bluuebunny/crossref_metadata_2025 huggingface dataset:
Large-scale stratiform and intrusive sedimentary breccias of the lower Proterozoic Goulburn Group, Bathurst Inlet, N.W.T.
Authors: Cecile M. P. , Campbell F. H. A.
Published: April 2011

Two types of sedimentary breccia have been identified in the lower Proterozoic (1.7 to 2.5 Ga) Goulburn Group, Bathurst Inlet, N.W.T. One type is a single unit of strata-bound breccia consisting predominantly of sedimentary clasts surrounding large (up to 500 m in length) sheets of chaotically folded and brecciated allochthonous carbonates. This breccia, the Omingmaktook member of the Brown Sound Fm., is an olistostrome interpreted to have formed by slumping of carbonate sediments during differential basin subsidence and (or) evaporite solution. The other type of breccia occurs as intrusive dykes and large cylindrical bodies (up to 1 km in diameter) that cut through more than 2000 m of Goulburn strata. The intrusive breccias also cross-cut and rework the olistostrome. These intrusive breccias: are of entirely sedimentary composition, and restricted to the upper Goulburn Group; are generally unsorted and exhibit both massive and flowage-layered textures; and contain quartz, dolomite, and minor tourmaline crystals. The intrusive breccias are interpreted as exhumed conduits through which trapped intrastratal fluids migrated to a post-Goulburn paleosurface. Intrusion of the breccia is interpreted to have been produced by the accumulation of pools of intrastratal fluids in structural traps, which under pressure intruded and stoped into overlying strata, eventually reaching a Goulburn paleosurface where they extruded mud flows and formed sedimentary volcanoes.
A theoretical study on electromagnetic probing of permafrost terrains
Authors: Sinha Ajit K.
Published: April 2011

A theoretical analysis has shown that a portable double dipole multifrequency electromagnetic system can be a viable tool for mapping the permafrost terrains of the northern areas for engineering purposes. In this analysis, the theoretical response of a two-layer permafrost terrain (with the frozen layer at the top underlain by the unfrozen sediments) has been obtained for three coil arrangement systems. Available data on the frequency variations of the electrical properties of the permafrost and the unfrozen layers have been considered in the simulations to make the models realistic.The performance of the horizontal coplanar system is seen to be the best for mapping purposes, closely followed by that of the inclined-parallel system which is a null-coupled configuration. The study also considers the effects of the presence of a transition layer between the permafrost and unfrozen layers. The results indicate that the effects are greater when the parameters in the transition layer vary in an exponential fashion rather than in a linear fashion. The quadrature parts of the mutual coupling ratios are, in all cases, less affected by the transition layer than the in-phase parts. However, the resolution is better for the in-phase part when the permafrost thickness and frequency values are large.
Problème de la limite Précambrien–Cambrien: étude radiochronologique par la méthode U–Pb sur zircons du volcan du Jbel Boho (Anti-Atlas marocain)
Authors: Ducrot J. , Lancelot J. R.
Published: April 2011

A 534 ± 10 Ma age has been obtained on zircons from Jbel Boho volcano by the U–Pb method; previous assumptions of older ages for the Anti-Atlas Infracambrien (Morocco) cannot be maintained. This formation belongs to the lower Paleozoic. A slight thermal event has affected the volcanic rocks during Variscan (or Hercynian) times and induced opening of the K–Ar and Rb–Sr systems; but the U–Pb system of the zircons has not been affected. These U–Pb data are further reasons to raise the Precambrian – Cambrian boundary to an age of 550–560 Ma.
Stratigraphic differentiation by sulfur isotopes between Upper Cambrian and Lower Devonian gypsum-bearing units, District of Mackenzie, N.W.T.
Authors: van Everdingen Robert O. , Krouse H. Roy
Published: April 2011

Sulfur isotope analyses of gypsum in outcrop and subsurface samples from the Lower Devonian Bear Rock Formation gave δ34S values ranging from + 10.3 to + 21.8‰ (mean + 16.1‰, standard deviation 2.85‰); samples from the Upper Cambrian Saline River Formation gave δ34S values ranging from + 24.7 to + 40.2‰ (mean + 30.3‰, standard deviation 3.65‰). The lower portion of one outcrop section of 532 ft (162.2 m) on the northeast side of the Norman Range (Franklin Mountains), mapped as Saline River Formation, showed anomalous δ34S values (+ 10.3–+ 18.7‰), suggesting correlation with the Bear Rock Formation. It is likely that at least 97 ft (29.6 m) of Bear Rock strata are present in this section, overlain by a maximum of 435 ft (132.6 m) of gypsiferous Saline River strata that form the base of the main thrust plate of the Norman Range in this locality.
Tors, felsenmeer, and glaciation in northern Cumberland Peninsula, Baffin Island
Authors: Sugden D. E. , Watts S. H.
Published: April 2011

On the basis of two case studies in eastern Baffin Island it is suggested that tors and felsenmeer have survived beneath the Laurentide ice sheet. These features, therefore, need not be diagnostic of areas that escaped glaciation. Rather, the existence of tors and felsenmeer may reflect situations where the overlying Laurentide ice sheet was cold-based.
Algues siluriennes de la Formation de Sayabec (Lac Matapédia, Québec)
Authors: Héroux Y. , Hubert C. , Mamet B. , Roux A.
Published: April 2011

