bluuebunny/crossref_metadata_2025 huggingface dataset:
Geochemistry of the upper Snooks Arm Group basalts, Burlington Peninsula, Newfoundland: evidence against formation in an island arc
Authors: Jenner G. A. , Fryer B. J.
Published: April 2011

The Snooks Arm Group of the Newfoundland Appalachians, which includes the Betts Cove ophiolite at its base, has been interpreted as oceanic crust overlain by island arc volcanic and sedimentary rocks. The limited geochemical data available on the upper Snooks Arm Group basalts have been used as evidence for and against their formation in an island arc environment.Reinvestigation of the chemistry of the basaltic rocks of the upper Snooks Arm Group establishes them as large ion lithophile enriched tholeiites. Similar basalts have been found in oceanic islands, on aseismic ridges, and possibly in back-arc basins. Chemically analogous rocks are notably lacking from island arc settings.The geochemistry and geology of the upper Snooks Arm Group suggest that these rocks may have formed in either an oceanic island setting or, as recently suggested by Upadhyay and Neale, as part of a marginal basin. It is not possible to distinguish between these alternate models, although the most similar basaltic rocks occur in the former environment. It is most unlikely that these rocks formed in an early island arc setting and indeed there may be no need for them to be associated with a major subduction zone.
Buried ocean crust and continental crust geomagnetic induction anomalies: a possible association
Authors: Drury M. J. , Niblett E. R.
Published: April 2011

Geomagnetic induction surveys have indicated the presence of several areas where electrical resistivity in the continental crust is abnormally low. Several such anomalies occur either along present continental margins or over postulated aulacogens (failed rifts), where the low resistivities cannot be explained by elevated temperatures. This implies a close association between the site of anomalies and former plate boundaries, areas where buried ocean crust might occur in the present continental crust. It is suggested that the low inferred resistivities might arise from the presence of such buried hydrated ocean crust. A resistivity profile model for a layer of ocean crust embedded in continental crust is developed, and a number of induction anomalies which might be explained by the model are discussed.
The origin of hummocks, western Arctic coast, Canada
Authors: Mackay J. Ross
Published: April 2011

Hummocks (nonsorted circles) are widely distributed in arctic and subarctic regions. The hummocks under discussion are composed of fine-grained frost-susceptible soils; the late summer frost table is bowl-shaped; and the hummocks grade from those which are completely vegetated (earth hummocks) to those with bare centres (mud hummocks). The mound form is usually attributed to an upward displacement of material resulting from cryostatic (freeze-back) pressure generated in a confined, wet, unfrozen pocket of the active layer. Theoretically, cryostatic pressure should not develop in a frost-susceptible hummock soil, because ice lensing at the top and (or) bottom of the active layer will desiccate the last unfrozen pocket so that the pore water is under tension, not pressure. Field observations carried out at Garry Island, Northwest Territories, for 1965–1979 and for 1967–1979 at Inuvik, Northwest Territories, involving: summer and winter excavations; the measurement of the deformation of tubes, soil pressure, soil temperature, soil heave, soil moisture migration; and observations on hummock stability provide no field evidence for the cryostatic theory. An alternative model of hummock growth, based upon field observations, is here proposed. The upward displacement of material is believed caused by freeze–thaw of ice lenses at the top and bottom of the active layer with a gravity-induced cell-like movement, because the top and bottom freeze–thaw zones have opposite curvatures. The cell circulation is evident from the grain-size distribution of hummock soils and from upward-moving tongues of saturated soil observable in late summer. The most active period is in late summer. Model experiments in the laboratory have been successful in producing mounds by freeze–thaw of a kaolin slurry in a bowl-shaped container in support of the proposed theory.
Impregnation technique using colored epoxy to define porosity in petrographic thin sections
Authors: Gardner Kenneth L.
Published: April 2011

This vacuum-assisted technique for colored impregnation of all rock types clearly defines porosity, even in low-permeability, very fine grained, or semifriable material. The technique is also suitable for use with water-soluble and heat-sensitive material. The technique is trouble-free and provides a practical way of visually reproducing rock pore space less than 1 μm in size.
Evolution of physiography and drainage in southern Yukon
Authors: Tempelman-Kluit Dirk
Published: April 2011

The physiography of southern Yukon is dominated by upland plateaux and plateau remnants that probably evolved in the Tertiary, culminating in a mature erosion surface about Miocene time. Variations in the elevation of this surface are thought to result from uneven uplift and faulting in the Late Miocene or Pliocene. The Tintina and Shakwak Trenches are young grabens superposed on the upland and the mountain ranges are youthful dissections of raised parts of the plateau.In the Miocene, water from central Yukon probably drained to the coast across the region occupied by the St. Elias and Coast Mountains. About the late Miocene, general uplift occurred and the St. Elias and Coast Mountains rose unevenly above interior parts of the Yukon. As a consequence, the drainage became entrenched. During deglaciation, ice in the St. Elias outlasted that in the interior and this forced derangements of the entrenched stream system. It was abandoned in favour of the less direct northwest drainage of today. The northwest drainage persists, but is unstable and in danger of capture by more vigorous streams that flow directly to the coast.
Reinterpretation of the North American apparent polar wander curve for the interval 800–1500 Ma
Authors: Berger Glenn W. , York Derek
Published: April 2011

