bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of diagenetic microfabric on oil sands behaviour
Authors: Barnes Deborah J. , Dusseault Maurice B.
Published: April 2011

The diagenetic processes of pressure solution and authigenic crystal overgrowth have altered the arenaceous oil sand materials of northeastern Alberta, creating sands with a decreased porosity and interlocking grain contacts. Examination of specimens in the scanning electron microscope indicates that a large number of the grain contacts in the materials have been altered from tangential to long and concavo-convex. Except for infrequent isolated bands, the materials are free from true grain-to-grain mineral cement.Strength, compressibility, and index tests (density, grain size) were performed in the laboratory on oil-free samples of the McMurray and Grand Rapids Formations, two of the Alberta oil-bearing strata. Results indicate that increased grain contact area and grain interlock cause a reduction in the compressibility and an increase in the shear strength of the materials.The influence of porosity, mineralogy, grain size, and degree of diagenetic alteration on the behaviour of granular materials is discussed, and a qualitative classification for degree of diagenetic alteration and its influence on shear strength is presented.The recognition of the geological processes reponsible for the unusual engineering behaviour of oil sands will provide a valuable predictive capacity for all friable sandstone behaviour. On the other hand, the relatively straightforward properties of relative density and compressibility can serve as effective measures of geological diagenetic history for future process quantification.
Weighted vector analysis applied to surge deposits from the May 18, 1980 eruption of Mount St. Helens, Washington
Authors: Hickson Catherine J. , Hickson Paul , Barnes William C.
Published: April 2011

The so-called "lateral blast" associated with the May 18, 1980 eruption of Mount St. Helens was witnessed by two of us (C.H. and P.H.), and its deposits were later studied. Oriented samples were collected on a ridge 14 km northwest of the mountain. The thickness of the deposit at this locality ranges from 40 cm to more than 1 m. The surface of the deposit was sculpted by the flow into large elongate bedforms aligned parallel with the flow, with their positions being partly controlled by small features beneath the deposit. The deposit consists of a very poorly sorted basal unit that may locally be divided into a lower massive layer and an upper crudely lenticular laminated layer, overlain by a unit of accretionary lapilli ranging from a few millimetres to several centimetres in thickness. The lower layer contains elongate organic clasts aligned parallel to the flow. The rock fragments that make up the remainder of the layer are more equant and have no obvious preferred orientation on a macroscopic scale.Oriented samples of the lower, poorly sorted layer were resin-impregnated and thin sectioned for grain orientation analysis. The vector orientation data were analyzed both unweighted and weighted by the eccentricity and elongation of the grains. One sample was successfully impregnated and analysis has shown that the grains have a statistically significant orientation parallel to the flow direction as determined by blown down timber and abrasion of stumps. These results are consistent with the rapid accumulation of the deposit from a high velocity, moderate particle density, low fluid viscosity flow analogous to pyroclastic surges observed elsewhere on a smaller scale.
Precise U–Pb zircon ages from the Gamitagama greenstone belt, southern Superior Province
Authors: Krogh T. E. , Turek A.
Published: April 2011

Volcanism in the Gamitagama Lake greenstone belt, 50 km south of Wawa, Ontario, on the east shore of Lake Superior, took place [Formula: see text] ago at the same time as similar volcanism in the much larger Abitibi greenstone belt to the east. Two post-orogenic intrusions in the metavolcanic–metasedimentary terrain are coeval at [Formula: see text] and [Formula: see text] and could very well be comagmatic as suggested by Ayres. A granitic sill in a metasedimentary–granitic migmatite terrain that borders the greenstone belt to the southwest has an age of 2615 ± 10 Ma and is much younger than the post-orogenic plutons to the northeast. This migmatite region represents either an uplifted deep zone that remained hot long after volcanism or a region that accumulated heat as a result of its sedimentary cover.
Infidélité paléomagnétique observée dans une formation lacustre varvée quaternaire dite: "argiles d'Eybens" (Grenoble, France)
Authors: Biquand Daniel
Published: April 2011

We have investigated the properties of natural magnetization of a lacustrine interglacial Riss–Würm deposit near Grenoble (France). Made up of accumulated argillite 250 m thick, this deposit comprises annual varves with an average thickness of 0.5 cm.The magnetic viscosity of this sediment is not very high, and we have demonstrated that the characteristic magnetization, measured after a moderate thermal treatment (between 160 and 220 °C) followed by alternating field demagnetization with maximum intensity at 200 Oe (15.9 × 103 A/m), is possibly a detrital magnetization carried by the magnetite (thermomagnetic and strong continuous field studies).On a local scale (area of about 100 m2), the direction of this magnetization remains very homogeneous within each horizon; sampling restricted to about 10 sites 1 m apart indicates for each level a mean direction of magnetization with a high accuracy: α95 = 1–2°, k = 500–2500. The aveage direction calculated by this method for different levels indicates significant stratigraphic variations (attaining an inclination of 20° and a declination of 50°), which are reached rapidly (from 1 to few degrees per year). Such variations cannot be reasonably attributed to changes in the directions of the Earth's magnetic field.A study of the acquired anisotropy of the thermal remanent magnetization indicates a magnetic anisotropy that is related to the lithological structure of the sediment and shows a strong intensity: the maximum divergence between the field direction and the acquired thermal remanent magnetization direction in this field varies, with individual samples, between 9 and 50°. The study of the properties of this anistotropy demonstrates the "infidelity" of the detrital magnetization: for one of the small vertical sequences studied for anisotropy the characteristic magnetization of a specified level has a direction nearer the axial direction of easy magnetization when the anisotropic intensity is large. This infidelity may be caused by different factors influencing the deposition of the sediment, particularly the variable directions of water flows determining the particle orientation. [Journal Translation]
General geology and genesis of silver and gold veins in the Beaverdell area, south-central British Columbia
Authors: Watson P. H. , Godwin C. I. , Christopher P. A.
Published: April 2011

