bluuebunny/crossref_metadata_2025 huggingface dataset:
Geotectonics of Cretaceous and Eocene plutons in British Columbia: a paleomagnetic fold test
Authors: Symons D. T. A.
Published: April 2011

A total of 295 cores (590 specimens) were collected at 59 sites in the Coast plutonic complex along an E–W section southwest of Kitimat, British Columbia. The sites represent the Ponder, Alastair Lake, and Quottoon plutons in the 40–50 Ma eastern K–Ar age zone and the Ecstall and Butedale plutons in the 64–80 Ma central age zone. After af demagnetization a stable remanent magnetization was isolated at 32 sites and these data were combined with available data from the Skeena River section about 100 km to the north. The remanence directions in sites from the NNW-trending north and south limbs of the Hawkesbury Warp provide a positive fold test when compared to the WNW-trending centre limb directions.In the Eocene eastern age zone the NNW limbs give a concordant pole position relative to the cratonic North American pole whereas the centre limb has undergone ≈ 50° of the counter-clockwise rotation and ≈ 10° of upward tilt of its western end to give a discordant pole. In the late Upper Cretaceous central age zone, the Ecstall–Butedale pluton was tilted 15° to the west on all limbs before the Eocene intrusion and Hawkesbury Warp deformation events to give a NNW-trend pole and WNW-trend pole diverging in opposite directions from the cratonic reference pole.The geologic field evidence from structural trends, from fault, fold, contact, and foliation attitudes, and from distribution of plutonic phases is consistent with the structural model. The regional geotectonic events are related to possible Cenozoic plate interactions on the western margin of the North American plate. This combination of concordant and discordant poles cannot be explained in terms of an excursion of the geomagnetic paleopole during intrusion, a large scale northward translation of the western Cordillera during the Cenozoic, or a combination of clockwise rotations and northward translations on the margin of the advancing North American plate. The fold test and polarity reversal pattern indicate that all plutons acquired a primary thermoremanent magnetization (TRM) during cooling and probably within ≈ 1 Ma after emplacement.
A marine deep seismic sounding system
Authors: Clowes Ron M.
Published: April 2011

A marine seismic system for recording near-vertical incidence to wide-angle reflected waves and refracted waves with penetration from the ocean bottom to the upper mantle has been developed. Operations require two ships, one the receiving vessel, the other the shooting ship. Seismic signals are received by six individual hydrophone assemblies suspended at 45-m depth from a neutrally buoyant 610-m cable trailed from the receiving vessel. After filtering and amplification, the seismic data plus the WWVB radio time code are recorded on a multichannel, 14-bit digital data acquisition system. The shooting ship detonates explosive charges as it proceeds along a predetermined course. In order to calculate origin times and to monitor the source signature, the signal from a single hydrophone and the WWVB time code are recorded on a 2-channel chart recorder and 4-channel FM analog tape transport. The digital recording and multiple receivers provide increased dynamic range relative to analog methods, improve the capability for detecting subcritical incidence reflections, and enable the use of data processing techniques, including stacking of weak refraction arrivals. Examples of an expanding reflection record section from a deep water sedimentary basin west of Vancouver Island and of a refraction record section recorded across Explorer Ridge spreading centre show the quality of data which are acquired with the marine seismic system.
Northern extent of Lake Agassiz in eastern Saskatchewan
Authors: Langford F. F.
Published: April 2011

Surveys for a proposed hydroelectric dam, disclosed extensive deposits of late Pleistocene lacustrine clay in the valleys of the Churchill and Reindeer Rivers. The presence of montmorillonite in these clays and the topographic configuration suggest continuous connection to the main body of Glacial Lake Agassiz. The presence of till layers above the lacustrine deposits is explained by subaqueous slumping rather than read vance of the glacier, which retreated from this area between 10 000 and 9 000 years ago.
Paléomagnetisme de la formation des 'grès-à-Voltzia' (Buntsandstein supérieur) du Massif des Vosges (France)
Authors: Biquand Daniel
Published: April 2011

The results of a paleomagnetic study of 99 samples (156 specimens) from 6 quarries spread over an area of 6000 km2 in the Lower Triassic Voltzia sandstone formation from the Vosges (France) are presented. More precisely, this paper is limited to a detailed statistical study of magnetization directions at different stages of physical treatment of the magnetized material: exposure in null field for long time periods, up to 18 months; attack with moderate alternative fields (600 Oe (4.8 × 104 A/m) eff. maximum), then strong fields (1600 Oe (12.7 × 104 A/m) eff.); thermal treatment to 670 °C.Here is a summary of the results:(1) Strong alternative field attack or moderate thermal treatment (≤400 °C) do not result in the acquisition of parasitic magnetization, however weak, of preferred orientation, but seem to cause a random scatter of magnetization directions.(2) Thermal treatment seems preferable to alternative field attack to completely destroy secondary magnetization, ubiquitous and intense, the direction of which is close to the present terrestrial field direction.(3) Primary magnetization usually shows inverse polarity. The coordinates of the corresponding virtual geomagnetic pole are: 43.1° N, 145.7° E; Dm = 4.9°; Dp = 2.5°.(4) This study allowed the testing of the validity of secondary magnetization cancellation method by vectorial calculus techniques using the two primary magnetization polarities obtained after long exposure in null field. [Journal Translation]
Episodic Holocene alluviation in meltwater channels near Calgary, Alberta
Authors: Osborn Gerald D.
Published: April 2011

