bluuebunny/crossref_metadata_2025 huggingface dataset:
Contribution of icing ablation to streamflow in a discontinuous permafrost area
Authors: Reedyk Sharon , Woo Ming-Ko , Prowse Terry D.
Published: April 2011

Icings, present in many small streams in the discontinuous permafrost environment, alter the seasonal water balance by redistributing a component of flow from the winter to the spring. Icing ablation continues to contribute to streamflow after the disappearance of the snowpack and constitutes an additional source of runoff. The temporal variability and significance of icing ablation to streamflow were examined with a combined water balance and isotope study in a tributary of Manners Creek, Northwest Territories. Icing accounted for 20% of the surface water available for melt. Over the spring study period, icing ablation accounted for 6% of total streamflow, while the total surface-water flux provided 8%. Shallow subsurface flow, which consisted of infiltrated snow meltwater and premelt groundwater, contributed the most to streamflow. At the end of the melt period, icing ablation was the only source of surface runoff to the stream and was similar in magnitude to the estimated evapotranspiration loss. Comparison with other studies revealed that on a regional scale, the hydrologic role of icing ablation is controlled by the interaction between the timing of melt, the magnitude of groundwater recharge, the spatial extent of permafrost, and the depth of seasonal frost.
Seismic reflection profiles across the "Mine Series" in the Noranda camp of the Abitibi belt, eastern Canada
Authors: Verpaelst Pierre , Péloquin A. Shirley , Adam Erick , Barnes Arthur E. , Ludden John N. , Dion Denis-Jacques , Hubert Claude , Milkereit Bernd , Labrie Michel
Published: April 2011

The Abitibi–Grenville Lithoprobe project completed a regional (line 21) and a high-resolution (line 21-1) seismic survey in the Noranda Central Volcanic Complex of the Blake River Group, Abitibi, Quebec. Line 21 provides a regional framework in which the Archean crust is divided into three layers, two of which are discussed here: the uppermost layer, which corresponds to the Blake River Group, is the least reflective, and lies above 4 s (12 km), and the mid-crustal layer, which is composed of a complex pattern of generally east-northeast-dipping reflectors and lies between 4 and 8 s. Within the regional data, the Mine Series of the Central Volcanic Complex is imaged as a semitransparent series of reflectors overlying a highly reflective east-facing structure interpreted as the subvolcanic Flavrian pluton. The high-resolution data (line 21-1) were collected in the vicinity of the Ansil mine. The seismic images in this region can be controlled by surface geology and extensive drill-hole data, and the project was designed to test the applicability of seismic reflection profiling in providing structural and stratigraphic information for use in mineral exploration: shallow-dipping reflectors correlate well with lithological variations or contacts in the volcanic sequence; strong subhorizontal reflectors correspond to diorite and gabbro dykes and sills; several abrupt lateral changes in the reflectivity coincide with known intrusive contacts such as the Lac Dufault pluton.
The geochemistry and geochronology of the gneisses and pegmatites of the Tollie antiform in the Lewisian complex of northwestern Scotland
Authors: Holland J. G. , Lambert R. StJ.
Published: April 2011

The Tollie antiform occupies a tectonic break between an area to the north, where remnants of Archaean structures are preserved, and an area to the south, characterized by substantial Proterozoic reworking. The antiform produced in this tectonic boundary is a multistage structure containing three components Creag Mhor Thollaidh in the north, faulted against a central zone, which passes southwards into the highly sheared and attenuated Buanichean gneisses of the southwestern limb. The compositions of gneisses in the antiform assign them unambiguously to the Archaean gneisses of the Gruinard and Lochinver areas to the north. Gneisses of this extensive area were brought together within the narrow confines of the Tollie antiform. As the antiform evolved, the Buanichean gneisses acted as an anatectic source to a set of shear-refined potash-rich pegmatites, which penetrated north into the central zone of the developing antiformal structure. In this central zone, some of the pegmatites were deformed into open folds, whereas others were unmodified. The pegmatites thus form a point of reference within the evolution of the Tollie antiform. Rb–Sr isotopic data on the pegmatites give an age for their intrusion and crystallization of 1660 Ma. Downward shear of the southwestern limb of the antiform continued until about 1500 Ma. By the time this episode of structural restyling in the Lewisian had been completed, a deep-rooted wedge of Proterozoic cover sediments had become encased in an Archaean basement.
Metamorphic discontinuities in the Pennsylvania – Delaware Piedmont: evidence for early Paleozoic assembly
Authors: Alcock J. , Wagner Mary Emma
Published: April 2011

Interpretation of the early Paleozoic tectonic history of the Appalachian Piedmont is commonly complicated by post-Taconian deformation that has disrupted and obscured early Paleozoic structure. Blocks that lie between zones where later deformation has been concentrated, however, may preserve evidence of Taconian high-grade metamorphism. In these cases, analysis of metamorphism allows an interpretation of the early Paleozoic tectonic history of the block and its surrounding region. A block of this type in the Pennsylvania–Delaware Piedmont includes three tectonic units: (1) the basement-cored massifs of southeastern Pennsylvania with Grenvillian gneiss unconformably overlain by the Setters Formation and Cockeysville Marble; (2) the Wilmington Complex arc terrane; and (3) the Wissahickon Group and associated metaigneous rocks. A metamorphic gradient and inferred temperature inversion within the Wissahickon Group and a metamorphic discontinuity at the Wissahickon Group–Cockeysville Marble contact are used to establish that the Wilmington Complex was first joined with the Wissahickon Group and that the two units were then emplaced together onto the rocks now exposed in the massifs. An observed correlation of amphibolite-facies mineral assemblages in the Cockeysville Marble with their distance from the Wissahickon Group indicates that peak metamorphism of the marble occurred after the metapelites were emplaced. As amphibolite-facies metamorphism of the basement-cored massifs has been previously dated as Taconian, it follows that the assembly of these tectonic units occurred in the early Paleozoic.
Transition from oceanic to continental crustal structure: seismic and gravity models at the Queen Charlotte transform margin
Authors: Spence G. D. , Long D. T.
Published: April 2011

