Southeastern Yukon Research Articles

Continent-wide population genomic structure and phylogeography of North America's most destructive conifer defoliator, the spruce budworm (Choristoneura fumiferana).

The spruce budworm, Choristoneura fumiferana, is presumed to be panmictic across vast regions of North America. We examined the extent of panmixia by genotyping 3,650 single nucleotide polymorphism (SNP) loci in 1975 individuals from 128 collections across the continent. We found three spatially structured subpopulations: Western (Alaska, Yukon), Central (southeastern Yukon to the Manitoba–Ontario border), and Eastern (Manitoba–Ontario border to the Atlantic). Additionally, the most diagnostic genetic differentiation between the Central and Eastern subpopulations was chromosomally restricted to a single block of SNPs that may constitute an island of differentiation within the species. Geographic differentiation in the spruce budworm parallels that of its principal larval host, white spruce (Picea glauca), providing evidence that spruce budworm and spruce trees survived in the Beringian refugium through the Last Glacial Maximum and that at least two isolated spruce budworm populations diverged with spruce/fir south of the ice sheets. Gene flow in the spruce budworm may also be affected by mountains in western North America, habitat isolation in West Virginia, regional adaptations, factors related to dispersal, and proximity of other species in the spruce budworm species complex. The central and eastern geographic regions contain individuals that assign to Eastern and Central subpopulations, respectively, indicating that these barriers are not complete. Our discovery of previously undetected geographic and genomic structure in the spruce budworm suggests that further population modelling of this ecologically important insect should consider regional differentiation, potentially co‐adapted blocks of genes, and gene flow between subpopulations.

Sedimentology and regional significance of the ‘argillite unit’, a probable Cryogenian map unit in southeast Yukon, Canada

AbstractAn unnamed succession of volcaniclastic argillite, sandstone, and conglomerate (the ‘argillite unit’) is exposed in an inlier in southeastern Yukon (NTS 95C/5). These strata were hornfelsed during emplacement of the Pool Creek syenite (ca. 640–650 Ma) and are correlated with the late Cryogenian Hay Creek Group of the Mackenzie Mountains based on lithostratigraphic evidence and published constraints from detrital zircons. The unit preserves three argillite lithofacies, two sandstone lithofacies, and two conglomerate lithofacies. The argillite and sandstone can be grouped into three facies associations, reflecting differing volumes of sandstone and the presence or absence of chaotic bedding. Deposition was mainly from sediment‐gravity flows, particularly turbidity currents and debris flows. Post‐depositional slumping was common, and the succession is interpreted to have been deposited on a slope that trended NNW and dipped to the ENE. This orientation was subparallel to but facing towards the contemporaneous slope of the Hay Creek Group in the Mackenzie Mountains. Conglomeratic facies are dominated by angular to poorly rounded clasts of subalkali basalt that probably were entrained in debris flows during or soon after eruption and otherwise saw little transport or weathering. Geochemistry of the clasts is permissive of a rift‐related setting. Following deposition, but prior to deposition of overlying Cambro‐Ordovician strata, the argillite unit underwent compression that produced broad, open folds, consistent with recent proposals for late Neoproterozoic transtension–transpression on the present‐day northwest margin of Laurentia. The argillite unit provides a snapshot of the geological evolution of southeast Yukon during the late Cryogenian, providing a new data point for reconstructing the protracted and complex rifting history of Rodinia in western Canada. © 2016 Her Majesty the Queen in Right of Canada Geological Journal © 2016 John Wiley & Sons, Ltd.

Examination of the interplay between glacial processes and exhumation in the Saint Elias Mountains, Alaska