Sheetlike layers of sediment consisting of coarse clasts in a fine-grained matrix occur at the bases of steep meltwater-channel slopes north and northwest of Calgary. Individual layers are separated by thin organic horizons which are probably accumulations of water-transported burned organic matter. The deposits are interpreted to be products of a series of unchannelled water–sediment slurries created whenever heavy rains fell on denuded or destroyed grass cover stripping the soil from the steep upper parts of the valley slopes. Fire was most likely responsible for periodically destroying the grass cover. At least 24 erosion–alluviation events occurred in one of the channels in the last 15 000 years. These alluviation events seem to be the main process by which the meltwater channels are being infilled.
Mesozoic – early Cenozoic volcanism, plutonism, and mineralization in southern British Columbia: A plate tectonic synthesis
Authors: Griffiths John R.
Published: April 2011

Three time–space profiles have been constructed using geologic data from British Columbia between 49° N and 56° N. They illustrate variations across the Cordillera, (1) in the stratigraphic and tectonic setting of volcanism, (2) in the age and modal type of granitoids, and (3) in the distribution and types of copper and lead deposits related to volcanic and plutonic rocks. These profiles provide the basis for a plate tectonic synthesis of the Mesozoic–Cenozoic geology, illustrated by six true-scale cross sections.The preferred model has, in the Triassic, two eastward-dipping subduction zones, giving rise to the copper-rich Karmutsen and Nicola–Takla volcanics respectively. After collision of the two volcanic belts by the Early Jurassic, a single eastward-dipping subduction zone remained active until the Eocene. Magmas produced by partial melting and fractionation of subducted lithosphere occurred across the western 300 km of the Cordillera, leading to thickening of the crust, and eventually to anatectic melting to generate large batholiths now containing pendants of volcanics. Jurassic and later geologic and metallogenic events across the eastern 500 km of the Cordillera are the results of an increased heat flux through inhomogeneous crust of varying thickness, comprised of relict ocean floor, continental margin sediments, older volcanics, and ancient cratonic basement. This results in patterns of metamorphism, volcanism, and plutonism which have no simple spatial relationship to the subduction zone.
Rb–Sr ages and tectonic setting of some granite intrusions, coastal Labrador
Authors: Barton Jr. Jackson M.
Published: April 2011

Results of Rb–Sr isotopic and chemical analyses from five bodies of granite and from one body of granitic gneiss cropping out along the coast of Labrador between Nain and the Khaumayät (Kaumajet) Mountains are reported. These indicate that: (1) the Okhakh, Nänukhtut, and Saddle Island Granites were intruded between ~2400 Ma ago and ~2300 Ma ago, contemporaneously with the extrusion of volcanic rocks within the Mugford Group; (2) the Loon Granite was emplaced ~1576 Ma ago; and (3) the Operngeviksoakh and Manvers Granites crystallized ~1376 Ma ago and ~ 1280 Ma ago respectively, contemporaneously with the final stages of emplacement of the Nain Complex. These granites are characterized by large initial 87Sr/86Sr ratios, suggesting that they are of predominantly crystal origin. All of these granite bodies were emplaced post-tectonically and did not accompany any regional deformation or metamorphism.
Oxygen and carbon isotopic study of ammonites from the Late Cretaceous Bearpaw Formation in southwestern Saskatchewan
Authors: Forester R. W. , Caldwell W. G. E. , Oro F. H.
Published: April 2011

The sediments of the late Campanian – early Maestrichtian Bearpaw Formation were deposited during the last movements of the Cretaceous Western Interior seaway in what is now the southern Interior Plains of Canada. Biostratigraphic correlation of the Bearpaw beds in southwestern Saskatchewan is firmly established. The formation carries a rich faunal sequence, including well-preserved ammonites suitable for an oxygen and carbon isotopic study to determine the environment, particularly the temperatures, of the Bearpaw sea. Oxygen and carbon isotopic measurements were made on the aragonitic shells of Baculites rugosus, B. compressus robinsoni, B. cuneatus, B. reesidei, B. baculus, B. grandis, Hoploscaphites nodosus, and H. plenus. The average δ18O values (PDB) from the ammonite zones range from +0.06 to −2.14, with an average of −1.44, which translate into mean temperatures of about 17–27 °C, with an average of 23.2 °C. The δ13C values range from −5.71 to +2.92, with an average of −1.90. Although the δ18O values for the ammonites are consistent with the accepted marine habitat of these molluscs, an apparent correlation between the average δ18O and δ13C values of baculites from each of the zones in the Bearpaw Formation suggests small contributions of fresh water to the Western Interior seaway in southwestern Saskatchewan. Paleogeographical, paleontological, and sedimentological evidence points to such possible contributions as being local and periodic.
Geomorphology and Quaternary geology of Codroy Lowland and adjacent plateaus, southwest Newfoundland
Authors: Brookes Ian A.
Published: April 2011

