U–Pb zircon, monazite, and sphene ages for granitic orthogneiss of the Barkerville terrane, east-central British Columbia

1987 ◽  
Vol 24 (6) ◽  
pp. 1261-1266 ◽  
Author(s):  
J. K. Mortensen ◽  
J. R. Montgomery ◽  
J. Fillipone
Keyword(s):  
British Columbia ◽  
Metamorphic Event ◽  
Precise Estimate ◽  
Late Devonian ◽  
Second Phase ◽  
Combined Effects ◽  
East Central ◽  
Late Proterozoic

Granitic orthogneiss forms an important component of the Barkerville terrane of southeastern British Columbia. Rb–Sr whole-rock ages for the orthogneisses are ambiguous and range from Late Proterozoic to mid-Paleozoic, with large associated errors. U–Pb dating of zircon, monazite, and sphene has been employed in an attempt to establish precise crystallization ages for two of the orthogneiss bodies. U–Pb systematics for zircons from both bodies show the combined effects of inheritance of zircon cores and postcrystallization Pb loss. This complexity precludes a precise estimate of the age of emplacement of the granitic protoliths of the gneiss. The data do, however, constrain possible emplacement ages for the bodies to between 335 and 375 Ma (Late Devonian – mid-Mississippian).A U–Pb age of 174 ± 4 Ma for metamorphic sphene from one of the orthogneiss bodies is interpreted as dating the end of the second phase of deformation in the area. Two nearly concordant U–Pb ages of 114 and 117 Ma for monazite from the second body remain problematical. These data suggest either that the monazite grew during a relatively young shearing and (or) metamorphic event that locally affected the Barkerville terrane or that the closure temperatue for the U–Pb system in monazite is lower than had previously been inferred, or both.

Deformation of the western margin of the Omineca Belt near Crooked Lake, east-central British Columbia

1990 ◽  
Vol 27 (3) ◽  
pp. 414-425
Author(s):  
Jeffrey A. Fillipone ◽  
John V. Ross
Keyword(s):  
British Columbia ◽  
North America ◽  
Middle Jurassic ◽  
Phase 1 ◽  
Late Devonian ◽  
East Central ◽  
Western Margin ◽  
Metasedimentary Rocks ◽  
Narrow Zone ◽  
Minimum Age

The western margin of the Omineca Belt near Crooked Lake, British Columbia, consists of metasedimentary rocks (Snowshoe Group) and orthogneisses of the Barkerville terrane, structurally overlain by a mafic volcanic – sedimentary package of rocks belonging to the allochthonous Slide Mountain (Crooked Amphibolite) and Quesnel terranes (Triassic phyllite and Nicola Group). At least two episodes of regional deformational (phases 2 and 3) affected this composite package. Deformation and metamorphism (phase 1) in the Snowshow Group predate the formation of this package and are nowhere evident within the allochthonous terranes.Middle Jurassic metamorphism ranging from chlorite zone through sillimanite zone affected all units. Isograds are folded, together with the junction between the terranes, indicating that the metamorphic assemblages developed prior to folding of this boundary. Granitic orthogneiss (Boss Mountain, Quesnel Lake, and Perseus gneisses), having a minimum age of Late Devonian to Early Pennsylvanian, was intruded into and deformed with the Snowshoe Group during the earliest recognizable phase of deformation in the Barkerville terrane (phase 1). Slide Mountain terrane rocks occupy a narrow zone where large eastward displacement occurred during overthrusting of the Intermontane superterrane upon the western margin of North America in Middle Jurassic time.

scholarly journals Contrasting effects of the onset of spring on reproductive success of Arctic-nesting geese

The Auk ◽  
2019 ◽  
Vol 137 (1) ◽  
Author(s):  
Bart A Nolet ◽  
Kees H T Schreven ◽  
Michiel P Boom ◽  
Thomas K Lameris
Keyword(s):  
Population Dynamics ◽  
Late Onset ◽  
The Other ◽  
Second Phase ◽  
Combined Effects ◽  
Negative Effects ◽  
Early Snowmelt ◽  
The One ◽  
Winter Flocks ◽  
Breeding Propensity

