A Sm-Nd and U-Pb Detrital Zircon St

Research Paper

GEOSPHERE Northern Laurentian provenance for Famennian clastics of the Jasper Basin (Alberta, Canada): A Sm-Nd and U-Pb detrital GEOSPHERE; v. 13, no. 4 zircon study doi:10.1130/GES01453.1 Tyler E. Hauck1, Dinu Panǎ1, and S. Andrew DuFrane2 11 figures; 3 tables; 1 supplemental file 1Alberta Geological Survey, Alberta Energy Regulator, 402, Twin Atria Building, 4999 98 Avenue, Edmonton, Alberta T6B 2X3, Canada 2Department of Earth and Atmospheric Sciences, University of Alberta, 116 Street and 85 Avenue, Edmonton, Alberta T6G 2R3, Canada

CORRESPONDENCE: tyler.hauck@aer.ca

CITATION: Hauck, T.E., Panǎ, D., and DuFrane, S.A., ABSTRACT INTRODUCTION 2017, Northern Laurentian provenance for Famen- nian clastics of the Jasper Basin (Alberta, Canada): A Sm-Nd and U-Pb detrital zircon study: Geosphere, Within the carbonate-dominated Devonian succession of the Western Can- The Upper Devonian (Famennian) Sassenach Formation was mapped as v. 13, no. 4, p. 1149–1172, doi:10.1130/GES01453.1. ada Sedimentary Basin, sandstones of the Famennian Sassenach Formation a distinctive unit in the Front Ranges of the Canadian Cordillera, comprising a represent a sedimentological and isotopic anomaly inferred to be related to mixture of carbonates and calcareous shales along with a significant compo- Received 7 November 2016 western sources uplifted during Antler tectonism. Previously reported evi- nent of siltstone and subordinate fine-grained quartz sandstone (McLaren and Revision received 14 February 2017 Accepted 7 April 2017 dence for a changing tectonic regime along western Laurentia during depo- Mountjoy, 1962). The Sassenach was later identified in southwestern Alberta Published online 26 May 2017 sition of the Sassenach renders this unit an important potential link to shifts and southeastern British Columbia (Price, 1964). East of the town of Jasper, in source areas associated with this tectonism. We report the first set of U-Pb outcrops of the Sassenach Formation are exposed along a number of thrust detrital zircon ages and new Sm-Nd whole rock data from the Sassenach sheets in the Front Ranges of the Rocky Mountains (Fig. 1). Late Jurassic to Formation of the Jasper Basin in the Alberta Rocky Mountain fold-and-thrust early Eocene eastward propagation of the Rocky Mountains fold-and-thrust 147 144 belt. The Sm/ Nd ratios (0.109–0.122) and εNd values (–9.6 to –10.9) at the belt (Pană and van der Pluijm, 2015) has displaced the Devonian strata tens of time of deposition are within a narrow range that overlaps with published kilometers from the original Sassenach depocenter (Fig. 2).

data, confirming a post-Ordovician shift to more positiveε Nd values along the The presence of sandstone within the Sassenach Formation renders it northern and western Laurentian margin coinciding with the introduction of unique within the eastern Cordilleran Devonian stratigraphic succession, which more juvenile sources associated with Innuitian and Grenville sources. A pre- otherwise comprises carbonate reefs and their associated fine-grained off-reef

viously recognized subtle negative shift in εNd values in the Sassenach relative sediments. The Sassenach Formation was deposited in a western depocenter to underlying Frasnian deposits is also confirmed, which suggests a minor known as the Jasper Basin along the Devonian miogeocline of western Lau- contribution from more mature sources, opposite the overall post-Ordovician rentia (Fig. 2) (Mountjoy, 1980). The lack of comparable sandstones in eastern positive trend. Zircon ages show a wide spread (378–3506 Ma), with three subsurface equivalents, along with particular isotopic characteristics, has led broad age groups separated by a paucity of ages in the 700–900 Ma and 2100– to the interpretation that Sassenach clastics were derived from a newly up- 2500 Ma ranges: (1) a narrow Paleozoic to Neoproterozoic group (378–700 Ma), lifted western source (Mountjoy, 1980; Stevenson et al., 2000). This differs from (2) a broad Proterozoic group of scattered ages (900–2100 Ma), and (3) a narrow the interpreted northern and eastern source areas for the detrital component of Archean group (2500–2900 Ma). Paleozoic to Neoproterozoic detrital zircon the underlying strata (e.g., Stoakes, 1980; Patchett et al., 1999a). The proposed ages are absent from the western Laurentian record, and thus link the Sasse new western source would have been a highland related to the Antler orogeny nach Formation to the Arctic realm where terranes with zircons of these ages defined in the western U.S. are well known. Discordance modeling suggests a consistent Pb loss in the Much of the late Paleozoic record of western Laurentia has been obscured Sassenach zircon data set (ca. 390 Ma) that coincides with the first orogenic by Cordilleran tectonism associated with the formation of the Rocky Moun- pulse in Innuitian–Ellesmerian tectonics in the paleo-Arctic realm. Together tains fold-and-thrust belt. Detrital zircon provenance studies have proven use- these data suggest that the bulk of terrigenous sediment in the Jasper Basin ful in unravelling such complex histories and have shed light on source-area was recycled from Ellesmerian foreland strata and subsequently transported changes possibly linked to vestiges of Paleozoic tectonic activity. For example, southward along the margins of western Laurentia. Sediment transport may recent tectonic models (Colpron and Nelson, 2009, 2011; Beranek et al., 2010, For permission to copy, contact Copyright have been facilitated by southward-directed, shore-parallel shallow-marine 2016) have been used to interpret exotic terranes outboard of the Devonian– Permissions, GSA, or [email protected]. currents initiated by Northern Hemisphere wind patterns. Mississippian western Laurentia as a source for zircon ages of yet-unknown

118°W F o N ld in g M Thornton tn Haultain . Miette T h 6 r 1 u s

y t a

w gh Hi Chetamon

Cinquefoil 5 Morrow M 4 cC G o re n e n 53°N n e o ll c T k h T r h u 53°N r s u t C s o t Pyramid 3 lin C T he hr ta u mo st 2 n Th ru s 1 t Jasper Py Figure 1. Location of the study area and Signal ram sample locations in the Rocky Mountains id T 6 fold-and-thrust belt near Jasper, Alberta, hr u Canada. The Sassenach Formation crops Whistlers st out along a series of imbricate thrust J a S sheets in the Front Ranges. Map of geol- s na p ri ogy of Alberta from Prior et al. (2013). Inset er n 015 020 T g modified from Panǎ and Elgr (2013). h Th 118°W ru ru Kilometers st st Stratigraphy Mountain peak Devonian System Alberta Sassenach Formation

Sample locations Sm-Nd, U-Pb Grande Prairie 1 DP15-66 (Chetamon thrust sheet 1)

2 DP15-64 (Chetamon thrust sheet 2) Edmonton 3 DP15-73 (Jasper Transfer station)

4 DP15-77 (Snaring River bridge)

Calgary 5 DP15-76 (Morrow Peak traverse)

6 DP16-02 (Medicine Lake)

120°W 118°W 114°W 110°W Laurentian provenance. The detrital zircon record of parautochthonous Late 56°N Devonian strata in western Laurentia potentially records the erosional record of GROSMONT EROSIONAL such exotic terranes. For example, Kraft (2013) suggested that the Okanagan– EDGE Chilliwack composite terrane of Arctic affinity was a source for Silurian-aged zircons in the Chase Formation of southern British Columbia. A fundamental COOKING LAKE PLATFORM underpinning of this interpretation is that the Silurian-aged zircons are linked EROSIONAL PRA FRINGING GROSMONT to magmatic activity in the northern Alexander terrane (Kraft, 2013), and as REEF EDGE REEF COMPLEX D such the Okanagan–Chilliwack composite terrane was linked to, and subse- N

E R quently removed from, the Alexander terrane. Such an interpretation requires T

PRA F 56°N E the sinistral translation of Arctic-affinity terranes southward and outboard of LANDMASS E )

R T

N E the western Laurentian margin to locations adjacent to a back-arc basin—the

A M

S L model of Colpron and Nelson (2009). Similar interpretations based on the

N I same tectonic models are invoked for the detrital zircon record of Frasnian– G

L -

A U Famennian strata of the Pioneer Mountains in Idaho (USA) (Beranek et al., STURGEON C S ( 2016). In addition to the “Okanagan High” (Okanagan–Chilliwack composite TE ET K terrane of Kraft, 2013), the Arctic-affinity Eastern Klamath and Northern Sierra N O O M E O

I N R terranes are pointed to as potential sources. Importantly, these interpretations O WINDFALL 54°N S T B S W IG REDWATER hinge on the presence of Silurian to late Neoproterozoic zircons, including Late O Figure 2. Paleogeography of Frasnian car- ANCIENT B D A Devonian varieties, within the magmatic and detrital record of these terranes

E bonate buildups and basins, and strati- WALL D Edmonton N EST HALE M Hinton W S E - (Kraft, 2013; Beranek et al., 2016)—the crucial link to the paleo-Arctic realm. The graphic nomenclature from the mountains Y R EAST SHALE T BASIN BE and subsurface, Alberta and southeastern F possibility of a northern extension of the Antler orogen to Canadian latitudes, M E BASIN I D E N British Columbia, Canada. Blue shading e R Jasper fo R GI regardless of the style of tectonics, has been a longstanding question. The rm R represents carbonate buildups. Paleogeo- a A t M MIETTE io X presence of a short-lived orogen as a possible western source for clastic mate- graphic map compiled from Switzer et al. n E F N f L L r P IR o E (1994), Stevenson et al. (2000), and Hauck A n M H rial in Upper Devonian miogeoclinal strata would have profound implications t O S ASPER C C et al. (2017). Stratigraphic schematic modi J - K F M 52°N for the Paleozoic paleogeography, depositional setting, and tectonics of the S E A E fied from Stevenson et al. (2000). The Blue BASIN L E L H R L E I T N western margin of North America. U Ridge and Gramina Silt members are part N W K O A A of the Graminia Formation. Abbreviations: S H H Existing provenance studies based on radiogenic isotope systems from the C S A E PRA—Peace River Arch; Fm.—Formation; N B Jasper Basin are limited to Sm-Nd data (Boghossian et al., 1996; Stevenson LI Mbr.—Member. C et al., 2000) and one detrital zircon sample from the Sassenach Formation at FAIRHOLME Calgary COMPLEX an uncertain location in southern British Columbia (Gehrels and Pecha, 2014). ALBERTA-BRITISH COLUMBIA BORDER In this study, we use whole rock Sm-Nd coupled with a new set of detrital ? palinspastically restored zircon U-Pb data that provide more accurate ages of the source material to 50°N further constrain possible sources for the clastic component of the Sassen- ach Formation. We scrutinize the hypothesis that Sassenach sediments were Mountains Subsurface derived from western sources associated with Antler-age tectonics along the PALLISER FM. WABAMUN FM. GRAMINIA western margin of Laurentia, and provide evidence that the clastic component SILT MBR. LUE IDGE BR was sourced from the northern Innuitian-Franklinian Basin and recycled in the SASSENACH FM. RONDE MBR. B R M . .

