bluuebunny/crossref_metadata_2025 huggingface dataset:
Stable isotope constraints on the role of graphite in the genesis of unconformity-type uranium deposits
Authors: Kyser T. K. , Wilson M. R. , Ruhrmann G.
Published: April 2011

The Key Lake unconformity-type uranium deposit occurs in a shear zone where it intersects the unconformity between Archean and Aphebian gneisses and the overlying Proterozoic Athabasca Group sandstones. The roots of the Key Lake and many other unconformity-type uranium deposits in the Athabasca basin are close to gneisses rich in graphite and most deposits have small amounts of carbonaceous materials (bitumen and hydrocarbon buttons) within and around altered basement and sandstone ore zones. In many Athabasca uranium deposits, hydrothermal fluids have destroyed graphite disseminated in the strongly altered gneisses in the vicinity of the deposits, prompting some to suggest that graphite was converted to CH4, which reduced and precipitated the uranium and partially condensed to form bitumen. The δ13C values of graphite collected from unaltered and altered gneisses around the Key Lake deposit have a limited range (−25 ± 5) and are not a function of distance from the mineralization or the intensity of alteration or deformation. The uniformity of these δ13C values suggests that the destruction of graphite was due predominantly to oxidation by basinal fluids from the sandstone and that the graphite near the deposits did not react to form substantial amounts of 12C-rich phases such as CH4. Most of the bitumen samples, which have higher H/C ratios than the graphite, have δ13C values identical to those of the graphite (−25 ± 5). The similarity in the isotopic compositions of carbon in the bitumen and in the graphite indicates that the bitumen formed from degradation of graphite as a result of reactions with no significant isotopic fractionations, such as ones involving radiolysis of graphite. The hydrocarbon buttons and a few samples of bitumen have petrographic relations and 13C/12C ratios (δ13C values less than −30) that are indicative of reduction of graphite by H2 produced from water by radiolysis. Graphite in these deposits did not play a central role as a reducing agent for uranium, rather it represents a critical structural factor by providing shear zones along which fluid flow can be focussed.
Early Permian fossil vertebrate footprints and their stratigraphic setting in megacyclic sequence II red beds, Prim Point, Prince Edward Island
Authors: Mossman David J. , Place Craig H.
Published: April 2011

Vertebrate trace fossils are reported for the first time from red beds near the top of megacyclic sequence II at Prim Point in southwestern Prince Edward Island. They occur as casts of tetrapod trackways. The ichnocoenose also includes a rich invertebrate ichnofauna. The trackmakers thrived in an area of sparse vegetation and occupied out-of-channel river sediments, most likely crevasse-splay deposits.Amphisauropus latus, represented by three trackways, has been previously reported from Germany, Poland, and Czechoslovakia. It is here interpreted as the track of a cotylosaur. It occurs together with the track of Gilmoreichnus kablikae, which is either a captorhinomorph or possibly a juvenile pelycosaur. These facilitate the assignment of a late Early Permian (late Autunian) age to the strata. The third set of footprints, those of a small herbivorous pelycosaur, compare most closely with Ichniotherium willsi, known hitherto from the Keele beds (latest Stephanian) of the English Midlands.This ichnocoenose occurs in a plate-tectonically rafted segment of crust stratigraphically equivalent to the same association of ichnofauna in the English Midlands and central Europe. The community occupied piedmont-valley-flat red beds within the molasse facies of Variscan uplands.
New information on the pectoral girdle and vertebral column in Lupeosaurus (Reptilia, Pelycosauria)
Authors: Sumida Stuart S.
Published: April 2011

UCLA VP 1651, a new specimen from the Lower Permian Admiral Formation of Archer County, Texas, provides information on heretofore unknown portions of the postcranial skeleton of the large pelycosaur Lupeosaurus. Presacral neural spines are elongate and have a subcircular cross section. Laterally directed tubercles are not present on any of the neural spines. Cervical vertebrae appear to have elongate neural spines and sharply keeled centra. Transverse processes are positioned relatively high above the bases of the centra through the length of axial column. The pattern of tilting of the neural spines is similar to that in the primitive edaphosaur Ianthasaurus hardestii. The proximal end of the first sacral rib contributes significantly to the intervertebral articular facet usually formed by the centra. The sacral ribs do not appear to fuse with one another distally. The ventral clavicular plate is greatly expanded anteriorly. The posterior edge of the subcoracoscapular fossa is very well defined. The available morphological information does not warrant a separate familial designation for the genus Lupeosaurus. Despite the lack of laterally directed tubercles of the neural spines, Lupeosaurus appears to be referrable to the Edaphosauridae. However, in the absence of cranial materials, this association must remain tentative. Although this description adds new information for only a restricted portion of the skeleton, it does appear to confirm the existence of a distinct, albeit rare, pelycosaur from the extensively studied fauna of the Lower Permian.
The first radiometric ages from the Judith River Formation (Upper Cretaceous), Hill County, Montana
Authors: Goodwin Mark B. , Deino Alan L.
Published: April 2011

