bluuebunny/crossref_metadata_2025 huggingface dataset:
Geochemistry of cobalt, nickel, chromium, and vanadium in the sediments of the estuary and open Gulf of St. Lawrence
Authors: Loring D. H.
Published: April 2011

Total Co (3–22 ppm), Ni (4–160 ppm), V (4–168 ppm), and Cr (8–241 ppm) concentrations vary regionally and with textural differences in the sediments of the St. Lawrence estuary and Gulf of St. Lawrence. They are, except for local anomalies, at or near natural levels relative to their source rocks and other marine sediments.Chemical partition and mineralogical analyses indicate that small but biochemically significant quantities (2–24%) of the total element concentrations are potentially available to the biota and are most likely held by fine-grained organic material, hydrous iron oxides, and ion exchange positions in the sediments. In the upper estuary, nondetrital Ni, Cr, and V supplied from natural and anthropogenic (Cr) sources are apparently preferentially scavenged from solution by terrestrial organic matter and hydrous oxides and concentrated in fine-grained sediments deposited below the turbidity maximum. In the lower estuary, the fine-grained sediments are relatively enriched in nondetrital V supplied from anthropogenic sources in the Saguenay system. Elsewhere the sedimentation intensities of the nondetrital elemental contributions have remained relatively constant with fluctuations in total sediment intensity.Seventy-six to 98% of the total Co, Ni, Cr, and V is not, however, available to the biota, but held in various sulphide, oxide, and silicate minerals. The host minerals have accumulated at the same rate as other fine-grained detrital material except for some local anomalies. In the upper estuary, detrital V concentrations are highest in the sands as an apparent result of an enrichment of ilmenite and titaniferous magnetite from a nearby mineral deposit. In the open gulf, relatively high concentrations of Ni, Cr, and V occur in sediments from the Bay of Islands, Newfoundland, and probably result from the seaward dispersal of detrital Ni, Cr, and V bearing minerals from nearby ultrabasic rocks.
Effects of pressure, temperature, and grain size on the kinetics of the calcite → aragonite transformation
Authors: Brar N. S. , Schloessin H. H.
Published: April 2011

Single crystals and polycrystalline samples of transparent calcite (Iceland spar) were used to investigate the effects of pressure (p), temperature (T), pressure beyond an accepted equilibrium value (Δp), and grain size (D) on the kinetics of the calcite–aragonite transformation. Transformed mass fractions x(t), produced after different times of exposure to constant pressure ranging from 14 to 25 kbar (1.4 to 2.5 GPa) and constant temperature from 300 to 600 °C, were determined from integrated X-ray peak intensities of the (012), (021), and (111) reflections of aragonite. Values for the rale constant K and the exponent n characterizing the transformation were computed from the x(t) data using Cahn's nucleation and growth model for solid–solid transformations. At 17 kbar(1.7 GPa), K(s−1) increases from 2.00 × 10−5 at 300 °C to 1.39 × 10−3 at 600 °C. The exponent n, of the order of 1, mostly <1, indicates that the nucleation stage is terminated rapidly by site saturation and that most of the transformation takes place thereafter by growth as expected from theory. For single crystals the relationship between x(t) and Δp, for a period of 1 hour is almost linear. At 600 °C the relative increase of x(t) amounts to 0.1 kbar−1 (1 × 107 Pa−1). For a given time, x increases nearly exponentially with T. The apparent activation energy for the transformation, at 17 kbar (1.7 GPa), is 16 kcal mol−1. For polycrystals x(t) decreases as [Formula: see text]. This somewhat surprising result may be related to deviatoric stresses and stress concentration by the already transformed volume fractions, which act as misfitting, ellipsoidal, inclusions.
δ18O variations in snow on the Devon Island ice cap, Northwest Territories, Canada
Authors: Koerner R. , Russell R. D.
Published: April 2011

A study of δ18O variations of snow samples taken on traverses across the Devon Island ice cap in June 1971, 1972, and 1973 has shown a difference between the accumulation conditions on the southeast and northwest sides of the ice cap. On the southeast side there is an increasing depletion of 18O in the snow with increasing elevation. This pattern is attributed to the effect of orographic uplift of air masses moving over the ice cap from the southeast, which promotes condensation and precipitation due to adiabatic cooling. On the northwest side of the ice cap there is no evidence of any further depletion of 18O in snow, neither with increasing distance from the possible moisture source in Baffin Bay to the southeast nor with increasing elevation if the air mass comes from the northwest. In this case condensation is due to isobaric cooling so that precipitation is generally from level cloud bases. The changes inferred for the isotopic composition of the water vapour as it rises up the southeast slope are found to be consistent with its depletion through precipitation under near-equilibrium conditions. It is calculated that approximately 30% of the moisture at sea level on the southeast side of the ice cap and 8% at the top of the ice cap are of local origin. Lower temporal and aerial variabilty of the δ values on the southeast side of the ice cap is attributed to dominance of the Baffin Bay low on that side effecting consistency of storm conditions there.The δ values of ice in the ablation zone on the Sverdrup Glacier show the combined effect of ice movement from the accumulation to the ablation zone and climatic change during the period of movement from cold to warm and back to cold conditions again.
Rock stratigraphy and clay mineralogy of volcanic ash beds from the Black River and Trenton Groups (Middle Ordovician) of southern Quebec
Authors: Brun J. , Chagnon A.
Published: April 2011

