bluuebunny/crossref_metadata_2025 huggingface dataset:
An assessment of the St-Urbain and other Grenville paleopoles
Authors: Roy Jean L. , Robertson P. Blyth
Published: April 2011

The significance of Grenville poles and the validity of some of the models that have been postulated to explain their apparent incompatibility with the North American apparent polar path are examined. Different models are briefly reviewed in terms of the Grenville St-Urbain pole (StU) which simply falls in its expected location on the most probable North American path. The StU pole derived from a hematite remanence is associated more closely with magnetite poles than hematite poles and this poses serious objections to some of the models reviewed. A few problems inherent to the study of multicomponent remanences are discussed: the recognition of all components, the sequence of remanence acquisition of the components, the absolute age and origin of each component, and most importantly the clear separation of the components. As they can be isolated by thermal treatment. hematite remanences are usually more accurate indicators of the magnetizing field than magnetite remanences which may be biased by an underlying hematite remanence. Furthermore, magnetite remanences obtained from limited experimental work may not be the initial remanences. Of much interest in the discussion of some models is the resolution that can be expected from paleomagnetic data, and which is not expressed statistically. The relatively simple (single remanence) St-Urbain results are inspected in some detail and used to demonstrate the inaccuracies in pole determination that may evolve from dual polarity remanences. They also raise questions about the validity of closely spaced sequential poles. The St-Urbain and other recent results from Interior Laurentia show that most of the Grenville poles can be explained without necessitating any special modelling. At the present, only the most southerly Grenville poles cannot be accounted for and it is suggested they may belong to a segment of a yet incomplete North American apparent polar path.
Geochemical discrimination between ocean-floor and island-arc tholeiites—application to some ophiolites
Authors: Beccaluva L. , Ohnenstetter D. , Ohnenstetter M.
Published: April 2011

Two discriminative diagrams are proposed to separate island-arc tholeiites (1AT) and ocean-floor tholeiites (OFT). The first diagram, Ti/Cr vs. Ni, has been drawn using 84 island-arc (IAT) and 178 ocean-floor (OFT) samples with silica contents between 40 and 56%. About 97% of OFT and 93% of IAT samples fall, respectively, on opposite sides of the empirical boundary. In the second diagram, where the Ba/Y is less than 4.4 for the OFT and more than 3.9 for the IAT, the overlap between the two groups is about 6%.Owing to alteration effects, only the discrimination diagram Ti/Cr vs. Ni has been applied to ophiolitic basalts from the Mediterranean belts, Newfoundland, Central and North America, and Mongolia. The effusive and hypabyssal formations plotting either in one group or in the other lead to the suggestion that they have been formed in several possible geotectonical environments. It appears that ophiolites generated in a mid-oceanic ridge are scarce in opposition to those formed in an island-arc setting. In this latter case, ophiolite associations may correspond to the juxtaposition of either island-arc – marginal basin or island-arc – offshore oceanic crust formations.
A mixed Atlantic–Pacific province Middle Ordovician graptolite fauna in western Newfoundland
Authors: Finney Stanley C. , Skevington David
Published: April 2011

A recently excavated quarry in the middle Table Head Formation (Middle Ordovician) on the Port-au-Port Peninsula, western Newfoundland, has provided a rich and varied fauna of graptolites associated with trilobites, inarticulate brachiopods, and crustacean remains. The graptolite fauna includes Atlantic province species in an otherwise characteristically Pacific assemblage, thereby enabling the correlation of provincially distinct zonal classifications.
A regional paleomagnetic study of Archean rocks from the Superior Geotraverse area, northwestern Ontario
Authors: Dunlop David J.
Published: April 2011

Preliminary paleomagnetic data are reported for Archean metavolcanics, felsic and mafic intrusives, gneisses, and iron formations from the Quetico, Shebandowan, and Wabigoon belts in the western Superior Structural Province. Eleven of the 23 formations sampled have been studied in detail using stepwise alternating-field demagnetization and, in some cases, thermal demagnetization. Two characteristic components of magnetization are revealed. One is widespread in occurrence and reasonably well grouped (D = 4.5°, I = + 55.7°, k = 17.9, α95 = 5.4°, N = 40 samples for the Shelley Lake granite for example). It is a regional magnetic overprint due to the Kenoran orogeny, acquired, according to the position of its paleopole (71.7°E, 77.3°N, δp = 5.5°, δm = 8 °for the Shelley Lake granite) on the Laurentian apparent polar wander path and to independent radiometric evidence, about −2600 Ma. The second magnetic component is spotty in occurrence, more prevalent in the Wabigoon belt than elsewhere, and everywhere rather scattered. The only fully reliable determination is D = 66.0°, I = −5.1 °(k = 10.2, α95 = 15°, N = 11 samples) for the Wabigoon gabbro. The corresponding paleopole is either 17.8°E, 13.1°N (δp = 7.5°, δm = 15°) falling at about −2800 Ma on the apparent polar wander path or the antipole of this direction, dating between −1350 and −1250 Ma. The younger date, implying a late ProterQzoic metamorphic event in the region, is more likely than the older age, which would require that the magnetization be primary or a pre-Kenoran overprint. The metamorphism seems to have occurred too early to have been caused by igneous activity ca. 1100 Ma in the nearby Keweenawan basin. About −2600 Ma, the region was in its present orientation, but at a latitude of 20 to 35°N and probably drifting northward. About −1250 Ma, the region was equatorial but rotated 90°, so that presently east–west trending greenstone belts were north–south. It is possible, but un-proven, that a paleoocean existed between the Wabigoon subprovince and the other belts about −1250 Ma, the Wabigoon region having since moved > 500 km westward (present-day direction) to its present location.
Heat flow measurements under some lakes in the Superior Province of the Canadian Shield
Authors: Allis R. G. , Garland G. D.
Published: April 2011