Seismic refraction data have been interpreted along a line crossing the Queen Charlotte transform, just north of the triple junction where the Explorer Ridge intersects the continental margin. These data, observed at three onshore sites, help to define the structure of the continental crust beneath the Queen Charlotte sedimentary basin. Sediment thicknesses of up to 4 km were determined from a coincident multichannel reflection line. Beneath the sediments, velocities increase from about 5.5 to 6.3 km·s−1 at 8 km depth, then increase from 6.5 to 6.7 km·s−1 at 18 km depth. Below this depth, the lower crust is partly constrained by Moho wide-angle reflections at the three receiving sites, which indicate a lower crust velocity of 6.8–6.9 km·s−1 and a Moho depth of 26–28 km. The crustal velocity structure is generally similar to that in southern Queen Charlotte Sound. It is in contrast to the velocity structure across Hecate Strait to the north, where a prominent mid-crust interface at ~15 km depth was observed. Seismic velocity models of the continental crust provide constraints that can be used in modelling gravity data to extend structures across the ocean–continent boundary. Along the profile just north of the Queen Charlotte triple junction, the gravity "edge effect" is very subdued, with maximum anomalies of < mGal (1 mGal = 10−3 cm·s−2). To satisfy the gravity data along this profile, the modelled crustal thickness must decrease to oceanic values (5–6 km) over a horizontal distance of 75 (±10) km, which gives a Moho dip of about 14°. Farther north, refraction models across Hecate Strait provide similar constraints for gravity modelling; the gravity data indicate horizontal transition distances from thick to thin crust of 45 (±10) km, comparable with, but slightly smaller than, those nearer the triple junction, and Moho dips at an angle of 18–22°. The greater thinning near the triple junction is consistent with mass flux models in which ductile flow in the lithosphere is induced by the relative motion between oceanic and continental plates.
The Sisters Creek Formation: Pleistocene sediments representing a nonglacial interval in southwestern British Columbia at about 18 ka
Authors: Hicock Stephen R. , Lian Olav B.
Published: April 2011

Sisters Creek Formation is formally defined, stratotypes are established for it, and the time–space chart is updated for the Fraser Lowland, southwestern British Columbia. The Sisters Creek is a Pleistocene formation comprising in situ and reworked organic-rich sediments, and nonorganic silt, sand, and gravel. The formation was deposited during the Port Moody interstade (within the Late Wisconsinan Fraser Glaciation; δ18O stage 2) between the Coquitlam stade (early Fraser Glaciation) and the main Vashon stadial maximum that occurred about 14.5 ka. The Sisters Creek Formation represents a glacial recession in southwestern British Columbia that generally coincided with the timing of the last global glacial maximum. The new time–space chart implies that, in Fraser Lowland, the Fraser Glaciation represents the rapid advances and retreats of glacial lobes issuing from surrounding mountains, which remained ice-covered during interstades.
Silurian orogenesis in the western Penobscot Bay region, Maine
Authors: West Jr David P. , Guidotti Charles V. , Lux Daniel R.
Published: April 2011

New 40Ar/39Ar mineral ages from rocks collected west of Penobscot Bay, Maine, indicate this region was regionally deformed, metamorphosed to amphibolite facies conditions, and intruded by plutons in Silurian times rather than in the Devonian as previously assumed. Disturbed hornblende age spectra, along with the presence of some Devonian felsic plutons and extensive retrograde metamorphic textures do suggest, however, that these rocks were subsequently affected by low-grade Devonian thermal events. In sharp contrast, rocks west of the Sennebec Pond thrust fault, a major tectono-stratigraphic boundary in this region, lack a significant Silurian tectono-thermal signature, and instead record the effects of intense Devonian deformation and high-grade regional metamorphism. The data suggest the two regions experienced very different pre-Devonian histories and were most likely juxtaposed by the Sennebec Pond thrust fault in latest Silurian to Early Devonian time. Rocks now exposed east of the Sennebec Pond fault probably occupied much higher structural levels during Devonian orogenesis and were not subjected to the same intense Devonian deformation and metamorphism as those rocks now found to the west of this structure. The Silurian tectonism now recognized in this region bears striking resemblance to events of similar age recorded along the northwest margin of the Avalon composite terrane throughout much of Atlantic Canada. This greatly extends the zone of Silurian orogenesis in the northern Appalachians and requires that previous models of New England middle Paleozoic tectonism be significantly revised.
Magmatisme fissural triasico-liasique dans l'ouest du Massif armoricain (France): pétrologie, géochimie, âge, et modalités de la mise en place
Authors: Caroff Martial , Bellon Hervé , Chauris Louis , Carron Jean-Paul , Chevrier Stéphane , Gardinier Alain , Cotten Joseph , Moan Yann Le , Neidhart Yseult
Published: April 2011