The Black River and Trenton Groups (Middle Ordovician) of southern Quebec contain several beds of swelling claystone which do not resemble the normal marine shales present in these units. The stratigraphic analysis of these units shows that these peculiar beds correspond to several well defined horizons which correlate over large distances, and are thus very good marker horizons. The clay mineralogic analysis of these beds shows that the main clay mineral is a mixed-layer of illite–smectite type having 20–40% of expandable layers. These claystones are identified as 'K-bentonites.' They are interpreted as being the result of the sedimentation and lithification of volcanic ash ejected during a series of eruptions contemporaneous with the deposition of the sediments.
Fracture-trace influenced stream orientation in glacial drift, northwestern Pennsylvania
Authors: Cox Jason C. , Harrison Samuel S.
Published: April 2011

The orientation of streams in the Geneva quadrangle, northwestern Pennsylvania, was studied in order to determine if their orientation has been influenced by fracture traces. Of the 151 visible fracture traces in the study area, 83% are oriented N30°W–N60°W or N30°E–N60°E. Measurement of over 2500 stream segments revealed that 43% of the segments are oriented 30–60° east or west of north, whereas random orientation of streams would result in only 33% of the segments having these trends. This preferred orientation is statistically highly significant (0.001 level). Contrary to expectations, the degree to which stream orientation was influenced by fracture traces does not appear to decrease with increasing drift thickness within the 0–500 ft (0–152 m) range present in the quadrangle.
An expanding spread seismic reflection survey across the Snake Bay–Kakagi Lake greenstone belt, northwestern Ontario
Authors: Green A. G. , Anderson N. L. , Stephenson O. G.
Published: April 2011

An expanding spread seismic reflection survey has been conducted across the Snake Bay–Kakagi Lake greenstone belt in northwestern Ontario. Receiver and shot arrays with multiple shots per location helped to maintain a high signal to noise ratio in most of the data. Distances between the shots and receivers ranged from 1.04–8.48 km and the total charge per shot location varied from 26–86 kg. After computer processing the data, numerous coherent reflections were observed from near vertical and near horizontal discontinuities.Prominent early reflections were used to map a granite–greenstone contact to the south of the profile and a section of the Long Bay fault zone to the northeast of the profile. A noticeable absence of reflections from the Aulneau granite batholith–greenstone contact suggests that this contact dips westwards, towards the centre of the batholith.From the later reflections a model of the deep crust beneath the Snake Bay–Kakagi Lake greenstone belt was derived. This model, which represents a lateral extension of the Aulneau crustal model, consists of a three-layered crust. The top crustal layer is 19 km thick with Pg and Sg velocities of 6.2 and 3.5 km/s respectively, the middle layer is 3 km thick, and the lower layer extends to the Mohorovicic discontinuity at 38 km depth.
Deepwater sculpin, Myoxocephalus thompsoni (Girard) from a Pleistocene nodule, Green Creek, Ontario, Canada
Authors: Champagne Donald E. , Harington C. R. , McAllister Don E.
Published: April 2011

A nodule containing the cranium of a deepwater sculpin, Myoxocephalus thompsoni (Girard), was discovered in Pleistocene Champlain Sea deposits at Green Creek, 10 km east of Ottawa, Ontario, Canada, and represents the first fossil reported for the species. It provides an additional basis for refuting derivation of the species from a post-Wisconsin marine submergence and suggests an origin at the beginning of the Wisconsin or earlier. Habitat preferences of the species favour an oligotrophic lacustrine environment with bottom summer temperatures below 8 °C in the Champlain Sea or nearby lake basin. The head length of the fossil is 28 mm, the estimated standard length 86 mm. Use of a longwave ultraviolet lamp with the fossil improved contrast between the bones and the clay matrix in photographs. Scanning electron microscopy (SEM) analysis of bone in the fossil failed to detect the presence of strontium.
Extension of the Superior–Churchill boundary zone into southern Canada
Authors: Green A. G. , Cumming G. L. , Cedarwell D.
Published: April 2011

A regional magnetic map for southwestern Manitoba and southeastern Saskatchewan (areas not covered by the Federal–Provincial aeromagnetic maps) has been compiled. After a review of the geological and geophysical characteristics of the Superior–Churchill boundary zone in northern Manitoba, the new compilation magnetic map was used as a guide for tracing the boundary zone southwards to the Canada–U.S.A. border.By comparing the patterns on the new magnetic map with those on the neighbouring Federal–Provincial aeromagnetic maps, the major east–west trending crustal belts in the Superior Province have been extended farther west than was previously possible. In addition, a major granite/greenstone terrain, which extends in a southerly direction from a region near Flin Flon to the Canada–U.S.A. border, has been delineated in the Churchill Province. To the west of this granite/greenstone terrain, in central Saskatchewan, there is an extensive region of low magnetic relief, similar to that observed across the Kisseynew gneiss belt in northern Manitoba.
The stratigraphy and structure of the Laurentian Cone region
Authors: Uchupi Elazar , Austin Jr. James A.
Published: April 2011

