bluuebunny/crossref_metadata_2025 huggingface dataset:
Deep-water facies and depositional setting of the lower Conception Group (Hadrynian), southern Avalon Peninsula, Newfoundland
Authors: Gardiner S. , Hiscott R. N.
Published: April 2011

The lower part of the Hadrynian Conception Group is exposed in coastal outcrops near Holyrood Pond, St. Mary's Bay. Deep-water sediments of the Mall Bay Formation (>800 m) are overlain by glaciogenic debris flows of the Gaskiers Formation (250–300 m) and then by renewed turbidite deposition in the lower part of the Drook Formation (1000 m examined; formation thickness 1500 m). The main facies in the Mall Bay and Drook formations are thinly to very thickly bedded sand stone–mudstone couplets (turbidites), amalgamated in the thicker and coarser beds, and graded-stratified siltstones–mudstones. These are interpreted as deposits on an extensive basin floor and on the lower and middle parts of small-scale submarine fans that prograded from fringing volcanic islands. Paleocurrent data indicate a complex paleogeography dominated by active volcanic islands, probably like some modern volcanic arcs. The Gaskiers Formation was generated by glaciation of these islands.The Malll Bay Formation contains lenticular and wavy bedded siltstones–mudstones interpreted as the deposits of bottom currents, perhaps flowing parallel to the contours of the volcanic islands. In Phanerozoic sediments, bottom-current deposits in this setting would probably be thoroughly bioturbated.
An Ibexian (Early Ordovician) trilobite faunule from the type section of the Rabbitkettle Formation (southern Mackenzie Mountains, Northwest Territories)
Authors: Pratt Brian R.
Published: April 2011

The Rabbitkettle Formation is a widespread lower Paleozoic unit in the northern Cordillera. A trilobite faunule collected from the middle part of the type section and described here documents an early Ibexian (Early Ordovician) age for this interval and provides the first biostratigraphic reference point for the type section. This faunule is dominated by the agnostoid Micragnostus, the leiostegiid Leiostegium, and the remopleuridid Kainella. These genera and rarer taxa have North American, South American, and Austral-Asian affinities. A new species, Kainella eleutherolfi, is established.
Pb–Zn occurrences and their Pb-isotopic signatures bearing on metallogeny and mineral exploration—Paleozoic sedimentary rocks, northern Appalachians, Quebec
Authors: Schrijver K. , Marcoux E. , Beaudoin G. , Calvez J. Y.
Published: April 2011

Galena Pb-isotope ratios of epithermal vein and disseminated sulfide occurrences in the Taconian Orogen and Siluro-Devonian basin cluster around 17.90–18.05 for 206Pb/204Pb and 37.70–38.00 for 208Pb/204Pb. The major source of Pb in most, if not all, occurrences is a fairly common continental crust, a characteristic found in published analyses of Grenville feldspar Pb. A southwest to northeast increase in galena 206Pb/204Pb ratios is ascribed to the supply of several types of detritus from Grenville basement during the Cambro-Ordovician: coarse-grained, K-feldspar-bearing in the southwest, grading into fine-grained phyllitic, and relatively more highly radiogenic in the northeast.Emplacement (i) of Pb–Zn–barite veins and disseminations, commonly of homogeneous crustal Pb-isotopic signature, was late Taconian; (ii) of Pb–Zn–quartz veins, of less homogeneous signature, was post-Taconian; and (iii) of Pb–Zn–carbonate veins, relatively highly radiogenic and commonly homogeneous, was late or post-Acadian. Signatures of the first-mentioned group seem to be most useful in exploration.
Sediment characteristics and sea-level history of Royal Roads Anchorage, Victoria, British Columbia
Authors: Linden R. H. , Schurer P. J.
Published: April 2011

High-resolution and airgun seismic-reflection mapping of the approaches to Esquimalt Harbour, Juan de Fuca Strait, reveal that offshore, sea-floor sediments consist of a widespread glaciomarine unit recognizable to the entrance of the strait. The upper part of the unit has been dated at approximately 10 000 radiocarbon years BP. An early postglacial sea-level low of at least −50 m appears to have formed a widespread unconformity. Nearshore sediments above the unconformity consist of sands, muddy fine sands, and minor gravel that were deposited in a prograding marine environment. Sediments have been accumulating off Esquimalt Harbour at a rate of approximately 1.9 cm per 100 years.
Automated editing and true-amplitude stacking of seismic data
Authors: Mayrand Louis J. , Milkereit Bernd
Published: April 2011

Lateral changes in recording conditions often require that trace amplitudes be balanced, with consequent loss of information on the lateral amplitude variation of reflected energy. We present a quality-control and automated editing algorithm that recognizes source and geophone coupling problems and different noise levels along the survey line. Problem traces are discarded, and true-amplitude stacking of the remaining ones is possible with constant scaling factors. Application of the algorithm to one of the Vancouver Island LITHOPROBE profiles gives a nominal signal-to-noise improvement of 15 dB and a better understanding of recording problems in the field. Our analysis shows that the varying strength of a reflection from near the top of the subducting Juan de Fuca plate cannot be explained by changing recording conditions alone. Results suggest that the extra effort involved in the automated optimization of common midpoint stacks of low signal-to-noise deep seismic data is warranted only if lateral amplitude information is to be preserved.
Volcanism on the passive margin of Laurentia: an early Paleozoic analogue of Cretaceous volcanism on the northeastern American margin
Authors: Kumarapeli Stephen , Seymour Karen St. , Pintson Hillar , Hasselgren Elizabeth
Published: April 2011

