bluuebunny/crossref_metadata_2025 huggingface dataset:
Alberta bolide of June 1, 1982: interpretation of photographic and seismic records
Authors: Cumming G. L.
Published: April 2011

Passage of a bright bolide northeast of Edmonton near midnight on the evening of June 1, 1982, was recorded both photographically by three cameras of the Meteorite Observation and Recovery Project of the National Research Council of Canada and by seismic recording stations at Edmonton and Cold Lake. The photographic data indicate a path towards the northwest at an average height of about 80 km and an average speed of 28 km/s. The Cold Lake data make possible the determination of direction and velocity of approach of the sound wave as well as wave-front curvature in the horizontal plane. The data indicate an essentially zero curvature and a speed across the array of 337.8 m/s for the sound arrival.Wave-front curvature indicates a line source, being the nearly cylindrical shock wave from the hypervelocity bolide. Directions of approach at both Cold Lake and Edmonton, however, seem to indicate a direction more consistent with the end of the brightest segment of the meteor photograph.The discrepancy is not resolved at present, nor is the very slow apparent velocity towards both Cold Lake and Edmonton as derived from the traveltimes to each of the seismic stations.
Petrology and age of volcanic-arc rocks from the continental margin of the Bering Sea: implications for Early Eocene relocation of plate boundaries
Authors: Davis Alicé S. , Pickthorn Leda-Beth G. , Valuer Tracy L. , Marlow Michael S.
Published: April 2011

Eocene volcanic flow and dike rocks from the Beringian margin have arc characteristics, implying a convergent history for this region during the early Tertiary. The extrusive rocks are basalt, basaltic andesite, andesite, and minor dacite and rhyolite. The intrusive sample is from a quartz diorite dike intruding serpentinized peridotite. Major-element oxide contents, particularly FeO*/MgO versus SiO2, identify both tholeiitic and calc-alkalic basalt; more silicic lavas have calc-alkalic affinities. Consistent with volcanic-arc compositions, spidergrams show pronounced Nb–Ta depletion and alkali enrichment relative to light-rare-earth-element (LREE) abundance. Chondrite-normalized REE plots show relatively flat patterns, with only slight LREE enrichment for tholeiitic compositions and greater LREE enrichment and lower heavy-rare-earth-element (HREE) abundance for calc-alkalic compositions. The samples, particularly those with calc-alkalic compositions, are rich in plagioclase that is strongly zoned; the more silicic samples contain orthopyroxene, clinopyroxene, and primary amphibole. The quartz diorite dike contains iron-rich almandine phenocrysts that appear to be magmatic, suggesting emplacement at great depth near the base of the crust or upper mantle.Chemical and mineralogical compositions are similar to those of modern Aleutian-arc lavas. They also resemble volcanic-arc compositions from western mainland Alaska, although greater chemical diversity and a stronger continental influence are observed in the Alaskan mainland rocks.Early Eocene ages of 54.4–50.2 Ma for the Beringian samples are well constrained by conventional K–Ar ages of nine plagioclase separates and by concordant 40Ar/39Ar incremental heating and total-fusion experiments. A concordant U–Pb zircon age of 53 Ma for the quartz-diorite dike is in good agreement with the K–Ar data.Plate motion studies of the North Pacific Ocean indicate more northerly directed subduction prior to the Tertiary and a continuous belt of arc-type volcanism extending from Siberia, along the Beringian margin, into mainland Alaska. Around 56 Ma (chron 25–24), subduction changed to a more westerly direction and subduction-related volcanism ceased for most of mainland Alaska. The increasingly oblique angle of convergence should have ended subduction along the Beringian margin as well. However, consistent ages of 54–50 Ma indicate a final pulse in arc-type magmatism during this period of plate adjustment, which may be explained by three different models: (1) The northern and central part of the Beringian margin maintained a higher angle of convergence, allowing a final pulse of arc-type magmatism. (2) The rocks erupted in an early, or proto, Aleutian arc and were rafted against the continental margin along transform faults. (3) The rocks erupted along a leaky transform fault, analogous to calc-alkalic volcanism in the southern California borderland.
The Queen Charlotte Islands refraction project. Part II. Structural model for transition from Pacific plate to North American plate
Authors: Mackie D. J. , Clowes R. M. , Dehler S. A. , Ellis R. M. , Morel-À-l'Huissier P.
Published: April 2011