Six heat flow values have been obtained from measurements made in the sediments of thermally-stable lakes in four major structural belts of northwestern Ontario. Each heat flow is the average of measurements from 3–6 neighbouring lakes. Corrections for the thermal history, lateral heat flow, sedimentation, and refraction effects have been applied. High heat flows which were measured in the Quetico gneiss superbelt (77 mW/m2) and on the Indian Lake intrusion in the Wabigoon superbelt (64 mW/m2) are related to above-average heat productivities at these locations, but the extent in depth of the sources is shown to be very different in the two cases. The consistency of the lake results with borehole measurements, on a heat flow – heat productivity plot, strongly suggests that the former are not perturbed by recent climatic variations.
Electrical properties of Athabasca Oil Sands
Authors: Chute F. S. , Vermeulen F. E. , Cervenan M. R. , McVea F. J.
Published: April 2011

The results of a series of laboratory measurements of the electrical properties of samples of oil sand from the Athabasca deposit in northeastern Alberta are reported. The electrical conductivity and relative dielectric constant of the samples have been determined over a frequency range extending from 50–109 Hz. The measurements were performed on samples with a wide range of moisture content and over a temperature range from about 3–150 °C. A discussion of the methods and apparatus used is included.Sufficient data have been collected to permit correlation of the electrical properties of oil sand with density, moisture content, and temperature, and hence to indicate how the laboratory results can be extended to estimate in situ conductivities and dielectric constants. The results of these correlations, which are presented in graphical form, are of fundamental importance in any realistic assessment of the viability of electromagnetically heating large in situ deposits of oil sand.
Troublesome definition of the Lower/Middle Jurassic boundary
Authors: Westermann G. E. G.
Published: April 2011

Recent North American usage of the series boundary is divided: (1) following English tradition it is placed between the Toarcian and the Bajocian s.l. stages; (2) following central European tradition it is placed at the same position, but with the distinction of the Aalenian stage = Lower Bajocian s.l.; (3) following the resolution of the 1st Luxembourg Colloquium it is placed at the Aalenian/Bajocian s.str. boundary. Subsequent resolutions of the Cassis Meeting and, equivocally, of the 2nd Luxembourg Colloquium, however, rescinded the third usage because it conflicts with the original series definition and with the Lias/Dogger boundary; they also supported the Aalenian stage. Although no decision has as yet been taken by an internationally recognized body, the second alternative is strongly recommended in the meantime.
Paléomagnétisme et datation du volcanisme permien, triasique et crétacé du Maroc
Authors: Westphal M. , Montigny R. , Thuizat R. , Bardon C. , Bossert A. , Hamzeh R. , Rolley J. P.
Published: April 2011

Paleomagnetism and K–Ar dating of Permian, Triassic, and Cretaceous rocks from Morocco. We have sampled and studied volcanic rocks from the whole of Morocco. Permo-Carboniferous rocks give a magnetic pole situated at 36°N and 238°E (four sites, K = 23, A95 = 20°). Triassic dolerites dated on plagioclases from 205–180 Ma have a mean pole at 72°N, 218°E (34 sites, K = 17, A95 = 6°). Middle Jurassic and Lower Cretaceous basalts and dolentes from l'Atlas de Beni Mellal (ages from 170–120 Ma) have a pole at 45°N and 251°E (13 sites, K = 26, A95 = 8°).The results may be interpreted by clockwise rotation within Morocco. We compare them also with those from other continents.
Cleavage in Triassic rocks of southern New Brunswick, Canada
Authors: Stringer Peter , Lajtai Emery Z.
Published: April 2011

Cleavage is sporadically developed in Late Triassic redbeds of the Lepreau Formation in folds and in areas of uniform northwestward dip in the lower Lepreau River – Lepreau Harbour half-graben. The cleavage in shaly siltstone beds is a composite incipient fabric defined by patchily developed crenulated bedding laminae, pressure solution planes, and mineral orientation parallel to the cleavage direction; cleavage in sandstone beds is defined by alignment of submicroscopic cracks inferred from laboratory tests. The cleavage fabrics are subvertical trending northeast–southwest, and resulted from horizontal northwest–southeast compression. Closely spaced fractures subparallel to the cleavage fabric in both shaly siltstones and sandstones are interpreted as later structures formed during relaxation of tectonic stresses. The cleavage fabrics and fractures are also present in intraformational clasts of shaly siltstone and rare sandstone clasts within conglomerate beds. A distinct shape orientation of the shaly siltstone clasts parallel to their cleavage within relatively undeformed conglomerate is attributed to compression during folding of unconsolidated conglomerate beds. The mean cleavage orientation varies from coplanar to noncoplanar with fold axial surfaces. The folds and cleavage formed during lateral compression probably related to wrench faulting which postdates the formation of the Triassic grabens.
Atrypoidea zonation of the Upper Silurian Read Bay Formation of Somerset and Cornwallis Islands, Arctic Canada
Authors: Jones Brian
Published: April 2011

