bluuebunny/crossref_metadata_2025 huggingface dataset:
The Mings Bight Ophiolite Complex, Newfoundland: Appalachian oceanic crust and mantle
Authors: Kidd W. S. F. , Dewey John F. , Bird John M.
Published: April 2011

The Mings Bight Ophiolite Complex, of probable early Ordovician age, is disposed in four major thrust sheets with an eastward vergence at the northern end of the Baie Verte Lineament. This narrow ophiolitic belt, and (to the south) an adjacent zone of early Devonian volcanic rocks and sediments, were affected by a strong Acadian (Middle Devonian?) deformation between more resistant blocks consisting mainly of rocks that were deformed and regionally metamorphosed, prior to the development of the ophiolites and overlying mafic sediments and volcanic rocks, probably in Late Cambrian to earliest Ordovician. The ophiolite sequence and conformably overlying sedimentary and volcanic sequence define an overturned synclinal structure with an eastward vergence; the three western thrust sheets contain an inverted sequence, the eastern sheet is upright. The thick mafic volcaniclastic and pillow lava sequence overlying the ophiolite complex suggests that the ophiolite complex was generated as the the floor of a small rear-arc or intra-arc basin. The ophiolite complex, although dissected by faults, consists of an ordered sequence from non-cumulate tectonite harzburgite through cumulate ultramafic rocks, gabbro and sheeted dike complex to pillow lavas. The continuous, coastal exposures show the relationships between the lithologies of the ophiolite complex unusually clearly, and these are described in some detail. In particular, the relationships between the sheeted dikes and both the homogeneous upper gabbro and the pillow lavas, and the intrusive complexities and the high-temperature deformation in the layered gabbros and ultramafics, are very clearly displayed. An ocean floor fault containing diapiric serpentinite is preserved in one thrust sheet. Two new formations are proposed, for the mafic volcaniclastic sediments (Big Head Formation) and for the overlying pillow lavas (Barry–Cunningham Formation) above the ophiolite complex.
Devonian alkalic basalt dikes of northeastern Newfoundland: evidence of a tensional environment
Authors: Jayasinghe N. R.
Published: April 2011

A suite of diabase dikes intrudes granites and migmatites in the northeastern Gander Zone of Newfoundland. Rb–Sr dates on granites pre-dating and post-dating the diabases show that the dikes were emplaced in the Devonian. The mineralogy and the major and minor element chemistry of the dikes indicate that they are alkalic basalts that may have been intruded during a period of tension.
Holocene and latest Pleistocene cirque glaciations in the Shuswap Highland, British Columbia
Authors: Duford J. M. , Osborn G. D.
Published: April 2011

Ages of glacial deposits in cirques of the Shuswap Highland, British Columbia are approximated or bracketed using tephrochronology, radiocarbon dating and lichenometry. There is evidence for two minor Holocene glacial advances. The younger, named the Raft Mountain Advance, is defined by the type Raft Mountain moraine, which is about 100 years old judging from Rhizocarpon lichens. No volcanic ash is found on the moraine or its equivalents. The older, named the Dunn Peak Advance, is defined by the type Dunn Peak moraine and equivalent deposits in the Dunn Peak area. These deposits bear Mazama ash and are thus older than 6600 years; one of the moraines has a minimum radiocarbon age of about 7400 years. The deposits are younger than the Late Wisconsin deglaciation in southern B.C. (about 11 000 years BP). In addition, an earlier event, possibly a stillstand, is represented by a moraine (the Harper Creek moraine) downstream of the type Dunn Peak moraine. This moraine is also bracketed between 6600 and 11 000 years in age. The Dunn Peak Advance may be correlative with an Early Holocene Advance reported from the Canadian Rockies and northern American Rockies, and the Raft Mountain Advance is correlative with very recent advances reported from several parts of the world.
Plate tectonics in the Phanerozoic
Authors: Kanasewich E. R. , Havskov J. , Evans M. E.
Published: April 2011

Paleomagnetic observations, oceanic magnetic lineations, and the present continental margins are combined in an interactive computer program to generate maps for seven periods in the Phanerozoic Era. The results are presented in the familiar Mercator projection and with less distortion on other projections. On an azimuthal-equidistant map projection with origin on the centroid of the continental lithosphere the boundaries display a high degree of symmetry and order. By using geological evidence on the position of geosynclines, volcanic assemblages, and zones of diastrophism an attempt is made to model a reconstruction of major plate boundaries in the past. During the Cambrian and Ordovician Periods the continental segments were as widely dispersed as at present and formed a ring of plates on the paleoequator but with North Africa and South America contiguous and close to the south pole. In these, as in other periods, there is symmetry about the spin axis. Extensive plate motion occurred at about the time of the Caledonian Orogeny when the continental segments evolved toward the formation of a single large group called Pangaea by Wegener. This evolution occupied much of the late Paleozoic and Mesozoic Eras. Toward the end of the Cretaceous Period a more dispersed form began to develop yielding the present pattern of two antipodal quasi-circular plates separated by a ring of more irregular quasi-elliptical plates. The results suggest the presence of a slowly evolving mantle-wide convection system that is symmetric about the Earth's spin axis. The dominant pattern during the late Paleozoic and the Cenozoic was of plates with dimensions of 60–120° in which the convective pattern may be described in terms of spherical harmonics of the third order. In the Mesozoic and late Paleozoic the plate sizes were of the order of 90–180° and physical parameters describing convection were presumably dominated by second order terms.
The geomorphology and origin of Point Pelee, southwestern Ontario
Authors: Trenhaile A. S. , Dumala R.
Published: April 2011