The paper presents an interpretation of preglacial and glacial landforms and Quaternary sediments of approximately 2000 km2 of southwest Newfoundland. The area comprises lithologically controlled Codroy Lowland, floored by Late Wisconsinan glacial deposits, flanked by Long Range and Anguille Mountains plateaus, which bear pre-Quaternary fluvial denudation surfaces and evidence in weathering zones of multiple Quaternary glaciation. Part of Long Range Mountains bears no evidence of glaciation, and extensive areas there, including all of the Anguille Mountains, were ice-free at the Late Wisconsinan glacial maximum. The maximum glacial condition for which evidence is preserved prevailed some time before the Late Wisconsinan and surfaces exposed since then have not passed through an interglacial weathering regime, so that this condition probably can be assigned to an Early Wisconsinan glacial stade.Coastal cliffs on Cabot Strait expose a Late Wisconsinan drift sequence which indicates: (1) advancing ice moved perpendicular to the coast, striating rock and depositing till; (2) subsequently the coast was deglaciated and marine overlap ensued, approximately 14 000 years ago; (3) ice readvanced, probably down Codroy Lowland with a halt near the present coast, and deposited moraines at about 12 600 years ago.Total postglacial isostatic rebound has raised marine features only 5–10 m above rising sea level. The shoreline has likely been submerging since about 11 000 years BP under the combined influences of eustatic sea level rise, dominant over rebound, and possible subsidence beneath the load of more than 500 m of water in Laurentian Channel, only 30 km offshore.
Enigmatic trace fossils from the Silurian Chaleurs Group of the southeastern Gaspé Peninsula, Quebec
Authors: Pickerill R. K. , Roulston B. V.
Published: April 2011

A series of enigmatic trace fossils from the Silurian Chaleurs Group (Gascons Formation) of the southeastern Gaspé Peninsula, Quebec, is described in detail. Two types of trace fossil are present and are herein referred to as Form A and Form B. Form A burrows are essentially horizontal branching tunnel networks, typically showing Y-shaped branching patterns and 'turn arounds'. It is suggested that the burrows are feeding and dwelling burrows of some unknown arthropod group, possibly primitive crustaceans. Form B burrows are vertical bulbous structures consisting of an enlarged spherical or subspherical bulbous base which extends upward into an upward tapering vertical shaft. It is suggested that these structures may represent brood structures of the same arthropod group, tubules on the bulb representing juvenile migration exits and tubercles possibly representing poorly preserved and incomplete migration exits or alternatively repositories for fecal material.
Glacier movement, ice structures, and medial moraine form at a glacier confluence, Berendon Glacier, British Columbia, Canada
Authors: Eyles N. , Rogerson R. J.
Published: April 2011

On Berendon Glacier, Canada, at the asymmetric Y junction of two large valley glaciers, observations of ice velocity, strain rate, and ice structures indicate that the form of a medial moraine is determined by severe lateral compression between the two ice streams. Debris of the moraine is recycled along complex transport paths determined by ice structures. For example, supraglacial debris is precipitated into the confluence zone between the two glaciers forming a subglacial debris reservoir. Debris is evacuated from the reservoir by shearing between the two glaciers and is revealed on the glacier surface as debris dykes and melt-out tills along the contact plane. Important implications regarding the sedimentology of the moraine can be stated. Elsewhere debris is precipitated into transverse crevasses subsequently resulting in transverse till ridges at the glacier surface.Annually-formed wave ogives, bulges in surface ice, and overriding along the glacier contacts result from severe lateral compresssion, and add further diversity to the moraine.Downglacier, confluence ice structures are destroyed by ablation, the pattern of ice flow becomes less complex, unified flow between the two glaciers is established, and a distinct structurally-determined moraine morphology is replaced by one dependent upon the differential ablation of debris covered and clean ice.
Determination of radioactive disequilibrium in uranium-bearing rocks
Authors: Szöghy I. M. , Kish L.
Published: April 2011

A method is presented to determine the radio-equilibrium of the uranium–actinium series in rock samples by low energy photon spectroscopy. The equilibrium pattern is indicated by the relative abundance of the isotopes 238U, 231Pa, 226Ra, 222Rn and 210Pb. For whole rock analysis no elaborate sample preparation is needed and the measurements can be performed in the field. On chemically separated material the uranium-234, -235 and -238 ratio can also be determined by the present method. A practical table for radioactive rock analysis, listing intense photons below 250 keV energy, is also included.Measurements on uranium-bearing rocks indicate that radioactive disequilibrium is common, especially in near-surface specimens. This should be taken into consideration in calculating equivalent uranium (eU) values from scintillometric measurements, and in interpreting anomalies by radon geochemistry. The deduced isotopic ratios can be used for age determination and to monitor industrial enrichment of uranium-235.
A new Silurian Astylospongid sponge from Baillie-Hamilton Island, Canadian Arctic Archipelago
Authors: Rigby J. Keith , Lenz Alfred C.
Published: April 2011

The new sponge, Astylospongiella megale, is described from rocks of the Ludlovian Neodiversograptus nilssoni Zone of the Cape Phillips Formation from southern Baillie-Hamilton Island, Arctic Canada. The genus is included in Astylospongiidae because its skeletal net is composed of sphaeroclones, which in this species, are of relatively uniform size throughout the sponge. The new sponge also has irregularly placed radiating canals which are subparallel to the upper surface, and which are cross-connected by upward fanning canals that are approximately normal to the sponge surface and the radiating canals.
The Ordovician cystoid, Amecystis cordiformis Sinclair
Authors: Broadhead Thomas W.
Published: April 2011

The rhombiferan cystoid species, Amecystis cordiformis described by G. W. Sinclair from the Ordovician (Caradocian) near Pont Rouge, Quebec, is a junior synonym of Amecystis laevis (Raymond), the type-species of the genus.
The Somerset Island Formation: an upper Silurian to ?Lower Devonian intertidal/supratidal succession, Boothia Uplift region, Arctic Canada
Authors: Miall A. D. , Kerr J. Wm. , Gibling M. R.
Published: April 2011

