Proterozoic strata in the northwestern Canadian Cordillera are preserved in erosional windows separated by 40–80 km of Phanerozoic cover (termed ‘inliers’; Fig. 1). The inliers of the Ogilvie Mountains are situated on the ‘Yukon block’ (Jeletsky 1962), which is an isostatically independent crustal block separated on its eastern margin from the North American autochthon by the Cretaceous to Paleogene Richardson Fault Array (Norris 1997; Hall and Cook 1998). This NNW–SSE zone of crustal weakness roughly outlines large Paleozoic facies changes that define the Richardson Trough (Cecile 1982, 2000; Cecile et al. 1997), large Neoproterozoic facies changes in the Windermere and Mackenzie Mountains Supergroups (Eisbacher 1981; Norris 1997), and the easternmost extent of exposure of the Pinguicula Group and Wernecke Supergroup (Delaney 1981; Eisbacher 1981). To the east of the Richardson Fault Array, Neoproterozoic rocks out-crop in the arcuate Mackenzie Mountains fold belt (Aitken and Long 1978; Park et al. 1989). The Yukon block is bound to the south by the Cretaceous to Paleogene Dawson Fault, which separates it from the Selwyn Basin (Gordey and Anderson 1993), and to the north and west by the Cenozoic Kaltag Fault (Fig. 1). Early Neoproterozoic strata equivalent to the platformal rocks exposed in the inliers have not been identified south of the Dawson Fault (Abbott 1997). Abrupt facies changes occur across the Dawson Fault in late Neoproterozoic and Paleozoic strata, suggesting that it was also a long-lived basement structure that originated during the Proterozoic and was sporadically reactivated in the Phanerozoic (Thompson et al. 1987; Abbott 1997; Norris 1997).

Since the early recognition that similar stratigraphic sequences were exposed throughout NW Canada (Fig. 2; Gabrielse 1972; Young 1977, 1981; Young et al. 1979), correlation of units between the Tatonduk (Young 1982), Coal Creek (Thompson et al.,1987), Hart River (Abbott 1997), and Wernecke (Eisbacher 1981; Delaney 1981) inliers of the Ogilvie and Wernecke Mountains of Yukon (Eisbacher 1981; Thorkelson 2000; Thorkelson et al. 2005), the Mackenzie Mountains fold belt of the Northwest Territories (NWT) (Aitken 1981), and the Amundsen Basin of Nunavut and NWT (Young 1981; Rainbird et al. 1996) has been a principal goal in geological mapping and stratigraphic analysis. Recent mapping and stratigraphic, geo-chemical, and geochronological analyses (Turner and Long 2008; Furlanetto et al. 2009; Jones et al. 2010; Macdonald and Roots 2010; Macdonald et al. 2010b, 2011; Medig et al. 2010; Martell et al 2011; Turner 2011; Halverson et al. 2012) have resulted in important new constraints on these successions. However, a comprehensive regional synthesis of Proterozoic stratigraphy has remained elusive due to the scarcity of isotopically dateable rock types, significant along-strike facies changes, poorly understood structural complications between inliers, and the lack of detailed descriptions of Proterozoic stratigraphy exposed in Yukon.

No crystalline basement is exposed in the Ogilvie, Wernecke, or Mackenzie mountains. The oldest exposed rocks belong to the Paleoproterozoic Wernecke Supergroup, which is only present on the Yukon block. The Wernecke Supergroup corresponds to Sequence A of Young et al. (1979, 1981) and consists of over 10 km of polydeformed carbonate and siliciclastic rocks (Delaney 1981). The Wernecke Supergroup was previously considered to be pre-1.71 Ga (Thorkelson et al. 2005); however, this constraint has become ambiguous following the new geochronological data of Furlanetto et al. (2009) which include ca. 1.65 Ga zircons in the Fairchild Lake, Quartet, and Gillespie Lake groups. Thus, it appears that the Wernecke Supergroup was deposited in a syn-tectonic basin immediately prior to the ca. 1.60 Ga Racklan orogeny and emplacement of the mineralized Wernecke breccia (Thorkelson et al. 2001a, 2005). Mafic intrusions cutting the Wernecke Supergroup are likely correlative with the ~1380 Ma Hart River sills in the Hart River inlier (Abbott 1997) or the ~1270 Ma Bear River dykes (Thorkelson 2000; Schwab et al. 2004).

