ABSTRACT The Windermere Supergroup in southern British Columbia and its correlatives (such as the Pocatello Formation and lower Brigham Group in southeastern Idaho) along the western North American Cordilleran margin are an archetype of Neoproterozoic to early Paleozoic tectonic, sedimentary, and climatic processes. The central Idaho portion of the margin remains relatively understudied when compared to regions to the south in southeastern Idaho or to the north in northeastern Washington. This is in part a legacy of early workers, who identified the absence of Neoproterozoic and Cambrian strata in east-central Idaho across the Lemhi arch. However, Neoproterozoic and Cambrian rocks are indeed present west of the Lemhi arch within the central Idaho section of the Cordillera. Here, we summarize recent advances in our understanding of these strata within central Idaho and correlate the Pocatello Formation and Brigham Group rocks from northern Utah/southeastern Idaho through central Idaho to northeastern Washington. We also provide new constraints that link Cambrian strata from central Idaho across the Lemhi arch to southwestern Montana. Collectively, this emerging tectono-stratigraphic framework suggests extensive, some likely diachronous, stratigraphic boundaries and magmatic events relating to (1) widespread rifting ca. 720–680 Ma; (2) early and late Cryogenian (Sturtian and Marinoan) glacial sedimentation; (3) base-level drawdown and formation of incised valleys, previously correlated to the Marinoan glacial interval, but which now appear to be younger (ca. 600 Ma) and perhaps related to tectonic activity; (4) onset of the Sauk I transgression 560–530(?) Ma; (5) the ca. 515 Ma Sauk II lowstand, perhaps related to final rifting in southern Laurentia; and (6) the Sauk III lowstand coeval with exhumation of 500–490 Ma Beaverhead plutons within the Lemhi arch. Magmatism occurred ca. 680 Ma, 660 Ma, 600 Ma, and 500 Ma, providing age ties. These observations suggest that Neoproterozoic and lower Paleozoic strata in the central Idaho sector of the North American Cordillera record similar processes and sedimentation as strata elsewhere along the margin.

Abstract Detailed sedimentological and stratigraphic analyses of a c. 1500 m thick, siliciclastic-dominated slope succession in the Neoproterozoic Isaac Formation at the Castle Creek study area (southern Canadian Cordillera) reveals the occurrence of four well-preserved mass-transport complexes (MTCs) composed principally of slide/slump and debris-flow deposits. The stratigraphically lowest of these complexes is about 60 m thick and crops out for >2.5 km laterally, consisting of slide and debrite. The slide has an irregular erosive base with ramp-and-flat geometry. This is overlain locally by boulder-sized blocks of slightly to moderately deformed strata, bounded by shear surfaces. The slide is overlain by a debrite that pinches and swells laterally, consisting of matrix-supported conglomerate with common metre-scale clasts of mudstone and coarse-grained sandstone embedded in a mudstone-rich matrix with dispersed, pebble quartz grains. Based on its stratigraphic position at the base of the slope, vertical stacking of slide-debrite, lithological distribution, considerable thickness and lateral extent, this MTC is interpreted to be associated with a major episode of continental slope instability and submarine mass-wasting. The close association between the MTC and underlying/overlying mixed carbonate-siliciclastic strata suggests that sea level most likely exerted a key control on sediment supply, which ultimately led to the emplacement of this MTC.

Abstract Deep marine rocks of the Windermere Supergroup record a several km-thick sedimentary pile that accumulated along the passive continental margin of Neoproterozoic Laurentia (ancestral North America). The succession comprises mostly siliciclastic sedimentary rocks intercalated with carbonate and mixed carbonate-siliciclastic intervals that range up to a few 100 m in thickness. Observations along a several 100 km-long depositional transect that stretches from upper slope canyons to deep basin-floor deposits shows a number of systematic changes that appear to be principally controlled by changes of eustasy. Significantly, these changes are only recognized in the slope part of the transect. Slope deposits form a ~2 km-thick succession dominated by thin-bedded turbidites that locally are intercalated with up to >100 m-thick by several km-wide erosional and leveed channel complexes. Channels exhibit two end member kinds of fill: aggradational and laterally accreting. Aggradationally filled channels are flanked by well developed sandy levees compared to mud-rich levees in the case of laterally accreting channels. Unlike aggradationally filled channels and laterally accreting channels are associated with the input of carbonate sediment, typically in the form of carbonate-cemented sandstone and mudstone clasts. Additionally, evidence of mass wasting, evidenced by thickly developed and areally extensive debrites, slump, and slide deposits, become an important component in the stratigraphy. Fragments within these strata, namely stromatolite and oolite fragments, in addition to abundant carbonate-cemented sandstone and mudstone clasts, indicates the resedimentation of debris sourced from an upslope shallow-water carbonate platform under late transgressive, highstand and possibly also early falling stage conditions. Specifically, the rise of eustasy is interpreted to have not only initiated the development of a carbonate platform, and thereby the input of carbonate sediment, but more importantly changed the make-up of the siliciclastic sediment supply, principally in terms of its grain size and grain-size distribution.

