bluuebunny/crossref_metadata_2025 huggingface dataset:
Tectonic setting and syndepositional deformation of molasse and other nonmarine-paralic sedimentary basins
Authors: Miall Andrew D.
Published: April 2011

Molasse is a distinctive sedimentary facies consisting of alluvial and shallow marine deposits derived from source areas undergoing rapid uplift and erosion. The characteristic setting of molasse is within or adjacent to fold belts, and most molasse basins can be classified as foreland basin (external) or intermontane (internal) in type. Thick alluvial and shallow marine sequences in cratonic settings (e.g., taphrogenic troughs) have been classified as molasse by some workers, but this is not generally accepted.Most molasse is synorogenic, and the interdependence of sedimentation and tectonism results in structural and stratigraphic complexity. Intermontane basins generally are tensional in origin and are bounded by high angle (commonly normal) faults. Facies distributions adjacent to each fault depend on relative rates of differential movement, erosion, and sedimentation; accelerated source area uplift causes segmentation and progradation of alluvial fans and generates coarsening-upward sedimentary cycles. Complications are introduced if tectonism occurs in discrete pulses and if basins enlarge themselves along systems of stepped faults.Basins of compressional origin, such as those in a foreland setting, show a greater variety of internal complexity. Facies belts and trends of maximum thickness move progressively out from the core of the fold belt in response to a migration of the zone of active deformation. Conversely, broad structural warps may develop in response to a locally increased sedimentary load, such as a major delta. Folds or thrust faults growing within the basin cause local thinning or unconformable relationships, and may breach the surface so as to isolate parts of the alluvial plain as a synorogenic intermontane basin. Uplift of the fold belt may be discontinuous, causing the generation of stacked sedimentary megacycles. Basin margins commonly are characterized by intraformational angular unconformities and syndepositional folds.Rates of alluvial sedimentation and tectonic movement measured in modern environments are one to two orders of magnitude higher than rates deduced from ancient nonmarine sequences. This lends support to the idea that much sedimentation may be very episodic in nature, but it could also imply that alluvial sequences are deposited much more rapidly than current interpretations of the ancient record would imply, based as they are on relatively crude dating techniques. Only in some wrench-fault basins do calculated sedimentation rates compare with those measured in modern environments.
A coiled nautiloid preserved in life orientation from the Middle Ordovician of Ontario
Authors: Collins Desmond
Published: April 2011

The occurrence of a coiled nautiloid embedded in life orientation in the Middle Ordovician Bobcaygeon Formation just north of Manitoulin Island indicates that the sea was less than 10 m deep in this area at that time.This is the first documentation of preservation of a coiled cephalopod in life orientation in Ontario and probably in Canada.The nautiloid, Campbelloceras clochense, n.sp., extends the range of the Tarphyceratidae one complete stage from the Chazy to the top of the Black River.
Carbonate-hosted lead–zinc occurrences in northeastern British Columbia with emphasis on the Robb Lake deposit
Authors: Macqueen R. W. , Thompson R. I.
Published: April 2011

In the Rocky Mountains of northeastern British Columbia, a Lower and Middle Devonian platform carbonate succession of six formations and [Formula: see text] total thickness gives way laterally north and west to shales, siltstones, and carbonaceous limestones of the Besa River Formation, of deeper water origin. Promising mineralization, dominantly sphalerite with some galena, is located in carbonates near the platform margin, within the Muncho–McConnell–Stone, Pine Point – Sulphur Point, and Slave Point Formations. Mineralization is not obviously related to structure, unconformities, or evaporite solution. Sphalerite and galena are closely associated with white sparry dolomite and commonly accompanied by quartz and thermally altered reservoir bitumen. Sulphur isotope ratios of galena and sphalerite range from + 5.0 to + 17.5 δ34S‰, consistent with a reduced sulphate or petroleum-derived hydrogen sulphide source for sulphur.At Robb Lake, mineralization occurs within broadly conformable breccias in the Stone, Muncho–McConnell interval; sparry dolomite forms the breccia matrix; and bitumen is common although rare elsewhere in the interval. Maximum paleotemperatures of host carbonates at Robb Lake appear to have been about 200–230 °C, as determined by bitumen characteristics, fluid inclusion filling temperatures in quartz, and illite crystallinity from illite in Besa River Formation shales. The Paleozoic and Mesozoic sedimentary section in the region suggests that the Middle Devonian of the Robb Lake area reached a maximum burial depth of about 5 km during mid-Cretaceous time. Physical proximity of bitumen and sulphide mineral deposits suggests that similar processes were involved in petroleum maturation–migration, and metallic mineral precipitation. Besa River shales are seen as probable sources for both petroleum and metals; sulphide sources appear to have been hydrogen sulphide generated within carbonate host rocks. A genetic association of petroleum and metals implies that mineralization took place relatively late (?early Mesozoic), and under deep subsurface conditions.Ground preparation in the form of brecciation and fracturing is problematical; at Robb Lake it may be a consequence of hydraulic fracturing due to high pore pressures generated by dewatering of the fine clastic facies that envelope the host dolomites. A better knowledge of time of origin of these deposits will contribute greatly to an understanding of their genesis. Meanwhile, consideration of the burial and thermal history of the host rocks offers a useful framework within which the mineral deposits and their genesis may be assessed.
The development of limestone cave systems in the dimensions of length and depth
Authors: Ford D. C. , Ewers R. O.
Published: April 2011

