bluuebunny/crossref_metadata_2025 huggingface dataset:
Two decades of Geological Survey of Canada petroleum resource assessments
Authors: Lee P. J.
Published: April 2011

The Geological Survey of Canada has conducted petroleum resource assessments of Canadian sedimentary basins to respond to a need for information concerning the extent of Canada's energy endowment. The evolution of these activities and methods, which began in the 1970's and continue to the present, is discussed in this paper. The first assessment of Canadian basins was conducted in the 1970's using a volumetric yield method, whereby the volume of sedimentary rock in a basin was multiplied by a hydrocarbon yield per unit volume factor. Later, a Monte Carlo approach was used. It required a knowledge of the exploration plays in a given basin and made use of a variety of pool parameters expressed as cumulative probability distributions. The Monte Carlo method did not account for the biased data-set problem that came from using a selective exploration process. A third assessment method was based on geochemical data and was used to estimate the amount of hydrocarbon generated and the expulsion efficiencies. The results from each of the three methods defied detailed economic analysis.Advanced statistical methods were gradually developed in the 1980's. By the end of this period, PETRIMES (the Petroleum Exploration and Resource Evaluations System) was developed. This system evaluates hydrocarbon potential by means of an exploration play definition coupled with compiled play data used to estimate undiscovered pool sizes. During this period, discovery process models were developed to account for the biased data. Estimations of individual pool sizes in the play were made and displayed graphically so that undiscovered pools could be identified in a statistically derived population of pools. Summed quantities of petroleum in undiscovered pools were used to define remaining expected play potential.The estimated undiscovered individual pool sizes inferred from assessments serve as direct input to economic analyses that examine which pools are viable prospects under specific economic conditions. This knowledge is useful to governments formulating energy policies and to petroleum companies setting exploration priorities.
A late Quaternary moraine sequence dated by rock weathering rinds, Craigieburn Range, New Zealand
Authors: Ricker K. E. , Chinn T. J. , McSaveney M. J.
Published: April 2011

Basins draining the Craigieburn Range, New Zealand, preserve a nearly complete late Quaternary moraine sequence. There are no radiocarbon dates, but moraine ages were determined by weathering-rind dating using thicknesses of rinds on surface-exposed sandstone boulders. Periods of expanded glaciers occurred 0.53, 0.66–2.5, 2.8–4.2, 5.9–9.7, and 16 thousand calendar (sidereal) years ago. Earlier periods of expanded glaciers in the region are dated by inference, largely from the ocean oxygen-isotope record, at 21–23.3, 25.5, and 56–70 ka.
Paleomagnetism of the Abitibi dyke swarm, southern Superior Province, and implications for the Logan Loop
Authors: Ernst Richard E. , Buchan Kenneth L.
Published: April 2011

The trace of the Middle Proterozoic Logan Loop of the North American apparent polar wander path is controversial. The older 1270–1110 Ma limb of the loop is poorly constrained, while the depth of the loop, based on the 1110–1080 Ma Keweenawan data of the younger limb, is thought by some to be largely an artifact of reversal asymmetry in the Earth's magnetic field. Paleomagnetism of the 1141 Ma Abitibi mafic dyke swarm is one of the keys to constraining the geometry of the Logan Loop.Unfortunately, previous paleomagnetic studies failed to distinguish dykes of the northeast-trending Middle Proterozoic olivine-bearing Abitibi swarm from subparallel Early Proterozoic olivine-free Biscotasing (formerly Preissac) dykes, and hence paleomagnetic poles determined in these studies should no longer be used. In the present study, sampling of eight Abitibi dykes has identified 23 normally magnetized sites in four dykes and, for the first time, five reversely magnetized sites in three dykes. One of the normally magnetized sites corresponds to the locality for which a high-precision U–Pb age was previously reported. A baked contact test establishes that the characteristic remanence of one normally magnetized dyke is primary. In addition, sites along individual dykes exhibit much smaller secular variation than is observed between dykes, indicating that the remanences of the other dykes are also primary. One of the normally magnetized dykes, the 700 km long Great Abitibi dyke, exhibits two primary directions that correspond to two geochemically distinct magma pulses. The five normally magnetized units, which consist of four separate dykes plus the second pulse of the Great Abitibi dyke, yield a well-defined mean paleomagnetic pole at 42.8°N, 151.5°W, dm = 16.3°, dp = 12.5°. It falls close to the reversely magnetized poles from the Keweenawan Track and establishes a minimum depth for the Logan Loop of about 40°. The reversed-polarity data from three other dykes are more scattered and may not average out secular variation. Hence, the present study is inconclusive regarding asymmetry of the Earth's magnetic field at 1141 Ma, even though a mean pole based on combined normal-and reversed-polarity dykes is indistinguishable from that based on normal-polarity dykes alone.
Age and origin of Late Jurassic and Paleocene granitoids, Nelson Batholith, southern British Columbia
Authors: Sevigny J. H. , Parrish R. R.
Published: April 2011

