bluuebunny/crossref_metadata_2025 huggingface dataset:
Lithotectonic elements and tectonic evolution of Torngat Orogen, Saglek Fiord, northern Labrador
Authors: Mengel Flemming , Rivers Toby , Reynolds Peter
Published: April 2011

A cross section of the eastern part of the Early Proterozoic Torngat Orogen is exposed along Saglek Fiord in northern Labrador. It shows the transition from a foreland, through a frontal zone to the internal zone of the orogen, the latter being composed of two lithologically distinct terranes that are part of Abloviak shear zone, a crustal-scale transcurrent shear zone with a sinistral sense of displacement. One of these terranes is parautochthonous with respect to the foreland, the other is allochthonous and interpreted as being separated from the parautochthon by a cryptic suture.Ramah Group, an Early Proterozoic supracrustal sequence that lies unconformably on Archean gneisses in the foreland, can be traced across the frontal zone, but does not occur in Abloviak shear zone in the Saglek area.Tectonic evolution of Torngat Orogen involved crustal thickening to approximately double normal thickness, with transcurrent shearing of the thickened crust taking place during peak metamorphic conditions. Synmetamorphic uplift occurred synchronously with transcurrent shearing, and was followed by imbrication of orogenic zones along late thrust–reverse faults. Available age determinations suggest that peak metamorphism predated uplift by about 50 Ma. 39Ar/40Ar dating of hornblende from Abloviak shear zone has yielded ages of 1790–1750 Ma, some 15–65 Ma younger than recent estimates of the age of late faults, thus indicating slow and irregular uplift throughout the orogen.The orogenic history of Torngat Orogen is compatible with evolution in an oblique collision zone between two Archean cratonic blocks, and their subsequent welding into a single continental fragment that itself became incorporated into proto-Laurentia.
Ground penetrating radar of northern lacustrine deltas
Authors: Jol Harry M. , Smith Derald G.
Published: April 2011

Ground penetrating radar (GPR) was used in several selected deltaic sedimentary environments to better understand subsurface stratigraphy and reconstruct former depositional environments. The profiles provide high-resolution, continuous subsurface data on facies thickness and depths, orientation of major sedimentary structures, postdepositional failure planes, and depth of peat deposits.Field experiments were carried out on six river deltas. Records from four of the deltas exhibit sedimentary facies; a record from one delta shows a possible slump; and records from another delta reveal the thickness and stratigraphic relationships of peat deposits. The delta types are (i) sandy, wave influenced; (ii) sandy, immature wave influenced (steeper middle and lower shoreface); (iii) sandy braided; and (iv) gravelly, fan–foreset.In areas of limited subsurface control (stratigraphic logs from drill core, cutbank exposure, or geophysical logs), radar profiles can provide ''big picture'' perspectives of the subsurface, a view only available in laterally extensive exposures. High-resolution profiles of subsurface stratigraphy and sedimentary facies from GPR provide an opportunity for geomorphologists and sedimentologists to further advance field research. Although GPR has limited success in silt and clay, results from sand and gravel deposits often reveal detailed facies assemblages.
Multiple alteration events in the history of a sub-Huronian regolith at Lauzon Bay, Ontario
Authors: Sutton S. J. , Maynard J. B.
Published: April 2011

Confusion exists over the usefulness of chemical data from Precambrian weathering profiles in constraining models of atmospheric evolution. One difficulty is in correctly identifying ancient weathering effects and isolating them from numerous other processes that are likely to have affected such ancient rocks. In this study of a middle Precambrian granitic weathering profile, we have used several analytical techniques to separate weathering-related chemical and mineralogical changes from those resulting from other processes. The profile is exposed beneath the Huronian at Lauzon Bay in the Blind River area of Ontario and has a complex history of alteration events, addition of allochthonous material, and low-grade metamorphism. Much of this history can be deciphered, and changes in mineralogy and bulk and mineral chemistry can be assigned to separate alteration events. Specifically, the granite has undergone preweathering albitization, resulting in Na enrichment, followed by chemical weathering that corroded K-feldspar and nearly destroyed plagioclase feldspar and mica in the regolith. Clay minerals replaced feldspars, resulting in enrichment in Al, Ti, and Zr and depletion in Na, Ca, Sr, and K. Fe has also been leached. After weathering, a fine-grained 0.5 m layer of strongly weathered allochthonous material was deposited on the regolith, followed by deposition of the Matinenda Formation. Sometime after Matinenda deposition, K- and Rb-metasomatim affected the regolith and overlying sediments, converting some clays to illite and depositing secondary K-feldspar. Greenschist-facies metamorphism probably postdated this metasomatism and converted clay minerals to white mica and chlorite.
173 Ma U–Pb age of felsite sills (Kaslo River intrusives) west of Kootenay Lake, southeastern British Columbia
Authors: Smith Moira T. , Gehrels George E. , Klepacki David W.
Published: April 2011

U–Pb geochronological analyses of five zircon fractions from a lineated and foliated monzonite sill on the west side of Kootenay Lake are discordant and yield a lower intercept age of 173 ± 5 Ma, interpreted as the minimum crystallization age. An upper intercept of 1710 ± 180 Ma is interpreted as the average age of inherited components, and is consistent with contamination by Middle Proterozoic detritus in Upper Proterozoic to lower Paleozoic strata. The sills are interpreted as pre- to syn-kinematic with respect to regional second-phase or possibly third-phase deformation, thus further constraining the timing of Mesozoic orogeny in the Kootenay Arc, and may represent an early, foliated phase of the Nelson Batholith.
Caymanite, a cavity-filling deposit in the Oligocene–Miocene Bluff Formation of the Cayman Islands
Authors: Jones Brian
Published: April 2011