The combination of large, temperate glaciers and rapid crustal convergence in the Saint Elias Mountains (southeastern Alaska, USA, and Yukon Territory and British Colombia, Canada) provides an exceptional opportunity to study the interactions between the tectonic and surface processes that have shaped most active orogens on Earth during much of the Quaternary. This research first provides a review of thermochronometric data sets recording exhumation under two major glacier systems of the Saint Elias Mountains, the Bagley-Bering and the Seward-Malaspina systems. These data sets are integrated over the single glacier systems and used in conjunction with glaciological data to investigate the interactions of glacial erosion and tectonics. Despite their proximity, the glaciological processes and geological settings of these two glacial systems differ significantly. On the east side of the orogen, sediments eroded from bedrock underneath the Malaspina Glacier reflect regions of rapid erosion under the slowly moving Seward Ice Field. Because the Seward Ice Field overlies a localized zone of major faulting and rapid exhumation, the strained and fractured bedrock is primed for erosion. On the west side, the Bering Glacier is the primary outlet for the Bagley Ice Field, which covers half of the crest of the orogen; however, few if any of the sediments at its terminus originate from under the Bagley Ice Field. Sediment transport is likely hindered by subglacial freeze-on processes that reduce the sediment-carrying capacity of subglacial rivers, though glacial surges are likely exceptions that deposit sediment far beyond the active margin of the glacier. Our study concludes that the widely invoked concepts of glacial erosion should be used with caution, as oversimplification can fail to account for important site-specific differences in geologic and glacial conditions.

Spatial distribution of meadow jumping mice ( Zapus hudsonius) in logged boreal forest of northwestern Canada

Most studies of small mammal responses to habitat alterations focus on dominant species, with a resulting lack of information for rare species. Jumping mice (Order Rodentia: Dipodidae) tend to be rare in small mammal trapping studies; thus, little is known of their response to habitat alterations, such as clear-cut logging. We examined the spatial distribution of meadow jumping mice ( Zapus hudsonius) captured in 3 upland habitat types (forest interior, forest edge, and logged forest) in the boreal forest of southeastern Yukon, Canada. Meadow jumping mice were the third most common rodent captured, and consistently constituted 19.7% of captures in all of the habitat types. Meadow jumping mice may not be rare in some boreal mammal assemblages. Significantly less animals were captured in the forest interior compared to the forest edge or logged forest ( P < 0.05). A preference or avoidance of sharp habitat edges created by logging was not detected. Logged areas may be more preferred over unlogged areas by meadow jumping mice because they provide relatively diverse and abundant food resources and cover. To provide data more useful for biodiversity conservation, we suggest that studies of small mammals in forest ecosystems deploy a variety of trap types and sample at sufficient intensity to provide information on both dominant and rare species.

Trace-fossil assemblages in the Lower Triassic Toad Formation, La Biche River map area, southeastern Yukon

Abstract Two outcrop sections of the Lower Triassic (Griesbachian = Early Induan) Toad Formation in southeastern Yukon (La Biche River map area; NTS 95 C) contain well-preserved trace fossils. Strata consist of interbedded shale, siltstone, and sandstone in varying proportions and are interpreted to record deposition on a wave-dominated shelf. Trace-fossil diversity and abundance are low in facies interpreted to be of distal-shelf origin but are moderate to high in offshore-transition and lower-shoreface strata. Sandstone packages interpreted as shoreface deposits are effectively barren. The most common ichnofossils are dwelling networks (Spongeliomorpha), infaunal feeding traces (most commonly Planolites), and arthropod-produced furrowing traces (Cruziana). Ichnotaxonomic diversity of the Toad Formation is high relative to many well-documented Griesbachian successions. This supports suggestions that infauna recovered more rapidly in high-paleolatitude regions than in low-paleolatitude regions following the end-Permian extinction. The studied strata are an outcrop analogue for correlative, gas-producing strata (Montney Formation) in the Ring/Border Field of northeastern British Columbia and the Pedigree Field of northwestern Alberta. Similarities in sedimentology and ichnology between the two successions suggest that prospective reservoir strata may be present regionally in the Lower Triassic.

Provenance of North American Triassic strata from west-central and southeastern Yukon: correlations with coeval strata in the Western Canada Sedimentary Basin and Canadian Arctic Islands