A new isotopic age of ca. 78 Ma was obtained by the conventional K–Ar method and by laser-fusion 40Ar/39Ar analysis of biotite and sanidine crystals from two bentonites in the Judith River Formation of Kennedy Coulee, Hill County, Montana. The 40Ar/39Ar analyses yielded weighted mean ages of 78.2 ± 0.2 Ma (biotite) and 78.2 ± 0.2 Ma (sanidine) for sample 84MG8-3-4, and 79.5 ± 0.2 Ma (biotite) and 78.5 ± 0.2 Ma (sanidine) for sample 85MG7-16-1. These are the first isotopic age determinations from the Judith River Formation. The dated bentonites in Kennedy Coulee bracket two significant Judithian "age" mammal localities, UCMP V77083 and V81234.The radioisotopic age of ca. 78 Ma for the Hill County local faunas and correlations of other Judithian local faunas with marine units suggest that the duration of the Judithian was at least 5 Ma. Judithian local faunas are probably correlative with the late Campanian of the Western Interior. Similarities in the principal Judithian mammalian faunas from Alberta, Montana, and Wyoming can now be interpreted as documenting a low rate of evolutionary change rather than individual or populational variation of approximately contemporaneous local faunas.
The Lac des Iles Complex, Ontario: petrology and platinum-group-elements mineralization in an Archean mafic intrusion
Authors: Sutcliffe R. H. , Sweeny J. M. , Edgar A. D.
Published: April 2011

The Lac des Iles Complex is a late Archean, mafic to ultramafic complex that is host to 20.4 × 106 t Pt, Pd, and Au mineralization with an average grade of 6.34 g/t platinum-group elements (PGE). The 30 km2 complex, located in the Wabigoon Subprovince, consists of several coalescing mafic to ultramafic intrusive centers. The complex is emplaced into early gneissic tonalite and is contemporaneous with late granitoids.The magmatic evolution of the complex reflects the emplacement of multiple pulses of previously fractionated magma, some of which underwent subsequent in situ fractionation. Distinct magma sequences are recognized on the basis of intrusive relationships, differences in the cumulus minerals, crystallization order, and trace-element chemistry. These sequences are (1) hornblende gabbro, (2) gabbro and gabbronorite, and (3) ultramafic. Where there is evidence of intrusive relations, the most primitive sequences are emplaced late and occur toward the north end of the complex. Microprobe analyses indicate the following compositional ranges of mineral phases within the complex: olivine–Fo84–76, orthopyroxene—En82–67Fs15–30Wo2–3, and clinopyroxene—En53–46Fs3–12Wo41–51. Cyclic layering is developed only in the northern ultramafic part of the complex where several cycles of mesocumulate- to adcumulate-textured wehrlite, clinopyroxenite, and websterite are identified.Although the parental magma compositions are not well constrained, model calculations using major-element and rare-earth-element (REE) contents of cumulus phases and adcumulate rocks indicate that the parental magmas had mol MgO/(MgO + FeO) ranging from at least 0.61 to 0.54 and had fractionated REE abundances with CeN/YbN of approximately 5.0. Mineral chemistry and crystallization sequences indicate that the ultramafic and gabbroic parts of the complex had tholeiitic basalt parental magmas of picritic and high-alumina affinities, respectively.The major PGE mineralization at Lac des Iles occurs in the Roby Zone along the interface between the gabbro and gabbronorite in the southern part of the complex. This interface has been intruded by a sheet of pyroxene cumulate, which is probably part of the ultramafic sequence. The PGE sulphide mineralization in the Roby Zone is associated with disseminated chalcopyrite, pyrrhotite, pentlandite, pyrite, and altered silicates in (1) the pyroxene cumulate sheet, (2) the mixed gabbro–gabbronorite, and (3) the gabbroic pegmatite dikes and breccia zones. Cl-rich apatite and monazite are accessory phases associated with PGE mineralization PGE occurrences are also present within sulphide-bearing orthopyroxene–clinopyroxene cumulates in the northern ultramafic part of the complex. The Roby Zone mineralization is localized by mixing the PGE and sulphide-rich gabbronorite and pyroxene cumulates with the volatile-rich gabbro. The PGE are redistributed by late magmatic volatile activity, which generated mineralized gabbroic pegmatites and breccia zones.
Ichthyosaurs (Reptilia, Ichthyosauria) from the Lower and Middle Triassic Sulphur Mountain Formation, Wapiti Lake area, British Columbia, Canada
Authors: Callaway Jack M. , Brinkman Donald B.
Published: April 2011

Ichthyosaurs are found in the Lower and Middle Triassic members of the Sulphur Mountain Formation in the Wapiti Lake area, British Columbia. Three species are recognized: Pessosaurus sp. in the family Shastasauridae from the Middle Triassic, Mixosaurus cf. M. nordenskioeldii in the family Mixosauridae from the Lower and Middle Triassic, and Phalarodon cf. P. fraasi in the family Omphalosauridae from the Middle Triassic. Other ichthyosaur material in the Lower Triassic (Smithian) member is the oldest known from North America and coeval with the oldest known elsewhere but cannot be identified confidently at this time. This material provides new information relative to the paleobiogeography of early ichthyosaurs and additional confirmation that ichthyosaurs were already highly specialized and quite diverse by the Early Triassic.
Crustal thickness under the Gulf of St. Lawrence, northern Appalachians, from gravity and deep seismic data
Authors: Marillier F. , Verhoef J.
Published: April 2011

