bluuebunny/crossref_metadata_2025 huggingface dataset:
Paleogeographic conditions in the western Pelagonian margin in Greece during the initial rifting of the continental area
Authors: Mountrakis D. , Sapountzis E. , Kilias A. , Eleftheriadis G. , Christofides G.
Published: April 2011

The uppermost Paleozoic metaclastic sequences of the Pelagonian zone in northern Greece are connected to the western margin of the zone. They represent paleogeographic conditions of a deltaic environment and continental slope, which are related to the separation of the Paleozoic continent and the initial rifting in the western ophiolite belt in Greece. The metaclastic sequences define the western (external) boundary of the Pelagonian zone, and are used to find the continuation of this boundary in the Sporades and Oinouses islands in the Aegean Sea, in order to help answer the question of the connection between the Hellenides and the Taurides in Turkey.
An application of photoelastic models to explain microfractures and joints in carbonate strata
Authors: Gupta U. Das , Currie J. B.
Published: April 2011

A two-dimensional photoelastic model constructed of Araldite and Hysol plastic is used to study how preferentially oriented microfractures originate in carbonate rocks. The model experiments suggest that orthogonal sets of microfractures should trend parallel to principal tectonic axes and that when diagenetic changes, such as dolomitization, are intense microfractures could be generated during both loading and unloading episodes in the history of a sedimentary basin.Petrographic observation of carbonates in the Turner Valley Formation illustrates the occurrence of microfractures. Laboratory tests demonstrate their preferred alignment in principal tectonic directions. Field measurement of joints in Turner Valley strata along Elbow River in southwest Alberta shows that the pattern of larger fractures can also consist of orthogonal fracture sets.The model experiments indicate therefore that development of preferentially oriented sets of microfractures in carbonates is probably a usual result of diagenetic and tectonic events that most of these rocks undergo during basinal evolution.
The late Tertiary – Quaternary stratigraphic record of the Duck Hawk Bluffs, Banks Island, Canadian Arctic Archipelago
Authors: Vincent J.-S. , Occhietti S. , Rutter N. , Lortie G. , Guilbault J.-P. , Boutray B. de
Published: April 2011

The Duck Hawk Bluffs, of southwestern Banks Island in the Canadian Arctic Archipelago, record a succession of late Tertiary – Quaternary events. Organic-bearing sediments of eolian, fluvial, and lacustrine origin that overlie the Late Cretaceous Kanguk Formation and the Miocene Beaufort Formation record preglacial events of Pliocene and (or) early Quaternary age and are assigned to the Worth Point Formation. These are covered by glacial sediments of the Duck Hawk Bluffs Formation associated with the Banks Glaciation, the oldest of the three recognized glaciations to reach the island. Associated with the glacial deposits are marine or glaciomarine sediments deposited in the glacio-isostatically depressed area as the ice both advanced and retreated. These sediments are in turn covered by interglacial sediments (Morgan Bluffs Formation), by marine deposits (Big Sea sediments associated with the Thomsen Glaciation), and by younger interglacial sediments (Cape Collinson Formation). Events associated with the early Wisconsinan M'Clure Stade of the last or Amundsen Glaciation are recorded in a coastal section east of the Duck Hawk Bluffs. There, marine deposits (pre-Amundsen Sea sediments) are covered by glacial deposits (Sachs Till) of the M'Clure Stade, D/L ratios of aspartic acid in fossil wood from the Morgan Bluffs and Cape Collinson interglacial sites, respectively, vary between 0.22 and 0.31 and 0.12 and 0.13, while Holocene wood is 0.08. A composite section is proposed for these bluffs that record some of the oldest events in the Canadian Quaternary and the various units are correlated with the previously published Quaternary framework for Banks Island.
Progressive metamorphism of pelitic and quartzofeldspathic rocks in the Grenville Province of western Labrador — tectonic implications of bathozone 6 assemblages
Authors: Rivers T.
Published: April 2011

Aphebian metapelites and quartzofeldspathic rocks from the Grenville Province south of the Labrador Trough display progressive changes in mineral assemblages as a result of Grenvillian metamorphism, consistent with variation in grade from greenschist to upper amphibolite facies. The following metamorphic zones have been delineated: (i) chlorite–muscovite; (ii) chlorite–muscovite–biotite; (iii) chlorite–muscovite–biotite–garnet; (iv) muscovite–staurolite–kyanite; (v) muscovite–garnet–biotite–kyanite; (vi) muscovite–garnet–biotite–kyanite–granitic veins; (vii) K–feldspar–kyanite – granitic veins; (viii) K-feldspar–sillimanite–granitic veins. Reactions linking the lower grade metamorphic zones are interpreted to be dehydration phenomena, whilst anatectic reactions occur at higher grades. At lower metamorphic grades aH2O was high [Formula: see text] but it declined progressively as water entered the melt phase during higher grade anatectic reactions. With the onset of vapour-absent anatexis, the restite assemblage became essentially "dry" [Formula: see text], and biotite breakdown occurred in granulite-facies rocks east of the study area. Consideration of available experimental data suggests that metamorphic temperatures ranged from approximately 450 to 750 °C across the study area. Lithostatic pressure during metamorphism reached about 8 kbar (800 MPa) in the high-grade zones, with estimates at lower grades being poorly constrained; however, a steep pressure gradient across the map area is postulated.This is the first reported occurrence of bathozone 6 assemblages from a progressive metamorphic sequence, and it indicates the presence of an unusually great thickness of supracrustal rocks during the Grenvillian Orogeny. This was achieved by imbricate stacking of thrust slices, perhaps doubling the thickness of the crust in the Grenville Front Tectonic Zone, creating a huge gravity anomaly of which a remnant still persists today.
Patterns of total and incremental strain in subsiding troughs: experimental centrifuged. models of inter-diapir synclines
Authors: Dixon J. M. , Summers J. M.
Published: April 2011