Karst caves are defined as solutional cavities >5–16 mm in diameter and discussion is limited to cases where such continuously extend to a surficial input or output or both. Three opposed sets of general genetic hypotheses ('the classical hypotheses') have been presented for such caves, arguing that the majority develop (1) in the vadose zone, (2) in the phreatic zone, or (3) proximate and parallel to a water table. It is contended here that vadose, phreatic, and water-table caves are all of common occurrence and may be linked in one genetic theory. A four state model is proposed in which ideal phreatic and water-table caverns are end members; in a given massif of soluble rock the state (cave type) that develops is a function of the frequency of fissures penetrable by groundwater. The water-table type is the high frequency end member. Fissure frequency increases with passage of time after onset of karstification and gradational features may also develop to modify phreatic types. Vadose caves may be of 'drawdown' type (following an initial phreatic path) or 'invasion' type (developing a new path through rock drained by earlier caves). Extensive cave systems may comprise vadose, phreatic, and (or) water-table components developed contemporaneously.
Mean flow structure in meanders of the Squamish River, British Columbia
Authors: Hickin Edward J.
Published: April 2011

The primary velocity field and pattern of secondary flow are described for nine consecutive bends of the Squamish River in southwest British Columbia.The velocity field largely can be explained in terms of variation in channel form, advective acceleration responses, and water transfers by secondary flow.The pattern of secondary flow accords with the general model of spiral flow in meanders. Divergences from this ideal pattern can be explained by bend–flow interaction induced by the variable planform geometry of the channel.The strength of secondary circulation increases rapidly as the ratio of the radius of bend curvature to channel width (rm/w) declines from 4.0 to the data minimum of 1.41. There is no discontinuity phenomenon in the flow structure over the measured range of rm/w; the Bagnold separation–collapse model does not apply to the Squamish River.As rm/w declines to values less than 3.0, the maximum velocity filament shifts from the concave to the convex bank zone. The resulting high shear stresses over the point bar and declining shear stresses at the concave bank markedly reduce the channel migration rate.Separation zones developed at the concave bank of tightly curved bends provide the mechanism for completely halting (and indeed reversing) the process of channel migration.
A major Aphebian–Helikian unconformity within the Central Mineral Belt of Labrador: definition of new groups and metallogenic implications
Authors: Smyth W. R. , Marten B. E. , Ryan A. B.
Published: April 2011

The Central Mineral Belt of Labrador consists of a belt of supracrustal rocks that occupies the northern foreland region of the Grenville Province of the Canadian Shield. Recent mapping in this belt has shown that the Proterozoic Croteau Group consists of two distinct sequences separated by an observed angular unconformity. It is therefore proposed that the name Croteau Group be abandoned and that the lower, Aphebian, marine sequence of sandstone, dolostone, slate, argillite, and mafic volcanic rocks be named the Moran Lake Group and that the upper, Helikian, continental sequence of conglomerate, tuffaceous sandstone, and a calc-alkalic volcanic assemblage be named the Bruce River Group.The Moran Lake Group underwent polyphase deformation, which has been assigned to the Hudsonian Orogeny, prior to deposition of the Bruce River Group around 1474 Ma. The Bruce River Group was intruded by a large granitic batholith, the Otter Lake Granite, for which a preliminary Rb–Sr isochron age of 1445 Ma has been obtained; this age correlates with the Elsonian magmatic event, an event well documented in northern Labrador. The Seal Lake Group, a Neohelikian (1278 Ma) sequence of quartzites, conglomerates, and intercalated mafic lava flows, was unconformably deposited upon the Bruce River Group and the Otter Lake Granite. During the Grenvillian Orogeny, the Bruce River and Seal Lake Groups were deformed together into a major easterly trending syncline. Deformation and metamorphism decrease across these groups to the north.The Bruce River Group forms part of the Labrador uranium area and hosts 14 known uranium occurrences. Occurrences are concentrated in the basal sandstones and conglomerates of the group, above the Aphebian–Helikian unconformity, and in ignimbrites and acid tuffs near the top of the group. No uranium occurrences are known from the Moran Lake Group except in fault-related fractures below the unconformity.
Paleoecological succession leading to a late Ordovician biostrome on Manitoulin Island, Ontario
Authors: Copper Paul , Grawbarger David J.
Published: April 2011

A 4 m thick section in the late Ordovician sequence on Manitoulin Island revealed four successively shallowing carbonate environments, each with a distinctive fossil assemblage. The lowermost quieter water, muddy level bottom community was dominated by the brachiopod Zygospira. Next, increased laminar current action attracted smaller colonies of the tabulate corals Tetradium and Columnopora, and locally small banks of corals and stromatoporoids were built up. In the protected shallow subtidal community following, encrusting algae (Girvanella) and upright match-stick Hedstroemia were more important, alongside Columnopora, cup corals, and a diverse association of thick-shelled bivalves and gastropods. The short-term paleoecological succession terminated under turbulent conditions with large colonies of Labechia, rugose coral colonies of Cyathophylloides, and tabulate corals such as Tetradium forming what is called the Wekwemikong biostrome.
Anomalous Li in Keweenawan rhyolites, Ontario
Authors: Jackson M. R. , Shaw D. M. , Massey N. W. D.
Published: April 2011

