bluuebunny/crossref_metadata_2025 huggingface dataset:
The Abitibi-Grenville Lithoprobe transect part III: introduction
Authors: Ludden John , Hynes Andrew
Published: April 2011

This is the third and final compendium of papers on the Abitibi-Grenville Lithoprobe transect. Much of the focus is on the Grenville Province, complementing the previous compendia which focussed on the Abitibi subprovince. There are, however, papers on the Abitibi subprovince concerning detailed gravity studies, granitoid geochemistry, and fluid evolution. The evolution of the Grenvillian orogen is examined in a series of papers combining observations from seismic studies, isotopic characteristics, geochronology, petrology, and structural geology. There are papers discussing the heat flux, teleseismic attributes, and electromagnetic characteristics across the entire region of the Lithoprobe transect, and an overview of Lithoprobe studies of the Sudbury region. A synthesis paper contrasts the Archean tectonic evolution of the Abitibi subprovince with the Mesoproterozoic evolution of the Grenville Province.
Age and origin of advanced argillic alteration zones and related exotic limonite deposits in the Limonite Creek area, central British Columbia
Authors: Deyell C L , Thompson J FH , Friedman R M , Groat L A
Published: April 2011

The Limonite Creek property in north-central British Columbia contains several zones of silicic and acid-sulphate alteration. These zones grade through advanced argillic and aluminous mineral assemblages to sericitic and regional propylitic alteration. Alteration assemblages are characteristic of high-sulphidation systems, although the abundance of pyrophyllite and andalusite suggests formation at depths below typical epithermal environments. Alteration occurred between 212 and 52 Ma as determined from field relations and U-Pb dating of intrusions. The deformed nature of the alteration assemblages and a minimum age of alunite (144 ± 8 Ma) suggest formation in latest Triassic to Middle Jurassic time. Based on these age constraints, alteration zones at Limonite Creek are significantly older than the Eocene Equity Silver deposit (ca. 60 Ma), despite the latter's proximity and similar styles of alteration. Based on the new dates, host rocks at Limonite Creek are Late Triassic or older, and hence regional stratigraphy needs reassessment. Extensive exotic limonite deposits occur around the alteration zones and at lower elevations to the south. Radiocarbon dating indicates that the deposits have been accumulating for at least 8000 years. Iron released during weathering was transported in low-pH waters and precipitated initially as ferrihydrite, with subsequent conversion to goethite. Water chemistry confirms that the process is still active. In addition to iron, the limonite contains minor copper and zinc. The formation of low-pH waters and the transport of iron resulted from weathering of pyrite-rich alteration assemblages with negligible buffering capacity.
Some graptolites from the late Tremadoc and early Arenig of Yukon, Canada
Authors: Jackson D E , Lenz A C
Published: April 2011

Ten graptolite species from upper Tremadoc and lower Arenig strata are described from a 160 m thick, homoclinal, totally exposed section of the Road River Group in the Upper Canyon of Peel River, Yukon. This is believed to be one of the most complete sequences of this age range known to science. Graptolites were collected from 40 levels in the (lowest to highest) Adelograptus antiquus, Kiaerograptus pritchardi, Paradelograptus kinnegraptoides, Tetragraptus approximatus, and Pendeograptus fruticosus biozones. Two new species described are Paradelograptus rallus sp.nov. from the K. pritchardi Biozone and Kinnegraptus reclinatus sp.nov. from the Tetragraptus fruticosus Biozone.
Walker Creek fault zone, central Rocky Mountains, British Columbia-southern continuation of the Northern Rocky Mountain Trench fault zone
Authors: McMechan M E
Published: April 2011

Walker Creek fault zone (WCFZ), well exposed in the western Rocky Mountains of central British Columbia near 54°, comprises a 2 km wide zone of variably deformed Neoproterozoic and Cambrian strata in fault-bounded slivers and lozenges. Extensional shear bands, subhorizontal extension lineations, slickensides, mesoscopic shear bands, and other minor structures developed within and immediately adjacent to the fault zone consistently indicate right-lateral displacement. Offset stratigraphic changes in correlative Neoproterozoic strata indicate at least 60 km of right-lateral displacement across the zone. WCFZ is the southern continuation of the Northern Rocky Mountain Trench (NRMT) fault zone. It shows a through going, moderate displacement, strike-slip fault system structurally links the NRMT and the north-central part of the Southern Rocky Mountain Trench. Strike-slip motion on the WCFZ occurred in the Late Cretaceous to Early Eocene at the same time as northeast-directed shortening in the fold-and-thrust belt. Thus, oblique convergence in the eastern part of the south-central Canadian Cordillera was apparently resolved into parallel northwest-striking zones of strike-slip and thrust faulting during the Late Cretaceous to Early Eocene. The change in the net Late Cretaceous to Early Eocene displacement direction for rocks in the Rocky Mountain trenches from north (56-54°N) to northeast (52-49°N) suggests that the disappearance of strike-slip displacement and increase in fold-and-thrust belt shortening in the eastern Cordillera between 56° and 49°N is largely the result of a north-south change in relative plate motion or strain partitioning across the Cordillera, rather than the southward transformation of right-lateral strike-slip displacement on the Tintina - NRMT fault system into compressional deformation.
A new ammonite and coccolith fauna from the lowermost Fernie Formation (Hettangian) in northwestern Alberta, Canada
Authors: Hall Russell L , Kendall Debra R , Taylor David G , Craig James
Published: April 2011

