bluuebunny/crossref_metadata_2025 huggingface dataset:
The Vancouver Island Seismic Project: a co-CRUST onshore–offshore study of a convergent margin
Authors: Ellis R. M. , Spence G. D. , Clowes R. M. , Waldron D. A. , Jones I. F. , Green A. G. , Forsyth D. A. , Mair J. A. , Berry M. J. , Mereu R. F. , Kanasewich E. R. , Cumming G. L. , Hajnal Z. , Hyndman R. D. , McMechan G. A. , Loncarevic B. D.
Published: April 2011

The seismic structure of the British Columbia continental margin has been investigated using four reversed refraction profiles. The profile across strike extended 350 km from the volcanic arc on the continent to the deep ocean of the Juan de Fuca Plate; the three profiles along strike were located on Vancouver Island, on the continental shelf, and in the deep ocean on the Juan de Fuca Plate. Interpretation of the profile along Vancouver Island yields a well constrained model for the upper crust with velocity increasing from ~5.3 km/s at the surface to ~6.4 km/s at 2 km depth to ~6.75 km/s at 15.5 km depth where the velocity increases sharply to ~7 km/s. The velocity structure of the deep crust and the crustal thickness are poorly constrained. Four possible velocity functions, based on ambiguous first arrivals and (or) secondary phases interpreted as Moho reflections, are presented. The preferred one includes a deep crustal low velocity zone with a crustal thickness of 37 km; models with a constant 7.1 km/s deep crust require thicknesses of 52 km. Preliminary results from the profile across strike show the dip of the basement towards the continent steepens from approximately 1.4° immediately west of the continental rise to ~4° beneath the rise. Sediment velocities increase as the sedimentary layer thickens towards the shelf. The Moho, with velocity near 8 km/s, appears to dip at similar angles in this region; the dip is ~6° from the edge of the shelf to the central portion of Vancouver Island; here there is an abrupt thickening of the continental crust by about 10 km with a flat-lying Moho to the east. This suggests a contact between subducting oceanic Moho and continental Moho. A small positive velocity gradient is required in the mantle.Two short reflection lines, one using explosives and the other a large air gun fired in an inlet, were recorded on a land-based multichannel reflection system. These were run to test the feasibility of obtaining coherent reflections to upper mantle depths in this complex geological environment, and of acquiring deep reflection data in coastal areas with an air-gun source. The preliminary explosion section showed reflections near 4.4 and 6.8 s. The depths of these reflections correspond closely to the 15.5 km crustal refractor and the top of the subducting oceanic lithosphere, respectively. Dip on the deeper reflector is close to that estimated from the refraction profile. Without stacking or velocity filtering, the air-gun recordings on a line adjacent to the explosion profile show arrivals of energy at similar times.
Palynology and paleoecology of postglacial sediments in an anoxic basin, Saanich Inlet, British Columbia
Authors: Heusser Linda E.
Published: April 2011

Varved, black clayey silts deposited in the marine waters of Saanich Inlet yield unusually abundant and diverse pollen assemblages derived from the coastal Douglas-fir (Pseudotsuga) and western hemlock (Tsuga heterophylla) forests of southwestern British Columbia. The 12 000 year palynological record chronicles the development of vegetation since ice left Saanich Inlet: the succession of pine (Pinus contorta) and alder (Alnus rubra) woodlands by forests characterized by Douglas-fir and oak (Quercus) and later by western hemlock and red cedar (Thuja plicata). Rapid deposition of annual layers of pollen, charcoal, and other terrigenous particles provides detailed evidence of changes in land use during the past few hundred years: settlement, logging, farming, and urbanization. Vegetational and climatic changes inferred from pollen spectra in the marine sediments of Saanich Inlet compare favorably with changes inferred from correlative pollen assemblages previously described from adjacent parts of Vancouver Island and the Fraser River valley.
UHF radar system for airborne surveys of ice thickness
Authors: Narod B. Barry , Clarke Garry K. C.
Published: April 2011

We describe an 840 MHz pulsed radar system developed for airborne sounding of polar glaciers and ice caps. The system performance (ratio of transmitter power to minimum detectable signal) is 126 dB. A sampling time base converts the received signal to audio frequencies, and data are recorded in analogue form on magnetic tape. Computer-enhanced time sections for a glacier and an ice shelf are presented as examples.
Pleistocene ice and sand wedges, Hooper Island, Northwest Territories
Authors: Mackay J. Ross , Matthews Jr. J. V.
Published: April 2011

Buried ice and sand wedges have been found in glacially deformed sediments that can be no younger than the early Wisconsinan. The environmental conditions at the time of ice-wedge cracking have been inferred from the number of elementary ice veinlets, the vertical extent of the wedges, collapse structures, oxygen isotope ratios, and macrofossils of plants and insects. The winter ground and summer climates were probably as warm or warmer than the present. The preservation of the ice in the ice wedges shows that permafrost has been present at Hooper Island since at least the early Wisconsinan.
Lacustrine stromatolites and algal laminites in a Pennsylvanian coal-bearing succession near Sydney, Nova Scotia, Canada
Authors: Masson A. Guy , Rust Brian R.
Published: April 2011

