bluuebunny/crossref_metadata_2025 huggingface dataset:
The Ordovician–Silurian boundary at the eastern end of Anticosti Island
Authors: Cocks L. R. M. , Copper P.
Published: April 2011

A Hirnantia fauna is recorded for the first time from Anticosti Island, situated 6 m below the beds interpreted here as representing the maximum regression at the eastern end of the island, the latter coinciding with the local top of the revised Ellis Bay Formation. The Ordovician–Silurian boundary on the island is discussed.
Columbia River fault zone: southeastern margin of the Shuswap and Monashee complexes, southern British Columbia
Authors: Read Peter B. , Brown Richard L.
Published: April 2011

The Columbia River fault zone extends for 250 km from south of Nakusp, through Revelstoke, to north of Bigmouth Creek. It is a composite fault zone, which dips 20–30° easterly and separates major tectonic elements. The structurally lowest element is the Monashee Complex, which includes the culminations of Pinnacle Peaks, Thor–Odin, and Frenchman Cap. At Hoskins Creek, the Monashee décollement splays westward from the fault zone and then runs southward along the western margin of the Monashee Complex. On the east side, the Selkirk allochthon is a composite of four tectonic slices. Its western part consists of Clachnacudainn, Goldstream, and French Creek slices forming the hanging wall of the Columbia River fault zone. The remainder of the allochthon forms the highest and largest Illecillewaet slice, which may be composite.The fault zone retains evidence of a long history of movement extending from the mid-Mesozoic to Eocene. Early deformation formed a mylonite zone up to 1 km wide in which rocks recrystallized under greenschist facies conditions. The displacement truncated major folds and metamorphic isograds that had developed in the Middle Jurassic. Orientation of slickensides, fiber growth, and strain features in the mylonite indicates normal, dip-slip displacement with the slices of the hanging wall moving eastward. South of Revelstoke, the Galena Bay stock, dated at 150 Ma, apparently intruded the zone and gives a minimum age for early displacement that must be in the Late Jurassic.Late displacement caused intense fracturing, folding of mylonite, and development of gouge zones. These features are well exposed at the Revelstoke damsite, continue north of Revelstoke, but diminish in importance southward. Late movement was again normal, dip-slip with the hanging wall moving eastward; it probably ended in the Eocene. No fault scarps or disrupted drainages have been observed, and at several localities glacial sediments lie undisturbed across the fault zone, indicating a lack of postglacial movement.Metamorphic zones, juxtaposed along the fault, imply a minimum dip-slip displacement of 15–25 km. Displacement in this range poses stratigraphic and metamorphic problems, which are alleviated if displacement is in excess of 80 km. The tectonic slices east of the Columbia River fault zone are part of an allochthonous cover that was transported at least tens of kilometres eastward over the Shuswap and Monashee complexes during the Late Jurassic.
Geology and geochronology of Helikian magmatism, western Labrador
Authors: Brooks Christopher , Wardle Richard J. , Rivers Toby
Published: April 2011

The Shabogamo intrusive suite, a predominantly gabbroic magma series intrusive into a variety of Archean, Aphebian, and Helikian units in the Churchill and Grenville Provinces of western Labrador, is reliably dated at circa 1375 Ma using both the Rb/Sr and Sm/Nd methods on whole rocks and mineral separates. The suite is thus synchronous with Elsonian magmatism in Labrador, which is characterized by the intrusion of large volumes of gabbroic, anorthositic, and associated magma, and so invites petrogenetic correlations on a regional scale.Gabbros of the Shabogamo intrusive suite are emplaced into volcanics and volcaniclastics of the Blueberry Lake group, which are provisionally dated at 1540 ± 40 Ma. The volcanic rocks are therefore of similar age to, and probably correlative with, the upper Petscapiskau Group and Bruce River Group felsic volcanics, which occur further east in a narrow belt within the Grenville Foreland zone. The linear disposition of centres of felsic volcanism in the Grenville Foreland zone about 1500 Ma ago is suggestive of the development of a major ensialic rift at least 300 km in length at that time. A twofold magmatic history during the Helikian of this part of Labrador is now emerging from the field mapping and geochronological studies. Early extrusive felsic volcanism about 1500 Ma ago confined to a linear belt immediately north of the Grenville Province was followed by voluminous mafic magmatism (with emplacement of gabbroic, anorthositic, and associated rocks) occurring over a wide area both within and outside of the present location of the Grenville Province.Rb/Sr dating of Aphebian quartzofeldspathic schists from within the Grenville Province near Wabush – Labrador City shows that the high-grade metamorphism and development of a penetrative schistosity were Grenvillian features formed about 1000 Ma ago. This result effectively precludes the possibility of a Hudsonian metamorphic imprint, a feasible interpretation that was raised during regional mapping of the area.
Deposition of the Cambrian continental rise: the St. Roch Formation near St. Jean-Port-Joli, Quebec
Authors: Strong Percy G. , Walker Roger G.
Published: April 2011

