complex; redeposited as Bouma AB carbonate grain flows in the Rapitan Group and Durkan Member

Eagle Creek Formation, Mt. Profeit Dolostone, Durkan Member, Ravensthroat Formation

Isolated carbonate platform high. Common wavegenerated scours and association with F9.

Mt. Profeit Dolostone

Subaerial exposure and karst development associated with uplift and fault breccia in some localities

Mt. Profeit Dolostone, Hay Creek Group

Commonly associated with ubaerial exposure surfaces in coarser-grain lithologies, but also likely due to later fluid event

Mt. Profeit Dolostone, Ravensthroat Formation

Fabric replacement due to later fluid event

Mt. Profeit Dolostone

Table 2. Formalization of the Eagle Creek Formation Name

Eagle Creek Formation

Name Derivation

Type area located south of Eagle Creek, western Ogilvie Mountains, Yukon Territory; Dawson Quadrangle (NTS 116BC)

Category and Rank Type Area Unit Type Section

Lithostratigraphic Formation Situated south of Eagle Creek on north facing slope, western Ogilvie Mountains, Yukon Territory, Canada Green shelter, composite sections F918, F919, and F920 of this paper (Figures 11 and 18, this paper) Located on north facing slope ~20 km NW of Mount Harper (N64°46', W-140°08') Lower boundary: sharp contact of matrix supported diamictite above massive basaltic flows of Mount Harper Volcanics Upper boundary: covered, transition into shale, siltstone, and limestone of Hay Creek Group

Unit Description

Interbedded yellow weathering dolomite clast supported conglomerate and yellow, black, green, or maroon weathering matrix supported glacigenic diamictite. Yellow weathering dolomite clast conglomerates form ~100 m thick coarsening upward sequences of fanglomerate facies with south-directed paleoflow. Volcaniclastic diamictites are more common to the south and are present in both massive and stratified facies interpreted as glacigenic debris flows. Evidence for a glacial origin of these strata is provided by common bed-penetrating dropstones interpreted as ice rafted debris, and rare striated clasts and till pellets.

Unit Reference Sections

1. Green Shelter composite section (F918-F920; this paper), which is near section 8 of Mustard and Roots (1997). 2. Section T1401 (this paper), which is equivalent to section 9 of Mustard and Roots (1997).

Dimensions

115 m thick in composite type section at Green Shelter (F918-F920; this paper), and >270 m thick in reference section T1401. A maximum thickness was estimated at ~400 m (Mustard and Roots, 1997)

Geologic Age

Regional Correlations

Cryogenian (<717, >~660 Ma). Underlying Mount Harper Volcanics dated at 717.43 ± 0.14 Ma, and a tuff near the base of the Eagle Creek Formation was dated at 716.47 ± 0.24 Ma (U/Pb ID-TIMS zircon dates; Macdonald et al., 2010). Base of overlying Hay Creek Group dated in Mackenzie Mountains with Re/Os at 662.4 ± 3.9 Ma (Rooney et al., 2014). Unnamed equivalents in the Tatonduk and Hart River inliers; Rapitan Group in the Wernecke inlier; Mt. Berg, Sayeuni, and Shezal formations of the Rapitan Group in the Mackenzie Mountains

Table 3. CA-IDTIMS U-Pb age summary Formation Sample Eagle Creek Formation F840A* F917-1 Mount Harper Volcanics F837B* F837C F837A 15PM06 15PM08

206

Locale

Pb/238U age Ma

MSWD†

N

Tango Tarn Tango Tarn

716.5 ± 0.2(0.4)[0.8] 716.9 ± 0.4(0.5)[0.9]

0.04 1.5

6 of 14 5 of 16

Bald Hill Bald Hill Bald Hill

717.4 ± 0.2(0.4)[0.8] 717.7 ± 0.3(0.5)[0.9] 717.8 ± 0.2(0.4)[0.8] 718.1 ± 0.3(0.5)[0.9] 718.1 ± 0.2(0.4)[0.8]

0.67 0.29 0.64 0.42 0.98

6 of 10 3 of 4 4 of 9 4 of 5 6 of 6

Notes: *All weighted mean ages at the 95% confidence interval, as calculated from the internal 2 errors expanded by the square root of the MSWD and the Student’s T multiplier of n-1 degrees of freedom. Uncertainties are quoted as analytical (analytical+tracer) [analytical+tracer+decay constant]. †mean squared weighted deviations.

