bluuebunny/crossref_metadata_2025 huggingface dataset:
Age and radiogenic isotopic systematics of the Borden carbonatite complex, Ontario, Canada
Authors: Bell Keith , Blenkinsop John , Kwon S. T. , Tilton G. R. , Sage R. P.
Published: April 2011

Rb–Sr and U–Pb data from the Borden complex of northern Ontario, a carbonatite associated with the Kapuskasing Structural Zone, indicate a mid-Proterozoic age. A 207Pb/206Pb age of 1872 ± 13 Ma is interpreted as the emplacement age of this body, grouping it with other ca. 1900 Ma complexes that are the oldest known carbonatites associated with the Kapuskasing structure. A 206Pb–238U age of 1894 ± 29 Ma agrees with the Pb–Pb age but has a high mean square of weighted deviates (MSWD) of 42. A Rb–Sr apatite–carbonate–mica whole-rock isochron date of 1807 ± 13 Ma probably indicates later resetting of the Rb–Sr system.An εSr(T) value of −6.2 ± 0.5 (87Sr/86Sr = 0.70184 ± 0.00003) and an εNd(T) value of +2.8 ± 0.4 for Borden indicate derivation of the Sr and Nd from a source with a time-integrated depletion in the large-ion lithophile (LIL) elements. These closely resemble the ε values for Sr and Nd from the Cargill and Spanish River complexes, two other 1900 Ma plutons. The estimated initial 207Pb/204Pb and 206Pb/204Pb ratios from Borden calcites plot significantly below growth curves for average continental crust in isotope correlation diagrams, a pattern similar to those found in mid-ocean ridge basalts (MORB) and most ocean-island volcanic rocks, again suggesting a source depleted in LIL elements. The combined Nd and Sr, and probably Pb, data strongly favour a mantle origin for the Borden complex with little or no crustal contamination and support the model of Bell et al. that many carbonatites intruded into the Canadian Shield were derived from an ancient, LIL-depleted subcontinental upper mantle.
The Shebandowan group: "Timiskaming-like" Archean rocks in northwestern Ontario
Authors: Borradaile G. , Brown H.
Published: April 2011

This group of Archean volcanic and metasedimentary rocks is generally considered to be younger than the Keewatin metavolcanic rocks. The metasedimentary rocks are disposed in tight to isoclinal folds with strong plunge variations that are mainly due to a primary tectonic event. The folds are accompanied by a single, penetrative tectonic microfabric and a coplanar magnetic fabric. The contacts of the group with the adjacent Keewatin rocks are unexposed but are inferred to be faulted, at least in part.
Analysis of strained sedimentary fabrics: review and tests
Authors: Borradaile G. J.
Published: April 2011

Accurate analysis of the homogeneous strain of ellipsoidal objects requires that certain premises are met. These are (1) coaxiality of strain increments, (2) accurate definition of finite strain axes, and (3) perfectly passive behaviour of the objects with respect to the matrix. The [Formula: see text] equations provide a mathematical model for this idealized scenario.In practice the analysis is limited to data from plane surfaces, and its success depends upon the type of initial fabric of the objects, the frequency distribution of their initial shapes, and errors of measurement of the final shapes (Rf1/2) and of final orientations [Formula: see text]. Together with the difficulty in locating the finite strain axes, these factors greatly affect the outcome of the analysis, and their combined effects have not been studied previously.Detailed observations on the orientations of strain and of the orientation–distribution of the objects' long axes sometimes indicate that the [Formula: see text] model is incompatible with the data. Strain analysis is then not possible by the present methods. If the data are compatible with the [Formula: see text] model and if the original fabric can be shown to have been random or had a preferred orientation parallel to bedding, it is possible to determine the strain accurately to within a few percent. This has been partly confirmed in practical examples in which the strain has been independently determined using the tectonic distortion of rims of individual clasts.
Special session: Rocks, minerals, and materials science Session
Authors: White Joseph Clancy , Williams Paul F.
Published: April 2011

"Rocks, Minerals, and Materials Science," a special session of the Geological Association of Canada and Mineralogical Association of Canada joint annual meeting, was convened in Fredericton, May 16, 1985, under the auspices of the Geological Association of Canada. The special session was supported by a Natural Sciences and Engineering Research Council of Canada (NSERC) conference grant. The intention of the session was to foster a multidisciplinary approach to geological and mineralogical studies by bringing together researchers from classically divergent disciplines who nonetheless follow similar experimental approaches based on consideration of the physical and chemical processes responsible for the phenomena they study. Authors of contributed papers included mineralogists, petrologists, field and experimental structural geologists, material scientists, and physicists. Several of the papers follow.Although such unifying approaches are not new, it was appreciated by the organizers of the special session that there still exists in the geological sciences a tendency to fall back into established niches and to de-emphasize the usefulness of "cross-pollenating" ideas and methods. As indicated by the title, this approach is well recognized in nongeological studies, such as materials science, the principles of which are fundamental to everything from petrology (by way of ceramic phase chemistry) to modern structural geology (by way of the physics of polycrystalline deformation). Because of the relative simplicity of many nongeological materials systems, concepts and methods often have been developed for such systems first and then applied to more complex geological problems. This is well illustrated by the adaptation of electron microscopy to various geological studies to characterize atomistic and grain-scale processes and associated features. As emphasized in several of the included papers, the application of the materials-science approach is ultimately constrained by the unique geological problem of long and complicated chemical and physical histories, developed over an extreme range of temperatures, pressures, and chemical environments. The necessity for integrated field observations remains as always vital.
Nonhydrostatic thermodynamics in deforming rocks
Authors: Bayly Brian
Published: April 2011

