Response of Recent Benthic Foraminiferal Assemblages to Contrasting Environments in Baffin Bay and the Northern Labrador Sea, Northwest Atlantic

Modern deep-water benthic foraminiferal assemblages in Baffin Bay and the northern Labrador Sea, Western North Atlantic, were sampled from box cores and analyzed to determine assemblage composition. The two marine basins are separated by the shallow waters of Davis Strait. Assemblages of Baffin Bay contained only agglutinated foraminifera, whereas samples from the Labrador Sea contained both calcareous and agglutinated species, which resulted in significantly higher species richness. The absence of benthic calcareous taxa in Baffin Bay is attributed to cold, saline, CO2-rich bottom waters related to the Baffin Bay Bottom Water and the Baffin Bay Atlantic Water. Modern foraminiferal assemblage distribution supports the model of increased organic flux under seasonal open-water conditions that feed a rich agglutinated assemblage, but lead to oxidation of organic matter and increased carbonate dissolution. Deep-water sediments contain ice-rafted coarse-grained components and biogenic elements such as sponge spicules that are heavily used by numerous agglutinated species for test construction. Robust, tubular suspension feeders occupy regions under the influence of bottom currents that deliver nutrients. Although disturbances of the sediment-water interface cannot be excluded with sampled box cores, small-scale patchiness can be confirmed by varying abundances of infaunal taxa. Absolute counts of specimens in subsamples vary signif­icantly, whereas species evenness among subsamples is less variable. These findings call for caution when interpreting lateral faunal changes on the basis of small core samples.Nous avons échantillonné des assemblages modernes de foraminifères benthiques d’eau profonde prélevés dans la baie de Baffin et le nord de la mer du Labrador, Atlantique du Nord-Ouest, à partir de carottes à boîte, puis nous les avons analysés afin d’en déterminer la composition. Les deux bassins marins sont séparés par les eaux peu profondes du détroit de Davis. Les assemblages de la baie de Baffin ne renfermaient que des foraminifères agglutinants, tandis que les échantillons de la mer du Labrador contenaient à la fois des espèces calcaires et des espèces agglutinantes, ce qui a donné lieu à une richesse d’espèces considérablement supérieure. L’absence de taxons calcaires benthiques dans la baie de Baffin s’explique par la présence d’eau de fond froide, saline et riche en CO2 provenant de l’eau de fond de la baie de Baffin et de l’eau atlantique de la baie de Baffin. La répartition des assemblages foraminifères modernes cadre avec le modèle du flux organique accru moyennant des conditions saisonnières en eaux libres qui alimentent un riche assemblage agglutinant, mais qui se traduisent par l’oxydation de la matière organique et l’intensification de la dissolution du carbonate. Les sédiments en eau profonde contiennent des composantes glacielles à grains grossiers et des éléments biogènes tels que le spicule de spongiaire dont dépendent de nombreuses espèces agglutinantes pour la construction de tests. Des suspensivores robustes et tubulaires occupent les régions sous l’influence de courants de fond qui déposent des nutriments. Bien que la perturbation de l’interface sédiment-eau ne puisse pas être excluse à l’aide des carottes à boîte, une microrépartition à petite échelle peut être confirmée au moyen de l’abondance variable des taxons benthiques. Les dénombrements absolus de spécimens des sous-échantillons varient considérablement, tandis que l’homogénéité des espèces parmi les sous-échantillons est moins variable. Ces constatations font appel à la prudence quand vient le temps d’interpréter les changements fauniques latéraux en fonction de petites carottes

U-Pb (zircon) age, petrology, and tectonic setting of the Canaan River pluton, southeastern New Brunswick, Canada

 The Canaan River pluton comprises megacrystic monzogranite and quartz diorite to monzodiorite that is exposed in several small inliers on the Carboniferous New Brunswick Platform west of Moncton in southeastern New Brunswick. Its distinct geophysical signature and borehole data suggest that the Canaan River pluton is part of a large buried felsic to mafic intrusive body that lies at relatively shallow depths beneath flat-lying Pennsylvanian sandstone on the platform. New laser ablation ICP-MS in situ analysis of the megacrystic monzogranite yielded a U-Pb zircon concordia age of 412.6 ± 2.1 Ma, indicating that the intrusion is of Early Devonian (upper Lochkovian) age.The new radiometric data along with lithological, geochemical, and isotopic data suggest that the Canaan River pluton is most like the megacrystic Hawkshaw Granite of upper Lochkovian age in the Pokiok Batholith in southwestern New Brunswick. The similarities shown by these granites suggests that they may have been generated in the same complex tectonomagmatic setting related to the successive arrival of the leading edge of Ganderia and Avalonia at the composite Laurentian margin during the Salinic and Acadian orogenies.