ARCS MBR. M Ellesmerian orogen. This source is traced with Sm-Nd data, U-Pb detrital zir- ISKU CALMAR

F N INTERBURN FM. FM. con ages, and potential timing of tectonism (timing of a Pb loss event) in the MOUNT HAWK GROTTO MBR. W FM. ROUP source area derived from discordance modeling (Reimink et al., 2016). G UPPER IRETON

PEECHEE OUTHESK MBR. ROUP LEDUC FM. G .S M AIRHOLME LOWER UVERNAY F

F D PERDRIX FM. UPPER REGIONAL PALEOGEOGRAPHY AND STRATIGRAPHY LEDUC FM. MBR. OODBEN D AIRN W MALIGNE FM. C COOKING LAKE FM. The latest Neoproterozoic to Middle Jurassic Cordilleran miogeocline assem FLUME FM./MBR. BEAVERHILL LAKE GROUP blages formed a westward-prograding continental margin terrace wedge (~10– 15 km combined maximum thickness), which marked the interface between

the ancient North American craton and the adjacent proto-Pacific (Panthalas- (Fig. 2). Carbonate complexes were bordered by off-reef basins known as sic) ocean basin (Price, 1994). The Paleozoic paleogeography is widely viewed the East Shale, West Shale, and Jasper basins, which were dominated by the as a passive margin that included a platform and shelf, dominated by carbon- accumulation of considerable thicknesses of detrital carbonates mixed with ate rocks with subordinate clastic rocks that passed laterally westward into an terrigenous clastics, mostly in the form of mudstones and shales (Fig. 2). The oceanic basin with finer-grained, deeper-water facies (the Cordilleran miogeo- stratigraphic nomenclature varies from outcrop to subsurface for both the car- cline). Elaborating on the concept of episodic (Proterozoic to mid-Paleozoic) bonates and the basinal strata, but stratigraphic equivalencies are generally heterogeneous thinning of the western margin of North America (Okulitch, well established (Fig. 2). Mountain terminology will be used herein. 1984; Struik, 1986), Thompson et al. (2006) argued that the outboard (western) During the Late Devonian, Frasnian carbonate buildups in the Jasper area, side of the Neoproterozoic through early Mesozoic North American margin and further east on the Laurentian platform, attained substantial bathymetric was defined by a “ribbon” of continental crust called the “Okanagan High” relief during overall transgressive global depophases IIb, IIc, and IId of John- at least 200 km wide and several hundred kilometers long. The Okanagan son et al. (1985). During maximum transgression in the Frasnian, the organic- High would include the Monashee and Selkirk metamorphic sequences and rich shales of the Perdrix Formation were deposited outboard of the coeval most of the basement of the Quesnel volcanic arc. Therefore, the continental Cairn and Southesk Formation buildups (Fig. 2). Basinal anoxia gave way to margin prism (all rocks deposited along the ancestral margin) developed on oxygenated conditions with the deposition of argillaceous carbonates and cal- and between the Laurentian craton to the east and the Okanagan High to the careous shales of the Mount Hawk Formation during the remainder of Cairn west. Alternatively, the Late Devonian to Early Mississippian architecture of and Southesk deposition. A relative sea-level fall—global sea-level fall at the the Cordilleran miogeocline at Canadian latitudes was variously interpreted end of depophase IId of Johnson et al. (1985)—is interpreted to have preceded as a west-facing active compressional continental margin related to the Antler the deposition of the unconformably overlying Sassenach Formation and its orogeny: (1) the foreland basin of the Antler orogen (Smith et al., 1993; Root, equivalent to the east (Graminia Silt). In the Rocky Mountains, this event is 2001); (2) a sinistral transpressional fault system located outboard of the pre- recorded by erosion on the carbonates of the Fairholme Group (McLaren and served margin of the miogeocline and extending from the Arctic to south of Mountjoy, 1962; MacKenzie, 1965) (Fig. 2). Nevada (USA) (Eisbacher, 1983; Gordey et al., 1987; Ketner, 2012) and respon- Off-buildup basins record a pattern of accumulation from north and east to- sible for both compression (resulting in highlands) and tension (resulting in ward the south and west in gentle clinoforms during regressive and stillstand pull-apart basins); (3) a back-arc basin above an east-dipping subduction zone phases of deposition (Stoakes, 1980; Wendte, 1992). To the west, strata of the (e.g., Nelson et al., 2002; Thompson et al., 2006); and finally (4) a combination Perdrix and Mount Hawk formations now exposed in the thrust sheets of of eastward subduction and sinistral transpression (Colpron and Nelson, 2009, the Rocky Mountains had not completely filled the accommodation space lee- 2011; Beranek et al., 2016). ward (present-day west) of the Fairholme Group buildups due to the east-west Paleozoic to Mesozoic pericratonic sequences were deposited mainly above progradation of basinal strata, leaving a depocenter known as the Jasper Basin the Neoproterozoic Windermere Supergroup (and possibly older metamor- (Mountjoy, 1980; Stevenson et al., 2000). During the Famennian, the Jasper phic sequences to the west), on cratonic basement inboard of the Windermere, Basin was filled by mixed detrital carbonates and siliciclastics, including sand- and over part of the Mesoproterozoic Belt-Purcell Supergroup assemblages to stone of the Sassenach Formation. Whereas the eastern margin of the Jasper the south. The Paleozoic to Middle Jurassic sequences of the Western Canada Basin can be observed through onlapping relationships with Frasnian strata Sedimentary Basin are made up of several tectono-stratigraphic packages: proximal to the Ancient Wall, Miette, and Southesk-Cairn buildups (Fig. 2), (1) the lower Paleozoic sequence consisting predominantly of platform and the western, northern, and southern extents of the basin have been obscured shelf carbonate buildups with subordinate shale that pass laterally westward through later erosion and thrust faulting. To the east, the equivalent Graminia into finer-grained, deeper-water facies; (2) middle and upper Paleozoic plat- Silt comprises a thin unit of silt and shale throughout a large portion of the form and shelf carbonate rocks and subordinate clastic rocks, which pass lat- subsurface of Alberta (Fig. 2). The Graminia Silt lacks the coarser-grained silici- erally westward into deeper-water facies; and (3) Triassic to Middle Jurassic clastics found in the Jasper Basin (Meijer Drees et al., 1998). shale, siltstone, sandstone, and carbonate units. The Sassenach Formation in the Jasper Basin is predominantly a silty carbonate, comprising distinct light-orange to buff-colored dolomitic or calcareous silts, interbedded with limestone, dolomitic limestone, calcareous JASPER BASIN PALEOGEOGRAPHY AND STRATIGRAPHY dolostone, and dolostone that show mudstone, wackestone, and packstone textures. The presence of the laminated silt- to sand-sized siliciclastic com- During the Frasnian, the Alberta Basin was positioned near the paleoequa- ponent gives a distinct ribbon-like appearance to portions of the Sassenach tor and saw widespread growth of biohermal and biostromal carbonates, Formation (Figs. 3C, 3D). In other areas, the formation is more argillaceous which are now located in the Alberta subsurface and in the thrust sheets of (Fig. 3E). Planar to wavy laminations and cross-bedding are common in the the adjacent Cordilleran foreland belt (Mountjoy, 1980; Switzer et al., 1994) siltstone and sandstone components. The Sassenach Formation can be sub-

A B

C D

Figure 3. Photos of the Sassenach For- mation in the Jasper region of Alberta, Canada. (A) Base of the Sassenach For- mation grading into the recessive calcareous shales (covered) of the Mount Hawk Formation, Morrow Peak traverse. (B) Silty and sandy limestone at Morrow Peak (sample DP15-76). (C) Weathered ribbon-like silty dolomitic limestone (silty beds are more resistant) at Medicine Lake (sample DP16-02). (D) Ribbon-like silty dolomitic limestone (silt weathers light-orange color) at the Jasper Transfer Station (sample DP15-73). (E) Recessive, argillaceous silty limestone east of rail tunnel at Pyramid thrust within the Chetamon thrust sheet (sample DP15-64). (F) Dolo- mitic-calcareous siltstone to fine-grained E F sandstone near Snaring River bridge on Highway 16 (sample DP15-77). Hammer is 33 cm long; pencil is 15 cm long.

divided into a lower silty member and an upper sandy member (McLaren and Mountjoy, 1962) (Fig. 4). The regressive character of this formation suggests a Morrow Peak transition from distal to more proximal facies upsection. The Famennian age of the Sassenach Formation in the Jasper Basin is well constrained by conodont 200 m dating (Wang and Geldsetzer, 1995; McCracken, 1996). Palliser Fm. The Sassenach Formation has been studied intermittently since its for- mal naming (McLaren and Mountjoy, 1962). Because of hydrocarbon pro- DP15-77 spectivity of Frasnian Fairholme Group carbonate strata in the subsurface of Alberta (Fig. 2), early Cordilleran studies focused on their stratigraphy and 175 sedimentology and only treated the Sassenach Formation peripherally (Price, 1964; Belyea and McLaren, 1964; MacKenzie, 1965; Mountjoy, 1965; Coppold, 1976). Subsequently, due to the relationship of the Sassenach Formation to the Frasnian-Famennian boundary, a number of studies have investigated 150 the strata for clues as to the extinction events associated with the boundary Sassenach Fm. (Geldsetzer et al., 1987; Goodfellow et al., 1988; Whalen et al., 2002; Bond Upper Member et al., 2013). Becker (1997) and Mountjoy and Becker (2000) reexamined the sedimentology and stratigraphy of the Sassenach Formation in the context of sequence-stratigraphic concepts. Published studies on subsurface equiv- 125 alents of the Sassenach Formation are lacking, with only Meijer Drees et al. (1998) assessing the subsurface correlative Graminia Silt (Fig. 2). Prior to isotopic work, northern Canadian Arctic orogens have been suggested as the source for fine terrigenous clastics deposited in the Alberta Basin and the miogeocline of the Cordillera during the late-Middle to Late Devonian (e.g., 100 Slumped / contorted Stoakes, 1980). Deposition of the Sassenach Formation and filling of the Jas- S per Basin coincided with the earliest interpreted ages of the Antler orogeny in bedding western United States. The westward thickening (Coppold, 1976) and upward DP15-76 coarsening of the Sassenach sediments, and the presence of feldspar, were interpreted to imply that a western source exposing older crust to erosion was 75 Argillaceous dolomite Sassenach Fm. either approaching or being increasingly uplifted (Savoy and Mountjoy, 1995; S Stevenson et al., 2000). Lower Member Dolomitic siltstone / ne-grained sandstone PREVIOUS PALEOZOIC PROVENANCE STUDIES IN THE REGION 50 Sandy limestone Provenance studies of western Canadian miogeoclinal strata (Ross et al., 40 1993; Gehrels and Ross, 1998) have drawn from previous geochronology work 30 S Silty limestone on Precambrian terranes across Laurentia (e.g., Hoffman, 1989; Ross et al., S (dolomitic; sandy) 1991; Ross and Parrish, 1991; Burwash et al., 1994). In particular, geochro- 20 S nology work by Ross et al. (1991) and Villeneuve et al. (1993) on the cratonic recessive Calcareous shale basement under the Western Canada Sedimentary Basin formed the basis for 10 covered interval subsequent interpretations of potential sources of detrital zircon and Nd sig- Mount Hawk Fm. natures for sediments in the western miogeocline. A number of studies have 0 m previously assessed the Nd isotopic values from Devonian miogeoclinal strata in western Canada (Boghossian et al., 1996; Garzione et al., 1997; Patchett et al., Figure 4. Location of samples DP15-76 and DP15-77 on the measured Sassenach Formation (Fm.) section at Morrow Peak west of Cold Sulfur Springs, Alberta, Canada (modified from 1999a, 1999b), and one Nd isotope study focused in greater detail on the Upper Becker, 1997). Devonian basinal strata in the Jasper Basin, including the Sassenach Forma- tion (Stevenson et al., 2000).

