bluuebunny/crossref_metadata_2025 huggingface dataset:
Sediments of the Rimouski shelf region, lower Saint Lawrence estuary
Authors: Silverberg Norman
Published: April 2011

The Rimouski shelf is a smooth-surfaced, gently sloping platform which gives way to the north to a steep, sometimes irregular margin of the Laurentian Trough. The surficial sediments are sandy and change rapidly over short distances particularly in areas close to the shore. A zone of well-sorted medium sands, littered in places with gravel, and surrounded by bands of finer, more poorly sorted sediment occupies the western half of the shelf. The central part of the shelf is also banded but fine-grained sediment is more abundant. Sand deposits reappear on the eastern edge of the study area, while uniform muds occur over the slope. These surface deposits are thin and appear to be related to modern shelf currents, ice rafting from the shore, and local sources of mud. Below the surface the deposits become more sandy and are often in sharp contact with a dense clay. The latter is correlated with the Goldthwait Sea clays of 9–12000 years BP. Available information suggests that the Goldthwait Sea regression continued past the present shorelines to permit the emplacement of the sandy deposits and then transgressed once more to about the present sea level during the last 9000 years.
Examples of the variability of disequilibrium and the emanation factor in some uraniferous materials
Authors: Levinson A. A. , Bland C. J.
Published: April 2011

The U3O8 and eU3O8 contents, and the activities of 226Ra and 214Bi, have been determined for samples from two distinctly different geological and environmental localities (Thailand and southern Africa). In both cases, most of the samples show significant disequilibrium. On the basis of these data, the potential difficulties which would be encountered if gamma ray spectrometers (either airborne or surface) were used in the exploration for uranium in these situations are discussed.Using the same data, as well as information from the literature, it is shown that only a limited, variable, and unpredictable amount of 222Rn produced during the decay of 238U (and its daughters) escapes from geological material; this amount is called the emanation factor (E). Thus, in attempting to use 222Rn for exploration purposes, not only must the short half-life (3.8 days) and other problems be considered, but at least of equal importance is the amount of 222Rn which can escape from any sample.
A unique stratigraphic record of late Tertiary–Quaternary events in southeastern Yukon
Authors: Klassen R. W.
Published: April 2011

A succession of fluvial sediments with minor coal, basaltic lava, five tills, and fossiliferous intertill sediments exposed along the Liard River where it crosses the Liard Plain provides a remarkably continuous record of geologic–climatic events in this region. The coal bearing sediments and lava were previously described and interpreted as Tertiary–Quaternary in age. The Quaternary sediments record four major intervals of glaciation and three nonglacial intervals not previously recognized in this region.
Oxide minerals in the Turnagain ultramafic complex, northwestern British Columbia
Authors: Clark Thomas
Published: April 2011

The oxide minerals in the Turnagain ultramafic complex, an Alaskan-type intrusion of possible Upper Triassic age in northwestern British Columbia, offer some important clues concerning the composition of magmas from which they separated and the chemical changes that they underwent during the cooling process. Chromite occurs as disseminations and vein-like concentrations in dunite, and as disseminations in wehrlite and olivine clinopyroxenite. Ilmenite is found in hornblendite. A small amount of primary magnetite is associated with intercumulus sulfide. Chrome spinel exhibits a very wide range of compositions. The ratio 100 Mg/(Mg + Fe2+) ranges from 69.7–3.6, and this is paralleled by a decrease in Cr2O3 (60.1–9.3%), and by increases in Fe2O3, TiO2, and MnO. Chromite rims are poorer in Cr and richer in Fe3+ than chromite cores. Magmatic differentiation was responsible for most of these variations. Subsolidus re-equilibration caused Mg/Fe2+ zoning in coexisting chromite and olivine, the ratio decreasing in chromite rims and increasing in rims of contacting olivine grains. Subsolidus re-equilibration was probably responsible for the enrichment in Mg of the minerals in a chromite-rich layer relative to those in the adjacent dunite. Disseminated chromite originated by cotectic crystallization; chromite-rich layers may have been deposited by magmatic turbidity currents. Several mineralogical and chemical features suggest that oxygen fugacity in the magmas was relatively low.
Fission track etching and annealing phenomenon in phlogopite and their applications
Authors: Parshad Rajinder , Saini H. S. , Nagpaul K. K.
Published: April 2011

Systematic annealing experiments on fission tracks in phlogopite have been carried out under standard etching conditions to obtain the correction curve for the ages of phlogopite, which might have been lowered due to geological annealing of fossil fission tracks. Variation of fission track density with etching time at different annealing temperatures has been analysed in order to standardize the etching conditions. All the tracks in phlogopite are annealed by heating at 590 °C for 1 h. Extrapolation of experimental data suggests that a temperature of 215 °C would be required for 1 Ma to remove all the tracks. The corrected age of a phlogopite sample from Neyyur village, Kanya Kumari District, India, is 395 ± 20 Ma. The mean values of fission fragment range for induced 235U fission tracks, uranium concentration, activation energy, and an effective paleoisotherm for fission track clock in the Neyyur village phlogopite are 17.7 ± 2.0 μm, 3.12 × 10−9 g/g, 1.8 eV, and 150 °C, respectively.
Morphology and paleoecology of Ordovician tetradiid corals from the Manitoulin District, northern Ontario
Authors: Copper Paul , Morrison Robin
Published: April 2011