In the Middle Jurassic Nelson Batholith, southern British Columbia, young 40Ar/39Ar ages (i.e., 50–60 Ma) and distorted isobaric surfaces in the batholith suggest the possibility of Paleocene granitic plutonism. We present the results of a study undertaken to evaluate this possibility. Geochemical criteria successfully distinguish a suite of granitoids within the Nelson Batholith that differ from Nelson granites of similar SiO2 content. The granitoid suite is composed of 71.6–75.7 wt.% SiO2 leucocratic biotite granite and quartz monzonite with strong enrichments in alkaline, alkaline earth, and rare earth elements. Nd and Pb isotopic compositions suggest that biotite granite and quartz monzonite are not related. Biotite granite yields a U–Pb age of 158.9 ± 0.6 Ma (concordant zircons). Quartz monzonite crystallized at 61 ± 1 Ma, based on interpretation of titanite and zircon analyses. Zircons from this sample lie along a line from 61 to 160 Ma and demonstrate the presence of Middle Jurassic inheritance. Based on its petrographic and isotopic similarity to other Middle Jurassic plutons in the Nelson Batholith – Valhalla Complex area, we include the 159 Ma biotite granite with the Jurassic plutonic suite. This result demonstrates that magmatism in southern British Columbia was active at least until the early Late Jurassic (Oxfordian). The Paleocene (61 Ma) quartz monzonite that intrudes the southern Nelson Batholith is the structurally highest occurrence of "Ladybird" granite yet documented in southern British Columbia. Comparison of new and published geochemical and isotopic data for Paleocene granitoids throughout the southern Omineca Belt, British Columbia, suggests that these granitoids were not derived from a single, old crustal source.
Paleomagnetism of the Uairen Formation, Roraima Group, southeastern Venezuela: evidence for one of the oldest (Middle Proterozoic) depositional remanent magnetizations
Authors: Castillo Jesús H. , Costanzo-Alvarez Vincenzo
Published: April 2011

This study reports paleomagnetic results from nine localities (22 sites) of the Uairen Formation, the basal and oldest unit of the Roraima sedimentary sequence (Roraima Group) in the Precambrian Guayana shield (southeastern Venezuela). Three distinct natural remanent magnetizations (NRM's), U1N, U1R, and U2, were isolated by alternating-field and thermal demagnetization. U1N and U1R NRM's have mean directions D = 342°, I = 6° (k = 14, α95 = 10°, N = 14 sites) and D = 155°, I = 10° (k = 8, α95 = 17°, N = 8 sites), respectively. Because of their high coercivities (HC) and high (>580 °C) laboratory unblocking temperatures (TUB), it is believed that these NRM's are carried mainly by fine-grained magnetite and (or) hematite. The U2 NRM has D = 338°, I = −7° (k = 5, α95 = 25°, N = 6 sites). U2 is a low-HC (20 mT) and low-TUB (<300 °C) NRM carried by coarse-grained magnetite. Despite its low Fisher's k value, the U2 grand mean closely resembles that for U1N. Directional similarities between U1N, U1R, and U2 to groups I and II previously reported for diabase dikes and sills that intruded the Roraima sedimentary sequence (Roraima Intrusive Suite) suggest that primary NRM's of these sediments have been completely overprinted by thermal and hydrothermal effects associated with the intrusive suite. The apparent absence of diabase intrusions at the sampled localities, but mainly the low metamorphic grade of the Uairen samples revealed by thin-section analyses, lead to the alternative conclusion that U2 is a primary detrital remanent magnetization (DRM) dating from the time of deposition of the Uairen sediments, and U1N and U1R are later thermochemical overprints (TCRM's) acquired shortly after deposition by oxidation of fine-grained magnetite. Directional scatter of U2 could be explained as the consequence of misaligning effects of mechanic over magnetic torques acting on coarse-grained magnetite. An age between 1580 and 1960 Ma, derived from radiometric constraints, is suggested for the Uairen components. Thus U2 would be one of the oldest DRM's ever reported.
Seismic images of a tectonic subdivision of the Grenville Orogen beneath lakes Ontario and Erie
Authors: Forsyth D. A. , Milkereit B. , Davidson A. , Hanmer S. , Hutchinson D. R. , Hinze W. J. , Mereu R. F.
Published: April 2011

New seismic data from marine air-gun and Vibroseis profiles in Lake Ontario and Lake Erie provide images of subhorizontal Phanerozoic sediments underlain by a remarkable series of easterly dipping reflections that extends from the crystalline basement to the lower crust. These reflections are interpreted as structural features of crustal-scale subdivisions within the Grenville Orogen. Broadly deformed, imbricated, and overlapping thrust sheets within the western Central Metasedimentary Belt are succeeded to the west by a complex zone of easterly dipping, apparent thrust faults that are interpreted as a southwest subsurface extension of the boundary zone between the Central Metasedimentary Belt and the Central Gneiss Belt. The interpreted Central Metasedimentary Belt boundary zone has a characteristic magnetic anomaly that provides a link from the adjacent ends of lakes Ontario and Erie to structures exposed 150 km to the north. Less reflective, west-dipping events are interpreted as structures within the eastern Central Gneiss Belt. The seismic interpretation augments current tectonic models that suggest the exposed ductile structures formed at depth as a result of crustal shortening along northwest-verging thrust faults. Relatively shallow reflections across the boundary region suggest local, Late Proterozoic extensional troughs containing post-Grenville sediments, preserved possibly as a result of pre-Paleozoic reactivation of basement structures.
Tomodensitométrie axiale: relation entre l'intensité tomographique et la densité de la matière
Authors: Boespflug X. , Ross N. , Long B. , Dumais J. F.
Published: April 2011