Species of the brachiopod genus Atrypoidea have a distinct distribution in carbonate rocks of the late Silurian Read Bay Formation of Arctic Canada. Atrypoidea phoca occurs in the basal part of the formation and this species is succeeded by Atrypoidea foxi forma B at higher levels. The ranges of the two species overlap, defining a third useful zone. Locally, as in the Pressure Point area of northwestern Somerset Island, Atrypoidea foxi forma B is succeeded by Atrypoidea foxi forma A. Atrypoidea foxi forma A is generally restricted to carbonates with a low content of detrital material and has a significantly larger shell than Atrypoidea foxi forma B. A higher zone is defined by Atrypoidea erebus which occurs in the basal part of the Somerset Island Formation on Somerset Island and in the basal part of member C of the Read Bay Formation at Goodsir Creek on Cornwallis Island. At the latter locality, Atrypoidea foxi forma A is found with Atrypoidea erebus, thereby demonstrating their overlapping ranges.The overlapping ranges of Atrypoidea phoca and Atrypoidea foxi forma B occur in the middle to late Ludlovian ploeckensis–siluricus conodont zones. On Somerset Island, Atrypoidea foxi forma B and Atrypoidea foxi forma A range through the ploeckensis–siluricus conodont zone. Atrypoidea erebus occurs in late Ludlovian and (or) early Pridolian strata.
Biostratigraphy and paleoecology of Upper Cretaceous (Campanian and Maestrichtian) foraminifera from the Upper Lambert, Northumberland, and Spray Formations, Gulf Islands, British Columbia, Canada
Authors: McGugan Alan
Published: April 2011

The Maestrichtian Bolivina incrassata fauna (upper part of Upper Lambert Formation) of Hornby Island (northern Comox Basin) is now recognized in the southern Nanaimo Basin on Gabriola and Galiano Islands. The Maestrichtian planktonic index species Globotruncana contusa occurs in the Upper Northumberlahd Formation of Mayne Island and Globotruncana calcarata (uppermost Campanian) occurs| in the Upper Northumberland Formation of Mayne Island and also in the Upper Lambert Formation at Manning Point on the north shore of Hornby Island (Comox Basin).Very abundant benthonic and planktonic foraminiferal assemblages from the Upper Campanian Lower Northumberland Formation of Mayne Island enable paleoecological interpretations to be made using the Fisher diversity index, triangular plots of Texturlariina/Rotaliina/Miliolina, calcareous/agglutinated ratios, planktonic/benthonic ratios, generic models, and associated microfossils and megafossils. Combined with local geology and stratigraphy a relatively shallow neritic depositional environment is proposed for the Northumberland Formation in agreement with Scott but not Sliter who proposed an Outer shelf/slope environment with depths of 300 m or more.
The 2.5 Ga Duxbury massif, Quebec : a remobilized piece of pre-3.0 Ga sialic basement(?)
Authors: Verpaelst P. , Brooks C. , Franconi A.
Published: April 2011

The Duxbury massif, Eastmain District, Quebec, is a complex tonalitic intrusion that is internally divisible into a homogeneous border zone of granodiorite (Rb–Sr total-rock isochron age = 2500 ± 85 Ma; initial 87Sr/86Sr = 0.7023 ± 0.0003) and a heterogeneous core zone of tonalite (Rb–Sr total-rock errorchron age = 3060 ± 180 Ma; initial 87Sr/86Sr = 0.7014 ± 0.0003). The geologic, petrographic, and isotopic data are consistent with a model of remobilization of 3.1 Ga sialic basement during the Kenoran orogeny at 2.5 Ga. Evidence suggests that the source material was of tonalitic composition, that it was never more deeply buried than 15–20 km, and that it was remobilized in a plastic to brittle subsolidus state. Slab-sample studies of the tonalite indicate the 3.1 Ga age is a metamorphic one, and that the source material had a pre-history at that time. Sr-isotope constraints imply source region formation as juvenile material from the mantle at between 3.5 and 3.6 Ga. The Duxbury massif, hence, records a history of crustal development spanning at least 600 Ma and possibly more than 1 Ga. These results may be applicable on a larger scale to many of the regional tonalite massives found in the Superior Province of Canada and elsewhere.
Dynamics of a fluid core with inward growing boundaries
Authors: Schloessin H. H. , Jacobs J. A.
Published: April 2011