Within western Canada miogeoclinal strata, Boghossian et al. (1996) et al., 1993) (Fig. 1). These sediments were dispersed >2000 km along the

showed that eNd(T ) (T—at time of deposition) values increase from lows rang- western miogeocline as far south as California and Nevada (USA) and Sonora ing from –22.0 to –15.8 in Precambrian–Ordovician rocks, representing Archean (Mexico) (Gehrels and Pecha, 2014). Isotopic signatures of the Upper Devonian and Proterozoic basement sources of the Canadian Shield, to –9.5 to –6.4 in the to Triassic strata shift back to local sources, including recycled miogeoclinal Devonian–Triassic sequences, which required mixing with detritus from more strata, along with significant proportions of detritus derived from the northern juvenile sources. Possible juvenile sources include: (1) the Cordilleran miogeo- Innuitian-Franklinian orogen (Gehrels and Pecha, 2014). cline related to Antler-age tectonism; (2) the Appalachians, with detritus trans- In recent years, detrital zircon geochronology and provenance studies of ported by drainage systems across the craton; or (3) the northern Innuitian and Paleozoic strata from the Canadian Arctic and the northern Canadian Cordillera Ellesmerian orogens in the Canadian Arctic, with detritus transported south- have greatly contributed to our understanding of the evolution of the northern ward along the Cordilleran margin. Garzione et al. (1997) confirmed this posi- margin of Laurentia and its possible contribution to sediments within Alberta tive shift in northern British Columbia from the westerly derived Middle Devo- and along the western miogeocline. In particular, linkages have been proposed nian to Mississippian Earn Group (–6.6 to –12.9) and its eastern and southern with parts of Siberia and Baltica through terrane accretion along northern Lau- fringe in the Cordilleran miogeocline, the Besa River Formation (–8 to –10.5). rentia, as suggested by zircon ages anomalous for Laurentia (Beranek et al., They interpreted the Sm-Nd systematics in the Ordovician to Lower Devonian 2010, 2015; Lemieux et al., 2011; Anfinson et al., 2012a, 2012b). These include strata as a mixture of Canadian Shield sources with locally erupted, juvenile detrital zircon populations with Grenville-Sveconorwegian (1000–1300 Ma) and volcanics, and inferred a contribution from the Innuitian orogen of the Cana- Silurian to Neoproterozoic (ca. 420–700 Ma) ages that are found within clastic dian Arctic in the post–Middle Devonian strata. Patchett et al. (1999a, 1999b) strata along the northern and western margin of the continent. In the northern reported Sm-Nd data from North American strata that included Arctic Canada. Cordillera, the presence of these non-Laurentian zircon populations was ex-

They interpret the positive eNd shift to represent: (1) Grenville-age signatures plained by recycling and dispersal of these detrital zircons into Devonian strata indirectly sourced from the Caledonian orogen along eastern Greenland into (Beranek et al., 2010; Lemieux et al., 2011). The presence of such populations the Franklinian Basin and subsequent mobile belt of the Canadian Arctic, and as far south as Eastern Klamath and Northern Sierra terranes of the western ultimately into the western Canadian miogeocline; or alternatively (2) a com- U.S. prompted Colpron and Nelson (2009) to invoke southward translation of bination of Arctic orogenic material with arc- or extension-related magmatic Arctic affinity terrane(s) to central Cordilleran paleolatitudes along a Devonian sources along the Cordilleran margin. sinistral transpressional fault system located outboard of the miogeocline. The The shift from older cratonic to younger Grenville-aged sources, as recog- model offered a possible source of exotic (Arctic) zircon subsequently found in nized in Nd isotopes, occurred at ca. 450 Ma (Late Ordovician) across North the parautochthonous strata in southern British Columbia (Chase Formation; America due to the overwhelming input from Caledonian-Appalachian oro- Kraft, 2013; Beranek et al., 2016) and the Sassenach Formation of the cratonic

genic sources (Patchett et al., 1999a). Stevenson et al. (2000) reported eNd(T ) platform (Beranek et al., 2016). values from the Upper Devonian stratigraphy in the Jasper area that confirmed the post-Ordovician overall positive shift. They also noted a deviation to slightly more negative values (–8.5 to –11) in the Famennian Sassenach For- SAMPLE LOCATIONS mation compared to strata above and below it. This excursion to more nega-

tive eNd(T ) values—which requires a contribution of detritus from older rocks— Six samples, ~25 kg each, were collected from outcrops of the Sassenach corroborated with sedimentological evidence suggesting a western source, Formation from the Colin and Chetamon thrust sheets along the Athabasca was interpreted to record derivation of the Sassenach clastics from sources River valley and near Medicine Lake east of the town of Jasper, Alberta (Fig. 1). exposed in the Antler orogen at or near Canadian latitudes. At each location, we attempted to sample the coarsest, or most siliciclastic-rich, A general pattern of the evolution of source areas for detrital zircons in part of the Sassenach Formation such as the silty beds of the ribbon stone (Figs. the western miogeocline has emerged in recent years, with sedimentary re- 3C, 3D). Rock description and sample site coordinates are compiled in Table 1. cycling as a common theme (Ross et al., 1993; Gehrels et al., 1995; Gehrels and Ross, 1998; Gehrels and Pecha, 2014). Neoproterozoic through Middle Devonian strata are dominated by sediments shed from local basement rocks ANALYTICAL TECHNIQUES and clastic rocks with Grenville orogen signatures. Grenville-sourced material has been recognized in basins as old as the Neoproterozoic along the western Sm-Nd part of the Canadian Arctic as well as correlative strata in the Canadian miogeocline (Rainbird et al., 1992). A shift in dominant source areas is observed Samarium-neodymium isotopic analysis was performed on the six Sasse in Ordovician rocks, where miogeocline strata were influenced by sediments nach samples collected from the Jasper Basin. Analyses were performed on a originating from the emergent Peace River Arch in west-central Alberta (Ross Triton-TI mass spectrometer at GeochronEx Analytical Services and Consult-

TABLE 1. LOCATION AND DESCRIPTION OF SAMPLES COLLECTED FROM THE SASSENACH FORMATION IN THE JASPER REGION, ALBERTA, CANADA Location Sample Latitude Longitude number (°N) (°W) Location descriptionSample description DP15-64 52.920564 118.052719 East of rail tunnel at Pyramid thrust (off Highway 16) Shaly, resistant silty dolomitic limestone beds (<1 cm thick) (Fig. 3E) DP15-66 52.919251 118.052948 Near rail tunnel at Pyramid thrust (off Highway 16) Ribbon rock, dolomitic limestone with light-orange wavy siltstone partings DP15-73 52.940650 118.045080 Jasper Transfer Station (north of Highway 16) Ribbon rock, interbedded dolomitic limestone and wavy bedded silty dolomitic limestone (Fig. 3D) DP15-76 53.041825 118.083158 Traverse at Morrow Peak, west of Cold Sulphur Springs (off Highway 16) Centimeter-bedded silty limestone with fine-grained sandstone beds (cross-bedded) (Fig. 3B) DP15-77 53.041639 118.087772 Parking lot at Snaring River bridge on Highway 16Calcareous to dolomitic silty sandstone, cross-bedded, some limestone interbeds (Fig. 3F) DP16-02 52.850045 117.725232 North of Medicine Lake off Maligne Lake Road Ribbon rock, interbedded dolomitic limestone and wavy bedded silty dolomitic limestone (Fig. 3C)

Determination of Maximum Depositional Age (MDA) of the Sassenach Formation, Jasper Basin ing (Burlington, Ontario, Canada). Complete details on analytical techniques The maximum depositional age (MDA) was determined with Isoplot (Lud- Analytical Methods used at GeochronEx are listed in the Supplemental Materials1. A depositional wig, 2003). The MDA is derived from the mean square weighted deviation For determination of the Maximum Depositional Age (MDA), the procedures outlined by the Arizona Laserchron Center were followed age of 365 Ma was assigned to all samples for eNd(T ) calculations, which al- of the youngest three detrital zircon ages within our samples (Supplemental (https://docs.google.com/document/d/1MYwm8GcdYFOsfNV62B6PULb_- g2r1AS3vmm4gHMOFxg/preview). lowed for comparisons with previously reported eNd(T) values for the Sasse Materials [see footnote 1]) (see Spencer et al., 2016, for a discussion on deter- Supplemental material regarding such procedures can be found in Spencer and Kirkland (2016)

Based on these procedures, we chose to use the MSWD approach. The youngest three (<10%discrodant) nach of the Jasper Basin (Stevenson et al., 2000). Uncertainty of eNd values is mining MDA). grains from the Sassenach were used. The Isoplot software of Ludwig (2003) was used for the MSWD analysis. ~0.5 eNd units. Lower intersection ages were assessed using the discordance modeling Youngest three Sassenach zircons: program of Reimink et al. (2016) within the computer software R (R Core Team, Age (Ma) 2σ

378.4472 15.59104 2014). It is common practice in single-grain detrital zircon provenance studies 380.0437 13.89285 394.2211 13.81808 U-Pb to discard U-Pb analyses with relatively high discordance (usually 5%–30% dis-

MSWD cordance). The modeling program from Reimink et al. (2016) includes all data

Mean = 384.7±8.3 [2.2%] 2σ Wtd by data-pt errs only, 0 of 3 rej. In situ U-Pb zircon data were collected using laser ablation–multicollector– from a detrital zircon U-Pb geochronology study in a statistical analysis aiming MSWD = 1.5, probability = 0.22 inductively coupled plasma–mass spectrometry (LA-MC-ICP-MS) at the Cana- to define probable discordia lines and their associated lower and upper inter- data-point error symbols are 2σ 415 dian Centre for Isotopic Microanalysis at the University of Alberta using pro- cept ages on concordia diagrams. Providing hints on both the timing of zircon 405