The calibration of an axial tomodensitometer, used in sedimentology, was carried out on minerals and liquid samples. This study, taking into consideration the interactions between X rays and matter, revealed (i) a good correlation between the density of samples containing elements with low atomic number, which undergo only Compton scattering, and the intensity readings obtained by computer tomography and (ii) readings higher than predicted by linear correlation for samples containing elements with high atomic number, which undergo both Compton scattering and photoelectric absorption. An empirical model is used to correct the readings and correlate them with the density.
Age and depositional environment of the Rock River coal basin, Yukon Territory, Canada
Authors: Long D. G. F. , Sweet A. R.
Published: April 2011

Poorly exposed Late Eocene strata in the Rock River basin, 115 km northeast of Watson Lake, accumulated in an intermontane valley with a geometry and history controlled by subsidence associated with the Rock River Fault. The sequence, as seen in one outcrop and five borehole sections, is dominated by drab mudrocks with minor sandstones and some thick lenses of coal. The mudrocks accumulated in floodplain marsh and pond settings associated with a low-gradient, possibly anastomosed, fluvial system. River banks were stable owing to the abundance of plant roots in the channel walls. Although channel sandstone and conglomerate were not identified in the core, the abundance of coarsening- and fining-upwards sets of sandstone of splay origin indicates pronounced levee development. Woody coals accumulated in areas well away from the main channel, in a series of elongate forested swamps, which were periodically inundated by flood water.The overall palynological assemblage is typical of the Eocene and Early Oligocene. A Late Eocene age is inferred from the presence of Gothanipollis in combination with the absence of index species for the Early–Middle Eocene and the latest? Eocene and Oligocene. The low miospore diversity indicates a temperate climate. The dominance of the palynological assemblage by Taxodiaceae–Cupressaceae pollen indicates wet–humid conditions.
Mid-Cambrian (Marjuman) trilobites from the Pika Formation, southern Canadian Rocky Mountains, Alberta
Authors: Melzak Adam , Westrop Stephen R.
Published: April 2011

The carbonates and fine siliciclastics of the Mid-Cambrian (Marjuman) Pika Formation in the southern Canadian Rocky Mountains provide an important record of inner-shelf trilobite biofacies. The faunas are characterized by low diversity and, in contrast to the more diverse open-shelf faunas of other parts of North America, agnostid trilobites are absent. A new biostratigraphic framework of two zones and two informal faunas is proposed for use in inner-shelf settings. Twenty-seven collections from three sections yielded at least eight genera and thirteen species; Marjumia bagginsi is a new species.
Finite element study of uplift and strain across Vancouver Island
Authors: Wang Kelin , Dragert Herb , Melosh H. Jay
Published: April 2011

Geological evidence for sudden coastal subsidence along the west coast of southern Vancouver Island points to the occurrence of great prehistorical subduction earthquakes. Contemporary uplift and crustal shortening patterns in southern Vancouver Island appear to indicate that the subduction megathrust fault is currently locked. To understand better the dynamics of the observed surface deformation, we develop a finite element model of earthquake cycles for the northern Cascadia subduction zone across southern Vancouver Island, using a linear viscoelastic rheology. The model consists of the continental and oceanic lithospheres, the asthenospheric mantle with a viscosity of 5 × 1019 Pa∙s, and a low-viscosity (1018 Pa∙s) mantle wedge between the subducted oceanic plate and the overlying continental plate. The shallow geometry of the subducted Juan de Fuca plate is well defined by the results of various geophysical surveys, and the deep geometry is constrained by the results of seismic tomography. The model megathrust fault has a stick-slip zone near the surface, a viscoelastically weakly coupled zone (viscosity 7 × 1017 Pa∙s) at depth, and a narrow free-slip zone in between. Earthquakes are allowed to occur every 500 years. Varying the recurrence time does not greatly affect the surface deformation in the later part of the interseismic period. Experiments varying the width of the stick-slip zone lead to the conclusion that a width of about 70 km satisfies both the observed coseismic coastal subsidence and the contemporary surface deformation pattern. The results of a simple elastic dislocation model for thrust earthquakes that had been previously applied to the region are compared with the solutions of the viscoelastic model. Despite its simplicity, the elastic model approximates well the surface deformation of the viscoelastic model in the second half of the interseismic period, although it predicts a slightly narrower stick-slip zone of the fault. The present viscoelastic model is limited principally by the two-dimensional approach, the assumptions of purely stick-slip behaviour of the thrust fault, and the uncertainties in rock rheology.
Provenance memories and maturity of holocene sands in northwest Mexico
Authors: Carranza-Edwards Arturo , Rosales-Hoz Leticia , Santiago-Pérez Susana
Published: April 2011

Beach and fluvial sediments from the region around Todos Santos Bay, Baja California, have been studied to determine their maturity, provenance, chemical alteration, and tectonic relationships. Analysis of the CaO–Na2O–K2O content of several samples demonstrated a difference between those from a beach environment and those from a fluvial environment. Transport affects the characteristics of the sediment, producing an enrichment of material resistant to chemical and physical attack on the beach area. The beach sand samples are mineralogically and chemically more mature than those from the fluvial sands. The provenance index (feldspar/rock fragments) gives relatively low average values for fluvial sands, provided that they are richer in rock fragments. The chemical index of alteration has low average values for beach sands because the minerals are more resistant to energy from waves and currents. Tectonic settings, defined through the binary diagram from Roser and Korsch, suggest that the samples belong to active continental margin and arc domains. When tectonic fields are assigned, based on a Q–F–L triangular diagram analysis, the sediments from the study area fall in an active magmatic arc field, even though this region is not presently subject to subduction.
Plutonic rocks of the Thirtymile Range, Dorsey Terrane: ultrafractionated tin granites in the Yukon
Authors: Liverton T. , Alderton D. H. M.
Published: April 2011