New detrital mineral age and whole-rock geochemical data provide the first constraints on the composition and source of North American Triassic strata in the northern Canadian Cordillera. Conodont-bearing Triassic strata collected from five locations across west-central to southeastern Yukon contain trace-element ratios ((La/Yb)N = ∼8; Eu/Eu* = ∼0.66), εNd(248 Ma) values (–9 to –10), and detrital zircon ages (400–680, 980–1200, 1500–1650, 1800–2000 Ma) that correspond with those of coeval rocks in the Canadian Arctic Islands and the Western Canada Sedimentary Basin of British Columbia and Alberta. The majority of detrital zircons were cannibalized from Ellesmerian clastic wedge and western Laurentian margin strata and recycled into Triassic rocks. Conspicuous early Paleozoic and Neoproterozoic detrital zircons may have been ultimately derived from allochthonous rocks of Caledonian–Baltican affinity in northern North America, such as the Pearya and Arctic Alaska – Chukotka terranes. One Early Triassic unit in eastern Yukon contains ca. 360 Ma detrital muscovite, and samples from several localities include single-grain occurrences of Mississippian detrital zircon. Mississippian detrital mineral ages likely record a partial source from mid-Paleozoic rocks of the allochthonous Slide Mountain and Yukon–Tanana terranes following their Late Permian – Early Triassic emplacement onto the Cordilleran margin. More substantial evidence of terrane-derived sediment deposited along the North American margin may be further identified within Triassic strata that are exposed to the west (outboard) of our sample sites, immediately adjacent to the Slide Mountain and Yukon–Tanana terranes.

Apparent Predation of an American Water Shrew, &lt;em&gt;Sorex palustris&lt;/em&gt;, by an American Marten, &lt;em&gt;Martes americana&lt;/em&gt;

Little is known of the natural history of American Water Shrews, Sorex palustris, including their predators. We document an apparent case of predation of an American Water Shrew by an American Marten, Martes americana, in the boreal forest of southeastern Yukon.

Sequences in the Sikanni Formation in the frontier Liard Basin of northwestern Canada—evidence for high frequency late Albian relative sea-level changes

The frontier Liard Basin is a relatively unexplored basin in northeastern British Columbia, southwestern Northwest Territories and southeastern Yukon Territory. Although it preserves a thick Cretaceous sedimentary succession, the relationships of these strata to those to the south in the Western Canada Sedimentary Basin (WCSB) are poorly understood. Outcrop sedimentary analysis along with foraminiferal micropaleontology and Rock-Eval pyrolysis are used to investigate the relative sea level and palaeoenvironmental changes that accompanied deposition of the upper Albian Sikanni Formation. Analysis of proximal and distal facies from three outcrops of the Sikanni Formation within the Liard Basin indicates that four sequences can be identified in offshore, wave-dominated shoreline, prodeltaic, delta front and delta plain litho- and biofacies. The identification of 10 5 yr cyclicity relative sea level changes that punctuated Sikanni deposition is supported by the presence of chert pebble lag deposits at surfaces interpreted as sequence boundaries. These sequences are regionally correlative in outcrops and well logs of the Sikanni Formation and indicate a previously unrecognized cyclicity in the upper Albian of the WCSB. Among the two causal mechanisms considered to have possibly driven the cycles, high frequency changes in flexural loading is probably responsible for the cyclicity observed, as evidence of basin-wide relative sea level changes necessary to support a eustatic interpretation is lacking in the late Albian of the WCSB.

Yukon–Tanana terrane in the southern Campbell Range, Finlayson Lake belt, southeastern Yukon: the geological setting of retrogressed eclogite of the Klatsa metamorphic complex

Yukon–Tanana terrane in the southern Campbell Range is composed of rocks that have different metamorphic, exhumation, and structural histories, and that have formed in disparate parts of the Paleozoic Yukon–Tanana volcanic arc. The geological relationships in the southern Campbell Range reveal the tectonic and structural history of the Klatsa metamorphic complex, which represents the remnants of an Early Mississippian subduction zone beneath the Yukon–Tanana arc. The Klatsa metamorphic complex is composed of foliated to massive serpentinite, leucogabbro, amphibolite, and retrogressed eclogitic quartz–muscovite schist with lenses of metabasite. It was structurally juxtaposed on Upper Mississippian to Lower Permian metasedimentary rocks of the White Lake, King Arctic, and Money Creek formations. Regional and local structural and stratigraphic relationships suggest that the Klatsa metamorphic complex is part of the Cleaver Lake thrust sheet, the structurally highest thrust sheet in a north- to northeast-vergent thrust belt that deformed the Yukon–Tanana terrane during the Early Permian. Restoration of the displacement on the Cleaver Lake and underlying thrust faults places the Klatsa metamorphic complex on the western margin of Yukon–Tanana terrane. Late Devonian to Early Mississippian subduction is thought to have occurred along this margin based on previous paleogeographic reconstructions. Generally north- to northeast-vergent D1 to D3 folds deformed the Klatsa metamorphic complex and adjacent metasedimentary rocks. Jurassic(?) D4 imbricate thrust faulting has, in part, reactivated the Cleaver Lake thrust fault contacts and imbricated the Klatsa metamorphic complex with metasedimentary rocks in fault panels that are repeated at a scale of 10 to hundreds of metres.