A series of single and multichannel seismic reflection profiles combined with well data from the adjacent shelves and deep sea and published geophysical profiles permit the reconstruction of the geologic development of the Laurentian Cone. The cone's sediments can be divided into two megasequences, a lower one of Early Jurassic to Eocene age, which extends from a transitional and oceanic basement to horizon AT, and an upper sequence of early-middle Miocene to Holocene age extending from horizon AT to the sea floor. Plastic flow of Early Jurassic salt at the base of the lower megasequence has resulted in the deformation of the strata above, and the formation of a ridge that extends along the continental rise from Georges Bank to the Grand Banks. Horizon AT, separating the two sequences, is the surface of a fan deposited by turbidity currents during a latest Cretaceous and a late Eocene–Oligocene regression; these regressions may be due to the onset of continental glaciation. Deposition of this regressive wedge initiated the emplacement of the Laurentian Cone. The upper terrigenous megasequence, composed of three coalescing fans, was emplaced through the action of turbidity currents, and reflects the rapidly fluctuating climatic conditions associated with the waxing and waning of continental glaciers from latest Miocene to Holocene. The cone is not being supplied with sediments from the continent at present, but sediment continues to move down-cone in response to sporadic seismic activity.
Paragneisses in the Pakwash Lake area, English River Gneiss Belt, Northwest Ontario
Authors: Kamp P. C. van de , Beakhouse G. P.
Published: April 2011

A 4000 to 7000 m sequence of amphibolite-facies Archean layered gneisses in the Pakwash Lake – Lac Seul area of Northwest Ontario has been examined to determine its origin. The micaceous, relatively fine grained gneisses are concluded to be metasedimentary rocks. They were probably deposited from aqueous suspension as graded beds. The provenance of the detrital material was dacitic volcanics. Apparently there was little chemical alteration prior to metamorphism. An unmetamorphosed analog for these deposits is the volcaniclastic Eocene Ohanapecosh Formation in the Mt. Rainier area of Washington, U.S.A. Seventeen new chemical analyses are used to describe the rocks and decipher their origin.Similar rocks occur for at least 100 km east and west from the area of detailed study, suggesting a major sedimentary basin or series of basins in the area of the present English River Gneiss Belt.
Magnetic spherules in Arctic Ocean sediments
Authors: Bornhold B. D. , Bonardi M.
Published: April 2011

Five types of spherule were found in Quaternary sediments from the Canada Abyssal Plain. They include: type A spherules composed of magnetite and hematite surrounding metallic iron cores, exsolution blebs, or veinlets (Ni, Fe, Co); type B, of nearly pure homogeneous magnetite; type C, displaying intergrowths of magnetite and hematite and containing minor Ti (< 1%); type D, composed predominantly of magnetite with significant amounts of Ti (up to 4.8%); and type E, consisting of ilmenite and rutile with Ti, Si, Fe, Mn, Al, K, and Mg as major elements and Cr, Ca, and Na as minor elements. Ni and Co were detected only in a small metallic veinlet (with Fe) surrounded by magnetite containing significant amounts of Ti.Three possible sources are considered: industrial, volcanic, and extraterrestrial. Industrial input is unlikely in view of the great distances to possible sources and the relatively large size of the particles. The high Ti content of most of the spherules suggests a volcanic origin. The five type B spherules are the only possible candidates for a cosmic origin.
Petrology, composition, and age of intrusive rocks associated with the Quartz Hill molybdenite deposit, southeastern Alaska
Authors: Hudson Travis , Smith James G. , Elliott Raymond L.
Published: April 2011

A large porphyry molybdenum deposit (Quartz Hill deposit) was recently discovered in the heart of the Coast Range batholithic complex about 70 km east of Ketchikan, southeastern Alaska. Intrusive rocks associated with the mineral deposit form two composite epizonal to hypabyssal stocks and many dikes in country rocks. The stocks are characterized by a variety of textural rock types varying from equigranular or weakly seriate biotite granite to porphyries with aphanitic or very fine grained and aplitic groundmasses. These rocks contain about equal amounts of quartz, albitic plagioclase, and microperthitic microcline and less than 2.5% biotite. Unaltered rocks contain between 0.2 and 1% CaO, less than 1.7% combined Fe2O3, FeO, and MgO, and 74.4 to 77.7% SiO2. Total alkalis are between 8 and 9%, and K2O/Na2O is about 1.1. The range of major-oxide variation is small, but it is systematically related to lithology. Many trace-elements, including B, Pb, Sn, and Li have low concentrations. Intrusive rocks associated with the Quartz Hill deposit are more albitic and possibly trace-element depleted compared to some other rocks associated with porphyry molybdenum deposits.All observed metallization and alteration is within the Quartz Hill stock. Molybdenite forms fracture coatings and occurs in veins with quartz. Alteration is widespread and includes development of secondary quartz, pyrite, K-feldspar, biotite, white mica, chlorite, and zeolite. Field relations indicate that the stocks were emplaced after regional uplift and erosion of the Coast Range batholithic complex, and K–Ar data show that intrusion and alteration took place in late Oligocene time, about 27 to 30 Ma ago. Data from the Ketchikan quadrangle indicate that porphyry molybdenum metallization in the Coast Range batholithic complex is associated with regionally extensive but spotty, middle Tertiary or younger, felsic magmatism.
Chemical demagnetization: methods, procedures, and applications through vector analysis
Authors: Henry Steven G.
Published: April 2011