A study of granitoid plutons of the western part of the Dorsey terrane in the southern Yukon has shown that two distinct suites exist on the basis of their mineralogy, chemistry, and metallogeny. Hornblende-rich granodiorite and granodiorite with minor gabbro and diorite form the NW and SW Thirtymile stocks, respectively. These are similar to many calc-alkaline Cordilleran intrusions and are not associated with any mineralization. The Thirtymile and Ork stocks are composed of highly evolved granite that contains hornblende only in the least evolved, volumetrically minor, lithofacies. Biotite granite forms the bulk of the Thirtymile stock, and it displays major- and trace-element trends that correspond to those shown by the adjacent Hake and Seagull batholiths. These latter granites are interpreted to be one magmatic suite, which is associated with F–B-rich skarn tin–tungsten mineralization. The most evolved lithofacies of the Ork and Thirtymile stocks is an alkali-feldspar-rich zinnwaldite–topaz–fluorite leucogranite that has an extremely evolved chemistry (differentiation index up to 99.4 and Rb/Sr ratio > 3000), with trace-element contents normally associated with "A-type" granites. This is interpreted to be the result of ultrafractionation of a halogen-rich residual granitic melt.
Geological and geophysical studies of buried valleys and their fills near Elora and Rockwood, Ontario
Authors: Greenhouse J. P. , Karrow P. F.
Published: April 2011

Buried bedrock valleys are of economic interest for groundwater and engineering studies, and of scientific interest for the sedimentary sequences they may contain. Two buried valleys, about 60 m deep, north and northeast of Guelph, Ontario, are tributary to the major Dundas Valley southwest of Guelph. Located initially from water well data, their locations and geometry were refined with surface geophysics, including very low frequency resistivity, terrain conductivity, resistivity, transient electromagnetic, gravity, and seismic methods. Useful data are obtained roughly in proportion to cost. Cored and rotary holes in the two valleys were followed by geophysical downhole logging with normal electric, spontaneous potential, single-point resistance, calliper, neutron – epithermal neutron, gamma–gamma, and natural gamma methods. Cores revealed multi-till sequences in the upper parts of the holes and, together with geophysical logs and their interpreted electrofacies, indicate the presence of underlying uniform, pollen-bearing (pine and spruce dominate) lacustrine fills. These fills and the buried valleys containing them are interpreted to be perhaps as old as the last interglacial. Buried valleys are fruitful targets for the discovery of older Quaternary sequences.
Development of inverted metamorphic gradient in the internal domain of the Taconian belt, Gaspé Peninsula
Authors: Camiré G.
Published: April 2011

The Mont Logan Nappe is part of the Taconian internal domain of the Quebec Appalachians, and is entirely made up of synrift to passive margin elastics and volcanics of the Shickshock Group. Rocks of the Mont Logan Nappe were affected by both Taconian and Acadian deformations but regional prograde metamorphism is Taconian and limited to the D1 deformational event. Thermobarometry and mineral assemblages indicate that the metasedimentary and metavolcanic rocks of the Mont Logan Nappe have recorded peak temperatures in the range 610–700 °C under pressures of approximately 600–700 MPa, and that prograde metamorphism was accompanied by the development of an inverted metamorphic gradient of −40 to −75 °C/km. The preferred interpretation of the cause of the inverted gradient is dissipative heating accompanying deformation along an intracontinental synmetamorphic thrust fault located at the top of the inverted metamorphic sequence.
The sedimentary record of Moose Lake: implications for glacier activity in the Mount Robson area, British Columbia
Authors: Desloges Joseph R. , Gilbert Robert
Published: April 2011

The postglacial sedimentary environment of Moose Lake was investigated using 3.5 kHz subbottom profiles and cores from the sediment surface. A late phase in the deglaciation of the upper Fraser River valley involved a valley glacier that flowed east to west and that terminated near the present-day outlet of Moose Lake. The overdeepened Fraser valley was infilled with ice-contact sediments, including terminal and recessional moraines, thereby damming westward drainage and forming Moose Lake. Eastward glacier retreat resulted in the deposition of ice blocks in the shallow west zone of the lake, where subsequent melting disturbed conformable glaciolacustrine deposits. The main Moose Lake basin records a transition from proximal to distal proglacial environments. However, late glacial and postglacial sediments are dominated by settling from suspension. Coarse, but localized, sediment inputs are derived from the Thunder Creek fan-delta and avalanche activity on the north-facing slope of the south shore. Depths to major acoustic reflectors and known modern accumulation rates of 2.7 mm a−1 indicate that the upper 15.5 m of sediment fill represents deposition during the Holocene and accounts for less than one third of the total late glacial and postglacial sediment yield. Sedimentary structures visible in cores and 14C dating confirm the varved nature of the upper 3 m of sediment. Extreme positive departures in varve thickness are related to above-average discharge to Moose Lake following persistent, glacier-melt-augmented summer flows. The Moose Lake varve chronology confirms the general pattern inferred from other regional evidence of climate deterioration after 1600 AD, which led to glacier advance and moraine emplacement in the Canadian Rocky Mountains.
The Paleoproterozoic upper Gowganda Formation, Whitefish Falls area, Ontario, Canada: subaqueous deposits of a braid delta
Authors: Junnila R. M. , Young G. M.
Published: April 2011