We have reviewed the geochronology of rocks having paleopoles in the interval 800–1500 Ma from North America, Greenland, and the Baltic Shield. The present uncertainties in the acquisition times of the remanent magnitizations allow the construction of a simplified apparent polar wander curve for North America that incorporates Sveconorwegian paleopoles in a Grenville Loop, and that places poles from the El Paso, Stoer Group, and Aillik Bay rocks on the Logan Loop. Furthermore, the sense of motion through poles older than ~ 1.3 Ga is reversed to permit the shortest connection to poles older than 1.6 Ga. As well, the timing and shape of the Hadrynian Track are modified so that it begins in the Atlantic hemisphere at ~ 800 Ma and terminates in the Pacific at ~ 650 Ma, representing a minimum average continental drift rate of ~ 10 cm/year for this interval.
The Nipissing transgression around southern Lake Huron
Authors: Karrow P. F.
Published: April 2011

South of the Lake Algonquin hinge line through Bad Axe, Michigan, and Grand Bend, Ontario, a prominent lake terrace at about 183 m (600 ft) has been previously attributed to formation by Lake Algonquin about 11 000 years ago. Radiocarbon dates and mollusc assemblages in near-shore lacustrine sediments on the terrace indicate formation by the Nipissing stage, about 5000 years ago. The gradual and vigorous Nipissing transgression extensively removed and destroyed the older Algonquin features.
A cluster analysis interpretation of Middle Ordovician biofacies, southern Mackenzie Mountains
Authors: Hayes Brad J. R.
Published: April 2011

Collections of fossil trilobites, ostracods, bryozoans, and conodonts from Chazyan and Blackriveran strata of the southern Mackenzie Mountains are analyzed in an attempt to define biofacies, in terms of areal extent and faunal composition. Q-mode and R-mode cluster analyses, using Jaccard's coefficient and the unweighted pair-group method of clustering, are employed to delineate five biofacies. The interpretation of sedimentological features and composition of faunal assemblages shows that one nearshore biofacies, three progressively deeper shelf biofacies, and one continental slope biofacies are represented. A plot of biofacies succession through time in each measured section provides added support for the biofacies interpretations.
Late-glacial regional ice-flow patterns in eastern Ontario
Authors: Gadd Nelson R.
Published: April 2011

Reconnaissance of eastern Ontario regions lying between the late-glacial positions of Lake Iroquois and the Champlain Sea provides new information on ice-flow patterns as represented by striae and other streamline phenomena. This is related to the distribution of ice-marginal deposits and to structurally controlled topography. Two ice lobes, Madawaska Highland lobe and Ottawa – Lake Ontario lobe, are identified, and the Oak Ridges interlobate moraine system is extended. Discussion of apparent sequences of events allows for a new working hypothesis, including the concept of a calving bay in Ottawa Valley, for the development of the Champlain Sea, and for the timing of the drainage of Lake Iroquois. It reconciles radiocarbon dates previously thought to be anomalous.
Bridge River tephra: revised distribution and significance for detecting old carbon errors in radiocarbon dates of limnic sediments in southern British Columbia
Authors: Mathewes Rolf W. , Westgate John A.
Published: April 2011

Ash-grade Bridge River tephra, identified as such on the basis of shard habit, modal mineralogy, and composition of ilmenite, occurs in sedimentary cores from three lakes located to the south of the previously documented plume and necessitates a significant enlargement of the fallout area of that tephra in southwestern British Columbia.These new, more southerly occurrences are probably equivalent to the ~2350 year old Bridge River tephra, although it can be argued from the evidence at hand that the 14C dates and biotite-rich nature support relationship to a slightly earlier Bridge River event.Large differences exist in the 14C age of sediments immediately adjacent to the Bridge River tephra at these three lake sites; maximum ages of 3950 ± 170 years BP (GX-5549) and 3750 ± 210 years BP (I-10041) were obtained at Phair and Fishblue lakes, respectively, whereas the corresponding age at Horseshoe Lake is only 2685 ± 180 years BP (GX-5757). The two older dates are considered to be significantly affected by old carbon contamination for the bedrock locally consists of calcareous sedimentary rocks and the lacustrine sediments are very calcareous. The 14C date from Horseshoe Lake, which occurs in an area of igneous rocks, appears to be only slightly too old relative to the ~2350 year old Bridge River tephra.Well-dated tephra beds, therefore, can be very useful in assessing the magnitude of old carbon errors associated with radiocarbon dates based on limnic sediments. Calcareous gyttja deposits beneath Bridge River tephra within the study area exhibit old carbon errors of the order of 1350–1550 years.
Correlation of gravity anomalies with Yellowknife Supergroup rocks, North Arm, Great Slave Lake
Authors: Gibb R. A. , Thomas M. D.
Published: April 2011

A gravity map compiled from observations made on the frozen surface of Great Slave Lake shows that the positive gravity anomaly associated with the Yellowknife greenstone belt extends offshore into the North Arm of the lake. On the western shore of Yellowknife Bay the axis of the anomaly coincides with mafic volcanic rocks of the Kam Formation. Offshore the axis continues southwards for about 10 km to the West Mirage Islands where it takes a dramatic turn to the southeast and continues for a further 60 km to the Outer Whaleback Rocks. Using the geology and rock density determinations on land for control, a three-dimensional geological model comprising a large number of prismatic blocks was derived from the gravity anomalies. In the model the simplifying assumption has been made that the greenstone belt is everywhere floored by granodiorite similar to the adjacent Western and South-east granodiorites. According to the model, mafic volcanic rocks of the Kam Formation are generally 1–3 km thick with a maximum thickness of 7 km at the mouth of Yellowknife Bay. Greywacke and mudstone of the Burwash Formation vary in thickness from 1 to 3 km. Locally these sedimentary rocks attain a thickness of 8 km but this is probably an overestimated value as they may very well be underlain by volcanic rocks of the Kam Formation. The presence of a third pluton of granodiorite flanking the belt to the southwest is also inferred from the gravity data. Previous seismic work indicated a greenstone basin with an average thickness of about 10 km. However, reexamination of the seismic records suggests that weak arrivals interpreted as originating from the base of the greenstone belt are more likely to be pulses associated with earlier arrivals.
Mobility of Morocco
Authors: Sichler Bertrand , Olivet Jean-Louis , Auzende Jean-Marie , Jonquet Hélène , Bonnin Jean , Bonifay Alain
Published: April 2011