The grain size of sediments from shallow boreholes (1–4 m) was used to determine the origin of four landscape elements on Point Pelee, southwestern Ontario. The sand plains, an area of low relief near the interior of the point, are composed of sediments derived from the lake floor and washed onto the Pelee–Lorain moraine by rising postglacial lake levels. The dune and beach ridge formations on the western flank of the point were built in the last 1000 years, with sediment eroded and moved alongshore from the bluffs to the north. The presence of several truncated ridges at the southern end of the enclosed marsh was confirmed. A new theory for the development of Point Pelee is proposed, in which alongshore transport of material is considered to be insignificant during the initial development of the point, but dominant during its later history.
Seismicity of western Canada
Authors: Milne W. G. , Rogers G. C. , Riddihough R. P. , McMechan G. A. , Hyndman R. D.
Published: April 2011

The seismicity of western Canada has been studied for the period 1899–1975. The quality of the data collected improved through this period as the number of recording stations increased and the location and analysis methods developed, but significant uncertainties and biases remain. Although these restrictions limit detailed correlation of seismic events with specific tectonic features, in general the most active earthquake areas correspond to the boundaries between the major lithospheric plates. These are the Queen Charlotte – Fairweather fault system (Pacific–America plates), the offshore ridge-fracture zone system (Pacific – Juan de Fuca plates), and the Vancouver Island – Puget Sound region (Juan de Fuca – America plates). Strain release calculations show that most seismic energy is released along the Queen Charlotte – Fairweather fault system and that at present a significant accumulation of strain may be available for release as earthquakes in the Vancouver Island – Puget Sound area. Except for the absence of thrust earthquakes along the apparently converging margin, focal mechanisms are in good agreement with the postulated plate motions. The b values in the frequency–magnitude recurrence relation for different areas within the region range from 0.65 to 0.82.
A slice of basement in the western margin of the Appalachian orogen, Saint-Malachie, Quebec
Authors: Vallières A. , Hubert C. , Brooks C.
Published: April 2011

Slivers of gneisses and amphibolites (termed the Sainte-Marguerite Complex) having a minimum isotopic age of 900 Ma are interpreted to represent thrust slices of Grenvillian-type basement within the western margin of die internal domain of the Appalachian orogen. These slices constitute the basement to a series of spilitized volcanic rocks and interbedded shallow-water sandstones (termed the Montagne de Saint-Anselme Formation) which are interpreted to be Precambrian to Cambrian(?) rift-related precursors to the filling of the Appalachian mobile belt.
Petrogenesis of spilite and keratophyre from a Permian and Triassic volcanic arc terrane, eastern Oregon and western Idaho, U.S.A.
Authors: Vallier T. L. , Batiza Rodey
Published: April 2011

Spilite, keratophyre, and quartz keratophyre from a Permian and Triassic volcanic arc assemblage in eastern Oregon and western Idaho originally were low-potassium basalt, andesite, dacite, and possibly rhyolite. Amphibolite from an abyssal sea floor or marginal basin environment of either Permian or Triassic age originally was low-potassium basalt. Present mineralogies are characteristic of the greenschist and amphibolite facies of regional metamorphism. Greenschist facies minerals are mostly albite, epidote, chlorite, calcite, and quartz, whereas amphibolite facies minerals are predominantly hornblende, plagioclase (andesine), and epidote. In the volcanic arc assemblage, mineralogies of the Permian rocks are nearer equilibrium in the greenschist facies than those of the overlying Triassic rocks, probably reflecting deeper burial. Bulk compositions indicate extensive ion mobility, but there has been a general internal mass balance of most components. Na2O, CO2, and H2O were probably added to most rocks, but the source of those components has not been established.
Magnetic overprinting in the Thanet gabbro complex, Ontario
Authors: Buchan Kenneth L.
Published: April 2011

Multi-component paleomagnetic remanences are reported for the Thanet gabbro complex of the Grenville Province in Ontario. Forty-five samples (10 sites) attain stable reversed (A) directions in AF's (alternating fields) of 150 Oe (1.2 × 104 A/m) or less. Blocking temperatures (TB's) are 300–350 °C (5 sites) and 525–560° (5 sites). The A1 paleopole of 158.4°E, 38.0°S (k = 593, α95 = 3.1°) for the low TB sites differs significantly at the 95% confidence level from the A2 pole of 172.0°E, 32.3°S (k = 151, α95 = 6.2°) for the high TB sites. Directions from 18 additional samples (at 8 sites) follow great circle paths towards the A direction upon AF demagnetization to 1000 Oe (8.0 × 104 A/m). TB's of the lower coercivity (B) component are 560–580 °C, above TB's of both A components. Upon thermal demagnetization, directions swing away from the A direction and endpoints reached above 560 °C define a normal B paleopole at 159.3°E, 20.3°N (k = 9.6, α95 = 11.7°).If the A and B components are both of thermal origin, B predates A, and was overprinted by A during a regional metamorphic event which reset components with TB's <560 °C but left those unaffected with TB's > 560°C. The difference in the A2 and A1 directions represents apparent polar wander during cooling from above 500 °C to less than 300 °C. If the B component, however, was generated as a low temperature (<300 °C) chemical remanence, the relative age of A and B are reversed—B is younger than A. The applicaton of Thanet paleopoles to the problems of Grenville and Sveconorwegian tectonics is described.
On the nature of the crust in the vicinity of the southeast Newfoundland Ridge
Authors: Sullivan K. D. , Keen C. E.
Published: April 2011