Seventeen genera of algae, seven of which are codiaceans, and twenty-six species (three of which are new) occur in the reef, reefoid, and lagoonal facies of the Silurian Sayabec Formation in the Lake Matapedia region.
Asian freshwater mollusks from Pleistocene deposits in the Old Crow Basin, Yukon Territory
Authors: Clarke Arthur H. , Harington C. R.
Published: April 2011

Approximately 15 species of terrestrial and freshwater mollusks are reported from Pleistocene deposits in the unglaciated Old Crow Basin of the northern Yukon Territory. Of those species, Bulimus leachi (Sheppard), a widespread Eurasian species; and Valvata piligera yukonensis (n. ssp.), closely related to an unusual Valvata now confined to Lake Baikal, U.S.S.R., are recorded from North America for the first time. Possible causes for the failure of these species of freshwater mollusks to become established in North America are considered.
Multiple water reflections recorded at the ocean bottom
Authors: McMechan George A.
Published: April 2011

The use of direct arrivals and multiple reflections that have travelled completely in water from source to receiver to determine epicentral distances is a standard technique in the analysis of marine seismic profiles. The configuration of a source at the air–water interface and a seismometer at the water–sediment interface is investigated in the ray parameter – distance plane and the travel time – distance plane. Vertical component synthetic seismograms are computed by the Cagniard – de Hoop algorithm and are compared with seismograms recorded at the ocean bottom. The results explain the prominent features of the observed wavetrains, including the asymptotic behaviour of arrivals, the location of caustics and the variable observability of arrivals as a fu nction of distance.
Depositional environments of a thick Proterozoic sandstone: the (Huronian) Mississagi Formation of Ontario, Canada
Authors: Long Darrel G. F.
Published: April 2011

The Mississagi Formation is a thick (up to 3.4 km) Proterozoic arenite sequence that forms part of the Huronian (lower Aphebian [Formula: see text]) succession of the north shore of Lake Huron, Ontario. The formation is characterized by planar and to a lesser extent trough cross-stratified medium to coarse feldspathic arenites, with only minor amounts of argillite and conglomerate. Although the formation lacks any regular systematic cyclicity, both thinning upward and fining upward sequences can be recognized in some sections. Paleocurrent roses for individual outcrops are typically unimodal, although some bimodal distributions are recognized. The bulk of the formation is interpreted to be the result of deposition in a fluvial environment, principally from bed load and mixed load streams. These rivers were probably marked by a braided stream pattern in which channels were characterized by intermediate to low sinuosities and high width to depth ratios. Regional paleocurrent and petrographic trends indicate that two major river systems were operative. One system flowed east and south from the Sault Ste. Marie – Elliot Lake region to meet a second, southwesterly flowing system originating in the Cobalt Plain. These systems met in the southern Huronian area, from where the coalescing river systems flowed south.
Geochemistry of volcanic rocks from the Tetagouche Group, Bathurst, New Brunswick, Canada
Authors: Whitehead R. E. S. , Goodfellow W. D.
Published: April 2011

The volcanic rocks of the Tetagouche Group are predominantly dacitic to rhyolitic pyroclastics and lavas; mafic alkaline and tholeiitic volcanic rocks are less abundant. Lavas representing the intermediate range (such as andesites) are uncommon.As a consequence of intense Na2O and K2O metasomatism, the mafic volcanic rocks have been classified on the basis of relatively immobile elements such as Ti, Y, Zr, Nb, Ni and Cr.By reference to volcanic suites described elsewhere for varying geologic and tectonic environments, the Tetagouche Group appears to represent two geologic environments. It is proposed that the deposition of tholeiitic and alkaline basalts accompanied the rifting associated with the opening of the Proto-Atlantic, which began during Hadrynian times. However the calc-alkaline felsic volcanic rocks were deposited on the top of the basaltic sequence along a mature island arc system that developed with the closing of the Proto-Atlantic during Middle Ordovician time.
Lherzolite nodules from a Pleistocene cinder cone in central Yukon
Authors: Sinclair P. D. , Tempelman-Kluit D. J. , Medaris Jr. L. G.
Published: April 2011

Fresh spinel lherzolite nodules occur in basaltic tuff on the flank of a Pleistocene cinder cone built on Selkirk Lavas in central Yukon. The nodules are mineralogically and chemically similar to others from diverse localities. The texture and mineral chemistry are consistent with an upper mantle origin for the Selkirk nodules. Equilibration temperatures for the nodules have been determined to be about 1100 °C.
An analytical representation of the geomagnetic field in Canada for 1975. Part II: The secular change
Authors: Dawson E. , Newitt L. R.
Published: April 2011