The experimental technique of centrifuge modelling has been used to elucidate patterns of total strain and progressive deformation associated with troughs that form by gravitational subsidence of a dense cover into a less dense basement. Model structures are analogous to synclines found between mantled gneiss domes, and the models provide data with which to test the hypothesis that Archean greenstone belts are products of vertical gravity tectonics.Experimental results include the following. (1) Strain within the main body of subsiding belts is dominated by strong horizontal contraction and vertical extension. In natural structures this strain pattern would produce vertical foliation and steeply plunging mineral lineation. (2) Within cover units near trough margins the flattening plane trends parallel with or at a low angle to the cover–basement interface at all levels in the trough. (3) Patterns of strain within subsiding troughs, at least as expressed in surface deformation, reflect the geometry of the cover–basement interface at depth. Flow within the cover units converges towards points of maximum trough subsidence to produce local vertical constrictive strain. Deformation above trough saddles is characterized by vertical flattening strain. (4) Horizontal shortening within a subsiding, stratified cover sequence produces early folds with horizontal axes and steep axial surfaces. Where the stratified sequence forms a relatively low-density unit within the cover, folds and thrusts verge consistently away from the trough axis. Continued subsidence and horizontal contraction tend to rotate initially shallowly dipping structures into steeply dipping attitudes.
Analyse dendrochronologique d'un glissement de terrain de la région du Lac à l'Eau Claire (Québec nordique)
Authors: Bégin Christian , Filion Louise
Published: April 2011

A landslide in Clearwater Lake has been dated to spring of 1933 from tree-ring analysis (reaction wood, growth suppression, and corrosion scars). From the 52 sampled trees, seven peak periods of movement were registered within the site before landslide occurrence: 1785, 1815, 1827, 1829, 1852–1853, 1871–1872, 1897, and 1926. After a slow progression lasting 200 years, the slope movements accelerated in 1926, as indicated by suppressed growth rings. It is proposed here that the landslide was the outcome of a long-term slope development partly controlled by climate (precipitation). Postdisturbance forest regeneration (between 1950 and 1976) on the newly exposed substrate is also related to climatic conditions.
Middle to Upper Ordovician graptolite biostratigraphy of Peel River and other areas of the northern Canadian Cordillera
Authors: Lenz A. C. , Xu Chen
Published: April 2011

Middle to Upper Ordovician (Darriwilian to Bolindian) graptolite zones of the northern Canadian Cordillera comprise the following: Glyptograptus euglyphus Zone of late Darriwilian (Llandeilo) age, Nemagraptus gracilis Zone of early Gisbornian (late Llandeilo and earliest Caradoc) age, Climacograptus bicornis and Dicranograptus clingani? zones of early to mid-Gisbornian (early to mid-Caradoc) age, Orthograptus quadrimucronatus Zone of Eastonian (late Caradoc) age, and Dicellograptus ornatus zone of Bolindian (Ashgill) age.A prominent biostratigraphic break equivalent to the spiniferus to hians kirki zones (Eastonian) is shown to exist between the clingani? Zone and the overlying quadrimucronatus Zone.Thirty eight common and (or) important species are illustrated, of which one new species, Orthograptus expansus n. sp., is described and figured.
A study of joints and stress-release buckles in Palaeozoic rocks of the Niagara Peninsula, southern Ontario
Authors: Williams Howard R. , Corkery D. , Lorek E. G.
Published: April 2011

Joint sets in Palaeozoic bedrock of the Niagara Peninsula occur at 005, 045, 085, and 135° orientations. There is no consistent change in joint orientation with lithology, rock age, or location within the area. Drainage pattern analysis using airphotos and topographic maps indicates that glacial drift effectively masks underlying joint systems. Rare calcite and gypsum mineralization occurs along joints of 085 and 135° trend. Stress-relief buckles indicate a contemporary maximum principal stress along an 050° trend. Joint systems in the Niagara Peninsula are similar in trend to those on the Appalachian Plateau.
Thermoluminescence dating studies of rapidly deposited silts from south-central British Columbia
Authors: Berger Glenn W.
Published: April 2011

To determine whether Quaternary sediments from small lake and fan deposits can be dated by thermoluminescence (TL) methods, I have applied recently proposed techniques for TL dating to known-age, rapidly deposited silts and have examined the sensitivity of the TL of fine-grain feldspars and quartz to light. These feldspar-dominated silts exhibited little or no detectable anomalous fading. The TL of quartz was observed to be very resistant to light with wavelengths above ~400 nm, whereas that of feldspars was sensitive to all visible wavelengths. No significant resetting of the TL of the 11 ka old glaciolacustrine silt (deposition rate [Formula: see text]) could be detected with these techniques, implying that silts deposited at such rates into small, glacier-bordered lakes cannot be dated by these methods. However, accurate equivalent doses were measured for the derivative 7.5 ka old mudflow silts (~1 mm/year), but only with the use of the R–Γ technique applied to the feldspars.
Silurian (Llandovery–Wenlock) conodonts from the base of the Heceta Limestone, southeastern Alaska
Authors: Savage Norman M.
Published: April 2011