The oceanic-continental boundary west of the Queen Charlotte Islands is marked by the active Queen Charlotte Fault Zone. Motion along the fault is predominantly dextral strike slip, but relative plate motion and other studies indicate that a component of convergence between the oceanic Pacific plate and the continental North American plate presently exists. This convergence could be manifest through different types of deformation: oblique subduction, crustal thickening, or lateral distortion of the plates. In 1983, a 330 km offshore–onshore seismic refraction profile extending from the deep ocean across the islands to the mainland of British Columbia was recorded to investigate (i) structure of the fault zone and associated oceanic–continental boundary and (ii) lithospheric structure beneath the islands and Hecate Strait to define the regional transition from Pacific plate to North American plate and thus the nature of the convergence. Two-dimensional ray tracing and synthetic seismogram modelling of many record sections enabled the derivation of a composite velocity structural section along the profile. The structural section also was tested with two-dimensional gravity modelling. Part I of the study addressed the structure of the fault zone; part II addresses lithospheric structure extending eastward to the mainland.The derived velocity structure has some important and well-constrained features: (i) anomalously low crustal velocities (5.3 km/s with a 0.2 km/s per km gradient) underlain by a steep, 19 °eastward-dipping boundary above the mantle in the terrace region west of the main fault; (ii) a thin crust of 21–27 km beneath the Queen Charlotte Islands; and (iii) a gentle 4 °eastward dip of the Moho below Hecate Strait as crustal thickness increases from 27 km to 32 km. The gravity modelling requires that mantle material extend upwards to a depth of about 30 km below the mainland and indicates that an underlying subducted slab, if it exists, extends eastward no farther than the mainland.Unfortunately, the velocity structure delineated by this study could not unambiguously determine the mode of deformation, because the lowermost crustal block beneath Queen Charlotte Islands and Hecate Strait can be interpreted as subducted oceanic crust or middle to lower continental crust. Thus, two different tectonic models for the transition from Pacific plate to North American plate are discussed: in one, oblique subduction is the principal characteristic; in the other, oceanic lithosphere juxtaposed against continental lithosphere across a narrow boundary zone along which only transcurrent motion occurs is the dominant feature. Based on the thin crust beneath the Queen Charlotte Islands, the lack of a wide zone of deformation along the plate boundary region, and other geological and geophysical characteristics, oblique subduction is the more plausible model.
Holocene evolution of the Assiniboine River paleochannels and Portage la Prairie alluvial fan
Authors: Rannie W. F. , Thorleifson L. H. , Teller J. T.
Published: April 2011

The Portage la Prairie alluvial fan was constructed by numerous successive paleochannels of the Assiniboine River along the western side of the Lake Agassiz basin as the level of the lake rapidly declined beginning 9500 years ago. The history of the paleochannels during the first several thousand years is not known. Paleochannel morphologies and cross-cutting relations, soil maturity, and radiocarbon dates, however, indicate that by 6000–7000 years ago flow was northward into Lake Manitoba. This direction was maintained until about 3000 years ago, when avulsion redirected the Assiniboine eastward to the Red River near Winnipeg. The morphologies of the paleochannels suggest that channel-forming discharges and sediment loads of the ancestral rivers have not differed significantly from the modern values despite palynological evidence that the climate was warmer and drier during much of the Holocene.
Determination of the finite-strain ellipsoid from deformed porphyroblastic mineral aggregates and preferentially oriented feldspars in a mylonitized metamafic dyke
Authors: Owen J. Victor
Published: April 2011

Strain in a narrow mylonite zone has been estimated from deformed garnetiferous porphyroblastic aggregates and from preferentially oriented plagioclase porphyroclasts with high aspect ratios. In the undeformed metamafic dyke hosting the mylonite, the mineral aggregates have spheroidal to slightly oblate shapes, and plagioclase is nearly randomly oriented. In the mylonite, the mineral aggregates are prolate ellipsoids, and plagioclase in the aggregates and matrix is symmetrically oriented about the mylonitic planar fabric. Comparison with the radii of spheres of equal volume shows that the ellipsoidal mineral aggregates underwent triaxial strain, with maximum extension of 50–140% parallel to X and with shortening of up to −30 and −45% parallel to Y and Z, respectively. The maximum strain ratio varies between 1.9 and 4.2 (mean of 10 measurements = 3.1). The orientation and aspect ratios of elongate plagioclase grains measured in the X–Z plane indicate an intermediate value (2.7) for the strain ratio. Plagioclase deformation was apparently accommodated by dislocation glide on (010), recovery processes (subgrain rotation), and microcracking. The effects of mechanical anisotropy in plagioclase, however, were subordinate to the strain regime, strain ratio, and initial aspect ratio of grains in determining the final aspect ratio and rest position of these porphyroclasts.Both the deformed garnetiferous aggregates and the plagioclase porphyroclasts record state of strain in the mylonite. This suggests that the preferred orientation of densely packed feldspars of high aspect ratio potentially may be used to estimate strain in tectonites.
Distinguishing buried alluvium from till by using detailed total-magnetic-field data
Authors: Schwarz Erik J.
Published: April 2011

Total-magnetic-field and vertical-magnetic-gradient profiles are characteristically different over alluvial and glacial sediments. Positive magnetic anomalies elongated in the river-valley direction but not in the structural trend of the underlying bedrock indicate the occurrence of magnetite enrichments within the alluvium. No evidence for such anomalies is found in survey data obtained in gravel pits located in tills. The logarithm of the power of the total-field profiles over the river terraces plotted against spatial frequency is structured, which is indicative of the presence of magnetic sources of certain depth and width. However, the power spectra over till may also show similar features if high-frequency bedrock anomalies are present in the data, so these spectra are not a reliable means of distinguishing between buried alluvium and till. The results show that magnetic analysis allows the discrimination between buried tills and alluvium in which magnetite concentrations of considerable lateral extent were formed.
Practical numerical considerations for the Alekseev–Mikhailenko method
Authors: Daley P. F. , Hron F.
Published: April 2011

