bluuebunny/crossref_metadata_2025 huggingface dataset:
Major and minor element lithogeochemical anomalies surrounding the Louvem copper deposit, Val d'Or, Quebec
Authors: Spitz Guy , Darling Richard
Published: April 2011

Major element distributions in meta-rhyodacitic flows and fragmental rocks surrounding the Louvem volcanogenic copper deposit show a broad linear anomaly parallel to the local strike. At least 420 m long and up to 210 m wide, this altered area contains rocks that have high Fe+2, S, and low Na2O, CaO, and CO2 values. Included in the central portion of this large anomaly is a 100 m by 50 m highly altered area that contains rocks with high H2O and MgO values and crudely outlines the ore deposit.Element-ratio maps and a map showing percentage peraluminous character all display easily recognizable anomalies that mark the zone of altered rocks enclosing the ore deposit. Of the element ratios investigated at Louvem, Al2O3/Na2O appears to offer the most practical tool for mineral exploration.The chemical zoning of the altered fragmental layer that includes the copper ore is symmetrical about the long axis of the stratigraphically concordant orebody, but in a longitudinal direction this symmetry is absent. Instead, the alteration changes progressively from dominantly chloritic at the western end to pyritic at the eastern end of the study area. This alteration pattern seems to suggest that ore deposition was effected by hydrothermal solutions moving along the layer of now-altered fragmental rocks. By analogy with the chloritic alteration pipes underlying pyritic volcanogenic deposits, it seems probable that the direction of fluid flow was from west to east.
Sub-pingo water lenses, Tuktoyaktuk Peninsula, Northwest Territories
Authors: Mackay J. Ross
Published: April 2011

In 1976 and 1977 three growing pingos were drilled for the purpose of measuring sub-pingo water pressures beneath aggrading permafrost. All holes drilled through permafrost in the pingos and adjacent lake flats produced artesian flow. The flow from the pingos was clear and as the gushers rose to a maximum height of 3 m above ground level, large sub-pingo water lenses under pressure seemed evident. The existence of the lenses was confirmed by sounding their depths once permafrost was penetrated.One pingo had a 2.2 m deep water lens beneath the top. Pressure transducers, installed in the sub-pingo water lenses or in the unfrozen sands beneath, all indicated pressure heads above the tops of the pingos. Precise levelling of bench marks showed that the top of one pingo subsided 60 cm from drill hole water loss. Calculations for one pingo show that the water lens has likely been present since the birth of the pingo. Recharge from a distant source cannot account for the high pressures because the hydrostatic heads are above the pingo tops and as the pingo tops are usually the highest features in Tuktoyaktuk Peninsula, there can be no available higher source area; even if there were distant sources, the countless intervening lakes would quickly release any artesian pressures; and numerous pingos have grown up in drained lakes which are either too small or too young to have through-going taliks beneath them. Therefore, the observed water lenses and high sub-pingo pore water pressures cannot be attributed to recharge but provide strong field evidence for pressure generated by pore water expulsion.
Anorthosite and associated plutons, southern Nain complex, Labrador
Authors: Wiebe Robert A.
Published: April 2011

Plutonic rocks in a southern area of the Nain anorthosite complex consist of leuconorite, anorthosite, granite, and subordinate diorite. An older anorthosite intrusion (CI < 10) has been invaded and broken up by an extensive leuconorite intrusion (CI = 15). Ferrodiorite occurs as small bodies within or adjacent to the leuconorite and is a late stage differentiate of leuconorite, Large granitic plutons of separate crustal origin were emplaced prior to complete solidification of the leuconorite. Where these intrusions invaded leuconorite a marginal hybrid (diorite–granite) zone of heterogeneous matrix developed with chilled pillows of residual magma (mainly ferrodiorite) filter-pressed from the leuconorite. Chilled leuconorite dikes indicate that the parent magma of one leuconorite intrusion was approximately equivalent to its average composition. The older anorthosite body most probably represents a concentration of plagioclase crystals from a different magma; deformation of plagioclase crystals suggest that the mechanism of concentration was filter pressing.
Determination of stratigraphic thickness of strained units
Authors: Schwerdtner W. M.
Published: April 2011

Given the state of homogeneous total strain or average total strain of a deformed unit, its stratigraphic thickness can be readily determined. The necessary theoretical development is presented herein, together with a general discussion of the necessary equations. It is shown that the practice of destraining lines of true thickness of deformed strata is theoretically sound only if the bedding surface is a principal plane of deformation.
The structural relationship between Archean granite–greenstone terrains and late Archean mafic dikes
Authors: Halls H. C.
Published: April 2011

Examples of Archean shield areas from Canada and Australia are used to demonstrate a consistent orthogonality in trend between late Archean mafic dikes (~2.5 Ga old) and the structure of granite–greenstone terrains whose orogenic history terminated no more than about 0.2 Ga prior to dike injection. The simplest explanation of this relationship is that the regional structural grain of the granite–greenstone terrains was formed by horizontal crustal compression, and that the direction of maximum horizontal stress remained unchanged up to and including the time of dike emplacement.
Shallow crustal sounding in the Superior Province by audio frequency magnetotellurics
Authors: Koziar A. , Strangway D. W.
Published: April 2011