Caymanite is a laminated, multicoloured (white, red, black) dolostone that fills or partly fills cavities in the Bluff Formation of the Cayman Islands. The first phase of caymanite formation occurred after deposition, lithification, and karsting of the Oligocene Cayman Member. The second phase of caymanite formation occurred after joints had developed in the Middle Miocene Pedro Castle Member. Caymanite deposition predated dolomitization of the Bluff Formation 2–5 Ma ago.Caymanite is formed of mudstones, wackestone, packstones, and grainstones. Allochems include foraminifera, red algae, gastropods, bivalves, and grains of microcrystalline dolostone. Sedimentary structures include planar laminations, graded bedding, mound-shaped laminations, desiccation cracks, and geopetal fabrics. Original depositional dips ranged from 0 to 60°. Although caymanite originated as a limestone, dolomitization did not destroy the original sedimentary fabrics or structures.The sediments that formed caymanite were derived from shallow offshore lagoons, swamps, and possibly brackish-water ponds. Pigmentation of the red and black laminae can be related to precipitates formed of Mn, Fe, Al, Ni, Ti, P, K, Si, and Ca, which occur in the intercrystalline pores. These elements may have been derived from terra rossa, which occurs on the weathered surface of the Bluff Formation. Caymanite colours were inherited from the original limestone. Stratigraphic and sedimentologic evidence shows that sedimentation was episodic and that the sediment source changed with time. Available evidence suggests that caymanite originated from sediments transported by storms onto a highly permeable karst terrain. The water with its sediment load then drained into the subsurface through joints and fissures. The depth to which these waters penetrated was controlled by the length of the interconnected cavity system. Upon entering cavities, sedimentation was controlled by a complex set of variables.
Jurassic and Cretaceous plutonic and structural styles of the Eagle Plutonic Complex, southwestern British Columbia, and their regional significance
Authors: Greig Charles J.
Published: April 2011

The Eagle Plutonic Complex is an elongate north-northwest-trending body of deformed Middle to Late Jurassic and middle Cretaceous rocks which underlies the southwestern margin of the Intermontane terrane. New mapping of the complex and its country rocks, in concert with geochronometry, has defined episodes of contractional, ductile deformation in the Middle to Late Jurassic and middle Cretaceous, as well as brittle deformation in Tertiary time. Synkinematic Middle to Late Jurassic Eagle tonalite at the eastern margin of the Eagle Complex intrudes mylonitic Nicola Group rocks and structurally overlies them along a southwest-dipping belt of high strain (Eagle shear zone) with a structural thickness of > 1 km and a strike length of > 100 km. In the central and western Eagle Complex, Eagle tonalite grades into tonalite orthogneiss (Eagle gneiss), and both are crosscut by mid-Cretaceous, muscovite-bearing plutons of the Fallslake Plutonic Suite. Fallslake Suite rocks are themselves ductilely deformed along the Pasayten fault, which bounds the Eagle Complex on the west and was active mainly in the mid-Cretaceous (ductile deformation with sinistral, east-side-up, reverse displacement). The Jurassic and Cretaceous episodes of deformation may reflect the respective initial and final stages of the accretion of the Insular terrane to the North American margin. West of the Pasayten fault, Middle to Late Jurassic and older(?) rocks of the Zoa Complex are structurally overlain, in part, by deformed Middle Eocene and middle Cretaceous sedimentary rocks. In the north, the Middle Eocene rocks are intruded on their west side by the Middle Eocene Needle Peak pluton.
Postglacial emergence in the Canadian High Arctic: integrating glacioisostasy, eustasy, and late deglaciation
Authors: England John
Published: April 2011

Throughout the last glaciation, the Innuitian Sea, rather than glaciers, occupied many fiords and channels of the Queen Elizabeth Islands. Two alternative hypotheses, which constitute end members, are presented to account for the transgression of the Innuitian Sea between 18 and 8.8 ka, at which time it reached marine limit. Hypothesis A proposes that the last ice load was fully established by 18 ka and that it remained stable while sea level rose eustatically from approximately 60 m asl to marine limit by 8.8 ka. Hypothesis B proposes an advance of glaciers from present-day positions after 14 ka, when increased precipitation allowed rapid glacial loading to accompany the eustatic sea-level rise. By the early Holocene (when glaciers stood at the last ice limit) evidence suggests maximum warming and a shift to a negative mass balance.It is now recognized that the stable relative sea level at marine limit must record the balance between the rate of eustatic rise and the rate of uplift due to glacial unloading (thinning) between 8.8 and 7.8 ka. The rate of glacial unloading during this interval was low, approximately 1 m/100 years. Although the sea first penetrated inside the last ice limit by 8 ka, the first observed emergence was delayed until after 7.8 ka. By 7.6 ka many of the largest outlet glaciers from the Agassiz Ice Cap had retreated to positions equivalent to, or upvalley from, present-day margins. Nonetheless, between 7.8 and 7.2 ka, emergence progressed slowly (2 m/100 years), indicating that the large outlet glaciers retreated by calving, causing little change in the ice load. After 7.2 ka emergence was rapid, indicating that the regional glacial unloading was also rapid.It is proposed that the late deglaciation (Holocene) of the High Arctic favoured substantial postglacial emergence because the countering effect of the eustatic rise was largely completed by this time. Isobases drawn on the limit of the Innuitian Sea (the 8 ka shoreline) show a plunging ridge aligned with the south shore of Greely Fiord. It parallels the structural trends, suggesting the possibility of a tectonic component to the postglacial uplift.It is apparent that the style of ice advance and retreat in the High Arctic was controlled by several factors in addition to climatic change. These factors include topography, glacier dynamics, fiord bathymetry, sea-ice stability, and eustatic sea level.
Peatland development in relation to Holocene climatic change in Manitoba and Saskatchewan (Canada)
Authors: Kuhry P. , Halsey L. A. , Bayley S. E. , Vitt D. H.
Published: April 2011