Lithotectonic Framework of the Core Zone, Southeastern Churchill Province, Canada

The Core Zone, a broad region located between the Superior and North Atlantic cratons and predominantly underlain by Archean gneiss and granitoid rocks, remained until recently one of the less well known parts of the Canadian Shield. Previously thought to form part of the Archean Rae Craton, and later referred to as the Southeastern Churchill Province, it has been regarded as an ancient continental block trapped between the Paleoproterozoic Torngat and New Quebec orogens, with its relationships to the adjacent Superior and North Atlantic cratons remaining unresolved. The geochronological data presented herein suggest that the Archean evolution of the Core Zone was distinct from that in both the Superior and North Atlantic (Nain) cratons. Moreover, the Core Zone itself consists of at least three distinct lithotectonic entities with different evolutions, referred to herein as the George River, Mistinibi-Raude and Falcoz River blocks, that are separated by steeply-dipping, crustal-scale shear zones interpreted as paleosutures. Specifically, the George River Block consists of ca. 2.70 Ga supracrustal rocks and associated ca. 2.70–2.57 Ga intrusions. The Mistinibi-Raude Block consists of remnants of a ca. 2.37 Ga volcanic arc intruded by a ca. 2.32 Ga arc plutonic suite (Pallatin) and penecontemporaneous alkali plutons (Pelland and Nekuashu suites). It also hosts a coarse clastic cover sequence (the Hutte Sauvage Group) which contains detrital zircons provided from locally-derived, ca. 2.57–2.50 Ga, 2.37–2.32 Ga, and 2.10–2.08 Ga sources, with the youngest concordant grain dated at 1987 ± 7 Ma. The Falcoz River Block consists of ca. 2.89–2.80 Ga orthogneiss intruded by ca. 2.74–2.70 granite, tonalite, and granodiorite. At the western margin of the Core Zone, the George River Block and Kuujjuaq Domain may have been proximal by ca. 1.84 Ga as both appear to have been sutured by the 1.84–1.82 Ga De Pas Batholith, whereas at its eastern margin, the determination of metamorphic ages of ca. 1.85 to 1.80 Ga in the Falcoz River Block suggests protracted interaction with the adjacent Lac Lomier Complex during their amalgamation and suturing, but with a younger, ‘New Quebec’ overprint as well. The three crustal blocks forming the Core Zone add to a growing list of ‘exotic’ Archean to earliest Paleoproterozoic microcontinents and crustal slices that extend around the Superior Craton from the Grenville Front through Hudson Strait, across Hudson Bay and into Manitoba and Saskatchewan, in what was the Manikewan Ocean realm, which closed between ca. 1.83–1.80 Ga during the formation of supercontinent Nuna.RÉSUMÉLa Zone noyau, une vaste région située entre les cratons du Supérieur et de l’Atlantique Nord et reposant principalement sur des gneiss archéens et des roches granitiques, est demeurée jusqu’à récemment l’une des parties les moins bien connues du Bouclier canadien. Considérée auparavant comme faisant partie du craton archéen de Rae, puis comme la portion sud-est de la Province de Churchill, on l’a perçue comme un ancien bloc continental piégé entre les orogènes paléoprotérozoïques des Torngat et du Nouveau-Québec, ses relations avec les cratons supérieurs adjacents et de l’Atlantique Nord demeurant nébuleuses. Les données géochronologiques présentées ici permettent de penser que l’évolution archéenne de la Zone noyau a été différente de celle des cratons du Supérieur et de l’Atlantique Nord (Nain). De plus, la Zone noyau elle-même se compose d’au moins trois entités lithotectoniques distinctes avec des évolutions différentes, appelées ici les blocs de la rivière George, de Mistinibi-Raude et de la rivière Falcoz, lesquels sont séparées par des zones de cisaillement crustales à forte inclinaison, conçues comme des paléosutures. Plus précisément, le bloc de la rivière George est constitué de roches supracrustales d'env. 2,70 Ga, et d’intrusions connexes d'env. 2,70–2,57 Ga. Le bloc Mistinibi-Raude est constitué de vestiges d’un arc volcanique d'env. 2,37 Ga, recoupé par une suite plutonique d’arc d'env. 2,32 Ga (Pallatin) et de plutons alcalins péné-contemporains (suites Pelland et Nekuashu). Il contient également une séquence de couverture clastique grossière (le groupe Hutte Sauvage) renfermant des zircons détritiques de sources locales, âgés d'env. 2,57–2,50 Ga, 2,37–2,32 Ga et 2,10–2,08 Ga, le grain concordant le plus jeune étant âgé de 1987 ± 7 Ma. Le bloc de la rivière Falcoz est formé d’un orthogneiss âgé d'env. 2,89–2,80 Ga, recoupé par des intrusions de granite, tonalite et granodiorite âgées d'env. 2,74–2,70 Ga. À la marge ouest de la Zone noyau, le bloc de la rivière George et du domaine de Kuujjuaq peuvent avoir été proximaux il y a 1,84 Ga env., car les deux semblent avoir été suturés par le batholithe De Pas il y a environ 1,84–1,82 Ga, alors qu’à sa marge est, la détermination des datations métamorphiques de 1,85 à 1,80 Ga dans le bloc de la rivière Falcoz suggère une interaction prolongée avec le complexe adjacent du lac Lomier durant leur amalgamation et leur suture, mais affecté aussi d’une surimpression « Nouveau Québec » plus jeune. Les trois blocs crustaux formant la Zone noyau s’ajoutent à une liste croissante de micro-continents et d’écailles crustales « exotiques » archéennes à paléoprotérozoïques très précoces qui s’étalent autour du craton Supérieur depuis le front de Grenville jusqu’au Manitoba, à travers le détroit d’Hudson, la baie d’Hudson jusque dans le Manitoba et la Saskatchewan, là où s’étendait l’océan Manikewan, lequel s’est refermé il y a environ 1,83–1,80 Ga, pendant la formation du supercontinent Nuna