Twenty-five samples of altered silicic volcanic rocks associated with the Keweenawan altered basalts at Mamainse Point, Ontario, were analysed for major elements, Li, Rb, Sr, and Ba.Although other elements show no unusual abundances, Li is enriched in most samples, averaging 98 ppm, in comparison with equivalent fresh rocks elsewhere. It is probable that this enrichment took place during the alteration process.
Oxidation–reduction sequences in ground water flow systems
Authors: Champ D. R. , Gulens J. , Jackson R. E.
Published: April 2011

Hydrogeologists and ground water geochemists have observed a decline in the measured (platinum electrode) potential, EH, of ground water as it migrates from upland recharge areas to lowland discharge areas under confined conditions. Such variations in EH and variations in concentrations of elements with variable oxidation states (e.g., oxygen, nitrogen, iron, manganese, sulfur, and carbon) can be accounted for by a sequence of oxidation–reduction reactions occurring in the flow systems, the sequence being based on thermodynamic principles as outlined by Stumm and the microbial catalysis of such reactions. This sequence of reactions results in the identification of three redox zones in ground water flow systems: (1) oxygen–nitrate, (2) iron–manganese, and (3) sulfide. The mobility and concentration of most transition metal and nonmetal ions vary according to zone—a matter of considerable significance in exploration geochemistry and in ground water pollution studies.
Geology and petrochemistry of lower Aphebian (2.4–2.0 Ga) alkaline plutonic and hypabyssal rocks in the East Arm of Great Slave Lake, Northwest Territories
Authors: Badham J. P. N.
Published: April 2011

Two alkaline igneous complexes and three lines of diatreme breccias were emplaced in the East Arm of Great Slave Lake during the lower Proterozoic. Field relationships suggest that those rocks are broadly cogenetic and were emplaced about 2.1 Ga ago.One of the intrusions, the Easter Island dyke, was rotated subsequent to emplacement such that both top and bottom are now exposed. Field and petrographic data are indicative of progressive differentiation along (i.e., up) the dyke and are substantiated by chemical data. The differentiation history of the early gabbros of the Blachford Lake complex is similar. Late differentiates of both complexes closely resemble the igneous matrices of the breccias and petrographic and chemical data support the proposal of cogenesis and contemporaneity.The field data show that there was a period of significant faulting and concomitant alkaline igneous activity in the East Arm area in the lower Proterozoic.
Precambrian biota from the Little Dal Group, Mackenzie Mountains, northwestern Canada
Authors: Hofmann H. J. , Altken J. D.
Published: April 2011

Well preserved Precambrian algal microfossils and megafossils have been recovered in the northern Mackenzie Mountains from several levels and localities in a basinal, limestone-dominated rhythmite formation of the Little Dal Group. The microbiota includes the filaments Archaeotrichion, Taeniatum and Siphonophycus, and the sphaeromorph acritarchs Kildinella, Trachysphaeridium, Nucellosphaeridium, and Chuaria circularis. The megafossils, ail of probable algal affinities, comprise large carbonaceous ribbons assigned to the new vendotaenid species Tawuia dalensis n.g. n. sp., and the irregular compressions Mariana? antiqua and Beltina danai. The same formation has also yielded a dubiofossil probably representing traces on bedding planes made by small cylindrical, discoid, or spheroidal organisms, questionably referred toBergaueria. The biota suggests a late Helikian to early Hadrynian age (1.1–0.8 Ga) for the Little Dal Group, and adds to the growing body of evidence for the existence of eucaryotic organisms at that time.
Paleomagnetism and orogenic history of the Botwood Group and Mount Peyton Batholith, Central Mobile Belt, Newfoundland
Authors: Lapointe P. L.
Published: April 2011

This is the first palcomagnetic result from the Paleozoic Botwood Central Zone of Newfoundland. Two Lower Paleozoic rock units were sampled: the Botwood Group (rhyolite and red sandstone) at 16 sites and the Mount Peyton Batholith (dioritic and granitic phases) at 12 sites. Two phases are recognized in this intrusion: dioritic (420 Ma) and granitic (380 Ma). Four distinct magnetization directions were observed during the study. In the Lawrenceton Formation (Bot-wood Group, rhyolite) the direction obtained after tilt correction (180°, + 47°) gives a pole at 125°E, 13°N, probably of Lower Silurian age. The overlying Wig Wam Formation of the Botwood Group (red sandstone) was magnetized during a reversal. Detailed demagnetization techniques (thermal, chemical, and alternating field) were used to separate the normal and reversed directions in composite magnetizations; with a mean direction of 194°, + 28°, the pole (100°E, 25°N) obtained after tilt correction is related to a Silurian age. Two magnetizations were found in the Mount Peyton Batholith: the first one (pole at 68°E, 15°S) is associated with the dioritic phase with an age of 420 Ma. The second one (pole at 125°E, 63°S) is associated with the granitic phase at 380 Ma.
The Wisconsinan deglaciation, of southern Saskatchewan and adjacent areas
Authors: Christiansen E. A.
Published: April 2011

