bluuebunny/crossref_metadata_2025 huggingface dataset:
A pseudo-tactite assemblage in the footwall of a massive sulfide occurrence, Savant Lake – Sturgeon Lake Greenstone Terrains, Ontario
Authors: Kissin S. A. , Turner G. W.
Published: April 2011

A mineral assemblage consisting of calcite–tremolite–quartz–clinozoisite–diopside–muscovite has been found associated with a small, stratiform pod of galena–sphalerite–chalcopyrite–pyrite–pyrrhotite. This alteration assemblage resembles that of a skarn, although lacking, significantly, some typical minerals including garnet, wollastonite, and vesuvianite. Limits on possible condition of T, Pfluid, and [Formula: see text] can be estimated for the formation of the assemblage. The assemblage must have formed in a water-rich fluid, as [Formula: see text] is sharply restricted by the reaction 2 clinozoisite + CO2 = calcite + 3 anorthite + H2O. In Pfluid–T space, the assemblage is stable between the univariant curves for the assemblages tremolite + calcite + quartz + diopside at fixed [Formula: see text] and clinozoisite + anorthite + grossular + quartz + calcite. These curves bracket the kyanite–sillimanite boundary. As kyanite and sillimanite occur in the wall rocks, the minimum Pfluid–T are those of the aluminosilicate triple point. Measurement of sphalerite–sphalerite/galena dihedral angles in the thermally annealed area yielded a calculated temperature of 390 °C. Metamorphic conditions suggest that a sequence of progressive contact metamorphic reactions of an original talc and (or) chlorite–quartz–calcite assemblage produced the presently observed assemblage. Proximity to a later granitic batholith is believed to have brought about these changes by reactions in the original alteration mineral assemblage.
A study of slowness anomalies around London, Ontario from University of Western Ontario seismic array observations
Authors: Mok K. H. , Mereu R. F. , Yapp A. P.
Published: April 2011

A detailed analysis was made of over 100 earthquake P signals that were recorded at the short-period tripartite seismic array near London, Ontario. Deviations of measured values of slowness and azimuth from the theoretical values for a spherically symmetric Earth form a well defined anomaly pattern around the array. The pattern to the north of the array is consistent and significantly different from the weak pattern to the south and is a direct result of the relative station travel-time residuals, which were found to be as large as 0.3 s. Although a unique interpretation is not possible, the consistency of the pattern for travel paths that cover large regions of the Earth suggests that its cause is localized in the crust near the array. Numerical experiments also indicate that the residuals are not caused by slopes on any major seismic discontinuity such as the Precambrian or Mohorovičić, but are more likely to be the result of path lengthening effects that occur as the seismic energy is transmitted through a crust with small lateral and vertical velocity variations.
The age of the Hartman moraine and the Campbell beach of Lake Agassiz in northwestern Ontario
Authors: Nielsen Erik , McKillop W. Brian , McCoy James P.
Published: April 2011

Fluctuations in the level of Lake Agassiz are dated at two sites in northwestern Ontario. A radiocarbon date on a modern shell sample indicates dates on freshwater molluscs from the area are about 440 ± 100 years (GSC-3281) too old due to the hard-water effect. An adjustment of 400 years to two fossil freshwater mollusc dates of 11 400 ± 410 (GSC-3114) and 10 400 ± 100 years BP (GSC-2968) makes them compatible with radiocarbon dates on wood from deposits in other parts of the Lake Agassiz basin. The two new dates indicate the beginning of the low-water Moorhead Phase of Lake Agassiz started about 11 000 years BP. The high-water Emerson Phase started when the water level rose to form the Upper Campbell beach approximately 10 000 years BP. The red clay widely distributed throughout northwestern Ontario was deposited during the Emerson Phase when the ice margin lay along the Hartman, Dog Lake, and Marks moraines.
The paleomagnetism and U–Th dating of three Canadian speleothems: evidence for the westward drift, 5.4–2.1 ka BP
Authors: Latham Alf. , Schwarcz H. P. , Ford D. C. , Pearce G. W.
Published: April 2011

Three speleothems from western Canada have been analyzed for their paleomagnetism and U–Th activity ratios. These cave deposits do not appear to show the kind of depositional effects on the recorded magnetic signal as is often the case with sediments. In addition the signal may be referred directly to geographic coordinates so that virtual geomagnetic pole plots may be constructed. This in turn has allowed assessment of any possible bias of the paleofield.The U–Th activity ratios of two flowstones from the Crowsnest Pass area of British Columbia indicated ages greater than the 350 ka dating limit of the dating method. One of the samples was reversely magnetized. Besides their use in the study of the ancient field, these samples have useful geomorphic applications. A stalagmite from Vancouver Island was shown to have recorded [Formula: see text] clockwise loops of the field vector in the period 5.4–2.1 ka BP. This implies a mainly westward drift of the paleofield for this period; the corresponding VGP's were mostly far-sided and slightly left-handed.
Mineralogy of clay marker seams in some Saskatchewan potash mines
Authors: Mossman D. J. , Delabio R. N. , Mackintosh D.
Published: April 2011