Stromatolitic limestone units in the Pennsylvanian Morien Group near Sydney, Nova Scotia occur within mudstones in repetitive fining-upward, coal-bearing sequences, interpreted as meandering fluvial cyclothems. The fluvial association, presence of a non-marine fauna, and the lack of marine fossils indicate a lacustrine environment for the algal units. Horizontally laminated and domal forms are present, the latter encrusted on oncoids, which are attributed to moderate wave agitation. The stromatolites occupy a position analogous to the marine bands in paralic coal sequences and represent repetitive lacustrine development within the fluvial cyclothems of the Sydney Basin.
Loess in the Cypress Hills, Alberta, Canada
Authors: Catto N. R.
Published: April 2011

Loess deposits in the Cypress Hills were derived from a single, local source located adjacent to the southwestern margin of the plateau. The distributions of sand, clay, and heavy minerals, the changes in thickness of the deposits, and the orientation of the clasts all indicate that the direction of transport was from southwest to northeast. The changes in the textural composition of the loess are reflected in variations in the sorting, with the best sorted material being located in intermediate positions. The loess is depleted in feldspar relative to the source sediments. This depletion is due to the combined effects of weathering of the feldspar to hydrous mica clays and aeolian sorting. The platy clay mineral grains would be less likely to be incorporated into the aeolian load than the spherical and bladed angular quartz grains, and the partially weathered feldspar grains would be similarly preferentially winnowed. The variations noted indicate that loess deposits formed from a single local source will not have uniform textural characteristics, but will vary in texture, sorting, and mineralogy. Similar variations would be expected in continent-wide loess sheets, although the effects of each local source would be masked by the long-distance transport component of the sediment.
Foraminifera of the lower part of the Sully Formation (upper Albian), northeastern British Columbia
Authors: Stelck C. R. , Hedinger A. S.
Published: April 2011

An extensive microfauna of over 25 genera and 40 species of arenaceous foraminifera occurs in the lower Sully Formation on the Sikanni Chief River and consists of Bathysiphon spp., Hyperammina sp., Saccammina spp., Lituotuba? sp., Glomospira sp., Ammodiscus sp., Reophax spp., Haplophragmoides spp., Bigenerina sp., Ammobaculites spp., Ammotium sp., Haplophragmium spp., Trochammina spp., Ammobaculoides sp., Textulariopsis spp., Gaudryina sp., Orientalia sp., Eggerella sp., Gravellina sp., Verneuilinoides sp., Uvigerinammina sp., Pseudobolivina sp., Dorothia sp., Miliammina spp., and Psamminopelta sp.The suite occurs below the fish-scale marker bed of the Cretaceous Colorado Shale within the uppermost Albian portion of the Neogastroplites Zone. The assemblage defines the Haplophragmium swareni Subzone of the Miliammina manitobensis Zone of the Colorado Group. It is correlative with the middle Mowry Shale fauna of Wyoming.The suite is deep neritic (200 m) with some suggestion of salinity lessened slightly below normal marine. It is accompanied by an extensive microflora of pollen, spores, and dinoflagellates. The suite represents biofacies intermediate between those previously found at similar stratigraphic horizons within the Cruiser Shale of the Moberly Lake area of British Columbia (a shallower fauna) and within the type Shaftesbury Formation of Peace River, Alberta (deeper, or farther offshore).
Homomorphic deconvolution of potential field data in one and two dimensions
Authors: Jensen Oliver G. , Papazis Pandelis P.
Published: April 2011

A signal in a non-dispersive reverberent environment can generally be represented as the sum of overlapping delayed replicas of a basic wave form. This convolutional data model has long been employed in seismic analysis and can be usefully extended for the analysis of gravity and magnetic potential field data along with a host of other geophysical measurements. The deconvolution of gravity or magnetic data requires the separation of two basic components of the potential fields: one component represents a basic irreducible wave form or signature of the potential field, and the other represents the position and scale or distribution of this wave form throughout the area of measurement. The basic wave form often derives from the process of geophysical measurement (e.g., the upward-continuation operator) but may also be due to an inherent, common character of the geological structure of an area.Oppenheim obtained the formalism for a generalized theory of superposition that allows for a description of the deconvolution process in terms of non-linear homomorphic transformations. These methods have already found application in the geophysical analysis of seismic data; it now provides a useful tool for the deconvolution of geophysical potential field data.
Rb–Sr and U–Pb dating of bentonites
Authors: Baadsgaard H. , Lerbekmo J. F.
Published: April 2011

A 6 in. (15 cm) bentonite in the Z coal (Cretaceous–Tertiary boundary) in eastern Montana was sampled at four different places, and biotite, sanidine, and zircon were separated from the clay. U–Pb analyses of purified zircons yielded small systematic variations from concordant U–Pb dates. Plotting the data on a concordia diagram, a short linear discordia line intersects the concordia at [Formula: see text] with an MSWD of 1.16. The systematic variation of the four sets of zircon U–Pb data on the concordia plot may be an artifact of the sampling and purification procedure, or could result from natural sample variation from minor contamination. Biotite fractions of varying specific gravity were obtained for each of the four Z coal bentonite samples and (together with the matching purified sanidine fraction) were analysed for Rb–Sr dating. Excluding those lighter biotite fractions found to have lost 30% or more of their original Rb, an isochron was obtained giving an age of 63.7 ± 0.3 Ma with an initial 87Sr/86Sr ratio of 0.7061 ± 1 and an MSWD of 1.07.To investigate further the Rb–Sr variations in altered bentonite biotite, a large biotite sample from the Ordovician Kinnekulle A1 bentonite of southwestern Sweden was separated into 11 fractions of decreasing specific gravity. Rb–Sr analysis of these fractions also showed a departure from a linear isochron when more than about 30% of the original Rb had been lost. Chemical analysis and X-ray diffraction revealed the biotite-alteration process to be vermiculitization, but gave no definite reason why biotites that retain more than 70% of their original Rb give usable Rb–Sr data. Though some of the alteration may have taken place when the bentonite was deposited as an ash, most of the alteration probably occurred in recent times. The Kinnekulle A1 bentonite Rb–Sr isochron for biotite and sanidine gives an age of 447 ± 1 Ma with an initial 87Sr/86Sr ratio of 0.7094 ± 0.0003 and an MSWD of 3.7.
Uranium–lead dates from the Central Gneiss Complex and Ecstall pluton, Prince Rupert map area, British Columbia
Authors: Woodsworth G. J. , Loveridge W. D. , Parrish R. R. , Sullivan R. W.
Published: April 2011