The occurrence of the ammonite Discamphiceras cf. silberlingi Guex in a core 25 cm above the base of dark, bituminous shales of the lowermost Fernie Formation in the subsurface of northwestern Alberta establishes their middle to late Hettangian age. Associated coccoliths suggest a possible late Hettangian to early Sinemurian age, which is the oldest so far assigned to these shales and differs considerably from both the Sinemurian age of the type Nordegg Member of the outcrop belt and the Pliensbachian age of its supposed basinal equivalents ("Nordegg Member" of some recent authors).
Mantle flow mechanisms of epeirogeny and their possible role in the evolution of the Western Canada Sedimentary Basin
Authors: Pysklywec R N , Mitrovica J X
Published: April 2011

Otherwise stable cratons periodically experience enigmatic episodes of large-scale uplift and subsidence that may result in widespread marine transgressions and the subsequent formation of sedimentary basins. Strata in the Western Canada Sedimentary Basin, for example, record flooding events that reached deep into the interior of the continent during the Devonian to Carboniferous. The epeirogenic motion which caused this deposition was contemporaneous with compressive tectonic events along the western plate margin of Laurussia. We propose that the long-wavelength component of inferred subsidence and uplift across the basin was the result of mantle flow-induced dynamic topography. In particular, we investigate the epeirogenic signals associated with the coupled mantle processes of near-surface subduction and later stage penetration of accumulated slab material through the endothermic phase change at 660 km depth. Numerical simulations of convection are presented to model the thermo-mechanical evolution of subduction in the mantle. The associated dynamic topography is initially characterized by tilting of the continental margin and submergence approximately 1000 km from the trench due to viscous effects associated with the subduction. A more extensive transgression onto the continental platform follows as accumulating slab material penetrates through the endothermic phase change. We argue that the predicted subsidence and uplift is broadly consistent with the inferred record of DevonianCarboniferous epeirogeny across western Canada, and thus that the evolution of the Western Canada Sedimentary Basin may be intimately connected to mantle flow processes occurring contemporaneously beneath the craton.
The last glaciation of east-central Ellesmere Island, Nunavut: ice dynamics, deglacial chronology, and sea level change
Authors: England John , Smith I Rod , Evans David JA
Published: April 2011

During the last glacial maximum of east-central Ellesmere Island, trunk glaciers inundated the landscape, entering the Smith Sound Ice Stream. Accelerator mass spectrometry (AMS) dates on individual shell fragments in till indicate that the ice advanced after 19 ka BP. The geomorphic and sedimentary signatures left by the trunk glaciers indicate that the glaciers were polythermal. The configuration and chronology of this ice is relevant to the reconstruction of ice core records from northwestern Greenland, the history of iceberg rafting of clastic sediments to northern Baffin Bay, the reopening of the seaway between the Arctic Ocean and Baffin Bay, and the regional variability of arctic paleoenvironments. Deglaciation began with the separation of Ellesmere Island and Greenland ice at fiord mouths ~8-8.5 ka BP. Ice reached fiord heads between 6.5 and 4.4 ka BP. Trunk glacier retreat from the fiords of east-central Ellesmere Island occurred up to 3000 years later than in west coast fiords. This later retreat was favoured by (1) impoundment by the Smith Sound Ice Stream in Kane Basin until ~8.5 ka BP, which moderated the impact of high summer melt recorded in nearby ice cores between ~11.5 and 8.5 ka BP; (2) the shallow bathymetry and narrowness (<2 km) of the east coast fiords, which lowered calving rates following separation of Innuitian and Greenland ice; and (3) the likelihood of higher precipitation along east Ellesmere Island. Glaciers throughout the field area readvanced during the late Holocene. The greater advance of coastal glaciers is attributed to their proximity to the North Water polynya in Baffin Bay.
Age and composition of the Ruisseau Isabelle Mélange along the Shickshock Sud fault zone: constraints on the timing of mélanges formation in the Gaspé Appalachians
Authors: Malo Michel , Cousineau Pierre A , Sacks Paul E , Riva J FV , Asselin Esther , Gosselin Patrice
Published: April 2011

Mélanges are common in the Humber and Dunnage zones of the Quebec Appalachians. Humber Zone mélanges are spatially associated with Taconian nappes and believed to be of tectonic origin. Dunnage Zone mélanges are interpreted as relicts of an Ordovician accretionary prism. The Ruisseau Isabelle Mélange (RIM) in the Gaspé Appalachians was first interpreted as a Dunnage Zone mélange, because of its tectonic position along the Baie Verte  Brompton Line and lithological components, such as dark mudstone, blocks of ultramafic rocks, and greenish chromite-bearing sandstone. The RIM comprises sedimentary rock assemblages (Composite Shale, Black Shale, and Chromite-Bearing Sandstone assemblages), an Exotic Block, a Pebbly Mudstone Assemblage and slivers of Serpentinized Peridotite, and Metamorphic Tectonite. Most mélanges of the Dunnage Zone in the Quebec Appalachians contain partly similar rocks, but their age is not well constrained. Recent work on the RIM and Cap-Chat Mélange of the Humber Zone and new fossil finds in the RIM rock assemblages allow us to conclude that previous distinction between mélanges of the Dunnage and Humber zones on the basis of rock-type associations is not valid. According to the age of the RIM rock assemblages, mélanges in the northern Gaspé Appalachians continued forming after the mid-Caradocian, later than the Dunnage Zone mélanges of southern Gaspé Appalachians. The juxtaposition and structural features of the RIM rock assemblages result from repeated faulting along the Shickshock Sud fault from Late Ordovician to Middle Devonian.
A Cretaceous back-arc basin in the Coast Belt of the northern Canadian Cordillera: evidence from geochemical and neodymium isotope characteristics of the Kluane metamorphic assemblage, southwest Yukon
Authors: Mezger Jochen E , Creaser Robert A , Erdmer Philippe , Johnston Stephen T
Published: April 2011