The dolerite dykes at the western end of Britanny (France), which is located on the North Atlantic margin, were emplaced in a NW–SE field of faults at the Trias–Lias time limit, between 210 and 195 Ma. These rocks are quartz tholeiites enriched in TiO2, with a trace element composition close to that of the Deccan basalts. The initial concentrations of Ba, K, and Rb, though slightly modified by the alteration, and of Nb seem to have been affected by crustal contamination during the magma transfer. These dykes are comparable, in age and composition, to the tholeiitic dykes exposed in the Iberian Peninsula, in the Moroccan Atlas and in the Northern Appalachians; they however have a different orientation. Furthermore, these various domains differ in their postintrusion history: the rifting leading to the opening of the Central Atlantic occurred soon after the intrusions of the dykes, whereas the opening of the North Atlantic began several tens of millions of years later, following the direction of the Armorican array of dykes. The study of the mode of emplacement of the intrusions shows evidence of two sets of dykes: "simple dikes", 5 to 10 m thick, resulting from a single magmatic injection and "multiple dykes", about 30 m thick, composed of five magmatic units that are individually 5 to 10 m wide. The western Armorican dyke field is the result of the intrusion of successive sets of dolerite having a uniform thickness and composition, suggesting a cyclic magmatic supply from homogeneous source. [Journal Translation]
In situ silicification of an Icelandic hot spring microbial mat: implications for microfossil formation
Authors: Schultze-Lam S. , Ferris F. G. , Konhauser K. O. , Wiese R. G.
Published: April 2011

Transmission electron microscopy and energy-dispersive x-ray analysis revealed that filamentous phototrophic bacteria resembling Chloroflexus aurantiacus underwent rapid silicification in an Icelandic hot spring microbial mat. The mineralization associated with the cells occurred both extracellularly, within and on the external sheaths of the bacteria, and intracellularly, within the cytoplasm. The exceptional preservation of the bacterial sheaths is due to the presence of distinct mineral nucleation sites. This results in the production of silica casts of the bacteria, which bear a striking resemblance to microbial remains in ancient microfossil assemblages.
Structural evolution of a major fault zone: the Cape Ray Fault Zone, southwestern Newfoundland, Canada
Authors: Dubé Benoît , Lauzière Kathleen
Published: April 2011

The Cape Ray Fault Zone is a major Paleozoic structure in southwestern Newfoundland, and occurs at or close to the boundary between two major continental blocks, Laurentia and Avalonia. A detailed structural analysis demonstrates that the fault records early reverse-sinistral thrusting of the Grand Bay Complex at amphibolite grade (D2), followed by a protracted event (D3) characterized by reverse-dextral thrusting of the Grand Bay Complex rocks on top of the supracrustal rocks of the Windsor Point Group and retrogression to greenschist facies, as well as a pre-384 Ma orogen-parallel dextral transcurrent mylonite (D4) during the later stages of the collision. Regional-scale strain partitioning induced heterogeneity of strain both along and across the strike of the Cape Ray Fault Zone. The east–west-oriented segment of the Cape Ray Fault Zone is a tear fault that accommodated differential displacement along the length of the fault. Later stages of the deformation include post-384 Ma sinistral transcurrent reactivation of the dextral mylonite and extension. The reverse-sinistral thrusting and the reverse-dextral motion occurred between 415 and 386 Ma and correspond to the two-phase Acadian orogeny recognized at the scale of the orogen and believed to be related to collision between Laurentia and Avalonia. The Cape Ray Fault Zone preserves evidence of large-scale geodynamic processes affecting rocks where the kinematics and the timing are well constrained.
Sulphur isotope composition of the Brunswick No. 12 massive sulphide deposit, Bathurst Mining Camp, New Brunswick: implications for ambient environment, sulphur source, and ore genesis
Authors: Goodfellow Wayne D. , Peter Jan M.
Published: April 2011

The Brunswick No. 12 massive sulphide deposit occurs within a Middle Ordovician bimodal volcanic and sedimentary sequence that is thought to have formed in a continental back-arc rift covered with a thick succession of carbonaceous hemipelagic and turbiditic sedimentary rocks. The deposit consists of three en echelon lenses that are zoned from Vent Complex to Bedded Ore and Bedded pyrite facies. The Bedded Ore facies has the lowest average δ34S values (14.2[Formula: see text]), but are only slightly less positive than laminated pyrite in footwall sedimentary rocks (δ34Smean = 15.1[Formula: see text]). δ34S values for the bedded sulphides show an upward increase from 14.2[Formula: see text] in Bedded Ore to 16.5[Formula: see text] in Bedded Pyrite. Average δ34S values for Vent Complex (15.8[Formula: see text]) and underlying stringer sulphides (16.1[Formula: see text]) are consistently more positive than those for Bedded Ore. In carbonaceous shales and siltstone of the Patrick Brook Formation that underlie the deposit, δ34S values that range between 13.8 and 25.6[Formula: see text], and the similarity of these values to those of the Brunswick No. 12 deposit indicate major bacterial reduction of sulphate to sulphide under closed or partly closed conditions, and that most of the S in the deposit originated from ambient sulphidic bottom waters. Furthermore, the average δ34S value for Brunswick No. 12 bedded ores lies on the Selwyn Basin pyrite evolutionary curve and indicates that anoxic conditions within the Tetagouche back-arc basin reflect a global anoxic episode. The Brunswick No. 12 deposit probably formed, therefore, by the mixing of hydrothermal metals with dissolved sulphide of seawater origin during periods of ocean anoxia. The increase of δ34S values towards the Vent Complex may reflect the addition of isotopically heavy S formed by the inorganic reduction of seawater sulphate.
A new species of Zangerlia (Testudines: Nanhsiungchelyidae) from the Upper Cretaceous redbeds at Bayan Mandahu, Inner Mongolia, and the relationships of the genus
Authors: Brinkman Donald , Peng Jiang-Hua
Published: April 2011

