bluuebunny/crossref_metadata_2025 huggingface dataset:
Geology and footwall alteration of the South Bay massive sulphide deposit, northwestern Ontario, Canada
Authors: Urabe Tetsuro , Scott S. D.
Published: April 2011

South Bay is an Archean volcanogenic massive Cu–Zn sulphide deposit having many features in common with the Kuroko deposits of Japan. The ore lenses overlie a quartz–feldspar porphyritic rhyolite (QFP) lava dome and are covered by or occur within rhyolitic tuff breccia that, together with rhyolite tuffs and lavas, is contained within a caldera-like structure.Footwall hydrothermal alteration at South Bay is detectable for several hundred metres from ore. "Unaltered" footwall QFP lava dome contains a mineral assemblage of quartz + two feldspars + two micas + epidote + calcite + ilmenite. Closer to the orebodies, K-feldspar, epidote, and biotite disappear first, followed by consumption of calcite, ilmenite, and albitized plagioclase. The most altered QFP has an assemblage of quartz + paragonite + phengitic muscovite + chlorite + dolomite + sphene + rutile. The ratio Fe/(Fe + Mg) in dolomite, muscovite (phengite), and chlorite decreases consistently towards the orebodies. Neither bulk chemistry (except for Na2O) nor oxygen isotopic ratio shows consistently systematic lateral changes within the alteration halo. Quartz from the stringer zone, from lenses in massive ore, and from ore-horizon chert all have a very narrow δ18O range of +9.0 to +11.3‰. The δ18O of the QFP is +9.3 to +9.4‰, regardless of the degree of alteration.The temperature of ore formation is estimated to have been around 300 °C based on the paragonite–muscovite geothermometer and the carbonate geothermometer. The δ18O value of the ore-forming solution at 300 °C would have been between +2.1 and +4.4‰, which is similar to that of the Kuroko deposits.
Cretaceous sedimentation and tectonics, Tyaughton–Methow Basin, southwestern British Columbia
Authors: Kleinspehn Karen L.
Published: April 2011

The Mesozoic Tyaughton–Methow Basin straddles the Fraser–Yalakom–Pasayten – Straight Creek (FYPSC) strike-slip fault zone between six tectono-stratigraphic terranes in southwestern British Columbia. Data from Hauterivian–Cenomanian basin fill provide constraints for reconstruction of fault displacement and paleogeography.The Early Cretaceous eastern margin of the basin was a region of uplifted Jurassic plutons and active intermediate volcanism. Detritus shed southwestward from that margin was deposited as the marine Jackass Mountain Group. Albian inner to mid-fan facies of the Jackass Mountain Group can be correlated across the Yalakom Fault, suggesting 150 ± 25 km of post- Albian dextral offset. Deposits of the Jackass Mountain Group overlap the major strike- slip zone (FYPSC). If that zone represents the eastern boundary of the tectono-stratigraphic terrane, Wrangellia, then accretion of Wrangellia to terranes to the east occurred before late Early Cretaceous time.The western margin of the basin first became prominent with Cenomanian uplift of the Coast Mountain suprastructure. Uplift is recorded by dispersal patterns of the volcaniclastic Kingsvale Group southwest of the Yalakom Fault.Reversing 110 km of Late Cretaceous – early Tertiary dextral motion on the Fraser – Straight Creek Fault followed by 150 km of Cenomanian – Turonian motion on the Yalakom – Ross Lake Fault restores the basin to a reasonable depositional configuration.
Late glacial to Recent stratigraphy, paleontology, and sedimentary processes: Newfoundland continental slope and rise
Authors: Schafer C. T. , Tan F. C. , Williams D. F. , Smith J. N.
Published: April 2011

Micropaleontology, pollen, sediment, and δ18O studies point to considerable variation in sedimentary processes and water-mass characteristics on the northeast Newfoundland slope and rise during late glacial and Holocene time. Allochthonous shelf and upper slope foraminiferal species suggestive of turbidity current activity occur relatively frequently in rise sediments during a postglacial interval, dated by extrapolation from a probable 9300 year old ash horizon. A single late glacial turbidity current deposit involved a much larger volume of sediment than that noted for the earlier events and it appears to have originated primarily on the middle slope. In conjunction with a widespread late glacial interval of fecal pellet deposition, this larger event suggests an increased flux of material in the form of suspended particulate matter to the continental margin following the late Wisconsinan glacial maximum. Oceanographic conditions during late glacial time appear to have stimulated the productivity of zooplankton in the waters off northeastern Newfoundland.Within the late Holocene interval of the rise sediments, there is some micropaleontological and sedimentological evidence for an intensification of the Western Boundary Undercurrent that appears to have started about 1000–2000 years BP. Over the same period of time, the surface water circulation seaward of the northeast Newfoundland shelf appears to have changed from a mode that was dominated occasionally by a northern component of relatively warm North Atlantic drift water to one that is dominated today exclusively by Labrador Current water.
Vashon Drift: definition of the formation in the Georgia Depression, southwest British Columbia
Authors: Hicock Stephen R. , Armstrong John E.
Published: April 2011