The mobility of Morocco relative to Africa during the early history of the Atlantic has long been debated: arguments have been developed from Atlantic kinematic considerations and from paleomagnetic results. Both types of arguments are reexamined here. Using a new model of the Atlantic Ocean evolution described elsewhere, it is shown that the reconstructions of the positions of Africa relative to North America before the Atlantic opening, and at the times of magnetic anomalies M22 and J, do not imply a major motion of Morocco independent of Africa during these periods of time. The corresponding geomagnetic paleopoles have been recomputed from sample sites located on both "mobile" Morocco and "stable" Africa. The results indicate that the virtual geomagnetic pole of "mobile" Morocco for the Liassic falls within the 95% confidence cone of "stable" Africa. It is thus concluded that no major movement has occurred between "mobile" Morocco and "stable" Africa during the early phases of opening of the central Atlantic Ocean. This is in accordance with the field geological observations on the South Atlas fault; however, limited motion along this lineament, as observed in the field, is still compatible with the above conclusion, owing to the limited resolving power of both kinematic and paleomagnetic methods.
Geomagnetic depth sounding over the central Arctic Islands, Canada
Authors: DeLaurier Jon M. , Niblett E. R. , Plet F. , Camfield P. A.
Published: April 2011

In the spring of 1973, 3 days of simultaneous geomagnetic observations were obtained at six recording sites over the central Arctic Islands. The northern site, Isachsen, displayed the strong suppression of the amplitudes of short-period temporal variations in the vertical component that has been observed at Mould Bay, about 500 km to the southwest. One-dimensional conductivity models suggest high conductivities in the upper crust. Parkinson's arrows for short periods point to the inter-island channels of sea water but for long periods the arrows rotate to point to the deep Arctic Ocean. A large spatial variation of the in-phase correlated Z/H ratios is also observed along a profile across the central Arctic Islands. These ratios peak at the Cameron Island site, which is near the Sverdrup Basin – Franklinian Geosyncline geological boundary. In well-log resistivity data, a conductivity contrast of two orders of magnitude is observed across this margin. Electric currents therefore flow in the conductive sediments of the Sverdrup Basin and in the sea water in the inter-island channels. The electromagnetic response is similar to that near an ocean–continent margin but the peak response occurs "inland" by 300–400 km. Consequently, the margin of the resistive continent is located near the Franklinian – Sverdrup Basin boundary in the central Arctic Islands.
Paleomagnetism of Siluro-Devonian rocks from eastern Maine
Authors: Kent Dennis V. , Opdyke Neil D.
Published: April 2011

A diverse suite of rocks was collected for paleomagnetic study from two formations in the Eastport area of northeastern Maine: 18 sites (103 samples) from redbeds and diabase sills of the Hersey Formation (uppermost Silurian to Lower Devonian) and 14 sites (74 samples) from lavas, redbeds, and calcareous nodules of the Eastport Formation (Lower Devonian; Rb/Sr age 412 Ma). Characteristic magnetizations based on AF and thermal demagnetization analyses give mean directions, after simple correction for bedding tilt, of D = 163.6°, I = 41.3°, α95 = 6.3°, for N = 16 sites in the Hersey, and D = 179.3°, I = 38.0°, α95 = 9.4°, for N = 14 sites in the Eastport Formation. Baked contact relations, the presence of opposite polarities, and the similarity in directions over different rock types and magnetic carriers point to an acquisition of magnetization near to the time of rock formation. The mean directions correspond to (south) paleopole positions at 19.8°S lat., 308.8°E long. (δp, δm = 4.7°, 7.7°) for the Hersey and 23.7°S lat., 293.7°E long. (δp, δm = 6.6°, 11.1°) for the Eastport Formation.These paleopoles are removed from the Upper Silurian Bloomsburg Formation pole, but are in reasonable agreement with similar age results from central Newfoundland, suggesting that the Acadia displaced terrain encompassed these areas. Siluro-Devonian paleopoles from intrusive rocks in northeastern North America are generally widely divergent and these may not be providing an accurate record of paleomagnetic field in all cases.
Conditions of metamorphism in high-grade pelitic gneisses from the Frontenac Axis, Ontario, Canada
Authors: Lonker Steven
Published: April 2011