The Somerset Island Formation of Somerset Island is a newly defined unit consisting of interbedded fine-grained, grey, planar-laminated dolomite and limestone, grey mottled limestone and dolomite, red quartzose siltstone and red dolosiltite. It forms a transitional unit between the limestone and dolomite of the underlying Read Bay Formation and the sandstone and conglomerate of the overlying Peel Sound Formation, and ranges in thickness from 150 to more than 400 m. The formation was formed predominantly in intertidal and supratidal environments and forms the lowest part of a regressive sequence that culminates in boulder conglomerates of alluvial fan origin in the Peel Sound Formation. The Somerset Island Formation is predominantly Pridolian in age, but may include some strata of Ludlovian and Gedinnian age.The regressive sequence reflects a major pulse of the Cornwallis Disturbance of Boothia Uplift. A similar sequence occurs in Prince of Wales Island, although the lower part of the succession there contains conglomerate and sandstone, rock types that are absent in Somerset Island. These rocks are formally assigned to the Lower Peel Sound Formation but are of similar age to the Somerset Island Formation of the type area.Rocks of similar facies to the Somerset Island Formation of Somerset Island comprise the upper member of the Drake Bay Formation on Russell Island and Member D of the Read Bay Formation on Cornwallis Island. The latter unit is younger than the Somerset Island Formation, reflecting a later commencement of regression in that area.
Paleomagnetism of some late Precambrian and lower Paleozoic sediments from L'Adrar de Mauritanie, West Africa
Authors: Morris W. A. , Carmichael C. M.
Published: April 2011

Palaeomagnetic results are reported from three formations from the late Precambrian to lower Paleozoic sedimentary sequence of L'Adrar de Mauritanie, on the West African Craton. Each of the formations recorded complex magnetizations, the sequence of which could only be resolved after detailed thermal and chemical cleaning. Most of these complexities have arisen from post depositional hematite coating on both magnetic and non-magnetic grains. Formation I2 with a probable age of 1020 Ma records an early, presumably original remanence directed along D = 034°, I = +60° (α95 = 6°) and a later remanence D = 336°, I = +37° (α95 = 11°). Specimens from formations CO8 and CO10 (Cambro–Ordovician boundary) record a common late phase remanence at D = 128°, I = +24° (α95 = 8°). The CO10 early phase remanence is D = 033°, I = +61° (α95 = 7°), whereas the poorly isolated early phase remanence of CO8 approximates D = 060°, I = +51° (α95 = 20°).
Paleomagnetic results from the Nain anorthosite and their tectonic implications
Authors: Murthy G. S.
Published: April 2011

As part of studies of anorthosites from the northern hemisphere, the paleomagnetism of the Nain anorthosite from Labrador is described. A total of 113 samples were collected from 21 sites comprising both dark and pale facies types. Although AF (alternating field) demagnetization was not useful in obtaining a stable component of magnetization, it was possible to isolate two oppositely directed (easterly and westerly) magnetizations through thermal demagnetization. Quite often, both magnetizations are found in the same specimen. On the basis of thermal demagnetization, the 18 sites of dark facies anorthosite are found to possess stable remanence at D = 278.2°, I = 15.8°, k = 174, α95 = 2.6° with the corresponding paleomagnetic pole of mixed polarity at 11?N, 149°W (δp, δm = 1.5°, 3°). A magnetization with D = 275.3°, I = 27.2°, k = 92, α95 = 12.9° with the corresponding paleomagnetic pole at 15°N, 148°W (δp, [Formula: see text], 14°) was isolated for the pale facies anorthosite. Comparison of the Nain results with those of other plutons from Labrador suggests a significant difference in pole positions for the various anorthosite bodies north of the Grenville Front, which may represent a slight north–south polar shift during the time interval of intrusion of these bodies.
Distribution and characteristics of rock glaciers in the southern part of Jasper National Park, Alberta
Authors: Luckman B. H. , Crockett K. J.
Published: April 2011

One hundred and nineteen rock glaciers were identified in an aerial photograph inventory of 4632 km2 in Jasper National Park, Alberta. Morphological subdivision indicated 33 lobate, 76 tongue-shaped and 10 spatulate rock glaciers, whereas a 'genetic' classification identified 65 'glacial' (ice-cored) and 54 'non-glacial' (ice-cemented) rock glaciers. Head elevations of the glacial group (mean 2318 m) are significantly higher than the non-glacial group (mean 2256 m). The total elevation range of rock glaciers is 1710–2670 m.Optimal rock glacier sites are below north- or northeast-facing quartzite cliffs in cirques or on valley walls. These topographic and geologic controls produce a greater concentration of rock glaciers in the Main Ranges than the Front Ranges. Rock glacier head elevations rise eastwards and, to a lesser extent, southward across the area in response to regional climatic and latitudinal effects. Two phases of pre-'Little Ice Age' rock glacier activity are recognized on morphologic grounds and, since Little Ice Age glaciers overrode most of the evidence of Holocene glacier fluctuation, provide a major source of information on Holocene climatic fluctuations. Preliminary data suggest most rock glacier activity pre-dates the Little Ice Age and the oldest phases probably occurred between 6600 and 9000 BP.
A trace fossil preserving its producer (Trentonia shegiriana) from the Trenton Limestone of the Quebec City area
Authors: Pickerill R. K. , Forbes W. H.
Published: April 2011