The tetradiids were the most common tabulate coral component of the Ordovician (Caradocian–Ashgillian) sequence in the Manitoulin District, locally abundant enough to form biostromal accumulations. Five species, assigned to four genera, including a new subgenus Paenetetradium, are recognized in the section. In sequence, from oldest to youngest, these species are: Tetradium (Tetradium) undulatum n.sp. from the Cloche Island Formation; Rhabdoietradiitm giganteum n.sp., Paratetradium capella n.sp., and Phytopsis cf. racemosum (Raymond) from the Cobourg Formation; and T. (Paenetetradium) huronensis (Billings) n.subgen. from the Meaford and Kaguwong Formations, Broad trends include the development of tabulale from atabulate forms, reduction in corallite sizes, and dominance of cerioid forms by the late Ordovician. Tetradiids were commonly overgrown by stromatoporoids, calcareous algae, or bryozoans, and, in biostrome concentrations, grew in very shallow waters.
Dating of igneous and metamorphic events in the Fiskenaesset region of southern west Greenland
Authors: Pidgeon R. T. , Kalsbeek F.
Published: April 2011

U–Pb measurements on zircons from gneisses, which closely resemble Amitsoq gneisses, from nunataks from the Frederikshåbs Isblink show that they are in fact much younger, probably ca. 3000 Ma old. A direct measurement of the age of the granulite facies metamorphism in the northern part of the Fiskenaesset area, of [Formula: see text], has been achieved by U–Pb analyses on: (1) a large euhedral zircon from an ultrabasic pod considered to have crystallized during the granulite facies metamorphism; (2) zircons from the Ilivertalik granite, which is considered to have been emplaced shortly before the end of the granulite facies metamorphism; and (3) zircons from an anthophyllite–gedrite rock considered to have grown during the amphibolite facies retrogression following granulite facies metamorphism.A maximum age of 2660 ± 20 Ma for the end of the low grade amphibolite facies overprinting in the southern part of the Fiskenaesset area is given by a zircon U–Pb measurement on intrusive granitic sheets.
Copper mineralization near an intra-Rapitan unconformity, Nite copper prospect, Mackenzie Mountains, Northwest Territories, Canada
Authors: Helmstaedt Herwart , Eisbacher G. H. , McGregor J. A.
Published: April 2011

Copper minerals are known from at least five stratigraphic levels above and below an angular unconformity recognized within rocks of the Rapitan Group on and near the Nite copper prospect, Mackenzie Mountains. The main showing on the prospect is structurally controlled and occurs in siliceous dolostone near the top of the folded and faulted Coppercap Formation, directly beneath an unconformity separating two local members of the Sayunei Formation (Rapitan Group). The copper was emplaced in tectonically fractured dolostone, precipitated from solutions that may have descended from copper-bearing conglomerates in the Rapitan Group above the unconformity, or ascended from weakly mineralized carbonates below. Mechanical reworking of older strata-bound copper deposits is indicated by significant copper content in clasts eroded from older rocks of the northeastern Mackenzie Mountains. The ultimate source of copper can probably be sought in basaltic dikes and flows emplaced prior to deposition of Redstone River and Coppercap formations during an early phase of crustal extension in the northern part of the Cordilleran miogeosyncline.
Early recumbent folding in some westernmost exposures of the Shuswap Complex, southern Okanagan, British Columbia
Authors: Ross John V. , Christie James S.
Published: April 2011

A sequence of three phases of recumbent folding has been established within some western-most exposures of gneiss of the Shuswap Complex, near Vaseaux Lake, in the southern Okanagan Valley of British Columbia. These three structural events comprise large northerly trending recumbent folds (Phase 1) that have been refolded, first about northeasterly dipping axial surfaces (Phase 2) and secondly about southerly dipping axial surfaces (Phase 3).Much of the ductile strain visible in these rocks appears associated with Phase 2. Strain analysis of plastically deformed garnets, originally synkinematically developed during early stages of Phase 2, indicates that the growth of Phase 2 recumbent folds was associated with extreme flattening strain across their axial surfaces, accompanied by intense constriction subparallel with their hinge lines. A similar but less intense mode of strain appears associated with Phase 3 folds. No useful strain markers are associated with Phase 1 and perhaps this was a translational phase of strain.The Phase 3 event probably is an early part of the Columbian Orogeny, with Phases 1 and 2 being formed either during or earlier than the Permo-Triassic.Early Tertiary events have gently warped and fractured these three early main structures.
Zircon age measurements for Uivak II gneisses from the Saglek area, Labrador
Authors: Wanless R. K. , Bridgwater D. , Collerson K. D.
Published: April 2011

Three different zircon size fractions, prepared from a single sample of Uivak II gneiss, yielded highly discordant lead–uranium isotopic ratios. The data define a discordia chord which intersects concordia at 3760 ± 150 Ma and about 2500 Ma. The upper intersection is interpreted as the time when the rocks were metamorphosed while the lower intersection records a major episodic lead loss event coincident with the youngest granitic activity in the area.
Stromatolite morphogenesis—progress and problems
Authors: Semikhatov M. A. , Gebelein C. D. , Cloud Preston , Awramik S. M. , Benmore W. C.
Published: April 2011