Water-insoluble material is present mainly as thin stratigraphic layers throughout the potash ore zone(s) of the Prairie Evaporite. These clay seams constitute about 6% of the ore as mined. After clay minerals, which make up about one third of the total, the main water-insoluble constituents, in approximate order of decreasing abundance, are anhydrite, dolomite, hematite, quartz, potassium feldspar, hydrocarbon, and sporadic non-diagnostic palynomorphs.Clay mineralogy in the following mines has been studied: Cominco (Vanscoy); Central Canada Potash Co. Ltd. (Colonsay); and Potash Corporation of Saskatchewan (Allan and Lanigan). A total of 49 samples has been examined. In each sample, following concentration of clay minerals by centrifuging, X-ray diffractograms were obtained for untreated, glycolated, and heat-treated material (300, 450, 580, 650, and 725 °C). Additional runs were made on several samples under conditions of controlled humidity.The main clay minerals are Fe–Mg chlorite (14 Å (1.4 nm)), illite, and Mg-septechlorite (7 Å (0.7 nm)). Of the two chlorites, septechlorite is the more thermally stable. One or more of sepiolite, smectite, mixed layer (chlorite–smectite), and possibly traces of vermiculite are also present in some samples. The septechlorite, sepiolite, and vermiculite very likely originated as direct products of evaporation under hypersaline conditions, or are the result of diagenesis. Absence of otherwise ubiquitous septechlorite in a sample from Second Red Beds west of the 0-edge of the evaporite basin supports this concept. The proportions and kinds of clay minerals present in the ore zone(s) seem to reflect the extent to which hypersaline conditions were developed. The illite and 14 Å (1.4 nm) chlorite are of regional (detrital) origin.
Fission-track ages of late Cenozoic distal tephra beds in the Yukon Territory and Alaska
Authors: Naeser Nancy D. , Westgate John A. , Hughes Owen L. , Péwé Troy L.
Published: April 2011

Six distal tephra beds from the Yukon Territory and Alaska have been dated by the fission-track method. Zircon and glass ages were determined for the Fort Selkirk and Lost Chicken tephra beds, but only glass ages for the others.Assuming that no track fading has occurred in the glass, Old Crow and Dawson tephra beds are younger than 120 000 and 52 000 years BP, respectively. Mosquito Gulch tephra is 1.22 Ma old, Fort Selkirk tephra is about 1 Ma old, the Ester Ash Bed is 0.45 Ma old, and the best estimate of the age of Lost Chicken tephra is the range 1.7–2.6 Ma.It is evident from these results and from the known abundance of tephra beds within late Cenozoic deposits of the Yukon Territory and Alaska that application of the fission-track method to distal tephra, in conjunction with detailed characterization studies, offers great potential for elucidation of the late Cenozoic geologic history of Alaska and the Yukon Territory.
Ordovician Pterygometopidae (Trilobita) of North America
Authors: Ludvigsen Rolf , Chatterton Brian D. E.
Published: April 2011

Pterygometopidae are common trilobites in Middle and Upper Ordovician rocks of North America, northern Europe, and Siberia and they have considerable biogeographic usefulness. The subfamilies Pterygometopinae and Chasmopinae characterize Baltica, the Eomonorachinae characterizes Laurentia, and the Monorakinae characterizes Siberia. In North America, pterygometopids occur in strata of Whiterockian to Gamachian (Llanvirn to Ashgill) age. The Pterygometopinae is represented by Achatella Delo, the Monorakinae by Monorakos Schmidt, the Chasmopinae by Toxochasmops McNamara, and the Eomonorachinae by Eomonorachus Delo, Calyptaulax Cooper, Sceptaspis n. gen., Denella n. gen., and Tricopelta n. gen. Isalaux Frederickson and Pollack is not assigned to a subfamily. The north European Pterygometopus Schmidt was probably ancestral to Calyptaulax, which, in turn, gave rise to a modest North American radiation of eomonorachines in the Blackriveran to Edenian interval. The eomonorachines display both sphaeroidal and uncoiled spiral enrollment patterns, as well as a new intermediate pattern. A neotype is chosen for Eomonorachus intermedius (Walcott). Denella cumera and Tricopelta mackenziensis are new.
A new specimen of Taricha (Amphibia: Caudata) from the Oligocene of Washington
Authors: Naylor Bruce G.
Published: April 2011

A nearly complete fossil salamander, including part and counterpart, is referred to Taricha. The specimen is of a post-metamorphic individual and is a member of the more primitive subgenus Palaeotaricha as well as being the oldest known member of the genus. This documented congruence between age and primitiveness supports the validity of the paleontological approach to phylogenetic analysis.
Paraglacial origin for terraced river sediments in Bow Valley, Alberta
Authors: Jackson Jr. Lionel E. , MacDonald Glen M. , Wilson Michael C.
Published: April 2011