The Frontenac Axis is a southeasterly extension of the Grenville province of the Canadian Shield, which connects to the Adirondack Mountains in New York. A mineralogic and petrologic study of the high-grade pelitic gneisses in three sampled areas in the Westport and Gananoque map areas was undertaken to examine the dynamic nature of metamorphic and postmetamorphic history in the area. The mineral assemblages indicate pressures of 4–6 kbar, (4–6 × 105 kPa), temperatures of 675–800°C, and [Formula: see text] during peak metamorphism based on experimentally determined phase equilibria. Chemographic relations reveal that the highest grade rocks in southeastern Ontario (cordierite–orthopyroxene zone) are in the northeast corner of the Gananoque map area and in the area northwest of Gananoque. On the scale of a thin section, chemical equilibration has not been achieved as supported by chemical zoning, chemical heterogeneity, and absence of exchange equilibrium. On the scale of a rock, graphical analysis indicates that the continuous variation in the Mg/(Mg + Fe) ratio of ferromagnesian phases (assemblage: biotite + sillimanite + cordierite + garnet + quartz + alkali feldspar) is in response to temperature, which conceals any evidence of local gradients in [Formula: see text]. Different temperatures are recorded across a rock because of reequilibration during cooling. The direction of displacement of reactions that produce (1) the corona textures; (2) the chemical zoning associated with corona textures; and (3) the chemical zoning related to exchange reactions between adjacent phases, is consistent with a decrease in temperature, pressure, or both. Intermingling of incompatible assemblages and the widespread occurrence of six-phase AFM assemblages are due to disequilibrium produced by incomplete reaction during uplift and cooling.
The Flinton Group: a late Precambrian metasedimentary succession in the Grenville Province of eastern Ontario
Authors: Moore Jr. John M. , Thompson Peter H.
Published: April 2011

Clastic and carbonate metasediments, preserved in narrow synclines, have been correlated over an area of 2000 km2. These strata, the Flinton Group, lie unconformably on metamorphosed volcanic, clastic, and carbonate rocks, and on large granitic intrusions. The group, which comprises six formations, has undergone at least two major folding episodes and one main regional metamorphism of varying grade. The only post-Flinton intrusions are pegmatites at high grade and one tectonically emplaced ultramafic slice.Depositional environment ranged from fluvial to moderate-depth marine. Rapid facies changes, coupled with persistence of some units along strike and close relationships between facies and underlying lithology, point to local sources and local tectonic control of deposition basins. At the onset of sedimentation, a deeply weathered source terrain yielded mature basal redbeds, which were succeeded by less mature clastics as block faulting caused increase of relief between sources and basins. These facies passed offshore into finer, more reduced sediments. Deposition took place between 1050 and 1080 (±25) Ma ago, after arc volcanism, plutonism, uplift, and erosion, and before major regional metamorphism. All these events can be grouped within the Grenvillian orogenic cycle, spanning at least the interval 1300–1000 Ma and including, in eastern Ontario, the pre-Flinton Elzevirian Orogeny and post-Flinton Ottawan Orogeny.
Precision of measurement of remanent magnetization
Authors: Briden J. C. , Arthur G. R.
Published: April 2011

Confidence limits on the magnitude and direction of remanent magnetization measurements are derived as[Formula: see text]and[Formula: see text]where[Formula: see text]p is probability; n is the number of unbiased independent measurements Xi, Yi, Zi, of each Cartesian component x, y, z, and [Formula: see text] is the calculated magnitude of the remanence. Comparable expressions are derived for the confidence limits on the difference between two vectors. An approximate test for randomness is described. The errors commonly amount to more than 2% in magnitude and 2° in direction, and are greater for inhomogeneously magnetized samples and for vector magnitudes close to the sensitivity limit of the magnetometer. The effect of inhomogeneity of remanence requires special attention for most magnetometers. Applications of the methods to elimination of imprecise data, and assessing whether data conform to particular directional and stability-spectra models, are described.
A closer look at the September 16, 1732, Montreal earthquake
Authors: Leblanc Gabriel
Published: April 2011

The September 16, 1732, earthquake ranks among the three largest events in the western Quebec zone of earthquake occurrence and thus plays a controlling role in seismic hazard studies of the region. Its epicentral intensity has been estimated differently by various authors of earthquake catalogues, mostly because limited information was available. Recently, additional evidence was uncovered and evaluated. It suggests that an epicentral intensity VIII (modified Mercalli) is adequately representative of the damage observed in Montreal and agrees well with the other distant felt reports. On that basis, the intensity IX (MM) found in some catalogues should be revised; on the other hand, the Montreal location appears to be the most acceptable. It is proposed that the event be also characterized in terms of an estimated magnitude range, i.e., 5.6–6.0 [Formula: see text].
Remagnetization in Keweenawan rocks. Part I: conglomerates
Authors: Palmer H. C. , Halls H. C. , Pesonen L. J.
Published: April 2011

Conglomerate tests are used to show that Late Precambrian Keweenawan conglomerates on the Keweenaw Peninsula, Michigan and at Mamainse Point, Ontario have suffered a partial chemical remagnetization that predated tectonic tilting. At Mamainse Point the overprint was acquired during the final normal polarity stage of Keweenawan volcanism, whereas on the Keweenaw Peninsula it occurred after cessation of volcanism and has a maximum Late Freda Sandstone age. The extent of overprinting on the Keweenaw Peninsula increases westwards along a 40 km strike length in the Copper Harbor Conglomerate, and may at least in part be related to secondary mineral zonation (including native copper) in the underlying Portage Lake volcanics. It is shown that neither of the two overprinting episodes can be responsible for the reversal asymmetry observed in Keweenawan igneous rocks.
Crustal structure and velocity anisotropy beneath the Beaufort Sea
Authors: Mair J. A. , Lyons J. A.
Published: April 2011