Detailed mapping between Plage Victor and St. Jean-Port-Joli has enabled us to add a 550 m section to the top of the existing 450 m section of Hubert, making the longest continuous section anywhere in the Cambrian continental rise, Iapetus margin of North America. Our section can be divided into four main facies. The red mudstone facies makes up 30% of the section, and contains thin classical turbidites with easterly flow directions. The classical turbidite facies include both calcareous and siliceous turbidites, mostly Bouma BCE types, in beds up to about 1 m thick. Flow directions are again mostly to the east. The massive and pebbly sandstone facies occurs in units up to nearly 100 m thick, and contains both massive and normally graded beds with many fluid-escape features and rare trough cross-bedding. Occurrences of this facies normally have channelled bases, and there are several 5–10 m thick thinning- and fining-upward sequences. Paleoflow directions are southeasterly. The slurry facies includes massive to graded slurry beds, interpreted as debris flow deposits, and slurry breccias that incorporate slabs of interbedded sandstone.We interpret the red mudstones and classical turbidites as base-of-slope, continental rise deposits. The generally easterly and east-southeasterly flow directions suggest a local dip of the continental rise in that direction. The massive and pebbly sandstones represent the fill of feeder channels incised into the rise with southeast, oblique-to-maximum-dip, directions. The absence of thickening-upward sequences in the various turbidite facies suggests the absence of conventional submarine fans, perhaps due to the dominantly fine-grained material forming the lower slope and rise in this area.
Coquitlam Drift: a pre-Vashon Fraser glacial formation in the Fraser Lowland, British Columbia
Authors: Hicock Stephen R. , Armstrong John E.
Published: April 2011

Coquitlam Drift is formally defined and stratotypes established for it in the Coquitlam – Port Moody area, B.C. It is a Pleistocene formation consisting of till, glaciofluvial, ice-contact, and glaciomarine sediments deposited between 21 700 and 18 700 years BP, during the Fraser Glaciation (late Wisconsin) and prior to the main Vashon glacial maximum at about 14 500 years BP. The drift was deposited in short pulses by valley and piedmont glaciers fluctuating into the Fraser Lowland from the Coast Mountains to the north and Cascade Mountains to the east.
Estimates of the magnitude of glacier outburst floods from Lake Donjek, Yukon Territory, Canada
Authors: Clarke G. K. C. , Mathews W. H.
Published: April 2011

Lake Donjek was a large reservoir formed when Donjek Glacier dammed Donjek River. Although the basin is empty at present, a minor advance of Donjek Glacier could again dam the river and impound approximately 234 × 106 m3 of water. Ice-dammed lakes are commonly unstable, giving rise to destructive floods called "jökulhlaups," or glacier outburst floods. Our aim in this paper is to estimate the likely magnitude of outburst floods from Lake Donjek so that the danger to downstream installations can be assessed.In attempting to estimate the maximum discharge from Lake Donjek, we use both the empirical formula of Clague and Mathews and a computer simulation model based on theoretical contributions by Nye. The September 1967 outburst flood from Summit Lake, B.C. is taken as a reference event against which predictions of the simulation model are compared. Our estimates for peak discharge from Lake Donjek lie in the range 677–5968 m3 s−1 with values in the range 3968–5968 m3 s−1 being considered most probable.
Geologic history of the Saguenay region, Quebec (Central Granulite Terrain of the Grenville Province): a working hypothesis
Authors: Dimroth Erich , Woussen Gerard , Roy Denis W.
Published: April 2011

The Saguenay region is divided into three lithostructural units, namely (1) a gneiss complex; (2) batholithic anorthosite and mangerite complexes; and (3) late- to post-kinematic plutons. Three age groups of rocks in the gneiss complex are defined by increasing complexity of structure and mobilizates. Rocks of age group I (paragneiss, granite I) show extremely complex structure and contain three generations of mobilizates. Structures in rocks of age group II (granite II, amphibolite II dykes) are less complex and two generations of mobilizates are present. Rocks of age group III (granite III, amphibolite III dykes) contain one foliation and one generation of mobilizates. Metamorphosed mafic dykes are stratigraphic markers permitting correlation of age groups over vast tracts of terrain.Well-preserved igneous structures (cumulate layering) and textures (cumulate textures, ophitic textures) prove that anorthosite and mangerite crystallized from magmas. Anorthosite has been granulated and foliated, metamorphosed at high pressure with formation of orthopyroxene–spinel coronas by reaction of olivine and plagioclase, and intruded by three successive generations of mafic dykes (diorite, leucotroctolite, amphibolite IIIa).Mineral associations in the gneiss complex suggest metamorphism during slow cooling at about 5 kbar (500 MPa) pressure. Successive mineral associations in anorthosite and its cross-cutting dykes suggest a history of decreasing pressure (from >7–9 kbar (700–900 MPa)) and temperature (from 1200–1400 °C). Thus the anorthosite was emplaced at its present level by diapirism. Structures in the gneiss complex and anorthosite are consistent with the model of diapiric rise of anorthosite and mangerite plutons, but suggest presence of a generation of orogenic structures prior to diapirism.
40Ar/39Ar ages from the Botwood – Mount Peyton region, Newfoundland: possible paleomagnetic implications
Authors: Reynolds P. H. , Taylor K. A. , Morgan W. R.
Published: April 2011