Vashon Drift was deposited during the Fraser Glaciation (late Wisconsinan) at the time of maximum expansion of the southwestern part of the Cordilleran ice sheet when it filled the Georgia Depression about 14 500 years ago. The drift is present throughout the depression and comprises till and glaciofluvial and glaciolacustrine sediments derived from source areas surrounding the coastal trough. It is overlain by Capilano Sediments and underlain by Quadra Sand, also of Fraser age. Drift deposition was diachronous and complex, probably caused by alpine glaciers coalescing in the trough with the ice margin repeatedly grounding and floating in seawater. Studies of bedrock striae, till fabrics, and clast provenance reveal that Vashon ice movement was generally southward, although locally controlled by topography. A time–space diagram is presented that confirms the long-held hypothesis that advance and decay of Vashon ice were rapid.
Geochemistry and geochronology of the gneisses east of the Southern Rocky Mountain Trench, near Valemount, British Columbia
Authors: Chamberlain V. E. , Lambert R. St J. , Holland J. G.
Published: April 2011

Petrographic, geochemical, and geochronological data are presented on the gneisses of the Bulldog Creek block, the Mount Blackman block, and the Hugh Allan Creek block, which lie to the east of the Southern Rocky Mountain Trench (SRMT) south of Valemount, British Columbia.Petrographical and geochemical data, especially immobile-trace-element ratios (Nb: Y, Ti: Zr), and CaO versus Y and AFM plots are used to deduce the probable origins and protoliths of the gneisses. The Mount Blackman block consists of a psammitic paragneiss, probably derived from an immature arkosic sedimentary protolith, intruded by sills of tholeiitic basalt, now amphibolites. The Bulldog Creek block consists of felsic orthogneisses of calc-alkaline affinity, which are structurally concordant with mafic orthogneisses of possible tholeiitic basalt parentage. The Hugh Allan Creek block consists of a felsic orthogneiss with a probable alkaline granite protolith.Rb–Sr, and some U–Pb analyses show that each block has experienced a separate geological history. The Mount Blackman block psammitic paragneisses are the only analysed gneisses east of SRMT with a probable Archean Rb–Sr model crustal residence age. U–Pb analyses on zircons from these gneisses give a 1950 Ma minimum source rock age, and Rb–Sr whole-rock analyses suggest a 1860 ± 50 Ma age for amphibolite-facies metamorphism of both paragneisses and amphibolites. The Bulldog Creek block gneisses have a metamorphic age of at least 640 Ma, but their Rb–Sr systematics have been extensively disturbed, possibly during Mesozoic retrogressive metamorphism. The Hugh Allan Creek block gneisses have a Rb–Sr model crustal residence age of ~900 Ma and a metamorphic age of 805 ± 11 Ma. It is not possible to correlate any of these lithologies or events across the SRMT with the Malton block, and it is concluded that the SRMT is the site of a major fault or faults at this latitude.
Chronology and significance of a Holocene sedimentary profile from Clear Creek, Lake Erie shoreline, Ontario
Authors: Barnett P. J. , Coakley J. P. , Terasmae J. , Winn C. E.
Published: April 2011

An abandoned channel of Clear Creek, cut approximately 5 m below the present level of Lake Erie, was cored and the infilling sediments were examined. The postglacial history of this channel was reconstructed based on sedimentological, palynological, and chronological studies.The channel was cut initially some 15 m into Wentworth Till during the low-water Early Lake Erie stage. The infilling or aggradation of the channel began about 9500–9000 years BP, probably in response to rising water levels in the Lake Erie basin.This channel was cut off from the main channel shortly afterwards and an oxbow lake formed. By 7000 years BP, complete cutoff of the channel from the main stream system had occurred, allowing peat to accumulate. Eventually trees grew on this site, 4000 years BP.The diversion of glacial Lake Nipissing drainage into the Lake Erie basin may be reflected in the greater abundance of silt laminations in the peat of the upper part of the channel fill between 5975 ± 150 (BGS-899) and 3900 ± 100 (BGS-898) years BP.A rise in water level in the Lake Erie basin possibly over the Clear Creek site is recorded by the "drowning" of the forest shortly after 3900 ± 100 (BGS-898) years BP and the truncation of the Clear Creek site pollen diagram.
Geochemistry and tectonic significance of the mafic volcanic blocks in the Dunnage mélange, north central Newfoundland
Authors: Wasowski Janusz J. , Jacobi Robert D.
Published: April 2011

Abundant volcanic blocks are present in the Dunnage mélange. These mafic volcanic rocks consist predominantly of pillow lava, tuff breccia, isolated pillow–tuff breccia, and minor amounts of ropy lava.Major- and trace-element compositions of the basalts reveal that these volcanics do not resemble calc-alkaline or low-potassium island-arc suites. Rather, the majority of the samples are enriched-type ocean-floor tholeiites, whereas some show alkali basalt affinities. Discrimination diagrams suggest that these basalts may have been erupted as within-plate basalts. However, the chemical composition of the volcanic blocks is most similar to that of basalts generated at bathymetric highs located astride (or slightly off) mid-ocean ridges.The geochemistry of the Dunnage mélange basalts is very similar to that of the mafic volcanic rocks from the nearby Summerford Group and the Lawrence Head Formation. This correlation is further supported by sedimentary and petrographic evidence and by partial age equivalency.
Is the Cape Smith Belt (northern Quebec) a klippe?
Authors: Hoffman Paul F.
Published: April 2011

