bluuebunny/crossref_metadata_2025 huggingface dataset:
The movement of isolated boulders on tidal flats by ice floes
Authors: Drake John J. , McCann S. B.
Published: April 2011

The ability of ice floes to move isolated boulders on tidal flats by flotation and by pushing and (or) rolling them along the bed is considered in the standard format of sediment movement (entrainment, transport, and deposition). Analysis shows that flotation competence depends on ice thickness and floe size, and is sufficient to transport most of the boulders reported from eastern Canadian tidal flats. However, a limiting factor in the transportation of large boulders by this mode is likely to be the entrainment mechanism. Analysis of movement of grounded boulders by lateral ice thrust shows that, on both deformable and non-deformable beds, rolling rather than sliding will occur. Rolling competence depends on floe size, ice roughness, the ice–rock coefficient of friction, and current and (or) wind strength. Resistance to movement is a function of the embedment ratio and bed properties. Rolling could account for most of the observed short-distance transport of large boulders.
The upper Batinah Complex, Oman: allochthonous sediment sheets above the Semail ophiolite
Authors: Woodcock N. H. , Robertson A. H. F.
Published: April 2011

The upper Batinah Complex consists of allochthonous sedimentary sheets that structurally overlie both the Semail ophiolite and its cover of mélange (lower Batinah Complex). Sequences represent a former sedimentary transition across the outer part of a passive Mesozoic continental margin. From proximal to distal, units include redeposited quartzitic sandstones and shallow-water limestones, large carbonate buildups floored by Triassic mafic lavas, and pelagic radiolarites or hemi-pelagic calcilutites also underlain by Triassic mafic lavas. Sheets of these upper Batinah Complex sequences were emplaced onto the upper surface of the Semail ophiolite in Late Cretaceous time, during or soon after the advance of the Semail Nappe onto the Arabian margin. Emplacement was along subhorizontal fault zones, with sheets of distal facies followed by successively more proximal sheets. Structural style suggests a low overburden during deformation, with ductile flow of argillaceous material but more brittle behavior of other lithologies. Large recumbent folds are present. Fold orientations imply sheet transport from between northeast and southeast.We conclude that the Batinah sheets represent part of the passive margin to a continental mass originally northeast of the main Arabian margin, but which is no longer present. We favour high-level gravity emplacement of Batinah sheets, and argue against trench accretion as an emplacement mechanism for either the sheets or the Semail Nappe itself.
Évolution géochimique superficielle naissante des anorthosites. Cas du profil de Château-Richer (Québec), Canada
Authors: Dejou J. , Kimpe C. R. De , Lasalle P.
Published: April 2011

The initial stages of the superficial geochemical weathering of anorthosites have been investigated in a deposit at Château-Richer, Québec. The parent rock consists almost exclusively of andesine and is weathered to a thickness of about 120 cm. A till overburden indicates that the profile was truncated by the Wisconsinian ice. The rock is not extensively disintegrated, but the chemical weathering is rather intense. The Parker diagram shows a strong decrease of the weathering index from the parent rock to the weathering zone. While this is not the case for other crystalline rocks in the area, it may be accounted for by the fragility of the plagioclase.The < 2 μm fraction, which amounts to 2% of the soil, presents an evolution that is influenced by the site, especially the drainage conditions. At the base of the profile, drainage is poor and 2:1 minerals, smectite and vermiculite, are present in addition to 40% kaolinite. The 1:1 mineral increases to 60% near the contact with the till, while the amount of 2:1 minerals decreases because of the better internal drainage conditions.
Structure, petrology, and tectonic history of the Leech River complex northwest of Victoria, Vancouver Island
Authors: Fairchild Lee H. , Cowan Darrel S.
Published: April 2011

The Leech River complex 45 km northwest of Victoria consists of metamorphosed pelitic rocks, sandstone, and minor volcanic rocks, chert, and conglomerate of probable Late Jurassic to Cretaceous age. The assemblage experienced two similar deformational events during which regional shortening induced macroscopic east-plunging folds and related coaxial, mesoscopic linear structures, parasitic folds, and axial-plane cleavages. Fragmentation along the developing cleavages disrupted layering and eventually led to transposition during both events. Regional, progressive, low-pressure greenschist- to amphibolite-facies (andalusite–staurolite–biotite) metamorphism began during the first deformation and extended into the waning stages of the second. Intrusion of composite felsic sills was synchronous with deformation and metamorphism, which concluded about 39–41 Ma, according to K–Ar data. The Leech River fault, which forms the southern boundary of the complex, is a zone of two to four subparallel faults. All are relatively straight, narrow faults that appear to dip steeply. This structure is interpreted to be a left-lateral strike-slip fault, active exclusively after the 39–41 Ma conclusion of metamorphism and deformation.The Leech River complex originally may have accumulated somewhere along a late Mesozoic convergent margin, but there is no evidence that it either constitutes a subduction complex per se or was metamorphosed in such a setting in early Tertiary time. The Leech River complex is interpreted to be allochthonous with respect to the bulk of Vancouver Island, since neither older rocks of the Insular Belt (Wrangellia) to the north nor coeval rocks in northwestern Washington record the early Tertiary deformations and synkinematic low-pressure metamorphism. The complex apparently was derived from a cryptic terrane to the west and emplaced against Vancouver Island by left-lateral slip on the San Juan fault after 39–41 Ma.
40Ar/39Ar incremental-release age of biotite from a gabbro of the Shabogamo intrusive suite, southwestern Labrador
Authors: Dallmeyer R. D.
Published: April 2011