Abstract The Neoproterozoic Windermere Supergroup (WSG) is exposed over an area of 35 000 km 2 in the southern Canadian Cordillera, and consists primarily of deep-marine meta-sedimentary rocks interpreted to have been deposited during rifting and subsequent post-rift thermal relaxation. The main exposures of the WSG occur within thrust panels and structural culminations of the eastern Cordilleran orogen. Within the thick stratigraphic succession ( c. 9 km) are three units of glaciogenic affinity: Toby, Vreeland and Old Fort Point (OFP) formations. The Toby Formation (Fm.) is composed of up to 2500 m of diamictite, interbedded with conglomerate, sandstone, mudstone, carbonate and mafic volcanic rocks. The Vreeland Formation ranges from 350 m to 2000 m in thickness and consists of diamictite, interbedded with mudstone, sandstone and conglomerate. The OFP ranges from 60 to 450 m in thickness and consists of a distinctive threefold stratigraphic package of basal siltstone grading upward into limestone–siltstone rhythmite, organic-rich mudstone and an overlying heterolithic unit of diamictite, breccia, conglomerate, sandstone, siltstone to mudstone and limestone. A locally prominent unconformity marks the base of the OFP upper member. Both the Toby and Vreeland formations represent remobilized glacially derived marine sediments deposited by sediment-gravity flows. Deposition of the Toby Fm. was fault-controlled during an active tectonic phase (rifting), whereas the Vreeland Fm. accumulated during the subsequent quiescent phase (post-rift) with limited structural control. The OFP is interpreted to be a regionally extensive deep-marine post-glacial marker temporally associated with the glaciogenic Vreeland Fm. Although direct geochronological ages for WSG units in southwestern Canada are generally absent, high-precision radiometric ages of underlying and overlying igneous events constrain the relative maximum and minimum timing of deposition from c. 740–728 Ma to c. 569 Ma. At the base of the WSG succession, the Toby Fm. may be as young as c. 685 Ma based on ages obtained from potential stratigraphic correlatives in the USA. There is no direct age constraint for the deposition of the Vreeland Fm.; its minimum timing is based on its stratigraphic relationship with the post-glacial OFP. The middle member of the OFP was precisely dated at 607.8±4.7 Ma using the Re–Os method, placing it in the Ediacaran Period. Published geochemical and stable isotopic data are similarly limited for all three units with only some δ 34 S py values available from one section of the OFP. Recent work has focused on detailed sedimentological and stratigraphic studies of the Toby and OFP formations with future efforts being directed towards integrated geochemical and isotopic research. Additional geochronological constraints are needed to refine palaeogeographical models and strengthen regional correlations with other North American Cordilleran glaciogenic units.