Programs that utilize the Alekseev–Mikhailenko method are becoming viable seismic interpretation aids because of the availability of a new generation of supercomputers. This method is highly numerically accurate, employing a combination of finite integral transforms and finite difference methods, for the solution of hyperbolic partial differential equations, to yield the total seismic wave field.In this paper two questions of a numerical nature are addressed. For coupled P–Sv wave propagation with radial symmetry, Hankel transforms of order 0 and 1 are required to cast the problem in a form suitable for solution by finite difference methods. The inverse series summations would normally require that the two sets of roots of the transcendental equations be employed, corresponding to the zeroes of the Bessel functions of order 0 and 1. This matter is clarified, and it is shown that both inverse series summations may be performed by considering only one set of roots.The second topic involves providing practical means of determining the lower and upper bounds of a truncated series that suitably approximates the infinite inverse series summation of the finite Hankel transform. It is shown that the number of terms in the truncated series generally decreases with increasing duration of the source pulse and that the truncated series may be further reduced if near-vertical-incidence seismic traces are avoided.
Selachians from the Niobrara Formation of the Upper Cretaceous (Coniacian) of Carrot River, Saskatchewan, Canada
Authors: Case Gerard R. , Tokaryk Tim T. , Baird Donald
Published: April 2011

Acid etching of a shell-bed zone has enabled us to reclaim numerous fish remains for the Niobrara Formation (Coniacian) of east-central Saskatchewan, including teeth of the following new taxa: Odontaspis saskatchewanensis sp.nov., Synodontaspis lilliae sp.nov., and Cretomanta canadensis gen. et sp. nov. These are associated with remains of Ptychodus cf. Ptychodus rugosus Dixon, Cretodus sp., Cretoxyrhina mantelli (Agassiz), Squalicorax falcatus (Agassiz), and Rhinobatos sp. This is the most northern occurrence from Canada of a Niobrara-age selachian fauna.
Dolomitization of the Oligocene–Miocene Bluff Formation on Grand Cayman, British West Indies
Authors: Pleydell Suzanne M. , Jones Brian , Longstaffe F. J. , Baadsgaard H.
Published: April 2011

The Oligocene–Miocene Bluff Formation on Grand Cayman is formed of hard, white, finely crystalline dolostone in which the precursor textures and fossil microstructures are commonly preserved. The dolostones have a high porosity (up to 25%) because of leaching of skeletal material, which was originally aragonite, and dissolution of the bedrock during the various phases of exposure and karst development.A major disconformity divides the Bluff Formation into the Cayman Member (Oligocene) and Pedro Castle Member (Middle Miocene). Cavities in the Cayman Member are commonly filled or partly filled with caymanite, dolomitized skeletal grainstone, terra rossa, and flowstone. Available evidence suggests that the caymanite and skeletal grainstone were emplaced prior to deposition of the Pedro Castle Member in Middle Miocene times, whereas the emplacement of the terra rossa and flowstone postdates dolomitization of the Bluff Formation.Petrographic and geochemical data suggest that there was only one phase of dolomitization that was mediated by normal seawater. There is no signifiant difference among 87Sr/86Sr ratios of the dolostones of the Cayman and the Pedro Castle members. The average 87Sr/86Sr ratio of 0.70905 for these dolostones is significantly lower than the average 87Sr/86Sr ratio of 0.70917 obtained from modern seawater around Grand Cayman. The 87Sr/86Sr ratios for the dolostones of the Bluff Formation, ranging from 0.70900 to 0.70914, suggest the dolomitization occurred 2–5 Ma ago. The underlying cause of the pervasive dolomitization is uncertain. Although it appears that "normal" seawater was responsible for that dolomitization, there is little evidence pointing to why it occurred 2–5 Ma ago.
The Melville Moraine: sea-level change and response of the western margin of the Foxe Ice Dome, Melville Peninsula, Northwest Territories
Authors: Dredge L. A.
Published: April 2011

Marine-limit elevations and radiocarbon dates from Melville Peninsula suggest rapid deglaciation of Committee Bay about 9100 years ago when sea level was 235 m higher than present. During deglaciation, an extensive prominent moraine with both terrestrial and glaciomarine segments developed along the western margin of the Foxe Ice Dome. It developed between 8500 and 6500 years ago as glaciologic response to the opening of the bay. By the time ice had receded from the moraine, sea level had dropped to about 140 m. Garry Bay was not deglaciated until ice lay east of the Melville Moraine. Lithologic evidence and the persistence of ice in this lowland area suggest that the outer part of Garry Bay was the calving terminus of a major ice stream flowing westwards across the peninsula. Four well-controlled emergence curves, based on 37 radiocarbon dates, are presented. The Baker Bay and Brevoort curves depict disjunct emergence patterns in which the disjunction corresponds in time and elevation to the formation of the moraine; the other two cover only the last 7000 years and depict a normal exponential style of emergence. Differences in timing and amount of emergence in the curve from Fury and Hecla Strait are attributed to a late ice flow southwards from Baffin Island. The Melville Moraine is younger than the age initially proposed for the Cockburn moraine system, of which it forms a part. It formed as a glaciodynamic response to a shift from marine-based to terrestrially grounded ice margin, rather than to climatic factors.
Precambrian terrane of north-central Wisconsin: an aeromagnetic perspective
Authors: King Elizabeth R.
Published: April 2011