Fluvial terraces flank the course of the Bow River for 100 km from the eastern margin of the Rocky Mountain Front Ranges to Calgary and beyond. The terraces are cut predominantly in gravel fill, which ranges in thickness from approximately 10 m in the Calgary area to 30 m near the mountain front. Sedimentary structures in the gravels indicate a braided stream sedimentary environment in contrast to the present quasi-stable, sinuous, single-channel form of the Bow River. Radiocarbon dates on ungulate remains from the gravels indicate the main period of fill occurred ca. 11 500–10 000 RCYBP (radiocarbon years before present). Previous workers have postulated that the gravels originated directly as outwash from a glacial advance to or beyond the mountain front. This explanation has been refuted by recent stratigraphic and palynological investigations. A complex nonglaciofluvial origin is proposed for these terraces and the sediments that form them. The last glacial advance to reach the mountain front was well into retreat by as early as ca. 13 400 RCYBP. Spruce and pine forest was established in the Bow River drainage by ca. 10 400–10 000 RCYBP and glaciers were restricted to high cirques. It is probable that the early period of fill deposition (ca. 11 500–10 000 RCYBP) was initiated when mountain tributary trunk streams of the Bow River were choked with debris-flow-delivered sediment during the construction of paraglacial debris fans and related phenomena. The debris flows were distinctive features of early nonglacial times, when landforms left unstable by ice retreat mass-wasted into the valleys. Paraglacial processes explain the early postglacial history of the Bow drainage and this example provides a model readily applicable to other drainages in formerly glaciated terrain.
U–Pb geochronology of the Bokan Mountain peralkaline granite, southeastern Alaska
Authors: Saint-Andre Bruno de , Lancelot Joël R. , Collot Bernard
Published: April 2011

The Bokan Mountain arfvedsonite–aegirine granite is the only peralkaline acid intrusion actually known on the margin of the Canadian Cordillera. It is the end product of a peralkaline magmatic evolution and is characterized by genetically associated concentrations of U and Th. The U–Pb method on zircons has been used to date two samples: one from a barren peralkaline granite and one from a low-grade U–Th mineralized albitite. A typological study has revealed two genetically different populations of zircons in the barren granite. The upper intercept age of 171 ± 5 Ma obtained on a concordia diagram dates the emplacement of the peralkaline granite. Acid wash experiments on zircons have allowed us to remove important quantities of common lead; this point is discussed as well as the abnormally low Pb content of the feldspar extracted from the barren granite.A Jurassic period of magmatic activity must be integrated into the geological history of Prince of Wales Island. Peralkaline magmatism may have occurred when the Alexander Terrane rifted away from its more southerly area of origin.
Paleomagnetism of the Lac St-Jean anorthosite and related rocks, Grenville Province, Quebec
Authors: Buchan K. L. , Fahrig W. F. , Freda G. N. , Frith R. A.
Published: April 2011

Alternating field and thermal demagnetization study of the Lac St-Jean anorthosite and related rock units in the central portion of the exposed Grenville Province reveals two components of magnetization, one of reversed and the other of normal polarity. Both components are thought to have been acquired during the last regional metamorphism, which was sufficiently intense in this area (mostly amphibolite grade) to reset any earlier magnetization. Corresponding paleopoles at 193°W, 8°S (dm = 7.3°, dp = 4.6°) and 213°W, 19°S (dm = 10.5°, dp = 8.5°) lie along the 950–900 Ma segment of the recently calibrated Grenville track of the North American apparent polar wander path, a track that has thus far been defined largely by results from rock units of the western Grenville.
Paleomagnetism of the Borden dykes of Baffin Island and its bearing on the Grenville Loop
Authors: Christie K. W. , Fahrig W. F.
Published: April 2011

Northern Baffin Island is intersected by spectacular swarms of predominantly northwesterly trending diabase dykes. Cross-cutting relationships, K–Ar ages, and paleomagnetic contact tests indicate that these dykes represent at least two major episodes of Hadrynian igneous activity. The Borden dykes were emplaced during the earlier of these episodes. They are about 950 Ma old and have a paleomagnetic pole position of 153.3°E, 26.7°S, δm = 8.6e, δp = 6.1°. The later episode saw the emplacement of the previously defined Franklin dykes, which are about 750 Ma old. The newly defined Borden pole lies at the southern extremity of the Grenville Loop and has an age consistent with poles of similar position that were derived from rocks of the Grenville Province.All of the dykes probably reflect tension acting in an east-northeast–west-southwest direction. The directions of thick northwest trending dykes, which form a considerable angle to that expected from east-northeast tension, are thought to have been controlled by earlier (circa 1200 Ma) fractures of the Borden fault zones. The two main surges of magma may coincide with two -periods of Hadrynian uplift in the Boothia Peninsula area to the west.
Quartz surface microtextures and grain-size characteristics of Quaternary sediments in the Porcupine Strand area of coastal Labrador, Newfoundland, Canada
Authors: Rogerson R. J. , Hudson H. M.
Published: April 2011

Sand-sized quartz grains from five Quaternary environments on the coast of Labrador were scrutinized under a scanning electron microscope. Various surface textural characteristics defined in previous literature were noted and "counted" in a systematic fashion. Multivariate statistical analysis of the data reveals that certain groups of surface textures provide for significant environmental identification, but no single surface texture is unique to any one environment. Absolute recognition of a particular environment from the presence of "diagenetic" features on several grains is not recommended for areas such as this. Yet the statistical pattern of scores for some features results in a position of individual samples and groups similar to the patterns obtained from the analysis of grain-size distribution data. The glacial environment appears to be no harder to define than most others in this type of analysis.
Morphometry of open rock basins, Kananaskis area, Canadian Rocky Mountains
Authors: Sauchyn David J. , Gardner James S.
Published: April 2011