Seventy-live samples from the Freda sandstone (1050 Ma old) have been drilled from the same slab in order to investigate the best method of sample preparation and to optimize procedures for chemical demagnetization of red sandstones, Expanding on the chemical demagnetization procedures used by Park, several variables have been tested. These include: multicoring or slotting of samples to permit access of the acid, temperature and normality of the acid, zero-magnetic field during leaching, and vacuum conditions before leaching steps. Through proper sample preparation and leaching procedures, it is possible to separate the solubility spectra and associate the components of magnetization with particular magnetic carriers.Visual inspection of cores sectioned during progressive chemical demagnetization has allowed the comparison of the solubility spectra to the blocking temperature spectra of thermal demagnetizations. This comparison has linked the coarser-grained specularite to the highest blocking temperatures, and the fine-grained hematilic cement to intermediate blocking temperatures. There exists a component of magnetization which appears to be insoluble lo the leaching process. It has been shown to be carried by detrital titanomagnetite. Through the combined use of chemical, thermal, and alternating field demagnetization a magnetic history involving deposition. lithilication. and later overprinting has been unraveled from this slab of Freda.
Stone rosettes as indicators of ancient shorelines: examples from the Precambrian Belcher Group, Northwest Territories
Authors: Rlcketts B. D. , Donaldson J. A.
Published: April 2011

Flat-pebble conglomerates in the McLeary Formation of the Belcher Group display close packing of intraformational slabs in near-vertical arrays that appear distinctively polygonal in sections parallel to bedding. Such arrangements of flat pebbles, known by names such as stone rosettes and slone packings, are common on modem beaches, especially within the swash and backwash zone of shore platforms. Association of the McLeary stone rosettes with sedimentary features suggestive of shallow subtidal to supratidal origin (herringbone cross-bedding, reactivation surfaces, desiccation cracks, tepee structures, gypsum casts, oncolites, stromatolites, and probable beachrock) supports a hydrodynamic origin for these polygonal arrays of flat pebbles, an origin that has been demonstrated for modern occurrences. Where associated structures corroborate interpretation of a shallow-water origin, such stone rosettes provide evidence for ancient strandlines, and the designation "beach rosettes" is suggested as appropriate to distinguish them from stone rosettes formed by periglacial processes.
Aeromagnetic anomaly pattern in the English River gneiss belt, Superior Province
Authors: Urquhart W. E. S. , West G. F.
Published: April 2011

Aeromagnetic mapping of the English River gneissic belt (northwestern Ontario) reveals a pattern of sinuous east–west trending anomalies that help distinguish the gneissic belt from the more typical Archean metavolcanic–plutonic terrain. To study the significance of the pattern, a ground follow-up study was made where Lac Seul provides good access and outcrop. Field work consisted of (1) magnetometer profiling on the lake; (2) detailed searching for outcrop of anomaly-causing material and sampling; and (3) regional geological mapping and sampling. Thin section studies and physical property measurements were made in the laboratory as well as an interpretative study of the aeromagnetics using an "apparent susceptibility" data transformation.The main results are: (1) metamorphism is in upper amphibolite to granulite facies; (2) on average, rocks of the area have higher susceptibilities than are typical of the metavolcanic–plutonic regions; (3) the aeromagnetic anomalies are caused by bands of pyroxene–amphibolite gneiss; (4) the study area may be interpreted as a volcanic and sedimentary sequence deformed into a large, east–west striking, nearly isoclinal fold structure which has been intruded and highly metamorphosed; and (5) aeromagnetic data can be used to extend and complete geological mapping in the area.
Geochronology and geochemistry of felsic rocks in an Archean volcanic–plutonic suite in the Wabigoon belt, northwestern Ontario
Authors: Wolff J. M. , Crocket J. H.
Published: April 2011

Selected rock units of an Archean volcanic–plutonic assemblage from the Kakagi Lake area, northwestern Ontario, were sampled for geochronological and geochemical studies. The units sampled were felsic metavolcanic rocks from the upper third of the sequence (Middle Felsic Group) and a felsic pluton (the Stephen Lake stock) intruded into these metavolcanics. A Rb/Sr whole rock isochron from the Stephen Lake stock yielded an age of 2534 ± 96 Ma with an initial 87Sr/86Sr ratio of 0.7015. This date is interpreted as a minimum age for the end of volcanism in the Kakagi Lake area, and the low initial ratio indicates that older sialic material was not a significant contributor to the Stephen Lake magma.Major and trace element (Rb, Sr, Ba, Zr, Y, Ce) compositions show that the Kakagi Lake felsic metavolcanics are similar to high-alkali andesite and depleted siliceous volcanics as recognized by Condie. Geochemical indicators such as K/Rb, the potash index, and the Rb/Sr thickness grid index suggest that the Stephen Lake pluton is not simply the intrusive equivalent of the felsic metavolcanics, but that different magma sources are probably required.
SH waves in layered transversely isotropic media—a wave approach
Authors: Daley P. F. , Hron F.
Published: April 2011