Two peat cores from the southern boreal forest in south-central Manitoba and central Saskatchewan (Canada) were analyzed for microfossils, macrofossils, and physicochemical properties. Regional vegetation and local peatland development at these sites show the influence of warm and dry climatic conditions during the middle Holocene. Pollen assemblages at the base of the Manitoba site indicate the presence of grassland–parkland vegetation in the area prior to 4230 BP. At the Saskatchewan site, boreal forest was present throughout the development of the peatland from before 5020 BP to present. Both the Manitoba and Saskatchewan records suggest a more open – deciduous character of the regional vegetation cover during the middle Holocene in the southernmost part of the expanding boreal forest, in comparison with the modern southern mixed-wood boreal forest. The presence of a Typha latifolia-domimted marsh phase in the initial stages of development of both peatlands is indicative of marked water level fluctuations, likely due to frequent and severe periods of drought. Highest accumulation rates (1.24 mm peat/a, and 69 g carbon/(m2∙a)) occur in the forested fen phase (4290–3710 BP) of the Saskatchewan site. Low accumulation rates (0.24 mm peat/a, and 12 g carbon/(m2∙a)) in the bog phase (3710–960 BP) at this site are probably due to interruption of peat deposition or even surficial erosion of the deposits. Accumulation rates at the Manitoba site (4230–0 BP) are less variable, ranging from 0.30 to 0.82 mm peat/a and from 19 to 28 g carbon/(m2∙a). Changes in accumulation rates at the Saskatchewan and Manitoba sites are not synchronous in spite of similarities in general development, indicating that, in addition to climate, local factors have played roles in the developmental histories of these peatlands.
Paleomagnetism of Eocambrian Long Range dykes and Double Mer Formation from Labrador, Canada
Authors: Murthy G. , Gower C. , Tubrett M. , Pätzold R.
Published: April 2011

A paleomagnetic study was carried out on two post-Grenvillian units in the Grenville Province of southeast Labrador. These are (i) a swarm of northeast-trending mafic dykes inferred to be part of the Long Range suite and (ii) the Double Mer Formation, which is an undated rift-related red-bed sequence. Three of six mafic dykes investigated, including two having K–Ar (minimum) ages of 514 ± 8 and 553 ± 22 Ma, carry an interpreted primary remanence of declination (D) = 124.8°, inclination (I) = 55.5° (k = 48, α95 = 18.0°), with the corresponding paleopole at 10.8°S, 164.3°E. Three dykes, including one previously dated at 615 ± 2 Ma (U–Pb), yielded anomalous results. Nevertheless, because all six dykes show similar field, petrographic, and chemical characteristics, we consider that they belong to a single swarm. The anomalous directions are interpreted as disturbed paleomagnetic signatures, and the 615 Ma age is extrapolated as dating the primary remanence in the undisturbed dykes. The Double Mer Formation yields a mean direction for five sites at D = 110.8°, I = 50.1° (k = 24.6, α95 = 15.7°), with a corresponding paleopole at 13.0°S, 178.6°E. The similarity of this direction with that for mafic dykes is the first quantitative indication of its previously suspected Eocambrian age. Combining the Long Range dyke and Double Mer data, the paleolatitude of Eocambrian southeast Labrador is estimated to be 26 ± 5°S.
Stable isotope geochemistry and palynology of the late Precambrian to Early Cambrian sequence in Newfoundland
Authors: Strauss Harald , Bengtson Stefan , Myrow Paul M. , Vidal Gonzalo
Published: April 2011

A sequence of clastic sediments in southeastern Newfoundland straddling the Precambrian–Cambrian boundary has been investigated for its stable isotope geochemistry of carbon and sulfur and acid-resistant organic-walled microfossils. A detailed study of the Chapel Island Formation, which includes the boundary interval, has revealed fluctuations in the isotopic composition of organic carbon. These are largely interpreted as caused by differences in the depositional environments. Highly variable sulfur isotopic compositions indicate bacterial sulfate reduction as a pyrite-forming process, sometimes under sulfate-limited conditions. Palynological results are quite limited with respect to diagnostic microfossils.
Lower Ordovician (Arenig–Llanvirn) graptolites from the Notre Dame Subzone, central Newfoundland
Authors: Williams S. Henry
Published: April 2011