The Wisconsinan deglaciation of southern Saskatchewan and adjacent areas of Alberta, Manitoba, Montana, and North Dakota is depicted in nine phases of glacial advance, readvance, and retreat. Althouth there is some uncertainty whether Phase 1 or 2 represents the Classical Wisconsin (Woodfordian) terminus, the glacial history from about 17 000–10 000 years ago is considered.Although the glacier margin retreated at an increasing rate in Saskatchewan, the volume of meltwater released by the melting glacier decreased with time. The large meltwater channels south of the Cypress Hills as compared to those to the north and the fact that most of the glacial lake deposits north of the Cypress Hills came from extraglacial rivers suggest there was much more glacial meltwater activity south of the Cypress Hills than north of them. This in turn suggests that much of the ice melted before significant retreat of the ice front took place.
Crustal structure from a seismic refraction profile across southern British Columbia
Authors: Cumming W. B. , Clowes R. M. , Ellis R. M.
Published: April 2011

A partially reversed seismic refraction profile utilizing mine blasts as sources was recorded across southern British Columbia from Sparwood to the Highland Valley. The westwardly directed profile consisted of 32 short period seismograms covering 440 km, while the reversed line extended 330 km with 41 seismograms. From a starting model based on first arrival times and previous geological and geophysical data, a seismic structural section is developed using both synthetic seismograms and a program for ray tracing through inhomogeneous media.The refraction data indicate that the M-discontinuity dips to the east from an approximate depth of 30 km east of the Highland Valley to in excess of 40 km beneath the Purcell Anticlinorium. Undulations of about 165 km wavelength and several kilometres amplitude characterize the crust–mantle boundary. The Pn velocity is 7.8 km/s. Above the M-discontinuity, secondary arrivals are interpreted to be from a lower crustal layer of thickness near 12 km and velocity 6.9 km/s. The upper boundary of this layer also dips gently to the east.The seismic structure of the upper crust correlates closely with the regional geology as evidenced by traveltime and amplitude anomalies where the profile crosses the Rocky Mountain Trench and the Interior Plateau – Eastern Metamorphic Belt boundaries. The crustal P and S phases in the Interior Plateau yield a relatively low value of Poisson's ratio of 0.23. The detailed data close to the Highland Valley indicate significant velocity heterogeneity. For the Guichon Creek batholith, the inner Bethlehem phase is found to have a higher velocity than the surrounding Highland Valley phase.
Regional geochemical mapping in areas lacking surface drainages: Cu, Fe, Mn, and Zn content of overburden and soil in south-central Saskatchewan
Authors: Doyle P. J. , Fletcher W. K.
Published: April 2011

An approach to regional geochemical mapping is outlined utilizing differences among mean metal concentrations for soil associated with individual parent materials. Initially the area of study is divided into parent material-based subareas for soil collection. Separate mean and variance metal values are estimated for each parent material and Duncan's Multiple Range Test is used to evaluate the statistical significance of among mean differences. Results are summarized in map form showing only compositionally distinctive parent materials or parent material groups and their associated mean and range values.This approach was tested in the Rosetown–Outlook area of south-central Saskatchewan. Results suggest that, in total, fewer than 10 samples are required per parent material to produce stable maps for copper, iron, manganese, and zinc in this 10 000 km2 area. Because of the limited number of samples needed, the method is both rapid and relatively inexpensive. It is therefore ideally suited for regional geochemical surveying, particularly in relatively arid areas where conventional lake and stream sediment-based procedures are not applicable.
A Late Pleistocene plant-bearing deposit in Currie Township, near Matheson, Ontario
Authors: Brereton W. E. , Elson J. A.
Published: April 2011

Two overburden test holes drilled to bedrock in Currie Township, southwest of Matheson, Ontario, penetrated stratified beds containing fossil plant detritus resting on an oxidized substrate, which are between two till sheets underlying glacial Lake Ojibway-Barlow varved clays. The fossil plants, chiefly mosses, represent an environment that is common in the region today, and are radiocarbon dated (GSC-2148) as older than 37000 years. The interglacial deposit is tentatively correlated with the Missinaibi Formation in the Moose River basin of the James Bay lowlands, probably of Sangamon age.
Catagenesis in shales and occurrence of authigenic clays in sandstones, North Sabine H-49 well, Canadian Arctic Islands
Authors: Foscolos A. E. , Powell T. G.
Published: April 2011

Authigenic clays in eight sandstone samples from the North Sabine H-49 well in the Sverdrup Basin, N.W.T., have been studied by X-ray diffraction and scanning electron microscopy. The following sequence of authigenic minerals was observed with increasing burial depth: quartz–kaolinite, illitic 2:1 layer silicates, and chlorite. It is suggested that the formation of authigenic clays in sandstones can be considered in the context and as a product of catagenesis of adjacent shales. Upon burial, water is released from the shales by compaction, clay dehydration, and clay destruction. Continuing compaction carries the products of clay transformation to the sandstones where they precipitate to form authigenic clays. The nature of the authigenic clay is directly related to the physico-chemical conditions existing at various depths.
Facies of supraglacial sedimentation on Icelandic and Alpine temperate glaciers
Authors: Eyles Nicholas
Published: April 2011