Annual mean values of the north (X), east (Y) and vertical (Z) components of the magnetic field from 20 observatories in Canada and adjacent countries for the period 1955–1976 are used to test secular change derived from cubic time terms in a polynomial model. This model was used to derive the main magnetic field charts of Canada for 1975. The rms deviation in the secular change for 1975 (annual change) is a disappointing 16 nT. Graphs of observed and computed annual means show that this fit will worsen with time, especially in Y and Z. For these reasons the annual change contours on the above-mentioned charts were derived by conventional graphical methods. Graphs of the magnetic declination (D), the horizontal intensity (H) and Z were drawn for 20 observatories and 157 Canadian and American repeat stations. Values were extrapolated to 1975 and contoured. A comparison of graphical and polynomial methods show that this simple graphical extrapolation is more sensitive to small significant secular changes than a polynomial extrapolation. We show annual change charts in X, Y and Z constructed by this method.The movement of centres of intense secular change, called isoporic foci, in X, Y and Z, are examined to determine their influence on the secular change pattern in Canada. These indicate that Y and D will continue to decrease, while X and H will continue to increase over most of the country. The total intensity (F), the magnetic inclination (I), and Z will all decrease rapidly in southern Canada.
The Cretaceous–Tertiary boundary in south-central Alberta — a reappraisal based on dinosaurian and microfloral extinctions
Authors: Russell Dale A. , Singh Chaitanya
Published: April 2011

A major microfloral change takes place at the top of the Nevis coal seam in south-central Alberta. This change corresponds to a regional microfloral break recorded at the Cretaceous–Paleocene boundary in the northwestern interior of the United States. However, dinosaurs cf. Tyrannosaurus rex and Triceratops albertensis have been found in strata between the Nevis and Ardley coal seams at a stratigraphically higher level than that at which palynofloral change occurs in Alberta. This indicates that the floral extinctions slightly preceded the dinosaurian extinction and also implies that the two events were not linked in a direct cause and effect relationship. The presence of dinosaur remains a few metres above the level of microfloral change signifies that the floral change occurred slightly before the end of Cretaceous time. In the northwestern interior of the United States, however, the dinosaurian extinction apparently coincides with the regional palynofloral change recorded at the Cretaceous–Paleocene boundary. It seems that the lime relationship of the microfloral change and the dinosaurian extinction cannot be clearly seen in condensed sections, where they appear to coincide. This relationship becomes more evident in expanded clastic intervals, rapidly deposited under fluviatile sedimentary regimes, in which the datum marking the microfloral change clearly precedes the reptilian extinctions. The corroborative evidence of radiometric age, youngest dinosaur remains and regional microfloral change favours placing of the Cretaceous–Paleocene boundary at the base of the Ardley seam No. 14 in Alberta.
The petrology of the Tilting Harbour igneous complex, Fogo Island, Newfoundland
Authors: Cawthorn R. Grant
Published: April 2011

The Tilting Harbour complex, Fogo Island, Newfoundland, displays a mineralogical range from olivine-bearing pyroxenites to diorites. The engulfing granite is not genetically related to the complex. On field, petrographic and chemical evidence the complex can be divided into two distinct series. The older magma is of quartz tholeiite composition with an Mg/(Mg + Fe) ratio consistent with derivation directly from the mantle by melting under fairly low pressure (10 kbar (10 × 105 kPa)) under hydrous conditions. The second magma is of olivine tholeiite composition and produced magnetite-rich gabbros. It is not a primary melt from the mantle. Subsequent differentiation produced a range of liquids from olivine-normative to silica-rich, which is best explained by hornblende fractionation. Both magma series gave rise to websterite cumulates. However, the removal of pyroxene did not produce a significant change in residual liquid composition. The Ni content of the quartz-tholeiite magma is 75 ppm and suggests a partition coefficient of about 40 between mantle olivine and the liquid. The pyroxenes that crystallized from both liquids contained five times the Ni content of the magma. The partition coefficients for Ni and Cr between hornblende and liquid, determined from the chemical variation of the magnetite-rich gabbro suite, are both approximately 2.The contamination of the granite by melting of microdiorite was selective, only the fusible constituents being assimilated while refractory components were not incorporated.
Détermination du bore inorganique dans l'Estuaire du Saint-Laurent
Authors: Pelletier E. , Lebel J.
Published: April 2011

A precise and accurate method for the determination of inorganic boron in estuarine and coastal waters has been developed. The method takes into account the effects of ionic interactions in seawater on the electrode's junction potential, and on the ionization constant of the mannitol–borate complex. The analytical error is less than ±0.3% over the range of 0.35–4.45 mg B/kg seawater. This method, applied to 42 samples from the St. Lawrence Estuary, has allowed us to show that the B–Cl ratio varies in the region studied, and to localize regions that are deficient in dissolved inorganic boron.
The Gander Lake and Davidsville Groups of northeastern Newfoundland: a re-examination
Authors: Pajari G. E. , Currie K. L.
Published: April 2011

The three-fold division of supracrustal rocks in northeastern Newfoundland into gneiss complex, Gander Lake Group and Davidsville Group is valid and useful. The gneiss complex and Gander Lake Group are separated from the Davidsville Group by a steeply west-dipping reverse fault that was active in Devonian time, but inactive by Carboniferous. Northwest of the fault the ocean floor sequence of ultramafites, mafic volcanic rocks with minor plagiogranites and turbidites of the Davidsville Group proper were disturbed by olistostromes and tectonic slides beginning in late Ordovician time. However, the peak of progressive metamorphism, accompanied by granitoid intrusion and final tectonic emplacement, occurred in the Devonian. Southeast of the fault, the gneiss complex was metamorphosed to sillimanite grade before deposition of the Gander Lake Group. Later metamorphism, affecting both the gneiss complex and Gander Lake Group, was associated with emplacement of megacrystic granite and extended from Devonian into early Carboniferous time. The Gander Lake Group may be time-equivalent to the Davidsville Group. There is no direct evidence either for or against a previously reported late Precambrian to early Phanerozoic orogeny. The observed relations are compatible with obduction of oceanic material in late Ordovician time.
Foraminifera–mollusc associations in eastern Chaleur Bay
Authors: Schafer C. T. , Wagner F. J. E.
Published: April 2011