Hornblende and biotite from the freshest available sample of the gabbroic (early) phase of the Mount Peyton batholith have both yielded 40Ar/39Ar apparent age plateaus. An age of 420 ± 8 Ma is suggested for this phase. This means that there is a resolvable age difference between the mafic and the acidic rocks of the batholith (Rb/Sr age of the latter is 390 ± 15 Ma). Biotite and hornblende from a gabbroic inclusion and biotite from the latter's granitic matrix have all yielded very disturbed age spectra and variable total gas ages. Previously published paleomagnetic data suggest that these inclusions were remagnetized at the time of granite intrusion. The present radiometric data give some support to this interpretation, but do not clearly indicate the timing of any such event. A whole-rock sample from the (Lower Silurian?) Botwood Group rhyolite has also yielded a disturbed age spectrum; its total gas age is 385 ± 13 Ma. The Botwood pole is distinct from the granite pole, so either remagnetization did not occur in this case or it occurred at a later time, a time not clearly revealed in the present radiometric data.On the basis of previously published magnetic data and the now improved age control on the Mount Peyton complex, it appears that the 400 Ma paleopole for Newfoundland may differ substantially from other North American poles.
Amphibolite associated with the Thetford Mines Ophiolite Complex at Belmina Ridge, Quebec
Authors: Feininger Tomas
Published: April 2011

Amphibolite in the Quebec Appalachians at Belmina Ridge (45°58′N; 71°28′W) constitutes a steeply dipping, allochthonous sheet as much as 800 m thick, between the obducted Thetford Mines Ophiolite Complex to the east and rocks of the allochthonous Caldwell Group to the west. The amphibolite, which structurally and chemically is unlike amphibolite in the adjacent Caldwell, is fresh, coarse to fine grained, and massive to layered. It is composed chiefly of edenitic to pargasitic amphibole, pyrope- and grossular-rich almandine, salite, and epidote, with small amounts of quartz, plagioclase, and accessory minerals. Metamorphism ranged from [Formula: see text] at the base of the sheet to T ~ 780 °C at the top, near the tectonic contact with rocks of the superjacent ophiolite complex, under a Barrovian facies series with Ptotal between 5 and 7 kbars (500–700 MPa).The amphibolite is interpreted to have been derived from ocean-floor basalt that was metamorphosed under a 20 km thick, westward-directed, obducted allochthon of oceanic lithosphere. With a thermal gradient of 40 °C∙km−1, the temperature at the base of the allochthon would have been 800 °C, whereas the temperature at the base of the Thetford Mines Ophiolite Complex (the uppermost third of the allochthon) would have been 312 °C or less, in agreement with the serpentinization history of the complex. The dynamic environment during obduction could continually furnish "fresh" (hot) lithosphere to override the site of metamorphism of the amphibolite. At the site, the temperature of the base of the allochthon rose progressively, and a relatively high temperature was maintained for ample time, of the order of 1 Ma, to have continuously heated the underlying rocks to raise them to a high temperature without the allochthon ever having been unrealistically hot. The allochthon was dismembered tectonically toward the close of obduction. The amphibolite was thrust westward and upward, to be emplaced at relatively little depth on rocks of the Caldwell Group, and under the ophiolite complex. The petrogenesis proposed for the amphibolite at Belmina Ridge is consistent with the apparently simple metamorphic history of the rock.
Two high precision U–Pb zircon ages for the Sudbury Nickel Irruptive
Authors: Krogh T. E. , McNutt R. H. , Davis G. L.
Published: April 2011

Two independent U–Pb zircon ages were measured using norite samples from the North and South Ranges of the Sudbury Nickel Irruptive. Ages of [Formula: see text] and [Formula: see text] Ma were obtained with a probability of fit within experimental error of 51 and 57%, respectively.Previous determinations by the Rb–Sr whole-rock method gave ages between about 1700 and 2000 Ma, with errors of the order of ± 100 Ma. The difference in precision is inherent in the two methods: zircons from the norite are highly radiogenic and almost concordant whereas Rb–Sr whole-rock ages are determined by very small increments in radiogenic 87Sr.The two zircon ages have completely different discordia so that all simple models for lead loss by continuous diffusion can be excluded.
Volcaniclastic rocks and volcaniclastic facies in the Middle Precambrian (Aphebian) Belcher Group, Northwest Territories, Canada
Authors: Ricketts B. D. , Ware Michael J. , Donaldson J. Allan
Published: April 2011

The Middle Precambrian Flaherty Formation consists of a thick sequence of volcanic rocks of both effusive and explosive origin, derived from a source area west of the Belcher Islands. The effusive volcanic facies are made up of thick, massive lava flows, some of which are compound, that are intercalated with thick lenticular units of pillowed lava. Facies of explosive origin, the volcaniclastic rocks, are a product of phreatic and phreatomagmatic eruptions. A variety of volcaniclastic facies are recognized on the basis of bed geometry, sedimentary structures, and textural characteristics, and include: thinly bedded tuffs and lapillistones that were deposited by fallout from vertical ash columns (some tuffs contain accretionary lapilli and hence originated from subaerial eruption columns); pillow talus deposits (hyaloclastites) resulting from the rapid quenching of lava in water; volcaniclastic turbidites representing relatively deep-water resedimented tephra; and a single massive pyroclastic flow that was emplaced during a single depositional event, and may have been derived from a Plinian eruption or series of Surtseyan eruptions. Systematic variations in these volcaniclastic facies, for example an increase in the proportion of turbidite units towards eastern Belcher Islands, indicate that water depth increased eastward.Based on physical volcanological aspects, the Flaherty Formation is compared with some modern and ancient analogues. The style of volcanism envisaged for the Flaherty is similar to that of Iceland, or possibly to an immature stage of island arc development. From a tectonic viewpoint, the comparison with Iceland is problematical because it is part of an oceanic regime, whereas the Flaherty Formation is more closely related to an ensialic regime. Direct comparison with an island arc also is difficult because little is known about volcanic facies relationships in the early growth stages of such arcs.
Paleoecology and biostratinomy of solitary rugose corals in the Stony Mountain Formation (Upper Ordovician), Stony Mountain, Manitoba
Authors: Elias Robert J.
Published: April 2011