The Beaverdell silver, lead, and zinc vein camp is in south-central British Columbia. Granodiorite of the Jurassic(?) Westkettle batholith underlies much of the area, and has been intruded by stocks of Tertiary quartz monzonite including the Beaverdell stock. Remnants of pendants and (or) screens of metamorphosed sediments and volcanics of the Permian(?) Wallace Formation are contained in the granodiorite. Silver vein mineralization, characterized by the Beaverdell deposits on Wallace Mountain, are mainly within the Westkettle batholith. Gold mineralization, characterized by the Carmi mine, is commonly found near the contact of Westkettle granodiorite and Wallace Formation.Geological information, including K–Ar dating, provides constraints for the evaluation of galena-lead isotope data. Plots of the galena-lead analyses on 206Pb/204Pb versus 207Pb/204Pb and 206Pb/204Pb versus 208Pb/204Pb diagrams fall into two distinct clusters, group A and group B. Group A is characterized by Carmi gold mineralization and group B includes Beaverdell silver mineralization. Three geological models for the generation of the lead in these deposits are evaluated based on three possible ages of mineralization, viz. Permian (0.27 Ga), Jurassic (0.15 Ga), and Tertiary (0.05 Ga). However, we favour the model that indicates that group A and group B deposits formed at different times, under markedly different geological conditions. Specifically, group A vein mineralization is probably Jurassic in age and formed as a result of the intrusion of the mesozonal Westkettle batholith, and group B vein mineralization is likely Tertiary in age and is genetically linked to Tertiary intrusions such as the Beaverdell stock.Exploration for the two specific types of deposits in the Beaverdell area, represented by groups A and B, can be guided by galena-lead isotope analyses, because galena-lead isotopes for group A are substantially different from those for group B deposits.
Transitional basalts in the Keweenawan Rift
Authors: Massey N. W. D.
Published: April 2011

Transitional basalt suites have been recognised in Keweenawan lava sequences at Mamainse Point and Shesheeb Bay, Ontario. These are similar to their accompanying tholeiites in major element chemistry, but have higher, more alkalic contents of incompatible elements. They are believed to be derived from primary mantle melting and illustrate the complexity of magmatic processes within an immature proto-oceanic rift.
Seismological studies in a rock body at Chalk River, Ontario and their relation to fractures
Authors: Wright C.
Published: April 2011

Seismological experiments have been undertaken at a test site near Chalk River, Ontario that consists of crystalline rocks covered by glacial sediments. Near-surface P and S wave velocity and amplitude variations have been measured along profiles less than 2 km in length. The P and S wave velocities were generally in the range 4.5–5.6 and 2.9–3.2 km/s, respectively. These results are consistent with propagation through fractured gneiss and monzonite, which form the bulk of the rock body. The P wave velocity falls below 5.0 km/s in a region where there is a major fault and in an area of high electrical conductivity; such velocity minima are therefore associated with fracture systems. For some paths, the P and 5 wave velocities were in the ranges 6.2–6.6 and 3.7–4.1 km/s, respectively, showing the presence of thin sheets of gabbro. Temporal changes in P travel times of up to 1.4% over a 12 h period were observed where the sediment cover was thickest. The cause may be changes in the water table. The absence of polarized SH arrivals from specially designed shear wave sources indicates the inhomogeneity of the test site. A Q value of 243 ± 53 for P waves was derived over one relatively homogeneous profile of about 600 m length. P wave velocity minima measured between depths of 25 and 250 m in a borehole correlate well with the distribution of fractures inferred from optical examination of borehole cores, laboratory measurements of seismic velocities, and tube wave studies.
Melt-out till in the Edmonton area, Alberta, Canada
Authors: Shaw John
Published: April 2011

Till at two localities in the Edmonton area, Alberta was formed mainly by passive melt-out from glacier ice and not by lodgment by active ice or as a result of supraglacially derived flows. This interpretation is based on the implications of in situ stratified glacial sediment below and within till and of large unlithified clasts of sediment derived from subtill deposits. The interpretation is also supported by more general regional, stratigraphic, and structural observations. Such associated properties as subtill deformation, a sharply planar till – preglacial sediment contact, sole marks, and fabric support formation by melt-out or illustrate local exceptions to this process. Regionally consistent preferred orientation of clasts is interpreted to represent preferred englacial orientation. Collective analysis of the principal eigenvectors of individual englacial fabrics and flow or resedimented till fabrics from a modern glacial environment and similar analysis for till at Villeneuve near Edmonton show the Edmonton till to occupy the intermediate position in terms of orientation strength predicted by the melt-out hypothesis. In places, preferred orientation is considered to have been disturbed by flow and diapirism induced by the process of thaw–consolidation. Thus, preferred clast orientation in till may show considerable deviation from a regional trend. Stratigraphy and sedimentology are used to classify the till and to relate individual exposures to regional environments of deposition.
Evolution of the south-central part of the Archean Abitibi Belt, Quebec. Part I: Stratigraphy and paleogeographic model
Authors: Dimroth Erich , Imreh Laszlo , Rocheleau Michel , Goulet Normand
Published: April 2011