395 cedures modified from Simonetti et al. (2005). Analytical techniques can be crystallization (upper intercept age) and Pb-loss event (lower intercept age) 385 found in the Supplemental Materials (see footnote 1). Additionally, isotopic in the analyzed population may significantly contribute to a more plausible 375

365 ratios and apparent ages are found in Table S1 in the Supplemental Materials. identification of the source area where both emplacement and tectonothermal 355 Data points were discarded if it was obvious that an inclusion contributed to evolution is known. analysis, there was extreme common Pb component, or the grain was in fact not zircon. For plotting purposes, data were filtered using a 10% discordance 1 Supplemental Materials. Detrital zircon U-Pb analy filter. For ages >600 Ma, the207 Pb/206Pb age was used if <10% discordant, other RESULTS ses from the Sassenach Formation of the Jasper re- 206 238 gion, Alberta, Canada. Please visit http://doi.org/10 wise the Pb/ U age was used. We assessed concordance by comparing .1130/GES01453.S1 or the full-text article on www 206Pb/238U and 207Pb/206Pb ages except for analyses <500 Ma, where 207Pb/235U Sm-Nd .gsapubs.org to view the Supplemental Materials. and 206Pb/238U ages were compared. All zircon age plots—kernel density estimations (KDE) and probability Our sample lithologies range from slightly calcareous siltstones to slightly density functions (PDF)—were generated using the software DensityPlotter argillaceous limestones (Table 1; Fig. 3). All samples are fine grained and con- (Vermeesch, 2012). Multi-dimensional scaling was employed to compare data tain variable proportions of carbonate debris from adjacent carbonate com- sets (Vermeesch, 2013; Spencer and Kirkland, 2015; Saylor and Sundell, 2016). plexes and siliciclastics derived from outside the Jasper Basin. The Sassenach This statistical approach constrains our correlations with other zircon data sets Formation is generally fine grained, does not contain turbidite flows, and using a Kolmogorov-Smirnov (K-S) test, which measures the maximum dis- shows coherence of the Nd isotopic system, hence its Nd isotopic composition tance between two cumulative probability functions (Spencer and Kirkland, represents the average Nd composition of the contributing sources (e.g., Nel- 2015). A dissimilarity matrix can then be produced for all data sets, which pro- son and DePaolo, 1988; Gleason et al., 1995; Stevenson et al., 2000). vides an objective comparison of the likeness of detrital zircon age spectra 147Sm/144Nd ratios for all Sassenach samples fall within a narrow range of (see treatment in Vermeesch, 2013; Spencer and Kirkland, 2015). Dissimilarity 0.11–0.12 (Table 2). As currently defined, the boundaries of the Famennian matrices were produced using the Microsoft Excel macro (K-S Test) developed Stage are 372.2 ± 1.6 Ma and 358.9 ± 0.4 Ma (International Chronostratigraphic at the Arizona Laserchron Center (Guynn and Gehrels, 2010). Chart, version 2016/04, online update from Cohen et al., 2013). We have used

TABLE 2. SUMMARY OF Sm-Nd DATA FROM THE SASSENACH FORMATION IN THE JASPER REGION, ALBERTA, CANADA Sm Nd Error 147 144 143 144 Sample (ppm) (ppm) Sm/ Nd Nd/ Nd (±2σ) εNd(0)* εNd(365)* TDM(0) TDM(365) Location in Sassenach Formation DP15-64 3.33 18.32 0.1100 0.5120790.000002 –10.9–6.91572 1700 Upper half DP15-66 2.04 10.55 0.1171 0.5119470.000004 –13.5–9.81893 1941 Lower half DP15-73 1.23 6.25 0.1192 0.5119530.000002 –13.4–9.81927 1940 Lower half DP15-76 0.88 4.88 0.1088 0.5119360.000007 –13.7–9.61762 1927 Middle of upper half DP15-77 0.79 3.90 0.1218 0.5119000.000006 –14.4–10.92067 2035 7–10 m below base of Palliser Formation DP16-02 1.10 5.43 0.1222 0.5119500.000004 –13.4–10.01994 1956 Upper half

*Uncertainty of εNd values is approximately 0.5 εNd units. (0)—present-day; (365)—timing of deposition (365 Ma).

the deposition age of 365 Ma for the calculation of eNd(T ) and depleted-mantle (378 Ma) to Archean (3506 Ma) and show a general lack of well-defined, nar- model ages in order to directly compare our data to those reported by Steven row clustering (Fig. 6). The number of concordant zircon ages used for each of

son et al. (2000) and Boghossian et al. (1996). The eNd(T ) values are very consis- the six plots ranges from 30 to 92 (Fig. 6). The small number of zircon grains in tent, with five out of six samples varying within 1.3 epsilon units (–9.6 to –10.9). some of the samples results in a lack of similarity observed between some of One exception is sample DP15-64, with a less negative value of –6.9 collected the samples in the KDE plots (e.g., Fig. 6, sample DP15-76). This is in part a re- from a thinly bedded, silty dolomitic limestone interbedded with calcareous sult of the fine-grained nature of the Sassenach Formation, with some samples shales (Fig. 3E) in the upper half of the Sassenach Formation exposed along containing a small number of very small zircons (Fig. 5). However, the distribu-

the rail tracks north of the town of Jasper. Depleted-mantle model ages (TDM) tion of the zircon dates is broadly consistent between samples, in that nearly also show a narrow range from ca. 1.94 to 2.04 Ga, with the exception of the all of the samples show a paucity of ages in the 700–900 Ma and 2100–2500 Ma same sample DP15-64, which yielded an anomalously young model age of ranges. Based on these age gaps and peaks within the plots, three detrital

1.7 Ga. The most negative epsilon value of –10.9 and oldest TDM of 2067 Ma is zircon age clusters are interpreted from these data: (1) a Paleozoic to Neo from a silty, dolomitic fine-grained sandstone ~5 m below the Sassenach For- proterozoic cluster (378–700 Ma), (2) a broad Proterozoic group (900–2100 Ma), mation–Palliser Formation contact exposed in the parking lot east of Snaring and (3) an Archean group (2500–2900 Ma). A number of zircon ages fall out- River bridge (sample DP15-77, Fig. 3F). side these general age groups. Most notable are five detrital zircon grains with Archean ages scattered from 3100 to 3500 Ma (Fig. 6). U-Pb

We analyzed a total of 548 individual zircon grains from the six Sassenach DISCUSSION samples collected in the Jasper Basin. Raw analytical data are in the Supple- mentary Materials (see footnote 1). The size of recovered zircon grains varies Prior to radiogenic isotope studies, a western, Antler-related source for between sample sites, and generally increases toward the top of the Sasse the clastic component of the Sassenach Formation had been inferred based nach Formation (compare the stratigraphically lower sample DP15-76 and up- on sedimentological and stratigraphic evidence (Mountjoy, 1980; Savoy and per sample DP15-77; Fig. 5). Many of the zircon grains are very small (<40 mm). Mountjoy, 1995; Becker, 1997; Mountjoy and Becker, 2000). A switch from Average grain size of concordant to sub-concordant (<10% discordant) grains northern and eastern sources to a western source for the siliciclastic compo- is 75 mm. Concordant grains are colorless or colored light pink, medium pink, nent of the Sassenach Formation was deduced from the lack of a comparable and dark pink. The morphology of these grains includes rounded, subhedral, sand-sized fraction in the correlative Graminia Silt to the east and a general and euhedral varieties. Rounded grains are most common, followed by subor- western coarsening and increase in feldspar content within the Jasper Basin dinate subhedral grains, suggesting that sedimentary recycling dominates the (Mountjoy, 1980; Mountjoy and Becker, 2000). In addition, the eastward onlap- population. Only four euhedral grains were noted amongst the selected <10% ping relationship with carbonate buildups recognized in the Jasper–Saskatche- discordant grains (Fig. 5). A maximum depositional age of 384.7 ± 8.3 Ma was wan Crossing region is opposite of the general westward downlapping trend of determined from the three youngest detrital zircons (<10% discordant) sam- Perdrix–Mount Hawk shales and their equivalent strata from the east (Mount- pled from the Sassenach Formation. joy, 1980; Stoakes, 1980). The results of geochemical and Nd isotope studies For interpretation on KDE and PDF plots, we have used 354 analyses and have been interpreted to support the concept of a western source (Savoy et al., discarded 194 analyses with >10% discordance (35% of the 548 analyzed 2000; Stevenson et al., 2000). However, none of these studies incorporated grains). Single-grain ages in our Sassenach data set vary widely from Frasnian detrital zircon provenance to further elucidate potential source areas.

Figure 5. Detrital zircons from the Sas- 0.5 mm senach Formation samples examined in 0.5 mm this study (see Table 1). Zircon grain sizes DP15-76 vary between sample locations and with 0.5 mm DP15-77 stratigraphic position within the Sas senach Formation (generally larger toward DP15-64 the top). The majority of zircon grains are rounded, with low to medium sphericity. Subhedral grains are common, whereas euhedral crystals are rare (e.g., grain E in the enlarged area “i” of sample DP15-64) i and appear to be associated with samples that contain a greater proportion of large zircon grains. Blue coloration of DP16‑02 results from a different colored zircon mounting resin. 0.5 mm E DP15-66

0.05 mm 0.5 mm DP15-73 0.5 mm DP16-02

Significance of Sm-Nd Data DP15-64 n=61/100 Our Sm-Nd data are consistent with previously reported data from the Sas- senach Formation and are typical of continental shale-siltstone and mudstone (Stevenson et al., 2000; Boghossian et al., 1996; Dia et al., 1990) (Fig. 7). The 147Sm/144Nd ratios reported here (0.109–0.122) are within the narrow range of 0.107–0.123 reported by Stevenson et al. (2000) from 11 Sassenach samples which also encompasses the two ratios of 0.121 and 0.117 previously reported

by Boghossian et al. (1996). The eNd(365) range of –6.9 to –10.9 obtained in

DP15-66 this study partly overlaps with the values from other studies: two eNd values of n=66/110 –9.4 and –9.5 reported by Boghossian et al. (1996) and the –8.6 to –10.6 range

reported in Stevenson et al. (2000). Finally, TDM(365) values in the 1.7–2.04 Ga range (Table 2) encompass the previously reported values ranging between 1.7 and 1.8 Ga (Stevenson et al., 2000; Boghossian et al., 1996). DP15-73 Sampling across several intervals of the Devonian stratigraphy, Stevenson Probability density function et al. (2000) noticed a trend to more negative e (T ) values and older model n=69/110 Nd ages upward from Perdrix (eNd(T ) of –7.6 to –7.8 and TDM of 1.4–1.5 Ga) to Mount e Kernel density estimation Hawk ( Nd(T ) of –6.5 to –8.7 and TDM of 1.4–1.7 Ga) into the Sassenach Forma- tion (–8.6 to –10.6 and 2.0 Ga). Our data confirm the more negative eNd(T ) val- Figure 6. Detrital zircon plots (probability ues and older model ages (–9.6 to –10.9 and 1.76–2.07 Ga) from the Sassenach density function and kernel density esti- Formation. These more negative e values correlate with a greater proportion mation) for the six samples collected in Nd this study (see Supplemental Materials of older terrigenous material (siltstone and sandstone) and an overall upward- [footnote 1] for data tables). Three general coarsening trend into the Sassenach Formation (McLaren and Mountjoy, 1962; age clusters (gray shading) are interpreted: Becker, 1997; Stevenson et al., 2000). This may indicate a more vigorous input (1) 700–378 Ma, Neoproterozoic to Paleo- DP15-76 zoic; (2) 2100–900 Ma, Proterozoic; and of clastics and/or a decreasing source-to-sink distance during the deposition of (3) 2900–2500 Ma, Archean. n—number of n=30/60 the Sassenach Formation. zircons used (< 10% ± discordant) out of total The correlatives of the Sassenach, Mount Hawk, and Perdrix formations zircons analyzed. to the east in the subsurface of the Alberta Basin show comparable Sm-Nd systematics (Stevenson et al., 2000; Boghossian et al., 1996). Thus, a drill e DP15-77 core sample from the Graminia Silt yielded an Nd value of –10.0 and a TDM of 1.8 Ga, within the range of the correlative Sassenach Formation. The sim- n=36/59 ilar Sm-Nd systematics of the Sassenach Formation and its eastern correla tive—the Graminia Silt—suggest a common source. Similarly, the subsurface