To understand how deformation and the chemical processes of metamorphism interrelate, we need the concept of chemical potential. The state of stress of any material involved is likely to be nonhydrostatic; hence, to define chemical potential, we need the idea of an associated equilibrium state and need to recognize that the associated equilibrium state changes with the orientation of the plane considered. Along these lines, chemical potential appears as an attribute of a plane through a point, like the normal component of the stress.Given these ideas, a potential surface is envisaged; it can be represented in three dimensions if we use only one axis for spatial position and one axis for the inclination of a plane of interest to the principal stress directions. Diagrams of this type, while obviously limited, can show (i) the potential surface for simple diffusion (without deformation) and (ii) the potential surface for simple deformation (with no concurrent chemical change) and various states where deformation and chemical change go on concurrently.When a megacryst that is stiffer than its surroundings sits in a nonhydrostatic stress field, it creates stress shadows, and mobile material tends to migrate toward the shadows, through the megacryst and through the intergranular phase. In two alkali-feldspar gneisses, the potassium distribution is nonhomogeneous in ways possibly related to the foregoing theory.
Geology of Annette, Gravina, and Duke islands, southeastern Alaska
Authors: Gehrels George E. , Saleeby Jason B. , Berg Henry C.
Published: April 2011

Geologic mapping, U–Pb (zircon) geochronometry, and conodont studies indicate that the major pre-Jurassic assemblages on Annette, Gravina, Duke, and adjacent smaller islands include pre-Middle Ordovician metavolcanic and metasedimentary rocks (Wales metamorphic suite); Cambrian metaplutonic rocks; Ordovician – Early Silurian volcanic (Descon Formation), dioritic, and gabbroic rocks; Silurian trondhjemitic plutons; Early Devonian sedimentary (Karheen Formation) and volcanic rocks; Late Triassic sedimentary and volcanic rocks (Hyd Group); and a large body of Late Triassic pyroxene gabbro.Stratigraphic, structural, and intrusive relations record episodes of regional deformation, metamorphism, and uplift during Middle Cambrian – Early Ordovician time (Wales orogeny) and during middle Silurian – earliest Devonian time (Klakas orogeny). Upper Triassic strata were apparently deposited during a latest Paleozoic(?) – Triassic rifting event.Comparison with the geology of Prince of Wales Island indicates that the Annette and Craig subterranes of the Alexander terrane belong to the same tectonic fragment and that the Clarence Strait fault has ~15 km of right-lateral displacement at this latitude. Our geochronologic data indicate that the pyroxene gabbro on Duke Island is Triassic in age and therefore probably unrelated to nearby Cretaceous(?) zoned ultramafic bodies.
The graptolite Amplexograptus praetypicalis n. sp. and the origin of the typicalis group
Authors: Riva John
Published: April 2011

The graptolite Amplexograptus praetypicalis n. sp. is described and assigned to a more precisely defined and amended genus Amplexograptus Elles and Wood. This graptolite ranges through the lower half of the Climacograptus spiniferus Zone of northeastern North America and evolves, through a distinct process of phyletic gradualism, into the better known Climacograptus typicalis Hall. Climacograptus typicalis ranges through the upper half of the C. spiniferus Zone and the succeeding Climacograptus pygmaeus Zone, giving rise to three related species: the dwarfish Climacograptus pygmaeus Ruedemann, the gigantic Climacograptus magnificus Twenhofel, and the atavistic Climacograptus posterus Ruedemann. Together, these four species form a distinct group, termed the typicalis group, and a distinct lineage that had a brief existence from the late Middle to the early Late Ordovician. The genus Uticagraptus n. g. is here proposed for the graptolites of the typicalis group. This group is characterized by an advanced prosoblastic type of proximal-end development and an aseptate rhabdosome and, thus, differs fundamentally from Climacograptus bicornis (Hall), the type species of Climacograptus, with a more primitive diplograptid type of proximal-end development and a septate rhabdosome.
Paleogeographic evolution of the United States Pacific Northwest during Paleogene time
Authors: Heller Paul L. , Tabor Rowland W. , Suczek Christopher A.
Published: April 2011

Paleogeographic reconstructions for Oregon and Washington during Paleogene time illustrate a major transition from a dominantly compressional (prior to middle Eocene time) to an extensional tectonic regime. This transition resulted in the development of three phases of Paleogene basin evolution in the United States Pacific Northwest. During the initial phase, basins formed along the continental margin during collision of oceanic islands. Sediments in these basins were derived from nearby orogenic highlands. The second phase of basin development began in middle Eocene time and consisted of rapid subsidence of individual basins that formed within a broad forearc region. Nonmarine basins that formed during this phase were caused by extension possibly associated with transcurrent faulting. Rapid sedimentation in both marine and nonmarine basins during this time consisted dominantly of sandstone derived from Cretaceous plutonic sources far to the east. The final stage of basin development was the modification of previous basin configurations by the growth of the Cascade volcanic arc, which was initiated in early Oligocene time. The rising Cascade Range diverted streams carrying eastern-derived material, thereby reducing overall sedimentation rates in the coastal basins and providing a local source of volcanic detritus.
Petrology of ultramafic xenoliths from Rayfield River, south-central British Columbia
Authors: Canil Dante , Brearley Mark , Scarfe Christopher M.
Published: April 2011