Biotite from a gabbro sill of the Shabogamo intrusive suite in southwestern Labrador records a well defined 40Ar/39Ar plateau age of 1353 ± 17 Ma. This is similar to the 1375 ± 60 Ma dates recorded by Sm–Nd and Rb–Sr whole-rock isotopic systems of the suite. Together, recent radiometric results suggest that members of the suite were emplaced at approximately 1375 Ma and cooled quickly at shallow crustal levels.
Étude de quelques coelentérés de la base du Mésozoïque du Canada occidental
Authors: Beauvais Louise
Published: April 2011

The study of some Coelenterata from the Triassic through Middle Jurassic of Canada, preserved in the collections of the Institute of Sedimentary and Petroleum Geology, Geological Survey of Canada, Calgary, Alberta, permitted one to specify the stratigraphical position of the studied material. Two new species of Scleractinia from Dogger outcrops are described. Paleoecological conclusions are made, showing the non-reefal character of this material.
Geochemistry of the alteration pipe at the Amulet Upper A deposit, Noranda, Quebec
Authors: Hall B. V.
Published: April 2011

The Amulet Upper A orebody is a stratiform pyritiferous copper–zinc deposit situated within a sequence of andesitic pillow lavas. Underlying the massive sulphides is a cylindrical alteration pipe containing sulphides plus cordierite–anthophyllite-bearing rock. Hydrothermal alteration considered coincident with the formation of the overlying massive sulphides resulted in the development of a chlorite–quartz assemblage occupying the center of the alteration pipe, with a sericite–epidote–quartz assemblage at the fringes. Contact metamorphism resulting from the intrusion of the Lac Dufault granodiorite isochemically transformed the chlorite–quartz assemblage to cordierite–anthophyllite, and the sericite–epidote–quartz assemblage to biotite–epidote–quartz. This caused the development of four mineralogical zones within the alteration pipe: (1) anthophyllite zone, (2) cordierite zone, (3) biotite zone, and (4) stockwork zone.Pillows within the alteration pipe and exterior to it were studied using whole-rock analyses. A statistically balanced sampling procedure was adopted such that chemical and mineralogical variations within a single pillow could be compared with variations between adjacent pillows and finally with pillows situated in different locations within the deposit area. The largest source of variation was found to be a function of sample position within the alteration pipe. Ancillary variations include: (1) variations on the scale of an individual pillow resulting from the inward penetration of hydrothermal solutions and (2) variations between adjacent pillows due to differing degrees of alteration and veining.Proceeding into the alteration pipe, CaO, Na2O, Ba, Cr, Ni, and Sr were removed, Fe2O3T, MgO, K2O, H2O+, S2−, Cd, Cu, Li, and Zn were added, and Al2O3, TiO2, and V remained relatively constant. These changes were largely a chemical manifestation of the introduction of sulphides, plus the breakdown of plagioclase and pyroxene to form chlorite and quartz in the center of the alteration pipe, and sericite, epidote, and quartz at the fringes. Temperature appears to have been the dominant factor in controlling the distribution of the alteration assemblages, although sulphur fugacity did have an effect on the sulphide assemblages.
Paleomagnetism and structural history of the Ghost Range intrusive complex, central Abitibi Belt, Ontario: further evidence for the Late Archean geomagnetic field of North America
Authors: Geissman John Wm. , Strangway David W. , Tasillo-Hirt Ann M. , Jensen Larry S.
Published: April 2011

On the basis of their remanence properties, the lithologies of the Late Archean (2710–2703 Ma) Ghost Range Complex, an east–west-trending layered mafic–ultramafic extrusive sequence in the central Abitibi Greenstone Belt, can be divided into three groups. Group 1 units contain a high-coercivity, high-blocking temperature (greater than 520 °C) magnetite-dominated remanence characteristic of the complex (D = 280°, I = 2°, k = 5.5, α95 = 11.8°, virtual geomagnetic pole = 13°E, 7°S; isolated by both AF and thermal methods), in good agreement with the few previous results bearing on the Late Archean apparent polar wander path for North America. Group 2 units contain a low-coercivity, low-blocking-temperature (less than 310°C) scattered remanence residing in pyrrhotite. Often, both remanences coexist in a single lithology at a given site. Group 3 units contain distributed coercivity and blocking-temperature remanences, again residing in magnetite, that are more scattered but statistically identical to the mean group 1 direction. The order of magnetic blocking appears to have been group 1 before group 3 before group 2. The geologic setting of the Ghost Range suggests that it has remained essentially stable since emplacement and therefore the group 1 direction appears to reliably represent a Late Archean paleomagnetic pole.
Age of the Brookville Gneiss and associated rocks, southeastern New Brunswick
Authors: Olszewski Jr. William J. , Gaudette Henri E.
Published: April 2011