The region comprises parts of the southern zone of the Abitibi greenstone belt and of the Bellecombe gneiss belt, and the Belleterre–Angliers greenstone belt. The stratigraphic sequence of the Abitibi Belt consists of (1) a lower ultramafic division; (2) a middle tholeiitic division; and (3) an upper diverse division; these divisions lap onto an older volcanic sequence to the north and west. In the Bellecombe Belt, sediments overlie the lower ultramafic division; these sediments coarsen toward the Abitibi Belt and toward the stratigraphic top. The volcanic rocks of the Belleterre–Angliers Belt overlie the sediments of the Bellecombe Belt.Five paleogeographic phases have been recognized. During phase I, a deep marine ultramafic lava plain covered the south part of the Abitibi Belt and the Bellecombe Belt. Faulting took place at the Duparquet–Destor break. During phase II, tholeiitic basalts formed a deep marine lava plain in the west of the Abitibi Belt, whereas flows erupted mainly from central volcanic complexes in the east. Simultaneously, sediments derived from a volcanic–plutonic hinterland to the north began to accumulate in the Bellecombe Belt. In phase III, lavas of the upper diverse division erupted from well defined central volcanic complexes in the Abitibi Belt, and sedimentation continued in the Bellecombe Belt. In phase IV, volcanic centers built above sea level, and local fans of tuff and of volcanic-derived conglomerate and sandstone interfingered with the volcanic–plutonic-derived sediments at the southern limit of the Abitibi Belt. The volcanic sequence was uplifted at the Cadillac break during phase V, with consequent progradation of coarse conglomerates southward.The stratigraphic and paleogeographic evolution of the Abitibi Belt is comparable to the evolution of immature oceanic island arcs in the Cenozoic.
The Upper Carboniferous Clifton Formation of northern New Brunswick: coal-bearing deposits of a semi-arid alluvial plain
Authors: Legun Andrew S. , Rust Brian R.
Published: April 2011

Two contiguous successions within Member B of the Westphalian Clifton Formation are exposed on the coast of Chaleur Bay east of Bathurst, New Brunswick. The upper succession is dominated by sandstone, and the lower by shale, which encloses isolated channel and lenticular sandstone bodies. Distinctive features of the shale are thin coals, casts of tree trunks, calcareous paleosols, and deep desiccation cracks with calcareous coatings. Markov chain analysis of the shale-dominated succession defines a repetitive sequence of shale, rippled fine-grained sandstone, paleosol, and coal. This sequence is attributed to filling of flood basins followed by emergence and pedogenesis under semi-arid conditions, which prevented thick coal accumulation. The major sandstone bodies are interpreted as channels, associated with lenticular levee, crevasse-splay, or mouth-bar deposits of a semi-arid alluvial plain on which anastomosing channels dominated. The Okavango River of south-central Africa and Cooper's Creek in central Australia are proposed as modern analogues.The upper succession of Member B is characterized by sheet sandstones made up of top-truncated trough and planar cross-stratified units, with abundant plant litter and calcareous intraclasts. The rocks are interpreted as braided-fluvial sand sheet deposits that blanketed the lower succession floodplain. Petrographic and paleocurrent data suggest a common source for both successions. The progradation of the braided sand sheet may reflect a sedimentary response to climate change, tectonic rejuvenation, or a combination of both.
Implications of Early Devonian poles from the Canadian Arctic Archipelago for the North American apparent polar wander path
Authors: Dankers Peter
Published: April 2011

Lower Devonian red beds from the upper member of the Peel Sound Formation at Prince of Wales Island (Canadian arctic) yield two different paleopoles at 25N 099E and at 01N 091E, the first one being older than the second one. The magnetic directions from which the poles are calculated are derived from vector analysis of thermal, chemical, and alternating magnetic field demagnetization results. Normal and reversed polarities are recorded for the northerly pole, whereas the pole at the equator reveals mainly a normal polarity. The position of the pole close to the equator has significant implications for the early Paleozoic apparent polar wander path of the North American craton. It appears that from the Late Cambrian to Early Devonian the craton moved continuously in a counter-clockwise direction that ended abruptly in the Early Devonian when the direction of the motion of the continent was reversed in a very similar manner to what occurred in Late Cambrian times.
First report of Ordovician (Caradoc–Ashgill) palynomorphs from Orphan Knoll, Labrador Sea
Authors: Legault J. A.
Published: April 2011

Acritarchs and chitinozoans of Late Ordovician age have been recovered from probable bedrock on Orphan Knoll.
Late Quaternary inter-till paleosol and biota at Guelph, Ontario
Authors: Karrow P. F. , Hebda R. J. , Presant E. W. , Ross G. J.
Published: April 2011