Many lower Paleozoic rocks in the Notre Dame Subzone of central Newfoundland are of unknown or imprecise age. Several new Lower Ordovician graptolite occurrences are here reported and earlier records revised. New graptolite localities in the Balsam Bud Cove Formation at Snooks Arm on the Baie Verte Peninsula, previously recorded as "early Ordovician (Arenig)" have yielded an assemblage identical to that found in the middle part of Bed 11 of the Cow Head Group, western Newfoundland, indicating a probable lower Didymograptus bifidus Zone age. At Corner Pond, southeast of Corner Brook, an abundant, diverse fauna from the Corner Pond formation indicates a marginally older age for the black shales than those at Snooks Arm (Pendeograptus fruticosus Zone, equivalent to lower Bed 11). Black shales associated with felsic volcanics and limestone breccia belonging to the Cutwell Group at Lushes Bight, on Long Island, western Notre Dame Bay, which were previously assigned to the widespread black shales of the Lawrence Harbour Formation and equivalents in the Exploits Subzone, contain a rich lower Llanvirn (Paraglossograptus tentaculatus Zone) graptolite assemblage. This agrees with ages established using other macrofossils and conodonts from the associated limestones. In contrast, a lower shale unit from older strata at Southern Head on the eastern end of the island yields a late Arenig Isograptus victoriae maximus Zone assemblage. These newly discovered graptolite faunas provide precise ages for the upper and lower parts of the volcano-sedimentary sequence on Long Island. Interestingly, all four graptolite assemblages discussed here are of open-ocean affinity, permitting accurate correlation with localities not only in western Newfoundland but also elsewhere in the world.
Lithoprobe onshore seismic reflection transects across the Newfoundland Appalachians
Authors: Quinlan Garry M. , Hall Jeremy , Williams Harold , Wright James A. , Colman-Sadd Stephen P. , O'Brien Sean J. , Stockmal Glen S. , Marillier François
Published: April 2011

Vibroseis seismic reflection data have been recorded to 18 s two-way traveltime along three transects across the island of Newfoundland. The upper crust has both steep and subhorizontal reflectors consistent with a ramp–flat style of deformation, whereas the middle and lower crust are largely free of regional flats. Reflectors descend through ca. 20 km of vertical section in the middle and lower crust to flatten into the Moho or perhaps cut through it in places. The Moho is interpreted to be no younger than the dipping reflectors. Reflection fabrics, interpreted to be indicators of dominantly Mid-Ordovician to Mid-Silurian strain, show consistent orientations among the transects and divide the crust into two blocks. A northwestern block is characterized by upper and middle crustal reflectors dipping mostly southeast at variable angles. This block is underlain to the southeast by supposedly younger and dominantly northwesterly dipping reflectors that define a northwest-tapering, wedge-shaped block floored by the Moho. This latter block is cut by isolated southeast-dipping, upper crustal reflectors near the southeast ends of the seismic transects. One of these reflectors is spatially correlated with the Bay d'Est Fault, on which the last ductile motion was south over north thrusting of Mid-Silurian age. The two crustal blocks are proposed to represent the Laurentian and Gondwanan plates juxtaposed during closure of the Iapetus Ocean. The Gondwanan plate appears to be underthrust westward beneath the Laurentian plate, perhaps by as much as 200 km.
Quaternary stratigraphy, paleoecology, and glacial geology, Îles de la Madeleine, Quebec
Authors: Dredge L. A. , Mott R. J. , Grant D. R.
Published: April 2011

On the Îles de la Madeleine, a rock platform as much as 20 m asl, locally with clam borings, is correlated to the regional interglacial surface at 2–8 m; its anomalous height may be a consequence of salt tectonics. Overlying lagoonal and paludal organic beds, one with Th/U ages of 89–101 ka, record the Sangamonian climatic optimum (substage 5e), which culminated in forest more thermophilous than that of the Holocene optimum. Overlying littoral gravel and sand, considered analogous to sediments in present-day tombolos, and organic beds with less temperate pollen types were deposited during the marine transgressive climax of substage 5e and thus indicate that sea level remained high after the thermal optimum, as in Holocene time. Cold-based Early Wisconsinan ice, probably centred on the Magdalen Shelf, tectonized bedrock and interglacial beds and deposited till upon them. Periglacial features indicate a subsequent long cold period. An organic bed dating from 11.3 to 10.6 ka records a warm interval followed by cooling. Buried peat, a submerged fossil sea cliff, and barrier beaches record a marine transgression during the late Holocene.
The late Quaternary sedimentary record of Stave Lake, southwestern British Columbia
Authors: Gilbert Robert , Desloges Joseph R.
Published: April 2011

The postglacial sedimentary record of 59 km2 Stave Lake was investigated using 3.5 kHz subbottom profiles and cores from the sediment surface. The acoustic data show a thin cover of acoustically transparent sediment (unit 1) overlying bedrock or glacial sediment on the floor of the lake. Overlying acoustically stratified sediment is divided into unit 2, which thins from 28 m in the south of the lake to less than 12 m in the north, and unit 3, which thins from 20 m in the north to about 12 m in the south. Unit 1 is interpreted as resulting from deposition in a relatively quiet lacustrine or marine environment following retreat of Vashon glaciers about 13 ka ago. Unit 2 is ascribed to deposits of sediment in runoff to Stave Lake from the Sumas ice sheet in the Fraser Valley and connecting valleys to the Stave Basin. Following the retreat of the Sumas ice about 11 ka ago, deposition of unit 3 resulted almost entirely from sediment input from Stave River entering at the north end of the lake. Raising the lake in 1912 by damming for hydroelectric generation resulted in deposition of a thin but distinct marker horizon in the sediment, from which modern rates of accumulation averaging 3 mm/a are estimated. These are more than twice the average rates for the Holocene estimated from the total thickness of unit 3. The rates of sediment yield calculated from accumulation in Stave Lake are 4.5 × 105 kg∙km−2∙a−1 (modern) and less than 2 × 105 kg∙km−2∙a−1 (averaged over the Holocene).
A new Lower Ordovician (Arenig) faunule from the Coy Pond Complex, central Newfoundland, and a refined understanding of the closure of the Iapetus Ocean
Authors: Williams S. Henry , Boyce W. Douglas , Colman-Sadd Stephen P.
Published: April 2011