Abstract In central Idaho, Neoproterozoic stratified rocks are engulfed by the Late Cretaceous Idaho batholith and by Eocene volcanic and plutonic rocks of the Challis event. Studied sections in the Gospel Peaks and Big Creek areas of west-central Idaho are in roof pendants of the Idaho batholith. A drill core section studied from near Challis, east-central Idaho, lies beneath the Challis Volcanic Group and is not exposed at the surface. Metamorphic and deformational overprinting, as well as widespread dismembering by the younger igneous rocks, conceals many primary details. Despite this, these rocks provide important links for regional correlations and have produced critical geochronological data for two Neoproterozoic glacial periods in the North American Cordillera. At the base of the section, the more than 700-m-thick Edwardsburg Formation (Fm.) contains interlayered diamictite and volcanic rocks. There are two diamictite-bearing members in the Edwardsburg Fm. that are closely related in time. Each of the diamictites is associated with intermediate composition tuff or flow rocks and the diamictites are separated by mafic volcanic rocks. SHRIMP U–Pb dating indicates that the lower diamictite is about 685±7 Ma, whereas the upper diamictite is 684±4 Ma. The diamictite units are part of a cycle of rocks from coarse clastic, to fine clastic, to carbonate rocks that, by correlation to better preserved sections, are thought to record an older Cryogenian glacial to interglacial period in the northern US Cordillera. The more than 75-m-thick diamictite of Daugherty Gulch is dated at 664±6 Ma. This unit is preserved only in drill core and the palaeoenvironmental interpretation and local stratigraphic relations are non-unique. Thus, the date for this diamictite may provide a date for a newly recognized glaciogenic horizon or may be a minimum age for the diamictite in the Edwardsburg Fm. The c . 1000-m-thick Moores Lake Fm. is an amphibolite facies diamictite in which glacial features have not been observed. However, it is part of a sedimentary cycle from unsorted siliclastic deposits to mud and carbonate deposits. Using lithostratigraphy and available geochronology, the Moores Lake Fm. is correlated with a younger succession of Cryogenian glaciogenic rocks in southeastern Idaho. Traditional correlations of Neoproterozoic rocks in the Cordillera recognize two levels of Cryogenian diamictites. The Edwardsburg and Moores Lake diamictites along the middle Cordillera fit well into the scenario of two glacial events. Because of the correlations, dates that provide ages for the diamictites in central Idaho (and corroborated in southeastern Idaho, Link & Fanning 2008 ) could constrain the age of correlated glaciogenic deposits elsewhere in the Cordillera. However, in the absence of dates for the glaciogenic diamictites in Canadian and southern US Cordilleran sections, the correlations are considered possible but uncertain.

Abstract The Windermere Supergroup (WSG) is exposed extensively throughout western North America, extending from northwestern Mexico northward through the western United States, along the length of the Canadian cordillera ( Figure 1 ), and into the Yukon-Alaska border region ( Ross et al., 1989 ). The term Windermere Supergroup was coined by Walker (1926) for the mostly sedimentary rocks exposed in the Windermere Valley of southern British Columbia. Subsequent stratigraphic studies, however, have used a variety of terms to describe these rocks, including Miette Group in the western Rocky Mountains, Horsethief Creek Group for exposures in the Purcell Mountains, Kaza and Cariboo Groups in the Cariboo Mountains, and locally Mica Creek assemblage in high grade rocks of the Monashee Complex. Stewart (1972) was the the first to suggest that the WSG consisted of two parts: A lower sequence comprising laterally discontinuous strata that accumulated synchronous with rifting, and an upper sequence characterized by laterally continuous units interpreted to have accumulated during postrift thermal relaxation. Subsequently, Ross (1991) suggested that the Windermere comprises the sedimentary and volcanic record following the break-up of the supercontinent Rodinia and the formation of the proto-Pacific Ocean >700 Ma. Present-day preservation and exposure of the WSG is the result of Mesozoic deformation during formation of the cordilleran orogenic belt. In the southern Canadian cordillera, the WSG unconformably overlies Mesoproterozoic sedimentary rocks of the Belt-Purcell Supergroup (1.5–1.4 Ga; Evans et al., 2000 ) or crystalline basement that ranges in age from 2.2–0.73 Ga ( Crowley, 1999 ).

Abstract Unconfined, sand-rich, basin-floor submarine fan deposits have been identified in the Upper Kaza Group of the Windermere Supergroup and are well exposed at the Castle Creek locality, British Columbia, Canada ( Figure 1 ). Regional time slices through the Upper Kaza Group are interpreted to indicate a distal-basin-floor setting for the Castle Creek study area. Correlative strata, becoming more proximal to the continental slope over approximately 300 km (186 mi) in a southeast direction occur at Lake Louise, Alberta ( Figure 1A ). The distribution of facies (Figures 3, 4) has led to a threefold subdivision of the ~600-m (~1968-ft)-thick section which displays an upward decrease in the percentage of sandstones from 67.1% to 60.2% to 58.5%, respectively. This overall decrease in sandstone upwards is associated with a general thinning- and fining-upward trend at the scale of the outcrop. The vertical pattern is interpreted to reflect a change from an axial zone of sandstone deposition to an off-axis area with less sandstone and more mudstone or alternatively, an overall backstepping of the basin-floor-fan system. The lower Upper Kaza is characterized by amalgamated medium- to coarse-grained sandstone turbidites with scoured contacts. Lateral changes in sandstone to mudstone and character of outcrop gamma-ray profiles are interpreted as a change from a channelized lobe-interior to lobe-margin (lobe-fringe to interlobe). The presence of significant bypass facies (mudstone breccias and medium-scale cross-stratified sandstone) and scour surfaces differentiate the middle Upper Kaza from the lower Upper Kaza and mark a change to sediment bypass and scouring

