bluuebunny/crossref_metadata_2025 huggingface dataset:
Pleistocene stratigraphy of the Saskatoon area, Saskatchewan, Canada: an update
Authors: Christiansen E. A.
Published: April 2011

Pleistocene deposits in the Saskatoon area are divided into the Sutherland and Saskatoon groups. The Sutherland Group is divided into the Mennon, Dundurn, and Warman formations, and the Saskatoon Group is divided into the Floral and Battleford formations. The Floral Formation is subdivided into the lower till, the Riddell Member, and the upper till. Each formation is composed of a sequence of deposits, including basal proglacial sediment, till, upper proglacial sediment, and nonglacial sediment. Each formation is defined primarily on the basis of carbonate content and stratigraphic position of its till, and commonly it is bounded by weathered zones and (or) nonglacial sediments. The Sutherland Group is pre-Illinoian in age, and the lower till of the Floral Formation is Illinoian in age. The Riddell Member, between the lower and upper tills of the Floral Formation, is late Rancholabrean, probably Sangamon, in age. Radiocarbon ages of sediments lying between the upper till of the Floral Formation (Early Wisconsin) and the Battleford Formation (Late Wisconsin) range from more than 38 000 to 18 000 BP. The dissipating ice sheet margin stood in the vicinity of Saskatoon about 12 000 BP.
Kinematical and rheological evolution of a crustal-scale ductile thrust zone, Central Metasedimentary Belt, Grenville orogen, Ontario
Authors: Hanmer Simon , McEachern Sally
Published: April 2011

The Central Metasedimentary Belt boundary thrust zone is a 10 km thick, 200+ km long, stack of crystalline thrust sheets, enclosed by an anastomosing network of ductile thrust zones, formed at mid- to deep-crustal depths in the southwest Grenville orogen, Ontario. It has behaved as a coherent upper amphibolite facies thrust zone, accommodating northwestward transport of the Central Metasedimentary Belt, the largest lithotectonic entity in this part of the orogen, by coherent and contemporaneous displacements. The earliest thrusting was well under way by ca. 1.19–1.18 Ga and the boundary thrust zone was reactivated at ca. 1.08–1.05 Ga. The early thrusting records the closure of a back-arc basin within the Central Metasedimentary Belt, which closed at ca. 1.19–1.18 Ga. The younger thrusting may reflect continental collision to the southeast of the exposed Grenville and represent intraplate reactivation of the boundary thrust zone, which acted as an older, crustal-scale zone of weakness. Transverse mid- to deep-crustal thrusting was apparently contemporaneous with longitudinal (orogen-parallel) shearing at higher structural levels. The rheological behaviour of the deforming media may have influenced the localization of both the upper and lower limits of the boundary thrust zone at the time of its initiation. The upper limit coincides with a chain of relatively stiff metagabbro bodies, which may have acted as a barrier to the upward migration of fluids responsible for syntectonic nephelinization at the top of the thrust zone.
Interaction of submarine volcanic and high-temperature hydrothermal activity proposed for the formation of the Agrokipia, volcanic massive sulfide deposits of Cyprus
Authors: Hall James M.
Published: April 2011

The results of drilling near the spreading-ridge-type, volcanic-hosted, massive sulfide deposits of Agrokipia, Cyprus, are described. Mineralization and associated argillic hydrothermal alteration occur over intervals of 5–130 m and at depths of 80–230 m beneath the original surface of the oceanic crust. Mineralization occurs in massive flows that probably represent a locally ponded sequence up to 300 m thick. Abundant glass–aphanitic basalt transitions are present from about 100 m below the surface of the ponded sequence, with glass abundances locally reaching 60% of the section. A novel hypothesis, involving the presence of active, high-temperature hydrothermal vents beneath the cooling ponded sequence, with the passage of hydrothermal fluids through the still molten lava, is proposed to account for the observations. While this hypothesis is reasonable, the inferred processes have not, as yet, been demonstrated under either laboratory or field conditions. The seafloor expression of this system was probably one of widely distributed, low-temperature, fluid emission over the surface of a lava pond in the axial graben of a spreading ridge.
Geological interpretation of a high resolution reflection seismic survey at the Buchans mine, Newfoundland
Authors: Thurlow J. G. , Spencer C. P. , Boerner D. E. , Reed L. E. , Wright J. A.
Published: April 2011

Sixteen kilometres of high resolution Vibroseis reflection seismic data have been acquired in the vicinity of the former Buchans mine. Direct identification of the cause of several reflectors is possible because the geology is tightly constrained by underground workings and drill holes both of which locally exceed 1 km depth. Many of the mine-scale thrust faults are imaged as reflectors but conformable and intrusive contacts generally responded poorly. A significant shallow-dipping thrust, the Powerline Fault, is recognized below the orebodies and traced throughout the Buchans area, primarily as a result of the seismic survey. It truncates ore stratigraphy and forms the floor thrust of a large duplex–stack, which hosts all the orebodies. Its presence has negative implications for exploration in the immediate mine area. Several lines of evidence suggest that this fault has a significant component of out-of-sequence movement. A strong reflector 4.5 km below Buchans is correlated with the surface expression of the Victoria River Delta Fault, an important regional structure, newly recognized southeast of Red Indian Lake. This shallow, north-dipping sole thrust forms the structural base of the Buchans Group and brings it above a younger fossiliferous Llanvirn volcanic sequence. This fault is not itself the Red Indian Line but is one of a series of faults that collectively effect substantial geological contrasts in central Newfoundland. The seismic survey was a cost-efficient means of gaining knowledge of Buchans structure, which might otherwise have been acquired at much higher cost and over a longer period of time.
The application of reflection seismology to the investigation of the geometry of near-surface units and faults in the Blake River Group, Abitibi Belt, Quebec
Authors: Adam Erick , Milkereit Bernd , Mareschal Marianne , Barnes Arthur E. , Hubert Claude , Salisbury Matthew
Published: April 2011