The Brookville Gneiss is a medium- to high-grade quartz–feldspar–biotite and hornblende–quartz–feldspar–biotite gneiss found north and northeast of Saint John, New Brunswick. The Green Head Group, a sequence of low-grade metasediments, surrounds the Brookville Gneiss. Analyses of zircons with euhedral to subhedral overgrowths and rounded to subrounded cores from the Brookville Gneiss yield an upper intercept age on concordia of 1641 Ma, considered to be the age of the source area for the zircons. The zircon analyses also indicate two Pb-loss events at approximately 780 and 370 Ma. These ages are confirmed by zircon analyses of a quartz diorite gneiss from Green Head Island, which yields ages of 827 and 333 Ma. A small euhedral single zircon from the Brookville Gneiss, believed to be formed during metamorphism, gives a concordant age of 814 Ma corresponding to the first Pb-loss event. Rb–Sr whole-rock analyses of a granite from the east side of Musquash Harbour southwest of Saint John give an age of 392 Ma and an initial Sr ratio of 0.7187 substantiating the second Pb-loss event.The results indicate that the Brookville Gneiss and Green Head Group are older than 800 Ma and probably younger than 1200 Ma. The zircon source area age (1641 Ma) and first Pb-loss event (800 Ma) are similar to ages found in rocks of the eastern margin of the Appalachian orogen from Massachusetts and Cape Breton Island, respectively. They suggest a setting and tectonic event correlated in time for the Late Precambrian of the eastern margin distinct from the younger so-called "Avalonian."
The deglaciation of Atlantic Canada as reconstructed from the postglacial relative sea-level record
Authors: Quinlan Garry , Beaumont Christopher
Published: April 2011

The post-Wisconsinan relative sea-level record from Atlantic Canada is used to reconstruct the morphology of late Wisconsinan age ice cover during its retreat from the Atlantic region. The proposed reconstruction has little or no grounded ice in the southern Gulf of St. Lawrence, an ice dome over the north shore of the St. Lawrence, and thin ice, often less than 1 km thick, over much of the rest of the area. A sensitivity analysis shows that the proposed reconstruction is not unique in its ability to account for the relative sea-level record but that the thickness of ice in any individual area of the reconstruction is unlikely to be in error by more than a factor of two. The exact position of the ice margin in some areas is not well constrained by the model; an example is in southeastern Newfoundland.The numerical model used to relate ice morphology to postglacial relative sea level assumes that the ice sheets are isostatically equilibrated at the glacial maximum and, therefore, that load changes associated with earlier ice-sheet growth may be ignored. This assumption is shown to be reasonable. The same rapid relaxation of the Earth that allows one to ignore the effects of glacial accumulation, however, prohibits one from recognizing the effects of large-scale ablation that may have occurred prior to the assumed glacial maximum. For this reason the proposed reconstruction may be representative of only a late stage in the ablation of much more extensive and thicker ice sheets.Surfaces of relative sea level are presented for Atlantic Canada at various times in the past. These surfaces coincide with observational data where such data exist and are felt to provide reasonable estimates of relative sea level at all other locations for at least the last 13 000 years.
Progressive 18O depletion during CO2 separation from a carbon dioxide-rich hydrothermal fluid: evidence from the Grey River tungsten deposit, Newfoundland
Authors: Higgins N. C. , Kerrich R.
Published: April 2011

Oxygen isotope data for the Grey River tungsten prospect, Newfoundland, Canada, indicate a progressive depletion in δ18Ofluid during mineralization. Early veins with pegmatitic affinities were deposited at 470 °C and pressures greater than 1 kbar (100 MPa), from a fluid with a δ18O composition of 7.4‰, presumed to be of magmatic origin. Successive vein deposition, at progressively lower temperatures and pressures, culminated in the precipitation of wolframite-bearing veins at a temperature of 300 °C and pressures of 150–320 bar (15–32 MPa), from a low salinity fluid with a δ18O composition in the range 3.2–1.6‰.Low values of δ18O (and δDfluid) are recorded in many vein tungsten deposits and are normally interpreted as reflecting mixing of isotopically light meteoric fluids or formation brines with magmatic fluids. However, fluid-inclusion evidence for the Grey River mineralization indicates that a 40 mol% CO2 loss occurred by immiscibility and retrograde boiling of the hydrothermal fluid between 420 and 300 °C. Such a chemical change would have significantly altered the oxygen isotopic character of the hydrothermal fluid since CO2 fractionates 18O relative to coexisting water by ~10‰ at 400 °C and ~14‰ at 300 °C. Calculations using available CO2–H2O fractionation factors reveal that up to a 7‰ depletion in δ18O of the residual aqueous fluids may occur as a result of the 40 mol% CO2 loss from the hydrothermal fluid.
Structural interpretation of the eastern Notre Dame Bay area, Newfoundland: regional post-Middle Silurian thrusting and asymmetrical folding
Authors: Karlstrom K. E. , Pluijm B. A. van der , Williams P. F.
Published: April 2011