The Wernecke Supergroup is unconformably overlain by the Pinguicula Group, which was originally included with Sequence B strata of northwest Canada and thought to be equivalent with part of the lower MMSG (Young et al. 1979; Aitken and McMechan 1991; Rainbird et al. 1996). The Pinguicula Group was originally defined in the Wernecke Mountains near Pinguicula Lake and separated into units A–F (Eisbacher 1981). Abbott (1997) later described early Neoproterozoic strata in the Hart River inlier of the eastern Ogilvie Mountains that rested with an angular unconformity on the Gillespie Lake Group and Hart River sills and were overlain by the Callison Lake dolo-stone. He correlated these strata with units A–D of the Pinguicula Group in the Wernecke Mountains, but recognized an angular unconformity between units C and D. Refining earlier work in the Wernecke Mountains, Thorkelson (2000) upheld units A–C in the Pinguicula Group, but reassigned units D–F to the Hematite Creek Group. Turner (2011) subdivided the Hematite Creek Group and reassigned the uppermost units to the Katherine and Little Dal groups of the MMSG. The more restricted definition of units A–C of the Pinguicula Group permits correlation with the pre-1270 Ma Dismal Lake Group in the Coppermine homocline (Kerans et al. 1981; Thorkelson et al. 2005). This correlation stemmed from the identification of a dyke assigned to the ca. 1380 Ma Hart River Sills that cuts fine-grained clastic strata assigned to Pinguicula A in the Wernecke Mountains (Thorkelson 2000). However, the intruded strata were later reassigned to the Wernecke Supergroup (Medig et al. 2010), which raised the possibility that Pinguicula A–C is younger than 1270 Ma.

The Pinguicula Group is unconformably overlain by the MMSG. The MMSG correlates with the Shaler Supergroup on Victoria Island at a formation resolution (Rainbird et al. 1996; Jones et al. 2010), and as mentioned above, a portion of the MMSG can be correlated across the Richardson Fault Array into eastern Yukon (Turner 2011), however, how these strata extend to inliers in the Ogilvie Mountains has remained uncertain. Age constraints on the lower MMSG and its equivalents (Fig. 2) are provided by 1050±5 and 1059±3 Ma detrital zircons from unit PD1 and 1001±2 Ma detrital zircons from unit PD3 of the Hart River inlier (both units are assigned to the lower Fifteenmile Group), a 1079 ±2 Ma detrital zircon in unit K7 of the Katherine Group of the Mackenzie Mountains, and a 1077±2 Ma detrital zircon from the Nelson Head Formation of Victoria Island (Rainbird et al. 1997). An additional upper age constraint is given by the ca. 780 Ma mafic intrusions (assigned to the Gunbarrel igneous event) that cut the Little Dal Group up to the Gypsum Formation ( Jefferson and Parrish 1989; Harlan et al. 2003). These intrusions have been correlated geochemically with the Little Dal Basalt (Dudás and Lustwerk 1997), which separate the upper MMSG from the unconformably overlying Coates Lake Group and the Cryogenian–Ediacaran Windermere Supergroup (Sequence C of Young et al. 1979).

