Volume 49, 2013

EN:

Slope failures present a common hazard throughout the world and have considerable impact on transportation, forestry, coastal and urban development, and other human activities. Although little recognized in much of Atlantic Canada, mass movements have resulted in as many as 71 fatalities in Newfoundland. Due to the high relief of Newfoundland, rockfalls have caused several fatalities and damage to property is frequent. In the Ferryland disaster of ca. 1823, 42 fishermen were reportedly killed when a cave roof collapsed onto them. Debris torrents and flows are widespread particularly in areas of higher relief in Newfoundland and Cape Breton Island, and tend to be most hazardous for highway engineering and community development. Typically, a thin cover of till or colluvium overlies a steeply sloping and polished bedrock substrate. Failure is generally triggered by rainfall events. Rotational slumps of glaciomarine clays are particularly evident along the major river valleys of Labrador and are an important consideration for hydroelectric development such as along the lower Churchill River. Numerous sackungs have been identified, notably in the ultramafic rocks of western Newfoundland. In other areas of Atlantic Canada, earthflows frequently affect transportation routes and commonly involve movement of saturated sediment during spring thaw. Along the Gulf of St. Lawrence and Northumberland Strait and the Bay of Fundy coastlines, the combination of friable Carboniferous and Permian sediments, glaciotectonic activity, frost wedging, and coastal erosion has resulted in numerous small failures, along with incremental retreat of coastal cliffs. Ongoing climate change will have an impact on slope failure activity. The pattern of increasing summer frequency and intensity of thunderstorms and hurricane events, increased winter precipitation in some locations, and more erratic freeze-thaw events during late winter and spring, will result in an increase in debris torrents triggered by precipitation, and rockfalls triggered by freeze-thaw. Human utilization of coastal areas for recreation and residential construction is also increasing both the frequency and hazard of slope failures across Atlantic Canada.

EN:

The relationship between low-grade metasedimentary and high-grade paragneissic Precambrian rock units in the Bras d’Or terrane of central Cape Breton Island is a long-standing geological problem. Whole-rock geochemical and Nd isotopic data from representative components of these units in the Kellys Mountain area, the Glen Tosh formation and Kellys Mountain Gneiss, show strong similarity. Major and trace element characteristics suggest that protolith sediments for both units were wackes derived from felsic igneous sources and deposited at an active continental margin. Neodymium isotopic data in combination with previously published detrital zircon ages show that the sediments contained an ancient (ca. 2 Ga) end-member of recycled continental crust mixed with a juvenile component of Late Neoproterozoic age. The similarities suggest that the rocks represent the same sedimentary unit at different grades of metamorphism.