Stromatolites are laminated, lithified, sedimentary growth structures that accrete away from a point or limited surface of attachment. They are commonly, but not necessarily, of microbial origin and calcareous composition. Although familiar to geologists, they remain enigmatic as to origin and uncertain as to their full potential for historical geology.We summarize here the results of collective inquiry and discussion concerning central problems of stromatolite morphogenesis. We focus on relations between microstructure, laminar details, and gross morphology of ancient, probably biogenic, stromatolites and on the microbial composition and laminar characteristics of analogous modern microbial mats and sedimentary structures produced by them.The basic microstructure-determining unit of the modern stromatolite analog of biogenic origin is the mat-building community of organisms and particularly its dominant species, operating within a particular ecological setting. Biological factors dominate at the laminar and sublaminar level. Gross morphology probably reflects a balance between ecological processes and microbial activity.Nomenclatural clarity and stratigraphic utility turn on a proper understanding of morphogenesis. Although stromatolites will continue to function as stratigraphic and paleoecologic indicators, the reasons behind and limits to their applicability will remain obscure while morphogenetic processes remain uncertain. Finally, we outline some problems whose resolution could reduce that uncertainty.
Chemistry and prehnite–pumpellyite facies metamorphism of calc-alkaline Carboniferous volcanic rocks of southeastern New Brunswick
Authors: Strong D. F. , Dickson W. L. , Pickerill R. K.
Published: April 2011

Mafic pillowed and massive lavas of the Upper Carboniferous West Beach Formation, as exposed in the city of Saint John, southeastern New Brunswick, were metamorphosed under prehnite–pumpellyite facies conditions, possibly between 315 and 370 °C and 1 and 2.5 kbar (105 and 2.5 × 105 kPa). Petrographic and chemical data for 32 samples indicate that this metamorphism was accompanied by significant silicification of some samples and variable chloritization of most. These processes caused relatively minor chemical transfer of most elements other than silica, and calculations from averages assuming constant Al indicate that TiO2, P2O5, Zr, Rb, Nb, Ga, and Y are relatively immobile. However, ratio diagrams show anomalous concentrations of these elements in a few samples and illustrate the inherent flaws of quantitative estimates based on averages. Classifications using these elements in a variety of diagrams clearly and consistently indicate a primitive calc-alkaline nature for the lavas, contrary to what might be expected from their geological setting interbedded with plant-bearing paralic or continental sedimentary rocks.
The late depositional history of the western end of the Oak Ridges Moraine, Ontario
Authors: Duckworth Peter B.
Published: April 2011

The Oak Ridges Moraine lies about 25 km inland from the north shore of Lake Ontario and parallels the lake for about 160 km. The width varies from less than 1.6 to 14.5 km, and the maximum relief is about 150 m. Data from boreholes indicate that the maximum thickness of sediment in the moraine is about 215 m. Previous writers considered that the moraine was formed in several stages between lobes of the Laurentide glacier during the Wisconsinan or earlier.At the western end of the moraine up to 50 m of glaciofluvial outwash has been exposed. These upper sediments were deposited during and after the Port Bruce Stadial of the Late Wisconsinan Substage (< 15 000 years BP). In the central part of the moraine, in Uxbridge Township, the facies associations consist primarily of longitudinal gravel bars and well defined trough sets of dune origin, typical of the proximal portions of outwash plains. The finer grained distal facies occur to the west and northwest, and are characterized by transverse sand bars and sequences of ripple beds. The silt and clay fractions of the outwash were deposited mainly in proglacial lakes ponded against the north flank of the moraine south of Newmarket, and in King and Vaughan townships.
A structural interpretation across part of the northern Rocky Mountains, British Columbia, Canada
Authors: Thompson Robert I.
Published: April 2011

The northern Canadian Rocky Mountains, as exemplified by the Halfway River map-area (94B) in British Columbia, consists of a rugged and mountainous structurally complex Foothills subprovince of large amplitude box and chevron-style folds in rocks of late Paleozoic and Mesozoic age, and a structurally diverse Rocky Mountain subprovince with open folds and apparently inconspicuous thrust faults in upper Precambrian to upper Paleozoic rocks; separating them is a narrow topographically subdued and heavily vegetated 'transition interval' comprising more penetratively folded and faulted shales and thin-bedded carbonate rocks of late Devonian and Mississippian age.Flat thrust faults, with displacements in the order of 10 km, which occur under the eastern margin of the Rocky Mountain subprovince (mountain front) extend across the 'transition interval' and beneath the western margin of the Foothills subprovince. These faults terminate within a décollement along the Devonian and Mississippian Besa River shale, as the displacement on them is transformed into disharmonic kink-type box and chevron folds in overlying units and into tectonic thickening within the Besa River shale. Because most of the major thrust faults along the Rocky Mountains are 'blind' and cannot be traced to surface exposures, one is left with the erroneous impression that very little lateral displacement (foreshortening) has occurred in the northern Canadian Rocky Mountains.The basic change from a well organized thrust-fault terrane in the southern Rockies to a more diverse fold terrane with few large mappable thrusts in the north is consistent with changes in the stratigraphic character of the rock prism that was deformed: the proportion of thick incompetent shale units increases northward, and major lateral carbonate to shale facies transitions traverse the eastern margin of the Rocky Mountain subprovince.Despite the differences in structural style from south to north, strain patterns within the northern Rocky Mountains are consistent with the lateral eastward movement of a detached prism of sedimentary rocks, and support the basic tenets of thin-skinned tectonics.
Metamorphic evolution of Archean hyaloclastites, Noranda area, Quebec, Canada. Part I: Comparison of Archean and Cenozoic sea-floor metamorphism
Authors: Dimroth Erich , Lichtblau Andreas P.
Published: April 2011