Neoproterozoic strata in the Coal Creek inlier were originally separated from the Wernecke Supergroup by Norris (1978) and later mapped and described as the Fifteenmile Group (named after the headwaters of Fifteenmile River; Thompson et al. 1987, 1994) and the Mount Harper Group (Mustard and Roots 1997). The Fifteenmile Group was a provisional term used to distinguish older Neoproterozoic strata in the Coal Creek inlier from the Lower Tindir Group of the Tatonduk inlier and the Pinguicula Group in the Wernecke Mountains (Thompson et al. 1994). The Fifteen-mile Group was originally subdivided into upper and lower subgroups, containing three (PF1–PF3) and five (PR1–PR5) informally defined map units, respectively (these units are shown on the regional map of Thompson et al. (1994); see Figure 11 of Macdonald et al. (2011) for a chart comparing the old and new strati-graphic nomenclature). Previous workers suggested that the lower Fifteenmile Group was intruded by breccia (referred to as the ‘Ogilvie breccia’) equivalent to the ca. 1600 Ma Wernecke breccia (Thorkelson et al. 2001b) and hence was partly equivalent to the Pinguicula Group and Wernecke Supergroup of the Wernecke inlier (Thompson et al., 1987, 1994). However, Medig et al. (2010) demonstrated that map unit PR1 overlies a regolith formed on top of the Ogilvie breccia and that all of the lower Fifteenmile Group is younger. Moreover, a tuff recovered within strata previously mapped as PR4 (revised to PF1a to reconcile inconsistencies of previous mapping) was dated at 811.51 ± 0.25 Ma (U/Pb ID-TIMS; Macdonald and Roots 2010; Macdonald et al. 2010a). We follow Medig et al.’s (2010) suggestion that units PR1–PR3 are largely correlative with units A–C of the Pinguicula Group, which provides a distinct separation of the remaining Fifteenmile Group from the underlying Pinguicula Group.

Major revisions to the mapping in the Coal Creek inlier, including elimination of many inferred thrust faults in the lower Fifteenmile Group, led Macdonald et al. (2011) to propose a new subdivision of the Fifteenmile Group into an informal ‘lower assemblage’ of mixed shale and dolostone, overlain by the informal Craggy dolo-stone. Halverson et al. (2012) subsequently subdivided the lower assemblage into the informal Gibben and Chandindu formations and the overlying Reefal assemblage. Macdonald et al. (2011) also revised the stratigraphic nomenclature by removing the Callison Lake dolostone (Abbott 1997; Macdonald and Roots 2010) from the Fifteenmile Group. The Callison Lake dolostone is overlain by the Mount Harper Group, which includes the lower Mount Harper Group (LMHG) and the Mount Harper volcanic complex (MHVC; Macdonald et al. 2011; Fig. 2). A minimum age constraint on the Fifteenmile Group comes from rhyolite flows in the upper MHVC, which were dated at 717.43 ± 0.14 Ma (U/Pb ID-TIMS; Macdonald et al. 2010a). The MHVC is interbedded with and conformably succeeded by 716.47 ± 0.24 Ma glacial deposits of the Rapitan Group (U/Pb ID-TIMS; Macdonald et al. 2010a). In the Coal Creek inlier, the Rapitan Group is overlain by the Cryogenian Hay Creek Group and the Ediacaran to Early Cambrian ‘Upper’ Group (Macdonald et al. 2011; Chapter 3.3.4 in Martel et al. 2011), which are in turn unconformably overlain by the Cambrian to Devonian Bouvette Formation.

We measured 54 stratigraphic sections through the Pinguicula, Fifteenmile, Mount Harper, Rapitan, Hay Creek, and ‘Upper’ groups in the Coal Creek inlier. Carbonate lithofacies are defined (Table 1) and used in the lithostratigraphic descriptions below along with siliciclastic lithofacies differentiated by grain size and composition. These lithofacies are then grouped into facies assemblages (Table 2), which are used to track the evolving depositional environments and sequence architecture of the Fifteenmile Group. Sequences described are composed of parasequence sets that define systems tracts (Mitchum and Van Wagoner 1991), but without further age constraints, the order of these sequences remains uncertain. In the descriptions below we focus on the Fifteenmile Group, but to provide broader tectonostratigraphic context we also discuss the bounding stratigraphy in the Pinguicula Group, Callison Lake dolostone, and Mount Harper Group in the Coal Creek inlier.