In 1975 and 1976, excavations along Victoria Road in Guelph, Ontario exposed a paleosol and overlying fossiliferous sediments between tills. The site records a glacial advance and retreat with associated glaciofluvial outwash (early Wisconsinan or older), a long period of weathering, deposition of organic pond sediments (dated as >45 000 years) containing plants, ostracodes, molluscs, and insects, which indicate a cooler and drier climate than present, and a multiple till sequence probably including Catfish Creek and Port Stanley Tills of late Wisconsinan age (25 000–14 000 years old). The paleosol may be of early middle Wisconsinan age or older.
Metamorphism of the pelitic rocks of the Snyder Group in the contact aureole of the Kiglapait layered intrusion, Labrador: effects of buffering partial pressures of water
Authors: Speer J. Alexander
Published: April 2011

The petrography and mineral chemistries of the Aphebian Snyder Group pelitic rocks in the contact aureole of the Kiglapait layered intrusion, Labrador reveal a rapid increase in metamorphic grade over 1.7 km from the greenschist facies to the granulite facies. Three zones of metamorphic grade are defined by the aluminum silicates: I, andalusite; II, andalusite + sillimanite; and III, sillimanite. In addition to the succession in the aluminum silicates, progressive metamorphic mineral assemblages, with quartz, K-feldspar, and plagioclase, evolve from chlorite + biotite + muscovite through cordierite + biotite ± muscovite and garnet + cordierite + biotite to orthopyroxene + garnet + cordierite + biotite and eventually either orthopyroxene + cordierite ± biotite or orthopyroxene + garnet + cordierite. Anatectites, believed to be derived from pelitic rocks, intrude as small stocks in zone III. They comprise biotite + cordierite ± garnet ± orthopyroxene monzogranites or granodiorites with accessory ilmenite, rutile, monazite, and dumortierite.The contact metamorphism is isobaric with pressure just above the intersection of the muscovite + quartz decomposition with the andalusite–sillimanite transition. Most published geobarometers place the estimated pressure of metamorphism at 4 ± 1 kbar (400 ± 100 MPa), but use of the lower Holdaway triple point would put it at 2.25 kbar (225 MPa). The temperature ranges from 450 °C in zone I to 900 °C or more adjacent to the Kiglapait intrusion. The range of values of [Formula: see text] is estimated to be 0.1–0.9Ptotal. Because most reactions are dehydration reactions, conditions of [Formula: see text] less than Ptotal allow the metamorphic reactions to buffer the partial pressure of water. This results in the common occurrence of low-variance assemblages and leads to an apparent overlapping of mineral assemblages and mineral chemistries with increasing metamorphic grade.
Ordovician to Devonian sea-level changes in western and northern Canada
Authors: Lenz A. C.
Published: April 2011

Lower Paleozoic sediments of central, Cordilleran, and arctic Canada are dominated by two megafacies: supratidal to shallow subtidal carbonates and minor evaporites of the platformal (cratonic) areas, and deeper water dark shales and dark limestones of the slope and basinal areas. Large areas of the platform may be covered or exposed in response to relatively small changes in sea level, whereas sea-level changes in the slope and basinal areas are generally recognized only in changes in the sediments and organism content.Employing multiple lines of evidence from stratigraphic, sedimentologic, and paleontologic data, it is generally possible to recognize bathymetrie changes in local stratigraphic sequences, although present inadequate knowledge of fossil "communities" prevents incorporation of that form of paleobathymetric analysis.Composite sections of platformal areas of the central Mackenzie Valley and Williston Basin and of deformed areas of Cornwallis–Bathurst Islands, northern Yukon, central Mackenzie Mountains, and northeastern British Columbia, as well as central and southern Nevada were examined for indications of sea-level changes. Assuming reasonable correlations between sections of the seven areas, fairly good evidence exists for widespread sea-level changes. Sea-level rises (transgressions) are suggested for the Tremadoc and Arenig, early Caradoc and Ashgill, late early and later Llandovery and earliest Wenlock, latest Wenlock and Ludlow, to some extent the Zlichov and Daleje (Emsian), late Eifel and early Givet, and especially Frasne. Sea-level lowering (regression) is indicated possibly for about the middle Arenig, the Llandeilo, approximately the middle Llandovery, the middle Wenlock, the Pridoli, and the lower Lochkov, and approximately the middle Eifel. Anomalies, probably the result of local orogenic activities, are evident in lower Lochkov, Prag, and upper Givet strata of Nevada and the central Arctic Islands.
A new Late Devonian ostracode fauna and its bearing on the Frasnian–Famennian boundary in western Canada
Authors: Braun W. K. , Lethiers F.
Published: April 2011

A new ostracode assemblage, DFr6, characterizes the uppermost Frasnian rock sequences in western Canada. The assemblage or biozone contains elements of both the Frasnian and Famennian ostracode sequences and seems to be intermediate between both faunas, which in main aspects are strikingly different in composition. Similarities between the Devonian ostracodes of western Canada and their time-equivalent faunas of the Russian Platform and adjoining areas suggest the presence of a vast paleobiogeographic faunal province that is distinctly set apart from a "paleo-Tethyan" province whose ostracode representatives are found in central Europe and North Africa.The lower DFr6 subassemblage is contained in the Jean-Marie Member of the Redknife Formation, with the upper DFr6 ostracodes occurring in its upper member and in the Kakisa Formation. Both formations form prominent but lithologically similar carbonate sequences in the southwestern corner of the Northwest Territories and adjoining areas, causing problems in correlations, in particular in subsurface studies. Ostracodes of the upper DFr6 subzone were also recovered from the dolomites of the Winterburn Group of northern Alberta.
Acoustic interpretation of Quaternary sedimentation and erosion on the channelled upper Laurentian Fan, Atlantic margin of Canada
Authors: Piper David J. W. , Normark William R.
Published: April 2011