One hundred mantle xenoliths were collected from a hawaiite flow of Miocene–Pliocene age near Rayfield River, south-central British Columbia. The massive host hawaiite contains subrounded xenoliths that range in size from 1 to 10 cm and show protogranular textures. Both Cr-diopside-bearing and Al-augite-bearing xenoliths are represented. The Cr-diopside-bearing xenolith suite consists of spinel lherzolite (64%), dunite (12%), websterite (12%), harzburgite (9%), and olivine websterite (3%). Banding and veining on a centimetre scale are present in four xenoliths. Partial melting at the grain boundaries of clinopyroxene is common and may be due to natural partial melting in the upper mantle, heating by the host magma during transport, or decompression during ascent.Microprobe analyses of the constituent minerals show that most of the xenoliths are well equilibrated. Olivine is Fo89 to Fo92, orthopyroxene is En90, and Cr diopside is Wo47En48Fs5. More Fe-rich pyroxene compositions are present in some of the websterite xenoliths. The Mg/(Mg + Fe2+) and Cr/(Cr + Al + Fe3+) ratios in spinel are uniform in individual xenoliths, but they vary from xenolith to xenolith. Equilibration temperatures for the xenoliths are 860–980 °C using the Wells geothermometer. The depth of equilibration estimated for the xenoliths using geophysical and phase equilibrium constraints is 30–40 km.
Paleomagnetism and the age of copper mineralization in the Portage Lake Volcanics, Upper Peninsula, Michigan
Authors: Browning Timothy D. , Beske-Diehl Suzanne J.
Published: April 2011

The close association of hematite with native copper in the flow tops of the Portage Lake Volcanics invites the opportunity to establish the relative age of copper mineralization. For this purpose, we sampled 12 paleomagnetic sites representing six mineralized flow tops and their associated massive interiors on the Keweenaw Peninsula in Michigan. Three of the four less-altered flow interiors contained two components of magnetization: one was carried by primary magnetite, and therefore the other, carried by hematite, must be secondary. The hematite component was parallel to the single hematite component in the associated flow top, indicating that both components had a common secondary origin. The low between-site dispersion of the hematite component and the similarity of the mean direction to primary directions of other rocks of the same age (1100 Ma) suggest that hematization occurred over a period of time long enough to average out secular variation but before deposition of the overlying Nonesuch Shale, extensive tectonic tilting, and significant apparent polar wander. If copper mineralization and hematization were contemporaneous, then we have also dated the relative age of copper mineralization and the associated metamorphism. In contrast, paleomagnetic results from the two extensively altered flows (from below the Greenstone flow) are consistent with the mechanism of deuteric or auto-oxidation.
Princess Margaret Arch: re-evaluation of an element of the Eurekan Orogen, Axel Heiberg Island, Arctic Archipelago
Authors: Ricketts B. D.
Published: April 2011

It is argued on the basis of structural, stratigraphic, and sedimentologic criteria that Princess Margaret Arch developed during the principal phase of Eurekan thrusting and folding and therefore is no older than Middle Eocene. Sub-Eureka Sound Group unconformities on eastern Axel Heiberg Island are not associated with uplift on the eastern flank of this arch but are related to erosion of Mesozoic Sverdrup Basin strata over local evaporite diapir domes and ridges. Considerable disparity exists between levels of erosion on the flanks of the arch and the level of erosion along its axis, which cannot be explained by pre-Eocene uplift. Sedimentary facies and textural and petrographic characterisitics of Eureka Sound Group strata do not reflect proximity to an arch. Palynomorph assemblages in the west-derived, syntectonic Buchanan Lake Formation (Middle Eocene) contain reworked latest Cretaceous spores and pollen that were derived from Eureka Sound Group strata originally located on or close to the arch axis.Eureka Sound Group sedimentation in the Axel Heiberg Island – west Ellesmere Island region took place in a single, contiguous basin, rather than in smaller basins that were separated by ancestral Princess Margaret Arch.
Petrography and geochemistry of an unusual Fe-rich basaltic komatiite from Boston Township, northeastern Ontario
Authors: Stone W. E. , Jensen L. S. , Church W. R.
Published: April 2011