In the Coal Creek inlier, the Pinguicula Group is exposed in a syncline to the NW of Mt. Gibben (Fig. 3, section E1003) and along ridges north of Mount Harper, where it unconformably overlies the Wernecke Supergroup. The Pinguicula Group has been divided into a siliciclastic-dominated unit and a carbonate-dominated unit, referred to as Pinguicula A and Pinguicula B/C, respectively (Macdonald et al. 2011). On the north limb of the syncline near Mt. Gibben, Pinguicula A is composed of a lower ~320 m-thick unit of weakly foliated, brown to grey-coloured siltstone and shale with irregularly dispersed large dolostone blocks and conglomerates interpreted as olistostromes (Fig. 4a) and debris flows, respectively (Macdonald et al. 2011). On the south limb of the syncline, the distinct orange-coloured dolostone blocks are over 10 m in diameter and their internal bedding is discordant with the surrounding siliciclastic matrix. The olistostrome-bearing siliciclastic rocks are overlain by >500 m of yellow to blue-grey weathering dolostone of Pinguicula B/C. On the north side of the syncline, the carbonate rocks consist predominantly of grainstone and stromatolites (a facies characteristic of Pinguicula C in the Hart River and Wernecke inliers), whereas on the south side of the syncline the dolostones are characterized by laminated dolomicrite and dolosparite with rare lime mudstone (a facies characteristic of Pinguicula B in the Hart River and Wernecke inliers). These facies are gradational in the Coal Creek inlier; hence we mapped them together and refer to this sequence as Pinguicula B/C because they represent one depositional package with distinct lateral facies changes. At the top of Pinguicula B/C, stromatolites with high synoptic relief are overlain with black shale and minor dolomicrite, and green-weathering flat-laminated silt-stone, which we include with Pinguicula B/C.

North of Mount Harper (Fig. 3; section G135), the Pinguicula Group is represented by a thick dolostone capped by a spectacular assemblage of Minjaria, Tungussia, and Conophyton stromatolites (Halverson et al. 2012). The stromatolitic dolostone in this section is overlain by green siltstone. The Pinguicula Group tapers out to the NW of section G135 by a combination of onlap onto the unconformably underlying Gillespie Lake Group (upper Wernecke Supergroup) and truncation beneath an erosional unconformity at the base of the Fifteenmile Group (section G130, Fig. 3).

The Fifteenmile Group is exposed in the Tatonduk, Coal Creek, and Hart River inliers. We recently proposed a revised subdivision of the Fifteenmile Group into four informally defined formations: the Gibben and Chandindu formations, which constitute the lower Fifteenmile Group, and the Reefal assemblage and Craggy dolo-stone, which constitute the upper Fifteenmile Group (Macdonald et al. 2011; Halverson et al. 2012). Because of large lateral facies change within the Fifteenmile Group, we use a sequence stratigraphic approach to attempt the correlation of time-equivalent surfaces across the basin and help interpret the basin fill. Where subaerial unconformi-ties are apparent, depositional sequences are defined. Elsewhere, particularly in more distal environments, the maximum regressive surface (MRS) is used as the correlative sequence boundary.

The uppermost sequence of the Reefal assemblage is capped by a distinct sub-aerial exposure surface overlain by the heavily silicified and informally named Craggy dolostone. The Craggy dolo-stone forms a conspicuous, ridge-forming, >500-m-thick white dolo-stone and consists predominantly of thick bedded and massively recrystallized and silicified sucrosic dolostone. Microbialaminite and low-relief stromatolites (up to 10 cm of relief) are variably preserved through the pervasive and multigenerational silicification and recrystallization. Ooids, coated grains, brecciated teepee structures, tabular clast conglomerates, intraclast breccia, and low-angle crossbeds have also been observed. Silicification is particularly intense near the upper unconformity that separates the Craggy dolo-stone from the overlying Callison Lake dolostone. Although the pervasive silicification and recrystallization challenge any comprehensive facies and sequence stratigraphic analyses of the Craggy dolostone, it is evident that it records the development of a broad and stable carbonate platform following the filling of residual sub-basin bathymetry in the Reefal assemblage.