Allochthonous masses of basaltic lava flows and related tuffs are present in several localities in an approximately 30 km long segment of the western margin of the Granby Nappe, in southeastern Quebec. They occur either as numerous small blocks in the Drummondville wildflysch related to the nappe or as larger masses intercalated with sedimentary sequences of limestone and shale of probable Late Cambrian to Early Ordovician age. These latter occurrences and the associated sedimentary units form "island-like" areas within lithologies of the Granby Nappe consisting of Cambrian sediments that accumulated on the continental rise. Their overall characteristics suggest that they represent slabs derived from the shelf margin of Laurentia and incorporated into the cratonward-moving nappes during the Middle Ordovician Taconian Orogeny.The volcanic rocks are mainly transitional but include some alkali olivine basalts. There are some indications that their affinities are to basaltic rocks of seamount chains localized along leaky transform faults. The segment of the continental margin from which the volcanic rocks were derived originated in the latest Precambian times, by rifting involving a rift–rift–rift (RRR) triple junction. Thus, it was a likely location for deep-seated transverse fracture zones linked to ridge-to-ridge transform faults of Iapetus. Therefore, the best explanation of the volcanism is that it was localized along such fracture zones. This episode of Late Cambrian – Early Ordovician volcanism related to the Iapetus cycle is probably analogous to the recently documented Early Cretaceous volcanism related to the Atlantic cycle on the northeastern American margin.
Seismic stratigraphy of late Cenozoic sediments in the northern Labrador Sea: a history of bottom circulation and glaciation
Authors: Myers Robert A. , Piper David J. W.
Published: April 2011

The seismicstratigraphy of the upper 1 km of sediment in the northern Labrador Sea has been determined from the examination of about 26 000 line kilometres of seismic profiles. Four key reflectors (A to D) have been correlated with Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) holes and range in age from mid-Pliocene to approximately mid-Pleistocene. Ten seismic facies have been distinguished and are interpreted as resulting from slope progradation, turbidite deposition in channels and on the basin floor, and widespread contourite deposition.Tertiary sediments are predominantly hemipelagic or contourite, but in the mid-Pliocene, turbidite deposition began in the northeast Labrador Basin, which might reflect either Greenland glaciation or lowering of sea level. At the same time, widespread erosion and buildup of drift deposits indicate that there was an intensification of bottom-water circulation, probably reflecting high-latitude cooling. This was followed by a return to less dynamic conditions as increased sea-ice cover reduced bottom-water generation in high-latitude seas. A turbidite deep-sea fan developed off Hudson Strait in the Early Pleistocene. In the mid- and late Quaternary, there was a major increase in the supply of turbidites from the Labrador margin, accompanied by the development of an extensive channel system on the continental margin. This was a consequence of glacial ice sheets extending to the top of the continental slope and discharging sediment directly to deep water.
Eocene sedimentation and volcanism in the Fig Lake Graben, southwestern British Columbia
Authors: Thorkelson Derek J.
Published: April 2011

The Fig Lake Graben is a narrow, complex Eocene basin that developed along part of the Coldwater fault system in southwestern British Columbia. Its origin as a pull-apart basin is probably related to dextral wrench faulting along the Fraser Fault and low-angle normal faulting of the Okanagan shear zone. Within the graben are Kamloops Group volcanic and sedimentary rocks, the thickness of which implies that one fault block has been downthrown at least 4.5 km. Geochemical interpretation of previously published analyses of Kamloops Group volcanic rocks indicates that magma production was genetically related to both extension and subduction.
The continent–ocean boundary south of Flemish Cap: constraints from seismic refraction and gravity
Authors: Todd B. J. , Reid I.
Published: April 2011

A seismic-refraction survey providing deep crustal structural information on the continent–ocean boundary south of Flemish Cap on the east coast of Canada was carried out using large air-gun sources and ocean-bottom seismometers. The seismic-refraction results and gravity modelling suggest that thinned continental crust extends 25 km seaward of the shelf break. The transition from continental to oceanic crust with a main crustal layer p-wave velocity of 7.3 km/s extends seaward over 100 km to the south. One refraction profile with thin (~4 km) oceanic crust was probably shot on, or very near, the trace of a fracture zone. Previous plate reconstructions have suggested that Cretaceous-age sea-floor spreading south of Flemish Cap occurred as a series of short spreading segments offset by transform fauits, or by asymmetric rifting between Iberia and Flemish Cap. This study suggests that an oblique shear margin may have formed south of Flemish Cap. possibly as a result of transcurrent motion between Flemish Cap and Iberia.
Bedforms, bed material, and bedload transport in a salt-wedge estuary: Fraser River, British Columbia
Authors: Kostaschuk R. A. , Church M. A. , Luternauer J. L.
Published: April 2011