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Lower greenschist-facies metasedimentary rocks of the Middle Cambrian Conanicut Group occur in and around Beavertail State Park, Rhode Island. Detailed structural mapping (1:1000-scale) and petrology of these rocks indicate an early fold generation (F1) and axial planar metamorphic foliation (S1). F1 is folded by a more prominent, E-verging, NNE- to NNW-trending, non-coaxial fold generation (F2) and an associated pressure solution-enhanced crenulation cleavage (S2). A third map-scale fold generation is inferred from NNE-trending broad folding of F2 and S2. N-S extension resulted in boudins that deformed S2 on a scale of 1–10 m, whereas late planar quartz veins indicate NW-SE extension. All structures are cross cut by faults striking N- to NE- and ENE-to ESE that show dominantly normal motion with minor sinistral or dextral components. Kink bands associated with faulting trend NNE to ENE with WNW to NNW side up. The vertical Beaverhead shear zone juxtaposes the Cambrian rocks with Pennsylvanian rocks of the Narragansett Basin, and deflects S2 in a dextral sense, consistent with motion recorded elsewhere.The Cambrian rocks record the same deformation and metamorphism as the adjacent Narragansett Basin rocks. No evidence was found for pre-Alleghanian deformation or for northwest- or north-directed thrusting and accretion of a Meguma-like terrane during the Alleghanian orogeny. If the Beaverhead shear zone was a preexisting terrane boundary within Avalonia, both the Cambrian and Pennsylvanian Narragansett Basin sediments were deposited aſter terrane accretion.RÉSUMÉDes roches profondes métasédimentaires du faciès des schistes verts, que l’on retrouve dans le groupe Conanicut du Cambrien moyen, sont présentes dans le Beavertail State Park, au Rhode Island, et dans les environs. Une cartographie structurale détaillée (à l’échelle 1:1 000) et la pétrologie de ces roches indiquent la formation précoce d’un pli (F1) et une foliation métamorphique (S1) de plan axial. Le F1 est causé par la formation d’un pli (F2) non coaxial plus dominant, à vergence est et d’orientation NNE-NNO ainsi que par une schistosité de crénulation (S2) amplifiée en raison d’une dissolution par pression connexe. La formation d’un troisième pli à l’échelle cartographique est provoquée par un vaste plissement du F2 et de la S2 d’orientation NNE. Une extension N-S a produit des boudins qui déforment la S2 sur l’échelle de 1 à 10 m, tandis que des veines de quartz planes formées ultérieurement indiquent une extension NO-SE. Toutes les structures sont traversées par des failles orientées N-NE et ENE-ESE montrant un mouvement normal dominant accompagné de composantes senestres et dextres peu importantes. Les bandes froissées associées à ces failles sont orientées NNE-ENE et présentent une tangente verticale ONO-NNO. Dans la zone de cisaillement verticale de Beaverhead, les roches du Cambrien sont juxtaposées aux roches de la Pennsylvanie du bassin Narragansett, et la S2 dévie en un mouvement dextre, ce qui concorde avec le mouvement enregistré ailleurs.Les roches du Cambrien montrent la même déformation et le même métamorphisme que les roches du bassin Narragansett adjacent. On n’a trouvé aucune donnée appuyant la création d’une déformation avant l’orogenèse alléghanienne ni celle d’un chevauchement et d’une accrétion orientés vers le nord ou le nordouest d’un terrane semblable à la zone de Meguma lors de l’orogenèse alléghanienne. Si la zone de cisaillement verticale de Beaverhead constituait une limite de terrane qui existait avant l’orogenèse de l’Avalonien, les sédiments cambriens et pennsylvaniens du bassin Narragansett se sont déposés après l’accrétion du terrane.[Traduit par la redaction]

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Donald Baird (1926–2011), an influential and innovative vertebrate paleontologist with a scientific career spanning nearly 50 years, had an exceptional breadth of expertise in the study of late Paleozoic and Mesozoic vertebrates and their life traces. Beginning in 1956, Baird conducted fieldwork in the Carboniferous and Triassic-Jurassic of Nova Scotia, making a total of 21 trips in 30 years. His many scientific contributions include the discoveries of important assemblages of Carboniferous vertebrates as well as an unexpectedly diverse record of early Mesozoic tetrapods and their trackways in the province. Baird also encouraged and supported fieldwork by other vertebrate paleontologists as well as amateurs in Nova Scotia and elsewhere. His career-long commitment to the vertebrate paleontology of the province was instrumental in establishing it as an important source of fossils of Carboniferous and early Mesozoic continental vertebrates.RÉSUMÉDonald Baird (1926–2011), paléontologiste des vertébrés influent et novateur dont la carrière scientifique s’est échelonnée sur près de 50 ans, a acquis un savoir-faire exceptionnel dans l’étude des vertébrés du Paléozoïque tardif et du Mésozoïque et des vestiges de leur vie. À partir de 1956, M. Baird a mené des études sur le terrain du Carbonifère et du Trias-Jurassique en Nouvelle-Écosse, où il s’est rendu au total 21 fois en 30 ans. Ses nombreuses contributions scientifiques comprennent notamment les découvertes d’importants assemblages de vertébrés du Carbonifère ainsi que d’un nombre étonnamment diversifié de tétrapodes du Mésozoïque inférieur et de leurs traces dans la province. M. Baird a en outre encouragé et soutenu les études sur le terrain d’autres paléontologistes des vertébrés et d’amateurs du domaine en Nouvelle-Écosse et ailleurs. Pendant toute sa carrière, il s’est consacré à la paléontologie des vertébrés de la province, ce qui a contribué à la réputation de la Nouvelle-Écosse en tant que source importante de fossiles de vertébrés continentaux du Carbonifère et du Mésozoïque inférieur.