A shaded relief magnetic map covering most of the region of exposed Precambrian rocks of north-central Wisconsin shows the structural grain and many lithologic units with clarity and comprehensive detail. The area includes part of the volcanic sequence of the Keweenawan Supergroup south of Lake Superior, the southern margin of the Archean Superior Province, the accreted island-arc terranes of the Penokean Orogen, and the Wolf River batholith. Numerous dikes are evident in the shaded relief, some being more than 200 km in length. Many of the longer dikes are reversely magnetized Keweenawan diabase associated with early extension of the Midcontinent Rift; some apparently were intruded along preexisting faults. A northwest system of dikes and faults indicated by the shaded relief map may be related to later stages of Keweenawan rifting. The Wolf River batholith is characterized by low magnetic relief associated with the predominant granitoids but includes circular plutons of highly magnetic anorthosite and a large area of magnetic rock having a signature different from the mapped anorthosite bodies. A fault bounding the western side of the batholith is paralleled by an apparent system of faults or dikes in the older terrane to the west. The magnetic map covering the Wisconsin magmatic terranes and the Archean Superior Province margin to the north is dominated by east-northeast-trending Penokean rocks. Large units of magnetic mafic rocks and less magnetic granitoid rocks are cut by a system of well-defined northeast shear zones and a more easterly trending, possibly younger set of faults, some of which contain dikes along parts of their lengths. Although the sutures bounding the magmatic terranes generally follow the magnetic trends, they do not have distinctive magnetic signatures.
Metamorphism in the Solitude Range, southwestern Rocky Mountains, British Columbia: comparison with adjacent Omineca Belt rocks and tectonometamorphic implications for the Purcell Thrust
Authors: Gal L. P. , Ghent E. D.
Published: April 2011

Rocks of the Solitude Range, British Columbia, have been metamorphosed from chloritoid–chorite-zone to kyanite-zone conditions. The grade of metamorphism increases southwestward toward the Rocky Mountain Trench (RMT) and the Omineca Belt. Isograds crosscut lithologies and trend more northerly than deformation 2 (D2) structures and the RMT. They are thought to have been quenched syn- to post-D2. Pelitic (Mahto Formation) and calc-pelitic (Tsar Creek unit) rocks contain assemblages that reflect the increase in metamorphic grade. Physical conditions of metamorphism are estimated to be approximately 450–540 °C from the garnet to the kyanite zone; pressures averaged 6–7 kbar (1 kbar = 100 MPa). The pressures, temperatures, and metamorphic assemblages are very similar to those of the Adamant Range, which lies across the Purcell Thrust, to the southwest. This is in contrast with the Big Bend area, to the northwest, where differences in pressure across the Purcell Thrust (PT) have been documented. Two possible models to explain these contrasting relationships are presented. One model suggests that there was post-movement heating on the PT, which reduced the metamorphic contrast across the PT. The second model suggests that a combination of thrust and normal faulting, including warping of isobaric surfaces, has produced an apparently unbroken metamorphic sequence across the PT.
Faulting of a Middle Jurassic, ultramafic dyke in the Picton Quarry, Picton, southern Ontario
Authors: McFall G. H.
Published: April 2011

A fault zone coinciding with a Middle Jurassic, ultramafic dyke exposed in the Picton Quarry in Prince Edward County, Ontario, is marked by steeply dipping, generally east–west-striking fractures. The dyke has been affected by faulting, as evidenced by the presence of subhorizontal slickensides on fractures cutting the dyke rock. This discovery constitutes the first known example of Middle Jurassic or younger faulting having affected Paleozoic strata of southern Ontario and indicates that the structural and tectonic history of the region is more complex than commonly believed.
Major-, trace-, and rare-earth-element geochemistry of the Archaean Maggo gneisses, southern Nain Province, Labrador
Authors: Finn Gregory C.
Published: April 2011

The early middle Archaean Maggo gneisses of the southern Nain Province, Labrador, form the southwest portion of the once contiguous North Atlantic (Nutak) Craton (NAC). The gneisses and their late middle Archaean metamorphosed and migmatized equivalents are typical of grey gneiss terranes exposed worldwide. Geochemically the gneisses exhibit a continuous range of composition from 53.7 to 78.4 wt.% SiO2 and straddle the boundary between low- and high-Al trondhjemites. Major-element distributions are comparable to those of other Archaean-aged NAC gneisses (Amîtsoq, Uivak, and Nûk gneisses), however, the Na2O and K2O contents are scattered. The gneisses are depleted in K, Rb, and Ba, are enriched in Sr, and have high-field-strength-element distributions similar to those for NAC gneisses.Rare-earth-element (REE) patterns of Maggo gneisses can be subdivided, on the basis of the nature of the Eu anomaly, into two groups of samples: (i) with negative Eu anomalies and higher Σ REE contents and (ii) with positive to normal Eu anomalies and lower Σ REE contents. The subdivision reflects differentiation processes in the parent magma of the Maggo gneisses. REE patterns are similar to those reported for NAC grey gneiss complexes. On the basis of the (La/Yb)N and (Yb)N values, the Maggo gneisses parent magma is interpreted as being derived by partial-melting processes from preexisting, high-grade (granulite to amphibolite facies) sialic continental crust equivalent to the early Archaean lithologies preserved elsewhere in the NAC.
Deformation of the Archean Quetico–Shebandowan subprovince boundary in the Canadian Shield near Kashabowie, northern Ontario
Authors: Borradaile Graham , Spark Robert
Published: April 2011