There are many reports in the literature of anomalies in traveltime data when an isotropic homogeneous Earth model is used to interpret field data. In several cases, the introduction of a layered transversely isotropic model has successfully explained these kinematic irregularities. However, it is useful, in fact essential, to confirm the kinematic fit with a dynamic (amplitude) comparison.In this paper the problem of SH waves propagating in a transversely isotropic plane layered medium is discussed through the use of integral transforms and evaluation by steepest descents. This procedure yields not only the asymptotic solution which is also attainable using an asymptotic ray series approach, but also allows for the investigation of the interference of the reflected and head waves in the vicinity of the critical point (point of critical refraction). It is in this region that asymptotic ray theory breaks down or at least introduces significant error in the displacement amplitudes.It can be shown that a simple transformation will reduce this problem to one that may be solved exactly by the Cagnaird de Hoop technique but it is instructive to examine nonspherical wave-fronts in order to obtain an insight into more complicated anisotropic media.
Diagenetic and postdiagenetic changes in the composition of an Archean pillow
Authors: Baragar W. R. A. , Plant A. G. , Pringle G. J. , Schau Mikkel
Published: April 2011

An Archean basaltic pillow of greenschist metamorphic facies and a modern sea-floor pillow with minor diagenetic alteration are comparably zoned from rim to core as follows: a 'glassy' rim, a zone of incipient crystallization, and a crystalline interior, but the petrography of each is appropriate to its metamorphic stage. The Archean pillow varies markedly in composition inward, with the major changes taking place at the rim and at the margin of the crystalline interior; the centre is a broad zone of fairly uniform composition. Relative to the centre zone, alkalis and silica are greatly depleted and iron, lime, and magnesia greatly enriched at the rim, whereas the proportions are approximately reversed at the margin of the crystalline interior. The abundance and, in part, composition of metamorphic minerals reflect the same zoning: chlorite and epidote predominate at the rim, and feldspars concentrate at the margin of the crystalline interior. The bulk of the crystalline interior is a uniform intergrowth of actinolite–epidote–chlorite–albite–sphene–quartz–calcite. Epidote is iron–enriched and iron–depleted at the rim and the margin of the crystalline interior respectively. These variations can be attributed to a pre-existing diagenetic alteration analogous to that recognized in the modern pillow where palagonitization of the glassy rim is attended by oxidation of iron and a concentration of certain elements, notably alkalis, at the pillow margins. With metamorphism, epidote develops at the pillow rims because of oxidation induced by palagonitization and the residual glass is replaced by chlorite. Elements incompatible with these minerals migrate to the margin of the crystalline interior where they can be accommodated in the developing metamorphic assemblage. Little net change in the composition of the pillow is evident.
The paleomagnetism of Keweenawan dikes from Baraga and Marquette Counties, northern Michigan
Authors: Pesonen Lauri J. , Halls Henry C.
Published: April 2011

A paleomagnetic study involving alternating field (AF) and thermal cleaning, baked contact tests, and the measurement of hysteresis and other magnetic properties has been carried out on 21 Keweenawan diabase dikes (age ~1.1 Ga) from Baraga and Marquette Counties, northern Michigan. The main results are as follows.(1) The dikes exhibit a steep, negatively inclined remanence, which is shown to be a thermoremanent magnetization (TRM) acquired parallel to the ambient field at the time of initial magma cooling.(2) A secondary component, more resistant to magnetic cleaning than the primary TRM, and with west-northwest declination and positive inclination is occasionally found in the dikes, especially those from Baraga County.(3) Despite an early pole position obtained by Graham, which suggested that the dikes in Michigan were potentially important in defining the depth of the Logan Loop, most of them, from Marquette County, yield a pole that lies on the loop's western arm. The region of the projected apex of the loop thus still remains without reliable data.(4) The pole position of the Marquette dikes (48.4°N, 213.5°E; dp = 5.2°; dm = 6.2°) obtained from 14 sites is virtually identical to that obtained from 17 reversely magnetized dikes from the Thunder Bay district in Ontario, but appears to be distinct from poles derived from other Keweenawan units. Both dike swarms are thus interpreted to represent parts of the same magmatic pulse, and one that occurred in the centre of Lake Superior during an early opening phase of the Keweenawan rift system.
Amplitudes of oceanic magnetic anomalies and the chemistry of oceanic crust: Synthesis and review of 'magnetic telechemistry'
Authors: Vogt P. R.
Published: April 2011

A growing body of evidence suggests that certain areas of high-amplitude (H) sea-floor spreading-type magnetic anomalies reflect FeTi-enriched basalts of high remanent magnetization. A worldwide tabulation of these 'H-zones' is presented, together with a review of pertinent geochemical, rock magnetic, and deep-tow data relevant to the hypothesis of magnetic telechemistry.' H-zones are found in two tectonic settings: (1) along 102–103 km long sections of spreading axis close to hot spots; and (2) in narrow bands extending a few hundred kilometres along the edges of some fracture zones. Amplitudes in both provinces are 1.5 to 5, typically 2 to 3 times normal, and the hot spot H-zones are known from spreading half-rates of 0.6 to 3.7 cm yr−1 The highest amplitudes, magnetizations, and FeTi enrichment (up to 15–18% FeOT and 2–3% TiO2) seem to occur where both provinces overlap, i.e., where fracture zones occur near hot spots, for example along the Blanco Fracture Zone south of the Juan de Fuca hot spot and along the Inca Fracture Zone east of the Galapagos hot spot. The FeTi enrichment appears to reflect shallow-depth crystal fractionation (plagioclase, augite, and olivine), which is more extensive near hot spots, and more generally for fast-spreading ridges. H-zones presently affect at least 2.6 × 103 km, or 6.5% of the Mid-Ocean Ridge axis. However, the total known H-area of 8.5 × 105 km2 represents only 0.3% of oceanic crust. This suggests that older H-zones remain to be discovered, or/and that conditions favoring the formation of FeTi basalt and H-anomalies are more prevalent now than they have been on the average for the last 108 years. Evidence for the latter is provided by the known expansion of the magnetically well surveyed Juan de Fuca, Galapagos, and Yermak (Arctic) H-zones in the last 5 million years.
Heavy minerals in stream sediments from Churchill Falls, Labrador—an aid in bedrock mapping
Authors: Callahan John Edward
Published: April 2011