Digital elevation data have been obtained for 54 open rock basins from aerial diapositives using an analytical stereoplotter. The term "open rock basin" is used to distinguish these basins from the closed rock basins of classical glacial cirques. Whereas closed basin cirques have been subjected to considerable morphometric analysis, open rock basins, which are equally prevalent in mountain environments, have not. The morphometric analyses in this paper are based on nine indices: length, width, area, relief, length/width, length/relief, width/relief, area/relief, and compactness. Cluster analysis of compactness and area/relief data indicates five distinct clusters of open rock basins, which are attributed to variations in topoclimate and geologic structure. The three largest clusters are labelled rockfall chutes, rockfall funnels, and open cirques. The cirque cluster is compared with glacial cirques for which published morphometric data exist. Comparable length/width ratios suggest an equilibrium in rock basin planimetric shape. However, the considerably greater relief and lower area/relief values of the open cirques suggest that glaciation of these rock basins has been limited to their upper reaches in the form of niche glaciers.
Regional stratigraphy and age of Chilcotin Group basalts, south-central British Columbia
Authors: Bevier Mary Lou
Published: April 2011

Mio-Pliocene Chilcotin Group basalt flows form a 50 000 km2 lava plateau in south-central British Columbia. Two periods of eruptive activity at 2–3 and 6–10 Ma are indicated by a compilation of available age data, including 10 new K–Ar age determinations, and basalts from these two periods are chemically indistinguishable. The Chilcotin Group consists of thin, crudely columnar-jointed pahoehoe flows, some thick, tiered flows, pillow lava and pillow breccia, and rare silicic tephra layers. The presence of many vesicle sheets and cylinders and collapsed pahoehoe toes suggests that the basalts were volatile-rich. Known vents (gabbro and basalt plugs) for the basalt flows form a northwest trend along the axis of the lava plateau. The plateau appears to have formed from the overlap of many low-profile shield volcanoes and is similar in morphology to other plains basalts such as the Snake River Plain and parts of Iceland. Glaciation has stripped off an unknown volume of the flat-lying basalt flows.
Enriched 13C composition of interstitial waters in sediments of a freshwater lake
Authors: Turner J. V. , Fritz P.
Published: April 2011

The DIC (dissolved inorganic carbon) of interstitial waters from sediments of a small carbonate-precipitating lake in southern Ontario has highly enriched δ13C values of up to +13‰ relative to PDB (Peedee belemnite). This post-depositional isotopic enrichment is attributed to the metabolism of methanogenic bacteria. The δ13C values of marl in the sediment profile are also enriched by an average of +3 to +4‰ relative to the associated molluscs.Photosynthetically induced carbonate precipitation and post-depositional recrystallization are among the processes that are considered to contribute to the isotopically enriched marls. Evidence for the latter process is drawn from geochemical analyses on interstitial waters, which show them to be at or very close to saturation with respect to calcite, indicating that net calcite dissolution has occurred, probably under the influence of high pCO2's generated by methanogenic bacteria. Such freshwater carbonate sediments with interstitial waters enriched in 13C provide a unique environment for study of isotope relations during carbonate diagenesis under accessible conditions and with a time scale of geologic relevance.
Stratigraphy and deformational history of the Scrip Nappe, Monashee Mountains, British Columbia
Authors: Raeside Robert P. , Simony Philip S.
Published: April 2011

The Scrip Nappe, a large recumbent anticline that occupies the northern Selkirk and northern Monashee Mountains, has an inverted lower limb, some 50 km in length across strike, and comprises stratigraphic divisions of the Hadrynian Horsethief Creek Group, which can be traced southward with decreasing metamorphic grade through the Selkirk Mountains to the northern Purcell Mountains. The Scrip Nappe has a southwesterly vergence and it formed that way during the first folding phase of the Mesozoic Columbian Orogeny. Metamorphism no greater than biotite zone accompanied that first deformation. The nappe was subsequently refolded into tight northeast verging folds. Metamorphism rose to upper amphibolite facies late in the second deformation phase. After the metamorphic climax, northeast verging buckle folds and associated crenulation cleavage formed locally during a third folding episode. The entire nappe complex was then carried northeastward, on the Purcell thrust, over the folds and thrusts of the western Rocky Mountains.
Geochemistry and petrogenesis of basaltic rocks from Coppermine River area, Northwest Territories
Authors: Dostal J. , Baragar W. R. A. , Dupuy C.
Published: April 2011

Proterozoic basaltic flows (> 2000 m thick) and associated dykes and sills from the Coppermine River area, Northwest Territories have chemical compositions typical of continental tholeiites. The low Mg/Fe ratio and abundances of Ni and Cr indicate that the lavas were extensively fractionated prior to extrusion. The variations of incompatible elements such as K, Rb, REE, Y, Zr, Nb, and Th suggest that the rocks were affected by interaction with continental crust. The samples least affected by contamination have trace-element compositions very similar to those of P-type mid-ocean ridge basalts. It is suggested that continental tholeiites have been generated from the same source as P-type oceanic tholeiites, and geochemical features, such as the enrichment of some lithophile elements in many of these rocks, may be related to crustal contamination. The variations within the volcanic pile of the Coppermine River area are related to those of an exposed part of the Muskox layered intrusion.
The Archean gneiss complex of northern Labrador. 2. Mineral ages, secondary isochrons, and diffusion of strontium during polymetamorphism of the Uivak gneisses
Authors: Collerson Kenneth D.
Published: April 2011