A newly discovered fossiliferous horizon within sediments belonging to the Coy Pond Complex of the Exploits Subzone in central Newfoundland yields the graptolite Undulograptus austrodentatus s.l. and cyclopygid trilobite Cyclopyge grandis brevirhachis. This late Arenig faunule constrains the upper age limit of the ophiolite complex and is the first record of an Early Ordovician cyclopygid trilobite in North America. This is consistent with a paleogeographic affinity for south-central Newfoundland with the northern oceanic margin of Avalonia in a peri-Gondwanan position during the Early Ordovician and contrasts with coeval shelly and graptolitic faunas from the Notre Dame Subzone of central Newfoundland, which show marked Laurentian affinities. The Exploits Subzone is generally considered equivalent to the region of Scotland lying south of the Southern Upland Fault. The Newfoundland discovery, which is supported by faunal data from elsewhere in Newfoundland and in Ireland, suggests that the region around the Southern Upland Fault, rather than the Solway Firth, represents the location of the "Iapetus suture" in Britain in Lower Ordovician rocks.
The aeromagnetic survey program of the Geological Survey of Canada: contribution to regional geological mapping and mineral exploration
Authors: Teskey D. J. , Hood P. J. , Morley L. W. , Gibb R. A. , Sawatzky P. , Bower M. , Ready E. E.
Published: April 2011

The aeromagnetic survey operations of the Geological Survey of Canada (GSC) began in 1946, utilizing a magnetometer in a bird system towed by a Royal Canadian Air Force Anson. Subsequent early operations were carried out by the GSC-operated Canso and Aero Commander aircraft. In 1961, the GSC in-house survey team formed the nucleus of a contract surveys group set up to monitor a new program established to complete the aeromagnetic mapping of the Canadian Shield in 12 years on a cost-sharing basis with the provinces. Today, surveys are carried out under contract by light twin-engine aircraft such as the Cessna 404 and even, in some cases, single-engine aircraft that utilize compact computer-controlled data acquisition and navigation systems and inboard magnetometer installations. Early systems were capable of resolution of only a few nanoteslas (nT) compared to the current standard of 0.1 nT or less, and flight path positioning with 35 mm film and photomosaics or topographical maps was extremely challenging. Despite these limitations, the careful selection of survey parameters and attention given to quality control have resulted in a world-class aeromagnetic data base that has contributed significantly to regional geological mapping and to mineral and oil exploration in Canada. Concurrently, the GSC carried out research programs into the development of instrumentation and into processing, interpretation, and enhancement techniques. In 1968, the GSC acquired its own platform, a Beechcraft B80 Queenair, which was used to develop high-sensitivity techniques, and an inboard gradiometer system, which was transferred to private industry in 1983. The GSC, in cooperation with the Flight Research Laboratory of the National Research Council of Canada, has also conducted a program of research into magnetometry and navigation combined with aeromagnetic studies of the Arctic since 1962.
Gypsum facies in the Badenian (Middle Miocene) of southern Poland
Authors: Kasprzyk Alicja
Published: April 2011

Middle Miocene sulfate sediments south of the Holy Cross Mountains, southern Poland, comprise deep- and shallow-water as well as subaerial facies, accompanied by carbonates and siliciclastics. In the gypsum section, 18 lithostratigraphic units have been distinguished. The facies variety reflects distinct sedimentary conditions in the peripheral area of the evaporitic basin, where the maximum water depth never exceeded some tens of meters. The succession of facies is regressive and comprises six sedimentary cycles that reflect relative changes in sea level and in the physicochemical regime of the basin, both of which were controlled by tectonic and climatic factors. Sea level fell five times during sulfate sedimentation; the last sea-level drop led to the almost total desiccation of the sea in the peripheral part of the basin.
Paleomagnetism of the late Paleozoic Slide Mountain terrane, northern and central British Columbia
Authors: Richards David R. , Butler Robert F. , Harms Tekla A.
Published: April 2011

Paleomagnetic samples were collected from Mid-Pennsylvanian to Lower Permian red argillaceous cherts at two localities of the Slide Mountain terrane: 18 sites from the Sylvester allochthon in northern British Columbia and 11 sites from Sliding Mountain in central British Columbia. A secondary component of natural remanent magnetization in the Sylvester samples yields a paleomagnetic pole that can be brought into coincidence with the Jurassic portion of the North American apparent polar wander path by inferring vertical-axis rotation during obduction of the allochthon. Both localities yield a characteristic component (ChRM) with unblocking temperatures from 650 to 680 °C. After structural correction for bedding tilt, all inclinations of ChRM are negative, consistent with magnetization during a reversed-polarity interval in the northern hemisphere. Site-mean ChRM directions show consistent inclinations but distinct stratigraphic groupings of declinations. Inclination-only statistics indicate that the ChRM passes a tilt test within the Sylvester allochthon and regionally between the two localities. The ChRM was apparently acquired prior to structural imbrication within the Sylvester section and regional differential tilting. We interpret the ChRM to be a primary magnetization acquired at or soon after deposition during the Permo-Carboniferous reversed-polarity superchron. The mean ChRM inclination of −16.7° ± 6.0° from the Sylvester allochthon indicates a paleo-latitude of 8.8° ± 3.4°N, which is corroborated by a paleolatitude of 1.9° ± 1.5°N from the Sliding Mountain locality. When compared with expected Pennsylvanian–Permian paleolatitudes, a net poleward translation of 20.3 ± 3.7° is implied for at least the sampled lithotectonic component of the Sylvester allochthon.
U–Pb age constraints for the magmatic and tectonic evolution of the Pontiac Subprovince, Quebec
Authors: Mortensen J. K. , Card K. D.
Published: April 2011