Detrital zircon geochronology and provenance of the southeastern Yukon–Tanana terrane

Two samples of late Paleozoic grit and Late Mississippian quartzite–chert conglomerate collected from southeastern Yukon–Tanana terrane (YTT) — a composite thrust sheet resting structurally above North American parautochthonous strata and intervening imbricate sheets of the late Paleozoic oceanic Slide Mountain terrane — yielded, respectively, 89 and 74 concordant or nearly concordant (&lt;20% discordant) U–Pb ages on single detrital zircons. They provide constraints on the provenance of this allochthonous pericratonic terrane. Zircons in the grit range from 1770 to 2854 Ma, with a well-defined Early Proterozoic peak between 1800 and 2100 Ma. Precambrian zircons in the conglomerate also show a dominant peak between 1800 and 2100 Ma and smaller peaks between 2200 and 3200 Ma, with a few older grains, and younger grains with ages of 998, 1219, 1255, 1256, and 1417 Ma. The conglomerate also yielded three Devonian grains, with ages of 366 ± 23, 373 ± 12, and 379 ± 23 Ma. Their ages are approximately coeval with the oldest felsic to intermediate arc- and rift-related magmatism in the YTT. The age spectra from southeastern YTT units compare closely with those from Mississippian and older pericratonic units in the Coast Mountains, confirming correlations previously made on lithologic grounds. They also strongly resemble detrital zircon populations from craton-derived Paleozoic units of the northern North American autochthon. This robust U–Pb data set lends support to the idea that YTT once formed part of the outer, active margin of the North American continent, prior to Mississippian rifting and marginal ocean basin development.

First Records of the Southern Red-backed Vole, &lt;em&gt;Myodes gapperi&lt;/em&gt;, in the Yukon

Twenty Southern Red-backed Voles, Myodes gapperi, were collected in July 2004 in the LaBiche River valley of southeastern Yukon. Specimens were identified using morphological characteristics and analysis of cytochrome b gene sequences. These are the first records of this species in the Yukon. No Northern Red-backed Voles, M. rutilus, were collected and it is not known whether the two species are sympatric or parapatric in the Yukon. Further survey work is needed in southeastern Yukon to better delineate the extent of the northwestern range of this species and the extent, if any, of introgression with M. rutilus.

First Records of the Northern Long-eared Bat, &lt;em&gt;Myotis septentrionalis&lt;/em&gt;, in the Yukon Territory

Three adult male Northern Long-eared Bats, Myotis septentrionalis, were captured in mist nets in July 2004 in the LaBiche River Valley, southeastern Yukon. These are the first records of M. septentrionalis in the Yukon. Further survey work is needed to delineate the extent of the range and population structure of this and other species of bats in northwestern North America.

First Confirmation of Cougar, &lt;em&gt;Puma concolor&lt;/em&gt;, in the Yukon

Cougar (Puma concolor) have been reported from the Yukon as early as 1944. Despite many sightings, no indisputable, physical evidence of Cougar being present in the Yukon had been obtained. Here, we report on the first. In November 2000, a specimen was secured from near Watson Lake, in southeastern Yukon. Whether this specimen, and the numerous sighting records, are indicative of a low-density breeding population in the Yukon, or represent transients, is unknown.

Mortality of Deer Mice, &lt;em&gt;Peromyscus maniculatus&lt;/em&gt;, in Wire Mesh Live-Traps: A Cautionary Note

Live-capture of animals occasionally results in the death of some individuals. Here, we report upon an unusual occurrence of trap-related mortality observed in Deer Mice (Peromyscus maniculatus) captured in wire mesh live-traps during field sampling in southeastern Yukon. Eight of 85 marked individuals (9.4%) were found with their snouts caught in the wire mesh of our live-traps; four of these individuals were found dead. We suggest a modification to Ugglan live-traps that would likely decrease such incidents.