The four species of solitary Rugosa known from the Stony Mountain Formation at Stony Mountain in southern Manitoba belong to different genera, and differ from one another in external form. The distribution and abundance of taxa and their frequency with respect to one another were related to the degree of environmental restriction. The boundary between the Gunn Member and overlying Penitentiary Member corresponds to a marked increase in overall abundance and change in relative frequency. Helicelasma and Bighornia are dominant in the Gunn and lower Penitentiary, respectively. Deiracorallium and Lobocorallium decrease in frequency at the boundary.Larvae of these solitary Rugosa attached to the substrate with their cardinal side. Coralla of Helicelasma, Deiracorallium, and Lobocorallium were oriented in the sediment with the top of the convex cardinal side at or near the substrate surface and the upper part of the concave counter side exposed above it during life. Bighornia lay with the convex counter side in the sediment and the concave cardinal side at least partly exposed. Epizoic bryozoans generally became associated with live hosts, and were especially common on the exposed side of relatively large individuals. Microscopic boring algae infested the outer wall of most corals in the Gunn Member, usually while the hosts were alive. Responses of the polyp to stress and injury are indicated by redirection of the growth axis, constriction of the calice rim, and repair of broken calice rims. The attitudinal and directional orientations of solitary corals suggest that most and possibly all were transported after death. Differences in depositional orientation among the taxa are related to coral form. Currents were unidirectional from the present southeast during Gunn time, and either unidirectional from the southeast or northwest, or oscillating from both directions in early Penitentiary time. Abrasion of coral exteriors was primarily a post-mortem event associated with transportation. Trypanites borings were probably produced by one species of annelid after deposition of the corals. The degree of abrasion and frequency of annelid borings tended to increase with coral size and the duration of exposure before burial.
The Broughton Trough on the continental shelf of eastern Baffin Island, Northwest Territories
Authors: Gilbert R.
Published: April 2011

Bathymetric and seismic surveys of the trough across the continental shelf of Baffin Island at Broughton Island indicate that there were four stages in its development. The first involved deposition of Cretaceous and early Tertiary marine sediments before and during formation of a graben associated with the opening of Baffin Bay. With the uplift of Baffin Island, extensive deltaic deposits at the distal end of the trough were laid down in the second stage. These deposits are thought to represent the products of a river system raised much above grade, flowing in the trough and the fiords to the southwest, and depositing in a sea with a relative level 300–400 m below present. In the third stage during Pliocene–Pleistocene glaciation, the proximal regions of the trough were eroded to more than 700 m below present sea level. Lateral moraines indicate the extension of ice to the edge of the continental shelf, although the relatively small amount of erosion in the distal region suggests that the ice may have been partially floating. Glaciomarine and marine sedimentation following glaciation is the final stage in the evolution of the trough.
Thermometry and barometry of some amphibolite–granulite facies rocks from the Otter Lake area, southern Quebec
Authors: Perkins III Dexter , Essene Eric J. , Marcotty Louise Annette
Published: April 2011

Grenville rocks from a 2500 km2 area centered on Otter Lake, Quebec (some 75 km northwest of Ottawa) are in the uppermost amphibolite to lower granulite facies; orthopyroxene occurs occasionally in both metabasic and charnockitic rocks. The temperature of metapmorphism was approximately 675 °C, based upon oxide, feldspar, and garnet–clinopyroxene thermometry. Little thermal gradient could be detected across the area. Carbonate thermometry, using reintegrated calcite compositions, yielded lower temperatures of 600 °C (maximum), while garnet–biotite and other Kd thermometers yielded scattered and for the most part unreasonable results. Metamorphic pressure, calculated from the reaction anorthite = grossular + sillimanite + quartz, was 5.0 ± 0.5 kbar(500 ± 50 MPa). Similar calculations based upon the reactions garnet + quartz = anorthite + orthopyroxene and garnet + quartz = anorthite + clinopyroxene yielded pressures of 5.5–7.0 kbar (550–700 MPa). Pressure calculations based upon assemblages of cordierite–garnet–sillimanite–quartz were less precise, but agreed with the outer estimates. Similar metamorphic temperatures and slightly lower pressures have been estimated for the Adirondack Lowlands of New York. In the Morin Highlands, 100 km east of Otter Lake, and in the Adirondack Highlands, 100 km east of the Adirondack Lowlands, temperatures of metamorphism (700–800 °C) and pressures of metamorphism (6–9 kbar (600–900 MPa)) are both higher. Thus it appears that over an approximate 300 km north–south direction nearly constant metamorphic conditions prevailed at Grenville time. In the east–west direction significant variations in metamorphic grade are recorded; both temperature and pressure markedly increase to the east.
Quaternary sequences along the north shore of Lake Ontario: Oshawa – Port Hope
Authors: Brookfield M. E. , Gwyn Q. H. J. , Martin I. P.
Published: April 2011