Audio frequency magnetotelluric soundings in the frequency range of 10 Hz to 10 kHz have been carried out over a section of the Superior Province of the Precambrian Shield in northwestern Ontario. Measurements were made in the English River sub-province, which is mainly a gneissic belt. Resistivity values over gneissic rocks and granitic intrusives were found to be generally very high. Resistivity values over greenstone belts were lower. In addition, there was a distinct conductive layering to the crust that was independent of the surface rock type.At the surface there is a thin conducting layer due to water in the surface soils and fractured rocks. Below a few tens of metres, the resistivity rises to values typically between several thousand and 100 000 ohm∙m. This is undoubtedly due to the presence of massive, unfractured rock with little water content. Beyond a depth of 7 km the resistivity drops sharply to values of 100–1000 ohm∙m. One explanation of this drop is the presence of small amounts of trapped pore-space fluids.
Provenance of Mesozoic and Cenozoic sediments from the Labrador and western Greenland continental margins
Authors: Higgs Roger
Published: April 2011

Forty-two Cretaceous and Paleocene sand samples from offshore Labrador and onshore western Greenland were examined petrographically. The sands were found to be mineralogically and texturally immature, reflecting rapid erosion and transportation from local, high-relief source areas. The principal source-rock types were acidic plutonics and amphibolite-facies metasediments and metavolcanics. Basic igneous rocks provided minor quantities of detritus, whereas contributions from sedimentary and low-grade-metamorphic sources were negligible. Cretaceous and Paleocene sediment transport was essentially perpendicular to the axis of the 'Labrador–Baffin rift system.In view of the apparent local abundance of amphibolite-facies supracrustal rocks during the Cretaceous and Paleocene, extensive post-Paleocene denudation in Labrador, Baffin Island, and western Greenland is invoked to account for the present scarcity of such rock types.
Decolourization of heavy liquids — an economic assessment
Authors: Bitter P. H. von , Plint-Geberl H. A. , Miller A. A. L.
Published: April 2011

The cost effectiveness of silica gel, Fuller's earth, 'Kitty Litter', kaolinite, decolourizing carbon, and sodium hydroxide as decolourizing agents for darkened tetrabromoethane were evaluated. The 30/60 grade of attapulgus clay, or attapulgite, the principal member of the group known as Fuller's earth, proved to be the most effective when taking into account the cost of decolourizing agent per test run, the amount of tetrabromoethane lost through absorption, the time required per run, and the degree of decolourization.
Trace fossils from late Pleistocene glacial lake sediments in southwestern Ontario, Canada
Authors: Gibbard P. L. , Dreimanis A.
Published: April 2011

Nine types of crawling traces and one resting trace, attributed to isopods, water beetles and their larvae, crustaceans, and nematodes, were found along the partings of silty laminae in varved glaciolacustrine clayey silts of Late Wisconsinan age at Iona, St. Mary's, and Union, southwestern Ontario. They lived in proglacial lakes, at distances of about 1–100 km from the glacial margin.
Mammals from the Upper Cretaceous Oldman Formation, Alberta. III. Eutheria
Authors: Fox Richard C.
Published: April 2011

Eutherian mammals from the Upper Cretaceous Oldman Formation, Alberta, are described. These include the leptictid proteutherian Gypsonictops lewisi Sahni, which has five lower premolars and was probably the direct lineal ancestor of G. hypoconus Simpson of Lancian age; a new genus and species of primitive and generalized erinaceoid insectivore, which is the most adequate dental ancestor known for all Lipotyphla, Tupaiidae, Primates, Dermoptera, Chiroptera, and all of the ungulate mammals; and the first pre-Lancian occurrence in North America of the Family Palaeoryctidae.
A paleoecological analysis of Quadra Sand at Point Grey, British Columbia, based on indicator pollen
Authors: Mathewes Rolf W.
Published: April 2011

Pollen and spore percentages and concentrations were determined from six peaty zones about 24500 radiocarbon years old at the Point Grey sea cliffs. All samples are dominated by nonarboreal pollen, especially Cyperaceae of local origin and Gramineae. Analysis of 'indicator pollen' suggests that two floristic elements were present, a local wetland component and a montane to subalpine element. This study supports the geological contention that the Quadra Sand was deposited in a braided river environment under a cooler maeroclimate than exists at present. Pollen concentrations in the samples are within the range of some bog and lake sediments presently accumulating in the Fraser Lowland area of southwestern British Columbia, suggesting that climatic conditions were not of alpine severity around 24 500 BP, although the indicator pollen assemblage suggests a climatic regime similar to present-day midmontane or subalpine conditions.
K–Ar isochron age of the North Mountain Basalt, Nova Scotia
Authors: Hayatsu A.
Published: April 2011

Ages of five whole rock samples from the North Mountain Basalt, Nova Scotia, determined by Isotopes, Inc. in 1967, were discordant and indicated the effect of initial argon with a high 40Ar/36Ar ratio. Reanalysis of the same samples has yielded a 191 Ma isochron with a low initial 40Ar/36Ar ratio. Although the isochron age is similar to the value previously assigned to the basalt, the result suggests that application of the K–Ar isochron method may improve the precision of K–Ar age determination considerably.
Magnetites from a new unidentified tephra source, Banff National Park, Alberta
Authors: Brewster G. R. , Barnett R. L.
Published: April 2011