Reprocessing of part of a Lithoprobe high-resolution seismic reflection line across the southern part of the Abitibi Belt has improved the imaging of shallow reflections and allowed correlation of the data with surface geology. Enhancement of early reflections was accomplished by focusing on the high-frequency content of the data. This improved resolution of reflections at two-way traveltime as early as 0.3 s and attenuated noise such as shear waves. The shallow reflections are interpreted as impedance contrasts at the contact between a metadiabase–diorite body and metavolcanics rocks. Offsets of the reflectors correlate with faults mapped at the surface and indicate a downdropped block, which may be of interest for mineral exploration.
Canadian Cordilleran tectonics: from geosynclines to crustal collage
Authors: Monger James W. H.
Published: April 2011

The major contributions by the Geological Survey of Canada in the Canadian Cordillera—systematic mapping and definition of the regional geological framework—led directly to tectonic syntheses that attempted to explain its origin. From the late 1800's until the 1960's, Cordilleran mountain building was viewed as the end result of geosynclinal deposition. Early workers felt that a connection existed between mountain building and the Pacific basin, but its nature was never clear because little was known about ocean basins and their relationships to continental margins. In the 1950's, the nature of the oceanic lithosphere and ocean–continent relationships became better known; the knowledge led to formulation of the plate-tectonic hypothesis in the 1960's, a time fortuitously coinciding with completion, by the Survey, of most of the regional geological mapping (scale 1: 250 000). Geosynclinal rock units were reinterpreted in terms of their possible modern analogues (oceanic, island-arc, continental shelf – slope assemblages) and paleontological and paleomagnetic studies were used to support a mobilistic view of Cordilleran paleogeography, rather than the relatively fixed paleogeography tacitly assumed in earlier interpretations. In contrast with deterministic geosynclinal theory, it was recognized that plate-tectonic processes applied over a long time have enormous potential to create disorder; the result is an orogenic collage to be analyzed as a series of time – space events each of whose geodynamic settings may have been very different from one another. This aspect is especially important in the long-lived Cordillera, which was initiated as a continent–ocean boundary in latest Proterozoic time, evolved through the entire Phanerozoic, and today is a convergent-transform continen – ocean plate margin. Interactions between various oceanic plates and the North American plate, shown by the Cordilleran record of accretionary complexes, as well as results of possible arc–continent collisions and continental margin arc magmatism, formed new continental crust.
Optimum microfossil sequences and cyclic sediment patterns in Early Cretaceous pelagic strata
Authors: Gradstein Felix M. , Huang Zehui , Kristiansen Inger L. , Ogg James G.
Published: April 2011

Three sequencing methods were used to calculate the most likely biozonation and the periodicity of sedimentary cycles in Lower Cretaceous pelagic strata of the Atlantic and Indian oceans.A database was built of 378 first and last stratigraphic occurrences of calcareous nannofossils, dinocysts, foraminifers, and geomagnetic reversals in highest Jurassic through Lower Cretaceous deep marine strata at 10 Atlantic Ocean and 3 Indian Ocean drilling sites. There are 135 different events in total, about one third of which are unique to either ocean. Using the complete data set, the quantitative stratigraphy methods STRATCOR and RASC calculated closely comparable optimum sequences of average first- and last-occurrence positions. The preferred zonal solution, based on the STRATCOR method, includes 56 events, each of which occurs at three or more sites. The events comprise 6 geomagnetic reversals, 25 nannofossils, 5 planktonic foraminifera, 8 benthic foraminifera, and 12 dinocysts occurrences. Nine assemblage zones have been recognized of Tithonian through Albian age. All but 2 of 18 nannofossil events in the Atlantic Ocean optimum sequence were reported in the same stratigraphic order in a standard Mesozoic nannofossil zonation.Our quantitative examination, using Walsh spectral analysis, of the Lower Cretaceous cyclic sequences at three Deep Sea Drilling Project (DSDP) sites in the Atlantic Ocean generally supports the hypothesis that they are the product of cyclic climatic changes controlled by the Milankovitch orbital cycles. The peaks in the power spectra usually can be related to obliquity and precession cycles; some peaks seem to correspond to the eccentricity cycle. Obliquity seems to be the most important and persistent orbital element responsible for cyclic sedimentation in the Early Cretaceous Atlantic Ocean.The actual pelagic sedimentation rates were calculated for some cores using the results of spectral analysis. The correlation of the actual pelagic sedimentation rate with cyclic patterns and the occurrence of calcareous turbidites indicate that the changes in cycle pattern are the reflection of changes in the oceanographic setting. The changes in oceanographic setting are related to relative-sea-level fluctuations. The intervals dominated by laminated limestone were deposited during higher sea-level periods.
Holocene geomorphology and stratigraphy of the lower Falcon valley, Dinosaur Provincial Park, Alberta, Canada
Authors: O'Hara Sarah L. , Campbell Ian A.
Published: April 2011