The lower main channel of the Fraser River, British Columbia, is a sand-bed, salt-wedge estuary in which variations in velocity, discharge, and bedform characteristics are contolled by river discharge and the tides. Bed-material composition remains consistent over the discharge season and in the long term. Changes in bedform height and length follow but lag behind seasonal fluctuations in river discharge. Migration rates of bedforms respond more directly to river discharge and tidal fall than do height and length. Bedform characteristics were utilized to estimate bedload transport in the estuary, and a strong, direct, but very sensitive relationship was found between bed load and river discharge. Annual bedload transport in the estuary is estimated to be of the order of 0.35 Mt in 1986. Bedload transport in the estuary appears to be higher than in reaches upstream, possibly because of an increase in sediment movement along the bed to compensate for a reduction in suspended bed-material load produced by tidal slack water and the salt wedge.
A Lower Cambrian Eotebenna (Mollusca) from Arctic North America
Authors: Peel John S.
Published: April 2011

The helcionellacean mollusc Eotebenna Runnegar and Jell, 1976 is described from the Lower Cambrian Henson Gletscher Formation of central North Greenland, part of the Franklinian Basin sequence of Arctic Canada and adjacent northern Greenland. The Henson Gletscher Formation specimens of Eotebenna are the first Lower Cambrian and North American records of a genus originally described from the Middle Cambrian of Australia. A new species, Eotebenna arctica, is described.
40Ar/39Ar mineral ages from Kellys Mountain, Cape Breton Island, Nova Scotia: implications for the tectonothermal evolution of the Avalon composite terrane
Authors: Keppie J. Duncan , Dallmeyer R. D.
Published: April 2011

Hornblende from a diorite stock within the Kellys Mountain plutonic complex within the Avalon composite terrane, and hornblende, muscovite, and biotite from amphibolite and gneiss within the contact aureole record similar 40Ar/39Ar plateau ages of 493–498 Ma. These data indicate relatively rapid cooling through the contrasting temperatures appropriate for intracrystalline retention of argon in the different minerals. This is consistent with the relatively high level of intrusion of the pluton (3–10 km) suggested previously from the study of mineral assemblages developed in the contact aureole. These relationships suggest that intrusion of the Kellys Mountain complex took place at approximately 500 Ma, indicating an age close to the Cambro-Ordovician boundary. The complex may have formed in the same within-plate rifting regime as the Middle Cambrian Bourinot Group volcanic sequences exposed within the Avalon composite terrane.
Structural geometry and kinematic evolution of the eastern Cascades foldbelt, Washington and British Columbia
Authors: McGroder Michael F.
Published: April 2011

The eastern Cascades foldbelt is one of three structural domains lying within the complex collision zone between the Insular and Intermontane composite terranes in northern Washington and southern British Columbia. The foldbelt resides between the high-grade metamorphic backbone of the Cascade orogen on the west and rocks of the composite Intermontane terrane to the east. It encompasses the stratigraphically coherent, basalt-floored Jura–Cretaceous Methow basin as well as more chaotically disposed Permian–Jurassic oceanic rocks of the Hozameen terrane. Methow basin rocks are thought to have been sutured above the oceanic rocks prior to the middle Cretaceous contractional episode described in this report.Based on the analysis presented herein, between ca. 100 and 88 Ma the rocks in the foldbelt underwent shortening in an east-northeast – west-southwest direction by 50 km or more, largely by displacement on the east-vergent Jack Mountain – Chuwanten thrust system. The early stages of contraction occurred by the process of tectonic wedging, whereby rocks of the Hozameen terrane and western Methow basin translated eastward by delaminating eastern Methow basin strata along west-vergent thrusts. In later stages of shortening, the tectonic wedge became inactive and was carried piggyback atop the east-vergent Cascade Crest and Chuwanten faults.Presently available geochronologic data indicate overlap in the time periods during which eastern and western Cascades foldbelts were deforming and the Cascade metamorphic core was undergoing amphibolite-facies regional metamorphism. Therefore, contraction of rocks in the eastern foldbelt was an important product of the middle Cretaceous orogeny in the Cascades and must be considered in any regional tectonic model for orogenesis. The eastern foldbelt clearly accommodated substantially less shortening than the western foldbelt and is herein proposed to be a backthrust system in the rear of the predominantly west-vergent Cascade orogen.
Petrochemistry of the Yellowknife volcanic suite at Yellowknife, N.W.T.
Authors: Cunningham M. P. , Lambert R. St J.
Published: April 2011

The petrochemistry of the Yellowknife volcanic belt at Yellowknife (Kam, Duck and Banting formations) shows the suite to be more chemically complex than previously thought. The Kam Formation (65% basalt, 27% basaltic andesite, 17% andesite, and 2% dactite) has a strong tholeiitic trend, involving pyroxene fractionation, which shows iron enrichment to FeO/(FeO + MgO) = 0.75. After altered samples are removed from consideration, it can be shown that the Kam is chemically analogous to modern ocean-floor or ocean-rise tholeiites. The andesitic members of the Kam were partially melted from a hornblendic region, presumably former oceanic crust, possibly with a slight sialic component. The Duck Formation (11% basalt, 21% basaltic andesite, 59% andesite, and 9% dacite) shows considerable evidence of alkali mobility, with varied carbonate content. It is thought to have been largely derived as partial melts from former oceanic crust via hornblende fractionation. The Banting Formation (14% basalt, 7% basaltic andesite, 38% andesite, and 41% dacite) was also derived from an ocean-crust parent, with hornblende fractionation forming a calc-alkaline suite. There is also consistent major- and trace-element evidence that the relationship between Kam parental magmas and Duck–Banting parental magmas involved magnetite as well as hornblende. A petrogenetic model, starting from garnet or spinel lherzolite, with extensive fractionation and (or) partial melting of a preexisting oceanic crust, which may be either true oceanic crust or the lower part of a thin continental crust, is proposed. The whole suite appears to have been formed in one series of related events, developing a rifted ensialic environment at a late stage in the evolution of the Slave craton. It is shown that major- and trace-element discrimination diagrams yield highly varied tectonic conclusions about this sequence, and it is concluded that in general the diagrams are inapplicable to Archean volcanic sequences.
Carbonate till as a soft bed for Pleistocene ice streams on the Canadian Shield north of Lake Superior
Authors: Hicock Stephen R. , Kristjansson Fridrik J. , Sharpe David R.
Published: April 2011