The Cape Smith Belt is one of the most interesting and controversial of the proposed geosutures in the Canadian Shield. A new tectonic model is presented in which the mafic–ultramafic thrust sheets of the belt constitute a klippe, 20 000 km2 in area, separated from underlying basement of Superior Province and its thin autochthonous cover by a continuous décollement exposed along the north margin and the plunging eastern end of the belt. Thrusting is directed southward, and the entire stack is folded into a regional antiform (north of the belt) and synform (the belt itself). It is proposed that the décollement is rooted 30–90 km north of the belt, in a zone paralleling Sugluk Inlet, across which there is a major positive deflection in the Bouguer gravity field, an abrupt switch from broad north–south to narrow east–west magnetic anomalies, and a change in metamorphic grade from amphibolite to granulite facies from south to north. In the model, this zone is a north-dipping ductile shear zone juxtaposing crusts of two collided continents. Accordingly, granulite north of the zone represents lower crust of the overriding plate, whereas granulite between the zone and the klippe occurs in antiformal culminations in the underriding plate. One test of the model is that the south-dipping shear zone observed at the north margin of the belt should have a normal sense of slip. Another is that north-dipping banded gneiss at Sugluk Inlet should mark a ductile shear zone, also having a south-directed sense of overthrusting. A structural profile of the belt and its relation to basement can best be worked out by down-plunge projection of the eastern end of the belt.
The Iceland Research Drilling Project Crustal Section: Physical properties of some basalts from the Reydarfjordur borehole, Iceland
Authors: Drury Malcolm J.
Published: April 2011

Thermal, electrical, and other physical property data are reported for a suite of basalts from the core of a 1.9 km hole at Reydarfjordur, eastern Iceland. The principal aim is to add to the literature thermal diffusivity data on basalts. Both lava-flow and dyke-intrusion samples have been measured, in roughly the proportion of their abundances in the drilled section. Density and porosity measurements are in good agreement with values published previously by others. Thermal conductivity values are approximately 10% higher than those published by others, probably because of differences in measurement techniques. Porosity of the samples generally decreases with depth because of increasing infilling of voids and cracks with alteration products. Density, thermal conductivity, thermal diffusivity, and the derived properties grain density and grain conductivity increase with depth, whereas electrical resistivity decreases. Bulk properties of the section have been estimated. They are thermal diffusivity, 0.70 mm2/s (0.70 × 10−6 m2/s); thermal conductivity, 1.97 W/m∙K; bulk density, 2.82 Mg/m3; and porosity, 0.039 (3.9%). Curves modelling in situ electrical resistivity indicate values in the range 50–3000 ?∙m. The electrical structure of the crust in the Reydarfjordur area is apparently different from that in southwest Iceland, probably reflecting a different history of hydrothermal circulation and alteration.
The pachypleurosaurid Dactylosaurus schroederi (Diapsida: Sauropterygia)
Authors: Sues Hans-Dieter , Carroll Robert L.
Published: April 2011

Redescription of the small pachypleurosaurid nothosaur Dactylosaurus schroederi Nopsca, 1928, from the Muschelkalk of Upper Silesia (Gorny Slask), Poland, indicates that it closely resembles Neusticosaurus but differs from the latter in a number of features. The forelimb, especially the antebrachium, is very gracile. Dactylosaurus achieves a high degree of ossification at a much smaller body size than other Pachypleurosauridae. The pattern of interzygapophyseal articulation in the trunk region suggests that lateral flexion was largely suppressed. The Pachypleurosauridae represent a distinct radiation of Triassic sauropterygians and combine certain resemblances to plesiosaurs with a number of plesiomorphous features.
Geochronology of ophiolites of the Newfoundland Appalachians
Authors: Dunning G. R. , Krogh T. E.
Published: April 2011

Precise U/Pb zircon ages (2σ errors) are reported for four ophiolite complexes from the Newfoundland Appalachians.Zircons from trondhjemite from Blow Me Down Mountain, Bay of Islands Complex, give an age of [Formula: see text] (five points). Those from gabbro from Blow Me Down Brook give a minimum 207Pb/206Pb age of 480 Ma (one point), confirming that this is the age of the main plutonic episode. These data refute previously determined latest Cambrian U/Pb zircon and Sm/Nd (mineral–rock isochron) ages of 504 ± 10 and 505 Ma for the complex.Gabbro from the Betts Cove Complex yielded zircon that gives an age of [Formula: see text] (four points). This refutes the interpretation of an earlier U/Pb (zircon) age of 463 ± 6 Ma for a trondhjemite dyke as the age of the ophiolite. It was inconsistent with the presence of Arenigian graptolites in the overlying Snooks Arm Group.Two zircon ages from a pegmatitic and medium-grained trondhjemite of the Annieopsquotch Complex are [Formula: see text] (five points) and [Formula: see text] (two points). Zircon from trondhjemite of the Pipestone Pond Complex of central Newfoundland gives an age of [Formula: see text] (five points). Analysis of a single zircon fraction from the Coy Pond Complex gives a minimum 207pb/206pb age of 489 MaThe ages are comparable to those of the Lushes Bight Terrane, Newfoundland, the M'Clintock West Massif, Arctic Canada, and the Ballantrae Complex, Scotland, and together span 18 Ma of the Tremadocian and Arenigian stages. This short age range may imply that only young "hot" oceanic crust was emplaced and preserved in the Appalachian–Caledonian mountain belt.
Description d'un appareil à désaimanter par champs alternatifs; élimination de l'aimantation rémanente anhystérétique parasite
Authors: Goff Maxime Le
Published: April 2011

We give a description of a 400 Hz alternating field demagnetizer producing high fields, up to 280 mT, with a spiral mu metal magnetic shield and having the ability to eliminate the parasitic effect of the second harmonic in the alternating current supplying the field coil.
Shelf-facies microbiotas from the Odjick and Rocknest formations (Epworth Group; 1.89 Ga), northwestern Canada
Authors: Hofmann H. J. , Grotzinger J. P.
Published: April 2011