The Boston Creek Flow is a thick, Archean layered basaltic komatiite lava flow located 16 km south of Kirkland Lake, Ontario, within the Abitibi greenstone belt. It is superficially similar to the layered flows of Munro Township in that it consists of a basal pyroxenite overlain sequentially by peridotite, pyroxenite, gabbro, and pyroxene spinifex-textured rock and exhibits the typical cumulate komatiite crystallization sequence: olivine–clinopyroxene–plagioclase. The spinifex-textured unit is, however, unusually thick (33 m), and in comparison with other Archean lavas of similar magnesium content, the flow is Fe and Ti enriched and Al and Y depleted. CaO/Al2O3 and Al2O3/TiO2 ratios of 2–3 and 5, respectively, also distinguish it from other Archean magnesium-rich volcanic rocks.The preservation of typical tholeiitic chemistry in lavas underlying the Boston Creek Flow precludes metamorphism and metasomatism as explanations of the flow's enigmatic geochemistry. This is supported further by relict igneous textures exhibited by Ti-bearing oxides in the pyroxenite, gabbro, and spinifex-textured units of the flow. The presence of trellis-textured ilmenite lamellae in titanomagnetite, the textural evidence for symplectic intergrowth of titanomagnetite and clinopyroxene during crystallization, and the failure of assimilation models to explain the coupling of Fe and Ti enrichment with Al depletion suggest rather that the unusual geochemistry of the flow is a primary igneous feature. The Boston Creek Flow is more Al depleted and Fe and Ti enriched than Barberton and Minnesota Al-depleted komatiites (ADK) of the same magnesium number. It is therefore an Fe-rich, layered ADK.
Solute sources and transport in an ephemeral badland catchment, southeastern Alberta, Canada
Authors: Sutherland Ross A. , Bryan Rorke B.
Published: April 2011

This study was carried out as part of an investigation of water and sediment budgets in an ephemeral catchment in Dinosaur Provincial Park badlands, Alberta. These badlands have developed in Cretaceous mudstones, siltstones, and sandstones, with some glacial and postglacial surficial deposits. Study objectives were (i) to identify major solute sources, (ii) to show how these change with storm characteristics, and (iii) to assess the proportion of solutes in the total stream budget. Field examination, rainfall-simulation tests, and laboratory experiments showed marked variations in solute production on different lithologic surfaces. This information, when combined with data on threshold precipitation for runoff production from previous experiments, made it clear that solute production in the catchment is significantly influenced by storm characteristics. Observations indicate that in brief, low-intensity storms, runoff occurs only on sandstone, miniature-pediment, and stream-channel surfaces. Solute production on these surfaces is limited and is dominated by flushing of salts previously precipitated on the surface. In high-intensity or prolonged storms, runoff also occurs on mudstone surfaces and from subsurface tunnels. In both cases solute production is higher and increases with storm duration because of progressive mudstone dispersion. During the 12 storms monitored, the average stream-solute concentration was 308 mg L−1, which is approximately 1.4% of the total stream load.
Stratigraphy of the North Cliff section, Wellsch Valley site, Saskatchewan
Authors: Mahaney William C. , Stalker A. MacS.
Published: April 2011

Eight separate till sheets are displayed at the North Cliff, which is part of the Wellsch Valley site in Saskatchewan. Those tills are differentiated by using physical characteristics, particle size, clay and primary mineralogy, and sediment chemistry. Grain size tends to fine downward in the section, and a significant increase in the mean [Formula: see text] centre of gravity indicates that some weathering occurred after deposition of the tills. Within the clay mineral suites, smectite tends to dominate in all eight tills, indicating that the paleoclimate was generally as dry as the present-day climate. Only till number 4 (counting from the bottom) contains halloysite; this halloysite may have been entrained from a preweathered surface by the glacier, or it may have formed in situ following deposition. Among the primary minerals, quartz dominates throughout the section, whereas plagioclases are least abundant in tills 4 and 5, possibly as a result of postdepositional weathering. Element composition shows only minor changes for Cu, Pb, Zn, Co, and Ni, whereas Mo increases upward in the section, Cr remains uniform in tills 1, 2, 3, 7, and 8 but increases slightly in tills 4–6, and Mn increases downward, possibly as a response to fluctuating amounts of groundwater. Till 4 forms the best stratigraphic marker in the sequence because of its high Mn content and the presence of halloysite, but till 5 also contains distinctive features in its element composition.The clay composition of the surface soil, which has formed in the top till since the departure of the last glacier, resembles that found in the underlying tills, whereas quartz and plagioclase are present in lesser amounts. These properties reflect both weathering in a semiarid climate and the presence of preweathered material from earlier paleosols.
U–Pb and Rb–Sr geochronology of the Wedgeport granitoid pluton, southwestern Nova Scotia
Authors: Cormier R. F. , Keppie J. D. , Odom A. L.
Published: April 2011

Zircons from biotite monzogranite of the Wedgeport Pluton, intrusive into deformed metasediments of the Cambrian(?) Goldenville Formation in the southwestern Meguma Terrane of Nova Scotia, yield concordant U–Pb ages of 316 ± 5 Ma. This is interpreted as the time of intrusion and crystallization. Within the error limits, the 323 ± 12 Ma Rb–Sr whole-rock isochron age is identical and gives an initial 87Sr/86Sr ratio of 0.7137 ± 0.0056. Rb–Sr analyses of mineral separates of biotite, potassium feldspar, and quartz–plagioclase from several samples yield subparallel, internal isochrons with an average age of 257 ± 8 Ma. Initial ratios of the internal isochrons range from 0.716 to 0.759. A slow-cooling model for these latter data is discarded because the mineral data fall on straight lines. Instead, a reheating event related to plutonism ca. 257 Ma ago, which was sufficient to cause local grain-to-grain migration and reequilibration of strontium and rubidium but not large-scale redistribution, is invoked. This reheating is also inferred to be responsible for the hydrothermal alteration and Sn–U mineralization concentrated along the northwestern margin of the pluton. A dextral northeast–southeast shear zone cutting the pluton is also inferred to be ca. 257 Ma old. It may be related to the last stages of westward obduction of the Meguma Terrane.These results provide a clear example of Permo-Carboniferous plutonism in the southwestern Meguma Terrane and suggest a similar interpretation may apply to other anomalously young ages recorded in this area. In light of these results, the Permo-Carboniferous age of the large East Kemptville tin deposit and its location in a dextral shear zone suggest that the association of younger plutonism and shear zones may be a significant factor for economic mineralization.
Late Glacial landforms of Wollaston Peninsula, Victoria Island, Northwest Territories: product of ice-marginal retreat, surge, and mass stagnation
Authors: Sharpe David R.
Published: April 2011