Calmar Formation (Fig. 2) of the Alberta Basin has an eNd value of –9.1 and

a TDM of 1.7 Ga, which are consistent with the most negative eNd values and

oldest TDM ages found in the partly correlative Mount Hawk Formation in the Rocky Mountains (Fig. 2). One sample from the subsurface Duvernay Forma-

tion (Boghossian et al., 1996) yielded a similar TDM (1.55 Ga) but a slightly more

negative eNd(T ) (–9.0) value compared to its exposed equivalent in the Rockies, DP16-02 namely the Perdrix Formation (1.4 and 1.5 Ga, and eNd values of –7.6 and –7.8). n=92/110 To the southwest of the Jasper Basin in southern British Columbia, the Fras- nian–Famennian Chase Formation (Lemieux et al., 2007; Kraft, 2013) on the

western side of the miogeocline displays very similar eNd values (–6.7 to –10.8) to the Sassenach in the Jasper Basin (Fig. 8G), suggesting that both had access to more mature crustal material. 0400 8001200160020002400280032003600 The interpreted source for much of the Devonian miogeoclinal basin fill Age (Ma) in Alberta (i.e., Mount Hawk Formation and equivalents) is the Franklinian

COSTIGAN MEMBER PALLISER FORMATION MORRO MEMBER FAMENNIAN –9.5 –10.0 –10.9 –10.5 –10.4 –9.4 –6.9 –9.8 –9.9 SASSENACH –9.8 –9.6 –9.8 FORMATION –9.7 –10.6 372 Ma –8.4 –10.1 –8.6 SIMLA / RONDE MEMBER –8.6 ARCS MEMBER TIO N R –8.2 GROTTO MEMBER MOUNT HAWK FORMATION UPPE –6.8 –6.5

Figure 7. Existing Upper Devonian εNd(365) AN PEECHEE values placed at their approximate strati- MEMBER graphic position, except for the samples FRASNIAN SOUTHESK FORMA –8.7 analyzed by Boghossian et al. (1996), who PERDRIX –7.8 did not specify the stratigraphic position of their samples within a given formation. IRHOLME GROU P FORMATION –9.0 –7.6 (εNd at time of deposition of 365 Ma). DEVONI FA

IO N UPPER (DUVERNAY FORMATION)

AT MEMBER MALIGNE FORMATION

FLUME MEMBER CAIRN FORM FLUME FORMATION 382 Ma

–7.8 εNd(365) LE GIVETIAN Boghossian et al., 1996 (no stratigraphic depth implied) MIDD Stevenson et al., 2000

388 Ma This study

mobile belt in the Canadian Arctic (Patchett et al., 1999a). There, lower Cam- Jurassic, and Garzione et al. (1997) confirmed the general positive trend from

brian to Upper Devonian clastic strata show an abrupt shift in eNd values in the Precambrian into the Permian in the Yukon, Northwest Territories, and the Late Ordovician (ca. 450 Ma) from –25 to –17 in older rocks to –13 to –5 British Columbia. These data led Patchett et al. (1999b, p. 578) to infer that the in younger rocks (Patchett et al., 1999b). The ultimate source of these sedi- foreland clastic wedge of the Franklinian orogen propagated southwestward ments was inferred to be the Caledonian orogen (Patchett et al., 1999b). To the into the Cordilleran miogeocline “to give rise to the thick Upper Devonian south, in the Cordilleran miogeocline of Canada, Boghossian et al. (1996) had Imperial Assemblage in the north and to thinner Devonian clastic rocks over

previously noted a similar positive shift in eNd(T ) values from the Late Ordo- a wide region of the miogeocline and continental interior, at least as far south vician to Late Devonian time lasting until foreland basin formation in the Late as Alberta”.

GEOSPHERE | Volume 13 | Number 4 Hauck et al. | Famennian Sassenach Formation provenance, Jasper Basin, Alberta Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/13/4/1149/3995126/1149.pdf 1160 by guest on 01 October 2021 Research Paper 500–700 Ma εNd(T) A Parry Islands Fm. (8) NAMG –5.1, –5.3, –5.3, –7.4 n=636 (–5.8) latest Frasnian–Famennian Canadian Beverly Inlet Fm. B Beverly Inlet (3), Fram (3), Hecla Bay (4), Strathcona Fiord (2), Bird Fiord (1) Fms. –10.1 n=909 Hecla Bay Fm. Figure 8. Detrital zircon plots (probability Eifelian–Frasnian –9.0, –12.1 (10.6) Arctic density function and kernel density esti- Bird Fiord Fm. mation) and εNd(T ) (T is timing of depo- –11.4 sition) for Devonian strata from northern and western Laurentia. Light gray bands represent age clusters interpreted from the Jasper Basin Sassenach Formation –8.1 C Blackley Fm. (2) data. Light orange bands represent the 500–700 Ma zircon ages of Arctic affinity, n=164 and the North American magmatic gap Eifelian (NAMG; van Schmus et al., 1993). Num- ber in parentheses after a formation name Yu Northwes t T represents number of sample locations. erritories

–5.0, –5.9, –6.3, –6.8, D Imperial Fm. (2) kon and Average of two or more εNd(T) values is in –6.8, –7.3, –11.4 parentheses. See Figure 11 for general lo- n=122 cation of samples A to H. (A, C) Data from (–7.1) Frasnian–Famennian Anfinson et al. (2012b);ε Nd for the Parry We Islands and Blackley Formations are as re- –6.9, –9.6, –9.8, –9.8, Albert a E Sassenach Fm. Jasper Basin (6) st-central –10.0, –10.9 ported in Patchett et al. (1999b). (B) Data (–9.5) n=354 from Anfinson et al. (2012a); εNd for the Famennian Beverly Inlet, Hecla Bay, and Bird Fiord Formations are as reported in Patchett F et al. (1999b). (D) Data from Beranek et al. Sassenach Fm. Southern B.C. (1) (2010) and Lemieux et al. (2011); εNd values n=100 are as reported in Garzione et al. (1997). Southern British Columbia Famennian (E) Sassenach data from the Jasper Basin (this study). (F) Sassenach data reported in Gehrels and Pecha (2014); sample is reported from southern British Columbia, although precise location is unknown. (G) Chase Formation data reported in –6.7, –7.4, –7.9, –8.5, G Lemieux et al. (2007) and Kraft (2013). Chase Fm. (2) Sample 04TWL072 of Lemieux et al. (2007) –8.8, –9.6, –10.1, n=142 is excluded from the data set as it is likely –10.6, –10.8 Famennian(?) part of the Mississippian Milford Group (–8.9) (Kraft, 2013). (H) Data from Beranek et al. (2016). Abbreviations: B.C.—British Colum- bia; Fm.—Formation; Sst.—sandstone. H Jefferson Fm.(1), Milligen Fm. Independence Sst. (1)

Probability density function n=161 Idaho, US A Frasnian–Famennian Kernel density estimation

0 400 800 1200 1600 2000 2400 2800 3200 3600 Age (Ma)

A second-order shift to more negative eNd values (–11.4) in the otherwise some sample locations. These data suggest that in addition to the effects of positive regional shift can be noticed in the uppermost Frasnian to Famennian sample size, the Sassenach Formation, which can reach thicknesses >200 m in Imperial Formation of the northern Cordilleran miogeocline (Garzione et al., some areas, can have varying proportions of contributing material both geo- 1997). Here, from the underlying Canol Formation (–4.8 to –5.0) into the Impe- graphically and over the time span of its deposition, which cautions against the

rial Formation (–5.0 to –11.4; Fig. 8D), there is a negative shift in eNd values sim- use of a single sample location and stratigraphic level for comparative analysis ilar to that observed in the Perdrix–Mount Hawk to Sassenach formations of (see Fedo et al., 2003, for a discussion of spatial and stratigraphic variability).

the Jasper Basin. Whereas this negative shift in eNd values of Famennian strata However, the composite U-Pb spectrum of our detrital zircon samples defines within the Cordilleran miogeocline has not been noticed in the Franklinian three age populations, (1) 378–700 Ma, (2) 900–2100 Ma, and (3) 2500–2900 Ma, data set (Patchett et al., 1999b), the Eifelian Bird Fiord and Givetian Hecla Bay that are similar to those of the single Sassenach sample reported by Gehrels and

Formations have negative eNd values (as low as –11.4 and –12.1, respectively) Pecha (2014) from an uncertain location in southern British Columbia (Fig. 8F). similar to negative values observed in Imperial and Sassenach strata (Fig. 8).