Crustal-scale seismic refraction data obtained in the Beaufort Sea during 1976 reveal a 4–5 km thick sedimentary layer overlying an oceanic crust that thickens rapidly as it approaches the continental terrace of Alaska. A synthetic seismogram analysis of multiple reflected, water-wave events indicates that the upper sedimentary layer has a compressional velocity of 1.8 km/s and a shear velocity of about 0.2 km/s. An oceanic layer 2A of 4.3 km/s, a layer 3A of 6.6 km/s, and a layer 3B of 7.6 km/s overlying an anisotropic (3%) upper mantle with a median velocity of 8.3 km/s are interpreted. The direction of maximum upper-mantle velocity appears to be approximately north–south in the area surveyed, suggesting that a rotation of the Northwind Ridge–Chukchi Plateau away from the Barrow–Martin Point sector of Alaska may have occurred.
Stratigraphy of eastern Bay of Exploits, Newfoundland
Authors: McKerrow W. S. , Cocks L. R. M.
Published: April 2011

Fossils from the Fanners Island Formation (new name) show that, southwest of New World Island, Newfoundland, a thick (over 3 km) sequence of late Llandeilo turbidites and basalts overlies the Dunnage mélange. These are overlain by a thicker (6 km) sequence of turbidites, conglomerates, and associated olistostromes assigned to the Sansom Formation. The recognition of olistostromes in the Upper Ordovician (Caradoc and Ashgill) Sansom Formation (some of which contain olistoliths with early Ordovician fossils) eliminates the necessity of postulating repeated stratigraphic sequences by major faults. The field evidence indicates that the olistoliths slipped into a basin with more or less continuous sedimentation of turbidites and debris-flow conglomerates. Major faults separate distinct sequences of turbidites and olistostromes, suggesting that some of the faulting may have been contemporaneous with sedimentation.
Cardium Formation (U. Cretaceous) at Seebe, Alberta—storm-transported sandstones and conglomerates in shallow marine depositional environments below fair-weather wave base
Authors: Wright Marsha E. , Walker Roger G.
Published: April 2011

As a result of detailed mapping at Seebe, Alberta, we have defined five coarsening-upward sequences in the Turanian Cardium Formation. The sequences begin with bioturbated mudstones and coarsen into sandstones, commonly with conglomeratic veneers on top. In sequence 2, the conglomerate is up to 20 cm thick, and has been molded into sand waves a few centimetres high and with wavelengths of about 1 m.The sandstones are dominated by hummocky cross-stratification (HCS), a broad, low-angle undulating stratification now believed to be formed below fair-weather wave base by long-period storm waves. Sandstones with HCS occur in the upper parts of sequences 1, 2, 3, and 5, suggesting that all of these sequences terminate in water deeper than fair-weather wave base (10–15 m). The trace fossil assemblage of abundant Zoophycos and long, horizontal Rhizocorallium suggests similar depths. Foraminifera in sequences 3 and 4 show a high diveristy of agglutinated species, also suggesting deposition below fair-weather wave base.In view of the physical and biological evidence for deposition in a few tens of metres of water, and the total absence of medium-scale cross-bedding, we suggest that the entire Cardium Formation at Seebe was deposited below fair-weather wave base. The sandstones were emplaced by storm-generated density currents, the same storm both generating the flow and imprinting HCS on the deposit. Finally, we suggest that the conglomerates were also moved rapidly out to sea by density currents, there being no evidence for the traditional beach or transgressive lag interpretation of these rocks.
Petrology of the Fort Smith - Great Slave Lake radiometric high near Pilot Lake, N.W.T.
Authors: Burwash R. A. , Cape D. F.
Published: April 2011

Near Pilot Lake, the east boundary of the Fort Smith – Great Slave Lake radiometric high coincides with the contact of a well-foliated, porphyroblastic microcline–plagioclase–quartz-garnet–biotite gneiss1 (Pilot Lake Gneiss) with a hybrid assemblage of quartzite, mica schist, garnet–cordierite gneiss, and minor amphibolite (Variable Paragneiss). Anomalously high concentrations of uranium and thorium are associated with mafic-rich, lenticular bodies with a mineral assemblage biotite + monazite + zircon + ilmenite + hematite ± apatite ± plagioclase ± quartz. The mafic pods occur within both the Variable Paragneiss and the Pilot Lake Gneiss. Corundum and spinel occur in the mafic lenses and sillimanite, kyanite, and hypersthene in other inclusions in the Pilot Lake Gneiss.The ilmenite–magnetite–monazite–zircon–apatite assemblage is interpreted as a "black sand" concentration in a clastic sedimentary sequence subsequently metamorphosed by a regional granulite facies event. A granitic pluton intruded during the same orogenic cycle assimilated the clastic metasedimentary rocks containing black sand interlayers, becoming enriched in thorium from the monazite. A second metamorphic event at lower P–T conditions, accompanied by strong cataclasis, developed the texture of the Pilot Lake Gneiss as now observed. Shearing within the gneiss locally concentrated hematite + quartz + uranium.Regional tectonic extrapolations suggest that the pyroxene granulite event was Kenoran and the later amphibolite event Hudsonian.
Metamorphism and geothermometry near Coniston, Ontario: a clue to the tectonic evolution of the Grenville Front
Authors: La Tour Timothy E.
Published: April 2011