An analysis of glacial landforms on a regional scale leads to an interpretation of the dynamics of Late Wisconsinan glaciation on Wollaston Peninsula, Victoria Island, Northwest Territories. The glacial record is dominated by four adjacent belts of landforms: (I) ground moraine (till plains and ice-marginal drainage features), (II) hummocky moraine, (III) lateral and shear moraine, and (IV) streamlined landforms. The landform belts are considered as representing four distinct glacial ice conditions or regimes: (1) ice-margin retreat during extending flow of thin, active ice; (2) marginal ice stagnation following compressional flow; (3) a surging ice margin producing massive shear moraines; and (4) large-scale flooding and mass ice stagnation following a surge. These landform belts were arranged in zones by topographically controlled glacial dynamics, the latter two defining a former ice stream.Glaciological inferences can be extended by examining the sediments and processes that produced each landform set. Ground-moraine sediments were produced mainly subglacially from melt out or lodgment of glacial debris. Hummocky moraine resulted from debris flow and meltwater deposition controlled by ice, from resedimentation by sediment gravity flow, and from slump. Compressional shearing stacked thick deposits of drift prior to resedimentation. Simple lateral or end moraines may comprise interbedded sediment gravity flows deposited at static ice margins. Deformed lateral moraines resulted from intense marginal compressive flow that sheared and stacked thick, coarse sediment ridges or plates. This lateral shearing may be attributed to streaming or large ice surges. Drumlin exposures showed undeformed, interbedded, stratified sediments that appear to have accumulated in a subglacial cavity; there is no deformation related to high subglacial stress. Subglacial meltwater floods may have followed glacier surge. The greatly extended and thinner ice mass produced by the surge melted in place as clean (debris-free) ice.
Deformational geometry and tectonic significance of a portion of the Chilliwack Group, northwestern Cascades, Washington
Authors: Smith Moira
Published: April 2011

The northwestern Cascades structural province can be interpreted as an accretionary complex comprising fault-bounded blocks of pre-Tertiary metamorphic rocks of diverse age and lithologic type. This paper documents the deformation in a portion of the Chilliwack Group, a unit in this complex. The Chilliwack Group is a thick sequence of volcaniclastic sedimentary rocks, calc-alkaline volcanic rocks, and limestone that is metamorphosed to low-grade blueschist facies. The rocks underwent ductile deformation during a Late Cretaceous orogenic event, producing a subhorizontal foliation and, in appropriate lithologies, subhorizontal stretching lineations that trend N20°W. Finite strain sustained by coarse clastic rocks produced RXZ values averaging 3.5. The deformation at least partially postdates the high pressure metamorphic event, based on the presence of bent and broken high-pressure mineral grains. Although early studies postulated west-vergent thrust imbrication of units in the northwest Cascades, the N20°W direction of apparent elongation in the Chilliwack Group, consistent with the direction of motion along segments of the Shuksan fault elucidated in other more recent studies, may reflect significant, highly oblique components of convergence during formation of the western North Cascades collisional orogen.
Out-of-phase Holocene terraces in part of the North Saskatchewan River basin, Alberta
Authors: Rains Bruce , Welch James
Published: April 2011

This study focuses on alluvial terraces in part of the North Saskatchewan River valley, near Edmonton, and in the small tributary valleys of Whitemud and Strawberry creeks. The characteristic terrace morphologies and alluvial sediment sequences are briefly described, but most importantly, the deposits are radiocarbon dated for many sites. Twenty-seven new 14C dates on bone, wood, charcoal, and shell materials, along with previously reported dates, provide the chronological framework for the study. Occurrences of the Mazama ash marker bed in terrace alluvium offer additional geochronological evidence. The small tributary valleys have clearly developed in an out-of-phase manner relative to the main river valley, which acts as their local base level. Despite the comparatively abundant geochronological evidence described here, the explanation of alluvial terrace development, in terms of predominant causal factors, remains tantalizingly elusive.
Rock pingos in northern Ungava Peninsula, Quebec, Canada
Authors: Seppälä Matti
Published: April 2011

The author reports the first pingos found in Ungava Peninsula, Quebec. The pingos, 15–30 m high, are open-system rock pingos built of very fractured schist and hornblende gabbro. At the time of observation, water was draining out of their slopes. Peat from the top of the smaller pingo was dated at 2880 ± 100 years BP.
Subglacial erosional marks, Wilton Creek, Ontario
Authors: Shaw John
Published: April 2011