The base of the Heceta Limestone, exposed on Cap Island in southeastern Alaska, appears to lie close to the top of the celloni Zone. The succeeding 8 m of strata lies within the amorphognathoides Zone and part of the ranuliformis Zone. This Cap Island faunal sequence consists of 12 previously described and largely cosmopolitan taxa and nine new, possibly more provincial, taxa. It is particularly characterized by the distinctive new taxa Tuxekania barbarajeanae, Neospathognathodus chapini, Tokeenia furcata, and Aspelundia capensis. The section is of late Llandovery to early Wenlock (Silurian) age.
Geochronology of the Narakay Volcanic Complex: implications for the age of the Coppermine Homocline and Mackenzie igneous events
Authors: Bowring Samuel A. , Ross Gerald M.
Published: April 2011

U–Pb isotope analysis of four zircon separates from a rhyolite porphyry that is part of the bimodal Narakay Volcanic Complex (Dease Arm, Great Bear Lake) yields an age of 1663 ± 8 Ma. East-trending feldspar-phyric dykes that cut the complex yield zircons that are, within analytical error, the same age as the porphyry. The Narakay Volcanic Complex occurs in the upper part of the Hornby Bay Group, the lowermost group of the Coppermine Homocline, and the stratigraphic position of the dated rocks indicates that 1663 Ma is the depositional age of the upper Hornby Bay Group.This is the first U–Pb zircon age determined from rocks of the Coppermine Homocline and has important implications for previous geochronology and extrabasinal correlation. Earlier Rb–Sr dates from the conformably overlying Coppermine River Group basalts of ca, 1200 Ma, when taken together with the new data, suggest that the Dismal Lakes Group, which conformably overlies the Hornby Bay Group, was deposited during a period of more than 400 Ma. Given that the Dismal Lakes Group is a relatively thin, transgressive shallow platformal succession, this amount of time for deposition is interpreted to be excessive. If this interpretation is correct, then it follows that either there are many unrecognized diastems in the Dismal Lakes Group, or presently available dates for rocks of the Mackenzie magmatic event in the Coppermine Homocline region may be too young by several hundred million years.
Variability within a saprolite deposit near Quebec City, Canada
Authors: Kimpe Christian De , Wang Chang , Laverdière Marc , LaSalle Pierre
Published: April 2011

Samples were collected in two trenches opened in a saprolite developed in a mylonite derived from biotite–garnet gneiss near Quebec City in order to investigate the spatial variability from the points of view of morphological, physical, mineralogical, and chemical properties. Phyllosilicate assemblages were: (a) kaolinite, (b) mica, (c) kaolinite + mica, and (d) mica + interstratified minerals (+ smectite). Grouping of the samples according to prominent colour in the matrix showed a relation between chroma and kaolinite content. Total chemical analyses were in good agreement with mineral assemblages. The spatial distribution of these assemblages corresponded to the degree of transformation of the gneiss into mylonite.
The Border Ranges ultramafic and mafic complex, south-central Alaska: cumulate fractionates of island-arc volcanics
Authors: Burns Laurel E.
Published: April 2011

A discontinuous, elongate zone of mafic and ultramafic plutonic rock crops out in south-central Alaska for a distance of more than 1000 km. Intermediate- and detailed-scale geologic mapping, petrographic study, and compositional data suggest that the plutonic rocks are compositionally, petrologically, and mineralogically distinct from rocks in mid-ocean ridge and back-arc basin ophiolites. The mafic and ultramafic rocks instead represent part of the plutonic core of an intraoceanic island arc.The mafic–ultramafic zone, referred to as the Border Ranges ultramafic and mafic complex (BRUMC), is composed of ultramafic cumulates, gabbronorite cumulates, and massive gabbronorites. A very minor amount of tectonized ultramafic rock of mantle origin is present in the southern part of the BRUMC. A thick sequence of andesitic volcanic rocks, the Talkeetna Formation of Early Jurassic age, lies to the north of and structurally above the mafic–ultramafic zone. Voluminous calcalkaline plutons composed of quartz diorite, tonalite, and minor granodiorite intrude both the mafic plutonic complexes and the andesitic volcanic rocks.The cumulate ultramafic sections are largely composed of dunite ± chromite, wehrlite, clinopyroxenite, and websterite and are characterized by a wide range of Mg–Fe silicate compositions (Fo90–81; En45–50, Fs1–7, Wo45–49; En88–82, Fs11–17), chrome-rich spinels, and a lack of plagioclase. The gabbroic sections are composed of gabbronorites with up to 10–15% magnetite ± ilmenite. Hornblende, if present, is a very minor phase in most gabbroic rocks. The coexisting mineral compositions seen in the gabbroic rocks of the BRUMC (relatively iron-rich pyroxene—Fs6–13, En45–40; En81–63 —and calcic plagioclase An75–100) and their association with magnetite are common in plutonic xenoliths in island-arc rocks.The mineralogy and composition of the gabbroic rocks in the BRUMC are consistent with the fractional crystallization products predicted to be associated with the formation of andesite from a basaltic magma. Consideration of additional data, including detailed and regional field mapping of the plutonic and volcanic rocks and geochronology of the BRUMC and the nearby Talkeetna arc volcanic rocks, strongly suggests that the BRUMC represents relatively deep fractional crystallization products of magmas that produced the Talkeetna Formation volcanic rocks. Field relationships also indicate that intrusion of quartz diorites, tonalites, and granodiorites of batholithic proportions occurred slightly later than formation of the BRUMC.
Geochemistry and origin of the Regan Intrusive Suite and other granitoids in the northeastern Slave Province, northwest Canadian Shield
Authors: Frith R. A. , Fryer B. J.
Published: April 2011