Highlights: We present new geological, geochronological and geochemical data from Cryogenian rocks in the Yukon that provide needed geological context to the critical dates from the Yukon that constrain the onset of the Sturtian glaciation. Onset of the Sturtian glaciation is constrained between 716.9 ± 0.4 and 717.4 ± 0.2 Ma. A major unconformity developed throughout northwest Laurentia between the end of the Sturtian glaciation at 660 Ma and the end of the Marinoan glaciation at 635 Ma. Tonian to Cryogenian sections in the Yukon contain important fossil assemblages and Re-Os geochronological constraints in the underlying Callison Lake, the global Islay negative carbon isotope excursion, paleomagnetic constraints, and the most robust geochronological framework of any early Cryogenian succession, and should thus be considered in defining the base of the Cryogenian Period.

e

ns

City

Ti

nt

ina

65 00’00”N

Norman Wells

zi

fau

lt

Selwyn Basin Yukon River

.T. N.W N KO YU

0

63 00’00”N

65 00’00”N

en

ai

Sna Platea ke R u Fa iver ult Fau lt

ck

nt

ALASKA YUKON

Ma

ou

64 00’00”N

Mackenzie River

M

Richardson-Hess Figure 14 Fault array Tatonduk Inlier Y u k o n b l o c k Figure 9 Coal Creek Inlier Hart River Daw Inlier son Figure 3 thru st Wernecke Figure 6 Inlier Dawson

130 00’00”W

64 00’00”N

135 00’00”W

140 00’00”W

100 km Mackenzie Mtns. Supergroup (Tonian)

Hyland Group (Ediacaran-Cambrian)

Pinguicula Group (Meso-Neoproterozoic) Wernecke Supergroup (Paleoproterozoic)

Windermere Supergroup (Cryogenian-Cambrian) Map/Figure Outline

Cretaceous–Paleogene (Laramide)Thrust Fault Cretaceous–Paleogene (Laramide) Strike-Slip Fault Cretaceous–Paleogene Fault (Laramide) Undefined Fault Late Proterozoic Normal Fault

Yukon CANADA

U.S.A.

Rap.

811.5±0.1 Ma 0 km Re/Os organic-rich mudstone date Conglomerate CA-IDTIMS U/Pb zircon date (this paper) Sandstone-siltstone Shale U/Pb detrital zircon or multigrain fraction date

L.D.

Iron formation Evaporite Carbonate

Mackenzie Mountains Sheepbed

MMSG Little Dal Group

Windermere Supergroup Coates L Rapitan Hay Creek Group Group Group

Rap.

Ice Brook

“Upper” group

751.2±5.1 Ma

Mt. Profeit Dolostone

716.5±0.2 Ma 716.9±0.4 Ma 717.4±0.1 Ma 717.7±0.3 Ma 717.8±0.2 Ma 718.1±0.3 Ma 718.1±0.2 Ma 739.9±6.1 Ma

Katherine Group

1

Tonian Fifteenmile Group

2

Wernecke Inlier

Hay Creek?

Rap. E.C.

P.C.

Hart River Inlier

Fifteenmile Callison Group Lake Fm.

“Upper” group

Rap.

Mount Harper Group

H.C.

Fifteenmile Group

3

H.C.

Cryogenian

4

Coal Creek Inlier

Ediacaran “Upper” group

Tatonduk Inlier

Diamictite Basalt/gabbro Rhyolite

632.0±5.0 Ma

Keele Twitya

662.4±3.9 Ma

Shezal Sayunei Mt. Berg Cu-cap Red. River Thund. Ram 778 Ma Head T.S. S.S. Gayna S.K./Silver.