About 1000 km of single-channel seismic-reflection profiles from a 50 km × 100 km area on the upper Laurentian Fan shows no evidence of the large slumps interpreted by previous workers in this area. Our detailed profile grid indicates that slump-like masses are commonly in depositional continuity with definite autochthonous sediments, and surfaces previously interpreted as slide planes are either facies changes or the result of valley-wall erosion. Only a few small slump blocks of relatively consolidated sediment are found on the uppermost fan. Acoustic-facies distribution shows a single Early (?) Pleistocene fan valley crossing the northeast part of the survey area with thick overbank sediments to the southwest. In the middle (?) Pleistocene this valley became incised. Its upper reaches then ceased to receive sediment, and a new valley was cut extending southward from the upper slope and intercepting the lower reaches of the old fan valley. This channel diversion was probably related either to the glacial excavation of the Laurentian Channel or to a major slump scar that formed east of the survey area. Most of the old abandoned channel was plugged by overbank deposits from the new master channel. Two other valleys farther west also developed at this time or somewhat earlier. In Late Pleistocene time, all three valleys were incised and more than 1 km of sedimentary material was stripped from much of the uppermost part of the fan, probably as a result of headward erosion of submarine canyons and general thalweg lowering.
Optimum linear regression and error estimation applied to U–Pb data
Authors: Davis Donald W.
Published: April 2011

A method is presented for the estimation of age errors for U–Pb zircon data based on Bayesian confidence intervals. The optimum regression problem is first solved using the formalism of maximum probability. The correlation between errors is removed by applying a separate rotation and translation operator for each point. A probability density function is then defined in terms of two straight-line parameters, slope and y intercept, and the optimum line is found by maximizing this function. The intercept parameter is then transformed into an age t, determined by the upper concordia intercept of the given line, and the function is redefined in terms of the slope and t. By integrating this function over the slope parameter, a function of probability versus t is obtained. The age errors then have a natural expression in terms of the width of this function. The results are compared with an approximative method based on confidence-interval theory. A model is then presented to estimate ages and errors for U–Pb data that do not fit a line within error. The error ellipses of the data points are expanded by an amount proportional to discordance until a good fit is obtained. A Student's t factor is applied only to the residuals in the resulting age errors.
Archean metavolcanics from the Rouyn–Noranda district, Abitibi Greenstone Belt, Quebec. 2. Mobility of trace elements and petrogenetic constraints
Authors: Ludden John , Gélinas Léopold , Trudel Pierre
Published: April 2011

Qualitative evaluation of altered mafic pillows from the Rouyn–Noranda district of the Abitibi metavolcanic belt reveals that, for low-grade metamorphism, the high field strength elements (HFS: Zr, Y, Ti) and the rare earth elements (REE) are immobile. However, where alteration is extreme, the REE elements are leached and redeposited by carbonate-rich and K-rich metasomatic fluids whilst Zr/Y and Zr/Ti remain unchanged. Rubidium, Ba, and, to a lesser extent, Sr are mobile at all levels of alteration. However, provided certain filters are applied, the original geochemical values of the lavas for the alkaline elements, the HFS elements, and the REE can be defined.The geochemical variations thus identified for the volcanic series of the Rouyn–Noranda district are ascribed to a combination of contamination and fractional crystallization of a primitive tholeiitic magma.
Occurrence of surface flow on arctic slopes, southwestern Cornwallis Island
Authors: Woo Ming-Ko , Steer Peter
Published: April 2011

Surface flow on arctic slopes is due to a rise of the suprapermafrost water table above the ground surface. The active layer therefore has to be saturated, or surface flow will be lost to infiltration.In spring, snowmelt supplies abundant water to the slopes, but a shallow frost table restricts the active layer storage capacity. This produces extensive surface flow, delivering considerable volumes of water downslope as overland flow or rill runoff. As the snowpacks are reduced and ground thaw increases the subsurface storage capacity, surface flow declines in magnitude and in areal coverage. During most summers, subsurface flow dominates, except when occasional rainstorms of high intensity raise the water table above the ground to rejuvenate surface runoff.The occurrence of surface flow is controlled by slope material, slope profile, and the water balance. Spatial and temporal changes in these controlling variables always result in a highly dynamic pattern of surface flow on arctic slopes.
A thermodynamic approach to the understanding of the supergene alteration at the Afton copper mine, south-central British Columbia
Authors: Kwong Y. T. J. , Brown T. H. , Greenwood H. J.
Published: April 2011