The Regan Intrusive Suite of about 100 plutons of tonalite, granodiorite, and quartz diorite intruded the Yellowknife Supergroup and migmatite terrain in the northwest Slave Structural Province 2.59 Ga ago. Rare-earth-element (REE), trace-element, and major-element analyses from 39 representative whole rocks from the suite suggest it was derived by batch melting of the crust, producing a parental magma of tonalitic or granodioritic composition. By analysing REE from different parts of a zoned pluton, it was concluded that REE distribution was controlled by early separation of quartz diorite from the parent magma by flow differentiation and that the bulk of the REE were contained in early, cumulate, accessory apatite and monazite. The residual magma was further fractionated in pipelike magma chambers during ascent into more leucocratic rocks. Chondrite-normalized REE patterns of single-lithology plutons are similar to lithologies in zoned plutons, and it is proposed they initially segregated during ascent. It was found that granites, which were formerly grouped with the suite, formed in three ways, only one of which is related to the Regan Intrusive Suite.Study of 2.67 Ga old synvolcanic tonalite pluton revealed a strong covariance of light REE with those of the bimodal, calc-alkaline Hackett River Group of volcanic rocks. The data imply a common crustal source, but mass balance requires larger volumes of felsic volcanic rocks than are presently preserved, suggesting that much of the erupted felsic pyroclastic rocks were eroded. Partial melts from synvolcanic tonalite during subsequent regional metamorphism differentially depleted host rocks in REE and concentrated Eu and heavy rare-earth elements (HREE) in trondhjemite pegmatites.
Tectonic evolution of southwestern Newfoundland as indicated by granitoid petrogenesis
Authors: Wilton Derek H. C.
Published: April 2011

Four granitoid suites are recognized in the region of the Cape Ray Fault Zone of southwestern Newfoundland. The two oldest (Ordovician–Silurian (?)) suites represent partial melts of their enclosing host rocks. The Port aux Basques granite is modelled as a partial melt of the gneissic component of its host, Port aux Basques Complex. The Cape Ray granite forms a dominantly tonalitic terrane derived by partial melting of ophiolitic material. The Red Rocks granite and a megacrystic phase of the Cape Ray granite form coherent lines of geochemical descent from the parental tonalite but show evidence of some continental crust contamination.The Late Devonian Windowglass Hill granite is a subvolcanic equivalent of felsic volcanic rocks in the Windsor Point Group. Both units were derived as partial melts of continental crust.The post-tectonic, Late Devonian to Early Carboniferous Strawberry and Isle aux Morts Brook granites constitute the youngest granitoid suite in the region. These A-type granitoids were derived as partial melts of an underlying depleted granulitic (felsic) crust. The depleted nature of the source may have resulted from previous generation of the Windowglass Hill granite and Windsor Point Group. The only possible protolith for the granulitic source is Precambrian Grenvillian gneiss. The presence of this gneiss beneath the Cape Ray Fault Zone of southwestern Newfoundland implies that the complete series of lithologies is allochthonous.
The spore genus Archaeoperisaccus and its occurrence within the Upper Devonian Imperial Formation, District of Mackenzie, Canada
Authors: Braman D. R. , Hills L. V.
Published: April 2011

The miospore genus Archaeoperisaccus is restricted to the late Givetian – possibly early Famennian, is most common in the Frasnian, and is known from northern Canada, Spitsbergen, western and eastern USSR, and China. Twenty-three species are briefly discussed and three, A. art us, A.regalis, and A. signus, are described as new. Eight species occur in the Frasnian portion of the Imperial Formation, District of Mackenzie.
Scoliomus puercensis Williston and Case, 1913, identified as a junior synonym of Sphenacodon ferox Marsh (Reptilia, Pelycosauria)
Authors: Reisz Robert R. , Berman David S.
Published: April 2011

The pelycosaurian reptile Scoliomus puercensis Williston and Case, 1913, based on several postcranial elements from the Permo-Pennsylvanian redbeds of the Cutler Formation of north-central New Mexico, proves on comparative study to be a junior synonym of Sphenacodon ferox of the family Sphenacodontidae. As Romer and Price noted, features originally cited as unique to the holotype are attributable to imperfect restoration. Although correctly recognizing S. puercensis as belonging to the suborder Sphenacodontia, they mistakenly assigned it to the family Varanopseidae, mainly on the basis of its small size.
A petrologic and Rb–Sr isotopic study of intrusive rocks near Fairbanks, Alaska
Authors: Blum Joel D.
Published: April 2011