The Coast Belt of the northern Cordillera in Canada is the locus of the boundary between accreted and ancient North American margin rocks. The largest exposure of metasedimentary rocks in the Coast Belt is the Kluane metamorphic assemblage (KMA), a northwest-striking belt 160 km long of graphitic micaquartz schist and gneiss with minor interfoliated olivine serpentinite. The KMA does not appear to correlate with other sedimentary or metamorphic rock assemblages in the Canadian Cordillera. To determine its tectonic setting and protolith provenance, we analyzed trace element, rare earth elements, and neodymium isotope compositions of the KMA, of the adjacent pericratonic Aishihik metamorphic suite (AMS) of the YukonTanana terrane, and of adjacent slates of the Dezadeash Formation (DF), filling a Late Jurassic  Early Cretaceous flysch basin. The εNd(0) values of analyzed KMA samples range from 1.4 to 5.6 and depleted mantle model ages (TDM) range from 1.16 to 1.45 Ga. KMA samples are intermediate between more evolved AMS samples (average εNd(0) 25, TDM = 2.6 Ga) and more juvenile DF samples (εNd(0) = +1.9, TDM = 0.95 Ga). The intermediate characteristics of the KMA samples cannot be linked to a known source region and are interpreted to reflect homogeneous mixing from predominantly juvenile and minor evolved sedimentary sources. A compatible tectonic setting is a back-arc basin within influence of a continental source. Eastward subduction of the KMA beneath ancient North America collapsed the back-arc basin by latest Cretaceous time.
A comparative 40Ar/39Ar conventional and laserprobe study of muscovite from the Port Mouton pluton, southwest Nova Scotia
Authors: Fallon Raymond P , Reynolds Peter H , Clarke D Barrie
Published: April 2011

We report 40Ar/39Ar age spectrum and laserprobe data for primary magmatic or fluido-magmatic muscovite minerals from the Port Mouton pluton, one of several weakly peraluminous peripheral plutons in the Meguma terrane, southwestern Nova Scotia. Laserprobe data from the cores of thin grain fragments suggest that this pluton cooled rapidly following intrusion at 373 ± 1 Ma, the UPb monazite age. The rims of thicker more complete grains record ages of 315325 Ma, even in cases where there have been no apparent changes in grain rim chemistry and where deformation is minimal. The observed age gradients may be the result of prolonged reheating during the Late Carboniferous Alleghanian Orogeny or, alternatively, the result of rapid cooling at this time to temperatures below the closure value for muscovite rims. Conventional age spectra obtained from muscovite separates record neither the older intrusion age nor the younger resetcooling age. Instead, these intermediate ages appear to reflect the averaging of intragrain (corerim) age variations in thick grains and thus have no chronological significance. For these Port Mouton muscovite minerals, the record of initial cooling appears to reside only in certain limited regions of a given grain, a record that can be recovered by the laserprobe technique applied to carefully prepared subgrain fragments. A contrast in the early tectono-thermal histories of plutonic rocks in southwestern Nova Scotia relative to those in the northeast may be the result of perturbation by a mantle plume.
Ammonoid faunas from the Cardium Formation (Turonian-Coniacian, Upper Cretaceous) and contiguous units, Alberta, Canada: I. Scaphitidae
Authors: Braunberger Wayne F , Hall Russell L
Published: April 2011

While the Cardium Formation (TuronianConiacian, Upper Cretaceous) is one of the major hydrocarbon sources, and consequently one of the most intensely studied siliciclastic formations in the Western Canada Sedimentary Basin, it remains one of the more controversial units in terms of understanding the depositional environments and processes it represents, and correlations between subsurface and outcrop. Proposed subsurface subdivisions based on sequence stratigraphic concepts, and relation of these allomembers to long-established members of the outcrop belt, have provoked further disagreements. The general lack of biostratigraphic data within the Cardium Formation makes it difficult to test different models and to resolve conflicting proposals. This paper provides stratigraphic and taxonomic information on all known scaphitid ammonoids from the Cardium Formation and correlation of these faunas with the Turonian and Coniacian zonal scheme established in the United States Western Interior; future publications will provide similar treatments of the collignoniceratid ammonites and inoceramid bivalves.
Modes of extinction in two Devonian ostracode faunas of western Canada
Authors: Braun Willi K
Published: April 2011

The development of a prominent Middle Devonian Eifelian and an Upper Devonian Frasnian ostracode faunal sequence of western Canada is used to trace their evolutionary pathways, to illustrate evolutionary dynamics, and to evaluate the most probable causes and implications of the major and minor changes, which are clearly expressed in two sets of charts. A connection between sedimentary transgressiveregressive and evolutionary cycles is evident and documented in sample-for-sample accounts. Major changes in sea level were the primary cause for the most obvious breaks and trends in the faunal sequences and were responsible for the cyclic development of both the sedimentary and ostracode records. In contrast, numerous subordinate faunal breaks impart a distinctly punctuated pattern to both extinction and speciation pathways. Their regular spacing point to rhythmic influences that are interpreted to reflect primarily temperature fluctuations to which ostracodes are known to react in direct and indirect ways. In turn, the periodicity of the changes falls within the time frame of the Milankovitch Effect or to any one, or a combination, of its three variables. By combining the overall cyclic development with the punctuated progression of both extinction and speciation events in an "event-stratigraphic chart," a blueprint of the evolutionary dynamics emerges, which can be directly applied in sequence-stratigraphic reconstructions.
Geology and tectonic setting of Paleoproterozoic granitoid suites in the Island Harbour Bay area, Makkovik Province, Labrador
Authors: Barr S M , White C E , Culshaw N G , Ketchum J WF
Published: April 2011