Moderately well preserved microfossils are reported from two formations of the Epworth Group in the Wopmay Orogen. An assemblage in a stromatolitic unit in the uppermost part of the Odjick Formation contains the microfossils Huroniospora spp., Gunflintia sp., and Frutexites sp. This assemblage, which is remarkable for its preservation in a carbonate matrix, is similar to one found in a stromatolitic chert facies in the Gunflint Iron Formation of Ontario. Taxa in four members of the overlying Rocknest Formation are preserved in cherty dolomites of inner-shelf shallowing-upward cycles capped by small digitate stromatolites. These assemblages comprise the spheroidal taxa Huroniospora spp., Melasmatosphaera magna, Sphaerophycus sp., and Palaeoanacystis sp., the filamentous taxa Archaeotrichion sp., Eomycetopsis sp., Siphonophycus sp., Brevitrichoides sp., Biocatenoides incrustata, Gunflintia? sp., and Archaeonema sp., the acritarch Eomicrhystridium sp., and rare specimens of two unidentified and problematic taxa.
A large convex lens can provide stereoscopic views of maps colour coded in spectral order
Authors: Hodych J. P.
Published: April 2011

Geophysical maps are often colour coded in spectral order, that is, with violet, blue, green, yellow, orange, and red representing successively higher values of the mapped data. Viewing such maps with both eyes through a large convex lens can aid interpretation by making the colours appear to lie at successively higher levels in spectral order: red appears highest above the map plane and violet lowest. This colour stereoscopy (induced by chromatic aberration in the lens) will be in spectral order if saturated colours are separated by black contours. However, white separating uniform, saturated colours causes green to appear highest, with blue, red, and then yellow below. Fortunately, an overlay of fine black dots can restore spectral order to lens-induced colour stereoscopy in maps lacking black contours. Hence, I recommend that colour-coded maps use spectral order with red representing the highest values of mapped data and that an array of just visible black dots be printed over the colours if black contours are absent. Then viewing through a large magnifying glass will provide effortless perception of the map's implied third dimension.
40Ar/39Ar ages for minerals from the amphibolite dynamothermal aureole, Mont Albert, Gaspe, Quebec
Authors: Lux Daniel R.
Published: April 2011

New 40Ar/39Ar ages are presented for two hornblendes and one biotite from the dynamothermal aureole that is situated at the base of the Mont Albeit ophiolite. Analysis by the incremental release technique reveals a small component of excess 40Ar in one hornblende, though both exhibit plateau-type spectra. The biotite was analyzed by the total fusion technique. All apparent ages are concordant and average 456 ± 3 Ma.Dynamothermal aureoles form during the obduction process, which juxtaposes ophiolites and amphibolite protoliths during a compressional tectonic event at a plate margin: in this instance, thrusting of the Mont Albert ophiolite over rocks of the Shickshock Group. The concordance of biotite and hornblende ages indicates rapid postmetamorphic cooling and firmly dates obduction at 456 ± 3 Ma ago, an age younger than any of the other northern Appalachian ophiolites. The high-pressure metamorphism of the amphibolite is inconsistent with the present high structural level of the composite Mont Albert – Shickshock allochthon. This implies that obduction and assembly of the allochthon took place in a different environment prior to emplacement in its present high-level position. The age presented here is therefore a maximum limit for the late thrusting event. A north–south diachronism of Humber Zone ophiolite obduction is supported by the new data.
Glacial geomorphology and chronology in the Selamiut Range – Nachvak Fiord area, Torngat Mountains, Labrador
Authors: Evans David J. A. , Rogerson Robert J.
Published: April 2011

The Selamiut Range of the Torngat Mountains, northern Labrador, rises to over 1700 m above sea level and constituted a barrier to eastward-flowing Laurentide ice during former glaciations. Local and regional ice has left an assemblage of landforms exhibiting cross-cutting relationships. Three glacial phases are recognized in the area. The oldest and most extensive (the Ivitak phase) is marked by high-elevation till deposited when regional and local ice coalesced. At this time regional ice flowed eastward down Nachvak Fiord while interfiord highlands extended above the ice as nunataks. During a late Ivitak phase a large proglacial lake was dammed in the lower McComick Valley at 80 m above sea level when regional and local ice in Nachvak Fiord blocked the local drainage. During the subsequent Nachvak phase, lakes were dammed in the lower McCornick Valley at 67 and 53 m above sea level for ca. 3000 years by Laurentide ice alone. The Superguksoak had three subphases when local cirque glaciers expanded up to 5 km beyond their present limits. The Holocene marine limit around 33 m reflects the small ice load influencing Nachvak Fiord, or very late deglaciation of the Ivitak Cove area.The chronology of these glacial and proglacial deposits is based on their spatial relationships as well as pedology and lichenometry. Seventy-nine soil pits excavated to the base of the Cox horizon indicate the relative duration of weathering since deglaciation. Absolute ages for the soils are estimated to be > 40–40 ka BP for the Ivitak phase, 23–17 ka BP for the Nachvak phase, and 12–5 ka BP for Superguksoak I. Measurements of Rhizocarpon geographicum indicate that prominent Superguksoak-phase moraines bordering the present-day cirques were abandoned approximately > 4000, 3000, and 1500 years BP. Collectively these data are compared with earlier fieldwork in northern Labrador, and some discrepancies are discussed.
A gravity survey of the Dundas buried valley west of Copetown, Ontario
Authors: Greenhouse John P. , Monier-Williams Mark
Published: April 2011