This paper presents new seismic reflection, refraction, gravity, and magnetic data bearing on the nature of the crust in the vicinity of the Newfoundland Ridge and the J-anomaly Ridge, immediately south of the Grand Banks. This area experienced a complicated plate tectonic history being the focal point for interactions of the North American, African, and Iberian plates. New data have recently been published for this region and conflicting interpretations have been offered in relation to the oceanic or continental origin of the crust there. The data presented here show that the seismic structure and the most reasonable models for the magnetic anomalies are more consistent with an oceanic origin. The trends and offsets in the magnetic lineations and possible differences in subsidence, north and south of the Newfoundland Ridge, are discussed in relation to possible modes of formation of this feature. It is proposed that similar subsidence histories since mid-Cretaceous time on the Grand Banks and J-anomaly Ridge are related to a similarity in the thermal history of the lithosphere beneath these areas, as the ridge crest migrated eastwards, and do not require the same type of crust to underlie both areas.
Geophysical measurements in the region of the Explorer ridge off western Canada
Authors: Hyndman R. D. , Rogers G. C. , Bone M. N. , Lister C. R. B. , Wade U. S. , Barrett D. L. , Davis E. E. , Lewis T. , Lynch S. , Seemann D.
Published: April 2011

The region of the Explorer spreading centre off Vancouver Island, British Columbia, has been studied through a marine geophysical survey. Earthquake epicentres located by three ocean bottom seismometers confirm that the boundary between the Pacific plate and the Explorer plate (the northern extension of the Juan de Fuca plate) at present lies along the Sovanco fracture zone, the Explorer ridge, and the Dellwood Knolls. The epicentres of earthquakes in this area as determined by the onshore seismic network are found to be subject to significant errors. The ocean bottom seismometers also have been used for a detailed seismic refraction line just to the north of the Explorer spreading centre employing explosives and a large airgun as sources. A preliminary analysis of the data indicates a fairly typical crustal structure but a shallow and low velocity mantle near the ridge crest, and illustrates the value of ocean bottom seismometers in oceanic refraction studies. A new geothermal heat flux probe was employed in this study that permitted repeated 'pogostick' penetrations without raising the instrument to the surface. Six profiles with a total of 112 penetrations provided valuable data on the nature of hydrothermal circulation in the oceanic crust. Eleven standard heat probe stations provided some restraints on the poorly known age of the oceanic crust along the margin. Seismic reflection profiles using a 3.5 kHz system, a high resolution pulser profiler, and a large airgun were used as aids in the interpretation of the seismic and heat flow data.
Simple graphical methods for estimating the confidence region about the orientation of the intersection of two planes
Authors: Cruden D. , Kelker D.
Published: April 2011

We give a simple graphical method for the construction on a stereonet of the confidence region for the orientation of the line of intersection of two planes. The method applies when the poles to the planes have been estimated by large and approximately equal numbers of measurements which may be treated as samples from two Fisher distributions of equal and large precision parameters. The method requires the estimation of the acute angle between poles to the planes and the range of the plunges of the poles.When the samples of poles are samples of large size from two Bingham distributions tightly clustered about their common plane, a more complex graphical construction is available. It requires the estimation of scatter of the poles in and perpendicular to the common plane and some simple calculations.The methods are applicable to a variety of problems in structural geology and rock mechanics.
The feasibility of delineating non-layered anomalous velocity zones by a combination of fan shooting and least-squares analysis
Authors: Waboso C. E. , Mereu R. F.
Published: April 2011

Laboratory velocity measurements on nickel-sulphide samples show that the velocity contrast between a sulphide body and rocks typical of the Canadian Shield can be fairly large. In view of this, the feasibility of delineating the sulphide body by means of a combination of fan shooting and least-squares analysis was examined by both computer model simulation and field experimentation. The method consists, essentially, of shooting several fans emanating from the perimeter of a rectangle around the suspected location of a deposit, and measuring the corresponding first arrival times. The rectangle is then divided into grid units, and the apparent velocity in each grid unit is found by least-squares solutions of an overdetermined system of linear equations.The computer model tests indicate that in cases where the velocity contrast between the surrounding medium and the anomalous zone is good, and each medium homogeneous, the method is a potentially useful auxiliary technique for mining exploration. However, field tests show that these requirements (i.e., good velocity contrast and homogeneity of each medium) may constitute a serious limitation of the method.
Groundwater temperatures in the Athabasca Oil Sands area, Alberta
Authors: Hackbarth D. A.
Published: April 2011