New U–Pb zircon, titanite, and monazite ages help constrain the history of magmatism and tectonism within the Pontiac Subprovince of western Quebec. The Pontiac Subprovince resembles other metasedimentary belts of the Superior Province; however, the stratigraphic relationships between the dominantly sedimentary rocks of the Pontiac and the adjacent, volcanic-dominated Abitibi belt to the north and west remain controversial. Volcanic rocks of the Belleterre volcanic zone in the southern part of the Pontiac Subprovince have been interpreted by other workers as klippen of Abitibi strata that were thrust southward onto the Pontiac Subprovince. However, volcanic rocks in the Belleterre zone give crystallization ages of 2689–2682 Ma, which are younger than any extrusive rocks dated thus far from the Abitibi belt. Single detrital zircon grains from Pontiac sedimentary rocks give ages as young as 2683 Ma, indicating that the sediments are similar in age, or younger than, the volcanic units. The volcanic rocks probably represent distal facies of small volcanic arcs deposited within a large turbidite basin.The Lac des Quinze tonalitic gneiss body gives U–Pb zircon and titanite ages of 2695 ± 1 Ma and 2673 ± 4 Ma, respectively. Although the gneiss may represent basement to the supracrustal units, field relationships indicate that it was tectonically juxtaposed against the supracrustal package. Alkaline intrusive rocks in the Pontiac Subprovince yield U–Pb ages that overlap with the youngest ages obtained from the volcanic units. This attests to a very short-lived cycle of sedimentation and arc magmatism, followed by late tectonic and posttectonic alkaline plutonism.
The youngest Paleozoic plutonism of the Newfoundland Appalachians: U–Pb ages from the St. Lawrence and François granites
Authors: Kerr A. , Dunning G. R. , Tucker R. D.
Published: April 2011

The posttectonic St. Lawrence and François granites have long been regarded as the youngest Paleozoic plutonic suites of the Newfoundland Appalachians. Their U–Pb ages of 374 ± 2 and 378 ± 2 Ma, respectively, define a Middle to Late Devonian magmatic event. Mid-Carboniferous magmatic and (or) rifting events, suggested on the basis of earlier Rb–Sr dating of the St. Lawrence Granite, are not supported by these new data. Both granites intrude major ductile and brittle structures that were active during the early Paleozoic, and they provide a younger age limit for major tectonic activity in the Avalon Zone and on the south coast of Newfoundland. The granites may correlate with plutons of closely similar age reported from the Aspy and Mira terranes of Cape Breton Island, Nova Scotia.
Early Devonian age of the Detroit River Group, inferred from Arctic stromatoporoids
Authors: Prosh Eric C. , Stearn Colin W.
Published: April 2011

The Detroit River Group of southwestern Ontario and the adjacent United States has traditionally been considered mostly or entirely Middle Devonian in age. Detroit River Group faunas are, however, highly endemic and difficult to correlate to the chronostratigraphic standard; widely accepted conodont-based ages are similarly constrained by endemism and rely heavily upon inferential correlations. Recent evidence from the Blue Fiord Formation of southwestern Ellesmere Island suggests an Emsian (late Early Devonian) age for the full Detroit River Group, based upon shared stromatoporoid species. Four Detroit River Group species, Stromatoporella perannulata Galloway and St. Jean, Stictostroma mamilliferum Galloway and St. Jean, Habrostroma proxilaminata (Fagerstrom), and Parallelopora campbelli Galloway and St. Jean, are recognized for the first time in the Arctic. In addition, Blue Fiord Formation (and younger) species of Trupetostroma and Pseudoactinodictyon demonstrate close relationships to Detroit River Group species. Together, the stromatoporoid evidence and the available conodont data imply a serotinus age for the Amherstburg Formation and a serotinus to patulus age for the Lucas Formation. This is the first direct species-level correlation of a Detroit River Group "endemic" to a globally dateable level and the first regional application of stromatoporoid biostratigraphy in North America.
Seismic images of the Grenville Orogen in Ontario
Authors: White D. J. , Easton R. M. , Culshaw N. G. , Milkereit B. , Forsyth D. A. , Carr S. , Green A. G. , Davidson A.
Published: April 2011