Supraglacial debris transported by temperate valley glaciers is classified as supraglacial morainic till, distinct from lodgement till, and melt-out and flow till species on polar glaciers. In Iceland and the Alps, where annual discharges of supraglacial morainic till vary from 200–2000 m3 (compared with a maximum discharge of 26 000 m3 of lodgement till), till is deposited as three facies.Fades 1 occurs where supraglacial morainic till slows the rate of ice melt such that till is slowly superimposed on the subglacial surface in the form of stagnation or disintegration topography. The rate of deposition shows an initial slowing phase in response to (1) soil formation and (2) melt-out of englacial debris, followed by accelerated deposition accompanying the formation of thaw lakes. Continued mass movement of till on lake margins (backwasting) is more effective in destroying the ice-core than either top or bottom melt and prohibits accumulation of a distinct melt-out sediment. This situation can be contrasted with the style of sedimentation at polar glaciers. Where the depositing glacier is inactive and uncontrolled an unlineated till surface, typical of stagnation or disintegration topography, develops. Significantly, in terms of Pleistocene reconstructions, tracts of stagnation topography are being constructed at the margins of certain active Icelandic glaciers by sequential stagnation of a marginal rim of ice as the active glacier retreats up-valley.Fades 2 occurs where the till cover is too thin or too coarse and ice melt is unretarded and supraglacial morainic till is deposited as a dispersed bouldery veneer by dumping during which gravity sorting occurs. Dump moraine ridges frequently show internal bedding being ice-contact screes at time of formation but are not ice-cored. An active glacier produces a controlled distribution of landforms resulting in a lineated till surface.Facies 3 refers to those stratigraphic sequences where irregular or lensate till horizons alternate repeatedly with ice-contact outwash. The stratigraphic sequence as a whole is defined here as a supraglacial morainic till complex. Well-sorted, clast-supported outwash sediments occur within complexes deposited at inactive low-angled ice margins. At active steep-fronted glaciers, where areas of the till-covered ice front are only episodically scoured, distinct flood-deposited matrix-supported outwash units are found. Their subaerial formation runs counter to recent published interpretation of sediments in certain Pleistocene eskers.
Dynamic properties of reflected and head waves near the critical point
Authors: Marks Larry W. , Hron F.
Published: April 2011

The classical problem of the incidence of spherical waves on a plane boundary has been reformulated from the computational point of view by providing a high frequency approximation to the exact solution applicable to any seismic body wave, regardless of the number of conversions or reflections from the bottoming interface. In our final expressions the ray amplitude of the interference reflected-head wave is cast in terms of a Weber function, the numerical values of which can be conveniently stored on a computer disk file and retrieved via direct access during an actual run. Our formulation also accounts for the increase of energy carried by multiple head waves arising during multiple reflections of the reflected wave from the bottoming interface. In this form our high frequency expression for the ray amplitude of the interference reflected-head wave can represent a complementary technique to asymptotic ray theory in the vicinity of critical regions where the latter cannot be used. Since numerical tests indicate that our method produces results very close to those obtained by the numerical integration of the exact solution, its combination with asymptotic ray theory yields a powerful technique for the speedy computation of synthetic seismograms for plane homogeneous layers.
A simple method for tilt corrections in X-ray pole figure goniometry in the reflection mode
Authors: Ballestracci Régis , Astier Gérard , Lamouroux Christian
Published: April 2011

X-ray texture goniometry is widely used to determine preferred orientations in rocks. The main difficulty is to correct the observed intensities for some physical effects (particularly X-ray absorption, volume variation of the irradiated specimen, and defocusing) which depend on the inclination α of the sample slab with respect to the plane of the incident and diffracted beams. The method presented in this paper makes it possible to determine, experimentally, a general correction factor ρ(α) for the measured intensities. A ρ(α) curve, is obtained by comparing the intensities of one pole measured in two differently oriented slabs. The general correction factor ρ(α) has been determined for labradorite in a calc-alkaline basalt and for the quartz in a mylonitized granodiorite.
Morphology and dynamics of a barrier breach: a study in stability
Authors: Greenwood Brian , Keay Patricia A.
Published: April 2011

A small barrier breach in Kouchibouguac Bay, New Brunswick, is examined with respect to: (a) origin, (b) morphological development, and (c) hydraulic characteristics. The small tidal inlet was formed in 1970 by storm conditions which have a return period of between 5 and 12 years, based upon two different storm intensity indices. Barrier breaching is not a catastrophic event in the temporal sense in the bay and the return period of the initiating storm conditions is close to the average interval between breaching episodes for this barrier system. A threshold barrier morphology is suggested as a more important variable than storm magnitude. Traced from its inception to closure (a period of 6 years), the barrier breach cited revealed: (a) flood domination generating a transfer of large volumes of sedimentary material from the littoral drift system into the lagoon, (b) gradual reduction in tidal prism associated with flood delta growth and infilling of tidal channels, and (c) migration (30 m year−1) and increasing reorientation of the inlet neck under a strong preferred littoral drift direction.
A study of the effects of pore-water salinity on some physical properties of sedimentary rocks at permafrost temperatures
Authors: Pandit B. I. , King M. S.
Published: April 2011