We have determined crustal thickness in the Gulf of St. Lawrence, an area that corresponds to an offset of the main northern Appalachians units. A "complete" Bouguer anomaly was calculated from recent depth-to-basement compilations and sediment densities from well data. The Moho surface was obtained by inverting the Bouguer anomaly, assuming a single density contrast at depth, and using an average depth provided by deep reflection seismic data. The resulting crustal model shows a Moho depth of 42–44 km beneath the Grenville Craton, north of the Appalachian deformation front. South of this front, the depth to Moho displays a pronounced thinning of the crust beneath the Carboniferous Magdalen Basin. This is in striking contrast to the deep seismic data, which give a Moho depth of about 43 km. The modelling of the Bouguer anomaly in the Magdalen Basin, taking into account the seismic reflection and refraction data, reconciles these different results and suggests that a 43 km deep Moho beneath the basin is associated with a lower crustal layer about 13 km thick, with high velocity (7.35 km/s) and density (3.05 g/cm3). The Bouguer anomaly suggests that the lateral extent of this high-density layer is confined roughly to the Magdalen Basin. We suggest that this layer is due to mantle underplating of the crust as a result of the Carboniferous-age formation of the Magdalen Basin, and that it is not a feature related to the early to middle Paleozoic development of the Appalachian Orogen.
40Ar/39Ar dating of the Mealy dykes of Labrador: paleomagnetic implications
Authors: Reynolds P. H.
Published: April 2011

40Ar/39Ar age spectrum data are presented for amphibole and biotite from four dykes representing the diabase swarm in the Mealy Mountains Terrane, Grenville Province, Labrador. An amphibole plateau age of ca. 1215 Ma is recorded by two of the dykes. A third amphibole records a younger age (ca. 1150 Ma) through an apparent veil of excess radiogenic argon. It is suggested that the ca. 1215 Ma age may closely approximate the time of dyke intrusion; the third amphibole, from a dyke relatively close to the terrane boundary, may have been significantly overprinted by heat associated with the Grenville Orogeny. Two of the four biotite age spectra are discordant; apparent ages range from ~980 to 1060 Ma. It is suggested that Grenvillian reheating caused gas loss from all four biotites, the loss having been complete in two, including the one closest to the terrane boundary.Mealy dyke B paleopoles plot on and about the Grenville Track close to the calibrated 980 Ma point. This observation is consistent with observed magnetic "unblocking" temperatures, taken in conjunction with the extent of Grenvillian reheating as estimated from the biotite data. It is suggested that the Mealy A magnetization is much older and cannot be used to define the eastern (descending) arm of the Grenville apparent polar wander track. A plausible structural correction (to compensate for Grenvillian thrusting) could bring the A paleopoles close to the ca. 1200–1250 Ma point on the North American polar wander track; the latter is considered to be the most likely age.
Some northern sources of atmospheric methane: production, history, and future implications
Authors: Nisbet E. G.
Published: April 2011

Northern sources, including wetlands and perhaps gas hydrates, contribute significantly to the CH4 content of the atmosphere. Methane production from northern wetlands, including bogs, swamps, and ponds, is probably very seasonal, being most important in late summer, with significant evasion in autumn as lakes overturn. The strong recovery of beaver populations in Canada, from near-extinction 50 years ago to present abundance, may also be important, both in creating new wetlands and in the alteration of them; wetlands that have been altered by beaver activity produce orders of magnitude more methane than beaver-free wetlands. In the Arctic, methane gas hydrates represent a significant source of methane, which may become more important if Arctic warming occurs as part of global climate change. The danger of a thermal runway caused by CH4 release from permafrost is minor, but real. Other high-latitude sources of CH4 include Arctic peat bogs, and losses from natural gas production, especially in the Soviet Union.
Glacially redeposited pollen in tills of southern Ontario, Canada
Authors: Dreimanis Aleksis , Liivrand Elsbet , Raukas Anto
Published: April 2011

According to published opinion based on analytical data, the secondary pollen of subglacial till in the eastern Baltic region of Europe reflect the pollen assemblages of the preceding interstadial or interglacial sediment, including abundant thermo-philous pollen. Tills and glaciolacustrine sediments from 10 sites in southern Ontario, including the Don Valley Brickyard section at Toronto, where polynologically investigated to compare the pollen content in glacigenic deposits of various ages. Only one site (upper Bradtville till) contained a secondary pollen assemblage with abundant deciduous pollen, like those found in a Yarmouthian interglacial deposit in Indiana. In all the others, pine (Pinus) pollen dominate. This phenomenon is explained by glacial incorporation of sediments enriched in overproduced Pinus pollen, which had accumulated during either (i) a lengthy cool transitional period between the warm phase of the Sangamonian Interglacial and the first major Early Wisconsinan glacial advance, (ii) the interstadial Middle Wisconsinan, or (iii) the cool nonglacial episode of Illinoian and pre-Illinoian time. Therefore, the northern European model for distinguishing tills of different ages by their secondary pollen assemblages is applicable to southern Ontario only in exceptional cases. Pollen in the glaciolacustrine Early Wisconsinan Sunnybrook Drift sediments resembles those of Sunnybrook till, but are more variable in their preservation and composition and contain more pre-Quaternary palynomorphs.
Holocene vegetation, climate, and lake-level changes in the Interior Douglas-fir Biogeoclimatic Zone, British Columbia
Authors: Mathewes Rolf W. , King Miriam
Published: April 2011

Chilhil, Phair, Fishblue, and Horseshoe lakes in the southern interior of British Columbia were cored and analyzed for pollen. Phair Lake was also examined for plant macrofossils and aquatic molluscs. Two dated volcanic tephras (Mazama and Bridge River) are present in three of the four lakes and, together with radiocarbon dates, provide an absolute chronology for pollen-influx calculations and stratigraphic correlation. Abrupt changes in sediment type at Phair Lake about 5650 and 2000 years ago correlate with Neoglacial advances near the coast–interior transition. Pollen changes suggestive of moister conditions and the presence of an aquatic mollusc (Valvata sincera helicoidea) at Phair and Chilhil lakes are consistent with the Neoglacial evidence of cooler and wetter conditions after about 2400 years ago. The driest part of the Holocene was the early, pre-Mazama (ca. 6600–6800 years ago) interval, when the vegetation was more open and herb rich and the lake levels were lower than at present. Wetter climatic conditions appear in post-Mazama time, indicated by regional increases in the pollen of Tsuga heterophylla and other coastal and subalpine trees. Pollen-influx values for the Interior Douglas-fir Zone are broadly consistent at all sites, with values of < 2000 –8000 grains cm−2 year−1. Douglas-fir (Pseudotsuga menziesii) has been an important forest species in the study region throughout the Holocene.
Paleomagnetism and the origin of the Mackenzie Arc of northwestern Canada
Authors: Park John K. , Norris Donald K. , Larochelle André
Published: April 2011