Detailed petrographic comparison of Archean and Cenozoic hyaloclastites and pillows permits us to outline an analogous history of sea-floor metamorphism. The Cenozoic hyaloclastites have been replaced by palagonite (hydrated and oxidized glass), smectites, zeolites, calcite and, locally, by silica. Present minerals in Archean hyaloclastites formed during a phase of load metamorphism, but relict textures permit one to recognize textures of palagonite, former zeolites and smectites, followed by replacement by chlorite, carbonate, and silica. Most pillows of Cenozoic and Archean age consist of three zones: a border zone consisting of palagonitized or chloritized glass; a rim defined by the presence of feldspar spherulites; and a microlitic core. Chloritization, carbonatization, and silicification follow the growth of feldspar spherulites.The evidence indicates that Archean and Cenozoic sea-floor metamorphism took place under identical conditions. In particular Archean palagonite is highly oxidized.
Analyse isotopique de concrétions sous-glaciaires de l'inlandsis laurentidien et teneur en oxygène 18 de la glace
Authors: Hillaire-Marcel Claude , Soucy Jean-Marc , Cailleux André
Published: April 2011

Calcareous concretions occurring on Grenvillian gneiss have been discovered north of Hull, Quebec. Their structure and isotopic composition ([Formula: see text]; [Formula: see text]; 14C age > 35 000 BP) indicate subglacial conditions of precipitation. It is concluded that they were deposited at the base of the Laurentide ice sheet. Assuming equilibrium conditions with the subglacial film of water during precipitation of calcite, it is possible to define a −27.5 to −31.8‰ (vs. "standard mean ocean water" (SMOW)) range for the oxygen-18 content of the ice.
Crustal structure of the central Sverdrup Basin
Authors: Forsyth D. A. , Mair J. A. , Fraser I.
Published: April 2011

A synthesis of refraction data recorded in 1972 and 1973 in the central Sverdrup Basin with other geophysical data shows major features which correlate well with the regional geological structure. The record sections from the Arctic Archipelago show little coherent secondary energy compared with those from other areas of Canada. Normalization of the sections to remove effects of varying shot size and instrument gain has revealed a significant loss of amplitude and coherence of the upper and mid-crustal phases of the seismic energy on traversing a major northeast-trending structure between Melville and Lougheed Islands. The upper mantle phase (Pn), however, is not abnormally attenuated in its travel beneath the area. The aeromagnetic data reveal a major series of dykes or minor graben, a likely cause of scattering and attenuation of the seismic energy travelling within the crust. These seismic effects and the focal depths of earthquakes suggest that lateral heterogeneities in the crust may extend to near-mantle depths in this area. The age dates available suggest fracture or dyke development progressed from south to north beginning in the Early Cretaceous. The correlation of the recorded seismicity with these structures provides one of the better examples of an active, intraplate tectonic feature.East of King Christian Island (KCI) the refraction results concur with gravity and regional geology in suggesting a major change in crustal and upper mantle structure. Models derived using ray theory indicate a crust which thins from near 40 km beneath the eastern Sabine Peninsula to 32 km west of KCI. East of KCI the Moho may lie at 40 km beneath a complex crustal structure. The average crustal compressional wave velocity is between 5.9 and 6.4 km s−1 and the mean upper mantle velocity is 8.2 km s−1. The present study does not support the existence of a distinct mid-crustal layer with a velocity of about 7.3 km s−1.
Use of long-term automatic time-lapse photography to measure the growth of frost blisters
Authors: Everdingen Robert O. van , Banner James A.
Published: April 2011

The use of automatic time-lapse camera systems, taking daily photographs at solar noon between 26 September 1977 and 3 May 1978, has made it possible to determine the time and rate of growth of frost blisters at Bear Rock near Fort Norman, N.W.T. The daily negatives have been printed and refilmed to produce a time-lapse motion picture covering the full 220 day observation period. The use of paired cameras allowed production and viewing of daily stereo pairs.
Early Silurian volcanic rocks at Arisaig, Nova Scotia
Authors: Keppie J. Duncan , Dostal J. , Zentilli M.
Published: April 2011

Petrochemical data for the Early Llandovery subaerial volcanic rocks at Arisaig, Antigonish Highlands, Nova Scotia, show that they are a bimodal suite of altered rhyolites and basalts of tholeiitic affinity with some alkaline tendencies extruded in a nonorogenic extensional environment within a continental plate. These data do not support the island arc origin frequently inferred for these rocks but are consistent with recent petrological data from the Silurian – Lower Devonian Coastal Volcanic Belt in southern Maine, which may be a strike continuation of the Arisaig volcanics. The close spatial and temporal association of basalts and rhyolites is attributed to anatexis of the crust upon contact with the rising basaltic magma.
Isotopic dates and strontium isotopic ratios for plutonic and volcanic rocks in the Quesnel Trough and Nicola Belt, south–central British Columbia
Authors: Preto V. A. , Osatenko M. J. , McMillan W. J. , Armstrong R. L.
Published: April 2011