The effect of pore-water salinity on the elastic wave velocities and electrical resistivities of frozen, saturated specimens of two sandstones and a limestone have been studied in the temperature range −15 to +4 °C. The specimens were saturated with solutions whose salinities varied from 0.0 M (distilled water) to 1.0 M NaCl.An increase in pore-water salinity reduces the effect of sharp increases in velocity as the temperature is reduced below 0 °C. The ratio of compressional to shear-wave velocities shows a weak dependence on temperature and salinity. Calculations of the ice content showed that the pore spaces were not completely filled with ice, even at the lowest temperature (−15 °C) reached.An increase in either temperature or salinity was found to lower the complex resistivity, and to extend the range of frequency over which the resistive behavior, rather than the dielectric, was dominant. The decrease in resistivity was observed to be most rapid when the pore water salinity was increased from 0.0–0.3 M. The ratio of the resistivity of a rock when frozen (ρf) to that when thawed (ρt) can be shown to be related to the fraction (Sw) of the water remaining unfrozen at subzero temperatures by ρf/ρt = (Sw)1−n. By combining the results of the velocity and resistivity measurements, it was found that n = 0.9 log pf/pt + 2.3.
Isotopic studies of lead-depleted pitchblende, secondary radioactive minerals, and sulphides from the Rabbit Lake uranium deposit, Saskatchewan
Authors: Cumming G. L. , Rimsaite J.
Published: April 2011

Uranium–lead and lead isotopic studies have been made on different types of pitchblende, on secondary Pb-rich and Pb-poor uranium-bearing minerals, and on sulphides (radiogenic galena and pyrite) from the Rabbit Lake uranium deposit in northern Saskatchewan. Most specimens have been selected on the basis of their mineralogy and Pb/U ratios as determined by electron microprobe analyses. The Pb/U ratio varied between 1/2 and 1/665 as a result of diverse episodes of crystallization, differential losses of uranium and radiogenic lead, recrystallization of remobilized uranium and lead in different proportions in secondary radioactive minerals, and possible loss or enrichment of radon gas.All concentrates yielded discordant ages. Six samples contained an excess of radiogenic lead and yielded Pb/U ratios above the concordia curve. P-1 (primary) pitchblende samples were found to be depleted of radiogenic lead, thus grading into the Pb-depleted pitchblende of type P-2, and the data on even the "best" material can, thus, only be interpreted in terms of a discordia line which yields intersections at about 1281 and 440 Ma.A second discordia intersects the concordia curve at 1085 Ma and was obtained on concentrates containing several types of pitchblende including some samples difficult to distinguish in polished section from those of the 1281–440 Ma line, and secondary Pb-rich and Pb-poor uranyl-bearing aggregates that fell above, and at the lower end of, the concordia curve. This discordia intersection agrees well with previously published ages.The important event related to the replacement of pitchblende by sulphides, selenides, and arsenides, accompanied by marked losses of radiogenic lead and mobilization of uranium from the partly-resorbed "primary" pitchblende of type P-1, took place at a time no greater than 800–900 Ma ago. Reactions between remobilized uranium and altered silicates, and between the uranium and silica to form uraniferous phyllosilicates and coffinite, occurred 440 and ca. 200 Ma ago. Crystallization of hydrous uranyl-bearing aggregates, including precipitation of amorphous crusts in fractures of argillized rocks, continues at the present time.The Rabbit Lake deposit has been affected by superimposed alterations and recurring fracturing leaving fragments of partly resorbed and Pb-depleted pitchblende as the only remnants of the original intensive and widespread uranium mineralization.
The Cretaceous–Tertiary boundary in south-central Alberta—a revision based on additional dinosaurian and microfloral evidence
Authors: Lerbekmo J. F. , Singh Chaitanya , Jarzen D. M. , Russell D. A.
Published: April 2011

Recent field observations indicate that no dinosaur remains are known to occur above the Nevis coal seam. Therefore, previous conclusions which placed the Cretaceous–Tertiary boundary at the base of the Ardley coal seam are modified. A microfloral change recorded at the top of the Nevis seam in south-central Alberta corresponds to similar palynofloral changes at the Maestrichtian–Paleocene boundary in the northwestern interior of the United States. This microfloral change is considered synchronous in the region stretching from Alberta to Colorado and coincides with the dinosaurian extinction at the Maestrichtian–Paleocene boundary. In the light of this new evidence, it is proposed that the Cretaceous–Paleocene boundary be placed at the top of the Nevis coal seam in Alberta.
Ichnology of the Trenton Group in the Quebec City area
Authors: Plckerill R. K. , Forbes W. H.
Published: April 2011

Marine limestones of the Middle Ordovician (Caradocian) Trenton Group in the Quebec City area are extensively burrowed. Traces referable to Anconichnus horizontalis, cf. Biformites, Bifungites cf. halli, Chondrites, Cruziana cf. pudica, Cruziana, Isopodichnus, Palaeophycus, Planolites, ? Rhizocorallium cf. R. irregulare, Rusophycus, Teichichnus cf. rectus, Tomaculum and Trichichnus are described in detail. Miscellaneous traces, those not morphologically distinct and (or) sufficiently abundant to warrant formal taxonomic treatment, are briefly described. The trace fossil assemblage can be broadly equated with the Cruziana ichnofacies. Southwest of Quebec City the Trenton Group was deposited in a gradually deepening offshore bar to shallow inner shelf situation, whereas to the northeast deposition occurred in a shallow inner shelf to deeper outer shelf – upper slope environment. The spatial and temporal distribution and abundance of the trace fossils are examined in relation to these broad environmental changes. The observed patterns are perhaps best related to variation in energy conditions, substrate stability, and food availability, parameters all broadly related to water depth. The trace fossil density and diversity patterns are analogous to those exhibited by modem and ancient shelly macrobenthos, where in shallow subtidal regimes they are low, then peak in slightly deeper subtidal situations, and gradually decrease seawards with increasing depth and distance from shore.
A new and unusual skeletal organism from the Lower Cambrian of Labrador
Authors: Kobluk David R.
Published: April 2011