Corn Creek folds Olistoliths Unconformity

<711 Ma 732.2±3.9 Ma

774.9±0.5 Ma 777.7±2.5 Ma

Scale microfossils VSM Rusty Assemblage

65°02'N

133°20' W

133°10' W

Eis

R

A1414,F1426 T1405 T1408

Gra

5

133°0' W 2.5

0

5 km

be

n

F1427

Pu

T

R T

R

R

North

64°58'N

W

Sn

T

ak eR

W

iv er

64°54'N

W

Eu

D

Eu

F852

P

64°50'N

F849

W8

F851

Go zA

F1228

F848

Eu Pu

Pc

64°46'N

HC

Eu

Mt . Pr ofe

P

it

HC

F1224

HC

F855

LD

64°42'N

Fa u

lt

D

F1226

HC Paleozoic undifferentiated Ediacaran undifferentiated Hay Creek Group Ravensthroat formation Ice Brook Formation Stelfox Member Mt. Profeit dolostone Keele Formation Twitya Formation

K

F854 F853

R LD K HC P W

Eu

Go zB Eu

Rapitan Group Little Dal Group Katherine Group Hematite Creek Group Pinguicula Group Wernecke Supergroup Fault Camp Dike Fold Measured section

Goz A W8, F851, F852

δ13C carb(‰ VPDB)

-10

-5

0

S. Goz A F1228, F848

δ13C carb(‰ VPDB)

-20 -15 -10 -5

5 10

0

δ13C carb(‰ VPDB)

5 10

-10 -5

0 5 10

Mount Profeit F1224

Goz B F853, F854, F855, F1226

δ13C carb(‰ VPDB)

δ13C carb(‰ VPDB)

-10 -5 0 5 10 Ravensthroat and Hayhook formations

-10

-5

0

5

EDIACARAN

Eis Graben A1414, F1426, F1427, T1405, T1408

Southeast

Stelfox Member

“Upper” Ice Brook Sheepbed

Northwest

500

500 0

900

0(m)

-10

100

0(m)

Mount Profeit

siliciclastic: m s m c vc g cgl carbonate: m c w g b br

5

0 5

-10

δ13C carb(‰ VPDB)

siliciclastic: m s m c vc g carbonate: m c w g b br

Clastic lithofacies:

L1: Massive diamictite L2: Stratified diamictite L3: Conglomerate L4: Sandstone L5: Siltstone L6: Shale Yellow dolomite matrix Brown-green siliciclastic matrix Purple-maroon siliciclastic matrix

-5

0

5

300

0(m) siliciclastic: m s m c vc g m c w g b br carbonate:

Carbonate & diagenetic lithofacies:

L7: Rhythmite L8: Ribbonite L9: Grainstone L10: Stromatolitic dolostone L11: Breccia L12: Recrystalized dolostone L13: Saddle dolomite Dolostone Limestone

Micritic cement Giant ooids Flooding surface Olistoliths Jaspilitic chert clast Erosive surface Cover Correlative surface

200

100

0(m)

siliciclastic: m s m c vc g cgl carbonate: m c w g b br

TONIAN

-20 -15 -10 -5

folded

Katherine Gp.

0

-40 -35 -30 -25 -20 δ13Corg(‰ VPDB)

M.P.

Rapitan Group

100

-5

δ13C carb (‰ VPDB)

siliciclastic: m s m c vc g carbonate: m c w g b br

Rapitan conglomerate (informal)

100

5

Little Dal Group (Stone Knife Fm.)

Shezal Formation

300

0(m)

200

0

400

400

300

-5

Rapitan Group ?

-10

s

Thickness Approximated

5 10

0 (m) 10

folded

0

200 500

100

300

200

600

200

CRYOGENIAN

400

Mount Profeit dolostone

500

500

-10 -5

700

Mount Profeit Dolostone

Thickness Approximated

Ice Brook Formation

600

Ice Brook Formation

Thickness Approximated

700

300

Hematite Creek Group

800

800

~1 km not shown

Twitya

Hay Creek Group Keele

400

137°00 'W

136°45'W

136°30'W

136°15'W

CDb CDb

nPFU

0

CDb

2.5

5

7.5

10 km

64°35'N

CDb CDb

CDb

nPHcl nPHcl

F936

PW

PPu

nPFu

F937

F934, J906 nPFu

Psh nPFu Psh

nPChu

nPHcl nPRu

64°30'N

CDb nPChu

Measured sections Psh: Paleozoic shale undifferentiated COv: Dempster volcanics nPChu CDb: Bouvette Formation PChu: Hyland Group nPHCu: Hay Creek/Upper gps undifferentiated

nPRu

nPRu: Rapitan Group nPHcl: Callison Lake Fm

PPu

nPFu: Fifteenmile Group PPu: Pinguicula Group PHRsv: Hart River sills/volcanics PW: Wernecke Supergroup

nPChu

Psh

West

East

F936

F10: Massive stromatolitic dolostone Yellow dolomite matrix Cover Brown-green siliciclastic matrix Purple-maroon siliciclastic matrix F1: Massive bedded matrix supported diamictite F2: Thin bedded matrix supported diamictite F3: Clast supported conglomerate Fault F4: Sandstone Striated clast F12: Breccia Soft sediment deformation Fe Ironstone Ripple cross-lamination Erosive surface

150

F934, J906

F937

50

100

Rapitan Group

50

100

Rapitan Group

100

50

Rapitan Group?