Epizonal granodiorite and granite plutons intrude the northwestern portion of the Yukon Crystalline Terrane near Fairbanks, Alaska. Mineralogic, major-oxide, and trace-element studies indicate that the plutons represent a comagmatic fractionation suite. A Rb–Sr whole-rock isochron for one pluton yields an age of 90.9 ± 0.9 Ma, in agreement with previous K–Ar dating of biotite and hornblende and an initial 87Sr/86Sr ratio of 0.71238 ± 0.00014. The elevated initial 87Sr/86Sr ratio suggests that the plutons may have had a different source from that of the belt of subduction-related, mid-Cretaceous plutonic rocks found farther to the southeast in the Yukon Crystalline Terrane. In contrast, they appear to have been formed at least in part by anatectic melting of Late Proterozoic or early Paleozoic crustal rocks. Comparison of aplite dike compositions with the synthetic granite system, estimates of average uplift rate, and K–Ar cooling ages of surrounding schists all indicate that the magmas that formed the plutons near Fairbanks intruded much higher into the crust after anatectic melting and crystallized at a relatively shallow depth of 3–5 km.
Cranial anatomy of the primitive reptile Procolophon
Authors: Carroll Robert L. , Lindsay William
Published: April 2011

The skull of the Lower Triassic reptile Procolophon is described on the basis of newly prepared specimens in the collection of the British Museum (Natural History) and from casts made from high-fidelity natural molds. It is concluded that this genus had a large tympanum supported by the supratemporal, squamosal, and quadratojugal. The stapes remains incompletely known but probably functioned as part of an impedance-matching system comparable with that of modern lizards. The teeth of the upper and lower jaws are inset from the margin of the skull, suggesting the presence of cheeks. Jaw movement is confined to the vertical plane. Neither resorption pits nor weakly attached crowns provide evidence of tooth replacement. The position of the teeth is controlled so that the upper and lower teeth interdigitate exactly, with wear facets on the anterior and posterior surfaces. A natural cast of the nasal cavities resembles that of Triassic cynodont therapsids, suggesting the presence of turbinais and extensive olfactory epithelium. Procolophonoids may have evolved from the primitive, protorothyrid reptiles. They show no close affinities with other anapsids.
Structural history of continental margin sediments beneath the Bay of Islands Ophiolite, Newfoundland
Authors: Waldron John W. F.
Published: April 2011

Deformed continental margin sediments of the Curling Group underlie the Bay of Islands Ophiolite in the Humber Arm allochthon of western Newfoundland. Within the allochthon, tectonic slices of sediments are separated by zones of mélange. The earliest structures in the slices are synsedimentary features produced by soft-sediment deformation on the continental slope or rise. Later, west-facing asymmetrical F1 folds without penetrative axial plane cleavage were probably produced during the emplacement of the allochthon in the Middle Ordovician Taconic Orogeny. Associated extensional structures include shear-fracture and extension-fracture boudins. Pervasive cataclastic shearing of shale and boudinage of competent beds produced mélange between slices. Shear surfaces and the original bed-parallel fissility of the shale both contribute to the anastomosing fabric of the mélange matrix.A subsequent folding event of probable Acadian age produced upright to moderately inclined F2 folds with axial-plane cleavage increasing in intensity eastwards across the allochthon. This event refolded the folds, thrust slices, and mélange zones produced during emplacement. Later, gentle cross folds, associated with sporadic development of crenulation cleavage, produced culminations and depressions on the F2 fold hinges.
Cranial anatomy of Stenonychosaurus inequalis (Saurischia, Theropoda) and its bearing on the origin of birds
Authors: Currie P. J.
Published: April 2011

The discovery in recent years of additional skull material of the rare carnivorous dinosaur Stenonychosaurus inequalis prompts the first thorough description of this animal. This species, known only from the Upper Cretaceous strata of North America, is closely related to, but distinct from, the two described species of Saurornithoides from Mongolia. A derived characteristic, an inflated parasphenoid capsule, is found in both the saurornithoidids and ornithomimids, strongly suggesting shared ancestry. The middle ear cavity is well defined and is connected to at least two systems of sinuses in the skull bones. Periotic sinuses like these have not been described in theropods, and their presumed absence has been used as evidence against theropod ancestry of birds. Although these and other cranial characteristics of Stenonychosaurus do not prove that birds descended from theropods, they strengthen the claim that small carnivorous dinosaurs are more plausible bird ancestors than either pseudosuchians or crocodiles:
Uranium uptake by algae: experimental and natural environments
Authors: Mann H. , Fyfe W. S.
Published: April 2011

Monocultures of the freshwater green algae Ankistrodesmus sp. grown at pH 8.1–8.2 and 13–16 °C, in solutions containing 2 ppm U chelated with EDTA, acquired 1000 – 10 000 ppm uranium by dry weight. In some algae, a uranium mineral of cubic habit was detected. At Elliot Lake, Ontario, Euglena sp. thriving in tailings discharge contain on average 184 ppm U. Tailings waters contain high concentrations of dissolved uranium, on average 273 ppb. In natural drainage waters, above and below tailings, dissolved U averages 0.23 ppb. Thames River algae average 28 ppm U, whereas waters have an average dissolved U of 1.46 ppb, representing about twice the global mean riverine value of 0.6 ppb U.
Hydrothermal petroleum: genesis, migration, and deposition in Guaymas Basin, Gulf of California
Authors: Simoneit Bernd R. T.
Published: April 2011

