bluuebunny/crossref_metadata_2025 huggingface dataset:
Multicomponent magnetizations in Nipissing diabase near Temagami, Ontario, and structural and thermal history of the Grenville Front
Authors: Hyodo Hironobu , Dunlop David J.
Published: April 2011

The Nipissing diabase (ND), sampled 2 km northwest of the Grenville Front near Temagami, Ontario, has four distinct components of natural remanent magnetization (NRM). The lowest unblocking temperature (TUB) component is attributed to the present Earth's field, whereas the second lowest TUB component is due to overprinting during the late stages of the Grenvillian Orogeny (~900 Ma). Similar Grenvillian overprint directions of NRM are found in Archean (~2600 Ma) country rock. The second highest TUB component (B) has an unknown origin. Low-temperature demagnetization (LTD) reveals that this component is significantly contaminated by overlap with the Grenvillian overprint and with the highest TUB component (A). If the A NRM is primary, its direction should agree with previously published ND poles after structural correction for subvertical tilting of sites. However, the structurally corrected A direction does not agree with known ND primary directions without additional rotation about a vertical axis. This may indicate sequential block rotation and tilting or could be caused by a single tectonic rotation about an inclined axis. The ND in the Temagami area shows a variety of characteristic magnetizations, which may reflect a complicated structural history and (or) hydrothermal activity before Grenvillian uplift, whereas west of Lake Temagami and in the Wanapitei Lake area ND results agree with the previously reported N1 paleopole. This contrast suggests quite different tectonic histories east and west of Lake Temagami.
Gravity modelling of the Saint George Batholith and adjacent terrane within the Appalachian Orogen, southern New Brunswick
Authors: Thomas M. D. , Willis C.
Published: April 2011

The geometry of the Saint George Batholith has been investigated along three detailed (1–2 km station spacing) north–south gravity traverses surveyed in conjunction with a geothermal study. Modelling of corresponding gravity profiles indicates that the batholith is 6.6, 4.3, and 7.0 km thick along the western, central, and eastern traverses, respectively. The western profile crosses the buried western granitic extension of the batholith and the exposed mafic Bocabec complex, modelled as a sheet 200–400 m in thickness. The central profile crosses the western half of the exposed batholith, and the eastern profile crosses the eastern half near a borehole used for heat-flow measurements.Two other gravity profiles, defined by detailed and regional (average station spacing about 5 km) observations, were also modelled. One trends northeast across the eastern margin of the batholith and passes directly through the borehole site, at which the batholith is modelled as 6.5 km thick. Here, geothermal calculations suggest that the thickness of radiogenic granite lies in the range 1.4–3.3 km. The large discrepancy between gravity and geothermal estimates supports suggestions that radiogenic elements have been concentrated in the upper part of the batholith, probably by circulating groundwater. The second profile crosses the Pleasant Ridge and Sorrel Ridge granitic intrusions, located northwest of the batholith. Modelling indicates that these intrusions are rooted in the buried roof of the Saint George Batholith at depths of about 1.1 km.Relatively high levels of the gravity field south of the batholith are attributed to dense Precambrian rocks, which are modelled as forming the wall rocks along much of the southern margin of the batholith. The walls in places are steep, suggesting control by major faults that step the Precambrian rocks down to the north, where they apparently floor the batholith and (or) lower Palaeozoic rocks at a depth of about 7.6 km. This picture of block faulting is supported by interpretation of a regional gravity profile located northeast of the Saint George Batholith and running northwest from the Bay of Fundy to the Miramichi Massif.
Late Quaternary stratigraphy, sedimentology, and history of the Jasper townsite area, Alberta, Canada
Authors: Levson V. M. , Rutter N. W.
Published: April 2011

Geomorphic, stratigraphic, and sedimentologic evidence obtained from Quaternary sediments near Jasper, Alberta, is used to reconstruct depositional environments in the vicinity of two former confluent valley glaciers. Sedimentation occurred mainly in the valley centre in a pre-existing river channel. Lateral ice-marginal sedimentation along the inset valley walls was important during both the advance and the retreat stages. Prior to and during glacial advance, horizontally stratified gravels, sands, and silts were deposited in a braided stream. Near the valley bottom, diamictons containing trough-shaped sand lenses were deposited by subsequent proglacial debris flows and intermittent fluvial activity. At higher stratigraphic positions, outwash deposits confined to the valley wide are unconformably overlain by massive diamicton, interpreted as subglacial till, deposited as ice began to override the area. The diamicton grades towards the valley side into ice-contact debris deposited at the margins of the expanding glacier by water and sediment flows from the ice surface. Glaciers eventually overrode the entire area. During deglaciation, thick sequences of normally faulted, steeply dipping sand, gravel, and clast-rich diamicton were deposited in a kame terrace west of Jasper townsite. The orientation of bedding and faults and the nature of the sediments indicate they were derived from, and deposited in contact with, a linear belt of stagnating, debris-covered ice that extended along the valley centre east of Jasper. It is postulated that the stagnating ice originated from a well-developed medial moraine and debris septum that formed at the confluence of the large Athabasca and Miette valley glaciers. The knob-and-kettle topography, which eventually developed in the valley centre, was obscured by glaciofluvial and fluvial activity. A linear chain of kettle lakes remains as evidence of the possible existence of the moraine. Kettle chains and hummocky topography, formed in the positions of both medial and lateral moraines, may be relatively common geomorphic features in glaciated mountain valleys.
Ion probe U–Th–Pb zircon dating of polymetamorphic orthogneisses from northern Labrador, Canada
Authors: Schiøtte L. , Compston W. , Bridgwater D.
Published: April 2011