Bottom-hole temperatures were measured in groundwater observation wells in the Athabasca Oil Sands area of Alberta. Depth of observation varies from 6–581 m in rocks of Holocene, Cretaceous, and Devonian age. Observations of temperature at various depths at a particular location were made in individual wells.At depths of 300 and 400 m, a correlation of both hydraulic head-loss and temperature with the elevation of the land surface at the observation well indicates that groundwater flow is the dominant parameter controlling subsurface temperatures. The control of groundwater flow on temperature and the location of observation wells in different positions in the groundwater flow system means that temperatures are not well correlated with depth.Bottom-hole temperatures from geophysical logs made in the area are significantly higher than values observed nearby at similar depths during this study. Published thermal gradient maps based upon information from geophysical logs give values which are about twice as high as those calculated with the present data.At depths less than about 60 m temperatures varied widely and at many well sites declined with depth. The average temperature of shallow groundwater was 5.9 °C at an average depth of 12.7 m. This fact indicated that the mean annual air temperature of −0.6 °C should not be used to approximate the temperature of shallow groundwater.
40Ar/39Ar dating of dikes from the Frontenac Axis and implications for Grenville paleomagnetism
Authors: Reynolds P. H. , Olojo E. O. , Stukas V. J. , Clay W.
Published: April 2011

Stepwise outgassing experiments have been carried out on nine whole rock samples of material from these diabase dikes. None of the samples is entirely free of alteration and all of the age spectra exhibit at least some degree of discordance. Over the intermediate temperature interval (775–1025 °C, arbitrarily defined), apparent age plateaus (or plateau-like features) appear to be the rule. The mean apparent age of gas released at these temperatures for six of the samples is ~900–910 Ma; the average apparent Ca/K ratio is ~3. These samples have a mean total gas age of ~910 Ma and total gas apparent Ca/K ratios ranging from ~5 to ~7. The above value is interpreted as a probable minimum age for K-rich phases (biotite and sericite).The dikes were intruded into the host gneisses probably while they were still above the temperature at which argon is quantitatively retained in biotites. Although the magnetic blocking temperatures of the dikes are not known, the Frontenac paleopole is probably in the vicinity of ~900 Ma old. This value is consistent with other recent estimates of the age of this middle portion of the Grenville apparent polar wander track.
Pre-Carboniferous basement near Trail, British Columbia
Authors: Simony Philip S.
Published: April 2011

In the Columbia Valley north of Trail, the Carboniferous Mount Roberts Formation is underlain by a mass of gneiss. This, the Trail Gneiss, consists of amphibolite, grey biotite gneiss with minor mica schist, and marble, cut by hornblende and biotite quartz diorite orthogneiss, all laced by abundant pegmatite and aplite. Siltstone, slate, and greywacke with chert pebble conglomerate and limestone lenses of the Mount Roberts Formation face away from the Trail Gneiss, separated by a recrystallized mylonite zone, which may represent an unconformity between basement and cover, tectonized during décollement of the cover. The Trail Gneiss likely is a partially reworked and possibly allochthonous piece of the Precambrian North American craton. An upper Paleozoic to Jurassic sequence of 'arc-type' clastic, andesitic volcanic, and volcaniclastic rocks accumulated on this basement and was probably over-thrust by it in the Jurassic.The Trail Gneiss and its cover pass northward through a zone of increasing metamorphic grade into augen gneiss and pegmatite incorporating slabs and sheets of Trail Gneiss. This younger complex, the Castlegar Gneiss, closely resembles the upper sheet of mixed gneiss in Valhalla Dome and is nearly continuous with it. The Trail and Castlegar Gneisses outline a broad antiform continuous with Valhalla Dome.
The petrology of sands in the uppermost Cretaceous and Palaeocene of southern Saskatchewan: a study of composition influenced by grain size, source area, and tectonics
Authors: Misko Ronald M. , Hendry Hugh E.
Published: April 2011

The sands of the Frenchman Formation (Maastrichtian) and the Ravenscrag Formation (Palaeocene) in southwestern Saskatchewan are mineralogically immature lithic arenites and wackes. Volcanic rock fragments, which in the Frenchman Formation make up to 30% of the fraction coarser than 0.0625 mm, are less common in the Ravenscrag Formation, where quartz and carbonate rock fragments are significantly more abundant in the same size fraction. Sand composition is influenced by grain size in both formations. Over the range from 0.59–0.074 mm there is, in general, a decrease in the percentage of rock fragments and an increase in the percentage of quartz, with decreasing grain size. Although the Ravenscrag sands mostly are finer grained than those of the Frenchman, compositions of the fraction coarser than 0.0625 mm fall into separate but overlapping fields in a conventional quartz – feldspar – rock fragment (QFR) diagram. Differences, in terms of QFR ratios, between the formations, are clearer if compositions of limited size ranges (six size ranges between 0.59 and 0.074 mm) are considered, but there is still overlap. Significant compositional differences are obvious only when the relative amounts of different types of rock fragment are taken into account.Grain-size distributions of different components in the sands are, for the most part, the same in both formations, and reveal trends that are anticipated by studies of sand transport in modern streams. The proportions of quartz and detrital carbonate grains increase with decreasing grain size, whereas relative amounts of nonvolcanic rock fragments and chert decrease with decrease in grain size. Volcanic rock fragments and feldspar show an irregular increase with decreasing grain size in the Frenchman sands, and an increase followed by a decrease in the Ravenscrag sands. The differences in the latter two components between the sands of the two formations are attributed to a reduction in both the abundance and the variety of volcanic detritus supplied to the area in Palaeocene times.The bulk of the volcanic material in both formations likely was derived from western Montana. In particular, the Elkhorn Mountain Volcanics (Campanian) and the Adel Mountain Volcanics (Maastrichtian to ?Palaeocene) probably were important sources. The uplift of Palaeozoic carbonate rocks and Mesozoic clastic deposits in the Front Ranges of the Rocky Mountains may account for the relative reduction in supply of volcanic rock fragments and feldspar, and the increased contribution of detrital carbonate and quartz, to the sands of the Ravenscrag Formation.
Mammals from the Upper Cretaceous Oldmae Formation, Alberta. I. Alphadon Simpson (Marsupialia)
Authors: Fox Richard C.
Published: April 2011