In both physical and mathematical models of the Earth's core it has been difficult, so far, to discuss all the terms in the magneto-hydrodynamic energy equation under one unifying theory and to relate all the physical mechanisms involved in a specific model. The reason for this is mainly the uncertainty about the energy sources, or, when they could be accounted for, with uncertainty about their location. In the following article we deduce and examine a model of the Earth's core which can be regarded as a sequel to theories of the formation of a fluid core in the course of the Earth's thermal evolution.General cooling and pressure-freezing cause the formation of solid phases at the boundaries of the fluid core, leading to a solid inner core (IC) and a lower mantle shell (Bullen's D″ layer) from slow overgrowth at the mantle–core (MC) boundary. For simplicity, the core fluid is assumed to consist of two major phases, one conducive to solid metallic core formation, and the other to crystallization of a lower mantle phase from "solution" in a metal "solvent." The presence of a third, minor constituent, by selective partitioning between phases, acts as a solid phase growth regulator.On the basis of this model the energy available for fluid core motion and thereby for maintenance of the magnetic field, is related directly to the time rate of change of the growth of the solid phases at the IC and MC boundaries. Most of the available energy is gravitational and is associated with density and concentration currents which offset density inhomogeneities caused by selective acceptance and rejection of the fluid core constituents by the two solid phases.A very conservative estimate of the net gain per second in gravitational potential energy resulting from the mass redistribution via density currents and solid phase formation is 2.6 × 1013 W which may become available in different forms. The fraction which is converted into kinetic energy associated with differential circulatory motion around the rotation axis amounts to 3.4 × 1011 W, based on radial interchange with respect to the Earth's centre. The heat liberated as a result of IC solidification is 2.7 × 1011 W, assuming that the metallic phase is mainly iron. Since our ideas of other constituents of the core fluid are less definite we can draw only very general conclusions about the MC boundary. If silicates and oxides are likely candidates, it is possible that in the crystallization of the mantle phase from the core fluid, heat is being absorbed, thus creating a heat sink at the MC boundary. An estimate of the net strain energy associated with compression of IC material by about 1.4% and expansion of MC material by, on the average, 0.4% gives 1.5 × 1011 W.Magnetic polarity reversals might be explained as due to epochs during which the solid phase growth rate which dominates the fluid motion shifts from the IC to the MC boundary and vice versa. Intensity changes might be due to significant variations in the ratio of the radial and horizontal velocity components of the fluid motion.
Oxygen isotope evidence for the genesis of Upper Paleozoic granitoids from southwestern Nova Scotia
Authors: Longstaffe F. J. , Smith T. E. , Muehlenbachs K.
Published: April 2011

The oxygen isotope ratios for 127 rocks and coexisting minerals from Paleozoic granitoids and clastic metasedimentary rocks of southwestern Nova Scotia have been measured. The whole-rock δ18O values for samples of the South Mountain batholith range from 10.1–12.0‰.But discrete granitoid plutons, located to the south of the South Mountain batholith, have lower δ18O values (7.8–10.4‰). Coexisting minerals from the Nova Scotia granitoids are near isotopic equilibrium, indicating that the whole-rock δ18O values primarily reflect the δ18O of the magma, rather than secondary alteration processes. The Meguma Group clastic metasedimentary rocks that host the Nova Scotia granitoids range in δ18O from 10.1–12.9‰. These clastic metasedimentary rocks show no systematic geographic variation in δ18O. The greenschist facies Meguma Group rocks that host the South Mountain batholith have similar δ18O values to the amphibolite facies equivalents located about the southern discrete plutons. Large scale isotopic exchange between the Meguma Group and the South Mountain batholith, or the southern plutons, is not evident.The relatively high δ18O values of the peraluminous South Mountain batholith (10.1–12.0‰) indicate that it formed by anatexis of 18O-rich clastic metasedimentary rocks. The southern plutons were also derived by partial melting of clastic metasedimentary rocks, but their lower δ18O values reflect exchange of the source material with a low 18O reservoir (mafic magmas?) prior to, or during anatexis.The sheared Brenton pluton is much lower in δ18O (5.0‰) than any of the other rocks, probably because of exchange with low 18O fluids during shearing.
Deep Drill 1972: a paleomagnetic study of the Bermuda Seamount
Authors: Rice Philip D. , Hall James M. , Opdyke Niel D.
Published: April 2011

The rock and paleomagnetic character of an 802 m core drilled on the Bermuda Seamount is described. Intrusion of highly evolved, limburgitic Tertiary sheets, which comprise 40% of the core, into older tholeiitic submarine lavas has produced extensive stable additional magnetization in the flows. Original and later components of the supposed polyphase magnetization of the flows have not yet been separated by the alternating field or thermal methods of remanence analyses. It is thought that both remanence components are held in nearly pure magnetite with similar grain size distributions.Development of additional magnetization in the high temperature hydrothermal conditions experienced by the flows is volumetrically much more extensive than baked thermal remagnetization, and could, in appropriate circumstances, provide a uniformly magnetized, lower layer 2 source for the linear magnetic anomaly patterns of the ocean basins.
Conodonts from the Davidsville Group, northeastern Newfoundland
Authors: Stouge Svend
Published: April 2011

Conodonts from the basal part of the Davidsville Group, Botwood Zone of Newfoundland, are assigned a late Llanvirn to early Llandeilo age. Other fossil groups suggest a time range of Llanvirn to early Caradoc, and the conodonts are in accordance with the previous datings. The conodont fauna is contemporaneous with that of Cobbs Arm Limestone, central Newfoundland, and no major difference between the two faunas exists.
Borings in solitary rugose corals of the Selkirk Member, Red River Formation (late Middle or Upper Ordovician), southern Manitoba
Authors: Elias Robert J.
Published: April 2011

Borings occur in solitary rugose corals from the Selkirk Member of the late Middle or Upper Ordovician Red River Formation in southern Manitoba. They are assigned to Dictyoporus garsonensis n. ichnosp., which was produced by algae, and Trypanites weisei Mägdefrau 1932, made by spionid polychaete annelids. Most, and possibly all, boring occurred while the host corals were alive and in life position. The location and relative abundance of borings support interpretations that unattached curved solitary corals lay with the convex cardinal side in the sediment and the concave counter side facing upward during life, whereas straight conical forms were oriented upright in the sediment. These ichnospecies suggest that host corals lived in very shallow marine environments.
Shallow core snow chemistry of Athabasca Glacier, Alberta
Authors: Butler Danna , Lyons W. Berry , Hassinger Jon , Mayewski Paul A.
Published: April 2011