The overlying Frasnian Beverly Inlet Formation has comparable negative eNd Lower Neoproterozoic to Archean Zircons (900–3500 Ma) values (–10.1) (Fig. 8B). Thus, the northern Laurentian strata younger then Mid- dle Devonian appear to have had access to sources comprising older crustal A significant number of zircons (64%) from the Sassenach in the Jasper material. The Franklinian margin strata are interpreted to have been uplifted Basin fall within the 900–2100 Ma age cluster. An additional 15% of zircons fall during the Ellesmerian orogeny and subsequently distributed southward (e.g., within the 2100–2900 Ma age population (Fig. 8E). Direct derivation of Paleo-

Lemieux et al., 2011). The negative eNd values reported in these strata may have proterozoic and older zircon grains from the Canadian Shield into the Jasper

contributed to similar eNd values observed in the Sassenach of this study. How- Basin is unlikely. However, the shield was the primary source for the pre-Devo- ever, the westward coarsening both in the northern Cordilleran miogeocline nian terrigenous units at the western margin of Laurentia, hence any highland from fine-grained Besa River Formation to Imperial Formation (partly equiva- to the west of the Jasper Basin could have exposed the underlying strata that lent to the Earn Group) and in the Jasper Basin from the Graminia Silt to the may have acted as secondary sources of cratonic zircon grains into the Sas- western Sassenach, corroborated with the lack of such a second-order shift in senach Formation.

the Arctic, suggests that the Late Devonian negative shift in eNd values within The location of Belt-Purcell Supergroup strata at the western edge of Lau- the northern Cordilleran miogeocline may be related to an additional western rentia (Ross and Villeneuve, 2003) makes it a potential source of Precambrian source for these sediments. zircons for the younger strata along the western margin of Laurentia. All of

The subtle negative eNd shift recorded in the Sassenach Formation requires the pre-Mesoproterozoic detrital zircon age groups we have obtained from the

contributions from pre–Late Ordovician rocks with negative eNd values. The na- Sassenach samples have been reported from the Mesoproterozoic Belt-Purcell ture of the Sm-Nd isotopic system, namely the averaging of the isotopic com- Supergroup (Ross and Villeneuve, 2003), including grains in the 1610–1490 Ma position and age of source rocks, leaves some ambiguity in the interpretation North American magmatic gap (NAMG), which are atypical for Laurentia (van

of eNd values for provenance from Devonian miogeoclinal strata of western Schmus et al., 1993). A number of zircon grains (19) in our Sassenach sam-

Laurentia. Mixing of even small amounts of very negative eNd(T ) values from ples yielded ages that fall within the NAMG (Fig. 8); however, such zircon ages uplifted Neoproterozoic Windermere Supergroup (–20 to –22) and/or lower are known in the Prichard Formation of the Belt Supergroup where they were Paleozoic strata (–21 to –29) to the west could have produced the second-order interpreted to represent an influx of sediment from a western, subsequently

Late Devonian shift to more negative eNd(T ) in the Sassenach Formation. At the tectonically removed source (Ross and Villeneuve, 2003). same time, the Givetian to Frasnian Canadian Arctic strata and the Frasnian The detrital zircon budget of the Horsethief Creek Group (the southern strata of the Northwest Territories and Yukon (Imperial Formation) have nega- metamorphosed portion of the Neoproterozoic Windermere Supergroup)

tive eNd values overlapping with those of the Sassenach. appears dominated by late Paleoproterozoic (1753–1874 Ma) and random Archean (2564–3085 Ma) grains (Gehrels and Ross, 1998). To the north, in the Significance of Detrital Zircon Data Cariboo Mountains, two samples from the Kaza Group, the local representa- tive of the Windermere Supergroup, yielded zircon ages with a bimodal distri- There are a number of visual and statistical differences between zircon bution: 1.6–2.16 Ga and >2.5 Ga, with a distinct lack of ages between 2.1 and spectra of the six Sassenach samples from the Jasper Basin (Fig. 6). While the 2.5 Ga (Ross and Parrish, 1991). Although grits of these Neoproterozoic units general age gaps of 700–900 Ma and 2100–2500 Ma are mostly consistent, some were inferred to be derived from erosion of Laurentian source rocks to the samples contain a few ages within these troughs (three and 10 zircon ages, re- east, which include extensive 2.1–2.4 Ga rocks (particularly 2.3–2.5 Ga rocks spectively). Data density (shown in KDE plots) varies between samples within of the Arrowsmith orogeny; Berman et al., 2013), this age gap remained unex- the age clusters outlined in gray in Figure 6, which is in part due to the fine- plained. Noteworthy is that a similar age gap is obvious in the zircon spectrum grained nature of the sediment and the small zircon numbers retrieved from of our Sassenach samples (Fig. 8E).

There is no data set for the clastic strata of the Cambrian Gog Group, but Late Devonian–Early Mississippian (ca. 360 Ma) one sample from the Hamill Group, its correlative to the west in the Omineca belt, yielded a pattern almost identical to that of the underlying Neoprotero- 45°N zoic Horsethief Creek dominated by zircon ages in the 1750–1859 Ma range AX (Gehrels and Ross, 1998). The Middle to Upper Ordovician Mount Wilson For- mation yielded cogenetic zircons of 1030 Ma and 1053 Ma, ranges of 1816– 1967 Ma and 2025–2110 Ma, and a few isolated grains in the 2276–2598 Ma Innuitian hinterland AA range (Gehrels and Ross, 1998). Although a few grains with these ages are also present in the Sassenach Formation, there are no clear criteria to assign these 30°N CL grains to the underlying stratigraphic units. YT The large Proterozoic populations in the 1000–2100 Ma age range are very PT QN BAR. E common in the kilometers-thick clastic deposits of the Neoproterozoic Winder- L L mere and clastic Cambrian to Ordovician deposits. Mesoproterozoic and older E S zircon grains were also available from the Belt-Purcell strata. Paleoproterozoic- M E (older than ca. 1800 Ma) and Archean-age zircons including those defining 15°N R BALTICA I AN the 2500–2900 Ma cluster likely reflect Canadian Shield sources; the Meso- to Paleoarchean zircon ages (3100–3500 Ma) that fall outside the clusters are EK LAURENTIA likely multiply recycled from ancient basement provinces of the western Cana- NS dian Shield (Gehrels and Ross, 1998). The Neoproterozoic to Archean zircons in the Sassenach samples share ANTLER common ages with those of Devonian clastic strata of the northern and western margins of Laurentia (Fig. 8), although the proportion of zircons in the Jasper Basin Peri-Laurentian terranes age populations varies. These old populations do not offer clear discrimina- Plate vector tion criteria between western versus northern sources. As described above, Terranes of Caledonian, Baltican, or Siberian affinity many of these zircon ages can be explained by indirect (recycled) provenance Ellesmerian sediment from the Laurentian craton. The 900–1200 Ma populations, in addition to po- transport direction Early and mid-Paleozoic orogeny tential sources from Windermere and Cambrian deposits along the western Recycled Ellesmerian Laurentian margin, may be sourced from Arctic terranes, such as Crockerland sediment transport (Fig. 9), which has been interpreted to record zircons produced during the direction Grenville-Sveconorwegian orogenies (Anfinson et al., 2012b). Figure 9. A model for Late Devonian to Early Mississippian paleogeography of western and In reviewing the published data sets from the older clastic units in the adja- northern Laurentia (modified from Beranek et al., 2010). Abbreviations: AX—Alexander terrane; cent Cordilleran miogeocline, the identification of uniquely characteristic fea- AA—Arctic Alaska–Chukotka terrane; CL—Crockerland; PT—Pearya terrane; BAR.—Barentsia; tures in the underlying clastic strata is not possible at this time. YT—Yukon-Tanana terrane; QN—Quesnellia terrane (includes Okanagan subterrane); EK—East- ern Klamath terrane (includes Yreka-Trinity subterrane); NS—Northern Sierra terrane (includes Sierra City–Shoo Fly subterrane). Neoproterozoic to Paleozoic Zircons (378–700 Ma)

In contrast to the lower Neoproterozoic to Archean zircon populations, and Timanian orogenic belts (Beranek et al., 2010; Lemieux et al., 2011; Anfin there are unique features in the zircon age spectra obtained from the Sassen- son et al., 2012a, 2012b; Beranek et al., 2016). In particular, the 500–700 Ma ach Formation between 378 Ma and 700 Ma that are similar to those reported cluster is an age range atypical for Laurentia, but characteristic of granitoids from Middle and Upper Devonian strata of the Canadian Arctic, the northern associated with the Timanide orogen of Baltica. The oldest influx of Timanian and southern Canadian miogeocline, and south-central Idaho that link these zircons to Laurentia is recorded in upper Silurian deposits of Franklinian mar- strata to the paleo-Arctic region of northern Laurentia (Figs. 8A–8C). Zircons gin strata (Beranek et al., 2015). Subsequent uplift of Franklinian margin strata in this age group can be tied to terranes that accreted to the northern margin during Ellesmerian orogenesis in the mid-Paleozoic is recorded by Timanian of Laurentia, such as Arctic Alaska–Chukotka, Pearya, and Crockerland (Fig. 9) zircon ages in Devonian strata of the Arctic archipelago (Anfinson et al., 2012b) (Colpron and Nelson, 2009; Beranek et al., 2010, 2015; Anfinson et al., 2012a, and Devonian to Lower Mississippian strata of the Northwest Territories and 2012b; Lemieux et al., 2011). These terranes contain non-Laurentian zircon pop- Yukon (Beranek et al., 2010; Lemieux et al., 2011). Recycling of the Ellesmerian ulations, particularly in the 430–700 Ma range, sourced from the Caledonian clastic wedge containing the exotic Caledonian and Timanide zircon popula-

tions is recorded in Lower Mississippian strata (Keno Hill Quartzite and Tsichu Comparing Zircon Ages along Northern and Western Laurentia Formation) in the Yukon (Beranek et al., 2010). Our finding of exotic Caledonian and Timanide zircons in the Sassenach Formation of the Jasper Basin could In comparing the geographically disparate Devonian detrital data sets be interpreted as the oldest (Famennian) evidence for recycled Ellesmerian (Fig. 8), it is clear that in general all share the three age clusters described strata in the Cordilleran miogeocline. Older Devonian clastics on the North above (378–700 Ma, 900–2100 Ma, and 2500–2900 Ma). Kernel density estima- American shelf of the Cordilleran miogeocline are included in the Eifelian– tions, however, highlight the variation in data density in each age cluster. For Givetian Mount Forster Formation, but they do not contain the northern Lau- example, the Chase Formation from southern British Columbia and the Jeffer rentian signature (Kraft, 2013). son and Milligen Formations from Idaho have relatively low data densities Beranek et al. (2016) suggested an alternative hypothesis for the prove- in the Paleozoic to Neoproterozoic age group, particularly in the 500–700 Ma nance of detrital material for the Sassenach and Chase formations in south- range (Figs. 8G, 8H). The number of 500–700 Ma zircons increases to the north ern British Columbia, based on similarity to zircon populations in Upper from the Jasper Basin of this study toward Eifelian to Famennian strata of the Devonian strata of the Pioneer Mountains in Idaho. In addition to the Sas- Yukon, Northwest Territories, and the Canadian Arctic archipelago. Zircon age senach and Chase formations, Upper Devonian strata in Idaho contain data density also varies within the broad Proterozoic group (900–2100 Ma). For zircon populations with Arctic affinities as described above (Figs. 8E–8H). example, zircon ages from the uppermost Frasnian–Famennian Parry Islands Rather than direct marine current transport from the paleo-Arctic, Beranek Formation have fewer zircons in the 900–2100 Ma range but many more in the et al. (2016) attributed source areas to Arctic terranes that were translated Paleozoic to Neoproterozoic group, which was interpreted to reflect the over- southward along a sinistral transpressional system developed outboard of whelming input from younger source terranes colliding with northern Lauren- the western side of the Laurentian miogeocline during the Middle to Late tia over eastern Caledonian sediment sources (Anfinson et al., 2012b). Devonian (Fig. 9). The sinistral transcurrent system is interpreted to be re- Kraft (2013) noticed a peculiar Proterozoic age gap in the Chase Formation lated to the Antler orogeny along western Laurentia (Colpron and Nelson, from 1.22 Ga to 1.32 Ga (Fig. 8G). This age gap is also present in the Milligen 2009, 2011; Beranek et al., 2016). Three terranes in particular are pointed to and Jefferson Formations of Idaho (Fig. 8H; Beranek et al., 2016). However, this as sources for Upper Devonian sediments laying on the western Laurentian age gap is not present in the Sassenach or the rest of the Devonian strata in margin, including the Sassenach and Chase formations of southern British areas northward of the Jasper Basin (Figs. 8A–8F), which suggests potential Columbia and the Milligen and Jefferson formations in south-central Idaho differences in sources containing Proterozoic zircons. (Figs. 8E–8H) (Beranek et al., 2016): the Okanagan subterrane of the Ques The differences between the data sets, as described above, are borne out nellia terrane (part of the “Okanagan High”), the Trinity-Yreka subterrane of by K-S tests (Table 3). The Sassenach appears to correlate best with the partly the Eastern Klamath terrane, and the Sierra City–Shoo Fly subterrane of the coeval Imperial Formation of the Yukon and Northwest Territories and the Eifel Northern Sierra terrane (Fig. 9). ian Blackley Formation of the Arctic region, whereas the Jefferson and Milligen