Common associations of mollusc and Foraminifera species were investigated in eastern Chaleur Bay, Gulf of St. Lawrence. Three depth-related biotopes are recognized. The distribution of species in this open bay environment appears to be controlled by substrate and (or) water mass characteristics. North–south differences in shallow water assemblages are related to summer bottom water temperature; calcareous Foraminifera and molluscs dominate in relatively high temperature environments. The influx of cold water (<1 °C) at intermediate depths (40–80 m) is reflected by an increase in the abundance of arenaceous Foraminifera species such as Reophax scottii, and by the absence of numerous mollusc species that are found at these depths elsewhere. A deep bay biotope (>80 m) can be recognized primarily on the basis of the mollusc species Yoldia limatula and Periploma fragile in association with the Foraminifera species Islandiella islandica. The observed mollusc–Foraminifera associations can be applied to paleoenvironmental and biostratigraphic studies of north temperate Holocene marine sediments.
Paleoecology of Dinosaur Provincial Park (Cretaceous), Alberta, interpreted from the distribution of articulated vertebrate remains
Authors: Béland P. , Russell D. A.
Published: April 2011

The distribution of articulated remains of fossil vertebrates is not uniform within the Oldman Formation (Campanian, Cretaceous) of Dinosaur Provincial Park, Alberta. The mesofauna gradually declines in importance from the west to the east, but a corresponding decline in megafauna does not occur until the eastern limit of the park is reached. The mesofauna is also impoverished low in the exposed section, although the megafauna is as abundant there as in higher levels. Woody vegetation may have supported 88% of the megafaunal herbivore biomass. A fine-grained mosaic of several vegetational types was superimposed on a broader west–east gradient of marsh–forest with an abundant mesofauna to an open woodland dominated by hadrosaurids. High densities of large ectothermic dinosaurs would have made intensive use of available vegetation and profoundly influenced landscapes. Distributions of vertebrates in sedimentary units resulting from normal environmental gradients should be distinguished from those postulated to be associated with the onset of changes that brought the Mesozoic to a close.
Nature and genesis of mudboils, central Keewatin, Canada
Authors: Shilts William W.
Published: April 2011

Mudboils are round lo elongate, 1–3 m diameter bare soil patches that form on perennially frozen till, marine clayey silt, colluvium, or other poorly sorted sediments (muds) with significant silt and (or) clay content. In Keewatin these muds have low liquid limits (< 20%) and limited plasticity indices (< 10%). Natural moisture contents are very near the liquid limit so that the muds liquefy and flow readily in response to slight changes in moisture content or slight internal or external stresses. When the stresses cannot be readily relieved by downslope movement, mud may burst through a rigid surface layer or carapace, creating or maintaining a mudboil.Ideally, the structures of a mudboil include: (1) an outer turf or stone ring, the type of ring depending on the stoniness of the mud and severity of the climate; (2) a thawed mud substrate (TMS), lying between the permafrost table and a rigid surface layer; (3) a carapace, a semi-rigid, sandy, desiccated layer averaging 30–40 cm thick; and (4) a diapir, in the case of active mudboils, which marks a zone of intrusion of mud from the TMS through the carapace.Driving pressures for diapirism may result from hydrostatic or artesian pressures on a slope, from excess pore-water pressures due to rain or thawing ice lenses, or from loading by animals or man.The shapes of mudboils are controlled principally by slope, the steeper the slope, the more elongate the boil; the nature of their borders depends on the texture of mud, its thickness over bedrock, exposure to tundra fires, and on the suitability of local climate for growth of vegetation.The degree of activity of a mudboil is largely related to the amount of clay and silt in the mud, the steepness of the slope on which it is located, and the amount of moisture available to the mud during the thaw season.
A critical appraisal of Archean basin–craton complexes
Authors: Walker Roger G.
Published: April 2011

Attempts have recently been made to define basins in the Superior Province. Criteria for outlining basin margins include the presence of oxide iron-formations, coarse clastic deposits, and felsic volcanics. However, oxide iron-formations commonly occur with turbidites in deep water, and do not define basin margins. Coarse clastics occur in two environmental settings in the Superior Province — subaerial alluvial fans and deep water submarine fans. They can only be used as basin margin indicators in the most general way. In many areas, submarine fan conglomerates stratigraphically overlie alluvial fan conglomerates, implying rapidly migrating 'basin margins' through time. An unjustified assumption has also been that the coarse clastics in any one 'basin' are time-equivalent. If they are diachronous, they do not necessarily define any one particular basin margin. There appears to be no a priori reason why felsic volcanics should mark basin margins unless the tectonic style of the basin has been assumed beforehand.Published maps of Archean basins purport to show the above facies associations at the 'margins'. Reexamination of the data shows that outlining the 'basins' is highly subjective, and that even in well mapped areas (Abitibi and Wabigoon basins), interpretation is ambiguous. Instead of an Archean craton in the Superior Province with many small basins, the data also suggest an Archean ocean with many small landmasses. Some of these are sialic and quiescent, some sialic with active volcanism, and some are entirely volcanic.
Computer simulation and sedimentological implications of burrowing by Axius serratus
Authors: Risk Michael J. , Venter Ronald D. , Pemberton S. George , Buckley Dale E.
Published: April 2011