Paleoproterozoic granitoid rocks in the Island Harbour Bay area (Kaipokok domain, Makkovik Province, Labrador) are divided into four separate suites on the basis of field relations, petrology, and age. The redefined Island Harbour Bay plutonic suite consists of ca. 18951870 Ma dioritic to granitic (mainly granodioritic and granitic) units. The rocks are variably foliated as a result of emplacement under amphibolite-facies conditions in a dextral transpressive regime during Andean-type subduction. The dominant mafic mineral is biotite, and accessory epidote, allanite, and titanite are abundant. The suite is calc-alkalic, but with rare-earth element patterns similar to those of Archean tonalitictrondhjemiticgranodioritic suites. It is interpreted to have formed deep in an Andean-type magmatic arc at the margin of the Nain continent. In contrast, the younger Hares Islands and Drunken Harbour granites (emplaced at ca. 1805 and 1790 Ma, respectively) were part of widespread late-orogenic magmatic activity in the Makkovik Province. In contrast to the Island Harbour Bay plutonic suite, these units retain igneous textures and are either unfoliated or display magmatic foliation, locally modified by emplacement in active shear zones. The ca. 1716 Ma Blacklers Bight granite varies from porphyritic to equigranular, is fluorite-bearing, and has chemical features approaching those of continental A-type granites. Similar granite occurs farther south in the Makkovik Province, reflecting widespread anorogenic magmatic activity at that time, perhaps related to mafic magma underplating. Variable interaction with Archean (Nain Province) crust by granitic magmas of all three ages is evidenced by εNd values ranging from 7.2 to 2.5.
Late Wisconsinan stratigraphy and chronology of southern St. George's Bay, Newfoundland: a re-appraisal
Authors: Bell Trevor , Liverman David GE , Batterson Martin J , Sheppard Kevin
Published: April 2011

Almost sixty years after the initial mapping of extensive Quaternary sediments along the coast of St. George's Bay, Newfoundland, a revised stratigraphic section is presented which identifies five main sediment types (diamicton, mud, sand, gravelly sand, gravel) and their stratigraphical position along 39 km of coastline from Highlands to Flat Bay. Most of the sediments overlying a basal till (St. George's River Drift) are interpreted to have been deposited in an ice-proximal to ice-distal glaciomarine environment by debris flow, underflow, current flow, or suspension settling, and capped by glaciofluvial outwash (Bay St. George Delta). For the most part, sections display a relatively simple deglacial sequence in a shallowing marine to fluvial environment. Where hummocky ridges intersect the coast, however, the sedimentary sequences are more complex and the variability in depositional style is typical of grounding line fans at a tidewater glacier margin. The occurrence of an upper diamicton or coarse gravels (Robinsons Head Drift) was generally observed only in grounding-line fan sequences and is interpreted here in the context of marginal fluctuations of a quasi-stable tidewater glacier, and not necessarily a climatically-induced readvance of a land-based ice margin (Robinsons Head readvance). Radiocarbon dates on marine shells from varied stratigraphic positions and sedimentary units suggest rapid deposition occurred in a glaciomarine environment between 14 and 13 ka BP.
Quaternary geology of the Babine porphyry copper district: implications for geochemical exploration
Authors: Levson Victor M
Published: April 2011

The Quaternary stratigraphy of the Babine Lake region is characterized by a Late Wisconsinan succession of advance-phase glaciolacustrine sediments, glaciofluvial deposits, and till. Pollen data from a rare new interglacial site suggest a colder than present Middle Wisconsinan climate. Ice flow during the last glaciation was dominantly southeasterly, but in the Babine Range a regional, westerly ice-flow event occurred. Evidence for westerly flow diminishes eastward of Babine Lake, suggesting that the valley was near the eastward limit of an interior ice divide. Deglacial sediments include ice-marginal debris-flow, glaciofluvial, and glaciolacustrine sediments. Raised-delta elevations indicate that Glacial Lake Babine extended nearly 150 m above present lake level to 850 m asl, and higher, earlier phases may have existed locally. A variety of Holocene deposits cap the Quaternary succession. Glaciation has important implications for exploration in this copper-producing area. Southeasterly glacial dispersal patterns dominate, despite a regionally complex ice-flow history. Highly anomalous concentrations of copper occur in tills down-ice of most known bedrock copper occurrences, and a number of similarly anomalous till sites with no known copper sources have been identified in drift-covered areas. Exploration problems due to the thick and complex surficial cover can be overcome by selective sampling of basal tills, the composition of which clearly reflects the presence of buried mineral deposits. The effectiveness of till geochemistry as a method for locating buried mineralization in the region will be enhanced by careful selection of sample media and by a clear understanding of the glacial history.
Quaternary stratigraphy and history of the Ootsa Lake - Cheslatta River area, Nechako Plateau, central British Columbia
Authors: Mate D J , Levson V M
Published: April 2011