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Carbonaceous compressions from the Pridolian to middle Lochkovian Indian Point Formation in the Flatlands area of New Brunswick comprising a central axis with irregularly arranged unbranched appendages are assigned to Medusaegraptusmirabilis. This is the first report of intact thalli of this noncalcified macroalgal taxon from a locality outside of western New York. The biotic composition, stratigraphic context, and sedimentology of this occurrence suggest a shallow-marine depositional setting roughly comparable to that for the type material of Medusaegraptus mirabilis from Gasport, New York.RÉSUMÉRÉSUMÉLes fossiles carbonés comprimés de la formation d’Indian Point, située dans la région de Flatlands du Nouveau-Brunswick et qui date du Pridolien au Lochkovien moyen, sont attribués àMedusaegraptus mirabilis; ils présentent un axe central avec des appendices non ramifiés et disposés de façon irrégulière. C’est la première fois qu’on signale la présence de thalles intacts de ce taxon de macroalgues non calcifiées dans une localité ailleurs que dans l’ouest de l’État de New York. La composition biotique, le contexte stratigraphique et les données sédimentologiques permettent de penser à un dépôt marin peu profond à peu près comparable à ce qu’on trouve dans le cas de Medusaegraptus mirabilis de Gasport, dans l’État de New York.[Traduit par la redaction]

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The Mount Pleasant granite-related polymetallic deposit, located on the southwestern margin of the Late Devonian to Early Carboniferous Mount Pleasant Caldera Complex in southwestern New Brunswick, contains a significant resource of tin, tungsten, molybdenum, zinc, indium, and bismuth. The Caldera Complex comprises Intracaldera, Exocaldera, and Late Caldera-Fill sequences and associated subvolcanic granitic rocks. Three granitic phases of the Mount Pleasant Granitic Suite (Granite I, II, and III) are recognized in the vicinity of the Mount Pleasant deposit and are interpreted to be fractionates of the more regionally exposed McDougall Brook Granitic Suite. Granite I and Granite II are associated with tungsten-molybdenum-bismuth, and tin-zinc-indium mineralization, respectively. Despite extensive research within the Caldera Complex, the exact age of mineralization at Mount Pleasant has never been firmly established. An inferred age of 363 ± 2 Ma was based on the proposed synchronicity of the U-Pb dated Bailey Rock Rhyolite of the Exocaldera Sequence with that of the undated McDougall Brook Granitic Suite, which intrudes the Intracaldera Sequence. Here, we present Re-Os dating of two molybdenite samples associated with the tungsten mineralization related to Granite I at the Fire Tower Zone, that constrain the initial onset of mineralization at Mount Pleasant to be between 369.7±1.6 Ma and 370.1±1.7 Ma. The new Re-Os ages clearly indicate that the McDougall Brook Granitic Suite, which pre-dates mineralization, must be at least seven million years older than the Bailey Rock Rhyolite, whose type-section is located within the Exocaldera Sequence. A re-examination of the gradational relationship between the McDougall Brook Granitic Suite and purported rocks of Bailey Rock Rhyolite within the Intracaldera Sequence revealed that the latter should instead be assigned to the Seelys Formation. Thus, deposition of the polymetallic mineralization likely took place contemporaneously with caldera collapse and an early phase of resurgent doming in response to degassing of the magma chamber rather than being coincident with erosion of the volcanic edifice as inferred from previous modeling of the eruptive history at Mount Pleasant.