Examination of concentrations of several chemical species in a 7.37 m deep pit excavated close to the 1978 summer equilibrium line altitude (ELA) of Athabasca Glacier (2694 m) suggests that: (1) aerosol forms of NO3−, PO43−, and reactive SiO2 entered this area in diluted concentrations compared to values for Edmonton, Alberta, the closest heavily populated area; (2) Fe values were similar to those in Edmonton; and (3) the glacier's yearly net mass balance for the sample area was 1.5 and 2.4–2.7 m H2O equivalent for the 1976–1977 and 1977–1978 mass balance years.
Fold fabrics and emplacement of an Archean granitoid pluton, Cleft Lake, Northwest Territories
Authors: Fyson W. K.
Published: April 2011

The axial-plane foliation of early-phase folds in metagreywacke is commonly obliterated by a secondary, regional, crenulation cleavage or schistosity and quartz segregation layering. Nevertheless, remnants are preserved as quartz inclusion trails in biotite porphyroblasts. The trails deviate little in strike for over 20 km across traces of the early folds curving around a granodiorite pluton. Evidently the trails reflect trends existing before emplacement of the pluton. Later regional compression across the secondary cleavage apparently deflected folds around the pluton and thus displaced the porphyroblasts. These, however, were "locked" in orientation by the cleavage forming by a process of quartz diffusion.In a 10 km2 area near the pluton, the secondary cleavage is less pronounced and dips at shallower angles than elsewhere. This suggests a modification to the regional strain such as expected above a satellite pluton rising during formation of the cleavage.
Thermoluminescence dating of ocean sediments
Authors: Wintle A. G. , Huntley D. J.
Published: April 2011

We describe data on the thermoluminescence (TL) of ocean sediments which leads us to propose that exposure to sunlight prior to deposition reduces any previously acquired TL to a small "residual" value. Subsequent radiation from radionuclides in the sediment increases the TL and this increase is used for dating. Three methods of separating these two TL components are described. In the preferred one the reduction in TL (R) caused by a standard sunlamp exposure is measured as a function of an administered gamma dose; extrapolation to R = 0 yields the natural dose.An equation relating this dose to the age and to dose rates derived from radioactivity analyses is presented. The details are given for six samples from each of two cores and their TL ages calculated; these range from 9–140 ka. For one core independent dates from Cycladophora davisiana variations and an 18O/16O stratigraphic marker were available for comparison; the agreement is satisfactory. The TL age uncertainty is primarily set by the uncertainty in the water content.
Cooperative seismic surveys across the Superior–Churchill boundary zone in southern Canada
Authors: Green A. G. , Stephenson O. G. , Mann G. D. , Kanasewich E. R. , Cumming G. L. , Hajnal Z. , Mair J. A. , West G. F.
Published: April 2011

Three seismic surveying techniques have been employed in a study of the Superior–Churchill boundary zone in southwestern Manitoba and southeastern Saskatchewan. Two reversed refraction – wide angle reflection profiles, one north–south within the Superior tectonic province and one east–west traversing part of the Superior tectonic province, the boundary zone, and part of the Churchill tectonic province, were used to obtain information on the gross velocity structure of the crust over a large region. Preliminary results from these surveys suggest that the crust beneath the north–south profile is typical of previously published crustal models of the western Superior Province, while the crust beneath the east–west profile is similar to that reported for the Churchill Province in eastern Alberta and western Saskatchewan. Generally, the upper and middle crustal sections in the two tectonic provinces are quite similar, while the lower crust in the Churchill Province has a distinct ~7 km/s layer that is not observed in this part of the Superior Province. In addition, there is a marked thickening of the crust within the boundary zone from ~41 km in the Superior Province to ~46 km in the Churchill Province.A 72 km length of fourfold common reflection point coverage was collected in order to determine the fine structure of the crust over a relatively small region. Reliable stacking velocities that may be used for future processing of the common reflection point data were obtained from an expanding spread reflection survey. Various data processing techniques, including common reflection point stacking, linear and nonlinear velocity filtering, and velocity spectral analysis, have been successful in enhancing reflections from the middle and lower parts of the crust. From the preliminary results of the two reflection surveys, it may be concluded that those parts of the crust which are shown as relatively simple layers in the refraction derived models, may be quite complex when viewed on a smaller scale.
Stratigraphy and depositional setting of the Sibley Group, Thunder Bay district, Ontario, Canada
Authors: Franklin J. M. , McIlwaine W. H. , Poulsen K. H. , Wanless R. K.
Published: April 2011

The Sibley Group is a Neohelikian (1339 ± 33 Ma, RbSr, 87Rb = 1.42 × 10−11 year−1) red bed sequence located in an elongate basin extending northward for 150 km from Nipigon, Ontario. The lowest unit, the Pass Lake Formation (new name), is 50 m thick and consists of quartz arenite, deposited primarily in a shallow, quiet lacustrine environment. It is overlain by the Rossport Formation (new name), a unit of 135 m thickness consisting of a lower arenaceous red dolomite member, central chert–carbonate and stromatolite member, and an upper argillaceous red dolomite member. The Rossport Formation was deposited in a shallow, highly saline environment, in a basin of fluctuating size. The Kama Hill Formation (new name) is 50 m thick, and consists of purple shale composed of smectite, authigenic microcline, and quartz. It was deposited in a periodically dry mud flat, and is characterized by desiccation cracks, evaporite casts, and mud-chip microbreccias.Both the Rossport and Kama Hill Formations have an increased arenite content near the basin margins. Breccias cut the Rossport Formation and consist of stoped blocks of Rossport and Kama Hill rocks; these breccias are cut by sandstone dykes. The Sibley Group is situated in, and was possibly deposited in, a "failed arm" which radiates from a paleo-plume in the Keweenawan rift valley.
Structural and stratigraphic setting of the Downie slide, Columbia River valley, British Columbia
Authors: Brown Richard L. , Psutka John F.
Published: April 2011