The Trenton Limestone of the Quebec City area contains a moderately abundant and diverse ichnofauna including numerous simple trails that formed at the sediment–water interface. A rare specimen of one of these trails demonstrates that its producer was an errant polychaete annelid, Trentonia shegiriana gen. et sp. nov. It is suggested that T. shegiriana or a morphologically similar errant polychaete annelid was responsible for the production of not only the trails described herein but also the ichnospecies Walcottia rugose. Faunal, ichnofaunal and sedimentological evidence suggests that T. shegiriana inhabited a shallow water subtidal environment with water depths in the order of 10 m or less and preferred a calcisiltite substrate. In the absence of T. shegiriana these simple trails can therefore be utilized as useful palaeoenvironmental indicators.
Late Pleistocene Camelops from the Gallelli Pit, Calgary, Alberta: morphology and geologic setting
Authors: Wilson Michael , Churcher C. S.
Published: April 2011

A radiocarbon-dated gravel deposit in Calgary, Alberta, has yielded a large humerus referred to the extinct camelid, Camelops cf. hesternus. With a date of 11 300 ± 290 BP (RL-757) this is the first securely dated postglacial record of Camelops in Canada. Studies of the gravels show them to represent a period of rapid aggradation by a braided river, subsequent to the drainage of glacial Lake Calgary. The gravels are equivalent in age and characteristics to the Bighill Creek Formation of the Cochrane area, 30 km west of Calgary; and are therefore assigned to that formation. Later fill units are, however, excluded from the formation as they represent Holocene cut-and-fill events of differing hydrologic significance. Recent suggestions that Lake Calgary persisted until 9000 years BP can now be rejected on the basis of stratigraphy and radiocarbon dates. Studies of the camel humerus suggest some revisions in our views concerning morphologic variation in the species: the species was probably more plastic than has been accepted to date. Associated Bison bison antiquus and Equus conversidens from the same gravels (Gallelli and Galvin Pits) are briefly described. The ungulate fauna from these pits suggests a semiforest habitat with extensive shrub and grassland elements.
Zoned epidote nodules from sedimentary rocks of the Eastport Formation, southwest New Brunswick
Authors: Percival J. A. , Helmstaedt H.
Published: April 2011

Zoned epidote-rich nodules occur in shallow-water sedimentary rocks of the Eastport Formation in southwestern New Brunswick. The host rocks of the nodules are sandstone and shale displaying well preserved clastic texture and minimal metamorphic effects, whereas the recrystallized nodule cores consist of epidote and quartz, with minor proportions of prehnite and actinolite. Whole rock analyses show depletion of sodium, potassium, and magnesium in the nodule relative to the host as well as relative enrichment in calcium and iron. Chemical, mineralogical, and textural similarities to calcareous concretions lead to the conclusion that the nodules represent metamorphosed equivalents of ironstone concretions. The St. George pluton is thought to have been the source of heat for metamorphism. Differences in degree of recrystallization between the nodules and their host rocks are attributed to differences in original bulk composition. Although the primary textures in the pelitic and quartzofeldspathic host rocks remained essentially unchanged during very low grade metamorphism, the nodule cores, richer in calcium and iron, recrystallized into metamorphic assemblages.
Cap des Rosiers Formation at Grosses Roches, Quebec—deposits of the mid-fan region on an Ordovician submarine fan
Authors: Hendry Hugh E.
Published: April 2011

Resedimented deposits in the Ordovician Cap des Rosiers Formation near Grosses Roches, Quebec, are arranged in fining-upwards sequences, each with conglomerate at the base, and argillaceous sandstones, or interbedded sandstones and shales at the top. The conglomerates are primarily cobble-grade, and are poorly sorted; graded bedding and clast imbrication are poorly developed, and internal stratification is uncommon. They pass upwards and laterally to pebbly sandstones and sandstones, most of which are massive, but which contain cross-stratification, parallel stratification, or dish structure in places. The sandstones are overlain by finer-grained sandstones with many load-deformation and water-escape structures and at the top of some sequences there are sandstone and siltstone turbidites. The presence of large sediment slabs and soft clasts in the conglomerates and sandstones, and of the abundant shale chips in the argillaceous sandstones, provides evidence of penecontemporaneous erosion. Load casts, flame structures, dish structures, and other water-escape structures indicate relatively high rates of deposition. At the base of the section, 10–12 m of conglomerate and sandstone beds in the lowermost sequence onlap against the eroded pelites of a channel margin. The exposed bases of four other fining-upwards sequences are erosional, but no onlapping relationships are observable, and the eroded sediments are coarser grained than the pelites at the very base of the section.The sequences are considered to represent the back-filling of a channel-mouth in the mid-fan region of a submarine fan, and subsequent accumulation of fining-upwards lobes beyond the front of a principal channel which continued to supply sediment. The superposition of conglomerate-bearing fining-upwards sequences is interpreted as a result of fluctuations in supply from a tectonically active source.
Postglacial tilting of Akpatok Island, Northwest Territories
Authors: Løken Olav H.
Published: April 2011