The Craggy dolostone is succeeded by the Callison Lake dolostone (Abbott 1997), which was recently separated from the Fifteenmile Group (Macdonald et al. 2011) because it unconformably overlies the Fifteenmile Group (Macdonald and Roots 2010). Halverson et al. (2012) suggested placement in the Mt. Harper Group, but we leave it as an orphaned unit here awaiting formal formation and group designation. Near Mt. Gibben, the Callison Lake dolostone is ~500 m thick and consists of a basal siltstone and shale sequence with laterally discontinuous stromatolitic bioherms. This is overlain by medium-bedded dolostone interbedded with black shale that consists almost exclusively of sedimentary talc (Tosca et al. 2011). These strata (previously mapped as unit PF2; Thompson et al. 1994) are overlain by ~200 m of a silicified dolostone characterized by domal stromatolites (previously mapped as unit PF3). An additional ~25 m interval of interbedded black shale and dolostone occurs just below the contact with the lower Mount Harper Group. We map the entire shale–carbonate sequence as the Callison Lake dolostone because this succession appears to form a genetically continuous unit, minimizes new terminology and allows for straightforward stratigraphic correlation between the Coal Creek and Hart River inliers.

Two sets of mafic dykes are present in the Coal Creek inlier. One set is oriented WSW–ENE and predominantly intrudes the Wernecke Supergroup (Fig. 3). These dykes are likely correlative with the sheared mafic rocks that are in fault contact with the Fifteen-mile Group near Mt. Gibben in section E1002 (Fig. 3) and multiple intrusions associated with the WSW–ENE oriented Ogilvie breccias. In section E1003 (Fig. 3), an ESE–WNW oriented dyke also intrudes Pinguicula A.

A second set of dykes is oriented NNW–SSE and intrudes strata up through the lower MHVC. These dykes are associated with chaotic deformation in the Lower Mount Harper Group, indicating that these rocks were still soft sediments when the second suite was emplaced. No dykes have been observed to intrude the Rapitan Group. Thus, the NNW–SSE dykes appear to be associated with the ca. 717 Ma upper MHVC and predate the ca. 716 Ma Rapitan Group.

We report 1386 new carbonate carbon and oxygen isotope measurements (see data repository). Samples were cut perpendicular to lamination, revealing internal textures and between 5 and 20 mg of powder were micro-drilled from the individual laminations (where visible), avoiding veining, fractures, and siliciclastic components. Subsequent δ¹³C_carb and δ¹⁸C_carb analyses were performed on aliquots of this powder, acquired simultaneously on a VG Optima dual inlet mass spectrometer attached to a VG Isocarb preparation device (Micromass, Milford, MA), in the Harvard University Laboratory for Geochemical Oceanography. Micro-drilled samples were reacted in a common, purified H₃PO₄ bath at 90°C where evolved CO₂ was collected cryogenically and analyzed using an in-house reference gas. External error (1σ) from standards was better than ± 0.1‰ for both δ¹³C and δ¹⁸O. Samples were calibrated to VPDB (Vienna Pee-Dee Belemnite) using the Carrara Marble standard. Increasing the reaction times (~7 minutes) minimizes any potential memory effect resulting from the common acid-bath system, which is included in the precision estimates noted above. Carbon (δ¹³C) and oxygen (δ¹⁸O) isotopic results are reported in per mil notation of ¹³C/¹²C and ¹⁸O/¹⁶O, respectively, relative to the standard VPDB.

Carbon isotope chemostratigraphy of the Fifteenmile Group was performed to test local, regional, and global correlations through large facies changes. In the basal Gibben formation of the Fifteenmile Group, δ¹³C values rise from ~0 to +4‰, and is a consistent trend throughout the inlier (Figs. 5 and 6). Carbon isotope values in thin carbonate interbeds, within siliciclastic-dominated strata of the overlying Chandindu formation and lower portion of the Reefal assemblage, are highly variable. This is likely due, in part, to local re-mineralization of organic matter and proportionately greater contribution of ¹³C-depleted authigenic cements to the whole-rock carbonate content. Nonetheless, more carbonate-rich facies at the top of sequence 4b in the Mount Harper composite section (Fig. 5), show consistent values around 0‰ that rise steadily up-section to very heavy values (~+4‰).