Analysis of paleomagnetic data obtained from 1966 alternating-field treatment and from recent thermal demagnetization of the same samples of Late Proterozoic (770 Ma) diabase sills and dykes distributed about the Mackenzie Arc from northeastern British Columbia to the Alaskan border has revealed a primary magnetization in seven sites that is similar to existing data from 10 sites confined to the central Mackenzie Mountains region (N = 17 site poles; 222.2°W, 01.6°N; R = 16.73; K = 60; A95 = 5°). The diabases are confined to the dominantly clastic Late Proterozoic Tsezotene Formation and Katherine Group of the Mackenzie Mountains Supergroup. Tests of Carey's orocline hypothesis for the arc using linear regression and a plan-view application of the fold test suggest, in line with earlier structural studies, that the arc is largely nonrotational and that it is not an orocline resulting from the Cretaceous and early Tertiary Laramide Orogeny. Rather, it conforms to the arcuate foreland margin predating deposition of the Late Proterozoic Mackenzie Mountains Supergroup.
Facies anatomy of an Upper Cambrian grand cycle: Bison Creek and Mistaya formations, southern Alberta
Authors: Westrop Stephen R.
Published: April 2011

The Bison Creek and Mistaya formations form the youngest Cambrian sedimentary grand cycle exposed in Banff and Jasper national parks. The shaly half-cycle of the Bison Creek Formation records the displacement of a carbonate bank during a major rise in sea level that can be identified in other parts of North America. Lithofacies of the Bison Creek Formation fall into three recurrent associations that represent sedimentation in shallow, subtidal, storm-dominated shelf settings. The Mistaya Formation records the reestablishment of carbonate bank deposition, probably due to a decrease in the rate of sea-level rise, and includes two facies associations that represent a mosaic of shallow subtidal to supratidal environments. The grand cycle was terminated by a sea-level rise, possibly eustatic in nature, that drowned the carbonate platform. The overlying shales, mudstones, packstones, grainstones, and rudstones of the Survey Peak Formation mark a return to subtidal, storm-dominated shelf conditions.
U–Pb and Rb–Sr geochronology of Acadian plutonism in the Dunnage zone of the southeastern Quebec Appalachians
Authors: Simonetti Antonio , Doig Ronald
Published: April 2011

U–Pb zircon and (or) titanite or monazite ages have been obtained for five major, undeformed, calc-alkaline plutons of the Appalachians of southeastern Quebec. These are interpreted as ages of crystallization for the Scotstown (384 ± 2 Ma), Lac aux Araignées (383 ± 3 Ma), Winslow (377 ± 7 Ma), Aylmer (375 ± 3 Ma), and Ste-Cécile (374 ± 2 Ma) plutons. Many other titanite samples gave 206Pb/238U dates that are 2–16 Ma younger than the concordant zircon dates from the same samples, and this is probably the result of Pb loss. Variation in 207Pb/206Pb ages of titanite from some samples is attributed to incorrect common Pb correction.Rb–Sr data for the same plutons show considerable isotopic heterogeneity and correspondingly high errors in ages. The isotopic heterogeneity is likely caused by postsolidification metasomatic alteration by host rock fluids. Where the scatter is least (Ste-Cécile), the Rb–Sr age (364 ± 14 Ma) is similar to the U–Pb mineral age (374 ± 2 Ma). The 87Sr/86Sr initial ratios range from 0.7065 to 0.710 and are probably related to the source of the magmas. The relatively high initial ratios and the peraluminous nature of the plutons preclude a significant mantle contribution to the magmas. These undeformed plutons are probably the result of melting of the lower continental crust near the end of crustal thickening caused by compression during the Acadian Orogeny.
Geology and U–Pb geochronology of the Klondike District, west-central Yukon Territory
Authors: Mortensen J. K.
Published: April 2011