Axius serratus, a burrowing shrimp capable of living in areas so polluted that other benthic organisms are excluded, has a probable range along the Atlantic coast of North America from Massachusetts Bay to the Arctic. Results of computer simulation of burrowing patterns and rates, based on field data, suggest the possibility of extensive sediment reworking in regions of high Axius densities. Computed rates of sediment overturning, compared with core data, indicate that high densities of Axius in the Strait of Canso area are a recent phenomenon probably connected with recent environmental degradation. Axius serratus may have potential as a pollution-indicator species.
40Ar/39Ar incremental-release ages of hornblende and biotite from Grenville basement rocks within the Indian Head Range complex, southwest Newfoundland: their bearing on Late Proterozoic – Early Paleozoic thermal history
Authors: Dallmeyer R. D.
Published: April 2011

Hornblende and biotite from autochthonous basement rocks within the Indian Head Range complex of southwest, insular Newfoundland record undisturbed 40Ar/39Ar release spectra with average total-gas ages of 880 Ma (hornblende) and 825 Ma (biotite). These gas-retention ages date the times when this segment of the western Appalachian basement terrane cooled below hornblende and biotite argon retention temperatures (~500 °C and ~300 °C respectively) following culmination of the ~ 1150–1100 Ma Grenville metamorphism. Although these results indicate that elevated temperatures were maintained for a prolonged period following the Grenville thermal peak, once initiated, cooling must have been relatively rapid because hornblende and biotite record generally similar total-gas dates.The undisturbed release spectra of minerals within the Indian Head Range complex indicate that this segment of the western Appalachian basement terrane was not affected by Paleozoic metamorphism. This is consistent with recent tectonic models that indicate that the overlying Humber Arm allochthon was emplaced into its present position as a cold, already assembled structural unit. Lack of Paleozoic metamorphism within the Indian Head basement rocks is also compatible with suggestions that the obduction site of the Bay of Islands ophiolite lay considerably east of the Early Paleozoic continental margin of North America.
Oldest known brachiopod burrow: the Lower Cambrian of Labrador
Authors: Pemberton S. George , Kobluk David R.
Published: April 2011

A specimen of the ichnospecies Lingulichnus verticalis was recovered from the Lower Cambrian Bradore Formation of southern Labrador. The sample represents the only known Cambrian example of an in situ lingulid, and sheds light on the evolution of the ethology of lingulids. Prior to this it was assumed that Cambrian lingulids maintained a non-burrowing mode of life.
Viséan limestones front the Newfoundland Shelf
Authors: Jansa L. F. , Mamet B. , Roux A.
Published: April 2011

Three short cores of Windsor Group carbonates from the northeast Newfoundland Shelf yielded Late Viséan foraminifers of Zones 15 and 16Inf. This most northeastward occurrence of the marine Lower Carboniferous on the American continent has foraminifers identical to those reported from Windsor carbonates exposed in southwestern Newfoundland and Nova Scotia. The foraminifera belong to the North American realm and not to the Tethyan realm. The algae are exceptionally well preserved. Except for a single species, they are also 'American' and not Tethyan. This confirms that the proto-Atlantic effectively separates the North American and Euro–African continental blocks in Early Carboniferous time.
A Huronian outlier in the Goulais River area, District of Algoma, Ontario
Authors: Grunsky E. C. , Arengi J. T.
Published: April 2011

An outlier of sedimentary rock assigned to the Gowganda Formation of the Huronian Supergroup was discovered during field mapping in the Goulais River area, District of Algoma, Ontario. This outlier is the northernmost documented occurrence of Huronian sedimentary rocks in the Algoma region. The outlier is 53 m in stratigraphic thickness and consists of polymictic to oligomictic paraconglomerate and orthoconglomerate with interbeds of pink arkose, siltstone, and dark grey greywacke. The conglomerates contain metavolcanic fragments and altered feldspars that suggest part of the sediment had a nearby source. Hematite results in a pink matrix in both conglomerates and arkosic interbeds and may indicate that an oxidizing environment prevailed during deposition. Air photo interpretation may help locate other outliers in the vicinity of lineaments, faults, or topographic highs.
Compositional variability of Glacier Peak tephra and its stratigraphic significance
Authors: Westgate J. A. , Evans M. E.
Published: April 2011

Glacier Peak Volcano erupted many times during the period from ~11 000 to ~13 000 years ago and produced at least Three widespread tephra layers that serve as valuable stratigraphic markers in northwestern United States and the adjacent plains of southwestern Canada. Each of these units can be recognized by their stratigraphic, petrographic, and chemical attributes.Tephra was shed over eastern Washington, northern Idaho, western Montana, and southernmost Alberta during each of the eruptions responsible for the older two units; the other layer was deposited during the youngest and most violent event that directed tephra to the southeast as far as Yellowstone National Park, ~950 km from the volcano.Chemical data on glass, hornblende, hypersthene, feldspar, magnetite, and ilmenite show a systematic and unidirectional trend in tephra composition with age; earlier eruptions produced slightly more acidic tephra. This age–composition relationship is confirmed by palaeomagnetic data obtained from 116 specimens collected from two 5 m thick sections. It should therefore be possible to determine the relative age of Glacier Peak tephra samples by their composition alone.The chronology of the Glacier Peak eruptive sequence is still poorly understood. This is especially true of the oldest unit which has so far only been found in southeastern Alberta. Proximal occurrences should be sought in the bogs of eastern Washington where prospects of preservation and age definition are optimised.
Provenance of Ordovician deep-water sandstones, Tourelle Formation, Quebec, and implications for initiation of the Taconic orogeny
Authors: Hiscott Richard N.
Published: April 2011