Electron microprobe examination of glass-encased magnetites present within surficial volcanic ash deposits located in Banff and Jasper National Parks revealed five distinct magnetite populations. Three of the magnetite populations represented the Mazama, St. Helens Y, and Bridge River volcanic units previously identified in this area of the Canadian Rocky Mountains. The remaining two magnetite groups are characterized by glass-encased magnetites which have titanium oxide concentrations of 11.59 and 10.33%, values considerably higher than those characteristic of either Mazama, St. Helens Y, or Bridge River volcanic units. The high-titanium magnetites are of unknown provenance, and although the section provided no means for dating these volcanic groups, their distribution within the section suggests that they are older than Bridge River, and one group may predate Mazama.
Geochronology and tectonics of the northern Wolverine Complex, British Columbia
Authors: Parrish Randall R.
Published: April 2011

The Wolverine Complex is a metamorphosed and polydeformed sequence of Hadrynian clastic rocks that forms part of the Omineca Crystalline Belt in north-central British Columbia. Twenty-six Rb–Sr and K–Ar dates from an area at the north end of the complex are presented. Rb–Sr muscovite dates are the oldest, 70–166 Ma, and constrain the main metamorphic–deformational event to the Middle to Late Jurassic or earlier. K–Ar dates on muscovite and biotite are highly discordant and the dates of the minerals vary in the order Rb–Sr muscovite > K–Ar muscovite > K–Ar biotite. Many rocks show partial or complete homogenization of the isotopes during an early Tertiary thermal event, which has extensively reset K–Ar dates in part of the complex.The blocking temperatures of the isotopic systems when combined with the isotopic dates, other published dates, and estimated geothermal gradients, allow inference of thermal history and paleo-uplift rates. In the Chase Mountain area where the influence of Eocene resetting is either small or minimal, the rocks had cooled to 220 ± 40 °C by about 80 Ma ago or earlier. During their cooling from metamorphic temperatures of about 500 °C, they cooled at rates between 3 and 10 °C/Ma with an average minimum cooling rate of 4 °C/Ma. Using estimated geothermal gradients, corresponding uplift rates were 0.1–0.3 km/Ma or more.Because cooling of these rocks probably took place dominantly by advection resulting from uplift and erosion, a significant portion of the total uplift of these rocks was complete by the time they reached the biotite blocking temperature, 220 °C, at least 80 Ma ago. The predominantly Late Jurassic to Early Cretaceous uplift of the complex implied by these dates has important implications for regional tectonics and models of evolution for the Omineca Crystalline Belt and adjacent areas.
The eastern British Columbia earthquake of February 4, 1918
Authors: Rogers Garry C. , Ellis Robert M.
Published: April 2011

Based on damage, felt reports, and the number of instrumental observations, the February 4, 1918 earthquake in east-central British Columbia has in the past been assigned a location near Revelstoke and a magnitude of about 5. It is the largest historical earthquake that has occurred in the eastern part of the Canadian Cordillera. Re-examination of this earthquake using seismograms from Spokane (SPO), Saskatoon (SAS), and Ottawa (OTT), along with newspaper reports, indicates that the event was located approximately 150 km north of Revelstoke with a magnitude [Formula: see text] of 5.6 to 6.1. Examination of this and more recent events indicates that the Lg phase, which in general is not well observed at Cordilleran stations, may efficiently propagate along strike in this region.
The significance of the ammonoids Paratirolites and Otoceras in correlating the Permian–Triassic boundary beds of Iran and the People's Republic of China
Authors: Tozer E. T.
Published: April 2011

Chinese geologists have correctly interpreted the sequence in south China as including the youngest known marine Permian (Changxingian Stage), followed by earliest Triassic, strata with Otoceras (Griesbachian Stage, Gangetian Substage). Most of the Changxingian ammonoids are known only from China but one recently described species, Shizoloboceras fusuiense, is evidently congeneric with Paratirolites vediensis, which characterizes latest Permian (Dorashamian) beds of the south U.S.S.R. and Iran. This indicates that the youngest Permian beds of Iran and China are correlative. Alternative correlations which have been suggested, namely with Changxingian including beds younger than Dorashamian, and Gangetian correlative with Dorashamian, are rejected. Below the Changxingian is the Lopingian (or Wuchiapingan), characterized by a variety of early otocerataceans. Lopingian is more or less correlative with Dzhulfian.South China is the only known place where ammonoids of Dzhulfian (= Lopingian), Dorashamian (= Changxingian), and Gangetian (lowermost Triassic) ammonoids occur in a formational sequence. It does not necessarily follow that the Changxingian–Gangetian interval was one of faunal continuity and continuous deposition. Paleozoic-type brachiopods that locally occur in the basal metre of the Triassic formations do not establish that the relationship between the Permian and Triassic formations is transitional. The boundary between these formations is distinct. Probably, these brachiopods are derived from the subjacent Permian strata and are not natural members of the Triassic fauna.
A study of residual stress effects in sandstone
Authors: Lajtai E. Z. , Alison J. R.
Published: April 2011