A tributary of the Red Deer River in Dinosaur Provincial Park, southern Alberta, contains evidence of a sequence of valley cutting and the deposition of three alluvial fills and one eolian deposit. With the exception of the eolian deposit and minor amounts of Shield and Cordilleran rocks, the sediments are derived from local bedrock. Incision of the bedrock valley occurred in the early postglacial period about 14 000 – 12 000 BP by rapid drainage of proglacial lakes and meltwaters. The valley was subsequently partly infilled as locally fed stream discharges declined during the early to middle Holocene. By 6000–5000 BP alluvial fans had formed along the base of the valley walls. Fan development was followed by two phases of stream entrenchment and alluvial deposition, including the most recent phase of cutting and filling that began approximately 800 BP. The erosional and depositional events may reflect climatic changes as inferred in lacustrine deposits in southern Alberta and in valleys elsewhere in the Great Plains. Glacioisostacy conditions, however, at least in the early Holocene, may have had profound effects on stream base levels.
Late Ordovician mass extinction in the Selwyn Basin, northwestern Canada: geochemical, sedimentological, and paleontological evidence
Authors: Wang K. , Chatterton B. D. E. , Attrep Jr. M. , Orth C. J.
Published: April 2011

We present a detailed study of the trace element and stable isotope geochemistry, sedimentology, and fossil distributions in two Avalanche Lake (AV4B, AV1) Ordovician–Silurian boundary sections in the Selwyn Basin. Trilobites and conodonts indicate a profound extinction at the end of the Ordovician, which is constrained stratigraphically within a <60 cm interval at AV4B. Facies analysis suggests that the extinction interval coincides with the maximum shallowing (low stand of sea level), which was probably caused by a galcioeustatic regression induced by the Late Ordovician Gondwanan glaciation. The extinction crisis is also signalled by the change in carbonate δ13C: a sudden "Strangelove ocean" δ13C excursion (>3‰ in magnitude) is recorded in the extinction interval. Iridium abundances (<0.051 ppb) in the extinction interval are low and fail to provide evidence for an impact. The highest Ir abundance is found to be associated with reduced sedimentation in a condensed horizon. Cerium anomalies indicate a short period of basin ventilation in the otherwise anoxic Selwyn Basin. The extinction occurred during the time of this basin ventilation, which was probably caused by the cold climate during the glaciation. The ventilation may have triggered upwelling of the deep water through vertical advection, bringing up toxic material, poisoning the upper-water photic zone, and causing the extinction.
Massive sulfide deposits of the Noranda area, Quebec. V. The Corbet mine
Authors: Barrett T. J. , MacLean W. H. , Cattalani S. , Hoy L.
Published: April 2011

The Corbet deposit is located in the upper part of the Flavrian andesite, the lowest volcanic formation within cycle III of the Noranda Central Mine Sequence. The deposit consisted of one main lens of massive sulfides, and several smaller lenses, and contained 2.7 × 106 t of mineable ore at 2.92% Cu, 1.98% Zn, 20.6 g/t Ag, and 1.0 g/t Au. The orebody had a massive pyrrhotite–chalcopyrite core, which passed laterally into massive pyrite–sphalerite. The northwestern part of the ore-body is overlain by 50–100 m of Flavrian andesite, whereas the southeastern portion is overlain by Northwest rhyolite.Lavas within the Flavrian andesite and the lower Northwest rhyolite are low in K2O (<0.5%), and are partly of tholeiitic affinity, and partly of transitional affinity. The tholeiitic volcanic series has Zr/Y ratios of 2.8 to 4.5, whereas the transitional series has Zr/Y ratios of 4.5 to 7.1. The two series are also distinct in plots of Nb–Zr, Yb–Zr, Nb–Y, and the rare earth elements. These data indicate that two slightly different magma types existed in the chamber that fed this portion of the extrusive Central Mine Sequence.Alteration is most intense in the breccias of the upper Flavrian andesite, within ~50 m of the orebody, and is almost entirely chloritic. There is no zone of silicification, although moderate sericitization occurs lateral to and above the orebody. Mass-change calculations indicate that large amounts of SiO2 and CaO + Na2O were leached from the rocks by hydrothermal solutions, whereas large amounts of hydrothermal FeO and seawater MgO were added.Oxygen isotope depletions are among the largest in the Noranda area and extend laterally and vertically up to 300 m from the orebody. Within this volume, δ18O values of altered volcanic rocks have been decreased to values as low as 2 to −2‰. These depletions result from reactions with seawater at ~ 250–300 °C and from strong silica leaching, as indicated by mass-change calculations. The hydrothermal system at Corbet can be assessed using two lithogeochemical tools: calculated mass changes and oxygen isotope ratios, both of which are sensitive to water–rock ratio and temperature.
Stable-isotope, fluid-inclusion, and mineralogical studies relating to the genesis of amethyst, Thunder Bay Amethyst Mine, Ontario
Authors: McArthur J. R. , Jennings E. A. , Kissin S. A. , Sherlock R. L.
Published: April 2011