Four distinct igneous events of the southern Intermontane Belt are represented in new K–Ar and Rb–Sr dates. The first and regionally most important event is sharply defined by new K–Ar dates between 200 and 209 Ma for the Thuya, Wildhorse, Iron Mask, and Allison batholiths and a 205 ± 10 Ma Rb–Sr isochron for the Guichon Creek batholith. All these plutons were emplaced approximately at the change from Triassic to Jurassic time. The related and slightly older Nicola volcanic rocks are altered by addition of more radiogenic sedimentary Sr (Carnian Nicola limestones having 87Sr/86Sr = 0.7075 ± 1) and do not give an isochron date. The Coldwater stock is anomalously old (K–Ar dates range from 215–267 Ma).The Mid- to Late Jurassic igneous event is indicated by a 141 Ma K–Ar date for the Mount Martley batholith. Mid-Cretaceous volcanic rocks of the Kingsvale Group give a Rb–Sr isochron date of 112 ± 10 Ma and are postdated by the crosscutting and slightly younger Summers Creek stock (100 Ma by K–Ar).The final event straddles the Cretaceous–Tertiary boundary with the Nicola batholith emplaced about 60 Ma ago (K–Ar) and the Rey Lake stock perhaps slightly earlier (69 Ma by K–Ar).Initial 87Sr/S6sr ratios range from 0.7025–0.7046 with a mean and mode near 0.7037 which is within the range of modern circum-Pacific volcanoes. Initial ratios of 0.7034 ± 1 for the Guichon Creek batholith, 0.7035 ± 1 for the Iron Mask batholith, 0.70435 ± 10 for the Thuya batholith, and 0.70379 ± 4 for the Kingsvale volcanic rocks are the most precisely determined. The Coldwater stock is anomalously low at 0.7025. For the other plutonic bodies only scattered or single analyses are available. The Nicola volcanic rocks appear to have once been similar in initial ratio to the Guichon Creek batholith but their calculated initial ratios now scatter from 0.7034–0.7073.
K–Ar geochronology of the southwestern Brooks Range, Alaska
Authors: Turner Donald L. , Forbes Robert B. , Dillon John T.
Published: April 2011

The southern Brooks Range schist belt is characterized by metasediments with subordinate metabasites and metafelsites. Blueschists occur within the schist belt from the Chandalar Quadrangle westward to the Baird Mountains Quadrangle.We report 76 new 40K–40Ar mineral ages from 47 metamorphic and igneous rocks in the southwestern Brooks Range. The pattern of radiometric ages reflects the complex geologic history of this area. Local and regional radiometric ages provide evidence that the schist belt has, at least in part, undergone a Late Precambrian blueschist facies metamorphism. Silurian to Devonian carbonates and Middle Devonian felsic volcanics were later deposited on this Precambrian basement. Subsequent deformations produced the present pattern of isoclinal, recumbent folds, resulting in the interlayering of rocks of markedly different ages and lithologies.The entire schist terrane was metamorphosed to greenschist facies in Mesozoic time, probably as a result of Jurassic–Cretaceous northward overthrusting of oceanic crust and upper mantle, resulting in the resetting of most K–Ar mica ages to the mid-Cretaceous. A series of apparent 40K–40Ar ages intermediate between Late Precambrian and mid-Cretaceous are interpreted as indicating varying amounts of partial argon loss from older rocks during the Mesozoic metamorphism. Some glaucophanes contain excess radiogenic 40Ar.
The St-Donat, Quebec, earthquake sequence of February 18–23,1978
Authors: Horner R. B. , Wetmiller R. J. , Hasegawa H. S.
Published: April 2011

The St-Donat earthquake of February 18, 1978, occurred in a diffuse zone of significant seismicity in western Quebec. A field survey detected two aftershocks ([Formula: see text]) in a 3 day period following the magnitude mb(Lg) 4.1 main shock. These were followed by a magnitude mb(Lg) 3.4 earthquake on February 23, after the field stations were removed. Main shock and aftershock activity occurred within a small active volume located at 46 °19.2′N, 74°06.6′W, depth 7 km, with an estimated uncertainty of 1 km on all three hypocentral parameters. The main shock seismic moment was calculated to be 0.8 × 1022 dyne∙cm (8 × 1022 μN∙cm).The tremor was felt over an area of 70 000 km2 in western Quebec, eastern Ontario, and northern New York State with a maximum radius of perceptibility of 185 km and a maximum intensity of V in the St-Donat area. A comparison of the isoseismals of this and three other recent earthquakes of magnitude near 4 suggests a variation of maximum intensity inversely with focal depth; a significant area of intensity V is only observed when the focal depth is less than 10 km. There is also an indication of a systematic change in focal depths across the western Quebec zone, from shallow (upper crustal) depths north of Montreal to deeper (midcrustal) depths north of Ottawa.The P-nodal solution indicates almost pure thrust motion on a plane striking N20°W and dipping either 40°NE or 50°SW. The deviatoric compression axis is nearly horizontal, in a west-southwest direction. Similar results from the 1975 Maniwaki, Quebec, earthquake suggest that a uniform stress condition exists throughout western Quebec.
Interpretation of isotopic ages and 87Sr/86Sr initial ratios for plutonic rocks in the Whitehorse map area, Yukon
Authors: Morrison Gregg W. , Godwin Colin I. , Armstrong Richard L.
Published: April 2011