We describe six major stratigraphic units from the hitherto neglected Quaternary sequences along the north shore of Lake Ontario between Oshawa and Port Hope. These units, from the base upwards, consist of the following: a lowermost unit of silt till, apparently overlying bedrock; a complex unit of lacustrine and glaciofluvial sediments with several thin silt tills, usually unconformable on the lowermost unit; a glaciofluvial sand unit, filling valleys cut into the underlying units; a unit of two sandy pebbly tills; a silt till; and varved clays and sands of glacial Lake Iroquois.Though the sections show more erosional intervals, the above units can be correlated with the better known Scarborough sections as follows: the lowest unit with the Sunnybrook Till; the overlying complex unit with the Meadowcliffe Till and associated sediments; the two sandy pebbly tills with the lower Leaside Till; and the overlying silt till with the Halton Till.The inferred geological history is similar to that of the Scarborough area.
Stress-relief buckles in the McFarland quarry, Ottawa
Authors: Adams John
Published: April 2011

Six quarry-floor buckles in a west-end Ottawa bedrock quarry are described and a semi-quantitative estimate of the stress field is inferred from them. The maximum principal stress component is horizontal with an azimuth that is constrained to the northeast–southwest quadrants and has an upper limit that is of the order of a few tens of megapascals.
A numerical approach toward the classification of magnetites from tephra in southern Alberta
Authors: King R. H. , Kingston M. S. , Barnett R. L.
Published: April 2011

High-titanium glass-encased magnetites associated with intermixed tephras in upper subalpine soils in Banff National Park are shown to be characteristic of Mazama tephra and of regional significance. Similar magnetites occur in a Mazama layer above a paleosol at Fish Creek, Alberta and within a sample of Mazama ash (UA 396) from Windy Point, Alberta. Detailed sampling and analysis of the Fish Creek tephra indicate that the magnetites do not represent a separate eruptive event or an older ashfall. Cluster analysis of glass-encased magnetites from reference samples of Mazama, St. Helens Y, and Bridge River ashes revealed composite grouping of Mazama and Bridge River magnetites and separate and strong groupings of high-TiO2 magnetites. Discriminant analysis identifies MgO, TiO2, and Al2O3 as the most significant chemical discriminants between the various ashes. Discriminant function analysis identifies the high-titanium magnetites as Mazama in type and successfully classifies 96% of the tephra-derived magnetites in two soils developed from intermixed ashes. Numerical analysis confirms the utility of compositional variations in tephra-derived magnetites in providing a time-stratigraphic framework in the analysis of volcanic ash soils in western Canada.
Tidal deposits of the Lower Cambrian Random Formation, eastern Newfoundland: facies and paleoenvironments
Authors: Hiscott Richard N.
Published: April 2011

The Avalon tectonostratigraphic zone occupies about 25% of the area of insular Newfoundland. Late Precambrian development of the Avalon terrane is distinctly different than that of other parts of the Appalachian orogen and cratonic North America. Late Precambrian volcanism and tectonic instability gave way to deposition of about 2 km of Cambrian and Lower Ordovician dominantly epiclastic sediments on a slowly subsiding, relatively stable shelf platform.The Lower Cambrian Random Formation is part of the platformal sequence and is bounded by regional disconformities over much of the Newfoundland Avalon Zone, except around Fortune Bay where it is underlain by older terrestrial and shallow-marine sediments. The Random Formation was deposited during a time of global sea-level rise, and consists of up to 250 m of shoreline, nearshore, and open-shelf deposits that record macrotidal conditions and periodic storm activity. Cross-bedded quartzarenites occur in units to about 50 m thick (one exceptional unit is 110 m thick) that tend to have gradational bases and abrupt tops. Bimodal–bipolar paleocurrent data are best explained by reversing tidal currents. These sandstone units show no evidence of intertidal (beach) processes and are therefore interpreted as subtidal ridges or shoals. The intertidal environment is represented by a shaly unit, with thin sandstone beds, that is characterized by flaser and lenticular bedding, oscillation (wave) ripples, some flat-topped ripples, and abundant synaeresis (dehydration) cracks. A muddy shoreline and subtidal sands suggest a macrotidal setting.Storm deposits range from: (1) fine, micaceous, red sandstones with fiat, gently dipping lamination, low-angle truncation surfaces, rare hummocks, shale-clast horizons, granule lags, and steep-sided erosional gulleys believed to represent lower shoreface rip-current channels; to (2) mudstones with graded, sole-marked, glauconitic sandstone beds deposited on an open shelf by storm-generated density currents.
Evidence for multiple deformation during the Penokean Orogeny in the Middle Precambrian Thomson Formation, Minnesota
Authors: Holst T. B.
Published: April 2011