The Lower Ordovician Tourelle Formation crops out on the Gaspé Peninsula in the allochthonous external domain of the Quebec Appalachians. Coarse sandstone beds dominate this submarine fan deposit, and contain immature detritus (volcanic fragments, radiolarian chert, amphiboles, pyroxenes, chromite) shed from initial uplifts within the Taconic orogenic belt. Pre-Tourelle sediments were eroded directly from a Lower Paleozoic Grenville-type craton and its fringing carbonate bank. Recycling of these sediments provided the bulk of the detritus found in the Tourelle sandstones.Volcanic rock fragments comprise 4% of framework grains. They are intermediate to acid in average composition, contain primary biotite, and record prehnite–pumpellyite grade metamorphism in the source area. This volcanic source also contributed fresh angular plagioclase (albite) to the Tourelle sand fraction. The volcanic source was probably an ensialic arc associated with the closing of the Iapetus Ocean, and is tentatively identified with the Cambrian to Middle Ordovician Tetagouche volcanics of northern New Brunswick.In addition to rounded, recycled grains of zircon, tourmaline, garnet, and sphene, the Tourelle heavy mineral suite contains prismatic hornblende, hypersthene, and clinopyroxene. These minerals may have been derived from arc lavas, their intrusive equivalents, or from an obducted ophiolite sheet. Ophiolite obduction and erosion is preferred because the [Formula: see text] heavy mineral population contains 18% chromite, or 8.2 × 10−4 g Cr/cm3 sandstone. This is 1/15 the chromite concentration of peridotite, an essential component of any ophiolite suite.Provenance criteria for these syn-orogenic sandstones require a plate tectonic model involving southeastward subduction beneath a block of continental crust, and emplacement of ophiolite. Previous models for the Quebec Appalachians are unable to account for detrital composition of Tourelle sands and must undergo major modification.This paper reveals that sedimentary petrography is essential to satisfactory unravelling of orogenic history. Neglect of sediment composition may invalidate tectonic reconstructions based solely on stratigraphic and structural considerations.
Petrography and mechanism of eruption of the Archean Dalembert tuff, Rouyn–Noranda, Quebec, Canada
Authors: Dimroth Erich , Demarcke Janet
Published: April 2011

We investigated the petrography of the Dalembert tuff, an assemblage of pyroclastic flows, in two sections named the Dalembert and Reneault sections. Tuffs in the Dalembert section consist of pumice, plagioclase crystals, and a polymict assemblage of lithic fragments probably derived from sub-aerial lavas. The size of plagioclase quench crystals varies somewhat across a thick (about 15 m) graded unit, proving eruption of hot pumice flows, but the tuffs are unwelded. The features suggest the eruption of overflowing glowing avalanches, and emplacement of the cold tuff under the sea.Plagioclase-phyric basaltic andesite, very similar to the pumice of the Dalembert section except for its poor vesiculation, comprises more than 95% of the tuffs in the Reneault section. A few dacite fragments are the accessory component. These features suggest derivation from collapsing domes or spines.The Dalembert section is representative of the Dalembert tuff as a whole, whereas the facies exposed at Reneault is a local variant. We suggest that the eruption began with formation of an overflowing glowing avalanche from a fissure on a volcanic island. Volatile content of the magma decreased and viscosity increased during the eruption. Spines and domes of viscous andesite lava extruded in the terminal stage and their collapse produced a local mantle of debris represented by the tuffs at Reneault. The feeding fissure is located close to and south of the Reneault section.
Cretaceous marine Teleostei from the basal Kanguk Formation, Banks Island, Northwest Territories
Authors: Wilson Mark V. H.
Published: April 2011

A marine teleostean assemblage, from within 2 m of the base of the Upper Cretaceous Kanguk Formation on Banks Island, is dominated by scales of Osmeroides? transversus and Ichthyodectes ctenodon, as well as bones of a primitive teleost tentatively referred to the salmoniforms. The fish indicate a shallow, calm paleoenvironment. Possible mechanisms of deposition include aerobic flotation decay, scale loss by living fish, and deposition of carnivore feces. The assemblage indicates a Cenomanian or Turonian age for the basal Kanguk, with an Early Turonian age preferred by correlation with the late Early Turonian fishes of Lac des Bois, Northwest Territories.
Pleistocene grebes from the Old Crow Basin, Yukon Territory
Authors: Fitzgerald Gerald R.
Published: April 2011

Four grebe fossils of presumed late Pleistocene age are reported from the Old Crow Basin. They include one Red-necked Grebe (Podiceps grisegena), two Horned Grebes (Podiceps auritus) and an unidentified grebe (Podiceps sp.). Three of the specimens have a minimum age of approximately 10 700 years BP.
Rock and paleomagnetic evidence for the existence and nature of a Cayman Trough spreading center
Authors: Clark M. J. , Hall J. M. , Peirce J. W.
Published: April 2011