A thermodynamic reconstruction of the supergene alteration at the Afton copper mine, south-central British Columbia, demonstrates that the dominance of native copper and the lack of copper enrichment in the supergene zone are related to the relatively mafic composition of the wall rocks and the absence of abundant hypogene sulfides. Supergene alteration of porphyry copper deposits in general can be interpreted in terms of a [Formula: see text] plot. Two arbitary "limiting" curves characterized by extreme values of acidic and basic pH can be drawn. A reacting fluid evolving near the acidic limiting curve will produce a well developed leached cap with an enriched supergene ore blanket underneath. In contrast, a reacting fluid evolving near the basic limiting curve will lead to a spectrum of copper oxides and native copper with little enrichment, as typified by Afton.
The southern Caspian: A compressional depression floored by a trapped, modified oceanic crust"
Authors: Berberian Manuel
Published: April 2011

The south Caspian intracontinental depression, floored by oceanic basement, is a relatively stable block, with minor deformation, surrounded by active fold-thrust belts of arcuate form (Talesh, Alborz, and Kopeh Dagh Mountains), which have undergone intense late Cainozoic crustal shortening. The basin is interpreted as a Neogene–Quaternary "compressional depression," bounded by multi-role mountain-bordering reverse faults, and apparently floored by a late Paleozoic – Triassic or late Mesozoic – early Tertiary "modified oceanic crust" trapped along an old geosuture. It may be a relic of an old (Paleozoic–Triassic) ocean, or else a marginal sea developed behind a Mesozoic–Paleogene ocean, and analysis of geological and geophysical data enables a scheme to be suggested. The general arcuate shape of the Alborz and the Talesh bordering mountain belts follows the pattern of the supposed rigid and thickened ocean crust of south Caspian depression.A tectono-sedimentary study of the south Caspian region, coupled with the body-wave modelling of a recent earthquake along one of the bordering faults, may suggest a possible flattening of the fault with depth (listric thrust), and that the estimate of the focal depth of the regional earthquakes based on teleseismic arrival time data is not accurate. The difference in elevation between the depression and the bordering active fold-thrust belts is caused by a difference in crustal structure and reverse faulting during a dominant compressional tectonic regime.The study may add support to the idea that old continental deep-seated multi-role faults, which have controlled the sedimentary facies and basins during different geological times and were responsible for the formation of the present physiographic feature, are the site of the present seismic activity in the orogenic belts.
Inclinaison magnétique de roches basaltiques de la dorsale est-pacifique à 21°N et validité des critères de polarité
Authors: Smith Brigitte
Published: April 2011

Among the basaltic rocks sampled by submersible or dredged at the East-Pacific Rise axis around 21°N latitude (French–American–Mexican legs CYAMEX and RISE), 22 samples have been selected according to macroscopic, oriented criteria (elongation plane of feeder tubes in sheeted lavas, bubbles and gas cavities, stalactites, septa) from which the polarity of a sample, acquired in situ during its cooling, could be established.The natural remanent magnetization intensity of these generally voluminous samples (up to about 350 cm3) has a mean value of 11.35 ± 2.31 A∙m−1 (10−3 emu∙cm−3); the scatter of the values can be explained by the varying proportion of nonmagnetic material (glass, Mn) in the samples.The magnetic viscosity is always negligible and the stability of the remanent magnetization direction after alternating field demagnetization indicates that the stable direction determined is the direction of the original thermoremanence.Despite the relatively low latitude, which makes the occurrence of negative magnetic inclinations within a normal polarity period (Brunhes, in this case) more probable, no reverse polarity has been found. The mean inclination of the 22 samples is I = +41.8 ± 16.7° and becomes I = +42.2 ± 19.4° if the samples are grouped in 15 pin-point sampling sites; these values are not significantly different from those of the local dipole field, I = ±37.4°, or from those of the actual local field, I ~ +47°, which may be the result of effusions from the youngest lava flows.The scatter of the magnetic inclination values is more tightly bound to the quality of the polarity criteria than to the secular variation of the Earth ' s magnetic field, the latter interfering in only a few cases. It is obvious that the validity of the reorientation depends on (1) the morphological quality of the criteria used: those that are well developed, well represented in the sample, and apparently the most crystallized (glassy criterion has proved to be doubtful), permit a better reorientation of the sample; and (2) the principle of the criterion itself: criteria referring to vertical axes (stalactites) or vertical planes (septa) are more reliable than those based upon the determination of a horizontal plane (elongation plane of tubes in sheeted lavas).It appears from this study that macroscopic polarity criteria may be used in an almost systematic way to find the polarity of an in situ sample.
Sedimentology of Upper Ordovician – Silurian sequences on New World Island, Newfoundland: separate fault-controlled basins?
Authors: Arnott R. J.
Published: April 2011

Remapping of northeast New World Island, Newfoundland demonstrates that two major faults separate three distinct sedimentary sequences, Paleontology and sedimentology indicate that these sequences are partly equivalent in age but were deposited in separate basins of deposition that were adjacent to each other. Active Silurian faults, the Boyds Island and Byrne Cove Faults (new names), bounded the margins of these basins and directly influenced sedimentation by uplifting Ordovician volcanics, limestone, and black shale, which are found both in situ and as blocks within Silurian sediments. Silurian sediments deposited adjacent to these faults are dominated by pebbly mudstones and chaotic bedding interpreted as debris flow deposits and slumped horizons. Away from the fault scarps sedimentation was predominantly axial; it comprises resedimented conglomerates and thick- and thin-bedded sandstone turbidites.West of New World Island, similar synsedimentary faults are confined to a narrow belt south of the Lukes Arm – Sops Head Fault. Two stages of Acadian deformation overprint all structures associated with the Silurian faulting.
Chronology of tectonothermal activity in the western Avalon Zone of the Newfoundland Appalachians
Authors: Dallmeyer R. D. , Hussey E. M. , O'brien S. J. , O'Driscoll C. F.
Published: April 2011