Late glacial deposits on Akpatok Island are described. They include a major moraine system and numerous raised shore features. A survey of the marine limit at several locations shows that subsequent to its formation the island has been tilted up towards the southwest. The isobases trend 313° true and the former sea surface rises to the southwest at a rate of 0.62 m/km. The late glacial chronology is vague due to the absence of C-14 dates with clear chronological significance. The moraine system is tentatively correlated to the Kangalaksiorvik Phase of northernmost Labrador.
Palynology of Quaternary deposits of the lower Bogachiel River area, Olympic Peninsula, Washington
Authors: Heusser Calvin J.
Published: April 2011

The palynology and radiocarbon chronology of an interstadial peat exposure and a bog located in the lower Bogachiel River drainage area provide further basis for the reconstruction of Quaternary vegetation and environments of the western Olympic Peninsula. The interstadial peat with a finite age of 59 600 ± 700 a BP at the top is overlain by till, and the bog situated distally in relation to an end moraine was formed before 30 000 ± 800 a BP following emplacement of the moraine. Pollen spectra of the interstadial peat are of subalpine forest species succeeded by tundra – park tundra types. The pollen record of the bog shows rising proportions of arboreal species in the lower part consisting of mountain hemlock and pine at the beginning and later of western hemlock. Subsequently, there follows in sequence a return of mountain hemlock and pine, culminating around 20 000 a BP, domination by tundra – park tundra types, and finally a rise of Sitka spruce to a maximum in association with alder. After about 10 000 a BP, alder reaches peak proportions and is followed by a succession of lowland arboreal species characterized chiefly by western hemlock. The pollen stratigraphy of these deposits correlates with a previously established biostratigraphic scheme for Quaternary deposits in western Washington. Data indicate one or more glacier advances predating 30 000 and postdating 59 600 a BP in the lower Bogachiel Valley.
Vein geometry and hydrostatics during Yellowknife mineralisation
Authors: Kerrich R. , Allison I.
Published: April 2011

Three vein systems with distinct geometry and time relations are located within major ductile shear zones at Yellowknife. En échelon arrays of centimetre width quartz veins initiated at ~45° to the shear zone boundaries and normal to the schistosity during initial translation on the structures. These geometrical relations conform to the simple shear model of Ramsay and Graham. Orientation of the maximum principal stress was ~45° to the 70° dipping shear zone boundaries, implying that the horizontal stress in the crust was greater than the vertical stress.Gold-bearing quartz veins of metre dimensions are disposed parallel to the schistosity, cross cutting early veins. This geometry requires the stress regime to switch from the former orientation such that the maximum principal stress is parallel to the schistosity, and the effective stress normal to the schistosity is tensile. The change of stress orientation is attributed to transient high fluid pressure which generated hydraulic fracturing and correspondingly high values of permeability. Under these conditions the shear zones act as conduits for massive fluid discharge; quartz and gold were precipitated from solutions cooling along a temperature–pressure (TP) gradient. Crustal vertical stress was greater than horizontal stress.Late stage lenticular gold-bearing quartz veins of metre dimensions were emplaced as vertical arrays within the shear zones, oriented normal to schistosity. These tension fractures formed when the stress regime reverted to the ambient conditions for stage 1 veining during a second episode of displacement on the shear zones. Consideration of the kinetics of intergranular diffusion, with reference to the required transport distances of gold into a lode deposit, implies that long-range diffusive transport of gold into veins was not significant.
Tectonic evolution of two greenstone belts from the Superior Province in Manitoba
Authors: Park R. G. , Ermanovics I. F.
Published: April 2011

The Bigstone Lake and Stevenson Lake greenstone belts are two areas of supracrustal rocks surrounded by quartz diorite to granodiorite plutons and by small patches of tonalitic gneiss interpreted as basement to the greenstone belts. The supracrustal sequence is divided into a lower, mainly volcanic, group correlated with the Hayes River Group of Island Lake and an unconformable upper group with roughly equal proportions of sediments and volcanics correlated with the Island Lake 'Series'. The lower group consists of about 4600 m of basaltic and andesitic pillow lavas with minor greywackes and dacitic volcanics. It is partly replaced at the base by the bordering plutons and cut out at the top by the unconformable upper group, which consists of about 2300 m of greywackes, arkoses, and mudstones above a basal conglomerate containing boulders derived from the lower group and from the basement. A further 2100 m of volcanics overlies these sediments.The supracrustal rocks show three phases of deformation. The first, F1, produced major northeast–southwest and east–west synclines. S1 foliation was developed under greenschist facies to low amphibolite facies metamorphism. F2 produced smaller scale steep east–west folds with a crenulation cleavage. Subsequent deformation resulted in chevron folds and conjugate shear belts.The intrusion of the plutons commenced before the F1 deformation and partly controlled it, but a further period of plutonic intrusion occurred after F1 and before F2.The north–south compressive stress prevailing during F2 and later deformation under waning metamorphism implies that the batholiths in the vicinity of the greenstone belts had completely solidified and that the crust was rigid enough to transmit a uniform stress field. The dominance of east–west structural grain in this part of the Superior Province indicates that these conditions were general.
Diapiric structures and regional compression in an Archean greenstone belt, Island Lake, Manitoba
Authors: Fyson W. K. , Herd R. K. , Ermanovics I. F.
Published: April 2011