Strontium isotope systematics of minerals from the ca. 3600 Ma old Uivak gneisses and of compositionally layered Uivak I gneisses, which define secondary isochrons, are the result of Sr isotopic homogenization during thermal events ca. 2800, ca. 2500, and ca. 1800 Ma ago. The strontium isotope data provide information about the thermal history of the Archean gneiss complex in northern Labrador, the scale of Sr isotopic equilibration, and mechanisms of Sr diffusion during polymetamorphism.The mineral data indicate that biotite and amphibole were both partially open to Sr diffusion during the Hudsonian Orogeny ca. 1800 Ma ago. However, cooling rates and closure to diffusion of Sr in these phases varied throughout the terrane. Potassium feldspars were largely closed to diffusive loss of Sr during the 1800 and 2500 Ma events, and they record evidence of a ca. 2800–2900 Ma thermal event.Ages defined by secondary isochrons correlate with variations in the widths of the gneissic layers and correspond with geologically established events in the Nain and Churchill Provinces. The secondary isochrons developed as a result of local isotopic equilibration on different scales during these thermal events. The variable scales of equilibration reflect the effects of different Sr diffusion mechanisms. As a melt phase was not produced in the gneisses at the times indicated by the secondary isochrons, diffusion must have occurred under subsolidus conditions. Temperatures were therefore too low for extensive volume diffusion to have taken place. Exchange of Sr isotopes over distances greater than 5–10 cm must have involved grain boundary diffusion or some form of infiltration metasomatism.
A subsided island west of Flores, Azores
Authors: Ryall Patrick J. C. , Blanchard Marie-Claude , Medioli Franco
Published: April 2011

Investigation of a seamount 50 km west of Flores, in the Azores, has shown it to be a subsided island. This has been established by the fact that some of the cores recovered by a drill from the seamount at 450 m water depth were composed of subaerial basalt. The presence of Globoratalia truncatulinoides in some cores has dated them at less than 1.8 Ma. The basalt has been dated at 4.8 Ma. These facts give a subsidence rate faster than that of normal oceanic crust. The magnetic properties of the basalts have been measured and the results used in an attempt to calculate the anomaly of the seamount using its bathymetry. No calculated anomaly based on our models resembled the observed anomaly. The observed anomaly shows a linear trend typical of normal oceanic crust.
Postglacial vegetational history of Tonquin Pass, British Columbia
Authors: Kearney M. S. , Luckman B. H.
Published: April 2011

A pollen and macrofossil study of peat sediments in Tonquin Pass, British Columbia provides the oldest dated record of vegetational and climatic changes in the middle Canadian Rockies. Paleoecological interpretation of these events dated by tephrochronology and radiocarbon dating is facilitated by comparisons with other regional pollen profiles.Late Wisconsin ice receded from Tonquin Pass prior to 10 000 years BP. By 9700 years BP a Pinus contorta forest with an understory dominated by ferns had colonized the area. The climate of this period was cool and moist. Following this interval was a brief episode (9000–8040 years BP) of haploxylon pine dominance during which the climate became colder. A long warm period beginning by 8040 years BP was characterized by desiccation of local meadows and fens and invasions of these areas by trees, principally Picea. Dated fossil Picea and Abies logs from alpine bogs within Jasper National Park document that timberlines had advanced beyond present limits by 8770 years BP. These data indicate a considerable lag in the registration of this interval in the Tonquin record.During the last 4300 years the retreat of trees from meadows and increases in the representation of several alpine taxa indicate that generally moist and cool conditions have prevailed. Evidence for Holocene timberline fluctuations in the Jasper area suggests an overall lowering in timberline elevation and further cooling since 1700 years BP.
Holocene history of the estuarine area surrounding Portage, Alaska as recorded in a 93 m core
Authors: Bartsch-Winkler Susan , Ovenshine A. Thomas , Kachadoorian Reuben
Published: April 2011

A 93 m core obtained at Portage, Alaska records four prograding cycles of estuarine deposition for the past 8230 ± 100 years. Analyses of texture, mineralogy, paleontology, and sedimentary structures enable definition of eight lithologic units. Mineralogic studies show that past and present sedimentation at Portage has been largely mud and sand from the Susitna River on the northwest side of Cook Inlet. Six radiocarbon dates from concentrated organic debris in the core and on the surface enable determination of sedimentation rates for four intervals and show rates to be higher and to vary more at depth than rates nearer the surface. The glacier-carved Turnagain Arm fiord has been receiving sediment for at least the past 14 000 years, as estimated by extrapolation of calculated sedimentation rates to the thickness of unconsolidated sediment drilled at Portage, which totals approximately 300 m. Presently, deposition is accomplished "instantly" as the result of tectonic subsidence and compaction of sediment caused by periodic earthquakes, in combination with a turbid estuarine system.
Aliphatic carboxylic acids in buried Ah horizons in Alberta, Canada as paleoenvironmental indicators
Authors: Dormaar J. F.
Published: April 2011

In southern Alberta, a buried Ah horizon is frequently present beneath Mazama tephra (ca. 6600 years BP). Drainage conditions during the formation of such buried Ah horizons may determine the quality of the aliphatic carboxylic acids in the soil organic matter. The spectrum of aliphatic acids extracted from a number of buried Ah horizons indeed suggests either well drained or poorly drained conditions during soil formation regardless of the mode of deposition of materials before or after the soil-forming interval. The climate required for development of the well drained paleosols was inferred to be similar to the climate under which surficial Black Chernozemic Ah horizons were formed.
Rb–Sr whole-rock age of the Klondike Schist, Yukon Territory
Authors: Metcalfe P. , Clark G. S.
Published: April 2011