Uranium–lead dates for nine zircon fractions from six rock samples of Central Gneiss complex (CGC) are concordant between 65 and 85 Ma. Two fractions from a sample near the eastern edge of the CGC give discordant U–Pb dates between 108 and 171 Ma, but analytical uncertainties and geological complexities prohibit meaningful interpretation. Two fractions from two samples from the Ecstall pluton give concordant U–Pb dates of about 98 ± 4 Ma and date the emplacement of the Ecstall pluton. The concordant CGC dates indicate Late Cretaceous to early Tertiary peak metamorphism (granulite and amphibolite facies) of the CGC east of Work Channel lineament. This contrasts with a slightly older (mid-Cretaceous) peak metamorphism west of Work Channel lineament inferred from the synmetamorphic nature of the Ecstall pluton.
An enigmatic fossil of sponge affinities from Middle Ordovician rocks of western Newfoundland
Authors: Paquette Jeanne , Stearn Colin W. , Klappa Colin F.
Published: April 2011

A loaf-shaped, spongelike organism is described as Lapidipanis terranovae n. gen. n. sp. from the Table Point Formation. The organism is composed of poorly defined radial and concentric skeletal elements that are formed by spherules from 0.2 to 0.6 mm across. The spherules consist of radially arranged, wedge-shaped crystals of calcite that may appear to be isolated in a calcite mosaic or in contact with their neighbours. The organism is compared with the modern sclerosponge Astrosclera. If chaetetids and stromatoporoids are excluded from the class Sclerospongiae, Lapidipanis may be the oldest member of this class so far described.
Early Cambrian problematic fossils near June Lake, Mackenzie Mountains, N.W.T.
Authors: Hofmann H. J.
Published: April 2011

Compressed cylindrical remains of probable trace fossil affinities are described under the taxon Palaeophycus ferrovittatus n. sp. The structures are preserved as ornamented, reddish brown, rectilinear to curvilinear ribbons of iron oxide several centimetres long, several millimetres wide, less than 1 mm thick, and surrounded by an argillaceous envelope. They occur along bedding planes in greyish olive weathering mudstone interbedded with glauconitic quartz sandstone in the Backbone Ranges Formation straddling the Precambrian–Cambrian boundary. They are associated with other fossils similarly preserved by iron oxides, including cf. "Helminthoidichnites? meeki" Walcott and Planolites montanus Richter.
The Emerson Phase of Lake Agassiz, independently registered in northwestern Minnesota and northwestern Ontario
Authors: Björck Svante , Keister Claire M.
Published: April 2011

Two stratigraphically different sites have been analyzed in different ways, but the results may be interpreted as reflecting a common event: the transgressive Emerson Phase of Lake Agassiz. The southern site at Swift, Minnesota exposes a beach ridge underlain by lakeshore deposits and peat that have been 14C-dated from 10 050 to 9350 years BP. At the other site, a small pond 32 km southeast of Sioux Lookout in northwestern Ontario, lithologic, diatom, and pollen analyses and a radiocarbon age of 9740 years reveal the history of the pond and its basin in relation to Lake Agassiz. Despite more than 300 km of separation it seems probable that the two sites were influenced by the same transgression of Lake Agassiz. The effect and duration differ, however, perhaps because of isostatic adjustments within the Lake Agassiz basin.
A study of uranium-rich reduction spheroids in sandstones from Pugwash Harbour, Nova Scotia
Authors: Dyck W. , McCorkell R. H.
Published: April 2011

The concentration and distribution of U, its decay products, and other trace elements in reduction centres in sandstones of Late Pennsylvanian – Stephanian age from Pugwash Harbour, Nova Scotia were determined by chemical analyses and autoradiography.Bulk analyses showed U enrichment up to 150 times in reduction centres relative to oxidized host rock. In the host rock U and 226Ra were in radioactive equilibrium; in the reduction centres there was up to seven times as much U as 226Ra activity. Cu, Ni, As, and Hg were also more concentrated in the centres than in the host rock. Carbon was only slightly or not at all elevated and Fe was considerably depleted in the centres.Autoradiograph patterns from gamma rays, alpha particles, and fission tracks from the centres were found to be identical to each other, and the highest track densities coincided with the dark areas of the centres. In detail they revealed fine complex zoning. In dark bands U was concentrated in submicron grains from which fission tracks, too numerous to be counted, radiated. Alpha tracks from these areas gave calculated U concentrations of up to 13 000 ppm.The element disproportionation between host and centre and the disequilibrium between parent U and daughter 226Ra in the centres suggest microredox systems still active today.Chemical and microprobe analyses indicate oxides and sulfides of trace and minor elements to be responsible for the dark colouration of these centres.
Geochronology and tectonic implications of magmatism and metamorphism, southern Kootenay Arc and neighbouring regions, southeastern British Columbia. Part I: Jurassic to mid-Cretaceous
Authors: Archibald D. A. , Glover J. K. , Price R. A. , Farrar E. , Carmichael D. M.
Published: April 2011