Silty carbonate till derived from erosion of Paleozoic carbonate and Proterozoic rocks within and adjacent to Hudson Bay covers extensive areas of the Canadian Shield north of Lake Superior. It is hypothesized that this carbonate till could have acted as low-resistance substrata for overriding ice streams by deforming and (or) supporting high subglacial water pressures. Contrary to assumptions presented in some current models for ice flow within the Laurentide Ice Sheet, it need not be assumed that Shield terrain in these areas acted as a rigid bed, generating large basal shear stresses and inhibiting ice flow. Indeed, erratic-dispersal patterns, long-distance glacial transport, and splayed patterns of ice-flow indicators in areas of thick till cover may be better explained by rapid ice-flow events or ice streams, enhanced by the thickness, distribution, impermeability, and susceptibility to deformation of fine carbonate till.
Stratigraphic variations in carbon and oxygen isotopes in the dolostone of the Carswell Formation (Proterozoic) of northern Saskatchewan
Authors: Abell P. I. , McClory J. , Hendry H. E. , Wheatley K. L.
Published: April 2011

Petrographic and stable isotopic analyses of stromatolitic sediments deposited in nearshore environments provides us with some of the best information available on ancient environments. Diamond drill hole CAR 58 penetrated 110 m of sediments in the lowermost part of the Proterozoic (probably Helikian age) Carswell Formation of northern Saskatchewan and gave us such an opportunity. The rocks are mainly dolostone and include, in descending order of abundance, cyanobacterial laminites, stromatolites, dolomicrites, dolorudites, breccias, and oolites. Stromatolites and Cyanobacterial laminites increase in abundance up-section, and deposition is interpreted as having taken place in conditions of increasingly restricted water circulation through time. The carbon isotope ratios vary from about −0.5 to −1.5‰ (Pee Dee Belemnite (PDB)) in the section except near the base where they assume values near −2.5‰. The oxygen isotope ratios (vs. PDB) increase from about −9.3‰ at the base to −7‰ at the top, with anomolously high values, more positive than −7‰, at two positions in the sequence. Original depositional structures and textures are still visible in most of the rocks, but gypsum has been replaced by dolomite, there has been some silicification, and original features have been obliterated by dolomite rhombs in a few samples. The upward trend to less-negative values of the oxygen isotope ratios is interpreted in terms of changing depositional environment involving a deepening but more protected basin, with increased evaporational concentration of the heavier isotope. Scatter diagrams of carbon and oxygen isotope ratios place the Carswell Formation dolomites close to the mainstream of other Proterozoic stromatolites but indicating some evaporative alterations during deposition.
Le transport chimique de l'or dans les environnements de surface: formation d'un colloïde et complexation organique
Authors: Bergeron Mario , Harrison Yves
Published: April 2011

Two different categories of experiments were undertaken to determine the significance of humic substances in the chemical transport of gold. The experiments of the first category were designed to study Au(Cl)4− reduction by humic acid at pH 3.5, which is consistent with the formation of this ion in sulfide oxidation zones. These experiments were repeated with denaturated humic acid (obtained by heating in an acid medium). The results show that Au(Cl)4− is reduced by humic acid to an unstable colloid, but not by denaturated humic acid. The purpose of the second category of experiments was to study gold solubility in various organic materials: humic acid, fulvic acid, and potassium humate. Solutions of these substances and demineralized water (the latter served as the reference point) were placed in contact with metallic gold for 1 month at pH 7, the common pH in surface environments. The data indicate an increase in gold solubility according to the following order: humic acid < fulvic acid < potassium humate. A two-step gold chemical-transport mechanism for surface environments is proposed on the basis of our results. In the first step, unstable colloidal gold is formed from inorganic complexes produced in the sulfide oxidation zones (zones with acidic pH). After full oxidization, the pH moves to the normal value, causing the dissociation of functional groups in humic substances. In the second step, these humic substances, through the dissociated functional groups, could form organo-metallic complexes with gold, ensuring gold dispersion in surface environments. [Journal Translation]
Electromagnetic sounding and crustal electrical conductivity in the region of the Wopmay Orogen, Northwest Territories, Canada
Authors: Camfield P. A. , Gupta J. C. , Jones A. G. , Kurtz R. D. , Krentz D. H. , Ostrowski J. A. , Craven J. A.
Published: April 2011