A variety of p-forms are discussed in terms of the agent producing them. A general conclusion based on form and the location of striations relative to p-forms is that they are produced by meltwater rather than ice. Erosional marks in the Wilton Creek valley, Ontario, are different from earlier described p-forms. Their relationship to striations establishes them as being of subglacial origin, and their form similarity with flutes together with the partial or total absence of striations on them suggests a fluvial origin. Large-scale forms are interpreted as spindle-shaped flutes associated with flow separation. Small-scale forms are subdivided into straight spindle forms, curved spindle forms, braided forms, and scallops. They appear not to have followed the inverse relationship between size and flow velocity reported for some other erosional marks. Potential but speculative explanations for these small-scale forms are that they are related to Taylor–Görtler vortices, vortices on mixing layers, or trailing vortices behind bluff obstacles. A general conclusion is that the forms described indicate broad separation by meltwater of the glacier from its bed.
Cretaceous remagnetization in the Sylvester Allochthon: limits to post-105 Ma northward displacement of north-central British Columbia
Authors: Butler R. F. , Harms T. A. , Gabrielse H.
Published: April 2011

The Sylvester Allochthon of the Slide Mountain Terrane in northern British Columbia is a structurally interleaved assemblage of ocean-floor lithologies ranging in age from Late Devonian to Late Triassic. It is the most inboard of oceanic suspect terranes and rests as a vast klippe on miogeoclinal strata of the Cassiar Terrane. The Sylvester Allochton and the Cassiar Terrane lie west of the Northern Rocky Mountain Trench Fault. Both the Sylvester Allochthon and the Cassiar Terrane are intruded by mid-Cretaceous (105 Ma) granite of the Cassiar Batholith. Six oriented cores were collected at each of 12 sites in Guadalupian Parafusulina-bearing limestone of the Sylvester Allochthon at a location 4 km from the batholith. Isothermal remanent magnetization (IRM) acquisition and subsequent thermal demagnetization indicate that pyrrhotite is the dominant ferrimagnetic mineral. Least-squares line fitting to four thermal demagnetization steps between 150 and 310 °C was used to determine the characteristic natural remanent magnetization (NRM) directions that fail the fold test at the 99.5% confidence level. We interpret these observations as indicating that the NRM is a thermoremanent or thermochemical remanent magnetism associated with intrusion of the Cassiar Batholith. The resulting paleomagnetic pole location is latitude = 75.7°N, longitude = 171.7°E, α95 = 8.5°. When compared with the mid-Cretaceous pole for cratonic North America, a small but significant clockwise rotation (R ± ΔR = 23.9 ± 18.1 °) is evident, but poleward translation (p ± Δp = 5.3 ± 9.2°) is not significant at the 95% confidence level. The paleomagnetic results are consistent with geological evidence for moderate (700 km) northward transport of the Cassiar Terrane (along with the previously emplaced overlying Sylvester Allochthon) during mid-Cretaceous to Tertiary dextral transcurrent faulting.
Lithic geochemistry of the Claggett marine cyclothem in south-central Saskatchewan
Authors: Whittaker S. G. , Kyser T. K. , Caldwell W. G. E.
Published: April 2011

Sediments of the Lea Park Formation in south-central Saskatchewan were deposited in the Claggett sea during the Late Cretaceous (Campanian) Claggett marine cycle. Rocks of the Lea Park Formation have remained virtually unaffected by diagenetic alteration; hence, variations in mineralogical and chemical compositions result primarily from changes in the source of detritus. Quartz, feldspar, discrete illite, kaolinite, and chlorite were derived from weathering of the western highlands, whereas illite–smectite (I–S), the dominant clay phase, originated from volcanic ash. Changes in the proportions of these minerals suggest a large-scale volcanic episode during deposition of the Lea Park sediments, an episode that affected not only the detritus delivered to the seaway but also the chemical and isotopic compositions of the sea water itself. δ13C values of organic matter increase with little change in the quantity of organic carbon preserved through both the transgressive and regressive phases of the Claggett cyclothem, unlike other cyclothems in which δ13C values generally decrease through the regressive phase. The increase in δ13C values in the Claggett cyclothem suggests a partial contribution from volcanic emanations to the 13C/12C ratio of the sea. Dissolution of Mg-rich volcanic debris from a major volcanic episode resulted in anomalously high Mg/Ca ratios in the sea and in the shells of molluscs living in the sea at that time. Rocks containing the shells with anomalously high Mg/Ca ratios are not themselves unusually Mg rich, but a general increase in Mg/SiO2 ratios in the rocks points to an increase in volcanic influx. The similarity between the mineralogical composition of the Lea Park Formation in Canada and that of the coeval lower part of the Pierre Shale in the United States indicates that volcanic ash was an important detrital source for both formations.
History of sedimentation in the northwestern Lake Superior basin and its relation to Lake Agassiz overflow
Authors: Teller James T. , Mahnic Paul
Published: April 2011