Seven samples of metarhyolite from a measured section of the Klondike Schist, in the Yukon Crystalline Terrane, 5 km southwest of Dawson City, give a whole-rock Rb–Sr isochron age of 202 ± 11 Ma with an initial 87Sr/86Sr ratio of 0.7140 ± 0.0001. The high initial ratio suggests that this is a metamorphic age, recording the time of shearing of the metarhyolites. An estimated minimum age of formation of the protolith of approximately 260 Ma was obtained by rotating the isochron to an assumed primary initial 87Sr/86Sr ratio of 0.707.The siliceous cataclasites of the Klondike Schist may have formed as a forearc wedge of arkose with intercalated volcanics. The unit was intensely sheared in a subduction zone, prior to obduction onto the ancient North American continental margin. The results of this isotopic study suggest an age of formation of 260 Ma and an age of cataclasis of 202 Ma. The metarhyolites remained closed to Rb–Sr isotopic equilibration during obduction, though the thermal event is recorded in K–Ar isotopic data reported by other authors. The results of this study are consistent with theories of formation of this assemblage.
Isostatic adjustments in a full glacial sea
Authors: England John
Published: April 2011

During the last glaciation an ice-free corridor existed between the northeast Ellesmere Island and northwest Greenland ice sheets. This corridor constituted a peripheral depression in which the marine limit marks the uppermost extent of a full glacial sea. The full glacial sea is characterized by (1) 14C dates on in situ marine shells that predate initial emergence (unloading) followed by (2) synchronous emergence from the marine limit throughout the peripheral depression. Relative sea-level curves from the full glacial sea confirm previous morphostratigraphic and glacioisostatic evidence for limited ice extent during the last glaciation. These curves also document the history of glacial unloading and the form of the relative sea-level curve that one would theoretically expect in the peripheral depression. The form of the curves presented here is unlike any other published emergence curves from arctic Canada or from Fennoscandia.The relative sea-level curves for northeast Ellesmere Island show three segments: (1) an interval of stable relative sea level (isostatic equilibrium) at the marine limit between at least 11 000 and 8000 BP; (2) an interval of slow emergence from 8000 to 6200 BP during which northeast Ellesmere Island ice slowly retreated; and (3) an interval of rapid emergence, caused by rapid glacial unloading, after 6200 BP when a prominent amelioration was in progress. These relative sea-level curves are discussed in relation to other paleoclimatic changes and the deglacial history of northwest Greenland. These curves are of regional importance in that they provide a new means of distinguishing between areas that were ice covered and ice free during the last glaciation.
Slope hydrology as influenced by thawing of the active layer, Resolute, N.W.T.
Authors: Woo Ming-ko , Steer Peter
Published: April 2011

High arctic slopes have a shallow active layer that thaws unevenly during summer. The result is often a lack of agreement between the configuration of the frost table and the surface topography, and this has effects on the slope hydrology. (1) Areas with a shallow frost table favour surface runoff but areas with a deeper frost table require a thick zone of saturation to generate surface flow. Uneven thaw depths then cause alternating seepage and re-emergence of water down a slope. (2) The configuration of the frost table is highly dynamic, causing day to day changes in water storage capacity in the active layer. (3) A frost table with local depressions can pond up groundwater, which may be rapidly released when part of the frozen sill is breached by continual thawing. (4) The topographical drainage divide may not correspond with the subsurface drainage divide as defined by the frost table, thus allowing groundwater to drain laterally across topographical boundaries. These findings show that a knowledge of the frost table behaviour, both spatially and temporally, is essential to the study of slope hydrology in continuous permafrost terrains.
Distribution of mineral deposits in accreted terranes and cratonal rocks of western United States
Authors: Albers John P.
Published: April 2011

The western margin of the conterminous United States, covering roughly 300 000 mi2 (777 000 km2), is an agglomeration of tectonostratigraphic terranes accreted to the North American craton mainly during Mesozoic time. The terranes represent a number of fundamental crustal types: oceanic crust, island-arc crust, mélange, various combinations of the preceding three, batholithic, miogeoclinal, and platform.The distribution patterns of types of mineral deposits show that miogeoclinal terranes of the craton are characterized by replacement and vein-type lead–zinc–silver, skarn tungsten deposits, molybdenum, and tin, whereas accreted terranes contain all the known volcanogenic massive sulfide deposits, all chromite and chert-associated manganese, and all the large gold quartz-vein deposits, except Goldfield, Nevada. Carlin-type disseminated fine-grained gold deposits occur mostly in windows of Paleozoic miogeoclinal rocks in Nevada, but the only known fine-grained gold deposit in California is in very youthful volcanic rocks overlying oceanic-crust terrane. Large bedded-type barite deposits, although in the same general area and showing the same general trend as fine disseminated gold deposits in Nevada, are in allochthonous oceanic terrane. Mercury and antimony are dominantly in accreted terranes but antimony, in particular, also forms important deposits in cratonal rocks. Most of the large iron deposits are in the craton but a few are in accreted island-arc terranes.
A spectrum of alluvial deposits in the Lower Carboniferous Bonaventure Formation of western Chaleur Bay area, Gaspé and New Brunswick, Canada
Authors: Zaitlin Brian A. , Rust Brian R.
Published: April 2011