Stream sediments from a 13 000 km2 previously glaciated area in central Labrador near Churchill Falls were examined for their heavy mineral content. The minus 0.25 mm (60 mesh) nonmagnetic heavy mineral fraction from 846 stream sediment samples consists mainly of magnetite, ilmenite. garnet, hornblende, epidote and minor clinopyroxene, orthopyroxene. kyanite. sillimanite, biotite. apatite, and zircon. Changes in the frequency distribution of epidote, hornblende, garnet, and sillimanite in the stream sediments correspond well with those reported in previously mapped underlying bedrock lithologies. The occurrence of kyanite and sillimanite, high concentrations of garnet and opaques (mainly ilmenite), and lower concentrations of hornblende and epidote were used to determine grades of regional metamorphism, resulting in revision of the geologic map of this area. Heavy minerals in glacial drift or fluvial deposits may be useful as an aid in mapping in glaciated areas.
Regional implications of Upper Triassic metavolcanic and metasedimentary rocks on the Chilkat Peninsula, southeastern Alaska
Authors: Plafker George , Hudson Travis
Published: April 2011

A low-grade metamorphic sequence consisting of thick mafic volcanic rocks overlain by calcareous flysch with very minor limestone underlies much of the Chilkat Peninsula. Fossils collected from both units are of Triassic age, probably late Karnian. This sequence appears to be part of the Taku terrane, a linear tectono-stratigraphic belt that now can be traced for almost 700 km through southeastern Alaska to the Kelsall Lake area of British Columbia. The age and gross lithology of the Chilkat Peninsula sequence are comparable to Upper Triassic rocks that characterize the allochthonous tectono-stratigraphic terrane named Wrangellia. This suggests either that the two terranes are related in their history or that they are allochthonous with respect to one another and coincidentally evolved somewhat similar sequences in Late Triassic time.
Strain from repeated geodetic surveys by generalized inverse methods
Authors: Margrave G. F. , Nyland E.
Published: April 2011

Surveys of microgeodetic networks (apertures of a few kilometres or less) using relatively simple, inexpensive commercially available equipment are capable of measuring Earth strains of 2 × 10−6 or greater. Use of such networks for strain measurements offers many practical advantages over larger networks. Trilateration alone achieves virtually the same precision as combined trilateration and triangulation, with the expenditure of significantly less time and energy. Strain determinations can be made by estimating coefficients in low order polynomial expansions of the strain in the network. The technique uses the theory of generalized inverses for rectangular matrices to estimate polynomial coefficients.This method is used to investigate the resolution of microgeodetic networks using a com prehensive suite of synthetic data. Real data from a network in Peru show that a shear strain event of −3 microstrains occurred within this network during the period 1975–1976. A further shear strain event of +3 microstrains occurred during 1976–1978, possibly as a response to the first.
Quantitative evaluation of clast fabrics within the Catfish Creek Till, Bradtville, Ontario
Authors: May Ronald W. , Dreimanis A. , Stankowski W.
Published: April 2011

The analysis of the orientation of the long axis of clasts in till (till fabric) is used to assess aspects of its depositional history. The till fabric of the Catfish Creek Till has been analyzed in two sections located on Lake Erie for three particle sizes: 0.3–0.6 cm, 1–5 cm, and +5 cm, at approximately 1 m intervals within each section. Data were analyzed using Bingham's distribution. Results indicate different depositional histories for the upper and lower units of the till. There are also differences between the two sections.Comparison of the results from this fabric study with those of other investigators, both qualitatively and quantitatively, when combined with other local geological criteria, indicate a complex subglacial environment of deposition, probably involving meltout, debris flows, and lodgement. This complexity of processes would account for the poorly developed fabrics.
Late Wisconsin white spruce (Picea glauca (Moench) Voss) at Brampton, Ontario
Authors: Terasmae J. , Matthews H. L.
Published: April 2011

Study of late Wisconsin deposits in a small bog on the crest of Brampton esker (mantled by the Halton Till), about 30 km west of Toronto, Ontario, yielded a radiocarbon date of 12 320 ± 360 years BP (BGS-551) for a sample of white spruce cones that contained fully-developed seeds. This date on cones (in gyttja) provides an estimate of minimum age for the lower boundary of the spruce pollen zone in southern Ontario. Silty clay beneath the gyttja yielded leaves of Dryas integrifolia and pollen assemblages (a herb pollen zone) that indicate presence of a dwarf-shrub tundra (essentially treeless) type of vegetation.This study supports the Port Huron Stadial age (about 13 000 years BP) of the Halton Till that underlies the silty clay, and suggests an age of between 12 500 – 13 000 years BP for glacial Lake Peel in the Brampton area that preceded the glacial Lake Iroquois phase in the Lake Ontario basin.
A new shale-facies microbiota from the Middle Proterozoic Dismal Lakes Group, District of Mackenzie, Northwest Territories, Canada
Authors: Horodyski Robert J. , Donaldson J. Allan , Kerans Charles
Published: April 2011