Temporal variations of the three components of the geomagnetic field were recorded at eight sites along a 240 km profile across the Early Proterozoic Wopmay Orogen. After an empirical separation of these data into normal and anomalous parts, horizontal-to-vertical-field transfer functions in the period range 40–1200 s display evidence for a minor anomaly spatially located near the allochthonous shelf margin at the eastern edge of the Hepburn Batholith. The observations can be partially simulated by a two-dimensional 20 ? m body (30 km wide, 2 km thick) embedded in the surface of a very resistive layered Earth model derived from inversion of magnetotelluric sounding data at a central station. The body correlates spatially with metamorphosed graphitic pelites of the Odjick Formation (Epworth Group), a unit of deep-water facies interpreted as continental slope–rise deposits. Laboratory measurements on samples of the pelite yielded resistivity values of the order of 104 ?∙m, so the enhanced conductivity of the body is more likely caused by water filling cracks associated with the pelites' well-developed cleavage and schistosity, rather than by the graphite. A scalar audiomagnetotelluric survey across the Wopmay fault zone, a prominent structure that bisects the orogen, gave results very much distorted by three-dimensional effects. The electric-polarization apparent resistivities of these data indicate a shallow conductor 2 km east of the fault scarp, 1–2 km wide. Models of the feature suggest that its vertical extent is at least 1–2 km.
Age of the Firesand River carbonatite complex from paleomagnetism
Authors: Symons D. T. A.
Published: April 2011

The 2.3 km diameter Firesand River complex intrudes Archean volcanics and granites of the Wawa Subprovince in the Superior Province about 8 km east of Wawa, Ontario. It has given differing Middle Proterozoic K–Ar biotite ages of 1018 ± 50 and 1097 Ma. Alternating-field and thermal step demagnetization of specimens from three calcific carbonatite sites, five ferruginous dolomitic carbonatite sites, and one lamprophyre dike site isolated a stable mean direction of 290°, 33 °(α95 = 12°). Isothermal remanent magnetization tests indicate the remanence is held by single-to pseudosingle-domain magnetite and hematite in the carbonatite. The dike remanence is Keweenawan in age, thereby confirming its genetic relationship to the complex, and it gives a positive partial contact test with its host rock, indicating no postintrusive remagnetization. The blocking-temperature spectra indicate that postintrusive uplift has not exceeded about 4 km. The pole position for the complex is 183°E, 27°N (dp = 8°, dm = 13°). This pole lies directly on the well-dated Keweenawan apparent polar wander path, giving an age of 1090 ± 10 Ma, in agreement with the older K–Ar age. It also confirms geologic and aeromagnetic evidence that the complex has not been tectonically tilted since emplacement.
Gold mineralization in Lower Cambrian McNaughton Formation, Athabasca Pass, Canadian Rocky Mountains: structural, mineralogical, and temporal relationships
Authors: Shaw Robert P. , Morton Roger D.
Published: April 2011

Gold-bearing quartz veins were recently discovered in archimetamorphic quartzite–rudite and quartzite–pelite sequences of the Lower Cambrian McNaughton Formation in the main ranges of the central Canadian Rocky Mountains. There are two distinct vein types: an early syntectonic, syn- to postmetamorphic, auriferous, bedding-parallel type, generated during repeated northeast-directed compressive tectonism; and a late, postpenetrative deformational discordant type, which contains only minor gold (<500 ppb Au). Gold emplacement and discordant veining were confined to the onset of late compression leading to development of the Chatter Creek Fault.The spatial distribution and dimensions of the veins attest to mechanically founded lithologic anisotropy. Bedding-parallel veins are confined to less competent, volumetrically minor pelitic rock types. Discordant veins are confined to competent quartzitic units.Bedding-parallel vein filling took place in two paragenetic stages: a protracted, pre-gold stage (quartz ± minor white mica and pyrite) depositing over 90% of vein material; and a late gold-bearing–post-gold stage (quartz–pyrite–gold–galena ± white mica and Fe carbonate). Gold usually occurs in association with brecciated pelites and penecontemporaneous sulfides. Discordant veins (quartz ± minor pyrite) record a single stage of vein filling broadly coeval with gold deposition. Minor hydrothermal alteration (pyrite ± white mica ± carbonate) of adjacent wall rocks accompanied gold emplacement and is mineralogically congruent with the regional archimetamorphic and bedding-parallel vein assemblages.In terms of their setting and morphology, the Athabasca Pass gold lodes are viewed as a siliciclastic-hosted analogue of the turbidite-hosted class of gold deposits. Principle geochemical differences from published process models for turbidite-hosted gold deposits are a function of the mineralogical maturity of the siliciclastic host strata in the Athabasca Pass.
Proterozoic deformation beneath Banks Island: implications for the regional extent of the Racklan orogeny
Authors: Cook Frederick A.
Published: April 2011

Seismic reflection data from the northeast corner of Banks Island in arctic Canada show that Proterozoic layers were subjected to at least two deformational events prior to the Cambrian. The oldest of these events involved folding and faulting(?) from west-northwest to east-southeast. The ages of the layers that were subjected to this deformation are unknown; however, younger Proterozoic layers, probably correlative with the Shaler Group (ca. 1.1–0.8 Ga), unconformably overlie the folded and faulted layers, and were themselves regionally arched prior to the Cambrian. The relative position of the oldest deformed strata is thus the same as that of the strata observed to the south beneath the Anderson Plains, where thrust faulting and folding deformed pre-Mackenzie Mountains Supergroup (Shaler Group equivalent) layers during at the time of the Racklan orogeny (ca. 1.1–1.2 Ga). Distant effects of the Racklan orogeny may therefore extend to at least the northeast side of Banks Island.
Age of a K-feldspar megacrystic granite from the Burgeo intrusive suite, and timing of tungsten mineralization at Grey River, southern Newfoundland
Authors: Higgins N. C. , Halliday A. N. , Mitchell J. G.
Published: April 2011