Sixteen new K–Ar dates and four new Rb–Sr isochrons help define four plutonic suites in the Whitehorse map area, Yukon. The Triassic(?) suite, defined on stratigraphic evidence, is the southern extension of the Yukon Crystalline Terrane and is correlative with plutonic suites in the Intermontane Belt in British Columbia. The mid-Cretaceous (~100 Ma) suite in the Intermontane Belt in the Whitehorse map area is time equivalent to plutonic suites in the Omineca Crystalline Belt to the east. Late Cretaceous (~70 Ma) and Eocene (~55 Ma) suites include volcanic and subvolcanic as well as plutonic phases and are correlative with continental volcano–plutonic suites near the eastern margin of the Coast Plutonic Complex. The predominance of the mid-Cretaceous suite in the Intermontane Belt in Whitehorse and adjacent map areas in Yukon and northern British Columbia suggests that this area has undergone posttectonic magmatism more characteristic of the Omineca Crystalline Belt than of the Intermontane Belt elsewhere in the Canadian Cordillera.87Sr/86Sr initial ratio determinations suggest that the southern extension of the Yukon Crystalline Terrane in the western part of the Whitehorse map area and in northern British Columbia includes Precambrian crust separated from the North American craton by Paleozoic oceanic crust of the Intermontane Belt.
Clarification of two Mammuthus molars from the British Columbia Provincial Museum
Authors: Kool Richard
Published: April 2011

British Columbia Provincial Museum (BCPM) 712 from Sooke, British Columbia, and BCPM uncatalogued from Cobble Hill, British Columbia, are shown to have been incorrectly referred to as Mammuthus. The molars are found to have come from Loxodonta africana and Elephas indicus respectively.
Heavy mineral assemblages in tills and their use in distinguishing glacial lobes in the Great Lakes region
Authors: Gwyn Q. H. J. , Dreimanis A.
Published: April 2011

Two main source areas of heavy minerals in tills have been defined in the Great Lakes region: a source in the Superior and Southern Provinces and another in the Grenville Province. The Superior–Southern source is typified by low heavy mineral content and high epidote percentage in contrast to the Grenville source which has a high content of heavy minerals of which garnet, tremolite, and to a lesser extent sphene and orthopyroxene are characteristic. The Huron lobe tills have a mineral suite characteristic of the Superior–Southern source. Two subsources can be distinguished in the Superior–Southern area; however, they are too limited in extent to be characteristic of major glacial lobes. Two other subsources have been identified in the Grenville provenance area: a western Grenville subsource containing abundant garnet and having a low purple–red garnet ratio; and an eastern Grenville subsource distinguished by high garnet and tremolite content and a garnet ratio generally greater than one. The western and eastern Grenville subsources are the provenance areas for the tills of the Georgian Bay lobe and the Ontario–Erie lobe respectively. A possible third Grenville subsource in the Adirondack Mountains is distinguished from other Grenville sources by a lower heavy mineral content and more abundant orthopyroxene and magnetic minerals. This assemblage may be characteristic of the southern portion of the Ontario–Erie lobe.
Quelques Chitinozoaires et Acritarches ordoviciens supérieurs de la Formation d White Head en Gaspésie, Québec
Authors: Martin Francine
Published: April 2011

Chitinozoan and acritarch assemblages from Caradocian and Ashgillian strata forming part of the White Head Formation of the Percé region, Gaspé Peninsula, Québec, contain species known from the central United States, eastern Canada, and northwestern Europe. One new species, Orthosphaeridium gaspesianum, is described.
Magnetotelluric soundings across the Pemberton Volcanic Belt, British Columbia
Authors: Dragert H. , Law L. K. , Sule P. O.
Published: April 2011

Magnetotelluric soundings were carried out at three sites about 30 km apart in a line crossing the Lillooet Valley near Pemberton, British Columbia, to determine the regional conductivity structure and its relationship to the Meager Creek geothermal area. Telluric data were limited to a period band of 10–500 s, while geomagnetic data were recorded in this band as well as a longer period band of 5 min–3 h.Single-station vertical transfer functions indicate that no simple, two-dimensional conductivity discontinuity crosses the profile line or its immediate extension. Thus, the Pemberton volcanic line of plutons does not have an associated two-dimensional continuous conductivity anomaly. Impedance tensors calculated from the short period data are dominated by three-dimensional effects and surface structure effects at the western and eastern sites respectively. The results from the central site indicate a macro-anisotropy in horizontal conductivities, possibly produced by local fracture zones. One-dimensional modelling suggests a vertical conductivity structure consisting of a highly resistive upper crust 15–25 km thick, underlain by a conductive region. Though this conductive layer beneath Pemberton is more resistive, a similar layer has been noted in previous studies in southern British Columbia and appears to be a feature of the western Cordillera.
Pleistocene mammals from Lost Chicken Creek, Alaska
Authors: Harington C. R.
Published: April 2011

Ten species of Pleistocene mammals are represented in a collection of fossils from a placer mining site at Lost Chicken Creek. Among these are four extinct species, an extinct subspecies, two species now extinct in the region, and three species that still occupy the area. Bison crassicornis (large-horned bison), Equus (Asinus) lambei (Yukon wild ass), and Rangifer tarandus (caribou) remains are commonest. Equus (Asinus) cf. kiang (kiang-like wild ass) is recorded for the first time from Alaska.These mammals seem to have occupied a cool steppe-like grassland during late Wisconsin time. Bones of horse, wapiti, bison, and helmeted muskox (Symbos) have yielded radiocarbon dates between 27 000 and 10 000 years BP. The dated bison bone was modified by man, indicating that people were present, and probably hunting and butchering bison, in easternmost Alaska at the close of the Wisconsin glaciation.
The Proterozoic ultramafic and mafic lavas and tuffs of the Dalma greenstone belt, Singhbhum, eastern India
Authors: Gupta Anupendu , Basu Aniruddha , Ghosh Protip K.
Published: April 2011