Model tests were designed to simulate tectonic loading during cementation. Mixtures of sand, Portland cement, and water were subjected to uniaxial confined compression until solidification was complete. After unloading, the mortar blocks were tested to measure residual stress effects. Results of the model tests were compared with data measured on tectonically compressed sandstones.Sandstones which have been subjected to a tectonic force during the process of cementation preserve the direction of the force through a residual stress effect; on relaxation of the tectonic force a plane of low tensile strength, formed by preferentially oriented microcracks, develops perpendicularly to the direction of the tectonic force. The plane of microcracks is detectable by point- and line-loading, and through measurements establishing variations in compressional wave velocity and in stress–strain characteristics. A secondary weaker alignment of microcracks may develop in a plane perpendicular to the primary alignment. Load-parallel microcracks may form during the loading cycle. Alternatively, the lateral residual stresses may be large enough to produce microfractures parallel to the relaxing tectonic force. It is demonstrated that most microcrack alignments have macroscopic equivalents in the form of joints.
The distribution of surface magnetization in the English River and Kenora subprovinces of the Archean shield in Manitoba and Ontario
Authors: Hall D. H. , Coles R. L. , Hall J. M.
Published: April 2011

Surface magnetizations (induced and remanent) have been measured from almost 600 oriented cores collected over an area of 50 000 km2 covering portions of the Kenora, English River, and Red Lake subprovinces of the western Archean shield, between latitudes 49 and 51 °and longitudes 93 and 96°. These surface magnetizations reflect major geological provinces in the area, and throw light on the vertical distribution of magnetization and on the associated long wavelength magnetic anomalies. A major belt of high surface magnetization lies over the granodiorite–granite suite in the southern part of the English River subprovince and a major belt of low magnetization over the metasedimentary gneiss belt in the northern part of the subprovince. Remanent magnetization is prevalent, but is very unstable, apparently due to viscous remanence, and subparallel to the present-day geomagnetic field. This fact is of importance because rocks of this type, if deeply buried and at ambient temperatures above surface values, may lead to rather large intensities of magnetization. The magnetization is almost entirely due to magnetite, and titanomagnetite is only rarely encountered. The prevalent opaque minerals are magnetite, ilmenite, pyrite, pyrrhotite, and hematite.
Paleomagnetism of the Notre Dame Bay lamprophyre dikes, Newfoundland, and the opening of the North Atlantic Ocean
Authors: Lapointe P. L.
Published: April 2011

Lamprophyre dikes and the Leading Tickles dunite from Notre Dame Bay. Nfld., were sampled for a paleomagnetic study to define their age relationships and the tectonic implications of their emplacements. A single normal polarity direction (328°, +62°) was obtained by alternating field and thermal treatment, from 10 Cretaceous lamprophyre dikes. The paleopole (2I2°E, 67°N) derived from these dikes agrees with the cluster of North American Cretaceous paleopoles. On the other hand. I he Leading Tickles dunite recorded two magnetizations: one (206°, +32°) related to the time of intrusion and interpreted to be Ordovician; the second one (000°, +66°). an overprint, is related to the intrusion of the lamprophyre dikes and interpreted to be Cretaceous. The polarity, paleopole, radiometric age, and tectonic setting of the lamprophyre dikes when compared with the Isachsen dikes. N.W.T., suggest the opening of the North Atlantic Ocean was initiated in the Lower Cretaceous.
Combustion metamorphism in the Hat Creek area, British Columbia
Authors: Church B. N. , Matheson A. , Hora Z. D.
Published: April 2011

An area of several square kilometres of subbituminous coal at Hat Creek has been burnt in prehistoric times, probably as a result of spontaneous combustion. The product of this combustion is a yellow and reddish partly fused rock with high temperature minerals and chemical composition unlike volcanic rocks. The effect of thermal metamorphism within a few hundred feet of the burnt zone is an apparent slight increase in coalification levels above regional metamorphic grades.
40Ar–39Ar dating of multicomponent magnetizations in the Archean Shelley Lake granite, northwestern Ontario
Authors: Berger Glenn W. , York Derek
Published: April 2011

The Shelley Lake granite yields two paleopoles which could represent either of two scenarios: both poles were acquired early, SL2 at 2.7 Ga and SL1 during metamorphic overprinting near 2.6 Ga; pole SL1 was acquired first on cooling at 2.6 Ga while the SL2 antipole represents a late Proterozoic remagnetization. We chose biotite and K-feldspars from the available cores — biotite to record high temperature events and K-feldspars to detect any weak late Proterozoic reheating event. The biotite 40Ar/39Ar age spectrum is flat for 80% of the released Ar, indicating closure to Ar loss at 300 °C 2.60 Ga ago. The two feldspars show coincident minima in their age spectra at ca. 1.1 Ga, indicating a low-level heating event near that time with temperatures in the interval 150–300 °C and a duration less than ca. 1 Ma. Diffusion calculations show that the biotite could have been totally outgassed during the Kenoran orogeny and so we are unable to decide unambiguously between the two paleomagnetic scenarios. Nevertheless, we have detected a weak late Proterozoic thermal event that would otherwise have escaped notice and have thereby demonstrated the power of this dating technique when applied to K-feldspars from polymetamorphic terranes.
The significance of radiometric ages from the Gulquac Lake area of New Brunswick
Authors: Fyffe L. R. , Cormier R. F.
Published: April 2011