Erosion along the Nechako Reservoir and Cheslatta River Spillway has resulted in unusually well-exposed late Quaternary and Holocene stratigraphy. Surficial sediments in the study area are mostly products of Late Wisconsinan glaciation. However, evidence for pre-Late Wisconsinan sedimentation has been found along the shores of the Nechako Reservoir, including till of an older glaciation and organic-bearing, blue-grey, lacustrine sediments of probable Middle Wisconsinan age. Stratigraphic correlation of the lake sediments suggests that an extensive lake system occurred in the region during the Olympia Nonglacial Interval. Late Wisconsinan ice initially moved along major valleys, with glaciofluvial outwash deposited in front of the advancing ice. Advance-phase glaciolacustrine sediments are rare but significant, as slope failures are spatially associated with areas where they are preserved. The distribution of these sediments and associated deltaic deposits indicates that advance-phase glacial lakes occurred up to approximately 855 m asl, at least several metres above the modern reservoir level. Sediments deposited in front of the ice margin were overridden during ice advance and are best preserved in large valleys. At the glacial maximum, ice flowed northeasterly throughout the study region. Crag and tails, flutings, and drumlinoid ridges with a generally consistent northeast trend are the dominant landforms. Till is the most common Pleistocene surficial sediment, covering approximately 80% of the area; large areas of exposed bedrock are rare. Late-glacial glaciofluvial and Holocene fluvial deposits are uncommon and occur mainly along the Cheslatta River valley.
A new genus of ichthyosaur from the Late Triassic Pardonet Formation of British Columbia: bridging the Triassic Jurassic gap
Authors: Nicholls Elizabeth L , Manabe Makoto
Published: April 2011

Both the genus Shastasaurus and the family Shastasauridae have long been hard to define due to the fragmentary nature of the type specimens. Consequently, recent interpretations of the genus have been based almost entirely on Shastasaurus neoscapularis from the Late Triassic Pardonet Formation of British Columbia. Two new specimens of this taxon, from Pink Mountain, British Columbia, demonstrate that it does not belong in the genus Shastasaurus. This paper describes the new specimens, and refers the species to Metashastasaurus gen nov. Post-cranially, the skeleton of Metashastasaurus resembles that of shastasaurids, differing primarily only in the shape of the scapula and fibula. However, the skull has a unique combination of characters, including large diamond-shaped frontals that enter the supratemporal fenestrae, and very narrow posterior extensions of the nasals, which contact the postfrontals. It also differs from the skull of Shastasaurus in the presence of both a parietal ridge and postparietal shelf. This is a combination of derived characters previously known only in Jurassic forms. The front limb has four proximal carpals and four digits, indicating that previous reconstructions were based on incomplete material. Shastasaurus pacificus Merriam 1895, the type species of the genus Shastasaurus, must be considered a nomen dubium, making the genus Shastasaurus invalid. Until this problem is clarified, the use of the generic name Shastasaurus should be restricted to Merriam's type specimens, of which only Shastasaurus alexandrae and Shastasaurus osmonti are based on adequate material.
Ammonoid faunas from the Cardium Formation (TuronianConiacian; Upper Cretaceous) and contiguous units, Alberta, Canada: II. Collignoniceratidae and Placenticeratidae
Authors: Braunberger Wayne F , Hall Russell L
Published: April 2011

Ammonite species of the genera Prionocyclus, Subprionocyclus, and Collignoniceras described here from the Cardium Formation, in combination with scaphitid ammonoids and inoceramid bivalves, allow recognition of all biozones for the Turonian Stage (Upper Cretaceous) established farther south in the United States Western Interior Basin. Although many of the species used in this zonation were endemic to the Western Interior seaway, more cosmopolitan forms at some levels do allow correlation with western European sequences. The presence of Prionocyclus germari Reuss is firmly established in the lower parts of the Leyland Member, confirming the position of the Turonian-Coniacian boundary and earlier proposed constraints on the duration of the CardinalLeyland hiatus.
Crustal structure of the Grenville Province in southeastern Labrador from refraction seismic data: evidence for a high-velocity lower crustal wedge
Authors: Funck Thomas , Louden Keith E , Reid Ian D
Published: April 2011

The crustal structure of the eastern Grenville and Makkovik provinces was determined using two onshoreoffshore refraction seismic lines of the Lithoprobe Eastern Canadian Shield OnshoreOffshore Transect (ECSOOT). A gravity high in the Hawke River terrane correlates with increased P-wave velocities in the upper 30 km of the crust (6.26.7 km/s in the upper and middle crust and 6.97.1 km/s below) which we interpret as structure inherited from the Labradorian orogen. Velocities in the adjacent Groswater Bay terrane are 6.06.55 km/s in the upper and middle crust and 6.66.95 km/s in the lower crust. The entire Grenville crust is underlain by a 1520 km thick high-velocity lower crustal (HVLC) wedge consisting of an upper layer (7.17.4 km/s) and a lower layer (7.67.8 km/s). The HVLC wedge is interpreted as an underplated layer formed during Iapetan rifting. This interpretation is based on the correlation with the 615 Ma Long Range dykes onshore and the eastward termination of the wedge at the Cartwright Arch. Similar HVLC layers are found offshore western Newfoundland, suggesting that the underplating may be a continuous feature along the passive Grenvillian margin. The Cartwright Arch is characterized by velocities of 6.4 km/s and 4 km thick sediment sequences (4.35.7 km/s) in the surrounding basin, interpreted as an extensional basin with basaltic magmatism within the arch. The Grenville front is clearly marked by a decrease of velocities in the Makkovik Province (5.86.4 km/s in the upper and middle crust, 6.656.85 km/s in the lower crust) and a gradual thickening of the crust (not including the HVLC layer) from 30 km in the Grenville Province to 35 km in the Makkovik Province.
Archean rocks in the southern Rottenstone Domain: significance for the evolution of the Trans-Hudson Orogen
Authors: Bickford M E , Hamilton M A , Wortman G L , Hill B M
Published: April 2011