The Thunder Bay Amethyst Mine exploits a vein system in which the main zoned sequence consists of chalcedony, colorless quartz, and three to four stages of amethyst. The main sequence surrounds fragments of a brecciated earlier sequence containing chalcedony, colorless quartz, and prasiolite, which appears to be thermally bleached amethyst. The vein system occupies a fault in Archean granodiorite and is associated with a narrow zone of chloritic and hematite alteration overprinted by weak argillic alteration. Fragments of Proterozoic (1339 Ma) Sibley Group rocks occur in the vein system, indicating the former presence of a shallow cover during deposition of quartz and limiting the maximum age of the deposit. These downfallen fragments and the abundance of vugs indicate near-surface formation of the deposit.Main-stage fluid-inclusion homogenization temperatures are in the range from 91.2 to 40.9 °C (mean 68.4 °C) in amethyst, whereas in colorless quartz homogenization temperatures range from 146.5 to 114.7 °C (mean 132.1 °C). Eutectic temperatures fall in three ranges with means of −50.9, −48.7, and −43.9 °C, which are related to paragenetic position and indicate an NaCl–CaCl2–H2O system, with possible additional components in later inclusions. Salinities in amethyst-hosted inclusions decrease in the growth direction from 22.9 to 15.3 equiv.wt% NaCl.Trace sulfide and other mineral inclusions indicate a trend of decreasing Eh and pH from an initially rather oxidized (sulfate stable) to a reduced (sulfide stable) condition during deposition. Sulfur isotopic composition in pyrite and chalcopyrite ranges from δ34S = −0.4 to −1.4‰ and is similar to values obtained from lead–zinc–barite in other vein deposits surrounding the Sibley depositional basin. Oxygen isotopes in quartz range from δ18O = +12.7 to +17.1‰, corresponding to δ18O(H2O) = −2.1 to −12.8‰ using fluid-inclusion temperatures. Fresh quartz monzonite wall rock (δ18O = +11.82‰) and altered quartz monzonite (δ18O = +11.01‰) do not seem to have undergone significant isotopic exchange with the hydrothermal solution, and the trend of isotopic change does not account for the trend of δ18O(H2O) determined in quartz. Rather, mixing of local meteoric water with a basinal brine appears to explain the observed trend.The amethyst deposits are believed to have been formed by basinal brines expelled from Sibley Group sediments. The brines dissolved silica by alteration processes accompanying their passage through granitic basement rocks in basin marginal faults. Amethyst was deposited on mixing with meteoric water. The temperature interval for amethyst formation appears to be restricted to less than ~90 °C. Temperatures causing thermal bleaching of amethyst are as low as 145 °C, and possibly 115 °C, as indicated by these results. This low range of temperature is not in agreement with bench-type experiments indicating bleaching at hundreds of degrees Celsius.
Hydrothermal zircon and baddeleyite in Val-d'Or Archean mesothermal gold deposits: characteristics, compositions, and fluid-inclusion properties, with implications fortiming of primary gold mineralization
Authors: Kerrich Robert , King Robert
Published: April 2011

Zircon and baddeleyite occur within quartz–tourmaline veins at four gold deposits in the Val-d'Or district of the Archean Abitibi Southern Volcanic Zone. Host rocks have experienced intense metasomatic enrichment of Zr, Hf, Y, and rare earth elements. The zircons contain primary inclusions of quartz, tourmaline, pyrite, albite, K-mica, scheelite, and gold, and gold occurs in primary fluid inclusions in zircons. Magmatic zircons in host rocks do not have this suite of inclusions; consequently a wall-rock inheritance model for the vein zircons is implausible. Compositionally, the zircons feature pronounced interzone and intergrain variations of Hf, Y, Yb, Th, and U, and sporadic anomalous Ce contents of ~ 1100 ppm, distinct from magmatic counterparts. Two principal types of primary fluid inclusion occur in the vein zircons. Type 1 H2O–CO2 inclusions have low salinities, variable quantities of CO2 and homogenization temperatures of 260–380 °C, and type 2 CO2 rich inclusions contain minor H2O and CH4. The vein zircons coprecipitated at 260–380 °C and ~ 2 kbar (1 kbar = 100 MPa) with coexisting minerals of undisputed hydrothermal origin, such as vein quartz and gold. In the Superior Province, mesothermal gold deposits are related in space and time to translithospheric structures that mark the diachronous accretion of allochthonous subprovinces from north to south between ~ 2710 and 2680 Ma. Consequently, vein zircon ages of ~ 2680 Ma record the primary mineralizing event, whereas aberrantly young ages for rutile, titanite, scheelite, and micas in the same vein systems, that scatter over 2630–2579 Ma, reveal the age of secondary remobilization events.
Changes in the silt- and clay-size mineralogy of sediments at Ocean Drilling Program site 645B, Baffin Bay
Authors: Andrews J. T.
Published: April 2011

Site 645B, Ocean Drilling Program (ODP) leg 105, was cored in 2010 m water depth off the eastern margin of Baffin Island. A 279 m core was dated as extending back to ca. 2 Ma. Samples of sediment were analyzed for their silt- and clay-size mineralogy using X-ray diffraction techniques. Constrained cluster analysis on these data defined three units, which indicated that significant changes in mineralogies occurred at approximately 75 m below sea floor (bsf) (ca. 0.5 Ma) and 155 m bsf (ca. 1.15 Ma). These boundaries coincide closely with units IA–IB and IB–II as designated in the ODP shipboard reports, and which were based on detrital carbonate and sand contents. Unit II (1.2–2 Ma) is characterized by zero clay-size calcite and high amounts of clay-size smectite and silt-size mica. Unit IB (0.5 – 1.15 Ma) is noteworthy for the first presence of clay-size calcite, high amounts of detrital dolomite, and a peak in clay-size kaolinite. The uppermost unit IA (0–0.5 Ma) is characterized by consistently high values of clay-size dolomite and sand. Compared with sediments on the adjacent eastern Baffin Island shelf and fiords, the sediments at ODP site 645B are enhanced in the amounts of carbonate, smectite, and kaolinite, and depleted in both silt- and clay-size mica and feldspar. This pattern suggests a limited supply of sediment is transported from Baffin Island into Baffin Bay.
Geology, geochemistry, and geochronology of the central Giants Range batholith, northeastern Minnesota
Authors: Boerboom Terrence J. , Zartman Robert E.
Published: April 2011