Long-distance Movement of a Dispersing Deer Mouse, &lt;em&gt;Peromyscus maniculatus&lt;/em&gt;, in the Boreal Forest

We report an apparent long-distance, non-homing movement of 3044 ± 60 m made by a dispersing subadult male Deer Mouse, Peromyscus maniculatus, in southeastern Yukon. Our observation is nearly twice the maximum distance previously recorded for non-homing Deer Mice, and apparently the longest dispersal movement recorded for this species.

Geological mapping and analogue modeling of the Liard, Kotaneelee and Tlogotsho ranges, Northwest Territories

Abstract The Liard, Kotaneelee and Tlogotsho Ranges lie within the southern Franklin Mountains of the southwestern Northwest Territories and southeastern Yukon Territory. Within the study area, the Liard and Kotaneelee Ranges exhibit a major change in trend from south to north. In the south, the ranges trend northwest while in the north they trend north-northeast. Geological field mapping was carried out during the summers of 2001 and 2002 to document the large-scale structures in the study area. The bedrock units exposed at the surface range in age from Late Devonian to Early Cretaceous. The topography of the study area is structurally controlled, with the Paleozoic, more resistant rocks forming the main parts of the ranges, and the Mesozoic, more recessive rocks occupying the valleys. The ranges are dominated by large-scale box anticlines and synclines, with less significant thrust faults. East–west and north–south stratigraphic variations have been documented and may have influenced the geometry of the ranges. Physical analogue modeling was carried out at the Queen's University Experimental Tectonics Laboratory to investigate the relationships between the mechanical stratigraphy and the structure of the study area and to identify potential causes of the dramatic change in trend of the ranges. Three possible controls on the change in trend were tested: (1) a transverse structure (the Beaver River structure); (2) changes in basement (Precambrian) elevation; and (3) stratigraphic facies variations. On the basis of the modeling it is concluded that the change in trend can be attributed to a change in basement elevation with a lesser effect due to facies changes.

New 42 Ma cratonic North American paleomagnetic pole from the Yukon underscores another Cordilleran paleomagnetism-geology conundrum

Eocene posttectonic plutons of the Beaver River alkalic complex in southeastern Yukon intruded Devonian–Mississippian and Triassic sandstones in the Foothills of the Canadian Cordillera. A paleomagnetic collection of 27 sites from three separate plutons produced 326 specimens that were analyzed using alternating field and thermal step demagnetization methods. The A component characteristic remanent magnetization (ChRM) resides in magnetite with normal polarity in the 42.6 ± 0.8 Ma Beaver River pluton, reversed polarity in the 42.1 ± 0.7 Ma Larson Creek East pluton, and both polarities in the 41.3 ± 0.4 Ma Larson Creek West pluton, corresponding with magnetic polarity chrons 20n, 19r, and the boundary between chron 19r and 18n, respectively. The ChRMs of the plutons are indistinguishable (2σ) with a mean for the 42.0 ± 0.5 Ma complex of D = 158.8°, I = –73.1° (N = 21 sites, α95 = 3.0°, k = 116.8). A positive paleomagnetic contact test shows the A component to be primary, and the poorly isolated B component suggests the host rocks for Larson Creek West are Early to Middle Devonian. The paleopole for the Beaver River complex at 79.2°N, 145.8°E (N = 21, dp = 4.8°, dm = 5.4°; Q = 7) is concordant with interpolated 42 Ma reference poles for the North American craton. In contrast, paleopoles from the accreted Intermontane and eastern Coast Belt terranes record clockwise rotations of 24° ± 10° (Eocene) and 13° ± 5° (Oligocene–Pliocene), indicating that the allochthonous Intermontane terranes have been progressively driven ~240 ± 120 km eastwards up and over pericratonic and cratonic North American lower crust by Pacific plate subduction since the mid-Eocene.