K–Ar dates and U–Pb zircon dates define three periods of igneous activity in the southern Kootenay Arc: (1) emplacement of late-synkinematic to post-kinematic granodioritic plutons in mid-Jurassic time (170–165 Ma) accompanying amphibolite-facies regional metamorphism; (2) emplacement of post-kinematic granitic plutons in mid-Cretaceous time (~100 Ma); and (3) emplacement of small bodies of syenite in Eocene time (~50 Ma) in the western part of the area. Micas from mid-Jurassic plutons that yield the oldest K–Ar dates (158–166 Ma) also yield plateau-shaped 40Ar/39Ar age spectra. Age spectra for biotites younger than these but older than 125 Ma reflect thermal overprinting.In southeastern British Columbia, the Kootenay Arc marks the transition from the North American rocks of the Cordilleran miogeocline to the tectonic collage of allochthonous terranes that have been accreted to it.Deformation, metamorphism, and plutonism recorded in rocks of the southern Kootenay Arc commenced in mid-Jurassic time as a composite allochthonous terrane was accreted to and overlapped the western margin of North America. The geochronology and metamorphic geothermobarometry show that in less than 10 Ma between 166 and 156 Ma: (1) rocks as young as the late Proterozoic Windermere Supergroup and the early Paleozoic Lardeau Group were carried rapidly to depths of 20–24 km while being deformed and intruded by granitic rocks of a hornblende–biotite suite that were also being emplaced at a much shallower level in the overriding allochthonous terrane; and (2) the miogeoclinal rocks of the Windermere Supergroup in the southern Kootenay Arc were then uplifted by more than 7 km at an estimated rate of 2 mm/year, and thrust over the allochthonous terrane prior to being intruded by post-kinematic granitic rocks, many of which belong to the two-mica suite of mid-Cretaceous age..
Ordovician intracratonic sediments from the Lac-St-Jean and Chicoutimi areas, Quebec, eastern Canada
Authors: Harland T. L. , Pickerill R. K. , Fillion D.
Published: April 2011

The transgressive sequence of the Ordovician intracratonic basin of the present-day Lac-St-Jean and Chicoutimi areas is characterized by a variety of sediments that were deposited in a number of environments. Marginal and nearshore sediments of the basin were a complicated system of clastics derived from the adjacent rugged coastal hinterland and intertidal and shallow subtidal carbonates with variably admixed clastics. Farther from shore, in sheltered bays or lagoons partly enclosed by offshore shoals and bars of skeletal lime sands, fine-grained carbonates with coral–algal–bryozoan thickets accumulated. These sediments exhibit numerous submarine hardgrounds or firm grounds. Variations in sedimentation rate and the development of periodically exposed banks of sediment also resulted in the formation of subaerial microkarstic surfaces. The offshore skeletal shoals and bars, which were composed mainly of pelmatozoan debris but included patches of incipient reef growth, provided an incomplete barrier to circulation. Deeper water offshore subtidal sediments consisted of mixed carbonate and argillaceous muds.Sudden increased rates of transgression, probably related to isostatic movements, resulted in the drowning of these coastal environments and the deposition of dark-coloured argillaceous shales in deeper water. These shales are partly of latest Utica and mainly Lorraine in age and it is likely that the initial submergence of this part of the Canadian Shield was much later than that in the St. Lawrence Lowland, probably occurring in Cobourg time.
Observations on the operculum of Oriostoma (Silurian Gastropoda)
Authors: Rohr David M. , Boucot A. J.
Published: April 2011

Opercula of Paleozoic gastropods are rarely found together in great numbers and may occur separated from their shells, making their identification with a particular species or genus uncertain. An unusually large collection of 27 opercula from one locality in the Lower Silurian (Llandoverian) of Quebec permits documentation of their variation and ontogeny. Comparisons of these opercula with previously reported specimens from Gotland indicate that the operculum of Oriostoma can be distinguished by its unique sculpture. The exterior surface of Oriostoma has counterclockwise multispiral coiling, whereas the interior has an opposing counterclockwise paucispiral coiling.
Microfossils from the Early Proterozoic Hornby Bay Group, District of Mackenzie, Northwest Territories, Canada
Authors: Horodyski Robert J. , Dudek Kathleen B. , Ross Gerald M. , Donaldson J. Allan
Published: April 2011

Spheroidal and filamentous organic-walled microfossils have been detected in ca. 1.7 Ga old cherts of the Hornby Bay Group, Northwest Territories, Canada. The majority of the spheroidal forms range from 1 to 4 μm in diameter, are referable to the genus Sphaerophycus, and probably represent the preserved sheaths of chroococcacean cyanophytes. A single, robust-walled, 27 μm diameter, spheroidal microfossil of undetermined affinity is also present. The filamentous forms are tubular, unbranched, and range from 1 to 8 μm in diameter. They appear to represent the preserved sheaths of nostocalean cyanophytes or filamentous bacteria. The filaments illustrate the relationship between matrix mineralogy and the fidelity of preservation of organic-walled microfossils. Where they occur in silica the filaments are preserved as three-dimensional tubular micro-structures, which are readily recognized as microfossils. In contrast, where they extend from silica into adjacent dolomite they are highly compressed and not readily discernable as microfossils. This compression appears to have been caused by aggrading neomorphism and pressure dissolution of the carbonate minerals, and it illustrates the contribution of diagenesis, in addition to decomposition of organic material, in causing the paucity of microfossils in Precambrian carbonate rocks.
An improved estimate of lithospheric thickness based on a reinterpretation of tilt data from Pleistocene Lake Algonquin
Authors: Wolf Detlef
Published: April 2011