The Giants Range batholith is a large composite granitoid body that intrudes deformed supracrustal rocks in the western part of the Wawa Subprovince of the Archean Superior Province. Peak fabric development in the supracrustal rocks coincides with D2 deformation, the product of regional transpression across the southern Superior Province. U–Pb zircon ages on two phases of the Giants Range batholith bracket D2 deformation to an interval between 2685 and 2669 Ma. Two well-exposed components of the central part of the Giants Range batholith are the pre- to syn-D2 Britt granodiorite, which contains a linear D2 metamorphic fabric, and the syn- to post-D2 Shannon Lake granite, which cuts deformation fabrics in the Britt granodiorite and the supracrustal rocks. Geochemical discrimination plots imply emplacement of the Britt granodiorite in an arc environment and the Shannon Lake granite in a collision setting. Zircons yield U–Pb ages of 2681 ± 4 and 2685 ± 4 Ma for the Britt granodiorite and 2674 ± 5 and 2674 ± 27 Ma for the Shannon Lake granite. Timing of D2 deformation near the Giants Range batholith corresponds well with similar rocks exposed along strike 170 km to the east near Shebandowan Lake, Ontario, where the end of D2 deformation has been bracketed between 2692 and 2681 Ma. The slightly younger ages for D2 deformation in Minnesota reflect later volcanic-arc development and associated plutonism than at Shebandowan Lake, possibly due to oblique convergence along a westward-migrating tectonic front.
Age and implications of Early Ordovician (Arenig) plutonism in the type area of the Bay du Nord Group, Dunnage Zone, southern Newfoundland Appalachians
Authors: Tucker R. D. , O'Brien S. J. , O'Brien B. H.
Published: April 2011

In south Newfoundland, an extensive tract of metamorphosed Ordovician metavolcanic, metasedimentary, and granitoid rocks (Bay du Nord Group) lies north of a late Precambrian basement inlier of peri-Gondwanan affinity, separated from the latter by Silurian rocks. In the Bay du Nord Group type area, the metavolcanic and metasedimentary rocks were ductilely sheared and locally fault imbricated with metagabbro prior to emplacement of the Baggs Hill Granite, herein dated at 477.6 ± 1.8 Ma. Some of the volcano-sedimentary strata within this succession, however, contain foliated clasts of Baggs Hill Granite, and these strata must comprise a younger stratigraphic sequence which, in this area, is thrust northwestward over the older rocks.The pre-477.6 ± 1.8 Ma tectonic interleaving of the Dunnage Zone gabbro and stratified rocks is significantly earlier than the Llandovery (early Salinic) recumbent folding and thrusting of Middle Ordovician Exploits Subzone rocks in the east-central Hermitage Flexure. In both areas, the Dunnage Zone rocks were inhomogeneously thickened and tectonically telescoped north of a rigid block of late Precambrian peri-Gondwanan basement. The emplacement of the Baggs Hill Granite is coeval with intrusion of similar Ordovician granite into ophiolites obducted southeastward onto the Gondwanan margin during Arenigian (Penobscot) orogenesis.
Paleo-Proterozoic thick-skinned tectonics: Lithoprobe seismic reflection results from the eastern Trans-Hudson Orogen
Authors: White D. J. , Lucas S. B. , Hajnal Z. , Green A. G. , Lewry J. F. , Weber W. , Bailes A. H. , Syme E. C. , Ashton K.
Published: April 2011

New seismic reflection data collected by Lithoprobe across the Trans-Hudson Orogen (Manitoba and Saskatchewan) provide striking images of juvenile paleo-Proterozoic arc rocks (Flin Flon and Kisseynew belts) juxtaposed against the deformed northwestern margin of the Archean Superior craton. Crustal imbrication on a scale imaged in few other orogens is observed within the Flin Flon Belt where a package of shallowly east-dipping reflections extends from the surface to 14 s. These reflections are attributed to middle to lower crustal arc rocks that appear to have been stacked below a major detachment that underlies the upper crustal rocks of the Flin Flon Belt. Surprisingly, the seismic images show the juvenile arc rocks dipping moderately eastward beneath the craton in apparent contradiction to existing tectonic models. Geological and geochronological evidence suggest that the observed crustal imbrication probably reflects late-collisional or postcollisional convergence rather than earlier oceanic subduction polarity. The east-dipping reflection fabric, marking a Hudsonian tectonic overprint, extends across the Superior Boundary Zone up to the Pikwitonei Granulite Belt where upper crustal reflections are west dipping. An east-dipping seismic boundary between these domains, which soles into the mid-crust, may represent a west-verging thrust fault along which the crust of the Archean Superior craton was uplifted.
Transformation of Archean structural inheritance at the Grenvillian Foreland Parautochthon Transition Zone, Chibougamau, Quebec
Authors: Daigneault Real , Allard Gilles O.
Published: April 2011