Hydrothermal activity and seabed mounds have been explored in Guaymas Basin by the Deep Sea Drilling Project (DSDP), piston coring, dredging, and diving with the Deep Submersible Research Vessel (DSRV) Alvin. Sedimentary organic matter, derived primarily from immature, degraded microbial detritus, is easily converted to petroleum under the hydrothermal regime. These petroleums are mature and migrate in the fluids and by diffusion to the seabed. The fluid migration is aided by near-critical aqueous solution and supercritical carbon dioxide and hydrocarbons. Petroleum compositions vary from condensates to naphthenic to waxy, all with significant amounts of asphaltenes and hydrothermal products such as olefins and toxic polynuclear aromatic hydrocarbons (PAH). The heavy ends condense at the seabed, depositing mainly as a cement with the sulfides and other minerals and to a lesser extent as entrapped oil and crystalline wax in vugs and conduits of the mounds. The PAH are high-temperature resynthesis-aromatization products from residual organic matter, and they are present in all oils but also deposit as discrete trace fractions in the hottest regions of the vent systems. Preliminary estimates of total hydrocarbon generation during hydrothermal alteration indicate that this process has a significant petroleum potential.
Occurrence and regional geological setting of Paleozoic rocks on the Grand Banks of Newfoundland
Authors: King Lewis H. , Fader Gordon B. J. , Jenkins W. A. M. , King Edward L.
Published: April 2011

Analyses of seismic reflection profiles supported by lithological and palynological studies of core samples from submarine outcrops indicate that the lower Paleozoic succession of the Avalon Terrane, southeast Newfoundland, is continuous offshore. The succession crops out over an area greater than 30 000 km2 and is approximately 8 km thick. The sequence is dominantly siltstone and is of Late Cambrian to ?Devonian or younger age. It is relatively unmetamorphosed, underlain by Hadrynian acoustic basement, and overlain along its eastern and southern margins by a Mesozoic–Cenozoic succession that is economically important from an oil and gas perspective.Lithofacies studies indicate that in Early Ordovician time restricted shallow-marine conditions probably prevailed over a vast area of the Avalon Terrane. Upper Ordovician and Silurian siltstones show evidence of deposition under more-dynamic and well-oxygenated conditions and probably represent a normal shallow-marine environment. Redbeds of possible Devonian or younger age are interpreted to be of continental origin. Black shales of Ordovician age are potential source rocks for the generation of hydrocarbons.
Isotope geochemistry of frost-blister ice, North Fork Pass, Yukon, Canada
Authors: Michel Frederick A.
Published: April 2011

Oxygen-18 and deuterium abundances vary with depth in ice from a frost blister at a spring site near North Fork Pass, Yukon. They indicate that the ice was formed by continuous downward freezing under nearly ideal, closed-system conditions in a water-filled cavity. Weighted mean values of δ18O and δ2H for the ice samples indicate that the frost–blister ice was formed from groundwater similar to that of nearby springs. The slope of the regression line (5.1) for the 18O and 2H data of the frost–blister ice suggests that nonequilibrium fractionation conditions existed during freezing. Tritium concentrations in the ice show irregular variations with depth; the weighted mean 3H concentration for the ice is, however, similar to that of the spring water.
Metamorphic conditions of late Archean high-grade gneisses, Minnesota River valley, U.S.A.
Authors: Moecher D. P. , Perkins III D. , Leier-Englehardt P. J. , Medaris Jr. L. G.
Published: April 2011

A detailed, comparative geothermobarometric analysis for the Minnesota River valley (MRV) Archean gneiss and migmatite terrane yields temperature and pressure ranges of 650–750 °C and 4.5–7.5 kbar (450–750 MPa), based on garnet–biotite, two-feldspar, garnet–clinopyroxene, garnet–cordierite, orthopyroxene–clinopyroxene, and magnetite–ilmenite thermometry and garnet–cordierite–sillimanite–quartz and garnet–orthopyroxene–plagioclase–quartz barometry. The temperature variation observed is interpreted to be primarily a result of varying degrees of re-equilibration of assemblages with falling temperature but may include real temperature variations between areas exhibiting granulite facies versus upper amphibolite facies–migmatitic lithologies. The large pressure range is primarily a result of differences among the pressure calibrations applied but may also record variations in pressure within the terrane. Lower pressures are consistent with the occurrence of cordierite-bearing assemblages at Granite Falls and Delhi. Based on the compositional zoning patterns determined in garnet adjacent to clinopyroxene, orthopyroxene, cordierite, and biotite and in orthopyroxene adjacent to garnet, the granulites are interpreted to have experienced nearly isobaric cooling, suggesting a magmatically influenced thermal regime may have been responsible for the high-grade conditions and relatively high transient metamorphic gradient (32 °C/km) attained in the MRV.
The Mont Saint Hilaire plutonic complex: occurrence of excess 40Ar and short intrusion history
Authors: Gilbert Lisa A. , Foland K. A.
Published: April 2011