Rounded zircons included within igneous zircons from the Uivak I gneisses, northern Labrador, have ages of up to 3863 ± 12 Ma (2σ), showing the (former) existence of rocks that predate the Uivak gneisses by more than 100 Ma. The igneous zircons themselves have experienced varying amounts of early Pb loss, but age estimates based on maximum 207Pb/206Pb from three separate gneiss samples agree to within error at 3732 ± 6 Ma (2σ), which is taken as the age of emplacement of the igneous precursor to the dominant component of the Uivak gneisses. A new generation of zircons was formed during migmatization at ca. 3620 Ma. The volumetrically less important Lister gneiss was emplaced at 3235 ± 8 Ma (2σ). In the late Archaean, different parts of the gneiss complex were subjected to different grades of metamorphic overprinting. The zircon chronology of gneisses affected by granulite facies metamorphism suggests a rapid sequence of events, with simultaneous recrystallization of old zircons and growth of new U-poor zircons at 2766 ± 17 Ma (2σ), followed by partial melting at 2744 ± 4 Ma (2σ), and further recrystallization and growth of U-poor zircons afterwards. No late Archaean zircon growth has been recorded from orthogneisses unaffected by granulite fades metamorphism.
Hydrology of small tributary streams in a subarctic wetland
Authors: Woo Ming-ko , diCenzo Peter D.
Published: April 2011

Rivers traversing subarctic wetlands are fed by numerous small tributary creeks, which carry much of the wetland runoff into the rivers during the snow-free season. The wetlands, being saturated, generate abundant surface flow in the spring melt season. This amount of water cannot be accommodated by the tributary creeks and, together with general flooding of the rivers, there is little distinction between overland flow and channelled flow across the wetland, the feeder tributaries, and the major rivers. After snowmelt, the water level subsides, and most of the overland flow from the wetland is funnelled into the feeder creeks. The feeders can usually respond quickly to rainstorms and recessions are short unless surface flow is sustained by extensive marshy depressions. Along the lower reaches of the major rivers, the small tributary creeks are the main conveyors of wetland runoff to the rivers and therefore strongly modify the runoff characteristics of the rivers.
Llandovery graptolite biostratigraphy and paleobiogeography, Cape Phillips Formation, Canadian Arctic Islands
Authors: Melchin Michael J.
Published: April 2011

Llandovery graptolites have been collected from 11 sections in the Cape Phillips Formation of the Canadian Arctic Archipelago: Melville, Bathurst, Truro, Cornwallis, Devon, and Ellesmere islands. The Cape Phillips Formation appears to have been deposited in a distinct subbasin, here termed the Cape Phillips Basin, under deep-shelf to shallow-basin conditions intermediate in position between the Arctic Platform to the south and east and the deeper Hazen Trough to the northwest.A total of 170 graptolite species and a further 25 subspecies have been identified. Their stratigraphic distribution allows the recognition of 11 graptolite zones: the acuminatus, atavus, acinaces, cyphus, curtus, convolutus, minor, turriculatus, crispus, griestoniensis, and sakmaricus zones. The curtus Zone can be subdivided into the pectinatus and orbitus subzones. The zones can be correlated with graptolite sequences worldwide.The Canadian Arctic faunas show strong affinities with those of Siberia, China, and the northern Canadian Cordillera. It may be possible to recognize a circum-equatorial faunal province in northern North America, Siberia, and China based on the occurrence of distinctive forms including Agetograptus and "Paramonoclimacis" in the middle Llandovery and certain Cyrtograptus species (especially C. sakmaricus) in the upper Llandovery.
Northeastern extension and crustal expression of terranes from Cape Breton Island, Nova Scotia, based on geophysical data
Authors: Loncarevic B. D. , Barr S. M. , Raeside R. P. , Keen C. E. , Marillier F.
Published: April 2011

The narrowest section of the Appalachian Orogen in Atlantic Canada (from Grenville-age basement in the west to the Avalon Terrane in the east) is preserved in Cape Breton Island, where components of four terranes display distinctive stratigraphic, igneous, metamorphic, aeromagnetic, and gravity characteristics. The Blair River Complex of northwestern Cape Breton Island is a fragment of Grenvillian rocks that is similar to units in western Newfoundland. The Aspy Terrane is characterized by mid-Paleozoic granitic rocks and high-pressure paragneisses and appears to continue across the Cabot Strait as the Gander Terrane of the Hermitage Flexure in Newfoundland. The Bras d'Or Terrane is composed of Hadrynian to Early Cambrian low-pressure metasedimentary units and dioritic to granitic plutonic rocks. As indicated by aeromagnetic anomalies, this terrane continues across the Laurentian Channel to the south coast of Newfoundland, where it may be terminated by the Hermitage Fault. The Avalon Terrane of southeastern Cape Breton Island bears many similarities to the Avalon Terrane of Newfoundland.A seismic reflection profile obtained as part of the Lithoprobe-East project shows that the Blair River Complex is juxtaposed against the Aspy Terrane by steeply dipping fault systems that cut through the entire crust and that the Bras d'Or Terrane is similarly juxtaposed with the Avalon Terrane. The nature of the boundary between the Aspy and Bras d'Or terranes is less clear, although metamorphic conditions and the seismic reflection profile both suggest that the Aspy Terrane represents a deeper crustal level, over which the Bras d'Or Terrane has been emplaced.
Out-of-sequence thrust faulting and duplex formation in the Lewis thrust system, Spot Mountain, southeastern Glacier National Park, Montana
Authors: Hudec Michael R. , Davis Gregory A.
Published: April 2011