Radiometric dating of igneous rocks in the Gulquac Lake area of west-central New Brunswick confirms that rhyolitic volcanism and shallow granitic intrusive activity were closely associated in time. Rb–Sr whole rock isochrons yield an age of 409 ± 35 Ma for the volcanic rocks and 409 ± 25 Ma from the intrusive rocks (λ = 1.42 × 10−11 year−1). Structural relationships in the area show that emplacement of the granite coincided with an episode of intense faulting and uplift of sillimanite-grade Cambro–Ordovician terrain.The combined radiometric data indicate a minimum age for the Silurian–Devonian boundary of 409 ± 20 Ma.
Abundance and distribution of Hg and As in the polymetamorphic Precambrian basement of western Canada
Authors: Burwash R. A. , Culbert R. R.
Published: April 2011

mean values of Hg and As in the subsurface Precambrian basement of western Canada are 66 ppb and 1.42 ppm respectively (183 samples). Both figures are close to accepted crustal averages. Plots of cumulative frequency vs. log ppm approach log-normality, but with evidence of small populations enriched in Hg and As and 23% of samples depleted in Hg.Trend surface mapping shows that both Hg and As have regional highs and lows. Several types of multivariate analyses, when applied to petrologic and chemical variables, show that Hg was depleted during both cataclasis and K-metasomatism related to the Hudsonian orogeny. A model for Hg mobility is suggested, with the McDonald–Hay River fault system acting as a conduit for westward migration during the Hudsonian metasomatism. This northeast trending system bisects the Pinchi Lake district Hg ore deposits, which occur along the northwest trending Pinchi fault zone. Mesozoic reactivation of Hudsonian crystalline basement beneath the Omineca crystalline belt may have produced these economic deposits.Multivariate analysis of As values in relation to petrologic variables suggests that As is mobilized during the earlier stages of cataclasis, but finally concentrates locally along major shear zones. The As trend surface high coincides with the area of maximum mylonization along the McDonald fault zone. Concentration of As in major shear zones matches known distributions of niccolite, rammelsbergite, and arsenopyrite in several ore deposits of the western Canadian Shield.
Late Wisconsinan glacial stratigraphy and history of southeastern Manitoba
Authors: Teller James T. , Fenton Mark M.
Published: April 2011

The history of Late Wisconsinan glaciation in southwestern Manitoba has been established by identifying and correlating ice-laid lithostratigraphic units in the subsurface. Five Late Wisconsinan tills are defined on the basis of their texture, mineralogic composition, and stratigraphic position. These new formations are, from youngest to oldest, Marchand, Whitemouth Lake, Roseau, Senkiw, and Whiteshell Formations.Late Wisconsinan ice first invaded southeastern Manitoba 22 000 to 24 000 years ago. This Laurentide glacier advanced from the northeast across the Precambrian Shield and deposited the sandy Whiteshell and Senkiw tills, which contain abundant Precambrian rock fragments and minerals and few Paleozoic carbonate grains. Shortly after this, Keewatin ice advanced from the northwest over Paleozoic carbonate rocks, depositing the loamy carbonate-rich Roseau Formation throughout most of the area. This ice remained over southeastern Manitoba until after 13 500 years ago, when it rapidly retreated northward with Lake Agassiz on its heels. Two brief glacial readvances occurred. The first overrode Lake Agassiz lacustrine sediment as far south as central North Dakota shortly after about 13 000 years ago. The clayey Whitemouth Lake till was deposited in southern Manitoba at this time. After a rapid retreat, the ice briefly pushed southward over southeastern Manitoba about 12 000 years ago to just south of the International Boundary. The sandy carbonate-rich Marchand Formation was deposited at this time as the ice overrode its own sandy outwash. By 11 000 years ago, ice had disappeared from southeastern Manitoba.
Spontaneous carbonization of oxidized high-volatile coal by a lightning strike
Authors: Pearson David E. , Creaney Stephen
Published: April 2011

Five 1 m diameter pods of very high-rank coal (meta-anthracite) have been discovered in a normally high-volatile coal seam on Eagle Mountain, Elk Valley Coalfield, British Columbia. Two zones of colour alteration occur on the surface of local siltstones in the immediate vicinity of this occurrence and a thin overlying seam is reduced to ash. A study of the mineralogy of low-temperature coal ash (LTA) and also of the petrography of these high-rank pods provides evidence of localized temperatures of around 800 °C together with extreme rank gradients of 0.07% [Formula: see text]and supports a hypothesis that one or more lightning strikes were responsible for this occurrence.
Brachiopod assemblages from the Upper Permian and Permian–Triassic boundary beds, South China
Authors: Zhuo-Ting Liao
Published: April 2011

Uppermost Permian (Changhsingian) brachiopods are abundant and diverse in South China; thus far, 60 genera and 130 species have been described from the Changhsing Formation. Two distinctive brachiopod faunas can readily be identified from a single Changhsingian zone, the Peltichia zigzag–Paryphella sulcatifera Assemblage Zone. The abundance and diversity of the faunas are controlled to a large degree by lithofacies. The Peltichia zigzag, Spinomarginifera alpha fauna occurs in a limestone facies and the Paryphella sulcatifera, Paracrurithyris pigmea fauna occurs in a clastic (siliceous) facies. At many locations in South China, a "mixed fauna," containing Permian-like brachiopods and Lower Triassic ammonoids and bivalves, occurs directly above the Permian–Triassic boundary. The association of Permian elements mixed with Triassic elements suggests that deposition was more or less continuous across the Permian Triassic boundary and that an unconformity does not occur at the boundary in much of South China.
Oldest known Esox (Pisces: Esocidae), part of a new Paleocene teleost fauna from western Canada
Authors: Wilson Mark V. H.
Published: April 2011