Zangerlia neimongolensis sp.nov. is described on the basis of material from the Upper Cretaceous redbeds at Bayan Mandahu in Inner Mongolia. Zangerlia neimongolensis is similar to Zangerlia testudinimorpha in the proportions of the carapace and plastron and presence of a knob at the posterior end of the neural series, but differs from it in the arrangement of scutes covering the bridge. The placement of Zangerlia in the Nanhsiungchelyidae is supported by derived features of the bridge peripherals and plastral scutes shared by Z. neimongolensis, Basilemys, and Nanhsiungchelys. These are the presence of ventrally expanded sixth inframarginal scutes, humeral scutes that are narrow at the midline and expanded laterally, pectoral scutes that are wide at the midline and narrow laterally, and large rectangular abdominal scutes. The skull of Zangerlia is more primitive than that of Nanhsiungchelys, the only other member of the family for which a skull is known. It shows extensive emargination of the temporal and cheek regions and the absence of a large, tubular external narial opening. A cladistic analysis of the Trionychoidea using Zangerlia as the representative of the Nanhsiungchelyidae suggests a sister-group relationship between the Nanhsiungchelyidae and Adocidae.
Sineoamphisbaena hexatabularis, an amphisbaenian (Diapsida: Squamata) from the Upper Cretaceous redbeds at Bayan Mandahu (Inner Mongolia, People's Republic of China), and comments on the phylogenetic relationships of the Amphisbaenia
Authors: Wu Xiao-Chun , Brinkman Donald B. , Russell Anthony P.
Published: April 2011

Sineoamphisbaena hexatabularis Wu et al., 1993 is the earliest known amphisbaenian represented by well-preserved cranial and postcranial material. It reveals a mosaic of generalized lizard-like features and amphisbaenian characters. Most distinctive of the latter are features of cranial consolidation adaptive for a fossorial way of life. Phylogenetic analyses strongly confirm the monophyly of the Amphisbaenia inclusive of S. hexatabularis. The Amphisbaenia is diagnosed by a suite of apomorphic characters. The available evidence suggests a probable Amphisbaenia–Macrocephalosauridae relationship within the Scincomorpha. This is supported primarily by the unique modifications of the palate and temporal region of the skull. It is argued here that the Amphisbaenia evolved in Central Asia during the Cretaceous, in response to the transition from a perennial lacustrine environment to a dry, semiarid eolian environment. The relatively primitive morphology indicates that S. hexatabularis was not permanently subterranean. The further derived modifications of later forms are associated with tunneling in an environment of more compact soils.
Influence of ground ice and permafrost on coastal evolution, Richards Island, Beaufort Sea coast, N.W.T.
Authors: Dallimore Scott R. , Wolfe Stephen A. , Solomon Steven M.
Published: April 2011

A long-term sediment budget (1947−1985) for northern Richards Island shows that, when ground ice and offshore erosion are accounted for, there is a near balance between headland erosion and coastal deposition. Excess ice constitutes about 20% of the total volume of eroded material from the headlands, with massive ground ice contributing nearly 9% and segregated ice lenses and ice wedges making up the remainder. Coastal response to major storms in 1987 and 1993 suggests that erosion is episodic, with short periods of intense disruption followed by readjustment of cliff profiles. Processes characteristic of this environment include mechanical erosion of ice-bonded sediments creating unstable erosional niches, mechanical failure of niches along ice-wedge planes, and longer term thermal erosion of ice-bonded sediments. Where ice contents are high, localized thaw slumps initiated by coastal erosion may retreat at rates substantially higher than those observed at other sections of the coast. Cliff-top retreat rates may be out of phase with storm-event chronology.
Glacier dynamics and paleoclimatic change during the last glaciation of eastern Ellesmere Island, Canada
Authors: England John
Published: April 2011

A 300 km transect along the east coast of Ellesmere Island fills a major gap in the late Quaternary data base of the Canadian High Arctic. The last glacial maximum (LGM) is marked by prominent moraines and meltwater channels that terminate within 30 km of modern ice margins. Shells in glaciomarine deposits, collected beyond the LGM, indicate deglaciation by more extensive ice prior to 35 ka BP. More than 60 14C dates from glaciomarine sediments provide a chronology for past ice dynamics during the LGM. To the north, while many areas remained ice free due to severe aridity, several glaciers remained in contact with the sea until 7.1 ka BP. Farther south, most glaciers reached the coast and significantly infilled several fiords. This southward increase in glacier extent is due to larger glacial catchment basins and increased precipitation towards storm tracks in northern Baffin Bay. The earliest dates on deglaciation along the transect range from 8.1 to 7.7 ka BP. Initial retreat was controlled by the extent of the marine-based ice margins, which were destabilized by calving. Once landward of the sea, many glaciers stabilized until ~6.5 ka BP. Considerable interfiord variability in glacier dynamics is apparent. A paleoclimatic model is proposed linking past glacier activity in the Canadian High Arctic with the available ice core record. Greenland ice cores show that colder intervals, with depleted δ18O, were associated with reduced precipitation and storminess, which may have constrained ice buildup prior to ~15 ka BP. In contrast, the abrupt rise in δ18O after ~15 ka signals the onset of regional warming associated with increased storminess and precipitation (up to 200%). This may have occasioned a late buildup of High Arctic glaciers, which remained close to the last ice limit well into the Holocene.
Postorogenic alkali feldspar granite and associated pegmatites in West Avalonia: the petrology of the Neoproterozoic Georgeville Pluton, Antigonish Highlands, Nova Scotia
Authors: Murphy J Brendan , Anderson Alan J , Archibald Doug A
Published: April 2011