New mammalian fossils from the Upper Cretaceous Oldman Formation, Alberta, pertain to three species of the marsupial Alphadon Simpson. One of these species, A. praesagus (Russell), is ancestral to the Lancian A. rhaister Clemens. The second, closely related but not ancestral to the Lancian A. marshi Simpson, is new, and the third, A. halleyi Sahni, is closely related to the Lancian A. lulli Clemens, as had been earlier supposed from fossils from the Judith River Formation, Montana. The phylogenetic relationships of Alphadon are discussed.
A creep instability analysis of the Antarctic and Greenland ice sheets
Authors: Gary P. W. , Clarke G. K. C. , Peltier W. R.
Published: April 2011

Creep instability, the runaway increase of temperature and deformation due to internal strain heating, is analysed with a very simple model of one-dimensional heat transfer to estimate the stability of the Antarctic and Greenland ice sheets. Derived stability maps indicate that for the assumed rheology both ice sheets are completely stable; however, the stability of the coastal region of Wilkes Land in Antarctica is only marginal and cannot be accurately determined because of uncertainties in the data, especially basal shear stress.
Submarine carbonate breccia beds—a oppositional model for two-layer, sediment gravity flows from the Sekwi Formation (Lower Cambrian), Mackenzie Mountains, Northwest Territories, Canada
Authors: Krause F. F. , Oldershaw A. E.
Published: April 2011

In the Sekwi Formation, carbonate breccia beds interbedded with slope sediments are interpreted as submarine sediment gravity flows that formed a two-layer deposit during a single transport event. They are intermediate between true slumps and turbidites and may initiate by slumping anywhere on the continental slope and rise. Textural characteristics of the deposits are a function of downslope transport distance.
Seismotectonics of the Beaufort Sea
Authors: Hasegawa H. S. , Chou C. W. , Basham P. W.
Published: April 2011

Earthquake data are utilized in conjunction with bathymetry and gravity measurements to study the seismotectonics of the Beaufort Sea area. The epicentre cluster in the Beaufort Sea is confined to the continental slope between the 200 and 2400 m bathymetry contours and falls between the seaward −20 mGal and the landward + 40 mGal contours of an elliptically shaped free-air gravity anomaly. The cluster, which experiences an average of one earthquake magnitude ≥ 4 per year, is shown by epicentre relocation studies to be a distinct zone and not the result of mislocations of earthquakes originating from a spatially confined source. Theoretical calculations of the stress field under the region where the gravity anomaly is most pronounced show that the horizontal component of the stress field is deviatoric tension normal to the axis of the continental margin; focal parameters of the June 14, 1975, mb 5.1, Ms 4.2 Beaufort Sea earthquake indicate deviatoric tension in the same (east–west) direction at a depth of 40 km. The relatively small surface waves from this and other Beaufort Sea earthquakes, compared to other on-shore Arctic earthquakes, are probably due to this deeper focus at the continental margin. The horizontal component of the deviatoric compression of this earthquake is north–south; a horizontal compressive stress from the north may be transmitted through the Arctic Ocean lithosphere from the Nansen–Gakkel spreading ridge. It is suggested that these stresses are acting on localized zones of weakness.
Observations on depositional environments and benthos of the continental slope and rise, east of Newfoundland
Authors: Carter Lionel , Schafer Charles T. , Rashid M. A.
Published: April 2011

Sedimentologic, biologic, and morphologic criteria permit recognition of four depositional environments on the continental slope and rise, east of Newfoundland. The 'upper slope' (300–700 m) has a hummocky substrate with a mantle of terrigenous, gravelly muddy sand which is a mixture of ice-rafted detritus and sediment reworked from underlying glacial drift deposits. Reworking presumably took place during the last major lowering of sea level and it is continuing today under the influence of the Labrador Current and other oceanographic and biologically-related forces. The featureless bottom of the 'middle slope' (700–2000 m) is the principal depositional site of Recent mud. Fines, reworked from shelf and upper slope sediments, settle out together with fines transported to the area by the southeast-flowing Western Boundary Under-current (WBU). Compared to the upper slope this deeper environment receives less ice-rafted clasts, supports a richer macrofauna, and has a higher total species diversity of foraminifera. The 'lower slope' (2000–2500 m) is characterized by higher amounts of gravel and sand mixed with the mud, increasing numbers of current bedforms, and a more diverse foraminiferal assemblage, all of which correlate with the increasing power of the WBU with depth. The gravel was ice rafted probably at the end of the late Wisconsin to early Holocene and its presence on the seabed reflects the power of the WBU to inhibit deposition of Recent mud. The 'rise' (2500 to > 3000 m) is heralded by a subtle break in slope at about 2500 m. A high speed core of the undercurrent is situated in this area as indicated by the coarseness of the sediments (gravelly muddy sand) and the observed current bedforms. A marked increase in the numbers of benthonic and planktonic foraminifera is related primarily to the winnowing capacity of WBU. Numerous arenaceous deep sea forms first occur between 2500 and 3000 m and appear to reflect the reduced salinity, low temperature, high dissolved oxygen characteristics of the watermass that is associated with this depth interval.
Further paleomagnetic results from the Seal Group igneous rocks, Quebec
Authors: Park J. K. , Roy J. L.
Published: April 2011