The Downie slide is a late to postglacial rockslide situated on the western slope of the Columbia River valley about 70 km north of Revelstoke, British Columbia. It attains a maximum thickness of 270 m and is estimated to involve 1.5 × 109 m3 of rock and debris. The head of the slide is bounded by a nearly vertical escarpment reaching heights of more than 125 m; its lateral boundaries are defined by a prominent east–west trending scarp on the south and a more subdued linear northeast trending ridge on the north. The toe forms the west bank of the Columbia River in this area.The slide occurs within a compositionally anisotropic formation of high-grade pelitic and semipelitic schists and psammites. The main shear zone at the base of the slide is located in pelitic schists. Minerals in the rock of the shear zone have been mechanically crushed and locally reduced to a fine-grained gouge.Three distinct phases of deformation are recognized in the Downie slide region. The location and attitude of the second and third fold phases and their associated fabrics controlled the external geometry of the slide.Along the western slopes of this part of the Columbia River valley the second phase of deformation has been dominant. Within the formation that contains the slide, bedding is extensively deformed by tight to isoclinal second phase minor folds that exhibit a penetrative axial plane foliation. At Downie slide this foliation dips approximately 20° eastward towards the Columbia River, and nearly parallels the slope of the hillside; the basal shear zone of the slide developed parallel to the axial plane foliation.West of the slide, third phase major and minor folds have been superimposed on the second phase geometry, but they die out eastward, and are of only minor significance within the main body of the slide. The eastern limit of major superposition coincides with the head scarp of the slide. The slide mass broke away along the hinge zone of the first major monoclinal flexure fold associated with this front of phase 3 folding.Late fracturing probably influenced the position of the northern and southern lateral boundaries of the slide.
Geology and origin of the Brandon Hills, southwest Manitoba
Authors: Welsted J. , Young H. R.
Published: April 2011

The Brandon Hills, formed during the deglaciation of southwestern Manitoba in Late Wisconsinan time, are usually mapped as end moraine, although glaciofluvial deposits are common and are responsible for some distinctive landforms. In the central and western part of the study area a series of subparallel ridges, composed of glaciofluvial deposits overlain by up to 5 m of till, are believed to have originated when sediments were deposited in a series of tunnels within or beneath the ice. Near the eastern end of the hills, a prominent ridge, 4 km long and up to 60 m high, exhibits many of the attributes of an esker. A smaller ridge on the south side of the hills is also esker-like in form.The pebble lithology of the till and of the glaciofluvial deposits is similar and is dominated by material derived from the Precambrian Shield and the Paleozoic outcrop belt to the northeast rather than from local shale bedrock. Dolomite in the till exhibits bimodal frequency distribution with the terminal grade < 0.062 mm.
Gravity model of the Aulneau batholith, northwestern Ontario
Authors: Brisbin W. C. , Green A. G.
Published: April 2011

A gravity survey over the Aulneau batholith, northwestern Ontario, shows that the batholith is expressed as a gravity low of approximately 40 mGal relative to the level of the gravity field over neighbouring greenstone rocks. Assuming that surface density contrasts extend to depth, then three-dimensional modelling of the gravity data indicates that the floor of the batholith, in general, is located between depths of 4.5–7 km. Locally, in two regions, prominent plugs extend to 11–12 km depth. The modelling also suggests that the wall contacts of the batholith are generally steep and inward dipping, a picture supported by earlier seismic studies.
Palynology of the Windsor Group (Mississippian) in a borehole at Stewiacke, Shubenacadie Basin, Nova Scotia
Authors: Utting J.
Published: April 2011

A palynological investigation of core samples from borehole SB-1 at Stewiacke, Nova Scotia, suggests that three miospore zones may be recognized. In terms of Bell's macrofaunal zonation, assemblage-zone I occurs in Lower Windsor subzones A and B, assemblage-zone II occurs in Upper Windsor subzones C, D, and E, and assemblage-zone III occurs in argillaceous beds containing intercalations of gypsum, which overlie the uppermost marine carbonate of the Upper Windsor subzone E. Slight differences distinguish miospore assemblages in macrofaunal subzones A and B, but the differences may be partly, or wholly, the result of reworking from the Horton Group. Preservation is very poor in the lower part of subzone A. Consequently, assemblages from these beds have been assigned only tentatively to assemblage-zone I(?).Tentative biostratigraphic correlation of the proposed miospore zones with the British Viséan suggests that assemblage-zone I is no older, and may be younger, than the upper part of the Upper Caninia (C2S1) Zone; assemblage-zone II possibly is similar in age to the Lower Dibunophyllum (D1) Zone; and assemblage-zone III is probably no older than the Upper Dibunophyllum (D2) Zone, although it may be younger. However, there is no palynological evidence to indicate that it is younger than the Upper Posidonia (P2) Zone of late Viséan age.The nature and thermal alteration of the organic matter suggest a source-rock potential for liquid hydrocarbons, but this potential is reduced by the abundance of halite, gypsum and (or) anhydrite in the succession.
Displacement of Vancouver Island: paleomagnetic evidence from the Karmutsen Formation
Authors: Yole R. W. , Irving E.
Published: April 2011