Abstract The outcrop consists of the inner-bend deposits of two sharp-based, laterally accreting sinuous channels (C1, C2) that are oriented perpendicular and moderately oblique to the outcrop, respectively. Many important channel attributes can be measured because of the perpendicular orientation of C1. Lateral-accretion deposits, although well developed in both channel fills, are inclined at 7–12° to the channel base in C1, and based on geometry, are of the order of 120–140 m (394–460 ft) long. Lateral-accretion deposits show negligible change in grain size along their length or stratigraphically upward (although beds generally thin upward. They consist of subparallel but inclined, decimeter (0.3 ft)-thick beds composed of very coarse-grained sandstone to granule conglomerate grading upward to medium-grained sandstone. Near the updip terminus of each lateral accretion layer, strata are ungraded and distinctively poorly sorted. In addition, traction sedimentary structures, mostly dune cross-stratification, occur in the upper half, or more commonly, upper third of the lateral accretion deposit. Mudstone (silty slate) is generally absent in all channel fills. Where present, it occurs typically as isolated patches of intraclast breccia in the lower third of the channel fill. These clasts were probably derived from erosion of local mudstone layers, and, as a consequence, coarser grained beds amalgamate in the lower part of the channel fill. At the top of the channel fills, mudstone intertongues with typically very coarse-grained sandstone that thins and pinches out, commonly abruptly, into mudstone. The mudstone interval consists of thinly bedded, single-set-thick, fine-grained sandstone Tc turbidites interstratified with silty mudstone

Abstract Isaac channel 3 in the Castle Creek South study area ( Figure 1 ) exposes a leveed-channel system that is up to 90 m (300 ft) thick and extends at least 1.6 km (1 mi) laterally ( Figure 2 ) (For an overview see Arnott and Ross, chapter 22, this volume). The channel-levee system overlies an areally extensive, up to 80-m (260-ft)-thick, carbonate-clast-rich debrite (D1). Locally, the debrite is overlain by an up to 3-m (10-ft)-thick, sheetlike, coarse-grained, sand-rich, heterolithic assemblage (L0 ) that is interpreted to have been deposited by relatively unconfined, high-density flows. These strata, in addition to topography along the top of the debrite, helped focus subsequent flows that ultimately formed Isaac channel 3. Isaac channel 3 consists of four channel-fill units (C1 to C4) that stack in a lateral-offset pattern toward the northwest ( Figure 2 ). These fills vary from 7 to 30 m (23–99 ft) thick, and have high net-to-gross (N:G) ratios (70–100%). In their axes, channel-fill strata typically consist of thick-bedded (up to 3 m [10 ft]), massive to graded, pebble conglomerate and very coarse- to medium- grained sandstone, and mudstone-clast breccia that were deposited by high-concentration, gravel- and sand-rich turbidity currents. In the upper part of Isaac channel 3 (C3 and C4), strata near the margin of the channel consist of thick-bedded (up to 1.5 m [up to 5 ft]) amalgamated sandstone that laterally becomes progressively more interbedded with siltstone and very fine- to fine-grained sandstone. These strata were deposited by low- to moderate-concentration flows.

Abstract A detailed architectural analysis was conducted on Isaac channel 5 in the Castle Creek area (east-central British Columbia, Canada, Figure 1 ). Isaac channel 5 developed within a Neoproterozoic slope turbidite system along the passive western margin of North America where debris flows and mass movements were common (see Arnott and Ross, chapter 22, this volume). Isaac channel 5 crops out across a 3.5-km (2.1-mi)-long section oriented oblique to mean paleoflow (toward the northwest) and represents an enduring transport and depositional pathway that accumulated ~100 m (~330 ft) of mostly sand sediment (Figures 2, 3). It consists of three stacked, high net-to-gross channel-complex fills (each 8–30 m [25–100 ft] thick) that correspond to shorter term flow conduits (C1, C2, and C3; Figures 2, 3). channel complexes are multistory units that consist mainly of thick-bedded, Bouma Ta and Tab divisions, mudstone-clast breccia, and medium-bedded, dune cross-stratified sandstone. Granule conglomerate to medium-grained sandstone is the most common grain-size range. Five different channel-fill elements were identified within the channel complexes. Each consists of a different assemblage of facies, stratal patterns, and/or lateral dimensions, and unique reservoir characteristics ( Figure 12 ). The development of channel-fill elements is linked to specific combinations of flow and sediment flux conditions that controlled aggradation and erosion within channels. channel complexes are capped by siltstone-rich, thin-bedded units (T3 and T4; Figures 2, 3) that represent intervening episodes of overbank and levee sedimentation (local channel-complex deactivation). Additionally, debrite deposits (D1 and D2), which occur typically at the base of channels and channel complexes, are the result of