The Lower Carboniferous Bonaventure Formation of western Chaleur Bay, Gaspé and New Brunswick, is a terrestrial redbed succession with abundant calcretes, deposited in a semi-arid paleoclimate. Facies can be grouped into three associations, conglomeratic, sandstone, and mud-dominated, within two 100–150 m upward-fining megasequences. The megasequences are attributed to alluvial fan progradation due to tectonic rejuvenation.Vertical facies relationships and internal structures indicate that varied alluvial environments are represented. Alluvial fans formed on steep slopes adjacent to fault scarps and are dominated by deposits of the conglomeratic association. Lateral and downslope coalescence of fans into a braid plain is represented by transition from the conglomeratic to the sandstone facies association. Distally, the braid plain is transitional into deposits of the mud-dominated association.Paleocurrents and clast compositions show that sediment in the Gaspé outcrops was derived from the northwest, and that in New Brunswick from the southwest. This indicates that Chaleur Bay is an exhumed Carboniferous paleovalley, with axial drainage to the east.
Kink folds at Upper Manitou Lake, northwestern Ontario
Authors: Wallace P. I. , Clifford P. M.
Published: April 2011

Two sets of conjugate kink folds occur in the greenstones of Upper Manitou Lake, northwestern Ontario. One set is sparsely developed; the later set is developed over the entire area, concentrating in the neighbourhood of the Manitou Straits Fault. This second set of kink folds is asymmetrically developed and seems to be associated with sinistral movement along the fault.The mechanism of fold development involved rotation of kinked foliae between kink fold boundaries, but lateral migration of these boundaries and of the tip of the kink fold is a necessary part of the mechanism. The folds developed at relatively low confining stresses by shear along closely spaced schistosity planes.
Application géophysique à l'interprétation structurale de la région du lac Bécancour, Thetford Mines, Québec
Authors: Seguin Maurice K.
Published: April 2011

The present study, based on detailed gravity anomaly (Bouguer and residual) and magnetic maps of the Thetford Mines area, seeks to explain the mechanism by which the Lac Bécancour structural unit was emplaced. The Bouguer anomaly map shows: (1) generally more positive anomalies toward the northwest; (2) local positive anomalies in the southwest and north-northwest; and (3) a small local positive anomaly in the east. Residual anomalies are characterized by a weak high of the order of 2–3 × 10−5 m/s2 (2–3 mgal) over the center of the structure. The magnetic map shows: (1) negative to neutral intensities over the center of the structure; (2) two small positive anomalies on the inner border of the structure; (3) a large magnetic mass (the ophiolite complex) in the west-northwest; and (4) small and isolated magnetic masses to the southwest and east.The hypothesis of diapir-like rise caused by an underlying serpentinite mass, as proposed by some geologists, is refuted by the absence of a positive magnetic anomaly over the structure. A second hypothesis, which calls on post-nappe granitization of the core of the structure at depth, is unlikely as gneiss is now here exposed in the area and the structure is bounded by faults. Instead, the geophysical data suggest that the Lac Bécancour structural unit is an old (Early Cambrian or Eocambrian) block that has undergone polyphase deformation during the Taconic Oxogeny rather than being a horst-like body emplaced by vertical rise. Identical overthrust slices of Hadrynian basement in the centers of imbricated blocks and nappes of lower Paleozoic rocks are commonly observed in the Caledonides of Norway and Sweden where they generally have the appearance of antiforms or synforms. [Journal Translation]
New paleomagnetic data for the Triassic Guichon batholith of south-central British Columbia and their bearing on Terrane I tectonics
Authors: Symons D. T. A.
Published: April 2011

The 198 Ma Guichon batholith outcrops in the southern end of the Intermontane Belt or composite Terrane I of the western North American Cordillera. Thermal demagnetization of specimens from 19 sites at 200, 450, and 560 °C isolates a stable primary component at 560 °C in 13 sites, giving a pole position of 347°W, 52°N (δp = 5°, δm = 9°). These data support earlier results obtained by the author that indicate the batholith has undergone a clockwise rotation about a vertical axis of ~43 ± 7°. They also show that the batholith has undergone northward motion of 13 ± 6°, which supports recent arguments that the terrane underwent 14 ± 2° of northward translation between Late Cretaceous and pre-Miocene time.
A new species of the artiodactyl Heptacodon from the Cypress Hills Formation, Lac Pelletier, Saskatchewan
Authors: Storer John E.
Published: April 2011

Heptacodon pellionis sp. nov. (Artiodactyla, Anthracotheriidae) occurs in the Cypress Hills Formation of Lac Pelletier, Saskatchewan. Its closest resemblances are to a specimen from the earliest Chadronian Yoder fauna of Wyoming, and I tentatively place the record in the early Chadronian (Early Oligocene).
Eclogite from central Yukon: a record of subduction at the western margin of ancient North America
Authors: Erdmer Philippe , Helmstaedt Herwart
Published: April 2011