Response of recent benthic foraminiferal assemblages to contrasting environments in baffin bay and the northern labrador sea, Northwest Atlantic

Modern deep-water benthic foraminiferal assemblages in Baffin Bay and the northern Labrador Sea, Western North Atlantic, were sampled from box cores and analyzed to determine assemblage composition. The two marine basins are separated by the shallow waters of Davis Strait. Assemblages of Baffin Bay contained only agglutinated foraminifera, whereas samples from the Labrador Sea contained both calcareous and agglutinated species, which resulted in significantly higher species richness. The absence of benthic calcareous taxa in Baffin Bay is attributed to cold, saline, CO2-rich bottom waters related to the Baffin Bay Bottom Water and the Baffin Bay Atlantic Water. Modern foraminiferal assemblage distribution supports the model of increased organic flux under seasonal open-water conditions that feed a rich agglutinated assemblage, but lead to oxidation of organic matter and increased carbonate dissolution. Deep-water sediments contain ice-rafted coarse-grained components and biogenic elements such as sponge spicules that are heavily used by numerous agglutinated species for test construction. Robust, tubular suspension feeders occupy regions under the influence of bottom currents that deliver nutrients. Although disturbances of the sediment-water interface cannot be excluded with sampled box cores, small-scale patchiness can be confirmed by varying abundances of infaunal taxa. Absolute counts of specimens in subsamples vary significantly, whereas species evenness among subsamples is less variable. These findings call for caution when interpreting lateral faunal changes on the basis of small core samples

Granitoid plutons in peri-Gondwanaan terranes of Cape Breton Island, Nova Scotia, Canada: new U-Pb (zircon) age constraints