The 579.8 ± 2.2 Ma (40Ar-39Ar, muscovite) Georgeville Pluton in mainland Nova Scotia is an epizonal body consisting of alkali feldspar granite and related pegmatite. The pluton intrudes the ca. 619-608 Ma arc-related rocks of the Georgeville Group, which comprises part of West Avalonia, the largest terrane in the Canadian Appalachians. The granite is characterized by above-average SiO2, Th, Nb, Y, and Zr; very low CaO, TiO2, MgO, FeO, and MnO; and most notably by positively sloped rare earth element (REE) profiles generated by extreme light REE depletion. Tectonic discrimination diagrams suggest a within-plate environment, with many, but not all, geochemical and mineralogical features resembling A-type granites. Numerous local and regional geological constraints indicate that the pluton was intruded in a trancurrent setting following the cessation of Neoproterozoic arc-related magmatism along the West Avalonian portion of the Gondwanan continental margin. Geochemical data are consistent with derivation by partial melting of depleted crust or upper mantle followed by extreme fractionation, including REE-rich accessory phases.
Continental collision including a weak zone: the vise model and its application to the Newfoundland Appalachians
Authors: Ellis Susan , Beaumont Christopher , Jamieson Rebecca A , Quinlan Garry
Published: April 2011

Continental collision generally occurs after a protracted history of rifting, sedimentation, and subduction. Inherited material heterogeneities and thermal effects from terrane accretion and amalgamation may control subsequent collisional deformation. Such strength contrasts may have played an important role in the Silurian evolution of the Newfoundland Appalachians. A cross-sectional plane-strain numerical model is used to investigate the effect of a weak zone embedded between stronger model crust (the "vise") on the deformation style of orogens. In contrast to collision of uniform strong crust in which deformation is directly related to the underlying subduction of mantle lithosphere, deformation in vise models can propagate out to the ends of the vise in a diffuse manner. This distributed tectonic style depends on the relative strength of the embedded weak zone, the degree of coupling of this zone to underlying layers, and the effect of gravity acting on thickened crust. For weak coupling at the base of the crust, results are insensitive to the behaviour of the underlying model mantle (e.g., subduction, subduction retreat, or pure-shear thickening). Vise model results are in first-order agreement with the following characteristics of Newfoundland Silurian tectonics: (i) a diffuse deformation style distributed over a weak core zone more than 100 km wide, (ii) lack of indirect evidence of mantle dynamics from crustal reflectivity fabric, and (iii) lack of clear evidence for significant crustal thickening during orogeny.
Geomorphic and sedimentary signatures of early Holocene deglaciation in High Arctic fiords, Ellesmere Island, Canada: implications for deglacial ice dynamics and thermal regime
Authors: Cofaigh Colm Ó
Published: April 2011

Integrated studies of glacial geomorphology, sedimentology, marine-limit elevations, and radiocarbon dating in two adjacent fiords on southwestern Ellesmere Island indicate that early Holocene regional deglaciation was characterized by a two-step retreat pattern, where initial rapid breakup of marine-based ice preceded slower, terrestrial retreat. These data also indicate interfiord variations in early Holocene deglacial thermal regime, and illustrate the role of fiord topography as a control on glacier retreat. In Starfish Bay, deglacial landform-sediment associations are preferentially located at fiord-side topographic irregularities, and record ice-proximal glaciomarine sedimentation during stillstands at pinning points. Abundant fine-grained subaquatic outwash indicates that the retreating trunk glacier was characterized by a warm-based thermal regime. The discrete location of these deposits and associated radiocarbon dates suggest rapid early Holocene deglaciation of the outer and middle fiord, interrupted by brief stillstands at pinning points, and subsequent stabilization and slower retreat in the inner fiord. Similar rapid early Holocene deglaciation occurred in Blind Fiord. However, the dominance of lateral meltwater channels and lack of fine-grained subaquatic outwash in this fiord suggest that trunk ice was predominantly cold-based during retreat. Initial rapid deglaciation was succeeded by stabilization and slower, terrestrial retreat when the trunk glacier reached the inner fiord. A prominent belt of glaciogenic landforms at the heads of both fiords is inferred to mark this stabilization.
Terrestrial palynomorph biostratigraphy of the Cypress Hills, Wood Mountain, and Turtle Mountain areas (Upper Cretaceous - Paleocene) of western Canada
Authors: Braman D R , Sweet A R
Published: April 2011