The structural geometry of the eastern Notre Dame Bay area is that of an allochthonous sequence (related to F1 thrusting and folding), folded by F2 asymmetrical folds, and offset by F3-related high-angle faults. F1 folds are isoclinal and commonly intrafolial. F2 folds are asymmetrical (generally tight) with axial surfaces that dip 30–85° southeast. The prominent northeast-striking, penetrative cleavage (S2) is axial planar to F2 folds. F3 structures include chevron folds, box folds, kink bands, and local S3 crenulation cleavage.F1 folds are overprinted by F2 folds producing coaxial and mushroom interference patterns. This and the subhorizontal enveloping surface of F2 indicate that F1 folds were recumbent prior to F2. A zone of F1 folds separating Silurian turbidites from subaerial volcanics on the Port Albert Peninsula suggests F1 was related to macroscopic thrusting, as does the association of F1 with mesoscopic thrust faults.F2 folds are the most obvious structures in the area. Macroscopic examples include an anticline–syncline pair on Milleners Peninsula; an anticlinorium cored by the Dunnage mélange, and a synclinorium cored by subaerial sandstones on the Port Albert Peninsula. These folds repeat the stratigraphy across areas that have been incorrectly interpreted in terms of fault-bounded, north-younging homoclines. A shallow enveloping surface for F2 is supported by the uniformly low metamorphic grade in the area and detailed structural profiles. In view of the shallow dip of the enveloping surface, it is possible to correlate the Dunnage mélange, the Carman ville mélange, and other mélanges in the area.Contrary to prevailing interpretations of a structural setting involving fault-bounded tectonostratigraphic zones, we demonstrate a similar deformational history and a general continuity of macroscopic F2 folds throughout our area. Rectilinear faults on geologic maps, used by previous workers as the boundaries between tectonostratigraphic zones, are post-F2 features. They cross-cut F2 folds and are at a high angle to the F2 enveloping surface. These include the Chanceport, Lukes Arm, Dildo, and Reach Faults.All three fold generations affect rocks ranging in age from Ordovician to Middle Silurian. Thus, irrespective of when the earliest deformation began, it continued into Silurian times.
Gravimetric terrain corrections in western Canada
Authors: Blais J. A. R. , Lodwick G. D. , Ferland R.
Published: April 2011

Terrain corrections for gravimetric measurements have been studied in terms of accuracy requirements and automated computations. Geodetic and geophysical applications in western Canada have been considered specifically because of complications arising from the rugged topography. Comparing the computation methods of Nagy and Mathisen in relation to the theoretical results, the former is shown to be more reliable with simulated accidented topography. Other approaches are also briefly discussed and general recommendations are made for an optimal technique to compute gravimetric terrain corrections in western Canada.
Uranium and thorium in Paleozoic rhyolites of Nova Scotia
Authors: Dostal J. , Dupuy C. , Keppie J. D.
Published: April 2011

The concentrations of U and Th in Paleozoic rhyolites of Nova Scotia are closely related to their contents of K. The rhyolites were affected by secondary processes including low-grade metamorphism that could lead either to enrichment or depletion of these elements. The average abundances of U (ppm), Th (ppm), and K (%) in rhyolites are: Cambrian—2.69, 9.77, and 2.58, respectively; Silurian—4.50, 17.3, and 4.09, respectively; and Devono-Carboniferous—4.64, 18.3, and 5.67, respectively. The depletion of U, Th, and K in Cambrian rocks compared with younger Paleozoic rhyolites is probably related to secondary processes. In Silurian and Devono-Carboniferous rhyolites, these elements were mainly redistributed during the secondary processes, but not removed.
Hudson Bay river sediments and regional glaciation: I. Iron and carbonate dispersal trains southwest of Hudson and James Bays
Authors: Adshead J. D.
Published: April 2011

Sands deposited from rivers draining the southwesterly trending watershed of the Cape Henrietta Maria area are enriched in calcite and are characterized by higher calcite/dolomite ratios than the sands from rivers north and south of the cape. This pattern suggests that a train of drift with distinctive carbonate composition extends southwest of Cape Henrietta Maria, indicating a dominant pattern of southwesterly ice flow in this region.Iron contents are highest for sands from rivers on Cape Henrietta Maria, suggesting iron enrichment in the sand fraction of tills in the cape area, and the existence of a broad dispersal train extending southwest of the cape. The dispersal train inferred from the calcite/dolomite ratios overprints part, but not all, of the dispersal train inferred from the iron content.
Hudson Bay river sediments and regional glaciation: II. Comparison of carbonate mineralogy of size fractions for ice movement inference
Authors: Adshead J. D.
Published: April 2011

Comparison of the carbonate mineralogy of sand, coarse silt, fine silt, and coarse clay fractions of river sediments from the Hudson Bay region demonstrates that dolomite is more abundant than calcite in the coarse silts but is less abundant than calcite in other size fractions. In coarse silts, dolomite commonly occurs as single crystals in the shape of well defined rhombs, whereas calcite is present as equant to subequant grains (few rhomb-shaped crystals). Dolomite grains appear to have greater resistance to abrasion than calcite grains after particles have been reduced to sizes lying in the coarse silt range. Although differing physical properties may play a role, it appears likely that the primary control on the particle size distributions of the carbonate minerals is their original crystal size in the source bedrock.The calcite/dolomite ratio for dolomite-enriched coarse silt parallels the regional distribution observed for sand, fine silt, and coarse clay, with highest values occurring in the Cape Henrietta Maria area. Carbonate mineral ratios for silt and clay fractions corroborate the results obtained for sands and provide further evidence for the existence of a carbonate dispersal train extending southwest of the cape. These results further demonstrate that fluvial carbonates can be useful indicators of regional drift dispersal and ice-flow patterns.The widespread use of silt or combined silt and clay fractions for calcite and dolomite determinations in drift provenance studies is not upheld by the results of this investigation. Coarse silts, which have been enriched in dolomite due to abrasion processes, provide a substantially distorted interpretation of source bedrock composition. Use of the sand-size grade is advocated. Sands, unlike coarse silts, reflect the major occurrence of limestones and minor dolostones in Paleozoic basins of the region.
Late Quaternary glacial history of the Hermitage area of southern Newfoundland
Authors: Leckie D. A. , McCann S. B.
Published: April 2011