Following the Marquette glacial advance, which blocked the eastern outlets of Lake Agassiz and reached northern Michigan about 10 000 years BP, the ice margin wasted back toward the northeast, eventually allowing Lake Agassiz to overflow into the Lake Superior basin through a series of channels. Sediments deposited east of Thunder Bay near the mouth of the Wolf, Wolfpup, Shillabeer, and Black Sturgeon channels reflect three phases in the history of Lake Superior and provide the basis for reconstructing the early postglacial history of the region.The lower part of the sedimentary sequence in the northwestern Superior Basin consists of a distinctive red, stoney, sandy till deposited during the Marquette glacial advance and is overlain by pink rhythmites deposited in Lake Superior when it was a deep proglacial lake at the Minong level. The nearly 300 rhythmites deposited at this time typically consist of 4 cm thick silt + clay couplets, which are punctuated by silt laminae and sandy turbidites that probably represent major thaw periods or storms. These are seasonal rhythmites, deposited prior to the reopening of the Lake Agassiz outlets into the Superior Basin, and they display a decrease in dropstones, grain size, and thickness upsection that reflects a receding ice margin.The first eastern outlets of Lake Agassiz were uncovered around 9500 years BP, and water began overflowing into the Superior Basin in a series of catastrophic floods. Subaqueous fans developed at the Wolf, Wolfpup, and Shillabeer confluence and at the mouth of the Black Sturgeon channel. Large sandy turbidites, 45–65 cm thick, were deposited in the proximal part of these fans, with scouring and large (1 m) trough cross-beds resulting from the largest Lake Agassiz floods. These sediments are transitional to distal, clayey silt rhythmites, 10–22 cm thick. A gradual decrease in flooding from Lake Agassiz is reflected in the upward decrease in rhythmite thickness to 1–3 cm by about 8200 years BP. The final sequence of sediments shows a transition to sandy units as water levels dropped in the Superior Basin and the influence of nearshore processes increased.
Age of the Frenchman Valley and associated drift south of the Cypress Hills, Saskatchewan, Canada
Authors: Christiansen E. A. , Sauer E. K.
Published: April 2011

Frenchman Valley extends about 340 km from the Cypress Hills, Saskatchewan, to its confluence with the Milk River in Montana. In one area, the valley is 3 km wide, and it was 180 m deep prior to deposition of as much as 80 m of landslide debris, channel sand and gravel, and alluvial and colluvial deposits. Six radiocarbon ages ranging from 3440 to 11 460 BP suggest the Frenchman Valley is Wisconsinan. The Frenchman Valley could not have formed in its side-hill position if Late Wisconsinan ice had not been present south at the Cypress Hills.
A pre-Paris ice-sheet limit near Guelph, southern Ontario
Authors: Straw Allan
Published: April 2011

The Guelph Moraine, a previously undesignated end moraine between Hespeler and Rockwood, is described and shown to be the consequence of a limited readvance that interrupted the general recession from the Guelph area of ice that deposited the Port Stanley Till rather than of a precursive advance of younger ice that laid down the Wentworth Till and eventually produced the Paris Moraine.From Rockwood and following broadly the Eramosa–Speed river a gravelly outwash train is traced southwest toward Hespeler, where it appears to merge with sandier deposits of Grand River provenance and to pass into an extensive sand "plateau" south of the town. These pre-Guelph sands and gravels were overridden by ice at Rockwood and southwest of Guelph during the readvance. Meltwaters were forced at first to detour westward along the upper Speed River and Ellis Creek valleys but later found their way beneath ice at Rockwood to initiate subglacial erosion of the gorges and adjacent dry-valley systems.The Eramosa–Speed "spillway" was therefore established during the Guelph stage, and the Eramosa–Speed river adopted its present course during recession from the Guelph Moraine. Paris stage meltwaters deposited extensive outwash plains along the southeast side of the Guelph Moraine and had to break through this moraine to reach the Eramosa–Speed system. All events took place during the Port Bruce Stade.
New isotopic data and a preliminary age for volcanics near the base of the Windermere Supergroup, northeastern Washington, U.S.A.
Authors: Devlin William J. , Brueckner Hannes K. , Bond Gerard C.
Published: April 2011

New Sm–Nd and Rb–Sr data are presented from the volcanic member of the Huckleberry Formation, a unit near the base of the upper Proterozoic Windermere Supergroup in northeastern Washington. The isotopic data are compatible with a rift setting during deposition of Windermere strata. A best-fit line through all the data yields an age of 795 Ma with a large error of ±115 Ma (2σ). However, a preliminary Sm–Nd mineral–whole-rock age of 762 ± 44 Ma (2σ) obtained from a least-altered basalt is within error of other age information from the Canadian Cordillera that broadly constrains the initiation of Windermere deposition to ~750 (±30) Ma. A synthesis of isotopic data, of the results of tectonic subsidence analyses, and of geologic relations within the Windermere Supergroup and the immediately overlying uppermost Proterozoic – Lower Cambrian strata leads to the conclusion that the Windermere Supergroup does not represent the rift deposits that led directly to the initiation of the early Paleozoic miogeocline. Instead, Windermere sedimentation occurred as a result of a protracted, episodic rift history that culminated with latest Proterozoic – Early Cambrian rifting associated with the onset of thermal subsidence in the ancient passive margin.
The geochemistry and structural significance of a set of Middle Precambrian diabase dikes from the Highland Range, southwestern Montana
Authors: Johnson Eric Lee , Swapp Susan M.
Published: April 2011