In southeastern Glacier National Park the Lewis thrust is discordant to structures in its hanging wall, strongly suggesting that it formed out of sequence. Faults that are truncated downward against the Lewis thrust are inferred to have originally soled into a structurally lower thrust fault, in which case displacement must have shifted out of sequence from this original fault (here named the Lewis I thrust) to the present-day, structurally higher surface (the Lewis II thrust) at some time during the evolution of the Lewis thrust system. Because of variations in the geometry of the Lewis thrust system along its 450 km strike length, it is likely that the formation of such out-of-sequence thrusts varied in time and in space. Consequently the present-day Lewis thrust may be a composite surface, composed of numerous segments that were not all active at the same time.Many of the fold and fault structures in the study area that are truncated downward agains the Lewis thrust lie within the Spot Mountain duplex, in the basal part of the Lewis allochthon. The Spot Mountain duplex is noteworthy in that both its roof thrust (the Spot Mountain fault) and its floor thrust (the Lewis thrust) formed out of sequence, after most of the structures within the duplex. The term "duplex" in this case has no genetic connotations but refers only to a geometry in which the highly deformed rocks constituting the base of the Lewis thrust plate are separated from less deformed rocks by an enveloping pair of thrust faults.
Geological and geophysical characteristics of the Tuzo Wilson Seamounts: implications for plate geometry in the vicinity of the Pacific – North America – Explorer triple junction
Authors: Carbotte S. M. , Dixon J. M. , Farrar E. , Davis E. E. , Riddihough R. P.
Published: April 2011

SeaMARC II imagery, SEABEAM bathymetry, seismic reflection profiles, and gravity and magnetic data are used to establish the tectonic significance of the Tuzo Wilson Seamounts, two submarine volcanic edifices located southwest of the southern end of the Queen Charlotte transform fault. SeaMARC II imagery reveals a parallel transform fault, an extension of the Revere–Dellwood Fault, bordering the southwest end of the Dell wood Knolls and terminating at the southwest end of the Tuzo Wilson Seamounts. This transform-fault system links spreading at the north end of Explorer Ridge to extension at the Tuzo Wilson Seamounts. An inactive continuation of this transform 50 km to the northwest of Tuzo Wilson Seamounts is inferred from seismic profiles. Between Dellwood Knolls and Tuzo Wilson Seamounts, this transform fault has offset Pleistocene (ca. 10 000 a) sea-bed features in a right-lateral sense by 250 m and has offset part of the Dellwood Knolls volcanic edifice by 6–8 km. Numerous normal faults at the Tuzo Wilson Seamounts and Dellwood Knolls are roughly orthogonal to the Queen Charlotte and Revere–Dellwood transforms and indicate rifting in an extensional jog between the transforms. Seismic profiles reveal sediments and basement back-tilted northwest and southeast away from the Tuzo Wilson Seamounts, also consistent with extension. Acoustic imagery indicates that the Tuzo Wilson Seamounts are surrounded by basalt flows that are largely free of sediment cover and thus postdate recent rapid sedimentation (< 10 000 a). In contrast, few of the flows around Dellwood Knolls are free of sediment. Basalts from the Tuzo Wilson Seamounts have high magnetizations (average 35 A/m) and are free of manganese encrustation. Tuzo Wilson Seamounts have a + 1000 nT magnetic anomaly, which can be modelled with normal, high-intensity (up to 40 A/m) magnetization and with geometry and depth matching the topography of the seamounts and surficial basalt flows. Their small, positive free-air gravity is largely accounted for by their topography; no appreciable local density contrast exists below the surrounding sea floor.The Tuzo Wilson Seamounts and Dellwood Knolls are separate sites of sea-floor spreading, although the partition of spreading between them is indeterminate. The 50 km inactive continuation of the Revere–Dellwood transform requires that a total of at least 100 km of sea floor has been created at the Tuzo Wilson and Dellwood spreading centres, probably within the last 2.5 Ma. The sea floor between the Tuzo Wilson Seamounts and Dellwood Knolls either is a separate microplate or is under going distributed strain. The triple junction of the Pacific, North America, and Explorer plates is not a discrete point; rather it occupies the strained and seismically active region between the northern Explorer Ridge and the Tuzo Wilson Seamounts.
Stratigraphy and structure of the Early Proterozoic Wilson Island Group, East Arm thrust-fold belt, N.W.T.
Authors: Johnson Bradford J.
Published: April 2011