A detailed petrochemical study of the Proterozoic "Dalma Epidiorites" of Singhbhum leads to a completely new interpretation of this dominantly volcanic belt. The initial igneous activity is represented by mafic and ultramafic intrusives and lavas of tholeiitic. alkaline, and komatiitic affinities. Interlayered are lithic tuffs and tuffaceous sediments. Also present is an analcite basalt heretofore unreported from the Dalma. This suite is overlain by a high-magnesian vitric tuff horizon, which along with its comagmatic intrusives shows quench textures and its chemistry is closely comparable to peridotitic-pyroxenitic komatiites of Archean greenstone terrains. It is noteworthy that the komatiitic magma in this belt is dominantly pyroclastic. The vitric tuff horizon is followed upwards by a thick sequence of high-iron, low-potassium, pillowed tholeiites with ocean-floor affinities.The proposed evolutionary model of the Dalma belt suggests that stretching of Archean proto-continental crust gave rise to the Dalma graben within the Proterozoic (Chaibasa) basin and unique thermal conditions coupled with a disrupted crust led to a high degree of melting and direct tapping of the mantle producing the komatiitic extrusives at a particular stage of the development of the belt.
Rubidium–strontium ages from the Oxford Lake – Knee Lake greenstone belt, northern Manitoba
Authors: Clark G. S. , Cheung S.-P.
Published: April 2011

Rb–Sr whole-rock ages have been determined for rocks from the Oxford Lake – Knee Lake – Gods Lake greenstone belt, in the Superior Province of northeastern Manitoba.The age of the Magill Lake Pluton is 2455 ± 35 Ma (λ87Rb = 1.42 × 10−11 yr−1), with an initial 87Sr/86Sr ratio of 0.7078 ± 0.0043. This granitic stock intrudes the Oxford Lake Group, so it is post-tectonic and probably related to the second, weaker stage of metamorphism.The age of the Bayly Lake Pluton is 2424 ± 74 Ma, with an initial 87Sr/86Sr ratio of 0.7029 ± 0.0001. This granodioritic batholith complex does not intrude the Oxford Lake Group. It is syn-tectonic and metamorphosed.The age of volcanic rocks of the Hayes River Group, from Goose Lake (30 km south of Gods Lake Narrows), is 2680 ± 125 Ma, with an initial 87Sr/86Sr ratio of 0.7014 ± 0.0009.The age for the Magill Lake and Bayly Lake Plutons can be interpreted as the minimum ages of granitic intrusion in the area.The age for the Hayes River Group volcanic rocks is consistent with Rb–Sr ages of volcanic rocks from other Archean greenstone belts within the northwestern Superior Province.
A soft substrate community with edrioasteroids, from the Verulam Formation (Middle Ordovician) at Gamebridge, Ontario
Authors: Waddington Janet B.
Published: April 2011

The edrioasteroids Isorophusella incondita (Raymond) and Cryptogoleus chapmani (Raymond) occur in profusion on one horizon in the lower member of the Verulam Formation (Middle Ordovician) near Gamebridge, Ontario. The associated fauna, including brachiopods, trilobites, and gastropods, suggests a smothered life assemblage from soft bottom shallow marine platform conditions. The edrioasteroids settled on overturned shells of Rafinesquina alternata and on local hard surfaces provided by previously formed internal moulds of molluscs.
Petrology of the Turnagain ultramafic complex, northwestern British Columbia
Authors: Clark Thomas
Published: April 2011

The Turnagain ultramafic complex is an Alaskan-type complex of possible Late Triassic age. It has a central zone of dunite and an outer zone of wehrlite, olivine clinopyroxenite, clinopyroxenite, dunite, hornblendite (rare), and basic hornblende and plagioclase-bearing rock (rare). The complex is largely fault-bounded. The central dunite intrudes the pyroxene-bearing rocks in one area; elsewhere the two zones are gradational. Small-scale layering occurs locally, and is most common in the outer zone. Layering dips steeply due to folding during regional deformation. The ultramafic rocks are generally only partly serpentinized, and consist largely of olivine, clinopyroxene, pargasite, phlogopite, and chrome spinel. The outer zone contains sporadic concentrations of iron–nickel–copper sulfides. Olivine is most magnesian (Fo94.9) in the central dunite, and most iron-rich (Fo80.2) in olivine clinopyroxenite. Clinopyroxene is diopside and follows an iron-enrichment trend. Minor-element contents of minerals indicate that crystallization caused magmatic impoverishment in Ni and Cr, and enrichment in Ti and Al. The primitive Turnagain magma was probably ultrabasic, extremely magnesian, and poor in Al and Ti. Differentiation followed an alkalic trend, possibly at relatively low oxygen fugacity compared to other Alaskan-type complexes. The complex may have formed in a subvolcanic magma chamber, and thus be related to nearby Upper Triassic volcanic rocks.
The Apollo structure in Tofino Basin, Canadian Pacific continental shelf
Authors: Yorath C. J.
Published: April 2011

The Apollo structure of Torfino Basin, Vancouver Island continental shelf, represents a gentle fold that developed within Neogene marine mudstones and siltstones during the Pleistocene. Interpretations derived from side-scan sonar, single and multichannel seismic, and 3.5 kHz profiles, in addition to observations made during submersible traverses as well as lithostratigraphic and biostratigraphic information from dart cores and the Shell Anglo Apollo J-14 well, provide the basis for a structural and kinematic analysis of the structure.At the surface the structure is expressed as a curvilinear anticline, the axis of which is offset by a left-lateral wrench fault. Rotated conjugate left-lateral and minor right-lateral shears developed from the main wrench and dislocate strata within the structure's core. The anticline developed above a shallow detachment surface enclosed within the Neogene and Pleistocene successions. Motion along this surface was possibly induced by earthquake activity associated with the Nootka Fault and thus the structure possibly represents the effects of a gravitational slide.
Halysitid corals from Silurian and Devonian rocks of Québec
Authors: Wright A. J. , Bourque P.-A.
Published: April 2011