The sequence of structures affecting rocks of the Island Lake greenstone belt suggests a progression from structures attributable to emplacement of granitic plutons to those that are of regional extent. Early homoclines (D0 deformation) and isoclinal folds (D1) are overturned or face away from marginal plutons which partly truncate the folds. Granitic offshoots display an S1 foliation. Syn-D1 emplacement of the granite is implied, and the pattern of homoclines and folds is consistent with deformation due to diapiric uplift.Later upright folds (D2) and a widespread subvertical schistosity S2 trend eastward throughout most of the region. S2 passes with little deflection into the granites. D1 folds are rotated towards S2 and clasts and volcanic vesicles are flattened, except within a zone of low strain extending 15 km east–west between two plutons. Evidently during D2 deformation the plutons acted as relatively rigid massifs between which a large 'pressure shadow' developed in response to regional north–south compression.
Crystal growth and nucleation in flash-injected diabase dikes
Authors: Gray Norman H.
Published: April 2011

Z, the number of either plagioclase, clinopyroxene, or opaque oxide crystals per unit volume, varies across the widths of 10 'flash-injected' diabase dikes in a manner which is well described by the equation[Formula: see text]where y is the distance from the contact. This relationship can be shown to be a consequence of the interaction of crystal growth and nucleation during the cooling of the dikes if[Formula: see text]The value of the exponent n in [i] is a function both of m in [ii] and the dominant growth-controlling mechanism during the main nucleation period. The n values of the minerals in the dikes examined cluster around −0.9, −1.5, and −2.2. On the basis of these data it appears that m is approximately constant and equal to 3.0 in basaltic melts. On the other hand, it appears that the dominant growth-controlling mechanism during nucleation is dependent on the exact composition of the melt. For example, the clinopyroxenes in the quartz and olivine tholeiitic diabases studied, differ significantly both in their crystal shape and n values. Departures from [i] are found within a few centimetres of the contact where, because of the rapid cooling, the assumption of constant m in [ii] is not valid.
The structural and metamorphic history of the Taconic unconformity in western Massachusetts
Authors: Uzuakpunwa A. B. , Brownlow Arthur H.
Published: April 2011

Evidence from detailed structural and petrographic studies in western Massachusetts shows that the Cambro-Ordovician Rowe Schist and the Middle Ordovician Moretown Formation have different depositional, structural, and metamorphic histories and are separated by a pre-Taconic angular unconformity. The Rowe Schist (pelitic and semi-pelitic schists and minor lenticular amphibolites) underwent multiple periods of deformation and amphibolite facies grade of metamorphism before the deposition of the Moretown Formation. The latter is composed of the Chester Amphibolite, chlorite–muscovite schist, and staurolite–garnet–biotite schists. The predominant structures and metamorphism in the Moretown Formation are those of the Acadian Orogeny. Both the Rowe Schist and the Moretown Formation are transected by a foliated pegmatitic granite (Middlefield – Blair Pond Pluton). A dyke of the granite cuts the composite tectonic fabric in the Rowe Schist (which it post-dates), but it is generally deformed by the earliest and regional schistosities found in the Moretown Formation (which it pre-dates). The base of the Moretown Formation is defined by the Chester Amphibolite. It represents a recrystallized basic volcanic rock associated with an island arc system.
Rb/Sr chronology of the Rainy Lake Archean granitoid batholith, Wabigoon Belt, northwestern Ontario
Authors: Birk Dieter
Published: April 2011

In the Lake Despair area, the Rainy Lake batholithic complex subdivides into three syntectonic, foliated to migmatized granitoids (Jackfish Lake Complex, Northwest Bay Complex, Footprint Lake Gneiss). Field relationships predate the high level, late tectonic, granitoid stocks lying within adjacent supracrustal rocks. The three units give a 10 point York I Rb/Sr whole-rock isochron age of 2616 ± 66 Ma (R0 = 0.7012 ± 0.0005).This age is statistically indistinct from a pooled isochron for seven late tectonic Wabigoon stocks. One geochemical outlier, from Footprint, lies on a 3241 Ma reference line, interpreted as a pseudoisochron.The Wabigoon Belt formed at about 2.6 Ga as one geotectonic cycle of supracrustal accumulation, plutonism, and metamorphism. The hiatus between syntectonic and late-tectonic activity is less than 60 Ma and is indistinguishable radiometrically from multiple intrusion.R0 locates on a single stage, linear mantle Sr evolution model, indicating that the granitoids originated directly from the upper mantle or as low Rb/Sr material from the lower crust, in residence for less than about 50 Ma.
Rare-earth and other trace element data bearing on the origin of Archaean granitic rocks from Yellowknife, Northwest Territories
Authors: Drury S. A.
Published: April 2011

Trace element data, including rare-earth elements, for six granitic rocks and two metasediments from the Archaean granite–greenstone terrain of Yellowknife, Northwest Territories are presented. Three granodiorites from the synkinematic Western and South-east plutons show similar Rb, Sr, Th, Rb/Sr, and K/Rb to many high level granodiorites, but are enriched in Ba. Their rare-earth element (REE) patterns show enrichment of light REE relative to heavy REE, and lack Eu anomalies. These features, together with Sr isotope data, are compatible with their origin by partial melting of mantle depth garnet-bearing basaltic source rocks, and little if any detectable fractionation of the rising magma. Potassic granites from post-kinematic plutons, such as the Prosperous Lake granite, are enriched in Th, depleted in Sr and Eu, and have very high Rb/Sr ratios and low K/Rb ratios. Their REE patterns, except for Eu, are very similar to those of metasediments which they intrude. These features, together with Sr isotope data, suggest that high degrees of partial melting of metasediments, leaving a plagioclase-rich residue, are the most likely origin for the post-kinematic granites. The REE patterns of the Archaean metasediments, in particular their high CeN/YbN ratios, suggest that they contain a high proportion of material derived from earlier sialic crust, and that local metavolcanic rocks are not clearly reflected in the composition of the stratigraphically younger metasediments.
Observations in the turbidity maximum of the St. Lawrence Estuary
Authors: Silverberg Norman , Sundby Bjørn
Published: April 2011