Eclogite occurring in central Yukon, at Faro and near Last Peak, as lenses interleaved with muscovite–quartz blastomylonite has the chemical and field characteristics of group C rocks. From sigmoidal inclusion trails in garnet, from geothermometry and geobarometry, and from mineral parageneses, the eclogite is inferred to have a crustal protolith and to have followed a hysteretic, subduction-cycle P–T trajectory. Transformation of basic igneous rock into schist was followed by eclogite metamorphism during which pressure was at least 1000 MPa and temperature was between 600 and 700 °C. Uplifting involved passage through the stability field of glaucophane; the eclogite and its host rocks were then subjected to greenschist fades metamorphism and deformation, with temperature at approximately 400 °C. The rocks were emplaced as thrust sheets against or onto the western North American cratonal margin. The tectonic boundary ranges from nearly vertical, where it is outlined by a zone of steeply dipping mélange, to nearly horizontal beneath klippen of cataclastic rocks that lie on North American miogeoclinal strata. Together with occurrences of eclogite on strike, in Yukon, near Fairbanks (Alaska), and near Pinchi Lake (British Columbia), eclogite at Faro and near Last Peak implies that the Yukon Cataclastic Complex is a deeply eroded collision mélange that borders over 1000 km of the ancient continental margin.
Breakouts in Alberta and stress in the North American plate
Authors: Fordjor C. K. , Bell J. S. , Gough D. I.
Published: April 2011

The paper reports a detailed statistical study of breakout azimuths in 48 oil wells widely distributed in the Alberta sedimentary basin, bringing the number of oil wells contributing azimuths to 94 for the western Canadian basin. The azimuths show significant regional variation between the northern, central, and southern parts of the basin. Twenty-one wells, in which breakouts cover depth ranges greater than 600 m, were used to investigate regression of breakout azimuths on depth. Ten wells give positive regression coefficients, 11 are negative, and no coefficient is significant at 95% confidence level. If the dominant northwest–southeast orientation of the long axes of breakouts gives the orientation of the lesser horizontal principal stress Sh, following the hypothesis of Bell and Gough, the inferred stress orientations indicate that throughout the whole basin the direction of the maximum horizontal stress SH is northeast–southwest. Stress measurements, by strain-relief techniques in a mine and from hydraulic fracture in wells, support the stress orientation given by the breakouts. The insignificant regression of breakout azimuths on depth supports the view that the orientation data represent stress in the lithosphere rather than in the sediments only. Directions of the lesser horizontal compression Sh, from Zoback and Zoback in the United States and from breakout studies in western Canada, are combined to suggest that the Mid-Continent stress province of North America may include the western Canadian basin and the Canadian Shield as well as the central United States. Coherent stress with the observed orientation, over the continent east of the Rocky Mountains, would result from northeastward basal drag on the North American plate, as Zoback and Zoback have pointed out. Basal drag to the northeast could arise either if the plate were sliding southwestward over a passive asthenosphere, as suggested by Zoback and Zoback, or if northeastward mantle flow were driving the asthenosphere and the plate northeastward.
Pillow shelves: determination of bedding direction and structural facing direction from shelves in deformed pillow lavas
Authors: Sawyer E. W. , Barnes Sarah-Jane , Buck Marcus J.
Published: April 2011

Pillow shelves form in the upper parts of pillows or lava tubes, and record pauses in their drainage. Thus the recognition of pillow shelves in tectonically deformed pillows allows both the palaeohorizontal (i.e., bedding) direction and approximate way-up direction to be determined. This is demonstrated in an example from the Cape Smith Fold Belt of northern Quebec, where way up and bedding were independently determined. The establishment of way up in strongly deformed pillow sequences enables structural facing direction to be determined and is a crucial step in the elucidation of the structural history in terrains where pillowed basic volcanics predominate, e.g., greenstone belts.
Notes on the North American Tertiary marsupials Herpetotherium and Peradectes
Authors: Fox Richard C.
Published: April 2011

New specimens of the North American Tertiary didelphid marsupials Herpetotherium fugax Cope and Peradectes elegans Matthew and Granger are described. Herpetotherium is shown to be a valid genus, distinct from Peratherium Aymard and Amphiperatherium Filhol, possessing procumbent lower incisors, the first two of which are enlarged. The associated upper and lower dentition of Herpetotherium shows H. fugax to have been a small didelphine of probable insectivorous habits; its molar function centered on a wearing of the crowns in near-horizontal planes and on orthal prevallid–postvallum shear. In P. elegans, by contrast, the lower incisors are unspecialized; P1 is crowded against a robust canine, the posterior lower premolars are trenchant, the molar trigonids are erect, and the talonids anteroposteriorly shortened. Shear in near vertical planes was a more important dental function than in H. fugax. The dental anatomy of H. fugax and P. elegans corroborates recognition of the tribes Didelphini and Peradectini; the last common ancestor of these clades was probably Late Cretaceous in age.
Late Quaternary lacustrine and deltaic sedimentation near Banff, Alberta
Authors: Kostaschuk R. A. , Smith D. G.
Published: April 2011

Evidence provided by surface morphology, exposures, cores, and the stratigraphic positions of Mazama (6600 years BP) and Bridge River (2500 years BP) ashes was used to interpret the origin and late Quaternary history of lacustrine and deltaic sediments in the Bow River valley near Banff, Alberta.There were three distinct stages of Lake Vermilion occupying the study area from Late Pleistocene to mid-Holocene times. The earliest stage was ice dammed, deposited beach gravel and nearshore sand, and drained along the present course of the Cascade River to the east. The second, proglacial stage is associated with thick subsurface deposits of non-organic clay and drained to the east along the course of the modern Bow River. The final stage is suggested by point bar and aeolian beach dune sediments.With the stabilization of the final stage of Lake Vermilion the low-energy, river-dominated Bow Delta prograded into the lake from the west. Progradation of the delta through three depositional zones produced the present Vermilion Lakes.