An assemblage of filamentous microfossils is preserved in black shales of the approximately 1.2 Ga old Dismal Lakes Group from a locality about 110 km west-southwest of Coppermine, Northwest Territories, Canada. These microfossils occur as empty, 1–13 μm wide, tubular structures which are compressed parallel to lamination. The wider filaments probably represent the empty sheaths of Lyngbya-like oscillatoriacean cyanophytes, whereas the narrower filaments could represent either oscillatoriacean filaments or bacterial filaments. Filaments 3.0–7.0 μm wide are comparable to Siphonophycus crassiusculum and rare filaments 10.5–13.0 μm wide are comparable to Siphonophycus beltensis, both from shales of the Middle Proterozoic Belt Supergroup, Montana. Sphaeromorphs are rare and lack distinctive surface features which would permit their assignment to particular taxa.This shale-facies microbiota appears to consist entirely of organisms that had relatively thick sheaths which were highly resistant to degradation and diagenetic alteration. This microfossil assemblage, as well as other Proterozoic shale-facies assemblages, probably are biased toward degradation-resistant taxa and may not be representative of the original microbial communities from which they were derived, nor of the Proterozoic biosphere. Nevertheless, such microfossils offer promise for intercontinental biostratigraphic correlation and provide data useful in understanding the evolution of Precambrian life.
Geology and geochemistry of the molybdenite showings of the Ackley City batholith, southeast Newfoundland
Authors: Whalen J. B.
Published: April 2011

The Ackley City batholith of southeast Newfoundland is an oval-shaped granitoid of approximately 5400 km2 which intruded Ordovician and Precambrian rocks of the Gander and Avalon tectonic zones, respectively, about 345 Ma ago. It is a composite body, consisting mainly of K-feldspar megacrystic granite and alaskite. Spatially related to the southeast contact of the alaskite are younger aplites and pegmatites within which are six separate molybdenite showings. The showings vary in their type of host rocks and in features of mineralization and alteration, but can all be classed as being of aplite–pegmatite type.This notably felsic (SiO2 > 71.8%) pluton has alkaline affinities and features indicative of derivation from an igneous source (I-type). Some major and trace elements exhibit considerable variations. These variations and other geological features indicate that aplites and pegmatites formed by in situ fractional crystallization of the alaskite at shallow depths (1.8 to 3.7 km) to produce a roof-zone complex. Mo is localized in these rocks, which formed from the final residual melt and coexisting vapour phase, and is considered to be closely genetically related to them.
A rock labyrinth in the Front Ranges of the Rockies, Alberta
Authors: Simmons J. V. , Cruden D. M.
Published: April 2011

A rock labyrinth, a regular arrangement of large, joint-bounded chert blocks, separated by streets up to 15 m wide occurs on a dip slope of Upper Palaeozoic rocks in the Front Ranges of the Rocky Mountains, adjacent to the Red Deer River in Alberta. It is believed to be caused by the development of ice wedges under earlier, periglacial conditions and to have been disturbed by later creep along weak units in the sedimentary succession. Labyrinth development may be a typical response of gentle dip slopes in cohesive rock units to periglacial conditions, particularly if systematic jointing exists perpendicular to the slope.
Radio-frequency electrical properties of Green River oil shales
Authors: Rajeshwar K. , DuBow J. , Thapar R.
Published: April 2011

Laboratory measurements on the radio-frequency (10–103 MHz) electrical behavior of Green River oil shales were carried out using an automated frequency domain technique. Data are presented which show the variation of the relative dielectric constant (ε′), dielectric loss (ε″), and loss tangent (tan δ) with shale oil yield, frequency, temperature, and water content. The magnitude of these electrical parameters is shown to be sensitive to water content and possibly to varve geometry. The ε′ values tend to decrease and tan δ increases with increasing oil yield for shales subjected to prior thermal treatment at ~110 °C for 1–2 weeks. A systematic variation is observed in the degree of scatter and in the extent of correlation of tan δ and ε′ as a function of oil yield with each subsequent thermal treatment cycle. The manner in which variations in shale water content and (or) varve geometry influence the magnitude of the measured dielectric parameters is illustrated by duplicate measurements on samples with identical organic content. Such effects are shown to be important at low measurement frequencies (< 200 MHz). The temperature dependence of ε′ and ε″ is seen to be weak in the range 25–250 °C and appears to be largely dominated by temperature-induced changes in the water content of the shale.
An early Holocene Solodic paleosol near Priddis, Alberta
Authors: Sanborn P. , Pawluk S.
Published: April 2011

An early Holocene paleosol was found beneath Mazama Ash (ca. 6600 BP) near Priddis, Alberta. The paleosol pedon has strong textural and morphological differentiation, with an eluvial surface horizon, thick prismatic transitional horizon, and a Btb horizon containing both illuvial clay and organic matter. A Solonetz to Solod genetic sequence is inferred, probably related to changes in groundwater regime caused by stream entrenchment.
Macgowanella gen. nov., possible bryozoan holdfasts, Mississippian of southern Canadian Rocky Mountains, Alberta
Authors: Nelson Samuel J. , Bolton Thomas E.
Published: April 2011