The southern boundary of the Quetico metasedimentary subprovince of the Superior Province of the Canadian Shield near Kashabowie, Ontario, is a vertical, east–west feature affected by dextral transpression that had a north-northwest – south-southeast compressional component. A synmetamorphic, locally D1 microfabric and magnetic-susceptibility fabric with an east-directed extension lineation is kinematically compatible with this pattern. It shows the same bedding–cleavage relationship and the same direction of structural facing on D1 in both the Quetico metasediments and the Shebandowan greenstone subprovince on the south side of the Quetico subprovince. In the low-grade rocks of the study area, there is a single phase of penetrative deformation, giving a nearly vertical schistosity at a consistent angle, anticlockwise with respect to the now nearly vertical east–west-striking strata. The absence of penetrative polyphase deformations may be due to the near parallelism of the subprovince boundary with the shear component of dextral transpression. Strain analysis indicates that the minimum shortening of the greywackes is 40% in a north–south direction. It is tentatively suggested that the shortening, the steepening of strata into a vertical position, and some of the S1 fabric development may have occurred prior to the climax of metamorphism and transpression. If this sequence is correct, the strata would have dipped gently to the north prior to the steepening event, with the embryonic schistosity dipping to the west.
Deformation at an Archean subprovince boundary, northern Minnesota
Authors: Tabor John R. , Hudleston Peter J.
Published: April 2011

Structural analysis in the northern margin of the Quetico subprovince (part of the Archean Superior Province of the Canadian Shield) in Minnesota reveals that the main deformation involved polyphase folding (F1 recumbent and nappe-like, and F2 upright, east–west trending, and tight to isoclinal) during regional ductile transpression and amphibolite-facies metamorphism. A younger deformation, developed during the latter stages of regional transpression, resulted in the generation of localized ultraphyllonites along the steeply dipping Rainy Lake – Seine River fault (RLSRF), the major fault separating the Quetico subprovince from the Rainy Lake wrench zone (a wedge-shaped block between the Quetico and Wabigoon subprovinces). The transpression involved north–south shortening and east–west dextral shear. The presence of shear zones in amphibolite-facies wall rock south of the fault and in lower grade ultraphyllonites within the RLSRF suggests that localization of shear occurred by work and (or) reaction softening, possibly enhanced by the influx of fluids during regional cooling. The youngest structures in the wall rock are conjugate brittle faults oriented similarly to the youngest ductile shear structures in the RLSRF, indicating that the zone of transpression widened following the stage of strain localization, possibly due to work hardening during continued regional cooling. Widening of the zone of deformation was accompanied by an increase in the relative intensity of the north–south shortening component of transpression, revealed by chloritized necks of boudinaged quartz ribbons, quartz and calcite microfabrics, and flattening strains. Protracted ductile flow and localized greenschist-facies conditions in the RLSRF, which occurred during widening of the zone of deformation and rotation of the kinematic frame (to produce north–south shortening structures), are best explained by an influx of fluid phases.Mesostructures and quartz microfabrics in late tectonic (but synkinematic) peraluminous leucogranitoid intrusions and host schist 10 km south of the RLSRF record north–south shortening, but not east–west dextral shear, and further support late north–south shortening across the RLSRF.Tectonic settings for the RLSRF include (i) a suture between distinct lithotectonic terranes or (ii) a zone of localization of deformation within the northern margin of the Quetico subprovince following collision between the Quetico and Wabigoon terranes.
Stratigraphic evolution of the Paleozoic Stikine assemblage in the Stikine and Iskut rivers area, northwestern British Columbia
Authors: Brown Derek A. , Logan James M. , Gunning Michael H. , Orchard Michael J. , Bamber Wayne E.
Published: April 2011

The Stikine assemblage, the "basement" of Stikinia, extends 500 km along the western flank of the Intermontane Belt, east of younger Coast Belt plutons. Four different stratigraphic successions are characteristic of Lower to Middle Devonian, Carboniferous and Permian rocks in the Stikine and Iskut rivers area. West of Forrest Kerr Creek are penetratively deformed Lower to Middle Devonian island-arc volcaniclastic rocks, coralline limestone, and felsic tuff. Fringing carbonate buildups in an arc setting are best illustrated in the sequence at Round Lake where Lower Carboniferous mafic-dominated, bimodal submarine volcanic rocks grade upward into two distinctive coarse echinoderm limestone units and medial siliceous siltstone and limestone conglomerate. Conodont colour alteration indices for Lower Carboniferous rocks near Newmont Lake indicate an anomalously low-temperature thermal history. Upper Carboniferous–Permian polymictic volcanic conglomerate and Lower Permian limestone overlie these strata there. The Scud River sequence is distinguished by subgreenschist- to greenschist-grade Carboniferous(?) volcanic and sedimentary rocks overlain by a structurally thickened package (greater than 1000 m) of Lower Permian limestone. Local calcalkaline pyroclastic rocks interfinger with limestone near the top of the Scud River sequence. Basinal, shelf, and shallow-water carbonate facies developed in the Early Permian, giving way to calcalkaline volcanism in Late Permian followed by deposition of deep-water chert and argillite.The tectonic setting during the Devonian and Carboniferous is comparable with modern Pacific volcanic arcs and atolls, but there is no modern analogue for the shelf-carbonate accumulation during the Early Permian which characterizes the Stikine assemblage and permits Cordilleran-scale correlations. Permian fusulinid and coral species have very close affinity to those of the McCloud Limestone of the eastern Klamath Mountains, California. Other geologic events common to both Stikinia and the Eastern Klamath terrane are Devonian limestone breccia deposition, Lower Permian limestone accumulation with McCloud faunal affinity, Carboniferous and Permian calcalkaline volcanism, and Upper Permian tuffaceous limestone. Stratigraphic differences include the absence of quartz detritus in Devonian strata and lack of thick Upper Permian volcanic rocks in the Stikine River area.
Paleomagnetism of dykes from the Groundhog River Block, northern Ontario: implications for the uplift history of the Kapuskasing Structural Zone
Authors: Bates M. P. , Halls H. C.
Published: April 2011