Mont Saint Hilaire is an approximately 10 km2 alkaline plutonic complex in the Monteregian petrographic province of Quebec. The complex consists of an older, western half of alkali gabbros and an eastern portion of nepheline syenites and magmatic breccias. The intrusives were emplaced at depths of no more than a few kilometres into Paleozoic sedimentary rocks through the underlying Grenville basement. 40Ar/39Ar analyses of amphibole yield complex age spectra in which the apparent ages decrease with increasing heating temperature. Conventional K–Ar analyses of amphibole, pyroxene, and feldspar yield anomalously old dates. These data indicate the presence of small yet significant amounts (up to 8 × 10−11 mol/g) of excess 40Ar. The quantities of excess argon are variable between rocks and minerals from the same rock. In contrast, biotites yield concordant plateaus and consistent ages ranging only from 124.1 to 124.6 Ma. These data define the age of the complex (124.4 ± 1.2 Ma) and imply a short time span of emplacement of about 0.5 Ma or less. The restricted time interval suggests the various lithologies are cogenetic. The nature of the amphibole 40Ar/39Ar spectra indicates that excess 40Ar was acquired after crystallization. The 40Ar could have been present in the initial magma either from crustal assimilation or from a mantle source. Alternatively, it could have been derived from outgassing of older crustal rocks. The occurrence of excess 40Ar in epizonal plutons may be a more widespread phenomenon than commonly recognized.
Ground ice conditions near Rea Point and on Sabine Peninsula, eastern Melville Island
Authors: French H. M. , Bennett L. , Hayley D. W.
Published: April 2011

Using data obtained in the winter of 1981–1982 from trench excavations in the vicinity of Rea Point, volumetric ice contents with depth have been calculated for Paleozoic age (Weatherall, Griper Bay, and Hecla Bay formations) and Quaternary age (alluvium and deltaic sands) sediments. In addition, borehole data from Sabine Peninsula and observations from the Panarctic Sherard Bay exploratory wellsite sump in the late winter of 1982–1983 enable similar values to be calculated for Mesozoic age (Christopher Formation) sediments. Although these data are believed typical of large areas of eastern Melville Island, they are only first estimates, since considerable site-specific variability may be present. Shale of the Christopher Formation possesses the highest ice content, typically between 30 and 70% by volume throughout the profile. Weatherall and Griper Bay siltstones and sandstones also contain locally significant ice contents (50–70%) at depths of 0.5–1.5 m. Pore and segregated ice are the dominant ice types. Ice-wedge ice is a relatively insignificant component of total ice content in any of the sediments examined.
The morphology, mineralogy, and behavior of u "fine-grained" gold from placer deposits of Alberta: sampling and implications for mineral exploration
Authors: Giusti L.
Published: April 2011

The morphology of a large number of gold grains from stream sediments of the North Saskatchewan River and the Athabasca River was studied, together with the partitioning of the placer gold between various size fractions.Two major morphological varieties of gold were observed: (1) flaky, scaly gold, with folded and hammered edges, and with crystals or crystal faces still visible on the surface; and (2) "sandwiched," droplike particles, sometimes toroidal. About 5% of both types of gold were found to be coated with "new," secondary gold.The size of the majority of the gold grains studied varies between 0.500 and 0.010 mm. The most frequent size range in the North Saskatchewan River is 0.125–0.250 mm, whereas in the Athabasca River it is 0.063–0.125 mm. An important fraction of the gold from both rivers is smaller than 0.063 mm.The average Corey shape factor (CSF) of the gravity-recovered gold increases as the particle size decreases, whereas the gold grains lost to the tailings indicate very low average shape factors (i.e., high degree of flattening). This apparent increase in CSF for the smallest fractions recovered when using mechanical techniques is due to the fact that the flaky gold particles are more difficult to recover than the more spherical ones. Moreover, the presence of a gold-rich rim on all the gold grains increases their hydrophobicity.The sampling procedure to be adopted in Alberta and, more generally, in glaciated terrains is discussed. In particular, the use of the −63 μm fraction for routine sampling of stream sediments is suggested.
Fluids in cupriferous dolostones and dolomite veins, Proterozoic Dunphy Formation, Labrador Trough
Authors: Schrijver K. , Bertrand R. , Chagnon A. , Tassé N. , Chevé S. R.
Published: April 2011

The metamorphosed, cryptalgal dolostones contain Cu–Fe-sulfides in dolospar-filled fenestrae and in metamorphic dolospar–quartz veins. Locally, dolostones and veins are altered to pink dolomite, with sulfides replaced by goethite. Analyses of fluid inclusions, isotopic composition of C and O, and phyllosilicates were made to try to determine the properties of fluids involved in bringing about these features.Dolospar and vein quartz contain "workable" fluid inclusions (2–10 μm). A crystal of salt is present in most inclusions in quartz and probably in dolospar (Tmice: −30 to −20 °C). Inclusions in veins have CO2/H2O and CH4/H2O mole ratios of 0.005 and 0.0004, Th (liquid) 242–312 °C, and Tf (dissolution of salt) 143–250 °C. Th and Tf are linearly correlated. The range of Th in dolostones is 225–290 °C, significantly lower than that of veins. This difference is probably due to strain-induced leakage in vein inclusions subsequent to trapping of the brine present during metamorphism. The pink dolomites are characterized by fluid inclusions with ~6 wt.% NaCl equiv. and Th of ~160 °C. Partial equilibration with oxidizing waters during a post-metamorphic event is inferred. A δ13CPDB of +15.5‰ for dolomite is ascribed to an early diagenetic stage of microbial methanogenesis. Isotopic ratios were preserved in veins and lowered by ~2‰ in portions of the pink dolomite.
Multiple folding and pluton emplacement in Archean migmatites of the southern Vermilion granitic complex, northeastern Minnesota
Authors: Bauer Robert L.
Published: April 2011