Geochemistry and tectonic significance of alkalic mafic magmatism in the Yukon-Tanana terrane, Finlayson Lake region, Yukon

This paper provides an integrated field and geochemical study of weakly alkalic, ~360 Ma mafic rocks from the Yukon–Tanana terrane in the Finlayson Lake region, southeastern Yukon. These mafic rocks occur as dykes and sills that crosscut older felsic metavolcanic rocks and metasedimentary rocks (Kudz Ze Kayah unit) or as flows interlayered with carbonaceous metasedimentary rocks. The mafic rocks have signatures similar to those of ocean-island basalts, moderate TiO2 and P2O5 contents, elevated high field strength element and light rare earth element contents, and εNd350 = +1.1. A subset of the dykes (group 4b) has similar geochemical characteristics but with higher Th/Nb and lower Nb/U ratios, higher Zr and light rare earth element contents, and εNd350 = –2.8. The geochemical and isotopic attributes of these rocks are consistent with formation from either lithospheric or asthenospheric sources during decompression melting of the mantle, with some rocks exhibiting evidence for crustal contamination (group 4b). The alkalic basalts are interpreted to represent ~360 Ma ensialic back-arc rifting and basin generation. It is envisioned that east-dipping subduction, represented by slightly older magmatic suites (Fire Lake unit), was disrupted by subduction hinge roll-back, westward migration of arc magmatism, and the onset of back-arc extension. Decompression melting of the mantle associated with back-arc generation resulted in mantle melting and the formation of the alkalic basalts. The spatial association of this mafic magmatism with crustally derived felsic volcanic rocks and contained volcanogenic massive sulphide mineralization suggests that the associated deposits (Kudz Ze Kayah, GP4F) formed within an ensialic back-arc environment.

Pressure, temperature and fluid conditions during emerald precipitation, southeastern Yukon, Canada: fluid inclusion and stable isotope evidence

The Crown emerald veins are somewhat enigmatic, displaying characteristics that are common to emerald deposits of tectonic–hydrothermal origin and of igneous origin. The veins cut the Fire Lake mafic meta-volcanic rocks, occurring within 600 m of an outcrop of Cretaceous S-type granite. Field work and vein petrography are consistent with a polythermal origin for the veins. The primary vein mineralogy is quartz and tourmaline with variable sized alteration haloes consisting of tourmaline, quartz, muscovite, chlorite and emerald. The veins weather a buff brown colour due to jarosite, scheelite and minor lepidocrocite, which were precipitated during the waning stages of vein formation. Microthermometic studies of primary fluid inclusions within emerald growth zones are consistent with emerald precipitation from H 2O–CO 2–CH 4 (±N 2±H 2S) bearing saline brines. The estimated fluid composition is approximately 0.9391 mol% H 2O, 0.0473 mol% CO 2, 0.0077 mol% CH 4 and 0.0059 mol% NaCl (∼2 wt.% NaCl eq.). Fluid inclusion and stable isotope studies are consistent with vein formation in the temperature range 365–498 °C, with corresponding pressures along fluid inclusion isochore paths ranging from 700 to 2250 bars. These data correlate with a very slow uplift rate for the region of 0.02–0.07 mm/year. Emerald deposits are generally formed when geological conditions bring together Cr (±V) and Be. Cr and V are presumed to have been derived locally from the mafic and ultramafic rocks during hydrothermal alteration. The Be is most likely derived from the nearby Cretaceous granite intrusion.

Map symbology and analysis of box and polyclinal folds, with examples from the Rocky Mountain Foothills of northeastern British Columbia and the Liard Ranges of southeastern Yukon Territory and southwestern Northwest Territories

The hinge surface traces of some types of folds cannot be portrayed adequately on maps using traditional symbology. Specifically, there are no widely accepted symbols suitable for hinge surfaces of (1) box folds (a class of polyclinal folds with two hinges), (2) folds whose limbs both dip in the same direction, or (3) overturned folds whose limbs dip in opposite directions. The latter two cases are not uncommon for hinges within polyclinal or composite folds. An unambiguous symbology is proposed, illustrated using hypothetical examples, and applied to the analysis of kilometre-scale folds mapped in the Rocky Mountain Foothills of northeastern British Columbia and the Franklin Mountain Liard Ranges of southeastern Yukon Territory and southwestern Northwest Territories.