A series of 13 and 25 h anchor stations and individual stations were occupied along the axis of the North Channel of the St. Lawrence Estuary during periods of both high and low river runoff. The data collected have permitted a detailed examination of the variations in salinity, suspended matter concentrations, and the size distributions of the suspended matter and the bottom sediments of the maximum turbidity zone. The high turbidity appears to be maintained by a complex density-driven circulation in combination with the resuspension of bottom sediments near the head of the estuary. The phenomenon may be aided by the breaking of internal waves. A longitudinal structure, which is only slightly influenced by changes in river discharge, is discernible for the zone. The highest concentrations of suspended matter occur in a well mixed region at the head of the estuary and suspended particulate matter levels decrease seaward as a two-layer estuarine circulation becomes better developed.
Some observations on rock weathering, Cumberland Peninsula, Baffin Island
Authors: Waits Stephen H.
Published: April 2011

A variety of bedrock weathering features—both modern and remnant—including surface grus, polygonal cracks, siliceous glaze, tors, weathering pits, and tafoni typify upland outcrops on the Cumberland Peninsula. Tor ridges are particularly prevalent and at lower elevations they show significant modification and streamlining by flowing ice. On summit areas at elevations above 750 m, however, remnant corestones are preserved in situ, suggesting selective preservation of upland surfaces. Bedrock structure and composition, topographic position, and intensity of process strongly influence tor development. Weathering pits are common on high level, open summit surfaces where weathering occurs in response to both climate and continued removal of derived debris. Pit enlargement through lateral undercutting has been favoured by accumulation of protective bottom residua, mechanical weathering, and the presence of exfoliation crusts. It is postulated that salt crystallization plays a role in outcrop microweathering under present upland arctic conditions.
A detailed 40Ar/39Ar age study of an Abitibi dike from the Canadian Superior Province
Authors: Hanes J. A. , York Derek
Published: April 2011

40Ar/39Ar step-heating analyses were performed on 11 felsic and mafic mineral separates from a 90 m wide Precambrian diabase dike of the Abitibi swarm in the Superior Province of the Canadian Shield. Deuterically altered minerals from the dike interior define a primary age of 2150 ± 25 Ma. Updated ages, obtained from felsic separates within 30, and mafic within 1.5 m of the dike border, are evidence of a previously undetected 'Hudsonian' (1.7–1.8 Ga) hydrothermal event in the area. It is possible to distinguish the deuteric from the later hydrothermal alteration by both dating and petrographic methods. The data from this study demonstrate the successful application of 40Ar/39Ar dating to early Proterozoic dikes which have suffered low grade metamorphism. The ages support a north to south sense of motion of the Track 5 apparent polar wander path (APWP). A monotonic decrease in apparent age of felsic spectra indicates reactor induced recoil effects which are correlated with the fine-grained saussurite in the feldspar.
Ages of deformation in the Hellroaring Plateau area, eastern Beartooth Mountains, Montana
Authors: Mueller Paul A.
Published: April 2011

Samples of quartzo-feldspathic dikes that were intruded along fractures parallel to the axial planes of folds produced by major deformational events in the eastern Beartooth Mountains were dated by the Rb–Sr whole rock method. Despite relatively large errors associated with the individual dates, it is shown that the second of four recognized fold sets was generated roughly 2750 Ma ago and the third fold set prior to approximately 2565 Ma ago.
The western margin of the Coast Plutonic Complex on Hardwicke and West Thurlow Islands, British Columbia
Authors: Nelson Jo Anne
Published: April 2011

The western margin of the Coast Plutonic Complex, one of the major tectonic boundaries of the Canadian Cordillera, has been variously interpreted as an intrusive contact, a shear zone, and a suture zone joining the Early Mesozoic Insular Belt to the North American continent. A representative section of this boundary, exposed on islands in Johnstone Strait, is an intrusive contact along which a quartz diorite with peripheral mafic phases truncates Early Mesozoic sediments and volcanics of the Insular Belt. Concordant hornblende–biotite pairs and two whole rock biotite isochrons date the intrusion as Late Jurassic (151 Ma). Prior to intrusion the stratified units underwent prehnite–pumpellyite facies metamorphism and west-northwest block faulting.The contact aureole of the quartz diorite and its associated mafic phases involves greenschist and hornblende–hornfels facies assemblages. Total pressure in the upper Karmutsen Formation during contact metamorphism was less than 2.5 × 105 kPa. The maximum contact temperature was between 670 and 700 °C. Forcible emplacement of the intrusion caused penetrative deformation of wall rocks in the inner aureole. The maximum contact temperatures indicate that the plutonic bodies were at near-liquidus temperatures when emplaced.The contact on Hardwicke and West Thurlow Islands appears representative of most of the tectonic boundary between the southern Coast Plutonic Complex and the Insular Belt. The western margin of the Coast Plutonic Complex is thus a Late Mesozoic magmatic front, the western limit of the intense magmatism that generated the Coast Plutonic Complex. The formation of Georgia Depression over the province boundary was a later event, coeval with major uplift of the Coast Plutonic Complex.