A K-feldspar megacrystic biotite granite phase of the Burgeo intrusive suite, southern Newfoundland, has been dated by the Rb–Sr whole-rock method. The isochron age of 412 ± 5 Ma (initial 87Sr/86Sr ratio = 0.7086 ± 0.0004) is consistent with the younger of two U–Pb zircon ages obtained from other phases of the Burgeo intrusive suite. The southern margin of the granite is intensively deformed in a shear zone that also affects amphibolitic gneisses of the Grey River enclave. Data from deformed granite samples plot below the 412 Ma isochron and may have resulted from reaction and partial reequilibration of the samples with a hydrothermal fluid of low initial 87Sr/86Sr ratio during metasomatic reactions accompanying shear zone deformation. However, alternative hypotheses such as crustal contamination or derivation from two separate and isotopically distinct magmas cannot be discounted. Mica ages between 390 and 370 Ma associated with tungsten mineralization at Grey River confirm that the mineralization was unrelated to the Burgeo intrusive suite. They support previous conclusions, based on geological and geochemical data, that the mineralization was related to posttectonic leucogranite intrusions.
Paleomagnetism of the Mississippi Valley-type ores and host rocks in the northern Arkansas and Tri-State districts
Authors: Pan H. , Symons D. T. A. , Sangster D. F.
Published: April 2011

A paleomagnetic study has been done on 452 specimens from the Early Ordovician Cotter and Middle Ordovician Everton formations in the northern Arkansas Mississippi Valley-type (MVT) lead–zinc ore district and from the Mississippian Warsaw and Keokuk formations in the Tri-State MVT district. Progressive alternating-field and thermal demagnetization first removed a steep normal modern viscous remanence component, leaving an underlying stable remanence of very low intensity (0.3 × 10−5 – 3 × 10−5 A/m). In the Tri-State area, further demagnetization of unaltered host rocks at seven sites in the Warsaw Formation yields a B component with a mean direction of declination (D) 146°, inclination (I) 14 °(A95 = 13°), corresponding to a paleopole of 130°E, 31°N (Dp = 7°, Dm = 14°), which is a primary Mississippian remanence. In northern Arkansas further demagnetization reveals an A component at 9 sites with a mean direction of D 156°, I 30° (A95 = 7°) and a C component at 14 sites of D 160°, I 1 °(A95 = 9°), corresponding to pole positions of 116°E, 33°N (Dp = 4°, Dm = 8°) and 119°E, 49°N (Dp = 4°, Dm = 9°), respectively. Almost all of the A-component sites are from unmineralized dolomite, whereas all of the C-component sites are from mineralized locations. This correlation suggests that the A magnetization is related to Late Devonian secondary dolomitization and the C magnetization to Permian mineralization produced by brines migrating from the Arkom basin upon deformation and uplift during the Ouachita orogeny.
An application of ground penetrating radar to peat stratigraphy of Ellice Swamp, southwestern Ontario
Authors: Warner Barry G. , Nobes David C. , Theimer Brian D.
Published: April 2011

Ground penetrating radar (GPR) has been applied to the mapping of stratigraphy and peat thickness of a large bog in southwestern Ontario. The GPR survey was undertaken in conjunction with a conventional coring survey and measurement of peat physical properties. The results indicate that GPR responds to peat moisture content and bulk density, which vary with stratigraphic changes. In particular, the acrotelm–catotelm boundary and the basal clay are GPR reflectors. The presence of gyttja above the clay is indicated by complex basal reflections. Ground penetrating radar is a viable alternative to an intensive coring survey for evaluating peat depth and extent.
Late Quaternary movement of Aspy Fault, Nova Scotia
Authors: Grant Douglas R.
Published: April 2011

An emerged Sangamonian (125 ka) intertidal rock platform at +7 m asl is apparently upthrown to +22 m asl along Aspy Fault on Cape Breton Island. The 15 m displacement may be an isostatic response to rapid ice retreat or erosional unloading, or it may be a tectonic effect due to release of crustal stress stored during Wisconsinan glacier cover.
Thermochronologic constraints on ore formation at the Gays River Pb–Zn deposit, Nova Scotia, Canada, from apatite fission track analysis
Authors: Arne Dennis C. , Duddy Ian R. , Sangster Don F.
Published: April 2011