A reinterpretation of relative-uplift data associated with the deformed strandline of Pleistocene Lake Algonquin is presented. The new analysis is based on a dynamic model that allows for the finite rate of retreat of the Laurentide ice sheet and the viscous relaxation of the Earth's mantle. Attention is also paid to the effects of the shape of the load profile on the interpretation. In the context of this model the thickness of the lithosphere is constrained to be not more than 85 km. This value is based on the assumption of a model ice sheet with a parabolic cross section. If the load has a sharper edge, a thickness of 110 km is consistent with the data. These revised values slightly exceed Walcott's original estimate. They are, on the other hand, distinctly lower than the value of 200 km, which has recently been inferred by Peltier for the thickness of the North American lithosphere. The relations between the different estimates are briefly discussed. It is suggested that a reconciliation of the estimates may require that effects caused by geoidal perturbations be included in future analyses of strandline tilt.
Holocene tephrostratigraphy and glacial fluctuations in Waterton Lakes and Glacier national parks, Alberta and Montana
Authors: Osborn Gerald
Published: April 2011

Waterton Lakes National Park in Alberta and Glacier National Park in Montana lie along adjacent sections of the continental divide in the Rocky Mountains. In cirques or near divides there is evidence for two ages of glacial deposits. Younger deposits are generally well preserved, poorly vegetated, and bear no tephra and no or very small lichens. Older deposits are more poorly preserved, better vegetated, bear Rhizocarpon sp. lichens at least up to 92 mm in diameter, and bear tephra. The tephra often occurs in two different coloured horizons, but both are compositionally equivalent to Mazama tephra.The older advance has a minimum age of about 6800 14C years BP and a probable maximum age of about 12 000 14C years BP. It is correlated with the pre-Mazama Crowfoot Advance of the Canadian Rockies. Deposits of the younger advance are probably not too much older than mid-19th century, because some glaciers began retreating from the deposits about then. The younger advance is correlated to the Cavell Advance of the Canadian Rockies and the Gannett Peak Advance of the American Rockies.Both advances were minor. The older advance left moraines about 1.5 km or less beyond present glacier margins and depressed ELA's an average of 40 m below modern values.
Proterozoic basalt dikes in the Nain anorthosite complex, Labrador
Authors: Wiebe R. A.
Published: April 2011

Two sets of Proterozoic (between 1290 and 1042 Ma) alkali to transitional basaltic dikes occur sparsely in an area of at least 5000 km2 within the Nain anorthosite complex. Both are compositionally similar in terms of major elements, but the set that trends roughly north–south (HP dikes) contains much higher concentrations of incompatible elements than the more abundant dikes that trend roughly east-northeast–west-southwest (LP dikes). Both types have low normative clinopyroxene relative to olivine—a characteristic shared with widespread troctolitic rocks in the Nain complex. Low Mg numbers and low Ni contents suggest that the magmas producing these dikes have undergone extensive fractional crystallization. The low normative Di content of these dikes suggests that this fractional crystallization occurred at depths equivalent to at least 10 kbar (1000 MPa).High equilibration temperatures for coexisting Fe–Ti oxides in the matrices of these dikes indicate that the dikes cooled rapidly and were emplaced near the surface. The exposed level of the Nain anorthosite complex (emplaced at depths of 8–10 km) indicates that the anorthosites were uplifted and eroded relatively soon after their emplacement, i.e., prior to dike emplacement.
Age of magnetization of the Axelgold Gabbro, north-central British Columbia
Authors: Armstrong Richard Lee , Monger J. W. H. , Irving E.
Published: April 2011

K–Ar and Rb–Sr dates ranging from 101 ± 2 to 158 ± 6 Ma are reviewed to arrive at an absolute minimum age of 115–119 Ma and probable age of 125 ± 5 Ma for the Axelgold Gabbro, consistent with geologic evidence. The magnetization, with blocking temperature of 500–600 °C, was almost certainly acquired between these limits. The result provides an important constraint on the determination of the paleolatitudinal displacement of the Axelgold Gabbro with respect to the craton and supports the earlier contention of Monger and Irving that post-mid-Cretaceous displacement from the south was in excess of 1000 km.
East-directed imbrication and oblique-slip faulting in the Humber Arm Allochthon of western Newfoundland: structural and tectonic significance
Authors: Bosworth William
Published: April 2011