The groundhog River Block (GB) forms the central segment of the Kapuskasing Structural Zone a fault-bounded belt of Proterozoic crustal uplift in the southern Superior Province. Dykes adjacent to the GB carry a magnetization (D = 11°, I = 26°, α95 = 27°, N = 3) that is characteristic of 2.45 Ga Matachewan dykes. However, within the GB, dykes and high-grade gneissic host rocks carry a steep positive magnetization (D = 295°, I = 83°, α95 = 12°, N = 9) that also partially overprints the dykes immediately outside the GB. The boundaries between the contrasting paleomagnetic signatures coincide with boundary faults and changes in paleopressure that define the GB. The steep magnetization in the GB was acquired during uplift and cooling close to the time at about 1.95 Ga when a virtually antiparallel remanence of similar origin was being formed in the Chapleau Block, the southern segment of the Kapuskasing Structural Zone.
Geochemistry of two metavolcanic arc suites from the Central Metasedimentary Belt of the Grenville Province, southeastern Ontario, Canada
Authors: Harnois Luc , Moore John M.
Published: April 2011

Samples of two subalkaline metavolcanic suites, the Tudor formation (ca. 1.28 Ga) and the overlying Kashwakamak formation, have been analysed for major elements and 27 trace elements (including rare-earth elements). The Tudor formation is tholeiitic and contains mainly basaltic flows, whereas the Kashwakamak formation is calc-alkaline and contains mainly andesitic rocks with minor felsic rocks. The succession has been regionally metamorphosed to upper greenschist – lower amphibolite facies. Trace-element abundances and ratios indicate that rocks of the Tudor and Kashwakamak formations are island-arc type. Geochemical modelling using rare-earth elements, Zr, Ti, and Y indicates that the Tudor volcanic rocks are not derived from a single parental magma through simple fractional crystallization. Equilibrium partial melting of a heterogeneous Proterozoic upper mantle can explain the trace-element abundances and ratios of Tudor formation volcanic rocks. The intermediate to felsic rocks of the Kashwakamak formation appear to have been derived from a separate partial melting event. The data are consistent with an origin of the arc either on oceanic crust or on thinned continental crust, and with accretion of the arc to a continental margin between the time of extrusion of Tudor volcanic rocks and that of Kashwakamak volcanic rocks.
A Middle Cambrian trilobite faunule from the Meguma Group of Nova Scotia
Authors: Pratt Brian R. , Waldron John W. F.
Published: April 2011

The Meguma Group of southern Nova Scotia is a thick succession of mostly deep-water siliciclastic sedimentray rocks of uncertain age. Previous fossil finds have been in the Halifax Formation of the upper part of the sequence and have provided Early Ordovician ages. A newly discovered trilobite-bearing bed from the underlying Goldenville Formation yields Middle Cambrian taxa of Acado-Baltic affinity. Specimens belonging to Paradoxides (s.l.), Agraulos, Dorypyge, and Ellipsocephalidae indicate that the Meguma Group is an exotic succession with faunal similarity to the adjacent Avalon Terrane and to Middle Cambrian successions in Europe, the Middle East, and west Africa.
Reidentification of the Chadronian supposed didelphid marsupial Alloeodectes mcgrewi as part of the deciduous dentition of the canid Hesperocyon
Authors: Bryant Harold N.
Published: April 2011

Alloeodectes mcgrewi (Russell) 1984 is based on isolated teeth, from Chadronian (Late Eocene) localities in the Cypress Hills Formation of southwestern Saskatchewan, that were interpreted as the upper molars of a didelphid marsupial. These teeth are dP4,s of the canid Hesperocyon. The similarity between the last deciduous upper premolar of a canid and the upper molars of a peradectine didelphid results from (i) the differences between the deciduous and permanent dentitions in the Carnivora, and (ii) the apomorphic reduction in certain peradectines of features characteristic of the upper molars in didelphid marsupials.
Late Quaternary sedimentation in central Flemish Pass
Authors: Piper David J. W. , Pereira Christopher P. G.
Published: April 2011