A total of 243 Bouguer gravity readings have been completed over a 9 km2 area covering the terminus of the Dundas buried valley, a prominent reentrant in the Niagara Escarpment. A 1.5 mGal (15 μm s−2) Bouguer anomaly clearly defines an abrupt closure of the bedrock topography west of Copetown, confirming and extending the results of earlier seismic reflection and refraction surveys. An apparent tributary in the contoured gravity, entering the terminus from the south, is unfortunately poorly resolved. It underlies property to which access was denied. The Bouguer gravity data are transformed to a model of the bedrock depth via a three-dimensional model. The mean error between data and model gravity, after correcting the former for a regional gradient, is less than 0.1 mGal (1 μm s−2). The estimated error in the observations themselves is ± 0.11 mGal (1.1 μm s−2). The observed Bouguer gravity is compared with that which would be produced by the present Niagara Gorge were it to underlie the survey area. The magnitude and dimensions of the computed anomalies are remarkably similar.
Alluvial–playa sedimentation in the lower Keweenawan Sibley Group, Thunder Bay District, Ontario
Authors: Cheadle Burns A.
Published: April 2011

The Middle Proterozoic Sibley Group is a mixed clastic–carbonate red bed sequence located in the Thunder Bay – Nipigon area on the north shore of Lake Superior. The lowest unit, the Pass Lake Formation, consists of a basal paraconglomerate member, of probable alluvial debris-flow origin, overlain by 20–80 m of plane-bedded and cross-bedded quartz arenites, which were probably deposited by sheetfloods and eolian processes on alluvial outwash sand flats. The overlying Rossport Formation is dominated by red and buff dolomicritic mudstone. The association of these mudstones with relatively pure massive carbonate beds and sheetflood sandstone units is strongly suggestive of a playa lake depositional environment. Fluctuations in playa lake levels may have resulted in oscillations between carbonate-dominated and clastic-dominated sedimentation. The upper unit, the Kama Hill Formation, consists of horizontally laminated purple shales and ripple cross-laminated buff siltstones to fine sandstones. The presence of stacked "powering-down" sequences and abundant dessiccation features is suggestive of sheetflood deposition on a distal alluvial floodplain.The sequence of depositional environments suggests that the Sibley Basin formed by stretching and sagging of the Middle Proterozoic crust preceding the main period of volcanic activity along the Keweenawan Midcontinent Rift Zone. In this sense, the Sibley Group red beds represent the earliest products of Keweenawan rifting. They were not, however, deposited in a classical aulacogen or "failed arm."
Petrogenesis of the Natkusiak continental basalts, Victoria Island, Northwest Territories, Canada
Authors: Dostal J. , Baragar W. R. A. , Dupuy C.
Published: April 2011

The Natkusiak flows (~1100 m thick), sills, and dykes of Victoria Island, Northwest Territories, are part of an extensive, late Hadrynian magmatic event in the northern Canadian Shield. The flows are subaerially erupted plateau basalts and together with associated doleritic sills and dykes display many geochemical features typical of continental tholeiites. In addition to fractional crystallization, the rocks were affected by crustal contamination but to a smaller degree than usually encountered in continental tholeiites elsewhere. The basalts were derived from a depleted upper mantle source very similar to that of N-type mid-ocean ridge basalts, although it is suggested that the melting residue contained small amounts of garnet (~2%).
Revised 14C age for St. Helens Y tephra at Tonquin Pass, British Columbia
Authors: Luckman B. H. , Kearney M. S. , King R. H. , Beaudoin A. B.
Published: April 2011

The age of a Mount St. Helens set Y tephra at Tonquin Pass, British Columbia, previously assumed to be 4300 years BP, is revised to ca. 3400 years BP, based on bracketing 14C dates of 3140 ± 70 (Beta 13558) and 3680 ± 80 years BP (Beta 13559). The implications of this revision for tephrostratigraphy of this area are discussed.
A microcomputer program for the ASTM method of grain-size analysis
Authors: Mackenzie R. L. , Westgate J. A.
Published: April 2011

We describe a microcomputer program for the ASTM method (D422-63) of grain-size analysis. This multi-optioned program is written in Applesoft BASIC and can be run on any Apple II microcomputer with a disk drive and plotter. Gaussian rather than linear interpolations and extrapolations are used to construct the histogram and calculate the statistics.
Fish otoliths from the lower Tertiary of Ellesmere Island
Authors: Schwarzhans Werner
Published: April 2011

Fish otoliths of five species are present in lower Tertiary (Paleocene to Lower Eocene) rocks at Strathcona Fiord, Ellesmere Island. Two species are new, one is conspecific with a species known from the Lower Eocene of southern England, and two remain in open nomenclature.Paleobiogeographic and other implications of the fauna are that first, there is no resemblance to central European faunas; second, there is a resemblance to northern European faunas from Great Britain and the Soviet Union, pointing to cooler climatic conditions; and third, composition of the fauna suggests the prevalence of deeper shelf conditions.
Deformational history of an outlier of metasedimentary rocks, Coast Plutonic Complex, British Columbia, Canada
Authors: Douglas Bruce J.
Published: April 2011