This paleomagnetic study involves further demagnetization (alternating field, thermal) of specimens from part of the previously published Seal Group (volcanics and sills). A previous study uncovered two stable magnetizations nominated M2 (herein B) and M3 (herein A). In the present work, the A magnetization has been better defined, found to contain reversals of direction, and has been found also in the sills (6 sites, specimen unit weight; 289°, +11°; α95 = 11°) as well as the volcanics (5 sites; 293°, +13°; α95 = 13°) for a combined direction with respect to bedding of 291°, +12 °(11 sites, R = 10.76, α95 = 7°). Of the total number of specimen directions (63; 1 or 2 per sample), 17 were obtained by vector subtraction (VS); all but four of the latter were the means of at least two determinations. It is suggested that the A magnetization residing in hematite was acquired first, and B, residing in magnetite, later, as a result of remagnetization during the Grenville 'Orogeny'. At several sites, where there is no evidence of hematite, a reverse B direction may be present. The A pole is at 17°N, 195°E (δp = 4°, δm = 7°), near the Seal Group red bed pole (05°N, 205°E), and the B pole (direction with respect to horizontal) at 17°S, 158°E (7°, 9°).It is apparent in this and other studies that specimens that contain both normal and reverse magnetizations display a very characteristic behaviour under demagnetization. This behaviour and its implications for deriving good approximations to the true direction by the use of VS—even when remanent coercive force or unblocking temperature spectra overlap substantially—are revealed by means of a model using artificial data.
The Archean gneiss complex of northern Labrador. 1. Preliminary U–Th–Pb geochronology
Authors: Baadsgaard H. , Collerson K. D. , Bridgwater D.
Published: April 2011

Lithological and earlier isotopic studies suggest that several of the older rock units in the Archean gneiss complex of north Labrador can be correlated with those of the Godthaabsfjord area of west Greenland (West Greenland Correlation = WGC). However, comparison of zircon data from the two areas suggests major differences in the younger Archean geological development of the two areas. The Uivak I and II gneisses (WGC = the 3600 Ma Amitsoq gneisses) yield zircon 207Pb/206Pb ages of up to 3485 Ma but with an apparent high Pb-loss episodic disturbance pattern. Zircons from the Nulliak assemblage (WGC = Isua supracrustals and Akilia association, > 3800 Ma) give dates of ~2500 Ma and have been completely reset by thermal metamorphism accompanying the intrusion of post-tectonic granites at ~2520 Ma (WGC = Qôrqut granite 2520 Ma). A group of high Fe2O3 iron-rich minor intrusives of uncertain stratigraphic age yield zircon ages of 2500–2800 Ma. Sphene separated from all the above rock types gives essentially concordant U–Th–Pb ages at ~2530 Ma, while Uivak gneiss apatite is somewhat discordant at 2385 Ma. The whole rock, feldspar, and apatite Pb isotopic composition of the Uivak gneisses is quite different from that for the Amitsoq gneiss. The Uivak gneiss lead is much more radiogenic and probably acquired the radiogenic lead during later metamorphism between 2800–2500 Ma ago.
Determination of lacustrine sedimentation rates by radioactive fallout (137Cs), Pitt Lake, British Columbia
Authors: Ashley Gail M. , Moritz Lutz E.
Published: April 2011

The stratigraphic record of 137Cs activity levels found in Pitt Lake, British Columbia, mimics the radioactive fallout values for 137Cs and 90Sr recorded in milk from the adjacent Fraser Valley. The Pitt Lake record closely parallels the fallout values obtained in England, Alabama, and Lake Michigan. The presence of 137Cs in Pitt Lake sediments is unequivocable evidence for modern (since 1952) clastic deposition. Calculated sedimentation rates as great as 1.8 cm year−1 were made using the 137Cs technique. These values substantiate previous estimates based on varve thickness. The technique is shown to be a useful tool which can quickly and reliably determine modern lacustrine sedimentation rates.
A new species of Taricha (Caudata: Salamandridae), from the Oligocene John Day Formation of Oregon
Authors: Naylor Bruce G.
Published: April 2011

A new species of Taricha is described from the Oligocene John Day Formation of Oregon. The new species, represented by a single nearly complete skeleton, shows features intermediate between the subgenera Palaeotaricha and Taricha, but is closest to the latter taxon.
Quelques aspects pétrographiques et géochimiques du volcanisme archéen du Malartic en Abitibi (Province du Québec, Canada)
Authors: Alsac C. , Latulippe M.
Published: April 2011