An unusual carbonate skeletal organism is found in abundance in the upper of two archaeocyathid-rich horizons in the Lower Cambrian Forteau Formation of southern Labrador. The commonly cryptic organism consists of splaying and branching irregularly polygonal tubes which are open. Tabulae and dissepiments are absent; the walls are thick (200–950 μm) in relation to the diameter of the tubes (150 μm to 5 mm). Only very rarely is wall microstructure preserved. It consists of elongate calcite crystals perpendicular to the wall margin in vertical section. The wall is covered by a thin (20–35 μm) outer layer. Pore-like structures with curved necks are very rarely found perforating the wall outer layer.The affinities of this organism are unknown, but it does have features which are both coral-like and sponge-like. It is here placed in the Incertae Sedis.
A model for Archean tectonism. Part 2. Numerical models of vertical tectonism in greenstone belts
Authors: Mareschal Jean-Claude , West Gordon F.
Published: April 2011

A tectonic model that attempts to explain common features of Archean geology is investigated. The model supposes the accumulation, by volcanic eruptions, of a thick basaltic pile on a granitoid crust. The thermal blanketing effect of this lava raises the temperature of the granitic crust and eventually softens it enough that gravitational slumping and downfolding of the lava follows.Numerical models of the thermal and mechanical evolution of a granitoid crust covered with a thick lava sequence indicate that such an evolution is possible when reasonable assumptions are made about the temperature dependence of the viscosity in crustal rocks. These models show the lava sinking in relatively narrow regions while wider granite diapirs appear in between. The convection produces strong horizontal temperature gradients that may cause lateral changes in metamoprhic facies. A one order of magnitude drop in accumulated strain occurs between the granite–basalt interface and the center of the granite diaper at a depth of 10–15 km.
Storm-dominated shallow marine sediments of the Arisaig Group (Silurian–Devonian) of Nova Scotia
Authors: Cant Douglas J.
Published: April 2011

Shallow marine deposits of the Arisaig Group (Silurian–Devonian) of Nova Scotia consist of shaly sediments with varying proportions of coarser interbeds. Brachiopods, graptolites, crinoids, corals, and bivalves are present in parts of the group.One end-member lithology consists of black, fissile shale with few fossils. This grades into grayer, less fissile, more fossiliferous shale with coarse siltstone interbeds up to 5 cm thick. Higher in the group, nearer nonmarine beds, the background sediments consist of mottled, nonfissile silty mudstone with many large in situ brachiopods and lenses of coarse siltstone. The interbeds are composed of coarse siltstone or fine sandstone and, in some cases, have lenses of coquina within them. They range from 5–50 cm in thickness, but in places have amalgamated by scouring and locally comprise almost 100% of the section. Most of the coarse interbeds have sharp bases with horizontal or low angle laminations, but some thicker beds show sets of low angle, curving laminations which truncate other sets, termed “hummocky cross-stratification," The top surfaces of these beds are covered by interference ripples and burrows.The coarse interbeds were laid down rapidly by fractional seaward-flowing bottom currents during storms. Some of the coarse beds were later modified by bioturbation during fair weather periods when settling of sediment from suspension and faunal activity were the dominant processes. The Arisaig Group represents the deposits of a storm-dominated shelf and illustrates the range in variation which can occur in the sediments of this type of environment.
Chattermarked garnets and heavy minerals from the Late Paleozoic glacial deposits of southeastern Brazil
Authors: Gravenor C. P.
Published: April 2011

Heavy mineral suites from Late Paleozoic tillites from the southeastern part of the Paraná Basin are dominated by garnet. An analysis of the heavy minerals and chattermark trails found on the garnets suggests that the glacial sediments were transported over long distances, probably as a result of having been recycled many times.The heavy mineral suites are more complex than those found in the intensively glaciated regions of Australia and South Africa. This observation combined with an analysis of the chattermark trails on garnets suggests that glaciation was not as intense nor did it last as long as the glaciation over southern Africa, Antarctica, and Australia. The glaciers which deposited the tillites in the eastern side of the Paraná Basin were probably centered in southern Africa and moved northward and westward penetrating the eastern side of the Paraná Basin.
Chemistry and origin of the Eocene Metchosin Volcanics, Vancouver Island, British Columbia
Authors: Muller J. E.
Published: April 2011