During late Wisconsinan glaciation, the northern part of the Hermitage area was glaciated by Newfoundland-centred ice and the southern part by a small, complex, upland ice field, broken by nunataks. During deglaciation a lobe of Newfoundland ice dammed a lake at the head of Bay d'Espoir in which a series of small glaciolacustrine deltas were deposited. Valley glaciers from the southern ice cap reached the south coast at several locations, most notably near Harbour Breton, where a large glaciomarine delta was formed during deglaciation when sea level stood 22–24 m above present HWM. Except for three occurrences of till, no deposits were found that can be attributed to glacial events older than late Wisconsinan.
Découverte de concrétions calcaires striées dans le till de Gentilly, basses-terres du Saint-Laurent, Québec
Authors: Lamothe M. , Hillaire-Marcel C. , Pagé P.
Published: April 2011

The discovery of striated calcareous concretions in the Gentilly Till supports the hypothesis of an early episode of carbonate precipitation in a glaciolacustrine environment that occurred before the St. Lawrence Lowlands became covered by the last ice advance. Finite 14C ages have been obtained on two such concretions. These ages are in agreement with several others obtained previously on concretions from Lake Deschaillons varves. They suggest a maximum age of ca. 35 000 BP for the Gentilly Till deposition. Inasmuch as the underlying St. Pierre sediments have been dated at ca. 75 000 BP, the St. Lawrence Lowlands would have been ice-free during a large part of the Wisconsinan stage.
Etude du champ magnétique anormal d'origine intralithosphérique
Authors: Tarits P. , Menvielle M.
Published: April 2011

The separation of the anomalous magnetic field with respect to the depth of lateral contrasts of conductivity is discussed in this paper. It is shown that, for most geophysical cases, this separation is very simply performed for periods greater than 1800 s: the anomalous field of an intralithospheric source is the difference between the observed anomalous field and the one related to the lateral contrasts of conductivity in the superficial part of the crust (mostly the coast effect).Electromagnetic data observed in California are analysed using this method. An anomalous field of intralithospheric source is shown to exist. The study of this field provides us with indications about lateral variations of the physical and chemical conditions in the lithosphere; the obtained results are in good agreement with data drawn from other Earth sciences.Finally, we show that such results can be obtained in other tectonically active areas: Japan and Peruvian Andes.
Aeromagnetic interpretation of the Kirkland Lake – Larder Lake portion of the Abitibi Greenstone Belt, Ontario
Authors: Letros S. , Strangway D. W. , Tasillo-Hirt A. M. , Geissman J. W. , Jensen L. S.
Published: April 2011

High-resolution aeromagnetic data from the Larder Lake – Kirkland Lake region have been analyzed to develop optimum maps for geologic interpretation. The use of the apparent susceptibility technique has led to a map that shows clearly the major lithologies in a major synclinorium in the Abitibi Greenstone Belt. Calc-alkaline volcanics of the Blake River group are weakly magnetic, but show ring-like anomalies associated with intrusives where magnetite has been generated in the country rock. Alternating bands of Mg-rich and Fe-rich tholeiites of the Kinojevis Group show a strong magnetization associated with the Fe-rich phases. Gabbroic intrusions underlain by serpentine and peridotite give strong levels of magnetization.These various units have been sampled and it is shown that the susceptibility is not high enough to account for the anomalies. Rather, the anomalies are associated with the mean natural remanent magnetization in the formations sampled. These studies have led to a revised geological map of this region.
Paleomagnetism of the Middle Proterozoic Mount Nelson Formation: evidence for a regional remagnetization event in the Late Precambrian of the Cordillera
Authors: Morris W. A. , McMechan M. E.
Published: April 2011

Chemical and thermal demagnetization of 92 specimens from the Mount Nelson Formation (uppermost Purcell Supergroup) in the Purcell Mountains of southeastern British Columbia yields two distinct directional groups. MN-A, found by thermal and chemical demagnetization, has a mean direction of D = 274°, I = 19° (α95 = 10°, tilt corrected), which corresponds to a pole position at 156 °E, 10 °N, MN-A resides in fine-grained hematite and is similar to other overprint directions reported from middle and upper Belt–Purcell strata in the Glacier National Park – Clark Range area. Genesis of this overprint is related to some regional geological process, most probably the Goat River Orogeny [Formula: see text]. Direction MN-B, which is found after acid leaching of more than 250 h, has a mean direction of D = 331°, I = 47°(α95 = +4°, tilt corrected), corresponding to a pole at 119 °E, 59 °N. The MN-B pole is significantly different from all poles previously reported from the Belt–Purcell Supergroup (ca. 210 °E, 20 °S). As the age of the MN-B pole is unconstrained the significance of this marked discrepancy is at present uncertain.
Disintegration of shale by cyclic wetting and drying and frost action
Authors: Mugridge Samantha-jane , Young Harvey R.
Published: April 2011

Samples of siliceous shale from the Odanah Member of the Pierre Shale (Late Cretaceous, Campanian) collected from outcrops and gravel bars along the Souris River in southwestern Manitoba undergo disintegration when subjected to cyclic wetting and drying. Breakage of some fragments along curved surfaces indicates that fragmentation, believed to be related to stresses developed by ordered water in rock pores, is not bedding controlled. Breakdown of shale clasts subjected to cyclic wetting, freezing, thawing, and drying is more rapid than disintegration caused by wetting and drying only, because of the combined action of ice and adsorbed water.
Isotopic and geochemical composition of marl lake waters and implications for radiocarbon dating of marl lake sediments
Authors: Turner J. V. , Fritz P. , Karrow P. F. , Warner B. G.
Published: April 2011