New paleomagnetic results from the Karmutsen Formation (Late Triassic) of Vancouver Island confirm the presence of two families of magnetizations (X and Y), both of which are inconsistent with known Mesozoic and Cenozoic geomagnetic fields of cratonic North America. The X magnetizations have coherent directions with the exception of a subset of five sites (the B subset). We argue that the deviation of the B subset is caused either by a 31 ± 13 °anticlockwise rotation of a small block relative to the main sampling areas or by a short-term excursion of the field. The X magnetization has an overall mean direction 008°, −33 °α95 = 6 °based on results from 147 oriented samples (usually 2 specimens from each) collected at 28 sites spanning about 6000 m stratigraphically. We interpret this as the original Late Triassic magnetization. The corresponding X paleopole (21°N, 44°E A95 = 6°) is strongly far-sided and right-handed with respect to the Mesozoic apparent polar wander path for cratonic North America. The paleolatitude indicated for Vancouver Island in the Late Triassic is either 18°N or 18°S, the latter being preferred on the grounds that it yields a more consistent pattern for Cordilleran magnetizations, but the ambiguity is still not settled. In either case the results show that Vancouver Island was far south of its present position relative to North America in the Late Triassic, thus confirming the previous results of Irving and Yole. The Y magnetizations, with more heterogenous properties, occur at 14 sites (66 oriented cores, usually 2 specimens each). Y magnetizations are generally softer than X and for this and other reasons we regard them as secondary and post-Triassic in age. Individual site poles for the Y magnetization are, with minor exceptions, right-handed and slightly far-sided with respect to the apparent polar wandering path for cratonic North America. The mean paleopole for Y magnetizations is situated at 70°N, 15°W A95 = 11°. Both the X and Y magnetizations are consistent with either northward motion of the westernmost Cordilleran elements accompanied by clockwise rotation, or with oblique translation from the southwest. The northward component of motion derived from X directions would be the same in both instances and amounts to 1300 or 4900 km depending on whether the northern or the southern paleolatitude option is chosen. Our preference is for the latter and we present arguments which suggest that Vancouver Island may have been originally derived from a region near to eastern Gondwana or from a block east of Gondwana that might have included Malaysia. The procedures used for the tectonic analysis of aberrant paleopoles are described in the Appendix.
Gravitationally induced stresses at structural boundaries
Authors: Goodacre A. K. , Hasegawa H. S.
Published: April 2011

Prominent gravity anomalies, consisting of paired positive-negative belts, occur in Canada at structural boundaries between geological provinces. The associated anomalous masses produce what are termed gravitationally induced stresses. These stresses may contribute to the failure of rocks along preexisting faults, or other zones of weakness. In the case of a typical structural boundary, failure at shallow depths in the crust is likely to occur in the region outlined by the negative gravity anomaly, whereas failure deeper within the crust and upper mantle may occur beneath the positive anomaly. Along the lower St. Lawrence valley, good spatial correlation is found between regions of high seismicity and those negative free-air anomaly areas which are adjacent to prominent free-air gravity highs. It is suggested that in a heavily faulted region, such as the lower St. Lawrence valley, gravitationally induced stresses may be a contributing factor to the production of earthquakes in regions which are otherwise already close to failure.
Geochemical evolution in the Blake River Group, Abitibi Greenstone Belt, Superior Province
Authors: Smith I. E. M.
Published: April 2011

In well exposed, well developed greenstone belts of the Superior Province there is a clear progression from stratigraphically lower, geochemically primitive volcanic rock types (komatiites, tholeiites) to overlying geochemically evolved calc-alkaline volcanic rock types. In the western Blake River Group of the Abitibi Greenstone Belt the change from tholeiitic to calc-alkaline volcanics represents a geochemical discontinuity defined by an increase in incompatible elements and light/heavy rare-earth element fractionation in the overlying rocks. Quantitative modelling of the parameters of the discontinuity indicates that it can be explained by a change to very small amounts of melting of unmodified mantle lherzolite, although this is not a unique solution. In calc-alkaline suites showing high degrees of rare-earth element fractionation the calculated melt fraction required of unmodified mantle becomes unrealistically low and models involving a geochemically evolved source may have to be considered.
Stromatolites and fenestral fabric in Early Proterozoic Huronian Supergroup, Ontario
Authors: Hofmann H. J. , Pearson D. A. B. , Wilson B. H.
Published: April 2011

Crustose and columnar carbonate stromatolites from the Espanola Formation at Quirke Lake, and laminated dolostone with fenestral fabric from the Gordon Lake Formation at Plummer, are considered to be products of benthic microbial activity at isolated, carbonate accumulating sites in transitional environments characterized almost exclusively by arenaceous sedimentation.
Rheological properties of the upper mantle in Canada from olivine microrheology
Authors: Ranalli G.
Published: April 2011