Geological mapping and U–Pb geochronology of the Klondike District provide new information on the nature and evolution of the Yukon–Tanana terrane (YTT) in western Yukon. The area is underlain by a sequence of thrust panels of regional extent. A continuously mappable sequence of interlayered metasedimentary and metavolcanic rocks is intruded by a variety of deformed metaplutonic rocks within two of these thrust sheets. Layering in the metasediments and metavolcanics is considered to be at least in part transposed stratigraphy. Small bodies of greenstone and altered ultramafic rocks thought to be part of the Slide Mountain terrane occur discontinuously along the thrust faults.U–Pb age determinations indicate that the uppermost thrust panel (assemblage I), which underlies much of the Klondike District, consists largely of metamorphosed, mid-Permian felsic plutonic, subvolcanic, and tuffaceous rocks. Beneath assemblage I is a second thrust panel (assemblage II), also of large areal extent, of mid-Paleozoic or older metasedimentary and mafic and felsic metavolcanic rocks, intruded by a large body of latest Devonian – Early Mississippian granitic augen orthogneiss. U–Pb analyses of zircon from the orthogneiss reflect both lead loss and a significant inherited zircon component. A third structural unit (assemblage III), which consists mainly of carbonaceous schist and phyllite, crops out in the northern part and along the southwestern edge of the study area, where it underlies both assemblages I and II.The earliest stage of deformation and metamorphism that affected the area (F1) produced the pervasive recrystallization fabric characteristic of all of the metamorphic rocks in assemblages I, II, and III, and occurred between mid-Permian and Late Triassic time. Thrust faulting, presumed to be northerly or northeasterly directed, postdates Late Triassic but predates mid-Cretaceous. The second phase of deformation (F2) was either synchronous with or later than thrust faulting. Monazite ages for the augen orthogneiss indicate that at least local metamorphism and (or) deformation lasted until Early Cretaceous time.Close similarities between composition, U–Pb ages, as well as timing and style of deformation, documented in the Klondike District and observed elsewhere in the YTT in southeastern Yukon and east-central Alaska suggest that much of the YTT either evolved as a single entity or else shared a very similar history.
Postglacial paleoceanography of Hudson Bay: stratigraphic, microfaunal, and palynological evidence
Authors: Bilodeau Guy , Vernal Anne de , Hillaire-Marcel Claude , Josenhans Heiner
Published: April 2011

Cores containing representative sequences of postglacial sediments in northern and southern Hudson Bay were analyzed for their microfaunal (foraminifers and ostracods) and palynological (dinocysts, pollen, and spores) content in order to reconstruct the evolution of environments since the last glaciation.In southern Hudson Bay, the marine invasion of the Tyrrell Sea at ca. 8000 BP, following the Lake Ojibway episode, was accompanied by the development of an Arctic-type microflora and microfauna indicative of a dense seasonal sea-ice cover and stratified water masses. Shortly after 8000 BP, the establishment of subarctic conditions in surface waters was accompanied by more intense homogenization of water masses. Subarctic conditions have persisted throughout most of the postglacial interval despite a recent surface-water cooling.In northern Hudson Bay, micropaleontological and lithological data reveal a succession of proximal to distal glaciomarine environments characterized by low biogenic productivity, harsh Arctic conditions, and stratified water masses. An increase in dinocyst abundance and diversity, after 6000 BP, indicates the establishment of cool subarctic conditions in surface waters, while foraminifer assemblages suggest intensified mixing of water masses.The micropaleontological records of northern and southern Hudson Bay reveal a strong latitudinal gradient in biogenic productivity and water mass characteristics throughout the postglacial interval. "Interglacial" conditions, established in southern Hudson Bay very shortly after it was invaded by the sea, seem to have occurred much later in northern Hudson Bay.
Ludlow and Pridoli (Upper Silurian) graptolite biostratigraphy of the central Arctic Islands: a preliminary report
Authors: Lenz Alfred C.
Published: April 2011

A fauna, comprising slightly more than 30 species of Upper Silurian graptolites, has been recognized from the Arctic Islands. The following preliminary biostratigraphic biozones are recognizable: Lobograptus progenitor, Saetograptus fritschi linearis, and Bohemograptus bohemicus tenuis zones of Ludlow age; and the Pseudomonoclimacis parultinus, Pseudomonoclimacis ultimus, Monograptus bouceki, "Pristiogratpus" transgrediens, and Monograptus cf. birchensis zones of Pridoli age. The last-named zone may range into the Devonian. The faunal composition and zones are relatively close to coeval faunas of northern Yukon. They are, however, distinctly depauperate in comparison with the faunas of Poland, Czechoslovakia, or Kazakhstan.
Seismic reflection investigation of Kalamalka Lake: a "fiord lake" on the Interior Plateau of southern British Columbia
Authors: Mullins Henry T. , Eyles Nicholas , Hinchey Edward J.
Published: April 2011

A uniboom seismic reflection profile survey has revealed the nature of bedrock relief and the acoustic character of Pleistocene glacial sediment fill beneath Kalamalka Lake in southern British Columbia. Despite its continental interior setting, Kalamalka Lake basin has many attributes of coastal fiords, such as being overdeepened below sea level and having closed bedrock depressions and a thick sediment fill.The bedrock surface beneath Kalamalka Lake has been eroded as much as 417 m below lake level (26 m below sea level) and is characterized by a series of closed, glacially overdeepened depressions. We suggest that the location of the lake basin is structurally controlled but was overdeepened by rapidly flowing ice that drained the interior portions of the Cordilleran ice sheet during repeated Pleistocene glaciations.Up to 272 m of sediment has been deposited beneath Kalamalka Lake. The greatest thickness of the sediment fill (up to 237 m) is a seismically transparent unit that overlies a thin (up to 20 m), discontinuous lower stratified unit and is overlain by a thin (up to 15 m), continuous upper unit that is well stratified. The sedimentological nature of the lower stratified unit is not known but could represent a discontinuous coarse lag. The thick, middle transparent unit is interpreted as a massive silt deposited rapidly in a proglacial lake from suspended-sediment plumes during deglaciation. The thin overlying stratified unit may be correlative with laminated glaciolacustrine "white silt" deposits that outcrop extensively across central and southern British Columbia, suggesting a common history of deglaciation and sedimentation.An ambitious research program focused on seismic stratigraphic definition, coupled with direct drill-core sampling, is needed to take full advantage of the extensive sediment record that exists beneath the large, glacially overdeepened lakes of southern British Columbia.
Early development and flysch sedimentation in Ordovician Taconic foreland basin, west-central Newfoundland
Authors: González-Bonorino Gustavo
Published: April 2011