The staurolite and sillimanite isograds at the Grenville Front near Coniston, Ontario coincide with two discrete mylonite zones, MZ I and MZ II, respectively. MZ I is characterized by mylonitic fabrics and is associated with retrograde metamorphic features; MZ II is characterized by blastomylonitic fabrics and prograde metamorphic features. Garnet–biotite geothermometry yields a temperature of ~540 °C for staurolite-grade rocks and ~610 °C for sillimanite-grade rocks, and the spatial distribution of outcrops indicates an improbably high thermal gradient of at least 114 °C/km. This can be reconciled by recognizing that the mylonite zones represent structural discontinuities in a terrain otherwise characterized by a "normal" metamorphic gradient.MZ II is probably the older zone that formed at or near the peak of metamorphism during sustained heat flow and crustal thickening (orogeny). MZ I formed later as temperatures waned. The close proximity of MZ I to MZ II reflects epdisodic or continuous deformation confined by the northwestern boundary of the Greenville mobile belt. One of the unique characteristics of the Coniston area may be that late mylonitic deformation did not obliterate earlier blastomylonitic and phyllonitic features, making possible present-day distinction between the two mylonite zones.
On lake bottom dynamics—the energy–topography factor
Authors: Håkanson Lars
Published: April 2011

It is suggested that the areal distribution of erosion and transportation (aE + T) or accumulation (aA = 100 − aE + T) at the bottom of lakes is governed by: (1) an energy factor, [Formula: see text], where a is the lake area (km2), Dmax is the maximum depth (m); (2) a slope factor, [Formula: see text], where [Formula: see text] is the mean depth (m); and (3) a form factor, [Formula: see text]. This relationship may be given as: aE + T = 52.0ET + 19.3 where ET is the energy–topography factor; or[Formula: see text]This relationship is important since it provides a means by which to determine the percentage of a given lake area that is dominated by erosion and transportation processes (aE + T) or accumulation processes (aA) from only three morphometric standard parameters: lake area (a), mean depth ([Formula: see text]), and maximum depth (Dmax). The relationship may also be used as a tool to gain better insight into the difficult problem of distinguishing between net and total deposition, i.e., the resuspension problem, since resuspension in a lake depends on the energy, slope, and form factors.
Middle Ordovician (Chazy Group) cavity-dwelling boring sponges
Authors: Kobluk David R.
Published: April 2011

Microcavities in lower Middle Ordovician bryozoan mounds from the Laval Formation (Chazy Group) near Montreal, Quebec contain evidence that endolithic (boring) sponges were present. Ramose borings with scalloped walls and swellings resembling endolithic sponge galleries, faceted carbonate grains similar to modern sponge chips, and siliceous spicules both in situ on the cavity wall or roof and in the sediment, all point to the activities of endolithic sponges in the hard substrate of the wall and roof.Coelobiontic (cavity-dwelling) endolithic sponges therefore infested cavities in skeletal mounds and reefs in the Middle Ordovician and appear to have exploited the cavity habitat very soon after the appearance of metazoan skeletal reefs in the Ordovician.
Late Quaternary marine sediments at Chalk River, Ontario
Authors: Catto N. R. , Patterson R. J. , Gorman W. A.
Published: April 2011

The occurrence of marine clays and silts in the Chalk River area necessitates a revision of the previously accepted position of the northwestern extent of the Champlain Sea in the Ottawa Valley. The marine origin of these deposits is demonstrated by sedimentological, geochemical, and paleontological criteria. Boron and vanadium concentrations indicate a salinity for this part of the Champlain Sea of from 12 to 16 parts per thousand. Foraminifera present in the clays suggest a shallow brackish water environment. An evaluation of elevations of the marine limit indicates that the sea was present at Chalk River between about 11 300 and 11 100 years BP and thus was a relatively late phase of the Champlain Sea. It appears that ice cover in the area had prevented an earlier inundation by Champlain Sea waters.Till overlying the marine sediments is attributed to a minor readvance starting about 11 000 years ago. The timing and geographic location of this advance strongly indicate a correlation with the St. Narcisse event, well documented to the east of the Ottawa Valley. With the subsequent ice retreat, aeolian and lacustrine and, later, fluvial conditions prevailed, as isostatic recovery had elevated the area above the existing sea level.
A geodynamic model for some structures within and adjacent to the Okanagan Valley, southern British Columbia
Authors: Ross John V.
Published: April 2011

Detailed and reconnaissance mapping of areas along the east and west sides of the Okanagan Valley, from the International Boundary in the south to Kamloops in the north, has revealed a similarity in structural sequence and geometry in rocks ranging in age from Pennsylvanian (Harper Ranch, Anarchist, Kobau, Old Tom, and Shoemaker Groups) through Late Triassic – Early Jurassic (Nicola, Sicamous, and Slocan Groups).Earliest recognizable folds, F1, have northerly trending axes, are isoclinal in form, and are disrupted on all scales by a strongly penetrative second phase of deformation, F2. This second phase is characterized by northerly and southerly verging isoclinal folds having east–west axes that are very nearly parallel with a well-developed stretching lineation, L2. Mylonitic lamination is developed parallel with these F2 axial surfaces. A third phase of folding, F3, comprising more unright open structures having a consistent southerly vergence, deforms the earlier F1 and F3 structures. Later phases of deformation, F4 and F5, almost coeval, have produced the present foliation configuration outlining basins and domes and associated northerly trending normal faults.Progressive metamorphism accompanied F1, F2, and F3 deformations and peaked during F2. F4 and F5 are associated with a thermal event resulting in resetting of most radiometric ages within the region.F1 deformation is probably Permo-Triassic in age and associated with lower greenschist metamorphism, whereas F2 and F3, associated with a much higher metamorphism up to amphibolite facies, affect all the sedimentary rocks within the region and apparently terminated by about 178 Ma (K–Ar on hornblende), Triassic – Early Jurassic. The latest movements, F4 and F5, involve volcanic rocks whose age of crystallization is set radiometrically at about Eocene.A plate model involving easterly obduction during the Permo-Triassic, followed by easterly dipping subduction with associated dextral transform movement during the Late Triassic – Early Jurassic, is proposed to explain the observed geometry. A mantle diapir below the region is rationalized to explain the localized high heat flow during Eocene time.
Paleomagnetism of basic intrusions from the Brock Inlier, Northwest Territories, Canada
Authors: Park J. K.
Published: April 2011