The upper Gowganda Formation is part of the Paleoproterozoic Huronian Supergroup (ca. 2.5–2.2 Ga) of the north shore of Lake Huron. The upper Gowganda Formation rests with sharp conformable contact on glaciogenic rocks of the lower Gowganda Formation and is gradational with cross-bedded sandstones of the overlying Lorrain Formation. At the southern margin of the Huronian fold belt, in the Whitefish Falls area, the upper Gowganda Formation is 380–750 m thick, and consists of four coarsening-upward cycles from 30 to 300 m in thickness. Each is comprised of the succession (a) laminated argillite deposited from suspension on the prodelta, (b) argillite and cross-laminated sandstone laid down on the delta front by normal fluvial input and flood episodes, (c) fine-to coarse-grained, cross-bedded sandstone formed as distributary-mouth sand sheets influenced by shallow marine processes. Abundant soft-sediment deformation indicates rapid sedimentation and (or) contemporaneous fault-related seismicity. Erosional contacts between cycles resulted from marine reworking as sediment supply diminished. Each coarsening-upward cycle is interpreted as the subaqueous deposits of a braid delta that prograded into a moderately wave-influenced, tectonically active marine basin. In some respects, the succession of the deltaic deposits is comparable to those formed during the postglacial evolution of the Mississippi delta, but it is likely that the fluvial regime at the time of deposition of the Gowganda Formation was dominantly braided.
Pleistocene herpetofaunal remains from the East Milford mastodon site (ca. 70 000–80 000 BP), Halifax County, Nova Scotia
Authors: Holman J. Alan , Clouthier Shawn G.
Published: April 2011

The remains of a frog (Rana pipiens) and two turtles (Chrysemys picta and Clemmys insculpta) were recovered from an organically rich clay matrix in association with mastodon remains in Halifax County near East Milford, Nova Scotia. Preliminary stratigraphic studies and radiometric dating indicate an Early Wisconsinan age between 70 000 and 80 000 BP for the site. All of the herpetological species are cold-tolerant forms that inhabit Nova Scotia today. The turtles are important paleoclimatically, in that they suggest that the summers had a sufficient number of warm days for the successful incubation of their eggs. Together, the herpetological species indicate a quiet, well-vegetated pond or small lake, with peripheral meadows, and the presence of a meandering stream with sand or gravel banks.
Detrital zircon geochronology of a conglomerate in the northeastern Cape Breton Highlands: implications for the relationships between terranes in Cape Breton Island, the Canadian Appalachians
Authors: Chen Ya-Dong , Lin Shoufa , van Staal Cees R.
Published: April 2011

Cape Breton Island has been interpreted as consisting of four zones of pre-Carboniferous rocks, but the relationships among them are controversial. To help resolve the controversy, we have dated detrital zircons from a conglomerate (part of the Cheticamp Lake Gneiss) in the Aspy terrane in the northeastern Cape Breton Highlands using the U–Pb method. The following ages were obtained: 462 ± 2 Ma (Middle Ordovician); ~492–488 Ma (6 ages; Early Ordovician); 552 ± 3 Ma (latest Precambrian–Early Cambrian); 620 ± 13 and 687 ± 4 Ma (Cadomian); and 809 ± 17, 1423 ± 10, 1462 ± 12, 1605 ± 14, 1644 ± 4, and 1911 ± 5 Ma (Proterozoic). The Middle Ordovician age sets a maximum age limit for deposition of the conglomerate, and supports an Ordovician–Silurian age for the Cheticamp Lake Gneiss. The Early Ordovician, latest Precambrian–Early Cambrian, and Cadomian ages match published ages from the Bras d'Or terrane (and its correlatives) and the Mira terrane (and its correlatives), and indicate provenance of the conglomerate from both terranes. They also indicate that the Bras d'Or and Mira terranes had been connected by the time of deposition of the conglomerate. The combination of the Cadomian and the Proterozoic ages is typical of parts of South America, supporting a suggestion that the Avalon Composite Terrane was derived from South America.
Geochemical analysis through the "transitional zone" of conodont faunal turnover in the Ordovician – Silurian boundary interval, Anticosti Island, Quebec
Authors: Wang K. , Chatterton B. D. E. , Orth C. J. , Attrep Jr M.
Published: April 2011