Granitoid plutons are a major component of pre-Carboniferous rocks in Cape Breton Island and knowledge of the time and tectonic setting of their emplacement is crucial for understanding the geological history of the island, guiding exploration for granite-related economic mineralization, and making along-orogen correlations. The distribution of these plutons and their petrological characteristics have been used in the past for recognizing both Laurentian and peri-Gondwanan components in Cape Breton Island, and for subdividing the peri-Gondwanan components into Ganderian and Avalonian terranes. However, ages of many plutons were assumed on the basis of field relations and petrological features compared to those of the relatively few reliably dated plutons. Seventeen new U–Pb (zircon) ages from igneous units reported here provide enhanced understanding of the distribution of pluton ages. Arc-related plutons in the Aspy terrane with ages of ca. 490 to 475 Ma likely record the Penobscottian tectonomagmatic event recognized in the Exploits subzone of central Newfoundland and New Brunswick but not previously recognized in Cape Breton Island. Arc-related Devonian plutonic activity in the same terrane is more widespread, continuous, and protracted (445 Ma to 395 Ma) than previously known. Late Devonian magmatism in the Ganderian Aspy terrane is similar in age to that in the Avalonian Mira terrane (380 to 360 Ma) but the tectonic settings are different. In contrast, magmatic activity in the Bras d’Or terrane is almost exclusively arc-related in the Late Ediacaran (580 to 540 Ma) and rift-related in the Late Cambrian (520 to 490 Ma). The new data support the terrane distinctions previously documented

U-Pb (zircon) age, petrology, and tectonic setting of the Canaan River pluton, southeastern New Brunswick, Canada

The Canaan River pluton comprises megacrystic monzogranite and quartz diorite to monzodiorite that is exposed in several small inliers on the Carboniferous New Brunswick Platform west of Moncton in southeastern New Brunswick. Its distinct geophysical signature and borehole data suggest that the Canaan River pluton is part of a large buried felsic to mafic intrusive body that lies at relatively shallow depths beneath flat-lying Pennsylvanian sandstone on the platform. New laser ablation ICP-MS in situ analysis of the megacrystic monzogranite yielded a U-Pb zircon concordia age of 412.6 ± 2.1 Ma, indicating that the intrusion is of Early Devonian (upper Lochkovian) age. The new radiometric data along with lithological, geochemical, and isotopic data suggest that the Canaan River pluton is most like the megacrystic Hawkshaw Granite of upper Lochkovian age in the Pokiok Batholith in southwestern New Brunswick. The similarities shown by these granites suggests that they may have been generated in the same complex tectonomagmatic setting related to the successive arrival of the leading edge of Ganderia and Avalonia at the composite Laurentian margin during the Salinic and Acadian orogenies

Age and tectonic setting of granitoid plutons in the Chéticamp belt, western Cape Breton Island, Nova Scotia, Canada

Geological mapping in the Chéticamp granitoid belt in combination with petrographic and geochemical studies and U-Pb (zircon) dating by laser ablation inductively coupled plasma mass spectrometry have resulted in major reinterpretation of the geology in the western part of the Ganderian Aspy terrane of Cape Breton Island. Nine new U-Pb (zircon) ages show that the former “Chéticamp pluton” consists of 10 separate plutons of 5 different ages: Late Neoproterozoic (ca. 567 Ma), Cambrian-Ordovician (490-482 Ma), Ordovician-Silurian (442-440 Ma), mid-Silurian (ca. 428 Ma), and late Devonian (366 Ma). The three Late Neoproterozoic granodioritic to monzogranitic plutons are older than the adjacent metavolcanic and metasedimentary rocks of the Jumping Brook Metamorphic Suite, whereas the tonalitic to quartz dioritic Cambrian-Ordovician plutons intruded those metamorphic rocks. Petrographic characteristics and approximately 100 whole-rock chemical analyses show that with the exception of the mid-Silurian Grand Falaise alkali-feldspar granite which has A-type within-plate characteristics, the plutonic units have calc-alkaline affinity and were emplaced in a volcanic-arc tectonic setting. These results are evidence that fragments of a long history of episodic subduction-related magmatism and terrane collision is preserved in this small part of Ganderia. Eight new Sm-Nd isotopic analyses are consistent with the Ganderian affinity of the Chéticamp plutonic belt. The ca. 490-482 Ma plutons are the first direct evidence in Cape Breton Island for the Penobscottian event recognized in the Exploits subzone of central Newfoundland and in New Brunswick. However, the structural relationship of the Chéticamp plutonic belt to the rest of the Aspy and Bras d’Or terranes remains enigmatic, as is the apparent absence of effects of Devonian deformation and metamorphism in the older plutonic units.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author