Three cored test holes were drilled to study the stratigraphic interval spanning the Cretaceous-Tertiary boundary: one in the western Cypress Hills near Elkwater, Alberta; a second in the eastern portion of the Wood Mountain area near Killdeer, Saskatchewan; and a third on the western edge of Turtle Mountain near Goodlands, Manitoba. The terrestrial elements of the palynological assemblages are discussed. The Maastrichtian assemblages encompassed the Scollardia trapaformis Zone and two new subzones, Myrtipites scabratus - Aquilapollenites delicatus var. collaris and Porosipollis porosus - Aquilapollenites notabile within the Wodehouseia spinata Zone. The Paleocene zones encountered include the Aquilapollenites reticulatus Subzone of the W. spinata Zone, the previously described Wodehouseia fimbriata and Momipites wyomingensis zones, and the newly defined Tricolporopollenites kruschii Zone. These provide a biostratigraphy for the cored intervals which can be related to polarity chrons. The observations made demonstrate that existing zonations are not applicable basin wide, as there are chronologically distinct disconformity-bounded sequences in western and eastern basin sectors. Apparent diachronisms within the preserved assemblages were documented by earlier entry levels within the Momipites lineage and a significant upwards extention in the range of W. fimbriata in the eastern part of the basin.
Geological correlations between Cape Breton Island and Newfoundland, northern Appalachian orogen
Authors: Barr S M , Raeside R P , White C E
Published: April 2011

Geological correlations between Cape Breton Island and Newfoundland are apparent both in surface geology and at deeper crustal levels, based on similarities in Sm-Nd isotopic signatures. The Mira terrane of southeastern Cape Breton Island is part of the Avalon terrane sensu stricto and is composed of Neoproterozoic volcanic-sedimentary-plutonic belts and overlying Cambrian rocks directly comparable to those in the western part of the Newfoundland Avalon terrane. The Bras d'Or terrane is also mainly of Neoproterozoic age, but shows lithological and isotopic contrasts with the Mira terrane. Small areas of similar Neoproterozoic rocks occur in southern Newfoundland and to the north as inliers in the Exploits terrane. The Bras d'Or terrane and similar rocks in Newfoundland are interpreted to represent a peri-Gondwanan terrane where rocks of the Gander terrane were later formed. Hence this area is part of the Central Mobile Belt and distinct from Avalon terrane sensu stricto. The Aspy terrane is a complex area that may include fragments of Bras d'Or crust and components of the Gander, Exploits, and possibly Notre Dame terranes of Newfoundland. It formed by subduction and back-arc basin opening and closure during the Silurian to Early Devonian. The Blair River Inlier is a fragment of Grenvillian rocks, similar to those in the Grenvillian inliers in the Humber zone of western Newfoundland in terms of age, rock types, and isotopic composition. Silurian and Devonian promontory-promontory collision resulted in juxtaposition and stacking of these elements in Cape Breton Island, as in the Hermitage Flexure - Port aux Basques area of Newfoundland. Because the lower crust under Bras d'Or - Gander - Aspy terranes seems distinct from that under Avalon terrane sensu stricto, it is preferable to use the term peri-Gondwanan rather than Avalonian to refer to these areas.
The McEwan Lake fault: gravity evidence for a new structural element of the Kapuskasing zone
Authors: Halls H C , Mound J
Published: April 2011

The Chapleau block, the largest uplifted crustal block within the Kapuskasing zone, continues, after sinistral offset of about 20 km, for a further 60 km to the southwest of Chapleau. This newly discovered extension, referred to as the Pineal Lake block, terminates to the west in a north-south-trending, west-verging thrust, named the McEwan Lake fault. New gravity data suggest that the fault has a vertical displacement of at least 5 km, a dip of about 25°E, and a length of at least 30 km. It is not known whether the fault crosscuts the Kapuskasing structure, in which case it may represent a younger thrusting event, or represents a southerly extension of the Saganash Lake fault that bounds the northwestern side of the Kapuskasing zone in the Chapleau area.
Preglacial archaeological evidence at Grimshaw, the Peace River area, Alberta
Authors: Chlachula Jiri , Leslie Louise
Published: April 2011

An assemblage of quartzite cobbles with attributes of cultural flaking and utilization has been recorded at the base of a Laurentide till at the contact with underlying fluvial gravels in a section face of a gravel pit near Grimshaw in the course of Quaternary geology mapping of the Peace River area. The geological context, with secondarily redeposited stone artifacts, documents distortion of an early prehistoric site located in a nonglacial riverine setting by the expanding Late Wisconsinan continental ice from the north. The lithic assemblage provides further evidence for an earlier (pre-last glacial) occupation of North America, predating the earliest postglacial (<11 500 BP) Palaeoindian cultures, traditionally regarded as the hallmark of peopling of the New World.
Elemental and isotopic (Sr, Nd, and Pb) characteristics of Madeira Island basalts: evidence for a composite HIMU - EM I plume fertilizing lithosphere
Authors: Mata J , Kerrich R , MacRae N D , Wu T -W
Published: April 2011

The within-plate volcanic island of Madeira is considered a hot-spot originating from a mantle plume. Lavas range from basanites to mugearites. The majority of primitive lavas are nepheline normative and characterized by strongly fractionated rare-earth elements, where (La/Yb)n = 12-25, and by pronounced normalized negative K but positive Nb-Ta anomalies, similar to high 238U/204Pb (HIMU) type basalts. Madeira basalts are highly depleted in terms of Sr- and Nd-isotope ratios, which are negatively correlated and define a trend steeper than the mantle array. Pb-isotope ratios are moderately high (206Pb/204Pb up to 19.582), with almost all samples plotting close to the Northern Hemisphere Reference Line. Radiogenic isotope systematics demonstrate that the mantle source of Madeira basalts is the result of a multicomponent mixture where HIMU and enriched mantle I (EM I) plume components are diluted by a depleted component (DMM) which represents more than 85% of the source volume. The presence of DMM is considered to result from entrainment of asthenospheric depleted material by the plume. There is trace-element evidence for liquids having equilibrated with garnet and amphibole, the presence of the latter mineral reflecting lithospheric involvement in the genesis of the magmas. Such was done via assimilation, by plume (plus entrained asthenosphere) magmas, of melts generated from oceanic lithosphere and leaving amphibole as residue.
Magnetostratigraphy of the Canadian Continental Drilling Program Cretaceous-Tertiary (K-T) Boundary Project core holes, western Canada
Authors: Lerbekmo J F
Published: April 2011