The stromatolite reefs of sequence 5 of the Reefal assemblage have δ¹³C values that average ~+4‰. However, lateral gradients are present in coeval strata. Above the basal flooding surface of sequence 6, δ¹³C values increase further to ~+8‰. This sequence contains the 811.5 ± 0.1 Ma ash bed (Macdonald et al. 2010b). Above the ash bed, δ¹³C values decrease smoothly to values as low as -6‰ (Figs. 5 and 6). However, the full ~14‰ isotope excursion is not present in some sections because the interval is shale-dominated (e.g., in the Mount Harper composite section, Fig. 5). In other sections, the excursion is cut out by erosional surfaces (e.g., in the Mt. Gibben composite section, Fig. 5). The most complete section of the excursion is exposed at Reefer Camp (section G021), which was measured from a paleo-high developed above a reef core (Fig. 6). There, the S7a transgression is carbonate dominated, so the whole excursion is preserved along with two additional smaller excursions in the S7a highstand and S7c (Fig. 6). Although a weak covariance between δ¹³C and δ¹⁸O can be observed through these excursions (see data repository), lateral reproducibility through different facies precludes large-scale diagenetic alteration.

In the Craggy dolostone, δ¹³C values increase steadily up-section and plateau at ~4‰. Although these dolomites are dominated by cement and full of exposure surfaces, the δ¹³C trends are consistent along strike and show no covariance with oxygen isotopes (see data repository).

The exact timing and geometry for both the formation and the break-up of Rodinia has remained elusive. Situated at the NW corner of Laurentia, and in the centre of Rodinia (Li et al. 2008b), the Yukon occupies an important position for distinguishing between tectonic events occurring on the northern and western margins of Laurentia. Recent paleomagnetic studies provide a Rodinia reconstruction that is “longer-lasting and tighter-fitting” (Li and Evans 2011), and these data require that Australia and Lauren-tia came together after 1070 Ma with a ‘missing link’ presiding in-between, and subsequently separated between ca. 750 and 650 Ma. Paleomagnetic and geochronologic data indicate that South China may be the ‘missing link’ (Li et al., 1995, 2008b). South China is a composite Neoproterozoic continent consisting of the Cathaysia and Yangtze blocks, which converged during the ca. 835 Ma Sibao orogeny (Wang et al. 2012). In the ‘missing link’ model, the Cathaysia Block was a fragment of Mesoproterozoic Lauren-tia and the Yangtze Block provided westerly-derived 1600–1490 Ma zircons to the Belt Supergroup (Ross et al. 1992; Ross and Villeneuve 2003). The Sibao Orogeny may have also provided a more local source of Grenville-age 1.2–1.0 Ma zircons to the western margin of Laurentia (Li et al. 2008a) that have previously been attributed to a transcontinental river system (Rainbird et al. 1997). However, no early Neoproterozoic foreland basin or orogen has been identified on the western margin of Laurentia to suggest a link to this orogenic event. Possible exceptions occur in the Coppermine homo-cline (Fig. 1), where two sets of structures deform the ca. 1270 Ma Copper-mine River Group and predate the Shaler Supergroup (Hildebrand and Baragar 1991), and in the Wernecke Mountains, where NW-vergent folds in the Hematite Creek and Katherine groups have been assigned to the Corn Creek Orogeny (Eisbacher 1981; Thorkelson 2000; Thorkelson et al. 2005). Neoproterozoic folding has also been described in the Coates Lake and Rapitan groups in the Mackenzie Mountains (Helmstaedt et al.1979; Eisbacher 1981), and in the Shaler Supergroup on Victoria Island (Heaman et al. 1992; Bedard et al. 2012), but these structures appear to be too young to be correlative with the Sibao orogeny.