The Ackley granite was intruded into variably deformed and metamorphosed rocks within the Gander and Avalon Zones of the Newfoundland Appalachians. Biotite and hornblende from the pluton record internally concordant 40Ar/39Ar age spectra that define total-gas dates of 352–356 Ma. These are similar to a previously reported 355 ± 5 Ma Rb–Sr whole-rock isochron age, and indicate relatively rapid post-magmatic cooling, a feature consistent with the post-kinematic character of the pluton.In the western Avalon Zone, recrystallized, sericitic metavolcanic rocks from the Late Precambrian Love Cove and Marys-town Groups display variably discordant, whole-rock 40Ar/39Ar age spectra. However, the samples yield well defined plateau ages of 353–400 Ma (11 samples), which are interpreted to closely date the regional metamorphism and associated deformation in the western Avalon Zone. This chronology is similar to that of the easternmost Gander Zone, indicating that deformation and metamorphism in the western Avalon Zone occurred simultaneously with tectonic juxtaposition of the Gander and Avalon terranes during the Acadian Orogeny. Geochronological evidence of previously described Precambrian (Avalonian) tectonothermal activity has not been documented in this study.
New data on pachycephalosaurid dinosaurs (Reptilia: Ornithischia) from North America
Authors: Galton Peter M. , Sues Hans-Dieter
Published: April 2011

In this paper several new significant specimens of pachycephalosaurid dinosaurs from Upper Cretaceous strata of Canada and the United States are described and figured. The domes of an unusual pachycephalosaurid from the Judith River Formation (Campanian) of Alberta show a slightly thickened frontal with an ornamentation of bony tubercles; they are referred to a new genus. A new genus of Pachycephalosauridae is described from the Hell Creek Formation (Maestrichtian) of Montana; it has horn-like projections on the squamosal. Sutural fusion between the quadrate and squamosal of Pachycephalosaurus is reported; this is an unusual condition among the Ornithischia. The biological significance of certain cranial features is considered.
Depositional environments along a carbonate ramp to slope transition in the Silurian of Washington Land, North Greenland
Authors: Hurst John M. , Surlyk Finn
Published: April 2011

During the earliest Silurian, subsidence and tilting of a relatively flat carbonate platform produced a homoclinal carbonate ramp transitional to the slope of a deep-water basin. Further subsidence, associated with a flexure, differentiated the slope from the carbonate ramp. Subsequently, a linear reef tract developed along part of the flexure, producing a steep reef-scarp slope at the outer homoclinal carbonate ramp margin and accentuating the initial basin slope. Isolated reefs also developed on the slope. The reef tract, which influenced slope depositional environments considerably, marked the transition from the shallow homoclinal carbonate ramp facies to the deeper slope environments. Background slope sedimentation was primarily terrigenous mudstone deposited out of suspension and by very dilute muddy turbidity flows. Superimposed were calcarenites and conglomerates, derived from the carbonate ramp margin and reefs, deposited by low- to high-density turbidity flows, debris flows, and possibly grain and liquefied flows. Sedimentation patterns along the incipient slope reflect both shallow carbonate ramp and deep basinal influences. With continued subsidence and differentiation of slope and ramp, slumping of carbonate blocks occurred at the ramp margin. Disorganized talus wedges developed as circular fringes around reefs on the slope, and a fine-grained talus wedge developed along the base of the main precipitous reef scarp at the ramp margin. A large channel cut down and across the slope and eventually became choked with ramp-margin reef and top-of-slope material. Finally, abrupt subsidence, which generated an olistostrome containing a minimum of [Formula: see text] of debris, drowned all reefs and the slope became essentially starved of resedimented carbonate debris.
Biostratigraphic, paleogeographic, and tectonic implications of Late Ordovician conodonts from the Grog Brook Group, northwestern New Brunswick
Authors: Nowlan Godfrey S.
Published: April 2011

Diverse conodont faunas recovered from the Grog Brook Group in northwestern New Brunswick indicate a Late Ordovician, probably Gamachian, age. The conodonts are of mixed provincial affinity including components of the North Atlantic Province (e.g., Hamarodus, Icriodella, Periodon, and Protopanderodus) and taxa representing shallow (e.g., Rhipidognathus) to deeper water environments (e.g., Phragmodus) in the Midcontinent Province. Elements of Amorphognathus ordovicicus Branson and Mehl numerically dominate the faunas that together with sparse representatives of Gamachignathus ensifer McCracken, Nowlan and Barnes suggest a latest Ordovician age. The beds from which the conodont faunas have been recovered are interpreted as distal debris flows that originated at the basin margin and brought Midcontinent Province conodonts down the slope to mix with indigenous North Atlantic Province faunas. The faunas are correlative with those from the Matapedia Group (previously thought to overlie the Grog Brook Group) and their occurrence suggests at least partial lateral equivalence of the two units.The conodonts recovered are only slightly thermally altered. Two alternative hypotheses are proposed to explain the juxtaposition of relatively unaltered conodonts of the Grog Brook Group and highly altered forms from the Matapedia Group. The first suggests that thrust faulting took place in the Late Ordovician – Early Silurian and that this process and later normal faulting account for the unusual distribution of conodont colour alteration. The second possibility is that the strata of the Grog Brook Group in the section examined were deposited on a structural high and overlain by little or no sediment of the Matapedia Group; however, such a structural high must have had access to a source of Midcontinent Province conodonts. Acadian thrusting then brought higher grade Matapedia Group strata into contact with this part of the Grog Brook Group.
Some silicified Middle Silurian rostroconchs (Mollusca) from the Mackenzie Mountains, N.W.T., Canada
Authors: Johnston D. I. , Chatterton B. D. E.
Published: April 2011