The Penokean Orogeny, a major event that occurred at 1850–1900 Ma in the Great Lakes region, involved deformation, metamorphism, and igneous activity. In Minnesota, the effects of the Penokean deformation are most clearly seen in the Thomson Formation. Here, two main Penokean deformational events are recognized. The first involved isoclinal recumbent folds (F1) with a well developed axial-planar foliation (S1). The second deformation involved open, upright and subhorizontal folds (F2) which folded bedding (S0) and the first foliation (S1), and refolded the early folds. A crenulation cleavage (S2) developed axial planar to the F2 folds. Post-Penokean structural features include joints, kink bands, and basalt dikes.Evidence for the first Penokean deformation is found in the southern region of Thomson Formation outcrop, whereas the features associated with the second Penokean deformation are found throughout its outcrop area. Thus, the only Penokean-age structural features seen at the type locality of the Thomson Formation are from the second Penokean deformation.
Overview of regional geophysical studies in Manitoba and northwestern Ontario
Authors: Hall D. H. , Brisbin W. C.
Published: April 2011

This paper presents an overview of six geophysical projects (seismic reflection and refraction, gravity and magnetic anomaly interpretation, specific gravity and magnetic property measurements) carried out in an area in Manitoba and northwestern Ontario bounded by 93 and 96°W longitude, and 49 and 51°N latitude.The purpose of the surveys was to define crustal structure in the Kenora–Wabigoon greenstone belt, the Winnipeg River batholithic belt, the Ear Falls – Manigotagan gneiss belt, and the Uchi greenstone belt. The following conclusions emerge.In all of the belts, a major discontinuity divides the crust into the commonly found upper and lower crustal sections. At the top of the lower crust, a seismically distinct layer (the mid-crustal layer) occurs. Seismic velocities in this layer suggest either intermediate to basic igneous rocks or metamorphic rocks of the amphibolite facies.Crustal geophysical characteristics vary sufficiently among the four belts to justify the classification of all four as distinct subprovinces of the Superior Province.Cet article présente une vue générale sur six projets de géophysique (réflexion et réfraction sismique, interprétation d'anomalies de gravité et magnétiques, déterminations de densité et de propriétés magnétiques) réalisés dans une région du Manitoba et du nord-ouest de l'Ontario encadrée par les longitudes 93 et 96°O et les latitudes 49 et 51°N.
Paleomagnetism of drill cores from Labrador offshore wells
Authors: Pätzold Raymund R. , Deutsch Ernst R.
Published: April 2011

Values of the remanent magnetic intensity and inclination, initial susceptibility, and Koenigsberger ratios were obtained from basaltic material in four short core sections from three wells (Bjarni H81, two sections; Leif M48; Herjolf M92) drilled off Labrador. Published K–Ar dates are latest Jurassic to Early Cretaceous. Alternating-field (AF) demagnetization to 600 Oe (60 mT) and thermal demagnetization to 400 °C yielded stable, comparable remanent inclinations mostly of normal polarity for the Bjarni and Leif samples and revealed a change from reversed to normal polarity in the Bjarni well. Virtual pole position loci calculated from the paleoinclinations after AF and thermal treatment agree with published Early Cretaceous pole positions in the case of one Bjarni core, but the fit is poorer in the case of the second Bjarni core and the Leif core. These are the first paleomagnetic results from offshore Labrador.
Archean mafic metavolcanics from the Rouyn–Noranda district, Abitibi Greenstone Belt, Quebec. 1. Mobility of the major elements
Authors: Gélinas Léopold , Mellinger Michel , Trudel Pierre
Published: April 2011

In a suite of Archean mafic pillows from the Rouyn–Noranda region of Quebec's Abitibi Greenstoné Belt, including both tholeiitic and calc-alkaline varieties spanning the prehnite–pumpellyite to upper greenschist metamorphic facies, three types of alteration can be defined: (I) chlorite–epidote–actinolite; (II) chlorite–epidote; and (III) chlorite ± sericite; the number of mineral phases decreases as a result of progressive hydration from type I to type III alteration. Albitization, resulting from substitution of [Formula: see text], in calcic plagioclase, is highly variable in type I alteration, but in types II and III the plagioclase is totally albitized and in some cases silicified. Chloritization is closely linked to increasing hydration and Ca leaching with MgO and FeO substituting for CaO in ferromagnesian minerals.Calcium was mobilized and carried by solutions, as evidenced by the variable concentration of epidote at the margins of pillows. This calcium leaching generated an excess of Al2O3 with respect to the combined molecular proportions of Na2O, K2O, and CaO, and is shown by the presence of corundum in CIPW norm calculations. In some pillows showing substitution of [Formula: see text], the fo2 of the invading fluid appears to have remained constant, being buffered by the pillow composition; this would be favored by a low water/rock mass ratio. As a result, the initial pillow Fe2O3/FeO ratio remained constant. In other pillows, the fo2 appears to have been imposed by the invading fluid rather than by the mineral assemblage: the FeO/MgO ratios are thus no longer representative of the magmatic composition whereas the ΣFeO/MgO is still representative of the pristine magmatic value.Two types of substitution of CaO by FeO and (or) MgO have been observed: (1) preferential substitution restricted to type I alteration, of FeO over MgO, similar to low-temperature substitution in modern-day sea-floor alteration; and (2) the more common substitution in type II and III alterations in which MgO predominates over FeO, similar to the high-temperature substitution taking place at great depth on the ocean floor.Although the samples were collected to test mineral heterogeneities caused by chemical degradation, more than 40% of the pillows sampled retained their pristine ΣFeO/MgO ratios. The various alteration patterns are independent of the initial tholeiitic or calc-alkaline lineage; this was confirmed using rare earth elements (REE) and inert trace elements such as Zr, Y, and Ti. The chemical changes in the mafic metavolcanic rocks do not obliterate their tholeiitic or calc-alkaline chemical affinities.
Holocene history of Bedford Basin, Nova Scotia: foraminifera, dinoflagellate, and pollen records
Authors: Miller A. A. L. , Mudie P. J. , Scott D. B.
Published: April 2011