200

Fe

CL

CL

HRV

0 (m) m s w c vc g

m s w c vc g

m s w c vc g

64°50'N

140°15'W

Psh

64°45'N

Psh

Psh

Proterozoic dike MeasuredPshsections Psh: Paleozoic shale undivided COv: Dempster volcanics CDb CDb: Bouvette Formation nPChu: Hyland Group PCu nPU: Upper group nPHCu: Hay Creek Group nPec: Eagle Creek formation nPHv3: Mt. Harper Vol. (E-F) PCuHarper Vol. (D) nPHv2: Mt. nPHv1: Mt. Harper Vol. (A-C) nPHsp: Seela Pass Formation nPHcl: Callison Lake FmnPU

140°0'W

Psh CDb CDb

CDb

Mine Camp

F1010 nPF

nPU

J1011,G07 nPHv1

nPF

Green Shelter F918

F919 F841,F920

CDb

nPU

nPU

PW: Wernecke Supergroup Geochronology sample

CDb

PW nPHcl

nPec

nPF

F840,F917

F924

Tango Tarn

CDb

A’

nPHv1

nPU 64°40'N

PW

F1013

nPF: Fifteenmile Group

PCu

B

T1401

nPec

F1154 A1209 A1210

Bald Hill F837 nPHv2

15PM06

nPChu

B’

PW

A

15PM08

Psh

Mount Harper

nPHv2 nPChu

PW

Psh

Psh

64°35'N

COv COv

nPChu

Psh

nPChu

0COv

3

6

9

km

Southwest

700

500

member B

600

800 700 600

400

500

300 200

Sill 100 Pahoehoe Erosive surface 0(m)

400

member A

Diamictite Shale Sandstone Conglomerate Dolostone Rhyolite Andesite Basalt Brecciated

Mount Harper Volcanics member A member B

E.C. F837B,C F837A

300 200 F MC Flows Breccia

Re/Os date CA-IDTIMS U/Pb zircon sample

100 0(m)

Seela Pass Formation

800

Cal. Lake

15PM06 15PM08

Northeast A’

Mt. Harper F1154, A1209, A1210

Bald Hill F837 CD E

Southwest Inlier

mb D

A

739.9 ±6.1 Ma m s w c vc g

B Northwest

Southeast B’

T1401 Mine Camp F1010, G07, J1011

200

Not exposed thickness uncertain

Eagle Creek Formation

Not exposed thickness uncertain

F1013

150

100

-4-2 0 2 4

Upper

Hay Creek Upper

δ C (‰)

Hay Creek

250

F1: Massive bedded matrix supported diamictite F2: Thin bedded matrix supported diamictite F3: Clast supported conglomerate F4: Sandstone Striated clast F5: Siltstone Soft sediment deformation F6: Shale Ripple cross-lamination Yellow-grey dolomite matrix Green-black volcaniclastic matrix Green Shelter Coarsening-up F920, F841 Purple-maroon siliciclastic matrix F7: Thin bedded limestone rhythmite δ C (‰) Geochronology sample F9: Dolo-grainstone F10: Stromatolitic dolostone Rhyolite F11: Breccia Covered Andesite Dropstone Fault Basalt Erosive surface Pahoehoe Brecciated Massive flows Pillowed flows Tango Tarn Green Shelter Ash flow tuff F918 F924 F917 -4-2 0 2 4 Sill F840

F919 F840

m s w c vc g

50

C.L.

m s w c vc g

0 (m)

Bald Hill F837

m s w c vc g m s w c vc g m s w c vc g

F917-1

Mount Harper Volcanics m s w c vc g m s w c vc g m s w c vc g

F837B,C F837A

141°10'W

141°0'W

65°08'N

65°10'N

65°12'N

Alaska Yukon

65°14'N

43

A’