TABLE 3. P VALUES FROM KOLMOGOROV-SMIRNOV STATISTICAL TEST* North South Quesnellia Canadian Arctic Yukon and N.W.T. Jasper Basin Southern B.C. (Southern B.C.) South-central Idaho ABCDEFGH A 0.000 0.000 0.000 0.0000.000 0.0000.000 B 0.000 0.738 0.001 0.032 0.1070.118 0.001 C 0.000 0.738 0.147 0.0880.832 0.864 0.009 D 0.000 0.001 0.147 0.365 0.0190.012 0.000 E 0.000 0.032 0.088 0.365 0.0500.038 0.003 F 0.000 0.107 0.832 0.019 0.050 0.975 0.009 G 0.000 0.118 0.864 0.012 0.038 0.975 0.004 H 0.000 0.001 0.009 0.000 0.0030.009 0.004 Note: Sample locations: A—Parry Islands Formation (Anfinson et al., 2012a, 2012b); B—Beverly Inlet, Fram, Hecla Bay, Strathcona Fiord, Bird Fiord Formations (Anfinson et al., 2012a); C—Blackley Formation (Anfinson et al., 2012b); D—Imperial Formation (Beranek et al., 2010; Lemieux et al., 2011); E—Sassenach Formation (this study); F—Sassenach Formation (Gehrels and Pecha, 2014); G—Chase Formation (Lemieux et al., 2007; Kraft, 2013); H—Jefferson Formation and Independence sandstone (Milligen Formation) (Beranek et al., 2016). *P values greater than 0.05 (gray shading and bold values) considered statistically indistinguishable, and thus have the same provenance. P values of 0 have statistical certainty of different source areas.

Formations (Idaho) and the Parry Islands Formation (Arctic) do not appear to not explain the negative deviation of eNd values of the Sassenach Formation correlate to any other data sets despite visual similarity in PDF and KDE plots (Fig. 7). Moreover, the arch was mostly covered by Devonian sediments during (Table 3). The K-S tests suggest a closer link to partly coeval Devonian clastics the Famennian deposition of the Sassenach Formation and exposed only as a from northern areas of the western Laurentian margin. small island north of the Jasper Basin. Whereas the existing Nd isotope data from the Sassenach Formation sug- Discordance Modeling gest contributions from an older, possibly western source, the recognition of Arctic-affinity detrital zircon grains (500–700 Ma age range) and of a Pb-loss To further constrain the source, we have modeled our U-Pb data using event coincident with an Ellesmerian tectonic event are consistent with a Ca- the discordance modeling program by Reimink et al. (2016) (Fig. 10). The ca. nadian Arctic source for the detrital component of the Sassenach Formation. 390 Ma lower intercept derived from the discordia modeling is not an exact Whether these Arctic-affinity zircons were delivered directly from the Arctic age of the potential alteration of the zircons; it represents a peak with a like- through south-directed Late Devonian shore-parallel shallow-marine currents lihood that is larger than one-third of the maximum likelihood in the data set along western Laurentia, or alternatively from western sources, either high- (Reimink et al., 2016). However, the lack of any other conspicuous peaks in lands related to the Antler orogen or Arctic-affinity terranes that migrated the lower-intercept line (Fig. 10C) strengthens the interpretation of one major south and were tectonically juxtaposed against the western margin of Lauren- resetting event that has affected a significant proportion of the Sassenach zir- tia during the Middle to Late Devonian, will be discussed further below. cons with a range of crystallization ages. The 390 Ma lower-intercept age calculated here appears to be too old for Western Sources the Antler orogeny, although no precise dating constrains Antler-equivalent tectonism in the Canadian Cordillera. Instead, this early Eifelian age coincides The interpretation of a western source for the clastic material in the Sas- with the first of three tectonic loading events inferred in the Innuitian-Elles senach Formation has been intrinsically associated with the manifestation of merian orogen. There, accelerated subsidence at the initiation of unconformity- Antler tectonics at Canadian latitudes. Antler-age tectonism was inferred from bounded sequences in the foreland basin (early Eifelian–earliest Frasnian, early the Late Devonian through mid-Mississippian flooding of the Cordilleran mio- Frasnian–late Frasnian, and late Frasnian–mid-Famennian, followed by a con- geocline by westerly derived clastics, which required a highland to the west. cluding phase of deformation and uplift of the foreland basin in late Famen- This clastic influx is represented by the coarse clastics of the Guyet Formation nian–Tournaisian) has been triggered by three major thrusting pulses during at Alberta latitudes in the Cariboo Mountains (Campbell et al., 1973) and by southwestward propagation of the Ellesmerian orogenic belt (Embry, 1988). the Earn Group farther north in the Cassiar Mountains and the Yukon (Gordey et al., 1987), with their eastern fine fringe consisting of the Exshaw Forma- tion and Besa River Formation, respectively, which spread far into the interior POSSIBLE SOURCES FOR THE SASSENACH FORMATION of the platform from Frasnian to earliest Mississippian time (Campbell et al., 1973; Struik, 1986; Gordey et al., 1991). The western sequences that include In the context to the Western Canada Sedimentary Basin, potential source coarse sandstone and conglomerate are associated with growth faults and areas for the terrigenous-clastic component of the Sassenach Formation in the local alkali volcanic rocks of continental-rift geochemistry (Goodfellow et al., Jasper Basin include one, or a combination, of the following sources: (1) an 1995). Their original interpretation as deposited in half-grabens formed in the eastern source in the Canadian Shield, including the Peace River Arch; (2) the outer miogeocline (Tempelman-Kluit, 1979) has been reconsidered as depos- western Laurentian margin at paleolatitudes proximal to the Jasper Basin, its of pull-apart basins along a broad sinistral strike-slip fault zone (Eisbacher, such as the “Okanagan High” and/or an exotic terrane related to Antler tec 1983; Gordey et al., 1987; Ketner, 2012). The sediment sources could have been tonics; and/or (3) sediment recycling from Franklinian strata during the Elles- local uplifts (highlands) at compressional bends along the major fault zone merian orogeny along the western Laurentian margin. outboard of the preserved margin of the miogeocline, which were partly removed or obscured by subsequent tectonism. Eastern Sources Smith et al. (1993) postulated, however, that the Antler orogen of central Nevada and southern Idaho extended to the north, and that the Late Devo- Our detrital zircon and Sm-Nd data show that eastern, shield-derived nian and Mississippian extensional setting in the Canadian Cordillera is the sources alone can be discounted based on their lack of Neoproterozoic and expression of “foreland flexural extension” east of the advancing orogen. In younger zircons. The Peace River Arch, which exposed cratonic basement just spite of its highly speculative nature and striking differences between the west- north of the Jasper Basin, can also be discounted as the sole source based on ern U.S. and Canada (e.g., compressional versus extensional tectonic setting, zircon ages (lack of Neoproterozoic to Paleozoic zircon ages) and its less nega- well-defined fold-thrust belt versus modest local deformation, no foreland

tive eNd values (–9.7 to –5.6, average of –2.3; Thériault and Ross, 1991) that can- volcanics versus abundant volcanics, respectively), over time this extrapola-

1.0

data-point error ellipses are 2σ 4000

0.8 ) 3400 3000

U 0.6 300000

23 8 2600

Pb / 2200 2000

20 6 0.4

1800 wer Intercept (Ma Figure 10. Results of discordia modeling (Reimink et al., 2016) for 548 zircons ana Lo lyzed from the Sassenach Formation in

0.2 00 0 this study. (A) Discordia diagram for all zircons. Numbers along curve are age in Ma. (B) Two-dimensional likelihood A 0.0 map of normalized probability relative to 010203040 B the upper and lower intercept ages. The 01 darkest blue represents the highest like- 207 235 Pb/ U 0 1000 2000 3000 4000 lihood for the upper and lower intercept Upper Intercept (Ma) ages. Notice the narrow region associated with the lower intercept (ca. 390 Ma). 390 Ma 1570 Ma (C) Graph of binned upper and lower intercept ages and associated likelihood.