Investigation of the stratigraphy and structure of the 1.9 Ga Wilson Island Group has led to sedimentological and tectonic interpretations that are consistent with models for an Early Proterozoic collision between the Slave and Rae provinces. The lower part of the 8 km thick Wilson Island Group consists of alluvial clastic rocks and a bimodal volcanic suite. These are overlain by mixed siliciclastic and carbonate rocks that are inferred as representing a combination of alluvial and shallow-marine sedimentation. Finally, an upward-fining succession of feldspathic sandstone, ironstone, and mudstone records progradation of an alluvial system followed by a major transgression. Soft-sediment deformation structures, intrabasinal coarse detritus, and abrupt vertical facies changes collectively indicate that the early stages of deposition were tectonically controlled.Regional penetrative foliations and a steeply plunging stretching lineation reflect deformation concomitant with greenschist-facies to lower amphibolite-facies metamorphism. Open to tight, plunging, northwesterly overturned folds formed synchronously with axial-plane cleavage in quartzites and deformed an older cleavage in pelites. These synmetamorphic structures were refolded by postmetamorphic kinks and dissected by transcurrent and normal faults.The Wilson Island Group evolved during postcollisional convergence, when thrusting and dextral transcurrent shearing characterized the regional tectonic style. However, the bimodal volcanic suite indicates a component of crustal extension that, in the regional context, favours a pull-apart-basin origin for the Wilson Island Group.
Evidence for the subglacial meltwater origin and late Quaternary lacustrine environment of Bateau Channel, eastern Lake Ontario
Authors: Gilbert Robert
Published: April 2011

Bateau Channel is the smallest and most northerly of the three outlets of Lake Ontario. Near its narrowest point (125 m at present water level) it is 60 m deep, making it one of the deepest places in eastern Lake Ontario. Evidence is presented to show that the trench formed as a result of high-velocity subglacial meltwater flow over a scarp at the boundary of the Precambrian Shield and Ordovician limestones to the southeast, and concentrated along a glacial or preglacial depression. Similar trenches occur across this boundary to the northwest. During flooding by Lake Iroquois, the trench was partially filled with glacilacustrine sediment. During the low-level phase of early Lake Ontario, the channel was abandoned and subaerially exposed. Calculations based on the slopes of the isostatic surface and of Bateau Channel suggest that it was reinundated about 7 ka BP and parts of the trench were exhumed to bedrock. Shell fragments 1.7 m below the sediment surface in a core recovered from marly sediment forming a shelf along the channel sides dated at 3440 ± 80 BP (TO-1587), indicating that deposition of this shelf occurred during recent rising water levels.
Conformable Late Jurassic (Oxfordian) to Early Cretaceous strata, northern Bowser Basin, British Columbia: a sedimentological and paleontological model
Authors: MacLeod S. E. , Hills L. V.
Published: April 2011

The upper Jackson unit in the northern Bowser Basin includes marine strata of Late Jurassic (middle Oxfordian to Tithonian) age on the basis of the presence of Vaugonia doroschini (Eichwald), Buchia concentrica (Sowerby), Buchia mosquensis (Von Buch), Buchia piochii (Gabb), and Buchia fischeriana (d'Orbigny). Herzogina Chavan and plant macrofossils in the overlying Currier Formation indicate an Early Cretaceous age. Macrofloras of the overlying McEvoy and Devils Claw formations are most similar to Early Cretaceous, pre-Albian floras of the Western Interior Basin of North America.A model of continuous sedimentation from the Jurassic to Early Cretaceous time is proposed, with a progression from marine conditions of the Jackson unit to marginal marine conditions, with lower delta plant deposition in the Currier Formation, to nonmarine fluvial conditions, with upper delta plain deposition in the McEvoy Formation. This stratigraphic sequence culminated in alluvial deposits of the Devils Claw Formation.The present evidence indicates uninterrupted deposition from the Jackson unit to the Devils Claw Formation.
The Cold Spring Melange and a possible model for Dunnage–Gander zone interaction in central Newfoundland
Authors: Williams Harold , Piasecki M. A. J.
Published: April 2011

Structural relationships at Cold Spring Pond and the recognition of ophiolitic melange bear on the important questions of timing and style of structural superpositioning of Dunnage Zone rocks above Gander Zone rocks in central Newfoundland. The latest models emphasize ductile shear boundaries and orogen-parallel movements. Previous models proposed west-to-east or head-on obduction of Dunnage ophiolitic rocks across the Gander Zone.At the Dunnage (Exploits Subzone) – Gander (Meelpaeg Subzone) boundary at Cold Spring Pond, discrete, outcrop-size ultramafic blocks and smaller quartzite blocks are randomly distributed, and they are surrounded by, or are embedded in, homogeneous black graphitic shale or phyllite. The ultramafic blocks are typical of nearby Early Ordovician Dunnage ophiolite suites, the quartzite blocks are typical of adjacent Early Ordovician or earlier Gander clastic rocks, and the matrix black shales are similar to those of Middle or Early Ordovician age that occur throughout central Newfoundland. This chaotic mixture of almost coeval lithologies at Cold Spring Pond is interpreted as an olistostromal melange; the Cold Spring Melange. It resembles melanges that are dated as Ordovician elsewhere in Newfoundland.The Cold Spring Melange is overprinted by the full range of structures and metamorphic effects evident in adjacent rocks of the Exploits (Dunnage) and Meelpaeg (Gander) subzones. These include the development of lineations, cleavages, schistosities, zones of ductile shearing, regional metamorphism, and contact metamorphism. The oldest of these effects are interpreted as Silurian, based on isotopic dating in southern Newfoundland.The formation of olistostromal, ophiolitic melange implies disruption of the oceanic tract (Exploits Subzone of the Dunnage Zone), and in the case of the Cold Spring example, juxtapositioning or transport of Exploits Subzone ophiolite suites against or across the supracrustal rocks of the Meelpaeg Subzone (Gander Zone). The age and provenance of Cold Spring components, lack of post-Ordovician components, overprinting structural relationships, and comparison with other Newfoundland melanges all support an Ordovician age of formation. Overprinting relationships indicate that major ductile shears at other Dunnage–Gander zone boundaries postdate initial Dunnage–Gander superpositioning.
Silurian tabulate coral biostratigraphy and biofacies of northern New Brunswick and the southern Gaspé Peninsula
Authors: Young Graham A. , Noble James P. A.
Published: April 2011