Fission tracks in detrital apatites from the Cambro-Ordovician metasedimentary basement in the vicinity of the Carboniferous-hosted Gays River Pb–Zn deposit, Nova Scotia, provide a record of final cooling during uplift and erosion of the Meguma Zone and constrain the timing of ore formation. Apatite fission track ages range from 203 to 241 Ma, with typical uncertainties of ± 10 Ma. Mean confined track lengths generally vary between 12.0 and 13.4 μm and indicate that the apatites record "apparent" ages only. An inferred thermal history involving regional heating to paleotemperatures > 110 °C during late Paleozoic burial followed by cooling to ~ 110 °C prior to 240–220 Ma is suggested. A more recent phase or regional heating to paleotem-peratures probably in the range of 60–80 °C during Late Cretaceous – early Tertiary (ca. 100–50 Ma) burial is also indicated by the track length data. Apatite fission track ages and mean track lengths from drill-core samples immediately beneath the Gays River orebody are similar to those for regional outcrop samples. At minimum temperatures > 200 °C estimated for ore formation, sulphide mineralization must either have preceded or accompanied regional heating to paleotemperatures > 110 °C during the late Paleozoic. Sulphide mineralization at Gays River must therefore have taken place at some time after ca. 330 Ma (the stratigraphic age of the lower Windsor Group host rocks) but before ca. 240–220 Ma (the last cooling of Meguma Group basement below 110 °C). These constraints on the timing of ore formation at Gays River are compatible with previous suggestions that Pb–Zn mineralization of Carboniferous strata in Nova Scotia occurred at ca. 300 Ma.
Seasonal growth bands in pingo ice
Authors: Mackay J. Ross
Published: April 2011

Field studies of pingo ice show that alternating clear and bubble bands may grow when water freezes at the top of a subpingo water lens. A study of the banding at one excellent exposure of pingo ice shows that the clear bands probably grew during propagation of the cold winter temperature waves, the bubble bands, from the warmer summer temperature waves. The likely cause for the gradual transitions from clear to bubble bands followed by the abrupt transitions from bubble to clear bands was marked asymmetry of the periodic temperature waves in permafrost overlain by an active layer whose thermal properties varied seasonally. Pingo growth, as determined from the growth of bands, shows good agreement with Stefan's equation where growth varied as the square root of time. Geochemical profiles show no systematic change with depth. Stable-isotope profiles for δ18O and δD show linear trends with depth and a depletion of the heavy isotopes. The co-isotope slope of 7.2 suggests freezing, with the input being impoverished in the heavy isotopes.
Biostratigraphy of the Albian Paddy Member (Lower Cretaceous Peace River Formation), Goodfare, Alberta
Authors: Stelck C. R. , Leckie Dale A.
Published: April 2011

Thirty-seven taxa of arenaceous foraminifera, recovered from cores of the upper part of the Paddy Member (Peace River Formation) and the superjacent lower Shaftesbury Formation in the Goodfare area of northwestern Alberta, are assigned to the lower part of the Verneuilina canadensis Subzone of the Miliammina manitobensis Zone of the Lower Cretaceous (upper Albian). A stratigraphic hiatus of eight foraminiferal subzones is implied between the Paddy Member and subjacent Cadotte Member. Progressive transgression of the M. manitobensis sea is reflected by a succession of four faunules of foraminifera and trace fossils. Shallow-water facies and reduced salinity are indicated for the Paddy environment, and a return to normal salinity during deposition of the overlying Shaftesbury Formation. A distinctive Miliammina–Ammotium faunule is figured from the upper part of the Paddy Member.
Sulphide remobilization in Archean volcano-sedimentary rocks and its significance in Proterozoic silver vein genesis, Cobalt, Ontario
Authors: Smyk Mark C. , Watkinson David H.
Published: April 2011

The Archean volcano-sedimentary succession at Cobalt, Ontario, consists mainly of submarine andesitic flows and turbiditic interflow sedimentary rocks. Steeply dipping faults and large-scale, tight to isoclinar folds have developed in these basement rocks. The faults commonly host silver-vein-bearing structures that extend upward into overlying Proterozoic units. Synvolcanic and synsedimentary base metal sulphide deposits are ubiquitous in the Archean rocks. Epigenetic sulphide mineralization consists of remobilized and replacement sulphides and minor sulpharsenides. Epigenetic sulphides occur in permeable rocks and in fault and fracture zones, commonly in juxtaposition with silver veins.The coincidence of silver veins and structures containing remobilized sulphides suggests that sulphide remobilization from Archean basement rocks into Proterozoic vein-bearing structures predated or accompanied vein development. Sulphide remobilization may have also facilitated the mobilization (leaching) of metals from basement sulphides into the vein-forming hydrothermal fluids.
Oxygen-isotope composition and temperature of fluids involved in deposition of Proterozoic sedex deposits, Sudbury Basin, Ontario
Authors: Davies J. F. , Leroux M. V. , Whitehead R. E. , Goodfellow Wayne D.
Published: April 2011

Sedex Cu–Pb–Zn deposits in the Sudbury Basin were deposited on the sea floor from fluids in which δ18O = −1‰ and at temperatures around 170 °C. Distal Mn-bearing sediments were deposited in seawater in which δ18O ≈ −3‰ and at temperatures around 125 °C. The fluids at the vent site (δ18O ≈ −1‰) probably represent a mixture of normal seawater and isotopically positive hydrothermal fluid generated in the substrate by seawater–rock reactions. The heat source responsible for convection and venting onto the sea floor and into the water column was the underlying Sudbury Irruptive, which was emplaced immediately following deposition of the Onaping Formation, directly above which the sedex deposits lie.
Age of the Bowen Island Group, southwestern Coast Mountains, British Columbia
Authors: Friedman R. M. , Monger J. W. H. , Tipper H. W.
Published: April 2011