An augened, strongly flasered, and multiply folded monzonitic gneiss occurs in a structural dome in the Black Bear Island Lake region of northern Saskatchewan, within the ca. 1850 Ma Paleoproterozoic southern Rottenstone Domain of the Trans-Hudson Orogen (THO). A sample of this rock has yielded thermal ionization mass spectrometry (TIMS) and sensitive high-resolution ion microprobe (SHRIMP) zircon data consistent with a formation age of at least 2500 Ma. Zircons also show somewhat younger, ca. 2380 Ma overgrowths, indicating a complex history. The Nd model age (TDM) of 2726 Ma also confirms the late Archean age of the rock, as does the isotopic composition of common Pb from a K-feldspar sample. UPb analyses of titanites yield ages of ca. 1800 Ma, indicating recrystallization during terminal closure of the THO. It is unlikely that the Archean rocks are a part of the Archean Sask craton in the Glennie Domain, for Lithoprobe seismic sections indicate that the Sask craton dips westward beneath the La Ronge and Rottenstone domains. It is more likely that the rocks are part of a klippen of Hearne Province crust emplaced during closure of the THO, a large pendant in the ca. 1850 Ma Wathaman batholith, or a crustal fragment exotic to the orogen. Further study should shed light on the tectonic and paleogeographic history of the THO.
New information onShanshanosaurus huoyanshanensis, a juvenile tyrannosaurid (Theropoda, Dinosauria) from the Late Cretaceous of China
Authors: Currie Philip J , Zhiming Dong
Published: April 2011

Shanshanosaurus huoyanshanensis from the Subashi Formation (Upper Cretaceous) of Xinjiang in northwestern China has long been thought of as a distinctive genus of small theropod. Although usually assigned to its own family, it has generally been included in the tyrannosaurid subfamily Aublysodontinae in recent years. Restudy and description of the only known specimen reveal that it is not a small species, but is a juvenile tyrannosaurine, possibly Tarbosaurus. With a total estimated length of 2.3 m, it is the smallest tyrannosaurid skeleton known. Shanshanosaurus provides the best information available on ontogenetic changes in these enormous carnivores and reveals that young tyrannosaurids had long, low skulls, huge pubic boots, and well-developed limb joints. Evidence suggesting that young tyrannosaurs had relatively longer forelimbs than the adults is not supported by Shanshanosaurus.
Petrogenesis of the Early Proterozoic Matachewan dyke swarm, Canada, and implications for magma emplacement and subsequent deformation
Authors: Phinney W C , Halls H C
Published: April 2011

Major, minor, and rare-earth element analyses of fine-grained marginal material from 249 dykes of the Matachewan giant radiating swarm show that the range in compositions cannot be produced by any simple fractionation model. Instead a two-stage process is required, whereby melts were modified by both fractionation and assimilation of lower crustal material, before rising and ponding at shallower crustal levels (1520 km maximum), where a combination of fractional crystallization, plagioclase phenocryst formation, and periodic melt replenishment took place. These shallow crustal chambers acted as feeders for the numerous dykes. One hypothesis compatible with these observations involves an extensive rising plume that would provide heterogeneous melts over a large area accompanied by stresses that could produce a radial pattern of dykes. In a search for indications of lateral magma flow, a comparison of longitudinal variations in composition along four sample traverses across the western subswarm showed no truly consistent trends. However, Hf/Zr values are highest in the traverse nearest the focal region and lowest in the traverse 250 km away, suggesting a change in magma composition with distance from the focus of the swarm, the assumed plume centre. Given the presently available data, the variations cannot be attributed to progressive fractionation during lateral magma flow in the crust nor to a northward increase in amounts of contamination by known lower crustal assimilants, all of which have Hf/Zr ratios higher than the distal values recorded by the dykes. Instead the variations are thought to reflect a possible compositional zonation of the plume head. The distortion of the western subswarm from a simple radiating pattern may have been facilitated by a low viscosity lower crust, softened by Matachewan igneous activity, and is consistent with deformation by the Blezardian orogen at about 2.22.4 Ga.
New information on Cretaceous troodontids (Dinosauria, Theropoda) from the People's Republic of China
Authors: Currie Philip J , Zhiming Dong
Published: April 2011

Troodontid specimens were recovered from three localities in China by the Sino-Canadian expeditions between 1987 and 1990. These include a Lower Cretaceous form (Sinornithoides youngi), which is the most complete troodontid skeleton ever found, isolated bones from the Iren Dabasu Formation (?Turonian), and partial skeletons of Saurornithoides mongoliensis from Djadokhta-equivalent beds (?Campanian). These, and other specimens recently described from North America, allow a better assessment of the phylogenetic position of troodontids than has been possible before. Although troodontids have autapomorphies that eliminate them from consideration as bird ancestors, they are nevertheless one of the closest avian outgroups within the Theropoda.
Sequence stratigraphy, paleoclimate patterns, and vertebrate fossil preservation in JurassicCretaceous strata of the Junggar Basin, Xinjiang Autonomous Region, People's Republic of China
Authors: Eberth David A , Brinkman Donald B , Chen Pei-Ji , Yuan Feng-Tian , Wu Shao-Zu , Li Gang , Cheng Xian-Shen
Published: April 2011