The Canadian Continental Drilling Program (CCDP) Cretaceous-Tertiary Boundary Project cored three holes, to 160, 188, and 170 m in southern Alberta, Saskatchewan, and Manitoba, respectively, to intersect the Cretaceous-Tertiary boundary. One hundred and seventy to 200 samples from 50 to 60 levels were taken from each of these unoriented cores for magnetostratigraphy. Samples were subjected to both alternating field (AF) and thermal cleaning. AF demagnetization in steps of 5 mT up to 30 mT showed that samples from all three cores carried only a low-coercivity viscous overprint, which was largely removed at 10 mT. Thus, three samples from each depth were routinely demagnetized at 10 mT or 100°C. The magnetic inclination of the sample giving the smallest measuring error was chosen to indicate the polarity at that depth. With the aid of palynologic control, magnetochrons 29n to 30r inclusively, in the Ravenscrag, Frenchman, Battle, Whitemud, and Eastend formations, were identified in the Elkwater core hole, western Cypress Hills, Alberta (49°36'N, 110°18'W). The Cretaceous-Tertiary boundary is missing at the Frenchman-Ravenscrag contact. The Wood Mountain core hole (49°05'N, 106°16'W) spans the interval from magnetozone 28n to 30r in the Ravenscrag, Frenchman, Battle, Whitemud, Eastend, and Bearpaw formations. The Cretaceous-Tertiary boundary is present in 29r. The Turtle Mountain core (49°01'N, 100°33'W) has a number of significant disconformities; only magnetozones 28n, 28r, 29n, 30n, and 32n or 33n are present in the Turtle Mountain, Boissevain, and Pierre formations. At the Cretaceous-Tertiary contact near the base of the Turtle Mountain Formation, there is a hiatus of 0.6 × 106 to 0.8 × 106 years. At the Campanian-Maastrichtian contact, between the Odanah and Coulter members of the Pierre Formation, there is a time gap of at least 3 × 106 years but probably about 6 × 106 years.
Precise U-Pb dating of Meguma basement xenoliths: new evidence for Avalonian underthrusting
Authors: Greenough John D , Krogh Tom E , Kamo Sandra L , Owen J Victor , Ruffman Alan
Published: April 2011

U-Pb zircon and monazite dates for granulite-facies basement xenoliths from the Popes Harbour dyke on the eastern shore of Nova Scotia provide strong evidence that the Meguma terrane overlies Avalonian basement. Slightly discordant (1.6%), "facetted" zircons from a mafic granulite indicate a minimum crystallization age of ~629 Ma, with near-concordant (0.7%) rounded zircons suggesting a maximum age for the last metamorphic event affecting the zircons at ~575 Ma. Two near-concordant (-0.9 to 0.4%) monazite fractions from a pelitic granulite indicate a major metamorphic disturbance at 378 ± 1 Ma, ~10 Ma prior to dyke entrainment and coincident with Meguma regional metamorphism. Projections from 378 Ma through four highly discordant (15-42%) metapelite zircon fractions give provenance ages between 880 and 1050 Ma and two others project to maximum ages of ~1530 Ma. Unlike Meguma sediments which lack Grenvillian-age (~1 Ga) detrital zircons and are dominated by ~2000 Ma detrital zircons, these dates indicate a dominantly Grenvillian-age provenance for the pelitic xenoliths. The "Avalonian" igneous, metamorphic, and provenance ages from the xenoliths suggest the Meguma rests on Avalonian basement. Because Avalonian sediments need a Grenvillian provenance and Meguma sediments lack such a source but require a [Formula: see text]2.0 Ga component missing in the xenoliths, it seems unlikely the Meguma was deposited on Avalonian crust. Thus the dating places on firmer footing the suggestion from earlier structural, seismic, and geochemical work that the Meguma structurally overlies Avalonian terrane. Thrusting occurred between the time of earliest Meguma deformation (~400 Ma) and intrusion of the xenolith-bearing dyke (~370 Ma).
Evolution of the Paleoproterozoic Snow Lake arc assemblage and geodynamic setting for associated volcanic-hosted massive sulphide deposits, Flin Flon Belt, Manitoba, Canada
Authors: Bailes Alan H , Galley Alan G
Published: April 2011