During the Early to Late Ordovician the Taconic foredeep in west-central Newfoundland evolved from an underfilled to an overfilled state in response to cratonward advance, thickening, and erosion of the Taconic Orogen. Early orogen-derived sediment in the foreland basin consisted of middle(?) to lake Arenigian deep-water mudstones that accumulated on an inner (craton-facing) slope prism (uppermost parts of Shallow Bay and Green Point formations and correlative units). These deposits are interbedded with and overlie passive-margin slope sediments. In the middle Arenigian to early Llanvirnian, sand from the orogen formed several small, sand-rich submarine fans (Lower Head Formation and correlative units) on the lower reaches of the inner slope and basin plain. The fans may have been fed by closely spaced rivers draining the orogen, as presently occurs in western South America. Only proximal portions of these fans are now exposed. The flysch basin was narrow, constricted by the inner slope and the passive-margin slope, and located a short distance seaward from the buried hingeline of the proto-North American craton. As the orogen thickened sufficiently to override the crustal ramp, the carbonate shelf on the craton drowned, clastic depocentres migrated onto the foundered craton, and a thicker flysch (Mainland Sandstone) accumulated in Llanvirnian-Llandeilian time. In the Caradocian the foreland basin was overfilled with shallow-marine terrigenous sediments (Long Point Formation). Regional flysch dispersal was from a St. Lawrence promontory to a Quebec reentrant.
The distribution and possible biostratigraphic significance of the ichnogenus Oldhamia in the shales of the Blow Me Down Brook Formation, western Newfoundland
Authors: Lindholm Rosanne M. , Casey John F.
Published: April 2011

The Blow Me Down Brook Formation is a siliciclastic unit in the Humber Arm allochthon of western Newfoundland that was deposited on the ancient North American continental slope and rise during the early stages of the development of the Iapetus Ocean. This unit consists primarily of sand-rich turbidites that appear to be barren of body fossils. The shales, however, contain trace fossil assemblages dominated by the ichnogenus Oldhamia and also include Planolites, Gordia, and other indistinguishable simple forms. Oldhamia is considered as an index fossil for the Early Cambrian, and the validity of this age assignment is reviewed.Oldhamia traces have been found in the Blow Me Down Brook Formation at 27 localities along the length of the allochthon and occur beneath each of the four ophiolitic massifs. Together, the assemblages from this unit contain five Oldhamia ichnospecies including O. radiata, O. antiqua, O. smithi, O. flabellata, and the newly reported O. curvata. Different ichnospecies are dominant in the Oldhamia assemblages at the 27 localities and these differences appear to be systematic. In the northernmost localities of the Blow Me Down Brook Formation simple radial forms predominate, including O radiata and O. smithi, whereas in the southernmost localities dendritic forms such as O. flabellata are common. This north to south distribution from radial to dendritic forms may represent an evolutionary trend of feeding optimization.
Near-surface tilt response to steam injection into a tar sands formation
Authors: Rogers J. S. , Jones F. W. , Ertman M. E. , Thibault J.
Published: April 2011

Two biaxial mercury-level borehole tiltmeters located at moderate depth (20 m) and 91 m horizontally distant from the injection well have been used to monitor the effects of a fast hydraulic fracture and subsequent steam injection in a tar sands formation at a depth of 230 m. Tilt vectors are determined for the maximum tilts during the fracture, and the long-term tilt migration associated with the steam-injection process is monitored. The tilt associated with the fast fracture is of the order of 1–2 μrad, and the long-term tilt increased as much as 240 μrad over the 500 day monitoring period, and appeared to approach a limit. The long-term tilt migration generally follows the same orientation as the initial tilt due to the fast fracture.
U–Pb dating of monazite and its application to geological problems
Authors: Parrish Randall R.
Published: April 2011

Monazite is an underutilized mineral in U–Pb geochronological studies of crustal rocks. It occurs as an accessory mineral in a wide variety of rocks, including granite, pegmatite, felsic volcanic ash, felsic gneiss, pelitic schist and gneiss of medium to high metamorphic grade, and low-grade metasedimentary rocks, and as a detrital mineral in clastic and metaclastic sediments.In geochronological applications, it can be used to date the crystallization of igneous rocks, determine the age of metamorphism in metamorphic rocks of variable metamorphic grade, and determine the age and neodymium isotopic characteristics of source materials of both igneous and sedimentary rocks. It is particularly useful in the dating of peraluminous granitic rocks where zircon inheritance often precludes a precise U–Pb age for magmatic zircon. The U–Pb systematics of the mineral are not without complexity, however. Being a mineral that favors incorporation of Th relative to U, it can contain considerable amounts of excess 206Pb derived from initially incorporated 230Th, an intermediate decay product of 238U. Corrections for this effect can be made using the Th/U ratio of the host rock, but these corrections may not always be valid. Monazite is known to be capable of preserving inheritance in a manner similar to that of zircon, and it can lose Pb during episodic or prolonged heating events of uppermost amphibolite and granulite facies metamorphic grades. Monazite is less retentive of Pb than zircon during high-temperature igneous and metamorphic processes, and a few studies of its behavior suggest that its closure temperature is approximately 725 ± 25 °C. Examples of U–Pb systematics from most of the above situations are presented in this paper to illustrate both the utility and complexity of monazite in geochronological studies in an attempt to encourage more widespread application of this dating method.
Moraine formation in northwestern Ontario: product of subglacial fluvial and glaciolacustrine sedimentation
Authors: Sharpe David R. , Cowan W. R.
Published: April 2011