Radiocarbon dates on organic and calcareous fractions of sediment cores from marl lakes may yield anomalous ages due to the assumption of a constant hardwater correction factor along the sediment sequence. A study of eight marl lakes in southern Ontario that are actively precipitating calcium carbonate was conducted in order to assess those isotopic and aqueous geochemical parameters in modern lakes that may be utilized to estimate the history and extent of variations in the hardwater effect along such sediment sequences. Results show an increase in the δ13C composition of lake DIC (dissolved inorganic carbon) as approach to isotopic equilibrium with atmospheric CO2 occurs. Differences in the extent to which this equilibrium is established also appear responsible for observed differences in the 14C activity of DIC between lakes of as much as 20 pmc (percent modern carbon). These variations have been related to the relative residence times of water in each lake by examination of their corresponding seasonal variations in 18O and 2H content. Consequently δ13C and δ18O of marl and molluscs have been used to identify variations in the hardwater effect along the sediment profile. A profile of radiocarbon dates on marl from Little Lake in southern Ontario shows satisfactory agreement with an independently determined pollen chronology. Where certain criteria are met, marl deposits appear to be suitable material for establishing Quaternary chronology.
Rb–Sr isotopic study of Archean gneisses north of the Cape Smith fold belt, Ungava, Quebec
Authors: Doig Ronald
Published: April 2011

The Cape Smith volcanic fold belt extends across the Ungava Peninsula of Quebec, and is part of the Aphebian Circum-Ungava geosyncline. The contact with the Superior Province to the south is an unconformity, but the relationship with gneisses to the north has been obscured by Proterozoic metamorphism and deformation. Rb–Sr isochrons obtained from these gneisses yield ages ranging from 2934 to 2569 Ma, in part a result of the scale of sampling. Units interpreted to be granitic intrusions and migmatites yield ages of about 2750 Ma. All initial ratios are low (0.701–0.703) but seem to define an evolutionary path consistent with generation by melting of sialic crust with a Rb/Sr ratio of 0.14.Dominantly quartz-rich metasediments occur throughout the area of reworked Archean gneisses, and are tentatively considered to be temporally equivalent to the Proterozoic Cape Smith fold belt rocks.The simplest evolutionary model for this part of the Circum-Ungava belt would consist of a deep Proterozoic sedimentary basin to the north deposited on and deformed with Archean crust. The Cape Smith rocks would represent in part rift-related volcanism at the margin of the basin. There is no requirement for the opening of a broad ocean or for a suture between colliding Archean cratons.
Early Tertiary resetting of potassium–argon dates in the Kootenay Arc, southeastern British Columbia
Authors: Mathews W. H.
Published: April 2011

K–Ar analyses of rocks in the central Kootenay Arc indicate a Paleocene (or slightly earlier) thermal event, locally reaching 350 °C, that has reset this isotope clock. The area of resetting is nearly coincident with a north–south belt, 20 km wide, of metamorphic rocks resulting from an earlier (mid-Jurassic?) thermal event with temperatures reaching an estimated 625 °C. The strata involved in both high-grade metamorphism and resetting seem not to have been uplifted more than older weakly metamorphosed strata to the east. The mid-Jurassic? and Paleocene thermal events appear to be distinct in time from one another, but may both be related to some common control in the deeper crust or upper mantle.
Chitinozoaires du Llanvirn (formation de Table Head) de la partie occidentale de Terre-Neuve, Canada
Authors: Achab Aicha
Published: April 2011

A chitinozoan microfauna is described from the middle part of the Table Head Formation (Diplograptus decoratus Zone, Llanvirn age). It includes Fustichitina langei, Conochitina poumoti, Conochitina pirum, Conochitina subcylindrica, Conochitina cf. C. bulmani, and Desmochitina cf. D. lata. Considering the proposed synonymy, this microfauna appears to be similar to that previously described and assigned to the Caradoc by Neville. This resemblance suggests that Neville's microfauna is also of Llanvirn age. The absence of Lagenochitina baltica in both assemblages confirms the value of this species as a guide fossil for the late Caradoc – early Ashgill.The relationship between the Table Head microfauna and those of the upper Arenig (Zone D) Levis Formation and of the Llanvirn Goldwyer Formation of the Canning Basin of Australia is documented.
Correlation of metal occurrence and terrane attributes in the northwestern conterminous United States
Authors: Tooker Edwin W.
Published: April 2011

The regional distribution patterns for 20 critical metals derived by an areal-pattern recognition technique leads me to conclude that metals are regularly distributed preferentially in the accreted and cratonic terranes studied in and surrounding the state of Oregon in the northwestern United States. The distribution patterns along distinctively different zones differ in these contrasting crusts across a concealed boundary that is established by strontium isotope data. Copper and gold appear to be abundant in both terranes; nickel, cobalt, chromium, and the platinum-group metals predominate in accreted terranes; lead, zinc, tin, and tungsten are concentrated locally along the boundary zone along the edge and in the interior of the cratonic terrane. The association of metals with accreted terranes and with restricted areas or lineaments in the craton further supports the metallogenetic hypothesis that metal materials are derived mainly from underlying ensialic and ensimatic crusts, and anticipates the possibility for remobilization of these materials along the same broad linear zones over geologic time.
Haughton impact structure: structural and morphological aspects
Authors: Robertson P. B. , Sweeney J. F.
Published: April 2011