Geochemical analysis of the Ordovocian–Silurian boundary interval on Anticosti Island, Quebec, has revealed low Ir abundances for the lower Becscie Formation (0.005–0.039 ppb), comparable to those reported for the upper Ellis Bay Formation (0.005–0.058 ppb). When normalized as CaCO3-free values and ratioed to Al, a small amount of excess Ir (over background Ir levels) was observed in and on the upper surface of an oncolite platform bed in Member 7 (Laframboise) of the Ellis Bay Formation. Except for this bed, the abundances of Ir and other elements are relatively uniform throughout the section, but small enrichments are apparent in a few clay layers. As in other areas previously studied (South China, northwestern Canada, Scotland), the Ir maxima on Anticosti Island occur near the base of the graptolite persculptus Zone, and are attributable to condensation and slower sedimentation rates associated with the hardgrounds found within and on the upper surface of the oncolite platform bed. Although we cannot preclude a large extraterrestrial impact as the source for the Ir abundance maxima near the end of the Ordovician, which appear to be stratigraphically coeval and geographically widespread in the world, all of them are found to be associated with sedimentary condensation that may have resulted from glacio-eustatic sea-level fluctuations at the end of the Ordovician. From our data, we note that certain elements (e.g., Th, La, Lu, Sc, Cr, Ir, Fe, Al, Ca) show distinct abundance patterns in limestones, calcareous shales, and clays, apparently a result of increasing clay mineral contents.
Ferro-andesites in the Grande Ronde Basalt: their composition and significance in studies of the origin of the Columbia River Basalt Group
Authors: Lambert R. StJ. , Chamberlain V. E. , Holland J. G.
Published: April 2011

Flows from the Grande Ronde Basalt of the Columbia River Basalt Group include several with the chemical composition of ferro-andesites. These flows have SiO2 > 55%, MgO < 4%, and also have higher Fe/Mg than the average value for Grande Ronde Basalt. They are also distinctly richer in Cs, Rb, K, Ba, La, Ce, Th, and U than the remainder of the Grande Ronde Basalt flows, and possess small negative Eu anomalies. Their Pb isotopic compositions define a mixing line with a negative slope on a 206Pb/204Pb versus 207Pb/204Pb plot. Their Nd isotopic compositions lie between 143Nd/144Nd = 0.51252 and 0.51264, and their Sr isotopic compositions lie between 87Sr/86Sr = 0.7055 and 0.7060. These values define the enriched end of the Columbia River Basalt Group spectrum on a Sr–Nd epsilon diagram (excluding the Saddle Mountains Basalt). These ferro-andesite flows also form a compositional end member of the Columbia River Basalt Group and are sufficiently distinctive to warrant special consideration. We compare them with lavas from other tholeiitic provinces. Petrogenetically, they can be related to the Grande Ronde Basalt low-Mg basalts by plagioclase fractionation, or by clinopyroxene fractionation in partially melted eclogites. However, the situation may not be that simple, as their unique isotopic compositions are closely related to those of parental mantle materials, perhaps thus requiring separate reservoirs and (or) sources. Extending this argument to other parts of the Columbia River Basalt Group suggests that the origin of these basalts may be in a system of comparatively small magma chambers in the uppermost mantle, frequently replenished from a variety of sources.
Pb, Sr, and Nd isotopic systematics of rocks from the Galapagos Microplate
Authors: Cumming G. L. , Krstic D. , Puchelt H.
Published: April 2011

Pb, Sr, and Nd isotopic analyses were performed on a suite of compositionally variable rock samples representing an approximately 2500 m thickness of oceanic crustal lithologies from the deep rift valleys and spreading centers along the periphery of the Galapagos Microplate at the junction of the Pacific, Cocos, and Nazca plates. Samples were obtained from lower peridotite and gabbro layers, Fe–Ti basalts, very recent neovolcanic flows, and the thin sedimentary cover. The samples were dredged, cored, or video-grabbed during the research cruise Sonne 60. For unaltered igneous rocks, 206Pb/204Pb ratios range from 17.70 to 18.90, 87Sr/86Sr ratios from 0.7024 to 0.7035, clustering around 0.7027, while 143Nd/144Nd ratios range from 0.51307 to 0.51324. Based on these data, little systematic isotopic variation can be associated with any specific area or lithology of the microplate. One exception is a series of very thin volcanic flows from the Summit Graben area, where Pb and Nd isotope ratios change gradually, with each successive flow. The extent of the observed Pb isotopic variation covers almost the entire range of ratios for the East Pacific Rise mid-oceanic ridge basalts published to date, suggesting that the part of the mantle responsible for formation of the Galapagos Microplate rocks is no more isotopically homogeneous than the East Pacific Rise mantle as a whole, taken over a length of several thousands of kilometres.
A new and typically Jurassic ichthyosaur from the Upper Triassic of British Columbia
Authors: McGowan Chris
Published: April 2011

A new ichthyosaur species is described from the Upper Triassic (middle Norian) of Williston Lake, northeastern British Columbia. Aside from the foramen enclosed between the radius and ulna–a characteristic of Triassic ichthyosaurs–the new specimen is typical of Lower Jurassic forms. Indeed, if the specimen had been collected from the English lower Liassic, there would have been no hesitation in referring it to the common English genus Ichthyosaurus, a taxonomic course I follow here. Referring the new species to Ichthyosaurus extends the geological range of the genus by approximately 9 Ma, to the middle Norian. Ichthyosaurus janiceps sp. nov. has an abbreviated snout, like that of Ichthyosaurus breviceps, but it is a much larger species, and has a distinctly different forefin.
Mineralogy, bulk and rare earth element geochemistry of massive sulphide-associated hydrothermal sediments of the Brunswick Horizon, Bathurst Mining Camp, New Brunswick
Authors: Peter Jan M. , Goodfellow Wayne D.
Published: April 2011