Long, arcuate, stratified end moraines in northwestern Ontario may represent major and rapid sedimentation events in glacial Lake Agassiz. Rapid lowering of the lake or lift of a marginal ice dam may have triggered widespread outbursts of subglacial meltwater which deposited these end moraines as coalesced or broad subaqueous lacustrine fans. Moraine cores are of undeformed gravel, sand, and silty sand that fine upward. Coarse beds are massive to weakly stratified. Large-scale cross-stratification may be present. Sandy rhythmic beds are laterally transitional to silt–clay rhythmites (varves). Similar facies occur in adjoining eskers.Moraine sediments have the expected characteristics of rapid deposition on subaqueous fans and, therefore, may not represent either prolonged sedimentation or stable ice margins. Rather, they may reflect rapid sedimentation associated with large discharges that induced transient instability in the drainage network and (or) surging prior to marginal sedimentation. This explanation for moraine formation questions the traditional view that large end moraines represent climatically controlled stillstands.
Locomotion and feeding traces in Champlain Sea subaqueous outwash deposits near Ottawa, Canada
Authors: Naldrett Dana L.
Published: April 2011

Locomotion and feeding traces (repichnia and fodichnia) observed on bedding planes of rhythmically bedded subaqueous outwash deposits in the Brazeau sand pit, Nepean, Ontario, Canada, are the first bedding-plane traces described in detail from the western Champlain Sea. The Planolites–Palaeophycus-like and Taenidium-like traces are cylindrical with circular cross section, smooth sided, unlined, sinuous, sometimes branching, and sometimes meniscate. Organisms producing the traces are tentatively identified as errant polychaetes or nemerteans. The enclosing sediments are rhythmic couplets of alternating fine sand and silt layers overlain by silty clay and fine–medium silt layers. The occurrence of traces within the uppermost portion of the coarse unit, and within the coarser, upper portion of the overlying fine unit, and the rhythmic alternation of coarse and fine layers suggest these deposits may be varves. The traces formed during the more biologically suitable summer months but were preserved only during the latter portion of the summer. Traces are distributed on bedding planes in close association with bedforms and show a high correlation with the substrate and possibly the hydrodynamic regime. This is interpreted as indicating a strong preference in feeding behaviour. The presence of traces in the subaqueous outwash environment necessitates rethinking of the depositional environment to include the presence of errant polychaetes, nemerteans or similar organisms, and the lower life-forms such as epontic algae and bacteria on which they live.
Nd- and Sr-isotope systematics for the Kamiskotia–Montcalm area: implications for the formation of late Archean crust in the western Abitibi Subprovince, Canada
Authors: Barrie C. Tucker , Shirey Steven B.
Published: April 2011

Geochemistry and Nd isotopic compositions are used to characterize mantle and crustal sources and to provide constraints on petrogenetic models for tholeiitic, calc-alkalic, and lamprophyric suites in the Kamiskotia–Montcalm area. The Kamiskotia gabbroic complex (KGC) and cogenetic, bimodal volcanic rocks have εNd(t) = +2.2 to +2.6, consistent with a direct derivation from a long-term, light rare-earth element (LREE)-depleted mantle. The Montcalm gabbroic complex has decreasing εNd(t) upsection from +2.8 to +1.0, consistent with contamination by long-term, LREE-enriched (with respect to the long-term, LREE-depleted Abitibi mantle) crust during fractionation. Two calc-alkalic lamprophyre samples, characterized by large-ion lithophile element (LILE) and LREE enrichment and high MgO, Ni, and Cr contents, have εNd(t) of +2.5 and +2.8, indicating a derivation from a depleted mantle source that had undergone recent trace-element enrichment. A different lamprophyre suite is extremely LILE and LREE enriched and has an εNd(t) of +1.0, indicating a derivation from a slightly different source that had earlier LREE enrichment. Granitoid rocks internal and external to greenstone belt rocks have εNd(t) = +2.5 to +3.8 and +0.6 to −0.4, respectively. The lower values provide additional evidence for the existence of LREE-enriched crust in this area.Considering these data along with other radiogenic isotope studies, a petrogenetic and tectonic model is suggested for the crustal development of the southern Abitibi Subprovince. From >2740 to 2698 Ma—the major period of volcanic activity—komatiitic and tholeiitic suites and one lamprophyre suite were derived from a uniformly LREE-depleted mantle reservoir with εNd(t) = +2 to +3. Calc-alkalic granitoids were emplaced generally after 2700 Ma. Their long-term, LREE-depleted and LREE-enriched Nd isotopic signatures are similar to signatures in continental-arc settings (e.g., the Coastal Batholith of Peru). Form 2690 to 2670 Ma, when transpressional tectonism prevailed, mantle-derived magmatism was represented by long-term, LREE-enriched (εNd(t) = +1 to +2) lamprophyric and alkalic volcanic suites.The Kamiskotia suite has a seven-point, whole-rock – mineral isochron Sm–Nd age of 2710 ± 30 Ma, identical to U–Pb zircon ages for the suite, indicating closed-system behavior. An Rb–Sr mineral – whole-rock isochron age from one KGC sample is 2450 ± 30 Ma, identical to U–Pb ages for the Hearst–Matachewan dike swarm, a prominent feature in the KGC area. Regression of whole-rock and mineral-isotope data for one granitoid sample with a U–Pb zircon age of 2696 ± 1.5 Ma gives identical ages of 2530 ± 30 Ma in the Sm–Nd and Rb–Sr systems. The latter data add to an increasing body of evidence for cryptic, late thermal events after granitoid–greenstone belt development in the southern Abitibi Subprovince.
An investigation of Superior Shoal, central Lake Superior, with a manned submersible
Authors: Manson Matthew L. , Halls Henry C.
Published: April 2011