Haughton is a complex meteorite impact structure of Tertiary age on Devon Island in the Canadian Arctic. The 20.5 km diameter site was formed in essentially flat-lying Paleozoic carbonates, roughly 1700 m in thickness, overlying Precambrian gneisses. The structure comprises three concentric rings surrounding a central basin with interior peaks. The outer ring, diameter 20.5 km, is an annulus of peaks separating the Allen Bay dolomites of the regional plateau from the same unit that has been downdropped towards the crater interior along a series of circumferential faults. The middle ring of peaks, diameter 14–15 km, comprises both faulted Allen Bay dolomites and blocks of the underlying Bay Fiord Formation uplifted 250 m. Hills of the inner, elliptical ring, 3.5–5.5 km in diameter, are also formed from Bay Fiord Formation and the underlying Eleanor River Formation brought up 600 m. An interconnected series of normal faults occupies most of the annulus between the inner and outer rings. Within the central basin occur isolated hills of Bay Fiord and Eleanor River material, again raised a minimum of 700 m. Allochthonous impact breccia, containing shocked clasts of all sedimentary units and the Precambrian crystalline rocks, covers most of the central basin and the inner ring, and occurs in patches within the faulted annulus. A circular, −11 mGal (−11 × 10−5 m s−2) residual Bouguer gravity anomaly, diameter 25 km, is concentric with the structure. A more intense central "low" is tentatively correlated with allochthonous breccia up to 200 m in thickness. A 300 nT positive magnetic anomaly is situated at the crater's centre and possibly reflects the near-surface occurrence of crystalline rocks of the uplifted Precambrian basement. Most of the structural and morphological features at Haughton have counterparts in the thoroughly investigated Ries impact structure, Germany, and the allochthonous breccia is considered equivalent to the suevite deposits of the latter site.The transition between various morphologies in the crater populations of the cratered planets is a function of size, rock type, and planetary gravity. Scaling from lunar data indicates that a multi-ring impact basin in sedimentary rocks may form on Earth at a diameter not much larger than that of Haughton. The morphology of Haughton is considered intermediary between peak ring basins and multi-ring basins.
Relative sea-level rise and tidal development in the Fundy tidal system
Authors: Scott David B. , Greenberg David A.
Published: April 2011

Previous studies of sea-level and tidal amplification in the Bay of Fundy suggested a linear increase of tidal amplitude as relative sea level rose. New data presented here are used in a numerical tidal model in an effort to reproduce paleotidal regimes over the last 7000 years. Five new sea-level curves covering the last 4000 years and some previously published data extending the record back to 7000 years before present (BP) are used as the data base. These data, when used together with the tidal model, indicate that tidal amplitudes increased much more rapidly between 7000 and 4000 years ago than in the period 4000 years ago to present. It is also shown that changes in depth within the Bay of Fundy produce little effect on the tidal amplitudes, whereas such variations in water depth on Georges Bank account for almost all the change. This calculation of tidal-amplitude changes allows calibration of sea-level curves to be made for the Bay of Fundy using higher high-water (HHW) indicators.
Rb–Sr dating of Paleozoic(?), Mesozoic, and Cenozoic intrusive rocks, Okanagan Lake region, southern British Columbia, Canada
Authors: Medford G. A. , Armstrong Richard Lee , Osatenko M. J.
Published: April 2011

Sr isochron plots distinguish three different suites of granitic rocks in the vicinity of Okanagan Lake. Voluminous granites sampled over a large area east and west of the lake have scattered 87Sr/86Sr isotopic ratios (0.706–0.710) that indicate either a Paleozoic age (possibly as old as Devonian) or heterogeneous and high initial ratios in Mesozoic granites. The second suite, a composite from localities near Whiterocks Mountain, gives an isochron date of 150 ± 5 Ma with an initial 87Sr/86Sr ratio of 0.7039 ± 0.00015. The third suite, from the Whiteman Creek stock and granites along the shores of Okanagan Lake and Wood Lake, gives an isochron date of 59 ± 2 Ma with initial ratio 0.70515 ± 0.00015. The secular increase in initial ratios reflects crustal thickening and evolution. These new dates are consistent with Paleozoic (circa 400 Ma), Mesozoic (180 and 150–160 Ma), and Cenozoic (50 Ma) igneous episodes previously recognized in the border zone between the Intermontane and Omineca belts in southern British Columbia.
Age and contact-metamorphic effects of the Overflow Pond Granite: an undeformed pluton in the Dunnage Zone of the Newfoundland Appalachians
Authors: Dallmeyer R. D. , Kean B. F. , Odom A. L. , Jayasinghe N. R.
Published: April 2011