Abstract Breeding output of geese, measured as the proportion of juveniles in autumn or winter flocks, is lower in years with a late onset of spring in some species, but higher in at least one other species. Here we argue that this is because the timing of spring affects different stages of the reproductive cycle differently in different species. Because the effects on 2 different stages are opposite, the combined effects can result in either a positive or a negative overall effect. These stages are the pre-laying, laying, and nesting phase on the one hand; and the hatchling, fledgling, and juvenile phase on the other hand. The first phase is predominantly positively affected by an early snowmelt, with higher breeding propensity, clutch size, and nest success. The second phase in contrast is negatively affected by early snowmelt because of a mismatch with a nutrient food peak, leading to slow gosling growth and reduced survival. We argue that recognition of this chain of events is crucial when one wants to predict goose productivity and eventually goose population dynamics. In a rapidly warming Arctic, the negative effects of a mismatch might become increasingly important.

scholarly journals Seasonal Habitat Use and Movements of Mountain Goats, Oreamnos americanus, in East-central British Columbia

2003 ◽  
Vol 117 (4) ◽  
pp. 565 ◽  
Author(s):  
Kim G. Poole ◽  
Douglas C. Heard
Keyword(s):  
British Columbia ◽  
Adverse Effects ◽  
Home Range ◽  
Habitat Use ◽  
High Elevation ◽  
East Central ◽  
Oreamnos Americanus ◽  
Mountain Goats ◽  
Mineral Licks ◽  
Forest Use

To identify the potential for adverse effects of forest development on Mountain Goats (Oreamnos americanus), we documented the patterns of forest use by goats and the factors influencing goat habitat use. We used a combination of 15 very high frequency (VHF) and six global positioning system (GPS) radiocollars to document the distribution and movements of 21 (15 female, 6 male) goats from 1997 to 1999 in the mountains surrounding the Robson Valley in east-central British Columbia. Because canopy closure reduces the likelihood that a GPS receiver will obtain a location fix, we estimated that GPS collars underrepresented forest use by about 23%. Three goats used separate winter and summer ranges separated by 8–13 km, while most simply exhibited seasonal shifts in elevation. In winter, goats were more often at lower elevations, in commercial forest stands, on southerly aspects, and moved less each hour and over the course of the winter. Goat use declined in areas >500 m from escape terrain and goats were found lower in elevation from evening to dawn compared to daylight hours. Collared goats used high elevation licks, which were either within their home range, or in two cases, 6 and 14 km from their typical home range. We documented use of known mid-elevation mineral licks by three collared goats, but no use of known low elevation (valley bottom and lower slopes) mineral licks. Robson Valley goats appeared to be at relatively low risk from disturbances related to logging, because although forest use was documented during winter, it occurred primarily on high elevation, steep slopes where trees are currently of low commercial value, and goats made little use of low elevation mineral licks. We recommend that in this area a forested buffer of 500 m around cliffs be left to reduce the possibility of adverse effects on goats especially, on southerly aspects above 1300 m.

Temporal dynamics of snags and development of snag habitats in wet spruce–fir stands in east-central British Columbia

2008 ◽  
Vol 255 (10) ◽  
pp. 3613-3620 ◽  
Author(s):  
S. Craig DeLong ◽  
Glenn D. Sutherland ◽  
Lori D. Daniels ◽  
Ben H. Heemskerk ◽  
Ken Olaf Storaunet
Keyword(s):  
British Columbia ◽  
Temporal Dynamics ◽  
East Central

Structural relations at the eastern margin of the Shuswap Complex, near Revelstoke, southeastern British Columbia

1968 ◽  
Vol 5 (4) ◽  
pp. 831-849 ◽  
Author(s):  
John V. Ross
Keyword(s):  
British Columbia ◽  
Granite Gneiss ◽  
Early Paleozoic ◽  
Final Phase ◽  
Late Proterozoic ◽  
Eastern Margin ◽  
Deformational History ◽  
Facies Metamorphism ◽  
Absolute Age ◽  
Paleozoic Rocks

Three major phases of folding affected rocks of Late Proterozoic and Early Paleozoic age and members long assigned to the Shuswap Complex of southeastern British Columbia. The main and first phase of folding produced a large recumbent anticline, having a northerly trend, overturned to the east, that contains an exotic wedge of granite-gneiss within its core. This gneiss was mechanically emplaced into the Late Proterozoic and Early Paleozoic sediments, and already had a metamorphic and deformational history prior to its emplacement. Its age is possible Hudsonian equivalent. Metamorphism during this recumbent phase of folding was greenschist facies.Phase 2 folding was accompanied by amphibolite facies metamorphism, and caused refolding of the earlier composite recumbent anticline into open folds along southeasterly axes.A third and final phase of folding, associated with waning metamorphism, gave rise to folds along southeasterly striking axial-planes that dip steeply to the northeast. Thus, phase three folds caused tightening-up of the previously formed folds.The absolute age of these deformations is not yet known, but the Shuswap Complex, at its eastern margin, is shown to include Paleozoic rocks and some older gneisses, possibly of Hudsonian age.