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The Manzanillabeach in Cocos Bay, Trinidad is a barrier beach that protects the freshwaterNariva Swamp from the marine environment of the Atlantic. The Manzanilla beachis a very dynamic system owing to the open bay morphology, and its exposure tothe Atlantic Ocean. This study evaluated thespatial and temporal morphological and sedimentological characteristics,alongside hydrodynamic conditions operating on the beach. This studyinvestigates the beach’s response to tidal cycles diurnally, from spring toneap tide, and seasonally. Data from nine sites during the period December 2005to September 2007 are analyzed. Coastal parameters such as beach profiles,littoral data and sediment samples were obtained using standardgeomorphological techniques. The beach volumetric changes that occurred overthe tidal cycles are also quantified. Results indicate that wave height andwave energy were good predictors of beach change. The study showed that erosionwas linked to rising tide and accretion to falling tide diurnally. Erosionoccurred during spring tide conditions and accretion dominated during neaptides. Seasonally more erosion occurred in the winter period (dry season) andbeach changes in the summer period (wet season) were controlled by theformation and migration of bars.

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Fredericton, New Brunswick, is situated in an estuarine valley with its urban centre overlying up to 60 m of unconsolidated Late Wisconsinan-age glacigenic sediments. The discontinuous nature of units comprising the underlying sedimentary architecture represents challenges to engineering in the city. Major concerns have been the identification of pathways into the supply aquifer lying below the urban centre, and the sensitive nature of a buried fine-grained estuarine clay-silt unit. Results from a borehole drilled in the city centre were used to characterise the sediment units and recover samples from the estuarine unit for tests of engineering properties. These results and inclusion of published geophysical data represent the first detailed collection of engineering and sediment properties of the clay-silt unit at Fredericton.

EN:

Large fossiliferous glacial erratics occur scattered across the basalt of the Preakness Formation (Lower Jurassic) on High Mountain, Passaic County, New Jersey. These erratics are comprised of light tan to yellow, sandy limestone and contain fossiliferous beds with casts and molds of invertebrates. Analysis of these fossils including: rostroconchs, brachiopods, pelecypods, corals, bryozoans, nautiloid cephalopods and trilobites as well as the distinct lithology indicate that these erratics belong to the Lower Devonian Tristates Group and the Rickard Hill Facies of the Schoharie Formation. Outcrops of the Rickard Hill Facies of the Schoharie Formation occur in a narrow belt within the Helderberg Mountains Region of New York and due north of the High Mountain recovery location. Reconstruction of the glacial history across the Helderberg Mountains Region and New Jersey Piedmont indicates that the Rickard Hill Erratics have been transported tens of kilometers from their original source region during the Wisconsin glaciation. The Rickard Hill Erratics provide a unique opportunity to reconstruct additional elements of the complex surficial geology of the New Jersey Piedmont and High Mountain. Palynology of glacial kettle ponds adjacent to High Mountain along with cosmogenic-nuclide exposure studies on glacial erratics and the regional lake varve record indicate that the final deposition of the Rickard Hill Erratics occurred within a few thousand years after 18,500 YBP.

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A medullosalean-pteridosperm specimen, 22 cm long, from the Sydney Coalfield, Nova Scotia, Canada, illustrates the advantage of studying the fossilization history of compressed foliage freed from the rock matrix by hydrofluoric acid, as compared to the examination of compressions still in the rock matrix. The image of any freed frond segment of compression foliage that has been reprocessed digitally to represent its original structure is called a compression map. Interpretation of a compression map is reliant on a physicogeochemical model of preservation processes.RÉSUMÉRÉSUMÉUn spécimen fossile d’une ptéridospermée du genre Medulossa mesurant 22 cm de longueur et excavé dans le bassin houiller de Sydney, en Nouvelle-Écosse (Canada), illustre bien l’avantage d’étudier l’histoire géologique de fossiles de feuilles extraits de la matrice rocheuse au moyen de l’acide fluorhydrique plutôt que d’examiner des compressions qui sont encore dans la matrice. On désigne carte de compression l’image d’un segment de fronde compressé extrait de la matrice dont on a fait l’extrapolation numérique pour voir sa structure originale. L’interprétation d’une carte de compression repose sur un modèle physicogéochimique des processus de préservation.[Traduit par la redaction]