Paleocene freshwater teleostean fishes from the Paskapoo and Ravenscrag Formations of Alberta and Saskatchewan, dated as Tiffanian or about 62 Ma old, include pike (Esox) remains twice as old as any previously known. Esox tiemani sp. nov. is an elongate, narrow-snouted pike, indicating that this body form may be primitive for some Recent pike species, and casting doubt on hypotheses of geologically more recent dispersal of pike into North America from Eurasia.The pike remains occur in the Paskapoo Formation with a teleost fauna having Eocene affinities and including osteoglossids, hiodontids, gonorynchids, cyprinoids, percopsids, and asineopids, none of which has previously been recorded from the Paleocene of North America.
The age and geological history of the Wollaston, Peter Lake, and Rottenstone domains in northern Saskatchewan
Authors: Ray G. E. , Wanless R. K.
Published: April 2011

Three U–Pb zircon and four K–Ar mineral age determinations from national topographic system (NTS) area Geikie River (SE) in northern Saskatchewan are presented and the geology of the region is described. The area lies within the Churchill Province of the Canadian Precambrian Shield and includes parts of the Wollaston, Peter Lake, and Rottenstone domains; the relationship between the geological histories of these domains and the age determinations is discussed. Zircon age measurements suggest a period of late Archean magmatism ca. 2500 Ma was responsible for both the Wollaston domain granitic basement and a suite of basic plutons in the adjoining Peter Lake domain.The overall lithological differences of the presumed lower Proterozoic supracrustal rocks in the region are examined in the context of a plate tectonic model. This invokes late Archean continental rifting accompanied by limited volcanism close to the present Needle Falls Shear Zone, followed by continental separation and the generation of an Aphebian ocean basin. Deposition of shelf and deeper water sediments along the trailing edge of the Wollaston domain continental margin was followed by reversal of plate movement, oceanic subduction, and the formation of an island-arc complex. This marked the start of the Hudsonian Orogeny and was accompanied by the development of successive generations of granitic material, including the Wathaman batholith. The regional emplacement of this batholith ca. 1865 Ma ago is compared to other volcano-plutonic belts described elsewhere along Cordilleran-type continental margins.
Correlation of Cambrian–Ordovician boundary between Europe and North America: new data from western Newfoundland
Authors: Fortey Richard A. , Skevington David
Published: April 2011

The Cow Head Group in western Newfoundland includes a record of continuous graptolite evolution across the Cambrian–Ordovician boundary. In sections at Broom Point, interbedded breccias contain blocks with rich platform trilobite faunas which give a complete succession of North American zones. The stratigraphic relationship between graptolites and trilobites clearly establishes that the base of the type Tremadoc Series lies above that of the Missisquoia Zone. The sequence of earliest planktonic graptolites is the most complete known and serves to remove objections to the selection of Dictyonema flabelliforme, or one of its subspecies, as an index for the base of the Ordovician System.
Paleomagnetism of the Karmutsen basalts from southeast Vancouver Island
Authors: Schwarz E. J. , Muller J. E. , Clark K. R.
Published: April 2011

One hundred and twenty oriented drill cores were collected from 20 sites in the Karmutsen basalts of Karnian age in the eastern part of Vancouver Island. Alternating field and thermal demagnetization studies reveal stable endpoint directions in 13 sites which fall into the following groups: (1) northwest-up (four sites); (2) north-up (four sites); (3) north-northeast-down (four sites); and (4) easterly-up (one site). The northwest-up direction is observed in the least altered samples with only pure magnetite of high coercive force and blocking temperatures as a carrier. The north-up direction, which shows streaking in a east–west sense, is also observed in (other) least altered specimens, and shows a complex magnetic mineralogy with lower coercivity. The north-northeast-down direction occurs in definitely more altered specimens, and some specimens show a northerly flat magnetization at the end of the blocking temperature range. The easterly-up direction is poorly defined but may correspond to the direction reported for the Nicolai Greenstones in Alaska. The relation between these groups of directions is not clear, and only in a few specimens an indication for the separation of remanence components has been observed. The available evidence indicates that a northerly component is probably the oldest and that the northwest-up magnetization may represent this component. The pole position calculated for this magnetization is 90°E, 21°N which is about 40°S of the Triassic pole position for cratonic North America. The discrepancy would be larger still if the northwest-up direction is a single component secondary direction. The discrepancy can, of course, be explained by a northward shift of the Karmutsen from a source area near 10°N with or without a sinistral rotation.
Further immobile element data from altered volcanic rocks, Timmins mining area, Ontario
Authors: Vies J. F. Da , Whitehead R. E. S.
Published: April 2011

The relatively immobile trace elements TiO2, Zr, and Y prove useful for determining the original identity of, and for correlating, metamorphosed and metasomatized Archean volcanic rocks. More than 95% of 366 samples from the Timmins area were found to correspond to the lithostratigraphic units determined independently from structural and stratigraphic decisions based on lithology and top determinations. Trace-element data can be used for distinguishing volcanic units and as an aid in correlation regardless of any petrogenetic interpretations.
A Rb–Sr isotopic study of the Archean rocks of the eastern Lac Seul region, English River subprovince, northwestern Ontario
Authors: Wooden Joseph L. , Goodwin Alan M.
Published: April 2011