Flemish Pass is a basin in 1000 m water depth on the continental slope off the Grand Banks of Newfoundland and has a Quaternary fill principally of turbidites. The late Quaternary history of the pass has been investigated using mid-range side-scan sonargraphs, high-resolution seismic profiles, and cores dated using C-14. The sequence of facies in the cores reveals six lithostratigraphic units deposited in the past 40 ka. At 15–19 ka and ?25–30 ka, sedimentation was dominated by debris-flow and turbidite deposits, together with hemipelagic deposits of similar clay-size mineralogy, derived from the Grand Banks. At other times, ice-rafting and hemipelagic sedimentation, principally of carbonate-rich sediment transported by the Labrador Current, predominated. A late Quaternary regional unconformity on the slope may reflect the effects of ice sheets reaching the shelf break, probably in the Early Wisconsinan. Late Wisconsinan resedimentation was not related to ice-marginal processes and probably resulted from iceberg impacts.
Monitoring temporal change in conductivity in the central Vancouver Island region, an area with past large earthquakes
Authors: Auld D. R. , Dosso S. E. , Oldenburg D. W. , Law L. K.
Published: April 2011

Two major earthquakes, magnitude 7.0 in 1918 and magnitude 7.3 in 1946, have occurred this century in the central region of Vancouver Island, British Columbia, Canada. Levelling data in the region indicate relative uplift of 4 mm/year from 1977 to 1984, followed by subsidence at approximately the same rate over the next 2 years. In response to the observed elevation changes, a program was initiated to investigate if temporal changes in the geoelectrical conductivity might be associated with earthquake occurrence. Beginning in 1986, magnetotelluric (MT) data have been measured annually at a number of sites on central Vancouver Island to monitor the long-term variability of the conductivity of the crust and upper mantle in the region. Robust processing techniques now used in the analysis of MT data enhance the possibility of detecting changes in the conductivity.Past studies involving the monitoring of MT stations have considered temporal change only in terms of the measured responses. However, formulating the inverse problem of constructing conductivity–depth models that vary minimally from year to year allows quantitative investigation of the changes required in the models to accommodate the yearly variations in the data. This provides a method of evaluating the processes and depths involved in observed changes in the data. Our modelling study indicates a small but systematic yearly decrease in conductivity from 1987 to 1990 localized in a conductive zone overlying the subducting Juan de Fuca Plate.
Documentation of earthquake-induced disturbance of lake sediments using subbottom acoustic profiling
Authors: Shilts W. W. , Clague John J.
Published: April 2011

Subbottom acoustic profiling in lakes on the Canadian Shield and in the Canadian Cordillera has revealed disruptions in deltaic and lacustrine sediments that can be attributed to large historical earthquakes. The Timiskaming earthquake of 1935 (Magnitude 6.25) and the Vancouver Island earthquake of 1946 (Magnitude 7.2) triggered extensive slumping and flow of postglacial sediments in lakes located within a few tens of kilometres of the epicentres of these events. There is some evidence in one of the surveyed lakes for in situ mobilization of sediment on relatively gentle slopes, with minimal horizontal displacement; this may be a product of liquefaction induced by coseismic shaking or displacements along faults beneath the basin. In another lake, widespread coseismic slumping resuspended large amounts of fine sediment, which then settled out onto the lake floor to produce a texturally anomalous layer. Features similar to those produced by the 1935 and 1946 earthquakes can also result from a variety of nontectonic processes, for example, the collapse of sediment over buried ice blocks, depositional oversteepening of deltas, groundwater sapping, and variations in pore-water pressures due to lake-level fluctuations. Records of sediment disruption in lakes therefore must be interpreted with caution. In general, many lakes in a region should be surveyed and a variety of different features identified before sediment disruptions are attributed to an earthquake.
Stratigraphic comparison of the Lardeau and Covada groups: implications for revision of stratigraphic relations in the Kootenay Arc
Authors: Smith Moira T. , Gehrels George E.
Published: April 2011

The Lardeau Group is a heterogeneous assemblage of lower Paleozoic, outer continental margin strata present in the Kootenay Arc in southeastern British Columbia. From east to west, structurally lowest to highest, and what has been previously interpreted as stratigraphically lowest to highest, it consists of green and grey phyllite, argillite, limestone, and rare pillow flows (Index Formation); siliceous argillite and phyllite (Triune Formation); grey massive quartzite (Ajax Formation); siliceous argillite and phyllite (Sharon Creek Formation); alkalic(?) pillow basalt, breccia, and tuff (Jowett Formation); and quartzo-feldspathic wacke and phyllite (Broadview Formation).We propose a correlation between the Lardeau Group and the Covada Group and Bradeen Hill assemblage, both in north eastern Washington. The latter contain the same stratigraphic elements, in the same structural order, as those of the Lardeau Group. These include, from east to west, black and grey argillite and slate, chert, chert–quartz sandstone, limestone, and rare tuff, pillow flows, and quartz arenite (Bradeen Hill assemblage); alkalic(?) pillow basalt, breccia, tuff, and limestone (Butcher Mountain Formation); and quartzo-feldspathic wacke and slate (Daisy Formation). However, the sense of facing, and hence the stratigraphie sequence in the Covada Group and Bradeen Hill assemblage, is reversed in relation to the Lardeau Group, with the quartzo-feldspathic wacke unit the oldest and slate and argillite the youngest. Because the degree of preservation (and consequently the evidence for facing and age) of the units in northeastern Washington is superior to that of the Lardeau Group, we suggest that (1) the Lardeau Group may be inverted relative to the sequence as originally defined; (2)the Lardeau Group may range from Late Cambrian (Broadview Formation) to Devonian (Index Formation) in age; and (3)further work is warranted to test this hypothesis. This correlation unites lower Paleozoic stratigraphic units along several hundred kilometres of the ancient continental margin.
Early Silurian paleolatitude for central Newfoundland from paleomagnetism of the Wigwam Formation
Authors: Buchan Kenneth L. , Hodych Joseph P.
Published: April 2011