F8

65°16'N

141°20'W

Ha

ree

k

3

02

9

0 T7

65°04'N

1.5

0

3 km

River Fault Camp Dike Measured Section Anticline Syncline

10

Pass C reek

65°02'N

k

ree

C nt

GS

a Ple

3

T7

65°00'N

sa

T7

01 T7 06 T7

65°06'N

kC

4 8 GS 0 T7 1 7 GS 70 2 T GS

rd Lu c

Tatonduk River

A

Paleozoic undifferentiated Ediacaran undifferentiated Hay Creek Group Rapitan Group Pleasant Creek volcanics Fifteenmile Group Pinguicula Group

South

North

Fe Fe Fe Fe

m s m c vc g

100

50

Fe Fe Fe

100

50

250

Fe Fe

150

100

50

200

PCV m s m c vc g

m s m c vc g

0(m)

m s m c vc g

0(m)

m s m c vc g

Pleasant Creek Volcanics

Fe

-4-2 0 2 4

? HC Upper Group

0 -4-2 0 2 4

100

15 Rapitan

300

Fe

0(m)

International Border NW of Mt. Slipper T708, GS1, GS4 F843 Upper Group

Upper Group

300

Hay Creek Group

Pleasant Creek Volcanics

150 -4-2 0 2 4

Fe Fe

Hay Creek Group

150

Pleasant Creek T707, GS2

Pleasant Creek Volcanics

50

Fe Fe Fe

Rapitan Group

100

Rapitan Group

150

Rapitan Group HC Upper Group

-4-2 0 2 4

250

200

Hard Luck Creek T702, T709, GS3 T701, T706

Pleasant Creek Volcanics

Pass Creek T710 Upper Group

Upper Group

Tatonduk River

Upper Group

A

A’

0 -4-2 0 2 4

Fe Fe

m s m c vc g

F3: Conglomerate F4: Sandstone F5: Siltstone F6: Shale 150 F7: Rhythmite F9: Grainstone F11: Breccia Dolomite Limestone 100 Basalt Massive flows Pillowed flows Jaspilite clast m s m c vc g Dropstone Fe Ironstone F1: Massive diamictite Covered F2: Stratified diamictite Fault Yellow dolomite matrix Brown-green siliciclastic matrix Purple-maroon siliciclastic matrix

Nb x 50 Eagle Creek Fm F840A/B F917-1

950

Mt Harper Volcanics

T °C

900

F837A F837B F837C

850

Yellowstone

0.1

Mesa Falls Tuff Huckleberry Ridge Tuff

Nb/U

1000

0.03

0.01

800

750

0.003 700 0

0.05

0.1

0.15

Th/Y

0.2

0.25

Th

Y x 0.1

0.03

0.1

Th/Y

0.3

Pb/238U 206

Pb/238U 206

716

720

F917-1

720

1.03

720

1.04

720

720 0.1180

0.1175

720

1.04

0.1184

1.03

0.1165

F917-1

716

708

716

716

716

0.1155

704

1.01

Pb/235U 1.03

15PM08

F837C

712 1.01

712 1.02

712 1.01

712 1.02

712 1.01

207

1.02

Pb/235U

0.1168

0.99

15PM06

data-point error ellipses are 2σ

207

716

0.1172

F837A

0.1176

712

0

Mt. Profeit dolostone

-1 fanglomerate -2

0

Ka -3 Gtrherine Hematite oup Creek Group P -4 km 0 B. South

10 km

Ice Brook Formation

.

P

H.C

H.C.

Little Dal

5

H.C.

H.C.

Pinguicula Group

P

fanglomerate

P W P 5

Eis Graben Stelfox Member Keele Formation tion Twitya Forma Shezal

Wernecke Supergroup 10 km

North

Mine Camp

Bald Hill

0

. H.C cula i gu n i P

North Snake River Fault

Mount Profeit

Snake River Basin

A. South

Hay Creek Group

Eagle Creek Formation Mount Harper volcanics

-1 km

W

ormation la Pass F

See

635 Ma Ravensthroat formation 800-660 Ma thrust faults

on ke Formati Callison La Fifteenmile Group

Syn-Hay Creek, 660-635 Ma unconformity Sub-Rapitan, pre-660 Ma unconformity

High-angle faults (commonly reactivated)