A new U–Pb date of [Formula: see text] for foliated felsic metavolcanic rocks of the Bowen Island Group, from Mount Elphinstone in the southwesternmost Coast Mountains of British Columbia, indicates that there the age of this hitherto undated unit is early Middle Jurassic. These rocks grade along strike to the north-northwest into a more sedimentary facies, which north of Jervis Inlet contains a probable Sinemurian (Lower Jurassic) ammonite. The Bowen Island Group thus appears to include Lower and Middle Jurassic rocks and to be coeval in part with volcanic rocks of the Bonanza Formation on Vancouver Island to the west and the Harrison Lake Formation within the central Coast Mountains 75 km to the east.
Deep crustal structure beneath a rifted basin: results from seismic refraction measurements across the Jeanne d'Arc Basin, offshore eastern Canada
Authors: Reid I. D. , Keen C. E.
Published: April 2011

A crustal seismic refraction experiment was conducted across the south Jeanne d'Arc Basin, one of the rifted sedimentary basins on the Grand Banks, offshore eastern Canada, that developed in Mesozoic time in response to extension and rifting between the North American plate and the African, Iberian, and European plates. The primary objective of this experiment, which was carried out to correlate with an existing deep seismic reflection profile, was to delineate the deep crustal geometry below the basin. Ten ocean-bottom seismometers were deployed across the basin and recorded signals from a large air-gun array. The results show that the crust is primarily composed of two layers, with velocities of 5.8–6.1 and 7.2 km/s, respectively. There is very little relief on the Moho across the basin, with only a 2 km step, from a depth of 37 to 35 km, occurring west of the basin. There is, however, considerable complexity of crustal structure, particularly near Moho depths. These results are valuable when used in conjunction with other data in the region, in particular gravity and deep seismic reflection data. The seismic reflection and refraction data sets together give a fairly complete picture of crustal geometry in the crust. The flat Moho below the basin is compatible with the detachment of the major basin-bounding fault in the lower crust or at the Moho, as seen on the reflection data. The 7.2 km/s layer is not restricted to the zone of Mesozoic crustal extension below the basin, but occurs also below relatively unextended parts of the crust. This layer may represent basaltic intrusion or underplating during a rifting event. It may also correspond to the reflective lower crust observed on the deep seismic reflection data. These results provide strong constraints on models describing the origin and evolution of this and other rifted basins.
Coincident seismic-wave velocity and reflectivity properties of the lower crust beneath the Appalachian Front, west of Newfoundland
Authors: Marillier François , Dentith Mike , Michel Karin , Reid Ian , Roberts Brian , Hall Jeremy , Wright Jim , Louden Keith , Morel-à-l'Huissier Patrick , Spencer Carl
Published: April 2011

We have determined the seismic velocity structure of the crust in the vicinity of the Appalachian deformation front off western Newfoundland and the adjacent Gulf of St Lawrence. These measurements were made from two perpendicular wide-angle seismic refraction profiles, one of which is collinear with a previously recorded deep seismic reflection profile. The Grenville foreland crust, about 45 km thick, is characterized by velocities of 6.35 km/s in its upper part and 6.7 km/s in its lower part. Close to the coast of Newfoundland, a deep crustal reflective wedge is bounded by a northwest-dipping reflector and by the crust–mantle boundary, which is at only 39 km depth beneath the wedge. In the wedge, velocities of 7.2–7.3 km/s may indicate the presence of mafic and ultramafic rocks. We speculate that several processes could have caused the high velocities and the high reflectivity. The most attractive is perhaps crustal extension with consequent underplating during the formation of the Iapetus Ocean or during later reactivation by Carboniferous strike-slip movements.
A Mazama tephra marker bed in the Fraser Lowland, British Columbia
Authors: Williams Harry F. L. , D'Auria John
Published: April 2011

Drill cores from the Fraser River delta and western Fraser River floodplain, British Columbia, reveal a widespread tephra marker bed within silty floodplain deposits. Isolated tephra layers have been noted in previous studies in the Fraser Lowland and have been assumed to be Mazama tephra (ca. 6800 BP). This note presents the results of the first attempt to systematically identify a number of tephra samples from this area, based on X-ray energy spectroscopic analysis of their chemical compositions and bracketing radiocarbon ages. The results confirm that the tephra bed is Mazama, a finding of considerable utility to future studies in this area.
Two-stage evolution in an Archean tonalite suite: the Taschereau stock, Abitibi (Quebec, Canada)
Authors: Jébrak Michel , Harnois Luc
Published: April 2011

The Taschereau stock occurs north of Timmins and Val-d'Or, Quebec, in the Abitibi greenstone belt of the Superior Province. This late Archean composite pluton is composed mainly of diorite–tonalite–trondhjemite cut by granitic rocks. Gold–molybdenum occurrences are associated with a zone of albite-rich rocks surrounding the granitic rocks. Diabase dykes and shear zones postdate all rock units. Field and geochemical evidence suggests that the Taschereau stock was emplaced diachronously. Trace-element geochemical modelling shows that trace-element abundances (rare-earth elements, Ti, Zr) of Taschereau granitic rocks are consistent with partial melting of preexisting Taschereau tonalitic rocks and implies that these two rock types are not end members of a single magma that evolved through fractional crystallization.