Basic intrusions of the Brock Inlier of the Northwest Territories are shown by means of paleomagnetism to be related to the Franklin diabases (specifically the Coronation suite) of the Canadian Shield, thus verifying previous correlations made through geological considerations and radiometric dating. A predominantly reverse (AR) and occasionally normal (AN), presumably magnetite, magnetic component were resolved in single specimens from five separate sills (five sites) using alternating field and subsequent thermal treatment in conjunction with vector diagrams. A presumably hematite component antiparallel to AR was recovered at one site using converging great circles. The mean A direction is at 074°, −07° (k = 15) and the average of the site poles at 165°E, 02°S (N = 5, K = 40, A95 = 12°), close to that of the Coronation suite. Two specimens from a single dyke site yielded a normal AN-type pole similar to that of the Franklin dykes to the east of the Coronation suite.
Geological setting and tectonic significance of Mississippian felsic metavolcanic rocks in the Pelly Mountains, southeastern Yukon Territory
Authors: Mortensen James K.
Published: April 2011

The central Pelly Mountains in southeastern Yukon Territory consist of imbricate thrust sheets, which have undergone syn- and post-thrusting deformation and metamorphism. The local geology is further complicated by the intrusion of Late Cretaceous batholiths, and by strike-slip faulting related to the Tintina Fault, a major northwest-trending transcurrent fault of latest Cretaceous or early Tertiary age. This faulting disrupts the northeast edge of the study area.Upper Devonian and Mississippian strata are present in at least two of the structural packages, but the Mississippian metavolcanic rocks occur only in the lowermost package. Rb–Sr geochronology indicates a mid-Mississippian age for the igneous suite. The volcanic rocks consist of volcaniclastic material with minor interbedded flows, and were deposited in a submarine environment. Several coeval and cogenetic syenite and trachyte domes and small stocks are the remains of vent areas. Although the volcanic rocks are all highly altered and show evidence of widespread chemical mobility, trace element data indicate that the rocks are metaluminous trachytes, most closely resembling peralkaline volcanics generated in extensional environments. This suggestion of a predominantly extensional tectonic setting in mid-Mississippian time in the Pelly Mountains is consistent with recent tectonic syntheses for the area.
Neoglacial Lake Alsek
Authors: Clague John J. , Rampton V. N.
Published: April 2011

Lowell Glacier, a large valley glacier in the St. Elias Mountains of southwestern Yukon Territory, advanced across Alsek Valley and blocked south-flowing Alsek River many times during the Neoglacial interval. The resulting lake, termed Neoglacial Lake Alsek, extended east of the front of the St. Elias Mountains and inundated parts of Dezadeash Valley that presently are populated. Lake Alsek, at its maximum, was about 200 m deep at the glacier dam and over 100 km long. Staircase flights of beaches, wave-cut benches, layers of driftwood, and thin lacustrine sediments provide evidence of the former lake. Giant dunes and flood terraces on the floor of Alsek Valley indicate that the lake emptied catastrophically when the Lowell Glacier dam failed.Several phases of Lake Alsek have been identified. Each was preceded and followed by intervals during which the lake was empty and the present southward drainage pattern in Alsek Valley prevailed. Historical records, radiocarbon and tree-ring dates on driftwood, and radiocarbon dates on buried soils separating lacustrine units indicate that Lake Alsek extended into Dezadeash Valley sometime between A.D. 1848 and 1891, between A.D. 1736 and 1832, twice between 250 and 500 years ago, and at least once between 800 and 2900 years ago. In addition, a small lake may have existed in Alsek Valley after 1891, but before 1917, although the evidence for this is equivocal. During each ponding phase, Lake Alsek may have emptied and filled repeatedly, perhaps on a regular cycle, as is common for some existing glacier-dammed lakes.Lowell Glacier, during a future surge, might again block Alsek River and form a new lake. However, populated areas in Dezadeash Valley probably would not be inundated because Lowell Glacier has thinned and receded somewhat since Lake Alsek last extended beyond the St. Elias Mountains in the nineteenth century.
Significance of some geotechnical properties of continental slope and rise sediments off northeast Newfoundland
Authors: Schafer Charles T. , Asprey Kenneth W.
Published: April 2011

Shear strength measurements carried out on the 0–20 cm interval of continental slope and continental rise surficial sediments yielded mean values per station that ranged from 3.7 to 8.9 kPa. The factors controlling the bathymetric variation of sediment shear strength appear to be sediment texture (which is controlled locally by sediment spillover) on the upper slope, increased deposition of fines (silt- and clay-sized particles) from suspension and greater bioturbation activity on the middle slope, and bottom current sediment reworking on the base-of-slope and upper rise.Sediments deposited on the downslope side of the present presumed location of the Western Boundary Undercurrent (WBU) axis have comparatively high shear strength gradients that appear to denote the increased proportion of fine sediment deposition during early to middle Holocene time when the WBU axis may have been located further upslope than at present.
Northern Labrador Shelf glacial chronology and depositional environments
Authors: Fillon Richard H. , Harmes Robert A.
Published: April 2011