The Archean metavolcanic formations of the Malartic Group in Abitibi, northwestern Quebec (Canada), are several kilometres thick and made up of lavas and pyroclastic rocks, a large part of which are of submarine origin with pillows and hyaloclastites.The mafic phases, with ultramafic material (komatiites), dominate at the base of the unit, the felsitic flows and other derived material, locally associated with copper and zinc sulphides, are located towards the summit of the unit.The regional metamorphism of greenschist and locally amphibolite–almandine facies, has destroyed the magmatic paragenesis; on the other hand, the original textures and structures are generally well preserved.A geochemical study of major elements was carried out on 67 well chosen fine-grained lavas. These were retained for analysis after thin section examination showed them to be nonporphyritic, homogeneous, with a minimum of alteration, and a lack of secondary fillings of amygdales and microfissures. This study led to the following conclusions:(1) The original composition of the volcanic rocks of the Malartic Group is still identifiable in spite of the modification in the content of Na, K, Ca, S, H2O, CO2 and to a lesser degree of Mg and Fe.(2) The variable percentages, generally high in Na and low in K, give to this volcanic group a spilitic characteristic; this may simply be an accentuation of an original tendency for series poor in K.(3) Apart from the ultramafic flows and certain magnesian basalts for which a komatiitic relationship is considered, the Malartic volcanism has magmatic characteristics comparable to those of volcanic island arcs. It begins with dominantly mafic extrusions with a tholeiitic composition poor in K. It continues in the upper Malartic with eruptions in which felsitic phases, locally associated with copper–zinc mineralization, become more abundant; these products seem to belong to two different magmatic series: one tholeiitic, the other calc-alkaline, both poor in K. The phases of these two magmatic series are spatially tightly imbricated.
An inexpensive sieving method for concentrating pollen and spores from fine-grained sediments
Authors: Cwynar Les C. , Burden E. , McAndrews J. H.
Published: April 2011

A sieving method is described for concentrating pollen and spores from fine-grained sediments. The effectiveness of nylon screens with 5, 7, 10, and 15 μm meshes was tested in comparison with both standard digestion and sodium pyrophosphate suspension procedures.Sieving through 7 μm mesh screens recovers more pollen than any of the other methods tested and effectively removes fines with a negligible loss of pollen (0.4%). We recommend this method for general use with fine-grained minerogenic sediments. Thus, it is possible to process and count more reliably to statistically significant sums, clay and silt-rich samples previously considered either barren of pollen or too time consuming to count.
Regional deformations and emplacement of granitoid plutons in the Hackett River greenstone belt, Slave Province, Northwest Territories
Authors: Fyson W. K. , Frith R. A.
Published: April 2011

Regional foliations resulting from two main phases of deformation within the Archean Hackett River greenstone belt are generally steeply inclined, except near some granitoid plutons where one or both structures are shallow dipping. Inclinations decrease near the plutons with little deviation in regional strike. Near other plutons all structures are steep; in some cases steep second phase foliation passes into the granitoid rock. It is suggested that the shallow dips reflect modifications of regional strain induced solely by those plutons that were rising during the phases of regional deformation. From changes in the structural arrangement along the belt it can be inferred that plutons rose into higher grade metamorphic rocks earlier than into lower grade rocks.A domal structure in basal gneiss could have formed during a late stage of the second deformation. Shallow dipping foliation within the gneiss may, however, reflect not only strain modification during regional deformation and buoyant uplift, but also the initial configuration of an infrastructure.
Paleomagnetic results from three rock units of New Brunswick and their bearing on the Lower Paleozoic tectonics of North America
Authors: Roy J. L. , Anderson P. , Lapointe P. L.
Published: April 2011

Thermal, alternating field (AF), and two-stage (AF followed by thermal) experiments performed on one Silurian (Mascarene Group) and two Devonian (St. George and St. Stephen plutons) rock units indicate that considerable polar movement relative to New Brunswick took place in Siluro-Devonian times. The Mascarene Group yields a pole at 122°E, 02°S, the St. Stephen pluton, a pole at 136°E, 43°S, and the St. George pluton, two poles at 085°E, 38°S and 093°E, 29°N respectively. Although the southern poles lie some 70° south of most North American Silurian and Devonian poles, they are in agreement with poles obtained from two recent studies of Newfoundland rock units. It is unknown if this apparent polar displacement is representative of the entire North American craton or of its eastern margin only. A graphic representation of all available North American data is disconcerting and shows that little is known about the behaviour of the Lower Paleozoic field relative to North America and that many more data are needed to reconstruct the paleomagnetic record.The St. George pluton carries two dual polarity remanences which often are not easily discernible, especially since one of the remanences has an intensity much weaker than the other. The usefulness of vector diagrams for the analysis of multicomponent remanences is demonstrated. Examples are shown where the dual polarity of the weaker remanence, which might otherwise escape notice, can be readily detected on enlarged scale vector diagrams.
Geochemistry of metaanorthosites from a greenstone belt in Karnataka, India
Authors: Naqvi S. M. , Hussain S. M.
Published: April 2011

Sheet-like fine-grained metaanorthosite bodies occur in the 3.5–3.2 Ga greenstone belt of Holenarasipur, Karnataka, India. These bodies are associated with metaperidotitic komatiites, serpentinites, and amphibolites. In texture, grain size, major, and trace element composition, including rare-earth elements (REE), they resemble lunar anorthositic basalts and anorthositic microgabbros. On the basis of these resemblances, similar trends of geochemical evolution of the earth and moon during their early history are indicated. It is suggested that after the accretion of the earth, high temperature conditions might have existed to generate magmas enriched in Ca–Al at or near the surface which resulted in the formation of anorthite-rich basaltic and peridotitic lavas. The incomplete cumulation of the anorthite before and during the extrusion of the ultrabasic lava appears to have given rise to sheet-like anorthosite layers between the metaperidotitic and basaltic komatiites.
Crustal structure from a marine seismic survey off the west coast of Canada
Authors: Clowes Ron M. , Knize Stanislav
Published: April 2011