Multi-kilometre-thick JurassicCretaceous-age sedimentary successions exposed in the southern, northwestern, and northeastern regions of the Junggar Basin display a consistent and correlative stratigraphy comprising four, stacked second-order megasequences: Badaowan, Sangonghe, Shishugou, and Kalaza. Each consists of a basal erosional unconformity or discontinuity surface and lower, middle, and upper units that are interpreted as forestepping, backstepping, and aggradational systems tracts, respectively. Each megasequence is interpreted as recording an upsection shift from active tectonism and uplift to tectonic quiescence with associated changes in crustal response and sediment supply. Basin-wide analysis of megasequences indicates that tectonism was intermittent and regionally variable. A maximum phase of subsidence and sediment accommodation is recorded in the middle unit of each megasequence and correlates with a notable abundance of fossil vertebrates suggesting a primary tectonic and basin-response control on fossil preservation. Seasonally dry climatic conditions were developed first in the northeastern region of the basin during the Pliensbachian, followed by basin-wide seasonal dryness during the Bajocian. Seasonally dry climatic conditions were permanently established across the basin by the Oxfordian and intensified during the Early Cretaceous. A seasonally dry climate from Oxfordian through the Early Cretaceous correlates positively with the widespread presence of fossil vertebrates and suggests an additional climatic control on fossil preservation.
Stratigraphy, sedimentology, and environmental significance of late mid-Holocene dunes, Lauder Sand Hills, glacial Lake Hind Basin, southwestern Manitoba
Authors: Havholm Karen G , Running IV Garry L
Published: April 2011

Mid-Holocene eolian dune and sand-sheet deposits, rare in the northern Great Plains, are buried under a meter or more of younger sediment in the glacial Lake Hind Basin, southwestern Manitoba. Six facies observed in three cut-bank exposures allow reconstruction of sedimentary processes and resulting landscape at the study site in the basin center around 6100 cal (calibrated) BP. A mosaic of parabolic dunes with interdune and dune-marginal lightly vegetated sand sheets developed in the Souris River flood plain that was least partly covered with woodlands and wetlands. During floods, nearby interdune areas were inundated. Dune foreset orientation and stratification indicate a more easterly sand transport direction, lending support to the hypothesis that more pervasive westerly "zonal" flow contributed to mid-Holocene aridity evident elsewhere in the northern Great Plains. More arid conditions during the mid-Holocene may have helped trigger eolian activity. However, with the exception of a more active eolian component, the flood-plain environment may have been similar to that of the late Holocene. Mid-Holocene Gowen (Mummy Cave Complex) artifacts, the first found in Manitoba, indicate that people inhabited the resource-rich environment where eolian and flood-plain landforms occurred together. Protection of mid-Holocene dune and sand-sheet strata during late Holocene phases of eolian reactivation is attributed to rapid rise in the local water table soon after deposition.
A "SELF-CONSISTENT SOLUTION" METHOD FOR DETERMINING THE ELECTRICAL CONDUCTIVITY IN THE SUBSURFACE REGIONS OF THE EARTH
Authors: Watanabe Tomiya
Published: April 2011

The assumptions on which the so-called magneto-telluric method to determine the subsurface conductivity of the earth is based are examined and it is shown how the method can be revised to get rid of those assumptions which are not necessarily legitimate. The principle of this revised or generalized magneto-telluric method is that the magnetic and telluric field components which observation can provide over the entire surface of the earth are more than sufficient viewed as boundary conditions to determine the electromagnetic field inside the earth with a prescribed conductivity distribution and, therefore, the extra boundary conditions can be consistent with each other only by the correctly prescribed (or chosen) distribution of electrical conductivity. The purely magnetic method to determine the conductivity, which relies on the assumption that the magnetic field in space above the surface of the earth, is a potential field, is also revised to free it of the assumption which, does not hold true unconditionally.
MAGNETIC PROFILE ACROSS THE GRAND BANKS AND FLEMISH CAP OFF NEWFOUNDLAND
Authors: Hood Peter , Godby E. A.
Published: April 2011

This paper describes an aeromagnetic profile from Prince Edward Island, through the Cabot Strait to the Tail of the Grand Banks of Newfoundland, and subsequently over the Flemish Cap. It is inferred that Burgeo Bank off the southwest coast of Newfoundland is possibly a granite intrusion of Devonian age. A distinct magnetic anomaly, approximately 400 gammas in amplitude, appears to be associated with the edge of the continental shelf at the Tail of the Bank. A series of sharp shallow-source magnetic anomalies was recorded over the Flemish Cap, and this feature appears to have a negatively polarized core whose long dimension is oriented in a NNW.-SSE. direction.
SNARE–YELLOWKNIFE RELATIONS, DISTRICT OF MACKENZIE, N.W.T., CANADA
Authors: Ross John V. , McGlynn John C.
Published: April 2011

Within the District of Mackenzie, N.W.T., Canada, Snare Group rocks unconformably overlie Yellowknife Group; both groups of rocks are Precambrian in age. Snare deformation has modified the already deformed Yellowknife rocks and examples are given of Yellowknife "basement" response to the varying styles of Snare "cover" deformation.
PALAEOZOIC FLOOD BASALTS IN NORTHERN NEWFOUNDLAND AND LABRADOR
Authors: Clifford Paul M.
Published: April 2011