Analysis of folding in the southwestern Vermilion granitic complex suggests that F2 folds, which formed in a regional north–south compressional regime, were locally reoriented during pluton emplacement and were subsequently refolded by F3 folds generated by continuing north–south compression. An east–west-trending F2 antiform, crossing the boundary between the southern Vermilion granitic complex and the adjacent Vermilion district, was intruded by a tonalite pluton during the later stages of F2 folding. Either emplacement of the pluton or emplacement of the nearby Lac La Croix batholith is believed to have reoriented the F2 fold so that, subsequently, the pluton and the F2 antiform were refolded by a doubly plunging east–west-trending F3 fold, now cored by the pluton.A similar relationship occurs between F2 and F3 folds north of the Vermilion fault in the main portion of the complex. Here, F3 conical folds, not cored by plutons, refold F2 folds about northwest-trending vertex axes. Analysis of the refolding of minor F2 folds and L2 lineations in this area suggests they were nearly coaxial with the F3 folds prior to the F3 folding.
Late Quaternary vegetation history of the Fishhook Bend area, Porcupine River, Alaska
Authors: Edwards Mary E. , Brubaker Linda B.
Published: April 2011

Ped Pond is a lake lying in a Pleistocene scour channel of the Porcupine valley. The valley is considered to be a possible path of late Quaternary species migrations between interior Alaska and northwest Canada. Pollen in the oldest lake sediments (ca. 13 000 years old) indicates that shrub birch and willow probably occurred locally in a sparsely vegetated, herb-dominated landscape. Populus, Juniperus, and Typha latifolia increased about 10 000 years ago, suggesting particularly warm temperatures during the early Holocene. Picea glauca, which is presently common in the surrounding forests, first arrived near Ped Pond about 8500 years ago. This arrival date, together with existing evidence from other sites, indicates that spruce expanded rapidly across far-eastern Beringia 8000–9000 years ago. Other boreal forest taxa, Picea mariana, Betula papyrifera, and Alnus spp., became established locally between 7000 and 8000 years BP. A date of ca. 7500 years BP at Ped Pond suggests that the Alnus rise in northeast Alaska preceded that in adjacent Canada, possibly reflecting an eastward movement of alder. The vegetation history at Ped Pond suggests the Porcupine valley has been an important transition zone throughout the Holocene; some events are characteristic of northern Alaska and some of northwest Canada.
Black shale heaving at Sainte-Foy, Quebec, Canada
Authors: Bérubé Marc-André , Locat Jacques , Gélinas Pierre , Chagnon Jean-Yves , Lefrançois Paul
Published: April 2011

Oxidation of pyrite and crystallization of sulphate minerals in rock fractures have locally produced ground heaving in excess of 10 cm in the foundations of a college at Sainte-Foy, near Québec (Quebec). Black shales of the Sainte-Foy Formation are involved; they contain about 2% disseminated framboidal pyrite and 3% calcite. Reaction products identified with a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray chemical analyser (EDXA) are iron hydroxides and numerous sulphate minerals containing calcium, iron, potassium, aluminum, magnesium, manganese, barium, and strontium. In Ontario, heaving of black shales has been observed in the Ottawa area in particular; rock expansion there was mainly attributed to crystallization of gypsum along the bedding plane cleavages of the shales. At Sainte-Foy, fibroferrite, a fibrous iron–aluminum sulphate mineral, probably also contributed significantly to heaving.
The first 7 years (1978–1985) of ice wedge growth, Illisarvik experimental drained lake site, western Arctic coast
Authors: Mackay J. Ross
Published: April 2011

A large lake, measuring 600 m × 300 m and with a depth of nearly 5 m, was artificially drained on 13 August 1978. Observations on the formation, width, and depth of thermal contraction cracks for the first 7 years show that the crack profiles and ice wedge growth rates differ markedly from those of old ice wedges reported in the literature. The first winter's cracks had box-like profiles, with surface widths to 10 cm and depths to 2.5 m. Some cracks continued to widen and deepen, once opened in early winter, and then narrowed or even closed completely in summer. Mean growth rates for the ice wedges for the first few years have been as much as 3.5 cm/year. Temperature gradients at the time of first cracking have been in the range of 10–15 °C/m. The growth rate of young ice wedges is site specific and temperature dependent, varying with factors such as the temperature gradient, vegetation, and snow cover, so an estimate of the age of an ice wedge from its width will usually be impossible. A study of crack widths indicates that the apparent coefficient of linear expansion of frozen ground may be several times that of ice. Upward cracking has been proven.
The Lake Nipissing transgression in the Saginaw Bay region, Michigan
Authors: Monaghan G. W. , Lovis W. A. , Fay L.
Published: April 2011

Lake Nipissing phase deposits occur between two cultural zones in exposures at the Weber I archeological site along the Cass River in Saginaw County, Michigan. Radiocarbon dates from the lower cultural zone suggest that the Lake Nipissing transgression did not reach an altitude of 180.7 m before about 4600–5000 BP, whereas dates from the upper cultural zone indicate that the lake level was lowered to the 181.3 m Lake Algoma level before about 3000 BP.