The Metchosin Volcanics of southern Vancouver Island consist of submarine pillow lavas, tuffs, and breccias, overlain by subaerial flows of mainly tholeiitic composition. They overlie basaltic dyke complexes and gabbro and are interpreted as Eocene (and older?) oceanic floor and oceanic island tholeiites. They are separated by the fundamental Leech River Fault from the Paleozoic and Mesozoic rocks underlying Vancouver Island. Major and trace element chemical analyses of the volcanics and a few related intrusive rocks are compared with those of recent to late Tertiary tholeiites from known oceanic settings and with the coeval Crescent Volcanics of the Olympic Peninsula. Possible settings are: (1) oceanic ridge (e.g., mid-Atlantic, Juan de Fuca); (2) oceanic ridge-island (e.g., Iceland); (3) oceanic intra-plate island (e.g., Hawaii); and (4) oceanic island arc (e.g., Tonga–Kermadec). Alkali–silica and AFM diagrams clearly define the subalkaline and tholeiitic character but do not allow distinction of these four oceanic settings. Major element factor analysis yields doubtful results but could perhaps be improved by increased data base. Several orthogonal plots of abundances of Ti, Fe, Mg, Zr, and Cr seem to permit distinction of the four types of tholeiites.On geological and chemical bases Metchosin and Crescent formations correspond most closely to the Icelandic ridge-island setting; the Hawaiian intra-plate island setting is less probable in view of several chemical distinctions. The ocean floor setting, though chemically similar in several plots, is precluded at least for the upper, nonmarine parts of the formations. Lastly, an island arc setting is not indicated by either general lithology or chemistry.
Spatial variability of foraminifera and pollen in two nearshore sediment sites, St. Georges Bay, Nova Scotia
Authors: Schafer C. T. , Mudie P. J.
Published: April 2011

Spatial variability of sediment texture, foraminiferal, and pollen assemblages were studied at two core sites in St. Georges Bay, using data from replicate cores spaced about 1 m apart. Despite the similarity of water depth (22 m) and location (3.6 km offshore) of the two sites, correlatable sediment textural units could not be clearly distinguished except for the ubiquitous presence of a surface layer of fine-grained sediment. Textural parameters strongly indicate distinctive Holocene depositional histories at each site, which appear to be related to local submarine morphological features.Despite the between-site textural heterogeneity, the depositional histories of all the cores can be correlated spatially and temporally by means of selected paleontologic parameters. In all cores the top 20–30 cm of sediment was found to coincide with the historical weed pollen assemblage zone; hence, the uppermost fine sediment layer most probably reflects an increased influx of fine-grained sediment associated with deforestation and other local land use practices. At both sites, the ratio of common modern calcareous to arenaceous foraminifera species can be used to reveal comparable relative sea level records in each of the cores. However, critical evaluation of combined lithological and faunal data is necessary to distinguish an apparent decrease in water depth that can arise from an increased influx of nearshore sediment and species rather than a real change in relative sea level.Detailed statistical analysis of the variation in foraminiferal abundance parameters shows that absolute abundance data cannot be used for determining relative sedimentation rates in nearshore environments and suggests that biofacies correlations in these environments should be based on assemblages of comparatively abundant species. Within-site similarity in both foraminiferal and palynological assemblages is generally lower for the texturally more heterogeneous site at Linwood than at the more uniformly muddy site near Pomquet. However, relatively high within and between-site correlations of pollen taxa are evident throughout all sediment intervals that comprise more than 50% mud, regardless of differences in sediment sorting parameters and changes in paleodepths at the depositional sites.It appears that studies of the depositional histories of nearshore Holocene sediments in the Atlantic coastal region are most likely to yield results when analysis of combined textural, microfaunal, and palynological parameters is carried out on cores obtained from relatively low-energy depositional sites. It is predicted that for upper Holocene marine sediments, the coarser the texture of a core the less representative it will be of the overall paleoecological history of a region.
A microfauna associated with Early Cambrian trilobites of the Callavia Zone, norther Antigonish Highlands, Nova Scotia
Authors: Landing Ed , Nowlan Godfrey S. , Fletcher Terence P.
Published: April 2011

Trilobites of the Callavia Zone s.1. occurring together with phosphatic fossils in the Little Hollow Formation are the first known Early Cambrian faunas from mainland Nova Scotia. The tectono-stratigraphic affinity of the northern Antigonish Highlands with less intensely deformed portions of the Avalonian Platform is indicated by: (1) the Avalonian character of the trilobites and Early Ordovician brachiopods, (2) the nature of the lithologic sequence of the Iron Brook Group, and (3) local evidence for a Hadrynian orogeny.Rhombocorniculum cancellatum (Cobbold) is here informally designated a "pseudoconodont" based on its unique histology and is regarded as a conodontophorid-like organism. Eccentrotheca kanesia n. gen., n. sp. is a multiplated organism with apparent affinities to groups regarded as mitrosagophorans. Sunnaginia imbricata Missarzhevsky and possibly Turcutheca are demonstrated to occur in strata younger than Tommotian (lowest Lower Cambrian).
Revised stratigraphic nomenclature for Aphebian and other rock units, southern Labrador Trough, Grenville Province
Authors: Rivers T.
Published: April 2011

Stratigraphically equivalent Aphebian strata occurring in both the Churchill and Grenville Provinces have different group and formational names. The stratigraphy was first defined within the Churchill Province, and it is proposed that use of these names be extended to cover equivalent units within the Grenville Province. The nomenclature of the Knob Lake Group will thus replace that of the Gagnon Group. Two other changes in terminology are proposed in accordance with a recent amendment to the Code of Stratigraphic Nomenclature. Shabogamo Gabbro is renamed Shabogamo Intrusive Suite, and the name Ashuanipi Metamorphic Complex is proposed instead of Ashuanipi Complex.