Diverse Early and Late Silurian tabulate coral faunas occur in the Baie des Chaleurs region. Analysis of relative abundance data of tabulate corals from the Limestone Point and La Vieille formations of northern New Brunswick and the Anse à Pierre-Loiselle, La Vieille, and Gascons formations of the southern Gaspé Peninsula allowed the recognition of three recurrent large-scale biofacies: the Propora–Heliolites, Cystihalysites, and Syringopora biofacies. The Syringopora Biofacies lacks the characteristics that would allow a zonation to be produced, but in each of the other biofacies, two zones are erected. These can be applied throughout the Baie des Chaleurs region and may be used for correlation with other areas having faunal affinities with this region.
Contrasting U–Pb ages from plutons in the Bras d'Or and Mira terranes of Cape Breton Island, Nova Scotia
Authors: Barr S. M. , Dunning G. R. , Raeside R. P. , Jamieson R. A.
Published: April 2011

U–Pb dates from zircon, titanite, and monazite in plutons of the Bras d'Or and Mira terranes of southern Cape Breton Island, combined with 40Ar/39Ar and other radiometric age data, indicate that the Bras d'Or and Mira terranes had separate magmatic and metamorphic histories until at least the Middle Cambrian and possibly until the Devonian. The Bras d'Or Terrane is characterized by abundant late Precambrian (ca. 565–555 Ma) dioritic to granitic plutons, as exemplified by the Shunacadie granodiorite ([Formula: see text], U–Pb zircon). Early Ordovician granitic plutons, such as the Kellys Mountain leucogranite with a U–Pb (zircon) age of 498 ± 2 Ma, occur locally. Titanite and 40Ar/39Ar (hornblende) ages from plutons and metamorphic units suggest that widespread metamorphism may have occurred between these plutonic events and (or) during the Early Ordovician plutonism.Plutons in the Mira Terrane appear to have been emplaced at about 620 Ma or before, as exemplified by the Chisholm Brook granodiorite ([Formula: see text]), and to have been unaffected by younger thermal events, as indicated by close similarity of U–Pb (zircon and titanite) and 40Ar/39Ar (hornblende) ages. Plutons of Devonian age are localized in an easterly trending belt in the central part of the terrane. In contrast to the Bras d'Or Terrane, widespread latest Precambrian (ca. 565–555 Ma) to Early Ordovician plutonism and metamorphism appear to have been absent. It is unlikely that the Mira and Bras d'Or terranes were juxtaposed before the Early Ordovician.
Rock avalanches at Texas Creek, British Columbia
Authors: Ryder J. M. , Bovis M. J. , Church M.
Published: April 2011

At least two rock avalanches have occurred during Holocene time at the confluence of Texas Creek and Fraser River, about 300 km upstream from Vancouver. The morphological features of the avalanche debris are well preserved, and its stratigraphic relations are well exposed. Failures occurred in fractured argillites adjacent to a small pluton at a site where a steep slope is maintained as a result of undercutting by Fraser River. The first and largest (45 × 106 m3) avalanche occurred during middle to late Holocene time. Debris infilled the postglacial gorges of the streams and spread across a partly dissected alluvial fan. An anomalous ridge on the avalanche deposit reflects the influence of a buried scarp on debris motion and failure in underlying Pleistocene silts. A sharp contact between debris of differing lithologies suggests that the avalanche moved as a coherent mass. A second, smaller (about 7.2 × 106 m3) avalanche occurred about 120014C years ago.Archaeological and geological evidence from sites upstream suggests that the second avalanche impounded Fraser River, causing backwater sedimentation at Lillooet and blocking the migration of salmon. Another avalanche could occur at this site, with similar effects; sudden failure of the landslide dam could generate a catastrophic flood downstream.
Water-level fluctuations in Lake Ontario over the last 4000 years as recorded in the Cataraqui River lagoon, Kingston, Ontario
Authors: Dalrymple Robert W. , Carey John S.
Published: April 2011

The modern sediments in the Cataraqui River lagoon and marsh (Kingston, Ontario) consist of mixtures of organic material and clayey silts, the organic content of which increases as water depth decreases; gyttjas are accumulating in the deeper water parts of the lagoon, whereas peat is the dominant sediment in the very shallow water portion of the lagoon (< 0.7 m) and in the adjacent marsh. Cores show that one partial (modern) and two complete depositional cycles (gyttja passing upwards into peat) have formed within the last 4000 years. The contact between cycles (gyttja over peat) is abrupt. These cycles are interpreted as resulting from fluctuations in the level of Lake Ontario about the long-term rising trend. Radiocarbon dates show that relatively low levels prevailed from 4100 to 3300 BP and from 2300 to 1900 BP; rapid rises in water level, which are indicated by the abrupt contact between cycles, occurred at 3300–3100 BP and some time between 2000 and 1500 BP. These water-level changes are synchronous with those shown by other studies in Lake Ontario and with century-scale paleoclimatic events. The high stands correlate with wet periods, and perhaps also with warm periods in the eastern part of the Great Lakes basin, but an inverse relationship between precipitation and temperature in the western Great Lakes suggests that the Great Lakes basin does not respond uniformly to climatic changes.
Aeolian sandstones in the Copper Harbor Formation, Late Proterozoic, Lake Superior basin
Authors: Taylor Ian E. , Middleton Gerard V.
Published: April 2011