The easternmost portion of the Archean Abitibi greenstone belt adjacent to the Grenville Front in the Chibougamau area displays distinctive structural features related to crustal-scale contraction during the Grenvillian orogeny. The "Foreland parautochthon transition zone," (FPTZ) a 3–15 km wide zone of Archean rocks, shows a Grenvillian deformation and metamorphic history that overprint fabrics inherited from the Archean Kenoran orogeny. The deformation history of this zone can be divided into two stages. During stage 1, a major crustal-scale deformation zone is responsible for a first uplift episode of deep Archean crust. During this stage, the Grenvillian deformation reactivated and emphasized the Archean fabrics. Amphibolite-grade mylonitic fabrics are interpreted to be an enhancement of the Archean regional schistosity, which remains axial planar to the regional folds. Archean rocks with well-developed former fabrics are strongly affected by Grenvillian non-coaxial flow associated with southeast-dipping stretching lineations. The northwestward transport direction, deduced from shear-sense indicators, is compatible with the signature of the Grenvillian orogeny. Stage 2 is responsible for the formation of the N015°-trending, late Grenvillian faults that have dissected the stage 1 deformation zone. Steep east-dipping narrow zones of retrograde low-temperature mylonites indicate a reverse, east-side-up movement that has contributed to the uplift of deeper Archean structural levels. In a later stage of brittle deformation, pseudotachylite injections and cataclasis, resulting from sinistral lateral offsets in a dominantly brittle regime, are superimposed on the mylonitic structures in response to a modification of the transport direction at the end of the Grenvillian orogeny. Even if high-grade metamorphism can be partly explained by the uplift of deep Archean crust, the structural signature associated with amphibolite mylonites within the FPTZ is interpreted as a product of the Grenvillian orogeny.
Glacial-lake spillway incision and deposition of a coarse-grained fan near Watrous, Saskatchewan
Authors: Kehew Alan E. , Teller James T.
Published: April 2011

The Watrous spillway was rapidly incised during a short-lived outburst from glacial Lake Elstow. In its outlet area, the bed of Lake Elstow was composed of stagnant ice. The 40 km long spillway is incised across a divide, and terminates in the glacial Last Mountain Lake basin, where a coarse-grained fan, herein named the Little Manitou fan, was deposited. Clast sizes fine systematically from the mouth of the spillway across the surface of the fan, from boulders with a maximum mean intermediate diameter of 1.26 m to cobbles, over a distance of 7 km on the south lobe of the fan. Large clasts are concentrated on the surface, and probably represent deposition at peak discharge. The proximal margin of the south lobe of the fan is hummocky, suggesting that deposition of sediment at its apex was on stagnant ice with subsequent collapse. Paleovelocity, paleodischarge, and other parameters were estimated for the outburst flood using a critical shear stress approach. These approaches yielded paleodischarge estimates lower than those deduced from previous analyses of floods in channels of similar size in the region, and lower than values given by empirical equations relating shear stress to particle size. Due to the lack of high-water marks along the channel, the progressive flood erosion of the spillway floor, and the possible presence of stagnant ice in at least the headwater reach of the spillway during the flood, slope is the most difficult parameter to estimate for the flood.
The stratigraphic importance of species of Sumatradinium, Barssidinium, and Erymnodinium, Neogene dinoflagellate genera from offshore eastern Canada
Authors: Lentin Judith K. , Fensome Robert A. , Williams Graham L.
Published: April 2011

The Neogene strata of offshore eastern Canada contain a rich diversity of dinoflagellate cysts. Among the most distinctive are species of the peridinialean genus Sumatradinium and the related genera Barssidinium gen.nov. and Erymnodinium gen.nov. Sumatradinium and Erymnodinium have a reticulate wall, whereas Barssidinium has a smooth to granulate wall. Sumatradinium and Barssidinium have processes or pustules only; Erymnodinium has crests. The three genera and their constituent species are useful for biostratigraphic subdivision in the Miocene and Pliocene, as exemplified in the two wells Evangeline H-98 and Heron H-73; stratigraphic control for these wells is based on previously established palynologic data. To categorize the considerable morphological variation of these genera and promote their biostratigraphic usefulness, we propose five new species: Sumatradinium druggii, Sumatradinium pustulosum, Barssidinium evangelineae, Barssidinium graminosum, and Barssidinium wrennii. We also emend the generic diagnosis of Sumatradinium and the specific diagnosis of Sumatradinium hispidum.
Microstructural and geochemical investigations on Late Cretaceous archosaur teeth from Alberta, Canada
Authors: Bocherens Herve , Brinkman Donald B. , Dauphin Yannicke , Mariotti André
Published: April 2011

Microstructural and chemical composition studies on fossil reptile teeth from Upper Cretaceous localities of Alberta, Canada, show that the quality of preservation exhibits great variability within a formation, as well as within a locality or even a single tooth. The chemical composition of fossil enamel is close to that of modern enamel, whereas the chemical compositions of fossil and modern dentine are very different. It seems that fossil enamel may have retained some paleodietary information in its chemical composition, whereas dentine, as well as bone, likely did not. Paleodietary interpretations may thus be drawn from the chemical composition of some elements in tooth enamel, such as strontium, but more studies on recent reptiles are urged for comparison.
Glacial Lake Camelsfoot: a Late Wisconsinan advance stage proglacial lake in the Fraser River valley, Gang Ranch area, British Columbia
Authors: Huntley David H. , Broster Bruce E.
Published: April 2011