Well-preserved, enigmatic and striking, partially interlocking slender star-like structures from the Mississippian of the southern Canadian Rockies are incertae sedis, but may possibly be bryozoan holdfasts. They represent a new genus, Macgowanella, and belong to species previously referred to Evactinopora? tenuiradiata Warren and E.? stellata Warren.
Lead isochron dating of the Seton Formation, East Arm of Great Slave Lake, Northwest Territories
Authors: Cumming G. L.
Published: April 2011

Dating of "spilitic" basalts from the Proterozoic Seton Formation by the Pb/Pb method yields an age of 1804 ± 23 Ma (2σ), in excellent agreement with Rb–Sr data on the same rocks, when the latter ages are calculated with currently accepted decay constants. It seems unlikely that spilitization could have reset both the Rb–Sr and Pb/Pb systems to yield exactly the same ages with no geologic scatter about the isochrons in either case, and, therefore, it may be that the isochrons represent the true age of deposition of the lavas.
Pleistocene loons of the Old Crow Basin, Yukon Territory, Canada
Authors: Fitzgerald Gerald R.
Published: April 2011

Ten Pleistocene fossils representing loons of the species Gavia stellata, Gavia arctica, Gavia immer, and Gavia cf. adamsii are reported from the Old Crow Basin in the northern Yukon Territory, an area which is presently outside the range of G. adamsii. One specimen of G. arctica is from beds that correlate to beds dating > 54 000 years BP and are presumed to be of Sangamon interglacial age. Two specimens of G. stellata and one of G. cf. adamsii have minimum dates of about 10 700 years BP.
Anorthosites of diverse magma types in the Puttuaaluk Lake area, Nain complex, Labrador
Authors: Ranson W. A.
Published: April 2011

Helikian anorthositic rocks in the Puttuaaluk Lake area, Labrador are in contact with granitic rocks of similar age and basement granulites of Archean (?) age. Internal variation within the anorthositic rocks has led to their subdivision into anorthosite, leuconorite, and oxide-rich anorthosite, which suggests three separate intrusive events and at least three magma types. The major differences among the anorthositic rocks are that anorthosite typically carries augite, leuconorite carries orthopyroxene ± augite, and oxide-rich anorthosite carries ilmenite ± magnetite with minor orthopyroxene. Plagioclase compositions plotted in the system Ab–An–Or lie within 3 mol% Or of the Ab–An join, and regression analyses for anorthosite and leuconorite show a slight decrease of K with decreasing An. Hence a distribution coefficient DKplag–liq ≥ 1.0 is implied for the anorthositic parent magmas.The average modal composition of the leuconorite, assuming 1% ilmenite, is 23% orthopyroxene and 76% plagioclase (volume percent). This approaches the cotectic composition (25% Opx, 75% Plag) for leuconorite estimated for the system OI–Plag–SiO2 after correction for the effects of Ab, Fe2+, and pressure. It is concluded that the leuconorite unit represents on the average a cotectic composition or a composition slightly more plagioclase-rich than the cotectic. It is likely that the leuconorite magma composition lay in the plagioclase field near the Plag–Opx join and the average rock composition. The low color index of the anorthosite unit, with an average modal composition, assuming 1% ilmenite, of 6% pyroxene and 93% plagioclase, suggests that crystallization from a magma equivalent to the rock composition is highly unlikely. Flotation of plagioclase from a leucogabbroic magma could account for the extreme plagioclase richness of the anorthosite unit. The oxide-rich anorthosite with its calcic plagioclase and abundant ilmenite cannot be the logical daughter product of either the anorthosite or the leuconorite and is more likely a product of a magma enriched in Fe-Ti oxide components relative to the other two units.
Resedimented volcaniclastics in the Carmanville area, northeastern Newfoundland—depositional remnants of Early Palaeozoic oceanic islands
Authors: Pickerill R. K. , Pajari Jr. G. E. , Currie K. L.
Published: April 2011

The olistostromal Carmanville ophiolitic mélange of northeastern Newfoundland contains two extensive mafic volcanic and volcaniclastic rafts (4 km × 1 km, 11 km × 7 km), which were previously interpreted as an assemblage of lavas and pyroclastics. These rafts are ? Upper Cambrian – Arenigian in age and, prior to tectonic transport and subsequent resedimentation and incorporation into the submarine slides (olistostromes) of the Carmanville ophiolitic mélange, were originally deposited on the slopes of a volcanic edifice (volcanic islands). The primary sedimentation history and depositional environment of the volcanic and volcaniclastic rocks are examined in detail. Four volcaniclastic facies are now recognized (facies 1–4), each differentiated on the basis of megascopic descriptive and genetic criteria. The essential characteristics of each facies are described in detail. These facies essentially represent shallow-water mafic volcanic material resedimented into a deeper water submarine slope or fan valley system by mass-emplacement depositional mechanisms, which included debris, turbidity, and possibly fluidized sediment flows. Normal contour-following bottom currents could possibly have been responsible for depositing or at least reworking some of the volcaniclastic siltstones of facies 3. Facies 1–4 were introduced into a deeper water environment itself characterized by the formation of massive and pillowed lavas and their hyaloclastic equivalents (facies 5) envisaged as the end product of deposition from submarine seamounts and guyots.