Three piston cores from Bedford Basin, a silled coastal inlet, provide the basis for a micropaleontological study of postglacial to recent sediments. Five faunal units (four foraminiferal, one arcellacean) are found in core 79-11: a surface assemblage, followed by deep estuarine, marginal marine, transition, and freshwater (arcellacean) assemblages. The other cores contain only expanded marine sequences. The top of the transition zone in core 79-11 has a C-14 age of 5830 ± 230 years BP, indicating a rise in sea level of at least 20 m (the sill depth) during the Holocene.Four dinoflagellate assemblage zones are found in core 79-11. The first (O. centrocarpum – B. tepikiense) is typical of a silled basin with marine water of near-normal salinity; the second (P. conicoides – Cyst C) indicates a temperate marine environment with strong fluvial influence (marginal marine); the third (P. limbatum) is dominated by freshwater cysts, and the fourth (Dinocyst sp. A) is dominated by subarctic brackish water cysts.Four pollen assemblage zones are found in core 79-11. Zones C1–C3 indicate mixed boreal–deciduous forest vegetation. Zone B indicates early Holocene park–woodland vegetation, the base of which has a C-14 age of 7705 ± 550 BP. The palynozones in the marine sediment core are correlatable with C-14 dated stratigraphies from Nova Scotian lakes.Foraminifera and dinoflagellate assemblages in core 79-11 reflect the response of the microfauna and microflora to changes in water depth, salinity, and temperature, which have accompanied changes in sea level and climate during the past 8000 years. Major changes in the marine biota during the recent period of urban development may be due to increased sediment influx and effluent discharge. The effects of anthropogenic changes are small, however, compared to those accompanying the Holocene marine transgression.
Hudson Bay river sediments and regional glaciation: III. Implications of mineralogical studies for Wisconsinan and earlier ice-flow patterns
Authors: Adshead J. D.
Published: April 2011

Mineralogical studies of river sediments from the Hudson Bay and James Bay Lowlands suggest that the glacial erosion of pre-Devonian Paleozoic carbonate rocks played an important role in the production of calcite-enriched debris in the Cape Henrietta Maria watershed. Ice flowing southwesterly across Devonian basins in western Hudson Bay and the James Bay Lowlands would largely bypass the intervening cape area.Enrichment of iron in river sands of the cape watershed is attributed to Proterozoic ferruginous sources now largely submerged under the waters of eastern Hudson Bay. Distributional patterns of carbonates and iron indicate that the dominant flow of ice from eastern Hudson Bay was southwesterly toward Cape Henrietta Maria, without major flow from the area of Proterozoic bedrock into the Nelson River watershed. In the cape area, iron enrichment due to Proterozoic sources significantly overshadows possible contributions from siderite-bearing Devonian bedrock.The fluvial sediment data are consistent with a multiple dome model of glaciation with ice mass centres located east and west of Hudson Bay. However, quartz/(total carbonate) ratios indicate that, if independent ice masses existed in this configuration, the dominant position of their contact should be placed north of the Churchill–Nelson watershed boundary. Indications of K-feldspar enrichment in Churchill sands are not evident in cape localities where ice flow was southwesterly.Rivers sands are composite channel samples of a drift cover that includes several pre-Wisconsinan tills as well as Wisconsinan deposits. Well defined regional patterns of composite (fluvial) sediment composition suggest a consistency in dominant regional ice movements through time. Similarities between regional drift dispersal limits based on these composite sediments and on pebble dispersal patterns for Wisconsinan tills further indicate that dominant ice-flow patterns in central Canada were probably similar for Wisconsinan and earlier glaciations.
A multivariate approach to geochemical distinction between tin-specialized and uranium-specialized granites of southern Nova Scotia
Authors: Chatterjee A. K. , Strong D. F. , Muecke G. K.
Published: April 2011

Like most granitoid bodies that host significant granophile deposits, the South Mountain batholith (SMB) of Nova Scotia consists of an earlier suite intruded by a later suite of smaller plutons that are more silicic and peraluminous. The latter generally show a range of other geochemical features that readily identify them as "specialized" and allow for their separation from the earlier "non-specialized" granites. In the case of mineralization associated with the SMB we can go one step further and clearly separate the specialized granites into stanniferous and uraniferous series, which can be identified even where no Sn or U enrichment is present. Although this can be done successfully using simple histograms of a number of elements (Li, P, Sn, and F), we show that combining all elements in discriminant analysis guarantees 100% success in separating the two groups. R-mode factor analysis aids in accounting for the variance within each group, the most important effect being a "biotite factor" because of both its magmatic role and its early breakdown by hydrothermal fluids. The stanniferous series is marked by what we call the "lithophile factor" (heavily loaded by K2O, P2O5, Rb, F, Li, and W) and the uraniferous series by a "metallization factor" (loaded by Cu, Sn, Mn, and Zn). These can be interpreted in terms of dominantly magmatic processes for the former and dominantly hydrothermal processes for the latter. Furthermore, we emphasize that the separate suites do exhibit these independent characteristics even without mineralization being present.
Trace-element mobility during low-grade metamorphism and silicification of basaltic rocks from Saint John, New Brunswick
Authors: Dostal J. , Strong D. F.
Published: April 2011