Massive sulphides are spatially and temporally associated with iron formation (IF) and other hydrothermal sedimentary rocks in the vicinity of the Brunswick No. 12, Brunswick No. 6, and Austin Brook deposits, Bathurst Mining Camp. Sulphide-, carbonate-, oxide-, and silicate-predominant IF is present. Carbonate-predominant IF is best developed in and around the Brunswick No. 12 deposit, whereas hematite-bearing IF is absent here but prominent in the Austin Brook–Brunswick No. 6 area. The IF is composed dominantly of Si, CO2, Fe, Mn, and Ca. Minor constituents include Mg, P, Ti, Al, and S. Statistically significant interelement correlations between Eu, Fe, Mn, Pb, Zn, Cd, Au, Ca, Sr, Ba, P, CO2, and S indicate that these elements were precipitated from hydrothermal fluids vented onto the seafloor. Positive interelement correlations between Si, Ti, Al, Mg, K, Zr, rare earth elements (REE's) except Eu, Se, V, Y, Yb, Co, Ni, and Cr reflect the presence of detrital clastic mafic and aluminosilicate minerals and hydrogenous sedimentary components. Felsic volcanic and pyroclastic rocks are considered to be the source for the detritus. REE patterns of IF at Brunswick No. 12 display similarities with those of modern high-temperature hydrothermal vent solutions, sea water, and host rhyolitic tuff and sedimentary rocks. These patterns are largely controlled by the relative proportions of hydrothermal and detrital components. The IF formed from reduced hydrothermal fluids vented into a stratified marine basin. The mineral precipitates were widely dispersed from the sites of venting and massive sulphide accumulation.
New psittacosaur occurrences in Inner Mongolia
Authors: Russell Dale A. , Zhao X.-J.
Published: April 2011

Psittacosaur materials were collected from seven localities in the course of Dinosaur Project fieldwork in Inner Mongolia. Two new species of Psittacosaurus are recognized, bringing the number of well-defined species to six. One, based on a nearly complete skeleton, resembles Psittacosaurus mongoliensis, but is a smaller animal with a relatively larger head and longer tail. The other species possesses jugal horns, but exhibits a different combination of characters than Psittacosaurus sinensis and Psittacosaurus xinjiangensis. A larger matrix of taxa and characters than is presently available will be necessary to resolve adequately phylogenetic relationships within the genus. Psittacosaurs were small dinosaurs, the skeletons of which are preserved in unusual completeness in proximity to aeolian environments of deposition. Their small brain size relative to that of modern mammals of similar body size implies a relatively restricted behavioral repertoire.
Subsidence of the Atlantic Moroccan margin during the Mesozoic
Authors: Le Roy P , Guillocheau F , Piqué A , Morabet A M
Published: April 2011

This paper presents a combined study based on seismic interpretation, sequence stratigraphy, and the evaluation of subsidence that aims to characterize the structure and development of the Essaouira Basin in Morocco. Located in the coastal Meseta adjoining the continental margin, this basin records an initial Carnian-Hettangian deformation phase during rifting in the central part of the North Atlantic region. The geometry of the basin as a function of time shows a succession of half-grabens and horsts that developed westwards from reactivated Hercynian structures. The postrift stage is characterized by an aggrading sedimentary sequence, as shown by concordant seismic sequences stacking over the onshore part of the basin. The Upper Cretaceous coincides with a sequence showing a transition towards a prograding regime that leads to the topography of the present-day margin. Using the high-resolution analysis provided by sequence stratigraphy, it is possible to recognize fine-scale stratigraphic variations in the sedimentary succession. The well-to-well correlation of sedimentary cycles forms a dataset for evaluating subsidence. Residual subsidence curves reveal a differential behaviour between the present onshore and offshore areas. Although the computed subsidence rates are low across the onshore zone, curves for the western offshore part of the basin follow theoretical lithospheric cooling curves that are compatible with a stretch factor ( beta ) of nearly 1.4. Steep temporary gradients on the computed curves may be correlated with tectonic phases documented across the North Atlantic region that exerted a tight control on the development of the Essaouira Basin from Triassic rifting until the uplift of the Atlas Mountains during the Cenozoic.
Crustal geometry of the Abitibi Subprovince, in light of three-dimensional seismic reflector orientations
Authors: Bellefleur G , Calvert A J , Chouteau M C
Published: April 2011

We provide precise estimates of reflector orientations beneath the Archean Abitibi Subprovince, using two distinct approaches based on Lithoprobe seismic reflection data. In the first, we use the dip of reflections observed on intersecting profiles to establish the three-dimensional orientation of reflective structures. In the second, the strikes and dips of reflectors are estimated in the crooked parts of seismic reflection profiles by calculating a measure of coherency along the traveltime trajectories defined by a particular azimuth, dip, depth, and medium velocity. Mid-crustal reflectors define two areas with distinctive geometry: reflectors beneath the southern Abitibi belt are oppositely dipping, and convergent at depth, providing a V-shape aspect to the greenstone rocks; other reflectors beneath the northern Abitibi belt are, in general, subparallel, dipping at an average of 30° toward the north. These north-dipping reflectors are partly disrupted by a low-reflectivity zone, which is attributed to rocks of the Opatica Subprovince, located underneath the northern Abitibi belt. Lower-crustal reflectors have a similar, shallowly north-dipping orientation throughout the Abitibi Subprovince. The geometry of the reflectors recovered is consistent with the different tectonic histories proposed for the southern and northern Abitibi assemblages, until common deformation during a north-south shortening event. Attitudes recovered in the northern Abitibi belt are consistent with tectonic scenarios involving underthrusting of Abitibi middle and lower crustal terranes beneath the Opatica belt, whereas the oppositely dipping reflectors recovered in the middle crust beneath the southern Abitibi belt could be representative of a rifted volcanic arc environment.
A new scleritomous metazoan from the Late Ordovician Georgian Bay Formation, southern Ontario
Authors: Rudkin David M
Published: April 2011