A silicified rostroconch fauna is described from strata of Early (late Llandovery) to Middle (Wenlock to early Ludlow) Silurian age in the Mackenzie Mountains. Two new genera, Cassowarioides and Nehedia, and nine new species, Bigalea buskasi, B. tercierae, Bransonia foxi, Cassowarioides perryi, C. stelcki, Mulceodens schneideri, M. wilsoni, Nehedia bainsi, and N. grovesi, are proposed.An examination of the stratigraphic ranges of some of these taxa suggests that the rostroconchs may have some biostratigraphic utility during the Silurian.
The isotopic composition of western Canadian barites and the possible derivation of oceanic sulphate δ34S and δ18O age curves
Authors: Cecile M. P. , Shakur M. A. , Krouse H. R.
Published: April 2011

Seventeen samples of stratiform barite hosted in Middle Cambrian to middle Mississippian marine sedimentary rocks of the western Canadian Cordillera were analyzed to determine their δ34S and δ18O values. Whereas some samples had isotopic values close to those for time-equivalent evaporites, others were clearly more enriched in the heavy oxygen and sulphur isotopes. Samples with isotopic values close to the evaporite curve were from very thick stratiform barites hosted mainly in organic-rich shales, and from thin and nodular beds hosted in organic-free sedimentary strata. All samples enriched in heavy isotopes were collected from thin or nodular deposits hosted in organic-rich sedimentary strata. Enrichment of barite in heavy isotopes can be achieved by a barite precipitation–dissolution process that cycles barium between oxygenated and reduced zones in either redox-stratified wet sediment, or sea water. This cycles requires barite to either settle from oxygenated sea water into more reducing water or to precipitate within or settle into wet sediment where Eh values are decreasing in situ during sediment buildup. Because all anomalously isotopically heavy barites are hosted in organic-rich strata, barite dissolution during this cycle likely occurs through the bacterial metabolism of organic matter and sulphate, during which sulphate with 16O and 32S is preferentially broken down. The main products of this bacterial activity are CO2 and H2S, which can react to form carbonates or pyrite or can escape from the system, resulting in a depletion of light isotopes from the remaining aqueous sulphate. Because thick deposits of barite hosted in organic-rich shale, unlike smaller deposits hosted in the same strata, do not show heavy isotopic enrichment, the main factor controlling isotope fractionation is likely the rate of barite precipitation relative to barite dissolution and reduction. The δ34S versus δ18O values for six samples of Upper Devonian rocks plot fall on a line with a slope of 2. The data and observations presented here and in published reports indicate that alteration of the isotopic composition of stratiform barite strongly favours enrichment in heavy isotopes with respect to coeval sea-water sulphate. It should be possible then, to construct a barite sulphate isotopic composition age curve by averaging the lower δ18O and δ34S values for samples of the same age.
Cataraquicrinus elongatus, a new disparid inadunate crinoid from the Middle Ordovician of Ontario
Authors: Kolata Dennis R.
Published: April 2011

A new disparid inadunate crinoid, Cataraquicrinus elongatus n. gen., n. sp. has been discovered in the Blackriveran (Middle Ordovician) Gull River Formation near Kingston, Ontario. The new homocrinacean crinoid is characterized by a very small crown, isotomously branching arms that have as many as nine primibrachials per arm, large elongate anal tube, a proximally pentagonal stem, and a lichenocrinid holdfast. The new genus most closely resembles Tunguskocrinus from rocks of approximately the same age of the Siberian Platform.
Relations possibles entre la microseismicité récente et l'astroblème de Charlevoix
Authors: Roy Denis W. , DuBerger Reynald
Published: April 2011

The limit of the direct effects of the Charlevoix astrobleme in the upper part of the Earth's crust outlines approximately a revolution paraboloid about a vertical axis. It reaches 14 km in depth below the center of the astrobleme and exhibits a 27 km radius at the present-day ground surface. The microearthquakes, which reflect the regional crustal stresses in eastern North America, occur on the normal faults characteristic of the St. Lawrence Lowland tectonic terrain mainly near the astrobleme paraboloid or near a second paraboloid located 7.9 km outside the first one. This second one could result from some yet undefined interference between the crust–mantle boundary and the shock wave responsible for the formation of the astrobleme 350 Ma ago. The very low seismic activity in the vicinity of Petite-Rivière–Saint-François may imply that energy is now building up in that area.