The Fifteenmile Group and equivalent strata in the Mackenzie Mountains and Victoria Island, can be broadly correlated to the Shihuiding Formation of the Cathaysia Block, and the Ziajiang, Danzhou and Banxi groups of the Yangtzee Block (Wang et al. 2011), the lower Callana Group in South Australia, the Bitter Springs Formation and equivalents in central Australia (Walter et al. 1995). Like the Fifteenmile Group, these Chinese basins also contain ca. 810 Ma tuff horizons (Wang et al. 2012). The ‘missing link’ model predicts that more ca. 800 Ma grains from the Sibao orogeny will be discovered in the uppermost Fifteen-mile Group or overlying strata. Interestingly, significant ca. 800 Ma populations have been discovered in the Uinta Mountains Group of Utah (Dehler et al. 2010), which may have been sourced from South China. Additionally, new age constraints on successions in the western US indicate that there are no known basins that formed between 1.0 and 0.8 Ga between 62° N and Mexico (Dehler et al. 2010, 2011), such that the basin forming event that accommodated the Fifteenmile Group and equivalents in the Shaler Supergroup and MMSG is a phenomenon of the NW margin of Laurentia and cannot represent rifting on the whole of the western margin, contrary to the simple-shear rift model proposed to accommodate the MMSG (Turner and Long 2008). We suggest instead that the inferred NE–SW oriented faults in the MMSG of Turner and Long (2008) are coeval with the faults in the basal Fifteenmile Group and also represent normal faults rather than transfer faults. This is consistent with Aitken’s (1981) previous interpretation of the Little Dal Group, which suggested deepening to the NNW.

Based on the assumption that the early Neoproterozoic conjugate margin to Laurentia was South China, we propose a new model for the early Neoproterozoic tectonic evolution of northwest Canada. The coincidence between basin formation in South China, Australia, and NW Canada at ca. 830 Ma, and the emplacement of the Gubei and Gairdner LIPs in South China and Australia between 830 and 810 Ma (Wingate et al. 1998; Li et al. 1999; Wang et al., 2008) suggests a mechanistic link. We propose that these strata were accommodated by extension and the subsequent thermal decay associated with the passing of Rodinia over a plume. In this model, the Reefal assemblage and Craggy dolostone are associated with the thermal decay of this plume. Deposition culminated with the intrusion of the 780 Ma Gunbarrel dykes—the nature of this igneous event remains poorly understood. This model is further consistent with the inference of Rain-bird et al. (1996) that Sequence B formed in an intracratonic basin.

The ca. 717 Ma NNE-side down normal faults in the Coal Creek inlier represent a reactivation of the NW margin of Laurentia. Geological and geochronological data suggest that Siberia occupied a position north of the Yukon during the Neoproterozoic (Rainbird et al. 1998). Moreover, dykes of approximately Franklin age are present in southwestern Siberia (Glad-kochub et al. 2006; Bedard et al. 2012;). Rainbird (1993) further documented fault-bounded graben with coarse terrestrial fill in the upper Shaler Supergroup, immediately beneath the ca. 723 Ma Natkusiak basalts. Although a record of later Cryogenian thermal subsidence is not present in Victoria Island where there is no section present above the Natkusiak basalts (Rain-bird 1993), a Cryogenian passive margin succession on the northern margin of Laurentia may be recorded in the subsurface west of Melville Island (Helwig et al. 2011) and in the Katakturuk Dolomite on the parautochthonous North Slope subterrane (Macdonald et al. 2009). Thus, a scenario consistent with all of these data is that extension occurred in the early Neoproterozoic between Siberia and northwest Laurentia, creating space between the two cratons and separating their respective APW paths (Rainbird et al. 1998; Khudoley et al. 2001; Evans 2009); however this extension may not have manifested itself in full rifting with the development of oceanic crust, such that both margins were later affected by additional extension and the emplacement of the ca. 720 Ma Franklin LIP.

The nature of Cryogenian basin formation on the western margin of Laurentia remains enigmatic. As discussed above, the presence of both Cryogenian normal faults and folding implies a transtensional–transpressional setting for Windermere-age rifting (Jefferson and Parrish 1989). Transtension may further account for the irregular distribution of Cryogenian strata in Yukon (Macdonald et al. 2011) and the lack of significant crustal thinning until the latest Ediacaran (Colpron et al. 2002), consistent with thermal subsidence models that indicate final rifting in the earliest Cambrian (Bond and Kominz 1984). Full description of Cryogenian and Ediacaran basins is beyond the scope of this paper and the later Neoproterozoic tectonic evolution of NW Laurentia remains to be elucidated with future work.