Halysitid tabulate corals occur in the Silurian and Devonian rocks of northeastern Gaspé Peninsula, Québec. Silurian specimens from the Dartmouth River and Madeleine River areas are referred to Cystihalysites. A specimen from a possibly Early Devonian level in the Gascons Formation in the Dartmouth River area is assigned to Cystihalysites. Two specimens from different levels in the Early Devonian part of the West Point Formation in the Madeleine River area are assigned questionably to Quepora. The latter occurrences in the West Point Formation demonstrate that this group of tabulate corals lingered into the Devonian.
Provenance et modèle de dépôt de la Formation de la Rivière Nicolet : flysch taconique du Domaine autochtone et du Domaine externe des Appalaches du Québec
Authors: Beaulieu Jean , Lajoie Jean , Hubert Claude
Published: April 2011

The composition of the detrital fraction of the Nicolet River Formation suggests that the rocks of the Autochtonous and the External Domains of the Quebec Appalachians were mostly derived from the sedimentary nappes of the External Domain. The contribution from the metamorphic nappes and ophiolites of the Internal Domain was minor but it indicates that the dynamothermal metamorphism had been completed by the end of the Middle Ordovician (C. spiniferus Zone). Piling up of the nappes, each one progressively richer in feldspar, produced a source of high relief subject to subaerial erosion. The vertical evolution observed in the flysch probably results from tectonic activity at the source area rather than from deep-sea fan progradation. The stratigraphic relationships evince that the deposit accumulated in basins controlled by a series of horsts and grabens.
The origin and history of the Kapuskasing structural zone, Ontario, Canada
Authors: Watson Janet
Published: April 2011

Reexamination of geological, geophysical, and geochronological evidence suggests three principal conclusions. Firstly, the Kapuskasing line came into existence very shortly after the stabilization of the Superior Province. The upfaulting of strips of granulites and associated rocks, and probably the redistribution of densities in the lower crust responsible for the regional positive Bouguer anomaly, took place before the emplacement of the Matachewan dike swarm at ~2690 Ma. Secondly, relative movements along the line during this tectonic stage had an important sinistral transcurrent component and sinistral movements continued during the emplacement of the Matachewan swarm. Thirdly, displacements of various kinds took place on the Kapuskasing line during a number of later events spaced out over a period of more than 2000 Ma; some of their effects can be deduced from the relationship of regional dike swarms and of cratonic cover formations. These findings suggest that the Kapuskasing line did not originate as a rift structure. Analogies are seen with deep transcurrent shear zones of other continents.
Middle Ordovician Table Head Group of western Newfoundland: a revised stratigraphy
Authors: Klappa Colin F. , Opalinski Paul R. , James Noel P.
Published: April 2011

Lithostratigraphic nomenclature of early Middle Ordovician strata from western Newfound land is formally revised. The present Table Head Formation is raised to group status and extended to include overlying interbedded terrigenoclastic-rich calcarenites and shales with lime megabreccias. Four new formation names are proposed: Table Point Formation (previously lower Table Head); Table Cove Formation (previously middle Table Head); Black Cove Formation (previously upper Table Head); and Cape Cormorant Formation (previously Caribou Brook formation). The Table Point Formation comprises bioturbated, fossiliferous grey, hackly limestones and minor dolostones; the Table Cove Formation comprises interbedded lime mudstones and grey–black calcareous shales; the Black Cove Formation comprises black graptolitic shales; and the Cape Cormorant Formation comprises interbedded terrigenoclastic and calcareous sandstones, siltstones, and shales, punctuated by massive or thick-bedded lime megabreccias. The newly defined Table Head Group rests conformably or disconformably on dolostones of the Lower Ordovician St. George Group (an upward-migrating diagenetic dolomitization front commonly obscures the contact) and is overlain concordantly by easterly-derived flysch deposits. Upward-varying lithologic characteristics within the Table Head Group result from fragmentation and subsidence of the Cambro-Ordovician carbonate platform and margin during closure of a proto-Atlantic (Iapetus) Ocean.
Delineation of geologic contacts by seismic refraction with application to the fault zone between the Thompson nickel belt and the Churchill Tectonic Province
Authors: Green A. G.
Published: April 2011

Refracted P-wave and S-wave arrivals are studied from a fourfold multicoverage seismic experiment that has been conducted across a region that spans the contact between the Thompson nickel belt and the Churchill Province in northern Manitoba. A new technique for the calculation of accurate delay times and basement velocities for unreversed multicoverage data is introduced. In this technique, the times of rays between selected shots and receivers are combined to give initial delay time corrections and a subsequent iterative least-squares analysis yields the final delay time corrections and estimates of the basement P-wave velocities. The P-wave velocities correlate well with the basement geology and have been used to refine the location of the contact between the Moak Lake gneisses of the Thompson nickel belt and the Kisseynew gneisses of the Churchill Province. From the P-wave velocities and S-wave attenuation it is concluded that this contact is a fault zone.