Temporal development of decaying log habitats in wet spruce–fir stands in east-central British Columbia

2005 ◽  
Vol 35 (12) ◽  
pp. 2841-2850 ◽  
Author(s):  
S Craig DeLong ◽  
Lori D Daniels ◽  
Ben Heemskerk ◽  
Ken Olaf Storaunet
Keyword(s):  
British Columbia ◽  
Picea Glauca ◽  
Model Development ◽  
Wildlife Habitat ◽  
Abies Lasiocarpa ◽  
Time Since Death ◽  
Morphological Attributes ◽  
East Central ◽  
Subalpine Fir ◽  
Advanced Stages

Time since death and time since fall were estimated for hybrid spruce (Picea glauca (Moench) Voss × Picea engelmannii Parry ex Engelm.) and subalpine fir (Abies lasiocarpa (Hook.) Nutt.) logs to quantify temporal changes in log decay and habitat quality in east-central British Columbia. We sampled 136 logs (72 spruce and 64 fir) for species, size, and morphological attributes and used dendroecological techniques to estimate year of death (n = 97) and fall (n =  22). Time since death and time since fall of spruce and fir were similar in decay classes 1 and 2; fir was older than spruce in more advanced stages of decay. Discriminant analysis based on time since fall correctly classified logs into four decay classes for 67% and 80% of spruce and fir, respectively. Function as wildlife habitat changed significantly as logs decayed. Logs served as elevated runways for approximately 15 years and then increased in value as habitat for invertebrates and insectivores as wood softened and vegetation established. Concealed spaces increased as the wood decomposed but decreased when logs collapsed. We conclude that decay classes represent biologically and statistically significant stages of log decomposition that are relevant to wildlife habitat and therefore provide a useful construct for model development and field interpretation..

Early to middle Cretaceous paleogeography of north-central British Columbia: stratigraphy and basin analysis of the Skeena Group

1997 ◽  
Vol 34 (12) ◽  
pp. 1644-1669 ◽  
Author(s):  
Kari N. Bassett ◽  
Karen L. Kleinspehn
Keyword(s):  
British Columbia ◽  
Early Cretaceous ◽  
Tidal Basin ◽  
Second Phase ◽  
Western Basin ◽  
North Central ◽  
Devil’S Claw ◽  
Oblique Convergence ◽  
Basin Margin ◽  
Basin Fill

The Lower–middle Cretaceous Skeena Group records the Early Cretaceous evolution of the southern margin of the Jura-Cretaceous Bowser basin in north-central British Columbia. We formalize Skeena Group nomenclature and present interpretations of three distinct paleogeographic and tectonic phases. During the first phase (Neocomian–Aptian), Skeena deposition was limited to a restricted tidal basin represented by Laventie Formation black-shale deposits, surrounded by coal-swamp deltas of the lower Bulkley Canyon Formation. The lower Skeena Group, correlated to the McEvoy Formation (Bowser Lake Group) in the northern basin, represents final filling of the Bowser foredeep produced by Jurassic accretion of the Intermontane Superterrane to North America. In the second phase (early Albian – Early Cenomanian), marine deposition transgressed eastward and southward accompanied by intrabasinal Rocky Ridge volcanism shedding volcanic detritus into the Kitsuns Creek Member of the Bulkley Canyon Formation. The Rocky Ridge Formation does not correlate northward to other Bowser basin fill but represents intrabasinal volcanism in a transtensional setting along the Omineca continental arc. During the final phase (early–middle Cenomanian), red-bed chert-pebble fluvial deposits of the Rocher Deboule Formation prograded westward, shifting the shoreline to tide-dominated deltas on the far western basin margin. The Rocher Deboule Formation correlates to the Devil's Claw Formation (Bowser Lake Group), the lower member of the Tango Creek Formation (Sustut Group), and, tentatively, to the lower conglomeratic Kasalka Group, all attributed to transpressional Omineca uplift and cannibalization of older Bowser basin fill. Thus the southern basin margin evolved from an Early Cretaceous flexural foredeep to a middle Cretaceous arc setting dominated by oblique convergence, first transtensional then transpressional.

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