The Khutzeymateen assemblage records a portion of the polyphase deformation experienced by rocks within the core of the Coast Plutonic Complex. This series of deformational events probably took place during Late Cretaceous to Early Eocene regional orogenic activity. The Khutzeymateen assemblage is dominated by metamorphosed graywackes and volcaniclastic material. The earliest recognizable deformation involves thrust faulting that juxtaposed rocks of the Khutzeymateen assemblage and Central Gneiss Complex. The next deformational event produced isoclinal folds (F1), a penetrative foliation (S1), and a strong mineral lineation (L1). Both F1 and L1 have a 340°, 15 °orientation. Peak metamorphism (P = 450 ± 50 MPa, T = 650° ± 50 °C) was synchronous with this isoclinal folding event. F1 folding was followed by a brittle chevron folding event (F2) with a 335°, 20° orientation. There is a strong lithologic control on the development of F2 minor folds, which are developed predominantly within regularly layered quartzo-feldspathic lithologies. Open F3 folds (065°, 35°) may have developed by buckling related to differential uplift on the Larch Creek Fault. Post-F3 faults and minor shear zones are developed mostly in the eastern half of the area. The different deformational styles associated with the different deformational events probably reflect variations in the position of this group of rocks with respect to the surface during a single orogenic episode.
Professor Mathews, outburst floods, and other glaciological disasters
Authors: Clarke Garry K. C.
Published: April 2011

Misfortunes befalling the Granduc mining operation near Stewart, British Columbia, stimulated Professor Mathews' influential scientific contributions on subglacial hydrology. A series of violent floods from glacier-dammed Summit Lake menaced the transportation corridor between the Granduc ore concentrator and a tidewater dock at Hyder, Alaska. This unusual problem motivated the research of Mathews and later of Gilbert, who together laid the foundation for a greater understanding of the physics of outburst floods. The physical model that evolved from their research can be used to predict outburst flood magnitude and to cast light on the hydrology of ancient floods such as those from glacial Lake Missoula.
A method for determining the frequency of large-magnitude earthquakes using lake sediments
Authors: Doig Ronald
Published: April 2011

Eastern Canada has experienced at least five earthquakes of estimated Richter magnitude 6 or greater during the last 350 years. The epicentres are usually under the St. Lawrence River, some 100 km east of Quebec City. Historical records of the earthquake of 1663, possibly the largest of these events, describe high levels of silting in streams for up to several months. A silt horizon in normally organic-rich lake sediments has been found in lakes with separate drainage systems and is interpreted as the 1663 event on the basis of rough sedimentation rates obtained from observation of 137Cs fallout of the 1950's and the effects of a dam on one of the lakes. Two other silt layers correspond reasonably well to the next largest earthquakes of 1791 and 1860 + 1870 (combined). Two deep layers were found that by extrapolation of the assumed 1663 layer yield dates of about A.D. 1060 and 600 and are believed to represent prehistoric earthquakes, though possibly not as large as that in 1663. Chemical analyses of the cores show that organic material, Ti, and especially K are very useful for identifying these layers and others that are not visible in the cores.
An improved alpha scintillation counting method for determination of Th, U, Ra-226, Th-230 excess, and Pa-231 excess in marine sediments
Authors: Huntley D. J. , Nissen M. K. , Thomson J. , Calvert S. E.
Published: April 2011

In a previous paper it was shown that thick-source α counting is a simple means for determining Th, U, Th-230 excess, and Pa-231 excess concentrations, and hence sedimentation rates, for deep-sea sediments. Here it is shown that radon escape can lead to inaccurate results if powdered samples are used and that this problem can be overcome by preparing samples as a borate glass before measurement. Glassed samples also permit a novel measurement of the Ra-226 content by measurement of the post-fusion buildup of Rn-222, a determination shown to be necessary for near-surface sediments that have a deficit of Ra-226. It is also shown that Po-210 is lost during the fusion and that this loss can be allowed for in the calculations.The above observations are found on comparisons of measured and calculated α count rates for several Th and U standards and on comparisons with α spectrometry results from four sets of deep-sea core samples.
Late Devonian rugose corals and the Frasnian–Famennian crsis
Authors: Sorauf J. E. , Pedder A. E. H.
Published: April 2011

All well-dated occurrences of Upper Devonian septate corals (subclass Rugosa) are analyzed at species and higher taxonomic levels. Platform-dwelling corals are differentiated from the less numerous basin-dwelling corals.Through early and middle Frasnian time, evolution outpaced the extinction of rugose corals, so that late Frasnian faunas were more diverse than the earliest Frasnian faunas. This gradual increase of genera was terminated abruptly by an almost complete extinction of late Frasnian platform-dwelling Rugosa in uppermost gigas to lower Palmatolepis triangularis Zone time. None of the 151 species, and probably as few as two or three, at most five, of the 47 genera of late Frasnian shallow-water corals survived this event. The loss of coral biomass was equally devasting. Very few early Famennian platform-dwelling corals are known, although platform carbonates of this age were deposited in several regions. Platform faunas, comprising 66 species and 27 genera, reappeared in late Famennian time. These faunas were unrelated phylogenetically to known Frasnian faunas but were forerunners of shallow-water Carboniferous faunas.Basin-dwelling Rugosa were affected little by the late Frasnian extinction event: all 12 Frasnian genera survived it.Rugose coral data provide compelling evidence for a major late Frasnian extinction of shallow-marine benthos without suggesting a unique cause of it. The data are consistent with results expected of an asteroid impact or a rapid decline of ocean temperature, especially in regard to the very much higher survival rate among basin-dwelling corals. However, the data are not controlled by a sufficiently refined time scale to prove the geological instantaneity of such an event.
Late Quaternary glacial and sea-level events, Clements Markham Inlet, northern Ellesmere Island, Arctic Canada
Authors: Bednarski Jan
Published: April 2011