In the Gang Ranch area, British Columbia, interaction between the regional physiography and ice flow during the Late Wisconsinan Fraser Glaciation resulted in the formation of a proglacial lake confined to valleys of the Fraser River and its tributaries. Lithostratigraphic and geomorphic evidence suggests that ponding was initiated in the Big Bar Creek area where the Fraser River is confined to a deep canyon in the Camelsfoot Range. During ice advance, a proglacial lake system developed that progressively deepened and reached a minimum upper elevation of approximately 710 m asl prior to being overridden by ice. We propose that this system be formally named "Glacial Lake Camelsfoot." A composite stratotype, comprising lithostratigraphic units associated with Glacial Lake Camelsfoot, is described from eight reference sections along Fraser River, Churn, and Lone Cabin creeks in the Gang Ranch area. Additional geomorphic evidence indicates that at the Fraser Glaciation maximum, the Cordilleran Ice Sheet in the study area ranged from 600 to 2000 m in thickness.
A laser 40Ar–39Ar study of minerals across the Grenville Front: investigation of reproducible excess Ar patterns
Authors: Smith P. E. , York D. , Easton R. M. , Özdemir Ö. , Layer P. W.
Published: April 2011

40Ar–39Ar ages have been determined on single grains of biotite and amphibole from rocks on a 40 km traverse across the Grenville Front (GF) in the Temagami area, Ontario. Minerals in the vicinity of the GF contain excess Ar in varying amounts characterized by both anomalously high integrated and plateau ages. The excess Ar in biotite varies with distance from the GF, such that the overall age distribution along the GF forms an asymmetric wave-like pattern (an argonami) with two age maxima, one on either side of the GF. The integrated age maxima are 2.34 Ga for biotite and 3.21 Ga for amphibole located 6 and 0.2 km north of the GF, respectively, whereas maxima are 1.33 Ga for biotite and 1.50 Ga for amphibole 7 km south of the GF. This wave-like pattern of apparent ages shows a remarkable similarity with that seen in an earlier K–Ar study across the GF at Chibougamau, Quebec, and also with a small-scale pattern of excess Ar associated with the emplacement of a dyke. Variations in the magnitude of excess Ar in minerals can be interpreted in terms of the interaction of variable mineral blocking trajectories with the ambient partial pressure of Ar, and their patterns may also provide clues to underlying tectonic structures associated with the anomalies.The time–temperature relationships for minerals geographically located beyond the effects of significant excess Ar suggest that the crust in the Temagami area was subjected to more rapid cooling relative to gneisses of the interior of the Grenville Province.
Petrology of veined gneisses of the Otter complex, southern Grenville Province
Authors: Kretz Ralph
Published: April 2011

A prominent metamorphic complex composed mainly of K-feldspar gneiss, with many quartz–feldspar layers and veins, occurs in the Otter Lake terrane of the southern Grenville Province of the Canadian Shield. Intense deformation of the complex is indicated by folded and disjointed amphibolite dikes; many veins are also folded. The K-feldspar gneiss consists of quartz, plagioclase, K-feldspar, biotite, local garnet, and rare sillimanite. With few exceptions, the mineral assemblage of each vein is the same as that of the enclosing gneiss, including garnet and sillimanite, where present, and minor minerals, magnetite, zircon, apatite, and allanite. The volume fraction K-feldspar/(K-feldspar + plagioclase) ranges widely (from 0.05 to 0.90), but compared with adjacent gneiss, K-feldspar is always higher and biotite is lower. The chemical composition of veins is similar to that of enclosing gneiss, but K and Ba are higher and Mg, Fe, Mn, Ti, Zr, Rb, and P are lower. The bulk composition of veined gneiss where veins are numerous and that of adjoining gneiss where veins are scarce are virtually identical. Vein–gneiss differences in plagioclase and garnet composition are small or imperceptible.These results lead to the conclusion that many of the veins were locally derived. The rearrangement of atoms needed to produce a vein is considered in terms of Orville–Fisher exchange reactions, e.g., the transport of K, Al, and Si from gneiss to sites of vein growth, in exchange for Mg, Fe, and H. The Ramberg–Robin model of metamorphic differentiation, in which transport occurs by crystal-boundary diffusion, driven by pressure gradients, is proposed as the principal process of vein formation.
New geophysical data from the northern Cordillera: preliminary interpretations and implications for the tectonics and deep geology
Authors: Lowe C. , Horner R. B. , Mortensen J. K. , Johnston S. T. , Roots C. F.
Published: April 2011

In this paper we analyze recently acquired geophysical data from the northern Cordillera and their relation to the mapped geology. A prominent gravity high (> −45 mGal (1 Gal = 1 cm/s2)) coincides with a magnetic low and an aseismic region in west-central Yukon where the underlying geology is dominated by quartzo-feldspathic rocks having moderate densities. Extension (~15%), magmatic underplating, and accretion of the anomalous region onto oceanic crust are three possible explanations.Magnetic, gravity, and seismicity data all show significant differences in the physical state of the crust on either side of the Tintina Fault and, together with geological data indicating large offset, suggest it was once a major crustal-scale strike-slip fault. The new gravity data also delineate an arcuate zone of steep gradients (up to 1.4 mGal/km) in the miogeocline, which may correlate with a west-dipping Proterozoic basement ramp mapped on deep seismic sections farther to the north and a transition from thin (east) to thick sediment cover (west). Seismicity data show that current tectonic activity is concentrated along the Pacific – North America plate margin in southwestern Yukon and adjacent Alaska and, although there is a marked decrease in activity inland of this margin, notable concentrations occur along the Denali Fault System and in the eastern miogeocline. There is a distinct absence of earthquakes in parts of the Selwyn Basin and in the northern Yukon–Tanana Terrane. Limited field studies suggest activity is confined to the upper 10–15 km of the crust.
Lithostratigraphy and map-scale structure in the western Cape Smith Belt, northern Quebec: a tentative correlation between two tectonic domains
Authors: Barrette Paul D.
Published: April 2011