The majority of volcanogenic massive sulphide (VMS) deposits at the east end of the Paleoproterozoic Flin Flon "greenstone" belt occur in the 1.89 Ga Snow Lake arc assemblage. VMS deposits in this isotopically juvenile oceanic arc sequence are hosted within a 6 km thick monoclinal section that records in its stratigraphy and geochemistry a temporal evolution in arc development from primitive, through mature, to arc rift. VMS deposits occur in both the primitive and mature arc sequences and are interpreted to be products of arc extension and accompanying anomolously high heat flow, fracturing, and fluid circulation. Boninites, low-Ti tholeiites, and isotopically juvenile rhyolite flows, a rock association that has been attributed in both modern and Phanerozoic arcs to high-temperature hydrous melting of refractory mantle sources in an extensional and (or) proto-arc environment, forms the primitive arc. Indication that the mature arc also underwent extension includes voluminous volcaniclastic detritus (from fault scarps?), prominent synvolcanic dykes, isotopically juvenile rhyolite flows, and the fact that the mature arc is stratigraphically overlain by arc-rift basalts with MORB-like geochemistry. Interpretation of VMS deposits at Snow Lake as products of an extensional geodynamic setting suggests that the traditional Flin Flon Belt exploration model, invoking "pluton-generated" convective seawater, be augmented by the search for evidence of rifting. Economically significant rock associations at Snow Lake include geochemically primitive refractory mafic magmas (e.g., boninites), isotopically juvenile felsic magmas, bimodal basalt-rhyolite sequences, and arc-rift basalts.
Post-Younger Dryas seasonality in the North American midcontinent region as recorded in Lake Huron varved sediments
Authors: Godsey Holly S , Moore, Jr. Theodore C , Rea David K , Shane Linda CK
Published: April 2011

A sediment core from northwestern Lake Huron contains a sequence of red and gray layered sediments that are postglacial and early Holocene glaciolacustrine varves. Two hundred and sixty four couplets were identified and measured using a newly developed image-analysis technique that produces records of seasonal and total varve thickness. On the premise that changes in varve thickness can serve as a proxy for climate variability, we use this information, along with oxygen-isotope records and seismic reflection profile data, to characterize a period immediately following the Younger Dryas. A time-series analysis of the thickness data was performed using two different techniques to characterize changes in spectral density that occur throughout the time span of the record. The results indicate that there are concentrations in variance that occur in the same frequency band as the quasi-periodic El Niño - Southern oscillation (ENSO) and the quasi-biennial oscillation (QBO). The effects of ENSO-like variability have not previously been documented in the postglacial and early Holocene of the Great Lakes region.
Laser 40Ar/39Ar thermochronology of Archean rocks in Yellowknife Domain, southwestern Slave Province: insights into the cooling history of an Archean granite-greenstone terrane
Authors: Bethune Kathryn M , Villeneuve Michael E , Bleeker Wouter
Published: April 2011

Laser 40Ar/39Ar ages for hornblende, muscovite, and biotite from Archean plutonic rocks of Yellowknife Domain, southwestern Slave Province, complement U-Pb ages from minerals with higher closure temperatures (zircon, monazite, titanite). Together, the data indicate that the plutonic suites of different ages (Defeat, Prosperous, Morose) coring three major thermal culminations in the domain have distinct Archean cooling histories until below approximately 250°C (biotite closure). The cooling trajectories for successive suites appear to document a decrease in cooling rate over the course of orogeny, possibly reflecting the build-up of heat within the orogen, coupled with a transition to lower rates of exhumation and (or) erosion. Greater structural relief over the Sleepy Dragon basement culmination may be responsible for slower cooling of the Morose Granite situated in its core. At or below the closure temperature of biotite the cooling curves converge with one another, documenting a transition from "localized" to "regional" cooling. The fact that cooling was locality specific until at least the biotite closure temperature suggests that, just as intrusion and related peak metamorphism were diachronous across the region, so was cooling to approximately 250°C. Uniform regional isotherms thus were not established until >200 Ma after the youngest Archean plutonism. The variable disturbance of biotite Ar spectra, but generally not muscovite or hornblende, indicates that the Paleoproterozoic thermal disturbance of Archean rocks in Yellowknife Domain did not exceed 200-300°C.
U-Pb ages of plutonism, sedimentation, and metamorphism of the Paleoproterozoic Kisseynew metasedimentary belt, Trans-Hudson Orogen (Manitoba, Canada)
Authors: Machado N , Zwanzig H , Parent M
Published: April 2011

The Kisseynew Domain is a metasedimentary belt in the central Reindeer Zone of the Trans-Hudson Orogen. It is bounded by 1.92-1.86 Ga volcanic-plutonic belts to the north and south, by an Archean terrane to the east (Superior Province), and by a volcanic-plutonic terrane underlain by an Archean terrane to the southwest (Glennie Domain). The Kisseynew Domain developed in an arc-related setting in the final stages of plate convergence involving the northward migration of arc-ocean floor complexes toward the Archean Hearne Craton. Terminal collision, involving also the Superior Craton, originated multiple fold-thrust systems and high-grade metamorphism. U-Pb ages of 1874-1860 Ma for pretectonic plutonic units in southern Kisseynew Domain are identical to ages of plutonism intruding the arc-ocean floor accretionary complex in the Flin Flon domain (Amisk collage) and indicate its northern extension. Deposition of the Burntwood Group turbidites started at ca. 1860 Ma, indicating uplift and erosion of the volcanic complexes and was coeval with arc magmatism that succeeded the Amisk collage. From 1848 Ma, Burntwood sedimentation was coeval with deposition of Missi Group continental sediments, with continental arc magmatism and early deformation. New and published ages for detrital zircon indicate that sediments were derived both from local 1.89-1.84 Ga units and also from 2.55-2.36 Ga sources. The latter suggest that a Neoarchean-Paleoproterozoic cratonic block was undergoing erosion, remnants of which occur in the Flin Flon Belt. Basin closure started after 1823 Ma and is marked by regional high-grade metamorphism lasting for ca. 30 million years from 1818 Ma to 1785 Ma; late- to posttectonic metamorphic activity lasted until ca. 1775 Ma.