Sandstones with cross-sets up to 1.5 m thick occur within the Copper Harbor Formation, most prominently at Five Mile Point. In contrast to intercalated sandstones with smaller scale cross-stratification or horizontal lamination, pebbles are very scarce in the large-scale cross-stratified sandstones and, where present, are restricted to set bases. The large-scale cross-stratified sandstones are better sorted than intercalated sandstones and show a mean palaeocurrent direction at 90° to the mean for the interbedded sandstones.The large-scale cross-stratified sandstones are interpreted as the product of fields of small transverse aeolian dunes that formed on dry parts of alluvial fans bordering the Keweenawan rift. The aeolian palaeocurrent mean is along the rift valley, and tentatively may be interpreted as the result of topographically constrained palaeo-tradewinds.
Geology and tectonic development of the Bras d'Or suspect terrane, Cape Breton Island, Nova Scotia
Authors: Raeside Robert P. , Barr Sandra M.
Published: April 2011

The Bras d'Or Terrane is defined in Cape Breton Island and consists of four distinctive components, (i) Low-pressure, regionally metamorphosed aluminous and calcareous gneiss of the Proterozoic Bras d'Or metamorphic suite is restricted to the southeastern part of the terrane. (ii) Late Proterozoic clastic-volcanic-carbonate units (Blues Brook, Malagawatch, McMillan Flowage, and Benacadie Brook formations, and Barachois River and Bateman Brook metamorphic suites) occur throughout the terrane and are generally at low metamorphic grades, although sillimanite grade has locally been achieved, (iii) A suite of 555–565 Ma calc-alkalic dioritic to granitic plutons was emplaced at pressures ranging from about 900 to less than 100 MPa. (iv) Early Ordovician granitic plutonism and Ordovician 40Ar/39Ar ages record regional heating.The Bras d'Or Terrane docked with the Mira Terrane to the southeast no earlier than the Ordovician. Cambro-Ordovician sedimentary rocks of the Mira Terrane appear locally to be thrust over the Bras d'Or Terrane. Mississippian sedimentary rocks overlap both terranes. The present boundary, the Macintosh Brook Fault, is mainly a Carboniferous feature. Docking with the Aspy Terrane to the northwest occurred along the Eastern Highlands shear zone and is constrained by a 375 Ma stitching pluton, the Black Brook Granitic Suite. Docking may have been initiated as early as 415 Ma, as indicated by reset 40Ar/39Ar ages near the boundary. The three Proterozoic components of the Bras d'Or Terrane have been recognized in the Brookville Terrane of southern New Brunswick, and Late Proterozoic gneiss, Late Proterozoic – early Cambrian calc-alkalic plutons and Ordovician granitic plutons have been reported in parts of the Hermitage Flexure of southern Newfoundland. The Bras d'Or Terrane may therefore be a regionally significant component of the northern Appalachian Orogen.
A reconstruction of Holocene geomorphology and climate, western Cypress Hills, Alberta and Saskatchewan
Authors: Sauchyn David J.
Published: April 2011

The Cypress Hills of southwestern Saskatchewan and southeastern Alberta are a key area for Quaternary research because the permanent lakes and coniferous forest are sources of proxy paleoenvironmental data generally not available on the surrounding northern Great Plains. In this paper, the Holocene paleoclimate of the western Cypress Hills is reconstructed from the pollen and organic matter contents of a 9.6 m sediment core from Harris Lake, Saskatchewan. This climatic history is considerably longer than others from the semiarid Interior Plains of Canada. Chronological control consists of a basal conventional radiocarbon date of 9120 ± 250 BP, Mazama tephra, and three accelerator mass spectrometry dates from plant macrofossils. The data from Harris Lake indicate significant climatic change from the warm, dry altithermal, 7700–5100 BP, to cooler and moister conditions of the late Holocene. Low lake sediment organic matter from 3000 to 2400 BP is attributed to lower temperatures and coincides with a well-documented global neoglacial advance. Correlations among the proposed climatic history, sedimentation rates in Harris Lake, and dated soils and sediments described in the literature are the basis for a reconstruction of the Holocene geomorphology. This information suggests a transition in dominant geomorphic processes from fluvial and aeolian erosion before 5100 BP to rotational landsliding after 4500 BP.
Contrasts in the response to dextral transpression across the Quetico–Wawa subprovince boundary in northeastern Minnesota
Authors: Bauer Robert L. , Bidwell Matthew E.
Published: April 2011