Huntec deep-tow records, 3.5 and 12 kHz echo-sounder profiles backed by airgun reflection, cores, and 14C dates delineate 10 mappable acoustic/morphologic units between 57°N and 61°N on the northern Labrador Shelf. These include: I—section composed of numerous horizontal reflectors with minimal scattering and smooth microrelief; II—acoustically transparent section with numerous subparallel, draped reflectors at its base—it underlies unit I in basin centers; III—section marked by intense scattering, point reflectors, and a rough microrelief; IV—section exhibiting strong scattering as in III, but with smooth microrelief and obvious terraces; V(a,b)—outcropping portions of II-type sediments variably dissected; VI—outcrops of II exhibiting warping, acutely intersecting reflectors and undulating mesorelief; VII(a,b)—areas of strong macrorelief with ridges and wedge- or lens-shaped reflectors and strong scattering; VII—section exhibiting strong macrorelief as in VII(a,b) but with somewhat rougher microrelief.A thin (<1 m) ubiquitous surface-sediment veneer that is not clearly identifiable on acoustic profiles is 14C dated at [Formula: see text]. Unit II dates between 9770 and 8380 BP and unit III at 10 260 BP. These dates are based on shells. Unit I is inferred to span the interval <8380 to >6050 BP. Total organic carbon dates from units I and II are deemed too old by as much as 17 000 years because of the introduction of reworked older carbon.The data suggest the following sequence of glaciation and deposition: (1) ice grounds on the shelf and upper slope during the glacial maximum; (2) shelf-basinal and bank portions of the ice sheet begin basal melting before 9770 and ca. 10 260 BP, respectively; (3) degrounding of the ice in shelf basins and admission of sea water by 9770 BP, perhaps at first beneath ice shelves; (4) deposition of fine-grained glacial muds in basins as runoff from actively ablating valley glaciers on Labrador finds its way into fjord-like embayments in the ice sheet (ca. 9770–8380 BP); and (5) deformation of sediments on shallower portions of the shelf and upper slope possibly by Hudson Bay, Foxe Basin, or Ungava Bay surge ice exiting outer Hudson Strait, ca. 8380–7500 BP.
Conodont biostratigraphy of the Codroy Group (Lower Carboniferous), southwestern Newfoundland, Canada
Authors: Bitter P. H. von , Plint-Geberl H. A.
Published: April 2011

Four stratigraphically successive conodont assemblage zones have been recognized in the Lower Carboniferous Codroy Group of southwestern Newfoundland. The Diplognathodus Zone is confined to the basal Ship Cove Limestone, and to a highly fossiliferous correlative at Aguathuna. The overlying Taphrognathus Zone occurs in carbonates in the stratigraphic interval above the sequence of massive sulphates and thick clastics. The Taphrognathus Zone, as well as the successive Cavusgnathus Zone, has been recognized on Fischells Brook, as well as in the complex section south of Codroy. The highest conodont zone, the Gnathodus Zone, has been recognized in the Crabbes–Jeffreys Limestone of the St. George's Bay area, and from south of Codroy.The discovery of conodonts of the Diplognathodus Zone in marine strata that are stratigraphie and lithologie correlatives of the Macumber and the Gays River Formations of Nova Scotia now makes it possible to microfaunally characterize the A Subzone, a macrofaunal subzone established in the Windsor Group of Nova Scotia.The Taphrognathus and Cavusgnathus Zones of the Codroy Group of Newfoundland correlate with the lower and upper B Subzone of the Lower Windsor Group of Nova Scotia, respectively. The Gnathodus Zone correlates with the C, D, and E Subzones of the Upper Windsor Group of Nova Scotia.
The chemistry and isotopic composition of saline groundwaters from the Sudbury Basin, Ontario
Authors: Frape S. K. , Fritz P.
Published: April 2011

The results of geochemical and isotopic analyses are discussed for groundwater samples obtained from five mines and several shallow wells in the Sudbury Basin. Mine samples were usually obtained from abandoned diamond drill holes or fractures, which were found from depths of 152–1219 m (500–4000 ft). Two very distinctive water types are recognized in the subsurface environment. Fresh to brackish waters were found from surface to approximately 800 m (2600 ft) in depth. However, below 914 m (3000 ft) very saline or briny waters occur at most of the localities sampled. The geochemistry of the shallow waters shows gradual increases in concentration for most elements; locally effects from the proximity of sulphide ores or drill hole grouting were observed. Isotopic data (2H, 18O, and tritium) indicate that the major component of these waters is less than 30 years of age and represents local meteoric waters. The saline waters have dissolved loads often in excess of 200 g∙L−1 and are dominated by calcium and chloride. The chemistry and isotopic contents of the Sudbury brines are very distinct from highly saline waters or brines of sedimentary or geothermal origin. The brines appear to represent very old, stagnant "groundwaters," which may have undergone prolonged chemical and isotopic alteration since their original emplacement. At the present a variety of possible origins for the deep Sudbury waters can be postulated, but most models for brine formation found in the literature are unsatisfactory to explain the origin and genesis of these deep Canadian Shield brines.