A marine seismic system for recording near-vertical incidence to wide-angle reflected waves and refracted waves has been used to obtain detailed crustal structure off Canada's west coast. Profiles about 20 km in length were recorded in three regions: the Hudson '70 survey area near 51 °N, 133 °W; west of Queen Charlotte Sound; and in northern Cascadia basin, west of central Vancouver Island. In the first area, the interpretation was completely consistent with the Hudson '70 study, but more detail was provided for the upper crust. About 0.6 km of sediments with velocity 2.4 km/s overly layers 2A and 2B with velocities of 4.0 and 5.5 km/s and thicknesses of 1.1 and 1.5 km respectively. The oceanic layer has a velocity of 6.8 km/s. Off Queen Charlotte Sound, the sediments vary in thickness from 3–3.5 km and are divided into an upper sequence with low velocities (2.1 and 2.8 km/s) and a lower sequence with higher velocities (about 4.2 km/s). Basaltic basement beneath the sediments has a velocity of 5.85 km/s. The seismic data indicate that sediment deposition has been complex, possibly interspersed with thin basalt sills derived from a nearby spreading centre. On the basis of these and other data, Winona basin is proposed to extend northwestward as far as an imaginary line drawn landward from the trough between the Dellwood Knolls. In order to test this proposal and delineate in detail the total sedimentary section, high resolution reflection studies with greater than 2 s of subbottom penetration are required. In Cascadia basin, reflection and refraction interpretations gave consistent results. The entire sedimentary sequence has low velocity values (≤2.6 km/s) and is about 1.8 km thick. A thin layer (0.4–0.7 km) of basaltic basement with velocity ~5.1 km/s lies below the sediments, and in turn is underlain by a 2 km layer with velocity ~6.1 km/s. A near-vertical incidence profile recorded in this study and a stacked record section provided by an oil company show reflections to subbottom depths of ~4.5 km, corresponding to the top of layer 3. The latter is laterally variable and poorly defined. Reflections from within layer 2 are recorded and some may be related to flows of basalt during crustal formation.
Morphology of Archean metabasalt flows, Utik Lake, Manitoba
Authors: Hargreaves R. , Ayres L. D.
Published: April 2011

A 400 m thick sequence of Archean, apparently deep water subaqueous, aphyric, tholeiitic metabasalt flows is well exposed at Utik Lake. It comprises intimately interlayered pillowed and massive flows in about equal proportions, with each layer consisting of one or more flows of similar aspect. Flows were apparently linear in plan view with an average thickness of about 10 m and widths of about 1 km. Eruption of successive flows resulted in relief of up to 20 m on the surface of the volcano.Three flow types are present, and there is a lateral transition towards the flow margin from complex massive flows with autobrecciated flow tops, through simple massive flows, into pillowed flows. This lateral transition appears to represent a decrease in lava supply rate with most of the new lava being concentrated at the moving front of the flow, or an outward increase in viscosity due to cooling. The vertical interlayering of flow types may represent differences in flow rate or viscosity of flows erupted from the same vent, or pillowed flows may have been erupted from more distant vents. In the pillowed flows, most pillows are interconnected and apparently formed by budding and digital advance of lava tubes. Pillows also occur locally at the base of massive flows.
Paleomagnetic studies of bulk mineral separates from the Bark Lake diorite, Ontario
Authors: Buchan Kenneth L.
Published: April 2011

The separation of superimposed stable remanent magnetizations, increasingly a problem in the study of paleomagnetism of metamorphosed terrains, has usually been attempted using indirect techniques such as vector subtraction. In the coarse-grained Bark Lake diorite of the Grenville Province, two stable and one unstable component, often superimposed in individual samples, are shown to reside in different rock-forming mineral fractions. They are directly separated by orienting small aggregates of dark or light grains and are measured and demagnetized using standard paleomagnetic equipment.
Late Pleistocene history and geomorphology, southwestern Vancouver Island, British Columbia
Authors: Alley Neville F. , Chatwin Steven C.
Published: April 2011

The major Pleistocene deposits and landforms on southwestern Vancouver Island are the result of the Late Wisconsin (Fraser) Glaciation. Cordilleran glaciers formed in the Vancouver Island Mountains and in the Coast Mountains had advanced down Strait of Georgia to southeastern Vancouver Island after 19 000 years BP. The ice split into the Puget and Juan de Fuca lobes, the latter damming small lakes along the southwestern coastal slope of the island. During the maximum of the glaciation (Vashon Stade), southern Vancouver Island lay completely under the cover of an ice-sheet which flowed in a south-southwesterly direction across Juan de Fuca Strait, eventually terminating on the edge of the continental shelf. Deglaciation was by downwasting during which ice thinned into major valleys and the strait. Most upland areas were free of ice down to an elevation of 400 m by before 13 000 years BP. A possible glacier standstill and (or) resurgence occurred along Juan de Fuca Strait and in some interior upland valleys before deglaciation was complete. Glacial lakes occupied major valleys during later stages of deglaciation.