Folds and shear zones in the central and western Vermilion district greenstone belt (Wawa Subprovince) are consistent with deformation in a regime of regional dextral transpression. However, the shear strain associated with this deformation regime is only locally evident in the schist and migmatite of the adjacent southeastern Vermilion Granitic Complex (VGC) (Quetico Subprovince). We suggest that differential partitioning of shear and flattening strains between the two terranes was controlled by the lower ductility, higher competency contrast, and steeper dip of orogen-parallel rock units in the Vermilion district compared with the variably oriented rocks in the adjacent VGC. Contact strains adjacent to plutonic bodies played a greater role in the development of complex fold geometries in the VGC.In the central Vermilion district, northwest-directed subhorizontal shortening produced easterly striking zones of brittle-ductile dextral shear and northeast-trending en echelon folds. The en echelon folds with curvilinear axial traces formed in the greenstone and local iron formation layers. These units were steepened during folding and early stages of deformation and acted as rigid competent units during subsequent shearing. The shear zones were concentrated in units of tuff and graywacke between the more rigid, steeply dipping greenstone units.In the adjacent southeastern VGC, the same regional stress regime resulted primarily in folding with only rare indications of ductile dextral shear. The transpression event produced westerly trending F2 folds along the southern margin of the VGC. However, the F2 folds have more varied orientations along the margins of syntectonic to late-tectonic granitic plutons and were locally refolded by easterly trending F3 folds during continued northwest-directed shortening.
Trace-element and Nd isotopic variations in Early Proterozoic dyke swarms emplaced in the vicinity of the Kapuskasing structural zone: enriched mantle or assimilation and fractional crystallization (AFC) process?
Authors: Boily M. , Ludden J. N.
Published: April 2011

Several Early Proterozoic Hearst–Matachewan (2.454 Ga), Kapuskasing (2.14 Ga), and Preissac (2.04 Ga) dykes were emplaced within the Archean crust surrounding the Kapuskasing structural zone (KSZ). The dykes are composed of moderately to highly fractionated tholeiitic basalts (Mg number = 24–55) that exhibit trace-element characteristics similar to those of intraplate basaltic magmas or ocean–island basalts (e.g., Zr/Nb = 6–21, Zr/Y = 2–5, high TiO2 = 0.9–3.2 wt.%, and (Fe2O3)t = 12.4–18.7 wt.%). Their initial Nd isotopic compositions display a range of depleted [Formula: see text] to enriched [Formula: see text] values that are negatively correlated with the degree of light rare-earth element enrichment. We evaluate two models for the origin of these dykes: (i) The basaltic parental magmas were derived from two distinct sources, an isotopically depleted asthenospheric mantle (εNd = +4 and La/Sm = 2.7) and an isotopically enriched lithospheric(?) mantle (εNd = −4 to−8 and La/Sm = 5.1). The magmas subsequently underwent mixing and fractionation during ascent in the mantle or the lower crust. (ii) The parental magmas originated from a homogeneous Nd isotopically depleted asthenospheric mantle but later assimilated a substantial amount of Archean crustal material upon fractionation and ascent in the lower crust. Results derived for the latter model preclude any participation of the exposed crustal rocks in the KSZ, and the assimilation and fractional crystallization (AFC) model remains a viable hypothesis only if the parental magmas assimilated an older and perhaps more isotopically enriched crust than that represented in the KSZ.
Dinosaur footprints with skin impressions from the Cretaceous of Alberta and Colorado
Authors: Currie Philip J. , Nadon Gregory C. , Lockley Martin G.
Published: April 2011

Cretaceous dinosaur footprints discovered in the J Sandstone of the South Platte Formation (Dakota Group) in Colorado and the St. Mary River Formation of southwestern Alberta exhibit the first reported foot pad skin impressions of large ornithopods. The Canadian tracks occur as sandstone casts preserved in mudstones, whereas the Colorado tracks are natural impressions in a sandstone bed overlain by shale. The South Platte Formation tracks occur as impressions in a widespread "dinoturbated" sandstone bed representing low-gradient, delta plain – coastal plain facies assemblages associated with the upper member of the group, the J Sandstone. Only one of the many iguanodontid trackways exhibits good skin impressions.The St. Mary River Formation palaeoenvironment is interpreted as an anastomosed fluvial system that flowed northeast over a low-gradient floodplain from Montana. Footprints, often preserved in trackways, were left as dinosaurs walked across lake and marsh sediments that were relatively well drained or in various stages of dewatering. The quality of preservation is variable, depending on the properties of the substrate, and only one hadrosaur footprint includes clear casts of skin patches on the bottom of the footprint. Similar track-rich facies assemblages, representing lowland coastal plain and deltaic environments, are found in both the Lower (Gething Formation, British Columbia) and Upper Cretaceous (Mesa Verde, Colorado) successions of western North America. Few substrates of these depositional environments were suitable for the preservation of skeletal remains, so the information derived from tracks is palaeontologically significant.
Nouvelles observations sur l'environnement sédimentaire de la Formation d'Escuminac (Dévonien supérieur, Frasnien), Québec, Canada
Authors: Vézina Daniel
Published: April 2011

The comparison of certain genera representative of the ichthyofauna of the Escuminac Formation (Quebec, Canada) with those coming from contemporaneous deposits (Upper Devonian, Frasnian) located in the Baltic countries (U.S.S.R.), Western Australia, Nevada (U.S.A.), and Germany provides new evidence against a lacustrine origin of the Escuminac Formation. It is suggested that the Escuminac Formation was deposited in a coastal marine environment. This hypothesis is supported by results of a geochemical study.
Evidence from thermoluminescence dating for Middle Wisconsinan deglaciation in the Hudson Bay Lowland of Manitoba
Authors: Berger Glenn W. , Nielsen E.
Published: April 2011