In 1990, Lithoprobe acquired 240 km of seismic-reflection data across parts of the Central Gneiss Belt (CGB) and the Central Metasedimentary Belt (CMB) within the western Grenville Province of southern Ontario. Interpretation of these data in conjunction with geological constraints provided by bedrock mapping supports a model of northwest-directed thrusting and crustal shortening for the Grenville Orogen. Within the CGB, the Parry Sound shear zone is imaged as a 3 km wide zone of reflections dipping southeastward at 20–25° and soling at depths < 7 km in the north and < 3 km in the south beneath Parry Sound domain. Parry Sound domain and the immediately adjacent domains are underlain by a gently southeast-dipping reflective zone at 4.5–12.0 km depth interpreted as a detachment surface, likely associated with the central Britt shear zone. This zone may have accommodated northwesterly transport of Parry Sound, southern Britt, and northwestern Rosseau domains over Britt domain during Grenvillian thrusting.Within the CMB, the seismic data indicate that crustal shortening and imbrication have not been confined to domain and terrane boundaries, as presently defined. A 6 km wide band of reflections dips south at ~20° from the surface within Bancroft terrane, soling into a mid-crustal décollement beneath Elzevir terrane. Beneath and to the north of this planar reflective zone is a complex pattern of strong, south-dipping (10–40°) reflections that extends from the near surface to the lower crust above a less reflective wedge-shaped zone. The zone of complex reflectivity projects updip to the CMB boundary zone and into the CGB; together with the linear band of reflections affiliated with Bancroft terrane, they form the tectonized boundary between the CGB and the CMB. To the south of the linear reflective zone, prominent reflective packages are restricted to the middle and upper crust. The generally nonreflective uppermost crust beneath Elzevir terrane is underlain by a series of gently southeast-dipping, antiformal reflections that appear to sole into the mid-crustal décollement beneath Mazinaw terrane. These observations suggest that the collision between the CMB and the CGB resulted in a sequence of relatively thin (15–20 km thick) allochthonous terranes within the CMB being transported along a regional décollement and thrust northwestward over footwall rocks of the CGB along a penetratively deformed tectonic zone, while a lower crustal wedge may have delaminated the CMB lower crust. Crustal thickness where defined by the seismic data is 42.0–43.5 km in both the CGB and the CMB.
Tunnel channels and associated landforms, south-central Ontario: their implications for ice-sheet hydrology
Authors: Brennand Tracy A. , Shaw John
Published: April 2011

The Peterborough–Trenton drumlin field and associated meltwater erosion marks (s-forms) were interpreted as the products of erosion by turbulent separated flows within a catastrophically released subglacial meltwater sheet, the Algonquin event. Recent theoretical modelling of ice-sheet hydrology suggests progressive channelization of meltwater during the collapse of such a sheet. Inductive testing of this hypothesis using observations in south-central Ontario forms the crux of this paper. A geometric model of the interaction of rough ice base and bed surfaces gives inferred meltwater flow patterns. Such a rough interactive geometry is suggested as the bed is drumlinized, and flows responsible for drumlins may be expected to have eroded similar forms into the ice base. Three landforms in south-central Ontario; namely tunnel channels, megachannels, and late-stage sheet-flow scours, are described, and interpreted as evidence of progressive channelization and flow diversion processes, governed by the geometric interactions between the recoupling ice base and its bed and thermodynamic feedbacks within an increasingly discontinuous meltwater sheet. Some fields of transverse ridges within tunnel channels may record meltwater deposition towards the end of the Algonquin event. By contrast, eskers within tunnel channels record a return to seasonally driven meltwater drainage. The Dummer Moraine and the Oak Ridges complex are integrated into a new landform–vent sequence for south-central Ontario which provides a framework for further field testing.
Late Wisconsinan deglaciation of Emerald Basin, Scotian Shelf
Authors: Gipp Michael R.
Published: April 2011

Seismic surveys of the glacial and proglacial sediments of Emerald Basin show a systematic succession representing one complete cycle of deglaciation. The succession consists of a thin layer of acoustically incoherent sediments overlain by a thick sequence of acoustically stratified muds, capped by ponded, acoustically transparent Holocene sediments. The incoherent sediments, interpreted as a subglacial till, extend across the basin. The stratified proglacial sediments contain five erosional or nondepositional surfaces, thought to be of chronostratigraphic significance. These five surfaces are used to divide the proglacial sediments into lithosomes, each of which is influenced to varying degrees by three depositional mechanisms: suspension rain-out, ice rafting, and turbidity currents.Radiocarbon dating indicates that deglaciation started at about 18 ka. Although the main ice sheet retreated landward, deglaciation was locally complex, and a series of ice rises likely persisted until about 12 ka, grounded on the banks of the outer and central Scotian Shelf. Retreat of ice from the Scotian Shelf is recorded as a reduction of sedimentation rates, a decrease in the amount of coarse (> 500 μm) clasts supplied to the basin, the absence of iceberg scours in the upper sediments of the basin, and the disappearance of depocentres of proglacial sediments from the southern and eastern flanks of the basin by 11 ka.
A Late Ordovician to middle Wenlockian graptolite sequence from a borehole within the Rathkenny Tract, eastern Ireland, and its relation to the paleogeography of the Iapetus Ocean
Authors: Lenz Alfred C. , Vaughan Alan P. M.
Published: April 2011

A borehole drilled within the Rathkenny Tract, southwest of Navan, eastern Ireland, yielded a rich graptolite fauna, including three excellent basal Silurian graptolite assemblages, from a deep-water, pelagic and hemipelagic sequence, ranging in age from uppermost Caradocian to middle Wenlockian, from immediately below Carboniferous strata. Biostratigraphic analysis of the graptolites shows that there are eight, discrete faunal (biostratigraphic) units, and these, together with the lithology, indicate the graptolite-bearing sequence is mostly inverted and faulted at several levels.Biogeographic affinities of several of the Llandoverian and of the Wenlockian graptolite species, as well as some lithological data, suggest that the Rathkenny Tract lay on the southeast side of the Iapetus Ocean. The presence of the youngest graptolites further suggests that some element, at least, of the Iapetus Ocean, though probably narrow by this time, was clearly still in existence until at least middle Wenlockian.
New occurrences of Oldhamia and other trace fossils in the Cambrian of the Yukon and Ellesmere Island, arctic Canada
Authors: Hofmann H. J. , Cecile M. P. , Lane L. S.
Published: April 2011