Rb–Sr whole-rock data for the gneissic and granitic rocks of the eastern Lac Seul region, when combined with the U–Pb zircon dating of Krogh, document a history of multiple intrusion for the area. The oldest rocks are the Sen Bay plutonic complex gneisses which have complex Rb–Sr systematics. Interpretation of the Rb–Sr data yields model ages of 3000–3100 Ma which are in good agreement with a zircon age of 3040 Ma. The next oldest rocks are trondhjemitic–granodioritic gneisses with a Rb–Sr age of 2780 ± 90 Ma. The initial Sr ratio (I) of 0.7009 ± 4 for these rocks suggests that this age approximates the time of intrusion and that the magma was derived from lower crustal rocks with a very short residence lime in the crust. Following a period of deformation and metamorphism, granodioritic to granitic dikes, sills, and small plutons were intruded between 2660 and 2560 Ma ago. I values for these racks range from 0.7019–0.7027. If the I values of these rocks represent the source region for the granitic magmas, then one explanation for the I values would be that the magmas were derived from a source region of mixed lithology and age. The Sen Bay plutonic complex is considered to represent an earlier cycle of crustal formation which is distinct from a later 2800–2550 Ma old cycle which dominates much of the Superior Province.
The Dellwood knolls and their role in triple junction tectonics off northern Vancouver Island
Authors: Riddihough R. P. , Currie R. G. , Hyndman R. D.
Published: April 2011

The Dellwood knolls are two small topographic features on the ocean floor off northern Vancouver Island. They have been proposed as a spreading centre connecting the Explorer ridge to the Queen Charlotte fault and the location of a triple junction between the Pacific, American, and Juan de Fuca plate systems.Detailed geophysical surveys and ocean-bottom seismometer deployments confirm that they are the site of active seismicity and recent volcanism. Modelling of the magnetic anomaly field shows that it is almost entirely produced by normally magnetized material, supporting geological evidence that the knolls are probably less than 1 Ma old. Although the two knolls are separated by a narrow valley with some downfaulting, they do not form a clearly linear spreading rift.Assessment of their role in the plate tectonics of the region suggests that spreading at the knolls was initiated around 1 Ma ago in crust now 4.5 Ma old as part of a complex, northwesterly ridge migration process at the northern end of the Explorer ridge. Reconstruction of this process, which involves asymmetric spreading and ridge jumping, provides an explanation for the creation of the associated Paul Revere and Winona ridges.
A Rb/Sr age for the Cretaceous–Tertiary boundary (Z coal), Hell Creek, Montana
Authors: Baadsgaard H. , Lerbekmo J. F.
Published: April 2011

A Rb/Sr isochron age of 63.6 ± 0.4 Ma for bentonite biotite and sanidine at Hell Creek, Montana, dates a palynofloral change marking the Cretaceous–Tertiary boundary in west-central North America. Extensive Rb and Sr variations caused by alteration of the biotites does not seem to unduly affect the presumed crystallization age of the biotite.
Positive test of the paleomagnetic method for estimating burial depth using a dike contact
Authors: Symons D. T. A. , Hutcheson H. I. , Stupavsky M.
Published: April 2011

Detailed magnetic measurements were made on specimens from profiles across the contact zones of two unmetamorphosed Miocene diabase dikes. The dikes cut Cretaceous plutonic rocks of the Coast Crystalline Complex near Bella Bella, British Columbia. The dikes feed flat-lying basalts that outcrop nearby. This indicates post-Miocene uplift is less than 1 km in the area. Alternating field demagnetization, magnetic susceptibility, thermal demagnetization, and magnetic force balance measurements were made on the specimens. From them, the distance from the contact and the maximum reheated temperature of the magnetic hybrid zone were determined. Results are reported for the Thorburne Island contact only because the other contact had unsuitable remanence characteristics. Using standard conduction heat flow equations the ambient temperature of the host rock at the time of intrusion was found to be 18 ± 5 °C giving a determined depth for the present erosion surface at the time of intrusion of 0.3 ± 0.1 km. This is the first positive test of the magnetic paleogeobarometric method.
Two hundred and twenty million years of Archean evolution: a zircon U–Pb age stratigraphic study of the Uchi–Confederation Lakes greenstone belt, northwestern Ontario
Authors: Nunes P. D. , Thurston P. C.
Published: April 2011

Three metavolcanic units in the Uchi–Confederation Lakes greenstone belt have been dated by the zircon U–Pb method. Ages obtained reveal a time interval of [Formula: see text] separating the cycle I crystal tuff (2958.6 ± 1.7 Ma) from the cycle III rhyolite ([Formula: see text]). A cycle II rhyolite about 2794 Ma old lies between the other two units. Uranium-rich xenocrystic cores occur in the cycle I zircons and are indirect evidence of preexisting sialic material.A metamorphosed granodiorite, intrusive into the cycle III rhyolite, is about the same age as the rhyolite. A post-metamorphic quartz monzonite pluton is dated at 2729.6 ± 1.3 Ma. A period of dynamothermal metamorphism in this portion of the Superior Province indirectly dated at [Formula: see text] reflects the Kenoran orogeny.
Measurement and evaluation of the acoustic reflectivity of the sea floor
Authors: Parrott D. R. , Dodds D. J. , King L. H. , Simpkin P. G.
Published: April 2011