Clements Markham Inlet cuts into the Grant Land Mountains of the northernmost coast of Ellesmere Island. The head of the inlet is bounded on three sides by mountain ice caps that surround lowlands mantled by extensive raised marine deposits. Fieldwork and mapping of late Quaternary sediments were used to determine the limits of past glaciations and the nature of ice retreat from the inlet head. Forty-five radiocarbon dates on driftwood and marine shells provide a deglacial chronology and document related sea-level adjustments.High-level ice-marginal meltwater channels and mountain summit erratics indicate that ice once inundated all of Clements Markham Inlet. During at least one of these undated glaciations, ice flowed unconstrained by the local topography. In contrast, the most recent glaciation involved confluent trunk glaciers, which terminated near the head of the inlet. Beyond this terminus, smaller glaciers entering the sides of the inlet debouched into a glacioisostatically depressed sea (full glacial sea). Retreat from the last glaciation is documented by moraines, kame terraces, and ice-contact deltas.Inside the ice limit at the head of the inlet, sections commonly show that a marine transgression occurred immediately after the retreat of the ice. Conversely, sections outside the last ice limit, along the sides of the inlet, show complex intercalations of marine and glacigenic sediments. These indicate proximal ice-front conditions where small valley glaciers locally contacted the sea.The oldest date on the last ice limit is 9845 BP. After this, slow retreat was in progress, and some glaciers were within 6 km of their current positions by ca. 9700 BP. At the head of the inlet, the mouths of the confluent valleys became ice free by 8000 BP. After 8000 BP, glacial retreat accelerated greatly, so that the entire lowland became ice free within 400 years.Relative sea-level curves from the inlet indicate ice-load changes that confirm this pattern of ice retreat. Outside the last ice limit, the full glacial sea reached 124 m asl by at least 10 000 BP. Emergence from this sea occurred slowly between at least 10 000 and 8000 BP (0.72 m 100 year−1). This period was followed by "normal" rapid postglacial emergence, which decelerated to the present.The marine limit of the full glacial sea rises from 92 m asl, at the outer coast, to 124 m asl near the last ice limit at the head of the inlet. Initial emergence from the full glacial sea occurred simultaneously throughout the inlet. On the proximal side of the last ice limit, the marine limit descends in the up-ice direction and becomes progressively younger. Individual strandlines tilt up in a southwesterly direction towards the central Grant Land Mountains, suggesting a former centre of glacio-isostatic loading in that area.
The Cretaceous–Tertiary boundary in the central Alberta Foothills. II: Miospore and pollen taxonomy
Authors: Sweet A. R.
Published: April 2011

The miospore and pollen discussed populations are from samples bounding the Cretaceous–Tertiary boundary in both the central Alberta Foothills and southwestern Saskatchewan.Nine new species, Aquilapollenites immiser, A. vulsus, Cranweliia suhtilis, Myrtaceidites solidus, Penetetrapites inconspicuus, Polotricolporites rotundus, Racemonocolpites formosus, Retibrevitricolporites beccus, and Striatellipollis raidiata, and two new varieties, Poiotricoiporites rotundus var. rotundus and P. rotundus var. pumilus, are described. Five new combinations, Gabonisporis cristatus, Nyssoidites anulatus, Pandaniidites typicus, Retibrevitricolporites marginus, and Ulmoideipites hebridicus, are made. The morphology of five previously described species is discussed and a key to species of Ulmoideipites is presented.The definition of these taxa is to further aid in the understanding of the floral events associated with the Cretaceous–Tertiary boundary interval.
The role of contemporaneous faulting on Late Silurian sedimentation in the eastern M'Clintock Basin, Prince of Wales Island, Arctic Canada
Authors: Mortensen Paul S. , Jones Brian
Published: April 2011

During the Late Silurian, the eastern margin of the M'Clintock Basin was the site of slow sedimentation on a relatively stable carbonate platform. It is apparent, however, that contemporaneous (syndepositional) faults segmented this basin into several quasi-independent subbasins during deposition of the Cape Storm, Douro, and Somerset Island formations. Differential subsidence of these subbasins played a major role in controlling sedimentation patterns and stratigraphie thickness. These subbasins may have been sustained into the Early Devonian, as is evident from the facies of the overlying Peel Sound Formation. The east–west orientated, reactivated basement faults bounding the subbasins served as zones of weakness during the development of the Cornwall is Fold Belt and are evident in the present-day outcrop.
Former southwesterly ice flows in the Abitibi–Timiskaming region: implications for the configuration of the late Wisconsinan ice sheet
Authors: Veillette J. J.
Published: April 2011