Many of the dominant outcrop-scale structural features in the lower, clastic thrust sheets of the Humber Arm Allochthon were not generated during the westerly emplacement of the allochthonous terranes of western Newfoundland. Two general groups of structures are abundant in the Humber Arm rocks: (1) east-verging folds accompanied by a weakly to moderately developed slaty cleavage and cut by west-dipping thrust faults; and (2) northeast–southwest-striking high-angle faults, with predominantly normal oblique-slip motion and with larger faults down-stepping to the northwest. Evidence of the earlier, west-directed thrusting (refolded and downward-facing folds, folded thrusts, etc.) is uncommon in the Humber Arm area. Slaty cleavage-generation structures, however, appear to overprint the phacoidal fabrics of the mélange zones that exist between and within thrust slices of the allochthon, making the mélange fabrics the most readily identified features associated with the initial east over west imbrication and emplacement of the allochthon.These observations suggest that the original detachment of the rocks of the Humber Arm Supergroup from their basement (early Taconian deformation) occurred with only limited internal deformation. Mélange zones presently define some or all of the early surfaces of movement. The fully assembled and emplaced allochthonous terrane was subsequently reimbricated on a smaller scale through east-directed thrusting, at which time the allochthon was more pervasively deformed (regional slaty cleavage and fold formation). This may represent late Taconian back thrusting or Acadian shortening. The youngest deformation of the Humber Arm region appears to have been a regional extensional event, with a significant northeast–southwest strike-slip component of movement. This may correlate with the development of Carboniferous strike-slip basins in the present Gulf of St. Lawrence and western Newfoundland. Much of the present structural geometry in the Humber Arm region, including the contacts between ophiolitic and clastic thrust sheets, may have originated during these later two deformational sequences, rather than as a consequence of the initial emplacement history.
Upper crustal structure of southern Queen Charlotte Basin from sonobuoy refraction studies
Authors: Clowes Ron M. , Gens-Lenartowicz Ewa
Published: April 2011

The Queen Charlotte Basin, which lies on the west coast of Canada, was the location of a petroleum exploration program in the 1960's. Recently published tectonic models indicate that estimates of hydrocarbon potential require re-evaluation, and a renewed exploration interest has been expressed. In 1981, a seismic refraction survey of the upper crust using radio-telemetering sonobuoys and a 27 L air-gun source was carried out. A particular objective of the study was to determine the existence and depth extent of any sedimentary layer, hypothesized on the basis of other studies, beneath or within the Tertiary Masset volcanics in which some of the exploration wells had terminated. Three reversed profiles and one unreversed profile up to 40 km long were recorded. Interpretation of the data made use of the travel-time and amplitude information of the seismic sections by comparison with theoretical sections computed by two-dimensional ray tracing and a new asymptotic ray theory synthetic seismogram algorithm.Consistent with the earlier industry results, sediment thicknesses vary considerably throughout the southern Queen Charlotte Basin. The Tertiary Masset volcanics appear to be pervasive throughout the study area, with thicknesses varying from less than 1 km to greater than 3 km. On three of the four profiles a low-velocity layer, interpreted as Mesozoic sediments or sediments interbedded with volcanics, was found to lie beneath the volcanics. Thicknesses ranged from about 1 km to zero at a pinchout. The lowermost layer of all models is considered to be crustal rocks and is identified with the top of Wrangellia, an allochthonous terrane proposed to underlie the southern Queen Charlotte Basin. Along the profile for which no low-velocity layer sediments were interpreted, the Wrangellia terrane forms a dome rising to within 2 km of the surface. Other recent studies suggest that hydrocarbon sources could be associated with the Mesozoic rocks of Wrangellia and with any sediments underlying the Tertiary lavas, as well as with Tertiary marine sediments above the volcanics. Thus further exploration is warranted.
An Eocene Rb–Sr isochron for rhyolite plugs, Skukum area, Yukon Territory
Authors: Pride Monica J. , Clark George S.
Published: April 2011

A new Rb–Sr whole-rock isochron for the Skukum rhyolite is 53.3 ± 1.1 Ma with an initial ratio of 0.7053. The rhyolite forms small plugs spatially and probably genetically related to the Skukum volcanic complex in the southwestern Yukon. They were intruded into granitic rocks of the Coast Plutonic Belt. The intrusions are coeval and part of an Eocene plutonic, subvolcanic, and volcanic suite correlated with the Bennett Lake cauldron complex. The initial 87Sr/86Sr ratio matches interpretations of the tectonic evolution of Yukon Crystalline Terrane and Coast Plutonic Complex.
Olivine fabrics in the Bay of Islands Ophiolite: implications for oceanic mantle structure and anisotropy
Authors: Salisbury Matthew H. , Christensen Nikolas I.
Published: April 2011

Petrofabric analysis of oriented ultramafic and mafic rock samples from six traverses representing all four massifs of the Bay of Islands ophiolite complex, Newfoundland, indicate that the ultramafic rocks are tectonites displaying fabrics consistent with high-temperature plastic flow on the olivine (010) [100] and (0kl) [100] slip systems. The fabric orientation is uniform in three of the four massifs but varies between massifs, suggesting differential rotation before or during emplacement. Within North Arm Mountain, the olivine a axes are aligned approximately perpendicular to the sheeted dikes in both the ultramafic tectonites and the overlying gabbroic tectonites. In Blow Me Down Mountain, the olivine a axes in the gabbros are perpendicular to the dikes, but they are parallel to them in the ultramafic rocks. It is concluded that the ultramafic rocks on Blow Me Down Mountain were rotated 90° during emplacement or that local decoupling and rotation occurred between the crust and upper mantle prior to emplacement. Within the Lewis Hills, the olivine fabrics rotate and weaken near the shear zone in the center of the massif. A second deformation, perhaps associated with low-temperature plastic flow, appears to have obliterated the fabric patterns still observed in the ultramafic rocks to the east.
Stenonychosaurus inequalis (Saurischia: Theropoda) from the Judith River (Oldman) Formation of Alberta: new findings on metatarsal structure
Authors: Wilson Michael Clayton , Currie Philip J.
Published: April 2011