A new genus and species of articulated scleritomous metazoan, Curviconophorus andersoni, is described on the basis of a unique specimen from the Late Ordovician Georgian Bay Formation of southern Ontario. The affinities of the organism remain obscure, although the overall morphology of component sclerites suggests a possible relationship with the Agmata, an extinct phylum-level group so far known with certainty only from the Cambrian. Curved, conical elements of the scleritome are preserved as internal moulds and yield no details of ultrastructure or primary composition, precluding detailed comparisons with the aggultinated, internally laminated sclerites of agmatans. Curviconophorus gen.nov. has a scleritome architecture similar to that of the Early Ordovician putative agmatan Dimorphoconus granulatus, though it has fewer elements that are strictly monomorphic.
A Triassic sponge from Vancouver Island: possible holdover from the Cambrian
Authors: Stanley, Jr. George D
Published: April 2011

Tiny cap-shaped fossils recovered from silicified residues in Upper Triassic rocks of Vancouver Island (Wrangellia) are identified as a calcareous sponge Nucha? vancouverensis n. sp. nov. The genus Nucha Pickett and Jell was first reported from Middle Cambrian rocks of Australia. The Triassic example constitutes the first occurrence outside the Cambrian system and the continent of Australia. The absence of representatives in rocks between Triassic and Cambrian age suggests that it is a long-range refugium taxon. The occurrence of such a wide-ranging holdover organism reinforces the role of refugia in preferential survivorship over long periods of geologic time. Other holdover taxa are known from volcanic displaced terranes of western American Cordillera, and their study may help clarify neglected aspects of survival and evolution.
Evolution of the Appalachian Laurentian margin: Lithoprobe results in western Newfoundland
Authors: Waldron John WF , Anderson Scott D , Cawood Peter A , Goodwin Laurel B , Hall Jeremy , Jamieson Rebecca A , Palmer Sarah E , Stockmal Glen S , Williams Paul F
Published: April 2011

The Humber Zone of the western Newfoundland Appalachians represents the early Paleozoic Laurentian margin established by Neoproterozoic rifting. After a period of passive margin thermal subsidence, Taconian deformation began in the Early Ordovician with westward thrusting. Subsequently, an extensive foreland basin developed beneath the Gulf of St. Lawrence. It records rapid Late Ordovician to Early Silurian subsidence; mid-Silurian erosion; and renewed Late Silurian to Devonian subsidence. The Humber Zone was traversed by Lithoprobe seismic reflection profiles. Within the external part of the orogen, seismic reflections in the upper crustal section appear more coherent where seismic lines are parallel to fold hinges. Some subhorizontal reflectors are interpreted as thrust sheets of shelf limestone, but others probably represent intrabasement structures. A group of moderately northwest-dipping reflections probably represents late extensional shear zones. On the Baie Verte Peninsula, low-angle reflections passing beneath the Baie Verte Line are probably also late extensional shears, possibly reactivating earlier thrusts. Tectonism in the Humber Zone probably began with attempted eastward subduction of the Laurentian margin. Deep burial of the margin, accompanied by eclogite-facies metamorphism, probably coincided with rapid subsidence in the foreland basin. Later Barrovian metamorphism was associated with cleavage development and east-directed shear, and with dextral oblique slip, in Baie Verte Peninsula. Later Silurian sinistral transpression with thrusting east of the Baie Verte Line was followed by dextral transpression to transtension. "Acadian" thrusting dominated the western margin of the orogen in the Devonian and possibly earliest Carboniferous.
Stratigraphy and paleomagnetism of Late Pliocene and Pleistocene sediments in the Wellsch Valley and Swift Current Creek areas, southwestern Saskatchewan, Canada
Authors: Barendregt R W , Irving E , Christiansen E A , Sauer E K , Schreiner B T
Published: April 2011

The Late Pliocene and Pleistocene are represented in southern Saskatchewan by sequences of preglacial, glacial, and nonglacial deposits. These have been studied in surface exposures and bore cores and have been subdivided and correlated on the basis of their lithologies. In this study, new observations of magnetic polarity are presented. They reveal a lower preglacial sequence (Empress Group) with reversed polarity, and an upper normally magnetized sequence which contains glacial deposits of pre-Illinoian, Illinoian, and Wisconsinan age and which are correlative with the Saskatoon and Sutherland groups of central Saskatchewan. The reversed preglacial sequence is referred to the Matuyama Zone (Late Pliocene to Early Pleistocene: 2.58-0.78 Ma) and the normal glacial sequence to the Brunhes Zone (Middle to Late Pleistocene and Holocene: 0.78 Ma to present). In southern Saskatchewan there is no evidence of glaciation during the Late Pliocene and Early Pleistocene (Matuyama Chron) which is in marked contrast with parts of the Cordilleran region of western Canada where glaciations occur throughout this time.