The Overflow Pond Granite intrudes deformed sedimentary and volcanic sequences in the central part of the Dunnage Zone of the Newfoundland Appalachians. Zircon and biotite in the pluton record similar ages (U–Pb and 40Ar/39Ar, respectively), which suggest an emplacement date of ca. 390 Ma. The concordant isotopic systems require relatively rapid post-magmatic cooling and indicate intrusion at shallow crustal levels. The metasedimentary rocks show a marked increase in grade in the vicinity of the pluton. Biotite within the higher grade terrane records 40Ar/39Ar ages identical to those within the pluton and suggests that the high-grade assemblages developed in response to emplacement of the granite. Whole-rock phyllite samples from lower grade portions of the sequence display variable discordant 40Ar/39Ar release spectra. These indicate a complex tectonothermal history, including formation of a pressure solution cleavage at ca. 410 Ma (with associated folding) and a contact-metamorphic overprint by the Overflow Pond Granite.
Structural evolution of a section along the base of the St. Anthony Complex, northwest Newfoundland
Authors: Craw D.
Published: April 2011

The basal portion of the St. Anthony Complex is made up of structural slices 10–30 m thick, with unknown amounts of relative movement between them. The lowest rocks are variably deformed pillow lavas and related rocks with one pervasive foliation. These rocks are overlain by greenschists, phyllonites, and mylonites with up to three planar structural elements developed. At least one of these latter surfaces (the earliest) had formed before the schists were thrust over the underlying pillow lavas. The overthrusting event resulted in deformation of underlying pillow lavas. All deformation occurred under lower greenschist facies conditions. Fold axes in the least deformed rocks have variable orientations, and this variation decreases up-section until axes are parallel and plunge gently eastwards, parallel to the stretching lineation. Parallelism between fold axes and stretching lineation implies rotation of fold axes during progressive deformation and is consistent with the rocks being part of a high-strain zone developed during regional overthrusting from east to west.
A U–Pb zircon age from the Kuskanax batholith, southeastern British Columbia
Authors: Parrish Randall R. , Wheeler J. O.
Published: April 2011

U–Pb dates on three fractions of zircon from the foliated border zone of the southeast part of the Kuskanax batholith are slightly discordant and indicate emplacement of the batholith [Formula: see text] ago, assuming no subsequent zircon Pb loss. The analyses are slightly discordant and reflect the presence of inherited zircon Pb ~2060 ± 300 Ma old. This interpretation of the data is consistent with geological relationships and available K–Ar dates. A geologically derived maximum age for the batholith is about 185 Ma. This age determination has important implications for timing of deformation in the Kootenay Arc.
Paleomagnetic history of the Mealy dykes of Labrador, Canada
Authors: Park J. K. , Emslie R. F.
Published: April 2011

Paleomagnetic analysis of the Mealy diabase dykes of Labrador reveals magnetizations that predate the Grenville event at about 1000 Ma. These dykes intrude the Mealy Mountains anorthositic complex in the Grenville Structural Province. They are well south of the Grenville Front Tectonic Zone, but were apparently never subjected to temperatures as high as 500 °C during their post-consolidation history.Four distinct magnetic components were uncovered by thermal and alternating field treatments and a fifth remained unresolved. The major magnetic mineral present, titanomagnetite, is thought to record two magnetic directions acquired during cooling from magmatic temperatures. These are B (D = 305°, I = −76°; N = 18 sites; κ = 12; α95 = 11°) and A (D = 095°, I = +52°; N = 20 sites; κ = 46; α95 = 5°). Component B has much within-site dispersion. The other two components, C (D = 274°, I = −47°; N = 10 sites; κ = 15; α95 = 13°) and D (D = 292°, I = −74°; κ = 5; α95 = 31°), probably reside in magnetite and pyrrhotite, respectively. Component C, antiparallel to A, was probably acquired at about the same time as A. We suggest that C and A represent the first stable magnetizations retained by the dykes following an extensive period of cooling and re-equilibration of the magnetic minerals. Components B and D, which agree in direction, represent a later stage of cooling.Component B has a pole at 148°E, 34°S (δp = 18°, δm = 19°) in agreement with regional metamorphic poles from the Grenville; A, however, has a pole at 173°W, 23°S (δp = 5°, δm = 7°), which apparently "sees through" the peak in Grenville activity. The A site poles have a linear distribution along the Keweenawan Track and probably relate to an age between 1000 and 1150 Ma.
Forms of phosphorus and phosphorus–iron relationships in the suspended matter of the St. Lawrence Estuary
Authors: Lucotte Marc , d'Anglejan Bruno
Published: April 2011

The partition of phosphorus between the organic fraction (PORG) and both the detrital (apatite rich) and non-detrital (adsorbed) fractions (PAP and PCDB) was studied in the particulate matter of the St. Lawrence Estuary and two of its tributaries. The adsorption of the PCDB fraction on particulate iron was examined. PORG makes up about one third of the total particulate P, which ranges betweeen 44 and 64 μg∙at./g. Everywhere in the estuary, and regardless of salinity, the concentration of PAP represents twice that of PCDB. The hydroxide fraction (FeCDB) is on the average 25 and 29% of the total particulate iron in May and September, respectively, but is much higher in the tributaries. The atom ratio (Fe/P)CDB of hydroxide Fe to adsorbed P fluctuates around 16 for May and 19 for September. Low values (13–16) are characteristic of the turbidity maximum, whereas higher ones are found in the deeper, more saline waters (16–26) and in the tributaries (17–26). Although any iron precipitation in the low-salinity turbid zone is masked by sediment resuspension, the low values of the ratio there suggest some P uptake on Fe-rich particles. Dissolved phosphate being conservative with respect to the salinity, desorption does not take place, or is only minor seaward of the turbidy maximum.