Field investigations in the western part of the Cape Smith Belt outlined four fault-bounded lithological assemblages tectonically overlying foliated to gneissic granitoids of the Archean Superior Province. These assemblages comprise sequences of pillowed volcanic rocks, sedimentary rocks of pelitic and psammitic composition, and volcaniclastic rocks. They are juxtaposed along the Lanyan Lake Fault against a structurally thickened sequence of mafic to ultramafic pillowed volcanic suite belonging to the Chukotat Group. The occurrence of volcaniclastic horizons in the uppermost levels of the Chukotat Group may indicate a northward facies transition from sea-floor volcanism to arc sedimentation, the latter corresponding to the Parent Group. A major pluton intruding the upper Chukotat Group, if assigned to the younger Narsajuaq intrusive suite, provides support for an 1844 – 1826 Ma link between two tectonic domains, formerly considered "suspect." These domains lie on either side of the Bergeron Fault in the east and central parts of the Cape Smith Belt. This fault, formerly interpreted as extending to Hudson Bay, was not recognized in this work. Thrust faulting, involving three kilometre-thick imbricate slices enclosing the Superior Province, was followed by the development of the Cape Smith Synclinorium with overturning of its northern limb, forelimb faulting, and large-scale folding along northwest-trending axes.
Evidence of the Pacific Faunal Province in the northern Alexander Terrane, recognition of two Middle Ordovician graptolite zones in northwestern British Columbia
Authors: Norford B. S. , Mihalynuk M. G.
Published: April 2011

The Middle Ordovician Pseudoclimacograptus decoratus Zone (Llanvirn) and Climacograptus bicornis Zone (early Caradoc) of the Pacific Faunal Province are documented from the Tatshenshini River map area in the northern Alexander Terrane. Graptolites were collected from three separate localities of uncertain stratigraphic position within the informal unit 1Pza. The ages of the collections are critical to dating the stratigraphic succession of the Lower Paleozoic rocks within the highly deformed terrane.Regionally, unit 1Pza can be correlated with the Descon Formation of Prince of Wales Island, southeastern Alaska, which also forms part of the Alexander Terrane. The original position of the Alexander Terrane is uncertain, but there are broad similarities between the Paleozoic stratigraphic package of the terrane and those of the Sierra Nevada of the western United States, southeastern Australia, and eastern Siberia.
The age and origin of the North Shore Plutons in the Rae Province, Goldfields area, Saskatchewan
Authors: O'Hanley David S. , Kyser T. Kurtis , Sibbald Thomas I. I.
Published: April 2011

The North Shore Plutons are peraluminous granitoids emplaced within the Murmac Bay Group supracrustals exposed on the north shore of Lake Athabasca, Saskatchewan. 207Pb/206Pb ages obtained using the single-zircon Pb-evaporation technique indicate emplacement at 1952 ± 18 Ma, coeval with Taltson magmatism that occurred during the 1.9–2.0 Ga Thelon orogeny, which influenced the Rae Province. The granitoids inherited zircons from Archean source terranes dated at approximately 2.5 and 3.0 Ga. Detrital zircons from the younger source terrane were also identified in the Murmac Bay Group, thus constraining the maximum age of the group to the Paleoproterozoic.Rare earth element and incompatible element data and Rb–Sr and Sm–Nd isotope systematics from the North Shore Plutons and adjacent host rocks indicate that the plutons are crustal melts generated from melting of Murmac Bay Group rocks and Archean crust at deeper levels. Granitic gneisses described as "Older" Granites represent mixtures of variable amounts of magmatic fluids similar to those that formed the North Shore plutons and the Murmac Bay Group metasedimentary rocks.
Anatomy of an Upper Silurian transgressive–regressive cycle, Prince of Wales Island, Arctic Canada
Authors: Mortensen Paul S. , Jones Brian
Published: April 2011

The Ludlovian–Pridolian Cape Storm, Douro, and Somerset Island formations on eastern Prince of Wales Island form a transgressive–regressive succession that developed on the western flank of the active Boothia Horst. Sedimentation took place in a series of fault-bounded subbasins that were, at different times, characterized by abundant microbolites, rhodolites, brachiopods, and organisms that produced a diverse array of ichnofossils. Integration of paleoecological information from this succession provides a multifaceted paleoecological model, which can be applied to similar, lithologically monotonous successions throughout the world. Three main factors controlled the distribution of biota through the transgressive–regressive cycle. The most obvious factor was ever-changing depositional settings caused by progressive rise and fall in sea level. Superimposed on this general pattern, however, was the influence of water circulation and the influx of detrital quartz from the Boothia Horst. The microbolites and rhodolites were mutually exclusive; the microbolites developed in intertidal to shallow subtidal settings, whereas the rhodolites grew in subtidal settings. The exception is in the lower Somerset Island Formation, where oncolites and rhodolites are numerous, commonly in the same beds. The influx of detrital quartz grains into the intertidal and supratidal settings, common during the development of the lower part of the Cape Storm Formation and the upper part of the Somerset Island Formation, curtailed microbolite development. During the subtidal phase, circulation controlled the distribution of Atrypoidea-dominated brachiopod faunas, rhodolites, microbolites, and ichnofossils. Even subtle changes in the nature of the rhodolite associations were accompanied by changes in the Atrypoidea species and changes in the ichnofossil assemblages.