A partial foot of Stenonychosaurus from the Judith River (Oldman) Formation, Dinosaur Provincial Park, Alberta, shows features in the metatarsus that have not previously been recognized. These include compression of metatarsal II and exclusion of the proximal half of metatarsal III from the anterior (= dorsal) surface of the metatarsus. Exclusion from the anterior surface of metatarsal III to this extent is unprecedented among theropods and further underscores the distinctiveness of the Sauromithoididae.
Conodonts and associated graptolites from the late Early Devonian of east-central Alaska and western Yukon Territory
Authors: Savage Norman M. , Blodgett Robert B. , Jaeger Hermann
Published: April 2011

Samples from two closely placed localities in western Yukon Territory have yielded late Early Devonian conodonts characteristic of areas farther to the north and east in Alaska and Yukon Territory and also characteristic of central and northern Siberia. Conodonts from a nearby locality in east-central Alaska indicate an age that makes the associated graptolites of considerable interest: they are among the youngest graptolites known in North America.
Sulfate-reducing bacteria and silica solubility: a possible mechanism for evaporite diagenesis and silica precipitation in banded iron formations
Authors: Birnbaum Stuart J. , Wireman John W.
Published: April 2011

Selective replacement of sulfate-evaporite minerals by silica and the precipitation of silica in association with sulfide mineral phases in banded iron formations may be mediated by the metabolic activities of sulfate-reducing bacteria. Hydrogen sulfide is known to be a product of this metabolism and is often called upon as a source of sulfur for metallic sulfides in sedimentary rocks. We report here on the influence that chemical changes induced by bacterial sulfate reduction have on silica solubility.Controlled in vitro growth experiments with Desulfovibrio desulfuricans and silica show (1) this organism can grow in silica concentrations as great as 400 ppm with no inhibition and (2) growth in the presence of silica yields a decrease in dissolved silica.Growth experiments with 80 ppm silica produced a lowering in dissolved silica from 80 ppm to 60 ppm, a 25% decrease, in just 30 h. Control experiments in the absence of cells resulted in no effective decrease in dissolved silica. The ability of sulfate-reducing bacteria to remove silica from solution may be related to local changes in pH and to hydrogen bonding of amorphous silica followed by polymerization to higher weight molecules.
Carbon in Archean rocks of the Abitibi belt (Ontario–Quebec) and its relation to gold distribution
Authors: Springer Janet S.
Published: April 2011

In the Abitibi belt of Ontario and Quebec, sedimentary black argillites with carbon contents of up to 5% C contain up to 0.5 ppm gold. Sheared black argillites, now graphitic schists, reflect the values of the sedimentary precursors, although their appearance is very different. Gold values of 15 ppm and more are found in graphitic schists only where alteration, shown by quartz veins and increased carbonate content, gives independent evidence of a later hydrothermal event. Gold-rich graphitic schists are characterized by veining; raised gold values closely follow vein margins. As mass balancing shows gold leaching and redeposition to be unlikely, gold enrichment is interpreted to reflect introduction of gold and its preferential deposition in carbonaceous rocks by reduction at vein margins. Natural carbons in these rocks may have been surface activated by both shearing and hydrothermal fluids.
Age estimation of the Shulie Lake and Eatonville tills in Nova Scotia by pedogenic development
Authors: Wang C. , Stea R. R. , Ross G. J. , Holmstrom D.
Published: April 2011

The Shulie Lake Till (in which the Shulie soil developed) and Eatonville Till (in which the Westbrook soil developed) are commonly found at the surface of western Cumberland Country. The Shulie Lake Till is occasionally found overlying the Eatonville Till near the boundary of the two tills. The Shulie Lake Till is of late Wisconsinan age, but the age of the Eatonville Till is not known. Several pedons of the Shulie and Westbrook soils were observed and analyzed to determine the degree of their pedogenic development in order to estimate the relative ages of the two tills in which these soils had developed.The thickness of the solum and the amount of amorphous Fe and Al were found to be greater in the Westbrook soil than in the Shulie soil. This evidence indicates that the Eatonville Till is older than the Shulie Lake Till. However, the age difference between the tills is probably small because, after discounting differences in inherited kaolinite, the differences in composition and weathering of the clay minerals in the two soils are minor and common in Podzolic soils of late Wisconsinan age elsewhere in the Maritime Provinces. The combined pedogenic evidence indicates that the Shulie Lake and Eatonville tills are most probably of late Wisconsinan age.
Post-stack depth migration in the frequency–space domain
Authors: Kelamis Panos G. , Kjartansson Einar , Marlin E George
Published: April 2011

The 45 °monochromatic one-way wave equation, along with the thin-lens term, is used, and a depth-migration algorithm is developed in the frequency–space (ω, x) domain. Using this approach, an unmigrated stack section is directly transformed into a depth-migrated section taking into account both vertical and lateral velocity variations. In practice, the algorithm can accommodate steep events with dips of the order of 60–65°. The use of the frequency–space domain offers several advantages over the conventional time–space and frequency–wave-number domains. Time derivatives are evaluated exactly by a simple multiplication, while the use of the space (x, z) domain facilitates the handling of lateral velocity inhomogeneities. The performance of the depth-migration algorithm is tested with synthetic data from complicated models and real data from the Foothills area of western Canada.
The Quaternary stratigraphic record of British Columbia—evidence for episodic sedimentation and erosion controlled by glaciation
Authors: Clague John J.
Published: April 2011