Columnar basalt of the Cloud Hills in northern Newfoundland, previously regarded as of Keeweenawan age, now is thought to be post-Lower Cambrian, since it lies on coarse clastic rocks correlated with known Lower Cambrian strata nearby. A younger age limit is given by a whole rock K-A date of 334 m.y. Perhaps these and similar basalts in southern Labrador represent a flood basalt province, once much more continuous than now.
MAGNETIC PROVINCES OF LAKE HURON AND ADJACENT AREAS AND THEIR GEOLOGIC SIGNIFICANCE
Authors: Nwachukwu S. O. , Beck A. E. , Currie J. B.
Published: April 2011

A regional magnetic survey was conducted on Lake Huron, Georgian Bay, and land adjacent to them in Southwestern Ontario, Manitoulin Island, and Eastern Michigan. Study of its results indicates that the origin of the magnetic anomalies lies within the Precambrian basement complex and that the surveyed area is divisible into seven magnetic provinces. Anomaly trends are used to outline and extend the Grenville Front southward across Lake Huron into Michigan. There is evidence that structural trends within the basement near the southeastern part of Lake Huron may have localized the effects of epeirogenic movement during Paleozoic time and influenced the distribution of sediments and position of reefs.
THE SHAPE AND THICKNESS OF AN ARCHAEAN GREENSTONE BELT BY GRAVITY METHODS
Authors: Grant F. S. , Gross W. H. , Chinnery M. A.
Published: April 2011

The Red Lake greenstone belt is Archaean in age (older than 2.5 billion years) and is located in the Superior province of the Canadian Precambrian Shield. It is a fairly typical greenstone belt, being composed of a complex assemblage of lavas, sediments, and intrusives. The belt is completely surrounded, and therefore is isolated from other greenstone belts, by granitic batholiths and acid paragneiss. Generally speaking, greenstones are more dense than the surrounding granitic rocks and they therefore give positive gravity effects, the amplitudes of which give some indication of their shape and overall thickness.At Red Lake, the greenstone belt is approximately 35 mi long by 18 mi wide. Gravity readings taken across the width of the belt indicate that the greenstones taper sharply in depth to a maximum thickness of approximately 25 000 ft. These results appear to confirm, as most geologists feel intuitively, that greenstone belts are basin-shaped and are underlain by granitic batholiths and gneiss.
A STUDY OF SENSITIVITY IN LEDA CLAY
Authors: Penner E.
Published: April 2011

The sensitivity of Leda clay from the Ottawa area is relatively independent of the salt content in the pore water. Sensitivity values may vary between 10 and 1 000 in the low salt content range (less than 2 g/liter); at higher salt contents strong flocculating effects of the electrolyte limit the sensitivity, but values as high as 75 have been measured.A relationship has been determined experimentally between electrokinetic potential and sensitivity that is consistent with the theory of interparticle repulsion and attraction. The main deviations are attributable to differences in grain size.Chemical analyses of pore water show that large variations in sensitivity, particularly within one profile, are related to the nature of the pore water electrolyte in the low salt content range. Soils that are unusually sensitive have a high monovalent cation content. Large differences in sensitivity can be accounted for in this way, but the reason for small variations is still obscure.The electroosmosis technique used to determine electrokinetic potentials is discussed in detail. This apparatus was used also to verify Rosenqvist'a leaching theory of sensitivity for soils known to have had a marine origin.
THE PROPAGATION OF THE COMPRESSIONAL WAVE IN THE CRUST: I. A SIMPLE TREATMENT OF THE DATA
Authors: Keen M. J. , Tsong C. F. , Blanchard J. E.
Published: April 2011

Seismic experiments have been undertaken along the Atlantic coast of Nova Scotia, and an attempt has been made to determine by what mechanism the compressional wave which is recorded as the first event in the range of distance 10 km to 180 km propagates, and to describe its attenuation. In this part of the paper the change in amplitude of the first half-cycle of the first event is investigated, and compared with the change in amplitude which might be expected if propagation occurred as a "head wave", and if propagation occurred because of the presence of a velocity gradient in the upper few kilometers of the earth's crust. We find that we cannot distinguish between the two mechanisms of propagation with any certainty, and although the suggestion is made that the value of Q is in the range 90 to 300, depending upon the propagation mechanism, the assumptions which underlie the approach are criticized, and a more reasonable one put forward.
CHROMIAN SPINEL AS A PETROGENETIC INDICATOR: PART 1. THEORY
Authors: Irvine T. N.
Published: April 2011

Previous investigators have shown that natural chromium-bearing spinel solid solutions adhere closely to the general formula (Mg, Fe++) (Cr, Al, Fe+++)2O4 and may therefore be graphically portrayed in a triangular prism, the length of which represents the ratios MgO/FeO, and the cross section the relative proportions of Cr2O3, Al2O3, and Fe2O3. In this paper, theoretical expressions are derived whereby the prism may be "contoured" for conditions of isothermal–isobaric equilibrium according to (a) the spinel compositions that may coexist with olivine or pyroxene having specific MgO/FeO ratios; (b) the activity ratios of Cr/Al, Cr/Fe+++, or Al/Fe+++ that obtain in the environments in which the spinel solid solutions form, and (c) the oxygen fugacities that accompany formation of spinel in systems containing olivine (forsterite–fayalite) and orthopyroxene (enstatite–ferrosilite). Rough "working" values for the thermochemical coefficients involved are estimated from limited calorimetric data and chemical analyses of spinel–olivine and spinel–orthopyroxene pairs.