Upper Carboniferous basaltic lavas from Saint John, New Brunswick were metamorphosed under prehnite–pumpellyite conditions and some were also affected by extensive silicification. Silicification led to simple dilution of relatively immobile elements such as rare earths, Y, Zr, Hf, Th, and Sc. The chondrite-normalized REE patterns of the silicified rocks are parallel to those of basalts.
The oldest sequence of skeletal fossils in the Lower Cambrian of southeastern Newfoundland
Authors: Bengtson Stefan , Fletcher Terence P.
Published: April 2011

Sections on the Burin Peninsula in southeastern Newfoundland show a record of continuous sedimentation during the Late Precambrian–Early Cambrian transition. These may be correlated lithologically and biostratigraphically with less complete sequences on the Avalon and Bonavista Peninsulas. Below the oldest known trilobites in southeastern Newfoundland (of the Callavia Zone) two consecutive assemblages of skeletal fossils are recognizable: an Aldanella attleborensis assemblage and the succeeding Coleoloides typicalis assemblage. The shift between the two assemblages takes place within the Bonavista Formation in the Avalon–Bonavista region and in a similar succession of mudstones near St. Lawrence on the Burin Peninsula. The quartzitic Random Formation appears to have been deposited during a short interval within the time span represented by the A. attleborensis assemblage, and there is no conclusive biostratigraphical evidence of any major diachronism of this unit. The A. attleborensis assemblage contains taxa known from the lower part of the Tommotian Stage on the Siberian Platform. It is interpreted to be of Tommotian age, and the subsequent shift to the C. typicalis assemblage is tentatively correlated with the Tommotian–Atdabanian boundary as recognized in Siberia.
P-wave velocity structure of the Earth's crust beneath Vancouver Island
Authors: McMechan George A. , Spence George D.
Published: April 2011

Refraction data were recorded from three shot points out to a maximum distance of ~330 km as part of the 1980 Vancouver Island Seismic Project (VISP80). These vertical component data are partially reversed and so can be interpreted in terms of two-dimensional structures by iterative modeling of P-wave travel times and amplitudes. The structure of the upper crust is the best constrained part of the model. It consists, generally, of a gradually increasing velocity from ~5.3 km/s at the surface to ~6.4 km/s at 2 km depth to ~6.75 km/s at 15.5 km depth, where the velocity increases sharply to ~7 km/s. Below ~20 km depth, the model becomes speculative because the data provide only indirect constraints on velocities at these depths. An interpretation that fits the observed times and amplitudes has a low velocity zone in the lower crust and a Moho at 37 km depth. The only significant departure from this general structure is beneath the central part of Vancouver Island where the 15.5 km boundary in the model attains a depth of ~23 km, below which there appears to be a local high velocity anomaly.
A crystallographic approach to the calculation of orientation diagrams
Authors: Starkey John
Published: April 2011

Methods are described that use measured pole figures directly to calculate pole figures, inverse pole figures, and the crystal orientation matrix; this latter is a frequency distribution of the Euler rotations, which relate the crystal orientations in a polycrystalline aggregate to a standard crystallographic orientation. It is demonstrated that if data from crystal forms with different crystallographic multiplicities are to be compared the appropriate multiplicity factor must be applied to the data in the measured pole figures.These techniques are applied to computer-simulated fabrics and the data obtained are compared with data derived via the orientation distribution function. It is concluded that the data derived directly from the measured pole figures more closely represent the actual data. In the case of inverse pole figures the procedures based on the orientation distribution function yield results that are of doubtful geological significance.
New evidence on the relationships of the Tertiary insectivoran Ankylodon (Mammalia)
Authors: Fox Richard C.
Published: April 2011

Features of the snout, face, palate, and anterior upper dentition of the Tertiary insectivoran Ankylodon Patterson and McGrew are described for the first time. Instead of corroborating the widely held view (based on the anatomy of the molars) that Ankylodon is most closely related to the Adapisoricidae and, hence, to the Erinaceomorpha among the Insectivora, these features suggest that Ankylodon is most closely related to soricomorph insectivorans. The hypothesis that Ankylodon and the Tertiary soricomorph Centetodon Marsh represent insectivoran lineages that had been separate since the Late Cretaceous is shown to be largely based on differences between Ankylodon and advanced species of Centetodon, rather than between Ankylodon and primitive species of Centetodon as would a valid hypothesis require.
Fossil crabs in glacial drift at Bellingham, Washington: evidence of mid-Tertiary marine deposition
Authors: Mustoe G. E.
Published: April 2011

Three glauconite-rich arkose concretions have been found in glacial drift at Bellingham, Washington. Two concretions contain well preserved fossil crabs, Portunites alaskensis Rathbun, a species previously reported only from Oligocene rocks. No Tertiary marine sediments have been recognized in the source area for this glacial material, but these concretions provide evidence of as yet undiscovered Oligocene strata in the vicinity of the British Columbia – northwest Washington border.