Rock and paleomagnetic measurements have been made on a set of 54 basalts dredged from 17 stations located within the central valley of the Cayman Trough. Seventeen of the samples could be oriented with respect to the in situ vertical by the use of lava cooling ledges and stalactites.Peak remanent intensities in the Cayman Trough are lower than peak Mid-Atlantic Ridge values by a factor of 2 or 3 even after allowance is made for the latitudinal variation in geomagnetic field intensity. This difference is likely to be the result of the combined effects of relatively low saturation magnetization and more advanced low temperature oxidation of titanomagnetite in the Cayman Trough basalts.Five young, reversely magnetized basalts, similar to those found on the Mid-Atlantic Ridge, occur in the Cayman Trough sample set.Plots of the magnetic parameters of the pillow basalts with distance from the axis of the trough show broad highs or lows associated with the axis. Our interpretation is that crustal formation in the central valley has occurred recently, but it has either been rather diffuse or is now much disturbed tectonically on a small scale in comparison with the Mid-Atlantic Ridge. Analysis of the distribution of Curie temperatures suggests that crustal accretion has been slow (0.1–0.4 cm year−1 half-rate) and may have ceased in the area studied at about 0.6 Ma BP.
Radiocarbon dating of Nipissing Great Lakes events near Sault Ste. Marie, Ontario
Authors: Cowan W. R.
Published: April 2011

In 1863 Logan, Murray, Hunt, and Billings reported buried organic detritus near Goulais Bay, Ontario. Several exposures located along the Goulais River were examined in 1976. Radiocarbon analyses of wood from three sites gave dates of 6490 ± 100 (BGS-373); 6550 ± 100 (BGS-417); 7310 ± 110 (BGS-416), and 5430 ± 100 (BGS-498) (BGS:Brock University Geological Sciences). The wood was derived from silts and sands interpreted as overbank alluvium; these are overlain by deltaic sediments of the Nipissing Great Lakes. The alluvial sediments were deposited by a meandering river graded to lake levels in the Superior basin, which were initially about 15 m below the Nipissing shore (197 m at Sault Ste. Marie). This initial level was apparently controlled by the St. Marys River sill (now 181 ± m). Similar organic materials obtained from Garden River sections (Huron basin) were dated at 7260 ± 110 (BGS-413) and 5120 ± 100 (BGS-414); these occupy a similar stratigraphic position to those of Goulais River except they are 18–20 m below the Nipissing shoreline, i.e., related to a Huron basin outlet. A date of 4610 ± 90 (BGS-374) was obtained on a wood sample from the base of the Nipissing bluff at Sault Ste. Marie. The dates represent alluviation in meandering river systems from 7400–5000 years BP followed by burial as lake levels rose to the Nipissing level.
Three-dimensional gravity analysis of the Kiglapait layered intrusion, Labrador
Authors: Stephenson Randell , Thomas Michael D.
Published: April 2011

The Kiglapait basic layered intrusion in northern Labrador previously has been interpreted, on geological grounds, to be a lopolith with a maximum thickness of 8.7 km. It is associated with a large (~45 mGal) positive gravity anomaly that for the most part is very similar to a theoretical anomaly computed for the proposed lopolith model, except over the southeastern part of the exposure where the theoretical anomaly is significantly more positive. Model studies of the gravity data suggest that the form and dimensions of the lopolithic model predicted on geological criteria are essentially valid and that a granitic intrusion is present in the southeastern region of the lopolith causing the discrepancy between observed and theoretical anomalies. The latter intrusion is believed to be genetically related to the Manvers granite, which occurs throughout the southeastern region as dykes and small stocks. The presence of another buried granitic mass south of the Kiglapait intrusion is also suggested by the gravity data.
Discrimination between extrusive and intrusive Archean ultramafic rocks in the Shaw Dome area using selected major and trace elements
Authors: Muir T. L.
Published: April 2011

The ultramafic rocks in the Shaw Dome area, southeast of Timmins, Ontario, are divided on the basis of held criteria into two groups for the purpose of comparing their chemical compositions: (1) extrusive ultramafic rocks consisting of peridotitic komatiites and (2) intrusive ultramafic rocks, consisting of dunites and lherzolites.The two groups can be distinguished on a chemical basis by graphical and statistical methods which provide accuracies of extrusive–intrusive classification of about 92 and 96% respectively. Both methods provide qualitative and quantitative aspects of discrimination.The discriminating parameters were developed using samples which show all types and degrees of alteration that are common in ultramafic rocks. Preliminary studies indicate that the genera! procedure for chemical discrimination between extrusive and intrusive ultramafic rocks may be applicable to similar Archean rocks from other areas.In addition, the separation provides an aid to exploration for minerals such as nickel sulphides, asbestos, magnesite, and gold which may be largely restricted to either extrusive or intrusive ultramafic rocks.
Mammals from the Upper Cretaceous Oldman Formation, Alberta. II. Pediomys Marsh (Marsupialia)
Authors: Fox Richard C.
Published: April 2011