A Johnson-Sea-Link submersible was used to examine the geology of Superior Shoal in central Lake Superior. Here, glacially scoured, vertical cliffs, some more than 100 m high, are formed of 1.1 Ga middle Keweenawan basaltic lava flows displaying ophitic interiors and red amygdaloidal tops. Flat-lying sandstones, lithologically similar to the upper Keweenawan Bayfield–Jacobsville sequences, occur to the north of the volcanic rocks. These are inferred to have been downthrown along an eastward extension of the Isle Royale fault, a major boundary fault of the Midcontinent rift. The volcanic rocks are normally magnetized, supporting lithological evidence that they correlate with the middle Keweenawan sequence on Isle Royale. Paleomagnetic data suggest that the volcanics have a complex structure, possibly involving drag folding along the Isle Royale fault.
The Savage Lode magnesian skarn in the Marvel Loch gold–silver mine, Southern Cross greenstone belt, Western Australia. Part 1: Structural setting, petrography, and geochemistry
Authors: Mueller Andreas G.
Published: April 2011

The Marvel Loch mine in the Archean Yilgarn Block. Western Australia, has produced 9.70 t gold and 1.92 t silver from 3.28 × 106 t of oxide–sulphide ore. The deposit is located in the Southern Cross greenstone belt, and occurs within the medium-grade metamorphic aureole of the Ghooli Dome granitoid batholith, about 1.5 km from the granitoid–greenstone contact, The deposit is controlled by a broad ductile shear zone and spatially associated with late syn- to post-mineralization pegmatite dykes. The major orebodies, represented by the Savage Lode, are hosted by a uniform sequence of metakomatiites, and form zoned replacement bodies oriented subparallel to the steeply dipping foliation of the shear zone. Lens-shaped domains of pillowed metakomatiiles (hornblende + cummingtonite + chlorite) are locally preserved between the orebodies.The gangue of the Savage Lode is laterally zoned, and shows distinct similarities to Phanerozoic magnesian skarns. Calcite–olivine rock and calcite–phlogopite–chlorite schist occur in the centre, and are enveloped by three types of calcite-poor ore, namely banded diopside–amphibole rock, quartz–diopside veins, and tremolite–phlogopite schist. The latter grades laterally into subeconomic, outer tremolite–chlorite schists. Local retrogression of prograde alteration minerals is evident in the partial replacement of olivine by iddingsite and serpentine, and in the occurrence of late muscovite, clinozoisite, and prehnite. The gangue in the lode reflects strong carbon dioxide, calcium, and potassium metasomatism.Hydrothermal oxides and sulphides (2–5 vol.%) occur disseminated throughout the Savage Lode. The oxide assemblage includes hercynite–spinel, magnetite, ilmenite, and scheelite, whereas the sulphide assemblage is dominated by pyrrhotite, loellingite, and arsenopyrite. Native gold occurs as discrete grains (0.001–3 mm) intergrown with sulphides or enclosed in gangue minerals. The average magnesian ore skarn is characterized by a MgO–FeO ratio of 2.0:1, a Au–Ag ratio of 1.7:1, and low base metal (< 500 ppm), anomalous tungsten (20–40 ppm), and high arsenic (2900 ppm) contents. The Savage and other lodes in the Marvel Loch mine may be classified as gold or gold–silver skarns by economic metal content. The magnesian rather than calcic nature of the Marvel Loch skarns is related to the high magnesium content (21 wt.% MgO) of the precursor metakomatiite rocks.
The Scotia–Quaal metamorphic belt: a distinct assemblage with pre- early Late Cretaceous deformational and metamorphic history, Coast Plutonic Complex, British Columbia
Authors: Gareau S. A.
Published: April 2011

The Scotia–Quaal metamorphic belt extends from Hawkesbury Island to Work Channel between the early Late Cretaceous Ecstall and the Paleogene Quottoon plutons. The belt consists of a Proterozoic?–Paleozoic metasedimentary and metavolcanic sequence, the Middle Devonian Big Falls orthogneiss, Early Jurassic orthogneiss, and Jurassic or Cretaceous mafic and ultramafic intrusive rocks. The assemblage may be correlative with Nisling terrane lithologies and may have shared a common history, at least from Early Jurassic time on, with rocks of Stikine terrane.Strong planar and linear fabrics, abundant folds, and scarcity of kinematic indicators characterize the belt's deformational style. Development of a strong foliation followed by three episodes of folding occurred between emplacement of the Middle Devonian Big Falls orthogneiss and early Late Cretaceous Ecstall intrusion. Paleogene fabrics occur in the Quottoon pluton and in the easternmost 1.5 km of the Scotia-Quaal belt. If a major Paleogene shear zone is postulated to explain the disparity in cooling dates, metamorphic histories, and structural styles between the western and central Coast Plutonic Complex, then it does not traverse the Scotia–Quaal metamorphic belt, but must be located within or at the western edge of the Quottoon pluton.Medium-pressure, epidote–amphibolite to upper amphibolite facies metamorphic conditions are preserved in the central region. Metamorphic grade increases gradually across the belt from west to east and from south to north. Regional metamorphism outlasted regional deformation. Contact metamorphism associated with Quottoon and Ecstall intrusion is apparent only in rocks of the southern region where regional metamorphic grades are lowest.