The terrestrial Quaternary stratigraphic record of British Columbia is largely a product of brief depositional events separated by long periods of nondeposition and erosion. Thick, stratified Quaternary sediments are present mainly in valleys and coastal lowlands and accumulated during periods of growth and decay of the Cordilleran Ice Sheet. At glacial maxima, till was deposited over large areas of low and moderate relief. However, at the same time, much of the landscape was eroded by glaciers.Sedimentation has been more restricted and has occurred at lower rates during nonglacial periods than during glaciations. On land, the only important sediment accumulation sites during nonglacials have been lakes, floodplains, and fans. However, large amounts of sediment have accumulated offshore, especially in fjords and basins such as the Strait of Georgia. Because of the restricted aspect of sedimentation during nonglacials, the stratigraphic record of these periods is meagre. In most places, true nonglacial units are thin and discontinuous, or they are absent altogether. Commonly, a nonglacial period is recorded only by an unconformity produced when streams incised valley fills shortly after the end of the preceding glaciation.
The western Anahim Belt: root zone of a peralkaline magma system
Authors: Souther J. G.
Published: April 2011

The Anahim Volcanic Belt extends easterly across central British Columbia, where it includes three large shield volcanoes and numerous small monogenetic cones and lava flows. Potassium–argon dates on the lavas suggest that the onset of volcanic activity progressed from approximately 8 Ma in the west to less than 1 Ma in the east. A western extension of the belt into the strongly uplifted and deeply dissected Coast Mountains is defined by an east-trending zone of chemically distinctive, high-level plutons, dyke swarms, and remnants of eruptive breccia that yield K–Ar dates of 10–14 Ma. The lavas and dykes include both basic (alkali basalt and hawaiite) and salic (trachyte and sodic rhyolite) suites, which have remarkably similar major-element abundances. In addition, moderately to strongly peralkaline rocks (comendite and pantellerite) constitute a major part of the volcanic piles and a lesser proportion of the dykes. Epizonal plutons show an upward zonation from hypersolvus syenite to miarolitic, alkaline to mildly peralkaline soda granite. The plutonic, hypabyssal, and eruptive rocks of the western Anahim Belt are considered to represent different levels of exposure in the root zone of an alkaline magma system that gave rise to peralkaline end members. Uplift rates, based on fission track dates, suggest that fractionation leading to mildly peralkaline soda granite took place in crustal reservoirs emplaced at depths of 2.5–4.5 km below the surface and that additional enrichment in alkalis took place at still shallower depths.
Paleomagnetism of Early Cambrian redbeds on Cape Breton Island, Nova Scotia
Authors: Rao K. V. , Seguin M. K. , Deutsch E. R.
Published: April 2011

Results are reported from steeply dipping red sandstones collected at nine sites (45 samples) of the Lower Cambrian Morrison River and MacCodrum formations on southeast Cape Breton Island, which forms part of the Avalon terrane. Demagnetization studies indicate minimal overlap of stability spectra in thermal, alternating-field, and chemical treatments. A stable component (hematite) with high unblocking temperatures (680 °C) is dominant at all sites. Its mean direction corrected for geologic tilt is D = 281°, I = +32°, k = 97, giving a paleomagnetic pole (pole M) at 20°N, 146°W (dp, dm = 3°, 6°). The corresponding in situ direction is D = 147°, I = +59°, k = 97, with a pole M′ at 2°S, 39°W (dp, dm = 6°, 8°). Poles M and M′ were compared with published Paleozoic poles for the Avalon Zone and cratonic North America to test whether the magnetization originated before or after the Taconic (Ordovician) folding. It could have been acquired during deposition or early diagenesis (Early to Middle Cambrian), in which case the paleolatitude differences between Morrison River–MacCodrum and age-equivalent cratonic sites require a minimum 20° post-Early Cambrian displacement between Avalon Zone and craton. This is, however, difficult to verify, since a fold test is not possible and well-dated Cambrian poles from Avalonia are lacking. Three or four of the many post-Cambrian results from the Avalon and Gander zones were found to be comparable with pole M′, so that alternatively the Morrison River–MacCodrum magnetization could be a postfolding, Late Ordovician–Early Silurian or Late Devonian overprint.
Un exemple de métasomatisme alcalin albite–uranium dans le bassin des Monts Otish, Québec
Authors: Ruhlmann Francois , Raynal Michel , Lavoie Serge
Published: April 2011

Metallographic studies of uraniferous occurrences in the Otish basin (Quebec) have shown that these mineralizations are characterized by the association albite–uranium (successively, brannerite–uraninite). This paragenesis corresponds to a sodium metasomatic event related to Hudsonian (1730 ± 30 Ma) gabbroic sills and dykes that intrude both Archean granitic basement and the overlying Aphebian detritic cover. The mineralization (1723 ± 3 Ma) is interpreted as a late Hudsonian event and is in many ways comparable to other occurrences in the Precambrian shields of Brazil, Scandinavia, and the Ukraine. A comparison of these different occurrences with the Otish mineralization has resulted in the recognition of several characteristics common to late-orogenic metallogenic events from mid-Proterozoic time in Canada and elsewhere up to late Hercynien in Europe. To explain specific assemblages of tellurides, selenides, and sulphides within a dolomitic gangue, one suggests that deep basinal Na-rich brines were mobilized to form mineralizing fluids during a regional tectono-magmatic event. The pitchblende–calcite association in the Otish basin corresponds to the latest mineralized event (306 Ma) caused by a remobilization of the primary Na–U metallogeny.