Abstract The lower Isaac Formation of the Windermere Supergroup at Castle Creek South consists mostly of fine-grained slope strata, with intercalated conglomerate- and sandstone-filled channel complexes, and most likely represents a toe-of-slope depositional environment. The uppermost channel complex at Castle Creek, channel 6 ( Figure 1 ), is comprised of two vertically stacked channels (C1, C2), surrounded by proximal-levee sandstone (S1-S3), and debris-flow deposits (D1, D2). channel 6 illustrates the architectural relationships between slope channels, adjacent sand-rich levees, and debris flows ( Figure 2 ).

Abstract Deep-water deposits of the Isaac Formation, Windermere Supergroup, are well exposed in the Cariboo Mountains of British Columbia, Canada ( Figure 1 ). At a site referred to as Castle Creek, seven channel-levee complexes (numbered CC-1 through CC-7 in ascending stratigraphic order) have been mapped by Arnott and Ross (chapter 22, this volume). This paper focuses on the architecture of channel Complex 2 located on the north side of the Castle Creek glacier ( Figure 2A ). A photo of the exposure looking north from the glacier is shown in Figure 2B .

Abstract High-resolution seismic surveys of many modern deep-water channel systems suggest that channels commonly overlie a genetically related, sheetlike, sand-rich unit termed a high amplitude reflection package (HARP), which is interpreted to be the result of channel avulsion and flow diversion ( Hiscott et al., 1997 ). Because of their sand-prone composition, and sometimes poor conventional core recovery, knowledge of their stratigraphic and lithological attributes is limited ( Hiscott et al., 1997 ). However, at Castle Creek North, a deep-marine channel-fill complex and genetically related subjacent strata are well exposed in rocks of the Windermere Supergroup. At the base of Unit 13, thin-bedded, upper-division turbidites (Tc-e) are interstratified with thicker, coarser grained, more complete turbidites. Respectively, these strata are interpreted to be fine-grained levee and overbank-splay deposits related to an active but not exposed channel. These strata are then overlain abruptly by a 23-m (75-ft)-thick succession consisting of thin-bedded, fine- to medium-grained sandstone Ted turbidites intercalated with medium-bedded, graded (coarse-tailed), structureless, medium-grained sandstone. This succession is interpreted to be a proximal crevasse splay or HARP deposit related to the avulsion of an adjacent, previously active channel. High-energy turbulent suspensions, now diverted through the levee breach and into the interchannel area, expanded rapidly, lost transport capacity, and incrementally constructed the crevasse splay. Depending on the rate of turbulent suspension collapse, one of two lithofacies were deposited: Ted turbidites were deposited from low-concentration dispersions, whereas structureless sandstone accumulated rapidly from high-concentration suspensions formed in submerged hydraulic jumps (turbidites were deposited from reconstituted dispersions

Abstract The stratigraphy and geological setting of the Proterozoic Windermere Supergroup ( Figure 1 ) is discussed in detail in Arnott and Ross (chapter 22, this volume). The Isaac and Kaza Formations, part of the Windermere Supergroup ( Figure 1 ), are interpreted by Arnott and Ross (op. cit.) to represent an immense slope to toe-of-slope, passive-margin, clastic fan system with sediment transported into deep water across an exposed carbonate shelf. Seven compensatory channel-levee complexes with interstratified slope and mass-transport complexes (MTCs), sheet sands (high amplitude reflection packages [HARPs]) and intervening condensed sections have been mapped in the Isaac Formation within the study area exposures at Castle Creek, British Columbia ( Figure 2 A). The outcrop panel presented here focuses on channel Complex 4 (CC4) as shown in Figure 2 A.