Redbeds and minor volcanic rocks of the Early Silurian Wigwam Formation of the Botwood Group were sampled in the Exploits Subzone of the Dunnage Zone of central Newfoundland. At 18 sedimentary and 3 volcanic sites thermal demagnetization isolated a shallow northward (or southward) magnetization (D = 356.0°, I = −16.8°; k = 12.9; α95 = 9.2°; n = 21 site means) after correction for the tilt of bedding. A positive fold test demonstrates that this remanence predates regional Siluro–Devonian folding. A primary age for the remanence is indicated by positive conglomerate tests on volcanic clasts, and reversals correlated with sedimentary stratigraphy. Antiparallel remanence directions at sites of opposite polarity indicate that the primary remanence is not partially overprinted by a secondary component. The Exploits Subzone of the Dunnage Zone is interpreted to have been at low paleolatitudes (8.5°S ± 5°) during the Early Silurian. We reached a similar conclusion for the Notre Dame Subzone of the Dunnage Zone in a previous paleomagnetic study of Early Silurian redbeds and volcanic rocks of the King George IV Lake area. The low paleolatitudes obtained for the Wigwam and King George IV Lake rocks do not differ significantly and, hence, provide no evidence for a large ocean between the two subzones in the Early Silurian. However, the azimuthal orientation of the subzones at that time is still uncertain, and an ocean with its axis oriented in a north–south direction would not be detected by the paleomagnetic method.
Evidence for early fluid channelization, Pikwitonei granulite domain, Manitoba, Canada
Authors: Vry Julie K. , Brown Philip E.
Published: April 2011

The results of field mapping and carbon isotope and phase equilibria studies suggest that two different, locally controlled fluid regimes existed during at least the early phases of high-grade metamorphism in the north Cauchon Lake region, Pikwitonei granulite domain, Manitoba, Canada. During the prograde stages of high-grade "anticlockwise" regional metamorphism, rocks already metamorphosed to at least sillimanite grade were thermally metamorphosed at temperatures near 900 °C by the intrusion of a charnockitic magma. It is likely that this magma released an oxidizing, CO2-bearing, probably CO2-rich fluid phase while the region was still at relatively shallow depths. Fluid migration was channelized along the intrusive contact, and local fluid buffering characterized many of the country rocks. The light carbon isotope values of graphites (gr) and CO2 in cordierites (crd) in pelitic lithologies (δ13Cgr = −41.8 to −30.4; δ13Ccrd = −31.8 to −34.9), and the low oxygen fugacities in many samples rule out infiltration of these units by large amounts of an externally derived CO2-rich fluid phase. Texturally early CO2-rich fluid inclusions occur in the cores of garnets in a variety of rock types along the intrusive contact. These fluid inclusions were probably trapped during early garnet growth at high temperatures and relatively low pressures, and appear to have undergone limited or no subsequent reequilibration. They do not appear to provide direct information about the highest regional metamorphic temperature and pressure conditions to have affected the region (750 °C and 7 kbar (1 kbar = 100 MPa)) but may instead retain evidence of the prograde metamorphic path. These studies demonstrate the importance of local controls on the sources, compositions, timing, and transport of metamorphic fluids in the north Cauchon Lake region.
Holocene history of earthflow mass movements in south-central British Columbia: the influence of hydroclimatic changes
Authors: Bovis Michael J. , Jones Penny
Published: April 2011

Large earthflows in south-central British Columbia have exhibited regionally consistent fluctuations in their movement during the Holocene. Over the past 60 years, air photographs show that many earthflows were reactivated during the relatively wet period 1950–1985. Over the past 300 years, a fairly coherent relationship is established between periods of wetter climate, defined by the tree-ring record, and phases of slope movement, defined by the record of compression-wood development in conifers located near earthflow headscarps. On a time scale of several thousand years, stratigraphic evidence shows that many large earthflows in the region underwent significant reactivation of movement in the post-Mazama period, during the relatively wet, cool Neoglacial interval of the Holocene. These lines of evidence indicate that Holocene hydroclimatic changes have exerted an important influence on the regimen of large earthflows. Earthflows present a wealth of paleogeomorphic information, hitherto largely neglected, that allows a reconstruction of the changing rate of mass movement with time.
Implications of rapid sediment accumulation in a small New England salt marsh
Authors: Anderson R. Scott , Borns Jr. H. W. , Smith D. C. , Race C.
Published: April 2011

The sediment accumulation rate within a small Spartina alterniflora marsh in Maine has been determined by measuring the amount of peat accretion on top of human-produced boards protruding from an exposed face of the marsh. Boards are at depths of 50–140 cm, suggesting sediment accumulation rates of 6.2–7.0 mm/year. Based on these data and a review of other relevant studies, aggradation in small marshes such as Shipyard Cove should be able to keep pace marginally with the anticipated sea-level rise due to "greenhouse" warming, given sufficient sediment supply. Local 19th century land clearance and subsequent erosion, activities that are greatly reduced today, probably supplied the bulk of the inorganic marsh sediment.