The rheological properties of the upper mantle for geotherms representative of shield and Cordilleran regions are studied on the basis of olivine microrheology. The equation for power-law creep, where the strain rate is dependent upon the diffusion-controlled climb of edge dislocations, is found to yield realistic values of creep strength and viscosity, when the experimentally determined parameters for dry olivine are used. For grain sizes larger than 0.01 cm, power-law creep is predominant over linear creep in the upper mantle, but the increasing importance of grain-boundary diffusion with decreasing depth makes linear creep a very likely deformation mechanism in the upper lithosphere.The differences between shield and Cordilleran geotherms are reflected in lateral variations in the rheological properties of the lithosphere and upper mantle. The lithosphere is thinner, and the upper mantle softer, in the Cordilleran region. The lateral variations in effective viscosity in the 100–200 km depth range are between one and two orders of magnitude.
Paleomagnetism of Eocene igneous intrusions in the Valley and Ridge Province, Virginia and West Virginia
Authors: Ressetar Robert , Martin David L.
Published: April 2011

Paleomagnetic measurements from 11 small dikes and plugs in the Valley and Ridge Province of Virginia and West Virginia yield a mean magnetic direction of D = 176.3°, I = −60.9 °after AF cleaning. The geomagnetic pole position calculated from this direction lies at 85.5°N, 243.7°E. The proximity of this pole to others from North American rocks of Eocene age is consistent with radiometric age determinations. This provides further evidence that North America has undergone little apparent polar wander since early Tertiary time, and that the Appalachian Eocene activity covered a wider area than previously realized.
Correlation of the members of the Jurassic Snowshoe Formation in the Izee basin of east-central Oregon
Authors: Smith Paul L.
Published: April 2011

The lithostratigraphic terminology of the type Snowshoe Formation of the John Day inlier is revised. The lower member is correlated with and renamed the Warm Springs Member. The middle and upper members are renamed the Schoolhouse and South Fork Members respectively. A local zonal scheme based on ammonites and related to the standard schemes of North America and northwest Europe is applied to the interdigitating units deposited in the Izee basin. Marked diachronism is evident so that the depositional model of the Basey and Silvies Members synchronously providing sediment to the Izee basin must be rejected. It is replaced by a sequential model whereby an early Bajocian Basey-to-Schoolhouse-to-Warm Springs Member lateral transition eastward is followed by a late Bajocian Silvies-to-Schoolhouse Member lateral transition westward. This latter event together with the deposition of the succeeding South Fork Member of Bathonian age is represented south of the South Fork of the John Day River by an unconformity and as such denotes a major event in the Jurassic history of eastern Oregon.
The ellipsoidal form of clasts with practical applications to fabric and size analyses of fluvial gravels
Authors: Koster Emlyn H. , Rust Brian R. , Gendzwill Don J.
Published: April 2011

The widespread assumption that most water-worn gravel clasts approximate ellipsoids is confirmed by a statistical analysis of available data. The analysis demonstrates a Gaussian distribution of V/Ve ratios, centred on unit ratio, where V is clast volume and Ve the volume of a symmetric ellipsoid with equivalent triaxial dimensions. For internally isotropic and unbroken clasts, ellipsoidal form evolves as the rounding due to abrasion reaches its final stages. There appears to be no other major control on the tendency towards ellipsoidal geometry. The ellipsoidal tendency assists the interpretation of fluvial gravel deposits, which depends greatly on accurate description of clast size and fabric.Firstly, it facilitates calculation of Ap, the plane area projected upstream by clasts, a key parameter in bed–flow interactions such as preferred fabric. Formulae are derived to calculate Ap for ellipsoidal clasts with any configuration relative to flow direction. Viewing fabric in terms of the Ap variable supports and explains earlier conclusions concerning the controls on variability of imbrication angle.Secondly, an investigation of the relative merits of six size measures as descriptors of areal trends and predictors of nominal diameter, dn, concludes that (abc)1/3(the formula for dn of an ellipsoid) is superior. Other measures, namely, a, b, c, (a + c)/2, and (a + b + c)/3, are all subject to error in proportion to the degree of shape variation. Also, since downstream fining is typically accompanied by a changing proportion of oblate, bladed, prolate, and equant forms, dn is subject to inconsistent levels of under- or overestimation. The commonly used b dimension is endorsed as an acceptable predictor of dn, but a severely overestimates dn and should be abandoned. Information on errors in size analysis is presented as nomograms in the form of contoured c/b versus b/a plots and as probability distributions based on the typical range of shape variation in fluvial gravel.
Cavity-dwelling biota in Middle Ordovician (Chazy) bryozoan mounds from Quebec
Authors: Kobluk David R.
Published: April 2011

Bryozoan mounds, dominated by Batostoma chazyensis from the Laval formation of the Chazy Group (early Middle Ordovician) near Montreal, Quebec contain framework cavities that house a coelobiontic (cavity-dwelling) biota. Reports of coelobionts of Ordovician age are rare, and this is the first report of Chazy Group mounds containing coelobionts.Algae, sponges, and bryozoa (Batostoma) dominate the cavity biota, and are found encrusting cavity walls and roofs. The algae are represented by mammillary encrustations (now micrite), and Solenpora sp. on the roofs. The sponges are not identified, but occur both as isolated monaxial, triaxial, and six-rayed spicules, and as body fossils within the cavities. Coccoid cells, of unknown affinities, are also found. These cavities provide the first evidence of coelobiontic biological erosion. Trypanites, a compound morphogenus, is the only macroborer and is found in cavity walls; endolithic (boring) algae are present, and indicate that as early as the Middle Ordovician bio-erosion of reef and mound interior cavities was active and that micro- and macroendoliths had invaded the cavity habitat.