The effect of seabed character on the distribution of acoustic energy reflected from the seabed was studied using digitized data from a high resolution, broad band, seismic source (Huntec Deep Towed Seismic System, Reflected energy was measured in two lime windows representing the lop metre of the seabed, and normalized to correct for operational variables and spreading losses due to propagation in the water column. These energy values were used to calculate acoustic reflectivity as a percentage of the energy content of the original outgoing pulse, and were displayed as continuous profiles alongside the seismic section. Most of the surficial geology formations on the Scotian Shelf, established from previous investigations, are seen to have a characteristic range in reflectivity. Thus, the acoustic reflectivity profiles enhance the seismic section by providing quantitative information on the nature and distribution of the lithology of the seabed in addition to the stratigraphic information which is normally obtained.
Geology of the Coquihalla Volcanic Complex, southwestern British Columbia
Authors: Berman Robert G. , Armstrong Richard Lee
Published: April 2011

The Coquihalla Volcanic Complex consists of calc-alkaline acid to intermediate extrusive and intrusive rocks that have an areal extent of roughly 30 km2 near Hope, British Columbia. The oldest and most voluminous members of the complex are rhyolitic pyroclastic rocks that have an overall thickness of approximately 1600 m. Later igneous activity produced numerous andesite to dacite domes, dykes, and sills. A late stage diorite to quartz diorite stock forms the core of Coquihalla Mountain.Pyroclastic rocks rest unconformably on the Jurassic to Cretaceous Eagle pluton and Lower Cretaceous Pasayten Group rocks. Monolithologic avalanche breccias were deposited against a fault scarp of uplifted Pasayten Group rocks in the southwestern portion of the map area. In the southeastern part of the area, monolithologic granitic avalanche breccias formed in response to lilting and uplift of the underlying Eagle pluton as the basin subsided.Three K–Ar dates average 21.4 ± 0.7 Ma, and are concordant with a Rb–Sr isochron (22.3 ± 4 Ma with initial 87Sr/86Sr = 0.70370 ± 0.00008) based on seven whole-rock samples which span the entire compositional range of the suite. These results indicate that the Coquihalla Volcanic Complex is coeval with calc-alkaline centres in the Pemberton Volcanic Belt (PVB).The north-northwest trend of the PVB is parallel to, but roughly 75 km east, of the Pleistocene to Recent Garibaldi Volcanic Belt (GVB). Both volcanic belts appear to have formed as a result of subduction of the Juan de Fuca plate. Genetic models must explain the easterly displacement of the PVB, the development of larger volumes of rhyolitic compositions in this belt as compared to the GVB, and the decrease in age of igneous rocks from south to north within the PVB.
Geochemistry of Archean meta-igneous rocks, Lake Despair area, Wabigoon Subprovince, northwestern Ontario
Authors: Longstaffe Fred J. , McNutt Robert H. , Schwarcz Henry P.
Published: April 2011

The Lake Despair area, northwestern Ontario, is underlain by a series of igneous and meta-igneous rocks including mafic and felsic metavolcanic rocks, gneisses (Footprint gneiss), and plutonic granitoids (Jackfish Lake Plutonic Complex; Northwest Bay Complex). The metavolcanic sequence consists of a bimodal suite of interlayered metabasalts of tholeiitic character and metadacites with metamorphic grade ranging from greenschist to amphibolite facies. Trace element studies of the metabasalt, while indicating an oceanic provenance, do not uniquely distinguish between possible oceanic tectonic settings. The metadacites, the Footprint gneiss, and the Northwest Bay Complex are chemically similar to the high Al tonalitic rocks common in other Archean terrains. The Footprint gneiss, which forms part of the gneissic core of the Rainy Lake batholith, was derived from an igneous parent, and was quasi-isochemically metamorphosed.The youngest major intrusion, the Na-alkalic Jackfish Plutonic Complex, is composed of hornblende diorite and monzodiorite with minor leucodiorite, quartz monzodiorite, granodiorite, and Na-syenite. The diorite and monzodiorite crystallized from an intermediate magma formed by partial melting of a garnet and (or) amphibole-rich basaltic parent. Remaining residual liquids, enriched in alkalis and silica by amphibole fractionation, crystallized to form the more leucocratic rock types. Perthitic microcline megacrysts, characteristic of the quartz monzodiorite and granodiorite, formed near the end of magmatic processes. The Na-syenite was emplaced as a separate pulse of magma or possibly was produced by the interaction of alkalis and the upper portions of the solidified rim of the magma chamber.
Age of Ag–Pb–Zn mineralization, Keno Hill – Galena Hill area, Yukon Territory
Authors: Sinclair A. J. , Tessari O. J. , Harakal J. E.
Published: April 2011

Whole-rock K–Ar model ages of Keno Hill quartzite from small stockwork zones adjacent to Ag–Pb–Zn veins (Husky and Keno deposits) indicate that mineralization occurred at about 87 Ma. Regionally metamorphosed country rocks more distant from stockwork zones have potassium–argon model ages that are slightly but significantly older, indicating that mineralization postdated the main phase of Late Cretaceous regional metamorphism.