Likelihood is the normalized, raw summed 21 Upper intercept probability density of the dataset used as a relative metric. The lower intercept curve Lower intercept 18 is defined by a distinct peak ca. 390 Ma (corresponding to the blue in B), with no 15 other distinct peaks. These data suggest common alteration of the detrital zircon population during the Middle Devonian. 12

lihood 9

Li ke 6 3 C 0 0500 1000 1500 2000 2500 3000 3500 4000 4500 Age (Ma)

tion has propagated into the local literature (e.g., Stevenson et al., 2000; Root, both locations the structural interpretations are tenuous and will be briefly re- 2001). Various Silurian to Mississippian tectonic processes at the western mar- viewed here. gin of ancient North America have been conveniently assigned to the Antler Gehrels and Smith (1987) proposed that the Lardeau Group of the Kootenay orogeny (see Root, 2001). arc was an “Antler” allochthon correlative with the Covada Group in the Rob- Antler-age compressional deformation along the Canadian Cordillera has erts Mountains of the northwestern U.S., and that it was emplaced over mio- been assumed at two locations in southern British Columbia, one in the Koote geoclinal strata (Badshot Formation) during mid-Paleozoic time. Colpron and nay parautochthon and the other on the Middle Devonian “Purcell arch”. At Price (1995) showed instead that the Lardeau Group is depositionally linked

to and conformable with underlying rocks that form part of the North Ameri- Root (2001) interpreted the tectonic setting as “foreland basin during (early can Cordilleran miogeocline. Subsequent detailed mapping in the Kooteney Antler) contractional deformation”. Located inboard of the Lardeau trough, in arc (Thompson et al., 2006) has provided stratigraphic evidence that supports a back-arc (extensional) tectonic setting, the syn-depositional deformation in a change from a trough-like setting during the Lardeau deposition, to stable the Mount Forster Formation had a local character, and could not have been platform-like conditions in the mid-Devonian, to back-arc extension and mag- “part of an orogenic event of sufficient magnitude to generate a foreland basin… matism in the Late Devonian to Mississippian; in modern coordinates, the along the Devonian Cordilleran margin” (Kraft, 2013, p. 149). We consider Root’s west-facing continental margin arc developed on the Okanagan High above (2001) interpretation of an Antler fold-and-thrust belt to be tenuous at best and an east-dipping subduction zone (Thompson et al., 2006). According to Kraft its propagation into continental-scale paleoreconstructions invoking an Antler (2013), volcanic lithogeochemical data from the Kootenay arc show a progres- orogen all along western Laurentia (Smith et al., 1993) unwarranted. Although sion from early to mid-Paleozoic rift-related volcanism (in the Lardeau Group), we are well aware that the tectonic setting, timing of events, and structural style to Devonian and Early Mississippian arc-related volcanism (in the Mount may vary along a continental-scale orogenic belt, and that its vestiges could be Sproat assemblage), followed by Permian oceanic spreading-center volcanism obscured by Mesozoic–Cenozoic Cordilleran tectonics, the frequently invoked (in the Kaslo Group, the local expression of Slide Mountain “ocean”). Antler orogen has yet to be firmly established at Canadian latitudes. We favor the An episode of (middle Paleozoic?) contractional deformation in the Koote- interpretation of a local western highland(s) within or beyond the miogeocline. nay arc was inferred based on truncation of foliation surfaces, folds, and thrust The extensional, back-arc basin setting of the miogeoclinal-terrace wedge faults in the early Paleozoic Lardeau Group by the Lower Mississippian Mil- at the western margin of Laurentia throughout the middle to late Paleozoic ford Group (e.g., Read and Wheeler, 1975; Klepacki and Wheeler, 1985; Smith implies a west-facing magmatic arc on the outboard margin of Laurentia et al., 1993). Kraft (2013) has shown that old D1 compressional structures in the (Thompson et al., 2006). Arctic-origin terranes migrating to the south could Lardeau Group have only been observed in the northern Kootenay arc, and have been placed adjacent to the arc during the Late Devonian (Colpron and internal deformation in the Index Formation to the south (interpreted as a pos- Nelson, 2009) and shed Arctic zircons to the western Laurentian miogeocline, sible Mississippian thrust zone), were both manifestations of local shortening including the Jasper Basin (Beranek et al., 2016). Assuming that a transport due to heterogeneities in a back-arc environment. At southern Canadian Cordi mechanism could be imagined to deliver zircons from across the ~300-km- llera latitudes, the Slide Mountain basin was closed through thrusting and fold- wide back-arc basin (Thompson et al., 2006), it is striking that the Sassenach ing (the “Whitewater event”) as late as late Permian to Middle Triassic, and ob- Formation does not contain syndepositional zircon from the extensive Late duction would have occurred after Late Triassic–Early Jurassic arc magmatism, Devonian–Mississippian Eagle Bay magmatic suite of the Okanagan High hence too late to be assigned to the Antler orogeny (Thompson et al., 2006). (Paradis et al., 2006). It is also intriguing that the Chase Formation on the The other frequently cited evidence of Antler compression at Canadian Okanagan High at the western shoulder of the back-arc basin lacks syndeposi- latitudes is in the Purcell Mountains, where the geology within a very limited tional zircons from the proximal Eagle Bay Formation (Kraft, 2013). area (<10 km2) was interpreted to record the “most precise view of the nature Whereas a mixture of northern and western sources related to southward- and timing of the mid-Paleozoic deformation...in western Canada” (Root, 2001, migrating terranes cannot be discounted due to the potential masking of p. 17). At this location, the Neoproterozoic Horsethief Creek Group (Winder- western-derived zircons by the northern sources, the discordia modeling mere Supergroup) is overlain above a major regional unconformity by three herein suggests a common zircon alteration event ca. 390 Ma in the Sasse Middle Devonian formations (Eifelian to late Givetian conodont zones), each nach zircon population, which may be linked to Eifelian convergent tectonism separated by angular unconformities. In ascending order these are the Mount during Ellesmerian orogenic events along the northern margin of Laurentia. Forster, Harrogate, and Starbird formations. The Mount Forster Formation (and inferred correlatives to the east) comprises an easterly thinning wedge that Northern Sources pinches out against the West Alberta Ridge, which was the source for sandstone and conglomerate present in exposures near the eastern zero edge of the The interpretation of a common source for strata of the northern regions of sequence (Belyea and Norford, 1967). Root (2001, p. 17) described two faults Laurentia and those of the Jasper Basin requires significant southward trans- with uncertain sense of displacement: F2 was considered “poorly understood” port of sediments by shore-parallel, shallow-marine currents along the western but was mapped as a normal fault, and F3 was believed to be “a normal fault margin of the Laurentia (Fig. 11). Based on the Nd isotopic system, a northern that has created an omission of strata”, amongst other possibilities. The au- source for the mid-Devonian to Lower Jurassic sediments of the western North thor viewed “the structural and stratigraphic geometries (as being) produced American miogeocline has already been postulated (e.g., Boghossian et al., by Devonian syndepositional deformation…(with) abundant angular uncon 1996; Patchett et al., 1999a). Stoakes (1980) and Mountjoy (1980) suggested formities…created by syndepositional fold- and fault-related growth structures”. that the fine-grained terrigenous clastics of the Mount Hawk Formation of the Paradoxically, although an extensional depositional environment is suggested southern Canadian Rocky Mountains and its equivalent Ireton Formation in by the normal faults and by the volcanic flows in the Mount Forster Formation, the subsurface of Alberta were derived from the north, and Stoakes (1980)

Alexander Terranerrane

Arctic Alaska/Chukotka/ Pearya/Crockerland ogeogenn Terranes Baltica PlatPlatee

Caledonian Or Peri-Baltic-Siberia TTerranes Innuitian–Ellesmerian Or C

A and B ) ogen

erranes D Laurentian PlatPlatee Equator 1 (380–370 Ma

) Ma

Panthalassic ? Ocean ? PRA Equator 2 (365–355 Ma E Jasper BasiBasinn GrosmontGrosmont ? Platform e ogen ? Leduc Reefs ? F AB SK G? ? MT Avalon PlatPlate N Acadian Or ? H

1000 km LATE DEVONIAN — 375 Ma (380–370 Ma)

Figure 11. Late Devonian paleogeography of northern and western Laurentia (375 Ma) (modified from Ron Blakey, Colorado Plateau Geosystems Inc.). The Jasper Basin (Sassenach Formation) is located in the southern Canadian Cordillera, west of palinspastically restored Frasnian reef complexes. Arrows denote the general sediment pathways interpreted for the Frasnian–Famennian basin fill, including the Sassenach Formation (yellow arrows), from the Innuitian-Ellesmerian orogen in the Canadian Arctic. Two positions of the equator are shown for different 10 m.y. time slices: equator 1 is Late Devonian, whereas equator 2 is Late Devonian–Early Mississippian; see text. Locations A to H represent areas of existing Devonian detrital zircon chronology studies with zircon age spectra compiled in Figure 8. White line off NW Laurentia represents a hypothetical oceanic spreading ridge. Abbreviations: AB—Alberta, Canada; MT—Montana, USA; PRA—Peace River Arch; SK—Saskatchewan, Canada.

suggested the Franklinian orogen as a potential source. The Sassenach Forma- Devonian strata from the Yukon, Northwest Territories, and the Canadian

tion, however, is siltier and contains fine-grained sandstone, and its equivalent Arctic (Figs. 7, 8, and 11). The post-Ordovician eNd positive trend in Devonian in the subsurface, the Graminia Silt, is relatively thin and contains no signifi- strata is common in the Canadian Arctic and Canadian Cordilleran miogeo-

cant sandstone. The fact that the Graminia Silt and other northern Devonian cline. Furthermore, subtle negative eNd deviations in the post-Ordovician trend

sequences as old as the Eifelian contain eNd values that overlap with the most are recorded in both the Middle to Late Devonian northern strata and the Late negative values in the Sassenach suggests that they share a common source, Devonian Sassenach of the Jasper Basin. possibly Franklinian margin strata recycled through Ellesmerian orogenesis. A northern Laurentian source area for the Sassenach Formation is sup- One suggestion is that more vigorous shore-parallel currents were di- ported by similarity in detrital zircon age populations, specifically in non-Lau- rected along the outer shelf of Laurentia, west of the West Shale Basin (Fig. 2), rentian ages in the 500–700 Ma age range. Silurian to Devonian zircon ages during Famennian Sassenach deposition (Fig. 11). This scenario is consistent within the Sassenach are also common within the Devonian of northern Lau- with Northern-Hemisphere-clockwise currents (south-directed currents) set up rentia, with a common potential source in the Pearya terrane. Discordance along the western margin of Laurentia due to the Famennian shift of the Jasper modeling of the Sassenach zircons points to a common period of tectonother- Basin to the Northern Hemisphere. Similar processes were invoked for the mal overprinting at ca. 390 Ma, which corresponds to the first pulse in tec- distribution of zircons southward from the exposed Peace River Arch during tonism in Innuitian-Ellesmerian orogenic events. These data suggest that the the Ordovician (Gehrels and Ross, 1998; Gehrels and Pecha, 2014). Southward bulk of the clastic sediment in the Sassenach Formation was derived from the transport of coarser sediment may also have been facilitated by a significant recycled Ellesmerian foreland basin, and that this sediment propagated along relative sea-level fall at the Frasnian-Famennian boundary, recognized from the western side of Laurentia during the Famennian. numerous Devonian locales in Euramerica (top of transgressive-regressive cycle IId of Johnson et al. [1985]). Fairholme Group carbonates, which under- ACKNOWLEDGMENTS lie the Sassenach in the Cordillera, show evidence of erosion corresponding to this sea-level fall event (McLaren and Mountjoy, 1962; MacKenzie, 1965). The authors would like to acknowledge the financial support of the Alberta Energy Regulator– Alberta Geological Survey. The valued cartographic support of Kirk McKay and Rastislav Elgr of Stratal relationships suggest that the Sassenach filled the Jasper Basin during the Alberta Geological Survey is acknowledged. Robert Dokken (University of Alberta) is thanked the ensuing eastward transgression and continually onlapped the Fairholme for sample separation. Thoughtful and constructive reviews by L. Beranek, M. Blum, P. Link, and Group carbonate buildups (Mountjoy and Becker, 2000). Associate Editor C. Spencer significantly improved this paper. The detrital zircon budget of the Sassenach Formation of the Jasper Basin appears to be tied more closely to northern Devonian strata than to the south- REFERENCES CITED ern and western margin of Laurentia. 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