Trace fossil assemblages from green and maroon argillites at 34 localities in the British Mountains and Barn Mountains of northernmost Yukon, and 3 localities in the Grant Land Formation of northern Ellesmere Island contain abundant Planolites spp., Oldhamia curvata, Oldhamia flabellata, and Oldhamia radiata, and rare Oldhamia antiqua, Oldhamia? wattsi (n.comb.), Bergaueria hemispherica, Cochlichnus sp., Didymaulichnus? sp., Helminthoidichnites sp., Monomorphichnus sp., Protopaleodictyon sp., and Tuberculichnus? sp. Additionally, 11 new sites in the Selwyn Mountains of north-central Yukon have yielded an ichnofauna including Helminthorhaphe sp., O. curvata, O. flabellata, O. radiata, Plagiogmus? sp., Planolites spp., and unidentified small hemispherical traces. All these assemblages are interpreted as Early Cambrian to early Middle Cambrian, based on comparison with Oldhamia-bearing ichnofaunas of similar age in North America, Argentina, and western Europe, and on archaeocyathids and olenellids in overlying units.
Geometry and kinematics of a major crustal shear zone segment in the Appalachians of southern New Brunswick
Authors: Park Adrian F. , Williams Paul F. , Ralser Steven , Léger Albert
Published: April 2011

In southern New Brunswick the Kennebecasis Fault follows the northern boundary of a crystalline portion of the late Precambrian – Cambrian Avalon terrane. This low-grade crystalline complex forms the basement to a series of Carboniferous through Triassic basins. This complex also contains a major shear zone relic that is largely flat lying but upturned adjacent to the fault, and that with it defines the Pocologan–Kennebecasis fault zone. The orientation of the main composite foliation (S1) and the included mineral (stretching) lineation (L1) indicate that this geometry is a primary feature of the shear zone, representing a linked pair of horizontal and vertical detachments bounding an allochthonous unit. Kinematic indicators show that this allochthon moved parallel to the strike of the north Appalachian orogen, with top towards the west or west-southwest. The bounding shear zone is not uniform, but consists of a mylonite–phyllonite adjacent to the detachment. The upturned segment of the shear zone has been the site of later, brittle reactivation, one episode of which is represented by the Kennebecasis Fault. The main shear zone relic relates to more fundamental events, such as the accretion of the Avalon terrane.
Depositional facies and detrital composition of the Paleoproterozoic Et-Then Group, N.W.T., Canada: sedimentary response to intracratonic indentation
Authors: Ritts Bradley D. , Grotzinger John P.
Published: April 2011

Paleoproterozoic intracratonic compression across the Slave Province resulted in eastward indentation of the wedge-shaped Slave craton into the Thelon orogen. Indentation was accommodated by shortening and crustal thickening at the apex of the Slave wedge, bounded to the south by the right-lateral McDonald fault and to the north by the left-lateral Bathurst fault. The Paleoproterozoic, nonmarine Et-Then Group in the East Arm of Great Slave Lake records the history of this indentation. The Et-Then Group consists of two formations. The older Murky Formation is an alluvial-fan conglomerate deposited unconformably over older Paleoproterozoic sedimentary and igneous rocks and Archean metamorphic and igneous rocks. Clast composition indicates that the Murky Formation was derived from these older rocks, eroded during initial translation and uplift on the McDonald fault system. The younger Preble Formation conformably overlies the Murky Formation and is a braided fluvial sandstone. The modal framework composition indicates a granitoid source. On the basis of west-southwest paleocurrrents, modal composition, and depositional style, the Preble Formation is interpreted to be derived from the apex of the Slave wedge. Isostatic uplift at the apex of the Slave craton, due to crustal thickening, provided sufficient amounts of sediment to effectively bury local relief in the East Arm and change the depositional style from one of locally derived alluvial fans (Murky style) to a westward-sloping, regionally extensive braid plain (Preble style).
Structure profonde du mont Ross d'après la réfraction sismique (îles Kerguelen, océan Indien austral)
Authors: Recq Maurice , Roy Isabelle Le , Charvis Philippe , Goslin Jean , Brefort Daniel
Published: April 2011

Mont Ross is the main volcanic feature of the Kerguelen Archipelago (terres Australes et Antarctiques françaises). This newly formed volcano buildup over 2 Ma provides us with an outstanding model of volcanism occurring on an intraplate structure already aged 40 Ma. Mont Ross is the subaerial part of a plutonic complex located in Galliéni Peninsula. From seismic refraction studies, P-wave velocities within the upper crust range downward from 5.35 km/s at sea level to 6.60 km/s at a depth of 11 km. These are definitely higher than those encountered within surrounding basalts known as plateau basalts. These high velocities reveal, at first glance, an origin and composition of the basement of Mont Ross far distinct from those of tholeiitic or transitional lava flows generated near spreading centres. By comparison with plutonic ring complexes, it is reasonable to state that monzonite and syenite are the basic materials of the basement. Seismic velocities (6.85 to 7.30–7.35 km/s) and related Poisson ratio (σ = 0.30) within lower crust are consistent with gabbros as prominent material. The thickness of the lower crust below Mont Ross (6–7 km) is roughly the same as that below the archipelago. Gabbros are exposed around several plutonic ring complexes spread over the archipelago. The transition to mantle might be modelled by a 2 km thick transition zone, with high velocity gradient, already noticed below the archipelago. Velocities of 7.30–7.35 km/s at the base of the crust below Mont Ross do not preclude contamination of the lower crust by mantle material. Both gravity and seismic data substantiate the occurrence of high density (velocity) within the upper crust below Mont Ross. Isostatic compensation of Mont Ross is rather achieved by a flexural deflection of the lithosphere than by an Airy-type model. The structures of Mont Ross and Hawaiian volcanoes bear analogies likely related to their intraplate genesis.