Pediomys Marsh, a primitive marsupicarnivore, is the most common therian mammal known from the Upper Cretaceous Oldman Formation, Alberta, where it is represented by at least four species. The first, P. clemensi Sahni, appears closely related to the Lancian P. cooki Clemens; other species, poorly represented by fossils, resemble the Lancian P. elegans Marsh and P. hatcheri respectively; a final species, which is new, is interpreted as the direct ancestor of the Lancian P. krejcii Clemens. Pediomys shows trends toward enhancement of a crushing rather than a shearing function of the postcanine dentition and, consequently, seems not ancestral to the Cenozoic 'dog-like' marsupials of Australia and South America, contrary to recent suggestions elsewhere.
Ferromanganese concretions in Shebandowan Lakes, Ontario
Authors: Sozanski A. G. , Cronan D. S.
Published: April 2011

Shebandowan Lakes, Ontario, are the site of at least 49 shallow (2–12 m) ferromanganese concretion deposits, widely distributed throughout the 48 km of the watercourse.X-ray diffraction and Mössbauer methods have revealed the presence of goethite in some of the concretions. Chemical analyses of the acid soluble portions of 72 samples gave an average composition of 43.1% Fe and 5.65% Mn with a low content of trace elements. The Shebandowan concretions are among the richest in iron of lake concretions reported, possibly because only the acid soluble portion was analysed. Their low content of trace elements suggests rapid growth rates and a relatively young age. A positive correlation was found between Mn and K, Ca, Mg, Cu, Ni, and Co and the relationship between the last three and Mn was deemed significant. Zn was independent of association with either Mn and Fe, probably due to the presence locally of zinc sulphide deposits.Analyses of lake bottom and influent waters suggested that frequent resampling of the sites would be required throughout the year to permit meaningful interpretation of the effect of water composition on the composition of concretions. Analyses of sediment cores from 20 concretion sites indicated an upward increase in Fe and Mn and in the Mn/Fe ratio, consistent with the model of upward migration of the elements, where Mn is more mobile than Fe.This study concludes that a considerable proportion of the elements have been supplied to the Shebandowan concretions via the diagenetic process; generally a minor fraction of the elements has been abstracted directly from the superjacent water.
Late Precambrian ash-flow tuffs and associated rocks of the Harbour Main Group near Colliers, eastern Newfoundland: chemistry and magmatic affinities
Authors: Nixon G. T. , Papezik V. S.
Published: April 2011

The Colliers Peninsula, a typical area in the western part of the Harbour Main Group in eastern Newfoundland, is underlain by three steeply-dipping sequences of ash-flow tuffs 250–500 m thick, separated by clastic sediments, conformably overlain by subaerial mafic flows and cut by small bodies of high-level intrusive rocks rich in plagioclase phenocrysts. All rocks are of low metamorphic grade.The two lower pyroclastic sequences have a bulk composition of rhyolite and alkali rhyolite; they contain phenocrysts of albite, quartz, and biotite. Na/K ratios are highly variable; the albite crystals may be pseudomorphous after anorthociase. The upper sequence, rhyodacitic in bulk composition, has lower Si and higher Na; it lacks quartz and biotite phenocrysts but contains small amounts of calcic augite and altered olivine. The mafic flows (50% SiO2) show high Al and alkalies and low Ca and Ti. The porphyritic intrusives have 60–65% SiO2, but their bulk chemistry is otherwise similar to that of the ash-flow tuffs.The present composition of the rocks reflects complex chemical adjustments, both contemporaneous with and subsequent to the magmatic event. However, mineralogical and chemical data and trends considered to be a part of the original magmatic heritage are consistent with suggestions that the western (probably lower) part of the Harbour Main volcanic pile was formed in a continental, extensional tectonic environment.
Development of cleavage in the Banff Formation at Pigeon Mountain, Front Ranges, Canadian Rocky Mountains
Authors: Spang J. H. , Oldershaw A. E. , Stout M. Z.
Published: April 2011

Cleavage in the Mississippian Banff Formation at Pigeon Mountain in the Front Ranges of the Rocky Mountains, Alberta, makes an average angle to bedding of 25 °with the pole to the cleavage approximately parallel to the transport direction of the McConnell Thrust. Detailed examination of the microfabrics that define the cleavage indicates that mechanisms of formation include dissolution, local precipitation in strain shadows, and rigid body rotations. Dissolution includes pressure solution of host rock at the immediate contact with thin, parallel, and anastomosing clay seams and passive solution in a zone up to 100 μm wide adjacent to the seams. Lens shaped pods of carbonate in all stages of dissolution along the clay seams appear to form part of a sequence of progressive coalescence of dissolution zones to form well defined tight cleavage with characteristically strong preferred orientation of clay platelets. The cleavage probably formed at a temperature of 150–280 °C and under a lithostatic pressure of less than 2 kbar (2 × 105 kPa).
New occurrences of two Lower Devonian graptolites from northern Yukon
Authors: Lenz Alfred C.
Published: April 2011

Two species of Early Devonian graptolites are described from the Richardson Mountains, northern Yukon Territory; these are ?Pristiograptus sp. and Monograptus fanicus Koren', the latter being reported for the first time from the northern Canadian Cordillera. Associated grapto lites as well as the presence of M. fanicus indicate a Pragian age. The presence of M. fanicus helps fill the zonal gap between the late Lochkovian hercyniens Zone, and probable late Pragian thomasi and yukonensis Zones, and suggests that lower and upper Pragian substage divisions are possibly recognizable in the graptoiite facies.