We report here the first direct dating of the nonglacial, intertill Nelson River sediments from five sites in northern Manitoba. We used the thermoluminescence (TL) sediment-dating technique to obtain age estimates of 32–46 ka for four samples and 119 ka for the fifth, all samples previously correlated to the Sangamonian Stage (80–130 ka) Missinaibi Formation. We interpret the younger TL dates as being within 20–40% of the true deposition ages, but interpret the oldest TL date as an overestimate because of ineffective zeroing of the light-sensitive TL associated with observed pebble and sand detritus in that sample. Thus these younger direct dates imply a significant climatic warming and deglaciation in the heart of the Laurentide Ice Sheet area during Middle Wisconsinan time.
Two stages of CO2 metasomatism at the Munro mine, Munro Township, Ontario: evidence from fluid-inclusion, stable-isotope, and mineralogical studies
Authors: Schandl Eva S. , Wicks Frederick J.
Published: April 2011

The Munro asbestos mine is hosted by a differentiated ultramafic sill of Archean age. Localized carbonate alteration at the mine has resulted from two separate episodes of CO2 metasomatism, and the fluids were unrelated. The first episode affected only the serpentinized peridotite and occurred at 250 °C. The fluid was a saline brine (up to 24 wt.% NaCl–CaCl2), and had an oxygen isotopic composition of −3‰, and δ13C was equal to −7.8‰. Calcite veins were emplaced into the overlying, fractured pyroxenite at approximately 300–400 °C during the second episode. The salinity of this fluid was only 1–5 equiv. wt.% NaCl, the oxygen isotopic composition was +7.5‰, and δ13C equaled −3 to −5‰. The first episode was probably associated with burial metamorphism (diagenesis) and the second episode with regional metamorphism. The widespread occurrence of two separate stages of CO2 metasomatism in the Abitibi belt and in other well-documented Archean terranes, such as the Norseman–Wiluna greenstone belt in Western Australia, suggests that this may be an important factor in the tectonic evolution and metamorphic history of Archean greensone belts.
Implications of U–Pb and K–Ar geochronology for petrogenesis and cooling history of the McGerrigle Mountains plutonic complex, Gaspé, Quebec
Authors: Whalen J. B. , Mortensen J. K. , Roddick J. C.
Published: April 2011

The high-level McGerrigle Mountains plutonic complex consists of a compositionally diverse (gabbro to granite) hybrid suite at its northern end and a relatively homogeneous granite suite in its southern half. Field and geochemical evidence support formation by hybridization between at least three end-member magmas. New U–Pb zircon and titanite ages from these end members indicate that intrusion of all components took place at 391.3 ± 3.4 Ma. Eighteen new K–Ar mineral ages, which cover the range 370–390 Ma, suggest that the granite suite cooled quickly to < 500 °C in less than 2 Ma, whereas temperatures between 600 and 500 °C may have been maintained over an extended period (5–15 Ma) within the hybrid suite. The long-lived thermal anomaly associated with the hybrid suite may explain the large epimetamorphic (< 300 °C) halo surrounding this suite and the existence of hydrothermal mineralization (Madelaine (Cu) and Candego (Pb–Zn–Ag) deposits) adjacent to it.
Origin of complex upper mantle structures in the southern Lewis Hills (Bay of Islands Ophiolite, Newfoundland)
Authors: Suhr Günter , Calon Tom , Dunsworth Sherry M.
Published: April 2011

The Springers Hill area (Lewis Hills, Bay of Islands Ophiolite) may represent oceanic lithosphere created in close proximity to the nontransform segment of an oceanic fracture zone. Upper mantle rocks exposed on Springers Hill were investigated to establish whether their development was affected by the thermal and rheological changes associated with oceanic fracture zones. Harzburgites of the Springers Hill area reveal complex structural patterns. On a small scale, foliations defined by orthopyroxene grains intersect foliations defined by spinel grains at various angles. Olivine petrofabric work demonstrates that only the spinel foliation is related to the preserved flow plane. The orthopyroxene foliation appears to be the result of pull-apart of formerly larger grains during high-temperature deformation. On the larger scale, orientation patterns of foliation, lineation, and dykes suggest that strike-slip movement occurred parallel and at high angle to the fracture- zone contact at various stages of a complex flow history. Given its location adjacent to a nontransform segment of oceanic lithosphere, the origin of the strike-slip movement parallel to the fracture zone must be clarified. It can be accounted for by movement of the older lithosphere past asthenosphere of the young spreading ridge during plate-driven flow.
Stratigraphic position and conodonts of the early Middle Ordovician Melbourne Formation, Quebec
Authors: Marquis Robert , Nowlan Godfrey S.
Published: April 2011

A new fossil locality yielding rare conodonts of probable late Arenig to early Llanvirn age in the previously unfossiliferous Melbourne Formation of the Appalachian Humber Zone has been discovered in the Eastern Townships of Quebec. The presence of a continental-margin fauna at the northeast end of the Sutton Mountains Anticlinorium suggests a continuity of sedimentation, and this contradicts previous suggestions of a major disconformity between the Lower and Middle Ordovician rocks in this part of the Quebec Reentrant. Moreover, recent geological mapping shows that the contact between the conodont-bearing Melbourne Formation and the underlying Sweetsburg Formation of the Oak Hill Group is conformable and gradational. Consequently, it is proposed that the graphitic limestone of the Melbourne Formation represents the youngest unit of the Cambro-Ordovician Oak Hill Group.