Measurements at some 300 cross-striated sites in the Abitibi–Timiskaming area of Quebec and Ontario revealed two former directions of ice flow: an older west-southwest one (230–270°) in the extreme western part of the area, and a younger, widespread south-southwest one (180–220°) in the region west of the Harricana – Lake McConnell glaciofluvial complex. These sets of older striae, whether one or both on the same outcrop, are almost everywhere crossed by marks of a younger ubiquitous flow to the south-southeast (130–170°). On the basis of striae directions measured below an older till and of three dates obtained from intertill (below the surficial till) nonglacial sediments in the Timmins and Matheson areas in Ontario and the Selbaie mine area in Quebec, the oldest west-southwest (230–270°) striae are tentatively associated with the west-southwest flow that deposited this lowermost till in early to mid-Wisconsinan time or earlier.The Harricana – Lake McConnell glaciofluvial system extends from James Bay to the vicinity of North Bay Ontario and probably continues farther south to the Lake Simcoe area. It is strictly an interlobate deglaciation feature and does not result from the converging flows of two coalescing glaciers. At the last glacial maximum the dominant ice-flow direction in the area was probably toward the southwest, across the space occupied by this glaciofluvial system, confirming the flow lines shown by most models of the late Wisconsinan ice sheet. Because none of the cross-striated outcrops showing marks of the former south-southwest (180–220°) and of the last south-southeast (130–170°) movements show evidence of differential weathering and because glacial transport was due to the former southwest movement at several locations, it is proposed that the cross-striations result from the same ice mass subjected to (1) a general change in flow direction from the southwest to the southeast and (2) a complete scission that led ultimately to the deposition of the Harricana – Lake McConnell glaciofluvial system in the interlobate position.
Ice-push caves in platform limestones of the Montréal area
Authors: Schroeder J. , Beaupré M. , Cloutier M.
Published: April 2011

Continental-type glaciers, which covered the Montréal area, are known to have been responsible for bedrock deformation related to compressive forces. On the other hand, here we report cave systems hundreds of metres long that were caused by tension and shearing of the same bedrock. These voids were created in a low-relief area and in thin, interbedded limestone and shale. Their geometrical characteristics suggest that at least the uppermost 10 m of this limestone was broken up during middle Wisconsinan time and that this intersliding of stratified rock masses continued until the late Wisconsinan. Except for rare collapses, these voids, of unknown sizes until now, show almost no connection with the superficial geomorphology.
Additional K–Ar isotopic dates for the Carmacks Group (Upper Cretaceous), west central Yukon
Authors: Lowey G. W. , Sinclair W. D. , Hills L. V.
Published: April 2011

Three whole-rock K–Ar analyses on andesites from the Indian River area, west central Yukon, yielded dates of 69.0 ± 1.7, 65.2 ± 1.7, and 64.8 ± 1.7 Ma. These confirm earlier dates indicating the Carmacks Group is Late Cretaceous in age. A single date of 51.4 ± 3.9 Ma was obtained from a tuff in the Sixty Mile River area, west central Yukon, suggesting an Eocene age for these deposits. However, this date is considered equivocal because it is anomalous when compared with the other dates from the area.
Petrology of cogenetic silica-saturated and -oversaturated plutonic rocks in the Ruby geanticline of north-central Alaska
Authors: Blum Joel D. , Blum Alex E. , Davis Terry E. , Dillon John T.
Published: April 2011

Felsic plutonic rocks in the northwestern portion of the Ruby geanticline of north-central Alaska occur as two distinct rock suites: (1) silica-saturated monzonite and syenite and (2) silica-oversaturated granite. K–Ar mineral ages for each suite average 107 ± 6 Ma, and both suites plot along a single Rb–Sr whole-rock isochron that yields an age of 112 ± 4 Ma and an initial 87Sr/86Sr ratio of 0.70778 ± 0.00006. Whole-rock δ18O values range from + 6.75 to + 7.30‰. The two suites cannot be related by simple fractionation, yet they appear to have a chemically and isotopically similar parental magma. Based on chemical mixing calculations, observations of magma – wall-rock interaction and xenolith abundances, we suggest a model whereby a small amount of assimilation of siliceous wall rock by a portion of an originally silica-saturated magma caused an increase in silica saturation, which led to two distinct fractionation suites. The almost exactly silica-saturated composition and extremely high Sr concentrations indicate that the silica-saturated magma formed at high pressure. This evidence, combined with the initial 87Sr/86Sr ratio and δ18O values, leads us to suggest a lower crust or enriched mantle source for the magma. The silica-saturated suite may be representative of a parental magma that contributed to the melting of upper crustal siliceous wall rock throughout the Ruby geanticline. Whereas a small amount of crustal contamination led to the silica-oversaturated rocks that occur in the northwestern part of the Ruby geanticline, larger amounts of assimilation may have formed the largely anatectic granites of the same age that are found in the interior of the Ruby geanticline.
Optical and electron microscope investigation of temperature-dependent microstructures in anorthoclase
Authors: Smith K. L. , McLaren A. C. , O'Donnell R. G.
Published: April 2011

Optical and transmission electron microscopy has been used to study the cross-hatched microstructure (associated with the intersection of albite and pericline twin lamellae) that is characteristic of b*c* sections of anorthoclase. With the aid of a specimen-heating stage fitted to each microscope, the changes that occur in the microstructure on heating and subsequent cooling have been observed over the temperature range from ~20 to 950 °C. Observations of unheated crystals indicate that the cross-hatched microstructure consists of a chessboard pattern of triclinic areas (diagonal pairs of which are essentially albite-twin related) and of optically monoclinic areas that consist of domains of fine-scale albite-twin lamellae and domains of pericline-twin lamellae. The four-spot diffraction pattern characteristic of M twinning is observed only from volumes of specimen containing both types of domain. The complex twin interactions at the domain boundaries are described in detail. The changes in optical contrast of the twins when the crystals are heated are shown to be due to changes in the orientation of the refractive index ellipsoid; the disappearance of twins does not necessarily indicate a change to monoclinic symmetry. The observations also indicate that the relative stability of albite and pericline twins is a function of temperature, the pericline twin being more stable than the albite twin at high temperatures near the monoclinic–triclinic transformation and the opposite at room temperature. Evidence is also given that the twin microstructure that develops at the transformation is strongly influenced by external stress.