The Middle Precambrian diabase dikes of the Highland Range in southwestern Montana are moderate- to high-TiO2 continental tholeiites and are related along a differentiation trend involving strong iron enrichment. Postmagmatic metamorphism and K, Rb, and Sr metasomatism have altered the chemical composition of the igneous rocks of some of the samples. The metamorphic assemblage in the diabase dikes belongs to the low-pressure calcic plagioclase – actinolite hornfels facies, and we suggest that thermal effects associated with the intrusion of the Boulder Batholith are responsible for the metamorphic overprints in these rocks.Combined chemical data from the diabase dikes in the Highland Range, the Ruby Range, and the Tobacco Root Mountains produce smooth differentiation trends for most major oxides and trace elements, and we conclude that one magma was responsible for the dikes in the three ranges. Discrepancies in Rb–Sr age dates obtained for the dikes in the Tobacco Root Mountains can be explained if a Rb, Sr, and K metasomatic event like the one observed in the Highland Range had occurred in the Tobacco Root Mountains as well.Structurally, the diabase dikes in the Highland Range intruded into both east–west- and northwest-trending fractures at the same time. All dikes dip steeply to the north or northeast and are believed to have intruded into tensionally opened fractures related to the opening of the Belt Basin.
Davis Creek silt, an Early Pleistocene or Late Pliocene deposit in the Cypress Hills of Saskatchewan
Authors: Vreeken W. J. , Klassen R. W. , Barendregt R. W.
Published: April 2011

Davis Creek silt is the informal name for a previously unreported loess and its reworked detritus encountered at several locations to the south of the east and centre blocks of the Cypress Hills. This unit intervenes between a pediment with an estimated age of 10 Ma and Late Wisconsinan glacial deposits. Because the unit has reversed magnetization, it is older than 788 ka, the astronomical age of the Matuyama–Brunhes magnetic polarity reversal. The unit also contains an undated volcanic ash from the Pearlette ash family that could represent the Mesa Falls (1.27 Ma) or the Huckleberry Ridge (2.02 Ma) ash bed. Davis Creek silt overlies an oxidized weathering zone and contains large secondary carbonate nodules near its truncated top that were, in places, reworked into a lag deposit or stone line before accumulation of the glacial overburden. At one location Davis Creek silt is separated from this overburden by a unit of cryoturbated gravelly loam with remnants of a reddish-yellow paleosolic B horizon.
Taxonomic position and phylogenetic relationships of Colobomycter pholeter, a small reptile from the Lower Permian of Oklahoma
Authors: Laurin Michel , Reisz Robert R.
Published: April 2011

Redescription of Colobomycter pholeter Vaughn, a small amniote from the Lower Permian of Oklahoma, provides evidence that it is not a mammal-like reptile. Osteological features used to associate Colobomycter with the family Eothyrididae are also present in protorothyridids. Colobomycter has a large sheet-like jugal in the temporal region, precluding the presence of a pelycosaurian lateral temporal opening. Derived osteological features shared with members of the family Protorothyrididae suggest that Colobomycter might be a member of that family, but this assignment must remain tentative because of the fragmentary nature of the known specimens.
Reconstructed ice-flow patterns and ice limits using drift pebble lithology, outer Nachvak Fiord, northern Labrador
Authors: Bell Trevor , Rogerson Robert J. , Mengel Flemming
Published: April 2011

The geology of outer Nachvak Fiord provides an opportunity to differentiate lithologies originating in the Churchill Structural Province (central and inner fiord) from those in the sedimentary Ramah Group and the Nain Structural Province (outer fiord). As a result, the distribution of glacial erratics from the central and inner fiord depicts the former presence of regional Laurentide ice in the outer fiord, whereas the distribution of glacial deposits characterized by locally derived lithologies delimits the area of local glacier expansion.Based upon these criteria, the suggestion is made that regional ice at some time covered the deeply weathered mountain summits (900 m asl) in outer Nachvak Fiord. A later advance, confined to the fiord and valleys, deposited the highest moraines and till (180–115 m asl) recorded in the area. On the basis of geomorphic relationships, this advance is considered a discrete glacial event, separate from a later glaciation that was responsible for moraines and sediments at lower elevations (130–80 m asl). Two hypotheses are presented to explain the character of glacial features and sediments in the lower valleys.Hypothesis I requires that regional ice advanced through the study area and floated as ice shelves in the outer fiord and adjacent distributary valley. Sea level at this time was approximately 70 m higher than at present. Radiocarbon dates and amino-acid ratios from the shells in associated marine and glaciomarine sediments suggest a Middle Wisconsinan age for this event. During the Late Wisconsinan, regional Laurentide ice was restricted to the inner fiord while the sea (29–40 m above present) occupied the outer fiord area. The expansion of local cirque glaciers in upland areas may have occurred during both regional glaciations.In hypothesis II, the Middle Wisconsinan was characterized by extensive local glacier activity, depositing predominantly local material in the lower valleys, south of the fiord. Related fossiliferous sediments (same as above) provide the dating framework for this event. Late Wisconsinan regional ice advanced to the outer fiord and entered the distributary valley south of the fiord. Till deposited during this event is distinguished from the earlier local glaciation by the predominance of regional lithologies. Both Middle and Late Wisconsinan glaciations resulted in the formation of ice-shelf moraines at similar elevations. This implies similar relative sea-level responses to loading of the crust during both events, and consequently it is suggested that regional Laurentide ice had also advanced during the Middle Wisconsinan.Neither hypothesis conforms to a recently proposed Late Wisconsinan ice model for northern Labrador that requires extensive regional ice coverage in the outer fiord and on the Labrador Shelf.